Surface band structures on Nb(001).

Abstract

We report the joint studies of experimental and theoretical surface band structures of Nb(001). Angle-resolved photoelectron spectroscopy was used to determine surface-state dispersions along three high-symmetry axes \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}M\ifmmode\bar\else\textasciimacron\fi{}, \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}X\ifmmode\bar\else\textasciimacron\fi{}, and M\ifmmode\bar\else\textasciimacron\fi{}X\ifmmode\bar\else\textasciimacron\fi{} in the surface Brillouin zone. Ten surface bands have been identified. The experimental data are compared to self-consistent pseudopotential calculations for the 11-layer Nb(001) slabs that are either bulk terminated or fully relaxed (with a 12% contraction for the first interlayer spacing). The band calculations for a 12% surface-contracted slab are in better agreement with the experimental results than those for a bulk-terminated slab, except for a surface resonance near the Fermi level, which is related to the spin-orbit interaction. The charge profiles for all surface states or resonances have been calculated. Surface contraction effects on the charge-density distribution and the energy position of surface states and resonances will also be discussed.