Evidence for Isotopic Impuritons in Solid Helium

Abstract

Measurements of the spin diffusion coefficient $D$ and the NMR linewidth ${T_2}^{-1\mathrm{}}$ are reported for a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ impurity in solid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at molar volume 21 ${\mathrm{cm}}^3$. For $x_3<3\mathrm{}\times {10}^{-2\mathrm{}}$, $D{x}_3=(1.2\mathrm{}\pm 0.4)\times {10}^{-11\mathrm{}}$ ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$, where $x_3$ is the fractional impurity concentration, and for $x_3<2\mathrm{}\times {10}^{-3\mathrm{}}$, $T_2{x}_3=(1.1\mathrm{}\pm 0.3)\times {10}^{-4\mathrm{}}$ sec. These results conform with a model of "impuriton" excitations or "mass fluctuation waves" in which the quasiparticles move like a gas.