Extreme nonlinear damping by the quasiparticle gas in superfluidB3in the low-temperature limit

The resistance to motion of a wire in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$ has three contributions: that due to the internal friction of the resonator; that due to pair breaking; and that due to the quasiparticle gas. We have been able to separate quasiparticle contribution and find that it is highly nonlinear with velocity on the scale of the Landau velocity, Δ/${\mathrm{p}}_{\mathrm{F}}$, and falls with increasing velocity. This indicates that the quasiparticle resistance is also governed by the condensate, almost certainly through Andreev reflection in the flow field around the wire.