Ultraviolet photoemission study of single-crystal BaPb1-xBixO3

An ultraviolet photoemission study on single-crystal BaPb1-xBixO3 withx=0.15 (superconductor) and x=1.0 (semiconductor) has been presented. A clear Fermi-edge structure was observed for the first time for the superconducting compound. A rigid shift of the valence band by 0.3--0.4 eV between the superconductor and the semiconductor was observed although the shift is much smaller than predicted from the band-structure calculation. The ''mysterious 9-eV peak,'' whose origin has been controversial in cuprate superconductors, was found also for degraded crystal surfaces of BaPb1-xBixO3. Its origin was discussed in connection with the difference and similarity in the high-Tc mechanism between cuprate and noncuprate superconductors