Coupling lattice, charge and topological reconstructions at oxide interfaces

Abstract

Modern materials synthesis techniques allowfor the layer-by-layer assimilation of structurally similar, yet compositionally different materials into artificial crystals, with atomic scale precision. At the resulting heterointerfaces, structural, electronic and magnetic reconstructions can lead to physical phenomena that are otherwise absent in the individual constituents. Composing so-called heterostructures is therefore one of the key approaches towards realizing the ultimate goal of designer materials with tailored properties. In this context, perovskite oxides represent a promising class of materials, owing to the combination of a delicate balance among competing electronic and magnetic interactions, as well as excellent structural compatibility among its members. This thesis describes a collection of investigations into interface-driven reconstructions in heterostructures composed of such perovskite oxides. Chapters 1 provides a brief introduction to the field of complex oxide interfaces, as well as the Berry curvature and its relationship to the so-called anomalous Hall effect. Chapter 2 provides an overview of the main experimental techniques used throughout this thesis; pulsed-laser deposition, X-ray diffraction, lithographic device fabrication and cryogenic magnetotransport characterization. Chapter 3 focuses on heterostructures composed of spin-orbit semimetal SrIrO3 and the bandgap insulator SrTiO3. Aided by transport measurements, synchrotron X-ray diffraction and DFT calculations, we demonstrate a coupling of orthorhombic structural domains in the film to tetragonal domains in the substrate. The results extend to a variety of orthorhombic materials, opening up possibilities to manipulate structural domain patterns to a wide variety of materials through interaction with a tetragonal substrate. Chapters 4 and 5 focus on the itinerant ferromagnet SrRuO3 and its intriguing intrinsic anomalous Hall effect. We show that through interfacing SrRuO3 with SrTiO3, SrIrO3 and LaAlO3, the sign of the momentum-space Berry curvature can be controlled. We propose a simple two-channel model to account for the unusual field dependence of the anomalous Hall effect in asymmetric heterostructures. The findings in these chapters underline oxide interfaces as a versatile platform for manipulating the geometric properties of wavefunctions in solid-state systems, as well as the potential of ultrathin SrRuO3 for spintronic applications. In Chapter 6, we synthesize SrRuO3 thin films on SrTiO3 (111) substates. Transport measurements indicate a distinct effect of electronic confinement on the electronic properties of (111) oriented SrRuO3 thin films as compared to their (001) counterparts, producing bands with a hole-like character in the ultrathin limit. This highlights crystal orientation and heteroepitaxial growth as an effective tuning parameter for controlling the electronic properties of oxide heterostructures. The final chapter summarizes the findings of this thesis and provides a number of research directions to be further explored.