Within the family of II3V2 pnictides, cadmium arsenide (Cd3As2) is unique for hosting topologically non-trivial bands in its electronic structure. In the bulk limit, it is regarded as a model for topological Dirac semimetals because its inverted bands intersect each other along a 4-fold rotation axis, satisfying a linear dispersion relation without obstruction from nearby Fermi surfaces. When scaled to two-dimensions, the bulk topological bands of Cd3As2 can be further engineered to generate new electronic states.

This dissertation presents magnetotransport studies of (001) oriented Cd3As2 quantum wells that are grown by solid-source molecular beam epitaxy (MBE). Building on Chapter 1's introduction, Chapter 2 details the MBE growth and structural characterization of these thin film samples. This includes not only the Cd3As2 active region, but also the metamorphic (Al,In)Sb buffer, designed to accommodate the film/substrate misfit, and the GaSb capping layer, which is deposited at low temperatures. Chapter 3 then focuses on improvements made to both device fabrication and transport measurements of these quantum wells. This enabled the first demonstration of chemical potential-tuning across the bandgap of confined (001) Cd3As2 samples using an electrostatic top gate. Furthermore, an insulating v = 0 quantum Hall plateau, showing an unusual magnetic field dependence, was observed in an early generation quantum well. Higher mobility samples helped to resolve the nature of this state, and more important, provided evidence of subband inversion in a range of well thicknesses near 20 nm. Next, Chapter 4 investigates the influence of an in-plane (Zeeman) magnetic field on samples belonging to the band-inverted regime. The transport data are consistent with a predicted topological phase transition from the inverted phase to an emergent 2D Weyl semimetal phase (2D WSM), driven by the in-plane field. In particular, the 2D WSM shows saturated resistivities h/e^2 at charge neutrality, and a well-developed odd-integer quantum Hall effect under a small perpendicular magnetic field. These experimental findings are supported by a 4-band k-p model of Cd3As2 that incorporates first-principles, effective g factors. Chapter 5 shifts focus to provide a discussion of preliminary results on devices designed to evaluate hybrid interfaces between ex situ superconductors and (001) Cd3As2 quantum wells. Chapter 6 summarizes the key findings of this dissertation and describes future directions for MBE-grown Cd3As2 thin films.