Piezoacoustic Measurements of Electrons on Helium*

We report on simultaneous low-frequency transport and high-frequency piezoacoustic measurements of electrons on the surface of superfluid helium. By coupling a piezoacoustic surface wave to a nearby two-dimensional electron system we measure the high frequency conductivity of the electron system in a wave-vector selective manner. Additionally, a dynamical piezoelectric standing wave creates a modulated and tunable potential that can be used to simulate a two-dimensional system exhibiting commensurate-incommensurate transitions which can be detected via quasi-dc transport measurements.