He3Film Flow: Two-Dimensional Superfluidity

Abstract

${}_{}{}^3{}_{}{}^{}\mathrm{He}$ film flow has been observed. The maximum flow rate, at 0.7 mK, over a rim 0.9 mm above the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ level, was 1.2 ${\mathrm{mm}}^3$/h corresponding to an approximate flow velocity of 0.2 mm/sec. A flow rate of 0.2 ${\mathrm{mm}}^3$/h (∼0.1 mm/sec) was measured with the rim 14 mm above the level. The transition to superflow occurred at 3.5 ± 0.5 mK for the 0.9-mm film and 2.0 ± 0.5 mK for the 14-mm film. This flow is in a regime where the film thickness is less than or comparable to the bulk superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ coherence length (∼ 1000 Å at 0.8 mK) and the temperature is higher than the bulk ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ superfluid transition temperature (1.08 mK) and corresponds, we believe, to a two-dimensional superfluid phase of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$.