Cavity-assisted boosting of self-hybridization between excitons and photonic bound states in the continuum in multilayers of transition metal dichalcogenides

Strong coupling between excitons in transition metal dichalcogenides (TMDs) and quasibound states in the continuum (QBIC) has attracted much attention in recent years. However, the coupling strength is often limited due to the spatial mismatch at the location of the TMDs and the maximum field strength of the QBIC mode. Here, we report a cavity-assisted boosting of self-hybridization between excitons (X) and the QBIC mode at room temperature by embedding a two-dimensional (2D) metasurface composed of bulk ${\mathrm{WS}}_{2}$ into a microcavity. We demonstrate that the self-hybridized BIC-X coupling strength in this 2D metasurface can be dramatically enhanced with the assistance of a Fabry-P\'erot cavity. Full wave simulations demonstrate a giant Rabi splitting up to 240 meV, which is twice as high as the QBIC-X self-hybridization in the 2D metasurface system. A coupled oscillator model containing a $3\ifmmode\times\else\texttimes\fi{}3$ Hamiltonian matrix combined with a near-field analysis reveals the underlying mechanism of the greatly enlarged coupling strength: The cavity provides a strong out-of-plane field confinement and the QBIC mode concentrates in an in-plane electric field, which greatly facilitates the spatial overlap of excitons with the localized field. Importantly, we also demonstrate that the coupling strength of the hybrid system can be readily tuned by controlling the excitonic oscillator strength of the bulk TMD material. This provides a powerful approach for manipulating the self-hybridization process. We believe that the cavity-based configuration proposed in this paper can serve as a universal recipe for achieving strong light-matter interactions, thus paving the way for the design of tunable exciton-polariton photonic devices with high performance.