High T$_{c}$ electron doped Ca$_{10}$(Pt$_{3}$As$_{8})$(Fe$_{2}$As$_{2})_{5}$ and Ca$_{10}$(Pt$_{4}$As$_{8})$(Fe$_{2}$As$_{2})_{5 }$superconductors

In this talk, we will present the crystal structures and physical properties of two new iron arsenide superconductors, Ca$_{10}$(Pt$_{3}$As$_{8})$(Fe$_{2}$As$_{2})_{5}$ (the ``10-3-8 phase") which crystallizes in the triclinic structure and Ca$_{10}$(Pt$_{4}$As$_{8})$(Fe$_{2}$As$_{2})_{5}$ (the ``10-4-8 phase") which crystallizes in the tetragonal structure. They are very similar compounds for which the most important differences lie in the structural and electronic characteristics of the intermediary platinum arsenide layers. Electron doping through partial substitution of Pt for Fe in the FeAs layers leads to $T_{c}$ of 11 K in the 10-3-8 phase and 26 K in the 10-4-8 phase. The anisotropic H$_{c2}$ measurement indicates the multiband superconductivity in these compounds. The often-cited empirical rule in the arsenide superconductor literature relating $T_{c }$to As-Fe-As bond angles does not explain the observed differences in $T_{c}$ of the two phases; rather, comparison suggests the presence of stronger FeAs interlayer coupling in the 10-4-8 phase due to the two-channel interlayer interactions and the metallic nature of its intermediary Pt$_{4}$As$_{8}$ layer. The interlayer coupling is thus revealed as important in enhancing $T_{c}$ in the iron pnictide superconductors.