Unusual magnetotransport in twisted bilayer graphene

TL;DR

This study investigates magnetotransport in twisted bilayer graphene with a 1.38° twist, revealing unusual behaviors such as large quadratic magnetoresistance and Landau level gap splitting, linked to Hofstadter's butterfly phenomena.

Contribution

The paper reports novel magnetotransport phenomena in twisted bilayer graphene at a twist angle above the magic angle, connecting experimental observations with Hofstadter's butterfly model.

Findings

Large quadratic magnetoresistance around half filling

Splitting and bending of Landau level gaps

Reproduction of behaviors using Hofstadter's butterfly model

Abstract

We present transport measurements of bilayer graphene with 1.38{\deg} interlayer twist and apparent additional alignment to its hexagonal boron nitride cladding. As with other devices with twist angles substantially larger than the magic angle of 1.1{\deg}, we do not observe correlated insulating states or band reorganization. However, we do observe several highly unusual behaviors in magnetotransport. For a large range of densities around half filling of the moir\'e bands, magnetoresistance is large and quadratic. Over these same densities, the magnetoresistance minima corresponding to gaps between Landau levels split and bend as a function of density and field. We reproduce the same splitting and bending behavior in a simple tight-binding model of Hofstadter's butterfly on a square lattice with anisotropic hopping terms. These features appear to be a generic class of experimental manifestations of Hofstadter's butterfly and may provide insight into the emergent states of twisted bilayer graphene.