Atomistic theory of twist-angle dependent intralayer and interlayer exciton properties in twisted bilayer materials

I Maity and AA Mostofi and J Lischner, NPJ 2D MATERIALS AND APPLICATIONS, 9, 20 (2025).

DOI: 10.1038/s41699-025-00538-4

Twisted bilayers of two-dimensional materials have emerged as a highly tunable platform to study and engineer properties of excitons. However, the atomistic description of these properties has remained a significant challenge as a consequence of the large unit cells of the emergent moir & eacute; superlattices. To address this problem, we introduce an efficient atomistic quantum-mechanical approach to solve the Bethe- Salpeter equation that exploits the localization of atomic Wannier functions. We then use this approach to study intra- and interlayer excitons in twisted WS2/WSe2 at a range of twist angles. In agreement with experiment, we find that the optical spectrum exhibits three low- energy peaks for twist angles smaller than 2 degrees. The energy splitting between the peaks is described accurately. We also find two low-energy interlayer excitons with weak oscillator strengths. Our approach opens up new opportunities for the atomistic design of light- matter interactions in ultrathin materials.

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