Magneto-optical studies of graphite intercalation compounds

High field magnetoreflection measurements are reported on the first observation of interband Landau level transitions in residue and lamellar compounds of graphite intercalated with the halogens Br₂, IBr and ICl. These magnetoreflection spectra are interpreted to yield a model for the magnetic energy level structure of these intercalation compounds in the dilute limit corresponding to stage ≳5. In this dilute limit, the insensitivity of the magnetoreflection resonances to intercalate concentration shows that near the Fermi level for pure graphite the electronic structure of the intercalation compounds is essentially independent of intercalate concentration. This conclusion results from analysis of both infrared and far-infrared magnetoreflection spectra for Landau level transitions within ±0.1 eV of the graphite Fermi level. The model for the electronic structure deduced from the magnetoreflection spectra is supported by Raman scattering results presented for the in-plane lattice modes of carbon atoms in the graphitic layer planes.