| Project/Area Number |
13640316
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | University of Tsukuba |
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Principal Investigator |
NAKAO Kenji University of Tsukuba, Institute of Materials Science, Professor, 物質工学系, 教授 (30011597)
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| Co-Investigator(Kenkyū-buntansha) |
SUZUKI Shugo University of Tsukuba, Institute of Materials Science, Associate Professor, 物質工学系, 助教授 (90241794)
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| Project Period (FY) |
2001 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2003: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2002: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2001: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Keywords | Alkali Metal / C_<60> / Low Energy Excitation / Optical Properties Photoemission Spectrum / Superconductivity / Exciton / Electron-Phonon Interaction / 電子格子相互作用 / アルカリ金属ドープC_<60> / 有限温度 / 動的ヤーン-テラー効果 / スール-近藤機構 / エネルギーギャップ / 超伝導転移温度 / アルカリ金属ドープC60 / 電子間相互作用 / 電荷揺らぎ / 強相関電子系 / 強結合電子系 |
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| Research Abstract |
Alkali-metal-doped C60 is a material whose transition temperature of superconductivity is extraordinarily high among molecular crystals. Although the origin of superconductivity in this material is still controversial, we have claimed that the origin is the competition between the electron-electron interaction and the electron phonon interaction, where the dynamic Jahn-Teller effect plays an essential role for the latter interaction to overcome the former one. In the present study, we try to explain experimental facts from our point of view. We first investigate the anomalous behavior observed in the photoemission spectra in alkali-metal-doped C60 by using the dynamical mean field approximation. Consequently, we find that A4C60, where A is alkali metal, is a nonmagnetic insulator due to the cooperation between the electron-electron interaction and the electron-phonon interaction. The reason for the nonmagnetic nature is that the electron-phonon interaction is much stronger than the Hund coupling originated in the electron-electron interaction. Furthermore, a peak structure observed in the infrared reflection spectra of alkali metal-doped C60 is found to be originated in the exciton in this material. In particular, it is found that, in alkali-metal-doped C60, the spin-singlet exciton is energetically lower than the spin-triplet exciton in contrast with usual materials. We conclude that all the characteristic properties are due to the Jahn-Teller effect
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