Superconductivity and lattice dynamics of granular tin

The superconducting transition temperature was measured in samples of 45-Å Sn grains embedded in a tin oxide matrix. The Debye temperature of the same samples was measured by the Mössbauer effect in¹¹⁹Sn in order to detect possible changes in the phonon spectrum. It was found that T_c is enhanced by 10% and γ is decreased by 4% relative to the bulk. Both trends are found to fit quantitatively with McMillan's theory of strong-coupling superconductors. The microstructure and the chemical composition of the samples were thoroughly studied by electron microscopy and the Mössbauer hyperfine interaction. Several conclusions were derived on the nature of the grains and their interaction with the dielectric coating.