C-axis transport of pnictide superconductors

各向异性是所有高温超导体的一个关键问题。机理和应用的基本问题都敏感地依赖于各向异性输运参数。我们计划用直流测量来研究磷灰石单晶的输运各向异性，并用二维霍尔探针研究磁化强度的各向异性。当相干长度各向异性接近FeAs面间约瑟夫森耦合的极限时，可以预期有较高的c轴临界电流密度。这定义了一种新的本征约瑟夫森效应。本征直流和交流约瑟夫森效应以及宏观量子隧道效应将被研究。我们发现了一种相当壮观的效果。通过c轴方向的电流注入，我们可以相当有效地改变掺杂水平。我们将对超导层和绝缘层的改进进行表征。一个吸引人的目标是通过掺杂而不发生显著的晶格膨胀来提高临界温度。

Anisotropy is a critical issue for all high-Tc superconductors. Both fundamental questions of the mechanism and applications depend sensitively on anisotropic transport parameters. We plan to investigate the transport anisotropy of pnictide single crystals by dc measurements and the anisotropy of magnetization using 2DEG Hall-probes. As the coherence length anisotropy is near the limit of Josephson coupling between the FeAs planes, rather high c-axis critical current densities can be expected. This defines a new regime of intrinsic Josephson effects. Intrinsic dc and ac Josephson effects as well as macroscopic quantum tunnelling will be studied. We have discovered a rather spectacular effect. By current injection in c-axis direction, we can change the doping level rather effectively. We will characterize the modifications of the superconducting and insulating layers. One attractive goal would be increasing the critical temperatures by doping without significant lattice expansion.