Quantized Dispersion of Two-Dimensional Magnetoplasmons Detected by   Photoconductivity Spectroscopy
  We find that the long-wavelength magnetoplasmon, resistively detected by photoconductivity spectroscopy in high-mobility two-dimensional electron systems, deviates from its well-known semiclassical nature as uncovered in conventional absorption experiments. A clear filling-factor dependent plateau-type dispersion is observed that reveals a so far unknown relation between the magnetoplasmon and the quantum Hall effect. 
S. Holland, Ch. Heyn, D. Heitmann, E. Batke, R. Hey, K. J. Friedland,   and C. -M. Hu