Spin-orbit-interaction-induced surface resonance on W(011)

A surface resonance has been observed on the (011) surface of tungsten using angle-resolved photoemission. The resonance is located near the center of the surface Brillouin zone in a pseudogap opened by the spin-orbit interaction. It is degenerate with a bulk band, which in the absence of the spin-orbit interaction would have a different symmetry than a state in the gap. The resultant weak coupling leads to the formation of a well-defined resonance. These conclusions are supported by polarization- and photon-energy-dependent studies. The generality of our observations is discussed.