Soliton
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KAIST and Mainz Researchers Unveil 3D Magnon Control, Charting a New Course for Neuromorphic and Quantum Technologies
< Professor Se Kwon Kim of the Department of Physics (left), Dr. Zarzuela of the University of Mainz, Germany (right) >
What if the magnon Hall effect, which processes information using magnons (spin waves) capable of current-free information transfer with magnets, could overcome its current limitation of being possible only on a 2D plane? If magnons could be utilized in 3D space, they would enable flexible design, including 3D circuits, and be applicable in various fields such as next-generation neuromorphic (brain-mimicking) computing structures, similar to human brain information processing. KAIST and an international joint research team have, for the first time in the world, predicted a 3D magnon Hall effect, demonstrating that magnons can move freely and complexly in 3D space, transcending the conventional concept of magnons.
KAIST (President Kwang Hyung Lee) announced on May 22nd that Professor Se Kwon Kim of the Department of Physics, in collaboration with Dr. Ricardo Zarzuela of the University of Mainz, Germany, has revealed that the interaction between magnons (spin waves) and solitons (spin vortices) within complex magnetic structures (topologically textured frustrated magnets) is not simple, but complex in a way that enables novel functionalities.
Magnons (spin waves), which can transmit information like electron movement, are garnering attention as a next-generation information processing technology that transmits information without using current, thus generating no heat. Until now, magnon research has focused on simple magnets where spins are neatly aligned in one direction, and the mathematics describing this was a relatively simple 'Abelian gauge theory.'
The research team demonstrated, for the first time in the world, that in complex spin structures like frustrated magnets, magnons interact and become entangled in complex ways from various directions. They applied an advanced mathematical framework, 'non-Abelian gauge theory,' to describe this movement, which is a groundbreaking achievement.
This research presents the possibility of future applications in low-power logic devices using magnons and topology-based quantum information processing technologies, indicating a potential paradigm shift in future information technology.
In conventional linear magnetic materials, the value representing the magnetic state (order parameter) is given as a vector. In magnonics research based on this, it has been interpreted that a U(1) Abelian gauge field is induced when magnons move in soliton structures like skyrmions. This means that the interaction between solitons and magnons has a structure similar to quantum electrodynamics (QED), which has successfully explained various experimental results such as the magnon Hall effect in 2D magnets.
< Figure. Schematic diagram of non-Abelian magnon quantum chromodynamics describing the dynamics of three types of magnons discovered for the first time in this study.>
However, through this research, the team theoretically revealed that in frustrated magnets, the order parameter must be expressed not as a simple vector but as a quaternion. As a result, the gauge field experienced by magnons resembles an SU(3) non-Abelian gauge field, rather than a simple U(1) Abelian gauge field.
This implies that within frustrated magnets, there are not one or two types of magnons seen in conventional magnets, but three distinct types of magnons, each interacting and intricately entangled with solitons. This structure is highly significant as it resembles quantum chromodynamics (QCD) that describes the strong interaction between quarks mediated by gluons rather than quantum electrodynamics (QED) that describes electromagnetic forces.
Professor Se Kwon Kim stated, "This research presents a powerful theoretical framework to explain the dynamics of magnons occurring within the complex order of frustrated magnets," adding, "By pioneering non-Abelian magnonics, it will be a conceptual turning point that can influence quantum magnetism research as a whole."
The research results, with Dr. Ricardo Zarzuela of the University of Mainz, Germany, as the first author, were published in the world-renowned physics journal Physical Review Letters on May 6th.※ Paper title: "Non-Abelian Gauge Theory for Magnons in Topologically Textured Frustrated Magnets," Phys. Rev. Lett. 134, 186701 (2025)DOI: https://doi.org/10.1103/PhysRevLett.134.186701
This research was supported by the Brain Pool Plus program of the National Research Foundation of Korea.
2025.05.22 View 1519 -
Success in Real-Time Observation of the Formation Process of Topological Solitons, a Core Technology for Next-Generation Information Transfer
< From left) Geonhyeong Park (Ph.D. Candidate), Yun-Seok Choi (Ph.D.), Professor Dong Ki Yoon, and Changjae Lee (Ph.D. Candidate) of the Department of Chemistry >
Professor Dong Ki Yoon's research team in the Department of Chemistry at KAIST announced on the 11th that they have succeeded in controlling the formation of topological solitons in a regular, large-area manner through the self-assembly of chiral liquid crystal materials and observing their formation process in real-time.
A soliton refers to a phenomenon where a specific wave persists without dissipating through interaction with its surroundings. In particular, even when a wave is transmitted over long distances, it retains its unique information until it reaches the desired destination. Therefore, in today's digital society, which is susceptible to hacking, solitons are highly anticipated to be the core of future communication due to their inherent high stability. Furthermore, topological solitons created using organic liquid crystal molecules are expected to be utilized as next-generation anti-counterfeiting devices and memory elements due to their unique spin directionality.
Professor Yoon's team specifically revealed the formation process of topological solitons in this study, which had not been observable in real-time under mild conditions such as room temperature until now. This was made possible by using self-assembling chiral liquid crystal materials in a confined space created by air pillars.
This research, in which Geonhyeong Park (Ph.D. Candidate, Department of Chemistry) and Dr. Ahram Suh participated as co-first authors, and Dr. Yun-Seok Choi and Changjae Lee (Ph.D. Candidate) from the same group also participated, was published online in the international journal 'Advanced Materials' on June 5th and is scheduled to be featured as the back cover of the July issue. (Paper title: "Fabrication of Arrays of Topological Solitons in Patterned Chiral Liquid Crystals for Real-Time Observation of Morphogenesis")
< Figure 1. Schematic diagram of the research>
< Figure 2. Real-time observation of topological soliton formation using liquid crystals>
In this study, Professor Yoon's team implemented topological soliton structures at approximately 30 degrees Celsius, similar to room temperature, using chiral (asymmetric) liquid crystal materials instead of the conventional liquid crystal molecules widely used as core materials in liquid crystal displays (LCDs). Generally, complex equipment is required to control the formation of topological solitons, and their formation time is very short, which has hindered research into their formation process until now.
To achieve regular formation and control of topological solitons formed by chiral liquid crystal molecules, Professor Yoon's team precisely controlled a combination of vertical alignment layers, which can orient molecules vertically, and air pillars. Specifically, they prepared concave patterns based on circular silicon material, several micrometers (one-millionth of a meter) in size, coated with a vertical alignment layer, and a glass substrate. By adjusting the gap to several micrometers and injecting chiral liquid crystal material, air pillars were spontaneously formed on the concave patterns. Subsequently, the liquid crystal molecules were vertically aligned on all substrates, inevitably causing regular distortions between the substrates, and between the substrate and the air pillars, thus developing a system where chiral molecular structures, i.e., topological solitons, could be formed.
The key to the formation and control of topological solitons lies in controlling the thermal phase transition to occur regularly as desired when cooling from the isotropic phase temperature (approximately 40 degrees Celsius) to the liquid crystal phase temperature (approximately 30 degrees Celsius), where the liquid crystal material near the air pillars is cooler than the liquid crystal material between the glass substrate and the silicon patterned parts. This is consistent with the everyday wisdom of eating steamed eggs from a 'Ttukbaegi' (earthen pot) by starting from the relatively cooler part exposed to the air (near the air pillars) rather than the hot pot part (silicon or glass substrate part).
Through real-time analysis, the research team elucidated that topological defects are formed by the naturally formed air pillars through controlled thermal phase transition, and topological solitons are formed only at the locations of these defects. This analysis technique has the potential for application in various fields, including the interpretation of topological soliton formation found in other physical phenomena such as skyrmion particles in electromagnetism.
< Figure 3. Snapshots during the formation process of regularly arranged topological solitons>
Professor Dong Ki Yoon stated, "General topological solitons are known to be highly stable, capable only of generation or annihilation. Through the results of this research, we can understand the formation process of solitons in more detail, and they can be used as spintronics application technology, considered a next-generation semiconductor device for storing and recording information."
This research was conducted in collaboration with Professor Ivan Smalyukh's laboratory at the University of Colorado, Department of Physics, and was supported by the Multiscale Chiral Structures Research Center and strategic projects of the National Research Foundation of Korea under the Ministry of Science and ICT.
2022.07.11 View 46