On the influence of the structural phase transition on the superconducting gap edge

Within the anharmonic model of the high-temperature superconductivity the temperature dependence of the thermodynamic energy gap edge and the ratio 2Δ/Tc are calculated with the help of nonlinearized Eliashberg equations on the real axis. It is shown that in three possible cases Tc < T0, Tc > T0 > 0 and Tc > T0 = 0 (Tc - the superconducting transition temperature, Tc - the structural transition temperature) the behaviour of those parameters is qualitatively different because of different temperature dependence of the electron-phonon coupling constant and the average phonon frequency. The real and imaginary part of Δ(ω), and tunneling density of states N(ω)/N(0) are numerically studied. Simple method of calculating Tc from the linearized equations is proposed. (author). 26 refs., 8 figs