Highly tunable valley polarization of moiré excitons

Hetero-structures of transition metal dichalcogenide semiconductors stacked at near 0 (H) and 60 (R) degrees inherit the valley pseudo-spin from the monolayers. Here we investigate the valley properties of moiré excitons in the H- and R-stacked junctions and find that the valley polarization is highly tunable, much more so than the excitons in monolayer transition metal dichalcogenides. The exchange interaction is expected much weaker in the heterojunctions, due to the small overlap between electron and hole wavefunction for the interlayer exciton. Nevertheless, our experiments indicate that this weak exchange interaction can still play a dominant role in valley depolarization of the moiré excitons.