Spatial imaging of noise voltages by a quantum Hall scanning electrometer

We present a new application of the quantum Hall effect (QHE): a scanning sensor for imaging the spatial distributions of noise voltages. This technique is based on a scanning electrometer employing a QHE device, which utilizes capacitive coupling between electrometer and sample. By measuring local voltage fluctuations with the QHE electrometer, we have been able to produce the first image of a noise-voltage distribution in a QHE sample. We found that a high noise level occurs in the lower magnetic field region of a QHE plateau of Landau-level-filling factor 2, and that it is concentrated in a high-potential edge region of the Hall bar sample. These results show that our noise-imaging system serves as a useful tool for probing edge-state electrons in QHE systems.