Computational Quantum Matter Research Team

Principal Investigator

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

Outline

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 Sciences

Keywords

Strongly correlated electron system
Magnetism
Superconductivity
Computational condensed matter physics

Results

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.

Members

Seiji Yunoki

Team Leader yunoki[at]riken.jp R

Tomonori Shirakawa

Research Scientist

Shohei Miyakoshi

Postdoctoral Researcher

お問い合わせ

2-1 Hirosawa, Wako, Saitama 351-0198 Japan

E-mail:
yunoki[at]riken.jp

Links