Strongly correlated electron systems studied by strain-dependent angle-resolved photoemission spectroscopy

所有现代技术的基础都是量子理论的力量，它可以高精度地预测机械、光学和电学性质。带理论很好地描述了铜或硅等普通金属和半导体。相比之下，理解导致强相关电子材料（如高温超导性）显著特性的相互作用仍然具有很大的挑战性。在强相关电子系统中，自旋、轨道和晶格自由度的耦合导致了复杂的相图，这些相图的阶数相互交织或竞争。理解这样的相图对于制定有效的量子理论是必不可少的。角分辨光谱学（ARPES）通过直接获取电子能带结构，为我们理解相关材料做出了重要贡献。然而，ARPES与常见的非热调谐参数（如磁场、电场或压力）不兼容。由于这些调谐参数建立相图，从ARPES的微观信息经常丢失。我的目标是将各向异性应变作为定量的非热调谐参数与ARPES相结合，并将电子结构信息添加到量子材料的相图中。我已经为APRES开发了一个应变装置的原型，并进行了第一次成功的测试。我的提议旨在利用这项新技术来研究铁基超导体和钌酸锶。它们的热力学和输运性质可以通过各向异性应变来调节，这使它们成为主要的候选者。由应变相关ARPES得到的铁基超导体的向列磁化率将有助于确定向列相的驱动序参数，其与超导性的相互作用以及可能的量子临界行为。钌酸锶是在奇宇称超导性方面讨论的少数材料之一，我将能够阐明其超导序参数。这些研究将大大提高我们对这两种材料相图的认识。他们还将反馈现有应变装置的改进，并将其建立为强相关材料中ARPES的表征良好的调谐装置。

The foundation of all modern technology is the power of quantum theories to predict mechanical, optical and electrical properties with high precision. Common metals and semiconductors like copper or silicon are well described by band theories. In contrast, understanding the interactions that lead to the remarkable properties of strongly correlated electron materials such as high-temperature superconductivity remains deeply challenging. The coupling of spin, orbital and lattice degrees of freedom in strongly correlated electron systems leads to complex phase diagrams with intertwined or competing orders. Understanding such phase diagrams is essential for formulating effective quantum theories.Angle-resolved photoemission spectroscopy (ARPES) has contributed profoundly to our understanding of correlated materials by accessing the electronic band structure directly. However, ARPES is incompatible with common non-thermal tuning parameters like magnetic fields, electric fields, or pressure. Since these tuning parameters build-up phase diagrams, the microscopic information from ARPES is often missing.My goal is to combine anisotropic strain as a quantitative, non-thermal tuning parameter with ARPES and add electronic structure information to the phase diagram of quantum materials. I have developed a prototype of a strain apparatus for APRES and performed first successful tests. My proposal aims at employing this new technique to study iron-based superconductors and strontium ruthenate. Their thermodynamic and transport properties can be tuned by anisotropic strain, which makes them prime candidates. The nematic susceptibility in iron-based superconductors derived from strain-dependent ARPES will substantially contribute to identify the driving order parameter of the nematic phase, its interplay with superconductivity and possible quantum critical behavior. Strontium ruthenate is one of the few materials discussed in terms of odd-parity superconductivity and I will be able to shed light on its superconducting order parameter. These studies will considerably improve our understanding of the phase diagrams of these two materials. They will also feedback to the improvement of the current strain apparatus and establish it as a well characterized tuning device for ARPES in strongly correlated materials.