Spin orbit coupling, electron correlations and exotic magnetism in 5d complex Ir oxides

In 5d Iridium oxides, a large spin-orbit coupling of $\sim $ 0.5 eV, inherent to heavy 5d elements, is not small as compared with the width of d bands and often modifies the landscape of the electronic structure substantially. This is distinct from those of 3d transition metal oxides and gives rise to a variety of novel electronic phases. Layered Ir$^{4+}$ perovskite Sr$_{2}$IrO$_{4}$ is recently revealed to be a novel J$_{eff}$=1/2 Mott insulator [1,2], where even a moderate Coulomb U can open up a correlation gap because of the large spin-orbit coupling. In the three dimensional analogue of Sr$_{2}$IrO$_{4}$, SrIrO$_{3, }$ the large spin-orbit coupling manifests itself in a contrasted way, where the interplay of strong spin-orbit coupling and lattice distortions brings the system almost to a band insulator. SrIrO$_{3}$ is in fact a very low carrier density semimetal with unusual transport and magnetic properties. If J$_{eff}$=1/2 Ir$^{4+}$ is placed on a honeycomb lattice or a geometrically frustrated lattice such as pyrochlore lattice, even more exotic states might be anticipated, including a correlated topological insulator [3] and a Kiteav magnet [4]. Our attempt to explore such spin-orbit coupling induced states will be reported.\\[4pt] Work done in collaboration with T. Takayama, B.J.Kim, S.Fujiyama, K.Ohashi, J.Matsuno, H.Osumi and T.Arima. \\[4pt] [1] B.J.Kim et al., Phys Rev Lett 101, 076402 (2008). \\[0pt] [2] B. J. Kim, H. Ohsumi, T. Komesu, S. Sakai, T. Morita, H. Takagi, and T. Arima, Science 323, 1329 (2009). \\[0pt] [3] Shitade et al., Phys. Rev. Lett. 102, 256403 (2009). \\[0pt] [4] J. Chaloupka, G.Jackeli, and G.Khaliullin, Phys. Rev. Lett. 105, 027204 (2010)