Electronic states in the stage-3 mercury chloride graphite intercalation compound.

The electronic states of the stage-3 mercury chloride graphite intercalation compound (${\mathrm{HgCl}}_{2}$-GIC) were investigated by the de Haas\char21{}van Alphen (dHvA) effect in the temperature range from 1.4 to 4.2 K with magnetic fields from 3 to 5 T. Three prominent dHvA frequencies, ${\mathit{f}}_{1}$=142.6 T, ${\mathit{f}}_{2}$=533 T, and ${\mathit{f}}_{3}$=788 T are identified with the three modified graphite \ensuremath{\pi} bands expected for a stage-3 GIC. The cyclotron electron masses for the graphitic bands are measured, yielding ${\mathit{m}}_{1}^{\mathrm{*}}$=0.09${\mathit{m}}_{0}$,${\mathit{m}}_{2}^{\mathrm{*}}$=0.17${\mathit{m}}_{0}$, and ${\mathit{m}}_{3}^{\mathrm{*}}$=0.19${\mathit{m}}_{0}$. In addition, there is a low-frequency oscillation at ${\mathit{f}}_{0}$=82.5 T with ${\mathit{m}}_{0}^{\mathrm{*}}$=0.15${\mathit{m}}_{0}$. The determination of the fractional charge distribution along the ${\mathbf{k}}_{\mathit{z}}$ direction of the three graphite layers of the stage-3 compound indicates that there is a deficiency of charge in the internal graphite layer relative to the layers adjacent to the intercalant. The charge fraction on the internal graphite layer is determined to be 0.25. The low-frequency ${\mathit{f}}_{0}$ may result from the effect of an incommensurate superlattice, which forms a magnetic interferometer orbit.