Special Colloquium, January 22, 2004

Radiation-Induced Magnetoresistance Oscillations in a 2D Electron Gas

Adam Durst

Yale University

The electrical transport properties of a two-dimensional electron gas in a perpendicular magnetic field have been studied extensively over the past two decades in connection with the quantum Hall effects. So it came as quite a surprise when recent experiments, in which such systems are subjected to electromagnetic radiation, revealed an intriguing new phenomenon. In the presence of microwave radiation, the measured magnetoresistance exhibits a novel 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 transport 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.

1:30 p.m., Smith Laboratory, Room 1094