Penetration Depth and Quasiparticle Conductivity in Iron-based High-Temperature Superconductors

We measure the in-plane penetration depth and the quasiparticle conductivity in the newly discovered Fe-based high-temperature superconductors PrFeAsO_1-y[1] and Ba_1-xK_xFe₂As₂[2], using a sensitive superconducting resonator. We show that the penetration depth exhibits a very flat behavior at low temperatures in both compounds, which indicates that the superconducting gap opens up all over the Fermi surface. The temperature dependence of the superfluid density is well fitted with the two gap model, suggesting the multi-gap nature of superconductivity in this system. Moreover, the observed large enhancement of the quasiparticle conductivity suggests a suppression of the quasiparticle scattering, reminiscent of the superconductors in strongly correlated electronic systems.[1] K. Hashimoto et al., arXiv:0806.3149., [2] K. Hashimoto et al., arXiv:0810.3506.