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Electronic phases controllable with current

  • School of Science/Graduate School of Science
  • Department of Physics
  • (Laboratory of Condensed-Matter Physics of Functional Materials)

Ichiro Terasaki [Professor]

http://vlab-nu.jp/en/e_home.html

Outline of Seeds

Electrons in some transition-metal oxides and organic conductors move in a correlated manner owing to the poor screening of the Coulomb repulsion. Such systems are called strongly correlated electron systems, which are known to exbit various electronic ordered phases. We have discovered that some of the ordered phases such as charge ordered phase and Mott insulator phase are suppressed by external electrical current.

Novelty and originality of this research

A system with electricity or heat flow is not in thermal equilibrium, where physical properties are diffucult to predict because of our poor understanding of nonequilbrium states. In order to understand and control such nonequilibrium states, we need a typcal material exhibiting intrinscally nonequibrium phenomena. In Fig. 1, we show nonlinear resistance above room temperature in a correlated oxide.

Application and research area for Industry collaboration

Electronic phases controllable with electrical current can change resistance by a factor of 1000, and give colossal electro-striction 1000 times larger than conventional Piezo electric materials. These functions offer an essentially novel way of making electronic devices.

Key Takeaway

We are in an age of discovery, and have been searching for new materials which exhibit superior functions to semiconductors developed in the 50's. We have developed new materials and investigated their fundamental physics.

Keywords

transition-metal oxide, thermoelectrics, organic conductor, nonlinear conduction, ceramics, energy conversion, magnetic material, huge response, strongly correlated electron system, material development, function search in new materials

Technologies

  • Growth of single-crystal and polycrystalline samples of varisous oxides
  • Precise measurements of resistivity, thermopower, Hall effect, thermal conductivity, dielectric constant, magnetic susceptibility, optical reflectivity, specific heat
  • nonlinear conduction measurement using pyrometry, magnetoelectric/magnetopolarization measurement, thermoelectric measurement using Harman method

Equipment

  • Quantum Design PPMS, MPMS, Image futnace, X-Ray Diffractometer, FTIR, Box furnaces, TD-DTA, and many homemade equipments

Monographs, Papers and Articles

  • F. Sawano, I. Terasaki, H. Mori, T. Mori, M. Watanabe, N. Ikeda, Y. Nogami and Y. Noda, "An organic thyristor", Nature 437 (2005) 522-524
  • R. Okazaki, Y. Nishina, Y. Yasui, F. Nakamura, T. Suzuki, and I. Terasaki, "Current-induced gap suppression in the Mott insulator Ca2RuO4", J. Phys. Soc. Jpn. 82 (2013) 103702