Superconductivity of Small Tin Particles Measured by Tunneling

We have used tunneling to study the superconductivity of small Sn particles imbedded in an oxide film. In contradiction to existing theories, no lower size limit for superconductivity has been found down to a particle radius $\mathcal{r}=25\mathrm{}$ Å. The junction characteristic shows a large peak in resistance at zero bias even for normal particles. This resistance maximum can be explained in terms of a capacitor model of the particle.