Polaron motion in complex oxides and high-temperature superconductivity

Abstract

The novel mechanisms of polaron pairing in complex oxides and the possibility of high-temperature superconductivity as a result are reported. The peculiarity of complex oxides is taken into account by considerations of a medium with two optical phonon branches satisfying the adiabatic condition of the polaron theory and having different dispersions. The system of nonlinear motion equations for the coupled fields of carriers and polarization is solved. It is shown that two carriers localized because of their interaction with one phonon branch form a bipolaron owing to the interaction with the real phonons of another branch under the resonance condition. Such a novel bipolaron does not need a high static dielectric constant (SDC) for its formation, distinct from other bipolaron models. The novel bipolaron is energetically favourable compared with other bipolarons, when SDC is not high. By taking into account the peculiarity of bosons having a low maximum velocity, the expression for their condensation temperature is modified. As a result, the high-temperature Bose condensation of the novel bipolarons is shown to be possible at lower concentrations even if their effective mass is very large.