Pinning and vortex dynamics in superconducting (K,Ba)BiO 3 single crystals

Pinning and vortex dynamics have been investigated in the 3-dimensional copper free (K, Ba)BiO₃superconductor (T_c 31K) by magnetization and transport measurements up to 30 Tesla. The magnetization curves present a pronounced fishtail effect which persists for time scales down to 10^–4s (pulsed field measurements). We show that it is an intrinsic feature of the critical current which can in part be well described by the collective pinning theory. Furthermore, this system presents evidence for a vortex liquid /glass transition for vanishingly small currents. As the current density is increased, dissipation in the glass state is dominated by creep effects. The temperature and current dependence of the activation energy is discussed.