Orbital Selective Spin-Texture in a Topological Insulator

Three-dimensional topological insulators support a metallic non-trivial surface state with unique spin texture, where spin and momentum are locked perpendicular to each other. In this work, we investigate the orbital selective spintexture associated with the topological surface states in Sb2Te3, using the first principles calculations. Sb2Te3 is a strong topological insulator with a p-p type bulk band inversion at the G-point and supports a single topological metallic surface state with upper (lower) Dirac-cone has left (right) handed spin-texture. Here, we show that the topological surface state has an additional locking between the spin and orbitals, leading to an orbital selective spin-texture. The out-of-plane orbitals (pz orbitals) have an isotropic orbital texture for both the Dirac cones with an associated left and right handed spin-texture for the upper and lower Dirac cones, respectively. In contrast, the in-planar orbital texture (px and py projections) is tangential for the upper Dirac-cone and is radial for the lower Dirac-cone surface state. The dominant inplanar orbital texture in both the Dirac cones lead to a right handed orbital-selective spin-texture.