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arXiv · 2512.10856

Brightening of dark trions in monolayer WS$_2$ via localization of surface plasmons

Sreyan Raha·Tara Shankar Bhattacharya·Indrani Bose·Achintya Singha
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Abstract

Among all excitonic complexes in transition-metal dichalcogenides (TMDs), dark and semi-dark trions are poised to play a stellar role in future quantum technologies due to their long lifetimes, about two orders of magnitude greater than those of their bright counterparts. In monolayer (ML) tungsten disulphide (WS$_2$), accessing these states via a suitable brightening mechanism remains challenging, specially, at elevated temperatures. Here, we demonstrate the brightening of dark trions from ML WS$_2$ over the temperature range, 83 K-115 K, enabled by localized surface plasmon modes in a disordered gold substrate. The resulting photoluminescence (PL) spectrum reveals a distinct spectral doublet with the twin peaks of semi-dark and bright trion states, separated by $\sim$ 45 meV. The origin of the semi-dark trion state lies in intervalley electron-electron scatterings, while its visibility in the PL spectrum is made possible by the enhanced out-of-plane electromagnetic field associated with plasmon localization. We also report on the negative degree of circular polarization in ML WS$_2$ at the energy of the semi-dark trion state. Our results establish a scalable plasmonic route to access valley-polarized semi-dark trions, opening new opportunities for quantum and valleytronic applications.

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Sreyan Raha, Tara Shankar Bhattacharya, Indrani Bose, Achintya Singha. 2025-12-11. Brightening of dark trions in monolayer WS$_2$ via localization of surface plasmons. https://doi.org/10.1088/1361-648x%2Fae8948

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