Dynamical heterogeneities as fingerprints of a backbone structure in Potts models.

We investigate slow nonequilibrium dynamical processes in a two-dimensional q-state Potts model with both ferromagnetic and ±J couplings. Dynamical properties are characterized by means of the mean-flipping time distribution. This quantity is known for clearly unveiling dynamical heterogeneities. Using a two-times protocol we characterize the different time scales observed and relate them to growth processes occurring in the system. In particular we target the possible relation between the different time scales and the spatial heterogeneities originated in the ground-state topology, which are associated to the presence of a backbone structure. We perform numerical simulations using an approach based on graphis processing units (GPUs) which permits us to reach large system sizes. We present evidence supporting both the idea of a growing process in the preasymptotic regime of the glassy phases and the existence of a backbone structure behind this process.

Strong dynamical heterogeneities in the violation of the fluctuation-dissipation theorem in spin glasses.

We analyze numerically the violation of the fluctuation-dissipation theorem (FDT) in the +/-J Edwards-Anderson (EA) spin-glass model. Using single spin probability densities we reveal the presence of strong dynamical heterogeneities, which correlate with ground-state information. The physical interpretation of the results shows that the spins can be divided into two sets. In 3D, one set forms a compact structure which presents a coarseninglike behavior with its characteristic violation of the FDT, while the other asymptotically follows the FDT. Finally, we compare the dynamical behavior observed in 3D with 2D.

Signature of the ground-state topology in the low-temperature dynamics of spin glasses.

We numerically address the issue of how the ground-state topology is reflected in the finite temperature dynamics of the +/-J Edwards-Anderson spin glass model. In this system a careful study of the ground-state configurations allows us to classify spins into two sets: solidary and nonsolidary spins. We show that these sets quantitatively account for the dynamical heterogeneities found in the mean flipping time distribution at finite low temperatures. The results highlight the relevance of taking into account the ground-state topology in the analysis of the finite temperature dynamics of spin glasses.

Long-range effects in granular avalanching.

We introduce a model for granular flow in a one-dimensional rice pile that incorporates rolling effects through a long-range rolling probability for the individual rice grains proportional to r(-rho), r being the distance traveled by a grain in a single toppling event. The exponent rho controls the average rolling distance. We have shown that the crossover from the power law to the stretched exponential behaviors observed experimentally in the granular dynamics of rice piles can be well described as a long-range effect resulting from a change in the transport properties of individual grains. We showed that stretched exponential avalanche distributions can be associated with a long-range regime for 12, where the average rolling distance is independent of the system size.