  Experimental measurements of photoresistivity under terahertz (THz) radiation
in low magnetic fields at conditions of cyclotron resonance (CR) in
two-dimensional electron system (2DES) of GaAs/AlGaAs nanostructures are
presented and discussed. We report the experimental discovery of CR-vanishing
effect (CRV) in GaAs/AlGaAs heterostructures with high mobility as a
well-defined gap on CR-line that is independent on incident THz power. Our
analysis shows that the CRV may appear in systems with well correlated state of
2D electrons such as plasma waves and others. Fundamental nature of these
correlated states of electrons in 2DES is discussed. Future THz detectors
utilizing the new correlated states in 2DES may expand horizons for
supersensitive and selective detectors in sub-THz and THz frequencies ranges.
