Agreement between local and global measurements of the London penetration depth

TL;DR

This study compares local and global measurements of the London penetration depth in a superconductor, finding that discrepancies in previous studies are due to sample differences rather than measurement techniques.

Contribution

The paper demonstrates that local and global measurement techniques yield consistent results on the same sample, clarifying the source of previous discrepancies.

Findings

Local and global measurements agree on the same sample.

Discrepancies in prior studies are due to sample differences.

Measurement techniques are consistent when applied to the same sample.

Abstract

Recent measurements of the superconducting penetration depth in Ba(Fe_1-x Co_x)2As2 appeared to disagree on the magnitude and curvature of {\Delta}{\lambda}_{ab}(T), even near optimal doping. These measurements were carried out on different samples grown by different groups. To understand the discrepancy, we use scanning SQUID susceptometry and a tunnel diode resonator to measure the penetration depth in a single sample. The penetration depth observed by the two techniques is identical with no adjustments. We conclude that any discrepancies arise from differences between samples, either in growth or crystal preparation.