New sample architectures with Fe-based superconductors based on layer transfer of epitaxial films

• Applicant: Dr. Ruben Hühne
• Subject Area: Synthesis and Properties of Functional Materials ; Experimental Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 533424795

Fe based superconductors show a rich variety of electronic phases, which can be tuned by doping, pressure or strain. Typically, single crystals are used for detailed studies due to the detrimental effect of the grain boundaries in these materials. Within the last years, high-quality epitaxial thin films were grown in particular for FeSe and BaFe2As2 based materials showing a comparable quality as single crystalline materials. However, the clamping of these superconducting layers on the rigid substrates limits the application of such films for more advanced studies. Therefore, the major aim of this project is to open new pathways for the study of Fe-based superconductors by the realization of thin freestanding layers, which can be transferred to other templates. The central tool for this approach is the application of sacrificial layers, which are mainly used so far for perovskite-based oxide architectures. The main challenge is to optimize these sacrificial layer architectures for the growth, release and transfer of oxygen-free Fe based superconductor films. A key aspect will be the reduction of strain to avoid a high number of cracks during the removal of the sacrificial layer as well as the realization of clean interfaces. Besides the growth of these materials on sacrificial layer architectures, the layer transfer of the grown epitaxial films needs to be studied in detail, which includes the development of suitable etching procedures to avoid any deterioration of the superconducting properties itself as well as of an appropriate transfer strategy to achieve smooth and crack-free films on the new template. Within the project, different applications of the released Fe-based superconducting layers are targeted. At first, layers will be transferred to flexible polymer template to study the influence of strain on the superconducting transition by stretching or bending such templates. Secondly, films will be transferred to thin membranes, which allow to study these materials using a dedicated low-temperature stage inside a transmission electron microscope. Finally, such layers will be used to realize new layer architecture as for example by twisting the layers against each other or by combining the superconductor with other functional materials as magnets or ferroelectrics to create multifunctional heterostructures. In all cases, a proof-of-principle study is mainly targeted in collaboration with experienced partners for the selected applications. We expect that the proposed project creates new opportunities for basic studies on Fe-based superconductors, which might help to understand the mechanism of superconductivity in these materials better. At the same time, the developed approaches will enable the realization of new device architectures for potential applications of Fe-based superconductors in functional heterostructures.

• DFG Programme: Research Grants