Collision Drag Effect on Two-Fluid Hydrodynamics of Superfluid 3He in Aerogel

TL;DR

This paper investigates how collision-induced drag forces affect sound propagation in superfluid helium-3 within aerogel, providing explicit attenuation formulas and exploring the propagation of fourth sound in confined geometries.

Contribution

It introduces a two-fluid model incorporating collision drag effects and derives explicit expressions for sound attenuation in superfluid helium-3 in aerogel.

Findings

Drag force causes sound damping in superfluid helium-3 in aerogel.

Explicit formulas for longitudinal sound attenuation are provided.

Fourth sound can propagate in narrow pores due to normal fluid clamping by aerogel.

Abstract

Sound propagation in superfluid $^3$He in aerogel is studied on the basis of a two-fluid model taking into account the effect by the drag force due to collisions between $^3$He-quasiparticles and aerogel molecules. The drag force plays a role of frictional force between the aerogel and the normal-fluid component. In local equilibrium, they move together in accordance with McKenna {\it et al.}'s model. The deviation from the local equilibrium leads to the damping of sound. We give explicit expressions for the attenuation of longitudinal sounds in this system. We also discuss the sound propagation in a superfluid ${}^3$He-aerogel system embedded in a narrow pore. It is shown that the forth sound propagates in such a system because of the clamping of the normal fluid by the aerogel.