Critical currents in weakly textured MgB2: Nonlinear transport in anisotropic heterogeneous media

A model for highly non-linear transport in heterogeneous media consisting of anisotropic particles with a preferred orientation is proposed and applied to the current transport in weakly textured magnesium diboride, MgB2. It essentially explains why, unlike in conventional superconductors, a significant macroscopic anisotropy of the critical currents can be induced by the preparation of MgB2 tapes. The field and angular dependence of the critical current is calculated for various degrees of texture and compared to experimental data.