Effects of Weak Links in the Nonlinear Microwave Response of MgB2 Superconductor

TL;DR

This study investigates the microwave second-harmonic response of MgB2 superconductors, revealing that weak links significantly influence their nonlinear behavior, with effects varying based on sample preparation and purity.

Contribution

It provides experimental insights into how weak links affect the nonlinear microwave response of MgB2, highlighting the impact of preparation methods and material purity.

Findings

Weak links dominate low-temperature SH emission in MgB2.

Sample preparation and purity affect weak link presence and SH response.

Nonlinear processes from fluxon motion are negligible at low fields.

Abstract

We report experimental results of second-harmonic (SH) response at microwave frequency in several ceramic MgB2 samples, prepared by different methods. The SH signal has been investigated as a function of the temperature and DC magnetic field. The investigation has been carried out at low magnetic fields, where nonlinear processes arising from motion of Abrikosov fluxons are ineffective. We show that the low-temperature SH emission is ascribable to processes involving weak links. Comparison among the peculiarities of the SH signal radiated by the different samples shows that the presence of weak links strongly depends on the sample preparation method, as well as the purity and morphology of the components used for the preparation.