Magnetoelectric control of the topological phase in graphene

The appearance of topological states in antiferromagnetic (AFM) materials has recently aroused considerable attention, resulting in the emergent field of topological AFM spintronics. Here, we theoretically explore the effect of voltage-controlled AFM order in chromia (Cr₂O₃) on the emerging topological states in graphene coupled across the Cr₂O₃/graphene interface. Chromia is a magnetoelectric AFM insulator exhibiting surface magnetization, intrinsically coupled to theNéel vector, which can be switched by an electric field. We find that the proximity effect leads to the broken time-reversal symmetry and the Rashba spin-orbit coupling in graphene, producing the topologically nontrivial band gaps. The resulting topological states and the quantum anomalous Hall effect in graphene are switchable by voltage with the Néel vector in chromia. Interestingly, the band gaps near the K and K’ points in graphene are different due to the staggered coupling on the two sublattices, resulting in the non-vanishing valley current and the valley-polarized anomalous Hall state. The switchable Néel vectorpotentially produces a topological phase transition in graphene.