Structure of the Different Cu Sites in the Corrugated CuO2Plane in High TcSuperconductors

By using x-ray absorption spectroscopy different configurations of the Cu site structure in the CuO2plane of the Bi 2:2:1:2 high Tcsuperconductor are found. The different Cu sites are characterized by short 2.3 Å and long 2.45 Å Cu-O(apical) distances. The linear arrays of different Cu sites forming domains with a corrugated-iron-foil shape is proposed to be a key feature of superconducting domains in the CuO2plane. The wavelength ? of the modulation is close to the superconducting coherence length ? and kF·??2?. The ordering of the distorted Cu sites is suggested to be evidence for ordering of polarons driven by the pseudo Jahn Teller electron lattice interaction.