Superconductivity in Nd2-xCexCuO4-∂ System

The effects of Ce doping and reduction on the superconductivity and electronic state of Nd2-xCexCuO4-∂ were investigated through measurements of the magnetization and X-ray absorption near-edge structure of the Cu-K edge of specimens annealed at various oxygen pressures and temperatures. The superconduction onset temperature and diamagnetism reach a peak at a Ce content of x=0.15. We found that the d electron density as estimated from the edge shift of the Cu-K edge absorption also has a peak around x=0.15. In addition, the d electron density increases with increasing reduction of the sample, and the magnitude of the superconduction diamagnetism becomes constant above a certain level of reduction. It is concluded that a d electron density above a certain critical value is necessary for the occurrence of superconduction in this system.