Polarized x-ray absorption spectroscopy study of the symmetry of unoccupied electronic states near the Fermi level in the system

A study of the electronic states near the Fermi level in high- superconductors, which is so important to understanding the mechanism of superconductivity, has been carried out on well characterized single crystals of superconducting . A large number of polarized x-ray absorption spectra have been recorded with the E vector parallel to the a - b plane and perpendicular to it at the Dragon beam line at the Brookhaven Light Source using the fluorescence mode of detection. These bulk spectra of and O K are then analysed to obtain the density of the unoccupied and orbitals from the spectra and the density of the and orbitals from the O K spectra. The results clearly show the presence of orbitals in a substantial amount although the same cannot be said of the orbitals. Tight-binding calculations of the holes are also reported and compared with experimental results.