  We observe a new type of magneto-oscillations in the photovoltage and the
longitudinal resistance of a two-dimensional electron system. The oscillations
are induced by microwave irradiation and are periodic in magnetic field. The
period is determined by the microwave frequency, the electron density, and the
distance between potential probes. The phenomenon is accounted for by coherent
excitation of edge magnetoplasmons in the regions near the contacts and offers
perspectives for the development of new tunable microwave and terahertz
detection schemes and spectroscopic techniques.
