UPPER CRITICAL FIELDS OF SUPERCONDUCTING SUPERLATTICE

For the superconducting superlattices whose diffusion constant varies sinusoidally in one direction, we calculate the temperature dependence of the upper critical field H(c2), parallel to the layer plane. We further study the angular derivative dH(c2)(T,theta) /d-theta at theta = 0, where theta is the angle between the layer plane and the applied magnetic field. The results show that under certain conditions the center of order parameter changes continuously from the region with a large diffusion constant to that with a small one as the temperature decreases.