Depinning frequency in a heavily neutron-irradiated MgB2 sample

TL;DR

This study investigates the microwave surface resistance variations in heavily neutron-irradiated MgB2, analyzing the depinning frequency's field dependence and revealing higher values than in conventional superconductors.

Contribution

It provides the first detailed analysis of depinning frequency in neutron-irradiated MgB2 using the Coffey and Clem model, highlighting effects of irradiation on vortex pinning.

Findings

Depinning frequency increases with magnetic field and varies with temperature.

Irradiation causes the two gaps in MgB2 to merge into a single gap.

Depinning frequency at low temperatures exceeds that of typical low-temperature superconductors.

Abstract

The magnetic-field-induced variations of the microwave surface resistance have been investigated in a heavily neutron-irradiated MgB2 sample, in which the irradiation has caused the merging of the two gaps into a single value. The experimental results have been analyzed in the framework of the Coffey and Clem model. By fitting the experimental data, we have determined the field dependence of the depinning frequency, omega_0, at different values of the temperature. Although the pinning is not particularly effective, the value of omega_0 obtained at low temperatures is considerably higher than that observed in conventional low-temperature superconductors.