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

The work, published in Nature Materials, focuses on freestanding membranes of BaTiO3, one of the most intensively studied ferroelectric compounds in existence. Ferroelectrics possess a spontaneous electric polarization that can be reoriented between stable states by an external field, which is precisely why they dominate applications ranging from capacitors to nonvolatile memories and piezoelectric transducers. What makes BaTiO3 particularly attractive for the new experiment is that its polar state is intimately tied to a structural distortion of the crystal lattice: below its Curie temperature, the titanium ions shift off-center within their oxygen cages, breaking the symmetry of the lattice and creating the electrical polarization. Because phonons are themselves collective motions of this lattice, any manipulation of the polarization necessarily reshapes the entire vibrational landscape, including the subtle rotational motions that define chiral phonons.

The particular vibration studied here belongs to what the authors describe as the g-wave sector of the lattice dynamics, referring to a high-frequency branch of phonons whose atoms execute circular, swirling trajectories. In such modes, two conjugate forms of the vibration exist, left-handed and right-handed, which are mirror images of one another but otherwise identical in energy. In an unperturbed crystal that lacks a handedness of its own, these two forms are degenerate, meaning they coexist in equal measure and no net chirality is expressed. To observe or use chiral phonons, one therefore needs a way to break this degeneracy, to make the crystal prefer one rotational sense over the other, and, crucially, to switch that preference on demand. The new study demonstrates that in BaTiO3 membranes, the ferroelectric polarization does exactly this job, acting as an internal, field-tunable chiral axis for the lattice.

Demonstrating such control experimentally is far from trivial. Chiral phonons vibrate at frequencies of terahertz order, far too fast for conventional spectroscopies to resolve directly, and their signatures are embedded deep within the vibrational spectrum of the crystal. The technique of choice in this study was circularly dichroic resonant inelastic X-ray scattering, an advanced synchrotron method that combines the momentum-resolving power of inelastic X-ray scattering with the chiral sensitivity of circularly polarized light. In this scheme, an incoming X-ray photon tuned to an absorption edge of a constituent atom transfers a well-defined portion of its energy and momentum to the lattice, exciting a specific phonon, and the scattered photon is analyzed for its energy loss. By measuring how efficiently the phonon is excited when the X-ray beam’s circular polarization is reversed, researchers can determine the phonon’s own handedness with remarkable selectivity, effectively interrogating the crystal with one rotating probe to detect rotating excitations.

Using this approach on their BaTiO3 membranes, the researchers recorded phonon spectra with circularly polarized X-rays tuned to the titanium absorption edge and observed a clear dichroic signal at the energy of the g-wave phonon. The sign of this signal, which encodes the phonon’s chirality, flipped when the ferroelectric polarization of the membrane was reversed by an applied electric field. This is the central experimental result: the handedness of the lattice vibration is not a fixed property of the material but a state that follows the polarization direction and can be rewritten at will. Because ferroelectric polarization is nonvolatile, retaining its orientation after the field is removed, the phonon chirality it selects is likewise nonvolatile, opening a conceptual pathway toward devices in which information is stored in the rotational sense of atomic motion rather than in charge, spin, or conventional polarization alone.

The physics underlying this switching can be understood through the lens of symmetry. In the ferroelectric phase of BaTiO3, the off-center displacement of the titanium ions lowers the crystal symmetry and establishes a polar axis, transforming the material from an achiral environment into one that distinguishes between clockwise and counterclockwise rotation along that axis. The g-wave phonon’s circular atomic trajectories then couple differently to this polar lattice depending on their handedness, lifting the degeneracy between the left- and right-handed forms and determining which one dominates the measured dichroic response. When the electric field reverses the polarization, the symmetry operation connecting the two states acts like a mirror that interchanges the two chiralities, and the phonon population follows. The experiment thus provides a direct, momentum-resolved picture of how a macroscopic order parameter in a ferroelectric governs the microscopic rotation of atoms, a connection that had been theorized but was extraordinarily difficult to verify until the advent of chiral-sensitive inelastic X-ray techniques.

The significance of the result extends well beyond barium titanate itself. Chiral phonons have been proposed as carriers of angular momentum that can be transferred to electron spins, as mediators of a phonon contribution to the Edelstein and inverse Edelstein effects, and as a route to phonon-controlled magnetism in so-called phonon-magnetic materials. They also underpin emerging proposals for chiral phononics, in which the handedness of vibrations serves as an information carrier immune to some of the noise and leakage channels that plague charge-based electronics. What all of these proposals require is an efficient, reversible, and preferably electrically driven mechanism for writing and erasing phonon chirality. The demonstration that a ferroelectric gate can fulfill this role in a technologically mature material suggests that such mechanisms are not exotic laboratory curiosities but achievable engineering primitives.

The choice of freestanding membranes as the sample geometry is also consequential. Thin, released membranes of complex oxides can sustain electric fields and strain states that are difficult to impose in bulk crystals, and their reduced thickness minimizes the absorption and scattering losses that complicate soft X-ray measurements. In the study, the membrane format allowed the researchers to apply the switching field while maintaining optical access for the resonant scattering experiment, and it is consistent with the broader trend of integrating oxide ferroelectrics into thin-film heterostructures for next-generation electronic devices. The combination of a classic ferroelectric, a state-of-the-art synchrotron probe, and device-relevant sample geometry gives the result an unusually direct line from fundamental symmetry physics to potential applications.

Looking forward, the findings raise a series of compelling questions. How fast can the phonon chirality follow the polarization during a switching event, and what transient chiral dynamics unfold in the intermediate states of a ferroelectric domain wall as it sweeps through the membrane? Can the same circularly dichroic scattering technique resolve the interaction between chiral phonons and other quasiparticles, such as magnons or excitons, in heterostructures that couple ferroelectric and magnetic orders? And can the electrically written chirality be read out by faster, more compact means, perhaps through chirality-dependent optical or transport responses, so that phonon-handedness memory could one day be integrated into practical circuitry? The present work does not answer all of these questions, but by establishing electric-field switching as an experimental reality, it converts many of them from speculation into concrete research programs.

For decades, ferroelectricity has been understood as the electric-field control of where atoms sit. This new result reframes that familiar story: in BaTiO3, the same field control extends to how atoms move, determining the rotational sense of their collective dance. The ability to write, erase, and read the chirality of a lattice vibration with a voltage transforms chiral phonons from a fascinating spectroscopic observation into a controllable degree of freedom of condensed matter. As synchrotron and free-electron laser facilities continue to sharpen the tools of chiral X-ray scattering, and as oxide membranes become ever more integrated into device architectures, the swirling, handed vibrations of crystals may soon find themselves at the heart of technologies that store data, process signals, and manipulate angular momentum in ways their discoverers never imagined.

Subject of Research: Electric-field control of chiral g-wave phonons in ferroelectric barium titanate membranes

Article Title: Electric-field switching of g-wave phonon chirality in ferroelectric BaTiO3

Article References: Grimes, M., Ueda, H., Allington, C. J., Romao, C. P., Kummer, K., Kaur, P., Wang, L.-S., Chang, Y.-W., Yang, J.-C., Huang, S.-W., & Staub, U. (2026). Electric-field switching of g-wave phonon chirality in ferroelectric BaTiO3. Nature Materials. https://doi.org/10.1038/s41563-026-02737-w

Image Credits: AI Generated

DOI: 10.1038/s41563-026-02737-w

Keywords: phonon chirality, ferroelectricity, BaTiO3, electric-field switching, resonant inelastic X-ray scattering, X-ray circular dichroism, chiral phonons, functional materials, lattice dynamics, nonvolatile memory, phononics, membranes