Evidence for Isotopic Impuritons in Solid Helium

Measurements of the spin diffusion coefficient $D$ and the NMR linewidth ${{T}_{2}}^{\ensuremath{-}1}$ are reported for a $^{3}\mathrm{He}$ impurity in solid $^{4}\mathrm{He}$ at molar volume 21 ${\mathrm{cm}}^{3}$. For ${x}_{3}<3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$, $D{x}_{3}=(1.2\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$ ${\mathrm{cm}}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, where ${x}_{3}$ is the fractional impurity concentration, and for ${x}_{3}<2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, ${T}_{2}{x}_{3}=(1.1\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ sec. These results conform with a model of "impuriton" excitations or "mass fluctuation waves" in which the quasiparticles move like a gas.

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