Light Pulse Could Flip a 2D Material's Magnetism and Topology at Once, Monash Calculations Show
The ACS Nano prediction for MnBi₂Te₄ points to ultrafast switching without the heat of electrical circuits, but no experiment has tested it yet.
Researchers at Monash University in Australia have predicted that a single pulse of terahertz light can switch both the magnetism and the electronic topology of an atomically thin material at the same time. If experiments confirm it, the result could point toward devices that switch without the wasteful heat of conventional electrical circuits.
The study, published in ACS Nano, focuses on MnBi₂Te₄, a two-dimensional magnetic topological material. The team says the switching is possible through a hybrid light-matter excitation they call magnetophononic polaritons.
"Controlling magnetism and topology with light has long been a challenge in topological quantum materials research," said Dr. Enamul Haque, the study's first author, who did the work during his Ph.D. at Monash. "Our calculations show a way to achieve both at once, which could enable ultrafast on-off switching of topological states."
The finding comes from first-principles calculations, not a lab measurement. The team modeled a strong terahertz pulse 0.6 picoseconds long with a field of about 2 megavolts per centimeter. In their simulation, the pulse drives vibrations of the crystal lattice that switch the magnetic coupling between the two layers of a MnBi₂Te₄ sheet, 14 atomic layers thick, from antiferromagnetic to ferromagnetic while the lattice is being driven.
In that state, the sheet changes from an ordinary insulator to a topological one, with protected conducting channels along its edges. The effect needs low temperatures. The material is magnetic only below about 20 to 25 kelvin.
The mechanism rests on quasiparticles, the collective excitations that arise when electrons, atomic vibrations and magnetic moments interact. Phonon polaritons form when light couples to vibrations of the crystal lattice, which are called phonons. They squeeze light into very small spaces, which makes them attractive for nanophotonics. In MnBi₂Te₄, one of the polaritons compresses light to an effective wavelength of about 18 nanometers. Light of the same energy has a wavelength of about 65 micrometers in free space.
"What stands out in this result is that a single material can confine light tightly and also let that light control its magnetic and topological properties," said Professor Nikhil Medhekar, who supervised the research. "Our next step is to work with experimental colleagues to test the prediction at low temperature using terahertz pulses."
The authors say optically induced magnetic changes offer a route to ultrafast switching, and that confined polaritons suit miniaturized photonic components. Combining both in one material points to devices where light controls magnetic and topological electronic states. Possible uses they list include reconfigurable electronics, spintronics and nanophotonic switches.
The prediction has not yet been tested in the lab, and the cryogenic temperature requirement limits near-term applications. The paper is Haque et al., "Highly Confined Magnetophononic Polaritons and Electron-Phonon Interactions in Atomically Thin MnBi2Te4," ACS Nano (2026), DOI 10.1021/acsnano.6c06828.
