Electronic structure of high-temperature superconductors I. Y-Ba-Cu-O systems

摘要

The electronic structure of high-Tccopper based superconductors has been studied using the quasirelativistic INDO molecular orbital method. Model clusters of YBa2Cu3Oysystems have been investigated foryranging between 6·0 and 7·0. Monomeric units Ba8Cu3Oxqand Y4Ba8Cu4Oxq, dimeric units Ba12Cu6Oxqand Y6Ba12Cu8Oxqas well as tetrameric units Ba18Cu12Oxqover 300 valence orbitals have been studied. From the set of occupied molecular orbitals the density of states (DOS) function has been calculated along with its d-orbital projection. The highest occupied molecular orbitals cover the oxygen p-band whereas the copper d-band lies at lower energies. Superconducting phase models (y=6·75 to 7·0) have a higher d-DOS function at higher energies with respect to the non-superconducting phase (y=6