Octahedral tilting induced isospin reorientation transition in iridate heterostructures

Iridate heterostructures are gaining interest as their magnetic properties are much more sensitive to structural distortion compared to pure spin systems due to spin-orbital entanglement. While bulk monolayer and bilayer iridates show $ab$-plane canted and $c$-axis antiferromagnetic (AFM) order, recent experiments on layered iridate superlattices (SLs) have revealed striking properties, especially in the bilayer SLs. A spin model is presented to illustrate the proclivity towards $ab$-plane canted AFM order. A realistic Hubbard model including spin-dependent hopping terms is constructed for the bilayer SL, and magnetic excitations are investigated in the self-consistently determined magnetic state. The Hubbard model analysis confirms the spin model results and shows strongly reduced magnon energy gap and an isospin reorientation transition from $c$-axis to $ab$-plane canted AFM order with increasing tilting.