Spin Polarized Superfluid ³He A₁

Abstract

Under applied magnetic field, the originally single superfluid ³He transition near 3 mK in zero field splits into two transitions between which a new A₁ phase emerges. The two second order transitions are marked by abrupt changes in viscosity, zero sound attenuation and nuclear magnetic resonance. To date, the maximum magnetic field for producing A₁ phase is 15 T. The A₁ phase has been identified with a spin-polarized (ferromagnetic) superfluid system which breaks the relative symmetry between spin, orbit and gauge spaces. A superfluid mass current in A₁ is simultaneously a spin current resulting in the propagation of spin-entropy wave. Experiments with spin-entropy wave provide measurements of anisotropic superfluid density and strong coupling parameters, spin diffusion coefficient and texture transformations. Owing to the spin-polarized nature, superflows may be generated by applied magnetic field gradients and measured from the induced magnetic fountain pressure. The mechanical spin density detector is developed to measure the spin relaxation in A₁ phase. The observed unexpected temperature dependence of the spin relaxation time gives evidence that the A₁ phase contains a small amount of the predicted minority spin condensate from dipolar interaction energy.