Tailoring the band structure of thin films by strain and by the growth of artificial heterostructures

材料的电子能带结构决定了它的电子、光学、磁性和催化性质，因此，精确地调整能带结构对于广泛的应用是至关重要的。这需要全面了解能带结构与原子结构的相关性。调整薄膜能带结构的两种可能方法是人工异质结构的生长和施加机械应变。特别是，应变被认为是一种强有力的工具，因为在材料的弹性区域内，它具有可逆的原位电子能带结构工程的潜力，从而具有材料的功能性质。通过在超薄膜单轴拉伸测试中进行角度分辨光电子能谱，我们想要建立应变对拓扑绝缘体、拓扑晶体绝缘体和过渡金属二卤化物的能带结构的影响。结合薄膜微结构和应力状态的表征，这将使应变和破坏晶体对称性对能带结构的影响得到系统的量化，并为利用应变作为原位工具来定制能带结构铺平道路。此外，我们还计划研究超导体和拓扑绝缘体之间的邻近效应。通过角度分辨光电子能谱，我们将建立拓扑表面态和体带的邻近感生超导电性与拓扑绝缘层厚度以及温度的函数关系，从而揭示了邻近感生超导电性的机制和决定因素。

The electronic band structure of a material determines its electronic, optical, magnetic and catalytic properties and thus a precise adjustment of the band structure is of fundamental importance for a wide range of applications. This requires a comprehensive understanding of the correlation of the band structure with the atomic constitution. Two possible ways to tailor the band structure of thin films are the growth of artificial heterostructures and the imposing of a mechanical strain. In particular, strain is considered as a powerful tool, since, within the elastic regime of the material, it bears the potential for a reversible in-situ engineering of the electronic band structure and thus the functional properties of the material.By performing angle-resolved photoemission spectroscopy during uniaxial tensile testing of ultrathin films, we want to establish the effect of strain on the band structure of topological insulators, topological crystalline insulators and transition metal dichalcogenides. In combination with a detained characterization of the microstructure and the stress state of the thin films, this will enable a systematic quantification of the effect of strain and of breaking the crystal symmetry on the band structure and pave the way to use strain as an in-situ tool for tailoring the band structure. Furthermore, we plan to investigate the proximity effect between a superconductor and a topological insulator. By performing angle-resolved photoemission spectroscopy, we will establish the proximity-induced superconductivity in the topological surface state and the bulk bands as functions of the topological insulator film thickness as well as the temperature, shedding light on the mechanism and the decisive factors for the proximity-induced superconductivity.