Spin-Polarized Surface Resonances and Topological Surface States in Pb-Based Topological Insulators

Topological surface states are generated through band inversion in the bulk electronic structure and provide a characteristic spin-helical electronic state at the surface. In this study, we have investigated the spin-polarized surface electronic states of the Pb-based ternary topological insulator Pb(Bi1－xSbx)2Te4 using spin- and angle-resolved photoemission spectroscopy and first-principles calculations. In addition to the topological surface state, we identified spin-polarized surface resonances near the projected bulk bands in the occupied states. One branch of these surface resonances connects continuously to the topological surface state, while the neighboring branch exhibits the opposite spin polarization. These findings indicate that the spin-polarized electronic structure near the topological surface state should be understood by including the adjacent surface resonances.