Superlattice-induced insulating states and valley-protected orbits in twisted bilayer graphene

TL;DR

This paper investigates the electronic properties of twisted bilayer graphene, revealing superlattice-induced insulating states with larger-than-expected gaps and unique Fermi surface features due to suppressed interlayer hopping.

Contribution

It provides experimental evidence of insulating states at superlattice band edges and explains the band structure with suppressed interlayer hybridization effects.

Findings

Insulating states at superlattice band edges with large thermal activation gaps.

Presence of two intersecting Fermi contours with unhybridized crossing points.

Exponential suppression of interlayer hopping for large momentum transfers.

Abstract

Twisted bilayer graphene (TwBLG) is one of the simplest van der Waals heterostructures, yet it yields a complex electronic system with intricate interplay between moir\'{e} physics and interlayer hybridization effects. We report on electronic transport measurements of high mobility small angle TwBLG devices showing clear evidence for insulating states at the superlattice band edges, with thermal activation gaps several times larger than theoretically predicted. Moreover, Shubnikov-de Haas oscillations and tight binding calculations reveal that the band structure consists of two intersecting Fermi contours whose crossing points are effectively unhybridized. We attribute this to exponentially suppressed interlayer hopping amplitudes for momentum transfers larger than the moir\'{e} wavevector.