Self-organised quantum dots in marginally twisted MoSe$_2$/WSe$_2$ and MoS$_2$/WS$_2$ bilayers

TL;DR

This paper demonstrates that marginally twisted MoSe2/WSe2 and MoS2/WS2 bilayers form self-organized quantum dots at strain hot spots, enabling tunable single-photon emission and potential applications in quantum photonics.

Contribution

It reveals the formation of strain-induced quantum dots in marginally twisted TMDC bilayers and explores their optical properties and tunability.

Findings

Quantum dots form at strain hot spots in twisted bilayers.

Recombination lines are red-shifted, enabling tunable single-photon emission.

Strain hot spots reduce exciton energy, allowing selective population.

Abstract

Moir\'e superlattices in twistronic heterostructures are a powerful tool for materials engineering. In marginally twisted (small misalignment angle, $\theta$) bilayers of nearly lattice-matched two-dimensional (2D) crystals moir\'e patterns take the form of domains of commensurate stacking, separated by a network of domain walls (NoDW) with strain hot spots at the NoDW nodes. Here, we show that, for type-II transition metal dichalcogenide bilayers MoX$_2$/WX$_2$ (X=S, Se), the hydrostatic strain component in these hot spots creates quantum dots for electrons and holes. We investigate the electron/hole states bound by such objects, discussing their manifestations via the intralayer intraband infrared transitions. The electron/hole confinement, which is strongest for $\theta<0.5^{\circ}$, leads to a red-shift of their recombination line producing single photon emitters (SPE) broadly tuneable around 1\,eV by misalignment angle. These self-organised dots can form in bilayers with both aligned and inverted MoX$_2$ and WX$_2$ unit cells, emitting photons with different polarizations. We also find that the hot spots of strain reduce the intralayer MoX$_2$ A-exciton energy, enabling selective population of the quantum dot states.