2010/06/30 by Xiangang Wan, Ari Turner, Ashvin Vishwanath +1 · 6 citations
Physics and Astronomy · #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.83.205101
published as Phys. Rev. B 83, 205101 (2011) · 7pages + 2pages appendices. 7 figures; see also viewpoint article by L. Balents, "Weyl Electrons Kiss", at Physics 4, 36 (2011)
arxiv created 2010/06/30 · arxiv updated 2015/05/19
In 5d transition metal oxides such as the iridates, novel properties arise from the interplay of electron correlations and spin-orbit interactions. We investigate the electronic structure of the pyrochlore iridates, (such as Y2Ir2O7) using density functional theory, LDA+U method, and effective low energy models. A remarkably rich phase diagram emerges on tuning the correlation strength U. The Ir magnetic moment are always found to be non-collinearly ordered. However, the ground state changes from a magnetic metal at weak U, to a Mott insulator at large U. Most interestingly, the intermediate U regime is found to be a Dirac semi-metal, with vanishing density of states at the Fermi energy. It also exhibits topological properties - manifested by special surface states in the form of Fermi arcs, that connect the bulk Dirac points. This Dirac phase, a three dimensional analog of graphene, is proposed as the ground state of Y2Ir2O7 and related compounds. A narrow window of magnetic `axion' insulator, with axion parameter θ=π, may also be present at intermediate U. An applied magnetic field induces ferromagnetic order and a metallic ground state.