Magnetism of layered honeycomb iridates

Abstract: Mutual interactions among magnetic moments in magnetic materials are most frequently of Heisenberg type and thus isotropic in spin space. In Mott insulators containing ions characterized by a large spin-orbit coupling, the on-site entanglement of spin and orbital degrees of freedom translates the bond-directional nature of orbitals into bond-anisotropy of the interactions. Signatures of such bond-anisotropic interactions are found in layered honeycomb iridates such as Na₂IrO₃. We will study the corresponding spin model containing all the symmetry-allowed nearest-neighbor interaction terms. We will focus in particular on its hidden symmetry properties discovered using dual mappings of the Hamiltonian. Recent experimental results on Na₂IrO₃ and Li₂IrO₃ will be reviewed and by a comparison to the theoretical analysis we will localize the realistic parameter range in the global phase diagram of the general spin model.