Associate Professor Yoshihiro Iwasa

Associate Professor Yoshihiro Iwasa completed his graduate study with Prof. N. Miura in 1986 at the Institute for Solid State Physics, University of Tokyo. He joined JAIST in 1994 from the Department of Applied Physics, University of Tokyo, where he had been a research assosiate(1986-1991) and then a lecturer(1991-1994). Dr. Iwasa worked with Drs. G. A. Thomas and A. F. Hebard at AT&T Bell Laboratories, New Jersey,USA, as a visiting researcher (1993-1994).

[ Japanese/English ]

Specialities : Fullerene, Organic conductors, Materials science, Superconductivity

　

Dr. Iwasa and his team are researching new molecular or organic solids with novel functionalities. Although their interest in solid state physics and chemistry is very broad, their current interest is focused on two subjects. (1)Fullerenes and (2)BEDT-TTF based organic materials.
(1)Fullerenes, cage-shaped carbon molecules, are of significant interest due to their potential to form new materials. Among them, C₆₀ is the most popular molecule, having a succour ball-like structure. C₆₀ becomes a superconductor by intercalation of alkali or alkali earth metals. Fullerenes are also interesting due to their structual variety. By application of pressure, C₆₀ turns into a polymeric form. Amorphous C₆₀ and C₇₀, on the other hands, are extremely good photoconductors.
Iwasa's group is searching for new fullerides with novel functionalities. Particularly, they are interested in superconductors. Their strategy is in the synthesis of multinary complex fullerides, in which alkali metals, alkali earth metals and netutral molecules are involved. Contribution of the former two is the donation of one and two electrons per element respectively, resulting in a tunability of electron density without changing the structure. In multinary fullerides solids, the assembly of these elements with fullerenes, play on important role in investigating the mechanisms of high Tc in fullerene superconductors as well as forming new superconductors.
(2)BEDT-TTF(bis(ethylenedithio)terathiafulvalene) molecule is well-known to form many organic (molecular) superconductors. However, Iwasa's group is not satisfied with the simple BEDT-TTF superconductors, and now they are trying to give an additional degree of freedom or functionalities in BEDT-TTF based materials. His group's strategy is the synthesis of charge transfer (CT) compounds with organic anions. Compounds with organic anions are of potential interest, due to their structural variety and possible tunability of band-filling, which has been impossible in molecular conductors. The BEDT-TTF-based CT compounds are promising since there appears a possible interplay between the conducting and localized electrons. Synthesis, structural analysis, and investigation of electronic and magnetic properties are being made in collaboration with Institute for Molecular Science and the University of Tokyo.

Selected Publications

• ``Metallic reflection spectra of K₃C₆₀.'' Phys. Rev. Lett., 69, 2284 (1992).
  
• ``Dispersion relation in the third-order electric susceptibility for polysilane film.'' Phys. Rev. Lett., 70, 3724 (1993).
  
• ``New Phases of C₆₀ Synthesized at High Pressure.'' Science 264, 1570 (1994).
  
• Superconductivity in K₃Ba₃C₆₀. Y.Iwasa et al., Phys. Rev. B54, 14960 (1996).
  
• Metal-insulator transition in ammoniated K₃C₆₀. Y.Iwasa et al., Phys. Rev. B53, R8836 (1996).
  
• Superconductivity and normal-state properties of nonavalent fullerides Y.Iwasa et al., Phys. Rev. B57, 13395 (1998).

Current Research

Materials Science and Solid State Physics of fullerenes and molecular conductros.
Structural analysis of molecular materials.
Nonlinear optical properties of conducting polymers.

School of Materials Science