Theoretical predicted Janus SrAlGaTe4: effects of strain and electric field and its topological properties

Abstract The asymmetric Janus SrAlGaTe 4 , constructed from its parent SrGa 2 Te 4 monolayer, was predicted theoretically by first principle calculations. Its stability was confirmed by phonon structure without imaginary frequency and ab initio molecular dynamics (AIMD) simulations. The Janus structure reduces the symmetry of SrGa 2 Te 4 monolayer, which causes the absence of topological states in free-standing Janus SrAlGaTe 4 . To explore the possible electronic and topological properties, the effects of strain and external electric field, working as effective modulation methods for the electronic properties, were investigated. The SrAlGaTe 4 monolayer undergoes a direct-to-indirect bandgap transition when the in-plane biaxial compressive strain is −8%. When the tensile strain is 9% or the electric field is 0.5 V Å −1 , the Janus SrAlGaTe 4 monolayer exhibits topological insulator (TI) characters, which was confirmed by the evolution of the Wannier charge centers (WCC). And the critical values for the topological transition are 2% for the biaxial tensile strain, and 0.2 V/Å for the applied electric field. The asymmetric Janus structure induces a Rashba spin splitting not only in the valence band but also in the conduction band near the Fermi level when the spin–orbit coupling (SOC) is present. Our findings offer theoretical insights into the exotic physical properties of SrAlGaTe 4 and also provide guides to new spintronic device designs.