Optical study of orbital excitations in transition-metal oxides

Abstract

The orbital excitations of a series of transition-metal compounds are studied by means of optical spectroscopy. Our aim was to identify signatures of collective orbital excitations by comparison with experimental and theoretical results for predominantly local crystal-field excitations. To this end, we have studied TiOCl, RTiO3 (R=La, Sm, Y), LaMnO3, Y2BaNiO5, CaCu2O3, and K4Cu4OCl10, ranging from early to late transition-metal ions, from t_2g to e_g systems, and including systems in which the exchange coupling is predominantly three-dimensional, one-dimensional or zero-dimensional. With the exception of LaMnO3, we find orbital excitations in all compounds. We discuss the competition between orbital fluctuations (for dominant exchange coupling) and crystal-field splitting (for dominant coupling to the lattice). Comparison of our experimental results with configuration-interaction cluster calculations in general yield good agreement, demonstrating that the coupling to the lattice is important for a quantitative description of the orbital excitations in these compounds. However, detailed theoretical predictions for the contribution of collective orbital modes to the optical conductivity (e.g., the line shape or the polarization dependence) are required to decide on a possible contribution of orbital fluctuations at low energies, in particular in case of the orbital excitations at about 0.25 eV in RTiO3. Further calculations are called for which take into account the exchange interactions between the orbitals and the coupling to the lattice on an equal footing.

published version, discussion of TiOCl extended to low T, improved calculation of orbital excitation energies in TiOCl, figure 16 improved, references updated, 33 pages, 20 figures

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• Observation of two-magnon bound states in the two-leg ladders of (Ca,La)14Cu24O41
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• Quantum Versus Jahn-Teller Orbital Physics in YVO${}_3$ and LaVO${}_3$
• Orbital excitations in LaMnO${}_3$
• Holes in a Quantum Spin Liquid
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• Presence of 3d Quadrupole Moment in LaTiO3 Studied by 47,49Ti NMR
• Theory of orbital state and spin interactions in ferromagnetic titanates
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• Dynamics of the 1D Heisenberg model and optical absorption of spinons in cuprate antiferromagnetic chains
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• Unusual Symmetries in the Kugel-Khomskii Hamiltonian
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• Giant phonon anomalies in the pseudo-gap phase of TiOCl
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Cited by in corpus (30)

• How chemistry controls electron localization in 3d1 perovskites: A Wannier-function study
• Spin-orbit excitations and electronic structure of the putative Kitaev magnet $\alpha$-RuCl${}_3$
• Magnetoelastic coupling in RETiO3 (RE = La, Nd, Sm, Gd, Y)
• Symmetry analysis of magneto-optical effects: The case of x-ray diffraction and x-ray absorption at the transition metal L23 edge
• Zero-field incommensurate spin-Peierls phase with interchain frustration in TiOCl
• Momentum dependence of orbital excitations in Mott-insulating titanates
• Optical evidence for symmetry changes above the Neel temperature in KCuF3
• Mott-Hubbard exciton in the optical conductivity of YTiO3 and SmTiO3
• Anisotropic Susceptibility of La_2-xSr_xCoO_4 related to the Spin States of Cobalt
• Pressure-induced insulator-to-metal transition in low-dimensional TiOCl
• Two-Spinon and Orbital Excitations of the Spin-Peierls System TiOCl
• Spin dynamics in the low-dimensional magnet TiOCl
• Optically probing symmetry breaking in the chiral magnet Cu2OSeO3
• Orbital superexchange and crystal field simultaneously at play in YVO3: resonant inelastic x-ray scattering at the V L edge and the O K edge
• Collective orbital excitations in orbitally ordered YVO3 and HoVO3
• Symmetry disquisition on the TiOX phase diagram
• Electronic structure and anomalous band-edge absorption feature in multiferroic MnWO4: An optical spectroscopic study
• Mott-Hubbard versus charge-transfer behavior in LaSrMnO4 studied via optical conductivity
• Multiple Spin-Orbit Excitons and the Electronic Structure of $\alpha$-RuCl${}_3$
• Effect of pressure on the polarized infrared optical response of quasi-one-dimensional LaTiO${}_{3.41}$
• Temperature-dependent optical conductivity of layered LaSrFeO_4
• Pressure-induced metallization and structural phase transition of the Mott-Hubbard insulator TiOBr
• Theory of Raman and Resonant Inelastic X-ray Scattering from Collective Orbital Excitations in YTiO${}_3$
• Ab initio computation of d-d excitation energies in low-dimensional Ti and V oxychlorides
• The fate of orbitons coupled to phonons
• Cluster Dynamical Mean-field calculations for TiOCl
• Electronic excitations in $5d^4$ J=0 Os${}^{4+}$ halides studied by RIXS and optical spectroscopy
• Spin-orbit coupling in a half-filled $t_{2g}$ shell: the case of $5d^3$ K${}_2$ReCl${}_6$
• Spin-orbital-lattice entanglement in the ideal j=1/2 compound K${}_2$IrCl${}_6$
• Dynamics of photo-induced ferromagnetism in oxides with orbital degeneracy