Weak orbital ordering of Ir t(2g) states in the double perovskite Sr2CeIrO6

The electronic and magnetic properties of distorted monoclinic double perovskite Sr2CeIrO6 were examined based on both experiments and first-principles density functional theory calculations. From the calculations we conclude that low-spin-state Ir4+ (5d(5)) forms a rare weakly antiferromagnetic (AFM) orbital ordered state derived from alternating occupation of slightly mixed c(g)(pi) symmetry states in the presence of spin-orbit coupling (SOC). This orbital ordering is caused due to the competition between the comparable strength of Jahn-Teller structural distortion and SOC. We found both electron-electron correlation and SOC are required to drive the experimentally observed AFM-insulating ground state. Electronic structure investigation suggests that this material belongs to the intermediate-SOC regime, by comparing our results with the other existing iridates. This single active site double perovskite provides a rare platform with a prototype geometrically frustrated fcc lattice where among the different degrees of freedom (i.e., spin, orbital, and lattice) SOC, structural distortion, and Coulomb correlation energy scales compete and interact with each other.