Electrical noise study of spin glass dynamics in mesoscopic copper manganese

The electrical resistance of the archetypal spin glass $\underline{\rm Cu}$Mn is surprisingly sensitive to small changes in the spin configuration. This enhanced sensitivity results from long-range electron quantum interference at low temperatures. Due to this effect, substantial resistance noise is produced by spontaneous spin fluctuations below the spin-glass freezing transition. Described here are the results of noise experiments on extremely small 'mesoscopic' samples of $\underline{\rm Cu}$Mn. These samples are so small that only a handful of spin fluctuation events are observed during a measurement. Thus we have probed, for the first time, the glassy dynamics with sufficient microscopic detail to uncover the main features of the dynamical pattern. The results are incompatible with the simple 'droplet' picture of spin glasses which is currently in vogue. Noise statistics reveal instead very cooperative dynamics, closely resembling hierarchical dynamics models.U of I OnlyETDs are only available to UIUC Users without author permissio