Experimental evidence against zero temperature spin-wave damping in 3He

We have discovered unexpected features in the NMR signal of the He-3- He-4 mixture inside the mixing chamber of a He-4 circulating dilution refrigerator. The dilution process not only cools the liquid in the mixing chamber to 12-15 mK but also enhances the nuclear spin polarization of the concentrated as well as the dilute phase to nearly four times the equilibrium value in a magnetic field of 9.36 T. The NMR features are ascribed to standing spin waves trapped by falling dilute phase droplets. The temperature and polarization dependence of the quality factor of the spin-wave modes contradicts evidence from previous work that favored zero temperature spin-wave damping in moderately polarized degenerate Fermi liquids. (C) 2000 Elsevier Science B.V. All rights reserved.