Excitonic response in TMD heterostructures from first-principles: impact of stacking, twisting, and interlayer distance

TL;DR

This paper uses first-principles calculations to analyze how stacking, twisting, and interlayer distance affect excitonic properties in TMD heterostructures, revealing new insights into exciton behavior and potential applications.

Contribution

It provides a comprehensive first-principles analysis of excitonic responses in TMD heterostructures, including all transitions across the Brillouin Zone, and predicts tunable exciton energies and lifetimes.

Findings

Interlayer excitons with significant electron density in both layers.

Possible inverted order of excitonic states in some heterostructures.

Exciton peak positions vary by approximately 100 meV, with lifetimes from pico- to micro-seconds.

Abstract

Van der Waals heterostructures of two-dimensional transition metal dichalcogenides provide a unique platform to engineer optoelectronic devices tuning their optical properties via stacking, twisting, or straining. Using ab initio Many-Body Perturbation Theory, we predict the electronic and optical (absorption and photoluminescence spectra) properties of MoS$_2$/WS$_2$ and MoSe$_2$/WSe$_2$ hetero-bilayers with different stacking and twisting. We analyse the valley splitting and optical transitions, and explain the enhancement or quenching of the inter- and intra-layer exciton states. Contrary to established models, that focus on transitions near the high-symmetry point K, our results include all possible transitions across the Brillouin Zone. This result, for a twisted Se-based heterostructures, in an interlayer exciton with significant electron density in both layers and a mixed intralayer exciton distributed over both MoSe$_2$ and WSe$_2$. We propose that it should be possible to produce an inverted order of the excitonic states in some MoSe$_2$/WSe$_2$ heterostructures, where the energy of the intralayer WSe$_2$ exciton is lower than that in MoSe$_2$. We predict the variability of the exciton peak positions ($\sim$100 meV) and the exciton radiative lifetimes, from pico- to nano-seconds, and even micro-seconds in twisted bilayers. The control of exciton energies and lifetimes paves the way towards applications in quantum information technologies and optical sensing.