Ultraflatbands and Shear Solitons in Moiré Patterns of Twisted Bilayer Transition Metal Dichalcogenides

Ultraflatbands in twisted bilayers of two-dimensional materials have the 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 ultraflatbands at the valence band edge in twisted bilayer MoS₂, a prototypical transition metal dichalcogenide. The computed band widths, 5 and 23 meV for 56. 5° and 3. 5° twist angles, respectively, are comparable to that of twisted bilayer graphene near "magic" angles. Large structural transformations in the moiré patterns lead to formation of shear solitons at stacking boundaries and strongly influence the electronic structure. We extend our analysis for twisted bilayer MoS₂ to show that flatbands can occur at the valence band edge of twisted bilayer WS₂, MoSe₂, and WSe₂ as well.