Measurements of the time dependence of zero-field-cooled (ZFC) and field-cooled (FC) magnetization M in YBa2Cu3O7-δ single crystal have been performed as a function of temperature and magnetic field. The appearance of an echo-like feature in the decay rate S = dM/d ln t at an observing time t equal to the waiting time tw during which the specimen was prepared at a given field H0 and temperature T reveals aging effects in the superconducting state. Similar phenomena reported in spin glasses seem to validate the picture of a superconducting glass state in YBa2Cu3O7-δ.
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