Evidence for weak electronic correlations in iron pnictides

Yang, Wanli; Sorini, A. P.; Chen, Cheng-Chien; Moritz, Brian; Lee, W.-S.; Vernay, F.; Olalde-Velasco, P.; Denlinger, Jonathan D.; Delley, B.; Chu, Jiun‐Haw; Analytis, James; Fisher, I. R.; Ren, Zefeng; Yang, Jie; Lü, Wei; Zhao, Z.X.; Brink, Jeroen van den; Hussain, Zahid; Shen, Zhi‐Xun; Devereaux, T. P.

doi:10.1103/physrevb.80.014508

Cited by 190 publications

(203 citation statements)

References 66 publications

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“…As in the pnictide Fe-HTSC, the Fe 2p PES and Fe L 23 XAS spectra display signatures which are typical of delocalized, itinerant electrons, in agreement with other studies [29,30]. Specifically, …”

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confidence: 73%

Spectroscopic evidence for strong quantum spin fluctuations with itinerant character inYFe2Ge2

et al. 2015

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We report x-ray absorption and photoemission spectroscopy of the electronic structure in the normal state of metallic YFe2Ge2. The data reveal evidence for large fluctuating spin moments on the Fe sites, as indicated by exchange multiplets appearing in the Fe 3s core level photoemission spectra, even though the compound does not show magnetic order. The magnitude of the multiplet splitting is comparable to that observed in the normal state of the Fe-pnictide superconductors. This shows a connection between YFe2Ge2 and the Fe-based superconductors even though it contains neither pnictogens nor chalcogens. The implication is that the chemical range of compounds showing at least one of the characteristic magnetic signatures of the Fe-based superconductors is broader than previously thought.

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confidence: 73%

Spectroscopic evidence for strong quantum spin fluctuations with itinerant character inYFe2Ge2

et al. 2015

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“…The observed spectral broadening could stem from more itinerant electrons [35][36] and/or structural distortion 37 of the electrode material under delithiated states. We note that a direct measurement of the electronic conductivity of a cycled Li1-xNi0.5Mn1.5O4 material is non-trivial due to the existence of the conductive carbon.…”

Section: Results Andmentioning

confidence: 99%

Direct Experimental Probe of the Ni(II)/Ni(III)/Ni(IV) Redox Evolution in LiNi_0.5Mn_1.5O₄ Electrodes

et al. 2015

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KEYWORDS: high voltage spinel, LiNi0.5Mn1.5O4, Ni(III), soft x-ray spectroscopy.2 ABSTRACT LiNi0.5Mn1.5O4 spinel is an appealing cathode material for next generation rechargeable Li-ion batteries due to its high operating voltage of ~4.7 V (vs. Li/Li + ). Although it is widely believed that the full range electrochemical cycling involves the redox of Ni(II)/(IV), it has not been experimentally clarified whether Ni(III) exists as the intermediate state, or a double-electron transfer takes place. Here, combined with theoretical calculations, we show unambiguous spectroscopic evidence of the Ni(III) state when the LiNi0.5Mn1.5O4 electrode is half charged.This provides a direct verification of single-electron-transfer reactions in LiNi0.5Mn1.5O4 upon cycling, namely, from Ni(II) to Ni(III), then to Ni(IV). Additionally, by virtue of its surface sensitivity, soft x-ray absorption spectroscopy also reveals the electrochemically inactive Ni 2+and Mn 2+ phases on the electrode surface. Our work provides the long-awaited clarification of the single-electron transfer mechanism in LiNi0.5Mn1.5O4 electrodes. Furthermore, the experimental results serve as a benchmark for further spectroscopic characterizations of Nibased battery electrodes.3

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“…16 We also note that there exists at present appreciable uncertainty concerning the experimentally determined values of U and J . Whereas recent x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) on pnictides such as BaFe 2 As 2 180505-3 reveal U 2 eV and J ≈ 0.8 eV, 30 other XAS measurements suggest U ≈ 3, . .…”

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High-energy pseudogap induced by Hund coupling in a degenerate Hubbard model

Liebsch

2011

Phys. Rev. B

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Hund coupling in the degenerate five-band Hubbard model near n = 6 occupancy is shown to give rise to a significant depletion of spectral weight above the Fermi level. Calculations within dynamical mean-field theory combined with exact diagonalization reveal that this pseudogap is associated with a collective mode in the self-energy caused by spin fluctuations. The pseudogap is remarkably stable over a wide range of Coulomb and exchange energies, but disappears for weak Hund coupling. The implications of this phenomenon for optical spectra of iron pnictides are discussed. Introduction. The discovery of superconductivity in iron pnictides 1 has stimulated intense discussions concerning the role of correlation effects in these compounds. In contrast to high-T c cuprates, which have antiferromagnetic Mott insulators as parent compounds, pnictides are correlated magnetic metals that tend to show significant deviations from Fermi-liquid behavior. Moreover, as a result of the multiband nature of pnictides, the interplay of Coulomb and exchange interactions gives rise to phenomena not found in cuprates. The importance of Hund coupling in pnictides and chalcogenides was recently pointed out in several theoretical 2-6 and experimental studies. [7][8][9] Optical data on paramagnetic LaFePO (Ref. 10) and BaFe 2 As 2 (Refs. 7-9) reveal a high-energy pseudogap not compatible with normal metal behavior. This pseudogap differs fundamentally from the low-energy gap in the antiferromagnetic spin-density wave phase. Also, angleresolved photoemission spectra for doped BaFe 2 As 2 exhibit a depletion of spectral weight near the Fermi level that differs from the superconducting gap. 11 To investigate the influence of Coulomb correlations on the electronic properties of iron pnictides, various groups 2,6,12-21 have used dynamical mean-field theory 22 (DMFT) combined with single-particle Hamiltonians derived from densityfunctional theory. These calculations typically revealed moderate to strong effective mass enhancement, in agreement with experimental data. Correlations were also shown to give rise to nonzero low-energy scattering rates, 13,16,18 indicating bad metallicity. On the other hand, as a result of the complex band structure of pnictides, all five d bands are important, so that the many-body features exhibit a marked orbital dependence. Moreover, the Fe 3d density of states generally shows two main features separated by a deep minimum slightly above the Fermi energy. In view of these multiband characteristics, it is difficult to distinguish genuine many-body features from single-particle properties. For instance, it is presently not clear to what extent pseudogaps in the interacting density of states are induced by Coulomb correlations or band-structure effects.The aim of the present Rapid Communication is to unravel these competing influences. For this purpose we have performed DMFT calculations for a simplified Hamiltonian consisting of five degenerate semielliptical bands. Since the density of states is featureless, corre...

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Evidence for weak electronic correlations in iron pnictides

Cited by 190 publications

References 66 publications

Spectroscopic evidence for strong quantum spin fluctuations with itinerant character inYFe2Ge2

Spectroscopic evidence for strong quantum spin fluctuations with itinerant character inYFe2Ge2

Direct Experimental Probe of the Ni(II)/Ni(III)/Ni(IV) Redox Evolution in LiNi_0.5Mn_1.5O₄ Electrodes

High-energy pseudogap induced by Hund coupling in a degenerate Hubbard model

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Evidence for weak electronic correlations in iron pnictides

Cited by 190 publications

References 66 publications

Spectroscopic evidence for strong quantum spin fluctuations with itinerant character inYFe2Ge2

Spectroscopic evidence for strong quantum spin fluctuations with itinerant character inYFe2Ge2

Direct Experimental Probe of the Ni(II)/Ni(III)/Ni(IV) Redox Evolution in LiNi0.5Mn1.5O4 Electrodes

High-energy pseudogap induced by Hund coupling in a degenerate Hubbard model

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Direct Experimental Probe of the Ni(II)/Ni(III)/Ni(IV) Redox Evolution in LiNi_0.5Mn_1.5O₄ Electrodes