Novel and metastable arsenic free Fe based pnictide superconductors synthesized by reactive molecular beam epitaxy

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Even more than in the case of cuprates, the Fe-based superconducting pnictides encompassa huge variety of materials. Here we intend to investigate the interplay between thedifferent pnictide materials and their structural, magnetic and superconducting propertiesby using single-crystalline epitaxial thin films grown by oxide molecular beam epitaxy(MBE). Oxide MBE is used as a versatile crystal synthesis tool for low-temperature growthof (metastable) pnictides and, thereby, allows extensive doping and substitution studies.(Note that here MBE is not used as a mere growth method for thin film applicationsof known compounds). As a result, we will obtain a variety of superconductivity phasediagrams as a function of chemical doping (corresponding to hole and electron doping),and substrate or substitution induced structural distortions. This work will contribute toidentify new superconducting material systems, and allow to understand systematicallythe dependence of physical properties on material compositions. One can summarizeour intended choice of doping/substitutions by oxide MBE in the Fe-pnictide systems asfollows: La(K, Na, Sr, Ca, lanthanoides)O(N)Fe(Ni, d-transition metals)Bi(Sb). We arecurrently not aiming at the As-based pnictides due to their toxicity and the amount of theworld-wide already existing results.