Computational Quantum Matter Research Team

Principal Investigator

PI Name Seiji Yunoki
Degree D.Eng.
Title Team Leader
Brief Resume
1996 D.Eng., Nagoya University
1996 Postdoctoral Researcher, National High Magnetic Field Laboratory, USA
1999 Postdoctoral Researcher, Materials Science Center, Groningen University, Netherlands
2001 Postdoctoral Researcher, International School for Advanced Studies, Italy
2006 Long-Term Researcher and Research Assistant Professor, Oak Ridge National Laboratory and University of Tennessee, USA
2008 Associate Chief Scientist, Computational Condensed Matter Physics Laboratory, RIKEN
2010 Team Leader, Computational Materials Science Research Team, RIKEN Advance Institute for Computational Science
2013 Team Leader, Computational Quantum Matter Research Team, RIKEN Center for Emergent Matter Science (-present)
2017 Chief Scientist, Computational Condensed Matter Physics Laboratory, RIKEN (-present)
2018 Team Leader, Computational Materials Science Research Team, RIKEN Center for Computational Science (-present)
2021 Team Leader, Quantum Computational Science Research Team, RIKEN Center for Quantum Computing (-present)


Electrons in solids are in motion within the energy band reflecting the lattice structure of each material. The Coulomb interaction, electron-lattice interaction, and spin-orbit interaction have nontrivial effects on the motion of electrons and induce various interesting phenomena. Our aim is to elucidate the emergent quantum phenomena induced by cooperation or competition of these interactions, using state-of-the-art computational methods for condensed matter physics. Our current focus is on various functional transition metal oxides, topological materials, and heterostructures made of these materials. Our research will lead not only to clarify the mechanism of quantum phenomena in existent materials but also to propose novel materials.

Research Fields

Physics, Materials Science


Strongly correlated electron system
Computational condensed matter physics


Mechanism of novel insulating state and possible superconductivity induced by a spin-orbit coupling

Electrons in solids are moving around, affected by the Coulomb interaction, electron-lattice interaction, and spin-orbit interaction, which induces different behaviors characteristic of each material. Recently, the study for the spin-orbit coupling has greatly progressed and attracted much attention. In the 5d transition metal oxide Sr2IrO4, the spin and orbital degrees of freedom are strongly entangled due to the large spin-orbit coupling and the novel quantum state is formed. Sr2IrO4 is also expected to be a possible superconducting material with a great deal of similarities to the parent compound of cuprate high-temperature superconductivity

We have studied the detailed electronic properties of a 3-orbital Hubbard model for Sr2IrO4 with several computational methods. Our calculations have clearly shown that the ground state of this material is an effective total angular momentum Jeff=1/2 antiferromagnetic insulator, where J eff is “pseudospin”,formed by spin and orbital degrees of freedom due to the strong spin-orbit coupling (x-AFI in Fig. (a)). We have also proposed that the dx2-y2-wave “pseudospin singlet” superconductivity (SC in Fig. (b)) is induced by electron doping into the Jeff=1/2 antiferromagnetic insulator Sr2IrO4.


Ground state phase diagram of 3-orbital Hubbard model with a spin-orbit coupling. (a) Electron density n=5, (b) n>5.


Seiji Yunoki

Team Leader yunoki[at]

Kazuya Shinjo

Research Scientist


  1. H. Watanabe, T. Shirakawa, K. Seki, H. Sakakibara, T. Kotani, H. Ikeda, and S. Yunoki,

    Unified description of cuprate superconductors suing a four-band d-p model

    Phys. Rev. Research 3, 033157 (2021)
  2. F. Lange, S. Ejima, J. Fujimoto, T. Shirakawa, H. Fehske, S. Yunoki, and S. Maekawa

    Generation of current vortex by spin current in Rashba systems

    Phys. Rev. Lett. 126, 157202 (2021)
  3. K. Seki and S. Yunoki

    Emergence of a thermal equilibrium in a subsystem of a pure ground state by quantum entanglement

    Phys. Rev. Research 2, 043087 (2020)
  4. K. Seki, and S. Yunoki

    Thermodynamic properties of an S=1/2 ring-exchange model on the triangular lattice

    Phys. Rev. B 101, 235115 (2020)
  5. T. Kaneko, T. Shirakawa, S. Sorella, and S. Yunoki

    Photoinduced eta Pairing in the Hubbard Model

    Phys. Rev. Lett. 122, 077002 (2019)



#225 Main Research Build., 2-1 Hirosawa, Wako, Saitama 351-0198 Japan