Exciton transport in a moiré potential: From hopping to dispersive regime

Abstract

The propagation of excitons in transition metal dichalcogenide (TMD) monolayers has been intensively studied revealing interesting many-particle effects, such as halo formation and nonclassical diffusion. Initial studies have investigated how exciton transport changes in twisted TMD bilayers, including Coulomb repulsion and Hubbard-like exciton hopping. In this work, we investigate the twist-angle dependent transition of the hopping regime to the dispersive regime of effectively free excitons. Based on a microscopic approach for excitons in the presence of a moir\'e potential, we show that the hopping regime occurs up to an angle of approximately ${2}^{\ensuremath{\circ}}$ and is well described by a moir\'e intercell tunneling model. At large angles, however, this nearest-neighbor approximation fails due to increasingly delocalized exciton states. Here, the quantum-mechanical dispersion of free particles with an effective mass determines the propagation of excitons. Overall, our work provides microscopic insights into the character of exciton propagation in twisted van der Waals heterostructures.