Excitonic Magnetism at the intersection of Spin-orbit coupling and crystal-field splitting

Abstract

Excitonic magnetism involving superpositions of singlet and triplet states is expected to arise for two holes in strongly correlated and spin-orbit coupled $t_{2g}$ orbitals. However, uncontested material examples for its realization are rare. Applying the Variational Cluster Approach to the square lattice, we find conventional spin antiferromagnetism combined with orbital order at weak and excitonic order at strong spin-orbit coupling. We address the specific example of Ca${}_2$RuO${}_4$ using ab-initio modeling and conclude it to realize excitonic magnetism despite its pronounced orbital polarization.

arXiv commentsome material added, e.g. phase diagram

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• Electronic excitations in $5d^4$ J=0 Os${}^{4+}$ halides studied by RIXS and optical spectroscopy
• Suppression of effective spin-orbit coupling by thermal fluctuations in spin-orbit coupled antiferromagnets
• Magnetization dynamics fingerprints of an excitonic condensate $t_{2g}^4$ magnet
• Spin-orbit coupling and crystal-field splitting in Ti-doped Ca2RuO4 studied by ellipsometry
• On the electronic ground state of two non-magnetic pentavalent honeycomb iridates
• Magnetic phases for two $t_{2g}$ holes with spin-orbit coupling and crystal field
• Coupled spin-orbital fluctuations in a three orbital model for $4d$ and $5d$ oxides with electron fillings $n=3,4,5$ -- Application to $\mathrm{NaOs}{\mathrm{O}}_3$, $\mathrm{C}{\mathrm{a}}_2\mathrm{Ru}{\mathrm{O}}_4$, and $\mathrm{S}{\mathrm{r}}_2\mathrm{Ir}{\mathrm{O}}_4$
• Role of orbital off-diagonal spin and charge condensates in a three orbital model for $\mathrm{C}{\mathrm{a}}_2\mathrm{Ru}{\mathrm{O}}_4$ -- Coulomb renormalized spin-orbit coupling, orbital moment, and tunable magnetic order
• Collective mode excitations and simulated $L$-edge resonant-inelastic x-ray scattering spectra in antiferromagnetic Ca${}_2$RuO${}_4$
• Magnetic ordering in the $J_{\mathrm{eff}}$ = 0 Nickelate NiRh${}_2$O${}_4$ prepared via a solid-state metathesis
• Magnetic polarons due to spin-length fluctuations in ${\mathbf{d}}^4$ spin-orbit Mott systems