Electronic Structure and Superconductivity of Indium-Cadmium Alloys

Abstract

The superconducting transition temperatures (in zero magnetic field) of In-Cd alloys in the range 0-60 at.% cadmium have been measured. $T_c$ decreases from 3.406 to 3.245°K in the tetragonal solid solution and from 3.55 to 3.00°K in the cubic phase, with increasing Cd content. A kink in the $T_c$-versus-composition curve at 2 at.% Cd is attributed to Fermi-surface-Brillouin-zone interaction. This interpretation is supported by lattice-parameter determinations which show an anomaly at 2% Cd, and also by the magnetic susceptibility measurements of Verkin and Svechkarev. The existence of the superconductivity anomaly at $Z=2.98\mathrm{}$ supports a recent hypothesis of Svechkarev concerning the electronic structure of indium. Measurement of reduced resistance ratio $\rho \equiv \frac{{R_{4.2}}^{\circ }}{({R_{273}}^{\circ }-{R_{4.2}}^{\circ })}$ show $\rho$ to be linear in Cd concentration $x$ up to the solubility limit at 5 at.% Cd, with a slope of 0.042/(at.% Cd). The data for the tetragonal phase are not linear on a plot of $\frac{\Delta T_c}{x}$ versus $\ln x$, and thus do not fit the present theory of $T_c$ variation in primary solid solutions. At the tetragonal-cubic phase transition, $T_c$ jumps by 10% without change of electron/atom ratio, cell volume, or ionic mass. The superconductivity data are all consistent with the published phase diagram of Heumann and Predel.