Pair-breaking in superconductivity

Abstract

<p>We have examined within Eliashberg theory the effect of several pair-breaking mechanisms on superconducting properties. Many predictions are made, some of which have recently been confirmed experimentally. First, we present the strong coupling theory of the thin film critical current. Predictions for the temperature dependence of this property are made for the cases of strong inelastic scattering, spin fluctuations, and magnetic and non-magnetic impurity scattering. We next examine the recently proposed marginal Fermi liquid theory, which has been shown to account for the unusual normal state properties of the high Tc superconductors. Here we have calculated several superconducting properties in this model. The most important result arising from this work is the effect of the gapping of the spectrum of fluctuations. This produces a drop in the quasiparticle damping rate below Tc and a peak in the low frequency temperature dependent conductivity. These predictions have been recently confirmed by several experiments. Also, in the frequency dependent optical conductivity, no absorption is predicted up until 4Δ in the clean limit. The experimental observation of a lack of Holstein structure in the ratio of the superconducting to normal state optical conductivity is explained. Several electromagnetic properties of superconductors are calculated with the inclusion of spin fluctuations and paramagnetic impurities. Predictions are made for the optical conductivity in the clean limit with magnetic impurity scattering. In this latter case, the Holstein structure will be reduced from the pure case and absorption will occur below 2Δ. Finally, we have examined a model for a spin glass superconductor which leads to a temperature dependent scattering rate. Within this model several thermodynamic and electrodynamic properties have been examined, giving results which might be confirmed by experiment. Reentrant behaviour is predicted for a certain choice of parameters.</p>