Critical phenomena in a highly constrained classical spin system: Neel ordering from the Coulomb phase

TL;DR

This paper studies how weak interactions induce Neel order in highly degenerate Coulomb phases of frustrated antiferromagnets, revealing a unique universality class with long-range effects and potential discontinuous transitions.

Contribution

It demonstrates that the Neel transition from a Coulomb phase belongs to a distinct universality class characterized by effective long-range interactions.

Findings

The critical point differs from standard universality classes.

Long-range interactions influence the nature of the transition.

Uniaxial stress could realize this transition experimentally.

Abstract

Many classical, geometrically frustrated antiferromagnets have macroscopically degenerate ground states. In a class of three-dimensional systems, the set of degenerate ground states has power-law correlations and is an example of a Coulomb phase. We investigate Neel ordering from such a Coulomb phase, induced by weak additional interactions that lift the degeneracy. We show that the critical point belongs to a universality class that is different from the one for the equivalent transition out of the paramagnetic phase, and that it is characterised by effective long-range interactions; alternatively, ordering may be discontinuous. We suggest that a transition of this type may be realised by applying uniaxial stress to a pyrochlore antiferromagnet.