Momentum-space indirect interlayer excitons in transition metal dichalcogenide van der Waals heterostructures

TL;DR

This paper investigates a new type of momentum-space indirect interlayer exciton in TMDC heterostructures, combining spectroscopy and first-principles calculations to control and understand excitonic effects for advanced optoelectronic applications.

Contribution

It introduces the concept of a partially charge-separated interlayer exciton at $ ext{Γ}$ and $K$ valleys, expanding the understanding of excitons in TMDC heterostructures.

Findings

Identification of a partially charge-separated exciton at Γ and K valleys.

Control of exciton emission energy via layer orientation.

Enhanced understanding of excitonic effects in TMDC heterostructures.

Abstract

Monolayers of transition metal dichalcogenides (TMDCs) feature exceptional optical properties that are dominated by excitons, tightly bound electron-hole pairs. Forming van der Waals heterostructures by deterministically stacking individual monolayers allows to tune various properties via choice of materials and relative orientation of the layers. In these structures, a new type of exciton emerges, where electron and hole are spatially separated. These interlayer excitons allow exploration of many-body quantum phenomena and are ideally suited for valleytronic applications. Mostly, a basic model of fully spatially-separated electron and hole stemming from the $K$ valleys of the monolayer Brillouin zones is applied to describe such excitons. Here, we combine photoluminescence spectroscopy and first principle calculations to expand the concept of interlayer excitons. We identify a partially charge-separated electron-hole pair in MoS$_2$/WSe$_2$ heterostructures residing at the $\Gamma$ and $K$ valleys. We control the emission energy of this new type of momentum-space indirect, yet strongly-bound exciton by variation of the relative orientation of the layers. These findings represent a crucial step towards the understanding and control of excitonic effects in TMDC heterostructures and devices.