Ginzburg-Landau theory of layered superconductors: application to iron pnictides

We use the Ginzburg-Landau approach for a layered superconductor with a Josephson coupling between the layers to study the effects of fluctuations in recently discovered iron-based high temperature superconductors. While such effects are theoretically well understood in three- and particularly in two-dimensional systems, the special challenge posed by iron pnictides is their layered but still effectively three dimensional character. Using an approximation devised for this particular situation, we derive theoretical expressions for the fluctuation contributions to the free energy, magnetization, specific heat, and electrical conductivity. We compare our results with recent experimental data on the iron pnictide superconductors.