Spin-Orbit Coupled Ground State of Ir-Oxides: From Jeff = 1/2 State to Topological Insulator to Quantum Magnets

Jaejun Yu

Seoul National University/Osaka University

 

A novel Jeff=1/2 state in Sr2IrO4 was reported as a unique manifestation of the spin-orbit coupling and on-site Coulomb interaction effect in 5d transition metal oxides. The electron correlation combined with strong spin-orbit coupling under a large crystal field present is responsible for the observed peculiar electronic and magnetic properties. Based on LDA+SO+U calculations including both on-site U and SOC, we have investigated a series of 5d Ir oxide compounds including Sr2IrO4, Na2IrO3, and Li2IrO3. The results show that there is an interesting competition between local lattice distortion and spin-orbit coupling, which controls the degree of jeff = 1/2 component in the state near EF. We predict the topological quantum phase transitions from normal to topological insulators in 5d transition metal oxide Na2IrO3, driven by controlling the long-range hopping and the trigonal crystal field. If one can fine-tune the structural parameters in Ir oxides, these systems can be one of the most promising candidates due to the characteristic energy of spin-orbit coupling close to that of the Coulomb correlations. The TI phase realized in Na2IrO3 can be a good playground for the study of the interplay between spin-orbit coupling and on-site Coulomb interaction. We also discuss an intriguing character of effective magnetic exchange interactions.