Engineering of Topological Spin States in Epitaxial Alpha-Tin Layers

这个项目是解决一种新型的拓扑绝缘体（TI），迄今为止只在理论上提出。它是由外延生长在半导体InSb衬底上的应变α - sn形成的。这个TI的主要可行性最近已经被我们的小组证明了。外延方法开辟了多种途径来研究狄拉克表面态的性质，包括TI晶体的不同表面取向。特别感兴趣的是狄拉克带的性质随层厚的变化。原位制备还允许用额外的涂层装饰表面，特别是用重原子或磁性原子，这将改变TI界面的自旋轨道相互作用并影响狄拉克态的性质。揭示电子特性的实验方法是基于高分辨率角分辨光发射（ARPES）。这允许跟踪带色散随厚度的变化，范围从间隙的rashba型状态到具有狄拉克交叉的完全拓扑状态。通过掺杂可以精确地控制TI的费米能级，从而可以监测能带情况和费米面，甚至明显高于狄拉克点。自旋拓扑将通过使用自旋分辨ARPES来解决，其中可以揭示随厚度和表面涂层影响的演变。这些研究还得到了密度泛函和多体理论领域的合作伙伴的进一步支持。

This project is addressing a new type of topological insulator (TI) which has thus far only been proposed theoretically. It is formed by strained alpha-Sn grown epitaxially on a semi-conducting InSb substrate. The principal feasibility of this TI has recently been demonstrated by our group. The epitaxial approach opens various pathways to study the properties of the Dirac surface state, including different surface orientations of the TI crystal. Particular interest rests on the evolution of the nature of the Dirac bands as a function of layer thickness. The in situ preparation also allows to decorate the surface with an additional coating layer, specifically with heavy or magnetic atoms, which will alter the spin-orbit interaction at the TI interface and affect the properties of the Dirac state.The experimental approach to unveil the electronic properties is based on high-resolution angle-resolved photoemission (ARPES). This permits to track changes in the band dispersion with thickness, ranging from gapped Rashba-type states to the fully topological regime with a Dirac crossing. The Fermi level of the TI can be controlled precisely by doping, which allows to monitor the band situation and the Fermi surface even significantly above the Dirac point. The spin-topology will be addressed by using spin-resolved ARPES, where the evolution with thickness and under the influence of a surface coating can be unveiled. The studies are furthermore backed by collaboration partners in the field of density functional and many-body theory.