Scanning gate microscopy investigations on quantum point contacts.

摘要

A cryogenic scanning probe microscopy system capable of operating at a base temperature of 300 mK was assembled. With this system, scanning gate microscopy was performed on quantum point contacts (QPC) fabricated on different materials. Images taken in a QPC fabricated in an InGaAs/InAlAs heterostructure revealed a set of fluctuations that can be associated to sites where the local random potential can be observed. Images in this sample revealed a mapping of this disordered background potential when the channel is nearly depleted. In the case of QPCs fabricated in a high mobility GaAs/AlGaAs heterostructure, new structures with the shape of rings are observed when the conductance is lowered below 2e2/h. Although the theory is still developing for this phenomenon, some explorations are presented. At high magnetic fields, it is possible to see regions corresponding to the compressible and incompressible liquid formed by edge states in the quantum Hall effect, a result that is explored for both materials. This work ends with a brief comparative study between the QPCs and preliminary measurements obtained on a quantum dot.