Electron Correlations and Topological Phases in Iridium Oxides

Abstract

Topological aspects of matter have been extensively studied for materials with strong spin-orbit interaction, inspired by the seminal prediction of the topological insulator by Kane and Mele. Although the initial prediction ignored the electron correlation effects, the role of strong electron correlation in the topological properties of materials has been the subject of subsequent wide range of studies particularly for transition-metal as well as rare-earth compounds. The studies include those on the possibility of the topological insulators induced solely by the electron correlation effects. Among others, since the electron correlation and the spin orbit interaction compete, iridium oxides have been extensively studied. Sr_2IrO_4 isostructural to the copper oxide superconductors, R_2Ir_2O_7, which was predicted to show the Weyl semimetal and topological insulator characterized by the domain wall conduction in the magnetic ordered phase, and Na_2IrO_3 proposed as a candidate of Kitaev spin liquid are examples of hot topics for searching rich physics. We review recent studies on emergent phenomena and concepts generated by the interplay of spin-orbit interaction and electron correlation.