Laser Pulse Flips a Ferromagnet Without Heating in Breakthrough That Unites Three Pillars of Condensed Matter Physics
ETH Zurich and University of Basel researchers permanently reversed a ferromagnet's polarity using only laser light in twisted bilayer molybdenum ditelluride, published in Nature.
Overview
A team of physicists at ETH Zurich and the University of Basel has demonstrated that a single laser pulse can permanently reverse the polarity of a ferromagnet, without any heating, in a result published in Nature on January 28, 2026. The experiment used a specially engineered material made of two atomically thin layers of molybdenum ditelluride stacked with a slight twist, and it represents the first time an entire ferromagnet’s orientation has been flipped using light alone.
Conventional methods for switching a magnet’s polarity require heating the material above its critical temperature and then cooling it in an external magnetic field. The new approach bypasses that thermal process entirely, opening a path toward optically programmable magnetic circuits.
What We Know
The research was led by Ataç Imamoğlu, Professor of Physics at ETH Zurich, and Tomasz Smoleński, Professor at the University of Basel, with experimental measurements carried out by Olivier Huber and Kilian Kuhlbrodt at ETH Zurich, according to Phys.org.
The material at the center of the experiment consists of two wafer-thin layers of molybdenum ditelluride positioned at a slight angle relative to each other. This twisted stacking creates a moiré pattern that gives rise to unusual electronic behavior. In this configuration, strong interactions between electrons cause their spins to align in parallel, producing ferromagnetism, while the geometric twist introduces topological states, fundamentally distinct electronic configurations that resist smooth transformation into one another.
A laser pulse directed at the material collectively reorients the electron spins, permanently flipping the magnet’s polarity. A second, weaker laser beam confirms the switch by analyzing the reflected light pattern of the electron spin orientation, as reported by ScienceDaily.
“What’s exciting about our work is that we combine the three big topics in modern condensed matter physics in a single experiment: strong interactions between the electrons, topology and dynamical control,” Imamoğlu said, according to Phys.org.
Olivier Huber, the lead experimental researcher, noted that the switching was permanent and that the material’s topology directly influences the switching dynamics, as reported by AZoOptics. Previous work had shown that individual electron spins could be manipulated with light, but this study is the first to demonstrate the reversal of an entire ferromagnet at once.
What We Don’t Know
The experiment was performed under laboratory conditions on an engineered two-dimensional material, and the researchers have not yet demonstrated the technique at room temperature or at scales relevant to commercial devices. It remains unclear how quickly the switching can be repeated at high frequencies, a requirement for practical computing applications. The Nature paper does not address whether the method can be extended to other twisted bilayer materials or conventional bulk ferromagnets.
Analysis
The result is significant because it bridges three domains of condensed matter physics, electron interactions, topology, and optical control, within a single experiment. Topology-based electronic states are prized for their robustness; combining them with light-driven magnetic switching could eventually enable reconfigurable circuits that are written and rewritten optically rather than lithographically.
Smoleński outlined the longer-term vision: “In the future, we will be able to use our method to optically write arbitrary and adaptable topological circuits on a chip,” which could be used to create miniature interferometers capable of measuring extremely small electromagnetic fields, according to AZoOptics.
If the technique can be scaled and adapted to operate under less stringent conditions, it could inform the development of next-generation magnetic memory, reconfigurable photonic devices, and precision sensing instruments. For now, the work stands as a proof of concept that light alone can permanently and reversibly control macroscopic magnetic order in a quantum material.