  The influence of microwave radiation (1.2-140 GHz) on resistance of
high-mobility two-dimensional electron gas in GaAs quantum wells is studied.
Two series of microwave-induced magnetoresistance oscillations periodic in 1/B
were observed under microwave radiation. The periods of oscillations are
determined by the microwave frequency and power, correspondingly. The
experimental data is qualitatively explained by photon-assisted transport and
Zener tunneling between Landau orbits.
