CuK-edge studies of the charge carries in Th-doped cuprate system R2-xThxCuO4-delta (R = Nd, Sm and Gd)

To further study the charge carrier concentration in electron doped cuprate superconductors, a systematic x-ray absorption near edge structure (XANES) measurement has been carried out on Th-doped superconductor system R2-xThx CuO4-delta (R = Nd, Sm, and Gd). The XANES results show that, similar to th e Ce-doped compounds, while the intensity of the Cu1+ 4p(pi) feature increa se with the increase of the Th doping level x, the intensities of the Cu24p(pi) and 4p(sigma) features decreases. This clearly indicates that the el ectrons doped by the Th atoms are injected into the local Cu 3d-orbitals. T he normalized Cu1+ 4p(pi) intensity data show that the Cu1+ concentration i n the Th-doped compound series with different R-elements is linearly propor tional to the Th doping-level x. The data suggest that both Ce and Th donat e the same fraction of electrons into the Cu sites.