Microwave conductivity in the ferropnictides with specific application to Ba1-xKxFe2As2

We calculate the microwave conductivity of a two band superconductor with s(+/-) gap symmetry. Inelastic scattering is included approximately in a BCS model augmented by a temperature-dependent quasiparticle scattering rate assumed, however, to be frequency independent. The possibility that the s-wave gap on one or the other of the electron or hole pockets is anisotropic is explored including cases with and without gap nodes on the Fermi surface. A comparison of our BCS results with those obtained in the two-fluid model is provided as well as with the case of the cuprates where the gap has d-wave symmetry and with experimental results in Ba1-delta K delta Fe2As2. The presently available microwave conductivity data in this material provides strong evidence for large anisotropies in the electron pocket s-wave gap. While a best fit favors a gap with nodes on the Fermi surface this disagrees with some but not all penetration-depth measurements which would favor a nodeless gap as do also thermal-conductivity and nuclear-magnetic-resonance data.