Multiple topological phases in graphene via magnetoelectric proximity effect

Topological antiferromagnetic (AFM) spintronics have been drawn special attention for the next generation of non-volatile, ultra-fast, and low-power memory and storage devices. The key to realize the spintronic applications is to manipulate the topological electronic states via switching the AFM order parameter. Here we propose a new approach to control the topological electronic states of a two-dimensional material by the proximity of a magnetoelectric antiferromagnet. Using density functional theory and tight-binding Hamiltonian approaches, we investigate an interface between graphene and AFM magnetoelectric Cr₂O₃ (0001). Due to the proximity effect, the interface electronic structure exhibits non-trivial band gap openings in the graphene Dirac bands asymmetric between the K and K′ valleys. This gives rise to an unconventional quantum anomalous Hall effect (QAHE) and, in addition, the spin-polarized valley Hall effect (VHE). The quantum anomalous Hall effect (QAHE), the valley-polarized QAHE and the quantum valley Hall effect emerge in graphene across a 180 magnetic domain wall in chromia. We theoretically demonstrate that these topological properties are controlled by voltage through magnetoelectric switching of the AFM insulator with no need for spin-orbit torques.