Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2010-06-30
Phys. Rev. B 83, 205101 (2011)
Physics
Condensed Matter
Strongly Correlated Electrons
7pages + 2pages appendices. 7 figures; see also viewpoint article by L. Balents, "Weyl Electrons Kiss", at Physics 4, 36 (2011
Scientific paper
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 Y$_{2}$Ir$_{2}$O$_{7}$) 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 Y$_{2}$Ir$_{2}$O$_{7}$ and related compounds. A narrow window of magnetic `axion' insulator, with axion parameter $\theta=\pi$, may also be present at intermediate U. An applied magnetic field induces ferromagnetic order and a metallic ground state.
Savrasov Sergey Y.
Turner Ari
Vishwanath Ashvin
Wan Xiangang
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