Optically induced lattice dynamics probed with ultrafast X-ray diffraction

Lee, H.J.; Workman, J.; Averitt, Richard D.; Taylor, Antoinette J.; Roberts, J. P.; McCulloch, Q.; Hof, Douglas E.; Funk, David J.; Wark, J. S.; Hur, N.; Cheong, S. W.

doi:10.1109/qels.2005.1548925

Cited by 5 publications

(6 citation statements)

References 10 publications

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“…Instead, we find a splitting of the initial Bragg peak into two distinct reflections at intermediate times until the initial peak has disappeared. Similar Bragg peak splittings have been previously observed in photoexcited bulk crystals and thin films 4,43,44 , however, either the signatures were relatively weak compared to the bulk reflection or a thorough description of the underlying structural dynamics is missing. The comparison of the experimental results in Fig.…”

Section: Resultssupporting

confidence: 77%

Ultrafast x-ray diffraction studies of photoexcited coherent phonons in SrRuO$_3$ thin films

Schick¹,

Gaal²,

Bojahr³

et al. 2013

Preprint

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We present ultrafast x-ray diffraction experiments on thin films of metallic SrRuO3 (SRO) after their excitation with ultrashort intense laser pulses. Depending on the layer thickness, the data exhibit a transient splitting of the (002) SRO Bragg peak evidencing the generation and propagation of sharp acoustic strain waves. These distinct structural dynamics are due to the exceptionally fast electron-phonon relaxation that gives rise to a quasi-instantaneous thermal stress in SRO. The interpretation is corroborated by numerical simulations which show excellent agreement with the experimental findings. Despite the qualitatively different lattice dynamics for different SRO layer thicknesses, we identify a universal evolution of the transient average layer strain. The inferred discrepancy of the thermal stress profile from the excitation profile may hint toward a temperaturedependent effective Grüneisen parameter of SRO.

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Section: Resultssupporting

confidence: 77%

Ultrafast x-ray diffraction studies of photoexcited coherent phonons in SrRuO$_3$ thin films

Schick¹,

Gaal²,

Bojahr³

et al. 2013

Preprint

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“…The effective expansion coefficient valid for heating a thin epitaxial layer is based on the lattice constants and strains predicted from equilibrium thermal expansion coefficients, corrected according to the Poisson effect 53 . In cubic materials with (100) surface orientation the ratio of the observed ultrafast (uf) strain and the strain ε eq = α eq ( T )Δ T along the (100) direction calculated from equilibrium value (eq) is ε / ε eq = α uf ( T )/ α eq ( T ) = 1 + 2 C 12 / C 11 = 2.2 for Ni and would be 2.6 for Au.…”

Section: Methodsmentioning

confidence: 99%

Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction

et al. 2018

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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.

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“…Light-matter interactions can be utilized to induce ultrafast phenomena in correlated electron materials 1 for realizing functionalities that can neither be observed in bulk equilibrium 2 3 4 5 nor by means of static perturbations to the structure, including chemical substitution, mechanical strain, or digital heterostructures. Inducing nonequilibrium phonon modulations are of particular recent interest owing to their direct 6 and indirect 7 8 9 10 accessibility with high intensity femtosecond laser pulses ranging from the mid-infrared (IR) to terahertz regimes 11 . This athermal light-enabled structure–property control, for example, has been exploited in the superconducting cuprate family, where the electron pairing strength is related to the Cu-O intra-bilayer distance 12 : Mid-IR pulses are able to induce transient high- T C superconductivity from a nominally non-superconducting material 13 or melt charge order in a superconducting cuprate at subpicosecond timescales 14 by direct excitation of IR-active Cu–O bond stretching modes.…”

mentioning

confidence: 99%

Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides

Rondinelli

2016

Sci Rep

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We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.

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Optically induced lattice dynamics probed with ultrafast X-ray diffraction

Cited by 5 publications

References 10 publications

Ultrafast x-ray diffraction studies of photoexcited coherent phonons in SrRuO$_3$ thin films

Ultrafast x-ray diffraction studies of photoexcited coherent phonons in SrRuO$_3$ thin films

Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction

Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides

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