Theoretical Study on Anomalous Behaviors in Photoemission Spectra of Alkali-Metal-Doped C_<60>

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We study the spectral densities for alkali-metal-doped C_<60>, A_xC_<60> (A=K ; Rb, etc), at zero temperature to elucidate the origin of anomalous behaviors in photoemision spectra, based on the dynamical mean-field theory by using the exact diagonalization method. The results for A_2C_<60> and A_4C_<60> agree qualitatively with the results of Hartree-Fock calculations ; these materials are insulating due to the cooperation between the electron-electron and electron-phonon interactions. On the contrary, in A_3C_<60>, the competition between the electron-electron and electron-phonon interactions results in the charge fluctuation and consequently the material remains metallic. We find satellites at about 1.6eV below and above the Fermi level and the enhancement of the spectral intensity at the Fermi level in the spectral density for A_3C_<60>. These originate from the charge fluctuation. Furthermore, it is found that continuous features ranging from -1 eV to +1 eV are derived from the multiplet splitting of C^<2->_<60> and C^<4->_<60> molecules. Our results for A_3C_<60> successfully explain the anomalous behaviors in the photoemission spectra of A_3C_<60>. Moreover, we study the photoemission spectra of a C^<3->_<60> molecule in a particle bath at finite temperature. The result is in qualitative agreement with the observed temperature dependence of the photoemission spectra of A_3C_<60>.
社団法人日本物理学会の論文
2002-02-15