Exciton fine structure in twisted transition metal dichalcogenide heterostructures

TL;DR

This paper uses many-body perturbation theory to analyze how twist angles in TMD heterostructures affect exciton properties, revealing angle-dependent hybridization and a method to project excitonic states onto individual layer Brillouin zones.

Contribution

It introduces a general ab initio approach to unfold excitonic states in twisted TMD heterostructures, enabling detailed analysis of twist-induced excitonic phenomena.

Findings

Optical spectra are dominated by mixed interlayer and intralayer transitions.

Unexpected angle-dependent hybridization between excitons.

Method for projecting excitonic states onto layer-specific Brillouin zones.

Abstract

Moir\'e superlattices of transition metal dichalcogenide (TMD) heterostructures give rise to rich excitonic phenomena associated with the interlayer twist angle and induced changes in the involved quantum states. Theoretical calculations of excitons in such systems are typically based on model moir\'e potentials to mitigate the computational cost. However, an ab initio understanding of the electron-hole coupling dominating the excitations is crucial to realize the twist-induced modifications of the optical selection rules. In this work we use many-body perturbation theory to compute and analyze the relation between twist angle and exciton properties in twisted TMD heterostructures. We present a general approach for unfolding excitonic states from the moir\'e Brillouin zone onto the Brillouin zones of the separate layers. Applying this method to a twisted MoS$_2$/MoSe$_2$ bilayer, we find that the optical excitation spectrum is dominated by mixed transitions between electrons and holes with different momenta in the separate monolayers, leading to unexpected and angle-dependent hybridization between interlayer and intralayer excitons. Our findings offer a design pathway for tuning exciton layer-localization in TMD heterostructures as a function of twist angle.