Dimensional crossover and finite size effects in superconducting films

Using the Ginzburg-Landau description of dirty and anisotropic superconductors, the dependence of Tc and of the upper critical field H∥c2 on film thickness are traced back to a finite size effect, corresponding to a dimensional crossover. Since the strength of fluctuations increases with reduced dimensionality, their effect is to decrease the transition temperature. If the film thickness exceeds the low temperature value of the perpendicular correlation length, the crossover can also be seen in the temperature dependence of H∥c2. Our analysis of the experimental data for Fe/V/Fe sandwiches and Pb/Ge superlattices clearly reveals this crossover phenomenon. © 1991.