Abstract
Frustration in magnetic interactions can give rise to disordered ground states with subtle and beautiful properties. The spin ices and exemplify this phenomenon, displaying a classical spin-liquid state, with fractionalized magnetic-monopole excitations. Recently, there has been great interest in closely related “quantum spin-ice” materials, following the realization that anisotropic exchange interactions could convert spin ice into a massively entangled, quantum spin liquid, where magnetic monopoles become the charges of an emergent quantum electrodynamics. Here we show that even the simplest model of a quantum spin ice, the XXZ model on the pyrochlore lattice, can realize a still-richer scenario. Using a combination of classical Monte Carlo simulation, semiclassical molecular-dynamics simulation, and analytic field theory, we explore the properties of this model for frustrated transverse exchange. We find not one, but three competing forms of spin liquid, as well as a phase with hidden, spin-nematic order. We explore the experimental signatures of each of these different states, making explicit predictions for inelastic neutron scattering. These results show an intriguing similarity to experiments on a range of pyrochlore oxides.
1 More- Received 29 April 2017
DOI:https://doi.org/10.1103/PhysRevX.7.041057
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
For more than 100 years, we have known that matter is composed of atoms and that matter made of the same atoms can behave in many different ways. The different ways in which atoms (or molecules) behave are known as phases; we encounter three phases—solid, liquid, and gas—in everyday life. But, for a long time, researchers have also been interested in what other phases of matter might be possible. This question has become more important as we have learned how to study matter at very low temperatures. In recent years, scientists have become fascinated with the low-temperature properties of magnetic materials. One material in particular, “spin ice,” has attracted a lot of attention because its magnetic atoms behave like a liquid that never freezes no matter how cold it becomes. In this paper, we look at what happens to spin ice as it is cooled to absolute zero.
Using computer simulations, we study a model of spin ice in which magnetic atoms exert small forces on one another through the exchange of electrons. Contrary to expectations, we find that this model supports five different phases, including not one but three different kinds of liquid that never freeze. We also discuss what these different phases would look like in an experiment.
These results expand our ideas of what is possible in magnets at very low temperatures and may explain some of the puzzling features of experiments carried out on spin-ice-like magnets.