Contactless measurement of nonlinear conductivity in the radio-frequency range

TL;DR

This paper introduces a contactless system for measuring nonlinear conductivity in the radio-frequency range across various temperatures, utilizing non-resonant and resonant circuits for excitation and detection.

Contribution

It presents a novel contactless measurement method with adaptable procedures for high power excitation, validated on superconducting and nematic transitions.

Findings

Successful measurement of nonlinear response at superconducting transition

Effective detection of nematic transition in iron pnictide

System operates over a wide temperature range

Abstract

We have developed a system for contactless measurement of nonlinear conductivity in the radio-frequency band, and over a wide temperature range. A non-resonant circuit is used to electrically excite the sample, and the induced signal is detected by a resonant circuit whose natural frequency matches higher harmonics of the excitation. A simple modification of the probe allows non-resonant detection suitable for stronger signals. Two measurement procedures are proposed that allow significant excitation power variation, up to 150 W. The apparatus has been validated trough the measurement of the nonlinear response at the superconducting transition of a high-Tc superconductor, and the nematic transition of an iron pnictide.