Guimpel, J., M. E. de la Cruz, F. de la Cruz, H. J. Fink, O. Laborde, and J. C. Villegier. "Size dependence of the Superconducting critical temperature and fields of Nb/Al multilayers." Journal of Low Temperature Physics 63, no. 1-2 (1986): 151–165.
Abstract: The critical temperatureT cof Nb/Al multilayers decreases as the total sample thicknessd Tis decreased while the thickness of each Nb and Al layer is kept constant. To understand this behavior, models based on the proximity effect and on weak two-dimensional (2D) localization are employed. The latter uses a characteristic length, the thermal diffusion length, in relation tod Tto obtain 2D behavior and leads to a reasonable explanation ofT c(d T). It is also found that the slope atT c(d T) of the critical magnetic field perpendicular to the layers is independent ofd Twhen the Nb and Al layer thicknesses are kept constant. The angular dependence of the critical field is also measured.