Concentration dependence of the softening effect in Pb–Sn and Pb–Bi alloys at the superconducting transition point

A study has been made of the effects of small amounts of tin and bismuth on the softening effect δϵns for lead single crystals at the superconducting transition point. Experiment shows that the magnitude of the softening κδϵns shows a complicated nonmonotonic dependence on the impurity concentration in the superconductor; the measurements are compared with conclusions from existing theories of the effect.