Evidence for collective δ <i>T</i> _<b>c</b> pinning in superconducting (K,Ba)BiO ₃ single crystals

Abstract

The nature of pinning has been investigated in the three-dimensional high-Tcsuperconductor (K,Ba)BiO3. We show that the magnetic-field dependence of the critical current deduced from pulsed-field magnetization measurements can be well described by the collective-pinning theory on a large temperature range 0.06 < T/Tc < 0.62. This permits us to construct a nonequilibrium H-Tphase diagram including both the single-vortex and vortex bundle regimes. Furthermore, the temperature dependence of the collective-pinning length Lc is in excellent agreement with a model of flux pinning induced by spatial fluctuations of the critical temperature (δTc pinning model).