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Ultrafast modulation of electronic structure by coherent phonon excitations
J Weisshaupt1, A Rouzée1, M Woerner1
1Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, D-12489 Berlin, Germany.
Physical Review. B
|April 15, 2024
Summary
Ultrafast X-ray absorption spectroscopy reveals coherent phonon displacements in LiBH4. Laser excitation induces charge transfer, driving lattice vibrations via Coulomb forces.
Area of Science:
- Condensed matter physics
- Materials science
- Ultrafast spectroscopy
Background:
- Coherent phonon displacements are crucial for understanding material dynamics.
- Femtosecond X-ray absorption spectroscopy offers insights into ultrafast structural changes.
Purpose of the Study:
- To investigate ultrafast structural dynamics in LiBH4 using femtosecond X-ray absorption spectroscopy.
- To map changes in X-ray absorption driven by coherent phonon displacements.
Main Methods:
- Utilized femtosecond X-ray absorption spectroscopy with a laser-driven high-harmonic source.
- Employed impulsive Raman excitation to induce coherent phonon displacements.
- Analyzed Li K-edge X-ray absorption spectra and femtosecond X-ray diffraction data.
Main Results:
- Observed oscillatory changes in Li K-edge X-ray absorption correlated with 10 THz Ag phonon mode displacements.
- Femtosecond X-ray diffraction revealed laser-induced charge transfer from BH4- to Li+ ions.
- Identified a differential Coulomb force driving lattice vibrations in a virtual transition state.
Conclusions:
- Femtosecond X-ray absorption spectroscopy can track femtometer-scale coherent phonon displacements.
- Laser-driven charge transfer plays a key role in initiating lattice vibrations in LiBH4.
- The study provides a new method for probing ultrafast dynamics in materials.
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