Orbit- and Atom-Resolved Spin Textures of Intrinsic, Extrinsic and Hybridized Dirac Cone States

Combining first-principles calculations and spin- and angle-resolved photoemission spectroscopy measurements, we identify the helical spin textures for three different Dirac cone states in the interfaced systems of a 2D topological insulator (TI) of Bi(111) bilayer and a 3D TI Bi$_{2}$Se$_{3}$ or Bi$_{2}$Te$_{3}$. The spin texture is found to be the same for the intrinsic Dirac cone of Bi$_{2}$Te$_{3}$ or Bi$_{2}$Se$_{3}$ surface state, the extrinsic Dirac cone of Bi bilayer state induced by Rashba effect, and the hybridized Dirac cone between the former two states. Further orbit- and atom-resolved analysis shows that $S$ and $P_{z}$ orbits have the conventional helical spin texture; $P_{\mathrm{x}}$ and$ P_{\mathrm{y}}$ orbits show individually radial spin component, while the sum of the two shows a total in-plane helical spins. The orbit-dependent spin structure is a signature property of spin-orbit coupling, independent of topology.