Monash University researchers found a new way to control magnetism and topology in MnBi₂Te₄ using light. Dr. Enamul Haque said, "Our calculations show a way to achieve both at once, which could enable ultrafast on–off switching of topological states." This discovery could help build energy-efficient electronic devices in the future.
Envision a material whose magnetic properties and electronic topology can be toggled by exposure to light, paving the way for future electronic devices that do not rely on traditional electrical switching, which wastes energy by producing heat.
Researchers at Monash University have predicted that this kind of switching is possible in the two-dimensional magnetic topological material MnBi₂Te₄, through a type of hybrid light–matter excitation they call magnetophononic polaritons. The study is published in ACS Nano.
"Controlling magnetism and topology with light has long been a challenge in topological quantum materials research. Our calculations show a way to achieve both at once, which could enable ultrafast on–off switching of topological states," said Dr. Enamul Haque, the study's first author, who carried out the work during his Ph.D. at Monash University.
Using first-principles calculations, the researchers show that magnetophononic polaritons allow light to change both magnetic order and electronic topology. Their calculations indicate that a strong terahertz pulse, 0.6 picoseconds long with a field of about 2 MV/cm, drives lattice vibrations 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 (see image above).
In this state, the sheet changes from an ordinary insulator to a topological one, with protected conducting channels along its edges. The effect requires low temperatures, below about 20 to 25 kelvin, for the material to be magnetic.
In quantum materials, electrons, atomic vibrations and magnetic moments interact to produce collective excitations known as quasiparticles. Phonon polaritons are one such quasiparticle, formed when light couples to vibrations of the crystal lattice (phonons). They confine light into very small spaces, which makes them useful for nanophotonics. In MnBi₂Te₄, one of the polaritons compresses light to an effective wavelength of about 18 nanometers, compared with about 65 micrometers for light of the same energy 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. Our next step is to work with experimental colleagues to test the prediction at low temperature using terahertz pulses," said professor Nikhil Medhekar, who supervised the research at Monash University.
Optically induced magnetic changes offer a route to ultrafast switching, and confined polaritons suit miniaturized photonic components. Combining both in one material points to devices in which light controls magnetic and topological electronic states, with potential uses in reconfigurable electronics, spintronics and nanophotonic switches.
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Enamul Haque completed a PhD at Monash University in Australia, while also an associate PhD student affiliated with the ARC Center of Excellence in Future Low-Energy Electronics Technologies (FLEET). Haque is currently a Postdoctoral Research Fellow at the Polytechnic University of Cartagena (UPCT) in Spain, focusing on quantum materials, condensed matter physics, and light–matter interactions, with particular emphasis on magnetic and topological phenomena. Haque investigates how fundamental quantum interactions can be harnessed to control material properties and advance future quantum and electronic technologies.
Haque is particularly interested in elucidating complex physical phenomena at the microscopic level and in developing theoretical and computational methods to study them. More broadly, Haque aims to explore fundamental questions in condensed matter physics, foster connections across research areas, and translate theoretical insights into opportunities for technological innovation.