Strong coupling between hybrid plasmonic–photonic resonances and excitons in metallic photonic crystal–monolayer WS2 nanostructures

Nanostructures, supporting hybrid plasmonic–photonic modes that combine the advantages of the electromagnetic field enhancement of the localized plasmon resonances (LSPRs) and the higher quality factor of the photonic resonances, have served as flexible and efficient platforms for engineering strong light–matter interactions. Here, we demonstrate theoretically that the two-dimensional metallic photonic crystals (PhCs) as a class of hybrid plasmonic–photonic lattices play an active role in light–matter interaction. The metallic PhCs are composed of optical waveguides strongly coupled to periodically arranged metallic nanodisks, and this coupling gives rise to the formation of waveguide–plasmon polaritons. By combining two-dimensional semiconducting materials (WS2) and the metallic PhCs, we prove strong coupling between waveguide–plasmon modes and excitons at room temperature. The strong coupling includes three types of resonances: guided modes excited by diffractive gratings, LSPRs on individual nanodisks, and WS2 excitons. Using coupled oscillator models, we show that the mode composition and coupling strength between polaritons can be controlled effectively by tuning the geometrical factor of the lattice, and thus reveal the LSPR-mediated energy transfer process. Our reports are not only of fundamental interest but could also be useful for practical applications based on monolayer semiconductors