Four-point dc-resistance measurement apparatus for anisotropic crystals

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Abstract
We report on a four-point dc-resistance measurement apparatus to obtain the temperature dependence of the ratio of two components of the resistivity tensor of samples with hexagonal structure. We point out that this ratio, as well as the individual components, can be calculated. Problems arise for thin crystals having a small anisotropy. These can be solved by performing a resistance measurement with the technique of van der Pauw on the same sample. The achieved relative accuracy in the temperature-dependent anisotropy ratio is better than 1%. The absolute accuracy depends on the nonuniformity of the crystal thickness, and the determination of probe distances.