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Hillebrecht, F. U., Morozov, A., Kirschner, J.

Direct observation of electronic correlation in C60 by double photoemission
Physical Review B 71, (12),pp 125406/1-6 (2005)
We report the first direct observation of electronic correlation for C60 thin films on Cu by two-electron photoemission excited by a single photon. The energetic position of features associated with one step excitation of two electrons shows the influence of the electrostatic correlation energy between the two holes which are generated simultaneously on the same site. The correlation energy determined from this experiment for C60 is 1.6 eV. The correlation energy is consistent with estimates derived from Auger spectroscopy.