Spectroscopic Signatures of Moiré-Confined Excitons in Bilayer TMDCs from First Principles

Few-layer transition metal dichalcogenides (TMDCs) have emerged as the ideal experimental platform to study many-body interactions in low dimensions due to their weak dielectric screening, which enhances many-electron interactions, and straightforward optical characterization. When two layers of TMDCs are stacked with a finite twist angle, a superlattice-periodic moiré potential emerges that modulates the localized quasiparticle and optical excitations.  Up to now, however, the experimental characterization of moiré-localized excitons has been indirect. Here, we derive the spectroscopic signatures of moiré-confined excitons in twisted 2D materials that can be measured in current time-resolved angle-resolved photoemission spectroscopy (TR-ARPES) setups. We show that, by simultaneously measuring the distribution of the holes and electrons bound to the photoexcited excitons, it is possible to directly extract both the center-of-mass and internal structure of an exciton. Our calculations are in good agreement with recent experiments, showing that moiré excitons are surprisingly localized even for relatively small moiré unit cells with a moiré lattice parameter of ~ 6 nm. Finally, we comment on a new method to extract accurate moiré potentials from first principles.