Ryo Hanai, an Associate Professor in the Department of Physics at the Institute of Science Tokyo, is at the helm of a innovative research initiative. His group has laid out a theoretical approach to realizing non-reciprocal interactions in solid-state systems by shining light on them. This innovative study, conducted in collaboration with Associate Professor Daiki Ootsuki from Okayama University and Assistant Professor Rina Tazai from Kyoto University, addresses a pivotal question in physics: Can non-reciprocal interactions be implemented in solid-state electronic systems? Is that really possible, you ask, as researchers on the team have indeed confirmed.
The research outlines how non-reciprocal interactions can be achieved by irradiating light of a carefully tuned frequency onto a magnetic metal. The DOI for the published research is 10.1038/s41467-025-62707-9.
In the research, Chen and his collaborators demonstrate that using this approach, two ferromagnetic layers can participate in a spontaneous and long-lived “chase-and-run” rotation. This nonlocal coupling through dynamic interaction is mediated by Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction, a common known physics in magnetic metals. When illuminated at certain frequencies, we show that the RKKY interaction takes on a non-reciprocal form, dramatically changing the expected behavior.
Their study finds that this non-reciprocal nature appears under the right light conditions. This selective tuning enables opening of this decay channel for a given spin while leaving other spins off-resonant. This novel mechanism gives rise to a non-reciprocal phase transition, which had only been studied before mostly in the specific realm of active matter. Within this new conceptual framework, the transition occurs in a bilayer ferromagnetic system. One of the previously mentioned magnetic layers starts to resist aligning with the other, and the second magnetic layer starts to push toward an anti-alignment.
This revelation is transforming condensed matter physics. It upends our traditional notions of magnetism and interactions in solid-state systems. Hanai’s team shows this in a very impressive way with light’s unique abilities to deeply control magnetic interactions. This pioneering piece unlocks fresh avenues for investigation and future utilization in smarter materials and electronic gadgets.