Magnetoelectric Switching of Competing Magnetic Orders in Rhombohedral Graphene

Abstract: A finite Hall conductance under zero magnetic field implies time reversal symmetry (TRS) breaking due to magnetic ordering. In rhombohedral (RH) stacked graphene, the angular momentum breaking TRS can result from the orbital degree of freedom at the $K$ and $K'$ valleys. This leads to valley polarization and occupation-dependent anomalous Hall resistance (AHR) due to the chirality in Berry curvature between the valleys. We report magnetoelectric control of orbital magnetic order in crystalline rhombohedral hexalayer graphene (RHG), achieved without the introduction of a moir\'e superlattice. At moderate displacement fields and low carrier densities, we observe a non-volatile and hysteretic AHR that can be electrically toggled by sweeping either the carrier density or the displacement field. Upon the application of small perpendicular magnetic fields, the system reveals a characteristic double sign reversal of the AHR, indicating a competition between distinct magnetic ground states. This interplay between valley polarization, orbital magnetism, and electric and magnetic field tuning demonstrates the rich multiferroic behavior of RHG. Our findings present crystalline RHG as a minimal, tunable platform for studying symmetry-breaking phases and magnetic order in flat-band systems, offering insight into the coupling between electronic structure and magnetoelectric response.