Massless surface wave

TL;DR

This paper predicts a novel massless surface wave at the interface of two superfluid helium-3 phases, driven by spin supercurrents and magnetic field gradients, with potential for experimental observation.

Contribution

It introduces a new type of massless surface wave in superfluid helium-3, characterized by surface displacement due to phase transition without particle flow, expanding understanding of topological surface excitations.

Findings

Dispersion relation for the massless wave derived.

Conditions for observing the wave identified.

Dissipation mechanisms analyzed.

Abstract

An interface between two media is topologically stable two-dimensional object where 3D-symmetry breaks which allows for existence of many exotic excitations. A direct way to explore surface excitations is to investigate their interaction with the surface waves, such as very well known capillary-gravity waves and crystallization waves. Helium remains liquid down to absolute zero where bulk excitations are frozen out and do not mask the interaction of the waves with the surface states. Here we show the possibility of the new, massless wave which can propagate along the surface between two different superfluids phases of $^3$He. The displacement of the surface in this wave occurs due to the transition of helium atoms from one phase to another, so that there is no flow of particles as densities of phases are equal. We calculate the dispersion of the wave in which the inertia is provided by spin supercurrents, and the restoring force is magnetic field gradient. We calculate the dissipation of the wave and show the preferable conditions to observe it.