Spectrally Resolved Exciton Emission in Monolayer WSe₂ Encapsulated in h-BN

The reduced screening of Coulomb interactions in transition metal dichalcogenide (TMDC) monolayers leads to the presence of a wide range of many-body effects in the materials’ optical properties, including tightly bound exciton (two-body), trion (three-body), and biexciton (four-body) states. Recently, new crystal growth methods and encapsulation in hexagonal boron nitride (h-BN) has greatly improved the quality of TMDC samples and given rise to a series of new exciting observations, such as the exciton linewidths near their intrinsic limit, signatures of interlayer electron-phonon couplings, and exciton emission polarized perpendicular to the surface. Here we report on our effort to spectrally resolve all emission peaks in h-BN encapsulated monolayers of WSe2. The narrowest peak we observe is from dark exciton states and exhibits a linewidth in photoluminescence below one meV at cryogenic temperature. We identify the different physical origins of the peaks by means of their dependence on doping and excitation properties, as well as their emission pattern.