UPPER CRITICAL FIELDS FOR SUPERCONDUCTING SUPERLATTICES

For the superconducting superlattices whose diffusion constant changes continuously, we study the upper critical field H(c2) and its angular derivative dH(c2)(theta)/d-theta at theta = 0, where theta is the angle between the layer plane and the applied magnetic field. The latter quantity shows whether the order parameter has a preferential position relative to the sample. From H(c2) and dH(c2) (theta = 0)/d-theta, we discuss the difference of this model from the model whose diffusion constant changes discontinuously at the interfaces and the Josephson coupling model.