Resonant electron-exchange excitations in transition-metal oxides

Fromme, Bärbel; Möller, Marco; Bethke, C.; Brunokowski, U.; Kisker, E.

doi:10.1103/physrevb.57.12069

Cited by 14 publications

(16 citation statements)

References 37 publications

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“…The 0.870 and 2.3 eV peaks are in agreement with x-rays but the 1.84 eV excitation was not resolved with non-resonant xrays and is forbidden in the dipolar approximation, however it has been reported in other optical and x-ray studies such as RIXS and EELS that are sensitive to dipole forbidden cross sections. 38,[43][44][45][46][47] This result highlights the point that the 1.84 ±0.03 eV excitation is dipole forbidden and confirms our claim that we are sampling a quadrupolar matrix element in our neutron scattering experiments.…”

Section: A Comparison With Inelastic X-rays and Optical Techniquessupporting

confidence: 86%

Neutron scattering investigation of thed−dexcitations below the Mott gap of CoO

et al. 2013

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Neutron scattering is used to investigate the single-ion spin and orbital excitations below the Mott-Hubbard gap in CoO. Three excitations are reported at 0.870±0.009 eV, 1.84±0.03, and 2.30±0.15 eV. These were parameterized within a weak crystal field scheme with an intra-orbital exchange of J(dd)=1.3 ± 0.2 eV and a crystal field splitting 10Dq=0.94 ± 0.10 eV. A reduced spinorbit coupling of λ=-0.016± 0.003 eV is derived from dilute samples of Mg0.97Co0.03O, measured to remove complications due to spin exchange and structural distortion parameters which split the cubic phase degeneracy of the orbital excitations complicating the inelastic spectrum. The 1.84 eV, while reported using resonant x-ray and optical techniques, was absent or weak for non resonant x-ray experiments and overlaps with the expected position of a 4 A2 level. This transition is absent in the dipolar approximation but expected to have a finite quadrupolar matrix element that can be observed with neutron scattering techniques at larger momentum transfers. Our results agree with a crystal field analysis (in terms of Racah parameters and Tanabe-Sugano diagrams) and with previous calculations performed using local-density band theory for Mott insulating transition metal oxides. The results also demonstrate the use of neutron scattering for measuring dipole forbidden transitions in transition metal oxide systems.

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Section: A Comparison With Inelastic X-rays and Optical Techniquessupporting

confidence: 86%

Neutron scattering investigation of thed−dexcitations below the Mott gap of CoO

et al. 2013

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“…The ground state of the Co 2ϩ ion has a 4 T 1 character in O h symmetry. In order to take into account the polarization dependence and ͑super͒exchange interactions, the calculations were made in the C 4h basis set at 0 K. Two configurations were considered: 3d 7 9 L Ϫ2 configuration in the ground state was neglected here since its weight was estimated to be only in the order of ϳ1% in prior studies. 21 The single-impurity Anderson model ͑SIAM͒, 22 with full multiplet effects, was applied to describe the system.…”

Section: Calculational Detailsmentioning

confidence: 99%

“…6 However, another EELS publication assigned the ϳ2.0 eV loss feature to the 4 T 1g → 4 A 2g quartet-quartet transition. 7 In spectrum C, the shoulder at ϳ2.3 eV and the peak at ϳ3.2 eV are probably due to the 4 T 1g → 4 T 1g and 4 T 1g → 4 A 2g quartet-quartet transitions, respectively. However, the assignments are difficult and several calculations of measured energy-loss peaks in the energy region ϳ2.3-3.2 eV differ strongly for CoO, and are sometimes also referred to as quartet-doublet spin-flip transitions.…”

mentioning

confidence: 91%

“…In Table II, the assignments of the loss structures are compared to those of absorption data 4,5 and EELS. [6][7][8] The lowest loss structure at ϳ0.9 eV above the ground state, most clearly observed in spectra A and C and as a shoulder in spectrum B, is due to the 4 T 1g → 4 T 2g quartet-quartet transitions. The assignment of the ϳ2.0-eV loss structure in spectra B and C, also observed as a shoulder in spectrum A, is more difficult.…”

mentioning

confidence: 92%

“…4,5 These faint excitations can also be studied with electronenergy-loss spectroscopy ͑EELS͒, since the dipole selection rules are relaxed at low electron energies although these measurements are very surface sensitive. [6][7][8] While detailed resonant photoemission spectroscopy ͑RPES͒ measurements, aimed at 2p and 3p core levels, [9][10][11][12][13] confirmed the chargetransfer character of CoO, the spectra are mixed with the O 2 p band, and it is not clear to what extent the 3d 6 and screened 3d 7 L Ϫ1 final states reflect the electronic structure of the ground state. 2 Although these materials are known to exhibit charge-transfer insulator properties, this important mechanism is not yet fully understood.…”

Section: Introductionmentioning

confidence: 99%

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Electronic structure investigation of CoO by means of soft x-ray scattering

et al. 2002

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The electronic structure of CoO is studied by resonant inelastic soft x-ray scattering spectroscopy using photon energies across the Co 2p absorption edges. The different energy-loss structures in the Raman scattering spectra are identified as due to d-d and charge-transfer excitations. For excitation energies close to the L 3 resonance, the spectral features are dominated by quartet-quartet and quartet-doublet transitions of the 3d 7 configuration. At excitation energies corresponding to the satellites in the Co 2p x-ray-absorption spectrum of CoO, the emission features are instead dominated by charge-transfer transitions to the 3d 8 L Ϫ1 final state. The spectra are interpreted and discussed with the support of simulations within the single-impurity Anderson model with full multiplet effects which are found to yield consistent spectral functions to the experimental data.

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