Spin-Orbit Coupling Induced Surface Band Splitting in Li/W(110) and Li/Mo(110)

The broken symmetry at surfaces can give rise to a nonzero spin-orbit splitting of valence bands. We observe such a splitting of the $d$-derived surface state on W(110) and, to a lesser extent, on Mo(110), and follow the evolution of the splitting as monovalent atoms are adsorbed. The observed evolution is directly relevant to recent observations of altered orbital magnetic structure versus adsorbate coverage in magnetic materials. We propose a spin ordering for the associated Fermi contours which has important implications for spin excitations at surfaces.