ELECTRONIC STATES IN THE STAGE-3 MERCURY-CHLORIDE GRAPHITE-INTERCALATION COMPOUND

The electronic states of the stage-3 mercury chloride graphite interca lation compound (HgCl2-GIC) were investigated by the de Haas-van Alphe n (dHvA) effect in the temperature range from 1.4 to 4.2 K with magnet ic fields from 3 to 5 T. Three prominent dHvA frequencies, f(1)=142.6 T,f(2)=533 T, and f(3)=788 T are identified with the three modified gr aphite pi bands expected for a stage-3 GIC. The cyclotron electron mas ses for the graphitic bands are measured, yielding m(1)=0.09m(0),m(2) =0.17m(0), and m(3)*=O.19m(0). In addition, there is a low-frequency oscillation at f(0)=82.5 T with m(0)=0.15m(0). The determination of t he fractional charge distribution along the k(2) direction of the thre e graphite layers of the stage-3 compound indicates that there is a de ficiency of charge in the internal graphite layer relative to the laye rs adjacent to the intercalant. The charge fraction on the internal gr aphite layer is determined to be 0.25. The low-frequency f(0) may resu lt from the effect of an incommensurate superlattice, which forms a ma gnetic interferometer orbit.