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

2008年发现的铁基超导体在高达55K的温度下表现出超导性，目前正在全世界范围内进行深入的研究。它们的温度掺杂相图丰富，除了超导相外，还有磁性相和向列相。众所周知，由电子自由度引起的磁性和超导电性对晶格的各种形变很敏感。这种电子-晶格耦合是一个额外的复杂性，最重要的是由于电子-电子相互作用，这使得对这些系统的微观理解是一个巨大的挑战。该提议的目的是执行非常明确的理论项目，以便量化这些材料中不同类型的电子-晶格耦合，并更好地了解这些耦合在建立磁性和超导秩序方面的作用。这项研究的一个长期好处是，一旦人们很好地理解了电子-晶格耦合，原则上可以通过材料工程来调整电子-晶格耦合，以提高超导转变温度Tc。该提议的科学目标如下。(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取得了一些有趣的实验突破，但理论上这一领域目前还不够发达。一个目的是促进我们对这种泵浦探测结果的理论理解，并提取微观信息，如与电子-晶格耦合有关的信息，以及与奇异磁性C4相有关的信息。这将通过基于对称性的Landau-Ginzburg方法和更微观的方法的混合来实现，在这种方法中，使用动力学Bloch方程来捕捉短时间动力学。(Ii)第二个目标是研究非传统电子-晶格耦合如何影响这些系统的磁性和向列相性质，以及从理论上理解这种耦合是如何影响超导的。在这一研究领域中，对泵浦-探测数据进行建模的理论工作很少。同样，尽管已经有大量的实验证据表明，异常的电子-晶格耦合对FESC的磁相、向列相和超导相的影响在理论上仍未得到很大的探索。该项目分为三个任务和六个子任务。两名协调员每人负责三个子任务，这些任务将由该项目资助的两名博士生参与执行，法国和德国各一名。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赞扬，以满足要求。此外，他们已经证明了联合研究的记录。这确保了它们之间良好的协同效应。

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.