Application-oriented syntheses of FeSe-based superconductor films and studies of their critical parameters

该合作项目的目标是通过将不同的晶体结构、沉积方法和表征工具结合在一个项目中，加深对超导态的潜在物理机制以及铁基超导体(FBS)优良钉扎性能的了解。这是重要的一步，因为只有通过密集和定期的科学讨论，而不是仅仅从出版物中收集数据，才能增加对材料、模型和技术之间细微差异的理解。从长远来看，我们的目标是确定铁基超导体可能的目标应用。在这个项目中，我们将重点放在FBS的硫系分支，即FeSe基超导体上。我们从两个方面来解决这个问题，(Te掺杂)FeSe具有最短的c轴长度和最简单的晶体结构，以及(Mn掺杂)(Li，Fe)OHFeSe，一种由(Li，Fe)OH中间层沿c方向伸长的FeSe结构。在初步保证了用常用掺杂剂可重复性沉积高质量样品后，将分别制备和研究其他掺杂以及新的掺杂剂(如Co、Ni、Cu、Zn、S)。目标如下：1.在IoP-Cas2上用不同的单晶生长方法合成较大尺寸的K2Fe4Se5和Fe(Se、Te、S)单晶。在IoP-Cas3上用基质辅助水热外延(MHE)法合成了一系列高质量的(Li，Fe)OHFeSe薄膜。在ITEP-KIT4上用脉冲激光沉积法(PLD)合成了高质量的Fe(Se，Te)薄膜。确定这些薄膜和单晶的物理性质5。通过提供：(1)不同类型的外延、超导Fe(Se，Te)和(Li，(2)IoP-CAS和ITEP-KIT制备的一套薄膜的基本参数和面向应用的参数数据库(3)深入了解所研究材料和FBS中超导和涡旋物质背后的物理机制。本项目的结果对基础研究和潜在的技术应用具有影响。首先，结果将是这个项目的样本或分别生产它们的食谱。我们将在同行评议的期刊上发表我们的研究成果，并在国际会议上展示它们。另一方面，该项目可以加强中国和德国顶尖研究机构在空腹血糖研究方面的科学合作，培养年轻科学家，并在小组之间交流思想、工作方法和途径。

The goal of the proposed collaborative project is to deepen the knowledge about the underly-ing physical mechanisms for the superconducting state as well as the excellent pinning properties of Fe-based superconductors (FBS) by combining different crystal structures, deposition methods and characterization tools within one project. This is an important step because only through intensive and regular scientific discussions instead of mere collecting data from publications can the understanding in the subtle differences in materials, models and techniques increase. On a long run, we are aiming on identifying possible target applications of Fe-based superconductors. In this project, we are focussing on the chalcogenide branch of FBS, namely the FeSe-based superconductors. We tackle this issue from two sides, (Te-doped) FeSe with the shortest c-axis length and simplest crystal structure and (Mn-doped) (Li,Fe)OHFeSe, an FeSe structure elongated in c-direction by (Li,Fe)OH interlayers. After initial assurance of reproducible deposition of high-quality samples with the common dopants, the respective other dopants as well as new ones (e.g. Co, Ni, Cu, Zn, S) will be prepared and investigated.The objectives are the following:1. Synthesizing sizable K2Fe4Se5 and Fe(Se,Te, S) single crystals by various single crystal growth methods at IoP-CAS2. Synthesizing a series of high-quality (Li,Fe)OHFeSe films by matrix-assisted hydro-thermal epitaxy (MHE) at IoP-CAS3. Synthesizing high-quality Fe(Se,Te) films by pulsed laser deposition (PLD) at ITEP-KIT4. Determining the physical properties of these films and single crystals5. Determining critical parameters & mechanismsThe proposed work will have a significant and timely impact that will advance physical understanding and material research of the iron-based superconductors by providing: (1) Different types of epitaxial, superconducting Fe(Se,Te) and (Li,Fe)OHFeSe films and crystals of high structural quality which will be available also for follow-up projects(2) A data base of fundamental and application-oriented parameters for the set of films prepared at IoP-CAS and ITEP-KIT(3) A deep understanding of the physical mechanisms behind superconductivity and vortex matter in the materials investigated and of FBS in general.The results of this project have both impact on basic research and implications for potential technical applications. Firstly, the outcome will be the samples of this project or respectively the recipes to produce them. We will publish our findings in peer-reviewed journals and present them at international conferences.On the other hand, this project can strengthen the scientific collaboration between the leading institutes in China and Germany on FBS research, train young scientists and exchange ideas, working methods and approaches between the groups.