Nano-optical imaging of exciton-plasmon polaritons in WSe2/Au heterostructures

We report a nano-optical imaging study of exciton-plasmon polaritons (EPPs) in WSe2/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 (similar to 0.19 eV). Furthermore, we found a sensitive dependence of the polariton wavelength (lambda(p)) on WSe2 thickness (d). When d is below 40 nm, lambda(p) decreases rapidly with increasing d. As d reaches 50 nm and above, lambda(p) drops to 210 nm, which is over 4 times smaller than that of the free-space photons. Our simulations indicate that the high spatial confinement of EPPs is due to the strong localization of the polariton field inside WSe2. Our work uncovers the transport properties of EPPs and paves the way for future applications of these highly confined polaritons in nanophotonics and optoelectronics.

Automated summary

This study investigates exciton-plasmon polaritons in WSe2/Au heterostructures using scattering-type scanning near-field optical microscopy (s-SNOM). The dispersion diagram of the polaritons is constructed by mapping the interference fringes at different excitation energies, showing strong exciton-plasmon coupling. The polariton wavelength is found to be sensitive to the thickness of WSe2, with a drastic decrease below 40 nm.