Local structural features of the superconducting Bi₂Sr₂CaCu₂O_8+δ system: A polarized Cu K-edge XAS study

Local structure of CuO₂ plane of the superconducting Bi₂Sr₂CaCu₂O_8+δ (Bi2212) crystal at the optimum doping has been investigated by in-plane polarized Cu K-edge x-ray-absorption spectroscopy. We have determined the quadrupole character of the 1s⃗3d_x²-y² transition in the x-ray-absorption near-edge spectra by rotation of the in-plane polarization geometry by 45° from the Cu-O-Cu direction. The nonzero intensity of this transition in the polarization vector parallel to the Cu-O-Cu direction indicates local structural distortion of the CuO₄ square plane. The statistical distribution of the instantaneous Cu-O bonds is determined by polarized extended x-ray-absorption fine structure and discussed.