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SHUBNIKOV-DE HAAS EFFECT OF VERY THIN GRAPHITE CRYSTALS

Recently, the magnetic field dependence of the transverse magnetoresistance ∆ρ/ρ0 and the Hall coefficient RH was measured for the graphite films of various thickness ranging from around 20 to 110 nm at temperatures between 4.2K and 300K. High quality of the crystallinity of these graphite films prepared by cleaving could be confirmed from the observation of Shubnikov-de Haas oscillation in RH. The saturation tendency revealed in the resistivity ρ versus magnetic field B characteristics for graphite films thinner than about 50 nm in the strong magnetic field region at low temperature, while as for all graphite films in this study, ρ varied in proportion to B n (n >1) in the strong magnetic field region at high temperature. According to the simple two-carrier system of conductors in the strong magnetic field region, this saturation tendency should be due to the difference between electron and hole densities. It may be caused by some change of energy band structure in thin films. In this study we measured the magnetic field dependence of the Hall coefficient RH for the graphite films of various thickness ranging from around 20 to 100 nm at 1.8K to obtain the more detailed feature of Shubnikov de Haas oscillation .