Evidence against an Almeida-Thouless line in disordered systems of Ising dipoles

TL;DR

This study uses Monte Carlo simulations to investigate the existence of an Almeida-Thouless line in disordered dipolar Ising systems, finding evidence against its presence.

Contribution

It provides the first numerical evidence challenging the existence of the Almeida-Thouless line in dipolar Ising spin glasses.

Findings

No evidence of an AT line in dipolar Ising systems.

Comparison shows differences from the Sherrington-Kirkpatrick model.

Correlation length analysis supports the absence of a phase boundary.

Abstract

By tempered Monte Carlo simulations, an Almeida-Thouless (AT) phase-boundary line in site-diluted Ising spin systems is searched for. Spins interact only through dipolar fields and occupy a small fraction of lattice sites. The spin-glass susceptibility of these systems and of the Sherrington-Kirkpatrick model are compared. The correlation length as a function of system size and temperature is also studied. The results obtained are contrary to the existence of an AT line.