Change in Fermi Surfaces of Graphite by Dilute Acceptor Doping

The effect of doping graphite single crystals with the acceptor boron was studied in the dilute range from ≲0.1 ppm to 0.5% by measurements of the Hall effect and de Haas-van Alphen effect. The transition from a mixed electron and hole conduction in the narrow band overlap region (0.035 eV) to that of a single hole conduction produces a peak in the Hall coefficient that shifts to a lower boron concentration with a decrease in temperature. The increase in hole concentration is accompanied by a rapid decrease in mobility, demonstrating the importance of collision broadening. Preliminary de Haas-van Alphen results tentatively identify the major electron and hole Fermi surfaces by means of the period shift with increasing acceptor concentration. A new, very small ellipsoid-like Fermi surface was discovered. It is aligned along the hexagonal axis, having an anisotropy ratio of 9 with orbital masses of about 0.0023 m
0
for H ∥ C and 0.017 m
0
for H ⊥ C. Analysis strongly indicates that this surface contains minority holes. Three of these surfaces are considered to be aligned symmetrically like “outriggers” about the major hole surface, producing a total of six in the Brillouin zone. A comparison is made with the cyclotron resonance results and a possible interpretation of these minority Fermi surfaces is presented using the Slonczewski-Weiss band model.