Valley-protected one-dimensional states in small-angle twisted bilayer graphene

Abstract

© 2021 American Physical Society.Theory predicts that the application of an electric field breaks the inversion symmetry of AB and BA stacked domains in twisted bilayer graphene, resulting in the formation of a triangular network of one-dimensional valley-protected helical states. This two-dimensional network of one-dimensional states has been observed in several studies, but direct experimental evidence that the electronic transport in these one-dimensional states is valley protected is still lacking. In this paper, we report the existence of the network in small-angle twisted bilayer graphene at room temperature. Moreover, by analyzing Fourier transforms of atomically resolved scanning tunneling microscopy images of minimally twisted bilayer graphene, we provide convincing experimental evidence that the electronic transport in the counterpropagating one-dimensional states is indeed valley protected.