Time Evolution of the Microwave Second-Harmonic Response of MgB2 Superconductor

TL;DR

This study investigates the time-dependent microwave second-harmonic response of MgB2 superconductors, revealing fluxon diffusion initially and surface barrier relaxation over minutes, enhancing understanding of their dynamic magnetic properties.

Contribution

It provides the first detailed analysis of the transient second-harmonic response in MgB2, distinguishing fluxon motion and surface barrier effects over different timescales.

Findings

Initial seconds show fluxon diffusive motion influence.

Minutes-long response dominated by surface barrier relaxation.

Transient effects are significant for understanding superconductor dynamics.

Abstract

We report on transient effects in the microwave second-order response of two ceramic MgB2 samples. The time evolution of the second-harmonic signal is investigated for about 500 s after the sample has been exposed to a variation of the dc magnetic field. We suggest that during the first seconds the response is determined by diffusive motion of fluxons, while in the time scale of minutes it is ruled by magnetic relaxation over the surface barrier.