Impact of temperature on exciton-cavity detuning and polariton relaxation kinetics in monolayer Tungsten Disulphide (WS_2) based microcavity

摘要

Monolayer Tungsten Disulphide (WS2) with strongly confined 2D Wannier-Mott excitons exhibits a large binding energy and oscillator strength. This monolayer is currently emerging as a good candidate for studying strong light matter coupling at high temperature. Here, we investigate the formation of exciton-polaritons in a monolayer WS2 based semiconductor microcavity under non resonant excitation. Our results show that the cavity detuning changes from negative to positive values over a temperature range of 130-230 K, which allow the tuning of polariton dispersion. The Hopfield coefficient show that the Upper branch (UP) can be tuned from a more excitonlike (130 K), to a more photonlike (230 K) at small wave vector k. Thus, the UP states have a faster lifetime which enhances the relaxation mechanisms towards lower polariton (LP) states. A Rabi splitting of 40 meV is observed, which corresponds to energy of longitudinal optical (LO) phonon. To show how polaritons states are populated, we investigate a semiclassical model that treats the temporal dynamics of polaritons in which LO phonon-assisted polariton emission is taken into account. The results reveals that the UP occupation starts to decrease, for increasing the occupation factor in the LP branch.