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

TL;DR

This paper provides experimental evidence that small-angle twisted bilayer graphene hosts a valley-protected network of one-dimensional states, confirmed through microscopy and transport analysis at room temperature.

Contribution

It demonstrates the existence and valley protection of one-dimensional states in twisted bilayer graphene, filling a gap in direct experimental validation.

Findings

Existence of a valley-protected network of 1D states at room temperature

Fourier analysis of STM images confirms valley protection

Electronic transport in these states is valley-protected

Abstract

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 study, 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 tunnelling microscopy images of minimally twisted bilayer graphene, we provide convincing experimental evidence that the electronic transport in the counter-propagating one-dimensional states is indeed valley protected.