Charge and spin correlations in the Monopole Liquid

TL;DR

This paper investigates a monopole liquid in a pyrochlore lattice, revealing that spins are uncorrelated despite charge correlations, and explores how interactions influence spin and charge behaviors, shedding light on high-temperature correlations in spin ice.

Contribution

The study introduces a simple Hamiltonian for monopole liquids, analyzes their thermodynamics, and uncovers how interactions affect charge and spin correlations, providing new insights into monopole matter phases.

Findings

Spins in the monopole liquid are uncorrelated at all temperatures.

Nearest neighbor interactions induce spin correlations similar to spin ice at higher temperatures.

Ferromagnetic interactions enhance short-range charge and spin order.

Abstract

A \emph{monopole liquid} is a magnetic charge-disordered spin system defined over an Ising pyrochlore lattice, with one single topological charge or \emph{monopole} in each tetrahedron. We define a simple model Hamiltonian for this system and compare its thermodynamics at zero magnetic field with that of spin ice ---a phase free of these charges. In spite of the liquid-like correlations between charges, we find that spins in the charged phase are uncorrelated at all temperatures, like in a perfect paramagnet. The addition of nearest neighbors interactions favoring neutral `2in-2out' excitations as a perturbation has a peculiar effect. While they decrease charge-charge correlations, new spin correlations resembling those in spin ice appear on increasing temperature. This helps us understand why dipolar correlations are observed in spin ices at unexpectedly high temperatures, and the major role of double excitations in erasing the Coulomb phase correlations. Ferromagnetic interactions strengthen the charges short range order and its associated spin correlations. Finally, we discuss how the monopole liquid can be related to other systems and materials where different phases of \emph{monopole matter} have been observed.