Absorption of microwave radiation by two-dimensional electron systems associated with the excitation of dimensional Bernstein mode resonances

The magnetic field dependence of the amplitudes of Shubnikov–de Haas oscillations in GaAs/AlGaAs heterostructure samples with a two-dimensional electron system irradiated by microwave radiation in the range of 130–170 GHz has been studied. Two features of the radiation-induced suppression of amplitudes of oscillations having a field-resonance character have been revealed. One of the resonances appears in a magnetic field corresponding to the second harmonic of the cyclotron resonance, whereas the dependence of the existence, position, and amplitude of the second resonance on the radiation frequency is more complex. The detected resonance absorption of radiation at the second harmonic is apparently responsible for an anomalous peak of the magnetoresistance recently observed near this harmonic. The detected resonances can be explained by the excitation of standing magnetoplasma waves in a confined sample with the same the wavenumber but corresponding to different regions of their dispersion relation: an almost dispersionless region of the Bernstein mode and a cyclotron magnetoplasma mode.