We report on a new contribution to the microwave response of a two-dimensional electron system in magnetic field which originates from excitation of virtual Bernstein modes. These collective modes emerge as a result of interaction between usual magnetoplasmon mode and cyclotron resonance harmonics. The electrons are found to experience a strongly enhanced radiation field when its frequency falls in a gap of the Bernstein modes spectrum. This field can give rise to nonlinear effects, one of which, the parametric cyclotron resonance, is discussed. We argue that this resonance leads to a plasma instability in the ultraclean system. The instability-induced heating is responsible for the giant photoresistivity spike recently observed in the vicinity of the 2nd cyclotron resonance harmonic.
@article{arxiv.1305.1238,
title = {Bernstein modes and giant microwave response of two-dimensional electron system},
author = {V. A. Volkov and A. A. Zabolotnykh},
journal= {arXiv preprint arXiv:1305.1238},
year = {2014}
}