Summary of Research Project Results under JSPS FY2001
"Research for the Future Program"

1.Research Institution Gakushuin University
2.Research Area Physical and Engineering Sciences
3.Research Field Exploratory Research on Novel Artificial Materials and Substances for Next-Generation Industries
4.Term of Project FY 1997 〜 FY 2001
5.Project Number 97P00105
6.Title of Project Control of the Conduction Mechanism in Organic Conductors and Design of Novel Functional Material

7.Project Leader
Name Institution,Department Title of Position
Toshihiro, Takahashi Gakushuin University, Faculty of Science Professor

8.Core Members

Names Institution,Department Title of Position
Koji, Kajita Toho University, Faculty of Science Professor
Keizo, Murata Osaka City University, Graduate School of Science Professor
Kazushige, Nomura Hokkaido University, Graduate School of Science Professor

9.Summary of Research Results

Conducting organic molecular complexes, i.e., organic conductors, have high possibility of useful material in near future. The purposes of this project were to investigate the mechanism of large variety of conductivity in this system and to derive the guideline to design new materials controlling their physical properties on the basis of the systematic analysis of the existing materials. We have chosen the complexes based on BEDT-TTF molecule as a model system and have analyzed the correlation between the molecular arrangement and the electronic properties in this family of material, looking for the possibility of systematic control of their electronic properties. The most prominent results are as follows.
1. Discovery of Metal-Insulator Transition accompanied by Charge Ordering
It was confirmed that the insulating phases of non-dimerized BEDT-TTF salts of the α- and θ-type were accompanied by charge ordering and the pattern of the charge ordering with a stripe structure was first determined experimentally.
2. Characterization of New Conducting State with Constant Resistance
The α-type I3 salt of BEDT-TTF was found to become a narrow-gap semiconductor with extremely high mobility under pressure. This state was found to be stable in a wide pressure and temperature region, and also observed in three different materials, indicating the universality of this state.
3. Control of the various ground states by applying hydrostatic and uniaxial pressure
Pressure effects on the MI transition with charge ordering and the narrow-gap semiconducting state were examined. It was observed that the ground state can be controlled systematically among the normal metallic state, the insulating state (with charge ordering) and the narrow-gap semiconducting state by controlling the molecular arrangement with hydrostatic and uniaxial pressure.

10.Key Words

(1)Organic Molecular Conductor、(2)Structure-Function Correlation、(3)Metal-Insulator Transition
(4)Charge Ordering、(5)Narrow-Gap Semiconductor、(6)Electron Correlation
(7)13C-NMR、(8)Symmetry of Organic Superconductor、(9)Uniaxial Compression Effects