Profiling Spin And Orbital Texture Of A Topological Insulator In Full Momentum Space

We investigate the coupled spin and orbital textures of the topological surface state in Bi-2(Te,Se)(3)(0001) across full momentum space using spin- and angle-resolved photoelectron spectroscopy and relativistic one-step photoemission theory. For an approximately isotropic Fermi surface in Bi2Te2Se, the measured intensity and spin momentum distributions, obtained with linearly polarized light, qualitatively reflect the orbital composition and the orbital-projected in-plane spin polarization, respectively. In Bi2Te3, the in-plane lattice potential induces a hexagonal anisotropy of the Fermi surface, which manifests in an out-of-plane photoelectron spin polarization with a strong dependence on light polarization, excitation energy, and crystallographic direction.