The superfluid density and the transition temperature of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ filling the pores of packed powders of 3 different sizes, nominally 1.0, 0.3, and 0.05 μm, have been measured using fourth sound. Progressively larger depressions are observed for both the superfluid density and the transition temperature as the powder size is decreased. The depression in the transition temperature has been measured as a function of pressure and is found to be consistent with theoretical estimates of the superfluid coherence length.

• Received 13 August 1979

DOI:https://doi.org/10.1103/PhysRevB.21.3941