Non-Magnetic Localized State in Aluminum. I. Superconducting Transition Temperature

Abstract

The change in T c of the superconducting transition temperature of aluminum due to the addition of 3 d transitional impurities Ti, V, Cr, Mn, Fe and Ni is measured as a function of the residual resistance ratio ρ in the region of dilute concentrations ranging from 0.001 to 0.04 atomic percent. The contribution due to the smearing out of the energy gap anisotropy ( Δ T c ) anis is estimated by assuming that it can be accounted for by the theory of Markowitz and Kadanoff. ( Δ T c ) a anis thus estimated is found to depend only on the mean free path and very little on the type of impurity. The remaining part ( Δ T c ) v obtained by subtracting ( Δ T c ) anis from the observed change in the transition temperature, is found to be negative showing a dependence on impurity similar to that found for the residual resistance but differing that it shows a rather sharp minimum at Mn. Comparison with theories based on the Anderson model of localized states in metals are made. It is shown that the overall behavior shows fair agreement with theories which include the effect of the d - d coulomb correlation energy.