Spin-Ice Thin Films: Large- N Theory and Monte Carlo Simulations

• Published in: Physical review. X 2018-05, Vol.8 (2), p.021053, Article 021053
• Main Authors: Lantagne-Hurtubise, Étienne, Rau, Jeffrey G., Gingras, Michel J. P.
• Format: Article
• Language: English
• Subjects: Boundary conditions; Broken symmetry; Computer simulation; Crystallography; Electromagnetic fields; Electromagnetism; Ferromagnetism; Gauge theory; Low temperature; Magnetic moments; Magnets; Numerical methods; Optical communication; Optical fibers; Phases; Simulation; Spin ice; Spin liquid; Thin films
• ISSN: 2160-3308; 2160-3308
• DOI: 10.1103/PhysRevX.8.021053

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-Ntechniques 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 classicalZ2spin 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 unusualZ3classical spin liquid. Finally, we comment on open questions and promising avenues for future research.