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Sample records for gd123 bulk superconductors

  1. Effect of addition of soft magnetic alloy particles on the flux trapping in Gd123 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Tsuzuki, K.; Zhang, Y.; Kimura, Y.; Izumi, M.

    2010-06-01

    Pinning stability and the introduction of magnetic flux pinning is an essential problem in applications of high-Tc superconductors. Study on the role of addition of a variety of metal oxides into GdBa2Cu3O7-δ (Gd123) bulk superconductors was carried out. We found that the addition of 0.05 wt. % of soft magnetic alloy particles Fe-Cu-Nb-Si-Cr-B (Fe-B) into the Gd123 contributes to the enhancement of the critical current density (Jc) under a wide range of applied magnetic fields up to 3 T. The Fe-B particles refined less than 10 μm by ball milling indicate no remarkable contribution on the Jc under the magnetic field. The reduction of the Ba content resulted in the appearance of a peak of Jc which has been observed in the Gd/Ba solid solution with rich Ba content. These results let us discriminate the effect of the magnetic particles from other conventional flux pinning mechanism. The peak of Jc under magnetic field was not only observed in the part along the c-axis under the seed of the sample but also in the growth sector around the periphery of the Gd123 bulk with Fe-B addition. It indicates that the magnetic particles inclusions play an important role on the homogeneous enhancement of Jc and the high flux pinning performance.

  2. Enhanced flux pinning in GdBaCuO bulk superconductors by Zr dopants

    NASA Astrophysics Data System (ADS)

    Xu, C.; Hu, A.; Ichihara, M.; Sakai, N.; Izumi, M.; Hirabayashi, I.

    2007-10-01

    We, respectively, fabricated GdBa2Cu3O7-δ (Gd123) single domain superconductors by melt growth process in air with Gd2Ba4CuZrOx (GdZr2411) and nanosize ZrO2 dopants. The microstructures and superconducting properties were investigated by scanning/transmission electron microscopy (SEM/TEM) and SQUID. GdZr2411 and BaZrO3 particles with the average size of 50 nm were observed in the GdZr2411 and nanosize ZrO2 doped Gd123 bulks by TEM, respectively. Critical current density (Jc) was enhanced up to 100,000 A/cm2 at 77 K and self-field with 0.4 mol% nano-sized ZrO2. The present study also showed that small amount GdZr2411 dopants (8 mol%, ratio to Gd123) were effective to induce a δTc-type pinning.

  3. Large area bulk superconductors

    DOEpatents

    Miller, Dean J.; Field, Michael B.

    2002-01-01

    A bulk superconductor having a thickness of not less than about 100 microns is carried by a polycrystalline textured substrate having misorientation angles at the surface thereof not greater than about 15.degree.; the bulk superconductor may have a thickness of not less than about 100 microns and a surface area of not less than about 50 cm.sup.2. The textured substrate may have a thickness not less than about 10 microns and misorientation angles at the surface thereof not greater than about 15.degree.. Also disclosed is a process of manufacturing the bulk superconductor and the polycrystalline biaxially textured substrate material.

  4. Bulk Superconductors in Mobile Application

    NASA Astrophysics Data System (ADS)

    Werfel, F. N.; Delor, U. Floegel-; Rothfeld, R.; Riedel, T.; Wippich, D.; Goebel, B.; Schirrmeister, P.

    We investigate and review concepts of multi - seeded REBCO bulk superconductors in mobile application. ATZ's compact HTS bulk magnets can trap routinely 1 T@77 K. Except of magnetization, flux creep and hysteresis, industrial - like properties as compactness, power density, and robustness are of major device interest if mobility and light-weight construction is in focus. For mobile application in levitated trains or demonstrator magnets we examine the performance of on-board cryogenics either by LN2 or cryo-cooler application. The mechanical, electric and thermodynamical requirements of compact vacuum cryostats for Maglev train operation were studied systematically. More than 30 units are manufactured and tested. The attractive load to weight ratio is more than 10 and favours group module device constructions up to 5 t load on permanent magnet (PM) track. A transportable and compact YBCO bulk magnet cooled with in-situ 4 Watt Stirling cryo-cooler for 50 - 80 K operation is investigated. Low cooling power and effective HTS cold mass drives the system construction to a minimum - thermal loss and light-weight design.

  5. Recent developments in melt processed Gd-123 and MgB2 materials at RTRI

    NASA Astrophysics Data System (ADS)

    Muralidhar, M.; Fukumoto, Y.; Ishihara, A.; Suzuki, K.; Tomita, M.; Koblischka, M. R.; Yamamoto, A.; Kishio, K.

    2014-01-01

    In this contribution we will report on the current status, recent developments in GdBa2Cu3Oy "Gd-123" and MgB2 material processing, characterization, and applications at the Railway Technical Research Institute (RTRI). Batch-processing of Gd-123 bulk material grown in air was performed using novel thin film Nd-123 seeds grown on MgO crystals. In this way, we are able to fabricate materials with good quality, and uniform performance. We examined the technology of the uniform performance of the large 45 mm diameter, single grain Gd-123 bulks for use in application of NMR. For this purpose, four 5 mm thick pieces are cut vertically from a single grain Gd-123 material and the magnetic field distribution is measured using a scanning hall sensor. We found that all four pieces are single domain and exhibit a quite uniform field distribution. Furthermore, the batch-processed bulk materials are used for the construction of a chilled Maglev vehicle. On the other hand, to optimize the trapped field performance of bulk MgB2 material, several samples were prepared by solid state reaction at different temperatures ranging from 750 to 950 °C in pure argon atmosphere. X-ray diffraction results indicated that single phase and homogenous MgB2 bulks are produced when sintering them around 775 °C. Further, atomic force microscopy (AFM) and scanning electron microscopy (SEM) indicated that an uniform grain size results by controlling the processing temperature. So, higher trapped fields can be achieved in sintered MgB2 material.

  6. Applications of bulk high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Hull, J. R.

    The development of high-temperature superconductors (HTS's) can be broadly generalized into thin-film electronics, wire applications, and bulk applications. We consider bulk HTS's to include sintered or crystallized forms that do not take the geometry of filaments or tapes, and we discuss major applications for these materials. For the most part applications may be realized with the HTS's cooled to 77 K, and the properties of the bulk HTS's are often already sufficient for commercial use. A non-exhaustive list of applications for bulk HTS's includes trapped field magnets, hysteresis motors, magnetic shielding, current leads, and magnetic bearings. These applications are briefly discussed in this paper.

  7. Transmission Electron Microscopy and Atomic Force Microscopy Observation of Air-Processed GdBa2Cu3O7-δ Superconductors Doped with Metal Oxide Nanoparticles (Metal = Zr, Zn, and Sn)

    NASA Astrophysics Data System (ADS)

    Xu, Caixuan; Hu, Anming; Ichihara, Masaki; Izumi, Mitsuru; Xu, Yan; Sakai, Naomichi; Hirabayashi, Izumi

    2009-02-01

    Single-domain, c-axis-oriented 30-mm-diameter GdBa2Cu3O7-δ (Gd123) melt-textured bulk superconductors have been successfully grown by the top-seeded melt growth method from precursors of Gd123, Gd2BaCuO5, and Ag2O in air with doping of nanosized ZrO2, ZnO, or SnO2. Transmission electron microscopy (TEM) unveils a large amount of BaZrO3 or BaSnO3 particles with an average diameter of approximately 50 nm respectively embedded in ZrO2 or SnO2 doped samples, while no Zn-rich nanoparticles are observed in the ZnO-doped samples. The critical temperature Tc is almost unchanged up to a doping amount of 10 mol % for ZrO2- or SnO2-doped Gd123 melt-textured bulks, while ZnO-doped Gd123 becomes non-superconductive at this doping level. By atomic force microscopy (AFM), nanostripes with a wavelength of 15 nm are observed in the ZnO-doped Gd123 sample. Nanoscale particles in the grown Gd123 single domain, together with the micro-defects induced by nanoparticle doping, can account for the enhanced superconducting properties.

  8. Characterization of bulk superconductors through EBSD methods

    NASA Astrophysics Data System (ADS)

    Koblischka, M. R.; Koblischka-Veneva, A.

    2003-10-01

    The application of electron backscatter diffraction (EBSD) technique to bulk high- Tc superconductors is presented and reviewed. Due to the ceramic nature and the complex crystallographic unit cells of the perovskite-type high- Tc superconductors, the EBSD analysis is not yet as common as it deserves. We have successfully performed EBSD analysis on a variety of high- Tc compounds and samples including polycrystalline YBCO (pure and doped by alkali metals), melt-textured YBCO, thin and thick films of YBCO; the “green phase” Y 2BaCuO 5, thin film and melt-textured NdBa 2Cu 3O x and Bi-2212 single crystals and tapes. It is shown that the surface preparation of the samples is crucial due to the small information depth (up to 100 nm) of the EBSD technique. High quality Kikuchi patterns are the requirement in order to enable the automated EBSD mapping, which yields phase distributions, individual grain orientations and the misorientation angle distribution. The results can be presented in form of mappings, as charts, and as pole figures. These informations are required for a better understanding of the growth mechanism(s) of bulk high- Tc superconductors intended for applications.

  9. Characteristics of an electromagnetic levitation system using a bulk superconductor

    SciTech Connect

    Senba, A.; Kitahara, H.; Ohsaki, H.; Masada, E.

    1996-09-01

    It is beneficial to apply a high-Tc bulk superconductor as a large flux source to an electromagnetic levitation system, which needs large amounts of levitation force. The authors made an attractive-type electromagnetic levitation system using a hybrid magnet that mainly consisted of bulk superconductor and control coils to confirm the principle of the levitation, and obtained characteristics of its system by both experiment and numerical analysis with magnetic circuit calculation. This is applicable to maglev transportation systems.

  10. Factors affecting characterization of bulk high-temperature superconductors

    SciTech Connect

    Hull, J.R.

    1997-11-01

    Three major factors affect the characterization of bulk high-temperature superconductors in terms of their levitation properties during interaction with permanent magnets. First, the appropriate parameter for the permanent magnet is internal magnetization, not the value of the magnetic field measured at the magnet`s surface. Second, although levitation force grows with superconductor thickness and surface area, for a given permanent magnet size, comparison of levitation force between samples is meaningful when minimum values are assigned to the superconductor size parameters. Finally, the effect of force creep must be considered when time-averaging the force measurements. In addition to levitational force, the coefficient of friction of a levitated rotating permanent magnet may be used to characterize the superconductor.

  11. Materials processing and machine applications of bulk HTS

    NASA Astrophysics Data System (ADS)

    Miki, M.; Felder, B.; Tsuzuki, K.; Xu, Y.; Deng, Z.; Izumi, M.; Hayakawa, H.; Morita, M.; Teshima, H.

    2010-12-01

    We report a refrigeration system for rotating machines associated with the enhancement of the trapped magnetic flux of bulk high-temperature superconductor (HTS) field poles. A novel cryogenic system was designed and fabricated. It is composed of a low-loss rotary joint connecting the rotor and a closed-cycle thermosiphon under a GM cryocooler using a refrigerant. Condensed neon gas was adopted as a suitable cryogen for the operation of HTS rotating machines with field poles composed of RE-Ba-Cu-O family materials, where RE is a rare-earth metal. Regarding the materials processing of the bulks HTS, thanks to the addition of magnetic particles to GdBa2Cu3O7 - d (Gd123) bulk superconductors an increase of more than 20% in the trapped magnetic flux density was achieved at liquid nitrogen temperature. Field-pole Gd123 bulks up to 46 mm in diameter were synthesized with the addition of Fe-B alloy magnetic particles and assembled into the synchronous machine rotor to be tested. Successful cooling of the magnetized rotor field poles down to 35 K and low-output-power rotating operation was achieved up to 720 rpm in the test machine with eight field-pole bulks. The present results show a substantial basis for making a prototype system of rotating machinery of applied HTS bulks.

  12. Al addition effect of bulk MgB 2 superconductor

    NASA Astrophysics Data System (ADS)

    Shinohara, K.; Ikeda, H.; Yoshizaki, R.

    2007-10-01

    The properties of transport and magnetization have been investigated for bulk MgB2Alx superconductor with Al addition (x = 0, 0.5, 1 wt%). MgB2 bulk samples sintered at different temperatures at 650-740 °C were prepared in the undoped state. The temperature and applied field dependencies of resistivity and magnetization were measured for the samples. The sample sintered at 690 °C exhibited the highest critical current density (Jc) and the lowest resistivity. This undoped sample was chosen as a criterion sample, and the effect of Al addition on the MgB2 bulk was studied from the transport and magnetization properties in a magnetic field. For MgB2Alx bulk samples sintered at 690 °C, the resistivity increased and Jc decreased as amount of Al was increased.

  13. Permanent magnet with MgB{sub 2} bulk superconductor

    SciTech Connect

    Yamamoto, Akiyasu; Ishihara, Atsushi; Tomita, Masaru; Kishio, Kohji

    2014-07-21

    Superconductors with persistent zero-resistance currents serve as permanent magnets for high-field applications requiring a strong and stable magnetic field, such as magnetic resonance imaging. The recent global helium shortage has quickened research into high-temperature superconductors (HTSs)—materials that can be used without conventional liquid-helium cooling to 4.2 K. Herein, we demonstrate that 40-K-class metallic HTS magnesium diboride (MgB{sub 2}) makes an excellent permanent bulk magnet, maintaining 3 T at 20 K for 1 week with an extremely high stability (<0.1 ppm/h). The magnetic field trapped in this magnet is uniformly distributed, as for single-crystalline neodymium-iron-boron. Magnetic hysteresis loop of the MgB{sub 2} permanent bulk magnet was determined. Because MgB{sub 2} is a simple-binary-line compound that does not contain rare-earth metals, polycrystalline bulk material can be industrially fabricated at low cost and with high yield to serve as strong magnets that are compatible with conventional compact cryocoolers, making MgB{sub 2} bulks promising for the next generation of Tesla-class permanent-magnet applications.

  14. Magnetic lenses using different MgB2 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Z. Y.; Choi, S.; Matsumoto, S.; Teranishi, R.; Giunchi, G.; Figini Albisetti, A.; Kiyoshi, T.

    2012-02-01

    A magnetic lens allows the concentration of magnetic fields using the diamagnetism of superconductors. The important features of the magnetic lens are a tapered inner diameter from which the magnetic flux is extruded and a slit to suppress the circumference current that shields the magnetic flux. This concept was experimentally confirmed through the use of GdBaCuO bulks and a stack of NbTi/Nb/Cu sheets. We refer to this arrangement as a magnetic lens. The Mg-reactive liquid infiltration (Mg-RLI) process developed by Edison SpA is suitable for the production of large and high-density MgB2 bulks. Three MgB2 bulk magnetic lenses, each with a different microstructure, were fabricated following the Mg-RLI process. The properties of the MgB2 magnetic lenses were measured in a cryocooler system as well as in liquid helium. The results confirmed that the MgB2 bulk magnetic lenses could concentrate a magnetic field and that their field concentration properties were greatly affected by the temperature and the external field. In addition, the microstructure of the MgB2 bulk also had an influence on the magnetic properties at different external fields. The results indicated that the MgB2 lens might be utilized as a field amplifier in intermediate fields.

  15. Bulk Topological Insulators and Superconductors: Discovery and the new Frontiers

    NASA Astrophysics Data System (ADS)

    Hasan, M. Zahid

    2011-03-01

    While most known phases of matter are characterized by broken symmetries, the discovery of quantum Hall effects (1980s) revealed that there exists an organizational principle based on topology rather than broken symmetry. In the past few years, theory and experiments have suggested that new types of topological states of matter exist in certain bulk insulators without any applied magnetic field. These topological insulators are characterized by a full band gap in their bulk and gap-less conducting edge or surface states protected by time-reversal symmetry. Unlike the quantum Hall systems, the bulk 3D topological insulators can be doped into superconductors and magnets revealing the interplay between topological-order and broken-symmetry-order [Rev. Mod. Phys 82, 3045 (2010)]. In this talk, I will highlight the experimental observations and focus on recent experimental developments on bulk topological insulators. I will then draw connections between the topological physics and their potential applications in electronics and the emergent new frontiers in fundamental physics. Work in collaboration with D. Hsieh, Y. Xia, L. Wray, D. Qian, C.L. Kane, H. Lin, A. Bansil, D. Grauer, R.J. Cava, Y.S. Hor, J. H. Dil, F. Meier, L. Patthey, J. Osterwalder, A.V. Fedorov.

  16. Effect of nonsuperconducting particles on the effective magnetostriction of bulk superconductors

    NASA Astrophysics Data System (ADS)

    Yong, Hua-Dong; Zhou, You-He

    2008-08-01

    In this article, the dependence of effective magnetostriction of the bulk superconductors on the parameters including the elastic moduli and volume fraction is investigated. For a bulk superconductor of nonsuperconducting particles dispersed in a superconducting matrix, a simple and approximate model for effective magnetostriction is described. Based on the plane strain approach, the two-dimensional magnetostriction is obtained by implementing the continuity conditions of displacement and stress at the interface between the particle and the matrix. The results obtained show that the elastic moduli and volume fraction have obvious effects on the magnetostriction of bulk superconductors, which may explain why the experimental and the theoretical results have small differences.

  17. Magnetic Signals of High-Temperature Superconductor Bulk During the Levitation Force Measurement Process

    NASA Astrophysics Data System (ADS)

    Huang, Huan; Zheng, Jun; Qian, Nan; Che, Tong; Zheng, Botian; Jin, Liwei; Deng, Zigang

    2017-02-01

    In order to study the commonly neglected magnetic field information in the course of levitation force measurement process in a superconducting maglev system, a multipoint magnetic field measurement platform was employed to acquire magnetic signals of a bulk high-Tc superconductor on both the top and the bottom surface. Working conditions including field cooling (FC) and zero field cooling were investigated for these vertical down and up motions above a permanent magnet guideway performed on a HTS maglev measurement system. We have discussed the magnetic flux variation process based on the Bean model. A magnetic hysteresis effect similar to the levitation force hysteresis loop of the bulk superconductor was displayed and analyzed in this paper. What is more valuable, there exists some available magnetic flux on the top surface of the bulk superconductor, and the proportion is as high as 62.42% in the FC condition, which provides an experimental hint to design the superconductor bulk and the applied field for practical use in a more efficient way. In particular, this work reveals real-time magnetic flux variation of the bulk superconductor in the levitation application, which is the other important information in contrast to the macroscopic levitation and guidance force investigations in previous studies, and it enriches the existing research methods. The results are significant for understanding the magnetic characteristic of superconductors, and they can contribute to optimize the present HTS maglev system design.

  18. Superconductors, analysis and applications, with special reference to the utilisation of bulk (Re)BCO materials

    NASA Astrophysics Data System (ADS)

    Coombs, T. A.

    2010-11-01

    The Electrical Power and Energy Conversion (EPEC) superconductivity group at Cambridge University has been working on the application of superconductivity to large scale devices. This work is taking place over a range of areas which cover FCLs, motors and generators, SMES, accelerator magnets and MRI. The research is underpinned by advanced modelling techniques using both pure Critical State models and E-J models to analyse the behaviour of the superconductors. As part of the device design we are concentrating on the analysis of AC losses in complicated geometries such as are found in motor windings and the magnetisation of bulk superconductors to enable their full potential to be realised. We are interested in the full range of high-temperature superconductors and have measured and predicted the performance of YBCO, MgB2 and BSCCO at a range of temperatures and in wire, tape and bulk forms. This paper concentrates on recent work which includes: modelling of coils using formulations based on H and A. A critical state model for the analysis of coils in SMES; crossed field effects in bulk superconductors; a magnetic model together with experimental results which explain and describe the method of flux pumping whereby a bulk superconductor can be magnetised to a high flux density using a repeatedly applied field of low flux density and finally a new configuration for MRI magnets

  19. Development of superconducting magnetic bearing with superconducting coil and bulk superconductor for flywheel energy storage system

    NASA Astrophysics Data System (ADS)

    Arai, Y.; Seino, H.; Yoshizawa, K.; Nagashima, K.

    2013-11-01

    We have been developing superconducting magnetic bearing for flywheel energy storage system to be applied to the railway system. The bearing consists of a superconducting coil as a stator and bulk superconductors as a rotor. A flywheel disk connected to the bulk superconductors is suspended contactless by superconducting magnetic bearings (SMBs). We have manufactured a small scale device equipped with the SMB. The flywheel was rotated contactless over 2000 rpm which was a frequency between its rigid body mode and elastic mode. The feasibility of this SMB structure was demonstrated.

  20. Sintering of bulk high- Tc superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B. ); Nash, A.S. )

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  1. Sintering of bulk high-{Tc} superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B.; Nash, A.S.

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  2. Concepts for using trapped-flux bulk high-temperature superconductor in motors and generators

    NASA Astrophysics Data System (ADS)

    Hull, John R.; Strasik, Michael

    2010-12-01

    We review previous concepts for using bulk high-temperature superconductors (HTSs) in motors and generators and discuss methods for using trapped-flux (TF) HTSs in motors and generators that have been recently investigated in our laboratory. We examine the expected performance of a brushless motor/generator that uses TF bulk HTSs to provide magnetomotive force, where the stator windings are used to create the TF. A key feature is the use of dysprosium for the stator and rotor cores.

  3. A superconducting conveyer system using multiple bulk Y-Ba-Cu-O superconductors and permanent magnets

    NASA Astrophysics Data System (ADS)

    Kinoshita, T.; Koshizuka, N.; Nagashima, K.; Murakami, M.

    Developments of non-contact superconducting devices like superconducting magnetic levitation transfer and superconducting flywheel energy storage system have been performed based on the interactions between bulk Y-Ba-Cu-O superconductors and permanent magnets, in that the superconductors can stably be levitated without any active control. The performances of noncontact superconducting devices are dependent on the interaction forces like attractive forces and stiffness. In the present study, we constructed a non-contact conveyer for which the guide rails were prepared by attaching many Fe-Nd-B magnets onto an iron base plate. Along the translational direction, all the magnets were arranged as to face the same pole, and furthermore their inter-distance was made as small as possible. The guide rail has three magnet rows, for which the magnets were glued on the iron plate such that adjacent magnet rows have opposite poles like NSN. At the center row, the magnetic field at zero gap reached 0.61T, while the field strengths of two rows on the side edges were only 0.48T due to magnetic interactions among permanent magnets. We then prepared a cryogenic box made with FRP that can store several bulk Y-Ba-Cu-O superconductors 25 mm in diameter cooled by liquid nitrogen. It was found that the levitation forces and stiffness increased with increasing the number of bulk superconductors installed in the box, although the levitation force per unit bulk were almost the same. We also confirmed that these forces are dependent on the configuration of bulk superconductors.

  4. New method for introducing nanometer flux pinning centers into single domain YBCO bulk superconductors

    NASA Astrophysics Data System (ADS)

    Yang, W. M.; Wang, Miao

    2013-10-01

    Single domain YBCO superconductors with different additions of Bi2O3 have been fabricated by top seeded infiltration and growth process (TSIG). The effect of Bi2O3 additions on the growth morphology, microstructure and levitation force of the YBCO bulk superconductor has been investigated. The results indicate that single domain YBCO superconductors can be fabricated with the additions of Bi2O3 less than 2 wt%; Bi2O3 can be reacted with Y2BaCuO5 and liquid phase and finally form Y2Ba4CuBiOx(YBi2411) nanoscale particles; the size of the YBi2411 particles is about 100 nm, which can act as effective flux pinning centers. It is also found that the levitation force of single domain YBCO bulks is increasing from 13 N to 34 N and decreasing to 11 N with the increasing of Bi2O3 addition from 0.1 wt% to 0.7 wt% and 2 wt%. This result is helpful for us to improve the physical properties of REBCO bulk superconductors.

  5. Method for determining transport critical current densities and flux penetration depth in bulk superconductors

    NASA Technical Reports Server (NTRS)

    Israelsson, Ulf E. (Inventor); Strayer, Donald M. (Inventor)

    1992-01-01

    A contact-less method for determining transport critical current density and flux penetration depth in bulk superconductor material. A compressor having a hollow interior and a plunger for selectively reducing the free space area for distribution of the magnetic flux therein are formed of superconductor material. Analytical relationships, based upon the critical state model, Maxwell's equations and geometrical relationships define transport critical current density and flux penetration depth in terms of the initial trapped magnetic flux density and the ratio between initial and final magnetic flux densities whereby data may be reliably determined by means of the simple test apparatus for evaluating the current density and flux penetration depth.

  6. From granules to bulk superconductors using Richardson-Gaudin equations

    NASA Astrophysics Data System (ADS)

    Combescot, Monique; Crouzeix, Michel

    2016-07-01

    We provide a compact expression of the ground-state energy of N-Cooper pairs valid from small to large sample volumes, as checked by numerically solving Richardson-Gaudin equations which give the exact eigenstates of BCS superconductors. This expression contains a contribution linear in the potential amplitude, dominant for small samples, and an exponential contribution dominant when the number of states available for pairing gets larger than a material-dependent threshold independent from sample size. These "available states" are the states feeling the BCS potential, reduced by the Pauli exclusion principle through a "moth-eaten effect" which comes from the composite boson nature of Cooper pairs. This work also presents an elegant derivation of the N-Cooper pair energy obtained recently, which makes use of the roots of the degree-N Hermite polynomial.

  7. EBSD analysis of MgB2 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Schmauch, J.; Inoue, K.; Muralidhar, M.; Berger, K.; Noudem, J.

    2016-04-01

    The grain orientation, the texture and the grain boundary misorientations are important parameters for the understanding of the magnetic properties of the bulk MgB2 samples intended for super-magnet applications. Such data can be provided by electron backscatter diffraction (EBSD) analysis. However, as the grain size (GS) of the MgB2 bulks is preferably in the 100-200 nm range, the common EBSD technique working in reflection operates properly only on highly dense samples. In order to achieve a reasonably good Kikuchi pattern quality on all samples, we apply here the newly developed transmission EBSD (t-EBSD) technique to several bulk MgB2 samples. This method requires the preparation of TEM slices by means of focused ion-beam milling, which are then analyzed within the SEM, operating with a specific sample holder. We present several EBSD mappings of samples prepared with different techniques and at various reaction temperatures.

  8. Bulk YBa2Cu3O(x) superconductors through pressurized partial melt growth processing

    NASA Technical Reports Server (NTRS)

    Hu, S.; Hojaji, H.; Barkatt, A.; Boroomand, M.; Hung, M.; Buechele, A. C.; Thorpe, A. N.; Davis, D. D.; Alterescu, S.

    1992-01-01

    A novel pressurized partial melt growth process has been developed for producing large pieces of bulk Y-Ba-Cu-O superconductors. During long-time partial melt growth stage, an additional driving force for solidification is obtained by using pressurized oxygen gas. The microstructure and superconducting properties of the resulting samples were investigated. It was found that this new technique can eliminate porosity and inhomogeneity, promote large-scale grain-texturing, and improve interdomain coupling as well.

  9. Superconducting topological surface states in the noncentrosymmetric bulk superconductor PbTaSe2

    PubMed Central

    Guan, Syu-You; Chen, Peng-Jen; Chu, Ming-Wen; Sankar, Raman; Chou, Fangcheng; Jeng, Horng-Tay; Chang, Chia-Seng; Chuang, Tien-Ming

    2016-01-01

    The search for topological superconductors (TSCs) is one of the most urgent contemporary problems in condensed matter systems. TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface (or edge) states. Within each vortex core of TSCs, there exists the zero-energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. To date, no stoichiometric bulk material exhibits the required topological surface states (TSSs) at the Fermi level (EF) combined with fully gapped bulk superconductivity. We report atomic-scale visualization of the TSSs of the noncentrosymmetric fully gapped superconductor PbTaSe2. Using quasi-particle scattering interference imaging, we find two TSSs with a Dirac point at E ≅ 1.0 eV, of which the inner TSS and the partial outer TSS cross EF, on the Pb-terminated surface of this fully gapped superconductor. This discovery reveals PbTaSe2 as a promising candidate for TSC. PMID:28138520

  10. Superconducting topological surface states in the noncentrosymmetric bulk superconductor PbTaSe2.

    PubMed

    Guan, Syu-You; Chen, Peng-Jen; Chu, Ming-Wen; Sankar, Raman; Chou, Fangcheng; Jeng, Horng-Tay; Chang, Chia-Seng; Chuang, Tien-Ming

    2016-11-01

    The search for topological superconductors (TSCs) is one of the most urgent contemporary problems in condensed matter systems. TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface (or edge) states. Within each vortex core of TSCs, there exists the zero-energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. To date, no stoichiometric bulk material exhibits the required topological surface states (TSSs) at the Fermi level (EF) combined with fully gapped bulk superconductivity. We report atomic-scale visualization of the TSSs of the noncentrosymmetric fully gapped superconductor PbTaSe2. Using quasi-particle scattering interference imaging, we find two TSSs with a Dirac point at E ≅ 1.0 eV, of which the inner TSS and the partial outer TSS cross EF, on the Pb-terminated surface of this fully gapped superconductor. This discovery reveals PbTaSe2 as a promising candidate for TSC.

  11. Melt-growth bulk superconductors and application to an axial-gap-type rotating machine

    NASA Astrophysics Data System (ADS)

    Zhang, Yufeng; Zhou, Difan; Ida, Tetsuya; Miki, Motohiro; Izumi, Mitsuru

    2016-04-01

    The present manuscript addresses key issues in the course of our study of materials processing of bulk high-temperature superconductors, trapped flux and its application to a prototype axial-gap-type rotating machine. The TUMSAT group has conducted a series of studies since 2003 on the growth of GdBa2Cu3O7-δ bulk material and its application in a compact low-speed high-torque rotating machine. In the stage of material growth, gaining the advantage of a large motive torque density requires large integrated flux in the motor/generators. A large grain surface might be required with sophisticated techniques for the melt-growth texture in the bulk with optimal flux pinning. In the second stage, the in situ magnetization procedure for bulk superconductors in the applied machine is a crucial part of the technology. Pulsed current excitation by using an armature copper winding has magnetized field pole bulks on the rotor. The axial-gap flux synchronous machine studied in the past decade is a condensed technology and indicates that further scientific development is required for a future compact machine to be superior to conventional ones in accordance with the cryogenic periphery and flux stabilization.

  12. Physical property characterization of bulk MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Vajpayee, A.; Mudgel, M.; Ganesan, V.; Awasthi, A. M.; Bhalla, G. L.; Kishan, H.

    2008-04-01

    We report synthesis, structure/micro-structure, resistivity under magnetic field [ρ(T)H], Raman spectra, thermoelectric power S(T), thermal conductivity κ(T), and magnetization of ambient pressure argon annealed polycrystalline bulk samples of MgB2, processed under identical conditions. The compound crystallizes in hexagonal structure with space group P6/mmm. Transmission electron microscopy ( TEM) reveals electron micrographs showing various types of defect features along with the presence of 3 4 nm thick amorphous layers forming the grain boundaries of otherwise crystalline MgB2. Raman spectra of the compound at room temperature exhibited characteristic phonon peak at 600 cm-1. Superconductivity is observed at 37.2 K by magnetic susceptibility χ(T), resistivity ρ(T), thermoelectric power S(T), and thermal conductivity κ(T) measurements. The power law fitting of ρ(T) give rise to Debye temperature (ΘD) at 1400 K which is found consistent with the theoretical fitting of S(T), exhibiting Θ D of 1410 K and carrier density of 3.81 × 1028/m3. Thermal conductivity κ(T) shows a jump at 38 K, i.e., at Tc, which was missing in some earlier reports. Critical current density (Jc) of up to 105 A/cm2 in 1 2 T (Tesla) fields at temperatures (T) of up to 10 K is seen from magnetization measurements. The irreversibility field, defined as the field related to merging of M(H) loops is found to be 78, 68 and 42 kOe at 4, 10 and 20 K respectively. The superconducting performance parameters viz. irreversibility field (Hirr) and critical current density Jc(H) of the studied MgB2 are improved profoundly with addition of nano-SiC and nano-diamond. The physical property parameters measured for polycrystalline MgB2 are compared with earlier reports and a consolidated insight of various physical properties is presented.

  13. Some features of bulk melt-textured high-temperature superconductors subjected to alternating magnetic fields

    NASA Astrophysics Data System (ADS)

    Vanderbemden, P.; Molenberg, I.; Simeonova, P.; Lovchinov, V.

    2014-12-01

    Monolithic, large grain, (RE)Ba2Cu3O7 high-temperature superconductors (where RE denotes a rare-earth ion) are known to be able to trap fields in excess of several teslas and represent thus an extremely promising competing technology for permanent magnet in several applications, e.g. in motors and generators. In any rotating machine, however, the superconducting permanent magnet is subjected to variable (transient, or alternating) parasitic magnetic fields. These magnetic fields interact with the superconductor, which yields a reduction of the remnant magnetization. In the present work we quantify these effects by analysing selected experimental data on bulk melt-textured superconductors subjected to AC fields. Our results indicate that the non-uniformity of superconducting properties in rather large samples might lead to unusual features and need to be taken into account to analyse the experimental data. We also investigate the evolution of the DC remnant magnetization of the bulk sample when it is subjected to a large number of AC magnetic field cycles, and investigate the experimental errors that result from a misorientation of the sample or a mispositioning of the Hall probe. The time-dependence of the remnant magnetization over 100000 cycles of the AC field is shown to display distinct regimes which all differ strongly from the usual decay due to magnetic relaxation.

  14. Equality of bulk wave functions and edge correlations in some topological superconductors: a spacetime derivation.

    PubMed

    Shankar, R; Vishwanath, Ashvin

    2011-09-02

    For certain systems, the N-particle ground-state wave functions of the bulk happen to be exactly equal to the N-point spacetime correlation functions at the edge, in the infrared limit. We show why this had to be so for a class of topological superconductors, beginning with the p+ip state in D=2+1. Varying the chemical potential as a function of Euclidean time between weak and strong pairing states is shown to extract the wave function. Then a Euclidean rotation that exchanges time and space and approximate Lorentz invariance lead to the edge connection. This framework readily generalizes to other dimensions. We illustrate it with a D=3+1 example, superfluid 3He- B, and a p-wave superfluid in D=1+1. Our method works only when the particle number is not conserved, as in superconductors.

  15. Magnetic characterisation of large grain, bulk Y-Ba-Cu-O superconductor-soft ferromagnetic alloy hybrid structures

    NASA Astrophysics Data System (ADS)

    Philippe, M. P.; Fagnard, J.-F.; Kirsch, S.; Xu, Z.; Dennis, A. R.; Shi, Y.-H.; Cardwell, D. A.; Vanderheyden, B.; Vanderbemden, P.

    2014-07-01

    Large grain, bulk Y-Ba-Cu-O (YBCO) high temperature superconductors (HTS) have significant potential for use in a variety of practical applications that incorporate powerful quasi-permanent magnets. In the present work, we investigate how the trapped field of such magnets can be improved by combining bulk YBCO with a soft FeNi, ferromagnetic alloy. This involves machining the alloy into components of various shapes, such as cylinders and rings, which are attached subsequently to the top surface of a solid, bulk HTS cylinder. The effect of these modifications on the magnetic hysteresis curve and trapped field of the bulk superconductor at 77 K are then studied using pick-up coil and Hall probe measurements. The experimental data are compared to finite element modelling of the magnetic flux distribution using Campbell’s algorithm. Initially we establish the validity of the technique involving pick-up coils wrapped around the bulk superconductor to obtain its magnetic hysteresis curve in a non-destructive way and highlight the difference between the measured signal and the true magnetization of the sample. We then consider the properties of hybrid ferromagnet/superconductor (F/S) structures. Hall probe measurements, together with the results of the model, establish that flux lines curve outwards through the ferromagnet, which acts, effectively, like a magnetic short circuit. Magnetic hysteresis curves show that the effects of the superconductor and the ferromagnet simply add when the ferromagnet is saturated fully by the applied field. The trapped field of the hybrid structure is always larger than that of the superconductor alone below this saturation level, and especially when the applied field is removed. The results of the study show further that the beneficial effects on the trapped field are enhanced when the ferromagnet covers the entire surface of the superconductor for different ferromagnetic components of various shapes and fixed volume.

  16. Intergrain magnetic properties and critical currents of T1-1223 bulk and tape superconductors

    NASA Astrophysics Data System (ADS)

    Zalecki, R.; Kolodziejczyk, A.; Chmist, J.; König, W.; Gritzner, G.

    2000-11-01

    The magnetic field and the temperature dependencies of the dispersive and the absorption components of the low frequency ac magnetic susceptibility for Pb and Bi single doped bulk superconductors as well as for Pb and Bi co-doped Ag-sheathed superconducting T1-1223 tapes have been measured and analyzed. The studies were accompanied by optical and electron microscopic observations of the microstructure. The ac susceptibility measured at various ac magnetic field amplitudes showed both intergrain and intragrain features. The temperature dependencies of the intergrain critical current densities were extracted from the absorption susceptibility via a modified Bean model. They were at relevant temperatures one order of magnitude larger for the tape than for the bulk specimens.

  17. Development of superconducting magnetic bearing using superconducting coil and bulk superconductor

    NASA Astrophysics Data System (ADS)

    Seino, H.; Nagashima, K.; Arai, Y.

    2008-02-01

    The authors conducted a study on superconducting magnetic bearing, which consists of superconducting rotor and stator to apply the flywheel energy-storage system for railways. In this study, high temperature bulk superconductor (HTS bulk) was combined with superconducting coils to increase the load capacity of the bearing. In the first step of the study, the thrust rolling bearing was selected for application by using liquid nitrogen cooled HTS bulk. 60mm-diameter HTS bulks and superconducting coil which generated a high gradient of magnetic field by cusp field were adopted as a rotor and a stator for superconducting magnetic bearing, respectively. The results of the static load test and the rotation test, creep of the electromagnetic forces caused by static flux penetration and AC loss due to eccentric rotation were decreased to the level without any problems in substantial use by using two HTS bulks. In the result of verification of static load capacity, levitation force (thrust load) of 8900N or more was supportable, and stable static load capacity was obtainable when weight of 460kg was levitated.

  18. Magnetic property of a staggered-array undulator using a bulk high-temperature superconductor

    NASA Astrophysics Data System (ADS)

    Kinjo, Ryota; Mishima, Kenta; Choi, Yong-Woon; Omer, Mohamed; Yoshida, Kyohei; Negm, Hani; Torgasin, Konstantin; Shibata, Marie; Shimahashi, Kyohei; Imon, Hidekazu; Okumura, Kensuke; Inukai, Motoharu; Zen, Heishun; Kii, Toshiteru; Masuda, Kai; Nagasaki, Kazunobu; Ohgaki, Hideaki

    2014-02-01

    The magnetic field of a staggered-array undulator using a bulk high-temperature superconductor is calculated by analytical and numerical methods. Analytical formulas for the undulator field and the solenoid field required to generate the undulator field are derived from a simple two-dimensional model. The analytical calculation shows the degree of dependence of these fields on the undulator parameters, the generation of a high undulator field proportional to the critical current density of the bulk superconductor, and the good tunability of the undulator field over a wide range of values. The numerical calculation is performed in a three-dimensional geometry by two methods: the center field and energy minimization methods. The latter treats the current distribution inside the bulk, whereas the former neglects it as a natural extension of the analytical model. The calculation also reveals the dependence of the fields on the undulator parameters arising from the current distribution. From the comparison with experimental results, we find that the latter method reproduces the experimental results well, which indicates the importance of the current distribution inside the bulk. Therefore, we derive a semiempirical formula for the required solenoid field by modifying the analytical formula using the numerical results so as to include the effect of the current distribution. The semiempirical formula reproduces the numerical result with an error of 3%. Finally, we estimate the magnetic performance of the undulator as an example of using the formulas and values presented in this paper. The estimation shows that an undulator field twice as large as that of the present in-vacuum undulator but with an equal period and gap can be obtained at a temperature of approximately 20-40 K, and that deflection parameters (K values) of 1 and 2 can be achieved with periods of 5 and 10 mm at approximately 4-20 K.

  19. Superconductor-Mediated Modification of Gravity? AC Motor Experiments with Bulk YBCO Disks in Rotating Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Noever, David A.; Koczor, Ronald J.; Roberson, Rick

    1998-01-01

    We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. Podkietnov, et al (Podkietnov, E. and Nieminen, R. (1992) A Possibility of Gravitational Force Shielding by Bulk YBa2 Cu3 O7-x Superconductor, Physica C, C203:441-444.) have indicated that rotating AC fields play an essential role in their observed distortion of combined gravity and barometric pressure readings. We report experiments on large (15 cm diameter) bulk YBCO ceramic superconductors placed in the core of a three-phase, AC motor stator. The applied rotating field produces up to a 12,000 revolutions per minute magnetic field. The field intensity decays rapidly from the maximum at the outer diameter of the superconducting disk (less than 60 Gauss) to the center (less than 10 Gauss). This configuration was applied with and without a permanent DC magnetic field levitating the superconducting disk, with corresponding gravity readings indicating an apparent increase in observed gravity of less than 1 x 10(exp -6)/sq cm, measured above the superconductor. No effect of the rotating magnetic field or thermal environment on the gravimeter readings or on rotating the superconducting disk was noted within the high precision of the observation. Implications for propulsion initiatives and power storage flywheel technologies for high temperature superconductors will be discussed for various spacecraft and satellite applications.

  20. The size effect on the magnetic levitation force of MgB2 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Savaskan, B.; Koparan, E. T.; Güner, S. B.; Celik, S.; Yanmaz, E.

    2016-12-01

    In this study, the size effect on the magnetic levitation performance of disk-shaped MgB2 bulk superconductors and permanent magnets was investigated. MgB2 samples with varying diameters of 13 mm, 15 mm and 18 mm, each of which were 2 g in mass, were prepared by two-step solid state reaction method. Vertical levitation force measurements under both zero-field-cooled (ZFC) and field-cooled (FC) regimes were carried out at different temperatures of 20, 24 and 28 K. It was determined that the levitation force of the MgB2 strongly depends on both the diameters of the sample and the permanent magnet. In ZFC regime, the maximum levitation force value for the permanent magnet and the sample 18 mm in diameters reached to the 8.41 N at 20 K. In addition, in FC regime, attractive and repulsive force increased with increasing diameters of the sample and the permanent magnet. In that, the sample with 18 mm in diameter showed the highest attractive force value -3.46 N at 20 K and FC regime. The results obtained in this study are very useful in magnetic levitation devices as there is no detailed study on the size of superconductors and permanent magnets.

  1. Multiple seeding for the growth of bulk GdBCO-Ag superconductors with single grain behaviour

    NASA Astrophysics Data System (ADS)

    Shi, Y.; Durrell, J. H.; Dennis, A. R.; Huang, K.; Namburi, D. K.; Zhou, D.; Cardwell, D. A.

    2017-01-01

    Rare earth-barium-copper oxide bulk superconductors fabricated in large or complicated geometries are required for a variety of engineering applications. Initiating crystal growth from multiple seeds reduces the time taken to melt-process individual samples and can reduce the problem of poor crystal texture away from the seed. Grain boundaries between regions of independent crystal growth can reduce significantly the flow of current due to crystallographic misalignment and the agglomeration of impurity phases. Enhanced supercurrent flow at such boundaries has been achieved by minimising the depth of the boundary between A growth sectors generated during the melt growth process by reducing second phase agglomerations and by a new technique for initiating crystal growth that minimises the misalignment between different growth regions. The trapped magnetic fields measured for the resulting samples exhibit a single trapped field peak indicating they are equivalent to conventional single grains.

  2. Improving magnetic properties of MgB2 bulk superconductors by synthetic engine oil treatment

    NASA Astrophysics Data System (ADS)

    Taylan Koparan, E.; Savaskan, B.; Yanmaz, E.

    2016-08-01

    The present study focuses on the effects of standby time of the MgB2 samples immersed in synthetic engine oil on the critical current density (Jc(H)), magnetic field dependence of the pinning force density fp(b) and Tc performances of MgB2 bulk superconductors. Synthetic engine oil was used as a product which is cheap and a rich carbon source. Manufactured MgB2 pellet samples were immersed at different standby time of 30 min, 120 min, 300 min and 1440 min in synthetic engine oil after the first heating process. Finally, MgB2 samples immersed in synthetic engine oil were sintered at 1000 °C and kept for 15 min in Ar atmosphere. The critical current density of all of MgB2 samples immersed at different standby time in engine oil in whole field range was better than that of the pure MgB2 sample because of the number of the pinning centers. The MgB2 sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. The Jc value for the pure sample is 2.0 × 103 A/cm2, whereas for the MgB2 sample immersed at 300 min standby time in engine oil the Jc is enhanced to 4.8 × 103A/cm2 at 5 K and 3 T. The superconducting transition temperature (Tc) did not change with the increasing standby time of the samples in synthetic engine oil at all. The best diamagnetic property was obtained from the sample which kept in synthetic engine oil for 300 min. Synthetic engine oil treatment results in remarkable improvement of the critical current density and pinning force performances of MgB2 superconductors. It was found that all MgB2 samples have a different pinning property at different measuring temperatures. Using synthetic engine oil as a product which is cheap and a rich carbon source in MgB2 bulk superconductors makes MgB2 samples immersed in synthetic engine oil a good candidate for industrial applications.

  3. Flux jump-assisted pulsed field magnetisation of high-J c bulk high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Ainslie, M. D.; Zhou, D.; Fujishiro, H.; Takahashi, K.; Shi, Y.-H.; Durrell, J. H.

    2016-12-01

    Investigating, predicting and optimising practical magnetisation techniques for charging bulk superconductors is a crucial prerequisite to their use as high performance ‘psuedo’ permanent magnets. The leading technique for such magnetisation is the pulsed field magnetisation (PFM) technique, in which a large magnetic field is applied via an external magnetic field pulse of duration of the order of milliseconds. Recently ‘giant field leaps’ have been observed during charging by PFM: this effect greatly aids magnetisation as flux jumps occur in the superconductor leading to magnetic flux suddenly intruding into the centre of the superconductor. This results in a large increase in the measured trapped field at the centre of the top surface of the bulk sample and full magnetisation. Due to the complex nature of the magnetic flux dynamics during the PFM process, simple analytical methods, such as those based on the Bean critical state model, are not applicable. Consequently, in order to successfully model this process, a multi-physical numerical model is required, including both electromagnetic and thermal considerations over short time scales. In this paper, we show that a standard numerical modelling technique, based on a 2D axisymmetric finite-element model implementing the H -formulation, can model this behaviour. In order to reproduce the observed behaviour in our model all that is required is the insertion of a bulk sample of high critical current density, J c. We further explore the consequences of this observation by examining the applicability of the model to a range of previously reported experimental results. Our key conclusion is that the ‘giant field leaps’ reported by Weinstein et al and others need no new physical explanation in terms of the behaviour of bulk superconductors: it is clear the ‘giant field leap’ or flux jump-assisted magnetisation of bulk superconductors will be a key enabling technology for practical applications.

  4. AC susceptibility analysis on MgB2 bulk and Ti-sheathed wire superconductors

    NASA Astrophysics Data System (ADS)

    Çiçek, Özlem; Yetiş, Hakan; Gencer, Ali

    2014-09-01

    We report a comparative study for bulk MgB2 superconductors and monofilamentary Ti/MgB2 wires as functions of the boron powder purity, average particle size of magnesium, and applied pressure. The structural and magnetic characterizations of the bulk samples were performed by means of XRD and AC susceptibility measurements, respectively. We found that the applied pressure did not cause any significant change on the onset transition temperature Tc,onset and transition width. This is also confirmed by the calculation of the lattice parameters. On the other hand, Tc,onset values were measured as 37.3 K, 38.0 K, and 38.6 K for the samples prepared from the precursor boron powders with purities of 95.2%, ⩾95%, and >98%, respectively. However Mg-particle size (Mg1: AlfaAesar Mg powder, avg. par. size: -325 mesh, purity: 99.8%; Mg2: SigmaAldrich Mg powder, avg. par. size: 20-230 mesh, purity: 98%) did not affect the Tc,onset but increasing the Mg particle size caused a significant broadening at the superconducting transition width for all precursor boron powder purity levels. Magnetization measurements showed that the critical current density of Ti/MgB2 wire prepared from AlfaAesar Mg powder (avg. par. size: -325 mesh) and Aldrich B powder (amorphous, purity ⩾ 95%) is greater than that of prepared by SigmaAldrich Mg powder (avg. par. size: 20-230 mesh) and Pavezyum B powder (amorphous, avg. par. size: 0,3 μm (max), purity > 98%) as 2.6 × 105 A/cm2 and 1.4 × 105 A/cm2 at T = 10 K and μ0H = 0.5 T, respectively. In addition, SigmaAldrich Mg and Pavezyum B wire sample has a lower pinning force, Fp, value at each temperature.

  5. Influence of preparation conditions on 211 particle refinement in YBCO bulk superconductors with Ce addition

    NASA Astrophysics Data System (ADS)

    Diko, Pavel; Volochová, Daniela; Radušovská, Monika; Zmorayová, Katarína; Šefčiková, Martina; Antal, Vitalij; Jurek, Karel; Jirsa, Miloš; Kováč, Jozef

    2013-11-01

    The influence of CeO2 and BaCeO3 addition and the influence of processing conditions on Y2BaCuO5 (Y211) particle size and particle distribution in melt-processed YBa2Cu3O7/Y2BaCuO5 (Y123/Y211) bulk superconductors with nominal composition Y1.5Ba2Cu3Ox was investigated. Ce dissolved in the peritectic melt can actively hinder the Y211 particle growth by the Ostwald ripening process at melting stage. At sintering of intensively milled samples, Y211 particles in the charge free of CeO2 are smaller than Y211 particles formed in the charge with CeO2 addition and this behaviour can be related to the melt formation around added CeO2. The Y211 particle refinement in the mildly milled samples with large Y123 particles in the pressed green bodies is caused by very dense Y211 skeleton resistant to melt formation at the sintering stage. This skeleton is a barrier for pollution of the sample from the substrate and from the seed. BaCeO3 added instead CeO2 causes significant Y211 particle refinement also in the samples with homogenously distributed Y211 particles.

  6. Superconducting screening on different length scales in high-quality bulk MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Horvat, J.; Soltanian, S.; Pan, A. V.; Wang, X. L.

    2004-10-01

    High-quality bulk MgB2 exhibits a structure of voids and agglomeration of crystals on different length scales. Because of this, the superconducting currents percolate between the voids in the ensuing structure. Magnetic measurements reveal that the superconducting currents circulate on at least three different length scales, of ˜1μm, ˜10μm, and whole of the sample (˜millimeter). Each of these screenings contributes to the measured irreversible magnetic moment (Δm ). The analysis of the field dependence of Δm for samples of subsequently decreasing size showed that the critical current obtained using the simple critical state model is erroneous. This leads to the artifact of the sample size-dependent critical current density Jc and irreversibility field. Our data analysis enables the separation of the contribution of each of the screening currents to Δm. The field dependence of each of the currents follows a stretched exponential form. The currents flowing around whole of the sample give a dominant contribution to Δm in the intermediate fields (1T superconductors, and it seems to be connected with the percolation of the currents.

  7. High output power reluctance electric motors with bulk high-temperature superconductor elements

    NASA Astrophysics Data System (ADS)

    Kovalev, L. K.; Ilushin, K. V.; Penkin, V. T.; Kovalev, K. L.; Larionoff, A. E.; M-A Koneev, S.; Modestov, K. A.; Larionoff, S. A.; Poltavets, V. N.; Akimov, I. I.; Alexandrov, V. V.; Gawalek, W.; Oswald, B.; Krabbes, G.

    2002-05-01

    We present new types of electric machines with the rotors containing bulk high-temperature superconductor (HTS) - YBCO and Bi-Ag - elements. We discuss different schematics of hysteresis, reluctance, 'trapped field' and composed synchronous HTS machines. The two-dimensional mathematical models describing the processes in such types of HTS machines were developed on the basis of the theoretical analysis of the electrodynamic and hysteresis processes in the single-domain and polycrystal YBCO ceramic samples and plate shape Bi-Ag elements. We give the test results of the series of hysteresis, reluctance, 'trapped field' and composed with permanent magnets HTS motors with an output power rating of 0.1-18 kW and current frequencies 50 Hz and 400 Hz. These results show that in the media of liquid nitrogen the specific output power per one unit weight of the HTS motor is four to seven times better than for conventional electric machines. A comparison of the theoretical and experimental characteristics of the developed HTS motors show that they are in good agreement. We discuss the test results for a liquid nitrogen cryogenic pump system with a hysteresis 500 W HTS motor. We describe several designs of new HTS motors operating in the media of liquid nitrogen with an output power 125 kW (and more) and a power factor of more than 0.8. We discuss future applications of new types of HTS motors for aerospace technology, on-land industry and transport systems.

  8. A flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors.

    PubMed

    Egan, R; Philippe, M; Wera, L; Fagnard, J F; Vanderheyden, B; Dennis, A; Shi, Y; Cardwell, D A; Vanderbemden, P

    2015-02-01

    We report the design and construction of a flux extraction device to measure the DC magnetic moment of large samples (i.e., several cm(3)) at cryogenic temperature. The signal is constructed by integrating the electromotive force generated by two coils wound in series-opposition that move around the sample. We show that an octupole expansion of the magnetic vector potential can be used conveniently to treat near-field effects for this geometrical configuration. The resulting expansion is tested for the case of a large, permanently magnetized, type-II superconducting sample. The dimensions of the sensing coils are determined in such a way that the measurement is influenced by the dipole magnetic moment of the sample and not by moments of higher order, within user-determined upper bounds. The device, which is able to measure magnetic moments in excess of 1 A m(2) (1000 emu), is validated by (i) a direct calibration experiment using a small coil driven by a known current and (ii) by comparison with the results of numerical calculations obtained previously using a flux measurement technique. The sensitivity of the device is demonstrated by the measurement of flux-creep relaxation of the magnetization in a large bulk superconductor sample at liquid nitrogen temperature (77 K).

  9. A flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors

    NASA Astrophysics Data System (ADS)

    Egan, R.; Philippe, M.; Wera, L.; Fagnard, J. F.; Vanderheyden, B.; Dennis, A.; Shi, Y.; Cardwell, D. A.; Vanderbemden, P.

    2015-02-01

    We report the design and construction of a flux extraction device to measure the DC magnetic moment of large samples (i.e., several cm3) at cryogenic temperature. The signal is constructed by integrating the electromotive force generated by two coils wound in series-opposition that move around the sample. We show that an octupole expansion of the magnetic vector potential can be used conveniently to treat near-field effects for this geometrical configuration. The resulting expansion is tested for the case of a large, permanently magnetized, type-II superconducting sample. The dimensions of the sensing coils are determined in such a way that the measurement is influenced by the dipole magnetic moment of the sample and not by moments of higher order, within user-determined upper bounds. The device, which is able to measure magnetic moments in excess of 1 A m2 (1000 emu), is validated by (i) a direct calibration experiment using a small coil driven by a known current and (ii) by comparison with the results of numerical calculations obtained previously using a flux measurement technique. The sensitivity of the device is demonstrated by the measurement of flux-creep relaxation of the magnetization in a large bulk superconductor sample at liquid nitrogen temperature (77 K).

  10. The use of buffer pellets to pseudo hot seed (RE)-Ba-Cu-O-(Ag) single grain bulk superconductors

    NASA Astrophysics Data System (ADS)

    Shi, Yunhua; Namburi, Devendra Kumar; Zhao, Wen; Durrell, John H.; Dennis, Anthony R.; Cardwell, David A.

    2016-01-01

    Reliable seeding of the superconducting (RE)Ba2Cu3O7-δ (RE-123) phase is a critical step in the melt growth of large, single grain, (RE)BaCuO ((RE)BCO) bulk superconductors. Recent improvements to the top seeded melt growth (TSMG) processing technique, which is an established method of fabricating bulk (RE)BCO superconductors, based on the use of a buffer layer between the seed and green body preform, has significantly improved the reliability of the single grain growth process. This technique has been used successfully for the primary TSMG and infiltration melt growth of all compositions within the ((RE)BCO-Ag) family of materials (where RE = Sm, Gd and Y), and in recycling processes. However, the mechanism behind the improved reliability of the melt process is not understood fully and its effect on the superconducting properties of the fully processed single grains is not clear. In this paper, we investigate the effect of the use of a buffer pellet between the seed and green body on the microstructure, critical current, critical temperature and trapped field of the bulk superconductor. We conclude that the introduction of the buffer pellet evolves the melt growth process towards that observed in the technologically challenging hot seeding technique, but has the potential to yield high quality single grain samples but by a commercially viable melt process.

  11. BCS-BEC crossover physics in FeSe bulk superconductor

    NASA Astrophysics Data System (ADS)

    Shibauchi, Takasada

    The physics of the crossover between weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein-condensate (BEC) limits gives a unified framework of quantum bound (superfluid) states of interacting fermions. This crossover has been studied in the ultracold atomic systems, but is extremely difficult to be realized for electrons in solids. Through the superfluid response, transport, thermoelectric response, and quantum oscillations, we demonstrate that the Fermi energy of the bulk superconductor FeSe is extremely small, with the ratio of the gap to Fermi energy is of the order of unity, which qualifies FeSe to be deep inside the BCS-BEC crossover regime. Thus FeSe appears to be a key material to solve the longstanding issue in the crossover physics; the presence of preformed Cooper pairs giving rise to a pseudogap above the superconducting transition temperature Tc. We report experimental signatures of preformed Cooper pairing well above Tc = 8 . 5 K in clean single crystals of FeSe. Our torque magnetometry reveals distinct diamagnetic signal below T* ~ 20 K indicating that the superconducting fluctuations above the transition temperature are strongly enhanced from the standard Gaussian theory. The transport and thermoelectric coefficients also exhibit distinct anomalies at ~T* , signaling a possible pseudogap formation. The multiband nature with the electron-hole compensation in FeSe may highlight a fundamentally new aspect of the BCS-BEC crossover physics In collaboration with S. Kasahara, T. Yamashita, Y. Matsuda (Kyoto), Y. Mizukami (Tokyo), T. Wolf, F. Hardy, C. Meingast, H. v. Löhneysen (KIT), M. D. Watson, A. I. Coldea (Oxford), T. Terashima (NIMS), W. Knafo (Toulouse), T. Hanaguri (Riken).

  12. Electrical resistivity, Debye temperature, and connectivity in heavily doped bulk MgB2 superconductors

    NASA Astrophysics Data System (ADS)

    Susner, M. A.; Bhatia, M.; Sumption, M. D.; Collings, E. W.

    2009-05-01

    The measured transport critical current densities, Jc, of MgB2 superconductors fall short of their intrinsic Jcs on account of the grain boundary blockage, sausaging, and porosity seen in most powder-processed wire samples. Hence, it becomes important to understand and to be able to measure the degree of what can be referred to as "connectivity" in order to be able to assess the highest attainable Jc in a given class of samples. In this paper connectivity is determined with the aid of normal state resistivity in an extension of the model originally proposed by Rowell. The normal-state resistivity temperature dependence is fitted to a standard Bloch-Grüneisen (B-G) equation in the range 50-300 K. Such an approach leads not only to a connectivity parameter but also to other useful data: the actual intragrain residual resistivity (indirectly related to the upper critical field) and a resistively determined Debye temperature, θR. The latter quantity, coupled to the transition temperature, Tc, provides a measure (by way of the McMillan formula) of the electron-phonon coupling constant, usually designated λ. The B-G-based connectivity model was applied to our own experimental data on binary and heavily doped MgB2 samples as well as published resistivity data. To complete the study, low temperature specific heat measurements, performed on binary and doped bulk samples provided calorimetrically determined Debye temperatures, θD, for comparison to the resistively determined values and excellent agreement was found. Calorimetric measurements also probed the homogeneity of the doped samples in terms of the roundness of the electronic specific heat jump near Tc.

  13. Influence of crossed fields in structures combining large grain, bulk (RE)BCO superconductors and soft ferromagnetic discs

    NASA Astrophysics Data System (ADS)

    Philippe, M. P.; Fagnard, J. F.; Wéra, L.; Morita, M.; Nariki, S.; Teshima, H.; Caps, H.; Vanderheyden, B.; Vanderbemden, P.

    2016-03-01

    Bulk (RE)BCO superconductors are able to trap record magnetic fields and can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. When such superconducting (SC) “trapped field magnets” are combined to a ferromagnetic (FM) disc, the total magnetic moment is increased with respect to that of the superconductor alone. In the present work, we study experimentally the magnetic behaviour of such hybrid FM/SC structures when they are subjected to cycles of applied field that are orthogonal to their permanent magnetization, i.e. a “crossed-field” configuration. Experimental results show that the usual “crossed-field demagnetization” caused by the cycles of transverse field is strongly reduced in the presence of the ferromagnet.

  14. Topological superconductor with a large Chern number and a large bulk excitation gap in single-layer graphene

    NASA Astrophysics Data System (ADS)

    Wang, L.; Wu, M. W.

    2016-02-01

    We show that a two-dimensional topological superconductor (TSC) can be realized in a hybrid system with a conventional s -wave superconductor proximity coupled to a quantum anomalous Hall (QAH) state from the Rashba and exchange effects in single-layer graphene. With very low or even zero doping near the Dirac points, i.e., two inequivalent valleys, this TSC has a Chern number as large as 4, which supports four Majorana edge modes. More importantly, we show that this TSC has a robust topologically nontrivial bulk excitation gap, which can be larger or even 1 order of magnitude larger than the proximity-induced superconducting gap. This unique property paves a way for the application of QAH insulators as seed materials to realize robust TSCs and Majorana modes.

  15. Applied Hts Bulks and Wires to Rotating Machines for Marine Propulsion

    NASA Astrophysics Data System (ADS)

    Miki, M.; Felder, B.; Kimura, Y.; Tsuzuki, K.; Taguchi, R.; Shiliang, Y.; Xu, Y.; Ida, T.; Izumi, M.

    2010-04-01

    High-temperature superconductors allow a compact and efficient way to provide high-torque density to rotating machines with excellent operation. A field pole, providing flux density of more than 1.5 T around the armature, was initially designed for an axial-gap type with the flux parallel to the rotor axis. Melt-growth Gd-123 bulks as well as Bi-2223 wire windings have been successfully assembled on the rotor disk. No iron core was used, though being an auxiliary flux control found in most HTS motors. Both bulk and wire types have realized a practical motor operation within a limited output range. For bulks, a 15 kW, 720 rpm, synchronous motor was designed and tested in the group of TUMSAT, Kitano Seiki and University of Fukui. A bulk field pole was cooled down by liquid nitrogen and was magnetized in the motor. To enhance the output power to more than 30 kW, we developed a thermosyphon system using condensed neon. Another field pole with HTS wire for large-scale marine propulsion is also discussed on a 100 kW, 230 rpm tested machine. A closed-cycle condensed neon associated with thermal insulation is also reported.

  16. Bulk-SQUID effect in a discrete superconductor as a consequence of generation frequency locking in constituent josephson junctions

    SciTech Connect

    Ginzburg, S. L.; Nakin, A. V.; Savitskaya, N. E.

    2012-02-15

    The theory of the bulk-SQUID effect in discrete superconductors is constructed for the first time. It is shown that the bulk-SQUID effect emerges in the system of 2D intrinsically stochastic multijunction SQUID (i.e., with random values of critical currents of the junctions, injection currents, and the coupling coefficients between the junction) due to generation frequency locking in all junctions. It is demonstrated that the bulk-SQUID effect occurs in a wide range of random parameters of the system. This domain of variation of the system parameters can be divided into three subdomains. The first one is the subdomain of coherent dynamics of phases at the junctions, the second is the subdomain of incoherent dynamics, in which the phases of the junctions are not locked, but the bulk-SQUID effect persists, and the third is the subdomain of transient dynamics, in which coherent dynamics and the bulk-SQUID effect are observed in parts. A simple mathematical model of noninteracting junctions, which correctly describes basic features of the dynamics of the initial system and makes it possible to calculate some of its statistical characteristics, is proposed and analyzed.

  17. A portable magnetic field of >3 T generated by the flux jump assisted, pulsed field magnetization of bulk superconductors

    NASA Astrophysics Data System (ADS)

    Zhou, Difan; Ainslie, Mark D.; Shi, Yunhua; Dennis, Anthony R.; Huang, Kaiyuan; Hull, John R.; Cardwell, David A.; Durrell, John H.

    2017-02-01

    A trapped magnetic field of greater than 3 T has been achieved in a single grain GdBa2Cu3O7-δ (GdBaCuO) bulk superconductor of diameter 30 mm by employing pulsed field magnetization. The magnet system is portable and operates at temperatures between 50 K and 60 K. Flux jump behaviour was observed consistently during magnetization when the applied pulsed field, Ba, exceeded a critical value (e.g., 3.78 T at 60 K). A sharp dBa/dt is essential to this phenomenon. This flux jump behaviour enables the magnetic flux to penetrate fully to the centre of the bulk superconductor, resulting in full magnetization of the sample without requiring an applied field as large as that predicted by the Bean model. We show that this flux jump behaviour can occur over a wide range of fields and temperatures, and that it can be exploited in a practical quasi-permanent magnet system.

  18. Superconductors

    DOEpatents

    Newkirk, Lawrence R.; Valencia, Flavio A.

    1977-02-01

    The structural quality of niobium germanide as a high-transition-temperature superconducting material is substantially improved by the presence of about 5 at. % oxygen. Niobium germanide having this oxygen content may readily be prepared as a bulk coating bonded to a metallic substrate by chemical vapor deposition techniques.

  19. Behavior of bulk high-temperature superconductors of finite thickness subjected to crossed magnetic fields: Experiment and model

    NASA Astrophysics Data System (ADS)

    Vanderbemden, Ph.; Hong, Z.; Coombs, T. A.; Denis, S.; Ausloos, M.; Schwartz, J.; Rutel, I. B.; Hari Babu, N.; Cardwell, D. A.; Campbell, A. M.

    2007-05-01

    Crossed-magnetic-field effects on bulk high-temperature superconductors have been studied both experimentally and numerically. The sample geometry investigated involves finite-size effects along both (crossed-)magnetic-field directions. The experiments were carried out on bulk melt-processed Y-Ba-Cu-O single domains that had been premagnetized with the applied field parallel to their shortest direction (i.e., the c axis) and then subjected to several cycles of the application of a transverse magnetic field parallel to the sample ab plane. The magnetic properties were measured using orthogonal pickup coils, a Hall probe placed against the sample surface, and magneto-optical imaging. We show that all principal features of the experimental data can be reproduced qualitatively using a two-dimensional finite-element numerical model based on an E-J power law and in which the current density flows perpendicularly to the plane within which the two components of magnetic field are varied. The results of this study suggest that the suppression of the magnetic moment under the action of a transverse field can be predicted successfully by ignoring the existence of flux-free configurations or flux-cutting effects. These investigations show that the observed decay in magnetization results from the intricate modification of current distribution within the sample cross section. The current amplitude is altered significantly only if a field-dependent critical current density Jc(B) is assumed. Our model is shown to be quite appropriate to describe the cross-flow effects in bulk superconductors. It is also shown that this model does not predict any saturation of the magnetic induction, even after a large number (˜100) of transverse field cycles. These features are shown to be consistent with the experimental data.

  20. Improvement of persistent magnetic field trapping in bulk Y-Ba-Cu-O superconductors

    NASA Technical Reports Server (NTRS)

    Chen, In-Gann; Weinstein, Roy

    1993-01-01

    For type-II superconductors, magnetic field can be trapped due to persistent internal supercurrent. Quasi-persistent magnetic fields near 2 T at 60 K (and 1.4 T at 77 K) have been measured in minimagnets made of proton-irradiated melt-textured Y-Ba-Cu-O (MT-Y123) samples. Using the trapping effect, high-field permanent magnets with dipole, quadrupole, or more complicated configurations can be made of existing MT-Y123 material, thus bypassing the need for high-temperature superconductor (HTS) wires. A phenomenological current model has been developed to account for the trapped field intensity and profile in HTS samples. This model is also a guide to select directions of materials development to further improve field trapping properties. General properties such as magnetic field intensities, spatial distributions, stabilities, and temperature dependence of trapped field are discussed.

  1. Visualizing the morphology of vortex lattice domains in a bulk type-II superconductor

    NASA Astrophysics Data System (ADS)

    Reimann, T.; Mühlbauer, S.; Schulz, M.; Betz, B.; Kaestner, A.; Pipich, V.; Böni, P.; Grünzweig, C.

    2015-11-01

    Alike materials in the solid state, the phase diagram of type-II superconductors exhibit crystalline, amorphous, liquid and spatially inhomogeneous phases. The multitude of different phases of vortex matter has thence proven to act as almost ideal model system for the study of both the underlying properties of superconductivity but also of general phenomena such as domain nucleation and morphology. Here we show how neutron grating interferometry yields detailed information on the vortex lattice and its domain structure in the intermediate mixed state of a type-II niobium superconductor. In particular, we identify the nucleation regions, how the intermediate mixed state expands, and where it finally evolves into the Shubnikov phase. Moreover, we complement the results obtained from neutron grating interferometry by small-angle neutron scattering that confirm the spatially resolved morphology found in the intermediate mixed state, and very small-angle neutron scattering that confirm the domain structure of the vortex lattice.

  2. Visualizing the morphology of vortex lattice domains in a bulk type-II superconductor

    PubMed Central

    Reimann, T.; Mühlbauer, S.; Schulz, M.; Betz, B.; Kaestner, A.; Pipich, V.; Böni, P.; Grünzweig, C.

    2015-01-01

    Alike materials in the solid state, the phase diagram of type-II superconductors exhibit crystalline, amorphous, liquid and spatially inhomogeneous phases. The multitude of different phases of vortex matter has thence proven to act as almost ideal model system for the study of both the underlying properties of superconductivity but also of general phenomena such as domain nucleation and morphology. Here we show how neutron grating interferometry yields detailed information on the vortex lattice and its domain structure in the intermediate mixed state of a type-II niobium superconductor. In particular, we identify the nucleation regions, how the intermediate mixed state expands, and where it finally evolves into the Shubnikov phase. Moreover, we complement the results obtained from neutron grating interferometry by small-angle neutron scattering that confirm the spatially resolved morphology found in the intermediate mixed state, and very small-angle neutron scattering that confirm the domain structure of the vortex lattice. PMID:26522610

  3. The effect of processing parameters during heat treatment of bulk high-{Tc} superconductors

    SciTech Connect

    Cha, Y.S.; Dorris, S.E.; Hull, J.R.; Poeppel, R.B.

    1991-04-01

    Plastic extrusion is a promising method for producing the long lengths of high-{Tc} superconductor that will be necessary to meet many potential applications. A crucial phase of the extrusion method is removal of organic constituents. Incomplete removal can leave residual carbon at grain boundaries, which can adversely affect the superconducting properties, whereas excessively rapid removal of the organics can cause the extruded superconductor to disintegrate completely. In this paper, we analyze the effects of the following aspects of organics removal, as they apply to the firing of extruded YBa{sub 2}Cu{sub 3}O{sub x} coils: (1) total pressure in the furnace, (2) oxygen flow, (3) heat conduction, and (4) diffusion of volatile components during removal of organics.

  4. The effect of processing parameters during heat treatment of bulk high- Tc superconductors

    SciTech Connect

    Cha, Y.S.; Dorris, S.E.; Hull, J.R.; Poeppel, R.B.

    1991-04-01

    Plastic extrusion is a promising method for producing the long lengths of high-{Tc} superconductor that will be necessary to meet many potential applications. A crucial phase of the extrusion method is removal of organic constituents. Incomplete removal can leave residual carbon at grain boundaries, which can adversely affect the superconducting properties, whereas excessively rapid removal of the organics can cause the extruded superconductor to disintegrate completely. In this paper, we analyze the effects of the following aspects of organics removal, as they apply to the firing of extruded YBa{sub 2}Cu{sub 3}O{sub x} coils: (1) total pressure in the furnace, (2) oxygen flow, (3) heat conduction, and (4) diffusion of volatile components during removal of organics.

  5. The influence of post-growth thermal treatments on the critical current density of TSMG YBCO bulk superconductors

    NASA Astrophysics Data System (ADS)

    Diko, P.; Antal, V.; Zmorayová, K.; Šefčiková, M.; Chaud, X.; Kováč, J.; Yao, X.; Chen, I.; Eisterer, M.; Weber, H. W.

    2010-12-01

    Oxygenation and thermochemical post-growth treatments of top seeded melt-growth (TSMG) YBCO bulk superconductors can significantly influence critical current density. It is shown that, depending on oxygenation conditions and the size of 211 particles, different reductions of intrinsic critical current density values can be obtained due to the reduction in the sample cross-section caused by the presence of a/b-microcracks induced by 211 particles, and a/b- and a/c-cracks induced by oxygenation. The possibility of eliminating oxygenation cracks by high pressure oxygenation and consequently significantly increasing the macroscopic critical current density is demonstrated. An effective dopant concentration for chemical pinning is proposed and possible clustering of substitutions in the Y123 lattice by thermochemical treatments is shown.

  6. Topology of the planar phase of superfluid He3 and bulk-boundary correspondence for three-dimensional topological superconductors

    NASA Astrophysics Data System (ADS)

    Makhlin, Yuriy; Silaev, Mikhail; Volovik, G. E.

    2014-05-01

    We provide topological classification of possible phases with the symmetry of the planar phase of superfluid He3. Compared to the B phase [class DIII in classification of A. Altland and M. R. Zirnbauer, Phys. Rev. B 55, 1142 (1997), 10.1103/PhysRevB.55.1142], it has an additional symmetry, which modifies the topology. We analyze the topology in terms of explicit mappings from the momentum space and also discuss explicitly topological invariants for the B phase. We further show how the bulk-boundary correspondence for the three-dimensional (3D) B phase can be inferred from that for the 2D planar phase. A general condition is derived for the existence of topologically stable zero modes at the surfaces of 3D superconductors with class-DIII symmetries.

  7. Enhanced trapped field performance of bulk high-temperature superconductors using split coil, pulsed field magnetization with an iron yoke

    NASA Astrophysics Data System (ADS)

    Ainslie, M. D.; Fujishiro, H.; Mochizuki, H.; Takahashi, K.; Shi, Y.-H.; Namburi, D. K.; Zou, J.; Zhou, D.; Dennis, A. R.; Cardwell, D. A.

    2016-07-01

    Investigating and predicting the magnetization of bulk superconducting materials and developing practical magnetizing techniques is crucial to using them as trapped field magnets in engineering applications. The pulsed field magnetization (PFM) technique is considered to be a compact, mobile and relative inexpensive way to magnetize bulk samples, requiring shorter magnetization times (on the order of milliseconds) and a smaller and less complicated magnetization fixture; however, the trapped field produced by PFM is generally much smaller than that of slower zero field cooling or field cooling techniques, particularly at lower operating temperatures. In this paper, the PFM of two, standard Ag-containing Gd-Ba-Cu-O samples is carried out using two types of magnetizing coils: (1) a solenoid coil, and (2) a split coil, both of which make use of an iron yoke to enhance the trapped magnetic field. It is shown that a significantly higher trapped field can be achieved using a split coil with an iron yoke, and in order to explain these how this arrangement works in detail, numerical simulations using a 2D axisymmetric finite element method based on the H -formulation are carried to qualitatively reproduce and analyze the magnetization process from both electromagnetic and thermal points of view. It is observed that after the pulse peak significantly less flux exits the bulk when the iron core is present, resulting in a higher peak trapped field, as well as more overall trapped flux, after the magnetization process is complete. The results have important implications for practical applications of bulk superconductors as such a split coil arrangement with an iron yoke could be incorporated into the design of a portable, high magnetic field source/magnet to enhance the available magnetic field or in an axial gap-type bulk superconducting electric machine, where iron can be incorporated into the stator windings to (1) improve the trapped field from the magnetization process

  8. Comparative studies between the influence of single- and multi-walled carbon nanotubes addition on Gd-123 superconducting phase

    NASA Astrophysics Data System (ADS)

    Abou-Aly, A. I.; Anas, M.; Ebrahim, Shaker; Awad, R.; Eldeen, I. G.

    2016-12-01

    The effect of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) addition on the phase formation and the superconducting properties of GdBa2Cu3O7-δ phase has been studied. Therefore, composite superconductor samples of type (CNTs)x GdBa2Cu3O7-δ, 0.0 ≤ x ≤ 0.1 wt.% have been synthesized by a standard solid-state reaction technique. The samples have been characterized using X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results of XRD show an enhancement in the phase formation up to 0.06 wt.% and 0.08 wt.% for SWCNTs and MWCNTs, respectively. SEM and TEM reveal that CNTs form an electrical network resulting in well-connected superconducting grains. The electrical properties of the prepared samples have been examined by electric resistivity and I-V measurements, and their results reinforce the XRD, SEM and TEM. Consequently, both Tc and Jc improve as the addition percentage increases up to 0.06 wt.% and 0.08 wt.% for SWCNTs and MWCNTs, respectively.

  9. Bulk viscosity of spin-one color superconductors with two quark flavors

    SciTech Connect

    Sa'd, Basil A.; Shovkovy, Igor A.; Rischke, Dirk H.

    2007-03-15

    We consider the contribution of the Urca-type processes to the bulk viscosity of several spin-one color-superconducting phases of dense two-flavor quark matter. In the so-called transverse phases which are suggested to be energetically favorable at asymptotic densities, the presence of ungapped quasiparticle modes prevents that spin-one color superconductivity has a large effect on the bulk viscosity. When all modes are gapped, as for one particular color-spin-locked phase, the effect on the viscosity can be quite large, which may have important phenomenological implications.

  10. Significant flux trapping in single grain GdBCO bulk superconductor under off-axis field cooled magnetization

    NASA Astrophysics Data System (ADS)

    Li, Zhi; Ida, Tetsuya; Miki, Motohiro; Teshima, Hidekazu; Morita, Mitsuru; Izumi, Mitsuru

    2017-03-01

    A single grain bulk high-temperature superconductor (HTS) exhibits intensified flux trapping performance upon field cooled magnetization. The world record of trapped flux is 17.6 T achieved by using stacked two-fold GdBCO bulks. However, the majority of magnetization studies focused on the magnetization along the crystallographic c-axis. In the present study, we clarify the flux trapping performance under field cooled magnetization using an off-axis magnetic field with respect to the c-axis. The results show that the trapped flux is almost polarized along the applied field as expected. This tendency remains up to a high off-axis angle θ around 60°. It is worth mentioning that, with θ of 30°, the maximum trapped flux component B // max parallel to the c-axis significantly remains more than 96% of 1.6 T which occurs under on-axis magnetization. Meanwhile, the angular dependence of the c-axis parallel component exhibits that observed flux density is higher than that expected from 1.6 cosθ. In addition, to visualize the flux line upon magnetization at θ of 90°, we successfully demonstrate the continuous flux line trace using steel wires; different trapped flux behaviour appears when applied field penetrates the bulk through the growth sectors centre and along the growth sector boundary, respectively. We interpret these results may come from the microstructure as a result of melt growth. It is highly emphasized that the off-axis magnetization with the finite inclination angle is quite useful for introducing into the design of HTS applications.

  11. Superconducting properties of adipic-acid-doped bulk MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Vajpayee, Arpita; Awana, V. P. S.; Bhalla, G. L.; Bhobe, P. A.; Nigam, A. K.; Kishan, H.

    2009-01-01

    We report the effect of adipic acid (C6H10O4) doping on lattice parameters, microstructure, critical temperature (Tc), current density (Jc) and irreversibility field (Hirr) for an MgB2 superconductor. Actual carbon (C) substitution level for boron (B) is estimated to be from 0.40 at.% to 2.95 at.% for different doping levels. A reduction in Tc from 38.43 to 34.93 K and in lattice parameter a from 3.084(3) Å to 3.075(6) Å is observed for the 10 wt% C6H10O4 doped sample in comparison to pristine MgB2. This is an indication of C substitution at boron sites, with the C coming from the decomposition of C6H10O4 at the time of reaction. Interestingly the doped samples have resulted in significant enhancement of Jc and Hirr. All the doped samples exhibit the Jc value of the order of 104 A cm-2 at 5 K and 8 T, which is higher by an order of magnitude as compared to the undoped sample. This result indicates that C6H10O4 is a promising material for MgB2 for obtaining the excellent Jc values under higher magnetic fields.

  12. Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films.

    PubMed

    Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X J

    2016-02-08

    The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.

  13. Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films

    PubMed Central

    Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X. J.

    2016-01-01

    The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors. PMID:26853801

  14. Processing of Bulk YBa2Cu3O(7-x) High Temperature Superconductor Materials for Gravity Modification Experiments and Performance Under AC Levitation

    NASA Technical Reports Server (NTRS)

    Koczor, Ronald; Noever, David; Hiser, Robert

    1999-01-01

    We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of bulk-processed high temperature superconductor disks. Others have indicated that large annular disks (on the order of 25cm diameter) and AC levitation fields play an essential role in their observed experiments. We report experiments in processing such large bulk superconductors. Successful results depend on material mechanical characteristics, and pressure and heat treat protocols. Annular disks having rough dimensions of 30cm O.D., 7cm I.D. and 1 cm thickness have been routinely fabricated and tested under AC levitation fields ranging from 45 to 300OHz. Implications for space transportation initiatives and power storage flywheel technology will be discussed.

  15. Melt-processed bulk superconductors: Fabrication and characterization for power and space applications

    NASA Technical Reports Server (NTRS)

    Hojaji, Hamid; Barkatt, Aaron; Hu, Shouxiang; Thorpe, Arthur N.; Ware, Matthew F.; Davis, David; Alterescu, Sidney

    1991-01-01

    Melt-process bulk superconducting materials based on variations on the base YBa2Cu3O(x) were produced in a variety of shapes and forms. Very high values of both zero-field and high-field magnetization were observed. These are useful for levitation and power applications. Magnetic measurements show that the effects of field direction and intensity, temperature and time are consistent with an aligned grain structure with multiple pinning sites and with models of thermally activated flux motion.

  16. Radiation detector using a bulk high T[sub c] superconductor

    DOEpatents

    Artuso, J.F.; Franks, L.A.; Hull, K.L.; Symko, O.G.

    1993-12-07

    A radiation detector is provided, wherein a bulk high T[sub c] superconducting sample is placed in a magnetic field and maintained at a superconducting temperature. Photons of incident radiation will cause localized heating in superconducting loops of the sample destroying trapped flux and redistributing the fluxons, and reducing the critical current of the loops. Subsequent cooling of the sample in the magnetic field will cause trapped flux redistributed Abrikosov fluxons and trapped Josephson fluxons. The destruction and trapping of the fluxons causes changes in the magnetization of the sample inducing currents in opposite directions in a pickup coil which is coupled by an input coil to an rf SQUID. 4 figures.

  17. Numerical simulations of electromagnetic behavior and AC loss in rectangular bulk superconductor with an elliptical flaw under AC magnetic fields

    NASA Astrophysics Data System (ADS)

    Xia, Jing; Zhou, Youhe

    2015-07-01

    This paper presents a finite element model based on the H-formulation to solve the electromagnetic behavior and AC loss in rectangular bulk superconductor with an elliptical flaw in AC external field condition. Both the interior flaw and the edge flaw are considered. A modified E-J power law which is valid for an arbitrary current density range is adopted in order to predict the strong local enhancement of the current density in the vicinity of the flaw tip. The results for the usual E-J power law are calculated for comparison as well. The simulation results show that the existence of the flaw significantly blocks the flow of the induced current and forces the current to redistribute around it. Meanwhile, the strong local enhancement of the current density is observed in the vicinity of the flaw tip. Furthermore, the influences of the size and position of the flaw on the local enhancement of the current density in the vicinity of the flaw tip are investigated. In addition, it is found that the influence of the flaw on the AC loss of the sample is slight for both cases of the interior flaw and the edge flaw.

  18. Simulation studies on the magnetization of (RE)BCO bulk superconductors using various split-coil arrangements

    NASA Astrophysics Data System (ADS)

    Xu, Zhihan; Lewin, Richard; Campbell, Archie M.; Cardwell, David A.; Jones, Harry

    2012-02-01

    Simulation studies were conducted on the magnetization of (RE)BCO (RE-Ba-Cu-O, where RE represents a rare earth element) bulk superconductors using various split-coil arrangements by solving the critical state equation using the commercial software FlexPDE. A pair of coaxial coils of identical size is identified as an optimum arrangement for practical magnetization at 77 K by the ‘zero-field cooling’ technique. In general, the magnetization process is likely to be most effective when the outer radius of the coils lies between 100% and 50% of the sample radius. A relatively large coil pair is necessary for samples with either a smaller aspect ratio or larger values of Jc0. Two different regimes of flux penetration are found to be involved in the magnetization process. For a sufficiently small sample, the penetration field is determined by flux propagation from beneath the coil to the centre of the sample; for a sufficiently large sample, the definitive propagation route is from beneath the coil to the periphery of the sample. Effective split-coil magnetization occurs only in the former regime, and both penetration regimes are completely different from that involved in the solenoidal-coil magnetization process.

  19. Influence of lateral displacement on the levitation performance of a magnetized bulk high-Tc superconductor magnet

    NASA Astrophysics Data System (ADS)

    Liu, W.; Wang, J. S.; Ma, G. T.; Zheng, J.; Tuo, X. G.; Li, L. L.; Ye, C. Q.; Liao, X. L.; Wang, S. Y.

    2012-03-01

    Compared with the permanent magnet, the magnetized bulk high-Tc superconductor magnet (MBSCM) can trap higher magnetic field due to its strong flux pinning ability, so it is a good candidate to improve the levitation performance of high-Tc superconductive (HTS) maglev system. The trapped magnetic flux of a MBSCM is sustained by the inductive superconducting current produced by the magnetizing process and is susceptible to the current intensity as well as configuration. In the HTS maglev system, the lateral displacement is an important process to change the superconducting current within a MBSCM and then affects its levitation performance, which is essential for the traffic ability in curve-way, the loading capacity of lateral impact and so on. The research about influence of lateral displacement on the levitation performance of MBSCM is necessary when MBSCM is applied on the HTS maglev vehicle. The experimental investigations about the influence of lateral displacement on the levitation performance of a MBSCM with different trapped fluxes and applied fields are processed in this article. The analyses and conclusions of this article are useful for the practical application of MBSCM in HTS maglev system.

  20. Universal bulk charge-density-wave (CDW) correlations in the cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Tabis, Wojciech

    2014-03-01

    The recent observation of bulk CDW order in YBa2Cu3O8+δ(YBCO) in competition with superconductivity is a significant development. Using Cu L-edge resonant X-ray scattering, we also observe bulk CDW order in HgBa2CuO4+δ(Hg1201 Tc = 72K). The correlations appear below TCDW ~ 200K, well below the pseudogap temperature T* ~ 320K associated with unusual magnetism, but coincident with the onset of Fermi-liquid-like charge transport. In contrast to YBCO, we observe no decrease of the CDW amplitude below Tc, and the correlation length is short and temperature independent. CDW correlations therefore are a universal property of underdoped cuprates, enhanced by low structural symmetry and a magnetic field, but fundamentally not in significant competition with superconductivity. We also discuss the relationship between the CDW modulation wave vector and the Fermi surface area extracted from QO experiments. Work supported by DOE-BES. In collaboration with Y. Li, M. Le Tacon, L. Braicovich, A. Kreyssig, M. Minola, G. Dellea, E. Weschke, M. Veit, A. Goldman, T. Schmitt, G. Ghiringhelli, N. Barisic, M.K. Chan, C. Dorow, G. Yu, X. Zhao, B. Keimer, M. Greven.

  1. Comparison of the effects of platinum and CeO2 on the properties of single grain, Sm-Ba-Cu-O bulk superconductors

    NASA Astrophysics Data System (ADS)

    Zhao, Wen; Shi, Yunhua; Radušovská, Monika; Dennis, Anthony R.; Durrell, John H.; Diko, Pavel; Cardwell, David A.

    2016-12-01

    SmBa2Cu3O7-δ (Sm-123) is a light-rare-earth barium-cuprate (LRE-BCO) high-temperature superconductor (HTS) with significant potential for high field industrial applications. We report the fabrication of large, single grain bulk [Sm-Ba-Cu-O (SmBCO)] superconductors containing 1 wt% CeO2 and 0.1 wt% Pt using a top-seeded melt growth process. The performance of the SmBCO bulk superconductors containing the different dopants was evaluated based on an analysis of their superconducting properties, including critical transition temperature, T c and critical current density, J c , and on sample microstructure. We find that both CeO2 and Pt dopants refine the size of Sm2BaCuO5 (Sm-211) particles trapped in the Sm-123 superconducting phase matrix, which act as effective flux pinning centres, although the addition of CeO2 results in broadly improved superconducting performance of the fully processed bulk single grain. However, 1 wt% CeO2 is significantly cheaper than 0.1 wt% Pt, which has clear economic benefits for use in medium to large scale production processes for these technologically important materials. Finally, the use of CeO2 results generally in the formation of finer Sm-211 particles and to the generation of fewer macro-cracks and Sm-211 free regions in the sample microstructure.

  2. Radiation detector using a bulk high T.sub.c superconductor

    DOEpatents

    Artuso, Joseph F.; Franks, Larry A.; Hull, Kenneth L.; Symko, Orest G.

    1993-01-01

    A radiation detector (10) is provided, wherein a bulk high T.sub.c superconducting sample (11) is placed in a magnetic field and maintained at a superconducting temperature. Photons of incident radiation will cause localized heating in superconducting loops of the sample destroying trapped flux and redistributing the fluxons, and reducing the critical current of the loops. Subsequent cooling of the sample in the magnetic field will cause trapped flux redistributed Abrikosov fluxons and trapped Josephson fluxons. The destruction and trapping of the fluxons causes changes in the magnetization of the sample inducing currents in opposite directions in a pickup coil (12) which is coupled by an input coil (15) to an rf SQUID (16).

  3. Magnetic levitation and its application for education devices based on YBCO bulk superconductors

    NASA Astrophysics Data System (ADS)

    Yang, W. M.; Chao, X. X.; Guo, F. X.; Li, J. W.; Chen, S. L.

    2013-10-01

    A small superconducting maglev propeller system, a small spacecraft model suspending and moving around a terrestrial globe, several small maglev vehicle models and a magnetic circuit converter have been designed and constructed. The track was paved by NdFeB magnets, the arrangement of the magnets made us easy to get a uniform distribution of magnetic field along the length direction of the track and a high magnetic field gradient in the lateral direction. When the YBCO bulks mounted inside the vehicle models or spacecraft model was field cooled to LN2 temperature at a certain distance away from the track, they could be automatically floating over and moving along the track without any obvious friction. The models can be used as experimental or demonstration devices for the magnetic levitation applications.

  4. Enhancement of trapped field in single grain Y-Ba-Cu-O bulk superconductors by a modified top-seeded melt-textured growth

    NASA Astrophysics Data System (ADS)

    Tang, Tian-wei; Wu, Dong-jie; Xu, Ke-Xi

    2016-08-01

    The modified top-seeded melt-textured growth technique for fabricating single grain Y-Ba-Cu-O (YBCO) bulk superconductors with high field-trapping ability by using modified precursor pellets was reported. The modified precursor pellets are composed of different precursor powders YBa2Cu3O{}7-δ (Y123) + x mol% Y2BaCuO5 (Y211) + 1 wt% CeO2 without any further chemical doping. The modified YBCO bulks up to 25 and 34 mm in diameter were successfully fabricated from the modified precursor pellets. Microstructural observation results showed that the modified YBCO bulk exhibited a homogeneous distribution of Y211 phase particles, which was qualitatively explained by the solute diffusion growth model in combination with the trapping/pushing theory. As a result, it is notable that the peak trapped field values of 0.91 T (maximum 0.96 T) and 1.2 T (maximum 1.28 T) at 77 K were achieved for 25 and 34 mm modified YBCO bulks, respectively. In a word, the results from present work are very helpful to understand the melt growth mechanism and to further improve the properties of YBCO bulk superconductors for practical applications.

  5. Investigation on the levitation force behaviour of malic acid added bulk MgB2 superconductors

    NASA Astrophysics Data System (ADS)

    Savaskan, B.; Taylan Koparan, E.; Celik, S.; Ozturk, K.; Yanmaz, E.

    2014-07-01

    The effects of malic acid addition (from 0 to 15 wt% of the total MgB2) on the levitation force properties of bulk MgB2 have been investigated. All samples were prepared from magnesium powder, amorphous boron powder, malic acid (C4H6O5) and toluene (C7H8) by using two-step solid state reaction method. Vertical and lateral levitation force measurements that are under both zero-field-cooled (ZFC) and field-cooled (FC) regimes were carried out at different temperatures of 24, 28 and 32 K for samples with various adding level. It was found that the reasonable malic acid adding has a positive impact on the levitation properties. At 24 K and 28 K, the 4 wt% and 6 wt% malic acid added samples exhibits a higher levitation force than pure sample. In the case of the optimally additive 4 wt% sample, the maximum levitation force corresponds to 18.60 N, whereas the pure sample shows 16.95 N at 24 K for ZFC regime. In this study the enhancing effect of malic acid adding on the levitation force properties of MgB2 has been first time investigated and reported.

  6. Quenching characteristics of electrical contacts using YBaCuO bulk superconductor

    NASA Astrophysics Data System (ADS)

    Fukuda, K.; Fujita, H.; Ogawa, K.; Tomita, M.; Murakami, M.; Sakai, N.; Hirabayashi, I.; Sawa, K.

    2008-09-01

    A persistent current switch (PCS) is used for various superconducting applications, such as superconducting magnetic energy storage (SMES) system. The authors have proposed a mechanical switch of Y-Ba-Cu-O (YBCO) bulk as a PCS. In previous study, in order to investigate the contact characteristics of the switch, 50 A current test was performed and the contact resistance between two contacts was measured by four terminal method. As a result, it became clear that polishing and metal depositing on YBCO surface was effective to reduce the residual resistance, and the authors achieved to reduce this resistance to 0.27 μΩ, which was less than our target value of 1 μΩ. At the same time, the greater current test (above 50 A) was performed in order to examine the transition to normal conductive state in the YBCO contacts. As a result, it could be found that the current value when a local quench occurred (local quenching current: LQC) had a strong relationship with the layer thickness of deposited silver on YBCO surface. This paper focused on the relationship between the transition current to the normal conductive state in the YBCO (quenching current) and the layer thickness of deposited silver on YBCO surface. And it was also observed whether the number of current cycles affected the value of quenching current.

  7. Irreversibility Line Measurement and Vortex Dynamics in High Magnetic Fields in Ni- and Co-Doped Iron Pnictide Bulk Superconductors

    DOE PAGES

    Nikolo, Martin; Singleton, John; Zapf, Vivien S.; ...

    2016-07-20

    The de-pinning or irreversibility lines were determined by ac susceptibility, magnetization, radio-frequency proximity detector oscillator (PDO), and resistivity methods in Ba(Fe0.92Co0.08)2As2 ( Tc = 23.2 K), Ba(Fe0.95Ni0.05)2As2 ( Tc = 20.4 K), and Ba(Fe0.94Ni0.06)2As2 ( Tc = 18.5 K) bulk superconductors in ac, dc, and pulsed magnetic fields up to 65 T. A new method of extracting the irreversibility fields from the radio-frequency proximity detector oscillator induction technique is described. Wide temperature broadening of the irreversibility lines, for any given combination of ac and dc fields, is dependent on the time frame of measurement. Increasing the magnetic field sweep ratemore » (dH/dt) shifts the irreversibility lines to higher temperatures up to about dH/d t = 40,000 Oe/s; for higher dH/dt, there is little impact on the irreversibility line. There is an excellent data match between the irreversibility fields obtained from magnetization hysteresis loops, PDO, and ac susceptibility measurements, but not from resistivity measurements in these materials. Lower critical field vs. temperature phase diagrams are measured. Their very low values near 0 T indicate that these materials are in mixed state in nonzero magnetic fields, and yet the strength of the vortex pinning enables very high irreversibility fields, as high as 51 T at 1.5 K for the Ba(Fe0.92Co0.08)2As2 polycrystalline sample, showing a promise for liquid helium temperature applications.« less

  8. Influence of layered precursor pellets on the growth and properties of Y-Ba-Cu-O bulk superconductors by top-seeded melt-textured growth

    NASA Astrophysics Data System (ADS)

    Tang, Tian-wei; Wu, Dong-jie; Xu, Ke-Xi

    2016-03-01

    It is well known that a fine and homogeneous distribution of Y2BaCuO5 (Y211) phase particles in single-grain Y-Ba-Cu-O (YBCO) bulk superconductors is essential for improving field-trapping ability. However, the size and concentration of Y211 phase particles in the fully melt-processed superconducting bulk increase significantly with the distance from the seed, which results in the accumulation of Y211 phase particles and the degradation of superconducting properties. In this paper, we report a new method of fabricating single-grain YBCO using layered precursor pellets. Using the top-seeded melt-textured growth process, single-grain YBCO bulk superconductors of about 22 mm in diameter and 9 mm in thickness were fabricated from layered precursor pellets and standard precursor pellets, respectively. The layered precursor pellets consist of precursor powders with 40 mol% Y211 at the top, 30 mol% Y211 in the middle and 20 mol% Y211 at the bottom of the whole pellets, while standard precursor pellets are prepared from precursor powders with only 40 mol% Y211. The growth morphology, microstructure and magnetic flux properties of the layered samples and standard samples were comparatively studied. The results proved that the layered precursor pellets allow a sufficient growth in the c-growth sector and a more uniform distribution of the Y211 phase in the matrix. The distribution of Y211 phase particles is qualitatively explained by the prevalent trapping/pushing theory. The trapped field at 77 K reaches 0.8 T, nearly 29% higher than the standard sample. The present results are very valuable for further improving the properties of YBCO bulk superconductors.

  9. Irreversibility Line Measurement and Vortex Dynamics in High Magnetic Fields in Ni- and Co-Doped Iron Pnictide Bulk Superconductors

    SciTech Connect

    Nikolo, Martin; Singleton, John; Zapf, Vivien S.; Jiang, Jianyi; Weiss, Jeremy D.; Hellstrom, Eric E.

    2016-07-20

    The de-pinning or irreversibility lines were determined by ac susceptibility, magnetization, radio-frequency proximity detector oscillator (PDO), and resistivity methods in Ba(Fe0.92Co0.08)2As2 ( Tc = 23.2 K), Ba(Fe0.95Ni0.05)2As2 ( Tc = 20.4 K), and Ba(Fe0.94Ni0.06)2As2 ( Tc = 18.5 K) bulk superconductors in ac, dc, and pulsed magnetic fields up to 65 T. A new method of extracting the irreversibility fields from the radio-frequency proximity detector oscillator induction technique is described. Wide temperature broadening of the irreversibility lines, for any given combination of ac and dc fields, is dependent on the time frame of measurement. Increasing the magnetic field sweep rate (dH/dt) shifts the irreversibility lines to higher temperatures up to about dH/d t = 40,000 Oe/s; for higher dH/dt, there is little impact on the irreversibility line. There is an excellent data match between the irreversibility fields obtained from magnetization hysteresis loops, PDO, and ac susceptibility measurements, but not from resistivity measurements in these materials. Lower critical field vs. temperature phase diagrams are measured. Their very low values near 0 T indicate that these materials are in mixed state in nonzero magnetic fields, and yet the strength of the vortex pinning enables very high irreversibility fields, as high as 51 T at 1.5 K for the Ba(Fe0.92Co0.08)2As2 polycrystalline sample, showing a promise for liquid helium temperature applications.

  10. Control of Y-211 content in bulk YBCO superconductors fabricated by a buffer-aided, top seeded infiltration and growth melt process

    NASA Astrophysics Data System (ADS)

    Namburi, Devendra K.; Shi, Yunhua; Palmer, Kysen G.; Dennis, Anthony R.; Durrell, John H.; Cardwell, David A.

    2016-03-01

    Bulk (RE)-Ba-Cu-O ((RE)BCO, where RE stands for rare-earth), single grain superconductors can trap magnetic fields of several tesla at low temperatures and therefore can function potentially as high field magnets. Although top seeded melt growth (TSMG) is an established process for fabricating relatively high quality single grains of (RE)BCO for high field applications, this technique suffers from inherent problems such as sample shrinkage, a large intrinsic porosity and the presence of (RE)2BaCuO5 (RE-211)-free regions in the single grain microstructure. Seeded infiltration and growth (SIG), therefore, has emerged as a practical alternative to TSMG that overcomes many of these problems. Until now, however, the superconducting properties of bulk materials processed by SIG have been inferior to those fabricated using the TSMG technique. In this study, we identify that the inferior properties of SIG processed bulk superconductors are related to the presence of a relatively large Y-211 content (˜41.8%) in the single grain microstructure. Controlling the RE-211 content in SIG bulk samples is particularly challenging because it is difficult to regulate the entry of the liquid phase into the solid RE-211 preform during the infiltration process. In an attempt to solve this issue, we have investigated the effect of careful control of both the infiltration temperature and the quantity of liquid phase powder present in the sample preforms prior to processing. We conclude that careful control of the infiltration temperature is the most promising of these two process variables. Using this knowledge, we have fabricated successfully a YBCO bulk single grain using the SIG process of diameter 25 mm that exhibits a trapped field of 0.69 T at 77 K, which is the largest value reported to date for a sample fabricated by the SIG technique.

  11. Superconductor consolidation

    SciTech Connect

    Staudhammer, K.P.

    1988-01-01

    A program to develop explosively shock consolidated monoliths of YBa/sub 2/Cu/sub 3/O/sub 7/minus/x/ ceramic superconductors has been ongoing at Los Alamos National Laboratory since last year. Shock consolidation can produce a near 100% theoretical density, bulk superconductor that does not require a post anneal in oxygen. Shock compaction is also an excellent means of creating a good electrical contact weld between the ceramic superconductor and a metal such as copper. Elimination of the post anneal and low temperature shock welding of the cladding metal are unique advantages stemming from the shock compaction processing. Successful shock compaction processing will enable production of a wide variety of complex ceramic-superconductor forms tailored for specific defense application requirements. Shock compaction can be developed into industrial manufacturing processes. DuPont now makes diamond powder this way. Shock compacted superconductor billets can be used in applications where a solid superconductor form is required (e.g., magnetic bearings, bus bar for a niobium-tin FEL SMES, motor rotors, etc.), or they can be post processed by extrusion and other swaging processes to produce textured wires and tapes for electrical current carrying applications. 11 refs., 1 fig.

  12. Superconductor consolidation

    NASA Astrophysics Data System (ADS)

    Staudhammer, K. P.

    A program to develop explosively shock consolidated monoliths of YBa2Cu3O(sub 7-x) ceramic superconductors has been ongoing at Los Alamos National Laboratory since last year. Shock consolidation can produce a near 100 percent theoretical density, bulk superconductor that does not require a post anneal in oxygen. Shock compaction is also an excellent means of creating a good electrical contact weld between the ceramic superconductor and a metal such as copper. Elimination of the post anneal and low temperature shock welding of the cladding metal are unique advantages stemming from the shock compaction processing. Successful shock compaction processing will enable production of a wide variety of complex ceramic superconductor forms tailored for specific defense application requirements. Shock compaction can be developed into industrial manufacturing processes. Shock compacted superconductor billets can be used in applications where a solid superconductor form is required (e.g., magnetic bearings, bus bar for a niobium-tin FEL SMES, motor rotors, etc.) or they can be post processed by extrusion and other swaging processes to produce textured wires and tapes for electrical current carrying applications.

  13. The Fabrication of (bismuth, LEAD)(2) STRONTIUM(2) CALCIUM(2) COPPER(3) Oxygen(x) Superconductor in Bulk and Tape Forms

    NASA Astrophysics Data System (ADS)

    Lim, Hanjin

    High-T_{rm c}<=ad doped rm Bi_2Sr_2Ca_2Cu _2Cu_3O_{x} (BSCCO 2223) superconductor bulk materials were prepared using conventional powder metallurgy techniques, which were made from precursors having different histories. The ease of formation of superconducting phases was highly dependent on the processing of primitive powder. With the three -powder process that combines three kinds of calcined precursor powders, the formation of the BSCCO superconductor was accelerated and the amount of the secondary phase (e.g., Ca_2CuO_3) was reduced. The critical transition temperature (T _{rm c}) of the superconductor from the three-powder process is higher than that from the one-powder process. In lead-doped BSCCO 2223, positron trapping and annihilation evidently occur in the open BiO double layers rather than in the superconducting CuO_2 layers of the structure. Both positron annihilation parameters (tau_1, tau _2, overlinetau) and Doppler parameters (P, W, P/W) were insensitive to the superconducting transition in this material. This is quite opposite to the case of YBCO and Dy doped YBCO where positron annihilation is sensitive to the superconducting transition. High-T_{rm c} BSCCO superconducting tapes were fabricated using the powder -in-tube (PIT) method that includes heat treatments as well as mechanical processing such as drawing, rolling, and pressing. The highest critical current densities (J _{rm c}) at 5 and 77 K were 5.12 times 10^5 A/cm^2 and 1.77 times 10^4 A/cm^2 , respectively, for the tape sample which was solid state processed at 840^circC with three short sintering steps. J_{ rm c} values at 5 and 77 K of tape samples were 1 and 2 orders of magnitude higher than those of bulk samples, respectively. The preferred orientations of the BSCCO 2212 phase in the tape samples were basal and (1 1 13) textures; for the BSCCO 2223 phase preferred orientations were also basal and (1 1 19) textures. By taking the ratios of the texture coefficients (TCs) for (0 0 1) and

  14. A novel, two-step top seeded infiltration and growth process for the fabrication of single grain, bulk (RE)BCO superconductors

    NASA Astrophysics Data System (ADS)

    Namburi, Devendra K.; Shi, Yunhua; Palmer, Kysen G.; Dennis, Anthony R.; Durrell, John H.; Cardwell, David A.

    2016-09-01

    A fundamental requirement of the fabrication of high performing, (RE)-Ba-Cu-O bulk superconductors is achieving a single grain microstructure that exhibits good flux pinning properties. The top seeded melt growth (TSMG) process is a well-established technique for the fabrication of single grain (RE)BCO bulk samples and is now applied routinely by a number of research groups around the world. The introduction of a buffer layer to the TSMG process has been demonstrated recently to improve significantly the general reliability of the process. However, a number of growth-related defects, such as porosity and the formation of micro-cracks, remain inherent to the TSMG process, and are proving difficult to eliminate by varying the melt process parameters. The seeded infiltration and growth (SIG) process has been shown to yield single grain samples that exhibit significantly improved microstructures compared to the TSMG technique. Unfortunately, however, SIG leads to other processing challenges, such as the reliability of fabrication, optimisation of RE2BaCuO5 (RE-211) inclusions (size and content) in the sample microstructure, practical oxygenation of as processed samples and, hence, optimisation of the superconducting properties of the bulk single grain. In the present paper, we report the development of a near-net shaping technique based on a novel two-step, buffer-aided top seeded infiltration and growth (BA-TSIG) process, which has been demonstrated to improve greatly the reliability of the single grain growth process and has been used to fabricate successfully bulk, single grain (RE)BCO superconductors with improved microstructures and superconducting properties. A trapped field of ˜0.84 T and a zero field current density of 60 kA cm-2 have been measured at 77 K in a bulk, YBCO single grain sample of diameter 25 mm processed by this two-step BA-TSIG technique. To the best of our knowledge, this value of trapped field is the highest value ever reported for a sample

  15. Melting of SmBa2Cu3O7-y-seeds during preparation of YBCO Bulk Superconductors by Infiltration Growth Method

    NASA Astrophysics Data System (ADS)

    Vojtkova, L.; Diko, P.; Volochová, D.

    2016-03-01

    The conditions for single-grain growth of YBCO bulk superconductors by top seeded infiltration growth were tested. It is shown that the interaction of melt formed from BaCuO2 + CuO + Y2O3 precursor with the Sm123 seed causes dissolution of the seed at maximum melting temperature 1045 °C. Experiments with low weight Y211 pellet confirmed that the low concentration of Y in the infiltration melt is responsible for this effect. The most effective way suppressing the seed dissolution was shown to be the insertion of Y123 + Y211 buffer layer between the seed and the Y211 pellet. This buffer layer possesses the melt which is saturated with yttrium what prevents dissolution of the seed.

  16. Bulk evidence for single-Gap s-wave superconductivity in the intercalated graphite superconductor C6Yb.

    PubMed

    Sutherland, Mike; Doiron-Leyraud, Nicolas; Taillefer, Louis; Weller, Thomas; Ellerby, Mark; Saxena, S S

    2007-02-09

    We report measurements of the in-plane electrical resistivity rho and thermal conductivity kappa of the intercalated graphite superconductor C6Yb down to temperatures as low as Tc/100. When a field is applied along the c axis, the residual electronic linear term kappa0/T evolves in an exponential manner for Hc1

  17. Analysis of the levitation force of pure and starch/polystyrene/MWCNT added bulk MgB2 superconductors using frozen image model under zero field cooling condition

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Dey, T. K.

    2016-04-01

    The measurement of superconducting levitation force between permanent magnet and polycrystalline samples of pure and MgB2 added with starch, polystyrene (PS) and multiwall carbon nanotube (MWCNT) have been performed under zero field cooling (ZFC) condition at 20 K in both descending and ascending modes. For this, the bulk pellets were synthesized by conventional solid state sintering technique. The XRD data indicate well developed MgB2 phase. However, a decrease in lattice parameter 'a = b' have been observed for doped MgB2 samples. Superconducting transition temperature of MgB2 also decreases with starch/PS/MWCNT addition. Unlike MWCNT, the addition of starch/polystyrene is found to enhance the levitation force of MgB2 superconductor. The levitation force between PM and investigated pellets in ZFC condition is explained well in terms of the updated version of modified frozen image model and the magnetic moment originated due to vertical motion of the superconductors have been estimated. It may be noted that except for MWCNT, addition of starch/PS in MgB2 improves the magnetic moment generated by vertical movement of pure MgB2. However, this improvement is more pronounced for 1 wt.% of PS added MgB2, which indicates more flux trapping and hence better levitation properties in 1 wt.% of PS added MgB2. The vertical stiffness estimated for pure and starch/PS/MWCNT doped MgB2 samples indicate that the levitation force are more sensitive in the region close to the PM.

  18. Solid state synthesis and characterization of bulk FeTe0.5Se0.5 superconductors

    NASA Astrophysics Data System (ADS)

    Onar, K.; Yakinci, M. E.

    2016-01-01

    FeTe0.5Se0.5 polycrystalline superconductor samples were synthesized by solid- state reaction method at different heating temperatures. The morphological and structural characterization of FeTe0 5Se0.5 samples were carried out by X-rays Diffraction, Scanning Electron Microscope and Energy Dispersive X-ray Spectroscopy. The electrical, magnetic and thermal transport properties were investigated up to 8 T by using physical property measurement system. The results reveal that the sensitivity of electrical and magnetic properties strongly depends on the heat treatment cycles. The upper critical field, Hc2(0), was determined with the magnetic field parallel to the sample surface. It gives a maximum value of 36.3 T. The lower critical field, Hc1(T), was obtained as 210, 140 and 70 Oe at 5, 8 and 12 K, respectively. The coherence length, ξ, at the zero field, was calculated to be 1.94 nm and suggested a transparent intergrain boundaries peculiarity. The μ0Hc2(0)/kBTc rate shows higher value (3.36 T/K) than the Pauli limit (1.84 T/K) which suggests unconventional nature of superconductivity for the polycrystalline FeTe0.5Se0.5 superconducting samples.

  19. Majorana fermions in ferromagnetic chains on the surface of bulk spin-orbit coupled s-wave superconductors

    PubMed Central

    Hui, Hoi-Yin; Brydon, P. M. R.; Sau, Jay D.; Tewari, S.; Sarma, S. Das

    2015-01-01

    Majorana fermion (MF) excitations in solid state system have non-Abelian statistics which is essential for topological quantum computation. Previous proposals to realize MF, however, generally requires fine-tuning of parameters. Here we explore a platform which avoids the fine-tuning problem, namely a ferromagnetic chain deposited on the surface of a spin-orbit coupled s-wave superconductor. We show that it generically supports zero-energy topological MF excitations near the two ends of the chain with minimal fine-tuning. Depending on the strength of the ferromagnetic moment in the chain, the number of MFs at each end, n, can be either one or two, and should be revealed by a robust zero-bias peak (ZBP) of height 2 ne2/h in scanning tunneling microscopy (STM) measurements which would show strong (weak) signals at the ends (middle) of the chain. The role of an approximate chiral symmetry which gives an integer topological invariant to the system is discussed. PMID:25743763

  20. Process parameters, orientation, and functional properties of melt-processed bulk Y-Ba-Cu-O superconductors

    NASA Astrophysics Data System (ADS)

    Zakharchenko, I. V.; Terryll, K. M.; Rao, K. V.; Balachandran, U.

    1995-12-01

    This study compared the microstructure, texturing, and functional properties (critical currents) of YBa2Cu3O7-x-based bulk pellets that were prepared by the quench-melt-growth-process (QMGP), melt-textured growth, and conventional solid-state reaction approaches. Using two x-ray diffraction methods, θ-2θ, and rocking curves, we found that the individual grains of two melt-processed pellets exhibited remarkable preferred orientational alignment (best rocking curve width < 3.2‡). However, the direction of the preferred orientation among the grains was random. Among the three types of bulk materials studied, the QMGP sample was found to have the best Jc values, ≈4500 A/cm2 at 77K in a field of 2 kG, as determined from superconducting quantum interference device magnetic data.

  1. Pulsed field magnetization of 0°-0° and 45°-45° bridge-seeded Y-Ba-Cu-O bulk superconductors

    NASA Astrophysics Data System (ADS)

    Ainslie, M. D.; Zou, J.; Mochizuki, H.; Fujishiro, H.; Shi, Y.-H.; Dennis, A. R.; Cardwell, D. A.

    2015-12-01

    Large, single-grain (RE)BCO (where RE = rare earth or Y) bulk superconductors with complicated geometries are required for a variety of potential applications, such as rotating machines, magnetic bearings and magnetic separation. As a consequence, the top multi-seeded melt growth process has been studied over many years in an attempt to deliver large, single grains for practical applications. Among these techniques, the so-called bridge-seeding produces the best alignment of two seeds during melt processing of multi-seed samples. In this paper, the trapped field performance and magnetic flux dynamics of two bridge-seeded, multi-seed samples magnetized by pulsed field magnetization are analyzed: one with a 45°-45° and another with a 0°-0° bridge seed. Based on an analysis of the flux penetration across the seeds and in-between the seeds of the 45°-45° multi-seed sample, an estimated J c distribution over the ab-plane is determined, which provides the basis for further analysis via numerical simulation. A three-dimensional finite-element model, developed to qualitatively reproduce and interpret the experimental results, was employed to investigate the influence of the length of the bridge seed for such multi-seed samples. The simulation results agree well with the observed experimental results, in that the multi-seed sample’s particular inhomogeneous J c distribution acts to distort the trapped field profile from a traditional conical Bean’s profile, which is determined by the length and direction of the bridge seed on the bulk surface.

  2. Vortex flux dynamics and harmonic ac magnetic response of Ba(Fe0.94Ni0.06)2As2 bulk superconductor

    DOE PAGES

    Nikolo, Martin; Zapf, Vivien S.; Singleton, John; ...

    2016-07-22

    Vortex dynamics and nonlinear ac response are studied in a Ba(Fe0.94Ni0.06)2As2(Tc= 18.5 K) bulk superconductor in magnetic fields up to 12 T via ac susceptibility measurements of the first ten harmonics. A comprehensive study of the ac magnetic susceptibility and its first ten harmonics finds shifts to higher temperatures with increasing ac measurement frequencies (10 to 10,000 Hz) for a wide range of ac (1, 5, and 10 Oe) and dc fields (0 to 12 T). The characteristic measurement time constant t1 is extracted from the exponential fit of the data and linked to vortex relaxation. The Anderson-Kim Arrhenius lawmore » is applied to determine flux activation energy Ea/k as a function dc magnetic field. The de-pinning, or irreversibility lines, were determined by a variety of methods and extensively mapped. The ac response shows surprisingly weak higher harmonic components, suggesting weak nonlinear behavior. Lastly, our data does not support the Fisher model; we do not see an abrupt vortex glass to vortex liquid transition and the resistivity does not drop to zero, although it appears to approach zero exponentially.« less

  3. The influence of slow cooling on Y211 size and content in single-grain YBCO bulk superconductor through the infiltration-growth process

    NASA Astrophysics Data System (ADS)

    Ouerghi, A.; Moutalbi, N.; Noudem, J. G.; M'chirgui, A.

    2017-03-01

    Highly textured YBa2Cu3O7-δ (Y123) superconductors were produced using modified Textured Top Seeded Infiltration Growth (TSIG) process. The liquid source is made of only Y123 powder whereas the solid source is composed of Y2BaCuO5 (Y211) powder. We aim to control the amount of liquid that infiltrates the solid pellet, which in turn controls the final amount of Y2BaCuO5 particles in Y123 matrix. The effect of the slow cooling kinetics on sample morphology, on grain growth and on final microstructure was too investigated. It is shown that appropriate slow cooling time may also contribute to the control of the amount of Y211 inclusions in the final structure of Y123 bulk. We report herein the Y211 particle size and density distribution in the whole Y123 matrix. The present work proves that finest Y211 particles locate under the seed and that their size and density increase with distance from the seed.

  4. Fabrication and Properties of Bulk and Thick Film YTTRIUM(1) BARIUM(2) COPPER(3) OXYGEN(7-DELTA) Superconductors

    NASA Astrophysics Data System (ADS)

    Bailey, Andrew

    Many of the applications envisaged for the new high critical temperature cuprate superconductors require the ability to produce high quality material in layers of 1-100mum thickness which can be used as prepared, or after patterning into discrete forms. Among the possible applications in the foreseeable future are EMI/EMC shielding, pcb interconnects, inductances, stripline, mixers and resonators. Consequently it is important to establish methods of 'thick film' manufacture which provide the versatility necessary for the wide range of uses. During the course of this research, a variety of processing methods have been studied in an attempt to optimize the important film parameters of density, adhesion, strength and good stable superconducting characteristics. Details will be given of substrate-layer interaction for the various substrates that were studied, which included alumina, sapphire, single crystal (100)MgO and yttria stabilised zirconia together with a number of methods of substrate passivation. To date, the most successful substrate for Y_1Ba_2Cu_3O_{7-delta } thick film production has been yttria stabilised zirconia. This thesis will discuss the results of investigations, using yttria stabilised zirconia substrates, which have identified satisfactory means of obtaining superconducting layers with T_{c} = 91.5K and J_{c~ }3000 Acm^{-2} in zero applied magnetic field. At the time of writing, this value of critical current density remains the highest reported value for Y_1Ba_2Cu _3O_{7-delta} thick films. These high quality thick films were then used in a study of conduction mechanisms and the results are interpreted in terms of flux pinning and thermodynamic fluctuation theory. These results highlighted the complex nature of the conduction process in these new ceramics, which is dominated by the weak-link intergranular contacts. Finally, details are given of Josephson characteristics that were observed in variable thickness microbridges patterned into the

  5. Effects of Bi-2212 addition on the levitation force properties of bulk MgB2 superconductors

    NASA Astrophysics Data System (ADS)

    Taylan Koparan, E.; Savaskan, B.; Guner, S. B.; Celik, S.

    2016-02-01

    We present a detailed investigation of the effects of Bi2Sr2Ca1Cu2O8+κ (Bi-2212) adding on the levitation force and magnetic properties of bulk MgB2 obtained by hot press method. The amount of Bi-2212 was varied between 0 and 10 wt% (0, 2, 4, 6, 10 wt%) of the total MgB2. Moreover, we present MgB2 bulk samples fabricated by using different production methods including hot pressing method to our knowledge. All samples were prepared by using elemental magnesium (Mg) powder, amorphous nano-boron (B) powder and Bi-2212 powder which are produced by hot press method. As a result of hot press process, compact pellet samples were manufactured. The vertical and lateral levitation force measurements were executed at the temperatures of 20, 24 and 28 K under zero-field-cooled (ZFC) and field-cooled (FC) regimes for samples with various adding levels. At 24 K and 28 K under ZFC regime, the 2 wt% Bi-2212 added sample exhibits a higher vertical levitation force than the pure sample. Bi-2212 added MgB2 samples compared to the pure sample have lower attractive force values in FC regime. The magnetic field dependence of the critical current density J c was calculated from the M-H loops for Bi-2212 added MgB2 samples. The 2 wt% Bi-2212 added sample has the best levitation and critical current density performance compared to other samples. The critical temperature ( T c ) has slightly dropped from 37.8 K for the pure MgB2 sample to 36.7 K for the 10 wt% of Bi-2212 added sample. The transition temperature slightly decreases when Bi-2212 adding level is increased.

  6. Improvements in the processing of large grain, bulk Y-Ba-Cu-O superconductors via the use of additional liquid phase

    NASA Astrophysics Data System (ADS)

    Congreve, Jasmin V. J.; Shi, Yunhua; Dennis, Anthony R.; Durrell, John H.; Cardwell, David A.

    2017-01-01

    A major limitation to the widespread application of Y-Ba-Cu-O (YBCO) bulk superconductors is the relative complexity and low yield of the top seeded melt growth (TSMG) process, by which these materials are commonly fabricated. It has been demonstrated in previous work on the recycling of samples in which the primary growth had failed, that the provision of an additional liquid-rich phase to replenish liquid lost during the failed growth process leads to the reliable growth of relatively high quality recycled samples. In this paper we describe the adaptation of the liquid phase enrichment technique to the primary TSMG fabrication process. We further describe the observed differences between the microstructure and superconducting properties of samples grown with additional liquid-rich phase and control samples grown using a conventional TSMG process. We observe that the introduction of the additional liquid-rich phase leads to the formation of a higher concentration of Y species at the growth front, which leads, in turn, to a more uniform composition at the growth front. Importantly, the increased uniformity at the growth front leads directly to an increased homogeneity in the distribution of the Y-211 inclusions in the superconducting Y-123 phase matrix and to a more uniform Y-123 phase itself. Overall, the provision of an additional liquid-rich phase improves significantly both the reliability of grain growth through the sample thickness and the magnitude and homogeneity of the superconducting properties of these samples compared to those fabricated by a conventional TSMG process.

  7. Topological nonsymmorphic crystalline superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Qing-Ze; Liu, Chao-Xing

    2016-01-01

    Topological superconductors possess a nodeless superconducting gap in the bulk and gapless zero energy modes, known as "Majorana zero modes," at the boundary of a finite system. In this work, we introduce a new class of topological superconductors, which are protected by nonsymmorphic crystalline symmetry and thus dubbed "topological nonsymmorphic crystalline superconductors." We construct an explicit Bogoliubov-de Gennes type of model for this superconducting phase in the D class and show how Majorana zero modes in this model are protected by glide plane symmetry. Furthermore, we generalize the classification of topological nonsymmorphic crystalline superconductors to the classes with time reversal symmetry, including the DIII and BDI classes, in two dimensions. Our theory provides guidance to search for new topological superconducting materials with nonsymmorphic crystal structures.

  8. Topological Nonsymmorphic Crystalline Superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Qing-Ze; Liu, Chao-Xing

    Topological superconductors possess a nodeless superconducting gap in the bulk and gapless zero energy modes, known as ``Majorana zero modes'', at the boundary of a finite system. In this work, we introduce a new class of topological superconductors, which are protected by nonsymmorphic crystalline symmetry and thus dubbed ``topological nonsymmorphic crystalline superconductors''. We construct an explicit Bogoliubov-de Gennes type of model for this superconducting phase in the D class and show how Majorana zero modes in this model are protected by glide symmetry. Furthermore, we generalize the classification of topological nonsymmorphic crystalline superconductors to the classes with time reversal symmetry, including the DIII and BDI classes, in two dimensions. Our theory provides a guidance to search for new topological superconducting materials with nonsymmorphic crystal structures.

  9. Topological surface states in nodal superconductors.

    PubMed

    Schnyder, Andreas P; Brydon, Philip M R

    2015-06-24

    Topological superconductors have become a subject of intense research due to their potential use for technical applications in device fabrication and quantum information. Besides fully gapped superconductors, unconventional superconductors with point or line nodes in their order parameter can also exhibit nontrivial topological characteristics. This article reviews recent progress in the theoretical understanding of nodal topological superconductors, with a focus on Weyl and noncentrosymmetric superconductors and their protected surface states. Using selected examples, we review the bulk topological properties of these systems, study different types of topological surface states, and examine their unusual properties. Furthermore, we survey some candidate materials for topological superconductivity and discuss different experimental signatures of topological surface states.

  10. Superconductor developments

    SciTech Connect

    Larbalestier, D.

    1989-04-05

    I will cover the technology of the new oxide supeconductors and how they might relate to the existing superconductors. Fermilab and the high energy physics community in general have had much to do with the development of the ''old'' superconductors. Bednorz and M/umlt u/ller must be credited with the idea of setting out on the search for the new superconductors.

  11. Organic superconductors.

    PubMed

    Saito, Gunzi; Yoshida, Yukihiro

    2011-06-01

    The present status of organic superconductors of charge-transfer (CT) type based on donor molecules is reviewed. Along with the superconducting phases of such materials and also of oxide superconductors, reside spin-ordered phases such as spin-density wave (SDW) and antiferromagnetic (AF) phases. We briefly describe the recent development of superconductors having a superconducting phase next to a spin-disorder state (quantum spin liquid state). In addition to the CT type superconductors, there are a few single-component superconductors under high pressure.

  12. Temperature and Frequency Dependent Dielectric Properties of Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ Bulk Superconductor

    NASA Astrophysics Data System (ADS)

    Rahim, M.; Khan, Nawazish A.; Mumtaz, M.

    2013-07-01

    The temperature and frequency dependent dielectric properties of polycrystalline Cd-doped Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ ( y=0,0.25,0.5,0.75) bulk superconductor samples are investigated. The zero resistivity critical temperature { T c( R=0)} has decreased and normal state resistivity has increased with the increase of Cd-doping in Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ samples. The dielectric properties such as dielectric constants ( ɛ', ɛ″), dielectric loss tangent (tan δ) and ac-conductivity ( σ ac ) are investigated by measuring the capacitance (C) and conductance (G) in the frequency range of 10 KHz to 10 MHz at different temperature from 80 K to 300 K. The negative capacitance (NC) is observed in all Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ samples. The large values of NC observed at lower frequencies and temperatures may be due to reduced thermal vibrations and enhanced polarizability of the material. The effect of Cd-doping on bulk properties, dc-resistivity ( ρ) and ac-electrical conductivity ( σ ac ) of these superconductor samples are investigated. The polarization in Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ samples is most likely arising from the displacement of charges in CuO2/CdO2 planes relative to the static charges at Ba2+, Tl3+, and Cu2+ sites in Cu0.5Tl0.5Ba2O4- δ charge reservoir layers by external applied field.

  13. Granular Superconductors and Gravity

    NASA Technical Reports Server (NTRS)

    Noever, David; Koczor, Ron

    1999-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

  14. The effect of resolidification on preform optimized infiltration growth processed (Y, Nd, Sm, Gd)BCO, multi-grain bulk superconductor

    NASA Astrophysics Data System (ADS)

    Pavan Kumar Naik, S.; Seshu Bai, V.

    2017-01-01

    Controlling the microstructure of superconductors by incorporating the flux pinning centers and reducing the macro-defects to improve high field performance is the topic of recent research. In continuation, the preform optimized infiltration growth (POIG) processed YBa2Cu3O7-δ (YBCO) system, Y-site substituted with three mixed RE (Nd, Sm, Gd) elements is investigated. 20 wt.% of (Nd, Sm, Gd)2BaCuO5 were mixed with Y2BaCuO5 and POIG processed in reduced oxygen atmosphere to obtain YNSG superconductor. No seed is employed for crystal growth; hence the processed samples are multi-grained. Microstructural and compositional investigations on YNSG revealed the presence of different phases in the matrix as well as in precipitates which are of the order of submicron to 4 μm. A large fraction of macro-defects (∼6% of porosity) was observed in the YNSG sample. For reducing the unwanted macro-defects and refine the non-superconducting precipitates, processed YNSG sample is pressed and resolidified (by infiltrating the liquid phases once again) in an argon atmosphere and the structural, microstructural, elemental and superconducting properties are compared with YNSG and undoped samples. Due to spatial scatter in superconducting critical temperatures, caused by the distribution of different REBCO unit cells in YBCO, superconducting transition curve is sharp in YNSG, whereas the resolidified sample showed the broad transition due to solidified liquid phases.

  15. Organic Superconductors

    SciTech Connect

    Charles Mielke

    2009-02-27

    Intense magnetic fields are an essential tool for understanding layered superconductors. Fundamental electronic properties of organic superconductors are revealed in intense (60 tesla) magnetic fields. Properties such as the topology of the Fermi surface and the nature of the superconducting order parameter are revealed. With modest maximum critical temperatures~13K the charge transfer salt organic superconductors prove to be incredibly valuable materials as their electronically clean nature and layered (highly anisotropic) structures yield insights to the high temperature superconductors. Observation of de Haas-van Alphen and Shubnikov-de Haas quantum oscillatory phenomena, magnetic field induced superconductivity and re-entrant superconductivity are some of the physical phenomena observed in the charge transfer organic superconductors. In this talk, I will discuss the nature of organic superconductors and give an overview of the generation of intense magnetic fields; from the 60 tesla millisecond duration to the extreme 1000 tesla microsecond pulsed magnetic fields.

  16. Superconductor Composite

    DOEpatents

    Dorris, Stephen E.; Burlone, Dominick A.; Morgan; Carol W.

    1999-02-02

    A superconducting conductor fabricated from a plurality of wires, e.g., fine silver wires, coated with a superconducting powder. A process of applying superconducting powders to such wires, to the resulting coated wires and superconductors produced therefrom.

  17. Vortex flux dynamics and harmonic ac magnetic response of Ba(Fe0.94Ni0.06)2As2 bulk superconductor

    SciTech Connect

    Nikolo, Martin; Zapf, Vivien S.; Singleton, John; Jiang, Jianyi; Weiss, Jeremy D.; Hellstrom, Eric E.

    2016-07-22

    Vortex dynamics and nonlinear ac response are studied in a Ba(Fe0.94Ni0.06)2As2(Tc= 18.5 K) bulk superconductor in magnetic fields up to 12 T via ac susceptibility measurements of the first ten harmonics. A comprehensive study of the ac magnetic susceptibility and its first ten harmonics finds shifts to higher temperatures with increasing ac measurement frequencies (10 to 10,000 Hz) for a wide range of ac (1, 5, and 10 Oe) and dc fields (0 to 12 T). The characteristic measurement time constant t1 is extracted from the exponential fit of the data and linked to vortex relaxation. The Anderson-Kim Arrhenius law is applied to determine flux activation energy Ea/k as a function dc magnetic field. The de-pinning, or irreversibility lines, were determined by a variety of methods and extensively mapped. The ac response shows surprisingly weak higher harmonic components, suggesting weak nonlinear behavior. Lastly, our data does not support the Fisher model; we do not see an abrupt vortex glass to vortex liquid transition and the resistivity does not drop to zero, although it appears to approach zero exponentially.

  18. Experiments on Nanoscale Disordered Superconductor-Normal-Superconductor Arrays

    NASA Astrophysics Data System (ADS)

    Long, Zhenyi; Kouh, Taejoon; Stewart, Michael; Valles, James

    2003-03-01

    We are studying a quasi-two-dimensional system of nanoscale, superconducting grains (Pb) overlain by a normal metal (Ag), which can be described as an array of mesoscopic superconductor-normal-superconductor junctions. The Pb grains are smaller than the bulk Pb coherence volume and consequently, these arrays are expected to exhibit a superconductor to metal quantum phase transition [1]. Previous measurements of the decrease in critical temperature with increasing Ag thickness show clear deviations from the predictions of mean field theories of the proximity effect [2]. Our recent experiments on systems with even smaller Pb grains exhibit similar deviations. We will discuss these and our latest tunneling and transport results in terms of recent theories[1] and contrast them with the behavior of ultrathin, disordered films near the superconductor to insulator transition. [1] B.Spivak, A.Zyuzin, M.Hruska ,Phys. Rev. B. 64, 132502(2001) [2] Taejoon Kouh and James Valles Jr Breakdown of Cooper Limit Theory in Disordered Nanoscale Superconductor-Normal-Superconductor Arrays (cond-mat 0202104)

  19. Inhomogeneous oxygen interchange during annealing and cooling of textured bulk Bi2Sr2CaCu2O8+dgr superconductors

    NASA Astrophysics Data System (ADS)

    Natividad, E.; Angurel, L. A.; Andrés, J. M.; Mayoral, M. C.

    2004-03-01

    The optimized annealing of bulk Bi2Sr2CaCu2O8+dgr (Bi-2212) materials textured using the laser floating zone technique requires a two-step process, consisting of a first step at 870 °C and a second step at 801 °C. In this paper, we present an analysis of the changes induced within the samples along this thermal treatment and the subsequent cooling to room temperature. During the initial step the cationic diffusion takes place, while the oxygen content is adjusted during the second step, at lower temperature. The evolution of the superconducting properties reveals that the oxygen diffusion into the sample is not homogeneous and that the different oxygen contents along the annealing are also a consequence of a strong interchange between the central and the external sample regions. It has been shown that, at the different stages of the thermal process, the samples present different degrees of homogeneity in their superconducting properties, this being caused by the improvement of one region to the detriment of the other.

  20. Majorana Fermions and Topology in Superconductors

    NASA Astrophysics Data System (ADS)

    Sato, Masatoshi; Fujimoto, Satoshi

    2016-07-01

    Topological superconductors are novel classes of quantum condensed phases, characterized by topologically nontrivial structures of Cooper pairing states. On the surfaces of samples and in vortex cores of topological superconductors, Majorana fermions, which are particles identified with their own anti-particles, appear as Bogoliubov quasiparticles. The existence and stability of Majorana fermions are ensured by bulk topological invariants constrained by the symmetries of the systems. Majorana fermions in topological superconductors obey a new type of quantum statistics referred to as non-Abelian statistics, which is distinct from bose and fermi statistics, and can be utilized for application to topological quantum computation. Also, Majorana fermions give rise to various exotic phenomena such as "fractionalization", non-local correlation, and "teleportation". A pedagogical review of these subjects is presented. We also discuss interaction effects on topological classification of superconductors, and the basic properties of Weyl superconductors.

  1. Organic superconductors

    NASA Astrophysics Data System (ADS)

    Jérome, D.

    1994-10-01

    The discovery of organic superconductors in 1980 was an happy conclusion of a search for high T c superconductors (although T c was modestly in the Kelvin range). The first generation of organic superconductors belonged to a large family of quasi-one-dimensional conducting cation radical salts. Most of them exhibit a wide range of new phenomena, including the competition between ground states, the influence of a magnetic field on the non ordered phase of a quasi-one-dimensional electron gas and the onset of spin density wave phases at high magnetic field with quantized Hall effect. The extensive study of the (TM) 2X series has shown that electron interactions are repulsive and of the order of the electron bandwidth. However, the nature of the ground states relies essentially on the balance between charge localisation boosted by the Umklapp scattering and the interchain hopping intergal. Second and third generation organic superconductors are two and three dimensional molecular conductors respectively with maximum T c of 12K (ET) 2X and 33 K (fullerides).

  2. Superconductor cable

    DOEpatents

    Allais, Arnaud; Schmidt, Frank; Marzahn, Erik

    2010-05-04

    A superconductor cable is described, having a superconductive flexible cable core (1) , which is laid in a cryostat (2, 3, 4), in which the cable core (1) runs in the cryostat (2, 3, 4) in the form of a wave or helix at room temperature.

  3. Processing of YBCO superconductors for improved levitation force

    SciTech Connect

    Balachandran, U.; Zhong, W.

    1993-05-01

    One objective of the ANL superconductor program is to develop improved processing methods for production of YBCO superconductors with higher levitation forces suitable for low-friction, superconductor/permanent-magnet bearings and flywheel-energy-storage applications. From the standpoint of these applications, melt-processed bulk YBCO superconductors are of considerable interest. Levitation force and flux-pinning properties depend on microstructural features of the superconductors. We have added several chemical species to YBCO to alter the microstructure and have used a seeding technique to induce crystallization during melt processing. In this paper, we discuss the effects of various process parameters, additives, and a seeding technique on the properties of melt-processed bulk YBCO samples and compare the results with solid-state-sintered superconductors.

  4. Superconductor cable

    DOEpatents

    Smith, Jr., Darrell F.; Lake, Bill L.; Ballinger, Ronald G.

    1988-01-01

    A superconducting cable comprising an in-situ-formed type II superconductor, e.g. Nb.sub.3 Sn, in association with a stabilizing conductor both in heat transfer relationship with at least one passage adapted to carry liquified gaseous refrigerant. The conductor and said at least one passage are enclosed by a sheath comprising an alloy consisting essentially of about 49% nickel, about 4% chromium, about 3% niobium, about 1.4% titanium, about 1% aluminum, balance essentially iron.

  5. Chiral superconductors.

    PubMed

    Kallin, Catherine; Berlinsky, John

    2016-05-01

    Chiral superconductivity is a striking quantum phenomenon in which an unconventional superconductor spontaneously develops an angular momentum and lowers its free energy by eliminating nodes in the gap. It is a topologically non-trivial state and, as such, exhibits distinctive topological modes at surfaces and defects. In this paper we discuss the current theory and experimental results on chiral superconductors, focusing on two of the best-studied systems, Sr2RuO4, which is thought to be a chiral triplet p-wave superconductor, and UPt3, which has two low-temperature superconducting phases (in zero magnetic field), the lower of which is believed to be chiral triplet f-wave. Other systems that may exhibit chiral superconductivity are also discussed. Key signatures of chiral superconductivity are surface currents and chiral Majorana modes, Majorana states in vortex cores, and the possibility of half-flux quantum vortices in the case of triplet pairing. Experimental evidence for chiral superconductivity from μSR, NMR, strain, polar Kerr effect and Josephson tunneling experiments are discussed.

  6. Superconductor cable

    DOEpatents

    Allais, Arnaud; Schmidt, Frank (Langenhagen, DE

    2009-12-15

    A superconductor cable includes a superconductive cable core (1) and a cryostat (2) enclosing the same. The cable core (1) has a superconductive conductor (3), an insulation (4) surrounding the same and a shielding (5) surrounding the insulation (4). A layer (3b) of a dielectric or semiconducting material is applied to a central element (3a) formed from a normally conducting material as a strand or tube and a layer (3c) of at least one wire or strip of superconductive material is placed helically on top. The central element (3a) and the layer (3c) are connected to each other in an electrically conducting manner at the ends of the cable core (1).

  7. Topological properties of ferromagnetic superconductors

    DOE PAGES

    Cheung, Alfred K. C.; Raghu, S.

    2016-04-27

    Here, a variety of heavy fermion superconductors, such as UCoGe, UGe2, and URhGe exhibit a striking coexistence of bulk ferromagnetism and superconductivity. In the first two materials, the magnetic moment decreases with pressure, and vanishes at a ferromagnetic quantum critical point (qcp). Remarkably, the superconductivity in UCoGe varies smoothly with pressure across the qcp and exists in both the ferromagnetic and paramagnetic regimes. We argue that in UCoGe, spin-orbit interactions stabilize a time-reversal invariant odd-parity superconductor in the high pressure paramagnetic regime. Based on a simple phenomenological model, we predict that the transition from the paramagnetic normal state to themore » phase where superconductivity and ferromagnetism coexist is a first-order transition.« less

  8. Topological properties of ferromagnetic superconductors

    SciTech Connect

    Cheung, Alfred K. C.; Raghu, S.

    2016-04-27

    Here, a variety of heavy fermion superconductors, such as UCoGe, UGe2, and URhGe exhibit a striking coexistence of bulk ferromagnetism and superconductivity. In the first two materials, the magnetic moment decreases with pressure, and vanishes at a ferromagnetic quantum critical point (qcp). Remarkably, the superconductivity in UCoGe varies smoothly with pressure across the qcp and exists in both the ferromagnetic and paramagnetic regimes. We argue that in UCoGe, spin-orbit interactions stabilize a time-reversal invariant odd-parity superconductor in the high pressure paramagnetic regime. Based on a simple phenomenological model, we predict that the transition from the paramagnetic normal state to the phase where superconductivity and ferromagnetism coexist is a first-order transition.

  9. Superconductor bearings, flywheels and transportation

    NASA Astrophysics Data System (ADS)

    Werfel, F. N.; Floegel-Delor, U.; Rothfeld, R.; Riedel, T.; Goebel, B.; Wippich, D.; Schirrmeister, P.

    2012-01-01

    This paper describes the present status of high temperature superconductors (HTS) and of bulk superconducting magnet devices, their use in bearings, in flywheel energy storage systems (FESS) and linear transport magnetic levitation (Maglev) systems. We report and review the concepts of multi-seeded REBCO bulk superconductor fabrication. The multi-grain bulks increase the averaged trapped magnetic flux density up to 40% compared to single-grain assembly in large-scale applications. HTS magnetic bearings with permanent magnet (PM) excitation were studied and scaled up to maximum forces of 10 kN axially and 4.5 kN radially. We examine the technology of the high-gradient magnetic bearing concept and verify it experimentally. A large HTS bearing is tested for stabilizing a 600 kg rotor of a 5 kWh/250 kW flywheel system. The flywheel rotor tests show the requirement for additional damping. Our compact flywheel system is compared with similar HTS-FESS projects. A small-scale compact YBCO bearing with in situ Stirling cryocooler is constructed and investigated for mobile applications. Next we show a successfully developed modular linear Maglev system for magnetic train operation. Each module levitates 0.25t at 10 mm distance during one-day operation without refilling LN2. More than 30 vacuum cryostats containing multi-seeded YBCO blocks are fabricated and are tested now in Germany, China and Brazil.

  10. Order parameter fluctuations in the holographic superconductor

    NASA Astrophysics Data System (ADS)

    Plantz, N. W. M.; Stoof, H. T. C.; Vandoren, S.

    2017-03-01

    We investigate the effect of order parameter fluctuations in the holographic superconductor. In particular, following an introduction to the concept of intrinsic dynamics and its implementation within holographic models, we compute the intrinsic spectral functions of the order parameter in both the normal and the superconducting phase, using a fully backreacted bulk geometry. We also present a vector-like large-N version of the Ginzburg–Landau model that accurately describes our long-wavelength results in both phases. Our results indicate that the holographic superconductor describes a relativistic multi-component superfluid in the universal regime of the BEC–BCS crossover.

  11. Passivation of high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Vasquez, Richard P. (Inventor)

    1991-01-01

    The surface of high temperature superconductors such as YBa2Cu3O(7-x) are passivated by reacting the native Y, Ba and Cu metal ions with an anion such as sulfate or oxalate to form a surface film that is impervious to water and has a solubility in water of no more than 10(exp -3) M. The passivating treatment is preferably conducted by immersing the surface in dilute aqueous acid solution since more soluble species dissolve into the solution. The treatment does not degrade the superconducting properties of the bulk material.

  12. The use of high temperature superconductors to levitate lunar telescope

    NASA Technical Reports Server (NTRS)

    Brown, Beth A.

    1992-01-01

    The objective of this paper was to assist in the construction of a lunar telescope mirror model by conducting research on composite materials and other lightweight, rigid materials, and by determining how much weight can be levitated by available superconductors. It is believed that with the construction of four magnets suspended over four bulk superconductors (or vice versa), there should be no problems lifting a model mirror and stabilizing it at different positions. It may be necessary to increase the size and quality of the superconductors and/or magnets in order to achieve this.

  13. Study of the glass formation of high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin C.; Kaukler, William F.; Rolin, Terry

    1992-01-01

    A number of compositions of ceramic oxide high T(sub c) superconductors were elevated for their glass formation ability by means of rapid thermal analysis during quenching, optical, and electron microscopy of the quenched samples, and with subsequent DSC measurements. Correlations between experimental measurements and the methodical composition changes identified the formulations of superconductors that can easily form glass. The superconducting material was first formed as a glass; then, with subsequent devitrification, it was formed into a bulk crystalline superconductor by a series of processing methods.

  14. Observability of surface currents in p-wave superconductors

    NASA Astrophysics Data System (ADS)

    Bakurskiy, S. V.; Klenov, N. V.; Soloviev, I. I.; Kupriyanov, M. Yu; Golubov, A. A.

    2017-04-01

    A general approach is formulated to describe spontaneous surface current distribution in a chiral p-wave superconductor. We use the quasiclassical Eilenberger formalism in the Ricatti parametrization to describe various types of the superconductor surface, including arbitrary roughness and metallic behavior of the surface layer. We calculate angle resolved distributions of the spontaneous surface currents and formulate the conditions of their observability. We argue that local measurements of these currents by muon spin rotation technique may provide an information on the underlying pairing symmetry in the bulk superconductor.

  15. Fine uniform filament superconductors

    DOEpatents

    Riley, Jr., Gilbert N.; Li, Qi; Roberts, Peter R.; Antaya, Peter D.; Seuntjens, Jeffrey M.; Hancock, Steven; DeMoranville, Kenneth L.; Christopherson, Craig J.; Garrant, Jennifer H.; Craven, Christopher A.

    2002-01-01

    A multifilamentary superconductor composite having a high fill factor is formed from a plurality of stacked monofilament precursor elements, each of which includes a low density superconductor precursor monofilament. The precursor elements all have substantially the same dimensions and characteristics, and are stacked in a rectilinear configuration and consolidated to provide a multifilamentary precursor composite. The composite is thereafter thermomechanically processed to provide a superconductor composite in which each monofilament is less than about 50 microns thick.

  16. Superconductor rotor cooling system

    DOEpatents

    Gamble, Bruce B.; Sidi-Yekhlef, Ahmed; Schwall, Robert E.; Driscoll, David I.; Shoykhet, Boris A.

    2004-11-02

    A system for cooling a superconductor device includes a cryocooler located in a stationary reference frame and a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with a rotating reference frame in which the superconductor device is located. A method of cooling a superconductor device includes locating a cryocooler in a stationary reference frame, and transferring heat from a superconductor device located in a rotating reference frame to the cryocooler through a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with the rotating reference frame.

  17. Photothermal measurements of superconductors

    SciTech Connect

    Kino, G.S.; Studenmund, W.R.; Fishman, I.M.

    1996-12-31

    A photothermal technique has been used to measure diffusion and critical temperature in high temperature superconductors. The technique is particularly suitable for determining material quality and inhomogeneity.

  18. Superconductor rotor cooling system

    DOEpatents

    Gamble, Bruce B.; Sidi-Yekhlef, Ahmed; Schwall, Robert E.; Driscoll, David I.; Shoykhet, Boris A.

    2002-01-01

    A system for cooling a superconductor device includes a cryocooler located in a stationary reference frame and a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with a rotating reference frame in which the superconductor device is located. A method of cooling a superconductor device includes locating a cryocooler in a stationary reference frame, and transferring heat from a superconductor device located in a rotating reference frame to the cryocooler through a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with the rotating reference frame.

  19. Partial Meissner effect in superconductors with twins

    SciTech Connect

    Gurevich, A.L.; Mints, R.G. )

    1988-11-01

    Superconductivity of twinning planes, arising at critical temperature T/sub c/ exceeding the bulk point T/sub co/, may prove to be important for the understanding of the properties of high-temperature superconductors with well-developed twinning structure. This paper shows that regardless of a specific mechanism of superconductivity, twins at T/sub c/>T/sub co/ act as seeds for the growth of metastable superconducting domains whose order parameter phases differ by {pi}.

  20. Fabrication of high temperature superconductors

    DOEpatents

    Balachandran, Uthamalingam; Dorris, Stephen E.; Ma, Beihai; Li, Meiya

    2003-06-17

    A method of forming a biaxially aligned superconductor on a non-biaxially aligned substrate substantially chemically inert to the biaxially aligned superconductor comprising is disclosed. A non-biaxially aligned substrate chemically inert to the superconductor is provided and a biaxially aligned superconductor material is deposited directly on the non-biaxially aligned substrate. A method forming a plume of superconductor material and contacting the plume and the non-biaxially aligned substrate at an angle greater than 0.degree. and less than 90.degree. to deposit a biaxially aligned superconductor on the non-biaxially aligned substrate is also disclosed. Various superconductors and substrates are illustrated.

  1. Proposal of a Bulk HTSC Staggered Array Undulator

    SciTech Connect

    Kii, Toshiteru; Kinjo, Ryota; Bakr, Mahmoud A.; Sonobe, Taro; Higashimura, Keisuke; Masuda, Kai; Ohgaki, Hideaki; Yoshida, Kyohei; Zen, Heisyun

    2010-06-23

    We proposed a new type of undulator based on bulk high-T{sub c} superconductors (HTSC) which consists of a single solenoid and a stacked array of bulk HTSC. The main advantage of this configuration is that a mechanical structure is not required to produce and control the undulator field. In order to perform a proof of principle experiment, we have developed a prototype of bulk HTSC staggered array undulator using 11 pairs of DyBaCuO bulk superconductors and a normal conducting solenoid. Experimental results obtained by using the prototype undulator and numerical results obtained by a loop current model based on the Bean mode for a type-II superconductor were compared.

  2. Conductance of d-wave superconductor/normal metal/d-wave superconductor junctions

    NASA Astrophysics Data System (ADS)

    Pesin, Dmytro; Andreev, Anton; Spivak, Boris

    2008-03-01

    We develop a theory of the low-temperature conductance of superconductor/normal metal/superconductor junctions in which the superconductors have d-wave pairing symmetry. We show that at low temperatures the conductance of the junction is determined by the inelastic relaxation time of quasiparticles in the bulk of d-wave superconductors, GDND√&(d)circ;ɛ. Thus it greatly exceeds the conductance of the normal metal part of the junction, which is controlled by the elastic mean free path. This dependence of GDND on the inelastic relaxation time should be contrasted with that of the low-temperature conductance of the junction in the case of the s- wave superconductor leads, GSNS. In the latter case the conductance is proportional to the first power of the inelastic electron relaxation time in the normal metal part of the junction, GSNSτɛ^(n) [1]. [1] S. V. Lempitskii, Sov. Phys. JETP 58, 624 (1983); U. Gunsenheimer and A. D. Zaikin, Phys. Rev. B50, 6317 (1994); F. Zhou and B. Spivak, JETP Lett. 65, 369 (1997).

  3. Electronic structure and superconductivity of FeSe-related superconductors.

    PubMed

    Liu, Xu; Zhao, Lin; He, Shaolong; He, Junfeng; Liu, Defa; Mou, Daixiang; Shen, Bing; Hu, Yong; Huang, Jianwei; Zhou, X J

    2015-05-13

    FeSe superconductors and their related systems have attracted much attention in the study of iron-based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced to 37 K at high pressure. On the other hand, its cousin system, FeTe, possesses a unique antiferromagnetic ground state but is non-superconducting. Substitution of Se with Te in the FeSe superconductor results in an enhancement of Tc up to 14.5 K and superconductivity can persist over a large composition range in the Fe(Se,Te) system. Intercalation of the FeSe superconductor leads to the discovery of the AxFe2-ySe2 (A = K, Cs and Tl) system that exhibits a Tc higher than 30 K and a unique electronic structure of the superconducting phase. A recent report of possible high temperature superconductivity in single-layer FeSe/SrTiO3 films with a Tc above 65 K has generated much excitement in the community. This pioneering work opens a door for interface superconductivity to explore for high Tc superconductors. The distinct electronic structure and superconducting gap, layer-dependent behavior and insulator-superconductor transition of the FeSe/SrTiO3 films provide critical information in understanding the superconductivity mechanism of iron-based superconductors. In this paper, we present a brief review of the investigation of the electronic structure and superconductivity of the FeSe superconductor and related systems, with a particular focus on the FeSe films.

  4. Making High-Temperature Superconductors By Melt Sintering

    NASA Technical Reports Server (NTRS)

    Golben, John P.

    1992-01-01

    Melt-sintering technique applied to YBa2Cu3O7-x system and to Bi/Ca/Sr/Cu-oxide system to produce highly oriented bulk high-temperature-superconductor materials extending to macroscopically usable dimensions. Processing requires relatively inexpensive and simple equipment. Because critical current two orders of magnitude greater in crystal ab plane than in crystal c direction, high degree of orientation greatly enhances critical current in these bulk materials, making them more suitable for many proposed applications.

  5. Using high-temperature superconductors for levitation applications

    NASA Astrophysics Data System (ADS)

    Hull, John R.

    1999-07-01

    Melt-textured, bulk high-temperature superconductors are finding increasing uses in superconducting bearings, flywheel energy storage, and other levitational applications. This article reviews the use of these materials in magnetic-levitation applications. The behavior of levitational force, stiffness, damping, and rotational losses is discussed.

  6. Using high-temperature superconductors for levitation applications.

    SciTech Connect

    Hull, J. R.; Energy Technology

    1999-07-01

    Melt-textured, bulk high-temperature superconductors are finding increasing uses in superconducting bearings, flywheel energy storage, and other levitational applications. This article reviews the use of these materials in magnetic-levitation applications. The behavior of levitational force, stiffness, damping, and rotational losses is discussed.

  7. Electrocaloric Refrigeration for Superconductors

    DTIC Science & Technology

    1977-02-01

    CO rH CO © . NBSIR 76-847 ELECTROCALORIC REFRIGERATION FOR SUPERCONDUCTORS Ray Radebaugh and J.D. Siegwarth Cryogenics Division Institute...June 30, 1975 NBSIR 76-847 ELECTROULORIC REFRIGERATION FOR SUPERCONDUCTORS Ray Radebaugh and J.D. Siegwarth Cryogenics Division L Institute for...Field at Low Temperatures, Rev. Sei. Instrum. 42, 571 (1971). 8. Lawless, W. N., Radebaugh , R., and Soulen, R. J., Studies of a Glass- Ceramic

  8. Topological superconductors: a review.

    PubMed

    Sato, Masatoshi; Ando, Yoichi

    2017-04-03

    This review elaborates pedagogically on the fundamental concept, basic theory, expected properties, and materials realizations of topological superconductors. The relation between topological superconductivity and Majorana fermions are explained, and the difference between dispersive Majorana fermions and a localized Majorana zero mode is emphasized. A variety of routes to topological superconductivity are explained with an emphasis on the roles of spin-orbit coupling. Present experimental situations and possible signatures of topological superconductivity are summarized with an emphasis on intrinsic topological superconductors.

  9. Layered nickel based superconductors

    SciTech Connect

    Ronning, Filip; Bauer, Eric D; Park, Tuson; Kurita, Nobuyuki; Klimczuk, T; Movshovich, R; Thompson, J D; Sefat, A S; Mandrus, D

    2009-01-01

    We review the properties of Ni-based superconductors which contain Ni{sub 2}X{sub 2} (X=As, P, Bi, Si, Ge, B) planes, a common structural element to the recently discovered FeAs superconductors. We also compare the properties ofthe Ni-and Fe-based systems from a perspective ofelectronic structure as well as structure-property relations.

  10. Continuous lengths of oxide superconductors

    DOEpatents

    Kroeger, Donald M.; List, III, Frederick A.

    2000-01-01

    A layered oxide superconductor prepared by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon. A continuous length of a second substrate ribbon is overlaid on the first substrate ribbon. Sufficient pressure is applied to form a bound layered superconductor precursor powder between the first substrate ribbon and the second substrate ribbon. The layered superconductor precursor is then heat treated to establish the oxide superconducting phase. The layered oxide superconductor has a smooth interface between the substrate and the oxide superconductor.

  11. Application of shielding current in bulk HTS to control magnetic field distribution

    NASA Astrophysics Data System (ADS)

    Kii, T.

    2016-03-01

    Superconducting shielding current is excited when external field is applied to superconductor. In case for field cooling of bulk superconductor, shielding current is an origin of strong trapped field. When external field is changed to a properly arranged bulk HTS array, various magnetic field distribution can be formed by an excited shielding current in each bulk HTS. This paper presents a simple intuitively method to design magnetic field distribution using supercurrents in bulk high-temperature superconductor (HTS) array. In this method, an ideal current path for intended field distribution is represented by shielding currents in bulk HTS array. Expected performance can be roughly estimated by using Biot-Savart law. As examples, Maxwell coil pair and helical field generator are designed. This method can be applied to design various magnet devices using bulk HTS array.

  12. New class of topological superconductors protected by magnetic group symmetries.

    PubMed

    Fang, Chen; Gilbert, Matthew J; Bernevig, B Andrei

    2014-03-14

    We study a new type of three-dimensional topological superconductor that exhibits Majorana zero modes (MZM) protected by a magnetic group symmetry, a combined antiunitary symmetry composed of a mirror reflection and time reversal. This new symmetry enhances the noninteracting topological classification of a superconducting vortex from Z2 to Z, indicating that multiple MZMs can coexist at the end of one magnetic vortex of unit flux. Especially, we show that a vortex binding two MZMs can be realized on the (001) surface of a topological crystalline insulator SnTe with proximity induced BCS Cooper pairing, or in bulk superconductor InxSn1-xTe.

  13. Progress of research of high-T(sub c) superconductors

    NASA Technical Reports Server (NTRS)

    Tanaka, Shoji

    1990-01-01

    The research of high T(sub c) superconductors has made big progress in these last few years. New materials were found and the systematic investigations of these materials must contribute to understanding the mechanism of high T(sub c) superconductivity. The critical currents in thin films, bulks and tapes increased drastically, and the origin of flux pinning will be clarified in the near future. These progressions gives a view of a bright future of high T(sub c) superconductivity in both the basic and application research areas. Recent activities in research of high T(sub c) superconductivity and superconductors in Japan are overviewed.

  14. Progress of research of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Tanaka, Shoji

    1991-01-01

    Research in the area of of high T(sub c) superconductors has made great progress in the last few years. New materials were found and the systematic investigation of these materials has contributed to understanding the mechanism of high T(sub c) superconductivity. The critical currents in thin films, bulks, and tapes increased drastically, and the origin of flux pinning will be clarified in the near future. The future of high T(sub c) superconductivity, in both the basic and applied research areas, is very optimistic. Recent activities in research of high T(sub c) superconductivity and superconductors in Japan are overviewed.

  15. EDITORIAL: Focus on Superconductors with Exotic Symmetries FOCUS ON SUPERCONDUCTORS WITH EXOTIC SYMMETRIES

    NASA Astrophysics Data System (ADS)

    Rice, T. Maurice; Sigrist, Manfred; Maeno, Yoshiteru

    2009-05-01

    Behnia Pairing state at an interface of Sr2RuO4: parity-mixing, restored time-reversal symmetry and topological superconductivity Y Tada, N Kawakami and S Fujimoto Momentum-resolved superconducting gap in the bulk of Ba1-xKxFe2As2 from combined ARPES and μSR measurements D V Evtushinsky, D S Inosov, V B Zabolotnyy, M S Viazovska, R Khasanov, A Amato, H-H Klauss, H Luetkens, Ch Niedermayer, G L Sun, V Hinkov, C T Lin, A Varykhalov, A Koitzsch, M Knupfer, B Büchner, A A Kordyuk and S V Borisenko Cooper-pair formation by anharmonic rattling modes in the β-pyrochlore superconductor KOs2O6 Jun Chang, Ilya Eremin and Peter Thalmeier Doping-dependent optical properties of Bi2201 E van Heumen, W Meevasana, A B Kuzmenko, H Eisaki and D van der Marel Phase diagram and single-particle spectrum of CuO2 high-Tc layers: variational cluster approach to the three-band Hubbard model E Arrigoni, M Aichhorn, M Daghofer and W Hanke Heat transport as a probe of superconducting gap structure H Shakeripour, C Petrovic and Louis Taillefer Pressure-induced magnetic transition and volume collapse in FeAs superconductors: an orbital-selective Mott scenario Andreas Hackl and Matthias Vojta Orbital magnetic moment of a chiral p-wave superconductor James F Annett, B L Györffy and K I Wysokiński Magnetism and superconductivity in strongly correlated CeRhIn5 Tuson Park and J D Thompson Superconducting gap structure of heavy-Fermion compound URu2Si2 determined by angle-resolved thermal conductivity Y Kasahara, H Shishido, T Shibauchi, Y Haga, T D Matsuda, Y Onuki and Y Matsuda Polar Kerr effect as probe for time-reversal symmetry breaking in unconventional superconductors Aharon Kapitulnik, Jing Xia, Elizabeth Schemm and Alexander Palevski Influence of non-magnetic impurities on hole-doped two-leg Cu-O Hubbard ladders P Chudzinski, M Gabay and T Giamarchi Pairing in the iron arsenides: a functional RG treatment Christian Platt, Carsten Honerkamp and Werner Hanke Tracking anisotropic scattering in

  16. Lightning in superconductors.

    PubMed

    Vestgården, J I; Shantsev, D V; Galperin, Y M; Johansen, T H

    2012-01-01

    Crucially important for application of type-II superconductor films is the stability of the vortex matter--magnetic flux lines penetrating the material. If some vortices get detached from pinning centres, the energy dissipated by their motion will facilitate further depinning, and may trigger a massive electromagnetic breakdown. Up to now, the time-resolved behaviour of these ultra-fast events was essentially unknown. We report numerical simulation results revealing the detailed dynamics during breakdown as within nanoseconds it develops branching structures in the electromagnetic fields and temperature, with striking resemblance of atmospheric lightning. During a dendritic avalanche the superconductor is locally heated above its critical temperature, while electrical fields rise to several kV/m as the front propagates at instant speeds near up to 100 km/s. The numerical approach provides an efficient framework for understanding the ultra-fast coupled non-local dynamics of electromagnetic fields and dissipation in superconductor films.

  17. Microgravity Processing of Oxide Superconductors

    NASA Technical Reports Server (NTRS)

    Olive, James R.; Hofmeister, William H.; Bayuzick, Robert J.; Vlasse, Marcus

    1999-01-01

    Considerable effort has been concentrated on the synthesis and characterization of high T(sub c) oxide superconducting materials. The YBaCuO system has received the most intense study, as this material has shown promise for the application of both thin film and bulk materials. There are many problems with the application of bulk materials- weak links, poor connectivity, small coherence length, oxygen content and control, environmental reactivity, phase stability, incongruent melting behavior, grain boundary contamination, brittle mechanical behavior, and flux creep. The extent to which these problems are intrinsic or associated with processing is the subject of controversy. This study seeks to understand solidification processing of these materials, and to use this knowledge for alternative processing strategies, which, at the very least, will improve the understanding of bulk material properties and deficiencies. In general, the phase diagram studies of the YBaCuO system have concentrated on solid state reactions and on the Y2BaCuO(x) + liquid yields YBa2Cu3O(7-delta) peritectic reaction. Little information is available on the complete melting relations, undercooling, and solidification behavior of these materials. In addition, rare earth substitutions such as Nd and Gd affect the liquidus and phase relations. These materials have promising applications, but lack of information on the high temperature phase relations has hampered research. In general, the understanding of undercooling and solidification of high temperature oxide systems lags behind the science of these phenomena in metallic systems. Therefore, this research investigates the fundamental melting relations, undercooling, and solidification behavior of oxide superconductors with an emphasis on improving ground based synthesis of these materials.

  18. Bulk undercooling

    NASA Technical Reports Server (NTRS)

    Kattamis, T. Z.

    1984-01-01

    Bulk undercooling methods and procedures will first be reviewed. Measurement of various parameters which are necessary to understand the solidification mechanism during and after recalescence will be discussed. During recalescence of levitated, glass-encased large droplets (5 to 8 mm diam) high speed temperature sensing devices coupled with a rapid response oscilloscope are now being used at MIT to measure local thermal behavior in hypoeutectic and eutectic binary Ni-Sn alloys. Dendrite tip velocities were measured by various investigators using thermal sensors or high speed cinematography. The confirmation of the validity of solidification models of bulk-undercooled melts is made difficult by the fineness of the final microstructure, the ultra-rapid evolution of the solidifying system which makes measurements very awkward, and the continuous modification of the microstructure which formed during recalescence because of precipitation, remelting and rapid coarsening.

  19. Avoided valence transition in a plutonium superconductor

    PubMed Central

    Ramshaw, B. J.; Shekhter, Arkady; McDonald, Ross D.; Betts, Jon B.; Mitchell, J. N.; Tobash, P. H.; Mielke, C. H.; Bauer, E. D.; Migliori, Albert

    2015-01-01

    The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5—the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)—and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability—therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5. PMID:25737548

  20. Avoided valence transition in a plutonium superconductor.

    PubMed

    Ramshaw, B J; Shekhter, Arkady; McDonald, Ross D; Betts, Jon B; Mitchell, J N; Tobash, P H; Mielke, C H; Bauer, E D; Migliori, Albert

    2015-03-17

    The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5--the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)--and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability--therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5.

  1. Static Test for a Gravitational Force Coupled to Type 2 YBCO Superconductors

    NASA Technical Reports Server (NTRS)

    Li, Ning; Noever, David; Robertson, Tony; Koczor, Ron; Brantley, Whitt

    1997-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cc. Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating type II, YBCO superconductor, with the percentage change (0.05 - 2.1 %) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10' was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field. Changes in acceleration were measured to be less than 2 parts in 108 of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between static superconductors and gravity.

  2. Odd-parity topological superconductors: theory and application to CuxBi2Se3.

    PubMed

    Fu, Liang; Berg, Erez

    2010-08-27

    Topological superconductors have a full pairing gap in the bulk and gapless surface Andreev bound states. In this Letter, we provide a sufficient criterion for realizing time-reversal-invariant topological superconductors in centrosymmetric superconductors with odd-parity pairing. We next study the pairing symmetry of the newly discovered superconductor CuxBi2Se3 within a two-orbital model, and find that a novel spin-triplet pairing with odd parity is favored by strong spin-orbit coupling. Based on our criterion, we propose that CuxBi2Se3 is a good candidate for a topological superconductor. We close by discussing experimental signatures of this new topological phase.

  3. Odd-Parity Topological Superconductors: Theory and Application to CuxBi2Se3

    NASA Astrophysics Data System (ADS)

    Fu, Liang; Berg, Erez

    2010-08-01

    Topological superconductors have a full pairing gap in the bulk and gapless surface Andreev bound states. In this Letter, we provide a sufficient criterion for realizing time-reversal-invariant topological superconductors in centrosymmetric superconductors with odd-parity pairing. We next study the pairing symmetry of the newly discovered superconductor CuxBi2Se3 within a two-orbital model, and find that a novel spin-triplet pairing with odd parity is favored by strong spin-orbit coupling. Based on our criterion, we propose that CuxBi2Se3 is a good candidate for a topological superconductor. We close by discussing experimental signatures of this new topological phase.

  4. Heterostructures of Topological Insulators and Superconductors

    NASA Astrophysics Data System (ADS)

    Lababidi, Mahmoud

    Topological insulators (TI), such as Bi2Se 3, are a new class of quantum materials discovered recently. They are insulating in the bulk but can conduct on the surfaces. The robust surface states of three-dimensional strong TIs form a unique two-dimensional system of massless electrons, known as a helical metal, with a linear energy-momentum dispersion and spin-momentum locking. While these surface modes alone have spurred great interest, their interaction with superconductors (S) in close proximity has opened up opportunities to engineer topological superconductivity using TI-S heterostructures. This thesis is a microscopic, self-consistent theoretical investigation of the interplay between TI and superconductors. Three types of TI-based heterostructures with increasing complexity are studied in detail. We first present a detailed study of the coupling between a metal and a topological insulator. We compute the spin-active scattering matrix for electrons coming from the metal incident on the metal-TI interface. We find that there exists a critical incident angle, where perfect spin-flip occurs as the incoming electron is reflected. We discuss the origin of this phenomena and its potential implications in spintronics. We then compute the local spectrum at the metal-TI interface, and examine its evolution from the tunneling limit (bad contact) to the strong coupling limit (good contact). The calculations are done using two complementary approaches; in a continuum model based on a k·p Hamiltonian a wave function matching approach is taken and the lattice model requires the use of lattice Green's functions. The study of metal-TI interface lays the foundation for our subsequent theory of S-TI interface. Next we carry out microscopic, self-consistent calculations of the superconducting order parameter and pairing correlations near a S-TI interface, where S is an s-wave superconductor. We discuss the suppression of the order parameter by the topological insulator and

  5. Angle-resolved heat capacity of heavy fermion superconductors

    NASA Astrophysics Data System (ADS)

    Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige

    2016-09-01

    Owing to a strong Coulomb repulsion, heavy electron superconductors mostly have anisotropic gap functions which have nodes for certain directions in the momentum space. Since the nodal structure is closely related to the pairing mechanism, its experimental determination is of primary importance. This article discusses the experimental methods of the gap determination by bulk heat capacity measurements in a rotating magnetic field. The basic idea is based on the fact that the quasiparticle density of states in the vortex state of nodal superconductors is field and direction dependent. We present our recent experimental results of the field-orientation dependence of the heat capacity in heavy fermion superconductors CeTIn5 (T  =  Co, Ir), UPt3, CeCu2Si2, and UBe13 and discuss their gap structures.

  6. Angle-resolved heat capacity of heavy fermion superconductors.

    PubMed

    Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige

    2016-09-01

    Owing to a strong Coulomb repulsion, heavy electron superconductors mostly have anisotropic gap functions which have nodes for certain directions in the momentum space. Since the nodal structure is closely related to the pairing mechanism, its experimental determination is of primary importance. This article discusses the experimental methods of the gap determination by bulk heat capacity measurements in a rotating magnetic field. The basic idea is based on the fact that the quasiparticle density of states in the vortex state of nodal superconductors is field and direction dependent. We present our recent experimental results of the field-orientation dependence of the heat capacity in heavy fermion superconductors CeTIn5 (T  =  Co, Ir), UPt3, CeCu2Si2, and UBe13 and discuss their gap structures.

  7. Electrocaloric Refrigeration for Superconductors

    DTIC Science & Technology

    1974-12-31

    AD-A008 852 ELECTROCALORIC REFRIGERATION FOR SUPERCONDUCTORS Ray Radebaugh , et al National Bureau of Standards...for the period ending December 31, 1974 < Prepared by Ray Radebaugh , W. N. Lawless, and J. D. Slegwarth Cryogenics Division National Bureau of

  8. Quantum phenomena in superconductors

    SciTech Connect

    Clarke, J.

    1987-08-01

    This paper contains remarks by the author on aspects of macroscopic quantum phenomena in superconductors. Some topics discussed are: Superconducting low-inductance undulatory galvanometer (SLUGS), charge imbalance, cylindrical dc superconducting quantum interference device (SQUIDS), Geophysics, noise theory, magnetic resonance with SQUIDS, and macroscopic quantum tunneling. 23 refs., 4 figs. (LSP)

  9. Method for preparing superconductors

    DOEpatents

    Dahlgren, Shelley D.

    1976-01-01

    A superconductor having an equiaxed fine grain beta-tungsten crystalline structure found to have improved high field critical current densities is prepared by sputter-depositing superconductive material onto a substrate cooled to below 200.degree. C. and heat-treating the deposited material.

  10. Topological insulators/superconductors: Potential future electronic materials

    SciTech Connect

    Hor, Y. S.

    2014-03-05

    A new material called topological insulator has been discovered and becomes one of the fastest growing field in condensed matter physics. Topological insulator is a new quantum phase of matter which has Dirac-like conductivity on its surface, but bulk insulator through its interior. It is considered a challenging problem for the surface transport measurements because of dominant internal conductance due to imperfections of the existing crystals of topological insulators. By a proper method, the internal bulk conduction can be suppressed in a topological insulator, and permit the detection of the surface currents which is necessary for future fault-tolerant quantum computing applications. Doped topological insulators have depicted a large variety of bulk physical properties ranging from magnetic to superconducting behaviors. By chemical doping, a TI can change into a bulk superconductor. Nb{sub x}Bi{sub 2}Se{sub 3} is shown to be a superconductor with T{sub c} ∼ 3.2 K, which could be a potential candidate for a topological superconductor.

  11. Glass formability of high T(sub c) Bi-Sr-Ca-Cu-O superconductors

    NASA Technical Reports Server (NTRS)

    Kaukler, William F.

    1992-01-01

    A number of compositions of ceramic oxide high T(sub c) superconductors were evaluated for their glass formation ability by means of rapid thermal analysis during quenching, optical and electron microscopy of the quenched samples, and with subsequent DSC measurements. Correlations between experimental measurements and the methodical composition changes identified the formulations of superconductors that can easily form glass. The superconducting material was first formed as a glass, then with subsequent devitrification it was formed into bulk crystalline superconductor by a series of processing methods.

  12. Fermi Surface of the Most Dilute Superconductor

    NASA Astrophysics Data System (ADS)

    Lin, Xiao; Zhu, Zengwei; Fauqué, Benoît; Behnia, Kamran

    2013-04-01

    The origin of superconductivity in bulk SrTiO3 is a mystery since the nonmonotonous variation of the critical transition with carrier concentration defies the expectations of the crudest version of the BCS theory. Here, employing the Nernst effect, an extremely sensitive probe of tiny bulk Fermi surfaces, we show that, down to concentrations as low as 5.5×1017cm-3, the system has both a sharp Fermi surface and a superconducting ground state. The most dilute superconductor currently known therefore has a metallic normal state with a Fermi energy as little as 1.1 meV on top of a band gap as large as 3 eV. The occurrence of a superconducting instability in an extremely small, single-component, and barely anisotropic Fermi surface implies strong constraints for the identification of the pairing mechanism.

  13. Processing of R-Ba-Cu-O superconductors

    SciTech Connect

    Wu, H.

    1998-02-23

    Precipitation processes were developed to introduce second phases as flux pinning centers in Gd-Ba-Cu-O and Nd-Ba-Cu-O superconductors. In Gd-Ba-Cu-O, precipitation is caused by the decrease of the upper solubility limit of Gd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub 7} solid solution (Gd123ss) in low oxygen partial pressure. Processing of supersaturated Gd{sub 1.2}Ba{sub 1.8}Cu{sub 3}O{sub 7} in low oxygen partial pressure can produce dispersed second phases. Gd211 is formed as a separate phase while extensive Gd124 type stacking fault is formed instead of a separate CuO phase. As a result of the precipitation reaction, the transition temperature and critical current density are increased. In Nd-Ba-Cu-O, precipitation is caused by the decrease of the lower solubility limit of Nd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub 7} solid solution (Nd123ss) in oxygen. DTA results reveal the relative stability of Nd123ss in different oxygen partial pressures. In 1 bar oxygen partial pressure, Nd123ss with x = 0.1 is the most stable phase. In lower oxygen partial pressures, the most stable composition shifts towards the stoichiometric composition. The relative stability changes faster with decreasing oxygen partial pressure. Therefore, processing in oxygen and air tends to produce broad superconducting transitions but sharp transitions can be achieved in 0.01 bar and 0.001 bar oxygen partial pressures. While the lower solubility limits in 0.01 bar and 0.001 bar oxygen partial pressures remain at x = 0.00, the solubility limits in oxygen and air show a narrowing with decreasing temperature. Because of the narrowing of the solubility range in oxygen, oxygen annealing of Nd123 initially processed in low oxygen partial pressures will result in precipitation of second phases. The equilibrium second phase is BaCuO{sub 2} for temperature above 608 C, and at lower temperatures the equilibrium second phases are Ba{sub 2}CuO{sub 3.3} and Ba{sub 2}Cu{sub 3}O{sub 5+y}. However, annealing at

  14. Three-dimensional Majorana fermions in chiral superconductors.

    PubMed

    Kozii, Vladyslav; Venderbos, Jörn W F; Fu, Liang

    2016-12-01

    Using a systematic symmetry and topology analysis, we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-nondegenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum J formed by Bloch electrons with angular momentum j in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that the existence of bulk Majorana fermions in the vicinity of spin-selective point nodes is rooted in the nonunitary nature of chiral pairing in spin-orbit-coupled superconductors. We address experimental signatures of Majorana fermions and find that the nuclear magnetic resonance spin relaxation rate is significantly suppressed for nuclear spins polarized along the nodal direction as a consequence of the spin-selective Majorana nature of nodal quasiparticles. Furthermore, Majorana nodes in the bulk have nontrivial topology and imply the presence of Majorana bound states on the surface, which form arcs in momentum space. We conclude by proposing the heavy fermion superconductor PrOs4Sb12 and related materials as promising candidates for nonunitary chiral superconductors hosting three-dimensional Majorana fermions.

  15. Three-dimensional Majorana fermions in chiral superconductors

    PubMed Central

    Kozii, Vladyslav; Venderbos, Jörn W. F.; Fu, Liang

    2016-01-01

    Using a systematic symmetry and topology analysis, we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-nondegenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum J formed by Bloch electrons with angular momentum j in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that the existence of bulk Majorana fermions in the vicinity of spin-selective point nodes is rooted in the nonunitary nature of chiral pairing in spin-orbit–coupled superconductors. We address experimental signatures of Majorana fermions and find that the nuclear magnetic resonance spin relaxation rate is significantly suppressed for nuclear spins polarized along the nodal direction as a consequence of the spin-selective Majorana nature of nodal quasiparticles. Furthermore, Majorana nodes in the bulk have nontrivial topology and imply the presence of Majorana bound states on the surface, which form arcs in momentum space. We conclude by proposing the heavy fermion superconductor PrOs4Sb12 and related materials as promising candidates for nonunitary chiral superconductors hosting three-dimensional Majorana fermions. PMID:27957543

  16. Single Crystal Synthesis and STM Studies of High Temperature Superconductors

    NASA Technical Reports Server (NTRS)

    Barrientos, Alfonso

    1997-01-01

    This is a final report for the work initiated in September of 1994 under the grant NAG8-1085 - NASA/OMU, on the fabrication of bulk and single crystal synthesis, specific heat measuring and STM studies of high temperature superconductors. Efforts were made to fabricate bulk and single crystals of mercury based superconducting material. A systematic thermal analysis on the precursors for the corresponding oxides and carbonates were carried out to synthesized bulk samples. Bulk material was used as seed in an attempt to grow single crystals by a two-step self flux process. On the other hand bulk samples were characterized by x-ray diffraction, electrical resistivity and magnetic susceptibility, We studied the specific heat behavior in the range from 80 to 300 K. Some preliminary attempts were made to study the atomic morphology of our samples. As part of our efforts we built an ac susceptibility apparatus for measuring the transition temperature of our sintered samples.

  17. Ambient-pressure organic superconductor

    DOEpatents

    Williams, Jack M.; Wang, Hsien-Hau; Beno, Mark A.

    1986-01-01

    A new class of organic superconductors having the formula (ET).sub.2 MX.sub.2 wherein ET represents bis(ethylenedithio)-tetrathiafulvalene, M is a metal such as Au, Ag, In, Tl, Rb, Pd and the like and X is a halide. The superconductor (ET).sub.2 AuI.sub.2 exhibits a transition temperature of 5 K which is high for organic superconductors.

  18. Conformal energy currents on the edge of a topological superconductor

    NASA Astrophysics Data System (ADS)

    Self, Chris N.; Pachos, Jiannis K.; Wootton, James R.; Iblisdir, Sofyan

    2017-03-01

    The boundary of a two-dimensional topological superconductor can be modeled by a conformal field theory. Here we demonstrate the behaviors of this high level description emerging from a microscopic model at finite temperatures. To achieve that, we analyze the low-energy sector of Kitaev's honeycomb lattice model and probe its energy current. We observe that the scaling of the energy current with temperature reveals the central charge of the conformal field theory, which is in agreement with the Chern number of the bulk. Importantly, these currents can discriminate between distinct topological phases at finite temperatures. We assess the resilience of this measurement of the central charge under coupling disorder, bulk dimerization, and defects at the boundary, thus establishing it as a favorable means of experimentally probing topological superconductors.

  19. Vortex cutting in superconductors

    NASA Astrophysics Data System (ADS)

    Glatz, A.; Vlasko-Vlasov, V. K.; Kwok, W. K.; Crabtree, G. W.

    2016-08-01

    Vortex cutting and reconnection is an intriguing and still-unsolved problem central to many areas of classical and quantum physics, including hydrodynamics, astrophysics, and superconductivity. Here, we describe a comprehensive investigation of the crossing of magnetic vortices in superconductors using time dependent Ginsburg-Landau modeling. Within a macroscopic volume, we simulate initial magnetization of an anisotropic high temperature superconductor followed by subsequent remagnetization with perpendicular magnetic fields, creating the crossing of the initial and newly generated vortices. The time resolved evolution of vortex lines as they approach each other, contort, locally conjoin, and detach, elucidates the fine details of the vortex-crossing scenario under practical situations with many interacting vortices in the presence of weak pinning. Our simulations also reveal left-handed helical vortex instabilities that accompany the remagnetization process and participate in the vortex crossing events.

  20. Conceptual design of a novel insertion device using bulk superconducting magnet

    NASA Astrophysics Data System (ADS)

    Kii, T.; Kinjo, R.; Bakr, M. A.; Choi, Y. W.; Yoshida, K.; Ueda, S.; Takasaki, M.; Ishida, K.; Kimura, N.; Sonobe, T.; Masuda, K.; Ohgaki, H.

    2011-11-01

    An undulator or a wiggler with a strong magnetic field will play an important role in future synchrotron light sources, free electron lasers, and linear colliders. We proposed the bulk high critical temperature superconductor staggered array undulator (Bulk HTSC SAU) in order to generate a strong periodic field. The Bulk HTSC SAU consists of stacked bulk high-Tc superconductors (HTSs) and a solenoid magnet which is used to magnetize the bulk HTSs. A periodic magnetic field was produced and controlled using a prototype of the Bulk HTSC SAU using 11 pairs of REBaCuO bulk HTSs at 77 K. The expected performance at low temperatures around 20 K is calculated using a loop current model.

  1. Processing of Superconductor-Normal-Superconductor Josephson Edge Junctions

    NASA Technical Reports Server (NTRS)

    Kleinsasser, A. W.; Barner, J. B.

    1997-01-01

    The electrical behavior of epitaxial superconductor-normal-superconductor (SNS) Josephson edge junctions is strongly affected by processing conditions. Ex-situ processes, utilizing photoresist and polyimide/photoresist mask layers, are employed for ion milling edges for junctions with Yttrium-Barium-Copper-Oxide (YBCO) electrodes and primarily Co-doped YBCO interlayers.

  2. Theory of heterotic superconductor-insulator-superconductor Josephson junctions between single- and multiple-gap superconductors.

    PubMed

    Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio; Matsumoto, Hideki

    2009-06-12

    Using the functional integral method, we construct a theory of heterotic superconductor-insulator-superconductor Josephson junctions between one- and two-gap superconductors. The theory predicts the presence of in-phase and out-of-phase collective oscillation modes of superconducting phases. The former corresponds to the Josephson plasma mode whose frequency is drastically reduced for +/- s-wave symmetry, and the latter is a counterpart of Leggett's mode in Josephson junctions. We also reveal that the critical current and the Fraunhofer pattern strongly depend on the symmetry type of the two-gap superconductor.

  3. Superconducting RF materials other than bulk niobium: a review

    DOE PAGES

    Valente-Feliciano, Anne-Marie

    2016-09-26

    For the last five decades, bulk niobium (Nb) has been the material of choice for Superconducting RF (SRF) cavity applications. Thin film alternatives such as Nb and other higher-Tc materials, mainly Nb compounds and A15 compounds, have been investigated with moderate effort in the past. In recent years, RF cavity performance has approached the theoretical limit for bulk Nb. For further improvement of RF cavity performance for future accelerator projects, research interest is renewed towards alternatives to bulk Nb. Institutions around the world are now investing renewed efforts in the investigation of Nb thin films and superconductors with higher transitionmore » temperature Tc for application to SRF cavities. Our paper gives an overview of the results obtained so far and challenges encountered for Nb films as well as other materials, such as Nb compounds, A15 compounds, MgB2, and oxypnictides, for SRF cavity applications. An interesting alternative using a Superconductor-Insulator- Superconductor multilayer approach has been recently proposed to delay the vortex penetration in Nb surfaces. This could potentially lead to further improvement in RF cavities performance using the benefit of the higher critical field Hc of higher-Tc superconductors without being limited with their lower Hc1.« less

  4. Superconducting RF materials other than bulk niobium: a review

    SciTech Connect

    Valente-Feliciano, Anne-Marie

    2016-09-26

    For the last five decades, bulk niobium (Nb) has been the material of choice for Superconducting RF (SRF) cavity applications. Thin film alternatives such as Nb and other higher-Tc materials, mainly Nb compounds and A15 compounds, have been investigated with moderate effort in the past. In recent years, RF cavity performance has approached the theoretical limit for bulk Nb. For further improvement of RF cavity performance for future accelerator projects, research interest is renewed towards alternatives to bulk Nb. Institutions around the world are now investing renewed efforts in the investigation of Nb thin films and superconductors with higher transition temperature Tc for application to SRF cavities. Our paper gives an overview of the results obtained so far and challenges encountered for Nb films as well as other materials, such as Nb compounds, A15 compounds, MgB2, and oxypnictides, for SRF cavity applications. An interesting alternative using a Superconductor-Insulator- Superconductor multilayer approach has been recently proposed to delay the vortex penetration in Nb surfaces. This could potentially lead to further improvement in RF cavities performance using the benefit of the higher critical field Hc of higher-Tc superconductors without being limited with their lower Hc1.

  5. Nernst effect in high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Yayu

    This thesis presents a study of the Nernst effect in high temperature superconductors. The vortex Nernst measurements have been carried out on various high Tc cuprates to high magnetic fields. These results provide vital information about the properties and relations of the pseudogap phase and superconducting phase in high Tc superconductors. Our first finding is the existence of vortex-like excitations at temperatures much higher than Tc0, the zero filed transition temperature, in the underdoped cuprates. This result suggests that in the putative normal state of cuprates, although bulk Meissner effect is absent and resistivity looks normal, the amplitude of the Cooper pairing is still sizable. The transition at Tc0 is driven by the loss of long range phase coherence rather than the disappearance of superconducting condensate. The high field Nernst effect offers a reliable way to determine the upper critical field Hc2 of high Tc cuprates and many unusual properties are uncovered. For cuprates with relatively large hole density (x > 0.15), we found that H c2 is almost temperature independent for T < Tc0. This is in strong contrast to the Hc2 - T relation of conventional superconductors. Moreover, using a scaling analysis, we have demonstrated that H c2 increases with decreasing hole density x in this doping range, implying a stronger pairing potential at lower doping. In the severely underdoped regime (x < 0.12), some new features become apparent and they imply that the vortex Nernst signal is comprised of two distinct contributions. The first is from coherent regions with long range phase coherence and relatively low upper critical field, more like the superconducting phase; the second is from phase incoherent regions with much larger field scales, indicative of the pseudogap phase. As temperature rises, the superconducting phase gives weight to the pseudogap phase. Moreover, the upper critical field Hc2 of the superconducting phase scales with the onset

  6. Helical phases in superconductors

    NASA Astrophysics Data System (ADS)

    Sandhu, Raminder P. Kaur

    In conventional superconductors, the Cooper pairs are formed from quasiparticles with opposite momentum and spins because of the degeneracy of the quasiparticles under time reversal and inversion. The absence of any of these symmetries will have pronounced effects on superconducting states. Time reversal symmetry can be broken in the presence of magnetic impurities or by the application of a magnetic field. Similarly, the dislocation of crystal ions from their higher symmetric positions can cause broken inversion symmetry. We studied the effects of broken time reversal and inversion symmetries on unconventional superconductors, such as high temperature cuprates, Sr2RuO 4, and CePt3Si. In the cuprates, the superconducting state exists near the antiferromagnetic order. Sr2RuO4 and CePt3Si do not have spatial inversion, and the superconducting states coexist with magnetic order. In cuprates, the broken time reversal symmetry has been reported in the pseudogap phase which will effect the d-wave superconducting state of underdoped regime. On the basis of symmetry analysis we found that a mixture of spin-singlet and -triplet state, d+ip, which is shown to give rise to a helical superconducting phase. Consequences of this d+ip state on Josephson experiments are also discussed. Sr2RuO 4 is known to be another broken time reversal superconductor with spin triplet superconductivity. The widely believed superconducting state, the chiral p wave state, has been extensively studied through Ginzburg Landau theory, but the predictions for this state contradict some experimental observations like anisotropy in the upper critical field, and the existence of a second vortex state. We have formalize quasiclassical theory to find the origin of these contradictions, and also extended the theory to study other possible super-conducting states. Surprisingly, we find that a superconducting state corresponding to freely rotating in-plane d-vector explains the existing experimental results

  7. Surface superconductivity of dirty two-band superconductors: applications to MgB2.

    PubMed

    Gorokhov, Denis A

    2005-02-25

    The minimal magnetic field H(c2) destroying superconductivity in the bulk of a superconductor is smaller than the magnetic field H(c3) needed to destroy surface superconductivity if the surface of a superconductor coincides with one of the crystallographic planes and is parallel to the external magnetic field. While for a dirty single-band superconductor the ratio of H(c3) to H(c2) is a universal temperature-independent constant 1.6946, for dirty two-band superconductors this is not the case. I show that in the latter case the interaction of the two bands leads to a novel scenario with the ratio H(c3)/H(c2) varying with temperature and taking values larger and smaller than 1.6946. The results are applied to MgB(2) and compared with recent experiments (A. Rydh, cond-mat/0307445).

  8. Surface State Tunneling Signatures in the Two-Component Superconductor UPt3

    NASA Astrophysics Data System (ADS)

    Lambert, Fabian; Akbari., Alireza; Thalmeier, Peter; Eremin, Ilya

    2017-02-01

    Quasiparticle interference (QPI) imaging of Bogoliubov excitations in quasi-two-dimensional unconventional superconductors has become a powerful technique for measuring the superconducting gap and its symmetry. Here, we present the extension of this method to three-dimensional superconductors and analyze the expected QPI spectrum for the two-component heavy-fermion superconductor UPt3 whose gap structure is still controversial. Starting from a 3D electronic structure and the three proposed chiral gap models E1 g ,u or E2 u, we perform a slab calculation that simultaneously gives extended bulk states and topologically protected in-gap dispersionless surface states. We show that the number of Weyl arcs and their hybridization with the line node provides a fingerprint that may finally determine the true nodal structure of the UPt3 superconductor.

  9. High-temperature superconductors; Proceedings of the Symposium, Boston, MA, Nov. 30-Dec. 4, 1987

    NASA Astrophysics Data System (ADS)

    Brodsky, Merwyn B.; Dynes, Robert C.; Kitazawa, Koichi; Tuller, Harry L.

    Papers are presented on neutron diffraction studies of high-Tc superconductors, the preparation of bulk and thick films of YBa2Cu3O(7-y) using a solution technique, the effects of oxygen stoichiometry and oxygen ordering on superconductivity in Y1Ba2Cu3O(9-x), and the n-p transition in YBa2Cu3O(6.5+x). Also considered are high-Tc superconducting oxide films produced from solution precursors, the deposition, fabrication, and characteristics of high critical temperature devices, and the application of gel technology in the preparation of high-Tc perovskite superconductors. Other topics include high-Tc superconducting films from metalloorganic precursors, a photoemission study of the electronic structure of copper oxide superconductors, oxygen stoichiometry in La-Ba-Cu-O perovskites, and the advantages of barium peroxide in the powder synthesis of perovskite superconductors.

  10. Antenna applications of superconductors

    NASA Astrophysics Data System (ADS)

    Hansen, R. C.

    1991-09-01

    The applicability of superconductors to antennas is examined. Potential implementations that are examined are superdirective arrays; electrically small antennas; tuning and matching of these two; high-gain millimeter-wavelength arrays; and kinetic inductance slow wave structures for array phasers and traveling wave array feeds. It is thought that superdirective arrays and small antennas will not benefit directly, but their tuning/matching networks will undergo major improvements. Miniaturization of antennas will not be aided, but much higher gain millimeter-wave arrays will be realizable. Kinetic inductance slow-wave lines appear advantageous for improved array phasers and time delay, as well as for traveling-wave array feeds.

  11. Dynamics of interfaces in superconductors

    SciTech Connect

    Dorsey, A.T. )

    1994-08-01

    The dynamics of an interface between the normal and superconducting phases under nonstationary external conditions is studied within the framework of the time-dependent Ginzburg-Landau equations of superconductivity, modified to include thermal fluctuations. An equation of motion for the interface is derived in two steps. First, the method of matched asymptotic expansions is used to derive a diffusion equation for the magnetic field in the normal phase, with nonlinear boundary conditions at the interface. These boundary conditions are a continuity equation which relates the gradient of the field at the interface to the normal velocity of the interface and a modified Gibbs-Thomson boundary condition for the field at the interface. Second, the boundary integral method is used to integrate out the magnetic field in favor of an equation of motion for the interface. This equation of motion, which is highly nonlinear and nonlocal, exhibits a diffusive instability (the Mullins-Sekerka instability) when the superconducting phase expands into the normal phase (i.e., when the external field is reduced below the critical field). In the limit of infinite diffusion constant the equation of motion becomes local in time and can be derived variationally from a static energy functional which includes the bulk-free energy difference between the two phases, the interfacial energy, and a long range self-interaction of the interface of the Biot-Savart form. In this limit the dynamics is identical to the interfacial dynamics of ferrofluid domains recently proposed by S.A. Langer et al. As shown by these authors, the Biot-Savart interaction leads to mechanical instabilities of the interface, resulting in highly branched labyrinthine patterns. The application of these ideas to the study of labyrinthine patterns in the intermediate state of type-I superconductors is briefly discussed. 29 refs.

  12. Effects of fluctuating magnetic fields on a superconducting bulk rotor shielded with superconducting rings

    NASA Astrophysics Data System (ADS)

    Yamagishi, K.; Ogawa, J.; Tsukamoto, O.

    2014-05-01

    We study the effect of a fluctuating magnetic field, which is one of the technical problems for trapped magnetic fields in a bulk superconductor, to realize a practical bulk superconductor rotating machine. Previous research and other's research has shown that fluctuating magnetic fields reduce the strength of trapped magnetic fields in superconducting bulk modules [1, 2]. This deters development of applications of AC rotating machines because superconducting bulk modules are always exposed to a fluctuating magnetic field. Therefore, it is necessary to develop a method to control decrease of the trapped magnetic field. We propose a method to use the shielding ring of a superconducting wire to achieve this goal and the effects are confirmed experimentally [3]. We are now building test equipment for examining the performance of a shielding ring in a bulk rotating machine. This paper reports the test result for the shielding ring applied to the bulk superconducting rotor that is a part of the test equipment.

  13. Laser surface interactions of high-T(sub c) superconductors

    NASA Technical Reports Server (NTRS)

    Chen, C. H.; Mccann, M. P.; Phillips, R. C.

    1990-01-01

    During the past two years, one of the most exciting research fields in science has been the study of the newly discovered high-T(sub c) metal oxide superconductors. Although many theoretical models were proposed, there is no general agreement on any theory to explain these materials. One of the peculiar features of these high-T(sub c) materials is the noninteger number of oxygen atoms. The oxygen content is extremely critical to the superconductive properties. Take YBa2Cu3O(7-x) as an example. Its superconductive properties disappear whenever x is larger than 0.5. The existence of Cu(+ 3) was considered to account for x less than 0.5. However, results from mass spectroscopy of laser desorbed species indicate that significant quantities of oxygen molecules are trapped in the bulk of these high-T(sub c) superconductors. It appears that these trapped oxygen molecules may play key roles in superconductive properties. Preparation of superconductive thin films are considered very important for the applications of these new superconductors for the electronics industry. Fluorescence spectra and ion spectra following laser ablation of high-temperature superconductors were obtained. A real time monitor for preparation of superconductive thin films can possibly be developed.

  14. Laser surface interaction of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Chen, C. H.; Mccann, M. P.; Phillips, R. C.

    1991-01-01

    During the past two years, one of the most exciting research fields in science has been the study of the newly discovered high-T(sub c) metal oxide superconductors. Although many theoretical models were proposed, there is no general agreement on any theory to explain these materials. One of the peculiar features of these high-T(sub c) materials is the noninteger number of oxygen atoms. The oxygen content is extremely critical to the superconductive properties. Take YBa2Cu3O(7-x) as an example. Its superconductive properties disappear whenever x is larger than 0.5. The existence of Cu(+ 3) was considered to account for x less than 0.5. However, results from mass spectroscopy of laser desorbed species indicate that significant quantities of oxygen molecules are trapped in the bulk of these high-T(sub c) superconductors. It appears that these trapped oxygen molecules may play key roles in superconductive properties. Preparation of superconductive thin films are considered very important for the applications of these new superconductors for the electronics industry. Fluorescence spectra and ion spectra following laser ablation of high-temperature superconductors were obtained. A real time monitor for preparation of superconductive thin films can possibly be developed.

  15. Conventional magnetic superconductors

    SciTech Connect

    Wolowiec, C. T.; White, B. D.; Maple, M. B.

    2015-07-01

    We discuss several classes of conventional magnetic superconductors including the ternary rhodium borides and molybdenum chalcogenides (or Chevrel phases), and the quaternary nickel-borocarbides. These materials exhibit some exotic phenomena related to the interplay between superconductivity and long-range magnetic order including: the coexistence of superconductivity and antiferromagnetic order; reentrant and double reentrant superconductivity, magnetic field induced superconductivity, and the formation of a sinusoidally-modulated magnetic state that coexists with superconductivity. We introduce the article with a discussion of the binary and pseudobinary superconducting materials containing magnetic impurities which at best exhibit short-range “glassy” magnetic order. Early experiments on these materials led to the idea of a magnetic exchange interaction between the localized spins of magnetic impurity ions and the spins of the conduction electrons which plays an important role in understanding conventional magnetic superconductors. Furthermore, these advances provide a natural foundation for investigating unconventional superconductivity in heavy-fermion compounds, cuprates, and other classes of materials in which superconductivity coexists with, or is in proximity to, a magnetically-ordered phase.

  16. Vortex cutting in superconductors

    NASA Astrophysics Data System (ADS)

    Vlasko-Vlasov, Vitalii K.; Koshelev, Alexei E.; Glatz, Andreas; Welp, Ulrich; Kwok, Wai-K.

    2015-03-01

    Unlike illusive magnetic field lines in vacuum, magnetic vortices in superconductors are real physical strings, which interact with the sample surface, crystal structure defects, and with each other. We address the complex and poorly understood process of vortex cutting via a comprehensive set of magneto-optic experiments which allow us to visualize vortex patterns at magnetization of a nearly twin-free YBCO crystal by crossing magnetic fields of different orientations. We observe a pronounced anisotropy in the flux dynamics under crossing fields and the filamentation of induced supercurrents associated with the staircase vortex structure expected in layered cuprates, flux cutting effects, and angular vortex instabilities predicted for anisotropic superconductors. At some field angles, we find formation of the vortex domains following a type-I phase transition in the vortex state accompanied by an abrupt change in the vortex orientation. To clarify the vortex cutting scenario we performed time-dependent Ginzburg-Landau simulations, which confirmed formation of sharp vortex fronts observed in the experiment and revealed a left-handed helical instability responsible for the rotation of vortices. This work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division.

  17. Conventional magnetic superconductors

    DOE PAGES

    Wolowiec, C. T.; White, B. D.; Maple, M. B.

    2015-07-01

    We discuss several classes of conventional magnetic superconductors including the ternary rhodium borides and molybdenum chalcogenides (or Chevrel phases), and the quaternary nickel-borocarbides. These materials exhibit some exotic phenomena related to the interplay between superconductivity and long-range magnetic order including: the coexistence of superconductivity and antiferromagnetic order; reentrant and double reentrant superconductivity, magnetic field induced superconductivity, and the formation of a sinusoidally-modulated magnetic state that coexists with superconductivity. We introduce the article with a discussion of the binary and pseudobinary superconducting materials containing magnetic impurities which at best exhibit short-range “glassy” magnetic order. Early experiments on these materials led tomore » the idea of a magnetic exchange interaction between the localized spins of magnetic impurity ions and the spins of the conduction electrons which plays an important role in understanding conventional magnetic superconductors. Furthermore, these advances provide a natural foundation for investigating unconventional superconductivity in heavy-fermion compounds, cuprates, and other classes of materials in which superconductivity coexists with, or is in proximity to, a magnetically-ordered phase.« less

  18. Hybrid superconductor magnet bearings

    NASA Astrophysics Data System (ADS)

    Chu, Wei-Kan

    1995-04-01

    Hybrid superconductor magnet bearings (HSMB's) utilize high temperature superconductors (HTS's) together with permanent magnets to form a frictionless interface between relatively rotating parts. They are low mass, stable, and do not incur expenditure of energy during normal operation. There is no direct physical contact between rotor and stator, and hence there is no wear and tear. However, just as any other applications of HTS's, it requires a very cold temperature to function. Whereas this might be perceived as a disadvantage on earth, it is of no great concern in space or on the moon. To astronomers, the moon is an excellent site for an observatory, but the cold and dusty vacuum environment on the moon precludes the use of mechanical bearings on the telescope mounts. Furthermore, drive mechanisms with very fine steps, and hence bearings with extremely low friction are needed to track a star from the moon, because the moon rotates very slowly. All aspects considered, the HSMB is about the only candidate that fits in naturally. Here, we present a design for one such bearing, capable of supporting a telescope that weighs about 3 lbs on Earth.

  19. Hybrid superconductor magnet bearings

    NASA Technical Reports Server (NTRS)

    Chu, Wei-Kan

    1995-01-01

    Hybrid superconductor magnet bearings (HSMB's) utilize high temperature superconductors (HTS's) together with permanent magnets to form a frictionless interface between relatively rotating parts. They are low mass, stable, and do not incur expenditure of energy during normal operation. There is no direct physical contact between rotor and stator, and hence there is no wear and tear. However, just as any other applications of HTS's, it requires a very cold temperature to function. Whereas this might be perceived as a disadvantage on earth, it is of no great concern in space or on the moon. To astronomers, the moon is an excellent site for an observatory, but the cold and dusty vacuum environment on the moon precludes the use of mechanical bearings on the telescope mounts. Furthermore, drive mechanisms with very fine steps, and hence bearings with extremely low friction are needed to track a star from the moon, because the moon rotates very slowly. All aspects considered, the HSMB is about the only candidate that fits in naturally. Here, we present a design for one such bearing, capable of supporting a telescope that weighs about 3 lbs on Earth.

  20. Hybrid superconductor magnet bearings

    SciTech Connect

    Chu, W.

    1995-04-01

    Hybrid superconductor magnet bearings (HSMB`s) utilize high temperature superconductors (HTS`s) together with permanent magnets to form a frictionless interface between relatively rotating parts. They are low mass, stable, and do not incur expenditure of energy during normal operation. There is no direct physical contact between rotor and stator, and hence there is no wear and tear. However, just as any other applications of HTS`s, it requires a very cold temperature to function. Whereas this might be perceived as a disadvantage on earth, it is of no great concern in space or on the moon. To astronomers, the moon is an excellent site for an observatory, but the cold and dusty vacuum environment on the moon precludes the use of mechanical bearings on the telescope mounts. Furthermore, drive mechanisms with very fine steps, and hence bearings with extremely low friction are needed to track a star from the moon, because the moon rotates very slowly. All aspects considered, the HSMB is about the only candidate that fits in naturally. Here, the authors present a design for one such bearing, capable of supporting a telescope that weighs about 3 lbs on Earth.

  1. Superconductors (History & Advanced Research)

    NASA Astrophysics Data System (ADS)

    Khorrami, Mona

    2012-02-01

    Superconductors are materials that have no resistance to electricity's flow; they are one of the last great frontiers of scientific discovery. In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes When he cooled it to the temperature of liquid helium, 4 degrees Kelvin (-452F, -269C), its resistance suddenly disappeared. It was necessary for Onnes to come within 4 degrees of the coldest temperature that is theoretically attainable to witness the phenomenon of superconductivity. The next great milestone in understanding how matter behaves at extreme cold temperatures occurred in 1933. German researchers Walther Meissner and Robert Ochsenfeld discovered that a superconducting material will repel a magnetic field. A magnet moving by a conductor induces currents in the conductor. This is the principle on which the electric generator operates. But, in a superconductor the induced currents exactly mirror the field that would have otherwise penetrated the superconducting material - causing the magnet to be repulsed. This phenomenon is known as strong diamagnetism and is today often referred to as the ``Meissner effect'' (an eponym). In 1941 niobium-nitride was found to superconduct at 16 K. In 1953 vanadium-silicon displayed superconductive properties at 17.5 K. And, in 1962 scientists at Westinghouse developed the first commercial superconducting wire, an alloy of niobium and titanium (NbTi).

  2. Surface superconductivity of short coherence length superconductors

    NASA Astrophysics Data System (ADS)

    Watson Yang, T. J.; Chen, J. L.

    1994-12-01

    Based on the microscopic theory of Valls et al for short coherence length superconductors, the surface critical temperature Tcs is assumed to be higher than the bulk critical temperature Tcb and the term of surface energy is added in the Ginzburg-Landau (GL) free energy. A boundary condition is obtained and used to solve the GL equation exactly under zero magnetic field for various temperatures. Two examples are given. The critical temperature Tc will be enhanced by reducing the thickness of a superconducting thin film. The nucleation field Hc3(T) is proportional to Tcb-T near Tcb; and Hc3(T) is also proportional to (Tc-T)1/2 near Tc.>

  3. Surface superconductivity of short coherence length superconductors

    NASA Astrophysics Data System (ADS)

    Yang, T. J. Watson; Chen, J. L.

    1994-12-01

    Based on the microscopic theory of Valls et al for short coherence length superconductors, the surface critical temperature Tcs is assumed to be higher than the bulk critical temperature Tcb and the term of surface energy is added in the Ginzburg-Landau (GL) free energy. A boundary condition is obtained and used to solve the GL equation excactly under zero magnetic field for various temperatures. Two examples are given. The critical temperature Tc will be enhanced by reducing the thickness of a superconductig thin film. The nucleation field Hcs( T) is proportional to Tcb- T near Tcb; and Hcs( T) is also proportional to (T c-T) {1}/{2} near Tc.

  4. Correlations between Majorana Fermions Through a Superconductor

    NASA Astrophysics Data System (ADS)

    Zyuzin, A. A.; Rainis, Diego; Klinovaja, Jelena; Loss, Daniel

    2013-08-01

    We consider a model of ballistic quasi-one-dimensional semiconducting wire with intrinsic spin-orbit interaction placed on the surface of a bulk s-wave superconductor (SC), in the presence of an external magnetic field. This setup has been shown to give rise to a topological superconducting state in the wire, characterized by a pair of Majorana-fermion (MF) bound states formed at the two ends of the wire. Here, we demonstrate that besides the well-known direct-overlap-induced energy splitting, the two MF bound states may hybridize via elastic tunneling processes through virtual quasiparticle states in the SC, giving rise to an additional energy splitting between MF states from the same as well as from different wires.

  5. Theory of surface spectroscopy for noncentrosymmetric superconductors

    NASA Astrophysics Data System (ADS)

    Wennerdal, Niclas; Eschrig, Matthias

    2017-01-01

    We study noncentrosymmetric superconductors with the tetrahedral Td, tetragonal C4 v, and cubic point group O . The order parameter is computed self-consistently in the bulk and near a surface for several different singlet to triplet order parameter ratios. It is shown that a second phase transition below Tc is possible for certain parameter values. In order to determine the surface orientation's effect on the order parameter suppression, the latter is calculated for a range of different surface orientations. For selected self-consistent order parameter profiles the surface density of states is calculated showing intricate structure of the Andreev bound states as well as spin polarization. The topology's effect on the surface states and the tunnel conductance is thoroughly investigated, and a topological phase diagram is constructed for open and closed Fermi surfaces showing a sharp transition between the two for the cubic point group O .

  6. Spin manipulation in nanoscale superconductors.

    PubMed

    Beckmann, D

    2016-04-27

    The interplay of superconductivity and magnetism in nanoscale structures has attracted considerable attention in recent years due to the exciting new physics created by the competition of these antagonistic ordering phenomena, and the prospect of exploiting this competition for superconducting spintronics devices. While much of the attention is focused on spin-polarized supercurrents created by the triplet proximity effect, the recent discovery of long range quasiparticle spin transport in high-field superconductors has rekindled interest in spin-dependent nonequilibrium properties of superconductors. In this review, the experimental situation on nonequilibrium spin injection into superconductors is discussed, and open questions and possible future directions of the field are outlined.

  7. Materials design for new superconductors.

    PubMed

    Norman, M R

    2016-07-01

    Since the announcement in 2011 of the Materials Genome Initiative by the Obama administration, much attention has been given to the subject of materials design to accelerate the discovery of new materials that could have technological implications. Although having its biggest impact for more applied materials like batteries, there is increasing interest in applying these ideas to predict new superconductors. This is obviously a challenge, given that superconductivity is a many body phenomenon, with whole classes of known superconductors lacking a quantitative theory. Given this caveat, various efforts to formulate materials design principles for superconductors are reviewed here, with a focus on surveying the periodic table in an attempt to identify cuprate analogues.

  8. Magnetic levitation for hard superconductors

    SciTech Connect

    Kordyuk, A.A.

    1998-01-01

    An approach for calculating the interaction between a hard superconductor and a permanent magnet in the field-cooled case is proposed. The exact solutions were obtained for the point magnetic dipole over a flat ideally hard superconductor. We have shown that such an approach is adaptable to a wide practical range of melt-textured high-temperature superconductors{close_quote} systems with magnetic levitation. In this case, the energy losses can be calculated from the alternating magnetic field distribution on the superconducting sample surface. {copyright} {ital 1998 American Institute of Physics.}

  9. Superconductor and magnet levitation devices

    NASA Astrophysics Data System (ADS)

    Ma, K. B.; Postrekhin, Y. V.; Chu, W. K.

    2003-12-01

    This article reviews levitation devices using superconductors and magnets. Device concepts and their applications such as noncontact bearings, flywheels, and momentum wheels are discussed, following an exposition of the principles behind these devices. The basic magneto-mechanical phenomenon responsible for levitation in these devices is a result of flux pinning inherent in the interaction between a magnet and a type II superconductor, described and explained in this article by comparison with behavior expected of a perfect conductor or a nearly perfect conductor. The perfect conductor model is used to illustrate why there is a difference between the forces observed when the superconductor is cooled after or before the magnet is brought into position. The same model also establishes the principle that a resisting force or torque arises only in response to those motions of the magnet that changes the magnet field at the superconductor. A corollary of the converse, that no drag torque appears when an axisymmetric magnet levitated above a superconductor rotates, is the guiding concept in the design of superconductor magnet levitation bearings, which is the common component in a majority of levitation devices. The perfect conductor model is extended to a nearly perfect conductor to provide a qualitative understanding of the dissipative aspects such as creep and hysteresis in the interaction between magnets and superconductors. What all these entail in terms of forces, torques, and power loss is expounded further in the context of generic cases of a cylindrical permanent magnet levitated above a superconductor and a superconductor rotating in a transverse magnetic field. Then we proceed to compare the pros and cons of levitation bearings based on the first arrangement with conventional mechanical bearings and active magnetic bearings, and discuss how the weak points of the levitation bearing may be partially overcome. In the latter half, we examine designs of devices

  10. Materials design for new superconductors

    NASA Astrophysics Data System (ADS)

    Norman, M. R.

    2016-07-01

    Since the announcement in 2011 of the Materials Genome Initiative by the Obama administration, much attention has been given to the subject of materials design to accelerate the discovery of new materials that could have technological implications. Although having its biggest impact for more applied materials like batteries, there is increasing interest in applying these ideas to predict new superconductors. This is obviously a challenge, given that superconductivity is a many body phenomenon, with whole classes of known superconductors lacking a quantitative theory. Given this caveat, various efforts to formulate materials design principles for superconductors are reviewed here, with a focus on surveying the periodic table in an attempt to identify cuprate analogues.

  11. Topological Superconductivity on the Surface of Fe-Based Superconductors.

    PubMed

    Xu, Gang; Lian, Biao; Tang, Peizhe; Qi, Xiao-Liang; Zhang, Shou-Cheng

    2016-07-22

    As one of the simplest systems for realizing Majorana fermions, the topological superconductor plays an important role in both condensed matter physics and quantum computations. Based on ab initio calculations and the analysis of an effective 8-band model with superconducting pairing, we demonstrate that the three-dimensional extended s-wave Fe-based superconductors such as Fe_{1+y}Se_{0.5}Te_{0.5} have a metallic topologically nontrivial band structure, and exhibit a normal-topological-normal superconductivity phase transition on the (001) surface by tuning the bulk carrier doping level. In the topological superconductivity (TSC) phase, a Majorana zero mode is trapped at the end of a magnetic vortex line. We further show that the surface TSC phase only exists up to a certain bulk pairing gap, and there is a normal-topological phase transition driven by the temperature, which has not been discussed before. These results pave an effective way to realize the TSC and Majorana fermions in a large class of superconductors.

  12. A new aspect of single-layered cuprate superconductors — 90 K superconductors for Ca-doped Bi2Sr2CuO6+δ single crystals

    NASA Astrophysics Data System (ADS)

    Yoshizaki, R.; Yamamoto, T.; Ikeda, H.; Kadowaki, K.

    2012-12-01

    We found that the highest Tc (Tc max) of the superconductors in Bi-2201 phase was 80-90 K for the partially Ca substituted Bi2Sr2CuO6+δ for Sr. The superconductivity was confirmed to be bulk effect from a specific heat jump around Tc. By the findings the correlation between the structure and Tc max has been made clear and simple with respect to the distance between Cu and the apical oxygen for the single-layered cuprate superconductors in the hole doped system.

  13. Preparation of superconductor precursor powders

    DOEpatents

    Bhattacharya, Raghunath

    1998-01-01

    A process for the preparation of a precursor metallic powder composition for use in the subsequent formation of a superconductor. The process comprises the steps of providing an electrodeposition bath comprising an electrolyte medium and a cathode substrate electrode, and providing to the bath one or more soluble salts of one or more respective metals which are capable of exhibiting superconductor properties upon subsequent appropriate treatment. The bath is continually energized to cause the metallic and/or reduced particles formed at the electrode to drop as a powder from the electrode into the bath, and this powder, which is a precursor powder for superconductor production, is recovered from the bath for subsequent treatment. The process permits direct inclusion of all metals in the preparation of the precursor powder, and yields an amorphous product mixed on an atomic scale to thereby impart inherent high reactivity. Superconductors which can be formed from the precursor powder include pellet and powder-in-tube products.

  14. Manufacturing a Superconductor in School.

    ERIC Educational Resources Information Center

    Barrow, John

    1989-01-01

    Described is the manufacture of a superconductor from a commercially available kit using equipment usually available in schools or easily obtainable. The construction is described in detail including equipment, materials, safety procedures, tolerances, and manufacture. (Author/CW)

  15. Processing of Mixed Oxide Superconductors

    DTIC Science & Technology

    1990-07-01

    UROUP SUB-GROUP High Temperature Superconductivity , critical current -- 7-- 0superconductor, ceramic, magnetism 20 ’ I 19. ABSTRACT (Continue on...large intragrain currents and small intergrain currents . Magnetic separation works well for YBCO in liquid nitrogen. The technique can certainly be...between the intergrain and intragrain currents and that the short coherence length of oxide superconductors is not the main problem. The closest

  16. Multistrand superconductor cable

    DOEpatents

    Borden, A.R.

    1984-03-08

    Improved multistrand Rutherford-type superconductor cable is produced by using strands which are preformed, prior to being wound into the cable, so that each strand has a variable cross section, with successive portions having a substantially round cross section, a transitional oval cross section, a rectangular cross section, a transitional oval cross section, a round cross section and so forth, in repetitive cycles along the length of the strand. The cable is wound and flattened so that the portions of rectangular cross section extend across the two flat sides of the cable at the strand angle. The portions of round cross section are bent at the edges of the flattened cable, so as to extend between the two flat sides. The rectangular portions of the strands slide easil

  17. Stability of holographic superconductors

    SciTech Connect

    Kanno, Sugumi; Soda, Jiro

    2010-10-15

    We study the dynamical stability of holographic superconductors. We first classify perturbations around black hole background solutions into vector and scalar sectors by means of a 2-dimensional rotational symmetry. We prove the stability of the vector sector by explicitly constructing the positive definite Hamiltonian. To reveal a mechanism for the stabilization of a superconducting phase, we construct a quadratic action for the scalar sector. From the action, we see the stability of black holes near a critical point is determined by the equation of motion for a charged scalar field. We show the effective mass of the charged scalar field in hairy black holes is always above the Breitenlohner-Freedman bound near the critical point due to the backreaction of a gauge field. It implies the stability of the superconducting phase. We also argue that the stability continues away from the critical point.

  18. Stability of holographic superconductors

    NASA Astrophysics Data System (ADS)

    Kanno, Sugumi; Soda, Jiro

    2010-10-01

    We study the dynamical stability of holographic superconductors. We first classify perturbations around black hole background solutions into vector and scalar sectors by means of a 2-dimensional rotational symmetry. We prove the stability of the vector sector by explicitly constructing the positive definite Hamiltonian. To reveal a mechanism for the stabilization of a superconducting phase, we construct a quadratic action for the scalar sector. From the action, we see the stability of black holes near a critical point is determined by the equation of motion for a charged scalar field. We show the effective mass of the charged scalar field in hairy black holes is always above the Breitenlohner-Freedman bound near the critical point due to the backreaction of a gauge field. It implies the stability of the superconducting phase. We also argue that the stability continues away from the critical point.

  19. Observing Majorana bound states of Josephson vortices in topological superconductors

    PubMed Central

    Grosfeld, Eytan; Stern, Ady

    2011-01-01

    In recent years there has been an intensive search for Majorana fermion states in condensed matter systems. Predicted to be localized on cores of vortices in certain nonconventional superconductors, their presence is known to render the exchange statistics of bulk vortices non-Abelian. Here we study the equations governing the dynamics of phase solitons (fluxons) in a Josephson junction in a topological superconductor. We show that the fluxon will bind a localized zero energy Majorana mode and will consequently behave as a non-Abelian anyon. The low mass of the fluxon, as well as its experimentally observed quantum mechanical wave-like nature, will make it a suitable candidate for vortex interferometry experiments demonstrating non-Abelian statistics. We suggest two experiments that may reveal the presence of the zero mode carried by the fluxon. Specific experimental realizations will be discussed as well. PMID:21730165

  20. Surface resistance measurement of modified QMG superconducting bulks

    NASA Astrophysics Data System (ADS)

    Saito, A.; Sekiya, N.; Teshima, H.; Obara, H.; Noguchi, Y.; Hirano, H.; Hirano, S.; Ohshima, S.

    2006-10-01

    We investigated the microwave properties of high-temperature superconductor (HTS) bulks for high-power microwave applications. The HTS bulk samples of Dy-Ba-Cu-O and Gd-Ba-Cu-O, were prepared using the modified quench and melt growth (QMG) process. The relationship among the bulk surface mirror polishing process, oxygen annealing process, and surface resistance (Rs) was also investigated. The Rs of the HTS bulks was measured using the dielectric resonator method at 21.8 GHz for the TE011 mode. The measurement temperature was varied from 20 to 95 K. We found that the annealing after surface mirror polishing was more effective to obtain low Rs than polishing after annealing. Although the Rs value of the optimized Dy-Ba-Cu-O bulk sample at 20 K was twofold larger than that of the high-quality YBa2Cu3O7-δ thin film fabricated by THEVA GmbH, the Rs value was even low enough to be used for microwave devices. These results indicate that Dy-Ba-Cu-O bulk superconductors are feasible for applications to high-power transmit filters for mobile communication systems.

  1. Superconductor-Insulator Transition Induced by Electrostatic Charging in High Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Leng, Xiang

    Ultrathin YBa2Cu3O7-x films were grown on SrTiO3 substrates in a high pressure oxygen sputtering system to study the superconductor-insulator transition by electrostatic charging. While backside gating using SrTiO3 as a dielectric induces only small TC shifts, a clear transition between superconducting and insulating behavior was realized in a 7 unit cell thick film using an ionic liquid as the dielectric. Employing a finite size scaling analysis, curves of resistance versus temperature, R(T), over the temperature range from 6 K to 22 K were found to collapse onto a single function, which suggests the presence of a quantum critical point. However the scaling failed at the lowest temperatures indicating the possible presence of an additional phase between the superconducting and insulating regimes. In the presence of magnetic field, a cleaner superconductor-insulator transition was realized by electrostatic charging. A scaling analysis showed that this was a quantum phase transition. The magnetic field did not change the universality class. Further depletion of holes caused electrons to be accumulated in the film and the superconductivity to be recovered. This could be an n-type superconductor. The carriers were found to be highly localized. By changing the polarity of the gate voltage, an underdoped 7 unit cell thick film was tuned into the overdoped regime. This process proved to be reversible. Transport measurements showed a series of anomalous features compared to chemically doped bulk samples and an unexpected two-step mechanism for electrostatic doping was revealed. These anomalous behaviors suggest that there is an electronic phase transition in the Fermi surface around the optimal doping level.

  2. Performance and applications of quench melt-growth bulk magnets

    NASA Astrophysics Data System (ADS)

    Nariki, S.; Teshima, H.; Morita, M.

    2016-03-01

    This paper describes the progress in quench melt-growth (QMG) bulk magnets, developed by the Nippon Steel & Sumitomo Metal Corporation, which consist of single crystalline RE123 phase and finely dispersed RE211 particles. QMG bulks can trap high magnetic fields. The field-trapping ability of QMG bulks is largely increased with an improvement in its J c and size, promising the realization of various applications such as flywheel energy-storage systems, ship motors, NMR/MRI spectrometers, wind-power generators and so on. Intensive research has revealed that the optimal RE element is different depending on application requirements. Gd-QMG bulk is the most promising material for several high-field engineering applications. The trapped magnetic field of Gd-QMG bulk 60 mm in diameter at 77 K is twice as large as that of Y-QMG bulk with a similar size due to its excellent J c properties. The large Gd-based QMG bulks up to 150 mm in diameter are fabricated by incorporating the RE compositional gradient method. Compact NMR/MRI spectrometers are one of the promising applications of bulk superconductors. Eu-QMG bulks are suitable for NMR magnets. NMR applications require extremely homogeneous magnetic fields. In the Eu-system, the small paramagnetic moment of a Eu ion compared to a Gd ion improves the field homogeneity in the bulk. For the application of current leads, Dy-based QMG is available by utilizing a low thermal conductivity.

  3. Process for fabricating continuous lengths of superconductor

    DOEpatents

    Kroeger, Donald M.; List, III, Frederick A.

    1998-01-01

    A process for manufacturing a superconductor. The process is accomplished by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon, overlaying a continuous length of a second substrate ribbon on said first substrate ribbon, and applying sufficient pressure to form a bound layered superconductor precursor between said first substrate ribbon and said second substrates ribbon. The layered superconductor precursor is then heat treated to form a super conductor layer.

  4. Ferromagnet / superconductor oxide superlattices

    NASA Astrophysics Data System (ADS)

    Santamaria, Jacobo

    2006-03-01

    The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. With the (re)discovery of colossal magnetoresistance (CMR) materials, there has been renewed interest in heterostructures involving oxide superconductors and CMR ferromagnets where ferromagnetism (F) and superconductivity (S) compete within nanometric distances from the interface. In F/S/F structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for depressed magnetic and superconducting properties at the interface over nanometer length scales. In this talk I will focus in F/S/F structures made of YBa2Cu3O7 (YBCO) and La0.7Ca0.3MnO3 (LCMO). The high degree of spin polarization of the LCMO conduction band, together with the d-wave superconductivity of the YBCO make this F/S system an adequate candidate for the search of novel spin dependent effects in transport. We show that superconductivity at the interface is depressed by various factors like charge transfer, spin injection or ferromagnetic superconducting proximity effect. I will present experiments to examine the characteristic distances of the various mechanisms of superconductivity depression. In particular, I will discuss that the critical temperature of the superconductor depends on the relative orientation of the magnetization of the F layers, giving rise to a new giant magnetoresistance effect which might be of interest for spintronic applications. Work done in collaboration with V. Peña^1, Z. Sefrioui^1, J. Garcia-Barriocanal^1, C. Visani^1, D. Arias^1, C. Leon^1 , N. Nemes^2, M. Garcia Hernandez^2, S. G. E. te Velthuis^3, A. Hoffmann^3, M. Varela^4, S. J. Pennycook^4. Work supported by MCYT MAT 2005-06024, CAM GR- MAT-0771/2004, UCM PR3/04-12399 Work at Argonne supported by the Department of Energy, Basic

  5. Physics and chemistry of layered chalcogenide superconductors

    PubMed Central

    Deguchi, Keita; Takano, Yoshihiko; Mizuguchi, Yoshikazu

    2012-01-01

    Structural and physical properties of layered chalcogenide superconductors are summarized. In particular, we review the remarkable properties of the Fe-chalcogenide superconductors, FeSe and FeTe-based materials. Furthermore, we introduce the recently discovered BiS2-based layered superconductors and discuss their prospects. PMID:27877516

  6. Using metamaterial nanoengineering to triple the superconducting critical temperature of bulk aluminum.

    PubMed

    Smolyaninova, Vera N; Zander, Kathryn; Gresock, Thomas; Jensen, Christopher; Prestigiacomo, Joseph C; Osofsky, M S; Smolyaninov, Igor I

    2015-11-02

    Recent experiments have shown the viability of the metamaterial approach to dielectric response engineering for enhancing the transition temperature, Tc, of a superconductor. In this report, we demonstrate the use of Al2O3-coated aluminium nanoparticles to form the recently proposed epsilon near zero (ENZ) core-shell metamaterial superconductor with a Tc that is three times that of pure aluminium. IR reflectivity measurements confirm the predicted metamaterial modification of the dielectric function thus demonstrating the efficacy of the ENZ metamaterial approach to Tc engineering. The developed technology enables efficient nanofabrication of bulk aluminium-based metamaterial superconductors. These results open up numerous new possibilities of considerable Tc increase in other simple superconductors.

  7. Low-temperature rapid synthesis and superconductivity of Fe-based oxypnictide superconductors.

    PubMed

    Fang, Ai-Hua; Huang, Fu-Qiang; Xie, Xiao-Ming; Jiang, Mian-Heng

    2010-03-17

    Fe-based oxypnictide superconductors were successfully synthesized at lower reaction temperatures and with shorter reaction times made possible by starting with less stable compounds, which provide a larger driving force for reactions. Using ball-milled powders of intermediate compounds, phase-pure superconductors with T(c) above 50 K were synthesized at 1173 K in 20 min. This method is particularly advantageous for retaining F, a volatile dopant that enhances superconductivity. Bulk superconductivity and high upper critical fields up to 392 T in Sm(0.85)Nd(0.15)FeAsO(0.85)F(0.15) were demonstrated.

  8. Numerical analyses of levitation force and flux creep on high [Tc] superconductor

    SciTech Connect

    Tsuchimoto, M.; Kojima, T.; Takeuchi, H.; Honma, T. . Dept. of Electrical Engineering)

    1993-11-01

    Large levitation force and a stable equilibrium are obtained with a permanent magnet and a bulk high [Tc] superconductor (HTSC). Evaluation of the levitation force is important for many applications, such as magnetically levitated vehicles, magnetic bearing, flywheel and linear drive. Levitation force between a permanent magnet and a high [Tc] superconductor is examined by using two numerical methods. The levitation force to vertical direction is calculated by using the critical state model. Stiffness of restoring force to horizontal direction is calculated by using a frozen-in field model. Numerical solutions agree well with experimental results. Dynamic properties of the levitation force are also analyzed by combining the two methods.

  9. Multistrand superconductor cable

    DOEpatents

    Borden, Albert R.

    1985-01-01

    Improved multistrand Rutherford-type superconductor cable is produced by using strands which are preformed, prior to being wound into the cable, so that each strand has a variable cross section, with successive portions having a substantially round cross section, a transitional oval cross section, a rectangular cross section, a transitional oval cross section, a round cross section and so forth, in repetitive cycles along the length of the strand. The cable is wound and flattened so that the portions of rectangular cross section extend across the two flat sides of the cable at the strand angle. The portions of round cross section are bent at the edges of the flattened cable, so as to extend between the two flat sides. The rectangular portions of the strands slide easily over one another, so as to facilitate flexing and bending of the cable, while also minimizing the possibility of causing damage to the strands by such flexing or bending. Moreover, the improved cable substantially maintains its compactness and cross-sectional shape when the cable is flexed or bent.

  10. Tunneling in Superconductors

    NASA Astrophysics Data System (ADS)

    Giaever, Ivar

    2002-03-01

    It has been said that Thomas Edison's greatest invention was that of the "Research Laboratory" as a social institution. My greatest discovery was when I learned at 29 years of age that it was possible to work in such an institution and get paid for doing research. I had become interested in physics, gotten a job at General Electric Research Laboratory and found a great mentor in John C. Fischer, who besides instructing me in physics told me that sooner or later we all would become historians of science. I guess for me that time is now, because I have been asked to tell you about my second greatest discovery: Tunneling in superconductors. My great fortune was to be at the right place at the right time, where I had access to outstanding and helpful (not necessary an oxymoron) physicists. Hopefully I will be able to convey to you some of the fun and excitement of that area in this recollection. If you become real interested you may find a written version in my Nobel Prize talk: "Electron Tunneling and Superconductivity" Les Prix Nobel en 1973 or Science 183, 1253-1258 1974 or Reviews of Modern Physics 46 (2), 245-250 1974

  11. Randomly distributed spin induced suppression of superconducting properties in Gd-123

    NASA Astrophysics Data System (ADS)

    Biswas, B.; Haldar, S.; Mukherjee, I.; Kumar Ghosh, Ajay

    2017-02-01

    Suppression of superconducting property in presence of inhomogeneous spin distribution in GdBa2Cu3-xCoxO6.9 has been studied. A superconducting sample without Co exhibits superconducting transition at 56.1 K. The current-voltage (I-V) characteristics exhibit nonlinear to linear transformation above a certain temperature. Two other samples (i) with Co and (ii) without Cu are found to be nonsuperconducting with very high resistive in nature at lower temperature. Localization length decreases with the increase in Co substitution. Suppression of the superconducting transition has been attributed to the change in the magnetic fluctuations induced by the randomness in spin substitution. An exponent has been extracted to understand the current-voltage behaviour. Kosterlitz-Thouless (KT) transition may be affected strongly by the shifting of magnetic fluctuations.

  12. Torque magnetometry in unconventional superconductors

    NASA Astrophysics Data System (ADS)

    Li, Lu

    This thesis describes torque magnetometry studies on unconventional superconductors. Torque magnetometry measures the anisotropic magnetization of samples by recording their torque signals in a tilted magnetic field. Applied to superconductors, this method provides a reliable way to measure the field dependence of magnetization with high resolution under extreme conditions: DC magnetic fields from zero to 45.2 T, and temperature from 300 mK to 300K. The results can be used to determine many important parameters, such as the upper critical field H c2, the superconducting condensation energy, the onset temperature of diamagnetic signals, and so on. We carried out the torque magnetometry measurements on unconventional superconductors---high Tc superconductors and the p-wave superconductor Sr2RuO4---and uncovered new features that do not exist in conventional BCS superconductors. In high Tc superconductors, our torque magnetometry studies focus on the properties of the vortex liquid state. First, by comparing the observed magnetization curves with the Nernst effect results in Bi 2Sr2CaCu2O8+delta, we confirm that the unusually large Nernst effect signals originate from the surviving vortex liquid state above Tc. Second, the M-H curves near the critical temperature Tc suggest that the nature of the transition is the Kosterlitz-Thouless transition. Near Tc, the magnetization response at low field is strongly nonlinear, and the T dependence of the magnetic susceptibility in the low-field limit approaches the predicted curve from the Kosterlitz-Thouless transition. Third, the measurements in intense magnetic field up to 45 T reveal the unusual, weak T-dependence of Hc2. These observations strongly support the existence of the vortex liquid state above Tc. The superconducting state is destroyed by the phase fluctuation of the pair condensate, while the pair condensate keeps its amplitude above T c. Further studies in single-layered high Tc superconductors reveal more

  13. Resolving thermoelectric "paradox" in superconductors.

    PubMed

    Shelly, Connor D; Matrozova, Ekaterina A; Petrashov, Victor T

    2016-02-01

    For almost a century, thermoelectricity in superconductors has been one of the most intriguing topics in physics. During its early stages in the 1920s, the mere existence of thermoelectric effects in superconductors was questioned. In 1944, it was demonstrated that the effects may occur in inhomogeneous superconductors. Theoretical breakthrough followed in the 1970s, when the generation of a measurable thermoelectric magnetic flux in superconducting loops was predicted; however, a major crisis developed when experiments showed puzzling discrepancies with the theory. Moreover, different experiments were inconsistent with each other. This led to a stalemate in bringing theory and experiment into agreement. With this work, we resolve this stalemate, thus solving this long-standing "paradox," and open prospects for exploration of novel thermoelectric phenomena predicted recently.

  14. Thin film superconductor magnetic bearings

    DOEpatents

    Weinberger, Bernard R.

    1995-12-26

    A superconductor magnetic bearing includes a shaft (10) that is subject to a load (L) and rotatable around an axis of rotation, a magnet (12) mounted to the shaft, and a stator (14) in proximity to the shaft. The stator (14) has a superconductor thin film assembly (16) positioned to interact with the magnet (12) to produce a levitation force on the shaft (10) that supports the load (L). The thin film assembly (16) includes at least two superconductor thin films (18) and at least one substrate (20). Each thin film (18) is positioned on a substrate (20) and all the thin films are positioned such that an applied magnetic field from the magnet (12) passes through all the thin films. A similar bearing in which the thin film assembly (16) is mounted on the shaft (10) and the magnet (12) is part of the stator (14) also can be constructed.

  15. Heat transport in nonuniform superconductors

    NASA Astrophysics Data System (ADS)

    Richard, Caroline; Vorontsov, Anton B.

    2016-08-01

    We calculate electronic energy transport in inhomogeneous superconductors using a fully self-consistent nonequilibrium quasiclassical Keldysh approach. We develop a general theory and apply it to a superconductor with an order parameter that forms domain walls of the type encountered in the Fulde-Ferrell-Larkin-Ovchinnikov state. The heat transport in the presence of a domain wall is inherently anisotropic and nonlocal. The bound states in the nonuniform region play a crucial role and control heat transport in several ways: (i) they modify the spectrum of quasiparticle states and result in Andreev reflection processes and (ii) they hybridize with the impurity band and produce a local transport environment with properties very different from those in a uniform superconductor. As a result of this interplay, heat transport becomes highly sensitive to temperature, magnetic field, and disorder. For strongly scattering impurities, we find that the transport across domain walls at low temperatures is considerably more efficient than in the uniform superconducting state.

  16. Apparatus for fabricating continuous lengths of superconductor

    DOEpatents

    Kroeger, Donald M.; List, III, Frederick A.

    2001-01-01

    A process and apparatus for manufacturing a superconductor. The process is accomplished by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon, overlaying a continuous length of a second substrate ribbon on said first substrate ribbon, and applying sufficient pressure to form a bound layered superconductor comprising a layer of said superconducting precursor powder between said first substrate ribbon and said second substrates ribbon. The layered superconductor is then heat treated to establish the superconducting phase of said superconductor precursor powder.

  17. Apparatus for fabricating continuous lengths of superconductor

    DOEpatents

    Kroeger, Donald M.; List, III, Frederick A.

    2002-01-01

    A process and apparatus for manufacturing a superconductor. The process is accomplished by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon, overlaying a continuous length of a second substrate ribbon on said first substrate ribbon, and applying sufficient pressure to form a bound layered superconductor comprising a layer of said superconducting precursor powder between said first substrate ribbon and said second substrates ribbon. The layered superconductor is then heat treated to establish the superconducting phase of said superconductor precursor powder.

  18. Multifilamentary niobium tin superconductor tape

    NASA Technical Reports Server (NTRS)

    Brisbin, P. H.; Coles, W. D.

    1975-01-01

    In the method proposed for fabricating multifilamentary Nb3Sn tape, filamentary superconducting paths are produced in standard commercial superconductor tape by chemical milling of separator slots through the Nb3Sn layer. The multifilament configuration features a matrix of ten 1.2 mm wide parallel helical superconducting paths along the length of the tape. The paths are spaced 0.4 mm apart. Tapes tested as small pancake coils demonstrated the integrity and continuity of the matrix, and showed that critical current was sustained in direct proportion to retained superconductor.

  19. High temperature superconductor current leads

    DOEpatents

    Hull, John R.; Poeppel, Roger B.

    1995-01-01

    An electrical lead having one end for connection to an apparatus in a cryogenic environment and the other end for connection to an apparatus outside the cryogenic environment. The electrical lead includes a high temperature superconductor wire and an electrically conductive material distributed therein, where the conductive material is present at the one end of the lead at a concentration in the range of from 0 to about 3% by volume, and at the other end of the lead at a concentration of less than about 20% by volume. Various embodiments are shown for groups of high temperature superconductor wires and sheaths.

  20. High temperature superconductor current leads

    DOEpatents

    Hull, J.R.; Poeppel, R.B.

    1995-06-20

    An electrical lead is disclosed having one end for connection to an apparatus in a cryogenic environment and the other end for connection to an apparatus outside the cryogenic environment. The electrical lead includes a high temperature superconductor wire and an electrically conductive material distributed therein, where the conductive material is present at the one end of the lead at a concentration in the range of from 0 to about 3% by volume, and at the other end of the lead at a concentration of less than about 20% by volume. Various embodiments are shown for groups of high temperature superconductor wires and sheaths. 9 figs.

  1. Rotary bulk solids divider

    DOEpatents

    Maronde, Carl P.; Killmeyer, Jr., Richard P.

    1992-01-01

    An apparatus for the disbursement of a bulk solid sample comprising, a gravity hopper having a top open end and a bottom discharge end, a feeder positioned beneath the gravity hopper so as to receive a bulk solid sample flowing from the bottom discharge end, and a conveyor receiving the bulk solid sample from the feeder and rotating on an axis that allows the bulk solid sample to disperse the sample to a collection station.

  2. ROTARY BULK SOLIDS DIVIDER

    DOEpatents

    Maronde, Carl P.; Killmeyer JR., Richard P.

    1992-03-03

    An apparatus for the disbursement of a bulk solid sample comprising, a gravity hopper having a top open end and a bottom discharge end, a feeder positioned beneath the gravity hopper so as to receive a bulk solid sample flowing from the bottom discharge end, and a conveyor receiving the bulk solid sample from the feeder and rotating on an axis that allows the bulk solid sample to disperse the sample to a collection station.

  3. Nature of the superconductor-insulator transition in disordered superconductors.

    PubMed

    Dubi, Yonatan; Meir, Yigal; Avishai, Yshai

    2007-10-18

    The interplay of superconductivity and disorder has intrigued scientists for several decades. Disorder is expected to enhance the electrical resistance of a system, whereas superconductivity is associated with a zero-resistance state. Although superconductivity has been predicted to persist even in the presence of disorder, experiments performed on thin films have demonstrated a transition from a superconducting to an insulating state with increasing disorder or magnetic field. The nature of this transition is still under debate, and the subject has become even more relevant with the realization that high-transition-temperature (high-T(c)) superconductors are intrinsically disordered. Here we present numerical simulations of the superconductor-insulator transition in two-dimensional disordered superconductors, starting from a microscopic description that includes thermal phase fluctuations. We demonstrate explicitly that disorder leads to the formation of islands where the superconducting order is high. For weak disorder, or high electron density, increasing the magnetic field results in the eventual vanishing of the amplitude of the superconducting order parameter, thereby forming an insulating state. On the other hand, at lower electron densities or higher disorder, increasing the magnetic field suppresses the correlations between the phases of the superconducting order parameter in different islands, giving rise to a different type of superconductor-insulator transition. One of the important predictions of this work is that in the regime of high disorder, there are still superconducting islands in the sample, even on the insulating side of the transition. This result, which is consistent with experiments, explains the recently observed huge magneto-resistance peak in disordered thin films and may be relevant to the observation of 'the pseudogap phenomenon' in underdoped high-T(c) superconductors.

  4. Comparison of small-field behavior in Mg B2 , Low- and high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Pan, Alexey V.; Dou, Shi X.

    2006-02-01

    Different types of superconductors have been investigated at small magnetic fields (Ba) over wide temperature (T) ranges at different Ba orientations. It has been shown that the temperature dependence of the characteristic field (B*) , separating the Ba -independent critical current density (Jc) plateau (single vortex pinning regime) and the region with Jc(Ba) (collective pinning), can be attributed either to the temperature dependence of the magnetic penetration depth for Nb-film and MgB2 bulk superconductors, or to thermally activated processes for Bi-based superconductors and YBa2Cu3O7-δ superconducting films. In both cases the vortex pinning influence appears to have a secondary role, affecting the effective vortex depinning radius. An exception in such B*(T) behavior is considered for Nb film when the magnetic field has its considerable component applied perpendicular to the main surface of the film.

  5. Relaxation and pinning in spark-plasma sintered MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Jirsa, M.; Rames, M.; Koblischka, M. R.; Koblischka-Veneva, A.; Berger, K.; Douine, B.

    2016-02-01

    The model of thermally activated relaxation developed and successfully tested on high-T c superconductors (Jirsa et al 2004 Phys. Rev. B 70 0245251) was applied to magnetic data of a bulk spark-plasma sintered MgB2 sample to elucidate its magnetic relaxation behavior. MgB2 and the related borides form a superconductor class lying between classical and high-T c superconductors. In accord with this classification, the relaxation phenomena were found to be about ten times weaker than in cuprates. Vortex pinning analyzed in terms of the field dependence of the pinning force density indicates a combined pinning by normal point-like defects and by grain surfaces. An additional mode of pinning at rather high magnetic fields (of still unknown origin) was observed.

  6. Block copolymer self-assembly–directed synthesis of mesoporous gyroidal superconductors

    PubMed Central

    Robbins, Spencer W.; Beaucage, Peter A.; Sai, Hiroaki; Tan, Kwan Wee; Werner, Jörg G.; Sethna, James P.; DiSalvo, Francis J.; Gruner, Sol M.; Van Dover, Robert B.; Wiesner, Ulrich

    2016-01-01

    Superconductors with periodically ordered mesoporous structures are expected to have properties very different from those of their bulk counterparts. Systematic studies of such phenomena to date are sparse, however, because of a lack of versatile synthetic approaches to such materials. We demonstrate the formation of three-dimensionally continuous gyroidal mesoporous niobium nitride (NbN) superconductors from chiral ABC triblock terpolymer self-assembly–directed sol-gel–derived niobium oxide with subsequent thermal processing in air and ammonia gas. Superconducting materials exhibit a critical temperature (Tc) of about 7 to 8 K, a flux exclusion of about 5% compared to a dense NbN solid, and an estimated critical current density (Jc) of 440 A cm−2 at 100 Oe and 2.5 K. We expect block copolymer self-assembly–directed mesoporous superconductors to provide interesting subjects for mesostructure-superconductivity correlation studies. PMID:27152327

  7. Block copolymer self-assembly-directed synthesis of mesoporous gyroidal superconductors.

    PubMed

    Robbins, Spencer W; Beaucage, Peter A; Sai, Hiroaki; Tan, Kwan Wee; Werner, Jörg G; Sethna, James P; DiSalvo, Francis J; Gruner, Sol M; Van Dover, Robert B; Wiesner, Ulrich

    2016-01-01

    Superconductors with periodically ordered mesoporous structures are expected to have properties very different from those of their bulk counterparts. Systematic studies of such phenomena to date are sparse, however, because of a lack of versatile synthetic approaches to such materials. We demonstrate the formation of three-dimensionally continuous gyroidal mesoporous niobium nitride (NbN) superconductors from chiral ABC triblock terpolymer self-assembly-directed sol-gel-derived niobium oxide with subsequent thermal processing in air and ammonia gas. Superconducting materials exhibit a critical temperature (T c) of about 7 to 8 K, a flux exclusion of about 5% compared to a dense NbN solid, and an estimated critical current density (J c) of 440 A cm(-2) at 100 Oe and 2.5 K. We expect block copolymer self-assembly-directed mesoporous superconductors to provide interesting subjects for mesostructure-superconductivity correlation studies.

  8. Topological matter. Observation of Majorana fermions in ferromagnetic atomic chains on a superconductor.

    PubMed

    Nadj-Perge, Stevan; Drozdov, Ilya K; Li, Jian; Chen, Hua; Jeon, Sangjun; Seo, Jungpil; MacDonald, Allan H; Bernevig, B Andrei; Yazdani, Ali

    2014-10-31

    Majorana fermions are predicted to localize at the edge of a topological superconductor, a state of matter that can form when a ferromagnetic system is placed in proximity to a conventional superconductor with strong spin-orbit interaction. With the goal of realizing a one-dimensional topological superconductor, we have fabricated ferromagnetic iron (Fe) atomic chains on the surface of superconducting lead (Pb). Using high-resolution spectroscopic imaging techniques, we show that the onset of superconductivity, which gaps the electronic density of states in the bulk of the Fe chains, is accompanied by the appearance of zero-energy end-states. This spatially resolved signature provides strong evidence, corroborated by other observations, for the formation of a topological phase and edge-bound Majorana fermions in our atomic chains.

  9. Preparation of superconductor precursor powders

    DOEpatents

    Bhattacharya, R.

    1998-08-04

    A process for the preparation of a precursor metallic powder composition for use in the subsequent formation of a superconductor. The process comprises the steps of providing an electrodeposition bath comprising an electrolyte medium and a cathode substrate electrode, and providing to the bath one or more soluble salts of one or more respective metals which are capable of exhibiting superconductor properties upon subsequent appropriate treatment. The bath is continually energized to cause the metallic and/or reduced particles formed at the electrode to drop as a powder from the electrode into the bath, and this powder, which is a precursor powder for superconductor production, is recovered from the bath for subsequent treatment. The process permits direct inclusion of all metals in the preparation of the precursor powder, and yields an amorphous product mixed on an atomic scale to thereby impart inherent high reactivity. Superconductors which can be formed from the precursor powder include pellet and powder-in-tube products. 7 figs.

  10. Preparation of superconductor precursor powders

    DOEpatents

    Bhattacharya, Raghunath; Blaugher, Richard D.

    1995-01-01

    A process for the preparation of a precursor metallic powder composition for use in the subsequent formation of a superconductor. The process comprises the steps of providing an electrodeposition bath comprising an electrolyte medium and a cathode substrate electrode, and providing to the bath one or more soluble salts of one or more respective metals, such as nitrate salts of thallium, barium, calcium, and copper, which are capable of exhibiting superconductor properties upon subsequent appropriate treatment. The bath is continually energized to cause the metallic particles formed at the electrode to drop as a powder from the electrode into the bath, and this powder, which is a precursor powder for superconductor production, is recovered from the bath for subsequent treatment. The process permits direct inclusion of thallium in the preparation of the precursor powder, and yields an amorphous product mixed on an atomic scale to thereby impart inherent high reactivity. Superconductors which can be formed from the precursor powder include pellet and powder-in-tube products.

  11. A novel heat engine for magnetizing superconductors

    NASA Astrophysics Data System (ADS)

    Coombs, T. A.; Hong, Z.; Zhu, X.; Krabbes, G.

    2008-03-01

    The potential of bulk melt-processed YBCO single domains to trap significant magnetic fields (Tomita and Murakami 2003 Nature 421 517-20 Fuchs et al 2000 Appl. Phys. Lett. 76 2107-9) at cryogenic temperatures makes them particularly attractive for a variety of engineering applications including superconducting magnets, magnetic bearings and motors (Coombs et al 1999 IEEE Trans. Appl. Supercond. 9 968-71 Coombs et al 2005 IEEE Trans. Appl. Supercond. 15 2312-5). It has already been shown that large fields can be obtained in single domain samples at 77 K. A range of possible applications exist in the design of high power density electric motors (Jiang et al 2006 Supercond. Sci. Technol. 19 1164-8). Before such devices can be created a major problem needs to be overcome. Even though all of these devices use a superconductor in the role of a permanent magnet and even though the superconductor can trap potentially huge magnetic fields (greater than 10 T) the problem is how to induce the magnetic fields. There are four possible known methods: (1) cooling in field; (2) zero field cooling, followed by slowly applied field; (3) pulse magnetization; (4) flux pumping. Any of these methods could be used to magnetize the superconductor and this may be done either in situ or ex situ. Ideally the superconductors are magnetized in situ. There are several reasons for this: first, if the superconductors should become demagnetized through (i) flux creep, (ii) repeatedly applied perpendicular fields (Vanderbemden et al 2007 Phys. Rev. B 75 (17)) or (iii) by loss of cooling then they may be re-magnetized without the need to disassemble the machine; secondly, there are difficulties with handling very strongly magnetized material at cryogenic temperatures when assembling the machine; thirdly, ex situ methods would require the machine to be assembled both cold and pre-magnetized and would offer significant design difficulties. Until room temperature superconductors can be prepared, the

  12. Applications of high-temperature superconductors in power technology

    NASA Astrophysics Data System (ADS)

    Hull, John R.

    2003-11-01

    Since the discovery of the first high-temperature superconductors (HTSs) in the late 1980s, many materials and families of materials have been discovered that exhibit superconductivity at temperatures well above 20 K. Of these, several families of HTSs have been developed for use in electrical power applications. Demonstration of devices such as motors, generators, transmission lines, transformers, fault-current limiters, and flywheels in which HTSs and bulk HTSs have been used has proceeded to ever larger scales. First-generation wire, made from bismuth-based copper oxides, was used in many demonstrations. The rapid development of second-generation wire, made by depositing thin films of yttrium-based copper oxide on metallic substrates, is expected to further accelerate commercial applications. Bulk HTSs, in which large single-grain crystals are used as basic magnetic components, have also been developed and have potential for electrical power applications.

  13. Test Status for Proposed Coupling of a Gravitational Force to Extreme Type II YBCO Ceramic Superconductors

    NASA Technical Reports Server (NTRS)

    Noever, David; Li, Ning; Robertson, Tony; Koczor, Ron; Brantley, Whitt

    1999-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair electron density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (about 10-6 g/cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with the percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10(exp 4) was reported above a stationary (non-rotating) superconductor. In the present experiments reported using a sensitive gravimeter (resolution <10(exp -9) unit gravity or variation of 10(exp -6) cm/sq s in accelerations), bulk YBCO superconductors were stably levitated in a DC magnetic field (0.6 Tesla) subject to lateral AC fields (60 Gauss at 60 Hz) and rotation. With magnetic shielding, thermal control and buoyancy compensation, changes in acceleration were measured to be less than 2 parts in 10(exp 8) of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between high-Tc superconductors and gravity. Latest test results will be reported, along with status for future improvements and prospects.

  14. Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters.

    PubMed

    Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M

    2017-03-10

    Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id'-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id'-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id'-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry.

  15. Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters

    PubMed Central

    Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M.

    2017-01-01

    Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id′-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id′-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id′-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry. PMID:28281570

  16. Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters

    NASA Astrophysics Data System (ADS)

    Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M.

    2017-03-01

    Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id‧-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id‧-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id‧-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry.

  17. Interplay between Coulomb blockade and Josephson effect in a topological superconductor-quantum dot device

    NASA Astrophysics Data System (ADS)

    Lee, Yu-Li; Lee, Yu-Wen

    2016-05-01

    We study the behavior of a topological Josephson junction in which two topological superconductors are coupled through a quantum dot. We focus on the case with the bulk superconducting gap being the largest energy scale. Two parameter regimes are investigated: a weak tunneling between the dot and the superconductors, with the dot near its charge degeneracy point, and a strong-tunneling regime in which the transmission between the dot and the superconductors is nearly perfect. We show that in the former situation, the Andreev spectrum for each sector with fixed fermion parity consists of only two levels, which gives rise to the nontrivial current-phase relation. Moreover, we study the Rabi oscillation between the two levels and indicate that the corresponding frequency is a 4 π -periodic function of the phase difference between the two superconductors, which is immune to the quasiparticle poisoning. In the latter case, we find that the Coulomb charging energy enhances the effect of backscattering at the interfaces between the dot and the superconductors. Both the temperature and the gate-voltage dependence of the critical Josephson current are examined.

  18. Artificially engineered superlattices of pnictide superconductors.

    PubMed

    Lee, S; Tarantini, C; Gao, P; Jiang, J; Weiss, J D; Kametani, F; Folkman, C M; Zhang, Y; Pan, X Q; Hellstrom, E E; Larbalestier, D C; Eom, C B

    2013-05-01

    Significant progress has been achieved in fabricating high-quality bulk and thin-film iron-based superconductors. In particular, artificial layered pnictide superlattices offer the possibility of tailoring the superconducting properties and understanding the mechanism of the superconductivity itself. For high-field applications, large critical current densities (J(c)) and irreversibility fields (H(irr)) are indispensable along all crystal directions. On the other hand, the development of superconducting devices such as tunnel junctions requires multilayered heterostructures. Here we show that artificially engineered undoped Ba-122/Co-doped Ba-122 compositionally modulated superlattices produce ab-aligned nanoparticle arrays. These layer and self-assemble along c-axis-aligned defects, and combine to produce very large J(c) and H(irr) enhancements over a wide angular range. We also demonstrate a structurally modulated SrTiO3(STO)/Co-doped Ba-122 superlattice with sharp interfaces. Success in superlattice fabrication involving pnictides will aid the progress of heterostructured systems exhibiting new interfacial phenomena and device applications.

  19. Resonance tunneling of cooper pairs in a superconductor-polymer-superconductor josephson junction

    SciTech Connect

    Ionov, A. I.

    2013-05-15

    It is shown that the superconducting current flowing though a polymer in a superconductor-polymer-superconductor Josephson structure is due to resonant tunneling of Cooper pairs. The critical current and the thickness of the polymer in which the superconducting current is observed depend on the coherence length of a Cooper pair in the superconductor contacting the polymer.

  20. Current status of iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Kamihara, Yoichi

    2012-03-01

    Current status of iron-based superconductors is summarized. Although short range magnetic ordering and magnetic phase separation of Fe are controversial, (long range) magnetic and electronic phase diagrams of iron based superconductors can be classified into two-type. Antiferromagnetic ordering of itinerant Fe does not coexist with superconducting phase of SmFeAsO1 - xFx. The very large H c2 of iron-based superconductors attract us to attempts at applications.

  1. A Road Towards High Temperature Superconductors

    DTIC Science & Technology

    2013-08-01

    AFRL-AFOSR-UK-TR-2013-0040 A Road Towards High Temperature Superconductors Guy Deutscher Tel Aviv University Research... Superconductors 5a. CONTRACT NUMBER FA8655-10-1-3011 5b. GRANT NUMBER Grant 10-3011 5c. PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S...issue in trying to make useful high temperature superconductors is obviously to discover superconductivity at higher temperatures. But there is also

  2. Crystal growth and physical property of Bi-Sb-Te-Se topological insulator materials, and Cu-Bi-Se and Sn-In-Te topological superconductors

    NASA Astrophysics Data System (ADS)

    Gu, Genda; Yang, Alina; Schneeloch, J.; Zhong, R. D.; Xu, Z. J.; Tranquada, J. M.; Pan, Z. H.; Si, W. D.; Shi, X. Y.; Li, Q.; Valla, T.

    2013-03-01

    The discovery of 3D topological insulator materials and topological superconductor opens up a new research field in the condensed matter physics. We have grown a number of Bi-Sb-Te-Se topological insulator, and Cu-Bi-Se and Sn-In-Te topological superconductor single crystals. We have measured the physical properties on these single crystals. We have studied the effect of growth condition and impurity on the bulk electrical conductivity of these single crystals. We try to answer two questions for the topological insulator materials if it is possible to grow the bulk-insulating topological insulator single crystals and Which maximum resistivity of these topological insulator single crystals we can grow. For the topological superconductor, we have got the bulk superconducting single crystals with a maximum Tc =4.5K. DOE under Contract No. DE-AC02-98CH10886 and the DOE Center for Emergent Superconductivity.

  3. Recent progress on carbon-based superconductors.

    PubMed

    Kubozono, Yoshihiro; Eguchi, Ritsuko; Goto, Hidenori; Hamao, Shino; Kambe, Takashi; Terao, Takahiro; Nishiyama, Saki; Zheng, Lu; Miao, Xiao; Okamoto, Hideki

    2016-08-24

    This article reviews new superconducting phases of carbon-based materials. During the past decade, new carbon-based superconductors have been extensively developed through the use of intercalation chemistry, electrostatic carrier doping, and surface-proving techniques. The superconducting transition temperature T c of these materials has been rapidly elevated, and the variety of superconductors has been increased. This review fully introduces graphite, graphene, and hydrocarbon superconductors and future perspectives of high-T c superconductors based on these materials, including present problems. Carbon-based superconductors show various types of interesting behavior, such as a positive pressure dependence of T c. At present, experimental information on superconductors is still insufficient, and theoretical treatment is also incomplete. In particular, experimental results are still lacking for graphene and hydrocarbon superconductors. Therefore, it is very important to review experimental results in detail and introduce theoretical approaches, for the sake of advances in condensed matter physics. Furthermore, the recent experimental results on hydrocarbon superconductors obtained by our group are also included in this article. Consequently, this review article may provide a hint to designing new carbon-based superconductors exhibiting higher T c and interesting physical features.

  4. Suppression of superconductivity in mesoscopic superconductors.

    PubMed

    Sobnack, M B; Kusmartsev, F V

    2001-01-22

    We propose a new boundary-driven phase transition associated with vortex nucleation in mesoscopic superconductors (of size of the order of, or larger than, the penetration depth). We derive the rescaling equations and we show that boundary effects associated with vortex nucleation lower the conventional transition temperature in mesoscopic superconductors by an amount which is a function of the size of the superconductor. This result explains recent experiments in small superconductors where it was found that the transition temperature depends on the size of the system and is lower than the critical Berezinskĭ-Kosterlitz-Thouless temperature.

  5. Recent status of superconductors for accelerator magnets

    SciTech Connect

    Greene, A.F.

    1992-01-01

    A survey is given of superconductor wire and cable which has been or will be used for construction of dipole magnets for all of the large European and US superconducting accelerator rings. Included is a simplified view of the construction methods and operating requirements of an accelerator dipole magnet, with emphasis on required superconductor performance. The methods of fabricating Nb-Ti superconductors are described, including the critical parameters and materials requirements. The superconductor performance requirements are summarized in an effort to relate why these are important to accelerator designers. Some of the recently observed time dependent effects are covered briefly.

  6. Recent status of superconductors for accelerator magnets

    SciTech Connect

    Greene, A.F.

    1992-10-01

    A survey is given of superconductor wire and cable which has been or will be used for construction of dipole magnets for all of the large European and US superconducting accelerator rings. Included is a simplified view of the construction methods and operating requirements of an accelerator dipole magnet, with emphasis on required superconductor performance. The methods of fabricating Nb-Ti superconductors are described, including the critical parameters and materials requirements. The superconductor performance requirements are summarized in an effort to relate why these are important to accelerator designers. Some of the recently observed time dependent effects are covered briefly.

  7. Frontiers of organic conductors and superconductors.

    PubMed

    Saito, Gunzi; Yoshida, Yukihiro

    2012-01-01

    We review the development of conductive organic molecular assemblies including organic metals, superconductors, single component conductors, conductive films, conductors with a switching function, and new spin state (quantum spin liquid state). We emphasize the importance of the ionicity phase diagram for a variety of charge transfer systems to provide a strategy for the development of functional organic solids (Mott insulator, semiconductor, superconductor, metal, complex isomer, neutral-ionic system, alignment of chemical potentials, etc.). For organic (super)conductors, the electronic dimensionality of the solids is a key parameter and can be designed based on the self-aggregation ability of a molecule. We present characteristic structural and physical properties of organic superconductors.

  8. Oxygen diffusion in cuprate superconductors

    SciTech Connect

    Routbort, J.L.; Rothman, S.J.

    1995-01-01

    Superconducting properties of the cuprate superconductors depend on the oxygen content of the material; the diffusion of oxygen is thus an important process in the fabrication and application of these materials. This article reviews studies of the diffusion of oxygen in La{sub 2}{sub {minus}}{sub {times}}Sr{sub {times}}CuO{sub 4}, YBa{sub 2}Cu{sub 3}O{sub 7}{sub {minus}}{delta}, YBa{sub 2}Cu{sub 4}O{sub 8}, and the Bi{sub 2}Sr{sub 2}Ca{sub n}{sub {minus}}{sub 1}Cu{sub n}O{sub 2}{sub +}{sub 4} (n = 1, and 2) superconductors, and attempt to elucidate the atomic mechanisms responsible.

  9. High-Temperature Ceramic Superconductors

    DTIC Science & Technology

    1991-12-15

    magnetic susceptibility, Meissner effect and specific heat. Task 4 is an investigation of superconductor ceramic processing. Most of the important... effect of the additional heater on the microstructure is shown in Fig. 11. As the upper micrograph shows, hardly any alignment was induced with a single... effect in cal field,7 H 1 = 𔃻o In K/41TA 2, and magnetic field pene- limiting the current-carrying capability of the ceramic tration length, A. The

  10. Searching for ideal topological crystalline insulators and topological superconductors in the Pb-Sn-In-Te system

    NASA Astrophysics Data System (ADS)

    Gu, Genda

    The discovery of 3D topological insulator materials and topological superconductor open up a new research field in the condensed matter physics. In order to search for the ideal topological insulator, topological crystalline insulator and topological superconductor, we have grown a large number of the single crystals of Pb-system (Pb-Sn-In-Te) topological crystalline insulator and their topological superconductor . We have measured the physical properties on these single crystals by various techniques. We have studied the effect of crystal growth condition, impurity and composition on the bulk electrical conductivity of these single crystals. We try to find out which composition and crystal growth condition is the best for the ideal topological insulator, topological crystalline insulator and topological superconductor. We have got the bulk topological superconductor with Tc = 5 K . Work was supported by the Office of Basic Energy Sciences (BES), Division of Materials Sciences and Engineering, U.S. Department of Energy (DOE), through Contract No. DE-SC00112704.

  11. The Possibility of Improved and Higher Tc Superconductors in Hybrid Systems

    DTIC Science & Technology

    2014-10-15

    engineering 2d heterostructures to mimic the structure of bulk high temperature cuprate superconductors. Since these consist of CuO2 planes separated by...heterostructures is by looking at phase separated thin films where regions of overdoping and underdoping can be found. In such case local scanning...probes would have to be implemented to probe local variations in Tc. A means to control this phase- separation would be by looking carefully at crystal

  12. Edge instabilities of topological superconductors

    NASA Astrophysics Data System (ADS)

    Hofmann, Johannes S.; Assaad, Fakher F.; Schnyder, Andreas P.

    2016-05-01

    Nodal topological superconductors display zero-energy Majorana flat bands at generic edges. The flatness of these edge bands, which is protected by time-reversal and translation symmetry, gives rise to an extensive ground-state degeneracy. Therefore, even arbitrarily weak interactions lead to an instability of the flat-band edge states towards time-reversal and translation-symmetry-broken phases, which lift the ground-state degeneracy. We examine the instabilities of the flat-band edge states of dx y-wave superconductors by performing a mean-field analysis in the Majorana basis of the edge states. The leading instabilities are Majorana mass terms, which correspond to coherent superpositions of particle-particle and particle-hole channels in the fermionic language. We find that attractive interactions induce three different mass terms. One is a coherent superposition of imaginary s -wave pairing and current order, and another combines a charge-density-wave and finite-momentum singlet pairing. Repulsive interactions, on the other hand, lead to ferromagnetism together with spin-triplet pairing at the edge. Our quantum Monte Carlo simulations confirm these findings and demonstrate that these instabilities occur even in the presence of strong quantum fluctuations. We discuss the implications of our results for experiments on cuprate high-temperature superconductors.

  13. Fault current limiters using superconductors

    NASA Astrophysics Data System (ADS)

    Norris, W. T.; Power, A.

    Fault current limiters on power systems are to reduce damage by heating and electromechanical forces, to alleviate duty on switchgear used to clear the fault, and to mitigate disturbance to unfaulted parts of the system. A basic scheme involves a super-resistor which is a superconductor being driven to high resistance when fault current flows either when current is high during a cycle of a.c. or, if the temperature of the superconductive material rises, for the full cycle. Current may be commuted from superconductor to an impedance in parallel, thus reducing the energy dispersed at low temperature and saving refrigeration. In a super-shorted transformer the ambient temperature primary carries the power system current; the superconductive secondary goes to a resistive condition when excessive currents flow in the primary. A super-transformer has the advantage of not needing current leads from high temperature to low temperature; it behaves as a parallel super-resistor and inductor. The supertransductor with a superconductive d.c. bias winding is large and has small effect on the rate of fall of current at current zero; it does little to alleviate duty on switchgear but does reduce heating and electromechanical forces. It is fully active after a fault has been cleared. Other schemes depend on rapid recooling of the superconductor to achieve this.

  14. Nonlinear electrodynamics of high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Zutic, Igor

    We investigate the effects of nonlinear electrodynamics in unconventional superconductors. These effects can serve as fingerprints to identify the symmetry of the superconducting pairing state and to provide information about the unknown pairing mechanism in High Temperature Superconductors (HTSC). In the Meissner regime, at low temperatures, a nonlinear magnetic response arises from the presence of lines on the Fermi surface where the superconducting energy gap is very small or zero. This can be used to perform "node spectroscopy", that is, as a sensitive bulk probe to locate the angular position of those lines. We first compute the nonlinear magnetic moment as a function of applied field and geometry, assuming d-wave pairing and anisotropic penetration depth, for realistic finite sample. Our novel, numerically implemented, perturbative procedure exploits the small ratio of the penetration depths to the sample size and substantially reduces the computational work required. We next generalize these considerations to other candidates for the energy gap and to perform node spectroscopy. In calculating the nonlinear supercurrent response, we include the effects of orthorhombic distortion and a-b plane anisotropy. Analytic results presented demonstrate a systematic way to experimentally distinguish order parameters of different symmetries, including cases with mixed symmetry (for example, d+s and s+id). We finally extend our findings to the case of low frequency harmonic magnetic field. The nonlinear magnetic response for various physical quantities generates higher harmonics of the frequency of the applied field. We discuss how examination of the field and angular dependences of these harmonics allows determination of the structure of the energy gap. We show how to distinguish nodes from small minima ("quasinodes"). Gaps with nodal lines give rise to universal power law field dependences for the nonlinear magnetic moment and torque. They both have separable temporal

  15. Synthesis and characterization of superconducting ferropnictide bulks and wires

    NASA Astrophysics Data System (ADS)

    Weiss, Jeremy

    After nearly seven years of research effort since the discovery of iron-based superconductors, wires and tapes of K-doped BaFe2As2 have finally been developed by the inexpensive and scalable powder-in-tube technique with critical current densities reaching over 0.1 MAcm-2 at 4.2 K. Such progress relies heavily on the development of synthesis techniques that eliminate cracks and secondary phases. High energy ball milling, during which mechanochemical reactions take place, proves to be effective in producing high quality bulk material. The consolidation of high quality powders under high pressure produces bulk material with a fine grain microstructure and surprising high intergranular current density. We explore the dependence of doped Ba2Fe2As2 superconducting properties on sintering temperature in bulks, wires, and tapes to further optimize these materials and find that grain boundaries continue to act as weak-links, effectively blocking current, and limiting the intergranular critical current density in these materials. However, evidence for composition variation and impurity segregation across grain-boundaries suggests that the weak-linked behavior may still be of an extrinsic nature. Despite the current limiting effects of these weak-links, transport current is high enough in our fine grain material to demonstrate the first > 1 T magnet made out of an iron-based superconductor. These results provide a positive outlook for the potential future use of these materials to produce high field magnets.

  16. Bipolar electrical coil based on YBCO bulks: initial tests

    NASA Astrophysics Data System (ADS)

    Alvarez, A.; Suárez, P.; Ceballos, J. M.; Pérez, B.; Werfel, F.; Floegel-Delor, U.

    2008-02-01

    In the field of the application of HTS in electrical motors, most prototypes are made using superconducting coils based on tape and located in the position where copper coils work in a similar conventional motor. Other prototypes use superconducting bulks (usually disk-shaped) in those positions where normal magnets should work in similar conventional motors. But it is very unusual to find designs using electrical coils based on bulks. This is a challenge whose main problem is the difficulty in machining the superconductor bulks to get the proper shape because of the impossibility of bending the material to wind coils. The design of a bipolar single-turn coil made from a superconducting YBCO disk was proposed by the group of Electrical Application of Superconductors, at the University of Extremadura, several years ago to be an element for the design of a modular two-phase inductor for an air core axial-flux motor. The shape of each coil looks like an 'S'. When a current flows through the circuit, two opposite magnetic fields appear in the upper and lower halves of the piece. Until now, attempts to get a good superconducting circuit by cutting a YBCO disk into the required shape have failed because of cracks appearing in the crystal during the process. Last year, our group at the University of Extremadura began to work with ATZ GmbH who have improved the machining process and made the coils. In this paper we present the coil and the first tests carried out.

  17. Growth of layered superconductor β-PdBi2 films using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Denisov, N. V.; Matetskiy, A. V.; Tupkalo, A. V.; Zotov, A. V.; Saranin, A. A.

    2017-04-01

    Bulk β-PdBi2 layered material exhibits advanced properties and is supposed to be probable topological superconductor. We present a method based on molecular beam epitaxy that allows us to grow β-PdBi2 films from a single β-PdBi2 triple layer up to the dozens of triple layers, using Bi(111) film on Si(111) as a template. The grown films demonstrate structural, electronic and superconducting properties similar to those of bulk β-PdBi2 crystals. Ability to grow the β-PdBi2 films of desired thickness opens the promising possibilities to explore fascinating properties of this advanced material.

  18. Preparation of Bulky Bi(Pb)-Sr-Ca-Cu-O Superconductor by Magnetized Twin-Roll

    NASA Astrophysics Data System (ADS)

    Kawahara, Nobuaki; Kawabata, Sanemasa; Enami, Hiroyoshi; Shinohara, Toshiyuki; Hoshizaki, Hiroki; Hasegawa, Masashi; Asai, Shigeo; Imura, Toru

    1990-02-01

    A highly oriented (Bi, Pb)2Sr2Ca2Cu3Ox bulk superconductor has been prepared by magnetized twin-roll processing. In these bulks, plate-like crystal grains were highly oriented by a magnetic and mechanical force. The grain c-axes were parallel to the magnetic field and pressing directions. In fact, both critical current density (Jc) and orientation degree of the sample rolled under 2 T were higher than those of the sample rolled with no magnetic field. The magnetized twin-roll processing is effective not only in enhancing grain-orientation but also in packing to improve Jc.

  19. High temperature superconductors: A technological revolution

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The objectives are to demonstrate the Meissner effect through magnetic levitation, to demonstrate one application of the Meissner effect, the low friction magnetic rotation bearing, and to demonstrate magnetic flux penetration and the Type II nature of ceramic superconductors via the stacking of the superconductor disks. Experimental equipment and procedures are described.

  20. Enhancement of mechanical properties of 123 superconductors

    DOEpatents

    Balachandran, Uthamalingam

    1995-01-01

    A composition and method of preparing YBa.sub.2 Cu.sub.3 O.sub.7-x superconductor. Addition of tin oxide containing compounds to YBCO superconductors results in substantial improvement of fracture toughness and other mechanical properties without affect on T.sub.c. About 5-20% additions give rise to substantially improved mechanical properties.

  1. Enhancement of mechanical properties of 123 superconductors

    DOEpatents

    Balachandran, U.

    1995-04-25

    A composition and method are disclosed of preparing YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} superconductor. Addition of tin oxide containing compounds to YBCO superconductors results in substantial improvement of fracture toughness and other mechanical properties without affect on T{sub c}. About 5-20% additions give rise to substantially improved mechanical properties.

  2. Transport and Thermodynamic Properties of Various Superconductors Including Iron-based Superconductors, V3Si and a Bi2Te3/Fe1+yTe Interfacial Superconductor

    NASA Astrophysics Data System (ADS)

    Zheng, Yan

    This thesis focuses on several interesting aspects of various superconductors, which a special focus on iron-based superconductors. The choice of experimental probes under the influence of high pressure is very limited. In this thesis I am pioneering in measuring a large variety of physical quantities in pressure up to 10 GPa, including heat capacity and thermoelectric measurements. Heat capacity and resistivity experiments for CaFe2As 2 and underdoped Ba(Fe1--xCox)2As2 were performed under hydrostatic pressure conditions. The data supports the bulk nature of pressure-induced superconductivity in these iron-based pnictides, and reveals details on the pressure-induced structural transitions. It is observed that the maximum critical temperature and the superconducting condensation energy are strongly increased under pressure. Furthermore, detailed experimental data of various physical quantities are presented on Ba1-xK xFe2As2, which are rarely performed under pressure. These comprise heat capacity, resistivity, Nernst effect, Hall effect and Seebeck effect experiments. The data validates the existence of a new phase above the superconducting state under pressure. The data provides evidence that in this phase a spin-densitywave order and filamentary superconductivity coexist. The effect of thermal fluctuations is widely believed to be unobservable in classical superconductors. It will be shown that in V3Si fluctuations become significantly enhanced in magnetic fields of a few Teslas, because of the confinement of the electronic quasi particles in low Landau orbits. They become so strong that a vortex melting transition into a liquid vortex phase is observed in high-resolution specific heat experiments. Finally, Nernst effect data of a novel interfacial superconductor is presented, which occurs at the interface of a Bi2Te3/Fe 1+yTe heterostructure. It is superconducting below 12 K and shows a pronounced pseudogap up to 40 K. The data reveals that this pseudogap is of

  3. Magnetization of anisotropic Type II superconductors

    SciTech Connect

    Mints, R.G.

    1989-04-10

    Peculiarities of magnetization of anisotropic type II superconductors are of considerable interest in view of the discovery of high-T/sub c/ superconductors characterized by strongly asymmetric layered structure. Specifics of the penetration of magnetic flux into an anisotropic type II superconductor were discussed in the literature. This analysis gave the distribution of induction in an isolated vortex, its energy, and critical magnetic field H/sub c1/. However, the magnetization curve of anisotropic superconductors was not considered. This paper deals with the magnetic moment of uniaxial London superconductor in the interval H/sub c1/ /le/ H/sub 0/ << H/sub c2/, where H/sub 0/ is the external magnetic field strength.

  4. Properties of Superconductor-Normal Metal-Superconductor Microbridges.

    DTIC Science & Technology

    1980-07-21

    in superconducting microbridges. Both of these theories are based on the effect that non-paired electrons (quasiparticles) have on the density of...the superconductor, the electron does not simply cross the interface; instead, the electron from the normal metal combines with a quasiparticle in the... Electronic & Solid State Sciences PTogu -July 21- 1980 7 Code 427’- O ffice’ of. Naval Risear ch 13., MulligR or PAGIES 8W0 N.’ Ouincve Arlington- VA271 3 14

  5. Enhancing bulk superconductivity by engineering granular materials

    NASA Astrophysics Data System (ADS)

    Mayoh, James; García García, Antonio

    2014-03-01

    The quest for higher critical temperatures is one of the main driving forces in the field of superconductivity. Recent theoretical and experimental results indicate that quantum size effects in isolated nano-grains can boost superconductivity with respect to the bulk limit. Here we explore the optimal range of parameters that lead to an enhancement of the critical temperature in a large three dimensional array of these superconducting nano-grains by combining mean-field, semiclassical and percolation techniques. We identify a broad range of parameters for which the array critical temperature, TcArray, can be up to a few times greater than the non-granular bulk limit, Tc 0. This prediction, valid only for conventional superconductors, takes into account an experimentally realistic distribution of grain sizes in the array, charging effects, dissipation by quasiparticles and limitations related to the proliferation of thermal fluctuations for sufficiently small grains. For small resistances we find the transition is percolation driven. Whereas at larger resistances the transition occurs above the percolation threshold due to phase fluctuations. JM acknowledes support from an EPSRC Ph.D studentship, AMG acknowledges support from EPSRC, grant No. EP/I004637/1, FCT, grant PTDC/FIS/111348/2009 and a Marie Curie International Reintegration Grant PIRG07-GA-2010-268172.

  6. Fostered Thermomagnetic Stabilities and Boosted Mechanical Reliability Related to High Trapped Field in Composite Bulk YBa2Cu3O(7-δ) Cryomagnets.

    PubMed

    Kenfaui, Driss; Sibeud, Pierre-Frédéric; Gomina, Moussa; Louradour, Eric; Chaud, Xavier; Noudem, Jacques G

    2015-08-06

    In the quest of YBa2Cu3O(7-δ) (Y123) bulk superconductors providing strong magnetic fields without failure, it is of paramount importance to achieve high thermal stabilities to safeguard the magnetic energy inside them during the trapping-field process, and sufficient mechanical reliability to withstand the stresses derived from the Lorenz force. Herein, we experimentally demonstrate a temperature rise induced by dissipative flux motion inside an Y123 thin-wall superconductor, and a significant thermal exchange in a composite bulk Y123 cryomagnet realized by embedding this superconductor with high thermal-conductivity metal network. It resulted in stimulating the maximum trapped field Bm, which reached 6.46 T on 15.9 mm-diameter single disk superconductor after magnetization by field cooling to 17 K under 7 T, leading to an improvement of 18% compared to the thin-wall superconductor. The composite cryomagnet particularly revealed the potential to trap stronger fields if larger magnetic activation is available. By virtue of the pore-free and crack-free microstructure of this cryomagnet, its strength σR was estimated to be 363 MPa, the largest one obtained so far for Y123 bulk superconductors, thus suggesting a striking mechanical reliability that seems to be sufficient to sustain stresses derived from trapped fields stronger than any values hitherto reported.

  7. Oxide superconductors under magnetic field

    NASA Technical Reports Server (NTRS)

    Kitazawa, K.

    1990-01-01

    One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of the broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

  8. Oxide superconductors under magnetic field

    NASA Technical Reports Server (NTRS)

    Kitazawa, K.

    1991-01-01

    One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

  9. Nonlinear properties of multiphase high-temperature superconductors of the Bi-Sr-Ca-Cu-O system in the temperature range of the superconducting transition

    NASA Astrophysics Data System (ADS)

    Golev, I. M.; Sergeev, A. V.; Kalyadin, O. V.

    2017-01-01

    The nonlinear characteristics of high-temperature superconductors of the Bi-Sr-Ca-Cu-O system have been experimentally investigated in the temperature range of the superconducting transition under the influence of a harmonic alternating magnetic field. The effect of the generation of odd harmonics in the signal of response to a harmonic alternating magnetic field for multiphase high-temperature superconductors containing regions with different values of the critical temperature in their bulk has been observed for the first time. The mechanism of harmonic generation in a superconductor in the resistive state, which is associated with the switch effect, i.e., with the redistribution of eddy current density between the local regions of the superconductor, has been considered.

  10. Superconductor lunar telescopes --Abstract only

    NASA Technical Reports Server (NTRS)

    Chen, P. C.; Pitts, R.; Shore, S.; Oliversen, R.; Stolarik, J.; Segal, K.; Hojaji, H.

    1994-01-01

    We propose a new type of telescope designed specifically for the lunar environment of high vacuum and low temperature. Large area UV-Visible-IR telescope arrays can be built with ultra-light-weight replica optics. High T(sub c) superconductors provide support, steering, and positioning. Advantages of this approach are light-weight payload compatible with existing launch vehicles, configurable large area optical arrays, no excavation or heavy construction, and frictionless electronically controlled mechanisms. We have built a prototype and will be demonstarting some of its working characteristics.

  11. Vortex ice in nanostructured superconductors

    SciTech Connect

    Reichhardt, Charles; Reichhardt, Cynthia J; Libal, Andras J

    2008-01-01

    We demonstrate using numerical simulations of nanostructured superconductors that it is possible to realize vortex ice states that are analogous to square and kagome ice. The system can be brought into a state that obeys either global or local ice rules by applying an external current according to an annealing protocol. We explore the breakdown of the ice rules due to disorder in the nanostructure array and show that in square ice, topological defects appear along grain boundaries, while in kagome ice, individual defects appear. We argue that the vortex system offers significant advantages over other artificial ice systems.

  12. Microgravity Processing of Oxide Superconductors

    NASA Technical Reports Server (NTRS)

    Hofmeister, William H.; Bayuzick, Robert J.; Vlasse, Marcus; McCallum, William; Peters, Palmer (Technical Monitor)

    2000-01-01

    The primary goal is to understand the microstructures which develop under the nonequilibrium solidification conditions achieved by melt processing in copper oxide superconductor systems. More specifically, to define the liquidus at the Y- 1:2:3 composition, the Nd-1:2:3 composition, and several intermediate partial substitution points between pure Y-1:2:3 and Nd-1:2:3. A secondary goal has been to understand resultant solidification morphologies and pathways under a variety of experimental conditions and to use this knowledge to better characterize solidification phenomena in these systems.

  13. Noncentrosymmetric superconductors in one dimension

    NASA Astrophysics Data System (ADS)

    Samokhin, K. V.

    2017-02-01

    We study the fermionic boundary modes (Andreev bound states) in a time-reversal invariant one-dimensional superconductor. In the presence of a substrate, spatial inversion symmetry is broken and the electronic properties are strongly affected by an antisymmetric spin-orbit coupling. We assume an arbitrary even number of nondegenerate bands crossing the Fermi level. We show that there is only one possible pairing symmetry in one dimension, an analog of s -wave pairing. The zero-energy Andreev bound states are present if the sign of the gap function in an odd number of the bands is different from all other bands.

  14. Holographic superconductors with hyperscaling violation

    NASA Astrophysics Data System (ADS)

    Fan, ZhongYing

    2013-09-01

    We investigate holographic superconductors in asympototically geometries with hyperscaling violation. The mass of the scalar field decouples from the UV dimension of the dual scalar operator and can be chosen as negative as we want, without disturbing the Breitenlohner-Freedman bound. We first numerically find that the scalar condenses below a critical temperature and a gap opens in the real part of the conductivity, indicating the onset of superconductivity. We further analytically explore the effects of the hyperscaling violation on the superconducting transition temperature. We find that the critical temperature increases with the increasing of hyperscaling violation.

  15. A Scalable Superconductor Bearing System For Lunar Telescopes And Instruments

    NASA Astrophysics Data System (ADS)

    Chen, Peter C.; Rabin, D.; Van Steenberg, M. E.

    2010-01-01

    We report on a new concept for a telescope mount on the Moon based on high temperature superconductors (HTS). Lunar nights are long (15 days), and temperatures range from 100 K to 30 K inside shadowed craters. Telescopes on the Moon therefore require bearing systems that can position and track precisely under cryogenic conditions, over long time periods, preferably with no maintenance, and preferably do not fail with loss of power. HTS bearings, consisting of permanent magnets levitated over bulk superconductors, are well suited to the task. The components do not make physical contact, hence there is no wear. The levitation is passive and stable; no power is required to maintain position. We report on the design and laboratory demonstration of a prototype two-axis pointing system. Unlike previous designs, this new configuration is simple and easy to implement. Most importantly, it can be scaled to accommodate instruments ranging in size from decimeters (laser communication systems) to meters (solar panels, communication dishes, optical telescopes, optical interferometers) to decameters and beyond (VLA-type radio interferometer elements).

  16. Phenomenological models of holographic superconductors and hall currents

    NASA Astrophysics Data System (ADS)

    Aprile, Francesco; Franco, Sebastián; Rodríguez-Gómez, Diego; Russo, Jorge G.

    2010-05-01

    We study general models of holographic superconductivity parametrized by four arbitrary functions of a neutral scalar field of the bulk theory. The models can accommodate several features of real superconductors, like arbitrary critical temperatures and critical exponents in a certain range, and perhaps impurities or boundary or thickness effects. We find analytical expressions for the critical exponents of the general model and show that they satisfy the Rushbrooke identity. An important subclass of models exhibit second order phase transitions. A study of the specific heat shows that general models can also describe holographic superconductors undergoing first, second and third (or higher) order phase transitions. We discuss how small deformations of the HHH model can lead to the appearance of resonance peaks in the conductivity, which increase in number and become narrower as the temperature is gradually decreased, without the need for tuning mass of the scalar to be close to the Breitenlohner-Freedman bound. Finally, we investigate the inclusion of a generalized “theta term” producing Hall effect without magnetic field.

  17. Plastic superconductor bearings any size-any shape: 77 K and up

    NASA Technical Reports Server (NTRS)

    Reick, Franklin G.

    1991-01-01

    'Friction free' bearings at 77 K or higher are possible using the high T(sub c) copper oxide ceramic superconductors. The conventional method for making such bearings is to use a sintered ceramic monolith. This puts great restraints on size, shape, and postforming machining. The material is hard and abrasive. It is possible to grind up ceramic superconductors and suspend the granules in a suitable matrix. Mechanical properties improve and are largely dependent on the binder. The Meissner effect is confined to individual grains containing electron vortices. Tracks, rails, levitation areas, and bearings can be made this way with conventional plastic molding and extruding machines or by painting. The parts are easily machined. The sacrifice is in bulk electrical conductivity. A percolating wick feed for LN2 is used to cool remote superconductors and large areas quite effectively. A hollow spheroid or cylinder of superconductor material is molded with the internal surfaces shielded by the Meissner effect. It can be thought of as the DC magnetic analog of the Faraday cage and the inside is the 'Meissner space'. It is selective. The AC fields are transmitted with minor attenuation. Particle size and distribution have a profound effect on final magnetic and electrical characteristics.

  18. Striped superconductors: how spin, charge and superconducting orders intertwine in the cuprates

    NASA Astrophysics Data System (ADS)

    Berg, Erez; Fradkin, Eduardo; Kivelson, Steven A.; Tranquada, John M.

    2009-11-01

    Recent transport experiments in the original cuprate high temperature superconductor, La2-xBaxCuO4, have revealed a remarkable sequence of transitions and crossovers that give rise to a form of dynamical dimensional reduction, in which a bulk crystal becomes essentially superconducting in two directions while it remains poorly metallic in the third. We identify these phenomena as arising from a distinct new superconducting state, the 'striped superconductor', in which the superconducting order is spatially modulated, so that its volume average value is zero. Here, in addition to outlining the salient experimental findings, we sketch the order parameter theory of the state, stressing some of the ways in which a striped superconductor differs fundamentally from an ordinary (uniform) superconductor, especially concerning its response to quenched randomness. We also present the results of density matrix renormalization group calculations on a model of interacting electrons in which sign oscillations of the superconducting order are established. Finally, we speculate concerning the relevance of this state to experiments in other cuprates, including recent optical studies of La2-xSrxCuO4 in a magnetic field, neutron scattering experiments in underdoped YBa2Cu3O6+x and a host of anomalies seen in STM and ARPES studies of Bi2Sr2CaCu2O8+δ.

  19. Plastic superconductor bearings any size, any shape, 77 k and up

    NASA Technical Reports Server (NTRS)

    Reick, Franklin G.

    1990-01-01

    Friction free bearings at 77 k or higher are possible using the high T(sub c) copper oxide ceramic superconductors. The conventional method for making such bearings is to use a sintered ceramic monolith. This puts great restraints on size, shape and postforming machining. The material is hard and abrasive. It's possible to grind up ceramic superconductors and suspend the granules in a suitable matrix. Mechanical properties improve and are largely dependent on the binder. The Meissner effect is confined to individual grains containing electron vortices. Tracks, rails, levitation areas and bearings can be made this way with conventional plastic molding and extruding machines or by painting. The parts are easily machined. The sacrifice is in bulk electrical conductivity. A percolating wick feel for LN2 can be used to cool remote superconductors and large areas quite effectively. A hollow spheroid or cylinder of superconductor material can be molded with the internal surfaces shielded by the Meissner effect. It might be thought of as the dc magnetic analogue of the Faraday cage and the inside can be called the Meissner space. It's selective. The ac fields are transmitted with minor attenuation. Particle size and distribution have a profound effect on final magnetic and electrical characteristics.

  20. Odd-parity superconductors with two-component order parameters: Nematic and chiral, full gap, and Majorana node

    NASA Astrophysics Data System (ADS)

    Venderbos, Jörn W. F.; Kozii, Vladyslav; Fu, Liang

    2016-11-01

    Motivated by the recent experiment indicating that superconductivity in the doped topological insulator CuxBi2Se3 has an odd-parity pairing symmetry with rotational symmetry breaking, we study the general class of odd-parity superconductors with two-component order parameters in trigonal and hexagonal crystal systems. In the presence of strong spin-orbit interaction, we find two possible superconducting phases below Tc, a time-reversal-breaking (i.e., chiral) phase and an anisotropic (i.e., nematic) phase, and determine their relative energetics from the gap function in momentum space. The nematic superconductor generally has a full quasiparticle gap, whereas the chiral superconductor with a three-dimensional (3D) Fermi surface has point nodes with lifted spin degeneracy, resulting in itinerant Majorana fermions in the bulk and topological Majorana arcs on the surface.

  1. Losses of Superconductor Journal Bearing

    NASA Astrophysics Data System (ADS)

    Han, Y. H.; Hull, J. R.; Han, S. C.; Jeong, N. H.; Oh, J. M.; Sung, T. H.

    2004-06-01

    A high-temperature superconductor (HTS) journal bearing was studied for rotational loss. Two HTS bearings support the rotor at top and bottom. The rotor weight is 4 kg and the length is about 300 mm. Both the top and bottom bearings have two permanent magnet (PM) rings with an iron pole piece separating them. Each HTS journal bearing is composed of six pieces of superconductor blocks of size 35×25×10 mm. The HTS blocks are encased in a cryochamber through which liquid nitrogen flows. The inner spool of the cryochamber is made from G-10 to reduce eddy current loss, and the rest of the cryochamber is stainless steel. The magnetic field from the PM rings is < 10 mT on the stainless part. The rotational drag was measured over the same speed range at several chamber pressures. Results indicate that a chamber pressure of 0.4 mtorr is sufficiently low to minimize windage loss, and the 10 mT design criterion for the magnetic field on the stainless part of the cryochamber is too high.

  2. Highly crystalline 2D superconductors

    NASA Astrophysics Data System (ADS)

    Saito, Yu; Nojima, Tsutomu; Iwasa, Yoshihiro

    2016-12-01

    Recent advances in materials fabrication have enabled the manufacturing of ordered 2D electron systems, such as heterogeneous interfaces, atomic layers grown by molecular beam epitaxy, exfoliated thin flakes and field-effect devices. These 2D electron systems are highly crystalline, and some of them, despite their single-layer thickness, exhibit a sheet resistance more than an order of magnitude lower than that of conventional amorphous or granular thin films. In this Review, we explore recent developments in the field of highly crystalline 2D superconductors and highlight the unprecedented physical properties of these systems. In particular, we explore the quantum metallic state (or possible metallic ground state), the quantum Griffiths phase observed in out-of-plane magnetic fields and the superconducting state maintained in anomalously large in-plane magnetic fields. These phenomena are examined in the context of weakened disorder and/or broken spatial inversion symmetry. We conclude with a discussion of how these unconventional properties make highly crystalline 2D systems promising platforms for the exploration of new quantum physics and high-temperature superconductors.

  3. Method to improve superconductor cable

    DOEpatents

    Borden, A.R.

    1984-03-08

    A method is disclosed of making a stranded superconductor cable having improved flexing and bending characteristics. In such method, a plurality of superconductor strands are helically wound around a cylindrical portion of a mandrel which tapers along a transitional portion to a flat end portion. The helically wound strands form a multistrand hollow cable which is partially flattened by pressure rollers as the cable travels along the transitional portion. The partially flattened cable is impacted with repeated hammer blows as the hollow cable travels along the flat end portion. The hammer blows flatten both the internal and the external surfaces of the strands. The cable is fully flattened and compacted by two sets of pressure rollers which engage the flat sides and the edges of the cable after it has traveled away from the flat end portion of the mandrel. The flattened internal surfaces slide easily over one another when the cable is flexed or bent so that there is very little possibility that the cable will be damaged by the necessary flexing and bending required to wind the cable into magnet coils.

  4. Position-sensitive superconductor detectors

    NASA Astrophysics Data System (ADS)

    Kurakado, M.; Taniguchi, K.

    2016-12-01

    Superconducting tunnel junction (STJ) detectors and superconducting transition- edge sensors (TESs) are representative superconductor detectors having energy resolutions much higher than those of semiconductor detectors. STJ detectors are thin, thereby making it suitable for detecting low-energy X rays. The signals of STJ detectors are more than 100 times faster than those of TESs. By contrast, TESs are microcalorimeters that measure the radiation energy from the change in the temperature. Therefore, signals are slow and their time constants are typically several hundreds of μs. However, TESs possess excellent energy resolutions. For example, TESs have a resolution of 1.6 eV for 5.9-keV X rays. An array of STJs or TESs can be used as a pixel detector. Superconducting series-junction detectors (SSJDs) comprise multiple STJs and a single-crystal substrate that acts as a radiation absorber. SSJDs are also position sensitive, and their energy resolutions are higher than those of semiconductor detectors. In this paper, we give an overview of position-sensitive superconductor detectors.

  5. Electronic transport in unconventional superconductors

    SciTech Connect

    Graf, M.J.

    1998-12-31

    The author investigates the electron transport coefficients in unconventional superconductors at low temperatures, where charge and heat transport are dominated by electron scattering from random lattice defects. He discusses the features of the pairing symmetry, Fermi surface, and excitation spectrum which are reflected in the low temperature heat transport. For temperatures {kappa}{sub B}T {approx_lt} {gamma} {much_lt} {Delta}{sub 0}, where {gamma} is the bandwidth of impurity induced Andreev states, certain eigenvalues become universal, i.e., independent of the impurity concentration and phase shift. Deep in the superconducting phase ({kappa}{sub B}T {approx_lt} {gamma}) the Wiedemann-Franz law, with Sommerfeld`s value of the Lorenz number, is recovered. He compares the results for theoretical models of unconventional superconductivity in high-{Tc} and heavy fermion superconductors with experiment. The findings show that impurities are a sensitive probe of the low-energy excitation spectrum, and that the zero-temperature limit of the transport coefficients provides an important test of the order parameter symmetry.

  6. Vortex Molecules in Thin Films of Layered Superconductors

    NASA Astrophysics Data System (ADS)

    Buzdin, Alexander I.

    2014-01-01

    In bulk layered superconductors the vortices tilted with respect to the anisotropy axes attract each other at long distance, which leads to the vortex chains structures. In thin film the intervortex interaction is modified by an extremely slow decay of the supercurrent induced by a single vortex line (Pearl's effect). The interplay between these interactions in thin films is responsible for a formation of a minimum of the interaction potential vs. the intervortex distance. This minimum exists only for relatively strong tilting. Depending on the strength and the tilt of the magnetic field we may expect the formation of the vortex molecules rearranging in multiquanta flux lattices. The increase in the field tilting should be accompanied by the series of the phase transitions between the vortex lattices with different number of vortices per unit cell. The Lorentz microscopy technique seems to be an ideal tool to observe such effects.

  7. Generation of strong magnetic field using 60 mm∅ superconducting bulk magnet and its application to magnetron sputtering device

    NASA Astrophysics Data System (ADS)

    Yanagi, Y.; Matsuda, T.; Hazama, H.; Yokouchi, K.; Yoshikawa, M.; Itoh, Y.; Oka, T.; Ikuta, H.; Mizutani, U.

    2005-10-01

    To make a practical application of a superconducting bulk magnet (SBM), it is necessary that the SBM generates a strong and stable magnetic field in a working space and the magnet can be handled without any special care that would be needed because of the use of a superconductor. To satisfy these requirements, we have designed a portable and user-friendly magnet system consisting of a small air-cooled type refrigerator and a bulk superconductor. By using the stress-controlling magnetization technique, we could achieve a magnetic flux density of 8.0 T on the bulk surface and 6.5 T over the vacuum chamber surface of the refrigerator, when a 60 mm∅ Gd-Ba-Cu-O bulk superconductor reinforced with a 5 mm thick stainless steel ring was magnetized by field cooling in 8.5 T to 27 K. We have confirmed that the bulk magnet system coupled with a battery is quite portable and can be delivered to any location by using a car with an electric power outlet in the cabin. We have constructed a magnetron sputtering device that employs a bulk magnet system delivered from the place of magnetization by this method. This sputtering device exhibits several unique features such as deposition at a very low Ar gas pressure because the magnetic field is 20 times stronger than that obtained by a conventional device in the working space.

  8. Aeronautical applications of high-temperature superconductors

    NASA Technical Reports Server (NTRS)

    Turney, George E.; Luidens, Roger W.; Uherka, Kenneth; Hull, John

    1989-01-01

    The successful development of high-temperature superconductors (HTS) could have a major impact on future aeronautical propulsion and aeronautical flight vehicle systems. A preliminary examination of the potential application of HTS for aeronautics indicates that significant benefits may be realized through the development and implementation of these newly discovered materials. Applications of high-temperature superconductors (currently substantiated at 95 k) were envisioned for several classes of aeronautical systems, including subsonic and supersonic transports, hypersonic aircraft, V/STOL aircraft, rotorcraft, and solar, microwave and laser powered aircraft. Introduced and described are the particular applications and potential benefits of high-temperature superconductors as related to aeronautics and/or aeronautical systems.

  9. Circuit Theory of Unconventional Superconductor Junctions

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Nazarov, Yu. V.; Kashiwaya, S.

    2003-04-01

    We extend the circuit theory of superconductivity to cover transport and proximity effect in mesoscopic systems that contain unconventional superconductor junctions. The approach fully accounts for zero-energy Andreev bound states forming at the surface of unconventional superconductors. As a simple application, we investigate the transport properties of a diffusive normal metal in series with a d-wave superconductor junction. We reveal the competition between the formation of Andreev bound states and proximity effect that depends on the crystal orientation of the junction interface.

  10. Aeronautical applications of high-temperature superconductors

    NASA Technical Reports Server (NTRS)

    Turney, George E.; Luidens, Roger W.; Uherka, Kenneth; Hull, John

    1989-01-01

    The successful development of high-temperature superconductors (HTS) could have a major impact on future aeronautical propulsion and aeronautical flight vehicle systems. A preliminary examination of the potential application of HTS for aeronautics indicates that significant benefits may be realized through the development and implementation of these newly discovered materials. Applications of high-temperature superconductors (currently substantiated at 95 K) were envisioned for several classes of aeronautical systems, including subsonic and supersonic transports, hypersonic aircraft, V/STOL aircraft, rotorcraft, and solar, microwave and laser powered aircraft. Introduced and described are the particular applications and potential benefits of high-temperature superconductors as related to aeronautics and/or aeronautical systems.

  11. Synthesis of highly phase pure BSCCO superconductors

    DOEpatents

    Dorris, Stephen E.; Poeppel, Roger B.; Prorok, Barton C.; Lanagan, Michael T.; Maroni, Victor A.

    1995-01-01

    An article and method of manufacture of (Bi, Pb)-Sr-Ca-Cu-O superconductor. The superconductor is manufactured by preparing a first powdered mixture of bismuth oxide, lead oxide, strontium carbonate, calcium carbonate and copper oxide. A second powdered mixture is then prepared of strontium carbonate, calcium carbonate and copper oxide. The mixtures are calcined separately with the two mixtures then combined. The resulting combined mixture is then subjected to a powder in tube deformation and thermal processing to produce a substantially phase pure (Bi, Pb)-Sr-Ca-Cu-O superconductor.

  12. Synthesis of highly phase pure BSCCO superconductors

    DOEpatents

    Dorris, S.E.; Poeppel, R.B.; Prorok, B.C.; Lanagan, M.T.; Maroni, V.A.

    1995-11-21

    An article and method of manufacture (Bi, Pb)-Sr-Ca-Cu-O superconductor are disclosed. The superconductor is manufactured by preparing a first powdered mixture of bismuth oxide, lead oxide, strontium carbonate, calcium carbonate and copper oxide. A second powdered mixture is then prepared of strontium carbonate, calcium carbonate and copper oxide. The mixtures are calcined separately with the two mixtures then combined. The resulting combined mixture is then subjected to a powder in tube deformation and thermal processing to produce a substantially phase pure (Bi, Pb)-Sr-Ca-Cu-O superconductor. 5 figs.

  13. Kim model of stress induced by flux pinning in type-II superconductors

    NASA Astrophysics Data System (ADS)

    Yong, Hua-Dong; Zhou, You-He

    2008-06-01

    Magnetoelastic effects, which are caused by flux pinning in the superconductors, often induce fatal cracking of the bulk high temperature superconductors (HTS). In the present work, the Kim model is considered for the critical state in which the critical current density is assumed to depend on the flux density. Based on the plane strain approach, the analytic expression of the stress under the magnetic field is derived for a specimen having a slab geometry and infinitely along the other two directions. The stress field is obtained in the slab for the Kim model, and the stress behavior is discussed for two magnetization processes: the decreasing field and the field cooling. It is shown that the effects of the parameter p on the stress are related to the magnetization process. Compared to the Bean model, the results for the Kim model show the same trend with respect to the external field Ba during field cooling. Generally speaking, these results are of clear interest to experimentalists and to the successful application of bulk superconductors.

  14. Nematic antiferromagnetic states in bulk FeSe

    NASA Astrophysics Data System (ADS)

    Liu, Kai; Lu, Zhong-Yi; Xiang, Tao

    2016-05-01

    The existence of nematic order, which breaks the lattice rotational symmetry with nonequivalent a and b axes in iron-based superconductors, is a well-established experimental fact. An antiferromagnetic (AFM) transition is accompanying this order, observed in nearly all parent compounds, except bulk FeSe. The absence of the AFM order in FeSe casts doubt on the magnetic mechanism of iron-based superconductivity, since the nematic order is believed to be driven by the same interaction that is responsible for the superconducting pairing in these materials. Here we show, through systematic first-principles electronic structure calculations, that the ground state of FeSe is in fact strongly AFM correlated but without developing a magnetic long-range order. Actually, there are a series of staggered n -mer AFM states with corresponding energies below that of the single stripe AFM state, which is the ground state for the parent compounds of most iron-based superconductors. Here, the staggered n -mer (n any integer >1 ) means a set of n adjacent parallel spins on a line along the b axis with antiparallel spins between n -mers along both a and b axes. Moreover, different n -mers can antiparallelly mix with each other to coexist. Among all the states, we find that the lowest energy states formed by the staggered dimer, staggered trimer, and their random antiparallel aligned spin states along the b axis are quasidegenerate. The thermal average of these states does not show any magnetic long-range order, but it does possess a hidden one-dimensional AFM order along the a axis, which can be detected by elastic neutron scattering measurements. Our finding gives a natural account for the absence of long-range magnetic order and suggests that the nematicity is driven predominantly by spin fluctuations even in bulk FeSe, providing a unified description on the phase diagram of iron-based superconductors.

  15. Growth and superconductivity of REBCO bulk processed by a seed/buffer layer/precursor construction

    NASA Astrophysics Data System (ADS)

    Y Li, T.; Cheng, L.; Yan, S. B.; Sun, L. J.; Yao, X.; Yoshida, Y.; Ikuta, H.

    2010-12-01

    The buffer layer has been used, for the first time, in the cold-seeding melt-growth (MG) process for REBCO superconductor bulks. In this modified method, a mini pellet was inserted between the seed and the bulk precursor. Notably, the chemical contamination, from the seed material (either REBCO films or SmBCO/NdBCO crystals), was mostly absorbed by the mini pellet. Thus a uniformly high Tc REBCO bulk was readily gained. Secondly, the higher limits of the maximum processing temperature (Tmax) were evidently raised, which is promisingly beneficial for broadening the growth window and overcoming the self-nucleation in the growth of large-sized bulk. In short, the success of this work is that it protects the bulk from seed-induced contamination, and breaks the limit of Tmax caused by the intrinsic properties of the seed material. By means of this simple seed/buffer layer/precursor construction, we successfully fabricated a large single grain of GdBCO bulk superconductor with a diameter of 56 mm.

  16. Thermal properties of a cylindrical YBa2Cu3O x superconductor in a levitation system: triggered by nonlinear dynamics

    NASA Astrophysics Data System (ADS)

    Huang, Yi; Zhang, Xingyi; Zhou, You-He

    2016-07-01

    The vibration of a permanent magnet (PM) levitated upon a high temperature superconductor (HTS) shows anomalous motion under external disturbance. In this paper we construct a cantilevered beam experimental setup composed of a bulk PM and a thermally insulated cylindrical YBa2Cu3O x superconductor. When the levitation system is disturbed by vertical excitation, the thermal character of the superconductor surface could be measured directly. Our experiments on a clean and large single-domain superconductor show that a giant temperature spike appears once the levitated PM experiences period doubling oscillation. We develop a numerical simulation for the analysis of the nonlinear vibration of the levitated PM coupled with the nonlinear electromagnetic force between the PM and HTS, taking into account heat diffusion. Using this procedure, we explore the electromagnetic and thermal properties at the thermally insulated HTS surface when the levitated PM shows a period doubling vibration. We find a remarkable difference between the experimental results and simulation. In order to interpret this temperature difference, we suggest a type of flux motion triggered by the electromagnetic force when it is far larger than the pinning force of the superconductor. The quantitative approach is based on the analysis process of the partial flux jump as a result of the flux creep. Finally, the calculated result is shown to be very close to the experimental result.

  17. New twisted intermetallic compound superconductor: A concept

    NASA Technical Reports Server (NTRS)

    Coles, W. D.; Brown, G. V.; Laurence, J. C.

    1972-01-01

    Method for processing Nb3Sn and other intermetallic compound superconductors produces a twisted, stabilized wire or tube which can be used to wind electromagnetics, armatures, rotors, and field windings for motors and generators as well as other magnetic devices.

  18. Resistance domain in type II superconductors

    SciTech Connect

    Gurevich, A.V.; Mints, R.G.

    1980-01-05

    We show that traveling domains with a finite resistance can exist in type II superconductors in the presence of a transport current. An experiment in which this effect generates an alternating electric field and current is proposed.

  19. NEW APPROACHES: High temperature superconductor levitation motor

    NASA Astrophysics Data System (ADS)

    Abd-Shukor, R.; Lee, K. H.

    1998-01-01

    We show how it is possible to construct a high temperature superconductor levitation motor in an introductory physics laboratory. It is suitable for classroom demonstration and uses a simple yet efficient cooling method.

  20. Simultaneous constraint and phase conversion processing of oxide superconductors

    DOEpatents

    Li, Qi; Thompson, Elliott D.; Riley, Jr., Gilbert N.; Hellstrom, Eric E.; Larbalestier, David C.; DeMoranville, Kenneth L.; Parrell, Jeffrey A.; Reeves, Jodi L.

    2003-04-29

    A method of making an oxide superconductor article includes subjecting an oxide superconductor precursor to a texturing operation to orient grains of the oxide superconductor precursor to obtain a highly textured precursor; and converting the textured oxide superconducting precursor into an oxide superconductor, while simultaneously applying a force to the precursor which at least matches the expansion force experienced by the precursor during phase conversion to the oxide superconductor. The density and the degree of texture of the oxide superconductor precursor are retained during phase conversion. The constraining force may be applied isostatically.

  1. Superconductors for pulsed rf accelerators

    SciTech Connect

    Campisi, I.E.; Farkas, Z.D.

    1985-04-01

    The choice of superconducting materials for accelerator rf cavities has been determined in the past only in part by basic properties of the superconductors, such as the critical field, and to a larger extent by criteria which include fabrication processes, surface conditions, heat transfer capabilities and so on. For cw operated cavities the trend has been toward choosing materials with higher critical temperatures and lower surface resistance, from Lead to Niobium, from Niobium to Nb/sub 3/Sn. This trend has been dictated by the specific needs of storage ring cw system and by the relatively low fields which could be reached without breakdown. The work performed at SLAC on superconducting cavities using microsecond long high power rf pulses has shown that in Pb, Nb, and Nb/sub 3/Sn fields close to the critical magnetic fields can be reached without magnetic breakdown.

  2. Electrical resistivity of composite superconductors

    NASA Technical Reports Server (NTRS)

    Davis, J. H.; Lee, J. A.

    1983-01-01

    In addition to its superconducting properties, a superconductor is usually characterized by poor thermal conductivity and relatively high electrical resistivity in the normal state. To remedy this situation a study of superconducting properties of Cu-rich CU-Nb wires prepared by directionally solidified and cold-rolled technique was conducted. Some of the specimens were prepared by melting, directional solidification and diffusing in Tin. A total of 12 wire specimens was tested. Each specimen was analyzed by plotting experimental data into the following curves: the graph of the residual resistivity as a function of the specimen current at 4.3 K; and the graph of the electrical resistivity as a function of the temperature at a constant current.

  3. A Review of the Terahertz Conductivity of Bulk and Nano-Materials

    NASA Astrophysics Data System (ADS)

    Lloyd-Hughes, James; Jeon, Tae-In

    2012-09-01

    We review pioneering and recent studies of the conductivity of solid state systems at terahertz frequencies. A variety of theoretical formalisms that describe the terahertz conductivity of bulk, mesoscopic and nanoscale materials are outlined, and their validity and limitations are given. Experimental highlights are discussed from studies of inorganic semiconductors, organic materials (such as graphene, carbon nanotubes and polymers), metallic films and strongly correlated electron systems including superconductors.

  4. Search for Majorana fermions in topological superconductors.

    SciTech Connect

    Pan, Wei; Shi, Xiaoyan; Hawkins, Samuel D.; Klem, John Frederick

    2014-10-01

    The goal of this project is to search for Majorana fermions (a new quantum particle) in a topological superconductor (a new quantum matter achieved in a topological insulator proximitized by an s-wave superconductor). Majorana fermions (MFs) are electron-like particles that are their own anti-particles. MFs are shown to obey non-Abelian statistics and, thus, can be harnessed to make a fault-resistant topological quantum computer. With the arrival of topological insulators, novel schemes to create MFs have been proposed in hybrid systems by combining a topological insulator with a conventional superconductor. In this LDRD project, we will follow the theoretical proposals to search for MFs in one-dimensional (1D) topological superconductors. 1D topological superconductor will be created inside of a quantum point contact (with the metal pinch-off gates made of conventional s-wave superconductors such as niobium) in a two-dimensional topological insulator (such as inverted type-II InAs/GaSb heterostructure).

  5. Topological insulators and superconductors from string theory

    SciTech Connect

    Ryu, Shinsei; Takayanagi, Tadashi

    2010-10-15

    Topological insulators and superconductors in different spatial dimensions and with different discrete symmetries have been fully classified recently, revealing a periodic structure for the pattern of possible types of topological insulators and superconductors, both in terms of spatial dimensions and in terms of symmetry classes. It was proposed that K theory is behind the periodicity. On the other hand, D-branes, a solitonic object in string theory, are also known to be classified by K theory. In this paper, by inspecting low-energy effective field theories realized by two parallel D-branes, we establish a one-to-one correspondence between the K-theory classification of topological insulators/superconductors and D-brane charges. In addition, the string theory realization of topological insulators and superconductors comes naturally with gauge interactions, and the Wess-Zumino term of the D-branes gives rise to a gauge field theory of topological nature, such as ones with the Chern-Simons term or the {theta} term in various dimensions. This sheds light on topological insulators and superconductors beyond noninteracting systems, and the underlying topological field theory description thereof. In particular, our string theory realization includes the honeycomb lattice Kitaev model in two spatial dimensions, and its higher-dimensional extensions. Increasing the number of D-branes naturally leads to a realization of topological insulators and superconductors in terms of holography (AdS/CFT).

  6. Noncentrosymmetric superconductivity in a clean crystal of type II superconductor Bi-Pd

    NASA Astrophysics Data System (ADS)

    Ramakrishnan, Srinivasan; Pratap, Bhanu; Thamizhavel, A.

    2016-02-01

    In this work, we present the bulk superconductivity of a high-quality single crystal of monoclinic BiPd (α-BiPd, space group P21) below 3.8 K by studying its electrical resistivity, magnetic susceptibility, and heat capacity. This is the cleanest noncentrosymmetric superconductor (NCS) that display anisotropy due to spin-orbit scattering and also exhibits unusual superconducting properties due to s and p wave mixing as evidenced by the observation of Andreev bound state and multiple energy gaps via point contact measurements. In addition, Fermi surface studies suggest multiband superconductivity in this compound. Penetration depth studies and NQR investigations support mixing of s and p wave Copper paring in this crystal. Moroever, Muon spin rotation measurements indicate strong field dependence of the Ginzburg- Landau coefficient of this superconductor. Unusual pairing and multiband superconductivity are extremely sensitive to disorder and they can be observed only in cleanest (RRR > 170) single crystals.

  7. Kim model for flux-pinning-induced stress in a long cylindrical superconductor

    NASA Astrophysics Data System (ADS)

    Zeng, Jun; Wang, Xiaogui; Wu, Huaping; Xue, Feng; Zhu, Jun

    2016-07-01

    In this work, the flux-pinning-induced stress distribution in a circular cylinder of high-temperature superconductors is studied by adopting the Kim critical state model to describe the relationship between the magnetic flux density and induced current. Based on the plane strain approach, the analytic expressions of the radial and hoop stress in the cylinder are derived for the zero-field cooling and field cooling magnetization processes. It is shown that the stress distributions depend on the activation processes and the values of the dimensionless parameter p in the Kim model, and the overall maximums of the stresses appear at or near the center of the cylinder where cracking may be most likely initiated. In addition, the Kim model has wider applicability than the Bean model, and the influence of p on the stress depends on the activation process. Generally speaking, these results may be useful for understanding the magnetoelastic problem in practical application of bulk superconductors.

  8. Classification of two-dimensional topological crystalline superconductors and Majorana bound states at disclinations

    NASA Astrophysics Data System (ADS)

    Benalcazar, Wladimir A.; Teo, Jeffrey C. Y.; Hughes, Taylor L.

    2014-06-01

    We classify discrete-rotation symmetric topological crystalline superconductors (TCS) in two dimensions and provide the criteria for a zero-energy Majorana bound state (MBS) to be present at composite defects made from magnetic flux, dislocations, and disclinations. In addition to the Chern number that encodes chirality, discrete rotation symmetry further divides TCS into distinct stable topological classes according to the rotation eigenspectrum of Bogoliubov-de Gennes quasiparticles. Conical crystalline defects are shown to be able to accommodate robust MBS when a certain combination of these bulk topological invariants is nontrivial as dictated by the index theorems proved within. The number parity of MBS is counted by a Z2-valued index that solely depends on the disclination and the topological class of the TCS. We also discuss the implications for corner-bound Majorana modes on the boundary of topological crystalline superconductors.

  9. Remanent magnetization of ceramic and single-crystal high-Tc superconductors in tilted magnetic fields

    NASA Astrophysics Data System (ADS)

    Bugoslavsky, Yu. V.; Minakov, A. A.; Vasyurin, S. I.

    1996-02-01

    Dependence of the remanent magnetization (Mr) anisotropy on the structure and shape of the superconductor and on the magnetizing procedure was studied for a number of high-Tc superconductor ceramics and single crystals. The experiments were done by means of a vibrating-sample magnetometer with a rotatable sample holder. It was found that the main contribution to the anisotropic behavior of Mr is due to the surface screening currents, and therefore the anisotropy is subject to variation when sample shape is changed. The question is resolved, why the effective demagnetization factors for decoupled ceramic samples are different from those calculated in the inscribed-ellipsoid approximation. Influence of inhomogeneous grain magnetization and global bulk currents on the angular dependencies of Mr in ceramic samples is investigated. The evolution of remanence in YBCO single crystals with an increase of the magnetizing field is described within an extended Bean model.

  10. Levitation force of small clearance superconductor-magnet system under non-coaxial condition

    NASA Astrophysics Data System (ADS)

    Xu, Jimin; Jin, Yingze; Yuan, Xiaoyang; Miao, Xusheng

    2017-03-01

    A novel superconducting tilting-pad bearing was proposed for the advanced research of reusable liquid hydrogen turbopump in liquid rocket. The bearing is a combination of superconducting magnetic bearing and hydrodynamic fluid-film bearing. Since the viscosity of cryogenic fuel to activate superconducting state and form hydrodynamic fluid-film is very low, bearing clearance will be very small. This study focuses on the investigation of superconducting levitation force in this kind of small clearance superconductor-magnet system. Based on Bean critical state model and three-dimensional finite element method, an analysis method is presented to obtain the levitation force under such situation. Since the complicated operational conditions and structural arrangement for application in liquid rocket, center lines of bulk superconductor and magnet rotor will usually be in non-coaxial state. Superconducting levitation forces in axial direction and radial direction under non-coaxial situation are also analyzed by the presented method.

  11. Vortexlike excitations in the heavy-fermion superconductor CeIrIn5

    DOE PAGES

    Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; ...

    2016-05-05

    Here, we report a systematic study of temperature- and field-dependent charge (ρ) and entropy (S) transport in the heavy-fermion superconductor CeIrIn5. Its large positive thermopower Sxx is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal Sxy. By separating the off-diagonal Peltier coefficient αxy from Sxy, we find that αxy becomes positive and greatly enhanced at temperatures well above the bulk Tc. Compared with the nonmagnetic analog LaIrIn5, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn5. This study sheds light on the similarity ofmore » heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.« less

  12. Vortexlike excitations in the heavy-fermion superconductor CeIrIn5

    NASA Astrophysics Data System (ADS)

    Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; Thompson, J. D.

    2016-05-01

    We report a systematic study of temperature- and field-dependent charge (ρ ) and entropy (S ) transport in the heavy-fermion superconductor CeIrIn5. Its large positive thermopower Sx x is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal Sx y. By separating the off-diagonal Peltier coefficient αx y from Sx y, we find that αx y becomes positive and greatly enhanced at temperatures well above the bulk Tc. Compared with the nonmagnetic analog LaIrIn5, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn5. This study sheds light on the similarity of heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.

  13. Comprehensive comparison of the levitation performance of bulk YBaCuO arrays above two different types of magnetic guideways

    NASA Astrophysics Data System (ADS)

    Deng, Zigang; Qian, Nan; Che, Tong; Jin, Liwei; Si, Shuaishuai; Zhang, Ya; Zheng, Jun

    2016-12-01

    The permanent magnet guideway (PMG) is an important part of high temperature superconducting (HTS) maglev systems. So far, two types of PMG, the normal PMG and Halbach-type PMG, are widely applied in present maglev transportation systems. In this paper, the levitation performance of high temperature superconductor bulks above the two PMGs was synthetically compared. Both static levitation performance and dynamic response characteristics were investigated. Benefiting from the reasonable magnetic field distribution, the Halbach-type PMG is able to gain larger levitation force, greater levitation force decay during the same relaxation time, bigger resonance frequency and dynamic stiffness for the bulk superconductor levitation unit compared with the normal PMG. Another finding is that the Halbach-type PMG is not sensitive to the levitation performance of the bulk levitation unit with different arrays. These results are helpful for the practical application of HTS maglev systems.

  14. Magnetic-field-induced topological reorganization of a p -wave superconductor

    NASA Astrophysics Data System (ADS)

    Mercaldo, Maria Teresa; Cuoco, Mario; Kotetes, Panagiotis

    2016-10-01

    In this work, we illustrate the detrimental impact of the Cooper pair's spin structure on the thermodynamic and topological properties of a spin-triplet superconductor in an applied Zeeman field. We particularly focus on the paradigmatic one-dimensional case (Kitaev chain) for which we self-consistently retrieve the energetically preferred Cooper pair spin state in terms of the corresponding spin d vector. The latter undergoes a substantial angular and amplitude reorganization upon the variation of the strength and the orientation of the field and results to a modification of the bulk topological phase diagram. Markedly, when addressing the open chain we find that the orientation of the d vector varies spatially near the boundary, affecting in this manner the appearance of Majorana fermions at the edge or even altering the properties of the bulk region. Our analysis reveals the limitations and breakdown of the bulk-boundary correspondence in interacting topological systems.

  15. High Performance Bulk Thermoelectric Materials

    SciTech Connect

    Ren, Zhifeng

    2013-03-31

    Over 13 plus years, we have carried out research on electron pairing symmetry of superconductors, growth and their field emission property studies on carbon nanotubes and semiconducting nanowires, high performance thermoelectric materials and other interesting materials. As a result of the research, we have published 104 papers, have educated six undergraduate students, twenty graduate students, nine postdocs, nine visitors, and one technician.

  16. Effects of High Energy Electron Irradiation on a Yttrium Barium(2) Copper(3) Oxygen(7-delta) High Temperature Superconductor

    DTIC Science & Technology

    1991-09-01

    must be overcome however,is the relatively low current densities measured in bulk superconducting samples. Towards this goal, it is theorized that by...superconductor to its normal state. The value of that current which produces vortices sufficiently large enough to destroy the superconducting state is...Texas Center for Superconductivity at the University of Houston Houston, Texas 77204-5932 Defect Size Dependence of Critical Current Density

  17. Performance of ceramic superconductors in magnetic bearings

    NASA Technical Reports Server (NTRS)

    Kirtley, James L., Jr.; Downer, James R.

    1993-01-01

    Magnetic bearings are large-scale applications of magnet technology, quite similar in certain ways to synchronous machinery. They require substantial flux density over relatively large volumes of space. Large flux density is required to have satisfactory force density. Satisfactory dynamic response requires that magnetic circuit permeances not be too large, implying large air gaps. Superconductors, which offer large magnetomotive forces and high flux density in low permeance circuits, appear to be desirable in these situations. Flux densities substantially in excess of those possible with iron can be produced, and no ferromagnetic material is required. Thus the inductance of active coils can be made low, indicating good dynamic response of the bearing system. The principal difficulty in using superconductors is, of course, the deep cryogenic temperatures at which they must operate. Because of the difficulties in working with liquid helium, the possibility of superconductors which can be operated in liquid nitrogen is thought to extend the number and range of applications of superconductivity. Critical temperatures of about 98 degrees Kelvin were demonstrated in a class of materials which are, in fact, ceramics. Quite a bit of public attention was attracted to these new materials. There is a difficulty with the ceramic superconducting materials which were developed to date. Current densities sufficient for use in large-scale applications have not been demonstrated. In order to be useful, superconductors must be capable of carrying substantial currents in the presence of large magnetic fields. The possible use of ceramic superconductors in magnetic bearings is investigated and discussed and requirements that must be achieved by superconductors operating at liquid nitrogen temperatures to make their use comparable with niobium-titanium superconductors operating at liquid helium temperatures are identified.

  18. Performance of ceramic superconductors in magnetic bearings

    NASA Astrophysics Data System (ADS)

    Kirtley, James L., Jr.; Downer, James R.

    Magnetic bearings are large-scale applications of magnet technology, quite similar in certain ways to synchronous machinery. They require substantial flux density over relatively large volumes of space. Large flux density is required to have satisfactory force density. Satisfactory dynamic response requires that magnetic circuit permeances not be too large, implying large air gaps. Superconductors, which offer large magnetomotive forces and high flux density in low permeance circuits, appear to be desirable in these situations. Flux densities substantially in excess of those possible with iron can be produced, and no ferromagnetic material is required. Thus the inductance of active coils can be made low, indicating good dynamic response of the bearing system. The principal difficulty in using superconductors is, of course, the deep cryogenic temperatures at which they must operate. Because of the difficulties in working with liquid helium, the possibility of superconductors which can be operated in liquid nitrogen is thought to extend the number and range of applications of superconductivity. Critical temperatures of about 98 degrees Kelvin were demonstrated in a class of materials which are, in fact, ceramics. Quite a bit of public attention was attracted to these new materials. There is a difficulty with the ceramic superconducting materials which were developed to date. Current densities sufficient for use in large-scale applications have not been demonstrated. In order to be useful, superconductors must be capable of carrying substantial currents in the presence of large magnetic fields. The possible use of ceramic superconductors in magnetic bearings is investigated and discussed and requirements that must be achieved by superconductors operating at liquid nitrogen temperatures to make their use comparable with niobium-titanium superconductors operating at liquid helium temperatures are identified.

  19. Effects of densification of precursor pellets on microstructures and critical current properties of YBCO melt-textured bulks

    NASA Astrophysics Data System (ADS)

    Setoyama, Yui; Shimoyama, Jun-ichi; Motoki, Takanori; Kishio, Kohji; Awaji, Satoshi; Kon, Koichi; Ichikawa, Naoki; Inamori, Satoshi; Naito, Kyogo

    2016-12-01

    Effects of densification of precursor disks on the density of residual voids and critical current properties for YBCO melt-textured bulk superconductors were systematically investigated. Six YBCO bulks were prepared from precursor pellets with different initial particle sizes of YBa2Cu3Oy (Y123) powder and applied pressures for pelletization. It was revealed that use of finer Y123 powder and consolidation using cold-isostatic-pressing (CIP) with higher pressures result in reduction of residual voids at inner regions of bulks and enhance Jc especially under low fields below the second peak.

  20. Sealed glass coating of high temperature ceramic superconductors

    DOEpatents

    Wu, Weite; Chu, Cha Y.; Goretta, Kenneth C.; Routbort, Jules L.

    1995-01-01

    A method and article of manufacture of a lead oxide based glass coating on a high temperature superconductor. The method includes preparing a dispersion of glass powders in a solution, applying the dispersion to the superconductor, drying the dispersion before applying another coating and heating the glass powder dispersion at temperatures below oxygen diffusion onset and above the glass melting point to form a continuous glass coating on the superconductor to establish compressive stresses which enhance the fracture strength of the superconductor.

  1. Electron tunneling and point contact Andreev reflection studies of superconductors

    NASA Astrophysics Data System (ADS)

    Dai, Wenqing

    The energy gap is the most fundamental property of a superconductor. Electron tunneling spectroscopy and point contact spectroscopy (PCS) are powerful techniques for studying the density of states and energy gap features of superconductors. Two different superconducting systems, multiband superconductor MgB2 and proximity induced topological superconductor NbSe2/Bi 2Se3 heterostructures were studied using either quasiparticle tunneling in planar tunnel junctions or PCS in this work. (Abstract shortened by ProQuest.).

  2. Stop of magnetic flux movement in levitating superconductor

    NASA Astrophysics Data System (ADS)

    Smolyak, B. M.; Zakharov, M. S.

    2017-01-01

    A phenomenon of magnetic relaxation stopping in a levitating superconductor was studied. It was experimentally shown that magnetic flux creep (diffusion of flux lines to regions with lower vortex density) is absent in magnetic suspension of the superconductor. Magnetic relaxation arises, when a rigid constraint that fixes a position of the superconductor relative to a magnet is imposed on a levitating object. It is assumed that oscillations of magnetic structure, which is due to free oscillations of the levitating superconductor, stop magnetic relaxation.

  3. Quaternary borocarbides: New class of intermetallic superconductors

    NASA Technical Reports Server (NTRS)

    Nagarajan, R.; Gupta, L. C.; Dhar, S. K.; Mazumdar, Chandan; Hossain, Zakir; Godart, C.; Levy-Clement, C.; Padalia, B. D.; Vijayaraghavan, R.

    1995-01-01

    Our recent discovery of superconductivity (SC) in the four-element multiphase Y-Ni-B-C system at an elevated temperature (TC approximately 12 K) has opened up great possibilities of identifying new superconducting materials and generating new physics. Superconductivity with Tc (greater than 20 K) higher than that known so far in bulk intermetallics has been observed in multiphase Y-Pd-B-C and Th-Pd-B-C systems and a family of single phase materials RENi2B2C (RE= Y, rare earth) have been found. Our investigations show YNi2B2C to be a strong coupling hard type-II SC. HC2(T) exhibits an unconventional temperature dependence. Specific heat and magnetization studies reveal coexistence of SC and magnetism in RNi2B2C (R = Ho, Er, Tm) with magnetic ordering temperatures (Tc approximately 8 K, 10.5 K, 11 K and Tm approximately 5 K, approximately 7K, approximately 4 K respectively) that are remarkably higher than those in known magnetic superconductors . Mu-SR studies suggest the possibility of Ni atoms carrying a moment in TmNi2B2C. Resistivity results suggests a double re-entrant transition (SC-normal-SC) in HoNi2B2C. RENi2B2C (RE = Ce, Nd, Gd) do not show SC down to 4.2 K. The Nd- and Gd-compounds order magnetically at approximately 4.5 K and approximately 19.5 K, respectively. Two SC transitions are observed in Y-Pd-B-C (Tc approximately 22 K, approximately 10 K) and in Th-Pd-B-C (Tc approximately 20 K, approximately 14 K) systems, which indicate that there are at least two structures which support SC in these borocarbides. In our multiphase ThNi2B2C we observe SC at approximately 6 K. No SC was seen in multiphase UNi2B2C, UPd2B2C, UOs2Ge2C and UPd5B3C(0.35) down to 4.2 K. Tc in YNi2B2C is depressed by substitutions (Gd, Th and U at Y-sites and Fe, Co at Ni-sites).

  4. High levitation pressures with cage-cooled superconductors

    NASA Astrophysics Data System (ADS)

    Hull, John R.; Komori, Mochimitsu

    2002-05-01

    We present an analysis of and experimental results from a levitational system comprising a stationary, bulk high-temperature superconductor (HTS) and a levitated component (rotor) that consists of a cylindrical permanent magnet surrounded by an annular HTS. The rotor is cooled below the critical temperature of the HTS while surrounded by a ferromagnetic cage. When the ferromagnetic cage is removed, the flux from the permanent magnet is essentially excluded from the interior of the HTS. When brought into proximity with the HTS stator, the cage-cooled rotor experiences a levitational force. The levitational force may be calculated by applying magnetic circuit theory. Such calculations indicate that for a sufficiently high critical current density, the levitational pressure may exceed that between the permanent magnet and its mirror image. We constructed a rotor from an NdFeB permanent magnet and YBCO bulk HTS with a critical current density of ≈5 kA cm-2. A soft ferromagnetic steel cage was constructed in segments. The critical current density of the stator HTS was also ≈5 kA cm-2. Experimental results obtained with the cage-cooled rotor and stationary HTS show a significant increase in force over that of an equivalent PM rotor and stationary HTS.

  5. Rotating superconductor magnet for producing rotating lobed magnetic field lines

    DOEpatents

    Hilal, Sadek K.; Sampson, William B.; Leonard, Edward F.

    1978-01-01

    This invention provides a rotating superconductor magnet for producing a rotating lobed magnetic field, comprising a cryostat; a superconducting magnet in the cryostat having a collar for producing a lobed magnetic field having oppositely directed adjacent field lines; rotatable support means for selectively rotating the superconductor magnet; and means for energizing the superconductor magnet.

  6. Fermi surface deformation in a simple iron-based superconductor, FeSe

    NASA Astrophysics Data System (ADS)

    Coldea, Amalia; Watson, Matthew; Kim, Timur; Haghighirad, Amir; McCollam, Alix; Hoesch, Moritz; Schofield, Andrew

    2015-03-01

    One of the outstanding problems in the field superconductivity is the identification of the normal state out of which superconductivity emerges. FeSe is one of the simplest and most intriguing iron-based superconductors, since in its bulk form it undergoes a structural transition before it becomes superconducting, whereas its single-layer form is believed to be a high-temperature superconductor. The nature of the structural transition, occurring in the absence of static magnetism, is rather unusual and how the electronic structure is stabilized by breaking of the rotational symmetry is the key to understand the superconductivity in bulk FeSe. Here we report angle-resolved photoemission spectroscopy measurements on FeSe that gives direct access to the band structure and orbital-dependent effects. We complement our studies on bulk FeSe with low-temperature angular-dependent quantum oscillation measurements using applied magnetic fields that are sufficiently strong to suppress superconductivity and reach the normal state. These studies reveal a strong deformation of Fermi surface through the structural transition driven by electronic correlations and orbital-dependent effects. . This work was supported by EPSRC, UK (EP/I004475/1), Diamond Light Source, UK and HFML, Nijmegen.

  7. Fabrication of Bi2223 bulks with high critical current properties sintered in Ag tubes

    NASA Astrophysics Data System (ADS)

    Takeda, Yasuaki; Shimoyama, Jun-ichi; Motoki, Takanori; Kishio, Kohji; Nakashima, Takayoshi; Kagiyama, Tomohiro; Kobayashi, Shin-ichi; Hayashi, Kazuhiko

    2017-03-01

    Randomly grain oriented Bi2223 sintered bulks are one of the representative superconducting materials having weak-link problem due to very short coherence length particularly along the c-axis, resulting in poor intergrain Jc properties. In our previous studies, sintering and/or post-annealing under moderately reducing atmospheres were found to be effective for improving grain coupling in Bi2223 sintered bulks. Further optimizations of the synthesis process for Bi2223 sintered bulks were attempted in the present study to enhance their intergrain Jc. Effects of applied pressure of uniaxial pressing and sintering conditions on microstructure and superconducting properties have been systematically investigated. The best sample showed intergrain Jc of 2.0 kA cm-2 at 77 K and 8.2 kA cm-2 at 20 K, while its relative density was low ∼65%. These values are quite high as for a randomly oriented sintered bulk of cuprate superconductors.

  8. The color of polarization in cuprate superconductors

    NASA Technical Reports Server (NTRS)

    Hoff, H. A.; Osofsky, M. S.; Lechter, W. L.; Pande, C. S.

    1991-01-01

    A technique for the identification of individual anisotropic grains in a heterogeneous and opaque material involves the observation of grain color in reflected light through crossed polarizers (color of polarization). Such colors are generally characteristic of particular phases. When grains of many members of the class of hole carrier cuprate superconductors are so viewed at room temperature with a 'daylight' source, a characteristic color of polarization is observed. This color was studied in many of these cuprate superconductors and a strong correlation was found between color and the existence of superconductivity. Two members were also examined of the electron cuprate superconductors and it was found that they possess the same color of polarization as the hole carrier cuprate superconductors so far examined. The commonality of the characteristic color regardless of charge carrier indicates that the presence of this color is independent of carrier type. The correlation of this color with the existence of superconductivity in the cuprate superconductors suggests that the origin of the color relates to the origin of superconductivity. Photometric techniques are also discussed.

  9. Quantum interference in an interfacial superconductor

    NASA Astrophysics Data System (ADS)

    Goswami, Srijit; Mulazimoglu, Emre; Monteiro, Ana M. R. V. L.; Wölbing, Roman; Koelle, Dieter; Kleiner, Reinhold; Blanter, Ya. M.; Vandersypen, Lieven M. K.; Caviglia, Andrea D.

    2016-10-01

    The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO) has several intriguing properties that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (Tc; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-Tc superconductors. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.

  10. Quantum interference in an interfacial superconductor.

    PubMed

    Goswami, Srijit; Mulazimoglu, Emre; Monteiro, Ana M R V L; Wölbing, Roman; Koelle, Dieter; Kleiner, Reinhold; Blanter, Ya M; Vandersypen, Lieven M K; Caviglia, Andrea D

    2016-10-01

    The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO) has several intriguing properties that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (Tc; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-Tc superconductors. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.

  11. Conductance spectroscopy of topological superconductor wire junctions

    NASA Astrophysics Data System (ADS)

    Setiawan, F.; Brydon, Philip; Sau, Jay

    We study the zero-temperature transport properties of one-dimensional normal metal-superconductor (NS) junctions with topological superconductors across their topological transitions. Working within the Blonder-Tinkham-Klapwijk (BTK) formalism generalized for topological NS junctions, we analytically calculate the differential conductance for tunneling into two models of a topological superconductor: a spinless intrinsic p-wave superconductor and a spin-orbit-coupled s-wave superconductor in a Zeeman field. The zero-bias conductance takes nonuniversal values in the nontopological phase while it is robustly quantized at 2e2 / h in the topological regime. Despite this quantization at zero voltage, the zero-bias conductance only develops a peak (or a local maximum) as a function of voltage for sufficiently large interfacial barrier strength, or certain parameter regimes of spin-orbit coupling strength. Our calculated BTK conductance also shows that the conductance is finite inside the superconducting gap region because of the finite barrier transparency, providing a possible mechanism for the observed ``soft gap'' feature in the experimental studies. Work is done in collaboration with Sankar Das Sarma and supported by Microsoft Q, LPS-CMTC, and JQI-NSF-PFC.

  12. Surface Josephson plasma waves in layered superconductors above the plasma frequency: evidence for a negative index of refraction.

    PubMed

    Golick, V A; Kadygrob, D V; Yampol'skii, V A; Rakhmanov, A L; Ivanov, B A; Nori, Franco

    2010-05-07

    We predict a new branch of surface Josephson plasma waves (SJPWs) in layered superconductors for frequencies higher than the Josephson plasma frequency. In this frequency range, the permittivity tensor components along and transverse to the layers have different signs, which is usually associated with negative refraction. However, for these frequencies, the bulk Josephson plasma waves cannot be matched with the incident and reflected waves in the vacuum, and, instead of the negative-refractive properties, abnormal surface modes appear within the frequency band expected for bulk modes. We also discuss the excitation of high-frequency SJPWs by means of the attenuated-total-reflection method.

  13. Nanoscale magnetization of a single vortex in d-wave superconductors

    NASA Astrophysics Data System (ADS)

    Zakharchuk, I.; Januzaj, A.; Safonchik, M.; Traito, K. B.; Lähderanta, E.

    2017-01-01

    A finite-size scaling of the nanoscale magnetization m on size averaging R of a single vortex in d-wave bulk superconductor is developed using quasiclassical Eilenberger equations. Nanoscaling is anchoring around the linear London approximation for bulk superconductors. Comparing the results with those obtained in local nonlinear approach demonstrated the importance of the nonlocal contribution. Temperature dependences of two-point correlation function χ(T , R 1 , R 2) = m(T , R 2) / m(0 , R 2) - m(T , R 1) / m(0 , R 1) with R2 > R1 and one-point function χ(T, R1 → ∞, R2) are calculated. It is found that χ(T, R1, R2), R2 > R1, is a nonmonotonous function of temperature and changes sign at high temperatures. This nonmonotonous temperature dependence can be understood as a result of competition between various effects i) Volovik effect and nonlocal corrections to superconducting electron density dominating in low temperature range, and ii) current-induced suppression of the order parameter dominating at high temperatures. The introduced nonmagnetic disorder greatly suppresses the low temperature nonlocal and nonlinear effects, leaving the order parameter effects to prevail in the whole temperature range. Nonlocal pairing and tunneling effects are investigated at the superconductor - normal metal border by considering a d-wave superconducting dot (d-dot) inside a normal diffusive metal. These effects result in a suppression of the supercurrent in the vortex core and are essential in nanodots with relatively small sizes. At sizes larger than a temperature dependent characteristic length the nanoscale physics transforms into bulk solution.

  14. Quantum information aspects on bulk and nano interacting Fermi system: A spin-space density matrix approach

    NASA Astrophysics Data System (ADS)

    Afzali, R.; Ebrahimian, N.; Eghbalifar, B.

    2016-10-01

    By approximating the energy gap, entering nano-size effect via gap fluctuation and calculating the Green's functions and the space-spin density matrix, the dependence of quantum correlation (entanglement, discord and tripartite entanglement) on the relative distance of two electron spins forming Cooper pairs, the energy gap and the length of bulk and nano interacting Fermi system (a nodal d-wave superconductor) is determined. In contrast to a s-wave superconductor, quantum correlation of the system is sensitive to the change of the gap magnitude and strongly depends on the length of the grain. Also, quantum discord oscillates. Furthermore, the entanglement length and the correlation length are investigated. Discord becomes zero at a characteristic length of the d-wave superconductor.

  15. Electronic bands, Fermi surface, and elastic properties of new 4.2 K superconductor SrPtAs with a honeycomb structure from first principles calculations

    NASA Astrophysics Data System (ADS)

    Shein, I. R.; Ivanovskii, A. L.

    2011-10-01

    The hexagonal phase SrPtAs (s.g. P6/ mmm; #194) with a honeycomb lattice structure was recently declared as a new low-temperature ( T C ∼ 4.2 K) superconductor. Here, by means of first-principles calculations the optimized structural parameters, electronic bands, Fermi surface, total and partial densities of states, inter-atomic bonding picture, independent elastic constants, bulk and shear moduli for SrPtAs were obtained for the first time and analyzed in comparison with the related layered superconductor SrPt 2As 2.

  16. Studies of nonlinear electrodynamics of high-temperature superconductors

    SciTech Connect

    Lam, Quan-Chiu H.

    1991-08-01

    Nonlinear electrodynamics of high-{Tc} superconductors are studied both theoretically and experimentally. For powdered samples, a novel model is presented in which the metallographically observed superconducting grains in the powder are modeled as superconducting current loops of various areas with weak links. Surprising harmonic generation behavior in an arc field, H{sub 1} cos({omega}t), is predicted by the model; the power at high harmonics show sharp dips almost periodic in a superposing dc magnetic field, revealing flux quantization in the prototype loops in the model. Such oscillation of the harmonic power in dc magnetic field P{sub nf}(H{sub dc}), is indeed experimentally observed in powdered YBa{sub 2}Cu{sub 3}O{sub 7}. Other experimental aspects also agree with model predictions. For bulk sintered cylindrical samples, a generalized critical state model is presented. In this model, the nonlinear electrodynamics are due to flux-pinning, somewhat similar to low-temperature type-II superconductors, but with a more generalized critical current densities' dependence on magnetic field -- J{sub c}(H){approximately}H{sub local}{sup -{beta}}, with {beta} being an adjustable parameter. Experiments in ac and dc magnetic fields on a sintered cylindrical rod of YBa{sub 2}Cu{sub 3}O{sub 7} yield unambiguous evidence of independent inter- and intragranular contributions to the complex harmonic permeability {tilde {mu}}{sub n} = {mu}{prime}{sub n} -i{mu}{double prime}{sub n}. Temperature- dependence measurements reveal that, while the intragranular supercurrents disappear at {Tc}{ge}91.2 K, the intergranular supercurrents disappear at T{ge}86.6 K. This result is, to our knowledge, the first clear measurement of the phase-locking temperature of the 3-D matrix formed by YBa{sub 2}Cu{sub 3}O{sub 7} grains, which are in electrical contact with one another through weak links.

  17. Studies of nonlinear electrodynamics of high-temperature superconductors

    SciTech Connect

    Lam, Quan-Chiu H.

    1991-08-01

    Nonlinear electrodynamics of high-{Tc} superconductors are studied both theoretically and experimentally. For powdered samples, a novel model is presented in which the metallographically observed superconducting grains in the powder are modeled as superconducting current loops of various areas with weak links. Surprising harmonic generation behavior in an arc field, H{sub 1} cos({omega}t), is predicted by the model; the power at high harmonics show sharp dips almost periodic in a superposing dc magnetic field, revealing flux quantization in the prototype loops in the model. Such oscillation of the harmonic power in dc magnetic field P{sub nf}(H{sub dc}), is indeed experimentally observed in powdered YBa{sub 2}Cu{sub 3}O{sub 7}. Other experimental aspects also agree with model predictions. For bulk sintered cylindrical samples, a generalized critical state model is presented. In this model, the nonlinear electrodynamics are due to flux-pinning, somewhat similar to low-temperature type-II superconductors, but with a more generalized critical current densities` dependence on magnetic field -- J{sub c}(H){approximately}H{sub local}{sup -{beta}}, with {beta} being an adjustable parameter. Experiments in ac and dc magnetic fields on a sintered cylindrical rod of YBa{sub 2}Cu{sub 3}O{sub 7} yield unambiguous evidence of independent inter- and intragranular contributions to the complex harmonic permeability {tilde {mu}}{sub n} = {mu}{prime}{sub n} -i{mu}{double_prime}{sub n}. Temperature- dependence measurements reveal that, while the intragranular supercurrents disappear at {Tc}{ge}91.2 K, the intergranular supercurrents disappear at T{ge}86.6 K. This result is, to our knowledge, the first clear measurement of the phase-locking temperature of the 3-D matrix formed by YBa{sub 2}Cu{sub 3}O{sub 7} grains, which are in electrical contact with one another through weak links.

  18. The surface coordination chemistry of cuprate high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Xu, Feng

    The goals of the research described in this dissertation were: (1) to explore the surface coordination chemistry of cuprate high-temperature superconductors (HTSCs); (2) to develop chemical methodology for directly tailoring the surface and interfacial properties of cuprate HTSCs. This thesis documents the first survey of the surface coordination chemistry of a cuprate HTSC, YBa2Cu3O7-delta. Functional groups that can chemically bind to YBa2Cu3O 7-delta have been determined using cyclic voltammetry in conjunction with a series of redox-active ferrocenyl containing adsorbate molecules. Primary alkylamines have emerged as the optimum adsorbates for HTSCs, forming stable and robust monolayer films with no apparent damage to the bulk properties of the underlying superconductors. The interactions between alkylamine adsorbates and YBa2Cu3O7-delta have been shown to involve Cu(II)-NR3 coordination chemistry. The influence of organic monolayers on the properties of YBa2Cu3O 7-delta has been examined using cyclic voltammetry, X-ray powder diffraction, atomic force microscopy, and resistivity vs. temperature measurements. The presence of H2O in the soaking solution adversely affects the adsorption process due to a competing corrosion reaction. However, stable monolayers form on HTSC substrates under rigorously dry conditions. Significantly, monolayer modified HTSCs are substantially more stable to corrosion environmental reagents. The formation kinetics of redox-active alkylamine monolayers on ceramic YBa2Cu3O7-delta are proposed to involve two major processes: a fast adsorption process and a relatively slow pore diffusion process. Surface-solution adsorbate exchange is very dynamic and reversible, which appears to occur via an associative pathway. Monolayers on c-axis-oriented thin films have been shown to be more densely-packed and stable than those on ceramic substrates. Notably, the surface alkylamine "ligands" display traits of Cu(II)-based coordination chemistry

  19. High T(sub c) superconductors: Will they replace helium temperature superconductors for magnets

    NASA Astrophysics Data System (ADS)

    Green, Michael A.

    1988-07-01

    During the last two years, the maximum zero resistance critical temperature for superconductors has risen from 23 K to temperatures above 120 K. This paper presents a sober view of the usefulness of the high T sub c materials for generating magnetic fields in superconducting devices. The high T sub c materials are compared to conventional niobium titanium superconductors in the following areas: critical current density, adiabatic and dynamic stability, normal region propagation velocity, burn out integral, energy per unit volume to quench and the maximum cryogenic stability current density. A look at the whole picture suggests that for most superconducting magnet applications, conventional conductors would be the superconductors of choice for magnets.

  20. Non-volatile resistive switching in the dielectric superconductor YBa(2)Cu(3)O(7-δ).

    PubMed

    Acha, C; Rozenberg, M J

    2009-01-28

    We report on the reversible, non-volatile and polarity-dependent resistive switching between superconductor and insulator states at the interfaces of an Au/YBa(2)Cu(3)O(7-δ) (YBCO)/Au system. We show that, upon application of electric pulses, the superconducting state of YBCO in regions near the electrodes can be reversibly removed and restored. In addition, four-wire measurements reveal that pulsing also induces significant non-volatile changes in the bulk resistance. We argue that our observations are compatible with a scenario where the switching effect is due to migration of oxygen ions along grain boundaries that control the inter-grain superconducting coupling.

  1. Effective field theory for a p -wave superconductor in the subgap regime

    NASA Astrophysics Data System (ADS)

    Hansson, T. H.; Kvorning, T.; Nair, V. P.; Sreejith, G. J.

    2015-02-01

    We construct an effective field theory for the 2 d spinless p -wave paired superconductor that faithfully describes the topological properties of the bulk state, and also provides a model for the subgap states at vortex cores and edges. In particular, it captures the topologically protected zero modes and has the correct ground-state degeneracy on the torus. We also show that our effective field theory becomes a topological field theory in a well defined scaling limit and that the vortices have the expected non-Abelian braiding statistics.

  2. Method for preparing high transition temperature Nb/sub 3/Ge superconductors. [Patent application

    DOEpatents

    Newkirk, L.R.; Valencia, F.A.

    1975-06-26

    Bulk coatings of Nb/sub 3/Ge superconductors having transition temperatures in excess of 20/sup 0/K are readily formed by a chemical vapor deposition technique involving the coreduction of NbCl/sub 5/ and GeCl/sub 4/ in the presence of hydrogen. The NbCl/sub 5/ vapor may advantageously be formed quantitatively in the temperature range of about 250 to 260/sup 0/C by the chlorination of Nb metal provided the partial pressure of the product NbCl/sub 5/ vapor is maintained at or below about 0.1 atm.

  3. Persistent Current in Coils Made Out of Second Generation High Temperature Superconductor Wire

    DTIC Science & Technology

    2008-10-01

    stabilizer attached; only a 1–3 m thick silver coat- ing covered YBCO film deposited on 100 m thick Hastel- loy substrate. In each of the sections, a slit...1.2969798 In recent years there has been remarkable progress in manufacturing YBa2Cu3O7− YBCO coated superconductors.1 It is important to find...magnetic resonance imaging machines to electric motors and superconducting bearings,5,6 where they can replace bulk YBCO , to more exotic applications such

  4. Ac Permeability Measurement for Inter- and Intragrain Critical Current Densities in Oxide Superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, Teruo; Ni, Baorong

    1989-03-01

    A simple measuring method to discriminate between inter- and intragrain current densities in oxide superconductors under given magnetic fields and temperatures is proposed. This is a measurement of the imaginary part of the ac permeability or susceptibility as a function of the ac field amplitude. In this method, the analysis used to derive the penetration depth of the ac field in Campbell’s method or the waveform analysis method is not necessary. This method is useful when the value of the penetration field into the grains and that into the bulk specimen are remarkably different.

  5. Method for preparing high transition temperature Nb.sub.3 Ge superconductors

    DOEpatents

    Newkirk, Lawrence R.; Valencia, Flavio A.

    1977-01-01

    Bulk coatings of Nb.sub.3 Ge superconductors having transition temperatures in excess of 20 K are readily formed by a chemical vapor deposition technique involving the coreduction of NbCl.sub.5 and GeCl.sub.4 in the presence of hydrogen. The NbCl.sub.5 vapor may advantageously be formed quantitatively in the temperature range of about 250.degree. to 260.degree. C by the chlorination of Nb metal provided the partial pressure of the product NbCl.sub.5 vapor is maintained at or below about 0.1 atm.

  6. The magnetostriction in a superconductor-magnet system under non-uniform magnetic field

    NASA Astrophysics Data System (ADS)

    Li, Xueyi; Jiang, Lang; Wu, Hao; Gao, Zhiwen

    2017-03-01

    This paper describes a numerical model to examine the magnetostriction of bulk high-temperature superconductor (HTS) under non-uniform magnetic field in conjunction with finite element analysis. Through this model, the magnetostriction of homogeneous and nonhomogeneous HTS can be implemented under non-uniform magnetic field. Further, the effects of critical current density, applied field frequency and amplitude are also considered. The computational study can provide a fundamental mechanistic understanding the effects of non-uniform magnetic field on magnetostriction of HTS.

  7. Radiation shielding effectiveness of newly developed superconductors

    NASA Astrophysics Data System (ADS)

    Singh, Vishwanath P.; Medhat, M. E.; Badiger, N. M.; Saliqur Rahman, Abu Zayed Mohammad

    2015-01-01

    Gamma ray shielding effectiveness of superconductors with a high mass density has been investigated. We calculated the mass attenuation coefficients, the mean free path (mfp) and the exposure buildup factor (EBF). The gamma ray EBF was computed using the Geometric Progression (G-P) fitting method at energies 0.015-15 MeV, and for penetration depths up to 40 mfp. The fast-neutron shielding effectiveness has been characterized by the effective neutron removal cross-section of the superconductors. It is shown that CaPtSi3, CaIrSi3, and Bi2Sr2Ca1Cu2O8.2 are superior shielding materials for gamma rays and Tl0.6Rb0.4Fe1.67Se2 for fast neutrons. The present work should be useful in various applications of superconductors in fusion engineering and design.

  8. Charge and spin transport in mesoscopic superconductors

    PubMed Central

    Wolf, M J; Hübler, F; Kolenda, S

    2014-01-01

    Summary Background: Non-equilibrium charge transport in superconductors has been investigated intensely in the 1970s and 1980s, mostly in the vicinity of the critical temperature. Much less attention has been paid to low temperatures and the role of the quasiparticle spin. Results: We report here on nonlocal transport in superconductor hybrid structures at very low temperatures. By comparing the nonlocal conductance obtained by using ferromagnetic and normal-metal detectors, we discriminate charge and spin degrees of freedom. We observe spin injection and long-range transport of pure, chargeless spin currents in the regime of large Zeeman splitting. We elucidate charge and spin transport by comparison to theoretical models. Conclusion: The observed long-range chargeless spin transport opens a new path to manipulate and utilize the quasiparticle spin in superconductor nanostructures. PMID:24605283

  9. High-temperature superconductor antenna investigations

    NASA Astrophysics Data System (ADS)

    Karasack, Vincent G.

    1990-10-01

    The use of superconductors to increase antenna radiation efficiency and gain is examined. Although the gain of all normal-metal antennas can be increased through the use of superconductors, some structures have greater potential for practical improvement than others. Some structures suffer a great degradation in bandwidth when replaced with superconductors, while for others the improvement in efficiency is trivial due to the minimal contribution of the conductor loss mechanism to the total losses, or the already high efficiency of the structure. The following antennas and related structures are discussed: electrically small antennas, impedance matching of antennas, microstrip antennas, microwave and millimeter-wave antenna arrays, and superdirective arrays. The greatest potential practical improvements occur for large microwave and millimeter-wave arrays and the impedance matching of antennas.

  10. High-temperature superconductor antenna investigations

    NASA Technical Reports Server (NTRS)

    Karasack, Vincent G.

    1990-01-01

    The use of superconductors to increase antenna radiation efficiency and gain is examined. Although the gain of all normal-metal antennas can be increased through the use of superconductors, some structures have greater potential for practical improvement than others. Some structures suffer a great degradation in bandwidth when replaced with superconductors, while for others the improvement in efficiency is trivial due to the minimal contribution of the conductor loss mechanism to the total losses, or the already high efficiency of the structure. The following antennas and related structures are discussed: electrically small antennas, impedance matching of antennas, microstrip antennas, microwave and millimeter-wave antenna arrays, and superdirective arrays. The greatest potential practical improvements occur for large microwave and millimeter-wave arrays and the impedance matching of antennas.

  11. Practical superconductor development for electrical power applications

    SciTech Connect

    Goretta, K.C.

    1991-10-01

    Development of useful high-critical-temperature (high-{Tc}) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes technical progress of research and development efforts aimed at producing superconducting components based on the Y-Ba-Cu, Bi-Sr-Ca-Cu, Bi-Pb-Sr-Ca-Cu, and Tl-Ba-Ca-Cu oxides systems. Topics discussed are synthesis and heat treatment of high-{Tc} superconductors, formation of monolithic and composite wires and tapes, superconductor/metal connectors, characterization of structures and superconducting and mechanical properties, and fabrication and properties of thin films. Collaborations with industry and academia are also documented. 10 figs.

  12. Chemistry of high-temperature superconductors.

    PubMed

    Sleight, A W

    1988-12-23

    Spectacular advances in superconductors have taken place in the past two years. The upper temperature for superconductivity has risen from 23 K to 122 K, and there is reason to believe that the ascent is still ongoing. The materials causing this excitement are oxides. Those oxides that superconduct at the highest temperatures contain copper-oxygen sheets; however, other elements such as bismuth and thallium play a key role in this new class of superconductors. These superconductors are attracting attention because of the possibility of a wide range of applications and because the science is fascinating. A material that passes an electrical current with virtually no loss is more remarkable when this occurs at 120 K instead of 20 K.

  13. Practical superconductor development for electrical power applications

    SciTech Connect

    Goretta, K.C.

    1992-10-01

    Development of useful high-critical-temperature (high-[Tc]) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes the technical progress of research and development efforts aimed at producing superconducting components that are based on the Y-Ba-Cu, Bi-Sr-Ca-Cu, Bi-Pb-Sr-Ca-Cu, and (TI,Pb)-(Ba,Sr)-Ca-Cu oxide systems. Topics discussed are synthesis and heat treatment of high-[Tc] superconductors, formation of monolithic and composite wires and tapes, superconductor/metal connectors, characterization of structures and superconducting and mechanical properties, fabrication and properties of thin films, and development of prototype components. Collaborations with industry and academia are documented.

  14. Transverse acousto-electric effect in superconductors

    NASA Astrophysics Data System (ADS)

    Lipavský, P.; Koláček, J.; Lin, P.-J.

    2016-06-01

    We formulate a theory based on the time-dependent Ginzburg-Landau (TDGL) theory and Newtonian vortex dynamics to study the transverse acousto-electric response of a type-II superconductor with Abrikosov vortex lattice. When exposed to a transverse acoustic wave, Cooper pairs emerge from the moving atomic lattice and moving electrons. As in the Tolman-Stewart effect in a normal metal, an electromagnetic field is radiated from the superconductor. We adapt the equilibrium-based TDGL theory to this non-equilibrium system by using a floating condensation kernel. Due to the interaction between normal and superconducting components, the radiated electric field as a function of magnetic field attains a maximum value occurring below the upper critical magnetic field. This local increase in electric field has weak temperature dependence and is suppressed by the presence of impurities in the superconductor.

  15. Fracture toughness for copper oxide superconductors

    DOEpatents

    Goretta, Kenneth C.; Kullberg, Marc L.

    1993-01-01

    An oxide-based strengthening and toughening agent, such as tetragonal Zro.sub.2 particles, has been added to copper oxide superconductors, such as superconducting YBa.sub.2 Cu.sub.3 O.sub.x (123) to improve its fracture toughness (K.sub.IC). A sol-gel coating which is non-reactive with the superconductor, such as Y.sub.2 BaCuO.sub.5 (211) on the ZrO.sub.2 particles minimized the deleterious reactions between the superconductor and the toughening agent dispersed therethrough. Addition of 20 mole percent ZrO.sub.2 coated with 211 yielded a 123 composite with a K.sub.IC of 4.5 MPa(m).sup.0.5.

  16. Fracture toughness for copper oxide superconductors

    DOEpatents

    Goretta, K.C.; Kullberg, M.L.

    1993-04-13

    An oxide-based strengthening and toughening agent, such as tetragonal ZrO[sub 2] particles, has been added to copper oxide superconductors, such as superconducting YBa[sub 2]Cu[sub 3]O[sub x] (123) to improve its fracture toughness (K[sub IC]). A sol-gel coating which is non-reactive with the superconductor, such as Y[sub 2]BaCuO[sub 5] (211) on the ZrO[sub 2] particles minimized the deleterious reactions between the superconductor and the toughening agent dispersed therethrough. Addition of 20 mole percent ZrO[sub 2] coated with 211 yielded a 123 composite with a K[sub IC] of 4.5 MPa(m)[sup 0.5].

  17. Resolving thermoelectric “paradox” in superconductors

    PubMed Central

    Shelly, Connor D.; Matrozova, Ekaterina A.; Petrashov, Victor T.

    2016-01-01

    For almost a century, thermoelectricity in superconductors has been one of the most intriguing topics in physics. During its early stages in the 1920s, the mere existence of thermoelectric effects in superconductors was questioned. In 1944, it was demonstrated that the effects may occur in inhomogeneous superconductors. Theoretical breakthrough followed in the 1970s, when the generation of a measurable thermoelectric magnetic flux in superconducting loops was predicted; however, a major crisis developed when experiments showed puzzling discrepancies with the theory. Moreover, different experiments were inconsistent with each other. This led to a stalemate in bringing theory and experiment into agreement. With this work, we resolve this stalemate, thus solving this long-standing “paradox,” and open prospects for exploration of novel thermoelectric phenomena predicted recently. PMID:26933688

  18. Surface texturing of superconductors by controlled oxygen pressure

    DOEpatents

    Chen, N.; Goretta, K.C.; Dorris, S.E.

    1999-01-05

    A method of manufacture of a textured layer of a high temperature superconductor on a substrate is disclosed. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO{sub 2} atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO{sub 2} atmosphere to cause solidification of the molten superconductor in a textured surface layer. 8 figs.

  19. Thermomagnetic phenomena in the mixed state of high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Meilikhov, E. Z.

    1995-01-01

    Galvano- and thermomagnetic-phenomena in high temperature superconductors, based on kinetic coefficients, are discussed, along with a connection between the electric field and the heat flow in superconductor mixed state. The relationship that determines the transport coefficients of high temperature superconductors in the mixed state based on Seebeck and Nernst effects is developed. It is shown that this relationship is true for a whole transition region of the resistive mixed state of a superconductor. Peltier, Ettingshausen and Righi-Leduc effects associated with heat conductivity as related to high temperature superconductors are also addressed.

  20. Surface texturing of superconductors by controlled oxygen pressure

    DOEpatents

    Chen, Nan; Goretta, Kenneth C.; Dorris, Stephen E.

    1999-01-01

    A method of manufacture of a textured layer of a high temperature superconductor on a substrate. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO.sub.2 atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO.sub.2 atmosphere to cause solidification of the molten superconductor in a textured surface layer.

  1. Vortex core size in unconventional superconductors

    NASA Astrophysics Data System (ADS)

    Zakharchuk, I.; Belova, P.; Safonchik, M.; Traito, K. B.; Lähderanta, E.

    2013-01-01

    Influence of the order parameter symmetries on the cutoff parameter ξh and vortex core size ξ2 (the distance from the vortex center at which the current density reaches the maximum value) in the mixed state are investigated in the framework of Eilenberger theory for unconventional superconductors. The cutoff parameter determines the field distribution in the generalized London equation obtained as a projection of the quasiclassical theory. It is used for the fitting of the μSR and small-angle neutron scattering experimental data. Anisotropic dx2-y2 and isotropic s±-wave superconducting pairings are studied. These pairing symmetries can be realized in iron pnictide superconductors. Conventional s++ pairing mediated electron-phonon interaction is also considered. Temperature, field, and impurity scattering dependences of ξh/ξc2 are obtained. It is found that normalized ξ2/ξc2(B /Bc2) dependence is increasing with pair breaking impurity scattering (interband scattering for s±-wave and intraband impurity scattering for d-wave superconductors). Here, ξc2 is the Ginzburg-Landau coherence length determined from the relation Bc2=Φ0/2πξc22, where Bc2 is an upper critical field and Φ0 is a flux quantum. Two types of ξ2/ξc2(B /Bc2) dependences are obtained for s± superconductors. It has minimum at low temperatures and small impurity scattering transforming in monotonously decreasing function at strong scattering and high temperatures. The second kind of this dependence was also found for d-wave superconductors at intermediate and high temperatures. In contrast, impurity scattering results in decreasing of ξ2/ξc2 field dependence in s++ superconductors.

  2. Iron chalcogenide superconductors at high magnetic fields

    PubMed Central

    Lei, Hechang; Wang, Kefeng; Hu, Rongwei; Ryu, Hyejin; Abeykoon, Milinda; Bozin, Emil S; Petrovic, Cedomir

    2012-01-01

    Iron chalcogenide superconductors have become one of the most investigated superconducting materials in recent years due to high upper critical fields, competing interactions and complex electronic and magnetic phase diagrams. The structural complexity, defects and atomic site occupancies significantly affect the normal and superconducting states in these compounds. In this work we review the vortex behavior, critical current density and high magnetic field pair-breaking mechanism in iron chalcogenide superconductors. We also point to relevant structural features and normal-state properties. PMID:27877518

  3. Electrical connection structure for a superconductor element

    DOEpatents

    Lallouet, Nicolas; Maguire, James

    2010-05-04

    The invention relates to an electrical connection structure for a superconductor element cooled by a cryogenic fluid and connected to an electrical bushing, which bushing passes successively through an enclosure at an intermediate temperature between ambient temperature and the temperature of the cryogenic fluid, and an enclosure at ambient temperature, said bushing projecting outside the ambient temperature enclosure. According to the invention, said intermediate enclosure is filled at least in part with a solid material of low thermal conductivity, such as a polyurethane foam or a cellular glass foam. The invention is applicable to connecting a superconductor cable at cryogenic temperature to a device for equipment at ambient temperature.

  4. High temperature crystalline superconductors from crystallized glasses

    DOEpatents

    Shi, Donglu

    1992-01-01

    A method of preparing a high temperature superconductor from an amorphous phase. The method involves preparing a starting material of a composition of Bi.sub.2 Sr.sub.2 Ca.sub.3 Cu.sub.4 Ox or Bi.sub.2 Sr.sub.2 Ca.sub.4 Cu.sub.5 Ox, forming an amorphous phase of the composition and heat treating the amorphous phase for particular time and temperature ranges to achieve a single phase high temperature superconductor.

  5. Building blocks for correlated superconductors and magnets

    DOE PAGES

    Sarrao, J. L.; Ronning, F.; Bauer, E. D.; ...

    2015-04-01

    Recent efforts at Los Alamos to discover strongly correlated superconductors and hard ferromagnets are reviewed. While serendipity remains a principal engine of materials discovery, design principles and structural building blocks are beginning to emerge that hold potential for predictive discovery. Successes over the last decade with the so-called “115” strongly correlated superconductors are summarized, and more recent efforts to translate these insights and principles to novel hard magnets are discussed. While true “materials by design” remains a distant aspiration, progress is being made in coupling empirical design principles to electronic structure simulation to accelerate and guide materials design and synthesis.

  6. Aluminum-stabilized NB3SN superconductor

    DOEpatents

    Scanlan, Ronald M.

    1988-01-01

    An aluminum-stabilized Nb.sub.3 Sn superconductor and process for producing same, utilizing ultrapure aluminum. Ductile components are co-drawn with aluminum to produce a conductor suitable for winding magnets. After winding, the conductor is heated to convert it to the brittle Nb.sub.3 Sn superconductor phase, using a temperature high enough to perform the transformation but still below the melting point of the aluminum. This results in reaction of substantially all of the niobium, while providing stabilization and react-in-place features which are beneficial in the fabrication of magnets utilizing superconducting materials.

  7. A moving target: responding to magnetic and structural disorder in lanthanide- and actinide-based superconductors

    SciTech Connect

    Bauer, Eric D; Mitchell, Jeremy N; Booth, C H

    2009-01-01

    The effects of various chemical substitutions and induced lattice disorder in the Ce- and Pu-based 115 superconductors are reviewed, with particular emphasis on results from x-ray absorption fine structure (XAFS) measurements. The competition between spin, charge, and lattice interactions is at the heart of many of the strongly-correlated ground states in materials of current interest, such as in colossal magnetoresistors and high-temperature superconductors. This relationship is particularly strong in the CeTIn{sub 5} and PuTGa{sub 5} series (T = Co, Rh, Ir) of heavy-fermion superconductors. In these systems (figure 1), competition between bulk magnetic and non-magnetic ground states, as well as between superconducting and normal states, are directly related to local properties around the lanthanide or actinide ion, such as the nearest-neighbor bond lengths and the local density of states at the Fermi level. Tiny changes in the latter values can easily tip the balance from one ground state to another. This paper reviews recent work by the authors exploring the relationship between local crystal and electronic structure and ground state magnetic and conducting properties in the Ce- and Pu-based 115 materials.

  8. Stabilizing the spin vortex crystal phase in two-dimensional iron-based superconductors

    NASA Astrophysics Data System (ADS)

    O'Halloran, Joseph; Agterberg, D. F.; Chen, M. X.; Weinert, M.

    2017-02-01

    We present an investigation of the magnetic structure for iron-based superconductors (FeSCs) when inversion symmetry is broken, such as in substrate-supported monolayers or in the presence of a c -axis electric field. We perform group-, mean-field-, and density-functional-theoretic analyses on a model system of monolayer iron selenide (FeSe) on a strontium titanate [SrTiO3 (001)] substrate. Our group- and mean-field-theoretic calculations are more generally applicable to thin films of the rest of the 11 (e.g., FeSe) family of iron-based superconductors, as well as to thin films of the 111 (e.g., LiFeAs) and 1111 (e.g., LaOFeAs) families, as these all belong to the same space group. We find that in systems with a collinear antiferromagnetic phase in bulk, when inversion symmetry is broken, the transition is instead into a "spin vortex crystal" phase and that a further phase transition can occur at a lower temperature in some circumstances. The spin vortex crystal is a C4-symmetric magnetic phase which is related to this parent C2-symmetric collinear antiferromagnetic (stripe) phase which is ubiquitous among the iron-based superconductors.

  9. Observation of Majorana fermions in ferromagnetic atomic chains on a superconductor

    NASA Astrophysics Data System (ADS)

    Nadj-Perge, Stevan

    2015-03-01

    Majorana fermions are zero-energy excitations predicted to localize at the edge of a topological superconductor, a state of matter that can form when a ferromagnetic system is placed in proximity to a conventional superconductor with strong spin-orbit interaction. With the goal of realizing a one-dimensional topological superconductor, we have fabricated ferromagnetic iron atomic chains on the surface of superconducting lead. Using high-resolution spectroscopic imaging techniques, we show that the onset of superconductivity, which gaps the electronic density of states in the bulk of the chains, is accompanied by the appearance of zero-energy end-states. This spatially resolved signature provides strong evidence, corroborated by other observations and theoretical modeling, for the formation of a topological phase and edge-bound Majorana states in this system. Our results demonstrates that atomic chains are viable platform for future experiments to manipulate Majorana bound states and to realize other related 1D or 2D topological superconducting phases. This work has done in collaboration with Ilya K. Drozdov, Jian Li, Hua Chen, Sangjun Jeon, Jungpil Seo, Allan H. MacDonald, B. Andrei Bernevig and Ali Yazdani. We acknowledge ONR, NSF-MRSEC, ARO-MRUI, NSF-DMR and EU Marie Curie for support.

  10. Characteristic two-dimensional Fermi surface topology of high-Tc iron-based superconductors.

    PubMed

    Sunagawa, Masanori; Ishiga, Toshihiko; Tsubota, Koji; Jabuchi, Taihei; Sonoyama, Junki; Iba, Keita; Kudo, Kazutaka; Nohara, Minoru; Ono, Kanta; Kumigashira, Hiroshi; Matsushita, Tomohiro; Arita, Masashi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki; Wakita, Takanori; Muraoka, Yuji; Yokoya, Takayoshi

    2014-03-14

    Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors. Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-Tc). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-Tc materials remains unclear. Here we demonstrate a phase of electron-doped CaFe2As2 (La and P co-doped CaFe2As2) with Tc = 45 K, which is the highest Tc found for the AEFe2As2 bulk superconductors (122-type; AE = Alkaline Earth), possesses only cylindrical hole- and electron-like FSs. This result indicates that FS topology consisting only of two-dimensional sheets is characteristic of both hole- and electron-doped 122-type high-Tc superconductors.

  11. Strongly linked current flow in polycrystalline forms of the superconductor MgB2

    NASA Astrophysics Data System (ADS)

    Larbalestier, D. C.; Cooley, L. D.; Rikel, M. O.; Polyanskii, A. A.; Jiang, J.; Patnaik, S.; Cai, X. Y.; Feldmann, D. M.; Gurevich, A.; Squitieri, A. A.; Naus, M. T.; Eom, C. B.; Hellstrom, E. E.; Cava, R. J.; Regan, K. A.; Rogado, N.; Hayward, M. A.; He, T.; Slusky, J. S.; Khalifah, P.; Inumaru, K.; Haas, M.

    2001-03-01

    The discovery of superconductivity at 39K in magnesium diboride, MgB2, raises many issues, a critical one being whether this material resembles a high-temperature copper oxide superconductor or a low-temperature metallic superconductor in terms of its behaviour in strong magnetic fields. Although the copper oxides exhibit very high transition temperatures, their in-field performance is compromized by their large anisotropy, the result of which is to restrict high bulk current densities to a region much less than the full magnetic-field-temperature (H-T) space over which superconductivity is found. Moreover, the weak coupling across grain boundaries makes transport current densities in untextured polycrystalline samples low and strongly sensitive to magnetic field. Here we report that, despite the multiphase, untextured, microscale, subdivided nature of our MgB2 samples, supercurrents flow throughout the material without exhibiting strong sensitivity to weak magnetic fields. Our combined magnetization, magneto-optical, microscopy and X-ray investigations show that the supercurrent density is mostly determined by flux pinning, rather than by the grain boundary connectivity. Our results therefore suggest that this new superconductor class is not compromized by weak-link problems, a conclusion of significance for practical applications if higher temperature analogues of this compound can be discovered.

  12. Topologically protected surface states in a centrosymmetric superconductor β-PdBi2.

    PubMed

    Sakano, M; Okawa, K; Kanou, M; Sanjo, H; Okuda, T; Sasagawa, T; Ishizaka, K

    2015-10-13

    The topological aspects of electrons in solids can emerge in real materials, as represented by topological insulators. In theory, they show a variety of new magneto-electric phenomena, and especially the ones hosting superconductivity are strongly desired as candidates for topological superconductors. While efforts have been made to develop possible topological superconductors by introducing carriers into topological insulators, those exhibiting indisputable superconductivity free from inhomogeneity are very few. Here we report on the observation of topologically protected surface states in a centrosymmetric layered superconductor, β-PdBi2, by utilizing spin- and angle-resolved photoemission spectroscopy. Besides the bulk bands, several surface bands are clearly observed with symmetrically allowed in-plane spin polarizations, some of which crossing the Fermi level. These surface states are precisely evaluated to be topological, based on the Z2 invariant analysis in analogy to three-dimensional strong topological insulators. β-PdBi2 may offer a solid stage to investigate the topological aspect in the superconducting condensate.

  13. Microstructural refinement and enhanced transport properties in binary doped NdFeAsO superconductor

    SciTech Connect

    Aswathy, P. M.; Anooja, J. B.; Varghese, Neson; Syamaprasad, U.

    2014-02-07

    We report the synthesis of Nd{sub 1−x}Ca{sub x}FeAsO{sub 1−2x}F{sub 2x} superconductors using CaF{sub 2} as a binary dopant that provides both holes and electrons by simultaneous substitution of Ca{sup 2+} ions and F{sup −} ions at Nd{sup 3+} and O{sup 2−} sites, respectively. The sample with x = 0.2 exhibits a maximum critical temperature (T{sub C}) of 52.3 K and transport critical current density (J{sub C}) of 1240 A/cm{sup 2} at 12 K. An interesting feature observed for binary doped samples is the preferential alignment of (00l) planes and the refinement of microstructure both in terms of grain size and grain connectivity. NdFeAsO based superconductors are already known for their very high critical fields and field independent J{sub C}(H) performance. However, the development of the bulk superconductors with oriented large grains and good grain connectivity has not been reported so far and hence the present work will be definitely a step towards the progress in NdFeAsO based conductor development.

  14. Odd-frequency pairing and Ising spin susceptibility in time-reversal-invariant superfluids and superconductors

    NASA Astrophysics Data System (ADS)

    Mizushima, Takeshi

    2014-11-01

    We here illustrate the relation between odd-frequency spin-triplet even-parity (OTE) Cooper pairs and anomalous surface magnetic response in time-reversal-invariant (TRI) spin-triplet superfluids and superconductors. The spin susceptibility generally consists of two contributions: even-frequency odd-parity pair amplitudes and odd-frequency even-parity pair amplitudes. The OTE pair amplitudes are absent in the bulk region, but ubiquitously exist in the surface and interface region as Andreev bound states. We here clarify that additional discrete symmetries, originating from the internal symmetry and point-group symmetry, impose strong constraint on the OTE pair amplitudes emergent in the surface of TRI superfluids and superconductors. As a result of the symmetry constraint, the magnetic response of the OTE pairs yields Ising-like anisotropy. For the topological phase of the 3He -B in a restricted geometry, the coupling of the OTE pair amplitudes to an applied field is prohibited by an additional discrete symmetry. Once the discrete symmetry is broken, however, the OTE pairs start to couple to the applied field, which anomalously enhances surface spin susceptibility. Furthermore, we extend this theory to TRI superconductors, where the corresponding discrete symmetry is the mirror reflection symmetry.

  15. Topologically protected surface states in a centrosymmetric superconductor β-PdBi2

    PubMed Central

    Sakano, M.; Okawa, K.; Kanou, M.; Sanjo, H.; Okuda, T.; Sasagawa, T.; Ishizaka, K

    2015-01-01

    The topological aspects of electrons in solids can emerge in real materials, as represented by topological insulators. In theory, they show a variety of new magneto-electric phenomena, and especially the ones hosting superconductivity are strongly desired as candidates for topological superconductors. While efforts have been made to develop possible topological superconductors by introducing carriers into topological insulators, those exhibiting indisputable superconductivity free from inhomogeneity are very few. Here we report on the observation of topologically protected surface states in a centrosymmetric layered superconductor, β-PdBi2, by utilizing spin- and angle-resolved photoemission spectroscopy. Besides the bulk bands, several surface bands are clearly observed with symmetrically allowed in-plane spin polarizations, some of which crossing the Fermi level. These surface states are precisely evaluated to be topological, based on the Z2 invariant analysis in analogy to three-dimensional strong topological insulators. β-PdBi2 may offer a solid stage to investigate the topological aspect in the superconducting condensate. PMID:26460338

  16. Bulk Site Reference Materials

    SciTech Connect

    Barich, J.J. III; Jones, R.R. Sr.

    1996-12-31

    The selection, manufacture and use of Bulk Site Reference Materials (BSRMs) at hazardous waste sites is discussed. BSRMs are useful in preparing stabilization/solidification (S/S) formulations for soils, ranking competing S/S processes, comparing S/S alternatives to other technologies, and in interpreting data from different test types. BSRMs are large volume samples that are representative of the physical and chemical characteristics of a site soil, and that contain contaminants at reasonably high levels. A successful BSRM is extremely homogeneous and well-characterized. While not representative of any point on the site, they contain the contaminants of the site in the matrices of the site. Design objectives for a BSRM are to produce a material that (1) maintains good fidelity to site matrices and contaminants, and (2) exhibits the lowest possible relative standard deviation.

  17. Bulk material handling system

    DOEpatents

    Kleysteuber, William K.; Mayercheck, William D.

    1979-01-01

    This disclosure relates to a bulk material handling system particularly adapted for underground mining and includes a monorail supported overhead and carrying a plurality of conveyors each having input and output end portions with the output end portion of a first of the conveyors positioned above an input end portion of a second of the conveyors, a device for imparting motion to the conveyors to move the material from the input end portions toward the output end portions thereof, a device for supporting at least one of the input and output end portions of the first and second conveyors from the monorail, and the supporting device including a plurality of trolleys rollingly supported by the monorail whereby the conveyors can be readily moved therealong.

  18. Explosive bulk charge

    DOEpatents

    Miller, Jacob Lee

    2015-04-21

    An explosive bulk charge, including: a first contact surface configured to be selectively disposed substantially adjacent to a structure or material; a second end surface configured to selectively receive a detonator; and a curvilinear side surface joining the first contact surface and the second end surface. The first contact surface, the second end surface, and the curvilinear side surface form a bi-truncated hemispherical structure. The first contact surface, the second end surface, and the curvilinear side surface are formed from an explosive material. Optionally, the first contact surface and the second end surface each have a substantially circular shape. Optionally, the first contact surface and the second end surface consist of planar structures that are aligned substantially parallel or slightly tilted with respect to one another. The curvilinear side surface has one of a smooth curved geometry, an elliptical geometry, and a parabolic geometry.

  19. Bulk muscles, loose cables

    PubMed Central

    Liyanage, Chamari R D G; Kodali, Venkata

    2014-01-01

    The accessibility and usage of body building supplements is on the rise with stronger internet marketing strategies by the industry. The dangers posed by the ingredients in them are underestimated. A healthy young man came to the emergency room with palpitations and feeling unwell. Initial history and clinical examination were non-contributory to find the cause. ECG showed atrial fibrillation. A detailed history for any over the counter or herbal medicine use confirmed that he was taking supplements to bulk muscle. One of the components in these supplements is yohimbine; the onset of symptoms coincided with the ingestion of this product and the patient is symptom free after stopping it. This report highlights the dangers to the public of consuming over the counter products with unknown ingredients and the consequential detrimental impact on health. PMID:25326558

  20. Creating bulk nanocrystalline metal.

    SciTech Connect

    Fredenburg, D. Anthony; Saldana, Christopher J.; Gill, David D.; Hall, Aaron Christopher; Roemer, Timothy John; Vogler, Tracy John; Yang, Pin

    2008-10-01

    Nanocrystalline and nanostructured materials offer unique microstructure-dependent properties that are superior to coarse-grained materials. These materials have been shown to have very high hardness, strength, and wear resistance. However, most current methods of producing nanostructured materials in weapons-relevant materials create powdered metal that must be consolidated into bulk form to be useful. Conventional consolidation methods are not appropriate due to the need to maintain the nanocrystalline structure. This research investigated new ways of creating nanocrystalline material, new methods of consolidating nanocrystalline material, and an analysis of these different methods of creation and consolidation to evaluate their applicability to mesoscale weapons applications where part features are often under 100 {micro}m wide and the material's microstructure must be very small to give homogeneous properties across the feature.

  1. Bulk amorphous materials

    SciTech Connect

    Schwarz, R.B.; Archuleta, J.I.; Sickafus, K.E.

    1998-12-01

    This is the final report for a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this work was to develop the competency for the synthesis of novel bulk amorphous alloys. The authors researched their synthesis methods and alloy properties, including thermal stability, mechanical, and transport properties. The project also addressed the development of vanadium-spinel alloys for structural applications in hostile environments, the measurement of elastic constants and thermal expansion in single-crystal TiAl from 300 to 750 K, the measurement of elastic constants in gallium nitride, and a study of the shock-induced martensitic transformations in NiTi alloys.

  2. Giant supercurrent states in a superconductor-InAs/GaSb-superconductor junction

    SciTech Connect

    Shi, Xiaoyan Pan, W.; Hawkins, S. D.; Klem, J. F.; Yu, Wenlong; Jiang, Zhigang; Andrei Bernevig, B.

    2015-10-07

    Superconductivity in topological materials has attracted a great deal of interest in both electron physics and material sciences since the theoretical predictions that Majorana fermions can be realized in topological superconductors. Topological superconductivity could be realized in a type II, band-inverted, InAs/GaSb quantum well if it is in proximity to a conventional superconductor. Here, we report observations of the proximity effect induced giant supercurrent states in an InAs/GaSb bilayer system that is sandwiched between two superconducting tantalum electrodes to form a superconductor-InAs/GaSb-superconductor junction. Electron transport results show that the supercurrent states can be preserved in a surprisingly large temperature-magnetic field (T – H) parameter space. In addition, the evolution of differential resistance in T and H reveals an interesting superconducting gap structure.

  3. Revealing Surface States in In-Doped SnTe Nanoplates with Low Bulk Mobility.

    PubMed

    Shen, Jie; Xie, Yujun; Cha, Judy J

    2015-06-10

    Indium (In) doping in topological crystalline insulator SnTe induces superconductivity, making In-doped SnTe a candidate for a topological superconductor. SnTe nanostructures offer well-defined nanoscale morphology and high surface-to-volume ratios to enhance surface effects. Here, we study In-doped SnTe nanoplates, In(x)Sn(1-x)Te, with x ranging from 0 to 0.1 and show they superconduct. More importantly, we show that In doping reduces the bulk mobility of In(x)Sn(1-x)Te such that the surface states are revealed in magnetotransport despite the high bulk carrier density. This is manifested by two-dimensional linear magnetoresistance in high magnetic fields, which is independent of temperature up to 10 K. Aging experiments show that the linear magnetoresistance is sensitive to ambient conditions, further confirming its surface origin. We also show that the weak antilocalization observed in In(x)Sn(1-x)Te nanoplates is a bulk effect. Thus, we show that nanostructures and reducing the bulk mobility are effective strategies to reveal the surface states and test for topological superconductors.

  4. Influence of Critical Current Density on Magnetic Force of Htsc Bulk above Pmr with 3D-MODELING Numerical Solutions

    NASA Astrophysics Data System (ADS)

    Lu, Yiyun; Lu, Bingjuan; Ge, Yunwang; Chen, Wenqing

    Numerical electromagnetic field simulations of high-temperature superconductors (HTSC) bulk were carried out to calculate the magnetic force between the HTSC bulk and the permanent magnet railway (PMR). A 3D-modeling numerical calculation method is proposed using the finite element method. The model is formulated with the magnetic field vector (H-method). The resulting code was written with FORTRAN language. The electric field intensity E and the current density J constitutive relation of HTSC were described with E-J power law. The Kim macro-model is used to describe critical current density Jc of HTSC bulk. Two virtual HTSC bulks were used to solve the critical current density Jc anisotropic properties of HTSC materials. A superconducting levitation system composed of one HTSC bulk and PMR is successfully investigated using the proposed method. By this method, the influence of critical current density on magnetic levitation force of the superconducting levitation system is mathematically studied.

  5. Experimental Studies on Penetration Depth in Yttrium BARIUM(2)COPPER(3)OXIDE(7-DELTA) Superconductors

    NASA Astrophysics Data System (ADS)

    Lee, Juyoung

    There is growing evidence for a d-wave order parameter in high-T_{c} superconductors, which is of a great concern these days. The magnetic penetration depth lambda(T) of d-wave superconductors is predicted to be very sensitive to impurity effects: a rapid increase of lambda(0) and a decrease in the curvature of deltalambda(T) at low T should occur in disordered d-wave superconductors. Therefore, measurements of lambda(T) in deliberately disordered samples can lead to crucial information on the existence of a d-wave order parameter. We performed detailed penetration depth measurements on rm YBa _2Cu_3O_{7-delta} thin films by a two-coil method. Systematic oxygen depletion of the thin films is also made. lambda^2(0)/ lambda^2(T/T_{c}) vs T/T_{c} is the same for all films, even when oxygen is depleted. Also T _{c} vs 1/lambda^2(0) , reproduces the muSR results of Uemura et al. on bulk sample. This strongly suggests that the measured 1/lambda^2(T) is the property of superconducting grains, not the effect of "damaged" material like grain boundaries. There is extremely good agreement of lambda(T/T_{c}) between the thin films and Hardy's single crystal data above a crossover temperature of 25K, and also a deviation below the crossover temperature. The deviation at low T is quantified by two low T parameters: the increase of lambda(0) and the decrease in the curvature of lambda(T) at low T. Our result is consistent with the d -wave model analyzed by Hirschfeld et al., thus supporting a d-wave energy gap in high-T_{c} superconductors. This research has been supported by DOE Grant No. DE-FG02-90ER45427 through Midwest Superconductivity Consortium.

  6. Refined characterization of lattice Chern insulators by bulk entanglement spectrum

    NASA Astrophysics Data System (ADS)

    Chiou, Dah-Wei; Kao, Hsien-Chung; Lin, Feng-Li

    2016-12-01

    We have studied extensively the band-crossing patterns of the bulk entanglement spectrum (BES) for various lattice Chern insulators. We find that only partitions with dual symmetry can have either stable nodal lines or nodal points in the BES when the system is in the topological phase of a nonzero Chern number. By deforming the Hamiltonian to lift the accidental symmetry, one can see that only nodal points are robust. They thus should bear certain topological characteristics of the BES. By studying the band-crossing patterns in detail, we conclude that the topological characteristics of the BES are inherited from the topological order of the underlying Chern insulators, and the former can have more refined topological structures. We then conjecture that the sum of the vorticities in the BES in a properly chosen reduced Brillouin zone equals the Chern number of the underlying Chern insulator. This relation is beyond the usual classification scheme of topological insulators/superconductors.

  7. Enhancing critical current density of cuprate superconductors

    DOEpatents

    Chaudhari, Praveen

    2015-06-16

    The present invention concerns the enhancement of critical current densities in cuprate superconductors. Such enhancement of critical current densities include using wave function symmetry and restricting movement of Abrikosov (A) vortices, Josephson (J) vortices, or Abrikosov-Josephson (A-J) vortices by using the half integer vortices associated with d-wave symmetry present in the grain boundary.

  8. Monopoles and fractional vortices in chiral superconductors

    PubMed Central

    Volovik, G. E.

    2000-01-01

    I discuss two exotic objects that must be experimentally identified in chiral superfluids and superconductors. These are (i) the vortex with a fractional quantum number (N = 1/2 in chiral superfluids, and N = 1/2 and N = 1/4 in chiral superconductors), which plays the part of the Alice string in relativistic theories and (ii) the hedgehog in the ^l field, which is the counterpart of the Dirac magnetic monopole. These objects of different dimensions are topologically connected. They form the combined object that is called a nexus in relativistic theories. In chiral superconductors, the nexus has magnetic charge emanating radially from the hedgehog, whereas the half-quantum vortices play the part of the Dirac string. Each half-quantum vortex supplies the fractional magnetic flux to the hedgehog, representing 1/4 of the “conventional” Dirac string. I discuss the topological interaction of the superconductor's nexus with the ‘t Hooft–Polyakov magnetic monopole, which can exist in Grand Unified Theories. The monopole and the hedgehog with the same magnetic charge are topologically confined by a piece of the Abrikosov vortex. Such confinement makes the nexus a natural trap for the magnetic monopole. Other properties of half-quantum vortices and monopoles are discussed as well, including fermion zero modes. PMID:10716980

  9. Iron-based superconductors: Unity or diversity?

    SciTech Connect

    Kivelson, S. A.

    2010-02-24

    Superconductivity is among the most fascinating properties that a material can show. On the fundamental level, it represents a direct, macroscopic manifestation of coherent quantum mechanical behaviour, and its potential practical importance is almost unlimited, especially if new superconductors can be synthesized or discovered with still higher transition temperatures, Tc.

  10. Stripe phases in high-temperature superconductors

    PubMed Central

    Emery, V. J.; Kivelson, S. A.; Tranquada, J. M.

    1999-01-01

    Stripe phases are predicted and observed to occur in a class of strongly correlated materials describable as doped antiferromagnets, of which the copper-oxide superconductors are the most prominent representatives. The existence of stripe correlations necessitates the development of new principles for describing charge transport and especially superconductivity in these materials. PMID:10430848

  11. Stripe Phases in High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Emery, V. J.; Kivelson, S. A.; Tranquada, J. M.

    1999-08-01

    Stripe phases are predicted and observed to occur in a class of strongly correlated materials describable as doped antiferromagnets, of which the copper-oxide superconductors are the most prominent representatives. The existence of stripe correlations necessitates the development of new principles for describing charge transport and especially superconductivity in these materials.

  12. Stripe phases in high-temperature superconductors.

    PubMed

    Emery, V J; Kivelson, S A; Tranquada, J M

    1999-08-03

    Stripe phases are predicted and observed to occur in a class of strongly correlated materials describable as doped antiferromagnets, of which the copper-oxide superconductors are the most prominent representatives. The existence of stripe correlations necessitates the development of new principles for describing charge transport and especially superconductivity in these materials.

  13. Orientational order in disordered superconductors

    SciTech Connect

    Toner, J. )

    1991-05-13

    Orientational order in weakly pinned Abrikosov flux lattices is studied, taking into account two heretofore neglected effects: dislocations and orientational couplings to the underlying lattice. Without orientational couplings, arbitrarily weak pinning destroys long-ranged orientational order for all spatial dimensions {ital d}{lt}4. Orientational couplings stabilize long-ranged orientational order. For fields along an axis of {ital fourfold} symmetry, {ital sixfold} (hexatic) orientational order is described by a random-field Ising model, and so does not occur in {ital d}=2 (thin films) but does in {ital d}=3 (bulk).

  14. Organized Nanorod-Superconductor Composites.

    DTIC Science & Technology

    2007-11-02

    34 Preparation of Carbide Nanorods", 08/814,745, patent pending. 3. CM. Lieber and P. Yang, "Method of Producing Metal Oxide Nanorods", 08/790,824, patent...Growth of Nanowires Using Laser-Generated Nanoclusters ", Gordon Research Conference on Laser Interactions with Materials, Andover, NH, June 1998...to prepare MgO nanorods; (2) the preparation of MgO nanorod/HTS bulk composites with HTS = Bi2Sr2CaCu208 (BSCCO-2212) and Bi^Ca^O,,, (BSCCO-2223); (3

  15. A review of finite size effects in quasi-zero dimensional superconductors.

    PubMed

    Bose, Sangita; Ayyub, Pushan

    2014-11-01

    Quantum confinement and surface effects (SEs) dramatically modify most solid state phenomena as one approaches the nanometer scale, and superconductivity is no exception. Though we may expect significant modifications from bulk superconducting properties when the system dimensions become smaller than the characteristic length scales for bulk superconductors-such as the coherence length or the penetration depth-it is now established that there is a third length scale which ultimately determines the critical size at which Cooper pairing is destroyed. In quasi-zero-dimensional (0D) superconductors (e.g. nanocrystalline materials, isolated or embedded nanoparticles), one may define a critical particle diameter below which the mean energy level spacing arising from quantum confinement becomes equal to the bulk superconducting energy gap. The so-called Anderson criterion provides a remarkably accurate estimate of the limiting size for the destabilization of superconductivity in nanosystems. This review of size effects in quasi-0D superconductors is organized as follows. A general summary of size effects in nanostructured superconductors (section 1) is followed by a brief overview of their synthesis (section 2) and characterization using a variety of techniques (section 3). Section 4 reviews the size-evolution of important superconducting parameters-the transition temperature, critical fields and critical current-as the Anderson limit is approached from above. We then discuss the effect of thermodynamic fluctuations (section 5), which become significant in confined systems. Improvements in fabrication methods and the increasing feasibility of addressing individual nanoparticles using scanning probe techniques have lately opened up new directions in the study of nanoscale superconductivity. Section 6 reviews both experimental and theoretical aspects of the recently discovered phenomena of 'parity effect' and 'shell effect' that lead to a strong, non-monotonic size

  16. Spatial Complexity Due to Bulk Electronic Liquid Crystals in Superconducting Dy-Bi2212

    NASA Astrophysics Data System (ADS)

    Carlson, Erica; Phillabaum, Benjamin; Dahmen, Karin

    2012-02-01

    Surface probes such as scanning tunneling microscopy (STM) have detected complex electronic patterns at the nanoscale in many high temperature superconductors. In cuprates, the pattern formation is associated with the pseudogap phase, a precursor to the high temperature superconducting state. Rotational symmetry breaking of the host crystal (i.e. from C4 to C2) in the form of electronic nematicity has recently been proposed as a unifying theme of the pseudogap phase [Lawler Nature 2010]. However, the fundamental physics governing the nanoscale pattern formation has not yet been identified. Here we use universal cluster properties extracted from STM studies of cuprate superconductors to identify the funda- mental physics controlling the complex pattern formation. We find that due to a delicate balance between disorder, interactions, and material anisotropy, the rotational symmetry breaking is fractal in nature, and that the electronic liquid crystal extends throughout the bulk of the material.

  17. Bulk superconductivity at 2.6 K in undoped RbFe2As2

    NASA Astrophysics Data System (ADS)

    Bukowski, Z.; Weyeneth, S.; Puzniak, R.; Karpinski, J.; Batlogg, B.

    2010-12-01

    The iron arsenide RbFe2As2 with the ThCr2Si2-type structure is found to be a bulk superconductor with T=2.6K. The onset of diamagnetism was used to estimate the upper critical field H(T), resulting in μ0dH/dT≃-1.4T/K and an extrapolated μ0H(0)≃2.5T. As a new representative of iron pnictide superconductors, superconducting RbFe2As2 contrasts with BaFe2As2, where the Fermi level is higher and a magnetic instability is observed. Thus, the solid solution series (Rb, Ba)Fe2As2 is a promising system to study the cross-over from superconductivity to magnetism.

  18. Isotope and multiband effects in layered superconductors.

    PubMed

    Bussmann-Holder, Annette; Keller, Hugo

    2012-06-13

    In this review we consider three classes of superconductors, namely cuprate superconductors, MgB(2) and the new Fe based superconductors. All of these three systems are layered materials and multiband compounds. Their pairing mechanisms are under discussion with the exception of MgB(2), which is widely accepted to be a 'conventional' electron-phonon interaction mediated superconductor, but extending the Bardeen-Cooper-Schrieffer (BCS) theory to account for multiband effects. Cuprates and Fe based superconductors have higher superconducting transition temperatures and more complex structures. Superconductivity is doping dependent in these material classes unlike in MgB(2) which, as a pure compound, has the highest values of T(c) and a rapid suppression of superconductivity with doping takes place. In all three material classes isotope effects have been observed, including exotic ones in the cuprates, and controversial ones in the Fe based materials. Before the area of high-temperature superconductivity, isotope effects on T(c) were the signature for phonon mediated superconductivity-even when deviations from the BCS value to smaller values were observed. Since the discovery of high T(c) materials this is no longer evident since competing mechanisms might exist and other mediating pairing interactions are discussed which are of purely electronic origin. In this work we will compare the three different material classes and especially discuss the experimentally observed isotope effects of all three systems and present a rather general analysis of them. Furthermore, we will concentrate on multiband signatures which are not generally accepted in cuprates even though they are manifest in various experiments, the evidence for those in MgB(2), and indications for them in the Fe based compounds. Mostly we will consider experimental data, but when possible also discuss theoretical models which are suited to explain the data.

  19. Recrystallization of high temperature superconductors

    SciTech Connect

    Kouzoudis, Dimitris

    1996-05-09

    Currently one of the most widely used high Tc superconductors is the Bi-based compounds Bi2Sr2CaCu2Oz and Bi2Sr2Ca2Cu3Oz (known as BSCCO 2212 and 2223 compounds) with Tc values of about 85 K and 110 K respectively. Lengths of high performance conductors ranging from 100 to 1000 m long are routinely fabricated and some test magnets have been wound. An additional difficulty here is that although Bi-2212 and Bi-2223 phases exist over a wide range of stoichiometries, neither has been prepared in phase-pure form. So far the most successful method of constructing reliable and robust wires or tapes is the so called powder-in-tube (PIT) technique [1, 2, 3, 4, 5, 6, 7] in which oxide powder of the appropriate stoichiometry and phase content is placed inside a metal tube, deformed into the desired geometry (round wire or flat tape), and annealed to produce the desired superconducting properties. Intermediate anneals are often incorporated between successive deformation steps. Silver is the metal used in this process because it is the most compatible with the reacting phase. In all of the commercial processes for BSCCO, Ag seems to play a special catalytic role promoting the growth of high performance aligned grains that grow in the first few micrometers near the Ag/BSCCO interface. Adjacent to the Ag, the grain alignment is more perfect and the current density is higher than in the center of the tape. It is known that Ag lowers the melting point of several of the phases but the detailed mechanism for growth of these high performance grains is not clearly understood. The purpose of this work is to study the nucleation and growth of the high performance material at this interface.

  20. Hydrostatic pressure: A very effective approach to significantly enhance critical current density in granular iron pnictide superconductors

    PubMed Central

    Shabbir, Babar; Wang, Xiaolin; Ghorbani, S. R.; Shekhar, Chandra; Dou, Shixue; Srivastava, O. N.

    2015-01-01

    Pressure is well known to significantly raise the superconducting transition temperature, Tc, in both iron pnictides and cuprate based superconductors. Little work has been done, however, on how pressure can affect the flux pinning and critical current density in the Fe-based superconductors. Here, we propose to use hydrostatic pressure to significantly enhance flux pinning and Tc in polycrystalline pnictide bulks. We have chosen Sr4V2O6Fe2As2 polycrystalline samples as a case study. We demonstrate that the hydrostatic pressure up to 1.2 GPa can not only significantly increase Tc from 15 K (underdoped) to 22 K, but also significantly enhance the irreversibility field, Hirr, by a factor of 4 at 7 K, as well as the critical current density, Jc, by up to 30 times at both low and high fields. It was found that pressure can induce more point defects, which are mainly responsible for the Jc enhancement. Our findings provide an effective method to significantly enhance Tc, Jc, Hirr, and the upper critical field, Hc2, for other families of Fe-based superconductors in the forms of wires/tapes, films, and single crystal and polycrystalline bulks. PMID:25645351

  1. Critical Current Density and Bulk Pinning Force in RHQT-Processed Niobium-Aluminum Superconductors

    NASA Astrophysics Data System (ADS)

    Buta, F.; Sumption, M. D.; Collings, E. W.

    2004-06-01

    Transformation heat treatments with short excursions (1-10 min) to 1000°C preceding the conventional 800°C/10h were applied to jelly-roll Nb-Al samples that had been rapidly heated and quenched (RHQ) in bcc phase from high temperatures. The critical current density dependence on magnetic field at 4.2K in magnetic fields ranging from 0 to 8.5T was determined from magnetization measurements performed by Vibrating Sample Magnetometry. It was found that in this range of magnetic fields the highest critical current densities are not necessarily obtained for the samples with the highest initial heating rate of the transformation heat treatment as it is the case at magnetic fields in the vicinity of 20T. The highest pinning force density is present in samples that were transformed by rapid insertion in a furnace preheated to 1000°C and not in samples that were ohmically heated to 1000°C (the fastest heating rate employed).

  2. Preparation of a melt-processed La123 bulk superconductor with finely dispersed Y211 particle

    NASA Astrophysics Data System (ADS)

    Hee-Gyoun Lee; Il-Hyun Kook; Gye-Won Hong; Kyu-Won Lee; Yong-Il Kim; Chang-Soo Kim; Jong-Jin Kim; Myoung-Youp Song

    1995-02-01

    A high-magnetization La123 specimen with finely dispersed second-phase particles was successfully fabricated by a melt process under a reduced oxygen partial pressure. The dispersion of the fine second-phase particle was obtained by adding Y211 particles to the La123 specimen. The melt-down and the crack propagation were effectively suppressed in a melt-processed specimen with Y211 addition. The magnetization of the La123 specimen was clearly enhanced with Y211 addition. It is considered that the Y211 addition introduced extra flux-pinning centers in the La123 specimen.

  3. Interaction of Two Parallel Cracks in REBCO Bulk Superconductors under Applied Magnetic Field

    NASA Astrophysics Data System (ADS)

    Zhao-Xia, Zhang; Feng, Xue; Xiao-Fan, Gou

    2016-07-01

    Not Available Supported by the National Natural Science Foundation of China under Grant Nos 11372096 and 11402073, the National Research Foundation for the Doctoral Program of Higher Education of China, and the Natural Science Foundation of Jiangsu Province under Grant No BK20130824.

  4. Analysis of Magnetic Critical Fields in Iron-Based SmFeAsO0.85 HIGH-Tc Superconductor

    NASA Astrophysics Data System (ADS)

    Ahmad, Dawood; Song, Tae Kwon; Park, In Suk; Kim, G. C.; Ren, Zhi-An; Kim, Y. C.

    The magnetic properties of the newly discovered iron-oxypnictide SmFeAsO0.85 high-Tc superconductor with a Tc of around 55 K were investigated. Bulk SmFeAsO0.85 was prepared by a method for high-pressure synthesis. The lower critical field Hc1 was estimated from the magnetization at low fields; Hc1(0) was measured to be 212 Oe. A linear temperature dependence instead of saturation at low temperatures in Hc1(T) revealed unconventional superconductivity with a nodal gap structure in our SmFeAsO0.85 superconductor. The results showed that the well-known secondary peak in the temperature dependence of the critical current density Jc is absent in the SmFeAsO0.85 high-Tc superconductor. The irreversibility line Birr was fitted well by the power law dependence (1 - T/Tc)n with n ~ 1.5. This is indicative of the flux creep phenomena in the SmFeAsO0.85 high-Tc superconductor. In addition, within the range of measurement temperatures in this study, no crossover was observed in the temperature dependence of the irreversibility line Birr which may be due to low anisotropy in our SmFeAsO0.85 superconductor.

  5. MgB2 superconductors with abnormally improved Jc sintered after autoxidation of milled original powders

    NASA Astrophysics Data System (ADS)

    Ma, Zongqing; Liu, Yongchang; Huo, Jie; Gao, Zhiming

    2009-12-01

    An autoxidation treatment of short-time milled original powders was introduced for the synthesis of MgB2 superconductors and the critical current density Jc of the sintered MgB2 bulks was measured. It is unusually found that the undoped MgB2 bulks sintered with those autoxided milled original powder exhibit abnormally excellent Jc (above 1×104 A cm-2 even at 3.5 T, 20 K). Combined with the investigation of sintering process, it was found that the autoxidation treatment of the milled powders affects the subsequent sintering process dramatically and finally leads to the formation of MgB2 nanocrystalline with lots of dislocation and self-generated MgO nanoinclusions embedded in them. This unique microstructure brought up a significant improvement of Jc at high fields. Besides, the formation mechanism of this unique microstructure during the sintering process was also discussed in detail. It suggested that the MgO preformed by the reaction between Mg and B2O3 in the interface between Mg particles and B particles might serve as nuclei for the heterogeneous nucleation of the MgB2 phase and finally be included in the MgB2 grains as they grew up. The present method provides possible windows for the development of practical MgB2 superconductors without adopting expensive nanodopants.

  6. Flux-induced Nernst effect in low-dimensional superconductors

    NASA Astrophysics Data System (ADS)

    Berger, Jorge

    2017-02-01

    A method is available that enables consistent study of the stochastic behavior of a system that obeys purely diffusive evolution equations. This method has been applied to a superconducting loop with nonuniform temperature, with average temperature close to Tc. It is found that a flux-dependent average potential difference arises along the loop, proportional to the temperature gradient and most pronounced in the direction perpendicular to this gradient. The largest voltages were obtained for fluxes close to 0.3Φ0, average temperatures slightly below the critical temperature, thermal coherence length of the order of the perimeter of the ring, BCS coherence length that is not negligible in comparison to the thermal coherence length, and short inelastic scattering time. This effect is entirely due to thermal fluctuations. It differs essentially from the usual Nernst effect in bulk superconductors, that is induced by magnetic field rather than by magnetic flux. We also study the effect of confinement in a 2D mesoscopic film.

  7. The rich structure of Gauss-Bonnet holographic superconductors

    NASA Astrophysics Data System (ADS)

    Barclay, Luke

    2011-10-01

    We study fully backreacting, Gauss-Bonnet (GB) holographic superconductors in 5 bulk spacetime dimensions. We explore the system's dependence on the scalar mass for both positive and negative GB coupling, α. We find that when the mass approaches the Breitenlohner-Freedman (BF) bound and α → L 2 /4 the effect of backreaction is to increase the critical temperature, T c, of the system: the opposite of its effect in the rest of parameter space. We also find that reducing α below zero increases T c and that the effect of backreaction is diminished. We study the zero temperature limit, proving that this system does not permit regular solutions for a non-trivial, tachyonic scalar field and constrain possible solutions for fields with positive masses. We investigate singular, zero temperature solutions in the Einstein limit but find them to be incompatible with the concept of GB gravity being a perturbative expansion of Einstein gravity. We study the conductivity of the system, finding that the inclusion of backreaction hinders the development of poles in the conductivity that are associated with quasi-normal modes approaching the real axis from elsewhere in the complex plane.

  8. Theoretical study of pair density wave superconductors

    NASA Astrophysics Data System (ADS)

    Zheng, Zhichao

    In conventional superconductors, the Cooper pairs are formed from quasiparticles. We explore another type of superconducting state, a pair density wave (PDW) order, which spontaneously breaks some of the translational and point group symmetries. In a PDW superconductor, the order parameter is a periodic function of the center-of-mass coordinate, and the spatial average value of the superconducting order parameter vanishes. In the early 1960s, following the success of the BCS theory of superconductivity, Fulde and Ferrell and Larkin and Ovchinnikov (FFLO) developed theories of inhomogeneous superconducting states. Because of this Zeeman splitting in a magnetic field, the Cooper pairs having a nonzero center-of-mass momentum are more stable than the normal pairing, leading to the FFLO state. Experiments suggest possible occurrence of the FFLO state in the heavy-fermion compound CeCoIn5, and in quasi-low-dimensional organic superconductors. FFLO phases have also been argued to be of importance in understanding ultracold atomic Fermi gases and in the formation of color superconductivity in high density quark matter. In all Fermi superfluids known at the present time, Cooper pairs are composed of particles with spin 1/2. The spin component of a pair wave function can be characterized by its total spin S = 0 (singlet) and S = 1 (triplet). In the discovered broken inversion superconductors CePt3Si, Li2Pt3B, and Li2Pd3B, the magnetic field leads to novel inhomogeneous superconducting states, namely the helical phase and the multiple-q phase. Its order parameter exhibits periodicity similar to FFLO phase, and the consequences of both phases are same: the enhancement of transition temperature as a function of magnetic field. We have studied the PDW phases in broken parity superconductors with vortices included. By studying PDW vortex states, we find the usual Abrikosov vortex solution is unstable against a new solution with fractional vortex pairs. We have also studied the

  9. Low resistivity contact to iron-pnictide superconductors

    DOEpatents

    Tanatar, Makariy; Prozorov, Ruslan; Ni, Ni; Bud& #x27; ko, Sergey; Canfield, Paul

    2013-05-28

    Method of making a low resistivity electrical connection between an electrical conductor and an iron pnictide superconductor involves connecting the electrical conductor and superconductor using a tin or tin-based material therebetween, such as using a tin or tin-based solder. The superconductor can be based on doped AFe.sub.2As.sub.2, where A can be Ca, Sr, Ba, Eu or combinations thereof for purposes of illustration only.

  10. Ferrite-superconductor devices for advanced microwave applications

    SciTech Connect

    Dionne, G.F.; Oates, D.E.; Temme, D.H.; Weiss, J.A.

    1996-07-01

    Microwave devices comprising magnetized ferrite in contact with superconductor circuits designed to eliminate magnetic field penetration of the superconductor have demonstrated phase shift without significant conduction losses. The device structures are adaptable to low- or high-{Tc} superconductors. A nonoptimized design of a ferrite phase shifter that employs niobium or YBCO meanderlines has produced over 1,000 degrees of differential phase shift with a figure of merit exceeding 1,000 degrees/dB at X band. By combining superconductor meanderline sections with alternating T junctions on a ferrite substrate in a configuration with three-fold symmetry, a low-loss three-port switching circulator has been demonstrated.

  11. Method and apparatus to trigger superconductors in current limiting devices

    DOEpatents

    Yuan, Xing; Hazelton, Drew Willard; Walker, Michael Stephen

    2004-10-26

    A method and apparatus for magnetically triggering a superconductor in a superconducting fault current limiter to transition from a superconducting state to a resistive state. The triggering is achieved by employing current-carrying trigger coil or foil on either or both the inner diameter and outer diameter of a superconductor. The current-carrying coil or foil generates a magnetic field with sufficient strength and the superconductor is disposed within essentially uniform magnetic field region. For superconductor in a tubular-configured form, an additional magnetic field can be generated by placing current-carrying wire or foil inside the tube and along the center axial line.

  12. Sealed glass coating of high temperature ceramic superconductors

    DOEpatents

    Wu, W.; Chu, C.Y.; Goretta, K.C.; Routbort, J.L.

    1995-05-02

    A method and article of manufacture of a lead oxide based glass coating on a high temperature superconductor is disclosed. The method includes preparing a dispersion of glass powders in a solution, applying the dispersion to the superconductor, drying the dispersion before applying another coating and heating the glass powder dispersion at temperatures below oxygen diffusion onset and above the glass melting point to form a continuous glass coating on the superconductor to establish compressive stresses which enhance the fracture strength of the superconductor. 8 figs.

  13. Symmetry and topology of noncentrosymmetric superconductors

    SciTech Connect

    Samokhin, K.V.

    2015-08-15

    We present a detailed analysis of the pairing symmetry and the order parameter topology in superconductors without centre of inversion. Strong spin–orbit coupling of electrons with the crystal lattice leads to a large splitting of the Bloch bands, which makes it necessary to use a multiband description of superconductivity. We identify stable superconducting states and derive the Bogoliubov–de Gennes Hamiltonian, which determines the spectrum of fermionic quasiparticles. To develop a topological classification of the superconducting states we introduce two different types of topological invariants, the Chern numbers and the Maurer–Cartan invariants, and apply them to three-dimensional noncentrosymmetric superconductors, both with and without time reversal symmetry breaking.

  14. Surface superconductivity of short coherence length superconductors

    NASA Astrophysics Data System (ADS)

    Chen, J. L.; Yang, T. J.

    1994-09-01

    Based on the theory of Valls et al. for short coherence length superconductors, de Gennes' boundary theory for conventional superconductors with ξ 0≫ K-1F may be modified. We solve the G-L equation exactly under zero magnetic field for various temperatures. The order parameter Ψ( x) is not depleted but enhanced near the surface. We also obtain some interesting results: Tc will be enhanced by contracting of the thickness of a superconducting film. The nucleation field Hc3 ( T)∝( Tcb- T) near Tcb; and H c3(T)∝(T c-T) {1}/{2} near Tc. The critical current in SIS Josephson junctions Jc( T)∝( Tc- T)+√ 2 τ0( T0- T) for T< Tcb; and Jc( T)∝( Tc- T) for Tcb≤ T< Tc.

  15. Proximity effects in ferromagnet-superconductor structures

    NASA Astrophysics Data System (ADS)

    Halterman, Klaus Byron

    I present an extensive theoretical investigation of the proximity effects that occur in ferromagnet/superconductor systems. I use a numerical method to solve self consistently the Bogoliubov-de Gennes equations in the continuum. I obtain the pair amplitude and the local density of states (DOS), and use these results to extract the relevant lengths characterizing both the leakage of superconductivity into the magnet and to study spin splitting induced in the superconductor. These phenomena are investigated as a function of parameters such as temperature, magnet polarization, interfacial scattering, sample size and Fermi wave vector mismatch, all of which turn out to have an important influence on the results. These comprehensive results should help characterize and analyze future data, and are shown to be in agreement with existing experiments.

  16. Unconventional Disorder Effects in Correlated Superconductors

    NASA Astrophysics Data System (ADS)

    Gastiasoro, Maria N.; Bernardini, Fabio; Andersen, Brian M.

    2016-12-01

    We study the effects of disorder on unconventional superconductors in the presence of correlations, and explore a novel correlated disorder paradigm dominated by strong deviations from standard Abrikosov-Gor'kov theory due to generation of local bound states and cooperative impurity behavior driven by Coulomb interactions. Specifically we explain under which circumstances magnetic disorder acts as a strong poison destroying high-Tc superconductivity at the sub-1% level, and when nonmagnetic disorder, counterintuitively, hardly affects the unconventional superconducting state while concomitantly inducing an inhomogeneous full-volume magnetic phase. Recent experimental studies of Fe-based superconductors have discovered that such unusual disorder behavior seems to be indeed present in those systems.

  17. Method for preparing superconductors ceramic composition

    SciTech Connect

    Akinc, M.; Celikkaya, A.

    1990-03-06

    This patent describes a process of forming a superconductor ceramic of the formula: YBa{sub 2}Cu{sub 3}O{sub {ital x}} wherein x is from about 6.5 to bout 7.2. It comprises: heating a solid phase copper salt selected from the group of copper acetate and copper nitrate and solid phase barium hydroxide to a temperature high enough to form a meltphase; and adding to the melt a salt, hydroxide or oxide as a source of yttrium with stirring to provide a substantially homogeneous mixture, the quantities of each of said copper salt, barium hydroxide and yttrium source being sufficient to yield a Y:Ba:Cu ratio of about 1:2:3; and calcining the substantially homogeneous mixture of temperatures of from about 750{degrees} C. to about 1000{degrees} C. to form said superconductor ceramic.

  18. Neutron stars as type-I superconductors.

    PubMed

    Buckley, Kirk B W; Metlitski, Max A; Zhitnitsky, Ariel R

    2004-04-16

    In a recent paper by Link, it was pointed out that the standard picture of the neutron star core composed of a mixture of a neutron superfluid and a proton type-II superconductor is inconsistent with observations of a long period precession in isolated pulsars. In the following we will show that an appropriate treatment of the interacting two-component superfluid (made of neutron and proton Cooper pairs), when the structure of proton vortices is strongly modified, may dramatically change the standard picture, resulting in a type-I superconductor. In this case the magnetic field is expelled from the superconducting regions of the neutron star, leading to the formation of the intermediate state when alternating domains of superconducting matter and normal matter coexist.

  19. A Fifth Force: Generalized through Superconductors

    NASA Technical Reports Server (NTRS)

    Robertson, Glen A.

    1999-01-01

    The connection between the Biefield-Brown Effect, the recent repeat of the 1902 Trouton-Noble (TN) experiments, and the gravity shielding experiments was explored. This connection is visualized through high capacitive electron concentrations. From this connection, a theory is proposed that connects mass energy to gravity and a fifth force. The theory called the Gravi-Atomic Energy theory presents two new terms: Gravi-atomic energy and quantum vacuum pressure (QVP). Gravi-atomic energy is defined as the radiated mass energy, which acts on vacuum energy to create a QVP about a mass, resulting in gravity and the fifth force. The QVP emission from a superconductor was discussed followed by the description of a test for QVP from a superconductor using a Cavendish balance.

  20. Unconventional Disorder Effects in Correlated Superconductors.

    PubMed

    Gastiasoro, Maria N; Bernardini, Fabio; Andersen, Brian M

    2016-12-16

    We study the effects of disorder on unconventional superconductors in the presence of correlations, and explore a novel correlated disorder paradigm dominated by strong deviations from standard Abrikosov-Gor'kov theory due to generation of local bound states and cooperative impurity behavior driven by Coulomb interactions. Specifically we explain under which circumstances magnetic disorder acts as a strong poison destroying high-T_{c} superconductivity at the sub-1% level, and when nonmagnetic disorder, counterintuitively, hardly affects the unconventional superconducting state while concomitantly inducing an inhomogeneous full-volume magnetic phase. Recent experimental studies of Fe-based superconductors have discovered that such unusual disorder behavior seems to be indeed present in those systems.

  1. Ordering dynamics in type-II superconductors.

    PubMed

    Guttenberg, Nicholas; Goldenfeld, Nigel

    2006-12-01

    We use analytic and numerical methods to analyze the dynamics of vortices following the quench of a type-II superconductor under the application of an external magnetic field. In three dimensions, in the absence of a field, the spacing between vortices scales with time t with an exponent phi=0.414+/-0.01, in a thin sheet of a superconductor, the scaling exponent is phi=0.294+/-0.01. When an external magnetic field h is applied, the vortices are confined with respect to the length scale of the Abrikosov lattice, leading to a crossover between the power-law scaling length scale and the lattice length scale. From this we suggest a one-parameter scaling of r with h and r that is consistent with numerical data.

  2. Electrical bushing for a superconductor element

    DOEpatents

    Mirebeau, Pierre; Lallouet, Nicolas; Delplace, Sebastien; Lapierre, Regis

    2010-05-04

    The invention relates to an electrical bushing serving to make a connection at ambient temperature to a superconductor element situated in an enclosure at cryogenic temperature. The electrical bushing passes successively through an enclosure at intermediate temperature between ambient temperature and cryogenic temperature, and an enclosure at ambient temperature, and it comprises a central electrical conductor surrounded by an electrically insulating sheath. According to the invention, an electrically conductive screen connected to ground potential surrounds the insulating sheath over a section that extends from the end of the bushing that is in contact with the enclosure at cryogenic temperature at least as far as the junction between the enclosure at intermediate temperature and the enclosure at ambient temperature. The invention is more particularly applicable to making a connection to a superconductor cable.

  3. Energy gap structure of layered superconductors

    SciTech Connect

    Liu, S.H.; Klemm, R.A.

    1993-11-01

    We report the energy gap structure and density-of-states (DOS) of a model layered superconductor with one superconducting layer and one normal layer in a unit cell along the c-axis. In the physically interesting parameter range where the interlayer hopping strengths of the quasiparticles are comparable to the critical temperature, the peaks in the DOS curve do not correspond to the order parameter (OP) of the superconducting layer, but depend on the OP and the band dispersion in the c-direction in a complex manner. In contrast to a BCS superconductor, the DOS of layered systems have logarithmic singularities. Our simulated tunneling characteristics bear close resemblance to experimental results.

  4. Transport in ferromagnet/superconductor spin valves

    NASA Astrophysics Data System (ADS)

    Moen, Evan; Valls, Oriol T.

    2017-02-01

    We consider charge transport properties in realistic, fabricable, ferromagnet/superconductor spin valves having a layered structure F1/N /F2/S , where F1 and F2 denote the ferromagnets, S the superconductor, and N the normal-metal spacer usually inserted in actual devices. Our calculation is fully self-consistent, as required to ensure that conservation laws are satisfied. We include the effects of scattering at all the interfaces. We obtain results for the device conductance G , as a function of bias voltage, for all values of the angle ϕ between the magnetizations of the F1 and F2 layers and a range of realistic values for the material and geometrical parameters in the sample. We discuss, in the context of our results for G , the relative influence of all parameters on the spin valve properties. We also study the spin current and the corresponding spin-transfer torque in F1/F2/S structures.

  5. Asymmetric Ferromagnet-Superconductor-Ferromagnet Switch

    SciTech Connect

    Cadden-Zimansky, P.; Bazaliy, Ya.B.; Litvak, L.M.; Jiang, J.S.; Pearson, J.; Gu, J.Y.; You, Chun-Yeol; Beasley, M.R.; Bader, S.D.

    2011-11-04

    In layered ferromagnet-superconductor-ferromagnet F{sub 1} /S/F{sub 2} structures, the critical temperature T{sub c} of the superconductors depends on the magnetic orientation of the ferromagnetic layers F{sub 1} and F{sub 2} relative to each other. So far, the experimentally observed magnitude of change in T{sub c} for structures utilizing weak ferromagnets has been 2 orders of magnitude smaller than is expected from calculations. We theoretically show that such a discrepancy can result from the asymmetry of F/S boundaries, and we test this possibility by performing experiments on structures where F{sub 1} and F{sub 2} are independently varied. Our experimental results indicate that asymmetric boundaries are not the source of the discrepancy. If boundary asymmetry is causing the suppressed magnitude of T{sub c} changes, it may only be possible to detect in structures with thinner ferromagnetic layers.

  6. Method for fabrication of high temperature superconductors

    SciTech Connect

    Balachandran, Uthamalingam; Ma, Beihai; Miller, Dean

    2009-07-14

    A layered article of manufacture and a method of manufacturing same is disclosed. A substrate has a biaxially textured MgO crystalline layer having the c-axes thereof inclined with respect to the plane of the substrate deposited thereon. A layer of one or more of YSZ or Y.sub.2O.sub.3 and then a layer of CeO.sub.2 is deposited on the MgO. A crystalline superconductor layer with the c-axes thereof normal to the plane of the substrate is deposited on the CeO.sub.2 layer. Deposition of the MgO layer on the substrate is by the inclined substrate deposition method developed at Argonne National Laboratory. Preferably, the MgO has the c-axes thereof inclined with respect to the normal to the substrate in the range of from about 10.degree. to about 40.degree. and YBCO superconductors are used.

  7. High temperature superconductors applications in telecommunications

    NASA Technical Reports Server (NTRS)

    Kumar, A. Anil; Li, Jiang; Zhang, Ming Fang

    1995-01-01

    The purpose of this paper is twofold: (1) to discuss high temperature superconductors with specific reference to their employment in telecommunications applications; and (2) to discuss a few of the limitations of the normally employed two-fluid model. While the debate on the actual usage of high temperature superconductors in the design of electronic and telecommunications devices - obvious advantages versus practical difficulties - needs to be settled in the near future, it is of great interest to investigate the parameters and the assumptions that will be employed in such designs. This paper deals with the issue of providing the microwave design engineer with performance data for such superconducting waveguides. The values of conductivity and surface resistance, which are the primary determining factors of a waveguide performance, are computed based on the two-fluid model. A comparison between two models - a theoretical one in terms of microscopic parameters (termed Model A) and an experimental fit in terms of macroscopic parameters (termed Model B) - shows the limitations and the resulting ambiguities of the two-fluid model at high frequencies and at temperatures close to the transition temperature. The validity of the two-fluid model is then discussed. Our preliminary results show that the electrical transport description in the normal and superconducting phases as they are formulated in the two-fluid model needs to be modified to incorporate the new and special features of high temperature superconductors. Parameters describing the waveguide performance - conductivity, surface resistance and attenuation constant - will be computed. Potential applications in communications networks and large scale integrated circuits will be discussed. Some of the ongoing work will be reported. In particular, a brief proposal is made to investigate of the effects of electromagnetic interference and the concomitant notion of electromagnetic compatibility (EMI/EMC) of high T

  8. High temperature superconductors applications in telecommunications

    SciTech Connect

    Kumar, A.A.; Li, J.; Zhang, M.F.

    1994-12-31

    The purpose of this paper is twofold: to discuss high temperature superconductors with specific reference to their employment in telecommunications applications; and to discuss a few of the limitations of the normally employed two-fluid model. While the debate on the actual usage of high temperature superconductors in the design of electronic and telecommunications devices-obvious advantages versus practical difficulties-needs to be settled in the near future, it is of great interest to investigate the parameters and the assumptions that will be employed in such designs. This paper deals with the issue of providing the microwave design engineer with performance data for such superconducting waveguides. The values of conductivity and surface resistance, which are the primary determining factors of a waveguide performance, are computed based on the two-fluid model. A comparison between two models-a theoretical one in terms of microscopic parameters (termed Model A) and an experimental fit in terms of macroscopic parameters (termed Model B)-shows the limitations and the resulting ambiguities of the two-fluid model at high frequencies and at temperatures close to the transition temperature. The validity of the two-fluid model is then discussed. Our preliminary results show that the electrical transport description in the normal and superconducting phases as they are formulated in the two-fluid model needs to be modified to incorporate the new and special features of high temperature superconductors. Parameters describing the waveguide performance-conductivity, surface resistance and attenuation constant-will be computed. Potential applications in communications networks and large scale integrated circuits will be discussed. Some of the ongoing work will be reported. In particular, a brief proposal is made to investigate of the effects of electromagnetic interference and the concomitant notion of electromagnetic compatibility (EMI/EMC) of high T{sub c} superconductors.

  9. Semiconductor/High-Tc-Superconductor Hybrid ICs

    NASA Technical Reports Server (NTRS)

    Burns, Michael J.

    1995-01-01

    Hybrid integrated circuits (ICs) containing both Si-based semiconducting and YBa(2)Cu(3)O(7-x) superconducting circuit elements on sapphire substrates developed. Help to prevent diffusion of Cu from superconductors into semiconductors. These hybrid ICs combine superconducting and semiconducting features unavailable in superconducting or semiconducting circuitry alone. For example, complementary metal oxide/semiconductor (CMOS) readout and memory devices integrated with fast-switching Josephson-junction super-conducting logic devices and zero-resistance interconnections.

  10. Substrates For High-Temperature Superconductors

    NASA Technical Reports Server (NTRS)

    Shlichta, Paul J.

    1988-01-01

    Proposed hot-dipping process prepares materials well suited to serve as substrates for high-temperature superconductors. Makes it possible to produce substrates combining properties needed for given application, such as flexibility, strength, long grains, and <001> crystal orientation. Properties favor growth of superconductive films carrying high current and fabricated in variety of useful shapes. Used in making solar cells, described in "Hot-Dipped Metal Films as Epitaxial Substrates" (NPO-15904).

  11. Protection considerations for force-cooled superconductors

    SciTech Connect

    Dresner, L.

    1985-01-01

    This paper treats some hydrodynamic aspects of protecting magnets wound with force-cooled superconductors, namely, the rise in internal pressure and the forceful expulsion of helium during a quench. Two initial conditions are considered: an entire hydraulic path going normal all at once, and an initially small but nonrecovering normal zone. Formulas are given for the quench pressure and expulsion velocity in both cases and are compared with available experimental data.

  12. Electronic Properties of High-Temperature Superconductors

    DTIC Science & Technology

    1989-08-01

    presented at the International Superconductor Applications Convention, San Francisco, 1989 (unpublished). SJ. %I. Tranquada , S. 2M. Heald, A. R. Moodenbaugh...Lett. 62, 102 (1989). 151 J. M. Tranquada , D. E. Cox, WV. Kunnmann, H. Moudden, G. Shirane, %I. Suenaga, P. Zolliker, D. Vaknin, S. K. Sinha, M. S...Alvarez, A. J. Jacobson, and D. C. Johnston, Phys. Rev. Lett. 60, 136 (1988); J. M. Tranquada , A. H. Nioudden, A. 1. Goldman, P. Zolliker, D. E. Cox, G

  13. Spray-Deposited Superconductor/Polymer Coatings

    NASA Technical Reports Server (NTRS)

    Wise, Stephanie A.; Tran, Sang Q.; Hooker, Matthew W.

    1993-01-01

    Coatings that exhibit the Meissner effect formed at relatively low temperature. High-temperature-superconductor/polymer coatings that exhibit Meissner effect deposited onto components in variety of shapes and materials. Simple, readily available equipment needed in coating process, mean coatings produced economically. Coatings used to keep magnetic fields away from electronic circuits in such cryogenic applications as magnetic resonance imaging and detection of infrared, and in magnetic suspensions to provide levitation and/or damping of vibrations.

  14. Flywheel energy storage with superconductor magnetic bearings

    DOEpatents

    Weinberger, Bernard R.; Lynds, Jr., Lahmer; Hull, John R.

    1993-01-01

    A flywheel having superconductor bearings has a lower drag to lift ratio that translates to an improvement of a factor of ten in the rotational decay rate. The lower drag results from the lower dissipation of melt-processed YBCO, improved uniformity of the permanent magnet portion of the bearings, operation in a different range of vacuum pressure from that taught by the art, and greater separation distance from the rotating members of conductive materials.

  15. Magnetic impurities in spin-split superconductors

    NASA Astrophysics Data System (ADS)

    van Gerven Oei, W.-V.; Tanasković, D.; Žitko, R.

    2017-02-01

    Hybrid semiconductor-superconductor quantum dot devices are tunable physical realizations of quantum impurity models for a magnetic impurity in a superconducting host. The binding energy of the localized subgap Shiba states is set by the gate voltages and external magnetic field. In this work we discuss the effects of the Zeeman spin splitting, which is generically present both in the quantum dot and in the (thin-film) superconductor. The unequal g factors in semiconductor and superconductor materials result in respective Zeeman splittings of different magnitude. We consider both classical and quantum impurities. In the first case we analytically study the spectral function and the subgap states. The energy of bound states depends on the spin-splitting of the Bogoliubov quasiparticle bands as a simple rigid shift. For the case of collinear magnetization of impurity and host, the Shiba resonance of a given spin polarization remains unperturbed when it overlaps with the branch of the quasiparticle excitations of the opposite spin polarization. In the quantum case, we employ numerical renormalization group calculations to study the effect of the Zeeman field for different values of the g factors of the impurity and of the superconductor. We find that in general the critical magnetic field for the singlet-doublet transition changes nonmonotonically as a function of the superconducting gap, demonstrating the existence of two different transition mechanisms: Zeeman splitting of Shiba states or gap closure due to Zeeman splitting of Bogoliubov states. We also study how in the presence of spin-orbit coupling, modeled as an additional noncollinear component of the magnetic field at the impurity site, the Shiba resonance overlapping with the quasiparticle continuum of the opposite spin gradually broadens and then merges with the continuum.

  16. Superconductor Digital Electronics: -- Current Status, Future Prospects

    NASA Astrophysics Data System (ADS)

    Mukhanov, Oleg

    2011-03-01

    Two major applications of superconductor electronics: communications and supercomputing will be presented. These areas hold a significant promise of a large impact on electronics state-of-the-art for the defense and commercial markets stemming from the fundamental advantages of superconductivity: simultaneous high speed and low power, lossless interconnect, natural quantization, and high sensitivity. The availability of relatively small cryocoolers lowered the foremost market barrier for cryogenically-cooled superconductor electronic systems. These fundamental advantages enabled a novel Digital-RF architecture - a disruptive technological approach changing wireless communications, radar, and surveillance system architectures dramatically. Practical results were achieved for Digital-RF systems in which wide-band, multi-band radio frequency signals are directly digitized and digital domain is expanded throughout the entire system. Digital-RF systems combine digital and mixed signal integrated circuits based on Rapid Single Flux Quantum (RSFQ) technology, superconductor analog filter circuits, and semiconductor post-processing circuits. The demonstrated cryocooled Digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals, enabling multi-net data links, and performing signal acquisition from HF to L-band with 30 GHz clock frequencies. In supercomputing, superconductivity leads to the highest energy efficiencies per operation. Superconductor technology based on manipulation and ballistic transfer of magnetic flux quanta provides a superior low-power alternative to CMOS and other charge-transfer based device technologies. The fundamental energy consumption in SFQ circuits defined by flux quanta energy 2 x 10-19 J. Recently, a novel energy-efficient zero-static-power SFQ technology, eSFQ/ERSFQ was invented, which retains all advantages of standard RSFQ circuits: high-speed, dc power, internal memory. The

  17. Thallium 2223 high T(sub c) superconductor in a silver matrix and its magnetic shielding, hermalcycle and time aging properties

    NASA Technical Reports Server (NTRS)

    Fei, X.; He, W. S.; Havenhill, A.; Ying, Z. Q.; Xin, Y.; Alzayed, N.; Wong, K. K.; Guo, Y.; Reichle, D.; Lucas, M. S. P.

    1995-01-01

    Superconducting Tl2Ba2Ca2Cu3O10 (Tl2223) was ground to powder. Mixture with silver powder (0-80% weight) and press to desired shape. After proper annealing, one can get good silver-content Tl2223 bulk superconductor. It is time-stable and has good superconducting property as same as pure Tl2223. It also has better mechanical property and far better thermal cycle property than pure Tl2223.

  18. Holographic disorder driven superconductor-metal transition

    NASA Astrophysics Data System (ADS)

    Areán, D.; Pando Zayas, L. A.; Landea, I. Salazar; Scardicchio, A.

    2016-11-01

    We implement the effects of disorder on a holographic superconductor by introducing a random chemical potential on the boundary. We demonstrate explicitly that increasing disorder leads to the formation of islands where the superconducting order is enhanced and subsequently to the transition to a metal. We study the behavior of the superfluid density and of the conductivity as a function of the strength of disorder. We find explanations for various marked features in the conductivities in terms of hydrodynamic quasinormal modes of the holographic superconductors. These identifications plus a particular disorder-dependent spectral weight shift in the conductivity point to a signature of the Higgs mode in the context of disordered holographic superconductors. We observe that the behavior of the order parameter close to the transition is not mean-field type as in the clean case; rather we find robust agreement with exp (-A |T -Tc|-ν), with ν =1.03 ±0.02 for this disorder-driven smeared transition.

  19. Charge of a quasiparticle in a superconductor.

    PubMed

    Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas

    2016-02-16

    Nonlinear charge transport in superconductor-insulator-superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e = n, with n = 1-4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD ~ 2Δ, we found a reproducible and clear dip in the extracted charge to q ~ 0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure.

  20. Anomalous critical fields in quantum critical superconductors

    PubMed Central

    Putzke, C.; Walmsley, P.; Fletcher, J. D.; Malone, L.; Vignolles, D.; Proust, C.; Badoux, S.; See, P.; Beere, H. E.; Ritchie, D. A.; Kasahara, S.; Mizukami, Y.; Shibauchi, T.; Matsuda, Y.; Carrington, A.

    2014-01-01

    Fluctuations around an antiferromagnetic quantum critical point (QCP) are believed to lead to unconventional superconductivity and in some cases to high-temperature superconductivity. However, the exact mechanism by which this occurs remains poorly understood. The iron-pnictide superconductor BaFe2(As1−xPx)2 is perhaps the clearest example to date of a high-temperature quantum critical superconductor, and so it is a particularly suitable system to study how the quantum critical fluctuations affect the superconducting state. Here we show that the proximity of the QCP yields unexpected anomalies in the superconducting critical fields. We find that both the lower and upper critical fields do not follow the behaviour, predicted by conventional theory, resulting from the observed mass enhancement near the QCP. Our results imply that the energy of superconducting vortices is enhanced, possibly due to a microscopic mixing of antiferromagnetism and superconductivity, suggesting that a highly unusual vortex state is realized in quantum critical superconductors. PMID:25477044

  1. Synthesizing new, high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Weaver, Claire; Aronson, Meigan

    2015-03-01

    Currently, there is no accepted theory behind type-II, high-temperature superconductors, but there is a distinct relationship between anti-ferromagnetism and superconductivity. Our research focuses on synthesizing new superconducting materials by observing the link between atomic structure and magnetic moments of anti-ferromagnetic compounds and attempting to reproduce the molecular physics of these known materials in new compounds. Consider the square-planar arrangement of the transition metal Fe in the Fe-pnictide superconductors of the ZrCuSiAs ``11 11'' and the ThCr2Si2 ``122'' structure types. We believe that the physics behind this superconductor, where Fe has d6 valence electrons, contributes to the superconducting state, not the presence of Fe itself. For this reason, we are synthesizing materials containing neighboring transition metals, like Mn and Co, combined with other elements in similar crystal lattice arrangements, having ionization properties that hopefully impose d6 valence electrons on the transition metals. This project was supported in part by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships Program (SULI).

  2. Topology of nonsymmorphic crystalline insulators and superconductors

    NASA Astrophysics Data System (ADS)

    Shiozaki, Ken; Sato, Masatoshi; Gomi, Kiyonori

    2016-05-01

    Topological classification in our previous paper [K. Shiozaki and M. Sato, Phys. Rev. B 90, 165114 (2014), 10.1103/PhysRevB.90.165114] is extended to nonsymmorphic crystalline insulators and superconductors. Using the twisted equivariant K theory, we complete the classification of topological crystalline insulators and superconductors in the presence of additional order-two nonsymmorphic space-group symmetries. The order-two nonsymmorphic space groups include half-lattice translation with Z2 flip, glide, twofold screw, and their magnetic space groups. We find that the topological periodic table shows modulo-2 periodicity in the number of flipped coordinates under the order-two nonsymmorphic space group. It is pointed out that the nonsymmorphic space groups allow Z2 topological phases even in the absence of time-reversal and/or particle-hole symmetries. Furthermore, the coexistence of the nonsymmorphic space group with time-reversal and/or particle-hole symmetries provides novel Z4 topological phases, which have not been realized in ordinary topological insulators and superconductors. We present model Hamiltonians of these new topological phases and analytic expressions of the Z2 and Z4 topological invariants. The half-lattice translation with Z2 spin flip and glide symmetry are compatible with the existence of boundaries, leading to topological surface gapless modes protected by the order-two nonsymmorphic symmetries. We also discuss unique features of these gapless surface modes.

  3. Chemical stability of high-temperature superconductors

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.

    1992-01-01

    A review of the available studies on the chemical stability of the high temperature superconductors (HTS) in various environments was made. The La(1.8)Ba(0.2)CuO4 HTS is unstable in the presence of H2O, CO2, and CO. The YBa2Cu3O(7-x) superconductor is highly susceptible to degradation in different environments, especially water. The La(2-x)Ba(x)CuO4 and Bi-Sr-Ca-Cu-O HTS are relatively less reactive than the YBa2Cu3O(7-x). Processing of YBa2Cu3O(7-x) HTS in purified oxygen, rather than in air, using high purity noncarbon containing starting materials is recommended. Exposure of this HTS to the ambient atmosphere should also be avoided at all stages during processing and storage. Devices and components made out of these oxide superconductors would have to be protected with an impermeable coating of a polymer, glass, or metal to avoid deterioration during use.

  4. electric dipole superconductor in bilayer exciton system

    NASA Astrophysics Data System (ADS)

    Sun, Qing-Feng; Jiang, Qing-Dong; Bao, Zhi-Qiang; Xie, X. C.

    Recently, it was reported that the bilayer exciton systems could exhibit many new phenomena, including the large bilayer counterflow conductivity, the Coulomb drag, etc. These phenomena imply the formation of exciton condensate superfluid state. On the other hand, it is now well known that the superconductor is the condensate superfluid state of the Cooper pairs, which can be viewed as electric monopoles. In other words, the superconductor state is the electric monopole condensate superfluid state. Thus, one may wonder whether there exists electric dipole superfluid state. In this talk, we point out that the exciton in a bilayer system can be considered as a charge neutral electric dipole. And we derive the London-type and Ginzburg-Landau-type equations of electric dipole superconductivity. From these equations, we discover the Meissner-type effect (against spatial variation of magnetic fields), and the dipole current Josephson effect. The frequency in the AC Josephson effect of the dipole current is equal to that in the normal (monopole) superconductor. These results can provide direct evidence for the formation of exciton superfluid state in the bilayer systems and pave new ways to obtain the electric dipole current. We gratefully acknowledge the financial support by NBRP of China (2012CB921303 and 2015CB921102) and NSF-China under Grants Nos. 11274364 and 11574007.

  5. McMillan-Rowell like oscillations in a superconductor-InAs/GaSb-superconductor junction

    NASA Astrophysics Data System (ADS)

    Shi, Xiaoyan; Yu, Wenlong; Hawkins, S. D.; Klem, J. F.; Pan, W.

    2015-08-01

    We have fabricated a superconductor (Ta)-InAs/GaSb bilayer-superconductor (Ta) junction device that has a long mean free path and can preserve the wavelike properties of particles (electrons and holes) inside the junction. Differential conductance measurements were carried out at low temperatures in this device, and McMillan-Rowell like oscillations (MROs) were observed. Surprisingly, a much larger Fermi velocity, compared to that from Shubnikov-de Haas oscillations, was obtained from the frequency of MROs. Possible mechanisms are discussed for this discrepancy.

  6. McMillan-Rowell like oscillations in a superconductor-InAs/GaSb-superconductor junction

    SciTech Connect

    Shi, Xiaoyan Yu, Wenlong; Hawkins, S. D.; Klem, J. F.; Pan, W.

    2015-08-03

    We have fabricated a superconductor (Ta)-InAs/GaSb bilayer-superconductor (Ta) junction device that has a long mean free path and can preserve the wavelike properties of particles (electrons and holes) inside the junction. Differential conductance measurements were carried out at low temperatures in this device, and McMillan-Rowell like oscillations (MROs) were observed. Surprisingly, a much larger Fermi velocity, compared to that from Shubnikov-de Haas oscillations, was obtained from the frequency of MROs. Possible mechanisms are discussed for this discrepancy.

  7. McMillan-Rowell Like Oscillations in a Superconductor-InAs/GaSb-Superconductor Junction

    SciTech Connect

    Shi, Xiaoyan; Yu, Wenlong; Hawkins, Samuel D.; Klem, John F.; Pan, Wei

    2015-08-04

    We fabricated a superconductor (Ta)-InAs/GaSb bilayer-superconductor (Ta) junction device that has a long mean free path and can preserve the wavelike properties of particles (electrons and holes) inside the junction. Differential conductance measurements were also carried out at low temperatures in this device, and McMillan-Rowell like oscillations (MROs) were observed. A much larger Fermi velocity, compared to that from Shubnikov-de Haas oscillations, was obtained from the frequency of MROs. Possible mechanisms are discussed for this discrepancy.

  8. Non-equilibrium condensation process in holographic superconductor with nonlinear electrodynamics

    NASA Astrophysics Data System (ADS)

    Liu, Yunqi; Gong, Yungui; Wang, Bin

    2016-02-01

    We study the non-equilibrium condensation process in a holographic superconductor with nonlinear corrections to the U (1) gauge field. We start with an asymptotic Anti-de-Sitter (AdS) black hole against a complex scalar perturbation at the initial time, and solve the dynamics of the gravitational systems in the bulk. When the black hole temperature T is smaller than a critical value T c , the scalar perturbation grows exponentially till saturation, the final state of spacetime approaches to a hairy black hole. In the bulk theory, we find the clue of the influence of nonlinear corrections in the gauge filed on the process of the scalar field condensation. We show that the bulk dynamics in the non-equilibrium process is completely consistent with the observations on the boundary order parameter. Furthermore we examine the time evolution of horizons in the bulk non-equilibrium transformation process from the bald AdS black hole to the AdS hairy hole. Both the evolution of apparent and event horizons show that the original AdS black hole configuration requires more time to finish the transformation to become a hairy black hole if there is nonlinear correction to the electromagnetic field. We generalize our non-equilibrium discussions to the holographic entanglement entropy and find that the holographic entanglement entropy can give us further understanding of the influence of the nonlinearity in the gauge field on the scalar condensation.

  9. Theory of the spin-galvanic effect and the anomalous phase shift φ0 in superconductors and Josephson junctions with intrinsic spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Konschelle, François; Tokatly, Ilya V.; Bergeret, F. Sebastián

    2015-09-01

    Due to the spin-orbit coupling (SOC) an electric current flowing in a normal metal or semiconductor can induce a bulk magnetic moment. This effect is known as the Edelstein (EE) or magnetoelectric effect. Similarly, in a bulk superconductor a phase gradient may create a finite spin density. The inverse effect, also known as the spin-galvanic effect, corresponds to the creation of a supercurrent by an equilibrium spin polarization. Here, by exploiting the analogy between a linear-in-momentum SOC and a background SU(2) gauge field, we develop a quasiclassical transport theory to deal with magnetoelectric effects in superconducting structures. For bulk superconductors this approach allows us to easily reproduce and generalize a number of previously known results. For Josephson junctions we establish a direct connection between the inverse EE and the appearance of an anomalous phase shift φ0 in the current-phase relation. In particular we show that φ0 is proportional to the equilibrium spin current in the weak link. We also argue that our results are valid generically, beyond the particular case of linear-in-momentum SOC. The magnetoelectric effects discussed in this study may find applications in the emerging field of coherent spintronics with superconductors.

  10. Magnetic excitations in iron chalcogenide superconductors.

    PubMed

    Kotegawa, Hisashi; Fujita, Masaki

    2012-10-01

    Nuclear magnetic resonance and neutron scattering experiments in iron chalcogenide superconductors are reviewed to make a survey of the magnetic excitations in FeSe, FeSe1-x Te x and alkali-metal-doped Ax Fe2-y Se2 (A = K, Rb, Cs, etc). In FeSe, the intimate relationship between the spin fluctuations and superconductivity can be seen universally for the variations in the off-stoichiometry, the Co-substitution and applied pressure. The isovalent compound FeTe has a magnetic ordering with different wave vector from that of other Fe-based magnetic materials. The transition temperature Tc of FeSe increases with Te substitution in FeSe1-x Te x with small x, and decreases in the vicinity of the end member FeTe. The spin fluctuations are drastically modified by the Te substitution. In the vicinity of the end member FeTe, the low-energy part of the spin fluctuation is dominated by the wave vector of the ordered phase of FeTe; however, the reduction of Tc shows that it does not support superconductivity. The presence of same wave vector as that of other Fe-based superconductors in FeSe1-x Te x and the observation of the resonance mode demonstrate that FeSe1-x Te x belongs to the same group as most of other Fe-based superconductors in the entire range of x, where superconductivity is mediated by the spin fluctuations whose wave vector is the same as the nesting vector between the hole pockets and the electron pockets. On the other hand, the spin fluctuations differ for alkali-metal-doped Ax Fe2-y Se2 and FeSe or other Fe-based superconductors in their wave vector and strength in the low-energy part, most likely because of the different Fermi surfaces. The resonance mode with different wave vector suggests that Ax Fe2-y Se2 has an exceptional superconducting symmetry among Fe-based superconductors.

  11. Influence of the shielding currents lengthscale and anisotropy effects on the magnetic flux profiles of high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Vanderbemden, P.; Lovchinov, V.

    2012-12-01

    The so-called "magnetic flux profile" AC inductive technique is a powerful method for determining the critical current density Jc of bulk superconductors. In this work we aim at reporting analytical expressions for magnetic flux profiles of superconducting rectangular samples exhibiting a critical current density anisotropy. The results are used for examining the error resulting from approximating a rectangular cross-section by an "infinite cylinder" or "infinite slab" geometry. It is found that such approximations can lead to an artificial curvature of the flux profiles and errors of 10%-20% in the determination of Jc. Next, the effects of how planar defects (cracks, platelet boundaries,...) affect the magnetic flux profile signal are discussed. It is found that the magnetic flux profiles are much sensitive to the lengthscale of shielding currents, thereby providing means of investigation of the typical size of induced current loops in bulk superconductors. Finally some illustrative flux profile data measured on a bulk, large grain melt-processed YBCO single domain exhibiting Jc anisotropy are presented and discussed in relation with theoretical predictions.

  12. Proceedings of high-T sub c superconductors: Magnetic interactions

    SciTech Connect

    Bennett, L.H.; Flom, Y.; Vezzoli, G.C.

    1989-01-01

    This book contains the proceedings of the 1988 meeting on High-T{sub c} superconductors. Included are the following papers: Mechanism in high-T{sub c} superconductivity, Analysis of microwave surface resistance in high-T{sub c} superconductors, Patents and superconductivity.

  13. Controlled levitation of a large magnet above superconductors

    SciTech Connect

    Takamori, T.; Boland, J.J.; Dove, D.B. )

    1990-07-01

    The levitation of a permanent magnet over a type-II superconductor may be modified and controlled by the addition of a variable magnetic field to the magnet-superconductor system. Using this scheme, levitation of a magnet of significantly larger mass was established by the direct interaction of the additonal field with the levitating magnet.

  14. Peltier effect in the mixed state of high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Logvenov, G. Yu.; Ryazanov, V. V.; Ustinov, A. V.; Huebener, R. P.

    1991-04-01

    The Peltier and Seebeck effects in the mixed state of high- Tc superconductors are proportional to the resistivity due to flux motion. Therefore, both effects also show the broadening of the transition regime characteristic for these superconductors. The origin of the Peltier effect is discussed in detail, and the validity of the Thomson relation is confirmed, as expected.

  15. Texturing studies on ? bulk crystals

    NASA Astrophysics Data System (ADS)

    Prabhakaran, D.; Subramanian, C.

    1998-08-01

    Textured crystals of 0953-2048/11/8/013/img2 have been grown by the platinum strip heater-floating zone technique. Texturing ratio and phase purity (Bi-2212) of the grown crystals were calculated from the x-ray diffraction data. Chemical compositions of the grown crystals were quantified from the inductively coupled plasma analysis. 0953-2048/11/8/013/img3 was found to be increased by 2 K for a lower level of substitution and a superconductor to semiconductor transition was observed for the higher order Y substitution. Oxygen stoichiometries of the Y substituted crystals were quantified from the iodometry titration method. Micro-twinning along the growth axis was revealed during etching studies for the cleaved crystals.

  16. A Double-Decker Levitation Experiment Using a Sandwich of Superconductors.

    ERIC Educational Resources Information Center

    Jacob, Anthony T.; And Others

    1988-01-01

    Shows that the mutual repulsion that enables a superconductor to levitate a magnet and a magnet to levitate a superconductor can be combined into a single demonstration. Uses an overhead projector, two pellets of "1-2-3" superconductor, Nd-Fe-B magnets, liquid nitrogen, and paraffin. Offers superconductor preparation, hazards, and disposal…

  17. Method of manufacturing a high temperature superconductor with improved transport properties

    DOEpatents

    Balachandran, Uthamalingam; Siegel, Richard W.; Askew, Thomas R.

    2001-01-01

    A method of preparing a high temperature superconductor. A method of preparing a superconductor includes providing a powdered high temperature superconductor and a nanophase paramagnetic material. These components are combined to form a solid compacted mass with the paramagnetic material disposed on the grain boundaries of the polycrystaline high temperature superconductor.

  18. Precursor composites for oxygen dispersion hardened silver sheathed superconductor composites

    DOEpatents

    Podtburg, E.R.

    1999-06-22

    An oxide superconductor composite having improved texture and durability is disclosed. The oxide superconductor composite includes an oxide superconductor phase substantially surrounded with/by a noble metal matrix, the noble metal matrix comprising a metal oxide in an amount effective to form metal oxide domains that increase hardness of the composite. The composite is characterized by a degree of texture at least 10% greater than a comparable oxide superconductor composite lacking metal oxide domains. An oxide superconducting composite may be prepared by oxidizing the precursor composite under conditions effective to form solute metal oxide domains within the silver matrix and to form a precursor oxide in the precursor alloy phase; subjecting the oxidized composite to a softening anneal under conditions effective to relieve stress within the noble metal phase; and converting the oxide precursor into an oxide superconductor. 1 fig.

  19. Precursor composites for oxygen dispersion hardened silver sheathed superconductor composites

    DOEpatents

    Podtburg, Eric R.

    1999-01-01

    An oxide superconductor composite having improved texture and durability. The oxide superconductor composite includes an oxide superconductor phase substantially surrounded with/by a noble metal matrix, the noble metal matrix comprising a metal oxide in an amount effective to form metal oxide domains that increase hardness of the composite. The composite is characterized by a degree of texture at least 10% greater than a comparable oxide superconductor composite lacking metal oxide domains. An oxide superconducting composite may be prepared by oxidizing the precursor composite under conditions effective to form solute metal oxide domains within the silver matrix and to form a precursor oxide in the precursor alloy phase; subjecting the oxidized composite to a softening anneal under conditions effective to relieve stress within the noble metal phase; and converting the oxide precursor into an oxide superconductor.

  20. System and method for quench protection of a superconductor

    DOEpatents

    Huang, Xianrui; Sivasubramaniam, Kiruba Haran; Bray, James William; Ryan, David Thomas

    2008-03-11

    A system and method for protecting a superconductor from a quench condition. A quench protection system is provided to protect the superconductor from damage due to a quench condition. The quench protection system comprises a voltage detector operable to detect voltage across the superconductor. The system also comprises a frequency filter coupled to the voltage detector. The frequency filter is operable to couple voltage signals to a control circuit that are representative of a rise in superconductor voltage caused by a quench condition and to block voltage signals that are not. The system is operable to detect whether a quench condition exists in the superconductor based on the voltage signal received via the frequency filter and to initiate a protective action in response.

  1. Status of high temperature superconductor development for accelerator magnets

    NASA Technical Reports Server (NTRS)

    Hirabayashi, H.

    1995-01-01

    High temperature superconductors are still under development for various applications. As far as conductors for magnets are concerned, the development has just been started. Small coils wound by silver sheathed Bi-2212 and Bi-2223 oxide conductors have been reported by a few authors. Essential properties of high T(sub c) superconductors like pinning force, coherent length, intergrain coupling, weak link, thermal property, AC loss and mechanical strength are still not sufficiently understandable. In this talk, a review is given with comparison between the present achievement and the final requirement for high T(sub c) superconductors, which could be particularly used in accelerator magnets. Discussions on how to develop high T(sub c) superconductors for accelerator magnets are included with key parameters of essential properties. A proposal of how to make a prototype accelerator magnet with high T(sub c) superconductors with prospect for future development is also given.

  2. Disappearance of nodal gap across the insulator-superconductor transition in a copper-oxide superconductor.

    PubMed

    Peng, Yingying; Meng, Jianqiao; Mou, Daixiang; He, Junfeng; Zhao, Lin; Wu, Yue; Liu, Guodong; Dong, Xiaoli; He, Shaolong; Zhang, Jun; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Lee, T K; Zhou, X J

    2013-01-01

    The parent compound of the copper-oxide high-temperature superconductors is a Mott insulator. Superconductivity is realized by doping an appropriate amount of charge carriers. How a Mott insulator transforms into a superconductor is crucial in understanding the unusual physical properties of high-temperature superconductors and the superconductivity mechanism. Here we report high-resolution angle-resolved photoemission measurement on heavily underdoped Bi₂Sr₂-xLaxCuO(₆+δ) system. The electronic structure of the lightly doped samples exhibit a number of characteristics: existence of an energy gap along the nodal direction, d-wave-like anisotropic energy gap along the underlying Fermi surface, and coexistence of a coherence peak and a broad hump in the photoemission spectra. Our results reveal a clear insulator-superconductor transition at a critical doping level of ~0.10 where the nodal energy gap approaches zero, the three-dimensional antiferromagnetic order disappears, and superconductivity starts to emerge. These observations clearly signal a close connection between the nodal gap, antiferromagnetism and superconductivity.

  3. Influence of magnetic field change on the magnetization relaxation of YBa 2Cu 3O 7-δ superconductor

    NASA Astrophysics Data System (ADS)

    Hsu, S. W.; Chen, Y. C.; Lee, W. H.

    1990-12-01

    Measurements of time-dependent magnetization for the melt-textured YBa 2Cu 3O 7-δ bulk superconductor in the measuring field range H c1 ≪ H ≪ H ∗ at T > {1}/{2} T c reveal that the decay obeys a t {-2}/{3} or a t {-1}/{3} rather than a logarithmic law, depending on the measuring field which was applied by an increasing of a lower field or by a decreasing of a higher field.

  4. Thallium 2223 high Tc superconductor in a silver matrix and its magnetic shielding, hermal cycle and time aging properties

    SciTech Connect

    Fei, X.; He, W.S.; Havenhill, A.

    1994-12-31

    Superconducting Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} (Tl2223) was ground to powder. Mixture with silver powder (0--80% weight) and press to desired shape. After proper annealing, one can get good silver-content Tl2223 bulk superconductor. It is time-stable and has good superconducting property as same as pure Tl2223. It also has better mechanical property and far better thermal cycle property than pure Tl2223.

  5. A review of finite size effects in quasi-zero dimensional superconductors

    NASA Astrophysics Data System (ADS)

    Bose, Sangita; Ayyub, Pushan

    2014-11-01

    Quantum confinement and surface effects (SEs) dramatically modify most solid state phenomena as one approaches the nanometer scale, and superconductivity is no exception. Though we may expect significant modifications from bulk superconducting properties when the system dimensions become smaller than the characteristic length scales for bulk superconductors—such as the coherence length or the penetration depth—it is now established that there is a third length scale which ultimately determines the critical size at which Cooper pairing is destroyed. In quasi-zero-dimensional (0D) superconductors (e.g. nanocrystalline materials, isolated or embedded nanoparticles), one may define a critical particle diameter below which the mean energy level spacing arising from quantum confinement becomes equal to the bulk superconducting energy gap. The so-called Anderson criterion provides a remarkably accurate estimate of the limiting size for the destabilization of superconductivity in nanosystems. This review of size effects in quasi-0D superconductors is organized as follows. A general summary of size effects in nanostructured superconductors (section 1) is followed by a brief overview of their synthesis (section 2) and characterization using a variety of techniques (section 3). Section 4 reviews the size-evolution of important superconducting parameters—the transition temperature, critical fields and critical current—as the Anderson limit is approached from above. We then discuss the effect of thermodynamic fluctuations (section 5), which become significant in confined systems. Improvements in fabrication methods and the increasing feasibility of addressing individual nanoparticles using scanning probe techniques have lately opened up new directions in the study of nanoscale superconductivity. Section 6 reviews both experimental and theoretical aspects of the recently discovered phenomena of ‘parity effect’ and ‘shell effect’ that lead to a strong, non

  6. Majorana vortex-bound states in three-dimensional nodal noncentrosymmetric superconductors

    NASA Astrophysics Data System (ADS)

    Chang, Po-Yao; Matsuura, Shunji; Schnyder, Andreas P.; Ryu, Shinsei

    2014-11-01

    Noncentrosymmetric superconductors (NCSs), characterized by antisymmetric spin-orbit coupling and a mixture of spin-singlet and spin-triplet pairing components, are promising candidate materials for topological superconductivity. An important hallmark of topological superconductors is the existence of protected zero-energy states at surfaces or in vortex cores. Here we investigate Majorana vortex-bound states in three-dimensional nodal and fully gapped NCSs by combining analytical solutions of Bogoliubov-de Gennes (BdG) equations in the continuum with exact diagonalization of BdG Hamiltonians. We show that depending on the crystal point-group symmetries and the topological properties of the bulk Bogoliubov-quasiparticle wave functions, different types of zero-energy Majorana modes can appear inside the vortex core. We find that for nodal NCSs with tetragonal point group C4 v the vortex states are dispersionless along the vortex line, forming one-dimensional Majorana flat bands, while for NCSs with D4 point-group symmetry the vortex modes are helical Majorana states with a linear dispersion along the vortex line. NCSs with monoclinic point group C2, on the other hand, do not exhibit any zero-energy vortex-bound states. We show that in the case of the C4 v (D4) point group the stability of these Majorana zero modes is guaranteed by a combination of reflection (π rotation), time-reversal, and particle-hole symmetry. Considering continuous deformations of the quasiparticle spectrum in the presence of vortices, we show that the flat-band vortex-bound states of C4 v point-group NCSs can be adiabatically connected to the dispersionless vortex-bound states of time-reversal symmetric Weyl superconductors. Experimental implications of our results for thermal transport and tunneling measurements are discussed.

  7. Exploring intertwined orders in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Tranquada, John M.

    2015-03-01

    The concept of intertwined orders has been introduced to describe the cooperative relationship between antiferromagnetic spin correlations and electron (or hole) pair correlations that develop in copper-oxide superconductors. This contrasts with systems in which, for example, charge-density-wave (CDW) order competes for Fermi surface area with superconductivity. La2-xBaxCuO4 with x=0.125 provides an example in which the ordering of spin stripes coincides with the onset of two-dimensional superconducting correlations. The apparent frustration of the interlayer Josephson coupling has motivated the concept of the pair-density-wave superconductor, a state that theoretical calculations show to be energetically competitive with the uniform d-wave superconductor. Even at x=0.095, where there is robust superconductivity below 32 K in zero field, the coexistence of strong, low-energy, incommensurate spin excitations implies a spatially modulated and intertwined pair wave function. Recent observations of CDW order in YBa2Cu3O6+x and other cuprate families have raised interesting questions regarding the general role of charge modulations and the relation to superconductivity. While there are differences in the doping dependence of the modulation wave vectors in YBa2Cu3O6+x and La2-xBaxCuO4, the maximum ordering strength is peaked at the hole concentration of 1/8 in both cases. There are also possible connections with the quantum oscillations that have been detected about the same hole concentration but at high magnetic fields. Resolving these relationships remains a research challenge.

  8. Exploring intertwined orders in cuprate superconductors

    DOE PAGES

    Tranquada, John M.

    2014-11-22

    In this study, the concept of intertwined orders has been introduced to describe the cooperative relationship between antiferromagnetic spin correlations and electron (or hole) pair correlations that develop in copper-oxide superconductors. This contrasts with systems in which, for example, charge-density-wave (CDW) order competes for Fermi surface area with superconductivity. La2-xBaxCuO4 with x = 0.125 provides an example in which the ordering of spin stripes coincides with the onset of two-dimensional superconducting correlations. The apparent frustration of the interlayer Josephson coupling has motivated the concept of the pair-density-wave superconductor, a state that theoretical calculations show to be energetically competitive with themore » uniform d-wave superconductor. Even at x = 0.095, where there is robust superconductivity below 32 K in zero field, the coexistence of strong, low-energy, incommensurate spin excitations implies a spatially modulated and intertwined pair wave function. Recent observations of CDW order in YBa2Cu3O6+x and other cuprate families have raised interesting questions regarding the general role of charge modulations and the relation to superconductivity. While there are differences in the doping dependence of the modulation wave vectors in YBa2Cu3O6+x and La2-xBaxCuO4, the maximum ordering strength is peaked at the hole concentration of 1/8 in both cases. There are also possible connections with the quantum oscillations that have been detected about the same hole concentration but at high magnetic fields. Resolving these relationships remains a research challenge.« less

  9. Exploring intertwined orders in cuprate superconductors

    SciTech Connect

    Tranquada, John M.

    2014-11-22

    In this study, the concept of intertwined orders has been introduced to describe the cooperative relationship between antiferromagnetic spin correlations and electron (or hole) pair correlations that develop in copper-oxide superconductors. This contrasts with systems in which, for example, charge-density-wave (CDW) order competes for Fermi surface area with superconductivity. La2-xBaxCuO4 with x = 0.125 provides an example in which the ordering of spin stripes coincides with the onset of two-dimensional superconducting correlations. The apparent frustration of the interlayer Josephson coupling has motivated the concept of the pair-density-wave superconductor, a state that theoretical calculations show to be energetically competitive with the uniform d-wave superconductor. Even at x = 0.095, where there is robust superconductivity below 32 K in zero field, the coexistence of strong, low-energy, incommensurate spin excitations implies a spatially modulated and intertwined pair wave function. Recent observations of CDW order in YBa2Cu3O6+x and other cuprate families have raised interesting questions regarding the general role of charge modulations and the relation to superconductivity. While there are differences in the doping dependence of the modulation wave vectors in YBa2Cu3O6+x and La2-xBaxCuO4, the maximum ordering strength is peaked at the hole concentration of 1/8 in both cases. There are also possible connections with the quantum oscillations that have been detected about the same hole concentration but at high magnetic fields. Resolving these relationships remains a research challenge.

  10. Paramagnetic excited vortex states in superconductors

    NASA Astrophysics Data System (ADS)

    Gomes, Rodolpho Ribeiro; Doria, Mauro M.; Romaguera, Antonio R. de C.

    2016-06-01

    We consider excited vortex states, which are vortex states left inside a superconductor once the external applied magnetic field is switched off and whose energy is lower than of the normal state. We show that this state is paramagnetic and develop here a general method to obtain its Gibbs free energy through conformal mapping. The solution for any number of vortices in any cross-section geometry can be read off from the Schwarz-Christoffel mapping. The method is based on the first-order equations used by Abrikosov to discover vortices.

  11. NEW APPROACHES: High temperature superconductors take off

    NASA Astrophysics Data System (ADS)

    Gough, Colin

    1998-01-01

    This article describes the progress made towards real engineering applications of high temperature superconductors (HTS) in the ten years following the Nobel Prize winning discovery by Bednorz and Müller in August 1986. Examples include HTS wires and tapes for more efficient and powerful electric motors and for increasing the electrical power into the heart of modern cities, HTS permanent magnets for levitation, microwave filters for cellular telephone networks, SQUIDs (superconducting quantum interference devices) to monitor foetal heart and brain signals, and a new generation of superfast logic devices based on the flux quantum.

  12. Localization of resistive domains in inhomogeneous superconductors

    SciTech Connect

    Gurevich, A.V.; Mints, R.G.

    1981-01-01

    The properties of resistive domains due to the Joule heating in inhomogeneous superconductors with transport currents are studied. The equilibrium of a domain at an inhomogeneity of arbitrary type and with dimensions much smaller than the dimensions of the domain is investigated. It is shown that resistive domains can become localized at inhomogeneities. The temperature distribution in a domain and the current--voltage characteristic of the domain are determined. The stability of localized domains is discussed. It is shown that such domains give rise to a hysteresis in the destruction (recovery) of the superconductivity by the transport current.

  13. Potential aerospace applications of high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Selim, Raouf

    1994-01-01

    The recent discovery of High Temperature Superconductors (HTS) with superconducting transition temperature, T(sub c), above the boiling point of liquid nitrogen has opened the door for using these materials in new and practical applications. These materials have zero resistance to electric current, have the capability of carrying large currents and as such have the potential to be used in high magnetic field applications. One of the space applications that can use superconductors is electromagnetic launch of payloads to low-earth-orbit. An electromagnetic gun-type launcher can be used in small payload systems that are launched at very high velocity, while sled-type magnetically levitated launcher can be used to launch larger payloads at smaller velocities. Both types of launchers are being studied by NASA and the aerospace industry. The use of superconductors will be essential in any of these types of launchers in order to produce the large magnetic fields required to obtain large thrust forces. Low Temperature Superconductor (LTS) technology is mature enough and can be easily integrated in such systems. As for the HTS, many leading companies are currently producing HTS coils and magnets that potentially can be mass-produced for these launchers. It seems that designing and building a small-scale electromagnetic launcher is the next logical step toward seriously considering this method for launching payloads into low-earth-orbit. A second potential application is the use of HTS to build sensitive portable devices for the use in Non Destructive Evaluation (NDE). Superconducting Quantum Interference Devices (SQUID's) are the most sensitive instruments for measuring changes in magnetic flux. By using HTS in SQUID's, one will be able to design a portable unit that uses liquid nitrogen or a cryocooler pump to explore the use of gradiometers or magnetometers to detect deep cracks or corrosion in structures. A third use is the replacement of Infra-Red (IR) sensor leads on

  14. Magnetic refrigeration using flux compression in superconductors

    NASA Technical Reports Server (NTRS)

    Israelsson, U. E.; Strayer, D. M.; Jackson, H. W.; Petrac, D.

    1990-01-01

    The feasibility of using flux compression in high-temperature superconductors to produce the large time-varying magnetic fields required in a field cycled magnetic refrigerator operating between 20 K and 4 K is presently investigated. This paper describes the refrigerator concept and lists limitations and advantages in comparison with conventional refrigeration techniques. The maximum fields obtainable by flux compression in high-temperature supercoductor materials, as presently prepared, are too low to serve in such a refrigerator. However, reports exist of critical current values that are near usable levels for flux pumps in refrigerator applications.

  15. Superconductor coil geometry and ac losses

    NASA Technical Reports Server (NTRS)

    Pierce, T. V., Jr.; Zapata, R. N.

    1976-01-01

    An empirical relation is presented which allows simple computation of volume-averaged winding fields from central fields for coils of small rectangular cross sections. This relation suggests that, in certain applications, ac-loss minimization can be accomplished by use of low winding densities, provided that hysteresis losses are independent of winding density. The ac-loss measurements on coils wound of twisted multifilamentary composite superconductors show no significant dependence on ac losses on winding density, thus permitting the use of winding density as an independent design parameter in loss minimization.

  16. Vortex Core Structure in Multilayered Rashba Superconductors

    NASA Astrophysics Data System (ADS)

    Higashi, Y.; Nagai, Y.; Yoshida, T.; Yanase, Y.

    2014-12-01

    We numerically study the electronic structure of a single vortex in two dimensional superconducting bilayer systems within the range of the mean-field theory. The lack of local inversion symmetry in the system is taken into account through the layer dependent Rashba spin-orbit coupling. The spatial profiles of the pair potential and the local quasiparticle density of states are calculated in the clean spin-singlet superconductor on the basis of the quasiclassical theory. In particular, we discuss the characteristic core structure in the pair-density wave state, which is spatially modulated exotic superconducting phase in a high magnetic field.

  17. Fermi-liquid theory for unconventional superconductors

    SciTech Connect

    Sauls, J.A.

    1994-12-31

    Fermi liquid theory is used to generate the Ginzburg-Landau free energy functionals for unconventional superconductors belonging to various representations. The parameters defining the GL functional depend on Fermi surface anisotropy, impurity scattering and the symmetry class of the pairing interaction. As applications the author considers the basic models for the multiple superconducting phases of UPt{sub 3}. An important prediction of the leading order Fermi liquid theory for the two-dimensional representations of the hexagonal symmetry group is that the zero-field equilibrium state exhibits spontaneously broken time-reversal symmetry.

  18. Edge current in a small chiral superconductor

    NASA Astrophysics Data System (ADS)

    Suzuki, Shu-Ichiro; Asano, Yasuhiro

    2016-10-01

    We discuss a theoretical description of the edge current in a chiral superconductor. On the basis of the quasiclassical Green function formalism, we derive a useful expression of the chiral edge current which enable us to understand how Cooper pairs contribute to the electric current. We will show that the chiral edge current is carried by the combinations of two Cooper pairs belonging to different pairing symmetries. One Cooper pair belongs to the usual even-frequency pairing symmetry class. However, the other belongs to the odd-frequency symmetry class.

  19. Magnetic pinning in superconductor-ferromagnet multilayers

    SciTech Connect

    Bulaevskii, L. N.; Chudnovsky, E. M.; Maley, M. P.

    2000-05-01

    We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10{sup 6}-10{sup 7} A/cm{sup 2} at high temperatures (but not very close to T{sub c}) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics.

  20. Quantum oscillations in superconductors in magnetic field

    NASA Astrophysics Data System (ADS)

    Gvozdikov, Vladimir M.; Gvozdikova, Mariya V.

    2000-07-01

    The Aharonov-Bohm oscillations (ABO) of the free energy, the critical temperature, and the magnetic susceptibility in a stack of hollow mesoscopic cylinders are calculated. It is shown that sinusoidal (in flux) ABO crosses over to the parabolic Little-Parks oscillations (LPO) when the diameter of cylinders exceeds the coherence length. The exponential temperature behaviour of the magnetic susceptibility is like that found in Ag cylinders with thin Nb coating [Czech. J. Physics 46 (1996) 2317]. The formal analogy between oscillations of the free energy in the Aharonov-Bohm system in question and the de Haas-van Alphen oscillations (dHvAO) in layered superconductors is discussed.