Anomalous Attenuation of Transverse Sound in 3He

TL;DR

This paper reports the first measurements of transverse sound attenuation in superfluid 3He-B, revealing unexpectedly high attenuation likely due to surface Andreev bound states, contrasting with phase velocity behavior.

Contribution

It introduces the first experimental measurement of transverse sound attenuation in superfluid 3He-B and suggests a novel explanation involving surface bound states.

Findings

Attenuation is significantly larger than theoretical predictions.

Surface Andreev bound states likely cause the anomalous attenuation.

Phase velocity of transverse sound behaves differently from attenuation.

Abstract

We present the first measurements of the attenuation of transverse sound in superfluid 3He-B. We use fixed path length interferometry combined with the magneto-acoustic Faraday effect to vary the effective path length by a factor of two, resulting in absolute values of the attenuation. We find that attenuation is significantly larger than expected from the theoretical dispersion relation, in contrast to the phase velocity of transverse sound. We suggest that the anomalous attenuation can be explained by surface Andreev bound states.