Effect of randomly distributed anisotropic vortices on the critical current of a layered superconductor

We have studied the magnetic field dependence of the c-axis critical current of a layered superconductor when a pinned, disordered lattice of anisotropic vortices parallel to the superconducting planes is present. The model employed is based on the Josephson coupling picture of layered superconductors. In this case, the Josephson phase between adjacent layers varies randomly along the superconducting planes and its spatial correlations determine the value of an average critical current scale. We show that under these conditions the usual Fraunhofer oscillations are absent and this critical current is proportional to exp(−H ext / H ̃ 0) , where H ̃ 0 is crucially determined by the anisotropy and depends weakly on the size of the superconductor. The relevance of our results to transport properties recently observed in the high- T c cuprates is discussed.