SPIN SPLITTING OF AN AU(111) SURFACE-STATE BAND OBSERVED WITH ANGLE-RESOLVED PHOTOELECTRON-SPECTROSCOPY

High momentum resolution angle resolved photoemission spectra from the Au(lll) sp-derived surface state exhibit a doublet. The separation be tween the peaks increases linearly with k(parallel to), and reaches a maximum of 110 meV at 0.153 Angstrom(-1), when one of the bands crosse s the Fermi level. These results are interpreted as spin-split surface state bands, with the spins aligned in the plane of the surface perpe ndicular to the electronic momentum. The origin of the splitting is sp in-orbit coupling, which can break spin degeneracy in systems which la ck inversion symmetry.