Normal-Incidence-Excited Strong Coupling between Excitons and Symmetry-Protected Quasi-Bound States in the Continuum in Silicon Nitride–WS2 Heterostructures at Room Temperature

Room-temperature strong coupling between quasi-bound states in the continuum (q-BIC) of a silicon nitride metasurface and excitons in a WS₂ monolayer is investigated in detail by both numerical simulations and theoretical calculations. The strong coupling between the q-BIC mode and excitons leads to a remarkable spectral splitting and typical anticrossing behavior of the Rabi splitting, which can be realized in the absorption spectra by varying the grating thickness and asymmetry parameter of the silicon-nitride metasurface, respectively. In addition, both the line width of the q-BIC mode and local electric field enhancement are found to affect the strong coupling, which needs to be considered in detail in q-BIC metasurface designs. This work provides a possible way to enhance light-matter interactions in transition metal dichalcogenides monolayers and pave the way for future quantum and nanophotonic applications.