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

Abstract

We have measured the effect of dilute alloying on the strain ($\ensuremath{\epsilon}$) 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 $\frac{\ensuremath{\partial}{T}_{c}}{\ensuremath{\partial}\ensuremath{\epsilon}}$, but the addition of Cd had a large effect. The initial slope of the ${T}_{c}$-vs-$\ensuremath{\epsilon}$ curve, ${(\frac{\ensuremath{\partial}{T}_{c}}{\ensuremath{\partial}\ensuremath{\epsilon}})}_{\ensuremath{\epsilon}=0}$, 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, ${(\frac{\ensuremath{\partial}{T}_{c}}{\ensuremath{\partial}\ensuremath{\epsilon}})}_{\ensuremath{\epsilon}=0}$ increased to almost its value for pure In. The curves ${T}_{c}$ vs $\ensuremath{\epsilon}$ were linear in $\ensuremath{\epsilon}$ for $0\ensuremath{\le}x\ensuremath{\le}0.3$ and for $xg2$ at.%. For $0.3lx\ensuremath{\le}0.9$-at.% Cd, $\frac{{\ensuremath{\partial}}^{2}{T}_{c}}{\ensuremath{\partial}{\ensuremath{\epsilon}}^{2}}$ was negative, while for $0.9lxl2$-at.% Cd it was positive. For alloys with more than about 2.0-at.% Cd, ${T}_{c}$ was linear in $\ensuremath{\epsilon}$. This behavior is attributed to a change in the topology of the Fermi surface occurring at about 0.9-at.% Cd in In.