Coherence and Spin in GaAs Quantum Dots

This thesis describes a number of experiments performed in quantum dots as well as 2D systems fabricated in GaAs/AlGaAs 2D electron gases. The focus of the studies is set on spin, coherence and interaction effects of electrons in mesoscopic structures. Experiments investigating the rich physics of spin-orbit coupling in confined structures in presence of magnetic fields both perpendicular and parallel to the 2D plane, orbital effects of in-plane fields on average, variance and correlations of conductance as well as few electron physics focusing on the two electron system are presented. In situ control of spin-orbit coupling in coherent transport using a clean GaAs/AlGaAs 2DEG is realized, leading to a gate-tunable crossover from weak localization to antilocalization. The necessary theory of 2D magnetotransport in the presence of spin-orbit coupling beyond the diffusive approximation is developed and used to analyze experimental data. Spin-orbit coupling in ballistic GaAs quantum dots is investigated. Antilocalization that is prominent in large dots is suppressed in small dots, as anticipated theoretically. Effects of parallel fields on average and variance of conductance reflect novel spin-rotation symmetries, consistent with random matrix theory once orbital coupling of the parallel field is included. High sensitivity of mesoscopic conductance fluctuations to magnetic flux in large quantum dots is used to investigate changes in the two-dimensional electron dispersion caused by an in-plane magnetic field. In particular, changes in effective mass and the breaking of momentum reversal symmetry in the electron dispersion are extracted quantitatively from correlations of conductance fluctuations. New theory is presented, and good agreement