Lattice effects in quasi-2D Kondo systems

拟议的项目将集中在电子结构的三元重费米子化合物，包括大Z元素，特别是Bi和Sb。该项目是一个直接延续的工作，在第一阶段的研究单位，我们已经调查了电子结构的二元表面合金的基础上铈角分辨光电子能谱（ARPES）。正如几种金属间化合物合金所证明的那样，大Z元素引起强烈的自旋-轨道相互作用，从而引起电子表面态带的巨大Rashba分裂。我们将详细研究导带态的拉什巴分裂如何影响近藤晶格系统的性质。提升简并直接影响Ce“杂质”的4f态与导带之间的相互作用。据推测，这些表面合金的特殊情况导致增强的近藤效应，并在某些情况下，在费米能级的特征杂化带隙，例如在近藤绝缘体系统Ce 3Bi 4Pt 3或CeRhSb。最近有人提出，后者的材料代表弱拓扑绝缘体，其中强自旋轨道分裂与奇宇称波函数一起产生满足拓扑绝缘体（TI）标准的情况。在我们小组中建立的良好有序的4f表面合金的制备，将允许我们通过高分辨率光电子能谱（ARPES）和其他表面敏感技术（例如扫描隧道显微镜）来研究这一新的方面。此外，还原到表面系统具有各种关键的实验优势，例如通过避免光电发射终态效应和通过体和表面性质的解纠缠。然而，基于Ce的近藤绝缘体最有可能仅是弱拓扑的，即状态对于无序是相当不稳定的。因此，我们将在混合价态下，对其他材料的单晶体样品进行等效的高分辨率ARPES实验，以再次详细研究表面电子结构。该建议的表面合金与大块晶体4f和5 f材料的比较，这-与表面合金相反-可以通过体积敏感的方法来表征，以及，将是决定性的，以获得一个全面的图片的复杂的相互作用的结构，维数，和电子相关性的表面和薄膜系统。光电发射数据的分析和解释需要对电子能带结构和温度依赖的多体效应进行理论计算，因为这些计算可以在研究股的框架内进行。这种合作是必不可少的，以详细了解特定的单粒子性质（例如自旋轨道分裂，拓扑能带结构），在存在强大的多体效应导致近藤屏蔽和费米能级附近的重准粒子。

The proposed project shall focus on the electronic structure of ternary heavy-fermion compounds including large-Z elements, as in particular Bi and Sb. This project is a direct continuation of the work in the first period of the Research Unit in which we have investigated the electronic structure of binary surface alloys based on Ce by angle resolved photoemission spectroscopy (ARPES). As demonstrated for several intermetallic alloys, large-Z elements induce a strong spin-orbit interaction and therewith a huge Rashba splitting of the electronic surface state bands. It shall be investigated in detail how this Rashba splitting of the conduction band states influences the properties of the Kondo lattice system. The lifted degeneracy affects directly the interaction between the 4f states of the Ce “impurities” and the conduction bands. It is assumed that the peculiar situation in these surface alloys results in an enhanced Kondo effect and — under certain circumstances — in a characteristic hybridization band-gap at the Fermi level, as e.g. in the Kondo insulator systems Ce3Bi4Pt3 or CeRhSb. It was proposed recently that these latter materials represent weak topological insulators, where the strong spin-orbit splitting together with the odd-parity wavefunctions produces a situation where the criteria for a topological insulator (TI) are fulfilled. The preparation of well ordered 4f surface alloys, established in our group, will us allow to investigate this new aspect by high resolution photoemission spectroscopy (ARPES) and other surface sensitive techniques (e.g. scanning tunneling microscopy). Moreover, the reduction to a surface system has various crucial experimental advantages, as for example by avoiding photoemission final-state effects and by the disentanglement of bulk and surface properties. However, the Ce based Kondo insulators are most likely only weakly topological, i.e. the states are rather instable to disorder. Therefore, we shall have a look at equivalent highresolution ARPES experiments on single-crystalline bulk samples of other materials in the mixed-valence regime, to study again in detail the surface electronic structure. A comparison of the surface alloys of this proposal with bulk crystalline 4f and 5f materials, which — in contrast to the surface alloys—can be characterized by bulk sensitive methods as well, will be decisive to obtain a comprehensive picture of the complex interplay of structure, dimensionality, and electronic correlations in surface and thin film systems. The analysis and interpretation of the photoemission data requires theoretical calculations of the electronic band structure and temperature dependent many-body effects, as being accessible within the framework of the Research Unit. This collaboration is essential to give a detailed insight into the specific single-particle properties (e.g. spin-orbit splitting, topological band structure) in presence of strong many body effects leading to Kondo screening and heavy quasiparticles near the Fermi level.