Forced entanglement vs anisotropic dissipation in a vortex line liquid

We present evidence for forced topological entanglement of line-like vortices in the liquid regime of YBa2Cu3O7−δ with columnar defects. By splaying the defects within a fixed plane (in-fan) we create a c^– axis phase coherent vortex (string) structure which correlates with anisotropic dissipation. The high-field vortex motion is “easy” in fan and “hard” across fan in crystals–a signature of forced entanglement by a small angle splay. The high-field anisotropy is surprisingly reversed in thin films, where forced entanglement is absent. © 1997 American Physical Society.