Scanning gate tuning of mesoscopic transport in quantum-ring networks

Among the plethora of nano-objects, those conducting electricity attracted a great deal of attention with interesting transport properties such as electrical conductance quantization, electron interferences, single charge effects etc. This thesis aims to study puzzling electron transport signatures emerging as electrons flow through nanoscale electrically-conducting networks patterned within two-dimensional electron systems (2DES), where charge transport occurs in the ballistic and coherent regime at low temperature. These networks, constituted from connected nanowires, exhibit peculiar electrical conductance variations that we managed to associate with electron interferences within individual one-dimensional wires and two-dimensional ballistic electron scattering. Local-scale data on electronic transport were collected with scanning gate microscopy (SGM) - a near-field technique where an electrostatically biased nanoscale conductive tip, scanned in the vicinity of the network, is used to tune the electrostatic potential felt by electrons crossing the network. SGM allowed us to decrypt electron transport mechanisms at the local scale, to demonstrate the presence of an unidimensional electron interferometer in the network and to pinpoint a charge injection mechanism analogous to the two-dimensional Rutherford scattering both experimentally and in simulations. In turn, this work provides useful tools in the perspective of building ‘electron optics’ devices, where a local modulation of the electrostatic potential enables, on one hand, to control Fabry-Pérot electron resonances and, on the other hand, to redirect the electron flow in a similar way as an optical lens curves light rays, allowing to study Rutherford-like ballistic scattering mechanisms.
(FSA - Sciences de l'ingénieur) -- UCL, 2018