Direct Observation of Coherent Longitudinal and Shear Acoustic Phonons in TaAs Using Ultrafast X-Ray Diffraction
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of Rennes (France)
- SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States)
- Chinese Academy of Sciences (CAS), Beijing (China)
Here, 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.
- Research Organization:
- Ames Lab., Ames, IA (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Advancement of Topological Semimetals (CATS); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division; USDOE Laboratory Directed Research and Development (LDRD) Program
- Grant/Contract Number:
- AC02-07CH11358; 2018BU0083; 2018LANLBES16; AC02-76SF00515; SC0019126; AC02-05CH11231
- OSTI ID:
- 1864268
- Alternate ID(s):
- OSTI ID: 1871598; OSTI ID: 1878047
- Report Number(s):
- IS-J-10,781; LA-UR-20-29013; TRN: US2305963
- Journal Information:
- Physical Review Letters, Vol. 128, Issue 15; ISSN 0031-9007
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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