Fermi-Surface Topology Changes in In Alloys Deduced from the Behavior ofTcunder Strain

We have measured the effect of dilute alloying on the strain ($\epsilon$) dependence of the superconducting transition temperature $T_c$ of In whiskers. Alloy contents $x$ ranged up to 0.1-at.% Ag, 1.5-at.% Sn, and 3-at.% Cd. The addition of Ag and Sn did not affect $\frac{\partial T_c}{\partial \epsilon }$, but the addition of Cd had a large effect. The initial slope of the $T_c$-vs-$\epsilon$ curve, ${\left(\frac{\partial T_c}{\partial \epsilon }\right)}_{\epsilon =0\mathrm{}}$, decreased with increasing Cd content until at 0.9 at.% it was a minimum of 15 mK/%, one-fourth of its value for pure In. As $x$ increased from 0.9- to 2-at.% Cd, ${\left(\frac{\partial T_c}{\partial \epsilon }\right)}_{\epsilon =0\mathrm{}}$ increased to almost its value for pure In. The curves $T_c$ vs $\epsilon$ were linear in $\epsilon$ for $0\le x\le 0.3$ and for $x>\mathrm{}2\mathrm{}$ at.%. For $0.3<x\le 0.9$-at.% Cd, $\frac{{\partial }^2{T}_c}{\partial {\epsilon }^2}$ was negative, while for $0.9<x<\mathrm{}2\mathrm{}$-at.% Cd it was positive. For alloys with more than about 2.0-at.% Cd, $T_c$ was linear in $\epsilon$. This behavior is attributed to a change in the topology of the Fermi surface occurring at about 0.9-at.% Cd in In.