Spin-polarized semiconductor surface states localized in subsurface layers

Abstract

A pair of different surface-state and surface-resonance bands has been identified on $\text{Bi}/\text{Ge}(111)\text{\ensuremath{-}}(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ by a combined experimental and computational study. The wave functions of the states have negligible amplitude at Bi atoms and are extended over more than 20 subsurface layers. These bands exhibit characteristic spin structure, which is ascribed to the combined Rashba and atomic spin-orbit interaction (SOI). Unlike previously known surface Rashba systems, the spin polarization is induced by SOI of a light element (Ge) with negligible contribution of a heavier one (Bi).