Spin and charge dynamics in iron-based superconductors: A complementary neutron scattering and spectroscopic ellipsometry study

为了确定铁硫化物中的元素激发态，我们提出了用非弹性中子散射和椭圆偏振光谱相结合的方法对自旋和电荷激发谱进行综合研究。在我们的工作中，我们将利用内部生长的高质量单晶的独特组合，以及我们团队开发的和我们可以支配的先进实验工具，特别是ANKA的基于同步加速器的宽带光谱椭偏仪和FRM-II的具有自旋回波选项的中子谱仪，以实现μEV范围内的最高分辨率。我们将研究几个对库珀配对机制性质敏感的物理量：光学准粒子自能和散射率，它们是由耦合到配对模式决定的，以及描述磁激发的动态磁化率，作为一种潜在的配对模式。这些详细的信息将使我们能够表征配对模式的性质，特别是确定磁激发在配对机制中的作用。将特别强调研究广泛的温度和掺杂水平以及比较空穴和电子掺杂，因为彻底描述电子和磁性结构和动力学--也处于正常状态--对于完全理解这类新材料是必不可少的。

Aiming to identify the elementary excitations mediating superconductivity in the iron pnictides, we propose a comprehensive study of the spin and charge excitation spectra by the complementary techniques of inelastic neutron scattering and spectroscopic ellipsometry. In our work we will take advantage of the unique combination of high-quality single crystals grown in-house and the advanced experimental tools developed in our group and at our disposal, in particular a synchrotron-based wide-band spectroscopic ellipsometer at ANKA and a neutron spectrometer at FRM-II with a spin-echo option for highest resolution in the μeV range. We will study several physical quantities sensitive to the nature of the Cooper pairing mechanism: The optical quasi-particle self energy and scattering rate which are determined by coupling to the pairing mode, as well as dynamical magnetic susceptibility describing the magnetic excitations, as a prospective pairing mode. This detailed information will allow us to characterize the properties of the pairing mode, and in particular to determine the role of magnetic excitations in the pairing mechanism. A particular emphasis will be put on studying a wide range of temperatures and doping levels and on comparing hole and electron doping, since a thorough characterization of the electronic and magnetic structure and dynamics – also in the normal state – is indispensable for a complete understanding of this new class of materials.