Can Aging Phenomena Discriminate Between the Droplet Model and a Hierarchical Description in Spin Glasses?

We performed low-frequency ( f = 0.1 Hz) a.c. susceptibility measurements on the CdCr 1.7 In 0.3 S 4 insulating spin glass. The experiments were selected in an attempt to discriminate between the droplet model and a hierarchical picture characterized by a continuous splitting of the metastable states with decreasing temperatures. We studied the effect of small temperature changes on the aging of the out-of-phase susceptibility χ'' below the freezing temperature T g . We find that the predictions of the droplet model do not agree with some aspects of the results which appear as direct consequences of a hierarchical organization in phase space.