Observation of Josephson vortex lattice melting in a highly anisotropic superconductor

The Josephson vortex lattice state of the highly anisotropic high-T_c superconductor Bi₂Sr₂CaCu₂O₈ has been probed by measurements of the out-of-plane (c-axis) resistivity as a function of temperature, current density, magnetic field strength H and magnetic field orientation angle θ. Anomalous dissipation is observed below a critical temperature identified as the melting transition of the Josephson vortex lattice. The critical T-H and T-θ phase boundaries are determined. The melting transition is interpreted as a Kosterlitz-Thouless depairing of interlayer vortex/anti-vortex pairs. The same model accounts well for unusual in-plane dissipation observed previously in Bi₂Sr₂CaCu₂O₈.