Evidence for magnetoplasmon character of the cyclotron resonance   response of a two-dimensional electron gas
  Experimental results on the absolute magneto-transmission of a series of high density, high mobility GaAs quantum wells are compared with the predictions of a recent magnetoplasmon theory for values of the filling factor above 2. We show that the magnetoplasmon picture can explain the non-linear features observed in the magnetic field evolution of the cyclotron resonance energies and of the absorption oscillator strength. This provides experimental evidence that inter Landau level excitations probed by infrared spectroscopy need to be considered as many body excitations in terms of magnetoplasmons: this is especially true when interpreting the oscillator strengths of the cyclotron transitions. 
Cl\'ement Faugeras (LCMI), G\'erard Martinez (LCMI), A. Riedel (PDI),   Rudolf Hey (PDI), Klaus-Jurgen Friedland (PDI), Y. B...