Mobile orbitons in Ca${}_2$CuO${}_3$: crucial role of the Hund's exchange

Abstract

We investigate the Cu $L_3$ edge resonant inelastic x-ray scattering (RIXS) spectra of a quasi-1D antiferromagnet Ca${}_2$CuO${}_3$. In addition to the magnetic excitations, which are well-described by the two-spinon continuum, we observe two dispersive orbital excitations, the $3d_{xy}$ and the $3d_{yz}$ orbitons. We carry out a quantitative comparison of the RIXS spectra, obtained with two distinct incident polarizations, with a theoretical model. We show that any realistic spin-orbital model needs to include a finite, but realistic, Hund's exchange $J_H\approx 0.5$ eV. Its main effect is an increase in orbiton velocities, so that their theoretically calculated values match those observed experimentally. Even though Hund's exchange also mediates some interaction between spinon and orbiton, the picture of spin-orbit separation remains intact and describes orbiton motion in this compound.

arXiv comment13 pages, 10 figures

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• Fractional spin excitations in the infinite-layer cuprate CaCuO${}_2$
• Unraveling the orbital physics in a canonical orbital system KCuF${}_3$
• Collective nature of orbital excitations in layered cuprates in the absence of apical oxygens
• Unraveling higher-order corrections in the spin dynamics of RIXS spectra
• Ultrafast control of spin-orbital separation probed with time-resolved RIXS
• Electronic Excitations of Hematite Heteroepitaxial Films Measured by Resonant Inelastic X-Ray Scattering at the Fe L-edge
• Quantum entanglement, local indicators and effect of external fields in the Kugel-Khomskii model
• Excitonic wave-packet evolution in a two-orbital Hubbard model chain: A real-time real-space study
• A $j_{\mathrm{eff}}=1/2$ pseudospinon continuum in CaIrO${}_3$
• Observation of spin-conserving two-spinon continuum in the $S$=1/2 antiferromagnetic chain system Sr${}_2$CuO${}_3$ using Cu $K$-edge resonant inelastic x-ray scattering