General expression for the angular dependence of the critical field in layered superconductors

Starting from the Ginzburg-Landau equation we derive an analytical expression for the angular and temperature dependence of the critical field in layered superconducting materials, This formula is shown to reproduce as the limiting cases the well known results of Tinkham for the isolated film of finite thickness and of Lawrence-Doniach for the stacked array of films of zero thickness with its particular anisotropic Ginzburg-Landau limit. Since this general formula is very simple, we suggest that it should be used in all cases where the dimensional crossover of the critical field is studied.