Flow Induced Organization and Memory of a Vortex Lattice

We report on the evolution of a vortex state in response to a driving current in 2H-NbSe2 crystals. By using fast transport measurements we find that the current enables the system to reorganize and access new configurations. During this process the system exhibits a long-term memory: if the current is turned off the vortices freeze in place remembering their prior motion. When the current is restored the motion resumes where it stopped. The experiments provide evidence for a current driven structural change of the vortex lattice and a corresponding dynamic phase diagram that contains a previously unknown regime where the critical current can be either increased or decreased by applying an appropriate current. copyright 1999 The American Physical Society