Ferromagnetism in twisted bilayer graphene*

When two sheets of graphene are stacked at a small twist angle, the resulting flat superlattice minibands are expected to strongly enhance electron-electron interactions. These enhanced interactions have led to the observation of interesting correlated electronic states, such as superconductivity, where metallic behavior would otherwise be expected. Here we present evidence that near three-quarters (3/4) filling of the conduction miniband these enhanced interactions drive the twisted bilayer graphene into a ferromagnetic state. We suggest that the system is a Chern insulator. We further present magneto transport measurements in tilted field that may hold clues to the nature of the magnetism.