Rabi Splitting in a Plasmonic Nanocavity Coupled to a WS2 Monolayer at Room Temperature

A large Rabi splitting (∼145 meV) is demonstrated in a plasmonic nanocavity coupled to a WS2 monolayer at room temperature. The nanocavity is composed of a silver nanocube and a silver film with an Al2O3 spacer of a few nanometers, which belongs to a nanoparticle on mirror (NPoM) type. The surface plasmon resonance (SPR) of the nanocavity can be tuned by controlling the thickness of nanogap and the size of silver nanocubes, which allows to successively adjust the SPR to accurately match the exciton energy of WS2 monolayers (2.02 eV). A mode splitting can be clearly observed from the dark-field scattering spectrum of the single hybrid nanocavity, which is ascribed to a strong coupling between the nanocavity mode and the excitonic mode. Furthermore, the anticrossing curves of the hybrid system are obtained by recording the scattering spectra with varied sizes of silver nanocubes, which further validate the interaction regime. It presents a strong coupling platform for two-dimensional monolayers, which is of potential applications of the development of hybrid nanostructure devices.