London penetration depth measurements using tunnel diode resonators

TL;DR

This paper discusses the development and application of a tunnel-diode resonator technique for precise measurements of the London penetration depth in superconductors, aiding the understanding of their pairing mechanisms.

Contribution

It introduces a novel, highly sensitive method for measuring the London penetration depth in small superconducting samples, enhancing the study of unconventional superconductivity.

Findings

High-precision measurements of λ(T) in various superconductors

Application to copper oxides and iron-based superconductors

Widespread adoption of the technique by research groups

Abstract

The London penetration depth $\lambda$ is the basic length scale for electromagnetic behavior in a superconductor. Precise measurements of $\lambda$ as a function of temperature, field, and impurity scattering have been instrumental in revealing the nature of the order parameter and pairing interactions in a variety of superconductors discovered over the past decades. Here we recount our development of the tunnel-diode resonator technique to measure $\lambda$ as a function of temperature and field in small single crystal samples. We discuss the principles and applications of this technique to study unconventional superconductivity in the copper oxides and other materials such as iron-based superconductors. The technique has now been employed by several groups worldwide as a precision measurement tool for the exploration of new superconductors.