Observation of open quantum dot via low temperature scanning gate microscopy

Low temperature transport of a well-defined open-quantum dot has been studied via scanning gate microscopy (SGM). The open dot was fabricated on AlGaAs/GaAs heterostructure using trenches defined via electron beam lithography and a wet etching. The active size of the quantum cavity is approximately 1 μm × 1 μm. The SGM observation was performed at low temperature with a conductive piezolever, which is lifted up 50 nm above the surface with applied a negative voltage. During the scan of the tip, resistance across the dot is measured in a four-probe configuration and stored in a SPM controller synchronized with the position of the tip. The SGM response at zero-magnetic field shows a high resistance when the tip situates onto a line along the inlet and the outlet of the dot. The image could be understood as that the tip induced potential disturbs the current flow in the dot and it results in the increase of resistance. Such an image can be obtained even at more than 8 K, therefore this image would correspond to a classical transport. On the other hand, the image obtained at less than 2 K shows almost similar image as that observed at higher temperature. However, after subtracting the high temperature image as the back ground structure, which is achieved by a high pass filtering, conductance fluctuations are visualized in the low temperature image. These fluctuations would be attributed to a change of quantum interference condition as well as a manipulation of the wave-function confined in the open quantum dot.