  The optical spectra of transition metal dichalcogenide (TMDC) monolayers are
dominated by excitons and trions. Here we establish the dependences of these
optical transitions on disorder from hyperspectral imaging of h-BN encapsulated
monolayer MoSe2. While both exciton and trion energies vary spatially, these
two quantities are almost perfectly correlated, with spatial variation in the
trion binding energy of only ~0.18 meV. In contrast, variation in the energy
splitting between the two lowest energy exciton states is one order of
magnitude larger at ~1.7 meV. Statistical analysis and theoretical modeling
reveal that disorder results from dielectric and bandgap fluctuations, not
electrostatic fluctuations. Our results shed light on disorder in high quality
TMDC monolayers, its impact on optical transitions, and the many-body nature of
excitons and trions.
