On the theory of high-temperature superconductivity

The construction of a theory of the superconductivity of oxide metals based on the polar model is discussed. The matrix electron Green's function is calculated with allowance for both the electron–phonon interaction and strong Coulomb correlations. The possible raising of $T_c$ due to the lattice instability associated with strong anharmonicity of the oxygen ion vibrations in perovskitelike compounds is considered. Strong electron correlations are taken into account in a one-band $t - J$ model. Because of a local restriction that precludes doubly occupied states in a system with strong correlation, only $d$-wave pairing is possible.