Exciton-polariton properties in hBN-encapsulated transition metal dichalcogenides

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been remarked for their outstanding potential in photonics and optoelectronic devices. 2D TMDCs shows strong light-matter interactions due to increased excitonic effect in 2D limits and valley degrees of freedom as a result of broken inversion symmetry. These unique properties of TMDCs have led to studies of exciton-polaritons (EPs) demonstrated by cavity engineering. Further studies have shown that the formation of EPs is possible even in a bare structure of TMDCs due to their strong exciton-photon coupling. Hence, understanding of EPs is a key to unfold potentials in polariton-based optoelectronics.

Here, we demonstrated improved EPs properties in TMDCs with hexagonal-boron nitride (hBN). By encapsulating WS₂ with atomically thin hBN, WS₂ was isolated from charge disorders at the surface of substrate and maintained its flatness. We observed the presence of hBN reduces the inhomogeneous linewidth of exciton in the photoluminescence spectra. The reduced linewidth indicates a stronger excitonic resonance, improving properties of EPs. Therefore, to compare propagation properties of EPs depending on the presence of hBN, the spectra of EPs scattered at the sample edge were investigated as a function of the propagation length. The hBN enables us to study intrinsic optical properties of the polariton in TMDCs in details. The enhanced quality of EPs will contribute to further studies in photonics and optoelectronic devices.