  Piezoelectric surface acoustic waves (SAWs) are powerful for investigating
and controlling elementary and collective excitations in condensed matter. In
semiconductor two-dimensional electron systems SAWs have been used to reveal
the spatial and temporal structure of electronic states, produce quantized
charge pumping, and transfer quantum information. In contrast to
semiconductors, electrons trapped above the surface of superfluid helium form
an ultra-high mobility, two-dimensional electron system home to
strongly-interacting Coulomb liquid and solid states, which exhibit non-trivial
spatial structure and temporal dynamics prime for SAW-based experiments. Here
we report on the coupling of electrons on helium to an evanescent piezoelectric
SAW. We demonstrate precision acoustoelectric transport of as little as ~0.01%
of the electrons, opening the door to future quantized charge pumping
experiments. We also show SAWs are a route to investigating the high-frequency
dynamical response, and relaxational processes, of collective excitations of
the electronic liquid and solid phases of electrons on helium.
