  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.
