Single Crystal Break Junctions

Aminov, B. A.; Leonyuk, L.; Os'kina, T. E.; Piel, H.; Ponomarev, Ya. G.; Rachimov, H. T.; Sethupathi, K.; Sudakova, M. V.; Wehler, D.

doi:10.1007/978-4-431-68305-6_232

Cited by 10 publications

(8 citation statements)

References 7 publications

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“…Intrinsic multiple Andreev reflections effect, observed first in [22], takes place in Andreev arrays in layered superconductors, and is similar to intrinsic Josephson effect in S-I-S-I-…-S contact [23,24] (I = insulator). Since Andreev array is a stack of single SnS-junctions, its CVC and dynamic conductance spectra scale by a factor of N (where N is the number of contacts in the array); the SGS dips should occur at bias voltages…”

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confidence: 71%

Experimental study of the intrinsic multiple Andreev reflections effect in GdO(F)FeAs superconductor array junctions

Kuzmicheva¹,

Kuzmichev²,

Mikheev³

et al. 2013

EPL

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We report the first observation of the intrinsic multiple Andreev reflections effect (IMARE) in S-n-S-…-S-arrays (S = superconductor, n = normal metal) formed by "break-junction" technique in GdO(F)FeAs superconductor (T C = 48 ÷ 53 K). We show that superconducting gap peculiarities at dI/dV-spectra sharpen dramatically in the arrays as compared with that in the single-contact spectra; this enables to improve significantly accuracy of the bulk superconducting parameters determination. Using IMARE, we determined the large and the small gap values Δ L = 11.0 ± 1.1 meV and Δ S = 2.6 ± 0.4 meV. The BCS-ratio 2Δ L /k B T C local = 5.0 ÷ 5.9 > 3.52 (T C local is the contact area critical temperature) evidences for a strong electron-boson coupling. The results obtained agree well with our previous data by Andreev spectroscopy for single SnS-contacts.

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mentioning

confidence: 71%

Experimental study of the intrinsic multiple Andreev reflections effect in GdO(F)FeAs superconductor array junctions

Kuzmicheva¹,

Kuzmichev²,

Mikheev³

et al. 2013

EPL

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“…In ballistic mode, these arrays manifest intrinsic multiple Andreev reflections effect (IMARE) 43 which is similar to the intrinsic Josephson effect in cuprates. 44 In our experiment, after cleavage the two superconducting banks of the sample slide over each other touching at different terraces. By precise tuning of the sample holder one can probe tens of SnS-contacts as well as arrays (containing various number of contacts) in order to check reproducibility of the gap values.…”

Section: Methodsmentioning

confidence: 99%

Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap

et al. 2014

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Using two different experimental techniques, we studied single crystals of the 122-FeAs family with almost the same critical temperature, Tc. We investigated the temperature dependence of the lower critical field Hc1(T ) of a Ca0.32Na0.68Fe2As2 (Tc ≈ 34 K) single crystal under static magnetic fields H parallel to the c axis. The temperature dependence of the London penetration depth can be described equally well either by a single anisotropic s-wave-like gap or by a two-gaps model, while a d-wave approach cannot be used to fit the London penetration depth data. The intrinsic multiple Andreev reflection effect (IMARE) spectroscopy was used to detect bulk gap values in single crystals of the intimate compound Ba0.65K0.35Fe2As2, with the same Tc. We estimate the range of the large gap value ∆L = (6-8) meV (depending on small variation of Tc) and its k-space anisotropy about 30%, and the small gap is about ∆S ≈ (1.7±0.3) meV. This clearly indicates that the gap structure of our investigated systems is more likely to be of the two-gap nodeless s-wave type.

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“…Therefore, the bias voltage for any peculiarities (caused by bulk properties of the sample) in CVC and the dynamic conductance should be N times larger (where N is the number of junctions in the stack) for array contact in comparison with that of single ScS-contact. Such array contacts were for the first time observed on cuprates [76][77][78][79], and then on other layered superconductors [67][68][69][70][71][72]74,75]. In the Andreev mode (i.e.…”

Section: Methodsmentioning

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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Single Crystal Break Junctions

Cited by 10 publications

References 7 publications

Experimental study of the intrinsic multiple Andreev reflections effect in GdO(F)FeAs superconductor array junctions

Experimental study of the intrinsic multiple Andreev reflections effect in GdO(F)FeAs superconductor array junctions

Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap

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

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