THEORY OF HIGH-TEMPERATURE SUPERCONDUCTIVITY - APPLICATION TO YBCO SYSTEMS

In this paper the multiconfiguration self-consistent field method with configuration interaction is first described. Then this method is app lied to YBa2Cu3O7 (YBCO7) compound, and the key features of the calcul ated electronic structure are discussed and compared with those of La2 -xSrxCuO4 (LSCO) compounds previously calculated by Kamimura and Eto a nd also by Kamimura and Suwa. In LSCO the key feature of the electroni c state in the superconducting regime is a coherent state in a local a ntiferromagnetic (AF) order in which Zhan-Rice's spin-singlet state an d the spin-triplet state due to Hund's coupling appear alternately. Tn the present paper it is pointed out that, in order to realize such co herent state in YBCO7, the charge of Cu ion in the Cu-O chain must be in between 1.3 and 2.0. Finally, the important results of the effectiv e one-electron-type band structure, Fermi surfaces, the electron-phono n coupling constants, and the momentum-dependent spectral function cal culated for LSCO by Kamimura, Matsuno, Suwa, and Ushio are reviewed, a nd following them it is stated that even the phonon mechanism gives ri se to d-wave pairing when the AF local order exists.