Fluctuation conductivity of layered superconductors in a perpendicular magnetic field

The leading contributions to the c-axis conductivity of layered superconductors arising from superconducting fluctuations of the order parameter are discussed for arbitrary intralayer scattering. The contributions from fluctuations of the normal quasiparticle density of states are shown to be opposite in sign to the Aslamazov-Larkin and Maki-Thompson contributions, leading to a peak in the overall c-axis resistivity ${\mathrm{\rho }}_{\mathit{c}}$(T) above ${\mathit{T}}_{\mathit{c}}$. This peak is enhanced by a magnetic field H∥c^. With increasing H, the relative peak maximum in ${\mathrm{\rho }}_{\mathit{c}}$(T,H) increases in magnitude and is shifted to lower temperatures by an amount proportional to ${\mathit{H}}^2$ for weak fields and to H for strong fields. For comparison, the fluctuation conductivity parallel to the layers has been calculated including the fluctuations of the normal density of states. Our results are discussed in regard to recent experiments with ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$.