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 split ting 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 evolut ion of the splitting as monovalent atoms an adsorbed. The observed evolutio n is directly relevant to recent observations of altered orbital magnetic s tructure versus adsorbate coverage in magnetic materials. We propose a spin ordering for the associated Fermi contours which has important implication s for spin excitations at surfaces.