Excess current in point contacts on two-band superconductor MgB$_2$ in magnetic field

TL;DR

This study investigates the excess current in point contacts on MgB$_2$, a two-band superconductor, under magnetic fields up to 9 T, and compares experimental results with theoretical models for the mixed state.

Contribution

It provides experimental measurements of excess current in MgB$_2$ point contacts and analyzes them using a theoretical model for the mixed state of a two-band superconductor.

Findings

Magnetic field dependence of excess current was obtained.

Data qualitatively agree with theoretical behavior of $\sigma$ and $\pi$-band order parameters.

A simple model describes the excess current in the mixed state.

Abstract

Series of $I(V)$ characteristic and bias-dependent differential resistance $dV/dI(V)$ for point-contacts on the single crystals of two-band superconductor MgB$_2$ were measured in magnetic field up to 9 T. We have obtained magnetic field dependences of the excess current on the $I(V)$ curves and analyzed them using Koshelev and Golubov (Phys. Rev. Lett. {\bf 90}, 177002 (2003)) theoretical results for the mixed state of a dirty two-band superconductor. Introducing a simple model for the excess current in the point contact in the mixed state our data can be qualitatively described utilizing theoretical magnetic filed behavior of the $\sigma$ and $\pi$-band superconducting order parameters and the corresponding averaged electronic density of states in MgB$_2$.