U-graphite intercalation compound (GIC) was prepared in-situ by deposition
of U metal onto single-crystalline graphite(0001) and subsequent annealing.
The samples were studied by angle-resolved photoemission (PE) and resonant
PE at the 5d --> 5f excitation threshold. From a comparison of the experim
ental data with results of our LDA-LCAO calculations, the electronic struct
ure of the GIC may be understood in a first approach by a charge transfer f
rom the U atoms to unoccupied pi(0)* orbitals of graphite. The latter is re
lated to a shift to higher binding energies of all graphite-derived PE feat
ures and appearance of an additional rather narrow feature at the Fermi ene
rgy upon intercalation. This Fermi-level peak is superimposed by a sharp U
5f signal, that reveals no trace of multiplet splitting. Since our results
give clear evidence for a localized character of the U 5f states, we assume
that U is mixed-valent in this compound.