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

• Applicant: Dr. Jens Hänisch
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448625416

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.

• DFG Programme: Research Grants
• International Connection: China
• Partner Organisation: National Natural Science Foundation of China
• Cooperation Partner: Professor Xiaoli Dong, Ph.D.