Microscopic Mechanisms of Exciton Polariton Relaxation in Monolayer WS2 Microcavities.

Exciton polaritons in transition metal dichalcogenide (TMD) microcavities have garnered significant interest due to their strong spin-orbit coupling, large exciton binding energy, van der Waals heterointegration, and room-temperature stability. These properties make TMD microcavities a powerful platform for valleytronics, topological photonics, and ultrafast optoelectronics. A key factor in harnessing their potential is understanding the relaxation process, which governs condensation, transport, and nonlinear interactions. Here, we investigate the microscopic natures of these energy relaxation processes of exciton polaritons in monolayer WS2 microcavities. We find that the relaxation processes are dominated by two pathways, namely, thermally activated phonon scatterings and strong two-body polariton interactions, which have competing roles in different temperature regimes. We demonstrate that the dominance of these distinct mechanisms can be controlled by operating temperature and excitation power. Furthermore, numerical simulations provide robust validation of experimental observations, delivering essential theoretical foundations for the optimization of polaritonic devices in TMD systems.