Direct Observation of Coherent Longitudinal and Shear Acoustic Phonons in TaAs Using Ultrafast X-Ray Diffraction

• Main Authors: Chen, G.F (Author), De La Pena, G.A (Author), Huang, Y. (Author), Krapivin, V. (Author), Lee, M.-C (Author), Maznev, A. (Author), Nelson, K.A (Author), Pezeril, T. (Author), Prasankumar, R.P (Author), Qiu, X.G (Author), Reis, D.A (Author), Shi, J. (Author), Sirica, N. (Author), Teitelbaum, S.W (Author), Trigo, M. (Author), Tutchton, R. (Author), Xu, B. (Author), Yang, R. (Author), Yarotski, D.A (Author), Zhao, L.X (Author), Zhu, J.-X (Author)
• Format: Article
• Language: English
• Published: American Physical Society 2022
• Subjects: Acoustic deformation; Acoustic phonons; Acoustic-phonons; Crystal orientation; Deformation; Direct observations; Electromagnetic wave emission; Electronic structure; Electronic.structure; Femtosecond time-resolved; Phonons; Tantalum compounds; Time resolved x-ray diffractions; Time-resolved X-ray diffraction; Ultra-fast; X ray diffraction; X- ray diffractions
• Online Access: View Fulltext in Publisher

 Using femtosecond time-resolved x-ray diffraction, we investigated optically excited coherent acoustic phonons in the Weyl semimetal TaAs. The low symmetry of the (112) surface probed in our experiment enables the simultaneous excitation of longitudinal and shear acoustic modes, whose dispersion closely matches our simulations. We observed an asymmetry in the spectral line shape of the longitudinal mode that is notably absent from the shear mode, suggesting a time-dependent frequency chirp that is likely driven by photoinduced carrier diffusion. We argue on the basis of symmetry that these acoustic deformations can transiently alter the electronic structure near the Weyl points and support this with model calculations. Our study underscores the benefit of using off-axis crystal orientations when optically exciting acoustic deformations in topological semimetals, allowing one to transiently change their crystal and electronic structures. © 2022 American Physical Society.