Strain-tunable magnetism and topological states in layered VBi₂Te₄

Similar to the magnetic topological insulator of MnBi₂Te₄, recent studies have demonstrated that VBi₂Te₄ is also an ideal candidate to explore many intriguing quantum states. Different from the strong interlayer antiferromagnetic (AFM) coupling in layered MnBi₂Te₄, based on first-principles calculations, we find that the energy difference between AFM and ferromagnetic (FM) orders in layered VBi₂Te₄ is much smaller than that of MnBi₂Te₄. Specifically, it is found that the interlayer FM coupling can be readily achieved by applying strain. Further electronic band structures reveal that the VBi₂Te₄ bilayer is a time-reversal symmetry broken quantum spin Hall insulator with a spin Chern number of C_S = 1, which is essentially different from the QAH state with a Chern number of C = 1 in the MnBi₂Te₄ bilayer. Most strikingly, the topological states of the magnetic VBi₂Te₄ bilayer can be well tuned by strain, whose topological phase diagram is mapped out as a function of strain by employing continuum model analyses. All of these results indicate that the layered VBi₂Te₄ not only enriches the family of magnetic topological materials, but also provides a promising platform to explore more exotic quantum phenomena.