  We report the detection of the cyclotron(CR) and magneto-plasmon(MPR) resonances near the Fermi surface of high-mobility 2DES, by microwave photoresistance measurements. We observe large amplitude photoresistance oscillations originating from higher-order CR, transitions between non-adjacent Landau levels. Such transitions are drastically enhanced in low magnetic field as compared to those previously known in the high field limit. The scattering time of the CR is found to be nearly one order of magnitude higher than that of Shubnikov-de-Haas oscillations. Finally, distinct photoresistance peaks are observed in addition to the CR features. These are identified as resonances of the low-frequency MP modes at a cut-off wavelength determined by the width of the 2DES sample. 
Microwave Photoresistance Measurements of Magneto-excitations near a 2D   Fermi Surface