Mixed-State Dissipation in Zero Temperature Limit in $MgB_2$ Thin Films

TL;DR

This study reveals that MgB$_2$ thin films exhibit persistent vortex-related dissipation at zero temperature, driven by two-band superconductivity and quasiparticle proliferation, unlike single-gap superconductors.

Contribution

It demonstrates that two-band superconductivity in MgB$_2$ enhances vortex quantum fluctuations, leading to finite zero-temperature dissipation, a novel insight into vortex dynamics.

Findings

Finite zero-temperature dissipation due to vortex motion in MgB$_2$

Dissipation linked to quasiparticles from the $ ext{pi}$-band

Vortex quantum fluctuations are enhanced by two-band effects

Abstract

We have studied mixed-state dissipation in epitaxial MgB$_2$ thin films by measurements of resistive transition, current-voltage characteristics, Hall effect, and point-contact tunnelling spectrum. We found that unlike single gap superconductors with negligible vortex quantum fluctuations in which vortices are frozen at T=0 K, finite zero-temperature dissipation due to vortex motion exists in MgB$_2$ over a wide magnetic field range. This dissipation was found to be associated with proliferation of quasiparticles from the $\pi$-band of MgB$_2$. The result shows that the vortex fluctuations are enhanced by two-band superconductivity in MgB$_2$ and we suggest that the vortex quantum fluctuation is a possible cause of the non-vanishing zero-temperature dissipation.