A.A. Zabolotnykh, V.A. Volkov
Recent experiments on microwave-irradiated ultraclean 2D electron systems in quantizing magnetic field revealed a colossal, narrow photoresistivity peak in the vicinity of the second cyclotron resonance harmonic 2ωС. Here we propose a possible explanation of this puzzle phenomenon. It is shown that if microwave frequency is near 2ωС and the gradient of the amplitude of microwave electric field acting on electrons is sufficiently large then plasmon instability can arise in the high-mobility system. The instability development leads to the heating of the system, which in turn leads to the sharp photoresistivity peak.