Spin Dynamics of Dilute Polarized Quantum Systems.

Abstract Very dilute solutions of 3He in superfluid 4He behave as an almost ideal Fermi gas at millikelvin temperatures, which can be strongly polarized in high magnetic fields. This has enabled studies of their equilibrium, transport, and dynamical spin properties to be made over a wide range of temperatures, concentrations, and polarizations covering systems that are highly degenerate to those that are non-degenerate. This chapter discusses polarized Fermi gas, model theories, equilibrium theories, transport properties, and spin dynamics.Abstract Very dilute solutions of 3He in superfluid 4He behave as an almost ideal Fermi gas at millikelvin temperatures, which can be strongly polarized in high magnetic fields. This has enabled studies of their equilibrium, transport, and dynamical spin properties to be made over a wide range of temperatures, concentrations, and polarizations covering systems that are highly degenerate to those that are non-degenerate. This chapter discusses polarized Fermi gas, model theories, equilibrium theories, transport properties, and spin dynamics.

May 10, 20010 citations

Spin polarized quantum systems

Société française de physique

Jan 1, 19801 citation

Quantum spin transport in very dilute −43 He mixtures

Donald Candela, D. R. McAllaster, L-J. Wei +1 more

Transverse spin dynamics have been measured for a very dilute $^{3}\mathrm{\ensuremath{-}}^{4}$He mixture ( ${\mathit{x}}_{3}$ =1.82\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$) polarized by an 8-T magnetic field. The sample was confined to a small spherical resonator, resulting in well-defined spin-wave modes for temperatures below 50 mK. Results are presented for the spin-rotation parameter ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$ and spin-wave dispersion ${\mathit{D}}_{\mathrm{\ensuremath{\perp}}}$/${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$. It is found that ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$ increases monotonically as the temperature is decreased below the degeneracy temperature ${\mathit{T}}_{\mathit{F}}$ , in apparent disagreement with an earlier experiment.Transverse spin dynamics have been measured for a very dilute $^{3}\mathrm{\ensuremath{-}}^{4}$He mixture (${\mathit{x}}_{3}$=1.82\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$) polarized by an 8-T magnetic field. The sample was confined to a small spherical resonator, resulting in well-defined spin-wave modes for temperatures below 50 mK. Results are presented for the spin-rotation parameter ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$ and spin-wave dispersion ${\mathit{D}}_{\mathrm{\ensuremath{\perp}}}$/${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$. It is found that ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$ increases monotonically as the temperature is decreased below the degeneracy temperature ${\mathit{T}}_{\mathit{F}}$, in apparent disagreement with an earlier experiment.

Physical Review LettersJul 30, 199016 citations

Spin diffusion in paramagnetic quantum fluids

Andrei E. Ruckenstein, Laurent P. Lévy

We derive the linearized spin dynamics for paramagnetic quantum liquids. In these systems, the existence of quantum-mechanical exchange in the presence of (an externally induced) broken symmetry in spin space gives rise to a coherent precession of the spins damped by diffusion. Such collective oscillations occur as a result of the precession of the spin current about a macroscopic local exchange field generated either by an external polarizing magnetic field (as in dilute nondegenerate spin-polarized gases) or by the long-lived nonequilibrium polarization (as in degenerate Fermi liquids). We use a unified approach based on the Kadanoff-Baym formulation of the kinetic equations to describe these phenomena. The connection between strongly and weakly interacting paramagnetic systems is made obvious by considering two special cases: (1) a weakly interacting spin-polarized quantum gas and (2) a parametrization of strongly correlated degenerate Fermi liquids in terms a weakly interacting gas of ``quasiparticles.'' Transport coefficients are calculated with a novel method which may be generalizable to systems with no translational invariance.We derive the linearized spin dynamics for paramagnetic quantum liquids. In these systems, the existence of quantum-mechanical exchange in the presence of (an externally induced) broken symmetry in spin space gives rise to a coherent precession of the spins damped by diffusion. Such collective oscillations occur as a result of the precession of the spin current about a macroscopic local exchange field generated either by an external polarizing magnetic field (as in dilute nondegenerate spin-polarized gases) or by the long-lived nonequilibrium polarization (as in degenerate Fermi liquids). We use a unified approach based on the Kadanoff-Baym formulation of the kinetic equations to describe these phenomena. The connection between strongly and weakly interacting paramagnetic systems is made obvious by considering two special cases: (1) a weakly interacting spin-polarized quantum gas and (2) a parametrization of strongly correlated degenerate Fermi liquids in terms a weakly interacting gas of ``quasiparticles.'' Transport coefficients are calculated with a novel method which may be generalizable to systems with no translational invariance.

Physical review. B, Condensed matterJan 1, 198923 citations

Transverse spin dynamics have been measured for a very dilute $^{3}\mathrm{\ensuremath{-}}^{4}$He mixture (

{\mathit{x}}_{3}

=1.82\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$) polarized by an 8-T magnetic field. The sample was confined to a small spherical resonator, resulting in well-defined spin-wave modes for temperatures below 50 mK. Results are presented for the spin-rotation parameter ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$ and spin-wave dispersion ${\mathit{D}}_{\mathrm{\ensuremath{\perp}}}$/${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$. It is found that ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$ increases monotonically as the temperature is decreased below the degeneracy temperature

{\mathit{T}}_{\mathit{F}}

, in apparent disagreement with an earlier experiment.