Oscillations on free surface of superfluids at the inviscid limit are damped by quasiparticle scattering. We have studied this effect in both superfluids 3He and 4He 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 4He but significant deviation is found for 3He.
@article{arxiv.1410.4071,
title = {Quasiparticle Damping of Surface Waves in Superfluid $^3$He and $^4$He},
author = {Matti S. Manninen and Juho Rysti and Igor Todoshchenko and Juha Tuoriniemi},
journal= {arXiv preprint arXiv:1410.4071},
year = {2014}
}