First critical field measurements of superconducting films by third harmonic analysis

TL;DR

This paper introduces a contactless inductive method using third harmonic analysis to accurately measure the first critical magnetic field ($B_{C1}$) in superconducting thin films, validated on various materials.

Contribution

The study presents a novel, contactless technique for determining $B_{C1}$ in superconducting films using third harmonic voltage analysis, with detailed conditions for quantitative evaluation.

Findings

Accurate $B_{C1}$ measurements for Nb, NbN, MgB$_{2}$, and YBCO films.

Good agreement with literature and theoretical models.

Method is non-invasive and highly precise.

Abstract

The temperature behaviour of the first critical field ($B_{C1}$) of superconducting thin film samples can be determined with high accuracy using an inductive and contactless method. Driving a sinusoidal current in a single coil placed in front of the sample, a non zero third harmonic voltage $V_{3}$ is induced in it when Abrikosov vortices enter the sample. Conditions to be satisfied for the quantitative evaluation of $B_{C1}$ using this technique are detailed. As validation test, different type II superconductors (Nb, NbN, MgB$_{2}$ and Y$_{1}$Ba$_{2}$Cu$_{3}$O$_{7-d}$ under the form of thin films) have been measured. The comparison between experimental results, data presented in literature and theoretical predictions is presented and discussed.