Correlated Electronics Group


Group Outline and Primary Goal

The target of our research and development is to trigger innovation in electronics by establishing fundamentals in advanced state-of-the-art electronic devices for information and communication technologies, which will contribute to the creation of a low-carbon society.
Specifically, we develop technologies that control electric phase transitions where electric, magnetic, and optical properties change dramatically through external fields such as electric fields, magnetic fields, and lights, which is characteristic to strongly correlated electronic materials. 　　

Group website


Key Themes of Research

  1. Developments of state-of-the-art functional materials such as multiferroic materials with magnetic properties controlled by external voltage; colossal-magnetoresistance materials with a resistance change as large as several orders of magnitude; superconductors; thermoelectric materials with large figure of merit.
  2. Development of crystal growth technology of high-purity, low-defect, and large-diameter single crystals of β-Ga2O3 as a next-generation power semiconductor.
  3. Developments of prototypical electronic and neuromorphic devices such as Mott transistor utilizing a gate-controlled Mott transition (metal-insulator transition) of the strongly-correlated material; nonvolatile resistive random access memory (ReRAM) exploiting the switching of electric polarization in ferroelectric materials; their application to emerging computer technologies.
  4. Development of optical switch by a new mechanism combining silicon optical waveguide with strongly correlated material exhibiting a metal-insulator transition.
  5. Development of high-resolution magneto-optical microscope with time-resolved observation technique for magnetic domain dynamics by the stroboscope method.

    Schematic picture of originally developed crystal growth technique by the floating zone method using laser diodes as a heating source (LDFZ method)

    A large-sized single crystal of a room-temperature multiferroic material BiFeO3 using LDFZ method

    Schematic picture of ferroelectric resistance change memory device and scanning transmission electron microscope image of the cross section of the device

    Characteristics of rewriting data in ferroelectric resistance change memory devices by applying voltage pulses (arrows indicate the direction of electric polarization of the ferroelectric tunnel barrier layer)

Our Technologies

  • High-quality single-crystal growth of metal oxides utilizing the laser-diode-heated floating-zone (LDFZ) furnace
  • Fabrication of atomically flat heterojunctions and superlattices of strongly-correlated materials by pulsed laser deposition
  • Device fabrication process for new functional materials such as metal oxides
  • High resolution magneto-optical microscope

Articles

  • K. Shibuya et al.,“Epitaxial growth and polarized Raman scattering of niobium dioxide films”, AIP Advances 12, 055103 (2022).
  • T. Ito et al., “Purification of β-Ga2O3 crystals by the zone refining”, Jpn. J. Appl. Phys. 58, 110908 (2019).
  • Y. Tomioka et al., “Enhanced superconductivity close to a non-magnetic quantum critical point in electron-doped strontium titanate.”, Nat. Commun, 10, 738 (2019).
  • H. Yamada et al., “Growth and ferroelectric properties of yttrium-doped hafnium oxide/indium-tin oxide polycrystalline heterostructures with sharp and uniform interfaces”, J. Appl. Phys. 124, 105305 (2018).
  • T. Ogasawara et al., “Observation of frequency dependent resonances in magnetic vortex core gyration using time-resolved magneto-optical Kerr microscope with pulsed semiconductor laser illumination”, Jpn. J. Appl. Phys. 61, 018001 (2022).