Magnetic Monopole Dynamics in Spin Ice

TL;DR

This paper investigates the behavior of emergent magnetic monopoles in spin ice materials, analyzing their diffusive dynamics through models and simulations, and providing insights into their Coulomb interactions and quantum tunneling effects.

Contribution

It offers a detailed analysis of monopole dynamics in spin ice using both dipolar and Coulomb gas models, including quantum tunneling effects and constrained particle movement.

Findings

Monopoles exhibit diffusive behavior consistent with Coulomb interactions.

Quantum tunneling influences monopole dynamics in spin ice.

Modeling monopoles along Dirac string networks captures key experimental phenomena.

Abstract

One of the most remarkable examples of emergent quasi-particles, is that of the "fractionalization" of magnetic dipoles in the low energy configurations of materials known as "spin ice", into free and unconfined magnetic monopoles interacting via Coulomb's 1/r law [Castelnovo et. al., Nature, 451, 42-45 (2008)]. Recent experiments have shown that a Coulomb gas of magnetic charges really does exist at low temperature in these materials and this discovery provides a new perspective on otherwise largely inaccessible phenomenology. In this paper, after a review of the different spin ice models, we present detailed results describing the diffusive dynamics of monopole particles starting both from the dipolar spin ice model and directly from a Coulomb gas within the grand canonical ensemble. The diffusive quasi-particle dynamics of real spin ice materials within "quantum tunneling" regime is modeled with Metropolis dynamics, with the particles constrained to move along an underlying network of oriented paths, which are classical analogues of the Dirac strings connecting pairs of Dirac monopoles.