Insight into exciton polaritons of two-dimensional transition metal dichalcogenides with time-resolved spectroscopy

Exciton polaritons (EP) are quasi-particles formed via strong coupling between an exciton and a confined photon mode with tunable hybrid light-matter character. Low-dimensional transition metal dichalcogenides (TMD) are a promising platform for EP phenomena like strongly correlated physics, as well as for realization of tunable optoelectronic applications, at ambient temperatures. However, ultrafast relaxation timescales and the presence of long-lived reservoir states make unambiguous resolution of TMD EP properties, including nonlinearities, very challenging. In this prospective, we review recent progress in understanding TMD EP physics using time-resolved spectroscopies well suited for resolving complex optoelectronic behavior, highlight open questions, and discuss remaining experimental challenges.