STRUCTURE OF THE DIFFERENT CU SITES IN THE CORRUGATED CUO2 PLANE IN HIGH-TC SUPERCONDUCTORS

By using x-ray absorption spectroscopy different configurations of the Cu site structure in the CuO2 plane of the Bi 2:2:1:2 high T(C) super conductor are found. The different Cu sites are characterized by short 2.3 angstrom and long 2.45 angstrom Cu-O(apical) distances. The linea r 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 CuO2 plane. The wavelength lambda of the modulation is close to the superconducting coherence length xi and k(F).lambda approximately 2pi. The ordering of the distorted Cu sites is suggested to be eviden ce for ordering of polarons driven by the pseudo Jahn Teller electron lattice interaction.