Theoretical Study on Low-Energy Excitations in Alkali-Metal-Deped C_<60>

碱金属C_<60>低能激发的理论研究

• 批准号: 13640316
• 负责人: NAKAO Kenji
• 金额: $ 2.24万
• 依托单位: University of Tsukuba
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2003
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640316/
• 关键词: 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

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

碱金属掺杂的C_（60）是分子晶体中超导转变温度非常高的材料。虽然这种材料的超导电性的起源仍有争议，但我们认为其起源是电子-电子相互作用和电子-声子相互作用之间的竞争，其中动态Jahn-Teller效应对后者克服前者起着至关重要的作用。在本研究中，我们试图从我们的角度来解释实验事实。我们首先利用动态平均场近似研究了碱金属掺杂C60的光电子谱中观察到的反常行为。因此，我们发现，A_4C_60，其中A为碱金属，是一个介电绝缘体，由于电子-电子相互作用和电子-声子相互作用之间的合作。其原因是电子-声子相互作用比电子-电子相互作用产生的Hund耦合强得多。此外，在碱金属掺杂的C60的红外反射光谱中观察到的峰结构被发现起源于该材料中的激子。特别是，它被发现，在碱金属掺杂的C60，自旋单重态激子是能量低于自旋三重态激子与通常的材料相比。我们得出结论，所有的特征性质是由于Jahn-Teller效应

项目成果

Tadahiko Chida: "Theoretical Study on Anomalous Behaviors in Photoemission Spectra of Alkali-Metal-Doped C_<60>"Journal of Physical Society of Japan. 71. 525-537 (2002)

千田忠彦：“碱金属掺杂C_<60>光电发射光谱异常行为的理论研究”日本物理学会杂志。

Tadahiko Chida: "Role of Orbital Degree of Freedom in Photoenission Spectra in Alkali-Metal-Doped C_<60>"Journal of Physical Society of Japan(Supplement). 71. 205-207 (2002)

千田忠彦：“碱金属掺杂C_<60>中光电子光谱中轨道自由度的作用”日本物理学会杂志（增刊）。

Shugo Suzuki: "Role of Orbital Degree of Freedom in Superconductivity in Alkali-Metal-Doped C_<60>"Journal of Physical Society of Japan (Supplement). 71. 202-204 (2002)

铃木修吾：“碱金属掺杂C_<60>中轨道自由度对超导性的作用”日本物理学会杂志（增刊）。

Tadahiko Chida, Shugo Suzuki, Kenji Nakao: "Role of Orbital Degree of Freedom in Photoemission Spectrum Alkali-Metal-Doped C_<60>"Journal of Physical society of Japan. Vol.71 (Supplement). 205-207 (2002)

千田忠彦、铃木修吾、中尾健二：“轨道自由度在光电发射光谱碱金属掺杂 C_<60> 中的作用”日本物理学会杂志。

Tadahiko Chida, Shugo Suzuki, Kenji Nakao: "Theoretical Study on Anomalous Behaviors in Photoemission Spectra of Alkali-Metal-Doped C_<60>"Journal of Physical Society of Japan. Vol.71. 525-537 (2002)

千田忠彦、铃木修吾、中尾健二：“碱金属掺杂C_<60>光电子发射光谱异常行为的理论研究”日本物理学会杂志。