Mixed-State Dissipation in Zero Temperature Limit in $Mg{B}_2$ Thin Films

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 $\ddot{I}€$-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.

4 pages, 5 figures