title: Pairing mechanism for the high-TC superconductivity: symmetries and thermodynamic properties.
abstract: The pairing mechanism for the high-Tc superconductors based on the electron-phonon (EPH) and electron-electron-phonon (EEPH) interactions has been presented. On the fold mean-field level, it has been proven, that the obtained s-wave model supplements the predictions based on the BCS van Hove scenario. In particular: (i) For strong EEPH coupling and T < T(C) the energy gap (Δtot) is very weak temperature dependent; up to the critical temperature Δtot extends into the anomalous normal state to the Nernst temperature. (ii) The model explains well the experimental dependence of the ratio R(1) ≡ 2Δ(tot)(0)/k(B)T(C) on doping for the reported superconductors in the terms of the few fundamental parameters. In the presented paper, the properties of the d-wave superconducting state in the two-dimensional system have been also studied. The obtained results, like for s-wave, have shown the energy gap amplitude crossover from the BCS to non-BCS behavior, as the value of the EEPH potential increases. However, for T > T(C) the energy gap amplitude extends into the anomalous normal state to the pseudogap temperature. Finally, it has been presented that the anisotropic model explains the dependence of the ratio R(1) on doping for the considered superconductors.
authors.affiliation: Institute of Physics, Częstochowa University of Technology, Częstochowa, Poland. szczesni@wip.pcz.pl
authors.forename: Radosław
authors.initials: R
authors.lastname: Szczęśniak
mesh_terms: D000465:Algorithms; D004553:Electric Conductivity; D004583:Electrons; D006358:Hot Temperature; D060739:Phonons; D013816:Thermodynamics