On the structure of the superconducting order parameter in high-temperature Fe-based superconductors

Despite the fact that the Fe-based superconductors (FeSCs) were discovered nearly ten years ago, the community is still devoting a tremendous effort towards elucidating their relevant microscopic pairing mechanism(s) and interactions. At present, there is still no consistent interpretation of their normal state properties, where the strength of the electron-electron interaction and the role of correlation effects are under debate. Here, we examine several common materials and illustrate various problems and concepts that are generic for all FeSCs. Based on empirical observations and qualitative insight from density functional theory, we show that the superconducting and low-energy thermodynamic properties of the FeSCs can be described semi-quantitively within multiband Eliashberg theory. We account for an important high-energy mass renormalization phenomenologically, and in agreement with constraints provided by thermodynamic, optical, and angle-resolved photoemission data. When seen in this way, all FeSCs with T c < 40 K studied so far are found to belong to an intermediate coupling regime. This finding is in contrast to the strong coupling scenarios proposed in the early period of the FeSC history. We also discuss several related issues, including the role of band shifts as measured by the positions of van Hove singularities, and the nature of a recently suggested quantum critical point in the strongly hole-doped systems AFe 2 As 2 (A = K, Rb, Cs). Using high-precision full relativistic GGA-band structure calculations, we arrive at a somewhat milder mass renormalization in comparison with previous studies. From the calculated mass anisotropies of all Fermi surface sheets, only the ε-pocket near the corner of the BZ is compatible with the experimentally observed anisotropy of the upper critical field, pointing to its dominant role in the superconductivity of these three compounds.

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“…b). A similar T ‐dependence has been derived directly from tunneling measurements of nearly optimally or slightly underdoped doped

{Ba}_{1 - x} K_{x}

Fe 2 As 2 with

x < 0.4

. Here, the expected two large gaps with a BCS ‐like T ‐dependence from the dominant antiferromagnetically coupled pair of bands bearing probably the

s_{\pm}

mechanism of superconductuivity like in our case, were however experimentally not resolved.…”

Section: Weak Versus Strong Coupling In Fe ‐Based Superconductorssupporting

confidence: 77%

Constraints on the total coupling strengthto bosons in the iron based superconductors

Drechsler

Johnston

Grinenko

et al. 2017

Phys. Status Solidi B

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“…3. Experimentally observed gap anisotropy of 30% 47,48,50 approximately corresponds to the case of ∆ 1 β = 4 shown here. Evidently, decrease of the gap anisotropy leads to the increase of the spin resonance frequency.…”

Section: Second I Change the Gap Anisotropy On Electron Pockets By Vsupporting

confidence: 77%

“…However, the role of the gap anisotropy in the formation of the spin resonance peak is still an open question. For example, results of ARPES 47 and Andreev spectroscopy [48][49][50] demonstrate anisotropy of the larger gap as large as 30% in pnictides. On the qualitative level, the question was discussed in Ref.…”

Section: Introductionmentioning

confidence: 99%

Effect of gap anisotropy on the spin resonance peak in the superconducting state of iron-based materials

Korshunov

2018

Phys. Rev. B

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Spin resonance in the superconducting state of Fe-based materials within the multiorbital model with unequal anisotropic gaps on different Fermi surface sheets is studied. On the basis of the model gap function and the one calculated within the spin fluctuation theory of pairing, I show that the resonance peak shifts to higher frequencies with increasing the zero-amplitude gap magnitude. On the contrary, with increasing the gap anisotropy, it shifts to lower frequencies and lose some intensity.

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“…EuRbF e 4 As 4 single crystals were grown using the self-flux method as it has been done previously for Ni-doped Ba-122 [9,10]. The initial high purity components of Eu (99.95%), Rb (99.99%) and FeAs (99.98% Fe + 99.9999% As) were mixed in 1:1:12 molar ratio, placed in an alumina crucible and sealed in a niobium tube under 0.2 atm of residual argon pressure.…”

Section: Methodsmentioning

confidence: 99%

Vortex dynamic, pinning and irreversibility field investigation in EuRbFe4As4 superconductor

Vlasenko,

Pervakov,

Gavrilkin

2019

Preprint

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We performed systematic AC susceptibility and magnetic moment measurements to investigate the vortex dynamics and pinning in a EuRbF e 4 As 4 single crystal as a function of temperature, frequency and DC magnetic field. The vortex solid to vortex liquid line was determined and well fitted by H(T p ) = H 0 (1 − t p ) b with b=1.74-1.91 for H c indicating rather high pinning strength of vortex system.The field dependence of the activation energy U 0 is gained within the approach of thermally activated flux creep theory. A power law dependence of U ∼ H a with a = 0.52 is observed below 1T. The activation energy reaches 6700K at low fields, suggesting strong pinning in the material. Magnetic moment measurements also confirms the strong pinning in EuRbF e 4 As 4 . We show Eu 2+ magnetic ordering suppressed in magnetic fields about 3T.

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On the structure of the superconducting order parameter in high-temperature Fe-based superconductors

Cited by 19 publications

References 80 publications

Constraints on the total coupling strengthto bosons in the iron based superconductors

Constraints on the total coupling strengthto bosons in the iron based superconductors

Effect of gap anisotropy on the spin resonance peak in the superconducting state of iron-based materials

Vortex dynamic, pinning and irreversibility field investigation in EuRbFe4As4 superconductor

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