Topological domain-wall states from Umklapp scattering in twisted bilayer graphene

TL;DR

This paper reveals how intervalley Umklapp scattering in large-angle twisted bilayer graphene induces topological domain-wall states, driven by structural chirality, with potential for engineering novel electronic interfaces.

Contribution

It introduces a symmetry-constrained $k ext{-}p$ model for large-angle twisted bilayer graphene, highlighting the role of chirality in topological domain-wall state formation.

Findings

Chiral interlayer coupling leads to gapped spectra in $D_6$ configurations.

Chirality inversion creates topological domain-wall states.

Atomistic simulations confirm the robustness of these states.

Abstract

Twistronics, harnessing interlayer rotation to tailor electronic states in van der Waals materials, has predominantly focused on small-angle regime. Here, we unveil the pivotal role of intervalley Umklapp scattering in large-angle twisted bilayer graphene, which governs low-energy physics and drives unconventional band topology. By constructing symmetry-constrained effective $k\cdot p$ models for $\pm 21.8^{\circ}$-twisted bilayers, we demonstrate how structural chirality imprints distinct electronic responses. The $D_6$ configuration exhibits a gapped spectrum with chiral interlayer coupling, while $D_3$ symmetric stacking configuration displays semimetallic behavior. Crucially, chirality inversion creates topological domain-wall states, which manifest as counterpropagating pseudospin modes at interfaces between oppositely twisted regions. These states, absent in untwisted bilayers, emerge from a Jackiw-Rebbi-like mechanism tied to chirality reversal. Atomistic simulations confirm these topological states and demonstrate their robustness against symmetry-breaking perturbations. The interplay between twist-induced chirality and topology opens new pathways for engineering domain-wall states in twisted materials.