High frequency sound in superfluid 3He-B

TL;DR

This paper reports measurements of sound velocities in superfluid 3He-B, revealing insights into pairing interactions, collective modes, and energy gaps, advancing understanding of its quantum properties at low temperatures.

Contribution

It provides the first detailed measurements of phase velocities and attenuation in superfluid 3He-B, linking them to pairing interactions and collective modes.

Findings

Identification of the J=4- mode related to f-wave pairing

Establishment of lower bounds on the energy gap in B-phase

Agreement of attenuation measurements with pair-breaking energy estimates

Abstract

We present measurements of the absolute phase velocity of transverse and longitudinal sound in superfluid 3He-B at low temperature, extending from the imaginary squashing mode to near pair-breaking. Changes in the transverse phase velocity near pair-breaking have been explained in terms of an order parameter collective mode that arises from f-wave pairing interactions, the so-called J=4- mode. Using these measurements, we establish lower bounds on the energy gap in the B-phase. Measurement of attenuation of longitudinal sound at low temperature and energies far above the pair-breaking threshold, are in agreement with the lower bounds set on pair-breaking. Finally, we discuss our estimations for the strength of the f-wave pairing interactions and the Fermi liquid parameter, F4s.