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

We have measured the viscosity, , and the slip length, , 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 supports the existence of Andreev reflection even with⁴He film on the surface at 5 bar and 21 bar.