An apparatus for the investigation of the sintering of powder materials

Moskalenko, I. A.; Ostrik, P. N.; Popov, B. I.; Kas'yanova, T. N.

doi:10.1007/bf00796569

Cited by 7 publications

(15 citation statements)

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“…Our data show (see the Table) that the two condensates interact weakly, whereas namely due to λ LS,LS ≠ 0 the small gap does not vanish to zero until the local contact T C local ; indeed, for zero interband coupling, according to the theory [50][51][52], the small gap would close at its eigen T C S . Therefore, for temperatures exceeding T C S , superconductivity in the Δ S -condensate is induced by the "driving" Δ L -condensate (i.e., due to the k-space proximity effect).…”

Section: Discussionmentioning

confidence: 69%

“…[64,[67][68][69][70]72,74,75]). To analyze the measured temperature dependencies, we fitted them using two-gap system of equations by Moskalenko and Suhl [50,52] with renormalized BCSintegral (shown by the solid lines in Fig. 4).…”

Section: Resultsmentioning

confidence: 99%

“…At the same time, for La-1111, the large gap vanished abruptly already at ~2/3T C , whereas the small gap deviated from the BCS-like curve and linearly tended to zero at T C [49]. Such behavior of the gaps does not agree with the Moskalenko and Suhl system of gap equations [50][51][52] for two-gap superconductivity and was not confirmed in any subsequent works with Fe-based superconductors. The authors of Ref.…”

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confidence: 82%

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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: Discussionmentioning

confidence: 69%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 82%

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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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“…Therefore, we can consider two effective bands to estimate electron-boson coupling constants λ ij = V ij N j (V is interaction matrix element, N is normal carrier density of states (DOS) at the Fermi level, i, j = 1, 2, hereafter the effective band with the large gap is labelled as "1", that with the small gap -as "2") and to make some important conclusions concerning the two-gap superconductivity in FeSe 0.5 Te 0.5 . We used simple two-band model based on Moskalenko and Suhl system of equations [38,39] with a renormalized BCS integral to describe the experimental data in Fig. 5.…”

Section: Discussionmentioning

confidence: 99%

Direct evidence of two superconducting gaps in FeSe0.5Te0.5: SnS-Andreev spectroscopy and the lower critical field

et al. 2016

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We present direct measurements of the superconducting order parameter in nearly optimal FeSe0.5Te0.5 single crystals with critical temperature TC ≈ 14 K. Using intrinsic multiple Andreev reflection effect (IMARE) spectroscopy and measurements of lower critical field, we directly determined two superconducting gaps, ∆L ≈ 3.3 − 3.4 meV and ∆S ≈ 1 meV, and their temperature dependences. We show that a two-band model fits well the experimental data. The estimated electron-boson coupling constants indicate a strong intraband and a moderate interband interaction.

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“…Here we present di-rectly determined temperature dependences of the large and the small gaps in various 1111 compounds with the wide range of critical temperatures 21.5K ≤ T C ≤ 50K. The measured ∆ L,S (T ) dependences were fitted using a two-band BCS-like model with a renormalized BCS (RBCS) integral based on Moskalenko and Suhl system of gap equations [15,16,17]. The relative values of electron-boson coupling constants λ i,j /λ LL (i, j = L, S) are estimated.…”

Section: Introductionmentioning

confidence: 99%

Estimation of Intraband and Interband Relative Coupling Constants from Temperature Dependences of the Order Parameter for Two-Gap Superconductors

Kuzmichev

Kuzmicheva

Tchesnokov

et al. 2016

J Supercond Nov Magn

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We present temperature dependences of the large and the small superconducting gaps measured directly by SnS-Andreev spectroscopy in various Fe-based superconductors and MgB 2 . The experimental ∆ L,S (T ) are well-fitted with a two-gap model based on Moskalenko and Suhl system of equations (supplemented with a BCS-integral renormalization). From the the fitting procedure, we estimate the key attribute of superconducting state -relative electron-boson coupling constants and eigen BCS-ratios for both condensates. Our results evidence for a driving role of a strong intraband coupling in the bands with the large gap, whereas interband coupling is rather weak for all the superconductors under study.

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An apparatus for the investigation of the sintering of powder materials

Cited by 7 publications

References 0 publications

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

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

Direct evidence of two superconducting gaps in FeSe0.5Te0.5: SnS-Andreev spectroscopy and the lower critical field

Estimation of Intraband and Interband Relative Coupling Constants from Temperature Dependences of the Order Parameter for Two-Gap Superconductors

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