UC Santa Barbara

Complex oxides show a wide array of phenomena, including magnetic states, ferroelectricity, and superconductivity. Furthermore, the advent of atomic scale engineering of the oxides using molecular beam epitaxy (MBE) has facilitated the discovery of novel phenomena in thin films and heterostructures not seen in bulk. Complex oxide perovskite titanate heterostructures composed of both Mott and band insulators can be fabricated readily and exhibit unique properties, including interfacial two-dimensional electron gases (2DEGs), superconductivity, and magnetic ordering.

The objective of this Dissertation is to study the relationships between emergent phenomena and heterostructure design using advanced MBE growth techniques and characterization tools, with the intent of developing controllable states of matter. The impact of strain and octahedral connectivity in epitaxially mismatched heterostructures on magnetism and electrical transport is addressed, as well as proximity effects and the influence of magnetically ordered layers on neighboring low-dimensional itinerant systems.

The Dissertation begins with a motivational overview of materials and associated phenomena, describing the unique emergent properties associated with thin films. This is followed by a description of the organization of the remainder of the text. The methods implemented, including MBE and electrical transport characterization, are then discussed. Structure-magnetism and structure-transport correlations are demonstrated, as well as tunable emergent ferromagnetism in GdTiO₃/SrTiO₃ heterostructures and quantum critical behavior in SmTiO₃/SrTiO₃ heterostructures. Recent progress on devices based on GdTiO₃/SrTiO₃ are discussed. The dissertation closes with a brief summary and discussion of future works.