Plasmon-exciton Interactions in Gold-WSe2 Multilayer structures.

Van der Waals materials such as thin films of transition-metal dichalcogenides (TMDCs) manifest strongly bound exciton states in the visible spectrum at ambient conditions that provide an ideal platform for exciton-photon couplings. Utilizing semiconducting TMDCs in the form of multilayer structure combined with metals can increase significantly the light-matter interaction. In this way, the interaction between excitons and surface-plasmon polaritons emerge as a platform for transferring the electromagnetic energy at confined modal volumes. Here, we theoretically investigate how moving electrons can be used as a probe of hybrid exciton-plasmon polaritons of gold-WSe2 multilayers within the context of electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) spectroscopy. Interestingly, and in contrast to WSe2 slab waveguides where quasi-propagating photonic modes interact with only exciton A, in gold-WSe2 multilayer, exciton A and exciton B can both strongly interact with surface plasmon polaritons. Hence, we observe CL emission suppression at excitonic or plasmonic peaks, which reveals the energy transfer between excitons and plasmons in the form of nonradiating guided waves. Our work provides a systematic study for deeper understanding of the effect of the configuration and the thickness of layers on the photonic and plasmonic modes and hence on the strength of the coupling between excitons and surface-plasmon polaritons. Our findings pay the way for designing efficient photodetectors, sensitive sensors, and light emitting devices based on metal/semiconducting hybrid materials.