|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|
|6.Title of Project||Control of the Conduction Mechanism in Organic Conductors and Design of Novel Functional Material|
|Name||Institution,Department||Title of Position|
|Toshihiro, Takahashi||Gakushuin University, Faculty of Science||Professor|
|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.
(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