Critical Fields in Layered Superconducting Systems

Layered systems are considered which behave as single, but anisotropic superconductors. Supposing a second order transition in the presence of an external field, the critical fields Hc2 and Hc3 in the GL region are calculated. Hc2 is a function of the angle θ between the magnetic field and the direction perpendicular to the layers; Hc3 depends on θ in the same way as Hc2, the ratio Hc3/Hc2 being the same as in the isotropic case (Hc3/Hc2 = 1.69). In the limiting case of thin layers it is found that Hc2 is independent of the period of the layered structure, and is larger in the parallel (θ: π/2) then in the perpendicular (θ = 0) case.