CURRENT-DENSITY DEPENDENCE OF THE VORTEX PINNING ENERGY IN YBACUO

Measurements of the electrical resistivity, using pulsed currents of v arious magnitudes, in the mixed state of YBaCuO microbridges are repor ted. The onset of resistance follows a thermally activated behaviour o f flux line motion. The dependence of the pinning potential barrier U on the current density j was investigated revealing two distinctly dif ferent regions. At moderate current densities j < 10(4) A/cm2, no chan ge of U upon current density was observed. We associate this behaviour with thermally assisted flux flow. At high current densities, U decli nes logarithmically, in accordance with the flux creep picture and a p articular pinning potential well proposed by Zeldov et al.