  Magnetotransport phenomena in high-quality quantum wells often shed a light
on the nature of microscopic states of two-dimensional electrons in these
systems. In particular, the independence of photoresistance on the polarization
helicity of incident radiation have been treated an important puzzling result,
which had no well-established explanation up to now. Here we propose a
theoretical model of dynamics of a strongly non-ideal two-dimensional electron
liquid in moderate magnetic fields. In this system, in particular, successive
collisions of electrons joined in pairs are as important as single collisions
of statistically independent electrons. The resulting fluid photoresistance
exhibits an irregular shape of magnetooscillations, the absence of the
dependence on the helicity of the circular polarization of incident radiation,
and a large peak near the doubled cyclotron frequency. All these effects were
observed in experiments on best-quality GaAs quantum wells. We conclude that 2D
electrons in such nanostructures in moderate magnetic fields form a novel type
of highly correlated fluids.
