Dissipative Flux Motion in the High Temperature Superconductors

Thermally activated flux motion or flux creep is shown important for a description of the electromagnetic properties of the high-temperature superconductors. We have measured the resistance below T sub c of single crystals of several high T sub c materials in magnetic fields up to 12T. The resistive transition is dominated by intrinsic dissipation, which is thermally activated, resulting in an exponential temperature dependence of the resistivity well below T sub c. This dissipation is ohmic (=linear I-V-curves) and occurs for currents much smaller than the depinning critical current, limiting the current carrying capacity of the oxide superconductors in large magnetic fields at 77K.