Soft-x-ray absorption spectroscopy of Nd1+xBa2-xCu3O7+delta (x=0-0.6)

O K-edge and Cu L(23)-edge x-ray-absorption near-edge-structure spectra for the series of Nd1+xBa2-xCu3O7+delta compounds (x=0-0.6) were measured using a bulk-sensitive x-ray fluorescence yield technique. Near the O 1s edge, pre-edge peaks at similar to 527.5 and similar to 528.2 eV are ascribed to the excitations of O 1s electrons to O 2p holes located in the CuO3 ribbons and CuO2 planes, respectively. The peak at similar to 528.2 eV decreases in intensity with increasing the Nd doping, indicating the filling of holes in the CuO2 planes by the substitution of Nd3+ for Ba2+ in the Nd1+xBa2-xCu3O7+delta system. For low levels of Nd doping, the holes are located mainly in the CuO2 planes. At higher Nd doping, the holes are located predominantly in the CuO3 ribbons. The depression in T-c for the Nd1+xBa2-xCu3O7+delta system correlates closely with the hole concentration in the CuO2 planes and the number of disrupted fourfold-coordinated Cu on the chain sites. The high-energy shoulders in the Cu L(23)-edge absorption spectra arise from Cu3d(9)L defected states to Cu2p(-1)3d(10)L excited states, where L denotes the ligand hole on the CuO3 ribbons and CuO2 planes. With increasing the Nd doping, the shoulders shift to higher energy similar to 0.3 eV from x=0 to 0.6.