Direct Observation of Coherent Longitudinal and Shear Acoustic Phonons in TaAs Using Ultrafast X-Ray Diffraction
Min-Cheol Lee1, N Sirica1, S W Teitelbaum2,3
1Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Physical Review Letters
|May 2, 2022
Summary
We studied acoustic phonons in the topological semimetal TaAs using X-ray diffraction. Optically induced vibrations can transiently alter the material's electronic structure near Weyl points.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Solid-State Physics
Background:
- Topological semimetals like Tantalum Arsenide (TaAs) exhibit unique electronic properties governed by Weyl points.
- Optical excitation offers a route to dynamically control material properties.
Purpose of the Study:
- Investigate optically excited coherent acoustic phonons in the Weyl semimetal TaAs.
- Explore the influence of these acoustic deformations on the electronic structure.
Main Methods:
- Femtosecond time-resolved X-ray diffraction.
- Experimental probing of the (112) surface of TaAs.
- Computational simulations of acoustic mode dispersion.
Main Results:
- Simultaneous excitation and characterization of longitudinal and shear acoustic modes.
- Observed asymmetry in the longitudinal mode's spectral line shape, attributed to photoinduced carrier diffusion.
- Simulations closely matched experimental dispersion of acoustic modes.
Conclusions:
- Acoustic deformations can transiently modify the electronic structure near Weyl points in TaAs.
- Off-axis crystal orientations are beneficial for optically exciting acoustic deformations in topological semimetals.
- This technique allows for transient control over the crystal and electronic structures of topological semimetals.
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