Hopping induced ground-state magnetism in 6H perovskite iridates

Abstract

Investigation of elementary excitations has advanced our understanding of many-body physics governing most physical properties of matter. Recently spin-orbit excitons have drawn much attention, whose condensates near phase transitions exhibit Higgs mode oscillations, a long-sought physical phenomenon [Nat. Phys. {\bf 13}, 633 (2017)]. These critical transition points resulting from competing spin-orbit coupling (SOC), local crystalline symmetry and exchange interactions, are not obvious in Iridium based materials, where SOC prevails in general. Here, we present results of resonant inelastic x-ray scattering on a spin-orbital liquid Ba${}_3$ZnIr${}_2$O${}_9$ and three other 6H-hexagonal perovskite iridates which show magnetism, contrary to non-magnetic singlet ground state expected due to strong SOC. Our results show that substantial hopping between closely placed Ir${}^{5+}$ ions within Ir${}_2$O${}_9$ dimers in these 6H-iridates, modifies spin-orbit coupled states and reduces spin-orbit excitation energies. Here, we are forced to use at least a two-site model, to match the excitation spectrum going in line with the strong intra-dimer hopping. Apart from SOC, low energy physics of iridates is thus critically dependent on hopping, and may not be ignored even for systems having moderate hopping, where the excitation spectra can be explained using an atomic model. SOC which is generally found to be 0.4-0.5~eV in iridates, is scaled in effect down to $\sim$0.26~eV for the 6H-systems, sustaining the hope to achieve quantum criticality by tuning Ir-Ir separation.

12 Pages, Main text has 4 figures, SI which is added at the end of the main text has 5 figures and two tables

References in corpus (3)

• Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling in Sr2IrO4
• Spin--orbital interaction for face-sharing octahedra: Realization of a highly symmetric SU(4) model
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Cited by in corpus (9)

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• Spin-orbit effects in pentavalent Iridates: Models and materials
• Quasimolecular electronic structure of the spin-liquid candidate Ba${}_3$InIr${}_2$O${}_9$
• RIXS interferometry and the role of disorder in the quantum magnet Ba${}_3$Ti${}_{3-x}$Ir${}_x$O${}_9$
• Magnetization dynamics fingerprints of an excitonic condensate $t_{2g}^4$ magnet
• $J_{eff}$ states in a quasi one dimensional antiferromagnetic spin chain hexagonal Iridates Sr${}_3$MIrO${}_6$ (M=Mg, Zn, Cd): an $ab-initio$ comparative perspective
• On the electronic ground state of two non-magnetic pentavalent honeycomb iridates
• J = 0 nonmagnetic insulating state in K${}_2$Os$X_6$ (X = F, Cl and Br)