The upper critical field Hc2 anisotropy of Ca10(PtnAs8)(Fe2-xPtxAs2)5 (n = 3, 4) single crystals with long FeAs interlayer distance (d) was studied by angular dependent resistivity measurements. A scaling of the angular dependent resistivity was real
ized for both single crystals using the anisotropic Ginzburg-Landau (AGL) approach with an appropriate anisotropy parameter {gamma}. The AGL scaling parameter {gamma} increases with decreasing temperature and reaches a value of about 10 at 0.8Tc for both single crystals. These values are much larger than those of other iron-based superconductors (FeSCs). Remarkably, the values of {gamma}2 show an almost linear increase with the FeAs/FeSe interlayer distance d for FeSCs. Compared to cuprates, FeSCs are less anisotropic, indicating that two dimensionality of the superconductivity is intrinsically weak.
Superconductivity of Ca1-xLaxFe2As2 single crystals with various doping level were investigated via electromagnetic measurements for out-plane (H//c) and in-plane (H//ab) directions. Obvious double superconducting transitions, which can survive in ma
gnetic fields up to several Tesla, were observed in the medium-doped (x = 0.13) sample. Two kinds of distinct Hc2 phase diagrams were established for the low superconducting phase with Tc lower than 15 K and the high superconducting phase with Tc of over 40 K, respectively. Both the two kinds of phase diagrams exist in the medium-doped sample. Unusual upward curvature near Tc was observed in Hc2 phase diagrams and analyzed in detail. Temperature dependences of anisotropy for different doping concentrations were obtained and compared. Both superconducting phases manifest extremely large anisotropies, which may originate from the interface or intercalation superconductivity.
