Kelvin-Helmholtz instability of AB interface in superfluid 3He

TL;DR

This paper investigates the Kelvin-Helmholtz instability at the interface of superfluid 3He, demonstrating that classical stability conditions apply when accounting for magnetic effects on surface tension.

Contribution

It provides experimental validation of the modified Kelvin-Helmholtz stability criterion in superfluid 3He under magnetic fields and rotation.

Findings

Classic stability condition holds with magnetic field adjustments

Surface tension reduction affects interface stability

Instability observed down to 0.4 Tc

Abstract

The Kelvin-Helmholtz instability is well-known in classical hydrodynamics, where it explains the sudden emergence of interfacial surface waves as a function of the velocity of flow parallel to the interface. It can be carried over to the inviscid two-fluid dynamics of superfluids, to study different types of interfaces and phase boundaries in quantum fluids. We report measurements on the stability of the phase boundary separating the two bulk phases of superfluid 3He in rotating flow, while the boundary is localized with the gradient of the magnetic field to a position perpendicular to the rotation axis. The results demonstrate that the classic stability condition, when modified for the superfluid environment, is obeyed down to 0.4 Tc, if a large fraction of the magnetic polarization of the B-phase is attributed to a parabolic reduction of the interfacial surface tension with increasing magnetic field.