Charge ordering in Ir dimers in the ground state of Ba${}_5$AlIr${}_2$O${}_{11}$

Abstract

It has been well established experimentally that the interplay of electronic correlations and spin-orbit interactions in Ir${}^{4+}$ and Ir${}^{5+}$ oxides results in insulating J${}_{\mathrm{eff}}$=1/2 and J${}_{\mathrm{eff}}$=0 ground states, respectively. However, in compounds where the structural dimerization of iridum ions is favourable, the direct Ir $d$--$d$ hybridisation can be significant and takes a key role. Here, we investigate the effects of direct Ir $d$--$d$ hybridisation in comparison with electronic correlations and spin-orbit coupling in Ba${}_5$AlIr${}_2$O${}_{11}$, a compound with Ir dimers. Using a combination of $ab$ $initio$ many-body wave function quantum chemistry calculations and resonant inelastic X-ray scattering (RIXS) experiments, we elucidate the electronic structure of Ba${}_5$AlIr${}_2$O${}_{11}$. We find excellent agreement between the calculated and the measured spin-orbit excitations. Contrary to the expectations, the analysis of the many-body wave function shows that the two Ir (Ir${}^{4+}$ and Ir${}^{5+}$) ions in the Ir${}_2$O${}_9$ dimer unit in this compound preserve their local J${}_{\mathrm{eff}}$ character close to 1/2 and 0, respectively. The local point group symmetry at each of the Ir sites assumes an important role, significantly limiting the direct $d$--$d$ hybridisation. Our results emphasize that minute details in the local crystal field (CF) environment can lead to dramatic differences in electronic states in iridates and 5$d$ oxides in general.

5 pages with 3 figures

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Cited by in corpus (2)

• RIXS interferometry and the role of disorder in the quantum magnet Ba${}_3$Ti${}_{3-x}$Ir${}_x$O${}_9$
• Quasimolecular electronic structure of the trimer iridate Ba${}_4$NbIr${}_3$O${}_{12}$