Polarized resonant inelastic X-ray scattering from single-crystal transition metal oxides

Duda, Laurent; Nordgren, Joseph; Dräger, G.; Bocharov, S.; Kirchner, Th.

doi:10.1016/s0368-2048(00)00168-7

Cited by 35 publications

(34 citation statements)

References 28 publications

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“…In principle, d → d excitations provide a testing ground for the validity of conventional Raman selection rules within RIXS, and such excitations have been well studied with soft X-ray RIXS at the Cu L- [8][9][10]40,41 and M-edges, 11 with optical absorption, 42 with large-shift Raman scattering, 43 and with different theoretical methods. 44,45 Although for Nd 2 CuO 4 only the A 2g (d x 2 −y 2 → d xy ) Cu crystal-field excitation has been observed around 1.4 eV, 43 the crystal-field excitations of tetragonal Sr 2 CuO 2 Cl 2 have been extensively studied 10,11,42,44 and their energies should be similar to those of Nd 2 CuO 4 .…”

Section: Discussionmentioning

confidence: 99%

Polarization dependence and symmetry analysis in indirectK-edge RIXS

et al. 2010

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We present a study of the charge-transfer excitations in undoped Nd 2 CuO 4 using resonant inelastic X-ray scattering (RIXS) at the Cu K-edge. At the Brillouin zone center, azimuthal scans that rotate the incidentphoton polarization within the CuO 2 planes reveal weak fourfold oscillations. A comparison of spectra taken in different Brillouin zones reveals a spectral weight decrease at high energy loss from forward-to back-scattering. We show that these are scattered-photon polarization effects related to the properties of the observed electronic excitations. Each of the two effects constitutes about 10% of the inelastic signal while the '4p-as-spectator' approximation describes the remaining 80%. Raman selection rules can accurately model our data, and we conclude that the observed polarization-dependent RIXS features correspond to E g and B 1g charge-transfer excitations to non-bonding oxygen 2p bands, above 2.5 eV energy-loss, and to an E g d → d excitation at 1.65 eV.Raman scattering and optical spectroscopy have enabled tremendous contributions to the study of condensed matter systems. Both probes use ∼ 1 eV light and are limited to essentially zero momentum transfer. In order to investigate the charge response of a material throughout the Brillouin zone, photons in the X-ray regime must be used. X-ray Raman scattering, more commonly referred to as resonant inelastic X-ray scattering (RIXS), allows the measurement of the momentum dependence of charge excitations. Even though it has successfully been used to study the physics of a wide array of systems, 1-5 this resonant technique is relatively new and there is still much to learn about the details of its cross section.One of the strengths of conventional Raman scattering derives from the fact that the technique allows the determination of the symmetry of excitations by selecting the polarization of the incident and scattered photons. Only polarization dependent soft (or direct 6 ) X-ray RIXS studies, at the O K-edge or the Cu L-and M-edges of the cuprates, 7-11 have shown that photon polarization can be used to select different electronic excitations. In these cases, the photon polarization effects are understood to come from the direct interaction of the photoelectron, excited into the valence system, with the valence electrons. This is why this type of RIXS is commonly referred to as direct. 6 On the other hand, tuning the incident energy to the Cu K-edge excites the photoelectron into the Cu 4p band approximately 10-20 eV above the 3d valence levels. The relatively large separation in energy from the valence levels as well as the large spatial extent of the 4p orbital are believed to prevent the photoelectron from interacting with the valence system, and this type of RIXS is in turn referred to as indirect. 6 Accordingly, theoretical models of this type of RIXS accordingly do not include possible interactions of the 4p photoelectron with the valence system, 12-15 which is commonly referred to as the '4p-as-spectator' approximation.RIXS investigations of ...

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Section: Discussionmentioning

confidence: 99%

Polarization dependence and symmetry analysis in indirectK-edge RIXS

et al. 2010

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“…Particular energy loss features, as indicated by the gray lines, were enhanced at particular resonant energies, leading to very different lineshape. These energy loss features are signatures of dd-excitations 36 , details on which is not the topic of this paper. With better resolution, our RIXS data revealed more excitation modes than that in previous publications, covering the whole range of the optic absorption bands 37 .…”

Section: Xas and Rixs Measurementsmentioning

confidence: 98%

Evidence for weak electronic correlations in iron pnictides

et al. 2009

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Using x-ray absorption and resonant inelastic x-ray scattering, charge dynamics at and near the Fe L edges is investigated in Fe pnictide materials, and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show that Coulomb correlations are much smaller than in the cuprates, highlighting the role of Fe metallicity and strong covalency in these materials. Best agreement with experiment is obtained using Hubbard parameters U 2eV and J ≈ 0.8eV.

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“…The dispersionless behavior of the band edge intensity is not consistent with a coherent resonant inelastic X-ray scattering (RIXS) process in which the two-photon excitation and decay process is coupled to a lower-energy electronic transition. 57 Instead, it could represent a shake-up process in which valence electron excitations are stimulated during the relaxation of a core-level electron promoted by an X-ray photon to a state above the top of the CB. In this picture, the excess XES intensity is caused by normal fluorescence transitions from the excited states.…”

Section: Band Gap Measurements In Transition Metal Oxides By Soft-x-rmentioning

confidence: 99%

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

et al. 2010

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The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and soft X-ray absorption and emission spectroscopy to characterize the products of oxidizing uncoated and oleic-acidcoated magnetite nanoparticles in air. The oxidization of uncoated magnetite nanoparticles creates a material that is structurally and electronically indistinguishable from maghemite. By contrast, while oxidized oleic-acid-coated nanoparticles are also structurally indistinguishable from maghemite, Fe Ledge spectroscopy revealed the presence of interior reduced iron sites even after a 2-year period. We used X-ray emission spectroscopy at the O K-edge to study the valence bands (VB) of the iron oxide nanoparticles, using resonant excitation to remove the contributions from oxygen atoms in the ligands and from low-energy excitations that obscured the VB edge. The bonding in all nanoparticles was typical of maghemite, with no detectable VB states introduced by the long-lived, reduced-iron sites in the oleic-acid-coated sample. However, O K-edge absorption spectroscopy observed a ~0.2 eV shift in the position of the lowest unoccupied states in the coated sample, indicating an increase in the semiconductor band gap relative to bulk stoichiometric maghemite that was also observed by optical absorption spectroscopy. The results show that the ferrous iron sites within ferric iron oxide nanoparticles coated by an organic ligand can persist under ambient conditions with no evidence of a distinct interior phase, and exert an effect on the global electronic and optical properties of the material.This phenomenon resembles the band gap enlargement caused by electron accumulation in the conduction band of TiO 2 .

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Polarized resonant inelastic X-ray scattering from single-crystal transition metal oxides

Cited by 35 publications

References 28 publications

Polarization dependence and symmetry analysis in indirectK-edge RIXS

Polarization dependence and symmetry analysis in indirectK-edge RIXS

Evidence for weak electronic correlations in iron pnictides

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

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