Speaker
Description
Iridium oxides with $d^5$ configuration have attracted considerable interest in the last decade due to the realisation of spin-orbit-coupled (SOC) $j_{eff}=1/2$ insulating ground states. Recently, a new class of 5$d^4$ iridates with a singlet ($j_{eff}=0$) ground states have been realised in (Ba/Sr)$_2$YIrO$_6$. Here, we propose a new honeycomb lattice compound Ba$_3$CaIr$_2$O$_9$ in the $j_{eff}=0$ class of materials. Using ab initio methods including many-body wavefunction calculations we characterise the SOC ground and excited states and show that a a $j_{eff}=0$ singlet ground state is realised. Further, we find that the material hosts non-trivial electronic band structure with a well defined $Z_2$ topological invariant. We analyse the effect of electronic correlations on the non-trivial bands using the Gutzwiller wavefunction approach.
