Excitonic dispersion of the intermediate spin state in 
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 revealed by resonant inelastic x-ray scattering

Wang, Ru Pan; Hariki, Atsushi; Sotnikov, Andrii; Frati, Federica; Okamoto, Jun; Huang, Hung-Yi; Singh, Amol; Huang, D. J.; Tomiyasu, Keisuke; Du, Chao; Kuneš, J.; Groot, Frank M. F. de

doi:10.1103/physrevb.98.035149

Cited by 20 publications

(28 citation statements)

References 44 publications

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“…The comparison of L 2,3 -edge spectra in this study to references confirms the presence of Co 2+ in stable high-spin (HS) state 14 , Ni 3+ in the low-spin (LS) configuration 17 and different spin states of Co 3+ . Spin states of Co 3+ in LaCoO 3 have been subject to extensive debate in literature 13,18 , as Co 3+ may occur in the LS ground state, the first excited HS state, or excited states with intermediate spin 19 . Obtained spectra are equivalent to previous results related to a mixture of LS and HS states and spin state abundance was thus determined by a least squares fit of a linear combination of two reference spectra 13 representing a pure LS configuration and a mixed LS-HS state.…”

Section: Resultsmentioning

confidence: 99%

Electronic parameters in cobalt-based perovskite-type oxides as descriptors for chemocatalytic reactions

et al. 2020

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Perovskite-type transition metal (TM) oxides are effective catalysts in oxidation and decomposition reactions. Yet, the effect of compositional variation on catalytic efficacy is not well understood. The present analysis of electronic characteristics of B-site substituted LaCoO 3 derivatives via in situ X-ray absorption spectroscopy (XAS) establishes correlations of electronic parameters with reaction rates: TM t 2g and e g orbital occupancy yield volcanotype or non-linear correlations with NO oxidation, CO oxidation and N 2 O decomposition rates. Covalent O 2p-TM 3d interaction, in ultra-high vacuum, is a linear descriptor for reaction rates in NO oxidation and CO oxidation, and for N 2 O decomposition rates in O 2 presence. Covalency crucially determines the ability of the catalytically active sites to interact with surface species during the kinetically relevant step of the reaction. The nature of the kinetically relevant step and of surface species involved lead to the vast effect of XAS measurement conditions on the validity of correlations.

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Section: Resultsmentioning

confidence: 99%

Electronic parameters in cobalt-based perovskite-type oxides as descriptors for chemocatalytic reactions

et al. 2020

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“…Further details of the experiments can be found in the Supplemental Material of Ref. [42]. Figure 3(a) compares the fluorescence yield XAS spectra acquired from two orthogonal linear polarized incident beams.…”

Section: The 2p3d Rixs Experimentsmentioning

confidence: 99%

“…In an effort to contribute to the debate about the origin of magnetism in LaCoO 3 , we employ 2p3d resonant inelastic x-ray scattering (2p3d RIXS) to study the complex electronic configuration of the Co ions in a LaCoO 3 single crystal and strained thin films. 2p3d RIXS probes both the local [26][27][28][29][30][31][32][33][34] and collective excitations [35][36][37][38][39][40][41][42], including small lattice distortions [43][44][45]. In the case of LaCoO 3 , the 2p3d RIXS process in the ionic limit can be described as 3d 6 > 2p 5 3d 7 > 3d 6 transitions of Co 3+ ions, which allows us to distinguish the spin-state manifolds.…”

Section: Introductionmentioning

confidence: 99%

“…1(c)]. RIXS measurements on the single crystal LaCoO 3 indicate that the spin-state population is varying as a function of temperature, which suggests that the ground state is close to a degeneracy of LS 1 A 1g (O h ) and HS 5 T 2g (O h ) states [42,46]. Furthermore, different composition mixtures of LS and HS states have been found in the cuboidal (D 2h ) and trigonal (D 3d ) distorted LaCoO 3 films through 2p3d RIXS [45], which agrees with x-ray diffraction [10].…”

Section: Introductionmentioning

confidence: 99%

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Low-energy orbital excitations in strained LaCoO3 films

et al. 2019

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We present 90 meV resolved Co 2p3d resonant inelastic x-ray scattering linear dichroism spectra of strained LaCoO 3 films and a LaCoO 3 single crystal. A polarization-dependent low-energy excitation is observed at ∼0.2 eV on the tensile-strained LaCoO 3 /SrTiO 3 film, while it is not observed in either bulk LaCoO 3 or the compressive-strained LaCoO 3 /LaAlO 3 film. Guided by cluster calculations, we are able to distinguish the spin-state manifolds close to their transition point of Co 3+ ions in LaCoO 3 systems. Through a polarization analysis, we show that the spin state can easily flip from a low-spin 1 A 1g state in an octahedral symmetry to the high-spin 5 B 2g or 5 E g states with a small tetragonal distortion. A mixture of spin states suggests that the high-spin Co 3+ plays an important role in long-range ferromagnetic order on both tensile-and compressive-strained LaCoO 3 films.

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“…In the EI theories, the intermediate‐spin (IS) state generates the spatially mobile exciton as the source of dispersive spin‐state excitations . By contrast, the HS state is described as an immobile bi‐exciton consisting of two types of IS excitons with different site‐hopping directionality and results in the nondispersive excitations 6c,28. In this scheme, the HS condensation ranging multiple sites would lead to a novel bi‐excitonic insulating (bi‐EI) state with dual nature of immobility (localization) and site coherence (itinerancy).…”

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Quantum Paramagnet Near Spin‐State Transition

et al. 2018

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Spin‐state transition, also known as spin crossover, plays a key role in diverse systems, including minerals and biological materials. In theory, the boundary range between the low‐ and high‐spin states is expected to enrich the transition and give rise to unusual physical states. However, no compound that realizes a nearly degenerate critical range as the ground state without requiring special external conditions has yet been experimentally identified. This study reports that, by comprehensive measurements of macroscopic physical properties, X‐ray diffractometry, and neutron spectroscopy, the Sc substitution in LaCoO3 destabilizes its nonmagnetic low‐spin state and generates an anomalous paramagnetic state accompanied by the enhancement of transport gap and magneto‐lattice‐expansion as well as the contraction of Co─O distance with the increase of electron site transfer. These phenomena are not well described by the mixture of conventional low‐ and high‐spin states, but by their quantum superposition occurring on the verge of a spin‐state transition. The present study enables us to significantly accelerate the design of new advanced materials without requiring special equipment, based on the concept of quantum spin‐state criticality.

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Excitonic dispersion of the intermediate spin state in LaCoO3 revealed by resonant inelastic x-ray scattering

Cited by 20 publications

References 44 publications

Electronic parameters in cobalt-based perovskite-type oxides as descriptors for chemocatalytic reactions

Electronic parameters in cobalt-based perovskite-type oxides as descriptors for chemocatalytic reactions

Low-energy orbital excitations in strained LaCoO3 films

Quantum Paramagnet Near Spin‐State Transition

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