Electronic structure of graphite intercalation compounds of rare-earths and uranium

Graphite intercalation compounds (GICs) of rare-earths and U reveal interesting anisotropic electronic properties related to their characteristic layered structure. In this contribution we present a comparative angle-resolved photoemission (PE) study of single-crystalline R-GICs (R = La, Eu, Yb, U) together with band-structure calculations. The samples where prepared in situ by deposition of R metals onto clean graphite (0 0 0 1) substrates and subsequent annealing. Stage-2 GICs are formed with a B-A-R-A-B-R structure changing the A-B-A-B stacking sequence of graphite. The electron structure may be described in a first approach by simple charge transfer from the R metals to unoccupied pi* orbitals of graphite leading to a shift of all graphite-derived PE features to higher binding energies and to the appearance of an additional narrow feature at E-F. For uranium, this Fermi-level peak is superimposed by a sharp U 5f signal, that is located directly at E-F and reveals no trace of multiplet splittings. Since the band-structure calculation gives clear evidence for a localized character of the U 5f states, we assume that uranium behaves mixed-valent in this compound and can be described in the framework of a single-impurity Anderson model. (C) 1999 Elsevier Science B.V. All rights reserved.