Study on filled-skutterudite arsenide superconductors

由于这些化合物表现出多种强相关的电子行为，如非常规超导性、多极有序性或近藤半导体等，因此对填入的磷锑化合物进行了积极的研究。然而，由于样品的制备相当困难，迄今为止尚未对填充的方角铁矿砷化物进行研究。我们开发了利用同步辐射在高温高压下“原位”观察结晶的实验技术。利用该技术，我们确定了几种硫化物填充的合成条件，并成功地在高温高压下合成了高质量的硫化物填充化合物CeRu_4As_<12>, PrRu_4As_<12>, SmFe_4As_<12>的单相样品。CeRu_4As_<12>表现出半导体行为，活化能较小，为50K。磁性和热性能表明，CeRu_4As_<12>是近藤半导体。详细测量了在高压条件下制备的填充型方钨矿超导体PrRu_4As_<12> (Tc=2.3K)的比热。系统地比较了Pr基填充的方钨矿化合物和la基的参考材料，发现在Pr基填充的方钨矿超导体中，4f能级的晶体电场分裂对超导性能起着至关重要的作用。新化合物SmFe_4As_<12>显示铁磁性。

The filled skutterudite phosphides and antimonides have been actively studied because the compounds show wide variety of strongly correlated electron behaviors such as unconventional superconductivity, multipole ordering or Kondo semiconductor. However, filled skutterudite arsenides were not studied so far because a preparation of samples is quite difficult. We have developed the experimental technique of "in situ" observation for crystallization under high temperatures and high pressures using synchrotron radiation. Using the technique, we determined the synthesis conditions for several filled skutterudite arsenide and we have succeeded in synthesizing high quality single-phase samples of the filled skutterudite compounds CeRu_4As_<12>, PrRu_4As_<12>, SmFe_4As_<12> at high temperatures and high pressures. CeRu_4As_<12> exhibits a semiconducting behavior, with small activation energy of 50K. The magnetic and thermal properties suggest that CeRu_4As_<12> is a Kondo semiconductor. We measured specific heat of filled skutterudite superconductor PrRu_4As_<12> (Tc=2.3K) prepared under high pressure in detail. A systematic comparison among Pr-based filled skutterudite compounds and their La-based references reveals that crystalline electric field split of 4f levels play an essential role for superconducting properties in the Pr based-filled skutterudite superconductor. New compound SmFe_4As_<12> shows ferrimagnetism.