Noise from backscattered electrons in the integer and fractional quantized Hall effects

We report low-temperature experiments on noise (in equilibrium and in the presence of current flow) in Hall bars with 0.5-μm gates across them. The Hall bars were formed on high-mobility GaAs-${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructures, and by using the gate we were able to explore the noise characteristics both in the integer quantized Hall effect and for fractional filling factors. In the integer quantized Hall effect, the noise power exhibits plateaus where the resistance does, and it exhibits plateaus in spite of the lack of clear resistance plateaus when the filling factor is fractional beneath the gate. The excess noise found in the experiments is less than that predicted by the simple shot-noise formula.