Maxwell electromagnetism as an emergent phenomenon in condensed matter

TL;DR

This paper demonstrates how simple condensed matter systems of localized spins can emulate Maxwell electromagnetism at low energies, revealing emergent phenomena like magnetic monopoles and novel disordered magnetic states.

Contribution

It shows that non-relativistic spin systems can reproduce Maxwell electromagnetism and exhibit unique emergent phenomena not constrained by relativistic symmetry.

Findings

Emergence of Maxwell-like electromagnetism in spin systems

Existence of magnetic monopole excitations from fractionalization

Disorder-induced novel magnetic phases such as spin glasses

Abstract

The formulation of a complete theory of classical electromagnetism by Maxwell is one of the milestones of science. The capacity of many-body systems to provide emergent mini-universes with vacua quite distinct from the one we inhabit was only recognised much later. Here, we provide an account of how simple systems of localised spins manage to emulate Maxwell electromagnetism in their low-energy behaviour. They are much less constrained by symmetry considerations than the relativistically invariant electromagnetic vacuum, as their substrate provides a non-relativistic background with even translational invariance broken. They can exhibit rich behaviour not encountered in conventional electromagnetism. This includes the existence of magnetic monopole excitations arising from fractionalisation of magnetic dipoles; as well as the capacity of disorder, by generating defects on the lattice scale, to produce novel physics, as exemplified by topological spin glassiness or random Coulomb magnetism.