Sound experiments on superfluidity of He-3 in highly porous aerogels

We have carried out sound experiments on superfluid He-3 in three highly po rous aerogels with different porosities. Two of the acoustic cells contain aerogels inside the pores in roughly sintered silver powder to avoid the vi bration of the aerogel. In these acoustic cells we have detected fourth sou nd, and extracted the superfluid density from the fourth sound velocity. Th e effect of the sintered silver on superfluid He-3 was examined by using an other acoustic cell which contains the sintered silver without aerogel. The size of the pores in the sintered siltier was large enough not to show the size effect of super fluid He-3 and small enough to observe fourth sound o f He-3. In another cell without sintered silver, we have observed second-so und-like signal. The superfluid transition temperatures of He-3 are suppres sed more in higher density aerogel. The aerogel density dependence of the s uppression. of the superfluid transition temperature of He-3 in aerogel can be explained qualitatively by the simple s-wave scattering approximation. However, the superfluid density shows quite different pressure-dependence i n different porous aerogels.The reason of this phenomenon is not understood yet.