@article{BojahrGohlkeLeitenbergeretal.2015,
  author    = {Bojahr, Andre and Gohlke, Matthias and Leitenberger, Wolfram and Pudell, Jan-Etienne and Reinhardt, Matthias and Reppert, Alexander von 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{ZeuschnerMatternPudelletal.2021,
  author    = {Zeuschner, Steffen Peer and Mattern, Maximilian and Pudell, Jan-Etienne and Reppert, Alexander von and R{\"o}ssle, Matthias and Leitenberger, Wolfram and Schwarzkopf, Jutta and Boschker, Jos and Herzog, Marc and Bargheer, Matias},
  title     = {Reciprocal space slicing},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {1137},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-49976},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-499761},
  pages     = {13},
  year      = {2021},
  abstract  = {An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit (2θ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2.},
  language  = {en}
}
@article{ZeuschnerMatternPudelletal.2021,
  author    = {Zeuschner, Steffen Peer and Mattern, Maximilian and Pudell, Jan-Etienne and Reppert, Alexander von and R{\"o}ssle, Matthias and Leitenberger, Wolfram and Schwarzkopf, Jutta and Boschker, Jos and Herzog, Marc and Bargheer, Matias},
  title     = {Reciprocal space slicing},
  series = {Structural dynamics},
  volume    = {8},
  journal   = {Structural dynamics},
  number    = {1},
  publisher = {AIP Publishing LLC},
  address   = {Melville, NY},
  issn      = {2329-7778},
  doi       = {10.1063/4.0000040},
  pages     = {10},
  year      = {2021},
  abstract  = {An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit (2θ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2.},
  language  = {en}
}
@article{HerzogReppertPudelletal.2022,
  author    = {Herzog, Marc and Reppert, Alexander von and Pudell, Jan-Etienne and Henkel, Carsten and Kronseder, Matthias and Back, Christian H. and Maznev, Alexei A. and Bargheer, Matias},
  title     = {Phonon-dominated energy transport in purely metallic heterostructures},
  series = {Advanced functional materials},
  volume    = {32},
  journal   = {Advanced functional materials},
  number    = {41},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1616-301X},
  doi       = {10.1002/adfm.202206179},
  pages     = {8},
  year      = {2022},
  abstract  = {Ultrafast X-ray diffraction is used to quantify the transport of energy in laser-excited nanoscale gold-nickel (Au-Ni) bilayers. Electron transport and efficient electron-phonon coupling in Ni convert the laser-deposited energy in the conduction electrons within a few picoseconds into a strong non-equilibrium between hot Ni and cold Au phonons at the bilayer interface. Modeling of the subsequent equilibration dynamics within various two-temperature models confirms that for ultrathin Au films, the thermal transport is dominated by phonons instead of conduction electrons because of the weak electron-phonon coupling in Au.},
  language  = {en}
}
@misc{ReppertPuddellKocetal.2016,
  author    = {Reppert, Alexander von and Puddell, J. and Koc, A. and Reinhardt, M. and Leitenberger, Wolfram and Dumesnil, K. and Zamponi, Flavio and Bargheer, Matias},
  title     = {Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98710},
  pages     = {11},
  year      = {2016},
  abstract  = {We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the N{\´e}el temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost.},
  language  = {en}
}
@article{ReppertPudellKocetal.2016,
  author    = {Reppert, Alexander von and Pudell, Jan-Etienne and Koc, A. and Reinhardt, M. and Leitenberger, Wolfram and Dumesnil, K. and Zamponi, Flavio and Bargheer, Matias},
  title     = {Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet},
  series = {Structural dynamics},
  volume    = {3},
  journal   = {Structural dynamics},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {2329-7778},
  doi       = {10.1063/1.4961253},
  pages     = {11},
  year      = {2016},
  abstract  = {We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Neel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost. (C) 2016 Author(s).},
  language  = {en}
}
@article{ReppertPuddellKocetal.2016,
  author    = {Reppert, Alexander von and Puddell, J. and Koc, A. and Reinhardt, M. and Leitenberger, Wolfram and Dumesnil, K. and Zamponi, Flavio and Bargheer, Matias},
  title     = {Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet},
  series = {Structural dynamics},
  volume    = {3},
  journal   = {Structural dynamics},
  publisher = {AIP Publishing LLC},
  address   = {Melville, NY},
  issn      = {2329-7778},
  doi       = {10.1063/1.4961253},
  year      = {2016},
  abstract  = {We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the N{\´e}el temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost.},
  language  = {en}
}
@phdthesis{Reppert2021,
  author    = {Reppert, Alexander von},
  title     = {Magnetic strain contributions in laser-excited metals studied by time-resolved X-ray diffraction},
  doi       = {10.25932/publishup-53558},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-535582},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XV, 311},
  year      = {2021},
  abstract  = {In this work I explore the impact of magnetic order on the laser-induced ultrafast strain response of metals. Few experiments with femto- or picosecond time-resolution have so far investigated magnetic stresses. This is contrasted by the industrial usage of magnetic invar materials or magnetostrictive transducers for ultrasound generation, which already utilize magnetostrictive stresses in the low frequency regime. In the reported experiments I investigate how the energy deposition by the absorption of femtosecond laser pulses in thin metal films leads to an ultrafast stress generation. I utilize that this stress drives an expansion that emits nanoscopic strain pulses, so called hypersound, into adjacent layers. Both the expansion and the strain pulses change the average inter-atomic distance in the sample, which can be tracked with sub-picosecond time resolution using an X-ray diffraction setup at a laser-driven Plasma X-ray source. Ultrafast X-ray diffraction can also be applied to buried layers within heterostructures that cannot be accessed by optical methods, which exhibit a limited penetration into metals. The reconstruction of the initial energy transfer processes from the shape of the strain pulse in buried detection layers represents a contribution of this work to the field of picosecond ultrasonics. A central point for the analysis of the experiments is the direct link between the deposited energy density in the nano-structures and the resulting stress on the crystal lattice. The underlying thermodynamical concept of a Gr{\"u}neisen parameter provides the theoretical framework for my work. I demonstrate how the Gr{\"u}neisen principle can be used for the interpretation of the strain response on ultrafast timescales in various materials and that it can be extended to describe magnetic stresses. The class of heavy rare-earth elements exhibits especially large magnetostriction effects, which can even lead to an unconventional contraction of the laser-excited transducer material. Such a dominant contribution of the magnetic stress to the motion of atoms has not been demonstrated previously. The observed rise time of the magnetic stress contribution in Dysprosium is identical to the decrease in the helical spin-order, that has been found previously using time-resolved resonant X-ray diffraction. This indicates that the strength of the magnetic stress can be used as a proxy of the underlying magnetic order. Such magnetostriction measurements are applicable even in case of antiparallel or non-collinear alignment of the magnetic moments and a vanishing magnetization. The strain response of metal films is usually determined by the pressure of electrons and lattice vibrations. I have developed a versatile two-pulse excitation routine that can be used to extract the magnetic contribution to the strain response even if systematic measurements above and below the magnetic ordering temperature are not feasible. A first laser pulse leads to a partial ultrafast demagnetization so that the amplitude and shape of the strain response triggered by the second pulse depends on the remaining magnetic order. With this method I could identify a strongly anisotropic magnetic stress contribution in the magnetic data storage material iron-platinum and identify the recovery of the magnetic order by the variation of the pulse-to-pulse delay. The stark contrast of the expansion of iron-platinum nanograins and thin films shows that the different constraints for the in-plane expansion have a strong influence on the out-of-plane expansion, due to the Poisson effect. I show how such transverse strain contributions need to be accounted for when interpreting the ultrafast out-of-plane strain response using thermal expansion coefficients obtained in near equilibrium conditions. This work contributes an investigation of magnetostriction on ultrafast timescales to the literature of magnetic effects in materials. It develops a method to extract spatial and temporal varying stress contributions based on a model for the amplitude and shape of the emitted strain pulses. Energy transfer processes result in a change of the stress profile with respect to the initial absorption of the laser pulses. One interesting example occurs in nanoscopic gold-nickel heterostructures, where excited electrons rapidly transport energy into a distant nickel layer, that takes up much more energy and expands faster and stronger than the laser-excited gold capping layer. Magnetic excitations in rare earth materials represent a large energy reservoir that delays the energy transfer into adjacent layers. Such magneto-caloric effects are known in thermodynamics but not extensively covered on ultrafast timescales. The combination of ultrafast X-ray diffraction and time-resolved techniques with direct access to the magnetization has a large potential to uncover and quantify such energy transfer processes.},
  language  = {en}
}
@misc{PudellMaznevHerzogetal.2018,
  author    = {Pudell, Jan-Etienne and Maznev, Alexei and Herzog, Marc and Kronseder, M. and Back, Christian and Malinowski, Gregory and Reppert, Alexander von and Bargheer, Matias},
  title     = {Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction},
  series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe},
  number    = {797},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-42623},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-426233},
  pages     = {7},
  year      = {2018},
  abstract  = {Ultrafast heat transport in nanoscale metal multilayers is of great interest in the context of optically induced demagnetization, remagnetization and switching. If the penetration depth of light exceeds the bilayer thickness, layer-specific information is unavailable from optical probes. Femtosecond diffraction experiments provide unique experimental access to heat transport over single digit nanometer distances. Here, we investigate the structural response and the energy flow in the ultrathin double-layer system: gold on ferromagnetic nickel. Even though the excitation pulse is incident from the Au side, we observe a very rapid heating of the Ni lattice, whereas the Au lattice initially remains cold. The subsequent heat transfer from Ni to the Au lattice is found to be two orders of magnitude slower than predicted by the conventional heat equation and much slower than electron-phonon coupling times in Au. We present a simplified model calculation highlighting the relevant thermophysical quantities.},
  language  = {en}
}
@article{PudellMaznevHerzogetal.2018,
  author    = {Pudell, Jan-Etienne and Maznev, A. A. and Herzog, Marc and Kronseder, M. and Back, Christian H. and Malinowski, Gregory and Reppert, Alexander von and Bargheer, Matias},
  title     = {Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction},
  series = {Nature Communications},
  volume    = {9},
  journal   = {Nature Communications},
  publisher = {Nature Publ. Group},
  address   = {London},
  issn      = {2041-1723},
  doi       = {10.1038/s41467-018-05693-5},
  pages     = {7},
  year      = {2018},
  abstract  = {Ultrafast heat transport in nanoscale metal multilayers is of great interest in the context of optically induced demagnetization, remagnetization and switching. If the penetration depth of light exceeds the bilayer thickness, layer-specific information is unavailable from optical probes. Femtosecond diffraction experiments provide unique experimental access to heat transport over single digit nanometer distances. Here, we investigate the structural response and the energy flow in the ultrathin double-layer system: gold on ferromagnetic nickel. Even though the excitation pulse is incident from the Au side, we observe a very rapid heating of the Ni lattice, whereas the Au lattice initially remains cold. The subsequent heat transfer from Ni to the Au lattice is found to be two orders of magnitude slower than predicted by the conventional heat equation and much slower than electron-phonon coupling times in Au. We present a simplified model calculation highlighting the relevant thermophysical quantities.},
  language  = {en}
}
@article{KocReinhardtReppertetal.2017,
  author    = {Koc, A. and Reinhardt, M. and Reppert, Alexander von 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{WilligReppertDebetal.2019,
  author    = {Willig, Lisa and Reppert, Alexander von and Deb, Marwan and Ganss, F. and Hellwig, O. and Bargheer, Matias},
  title     = {Finite-size effects in ultrafast remagnetization dynamics of FePt},
  series = {Physical review : B, Condensed matter and materials physics},
  volume    = {100},
  journal   = {Physical review : B, Condensed matter and materials physics},
  number    = {22},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2469-9950},
  doi       = {10.1103/PhysRevB.100.224408},
  pages     = {6},
  year      = {2019},
  abstract  = {We investigate the ultrafast magnetization dynamics of FePt in the L1(0) phase after an optical heating pulse, as used in heat-assisted magnetic recording. We compare continuous and nano-granular thin films and emphasize the impact of the finite size on the remagnetization dynamics. The remagnetization speeds up significantly with increasing external magnetic field only for the continuous film, where domain-wall motion governs the dynamics. The ultrafast remagnetization dynamics in the continuous film are only dominated by heat transport in the regime of high magnetic fields, whereas the timescale required for cooling is prevalent in the granular film for all magnetic field strengths. These findings highlight the necessary conditions for studying the intrinsic heat transport properties in magnetic materials.},
  language  = {en}
}
@article{MatternReppertZeuschneretal.2022,
  author    = {Mattern, Maximilian and Reppert, Alexander von and Zeuschner, Steffen Peer and Pudell, Jan-Etienne and K{\"u}hne, F. and Diesing, Detlef and Herzog, Marc and Bargheer, Matias},
  title     = {Electronic energy transport in nanoscale Au/Fe hetero-structures in the perspective of ultrafast lattice dynamics},
  series = {Applied physics letters},
  volume    = {120},
  journal   = {Applied physics letters},
  number    = {9},
  publisher = {AIP Publishing},
  address   = {Melville},
  issn      = {0003-6951},
  doi       = {10.1063/5.0080378},
  pages     = {5},
  year      = {2022},
  abstract  = {We study the ultrafast electronic transport of energy in a photoexcited nanoscale Au/Fe hetero-structure by modeling the spatiotemporal profile of energy densities that drives transient strain, which we quantify by femtosecond x-ray diffraction. This flow of energy is relevant for intrinsic demagnetization and ultrafast spin transport. We measured lattice strain for different Fe layer thicknesses ranging from few atomic layers to several nanometers and modeled the spatiotemporal flow of energy densities. The combination of a high electron-phonon coupling coefficient and a large Sommerfeld constant in Fe is found to yield electronic transfer of nearly all energy from Au to Fe within the first hundreds of femtoseconds.},
  language  = {en}
}
@article{MatternReppertZeuschneretal.2023,
  author    = {Mattern, Maximilian and Reppert, Alexander von 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{SanderKocKwamenetal.2016,
  author    = {Sander, Mathias and Koc, A. and Kwamen, C. T. and Michaels, H. and Reppert, Alexander von and Pudell, Jan-Etienne and Zamponi, Flavio and Bargheer, Matias and Sellmann, J. and Schwarzkopf, J. and Gaal, P.},
  title     = {Characterization of an ultrafast Bragg-Switch for shortening hard x-ray pulses},
  series = {Journal of applied physics},
  volume    = {120},
  journal   = {Journal of applied physics},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0021-8979},
  doi       = {10.1063/1.4967835},
  pages     = {7},
  year      = {2016},
  abstract  = {We present a nanostructured device that functions as photoacoustic hard x-ray switch. The device is triggered by femtosecond laser pulses and allows for temporal gating of hard x-rays on picosecond (ps) timescales. It may be used for pulse picking or even pulse shortening in 3rd generation synchrotron sources. Previous approaches mainly suffered from insufficient switching contrasts due to excitation-induced thermal distortions. We present a new approach where thermal distortions are spatially separated from the functional switching layers in the structure. Our measurements yield a switching contrast of 14, which is sufficient for efficient hard x-ray pulse shortening. The optimized structure also allows for utilizing the switch at high repetition rates of up to 208 kHz. Published by AIP Publishing.},
  language  = {en}
}
@article{MatternPudellLaskinetal.2021,
  author    = {Mattern, Maximilian and Pudell, Jan-Etienne and Laskin, Gennadii and Reppert, Alexander von and Bargheer, Matias},
  title     = {Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3},
  series = {Structural dynamics},
  volume    = {8},
  journal   = {Structural dynamics},
  number    = {2},
  publisher = {AIP Publishing LLC},
  address   = {Melville, NY},
  issn      = {2329-7778},
  doi       = {10.1063/4.0000072},
  pages     = {9},
  year      = {2021},
  abstract  = {We use ultrafast x-ray diffraction to investigate the effect of expansive phononic and contractive magnetic stress driving the picosecond strain response of a metallic perovskite SrRuO3 thin film upon femtosecond laser excitation. We exemplify how the anisotropic bulk equilibrium thermal expansion can be used to predict the response of the thin film to ultrafast deposition of energy. It is key to consider that the laterally homogeneous laser excitation changes the strain response compared to the near-equilibrium thermal expansion because the balanced in-plane stresses suppress the Poisson stress on the picosecond timescale. We find a very large negative Gr{\"u}neisen constant describing the large contractive stress imposed by a small amount of energy in the spin system. The temperature and fluence dependence of the strain response for a double-pulse excitation scheme demonstrates the saturation of the magnetic stress in the high-fluence regime.},
  language  = {en}
}
@misc{MatternPudellLaskinetal.2021,
  author    = {Mattern, Maximilian and Pudell, Jan-Etienne and Laskin, G. and Reppert, Alexander von and Bargheer, Matias},
  title     = {Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-51571},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-515718},
  pages     = {11},
  year      = {2021},
  abstract  = {We use ultrafast x-ray diffraction to investigate the effect of expansive phononic and contractive magnetic stress driving the picosecond strain response of a metallic perovskite SrRuO3 thin film upon femtosecond laser excitation. We exemplify how the anisotropic bulk equilibrium thermal expansion can be used to predict the response of the thin film to ultrafast deposition of energy. It is key to consider that the laterally homogeneous laser excitation changes the strain response compared to the near-equilibrium thermal expansion because the balanced in-plane stresses suppress the Poisson stress on the picosecond timescale. We find a very large negative Gr{\"u}neisen constant describing the large contractive stress imposed by a small amount of energy in the spin system. The temperature and fluence dependence of the strain response for a double-pulse excitation scheme demonstrates the saturation of the magnetic stress in the high-fluence regime.},
  language  = {en}
}