Iron arsenides with three-dimensional FeAs layer networks: Can(n+1)/2(Fe1-xPtx)(2+3n)Ptn(n-1)/2 As(n+1)(n+2)/2 (n=2, 3)

We report the comprehensive studies between synchrotron X-ray diffraction, electrical resistivity and magnetic susceptibility experiments for the iron arsenides Can(n+ 1)/2(Fe1-xPtx)((2+ 3n)) Ptn(n-1)/2As(n+ 1)(n+ 2)/2 for n = 2 and 3. Both structures crystallize in the monoclinic space group P2(1)/m (# 11) with threedimensional FeAs structures. The horizontal FeAs layers are bridged by inclined FeAs planes through edge-sharing FeAs5 square pyramids, resulting in triangular tunneling structures rather than the simple layered structures found in conventional iron arsenides. n = 3 system shows a sign of superconductivity with a small volume fraction. Our first-principles calculations of these systems clearly indicate that the Fermi surfaces originate from strong Fe-3d characters and the three-dimensional nature of the electric structures for both systems, thus offering the playgrounds to study the effects of dimensionality on high T-c superconductivity.