Superconductivity and Electronic State of Nd-Ce-Cu-O System

Abstract

Effects of Ce-doping of reduction on the superconductivity and electronic state of Nd_2−x Ce_xCuO_4−δ have been investigated by measurements of magnetization and X-ray absorption near-edge structure of the Cu K-edge for the specimens annealed at various oxygen pressures and temperatures. The superconducting onset temperature and diamagnetization have a peak at Ce content x=0.15. We find that the electron density estimated from the edge shift of the Cu K edge absorption also shows a peak around 0.15. It is concluded that effect of Ce doping changes below and above x=0.15. Below x∼0.15 Ce-doping increases the electron density at Cu site and above that vice versa. The result suggests that the electronic state changes above and below x∼0.15 in this system.