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Polarized and narrow excitonic emission from graphene-capped monolayer WS2 through resonant phonon relaxation

Gupta, G and Majumdar, K (2023) Polarized and narrow excitonic emission from graphene-capped monolayer WS2 through resonant phonon relaxation. In: Physical Review B, 108 (7).

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Official URL: https://doi.org/10.1103/PhysRevB.108.075436


The broadening and polarization of excitonic luminescence in monolayer transition metal dichalcogenides largely suffer from inhomogeneity and temperature - an unresolved problem to date. In this work, through few-layer graphene encapsulation of monolayer WS2, we reduce the interexcitonic energy separation, which then can have a narrow resonance with a specific phonon mode of our choice. The resulting single-step exciton relaxation with the resonating phonon mode significantly suppresses the inhomogeneous broadening, allowing us to achieve the narrowest exciton linewidth of 1.06 meV (which translates to 0.19 meV after deconvolution with the excitation laser linewidth). The single-phonon resonance helps to achieve a high quantum efficiency despite graphene encapsulation. The technique is powerful in tuning the exciton polarization during relaxation by choosing a specific resonating phonon mode. For example, the valley coherence (polarization) improves from ∼68%(∼40%) to ∼90%(∼75%) on resonance with 2A1′ and A1′ modes, respectively. We further demonstrate a strong polarization reversal on resonance with a chiral phonon mode. Strikingly, the above features remain robust against temperature (up to 200 K) and sample age (a few months in ambient condition). The findings will lead to clean excitonic measurements without requiring cryogenic cooling. © 2023 American Physical Society.

Item Type: Journal Article
Publication: Physical Review B
Publisher: American Physical Society
Additional Information: The copyright for this article belongs to the Authors.
Keywords: Excitons; Graphene; Laser excitation; Phonons; Polarization; Transition metals; Tungsten compounds, Dichalcogenides; Energy separations; Excitonic emission; Excitonic luminescence; Few-layer graphene; Inhomogeneities; Narrow resonances; Phonon mode; Phonon relaxation; Resonant phonon, Monolayers
Department/Centre: Division of Electrical Sciences > Electrical Communication Engineering
Date Deposited: 17 Dec 2023 08:39
Last Modified: 17 Dec 2023 08:39
URI: https://eprints.iisc.ac.in/id/eprint/83448

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