Spin-dependent electron transport in GaAs- and InAs-based nanostructures

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The aim of this project is to investigate spin-dependent ballistic transport in nanoscale GaAs/AIGaAs field-effect heterostructures (FETs) of low spin-orbit coupling, and to extend the experimental studies to InAs/InGaAs field-effect heterostructures with an increased spinorbit coupling for a direct comparison. Starting materials are modulation doped heterostructures with two-dimensional electron gases of high mobilities (> 106 cm2/Vs for GaAs-based FETs and >105 cm2/Vs for InAs-based FETs) from which Aharonov-Bohm ring structures are prepared by electron-beam lithography and wet-chemical etching. Fourterminal measurements of current and voltage characteristics are taken äs a function of top voltages and magnetic fields at low temperatures (< 4.2 K). Local nanopatterned top-gates are used to control the electron densities in the electron waveguides of the ring. Quantum point contacts with large subband separations (>5-10 meV) are employed äs energy and mode filters and the injection of spin polarized electrons in the ring is planned by using a quantum point contact as spin filter element in inplane magnetic fields. The amplitude and phase of the Aharonov-Bohm conductance oscillations is investigated for different operating modes of the injecting quantum point contact. Up-to-date, the transport in the mode occupation below the first mode of a quantum point contact is discussed with spin-related mechanisms and remains an unresolved issue. The objective is the investigation of spinrelated dephasing mechanisms in the electronic quantum transport which is being approached by adding a single-electron transistor with tunable coupling to the ring structure.