The spin diffusion in normal and superfluid Fermi liquids

Abstract

Spin diffusion in paramagnetic spin systems is a dissipative process which acts so as to remove all spatial variation of the magnetization. In normal and superfluid Fermi liquids its physical origin lies in the nonconservation property of the macroscopic magnetization current associated with the thermal excitations, the Landau and Bogoliubov quasiparticles, respectively. In the hydrodynamic limit this dissipative process manifests itself in a constitutive relation connecting the decaying magnetization current with gradients in the magnetization density via a coefficient of spin diffusion. Exchange contributions to the quasiparticle interaction introduce, in addition, reactive processes, which can be associated with a rotation of the quasiparticle spin current about the direction of the spin polarization. This so-called spin current rotation—or Leggett-Rice effect—leads to nonhydrodynamic behavior of the spin diffusion whenever the exchange frequency becomes comparable to the inverse spin current relaxation time. In this article I would like to review our current understanding of diffusional spin transport, as influenced by nonhydrodynamic effects, in normal and superfluid Fermi systems.