How Tc can go above 100 K in the YBCO family

We report the results of the electronic structure calculation of a newly discovered member of the YBCO high-Tc family, i.e., Y3Ba5Cu8O18 (Y358) with Tc > 100, based on the full-potential linearized augmented plane waves method (FP-LAPW) of density functional theory in the generalized gradient approximation (GGA). The evolution of the number of hole carriers in different sites of the CuO2 planes and CuO chains has been investigated in comparison with the other YBCO family members, i.e., Y123, Pr123, Y124, and Y247. The results suggest that pumping hole carriers out of the chains toward the planes enhances the transition temperature. The band structure calculations have been performed for Y358, and the results show similar features with the other family members. Most notably, a van Hove singularity forms near the X point of the Brillouin zone below the Fermi level and within the energy of the buckling phonon mode, for which the interplay is discussed. PACS. 71.15.Mb Density functional theory, local density approximation, gradient and other corrections – 71.20.-b Electron density of states and band structure of crystalline solids – 74.72.-h Cuprate superconductors (high-Tc and insulating parent compounds)