Negative magnetoresistance in large-angle twisted bilayer graphene

Twisting two sheets of graphene can lead to a stunning array of new electronic properties. Most famously, twisted bilayer graphene (tBLG) at the magic angle of 1.1° exhibits superconductivity, orbital magnetism, and topological insulating states. At larger twist angles, the Dirac cones from the two graphene sheets become electronically decoupled owing to their large separation in momentum space. Large-angle tBLG therefore behaves approximately like monolayer graphene, but with an extra two-fold layer degeneracy that can be lifted by a perpendicular electric field. Here, we report the surprising observation of negative magnetoresistance (NMR) in such samples. We observe ubiquitous NMR when the two graphene layers are doped to the same carrier type, as well as at the charge neutrality point in the special case of zero displacement field. In the doped case, the NMR persists above room temperature. These observations contrast the typical transport properties of ultra-clean monolayer or Bernal bilayer graphene, necessitating a new theoretical framework for understanding their origin.