Iridium on the fcc lattice: new design principles for realizing <i>J</i>_eff = ½ moments and significant Kitaev interactions

Heavy transition metal magnets have been intensely investigated over the last decade due to their penchant for hosting a wide variety of exotic phases and phenomena. Of particular interest are systems with octahedrally-coordinated magnetic ions in a 5d⁵ electronic configuration, as the combination of large cubic crystal fields and strong spin-orbit coupling is expected to generate a J_eff = ½ electronic ground state that may be an essential ingredient for new classes of quantum spin liquids and superconductors. In this talk, I will discuss how spacing the iridium ions further apart and incorporating anions with low electronegativities into the crystal structure are useful design criteria for achieving unprecedented proximity to the ideal J_eff = ½ limit. One or both conditions are realized in the double perovskite iridate and iridium halide families, which have the general chemical formulas A₂BIrO₆ and A₂IrX₆ respectively. Notably, both structure types consist of a magnetic face-centered-cubic (fcc) sublattice, where nearest neighbor Kitaev interactions are symmetry-allowed through extended superexchange pathways. Therefore, I will also discuss the possibility of realizing significant Kitaev interactions in these families and their impact on the collective magnetic properties. Finally, I will explain how systems with J_eff = ½ moments on the fcc lattice can host exotic states of matter.