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

TL;DR

This study measures microwave penetration depth and quasiparticle conductivity in PrFeAsO$_{1-y}$ single crystals, providing evidence for a full superconducting gap and insights into the superfluid density and conductivity behavior.

Contribution

It presents experimental evidence for a full-gap superconducting state in PrFeAsO$_{1-y}$, challenging the nodal gap scenario in this material.

Findings

Flat low-temperature penetration depth indicates no nodes in the gap.

Superfluid density suggests a non-zero gap across the Fermi surface.

Enhanced microwave conductivity below $T_c$ exceeds coherence peak levels.

Abstract

In-plane microwave penetration depth $\lambda_{ab}$ 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. $\lambda_{ab}(T)$ shows flat dependence at low temperatures, which is incompatible with the presence of nodes in the superconducting gap $\Delta({\bf k})$. The temperature dependence of the superfluid density demonstrates that the gap is non-zero ($\Delta/k_BT_c\gtrsim 1.6$) 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.