Topological Phenomena Theory Research Team

Principal Investigator

PI Name

Shuichi Murakami

Title

Team Director

Brief Resume

1995	Research Associate, Department of Applied Physics, University of Tokyo
1999	Ph.D., University of Tokyo
1999	Visiting Scholar, Department of Physics, Stanford University
2007	Associate Professor, Department of Physics, Tokyo Institute of Technology
2007	PRESTO researcher, Japan Science and Technology Agency
2012	Professor, Department of Physics, Tokyo Institute of Technology
2016	Professor, Materials Research Center for Element Strategy, Tokyo Institute of Technology
2024	Professor, Department of Physics, Institute of Science Tokyo
2024	Specially Appointed Professor, International Institute for Sustainability with Knotted Chiral Meta Matter, Hiroshima University (-present)
2025	Professor, Department of Applied Physics, the University of Tokyo (-present)
2025	Team Director, Topological Phenomena Theory Research Team, RIKEN Center for Emergent Matter Science (-present)

Outline

Our team conducts theoretical research on emergent physical phenomena of electrons and quasiparticles in materials and waves in metamaterials, focusing on their topological structures. Our research methods are mainly analytical methods using models, and we find universal laws and phenomena from a broad perspective of quantum to classical systems. Our research activities cover a wide range of topics, from research on specific materials to the construction of theoretical frameworks for condensed matter and mathematical physics. Specifically, we are working in the fields such as topological phases, chiral phonons, electro-magnetic multipoles, non-Hermitian systems, and metamaterials.

Research Fields

Physics, Materials Sciences

Keywords

Topological insulator
Spintronics
Topological semimetal

Results

Theory of emergent phenomena by chiral phonons

Phonons are quantized vibrations of atoms in crystals, but in some materials, these phonons are accompanied by rotational motion. Such phonons are called chiral phonons. For example, in a system with a chiral crystal structure such as tellurium, the phonons are chiral phonons and involve angular momentum. We are theoretically studying new phenomena related to the angular momentum of such phonons. For example, we theoretically propose that in crystals with low symmetry, chiral phonons are induced when a temperature gradient is present in the crystal. Furthermore, we have theoretically shown that chiral phonons induce spin magnetization in electronic systems, noting that the angular momentum of phonons has the same symmetry as that of electron spin. This phenomenon is caused by the dynamical modulation of the electronic state by chiral phonons, which acquire a geometric phase (Berry phase) and induce spin polarization. Furthermore, we found that in localized spin systems such as ferromagnets and antiferromagnets, chiral phonons induce changes in magnon excitations. These indicate that chiral phonons act as an effective magnetic field for electrons and magnons.

Generation of spin polarization by chiral phonons.

Members

Shuichi Murakami	Team Director	shuichi.murakami[at]riken.jp