Theory of high-temperature superconductivity in doped polar insulators

Many high-temperature superconductors are highly polarizable ionic lattices where the Frohlich electron-phonon interaction (EPI) with longitudinal optical phonons creates an effective attraction of doped carriers virtually equal to their Coulomb repulsion. The general multi-polaron theory is given with both interactions being strong compared with the carrier kinetic energy so that the conventional BCS-Eliashberg approximation is inapplicable. The many-electron system is described by the polaronic t-J(p) Hamiltonian with reduced hopping integral, t, allowed double on-site occupancy, large phonon-induced antiferromagnetic exchange, J(p) >> t, and a high-temperature superconducting state of small superlight bipolarons protected from clustering. Copyright (C) EPLA, 2011