Bichromatic Microwave Photoresistance of Two-Dimensional Electron System

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We explore experimentally bichromatic (frequencies ω₁ and ω₂) photoresistance of a two-dimensional electron system in the regimes of microwave-induced resistance oscillations and zero-resistance states. We find bichromatic resistance to be well described by a superposition of ω₁ and ω₂ components, provided that both monochromatic resistances are positive. This relation holds even when the oscillation amplitudes are small and one could expect additive contributions from monochromatic photoresistances. In contrast, whenever a zero-resistance state is formed by one of the frequencies, such superposition relation breaks down and the bichromatic resistance is strongly suppressed.