High-pressure single crystal growth and characterization of the 1111-type iron-pnictide superconductors and related systems

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The single crystal growth of doped and undoped LnFeAsO (Ln=La, Ce,…) compounds was found to be very challenging, slowing down the scientific progress in this type of compounds. In this project within the priority program, we will use our particular experience with a high-temperature Sn-flux method which we have already developed for the homologue compounds CeTPO (T=Fe, Ru, Os, Co) to grow larger single crystals of the LnFeAsO materials. We will focus on the sustained optimization of the crystal growth parameters, e.g., the stoichiometry of the melt, the temperature profile, the material of the crucible, and others to obtain mm-size single crystals of highest possible quality. The quality of the crystals will be determined with various state of the art X-ray techniques as well as physical characterization including resistivity, specific-heat, and magnetization measurements. The single crystals will be the basis for many other projects within the priority program, e.g., photoelectron spectroscopy, neutron techniques, optical and ultrasonic measurements, thermal expansion, and quantum oscillations using partly long-standing collaborations with colleagues throughout Germany to significantly advance the understanding of this outstanding materials-class.