Strong coupling of monolayer WS2 excitons and surface plasmon polaritons in a planar Ag/WS2

This paper shows that the strong coupling regime between excitons in a WS${}_{2}$ monolayer and surface plasmon polaritons of a thin Ag film can be reached in a planar geometry of utmost simplicity. Total internal reflection ellipsometry provides a salient feature of strong coupling. The finding opens up the opportunity to engineer the light-matter interaction strength and even to tune the exciton-plasmon system between the weak and strong coupling regime via application of external stimuli.