Electronic structure of dilute graphite-bromine intercalation compounds: Magnetothermal oscillations and charge-density waves

Quantum magnetothermal oscillations in four different samples of residual graphite-bromine intercalation compounds are reported. Fourteen de Haas-van Alphen (dHvA) frequencies in the range 0.04×{}10⁵-6×{}10⁶ G have been observed. The frequencies are independent of the bromine concentration. These results are explained by a modulated electronic structure composed of an alternate sequence of two zones. One zone is pure three-dimensional graphite and the other is a two-dimensional metallic sandwich made of the bromine layer and the two adjacent carbon layers. This metallic structure is described in the nearly-free-electron approximation. A charge-density-wave state stabilized by the saddle points present in the Fermi surface allows one to explain all the observed dHvA frequencies. In particular, the charge-transfer rate is found to be 0.5.