PINNING AND VORTEX DYNAMICS IN SUPERCONDUCTING (K,BA)BIO3 SINGLE-CRYSTALS

Pinning and vortex dynamics have been investigated in the 3-dimensiona l copper free (K, Ba)BiO3 superconductor (T-c similar to 31K) by magne tization and transport measurements up to 30 Tesla. The magnetization curves present a pronounced fishtail effect which persists for time sc ales down to 10(-4)s (pulsed field measurements). We show that it is a n intrinsic feature of the critical current which can in part be well described by the collective pinning theory. Furthermore, this system p resents evidence for a vortex liquid/glass transition for vanishingly small currents. As the current density is increased, dissipation in th e glass state is dominated by creep effects. The temperature and curre nt dependence of the activation energy is discussed.