Imaging of quantum interference patterns within a quantum point contact

Direct visualization of quantum transport within the constriction of a quantum point contact (QPC) has been obtained using scanning gate microscopy (SGM). The SGM operates at 0.3 K using a PtIr-coated piezolever. Transmission through the QPC shows conductance quantization in units of 2 e2/h at 6 K; however, the plateaus are washed out by quantum fluctuations at 280 mK. Interference patterns within the QPC were observed by scanning the tip above the QPC. This is attributed to the presence of a random disorder potential. Near the pinch-off voltage, the technique allows us to directly image the disorder potential. At high magnetic fields, we observe quantized plateaus in the images, which may indicate a direct visualization of the edge states.