Time evolution of the microwave second-order response of YBaCuO powder

TL;DR

This study investigates the time-dependent microwave second-order response of YBaCuO powder, revealing different transient mechanisms at various time scales related to flux dynamics and magnetic relaxation.

Contribution

It provides a detailed analysis of the different physical processes governing the transient microwave response in YBaCuO powder over time.

Findings

Flux redistribution causes millisecond transient response.

Fluxon motion influences response within 10 seconds.

Surface barrier relaxation affects response over minutes.

Abstract

Transient effects in the microwave second-order response of YBaCuO powder are investigated. The time evolution of the second harmonic signal has been measured for about 300 s after the sample had been exposed to variations of the DC magnetic field. We show that in different time scales the transient response has different origin. In the time scale of milliseconds the transient response of samples in the critical state is ascribable to processes of flux redistribution induced by the switching on/off of the microwave field. At longer times, the time evolution of the second harmonic signal can be ascribed to motion of fluxons induced by the variation of the DC magnetic field. In particular, diffusive motion of fluxons determines the response in the first 10 seconds after the stop of the magnetic field variation; magnetic relaxation over the surface barrier determines the response in the time scale of minutes.