Tunable orbital Chern insulating states in crystalline Bernal-tetralayer graphene

Multilayer graphene systems, with their rich interplay of valley and layer degrees of freedom and associated order parmeters, host a variety of topological phenomena. Recent studies have induced moiré superlattices and spin-orbit proximity effects in multilayer graphene to realize quantum anomalous Hall (QAH) effects driven by orbital ferromagnetism. Here, we report the observation of a Hall resistance quantized at ±h/6e², which persists down to 20 mT, with an anomalous Hall effect in Bernal-stacked tetralayer graphene near charge neutrality. Experimental evidence of magnetic field, electric field and carrier density tunability of a ferromagnetic order provides convincing evidence for a Chern insulating state with a Chern number of 6. A theory reveals that this arises from an electric-field-driven topological phase transition enabled by a layer antiferro-valleytric order that couples the valley and layer degrees of freedom. Our findings uncover previously unrecognized layer-valley antiferroic orders and their resulting highly tunable orbital Chern insulating states in the single crystalline material, achieved without moiré engineering or spin-orbit coupling.