Multiphoton microwave photoresistance in a high-mobility two-dimensional electron gas

We report on experimental and theoretical studies of microwave-induced resistance oscillations in a two-dimensional electron gas over a wide range of microwave intensities. We observe a distinct crossover from linear to sublinear power dependence of the oscillation amplitude and a concomitant narrowing of the oscillation extrema. To explain our observations we propose a theory based on the quantum kinetic equation at arbitrary microwave power. Taken together, these findings demonstrate a crucial role of multiphoton processes at elevated microwave intensities.