TY - JOUR
A1 - Panchal, Gyanendra
A1 - Kojda, Sandrino Danny
A1 - Sahoo, Sophia
A1 - Bagri, Anita
A1 - Kunwar, Hemant Singh
A1 - Bocklage, Lars
A1 - Panchwanee, Anjali
A1 - Sathe, Vasant G.
A1 - Fritsch, Katharina
A1 - Habicht, Klaus
A1 - Choudhary, Ram Janay
A1 - Phase, Deodutta M.
T1 - Strain and electric field control of magnetic and electrical transport properties in a magnetoelastically coupled Fe3O4/BaTiO3 (001) heterostructure
JF - Physical review : B, Condensed matter and materials physics
N2 - We present a study of the control of electric field induced strain on the magnetic and electrical transport properties in a magnetoelastically coupled artificial multiferroic Fe3O4/BaTiO3 heterostructure.
In this Fe3O4/BaTiO3 heterostructure, the Fe3O4 thin film is epitaxially grown in the form of bilateral domains, analogous to a-c stripe domains of the underlying BaTiO3(001) substrate.
By in situ electric field dependent magnetization measurements, we demonstrate the extrinsic control of the magnetic anisotropy and the characteristic Verwey metal-insulator transition of the epitaxial Fe3O4 thin film in a wide temperature range between 20-300 K, via strain mediated converse magnetoelectric coupling.
In addition, we observe strain induced modulations in the magnetic and electrical transport properties of the Fe3O4 thin film across the thermally driven intrinsic ferroelectric and structural phase transitions of the BaTiO3 substrate.
In situ electric field dependent Raman measurements reveal that the electric field does not significantly modify the antiphase boundary defects in the Fe3O4 thin film once it is thermodynamically stable after deposition and that the modification of the magnetic properties is mainly caused by strain induced lattice distortions and magnetic anisotropy.
These results provide a framework to realize electrical control of the magnetization in a classical highly correlated transition metal oxide.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevB.105.224419
SN - 2469-9950
SN - 2469-9969
VL - 105
IS - 22
PB - The American Institute of Physics
CY - Woodbury, NY
ER -
TY - JOUR
A1 - Clark, Oliver J.
A1 - Wadgaonkar, Indrajit
A1 - Freyse, Friedrich
A1 - Springholz, Gunther
A1 - Battiato, Marco
A1 - Sanchez-Barriga, Jaime
T1 - Ultrafast thermalization pathways of excited bulk and surface states in the ferroelectric rashba semiconductor GeTe
JF - Advanced materials
N2 - A large Rashba effect is essential for future applications in spintronics. Particularly attractive is understanding and controlling nonequilibrium properties of ferroelectric Rashba semiconductors. Here, time- and angle-resolved photoemission is utilized to access the ultrafast dynamics of bulk and surface transient Rashba states after femtosecond optical excitation of GeTe. A complex thermalization pathway is observed, wherein three different timescales can be clearly distinguished: intraband thermalization, interband equilibration, and electronic cooling. These dynamics exhibit an unconventional temperature dependence: while the cooling phase speeds up with increasing sample temperature, the opposite happens for interband thermalization. It is demonstrated how, due to the Rashba effect, an interdependence of these timescales on the relative strength of both electron-electron and electron-phonon interactions is responsible for the counterintuitive temperature dependence, with spin-selection constrained interband electron-electron scatterings found both to dominate dynamics away from the Fermi level, and to weaken with increasing temperature. These findings are supported by theoretical calculations within the Boltzmann approach explicitly showing the opposite behavior of all relevant electron-electron and electron-phonon scattering channels with temperature, thus confirming the microscopic mechanism of the experimental findings. The present results are important for future applications of ferroelectric Rashba semiconductors and their excitations in ultrafast spintronics.
KW - ferroelectric semiconductors
KW - Rashba effect
KW - spin- and angle-resolved photoemission
KW - spin-orbit coupling
KW - time-resolved photoemission
KW - ultrafast dynamics
Y1 - 2022
U6 - https://doi.org/10.1002/adma.202200323
SN - 0935-9648
SN - 1521-4095
VL - 34
IS - 24
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Stefancu, Andrei
A1 - Nan, Lin
A1 - Zhu, Li
A1 - Chis, Vasile
A1 - Bald, Ilko
A1 - Liu, Min
A1 - Leopold, Nicolae
A1 - Maier, Stefan A.
A1 - Cortes, Emiliano
T1 - Controlling plasmonic chemistry pathways through specific ion effects
JF - Advanced optical materials
N2 - Plasmon-driven dehalogenation of brominated purines has been recently explored as a model system to understand fundamental aspects of plasmon-assisted chemical reactions. Here, it is shown that divalent Ca2+ ions strongly bridge the adsorption of bromoadenine (Br-Ade) to Ag surfaces.
Such ion-mediated binding increases the molecule's adsorption energy leading to an overlap of the metal energy states and the molecular states, enabling the chemical interface damping (CID) of the plasmon modes of the Ag nanostructures (i.e., direct electron transfer from the metal to Br-Ade).
Consequently, the conversion of Br-Ade to adenine almost doubles following the addition of Ca2+.
These experimental results, supported by theoretical calculations of the local density of states of the Ag/Br-Ade complex, indicate a change of the charge transfer pathway driving the dehalogenation reaction, from Landau damping (in the lack of Ca2+ ions) to CID (after the addition of Ca2+).
The results show that the surface dynamics of chemical species (including water molecules) play an essential role in charge transfer at plasmonic interfaces and cannot be ignored. It is envisioned that these results will help in designing more efficient nanoreactors, harnessing the full potential of plasmon-assisted chemistry.
KW - chemical interface damping
KW - Hofmeister effect
KW - hydration layer
KW - plasmonic chemistry
KW - specific ion effects
KW - surface-enhanced Raman scattering
Y1 - 2022
U6 - https://doi.org/10.1002/adom.202200397
SN - 2195-1071
VL - 10
IS - 14
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Yan, Xiaoli
A1 - Xue, Zhike
A1 - Jiang, Chaowei
A1 - Priest, E. R.
A1 - Kliem, Bernhard
A1 - Yang, Liheng
A1 - Wang, Jincheng
A1 - Kong, Defang
A1 - Song, Yongliang
A1 - Feng, Xueshang
A1 - Liu, Zhong
T1 - Fast plasmoid-mediated reconnection in a solar flare
JF - Nature Communications
N2 - Magnetic reconnection is a multi-faceted process of energy conversion in astrophysical, space and laboratory plasmas that operates at microscopic scales but has macroscopic drivers and consequences.
Solar flares present a key laboratory for its study, leaving imprints of the microscopic physics in radiation spectra and allowing the macroscopic evolution to be imaged, yet a full observational characterization remains elusive.
Here we combine high resolution imaging and spectral observations of a confined solar flare at multiple wavelengths with data-constrained magnetohydrodynamic modeling to study the dynamics of the flare plasma from the current sheet to the plasmoid scale. The analysis suggests that the flare resulted from the interaction of a twisted magnetic flux rope surrounding a filament with nearby magnetic loops whose feet are anchored in chromospheric fibrils. Bright cusp-shaped structures represent the region around a reconnecting separator or quasi-separator (hyperbolic flux tube).
The fast reconnection, which is relevant for other astrophysical environments, revealed plasmoids in the current sheet and separatrices and associated unresolved turbulent motions.
Solar flares provide wide range of observational details about fundamental processes involved. Here, the authors show evidence for magnetic reconnection in a strong confined solar flare displaying all four reconnection flows with plasmoids in the current sheet and the separatrices.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-022-28269-w
SN - 2041-1723
VL - 13
IS - 1
PB - Nature Publishing Group UK
CY - London
ER -
TY - JOUR
A1 - Morris, Paul J.
A1 - Bohdan, Artem
A1 - Weidl, Martin S.
A1 - Pohl, Martin
T1 - Preacceleration in the Electron Foreshock. I. Electron Acoustic Waves
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2 - To undergo diffusive shock acceleration, electrons need to be preaccelerated to increase their energies by several orders of magnitude, else their gyroradii will be smaller than the finite width of the shock. In oblique shocks, where the upstream magnetic field orientation is neither parallel nor perpendicular to the shock normal, electrons can escape to the shock upstream, modifying the shock foot to a region called the electron foreshock. To determine the preacceleration in this region, we undertake particle-in-cell simulations of oblique shocks while varying the obliquity and in-plane angles. We show that while the proportion of reflected electrons is negligible for theta (Bn) = 74.degrees 3, it increases to R similar to 5% for theta (Bn) = 30 degrees, and that, via the electron acoustic instability, these electrons power electrostatic waves upstream with energy density proportional to R (0.6) and a wavelength approximate to 2 lambda (se), where lambda (se) is the electron skin length. While the initial reflection mechanism is typically a combination of shock-surfing acceleration and magnetic mirroring, we show that once the electrostatic waves have been generated upstream, they themselves can increase the momenta of upstream electrons parallel to the magnetic field. In less than or similar to 1% of cases, upstream electrons are prematurely turned away from the shock and never injected downstream. In contrast, a similar fraction is rescattered back toward the shock after reflection, reinteracts with the shock with energies much greater than thermal, and crosses into the downstream.
Y1 - 2022
U6 - https://doi.org/10.3847/1538-4357/ac69c7
SN - 0004-637X
SN - 1538-4357
VL - 931
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Zaragoza-Cardiel, Javier
A1 - Gómez-González, Víctor Mauricio Alfonso
A1 - Mayya, Yalia Divakara
A1 - Ramos-Larios, Gerardo
T1 - Nebular abundance gradient in the Cartwheel galaxy using MUSE data
JF - Monthly notices of the Royal Astronomical Society
N2 - We here present the results from a detailed analysis of nebular abundances of commonly observed ions in the collisional ring galaxy Cartwheel using the Very Large Telescope (VLT) Multi-Unit Spectroscopic Explorer (MUSE) data set. The analysis includes 221 H II regions in the star-forming ring, in addition to 40 relatively fainter H a-emitting regions in the spokes, disc, and the inner ring. The ionic abundances of He, N, O, and Fe are obtained using the direct method (DM) for 9, 20, 20, and 17 ring H II regions, respectively, where the S++ temperature-sensitive line is detected. For the rest of the regions, including all the nebulae between the inner and the outer ring, we obtained O abundances using the strong-line method (SLM). The ring regions have a median 12 + log O/H = 8.19 +/- 0.15, log N/O = -1.57 +/- 0.09 and log Fe/O = -2.24 +/- 0.09 using the DM. Within the range of O abundances seen in the Cartwheel, the N/O and Fe/O values decrease proportionately with increasing O, suggesting local enrichment of O without corresponding enrichment of primary N and Fe. The O abundances of the disc H II regions obtained using the SLM show a well-defined radial gradient. The mean O abundance of the ring H II regions is lower by similar to 0.1 dex as compared to the extrapolation of the radial gradient. The observed trends suggest the preservation of the pre-collisional abundance gradient, displacement of most of the processed elements to the ring, as predicted by the recent simulation by Renaud et al., and post-collisional infall of metal-poor gas in the ring.
KW - galaxies: star clusters
KW - galaxies: individual
KW - galaxies: abundances
Y1 - 2022
U6 - https://doi.org/10.1093/mnras/stac1423
SN - 0035-8711
SN - 1365-2966
VL - 514
IS - 2
SP - 1689
EP - 1705
PB - Oxford University Press
CY - Oxford
ER -
TY - JOUR
A1 - Sposini, Vittoria
A1 - Chechkin, Aleksei
A1 - Sokolov, Igor M.
A1 - Roldan-Vargas, Sandalo
T1 - Detecting temporal correlations in hopping dynamics in Lennard-Jones liquids
JF - Journal of physics : A, Mathematical and theoretical
N2 - Lennard-Jones mixtures represent one of the popular systems for the study of glass-forming liquids.
Spatio/temporal heterogeneity and rare (activated) events are at the heart of the slow dynamics typical of these systems. Such slow dynamics is characterised by the development of a plateau in the mean-squared displacement (MSD) at intermediate times, accompanied by a non-Gaussianity in the displacement distribution identified by exponential tails.
As pointed out by some recent works, the non-Gaussianity persists at times beyond the MSD plateau, leading to a Brownian yet non-Gaussian regime and thus highlighting once again the relevance of rare events in such systems.
Single-particle motion of glass-forming liquids is usually interpreted as an alternation of rattling within the local cage and cage-escape motion and therefore can be described as a sequence of waiting times and jumps. In this work, by using a simple yet robust algorithm, we extract jumps and waiting times from single-particle trajectories obtained via molecular dynamics simulations.
We investigate the presence of correlations between waiting times and find negative correlations, which becomes more and more pronounced when lowering the temperature.
KW - glassy systems
KW - hopping dynamics
KW - jump detection
KW - rare events
Y1 - 2022
U6 - https://doi.org/10.1088/1751-8121/ac7e0a
SN - 1751-8113
SN - 1751-8121
VL - 55
IS - 32
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Grebenkov, Denis S.
A1 - Metzler, Ralf
A1 - Oshanin, Gleb
T1 - Search efficiency in the Adam-Delbruck reduction-of-dimensionality scenario versus direct diffusive search
JF - New journal of physics : the open-access journal for physics
N2 - The time instant-the first-passage time (FPT)-when a diffusive particle (e.g., a ligand such as oxygen or a signalling protein) for the first time reaches an immobile target located on the surface of a bounded three-dimensional domain (e.g., a hemoglobin molecule or the cellular nucleus) is a decisive characteristic time-scale in diverse biophysical and biochemical processes, as well as in intermediate stages of various inter- and intra-cellular signal transduction pathways. Adam and Delbruck put forth the reduction-of-dimensionality concept, according to which a ligand first binds non-specifically to any point of the surface on which the target is placed and then diffuses along this surface until it locates the target. In this work, we analyse the efficiency of such a scenario and confront it with the efficiency of a direct search process, in which the target is approached directly from the bulk and not aided by surface diffusion. We consider two situations: (i) a single ligand is launched from a fixed or a random position and searches for the target, and (ii) the case of 'amplified' signals when N ligands start either from the same point or from random positions, and the search terminates when the fastest of them arrives to the target. For such settings, we go beyond the conventional analyses, which compare only the mean values of the corresponding FPTs. Instead, we calculate the full probability density function of FPTs for both scenarios and study its integral characteristic-the 'survival' probability of a target up to time t. On this basis, we examine how the efficiencies of both scenarios are controlled by a variety of parameters and single out realistic conditions in which the reduction-of-dimensionality scenario outperforms the direct search.
KW - first-passage times
KW - Adam-Delbruck scenario
KW - dimensional reduction
KW - bulk
KW - and surface diffusion
Y1 - 2022
U6 - https://doi.org/10.1088/1367-2630/ac8824
SN - 1367-2630
VL - 24
IS - 8
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Agarwal, Ankit
A1 - Guntu, Ravikumar
A1 - Banerjee, Abhirup
A1 - Gadhawe, Mayuri Ashokrao
A1 - Marwan, Norbert
T1 - A complex network approach to study the extreme precipitation patterns in a river basin
JF - Chaos : an interdisciplinary journal of nonlinear science
N2 - The quantification of spatial propagation of extreme precipitation events is vital in water resources planning and disaster mitigation. However, quantifying these extreme events has always been challenging as many traditional methods are insufficient to capture the nonlinear interrelationships between extreme event time series. Therefore, it is crucial to develop suitable methods for analyzing the dynamics of extreme events over a river basin with a diverse climate and complicated topography. Over the last decade, complex network analysis emerged as a powerful tool to study the intricate spatiotemporal relationship between many variables in a compact way. In this study, we employ two nonlinear concepts of event synchronization and edit distance to investigate the extreme precipitation pattern in the Ganga river basin. We use the network degree to understand the spatial synchronization pattern of extreme rainfall and identify essential sites in the river basin with respect to potential prediction skills. The study also attempts to quantify the influence of precipitation seasonality and topography on extreme events. The findings of the study reveal that (1) the network degree is decreased in the southwest to northwest direction, (2) the timing of 50th percentile precipitation within a year influences the spatial distribution of degree, (3) the timing is inversely related to elevation, and (4) the lower elevation greatly influences connectivity of the sites. The study highlights that edit distance could be a promising alternative to analyze event-like data by incorporating event time and amplitude and constructing complex networks of climate extremes.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0072520
SN - 1054-1500
SN - 1089-7682
VL - 32
IS - 1
PB - American Institute of Physics
CY - Woodbury, NY
ER -
TY - JOUR
A1 - Clark, Oliver J.
A1 - Freyse, Friedrich
A1 - Yashina, L. V.
A1 - Rader, Oliver
A1 - Sanchez-Barriga, Jaime
T1 - Robust behavior and spin-texture stability of the topological surface state in Bi2Se3 upon deposition of gold
JF - npj quantum materials
N2 - The Dirac point of a topological surface state (TSS) is protected against gapping by time-reversal symmetry. Conventional wisdom stipulates, therefore, that only through magnetisation may a TSS become gapped. However, non-magnetic gaps have now been demonstrated in Bi2Se3 systems doped with Mn or In, explained by hybridisation of the Dirac cone with induced impurity resonances. Recent photoemission experiments suggest that an analogous mechanism applies even when Bi2Se3 is surface dosed with Au. Here, we perform a systematic spin- and angle-resolved photoemission study of Au-dosed Bi2Se3. Although there are experimental conditions wherein the TSS appears gapped due to unfavourable photoemission matrix elements, our photon-energy-dependent spectra unambiguously demonstrate the robustness of the Dirac cone against high Au coverage. We further show how the spin textures of the TSS and its accompanying surface resonances remain qualitatively unchanged following Au deposition, and discuss the mechanism underlying the suppression of the spectral weight.
KW - Electronic properties and materials
KW - Topological matter
Y1 - 2022
U6 - https://doi.org/10.1038/s41535-022-00443-9
SN - 2397-4648
VL - 7
IS - 1
PB - Nature Publishing Group
CY - London
ER -
TY - JOUR
A1 - Padash, Amin
A1 - Sandev, Trifce
A1 - Kantz, Holger
A1 - Metzler, Ralf
A1 - Chechkin, Aleksei
T1 - Asymmetric Levy flights are more efficient in random search
JF - Fractal and fractional
N2 - We study the first-arrival (first-hitting) dynamics and efficiency of a one-dimensional random search model performing asymmetric Levy flights by leveraging the Fokker-Planck equation with a delta-sink and an asymmetric space-fractional derivative operator with stable index alpha and asymmetry (skewness) parameter beta.
We find exact analytical results for the probability density of first-arrival times and the search efficiency, and we analyse their behaviour within the limits of short and long times.
We find that when the starting point of the searcher is to the right of the target, random search by Brownian motion is more efficient than Levy flights with beta <= 0 (with a rightward bias) for short initial distances, while for beta>0 (with a leftward bias) Levy flights with alpha -> 1 are more efficient.
When increasing the initial distance of the searcher to the target, Levy flight search (except for alpha=1 with beta=0) is more efficient than the Brownian search. Moreover, the asymmetry in jumps leads to essentially higher efficiency of the Levy search compared to symmetric Levy flights at both short and long distances, and the effect is more pronounced for stable indices alpha close to unity.
KW - asymmetric Levy flights
KW - first-arrival density
KW - search efficiency
Y1 - 2022
U6 - https://doi.org/10.3390/fractalfract6050260
SN - 2504-3110
VL - 6
IS - 5
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Grebenkov, Denis S.
A1 - Kumar, Aanjaneya
T1 - First-passage times of multiple diffusing particles with reversible target-binding kinetics
JF - Journal of physics : A, Mathematical and theoretical
N2 - We investigate a class of diffusion-controlled reactions that are initiated at the time instance when a prescribed number K among N particles independently diffusing in a solvent are simultaneously bound to a target region.
In the irreversible target-binding setting, the particles that bind to the target stay there forever, and the reaction time is the Kth fastest first-passage time to the target, whose distribution is well-known. In turn, reversible binding, which is common for most applications, renders theoretical analysis much more challenging and drastically changes the distribution of reaction times.
We develop a renewal-based approach to derive an approximate solution for the probability density of the reaction time.
This approximation turns out to be remarkably accurate for a broad range of parameters.
We also analyze the dependence of the mean reaction time or, equivalently, the inverse reaction rate, on the main parameters such as K, N, and binding/unbinding constants. Some biophysical applications and further perspectives are briefly discussed.
KW - first-passage time
KW - diffusion-controlled reactions
KW - reversible binding
KW - extreme statistics
Y1 - 2022
U6 - https://doi.org/10.1088/1751-8121/ac7e91
SN - 1751-8113
SN - 1751-8121
VL - 55
IS - 32
PB - IOP Publ.
CY - Bristol
ER -
TY - JOUR
A1 - Kölsch, Maximilian
A1 - Dietrich, Tim
A1 - Ujevic, Maximiliano
A1 - Brügmann, Bernd
T1 - Investigating the mass-ratio dependence of the prompt-collapse threshold with numerical-relativity simulations
JF - Physical review : D, Particles, fields, gravitation, and cosmology
N2 - The next observing runs of advanced gravitational-wave detectors will lead to a variety of binary neutron star detections and numerous possibilities for multimessenger observations of binary neutron star systems. In this context a clear understanding of the merger process and the possibility of prompt black hole formation after merger is important, as the amount of ejected material strongly depends on the merger dynamics. These dynamics are primarily affected by the total mass of the binary, however, the mass ratio also influences the postmerger evolution. To determine the effect of the mass ratio, we investigate the parameter space around the prompt-collapse threshold with a new set of fully relativistic simulations. The simulations cover three equations of state and seven mass ratios in the range of 1.0 <= q <= 1.75, with five to seven simulations of binary systems of different total mass in each case. The threshold mass is determined through an empirical relation based on the collapse time, which allows us to investigate effects of the mass ratio on the threshold mass and also on the properties of the remnant system. Furthermore, we model effects of mass ratio and equation of state on tidal parameters of threshold configurations.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevD.106.044026
SN - 2470-0010
SN - 2470-0029
VL - 106
IS - 4
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Emma, Mattia
A1 - Schianchi, Federico
A1 - Pannarale, Francesco
A1 - Sagun, Violetta
A1 - Dietrich, Tim
T1 - Numerical simulations of dark matter admixed neutron star binaries
JF - Particles
N2 - Multi-messenger observations of compact binary mergers provide a new way to constrain the nature of dark matter that may accumulate in and around neutron stars. In this article, we extend the infrastructure of our numerical-relativity code BAM to enable the simulation of neutron stars that contain an additional mirror dark matter component. We perform single star tests to verify our code and the first binary neutron star simulations of this kind. We find that the presence of dark matter reduces the lifetime of the merger remnant and favors a prompt collapse to a black hole. Furthermore, we find differences in the merger time for systems with the same total mass and mass ratio, but different amounts of dark matter. Finally, we find that electromagnetic signals produced by the merger of binary neutron stars admixed with dark matter are very unlikely to be as bright as their dark matter-free counterparts. Given the increased sensitivity of multi-messenger facilities, our analysis gives a new perspective on how to probe the presence of dark matter.
KW - numerical relativity
KW - dark matter
KW - neutron stars
KW - equation of state;
KW - gravitational-wave astronomy
KW - multi-messenger astrophysics
Y1 - 2022
U6 - https://doi.org/10.3390/particles5030024
SN - 2571-712X
VL - 5
IS - 3
SP - 273
EP - 286
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Dudi, Reetika
A1 - Adhikari, Ananya
A1 - Brügmann, Bernd
A1 - Dietrich, Tim
A1 - Hayashi, Kota
A1 - Kawaguchi, Kyohei
A1 - Kiuchi, Kenta
A1 - Kyutoku, Koutarou
A1 - Shibata, Masaru
A1 - Tichy, Wolfgang
T1 - Investigating GW190425 with numerical-relativity simulations
JF - Physical review : D, Particles, fields, gravitation, and cosmology
N2 - The third observing run of the LIGO-Virgo Collaboration has resulted in many gravitational wave detections, including the binary neutron star merger GW190425. However, none of these events have been accompanied with an electromagnetic transient found during extensive follow-up searches. In this article, we perform new numerical-relativity simulations of binary neutron star and black hole-neutron star systems that have a chirp mass consistent with GW190425. Assuming that the GW190425's sky location was covered with sufficient accuracy during the electromagnetic follow-up searches, we investigate whether the nondetection of the kilonova is compatible with the source parameters estimated through the gravitational -wave analysis and how one can use this information to place constraints on the properties of the system. Our simulations suggest that GW190425 is incompatible with an unequal mass binary neutron star merger with a mass ratio q < 0.8 when considering stiff or moderately stiff equations of state if the binary was face on and covered by the observation. Our analysis shows that a detailed observational result for kilonovae will be useful to constrain the mass ratio of binary neutron stars in future events.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevD.106.084039
SN - 2470-0010
SN - 2470-0029
VL - 106
IS - 8
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Gieg, Henrique
A1 - Schianchi, Federico
A1 - Dietrich, Tim
A1 - Ujevic, Maximiliano
T1 - Incorporating a Radiative Hydrodynamics Scheme in the Numerical-Relativity Code BAM
JF - Universe : open access journal
N2 - To study binary neutron star systems and to interpret observational data such as gravitational-wave and kilonova signals, one needs an accurate description of the processes that take place during the final stages of the coalescence, for example, through numerical-relativity simulations. In this work, we present an updated version of the numerical-relativity code BAM in order to incorporate nuclear-theory-based equations of state and a simple description of neutrino interactions through a neutrino leakage scheme. Different test simulations, for stars undergoing a neutrino-induced gravitational collapse and for binary neutron stars systems, validate our new implementation. For the binary neutron stars systems, we show that we can evolve stably and accurately distinct microphysical models employing the different equations of state: SFHo, DD2, and the hyperonic BHB Lambda phi. Overall, our test simulations have good agreement with those reported in the literature.
KW - numerical relativity
KW - binary neutron stars
KW - neutrinos
KW - leakage scheme
Y1 - 2022
U6 - https://doi.org/10.3390/universe8070370
SN - 2218-1997
VL - 8
IS - 7
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Ujevic, Maximiliano
A1 - Rashti, Alireza
A1 - Gieg, Henrique Leonhard
A1 - Tichy, Wolfgang
A1 - Dietrich, Tim
T1 - High-accuracy high-mass-ratio simulations for binary neutron stars and their comparison to existing waveform models
JF - Physical review : D, Particles, fields, gravitation, and cosmology
N2 - The subsequent observing runs of the advanced gravitational-wave detector network will likely provide us with various gravitational-wave observations of binary neutron star systems. For an accurate interpretation of these detections, we need reliable gravitational-wave models. To test and to point out how existing models could be improved, we perform a set of high-resolution numerical relativity simulations for four different physical setups with mass ratios q = 1.25, 1.50, 1.75, 2.00, and total gravitational mass M = 2.7 M???. Each configuration is simulated with five different resolutions to allow a proper error assessment. Overall, we find approximately second-order converging results for the dominant (2,2) mode, but also the subdominant (2,1), (3,3), and (4,4) modes, while generally, the convergence order reduces slightly for an increasing mass ratio. Our simulations allow us to validate waveform models, where we find generally good agreement between state-of-the-art models and our data, and to prove that scaling relations for higher modes currently employed for binary black hole waveform modeling also apply for the tidal contribution. Finally, we also test if the current NRTidal model used to describe tidal effects is a valid description for high-mass-ratio systems. We hope that our simulation results can be used to further improve and test waveform models in preparation for the next observing runs.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevD.106.023029
SN - 2470-0010
SN - 2470-0029
VL - 106
IS - 2
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Gerlach, Marius
A1 - Preitschopf, Tobias
A1 - Karaev, Emil
A1 - Quitian-Lara, Heidy Mayerly
A1 - Mayer, Dennis
A1 - Bozek, John
A1 - Fischer, Ingo
A1 - Fink, Reinhold F.
T1 - Auger electron spectroscopy of fulminic acid, HCNO
BT - an experimental and theoretical study
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - HCNO is a molecule of considerable astrochemical interest as a precursor to prebiotic molecules. It is synthesized by preparative pyrolysis and is unstable at room temperature. Here, we investigate its spectroscopy in the soft X-ray regime at the C 1s, N 1s and O 1s edges. All 1s ionization energies are reported and X-ray absorption spectra reveal the transitions from the 1s to the pi* state. Resonant and normal Auger electron spectra for the decay of the core hole states are recorded in a hemispherical analyzer. An assignment of the experimental spectra is provided with the aid of theoretical counterparts. The latter are using a valence configuration interaction representation of the intermediate and final state energies and wavefunctions, the one-center approximation for transition rates and band shapes according to the moment theory. The computed spectra are in very good agreement with the experimental data and most of the relevant bands are assigned. Additionally, we present a simple approach to estimate relative Auger transition rates on the basis of a minimal basis representation of the molecular orbitals. We demonstrate that this provides a qualitatively good and reliable estimate for several signals in the normal and resonant Auger electron spectra which have significantly different intensities in the decay of the three core holes.
Y1 - 2022
U6 - https://doi.org/10.1039/d2cp02104h
SN - 1463-9076
SN - 1463-9084
VL - 24
IS - 25
SP - 15217
EP - 15229
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Poelking, Carl
A1 - Benduhn, Johannes
A1 - Spoltore, Donato
A1 - Schwarze, Martin
A1 - Roland, Steffen
A1 - Piersimoni, Fortunato
A1 - Neher, Dieter
A1 - Leo, Karl
A1 - Vandewal, Koen
A1 - Andrienko, Denis
T1 - Open-circuit voltage of organic solar cells
BT - interfacial roughness makes the difference
JF - Communications physics
N2 - Organic photovoltaics (PV) is an energy-harvesting technology that offers many advantages, such as flexibility, low weight and cost, as well as environmentally benign materials and manufacturing techniques. Despite growth of power conversion efficiencies to around 19 % in the last years, organic PVs still lag behind inorganic PV technologies, mainly due to high losses in open-circuit voltage. Understanding and improving open circuit voltage in organic solar cells is challenging, as it is controlled by the properties of a donor-acceptor interface where the optical excitations are separated into charge carriers. Here, we provide an electrostatic model of a rough donor-acceptor interface and test it experimentally on small molecule PV materials systems. The model provides concise relationships between the open-circuit voltage, photovoltaic gap, charge-transfer state energy, and interfacial morphology. In particular, we show that the electrostatic bias generated across the interface reduces the photovoltaic gap. This negative influence on open-circuit voltage can, however, be circumvented by adjusting the morphology of the donor-acceptor interface.
Organic solar cells, despite their high power conversion efficiencies, suffer from open circuit voltage losses making them less appealing in terms of applications. Here, the authors, supported with experimental data on small molecule photovoltaic cells, relate open circuit voltage to photovoltaic gap, charge-transfer state energy, and donor-acceptor interfacial morphology.
Y1 - 2022
U6 - https://doi.org/10.1038/s42005-022-01084-x
SN - 2399-3650
VL - 5
IS - 1
PB - Nature portfolio
CY - Berlin
ER -
TY - JOUR
A1 - Vollbrecht, Joachim
A1 - Tokmoldin, Nurlan
A1 - Sun, Bowen
A1 - Brus, Viktor V.
A1 - Shoaee, Safa
A1 - Neher, Dieter
T1 - Determination of the charge carrier density in organic solar cells
BT - a tutorial
JF - Journal of applied physics
N2 - The increase in the performance of organic solar cells observed over the past few years has reinvigorated the search for a deeper understanding of the loss and extraction processes in this class of device. A detailed knowledge of the density of free charge carriers under different operating conditions and illumination intensities is a prerequisite to quantify the recombination and extraction dynamics. Differential charging techniques are a promising approach to experimentally obtain the charge carrier density under the aforementioned conditions. In particular, the combination of transient photovoltage and photocurrent as well as impedance and capacitance spectroscopy have been successfully used in past studies to determine the charge carrier density of organic solar cells. In this Tutorial, these experimental techniques will be discussed in detail, highlighting fundamental principles, practical considerations, necessary corrections, advantages, drawbacks, and ultimately their limitations. Relevant references introducing more advanced concepts will be provided as well. Therefore, the present Tutorial might act as an introduction and guideline aimed at new prospective users of these techniques as well as a point of reference for more experienced researchers. Published under an exclusive license by AIP Publishing.
KW - Electrical properties and parameters
KW - Organic semiconductors
KW - Solar cells
KW - Photoconductivity
KW - Capacitance spectroscopy
Y1 - 2022
U6 - https://doi.org/10.1063/5.0094955
SN - 0021-8979
SN - 1089-7550
SN - 1520-8850
VL - 131
IS - 22
PB - American Institute of Physics
CY - Melville, NY
ER -
TY - JOUR
A1 - Sun, Bowen
A1 - Sandberg, Oskar
A1 - Neher, Dieter
A1 - Armin, Ardalan
A1 - Shoaee, Safa
T1 - Wave optics of differential absorption spectroscopy in thick-junction organic solar cells
BT - optical artifacts and correction strategies
JF - Physical review applied / The American Physical Society
N2 - Differential absorption spectroscopy techniques serve as powerful techniques to study the excited species in organic solar cells. However, it has always been challenging to employ these techniques for characterizing thick-junction organic solar cells, especially when a reflective top contact is involved. In this work, we present a detailed and systematic study on how a combination of the presence of the interference effect and a nonuniform charge-distribution profile, severely manipulates experimental spectra and the decay dynamics. Furthermore, we provide a practical methodology to correct these optical artifacts in differential absorption spectroscopies. The results and the proposed correction method generally apply to all kinds of differential absorption spectroscopy techniques and various thin-film systems, such as organics, perovskites, kesterites, and two-dimensional materials. Notably, it is found that the shape of differential absorption spectra can be strongly distorted, starting from 150-nm active-layer thickness; this matches the thickness range of thick-junction organic solar cells and most perovskite solar cells and needs to be carefully considered in experiments. In addition, the decay dynamics of differential absorption spectra is found to be disturbed by optical artifacts under certain conditions. With the help of the proposed correction formalism, differential spectra and the decay dynamics can be characterized on the full device of thin-film solar cells in transmission mode and yield accurate and reliable results to provide design rules for further progress.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevApplied.17.054016
SN - 2331-7019
VL - 17
IS - 5
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Fritsch, Tobias
A1 - Kurpiers, Jona
A1 - Roland, Steffen
A1 - Tokmoldin, Nurlan
A1 - Shoaee, Safa
A1 - Ferron, Thomas
A1 - Collins, Brian A.
A1 - Janietz, Silvia
A1 - Vandewal, Koen
A1 - Neher, Dieter
T1 - On the interplay between CT and singlet exciton emission in organic solar cells with small driving force and its impact on voltage loss
JF - Advanced energy materials
N2 - The interplay between free charge carriers, charge transfer (CT) states and singlet excitons (S-1) determines the recombination pathway and the resulting open circuit voltage (V-OC) of organic solar cells.
By combining a well-aggregated low bandgap polymer with different blend ratios of the fullerenes PCBM and ICBA, the energy of the CT state (E-CT) is varied by 130 meV while leaving the S-1 energy of the polymer (ES1\[{E_{{{\rm{S}}_1}}}\]) unaffected.
It is found that the polymer exciton dominates the radiative properties of the blend when ECT\[{E_{{\rm{CT}}}}\] approaches ES1\[{E_{{{\rm{S}}_1}}}\], while the V-OC remains limited by the non-radiative decay of the CT state.
It is concluded that an increasing strength of the exciton in the optical spectra of organic solar cells will generally decrease the non-radiative voltage loss because it lowers the radiative V-OC limit (V-OC,V-rad), but not because it is more emissive.
The analysis further suggests that electronic coupling between the CT state and the S-1 will not improve the V-OC, but rather reduce the V-OC,V-rad.
It is anticipated that only at very low CT state absorption combined with a fairly high CT radiative efficiency the solar cell benefit from the radiative properties of the singlet excitons.
KW - external quantum efficiency
KW - organic photovoltaics
KW - ternary blends
KW - voltage losses
Y1 - 2022
U6 - https://doi.org/10.1002/aenm.202200641
SN - 1614-6832
SN - 1614-6840
VL - 12
IS - 31
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Vilk, Ohad
A1 - Aghion, Erez
A1 - Nathan, Ran
A1 - Toledo, Sivan
A1 - Metzler, Ralf
A1 - Assaf, Michael
T1 - Classification of anomalous diffusion in animal movement data using power spectral analysis
JF - Journal of physics : A, Mathematical and theoretical
N2 - The field of movement ecology has seen a rapid increase in high-resolution data in recent years, leading to the development of numerous statistical and numerical methods to analyse relocation trajectories. Data are often collected at the level of the individual and for long periods that may encompass a range of behaviours.
Here, we use the power spectral density (PSD) to characterise the random movement patterns of a black-winged kite (Elanus caeruleus) and a white stork (Ciconia ciconia). The tracks are first segmented and clustered into different behaviours (movement modes), and for each mode we measure the PSD and the ageing properties of the process.
For the foraging kite we find 1/f noise, previously reported in ecological systems mainly in the context of population dynamics, but not for movement data. We further suggest plausible models for each of the behavioural modes by comparing both the measured PSD exponents and the distribution of the single-trajectory PSD to known theoretical results and simulations.
KW - diffusion
KW - anomalous diffusion
KW - power spectral analysis
KW - ecological
KW - movement data
Y1 - 2022
U6 - https://doi.org/10.1088/1751-8121/ac7e8f
SN - 1751-8113
SN - 1751-8121
VL - 55
IS - 33
PB - IOP Publishing
CY - Bristol
ER -
TY - JOUR
A1 - Sajedi, Maryam
A1 - Krivenkov, Maxim
A1 - Marchenko, Dmitry
A1 - Sanchez-Barriga, Jaime
A1 - Chandran, Anoop K.
A1 - Varykhalov, Andrei
A1 - Rienks, Emile D. L.
A1 - Aguilera, Irene
A1 - Blügel, Stefan
A1 - Rader, Oliver
T1 - Is there a polaron signature in Angle-Resolved Photoemission of CsPbBr3?
JF - Physical review letters
N2 - The formation of large polarons has been proposed as reason for the high defect tolerance, low mobility, low charge carrier trapping, and low nonradiative recombination rates of lead halide perovskites. Recently, direct evidence for large-polaron formation has been reported from a 50% effective mass enhancement in angle-resolved photoemission of CsPbBr3 over theory for the orthorhombic structure. We present in-depth band dispersion measurements of CsPbBr3 and GW calculations, which lead to similar effective masses at the valence band maximum of 0.203 1 0.016 m0 in experiment and 0.226 m0 in orthorhombic theory. We argue that the effective mass can be explained solely on the basis of electron-electron correlation and largepolaron formation cannot be concluded from photoemission data.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevLett.128.176405
SN - 0031-9007
SN - 1079-7114
VL - 128
IS - 17
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Guo, Yingjie
A1 - Ni, Binbin
A1 - Fu, Song
A1 - Wang, Dedong
A1 - Shprits, Yuri Y.
A1 - Zhelavskaya, Irina
A1 - Feng, Minghang
A1 - Guo, Deyu
T1 - Identification of controlling geomagnetic and solar wind factors for magnetospheric chorus intensity using feature selection techniques
JF - Journal of geophysical research : A, Space physics
N2 - Using over-5-year EMFISIS wave measurements from Van Allen Probes, we present a detailed survey to identify the controlling factors among the geomagnetic indices and solar wind parameters for the 1-min root mean square amplitudes of lower band chorus (LBC) and upper band chorus (UBC).
A set of important features are automatically determined by feature selection techniques, namely, Random Forest and Maximum Relevancy Minimum Redundancy. Our analysis results indicate the AE index with zero-time-delay dominates the intensity evolution of LBC and UBC, consistent with the evidence that chorus waves prefer to occur and amplify during enhanced substorm periods. Regarding solar wind parameters, solar wind speed and IMF B-z are identified as the controlling factors for chorus wave intensity. Using the combination of all these important features, a predictive neural network model of chorus wave intensity is established to reconstruct the temporal variations of chorus wave intensity, for which application of Random Forest produces the overall best performance.
Plain Language Summary
Whistler mode chorus waves are electromagnetic waves observed in the low-density region near the geomagnetic equator outside the plasmapause. The dynamics of Earth's radiation belts are largely influenced by chorus waves owing to their dual contributions to both radiation belt electron acceleration and loss. In this study, we use feature selection techniques to identify the controlling geomagnetic and solar wind factors for magnetospheric chorus waves. Feature selection techniques implement the processes which can select the features most influential to the output.
In this study, the inputs are geomagnetic indices and solar wind parameters and the output is the chorus wave intensity. The results indicate that AE index with zerotime delay dominates the chorus wave intensity. Furthermore, solar wind speed and IMF B-z are identified as the most important solar wind drivers for chorus wave intensity.
On basis of the combination of all these important geomagnetic and solar wind controlling factors, we develop a neural network model of chorus wave intensity, and find that the model with the inputs identified using the Random Forest method produces the overall best performance.
Y1 - 2021
U6 - https://doi.org/10.1029/2021JA029926
SN - 2169-9380
SN - 2169-9402
VL - 127
IS - 1
PB - Wiley
CY - Hoboken, NJ
ER -
TY - JOUR
A1 - Prol, Fabricio S.
A1 - Smirnov, Artem G.
A1 - Hoque, M. Mainul
A1 - Shprits, Yuri Y.
T1 - Combined model of topside ionosphere and plasmasphere derived from radio-occultation and Van Allen Probes data
JF - Scientific reports
N2 - In the last years, electron density profile functions characterized by a linear dependence on the scale height showed good results when approximating the topside ionosphere. The performance above 800 km, however, is not yet well investigated.
This study investigates the capability of the semi-Epstein functions to represent electron density profiles from the peak height up to 20,000 km. Electron density observations recorded by the Van Allen Probes were used to resolve the scale height dependence in the plasmasphere.
It was found that the linear dependence of the scale height in the topside ionosphere cannot be directly used to extrapolate profiles above 800 km.
We find that the dependence of scale heights on altitude is quadratic in the plasmasphere. A statistical model of the scale heights is therefore proposed. After combining the topside ionosphere and plasmasphere by a unified model, we have obtained good estimations not only in the profile shapes, but also in the Total Electron Content magnitude and distributions when compared to actual measurements from 2013, 2014, 2016 and 2017.
Our investigation shows that Van Allen Probes can be merged to radio-occultation data to properly represent the upper ionosphere and plasmasphere by means of a semi-Epstein function.
Y1 - 2022
U6 - https://doi.org/10.1038/s41598-022-13302-1
SN - 2045-2322
VL - 12
IS - 1
PB - Macmillan Publishers Limited, part of Springer Nature
CY - London
ER -
TY - JOUR
A1 - Yuan, Jun
A1 - Zhang, Chujun
A1 - Qiu, Beibei
A1 - Liu, Wei
A1 - So, Shu Kong
A1 - Mainville, Mathieu
A1 - Leclerc, Mario
A1 - Shoaee, Safa
A1 - Neher, Dieter
A1 - Zou, Yingping
T1 - Effects of energetic disorder in bulk heterojunction organic solar cells
JF - Energy & environmental science
N2 - Organic solar cells (OSCs) have progressed rapidly in recent years through the development of novel organic photoactive materials, especially non-fullerene acceptors (NFAs). Consequently, OSCs based on state-of-the-art NFAs have reached significant milestones, such as similar to 19% power conversion efficiencies (PCEs) and small energy losses (less than 0.5 eV). Despite these significant advances, understanding of the interplay between molecular structure and optoelectronic properties lags significantly behind. For example, despite the theoretical framework for describing the energetic disorder being well developed for the case of inorganic semiconductors, the question of the applicability of classical semiconductor theories in analyzing organic semiconductors is still under debate. A general observation in the inorganic field is that inorganic photovoltaic materials possessing a polycrystalline microstructure exhibit suppressed disorder properties and better charge carrier transport compared to their amorphous analogs. Accordingly, this principle extends to the organic semiconductor field as many organic photovoltaic materials are synthesized to pursue polycrystalline-like features. Yet, there appears to be sporadic examples that exhibit an opposite trend. However, full studies decoupling energetic disorder from aggregation effects have largely been left out. Hence, the potential role of the energetic disorder in OSCs has received little attention. Interestingly, recently reported state-of-the-art NFA-based devices could achieve a small energetic disorder and high PCE at the same time; and interest in this investigation related to the disorder properties in OSCs was revived. In this contribution, progress in terms of the correlation between molecular design and energetic disorder is reviewed together with their effects on the optoelectronic mechanism and photovoltaic performance. Finally, the specific challenges and possible solutions in reducing the energetic disorder of OSCs from the viewpoint of materials and devices are proposed.
Y1 - 2022
U6 - https://doi.org/10.1039/d2ee00271j
SN - 1754-5692
SN - 1754-5706
VL - 15
IS - 7
SP - 2806
EP - 2818
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Rashti, Alireza
A1 - Fabbri, Francesco Maria
A1 - Brügmann, Bernd
A1 - Chaurasia, Swami Vivekanandji
A1 - Dietrich, Tim
A1 - Ujevic, Maximiliano
A1 - Tichy, Wolfgang
T1 - New pseudospectral code for the construction of initial data
JF - Physical review D
N2 - Numerical studies of the dynamics of gravitational systems, e.g., black hole-neutron star systems, require physical and constraint-satisfying initial data. In this article, we present the newly developed pseudospectral code ELLIPTICA, an infrastructure for construction of initial data for various binary and single gravitational systems of all kinds. The elliptic equations under consideration are solved on a single spatial hypersurface of the spacetime manifold. Using coordinate maps, the hypersurface is covered by patches whose boundaries can adapt to the surface of the compact objects. To solve elliptic equations with arbitrary boundary condition, ELLIPTICA deploys a Schur complement domain decomposition method with a direct solver. In this version, we use cubed sphere coordinate maps and the fields are expanded using Chebyshev polynomials of the first kind. Here, we explain the building blocks of ELLIPTICA and the initial data construction algorithm for a black hole-neutron star binary system. We perform convergence tests and evolve the data to validate our results. Within our framework, the neutron star can reach spin values close to breakup with arbitrary direction, while the black hole can have arbitrary spin with dimensionless spin magnitude ∼0.8.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevD.105.104027
SN - 2470-0010
SN - 2470-0029
VL - 105
IS - 10
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Kunert, Nina
A1 - Pang, Peter T. H.
A1 - Tews, Ingo
A1 - Coughlin, Michael W.
A1 - Dietrich, Tim
T1 - Quantifying modeling uncertainties when combining multiple gravitational-wave detections from binary neutron star sources
JF - Physical review D
N2 - With the increasing sensitivity of gravitational-wave detectors, we expect to observe multiple binary neutron-star systems through gravitational waves in the near future. The combined analysis of these gravitational-wave signals offers the possibility to constrain the neutron-star radius and the equation of state of dense nuclear matter with unprecedented accuracy. However, it is crucial to ensure that uncertainties inherent in the gravitational-wave models will not lead to systematic biases when information from multiple detections is combined. To quantify waveform systematics, we perform an extensive simulation campaign of binary neutron-star sources and analyze them with a set of four different waveform models. For our analysis with 38 simulations, we find that statistical uncertainties in the neutron-star radius decrease to 1250 m (2% at 90% credible interval) but that systematic differences between currently employed waveform models can be twice as large. Hence, it will be essential to ensure that systematic biases will not become dominant in inferences of the neutron-star equation of state when capitalizing on future developments.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevD.105.L061301
SN - 2470-0010
SN - 2470-0029
VL - 105
IS - 6
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Riese, Josef
A1 - Vogelsang, Christoph
A1 - Schröder, Jan
A1 - Borowski, Andreas
A1 - Kulgemeyer, Christoph
A1 - Reinhold, Peter
A1 - Schecker, Horst
T1 - The development of lesson planning skills in the subject of physics
T1 - Entwicklung von Unterrichtsplanungsfähigkeit im Fach Physik
BT - What influence does professional knowledge have?
BT - Welchen Einfluss hat Professionswissen?
JF - Zeitschrift für Erziehungswissenschaft
N2 - One main goal of university teacher education is the first acquisition of skills for theory-driven lesson planning.
According to models of teachers' professional competence, it is assumed that the acquired professional knowledge represents an essential basis for the development of planning skills.
Learning opportunities to apply this professional knowledge often occur in school internships, usually in advanced semesters of teacher education programs. It is also assumed that practical experience within lesson planning supports the formation of professional knowledge.
However, the relationship between the extent of professional knowledge and the development of skills to plan a lesson lacks evidence. There is a particular challenge in measuring lesson planning skills both authentically and standardized.
To evaluate the mentioned relationship, a longitudinal pre-post-study with prospective physics-teachers (N = 68 in the longitudinal section) was conducted at four German universities. Pre-service physics teachers' skills to plan a lesson were assessed with a standardized performance assessment at the beginning and at the end of a longterm-internship. This assessment consists of planning a physics lesson, conveying Newton's third Law, in a simulated and standardized way with limited time. In addition, content knowledge, pedagogical content knowledge and pedagogical knowledge has been assessed using standardized instruments.
Furthermore, additional information about the internship and the amount of learning opportunities was collected at the end of the internship. During the internship, both lesson planning skills and all components of professional knowledge increased. Cross-Lagged-Panel-Analyses reveal that in particular pre-service teachers' pedagogical content knowledge as well as pedagogical knowledge at the beginning of the internship influences the development of lesson planning skills.
N2 - Im Lehramtsstudium sollen Studierende grundlegende Fähigkeiten zur theoriegeleiteten Unterrichtsplanung erwerben.
In Übereinstimmung mit Modellen zur professionellen Handlungskompetenz von Lehrkräften wird hierbei meist angenommen, dass das im Studienverlauf erworbene Professionswissen eine wesentliche Grundlage für den Aufbau von Fähigkeiten zur Unterrichtsplanung bildet.
Lerngelegenheiten zur Anwendung dieses Professionswissens bieten vor allem schulpraktische Phasen im fortgeschrittenen Studienverlauf. Es wird aber ebenso angenommen, dass gerade Erfahrungen mit der Unterrichtsplanung den Aufbau von Professionswissen unterstützen.
Der Zusammenhang zwischen dem Ausmaß des Professionswissens und der Entwicklung von Planungsfähigkeit ist bisher unzureichend empirisch geklärt. Eine besondere methodische Herausforderung besteht darin, Planungsfähigkeiten sowohl möglichst authentisch als auch auf standardisierte Weise zu erfassen. Zur Untersuchung des genannten Zusammenhangs wurde eine längsschnittliche Studie im Prä-Post-Design bei angehenden Physiklehrkräften (N = 68 im Längsschnitt) an vier Universitäten durchgeführt.
Die Unterrichtsplanungsfähigkeit wurde mit Hilfe eines standardisierten Performanztests vor und nach dem Absolvieren eines Praxissemesters erfasst, indem als Standardsituation der Entwurf einer Unterrichtsstunde zum 3. Newton’schen Axiom unter definierten Zeitvorgaben im Praxissemester simuliert wurde. Zusätzlich wurden das fachliche, fachdidaktische und pädagogische Wissen der Studierenden mit Hilfe standardisierter Instrumente zu beiden Zeitpunkten erhoben, sowie die einschlägigen Lerngelegenheiten im Praxissemester über einen Fragebogen erfasst.
Sowohl für Unterrichtsplanungsfähigkeit als auch für alle Wissensvariablen können Zuwächse im Praxissemester beobachtet werden. Cross-Lagged-Panel-Analysen zeigen, dass insbesondere die Ausprägung des fachdidaktischen und pädagogischen Wissens der Studierenden am Beginn des Praxissemesters die Entwicklung von Unterrichtsplanungsfähigkeit begünstigt.
KW - teacher education
KW - physics
KW - lesson planning
KW - performance assessment
KW - professional knowledge
KW - longitudinal study
KW - Lehrerbildung
KW - Physik
KW - Unterrichtsplanung
KW - Performanztest
KW - Professionswissen
KW - Längsschnittstudie
Y1 - 2022
U6 - https://doi.org/10.1007/s11618-022-01112-0
SN - 1434-663X
SN - 1862-5215
IS - 4
SP - 843
EP - 867
PB - Springer VS/Springer Fachmedien Wiesbaden GmbH
CY - Wiesbaden
ER -
TY - JOUR
A1 - Oskinova, Lida
A1 - Schaerer, Daniel
T1 - Ionization of He II in star-forming galaxies by X-rays from cluster winds and superbubbles
JF - Astronomy and astrophysics : an international weekly journal
N2 - The nature of the sources powering nebular He II emission in star-forming galaxies remains debated, and various types of objects have been considered, including Wolf-Rayet stars, X-ray binaries, and Population III stars.
Modern X-ray observations show the ubiquitous presence of hot gas filling star-forming galaxies. We use a collisional ionization plasma code to compute the specific He II ionizing flux produced by hot gas and show that if its temperature is not too high (less than or similar to 2.5 MK), then the observed levels of soft diffuse X-ray radiation could explain He II ionization in galaxies.
To gain a physical understanding of this result, we propose a model that combines the hydrodynamics of cluster winds and hot superbubbles with observed populations of young massive clusters in galaxies. We find that in low-metallicity galaxies, the temperature of hot gas is lower and the production rate of He II ionizing photons is higher compared to high-metallicity galaxies. The reason is that the slower stellar winds of massive stars in lower-metallicity galaxies input less mechanical energy in the ambient medium.
Furthermore, we show that ensembles of star clusters up to similar to 10-20 Myr old in galaxies can produce enough soft X-rays to induce nebular He II emission. We discuss observations of the template low-metallicity galaxy I Zw 18 and suggest that the He II nebula in this galaxy is powered by a hot superbubble.
Finally, appreciating the complex nature of stellar feedback, we suggest that soft X-rays from hot superbubbles are among the dominant sources of He II ionizing flux in low-metallicity star-forming galaxies.
KW - galaxies
KW - ISM
KW - high-redshift
KW - bubbles
KW - X-rays
Y1 - 2022
U6 - https://doi.org/10.1051/0004-6361/202142520
SN - 0004-6361
SN - 1432-0746
VL - 661
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Sharma, Anjali
A1 - Bekir, Marek
A1 - Lomadze, Nino
A1 - Jung, Se-Hyeong
A1 - Pich, Andrij
A1 - Santer, Svetlana
T1 - Generation of local diffusioosmotic flow by light responsive microgels
JF - Langmuir
N2 - Here we show that microgels trapped at a solid wall can issue liquid flow and transport over distances several times larger than the particle size.
The microgel consists of cross-linked poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-AA) polymer chains loaded with cationic azobenzene-containing surfactant, which can assume either a trans-or a cis-state depending on the wavelength of the applied irradiation. The microgel, being a selective absorber of trans-isomers, responds by changing its volume under irradiation with light of appropriate wavelength at which the cis-isomers of the surfactant molecules diffuse out of the particle interior.
Together with the change in particle size, the expelled cis-isomers form an excess of the concentration and subsequent gradient in osmotic pressure generating a halo of local light-driven diffusioosmotic (l-LDDO) flow. The direction and the strength of the l-LDDO depends on the intensity and irradiation wavelength, as well as on the amount of surfactant absorbed by the microgel.
The flow pattern around a microgel is directed radially outward and can be maintained quasi-indefinitely under exposure to blue light when the trans-/cis-ratio is 2/1, establishing a photostationary state.
Irradiation with UV light, on the other hand, generates a radially transient flow pattern, which inverts from inward to outward over time at low intensities.
By measuring the displacement of tracer particles around neutral microgels during a temperature-induced collapse, we can exclude that a change in particle shape itself causes the flow, i.e., just by expulsion or uptake of water.
Ultimately, it is its ability to selectively absorb two isomers of photosensitive surfactant under different irradiation conditions that leads to an effective pumping caused by a self-induced diffusioosmotic flow.
Y1 - 2022
U6 - https://doi.org/10.1021/acs.langmuir.2c00259
SN - 0743-7463
SN - 1520-5827
VL - 38
IS - 20
SP - 6343
EP - 6351
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Mishurova, Tatiana
A1 - Stegemann, Robert
A1 - Lyamkin, Viktor
A1 - Cabeza, Sandra
A1 - Evsevleev, Sergei
A1 - Pelkner, Matthias
A1 - Bruno, Giovanni
T1 - Subsurface and bulk residual stress analysis of S235JRC+C Steel TIG weld by diffraction and magnetic stray field measurements
JF - Experimental mechanics : an international journal of the Society for Experimental Mechanics
N2 - Background
Due to physical coupling between mechanical stress and magnetization in ferromagnetic materials, it is assumed in the literature that the distribution of the magnetic stray field corresponds to the internal (residual) stress of the specimen.
The correlation is, however, not trivial, since the magnetic stray field is also influenced by the microstructure and the geometry of component.
The understanding of the correlation between residual stress and magnetic stray field could help to evaluate the integrity of welded components.
Objective
This study aims at understanding the possible correlation of subsurface and bulk residual stress with magnetic stray field in a low carbon steel weld.
Methods
The residual stress was determined by synchrotron X-ray diffraction (SXRD, subsurface region) and by neutron diffraction (ND, bulk region).
SXRD possesses a higher spatial resolution than ND. Magnetic stray fields were mapped by utilizing high-spatial-resolution giant magneto resistance (GMR) sensors.
Results
The subsurface residual stress overall correlates better with the magnetic stray field distribution than the bulk stress. This correlation is especially visible in the regions outside the heat affected zone, where the influence of the microstructural features is less pronounced but steep residual stress gradients are present.
Conclusions
It was demonstrated that the localized stray field sources without any obvious microstructural variations are associated with steep stress gradients.
The good correlation between subsurface residual stress and magnetic signal indicates that the source of the magnetic stray fields is to be found in the range of the penetration depth of the SXRD measurements.
KW - residual stress
KW - magnetic stray field
KW - synchrotron X-ray diffraction
KW - neutron diffraction
KW - TIG-welding
Y1 - 2022
U6 - https://doi.org/10.1007/s11340-022-00841-x
SN - 0014-4851
SN - 1741-2765
VL - 62
IS - 6
SP - 1017
EP - 1025
PB - Springer
CY - New York
ER -
TY - JOUR
A1 - Steigert, Alexander
A1 - Kojda, Sandrino Danny
A1 - Ibaceta-Jaña, Josefa Fernanda
A1 - Abou-Ras, Daniel
A1 - Gunder, René
A1 - Alktash, Nivin
A1 - Habicht, Klaus
A1 - Wagner, Markus Raphael
A1 - Klenk, Reiner
A1 - Raoux, Simone
A1 - Szyszka, Bernd
A1 - Lauermann, Iver
A1 - Muydinov, Ruslan
T1 - Water-assisted crystallization of amorphous indium zinc oxide films
JF - Materials today. Communications
N2 - Transparent conductive materials based on indium oxide remain yet irreplaceable in various optoelectronic applications. Amorphous oxides appear especially attractive for technology as they are isotropic, demonstrate relatively high electron mobility and can be processed at low temperatures. Among them is indium zinc oxide (IZO) with a large zinc content that is crucial for keeping the amorphous state but redundant for the doping. In this work we investigated water-free and water containing IZO films obtained by radio frequency sputtering. The correlation between temperature driven changes of the chemical state, the optical and electrical properties as well as the progression of crystallization was in focus. Such characterization methods as: scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, temperature dependent Hall-effect measurements and others were applied. Temperature dependent electrical properties of amorphous IZO and IZO:H2O films were found to evolve similarly. Based on our experience in In2O3:H2O (In2O3:H or IOH) we proposed an explanation for the changes observed. Water admixture was found to decrease crystallization temperature of IZO significantly from similar to 550 degrees C to similar to 280 degrees C. Herewith, the presence and concentration of water and/or hydroxyls was found to determine Zn distribution in the film. In particular, Zn enrichment was detected at the film's surface respective to the high water and/or hydroxyl amount. Raman spectra revealed a two-dimensional crystallization of w-ZnO which precedes regardless water presence an extensive In2O3 crystallization. An abrupt loss of electron mobility as a result of crystallization was attributed to the formation of ZnO interlayer on grain boundaries.
KW - IZO
KW - Thin films
KW - TCOs
KW - Crystallization
KW - Water-assisted crystallization
Y1 - 2022
U6 - https://doi.org/10.1016/j.mtcomm.2022.103213
SN - 2352-4928
VL - 31
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Lepri, Stefano
A1 - Pikovsky, Arkady
T1 - Phase-locking dynamics of heterogeneous oscillator arrays
JF - Chaos, solitons & fractals : applications in science and engineering ; an interdisciplinary journal of nonlinear science
N2 - We consider an array of nearest-neighbor coupled nonlinear autonomous oscillators with quenched ran-dom frequencies and purely conservative coupling. We show that global phase-locked states emerge in finite lattices and study numerically their destruction. Upon change of model parameters, such states are found to become unstable with the generation of localized periodic and chaotic oscillations. For weak nonlinear frequency dispersion, metastability occur akin to the case of almost-conservative systems. We also compare the results with the phase-approximation in which the amplitude dynamics is adiabatically eliminated.
KW - Ginzburg-Landau lattice
KW - Disorder
KW - Localized chaos
KW - Reactive coupling
Y1 - 2022
U6 - https://doi.org/10.1016/j.chaos.2021.111721
SN - 0960-0779
SN - 1873-2887
VL - 155
PB - Elsevier
CY - Oxford
ER -
TY - JOUR
A1 - Dudi, Reetika
A1 - Dietrich, Tim
A1 - Rashti, Alireza
A1 - Brügmann, Bernd
A1 - Steinhoff, Jan
A1 - Tichy, Wolfgang
T1 - High-accuracy simulations of highly spinning binary neutron star systems
JF - Physical review : D, Particles, fields, gravitation, and cosmology
N2 - With an increasing number of expected gravitational-wave detections of binary neutron star mergers, it is essential that gravitational-wave models employed for the analysis of observational data are able to describe generic compact binary systems. This includes systems in which the individual neutron stars are millisecond pulsars for which spin effects become essential. In this work, we perform numerical-relativity simulations of binary neutron stars with aligned and antialigned spins within a range of dimensionless spins of chi similar to [-0.28, 0.58]. The simulations are performed with multiple resolutions, show a clear convergence order and, consequently, can be used to test existing waveform approximants. We find that for very high spins gravitational-wave models that have been employed for the interpretation of GW170817 and GW190425 arc not capable of describing our numerical-relativity dataset. We verify through a full parameter estimation study in which clear biases in the estimate of the tidal deformability and effective spin are present. We hope that in preparation of the next gravitational-wave observing run of the Advanced LIGO and Advanced Virgo detectors our new set of numerical-relativity data can be used to support future developments of new gravitational-wave models.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevD.105.064050
SN - 2470-0010
SN - 2470-0029
VL - 105
IS - 6
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Smirnov, Artem
A1 - Shprits, Yuri Y.
A1 - Allison, Hayley
A1 - Aseev, Nikita
A1 - Drozdov, Alexander
A1 - Kollmann, Peter
A1 - Wang, Dedong
A1 - Saikin, Anthony
T1 - An empirical model of the equatorial electron pitch angle distributions in earth's outer radiation belt
JF - Space Weather: the International Journal of Research and Applications
N2 - In this study, we present an empirical model of the equatorial electron pitch angle distributions (PADs) in the outer radiation belt based on the full data set collected by the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard the Van Allen Probes in 2012-2019. The PADs are fitted with a combination of the first, third and fifth sine harmonics. The resulting equation resolves all PAD types found in the outer radiation belt (pancake, flat-top, butterfly and cap PADs) and can be analytically integrated to derive omnidirectional flux. We introduce a two-step modeling procedure that for the first time ensures a continuous dependence on L, magnetic local time and activity, parametrized by the solar wind dynamic pressure. We propose two methods to reconstruct equatorial electron flux using the model. The first approach requires two uni-directional flux observations and is applicable to low-PA data. The second method can be used to reconstruct the full equatorial PADs from a single uni- or omnidirectional measurement at off-equatorial latitudes. The model can be used for converting the long-term data sets of electron fluxes to phase space density in terms of adiabatic invariants, for physics-based modeling in the form of boundary conditions, and for data assimilation purposes.
KW - pitch angle
KW - radiation belt
KW - model
KW - magnetosphere
KW - van allen probes;
KW - electrons
Y1 - 2022
U6 - https://doi.org/10.1029/2022SW003053
SN - 1542-7390
VL - 20
IS - 9
PB - American Geophysical Union
CY - Washington, DC
ER -
TY - JOUR
A1 - Mayer, Dennis
A1 - Lever, Fabiano
A1 - Picconi, David
A1 - Metje, Jan
A1 - Ališauskas, Skirmantas
A1 - Calegari, Francesca
A1 - Düsterer, Stefan
A1 - Ehlert, Christopher
A1 - Feifel, Raimund
A1 - Niebuhr, Mario
A1 - Manschwetus, Bastian
A1 - Kuhlmann, Marion
A1 - Mazza, Tommaso
A1 - Robinson, Matthew Scott
A1 - Squibb, Richard J.
A1 - Trabattoni, Andrea
A1 - Wallner, Måns
A1 - Saalfrank, Peter
A1 - Wolf, Thomas J. A.
A1 - Gühr, Markus
T1 - Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy
JF - Nature communications
N2 - Imaging the charge flow in photoexcited molecules would provide key information on photophysical and photochemical processes. Here the authors demonstrate tracking in real time after photoexcitation the change in charge density at a specific site of 2-thiouracil using time-resolved X-ray photoelectron spectroscopy. The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220-250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-021-27908-y
SN - 2041-1723
N1 - Publisher correction: https://doi.org/10.1038/s41467-022-28584-2
VL - 13
IS - 1
PB - Nature Research
CY - Berlin
ER -
TY - JOUR
A1 - Mayer, Dennis
A1 - Lever, Fabiano
A1 - Picconi, David
A1 - Metje, Jan
A1 - Ališauskas, Skirmantas
A1 - Calegari, Francesca
A1 - Düsterer, Stefan
A1 - Ehlert, Christopher
A1 - Feifel, Raimund
A1 - Niebuhr, Mario
A1 - Manschwetus, Bastian
A1 - Kuhlmann, Marion
A1 - Mazza, Tommaso
A1 - Robinson, Matthew Scott
A1 - Squibb, Richard James
A1 - Trabattoni, Andrea
A1 - Wallner, Måns
A1 - Saalfrank, Peter
A1 - Wolf, Thomas J. A.
A1 - Gühr, Markus
T1 - Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy
JF - Nature Communications
N2 - The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220–250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-021-27908-y
SN - 2041-1723
N1 - These authors contributed equally: D. Mayer, F. Lever.
A Publisher Correction to this article was published on 09 March 2022.
This article has been updated.
VL - 13
PB - Springer Nature
CY - Berlin
ER -
TY - JOUR
A1 - Liu, Ji-Cai
A1 - Ignatova, Nina
A1 - Kimberg, Victor
A1 - Krasnov, Pavel
A1 - Föhlisch, Alexander
A1 - Simon, Marc
A1 - Gel'mukhanov, Faris
T1 - Time-resolved study of recoil-induced rotation by X-ray pump - X-ray probe spectroscopy
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Modern stationary X-ray spectroscopy is unable to resolve rotational structure.
In the present paper, we propose to use time-resolved two color X-ray pump-probe spectroscopy with picosecond resolution for real-time monitoring of the rotational dynamics induced by the recoil effect.
The proposed technique consists of two steps.
The first short pump X-ray pulse ionizes the valence electron, which transfers angular momentum to the molecule.
The second time-delayed short probe X-ray pulse resonantly excites a 1s electron to the created valence hole.
Due to the recoil-induced angular momentum the molecule rotates and changes the orientation of transition dipole moment of core-excitation with respect to the transition dipole moment of the valence ionization, which results in a temporal modulation of the probe X-ray absorption as a function of the delay time between the pulses.
We developed an accurate theory of the X-ray pump-probe spectroscopy of the recoil-induced rotation and study how the energy of the photoelectron and thermal dephasing affect the structure of the time-dependent X-ray absorption using the CO molecule as a case-study.
We also discuss the feasibility of experimental observation of our theoretical findings, opening new perspectives in studies of molecular rotational dynamics.
Y1 - 2022
U6 - https://doi.org/10.1039/d1cp05000a
SN - 1463-9076
SN - 1463-9084
VL - 24
IS - 11
SP - 6627
EP - 6638
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Voroshnin, Vladimir
A1 - Tarasov, Artem V.
A1 - Bokai, Kirill A.
A1 - Chikina, Alla
A1 - Senkovskiy, Boris V.
A1 - Ehlen, Niels
A1 - Usachov, Dmitry Yu.
A1 - Gruneis, Alexander
A1 - Krivenkov, Maxim
A1 - Sanchez-Barriga, Jaime
A1 - Fedorov, Alexander
T1 - Direct spectroscopic evidence of magnetic proximity effect in MoS2 monolayer on graphene/Co
JF - ACS nano
N2 - A magnetic field modifies optical properties and provides valley splitting in a molybdenum disulfide (MoS2) monolayer.
Here we demonstrate a scalable approach to the epitaxial synthesis of MoS2 monolayer on a magnetic graphene/Co system.
Using spin- and angle-resolved photoemission spectroscopy we observe a magnetic proximity effect that causes a 20 meV spin-splitting at the (Gamma) over bar point and canting of spins at the (K) over bar point in the valence band toward the in-plane direction of cobalt magnetization.
Our density functional theory calculations reveal that the in-plane spin component at (K) over bar is localized on Co atoms in the valence band, while in the conduction band it is localized on the MoS2 layer.
The calculations also predict a 16 meV spin-splitting at the (Gamma) over bar point and 8 meV (K) over bar-(K) over bar' valley asymmetry for an out-of-plane magnetization. These findings suggest control over optical transitions in MoS2 via Co magnetization. Our estimations show that the magnetic proximity effect is equivalent to the action of the magnetic field as large as 100 T.
KW - magnetic proximity effect
KW - MoS2
KW - monolayer
KW - graphene
KW - spin-resolved
KW - ARPES
Y1 - 2022
U6 - https://doi.org/10.1021/acsnano.1c10391
SN - 1936-0851
SN - 1936-086X
VL - 16
IS - 5
SP - 7448
EP - 7456
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Abiuso, Paolo
A1 - Holubec, Viktor
A1 - Anders, Janet
A1 - Ye, Zhuolin
A1 - Cerisola, Federico
A1 - Perarnau-Llobet, Marti
T1 - Thermodynamics and optimal protocols of multidimensional quadratic Brownian systems
JF - Journal of physics communications
N2 - We characterize finite-time thermodynamic processes of multidimensional quadratic overdamped systems.
Analytic expressions are provided for heat, work, and dissipation for any evolution of the system covariance matrix.
The Bures-Wasserstein metric between covariance matrices naturally emerges as the local quantifier of dissipation.
General principles of how to apply these geometric tools to identify optimal protocols are discussed.
Focusing on the relevant slow-driving limit, we show how these results can be used to analyze cases in which the experimental control over the system is partial.
KW - stochastic thermodynamics
KW - thermodynamic control
KW - thermodynamic length
KW - overdamped brownian systems
Y1 - 2022
U6 - https://doi.org/10.1088/2399-6528/ac72f8
SN - 2399-6528
VL - 6
IS - 6
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Stojkoski, Viktor
A1 - Sandev, Trifce
A1 - Kocarev, Ljupco
A1 - Pal, Arnab
T1 - Autocorrelation functions and ergodicity in diffusion with stochastic resetting
JF - Journal of physics : A, Mathematical and theoretical
N2 - Diffusion with stochastic resetting is a paradigm of resetting processes. Standard renewal or master equation approach are typically used to study steady state and other transport properties such as average, mean squared displacement etc.
What remains less explored is the two time point correlation functions whose evaluation is often daunting since it requires the implementation of the exact time dependent probability density functions of the resetting processes which are unknown for most of the problems.
We adopt a different approach that allows us to write a stochastic solution for a single trajectory undergoing resetting.
Moments and the autocorrelation functions between any two times along the trajectory can then be computed directly using the laws of total expectation. Estimation of autocorrelation functions turns out to be pivotal for investigating the ergodic properties of various observables for this canonical model.
In particular, we investigate two observables (i) sample mean which is widely used in economics and (ii) time-averaged-mean-squared-displacement (TAMSD) which is of acute interest in physics.
We find that both diffusion and drift-diffusion processes with resetting are ergodic at the mean level unlike their reset-free counterparts. In contrast, resetting renders ergodicity breaking in the TAMSD while both the stochastic processes are ergodic when resetting is absent. We quantify these behaviors with detailed analytical study and corroborate with extensive numerical simulations.
Our results can be verified in experimental set-ups that can track single particle trajectories and thus have strong implications in understanding the physics of resetting.
KW - autocorrelations
KW - ergodicity
KW - diffusion
KW - stochastic resetting
Y1 - 2022
U6 - https://doi.org/10.1088/1751-8121/ac4ce9
SN - 1751-8113
SN - 1751-8121
VL - 55
IS - 10
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Adolfs, Marjolijn
A1 - Hoque, Mohammed Mainul
A1 - Shprits, Yuri Y.
T1 - Storm-time relative total electron content modelling using machine learning techniques
JF - Remote sensing
N2 - Accurately predicting total electron content (TEC) during geomagnetic storms is still a challenging task for ionospheric models. In this work, a neural-network (NN)-based model is proposed which predicts relative TEC with respect to the preceding 27-day median TEC, during storm time for the European region (with longitudes 30 degrees W-50 degrees E and latitudes 32.5 degrees N-70 degrees N). The 27-day median TEC (referred to as median TEC), latitude, longitude, universal time, storm time, solar radio flux index F10.7, global storm index SYM-H and geomagnetic activity index Hp30 are used as inputs and the output of the network is the relative TEC. The relative TEC can be converted to the actual TEC knowing the median TEC. The median TEC is calculated at each grid point over the European region considering data from the last 27 days before the storm using global ionosphere maps (GIMs) from international GNSS service (IGS) sources. A storm event is defined when the storm time disturbance index Dst drops below 50 nanotesla. The model was trained with storm-time relative TEC data from the time period of 1998 until 2019 (2015 is excluded) and contains 365 storms. Unseen storm data from 33 storm events during 2015 and 2020 were used to test the model. The UQRG GIMs were used because of their high temporal resolution (15 min) compared to other products from different analysis centers. The NN-based model predictions show the seasonal behavior of the storms including positive and negative storm phases during winter and summer, respectively, and show a mixture of both phases during equinoxes. The model's performance was also compared with the Neustrelitz TEC model (NTCM) and the NN-based quiet-time TEC model, both developed at the German Aerospace Agency (DLR). The storm model has a root mean squared error (RMSE) of 3.38 TEC units (TECU), which is an improvement by 1.87 TECU compared to the NTCM, where an RMSE of 5.25 TECU was found. This improvement corresponds to a performance increase by 35.6%. The storm-time model outperforms the quiet-time model by 1.34 TECU, which corresponds to a performance increase by 28.4% from 4.72 to 3.38 TECU. The quiet-time model was trained with Carrington averaged TEC and, therefore, is ideal to be used as an input instead of the GIM derived 27-day median. We found an improvement by 0.8 TECU which corresponds to a performance increase by 17% from 4.72 to 3.92 TECU for the storm-time model using the quiet-time-model predicted TEC as an input compared to solely using the quiet-time model.
KW - ionosphere
KW - relative total electron content
KW - geomagnetic storms
KW - neural
KW - networks
KW - NTCM
KW - European storm-time model
Y1 - 2022
U6 - https://doi.org/10.3390/rs14236155
SN - 2072-4292
VL - 14
IS - 23
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Walker, Simon N.
A1 - Boynton, Richard J.
A1 - Shprits, Yuri Y.
A1 - Balikhin, Michael A.
A1 - Drozdov, Alexander
T1 - Forecast of the energetic electron environment of the radiation belts
JF - Space Weather: The International Journal of Research and Applications
N2 - Different modeling methodologies possess different strengths and weakness. For instance, data based models may provide superior accuracy but have a limited spatial coverage while physics based models may provide lower accuracy but provide greater spatial coverage. This study investigates the coupling of a data based model of the electron fluxes at geostationary orbit (GEO) with a numerical model of the radiation belt region to improve the resulting forecasts/pastcasts of electron fluxes over the whole radiation belt region. In particular, two coupling methods are investigated. The first assumes an average value for L* for GEO, namely LGEO* L-GEO* = 6.2. The second uses a value of L* that varies with geomagnetic activity, quantified using the Kp index. As the terrestrial magnetic field responds to variations in geomagnetic activity, the value of L* will vary for a specific location. In this coupling method, the value of L* is calculated using the Kp driven Tsyganenko 89c magnetic field model for field line tracing. It is shown that this addition can result in changes in the initialization of the parameters at the Versatile Electron Radiation Belt model outer boundary. Model outputs are compared to Van Allen Probes MagEIS measurements of the electron fluxes in the inner magnetosphere for the March 2015 geomagnetic storm. It is found that the fixed LGEO* L-GEO* coupling method produces a more realistic forecast.
KW - radiation belt forecasts
KW - data based NARMAX modeling
KW - verb simulations;
KW - geostationary orbit
KW - electron flux forecasts
Y1 - 2022
U6 - https://doi.org/10.1029/2022SW003124
SN - 1542-7390
VL - 20
IS - 12
PB - American Geophysical Union
CY - Washington
ER -
TY - JOUR
A1 - Haas, Bernhard
A1 - Shprits, Yuri Y.
A1 - Allison, Hayley
A1 - Wutzig, Michael
A1 - Wang, Dedong
T1 - Which parameter controls ring current electron dynamics
JF - Frontiers in astronomy and space sciences
N2 - Predicting the electron population of Earth's ring current during geomagnetic storms still remains a challenging task.
In this work, we investigate the sensitivity of 10 keV ring current electrons to different driving processes, parameterised by the Kp index, during several moderate and intense storms.
Results are validated against measurements from the Van Allen Probes satellites. Perturbing the Kp index allows us to identify the most dominant processes for moderate and intense storms respectively.
We find that during moderate storms (Kp < 6) the drift velocities mostly control the behaviour of low energy electrons, while loss from wave-particle interactions is the most critical parameter for quantifying the evolution of intense storms (Kp > 6). Perturbations of the Kp index used to drive the boundary conditions at GEO and set the plasmapause location only show a minimal effect on simulation results over a limited L range.
It is further shown that the flux at L & SIM; 3 is more sensitive to changes in the Kp index compared to higher L shells, making it a good proxy for validating the source-loss balance of a ring current model.
KW - ring current
KW - magnetosphere
KW - electron lifetimes
KW - electrons
KW - van allen probes (RBSP)
KW - ring current model
KW - verb
Y1 - 2022
U6 - https://doi.org/10.3389/fspas.2022.911002
SN - 2296-987X
VL - 9
PB - Frontiers Media
CY - Lausanne
ER -
TY - JOUR
A1 - Zeuschner, Steffen Peer
A1 - Wang, Xi-Guang
A1 - Deb, Marwan
A1 - Popova, Elena
A1 - Malinowski, Gregory
A1 - Hehn, Michel
A1 - Keller, Niels
A1 - Berakdar, Jamal
A1 - Bargheer, Matias
T1 - Standing spin wave excitation in Bi
BT - YIG films via temperature-induced anisotropy changes and magneto-elastic coupling
JF - Physical review : B, Condensed matter and materials physics
N2 - Based on micromagnetic simulations and experimental observations of the magnetization and lattice dynamics after the direct optical excitation of the magnetic insulator Bi : YIG or indirect excitation via an optically opaque Pt/Cu double layer, we disentangle the dynamical effects of magnetic anisotropy and magneto-elastic coupling. The strain and temperature of the lattice are quantified via modeling ultrafast x-ray diffraction data. Measurements of the time-resolved magneto-optical Kerr effect agree well with the magnetization dynamics simulated according to the excitation via two mechanisms: the magneto-elastic coupling to the experimentally verified strain dynamics and the ultrafast temperature-induced transient change in the magnetic anisotropy. The numerical modeling proves that, for direct excitation, both mechanisms drive the fundamental mode with opposite phase. The relative ratio of standing spin wave amplitudes of higher-order modes indicates that both mechanisms are substantially active.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevB.106.134401
SN - 2469-9950
SN - 2469-9969
VL - 106
IS - 13
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Padash, Amin
A1 - Aghion, Erez
A1 - Schulz, Alexander
A1 - Barkai, Eli
A1 - Chechkin, Aleksei V.
A1 - Metzler, Ralf
A1 - Kantz, Holger
T1 - Local equilibrium properties of ultraslow diffusion in the Sinai model
JF - New journal of physics
N2 - We perform numerical studies of a thermally driven, overdamped particle in a random quenched force field, known as the Sinai model. We compare the unbounded motion on an infinite 1-dimensional domain to the motion in bounded domains with reflecting boundaries and show that the unbounded motion is at every time close to the equilibrium state of a finite system of growing size. This is due to time scale separation: inside wells of the random potential, there is relatively fast equilibration, while the motion across major potential barriers is ultraslow. Quantities studied by us are the time dependent mean squared displacement, the time dependent mean energy of an ensemble of particles, and the time dependent entropy of the probability distribution. Using a very fast numerical algorithm, we can explore times up top 10(17) steps and thereby also study finite-time crossover phenomena.
KW - Sinai diffusion
KW - clustering
KW - local equilibrium
Y1 - 2022
U6 - https://doi.org/10.1088/1367-2630/ac7df8
SN - 1367-2630
VL - 24
IS - 7
PB - IOP Publishing
CY - Bristol
ER -
TY - JOUR
A1 - McKenna, Russell
A1 - Pfenninger, Stefan
A1 - Heinrichs, Heidi
A1 - Schmidt, Johannes
A1 - Staffell, Iain
A1 - Bauer, Christian
A1 - Gruber, Katharina
A1 - Hahmann, Andrea N.
A1 - Jansen, Malte
A1 - Klingler, Michael
A1 - Landwehr, Natascha
A1 - Larsén, Xiaoli Guo
A1 - Lilliestam, Johan
A1 - Pickering, Bryn
A1 - Robinius, Martin
A1 - Tröndle, Tim
A1 - Turkovska, Olga
A1 - Wehrle, Sebastian
A1 - Weinand, Jann Michael
A1 - Wohland, Jan
T1 - High-resolution large-scale onshore wind energy assessments
BT - a review of potential definitions, methodologies and future research needs
JF - Renewable energy
N2 - The rapid uptake of renewable energy technologies in recent decades has increased the demand of energy researchers, policymakers and energy planners for reliable data on the spatial distribution of their costs and potentials. For onshore wind energy this has resulted in an active research field devoted to analysing these resources for regions, countries or globally. A particular thread of this research attempts to go beyond purely technical or spatial restrictions and determine the realistic, feasible or actual potential for wind energy. Motivated by these developments, this paper reviews methods and assumptions for analysing geographical, technical, economic and, finally, feasible onshore wind potentials. We address each of these potentials in turn, including aspects related to land eligibility criteria, energy meteorology, and technical developments of wind turbine characteristics such as power density, specific rotor power and spacing aspects. Economic aspects of potential assessments are central to future deployment and are discussed on a turbine and system level covering levelized costs depending on locations, and the system integration costs which are often overlooked in such analyses. Non-technical approaches include scenicness assessments of the landscape, constraints due to regulation or public opposition, expert and stakeholder workshops, willingness to pay/accept elicitations and socioeconomic cost-benefit studies. For each of these different potential estimations, the state of the art is critically discussed, with an attempt to derive best practice recommendations and highlight avenues for future research.
KW - onshore wind
KW - resource assessments
KW - social acceptance
KW - planning constraints
KW - research priorities
Y1 - 2022
U6 - https://doi.org/10.1016/j.renene.2021.10.027
SN - 0960-1481
VL - 182
SP - 659
EP - 684
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Born, Artur
A1 - Johansson, Fredrik O. L.
A1 - Leitner, Torsten
A1 - Bidermane, Ieva
A1 - Kuehn, Danilo
A1 - Martensson, Nils
A1 - Föhlisch, Alexander
T1 - The degree of electron itinerancy and shell closing in the core-ionized state of transition metals probed by Auger-photoelectron coincidence spectroscopy
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Auger-photoelectron coincidence spectroscopy (APECS) has been used to examine the electron correlation and itinerance effects in transition metals Cu, Ni and Co.
It is shown that the LVV Auger, in coincidence with 2p photoelectrons, spectra can be represented using atomic multiplet positions if the 3d-shell is localized (atomic-like) and with a self-convoluted valence band for band-like (itinerant) materials as explained using the Cini-Sawatzky model.
For transition metals, the 3d band changes from band-like to localized with increasing atomic number, with the possibility of a mixed behavior.
Our result shows that the LVV spectra of Cu can be represented by atomic multiplet calculations, those of Co resemble the self-convolution of the valence band and those of Ni are a mixture of both, consistent with the Cini-Sawatzky model.
KW - spectra
KW - Ni
Y1 - 2022
U6 - https://doi.org/10.1039/d2cp02477b
SN - 1463-9076
SN - 1463-9084
VL - 24
IS - 32
SP - 19218
EP - 19222
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Kroh, Daniel
A1 - Eller, Fabian
A1 - Schötz, Konstantin
A1 - Wedler, Stefan
A1 - Perdigón-Toro, Lorena
A1 - Freychet, Guillaume
A1 - Wei, Qingya
A1 - Dörr, Maximilian
A1 - Jones, David
A1 - Zou, Yingping
A1 - Herzig, Eva M.
A1 - Neher, Dieter
A1 - Köhler, Anna
T1 - Identifying the signatures of intermolecular interactions in blends of PM6 with Y6 and N4 using absorption spectroscopy
JF - Advanced functional materials
N2 - In organic solar cells, the resulting device efficiency depends strongly on the local morphology and intermolecular interactions of the blend film. Optical spectroscopy was used to identify the spectral signatures of interacting chromophores in blend films of the donor polymer PM6 with two state-of-the-art nonfullerene acceptors, Y6 and N4, which differ merely in the branching point of the side chain. From temperature-dependent absorption and luminescence spectroscopy in solution, it is inferred that both acceptor materials form two types of aggregates that differ in their interaction energy. Y6 forms an aggregate with a predominant J-type character in solution, while for N4 molecules the interaction is predominantly in a H-like manner in solution and freshly spin-cast film, yet the molecules reorient with respect to each other with time or thermal annealing to adopt a more J-type interaction. The different aggregation behavior of the acceptor materials is also reflected in the blend films and accounts for the different solar cell efficiencies reported with the two blends.
KW - charge-transfer states
KW - Frank-Condon analysis
KW - morphology
KW - organic solar cells
Y1 - 2022
U6 - https://doi.org/10.1002/adfm.202205711
SN - 1616-301X
SN - 1616-3028
VL - 32
IS - 44
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Tockhorn, Philipp
A1 - Sutter, Johannes
A1 - Cruz Bournazou, Alexandros
A1 - Wagner, Philipp
A1 - Jäger, Klaus
A1 - Yoo, Danbi
A1 - Lang, Felix
A1 - Grischek, Max
A1 - Li, Bor
A1 - Li, Jinzhao
A1 - Shargaieva, Oleksandra
A1 - Unger, Eva
A1 - Al-Ashouri, Amran
A1 - Köhnen, Eike
A1 - Stolterfoht, Martin
A1 - Neher, Dieter
A1 - Schlatmann, Rutger
A1 - Rech, Bernd
A1 - Stannowski, Bernd
A1 - Albrecht, Steve
A1 - Becker, Christiane
T1 - Nano-optical designs for high-efficiency monolithic perovskite-silicon tandem solar cells
JF - Nature nanotechnology
N2 - Designing gentle sinusoidal nanotextures enables the realization of high-efficiency perovskite-silicon solar cells
Perovskite-silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite-silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%.
Y1 - 2022
U6 - https://doi.org/10.1038/s41565-022-01228-8
SN - 1748-3387
SN - 1748-3395
VL - 17
IS - 11
SP - 1214
EP - 1221
PB - Nature Publishing Group
CY - London [u.a.]
ER -
TY - JOUR
A1 - Stolterfoht, Martin
A1 - Lang, Felix
T1 - All-perovskite tandems get flexible
JF - Nature energy
N2 - Flexible all-perovskite tandem photovoltaics open up new opportunities for application compared to rigid devices, yet their performance lags behind. Now, researchers show that molecule-bridged interfaces mitigate charge recombination and crack formation, improving the efficiency and mechanical reliability of flexible devices.
Y1 - 2022
U6 - https://doi.org/10.1038/s41560-022-01087-6
SN - 2058-7546
VL - 7
IS - 8
SP - 688
EP - 689
PB - Nature Publishing Group
CY - London
ER -
TY - JOUR
A1 - Kaa, Johannes M.
A1 - Sternemann, Christian
A1 - Appel, Karen
A1 - Cerantola, Valerio
A1 - Preston, Thomas R.
A1 - Albers, Christian
A1 - Elbers, Mirko
A1 - Libon, Lelia
A1 - Makita, Mikako
A1 - Pelka, Alexander
A1 - Petitgirard, Sylvain
A1 - Plückthun, Christian
A1 - Roddatis, Vladimir
A1 - Sahle, Christoph J.
A1 - Spiekermann, Georg
A1 - Schmidt, Christian
A1 - Schreiber, Anja
A1 - Sakrowski, Robin
A1 - Tolan, Metin
A1 - Wilke, Max
A1 - Zastrau, Ulf
A1 - Konopkova, Zuzana
T1 - Structural and electron spin state changes in an x-ray heated iron carbonate system at the Earth's lower mantle pressures
JF - Physical review research
N2 - The determination of the spin state of iron-bearing compounds at high pressure and temperature is crucial for our understanding of chemical and physical properties of the deep Earth. Studies on the relationship between the coordination of iron and its electronic spin structure in iron-bearing oxides, silicates, carbonates, iron alloys, and other minerals found in the Earth's mantle and core are scarce because of the technical challenges to simultaneously probe the sample at high pressures and temperatures. We used the unique properties of a pulsed and highly brilliant x-ray free electron laser (XFEL) beam at the High Energy Density (HED) instrument of the European XFEL to x-ray heat and probe samples contained in a diamond anvil cell. We heated and probed with the same x-ray pulse train and simultaneously measured x-ray emission and x-ray diffraction of an FeCO3 sample at a pressure of 51 GPa with up to melting temperatures. We collected spin state sensitive Fe K beta(1,3) fluorescence spectra and detected the sample's structural changes via diffraction, observing the inverse volume collapse across the spin transition. During x-ray heating, the carbonate transforms into orthorhombic Fe4C3O12 and iron oxides. Incipient melting was also observed. This approach to collect information about the electronic state and structural changes from samples contained in a diamond anvil cell at melting temperatures and above will considerably improve our understanding of the structure and dynamics of planetary and exoplanetary interiors.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevResearch.4.033042
SN - 2643-1564
VL - 4
IS - 3
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Shayduk, Roman
A1 - Hallmann, Jörg
A1 - Rodriguez-Fernandez, Angel
A1 - Scholz, Markus
A1 - Lu, Wei
A1 - Bösenberg, Ulrike
A1 - Möller, Johannes
A1 - Zozulya, Alexey
A1 - Jiang, Man
A1 - Wegner, Ulrike
A1 - Secareanu, Radu-Costin
A1 - Palmer, Guido
A1 - Emons, Moritz
A1 - Lederer, Max
A1 - Volkov, Sergey
A1 - Lindfors-Vrejoiu, Ionela
A1 - Schick, Daniel
A1 - Herzog, Marc
A1 - Bargheer, Matias
A1 - Madsen, Anders
T1 - Femtosecond x-ray diffraction study of multi-THz coherent phonons in SrTiO3
JF - Applied physics letters
N2 - We report generation of ultra-broadband longitudinal acoustic coherent phonon wavepackets in SrTiO3 (STO) with frequency components extending throughout the first Brillouin zone. The wavepackets are efficiently generated in STO using femtosecond infrared laser excitation of an atomically flat 1.6 nm-thick epitaxial SrRuO3 film. We use femtosecond x-ray diffraction at the European X-Ray Free Electron Laser Facility to study the dispersion and damping of phonon wavepackets. The experimentally determined damping constants for multi-THz frequency phonons compare favorably to the extrapolation of a simple ultrasound damping model over several orders of magnitude.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0083256
SN - 0003-6951
SN - 1077-3118
VL - 120
IS - 20
PB - AIP Publishing
CY - Melville
ER -
TY - JOUR
A1 - Deb, Marwan
A1 - Popova, Elena
A1 - Jaffrès, Henri-Yves
A1 - Keller, Niels
A1 - Bargheer, Matias
T1 - Polarization-dependent subpicosecond demagnetization in iron garnets
JF - Physical review : B, covering condensed matter and materials physics
N2 - Controlling the magnetization dynamics at the fastest speed is a major issue of fundamental condensed matter physics and its applications for data storage and processing technologies. It requires a deep understanding of the interactions between the degrees of freedom in solids, such as spin, electron, and lattice as well as their responses to external stimuli. In this paper, we systematically investigate the fluence dependence of ultrafast magnetization dynamics induced by below-bandgap ultrashort laser pulses in the ferrimagnetic insulators BixY3-xFe5O12 with 1 xBi 3. We demonstrate subpicosecond demagnetization dynamics in this material followed by a very slow remagnetization process. We prove that this demagnetization results from an ultrafast heating of iron garnets by two-photon absorption (TPA), suggesting a phonon-magnon thermalization time of 0.6 ps. We explain the slow remagnetization timescale by the low phonon heat conductivity in garnets. Additionally, we show that the amplitudes of the demagnetization, optical change, and lattice strain can be manipulated by changing the ellipticity of the pump pulses. We explain this phenomenon considering the TPA circular dichroism. These findings open exciting prospects for ultrafast manipulation of spin, charge, and lattice dynamics in magnetic insulators by ultrafast nonlinear optics.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevB.106.184416
SN - 2469-9950
SN - 2469-9969
VL - 106
IS - 18
PB - American Institute of Physics, American Physical Society
CY - Woodbury, NY
ER -
TY - JOUR
A1 - Deb, Marwan
A1 - Popova, Elena
A1 - Jaffrès, Henri-Yves
A1 - Keller, Niels
A1 - Bargheer, Matias
T1 - Controlling high-frequency spin-wave dynamics using double-pulse laser excitation
JF - Physical review applied
N2 - Manipulating spin waves is highly required for the development of innovative data transport and processing technologies. Recently, the possibility of triggering high-frequency standing spin waves in magnetic insulators using femtosecond laser pulses was discovered, raising the question about how one can manipulate their dynamics. Here we explore this question by investigating the ultrafast magnetiza-tion and spin-wave dynamics induced by double-pulse laser excitation. We demonstrate a suppression or enhancement of the amplitudes of the standing spin waves by precisely tuning the time delay between the two pulses. The results can be understood as the constructive or destructive interference of the spin waves induced by the first and second laser pulses. Our findings open exciting perspectives towards generating single-mode standing spin waves that combine high frequency with large amplitude and low magnetic damping.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevApplied.18.044001
SN - 2331-7019
VL - 18
IS - 4
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Perdigón-Toro, Lorena
A1 - Le Quang Phuong,
A1 - Eller, Fabian
A1 - Freychet, Guillaume
A1 - Saglamkaya, Elifnaz
A1 - Khan, Jafar
A1 - Wei, Qingya
A1 - Zeiske, Stefan
A1 - Kroh, Daniel
A1 - Wedler, Stefan
A1 - Koehler, Anna
A1 - Armin, Ardalan
A1 - Laquai, Frederic
A1 - Herzig, Eva M.
A1 - Zou, Yingping
A1 - Shoaee, Safa
A1 - Neher, Dieter
T1 - Understanding the role of order in Y-series non-fullerene solar cells to realize high open-circuit voltages
JF - Advanced energy materials
N2 - Non-fullerene acceptors (NFAs) as used in state-of-the-art organic solar cells feature highly crystalline layers that go along with low energetic disorder.
Here, the crucial role of energetic disorder in blends of the donor polymer PM6 with two Y-series NFAs, Y6, and N4 is studied.
By performing temperature-dependent charge transport and recombination studies, a consistent picture of the shape of the density of state distributions for free charges in the two blends is developed, allowing an analytical description of the dependence of the open-circuit voltage V-OC on temperature and illumination intensity.
Disorder is found to influence the value of the V-OC at room temperature, but also its progression with temperature. Here, the PM6:Y6 blend benefits substantially from its narrower state distributions.
The analysis also shows that the energy of the equilibrated free charge population is well below the energy of the NFA singlet excitons for both blends and possibly below the energy of the populated charge transfer manifold, indicating a down-hill driving force for free charge formation.
It is concluded that energetic disorder of charge-separated states has to be considered in the analysis of the photovoltaic properties, even for the more ordered PM6:Y6 blend.
KW - energetic disorder
KW - non-fullerene acceptors
KW - open-circuit voltage
KW - organic solar cells
Y1 - 2022
U6 - https://doi.org/10.1002/aenm.202103422
SN - 1614-6832
SN - 1614-6840
VL - 12
IS - 12
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Marin-Beloqui, Jose
A1 - Zhang, Guanran
A1 - Guo, Junjun
A1 - Shaikh, Jordan
A1 - Wohrer, Thibaut
A1 - Hosseini, Seyed Mehrdad
A1 - Sun, Bowen
A1 - Shipp, James
A1 - Auty, Alexander J.
A1 - Chekulaev, Dimitri
A1 - Ye, Jun
A1 - Chin, Yi-Chun
A1 - Sullivan, Michael B.
A1 - Mozer, Attila J.
A1 - Kim, Ji-Seon
A1 - Shoaee, Safa
A1 - Clarke, Tracey M.
T1 - Insight into the origin of trapping in polymer/fullerene blends with a systematic alteration of the fullerene to higher adducts
JF - Journal of physical chemistry C
N2 - The bimolecular recombination characteristics of conjugated polymer poly[(4,4'-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,5-bis 3-tetradecylthiophen-2-y1 thiazolo 5,4-d thiazole)-2,5diy1] (PDTSiTTz) blended with the fullerene series PC60BM, ICMA, ICBA, and ICTA have been investigated using microsecond and femtosecond transient absorption spectroscopy, in conjunction with electroluminescence measurements and ambient photoemission spectroscopy. The non-Langevin polymer PDTSiTTz allows an inspection of intrinsic bimolecular recombination rates uninhibited by diffusion, while the low oscillator strengths of fullerenes allow polymer features to dominate, and we compare our results to those of the well-known polymer Si-PCPDTBT. Using mu s-TAS, we have shown that the trap -limited decay dynamics of the PDTSiTTz polaron becomes progressively slower across the fullerene series, while those of Si-PCPDTBT are invariant. Electroluminescence measurements showed an unusual double peak in pristine PDTSiTTz, attributed to a low energy intragap charge transfer state, likely interchain in nature. Furthermore, while the pristine PDTSiTTz showed a broad, low-intensity density of states, the ICBA and ICTA blends presented a virtually identical DOS to Si-PCPDTBT and its blends. This has been attributed to a shift from a delocalized, interchain highest occupied molecular orbital (HOMO) in the pristine material to a dithienosilole-centered HOMO in the blends, likely a result of the bulky fullerenes increasing interchain separation. This HOMO localization had a side effect of progressively shifting the polymer HOMO to shallower energies, which was correlated with the observed decrease in bimolecular recombination rate and increased "trap" depth. However, since the density of tail states remained the same, this suggests that the traditional viewpoint of "trapping" being dominated by tail states may not encompass the full picture and that the breadth of the DOS may also have a strong influence on bimolecular recombination.
Y1 - 2022
U6 - https://doi.org/10.1021/acs.jpcc.1c10378
SN - 1932-7447
SN - 1932-7455
VL - 126
IS - 5
SP - 2708
EP - 2719
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Vilk, Ohad
A1 - Aghion, Erez
A1 - Avgar, Tal
A1 - Beta, Carsten
A1 - Nagel, Oliver
A1 - Sabri, Adal
A1 - Sarfati, Raphael
A1 - Schwartz, Daniel K.
A1 - Weiß, Matthias
A1 - Krapf, Diego
A1 - Nathan, Ran
A1 - Metzler, Ralf
A1 - Assaf, Michael
T1 - Unravelling the origins of anomalous diffusion
BT - from molecules to migrating storks
JF - Physical review research / American Physical Society
N2 - Anomalous diffusion or, more generally, anomalous transport, with nonlinear dependence of the mean-squared displacement on the measurement time, is ubiquitous in nature. It has been observed in processes ranging from microscopic movement of molecules to macroscopic, large-scale paths of migrating birds. Using data from multiple empirical systems, spanning 12 orders of magnitude in length and 8 orders of magnitude in time, we employ a method to detect the individual underlying origins of anomalous diffusion and transport in the data. This method decomposes anomalous transport into three primary effects: long-range correlations (“Joseph effect”), fat-tailed probability density of increments (“Noah effect”), and nonstationarity (“Moses effect”). We show that such a decomposition of real-life data allows us to infer nontrivial behavioral predictions and to resolve open questions in the fields of single-particle tracking in living cells and movement ecology.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevResearch.4.033055
SN - 2643-1564
VL - 4
IS - 3
PB - American Physical Society
CY - College Park, MD
ER -
TY - JOUR
A1 - Ye, Fangyuan
A1 - Zhang, Shuo
A1 - Warby, Jonathan
A1 - Wu, Jiawei
A1 - Gutierrez-Partida, Emilio
A1 - Lang, Felix
A1 - Shah, Sahil
A1 - Saglamkaya, Elifnaz
A1 - Sun, Bowen
A1 - Zu, Fengshuo
A1 - Shoai, Safa
A1 - Wang, Haifeng
A1 - Stiller, Burkhard
A1 - Neher, Dieter
A1 - Zhu, Wei-Hong
A1 - Stolterfoht, Martin
A1 - Wu, Yongzhen
T1 - Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane
JF - Nature Communications
N2 - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-022-34203-x
SN - 2041-1723
VL - 13
PB - Springer Nature
CY - London
ER -
TY - JOUR
A1 - Brinkmann, Kai Oliver
A1 - Becker, Tim
A1 - Zimmermann, Florian
A1 - Kreusel, Cedric
A1 - Gahlmann, Tobias
A1 - Theisen, Manuel
A1 - Haeger, Tobias
A1 - Olthof, Selina
A1 - Tückmantel, Christian
A1 - Günster, M.
A1 - Maschwitz, Timo
A1 - Göbelsmann, Fabian
A1 - Koch, Christine
A1 - Hertel, Dirk
A1 - Caprioglio, Pietro
A1 - Peña-Camargo, Francisco
A1 - Perdigón-Toro, Lorena
A1 - Al-Ashouri, Amran
A1 - Merten, Lena
A1 - Hinderhofer, Alexander
A1 - Gomell, Leonie
A1 - Zhang, Siyuan
A1 - Schreiber, Frank
A1 - Albrecht, Steve
A1 - Meerholz, Klaus
A1 - Neher, Dieter
A1 - Stolterfoht, Martin
A1 - Riedl, Thomas
T1 - Perovskite-organic tandem solar cells with indium oxide interconnect
JF - Nature
N2 - Multijunction solar cells can overcome the fundamental efficiency limits of single-junction devices. The bandgap tunability of metal halide perovskite solar cells renders them attractive for multijunction architectures(1). Combinations with silicon and copper indium gallium selenide (CIGS), as well as all-perovskite tandem cells, have been reported(2-5). Meanwhile, narrow-gap non-fullerene acceptors have unlocked skyrocketing efficiencies for organic solar cells(6,7). Organic and perovskite semiconductors are an attractive combination, sharing similar processing technologies. Currently, perovskite-organic tandems show subpar efficiencies and are limited by the low open-circuit voltage (V-oc) of wide-gap perovskite cells(8) and losses introduced by the interconnect between the subcells(9,10). Here we demonstrate perovskite-organic tandem cells with an efficiency of 24.0 per cent (certified 23.1 per cent) and a high V-oc of 2.15 volts. Optimized charge extraction layers afford perovskite subcells with an outstanding combination of high V-oc and fill factor. The organic subcells provide a high external quantum efficiency in the near-infrared and, in contrast to paradigmatic concerns about limited photostability of non-fullerene cells(11), show an outstanding operational stability if excitons are predominantly generated on the non-fullerene acceptor, which is the case in our tandems. The subcells are connected by an ultrathin (approximately 1.5 nanometres) metal-like indium oxide layer with unprecedented low optical/electrical losses. This work sets a milestone for perovskite-organic tandems, which outperform the best p-i-n perovskite single junctions(12) and are on a par with perovskite-CIGS and all-perovskite multijunctions(13).
Y1 - 2022
U6 - https://doi.org/10.1038/s41586-022-04455-0
SN - 0028-0836
SN - 1476-4687
VL - 604
IS - 7905
SP - 280
EP - 286
PB - Nature Research
CY - Berlin
ER -
TY - JOUR
A1 - Ye, Fangyuan
A1 - Zhang, Shuo
A1 - Warby, Jonathan
A1 - Wu, Jiawei
A1 - Gutierrez-Partida, Emilio
A1 - Lang, Felix
A1 - Shah, Sahil
A1 - Saglamkaya, Elifnaz
A1 - Sun, Bowen
A1 - Zu, Fengshuo
A1 - Shoaee, Safa
A1 - Wang, Haifeng
A1 - Stiller, Burkhard
A1 - Neher, Dieter
A1 - Zhu, Wei-Hong
A1 - Stolterfoht, Martin
A1 - Wu, Yongzhen
T1 - Overcoming C-60-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane
JF - Nature Communications
N2 - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C-60 interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C-60 interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110mV, and retain >97% of the initial efficiency after 400h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells. Effective transport layers are essential to suppress non-radiative recombination losses. Here, the authors introduce phenylamino-functionalized ortho-carborane as an interfacial layer, and realise inverted perovskite solar cells with efficiency of over 23% and operational stability of T97=400h.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-022-34203-x
SN - 2041-1723
VL - 13
IS - 1
PB - Nature Publishing Group
CY - London
ER -
TY - JOUR
A1 - Pena-Camargo, Francisco
A1 - Thiesbrummel, Jarla
A1 - Hempel, Hannes
A1 - Musiienko, Artem
A1 - Le Corre, Vincent M.
A1 - Diekmann, Jonas
A1 - Warby, Jonathan
A1 - Unold, Thomas
A1 - Lang, Felix
A1 - Neher, Dieter
A1 - Stolterfoht, Martin
T1 - Revealing the doping density in perovskite solar cells and its impact on device performance
JF - Applied physics reviews
N2 - Traditional inorganic semiconductors can be electronically doped with high precision. Conversely, there is still conjecture regarding the assessment of the electronic doping density in metal-halide perovskites, not to mention of a control thereof. This paper presents a multifaceted approach to determine the electronic doping density for a range of different lead-halide perovskite systems. Optical and electrical characterization techniques, comprising intensity-dependent and transient photoluminescence, AC Hall effect, transfer-length-methods, and charge extraction measurements were instrumental in quantifying an upper limit for the doping density. The obtained values are subsequently compared to the electrode charge per cell volume under short-circuit conditions ( CUbi/eV), which amounts to roughly 10(16) cm(-3). This figure of merit represents the critical limit below which doping-induced charges do not influence the device performance. The experimental results consistently demonstrate that the doping density is below this critical threshold 10(12) cm(-3), which means << CUbi / e V) for all common lead-based metal-halide perovskites. Nevertheless, although the density of doping-induced charges is too low to redistribute the built-in voltage in the perovskite active layer, mobile ions are present in sufficient quantities to create space-charge-regions in the active layer, reminiscent of doped pn-junctions. These results are well supported by drift-diffusion simulations, which confirm that the device performance is not affected by such low doping densities.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0085286
SN - 1931-9401
VL - 9
IS - 2
PB - AIP Publishing
CY - Melville
ER -
TY - JOUR
A1 - Mattern, Maximilian
A1 - Reppert, Alexander von
A1 - Zeuschner, Steffen Peer
A1 - Pudell, Jan-Etienne
A1 - Kühne, F.
A1 - Diesing, Detlef
A1 - Herzog, Marc
A1 - Bargheer, Matias
T1 - Electronic energy transport in nanoscale Au/Fe hetero-structures in the perspective of ultrafast lattice dynamics
JF - Applied physics letters
N2 - We study the ultrafast electronic transport of energy in a photoexcited nanoscale Au/Fe hetero-structure by modeling the spatiotemporal profile of energy densities that drives transient strain, which we quantify by femtosecond x-ray diffraction. This flow of energy is relevant for intrinsic demagnetization and ultrafast spin transport. We measured lattice strain for different Fe layer thicknesses ranging from few atomic layers to several nanometers and modeled the spatiotemporal flow of energy densities. The combination of a high electron-phonon coupling coefficient and a large Sommerfeld constant in Fe is found to yield electronic transfer of nearly all energy from Au to Fe within the first hundreds of femtoseconds.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0080378
SN - 0003-6951
SN - 1077-3118
VL - 120
IS - 9
PB - AIP Publishing
CY - Melville
ER -
TY - JOUR
A1 - Le Corre, Vincent M.
A1 - Diekmann, Jonas
A1 - Peña-Camargo, Francisco
A1 - Thiesbrummel, Jarla
A1 - Tokmoldin, Nurlan
A1 - Gutierrez-Partida, Emilio
A1 - Peters, Karol Pawel
A1 - Perdigón-Toro, Lorena
A1 - Futscher, Moritz H.
A1 - Lang, Felix
A1 - Warby, Jonathan
A1 - Snaith, Henry J.
A1 - Neher, Dieter
A1 - Stolterfoht, Martin
T1 - Quantification of efficiency losses due to mobile ions in Perovskite solar cells via fast hysteresis measurements
JF - Solar RRL
N2 - Perovskite semiconductors differ from most inorganic and organic semiconductors due to the presence of mobile ions in the material. Although the phenomenon is intensively investigated, important questions such as the exact impact of the mobile ions on the steady-state power conversion efficiency (PCE) and stability remain. Herein, a simple method is proposed to estimate the efficiency loss due to mobile ions via "fast-hysteresis" measurements by preventing the perturbation of mobile ions out of their equilibrium position at fast scan speeds (approximate to 1000 V s(-1)). The "ion-free" PCE is between 1% and 3% higher than the steady-state PCE, demonstrating the importance of ion-induced losses, even in cells with low levels of hysteresis at typical scan speeds (approximate to 100mv s(-1)). The hysteresis over many orders of magnitude in scan speed provides important information on the effective ion diffusion constant from the peak hysteresis position. The fast-hysteresis measurements are corroborated by transient charge extraction and capacitance measurements and numerical simulations, which confirm the experimental findings and provide important insights into the charge carrier dynamics. The proposed method to quantify PCE losses due to field screening induced by mobile ions clarifies several important experimental observations and opens up a large range of future experiments.
KW - hysteresis
KW - mobile ions
KW - perovskite solar cells
Y1 - 2021
U6 - https://doi.org/10.1002/solr.202100772
SN - 2367-198X
VL - 6
IS - 4
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Zeiske, Stefan
A1 - Sandberg, Oskar J.
A1 - Zarrabi, Nasim
A1 - Wolff, Christian Michael
A1 - Raoufi, Meysam
A1 - Peña-Camargo, Francisco
A1 - Gutierrez-Partida, Emilio
A1 - Meredith, Paul
A1 - Stolterfoht, Martin
A1 - Armin, Ardalan
T1 - Static disorder in lead halide perovskites
JF - The journal of physical chemistry letters
N2 - In crystalline and amorphous semiconductors, the temperature-dependent Urbach energy can be determined from the inverse slope of the logarithm of the absorption spectrum and reflects the static and dynamic energetic disorder. Using recent advances in the sensitivity of photocurrent spectroscopy methods, we elucidate the temperature-dependent Urbach energy in lead halide perovskites containing different numbers of cation components. We find Urbach energies at room temperature to be 13.0 +/- 1.0, 13.2 +/- 1.0, and 13.5 +/- 1.0 meV for single, double, and triple cation perovskite. Static, temperature-independent contributions to the Urbach energy are found to be as low as 5.1 ?+/- 0.5, 4.7 +/- 0.3, and 3.3 +/- 0.9 meV for the same systems. Our results suggest that, at a low temperature, the dominant static disorder in perovskites is derived from zero-point phonon energy rather than structural disorder. This is unusual for solution-processed semiconductors but broadens the potential application of perovskites further to quantum electronics and devices.
KW - Cations
KW - External quantum efficiency
KW - Perovskites
KW - Solar cells
KW - Solar energy
Y1 - 2022
U6 - https://doi.org/10.1021/acs.jpclett.2c01652
SN - 1948-7185
VL - 13
IS - 31
SP - 7280
EP - 7285
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Doerries, Timo J.
A1 - Chechkin, Aleksei
A1 - Schumer, Rina
A1 - Metzler, Ralf
T1 - Rate equations, spatial moments, and concentration profiles for mobile-immobile models with power-law and mixed waiting time distributions
JF - Physical review : E, Statistical, nonlinear and soft matter physics
N2 - We present a framework for systems in which diffusion-advection transport of a tracer substance in a mobile zone is interrupted by trapping in an immobile zone.
Our model unifies different model approaches based on distributed-order diffusion equations, exciton diffusion rate models, and random-walk models for multirate mobile-immobile mass transport.
We study various forms for the trapping time dynamics and their effects on the tracer mass in the mobile zone.
Moreover, we find the associated breakthrough curves, the tracer density at a fixed point in space as a function of time, and the mobile and immobile concentration profiles and the respective moments of the transport.
Specifically, we derive explicit forms for the anomalous transport dynamics and an asymptotic power-law decay of the mobile mass for a Mittag-Leffler trapping time distribution.
In our analysis we point out that even for exponential trapping time densities, transient anomalous transport is observed.
Our results have direct applications in geophysical contexts, but also in biological, soft matter, and solid state systems.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevE.105.014105
SN - 2470-0045
SN - 2470-0053
VL - 105
IS - 1
PB - The American Institute of Physics
CY - Woodbury, NY
ER -
TY - JOUR
A1 - Herzog, Marc
A1 - Reppert, Alexander von
A1 - Pudell, Jan-Etienne
A1 - Henkel, Carsten
A1 - Kronseder, Matthias
A1 - Back, Christian H.
A1 - Maznev, Alexei A.
A1 - Bargheer, Matias
T1 - Phonon-dominated energy transport in purely metallic heterostructures
JF - Advanced functional materials
N2 - Ultrafast X-ray diffraction is used to quantify the transport of energy in laser-excited nanoscale gold-nickel (Au-Ni) bilayers.
Electron transport and efficient electron-phonon coupling in Ni convert the laser-deposited energy in the conduction electrons within a few picoseconds into a strong non-equilibrium between hot Ni and cold Au phonons at the bilayer interface.
Modeling of the subsequent equilibration dynamics within various two-temperature models confirms that for ultrathin Au films, the thermal transport is dominated by phonons instead of conduction electrons because of the weak electron-phonon coupling in Au.
KW - heterostructures
KW - nanoscale energy transports
KW - non-equilibrium
KW - thermal
KW - transports
KW - ultrafast phenomena
Y1 - 2022
U6 - https://doi.org/10.1002/adfm.202206179
SN - 1616-301X
SN - 1616-3028
VL - 32
IS - 41
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Warby, Jonathan
A1 - Zu, Fengshuo
A1 - Zeiske, Stefan
A1 - Gutierrez-Partida, Emilio
A1 - Frohloff, Lennart
A1 - Kahmann, Simon
A1 - Frohna, Kyle
A1 - Mosconi, Edoardo
A1 - Radicchi, Eros
A1 - Lang, Felix
A1 - Shah, Sahil
A1 - Pena-Camargo, Francisco
A1 - Hempel, Hannes
A1 - Unold, Thomas
A1 - Koch, Norbert
A1 - Armin, Ardalan
A1 - De Angelis, Filippo
A1 - Stranks, Samuel D.
A1 - Neher, Dieter
A1 - Stolterfoht, Martin
T1 - Understanding performance limiting interfacial recombination in pin Perovskite solar cells
JF - Advanced energy materials
N2 - Perovskite semiconductors are an attractive option to overcome the limitations of established silicon based photovoltaic (PV) technologies due to their exceptional opto-electronic properties and their successful integration into multijunction cells. However, the performance of single- and multijunction cells is largely limited by significant nonradiative recombination at the perovskite/organic electron transport layer junctions. In this work, the cause of interfacial recombination at the perovskite/C-60 interface is revealed via a combination of photoluminescence, photoelectron spectroscopy, and first-principle numerical simulations. It is found that the most significant contribution to the total C-60-induced recombination loss occurs within the first monolayer of C-60, rather than in the bulk of C-60 or at the perovskite surface. The experiments show that the C-60 molecules act as deep trap states when in direct contact with the perovskite. It is further demonstrated that by reducing the surface coverage of C-60, the radiative efficiency of the bare perovskite layer can be retained. The findings of this work pave the way toward overcoming one of the most critical remaining performance losses in perovskite solar cells.
KW - C60
KW - defects
KW - interface recombination
KW - loss mechanisms
KW - perovskites
KW - solar cells
Y1 - 2022
U6 - https://doi.org/10.1002/aenm.202103567
SN - 1614-6832
SN - 1614-6840
VL - 12
IS - 12
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Schwope, Axel
A1 - Pires, Adriana M.
A1 - Kurpas, Jan
A1 - Doroshenko, Victor
A1 - Suleimanov, Valery F.
A1 - Freyberg, Michael
A1 - Becker, Werner
A1 - Dennerl, Konrad
A1 - Haberl, Frank
A1 - Lamer, Georg
A1 - Maitra, Chandreyee
A1 - Potekhin, Alexander Y.
A1 - Ramos-Ceja, Miriam E.
A1 - Santangelo, Andrea
A1 - Traulsen, Iris
A1 - Werner, Klaus
T1 - Phase-resolved X-ray spectroscopy of PSR B0656+14 with SRG/eROSITA and XMM-Newton
JF - Astronomy and astrophysics : an international weekly journal
N2 - We present a detailed spectroscopic and timing analysis of X-ray observations of the bright pulsar PSR B0656+14. The observations were obtained simultaneously with eROSITA and XMM-Newton during the calibration and performance verification phase of the Spektrum-Roentgen-Gamma mission (SRG). The analysis of the 100 ks deep observation of eROSITA is supported by archival observations of the source, including XMM-Newton, NuSTAR, and NICER. Using XMM-Newton and NICER, we first established an X-ray ephemeris for the time interval 2015 to 2020, which connects all X-ray observations in this period without cycle count alias and phase shifts. The mean eROSITA spectrum clearly reveals an absorption feature originating from the star at 570 eV with a Gaussian sigma of about 70 eV that was tentatively identified in a previous long XMM-Newton observation. A second previously discussed absorption feature occurs at 260-265 eV and is described here as an absorption edge. It could be of atmospheric or of instrumental origin. These absorption features are superposed on various emission components that are phenomenologically described here as the sum of hot (120 eV) and cold (65 eV) blackbody components, both of photospheric origin, and a power law with photon index Gamma = 2 from the magnetosphere. We created energy-dependent light curves and phase-resolved spectra with a high signal-to-noise ratio. The phase-resolved spectroscopy reveals that the Gaussian absorption line at 570 eV is clearly present throughout similar to 60% of the spin cycle, but it is otherwise undetected. Likewise, its parameters were found to be dependent on phase. The visibility of the line strength coincides in phase with the maximum flux of the hot blackbody. If the line originates from the stellar surface, it nevertheless likely originates from a different location than the hot polar cap. We also present three families of model atmospheres: a magnetized atmosphere, a condensed surface, and a mixed model. They were applied to the mean observed spectrum, whose continuum fit the observed data well. The atmosphere model, however, predicts distances that are too short. For the mixed model, the Gaussian absorption may be interpreted as proton cyclotron absorption in a field as high as 10(14) G, which is significantly higher than the field derived from the moderate observed spin-down.
KW - stars: neutron
KW - X-rays: stars
KW - pulsars: individual: PSR B0656+14
Y1 - 2022
U6 - https://doi.org/10.1051/0004-6361/202141105
SN - 0004-6361
SN - 1432-0746
VL - 661
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Thapa, Samudrajit
A1 - Wyłomańska, Agnieszka
A1 - Sikora, Grzegorz
A1 - Wagner, Caroline E.
A1 - Krapf, Diego
A1 - Kantz, Holger
A1 - Chechkin, Aleksei V.
A1 - Metzler, Ralf
T1 - Leveraging large-deviation statistics to decipher the stochastic properties of measured trajectories
JF - New Journal of Physics
N2 - Extensive time-series encoding the position of particles such as viruses, vesicles, or individualproteins are routinely garnered insingle-particle tracking experiments or supercomputing studies.They contain vital clues on how viruses spread or drugs may be delivered in biological cells.Similar time-series are being recorded of stock values in financial markets and of climate data.Such time-series are most typically evaluated in terms of time-averaged mean-squareddisplacements (TAMSDs), which remain random variables for finite measurement times. Theirstatistical properties are different for differentphysical stochastic processes, thus allowing us toextract valuable information on the stochastic process itself. To exploit the full potential of thestatistical information encoded in measured time-series we here propose an easy-to-implementand computationally inexpensive new methodology, based on deviations of the TAMSD from itsensemble average counterpart. Specifically, we use the upper bound of these deviations forBrownian motion (BM) to check the applicability of this approach to simulated and real data sets.By comparing the probability of deviations fordifferent data sets, we demonstrate how thetheoretical bound for BM reveals additional information about observed stochastic processes. Weapply the large-deviation method to data sets of tracer beads tracked in aqueous solution, tracerbeads measured in mucin hydrogels, and of geographic surface temperature anomalies. Ouranalysis shows how the large-deviation properties can be efficiently used as a simple yet effectiveroutine test to reject the BM hypothesis and unveil relevant information on statistical propertiessuch as ergodicity breaking and short-time correlations.
KW - diffusion
KW - anomalous diffusion
KW - large-deviation statistic
KW - time-averaged mean squared displacement
KW - Chebyshev inequality
Y1 - 2020
U6 - https://doi.org/10.1088/1367-2630/abd50e
SN - 1367-2630
VL - 23
PB - Dt. Physikalische Ges. ; IOP
CY - Bad Honnef ; London
ER -
TY - JOUR
A1 - Teichmann, Erik
T1 - Using phase dynamics to study partial synchrony
BT - three examples
JF - European physical journal special topics
N2 - Partial synchronous states appear between full synchrony and asynchrony and exhibit many interesting properties. Most frequently, these states are studied within the framework of phase approximation. The latter is used ubiquitously to analyze coupled oscillatory systems. Typically, the phase dynamics description is obtained in the weak coupling limit, i.e., in the first-order in the coupling strength. The extension beyond the first-order represents an unsolved problem and is an active area of research. In this paper, three partially synchronous states are investigated and presented in order of increasing complexity. First, the usage of the phase response curve for the description of macroscopic oscillators is analyzed. To achieve this, the response of the mean-field oscillations in a model of all-to-all coupled limit-cycle oscillators to pulse stimulation is measured. The next part treats a two-group Kuramoto model, where the interaction of one attractive and one repulsive group results in an interesting solitary state, situated between full synchrony and self-consistent partial synchrony. In the last part, the phase dynamics of a relatively simple system of three Stuart-Landau oscillators are extended beyond the weak coupling limit. The resulting model contains triplet terms in the high-order phase approximation, though the structural connections are only pairwise. Finally, the scaling of the new terms with the coupling is analyzed.
Y1 - 2021
U6 - https://doi.org/10.1140/epjs/s11734-021-00156-3
SN - 1951-6355
SN - 1951-6401
VL - 230
IS - 14-15
SP - 2833
EP - 2842
PB - Springer
CY - Heidelberg
ER -
TY - JOUR
A1 - Rubio, Jesús
A1 - Anders, Janet
A1 - Correa, Luis A.
T1 - Global quantum thermometry
JF - Physical review letters / publ. by the American Physical Society
N2 - A paradigm shift in quantum thermometry is proposed. To date, thermometry has relied on local estimation, which is useful to reduce statistical fluctuations once the temperature is very well known. In order to estimate temperatures in cases where few measurement data or no substantial prior knowledge are available, we build instead a method for global quantum thermometry. Based on scaling arguments, a mean logarithmic error is shown here to be the correct figure of merit for thermometry. Its full minimization provides an operational and optimal rule to postprocess measurements into a temperature reading, and it establishes a global precision limit. We apply these results to the simulated outcomes of measurements on a spin gas, finding that the local approach can lead to biased temperature estimates in cases where the global estimator converges to the true temperature. The global framework thus enables a reliable approach to data analysis in thermometry experiments.
Y1 - 2021
U6 - https://doi.org/10.1103/PhysRevLett.127.190402
SN - 0031-9007
SN - 1079-7114
VL - 127
IS - 19
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Keles, Engin
T1 - Spectral signature of atmospheric winds in high-resolution transit observations
JF - Monthly Notices of the Royal Astronomical Society
N2 - The study of exoplanet atmospheres showed large diversity compared to the planets in our Solar system. Especially Jupiter-type exoplanets orbiting their host star in close orbits, the so-called hot and ultra-hot Jupiters, have been studied in detail due to their enhanced atmospheric signature. Due to their tidally locked status, the temperature difference between the day- and nightside triggers atmospheric winds that can lead to various fingerprints in the observations. Spatially resolved absorption lines during transit such as sodium (Na) could be a good tracer for such winds. Different works resolved the Na absorption lines on different exoplanets which show different line widths. Assuming that this could be attributed to such zonal jet streams, this work models the effect of such winds on synthetic absorption lines. For this, transiting Jupiter-type planets with rotational velocities similar to hot and ultra-hot Jupiter are considered. The investigation shows that high wind velocities could reproduce the broadening of Na-line profiles inferred in different high-resolution transit observations. There is a tendency that the broadening values decrease for planets with lower equilibrium temperature. This could be explained by atmospheric drag induced by the ionization of alkali lines that slow down the zonal jet streams, favouring their existence on hot Jupiter rather than ultra-hot Jupiter.
Y1 - 2021
U6 - https://doi.org/10.1093/mnras/stab099
VL - 502
IS - 1
SP - 1456
EP - 1468
PB - Oxford Univ. Press
CY - Oxford
ER -
TY - JOUR
A1 - Klein, Markus
A1 - Rosenberger, Elke
T1 - The tunneling effect for Schrödinger operators on a vector bundle
JF - Analysis and mathematical physics
N2 - In the semiclassical limit (h) over bar -> 0, we analyze a class of self-adjoint Schrodinger operators H-(h) over bar = (h) over bar L-2 + (h) over barW + V center dot id(E) acting on sections of a vector bundle E over an oriented Riemannian manifold M where L is a Laplace type operator, W is an endomorphism field and the potential energy V has non-degenerate minima at a finite number of points m(1),... m(r) is an element of M, called potential wells. Using quasimodes of WKB-type near m(j) for eigenfunctions associated with the low lying eigenvalues of H-(h) over bar, we analyze the tunneling effect, i.e. the splitting between low lying eigenvalues, which e.g. arises in certain symmetric configurations. Technically, we treat the coupling between different potential wells by an interaction matrix and we consider the case of a single minimal geodesic (with respect to the associated Agmon metric) connecting two potential wells and the case of a submanifold of minimal geodesics of dimension l + 1. This dimension l determines the polynomial prefactor for exponentially small eigenvalue splitting.
KW - Laplace-type operator
KW - Vector bundle
KW - WKB-expansion
KW - Quasimodes
KW - Tunneling
KW - Spectral gap
KW - Complete asymptotics
Y1 - 2021
U6 - https://doi.org/10.1007/s13324-021-00485-5
SN - 1664-2368
SN - 1664-235X
VL - 11
IS - 2
PB - Springer International Publishing AG
CY - Cham (ZG)
ER -
TY - JOUR
A1 - Bär, Christian
A1 - Mazzeo, Rafe
T1 - Manifolds with many Rarita-Schwinger fields
JF - Communications in mathematical physics
N2 - The Rarita-Schwinger operator is the twisted Dirac operator restricted to 3/2-spinors. Rarita-Schwinger fields are solutions of this operator which are in addition divergence-free. This is an overdetermined problem and solutions are rare; it is even more unexpected for there to be large dimensional spaces of solutions. In this paper we prove the existence of a sequence of compact manifolds in any given dimension greater than or equal to 4 for which the dimension of the space of Rarita-Schwinger fields tends to infinity. These manifolds are either simply connected Kahler-Einstein spin with negative Einstein constant, or products of such spaces with flat tori. Moreover, we construct Calabi-Yau manifolds of even complex dimension with more linearly independent Rarita-Schwinger fields than flat tori of the same dimension.
Y1 - 2021
U6 - https://doi.org/10.1007/s00220-021-04030-0
SN - 0010-3616
SN - 1432-0916
VL - 384
IS - 1
SP - 533
EP - 548
PB - Springer
CY - Berlin
ER -
TY - JOUR
A1 - Kluge, Lucas
A1 - Schewe, Jacob
T1 - Evaluation and extension of the radiation model for internal migration
JF - Physical review : E, Statistical, nonlinear and soft matter physics
N2 - Human migration is often studied using gravity models. These models, however, have known limitations, including analytic inconsistencies and a dependence on empirical data to calibrate multiple parameters for the region of interest. Overcoming these limitations, the radiation model has been proposed as an alternative, universal approach to predicting different forms of human mobility, but has not been adopted for studying migration. Here we show, using data on within-country migration from the USA and Mexico, that the radiation model systematically underpredicts long-range moves, while the traditional gravity model performs well for large distances. The universal opportunity model, an extension of the radiation model, shows an improved fit of long-range moves compared to the original radiation model, but at the cost of introducing two additional parameters. We propose a more parsimonious extension of the radiation model that introduces a single parameter. We demonstrate that it fits the data over the full distance spectrum and also-unlike the universal opportunity model-preserves the analytical property of the original radiation model of being equivalent to a gravity model in the limit of a uniform population distribution.
Y1 - 2021
U6 - https://doi.org/10.1103/PhysRevE.104.054311
SN - 2470-0045
SN - 2470-0053
SN - 2470-0061
VL - 104
IS - 5
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Gottwald, Georg A.
A1 - Reich, Sebastian
T1 - Combining machine learning and data assimilation to forecast dynamical systems from noisy partial observations
JF - Chaos : an interdisciplinary journal of nonlinear science
N2 - We present a supervised learning method to learn the propagator map of a dynamical system from partial and noisy observations. In our computationally cheap and easy-to-implement framework, a neural network consisting of random feature maps is trained sequentially by incoming observations within a data assimilation procedure. By employing Takens's embedding theorem, the network is trained on delay coordinates. We show that the combination of random feature maps and data assimilation, called RAFDA, outperforms standard random feature maps for which the dynamics is learned using batch data.
Y1 - 2021
U6 - https://doi.org/10.1063/5.0066080
SN - 1054-1500
SN - 1089-7682
VL - 31
IS - 10
PB - AIP
CY - Melville
ER -
TY - JOUR
A1 - Gaebel, Tina
A1 - Bein, Daniel
A1 - Mathauer, Daniel
A1 - Utecht, Manuel
A1 - Palmer, Richard E.
A1 - Klamroth, Tillmann
T1 - Nonlocal STM manipulation of chlorobenzene on Si(111)-7 x 7
BT - Potentials, kinetics, and first-principles molecular dynamics calculations for open systems
JF - The journal of physical chemistry : C, Nanomaterials and interfaces
N2 - We use quantum chemical cluster models together with constrained density STM Ph CI functional theory (DFT) and ab initio molecular dynamics (AIMD) for open system to simulate tip and rationalize nonlocal scanning tunneling microscope (STM) manipulation experiments for Philh ci chlorobenzene (PhCl) on a Si(111)-7 X 7 surface. We consider three different processes, namely, the electron-induced dissociation of the carbon-chlorine bond for physisorbed PhCl molecules at low temperatures and the electron- or hole-induced desorption of chemisorbed PhCl at 300 K. All processes can be induced nonlocally, i.e., up to several nanometers (nm) away from the injection site, in STM experiments. We rationalize and explain the experimental findings regarding the STM-induced dissociation using constrained DFT. The coupling of STM-induced ion resonances to nuclear degrees of freedom is simulated with AIMD using the Gadzuk averaging approach for open systems. From this data, we predict a 4 fs lifetime for the cationic resonance. For the anion model, desorption could not be observed. In addition, the same cluster models are used for transition-state theory calculations, which are compared to and validated against time-lapse STM experiments.
Y1 - 2021
U6 - https://doi.org/10.1021/acs.jpcc.1c02612
SN - 1932-7447
SN - 1932-7455
VL - 125
IS - 22
SP - 12175
EP - 12184
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Wiesner, Karoline
A1 - Ladyman, James
T1 - Complex systems are always correlated but rarely information processing
JF - Journal of physics. Complexity
N2 - 'Complex systems are information processors' is a statement that is frequently made. Here we argue for the distinction between information processing-in the sense of encoding and transmitting a symbolic representation-and the formation of correlations (pattern formation/self-organisation). The study of both uses tools from information theory, but the purpose is very different in each case: explaining the mechanisms and understanding the purpose or function in the first case, versus data analysis and correlation extraction in the latter. We give examples of both and discuss some open questions. The distinction helps focus research efforts on the relevant questions in each case.
KW - correlations
KW - information theory
KW - complex systems
KW - information
KW - processing
KW - self-organisation
Y1 - 2021
U6 - https://doi.org/10.1088/2632-072X/ac371c
SN - 2632-072X
VL - 2
IS - 4
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Clavier, Pierre J.
T1 - Borel-Écalle resummation of a two-point function
JF - Annales Henri Poincaré : a journal of theoretical and mathematical physics / ed. jointly by the Institut Henri Poincaré and by the Swiss Physical Society
N2 - We provide an overview of the tools and techniques of resurgence theory used in the Borel-ecalle resummation method, which we then apply to the massless Wess-Zumino model. Starting from already known results on the anomalous dimension of the Wess-Zumino model, we solve its renormalisation group equation for the two-point function in a space of formal series. We show that this solution is 1-Gevrey and that its Borel transform is resurgent. The Schwinger-Dyson equation of the model is then used to prove an asymptotic exponential bound for the Borel transformed two-point function on a star-shaped domain of a suitable ramified complex plane. This proves that the two-point function of the Wess-Zumino model is Borel-ecalle summable.
Y1 - 2021
U6 - https://doi.org/10.1007/s00023-021-01057-w
SN - 1424-0637
SN - 1424-0661
VL - 22
IS - 6
SP - 2103
EP - 2136
PB - Springer
CY - Cham
ER -
TY - JOUR
A1 - Diercke, Andrea
A1 - Kuckein, Christoph
A1 - Verma, Meetu
A1 - Denker, Carsten
T1 - Filigree in the surroundings of polar crown and high-latitude filaments
JF - Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics
N2 - High-resolution observations of polar crown and high-latitude filaments are scarce. We present a unique sample of such filaments observed in high-resolution H alpha narrow-band filtergrams and broad-band images, which were obtained with a new fast camera system at the Vacuum Tower Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope (ChroTel) provided full-disk context observations in H alpha, CaiiK, and Hei 10830 angstrom. The Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provided line-of-sight magnetograms and ultraviolet (UV) 1700 angstrom filtergrams, respectively. We study filigree in the vicinity of polar crown and high-latitude filaments and relate their locations to magnetic concentrations at the filaments' footpoints. Bright points are a well studied phenomenon in the photosphere at low latitudes, but they were not yet studied in the quiet network close to the poles. We examine size, area, and eccentricity of bright points and find that their morphology is very similar to their counterparts at lower latitudes, but their sizes and areas are larger. Bright points at the footpoints of polar crown filaments are preferentially located at stronger magnetic flux concentrations, which are related to bright regions at the border of supergranules as observed in UV filtergrams. Examining the evolution of bright points on three consecutive days reveals that their amount increases while the filament decays, which indicates they impact the equilibrium of the cool plasma contained in filaments.
KW - Chromosphere
KW - Quiet
KW - Granulation
KW - Magnetic fields
KW - Photosphere
KW - Prominences
KW - Quiescent
Y1 - 2021
U6 - https://doi.org/10.1007/s11207-021-01776-7
SN - 0038-0938
SN - 1573-093X
VL - 296
IS - 2
PB - Springer
CY - Dordrecht
ER -
TY - JOUR
A1 - Keles, Engin
A1 - Mallom, Matthias
A1 - von Essen, Carolina
A1 - Caroll, Thorsten A.
A1 - Alexoudi, Xanthippi
A1 - Pino, Lorenzo
A1 - Ilyin, Ilya
A1 - Poppenhäger, Katja
A1 - Kitzmann, Daniel
A1 - Nascimbeni, Valerino
A1 - Turner, Jake D.
A1 - Strassmeier, Klaus G.
T1 - The potassium absorption on HD189733b and HD209458b
JF - Monthly Notices of the Royal Astronomical Society: Letters
N2 - In this work, we investigate the potassium excess absorption around 7699 Å of the exoplanets HD189733b and HD209458b. For this purpose, we used high-spectral resolution transit observations acquired with the 2 × 8.4 m Large Binocular Telescope (LBT) and the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). For a bandwidth of 0.8 Å, we present a detection >7σ with an absorption level of 0.18 per cent for HD189733b. Applying the same analysis to HD209458b, we can set 3σ upper limit of 0.09 per cent, even though we do not detect a K-excess absorption. The investigation suggests that the K feature is less present in the atmosphere of HD209458b than in the one of HD189733b. This comparison confirms previous claims that the atmospheres of these two planets must have fundamentally different properties.
Y1 - 2021
U6 - https://doi.org/10.1093/mnrasl/slz123
VL - 489
IS - 1
SP - L37
EP - L41
PB - Oxford Univ. Press
CY - Oxford
ER -
TY - JOUR
A1 - Caruccio, Loredana
A1 - Deufemia, Vincenzo
A1 - Naumann, Felix
A1 - Polese, Giuseppe
T1 - Discovering relaxed functional dependencies based on multi-attribute dominance
JF - IEEE transactions on knowledge and data engineering
N2 - With the advent of big data and data lakes, data are often integrated from multiple sources. Such integrated data are often of poor quality, due to inconsistencies, errors, and so forth. One way to check the quality of data is to infer functional dependencies (fds). However, in many modern applications it might be necessary to extract properties and relationships that are not captured through fds, due to the necessity to admit exceptions, or to consider similarity rather than equality of data values. Relaxed fds (rfds) have been introduced to meet these needs, but their discovery from data adds further complexity to an already complex problem, also due to the necessity of specifying similarity and validity thresholds. We propose Domino, a new discovery algorithm for rfds that exploits the concept of dominance in order to derive similarity thresholds of attribute values while inferring rfds. An experimental evaluation on real datasets demonstrates the discovery performance and the effectiveness of the proposed algorithm.
KW - Complexity theory
KW - Approximation algorithms
KW - Big Data
KW - Distributed
KW - databases
KW - Semantics
KW - Lakes
KW - Functional dependencies
KW - data profiling
KW - data cleansing
Y1 - 2020
U6 - https://doi.org/10.1109/TKDE.2020.2967722
SN - 1041-4347
SN - 1558-2191
VL - 33
IS - 9
SP - 3212
EP - 3228
PB - Institute of Electrical and Electronics Engineers
CY - New York, NY
ER -
TY - JOUR
A1 - Gottwald, Georg A.
A1 - Reich, Sebastian
T1 - Supervised learning from noisy observations
BT - Combining machine-learning techniques with data assimilation
JF - Physica : D, Nonlinear phenomena
N2 - Data-driven prediction and physics-agnostic machine-learning methods have attracted increased interest in recent years achieving forecast horizons going well beyond those to be expected for chaotic dynamical systems. In a separate strand of research data-assimilation has been successfully used to optimally combine forecast models and their inherent uncertainty with incoming noisy observations. The key idea in our work here is to achieve increased forecast capabilities by judiciously combining machine-learning algorithms and data assimilation. We combine the physics-agnostic data -driven approach of random feature maps as a forecast model within an ensemble Kalman filter data assimilation procedure. The machine-learning model is learned sequentially by incorporating incoming noisy observations. We show that the obtained forecast model has remarkably good forecast skill while being computationally cheap once trained. Going beyond the task of forecasting, we show that our method can be used to generate reliable ensembles for probabilistic forecasting as well as to learn effective model closure in multi-scale systems. (C) 2021 Elsevier B.V. All rights reserved.
KW - Data-driven modelling
KW - Random feature maps
KW - Data assimilation
Y1 - 2021
U6 - https://doi.org/10.1016/j.physd.2021.132911
SN - 0167-2789
SN - 1872-8022
VL - 423
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Guggenberger, Tobias
A1 - Chechkin, Aleksei V.
A1 - Metzler, Ralf
T1 - Fractional Brownian motion in superharmonic potentials and non-Boltzmann stationary distributions
JF - Journal of physics : A, Mathematical and theoretical
N2 - We study the stochastic motion of particles driven by long-range correlated fractional Gaussian noise (FGN) in a superharmonic external potential of the form U(x) proportional to x(2n) (n is an element of N). When the noise is considered to be external, the resulting overdamped motion is described by the non-Markovian Langevin equation for fractional Brownian motion. For this case we show the existence of long time, stationary probability density functions (PDFs) the shape of which strongly deviates from the naively expected Boltzmann PDF in the confining potential U(x). We analyse in detail the temporal approach to stationarity as well as the shape of the non-Boltzmann stationary PDF. A typical characteristic is that subdiffusive, antipersistent (with negative autocorrelation) motion tends to effect an accumulation of probability close to the origin as compared to the corresponding Boltzmann distribution while the opposite trend occurs for superdiffusive (persistent) motion. For this latter case this leads to distinct bimodal shapes of the PDF. This property is compared to a similar phenomenon observed for Markovian Levy flights in superharmonic potentials. We also demonstrate that the motion encoded in the fractional Langevin equation driven by FGN always relaxes to the Boltzmann distribution, as in this case the fluctuation-dissipation theorem is fulfilled.
KW - anomalous diffusion
KW - Boltzmann distribution
KW - non-Gaussian distribution
Y1 - 2021
U6 - https://doi.org/10.1088/1751-8121/ac019b
SN - 1751-8113
SN - 1751-8121
VL - 54
IS - 29
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Beckus, Siegfried
A1 - Eliaz, Latif
T1 - Eigenfunctions growth of R-limits on graphs
JF - Journal of spectral theory / European Mathematical Society
N2 - A characterization of the essential spectrum of Schrodinger operators on infinite graphs is derived involving the concept of R-limits. This concept, which was introduced previously for operators on N and Z(d) as "right-limits," captures the behaviour of the operator at infinity. For graphs with sub-exponential growth rate, we show that each point in sigma(ss)(H) corresponds to a bounded generalized eigenfunction of a corresponding R-limit of H. If, additionally, the graph is of uniform sub-exponential growth, also the converse inclusion holds.
KW - Essential spectrum
KW - Schrodinger operators
KW - graphs
KW - right limits
KW - generalized eigenfunctions
Y1 - 2021
U6 - https://doi.org/10.4171/JST/389
SN - 1664-039X
SN - 1664-0403
VL - 11
IS - 4
SP - 1895
EP - 1933
PB - EMS Press, an imprint of the European Mathematical Society - EMS - Publishing House GmbH, Institut für Mathematik, Technische Universität
CY - Berlin
ER -
TY - JOUR
A1 - Kumar, Mohit
A1 - Rosenblum, Michael
T1 - Two mechanisms of remote synchronization in a chain of Stuart-Landau oscillators
JF - Physical review : E, Statistical, nonlinear and soft matter physics
N2 - Remote synchronization implies that oscillators interacting not directly but via an additional unit (hub) adjust their frequencies and exhibit frequency locking while the hub remains asynchronous. In this paper, we analyze the mechanisms of remote synchrony in a small network of three coupled Stuart-Landau oscillators using recent results on higher-order phase reduction. We analytically demonstrate the role of two factors promoting remote synchrony. These factors are the nonisochronicity of oscillators and the coupling terms appearing in the secondorder phase approximation. We show a good correspondence between our theory and numerical results for small and moderate coupling strengths.
Y1 - 2021
U6 - https://doi.org/10.1103/PhysRevE.104.054202
SN - 2470-0045
SN - 2470-0053
VL - 104
IS - 5
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Hannemann, Mandy
A1 - Wegner, Gino
A1 - Henkel, Carsten
T1 - No-slip boundary conditions for electron hydrodynamics and the thermal Casimir pressure
JF - Universe : open access journal
N2 - We derive modified reflection coefficients for electromagnetic waves in the THz and far infrared range. The idea is based on hydrodynamic boundary conditions for metallic conduction electrons. The temperature-dependent part of the Casimir pressure between metal plates is evaluated. The results should shed light on the "thermal anomaly," where measurements deviate from the standard fluctuation electrodynamics for conducting metals.
KW - dispersion force
KW - metal optics
KW - Drude model
KW - hydrodynamic model
KW - spatial
KW - dispersion
KW - viscosity
KW - non-contact heat transfer
Y1 - 2021
U6 - https://doi.org/10.3390/universe7040108
SN - 2218-1997
VL - 7
IS - 4
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Mutothya, Nicholas Mwilu
A1 - Xu, Yong
A1 - Li, Yongge
A1 - Metzler, Ralf
T1 - Characterising stochastic motion in heterogeneous media driven by coloured non-Gaussian noise
JF - Journal of physics : A, Mathematical and theoretical
N2 - We study the stochastic motion of a test particle in a heterogeneous medium in terms of a position dependent diffusion coefficient mimicking measured deterministic diffusivity gradients in biological cells or the inherent heterogeneity of geophysical systems. Compared to previous studies we here investigate the effect of the interplay of anomalous diffusion effected by position dependent diffusion coefficients and coloured non-Gaussian noise. The latter is chosen to be distributed according to Tsallis' q-distribution, representing a popular example for a non-extensive statistic. We obtain the ensemble and time averaged mean squared displacements for this generalised process and establish its non-ergodic properties as well as analyse the non-Gaussian nature of the associated displacement distribution. We consider both non-stratified and stratified environments.
KW - diffusion
KW - anomalous diffusion
KW - non-extensive statistics
KW - coloured
KW - noise
KW - heterogeneous diffusion process
Y1 - 2021
U6 - https://doi.org/10.1088/1751-8121/abfba6
SN - 1751-8113
SN - 1751-8121
VL - 54
IS - 29
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Henkel, Carsten
T1 - Heat transfer and entanglement
BT - non-equilibrium correlation spectra of two quantum oscillators
JF - Annalen der Physik
N2 - The non-equilibrium state of two oscillators with a mutual interaction and coupled to separate heat baths is discussed. Bosonic baths are considered, and an exact spectral representation for the elements of the covariance matrix is provided analytically. A wide class of spectral densities for the relevant bath modes is allowed for. The validity of the fluctuation-dissipation relation is established for global equilibrium (both baths at the same temperature) in the stationary state. Spectral measures of entanglement are suggested by comparing to the equilibrium spectrum of zero-point fluctuations. No rotating-wave approximation is applied, and anomalous heat transport from cold to hot bath, as reported in earlier work, is demonstrated not to occur.
KW - entanglement
KW - heat transfer
KW - non-equilibrium steady state
KW - master
KW - equation
KW - quantum thermodynamics
Y1 - 2021
U6 - https://doi.org/10.1002/andp.202100089
SN - 0003-3804
SN - 1521-3889
VL - 533
IS - 10
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Horovitz, Baruch
A1 - Henkel, Carsten
T1 - Spin entanglement via scanning tunneling microscope current
JF - Physical review : B, Condensed matter and materials physics
N2 - We consider a system of two spins under a scanning tunneling microscope bias and derive its master equation. We find that the tunneling elements to the electronic contacts (tip and substrate) generate an exchange interaction between the spins as well as a Dzyaloshinskii-Moriya interaction in the presence of spin-orbit coupling. The tunnel current spectrum then shows additional lines compared to conventional spin-resonance experiments. When the spins have degenerate Larmor frequencies and equal tunneling amplitudes (without spin orbit), there is a dark state with a vanishing decay rate. The coupling to the electronic environment generates significant spin-spin entanglement via the dark state, even if the initial state is nonentangled.
Y1 - 2021
U6 - https://doi.org/10.1103/PhysRevB.104.L081405
SN - 2469-9950
SN - 2469-9969
VL - 104
IS - 8
PB - American Physical Society
CY - Ridge, NY
ER -
TY - JOUR
A1 - Lever, Fabiano
A1 - Mayer, Dennis
A1 - Metje, Jan
A1 - Alisauskas, Skirmantas
A1 - Calegari, Francesca
A1 - Düsterer, Stefan
A1 - Feifel, Raimund
A1 - Niebuhr, Mario
A1 - Manschwetus, Bastian
A1 - Kuhlmann, Marion
A1 - Mazza, Tommaso
A1 - Robinson, Matthew Scott
A1 - Squibb, Richard J.
A1 - Trabattoni, Andrea
A1 - Wallner, Måns
A1 - Wolf, Thomas J. A.
A1 - Gühr, Markus
T1 - Core-level spectroscopy of 2-thiouracil at the sulfur L1 and L2,3 edges utilizing a SASE free-electron-laser
JF - Molecules
N2 - In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1- and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster–Kronig and Auger–Meitner emission at the L1- and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy.
KW - X-ray
KW - photoelectron
KW - sulfur
KW - thiouracil
KW - nucleobases
KW - Coster–Kronig
KW - Auger–Meitner
KW - NEXAFS
KW - FLASH
Y1 - 2021
SN - 1420-3049
VL - 26
IS - 21
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Feudel, Fred
A1 - Feudel, Ulrike
T1 - Bifurcations in rotating spherical shell convection under the influence of differential rotation
JF - Chaos : an interdisciplinary journal of nonlinear science
N2 - The bifurcations of thermal convection in a rotating spherical shell heated from the inner sphere and driven by the buoyancy of a central gravity field are studied numerically. This model of spherical Rayleigh-Benard convection describes large-scale convection in planets and in the outer zones of celestial bodies. In this work, the influence of an additionally imposed differential rotation of the inner sphere with respect to the outer one on the heat transfer and, more generally, on the whole bifurcation structure is investigated. In addition to numerical simulations, path-following techniques are applied in order to compute both stable and unstable solution branches. The dynamics and the heat transfer are essentially determined by a global bifurcation, which we have identified as a homoclinic bifurcation that consists of a collision of a stable modulated rotating with an unstable rotating wave.
Y1 - 2021
U6 - https://doi.org/10.1063/5.0063113
SN - 1054-1500
SN - 1089-7682
VL - 31
IS - 11
PB - AIP
CY - Melville
ER -
TY - JOUR
A1 - Köhler, Raphael H.
A1 - Handorf, Dörthe
A1 - Jaiser, Ralf
A1 - Dethloff, Klaus
A1 - Zängl, Günther
A1 - Majewski, Detlev
A1 - Rex, Markus
T1 - Improved circulation in the Northern hemisphere by adjusting gravity wave drag parameterizations in seasonal experiments with ICON-NWP
JF - Earth and Space Science : ESS
N2 - The stratosphere is one of the main potential sources for subseasonal to seasonal predictability in midlatitudes in winter. The ability of an atmospheric model to realistically simulate the stratospheric dynamics is essential in order to move forward in the field of seasonal predictions in midlatitudes. Earlier studies with the ICOsahedral Nonhydrostatic atmospheric model (ICON) point out that stratospheric westerlies in ICON are underestimated. This is the first extensive study on the evaluation of Northern Hemisphere stratospheric winter circulation with ICON in numerical weather prediction (NWP) mode. Seasonal experiments with the default setup are able to reproduce the basic climatology of the stratospheric polar vortex. However, westerlies are too weak and major stratospheric warmings too frequent in ICON. Both a reduction of the nonorographic, and a reduction of the orographic gravity wave and wake drag lead to a strengthening of the stratospheric vortex and a bias reduction, in particular in January. However, the effect of the nonorographic gravity wave drag scheme on the stratosphere is stronger. Stratosphere-troposphere coupling is intensified and more realistic due to a reduced gravity wave drag. Furthermore, an adjustment of the subgrid-scale orographic drag parameterization leads to a significant error reduction in the mean sea level pressure. As a result of these findings, we present our current suggested improved setup for seasonal experiments with ICON-NWP.
Plain Language Summary Although seasonal forecasts for midlatitudes have the potential to be highly beneficial to the public sector, they are still characterized by a large amount of uncertainty. Exact simulations of the circulation in the stratosphere can help to improve tropospheric predictability on seasonal time scales. For this reason, we investigate how well the new German atmospheric model is able to simulate the stratospheric circulation. The model reproduces the basic behavior of the Northern Hemisphere stratospheric polar vortex, but the westerly circulation in winter is underestimated. The stratospheric circulation is influenced by gravity waves that exert drag on the flow. These processes are only partly physically represented in the model, but are very important and are hence parameterized. By adjusting the parameterizations for the gravity wave drag, the stratospheric polar vortex is strengthened, thereby yielding a more realistic stratospheric circulation. In addition, the altered parameterizations improve the simulated surface pressure pattern. Based upon this, we present our current suggested improved model setup for seasonal experiments.
Y1 - 2021
U6 - https://doi.org/10.1029/2021EA001676
SN - 2333-5084
VL - 8
IS - 3
PB - American Geophysical Union
CY - Malden, Mass.
ER -
TY - JOUR
A1 - Pikovskij, Arkadij
T1 - Transition to synchrony in chiral active particles
JF - Journal of physics. Complexity
N2 - I study deterministic dynamics of chiral active particles in two dimensions. Particles are considered as discs interacting with elastic repulsive forces. An ensemble of particles, started from random initial conditions, demonstrates chaotic collisions resulting in their normal diffusion. This chaos is transient, as rather abruptly a synchronous collisionless state establishes. The life time of chaos grows exponentially with the number of particles. External forcing (periodic or chaotic) is shown to facilitate the synchronization transition.
KW - active particles
KW - chirality
KW - synchronization
KW - chaos
KW - transient chaos
Y1 - 2021
U6 - https://doi.org/10.1088/2632-072X/abdadb
SN - 2632-072X
VL - 2
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Zheng, Chunming
A1 - Toenjes, Ralf
A1 - Pikovskij, Arkadij
T1 - Transition to synchrony in a three-dimensional swarming model with helical trajectories
JF - Physical review : E, Statistical, nonlinear and soft matter physics
N2 - We investigate the transition from incoherence to global collective motion in a three-dimensional swarming model of agents with helical trajectories, subject to noise and global coupling. Without noise this model was recently proposed as a generalization of the Kuramoto model and it was found that alignment of the velocities occurs discontinuously for arbitrarily small attractive coupling. Adding noise to the system resolves this singular limit and leads to a continuous transition, either to a directed collective motion or to center-of-mass rotations.
Y1 - 2021
U6 - https://doi.org/10.1103/PhysRevE.104.014216
SN - 2470-0045
SN - 2470-0053
VL - 104
IS - 1
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Frieß, Fabian
A1 - Lendlein, Andreas
A1 - Wischke, Christian
T1 - Switching microobjects from low to high aspect ratios using a shape-memory effect
JF - Soft matter
N2 - Spherical particles from shape-memory polymers (SMP) can be stretched to ellipsoids with high aspect ratio (AR) and temporarily stabilized. They can switch back to low AR upon thermal stimulation. Here, the creation of an alternative shape-switching capability of particles from low to high AR is introduced, where a SMP matrix from polyvinyl alcohol (PVA) is used to create crosslinked high AR particles and to program the embedded micrometer-sized particles from a second SMP (oligo(epsilon-caprolactone) micronetworks, MN) with a low switching temperature T-sw. This programming proceeds through shape-recovery of the PVA matrix, from which the MN are harvested by PVA matrix dissolution. The use of a dissolvable SMP matrix may be a general strategy to efficiently create systems with complex moving capabilities.
Y1 - 2021
U6 - https://doi.org/10.1039/d1sm00947h
SN - 1744-6848
VL - 17
IS - 41
SP - 9326
EP - 9331
PB - Royal Society of Chemistry
CY - London
ER -
TY - JOUR
A1 - Scali, Stefano
A1 - Anders, Janet
A1 - Correa, Luis A.
T1 - Local master equations bypass the secular approximation
JF - Quantum : the open journal for quantum science
N2 - Master equations are a vital tool to model heat flow through nanoscale thermodynamic systems. Most practical devices are made up of interacting subsystems and are often modelled using either local master equations (LMEs) or global master equations (GMEs). While the limiting cases in which either the LME or the GME breaks down are well understood, there exists a 'grey area' in which both equations capture steady-state heat currents reliably but predict very different transient heat flows. In such cases, which one should we trust? Here we show that, when it comes to dynamics, the local approach can be more reliable than the global one for weakly interacting open quantum systems. This is due to the fact that the secular approximation, which underpins the GME, can destroy key dynamical features. To illustrate this, we consider a minimal transport setup and show that its LME displays exceptional points (EPs). These singularities have been observed in a superconducting-circuit realisation of the model [1]. However, in stark contrast to experimental evidence, no EPs appear within the global approach. We then show that the EPs are a feature built into the Redfield equation, which is more accurate than the LME and the GME. Finally, we show that the local approach emerges as the weak-interaction limit of the Redfield equation, and that it entirely avoids the secular approximation.
Y1 - 2021
U6 - https://doi.org/10.22331/q-2021-05-01-451
SN - 2521-327X
VL - 5
PB - Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften
CY - Wien
ER -