2003 Fiscal Year Final Research Report Summary
Neutral-ionic phase transition in two-dimensional organic semiconductor
| Project/Area Number |
13440088
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | National Institute of Advanced Industrial Science and Technology (AIST) (2003)
Hokkaido University (2001-2002) |
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Principal Investigator |
HASEGAWA Tatsuo National Institute of Advanced Industrial Science and Technology (AIST), Correlated Electron Research Center (CERC), Senior Researcher, 強相関電子技術研究センター, 主任研究員 (00242016)
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| Co-Investigator(Kenkyū-buntansha) |
MIZOGUCHI Kenji Tokyo Metropolitan University, Graduate School of Science, Professor, 理学研究科, 教授 (40087101)
NAKAMURA Takayoshi Hokkaido University, Research Institute for Electronic Science, Professor, 電子科学研究所, 教授 (60270790)
AKUTAGAWA Tomoyuki Hokkaido University, Research Institute for Electronic Science, Associate Professor, 電子科学研究所, 助教授 (60271631)
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| Project Period (FY) |
2001 – 2003
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| Keywords | Organic Semiconductor / Valence Instability / Neutral-Ionic Phase Transition / Crystal Structure Analysis / Electron Paramagnetic Resonance / Dielectric Properties / Quantum Critical Point / High-Pressure Measurement |
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| Research Abstract |
Valence instability or neutral-ionic (NI) phase transition in molecular semiconductor crystal, (BEDT-TTF)(ClMeTCNQ), is studied. We undertake to explore the new electronic phenomena based on the valence fluctuations around the quantum critical point, by studying the structural, magnetic, and dielectric properties of the compound under pressure and low temperature. The results of this project are summarized as follows;
1.Structure analyses:
We successfully developed the Be-based high pressure cell (application filed for a patent) for X-ray diffraction measurements under uniaxial pressure and low temperature. With use of this facility, we succeeded in the structural analyses below and above the NI transitions and observed the variation in the crystal symmetry and lattice constants.
2.ESR study:
By magnetic probe sensitive to the appearance of cation and anion radical 1/2-spins, we directly demonstrated how the NI phase transition develop in (BEDT-TTF)(ClMeTCNQ). By the analyses of the temper
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ature dependence of magnetic susceptibility under pressure, we observed the continuous evolution of the ionic domain fraction through the transition temperature. Particular finding is a presence of the thermoinduced NI meso-phase, where ionic radicals survive even at much higher temperature than the transitions. We conclude that this feature should be the origin of the drastic exponential increase of the magnetic susceptibility at room temperature with application of pressure.
3.Dielectric measurements:
Enhancement in dielectric response of (BEDT-TTF)(ClMeTCNQ) was observed around quantum critical point of the NI phase transitions. As the enhancement is temperature-and frequency-independent, we conclude that the enhancement should be ascribed to the quantum valence fluctuation between the neutral and ionic phases.
We also clarify the mechanism of magneto-lattice phase transitions in (BEDO-TTF)(Cl2TNCQ), which is an isomorphous compound with (BEDT-TTF)(ClMeTCNQ). Furthermore, the research is expanded to the new method for the valence control of molecular semiconductors with use of the FET device structures. Less
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