Enhanced Light-Matter Interaction with Bloch Surface Wave Modulated Plasmonic Nanocavities.

Strong coupling between nanocavities and single excitons at room temperature is important for studying cavity quantum electrodynamics. However, the coupling strength is highly dependent on the spatial light-confinement ability of the cavity, the number of involved excitons, and the orientation of the electric field within the cavity. By constructing a hybrid cavity with a one-dimensional photonic crystal cavity and a plasmonic nanocavity, we effectively improve the quality factor, reduce the mode volume, and control the direction of the electric field using Bloch surface waves. After transferring a monolayer of WSe sandwiched in the hybrid nanocavities, a Rabi splitting of approximately 186 meV is obtained and the number of excitons involved in the coupling is reduced to 8. This is the smallest number reported to date for transition metal dichalcogenide (TMD) based systems, with an effective coupling strength per individual exciton reaching 17.6 meV, which is nearly double the highest reported value.