Extremely Efficient Light-Exciton Interaction in a Monolayer WS2 van der Waals Heterostructure Cavity

Excitons in monolayer transition-metal-dichalcogenides dominate their optical response, however, the achieved light-exciton interaction strength have been far below unity, and a complete picture of its underlying physics and fundamental limits has not been provided. Using a van der Waals heterostructure cavity, we demonstrate near-unity excitonic absorption, together with efficient emission at ultra-low excitation powers. We find that the interplay between the radiative, non-radiative and dephasing decay rates plays a crucial role in this interaction, and unveil a universal absorption law for excitons in 2D systems.