Observation of Strong-Coupling Pairing with Weakened Fermi-Surface Nesting at Optimal Hole Doping in Ca
 0.33
 Na
 0.67
 Fe2As
 2

Shi, Yulan; Huang, Yaobo; Wang, Xiaoping; Shi, Xun; Roekeghem, Ambroise van; Zhang, Weilu; Xu, Na; Richard, P.; Qian, Tian; Rienks, E. D. L.; Thirupathaiah, S.; Zhao, Keyi; Jin, Changqing; Shi, M.; Ding, Hong

doi:10.1088/0256-307x/31/6/067403

Cited by 6 publications

(11 citation statements)

References 27 publications

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“…For x = 0.67, diluted and weak magnetism below 60-75 K as well as bulk superconductivity with T c = 34 K is found. The s-wave symmetry of the two superconducting gaps as well as the value of the larger gap agrees well with recent ARPES and specific-heat measurements [47,87].…”

Section: Discussionsupporting

confidence: 88%

Coexistence of superconductivity and magnetism inCa1−xNaxFe2As2: Universal suppression of the magnetic order parameter in 122 iron pnictides

et al. 2015

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We present a detailed investigation of the magnetic and superconducting properties of Ca 1−x Na x Fe 2 As 2 single crystals with x = 0.00, 0.35, 0.50, and 0.67 by means of the local probe techniques Mössbauer spectroscopy and muon spin relaxation experiments. With increasing Na-substitution level, the magnetic order parameter is suppressed. For x = 0.50 we find a microscopic coexistence of magnetic and superconducting phases accompanied by a reduction of the magnetic order parameter below the superconducting transition temperature T c. A systematic comparison with other 122 pnictides reveals a square-root correlation between the reduction of the magnetic order parameter and the ratio of the transition temperatures T c /T N , which can be understood in the framework of a Landau theory. In the optimally doped sample with T c ≈ 34 K, diluted magnetism is found and the temperature dependence of the penetration depth and superfluid density are obtained, proving the presence of two superconducting s-wave gaps.

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Section: Discussionsupporting

confidence: 88%

Coexistence of superconductivity and magnetism inCa1−xNaxFe2As2: Universal suppression of the magnetic order parameter in 122 iron pnictides

et al. 2015

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“…The fit of the experimental data to that previous gap function, illustrated in Fig. 11f, leads to ∆ 2 = 9.9 meV and ∆ z = 1.2 meV [109]. Interestingly, the ∆ 2 /∆ z = 8.3 ratio is similar to the J 2 /J z = 7 ratio determined by inelastic neutron scattering on the parent compound CaFe 2 As 2 [122].…”

Section: The Strong Coupling Approachsupporting

confidence: 74%

“…For example, a ratio of 7.5 was reported in Ba 0.6 K 0.4 Fe 2 As 2 for the hole-like α FS and the electron-like γ FS [43], a ratio that remains more or less constant as T c drops to 26 K upon underdoping [117] or to 22 K upon overdoping [107]. This ratio becomes 6.8 in Ca 0.33 Na 0.67 Fe 2 As 2 [109] and despite a much smaller T c of 15 K, a ratio of 9 was even reported for the α band in BaFe 1.5 Ru 0.5 As 2 [108]. Such large 2∆/k B T c ratios are not unique to the 122-ferropnictides.…”

Section: The Strong Coupling Approachmentioning

confidence: 99%

ARPES measurements of the superconducting gap of Fe-based superconductors and their implications to the pairing mechanism

Richard

Qian

Ding

2015

J. Phys.: Condens. Matter

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Its direct momentum sensitivity confers to angle-resolved photoemission spectroscopy (ARPES) a unique perspective in investigating the superconducting gap of multi-band systems. In this review we discuss ARPES studies on the superconducting gap of high-temperature Fe-based superconductors. We show that while Fermi-surface-driven pairing mechanisms fail to provide a universal scheme for the Fe-based superconductors, theoretical approaches based on short-range interactions lead to a more robust and universal description of superconductivity in these materials. Our findings are also discussed in the broader context of unconventional superconductivity.

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“…The three predicted gap values at

T = 0

Δ_{1} = 7.48

meV,

Δ_{2} = 2.35

meV, and

Δ_{3} = 7.5

meV, do nicely agree with the experimentally found values

Δ_{1} \approx Δ_{3} = 7.8

meV and

Δ_{2} = 2.3

meV from ARPES and

μ

SR data 6–6.7 meV and 0.6–0.8 meV. Another ARPES study arrived at somewhat enlarged gaps for a single crystal with the same

T_{c}

. The smallest gap occurs likely upon the outermost FSS with

d_{xy}

‐character.…”

Section: Superconducting State In the Strong Coupling Approximationsupporting

confidence: 79%

A multiband Eliashberg‐approach to iron‐based superconductors

Efremov

Drechsler

Rösner

et al. 2017

Physica Status Solidi (b)

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Since the discovery of the Fe-based superconductors (FeSC) a lot of efforts has been applied to elucidate the microscopic mechanism behind cooper pairing and the symmetry of the order parameter. Examination of effective interactions of electrons with spin-fluctuations in these systems yield that couplings are not weak and the materials have to be considered in a strong coupling scheme. In the present article, we review some aspects of the description of iron-based superconductors in the frame of the Eliashberg approach for multiband systems. The application of the Eliashberg scheme is demonstrated with two compounds Ba0.6K0.4Fe2As2 and Ca0.32Na0.68Fe2As2. In both cases, it was found that these materials are in the intermediate coupling regime. Further, we consider effects of impurities on physical properties of multiband superconductors. It is demonstrated that the impurities affect nontrivially the superconducting properties. In particular, they may trigger a symmetry change of superconducting order parameters. This effect can be used for determination of the superconducting order parameter. Finally, we consider KFe2As2 and show that its thermodynamic properties are consistent with a nodal superconducting order parameter

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Observation of Strong-Coupling Pairing with Weakened Fermi-Surface Nesting at Optimal Hole Doping in Ca _0.33 Na _0.67 Fe2As ₂

Cited by 6 publications

References 27 publications

Coexistence of superconductivity and magnetism inCa1−xNaxFe2As2: Universal suppression of the magnetic order parameter in 122 iron pnictides

Coexistence of superconductivity and magnetism inCa1−xNaxFe2As2: Universal suppression of the magnetic order parameter in 122 iron pnictides

ARPES measurements of the superconducting gap of Fe-based superconductors and their implications to the pairing mechanism

A multiband Eliashberg‐approach to iron‐based superconductors

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Observation of Strong-Coupling Pairing with Weakened Fermi-Surface Nesting at Optimal Hole Doping in Ca 0.33 Na 0.67 Fe2As 2

Cited by 6 publications

References 27 publications

Coexistence of superconductivity and magnetism inCa1−xNaxFe2As2: Universal suppression of the magnetic order parameter in 122 iron pnictides

Coexistence of superconductivity and magnetism inCa1−xNaxFe2As2: Universal suppression of the magnetic order parameter in 122 iron pnictides

ARPES measurements of the superconducting gap of Fe-based superconductors and their implications to the pairing mechanism

A multiband Eliashberg‐approach to iron‐based superconductors

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Observation of Strong-Coupling Pairing with Weakened Fermi-Surface Nesting at Optimal Hole Doping in Ca _0.33 Na _0.67 Fe2As ₂