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Observation of ~100% valley-coherent excitons in monolayer MoS2 through giant enhancement of valley coherence time

Gupta, G and Watanabe, K and Taniguchi, T and Majumdar, K (2023) Observation of ~100% valley-coherent excitons in monolayer MoS2 through giant enhancement of valley coherence time. In: Light: Science and Applications, 12 (1).

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Official URL: https://doi.org/10.1038/s41377-023-01220-4


In monolayer transition metal dichalcogenide semiconductors, valley coherence degrades rapidly due to a combination of fast scattering and inter-valley exchange interaction. This leads to a sub-picosecond valley coherence time, making coherent manipulation of exciton a highly challenging task. Using monolayer MoS2 sandwiched between top and bottom graphene, here we demonstrate fully valley-coherent excitons by observing ~100% degree of linear polarization in steady state photoluminescence. This is achieved in this unique design through a combined effect of (a) suppression in exchange interaction due to enhanced dielectric screening, (b) reduction in exciton lifetime due to a fast inter-layer transfer to graphene, and (c) operating in the motional narrowing regime. We disentangle the role of the key parameters affecting valley coherence by using a combination of calculation (solutions of Bethe-Salpeter and Maialle-Silva-Sham equations) and a careful choice of design of experiments using four different stacks with systematic variation of screening and exciton lifetime. To the best of our knowledge, this is the first report in which the excitons are found to be valley coherent in the entire lifetime in monolayer semiconductors, allowing optical readout of valley coherence possible.

Item Type: Journal Article
Publication: Light: Science and Applications
Publisher: Springer Nature
Additional Information: The copyright for this article belongs to the author.
Keywords: Design of experiments; Graphene; Landforms; Layered semiconductors; Molybdenum compounds; Monolayers; Sulfur compounds; Transition metals, reductions; Coherence time; Coherent manipulation; Combined effect; Degree of linear polarization; Dielectric screening; Exciton lifetime; Picoseconds; Steady state; Transition metal dichalcogenides (TMD), Excitons
Department/Centre: Division of Electrical Sciences > Electrical Communication Engineering
Date Deposited: 08 Aug 2023 05:16
Last Modified: 08 Aug 2023 05:16
URI: https://eprints.iisc.ac.in/id/eprint/82718

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