Large Rashba spin splitting of a metallic surface-state band on a semiconductor surface

The generation of spin-polarized electrons at room temperature is an essential step in developing semiconductor spintronic applications. To this end, we studied the electronic states of a Ge(111) surface, covered with a lead monolayer at a fractional coverage of 4 / 3, by angleresolved photoelectron spectroscopy (ARPES), spin-resolved ARPES and fi rst-principles electronic structure calculation. We demonstrate that a metallic surface-state band with a dominant Pb 6 p character exhibits a large Rashba spin splitting of 200 meV and an effective mass of 0.028 m e at the Fermi level. This fi nding provides a material basis for the novel fi eld of spin transport / accumulation on semiconductor surfaces. Charge density analysis of the surface state indicated that large spin splitting was induced by asymmetric charge distribution in close proximity to the nuclei of Pb atoms.