TY - JOUR A1 - Bojahr, Andre A1 - Gohlke, Matthias A1 - Leitenberger, Wolfram A1 - Pudell, Jan-Etienne A1 - Reinhardt, Matthias A1 - Reppert, Alexander von A1 - Rössle, Matthias A1 - Sander, Mathias A1 - Gaal, Peter A1 - Bargheer, Matias T1 - Second Harmonic Generation of Nanoscale Phonon Wave Packets JF - Physical review letters N2 - Phonons are often regarded as delocalized quasiparticles with certain energy and momentum. The anharmonic interaction of phonons determines macroscopic properties of the solid, such as thermal expansion or thermal conductivity, and a detailed understanding becomes increasingly important for functional nanostructures. Although phonon-phonon scattering processes depicted in simple wave-vector diagrams are the basis of theories describing these macroscopic phenomena, experiments directly accessing these coupling channels are scarce. We synthesize monochromatic acoustic phonon wave packets with only a few cycles to introduce nonlinear phononics as the acoustic counterpart to nonlinear optics. Control of the wave vector, bandwidth, and consequently spatial extent of the phonon wave packets allows us to observe nonlinear phonon interaction, in particular, second harmonic generation, in real time by wave-vector-sensitive Brillouin scattering with x-rays and optical photons. Y1 - 2015 U6 - https://doi.org/10.1103/PhysRevLett.115.195502 SN - 0031-9007 SN - 1079-7114 VL - 115 IS - 19 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Schründer-Lenzen, Agi A1 - Zimmermann, Matthias A1 - Görlich, Petra A1 - Horn-Conrad, Antje A1 - Geller, Katrin A1 - Eckardt, Barbara A1 - Hoffmann, Florian A1 - Pyanoe, Steffi A1 - Kampe, Heike A1 - Jäger, Sophie A1 - Reinhardt, Ragna T1 - Portal = Zwischen Freiheit und Verantwortung: Ethik in der Forschung BT - Das Potsdamer Universitätsmagazin N2 - Aus dem Inhalt: - Zwischen Freiheit und Verantwortung: Ethik in der Forschung - Die Grenzen der Grammatik - Ein Bild von einem Mann T3 - Portal: Das Potsdamer Universitätsmagazin - 02/2012 Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-440475 SN - 1618-6893 IS - 02/2012 ER - TY - JOUR A1 - Kühling, Matthias A1 - van Kempen, Britta A1 - Gebhardt, Thomas A1 - Hustedt, Thurid A1 - Ruberg, Björn A1 - Schenke, Ulrike A1 - Peter, Andreas A1 - Görlich, Petra A1 - Horn-Conrad, Antje A1 - Reinhardt, Ragna A1 - Walch, Claudia T1 - Portal = Was macht das Schaf an der Uni? Lange Nacht der Wissenschaften BT - Das Potsdamer Universitätsmagazin N2 - Aus dem Inhalt: - Was macht das Schaf an der Uni? Lange Nacht der Wissenschaften 2010! - Frauen am Dirigentenpult - Diplomaten auf Probe T3 - Portal: Das Potsdamer Universitätsmagazin - 02/2010 Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-440209 SN - 1618-6893 IS - 02/2010 ER - TY - JOUR A1 - Mangelsdorf, Birgit A1 - Görlich, Petra A1 - Heyer-Stuffer, Till A1 - Pohlenz, Philipp A1 - Schultz, Sebastian A1 - Sommer, Ute A1 - Horn-Conrad, Antje A1 - Klein, Armin A1 - Zimmermann, Matthias A1 - Peter, Andreas A1 - Reinhardt, Ragna T1 - Portal = Unverzichtbar: Drittmittel für die Forschung BT - Das Potsdamer Universitätsmagazin N2 - Aus dem Inhalt: - Unverzichtbar: Drittmittel für die Forschung - Auf Herz und Zähne geprüft - Tango mit Goethe T3 - Portal: Das Potsdamer Universitätsmagazin - 03/2010 Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-440211 SN - 1618-6893 IS - 03/2010 ER - TY - JOUR A1 - Szameitat, Ulrike A1 - Wilkens, Martin A1 - Görlich, Petra A1 - Horn-Conrad, Antje A1 - Zimmermann, Matthias A1 - Reinhardt, Kristin A1 - Kampe, Heike A1 - Jäger, Heidi A1 - Wenzel, Anna Theresa A1 - Scholz, Jana T1 - Portal = Unter einem Dach: Lehrerbildung und Bildungsforschung BT - Das Potsdamer Universitätsmagazin N2 - Aus dem Inhalt: - Unter einem Dach: Lehrerbildung und Bildungsforschung - Waldweit - Nicht ohne Eisen und Schwefel T3 - Portal: Das Potsdamer Universitätsmagazin - 02/2015 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-440634 SN - 1618-6893 IS - 02/2015 ER - TY - JOUR A1 - Kwamen, C. A1 - Rössle, Matthias A1 - Reinhardt, M. A1 - Leitenberger, Wolfram A1 - Zamponi, Flavio A1 - Alexe, Marin A1 - Bargheer, Matias T1 - Simultaneous dynamic characterization of charge and structural motion during ferroelectric switching JF - Physical review : B, Condensed matter and materials physics N2 - Monitoring structural changes in ferroelectric thin films during electric field induced polarization switching is important for a full microscopic understanding of the coupled motion of charges, atoms, and domainwalls in ferroelectric nanostructures. We combine standard ferroelectric test sequences of switching and nonswitching electrical pulses with time-resolved x-ray diffraction to investigate the structural response of a nanoscale Pb(Zr0.2Ti0.8)O-3 ferroelectric oxide capacitor upon charging, discharging, and polarization reversal. We observe that a nonlinear piezoelectric response of the ferroelectric layer develops on a much longer time scale than the RC time constant of the device. The complex atomic motion during the ferroelectric polarization reversal starts with a contraction of the lattice, whereas the expansive piezoelectric response sets in after considerable charge flow due to the applied voltage pulses on the electrodes of the capacitor. Our simultaneous measurements on a working device elucidate and visualize the complex interplay of charge flow and structural motion and challenges theoretical modeling. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevB.96.134105 SN - 2469-9950 SN - 2469-9969 VL - 96 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Reinhardt, Matthias A1 - Koc, Azize A1 - Leitenberger, Wolfram A1 - Gaal, Peter A1 - Bargheer, Matias T1 - Optimized spatial overlap in optical pump-X-ray probe experiments with high repetition rate using laser-induced surface distortions JF - Journal of synchrotron radiation N2 - Ultrafast X-ray diffraction experiments require careful adjustment of the spatial overlap between the optical excitation and the X-ray probe pulse. This is especially challenging at high laser repetition rates. Sample distortions caused by the large heat load on the sample and the relatively low optical energy per pulse lead to only tiny signal changes. In consequence, this results in small footprints of the optical excitation on the sample, which turns the adjustment of the overlap difficult. Here a method for reliable overlap adjustment based on reciprocal space mapping of a laser excited thin film is presented. KW - ultrafast X-ray diffraction KW - nanostructures KW - surface deformation KW - heat diffusion KW - optical pump Y1 - 2016 U6 - https://doi.org/10.1107/S1600577515024443 SN - 1600-5775 VL - 23 SP - 474 EP - 479 PB - International Union of Crystallography CY - Chester ER - TY - JOUR A1 - Koc, Azize A1 - Reinhardt, M. A1 - Reppert, Alexander von A1 - Roessle, Matthias A1 - Leitenberger, Wolfram A1 - Dumesnil, K. A1 - Gaal, Peter A1 - Zamponi, Flavio A1 - Bargheer, Matias T1 - Ultrafast x-ray diffraction thermometry measures the influence of spin excitations on the heat transport through nanolayers JF - Physical review : B, Condensed matter and materials physics N2 - We investigate the heat transport through a rare earth multilayer system composed of yttrium (Y), dysprosium (Dy), and niobium (Nb) by ultrafast x-ray diffraction. This is an example of a complex heat flow problem on the nanoscale, where several different quasiparticles carry the heat and conserve a nonequilibrium for more than 10 ns. The Bragg peak positions of each layer represent layer-specific thermometers that measure the energy flow through the sample after excitation of the Y top layer with fs-laser pulses. In an experiment-based analytic solution to the nonequilibrium heat transport problem, we derive the individual contributions of the spins and the coupled electron-lattice system to the heat conduction. The full characterization of the spatiotemporal energy flow at different starting temperatures reveals that the spin excitations of antiferromagnetic Dy speed up the heat transport into the Dy layer at low temperatures, whereas the heat transport through this layer and further into the Y and Nb layers underneath is slowed down. The experimental findings are compared to the solution of the heat equation using macroscopic temperature-dependent material parameters without separation of spin and phonon contributions to the heat. We explain why the simulated energy density matches our experiment-based derivation of the heat transport, although the simulated thermoelastic strain in this simulation is not even in qualitative agreement. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevB.96.014306 SN - 2469-9950 SN - 2469-9969 VL - 96 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Koc, A. A1 - Reinhardt, M. A1 - Reppert, Alexander von A1 - Rössle, Matthias A1 - Leitenberger, Wolfram A1 - Gleich, M. A1 - Weinelt, M. A1 - Zamponi, Flavio A1 - Bargheer, Matias T1 - Grueneisen-approach for the experimental determination of transient spin and phonon energies from ultrafast x-ray diffraction data: gadolinium JF - Journal of physics : Condensed matter N2 - We study gadolinium thin films as a model system for ferromagnets with negative thermal expansion. Ultrashort laser pulses heat up the electronic subsystem and we follow the transient strain via ultrafast x-ray diffraction. In terms of a simple Grueneisen approach, the strain is decomposed into two contributions proportional to the thermal energy of spin and phonon subsystems. Our analysis reveals that upon femtosecond laser excitation, phonons and spins can be driven out of thermal equilibrium for several nanoseconds. KW - ultrafast KW - x-ray diffraction KW - magnetostriction KW - nonequilibrium KW - spin KW - phonon KW - rare earth Y1 - 2017 U6 - https://doi.org/10.1088/1361-648X/aa7187 SN - 0953-8984 SN - 1361-648X VL - 29 SP - 5884 EP - 5891 PB - IOP Publ. Ltd. CY - Bristol ER -