1992 Fiscal Year Final Research Report Summary
High frequency electrical conductivity of Organic conductors
| Project/Area Number |
03452046
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性
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| Research Institution | Toho University |
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Principal Investigator |
KAJITA Koji Toho University,Faculty of Science,Professor, 理学部, 教授 (50011739)
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| Co-Investigator(Kenkyū-buntansha) |
NISHIO Yutaka Toho University,Faculty of Science,Associate Professor, 理学部, 助教授 (20172629)
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| Project Period (FY) |
1991 – 1992
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| Keywords | High Frequency Transport / alpha-(Bedt-TTF)_2I_3 / Metal-Non Metal Transition |
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| Research Abstract |
In the experiment, we did in 1992, we discovered that the microwave conductivity of alpha-(BEDT-TTF)_2I_3 shows an anomalous anisotropy when the system passes the phase boundary between the metallic state and the insulating state at 135K. In the electric field in the a-direction of the crystal axis, the conductivity decreases monotonically through the metal-insulator transition. While, in the field along the b-direction, the conductivity increases just above the transition and then decreases abruptly below the transition temperature.
The first experiment, we performed this year is to check if the anomalous anisotropy of the conductivity depends on the frequency in which we have measure the conductivity. We have adopted the Montgomery method by which we can measure the conductivity along the a-direction and the b-direction, simultaneously.
We found that the anomalous anisotropy of the conductivity is independent of the frequency. We also found that the phase transition at 135K is not so simple as we have expected. We have found that the anisotrpopy of the conductivity changes not only at the transition temperature(135K) but also at the temperature about 0.5K below the transition temperature.
The second experiment we have done is the survey of the metal-insulator transition under the pressures. In the investigation we did in 1992, we found that in a very high pressure, the metal-insulator transition is suppressed so that the system remains metallic down to low temperatures.
When we apply a magnetic field on such a system, we found that the metal-insulator transition appears again. We call this new phase as the "magnetic field induced insulating state".
We have done the Hall effect measurement for such systems. We found that in the magnetic field induced insulator phase, the carrier density becomes very low. The second discovery on the field induced insulator is that the carrier density at a constant temperature depends strongly on the strength of the magnetic field.
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