Surface state on clean Tb(0001)

Angle-resolved photoemission experiments on clean Tb(0001) reveal the existence of a state 0.5 eV below the Fermi level which has the properties of a surface state. It exhibits no dispersion with respect to the momentum component perpendicular to the surface in the photon-energy range between 15 and 55 eV; it is located in a band gap of the projected band structure at bar Γ; and it is very sensitive to oxygen contamination of the surface. The wave function of this surface state has Δ1 symmetry, as the intensity of the photoemission peak decreases when the p component of the exciting radiation is reduced. Both the very weak energy dispersion with respect to the parallel component k? of the momentum and the photon-energy dependence of the photoionization cross section indicate that the surface state has 5dz2 orbital character. The existence of this surface state can be explained by the same theory of surface core-level shifts that is related to the narrowing of the surface density of d states in transition metals