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Motional narrowing implies narrowing induced by motion, for example, in nuclear resonance, the thermally induced random motion of the nuclei in an inhomogeneous environment leads to counter-intuitive narrowing of the resonance line. Similarly, the excitons in monolayer semiconductors experience magnetic inhomogeneity: the electron-hole spinexchange interaction manifests as an in-plane pseudo-magnetic field with a periodically varying orientation inside the exciton band. The excitons undergo random momentum scattering and pseudospin precession repeatedly in this inhomogeneous magnetic environment – typically resulting in fast exciton depolarization. On the contrary, we show that such magnetic inhomogeneity averages out at high scattering rate due to motional narrowing. Physically, a faster exciton scattering leads to a narrower pseudospin distribution on the Bloch sphere, implying a nontrivial improvement in exciton polarization. The in-plane nature of the pseudomagnetic field enforces a contrasting scattering dependence between the circularly and linearly polarized excitons – providing a spectroscopic way to gauge the sample quality.

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  This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright © 2024 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.nanolett.3c04808.

Keyword: 2D materials, Exciton Pseudospin, Valley Decoherence, Motional Narrowing, Polarization Contrast, MoS2

Date published: 2024-05-08

Publisher: American Chemical Society (ACS)

Journal:

• Nano Letters (ISSN: 15306984) vol. 24 issue. 18 p. 5413-5419

Funding:

• Indian Space Research Organisation
• Ministry of Education, Culture, Sports, Science and Technology
• Science and Engineering Research Board
• Japan Society for the Promotion of Science 21H05233
• Japan Society for the Promotion of Science 23H02052
• Karnataka Innovation and Technology Society

Manuscript type: Author's version (Accepted manuscript)

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First published URL: https://doi.org/10.1021/acs.nanolett.3c04808

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Updated at: 2025-07-29 12:30:27 +0900

Published on MDR: 2025-07-29 12:21:26 +0900