Andreev Reflection of Quasiparticles by a Vortex Tangle in Superfluid 3He-B?

Abstract

We have made the surprising discovery that the thermal damping of a vibrating wire resonator in superfluid ³He-B at ultra low temperatures is considerably depressed when a second wire in the vicinity is driven supercritically. The damping of a vibrating wire resonator at low velocities in the B-phase arises from the scattering of quasiparticle excitations and has a temperature dependence proportional to the Boltzmann factor exp(−Δ/kT) at low temperatures. At higher velocities (v>v_L/3), the wire breaks Cooper pairs and emits a quasiparticle beam. At first sight it seems paradoxical that heating the superfluid can reduce the quasiparticle flux on a neighbouring wire. We can only understand this on the basis that vorticity emitted by the supercritical wire shields, via Andreev reflection, part of the background quasiparticle flux from reaching the other wire. If this interpretation is correct, these techniques will provide a sensitive probe of vortex dynamics in the ultra low temperature regime.