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Hdr Année : 2021

Scanning gate investigations of quantum transport phenomena

Résumé

The manuscript describes my research activities on quantum transport in electronic devices using an experimental technique called Scanning Gate Microscopy (SGM). This technique provides spatial information on electron density and electron flow in buried two-dimensional electron gases (2DEG) or to modify these quantities at specific positions in the 2DEG. We investigate III/V semiconductor heterostructures, such as GaAs/AlGaAs or InGaAs/InAlAs, which host 2DEGs with high electron mobility. At low temperature, the elastic mean free path is several microns and the electron transport is fully ballistic in nano-scale devices patterned by electron beam lithography. Since the transport is also phase coherent and the electron wavelength is large, quantum effects are observable and can be studied in various nanostructures forming constrictions, rings, cavities, etc... These effects are usually probed by transport or optical spectroscopy which give mainly access to the energy levels. The spatial distribution of the quantum states, however, cannot be observed directly in these buried nanostructures, as opposed to surface electronic systems where scanning tunneling microscopy can measure the local density of states. The aim of the SGM technique is thus to probe indirectly this spatial distribution by recording the effect of a local electrostatic perturbation on the transport properties of the nanostructure. The sharp tip of an atomic force microscope is used as a local gate which is scanned above the surface. The voltage applied on the tip with respect to the 2DEG induces a local change of the electrostatic potential in the 2DEG, affecting the electron states, and thus the device conductance if these states are involved in the conduction path. With this technique, the dream would be to image directly the wave function in any kind of nanostructure, but the resolution is unfortunately limited by the relatively large distance between the tip and the 2DEG, which is buried several tens of nanometers below the surface. On the other hand, the SGM technique provides very detailed images of conductance changes, with very fine features, because the quantum states are very sensitive to the potential landscape and thus to very small displacements of the tip. In my habilitation thesis, I first describe in details the SGM technique, then review the various experiments that we have done, and finally present a few research projects that are currently developed, or will be studied in the future, in particular on the Kondo effect in quantum dots and on the negative refraction in graphene.
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Dates et versions

tel-03276154 , version 1 (01-07-2021)

Identifiants

  • HAL Id : tel-03276154 , version 1

Citer

Hermann Sellier. Scanning gate investigations of quantum transport phenomena. Mesoscopic Systems and Quantum Hall Effect [cond-mat.mes-hall]. Université Grenoble Alpes, 2021. ⟨tel-03276154⟩

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