Rejuvenation and memory in model spin glasses in three and four dimensions

We numerically study aging for the Edwards-Anderson model in three and four dimensions using different temperature-change protocols. In D=3, time scales a thousand times larger than in previous work are reached with the Spin Update Engine SUE machine. Deviations from cumulative aging are observed in the nonmonotonic time behavior of the coherence length. Memory and rejuvenation effects are found in a temperature-cycle protocol, revealed by vanishing effective waiting times. Similar effects are reported for the D=3 site-diluted ferromagnetic Ising model without chaos. However, rejuvenation is reduced if off-equilibrium corrections to the fluctuation-dissipation theorem are considered. Memory and rejuvenation are quantitatively describable in terms of the growth regime of the spin-glass coherence length

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© 2007 American Physical Society.Depto. de Física TeóricaFac. de Ciencias FísicasTRUEpu

Study of the phase transition in the 3d Ising spin glass from out of equilibrium numerical simulations

Using the decay of the out equilibrium spin-spin correlation function we compute the equilibrium Edward-Anderson order parameter in the three dimensional binary Ising spin glass in the spin glass phase. We have checked that the Edward-Anderson order parameter computed from out of equilibrium numerical simulations follows with good precision the critical law as determined in experiments and in numerical studies at equilibrium. We have also studied the dependence of the order parameter with the lattice size. Finally we present a large time study of the scaling of the off-equilibrium fluctuation-dissipation relations.Comment: 14 pages, 7 Postscript figure

Simulating spin systems on IANUS, an FPGA-based computer

We describe the hardwired implementation of algorithms for Monte Carlo simulations of a large class of spin models. We have implemented these algorithms as VHDL codes and we have mapped them onto a dedicated processor based on a large FPGA device. The measured performance on one such processor is comparable to O(100) carefully programmed high-end PCs: it turns out to be even better for some selected spin models. We describe here codes that we are currently executing on the IANUS massively parallel FPGA-based system.Comment: 19 pages, 8 figures; submitted to Computer Physics Communication

Soft Modes, Localization, and Two-Level Systems in Spin Glasses

In the three-dimensional Heisenberg spin glass in a random field, we study the properties of the inherent structures that are obtained by an instantaneous cooling from infinite temperature. For a not too large field the density of states g(ω) develops localized soft plastic modes and reaches zero as ω^4 (for large fields a gap appears). When we perturb the system adding a force along the softest mode, one reaches very similar minima of the energy, separated by small barriers, that appear to be good candidates for classical two-level systems

IANUS: Scientific Computing on an FPGA-based Architecture

This paper describes the architecture and FPGA-based implementation of a massively parallel processing system (IANUS), carefully tailored to the computing requirements of a class of simulation problems relevant in statistical physics. We first discuss the system architecture in general and then focus on the configuration of the system for Monte Carlo simulation of spin-glass systems. This is the first large-scale application of the machine, on which IANUS achieves impressive performance. Our architecture uses large-scale on chip parallelism (~1000 computing cores on each processor) so it is a relevant example in the quickly expanding field of many-core architectures