Magnetic resonance in a high-frequency flow of a two-dimensional viscous electron fluid

Two-dimensional electrons in high-quality nanostructures at low temperatures can form a viscous fluid. We develop a theory of high-frequency magnetotransport in such a fluid. The time dispersion of viscosity should be taken into account at the frequencies about and above the rate of electron-electron collisions. We show that the shear viscosity coefficients as functions of magnetic field and frequency have the resonance at the frequency equal to the doubled cyclotron frequency. We demonstrate that such a resonance manifests itself in the plasmon damping. Apparently, the predicted resonance is also responsible for the peaks and features in photoresistance and photovoltage, recently observed on the ultra-high-mobility GaAs quantum wells. The last fact should be considered as important evidence for forming a viscous electron fluid in such structures.