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arXiv · 2602.01324

Population Metrology of a Hidden Exciton Reservoir: Quasi-Thermalization versus Localization

Guangyu Dai·Xinyu Zhang·Jiaxin Yu·Zi'ang Xing·Miao Cai·Zhaoqi Gu·Junyuan Zhang·Lin Dou·Fuxing Gu·Yiming Zhu·Songlin Zhuang
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Abstract

Long-lived dark states can dominate the lowest-energy manifold of optically driven quantum materials, yet their occupation remains difficult to quantify, leaving it unclear whether it reflects thermal redistribution or kinetic trapping. We combine microsphere-enabled far-field access with quantitative optical-response calibration to retrieve dark-to-bright population ratios in monolayer WSe2. Temperature-dependent measurements and controlled defect enhancement separate mobile and localized contributions. Near room temperature, the mobile dark-to-bright ratio reaches approximately 65% of its Boltzmann limit, indicating substantial but incomplete quasi-thermalization, whereas the low-temperature excess is dominated by defect-assisted localization. Dark-state dominance alone therefore does not establish equilibration, a distinction essential for interpreting transport and collective phases in optically hidden quasiparticle reservoirs.

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Guangyu Dai, Xinyu Zhang, Jiaxin Yu, Zi'ang Xing, Miao Cai, Zhaoqi Gu, Junyuan Zhang, Lin Dou, Fuxing Gu, Yiming Zhu, Songlin Zhuang. 2026-02-01. Population Metrology of a Hidden Exciton Reservoir: Quasi-Thermalization versus Localization. https://arxiv.org/abs/2602.01324

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