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

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 refrigerat or. 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 concentrat ed as well as the dilute phase to nearly four times the equilibrium value i n a magnetic field of 9.36 T. The NMR features are ascribed to standing spi n waves trapped by falling dilute phase droplets. The temperature and polar ization dependence of the quality factor of the spin-wave modes contradicts evidence from previous work that favored zero temperature spin-wave dampin g in moderately polarized degenerate Fermi liquids. (C) 2000 Elsevier Scien ce B.V. All rights reserved.