TRANSITION-TEMPERATURE AND UPPER CRITICAL FIELDS FOR SUPERCONDUCTING SUPERLATTICES

We numerically calculate the transition temperature and the upper critical fields for superconducting superlattices with spatial variations of the BCS interaction, the density of states and the diffusion constant. For the superlattices composed of thin layers, the Debye cutoff frequency plays a role to make the states with large eigen-values less important. By virtue of this, a simple expression for the perpendicular upper critical field H(c2) perpendicular to is obtained, if the diffusion constants are same in both thin layers.