QUANTUM TRANSPORT IN SEMICONDUCTOR NANOSTRUCTURES

Advances in complex oxide heterostructures have opened up a novel era in material sciences, and subsequently driven extensive physical research efforts to explore the underlying mechanisms. Material systems show a wide variety of phenomena such as superconductivity, magnetism, ferroelectricity, and spin-orbit coupling, all of which are gate-tunable. This facet demonstrates their significant importance, not only for science and research, but also for their substantial technological applications. One of the most promising systems is the LaAlO3/SrTiO3 heterostructure in which several unit cells of LaAlO3 are deposited on TiO2-terminated SrTiO3, giving rise to a two dimensional electron liquid (2DEL) at the interface region. In the case of 3-unit-cell (3 u.c.) LaAlO3/SrTiO3 interfaces, a conductive atomic force microscope (c-AFM) tip can be utilized to “write” and “erase” nanoscale devices, making LaAlO3/SrTiO3 a highly flexible platform application in novel nanoelectronics. In this thesis, the c-AFM lithography technique was employed to create various nanostructures at the LaAlO3/SrTiO3 interface. In parallel, their corresponding properties were also thoroughly investigated using quantum transport methods. Specifically, the mobility of these created nanostructures was investigated, and it was found that the mobility could be significantly enhanced in a 1D constrain configuration compared to the scenario of 2D structures. Nonlocal transport measurements were also performed on LaAlO3/SrTiO3 Hall bar structures in both normal state, and superconducting state. A novel transport property was revealed, and this property could be due to the spin and quasi-particles. Additionally, it is of note that quantum dot-like and quantum point-contact-like structures can be created via intentionally introducing barriers at the interface in LaAlO3/SrTiO3 nanowires. This can lead to various phenomena, such as electron paring without superconductivity, and conductance plateaus in transport measurements. The demonstrated c-AFM technique was also applied to a similar Al2O3/SrTiO3 material system, in which conducting channels were created at the interface. These channels show extremely high mobility at low temperature(s)