Moire flat bands in twisted 2D hexagonal vdW material

TL;DR

This paper theoretically explores a variety of twisted bilayer 2D hexagonal materials, revealing the presence of ultra-flat moire bands that could facilitate strong electron correlations and exotic quantum phenomena.

Contribution

It systematically investigates moire minibands in 22 different 2D bilayer materials beyond graphene, identifying systems with ultra-flat bands at large twist angles.

Findings

Flat bands with narrow bandwidth are common in studied systems.

Some materials host ultra-flat bands with bandwidth less than 20 meV.

Guidance for experimental exploration of strongly correlated 2D moire systems is provided.

Abstract

Moire superlattices in twisted bilayer graphene (TBG) and its derived structures can host exotic correlated quantum phenomena because the narrow moire flat minibands in those systems effectively enhance the electron-electron interaction. Correlated phenomena are also observed in 2H-transitional metal dichalcogenides moire superlattices. However, the number of moire systems that have been explored in experiments are still very limited. Here we theoretically investigate a series of two-dimensional (2D) twisted bilayer hexagonal materials (TBHMs) beyond TBG at fixed angles of 7.34 and 67.34 degree with 22 2D van der Waals (vdW) layered materials that are commonly studied in experiments. First-principles calculations are employed to systemically study the moire minibands in these systems. We find that flat bands with narrow bandwidth generally exist in these systems. Some of the systems such as twisted bilayer In2Se3, InSe, GaSe, GaS and PtS2 even host ultra-flat bands with bandwidth less than 20 meV even for such large angles, which make them especially appealing for further experimental investigations. We further analysis the characters of moire flat bands and provides guidance for further exploration of 2D moire superlattices that could host strong electron correlations.