Eliashberg equations with energy dependence of the normal density of states and quasiparticle tunneling in high-T-c superconductors

In the present paper the limits and the correct utilization of the standard program for the inversion of Eliashberg equations for the determination of the electron-phonon spectral function in high-T-c superconductors are discussed. In order to compare the calculated density of states with the experimental one that we recently measured in Bi2Sr2CaCu2O8+x single-crystal break junctions with T-c = 93K, we introduced the results of the standard inversion procedure in a direct program for the solution of Eliashberg equations. We explain most of the observed differences between theoretical and experimental curves at energy greater than the gap by a smooth energy dependence of the normal density of states that we introduced in the direct solution of the Eliashberg equations. The effects of the energy-dependent electron-phonon spectral function on the quasiparticle density of states are also presented in a simple particular case.