Non-trivial order parameter in Sr${}_2$IrO${}_4$

Abstract

Electronic structure calculations obtained with an approach with density functional theory with an enhanced local Coulomb interaction, DFT+$U$, are presented for the relativistic magnetic insulator Sr${}_2$IrO${}_4$. The results are in accordance with experiments with a band gap and a small moment anti-ferromagnetic ground state. This solution is thereafter thoroughly analyzed in terms of Landau theory where it is found that the ordered magnetic moments only form a secondary order parameter while the primary order parameter is a higher order magnetic multipole of rank five. It is further observed that the electronic structure in the presence of this order parameter is related to the earlier proposed $j_{\mathrm{eff}}=1/2$ model, but in contrast to that model the present picture can naturally explain the small magnitude of the ordered magnetic moments.

Cited by in corpus (1)

• Strange magnetic multipoles and neutron diffraction by an iridate perovskite (Sr2IrO4)