Spin-resolved spectro-microscopy of correlated surface and interface systems

在这个项目中，我们将进行自旋平均和自旋分辨的两类低维材料，都表现出电子相关性，即氧化物异质结构和二维近藤晶格的研究。为了实现对氧化物异质结构（例如LaAlO3/SrTiO3（LAO/STO）或LaVO3/SrTiO3（LVO/STO））的掩埋界面的访问，样品将在UHV条件下断裂以暴露其横截面。从而可以原位研究界面的结构和电子性质。将扫描隧道显微镜（STM）的原子分辨能力与自旋平均和自旋分辨扫描隧道光谱（STS）相结合，研究了（自旋相关的）态密度的横向分布。就单层而言，需要回答的关键问题是二维电子气的位置和空间分布。这些性质在多层结构中特别重要，因为多层结构中界面之间的耦合取决于层的周期性。我们将研究缺陷的影响，例如层厚度的缺陷和变化。结果将与光电子发射电子显微镜（P4），XMCD-PEEM（P7）和动态平均场理论（DMFT）计算（P8）进行比较。在本项目的第二部分，我们将研究二维近藤系统，如CePt合金，这也是项目P3，P7和P9的主题。虽然空间平均技术需要均匀的表面，STS的高空间分辨率也允许不同的本地Ce coverages.We的非均匀表面的表征将执行高分辨率的可变温度STS以上和以下的相干温度T * 这标志着单一杂质限制和相干重费米子带之间的过渡。此外，我们将进行光谱成像（SI）测量，通过k空间中的傅立叶变换来潜在地检测准粒子干涉（QPI）图案。虽然STS缺乏内在的k分辨率，但它是对其他光谱技术的补充，因为它在很宽的温度范围内提供高于和低于费米能级的高能量分辨率，并可选择施加高磁场。

In this project we will perform spin-averaged and spin-resolved studies of two classes of low- dimensional materials which both exhibit electron correlations, i.e. oxide heterostructures and two-dimensional Kondo lattices. To achieve access to the buried interfaces of oxide heterostructures, such as LaAlO3/SrTiO3 (LAO/STO) or LaVO3/SrTiO3 (LVO/STO), samples will be fractured under UHV conditions to expose their cross-section. Thereby structural and electronic properties of the interfaces can be studied in situ. Combining the atomic resolution capability of scanning tunneling microscopy (STM) with spin-averaging and spin-resolved scanning tunneling spectroscopy (STS) the lateral distribution of the (spin dependent) density of states will be investigated. As far as single layers are concerned key questions to be answered are the position and spatial distribution of the 2-dimensional electron gas. These properties are of particular relevance in multilayer structures where the coupling between the interfaces depends on the periodicity of the layers.We will study the impact of imperfections, such as defects and variations in layers thickness. The results will be compared with photoemission electron microscopy (P4), XMCD-PEEM (P7), and dynamic mean field theory (DMFT) calculations (P8). In the second part of this project we will investigate two-dimensional Kondo systems, such as CePt alloys which are also the subject of projects P3, P7, and P9. While spatially averaging techniques require homogeneous surfaces, the high spatial resolution of STS also allows for the characterization of inhomogeneous surfaces with different local Ce coverages.We will perform high-resolution variable temperature STS above and below the coherence temperature T* which marks the transition between the single impurity limit and coherent heavy-fermion bands. In addition, we will perform spectroscopic imaging (SI) measurements to potentially detect quasi-particle interference (QPI) patterns through Fourier transformation in k-space. Although STS lacks intrinsic k-resolution, it is complementary to other spectroscopic techniques as it offers high-energy resolution above and below the Fermi level for a wide temperature range with the option of applying high magnetic fields.