ISSP Stay report of Prof. Lee, Hyun-Yong
Hyun-Yong Lee
Division of Semiconductor Physics, Korea University, Sejong, Korea
Returning to ISSP as a visiting professor in Professor Naoki Kawashima’s group was deeply meaningful to me. I had previously spent more than three years at ISSP as a postdoctoral researcher, from 2016 to 2019. Six years after returning to Korea, I had the opportunity to come back for a stay from February to August 2026.
This time, my wife and our twin daughters accompanied me. I greatly enjoyed our life together in Kashiwa. Sharing this stay with my family made it different from my earlier years as a postdoc, and our time in Kashiwa was an important part of what made the visit so special.
Throughout my stay, I attended colloquia and theory seminars covering a broad range of topics. They gave me opportunities to learn about research at the forefront of different fields and to discuss it with researchers from both within and outside ISSP. I also gave a theory seminar and enjoyed the stimulating discussions that followed. Beyond ISSP, I participated in two international meetings in Japan: CompQMB2026 in Okinawa in March and the SQAI–NCTS Joint Workshop 2026 at Keio University in August. The perspectives I gained through these exchanges will be valuable for my future research.
Within the Kawashima group, I had many fruitful research discussions with Professor Kawashima and group members, including Feng-Feng, Jun, Zhi-Yao, Ryoma, and other students. Some of the ideas from these conversations developed into projects that are now ongoing. I plan to stay in touch and continue these discussions and collaborations after the visit.
During this stay, I had the pleasure of working with Professor Kawashima on a variety of interesting research topics. In our work on the spin-1 Baxter–Wu model, we addressed a question about its critical behavior that has remained open for more than four decades. Our results support the view that its unusual critical behavior arises from a slow flow away from the four-state Potts critical point, providing evidence toward resolving this longstanding question.
We also developed a quantics tensor-train approach to multiloop functional renormalization group for strongly correlated electrons, which makes these demanding calculations far more efficient. Tests on impurity models highlighted the importance of multiloop corrections.
With Zhi-Yao Ning, I began an ongoing project on the nature of the one-ninth magnetization plateau in the kagome antiferromagnet. Alongside these studies, I explored tensor-network models of spontaneous brain activity and long-lived active states in the Domany–Kinzel automaton, extending these methods to data modeling and nonequilibrium dynamics.
I am particularly grateful to Professor Kawashima and ISSP for making it possible for my postdoctoral researcher, Seungho Lee, and my student, Taeyoung Lee, to visit. Their visits gave us the opportunity to work in the same research environment.
This half-year was meaningful and productive for me, both in research and in my personal life. I sincerely thank Professor Kawashima and the members of his group for their support and our many discussions. I am also grateful to Itsuko Kuwabara, as well as Yuko Ishiguchi and Ayano Hashiguchi of the International Liaison Office, for their kind help throughout my stay. I hope to return to ISSP and see everyone again.
