Polarization Dependence of the Viscosity of Liquid 3He: A Comparison Between Experiments and Theory

Our recent measurements of the viscosity of spin polarized liquid 3 He revealed that, below 100mK, the relative enhancement of the viscosity is pressure independent and quadratic in polarization m up to m=70%. This simple behavior is remarkably close to that expected for a gas (i.e. isotropic scattering). For the dense liquid 3 He, the so-called s-p approximation is believed to give a more realistic description of scattering. Using the formalism developed by Anderson, Pethick and Quader, we have computed the expected polarization dependence in this case, assuming polarization independent collision probabilities. Surprisingly, this leads to an initial linear decrease of the viscosity with polarization, which is not observed experimentally. This may imply that the present description of transport in liquid 3 He is not complete.