The toy model for the high-Tc superconductivity

The simple microscopic model for the high-T_{C} superconductors based on the electron-phonon (EPH) and electron-electron-phonon (EEPH) interactions has been presented. On the {\it fold} mean-field level, it has been shown, that the obtained 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 (\Delta_{tot}) is very weak temperature dependent; up to the critical temperature \Delta_{tot} extends into the anomalous normal state to the Nernst temperature. (ii) The model explains well the experimental dependence of the ratio R_{1}\equiv 2\Delta_{tot}^{(0)}/k_{B}T_{C} on doping for the reported superconductors in the terms of the few fundamental parameters

Non-BCS temperature dependence of energy gap in thin film electron-doped cuprates

We investigate the dependence of the energy gap ($G$) on the temperature ($T$) for the electron-doped high-temperature superconductors. The following compounds, in the form of the thin films, have been taken into consideration: $\rm La_{2-x}Ce_xCuO_{4}$ (LCCO), $\rm Pr_{2-x}Ce_xCuO_{4}$ (PCCO), and $\rm Nd_{2-x}Ce_xCuO_4$ (NCCO). It was found that $G\left(T\right)$ deviates from the BCS prediction more, if a concentration of cerium assumes the lower values. For the lowest concentration (in the case of LCCO and NCCO), the function $G\left(T\right)$ is not quite like the BCS curve, which is connected with the existence of the residual Nernst region. Next, it has been pointed out that the NCCO superconductor becomes structurally unstable for the maximum concentration of cerium, which is leading to the anomalous dependence of the energy gap on the temperature and the induction of the wide Nernst region