Epitaxial oxides

All physical properties in solids come alive because of a specific interatomic arrangement, whether in crystalline or amorphous materials. For compounds such as metal oxides, additional parameters such as the metal valence state and the composition play a dominant role. While in principle one could imagine an infinite amount of atomic arrangements to be possible, it turns out that when a significant amount of atoms agglomerate together to form a crystal, only 230 different structural configurations are available because of symmetry reasons; these configurations are commonly known as space groups grouped in the 7 crystal lattices. Furthermore, it turns out that under ambient conditions only one specific structure is stable although other configurations are not far away - at least from a free energy point of view - which then results in phase transitions occurring at different temperatures or pressures. However, in reduced dimensions or in contact with other crystals through epitaxial strain, additional metastable structures can be formed. To explore both numerically and experimentally such metastable structures is the main focus of this PhD project. More specifically, since the discoveries around 2D graphene there has been a lot of progress in a plethora of other 2D materials. This also includes the appearance of novel topological properties that are uniquely related to this dimensionality such as the quantum anomalous Hall effect. While strong electron-electron correlations lead to a number of interesting physical properties in transition metal oxides such as high temperature superconductivity, colossal magnetoresistance, metal to insulator transitions etc., their role in 2D and their effect on the topological properties are not well known and will be the first pillar in this thesis. The second pillar will be to explore a range of unconventional straining methods in an attempt to create nanoscale single crystals. The methodology will include a series of numerical first principle methods in order to predict or explain the appearance of novel properties. Experimental results will be achieved through the growth of thin films using molecular beam epitaxy followed by extensive characterization methods such as x-ray diffraction, angle resolved x-ray photo emission, optical spectroscopies as well as magnetoelectric transport as a function of temperature.