Plasmon-exciton coupling in dielectric-metal hybrid nanocavities with an embedded two-dimensional material

The interaction between light and matter has long been the research topic in many scientific disciplines. So far, strong plasmon-exciton coupling has been demonstrated in a variety of plasmonic nanocavities with embedded two-dimensional materials. Here, we proposed a hybrid nanocavity, which is composed of a silicon (Si) nanoparticle and a thin gold (Au) film, to realize strong plasmon-exciton coupling with an embedded two-dimensional material (WS2 monolayer). It was found that the optical resonances of the hybrid nanocavity originate mainly from the coherent interactions of the Mie resonances supported by the Si nanoparticle and their mirror images induced by the Au film. Their optical properties, including electric field enhancements and damping rates, depend strongly on the excitation scheme of the nanocavity. It was revealed numerically and demonstrated experimentally that strong plasmon-exciton coupling can only be achieved by exploiting the optical mode formed by the interference of the electric dipole and its mirror image when the nanocavity is excited from the Au film side. Our findings pave the way for realizing strong plasmon-exciton coupling in dielectric-metal hybrid nanocavities and open new horizons for designing novel photonic devices in which the light-matter interaction can be manipulated.