Microwave penetration depth and quasiparticle conductivity of PrFeAsO1-y single crystals: evidence for a full-gap superconductor.

In-plane microwave penetration depthab and quaiparticle conductivity at 28 GHz are measured in underdoped single crystals of the Fe-based superconductor PrFeAsO1 y (Tc � 35 K) by using a sensitive superconducting cavity resonator. �ab(T) shows flat dependence at low temperatures, which is incompatible with the presence of nodes in the superconducting gap �(k). The temperature dependence of the superfluid density demonstrates that the gap is non-zero (�/kBTc & 1.6) all over the Fermi surface. The microwave conductivity below Tc exhibits an enhancement larger than the coherence peak, reminiscent of high-Tc cuprate superconductors.