抄録
We study the spectral densities for alkali-metal-doped C60, AxC60 (A=K, Rb, etc), at zero temperature to elucidate the origin of anomalous behaviors in photoemission spectra, based on the dynamical mean-field theory by using the exact diagonalization method. The results for A2C60 and A4C60 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 A3C60, 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 1.6 eV below and above the Fermi level and the enhancement of the spectral intensity at the Fermi level in the spectral density for A3C60. 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 C602- and C604- molecules. Our results for A3C60 successfully explain the anomalous behaviors in the photoemission spectra of A3C60. Moreover, we study the photoemission spectra of a C603- molecule in a particle bath at finite temperature. The result is in qualitative agreement with the observed temperature dependence of the photoemission spectra of A3C60.
