Tuning valleys and wave functions of van der Waals heterostructures by varying the number of layers: A first-principles study

TL;DR

This study uses first-principles calculations to show how varying the number of layers in van der Waals heterostructures can tune electronic properties and exciton dynamics, providing a new method for material engineering.

Contribution

It demonstrates how adding layers in TMDC heterostructures influences band edges and wave function localization, offering a novel approach to control electronic and excitonic properties.

Findings

Band edges shift from K to Q or G with additional layers

Q states become more delocalized with electron layers

Wave function extension affects exciton lifetime and dynamics

Abstract

In van der Waals heterostructures of two-dimensional transition-metal dichalcogenides (2D TMDCs) electron and hole states are spatially localized in different layers forming long-lived interlayer excitons. Here, we have investigated, from first principles, the influence of additional electron or hole layers on the electronic properties of a MoS2/WSe2 heterobilayer (HBL), which is a direct band gap material. Additional layers modify the interlayer hybridization, mostly affecting the quasiparticle energy and real-space extend of hole states at the G and electron states at the Q valleys. For a sufficient number of additional layers, the band edges move from K to Q or G, respectively. Adding electron layers to the HBL leads to more delocalized Q states, while G states do not extend much beyond the HBL, even when more hole layers are added. These results suggest a simple and yet powerful way to tune band edges and the real-space extend of the electron and hole wave function in TMDC heterostructures, strongly affecting the lifetime and dynamics of interlayer excitons.