Origin and stability of highly spin polarized surface resonances

铁磁材料在室温下的自旋极化大小是自旋电子学的一个重要性质。然而，对于大多数应用来说，它不是主体，而是材料的表面或界面，这是相关的。通过对Heusler化合物Co2MnSi的研究，我们最近观察到了一个高的自旋极化，这与深入到块体的大多数带中的稳定表面共振有关。在这里，我们想要研究这种高度自旋极化的表面共振的物理起源。本研究包括对不同Heusler及其相关化合物和表面取向的实验和理论研究。特别是，半金属体带结构是否是出现100%自旋极化表面共振的必要条件的问题应该得到回答。考虑到潜在的应用，如果用带有绝缘体或金属的界面取代自由表面，那么表面共振引起的高自旋极化是否保守是至关重要的。研究表面和界面态的主要实验方法是原位自旋分辨光电子能谱(SR-UPS)和较大探测深度的自旋积分高能X射线光电子能谱(HAXPES)。这些结果将与考虑了相对论、表面和高能效应的第一原理能带结构和光电子能计算相比较来解释。将特别强调电子关联以及有限温度效应，使用申请人主要开发的关于表面、温度和高能方面的最新方法。

The magnitude of the spin polarization of ferromagnetic materials at room temperature is a key property for spintronics. However, for most applications it is not the bulk, but the surface or interface of the material, which is relevant. Investigating the Heusler compound Co2MnSi we recently observed a high spin polarization, which is related to a stable surface resonance in the majority band extending deep into the bulk.Here we want to investigate the physical origin of such highly spin polarized surface resonances. This study includes experimental and theoretical investigations of different Heusler and related compounds and surface orientations. In particular, the question whether a half metallic bulk band structure is a necessary precondition for the appearance of a 100% spin-polarized surface resonance should be answered. Considering potential applications it is of major importance whether the high spin polarization due to a surface resonance is conserved, if the free surface is replaced by an interface with an insulator or metal.The main experimental method for the investigation of the surface and interface states will be in-situ spin resolved photoelectron spectroscopy (SR-UPS) and for a larger probing depth spin integrated high energy x-ray photoemission spectroscopy (HAXPES). The results will be interpreted in comparison with first-principles band structure and photoemission calculations which consider all relativistic, surface and high energy effects. Special emphasize will be put on electronic correlations as well as finite temperature effects using state of the art approaches mostly developed by the applicants concerning surface, temperature and high-energy aspects.