Imagine a world where the fundamental laws of physics, like Newton's third law of motion, can be bent or even broken. Sounds like science fiction, right? But here's where it gets controversial: researchers from Japan have discovered a way to do just that—using light. In a groundbreaking study, they’ve shown that by shining carefully tuned light on magnetic metals, they can create interactions that defy the principle of 'equal and opposite reactions.' This isn’t just a theoretical curiosity; it’s a potential game-changer for how we control materials at the quantum level.
Here’s the fascinating part: when light of a specific frequency hits a magnetic metal, it triggers a torque that sets two magnetic layers into a perpetual 'chase-and-run' motion. This phenomenon, known as photoinduced non-reciprocal magnetism, opens up a new frontier in non-equilibrium materials science. And this is the part most people miss—it’s not just about breaking the rules; it’s about harnessing this rule-breaking for innovative applications, like light-controlled quantum materials.
In equilibrium, physical systems follow the law of action and reaction, minimizing free energy. But in non-equilibrium systems—think biological processes or active matter—non-reciprocal interactions are surprisingly common. For example, the brain’s neurons interact in a non-reciprocal way, as do predators and prey. This raises a bold question: Can we replicate these non-reciprocal interactions in solid-state systems?
A team led by Associate Professor Ryo Hanai from the Institute of Science Tokyo, alongside collaborators from Okayama University and Kyoto University, says yes. They’ve developed a theoretical framework that uses light to induce non-reciprocal interactions in solids. Their findings, published in Nature Communications, demonstrate how the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction—a well-known magnetic phenomenon—can become non-reciprocal when exposed to light at specific frequencies. This light selectively activates decay channels for certain spins, creating an energy imbalance that drives non-reciprocal behavior.
But here’s the controversial bit: this approach challenges traditional condensed matter physics by borrowing concepts from active matter, a field typically associated with biological systems. By applying this dissipation-engineering scheme to a bilayer ferromagnetic system, the researchers predicted a unique non-equilibrium phase transition. One magnetic layer tries to align with the other, while the other resists, resulting in a continuous, chiral rotation of magnetization. This 'chase-and-run' dynamics is a direct consequence of broken action-reaction symmetry.
What’s even more exciting is that the light intensity required for this effect is within reach of current experimental capabilities. This means we could soon see practical applications, from new types of spintronic devices to frequency-tunable oscillators. Hanai emphasizes that this work not only provides a tool for controlling quantum materials with light but also bridges the gap between active matter and condensed matter physics.
Here’s a thought-provoking question for you: If we can manipulate materials at the quantum level by breaking fundamental laws, what other boundaries in physics might we redefine? Could this lead to technologies we haven’t even imagined yet? Let’s discuss in the comments—do you think this research is a step toward revolutionizing material science, or is it just a fascinating curiosity? Share your thoughts!
For more details, check out the study: Photoinduced non-reciprocal magnetism, Nature Communications (2025). DOI: 10.1038/s41467-025-62707-9. This research is protected by copyright, but fair use for study or research is permitted. The content is provided for informational purposes only.
