• electron transport
• Josephson effect
• low temperature-cryogenics
• nanotechnology and condensed matter physics
• quantum Hall effect
• Scanning Gate Microscopy (SGM) and Atomic Force Mi
• Superconductivity
• two-dimensional electron gas (2DEG)

This thesis is an experimental work performed at Laboratorio NEST in Pisa.
In this work we have started a long-term project regarding the study of nanofabricated superconductor-normal region-superconductor (SNS) hybrid junctions with the scanning gate microscopy technique (SGM).
As the normal region, we used a two-dimensional electron gas confined in an InAs quantum well, hosted in a semiconductor heterostructure. The superconductor is niobium.
The main feature of this kind of devices is that they are Josephson junctions (in our case S-2DEG-S), which means that a current (supercurrent) can pass through them without resistance.
Thanks to the use of 2DEGs as the normal region, these devices are ballistic and their supercurrent is tunable by means of side gates. Due to this feature, this kind of devices behaves like a transistor, in particular they are Josephson field effect transistors (JoFETs), consequently they are also extremely useful from the technological point of view.

The scanning gate microscope, which is a particular kind of atomic force microscope (AFM), uses a voltage-biased tip to locally change electron density and perturb charge trajectories in the 2DEG, therefore we were able to extract spatially-resolved information about the electron transport in these devices.

The experiment was performed in a 3-Helium cryostat with base temperature equal to 350mK and a superconductive magnet that can generate fields up to 9 Tesla. As a result, devices were studies in the Josephson, in the dissipative, and in the quantum Hall regimes.