Microwave Penetration Depth and Quasiparticle Conductivity of PrFeAsO1-y Single Crystals: Evidence for a Full-Gap Superconductor
In-plane microwave penetration depth λab and quasiparticle conductivity at 28 GHz are measured in underdoped single crystals of the Fe-based superconductor PrFeAsO1-y (Tc≈35K) by using a sensitive superconducting cavity resonator. λab(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 nonzero (∆/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.