Highly-confined exciton-polaritons in monolayer semiconductors

In this work, we predict the existence of a new type of in-plane propagating, highly-confined exciton-polariton, supported by monolayer transition-metal-dicalcogonides (TMDs) 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 twith those of surfaceplasmon-polaritons at the same spectral range reveals that the 2DEP exhibits two orders-of-magnitude larger wavelength confinement.