Measurement of the nonlinear Meissner effect in superconducting Nb films using a resonant microwave cavity: A probe of unconventional pairing symmetries

TL;DR

This paper reports the detection of the nonlinear Meissner effect in Nb superconducting films using a resonant microwave cavity, providing a new method to investigate unconventional pairing symmetries in superconductors.

Contribution

It introduces a novel experimental approach employing low power RF probing in thin films to observe NLME under equilibrium conditions, aligning with theoretical calculations.

Findings

NLME observed in Nb films via resonance frequency shifts

Method enables probing of unconventional pairing symmetries

Data matches Usadel equation calculations

Abstract

We report observation of the nonlinear Meissner effect (NLME) in Nb films by measuring the resonance frequency of a planar superconducting cavity as a function of the magnitude and the orientation of a parallel magnetic field. Use of low power rf probing in films thinner than the London penetration depth, significantly increases the field for the vortex penetration onset and enables NLME detection under true equilibrium conditions. The data agree very well with calculations based on the Usadel equations. We propose to use NLME angular spectroscopy to probe unconventional pairing symmetries in superconductors.