Large Rashba spin splitting of surface resonance bands on semiconductor surface

We have found a large spin splitting due to the Rashba spin-orbit interaction on the Bi/Ge(111)-(√3×√3)R30° surface by using angle-resolved photoelectron spectroscopy and first-principles electronic structure calculation. A surface resonance band derived from Bi exhibits the Rashba spin splitting with a large Rashba parameter (α_R) of 1.8 eV Å. The spin-split states have a considerable 6s-6p_z hybridized character, which leads to a strong perpendicular asymmetry of the charge density in close proximity of Bi nuclei. The result suggests that the magnitude of the Rashba splitting on Bi-adsorbed surfaces should depend crucially on the local-bonding geometry of Bi.