Radiation-induced magnetoresistance oscillations in a 2D electron gas

Recent measurements of a 2D electron gas subjected to microwave radiation reveal a magnetoresistance with an oscillatory dependence on the ratio of radiation frequency to cyclotron frequency. Oscillations grow with radiation intensity, with the minima saturating at zero resistance. We have performed a diagrammatic calculation which yields radiation-induced resistivity oscillations with the correct period and phase. Results are understood via a simple picture of photoexcited disorder-scattered electrons contributing to the DC conductivity. Sufficient intensity drives the calculated minima to negative resistivity, a situation shown by Andreev, Aleiner, and Millis to be unstable to the development of an inhomogeneous current distribution with zero resistivity. Hence, our result, taken together with theirs, provides an explanation for the experiments.