Low-temperature spin-glass behaviour in a diluted dipolar Ising system

TL;DR

This study uses Monte Carlo simulations to analyze the low-temperature spin-glass phase of a diluted dipolar Ising system, revealing sample-dependent spike distributions in the overlap parameter and comparing behavior with the Sherrington-Kirkpatrick model.

Contribution

It provides new insights into the spin-glass behavior of diluted dipolar systems, especially regarding spike distributions and size independence at low temperatures.

Findings

Spike distributions are sample-dependent and do not vary significantly with system size.

The average width of spikes remains consistent across different system sizes.

Comparison with the Sherrington-Kirkpatrick model highlights similarities in spike behavior.

Abstract

Using Monte Carlo simulations, we study the character of the spin-glass (SG) state of a site-diluted dipolar Ising model. We consider systems of dipoles randomly placed on a fraction x of all L^3 sites of a simple cubic lattice that point up or down along a given crystalline axis. For x < 0.65 these systems are known to exhibit an equilibrium spin-glass phase below a temperature T_sg proportional to x. At high dilution and very low temperatures, well deep in the SG phase, we find spiky distributions of the overlap parameter q that are strongly sample-dependent. We focus on spikes associated with large excitations. From cumulative distributions of q and a pair correlation function averaged over several thousands of samples we find that, for the system sizes studied, the average width of spikes, and the fraction of samples with spikes higher than a certain threshold does not vary appreciably with L. This is compared with the behaviour found for the Sherrington-Kirkpatrick model.