Special Issue "Layered Superconductors"

A special issue of Condensed Matter (ISSN 2410-3896).

Deadline for manuscript submissions: closed (30 September 2017)

Special Issue Editor

Guest Editor
Dr. Yoshikazu Mizuguchi

Department of Electrical and Electronic Engineering, Tokyo Metropolitan University, Hachioji, Tokyo, Japan
Website | E-Mail
Interests: superconductivity, thermoelectric material, new material, low- dimensional material, superconducting wire, crystal structure analysis

Special Issue Information

Dear Colleagues,

Layered superconductors have attracted much attention, due to the emergence of high-Tc and unconventional superconductivity. Thus, the discovery of new layered superconductors and understanding of superconductivity mechanisms are very important for exploring new high-Tc superconductors. In this special issue, we focus on the exploration of novel layered superconductors, such as Fe-based, Bi-based, and Ti-based layered superconductors. In addition, superconducting properties of high quality bulk and thin film samples will be explored in this special issue.

Dr. Yoshikazu Mizuguchi
Guest Editor

Manuscript Submission Information

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Keywords

  • layered superconductor
  • Fe-based superconductor
  • Bi-based superconductor
  • Ti-based superconductor
  • thin film
  • superconducting properties

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Published Papers (12 papers)

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Editorial

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Open AccessEditorial Layered Superconductors
Condens. Matter 2018, 3(1), 4; https://doi.org/10.3390/condmat3010004
Received: 10 January 2018 / Revised: 30 January 2018 / Accepted: 30 January 2018 / Published: 1 February 2018
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Abstract
Since the discovery of cuprates (Cu-oxide superconductors) in 1986 [1–4], layered superconductors have attracted much attention, due to the emergence of high-transition-temperature (high-Tc) and unconventional superconductivity. Full article
(This article belongs to the Special Issue Layered Superconductors)

Research

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Open AccessArticle Single Crystal Growth and Superconducting Properties of Antimony-Substituted NdO0.7F0.3BiS2
Condens. Matter 2018, 3(1), 1; https://doi.org/10.3390/condmat3010001
Received: 25 October 2017 / Revised: 18 December 2017 / Accepted: 19 December 2017 / Published: 27 December 2017
Cited by 1 | PDF Full-text (3655 KB) | HTML Full-text | XML Full-text
Abstract
Antimony (Sb) substitution of less than 8% was examined on a single crystal of a layered superconductor NdO0.7F0.3BiS2. The superconducting transition temperature of the substituted samples decreased as Sb concentration increased. A lattice constant along the c
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Antimony (Sb) substitution of less than 8% was examined on a single crystal of a layered superconductor NdO0.7F0.3BiS2. The superconducting transition temperature of the substituted samples decreased as Sb concentration increased. A lattice constant along the c-axis showed a large decrease compared with that along the a-axis. Since in-plane chemical pressure monotonically decreased as Sb concentration increased, the suppression of the superconductivity is attributed to the decrease in the in-plane chemical pressure. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessArticle Edge Contamination, Bulk Disorder, Flux Front Roughening, and Multiscaling in Type II Superconducting Thin Films
Condens. Matter 2017, 2(3), 27; https://doi.org/10.3390/condmat2030027
Received: 1 July 2017 / Revised: 9 August 2017 / Accepted: 11 August 2017 / Published: 21 August 2017
Cited by 2 | PDF Full-text (9778 KB) | HTML Full-text | XML Full-text
Abstract
We have investigated the effect of different types of disorder on the propagation, roughness, and scaling properties of magnetic flux fronts in a type II superconductor. A progression from the usual (Kardar–Parisi–Zhang-type) scaling to multiscaling is observed as the disorder strength is increased.
[...] Read more.
We have investigated the effect of different types of disorder on the propagation, roughness, and scaling properties of magnetic flux fronts in a type II superconductor. A progression from the usual (Kardar–Parisi–Zhang-type) scaling to multiscaling is observed as the disorder strength is increased. A hierarchy of disorder strengths is established for YBa 2 Cu 3 O 7 δ thin films. The results cast light on the physical origin of the roughening of flux fronts, and they are of interest for the design and elimination of flux noise in microscopic superconducting thin-film devices. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessArticle Time-Correlated Vortex Tunneling in Layered Superconductors
Condens. Matter 2017, 2(2), 21; https://doi.org/10.3390/condmat2020021
Received: 23 May 2017 / Revised: 13 June 2017 / Accepted: 15 June 2017 / Published: 17 June 2017
Cited by 1 | PDF Full-text (6105 KB) | HTML Full-text | XML Full-text
Abstract
The nucleation and dynamics of Josephson and Abrikosov vortices determine the critical currents of layered high-Tc superconducting (HTS) thin films, grain boundaries, and coated conductors, so understanding their mechanisms is of crucial importance. Here, we treat pair creation of Josephson and
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The nucleation and dynamics of Josephson and Abrikosov vortices determine the critical currents of layered high-Tc superconducting (HTS) thin films, grain boundaries, and coated conductors, so understanding their mechanisms is of crucial importance. Here, we treat pair creation of Josephson and Abrikosov vortices in layered superconductors as a secondary Josephson effect. Each full vortex is viewed as a composite fluid of micro-vortices, such as pancake vortices, which tunnel coherently via a tunneling matrix element. We introduce a two-terminal magnetic (Weber) blockade effect that blocks tunneling when the applied current is below a threshold value. We simulate vortex tunneling as a dynamic, time-correlated process when the current is above threshold. The model shows nearly precise agreement with voltage-current (V-I) characteristics of HTS cuprate grain boundary junctions, which become more concave rounded as temperature decreases, and also explains the piecewise linear V-I behavior observed in iron-pnictide bicrystal junctions and other HTS devices. When applied to either Abrikosov or Josephson pair creation, the model explains a plateau seen in plots of critical current vs. thickness of HTS-coated conductors. The observed correlation between theory and experiment strongly supports the proposed quantum picture of vortex nucleation and dynamics in layered superconductors. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessArticle Magnetoresistance, Gating and Proximity Effects in Ultrathin NbN-Bi2Se3 Bilayers
Condens. Matter 2017, 2(2), 14; https://doi.org/10.3390/condmat2020014
Received: 8 March 2017 / Revised: 19 April 2017 / Accepted: 21 April 2017 / Published: 25 April 2017
Cited by 3 | PDF Full-text (540 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Ultrathin Bi2Se3-NbN bilayers comprise a simple proximity system of a topological insulator and an s-wave superconductor for studying gating effects on topological superconductors. Here we report on 3 nm thick NbN layers of weakly connected superconducting islands, overlayed with
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Ultrathin Bi 2 Se 3 -NbN bilayers comprise a simple proximity system of a topological insulator and an s-wave superconductor for studying gating effects on topological superconductors. Here we report on 3 nm thick NbN layers of weakly connected superconducting islands, overlayed with 10 nm thick Bi 2 Se 3 film which facilitates enhanced proximity coupling between them. Resistance versus temperature of the most resistive bilayers shows insulating behavior but with signs of superconductivity. We measured the magnetoresistance (MR) of these bilayers versus temperature with and without a magnetic field H normal to the wafer (MR = [R(H) − R(0)]/{[R(H) + R(0)]/2}), and under three electric gate-fields of 0 and ± 2 MV/cm. The MR results showed a complex set of gate sensitive peaks which extended up to about 30 K. The results are discussed in terms of vortex physics, and the origin of the different MR peaks is identified and attributed to flux-flow MR in the isolated NbN islands and the different proximity regions in the Bi 2 Se 3 cap-layer. The dominant MR peak was found to be consistent with enhanced proximity induced superconductivity in the topological edge currents regions. The high temperature MR data suggest a possible pseudogap phase or a highly extended fluctuation regime. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessArticle Discovery of BiS2-Based Superconductor and Material Design Concept
Condens. Matter 2017, 2(1), 6; https://doi.org/10.3390/condmat2010006
Received: 25 November 2016 / Accepted: 26 January 2017 / Published: 31 January 2017
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Abstract
In 2012, we discovered new layered superconductors whose superconducting states emerge in the BiS2 layers. Since their crystal structure, composed of alternate stacks of BiS2 conduction layers and electrically insulating (blocking) layers, is similar to those of cuprate and Fe-based superconductors, many researchers
[...] Read more.
In 2012, we discovered new layered superconductors whose superconducting states emerge in the BiS2 layers. Since their crystal structure, composed of alternate stacks of BiS2 conduction layers and electrically insulating (blocking) layers, is similar to those of cuprate and Fe-based superconductors, many researchers have explored new BiS2-based superconductors and have studied the physical and chemical properties of the BiS2-based superconductors. In this paper, we present the histories of the discovery of the first BiS2-based superconductor, Bi4O4S3, and the second one, LaO1−xFxBiS2. The structural variation of the BiS2-based superconductor family is briefly introduced. Then, we show the material design concept for the emergence of bulk superconductivity in BiS2-based compounds. At the end, a possible strategy for the enhancement of the transition temperature in the BiS2-based superconductors is proposed. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Review

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Open AccessReview Crystal Growth Techniques for Layered Superconductors
Condens. Matter 2017, 2(4), 32; https://doi.org/10.3390/condmat2040032
Received: 23 August 2017 / Revised: 12 September 2017 / Accepted: 16 October 2017 / Published: 16 October 2017
Cited by 1 | PDF Full-text (3558 KB) | HTML Full-text | XML Full-text
Abstract
Layered superconductors are attractive because some of them show high critical temperatures. While their crystal structures are similar, these compounds are composed of many elements. Compounds with many elements tend to be incongruent melting compounds, thus, their single crystals cannot be grown via
[...] Read more.
Layered superconductors are attractive because some of them show high critical temperatures. While their crystal structures are similar, these compounds are composed of many elements. Compounds with many elements tend to be incongruent melting compounds, thus, their single crystals cannot be grown via the melt-solidification process. Hence, these single crystals have to be grown below the decomposition temperature, and then the flux method, a very powerful tool for the growth of these single crystals with incongruent melting compounds, is used. This review shows the flux method for single-crystal growth technique by self-flux, chloride-based flux, and HPHT (high-pressure and high-temperature) flux method for many-layered superconductors: high-Tc cuprate, Fe-based and BiS2-based compounds. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessReview In Search of Unambiguous Evidence of the Fulde–Ferrell–Larkin–Ovchinnikov State in Quasi-Low Dimensional Superconductors
Condens. Matter 2017, 2(3), 30; https://doi.org/10.3390/condmat2030030
Received: 9 August 2017 / Revised: 1 September 2017 / Accepted: 4 September 2017 / Published: 11 September 2017
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Abstract
In layered conductors with a sufficiently weak interlayer coupling in-plane magnetic field cause only small diamagnetic currents and the orbital depairing is strongly suppressed. Therefore, the Zeeman effect predominantly governs the spin-singlet superconductivity making the formation of the spatially modulated Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase
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In layered conductors with a sufficiently weak interlayer coupling in-plane magnetic field cause only small diamagnetic currents and the orbital depairing is strongly suppressed. Therefore, the Zeeman effect predominantly governs the spin-singlet superconductivity making the formation of the spatially modulated Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase possible in such materials. Despite decades of strenuous effort, this state still remains a profound mystery. In the last several years, however, there have been observed several hints indicating the experimental realization of the FFLO state in organic layered superconductors. The emergence of the FFLO phase has been demonstrated mainly based on thermodynamic quantities or microscopically with spin polarization distribution that exhibit anomalies within the superconducting state in the presence of the in-plane magnetic field. However, the direct observation of superconducting order parameter modulation is so far missing. Recently, there have been proposed theoretically several hallmark signatures for FFLO phase, which are a direct consequence of its main feature, the spatial modulation of the order parameter, and hence can provide incontrovertible evidence of FFLO. In this article, a review of these signatures and the underlying theoretical framework is given with the purpose to summarize the results obtained so far, omitting duplications, and to emphasize the ideas and physics behind them. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessReview Superconductivity in 122-Type Pnictides without Iron
Condens. Matter 2017, 2(3), 28; https://doi.org/10.3390/condmat2030028
Received: 1 August 2017 / Revised: 22 August 2017 / Accepted: 23 August 2017 / Published: 23 August 2017
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Abstract
The exploration of superconducting iron-free pnictides with a ThCr2Si2-type or related structure and the study of their superconducting properties are important in order to get a deeper understanding of the pairing mechanism of 122 iron pnictides. Here we review
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The exploration of superconducting iron-free pnictides with a ThCr2Si2-type or related structure and the study of their superconducting properties are important in order to get a deeper understanding of the pairing mechanism of 122 iron pnictides. Here we review the properties of 122-type iron-free pnictides superconductors with structures similar to that of BaFe2As2. Evidence of fully gapped nature of superconducting state has come from the specific heat and thermal conductivity measurements for BaNi2As2 and SrNi2P2, and nuclear magnetic and quadrupole resonance measurements for CaPd2As2 etc. Combined with the fact that no magnetism is observed in 122-type iron-free pnictides superconductors, the majority of evidence suggests that most of these compounds are conventional electron–phonon-mediated superconductors. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessReview Comparative Review on Thin Film Growth of Iron-Based Superconductors
Condens. Matter 2017, 2(3), 25; https://doi.org/10.3390/condmat2030025
Received: 3 April 2017 / Revised: 30 June 2017 / Accepted: 3 July 2017 / Published: 7 July 2017
Cited by 4 | PDF Full-text (7394 KB) | HTML Full-text | XML Full-text
Abstract
Since the discovery of the novel iron-based superconductors, both theoretical and experimental studies have been performed intensively. Because iron-based superconductors have a smaller anisotropy than high-Tc cuprates and a high superconducting transition temperature, there have been a lot of researchers working on the
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Since the discovery of the novel iron-based superconductors, both theoretical and experimental studies have been performed intensively. Because iron-based superconductors have a smaller anisotropy than high-Tc cuprates and a high superconducting transition temperature, there have been a lot of researchers working on the film fabrication of iron-based superconductors and their application. Accordingly, many novel features have been reported in the films of iron-based superconductors, for example, the fabrication of the epitaxial film with a higher Tc than bulk samples, the extraction of the metastable phase which cannot be obtained by the conventional solid state reaction, and so on. In this paper, we review the progress of research on thin film fabrications of iron-based superconductors, especially the four categories: LnFeAs(O,F) (Ln = Lanthanide), AEFe2As2 (AE = Alkaline-earth metal), FeCh (Ch = Chalcogen), and FeSe monolayer. Furthermore, we focus on two important topics in thin films of iron-based superconductors; one is the substrate material for thin film growth on the iron-based superconductors, and the other is the whole phase diagram in FeSe1-xTex which can be obtained only by using film-fabrication technique. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessReview Novel Electronic State and Superconductivity in the Electron-Doped High-Tc T’-Superconductors
Condens. Matter 2017, 2(3), 23; https://doi.org/10.3390/condmat2030023
Received: 28 April 2017 / Revised: 27 June 2017 / Accepted: 27 June 2017 / Published: 4 July 2017
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Abstract
In this review article, we show our recent results relating to the undoped (Ce-free) superconductivity in the electron-doped high-Tc cuprates with the so-called T’ structure. For an introduction, we briefly mention the characteristics of the electron-doped T’-cuprates, including the reduction annealing,
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In this review article, we show our recent results relating to the undoped (Ce-free) superconductivity in the electron-doped high- T c cuprates with the so-called T’ structure. For an introduction, we briefly mention the characteristics of the electron-doped T’-cuprates, including the reduction annealing, conventional phase diagram and undoped superconductivity. Then, our transport and magnetic results and results relating to the superconducting pairing symmetry of the undoped and underdoped T’-cuprates are shown. Collaborating spectroscopic and nuclear magnetic resonance results are also shown briefly. It has been found that, through the reduction annealing, a strongly localized state of carriers accompanied by an antiferromagnetic pseudogap in the as-grown samples changes to a metallic and superconducting state with a short-range magnetic order in the reduced superconducting samples. The formation of the short-range magnetic order due to a very small amount of excess oxygen in the reduced superconducting samples suggests that the T’-cuprates exhibiting the undoped superconductivity in the parent compounds are regarded as strongly correlated electron systems, as well as the hole-doped high- T c cuprates. We show our proposed electronic structure model to understand the undoped superconductivity. Finally, unsolved future issues of the T’-cuprates are discussed. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessReview Titanium Pnictide Oxide Superconductors
Condens. Matter 2017, 2(1), 4; https://doi.org/10.3390/condmat2010004
Received: 1 December 2016 / Revised: 30 December 2016 / Accepted: 3 January 2017 / Published: 12 January 2017
Cited by 3 | PDF Full-text (10545 KB) | HTML Full-text | XML Full-text
Abstract
In 2012, a novel superconductor BaTi2Sb2O was found in the layered titanium pnictide oxides ATi2Pn2O. A related superconductor BaTi2Bi2O was subsequently discovered in 2013. The structure of these materials consists
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In 2012, a novel superconductor BaTi2Sb2O was found in the layered titanium pnictide oxides ATi2Pn2O. A related superconductor BaTi2Bi2O was subsequently discovered in 2013. The structure of these materials consists of alternate stacking of superconducting Ti2Pn2O layers and Ba blocking layers, which is somewhat similar to high-Tc cuprates since the Ti2Pn2O layer contains an anti-CuO2-type Ti2O square lattice. In addition to the structural similarity to the well-known high-Tc superconductors, BaTi2Pn2O shows unique physical properties: two superconducting domes appear in the electronic phase diagram for solid solutions of BaTi2(Sb1‒xBix)2O and a unique density-wave instability which coexists with superconductivity. In this short review, the early studies of titanium pnictide oxides, the discovery of novel superconductors BaTi2Pn2O, and recent progress are summarized. Full article
(This article belongs to the Special Issue Layered Superconductors)
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