Nonlinear response of microwave-irradiated two-dimensional electron systems near the second harmonic of the cyclotron resonance

Recent experiments onmicrowave-irradiated high-mobility two-dimensional electron systems [Dai et al., Phys. Rev. Lett. 105, 246802 (2010); Hatke et al., Phys. Rev. B 83, 121301(R) (2011)] revealed a novel photoresistivity peak in the vicinity of the second cyclotron resonance harmonic. Here we report on the nonlinear transport measurements and demonstrate that the peak can be induced by modest dc fields and that its position is not affected even by strong dc fields, in contrast to microwave-induced resistance oscillations that shift to higher magnetic fields. These findings reinforce the notion that the peak cannot be described by existing models and provide important constraints for further theoretical considerations.