CU K-EDGE POLARIZED X-RAY-ABSORPTION NEAR-EDGE STRUCTURE OF BI2CASR2CU2O8

The linearly polarized Cu K-edge x-ray-absorption near-edge structure (XANES) of Bi2Sr2CaCu2O8+delta (Bi 2:2:1:2) has been measured, and the spectra are interpreted by the multiple-scattering approach in real space. The polarized spectra can be predicted in terms of a one-electron dipole (DELTA-l = +1) transition Cu 1s --> epsilon-p, probing the unoccupied p-like (l = 1) density of states projected on the Cu site with orbital angular momentum m(l) = 0 in the E parallel-to z spectra, and the m(l) = 1 in the E perpendicular-to c spectra. Therefore we show that the electronic structure of the high-energy conduction bands, beyond the Cu 3d band, are well described in terms of the one-electron approximation. Final-state effects induced by the core hole have been studied and calculated. A satellite 7 eV above the main K-XANES peak in both polarizations is shown to be a multielectron shake-up excitation, and it is enhanced going into the insulating phase. Structural information on the copper site in Bi2Sr2CaCu2O8+delta, and in Bi2Sr2YCu2O8+delta has been extracted from XANES spectra, providing evidence for the decrease of the Cu-O distance in the metallic phase.