Calorimetric evidence of multiband superconductivity in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mtext>Ba</mml:mtext><mml:msub><mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msub><mml:mrow><mml:mtext>Fe</mml:mtext></mml:mrow><mml:mrow><mml:mn>0.925</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mtext>Co</mml:mtext></mml:mrow><mml:mrow><mml:mn>0.075</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mn>2</mml:mn>

Hardy, F.; Wolf, Thomas; Fisher, Robert A.; Eder, R.; Schweiß, P.; Adelmann, P.; Löhneysen, H. v.; Meingast, C.

doi:10.1103/physrevb.81.060501

Cited by 113 publications

(129 citation statements)

References 39 publications

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“…It is worth to mention that γ r in our SC samples reaches 12.6%, 3.8%, and 6.5% of the normal state Sommerfeld coefficient γ n for x = 0.092, 0.096, and 0.10, respectively. A similar observation of (γ r /γ n ≈ 5.7%-24%) [47,49] was also reported in iron pnictide superconductors.…”

Section: Resultssupporting

confidence: 62%

“…In addition, γ n increases with Ni doping, illustrating the competition between magnetism and superconductivity. We believe, however, that the presence of multiple SC gaps may reduce the universal parameter, as evidenced in other 122 Fe-based superconductors [47]. It has been also well reported that the reduced jump in the specific heat C p /T c compared to that of a single-band s-wave superconductor might be related to a pronounced multiband character with rather different partial densities of states and gap values [24].…”

Section: Resultsmentioning

confidence: 98%

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Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case ofBaFe2−xNixAs2

Abdel-Hafiez

Zhang

et al. 2015

Phys. Rev. B

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The characteristics of Fe-based superconductors are manifested in their electronic, magnetic properties, and pairing symmetry of the Cooper pair, but the latter remain to be explored. Usually in these materials, superconductivity coexists and competes with magnetic order, giving unconventional pairing mechanisms. We report on the results of the bulk magnetization measurements in the superconducting state and the low-temperature specific heat down to 0.4 K for BaFe 2−x Ni x As 2 single crystals. The electronic specific heat displays a pronounced anomaly at the superconducting transition temperature and a small residual part at low temperatures in the superconducting state. The normal-state Sommerfeld coefficient increases with Ni doping for x = 0.092, 0.096, and 0.10, which illustrates the competition between magnetism and superconductivity. Our analysis of the temperature dependence of the superconducting-state specific heat and the London penetration depth provides strong evidence for a two-band s-wave order parameter. Further, the data of the London penetration depth calculated from the lower critical field follow an exponential temperature dependence, characteristic of a fully gapped superconductor. These observations clearly show that the superconducting gap in the nearly optimally doped compounds is nodeless.

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Section: Resultssupporting

confidence: 62%

Section: Resultsmentioning

confidence: 98%

Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case ofBaFe2−xNixAs2

Abdel-Hafiez

Zhang

et al. 2015

Phys. Rev. B

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“…Comparably small values of Δ 2 (0), as measured by α 2 , have been reported in electron-doped BaFe 2 As 2 -α 2 = 0.95 in Ref. 23 and α 2 = 0.957 in Ref. 24 -but, given the differences between the electron-and hole-doped compounds, the implications of this similarity in the values of α 2 are not clear.…”

Section: Discussionmentioning

confidence: 92%

Specific Heat of Ba_0.59K_0.41Fe₂As₂, an Fe-Pnictide Superconductor with T_c = 36.9 K, and a New Method for Identifying the Electron Contribution

et al. 2015

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We report measurements of the specific heat of Ba 0.59 K 0.41 Fe 2 As 2 , an Fe-pnictide superconductor with T c = 36.9 K, for which there are suggestions of an unusual electron pairing mechanism. We use a new method of analysis of the data to derive the parameters characteristic of the electron contribution. It is based on comparisons of α-model expressions for the electron contribution with the total specific heat, which give the electron contribution directly. It obviates the need in the conventional analyses for an independent, necessarily approximate, determination of the lattice contribution, which is subtracted from the total specific heat to obtain the electron contribution. It eliminates the uncertainties and errors in the electron contribution that follow from the approximations in the determination of the lattice contribution. Our values of the parameters characteristic of the electron contribution differ significantly from those obtained in conventional analyses of specific-heat data for five similar holedoped BaFe 2 As 2 superconductors, which also differ significantly among themselves. For Ba 0.59 K 0.41 Fe 2 As 2 the electron density of states is comprised of contributions from two electron bands with superconducting-state energy gaps that differ by a factor 3.8, with 77% coming from the band with the larger gap. The variation of the specific heat with magnetic field is consistent with extended s-wave pairing, one of the theoretical predictions. The relation between the densities of states and the energy gaps in the two bands is not consistent with a theoretical model based on interband interactions alone. Comparison of the normal-state density of states with band-structure calculations shows an extraordinarily large effective mass 2 enhancement, for which there is no precedent in similar materials and no theoretical explanation.

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“…To account this negligible variation, we use scaling coefficients close to unity. As an example, for Ba0.67K0.33Fe2As2 one may choose Ba(Fe0.847Co0.153)2As2 [46], Ba(Fe0.88Mn0.12)2As2 [47], BaFe1.75Ni0.25As2 [48].…”

Section: Specific Heat Measurementsmentioning

confidence: 99%

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

Kuzmicheva¹,

Muratov²,

Kuzmichev³

et al. 2017

Phys.-Usp.

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We discuss the synthesis, characterization, and comprehensive study of Ba-122 single crystals with various substitutions and various superconducting transition temperatures. We use five complementary techniques to obtain a self-consistent set of data on the superconducting properties of Ba-122. A major conclusion of our work is the coexistence of two superconducting condensates differing in the electron–boson coupling strength. The two gaps that develop in distinct Fermi surface sheets are nodeless in the kxky plane and exhibit s-wave symmetry; the two-band model suffices for the description of the main parameters of the superconducting state. A moderate interband coupling and a considerable Coulomb repulsion in the description of the two-gap superconducting state of barium pnictides favor the s++ model.

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Calorimetric evidence of multiband superconductivity inBa(Fe0.925Co0.075)2

Cited by 113 publications

References 39 publications

Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case ofBaFe2−xNixAs2

Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case ofBaFe2−xNixAs2

Specific Heat of Ba_0.59K_0.41Fe₂As₂, an Fe-Pnictide Superconductor with T_c = 36.9 K, and a New Method for Identifying the Electron Contribution

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

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Calorimetric evidence of multiband superconductivity inBa(Fe0.925Co0.075)2

Cited by 113 publications

References 39 publications

Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case ofBaFe2−xNixAs2

Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case ofBaFe2−xNixAs2

Specific Heat of Ba0.59K0.41Fe2As2, an Fe-Pnictide Superconductor with Tc = 36.9 K, and a New Method for Identifying the Electron Contribution

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

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Product

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Specific Heat of Ba_0.59K_0.41Fe₂As₂, an Fe-Pnictide Superconductor with T_c = 36.9 K, and a New Method for Identifying the Electron Contribution