Ultraflat bands and shear solitons in Moiré patterns of twisted bilayer transition metal dichalcogenides

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 MoS₂, a prototypical transition metal dichalcogenide. The computed band widths are comparable to that of twisted bilayer graphene near 'magic' angles. Large structural transformations in the Moiré patterns lead to the formation of shear solitons at stacking boundaries and strongly influence the electronic structure. We extend our analysis for twisted bilayer MoS₂ to show that flat bands can occur at the valence band edge of twisted bilayer WS₂, MoSe₂ and WSe₂ as well.