Functionalizing electronic and magnetic properties in oxide thin films and heterointerfaces: electric polarization and polar discontinuity

氧化物材料与层状结构的集成通常导致层和/或界面的有趣的、意想不到的电和磁性质。通常，观察到的现象是外在的，例如，由互扩散、缺陷和杂质引起。在这项提议中，我们计划研究两种类型的内在机制-及其可能的相互作用-最近作为控制薄膜和界面的电子和磁性的通用手段而成为关注的焦点。第一种是“电子重构”，即当具有不同极性的材料组合成层状结构时，电荷重新分配到界面，以补偿由于极性不连续而产生的静电势。第二种是伴随着结构重排的电极化，它可以被触发来补偿作为电子重构的替代或与电子重构竞争的内置电势，或者在铁电薄膜材料中自发形成。对于将要研究的材料选择，这些机制被认为是导致依赖于厚度的磁跃迁、自旋极化的界面电子系统以及使宿主异质结构具有光伏活性的特殊的电子层和界面性质。每种情况下起作用的微观机制都应通过先进的电子光谱学和显微方法相结合的方法加以阐明。

The integration of oxide materials with layered architectures often leads to intriguing, unexpected electronic and magnetic properties of layers and/or interfaces. Often the observed phenomena are of extrinsic nature and, e.g., caused by interdiffusion, defects, and impurities. Within this proposal we plan to investigate two type of intrinsic mechanisms – and their possible interplay –, which recently came into focus as generic means to control the electronic and magnetic properties of thin films and interfaces. The first is ‘electronic reconstruction’, i.e., the redistribution of charge to the interface in order to compensate the electrostatic potential due to the polar discontinuity when materials with different polar nature are combined in a layered architecture. The second is – concomitant with a structural rearrangement – electric polarization that either can be triggered to compensate a built-in potential as an alternative to or in competition with electronic reconstruction or forms spontaneously in a ferroelectric film material. For the materials selection to be studied these mechanisms are supposed to lead to thickness dependent magnetic transitions, spin-polarized interface electron systems and peculiar electronic layer and interface properties that make the hosting heterostructures photovoltaically active. The microscopic mechanisms at work in each case shall be elucidated by a combined approach of advanced electron spectroscopy and microscopy methods.