The A-B Transition of Superfluid Helium-3 in Aerogel and the Effect of Anisotropic Scattering

TL;DR

This study investigates the A-B phase transition of superfluid helium-3 in aerogel using high-frequency acoustic measurements, revealing phase coexistence influenced by anisotropic scattering.

Contribution

It provides experimental evidence of A-B phase coexistence in helium-3 within aerogel and links it to anisotropic scattering effects.

Findings

A and B phases coexist over ~100 micro-Kelvin range.

A-B transition observed on warming in zero magnetic field.

Anisotropic scattering influences phase stability.

Abstract

We report the results of high frequency acoustic shear impedance measurement on superfluid helium-3 confined in 98% porosity silica aerogel. Using 8.69 MHz continuous wave excitation, we measured the acoustic shear impedance as a function of temperature for the sample pressure of 28.4 and 33.5 bar. We observed the A-B transition on warming in zero magnetic field. Our observations show that the A and B phases in aerogel coexist in a temperature range of about 100 micro-Kelvin in width. We propose that the difference in the relative stability of the A and B phases, arising from anisotropic scattering, can account for our observations.