Induced superconductivity in Kondo alloys

The superconducting proximity effect between thin films of a superconductor and a Kondo alloy is analyzed theoretically, using the McMillan tunneling model to describe the proximity effect and the theory of Müller-Hartmann and Zittartz to describe the effect of Kondo impurities on superconductivity. The calculations are compared to measurements by Dumoulin, Guyon, and Nedellec for $\mathrm{Cu}\mathrm{Cr}$-Pb and other similar systems. Comparison of the tunneling density of states confirms that the bound state moves up towards the band edge more quickly than predicted by the Müller-Hartmann and Zittartz theory as the Kondo temperature increases. Fitting observed transition temperatures suggests the possibility of reentrant behavior at low temperatures. For both density of states and transition temperature, pair-breaking parameters approximately five times those expected theoretically are required to fit the data, possibly due to orbital degeneracy.