Spin-Orbit Induced Emergent Magnetic Phases in Iridium Based Oxides

We shall present our results on the electronic structure of 6H perovskite type quaternary iridates Ba$_{3}$MIr$_{2}$O$_{9}$, where Ir ions form structural dimers and non magnetic M provides a knob to tailor the valence of Ir. We shall first consider the d$^{4.5}$ insulator Ba$_{3}$YIr$_{2}$O$_{9}$ and explain the origin of the pressure induced magnetic transition to a spin-orbital liquid (SOL) state in this system. As a next example [2], we shall consider a pentavalent (d$^{4}$) 6H perovskite iridate Ba$_{3}$ZnIr$_{2}$O$_{9}$ and argue that the ground state of this system is a realization of novel SOL state. Our results reveal that such a system provides a very close realization of the elusive J=0 state where Ir local moments are generated due to the comparable energy scales of the singlet-triplet splitting driven by spin-orbit coupling (SOC) and the superexchange interaction mediated by strong intra-dimer hopping, however substantial frustrated interdimer exchange interactions induce quantum fluctuations favoring SOL phase at low enough temperature. [1] S.K. Panda, S. Bhowal, Ying Li, S. Ganguly, Roser Valenti, L. Nordstrom, and I. Dasgupta Physical Review B (Rapid Communication), 2015 (Accepted for Publication), [2] A. Nag et. al. arXiv:1506.04312 [cond-mat.str-el]