Probing the Superconducting Gap from Tunneling Conductance on NdFeAsO0.7 with T C=51 K

Miyakawa, Nobuaki; Minematsu, M.; Kawashima, Susumu; Ogata, Kazuma; Miyazawa, Keisuke; Kitô, Hijiri; Shirage, Parasharam M.; Eisaki, H.; Iyo, A.

doi:10.1007/s10948-010-0689-9

Cited by 12 publications

(8 citation statements)

References 26 publications

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“…In particular, similar situation is believed to be realized in MgB 2 [30] and LaO 0.9 F 0.1 FeAs [31]. The presence of the large superconducting gap characterized by 2∆ L /k B T c > 3.52 in the 1111-family compounds REOFeAs (RE = La, Sm, Nd) was confirmed by tunneling spectroscopy using break-junction technique [33], point-contact Andreev reflection spectroscopy [20,22,[35][36][37][38][39][40], scanning tunneling spectroscopy [21,33], and angle-resolved photoemission spectroscopy (ARPES) [34] (see Table 1). To the best of our knowledge, there is no other available data for Gd-1111.…”

supporting

confidence: 56%

Observation of multi-gap superconductivity in GdO(F)FeAs by Andreev spectroscopy

et al. 2011

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We have studied current-voltage characteristics of Andreev contacts in polycrystalline GdO0.88F0.12FeAs samples with bulk critical temperature Tc = (52.5 ± 1) K using break-junctions technique. The data obtained cannot be described within the single-gap approach and suggests the existence of a multi-gap superconductivity in this compound. The large and small superconducting gap values estimated at T = 4.2K are ∆L = 10.5 ± 2 meV and ∆S = 2.3 ± 0.4 meV, respectively.

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supporting

confidence: 56%

Observation of multi-gap superconductivity in GdO(F)FeAs by Andreev spectroscopy

et al. 2011

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“…In Refs. [42,43] NIS-spectra containing peculiarities cased by two isotropic gaps Δ L and Δ S were obtained with Nd-1111 polycrystalline samples. The BCS-ratio for the large gap was estimated as 2Δ L /k B T C = 6.2 ± 0.7, similar to that obtained by NS-spectroscopy [44], as well as the results presented here.…”

mentioning

confidence: 99%

Andreev spectroscopy of iron-based superconductors: temperature dependence of the order parameters and scaling of $ \Delta_{\rm L, S}$ with $ T_{\rm C}$

Kuzmicheva¹,

Kuzmichev²,

Mikheev³

et al. 2014

Phys.-Usp.

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IntroductionUnexpected discovery in 2006 [1] of the first layered Fe-based high-temperature superconductor (HTSC) -LnOFePn (where Ln -lanthanide, Pn -pnictide; hereafter referred to as "1111") becomes a key issue of modern solid state physics. Since 2008, the class of iron-based superconductors has much expanded: several families of iron pnictides and chalcogenides have been synthesized [2][3][4]. The crystal structure of oxypnictides recalls that of cuprates and is in fact a stack of the superconducting Fe-As layers alternating along the c-direction with spacers, the nonsuperconducting oxide blocks, Ln-O. In spite of the pronounced layered structure and anisotropic physical properties, the electron subsystem in Fe-based superconductors is less quasi-two-dimensional in comparison with that in cuprate HTSC, because the height of the Fe-As blocks exceeds the thickness of the Cu-O planes, whereas the distance between superconducting blocks in iron-based superconductors is significantly less than that in cuprates. The latter seems to be a reason [5] why the critical temperature of Fe-based superconductors, though being as high as T C ≈ 57.5 K [6] still does not reach the cuprate one. Superconductivity in novel materials emerges with the suppression of spin density wave ground state under doping of the superconducting Fe-As layers or under external pressure [7]. The key distinction from cuprates, however, is the multiband nature of newly-discovered superconductivity in iron-based materials. Band structure calculations showed (for a review, see [8]) the coexistence of the electron and the hole quasi-two-dimensional bands in these compounds, whereas the Fermi surfaces consist of slightly warped along the c-direction cylinders (near Γ and M points), where several superconducting condensates could form. Contrary to the observation of the strong isotope effect [9], an early theoretical study showed [10] that the high temperature superconductivity in Fe-based compounds could not to be based on the electron-phonon interaction solely. Although the latter plays an important role, it is incapable [10] to explain the observable values of T C in the framework of the Eliashberg theory [11]. Taking into account the nesting of the Fermi surface sheets along the Γ-M-direction, the vicinity of the antiferromagnetic state [12,13], and the appearance of the experimentally observed [14] peak of dynamic spin susceptibility ("magnetic resonance"), Mazin et al. suggested the theoretical description of the mechanism of superconductivity in iron pnictides and chalcogenides based on sign-changing (in different bands) order parameter -the so-called s ± -model. The simplest initial model considers two isotropic order parameters (in the electron and the hole bands, correspondingly), which have equal amplitudes but are in antiphase (i.e. having opposite signs). The strong interband interaction mediated by spin fluctuations along the Γ-M-direction plays the key role in this model, whereas the intraband electron-phonon coupling is an order of magnit...

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Section: Pcars In the Superconducting Statementioning

confidence: 99%

“…This led to the claim of a single, BCS gap in FeSC [8]. Others, including us, decided instead to treat these shoulders as if they were the hallmark of a second gap ∆ 2 [9,11,13,14] and thus fitted the PCARS spectra using a two-band BTK model (with two isotropic gaps), obtaining in many cases a very good fit in a wide energy range (as shown in Fig. 1a and b).…”

Section: Pcars In the Superconducting Statementioning

confidence: 99%

“…This, and the fact that most of the PCARS measurements have been performed in polycrystals -thus with random direction of current injection -seems to indicate that the small gap has a fairly good spatial homogeneity and is likely to show a small anisotropy in the k space. Although a few spectra show only the small gap features and can indeed be well fitted by a single-gap BTK model, [8,10,[12][13][14], in most cases additional features are also present in the spectra, in the form of more or less marked shoulders (see for example Fig.1 a and b), that prevent a single-gap BTK model from fitting the spectra in the whole energy range. The amplitude and the shape of these features can vary very much from contact to contact; interestingly enough, they seem to be weaker when the current is injected along the c axis, as in the case of PCARS in oriented films of La-1111 and Sm-1111 [15], while if the current is injected along the ab plane (as in the only PCARS measurements carried out in 1111 in single crystals so far) they are clearly detected [16].…”

Section: Introductionmentioning

confidence: 99%

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Point contact spectroscopy in Fe-based superconductors: Recent advancements and future challenges

Gonnelli¹,

Daghero²,

Tortello³

2013

Current Opinion in Solid State and Materials Science

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Iron-based superconductors (FeSC) present an unprecedented variety of features both in the superconducting and in the normal state. Different families differ in the value of the critical temperature, in the shape of the Fermi surface, in the existence or absence of quasi-nesting conditions, in the range of doping in which the antiferromagnetic (AFM) and the superconducting phase coexist and in the structure of the order parameter in the reciprocal space, and so on. In this paper the most important results of point-contact spectroscopy (PCS) in Fe-based superconductors are reviewed, and the most recent advances are described with the aim to discuss the future perspectives and challenges of this spectroscopic technique in the characterization of the superconducting properties of these complex compounds. One of the main challenges, faced so far only by a few researchers in the PCS field, is to fully explore the phase diagram of these materials, as a function of doping or pressure, to understand the interplay between superconductivity and magnetism, the effect of intrinsic or extrinsic inhomogeneities, the role of spin fluctuations (SFs) in the pairing, the symmetry and the structure of the order parameter(s).

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Probing the Superconducting Gap from Tunneling Conductance on NdFeAsO0.7 with T C=51 K

Cited by 12 publications

References 26 publications

Observation of multi-gap superconductivity in GdO(F)FeAs by Andreev spectroscopy

Observation of multi-gap superconductivity in GdO(F)FeAs by Andreev spectroscopy

Andreev spectroscopy of iron-based superconductors: temperature dependence of the order parameters and scaling of $ \Delta_{\rm L, S}$ with $ T_{\rm C}$

Point contact spectroscopy in Fe-based superconductors: Recent advancements and future challenges

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