Second harmonics and compensation effect in ceramic superconductors

A three-dimensional lattice of the Josephson junctions with a finite self-conductance is employed to model the ceramic superconductors. The nonlinear ac susceptibility and the compensation effect are studied by Monte Carlo simulations in this model. The compensation effect is shown to be due to the existence of the chiral glass phase. We demonstrate, in agreement with experiments, that this effect may be present in the ceramic superconductors which show the paramagnetic Meissner effect.Comment: 6 pages, latex, 4 figures, Phys. Rev. B (accepted

Strong rejuvenation in a chiral-glass superconductor

The glassy paramagnetic Meissner phase of a Bi$_2$Sr$_2$CaCu$_2$O$_x$ superconductor ($x$ = 8.18) is investigated by squid magnetometry, using ``dc-memory'' experiments employed earlier to study spin glasses. The temperature dependence of the zero-field-cooled and thermo-remanent magnetization is recorded on re-heating after specific cooling protocols, in which single or multiple halts are performed at constant temperatures. The 'spin' states equilibrated during the halts are retrieved on re-heating. The observed memory and rejuvenation effects are similar to those observed in Heisenberg-like spin glasses.Comment: REVTeX 4 style; 5 pages, 5 figure