Electronic correlations and topological states at the interface of twisted bilayer graphene and chromium oxychloride

When two layers of graphene are stacked with a twist angle of approximately 1.1°, strong interlayer coupling gives rise to a pair of flat bands in twisted bilayer graphene (TBG), resulting in pronounced electron–electron interactions. At half filling of the flat bands, TBG exhibits correlated insulating states. Here, we investigate the electrical transport properties of heterostructures composed of TBG and the antiferromagnetic insulator chromium oxychloride (CrOCl), and propose a strategy to modulate the correlated insulating states in TBG. During the transition from a conventional phase to a strong interfacial coupling phase, kink-like features are observed in the charge neutrality point (CNP), correlated insulating state, and band insulating state. Under a perpendicular magnetic field, the system exhibits broadened quantum Hall plateaus in the strong interfacial coupling regime. Electrons localized in the CrOCl layer screen the bottom gate, rendering the carrier density in TBG less sensitive to variations in the bottom gate voltage. These phenomena are well captured by a charge-transfer model between TBG and CrOCl. Our results provide insights into the control of electronic correlations and topological states in graphene moiré systems via interfacial charge coupling.