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其电子、光学、磁性和催化性能，因此精确调整能带结构对于广泛的应用具有重要意义。这需要对能带结构与原子构成的关系有全面的了解。定制薄膜带结构的两种可能方法是人工异质结构的生长和机械应变的施加。特别是，应变被认为是一个强大的工具，因为在材料的弹性范围内，它具有可逆的电子能带结构原位工程的潜力，从而具有材料的功能特性。通过在超薄膜单轴拉伸测试中进行角分辨光发射光谱，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硫族化合物的能带结构的影响。结合微观结构的表征和薄膜的应力状态，这将能够系统地量化应变和破坏晶体对称性对能带结构的影响，并为使用应变作为裁剪能带结构的原位工具铺平道路。此外，我们计划研究超导体和拓扑绝缘体之间的邻近效应。通过角分辨光谱学，我们将建立拓扑表面态和体带的邻近诱导超导性，并将其作为拓扑绝缘体膜厚度和温度的函数，揭示邻近诱导超导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.