Si/Si₃N₄/Ag hybrid nanocavity: a platform for enhancing light-matter interaction

High-index dielectric nanoparticles supporting strong Mie resonances, such as silicon (Si) nanoparticles, provide a platform for manipulating optical fields at the subwavelength scale. However, in general, the quality factors of Mie resonances supported by an isolated nanoparticle are not sufficient for realizing strong light-matter interaction. Here, we propose the use of dielectric-metal hybrid nanocavities composed of Si nanoparticles and silicon nitride/silver ( Si 3 N 4 / Ag ) heterostructures to improve light-matter interaction. First, we demonstrate that the nonlinear optical absorption of the Si nanoparticle in a Si / Si 3 N 4 / Ag hybrid nanocavity can be greatly enhanced at the magnetic dipole resonance. The Si / Si 3 N 4 / Ag nanocavity exhibits luminescence burst at substantially lower excitation energy (∼20.5 pJ ) compared to a Si nanoparticle placed on a silica substrate (∼51.3 pJ ). The luminescence intensity is also enhanced by an order of magnitude. Second, we show that strong exciton-photon coupling can be realized when a tungsten disulfide ( WS 2 ) monolayer is inserted into a Si / Si 3 N 4 / Ag nanocavity. When such a system is excited by using s-polarized light, the optical resonance supported by the nanocavity can be continuously tuned to sweep across the two exciton resonances of the WS 2 monolayer by simply varying the incident angle. As a result, Rabi splitting energies as large as ∼146.4 meV and ∼110 meV are observed at the A- and B-exciton resonances of the WS 2 monolayer, satisfying the criterion for strong exciton-photon coupling. The proposed nanocavities provide, to our knowledge, a new platform for enhancing light-matter interaction in multiple scenarios and imply potential applications in constructing nanoscale photonic devices.