Memory Effects in a Superconducting Y-Ba-Cu-O Single Crystal: A Similarity to Spin-Glasses

We report on memory effects observed in the time dependence of the magnetization $M(T, H)$ of a superconducting Y-Ba-Cu-O single crystal. As in spin-glasses, the decay rate $S=\frac{\mathrm{dM}}{d\ln t}$ is not uniquely determined. It exhibits a characteristic change at time $t$ equal to the waiting time $t_w$ during which the specimen was kept at a given temperature $T<\mathrm{}{T}_c$ and magnetic field $H$ before a field perturbation $\Delta H$ is applied at time $t=0\mathrm{}$. This phenomenon, seen for the first time in a superconductor, reveals the glassy nature of the superconducting state in the high-$T_c$ oxides.