Two-dimensional antiferromagnetic type-II Weyl fermions in monolayer ZnSb and type-I Weyl fermions and topological insulator in bilayer ZnSb

Two-dimensional (2D) topological materials have attracted extensive attention due to the discovery of graphene. In addition, their counterparts in magnetic materials are also a fascinating subject of research. However, it remains challenging to find 2D materials that have the desired topological phases. Here, based on first-principles calculations, we investigate the properties of a newly synthesized 2D material, monolayer/bilayer (ML/BL) ZnSb. We find that the ML ZnSb is antiferromagnetic (AFM) and that its magnetism can be changed by an external strain, from AFM to ferromagnetic. Without any external strain, the ML ZnSb can be considered as an almost ideal 2D type-II Weyl material with a pair of type-II Weyl fermions exactly located at the Fermi level. When taking into account spin-orbit coupling (SOC), a gap can be introduced at the Weyl point. We further show that by applying a biaxial strain to the BL ZnSb material, it is possible to open different gaps at the Weyl points, leading to a topological phase transition without breaking symmetry. When SOC is included, these Weyl points become topological insulators with a large bandgap, where the helical edge states can be identified. Overall, this study provides an example of a material that can be used to explore the physical consequences of 2D topological phases and provide a promising candidate for future research in this field.