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We investigated the upper critical fields of Ca10(Pt4As8)(Fe1.8Pt0.2As2)5 superconducting whiskers. The whiskers consist of several wire-like grains with diameter of around 200 nm, joined by grain boundaries whose misorientation angles are less than 5°. The upper critical fields along c-axis and in ab-plane were observed as 49 T at 12K and 50 T at 22K, respectively, which can be extrapolated to 81 and ~133 T at 0 K. The whisker demonstrated weak anisotropic factor and almost constant value of ~2 below 15 K. The impressive transport properties of the whisker may find applications in fields like superconducting micro- and meso-structure systems. [ABSTRACT FROM AUTHOR]

We studied the grain boundaries within mechanically formed polycrystalline BaKFe2As2 micro-bridges. By tunneling current across grain boundaries, current–voltage characteristics (IVCs) demonstrated the typical Josephson weak links behavior in micro-bridges. Shapiro steps were observed for the junctions under the microwave radiation at 10 GHz. The temperature dependence of the critical current Ic was observed as a shoulder, corresponding to a multi-gap symmetry but not a single-gap s-wave or d-wave. [ABSTRACT FROM AUTHOR]