Exploring the twist angle dependence of Bernal bilayer-trilayer graphene

In the family of twisted Bernal-stacked graphene moiré superlattices, bilayer-trilayer graphene hosts numerous correlation-driven states due to the strong moiré potential at the twisted interface. Prior work has revealed trivial and topological correlated insulators at integer and fractional fillings in samples with twist angles between 1.4° and 1.5°. At fractional fillings, it is hypothesized that the Chern insulators spontaneously break the discrete translational symmetry of the moiré superlattice. Moreover, the integer quantum anomalous Hall state at filling 𝜈 = ¼ appears to arise from a topologically trivial parent state at 𝜈 = 1, suggesting a nontrivial reordering of the Berry curvature. Bernal bilayer-trilayer graphene is thus a promising platform for topological phenomena, yet the evolution of these states outside a narrow twist angle range is not well understood. In this talk, I will present our ongoing investigation of Bernal bilayer-trilayer graphene twisted between 0.8° and 1.7°. Our measurements reveal that the Chern number of the 𝜈 = 1 state changes with twist angle and can also be tuned by displacement field at fixed angle. We also find evidence of zero-field Chern insulators at 𝜈 = 1/2, 5/2, and 3. These findings establish bilayer-trilayer graphene as a versatile platform for studying correlation-driven band restructuring.