Entropy-induced confinement in two-dimensional magnetic monopole gases

TL;DR

This paper demonstrates that entropy is the key factor in confining magnetic monopole quasiparticles to two dimensions at material interfaces, and shows how external conditions can manipulate their distribution.

Contribution

The study introduces an entropy-based model explaining 2D confinement of magnetic monopoles in spin ice interfaces, validated by spin model simulations.

Findings

Entropy favors 2D confinement of monopoles.

External magnetic field and temperature can manipulate monopole distribution.

Model accurately reproduces monopole distribution from spin simulations.

Abstract

Magnetic monopole quasiparticles in spin ice materials hold the potential for exploring new frontiers of physics that extend beyond Maxwell's equations. We have previously proposed a two-dimensional magnetic monopole gas (2DMG), confined at the interface between spin-ice ($R_2$Ti$_2$O$_7$, $R$ = Dy, Ho) and antiferromagnetic iridate ($R_2$Ir$_2$O$_7$, $R$ = Dy, Ho), which hosts monopoles with a net charge. The mechanism behind the 2D confinement of the monopole gas remains unclear. In this work, we demonstrate that entropy is a key factor in the 2D confinement of this monopole gas. We reveal that the competition between the entropy of spin-ice, which favors the 2D confinement, and the entropy of the monopoles' random walks, which favors the deconfinement, dictates the distribution of the monopoles within a few layers close to the interface. Our entropy-based model accurately reproduces the monopole distribution obtained from the spin model, affirming that 2D confinement is entropy-driven. We further employ both models to show that the monopole distribution can be manipulated by an external magnetic field and temperature, holding promise for next-generation devices based on magnetic monopoles. Our findings reveal the entropic mechanisms in 2DMG, enabling the manipulation of emergent quasiparticles at material interfaces.