CURRENT-INDUCED ORGANIZATION OF VORTEX MOTION IN TYPE-II SUPERCONDUCTORS

When a magnetic held is applied to a type-II superconductor, it penetr ates the sample in localized tubes of magnetic flux associated with qu antized current vortices; under appropriate conditions, these vortices form an ordered lattice, In a material free of crystal defects, trans port currents force this lattice to move and dissipate energy, giving the material a non-zero resistance, The presence of defects, however, can inhibit vortex motion, or even I pin vortices to specific location s. Thus, to engineer materials with improved properties it is importan t to understand the motion of a driven vortex lattice in the presence of different kinds of pinning defects(1,2). Recent research has invest igated vortex-lattice dynamics in the cases of weak, uniform pinning a nd strong but non-uniform pinning. Here we consider a different regime , in which the barriers to vortex motion at sample surfaces' also play a crucial role. Our experiments on dean, detwinned YBa2Cu3O7-delta cr ystals at temperatures around 80-90K reveal an interplay between surfa ce pinning and weak bulk pinning that leads to the formation of a defe ct superstructure in the vortex lattice, This current-induced organiza tion is similar to phenomena observed in the dynamics of sliding charg e-density waves, and represents a fundamentally new kind of vortex dyn amics.