Spin Ice, Fractionalization and Topological Order

TL;DR

This paper reviews spin ice materials, highlighting their emergent gauge fields, magnetic monopole excitations, and fractionalization phenomena, providing an accessible overview of their thermodynamics, dynamics, and topological properties.

Contribution

It offers an elementary introduction to spin ice concepts and surveys recent advances in understanding their thermodynamics, excitations, and emergent topological phenomena.

Findings

Spin ice exhibits emergent gauge fields.

Magnetic monopoles arise from fractionalization.

Observable Dirac strings and Coulomb plasma behavior are present.

Abstract

The spin ice compounds {\dys} and {\holm} are highly unusual magnets which epitomize a set of concepts of great interest in modern condensed matter physics: their low-energy physics exhibits an emergent gauge field and their excitations are magnetic monopoles which arise from the fractionalization of the microscopic magnetic spin degrees of freedom. In this review, we provide an elementary introduction to these concepts and we survey the thermodynamics, statics and dynamics---in and out of equilibrium---of spin ice from these vantage points. Along the way, we touch on topics such as emergent Coulomb plasmas, observable "Dirac strings", and irrational charges. We close with the outlook for these unique materials.