COMPARISON OF DYNAMIC RELAXATION IN COLUMNAR DEFECTED AND VIRGIN BI2SR2CACU2O8 CRYSTALS

The dynamic relaxation rates in virgin and columnar defected BSCCO 221 2 crystals have Seen studied as a function of field and Temperature be tween 8 K and 28 K. The dynamic response of Vortices is examined using the hysteresis loop scaling technique developed by Perkins and Caplin (1996 Phys. Rev. 8 54 12 551). Far both virgin and irradiated crystal s, power law field dependences are found for the characteristic curren t and energy scales, inconsistent with the predictions of collective p inning theory. in the virgin crystals the power law exponent is strong ly temperature dependent. The temperature dependence vanishes in the c olumnar defected crystals. In both cases the behaviour can be understo od in terms of plastic dislocation mediated flux creep. In columnar de fected crystals at fields less than the matching field, the Anderson-K im activation energy is extracted and found to be proportional to H-1. 2. Above the matching field. the characteristic energy is found to be proportional to H-1/2 in agreement with simple plastic behaviour.