New continuous model for intrinsic layered superconductors

We propose a new Ginzburg-Landau model for intrinsic layered superconductors. In this model the spatial dependent coefficients in the Ginzburg-Landau free energy are assumed to describe the layer structure. This model mediates between the homogeneous anisotropic effective mass model and the Lawrence-Doniach model. Solving the GL equations numerically, we calculated, we calculate the upper critical fields parallel and perpendicular to the layers, H_c2¹ and H_c2^∥. The temperature dependence of H_c2¹ shows the crossover behavior from 3D to 2D as temperature decreases. We also calculate the lower critical fields parallel and perpendicular to the layers in the high-k limit. In superconductors with strong layer nature the flux line state parallel to the layers may be unstable at high temperatures near T_c.