TRANSVERSE SPIN-DIFFUSION IN A DILUTE SPIN-POLARIZED DEGENERATE FERMIGAS

We re-examine the calculation of the transverse spin-diffusion coeffic ient in ct dilute degenerate spin-polarized Fermi gas, for rite case o f s-wave scattering. The special feature of this limit is that the dep endence of the spin diffusion coefficient on temperature and field can be calculated explicitly with no further approximations. This exact s olution uncovers a novel intermediate behaviour between the high field spin-rotation dominated regime in which D-perpendicular to proportion al to H-2, D-parallel to proportional to T-2, and the low-field isotro pic, collision dominated regime with D perpendicular to = D parallel t o proportional to T-2. In this intermediate regime, D perpendicular to ,parallel to proportional to T-2 but D perpendicular to not equal D pa rallel to. We emphasize that the low-field crossover cannot be describ ed,within the relaxation time approximation. We also present an analyt ical calculation of the self-energy in the s-wave approximation for a dilute spin-polarized Fermi gas, at zero temperature. This emphasizes the failure of the conventional Fermi-liquid phase space arguments for processes involving spin? flips. We close by reviewing the evidence f or. the existence of the intermediate regime in experiments on weakly spin-polarized He-3 and He-3-He-4 mixtures.