New mechanisms for irreversibility in high-T_c superconductors (invited)

We discuss the zero-field cooled (ZFC), field-cooled (FC), and remanent (rem) magnetization of YBaCuO crystals in the context of an extended Bean critical-state model. We introduce a novel way to include the reversible magnetization in this theory and show how this can explain the concave-downwards shape of the ZFC magnetization near Tc. We explain the persistence of remanence in a temperature range where FC and ZFC magnetizations merge in terms of a residual irreversibility arising from a step in the reversible B(H) curve. We also introduce the concept of a flux-trapping depth which helps explain the field dependence of the Meissner effect.