Transverse‐Electric‐Polarized Polaritons Propagating in a WS 2 /Si 3 N 4 /Ag Heterostructure

Strong light–matter interaction has attracted great interest due to its potential applications in photonic and plasmonic devices. So far, many studies focus on micro‐ and nanocavities with three‐dimensional confinement of light. Here, we investigate the coupling between the surface waves supported by a dielectric‐metal heterostructure and the excitons in a two‐dimensional material. It is revealed that the transverse‐electric (TE) polarized waves excited in the dielectric‐metal heterostructure possess significantly enhanced in‐plane electric field on the surface of the dielectric layer. This unique property makes it possible to realize strong photon–exciton coupling with the excitons in a two‐dimensional material. By using a tungsten disulfide (WS 2 )/silicon nitride (Si 3 N 4 )/silver (Ag) heterostructure, we demonstrate the strong coupling of the TE polarized waves with the two excitons (both A and B excitons) in the WS 2 monolayer, creating TE polarized polaritons propagating in the heterostructure. The strong photon–exciton coupling is revealed in the angle‐resolved reflection or scattering spectra with a Rabi splitting larger than the average damping rate of the TE polarized wave and the exciton. Our findings open new horizons for manipulating light–matter interaction in two‐dimensional nanostructures and indicate the potential applications of such propagating polaritons in photonic and plasmonic devices.