RESONANT PHOTOEMISSION-STUDY OF BA1-XKXBIO3 SINGLE-CRYSTALS

Single crystals of superconducting Ba0.6K0.4BiO3 and semiconducting Ba 0.9K0.1BiO3 have been studied by resonant photoemission. in the photon energy range 14-25 eV, a valence-band feature with a binding energy a round 2.6 eV becomes enhanced at the photon energies 16, 19, and 22.5 eV. In order to identify this possibly resonating feature, valence-ban d photoemission spectra were also measured at photon energies (90-120 eV) around the excitation threshold of the Ba 4d core level. A compari son between the results obtained at these different photon energy regi ons suggests that the valence-band enhancements at 16 and 19 eV can be assigned to resonating Ba states, while the comparatively weaker enha ncement at 22.5 eV is consistent with both a Ba and/or an O photoemiss ion resonance. The results also indicate Ba slates close to the Fermi level.