Strong coupling between excitons in a two-dimensional atomic crystal and quasibound states in the continuum in a two-dimensional all-dielectric asymmetric metasurface

We investigate the interaction between excitons in a two-dimensional atomic crystal and quasibound states in the continuum (q-BIC) in a two-dimensional all-dielectric asymmetric metasurface. By introducing coherent and incoherent coupling terms in a coupled oscillator model, we demonstrate the coexistence of coherent and incoherent coupling processes in the strongly coupled system and the resultant sub/superradiant polariton states. Based on the multipole decomposition method and near-field analysis of full wave simulations, we study the microscopic excitation of multipole components in q-BIC and their coupling to excitons. We reveal that not only the magnetic dipole but also the interference between electric dipole and its toroidal counterpart dominate in the exciton-BIC strong coupling regime. The fractions of the magnetic and electric dipole ingredients are modulated by the topology of the two-dimensional all-dielectric metasurface, exhibiting distinctly different features in the high- and low-energy hybrid modes in the strong coupling system. Our findings are expected to be of importance for both fundamental research in TMD-based light-matter interactions and practical applications in the design of novel, tunable exciton-polariton devices with high compactibility.