Surface Effects of 4He Coating on the Viscosity and the Slip Length of Normal and Superfluid 3He

We have measured the viscosity, η, and the slip length, ζ, of normal and superfluid3He using a torsional oscillator with a thick sample space. We coated the oscillating surface with 2.5 layers of4He film to study how the4He thin film changes the scattering mechanism of3He quasiparticles at the cell wall at 5 bar and 21 bar. In the normal phase, the temperature dependence of the viscosity was changed a little by the4He film at 21 bar but no change was observed at 5 bar. The slip length was enhanced by4He coating at 5 bar. This enhancement indicates the increase of specularity of3He quasiparticles scattering at the oscillating surface. On the other hand, a reduction of the slip length was observed at 21 bar. In the superfluid phase, the temperature dependence of ζ supports the existence of Andreev reflection even with4He film on the surface at 5 bar and 21 bar.