Exciton landscape in van der Waals heterostructures

TL;DR

This paper investigates the exciton landscape in van der Waals heterostructures of transition-metal dichalcogenides, identifying dominant exciton types and their spectral positions using advanced theoretical methods.

Contribution

It combines exciton density-matrix formalism with density-functional theory to identify the lowest-energy excitons and disentangle hybridization and layer polarization effects.

Findings

Identified the lowest-lying exciton states for various TMD heterostructures.

Clarified the contributions of hybridization and layer polarization to exciton energies.

Provided insights into the optical spectra of van der Waals heterostructures.

Abstract

van der Waals heterostructures consisting of vertically stacked transition-metal dichalcogenides (TMDs) exhibit a rich landscape of bright and dark intra- and interlayer excitons. In spite of a growing literature in this field of research, the type of excitons dominating optical spectra in different van der Waals heterostructures has not yet been well established. The spectral position of exciton states depends strongly on the strength of hybridization and energy renormalization due to the periodic moir\'e potential. Combining exciton density-matrix formalism and density-functional theory, we shed light on the exciton landscape in TMD homo- and heterobilayers at different stackings. This allows us to identify on a microscopic footing the energetically lowest-lying exciton state for each material and stacking. Furthermore, we disentangle the contribution of hybridization and layer polarization-induced alignment shifts of dark and bright excitons in photoluminescence spectra. By revealing the exciton landscape in van der Waals heterostructures, our work provides the basis for further studies of the optical, dynamical, and transport properties of this technologically promising class of nanomaterials.