Spin ice thin films: Large-N theory and Monte Carlo simulations

TL;DR

This paper investigates the effects of confinement and surface modifications on the Coulomb phase in spin ice thin films using large-N theory and Monte Carlo simulations, revealing new surface phenomena and phases.

Contribution

It combines analytic large-N techniques with simulations to analyze how thin film geometry and surface bonds influence spin ice's Coulomb phase and emergent spin liquids.

Findings

Pinch points indicative of 2D Coulomb phase in [001] films

Surface ferromagnetic bonds induce a Z_2 spin liquid

Predicted surface magnetic charges and novel spin liquids

Abstract

We explore the physics of highly frustrated magnets in confined geometries, focusing on the Coulomb phase of pyrochlore spin ices. As a specific example, we investigate thin films of nearest-neighbor spin ice, using a combination of analytic large-N techniques and Monte Carlo simulations. In the simplest film geometry, with surfaces perpendicular to the [001] crystallographic direction, we observe pinch points in the spin-spin correlations characteristic of a two-dimensional Coulomb phase. We then consider the consequences of crystal symmetry breaking on the surfaces of the film through the inclusion of orphan bonds. We find that when these bonds are ferromagnetic, the Coulomb phase is destroyed by the presence of fluctuating surface magnetic charges, leading to a classical Z_2 spin liquid. Building on this understanding, we discuss other film geometries with surfaces perpendicular to the [110] or the [111] direction. We generically predict the appearance of surface magnetic charges and discuss their implications for the physics of such films, including the possibility of an unusual Z_3 classical spin liquid. Finally, we comment on open questions and promising avenues for future research.