Magnetoreflection study of graphite under pressure

The magnetoreflection technique is applied to study Landau-level transitions in graphite under pressures up to 2 kbar to provide detailed information on the pressure dependence of the graphite electronic structure. In this pressure range the magnetoreflection spectra can be explained in terms of the Slonczewski-Weiss-McClure (SWMcC) band model with small changes in the band parameters that describe the graphite dispersion relations at atmospheric pressure. Using the SWMcC model and neglecting ${\gamma }_3$, a two-band model is developed to describe the $K$-point Landau levels and changes in these Landau levels produced by external perturbations. From this analysis a value for $\frac{\partial \ln {\gamma }_1}{\partial p}=0.024\mathrm{}\pm 0.004$ ${\mathrm{}\left(\mathrm{kbar}\right)\mathrm{}}^{-1\mathrm{}}$ is determined from the magnetoreflection spectra, in good agreement with recent pressure-dependent optical studies. Information on the pressure dependence of ${\gamma }_0$ and ${\gamma }_4$ is also presented. The implications of the present magnetoreflection results on previous pressure-dependent Fermi-surface studies are explored.