Electronic property and topological phase transition in a graphene/CoBr₂ heterostructure

Recently, significant experimental advancements in achieving topological phases have been reported in van der Waals (vdW) heterostructures involving graphene. Here, using first-principles calculations, we investigate graphene/CoBr2 (Gr/CoBr2) heterostructures and find that an enhancement of in-plane magnetic anisotropy (IMA) energy in monolayer CoBr2 can be accomplished by reducing the interlayer distance of the vdW heterostructures. In addition, we clarify that the enhancement of IMA energy primarily results from two factors: one is the weakness of the Co-dxy and Co-dx2 y2 orbital hybridization and the other is the augmentation of the Co-dyz and Co-dz2 orbital hybridization. Meanwhile, calculation results suggest that the Kosterlitz-Thouless phase transition temperature (TKT) of a 2D XY magnet Gr/CoBr2 (23.8 K) is higher than that of a 2D XY monolayer CoBr2 (1.35 K). By decreasing the interlayer distances, the proximity effect is more pronounced and band splitting appears. Moreover, by taking into account spin-orbit coupling, a band gap of approximately 14.3 meV and the quantum anomalous Hall effect (QAHE) are attained by decreasing the interlayer distance by 1.0 A degrees. Inspired by the above conclusions, we design a topological field transistor device model. Our results support that the vdW interlayer distance can be used to modulate the IMA energy and QAHE of materials, providing a pathway for the development of new low-power spintronic devices.