Cu K-Edge Studies of the Charge Carries in Th-Doped Cuprate System R_(2-x)Th_xCuO_(4-δ) (R = Nd, Sm amd 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 R_(2-x)Th_xCuO_(4-δ) (R=Nd, Sm, and Gd). The XANES results show that, similar to the Ce-doped compounds, while the intensity of the Cu^(1+)4pπ feature increase with the increase of the Th doping level x, the intensities of the Cu2+4pπ and 4pσ features decreases. This clearly indicates that the electrons doped by the Th atoms are injected into the local Cu 3d-orbitals. The normalized Cu^(1+)4pπ intensity data show that the Cu^(1+) concentration in the Th-doped compound series with different R-elements is linearly proportional to the Th doping-level x. The data suggest that both Ce and Th donate the same fraction of electrons into the Cu sites