Skip to Content

Physicists confirm existence of elusive quantum spin ice

Representation of spin ice

The original story is posted on the A&S News Website. You can read the original here.


A team of physicists from the University of Toronto and Rice University have uncovered the strongest evidence yet for the existence of a quantum spin ice — an exotic form of matter with potential applications in quantum computing and superconductors.

The discovery settles a long-standing question in condensed matter physics and provides a robust platform for exploring next-generation technologies.

“There have been many theoretical studies looking at these systems since they were first proposed decades ago,” says Yong Baek Kim, a professor of quantum materials in the Faculty of Arts & Science’s Department of Physics and a co-author of a paper describing the research.

“So, the basic theory is very well established and there have been many experiments over the years that have identified candidates for these systems.”

“But the challenge has been to make specific theoretical predictions that can be clearly tested in the experiments and also to find actual experimental evidence of such predictions,” says Félix Desrochers, a graduate student in the Department of Physics and a co-author of the paper. “And now we have it.”

The research of Kim, Desrochers and their collaborators is described in a paper published recently in the journal Nature Physics: ‘Neutron scattering and thermodynamic evidence for emergent photons and fractionalization in a pyrochlore spin ice.’

Spin ice is a magnetic material in which magnetic moments of electrons — coming from a property known as spin — are arranged in a lattice of connected tetrahedrons in three dimensional space. The spin configurations on the lattice are analogous to how water molecules align in a lattice when water is frozen.

We think this discovery, the clear identification of a quantum spin liquid, is an important new avenue for further research work in multiple different directions.

Quantum mechanical motion of these interacting spins gives rise to a quantum mechanical version of spin ice, dubbed quantum spin ice. This is a special kind of quantum spin liquid, a broader class of quantum spin states where the interacting spins do not order down to very low temperature due to quantum mechanical motions. This exotic state of matter can provide emergent photons — a massive collective motion of spins which resembles the motion of ordinary photons — and fractionalized particles called ‘spinons.’

The theoretical team at U of T provided predictions for definite signatures of emergent photons and fractionalized particles in the neutron scattering experiment. The experimental team at Rice University used state-of-the-art polarized neutron scattering techniques to isolate and identify the predicted signs of quantum spin ice behavior.

The measurements enabled them to discover emergent photon signals near zero energy — a key feature distinguishing quantum spin ice from other conventional phases in ordinary magnets. Complementary measurements of the compound’s specific heat at TU Vienna (Vienna University of Technology) provided further support, suggesting that the theoretically predicted emergent photons have a dispersion similar to how sound travels in a solid or how ordinary photons travel in a vacuum.

“There's a fundamental scientific interest in studying these exotic phases of matter,” says Desrochers. “But quantum spin liquids and quantum spin ice are also of interest for researchers studying quantum computing and other engineering innovations.”

Says Kim, “We think this discovery, the clear identification of a quantum spin liquid, is an important new avenue for further research work in multiple different directions.”

With files from Rice University.