An electronic structure study of c -axis orientedNdBCO (123) thin films using polarized soft x-ray absorption spectroscopy on Cu L3 and O K edges

Polarized x-ray absorption spectroscopic (XAS) measurements have been made on Cu L-3 and O K edges on four superconducting thin films of NdBCO with different T-c values to study the relative importance of the in-plane (Cu 3d(x2-y2) and O 2p(x,y) orbitals) and the out-of-plane (Cu 3d(z2) and O-2pz) orbitals in the mechanism of superconductivity. Our results clearly show that a significant number of out-of plane O 2p(z) and Cu 3d(z2)-r2 do exist in these films, still hardly affecting their T-c. T-c is found to depend more upon number of itinerant holes rather than the orientation or substrate of the film. However the out-of-plane holes perhaps do affect the superconducting fraction in the film. O K-edge spectra recorded for E parallel to ab to measure the density of itinerant holes in plane show a good agreement with the conclusion drawn from Cu L-3 data. The results have been compared with the XRD and the magnetic susceptibility measurement's reported on these films earlier and a good qualitative agreement found. From the present study we can confidently state that no direct correlation exists between T-c and out-of-plane covalent and doping hole densities and the models based on the premise that out-of-plane orbitals, if present, will destroy superconductivity also do not seem to be valid in these systems.