Microwave conductivity in the ferropnictides with specific application to Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$

Abstract

We calculate the microwave conductivity of a two band superconductor with $s^{\pm }$ 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 (TFM) is provided as well as with the case of the cuprates where the gap has d-wave symmetry and with experimental results in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$. 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 node-less gap as do also thermal conductivity and nuclear magnetic resonance data.

12 pages, 9 figures. Phys. Rev. B (submitted)

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• Optical conductivity of iron-based superconductors
• Nodes in the Order Parameter of Superconducting Iron Pnictides Observed by Infrared Spectroscopy
• Unusual microwave response and bulk conductivity of very thin fese0.3te0.7 films as a function of temperature
• On the determination of the quasiparticle scattering rate in unconventional superconductors by microwave surface impedance