Quasi-particle interference in surface- and bulk-doped topological insulators and Weyl semimetals

拓扑绝缘体的特征是无质量的狄拉克费米子，这些费米子受到拓扑保护，并由于自旋-轨道耦合而显示出螺旋自旋结构。这些独特的电子性质使它们成为未来自旋电子学应用的有前途的候选者。然而，对自旋分辨能带结构、散射事件和特定输运性质之间的关联仍然需要详细的了解。在本项目中，我们将继续研究磁性掺杂的拓扑绝缘体。通过自旋极化扫描隧道显微镜(STM)和光谱分析(STS)，我们将研究拓扑态在表面掺杂之间建立长程磁有序的机制。此外，我们还将对体相掺杂晶体进行XMCD和随温度变化的扫描探针实验，以更好地了解呈现量子反常霍尔效应的磁有序TiS的电子结构。我们将继续进行有机-TI混合界面的研究。我们在第一个资助期发现了这条新颖的路线，它有望通过自组装分子层对TI表面进行磁性掺杂，甚至可能实现门控。我们将继续我们的准粒子干涉(QPI)和STS实验来研究分子覆盖层的存在在多大程度上改变了TI表面态的电子性质。磁有序分子超结构是自旋电子学应用的里程碑之一，它的潜力将通过XMCD和自旋分辨STM实验进行仔细研究。我们将与Dresden(Yan，Felser)和Halle(Parkin)MPI的合作者合作，研究Weyl半金属的(自旋分辨)电子性质，这些Weyl半金属展示了动量空间中带有量子化Berry通量的拓扑单极子的Weyl点对。我们不仅将研究这些表面在真实空间中的散射态，还将研究当Weyl半金属表面被磁性掺杂时，局域隧道谱和QPI图案是如何变化的。

Topological insulators are characterized by massless Dirac fermions which are topologically protected and exhibit a helical spin structure due to spin-orbit coupling. These unique electronic properties make them promising candidates for future spintronics applications. However, a detailed understanding of the correlation between the spin-resolved band structure, scattering events, and specific transport properties is still due. In this project we will continue our investigations of magnetically doped topological insulators. By spin-polarized scanning tunneling microscopy (STM) and spectroscopy (STS) we will study the mechanisms that establish long-range magnetic order between surface dopants mediated by topological states. Furthermore, we will perform XMCD and temperature-dependent scanning probe experiments on bulk-doped crystals to better understand the electronic structure of magnetically ordered TIs exhibiting the quantum anomalous Hall effect. We will pursue our investigations of hybrid organic-TI interfaces. This novel route, which we dis- covered during the first funding period, holds the promise of magnetically doping and potentially even gating TI surfaces by means of self-assembled molecular layers. We will continue our quasiparticle interference (QPI) and STS experiments to study to what extent the presence of a molecular overlayer modifies the electronic properties of the TI surface state. The potential for magnetically ordered molecular superstructures, one of the milestones towards spintronics applications, will be scrutinized by XMCD and spin-resolved STM experiments. In cooperation with collaborators from MPIs at Dresden (Yan, Felser) and Halle (Parkin) we will study the (spin-resolved) electronic properties of Weyl semimetals which exhibit pairs of Weyl points which carry topological monopoles of quantized Berry flux in momentum space. We will not only study the scattering states of theses surfaces in real space, but also investigate how local tunneling spectra and the QPI pattern change once Weyl semimetal surfaces are magnetically doped.