Intralayer moiré exciton states in transition metal dichalcogenide heterostructures: a GW-BSE study*

Recent experimental measurements have shown signatures of novel exciton states in the moiré superlattices of transition metal dichalcogenide bilayer heterostructures. In the WS₂/WSe₂ heterostructure, the WSe₂ “A” exciton resonance is found to split into multiple peaks as the twist angle between the two layers approaches zero [1]. This splitting is directly correlated to the formation of a large-scale (~8.5 nm) moiré pattern at zero twist angle. Computing the optical properties of this system by brute force using first principles is intractable owing to the large number of atoms (~4000) in the moiré superlattice and the requirement of a fine k-point sampling of the Brillouin zone. We demonstrate an efficient approximation to solve the GW plus Bethe-Salpeter equation of the reconstructed moiré which yields excitations with meV accuracy relative to the traditional approach. Using this method, we study the twist-angle dependence of the absorption spectrum of intralayer excitons in the WS₂/WSe₂ moiré superlattice.

[1] C. Jin, et al. Nature 567, 76–80 (2019)