Strong Correlation Quantum Transport Research Team

Principal Investigator
Outline
Members
Publications
Articles

Principal Investigator

PI Name

Yoshinori Tokura

Degree

D.Eng.

Title

Team Leader

Brief Resume

1981	D. Eng., University of Tokyo
1986	Associate Professor, University of Tokyo
1994	Professor, Department of Physics, University of Tokyo
1995	Professor, Department of Applied Physics, University of Tokyo
2001	Director, Correlated Electron Research Center, AIST
2007	Group Director, Cross-Correlated Materials Research Group, RIKEN
2008	AIST Fellow, National Institute of Advanced Industrial Science and Technology (-present)
2010	Director, Emergent Materials Department, RIKEN
2010	Group Director, Correlated Electron Research Group, RIKEN
2013	Director, RIKEN Center for Emergent Matter Science (CEMS)
2013	Group Director, Strong Correlation Physics Research Group, Strong Correlation Physics Division, RIKEN CEMS (-present)
2014	Team Leader, Strong Correlation Quantum Transport Research Team, RIKEN CEMS (-present)
2017	Distinguished University Professor, University of Tokyo (-present)
2019	Special University Professor, University of Tokyo
2024	Special Advisor to the President, RIKEN (-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 Science

Keywords

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

Results

Quantum transport phenomena of surface Dirac states in thin film superstructures

The topological insulator is a new state of matter, whose bulk is a three-dimensional charge-gapped insulator but whose surface hosts a two-dimensional Dirac electron state. Surface Dirac states are characterized by massless electrons and holes whose spins are polarized perpendicular to their crystal momentum. As a result, the quantum transport phenomena stemming from their charge and spin degrees of freedom are promising for the applications to low-power consumption electronic devices. The well-known example for this is the quantum anomalous Hall effect (QAHE) in which one-dimensional conducting channel without any dissipation emerges at zero magnetic field. We established the growth of high quality thin film superstructure of topological insulator (Bi_xSb_1-x)₂Te₃sandwiched by ferromagnetic insulator (Zn,Cr)Te, by means of molecular beam epitaxy (MBE) method. We cooled down to cryogenic temperature, and successfully observed QAHE. We will make full use of the thin film superstructure to add functionality to topological materials. In particular, we now embark on the observation or control of the Majorana quasiparticle, which is expected to be applied to quantum computers.

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

Members

Yoshinori Tokura	Team Leader	tokura[at]riken.jp
Ilya Belopolski	Research Scientist	ilya.belopolski[at]riken.jp
Yuki Sato	Postdoctoral Researcher
Max Birch	Special Postdoctoral Researcher
Lixuan Tai	Postdoctoral Researcher
Yoshichika Onuki	Senior Visiting Scientist
Ayako Yamamoto	Visiting Scientist
Masataka Mogi	Visiting Scientist

Publications

M. Kawamura, M. Mogi, R. Yoshimi, T. Morimoto, K. S. Takahashi, A. Tsukazaki, N. Nagaosa, M. Kawasaki, and Y. Tokura

Laughlin charge pumping in a quantum anomalous Hall insulator

Nat. Phys. 19, 333–337 (2023)
M. Mogi, Y. Okamura, M. Kawamura, R. Yoshimi, K. Yasuda, A. Tsukazaki, K. S. Takahashi, T. Morimoto, N. Nagaosa, M. Kawasaki, Y. Takahashi, and Y. Tokura

Experimental signature of the parity anomaly in a semi-magnetic topological insulator

Nat. Phys. 18, 390–394 (2022)
K. Yasuda, T. Morimoto, R. Yoshimi, M. Mogi, A. Tsukazaki, M. Kawamura, K. S. Takahashi, M. Kawasaki, N. Nagaosa , and Y. Tokura

Large non-reciprocal charge transport mediated by quantum anomalous Hall edge states

Nat. Nanotechnol. 15, 831 (2020)
K. Yasuda, H. Yasuda, T. Liang, R. Yoshimi, A. Tsukazaki, K. S. Takahashi, N. Nagaosa, M. Kawasaki, and Y. Tokura

Nonreciprocal charge transport at topological insulator/superconductor interface

Nat. Commun. 10, 2734 (2019)
R. Yoshimi, K. Yasuda, A. Tsukazaki, K. S. Takahashi, M. Kawasaki, and Y. Tokura

Current-driven magnetization switching in ferromagnetic bulk Rashba semiconductor (Ge,Mn)Te

Sci. Adv. 4, aat9989 (2018)

Articles

Apr 18, 2023 Why exotic states of matter don’t need edges

Contrary to expectation, experiments show that edges are not needed to realize an unusual quantum effect
Dec 16, 2019 A new way to induce the quantum anomalous Hall effect

A ferromagnetic layer can induce the quantum anomalous Hall effect in a topological insulator
Mar 16, 2018 Domain walls allow dissipationless chiral edge conduction of electrons

Chiral edge states could offer a way to store and manipulate information in low-power electronic devices
Mar 02, 2018 Axion insulator exhibits giant magnetoresistance at low magnetic fields

The resistance of a new design of quantum material varies greatly with magnetic field, making it useful for novel devices
Feb 23, 2018 Chiral magnets show bulk diode effect due to spin fluctuation

Materials with left- and right-handed responses to current exhibit an intriguing diode effect
Oct 09, 2015 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 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 ....