Role of grain boundary networks in vortex motion in superconducting films

Abstract

We studied the vortex dynamics of the polycrystalline superconductors in the presence of both random point defects and the generated grain boundary (GB) networks with voronoi diagram. The synergistic effect of adjacent GBs on restricting the vortex motion in intragranular region is proposed and the corresponding intensity factor of the synergistic effect which characterizes the strength of the synergistic restriction of adjacent grain boundaries is also defined in the present paper. The interconnected GBs offer easy-flow channels for vortices in addition to pinning effects on the vortices. The combined channels and the vortex flow patterns in the superconducting film are analyzed in detail from molecular dynamics simulations. Furthermore, it is discovered that the critical current increases with decreasing magnetic field intensity, temperature, and the average grain size. The large number of vortices results in the enhanced repulsive interaction forcing the vortices moving out from the GBs. The thermal depinning from GBs leads to the lower Lorentz force range. The increase of the grain size causes the number of GBs decreasing. In summary, these effects result in the critical current being a decreasing function of magnetic field, temperature, and grain size.