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We have investigated the steady-sate valley polarization and valley coherence of encapsulated MoS2 monolayers as a function of the temperature and the power density of a continuous wave laser excitation. Both valley polarization and coherence exhibit a non-monotonic dependence on sample temperature, attaining a local maximum at T ≈ 40 K. This has been recently attributed to a motional narrowing effect: an enhancement of the valley relaxation time occurs when the scattering rate increases. At a fixed temperature of T = 6 K, a two-fold increase of the steady-state valley polarization is achieved by increasing the laser excitation power, which we attribute to a local heating induced by the energy relaxation of photoexcited excitons outside the light cone. In contrast, in the same power range only a moderate enhancement of valley coherence is observed. Further increasing the excitation power leads to a small reduction of valley polarization and a dramatic loss of valley coherence. Supported by spatial imaging of the excitonic luminescence and polarization, we attribute this behaviour to the detrimental role of exciton-exciton interactions on both the valley lifetime and the pure dephasing rate.

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• Creative Commons BY Attribution 4.0 International
  

Keyword: Valley polarization, MoS2 monolayer, exciton-exciton interactions

Date published: 2022-04-11

Publisher: Springer Science and Business Media LLC

Journal:

• npj 2D Materials and Applications (ISSN: 23977132) vol. 6 issue. 1 27

Funding:

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1038/s41699-022-00303-x

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Updated at: 2025-02-28 08:31:04 +0900

Published on MDR: 2025-02-28 08:31:04 +0900