Microwave Surface-Impedance Measurements of the Magnetic Penetration Depth in Single Crystal Ba1 xKxFe2As2 Superconductors: Evidence for a Disorder-Dependent Superfluid Density

4 pagesInternational audienceWe report high-sensitivity microwave measurements of the in-plane penetration depth ab and quasiparticle scattering rate 1= in several single crystals of the hole-doped Fe-based superconductor Ba1 xKxFe2As2 (x 0:55). While a power-law temperature dependence of ab with a power 2 is found in crystals with large 1= , we observe an exponential temperature dependence of the superfluid density consistent with the existence of fully opened two gaps in the cleanest crystal we studied. The difference may be a consequence of different levels of disorder inherent in the crystals. We also find a linear relation between the low-temperature scattering rate and the density of quasiparticles, which shows a clear contrast to the case of d-wave cuprate superconductors with nodes in the gap. These results demonstrate intrinsically nodeless order parameters in the Fe arsenides