@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}
}
@article{ShaydukHallmannRodriguezFernandezetal.2022,
  author    = {Shayduk, Roman and Hallmann, J{\"o}rg and Rodriguez-Fernandez, Angel and Scholz, Markus and Lu, Wei and B{\"o}senberg, Ulrike and M{\"o}ller, Johannes and Zozulya, Alexey and Jiang, Man and Wegner, Ulrike and Secareanu, Radu-Costin and Palmer, Guido and Emons, Moritz and Lederer, Max and Volkov, Sergey and Lindfors-Vrejoiu, Ionela and Schick, Daniel and Herzog, Marc and Bargheer, Matias and Madsen, Anders},
  title     = {Femtosecond x-ray diffraction study of multi-THz coherent phonons in SrTiO3},
  series = {Applied physics letters},
  volume    = {120},
  journal   = {Applied physics letters},
  number    = {20},
  publisher = {AIP Publishing},
  address   = {Melville},
  issn      = {0003-6951},
  doi       = {10.1063/5.0083256},
  pages     = {5},
  year      = {2022},
  abstract  = {We report generation of ultra-broadband longitudinal acoustic coherent phonon wavepackets in SrTiO3 (STO) with frequency components extending throughout the first Brillouin zone. The wavepackets are efficiently generated in STO using femtosecond infrared laser excitation of an atomically flat 1.6 nm-thick epitaxial SrRuO3 film. We use femtosecond x-ray diffraction at the European X-Ray Free Electron Laser Facility to study the dispersion and damping of phonon wavepackets. The experimentally determined damping constants for multi-THz frequency phonons compare favorably to the extrapolation of a simple ultrasound damping model over several orders of magnitude.},
  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{ZeuschnerWangDebetal.2022,
  author    = {Zeuschner, Steffen Peer and Wang, Xi-Guang and Deb, Marwan and Popova, Elena and Malinowski, Gregory and Hehn, Michel and Keller, Niels and Berakdar, Jamal and Bargheer, Matias},
  title     = {Standing spin wave excitation in Bi},
  series = {Physical review : B, Condensed matter and materials physics},
  volume    = {106},
  journal   = {Physical review : B, Condensed matter and materials physics},
  number    = {13},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2469-9950},
  doi       = {10.1103/PhysRevB.106.134401},
  pages     = {9},
  year      = {2022},
  abstract  = {Based on micromagnetic simulations and experimental observations of the magnetization and lattice dynamics after the direct optical excitation of the magnetic insulator Bi : YIG or indirect excitation via an optically opaque Pt/Cu double layer, we disentangle the dynamical effects of magnetic anisotropy and magneto-elastic coupling. The strain and temperature of the lattice are quantified via modeling ultrafast x-ray diffraction data. Measurements of the time-resolved magneto-optical Kerr effect agree well with the magnetization dynamics simulated according to the excitation via two mechanisms: the magneto-elastic coupling to the experimentally verified strain dynamics and the ultrafast temperature-induced transient change in the magnetic anisotropy. The numerical modeling proves that, for direct excitation, both mechanisms drive the fundamental mode with opposite phase. The relative ratio of standing spin wave amplitudes of higher-order modes indicates that both mechanisms are substantially active.},
  language  = {en}
}
@article{DebPopovaJaffresetal.2022,
  author    = {Deb, Marwan and Popova, Elena and Jaffr{\`e}s, Henri-Yves and Keller, Niels and Bargheer, Matias},
  title     = {Polarization-dependent subpicosecond demagnetization in iron garnets},
  series = {Physical review : B, covering condensed matter and materials physics},
  volume    = {106},
  journal   = {Physical review : B, covering condensed matter and materials physics},
  number    = {18},
  publisher = {American Institute of Physics, American Physical Society},
  address   = {Woodbury, NY},
  issn      = {2469-9950},
  doi       = {10.1103/PhysRevB.106.184416},
  pages     = {7},
  year      = {2022},
  abstract  = {Controlling the magnetization dynamics at the fastest speed is a major issue of fundamental condensed matter physics and its applications for data storage and processing technologies. It requires a deep understanding of the interactions between the degrees of freedom in solids, such as spin, electron, and lattice as well as their responses to external stimuli. In this paper, we systematically investigate the fluence dependence of ultrafast magnetization dynamics induced by below-bandgap ultrashort laser pulses in the ferrimagnetic insulators BixY3-xFe5O12 with 1 xBi 3. We demonstrate subpicosecond demagnetization dynamics in this material followed by a very slow remagnetization process. We prove that this demagnetization results from an ultrafast heating of iron garnets by two-photon absorption (TPA), suggesting a phonon-magnon thermalization time of 0.6 ps. We explain the slow remagnetization timescale by the low phonon heat conductivity in garnets. Additionally, we show that the amplitudes of the demagnetization, optical change, and lattice strain can be manipulated by changing the ellipticity of the pump pulses. We explain this phenomenon considering the TPA circular dichroism. These findings open exciting prospects for ultrafast manipulation of spin, charge, and lattice dynamics in magnetic insulators by ultrafast nonlinear optics.},
  language  = {en}
}
@article{DebPopovaJaffresetal.2022,
  author    = {Deb, Marwan and Popova, Elena and Jaffr{\`e}s, Henri-Yves and Keller, Niels and Bargheer, Matias},
  title     = {Controlling high-frequency spin-wave dynamics using double-pulse laser excitation},
  series = {Physical review applied},
  volume    = {18},
  journal   = {Physical review applied},
  number    = {4},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2331-7019},
  doi       = {10.1103/PhysRevApplied.18.044001},
  pages     = {7},
  year      = {2022},
  abstract  = {Manipulating spin waves is highly required for the development of innovative data transport and processing technologies. Recently, the possibility of triggering high-frequency standing spin waves in magnetic insulators using femtosecond laser pulses was discovered, raising the question about how one can manipulate their dynamics. Here we explore this question by investigating the ultrafast magnetiza-tion and spin-wave dynamics induced by double-pulse laser excitation. We demonstrate a suppression or enhancement of the amplitudes of the standing spin waves by precisely tuning the time delay between the two pulses. The results can be understood as the constructive or destructive interference of the spin waves induced by the first and second laser pulses. Our findings open exciting perspectives towards generating single-mode standing spin waves that combine high frequency with large amplitude and low magnetic damping.},
  language  = {en}
}