Magnetic Breakdown Effects in Two-Dimensional Periodic Systems

Two-dimensional electron systems subjected to a periodic background potential usually show large positive magnetoresistance that breaks down at a particular value of the magnetic field. Magnetoresistance oscillations periodic in the ratio of the diameter of the cyclotron orbit to the modulation period have been found above this field. The semiclassical theory is used to explain both effects. We show that the oscillations may be thought of as oscillations in the probability of magnetic breakdown.