Broken-symmetry states and divergent resistance in suspended bilayer graphene

Abstract

The presence of disorder makes it difficult to determine the intrinsic properties of graphene in its ideal form. Measurements of high-quality bilayer graphene flakes suspended above a substrate identify the persistence of quantum Hall behaviour at magnetic fields an order of magnitude lower than seen before, and previously unseen symmetry breaking of the lowest Landau level is also observed. Mono- and bilayer graphene have generated tremendous excitement owing to their unique and potentially useful electronic properties1. Suspending single-layer graphene flakes above the substrate2,3 has been shown to greatly improve sample quality, yielding high-mobility devices with little charge inhomogeneity. Here we report the fabrication of suspended bilayer graphene devices with very little disorder. We observe quantum Hall states that are fully quantized at a magnetic field of 0.2 T, as well as broken-symmetry states at intermediate filling factors ν=0, ±1, ±2 and ±3. In the ν=0 state, the devices show extremely high magnetoresistance that scales as magnetic field divided by temperature. This resistance is predominantly affected by the perpendicular component of the applied field, and the extracted energy gap is significantly larger than expected for Zeeman splitting. These findings indicate that the broken-symmetry states arise from many-body interactions and underscore the important part that Coulomb interactions play in bilayer graphene.