Domain wall motion in a polycrystalline vortex lattice*

We present transport measurements on superconductor-normal-superconductor (SNS) arrays studied in finite magnetic fields. By applying magnetic fields that correspond to an incommensurate filling factor (shifting the vortex lattice away from one that matches the SNS array), disorder within the system can be studied. By then driving vortex motion with applied current, we observed a two-step transition at the incommensurate fields, which demonstrates a transition from pinned vortices to lattice defect flow to lattice flow. This transport is suggestive of a polycrystalline structure with defects forming along the edges of the crystalline domain. These results inform the larger question of how disorder affects the vortex lattice.