Near-Tc second-harmonic emission in high-density bulk MgB2 at microwave frequency

TL;DR

This study investigates microwave second-harmonic generation in high-density MgB2, revealing how the harmonic signal varies with temperature and magnetic fields, and explaining the results with a two-fluid phenomenological model.

Contribution

It provides the first detailed analysis of second-harmonic emission in MgB2 using a two-fluid model considering temperature-dependent fluid densities.

Findings

Harmonic intensity varies with temperature and magnetic field amplitudes.

A linear temperature dependence of normal and superconducting fluid densities explains the results.

The phenomenological model successfully describes the experimental data.

Abstract

We discuss the microwave second-harmonic generation in high-density bulk MgB2, prepared by the reactive liquid Mg infiltration technology. The intensity of the harmonic signal has been investigated as a function of temperature and amplitudes of the DC and microwave magnetic fields. The results are discussed in the framework of a phenomenological theory, based on the two-fluid model, which assumes that both the microwave and static magnetic fields, penetrating in the surface layers of the sample, weakly perturb the partial concentrations of the normal and superconducting fluids. We show that, in order to account for the experimental results, it is essential to suppose that in MgB2 the densities of the normal and condensed fluids linearly depend on the temperature.