2003 Fiscal Year Final Research Report Summary
Theoretical Study on Low-Energy Excitations in Alkali-Metal-Deped C_<60>
| 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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| 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 |
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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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