Observation of moiré excitons in superlattices in heterostructures of van der Waals semiconductors

In Abstract

A new way to engineer properties of excitons in solids

Atomically thin layers of two-dimensional (2D) materials (e.g. graphene) can be assembled in vertical stacks that are held together by van der Waals forces. In such stacks, one can put together planes of atoms with incommensurate lattice constants and arbitrary mutual rotation, which is very different from bulk-grown solids with chemically bonded atoms, where the nearby layer repeat exactly the same crystalline structure. Stacks of incommensurate 2D crystals always feature periodic variations of the local atomic registry in the constituent layers, giving rise to the so called ”moiré superlattice”. Now, researchers from the Universities of Manchester and Sheffield assembled monolayers of molybdenum diselenide (MoSe₂) and tungsten disulfide (WS₂) to study how moire superlattice affects optical properties of semiconductor heterostructures and demonstrated (by the observation of additional absorption peaks ) that ”excitons” (bound hydrogen-like electron-hole pairs) in such a system acquire an intricate miniband dispersion prescribed by the moiré superlattice effects.

Read more here - DOI https://doi.org/10.1038/s41586-019-0986-9