Looking at the superconducting gap of iron pnictides

Dressel, Martin; Wu, Dan; Barišić, N.; Gorshunov, B.

doi:10.1016/j.jpcs.2010.10.004

Cited by 15 publications

(16 citation statements)

References 61 publications

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“…The obtained frequency is in line with the small gap values detected for other 122-iron pnictides with a similar T c [30,31]. Since in EuRbFe 4 As 4 several electronic bands cross the Fermi level, one may expect other gap(s) to be present, having the ratio 2∆ 0 /k B T c > 3.53 [32], similar to what is reported in 122 iron-based superconductors [30]. For CaKFe 4 As 4 with T c = 31-36 K, for instance, indications of two gaps, at 1-4 meV and at 6-9 meV have been reported [33].…”

supporting

confidence: 90%

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

et al. 2018

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Transport, magnetic and optical investigations on EuRbFe 4 As 4 single crystals evidence that the ferromagnetic ordering of the Eu 2+ magnetic moments at T N = 15 K, below the superconducting transition (Tc = 36 K), affects superconductivity in a weak but intriguing way. Upon cooling below T N , the zero resistance state is preserved and the superconductivity is affected by the in-plane ferromagnetism mainly at domain boundaries; a perfect diamagnetism is recovered at low temperatures. The infrared conductivity is strongly suppressed in the far-infrared region below Tc, associated with the opening of a complete superconducting gap at 2∆ = 10 meV. A gap smaller than the weak coupling limit suggests the strong orbital effects or, within a multiband superconductivity scenario, the existence of a larger yet unrevealed gap.New members of the iron-pnictide family, the so-called 1144-compounds, attract interest recently because the alternating layers of alkaline A and alkaline-earth B cations produce two different kinds of As sites [1][2][3][4]. These materials can be viewed as the intergrowth of A-122 and B-122 iron-pnictides and they are naturally hole doped. The parent compounds are superconducting with transition temperatures T c around 35 K, higher than most of the 122materials; no spin-density-wave order has been observed. Among all possible candidates, Eu-based 1144-systems are even more intriguing, since the Eu-sublattice orders ferromagnetically below a critical temperature T N ≈ 15 K [5,6], similar to the 122-counterpart EuFe 2 As 2 [7-11]. Ferromagnetic order deep inside the superconducting state is very rare, in general [12,13]; hence the "ferromagnetic superconductor" EuRbFe 4 As 4 might pave the way towards realization of a "superconducting ferromagnet" [14-16]. However, the exact nature of the Eu magnetic order and its effect on superconductivity is unresolved [5, 6] because single crystals have been synthesized only recently.In this Letter we focus on the interplay between superconductivity and ferromagnetism in EuRbFe 4 As 4 single crystals. We report comprehensive investigations comprising transport, magnetic and optical measurements combined with microscopic studies of the vortex dynamics. The infrared spectra show a clear gap opening around 80 cm −1 below T c = 36 K that is slightly reduced compared to the value expected from the BCS theory. We relate this small value to the multiband character of superconductivity as well as to the depairing (orbital) effects of super-currents screening the ferromagnetic domains. A surprisingly weak effect on the superconducting condensate has been observed upon magnetic ordering indicating a rather weak interaction between Eu-and Fe-sublattices.Single crystals of EuRbFe 4 As 4 are obtained according to Ref. [4,5,17,18]; they exhibit shiny ab-faces of approximately 1 mm in size. The structure of the compound is presented in Fig. 1(a). The crystals are characterized by x-ray, electrical transport, and magnetic susceptibility measurements. In Fig. 1(a) we plot the dc ...

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confidence: 90%

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

et al. 2018

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“…The three-band Eliashberg model adequately describes experimental temperature dependences of the superfluid density and penetration depth of the BaFe 1.91 Ni 0.09 As 2 film. The calculated values of the larger gaps fall within the range reported in [6,7,8,9,10], the smaller gap correlates well with that found in [10]. The London penetration depth found in [5] for a BaFe 1.9 Ni 0.1 As 2 film was somewhat smaller (λ L ∼ 226 ± 20 nm) compared to the present study, which can be ascribed to the different composition of our film.…”

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confidence: 90%

THz electrodynamics of BaFe_1.91Ni_0.09As₂ film analyzed in the framework of multiband Eliashberg theory

Ummarino¹,

Muratov²,

Kadyrov³

et al. 2020

Supercond. Sci. Technol.

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The temperature dependences of the plasma frequency, superfluid density and London penetration depth were determined from terahertz spectra of conductivity and dielectric permittivity of BaFe 1.91 Ni 0.09 As 2 film with critical temperature T c = 19.6 K. Part of experimental data were analyzed within a simple three-band Eliashberg model where the mechanism of superconducting coupling is mediated by antiferromagnetic spin fluctuations, whose characteristic energy Ω 0 scales with T c according to the empirical law Ω 0 = 4.65k B T c , and with a total electron-boson coupling strength λ tot = 2.17.

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“…6(a). [2,36]. It is interesting to compare our findings with one on Psubstituted EuFe 2 As 2 compounds where no gap was recognized in the optical response, because the samples are clean-limit superconductors [37].…”

Section: Eu(fe091ir009)2as2mentioning

confidence: 63%

Reentrant phases in electron-dopedEuFe2As2: Spin glass and superconductivity

et al. 2017

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We report evidence for a reentrant spin glass phase in electron-doped EuFe2As2 single crystals and first traces of the superconductivity re-entrance in optics. In the close-to-optimal doped Eu(Fe0.91Ir0.09)2As2 and Eu(Fe0.93Rh0.07)2As2 samples two magnetic transitions are observed below the superconducting critical temperature Tc ≈ 21 K: the canted A-type antiferromagnetic order of the Eu 2+ ions sets in around 17 K; the spin glass behavior occurs another 2 K lower in temperature. In addition, strong evidence for an additional transition is found far below the spin glass temperature. Our extensive optical and magnetic investigations provide new insight into the interplay of local magnetism and superconductivity in these systems and elucidate the effect of the spin-glass phase on the reentrant superconducting state.

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Looking at the superconducting gap of iron pnictides

Cited by 15 publications

References 61 publications

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

THz electrodynamics of BaFe_1.91Ni_0.09As₂ film analyzed in the framework of multiband Eliashberg theory

Reentrant phases in electron-dopedEuFe2As2: Spin glass and superconductivity

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Looking at the superconducting gap of iron pnictides

Cited by 15 publications

References 61 publications

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

Unique interplay between superconducting and ferromagnetic orders in EuRbFe4As4

THz electrodynamics of BaFe1.91Ni0.09As2 film analyzed in the framework of multiband Eliashberg theory

Reentrant phases in electron-dopedEuFe2As2: Spin glass and superconductivity

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THz electrodynamics of BaFe_1.91Ni_0.09As₂ film analyzed in the framework of multiband Eliashberg theory