Research
Research
I am interested in interplays between theories of hard condensed matter and soft matter. In particular, I have been studying topological materials in non-Hermitian and nonlinear systems and its applications to classical systems.
Active matter, a collection of self-propelled particles, have attracted much attention in biophysics and nonequiblium statistical physics. We have theoretically proposed active-matter counterparts of topological materials. Specifically, we have shown that an active-matter counterpart of the quantum anomalous Hall effect by using a kagome-lattice structure. We have also revealed that the non-Hermiticity inherent to active matter can be utilized to realize topological edge modes unique to non-Hermitian systems, namely, exceptional edge modes.
Papers: Phys. Rev. Lett. 123, 205502 (2019), Nat. Commun. 11, 5745 (2020)
Reciew article: arXiv:2407.16143
Non-Hermitian Hamiltonians are used to effectively describe the dynamics of open systems. We have revealed a unique mechanism to protect edge modes, which we term exceptional edge modes. The exceptional edge modes utilizes the nontrivial topology of band structures around exceptional points, gapless points unique to non-Hermitian systems. We have also proposed their applications to laser devices and active matter.
We have also studied topological invariants and phenomena unique to stochastic systems by considering the transition rate matrix as an effective Hamiltonian.
Papers: Nat. Commun. 11, 5745 (2020), Phys. Rev. B 105, 235426 (2022), Phys. Rev. Lett. 132, 046602 (2024), arXiv:2405.00458
Nonlinearity is ubiquitous in classical and interacting bosonic systems. However, since the conventional theory of topological materials relies on the linearity of equations, it is unclear whether the notion of topology can be extended to nonlinear systems.
We have proposed topological invariants characterizing nonlinear systems by extending the eigenvalue problem to nonlinear cases, and revealed their bulk-boundary correspondence. Furthermore, we have found unexpected connections between nonlinear physics and topological materials, such as topological synchronization and chaos transitions of edge modes.
Papers: Phys. Rev. Research 4, 023211 (2022), Nat. Phys. 20, 1164-1170 (2024), Nat. Commun. 16, 422 (2025), arXiv:2501.10087