Suppression of the Aharonov-Bohm effect in the quantized Hall regime

We have examined the suppression of oscillations due to the Aharonov-Bohm effect in the magnetoresistance of annuli fabricated in high-mobility Al_xGa_1-xAs/GaAs heterostructure. The oscillations, with a periodicity near zero field corresponding to a flux of hc/e through the average area of the annulus, decrease dramatically in amplitude and shift to a lower frequency as the magnetic field increases, and vanish near the resistance minima associated with plateaus in the Hall effect. Our observations show that the net current is carried by edge states in the quantized Hall regime, and the suppression of the Aharonov-Bohm effect is due to the absence of backscattering.