Theory of the diffusivity-mobility ratio in cadmium arsenide

Stimulated by the work of Chakravarti et al., the theory of the Einstein relation for the ratio of diffusivity, D, to mobility, μ, in cadmium arsenide crystals in a magnetic field at low temperatures is developed. D/μ shows characteristic de Haas-Shubnikov oscillations which vary considerably with orientation of the crystal due to its anisotropy. In fact, for low enough magnetic fields it is shown that it may oscillate as a function of the angle theta between the c-axis of the crystal and the field direction. Measurements of D/μ would thus constitute a sensitive test of anisotropy. By measuring the variation both, with respect to field and angle for a single sample, all the band parameters can be determined in principle. (author)