Strong light-matter interactions of exciton in bulk WS and a toroidal dipole resonance.

Exciton-polaritonic states are generated by strong interactions between photons and excitons in nanocavities. Bulk transition metal dichalcogenides (TMDCs) host excitons with a large binding energy at room temperature, and thus are regarded as an ideal platform for realizing exciton-polaritons. In this work, we investigate the strong coupling properties between high-Q toroidal dipole (TD) resonance and bulk WS excitons in a hybrid metasurface, consisting of SiN nanodisk arrays with embedded WS. Multipole decomposition and near-field distribution confirm that SiN nanodisk arrays support strong TD resonance. The TD resonance wavelength is easily tuned to overlap with the bulk WS exciton wavelength, and strong coupling is observed when the bulk WS is integrated with the hollow nanodisk and the oscillator strength of the WS material is adjusted to be greater than 0.6. The Rabi splitting of the hybrid device is up to 65 meV. In addition, strong coupling is confirmed by the anticrossing of fluorescence enhancement in the hybrid SiN-WS metastructure. Our findings are expected to be of importance for both fundamental research in TMDC-based light-matter interactions and practical applications in the design of high-performance exciton-polariton devices.