@article{MatternvonReppertZeuschneretal.2023, author = {Mattern, Maximilian and von Reppert, Alexander and Zeuschner, Steffen Peer and Herzog, Marc and Pudell, Jan-Etienne and Bargheer, Matias}, title = {Concepts and use cases for picosecond ultrasonics with x-rays}, series = {Photoacoustics}, volume = {31}, journal = {Photoacoustics}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2213-5979}, doi = {10.1016/j.pacs.2023.100503}, pages = {22}, year = {2023}, abstract = {This review discusses picosecond ultrasonics experiments using ultrashort hard x-ray probe pulses to extract the transient strain response of laser-excited nanoscopic structures from Bragg-peak shifts. This method provides direct, layer-specific, and quantitative information on the picosecond strain response for structures down to few-nm thickness. We model the transient strain using the elastic wave equation and express the driving stress using Gruneisen parameters stating that the laser-induced stress is proportional to energy density changes in the microscopic subsystems of the solid, i.e., electrons, phonons and spins. The laser-driven strain response can thus serve as an ultrafast proxy for local energy-density and temperature changes, but we emphasize the importance of the nanoscale morphology for an accurate interpretation due to the Poisson effect. The presented experimental use cases encompass ultrathin and opaque metal-heterostructures, continuous and granular nanolayers as well as negative thermal expansion materials, that each pose a challenge to established all-optical techniques.}, language = {en} } @article{GeistGallagherKotullaetal.2022, author = {Geist, Emily and Gallagher, John S. and Kotulla, Ralf and Oskinova, Lida and Hamann, Wolf-Rainer and Ramachandran, Varsha and Sabbi, Elena and Smith, Linda J. and Kniazev, Alexey and Nota, Antonella and Rickard, Matthew J.}, title = {Ionization and star formation in the giant H ii region SMC-N66}, series = {Publications of the Astronomical Society of the Pacific}, volume = {134}, journal = {Publications of the Astronomical Society of the Pacific}, number = {1036}, publisher = {IOP Publishing}, address = {Bristol}, issn = {0004-6280}, doi = {10.1088/1538-3873/ac697b}, pages = {11}, year = {2022}, abstract = {The NGC 346 young stellar system and associated N66 giant H ii region in the Small Magellanic Cloud are the nearest example of a massive star-forming event in a low metallicity (Z approximate to 0.2Z (circle dot)) galaxy. With an age of less than or similar to 3 Myr this system provides a unique opportunity to study relationships between massive stars and their associated H ii region. Using archival data, we derive a total H alpha luminosity of L(H alpha) = 4.1 x 10(38) erg s(-1) corresponding to an H-photoionization rate of 3 x 10(50) s(-1). A comparison with a predicted stellar ionization rate derived from the more than 50 known O-stars in NGC 346, including massive stars recently classified from Hubble Space Telescope far-ultraviolet (FUV) spectra, indicates an approximate ionization balance. Spectra obtained with SALT suggest the ionization structure of N66 could be consistent with some leakage of ionizing photons. Due to the low metallicity, the FUV luminosity from NGC 346 is not confined to the interstellar cloud associated with N66. Ionization extends through much of the spatial extent of the N66 cloud complex, and most of the cloud mass is not ionized. The stellar mass estimated from nebular L(H alpha) appears to be lower than masses derived from the census of resolved stars which may indicate a disconnect between the formation of high and low mass stars in this region. We briefly discuss implications of the properties of N66 for studies of star formation and stellar feedback in low metallicity environments.}, language = {en} } @article{PerottoniLimbergAmaranteetal.2022, author = {Perottoni, H{\´e}lio D. and Limberg, Guilherme and Amarante, Jo{\~a}o A. S. and Rossi, Silvia and Queiroz, Anna B. A. and Santucci, Rafael M. and P{\´e}rez-Villegas, Angeles and Chiappini, Cristina}, title = {The unmixed debris of Gaia-Sausage/Enceladus in the form of a pair of halo stellar overdensities}, series = {Astrophysical journal letters}, volume = {936}, journal = {Astrophysical journal letters}, number = {1}, publisher = {IOP Publishing}, address = {Bristol}, issn = {2041-8205}, doi = {10.3847/2041-8213/ac88d6}, pages = {7}, year = {2022}, abstract = {In the first billion years after its formation, the galaxy underwent several mergers with dwarf satellites of various masses. The debris of Gaia-Sausage/Enceladus (GSE), the galaxy responsible for the last significant merger of the Milky Way, dominates the inner halo and has been suggested to be the progenitor of both the Hercules-Aquila Cloud (HAC) and Virgo Overdensity (VOD). We combine SEGUE, APOGEE, Gaia, and StarHorse distances to characterize the chemodynamical properties and verify the link between HAC, VOD, and GSE. We find that the orbital eccentricity distributions of the stellar overdensities and GSE are comparable. We also find that they have similar, strongly peaked, metallicity distribution functions, reinforcing the hypothesis of common origin. Furthermore, we show that HAC and VOD are indistinguishable from the prototypical GSE population within all chemical-abundance spaces analyzed. All these evidences combined provide a clear demonstration that the GSE merger is the main progenitor of the stellar populations found within these halo overdensities.}, language = {en} } @article{PranavHultzschMusiienkoetal.2023, author = {Pranav, Manasi and Hultzsch, Thomas and Musiienko, Artem and Sun, Bowen and Shukla, Atul and Jaiser, Frank and Shoaee, Safa and Neher, Dieter}, title = {Anticorrelated photoluminescence and free charge generation proves field-assisted exciton dissociation in low-offset PM6:Y5 organic solar cells}, series = {APL materials : high impact open access journal in functional materials science}, volume = {11}, journal = {APL materials : high impact open access journal in functional materials science}, number = {6}, publisher = {AIP Publishing}, address = {Melville}, issn = {2166-532X}, doi = {10.1063/5.0151580}, pages = {8}, year = {2023}, abstract = {Understanding the origin of inefficient photocurrent generation in organic solar cells with low energy offset remains key to realizing high-performance donor-acceptor systems. Here, we probe the origin of field-dependent free-charge generation and photoluminescence in wnon-fullereneacceptor (NFA)-based organic solar cells using the polymer PM6 and the NFA Y5-a non-halogenated sibling to Y6, with a smaller energetic offset to PM6. By performing time-delayed collection field (TDCF) measurements on a variety of samples with different electron transport layers and active layer thickness, we show that the fill factor and photocurrent are limited by field-dependent free charge generation in the bulk of the blend. We also introduce a new method of TDCF called m-TDCF to prove the absence of artifacts from non-geminate recombination of photogenerated and dark charge carriers near the electrodes. We then correlate free charge generation with steady-state photoluminescence intensity and find perfect anticorrelation between these two properties. Through this, we conclude that photocurrent generation in this low-offset system is entirely controlled by the field-dependent dissociation of local excitons into charge-transfer states. (c) 2023 Author(s).}, language = {en} } @article{StojkoskiJolakoskiPaletal.2022, author = {Stojkoski, Viktor and Jolakoski, Petar and Pal, Arnab and Sandev, Trifce and Kocarev, Ljupco and Metzler, Ralf}, title = {Income inequality and mobility in geometric Brownian motion with stochastic resetting: theoretical results and empirical evidence of non-ergodicity}, series = {Philosophical transactions of the Royal Society A: Mathematical, physical and engineering sciences}, volume = {380}, journal = {Philosophical transactions of the Royal Society A: Mathematical, physical and engineering sciences}, number = {2224}, publisher = {Royal Society}, address = {London}, issn = {1364-503X}, doi = {10.1098/rsta.2021.0157}, pages = {17}, year = {2022}, abstract = {We explore the role of non-ergodicity in the relationship between income inequality, the extent of concentration in the income distribution, and income mobility, the feasibility of an individual to change their position in the income rankings. For this purpose, we use the properties of an established model for income growth that includes 'resetting' as a stabilizing force to ensure stationary dynamics. We find that the dynamics of inequality is regime-dependent: it may range from a strictly non-ergodic state where this phenomenon has an increasing trend, up to a stable regime where inequality is steady and the system efficiently mimics ergodicity. Mobility measures, conversely, are always stable over time, but suggest that economies become less mobile in non-ergodic regimes. By fitting the model to empirical data for the income share of the top earners in the USA, we provide evidence that the income dynamics in this country is consistently in a regime in which non-ergodicity characterizes inequality and immobility. Our results can serve as a simple rationale for the observed real-world income dynamics and as such aid in addressing non-ergodicity in various empirical settings across the globe.This article is part of the theme issue 'Kinetic exchange models of societies and economies'.}, language = {en} } @article{MayerLeverPicconietal.2022, author = {Mayer, Dennis and Lever, Fabiano and Picconi, David and Metje, Jan and Ališauskas, Skirmantas and Calegari, Francesca and D{\"u}sterer, Stefan and Ehlert, Christopher and Feifel, Raimund and Niebuhr, Mario and Manschwetus, Bastian and Kuhlmann, Marion and Mazza, Tommaso and Robinson, Matthew Scott and Squibb, Richard J. and Trabattoni, Andrea and Wallner, M{\aa}ns and Saalfrank, Peter and Wolf, Thomas J. A. and G{\"u}hr, Markus}, title = {Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy}, series = {Nature communications}, volume = {13}, journal = {Nature communications}, number = {1}, publisher = {Nature Research}, address = {Berlin}, issn = {2041-1723}, doi = {10.1038/s41467-021-27908-y}, pages = {9}, year = {2022}, abstract = {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.}, language = {en} } @article{LiuIgnatovaKimbergetal.2022, author = {Liu, Ji-Cai and Ignatova, Nina and Kimberg, Victor and Krasnov, Pavel and F{\"o}hlisch, Alexander and Simon, Marc and Gel'mukhanov, Faris}, title = {Time-resolved study of recoil-induced rotation by X-ray pump - X-ray probe spectroscopy}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {24}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {11}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/d1cp05000a}, pages = {6627 -- 6638}, year = {2022}, abstract = {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.}, language = {en} } @article{AbiusoHolubecAndersetal.2022, author = {Abiuso, Paolo and Holubec, Viktor and Anders, Janet and Ye, Zhuolin and Cerisola, Federico and Perarnau-Llobet, Marti}, title = {Thermodynamics and optimal protocols of multidimensional quadratic Brownian systems}, series = {Journal of physics communications}, volume = {6}, journal = {Journal of physics communications}, number = {6}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2399-6528}, doi = {10.1088/2399-6528/ac72f8}, pages = {15}, year = {2022}, abstract = {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.}, language = {en} } @article{VoroshninTarasovBokaietal.2022, author = {Voroshnin, Vladimir and Tarasov, Artem V. and Bokai, Kirill A. and Chikina, Alla and Senkovskiy, Boris V. and Ehlen, Niels and Usachov, Dmitry Yu. and Gruneis, Alexander and Krivenkov, Maxim and Sanchez-Barriga, Jaime and Fedorov, Alexander}, title = {Direct spectroscopic evidence of magnetic proximity effect in MoS2 monolayer on graphene/Co}, series = {ACS nano}, volume = {16}, journal = {ACS nano}, number = {5}, publisher = {American Chemical Society}, address = {Washington}, issn = {1936-0851}, doi = {10.1021/acsnano.1c10391}, pages = {7448 -- 7456}, year = {2022}, abstract = {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.}, language = {en} } @article{MillerCionideGrijsetal.2022, author = {Miller, Amy E. and Cioni, Maria-Rosa L. and de Grijs, Richard and Sun, Ning-Chen and Bell, Cameron P. M. and Choudhury, Samyaday and Ivanov, Valentin D. and Marconi, Marcella and Oliveira, Joana M. and Petr-Gotzens, Monika and Ripepi, Vincenzo and van Loon, Jacco Th.}, title = {The VMC survey - XLVII. Turbulence-controlled hierarchical star formation in the large magellanic cloud}, series = {Monthly notices of the Royal Astronomical Society}, volume = {512}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stac508}, pages = {1196 -- 1213}, year = {2022}, abstract = {We perform a statistical clustering analysis of upper main-sequence stars in the Large Magellanic Cloud (LMC) using data from the Visible and Infrared Survey Telescope for Astronomy survey of the Magellanic Clouds. We map over 2500 young stellar structures at 15 significance levels across similar to 120 square degrees centred on the LMC. The structures have sizes ranging from a few parsecs to over 1 kpc. We find that the young structures follow power-law size and mass distributions. From the perimeter-area relation, we derive a perimeter-area dimension of 1.44 +/- 0.20. From the mass-size relation and the size distribution, we derive two-dimensional fractal dimensions of 1.50 +/- 0.10 and 1.61 +/- 0.20, respectively. We find that the surface density distribution is well represented by a lognormal distribution. We apply the Larson relation to estimate the velocity dispersions and crossing times of these structures. Our results indicate that the fractal nature of the young stellar structures has been inherited from the gas clouds from which they form and that this architecture is generated by supersonic turbulence. Our results also suggest that star formation in the LMC is scale-free from 10 to 700 pc.}, language = {en} }