Anisotropic vortex dynamics in twinned YBa2Cu3O7 single crystal

Rotating continuously the applied vortex force and measuring the vortex vel ocity vector, we were able to directly determine the role of twin boundarie s in the vortex dynamics in YBa2Cu3O7 single crystals with unidirectional t wins. We show the different effect of these correlated pinning defects into the various vortex phases. In the entangled vortex liquid state, we observ e a linear response but with an anisotropic viscosity. On the other hand, a n anomalous guided motion by twin planes is found in the vortex solid. (C) 2000 Elsevier Science B.V. All rights reserved.