Theory of the self-diffusion (spin diffusion) coefficient of an electron gas

The self-diffusion (spin-diffusion) coefficient D of an electron gas is investigated by means of a proper connected diagram expansion which treats a collision in a medium (rather than in vacuum) in a natural manner. By calculating real and virtual interaction processes to the order e4 (second order in interaction strength), we obtain D = 0.3597 ℏ12 e-2(kBT)54 n0-12 M-34 for a non-degenerate gas where n0 represents the density. The square-root density (n0) dependence is noteworthy. In the calculation, no cut-off limiting low momentum transfer in collision is introduced; the screening effect which is important at higher densities, is neglected.