MANY-BODY EFFECTS IN X-RAY PHOTOEMISSION AND HIGH-T(C) SUPERCONDUCTIVITY OF CUPRATE SUPERCONDUCTORS

Many-body effects in Cu 2p x-ray photoemission of Bi2Sr2CaxCu1-xO6+2x (x=0,1,2), La2-xSrxCuO4 (x=0,0.13), and ErBa2Cu3O7-x,y (x<y) were obse rved and correlations between the many-body effects and high-T(c) supe rconductivity of cuprate superconductors were reviewed. For the Bi2Sr2 CaxCu1+xO6+2x (x=0,1,2) and La2-xSrxCuO4 (x=0,0.13) systems, proper hi gh-T(c) superconductivity was realized by increasing the transfer inte gral and the interaction strength of the Cu-O bond of the crystal dete rmined the superconducting properties. However, for the ErBa2Cu3O7-x a nd YBa2Cu3O7-x systems, 90 K superconductivity was realized by increas ing the charge transfer energy. The extended valence state including t he Cu, Ba, and O valence states in the crystal determined the supercon ducting properties of the ErBa2Cu3O7-x and YBa2Cu3O7-x systems.