Microwave Penetration Depth and Quasiparticle Conductivity in PrFeAsO_1-y Single Crystals : Evidence for a Full-Gap Superconductor

Abstract

In-plane microwave penetration depth $\hat{I}{»}_{ab}$ and quaiparticle conductivity at 28 GHz are measured in underdoped single crystals of the Fe-based superconductor PrFeAsO${}_{1-y}$ ($T_c\approx 35$ K) by using a sensitive superconducting cavity resonator. $\hat{I}{»}_{ab}(T)$ shows flat dependence at low temperatures, which is incompatible with the presence of nodes in the superconducting gap $\hat{I}”(\mathbf{k})$. The temperature dependence of the superfluid density demonstrates that the gap is non-zero ($\hat{I}”/k_B{T}_c\gtrsim 1.6$) all over the Fermi surface. The microwave conductivity below $T_c$ exhibits an enhancement larger than the coherence peak, reminiscent of high-$T_c$ cuprate superconductors.

4 pages, 3 figures. Version accepted for publication in Phys. Rev. Lett. For related results of hole-doped 122 system, see arXiv:0810.3506