Ultraflat bands and shear solitons in Moir\'e patterns of twisted bilayer transition metal dichalcogenides

TL;DR

This study demonstrates the emergence of ultraflat electronic bands in twisted bilayer transition metal dichalcogenides like MoS2, influenced by shear solitons and structural transformations, with potential for strong correlation effects.

Contribution

First principles calculations reveal ultraflat bands at the valence edge in twisted bilayer MoS2 and other TMDs, highlighting the role of shear solitons and structural changes.

Findings

Ultraflat bands with widths of 5-23 meV in twisted bilayer MoS2.

Structural transformations lead to shear solitons affecting electronic properties.

Flat bands also occur in twisted bilayer WS2, MoSe2, and WSe2.

Abstract

Ultraflat bands in twisted bilayers of two-dimensional materials have potential to host strong correlations, including the Mott-insulating phase at half-filling of the band. Using first principles density functional theory calculations, we show the emergence of ultraflat bands at the valence band edge in twisted bilayer MoS$_2$, a prototypical transition metal dichalcogenide. The computed band widths, 5 meV and 23 meV for 56.5$^\circ$ and 3.5$^\circ$ twist angles respectively, are comparable to that of twisted bilayer graphene near 'magic' angles. Large structural transformations in the Moir\'e patterns lead to formation of shear solitons at stacking boundaries and strongly influence the electronic structure. We extend our analysis for twisted bilayer MoS$_2$ to show that flat bands can occur at the valence band edge of twisted bilayer WS$_2$, MoSe$_2$ and WSe$_2$ as well.