Effects of Dy substitution for Ce on transport properties of (Pb2Cu)Sr2DyxCen-x-δCu2O2n+6 (n=5,6) epitaxial films

The crystal structure, in-plane resistivity, and thermopower for (Pb2Cu)Sr2DyxCen-x-δCu2O2n+6 (Pb-32n2 phase, n=5 or 6) have been studied as a function of Dy content, x, in the fluorite block to ascertain the limit of hole doping. The samples were grown by sequential deposition using the molecular beam epitaxy technique. For n=5, a single phase sample was obtained in the range of 0.91.6, resistivity and thermopower abruptly increased beyond the value for x=1.0, suggesting the electronic state change without changes in crystallinity. The ab-initio electronic structure calculations suggest that the substitution of Ln3+ for Ce4+ in the fluorite block has two effects detrimental to conducting properties and superconductivity: (a) creation of vacancy or the hole trap at the oxygen site in the fluorite block, and (b) decrease of the distance between Cu and apical oxygen. These effects may explain the experimental results. They are also considered to be the reasons for the absence of superconductivity in the layered cuprates having a multiple fluorite-type block with n≥3