Strong Correlation Theory Research Group

Principal Investigator

PI Name Naoto Nagaosa
Degree D.Sci.
Title Group Director
Brief Resume
1983Research Associate, University of Tokyo
1986D.Sci., University of Tokyo
1998Professor, University of Tokyo (-present)
2001Team Leader, Theory Team, Correlated Electron Research Center, National Institute of Advanced Industrial Science and Technology
2007Team Leader, Theoretical Design Team, RIKEN
2010Team Leader, Strong-Correlation Theory Research Team, RIKEN
2013Deputy Director, RIKEN Center for Emergent Matter Science (CEMS) (-present)
2013Division Director, Strong Correlation Physics Division, RIKEN CEMS (-present)
2013Group Director, Strong Correlation Theory Research Group, Strong Correlation Physics Division, RIKEN CEMS (-present)

Outline

We study theoretically the electronic states in solids from the viewpoint of topology and explore new functions, including non-dissipative currents. Combining first-principles electronic structure calculations, analytic methods of quantum field theory and numerical analysis of models for correlated systems, we predict and design magnetic, optical, transport and thermal properties of correlated electrons focusing on their internal degrees of freedom such as spin and orbital. In particular, we study extensively the nontrivial interplay between these various properties, i.e., cross-correlation, and develop new concepts such as electron fractionalization and non-dissipative quantum operation by considering the topology given by the relativistic spin-orbit interaction and/or spin textures.

Research Fields

Physics, Engineering, Materials Sciences

Keywords

Emergent electromagnetism
Magnetoelectric effect
Shift current
Non-reciprocal effect
Spin Hall effect
Interface electrons
Superconductivity

Results

Theory of shift current

Shift current, i.e., the photo-induce dc current in non-centrosymmetric crystal without the external electric field, is considered to be a promising candidate for the high efficiency photovoltaic effect in perovskite solar cells, attracts recent intensive attention. This current is one of the topological currents induced by the Berry phase of Bloch wavefunctions in solids,  and is essentially different from the conventional photocurrent. We have formulated this shift current in terms of the non-equilibrium Keldysh Green’s function, and studied the nonlinearity with respect to the strength E of the electric field of light, effects of the electron-electron interaction, and its non-locality. We have revealed the following nature of shift current. (i) We have determined the functional form of the shift current as a function of E, and found its saturation effect. (ii) The effect of exciton formation on the shift current is analyzed, and found that the shift current survives even when the optical excitation does not  create the free electron-hole pairs. (iii) We found that the shift current does not depend on the position of the photo excitation, which is in sharp contrast to the conventional photocurrent which is large when the photo excitation is near the electrodes. These results  have unveiled the unique nature of shift current as a kind of topological current, and offer  a guiding principles for the design of high efficiency solar cells.

Schematic figure of shift current
Photo-induced Floquet band structure, and its Berry phase structure induces the shift current.
T. Morimoto, and N. Nagaosa, Science Advances, 2, e1501524 (2016)

Members

Naoto Nagaosa

Group Director nagaosa[at]riken.jp R

Andrey Mishchenko

Senior Research Scientist

Wataru Koshibae

Senior Research Scientist

Ryota Nakai

Special Postdoctoral Researcher

Articles

  • Aug 04, 2017 RIKEN RESEARCH An uneven resistance
    Superconducting molybdenum disulfide exhibits a huge enhancement in the variability of resistance with field direction
  • Jul 21, 2017 RIKEN RESEARCH Flaws in zinc oxide films add magnetic twist
    Why does a non-magnetic material cause electrons to behave like they are interacting with a magnet?
  • Mar 03, 2017 RIKEN RESEARCH Weyl fermions, on the other hand
    Analogs of undiscovered elementary particles are predicted to exhibit an unusual effect in exotic materials
  • Jul 29, 2016 RIKEN RESEARCH A new tilt on an old particle
    When recreated in a solid, fundamental particles predicted over 80 years ago could exhibit more exotic properties than anticipated
  • Sep 25, 2015 RIKEN RESEARCH A magnetic memory bubbling with opportunity
    Ultrafast laser pulses can manipulate ‘bubble’ domains for future spintronic and logic devices
  • Sep 04, 2015 RIKEN RESEARCH Spins on the edge
    The edges of thin films could provide an ideal laboratory for studying the behavior of electron spins

お問い合わせ

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

E-mail:
nagaosa[at]riken.jp

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