Condensed Matter

284 KiB

Open AccessArticle

Numerical Solution of Maxwell Equations for S-Wave Superconductors

by Naoum Karchev and Tsvetan Vetsov

Condens. Matter 2017, 2(3), 31; https://doi.org/10.3390/condmat2030031 - 15 Sep 2017

Cited by 2 | Viewed by 3284

The present paper is a sequel to the paper by Karchev (Condensed Matter 20 February 2017). We report the numerical solutions of the system of equations, which describes the electrodynamics of s-wave superconductors without normal quasi-particles for time-independent fields and half-plane superconductor geometry. [...] Read more.

The present paper is a sequel to the paper by Karchev (Condensed Matter 20 February 2017). We report the numerical solutions of the system of equations, which describes the electrodynamics of s-wave superconductors without normal quasi-particles for time-independent fields and half-plane superconductor geometry. The results are: (i) the applied magnetic field increases the Ginzburg–Landau (GL) coherence length and suppresses the superconductivity; (ii) the applied electric field decreases GL coherence length and supports the superconductivity; (iii) if the applied magnetic field is fixed and the applied electric field increases, the London penetration depth of the magnetic field decreases. The main conclusion is that by applying electric field at very low temperature where there are no normal quasi-particles one increases the critical magnetic field. This result is experimentally testable. Full article

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1688 KiB

Open AccessReview

In Search of Unambiguous Evidence of the Fulde–Ferrell–Larkin–Ovchinnikov State in Quasi-Low Dimensional Superconductors

by Mihail D. Croitoru and Alexandre I. Buzdin

Condens. Matter 2017, 2(3), 30; https://doi.org/10.3390/condmat2030030 - 11 Sep 2017

Cited by 15 | Viewed by 4713

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 [...] Read more.

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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1915 KiB

Open AccessArticle

Correlated Disorder in Myelinated Axons Orientational Geometry and Structure

by Michael Di Gioacchino, Gaetano Campi, Nicola Poccia and Antonio Bianconi

Condens. Matter 2017, 2(3), 29; https://doi.org/10.3390/condmat2030029 - 11 Sep 2017

Cited by 4 | Viewed by 4160

Abstract

While the ultrastructure of myelin is considered a quasi-crystalline stable system, nowadays its multiscale complex dynamics appear to play a key role in its functionality, degeneration and repair processes following neurological diseases and trauma. In this work, we investigated the fluctuation of the [...] Read more.

While the ultrastructure of myelin is considered a quasi-crystalline stable system, nowadays its multiscale complex dynamics appear to play a key role in its functionality, degeneration and repair processes following neurological diseases and trauma. In this work, we investigated the fluctuation of the myelin supramolecular assembly by measuring the spatial distribution of orientation fluctuations of axons in a Xenopus Laevis sciatic nerve associated with nerve functionality. To this end, we used scanning micro X-ray diffraction (SμXRD), a non-invasive technique that has already been applied to other heterogeneous systems presenting complex geometries from microscale to nanoscale. We found that the orientation of the spatial fluctuations of fresh axons show a Levy flight distribution, which is a clear indication of correlated disorder. We found that the Levy flight distribution was missing in the aged nerve prepared in an unfresh state. This result shows that the spatial distribution of axon orientation fluctuations in unfresh nerve state loses the correlated disorder and assumes a random disorder behavior. This work provides a deeper understanding of the ultrastructure-function nerve relation and paves the way for the study of other materials and biomaterials using the SμXRD technique to detect fluctuations in their supramolecular structure. Full article

(This article belongs to the Special Issue Complex Nanoscale Geometry and Dynamics at the Frontier between Biology and Material Science)

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11896 KiB

Open AccessReview

Superconductivity in 122-Type Pnictides without Iron

by Pan Zhang and Hui-fei Zhai

Condens. Matter 2017, 2(3), 28; https://doi.org/10.3390/condmat2030028 - 23 Aug 2017

Cited by 11 | Viewed by 5564

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 [...] Read more.

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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9778 KiB

Open AccessArticle

Edge Contamination, Bulk Disorder, Flux Front Roughening, and Multiscaling in Type II Superconducting Thin Films

by Michel Geahel, Isabelle Jouanny, Dominique Gorse-Pomonti, Marie Poirier-Quinot, Javier Briatico and Cornelis Jacominus Van der Beek

Condens. Matter 2017, 2(3), 27; https://doi.org/10.3390/condmat2030027 - 21 Aug 2017

Cited by 4 | Viewed by 4568

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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5012 KiB

Open AccessArticle

X-Rays Writing/Reading of Charge Density Waves in the CuO₂ Plane of a Simple Cuprate Superconductor

by Gaetano Campi, Alessandro Ricci, Nicola Poccia, Michela Fratini and Antonio Bianconi

Condens. Matter 2017, 2(3), 26; https://doi.org/10.3390/condmat2030026 - 11 Aug 2017

Cited by 11 | Viewed by 4526

Abstract

It is now well established that superconductivity in cuprates competes with charge modulations giving an electronic phase separation at nanoscale. More specifically, superconducting electronic current takes root in the available free space left by electronic charge ordered domains, called charge density wave (CDW) [...] Read more.

It is now well established that superconductivity in cuprates competes with charge modulations giving an electronic phase separation at nanoscale. More specifically, superconducting electronic current takes root in the available free space left by electronic charge ordered domains, called charge density wave (CDW) puddles. This means that CDW domain arrangement plays a fundamental role in the mechanism of high temperature superconductivity in cuprates. Here we report about the possibility of controlling the population and spatial organization of the charge density wave puddles in a single crystal La₂CuO_4+y through X-ray illumination and thermal treatments. We apply a pump-probe method—based on X-ray illumination as a pump and X-ray diffraction as a probe—setting a writing/reading procedure of CDW puddles. Our findings are expected to allow new routes for advanced design and manipulation of superconducting pathways in new electronics. Full article

(This article belongs to the Special Issue Control and Enhancement of Quantum Coherence in Nanostructured Materials)

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7394 KiB

Open AccessReview

Comparative Review on Thin Film Growth of Iron-Based Superconductors

by Yoshinori Imai, Fuyuki Nabeshima and Atsutaka Maeda

Condens. Matter 2017, 2(3), 25; https://doi.org/10.3390/condmat2030025 - 7 Jul 2017

Cited by 21 | Viewed by 7463

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 [...] Read more.

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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2247 KiB

Open AccessArticle

The Road Map toward Room-Temperature Superconductivity: Manipulating Different Pairing Channels in Systems Composed of Multiple Electronic Components

by Annette Bussmann-Holder, Jürgen Köhler, Arndt Simon, Myung-Hwan Whangbo, Antonio Bianconi and Andrea Perali

Condens. Matter 2017, 2(3), 24; https://doi.org/10.3390/condmat2030024 - 7 Jul 2017

Cited by 18 | Viewed by 5495

Abstract

While it is known that the amplification of the superconducting critical temperature T_C is possible in a system of multiple electronic components in comparison with a single component system, many different road maps for room temperature superconductivity have been proposed for a [...] Read more.

While it is known that the amplification of the superconducting critical temperature T_C is possible in a system of multiple electronic components in comparison with a single component system, many different road maps for room temperature superconductivity have been proposed for a variety of multicomponent scenarios. Here we focus on the scenario where the first electronic component is assumed to have a vanishing Fermi velocity corresponding to a case of the intermediate polaronic regime, and the second electronic component is in the weak coupling regime with standard high Fermi velocity using a mean field theory for multiband superconductivity. This roadmap is motivated by compelling experimental evidence for one component in the proximity of a Lifshitz transition in cuprates, diborides, and iron based superconductors. By keeping a constant and small exchange interaction between the two electron fluids, we search for the optimum coupling strength in the electronic polaronic component which gives the largest amplification of the superconducting critical temperature in comparison with the case of a single electronic component. Full article

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1885 KiB

Open AccessReview

Novel Electronic State and Superconductivity in the Electron-Doped High-T_c T’-Superconductors

by Tadashi Adachi, Takayuki Kawamata and Yoji Koike

Condens. Matter 2017, 2(3), 23; https://doi.org/10.3390/condmat2030023 - 4 Jul 2017

Cited by 24 | Viewed by 5848

Abstract

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, [...] Read more.

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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Condens. Matter, Volume 2, Issue 3 (September 2017) – 9 articles

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