Exciton transport in a moir\'e potential: from hopping to dispersive regime

TL;DR

This paper explores how excitons in twisted TMD monolayers transition from localized hopping to dispersive propagation as the twist angle increases, revealing a shift from Hubbard-model behavior to free-particle dispersion.

Contribution

It provides a microscopic analysis of the twist-angle-dependent transition from exciton hopping to dispersive regimes in moiré potentials, highlighting the limitations of the Hubbard model at larger angles.

Findings

Hopping regime occurs up to ~2° twist angle.

Hubbard model describes exciton transport at small angles.

At larger angles, excitons become delocalized and follow free-particle dispersion.

Abstract

The propagation of excitons in TMD monolayers has been intensively studied revealing interesting many-particle effects, such as halo formation and non-classical 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{\deg} and is well described by the Hubbard model. At large angles, however, the Hubbard model 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.