Effect of Dissolved Manganese on Superconductivity of Pure and Impure Indium

Abstract

The superconducting critical temperature of indium decreases by ∼70°K per unit resistance ratio, $\frac{{\rho }_{4.2}}{{\rho }_{273°\mathrm{K}}}$, when doped with manganese. The addition of a third element, lead or tin, (just a few percent) progressively decreases the effect of the manganese and eliminates the effect completely when the mean free path is decreased to ∼500 Å. The data are explained on the basis of the Korringa model for the resistivity-minimum phenomenon found in dilute transition-metal solutions. It is assumed that the scattering of the conduction electrons undergoes a resonance (presumably caused by the localized moments) of width ∼1°K at the Fermi surface. The effect disappears when enough nonparamagnetic impurity is added to make the width of the electron energy levels large compared to that of the resonance. The technique and the model (if correct) opens a new way for investigating the resonance model for paramagnetic impurities.