Possible observation of impurity effects on conductance quantization

We report an experimental observation of impurity-induced conductance dips in quantized channels as predicted by previous theoretical studies. Our experiments use quantum point contacts on a two-dimensional electron gas in a modulation-doped GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructure. The electron gas has a sheet density of 1.2×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$ and a mobility of 4.6×${10}^5$ ${\mathrm{cm}}^2$/Vs measured at 50 mK. Our data, which are qualitatively very similar to those calculated with use of a two-dimensional Anderson model, strongly suggest that we are observing both the erosion of conductance quantization, and localization in the presence of an impurity-induced random potential.