Polarization and charge-separation of moir\'e excitons in van der Waals heterostructures

TL;DR

This paper investigates how atomic reconstruction in twisted TMD bilayers influences moiré excitons, revealing three regimes of exciton behavior and proposing experimental signatures and tuning methods for charge separation effects.

Contribution

It introduces a microscopic theory for intralayer charge-separation in reconstructed MoSe2-WSe2 heterostructures, identifying twist-angle-dependent exciton regimes and their unique hopping signatures.

Findings

Identifies three exciton regimes: localized, polarized, and charge-transfer.

Predicts a distinct twist-angle dependence of exciton hopping.

Shows dielectric engineering can tune charge separation effects.

Abstract

Twisted transition metal dichalcogenide (TMD) bilayers exhibit periodic moir\'e potentials, which can trap excitons at certain high-symmetry sites. At small twist angles, TMD lattices undergo an atomic reconstruction, altering the moir\'e potential landscape via the formation of large domains, potentially separating the charges in-plane and leading to the formation of intralayer charge-transfer (CT) excitons. Here, we employ a microscopic, material-specific theory to investigate the intralayer charge-separation in atomically reconstructed MoSe$_2$-WSe$_2$ heterostructures. We identify three distinct and twist-angle-dependent exciton regimes including localized Wannier-like excitons, polarized excitons, and intralayer CT excitons. We calculate the moir\'e site hopping for these excitons and predict a fundamentally different twist-angle-dependence compared to regular Wannier excitons - presenting an experimentally accessible key signature for the emergence of intralayer CT excitons. Furthermore, we show that the charge separation and its impact on the hopping can be efficiently tuned via dielectric engineering.