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Motion of Two-Dimensional Excitons in Momentum Space Leads to Pseudospin Distribution Narrowing on the Bloch Sphere

Gupta, G and Watanabe, K and Taniguchi, T and Majumdar, K (2023) Motion of Two-Dimensional Excitons in Momentum Space Leads to Pseudospin Distribution Narrowing on the Bloch Sphere. In: Nano Letters .

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

Abstract

Motional narrowing implies narrowing induced by motion; for example, in nuclear magnetic resonance, the thermally induced random motion of the nuclei in an inhomogeneous environment leads to a counterintuitive narrowing of the resonance line. Similarly, the excitons in monolayer semiconductors experience magnetic inhomogeneity: the electron-hole spin-exchange interaction manifests as an in-plane pseudomagnetic 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 rates 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. © 2024 American Chemical Society

Item Type: Journal Article
Publication: Nano Letters
Publisher: American Chemical Society
Additional Information: The copyright for this article belongs to American Chemical Society.
Keywords: Depolarization; Excitons; Layered semiconductors; Sulfur compounds, 2d material; Bloch sphere; Decoherence; Exciton pseudospin; Magnetic inhomogeneities; Motional narrowing; Polarization contrast; Pseudospin; Two-dimensional excitons; Valley decoherence, Molybdenum compounds
Department/Centre: Division of Electrical Sciences > Electrical Communication Engineering
Date Deposited: 22 May 2024 12:11
Last Modified: 22 May 2024 12:11
URI: https://eprints.iisc.ac.in/id/eprint/85074

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