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

铁基超导磷属元素化合物甚至比铜酸盐的情况更多地包含了种类繁多的材料。本文利用氧化物分子束外延（MBE）生长的单晶外延薄膜研究了不同磷属元素化物材料之间的相互作用及其结构、磁性和超导性能。氧化物分子束外延是一种多功能的晶体合成工具，用于低温生长（亚稳态）磷属元素，从而允许广泛的掺杂和取代研究。(Note这里MBE并不仅仅用作已知化合物的薄膜应用的生长方法）。因此，我们将获得各种超导相图作为化学掺杂（对应于空穴和电子掺杂）的函数，以及衬底或替代引起的结构畸变。这项工作将有助于识别新的超导材料系统，并允许系统地了解物理性能对材料成分的依赖性。在Fe-磷属元素化物系统中，我们可以总结出通过氧化物MBE掺杂/取代的预期选择如下：La（K，Na，Sr，Ca，镧系元素）O（N）Fe（Ni，d-过渡金属）Bi（Sb）。由于砷基磷化合物的毒性和世界范围内已有的研究结果，我们目前没有针对砷基磷化合物。

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.