Thermally activated depinning in an organic superconductor: Universal behavior of the flux-line lattice in layered superconductors

Abstract

With the vibrating reed technique we have measured the field dependence of the depinning temperature of the flux-line-lattice (depinning lines) in the organic superconductor κ-(BEDT-TTF) 2Cu(NCS) 2 for different magnetic field orientations. In a reduced temperature scale the depinning lines are similar to those measured in the high temperature superconductor Bi 2Sr 2CaCu 2O 8 in spite of a factor ten difference in the critical temperature. We find that the effective activation barriers for flux motion divided by the thermal energy at the critical temperature are similar for both superconductors. The results can be understood with the thermally activated flux flow model and suggest a rather universal behavior of the thermally activated depinning in layered superconductors. We further show that a small misalignment of the superconducting crystal with the applied magnetic field gives rise to two dissipation peaks; this effect can be quantitatively understood taking into account two diffusivity modes.