SPIN-ORBIT EFFECTS ON ELECTRONIC-STRUCTURES NEAR E(F) FOR NB(001)

We report the discovery of the bulk states resolved from the surface r esonance at GAMMABAR near the Fermi level (E(F)) for Nb(001) using a h igh-resolution angle-resolved photoelectron analyzer. Two surface band s merge from both the GAMMABAR XBAR and the GAMMABAR MBAR high-symmetr y axes and become the surface resonance at -60 meV. The topology of th ese surface bands suggests the possible influence of the spin-orbit in teraction. The bulk state has not been predicted by nonrelativistic bu lk-band calculations for Nb(001). We have carried out a relativistic c alculation with the augmented-plane-wave method to look for the filled hybridized bulk band splitting from GAMMA25'. The value of the bulk-s tate wave vector is determined to be 0.3GAMMAH. A pseudogap appears wi th a width around 0.10 eV, and the observed surface resonance is accom modated inside this gap.