Lattice Instability and Strong Electron-Phonon Coupling for High-TcSuperconductivity

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Abstract
Recent experiments revealing strong electron-phonon coupling in high-Tc superconductors are reviewed and the possibility of phonon-mediated superconductivity in then is discussed. Special emphasis in enhancing Tc is put on the lattice instability due to highly anharmonic oxygen vibrations in perovskite-type compounds. To describe the latter, a pseudospin model of the lattice dynamics is proposed and electron-phonon interaction in ion-type crystals is considered. It is argued that a strong coupling and high-Tc can be obtained due to instability of the ion lattice at a mode/rate value of electron-phonon interaction.