Strong Correlation Quantum Transport Research Team

Principal Investigator

PI Name Yoshinori Tokura
Degree D.Eng.
Title Team Leader
Brief Resume
1981D. Eng., University of Tokyo
1986Associate Professor, University of Tokyo
1994Professor, Department of Physics, University of Tokyo
1995Professor, Department of Applied Physics, University of Tokyo (-present)
2001Director, Correlated Electron Research Center, AIST
2007Group Director, Cross-Correlated Materials Research Group, RIKEN
2008AIST Fellow, National Institute of Advanced Industrial Science and Technology (-present)
2010Director, Emergent Materials Department, RIKEN
2010Group Director, Correlated Electron Research Group, RIKEN
2013Director, RIKEN Center for Emergent Matter Science (CEMS) (-present)
2013Group Director, Strong Correlation Physics Research Group, Strong Correlation Physics Division, RIKEN CEMS (-present)
2014Team Leader, Strong Correlation Quantum Transport Research Team, RIKEN CEMS (-present)
2017Distinguished Professor, University of Tokyo (-present)

Outline

We study various kinds of quantum transport phenomena which emerge in bulk materials and at hetero-interfaces of thin films, focusing on electron systems with strong correlation and/or strong spin-orbit interactions. Specifically, we try to clarify quantum states of Dirac electrons at surface/interfaces of topological insulators as well as in bulk Rashba system with broken inversion symmetry, by observing Landau level formation, quantum (anomalous) Hall effect, and various quantum oscillation phenomena at low temperatures and in high magnetic fields. Also, we synthesize high-temperature superconducting cuprates in bulk forms and various transition-metal oxides thin films, and measure transport properties under high pressure or high magnetic-field, aiming at increasing superconducting transition temperature and at finding novel magneto-transport properties.

Research Fields

Physics, Engineering, Materials Sciences

Keywords

Strongly correlated electron system
High-temperature superconductor
Spin-orbit interaction
Topological insulators
Interface electronic structure

Results

Quantum transport phenomena in surface Dirac states

The topological insulator is a new class of materials, whose bulk is a three-dimensional charge-gapped insulator but whose surface hosts a two-dimensional Dirac electron state. Dirac states are characterized by massless electrons and holes—known as Dirac fermions whose spins are polarized perpendicular to their crystal momentum. As a result, the quantum transport phenomena stemming from their charge or spin degrees of freedom are promising for the applications to low-power consumption electronic devices. The well-known example for this is the quantum Hall effect (QHE) in which one-dimensional conducting channel without any dissipation emerges at sample edges. We established the growth of high quality thin film of (BixSb1-x)2Te3, one of topological insulators, by means of molecular beam epitaxy (MBE) method. We fabricated “field effect transistor” structures for electric gating and successfully observed QHE, while changing the number of electrons in the sample. Furthermore, we synthesized a chromium-doped compound Crx(Bi1-ySby)2-xTe3, which shows a spontaneous gap opening in a Dirac state due to the ferromagnetic ordering. As a result, we observed the quantum anomalous Hall effect (QAHE), which is a quantum Hall state realized at zero magnetic field. We now embark on the observation or control of the quantum transport at a ferromagnetic domain wall as the edge state in the magnetic topological insulators.

Schematic of the quantum Hall effect on the surface of a topological insulator.

Members

Yoshinori Tokura

Team Leader tokura[at]riken.jp R

Minoru Kawamura

Senior Research Scientist
Ryutaro Yoshimi Special Postdoctoral Researcher ryutaro.yoshimi[at]riken.jp R

Maximilian Anton Hirschberger

Postdoctoral Researcher

Articles

  • Oct 09, 2015 RIKEN RESEARCH Characterizing electrons in the smallest devices
    A technique for investigating the magnetic properties of electrons in quantum point contacts leads to a better understanding of these quantum devices
  • Mar 14, 2014 RIKEN RESEARCH An exotic phase to manipulate spin
    In conducting materials, free electrons can move from one point to another, conveying their electrical charge to produce an electrical current. Electrons have another property, known as spin, tha ....

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E-mail:
tokura[at]riken.jp

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