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Proceedings Paper

Experimental observation of chiral phonons in monolayer WSe2
Author(s): Hanyu Zhu; Jun Yi; Ming-Yang Li; Jun Xiao; Lifa Zhang; Chih-Wen Yang; Sui Yang; Robert A. Kaindl; Lain-Jong Li; Yuan Wang; Xiang Zhang
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Paper Abstract

Chirality characterizes an object that is not identical to its mirror image. In condensed matter physics, Fermions have been demonstrated to obtain chirality through structural and time-reversal symmetry breaking. These systems display unconventional electronic transport phenomena such as the quantum Hall effect and Weyl semimetals. However, for bosonic collective excitations in atomic lattices, chirality was only theoretically predicted and has never been observed. We experimentally show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide, whose lattice breaks the inversion symmetry and enables inequivalent electronic K and -K valley states. The time-reversal symmetry is also broken when we selectively excite the valley polarized holes by circularly polarized light. Brillouin-zone-boundary phonons are then optically created by the indirect infrared absorption through the hole-phonon interactions. The unidirectional intervalley transfer of holes ensures that only the phonon modes in one valley are excited. We found that such photons are chiral through the transient infrared circular dichroism, which proves the valley phonons responsible to the indirect absorption has non-zero pseudo-angular momentum. From the spectrum we further deduce the energy transferred to the phonons that agrees with both the first principle calculation and the double-resonance Raman spectroscopy. The chiral phonons have significant implications for electron-phonon coupling in solids, lattice-driven topological states, and energy efficient information processing.

Paper Details

Date Published: 27 February 2019
PDF: 9 pages
Proc. SPIE 10916, Ultrafast Phenomena and Nanophotonics XXIII, 109160C (27 February 2019); doi: 10.1117/12.2510760
Show Author Affiliations
Hanyu Zhu, Univ. of California, Berkeley (United States)
Rice Univ. (United States)
Jun Yi, Univ. of California, Berkeley (United States)
Ming-Yang Li, King Abdullah Univ. of Science and Technology (Saudi Arabia)
Jun Xiao, Univ. of California, Berkeley (United States)
Lifa Zhang, Nanjing Normal Univ. (China)
Chih-Wen Yang, King Abdullah Univ. of Science and Technology (Saudi Arabia)
Sui Yang, Univ. of California, Berkeley (United States)
Robert A. Kaindl, Lawrence Berkeley National Lab. (United States)
Lain-Jong Li, King Abdullah Univ. of Science and Technology (Saudi Arabia)
Yuan Wang, Univ. of California, Berkeley (United States)
Xiang Zhang, Univ. of California, Berkeley (United States)
Lawrence Berkeley National Lab. (United States)
The Univ. of Hong Kong (Hong Kong, China)


Published in SPIE Proceedings Vol. 10916:
Ultrafast Phenomena and Nanophotonics XXIII
Markus Betz; Abdulhakem Y. Elezzabi, Editor(s)

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