Temperature, current, and magnetic-field dependence of the activation energy in the vortex-glass phase of (K, Ba single crystals

We have investigated the vortex dynamics of (K, Ba)(Formula presented) single crystals below the vortex liquid/glass transition. The activation energy U extracted from transport measurements presents a crossover from a (Formula presented) to a ln(J) behavior. The latter expression has been attributed to the existence of a glass transition regime which extends over a large part of the J-T phase diagram. We show that the temperature dependence of U lies entirely in μ(T): close to transition, the vortex glass structure is prevailing (μ→0.2), but becomes negligible at low temperature where creep effects may be controlled by the elastic properties of the vortex lattice (μ→1). The magnetic-field dependence of U is also discussed.