New Limits for Existence of Transverse Zero Sound in Fermi Liquid 3He

TL;DR

This study investigates the existence of transverse zero sound in Fermi liquid helium-3 using microfabricated acoustic cavities, finding no clear evidence due to high attenuation, and discusses theoretical reasons for the non-detection.

Contribution

The paper provides a novel experimental approach with microfabricated cavities to detect transverse zero sound and offers theoretical insights explaining the high attenuation observed.

Findings

No clear interference fringes observed, indicating high attenuation of transverse zero sound.

Attenuation likely exceeds 2000 cm^-1, preventing direct detection.

Theoretical analysis suggests the mode may still exist but is not detectable with current methods.

Abstract

Landau predicted that transverse sound propagates in a Fermi liquid with sufficiently strong Fermi liquid interactions, unlike a classical fluid which cannot support shear oscillations. Previous attempts to observe this unique collective mode yielded inconclusive results due to contributions from single particle excitations. Here, we have microfabricated acoustic cavities with a micron-scale path length that is suitable for direct detection of this sound mode. The interference fringes of these acoustic Fabry-Perot cavities can be used to determine both the real and imaginary parts of the acoustic impedance. We report a null-result in this search as no clear interference fringe has been observed in the Fermi liquid, indicating the attenuation of TZS is likely above 2000 cm^-1. We provide theoretical justification for why the sound mode may yet exist but not being directly detectable due to high attenuation.