Chasing Bose‐Einstein and Maxwell‐Boltzmann Distributions of Exciton‐Polaritons in a 2D Semiconductor Microcavity

ABSTRACT

Exciton polaritons (EPs) in two‐dimensional (2D) semiconductor microcavities have emerged as an attractive platform for high‐temperature polaritonic optoelectronics, owing to large exciton binding energies and superior thermal stability of transition‐metal dichalcogenides. Manipulating EP populations is crucial for understanding bosonic thermodynamics and developing tunable polaritonic devices. Most polariton devices employ lower‐polariton (LP) emission; by contrast, strong upper‐polariton (UP) emission remains a challenging yet highly desired counterpart for realizing controllable UP‐LP emitters. Here, we demonstrate tunable emission from primary LPs to robust UPs in a 2D semiconductor microcavity, revealing crossovers in polariton probability distributions between Bose‐Einstein (BE) and Maxwell‐Boltzmann (MB) statistics at elevated temperatures. Temperature‐dependent excitonic band renormalization and photonic cavity shrinkage lead to a reversal of the exciton‐photon detuning from negative to positive, reconstructing excitonic and photonic fractions in the formed EPs. At 318 K, the LP and UP populations follow BE and MB distributions, respectively. However, their statistical distributions are reversed at 378 K, where the thermal excitation assists the accumulation of the UP population and favors the BE distribution. Our findings provide insights into the basic thermodynamics of polaritonic populations, establishing a practical route to develop tunable LP‐UP devices.