V L Ginzburg and the development of experimental work on high-temperature superconductivity at LPI: 'iron superconductors'

Pudalov, V. M.; Omel’yanovskii, O. E.; Хлыбов, Е. П.; Sadakov, A.V.; Eltsev, Yu.; Mitsen, K. V.; Ivanenko, O. M.; Pervakov, K.S.; Gizatulin, D.R.; Usoltsev, A. S.; Dormidontov, A.S.; Gavrilkin, S.Yu.; Tsvetkov, A.Yu.; Ponomarev, Ya. G.; Kuzmichev, S. A.; Mikheev, M. G.; Chesnokov, S.N.; Shanygina, T. E.; Казаков, С. М.

doi:10.3367/ufnr.0181.201106h.0672

Cited by 9 publications

(6 citation statements)

References 54 publications

(4 reference statements)

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“…To the best of our knowledge, until now there are no experimental data on superconducting gaps value in Gd-oxypnictide, excepting our previous works [7,8,9]. As was shown theoretically in [31], the BCS-ratio is nearly independent on T C for oxypnictides.…”

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confidence: 69%

“…Our previous studies established the presence of two distinct superconducting gaps ∆ L = 10.5 ± 2 meV and ∆ S = 2.3 ± 0.4 meV in fluorine-doped GdFeAsO 1−x F x (T bulk C = 53 ± 1 K) [7,8,9]. Here we report temperature dependences of superconducting gaps ∆ L,S (T ) in oxygen-deficient GdFeAsO 0.88 measured by intrinsic multiple Andreev reflections effect (IMARE) spectroscopy of array superconductor -normal metal -superconductor (SnS) contacts.…”

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confidence: 79%

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Multigap Superconductivity in GdFeAsO0.88 Evidenced by SnS-Andreev Spectroscopy

Shanygina

Kuzmichev

Mikheev

et al. 2013

J Supercond Nov Magn

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Using intrinsic multiple Andreev reflection effect (IMARE) spectroscopy we studied superconducting properties of nearly optimal oxygen-deficient GdFeAsO 0.88 polycrystalline samples (bulk critical temperatures T bulk C = 49÷52 K). Temperature dependences for two superconducting gaps ∆ L,S (T ) (T local C = 48 ÷ 50 K) have been measured in the range from 4.2 to 50 K. The ∆ L,S (T ) dependences were found to deviate from the BCS-like function; this suggests an importance of the k-space (internal) proximity effect between the two condensates.GdFeAsO firstly reported in [1] belongs to oxypnictide high-temperature superconductors [2]. The stoichiometric compound is an antiferromagnetic metal with spin-density-wave (SDW) ground state [3], which can be turned into superconductivity under electron doping. The maximal critical temperatures up to T C = 56 K are achieved by O-deficiency, F introducing in-T.E. Shanygina · A.S. Usol'tsev Lebedev Physical Institute RAS,

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confidence: 69%

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confidence: 79%

Multigap Superconductivity in GdFeAsO0.88 Evidenced by SnS-Andreev Spectroscopy

Shanygina

Kuzmichev

Mikheev

et al. 2013

J Supercond Nov Magn

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“…In a case of a multi-gap superconductor several independent SGSs corresponding to the each gap should be observable (see Figs.2-5). Such two distinct SGSs were reported earlier at Andreev spectra of Mg(Al)B 2 break-junctions [33,34,35], LaO 0.9 F 0.1 FeAs [24], GdO(F)FeAs [36,37,38], and FeSe [39]. The main advantage of a symmetrical SNS-contact is that at any T < T C the gap energy can be defined directly from the bias voltages of the peculiarities at the dI/dV -curve making use of the formula (1).…”

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confidence: 78%

“…For the large gap, our experimental data lead to ratio 2∆ L /k B T C = (4.6 ÷ 5.6) which exceeds the standard one 3.52 for single-gap BCS superconductors in the weak coupling limit. At the same time, the BCS-ratio for the small gap 2∆ S /k B T C ≪ 3.52 indicates the superconductivity induced by interband coupling with the "driving" bands (characterized by the large gap ∆ L ) in the bands with ∆ S due to k-space (internal) proximity effect [51] between two condensates, which resembles the situation in Mg(Al)B 2 [33,34,35], and some Fe-based superconductors [24,36,37,38,39].…”

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confidence: 99%

Investigation of LiFeAs by means of “break-junction” technique

et al. 2012

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In our tunneling investigation using Andreev superconductor -normal metal -superconductor contacts on LiFeAs single crystals we observed two reproducible independent subharmonic gap structures at dynamic conductance characteristics. From these results, we can derive the energy of the large superconducting gap ∆L = (2.5 ÷ 3.4) meV and the small gap ∆S = (0.9 ÷ 1) meV at T = 4.2 K for the T local C ≈ (10.5 ÷ 14) K (the contact area critical temperature which deviation causes the variation of ∆L). The BCS-ratio is found to be 2∆L/kBTC = (4.6 ÷ 5.6), whereas 2∆S/kBTC ≪ 3.52 results from induced superconductivity in the bands with the small gap.The new class of superconducting rare-earth oxypnictides [1] is still not completely understood and therefore requires further investigation. The layered LiFeAs (111-system) [2] is one of the few stoichiometric Febased pnictides which shows neither magnetic nor structural transition but becomes superconducting at 18 K [3,4]. Band-structure calculations [5,6,7] show the Fermi surfaces for 111-system to be comprised of quasitwo-dimensional (2D) hole cylinders centered at the Γ-point and electron ones at the M-point of the first Brillouin zone that can be considered as two effective bands (so called minimal two-band model) [8,9]. The total density of states at the Fermi level is formed mainly by Fe 3d-states [10,11,12,13,14]. As was shown in [15], the superconducting transition temperatures T C for different types of iron-based superconductors correlate with the total density of states at the Fermi level. This fact and the strong Fe isotope effect, which was reported by [16] supports the phonon-mediated coupling importance [17] in these compounds [15,18]. The electron-phonon coupling is enhanced by an extended van Hove singularity [19] which was shown for iron pnictides and, in particular, for LiFeAs [20]. In this work, we present an investigation of the superconducting properties of LiFeAs single crystals by means of Andreev spectroscopy of superconductor -normal metal -superconductor (SNS) contacts, and the corresponding superconducting gaps.The LiFeAs single crystals were obtained by self-flux method. The synthesis and investigation of the composition and properties are detailed in [21]. A mixture of small lumps of the Li metal and powders of Fe and As in a molar ratio of Li : Fe : As = 3 : 2 : 3 was 1) e-mail: kuzmichev@mig.phys.msu.ru placed into an alumina crucible. All work on the reactive mixture preparation was carried out in a dry box under argon atmosphere. The crucible was inserted into a niobium container, which was welded in argon at 1.5 atm. The sealed Nb container was enclosed in a quartz ampoule. The sample was heated up to 1363 K, kept at this temperature and slowly cooled down to 873 K. At this temperature ampoule was extracted from the furnace and cooled in open air. The LiFeAs single crystals in the form of thin plates with lateral dimensions of (12 ± 6) × (12 ± 6) × (0.1 ± 0.05) mm 3 were separated from flux mechanically. According to the XRD, EDX, ICP MS, a...

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“…At large values of / J t 2 ³ (which usually are not realized in cuprates) the system becomes unstable towards extended s-wave pairing. For the set electron densities (optimal doping) and the values of / 1/2 J t we get the critical temperature of the d-wave pairing typical for high-TC We would like to summarize here both the early stage [42][43][44][45][46][47][48][49][50][51][52][53] and recent [54][55][56][57][58]…”

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confidence: 99%

Fermi-Bose Mixtures and BCS-BEC Crossover in High-Tc Superconductors

Kagan

Bianconi

2019

Condensed Matter

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In this review article we consider theoretically and give experimental support to the models of the Fermi-Bose mixtures and the BCS-BEC crossover compared with the strong-coupling approach, which can serve as the cornerstones on the way from high-temperature to room-temperature superconductivity in pressurized metallic hydrides. We discuss some key theoretical ideas and mechanisms proposed for unconventional superconductors (), superfluids and balanced or imbalanced ultracold Fermi gases in magnetic traps. We build a bridge between unconventional superconductors and recently discovered pressurized hydrides superconductors H3S and LaH10 with the critical temperature close to room temperature. We discuss systems with line of nodal Dirac points close to the Fermi surface and superconducting shape resonances, and hyperbolic superconducting networks which are very important for the development of novel topological superconductors, for the energetics, for the applications in nano-electronics and quantum computations.

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V L Ginzburg and the development of experimental work on high-temperature superconductivity at LPI: 'iron superconductors'

Cited by 9 publications

References 54 publications

Multigap Superconductivity in GdFeAsO0.88 Evidenced by SnS-Andreev Spectroscopy

Multigap Superconductivity in GdFeAsO0.88 Evidenced by SnS-Andreev Spectroscopy

Investigation of LiFeAs by means of “break-junction” technique

Fermi-Bose Mixtures and BCS-BEC Crossover in High-Tc Superconductors

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