High-order resonances in microwave-assisted magnetotransport of 2D electrons

Ivan Dmitriev

Karlsruhe University, Germany

Recent experiments on magnetoresistivity of irradiated 2D electron systems have reported novel resonant features and zero-resistance states located near fractional harmonics of the cyclotron resonance [1,2]. While in Ref.[2] the fractional features were observed only at radiation frequencies below a certain threshold, the other experiment didn't show any threshold behavior. We explain this apparent discrepancy as a result of competition of different mechanisms of the fractional photoresponce. Namely, at strong magnetic field the effect is due to multiphoton processes [3] while at weak field the resonances are dominated by a series of multiple single-photon transitions [2,4], giving rise to the observed thresholds. Interestingly, one more mechanism, associated with microwave induced sidebands in density of states, provides a comparable contribution to the fractional resonances at intermediate magnetic fields [3].
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