Electric and thermoelectric transport probes of metal–insulator and two-band magnetotransport behavior in graphite

We have investigated the nature of the magnetic field dependent metal–insulator (M–I) behavior in highly oriented pyrolytic graphite at low temperatures by electronic and thermoelectric transport. The experimental results are consistent with those of previous reports where a universal scaling relationship can describe the temperature dependent magnetotransport. However, thermopower measurements indicate that the material remains metallic over the entire region where the M–I transition is thought to occur, and hence there is no evidence for a gap. From van der Pauw measurements, we find that a simple two-band transport model can qualitatively describe the temperature and field dependence, without appealing to a M–I scaling description.