Interface engineering of charge-transfer excitons in 2D lateral heterostructures

TL;DR

This study combines theory and experiment to confirm the existence of bound charge transfer excitons at the interfaces of 2D lateral heterostructures, revealing how they can be engineered and observed through photoluminescence.

Contribution

It provides the first microscopic and experimental evidence of bound CT excitons in lateral heterostructures and explores how interface and dielectric engineering influence their formation.

Findings

Bound CT excitons appear at junction widths smaller than the Coulomb Bohr radius.

Theoretical predictions match experimental photoluminescence data.

Interface engineering can tune the properties of charge transfer excitons.

Abstract

The existence of bound charge transfer (CT) excitons at the interface of monolayer lateral heterojunctions has been debated in literature, but contrary to the case of interlayer excitons in vertical heterostructure their observation still has to be confirmed. Here, we present a microscopic study investigating signatures of bound CT excitons in photoluminescence spectra at the interface of hBN-encapsulated lateral MoSe$_2$-WSe$_2$ heterostructures. Based on a fully microscopic and material-specific theory, we reveal the many-particle processes behind the formation of CT excitons and how they can be tuned via interface- and dielectric engineering. For junction widths smaller than the Coulomb-induced Bohr radius we predict the appearance of a low-energy CT exciton. The theoretical prediction is compared with experimental low-temperature photoluminescence measurements showing emission in the bound CT excitons energy range. Our joint theory-experiment study presents a significant step towards a microscopic understanding of optical properties of technologically promising 2D lateral heterostructures.