Polarized X-ray Absorption Spectroscopy study of the Symmetry of Unoccupied States Near the Fermi Level in the Bi2Sr2CaCu2O8 System

A study of the electronic states near the Fermi level in high-T-c superconductors, which is so important to understanding the mechanism of superconductivity, has been carried out on well characterized single crystals of superconducting Bi2Sr2CaCu2O8+x Bi-2212. A large number of polarized x-ray absorption spectra have been recorded with the E vector parallel to the a-6 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 Cu L(3) and O K are then analysed to obtain the density of the unoccupied Cu 3d(z2) and Cu 3d(x2-y2) orbitals from the Cu L(3) spectra and the density of the O 2p(z) and O 2(x,y) orbitals from the O K spectra. The results clearly show the presence of O 2p(z) orbitals in a substantial amount although the same cannot be said of the 3d(z2) orbitals. Tight-binding calculations of the holes are also reported and compared with experimental results.