Critical fields of weakly and strongly coupled superconducting multilayers

The authors have compared the parallel (H c2 //) and perpendicular (H c2 perpendicular to ) upper critical field of superconducting multilayers with strong and weak interlayer coupling (Pb/Cu, Pb/Ge). The temperature dependence of H c2 // reflects the expected dimensionality of the multilayers and can be interpreted in terms of the Takahashi-Tachiki proximity coupling model. In contrast with the strongly coupled Pb/Cu multilayers, weakly coupled Pb/Ge multilayers exhibit a strong thickness dependence of H c2 perpendicular to . The electronic diffusion coefficient in Pb/Ge, obtained from H c2 perpendicular to data, is not in agreement with the value calculated from the normal state resistivity. The disagreement reflects the highly inhomogeneous nature of the weakly coupled Pb/Ge multilayers.