Helical trilayer graphene: a moiré platform for strongly-interacting topological bands – Part 2

The combination of strong electronic correlations and non-trivial band topology is fertile ground for exotic electronic phenomena. Here, we explore topological flat bands that emerge in magic angle helical trilayer graphene (HTG), which comprises three layers of graphene with successive layers rotated in the same direction by the same relative twist angle, θ_m ≈ 1.8°. We find correlated states and anomalous Hall effect at multiple integer and fractional electron fillings per moiré unit cell. At the filling of one electron per moiré unit cell, a time-reversal symmetric phase appears beyond a critical electric displacement field, indicating a topological phase transition. Finally, hysteresis upon sweeping carrier density points to first-order phase transitions across a spatial mosaic of Chern domains separated by a network of topological gapless edge states. We establish HTG as an ideal platform for exploring orbital magnetism with Chern domain walls, and a promising system for realizing exotic strongly interacting topological phases.