Spin-Orbital Excitations in Ca${}_2$RuO${}_4$ Revealed by Resonant Inelastic X-ray Scattering

Abstract

The strongly correlated insulator Ca${}_2$RuO${}_4$ is considered as a paradigmatic realization of both spin-orbital physics and a band-Mott insulating phase, characterized by orbitally selective coexistence of a band and a Mott gap. We present a high-resolution oxygen $K$-edge resonant inelastic X-ray scattering study of the antiferromagnetic Mott insulating state of Ca${}_2$RuO${}_4$. A set of low-energy ($\sim$80 and 400 meV) and high-energy ($\sim$1.3 and 2.2 eV) excitations are reported that show strong incident light polarization dependence. Our results strongly support a spin-orbit coupled band-Mott scenario and explore in detail the nature of its exotic excitations. Guided by theoretical modelling, we interpret the low-energy excitations as a result of composite spin-orbital excitations. Their nature unveil the intricate interplay of crystal-field splitting and spin-orbit coupling in the band-Mott scenario. The high-energy excitations correspond to intra-atomic singlet-triplet transitions at an energy scale set by the Hund's coupling. Our findings give a unifying picture of the spin and orbital excitations in the band-Mott insulator Ca${}_2$RuO${}_4$.

arXiv commentaccepted for publication in Physical Review X

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Cited by in corpus (32)

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• Observation of spin-orbit excitations and Hund's multiplets in Ca${}_2$RuO${}_4$
• Magnetic Anisotropy and Orbital Ordering in Ca${}_2$RuO${}_4$
• Emergence of a metallic meta-stable phase induced by electrical current in Ca_2RuO_4
• Keldysh space control of charge dynamics in a strongly driven Mott insulator
• Strong spin-phonon coupling unveiled by coherent phonon oscillations in Ca2RuO4
• Cooperative Interactions Govern the Fermiology of the Polar Metal Ca${}_3$Ru${}_2$O${}_7$
• Orbital-selective confinement effect of Ru $4d$ orbitals in SrRuO${}_3$ ultrathin film
• Van Vleck excitons in Ca${}_2$RuO${}_4$
• Tuning of the Ru${}^{4+}$ ground-state orbital population in the $4{\mathbf{d}}^4$ Mott insulator Ca${}_2$RuO${}_4$ achieved by La doping
• Multipole-fluctuation pairing mechanism of $d_{x^2-y^2}+ig$ superconductivity in Sr${}_2$RuO${}_4$
• Continuum excitation and pseudospin wave in quantum spin-liquid and quadrupole ordered states of Tb${}_{2+x}$Ti${}_{2-x}$O${}_{7+y}$
• Persistence of antiferromagnetic order upon La substitution in the $4d^4$ Mott insulator Ca${}_2$RuO${}_4$
• Pattern Formation by Electric-field Quench in Mott Crystal
• Magnetic reorientation transition in a three orbital model for $\mathrm{C}{\mathrm{a}}_2\mathrm{Ru}{\mathrm{O}}_4$ -- Interplay of spin-orbit coupling, tetragonal distortion, and Coulomb interactions
• Strain Healing of Spin-Orbit Coupling: A Cause for Enhanced Magnetic Moment in Epitaxial SrRuO3 Thin Films
• Electronic excitations in $5d^4$ J=0 Os${}^{4+}$ halides studied by RIXS and optical spectroscopy
• Resonant Inelastic X-ray Scattering Study of Ca${}_3$Ru${}_2$O${}_7$
• Spin-orbit coupling and crystal-field splitting in Ti-doped Ca2RuO4 studied by ellipsometry
• Photoemission Spectrum of Ca2RuO4: Spin Polaron Physics in an S=1 Antiferromagnet with Anisotropies
• Spin-orbit excitons and electronic configuration of the $5d^4$ insulator Sr${}_3$Ir${}_2$O${}_7$F${}_2$
• Spin-orbital mechanisms for negative thermal expansion in Ca2RuO${}_4$
• Mott-Insulator Ca2RuO4 under a static external electric field
• 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
• Anomalous orbital moment in the ferromagnetic phase of the Sr4Ru3O10
• 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 $\mathrm{S}{\mathrm{r}}_2\mathrm{Ir}{\mathrm{O}}_4$
• Competition of three-dimensional magnetic phases in Ca${}_2$Ru${}_{1-x}$Fe${}_x$O${}_4$: A structural perspective
• Anomalous Fermi pockets on Hund's metal surface of Sr2RuO4 induced by the correlation-enhanced spin-orbit coupling
• Collective mode excitations and simulated $L$-edge resonant-inelastic x-ray scattering spectra in antiferromagnetic Ca${}_2$RuO${}_4$
• Coexistence of insulator-like paramagnon and metallic spin-orbit exciton modes in SrIrO${}_3$
• Magnetic polarons due to spin-length fluctuations in ${\mathbf{d}}^4$ spin-orbit Mott systems