Abstract
We report high-sensitivity microwave measurements of the in-plane penetration depth and quasiparticle scattering rate in several single crystals of the hole-doped Fe-based superconductor (). While a power-law temperature dependence of with a power is found in crystals with large , 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 -wave cuprate superconductors with nodes in the gap. These results demonstrate intrinsically nodeless order parameters in the Fe arsenides.
- Received 20 October 2008
DOI:https://doi.org/10.1103/PhysRevLett.102.207001
©2009 American Physical Society