Emergent Device Research Team

Principal Investigator

PI Name Yoshihiro Iwasa
Degree Ph. D.
Title Team Leader
Brief Resume
1986Ph. D., University of Tokyo
1986Research Associate, Department of Applied Physics, University of Tokyo
1991Lecturer, Department of Applied Physics, University of Tokyo
1994Associate Professor, School of Materials Science, Japan Advanced Institute of Science and Technology
2001Professor, Institute for Materials Research, Tohoku University
2010Professor, Quantum-Phase Electronics Center, University of Tokyo (-present)
2010Team Leader, Strong-Correlation Hybrid Materials Research Team, RIKEN
2013Team Leader, Emergent Device Research Team, Supramolecular Chemistry Division, RIKEN Center for Emergent Matter Science (-present)

Outline

The purpose of Emergent Device Research Team is to discover novel quantum functionalities and create revolutionary energy materials based on two-dimensional (2D) materials, nanotube, and quantum dots of various oxides and chalcogenides. Specifically, control of quantum phase transitions and optimization of functionality are made by means of van der Waals heterostructures, and a wide range of carrier density tuning using electric double layer transistors. Such a unique combination of nanomaterials and iontronics concept enables us to realize 2D superconductivity, phase transitions of 2D materials, developments of new thermoelectric materials, and photovoltaics and nonreciprocal transport.

Research Fields

Physics, Engineering, Chemistry, Materials Sciences

Keywords

2D materials
Nanotubes
Quantum dots
Superconductivity
Thermoelectric effect
Nonreciprocal transport
Anomalous photovoltaic effect

Results

Quantum Materials and Their Nanodevices toward Revolutionary Energy Materials

FeSe is a unique 2D superconductor, where the critical temperature exhibits a dramatic jump from 8 K to 40 K by reducing the thickness from bulk to monolayer. However, due to the difficulty in fabrications, the transport properties has remained elusive. We fabricated FeSe monolayer films by means of an iontronic technique, and succeeded in the first measurement of thermoelectric properties.

Left figure shows an electric double layer transistor (EDLT) device of a FeSe monolayer. FeSe monolayer was obtained through the detailed control of electrochemical etching processes with temperature and gate voltages. Right figure summarizes the temperature dependence of thermoelectric power factor P for various materials including monolayer FeSe. We found that monolayer FeSe exhibits gigantic value of 250 μW/cm/K2 beyond that of well-known thermoelectric material Bi2Te3. Furthermore at low temperatures, record-high P values are observed exceeding all reported materials. This example unambiguously demonstrates that 2D and related materials are highly promising for our purposes.

Left: Monolayer FeSe device fabricated by an iontronic technique
Adapted from “Nature Communications 10, 825 (2019).”
Right: Temperature dependence of thermoelectric power factor of monolayer FeSe and other materials

 

Iontronics toward Revolutionary Energy Materials

  We are proposing a new concept “iontronics”, which means electronics controlled by motions and arrangements of ions. By introducing Iontronics, we are nowadays able to go beyond the conventional current switching devices and to realize voltage-controlled electronic phase transitions, including superconductivity, ferromagnetism, and metal-insulator transitions. Iontronics is growing up to an interdisciplinary field stemming from electrochemistry, materials science, condensed matter physics to energy materials.

A representative device iontronics is an electric double layer transistor (EDLT), which enables the high density carrier accumulation at the electrolyte-solid interfaces. Left figure shows the temperature-dependence of resistance of vanadium dioxide (VO2), demonstrating the field-induced insulator-metal transition with only 1 V. Right figure depicts the optimization of the thermoelectric power factor in zinc oxide (ZnO), an archetypal oxide semiconductor, as a function of carrier density, demonstrating a comparable power factor to that of the practically used Bi2Te3. These achievements are indicating novel routes toward the next generation low power consumption devices as well as revolutionary energy materials.

Left: Gate-induced esistance switching in VO2 EDLT.
Adapted from “Nature 487, 459-462 (2012).” with permission (© 2012 Nature)
Right: Optimization of thermoelectric power factor of ZnO with EDLT.
Adapted from “PNAS, 113, 6438-6443 (2016).” with permission

Members

Yoshihiro Iwasa

Team Leader iwasay[at]riken.jp R

Satria Bisri

Research Scientist satria.bisri[at]riken.jp R

Masaro Yoshida

Postdoctoral Researcher

Articles

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

TEL:+81-(0)48-467-8083

E-mail:
iwasay[at]riken.jp

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