Local antiferromagnetic correlations in the iron pnictide superconductors<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>LaFeAsO</mml:mtext></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mtext>F</mml:mtext><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mtext>Ca</mml:mtext><mml:msub>

Klingeler, R.; Leps, N.; Hellmann, I.; Popa, A.; Stockert, U.; Heß, Christian; Kataev, V.; Grafe, H.-J.; Hammerath, Franziska; Lang, Guillaume; Wurmehl, S.; Behr, G.; Harnagea, Luminita; Singh, S. J.; Büchner, B.

doi:10.1103/physrevb.81.024506

Cited by 124 publications

(124 citation statements)

References 45 publications

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“…For LaO 0.9 F 0.1 FeAs, the susceptibility ∆m p /V m ∆H linearly increases with the temperature which is typical for this compound where the AFM spin ordering has been completely suppressed. The absolute value of the susceptibility of the reference samples is similar to that reported by Klingeler et al 22 In contrast, for LaO 0.9 F 0.1 FeAs 1−δ the paramagnetic susceptibility is considerably higher and exhibits an unusual T-dependence.…”

Section: B T -Dependence Of the Paramagnetic Susceptibilitysupporting

confidence: 66%

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As vacancies, local moments, and Pauli limiting in LaFeAs1−δO0.9F0.1superconductors

et al. 2011

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We report magnetization measurements of As-deficient LaO0.9F0.1FeAs 1−δ (δ ≈ 0.06) samples with improved superconducting properties as compared with As-stoichiometric optimally doped La-1111 samples. In this As-deficient system with almost homogeneously distributed As-vacancies (AV), as suggested by the 75 As-nuclear quadrupole resonance (NQR) measurements, we observe a strong enhancement of the spin-susceptibility by a factor of 3-7. This observation is attributed to the presence of an electronically localized state around each AV, carrying a magnetic moment of about 3.2 µB per AV or 0.8 µB/Fe atom. From theoretical considerations we find that the formation of a local moment on neighboring iron sites of an AV sets in when the local Coulomb interaction exceeds a critical value of ∼ 1 eV in the dilute limit. Its estimated value amounts to ∼ 2.5 eV and implies an upper bound of ∼ 2 eV for the Coulomb repulsion at Fe sites beyond the first neighbor-shell of an AV. Electronic correlations are thus moderate/weak in doped La-1111. The strongly enhanced spin susceptibility is responsible for the Pauli limiting behavior of the superconductivity that we observe in As-deficient LaO0.9F0.1FeAs 1−δ . In contrast, no Pauli limiting behavior is found for the optimally doped, As-stoichiometric LaO0.9F0.1FeAs superconductor in accord with its low spin susceptibility.

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Section: B T -Dependence Of the Paramagnetic Susceptibilitysupporting

confidence: 66%

“…From the analysis of the experimental data reported in Ref. 22 one can see that at high temperature (above T N of the AFM ordering) the value of the susceptibility reduces only on 15% at the doping level of about ∼ 0.1. Therefore, one expects that χ …”

Section: B T -Dependence Of the Paramagnetic Susceptibilitymentioning

confidence: 99%

As vacancies, local moments, and Pauli limiting in LaFeAs1−δO0.9F0.1superconductors

et al. 2011

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“…Using the intrinsic susceptibility of polycrystalline LaFeAsO at 300 K of 3.3 × 10 −4 cm 3 /mol (see Table XXX), 207 the intrinsic magnetic moment of the 0.1 g LaFeAsO sample in H = 1 T is 0.0012 G cm 3 , whereas that of the saturated Fe impurity is 0.0042 G cm 3 which is a factor of 3.5 times larger than the intrinsic value. Thus the measured M/H for this hypothetical sample of LaFeAsO is a factor of 4.5 times larger than the intrinsic χ value.…”

Section: Influence Of Ferromagnetic and Paramagnetic Impurities On Mamentioning

confidence: 99%

The puzzle of high temperature superconductivity in layered iron pnictides and chalcogenides

Johnston

2010

Advances in Physics

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The response of the worldwide scientific community to the discovery in 2008 of superconductivity at Tc = 26 K in the Fe-based compound LaFeAsO1−xFx has been very enthusiastic. In short order, other Fe-based superconductors with the same or related crystal structures were discovered with Tc up to 56 K. Many experiments were carried out and theories formulated to try to understand the basic properties of these new materials and the mechanism for Tc. In this selective critical review of the experimental literature, we distill some of this extensive body of work, and discuss relationships between different types of experiments on these materials with reference to theoretical concepts and models. The experimental normal-state properties are emphasized, and within these the electronic and magnetic properties because of the likelihood of an electronic/magnetic mechanism for superconductivity in these materials. Contents

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“…15 The linear temperature dependence of high temperature susceptibility is a common feature in iron-based superconductors, which has been observed in NaFe 1−x Co x As, 15 Ba(Fe 1−x Co x ) 2 As 2 , 23 and LaFeAsO 1−x F x . 24 An explanation based on the J 1 -J 2 model of localized spins ascribes this behavior to the spin fluctuations arising from the local SDW correlation. 25 It is also argued that the behavior can be explained based on the spin susceptibiltiy of a 2D Fermi-liquid with nearly nested electron and hole pockets of the Fermi surface.…”

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confidence: 99%

Phase diagram and physical properties of NaFe1−xCuxAs single crystals

et al. 2013

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A series of high quality NaFe1−xCuxAs single crystals has been grown by a self-flux technique, which were systematically characterized via structural, transport, thermodynamic, and high pressure measurements. Both the structural and magnetic transitions are suppressed by Cu doping, and bulk superconductivity is induced by Cu doping. Superconducting transition temperature (Tc) is initially enhanced from 9.6 to 11.5 K by Cu doping, and then suppressed with further doping. A phase diagram similar to NaFe1−xCoxAs is obtained except that insulating instead of metallic behavior is observed in extremely overdoped samples. Tc's of underdoped, optimally doped, and overdoped samples are all notably enhanced by applying pressure. Although a universal maximum transition temperature (T max c ) of about 31 K under external pressure is observed in underdoped and optimally doped NaFe1−xCoxAs, T max c of NaFe1−xCuxAs is monotonously suppressed by Cu doping, suggesting that impurity potential of Cu is stronger than Co in NaFeAs. The comparison between Cu and Co doping effect in NaFeAs indicates that Cu serves as an effective electron dopant with strong impurity potential, but part of the doped electrons are localized and do not fill the energy bands as predicted by the rigid-band model.

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Local antiferromagnetic correlations in the iron pnictide superconductorsLaFeAsO1−xFxandCa

Cited by 124 publications

References 45 publications

As vacancies, local moments, and Pauli limiting in LaFeAs1−δO0.9F0.1superconductors

As vacancies, local moments, and Pauli limiting in LaFeAs1−δO0.9F0.1superconductors

The puzzle of high temperature superconductivity in layered iron pnictides and chalcogenides

Phase diagram and physical properties of NaFe1−xCuxAs single crystals

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