Effect of disorder on superconductive tunneling into A15 compounds

Abstract

One of the current explanations for the degradation of superconductivity in A15 compounds with disorder is in terms of the broadening of a peak in the electronic density of states N(ε) near the Fermi level. Here, the Eliashberg gap equations which incorporate both the energy dependence in N(ε) and the normal impurity scattering are solved on the real frequency axis at T=0 K for several impurity concentrations. The resulting tunneling characteristics are then inverted to obtain the effective electron-phonon spectral functions α 2(ohms)F(Ω) assuming that the usual Eliashberg theory ( N( ε)= const.) is applicable. The scale of the effective α 2 F-spectra diminishes with increasing disorder. At the same time there is a transfer of weight under the (α 2 F) eff to higher frequencies. This trend has been obeserved in tunneling experiments on A15 superconductors with compositional disorder.