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Talantsev, E F, E-mail: evgeny.talantsev@imp.uran.ru2019
AbstractAbstract
[en] The era of near-room-temperature superconductivity started after experimental discovery by Drozdov et al (2015 Nature 525 73) who found that compressed H3S exhibits superconducting transition at T c = 203 K. To date, the record near-room-temperature superconductivity stands with another hydrogen-rich highly compressed compound, LaH10 (Somayazulu et al 2019 Phys. Rev. Lett. 122 027001), which has critical temperature of In this paper, we analyse available upper critical field, B c2(T), data for LaH10 (Drozdov et al 2019 Nature 569 528) and report that this compound in all considered scenarios has the ratio of T c to the Fermi temperature, T F, 0.009 < T c/T F < 0.038, which is typical range for unconventional superconductors. In attempt to extend our finding, we examined experimental B c2(T) data for superconductors in the palladium-hydrogen system and surprisingly find that PdHx compounds have the ratio of 0.008 < T c/T F < 0.012. Taking in account that H3S has the ratio of 0.012 < T c/T F < 0.039 (Talantsev 2019 Modern Phys. Lett. B 33 1950195) we come to conclusion that in the Uemura plot all discovered to date hydrogen-rich superconductors, i.e. PdHx, H3S and LaH10, lie in same band as all unconventional superconductors, particularly heavy fermions, fullerenes, pnictides, and cuprates, and former should be classified as a new class of unconventional superconductors. (paper)
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Source
Available from http://dx.doi.org/10.1088/2053-1591/ab3bbb; Country of input: International Atomic Energy Agency (IAEA)
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Journal Article
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Materials Research Express (Online); ISSN 2053-1591;
; v. 6(10); [12 p.]

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AbstractAbstract
[en] We consider the superconducting transition in fermionic quantum critical systems. Assuming the validity of Migdal theorem, the gap equation can be written in terms of the retarded pair susceptibility. Instead of the usual BCS form, the pair susceptibility is now subject to scale invariance. The gap and transition temperature is thus of the algebraic form, totally different from the exponential behavior in BCS theory. Consequently, with reasonably small glue strength, we can get very large gap and transition temperature comparable to those discovered in cuprates. The ratio of the gap to retardation gets boosted by increasing retardation. We also find the upper critical field has a different scaling with the critical temperature. With a non-Lorentzian dynamical exponent, the upper critical field is greatly enhanced when approaching the critical point, though the critical temperature only changes modestly, in agreement with recent experiments on heavy fermions.
Source
9. international conference on materials and mechanisms of superconductivity; Tokyo (Japan); 7-12 Sep 2009; S0921-4534(09)00864-8; Available from http://dx.doi.org/10.1016/j.physc.2009.11.147; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
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AbstractAbstract
[en] The discovery of superconductivity is 100 years old but theoretical works are still necessary: the BCS theory does not apply to the new families of high temperature superconducting materials discovered after 1986. In 2001 it was discovered that MgB2 is superconducting at 39 K, this critical temperature is not the highest but MgB2 is easy to produce and cheap. Today's highest critical temperature under atmospheric pressure is that of the HgTlBaCaCuO compound: 138 K. The complexity and the cost of cryogenic systems restrain the applications of superconductivity. The author reviews the applications of superconducting in medical imaging, particle detectors, and in the safety systems of power networks. (A.C.)
Original Title
La supraconductivite a l'ere industrielle
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7 refs.
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Buisson, O.; Pannetier, B.
Proceedings of the International Conference on Transport Properties of Superconductors1990
Proceedings of the International Conference on Transport Properties of Superconductors1990
AbstractAbstract
[en] Published in summary form only
Source
Universidade Federal, Rio de Janeiro, RJ (Brazil). Inst. de Fisica; 82 p; 1990; p. 47; International Conference on Transport Properties of Superconductors; Rio de Janeiro, RJ (Brazil); 29 Apr - 4 May 1990; Available from the Library of Comissao Nacional de Energia Nuclear, RJ, Brazil
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Calan, C. de; Nogueira, F.S.
Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)1998
Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)1998
AbstractAbstract
[en] We consider a Ginzburg-Landau model for superconductivity with a Chern-Simons term added. The flow diagram contains two charged fixed points corresponding to the tricritical and infrared stable fixed points. The topological coupling controls the fixed point structure and eventually the region of first order transitions disappears. We compute the critical exponents as a function of the topological coupling. We obtain that the value of the v exponent does not vary much from the XY value, vxy = 0.67. This shows that the Chern-Simons term does not affect considerably the XY scaling of superconductors. We discuss briefly the possible phenomenological applications of this model. (author)
Source
Apr 1998; 15 p; ISSN 0029-3865;
; 24 refs., 8 figs.

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AbstractAbstract
[en] Published in summary form only
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Universidade Federal, Rio de Janeiro, RJ (Brazil). Inst. de Fisica; 58 p; 1988; p. 11; Latin-American Conference on High Temperature Superconductivity; Rio de Janeiro, RJ (Brazil); 4-6 May 1988; Available from the Library of Comissao Nacional de Energia Nuclear, RJ, Brazil
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AbstractAbstract
[en] A flux pinning model is presented which predicts the maximum critical current density attainable in superconductors. That such a limit must exist comes from the realization that flux pinning is strongest in regions of weak superconductivity, but these regions cannot carry a large supercurrent. Since the same regions within the superconductor cannot be used for both pinning and supercurrent conductions, there must be an optimum mix, leading to a maximum J/sub c/. Measurements on films and multilayers of NbN have verified many details of the model including anisotropy effects and a strong reduction in J/sub c/ for defect spacings smaller than the flux core diameter. In an optimized multilayer the pinning force reached /approximately/22% of the theoretical maximum. The implications of these results on the practical applications of NbN films and on the maximum critical current density in the new high temperature superconductors are also discussed. 24 refs., 4 figs
Source
Aug 1988; 9 p; Applied superconductivity conference; San Francisco, CA (USA); 21-25 Aug 1988; Available from NTIS, PC A02/MF A01 - OSTI; 1 as DE89003622; Portions of this document are illegible in microfiche products.
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AbstractAbstract
[en] Both critical current and Shapiro steps in Josephson ladders are found to show effects of vortex exclusion below a critical magnetic field. Vortices are excluded even though the flux itself is not screened out. When current is injected perpendicular to the ladder edges, the critical current is unchanged from its f=0 value up to a penetration field of fc1perpendicular≅0.12 flux quanta per plaquette. Similarly, there are only integer Shapiro steps below a critical c1 perpendicular *, where vortices first penetrate. A narrower critical current plateau also appears to form near f =1/2. No such plateaus occur when current is injected in the parallel direction. We attribute the exclusion in the perpendicular geometry to screening currents which flow along the edges of the ladder. copyright 1996 The American Physical Society
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Singh, Shiv J; Bristow, Matthew; Blundell, Stephen J; Coldea, Amalia I; Cassidy, Simon J; Clarke, Simon J, E-mail: shiv.singh@physics.ox.ac.uk, E-mail: amalia.coldea@physics.ox.ac.uk2020
AbstractAbstract
[en] CaKFe4As4 (1144) is a unique stoichiometric iron-based superconductor which harbors high upper critical fields and large critical current densities. In this work, we describe a study to optimize the synthesis conditions of stoichiometric polycrystalline samples of CaKFe4As4 and assess their structural, magnetic and transport properties. The samples were prepared over a wide temperature range (900 °C–1100 °C) and the pure phase formation is centered around 955 °C. Outside this temperature region, impurity phases of KFe2As2 and CaFe2As2 can also form. Magnetic susceptibility and resistivity measurements establish that the critical temperature reaches ∼34 K for the optimum synthesis conditions and the critical current reaches 2 × 104 A cm−2. The post-annealing process demonstrates the stability of the 1144 phase up to 500 °C, however, under higher temperature annealing, phase degradation occurs. Our study indicates that the formation of phase-pure 1144 occurs over a much narrower window and its highly prone to multi-phase formation as compared with the 122 family. As a result, the superconducting properties are enhanced for the pure 1144 phase but they are likely to be affected by the inter- and intra-granular behavior originating from the microstructural nature of polycrystalline CaKFe4As4, similar to other iron-based superconductors. Based on our study, we construct the phase diagram for polycrystalline 1144 and compared it with that reported for 1144 single crystal. (paper)
Source
Available from http://dx.doi.org/10.1088/1361-6668/ab58be; Country of input: International Atomic Energy Agency (IAEA)
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Aguilera-Navarro, V.C.; Llano, M. de
Instituto de Fisica Teorica (IFT), Sao Paulo, SP (Brazil)1991
Instituto de Fisica Teorica (IFT), Sao Paulo, SP (Brazil)1991
AbstractAbstract
[en] Weak-coupling BCS superconductivity theory is shown to admit a more general Tc formula wherein Tc approaches zero somewhat faster than with the BCS Tc formula. This allows some recent empirical values for ceramic superconductors of the gap-to-Tc ratio smaller than the universal BCS value of 3.53 not to be inconsistent with weak electron-boson coupling. Similarly, other universal constants related to specific heat and critical magnetic field will be modified. (author)
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Oct 1991; 15 p
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