Topological Domain-Wall States from Umklapp Scattering in Twisted Bilayer Graphene.

Twistronics, harnessing interlayer rotation to tailor electronic states in van der Waals materials, has predominantly focused on small-angle regimes. 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·p models for ±21.8°-twisted bilayers, we demonstrate how structural chirality imprints distinct electronic responses. The D6 configuration exhibits a gapped spectrum with chiral interlayer coupling, while the D3-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.