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arXiv · 2404.15120

Motion of 2D exciton in momentum space leads to pseudospin distribution narrowing on the Bloch Sphere

Garima Gupta·Kenji Watanabe·Takashi Taniguchi·Kausik Majumdar
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Abstract

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 spin-exchange 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 pseudo-magnetic 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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Garima Gupta, Kenji Watanabe, Takashi Taniguchi, Kausik Majumdar. 2024-04-23. Motion of 2D exciton in momentum space leads to pseudospin distribution narrowing on the Bloch Sphere. https://doi.org/10.1021/acs.nanolett.3c04808

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