ROLE OF PHONON HAVING A CHANGE IN COORDINATION-NUMBER OF VIBRATING ION IN HIGH-TC OXIDE SUPERCONDUCTORS

For those high-T(c) Cu-oxides whose crystalline unit is composed of a metal (M(c)) sheet sandwiched by two pyramidal CuO2 planes, a phonon-mediated superconductivity model is proposed in which a phonon having a change in the coordination number of a vibrating ion induces a charge-density wave in the CuO2 plane. The electron-phonon coupling constant in this mechanism is estimated and is shown to resonably reproduce the observed d ln T(c)/d ln r value given earlier (J. Phys. Soc. Jpn. 60 (1991) 3194) on the basis of the Eliashberg theory, where r denotes the M(c)-O bond length.