Short-Time Dynamics and Electron-Lattice Interaction in Iron Based Superconductors

铁基超导体于2008年被发现，在高达55 K的温度下表现出超导性，目前正在全球范围内进行深入研究。它们的温度-掺杂相图丰富，除了超导相外，还有磁性相和非磁性相。现在众所周知，由电子自由度引起的磁性和超导性对晶格的各种变形很敏感。这种电子-晶格耦合是一个额外的复杂性，在此之上，由于电子-电子相互作用，这使得微观理解这些系统是一个艰巨的挑战。IRONIC提案的目的是执行非常明确的理论项目，以量化这些材料中不同类型的电子-晶格耦合，并更好地理解这些耦合在建立磁性和超导秩序中的作用。这种研究的一个长期好处是，一旦很好地理解了电子-晶格耦合，原则上可以通过材料工程来调整，以提高超导转变温度Tc。(i)我们注意到，虽然在使用泵浦探测技术研究这些系统方面已经有了一些有趣的实验突破，但理论上这一领域目前还没有得到很好的发展。一个目标将是推进我们的理论理解，这样的泵探测结果，并提取微观信息，如那些相关的电子晶格耦合，和那些相关的外来磁C4相。这将通过一个混合的基于朗道-金兹伯格的方法，以及一个更微观的短时间动力学捕获使用动态布洛赫方程。(ii)第二个目标是研究非常规的电子-晶格耦合如何影响这些系统的磁性和磁性，以及从理论上理解这种耦合如何影响超导性。在这一研究领域，对泵浦探测数据进行建模的理论工作很少。类似地，尽管有大量的实验证据证明了这种相互作用，但不寻常的电子-晶格耦合对FeSC的磁相、超导相和超导相的影响在理论上仍然没有得到很大程度的探索。两名协调员分别负责三项子任务，这些任务将在项目资助的两名博士生（法国和德国各一名）的参与下执行。该项目需要几种类型的专业知识，两个合作伙伴的技能得到了很好的补充，以满足要求。此外，他们有共同研究的记录。这确保了它们之间的良好协同作用。

Discovered in 2008, iron-based superconductors show superconductivity at temperatures as high as 55 K, and are currently being studied intensely worldwide. Their temperature-doping phase diagram is rich, having magnetic and nematic phases in addition to the superconducting one. It is now well-known that the magnetism and the superconductivity, arising from the electronic degrees of freedom, are sensitive to various deformations of the crystalline lattice. This electron-lattice coupling is an additional complexity, on top of that due to the electron-electron interaction, which makes a microscopic comprehension of these systems a formidable challenge. The aim of the proposal IRONIC is to perform very well-defined theoretical projects in order to quantify the different types of electron-lattice couplings in these materials, and to understand better the role of these couplings in establishing magnetic and superconducting order. A long-term benefit of research such as that proposed here is that, once well-understood, the electron-lattice coupling can, in principle, be tuned by material engineering to raise the superconducting transition temperature Tc.The scientific goals of the proposal are the following. (i) We note that, while there have been severalinteresting experimental breakthroughs in the use of pump-probe technique to study these systems, theoretically this area is currently not as well-developed. One aim will be to advance our theoretical understanding of such pump probe results, and to extract microscopic information such as those related to electron-lattice coupling, and those related to the exotic magnetic C4 phase. This will be achieved through a mix of symmetry-based Landau-Ginzburg approach as well as a more microscopic one where short timedynamics is captured using dynamical Bloch equations. (ii) The second goal is to study how unconventional electron-lattice coupling affects magnetic and nematic properties of these systems, as well as to theoretically understand how such couplings affect superconductivity.The originality of the proposal is its subject matter. There has been very little theoretical work in modeling pump-probe data in this field of research. Similarly, the effect of unusual electron-lattice coupling on the magnetic, nematic and superconducting phases of the FeSC remains largely unexplored theoretically, even though there are ample experimental evidences of such interactions.The project is divided into three tasks and six sub-tasks. Each of the two coordinators is in charge of three sub-tasks, and the tasks will be executed with the participation of two PhD students financed by the project, one each from the French and the German sides. The project requires several types of expertise, and the skills of the two partners are well complimented to meet the requirements. Furthermore, they have proven record of joint research. This ensures good synergy between them.