Mobility of Negative Ions in SuperfluidHe3

We have found that the mobility of negative ions increases rapidly below $T_c$ in both superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ phases. The ratio $\frac{\mu }{{\mu }_N}$ of superfluid to normal mobility is larger in the $B$ phase than in the $A$ phase. A critical velocity consistent in magnitude with the Landau limit for pair breaking has also been observed. In the normal fluid we find a temperature-independent mobility between 30 mK and $T_c$ for all pressures between 0 and 28 bars.