The study of interactions within physical systems has long adhered to the principles established by Newton, particularly the concept of action and reaction. However, recent advancements in material science suggest that light could pave the way for interactions in solid-state systems that effectively violate these principles, leading to revolutionary consequences in quantum materials. Researchers from the Institute of Science Tokyo have recently developed a theoretical framework that predicts the emergence of non-reciprocal interactions, a phenomenon synonymous with non-equilibrium systems, which could redefine how we understand magnetic behavior in materials.
Light, a ubiquitous form of energy, has been shown to possess the capability to induce significant changes in the properties of materials, particularly magnetic metals. The research, led by Associate Professor Ryo Hanai and collaborators from various institutions, posits that by irradiating magnetic materials with light at specified frequencies, one can initiate a process that drives two magnetic layers into complex, synchronized motion, described as a “chase-and-run” dynamic. This revelation introduces a new paradigm in non-equilibrium materials science and opens avenues for innovative applications in areas such as spintronics and quantum computing.
In equilibrium, systems typically obey the laws of thermodynamics and mechanics, resulting in predictable interactions between components. Nevertheless, when we delve into non-equilibrium conditions—such as those encountered in biological systems or active matter—the interactions can display non-reciprocal characteristics. These interactions are evident in many natural occurrences, such as the behavior of neurons in the brain or interactions within ecosystems. The question arises: can we replicate these non-reciprocal characteristics within solid-state electronic systems, and the answer provided by this research is a resounding yes.
The researchers utilized a method, termed dissipation engineering, which involves manipulating how energy is dissipated within magnetic metals. By creating a scenario where certain spin states receive more energy than others, the researchers successfully initiated non-reciprocal interactions. The cornerstone of their findings is the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction, a well-known exchange interaction in magnetic systems. By targeting the interaction through light stimulation, they were able to introduce a non-reciprocal nature to a process traditionally governed by equilibrium and reciprocity.
As the team explored this idea further, they focused on bilayer ferromagnetic systems, which consist of two magnetic layers interacting with each other. When exposed to certain frequencies of light, these layers exhibited a non-reciprocal phase transition, an effect characterized by a dynamic where one layer tends to align while the other exhibits a tendency to anti-align. This creates a unique chiral phase, marked by continuous rotation of magnetization, defying the expected behavior according to Newton’s third law. The implications of such a finding are profound, hinting at the possibility of new materials and devices that leverage non-reciprocal interactions.
Furthermore, the research indicates that the light intensity required to induce these non-reciprocal phase transitions is not beyond current experimental capabilities. This aspect highlights an important transition from theoretical prediction to potential real-world application, as it opens the door for experimental validation and the discovery of new quantum materials that could enable advanced technologies.
The coupling between active matter phenomena and solid-state physics not only enriches the understanding of materials but may also contribute to the development of next-generation spintronic devices. These devices, leveraging the intrinsic spin of electrons, promise faster processing speeds and enhanced functionalities compared to their charge-based counterparts. As such, the pursuit of organized non-reciprocal dynamics could yield devices that are more efficient and represents a shift in how we manipulate information at the quantum level.
Moreover, the insights gained from these experiments could have beneficial impacts on various fields. For instance, exploring non-reciprocal interactions in Mott insulating phases of strongly correlated electrons could lead to the discovery of new superconducting mechanisms. Similarly, the interplay between light and magnetic states could facilitate the realization of frequency-tunable oscillators, thus enhancing communication technologies.
In conclusion, the exploration of non-reciprocal interactions within solid-state systems illuminated by light marks a significant leap forward in materials science. It invites researchers to rethink classical mechanics laws in the context of novel applications in both fundamental and applied physics. As scientists continue to unlock the mysteries of non-equilibrium systems, we may soon witness transformative changes that could revolutionize many technological landscapes—from quantum computing to advanced materials engineering.
This pivotal research sets the stage for future investigations into the intricate relationships between light, magnetic interactions, and the underlying physics governing them, indicating a promising frontier in both theoretical and applied science.
Subject of Research: Non-reciprocal interactions in solid-state systems induced by light.
Article Title: Photoinduced non-reciprocal magnetism.
News Publication Date: 18-Sep-2025.
Web References: https://doi.org/10.1038/s41467-025-62707-9
References: Fruchart, Hanai, et al., Nature, 2021; DOI: 10.1038/s41586-021-03375-9
Image Credits: Institute of Science Tokyo.
Keywords
Non-reciprocal interactions, magnetic materials, light-induced phenomena, quantum materials, spintronics, phase transitions, solid-state physics, non-equilibrium systems, RKKY interaction, chiral phase, dissipation engineering.
