| Semiconductor nanostructures are tunable systems and can serve as probes of strongly correlated electron behavior. These nanostructured devices are also promising candidates for building blocks of efficient, highly parallel nanoelectronic circuits and spin-qubit circuits. In this thesis, we present low-temperature transport measurements of semiconductor quantum dots and nanowires. We explore charge and spin effects in the context of the Coulomb blockade and the collective many-body phenomena of the Kondo effect and superconductivity.; In the first part of this thesis, we present experiments on quantum dots defined in GaAs/AlGaAs heterostructures containing two-dimensional electron gases. We investigate a triple quantum dot artificial molecule, where the three dots are arranged in a ring structure. When asymmetric coupling is introduced in the system, we show that the three coupled quantum dots in the Coulomb blockade regime act as an electron rectifier. This triple dot system can be used as a single-electron charge rectifier in single-electron circuits. A symmetric triple dot artificial molecule is also investigated. We supplement our experimental investigations with numerical calculations to determine the singlet-triplet splitting for a two electron triple quantum dot.; In a separate experiment, we investigate a quantum dot containing just one or two electrons in the Kondo regime. We observe several sharp peaks in the differential conductance, occurring at both zero and finite source-drain bias, for the one and two electron quantum dot. At zero source-drain bias, the temperature and magnetic field dependence of the conductance is consistent with a standard Kondo resonance. The peaks at finite-bias are related to a Kondo effect through excited states of the quantum dot. Measurements in an applied magnetic field were also performed to probe these additional Kondo resonances.; In the second part of this thesis, we present transport measurements of one-dimensional hole gases formed in Ge/Si core/shell heterostructure nanowires. When connected to superconducting aluminum electrodes, a dissipationless supercurrent flows through the semiconductor nanowire. By using a local top gate, which modulates the carrier density of the nanowire and the number of one-dimensional subbands populated, the critical current can be tuned. Resonant multiple Andreev reflections in the superconductor-nanowire-superconductor system is also observed. Finally, we investigate the interplay between one-dimensional quantum confinement and superconductivity. |
