Electronic structure and ultrafast dynamics of FeAs-based superconductors by angle- and timeresolved photoemission spectroscopy

本项目致力于测定铁基和硫系铁基高温超导体及其母体化合物的掺杂相关电子结构。这些材料的能带结构，特别是这些多能带系统的费米表面，是理解超导电性的主要因素，因为人们普遍认为，母体化合物的反铁磁顺序和掺杂化合物的超导电性与中心空穴和布里渊区边界的电子口袋之间的嵌套有关。在这些研究中，我们使用了可变光子能量(同步辐射)的高分辨率角度分辨光电子能谱(ARPES)和飞秒时间分辨ARPES的补充技术。这种独特的组合提供了直接访问空穴和电子分别在费米能级以下和之上的电子结构和准粒子散射动力学的途径。我们打算通过测量超导带隙的各向异性来分析超导带隙的对称性，这些带隙不仅平行于层，而且垂直于层。此外，还可以在频率和时间域中获得有关电荷载流子与玻色子激发(声子、自旋涨落)和电子-电子散射耦合的重要补充信息。这对于理解超导态是至关重要的。对于这些研究，预计将与优先方案内的其他实验和理论小组密切合作。我们的工作是基于在其他组中生长的单晶的可用性。

This project is focused on the determination of the doping-dependent electronic structure of iron-pnictide and iron-chalcogenide-based high-Tc superconductors and their parent compounds. The band structure of these materials and in particular the Fermi surface of these multiband systems is a major ingredient for the understanding of superconductivity, since it is generally believed that the antiferromagnetic order of the parent compounds and superconductivity in the doped compounds is related to a nesting between hole-pockets in the centre and electron pockets at the boundary of the Brillouin zone. For these studies we use both high-resolution angle-resolved photoemission spectroscopy (ARPES) with variable photon energies (synchrotron radiation) and the complementary technique of femtosecond time-resolved ARPES. This unique combination provides direct access to the electronic structure and quasiparticle scattering dynamics below and above the Fermi level for holes and electrons, respectively. We intend to analyze the symmetry of the superconducting gap by measuring the anisotropy of the gap not only parallel but also perpendicular to the layers. In addition important complementary information on the coupling of the charge carriers to bosonic excitations (phonons, spin fluctuations) and electron-electron scattering can be derived in the frequency and time domain. This is essential for the understanding of the superconducting state. For these investigations a close collaboration with other experimental and theoretical groups within the priority program is anticipated. Our work is based on the availability of single crystals grown in other groups.