Temperature dependence of X-ray absorption and nuclear magnetic resonance spectra: probing quantum vibrations of light elements in oxides

Nemausat, Ruidy; Gervais, Christel; Brouder, Christian; Trcera, Nicolas; Bordage, Amélie; Coelho-Diogo, Cristina; Florian, Pierre; Rakhmatullin, Aydar; Errea, Ion; Paulatto, Lorenzo; Lazzeri, Michele; Cabaret, Delphine

doi:10.1039/c6cp08393e

Cited by 18 publications

(16 citation statements)

References 90 publications

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“…In this case the major part of the excess energy is hosted by phonons since the specific heat of the lattice is considerable larger then the one of the electrons. The observed changes showcase that time-resolved XAS is also sensitive to phonons, in agreement with temperaturedependent changes observed in literature [37,42]. XAS thus allows us to track the electronic and phononic energy transfer and relaxation in all constituents of the heterostructure.…”

Section: A Ultrafast Soft X-ray Spectroscopysupporting

confidence: 89%

Microscopic nonequilibrium energy transfer dynamics in a photoexcited metal/insulator heterostructure

et al. 2019

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The element specificity of soft X-ray spectroscopy makes it an ideal tool for analyzing the microscopic origin of ultrafast dynamics induced by localized optical excitation in metal-insulator heterostructures. Using [Fe/MgO]n as a model system, we perform ultraviolet pump/soft X-ray probe experiments, which are sensitive to all constituents of these heterostructures, to probe both electronic and lattice excitations. Complementary ultrafast electron diffraction experiments independently analyze the lattice dynamics of the Fe constituent, and together with ab initio calculations yield comprehensive insight into the microscopic processes leading to local relaxation within a single constituent or non-local relaxation between two constituents. Besides electronic excitations in Fe, which are monitored at the Fe L3 absorption edge and relax within 1 ps by electron-phonon coupling, soft X-ray analysis identifies a change at the oxygen K absorption edge of the MgO layers which occurs within 0.5 ps. This ultrafast energy transfer across the Fe-MgO interface is mediated by high-frequency, interface vibrational modes, which are excited by hot electrons in Fe and couple to vibrations in MgO in a mode-selective, non-thermal manner. A second, slower timescale is identified at the oxygen K pre-edge and the Fe L3 edge. The slower process represents energy transfer by acoustic phonons and contributes to thermalization of the entire heterostructure. We thus find that the interfacial energy transfer is associated with non-equilibrium behavior in the phonon system. Because our experiments lack signatures of charge transfer across the interface, we conclude that phonon-mediated processes dominate the competition of electronic and lattice excitations in these non-local, non-equilibrium dynamics.

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Section: A Ultrafast Soft X-ray Spectroscopysupporting

confidence: 89%

Microscopic nonequilibrium energy transfer dynamics in a photoexcited metal/insulator heterostructure

et al. 2019

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“…We rather think that lattice displacements due to electron-phonon couplings are the main reason for the formation of the double peak. In a recent publication [45] it was demonstrated on the example of several light-element compounds that thermal vibrations can have noticeable effects on XANES and NMR spectra. Furthermore, in a recent synchrotron measurement [8] it was shown that a very small splitting of approximately 0.1 eV is observed for the first peak of the boron K-edge spectrum.…”

Section: Introductionmentioning

confidence: 99%

Effects of electron-phonon coupling on absorption spectrum: K edge of hexagonal boron nitride

et al. 2018

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A detailed analysis of the theoretical x-ray absorption near-edge structures (XANES) for the boron and nitrogen K edge in hexagonal boron nitride (h-BN) employing density-functional theory calculations is presented. The supercell core-hole method and the Bethe-Salpeter equation are used for the description of electron-hole interactions. The calculations are carried out with two different codes, the VASP and the WIEN2K codes, employing the projector augmented-wave and the full-potential linear augmented-plane-wave methods, respectively. We find close agreement between spectra obtained from the two codes and between calculations using the supercell core-hole method and the Bethe-Salpeter approach. All our calculations, as well as previous calculations using the ground-state structure, yield a single 2p σ * peak in the boron K-edge spectrum and hence fail to describe the experimental double-peak structure. We find that the inclusion of electron-phonon interactions is crucial to obtain the experimentally observed double-peak structure. We include these effects fully parameter free and ab initio using a one-shot sampling method and obtain excellent agreement with experiment.

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“…We generated different configurations by displacing randomly the atomic positions as in Ref. 42 and averaged the resulting Born effective charges.…”

Section: Discussionmentioning

confidence: 99%

Infrared reflectance, transmittance, and emittance spectra of MgO from first principles

2018

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By using density functional theory calculations we determined the influence of anharmonic effects on the infrared reflectance, transmittance and emittance of MgO. The goal is to determine the limit of validity of a perturbative (multi-phonon) approach. MgO is chosen as a test material because of the availability of different kinds of radiative properties measured experimentally. Non-analytic terms of the three-phonon scattering coefficients are explicitly calculated and do not provide measurable effects. The agreement is overall very good to such an extent that, already at room temperature, one can clearly identify regions in which four-phonon scattering processes are dominant with respect to the three-phonon ones. The influence of isotopic disorder at cryogenic temperatures is also settled.

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Temperature dependence of X-ray absorption and nuclear magnetic resonance spectra: probing quantum vibrations of light elements in oxides

Cited by 18 publications

References 90 publications

Microscopic nonequilibrium energy transfer dynamics in a photoexcited metal/insulator heterostructure

Microscopic nonequilibrium energy transfer dynamics in a photoexcited metal/insulator heterostructure

Effects of electron-phonon coupling on absorption spectrum: K edge of hexagonal boron nitride

Infrared reflectance, transmittance, and emittance spectra of MgO from first principles

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