NONOHMIC BEHAVIOR IN TL-2212 FILMS IN A WEAK MAGNETIC-FIELD

A power law, V similar to I-a, between voltage and current is reported in a T1-2212 thin film in a weak magnetic field (up to 300 mT) applie d perpendicularly to the layers. We find experimental support for the existence of a phase transition depending on magnetic field, below the zero magnetic field transition T-CO. We discuss these results in term s of a defect-mediated vortex-lattice (VL) melting leading to a Berezi nskii-Kosterlitz-Thouless transition type. Consistency is found with a logarithmic coupling energy U(r) = A In(r/r(o)) between VL defects wh ere the unrenormalized interaction constant A similar to T(Tco-T)(3/2) /H and the Abrikosov lattice parameter sets the cut-off r(o).