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Theoretical Study on Electron-Electron and Electron-phonon Interactions in Fullerene Compounds

富勒烯化合物电子-电子和电子-声子相互作用的理论研究

基本信息

批准号：
11165207
负责人：
NAKAO Kenji
金额：
$ 6.85万
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 on Priority Areas (A)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

In alkali-metal-doped C_<60>, the electron-electron and electron-phonon interactions play very important roles. We have already found that the two interactions open the band gaps in A_2C_<60> and A_4C_<60> cooperatively and make these materials insulating. On the contrary, A_3C_<60>, which is a phase between A_2C_<60> and A_4C_<60>, remains metallic although the electron-electron and electron-phonon interactions should also be strong in this material. This has been unsolved so far. In the present study, we have studied the reason why A_3C_<60> remains metallic in spite of the strong electron-electron and electron-phonon interactions by using the same model that has been used for studying A_2C_<60> and A_4C_<60>. As a result, we have found that, in A_3C_<60>, the electron-electron and electron-phonon interactions compete with each other and, consequently, this material remains metallic. This competition results in the charge fluctuation. In paticular, we have found that the charge fluctuation is the origin of a shoulder observed in the photoemission spectra in A_3C_<60>. Furthermore, we have studied the present model by the quantum Monte Carlo method and found that the shoulder disappears at high temperature. This result is in good agreement with experimental temperature dependence of the photoemission spectra. The present results are very important for understanding low energy excitation in A_3C_<60>. Finally, we have studied the phase diagrams of A_xC_<60> (x=1,-,5) and found that there exist paramagnetic metal, superconductor, orbital-palarized metal, and spin- and orbital-polarized metal in A_1C_<60>, A_3C_<60>, and A_5C_<60> while there exist paramagnetic metal, superconductor, orbital-polarized insulator in A_2C_<60> and A_4C_<60>.

在碱金属掺杂的C_2中<60>，电子-电子和电子-声子相互作用起着非常重要的作用。我们已经发现这两种相互作用协同打开了A_2C_1和A_4C_1的带隙<60><60>，使它们绝缘。而A_3C_<60>（A_2C_和A_4C_之间的一种相<60>）<60>则是金属相，尽管这种材料中的电子-电子和电子-声子相互作用也很强。到目前为止，这件事还没有解决。本文<60>采用与研究A_2C_3和A_4C_4相同的模型，研究了A_3C_3在强电子-电子和电子-声子相互作用下仍保持金属<60>性的原因<60>。结果表明，在A_3C_中<60>，电子-电子和电子-声子相互作用相互竞争，因此该材料保持金属性。这种竞争导致电荷波动。特别是在A_3C_2中，我们发现电荷涨落是在光电子谱中观察到的一个肩的起源<60>。此外，我们还用量子蒙特卡罗方法研究了该模型，发现肩在高温下消失。这一结果与光电子能谱的温度依赖性实验结果吻合得很好。这些结果对理解A_3C_2的低能激发具有重要意义<60>。最后，我们研究了A_xC_<60>（x=1，-，5）的相图，发现在A_1C_、A_3C_和A_5C_中存在顺磁金属、超导体、轨道极化金属、自旋极化金属和轨道极化金属<60><60>，<60>而在A_2C_和A_4C_中存在顺磁金属、超导体、轨道极化绝缘体<60><60>。