Consequences of the peculiar intrinsic properties of MgB2 on its macroscopic current flow

TL;DR

This paper investigates how MgB2's unique intrinsic properties, especially anisotropy and two-band superconductivity, affect its macroscopic current flow and critical current behavior in polycrystalline form.

Contribution

It provides a detailed analysis of MgB2's transport properties using a percolation model, highlighting the impact of anisotropy and fabrication techniques on critical current and pinning behavior.

Findings

Anisotropy of the upper critical field significantly affects current flow.

Two-band superconductivity has limited impact in practical conditions.

Grain boundary pinning dominates in MgB2 conductors.

Abstract

The influence of two important features of magnesium diboride on the macroscopic transport properties of polycrystalline MgB2 is discussed in the framework of a percolation model. While two band superconductivity does not have significant consequences in the field and temperature range of possible power applications, the opposite is true for the anisotropy of the upper critical field. The field dependence of the critical current densities strongly increases and the macroscopic supercurrents disappear well below the apparent upper critical field. The common scaling laws for the field dependence of the volume pinning force are altered and Kramer's plot is no longer linear, although grain boundary pinning dominates in nearly all polycrystalline MgB2 conductors. In contrast to the conventional superconductors NbTi and Nb3Sn, a significant critical current anisotropy can be induced by the preparation technique of MgB2 tapes.