Excitonic and Valley-Polarization Signatures of Fractional Correlated Electronic Phases in a WSe2/WS2 Moiré Superlattice

We have measured the reflectance contrast, photoluminescence, and valley polarization of a ${\mathrm{WSe}}_{2}/{\mathrm{WS}}_{2}$ heterobilayer moir\'e superlattice at gate-tunable charge density. We observe absorption modulation of three intralayer moir\'e excitons at filling factors $\ensuremath{\nu}=1/3$ and $2/3$. We also observe luminescence modulation of interlayer trions at around a dozen fractional filling factors, including $\ensuremath{\nu}=\ensuremath{-}3/2$, $1/4$, $1/3$, $2/5$, $2/3$, $6/7$, $5/3$. Remarkably, the valley polarization of interlayer trions is suppressed at some fractional fillings. These results demonstrate that electron crystallization can modulate the absorption, emission, and valley dynamics of the excitonic states in a moir\'e superlattice.