Nano-optical imaging of exciton-plasmon polaritons in WSe/Au heterostructures.

We report a nano-optical imaging study of exciton-plasmon polaritons (EPPs) in WSe/Au heterostructures with scattering-type scanning near-field optical microscopy (s-SNOM). By mapping the interference fringes of EPPs at various excitation energies, we constructed the dispersion diagram of the EPPs, which shows strong exciton-plasmon coupling with a sizable Rabi splitting energy (∼0.19 eV).