First-Principles Study on Cubic Pyrochlore Iridates Y2Ir2O7 and Pr2Ir2O7

Fully relativistic first-principles electronic structure calculations based on a noncollinear local spin density approximation (LSDA) are performed for pyrochlore iridates Y2Ir2O7 and Pr2Ir2O7. The all-in, all-out antiferromagnetic (AF) order is stablized by the on-site Coulomb repulsion U > U-c in the LSDA+U scheme, with U-c similar to 1.1 eV and 1.3 eV for Y2Ir2O7 and Y2Ir2O7, respectively. AF semimetals with and without Weyl points and then a topologically trivial AF insulator successively appear with further increasing U. For U = 1.3 eV, Y2Ir2O7 is a topologically trivial narrow-gap AF insulator having an ordered local magnetic moment similar to 0.5 mu(B)/Ir, while Pr2Ir2O7 is barely a paramagnetic semimetal with electron and hole concentrations of 0.016/Ir, in overall agreements with experiments. With decreasing oxygen position parameter x describing the trigonal compression of IrO6 octahedra, Pr2Ir2O7 is driven through a non-Fermi-liquid semimetal having only an isolated Fermi point of Gamma(+)(8), showing a quadratic band touching, to a Z(2) topological insulator.