Kaindl, Robert A.
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
Materials Science and Engineering Program
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AbstractChirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of clockwise and counterclockwise phonon modes at the corners of the Brillouin zone. We identified the phonons by the intervalley transfer of holes through hole-phonon interactions during the indirect infrared absorption, and we confirmed their chirality by the infrared circular dichroism arising from pseudoangular momentum conservation. The chiral phonons are important for electron-phonon coupling in solids, phonon-driven topological states, and energy-efficient information processing.
CitationZhu H, Yi J, Li M-Y, Xiao J, Zhang L, et al. (2018) Observation of chiral phonons. Science 359: 579–582. Available: http://dx.doi.org/10.1126/science.aar2711.
SponsorsWe thank F. Wang and Q. Niu for helpful discussions. This work was primarily supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231 within the van der Waals Heterostructures program (KCWF16) for sample preparation and theory and data analysis, and within the Subwavelength Metamaterials Program (KC12XZ) for optical design and measurement. R.A.K. was supported under the same contract within the Ultrafast Materials Science program (KC2203) for mid-IR frequency conversion. J.Y. acknowledges a scholarship from the China Scholarship Council (CSC) under grant no. 201606310094. L.Z. thanks M. Gao for helpful calculation and discussion and acknowledges support from the National Natural Science Foundation of China (grant no. 11574154). L.-J.L. acknowledges support from the King Abdullah University of Science and Technology through a Competitive Research Grant (CRG5) for monolayer WSe<INF>2</INF> synthesis. All data needed to evaluate the conclusions in the paper are present in the paper and the supplementary materials.