Spin-orbital excitons and their potential condensation in pentavalent iridates

Abstract

We investigate magnetic excitations in iridium insulators with pentavalent Ir${}^{5+}$ ($5d^4$) ions with strong spin-orbit coupling. We obtain a microscopic model based on the local Ir${}^{5+}$ multiplets involving $J=0$ (singlet), $J=1$ (triplet), and $J=2$ (quintet) spin-orbital states. We get effective interactions between these multiplets on square and face-centered-cubic (fcc) structures of magnetic ions in the layered-perovskites and the double-perovkites, in particular Ba${}_2$YIrO${}_6$. Further, we derive an effective spin-orbital Hamiltonian in terms of bond bosons and explore possible instabilities towards magnetic and quadrupole orderings. Additionally, we study charge excitations with help of the variational cluster perturbation theory and calculate the electronic charge gap as a function of hopping and Coulomb interactions. Based on both electronic and magnetic phase diagrams, we verify the possibility of excitonic magnetism due to condensation of spin-orbital excitons in Ir${}^{5+}$ iridates.

10 pages, 7 figures

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Cited by in corpus (6)

• Interplay between multipolar spin interactions, Jahn-Teller effect and electronic correlation in a $J_{eff}=\frac{3}{2}$ insulator
• Spin-orbit effects in pentavalent Iridates: Models and materials
• Hidden orders in spin-orbit entangled correlated insulators
• The effect of structural and magnetic disorder on the 3$d$-5$d$ exchange interactions of La${}_{2-x}$Ca${}_x$CoIrO${}_6$
• Magnetization dynamics fingerprints of an excitonic condensate $t_{2g}^4$ magnet
• Small moments without long-range magnetic ordering in the zero-temperature ground state of the double-perovskite iridate Ba${}_2$YIrO${}_6$