Abstract
In-plane microwave penetration depth and quasiparticle conductivity at 28 GHz are measured in underdoped single crystals of the Fe-based superconductor () by using a sensitive superconducting cavity resonator. shows flat dependence at low temperatures, which is incompatible with the presence of nodes in the superconducting gap . The temperature dependence of the superfluid density demonstrates that the gap is nonzero () all over the Fermi surface. The microwave conductivity below exhibits an enhancement larger than the coherence peak, reminiscent of high- cuprate superconductors.
- Received 20 June 2008
DOI:https://doi.org/10.1103/PhysRevLett.102.017002
©2009 American Physical Society