  Excitons, composite electron-hole quasiparticles, are known to play an
important role in optoelectronic phenomena in many semiconducting materials.
Recent experiments and theory indicate that the band-gap optics of the newly
discovered monolayer transition-metal dichalcogenides (TMDs) is dominated by
tightly bound valley excitons. The strong interaction of excitons with
long-range electromagnetic fields in these 2D systems can significantly affect
their intrinsic properties. Here, we develop a semi-classical framework for
intrinsic exciton-polaritons in monolayer TMDs that treats their dispersion and
radiative decay on the same footing and can incorporate effects of the
dielectric environment. It is demonstrated how both inter- and intra-valley
long-range interactions influence the dispersion and decay of the polaritonic
eigenstates. We also show that exciton-polaritons can be efficiently excited
via resonance energy transfer from quantum emitters such as quantum dots, which
may be useful for various applications.
