TY - JOUR A1 - Odziomek, Mateusz A1 - Giusto, Paolo A1 - Kossmann, Janina A1 - Tarakina, Nadezda A1 - Heske, Julian A1 - Rivadeneira, Salvador M. A1 - Keil, Waldemar A1 - Schmidt, Claudia A1 - Mazzanti, Stefano A1 - Savateev, Oleksandr A1 - Perdigon-Toro, Lorena A1 - Neher, Dieter A1 - Kühne, Thomas D. A1 - Antonietti, Markus A1 - Lopez-Salas, Nieves T1 - "Red Carbon": a rediscovered covalent crystalline semiconductor JF - Advanced materials N2 - Carbon suboxide (C3O2) is a unique molecule able to polymerize spontaneously into highly conjugated light-absorbing structures at temperatures as low as 0 degrees C. Despite obvious advantages, little is known about the nature and the functional properties of this carbonaceous material. In this work, the aim is to bring "red carbon," a forgotten polymeric semiconductor, back to the community's attention. A solution polymerization process is adapted to simplify the synthesis and control the structure. This allows one to obtain this crystalline covalent material at low temperatures. Both spectroscopic and elemental analyses support the chemical structure represented as conjugated ladder polypyrone ribbons. Density functional theory calculations suggest a crystalline structure of AB stacks of polypyrone ribbons and identify the material as a direct bandgap semiconductor with a medium bandgap that is further confirmed by optical analysis. The material shows promising photocatalytic performance using blue light. Moreover, the simple condensation-aromatization route described here allows the straightforward fabrication of conjugated ladder polymers and can be inspiring for the synthesis of carbonaceous materials at low temperatures in general. KW - carbon suboxide KW - carbonaceous materials KW - conjugated ladder polymers KW - covalent materials KW - photocatalysts Y1 - 2022 U6 - https://doi.org/10.1002/adma.202206405 SN - 0935-9648 SN - 1521-4095 VL - 34 IS - 40 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Yochelis, Arik A1 - Flemming, Sven A1 - Beta, Carsten T1 - Versatile patterns in the actin cortex of motile cells BT - self-organized pulses can coexist with macropinocytic ring-shaped waves JF - Physical review letters N2 - Self-organized patterns in the actin cytoskeleton are essential for eukaryotic cellular life. They are the building blocks of many functional structures that often operate simultaneously to facilitate, for example, nutrient uptake and movement of cells. However, identifying how qualitatively distinct actin patterns can coexist remains a challenge. Using bifurcation theory of a mass conserved activator-inhibitor system, we uncover a generic mechanism of how different actin waves-traveling waves and excitable pulses- organize and simultaneously emerge. Live-cell imaging experiments indeed reveal that narrow, planar, and fast-moving excitable pulses may coexist with ring-shaped macropinocytic actin waves in the cortex of motile amoeboid cells. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevLett.129.088101 SN - 0031-9007 SN - 1079-7114 VL - 129 IS - 8 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Kluge, Lucas A1 - Levermann, Anders A1 - Schewe, Jacob T1 - Radiation model for migration with directional preferences JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - The radiation model is a parameter-free model of human mobility that has been applied primarily for short-distance moves, such as commuting. When applied to migration, it underestimates the number of long-range moves, such as between different US states. Here we show that it additionally suffers from a conceptual inconsistency that can have substantial numerical effects on long-distance moves. We propose a modification of the radiation model that introduces a dependence on the angle between any two alternative potential destinations, accounting for the possibility that migrants may have preferences about the approximate direction of their move. We demonstrate that this modification mitigates the conceptual inconsistency and improves the model fit to observational migration data, without introducing any fitting parameters. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevE.106.064138 SN - 2470-0045 SN - 2470-0053 VL - 106 IS - 6 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Henkel, Carsten A1 - Folman, Ron T1 - Internal decoherence in nano-object interferometry due to phonons JF - AVS Quantum Science N2 - We discuss the coherent splitting and recombining of a nanoparticle in a mesoscopic "closed-loop" Stern-Gerlach interferometer in which the observable is the spin of a single impurity embedded in the particle. This spin, when interacting with a pulsed magnetic gradient, generates the force on the particle. We calculate the internal decoherence, which arises as the displaced impurity excites internal degrees of freedom (phonons) that may provide WelcherWeg information and preclude interference. We estimate the constraints this decoherence channel puts on future interference experiments with massive objects. We find that for a wide range of masses, forces, and temperatures, phonons do not inhibit Stern-Gerlach interferometry with micro-scale objects. However, phonons do constitute a fundamental limit on the splitting of larger macroscopic objects if the applied force induces phonons. Y1 - 2022 U6 - https://doi.org/10.1116/5.0080503 SN - 2639-0213 VL - 4 IS - 2 PB - AIP Publishing CY - Melville ER - TY - THES A1 - Novakovic-Marinkovic, Nina T1 - Optical control of bubble domains and skyrmions in thin films T1 - Optische Kontrolle von Blasendomänen und Skyrmionen in dünnen Schichten N2 - Laser induced switching offers an attractive possibility to manipulate small magnetic domains for prospective memory and logic devices on ultrashort time scales. Moreover, optical control of magnetization without high applied magnetic fields allows manipulation of magnetic domains individually and locally, without expensive heat dissipation. One of the major challenges for developing novel optically controlled magnetic memory and logic devices is reliable formation and annihilation of non-volatile magnetic domains that can serve as memory bits in ambient conditions. Magnetic skyrmions, topologically nontrivial spin textures, have been studied intensively since their discovery due to their stability and scalability in potential spintronic devices. However, skyrmion formation and, especially, annihilation processes are still not completely understood and further investigation on such mechanisms are needed. The aim of this thesis is to contribute to better understanding of the physical processes behind the optical control of magnetism in thin films, with the goal of optimizing material parameters and methods for their potential use in next generation memory and logic devices. First part of the thesis is dedicated to investigation of all-optical helicity-dependent switching (AO-HDS) as a method for magnetization manipulation. AO-HDS in Co/Pt multilayer and CoFeB alloys with and without the presence of Dzyaloshinskii-Moriya interaction (DMI), which is a type of exchange interaction, have been investigated by magnetic imaging using photo-emission electron microscopy (PEEM) in combination with X-ray magnetic circular dichroism (XMCD). The results show that in a narrow range of the laser fluence, circularly polarized laser light induces a drag on domain walls. This enables a local deterministic transformation of the magnetic domain pattern from stripes to bubbles in out-of-plane magnetized Co/Pt multilayers, only controlled by the helicity of ultrashort laser pulses. The temperature and characteristic fields at which the stripe-bubble transformation occurs has been calculated using theory for isolated magnetic bubbles, using as parameters experimentally determined average size of stripe domains and the magnetic layer thickness. The second part of the work aims at purely optical formation and annihilation of magnetic skyrmions by a single laser pulse. The presence of a skyrmion phase in the investigated CoFeB alloys was first confirmed using a Kerr microscope. Then the helicity-dependent skyrmion manipulation was studied using AO-HDS at different laser fluences. It was found that formation or annihilation individual skyrmions using AO-HDS is possible, but not always reliable, as fluctuations in the laser fluence or position can easily overwrite the helicity-dependent effect of AO-HDS. However, the experimental results and magnetic simulations showed that the threshold values for the laser fluence for the formation and annihilation of skyrmions are different. A higher fluence is required for skyrmion formation, and existing skyrmions can be annihilated by pulses with a slightly lower fluence. This provides a further option for controlling formation and annihilation of skyrmions using the laser fluence. Micromagnetic simulations provide additional insights into the formation and annihilation mechanism. The ability to manipulate the magnetic state of individual skyrmions is of fundamental importance for magnetic data storage technologies. Our results show for the first time that the optical formation and annihilation of skyrmions is possible without changing the external field. These results enable further investigations to optimise the magnetic layer to maximise the energy gap between the formation and annihilation barrier. As a result, unwanted switching due to small laser fluctuations can be avoided and fully deterministic optical switching can be achieved. N2 - Laser induziertes Schalten bietet eine attraktive Möglichkeit zur Manipulation kleiner magnetischer Domänen für zukünftige Speicher- und Logikbauteile auf ultrakurzen Zeitskalen. Darüber hinaus ermöglicht die rein optische Kontrolle der Magnetisierung ohne hohe angelegte Magnetfelder eine individuelle und lokale Manipulation magnetischer Domänen ohne teure Wärmeverluste. Eine der größten Herausforderungen bei der Entwicklung neuartiger optisch kontrollierter magnetischer Speicher- und Logikbauteile ist das zuverlässige Schreiben stabiler magnetischer Domänen, die unter Umgebungsbedingungen als Speicherbits dienen können. Magnetische Skyrmionen, topologisch nichttriviale wirbelf¨ormige Spin-Texturen, wurden seit ihrer Entdeckung aufgrund ihrer Stabilität und Skalierbarkeit in potenziellen spintronischen Bauelementen intensiv untersucht. Allerdings sind die Prozesse der Skyrmionenbildung und vor allem der Skyrmionenvernichtung noch immer nicht vollständig verstanden, so dass weitere Untersuchungen zu diesen Mechanismen erforderlich sind. Ziel dieser Arbeit ist es, zu einem besseren Verständnis der physikalischen Prozesse beizutragen, die der optischen Kontrolle magnetischer Texturen in dünnen Filmen zugrunde liegen, mit dem Ziel, die Materialparameter und Methoden für ihren potenziellen Einsatz in Speicher- und Logikbauteilen der nächsten Generation zu optimieren. Der erste Teil der Arbeit widmet sich der Untersuchung des rein optischen helizitätsabhängigen Schaltens (AO-HDS) als Methode zur Manipulation der Magnetisierung. AO-HDS wurde in Co/Pt-Multilayern und CoFeB-Legierungen mit und ohne DMI (Dzyaloshinskii-Moriya-Wechselwirkung), einer Art Austauschwechselwirkung, mittels magnetischer Bildgebung durch Photoemissions-Elektronenmikroskopie (PEEM) in Kombination mit magnetischem Röntgendichroismus (XMCD) untersucht. Die Ergebnisse zeigen, dass zirkular polarisiertes Licht in einem bestimmten Bereich der Laserfluenz einen Zug auf Domänenwände ausübt. Dies ermöglicht eine lokale deterministische Umwandlung des magnetischen Domänenmusters von Streifen zu Blasen Domänen in unmagnetisierten Co/Pt- Multilagen, die ausschließlich durch die Helizität der ultrakurzen Laserpulse gesteuert wird. Die Temperatur und die charakteristischen Felder, bei denen die Umwandlung von Streifen zu Blasen Domänen stattfindet, wurden mithilfe der Theorie für isolierte magnetische Blasen berechnet, wobei die experimentell ermittelte durchschnittliche Größe der Streifendom¨anen und die Dicke der magnetischen Schicht als Parameter verwendet wurden. Der zweite Teil der Arbeit zielt darauf ab, optimale Parameter zu ermitteln, die für das rein optische Schreiben und Löschen von magnetischen Skyrmionen in einem einzigen Laser Puls erforderlich sind. Das Vorhandensein einer Skyrmion-Phase in dafür verwendeten CoFeB-Legierungen wurde zunächst mit Hilfe eines Kerr-Mikroskops bestätigt. Dann wurde die helizitätsabhängige Skyrmion-Manipulation mittels AOHDS für verschiedene Laserfluenzen untersucht. Es zeigte sich, dass eine Schreiben oder Löschen einzelner Skyrmionen mittels AO-HDS zwar möglich ist, aber nicht immer zuverlässig, da Fluktuationen in der Laserfluenz oder Position den helizitätsabhängigen Effekt von AO-HDS leicht überschreiben können. Die experimentellen Ergebnisse und magnetischen Simulationen zeigten allerdings, dass die Schwellenwerte für die Laserfluenz zur Bildung und Vernichtung von Skyrmionen unterschiedlich sind. Für die Skyrmionenbildung wird eine höhere Fluenz benötigt, und bereits existierende Skyrmionen können durch Laser Pulse mit etwas geringerer Fluenz gelöscht werden. Dadurch bietet sich eine weitere Möglichkeit das Schreiben und Löschen von Skyrmionen durch die Laserfluenz zu kontrollieren. Mikromagnetische Simulationen liefern zusätzliche Erkenntnisse über den Schreib- und Löschmechanismus. Die Möglichkeit, den magnetischen Zustand einzelner Skyrmionen zu manipulieren, ist von grundlegender Bedeutung für magnetische Datenspeichertechnologien. Unsere Ergebnisse zeigen erstmalig, dass die optische Bildung und Vernichtung von Skyrmionen ohne Änderung des externen Feldes möglich ist. Diese Ergebnisse ermöglichen weitere Untersuchungen zur Optimierung der magnetischen Schicht, um die Energielücke zwischen Bildungs- und Vernichtungsbarriere zu maximieren. Dadurch kann unerwünschtes Schalten aufgrund kleiner Laserfluktuationen vermieden und vollständig deterministisches optisches Schalten erreicht werden. KW - Skyrmions KW - bubble domains KW - magnetism KW - Skyrmionen KW - Blasendomänen KW - Magnetismus KW - dünne Schichten KW - thin films Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-647069 ER - TY - JOUR A1 - Gonzalez Manrique, Sergio Javier A1 - Kuckein, Christoph A1 - Collados, M. A1 - Denker, Carsten A1 - Solanki, S. K. A1 - Gomory, P. A1 - Verma, Meetu A1 - Balthasar, H. A1 - Lagg, A. A1 - Diercke, Andrea T1 - Temporal evolution of arch filaments as seen in He I 10 830 angstrom JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. We study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them. Methods. We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10 830 angstrom spectral range. The He I triplet profiles were fitted with analytic functions to infer line-of-sight (LOS) velocities to follow plasma motions within the AFS. Results. We tracked the temporal evolution of an individual arch filament over its entire lifetime, as seen in the He I 10 830 angstrom triplet. The arch filament expanded in height and extended in length from 13 ' to 21 '. The lifetime of this arch filament is about 30 min. About 11 min after the arch filament is seen in He I, the loop top starts to rise with an average Doppler velocity of 6 km s(-1). Only two minutes later, plasma drains down with supersonic velocities towards the footpoints reaching a peak velocity of up to 40 km s(-1) in the chromosphere. The temporal evolution of He I 10 830 angstrom profiles near the leading pore showed almost ubiquitous dual red components of the He I triplet, indicating strong downflows, along with material nearly at rest within the same resolution element during the whole observing time. KW - Sun: chromosphere KW - Sun: activity KW - methods: observational KW - methods: data analysis KW - techniques: high angular resolution Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201832684 SN - 1432-0746 VL - 617 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Verma, Meetu A1 - Denker, Carsten A1 - Balthasar, H. A1 - Kuckein, Christoph A1 - González Manrique, Sergio Javier A1 - Sobotka, M. A1 - Gonzalez, N. Bello A1 - Hoch, S. A1 - Diercke, Andrea A1 - Kummerow, Philipp A1 - Berkefeld, T. A1 - Collados Vera, M. A1 - Feller, A. A1 - Hofmann, A. A1 - Kneer, F. A1 - Lagg, A. A1 - Löhner-Böttcher, J. A1 - Nicklas, H. A1 - Pastor Yabar, A. A1 - Schlichenmaier, R. A1 - Schmidt, D. A1 - Schmidt, W. A1 - Schubert, M. A1 - Sigwarth, M. A1 - Solanki, S. K. A1 - Soltau, D. A1 - Staude, J. A1 - Strassmeier, Klaus G. A1 - Volkmer, R. A1 - von der Lühe, O. A1 - Waldmann, T. T1 - Horizontal flow fields in and around a small active region The transition period between flux emergence and decay JF - Polymers N2 - Context. The solar magnetic field is responsible for all aspects of solar activity. Thus, emergence of magnetic flux at the surface is the first manifestation of the ensuing solar activity. Aims. Combining high-resolution and synoptic observations aims to provide a comprehensive description of flux emergence at photospheric level and of the growth process that eventually leads to a mature active region. Methods. The small active region NOAA 12118 emerged on 2014 July 17 and was observed one day later with the 1.5-m GREGOR solar telescope on 2014 July 18. High-resolution time-series of blue continuum and G-band images acquired in the blue imaging channel (BIC) of the GREGOR Fabry-Perot Interferometer (GFPI) were complemented by synoptic line-of-sight magnetograms and continuum images obtained with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Horizontal proper motions and horizontal plasma velocities were computed with local correlation tracking (LCT) and the differential affine velocity estimator (DAVE), respectively. Morphological image processing was employed to measure the photometric and magnetic area, magnetic flux, and the separation profile of the emerging flux region during its evolution. Results. The computed growth rates for photometric area, magnetic area, and magnetic flux are about twice as high as the respective decay rates. The space-time diagram using HMI magnetograms of five days provides a comprehensive view of growth and decay. It traces a leaf-like structure, which is determined by the initial separation of the two polarities, a rapid expansion phase, a time when the spread stalls, and a period when the region slowly shrinks again. The separation rate of 0.26 km s(-1) is highest in the initial stage, and it decreases when the separation comes to a halt. Horizontal plasma velocities computed at four evolutionary stages indicate a changing pattern of inflows. In LCT maps we find persistent flow patterns such as outward motions in the outer part of the two major pores, a diverging feature near the trailing pore marking the site of upwelling plasma and flux emergence, and low velocities in the interior of dark pores. We detected many elongated rapidly expanding granules between the two major polarities, with dimensions twice as large as the normal granules. KW - Sun: photosphere KW - Sun: magnetic fields KW - techniques: image processing KW - methods: data analysis Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201628380 SN - 1432-0746 VL - 596 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Gonzalez Manrique, Sergio Javier A1 - Kuckein, Christoph A1 - Pastor Yabar, A. A1 - Collados Vera, M. A1 - Denker, Carsten A1 - Fischer, C. E. A1 - Gömöry, P. A1 - Diercke, Andrea A1 - Gonzalez, N. Bello A1 - Schlichenmaier, R. A1 - Balthasar, H. A1 - Berkefeld, T. A1 - Feller, A. A1 - Hoch, S. A1 - Hofmann, A. A1 - Kneer, F. A1 - Lagg, A. A1 - Nicklas, H. A1 - Orozco Suarez, D. A1 - Schmidt, D. A1 - Schmidt, W. A1 - Sigwarth, M. A1 - Sobotka, M. A1 - Solanki, S. K. A1 - Soltau, D. A1 - Staude, J. A1 - Strassmeier, Klaus G. A1 - Verma, Meetu A1 - Volkmer, R. A1 - von der Lühe, O. A1 - Waldmann, T. T1 - Fitting peculiar spectral profiles in He I 10830 angstrom absorption features JF - Astronomische Nachrichten = Astronomical notes N2 - The new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple-component profiles are more commonly observed with these instruments. Particularly, the He i 10830 triplet presents such peculiar spectral profiles, which give information on the velocity and magnetic fine structure of the upper chromosphere. The purpose of this investigation is to describe a technique to efficiently fit the two blended components of the He i 10830 triplet, which are commonly observed when two atmospheric components are located within the same resolution element. The observations used in this study were taken on 2015 April 17 with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar telescope, located at the Observatorio del Teide, Tenerife, Spain. We apply a double-Lorentzian fitting technique using Levenberg-Marquardt least-squares minimization. This technique is very simple and much faster than inversion codes. Line-of-sight Doppler velocities can be inferred for a whole map of pixels within just a few minutes. Our results show sub-and supersonic downflow velocities of up to 32 km s(-1) for the fast component in the vicinity of footpoints of filamentary structures. The slow component presents velocities close to rest. (C) 2016 WILEY-VCH Verlag GmbH& Co. KGaA, Weinheim KW - Sun: chromosphere KW - methods: data analysis KW - techniques: spectroscopic KW - line: profiles Y1 - 2016 U6 - https://doi.org/10.1002/asna.201512433 SN - 0004-6337 SN - 1521-3994 VL - 337 SP - 1057 EP - 1063 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kamlah, Robert A1 - Verma, Meetu A1 - Diercke, Andrea A1 - Denker, Carsten T1 - Wavelength dependence of image quality metrics and seeing parameters and their relation to adaptive optics performance JF - Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics N2 - Ground-based solar observations are severely affected by Earth's turbulent atmosphere. As a consequence, observed image quality and prevailing seeing conditions are closely related. Partial correction of image degradation is nowadays provided in real time by adaptive optics (AO) systems. In this study, different metrics of image quality are compared with parameters characterizing the prevailing seeing conditions, i.e. Median Filter Gradient Similarity (MFGS), Median Filter Laplacian Similarity (MFLS), Helmli-Scherer mean, granular rms-contrast, differential image motion, and Fried-parameter r(0). The quiet-Sun observations at disk center were carried out at the Vacuum Tower Telescope (VTT), Observatorio del Teide (OT), Izana, Tenerife, Spain. In July and August 2016, time series of short-exposure images were recorded with the High-resolution Fast Imager (HiFI) at various wavelengths in the visible and near-infrared parts of the spectrum. Correlation analysis yields the wavelength dependence of the image quality metrics and seeing parameters, and Uniform Manifold Approximation and Projection (UMAP) is employed to characterize the seeing on a particular observing day. In addition, the image quality metrics and seeing parameters are used to determine the field dependence of the correction provided by the AO system. Management of high-resolution imaging data from large-aperture, ground-based telescopes demands reliable image quality metrics and meaningful characterization of prevailing seeing conditions and AO performance. The present study offers guidance on how retrieving such information ex post facto. KW - Granulation KW - Photosphere KW - Chromosphere KW - Image restoration KW - Adaptive KW - optics KW - Instrumentation and data management Y1 - 2021 U6 - https://doi.org/10.1007/s11207-021-01771-y SN - 1573-093X VL - 296 IS - 2 PB - Springer Science + Business Media B.V CY - Dordrecht [u.a.] ER - TY - JOUR A1 - Meyer, Dominique M.-A. A1 - Meliani, Zakaria T1 - Pulsar wind nebulae of runaway massive stars JF - Monthly notices of the Royal Astronomical Society. Letters N2 - A significant fraction of massive stars move at speed through the interstellar medium of galaxies. After their death as core-collapse supernovae, a possible final evolutionary state is that of a fast-rotating magnetized neutron star, shaping its circumstellar medium into a pulsar wind nebula. Understanding the properties of pulsar wind nebulae requires knowledge of the evolutionary history of their massive progenitors. Using two-dimensional magnetohydrodynamical simulations, we demonstrate that, in the context of a runaway high-mass red-supergiant supernova progenitor, the morphology of its subsequent pulsar wind nebula is strongly affected by the wind of the defunct progenitor star pre-shaping the stellar surroundings throughout its entire past life. In particular, pulsar wind nebulae of obscured runaway massive stars harbour asymmetries as a function of the morphology of the progenitor's wind-blown cavity, inducing projected asymmetric up-down synchrotron emission. KW - methods: MHD KW - stars: evolution KW - stars: massive KW - pulsars: general KW - ISM: supernova remnants Y1 - 2022 U6 - https://doi.org/10.1093/mnrasl/slac062 SN - 1745-3933 SN - 1745-3925 VL - 515 IS - 1 SP - L29 EP - L33 PB - Oxford Univ. Press CY - Oxford ER -