Analysis of the effects of annealing on the electron-doped cuprate superconductor Nd_(1.85)Ce_(0.15)Cu0_(4-__) using x-ray photoemission spectroscopy

摘要

We have studied the Cu 2p, Nd 3d and valence band x-ray photoemission spectra obtained for Nd_(1.85)Ce_(0.15)CuO_(4-__) single crystal under different annealing conditions. It is found that both the 2p_(3/2)3d~(10) and the 2p_(1/2)3d~(10) peaks of the Cu 2p core level appear obviously upon oxygen reduction. Nd 3d spectra move towards lower binding energy upon reduction. The valence band spectra show an increase in itinerant electrons with 3d character upon reduction. All the changes of the Cu 2p, Nd 3d and valence band spectra can be explained in terms of the delocalization of itinerant electrons. We suggest that an annealing process could remove excess oxygen and the associated disordered potential making the conductive electrons delocalized with the result that superconductivity becomes possible.