Critical Magnetic Fields of Cu-Pb-Cu Proximity-Effect Sandwiches Studied by Acoustic Surface Waves

The temperature dependence of the surface-wave attenuation in Cu-Pb-Cu sandwiches, in the absence of a magnetic field, agrees well with the BCS expression. We compare the temperature dependence of the parallel and perpendicular critical fields with expressions derived from the Ginzburg-Landau theory. We get satisfactory agreement, provided that for the thinner specimens we take the mean free paths in the proximity-effect sandwich to be somewhat smaller than the values found for monitor strips. This implies that some inter-diffusion between the Pb and the Cu is taking place.