Microwave Second-Harmonic Response of Ceramic MgB2 Samples

TL;DR

This study investigates the nonlinear microwave second-harmonic response of ceramic MgB2 samples, revealing different mechanisms at play across temperature ranges, including weak links at low temperatures and order parameter modulation near Tc.

Contribution

It provides a detailed analysis of the temperature-dependent nonlinear microwave response in MgB2, highlighting distinct mechanisms responsible for harmonic generation.

Findings

Nonlinear response at low temperatures is due to weak links.

Near Tc, harmonic emission is influenced by order parameter modulation.

Different mechanisms dominate in different temperature ranges.

Abstract

Nonlinear microwave response of different ceramic MgB2 samples has been investigated by the technique of second-harmonic emission. The second-harmonic signal has been investigated as a function of temperature, DC magnetic field and input microwave power. The attention has mainly been devoted to the response at low magnetic fields, where nonlinear processes arising from motion of Abrikosov fluxons are ineffective. The results show that different mechanisms are responsible for the nonlinear response in the different ranges of temperature. At low temperatures, the nonlinear response is due to processes involving weak links. At temperatures close to Tc, a further contribution to the harmonic emission is present; it can be ascribed to modulation of the order parameter by the microwave field and gives rise to a peak in the temperature dependence of the harmonic signal.