Size effects in He II as measured by fourth sound

Abstract

Fourth-sound measurements are used to determine the depletion in the superfluid

Superfluid Density in Porous Vycor Glass

“…For onset temperatures on the order of 2 K the fourth-sound measurements in packed powders indicate that the superfluid density approaches zero in a nearly linear fashion. 4 Both the depression of the onset temperature 5 and the temperature dependence of the superfluid density near onset 6 have been discussed in terms of the temperature-dependent healing length of 2 the Ginzburg-Pitaevskii-Mamaladze theory. 7 In this theory the healing length, |, is given by | = | 0 (1 -T/T x )" 2/3 .…”

Tortuosity of 4He Films on Aerogel

“…We found ε = 1.060 ± 0.013, to be compared with ε = 1.10 ± 0.02 for the 92%-porous aerogel. For comparison, the measured α(φ ) for liquid saturating non-fractal packed powders [8] and fused glass beads [3] of various porosities φ , give exponents between ε = 1/2 and ε = 2/3. The aerogels have a markedly different ε to the non-fractal porous media.…”

“…Tortuosity vs. helium filling fraction: (•) our data; (•) data for a 92%-porous sample which employed a transverse sound technique [2]; (△) and for 93.5%-porous aerogel [9]. For comparison helium saturating ( * ) fused glass beads [3] and (+) packed powders [8] are also shown. Solid lines are produced using an effective-medium theory for saturated porous media [10], for (ε = 1) self-similar needles orientated perpendicular to the flow, (ε = 2/3) self-similar needles randomly orientated, and (ε = 1/2) self-similar spheres.…”