Electronic band structure of the two-dimensional metallic electron system Au/Ge(111)

The two-dimensional electron system Au/Ge(111)-(root 3 x root 3)R30 degrees is studied in detail by angle-resolved photoemission and density functional theory calculations. In combining these results, we identify four metallic bands which are either of dominantly Au or Ge character, respectively. The largest Fermi surface sheet, originating from Au orbitals, is suggestive of a nesting condition due to its hexagonal shape. However, a charge density wave transition is not observed between room temperature and 10 K. The electronic structure obtained by density functional theory with inclusion of a self-energy correction is in good agreement with the experiment. These calculations also indicate that there is significant spin-orbit splitting, especially in the Au-related bands, which is partly of Rashba character.