Highly-confined 2D Exciton-polaritons in Monolayer Semiconductors

We predict the existence of a new type of in-plane propagating exciton-polaritons that are supported by monolayer transition-metal-dichalcogenides (TMDs), which can carry large momentum in the visible spectrum. This 2D exciton-polariton (2DEP) is a result of the coupling between the electromagnetic light field and collective oscillations of excitons in TMDs. We experimentally show that the conditions required for the excitation of the 2DEP are attainable if the TMD is encapsulated with hexagonal-boron-nitride (hBN) and is cryogenically cooled. In addition, a comparison of the properties of the 2DEP with those of surface-plasmon-polaritons at the same spectral range reveals that the 2DEP exhibits two orders-of-magnitude larger wavelength confinement.