Emergent Device Research Team

Principal Investigator

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


The purpose of our team is to discover novel properties and create revolutionary functions, based on nanodevices of two-dimensional (2D) materials, 1D nanotubes, and 0D quantum dots (QD) of various oxides and chalcogenides. Our focus is superconductivity, phase transitions, and nonreciprocal transport, using 2D materials and their van der Waals heterostructures, and a wide range of carrier density tuning using electric double layer transistors. We also develop several novel solution-processable QDs, assemble them into various arrangements, and realize various functionalities including thermoelectricity, photovoltaics, and charge storage.

Research Fields

Physics, Engineering, Chemistry, Materials Science


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


Bulk photovoltaic effect induced by symmetry control of two-dimensional materials

Our team is studying nonreciprocal transport in semiconductors and superconductors. One of them is a bulk photovoltaic effect, where the photoelectric conversion occurs without PN junctions. Monolayer transition metal dichalcogenides (TMDs) are two-dimensional materials with three-fold symmetry, which are known not to exhibit bulk photovoltaics. However, such a nanomaterial is capable of changing symmetry either by deforming or creating heterojunctions. This is a unique and important feature of nanomaterials that distinguishes them from bulk. Specifically, we have found strong bulk photovoltaic effects in the visible to infrared region in WS2 nanotubes, WSe2/black phosphorus van Waals heterojunctions, and strained MoS2 (Refs. 1, 3, 5). We found that the shift current mechanism plays an important role in this photovoltaic effect. Symmetry-controlled nanomaterials showing such large photovoltaic effects will be a promising new platform for high-efficiency photovoltaics and sensors.

Left: Symmetry controlled TMDs. From the top, TMD nanotube, van der Waals heterostructure, and strained device. Right: Wave length dependence of bulk photovoltaic coefficient for nano TMDs.
Copyright: Left: Adapted from “Nature Nanotechnology 18, 36 (2023).”


Quantum materials and their nanodevices toward revolutionary physical properties and energy functions

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


Yoshihiro Iwasa

Team Leader iwasay[at]riken.jp

Hideki Matsuoka

Special Postdoctoral Researcher hideki.matsuoka[at]riken.jp

 Ricky Dwi Septianto

Postdoctoral Researcher rickydwiseptianto[at]riken.jp

Retno Dwi Wulandari

International Program Associate retno.wulandari[at]riken.jp

Thanyarat Phutthaphongloet

International Program Associate thanyarat.phutthaphongloet[at]riken.jp

Alec Paul Romagosa

International Program Associate alec.romagosa[at]riken.jp

Satria Bisri

Visiting Scientist

Yuki Itahashi

Visiting Scientist


  1. Y. Dong, M.-M. Yang, M. Yoshii, S. Matsuoka, S. Kitamura, T. Hasegawa, N. Ogawa, T. Morimoto, T. Ideue, and Y. Iwasa

    Giant bulk piezophotovoltaic effect in 3R-MoS2

    Nat. Nanotechnol. 18, 36-41 (2022)
  2. Y. Nakagawa, Y. Kasahara, T. Nomoto, R. Arita, T. Nojima, and Y. Iwasa

    Gate-controlled BCS-BEC crossover in a two-dimensional superconductor

    Science 372, 190+ (2021)
  3. T. Akamatsu, T. Ideue, L. Zhou, Y Dong, S. Kitamura, M. Yoshii, D. Yang, M. Onga, Y. Nakagawa, K. Watanabe, T. Taniguchi, J. Laurienzo, J. Huang, Z. Ye, T. Morimoto, H. Yuan, Y. Iwasa

    A van der Waals interface that creates in-plane polarization and a spontaneous photovoltaic effect

    Science 372, 68-72 (2021)
  4. R. Miranti, D. Shin, R. D. Septianto, M. Ibanez, M. Kovalenko V, N. Matsushita, Y. Iwasa, and S. Z. Bisri

    Exclusive Electron Transport in Core@Shell PbTe@PbS Colloidal Semiconductor Nanocrystal Assemblies

    ACS Nano 14, 3242 (2020)
  5. Y. J. Zhang, T. Ideue, M. Onga, F. Qin, R. Suzuki, A. Zak, R. Tenne, J. H. Smet, and Y. Iwasa

    Enhanced intrinsic photovoltaic effect in tungsten disulfide nanotubes

    Nature 570, 349-353 (2019)



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