A topological insulating phase has theoretically been predicted for the thermodynamically unstable perovskite phase of YBiO 3 . Here, it is shown that the crystal structure of the Y-Bi-O system can be controlled by using a BaBiO 3 buffer layer. The BaBiO 3 film overcomes the large lattice mismatch of 12% with the SrTiO 3 substrate by forming a rocksalt structure in between the two perovskite structures. Depositing an YBiO 3 film directly on a SrTiO 3 substrate gives a fluorite structure. However, when the Y-Bi-O system is deposited on top of the buffer layer with the correct crystal phase and comparable lattice constant, a single oriented perovskite structure with the expected lattice constants is observed.Topological materials are at the focus of a relatively young field in material science, aiming to find both new topological materials as well as discovering novel applications for this new class of matter. The most prominent phenomena that emerge in topological materials include a chiral spin structure and topologically protected surface states. [1,2] The spin-momentum locking makes topological matter interesting for spintronic applications [1,3,4] and possibly quantum computation. [5] Therefore, global research is conducted towards further developing known topological materials and trying to find new compounds that have a non-trivial topology in their band structure.So far, only a handful of materials have been identified as topological insulators (TIs). Within a year after the theoretical prediction of Bernevig et al., [1] König et al. [3] observed the quantum spin Hall state in CdTe/HgTe/CdTe quantum wells À the first system known with a non-trivial band structure. Bi 1-x Sb x was the first three-dimensional TI that was experimentally observed, [6] followed by Bi 2 Se 3 , [7] and Bi 2 Te 3 . [4] The relatively heavy bismuth gives rise to strong spin-orbit coupling (SOC) effects, which in turn results in a band inversion at an odd

This work shows how itinerant electrons localize due to increased interactions across the Mott metal-insulator transition.

In the quest for topological insulators with large band gaps, heterostructures with Rashba spin–orbit interactions come into play. Transition metal oxides with heavy ions are especially interesting in this respect. We discuss the design principles for stacking oxide Rashba layers. Assuming a single layer with a two-dimensional electron gas (2DEG) on both interfaces as a building block, a two-dimensional topological insulating phase is present when negative coupling between the 2DEGs exists. When stacking multiple building blocks, a two-dimensional or three-dimensional topological insulator is artificially created, depending on the intra- and interlayer coupling strengths and the number of building blocks. We show that the three-dimensional topological insulator is protected by reflection symmetry, and can therefore be classified as a topological crystalline insulator. In order to isolate the topological states from bulk states, the intralayer coupling term needs to be quadratic in momentum. It is described how such a quadratic coupling could potentially be realized by taking buckling within the layers into account. The buckling, thereby, brings the idea of stacked Rashba system very close to the alternative approach of realizing the buckled honeycomb lattice in [111]-oriented perovskite oxides.

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An oxide topological insulator could be a possible building block for a new generation of consumer electronics, contributing to the need for more energy-efficient devices. A topological insulator is famous for its insulating bulk characteristics and metallic surface states. Various experimental realizations are known, but all with a relatively small energy band gap. Using oxide materials for artificially designed topological insulators potentially enlarges the size of the band gap or could enrich the functionality. Application at room temperature could become feasible and would open a route towards dissipationless electronics. In this dissertation, various design principles are explored as possible routes to achieve a nontrivial phase in oxide materials.