Fluxon dynamics by microwave surface resistance measurements in MgB2

TL;DR

This study investigates the microwave surface resistance in MgB2, revealing unconventional vortex behavior at low temperatures likely due to two-gap superconductivity, and confirming flux-flow dynamics near Tc with anisotropy considerations.

Contribution

It provides new insights into vortex dynamics in MgB2, highlighting the role of two-gap effects and anisotropy in microwave surface resistance behavior.

Findings

Unconventional Rs(H) features at low temperatures suggest two-gap vortex structure.

Near Tc, Rs(H) behavior aligns with flux-flow model considering anisotropy.

Results support the complex vortex dynamics in MgB2 due to its unique superconducting properties.

Abstract

Field-induced variations of the microwave surface resistance, Rs(H), have been investigated in high-density ceramic MgB2. At low temperatures, several peculiarities of the Rs(H) curves cannot be justified in the framework of models reported in the literature. We suggest that they are ascribable to the unconventional vortex structure in MgB2, related to the presence of two gaps. On the contrary, the results near Tc can be accounted for by the Coffey and Clem model, with fluxons moving in the flux-flow regime, provided that the anisotropy of the upper critical field is taken into due account.