Twist-angle dependent interlayer exciton diffusion in MoS₂-MoSe₂ heterobilayers

Heterobilayers (HBLs) of transition metal dichalcogenides can form a moiré superlattice with a periodic potential landscape, which can modulate the electronic structure and confine excitons. HBLs can host interlayer excitons (IXs) with electrons and holes separated in different layers, forming a dipolar exciton gas with repulsive Coulomb interactions among the aligned vertical dipoles. The presence of moiré superlattice further imposes an additional length scale that can change the dynamics and transport properties of IXs in HBLs. Here we study the influence of moiré periodicity on the IX diffusion in MoS₂-MoSe₂ HBLs. We prepared a series of HBLs with small twist angles by stacking monolayer MoSe₂ onto MoS₂ with well-aligned orientations grown by chemical vapor deposition. Twist-angle dependent photoluminescence (PL) energy of interlayer exciton (IX) were observed, signifying the formation of moiré potential. We further investigated the IX diffusion by time-resolved PL and spatially resolved PL imaging. The interplay between moiré potentials and dipole-dipole interactions of IX leads to exciton-density and twist-angle dependent diffusion length. Our results provide insights in understanding of the localization and delocalization of interlayer excitons in the moiré superlattice.