Exciton Polariton Interactions and Nonlinear Polariton Parametric Emission in Transition-metal Dichalcogenides Materials Microcavities

The monolayer transition-metal dichalcogenides have emerged as a new class of 2D semiconductors and attracted extensive research interests due to their sizable direct bandgap, remarkable optical and electronic properties. Here, we demonstrate a realization of nonlinear optical parametric polaritons in a WS₂ monolayer microcavity pumped at the inflection point and triggered in the ground state. We observed the formation of a phase-matched idler state and nonlinear amplification which preserves the valley population and survives up to room temperature. In addition, the layered structure can be assembled vertically to fabricate van der Waals heterostructure and enable new strategies for control of strong light-matter interactions. In this work, we demonstrate the systematic control of the coupling-strength by embedding multiple monolayers in a planar microcavity. The vacuum Rabi splitting is enhanced up to 72 meV for the 4 monolayer microcavity. Carrying out time-resolved pump-probe experiments at room temperature we investigate the nature of polariton interactions which are dominated by phase space filling effects. Furthermore, we also observe the presence of long-living dark excitations in the multiple monolayer superlattices. Our results not only provide fundamental understanding of the light-matter interaction in the integrated two-dimensional semiconductor and optical cavity system, but also show great promises for the application of polariton devices at room temperature