Electronic structure and many-body effects in interfaces of oxide heterostructures

超越了传统半导体的能力，氧化物界面提供了独特的机会来控制，增强和创造功能，如超导性，磁性，金属-绝缘体转变或拓扑相。突出的例子是在氧化物异质结构LaAlO 3/SrTiO 3（LAO/STO）和LaVO 3/SrTiO 3（LVO/STO）中超过临界膜厚度形成的相关界面电子系统。本项目致力于通过脉冲激光沉积制造这种混合系统，并通过高能光谱和扫描探针方法研究其化学和电子界面结构。要解决的重要问题包括映射的铁磁性和非磁性金属补丁在LAO/STO接口使用的对比度从X射线磁圆二色性在扫描X射线显微镜和现场调查的门控效应。共振技术和横截面扫描隧道光谱将被用来直接探测的界面状态，特别是带填充控制的莫特过渡LVO/STO。另一个重点将是调整的维度，因此，二维电子系统的相关性，使用邻基板的可能性。改变LAO的厚度和STO的错切角，一个维度的交叉已被预测导致在一维链。我们将系统地探索相关的参数空间，采用扫描隧道显微镜和光谱学以及角分辨光电子能谱。本课题将补充减少钛酸盐纳米线，可以稳定在裸露的STO表面的调查。最后一个方面涉及通过设计产生新相，如最近对于具有（111）取向的钙钛矿或钙钛矿型高Z金属氧化物双层所强调的。在存在大自旋轨道耦合的情况下，如果通过施加电场或通过在不同衬底之间堆叠双层来适当地调整能带拓扑，则可以产生拓扑绝缘体。

Transcending the capabilities of their conventional semiconductor counterparts, oxide interfaces provide the unique opportunity to control, enhance, and create functionalities such as superconductivity, magnetism, metal-insulator transitions, or topological phases. Striking examples are the correlated interface electron systems that form in the oxide heterostructures LaAlO3/SrTiO3 (LAO/STO) and LaVO3/SrTiO3 (LVO/STO) beyond a critical film thickness. This project is devoted to the fabrication of such hybrid systems by pulsed laser deposition and the study of their chemical and electronic interface structure by high-energy spectroscopies as well as scanning probe methods. Important questions to be addressed comprise the mapping of ferromagnetic and non-magnetic metallic patches at the LAO/STO interface using the contrast from x-ray magnetic circular dichroism in a scanning x-ray microscope and the in situ investigation of gating effects. Resonant techniques and cross-sectional scanning tunneling spectroscopy will be employed to directly probe the interface states, in particular the band-filling controlled Mott transition in LVO/STO. Another focus will be on the possibility to tune the dimensionality and hence the correlations of the two-dimensional electron system using vicinal substrates. Varying the LAO thickness and the STO miscut angle, a dimensional crossover has been predicted resulting in one-dimensional chains. We will systematically explore the relevant parameter space employing scanning tunneling microscopy and spectroscopy as well as angle-resolved photoelectron spectroscopy. This topic will be complemented by the investigation of reduced titanate nanowires which can be stabilized on bare STO surfaces. A last aspect concerns the creation of novel phases by design as has been highlighted lately for perovskite or perovskite-type high-Z metal oxide bilayers with (111)-orientation. In the presence of a large spin-orbit coupling topological insulators may result if the band topology is adjusted properly by applying an electric field or by sandwiching the bilayer between different substrates.