LOCAL STRUCTURAL FEATURES OF THE SUPERCONDUCTING BI2SR2CACU2O8- A POLARIZED CU K-EDGE XAS STUDY(DELTA SYSTEM )

Local structure of CuO2 plane of the superconducting Bi2Sr2CaCu2O8+del ta (Bi2212) crystal at the optimum doping has been investigated by in- plane polarized Cu K-edge x-ray-absorption spectroscopy. We have deter mined the quadrupole character of the 1s-->3d(x2-y2) transition in the x-ray-absorption near-edge spectra by rotation of the in-plane polari zation geometry by 45 degrees from the Cu-O-Cu direction. The nonzero intensity of this transition in the polarization vector parallel to th e Cu-O-Cu direction indicates local structural distortion of the CuO4 square plane. The statistical distribution of the instantaneous Cu-O b onds is determined by polarized extended x-ray-absorption fine structu re and discussed. [S0163-1829(98)05037-1].