Spin-orbital texture in topological insulators

For three-dimensional topological insulators in the Bi₂Se ₃ family, topological surface states with p_z orbitals have a left-handed spin texture for the upper Dirac cone and a right-handed spin texture for the lower Dirac cone. In this work, we predict a new form of the spin-orbital texture associated with the p_x and p_y orbitals. For the upper Dirac cone, a left-handed (right-handed) spin texture is coupled to the "radial" ("tangential") orbital texture, whereas for the lower Dirac cone, the coupling of spin and orbital textures is the exact opposite. The "tangential" ("radial") orbital texture is dominant for the upper (lower) Dirac cone, leading to the right-handed spin texture for the in-plane orbitals of both the upper and lower Dirac cones. A spin-resolved and photon polarized angle-resolved photoemission spectroscopy experiment is proposed to observe this novel spin-orbital texture.