Nearly flat Chern bands in moire superlattices

Topology and electron interactions are two central themes in modern condensed matter physics. Here, we propose graphene-based systems where both the band topology and interaction effects can be simply controlled with electric fields. We study a number of systems of twisted double layers with small twist angle where a moire superlattice is formed. Each layer is chosen to be either AB-stacked bilayer graphene, ABC-stacked trilayer graphene, or hexagonal boron nitride. In these systems, a vertical applied electric field enables control of the bandwidth, and interestingly also the Chern number. We find that the Chern numbers of the bands associated with each of the two microscopic valleys can be +/- 0, +/- 1, +/- 2, +/- 3 depending on the specific system and vertical electrical field. We show that these graphene moire superlattices are promising platforms to realize a number of fascinating many-body phenomena, including (fractional) quantum anomalous Hall effects. We also discuss conceptual similarities and implications for modeling twisted bilayer graphene systems.