Journal of Experimental and Theoretical Physics

Spectrum of spin waves in cold polarized gases

T. L. Andreeva

Published Feb 1, 2017• 0 citations

Abstract

The spin dynamics of cold polarized gases are investigated using the Boltzmann equation. The dispersion relation for spin waves (transverse component of the magnetic moment) and the spin diffusion coefficient of the longitudinal component of the magnetic moment are calculated without using fitting parameters. The spin wave frequency and the diffusion coefficient for rubidium atoms are estimated numerically.

DOI: 10.1134/s1063776117010010

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Journal of Experimental and Theoretical Physics

Spectrum of spin waves in cold polarized gases

T. L. Andreeva

Published Feb 1, 2017• 0 citations

Publisher

Abstract

DOI: 10.1134/s1063776117010010

Related papers

Spin waves in cold gases with nondegenerate levels

T. L. Andreeva, P. L. Rubin

Journal of Experimental and Theoretical PhysicsNov 1, 20081 citation

Theory of transverse spin dynamics in a polarized Fermi liquid and an itinerant ferromagnet

V. P. Mineev

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{k}^{2}

with a complex diffusion coefficient such that the damping has a finite value proportional to the quasiparticles scattering rate at

T=0

. This behavior of a polarized Fermi liquid contrasts with the behavior of a Heisenberg ferromagnet in the hydrodynamic regime where the transverse spin-wave attenuation appears in terms proportional to

{k}^{4}

. The reactive part of the diffusion coefficient in a paramagnetic state at

T=0

proves to be inversely proportional to the magnetization whereas in a ferromagnetic it is directly proportional to the magnetization. The dissipative part of the diffusion coefficient at

T=0

in the paramagnetic state is polarization independent, whereas in the ferromagnetic state it is proportional to the square of the magnetization. Moreover, the spin wave spectrum in a ferromagnetic Fermi liquid proves to be unstable demonstrating the difficulty of applying a Fermi liquid description to itinerant ferromagnetism.

{\mathit{T}}^{2}

. Spin waves would thus continue to be damped even to T=0 K.

Recent experiments in a mixture of two hyperfine states of trapped Bose gases show behavior analogous to a spin-

\frac{1}{2}

system, including transverse spin waves and other familiar Leggett-Rice-type effects. We have derived the kinetic equations applicable to these systems, including the spin dependence of interparticle interactions in the collision integral, and have solved for spin-wave frequencies and longitudinal and transverse diffusion constants in the Boltzmann limit. We find that, while the transverse and longitudinal collision times for trapped Fermi gases are identical, the Bose gas shows unusual diffusion anisotropy in both dipole and quadrupole modes. Moreover, the lack of spin isotropy in the interactions leads to the nonconservation of transverse spin, which in turn has significant effects on the hydrodynamic modes.