The World of Complex Systems Physics Research Driving Scientific and Technological Breakthroughs

Physics is often described as a "field for eccentrics." Using terms like atoms, energy, and interactions, it seeks to unravel phenomena beyond what we can see with the naked eye, making it seem distant from the real world.

However, Senior Researcher KIM Kyung Min defines the complex systems physics he studies as "a discipline that solves real-world problems." This interdisciplinary field integrates profound theories and large-scale simulations. Though invisible, the world we perceive as reality is composed of complex structures of numerous particles. Even plants and animals, which seem to exist naturally, have hidden order within them. Examples include the Fibonacci sequence in lilies and roses, or the golden ratio that signifies the most balanced proportions.

Complex systems physics interprets the intricate phenomena in nature, which cannot be explained by simple theories based on ideal conditions. Recently, Kim has gone beyond interpreting phenomena and proposed physical solutions applicable to real-world technologies, such as superconducting semiconductors. "I want to contribute to technological leaps through innovative research," says Kim, as we delve into his research journey.

Q. Please introduce yourself.
Hello, I am Kim Kyung-min, a senior researcher at the Center for Theoretical Physics of Complex Systems (PCS) within the Institute for Basic Science (IBS). Before joining IBS, I completed my Ph.D. in condensed matter theory at POSTECH. My specialization, quantum field theory in condensed matter, is often considered one of the most "theoretical" branches of condensed matter physics. It focuses on uncovering simple and fundamental principles rather than the complex and diverse properties that emerge in

Q. What led you to join IBS?
I felt the desire to challenge myself with new fields of study beyond the perspectives I had gained from condensed matter quantum field theory. At that time, simulation techniques utilizing computers were beginning to advance at an incredible pace. Naturally, I developed a strong aspiration to engage in research on more realistic and practical physical systems, such as complex systems, using computer simulations.

While searching for a research institute where I could pursue this new approach, I discovered the Center for Theoretical Physics of Complex Systems at IBS. Attending a conference hosted by the research group served as the catalyst for my interest. When I visited the center, I found many excellent researchers and well-equipped facilities for research. I felt that I could pave new research directions here. So, about four years ago, I began my postdoctoral research at the center.

Q. What is the Center for Theoretical Physics of Complex Systems like? 

The name "complex systems" might sound a bit ambiguous, but it can actually be described as the most "realistic" branch of physics. Traditional pure theoretical physics often assumes ideal conditions and explores the physical phenomena that occur within those scenarios. For example, researchers might study the physical behavior of a space containing only one or two particles.

However, the reality we live in is quite different. The materials that make up our world consist of countless particles, which interact with each other in complex ways. There exists a kind of network structure, akin to a spider web, among these particles. The Center for Theoretical Physics of Complex Systems is a place where scholars study phenomena within complex physical systems grounded in the real world. To effectively investigate complex systems, we employ a variety of methods, including effective modeling techniques and computer simulations.

Q: How is the atmosphere at the research group?
I was extremely satisfied. Since it’s an institution dedicated solely to research, it has better research facilities than educational institutions like universities.

However, what impressed me even more than the facilities was the research culture here. Researchers actively discuss each other's work and provide constructive feedback. During the process of multiple researchers gathering, asking questions, and exchanging ideas, I received sharp insights that I hadn’t thought of. I believe it’s the perfect environment for growth as a researcher.

Q. What kind of research did you want to pursue here?
I became interested in studying the complex and diverse characteristics that appear in real-world condensed matter systems, such as two-dimensional magnetic materials. By integrating various methods, including effective modeling techniques and computer-based simulations, I wanted to tackle challenging problems in condensed matter physics that had previously been difficult to approach. I believed that solving these practical physics problems could have a greater impact on the advancement of science and technology.

Q. What research did you do here? Can you share one of your key research accomplishments?
I was the first to successfully implement a method to stabilize unstable spin structures in two-dimensional magnetic materials (van der Waals magnets). A magnetic material is a substance that exhibits magnetism, and a spin structure refers to the arrangement of spins within the material according to complex rules.

Spin structures exhibit intricate patterns that are clearly distinct from their surroundings. They respond sensitively to external stimuli while maintaining a stable structure. Due to these unique characteristics, they have been actively researched as potential units for storing and transmitting information in semiconductor devices. However, until now, stable spin structures were known to only exist in magnetic materials with vertical anisotropy, where the magnetization direction is perpendicular to the surface.

discovered a method to stabilize spin structures in horizontally anisotropic magnetic materials by twisting and bonding two layers of magnets together. In horizontally anisotropic materials, a spin structure known as a "meron" forms, but in typical magnets, merons are unstable due to pair annihilation. This research marks the first time a method has been found to stabilize merons. The significance of this lies in the fact that it makes it possible to apply spin structures like merons, which had previously been too unstable to be used in memory devices, to semiconductor technology.

Q. This research must have been not easy.
hat's right. The twisted magnetic material dealt with in this research is a prime example of an unexplored field in complex systems. Globally, there are fewer than ten research groups studying it. In Korea, there are even fewer researchers, so when I faced challenges, there was no one to consult. Gathering the necessary knowledge and resources was also difficult. However, I believed that because it was an unexplored field, the opportunities and rewards would be great.

Although twisted magnetic materials are complex, the core principle I discovered after much deliberation is simple. To explain it simply: when two layers of magnetic materials are twisted and overlapped, a new type of "potential well" forms between the layers—something that doesn’t exist in ordinary magnetic materials. It’s like the deep valley that exists between two mountains. The meron pairs are trapped in this potential well, overcoming the instability caused by pair annihilation and ultimately becoming stabilized.

It took more than six months just to derive this result. Writing the code for the computer simulations also took a lot of time. Then, analyzing the results and writing the paper took more than another year. I remember constantly thinking about the research, whether I was walking or eating. Every stage was a challenge, but the intense happiness I felt when the results turned out as expected was incomparable to anything else.

Q. How was the response in the academia after your findings?
There was significant interest because it was a new discovery. Even experimental physicists reached out, asking if my theory could help explain some of their experimental results.

Q. It seems that this interest could lead to further research.
Yes. Since this theoretical research was not focused on a specific material, I believe that exploring how the theory applies to particular materials in future studies could lead to significant discoveries. I expect that collaboration with materials scientists and experimental physicists will help find ways to realize this theory in practical applications.

Q. What kind of support do you think is necessary to continue your research?
believe we need a delicate balance of support for both long-term, challenging research projects and short-term projects that can yield quick results. Additionally, I think a research culture that grants autonomy to researchers, allowing them to thoroughly study and fully understand their projects, is crucial to achieving breakthrough results.

Q. Any final thoughts you'd like to share?
The IBS Complex Systems Theory Research Group is a place where researchers can enjoy the freedom to lead and explore their own research topics. I hope more places like this emerge across Korea. Every scientist walking the path of research has their own dreams and ambitions, and I hope a stable research environment is created where they can deeply pursue those goals.