Boundary Scattering Effects on the Superconducting Transition Temperature of Indium

We have compared the superconducting transition temperature, $T_c$, of indium foils about 6 μ thick with that of an indium wire of diameter 250 μ. The foils were cold-rolled and then carefully annealed. At low temperatures the electron mean free path in the foils was primarily determined by scattering from the boundaries, as indicated by measurements of their residual resistivity. The transition temperature of the foils is lower than that of the wire by small but measurable amounts which agree with decreases in $T_c$ found in experiments with impure indium specimens of comparable resistivity. We conclude that the present measurements give additional support to the idea that limiting the electronic mean free path in indium results in a decrease in transition temperature independent of the mechanism determining the free path.