Frequency-dependent magnetoconductance quantisation in 2D systems-a disorder effect

Strong frequency dependence is shown in the quantised magnetoconductance in high-mobility silicon MOSFETs, with the loss of integer quantised plateaux and enhancement of fractional quantisation. Fractional plateaux observed are quantised to within 5%, which is within experimental accuracy. The frequency at which the onset of these phenomena is observed is shown to be dependent upon sample length and Landau level filling factor. The results are similar to those previously obtained using low-mobility GaAs heterostructures, though in the highest mobility cases no effect is seen up to 50 MHz. The roles of sample length and disorder are discussed.