TY - JOUR A1 - Shayduk, Roman A1 - Herzog, Marc A1 - Bojahr, Andre A1 - Schick, Daniel A1 - Gaal, Peter A1 - Leitenberger, Wolfram A1 - Navirian, Hengameh A1 - Sander, Mathias A1 - Goldshteyn, Jevgenij A1 - Vrejoiu, Ionela A1 - Bargheer, Matias T1 - Direct time-domain sampling of subterahertz coherent acoustic phonon spectra in SrTiO3 using ultrafast x-ray diffraction JF - Physical review : B, Condensed matter and materials physics N2 - We synthesize sub-THz longitudinal quasimonochromatic acoustic phonons in a SrTiO3 single crystal using a SrRuO3/SrTiO3 superlattice as an optical-acoustic transducer. The generated acoustic phonon spectrum is determined using ultrafast x-ray diffraction. The analysis of the generated phonon spectrum in the time domain reveals a k-vector dependent phonon lifetime. It is observed that even at sub-THz frequencies the phonon lifetime agrees with the 1/omega(2) power law known from Akhiezer's model for hyper sound attenuation. The observed shift of the synthesized spectrum to the higher q is discussed in the framework of nonlinear effects appearing due to the high amplitude of the synthesized phonons. Y1 - 2013 U6 - https://doi.org/10.1103/PhysRevB.87.184301 SN - 1098-0121 VL - 87 IS - 18 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Schick, Daniel A1 - Herzog, Marc A1 - Wen, Haidan A1 - Chen, Pice A1 - Adamo, Carolina A1 - Gaal, Peter A1 - Schlom, Darrell G. A1 - Evans, Paul G. A1 - Li, Yuelin A1 - Bargheer, Matias T1 - Localized excited charge carriers generate ultrafast inhomogeneous strain in the multiferroic BiFeO3 JF - Physical review letters N2 - We apply ultrafast x-ray diffraction with femtosecond temporal resolution to monitor the lattice dynamics in a thin film of multiferroic BiFeO3 after above-band-gap photoexcitation. The sound-velocity limited evolution of the observed lattice strains indicates a quasi-instantaneous photoinduced stress which decays on a nanosecond time scale. This stress exhibits an inhomogeneous spatial profile evidenced by the broadening of the Bragg peak. These new data require substantial modification of existing models of photogenerated stresses in BiFeO3: the relevant excited charge carriers must remain localized to be consistent with the data. Y1 - 2014 U6 - https://doi.org/10.1103/PhysRevLett.112.097602 SN - 0031-9007 SN - 1079-7114 VL - 112 IS - 9 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Shayduk, Roman A1 - Navirian, Hengameh A1 - Leitenberger, Wolfram A1 - Goldshteyn, Jevgenij A1 - Vrejoiu, Ionela A1 - Weinelt, Martin A1 - Gaal, Peter A1 - Herzog, Marc A1 - von Korff Schmising, Clemens A1 - Bargheer, Matias T1 - Nanoscale heat transport studied by high-resolution time-resolved x-ray diffraction JF - New journal of physics : the open-access journal for physics N2 - We report on synchrotron-based high-repetition rate ultrafast x-ray diffraction (UXRD) experiments monitoring the transport of heat from an epitaxial La(0.7)Sr(0.3)MnO(3)/SrTiO(3) superlattice (SL) into the substrate on timescales from 100 ps to 4 mu s. Transient thermal lattice expansion was determined with an accuracy of 10(-7), corresponding to a sensitivity to temperature changes down to 0.01 K. We follow the heat flow within the SL and into the substrate after the impulsive laser heating leads to a small temperature rise of Delta T = 6 K. The transient lattice temperature can be simulated very well using the bulk heat conductivities. This contradicts the interpretation of previous UXRD measurements, which predicted a long-lasting expansion of SrRuO(3) for more than 200 ps. The disagreement could be resolved by assuming that the heat conductivity changes in the first hundred picoseconds. Y1 - 2011 U6 - https://doi.org/10.1088/1367-2630/13/9/093032 SN - 1367-2630 VL - 13 IS - 11 PB - IOP Publ. Ltd. CY - Bristol 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 - Bojahr, Andre A1 - Gohlke, Matthias A1 - Leitenberger, Wolfram A1 - Pudell, Jan-Etienne A1 - Reinhardt, Matthias A1 - von Reppert, Alexander 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 - Goldshteyn, Jevgeni A1 - Bojahr, Andre A1 - Gaal, Peter A1 - Schick, Daniel A1 - Bargheer, Matias T1 - Selective preparation and detection of phonon polariton wavepackets by stimulated Raman scattering JF - Physica status solidi : Physica status solidi N2 - Wavevector-selective impulsive excitation of phonon-polaritons by a spectrally broad femtosecond transient grating produces wavepackets propagating in opposite directions. The photons in spectrally narrow probe pulses are scattered from these elementary excitations in lithium niobate (LiNbO3). Both elastically and inelastically scattered photons are simultaneously detected in a spectrometer. The Stokes- and anti-Stokes shifted probe pulses uniquely determine the propagation direction of the detected polariton wavepacket components and correspond to creation or annihilation of phonon-polaritons. Our experiments with spectrally broad pump and spectrally narrow probe pulses allows dissecting the four-wave-mixing process into two sequential stimulated Raman scattering events. Y1 - 2014 U6 - https://doi.org/10.1002/pssb.201350114 SN - 0370-1972 SN - 1521-3951 VL - 251 IS - 4 SP - 821 EP - 828 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Navirian, Hengameh A. A1 - Schick, Daniel A1 - Gaal, Peter A1 - Leitenberger, Wolfram A1 - Shayduk, Roman A1 - Bargheer, Matias T1 - Thermoelastic study of nanolayered structures using time-resolved X-ray diffraction at high repetition rate JF - Applied physics letters N2 - We investigate the thermoelastic response of a nanolayered sample composed of a metallic SrRuO3 electrode sandwiched between a ferroelectric Pb(Zr0.2Ti0.8)O-3 film with negative thermal expansion and a SrTiO3 substrate. SrRuO3 is rapidly heated by fs-laser pulses with 208 kHz repetition rate. Diffraction of X-ray pulses derived from a synchrotron measures the transient out-of-plane lattice constant c of all three materials simultaneously from 120 ps to 5 mu s with a relative accuracy up to Delta c/c = 10(-6). The in-plane propagation of sound is essential for understanding the delayed out-of-plane compression of Pb(Zr0.2Ti0.8)O-3. Y1 - 2014 U6 - https://doi.org/10.1063/1.4861873 SN - 0003-6951 SN - 1077-3118 VL - 104 IS - 2 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Schick, Daniel A1 - Shayduk, Roman A1 - Bojahr, Andre A1 - Herzog, Marc A1 - von Korff Schmising, Clemens A1 - Gaal, Peter A1 - Bargheer, Matias T1 - Ultrafast reciprocal-space mapping with a convergent beam JF - JOURNAL OF APPLIED CRYSTALLOGRAPHY N2 - A diffractometer setup is presented, based on a laser-driven plasma X-ray source for reciprocal-space mapping with femtosecond temporal resolution. In order to map out the reciprocal space, an X-ray optic with a convergent beam is used with an X-ray area detector to detect symmetrically and asymmetrically diffracted X-ray photons simultaneously. The setup is particularly suited for measuring thin films or imperfect bulk samples with broad rocking curves. For quasi-perfect crystalline samples with insignificant in-plane Bragg peak broadening, the measured reciprocal-space maps can be corrected for the known resolution function of the diffractometer in order to achieve high-resolution rocking curves with improved data quality. In this case, the resolution of the diffractometer is not limited by the convergence of the incoming X-ray beam but is solely determined by its energy bandwidth. Y1 - 2013 U6 - https://doi.org/10.1107/S0021889813020013 SN - 0021-8898 VL - 46 IS - 10 SP - 1372 EP - 1377 PB - WILEY-BLACKWELL CY - HOBOKEN ER - TY - JOUR A1 - Gaal, Peter A1 - Schick, Daniel A1 - Herzog, Marc A1 - Bojahr, Andre A1 - Shayduk, Roman A1 - Goldshteyn, Jevgeni A1 - Leitenberger, Wolfram A1 - Vrejoiu, Ionela A1 - Khakhulin, Dmitry A1 - Wulff, Michael A1 - Bargheer, Matias T1 - Ultrafast switching of hard X-rays JF - Journal of synchrotron radiation N2 - A new concept for shortening hard X-ray pulses emitted from a third-generation synchrotron source down to few picoseconds is presented. The device, called the PicoSwitch, exploits the dynamics of coherent acoustic phonons in a photo-excited thin film. A characterization of the structure demonstrates switching times of <= 5 ps and a peak reflectivity of similar to 10(-3). The device is tested in a real synchrotron-based pump-probe experiment and reveals features of coherent phonon propagation in a second thin film sample, thus demonstrating the potential to significantly improve the temporal resolution at existing synchrotron facilities. KW - ultrafast X-ray diffraction KW - thin film KW - coherent phonons KW - X-ray switching KW - pulse shortening KW - optical pump X-ray probe KW - time-resolved Y1 - 2014 U6 - https://doi.org/10.1107/S1600577513031949 SN - 0909-0495 SN - 1600-5775 VL - 21 SP - 380 EP - 385 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Koc, Azize A1 - Reinhardt, M. A1 - von Reppert, Alexander 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 -