@article{BojahrGohlkeLeitenbergeretal.2015,
  author    = {Bojahr, Andre and Gohlke, Matthias and Leitenberger, Wolfram and Pudell, Jan-Etienne and Reinhardt, Matthias and von Reppert, Alexander and R{\"o}ssle, Matthias and Sander, Mathias and Gaal, Peter and Bargheer, Matias},
  title     = {Second Harmonic Generation of Nanoscale Phonon Wave Packets},
  series = {Physical review letters},
  volume    = {115},
  journal   = {Physical review letters},
  number    = {19},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {0031-9007},
  doi       = {10.1103/PhysRevLett.115.195502},
  pages     = {5},
  year      = {2015},
  abstract  = {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.},
  language  = {en}
}
@misc{SchruenderLenzenZimmermannGoerlichetal.2012,
  author    = {Schr{\"u}nder-Lenzen, Agi and Zimmermann, Matthias and G{\"o}rlich, Petra and Horn-Conrad, Antje and Geller, Katrin and Eckardt, Barbara and Hoffmann, Florian and Pyanoe, Steffi and Kampe, Heike and J{\"a}ger, Sophie and Reinhardt, Ragna},
  title     = {Portal = Zwischen Freiheit und Verantwortung: Ethik in der Forschung},
  number    = {02/2012},
  organization    = {Universit{\"a}t Potsdam, Referat f{\"u}r Presse- und {\"O}ffentlichkeitsarbeit},
  issn      = {1618-6893},
  doi       = {10.25932/publishup-44047},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-440475},
  pages     = {42},
  year      = {2012},
  abstract  = {Aus dem Inhalt: - Zwischen Freiheit und Verantwortung: Ethik in der Forschung - Die Grenzen der Grammatik - Ein Bild von einem Mann},
  language  = {de}
}
@misc{KuehlingvanKempenGebhardtetal.2010,
  author    = {K{\"u}hling, Matthias and van Kempen, Britta and Gebhardt, Thomas and Hustedt, Thurid and Ruberg, Bj{\"o}rn and Schenke, Ulrike and Peter, Andreas and G{\"o}rlich, Petra and Horn-Conrad, Antje and Reinhardt, Ragna and Walch, Claudia},
  title     = {Portal = Was macht das Schaf an der Uni? Lange Nacht der Wissenschaften},
  number    = {02/2010},
  organization    = {Universit{\"a}t Potsdam, Referat f{\"u}r Presse- und {\"O}ffentlichkeitsarbeit},
  issn      = {1618-6893},
  doi       = {10.25932/publishup-44020},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-440209},
  pages     = {43},
  year      = {2010},
  abstract  = {Aus dem Inhalt: - Was macht das Schaf an der Uni? Lange Nacht der Wissenschaften 2010! - Frauen am Dirigentenpult - Diplomaten auf Probe},
  language  = {de}
}
@misc{MangelsdorfGoerlichHeyerStufferetal.2010,
  author    = {Mangelsdorf, Birgit and G{\"o}rlich, Petra and Heyer-Stuffer, Till and Pohlenz, Philipp and Schultz, Sebastian and Sommer, Ute and Horn-Conrad, Antje and Klein, Armin and Zimmermann, Matthias and Peter, Andreas and Reinhardt, Ragna},
  title     = {Portal = Unverzichtbar: Drittmittel f{\"u}r die Forschung},
  number    = {03/2010},
  organization    = {Universit{\"a}t Potsdam, Referat f{\"u}r Presse- und {\"O}ffentlichkeitsarbeit},
  issn      = {1618-6893},
  doi       = {10.25932/publishup-44021},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-440211},
  pages     = {47},
  year      = {2010},
  abstract  = {Aus dem Inhalt: - Unverzichtbar: Drittmittel f{\"u}r die Forschung - Auf Herz und Z{\"a}hne gepr{\"u}ft - Tango mit Goethe},
  language  = {de}
}
@misc{SzameitatWilkensGoerlichetal.2015,
  author    = {Szameitat, Ulrike and Wilkens, Martin and G{\"o}rlich, Petra and Horn-Conrad, Antje and Zimmermann, Matthias and Reinhardt, Kristin and Kampe, Heike and J{\"a}ger, Heidi and Wenzel, Anna Theresa and Scholz, Jana},
  title     = {Portal = Unter einem Dach: Lehrerbildung und Bildungsforschung},
  number    = {02/2015},
  organization    = {Universit{\"a}t Potsdam, Referat f{\"u}r Presse- und {\"O}ffentlichkeitsarbeit},
  issn      = {1618-6893},
  doi       = {10.25932/publishup-44063},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-440634},
  pages     = {46},
  year      = {2015},
  abstract  = {Aus dem Inhalt: - Unter einem Dach: Lehrerbildung und Bildungsforschung - Waldweit - Nicht ohne Eisen und Schwefel},
  language  = {de}
}
@article{KwamenRoessleReinhardtetal.2017,
  author    = {Kwamen, C. and R{\"o}ssle, Matthias and Reinhardt, M. and Leitenberger, Wolfram and Zamponi, Flavio and Alexe, Marin and Bargheer, Matias},
  title     = {Simultaneous dynamic characterization of charge and structural motion during ferroelectric switching},
  series = {Physical review : B, Condensed matter and materials physics},
  volume    = {96},
  journal   = {Physical review : B, Condensed matter and materials physics},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2469-9950},
  doi       = {10.1103/PhysRevB.96.134105},
  pages     = {6},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{KocReinhardtvonReppertetal.2017,
  author    = {Koc, Azize and Reinhardt, M. and von Reppert, Alexander and Roessle, Matthias and Leitenberger, Wolfram and Dumesnil, K. and Gaal, Peter and Zamponi, Flavio and Bargheer, Matias},
  title     = {Ultrafast x-ray diffraction thermometry measures the influence of spin excitations on the heat transport through nanolayers},
  series = {Physical review : B, Condensed matter and materials physics},
  volume    = {96},
  journal   = {Physical review : B, Condensed matter and materials physics},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2469-9950},
  doi       = {10.1103/PhysRevB.96.014306},
  pages     = {7},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{KocReinhardtvonReppertetal.2017,
  author    = {Koc, A. and Reinhardt, M. and von Reppert, Alexander and R{\"o}ssle, Matthias and Leitenberger, Wolfram and Gleich, M. and Weinelt, M. and Zamponi, Flavio and Bargheer, Matias},
  title     = {Grueneisen-approach for the experimental determination of transient spin and phonon energies from ultrafast x-ray diffraction data: gadolinium},
  series = {Journal of physics : Condensed matter},
  volume    = {29},
  journal   = {Journal of physics : Condensed matter},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {0953-8984},
  doi       = {10.1088/1361-648X/aa7187},
  pages     = {5884 -- 5891},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{ReinhardtKocLeitenbergeretal.2016,
  author    = {Reinhardt, Matthias and Koc, Azize and Leitenberger, Wolfram and Gaal, Peter and Bargheer, Matias},
  title     = {Optimized spatial overlap in optical pump-X-ray probe experiments with high repetition rate using laser-induced surface distortions},
  series = {Journal of synchrotron radiation},
  volume    = {23},
  journal   = {Journal of synchrotron radiation},
  publisher = {International Union of Crystallography},
  address   = {Chester},
  issn      = {1600-5775},
  doi       = {10.1107/S1600577515024443},
  pages     = {474 -- 479},
  year      = {2016},
  abstract  = {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.},
  language  = {en}
}