SUPERFLUIDITY OF PURE HE-3 AND MIXTURES OF HE-3 AND HE-4 IN AEROGEL

We describe new torsional oscillator experiments on He-3 confined in 9 8.2% open aerogel. In one, we monitored the superfluid fraction of pur e He-3 at T much less than T-c while we gradually changed the sample p ressure. The resulting change in density alters xi(0) of the superflui d He-3 relative to the distribution of the length scales (correlations ) of silica in the aerogel. We observed a T = 0 normal-to-superfluid t ransition at a pressure of about 6.5 bar, in marked contrast to the bu lk where liquid He-3 is superfluid at all pressures, rn the second exp eriment, we measured the temperature dependence of the He-3 rho(s) at a pressure of 21.6 bar with different amounts of He-4 present in the c ell. Adding 2-3% He-4 slightly increases both T-c and rho(s). We found that for He-4 concentrations between 2% and 34%, the He-3 T-c increas es by a very small amount. However, rho(s), which for pure He-3 in aer ogel at 0.5T(c) is no more than 11%, falls by another factor of 7. Thi s behavior (constant T-c, reduced rho(s)) is similar to that observed in granular superconducting films where the long-range order is contro lled by phase coherence between adjacent grains.