Anomalous Flux Flow Resistivity in Two Gap Superconductor MgB_2

TL;DR

This study measures the flux flow resistivity in MgB_2, revealing unusual field dependence due to its two-gap superconductivity, with distinct vortex dynamics and energy dissipation mechanisms.

Contribution

It provides the first detailed microwave surface impedance measurements of flux flow resistivity in MgB_2, highlighting the impact of two-gap superconductivity on vortex behavior.

Findings

Unusual field dependence of flux flow resistivity in MgB_2

Identification of a crossover field separating two flux flow regimes

Evidence that two superconducting gaps influence vortex dynamics

Abstract

The flux flow resistivity associated with purely viscous motion of vortices in high-quality MgB_2 was measured by microwave surface impedance. Flux flow resistivity exhibits unusual field dependence with strong enhancement at low field, which is markedly different to conventional s-wave superconductors. A crossover field which separates two distinct flux flow regimes having different flux flow resistivity slopes was clearly observed in H//ab-plane. The unusual H-dependence indicates that two very differently sized superconducting gaps in MgB_2 manifest in the vortex dynamics and almost equally contribute to energy dissipation. The carrier scattering rate in two different bands is also discussed with the present results, compared to heat capacity and thermal conductivity results.