Andreev reflection in rotating superfluid $^3$He-B

TL;DR

This paper reviews Andreev reflection of quasiparticles in superfluid $^3$He-B, demonstrating experimental agreement with theory, and reveals finite mutual friction at zero temperature through vortex dynamics analysis.

Contribution

It provides experimental validation of Andreev reflection in superfluid $^3$He-B and uncovers finite mutual friction at zero temperature, challenging existing theoretical assumptions.

Findings

Agreement between measured and calculated Andreev reflection.

Finite mutual friction observed at zero temperature.

Analysis of vortex decay reveals turbulent and laminar regimes.

Abstract

Andreev reflection of quasiparticle excitations from quantized line vortices is reviewed in the isotropic B phase of superfluid $^3$He in the temperature regime of ballistic quasiparticle transport at $T \leq 0.20\,T_\mathrm{c}$. The reflection from an array of rectilinear vortices in solid-body rotation is measured with a quasiparticle beam illuminating the array mainly in the orientation along the rotation axis. The result is in agreement with the calculated Andreev reflection. The Andreev signal is also used to analyze the spin down of the superfluid component after a sudden impulsive stop of rotation from an equilibrium vortex state. In a measuring setup where the rotating cylinder has a rough bottom surface, annihilation of the vortices proceeds via a leading rapid turbulent burst followed by a trailing slow laminar decay from which the mutual friction dissipation can be determined. In contrast to currently accepted theory, mutual friction is found to have a finite value in the zero temperature limit: $\alpha (T \rightarrow 0) = (5 \pm 0.5) \cdot 10^{-4}$.