  We study exciton-plasmon coupling in two-dimensional semiconductors coupled
with Ag plasmonic lattices via angle-resolved reflectance spectroscopy and by
solving the equations of motion (EOMs) in a coupled oscillator model accounting
for all the resonances of the system. Five resonances are considered in the EOM
model: semiconductor A and B excitons, localized surface plasmon resonances
(LSPRs) of plasmonic nanostructures and the lattice diffraction modes of the
plasmonic array. We investigated the exciton-plasmon coupling in different 2D
semiconductors and plasmonic lattice geometries, including monolayer MoS2 and
WS2 coupled with Ag nanodisk and bowtie arrays, and examined the dispersion and
lineshape evolution in the coupled systems via the EOM model with different
exciton-plasmon coupling parameters. The EOM approach provides a unified
description of the exciton-plasmon interaction in the weak, intermediate and
strong coupling cases with correctly explaining the dispersion and lineshapes
of the complex system. This study provides a much deeper understanding of
light-matter interactions in multilevel systems in general and will be useful
to instruct the design of novel two-dimensional exciton-plasmonic devices for a
variety of optoelectronic applications with precisely tailored responses.
