Anomalous Hall effect in superconductors near their critical temperatures

Measurements on epitaxial YBa2Cu3O7 thin films show that the Hall voltage just below the superconducting transition temperature has sign opposite to the Hall voltage in the normal state. This can result either from quasiparticle effects, or from unusual vortex motion. Because we observe a similar effect in Nb thin films, we argue that vortex motion is responsible. A simple interpretation of the Hall effect then requires that the vortex velocity have a component antiparallel to the transport current. This motion, while contrary to existing flux flow models, could result from vortex motion damping similar to that expected in superfluid 4He