Ab initio study of structural and electronic properties of ternary alkali-metal-based semimetal compounds

Based on the ab initio calculations, we propose a new class of three dimensional (3D) topological insulators in alkali-metals-based ternary intermetallic compounds X2YZ (X = alkali metals, Y = Ag, Z = Sb) with a highly ideal assumption that the X2YZ compounds would crystallize in a cubic lattice. The band topology of X2YZ is explored by using full-potential linear augmented plane wave method. The results reveal that the topological insulator state of X2YZ can be realized by applying a uniaxial tensile strain of greater than 3% along the [0 0 1] direction and the electronic structure exhibits a distinct band-inversion feature. This new X2YZ compounds provide an alternate platform for novel quantum phenomena and multifunctional topological devices.