Broken Symmetry and Nonequilibrium Superfluid 3He

TL;DR

This paper introduces non-equilibrium superfluid 3He, focusing on symmetry breaking and collective modes, including recent experimental observations of transverse sound waves supporting theoretical predictions.

Contribution

It provides a theoretical framework for understanding symmetry breaking effects on collective modes and discusses recent experimental detection of transverse sound in superfluid 3He.

Findings

Observation of transverse sound waves in superfluid 3He B-phase

Confirmation of Landau's prediction of shear waves in 3He

Analysis of symmetry breaking effects on collective mode dynamics

Abstract

These lecture notes provide an introduction to non-equilibrium superfluid 3He, with applications to high-frequency excitations, including aspects of symmetry breaking in 3He and its effects on collective mode dynamics. In 1957 Landau predicted that liquid 3He would support propagating shear waves at low temperatures, i.e. a transverse sound mode. Such waves have recently been observed at low temperatures in the superfluid B-phase of liquid 3He. These observations provide a beautiful example of the effect of spontaneous symmetry breaking in condensed matter. I discuss the theory of transverse wave propagation in 3He and the recent detection of these waves by magneto-acoustic rotation of the 3He polarization in a magnetic field.