K-point longitudinal acoustic phonons are responsible for ultrafast intervalley scattering in monolayer MoSe2

Soungmin Bae (), Kana Matsumoto, Hannes Raebiger, Ken-ichi Shudo, Yong-Hoon Kim, Ørjan Sele Handegård, Tadaaki Nagao, Masahiro Kitajima, Yuji Sakai, Xiang Zhang, Robert Vajtai, Pulickel Ajayan, Junichiro Kono, Jun Takeda () and Ikufumi Katayama ()
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Soungmin Bae: Tokyo Institute of Technology
Kana Matsumoto: Yokohama National University
Hannes Raebiger: Yokohama National University
Ken-ichi Shudo: Yokohama National University
Yong-Hoon Kim: Korea Advanced Institute of Science and Technology (KAIST)
Ørjan Sele Handegård: National Institute for Materials Science (NIMS)
Tadaaki Nagao: National Institute for Materials Science (NIMS)
Masahiro Kitajima: Yokohama National University
Yuji Sakai: Osaka University
Xiang Zhang: Rice University
Robert Vajtai: Rice University
Pulickel Ajayan: Rice University
Junichiro Kono: Rice University
Jun Takeda: Yokohama National University
Ikufumi Katayama: Yokohama National University

Nature Communications, 2022, vol. 13, issue 1, 1-8

Abstract: Abstract In transition metal dichalcogenides, valley depolarization through intervalley carrier scattering by zone-edge phonons is often unavoidable. Although valley depolarization processes related to various acoustic phonons have been suggested, their optical verification is still vague due to nearly degenerate phonon frequencies on acoustic phonon branches at zone-edge momentums. Here we report an unambiguous phonon momentum determination of the longitudinal acoustic (LA) phonons at the K point, which are responsible for the ultrafast valley depolarization in monolayer MoSe2. Using sub-10-fs-resolution pump-probe spectroscopy, we observed coherent phonons signals at both even and odd-orders of zone-edge LA mode involved in intervalley carrier scattering process. Our phonon-symmetry analysis and first-principles calculations reveal that only the LA phonon at the K point, as opposed to the M point, can produce experimental odd-order LA phonon signals from its nonlinear optical modulation. This work will provide momentum-resolved descriptions of phonon-carrier intervalley scattering processes in valleytronic materials.

Date: 2022
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DOI: 10.1038/s41467-022-32008-6

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