Quasi-one-dimensional taco-shaped bands in large-angle twisted bilayer transition metal dichalcogenides

TL;DR

This paper reports the discovery of quasi-one-dimensional flat bands at large twist angles in bilayer transition metal dichalcogenides, revealing new electronic properties and potential for correlated phases beyond small-angle moiré systems.

Contribution

It demonstrates the emergence of taco-shaped anisotropic flat bands at a large twist angle of 21.8°, expanding moiré engineering to large-angle twisted bilayer materials.

Findings

Flat bands with quasi-one-dimensional dispersion at large twist angles.

Six anisotropic channels with alternating spin textures.

Power-law density of states indicating enhanced correlations.

Abstract

Two-dimensional moir\'e materials offer a powerful, twist-tunable platform for engineering electronic bands and correlations, though most studies to date have focused on small twist angles where flat bands arise from symmetry-pinned monolayer momenta. Here, we observe the surprising emergence of flat electronic bands with a distinctive quasi-one-dimensional dispersion at large twist angles in bilayer transition metal dichalcogenides that originate from the $\Lambda$ valley states at generic momenta between $\Gamma$ and $K$ points. These taco-shaped anisotropic bands result from optimal interlayer hybridization between like-spin $\Lambda$ valleys at the conduction band minimum in the Brillouin zone, resulting in directional band flattening at a magic twist-angle of 21.8$^{\circ}$. The bands form six anisotropic channels with a sixfold alternating spin texture reminiscent of altermagnetic textures. At low energies, the density of states shows a power-law dependence due to the quasi-one-dimensional character, enhancing the potential for correlated phases. Our results provide a new platform for correlated phenomena and broaden the scope of moir\'e engineering to large twist angles in 2D materials.