Strong Light-Matter Coupling between Plasmons in Individual Gold Bi-pyramids and Excitons in Mono- and Multilayer WSe2

Monolayer transition-metal dichalcogenides (TMDCs) have attracted a lot of research attention recently, motivated by their remarkable optical properties and potential for strong light–matter interactions. Realization of strong plasmon–exciton coupling is especially desirable in this context because it holds promise for the enabling of room-temperature quantum and nonlinear optical applications. These efforts naturally require investigations at a single-nanoantenna level, which, in turn, should possess a compact optical mode interacting with a small amount of excitonic material. However, standard plasmonic nanoantenna designs such as nanoparticle dimers or particle-on-film suffer from misalignment of the local electric field in the gap with the in-plane transition dipole moment of monolayer TMDCs. Here, we circumvent this problem by utilizing gold bi-pyramids (BPs) as very efficient plasmonic nanoantennas. We demonstrate strong coupling between individual BPs and tungsten diselenide (WSe2) monolayers at ro...