Lower Critical Fields of Superconducting PrFeAsO$_{1-y}$ Single Crystals

TL;DR

This study investigates the lower critical fields of PrFeAsO_{1-y} single crystals, revealing insights into anisotropy and multiband superconductivity, and highlighting measurement considerations for accurate H_{c1} determination.

Contribution

It provides detailed measurements of H_{c1} in PrFeAsO_{1-y} crystals, demonstrating the multiband nature and anisotropic properties of this superconductor.

Findings

H_{c1} for H || c scales with in-plane penetration depth

Anisotropy of penetration lengths is approximately 2.5 at low temperatures

Local induction measurements near the crystal center may overestimate H_{c1}

Abstract

We have studied the lower critical fields H_{c1} of superconducting iron oxipnictide PrFeAsO_{1-y} single crystals for H parallel and perpendicular to the ab-planes. Measurements of the local magnetic induction at positions straddling the sample edge by using a miniature Hall-sensor array clearly resolve the first flux penetration from the Meissner state. The temperature dependence of H_{c1} for H || c is well scaled by the in-plane penetration depth without showing any unusual behavior, in contrast to previous reports. The anisotropy of penetration lengths at low temperatures is estimated to be ~ 2.5, which is much smaller than the anisotropy of the coherence lengths. This is indicative of multiband superconductivity in this system, in which the active band for superconductivity is more anisotropic. We also point out that the local induction measured at a position near the center of the crystal, which has been used in a number of reports for the determination of H_{c1}, might seriously overestimate the obtained H_{c1}-value.