@article{MatternPudellDumesniletal.2023, author = {Mattern, Maximilian and Pudell, Jan-Etienne and Dumesnil, Karine and von Reppert, Alexander and Bargheer, Matias}, title = {Towards shaping picosecond strain pulses via magnetostrictive transducers}, series = {Photoacoustics}, volume = {30}, journal = {Photoacoustics}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2213-5979}, doi = {10.1016/j.pacs.2023.100463}, pages = {7}, year = {2023}, abstract = {Using time-resolved x-ray diffraction, we demonstrate the manipulation of the picosecond strain response of a metallic heterostructure consisting of a dysprosium (Dy) transducer and a niobium (Nb) detection layer by an external magnetic field. We utilize the first-order ferromagnetic-antiferromagnetic phase transition of the Dy layer, which provides an additional large contractive stress upon laser excitation compared to its zerofield response. This enhances the laser-induced contraction of the transducer and changes the shape of the picosecond strain pulses driven in Dy and detected within the buried Nb layer. Based on our experiment with rare-earth metals we discuss required properties for functional transducers, which may allow for novel field-control of the emitted picosecond strain pulses.}, 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} } @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{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{MatternvonReppertZeuschneretal.2022, author = {Mattern, Maximilian and von Reppert, Alexander 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{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{MatternPudellLaskinetal.2021, author = {Mattern, M. and Pudell, Jan-Etienne and Laskin, G. and von Reppert, A. and Bargheer, Matias}, title = {Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3}, series = {Structural Dynamics}, journal = {Structural Dynamics}, 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} } @article{ZeuschnerMatternPudelletal.2021, author = {Zeuschner, S. P. and Mattern, M. and Pudell, Jan-Etienne and von Reppert, A. and R{\"o}ssle, M. and Leitenberger, Wolfram and Schwarzkopf, J. and Boschker, J. E. and Herzog, Marc and Bargheer, Matias}, title = {Reciprocal space slicing}, series = {Structural Dynamics}, volume = {8}, journal = {Structural Dynamics}, publisher = {AIP Publishing LLC}, address = {Melville, NY}, issn = {2329-7778}, doi = {10.1063/4.0000040}, pages = {11}, 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{LiebigSarhanBargheeretal.2020, author = {Liebig, Ferenc and Sarhan, Radwan Mohamed and Bargheer, Matias and Schmitt, Clemens Nikolaus Zeno and Poghosyan, Armen H. and Shahinyanf, Aram A. and Koetz, Joachim}, title = {Spiked gold nanotriangles}, series = {RSC Advances}, volume = {10}, journal = {RSC Advances}, number = {14}, publisher = {RSC Publishing}, address = {London}, issn = {2046-2069}, doi = {10.1039/d0ra00729c}, pages = {8152 -- 8160}, year = {2020}, abstract = {We show the formation of metallic spikes on the surface of gold nanotriangles (AuNTs) by using the same reduction process which has been used for the synthesis of gold nanostars. We confirm that silver nitrate operates as a shape-directing agent in combination with ascorbic acid as the reducing agent and investigate the mechanism by dissecting the contribution of each component, i.e., anionic surfactant dioctyl sodium sulfosuccinate (AOT), ascorbic acid (AA), and AgNO3. Molecular dynamics (MD) simulations show that AA attaches to the AOT bilayer of nanotriangles, and covers the surface of gold clusters, which is of special relevance for the spike formation process at the AuNT surface. The surface modification goes hand in hand with a change of the optical properties. The increased thickness of the triangles and a sizeable fraction of silver atoms covering the spikes lead to a blue-shift of the intense near infrared absorption of the AuNTs. The sponge-like spiky surface increases both the surface enhanced Raman scattering (SERS) cross section of the particles and the photo-catalytic activity in comparison with the unmodified triangles, which is exemplified by the plasmon-driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4'-dimercaptoazobenzene (DMAB).}, language = {en} } @article{vonReppertMatternPudelletal.2020, author = {von Reppert, Alexander and Mattern, Maximilian and Pudell, Jan-Etienne and Zeuschner, Steffen Peer and Dumesnil, Karine and Bargheer, Matias}, title = {Unconventional picosecond strain pulses resulting from the saturation of magnetic stress within a photoexcited rare earth layer}, series = {Structural Dynamics}, volume = {7}, journal = {Structural Dynamics}, number = {024303}, publisher = {AIP Publishing LLC}, address = {Melville, NY}, issn = {2329-7778}, doi = {10.1063/1.5145315}, pages = {13}, year = {2020}, abstract = {Optical excitation of spin-ordered rare earth metals triggers a complex response of the crystal lattice since expansive stresses from electron and phonon excitations compete with a contractive stress induced by spin disorder. Using ultrafast x-ray diffraction experiments, we study the layer specific strain response of a dysprosium film within a metallic heterostructure upon femtosecond laser-excitation. The elastic and diffusive transport of energy to an adjacent, non-excited detection layer clearly separates the contributions of strain pulses and thermal excitations in the time domain. We find that energy transfer processes to magnetic excitations significantly modify the observed conventional bipolar strain wave into a unipolar pulse. By modeling the spin system as a saturable energy reservoir that generates substantial contractive stress on ultrafast timescales, we can reproduce the observed strain response and estimate the time- and space dependent magnetic stress. The saturation of the magnetic stress contribution yields a non-monotonous total stress within the nanolayer, which leads to unconventional picosecond strain pulses.}, language = {en} }