Strain-Tuned Topological Insulator and Rashba-Induced Anisotropic Momentum-Locked Dirac Cones in Two-Dimensional SeTe Monolayers

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Rashba spin–orbit coupling (SOC) in topological insulators (TIs) is a very interesting phenomenon and has received extensive attention in two-dimensional (2D) materials. However, the coexistence of Rashba SOC and band topology, especially for materials with a square lattice, is still lacking. Here, by using first-principles calculations, we propose for the first time a SeTe monolayer as a 2D candidate with these novel properties. We find that the square lattice exhibits anisotropic band dispersions near the Fermi level and a Rashba effect related to large SOC and inversion asymmetry, which leads to a Dirac semimetal state. Another prominent feature is that SeTe can achieve a topological state under a tensile strain of only 1%, characterized by the Z 2 invariant and helical edge states. Our findings demonstrate that SeTe is a promising material for novel electronic and spintronics applications.