Chern insulators at integer and fractional filling in moiré rhombohedral pentalayer graphene: Part II

The interplay of topology and strong correlations has been used to great advantage in recent years in moiré systems, leading to the remarkable discoveries of integer and fractional quantum anomalous Hall effects (IQAHE/FQAHE) in twisted MoTe₂ and rhombohedral pentalayer graphene (RPG) aligned to boron nitride. However, the nature of these states and their relation to other theoretically predicted correlation-driven topological states remains unclear. In this presentation, we show that in a RPG sample aligned to boron nitride there is a topological state formed at fractional band filling ν = 2/3. Although this is reminiscent of the FQAH state reported in Ref. 1, the state we observe has integer, rather than fractional, quantized Hall conductance (with Chern number of C = 1). We see two additional C = 1 Chern insulators associated with ν = 1/4 and 1/3 upon applying a magnetic field. These states are most naturally explained by the formation of topological electronic crystals that spontaneously break the discrete translational symmetry of the moiré lattice. Within a narrow regime of parameter space at modest magnetic field, we further see signs of a weakly developed fractional Chern insulator that projects to ν = 2/3 filling at zero field. In the same sample, we also find a unique sequence of incipient Chern insulators arising over a broad range of incommensurate band filling near two holes per moiré unit cell. Our results establish moiré RPG as a fertile platform for studying the interplay of electronic crystallization and topological charge fractionalization.