EVIDENCE FOR A VORTEX-LATTICE MELTING TRANSITION IN AN ORGANIC SUPERCONDUCTOR

We have observed a step in the equilibrium magnetization for the organic superconductor ${\mathrm{\ensuremath{\kappa}}\ensuremath{-}(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{F})}_{2}{\mathrm{Cu}[\mathrm{N}(\mathrm{CN})}_{2}$]Br characteristic of a transition of the flux-line solid to a liquid of flux lines. The entropy variation at the transition is found larger than that expected from the theory of the flux-line lattice melting in an anisotropic superconductor. We interpret the decrease of the magnetization step magnitude upon a more rapid cooling of the material to be the consequence of the creation of some strong pins.