Switchable intervalley excitons with strong two-phonon scattering in bilayer WSe<sub>2</sub>

Fu Chen Hsiao
(Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan. Advanced Semiconductor Device and Integration Laboratory, Department of Electrical and Computer E)

Jeremiah van Baren
(University of California, Riverside)

Takashi Taniguchi
(International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki Tsukuba, Ibaraki 305-0044, Japan.)

Kenji Watanabe
(Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.)

Nathaniel M. Gabor
(Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA. Canadian Institute for Advanced Research, MaRS Centre West Tower, 661 University Avenu)

Yia Chung Chang
(Research Center for Applied Sciences, Academia Sin)

Chun Hung Lui
(Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA.)

Collaboration:

We thank Fatemeh Barati and Matthew Wilson for help in the project, Ao Shi for assistance in manuscript preparation, Kin Fai Mak and Jie Shan for discussion, Yong-Tao Cui for supporting E.L., Harry Tom for equipment support,

Abstract: We report the observation of QΓ intervalley exciton in bilayer WSe₂ devices encapsulated by boron nitride. The QΓ exciton resides at ~18 meV below the QK exciton. The QΓ and QK excitons exhibit different Stark shifts under an out-of-plane electric field due to their different interlayer dipole moments. By controlling the electric field, we can switch their energy order and control which exciton dominates the luminescence of bilayer WSe₂. Remarkably, both QΓand QK excitons exhibit unusually strong two-phonon replicas, which are comparable to or even stronger than the one-phonon replicas. By detailed theoretical simulation, we reveal the existence of numerous ( 14) two-phonon scattering paths involving (nearly) resonant exciton-phonon scattering in bilayer WSe₂. To our knowledge, such electric-field-switchable intervalley excitons with strong two-phonon replicas have not been found in any other two-dimensional semiconductors. They make bilayer WSe₂ a distinctive valleytronic material with potential novel applications.

*C.H.L. acknowledges support from the National Science Foundation Division of Materials Research CAREER Award No.1945660. YCC acknowledges support by the Ministry of Science and Technology (Taiwan) under Grant No. MOST 109-2112-M-001-046. N.M.G acknowledges support from the National Science Foundation Division of Materials Research CAREER Award No. 1651247, and from the United States Department of the Navy Historically Black Colleges, Universities, and Minority Serving Institutions (HBCU/MI) Award No. N00014-19-1-2574. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan and the CREST (JPMJCR15F3), JST. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation Cooperative Agreement No. DMR-1644779 and the State of Florida.

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Bulletin of the American Physical Society

APS March Meeting 2022

Volume 67, Number 3

Monday–Friday, March 14–18, 2022; Chicago

Session Q12: Optical Spectroscopic Measurements of 2D Materials I

Abstract: Q12.00012 : Switchable intervalley excitons with strong two-phonon scattering in bilayer WSe2*

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Abstract: Q12.00012 : Switchable intervalley excitons with strong two-phonon scattering in bilayer WSe₂*