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.
Highlights
The successful isolation and exploration of graphene [1,2] has led to a booming new research field in condensed matter physics
Bilayer graphene has a more complex band structure, which depends on the stacking order of the graphene layers
Our experiments reveal that intervalley scattering in the triangular network of 1D states is fully absent
Summary
The successful isolation and exploration of graphene [1,2] has led to a booming new research field in condensed matter physics. At twist angles smaller than the magic angle, another interesting phenomenon has been reported: Upon application of a perpendicular electric field, small-angle twisted bilayer graphene hosts a network of topologically protected states across the moiré pattern [14,15,16]. This network has previously been observed using scanning tunneling microscopy (STM) by Huang et al [14] at temperatures of 4.5 K. The latter implies that at an AA node each channel can only propagate in three out of the six possible directions and that
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