To determine the strength of essential electronic and magnetic interactions in the iridates Sr${}_2$IrO${}_4$ and Ba${}_2$IrO${}_4$—potential platforms for high-temperature superconductivity—we use many-body techniques from wave-function-based electronic-structure theory. Multiplet physics, spin-orbit interactions, and Ir-O hybridization are all treated on equal footing, fully ab initio. Our calculations put the lowest $d$-$d$ excitations of Sr${}_2$IrO${}_4$/Ba${}_2$IrO${}_4$ at 0.69/0.64 eV, substantially lower than in isostructural cuprates. Charge-transfer excitations start at 3.0/1.9 eV and the magnetic nearest-neighbor exchange coupling is 51/58 meV. Available experimental results are fully consistent with these values, which strongly constrains the parametrization of effective iridate Hamiltonians.

• Received 6 December 2011

DOI:https://doi.org/10.1103/PhysRevB.85.220402