PHASE-SLIP ANALYSIS OF THE NONOHMIC TRANSITION IN GRANULAR YBA2CU3O6.9

The resistive transition of granular YBa2Cu3O6.9 as a function of curr ent density (0.03 - 10 A/cm2) and magnetic field (0-75 G), applied per pendicular and parallel to the current direction, has been examined. T hese results are analyzed using the Ambegaokar-Halperin phase-slip the ory. By allowing the Josephson coupling energy (hI(c)BAR/e) to vary wi th current, temperature, and magnetic field, satisfactory agreement be tween theory and experiment has been obtained. Near T(c) we find the c oupling energy's temperature dependence to be (1-T/T(c))0.85 and its m agnetic field dependence to be H-1/2. This field and temperature depen dence is interpreted in terms of thermally activated flux creep.