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dc.contributor.authorZhu, Hanyu
dc.contributor.authorYi, Jun
dc.contributor.authorLi, Ming-yang
dc.contributor.authorXiao, Jun
dc.contributor.authorZhang, Lifa
dc.contributor.authorYang, Chih-Wen
dc.contributor.authorYang, Sui
dc.contributor.authorKaindl, Robert A.
dc.contributor.authorLi, Lain-Jong
dc.contributor.authorWang, Yuan
dc.contributor.authorZhang, Xiang
dc.date.accessioned2019-08-19T13:22:28Z
dc.date.available2019-08-19T13:22:28Z
dc.date.issued2019-02-28
dc.identifier.citationZhu, H., Yi, J., Li, M.-Y., Xiao, J., Zhang, L., Yang, C.-W., … Zhang, X. (2019). Experimental observation of chiral phonons in monolayer WSe2. Ultrafast Phenomena and Nanophotonics XXIII. doi:10.1117/12.2510760
dc.identifier.doi10.1117/12.2510760
dc.identifier.urihttp://hdl.handle.net/10754/656524
dc.description.abstractChirality 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.
dc.description.sponsorshipThis 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 by DOE BES, Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231 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. 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 WSe2 synthesis. All data needed to evaluate the conclusions in the paper are present in the paper and the supplementary materials.
dc.publisherSPIE-Intl Soc Optical Eng
dc.relation.urlhttps://www.spiedigitallibrary.org/conference-proceedings-of-spie/10916/2510760/Experimental-observation-of-chiral-phonons-in-monolayer-WSe2/10.1117/12.2510760.full
dc.rightsArchived with thanks to Proceedings of SPIE
dc.subjectChirality
dc.subjectphonon
dc.subjectvalley
dc.subjecttransition metal dichalcogenide
dc.subjecttime-reversal symmetry breaking
dc.subjectindirect absorption
dc.subjectzone-boundary
dc.subjectintervalence band transition
dc.titleExperimental observation of chiral phonons in monolayer WSe2
dc.typeConference Paper
dc.contributor.departmentMaterial Science and Engineering Program
dc.contributor.departmentPhysical Science and Engineering (PSE) Division
dc.conference.date2019-02-03 to 2019-02-06
dc.conference.nameUltrafast Phenomena and Nanophotonics XXIII 2019
dc.conference.locationSan Francisco, CA, USA
dc.eprint.versionPublisher's Version/PDF
dc.contributor.institutionNanoscale Science and Engineering Center, University of California, Berkeley, CA 94720, USA
dc.contributor.institutionDepartment of Materials Science and NanoEngineering, Rice University, Houston, TX 77005, USA
dc.contributor.institutionDepartment of Physics, Nanjing Normal University, Nanjing, Jiangsu 210023, China
dc.contributor.institutionMaterials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
dc.contributor.institutionPresident's Office, The University of Hong Kong, Hong Kong, China
kaust.personLi, Ming-yang
kaust.personYang, Chih-Wen
kaust.personLi, Lain-Jong
refterms.dateFOA2019-08-19T13:24:14Z
dc.date.published-online2019-02-28
dc.date.published-print2019-02-27


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