Quasiparticle Damping of Surface Waves in Superfluid $^3$He and $^4$He
  Oscillations on free surface of superfluids at the inviscid limit are damped by quasiparticle scattering. We have studied this effect in both superfluids $^3$He and $^4$He deep below the respective critical temperatures. Surface oscillators offer several benefits over immersed mechanical oscillators traditionally used for similar purposes. Damping is modeled as specular scattering of ballistic quasiparticles from the moving free surface. The model is in reasonable agreement with our measurements for superfluid $^4$He but significant deviation is found for $^3$He. 
Matti S. Manninen, Juho Rysti, Igor Todoshchenko, Juha Tuoriniemi
cond-mat.other