Electronic structure and superconducting mechanism of high T/sub c/ cupper oxide perovskite compounds

The authors' study concludes that satellite peaks marked with S and S' come from the electron transition from the 0 2p states to Cu 3d-hole states due to the inelastic scattering of the photoelectrons. The appearance of the satellite peaks is the evidence of the existence of the Cu 3d-holes. The life-time of the d-hole is estimated to be longer than the photoelectron transition-time (10/sup -15/ sec). It is possible that the d-holes act as attractors between the conductive electrons to form the Cooper pairs. The valence band spectra after annealing resembles strongly to those of ZrC, HfC. This suggests that the electronic structure of this oxide is possibly semimetallic like ZrC. The density of states (DOS) at the Fermi level is estimated to be as small as about one tenth of that (0.18 states/eV cell) of ZrC from the spectrum intensity. This study suggest two types of band models for oxidized and reduced superconductors. The top of the d-band with low energy-dispersion is under the Fermi level or the d-state localize. The valence fluctuation of Cu ions suggest the T/sub c/ enhancement by the exciton mechanism due to the creation and annihilation of the Cu 3d-hole resonating with vibration modes of the CuO/sub n/ (n=6, 5 and 4) clusters in addition to the phonon mechanism