Superconductivity

The superconducting and normal state properties are reviewed for exemplary matrix-impurity systems in the three distinct regimes of magnetic character of the impurity which have been identified. It is shown that these three regimes can be distinguished by thedetailed behavior of the depressions of 1) the superconducting transition temperatureT _c as a function of impurity concentrationn and 2) the specific heat jump ΔC atT _c as a function ofT _c . These systematics of superconductivity in the presence of local moments appear to be sufficiently well established that it is possible to 1) ascertain whether the solute spin is long-lived (magnetic) or short-lived (nonmagnetic) compared to thermal fluctuation lifetimes at superconducting temperatures, 2) determine the sign and magnitude of the conduction electron-impurity spin exchange interaction parameter ϑ and the temperature dependence of the exchange scattering of conduction electrons bylong-lived solute spins, 3) derive, in favorable cases, information pertaining to the energy level structure of rare earth ions in the crystalline electric field of their superconducting metallic host, and 4) observe magnetic-nonmagnetic transitions of an impurity induced by the application of an external pressure or variation of the composition of a binary alloy matrix. This article is based upon an invited presentation at the 1973 Summer meeting of the American Physical Society in East Lansing, Michigan, 18–20 June 1973 Bull. Amer. Phys. Soc.18, 779 (1973)]. Supported by the U.S. Energy Research and Development Administration under Contract No. ERDA E(04-3)-34 PA 227.