Periodic nanostructured pins and the anomaly in the critical depinning force

For the first time, molecular dynamic simulations based on dense nanostructured periodic arrays of pinning sites were carried out. The variables in the simulations were the vortex density, the temperature, the pinning strength, the size of pinning sites. An interesting dip was found to occur in the critical current density but only at zero temperature and for specific values of pinning strength. The properties of the dip were found to depend strongly on the initial positions of the vortices with respect to the positions of the pinning sites. The occurrence of the dip is attributed to the formation of one dimensional linear channels of moving vortices in the direction of the applied current. The pinning strength was also found to have an important role in determining the relative depth of the dip.