Influence of the upper critical field anisotropy on the transport properties of polycrystalline MgB${}_2$

Abstract

The intrinsic properties of MgB${}_2$ form the basis for all applications of this superconductor. We wish to emphasize that the application range of polycrystalline MgB${}_2$ is limited by the upper critical field H${}_{c2}$ and its anisotropy. In wires or tapes, the MgB${}_2$ grains are randomly oriented or only slightly textured and the anisotropy of the upper critical field leads to different transport properties in different grains, if a magnetic field is applied and the current transport becomes percolative. The irreversibility line is caused by the disappearance of a continuous superconducting current path and not by depinning as in high temperature superconductors. Based on a percolation model, we demonstrate how changes of the upper critical field and its anisotropy and how changes of flux pinning will influence the critical currents of a wire or a tape. These predictions are compared to results of neutron irradiation experiments, where these parameters were changed systematically.

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• Connectivity and Critical Currents in Polycrystalline MgB2
• Disorder effects and current percolation in FeAs based superconductors
• Application prospects of MgB${}_2$ in view of its basic properties
• Effect of $\alpha$-particle irradiation on a NdFeAs(O,F) thin film
• The influence of weak texture on the critical currents in polycrystalline MgB${}_2$
• Consequences of the peculiar intrinsic properties of MgB2 on its macroscopic current flow