Physicists Use Rotating Light to Reveal Hidden Eight-Pole Magnetism in Crystals

For more than a century, magnetism in everyday life has been a story of two poles. A compass needle points north and south, a refrigerator magnet clings to a door through opposing charges, and the underlying physics has seemed comfortably familiar. Yet deep inside certain crystalline materials, researchers are now finding magnetic arrangements that refuse to fit this simple picture. A team led by quantum physicists at the University of Toronto has established a new way to observe one of the strangest of these states, known as octupolar order, in which a pattern of particles locked into a crystal lattice behaves as though it carries eight magnetic poles rather than the familiar two. The work, published in Physical Review Letters, marks a critical first step toward putting these elusive magnetic states to work in practical technologies, from next-generation data storage to novel computing devices.

The challenge with octupolar magnetism has never been a shortage of theory. Quantum mechanics has long predicted that higher orders of magnetic organization should exist, and researchers have steadily uncovered evidence of them in exotic materials. The problem is detection. Ordinary magnetic probes, the instruments that readily reveal the north and south poles of a bar magnet, are essentially blind to these hidden configurations. Because the octupolar pattern does not produce the net magnetic signals that conventional measurements rely on, the state can hide inside a crystal even while shaping its electronic properties. As Arun Paramekanti, a professor in the Department of Physics and the Centre for Quantum Information & Quantum Control in the Faculty of Arts & Science at the University of Toronto and senior author of the study, explains, the team identified new signatures of a hidden type of magnetic state that cannot be detected using ordinary probes. He notes that the research opens up the possibility of using higher-order magnets in several applications, including controllable read-write memory elements found in everyday computers.

The Toronto-led team found a way around the invisibility problem by turning to light and to the tiny vibrations that ripple through a solid when its atoms are jostled. Their approach rests on a simple but powerful idea: shine light on a crystalline material, trigger minute vibrations within its atomic structure, and watch how those vibrations respond. In ordinary magnets, the answer is fairly predictable. But when an octupolar magnetic order is present, the vibrations carry a subtle imprint of the hidden pattern, one that conventional techniques would miss entirely. By reading that imprint, the researchers could effectively make the invisible visible, using the crystal’s own atomic motion as a messenger for the magnetic order buried within it.

The messengers in question are phonons, the packets of vibrational energy that move through a solid’s crystal lattice much like sound waves move through air. Every crystal supports a rich spectrum of these vibrations, and their behavior encodes information about the forces and symmetries that hold the material together. The researchers focused their attention on a special subset known as chiral phonons, vibrations that do not match their own mirror image. Rory Sutcliffe, a PhD candidate in the Department of Physics and lead author of the study, offers an intuitive comparison: just as a left hand cannot fit cleanly over a right hand even though they are mirror images, chiral phonons have a handedness and exist in distinct, non-matching forms. That handedness, it turns out, is precisely what makes them useful spies for hidden magnetism.

When the team examined how chiral phonons behave in materials on the verge of octupolar order, they found something remarkable. The onset of the hidden magnetic state imparts a distinct handedness to certain phonon modes, a property that would be absent in an ordinary magnet. Swati Chaudhary, a project research associate at the University of Tokyo and study co-author, describes these vibrations as behaving differently from those found in conventional magnets, which is why the team calls them pseudo-chiral phonons. According to Chaudhary, they provide a new way of identifying and studying hidden magnetic states. In other words, the crystal’s lattice itself becomes a detector: the moment octupolar order takes hold, the vibrations passing through it acquire a chiral character that light can read.

The optical side of the experiment is just as important as the phonon side. Rather than illuminating the material with ordinary light, the researchers directed a special type of rotating light at their magnetic samples. The rotation, a kind of twist in the light’s structure, couples to the handedness of the pseudo-chiral phonons. When the hidden octupolar order was present, the interaction produced a clear optical fingerprint, an unmistakable signature in how the light and vibrations responded to each other. That fingerprint is the key result of the study: a measurable, reproducible signal that betrays the presence of a magnetic state no conventional probe could see. It transforms the search for octupolar order from a matter of indirect inference into a direct optical measurement.

The implications reach well beyond the laboratory curiosity of seeing something new. Kathleen Hart, a PhD candidate in the Department of Physics and study co-author, explains that the work offers a new optical probe of hidden magnetic orders that are difficult to detect by standard techniques and lays the foundation for how such octupolar magnetism might eventually be controlled through atomic vibrations within a material. That last point deserves emphasis. Detection is only half the battle; if the pseudo-chiral phonons carry the signature of octupolar order, then in principle the same vibrations could be used to manipulate the order itself, switching it on and off or reorienting it at will. A magnetic state that can be both read and written through light and lattice vibrations is exactly the kind of tool that future memory technologies demand.

The connection to technology is not speculative decoration. Modern data storage relies on magnetic states that can be flipped between two configurations, and the density and speed of storage devices have been limited by the physics of conventional dipoles. Higher-order magnetic states offer a richer landscape: because octupolar order involves patterns of spins arranged across a crystal structure rather than a simple two-pole alignment, it could support memory elements that are more stable, more compact, or more resistant to the stray fields that scramble conventional bits. Paramekanti points specifically to controllable read-write memory elements of the kind found in everyday computers as a potential application. If the optical fingerprint discovered by the Toronto-led team can be turned into a reliable readout mechanism, and phonon control into a write mechanism, the path from fundamental discovery to device concept becomes considerably shorter.

There is also a broader significance for quantum materials research. The study, which the release notes was based on computational simulation and modeling, demonstrates a general principle: hidden orders of many kinds may reveal themselves not through their direct magnetic signals but through the way they reshape the vibrational life of the crystal. Chiral phonons have attracted growing attention in recent years for their role in exotic electronic behavior, and this work adds a new entry to that catalog by tying their handedness to a specific, technologically relevant magnetic order. Researchers hunting for octupolar phases in candidate materials now have a concrete experimental signature to look for, one that requires rotating light and vibrational spectroscopy rather than exotic new instruments. In that sense, the method could accelerate the discovery of octupolar magnets across a wide range of compounds.

The findings ultimately offer a new tool for uncovering and manipulating previously inaccessible forms of magnetism, opening new avenues for quantum technology development. What began as an attempt to detect a state that ordinary probes cannot see has ended with a recipe: find crystals whose phonons can become pseudo-chiral, illuminate them with rotating light, and read the fingerprint of eight-pole magnetic order written into their vibrations. For a field that has spent years theorizing about higher-order magnetism while struggling to observe it, that recipe may prove to be the turning point, converting one of quantum physics’ most elusive magnetic states from a hidden curiosity into an addressable component of future technologies.

Subject of Research: Detection of hidden octupolar magnetic order through pseudo-chiral phonons probed by rotating light in crystalline materials

Article Title: University of Toronto physicists identify ‘octupolar’ magnetism, with implications for quantum technologies

Article References: University of Toronto physicists identify ‘octupolar’ magnetism, with implications for quantum technologies. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: octupolar magnetism, chiral phonons, quantum magnetism, University of Toronto, Physical Review Letters, magnetic order, phonons, optical probe, quantum technologies, data storage, crystal lattice, spin textures