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Sample records for ndfe1-xrhx aso superconductor

  1. PREFACE: Atomic Spectra and Oscillator Strengths (ASOS9) Atomic Spectra and Oscillator Strengths (ASOS9)

    NASA Astrophysics Data System (ADS)

    Wahlgren, Glenn M.; Wiese, Wolfgang L.; Beiersdorfer, Peter

    2009-05-01

    For the first time since its inaugural meeting in Lund in 1983, the triennial international conference on Atomic Spectroscopy and Oscillator Strengths for Astrophysical and Laboratory Plasmas (ASOS) returned to Lund, Sweden. Lund has been a home to atomic spectroscopy since the time of Janne Rydberg, and included the pioneering work in laboratory and solar spectroscopy by Bengt Edlén, who presented the initial ASOS talk in 1983. The ninth ASOS was hosted by the Lund Observatory and Physics Department of Lund University, 7-10 August 2007, and was attended by 99 registrants. An encouraging sign for the field was the number of young researchers in attendance. This volume of Physica Scripta contains contributions from the invited presentations of the conference. For the first time, papers from the ASOS9 poster presentations have been made feely available online in a complementary volume of Journal of Physics: Conference Series. With these two volumes the character of ASOS9 is more evident, and together they serve as a review of the state of atomic spectroscopy for spectrum analysis and the determination of oscillator strengths and their applications. The goal of ASOS is to be a forum for atomic spectroscopy, where both the providers and the users of atomic data, which includes wavelengths, energy levels, lifetimes, oscillator strengths and line shape parameters, can meet to discuss recent advances in experimental and theoretical techniques and their application to understanding the physical processes that are responsible for producing observed spectra. The applications mainly originate from the fields of astrophysics and plasma physics, which includes fusion energy and lighting research. The oral presentations, all but one of which are presented in this volume, provided an extensive synopsis of techniques currently in use and those that are being planned. New to ASOS9 was the extent to which techniques such as cold, trapped atoms and molecules and frequency combs are

  2. The Lyman-alpha Solar Telescope for the ASO-S

    NASA Astrophysics Data System (ADS)

    Li, Hui

    2015-08-01

    The Lyman-alpha Solar Telescope (LST) is one of the payloads for the proposed Space-Borne Advanced Solar Observatory (ASO-S). LST consists of a Solar Disk Imager (SDI) with a field-of-view (FOV) of 1.2 Rsun, a Solar Corona Imager (SCI) with an FOV of 1.1 - 2.5 Rsun, and a full-disk White-light Solar Telescope (WST) with an FOV of 1.2 Rsun, which also serves as the guiding telescope. The SCI is designed to work at the Lyman-alpha waveband and white-light, while the SDI will work at the Lyman-alpha waveband only. The WST works both in visible (for guide) and ultraviolet (for science) white-light. The LST will observe the Sun from disk-center up to 2.5 solar radii for both solar flares and coronal mass ejections. In this presentation, I will give an introduction to LST, including scientific objectives, science requirement, instrument design and current status.

  3. Implications of ASOS winds on regulatory dispersion modeling applications

    SciTech Connect

    Jones, W.B.; Brower, R.P.

    1998-12-31

    With the advent of the Automated Surface Observing System (ASOS) throughout the United States during the 1990`s, an unprecedented level of meteorological data is now available. For the first time, observations of standard meteorological variables are available on a minute-by-minute basis. As a result, ASOS has tremendously increased the real-time data available for both weather forecasting and aviation purposes. However, the affect of the ASOS method of data collection on the dispersion modeling community is less clear. Because the hourly data now being reported at most stations across the country are being gathered in a fundamentally different way than previously, it is prudent to examine the differences between hourly meteorological observations gathered before and after ASOS. This paper scrutinizes wind speed and direction data gathered at Baltimore-Washington International Airport and Washington Dulles International Airport and quantifies the differences. Wind data are critical in determining the transport and dispersion of pollutant plumes. Relationships between manually gathered wind data and ASOS wind data are examined. Finally, potential ramifications on dispersion modeling applications are discussed.

  4. The evaluation of ASOS for the Kennedy Space Center's Shuttle Landing Facility

    NASA Technical Reports Server (NTRS)

    Yersavich, Ann; Wheeler, Mark; Taylor, Gregory; Schumann, Robin; Manobianco, John

    1994-01-01

    This report documents the Applied Meteorology Unit's (AMU) evaluation of the effectiveness and utility of the Automated Surface Observing System (ASOS) in terms of spaceflight operations and user requirements. In particular, the evaluation determines which of the Shuttle Landing Facility (SLF) observation requirements can be satisfied by ASOS. This report also includes a summary of ASOS' background, current configuration and specifications, system performance, and the possible concepts of operations for use of ASOS at the SLF. This evaluation stems from a desire by the Air Force to determine if ASOS units could be used to reduce the cost of SLF meteorological observations.

  5. The synthesis and characterization of 1 1 1 1 type diluted ferromagnetic semiconductor (La1-x Ca x )(Zn1-x Mn x )AsO

    NASA Astrophysics Data System (ADS)

    Ding, Cui; Guo, Shengli; Zhao, Yao; Man, Huiyuan; Fu, Licheng; Gu, Yilun; Wang, Zhouyang; Liu, L.; Frandsen, B. A.; Cheung, S.; Uemura, Y. J.; Goko, T.; Luetkens, H.; Morenzoni, E.; Zhao, Yang; Ning, F. L.

    2016-01-01

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor, (La1-x Ca x )(Zn1-y Mn y )AsO, with a layered crystal structure isostructural to that of the 1 1 1 1 type Fe-based high-temperature superconductor LaFeAsO and the antiferromagnetic LaMnAsO. With Ca and Mn codoping into LaZnAsO, the ferromagnetic ordering occurs below the Curie temperature {{T}\\text{C}}   ˜30 K. Taking advantage of the decoupled charge and spin doping, we investigate the influence of carrier concentration on the ferromagnetic ordering state. For a fixed Mn concentration of 10%, {{T}\\text{C}} increases from 24 K to 30 K when the Ca concentration increases from 5% to 10%. Further increase of Ca concentration reduces both the coercive field and saturation moment. Muon spin relaxation measurements confirm the ferromagnetically ordered state, and clearly demonstrate that (La1-x Ca x )(Zn1-y Mn y )AsO shares a common mechanism for the ferromagnetic exchange interaction with (Ga,Mn)As. Neutron scattering measurements show no structural transition in (La0.90Ca0.10)(Zn0.90Mn0.10)AsO below 300 K.

  6. Further investigations of automated surface observing system (ASOS) winds used in air quality modeling applications

    SciTech Connect

    Brower, R.P.; Jones, W.B.; Sherwell, J.

    1999-07-01

    Since 1992, a significant shift in the way standard surface meteorological data are observed and collected has occurred across the country. The National Weather Service, the Federal Aviation Administration, and the Department of Defense have been deploying the Automated Surface Observing System (ASOS) at nearly one thousand sites. Prior to ASOS, manual observation and recordation were the norm. With the advent of ASOS, an unprecedented level of meteorological data is now available; observations of standard meteorological variables are available almost real-time at more sites. However, with ASOS, meteorological data are being gathered in a fundamentally different way. New automated instruments sample, analyze, and record meteorological observations without human intervention. Many of these meteorological observations are key inputs to predictive air quality models. Reliable estimates of plume transport and dispersion require reliable and available meteorological data. The effect of the ASOS method of data collection on the dispersion modeling community is not clear. Because the hourly data now being reported at most stations across the country are being gathered in a fundamentally different way than previously, it is prudent to examine the differences between hourly meteorological observations gathered before and after ASOS. A preliminary analysis1 of pre-ASOS and ASOS data suggested that the differences in the observations could impact the data's application to air quality models. This expanded study examines more thoroughly the differences between wind data gathered before and after ASOS implementation in order to identify potential ramifications for air quality modeling. Pre-ASOS and ASOS data, from five stations in and around Maryland that represent the diversity of urbanization and topography of the region and that have a reasonably long record of ASOS observations, are examined.

  7. Rapid microwave synthesis of the iron arsenides NdFeAsO and NdFe{sub 0.9}Co{sub 0.1}AsO

    SciTech Connect

    Muir, Sean W.; Rachdi, Omar D.; Subramanian, M.A.

    2012-03-15

    Graphical abstract: For the first time, a rapid method for synthesizing NdFeAsO and NdFe{sub 0.9}Co{sub 0.1}AsO is reported. This method uses 2.45 GHz microwave radiation and an additional microwave susceptor to drive the reaction. The superconducting properties NdFe{sub 0.9}Co{sub 0.1}AsO of microwave synthesized materials match well with those reported previously. Highlights: Black-Right-Pointing-Pointer Microwave assisted solid state synthesis of NdFeAsO and NdFe{sub 0.9}Co{sub 0.1}AsO is reported. Black-Right-Pointing-Pointer Synthesis of high quality samples is achieved after 50 min microwave exposure. Black-Right-Pointing-Pointer Physical properties of microwave samples match those prepared conventionally. -- Abstract: The future of iron pnictide superconductors in technology is still undecided. While these materials are now known to possess relatively high critical temperatures and critical magnetic fields, processing methods for these superconductors are still in the development stage. Recently we have been investigating possible ways to speed up the synthetic process for obtaining polycrystalline iron arsenide superconductors and other transition metal pnictides. Here we report the synthesis of NdFeAsO and NdFe{sub 0.9}Co{sub 0.1}AsO in less than 1 h total exposure to microwave radiation using an additional microwave susceptor to surround the reaction ampoule. Structure and property measurements reveal the samples to be of high quality and superconducting when Co doped.

  8. 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.

  9. Analysis of Fumarole Acoustics at Aso Volcano, Japan

    NASA Astrophysics Data System (ADS)

    McKee, K. F.; Yokoo, A.; Fee, D.; Huang, Y. C.; Yoshikawa, S.; Utsugi, M.; Minami, T.; Ohkura, T.

    2015-12-01

    The lowermost portion of large eruption columns is the momentum-driven, fluid flow portion known as a volcanic jet. The perturbation of the atmosphere from this region produces a sound known as jetting or jet noise. Recent work has shown that this volcanic jet noise produced by a volcano has similar characteristics as the sound from jet and rocket engines. The study of volcanic jet noise has gained much from laboratory jet engine studies; however, jet engines have been engineered to reduce noise thereby limiting their use as a comparison tool to the complex, ever-changing volcanic jet. Previous studies have noted that fumaroles produce jet noise without further detailed investigation. The goal of this work is to enhance our understanding of large-scale volcanic jets by studying an accessible, less hazardous fumarolic jet. We aim to characterize the acoustic signature of fumaroles and evaluate if fumarolic jets scale to that of large volcanic jets. To investigate this, we deployed a 6-element acoustic array at two different locations along the edge of the crater wall at Aso Volcano, Japan from early July through mid-August 2015. Approximately two months before this deployment, the pyroclastic cone within Aso's crater partially collapsed into the vent. The cone was constructed during both ash venting and strombolian-style explosive activity in the last year. After the deployment, on July 13 a new small vent opened on the southwest flank of the pyroclastic cone. The vent is several meters in diameter and has consistent gas jetting which produces audible jet noise. To better capture the acoustic signature of the gas jetting we moved the array to the southwestern edge of the crater. The array is 230 meters from the vent and is positioned 54 degrees from the vertical jet axis, a recording angle usually not feasible in volcanic environments. Preliminary investigations suggest directionality at the source and the influence of topography along the propagation path as

  10. AgNa2Mo3O9AsO4

    PubMed Central

    Hamza, Hamadi; Zid, Mohamed Faouzi; Driss, Ahmed

    2011-01-01

    The title compound, silver disodium trimolybdenum(VI) nonaoxide arsenate, AgNa2Mo3O9AsO4, was prepared by a solid-state reaction at 808 K. The structure consists of an infinite (Mo3AsO13)n ribbon, parallel to the c axis, composed of AsO4 tetra­hedra and MoO6 octa­hedra sharing edges and corners. The Na and Ag ions partially occupy several independent close positions, with various occupancies, in the inter-ribbon space delimited by the one-dimensional framework. The composition was refined to Ag1.06(1)Na1.94(1)Mo3O9AsO4. PMID:22219728

  11. 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.

  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. 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.

  14. Development of antisense oligonucleotide (ASO) technology against Tgf-β signaling to prevent scarring during flexor tendon repair.

    PubMed

    Loiselle, Alayna E; Yukata, Kiminori; Geary, Michael B; Kondabolu, Sirish; Shi, Shanshan; Jonason, Jennifer H; Awad, Hani A; O'Keefe, Regis J

    2015-06-01

    Flexor tendons (FT) in the hand provide near frictionless gliding to facilitate hand function. Upon injury and surgical repair, satisfactory healing is hampered by fibrous adhesions between the tendon and synovial sheath. In the present study we used antisense oligonucleotides (ASOs), specifically targeted to components of Tgf-β signaling, including Tgf-β1, Smad3 and Ctgf, to test the hypothesis that local delivery of ASOs and suppression of Tgf-β1 signaling would enhance murine FT healing by suppressing adhesion formation while maintaining strength. ASOs were injected in to the FT repair site at 2, 6 and 12 days post-surgery. ASO treatment suppressed target gene expression through 21 days. Treatment with Tgf-β1, Smad3 or Ctgf ASOs resulted in significant improvement in tendon gliding function at 14 and 21 days, relative to control. Consistent with a decrease in adhesions, Col3a1 expression was significantly decreased in Tgf-β1, Smad3 and Ctgf ASO treated tendons relative to control. Smad3 ASO treatment enhanced the maximum load at failure of healing tendons at 14 days, relative to control. Taken together, these data support the use of ASO treatment to improve FT repair, and suggest that modulation of the Tgf-β1 signaling pathway can reduce adhesions while maintaining the strength of the repair. PMID:25761254

  15. Development of Antisense Oligonucleotide (ASO) Technology Against Tgf-β Signaling to Prevent Scarring During Flexor Tendon Repair

    PubMed Central

    Loiselle, Alayna E.; Yukata, Kiminori; Geary, Michael B.; Kondabolu, Sirish; Shi, Shanshan; Jonason, Jennifer H.; Awad, Hani A.; O’Keefe, Regis J.

    2015-01-01

    Flexor tendons (FT) in the hand provide near frictionless gliding to facilitate hand function. Upon injury and surgical repair, satisfactory healing is hampered by fibrous adhesions between the tendon and synovial sheath. In the present study we used antisense oligonucleotides (ASOs), specifically targeted to components of Tgf-β signaling, including Tgf-β1, Smad3 and Ctgf, to test the hypothesis that local delivery of ASOs and suppression of Tgf-β1 signaling would enhance murine FT healing by suppressing adhesion formation while maintaining strength. ASOs were injected in to the FT repair site at 2, 6 and 12 days post-surgery. ASO treatment suppressed target gene expression through 21 days. Treatment with Tgf-β1, Smad3 or Ctgf ASOs resulted in significant improvement in tendon gliding function at 14 and 21 days, relative to control. Consistent with a decrease in adhesions, Col3a1 expression was significantly decreased in Tgf-β1, Smad3 and Ctgf ASO treated tendons relative to control. Smad3 ASO treatment enhanced the max load at failure of healing tendons at 14 days, relative to control. Taken together, these data support the use of ASO treatment to improve FT repair, and suggest that modulation of the Tgf-β1 signaling pathway can reduce adhesions while maintaining the strength of the repair. PMID:25761254

  16. 78 FR 18314 - Foreign-Trade Zone 169-Manatee County, Florida; Application for Production Authority; ASO, LLC...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-03-26

    ... Foreign-Trade Zones Board Foreign-Trade Zone 169--Manatee County, Florida; Application for Production Authority; ASO, LLC; Subzone 169A (Textile Fabric Adhesive Bandage Coating and Production); Sarasota... facility is used for the production of plastic and textile fabric adhesive bandages. ASO is also...

  17. 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.

  18. Magma plumbing system at the beginning of repeated caldera eruption: A case study on Aso-1 erupted about 270 ky ago from Aso caldera, SW Japan

    NASA Astrophysics Data System (ADS)

    Miyagi, I.; Hoshizumi, H.; Miyabuchi, Y.

    2015-12-01

    In order to understand the commencement of magma plumbing system of a polygenetic caldera, we started petrological study on the earliest eruptive product of Aso caldera, SW Japan. Aso caldera is one of the active volcano in Japan which have produced four stages (Aso-1, -2, -3, -4) of large-scale pyroclastic flow deposits 270 to 90 ky. ago. A suite of samples were collected from the bottom of Aso-1 pyroclastic flow deposit and from the underlying tephra layer (Ono et al., 1979). The tephra comprises more than 10 pumice fall units inter-layered by dark gray volcanic ash. For whole rock chemistry, coarser pumice fragments were separated. For mineral and glass chemistry, phenocrysts and glass particles were handpicked from the sieved 500-1000 um fractions under a binocular microscope. This fraction consist of plagioclase, orthopyroxene, variably vesiculated volcanic glass fragments, and clinopyroxene phenocrysts. They were analyzed using an electron micro-probe. The suite of samples are similar and major temporal change is the chemical composition of orthopyroxenes; those from upper horizon are relatively Mg rich. Anorthite content of plagioclase phenocryst is bimodal 49-53 mol. % (major) and 57-70 mol. % (minor). Silica content of matrix glass fall in a narrow range 68-70 wt. %. Temperature and oxygen fugacity were estimated to be 865-905 deg-C and FMQ+2 log unit, respectively, using ILMAT (Lepage, 2003). Pressure and water content of the magma are estimated to be 5-7 kbar and 0.5-1 wt. % H2O, respectively, using rhyolite-MELTS (Gualda et al., 2012) on the most undifferentiated tholeiitic basalt of Aso 4KC-03 (Hunter, 1998) to reproduce the observed composition of matrix glass (68-70 wt. % SiO2) and plagioclase (An 49-53 mol. %). The calcic plagioclase (An 57-70 mol. %), however, suggest that the basalt was initially hydrous and require magma degassing before the differentiation. If we assume degassing by magma convection in a conduit (Kazahaya et al., 1994), the

  19. K(MoO2)4O3(AsO4)

    PubMed Central

    Jouini, Raja; Zid, Mohamed Faouzi; Driss, Ahmed

    2013-01-01

    A new compound with a non-centrosymmetric structure, potassium tetra­kis­[dioxomolybdenum(IV)] arsenate trioxide, K(MoO2)4O3(AsO4), has been synthesized by a solid-state reaction. The [(MoO2)4O3(AsO4)]+ three-dimensional framework consists of single arsenate AsO4 tetra­hedra, MoO6 octa­hedra, MoO5 bipyramids and bi­octa­hedral units of edge-sharing Mo2O10 octa­hedra. The [Mo2O8]∞ octa­hedral chains running along the a-axis direction are connected through their corners to the AsO4 tetra­hedra, MoO6 octa­hedra and MoO5 bipyramids, so as to form large tunnels propagating along the a axis in which the K+ cations are located. This structure is compared with compounds containing M 2O10 (M = Mo, V, Fe) dimers and with those containing M 2O8 (M = V) chains. PMID:23794968

  20. 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.

  1. 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. PMID:27088452

  2. Chiral superconductors

    NASA Astrophysics Data System (ADS)

    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.

  3. Magma plumbing system of the Aso-3 large pyroclastic eruption cycle at Aso volcano, Southwest Japan: Petrological constraint on the formation of a compositionally stratified magma chamber

    NASA Astrophysics Data System (ADS)

    Kaneko, Katsuya; Inoue, Kazuhisa; Koyaguchi, Takehiro; Yoshikawa, Masako; Shibata, Tomoyuki; Takahashi, Toshiro; Furukawa, Kuniyuki

    2015-09-01

    Aso volcano has the largest caldera (18 × 25 km in diameter) in the southwestern Japan Island Arc, and it formed as the result of four large (VEI = 6-7) pyroclastic-eruption cycles. We study the penultimate large eruption cycle, the Aso-3 cycle, which occurred 123 ka with an ejecta volume of more than 150 km3. The processes in the pre-eruptive magma chamber and the magma genesis of the Aso-3 cycle were inferred from geological data, phenocryst chemistry, and whole-rock chemical and Sr-, Nd-, and Pb isotopic analyses of juvenile clasts. The geological and petrological data indicate that the pre-eruptive magma chamber was stratified compositionally into three layers: from top to bottom, silicic, intermediate, and mafic magma layers. The three magma layers had a uniform isotope composition, suggesting that all the magmas were generated from a single source. The silicic and intermediate magmas were not generated from the mafic magma by fractional crystallization. The silicic magma has higher Ni content (compatible element) than the mafic magma. This suggests that these magmas were produced by partial melting of the same mafic crust but with differing amounts of partial melting: the silicic magma was produced by a low degree of partial melting of the source rock without fractional crystallization, and the mafic magma was produced by a large degree of partial melting followed by fractional crystallization. The intermediate magma compositions plot on the tie line between the silicic magma and the melt of the mafic magma in variation diagrams, and the intermediate magma has phenocrysts whose compositions are identical with those in the silicic magma. This observation indicates that, before the Aso-3 eruption cycle, a two-layer stratified magma chamber of the silicic and mafic magmas was formed as a result of melting of the mafic crust, which was followed by formation of the intermediate layer as a result of interfacial mixing between the silicic magma and the melt of

  4. Rupture process of the 2016 Kumamoto earthquake in relation to the thermal structure around Aso volcano

    NASA Astrophysics Data System (ADS)

    Yagi, Yuji; Okuwaki, Ryo; Enescu, Bogdan; Kasahara, Amato; Miyakawa, Ayumu; Otsubo, Makoto

    2016-07-01

    We constructed the rupture process model for the 2016 Kumamoto, Japan, earthquake from broadband teleseismic body waveforms (P-waves) by using a novel waveform inversion method that takes into account the uncertainty of Green's function. The estimated source parameters are: seismic moment = 5.1 × 1019 Nm (Mw = 7.1), fault length = 40 km, and fault width = 15 km. The mainshock rupture mainly propagated northeastward from the epicenter, for about 30 km, along an active strike-slip fault. The rupture propagation of the mainshock decelerated and terminated near the southwest side of the Aso volcano; the aftershock activity was low around the northeastern edge of the major slip area. Our results suggest that the rupture process of the mainshock and the distribution of aftershocks were influenced by the high-temperature area around the magma chamber of Mt. Aso.

  5. Steady subsidence of a repeatedly erupting caldera through InSAR observations: Aso, Japan

    NASA Astrophysics Data System (ADS)

    Nobile, Adriano; Acocella, Valerio; Ruch, Joel; Aoki, Yosuke; Borgstrom, Sven; Siniscalchi, Valeria; Geshi, Nobuo

    2016-04-01

    The relation between unrest and eruption at calderas is still poorly understood. Aso caldera, Japan, shows minor episodic eruptions, mainly phreatic, associated with steady subsidence. We analyse the recent deformation of Aso using SAR images from 1993 to 2011 and compare this with the eruptive activity. Although the dataset suffers from limitations (e.g., atmospheric effects, coherence loss, low signal to noise ratio), we observe a steady subsidence signal from 1996 to 1998, that suggests an overall contraction of a magmatic source below the caldera centre, from 4.5 to 7 km depth. Because of the similar volumes of the contracting source and erupted material, we propose that the contraction may have been induced by the release of the magmatic fluids feeding the eruptions. If confirmed by further data, this hypothesis suggests that degassing processes play a crucial role in triggering minor eruptions within open conduit calderas, as at Aso. These features underline the importance of defining any eruptive potential also from deflating magmatic systems with open conduit.

  6. NaAg(2)Mo(3)O(9)AsO(4).

    PubMed

    Hamza, Hamadi; Zid, Mohamed Faouzi; Driss, Ahmed

    2010-01-01

    The title compound, sodium disilver arsenatotrimolybdate, Na(0.93 (1))Ag(2.07 (1))Mo(3)AsO(13), was prepared by a solid-state reaction. In the crystal structure, isolated AsO(4) tetra-hedra share corners with groups of three edge-sharing MoO(6) octa-hedra. This arrangement leads to the formation of anionic (1) (∞)[Mo(3)AsO(13)](n) ribbons extending parallel to [100]. The three metal sites show occupational disorder by Ag(I) and Na(I) cations, each with a different Ag:Na ratio. The metal cations are situated in the space between the ribbons and are surrounded by terminal O atoms of the ribbons in the form of distorted MO(7) polyhedra (M = Ag, Na) for distances < 3.0 Å. The title compound shows weak ionic conductivity. Structural relationships between different compounds in the quaternary systems M-Sb-P-O, M-Nb-P-O and M-Mo-As-O (M is Ag or an alkali metal) are also discussed. PMID:21587345

  7. Wind Measurement and Archival under the Automated Surface Observing System (ASOS): User Concerns and Opportunity for Improvement.

    NASA Astrophysics Data System (ADS)

    Powell, Mark D.

    1993-04-01

    The National Weather Service, as a part of its modernization effort, is implementing the Automated Surface Observing System (ASOS). Much discussion has occurred about various aspects of ASOS versus the current system of manual and automated observations. Based upon a study of the ASOS specifications and an informal survey of potential ASOS winddata users, defects of the wind sampling and archival strategy chosen for ASOS are discussed in terms of their impact on various user groups. Limitations include: 1) hourly observation average periods that do not conform to international recommendations for wind reporting made by the World Meteorological Organization, 2) no regular archival of high-resolution data-potentially valuable research data are destroyed if not identified within a 12-h period, and 3) no emergency power for operation in severe weather conditions. An alternative sampling and archiving strategy is recommended that benefits a wider cross section of users, without detracting from aviation and forecast service requirements, at a cost of less than 1% of the original ASOS portion of the weather service modernization budget.

  8. Wind measurement and archival under the Automated Surface Observing System (ASOS): User concerns and opportunity for improvement

    SciTech Connect

    Powell, M.D. )

    1993-04-01

    The National Weather Service, as a part of its modernization effort, is implementing the Automated Surface Observing System (ASOS). Much discussion has occurred about various aspects of ASOS versus the current system of manual and automated observations. Based upon a study of the ASOS specifications and an informal survey of potential ASOS wind data users, defects of the wind sampling and archival strategy chosen for ASOS are discussed in terms of their impact on various user groups. Limitations include: (1) hourly observation average periods that do not conform to international recommendations for wind reporting made by the World Meteorological Organization, (2) no regular archival of high-resolution data-potentially valuable research data are destroyed if not identified within a 12-h period, and (3) no emergency power for operation in severe weather conditions. An alternative sampling and archiving strategy is recommended that benefits a wider cross section of users, without detracting from aviation and forecast service requirements, at a cost of less than 1 % of the original ASOS portion of the weather service modernization budget.

  9. 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).

  10. Combined absolute and relative gravity measurement for microgravity monitoring in Aso volcanic field

    NASA Astrophysics Data System (ADS)

    Sofyan, Yayan; Nishijima, Jun; Yoshikawa, Shin; Fujimitsu, Yasuhiro; Kagiyama, Tsuneomi; Fukuda, Yoichi

    2014-05-01

    Absolute measurement with a portable A10-017 absolute gravimeter at some benchmarks in the Aso volcanic field are valuable for reducing uncertainties of regional gravity variations and will be useful for delineating the long term trends of gravity changes. A10 absolute gravimeter is a new generation of portable absolute instrument and has accuracy 10 microGal. To further the development of a high precision gravity data, we also conducted measurement using two relative gravimeter (Scintrex CG-5 [549] and LaCoste type G-1016) to be combined with an A10 absolute gravimeter. The using absolute gravimeter along with relative gravimeter can reduce drift correction factor and improve the result of gravity change data in microgravity monitoring. Microgravity monitoring is a valued tool for mapping the redistribution of subsurface mass and for assessing changes in the fluid as a dynamic process in volcanic field. Gravity changes enable the characterization of subsurface processes: i.e., the mass of the intrusion or hydrothermal flow. A key assumption behind gravity monitoring is that changes in earth's gravity reflect mass-transport processes at depth [1]. The absolute gravity network was installed at seven benchmarks using on May 2010, which re-occupied in October 2010, and June 2011. The relative gravity measurements were performed at 28 benchmarks in one month before the eruption on May 2011 and then followed by series of gravity monitoring after the eruption in every three to five months. Gravity measurements covered the area more than 60 km2 in the west side of Aso caldera. Some gravity benchmarks were measured using both absolute and relative gravimeter and is used as the reference benchmarks. In longer time period, the combined gravity method will improve the result of gravity change data for monitoring in the Aso volcanic field. As a result, the gravity changes detected the hydrothermal flow in the subsurface which has a correlation to water level fluctuation in the

  11. Field Management System (FMS) user's manual. Atlanta Support Office Phase I, Version ASO-2

    SciTech Connect

    Not Available

    1985-06-01

    This manual describes the Field Management System (FMS) designed for the Department of Energy Atlanta Support Office (ASO). This manual is written for both the FMS manager and the first-time computer user. The manual is written and FMS is designed so that these users can operate FMS without learning a lot about the computer operations. The chapters of this manual have been arranged so that selected chapters can be combined into separate manuals for the needs of each user. This arrangement is as follows: Data Inspection; Data Entry; FMS Maintenance; and FMS Manager.

  12. FOREWORD: The 9th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas (ASOS 9)

    NASA Astrophysics Data System (ADS)

    Wahlgren, Glenn M.; Wiese, Wolfgang L.; Beiersdorfer, Peter

    2008-07-01

    For the first time since its inaugural meeting in Lund in 1983, the triennial international conference on Atomic Spectroscopy and Oscillator Strengths for Astrophysical and Laboratory Plasmas (ASOS) returned to Lund, Sweden. Lund has been a home to atomic spectroscopy since the time of Janne Rydberg, and included the pioneering work in laboratory and solar spectroscopy of Bengt Edlén, who presented the initial ASOS talk in 1983. The ninth ASOS was hosted by the Lund Observatory and the Physics Department of Lund University during from 8 to 10 August 2007 and was attended by nearly 100 registrants. An encouraging sign for the field was the number of young researchers in attendance. This volume contains the submitted contributions from the poster presentations of the conference, and represents approximately forty percent of the presented posters. A complementary volume of Physica Scripta provides the written transactions of the ASOS9 invited presentations. With these two volumes the character of ASOS9 is more fully evident, and they serve as a review of the state of atomic spectroscopy for spectrum analysis and the determination of oscillator strengths and their applications. The goal of ASOS is to be a forum for atomic spectroscopy where both the providers and users of atomic data, which includes wavelengths, energy levels, lifetimes, oscillator strengths, and line shape parameters, can meet to discuss recent advances in experimental and theoretical techniques and their application to understanding the physical processes that are responsible for producing observed spectra. The applications mainly originate from the fields of astrophysics and plasma physics, the latter including fusion energy and lighting research. As a part of ASOS9 we were honored to celebrate the retirement of Professor Sveneric Johansson. At a special session on the spectroscopy of iron, which was conducted in his honor, he presented his insights into the Fe II term system and his most recent

  13. Vibrational spectroscopic study of the mineral pitticite Fe, AsO 4, SO 4, H 2O

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; Xi, Yunfei; Tan, Keqin; Millar, Graeme J.; Palmer, Sara J.

    2012-01-01

    Some minerals are colloidal and show no X-ray diffraction patterns. Vibrational spectroscopy offers one of the few methods for the determination of the structure of these minerals. Among this group of minerals is pitticite, simply described as (Fe, AsO 4, SO 4, H 2O). In this work, the analogue of the mineral pitticite has been synthesised. The objective of this research is to determine the molecular structure of the mineral pitticite using vibrational spectroscopy. Raman and infrared bands are attributed to the AsO 43-, SO 42- and water stretching and bending vibrations. The Raman spectrum of the pitticite analogue shows intense peaks at 845 and 837 cm -1 assigned to the AsO 43- stretching vibrations. Raman bands at 1096 and 1182 cm -1 are attributed to the SO 42- antisymmetric stretching bands. Raman spectroscopy offers a useful method for the analysis of such colloidal minerals.

  14. A Rapid Turn-around, Scalable Big Data Processing Capability for the JPL Airborne Snow Observatory (ASO) Mission

    NASA Astrophysics Data System (ADS)

    Mattmann, C. A.

    2014-12-01

    The JPL Airborne Snow Observatory (ASO) is an integrated LIDAR and Spectrometer measuring snow depth and rate of snow melt in the Sierra Nevadas, specifically, the Tuolumne River Basin, Sierra Nevada, California above the O'Shaughnessy Dam of the Hetch Hetchy reservoir, and the Uncompahgre Basin, Colorado, amongst other sites. The ASO data was delivered to water resource managers from the California Department of Water Resources in under 24 hours from the time that the Twin Otter aircraft landed in Mammoth Lakes, CA to the time disks were plugged in to the ASO Mobile Compute System (MCS) deployed at the Sierra Nevada Aquatic Research Laboratory (SNARL) near the airport. ASO performed weekly flights and each flight took between 500GB to 1 Terabyte of raw data, which was then processed from level 0 data products all the way to full level 4 maps of Snow Water Equivalent, albedo mosaics, and snow depth from LIDAR. These data were produced by Interactive Data analysis Language (IDL) algorithms which were then unobtrusively and automatically integrated into an Apache OODT and Apache Tika based Big Data processing system. Data movement was both electronic and physical including novel uses of LaCie 1 and 2 TeraByte (TB) data bricks and deployment in rugged terrain. The MCS was controlled remotely from the Jet Propulsion Laboratory, California Institute of Technology (JPL) in Pasadena, California on behalf of the National Aeronautics and Space Administration (NASA). Communication was aided through the use of novel Internet Relay Chat (IRC) command and control mechanisms and through the use of the Notifico open source communication tools. This talk will describe the high powered, and light-weight Big Data processing system that we developed for ASO and its implications more broadly for airborne missions at NASA and throughout the government. The lessons learned from ASO show the potential to have a large impact in the development of Big Data processing systems in the years

  15. Synthesis and crystal structure of Na4Ni7(AsO4)6

    PubMed Central

    David, Rénald

    2016-01-01

    The title compound, tetra­sodium hepta­nickel hexa­arsenate, was obtained by ceramic synthesis and crystallizes in the monoclinic space group C2/m. The asymmetric unit contains seven Ni atoms of which two have site symmetry 2/m and three site symmetry 2, four As atoms of which two have site symmetry m and two site symmetry 2, three Na atoms of which two have site symmetry 2, and fifteen O atoms of which four have site symmetry m. The structure of Na4Ni7(AsO4)6 is made of layers of Ni octa­hedra and As tetra­hedra assembled in sheets parallel to the bc plane. These layers are inter­connected by corner-sharing between NiO6 octa­hedra and AsO4 tetra­hedra. This linkage creates tunnels running along the c axis in which the Na atoms are located. This arrangement is similar to the one observed in Na4Ni7(PO4)6, but the layers of the two compounds are slightly different because of the disorder of one of the Ni sites in the structure of the title compound. PMID:27308006

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Grounded electrical-source airborne transient electromagnetics (GREATEM) survey of Aso Volcano, Japan

    NASA Astrophysics Data System (ADS)

    Ito, Hisatoshi; Kaieda, Hideshi; Mogi, Toru; Jomori, Akira; Yuuki, Youichi

    2014-05-01

    Grounded electrical-source airborne transient electromagnetics (GREATEM), a type of semi-airborne electromagnetics, was used to examine Aso Volcano in south-west Japan, to verify its applicability to surveying deep subsurface resistivity structures. Comparison of the GREATEM resistivity values with those of ground-based transient electromagnetics (TEM) data, repeated GREATEM survey results at the same and different flight heights, and lithologic descriptions indicated that GREATEM can successfully identify underground structures as deep as ~800 m in rugged mountainous areas. An active volcanic region (Naka-Dake crater) was mapped as a low-resistivity zone from the surface to a depth of 100 m. This low-resistivity zone extended to the west-north-west, implying future volcanic activity in this area. Therefore, the GREATEM method is useful for surveying deep structures in large, inaccessible areas, such as volcanic provinces, in a quick, cost-effective way.

  1. Mineral and chemical variations within an ash-flow sheet from Aso caldera, Southwestern Japan

    USGS Publications Warehouse

    Lipman, P.W.

    1967-01-01

    Although products of individual volcanic eruptions, especially voluminous ash-flow eruptions, have been considered among the best available samples of natural magmas, detailed petrographic and chemical study indicates that bulk compositions of unaltered Pleistocene ash-flow tuffs from Aso caldera, Japan, deviate significantly from original magmatic compositions. The last major ash-flow sheet from Aso caldera is as much as 150 meters thick and shows a general vertical compositional change from phenocryst-poor rhyodacite upward into phenocryst-rich trachyandesite; this change apparently reflects in inverse order a compositionally zoned magma chamber in which more silicic magma overlay more mafic magma. Details of these magmatic variations were obscured, however, by: (1) mixing of compositionally distinct batches of magma during upwelling in the vent, as indicated by layering and other heterogeneities within single pumice lumps; (2) mixing of particulate fragments-pumice lumps, ash, and phenocrysts-of varied compositions during emplacement, with the result that separate pumice lenses from a single small outcrop may have a compositional range nearly as great as the bulk-rook variation of the entire sheet; (3) density sorting of phenocrysts and ash during eruption and emplacement, resulting in systematic modal variations with distance from the caldera; (4) addition of xenocrysts, resulting in significant contamination and modification of proportions of crystals in the tuffs; and (5) ground-water leaching of glassy fractions during hydration after cooling. Similar complexities characterize ash-flow tuffs under study in southwestern Nevada and in the San Juan Mountains, Colorado, and probably are widespread in other ash-flow fields as well. Caution and careful planning are required in study of the magmatic chemistry and phenocryst mineralogy of these rocks. ?? 1967 Springer-Verlag.

  2. Stabilin-1 and Stabilin-2 are specific receptors for the cellular internalization of phosphorothioate-modified antisense oligonucleotides (ASOs) in the liver

    PubMed Central

    Miller, Colton M.; Donner, Aaron J.; Blank, Emma E.; Egger, Andrew W.; Kellar, Brianna M.; Østergaard, Michael E.; Seth, Punit P.; Harris, Edward N.

    2016-01-01

    Phosphorothioate (PS)-modified antisense oligonucleotides (ASOs) have been extensively investigated over the past three decades as pharmacological and therapeutic agents. One second generation ASO, Kynamro™, was recently approved by the FDA for the treatment of homozygous familial hypercholesterolemia and over 35 second generation PS ASOs are at various stages of clinical development. In this report, we show that the Stabilin class of scavenger receptors, which were not previously thought to bind DNA, do bind and internalize PS ASOs. With the use of primary cells from mouse and rat livers and recombinant cell lines each expressing Stabilin-1 and each isoform of Stabilin-2 (315-HARE and 190-HARE), we have determined that PS ASOs bind with high affinity and these receptors are responsible for bulk, clathrin-mediated endocytosis within the cell. Binding is primarily dependent on salt-bridge formation and correct folding of the intact protein receptor. Increased internalization rates also enhanced ASO potency for reducing expression of the non-coding RNA Malat-1, in Stabilin-expressing cell lines. A more thorough understanding of mechanisms by which ASOs are internalized in cells and their intracellular trafficking pathways will aid in the design of next generation antisense agents with improved therapeutic properties. PMID:26908652

  3. Designing with superconductors

    SciTech Connect

    Hammond, R.B.; Hey-Shipton, G.L. ); Matthaei, G.L. )

    1993-04-01

    This article examines the basics of designing with superconducting microwave ICs. The topics of this article include high-temperature superconductors of copper-oxide compounds, the shortcomings of designing ICs with CAD, building small, high-Q bandpass or bandstop filters, combining high-temperature superconductors and conventional components, oscillator stability, tuning, digital interconnects, and cryogenic cooling options.

  4. 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.

  5. Superconductor as movie star

    SciTech Connect

    Pool, R.

    1993-12-03

    Japanese researchers have succeeded in producing a movie of changes in the magnetic flux lattice of a high-Tc superconductor as it is warmed. They used a technique called electron holography, in which electrons are passed through a superconductor, and flux lines are visualized as interference patterns induced by the electrons as they undergo a phase change as they pass to one side or another of the flux lines. The technique will have application in designing superconductors so that they do not lose their superconductivity when exposed to magnetic fields.

  6. Combined use of RFLP and PCR-ASO typing for HLA-DR-Dw and DQw typing.

    PubMed

    Bignon, J D; Bidwell, J L

    1991-01-01

    Due to some limitations of restriction fragment length polymorphism (RFLP) analysis in HLA-DR-DQ typing, we present a combined use of RFLP and polymerase chain reaction (PCR)-allele-specific oligonucleotide (ASO) typing. This scheme consists in selectively amplifying the few RFLP ill-defined genes (DR1/DR'Br' and DR4-Dw subsets) using PCR with allele specific primers to avoid cross-hybridization. PMID:1676910

  7. Heavy atom nitroxyl radicals. II: Spectroscopic detection of H2As=O, the prototypical arsenyl free radical

    NASA Astrophysics Data System (ADS)

    He, Sheng-Gui; Sunahori, Fumie X.; Yang, Jie; Clouthier, Dennis J.

    2009-09-01

    The previously unknown arsenyl (H2AsO) free radical has been identified in the gas phase through a combination of laser-induced fluorescence and single vibronic level emission spectroscopy in a supersonic expansion. Three isotopologues, H2AsO, HDAsO, and D2AsO have been detected as products of an electric discharge in mixtures of arsine or deuterated arsines, CO2, and argon. The observed spectra are assigned as due to the B˜ A2'-X˜ A2' electronic transition in which an electron in the ground state π orbital is promoted to the π∗ orbital. Rotational analysis of high-resolution spectra proves that the radical is nonplanar in both electronic states with the following r0 structures: r″(As-H)=1.513(4) Å, r″(As-O)=1.672(1) Å, θ″(HAsH)=101.8(4)°, ground state out-of-plane angle=63.1°; r'(As-H)=1.525(10) Å, r'(As-O)=1.806(3) Å, θ'(HAsH)=93.4(10)°, and excited state out-of-plane angle=70.7°. Small hyperfine splittings in the spectra have enabled the determination of the arsenic Fermi contact parameter in both states. The results of our ab initio studies of the ground and excited state of this radical (see immediately preceding paper) are in good agreement with the spectroscopic analysis.

  8. Disposition and Pharmacology of a GalNAc3-conjugated ASO Targeting Human Lipoprotein (a) in Mice.

    PubMed

    Yu, Rosie Z; Graham, Mark J; Post, Noah; Riney, Stan; Zanardi, Thomas; Hall, Shannon; Burkey, Jennifer; Shemesh, Colby S; Prakash, Thazha P; Seth, Punit P; Swayze, Eric E; Geary, Richard S; Wang, Yanfeng; Henry, Scott

    2016-01-01

    Triantennary N-acetyl galactosamine (GalNAc3)-conjugated antisense oligonucleotides (ASOs) have greatly improved potency via receptor-mediated uptake. In the present study, the in vivo pharmacology of a 2'-O-(2-methoxyethyl)-modified ASO conjugated with GalNAc3 (ISIS 681257) together with its unmodified congener (ISIS 494372) targeting human apolipoprotein (a) (apo(a)), were studied in human LPA transgenic mice. Further, the disposition kinetics of ISIS 681257 was studied in CD-1 mice. ISIS 681257 demonstrated over 20-fold improvement in potency over ISIS 494372 as measured by liver apo(a) mRNA and plasma apo(a) protein levels. Following subcutaneous (SC) dosing, ISIS 681257 cleared rapidly from plasma and distributed to tissues. Intact ISIS 681257 was the major full-length oligonucleotide species in plasma. In tissues, however, GalNAc sugar moiety was rapidly metabolized and unconjugated ISIS 681257 accounted > 97% of the total exposure, which was then cleared slowly from tissues with a half-life of 7-8 days, similar to the half-life in plasma. ISIS 681257 is highly bound to plasma proteins (> 94% bound), which limited its urinary excretion. This study confirmed dose-dependent exposure to the parent drug ISIS 681257 in plasma and rapid conversion to unconjugated ASO in tissues. Safety data and the extended half-life support its further development and weekly dosing in phase 1 clinical studies. PMID:27138177

  9. Analysis of Snow Albedo, Grain Size and Radiative Forcing based on the Airborne Snow Observatory (ASO) Imaging Spectroscopy Data

    NASA Astrophysics Data System (ADS)

    Seidel, F. C.; Painter, T. H.

    2013-12-01

    Climate is expected to be most vulnerable in mountainous and arctic regions where the atmosphere and the hydrosphere are directly linked to the cryosphere. A combination of modeling and large-scale observational efforts is required to investigate related scientific questions. NASA's Airborne Snow Observatory (ASO) at the Jet Propulsion Laboratory addresses some of these needs by establishing new quantitative observational capabilities in regional mapping of mountain snow properties. In addition, ASO's key products showed that we are able to achieve societal benefits by improving water resources management. We will show the first analysis of snow optical products (albedo, grain size, and radiative forcing) from the spring 2013 ASO campaign in the Sierra Nevada, CA, USA. In addition, we will present the retrieval methods used to derive these products based on airborne imaging spectroscopy, LiDAR, as well as radiative transfer models. The preliminary findings provide new important insights into the temporal and spatial aspects of Western US mountain snow and its melt.

  10. A European research infrastructure for the aerosol study on a continental scale: EARLINET-ASOS

    NASA Astrophysics Data System (ADS)

    Amodeo, Aldo; Pappalardo, Gelsomina; Bösenberg, Jens; Ansmann, Albert; Apituley, Arnoud; Alados-Arboledas, Lucas; Balis, Dimitris; Böckmann, Christine; Chaikovsky, Anatoly; Comeron, Adolfo; Freudenthaler, Volker; Gustaffson, Ove; Hansen, Georg; Mitev, Valentin; Nicolae, Doina; Papayannis, Alexandros; Perrone, Maria Rita; Pietruczuk, Aleksander; Pujadas, Manuel; Putaud, Jean-Philippe; Ravetta, Francois; Rizi, Vincenzo; Simeonov, Valentin; Spinelli, Nicola; Stoyanov, Dimitar; Trickl, Thomas; Wiegner, Matthias

    2007-10-01

    The present knowledge of the aerosol distribution is not sufficient to estimate the aerosol influence on global and regional environmental conditions and climate. This observational gap can be closed by using advanced laser remote sensing. EARLINET (European Aerosol Research Lidar Network) is the first aerosol lidar network, established in 2000, with the main goal to provide a comprehensive, quantitative, and statistically significant database for the aerosol distribution on a continental scale. EARLINET is a coordinated network of European stations (25 at present) using advanced lidar methods for the vertical profiling of aerosols. The network activity is based on simultaneous scheduled measurements, a rigorous quality assurance program addressing both instruments and evaluation algorithms, and a standardised data exchange format. Further observations are performed to monitor special events. EARLINET-ASOS (Advanced Sustainable Observation System) is a five year EC Project started in 2006, based on the EARLINET infrastructure. The main objectives are: to make EARLINET a world-leading instrument for the observation of the 4-D aerosol distribution on continental scale; to foster aerosol-related process studies, validation of satellite sensors, model development and validation, assimilation of aerosol data into operational models; and to build a comprehensive climatology of the aerosol distribution.

  11. Remote Monitoring of Aerosol Layers over Sofia in the Frame of EARLINET-ASOS Project

    NASA Astrophysics Data System (ADS)

    Grigorov, Ivan; Kolarov, Georgi; Stoyanov, Dimitar

    2010-01-01

    In this work we present some results of lidar remote sensing of aerosol layers in the atmosphere in Sofia region. The investigations were made using a lidar system equipped with a CuBr-vapor laser with high pulse repetition of 13 kHz and receiver in photon counting mode. These measurements were performed in frame of the project European Aerosol Research Lidar Network—Advanced Sustainable Observation System (EARLINET—ASOS). For some of presented results a conclusion about atmospheric aerosol's origins was made upon analyses of the information about the weather condition during the lidar measurements. Such information was obtained by the weather-forecast maps provided by the Atmospheric Modeling and Weather Forecasting Group of NTUA and the Forecast system of Barcelona Supercomputing Centre and accessible via Internet. Additional information is provided by calculations of the backward air mass trajectories, using online software of NOAA about HYSPLIT model (HYbrid Single-Particle Lagrangian Integrated Trajectory). A common database that automatically collects the data products provided by the individual lidar stations is build and makes data of measurements available to the scientific community.

  12. Bubble Coalescences Found in a Scoria from 2014-2015 Aso Eruption

    NASA Astrophysics Data System (ADS)

    Namiki, A.

    2015-12-01

    November 2014, Aso Volcano resumed the eruption after approximately 20 years quiescence. The main activity was ash eruption with silent large plumes, but Strombolian eruption of spouting scoriae without ash also was observed. Most of scoriae are highly vesiculated, and have low density (Yokoo and Miyabuchi, 2015). In order to understand the evolution of bubble texture, I observed the scoriae in three methods, the microscope, CT scan, and SEM those can observe different scales of 10 mm, 1 mm, 10μm, respectively. The microscope images show that larger bubbles (10mm) are surrounded by small bubbles (< 1mm), which shows elongated structure and suggesting that deformed by the large bubbles. CT images also show that larger bubbles (1mm) are surrounded by small bubbles (100μm). SEM images show that the bubble film thickness is approximately 1μm or less. According to the observation of pumices in other volcanoes, the typical bubble film thickness is estimated to be about 0.1-1μm (Nguyen, et al, 2013). In general, the volume fraction of bubbles and number density determine the thickness of the bubble films. For a smaller number density of bubbles, bubble size becomes larger in a same bubble volume fraction, so that the bubble film becomes thicker. In other words, the bubble films in the bubbly magma with a large number density reach the minimum thickness at a lower degree of bubble fraction. As a result, the bubble films rupture, or by coagulation, the larger bubble assimilates small bubbles. By the increase of the bubble size, thickness of the bubble film increases to be larger than the minimum thickness of 1μm. If such coalescences occur, the bubble size must have variety. From the varying bubble size and 1 1μm film thickness of scoriae, I infer that bubble coalescence occurred in the ascending bubbly magma in the conduit.

  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. Lightning in superconductors

    PubMed Central

    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. PMID:23185691

  15. Tunneling spectroscopy of anisotropic superconductors

    SciTech Connect

    Kashiwaya, Satoshi; Koyanagi, Masao; Kajimura, Koji; Tanaka, Yukio

    1996-12-31

    Tunneling spectroscopy of normal-insulator-superconductor junction is investigated theoretically. In anisotropic superconductors, differently from the case of isotropic superconductor, the effective pair potentials felt by quasiparticles depend on the direction of their motion. By taking this effect into account, it is shown that the conductance spectra strongly depend on the crystal orientation. Using Green`s function method, local density of states (LDOS) in superconductor is also calculated. The close relation between conductance spectra and LDOS is presented. The calculation is compared with experimental spectra of high-{Tc} superconductors.

  16. Superconductor materials engineering

    NASA Astrophysics Data System (ADS)

    Shumay, William C., Jr.

    1988-11-01

    The development status of the most promising high-temperature superconducting oxides is discussed with a view to the diversity of the compounds being investigated and the difficulties yet to be surmounted in their fabrication into commercially applicable products such as cables and thin films. Attention is given to R&D expenditures, laser processing methods for novel material phases, optimization methods for bulk superconductors, wire and filament production methods for large systems, explosive processing for matrix compatibility, the use of binders in tape casting and wire-forming, screen-printing of superconductor patterns, and thallium oxide-containing compositions promising higher transition temperatures.

  17. 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)

  18. 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.

  19. Heavy atom nitroxyl radicals. I: An ab initio study of the ground and lower electronic excited states of the H2As=O free radical

    NASA Astrophysics Data System (ADS)

    Tarroni, Riccardo; Clouthier, Dennis J.

    2009-09-01

    A series of ab initio calculations have been undertaken to predict the spectroscopic properties of the ground and first two excited states of the recently discovered arsenyl (H2AsO) free radical. This 13 valence electron species can be viewed as similar to the formaldehyde radical anion with a ground state electron configuration of ⋯(π)2(n)2(π∗)1. The arsenyl radical is nonplanar (pyramidal) in the ground state with a 59° out-of-plane angle and a 1.67 Å AsO bond length. It has a low-lying n-π ∗(Ã A2″) excited state (Te˜5000 cm-1) which has a much larger out-of-plane angle (86°) and longer AsO bond length (1.81 Å). The π-π ∗(B˜ A2') excited state at ˜20 500 cm-1 is less pyramidal (out-of-plane angle=70°) and has a somewhat shorter AsO bond (1.77 Å). Similar trends are found for the H2PO and H2NO free radicals, although the latter has a planar ground state, due to sp2 hybridization of the N atom, and a very long B˜ state AsO bond length. The geometric variations of the ground and excited states of the H2EO (E=N, P, As) radicals, as well as the ground states of the corresponding anions and cations, can be readily rationalized from the Walsh diagram of the anion. The variations in the E-O bond length are a result of changes in both the orbital occupancy and pyramidalization of the molecule. The results of the present work have been employed in the analysis of the B˜ A2'-X˜ A2' electronic band system of the H2AsO free radical as reported in the companion paper.

  20. Redetermination of eveite, Mn2AsO4(OH), based on single-crystal X-ray diffraction data

    PubMed Central

    Yang, Yongbo W.; Stevenson, Ryan A.; Siegel, Alesha M.; Downs, Gordon W.

    2011-01-01

    The crystal structure of eveite, ideally Mn2(AsO4)(OH) [dimanganese(II) arsenate(V) hydroxide], was refined from a single crystal selected from a co-type sample from Långban, Filipstad, Varmland, Sweden. Eveite, dimorphic with sarkinite, is structurally analogous with the important rock-forming mineral andalusite, Al2OSiO4, and belongs to the libethenite group. Its structure consists of chains of edge-sharing distorted [MnO4(OH)2] octa­hedra (..2 symmetry) extending parallel to [001]. These chains are cross-linked by isolated AsO4 tetra­hedra (..m symmetry) through corner-sharing, forming channels in which dimers of edge-sharing [MnO4(OH)] trigonal bipyramids (..m symmetry) are located. In contrast to the previous refinement from Weissenberg photographic data [Moore & Smyth (1968 ▶). Am. Mineral. 53, 1841–1845], all non-H atoms were refined with anisotropic displacement param­eters and the H atom was located. The distance of the donor and acceptor O atoms involved in hydrogen bonding is in agreement with Raman spectroscopic data. Examination of the Raman spectra for arsenate minerals in the libethenite group reveals that the position of the peak originating from the O—H stretching vibration shifts to lower wavenumbers from eveite, to adamite, zincolivenite, and olivenite. PMID:22199466

  1. Gaia16aso, Gaia16asq, Gaia16asu and Gaia16atb candidate supernovae near galaxies confirmed by Mercator/Maia imaging

    NASA Astrophysics Data System (ADS)

    Blanco-Cuaresma, S.; Roelens, M.; Semaan, T.; Palaversa, L.; Mowlavi, N.; Eyer, L.

    2016-07-01

    We report confirmation of Gaia Science Alerts transients Gaia16aso, Gaia16asq, Gaia16asu and Gaia16atb. Images were obtained in G and R bands of the Maia instrument mounted to the Flemish 1.2m Mercator telescope at Roque de los Muchachos observatory, La Palma, Canary Islands, Spain, on 2016 July 04 - 05. These new sources are supernovae candidates near galaxies and they are not visible in archival 2MASS and DSS images: Gaia16aso, Gaia16asq, Gaia16asu and Gaia16atb.

  2. Platform for engineering topological superconductors: Superlattices on Rashba superconductors

    NASA Astrophysics Data System (ADS)

    Lu, Yao; He, Wen-Yu; Xu, Dong-Hui; Lin, Nian; Law, K. T.

    2016-07-01

    The search for topological superconductors which support Majorana fermion excitations has been an important topic in condensed matter physics. In this work, we propose an experimental scheme for engineering topological superconductors. In this scheme, by manipulating the superlattice structure of organic molecules placed on top of a superconductor with Rashba spin-orbit coupling, topological superconducting phases can be achieved without or with little fine tuning of the chemical potential. Moreover, superconductors with different Chern numbers can be obtained by changing the superlattice structure of the organic molecules.

  3. "Fluctuoscopy" of Superconductors

    NASA Astrophysics Data System (ADS)

    Varlamov, A. A.

    Study of fluctuation phenomena in superconductors (SCs) is the subject of great fundamental and practical importance. Understanding of their physics allowed to clear up the fundamental properties of SC state. Being predicted in 1968, one of the fluctuation effects, namely paraconductivity, was experimentally observed almost simultaneously. Since this time, fluctuations became a noticeable part of research in the field of superconductivity, and a variety of fluctuation effects have been discovered. The new wave of interest to fluctuations (FL) in superconductors was generated by the discovery of cuprate oxide superconductors (high-temperature superconductors, HTS), where, due to extremely short coherence length and low effective dimensionality of the electron system, superconductive fluctuations manifest themselves in a wide range of temperatures. Moreover, anomalous properties of the normal state of HTS were attributed by many theorists to strong FL in these systems. Being studied in the framework of the phenomenological Ginzburg-Landau theory and, more extensively, in diagrammatic microscopic approach, SC FLs side by side with other quantum corrections (weak localization, etc.) became a new tool for investigation and characterization of such new systems as HTS, disordered electron systems, granular metals, Josephson structures, artificial super-lattices, etc. The characteristic feature of SC FL is their strong dependence on temperature and magnetic fields in the vicinity of phase transition. This allows one to definitely separate the fluctuation effects from other contributions and to use them as the source of information about the microscopic parameters of a material. By their origin, SC FLs are very sensitive to relaxation processes, which break phase coherence. This allows using them for versatile characterization of SC. Today, one can speak about the " fluctuoscopy" of superconductive systems. In review, we present the qualitative picture both of thermodynamic

  4. Superconductor stability 90: A review

    SciTech Connect

    Dresner, L.

    1990-01-01

    This paper reviews some recent developments in the field of stability of superconductors. The main topics dealt with are hydrodynamic phenomena in cable-in-conduit superconductors, namely, multiple stability, quench pressure, thermal expulsion, and thermal hydraulic quenchback, traveling normal zones in large, composite conductors, such as those intended for SMES, and the stability of vapor-cooled leads made of high-temperature superconductors. 31 refs., 5 figs.

  5. 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.

  6. Exploration and monitoring geothermal activity using Landsat ETM + images. A case study at Aso volcanic area in Japan

    NASA Astrophysics Data System (ADS)

    Mia, Md. Bodruddoza; Nishijima, Jun; Fujimitsu, Yasuhiro

    2014-04-01

    Thermal activity monitoring in and around active volcanic areas using remote sensing is an essential part of volcanology nowadays. Three identical approaches were used for thermal activity exploration at Aso volcanic area in Japan using Landsat ETM + images. First, the conventional methods for hydrothermal alteration mapping were applied to find the most active thermal region after exploring geothermal indicator minerals. Second, we found some thermally highly anomalous regions around Nakadake crater using land surface temperature estimation. Then, the Stefan-Boltzmann equation was used for estimating and also monitoring radiative heat flux (RHF) from the most active region of about 8 km2 in and around Nakadake crater in the central part of the Aso volcano. To fulfill the required parameter in the Stefan-Boltzmann equation for radiative heat flux, the NDVI (Normalized differential vegetation index) method was used for spectral emissivity, and the mono-window algorithm was used for land surface temperature of this study area. The NDVI value was used to divide land-cover in the study area into four types: water, bare ground, mixed and vegetated land. The bare land was found within the most active region. Vegetation coverage area showed an inverse relationship with total RHF in this study as health of thermally stressed vegetation supports this relationship. The spatial distribution of spectral emissivity ranged from 0.94 to 0.99 in our study. Land surface temperature was estimated using a mono-window algorithm and was highest LST in 2008 and lowest in 2011. The results of RHF showed that the highest pixel RHF was found to be about 296 W/m2 in 2008. Total RHF was obtained of about 607 MW in 2002 and the lowest was about 354 MW in 2008. The RHF anomaly area was found the highest in 2002 and was lowest in 2011. The highest total heat discharge rate (HDR) obtained about 3918 MW in 2002 and lowest total HDR about 2289 MW in 2008 from this study area. But in the case of

  7. 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.

  8. Overview of organic superconductors

    SciTech Connect

    Mori, Hatsumi . Nagoya Division)

    1994-01-10

    Organic materials which are usually used for insulators, were shown to be an electrical conductor by H. Akamatsu, H. Inokuchi, and Y. Matsunaga in 1954. Moreover, J.P. Ferraris et al. showed that TTF [center dot] TCNQ was stably metallic down to around 60 K in 1973. Because of a low dimensionality of organic compound, however, a stabilization of an electronic state and a destabilization of a periodic lattice constructed a charge density wave which led a metal-insulator transition (a Peierls transition). After overcoming this low dimensionality, D. Jerome et al. discovered the first organic superconductor, (TMTSF)[sub 2] PF[sub 6] ([Tc] = 0.9 K (12kbar)) in 1980. Then with the resisting up of [Tc] constantly, the superconductor [kappa]-(BEDT-TTF)[sub 2](NCS)[sub 2] ([Tc] = 10.4 K) was found in 1987 and the [Tc] of [kappa]-(BEDT-TTF)[sub 2]Cu[N(CN)[sub 2

  9. Probing Topological Superconductors

    NASA Astrophysics Data System (ADS)

    Schmeltzer, David

    2015-03-01

    The presence of attractive interaction on the surface of a 3D topological insulator which is characterized by spinors carrying a Berry phase of π gives rise to superconductivity that support space time half vortices (Majorana zero modes). We construct the effective dual action for the superconductor with the vortices, and show that the 2 n Majorana fermions are localized and can be replaced with n spinless fermions. The effect of the Majorana zero modes can be observed trough the the Andreev cross reflection when metallic leads are attached to the superconductor. The presence of the Majorana fermions can be detected with transverse sound waves. We have computed the effect of elastic strain fields and obtain an anomalous response indicating the presence of the Majorana fermions.

  10. Analytic holographic superconductor

    NASA Astrophysics Data System (ADS)

    Herzog, Christopher P.

    2010-06-01

    We investigate a holographic superconductor that admits an analytic treatment near the phase transition. In the dual 3+1-dimensional field theory, the phase transition occurs when a scalar operator of scaling dimension two gets a vacuum expectation value. We calculate current-current correlation functions along with the speed of second sound near the critical temperature. We also make some remarks about critical exponents. An analytic treatment is possible because an underlying Heun equation describing the zero mode of the phase transition has a polynomial solution. Amusingly, the treatment here may generalize for an order parameter with any integer spin, and we propose a Lagrangian for a spin-two holographic superconductor.

  11. Holographic Superconductor Vortices

    SciTech Connect

    Montull, Marc; Pomarol, Alex; Silva, Pedro J.

    2009-08-28

    A gravity dual of a superconductor at finite temperature has been recently proposed. We present the vortex configuration of this model and study its properties. In particular, we calculate the free energy as a function of an external magnetic field, the magnetization, and the superconducting density. We also find the two critical magnetic fields that define the region in which the vortex configurations are energetically favorable.

  12. Electronic properties of highly-active Ag3AsO4 photocatalyst and its band gap modulation: an insight from hybrid-density functional calculations.

    PubMed

    Reunchan, Pakpoom; Boonchun, Adisak; Umezawa, Naoto

    2016-08-17

    The electronic structures of highly active Ag-based oxide photocatalysts Ag3AsO4 and Ag3PO4 are studied by hybrid-density functional calculations. It is revealed that Ag3AsO4 and Ag3PO4 are indirect band gap semiconductors. The Hartree-Fock mixing parameters are fitted for experimental band gaps of Ag3AsO4 (1.88 eV) and Ag3PO4 (2.43 eV). The smaller electron effective mass and the lower valence band edge of Ag3AsO4 are likely to be responsible for the superior photocatalytic oxidation reaction to Ag3PO4. The comparable lattice constant and analogous crystal structure between the two materials allow the opportunities of fine-tuning the band gap of Ag3AsxP1-xO4 using a solid-solution approach. The development of Ag3AsxP1-xO4 should be promising for the discovery of novel visible-light sensitized photocatalysts. PMID:27502998

  13. Coordination of Advanced Solar Observatory (ASO) Science Working Group (SWG) for the study of instrument accommodation and operational requirements on space station

    NASA Technical Reports Server (NTRS)

    Wu, S. T.

    1989-01-01

    The objectives are to coordinate the activities of the Science Working Group (SWG) of the Advanced Solar Observatory (ASO) for the study of instruments accommodation and operation requirements on board space station. In order to facilitate the progress of the objective, two conferences were organized, together with two small group discussions.

  14. 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.

  15. The oscillation model of hydrothermal dynamics beneath Aso volcano, southwest Japan after small eruption on May 2011: A new understanding model using repeated absolute and relative gravity measurement

    NASA Astrophysics Data System (ADS)

    Sofyan, Yayan; Nishijima, Jun; Fujimitsu, Yasuhiro; Yoshikawa, Shin; Kagiyama, Tsuneomi; Ohkura, Takahiro

    2016-01-01

    At the end of 2010, the seismic activity in Aso volcano intensely increased and water level in the Nakadake crater decreased until early in 2011, then was followed by a small eruption in May 2011. After the eruption and heavy rain, the volcanic activity subsided to calm period, crater bottom was refilled with water, and water level increased in the Nakadake crater. The next tremor reappeared in 2014 and tracked to eruption in November 2014. This eruptive pattern and water level variation in the crater repeatedly appeared on the surface, and it should be related to the hydrothermal dynamics beneath Aso volcano. We initiated the gravity measurements in relation to hydrothermal dynamics in the subsurface of Aso volcano using Scintrex CG-5 (549) and LaCoste Romberg type G-1016 relative gravimeter at 28 benchmarks in April 2011, one month before the eruption. The repeated gravity measurements continue to monitor Aso volcano with a series of the measurement after the eruption in every three months to a half year. We analyze the gravity variation from 2011 to 2014 between the time of the phreatic and strombolian eruption. The measurements covered the area more than 60 km2 in the west side of Aso caldera. A new gravity network was also installed in May 2010 at seven benchmarks using A10-017 absolute gravimeter, which re-occupied in October 2010, June 2011 and two benchmarks in June 2014. As a result, the gravity changes distinguish hydrothermal dynamic in the subsurface, which has a direct correlation to water level fluctuation in the crater, after the first eruption and before the second discharge. The monitoring data notice large gravity changes between the surveys at benchmarks around Nakadake crater and Kusasenri area. The simple 3D inversion models of the 4-D gravity data deduce the density contrast distribution beneath Aso volcano. The inversion and mass change result generate the oscillation typical as a new understanding model. The variation of the mass shows a

  16. Li3Al(MoO2)2O2(AsO4)2

    PubMed Central

    Hajji, Mounir; Zid, Mohamed Faouzi; Driss, Ahmed

    2009-01-01

    Single crystals of trilithium(I) aluminium(III) bis­[dioxidomolybdenum(VI)] dioxide bis­[arsenate(V)], Li3AlMo2As2O14, have been prepared by solid-state reaction at 788 K. The structure consists of AsO4 tetra­hedra, AlO6 octa­hedra and Mo2O10 groups sharing corners to form a three-dimensional framework containing channels running respectively along the [100] and [010] directions, where the Li+ ions are located. This structure is compared with compounds having (MX 2O12)n chains (M = Mo, Al and X = P, As) and others containing M 2O10 (M = Mo, Fe) dimers. PMID:21582037

  17. Sudden changes in the amplitude-frequency distribution of long-period tremors at Aso volcano, southwest Japan

    NASA Astrophysics Data System (ADS)

    Sandanbata, Osamu; Obara, Kazushige; Maeda, Takuto; Takagi, Ryota; Satake, Kenji

    2015-12-01

    We observed the activity of long-period tremors (LPTs) with a period of ~15 s at Aso volcano, Japan, during a 3 year period including the 2014 eruptions. The number of LPTs detected systematically increased 3 months before the Strombolian eruptions. LPT activity can be divided into five stages based on rapid changes in the maximum LPT amplitude. The amplitude-frequency relation follows an exponential distribution during each stage before the Strombolian eruptions, with different characteristic amplitudes for each stage, indicating that the scale of the source property changed in stages. However, during a stage that persisted for 6 days after the onset of Strombolian activity, the amplitude-frequency relation temporarily followed a power law distribution, indicating that the LPT source process no longer had a characteristic scale. In the last stage, the amplitude-frequency relation returned to an exponential distribution. We therefore conclude that the physical source of volcanic LPTs changed during the eruption period.

  18. The mixed anion mineral parnauite Cu 9[(OH) 10|SO 4|(AsO 4) 2]·7H 2O—A Raman spectroscopic study

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; Keeffe, Eloise C.

    2011-10-01

    The mixed anion mineral parnauite Cu 9[(OH) 10|SO 4|(AsO 4) 2]·7H 2O from two localities namely Cap Garonne Mine, Le Pradet, France and Majuba Hill mine, Pershing County, Nevada, USA has been studied by Raman spectroscopy. The Raman spectrum of the French sample is dominated by an intense band at 975 cm -1 assigned to the ν1 (SO 4) 2- symmetric stretching mode and Raman bands at 1077 and 1097 cm -1 may be attributed to the ν3 (SO 4) 2- antisymmetric stretching mode. Two Raman bands 1107 and 1126 cm -1 are assigned to carbonate CO 32- symmetric stretching bands and confirms the presence of carbonate in the structure of parnauite. The comparatively sharp band for the Pershing County mineral at 976 cm -1 is assigned to the ν1 (SO 4) 2- symmetric stretching mode and a broad spectral profile centered upon 1097 cm -1 is attributed to the ν3 (SO 4) 2- antisymmetric stretching mode. Two intense bands for the Pershing County mineral at 851 and 810 cm -1 are assigned to the ν1 (AsO 4) 3- symmetric stretching and ν3 (AsO 4) 3- antisymmetric stretching modes. Two Raman bands for the French mineral observed at 725 and 777 cm -1 are attributed to the ν3 (AsO 4) 3- antisymmetric stretching mode. For the French mineral, a low intensity Raman band is observed at 869 cm -1 and is assigned to the ν1 (AsO 4) 3- symmetric stretching vibration. Chemical composition of parnauite remains open and the question may be raised is parnauite a solid solution of two or more minerals such as a copper hydroxy-arsenate and a copper hydroxy sulphate.

  19. Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor

    NASA Astrophysics Data System (ADS)

    Charnukha, A.; Thirupathaiah, S.; Zabolotnyy, V. B.; Büchner, B.; Zhigadlo, N. D.; Batlogg, B.; Yaresko, A. N.; Borisenko, S. V.

    2015-05-01

    In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature Tc ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe0.92Co0.08AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.

  20. Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor

    PubMed Central

    Charnukha, A.; Thirupathaiah, S.; Zabolotnyy, V. B.; Büchner, B.; Zhigadlo, N. D.; Batlogg, B.; Yaresko, A. N.; Borisenko, S. V.

    2015-01-01

    In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature Tc ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe0.92Co0.08AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors. PMID:25997611

  1. Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor.

    PubMed

    Charnukha, A; Thirupathaiah, S; Zabolotnyy, V B; Büchner, B; Zhigadlo, N D; Batlogg, B; Yaresko, A N; Borisenko, S V

    2015-01-01

    In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature Tc ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe(0.92)Co(0.08)AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors. PMID:25997611

  2. Conventional magnetic superconductors

    DOE PAGESBeta

    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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Plasmons in strong superconductors

    SciTech Connect

    Baldo, M.; Ducoin, C.

    2011-10-15

    We present a study of the possible plasmon excitations that can occur in systems where strong superconductivity is present. In these systems the plasmon energy is comparable to or smaller than the pairing gap. As a prototype of these systems we consider the proton component of Neutron Star matter just below the crust when electron screening is not taken into account. For the realistic case we consider in detail the different aspects of the elementary excitations when the proton, electron components are considered within the Random-Phase Approximation generalized to the superfluid case, while the influence of the neutron component is considered only at qualitative level. Electron screening plays a major role in modifying the proton spectrum and spectral function. At the same time the electron plasmon is strongly modified and damped by the indirect coupling with the superfluid proton component, even at moderately low values of the gap. The excitation spectrum shows the interplay of the different components and their relevance for each excitation modes. The results are relevant for neutrino physics and thermodynamical processes in neutron stars. If electron screening is neglected, the spectral properties of the proton component show some resemblance with the physical situation in high-T{sub c} superconductors, and we briefly discuss similarities and differences in this connection. In a general prospect, the results of the study emphasize the role of Coulomb interaction in strong superconductors.

  8. Enhanced superconductors. Final report

    SciTech Connect

    Olsen, R.B.

    1992-05-01

    One of the major challenges facing high temperature superconductors is the making of non-brittle materials. Based on the successful discovery of high temperature perovskite superconductors, a new class of superconducting materials is hypothesized. The proposed class will be mechanically tough and may have high critical temperatures. The proposed material will be inexpensive to manufacture and easily formed into wires and bands. The project's research goal was to detect a superconducting transition in a specific material within this proposed new class. Substantial progress was made toward this objective. In Phase I a major milestone, the bulk conversion of a precursor material, was successfully accomplished. The second model precursor polymer, Polychlorofluoroethylene (PCFE), was synthesized for this study. This allowed the possibility of making low defect polyfluoroacetylene. This synthesis route yielded poly(fluoroacetylene) with a significantly lower defect density when compared to HF-eliminated fluoropolymer films. The final phase of this work was directed to synthesis of poly(2,3,5,6-tetrafluoro-para-phenylene vinylene) (PTFPPV). While making significant progress in synthesizing conducting polymers with polar or polarizable groups, this study did not reach its ultimate goal of producing a model compound with all of the necessary chemical properties to test the exciton model of superconductivity.

  9. Attempt of volcanomagnetic change detection by repeated aeromagnetic survey aeromagnetic survey on Aso and Kuju volcano, central Kyushu Japan -

    NASA Astrophysics Data System (ADS)

    Utsugi, M.; Tanaka, Y.; Kagiyama, T.; Okubo, A.

    2006-12-01

    Recently, geomagnetic field observation is successfully applied to many active volcanos to detect the volcano- magnetic changes. These observations are usually based on the continuous or repeated observation stations setting on the ground near the active area. From these observations, we can obtain high accurate information about the temporal geomagnetic field changes. But we can obtain only limited information about the special distribution of field changes. To interpret the geomagnetic field changes to underground heat transfer, we have to know the special distribution of the geomagnetic changes. To obtain the detailed information about the spatial distribution, aeromagnetic survey is usually used. In our study, we tried to use this method to detect the volcanomagnetic change. The main problem of aeromagnetic repeated observation is the difficulty of the observation point control. In the two flights, it is impossible that quite the same place flies. So that, it is very difficult to separate a change according to the volcanic activity and a spatial change. But, if we know detailed 3-D distribution of geomagnetic field and we can estimate the field intensity on the arbitrary point, we can correct the spatial variation of the repeated aeromagnetic survey data caused by the difference of flight position, and it may be possible to detect the field changes associated with the volcanic activities. For this purpose, we made very high density and low altitude helicopter-borne aeromagnetic survey on Aso and Kuju volcano in July 2002 and Dec. 2004. Each observation was done by a different approach. On Aso volcano, an extremely high density aeromagnetic observation was carried out. The survey area was selected as NS1200 x EW1200 x 300m region above the Nakadake crater which is the most active area on Aso volcano. The flight was made in 8 heights. The total numbers of measurements were about 8200. Based on the equivalent anomaly method, which is usually used to calculate the

  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. Spin manipulation in nanoscale superconductors

    NASA Astrophysics Data System (ADS)

    Beckmann, D.

    2016-04-01

    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.

  12. 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. PMID:27001949

  13. 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.}

  14. The molecular structure of the multianion mineral hidalgoite PbAl 3(AsO 4)(SO 4)(OH) 6 - Implications for arsenic removal from soils

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; Palmer, Sara J.; Xi, Yunfei

    2011-11-01

    The objective of this research is to determine the molecular structure of the mineral hidalgoite PbAl 3(AsO 4)(SO 4)(OH) 6 using vibrational spectroscopy. The mineral is found in old mine sites. Observed bands are assigned to the stretching and bending vibrations of (SO 4) 2- and (AsO 4) 3- units, stretching and bending vibrations of hydrogen bonded (OH) - ions and Al 3+-(O,OH) units. The approximate range of O-H⋯O hydrogen bond lengths is inferred from the Raman and infrared spectra. Values of 2.6989 Å, 2.7682 Å, 2.8659 Å were obtained. The formation of hidalgoite may offer a mechanism for the removal of arsenic from the environment.

  15. Computational search of novel superconductors

    NASA Astrophysics Data System (ADS)

    Yin, Zhiping

    The recently discovered 200 K high temperature superconductivity in the hydrogen sulfur material under high pressure was first successfully predicted by first-principles computation in a quantitative fashion, demonstrating the power of computation in the search of new superconductors. With the rapid advancement of theory, algorithm, and computer power, computation will play an increasingly important role. In this talk, I will first summarize the key features of different families of high temperature superconductors, including the iron pnictide and chalcogenide superconductors, the transition metal chloronitrides, and Bi-based superconductors. Then I will show how to use the key features as guidance to design novel candidate materials of high temperature superconductivity by utilizing a combination of different computational methods and tools, including evolutionary structural search method, density functional theory and dynamical mean field theory. A few candidate materials will be given towards the end of the talk for interested experimentalists and theorists to test and explore

  16. 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.

  17. 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)

  18. A new method for As(V) removal from waters by precipitation of mimetite Pb5(AsO4)3Cl on Pb-activated zeolite

    NASA Astrophysics Data System (ADS)

    Manecki, Maciej; Buszkiewicz, Urszula

    2016-04-01

    A new method for removal of arsenate AsO43‑ ions from aqueous solutions is proposed. The principle of the method stems from precipitation of very insoluble crystalline lead arsenate apatite (mimetite Pb5(AsO4)3Cl) induced by bringing in contact Pb-activated zeolite and As-contaminated water in the presence of Cl‑. Zeolite is activated by sorption of Pb2+ followed by washing with water to remove the excess of Pb and to desorbe weakly adsorbed ions. Lead adsorbed on zeolite is bound strong enough to prevent desorption by water but weak enough to undergo desorption induced by heterogeneous precipitation of mimetite nanocrystals on the surface of zeolite. The experiment consisted of two steps. In the first step, aliquots of 0.5 g of natural clinoptilolite zeolite (from Zeocem a.s., Bystré, Slovak Republic) were reacted with 40 mL of solutions containing 20, 100, 500, and 2000 mg Pb/L (pH =4.5; reaction for 30 minutes followed by centrifugation). The amount of Pb sorbed was calculated from the drop of Pb concentration in solution. Centrifuged zeolite was washed three times by mixing with 10 mL of DDI water, followed by centrifugation. No Pb was detected in the water after second washing. Wet pulp resulting from this stage was exposed to solutions containing 70 mg/L Cl‑ and various concentrations of AsO43‑ (2 and 100 mg As/L; pH=4). Complete removal of As was observed for 2 mg As/L solutions mixed with zeolite-20 and zeolite-100. The precipitation of mimetite Pb5(AsO4)3Cl in the form of hexagonal crystals ca. 0.25 μm in size was observed using SEM/EDS. This work is partially funded by AGH research grant no 11.11.140.319.

  19. Be(3)(AsO4)2. 2H2O, a new berylloarsenate phase containing bridged tetrahedral 3-rings. Technical report, 1 June 1992-31 May 1993

    SciTech Connect

    Harrison, W.T.; Nenoff, T.M.; Gier, T.E.; Stucky, G.D.

    1993-02-15

    The high-temperature/high-pressure hydrothermal synthesis and X-ray single crystal structure of Be3(AsO4)2(dot)2H2O is described: the title compound contains a three-dimensional network of BeO4 and AsO4 tetrahedra. The structural motif includes infinite layers of bridged tetrahedral 3- and 4-rings. 9Be MAS NMR data are consistent with the Be-atom environments in the crystal structure.

  20. Organic conductors and superconductors

    NASA Astrophysics Data System (ADS)

    Jérome, D.; Schulz, H. J.

    2002-01-01

    This review attempts to present the most salient developments of research on organic conductors and superconductors during the past 10 years. A theoretical introduction treats instabilities of quasi-one-dimensional electron systems and associated precursor effects which are relevant to the experimental results on organic conductors. We then describe the characterization of quasi-one-dimensional organic conductors by their transport, optical and magnetic properties. Finally, two sections are devoted to the experimental investigation of the low temperature instabilities: lattice instability in TTF-TCNQ and related compounds, superconducting or antiferromagnetic instabilities in the (TMTSF)2X series. The importance of one-dimensional fluctuations is emphasized in both lattice and superconducting instabilities.

  1. 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

  2. Aperiodic Weak Topological Superconductors.

    PubMed

    Fulga, I C; Pikulin, D I; Loring, T A

    2016-06-24

    Weak topological phases are usually described in terms of protection by the lattice translation symmetry. Their characterization explicitly relies on periodicity since weak invariants are expressed in terms of the momentum-space torus. We prove the compatibility of weak topological superconductors with aperiodic systems, such as quasicrystals. We go beyond usual descriptions of weak topological phases and introduce a novel, real-space formulation of the weak invariant, based on the Clifford pseudospectrum. A nontrivial value of this index implies a nontrivial bulk phase, which is robust against disorder and hosts localized zero-energy modes at the edge. Our recipe for determining the weak invariant is directly applicable to any finite-sized system, including disordered lattice models. This direct method enables a quantitative analysis of the level of disorder the topological protection can withstand. PMID:27391744

  3. Aperiodic Weak Topological Superconductors

    NASA Astrophysics Data System (ADS)

    Fulga, I. C.; Pikulin, D. I.; Loring, T. A.

    2016-06-01

    Weak topological phases are usually described in terms of protection by the lattice translation symmetry. Their characterization explicitly relies on periodicity since weak invariants are expressed in terms of the momentum-space torus. We prove the compatibility of weak topological superconductors with aperiodic systems, such as quasicrystals. We go beyond usual descriptions of weak topological phases and introduce a novel, real-space formulation of the weak invariant, based on the Clifford pseudospectrum. A nontrivial value of this index implies a nontrivial bulk phase, which is robust against disorder and hosts localized zero-energy modes at the edge. Our recipe for determining the weak invariant is directly applicable to any finite-sized system, including disordered lattice models. This direct method enables a quantitative analysis of the level of disorder the topological protection can withstand.

  4. Raman spectroscopy of the multi-anion mineral schlossmacherite (H 3O,Ca)Al 3(AsO 4,PO 4,SO 4) 2(OH) 6

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; Palmer, Sara J.; Xi, Yunfei

    2012-02-01

    The mineral schlossmacherite (H 3O,Ca)Al 3(AsO 4,PO 4,SO 4) 2(OH) 6, a multi-cation-multi-anion mineral of the beudantite mineral subgroup has been characterised by Raman spectroscopy. The mineral and related minerals functions as a heavy metal collector and is often amorphous or poorly crystalline, such that XRD identification is difficult. The Raman spectra are dominated by an intense band at 864 cm -1, assigned to the symmetric stretching mode of the AsO 43- anion. Raman bands at 809 and 819 cm -1 are assigned to the antisymmetric stretching mode of AsO 43-. The sulphate anion is characterised by bands at 1000 cm -1 ( ν1), and at 1031, 1082 and 1139 cm -1 ( ν3). Two sets of bands in the OH stretching region are observed: firstly between 2800 and 3000 cm -1 with bands observed at 2850, 2868, 2918 cm -1 and secondly between 3300 and 3600 with bands observed at 3363, 3382, 3410, 3449 and 3537 cm -1. These bands enabled the calculation of hydrogen bond distances and show a wide range of H-bond distances.

  5. Synthesis and Characterization of Bismuth Magnesium Phosphate and Arsenate: BiMg 2PO 6 and BiMg 2AsO 6

    NASA Astrophysics Data System (ADS)

    Huang, Jinfan; Gu, Qiuyi; Sleight, Arthur W.

    1993-08-01

    Two new compounds, BiMg 2PO 6 and BiMg 2AsO 6, have been synthesized and structurally characterized by single crystal and powder X-ray diffraction. Both compounds crystallize in the orthorhombic space group Cmcm (No. 63) with four formula units per unit cell. They are isostructural with bismuth magnesium vanadate, BiMg 2VO 6. The cell parameters for BiMg 2PO 6 are a = 7.801(2), b = 11.888(3), c = 5.273(2) Å, V = 489.0(2) Å 3 and for BiMg 2AsO 6 are a = 7.9142(5), b = 12.1637(8), c = 5.3898(4) Å, V = 518.9(2) Å 3. The formula for this series of compounds may be written as (BiO 2)Mg AO 4 to emphasize the (BiO 2) 1- chains and the (AO 4) 3- tetrahedral groups isolated from one another. Between these chains and tetrahedral groups sit Mg 2+ cations in an unusual fivefold coordination to oxygen. No emission bands were observed from BiMg 2PO 6 and BiMg 2AsO 6 under excitation with UV or visible radiation. The IR spectra of these compounds are compared to that of BiMg 2VO 6.

  6. Origin and mode of emplacement of lithic-rich breccias at Aso Volcano, Japan: Geological, paleomagnetic, and petrological reconstruction

    NASA Astrophysics Data System (ADS)

    Furukawa, Kuniyuki; Uno, Koji; Shinmura, Taro; Miyoshi, Masaya; Kanamaru, Tatsuo; Inokuchi, Hiroo

    2014-04-01

    Takajosan breccia rocks are distributed around the southwestern caldera rim of the Aso Volcano in Japan. They are characterized by coarse lithic breccias with a pumiceous matrix. The proximal coarse lithic breccias are divided into the lower massive unit and the upper stratified unit. The lower massive lithic breccias tend to transform laterally into tuff breccias and pumiceous lapilli tuffs. Paleomagnetic results showed that all of the deposits were deposited at high temperatures of 175-560 °C. This was also supported by geological characteristics such as spatter clasts, clasts with a bread-crust texture, and weakly welded parts. These features clearly show that the deposits originated from pyroclastic density currents (PDCs). The dense lithic-rich lithofacies, low vesicularity of pumice, lack of plinian fall deposits, and radial distribution indicate that the deposits were derived from boil-over PDCs rather than plinian column-collapse PDCs. The SiO2 contents of the matrix glasses of the proximal lower massive breccia showed a progressive decrease from the bottom toward the upper part. We interpret that this chemical variation corresponds to chemical zonation of the magma chamber. This indicates that the massive deposits aggraded progressively from the base upwards (progressive aggradation), rather than through en masse freezing. The vertical lithofacies changes of the proximal breccias from the lower massive to the upper stratified units indicate that a sustained current in a quasi-steady state switched to an unsteady current with the progression of the volcanic activity.

  7. Raman spectroscopic study of the mineral arsenogorceixite BaAl3AsO3(OH)(AsO4,PO4)(OH,F)6

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; Xi, Yunfei; Pogson, Ross E.

    2012-06-01

    Arsenogorceixite BaAl3AsO3(OH)(AsO4,PO4)(OH,F)6 belongs to the crandallite mineral subgroup of the alunite supergroup. Arsenogorceixite forms a continuous series of solid solutions with related minerals including gorceixite, goyazite, arsenogoyazite, plumbogummite and philipsbornite. Two minerals from (a) Germany and (b) from Ashburton Downs, Australia were analysed by Raman spectroscopy. The spectra show some commonality but the intensities of the peaks vary. Sharp intense Raman bands for the German sample, are observed at 972 and 814 cm-1 attributed to the ν1 PO43- and AsO43- symmetric stretching modes. Raman bands at 1014, 1057, 1148 and 1160 cm-1 are attributed to the ν1 PO2 symmetric stretching mode and ν3 PO43- antisymmetric stretching vibrations. Raman bands at 764 and 776 cm-1 and 758 and 756 cm-1 are assigned to the ν3 AsO43- antisymmetric stretching vibrations. For the Australian mineral, the ν1 PO43- band is found at 973 cm-1. The intensity of the arsenate bands observed at 814, 838 and 870 cm-1 is greatly enhanced. Two low intensity Raman bands at 1307 and 1332 cm-1 are assigned to hydroxyl deformation modes. The intense Raman band at 441 cm-1 with a shoulder at 462 cm-1 is assigned to the ν2 PO43- bending mode. Raman bands at 318 and 340 cm-1 are attributed to the (AsO4)3-ν2 bending. The broad band centred at 3301 cm-1 is assigned to water stretching vibrations and the sharper peak at 3473 cm-1 is assigned to the OH stretching vibrations. The observation of strong water stretching vibrations brings into question the actual formula of arsenogorceixite. It is proposed the formula is better written as BaAl3AsO3(OH)(AsO4,PO4)(OH,F)6·xH2O. The observation of both phosphate and arsenate bands provides a clear example of solid solution formation.

  8. Modelling of bulk superconductor magnetization

    NASA Astrophysics Data System (ADS)

    Ainslie, M. D.; Fujishiro, H.

    2015-05-01

    This paper presents a topical review of the current state of the art in modelling the magnetization of bulk superconductors, including both (RE)BCO (where RE = rare earth or Y) and MgB2 materials. Such modelling is a powerful tool to understand the physical mechanisms of their magnetization, to assist in interpretation of experimental results, and to predict the performance of practical bulk superconductor-based devices, which is particularly important as many superconducting applications head towards the commercialization stage of their development in the coming years. In addition to the analytical and numerical techniques currently used by researchers for modelling such materials, the commonly used practical techniques to magnetize bulk superconductors are summarized with a particular focus on pulsed field magnetization (PFM), which is promising as a compact, mobile and relatively inexpensive magnetizing technique. A number of numerical models developed to analyse the issues related to PFM and optimise the technique are described in detail, including understanding the dynamics of the magnetic flux penetration and the influence of material inhomogeneities, thermal properties, pulse duration, magnitude and shape, and the shape of the magnetization coil(s). The effect of externally applied magnetic fields in different configurations on the attenuation of the trapped field is also discussed. A number of novel and hybrid bulk superconductor structures are described, including improved thermal conductivity structures and ferromagnet-superconductor structures, which have been designed to overcome some of the issues related to bulk superconductors and their magnetization and enhance the intrinsic properties of bulk superconductors acting as trapped field magnets. Finally, the use of hollow bulk cylinders/tubes for shielding is analysed.

  9. 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.

  10. 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

  11. Topological semimetals and nodal superconductors

    NASA Astrophysics Data System (ADS)

    Chang, Po-Yao

    Besides topological band insulators, which have a full bulk gap, there are also gapless phases of matter that belong to the broad class of topological materials, such as topological semimetals and nodal superconductors. We systematically study these gapless topological phases described by the Bloch and Bogoliubov-de Gennes Hamiltonians. We discuss a generalized bulk-boundary correspondence, which relates the topological properties in the bulk of gapless topological phases and the protected zero-energy states at the boundary. We study examples of gapless topological phases, focusing in particular on nodal superconductors, such as nodal noncentrosymmetric superconductors (NCSs). We compute the surface density of states of nodal NCSs and interpret experimental measurements of surface states. In addition, we investigate Majorana vortex-bound states in both nodal and fully gapped NCSs using numerical and analytical methods. We show that different topological properties of the bulk Bogoliubov-quasiparticle wave functions reflect themselves in different types of zero-energy vortex-bound states. In particular, in the case of NCSs with tetragonal point-group symmetry, we find that the stability of these Majorana zero modes is guaranteed by a combination of reflection, time-reversal, and particle-hole symmetries. Finally, by using K-theory arguments and a dimensional reduction procedure from higher-dimensional topological insulators and superconductors, we derive a classification of topologically stable Fermi surfaces in semimetals and nodal lines in superconductors.

  12. Transpiration characteristics of forests and shrubland under land cover change within the large caldera of Mt. Aso, Japan

    NASA Astrophysics Data System (ADS)

    Miyazawa, Y.; Inoue, A.; Maruyama, A.

    2013-12-01

    Grassland within a caldera of Mt. Aso has been maintained for fertilizer production from grasses and cattle feeding. Due to the changes in the agricultural and social structure since 1950's, a large part of the grassland was converted to plantations or abandoned to shrublands. Because vegetations of different plant functional types differ in evapotranspiration; ET, a research project was launched to examine the effects of the ongoing land use change on the ET within the caldera, and consequently affect the surface and groundwater discharge of the region. As the part of the project, transpiration rate; E of the major 3 forest types were investigated using sap flow measurements. Based on the measured data, stomatal conductance; Gs was inversely calculated and its response to the environmental factors was modeled using Jarvis-type equation in order to estimate ET of a given part of the caldera based on the plant functional type and the weather data. The selected forests were conifer plantation, deciduous broadleaved plantation and shrubland, which were installed with sap flow sensors to calculate stand-level transpiration rate. Sap flux; Js did not show clear differences among sites despite the large differences in sapwood area. In early summer solar radiation was limited to low levels due to frequent rainfall events and therefore, Js was the function of solar radiation rather than other environmental factors, such as vapor pressure deficit and soil water content. Gs was well regressed with the vapor pressure deficit and solar radiation. The estimated E based on Gs model and the weather data was 0.3-1.2 mm day-1 for each site and was comparable to the E of grassland in other study sites. Results suggested that transpiration rate in growing was not different between vegetations but its annual value are thought to differ due to the different phenology.

  13. Chern-Simons superconductor

    NASA Astrophysics Data System (ADS)

    Banerjee, Nabamita; Dutta, Suvankar; Roychowdhury, Dibakar

    2014-12-01

    We study the effect of a bulk Chern-Simons (CS) term on a (3+1) dimensional type II superconductor in the context of the AdS/CFT correspondence. We holographically compute the supercurrent and find that it is nonlocal in nature. It receives nontrivial corrections due to the presence of the CS term. Considering a large limit of a parameter λ (we call this limit the long wavelength limit), which is effectively the high temperature limit of the theory, we find that this nonlocal supercurrent boils down to a local quantity. The leading term (without the CS term) of this current matches the result of the Ginzburg-Landau (GL) theory. We compute the effect of the CS term on the GL current and find that the effect is greatly suppressed at high temperature (\\frac{1}{{{T}4}}). Finally, the free energy of the vortex configuration has been calculated. The free energy also receives nontrivial correction on the order of 1/{{λ }2} in the long wavelength approximation.

  14. 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.

  15. 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. PMID:26933688

  16. 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.

  17. 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. PMID:27214291

  18. 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.

  19. Thin film superconductor magnetic bearings

    SciTech Connect

    Weinberger, B.R.

    1995-12-26

    A superconductor magnetic bearing includes a shaft that is subject to a load (L) and rotatable around an axis of rotation, a magnet mounted to the shaft, and a stator in proximity to the shaft. The stator has a superconductor thin film assembly positioned to interact with the magnet to produce a levitation force on the shaft that supports the load (L). The thin film assembly includes at least two superconductor thin films and at least one substrate. Each thin film is positioned on a substrate and all the thin films are positioned such that an applied magnetic field from the magnet passes through all the thin films. A similar bearing in which the thin film assembly is mounted on the shaft and the magnet is part of the stator also can be constructed. 8 figs.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Raman scattering in cuprate superconductors

    SciTech Connect

    Devereaux, T.P.; Kampf, A.P.

    1997-07-20

    A theory for electronic Raman scattering in the cuprate superconductors is presented with a specific emphasis on the polarization dependence of the spectra which can infer the symmetry of the energy gap. Signatures of the effects of disorder on the low frequency and low temperature behavior of the Raman spectra for different symmetry channels provide detailed information about the magnitude and the phase of the energy gap. Properties of the theory for finite T will be discussed and compared to recent data concerning the doping dependence of the Raman spectra in cuprate superconductors, and remaining questions will be addressed.

  6. 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.

  7. Internally cooled cabled superconductors. I

    NASA Astrophysics Data System (ADS)

    Hoenig, M. O.

    1980-07-01

    A state of the art review and survey of work performed at the Massachusetts Institute of Technology in the area of internally cooled cabled superconductors (ICCS) is presented. Topics examined include original concepts, hollow concept, and heat transfer using supercritical helium. Attention is given to the ICCS conductor and coil design as well as experiments with niobium-titanium.

  8. Dynamics of vortices in superconductors

    SciTech Connect

    Weinan, E.

    1992-12-31

    We study the dynamics of vortices in type-II superconductors from the point of view of time-dependent Ginzburg-Landau equations. We outline a proof of existence, uniqueness and regularity of strong solutions for these equations. We then derive reduced systems of ODEs governing the motion of the vortices in the asymptotic limit of large Ginzburg-Landau parameter.

  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. ASO: Antistreptolysin O titer

    MedlinePlus

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  12. Crystal chemistry of anhydrous Li uranyl phosphates and arsenates. II. Tubular fragments and cation-cation interactions in the 3D framework structures of Li 6[(UO 2) 12(PO 4) 8(P 4O 13)], Li 5[(UO 2) 13(AsO 4) 9(As 2O 7)], Li[(UO 2) 4(AsO 4) 3] and Li 3[(UO 2) 7(AsO 4) 5O)

    NASA Astrophysics Data System (ADS)

    Alekseev, Evgeny V.; Krivovichev, Sergey V.; Depmeier, Wulf

    2009-11-01

    Single crystals of the new compounds Li 6[(UO 2) 12(PO 4) 8(P 4O 13)] ( 1), Li 5[(UO 2) 13(AsO 4) 9(As 2O 7)] ( 2), Li[(UO 2) 4(AsO 4) 3] ( 3) and Li 3[(UO 2) 7(AsO 4) 5O)] ( 4) have been prepared using high-temperature solid state reactions. The crystal structures have been solved by direct methods: 1—monoclinic, C2/ m, a=26.963(3) Å, b=7.063(1) Å, c=19.639(1) Å, β=126.890(4)°, V=2991.2(6) Å 3, Z=2, R1=0.0357 for 3248 unique reflections with | F0|≥4 σ F; 2—triclinic, P1¯, a=7.1410(8) Å, b=13.959(1) Å, c=31.925(1) Å, α=82.850(2)°, β=88.691(2)°, γ=79.774(3)°, V=3107.4(4) Å 3, Z=2, R1=0.0722 for 9161 unique reflections with | F0|≥4 σ F; 3—tetragonal, I4 1/ amd, a=7.160(3) Å, c=33.775(9) Å, V=1732(1) Å 3, Z=4, R1=0.0356 for 318 unique reflections with | F0|≥4 σ F; 4—tetragonal, P4¯, a=7.2160(5) Å, c=14.6540(7) Å, V=763.04(8) Å 3, Z=1, R1=0.0423 for 1600 unique reflections with | F0|≥4 σ F. Structures of all the phases under consideration are based on complex 3D frameworks consisting of different types of uranium polyhedra (UO 6 and UO 7) and different types of tetrahedral TO 4 anions ( T=P or As): PO 4 and P 4O 13 in 1, AsO 4 and As 2O 7 in 2, and single AsO 4 tetrahedra in 3 and 4. In the structures of 1 and 2, UO 7 pentagonal bipyramids share edges to form (UO 5) ∞ chains extended along the b axis in 1 and along the a axis in 2. The chains are linked via single TO 4 tetrahedra into tubular units with external diameters of 11 Å in 1 and 11.5 Å in 2, and internal diameters of 4.1 Å in 1 and 4.5 Å in 2. The channels accommodate Li + cations. The tubular units are linked into 3D frameworks by intertubular complexes. Structures of 3 and 4 are based on 3D frameworks composed on layers united by (UO 5) ∞ infinite chains. Cation-cation interactions are observed in 2, 3, and 4. In 2, the structure contains a trimeric unit with composition [OU(1)O]-U(13)-[OU(2)O]. In the structures of 3 and 4, T-shaped dimers are

  13. A Raman spectroscopic study of the arsenate mineral chenevixite Cu2Fe2(3+)(AsO4)2(OH)4⋅H2O.

    PubMed

    Frost, Ray L; López, Andrés; Scholz, Ricardo; Lana, Cristiano; Xi, Yunfei

    2015-01-25

    We have studied the mineral chenevixite from Manto Cuba Mine, San Pedro de Cachiyuyo District, Inca de Oro, Chañaral Province, Atacama Region, Chile, using a combination of scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDX) and vibrational spectroscopy. Qualitative chemical analysis shows a homogeneous composition, with predominance of As, Fe, Al, Cu, Fe and Cu. Minor amounts of Si were also observed. Raman spectroscopy complimented with infrared spectroscopy has been used to assess the molecular structure of the arsenate minerals chenevixite. Characteristic Raman and infrared bands of the (AsO4)(3-) stretching and bending vibrations are identified and described. The observation of multiple bands in the (AsO4)(3-) bending region offers support for the loss of symmetry of the arsenate anion in the structure of chenevixite. Raman bands attributable to the OH stretching vibrations of water and hydroxyl units were analysed. Estimates of the hydrogen bond distances were made based upon the OH stretching wavenumbers. PMID:25064502

  14. Influence of UV rays on Feulgen-type staining with azure A-SO2 prepared with normal hydrochloric acid and sodium thiosulphate.

    PubMed

    Dutt, M K

    1981-07-01

    This communication presents a new method for the preparation of azure A-SO2 for use in Feulgen procedure. The salient feature of this method lies in the fact that azure A-SO2 can be decolourised with normal hydrochloric acid and sodium thiosulphate. The pH of this dye reagent is 2.3 and it is of water colour after filtration. The pH of this dye-reagent is raised to 4.0 with an aqueous solution of sodium hydroxide. Nuclear colouration with this newly developed dye-reagent on acid-hydrolysed DNA of tissue sections becomes fairly satisfactory under the usual laboratory conditions. Staining with this dye-reagent under exposure to UV ray is, however, vastly improved within 5 minutes as compared with the control. Stained sections do withstand treatment in SO2 water without exhibiting any leaching of the dye from the nuclei. Possible mode of action of UV rays in increasing the intensity of staining as well as the speed of reaction has been suggested. PMID:6167839

  15. Synthesis, crystal structure, electrical properties, and sodium transport pathways of the new arsenate Na4Co7(AsO4)6

    NASA Astrophysics Data System (ADS)

    Ben Smida, Youssef; Marzouki, Riadh; Georges, Samuel; Kutteh, Ramzi; Avdeev, Maxim; Guesmi, Abderrahmen; Zid, Mohamed Faouzi

    2016-07-01

    A new sodium cobalt (II) arsenate Na4Co7(AsO4)6 has been synthesized by a solid-state reaction and its crystal structure determined from single crystal X-ray diffraction data. It crystallizes in the monoclinic system, space group C2/m, with a=10.7098(9) Å, b=14.7837(9) Å, c=6.6845(7) Å, and β=105.545(9)°. The structure is described as a three-dimensional framework built up of corner-edge sharing CoO6, CoO4 and AsO4 polyhedra, with interconnecting channels along [100] in which the Na+ cations are located. The densest ceramics with relative density of 94% was obtained by ball milling and optimization of sintering temperature, and its microstructure characterized by scanning electron microscopy. The electrical properties of the ceramics were studied over a temperature interval from 280 °C to 560 °C using the complex impedance spectroscopy over the range of 13 MHz-5 Hz. The ionic bulk conductivity value of the sample at 360 °C is 2.51 10-5 S cm-1 and the measured activation energy is Ea=1 eV. The sodium migration pathways in the crystal structure were investigated computationally using the bond valence site energy (BVSE) model and classical molecular dynamics (MD) simulations.

  16. A Raman spectroscopic study of the arsenate mineral chenevixite Cu2Fe23+(AsO4)2(OH)4ṡH2O

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; López, Andrés; Scholz, Ricardo; Lana, Cristiano; Xi, Yunfei

    2015-01-01

    We have studied the mineral chenevixite from Manto Cuba Mine, San Pedro de Cachiyuyo District, Inca de Oro, Chañaral Province, Atacama Region, Chile, using a combination of scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDX) and vibrational spectroscopy. Qualitative chemical analysis shows a homogeneous composition, with predominance of As, Fe, Al, Cu, Fe and Cu. Minor amounts of Si were also observed. Raman spectroscopy complimented with infrared spectroscopy has been used to assess the molecular structure of the arsenate minerals chenevixite. Characteristic Raman and infrared bands of the (AsO4)3- stretching and bending vibrations are identified and described. The observation of multiple bands in the (AsO4)3- bending region offers support for the loss of symmetry of the arsenate anion in the structure of chenevixite. Raman bands attributable to the OH stretching vibrations of water and hydroxyl units were analysed. Estimates of the hydrogen bond distances were made based upon the OH stretching wavenumbers.

  17. [{Ni4 (OH)3 AsO4 }4 (B-α-PW9 O34 )4 ](28-) : A New Polyoxometalate Structural Family with Catalytic Hydrogen Evolution Activity.

    PubMed

    Lv, Hongjin; Chi, Yingnan; van Leusen, Jan; Kögerler, Paul; Chen, Zheyuan; Bacsa, John; Geletii, Yurii V; Guo, Weiwei; Lian, Tianquan; Hill, Craig L

    2015-11-23

    A new structural polyoxometalate motif, [{Ni4 (OH)3 AsO4 }4 (B-α-PW9 O34 )4 ](28-) , which contains the highest nuclearity structurally characterized multi-nickel-containing polyanion to date, has been synthesized and characterized by single-crystal X-ray diffraction, temperature-dependent magnetism and several other techniques. The unique central {Ni16 (OH)12 O4 (AsO4 )4 } core shows dominant ferromagnetic exchange interactions, with maximum χm T of 69.21 cm(3)  K mol(-1) at 3.4 K. Significantly, this structurally unprecedented complex is an efficient, water-compatible, noble-metal-free catalyst for H2 production upon visible light irradiation (photosensitizer=[Ir(ppy)2 (dtbbpy)][PF6 ]; sacrificial electron donor=triethylamine or triethanolamine). The highest turnover number of approximately 580, corresponding to a best quantum yield of approximately 4.07 %, is achieved when using triethylamine as electron donor in the presence of water. The mechanism of this photodriven process has been probed by time-solved luminescence and by static emission quenching. PMID:26448510

  18. Design for a Superconductor Discovery Engine (SCODEngine)

    NASA Astrophysics Data System (ADS)

    Isikaku-Ironkwe, O. Paul

    2010-03-01

    One of the grand challenges of superconductivity is achieving a paradigm shift from discovery by serendipity to discovery by design. Periodic Table-based Maps that involve electronegativity, valence electrons and atomic number that correlate with superconducting transition temperature can be used to design novel superconductors. Combining these maps with experimental databases on superconductors, databases of crystal structures and integrating material design software engine, we can re-design many known superconductor families and predict novel systems. By adding search engine technology with a ``knowledge discovery engine'', we produce a superconductor discovery engine (SCODEngine). The SCODEngine enables us to discover novel superconductors with the accelerated speed of a Google search. We have produced a primitive SCODEngine that may revolutionize novel superconductor search and discovery.

  19. Holographic complexity in gauge/string superconductors

    NASA Astrophysics Data System (ADS)

    Momeni, Davood; Mansoori, Seyed Ali Hosseini; Myrzakulov, Ratbay

    2016-05-01

    Following a methodology similar to [1], we derive a holographic complexity for two dimensional holographic superconductors (gauge/string superconductors) with backreactions. Applying a perturbation method proposed by Kanno in Ref. [2], we study behaviors of the complexity for a dual quantum system near critical points. We show that when a system moves from the normal phase (T >Tc) to the superconductor phase (T

  20. Electromagnetic dark energy and gravitoelectrodynamics of superconductors

    NASA Astrophysics Data System (ADS)

    de Matos, Clovis Jacinto

    2008-02-01

    It is shown that Beck and Mackey electromagnetic model of dark energy in superconductors can account for the non-classical inertial properties of superconductors, which have been conjectured by the author to explain the Cooper pair’s mass excess reported by Cabrera and Tate. A new fundamental scale of nature (the Planck-Einstein scale) for gravitation in low temperature condensed matter is proposed to host the gravitoelectrodynamic properties of superconductors.

  1. Recent progress on carbon-based superconductors

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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.

  2. 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. PMID:27351938

  3. Topological properties of ferromagnetic superconductors

    DOE PAGESBeta

    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

  4. 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.

  5. Topological properties of ferromagnetic superconductors

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  6. Fidelity approach in topological superconductors

    NASA Astrophysics Data System (ADS)

    Yao, Dao-Xin; Tian, Wen-Chuan; Huang, Guang-Yao; Wang, Zhi

    We study topological superconductivity in the spin-orbit coupling nanowire system by using the fidelity approach. The wire is modeled as a one layer lattice chain with Zeeman energy and spin-orbital coupling, which is in proximity to a multi-layer superconductor. In particular, we study the effects of disorders and find that the fidelity susceptibility has multiple peaks. It is revealed that one peak indicates the topological quantum phase transition, while other peaks are signaling the pinning of the Majorana bound states by disorders. Our study shows that fidelity and fidelity susceptibility are very useful to investigate the topological quantum phase transition in superconductors. This work is supported by NSFC-11574404, 11275279, and NBRPC-2012CB821400.

  7. Quaternary borocarbides: Relatively high Tc intermetallic superconductors and magnetic superconductors

    NASA Astrophysics Data System (ADS)

    Mazumdar, Chandan; Nagarajan, R.

    2015-07-01

    Discovery of superconductivity in Y-Ni-B-C (Tc ∼ 13 K) gave rise to the class of quaternary rare earth transition metal borocarbide superconductors. Before the discovery of Fe-based arsenide superconductors, this was the only class of materials containing a magnetic element, viz., Ni, yet exhibiting Tcs > 5 K. Many members of this class have high Tc (>10 K). Tc of ∼23 K in Y-Pd-B-C system equaled the record Tc known then, for intermetallics. Another feature that sets this class apart, is the occurrence of the exotic phenomenon of coexistence of superconductivity and magnetism at temperatures >5 K. Availability of large and electronically 'clean' single crystals and large Ginzburg-Landau (G-L) parameter, κ, have enabled detailed investigation of nonlocal effects of superconductivity. Intermediate value of upper critical field Hc2, has enabled detailed investigation of superconductivity in this class, over the complete H-T plane. This has revealed details of anisotropy of superconductivity (e.g., a fourfold symmetry in the square a-b plane is found) and raised questions on the symmetry of order parameter. After a brief outline of the discovery, this article gives a summary of the materials and highlights of superconducting properties of this class of materials. Interesting results from studies, using various techniques, on YNi2B2C (Tc ∼ 15 K) and LuNi2B2C (Tc ∼ 16 K) are presented, including observation of unusual square vortex lattice and its structural transformation with H and T. With conduction electrons involved in the magnetic order of this class of superconductors, the interplay of superconductivity and magnetism is intimate in these magnetic superconductors. With Tc (∼11 K) > TN (∼6 K) in ErNi2B2C, Tc (∼8 K) = TN (∼8 K) in HoNi2B2C and Tc (∼6 K) < TN (∼11 K) in DyNi2B2C, and with other parameters being favorable as mentioned earlier, this class of magnetic superconductors have become ideal materials to investigate the coexistence

  8. Development of standards for superconductors

    NASA Astrophysics Data System (ADS)

    Clark, A. F.; Goodrich, L. F.; Fickett, F. R.; Minervini, J. V.

    1982-07-01

    Standard measurement practices for use in large scale applications of superconductivity were developed. The goal is the adoption of voluntary standards for the critical parameters and other characterizations of practical superconductors. The major effort was the development of a standard test method for critical current, the necessary back-up research, and the coordination of the adoption of the test method and a standard terminology.

  9. 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.

  10. Material properties of oxide superconductors

    SciTech Connect

    Phillips, J.C.

    1996-12-31

    The differences between the old (inter-) metallic superconductors and the new oxide superconductors are not limited to the much higher values of {Tc} attainable in the latter. There are many pervasive differences caused directly by oxide chemistry, quasi-perovskite local coordination configurations, and layered metal-semiconductor-metal{prime}-semiconductor-structures. When these differences are ignored, for instance in theoretical models which make effective medium approximations, many experiments appear to present anomalous results. These anomalies largely disappear when account is taken of the real materials properties of the cuprates and other new oxide superconductors, for instance in theoretical models which treat transport as a partially percolative process. This percolative process directly reflects the fact that the highest values of {Tc}, as well as the most anomalous normal-state transport properties, occur in materials vicinal to a metal-insulator transition. As the metallic and insulating regions alternate even in single-crystal samples, effective medium models, and most effective-medium parameters, lose their significance. Examples of attempts to measure microscopic properties illustrate the importance of filamentary effects on both normal-state and superconductive properties.

  11. Monoclinic structure of hydroxylpyromorphite Pb10(PO4)6(OH)2 - hydroxylmimetite Pb10(AsO4)6(OH)2 solid solution series

    NASA Astrophysics Data System (ADS)

    Giera, Alicja; Manecki, Maciej; Borkiewicz, Olaf; Zelek, Sylwia; Rakovan, John; Bajda, Tomasz; Marchlewski, Tomasz

    2016-04-01

    Seven samples of hydroxyl analogues of pyromorphite-mimetite solid solutions series were synthesized from aqueous solutions at 80° C in a computer-controlled chemistate: 200 mL aqueous solutions of 0.05M Pb(NO3)2 and 0.03M KH2AsO4 and/or KH2PO4 were dosed with a 0.25 mL/min rate to a glass beaker, which initially contained 100 mL of distilled water. Constant pH of 8 was maintained using 2M KOH. The syntheses yielded homogeneous fine-grained white precipitates composition of which was close to theoretical Pb10[(PO4)6‑x(AsO4)x](OH)2, where x = 0, 1, 2, 3, 4, 5, 6. High-resolution powder X-ray diffraction data were obtained in transmission geometry at the beamline 11-BM at the Advanced Photon Source (Argonne National Laboratory in Illinois, USA). The structure Rietveld refinements based on starting parameters of either hexagonal hydroxylpyromorphite or monoclinic mimetite-M were performed using GSAS+EXPGUI software. Apatite usually crystallizes in the hexagonal crystal system with the space group P63/m. For the first time, however, the lowering of the hexagonal to monoclinic crystal symmetry was observed in the hydroxyl variety of pyromorphite-mimetite solid solution series. This is indicated by better fitting of the modeled monoclinic structure to the experimental data. The same is not the case for analogous calcium hydroxylapatite series Ca5(PO4)3OH - Ca5(AsO4)3OH (Lee et al. 2009). Systematical linear increase of unit cell parameters is observed with As substitution from a=9.88, b=19.75, and c=7.43 for Pb10(PO4)6(OH)2 to a=10.23, b=20.32, and c=7.51 for Pb10(AsO4)6(OH)2. A strong pseudohexagonal character (γ ≈ 120° and b ≈ 2a) of the analyzed monoclinic phases was established. This work is partially funded by AGH research grant no 11.11.140.319 and partially by Polish NCN grant No 2011/01/M/ST10/06999. Lee Y.J., Stephens P.W., Tang Y., Li W., Philips B.L., Parise J.B., Reeder R.J., 2009. Arsenate substitution in hydroxylapatite: Structural characterization

  12. 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.

  13. 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.

  14. Neutron-scattering studies of magnetic superconductors

    SciTech Connect

    Sinha, S.K.; Crabtree, G.W.; Hinks, D.G.; Mook, H.A.; Pringle, O.A.

    1982-01-01

    Results obtained in the last few years obtained by neutron diffraction on the nature of the magnetic ordering in magnetic superconductors are reviewed. Emphasis is given to studies of the complex intermediate phase in ferromagnetic superconductors where both superconductivity and ferromagnetism appear to coexist.

  15. 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.

  16. 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.

  17. Method of fabricating a twisted composite superconductor

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

    A method of producing a twisted, stabilized wire or tube superconductor which can be used to wind electromagnets, armatures, rotors, field windings for motors and generators, and other magnetic devices which use a solenoid, toroidal, or other type winding is reported. At least one groove is formed along the length of a wire substrate which is then twisted into a helix and a layer of intermetallic superconducting material is formed in the groove. This layer can be formed by depositing the desired intermetallic compound into the groove or by diffusing one component of the superconductor into the groove formed in a substrate composed of the other component. The superconductor prepared by this method comprises a non-superconductor wire twisted into the shape of a helix, having at least one groove containing a layer of superconductor material along the length of the wire.

  18. 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.

  19. 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.

  20. MM wavecomponents - SIS (Superconductor-Insulator-Superconductor) mixers

    NASA Astrophysics Data System (ADS)

    Whiteley, Stephen R.

    1989-04-01

    Superconductor-Insulator-Superconductor (SIS) tunnel junction mixers are known to provide ultra-high sensitivity receiver applications above 30 GHz. In this two year (Phase 2) program, HYPRES, in collaboration with the National Radio Astronomy Observatory, developed novel fully integrated SIS mixer circuits, and demonstrated a unique high efficiency cooling system. The integrated SIS mixer chip contains, aside from the actual mixer elements, passive tuning components, an IF filter, a coplanar transmission line, and a waveguide coupler, necessary components heretofore realized off-chip. Fabrication of the integrated mixer required development of a nine level process and optimization of the process dependent electrical parameters of the SIS devices. The device performs efficiently in the range of 75-115 GHz. A novel dewar-based cooler, which makes use of the extremely low thermal conductivity of the fused silica chip substrate to achieve an incremental thermal load of 25 mW, was fabricated and demonstrated. Such a cryostat allows relatively long term unattended operation of SIS, or other, cryogenic devices.

  1. Development of standards for superconductors

    NASA Astrophysics Data System (ADS)

    Goodrich, L. F.; Minervini, J. V.; Clakr, A. F.; Fickett, F. R.; Ekin, J. W.

    1985-01-01

    A cooperative program with the Department of Energy, the National Bureau of Standards, and private industry is in progress to develop standard measurement practices for use in large scale applications of superconductivity. The goal is the adoption of voluntary standards for the critical parameters and other characterizations of practical superconductors. Progress for the period January 82 through December 1983 is reported. The major effort was the procurement, selection, and certification of the first superconducting wire for critical current measurements as a Standard Reference Material (SRM 1457). Other work reported here includes: effect of geometry on current transfer; lap-joint resistance; and ac losses.

  2. 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.

  3. 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.

  4. Periodic microwave absorption in superconductors

    SciTech Connect

    Martinek, J.; Stankowski, J. )

    1994-08-01

    A model explaining the presence of a periodic train of microwave absorption lines in the magnetic modulated microwave absorption (MMMA) spectra of high- and low-temperature superconductors is proposed. The model assumes the occurrence of regular superconducting current loops, closed by Josephson junctions, in these materials. The system of such loops is considered within the basic model of the rf superconducting quantum interference device taking into account the effect of thermal fluctuations. The magnetic-field and temperature dependencies of the MMMA obtained on the basis of the proposed model are in qualitative agreement with experimental data.

  5. 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.

  6. Two-band superconductor magnesium diboride

    NASA Astrophysics Data System (ADS)

    Xi, X. X.

    2008-11-01

    This review focuses on the most important features of the 40 K superconductor MgB2—the weakly interacting multiple bands (the σ and π bands) and the distinct multiple superconducting energy gaps (the σ and π gaps). Even though the pairing mechanism of superconductor MgB2 is the conventional electron-phonon coupling, the prominent influence of the two bands and two gaps on its properties sets it apart from other superconductors. It leads to markedly different behaviors in upper critical field, vortex structure, magnetoresistance and many other superconducting and normal-state properties in MgB2 from single-band superconductors. Further, it gives rise to new physics that does not exist in single-band superconductors, such as the internal Josephson effects between the two order parameters. These unique phenomena depend sensitively on scattering inside and between the two bands, and the intraband and interband scattering can be modified by chemical substitution and irradiation. MgB2 has brought unprecedented attention to two-band superconductivity, which has been found to exist in other old and new superconductors. The legacy of MgB2 will be long lasting because of this, as well as the lessons it teaches in terms of the search for new phonon-mediated higher Tc superconductors.

  7. Plasma oscillations in layered superconductors

    SciTech Connect

    Pokrovsky, V.L.

    1996-12-31

    Very soon after publication of the famous BCS work explaining the puzzle of the superconductivity, N.N. Bogolyubov and coworkers have proposed their version of the theory. One of the new results they obtained was the discovery of a collective mode--an oscillation of the Cooper pair density with the energy smaller than 2{Delta}. P.W. Anderson has indicated that this collective mode can not be found experimentally since the Coulomb forces neglected in the above mentioned work shift its energy to the plasma frequency, i.e., to the high-ultraviolet range in which the superconductivity is unessential. The interest for plasmons in superconductors revived a little in the search for the mechanism of the High-{Tc} superconductivity. However, a real surge of interest to this problem occurred after experimental observations of the plasma edge in the reflectivity of High-{Tc} superconductors La{sub 2{minus}x}Sr{sub x}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub 8{minus}y}. It is worthwhile to mention that a theoretical prediction had preceded the experiment. For external reasons, the paper was published a long time after its completion. Here the author presents a brief review of the experiments and theoretical developments in the field. The theoretical works will be presented in more detail, given the author`s specialization.

  8. 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.

  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. Modified entropic gravitation in superconductors

    NASA Astrophysics Data System (ADS)

    de Matos, Clovis Jacinto

    2012-01-01

    Verlinde recently developed a theoretical account of gravitation in terms of an entropic force. The central element in Verlinde’s derivation is information and its relation with entropy through the holographic principle. The application of this approach to the case of superconductors requires to take into account that information associated with superconductor’s quantum vacuum energy is not stored on Planck size surface elements, but in four volume cells with Planck-Einstein size. This has profound consequences on the type of gravitational force generated by the quantum vacuum condensate in superconductors, which is closely related with the cosmological repulsive acceleration responsible for the accelerated expansion of the Universe. Remarkably this new gravitational type force depends on the level of breaking of the weak equivalence principle for cooper pairs in a given superconducting material, which was previously derived by the author starting from similar principles. It is also shown that this new gravitational force can be interpreted as a surface force. The experimental detection of this new repulsive gravitational-type force appears to be challenging.

  11. 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.

  12. Application potential of Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Pallecchi, Ilaria; Eisterer, Michael; Malagoli, Andrea; Putti, Marina

    2015-11-01

    In this paper we report basic properties of iron-based superconductors and review the latest achievements in the fabrication of conductors based on these materials. We compare state-of-the-art results with performances obtained with low-T c and high-T c technical superconductors, evidencing in particular the most significant differences with respect to high-T c cuprate coated conductors. Although the optimization of preparation procedures is yet to be established, a potential range of applications for iron-based superconductors in the high field low temperature regime can be envisaged, where they may become competitors to RE-123 coated conductors.

  13. 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.

  14. 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.

  15. Complementary Variational Theorems for inhomogeneous superconductors

    NASA Astrophysics Data System (ADS)

    Choy, T. C.

    1997-03-01

    Complementary variational theorems are derived for an inhomogeneous London (local) superconductor in which both the magnetic permeability μ(r) and the London penetration length λ_L(r) vary randomly in space (T.C. Choy, Physical Review B (1997) (to appear)). An essential feature is the close coupling between magnetic and supercurrent polarisation effects, developed self-consistently in this work. Using these theorems and a suitable ansatz for the single particle polarisabilities, we obtained complementary bounds for a composite superconductor near Tc and T=0^circ K. Our results may be important for the empirical study of systems containing magnetic (normal) and superconducting mixtures, including the high Tc oxide superconductors.

  16. A New Platform for Engineering Topological Superconductors: Superlattices on Rashba Superconductors

    NASA Astrophysics Data System (ADS)

    Lu, Yao; Law, Kam Tuen

    The search for topological superconductors which support Majorana fermion excitations has been an important topic in condensed matter physics. In this work, we propose a new experimental scheme for engineering topological superconductors. In this scheme, by manipulating the superlattice structure of organic molecules placed on top of a superconductor with Rashba spin-orbit coupling, topological superconducting phases can be achieved without fine-tuning the chemical potential. Moreover, superconductors with different Chern numbers can be obtained by changing the superlattice structure of the organic molecules.

  17. Hilarionite, Fe{2/3+}(SO4)(AsO4)(OH) · 6H2O, a new supergene mineral from Lavrion, Greece

    NASA Astrophysics Data System (ADS)

    Pekov, I. V.; Chukanov, N. V.; Yapaskurt, V. O.; Rusakov, V. S.; Belakovsky, D. I.; Turchkova, A. G.; Voudouris, P.; Magganas, A.; Katerinopoulos, A.

    2014-12-01

    A new mineral, hilarionite, ideally Fe{2/3+} (SO4)(AsO4)(OH) · 6H2O, has been found in the Hilarion Mine, Agios Konstantinos, Kamariza, Lavrion district, Attiki Prefecture, Greece. It was formed in the oxidation zone of a sulfide-rich orebody in association with goethite, gypsum, bukovskyite, jarosite, melanterite, chalcanthite, allophane, and azurite. Hilarionite occurs as light green (typically with an olive or grayish tint) to light yellowish green spherulites (up to 1 mm in size) and bunches of prismatic to acicular "individuals" up to 0.5 mm long that are in fact near-parallel or divergent aggregates of very thin, curved fibers up to 0.3 mm long and usually lesser than 2 μm thick. The luster is silky to vitreous. The Mohs' hardness is ca. 2. Hilarionite is ductile, its "individuals" are flexible and inelastic; fracture is uneven or splintery. D(meas) = 2.40(5), D(calc) = 2.486 g/cm3. IR spectrum shows the presence of arsenate and sulfate groups and H2O molecules in significant amounts. The Mössbauer spectrum indicates the presence of Fe3+ at two six-fold coordinated sites and the absence of Fe2+. Hilarionite is optically biaxial (+), α = 1.575(2), γ = 1.64(2), 2 V is large. The chemical composition (electron microprobe, average of 7 point analyses; H2O determined by modified Penfield method) is as follows, wt %: 0.03 MnO, 0.18 CuO, 0.17 ZnO, 33.83 Fe2O3, 0.22 P2O5, 18.92 As2O5, 22.19 SO3, 26.3 H2O, total is 101.82%. The empirical formula calculated on the basis of 15 O is: (Fe{1.90/3+}Cu0.01Zn0.01)Σ1.92[(SO4)1.24(AsO4)0.74(PO4)0.01]Σ1.99(OH)1.01 · 6.03H2O. The X-ray powder diffraction data show close structural relationship of hilarionite and kaňkite, Fe{2/3+}(AsO4)2 · 7H2O. Hilarionite is monoclinic, space group C2/ m, Cm or C2, a = 18.53(4), b = 17.43(3), c = 7.56(1) Å, β = 94.06(15)°, V = 2436(3) Å3, Z = 8. The strongest reflections in the X-ray powder diffraction pattern ( d, Å- I[ hkl]) are: 12.66-100[110], , 5.00-10[22l], , 4

  18. 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. PMID:21952839

  19. Majorana fermions in nanowires without gating superconductors

    NASA Astrophysics Data System (ADS)

    Lin, Chien-Hung; Hui, Hoi Yin; Sau, Jay; Das Sarma, Sankar

    2011-03-01

    Majorana fermions have been proposed to be realizable at the end of the semiconductor nanowire on top of an s-wave superconductor [1,2]. These proposals require gating the nanowire directly in contact with a superconductor which may be difficult in experiments. We analyze [1,2] in configurations where the wire is only gated away from the superconductor. We show that some signatures of the Majorana mode remain but the Majorana mode is not localized and hence not suitable for quantum computation. Therefore we propose an 1D periodic heterostructure which can support localized Majorana modes at the end of the wire without gating on the superconductor. This work is supported by DARPA-QuEST, JQI-NSF-PFC, and LPS-NSA.

  20. 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.

  1. 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.

  2. A road to reality with topological superconductors

    NASA Astrophysics Data System (ADS)

    Beenakker, Carlo; Kouwenhoven, Leo

    2016-07-01

    Topological matter can host low-energy quasiparticles, which, in a superconductor, are Majorana fermions described by a real wavefunction. The absence of complex phases provides protection for quantum computations based on topological superconductivity.

  3. Metallic stripes in high-temperature superconductors

    SciTech Connect

    Salkola, M.I.; Emery, V.J.; Kivelson, S.A.

    1995-11-23

    A phenomenological approach is applied to explore signatures of disordered charge stripes and antiphase spin domains in single-particle properties of the high-temperature superconductors. Stripe phases are shown to explain many experimentally observed unusual features measured in angle-resolved photoemission and optical spectroscopy. It is argued that disordered and fluctuating stripe phases are a common feature of high-temperature superconductors, supported by the additional evidence from neutron scattering and NMR.

  4. Hexatic vortex glass in disordered superconductors

    SciTech Connect

    Chudnovsky, E.M. )

    1989-12-01

    It is shown that interaction of the flux-line lattice with randomly arranged pinning centers should destroy the long-range positional order in the lattice, but not the long-range orientational order. A new phase: hexatic vortex glass, is suggested for the mixed state of disordered, type-II superconductors. Relevance to amorphous and high-{ital T}{sub {ital c}} superconductors is discussed.

  5. Quantum rotor in nanostructured superconductors

    NASA Astrophysics Data System (ADS)

    Lin, Shi-Hsin; Milošević, M. V.; Covaci, L.; Jankó, B.; Peeters, F. M.

    2014-04-01

    Despite its apparent simplicity, the idealized model of a particle constrained to move on a circle has intriguing dynamic properties and immediate experimental relevance. While a rotor is rather easy to set up classically, the quantum regime is harder to realize and investigate. Here we demonstrate that the quantum dynamics of quasiparticles in certain classes of nanostructured superconductors can be mapped onto a quantum rotor. Furthermore, we provide a straightforward experimental procedure to convert this nanoscale superconducting rotor into a regular or inverted quantum pendulum with tunable gravitational field, inertia, and drive. We detail how these novel states can be detected via scanning tunneling spectroscopy. The proposed experiments will provide insights into quantum dynamics and quantum chaos.

  6. Quantum rotor in nanostructured superconductors.

    PubMed

    Lin, Shi-Hsin; Milošević, M V; Covaci, L; Jankó, B; Peeters, F M

    2014-01-01

    Despite its apparent simplicity, the idealized model of a particle constrained to move on a circle has intriguing dynamic properties and immediate experimental relevance. While a rotor is rather easy to set up classically, the quantum regime is harder to realize and investigate. Here we demonstrate that the quantum dynamics of quasiparticles in certain classes of nanostructured superconductors can be mapped onto a quantum rotor. Furthermore, we provide a straightforward experimental procedure to convert this nanoscale superconducting rotor into a regular or inverted quantum pendulum with tunable gravitational field, inertia, and drive. We detail how these novel states can be detected via scanning tunneling spectroscopy. The proposed experiments will provide insights into quantum dynamics and quantum chaos. PMID:24686241

  7. Quantum rotor in nanostructured superconductors

    PubMed Central

    Lin, Shi-Hsin; Milošević, M. V.; Covaci, L.; Jankó, B.; Peeters, F. M.

    2014-01-01

    Despite its apparent simplicity, the idealized model of a particle constrained to move on a circle has intriguing dynamic properties and immediate experimental relevance. While a rotor is rather easy to set up classically, the quantum regime is harder to realize and investigate. Here we demonstrate that the quantum dynamics of quasiparticles in certain classes of nanostructured superconductors can be mapped onto a quantum rotor. Furthermore, we provide a straightforward experimental procedure to convert this nanoscale superconducting rotor into a regular or inverted quantum pendulum with tunable gravitational field, inertia, and drive. We detail how these novel states can be detected via scanning tunneling spectroscopy. The proposed experiments will provide insights into quantum dynamics and quantum chaos. PMID:24686241

  8. 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.

  9. Fluctuation phenomena in layered superconductors

    SciTech Connect

    Klemm, R.A.

    1996-10-01

    Gaussian fluctuations in layered superconductors have been the subject of study for many years. Although the FD was studied in detail long ago, the FC (fluctuation conductivity) was studied only recently, since the MT and DOS diagrams were previously neglected. Recent comparisons with experiment on YBCO have shown that the DOS diagrams are important and can lead to qualitatively different behaviors for the FC parallel and perpendicular to the layers. In both cases, Gaussian fluctuations fit the data above {Tc} very well, even for YBCO. To date, nearly all calculations of fluctuation quantities were for B{parallel}{cflx c}. Nevertheless, it should be possible to treat an arbitrary B, but the evaluation of the required matrix elements for the fluctuation quantities will be more complicated.

  10. 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.

  11. 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).

  12. Topological insulators and superconductors from string theory

    NASA Astrophysics Data System (ADS)

    Ryu, Shinsei; Takayanagi, Tadashi

    2010-10-01

    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 θ 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).

  13. 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).

  14. Superconductor

    SciTech Connect

    Gleim, W.K.

    1982-07-27

    A superconductive article is described which comprises an electrically normal conductive metal cable having on the outer surface thereof a layer containing cobalt phthalocyanine and an alkali metal. The ratio of alkali metal atoms to cobalt phthalocyanine molecules in said layer is suitably about 8:1. The electrically normal conductive metal is preferably aluminum and the cable is preferably hollow.

  15. 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.

  16. Josephson Current in a Gapped Graphene Superconductor/Barrier/Superconductor Junction: Case of Massive Electrons

    NASA Astrophysics Data System (ADS)

    Suwannasit, Tatnatchai; Tang, I.-Ming; Hoonsawat, Rassmidara; Soodchomshom, Bumned

    2011-10-01

    The Josephson effect in a gapped graphene-based superconductor/barrier/superconductor junction is studied. The superconductivity in gapped graphene may be achieved by depositing conventional superconductor on the top of the gapped graphene such as graphene grown on SiC substrate. In gapped graphene system, the carriers exhibit massive Dirac fermions. We focus on the effect of pseudo-Dirac-like mass on the supercurrent. In contrast to that in the gapless graphene superconductor/barrier/superconductor junction, we find that the supercurrent exhibits dependency of the Fermi energy. Also, the massive supercurrent anomalously oscillates as a function of the gate potential. This novel behavior is due to the effect of electrons acquiring mass in gapped graphene.

  17. Infrared and Raman spectroscopic characterizations on new Fe sulphoarsenate hilarionite (Fe2((III))(SO4)(AsO4)(OH)·6H2O): Implications for arsenic mineralogy in supergene environment of mine area.

    PubMed

    Liu, Jing; He, LiLe; Dong, Faqin; Frost, Ray L

    2017-01-01

    Hilarionite (Fe2 (SO4)(AsO4)(OH)·6H2O) is a new Fe sulphoarsenates mineral, which recently is found in the famous Lavrion ore district, Atliki Prefecture, Greece. The spectroscopic study of hilarionite enriches the data of arsenic mineralogy in supergene environment of a mine area. The infrared and Raman means are used to characterize the molecular structure of this mineral. The IR bands at 875 and 905cm(-1) are assigned to the antisymmetric stretching vibrations of AsO4(3-). The IR bands at 1021, 1086 and 1136cm(-1) correspond to the possible antisymmetric and symmetric stretching vibrations of SO4(2-). The Raman bands at 807, 843 and 875cm(-1) clearly show that arsenate components in the mineral structure, which are assigned to the symmetric stretching vibrations (ν1) of AsO4(3-) (807 and 843cm(-1)) and the antisymmetric vibration (ν3) (875cm(-1)). IR bands provide more sulfate information than Raman, which can be used as the basis to distinguish hilarionite from kaňkite. The powder XRD data shows that hilarionite has obvious differences with the mineral structure of kaňkite. The thermoanalysis and SEM-EDX results show that hilarionite has more sulfate than arsenate. PMID:27391313

  18. The mineral tooeleite Fe6(AsO3)4SO4(OH)4ṡ4H2O - An infrared and Raman spectroscopic study-environmental implications for arsenic remediation

    NASA Astrophysics Data System (ADS)

    Liu, Jing; Cheng, Hongfei; Frost, Ray L.; Dong, Faqing

    2013-02-01

    The mineral tooeleite Fe6(AsO3)4SO4(OH)4ṡ4H2O is secondary ferric arsenite sulphate mineral which has environmental significance for arsenic remediation because of its high stability in the regolith. The mineral has been studied by X-ray diffraction (XRD), infrared (IR) and Raman spectroscopy. The XRD result indicates tooeleite can form more crystalline solids in an acid environment than in an alkaline environment. Infrared spectroscopy identifies moderately intense band at 773 cm-1 assigned to AsO33- symmetric stretching vibration. Raman spectroscopy identifies three bands at 803, 758 and 661 cm-1 assigned to the symmetric and antisymmetric stretching vibrations of AsO33- and As-OH stretching vibration respectively. In addition, the infrared bands observed at 1116, 1040, 1090, 981 and 616 cm-1, are assigned to the ν3, ν1 and ν4 modes of SO42-. The same bands are observed at 1287, 1085, 983 and 604 cm-1 in the Raman spectrum. As3d band at binding energy of 44.05 eV in XPS confirms arsenic valence of tooeleite is +3. These characteristic bands in the IR and Raman spectra provide useful basis for identifying the mineral tooeleite.

  19. Flux Pinning Properties and Magnetic Relaxation of Superconducting SmFe0.9Co0.1AsO

    NASA Astrophysics Data System (ADS)

    Zhuang, J. C.; Sun, Y.; Ding, Y.; Yuan, F. F.; Liu, J. T.; Shi, Z. X.; Li, X. W.

    2012-12-01

    Magnetic Co ion doped SmFeAsO polycrystal was synthesized via solid-state reaction. Resistivity, SEM and magnetic hysteresis loops (MHLs) were measured to investigate magnetic properties of the sample. Critical current densities as well as the flux pinning forces densities were estimated from MHLs. This paper reports for the first time the research of superconducting MHLs as well as magnetic relaxation properties of SmFe0.9Co0.1AsO. Results suggest that: (i) A tail effect in the resistivity measurement together with the rapid decrease in critical current densities at low fields shows the evidence for granularity of the sample; (ii) The asymmetry of the MHLs may be caused by the Bean-Livingstone (BL) surface pinning or granular nature, and none of theoretical models are suitable to the scaling behaviors of flux pinning forces densities; (iii) The anomalous tendency of the temperature dependence of magnetic relaxation rate as well as the effective pinning energy were observed, which may be attributed to the competition between the bulk pinning and the BL surface pinning.

  20. 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.

  1. 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.

  2. 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.

  3. Bernoulli effect and contact potential difference in superconductors

    SciTech Connect

    Omel'yanchuk, A.N.; Beloborod'ko, S.I.

    1983-10-01

    An expression is derived for the Bernoulli potential that arises in superconductors with an inhomogeneous current distribution. The expression is valid for arbitrary temperatures and superfluid velocities. In the superconductor--dielectric--superconductor system we consider the Bernoulli effect, which manifests itself in a contact potential difference between the superconductors. The potential difference is determined by the currents flowing through one plate of the contact and can be measured with a voltmeter in the quasi-stationary regime.

  4. 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.

  5. 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.

  6. 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.

  7. 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

    Superconductors can usefully be divided into two classes, those that are well described by the classic Bardeen-Cooper-Schrieffer (BCS) theory and its extensions and those which require a different microscopic description. The BCS theory of superconductivity solved the long standing mystery of this spectacular phenomenon and described all superconductors that were known when it was formulated in the 1950s. The key ingredient is an attractive interaction generated by the exchange of phonons between electrons which overcomes a Coulomb repulsion weakened by screening, to give a net attractive force on the low energy scale. In this case the simplest s-wave pairing always maximises the energy gain. There were speculations a little later that other types of electron pairing could be possible, but it took a quarter of a century until the first signs of superconductors with different and exotic pairing appeared. In the intervening thirty years many superconductors with exotic pairing have been and continue to be discovered and the study of their superconductivity has grown into a major subfield of condensed matter physics today. The importance of these exotic superconductors with unconventional symmetry is that their pairing is of electronic origin. As a result they are freed from the restrictions of low transition temperatures that go along with the phonon driven conventional superconductors. However in two of the main classes of the exotic superconductors, namely heavy fermion and organic superconductors, the intrinsic energy scales are very small leading to low temperature scales. The third class contains the small number of superconducting transition metal compounds with exotic pairing symmetry. The most studied of these are the high-Tc cuprates, the newly discovered iron pnictides and strontium ruthenate which is closely related to superfluid 3He. Although the basic electronic structure of these materials is well understood, the origin of the pairing is more complex

  8. 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.

  9. High-temperature ceramic superconductors

    NASA Astrophysics Data System (ADS)

    Mazdiyasni, K. S.

    1990-11-01

    The principal goals of this program are (1) to demonstrate fabrication of high-temperature ceramic superconductors via sol-gel method that can operate at or above 90 K with appropriate current density, J(sub c), in forms useful for application in resonant cavities, magnets, motors, sensors, computers, and other devices; and (2) to fabricate and demonstrate selected components made of these materials, including microwave cavities and magnetic shields. Chemical pathways for synthesis of 123 identified, process parameters window for sol-gel derived 123 fibers established, continuous flexible fibers 15 to 200 microns in diameter producted, fibers with T(sub c) is approximate or equal to 92.5 K, Delta T = 1.5 K, J(sub c) = 2000 A/sqcm at 77 K, 0 field; 4000 at 57K, 100 Oe was produced, formed adherent 123 oriented films on metals and ceramic substrates, achieved film T(sub c) is approximate or equal to 92 K, Delta T = 4 k, J(sub c) = 400 A/sq cm at 40 K, O field.

  10. Optical devices based on dye-coated superconductor junctions: An example of a composite molecule-superconductor device

    SciTech Connect

    Zhao, J.; Jurbergs, D.; Yamazi, B.; McDevitt, J.T.

    1992-03-25

    High-temperature superconductors provide new opportunities as materials used in the construction of hybrid molecule-superconductor components. Here, the authors describe fabrication methods for and operation of optical sensors based on molecular dye-coated superconductor junctions. Devices prepared from yttrium barium cuprates and using octaethylporphyrin, phthalocyanine, and rhodamine 6G as dyes have been prepared. 9 refs., 1 fig.

  11. Deviations from mean-field behavior in disordered nanoscale superconductor normal-metal superconductor arrays

    NASA Astrophysics Data System (ADS)

    Kouh, Taejoon; Valles, J. M.

    2003-04-01

    We have fabricated quasi-two-dimensional disordered arrays of nanoscale Pb grains coupled by an overlayer of Ag grains. Their temperature-dependent resistive transitions follow predictions for an array of mesoscopic superconductor normal-metal superconductor junctions. The decrease of their transition temperatures with Ag overlayer thickness systematically deviates from the Cooper limit theory of the proximity effect as the Pb grain size decreases. The deviations occur when the estimated number of Cooper pairs per grain is <1 and suggest the approach to a superconductor-to-metal transition.

  12. Fluxons in superconductor/ferromagnet/superconductor Josephson junction with external current

    NASA Astrophysics Data System (ADS)

    Alatas, Husin

    2016-03-01

    We discuss the existence of fluxons in superconductor/ferromagnet/superconductor Josephson junction with external current described by an inhomogeneous double sine-Gordon equation. Based on an extended Feynman's argument, we derived the corresponding current-phase relation from the nonlinear interaction of the macroscopic wavefunctions between the two superconductors. The result shows that the only solution that survive under the presence of external current are the bright and dark fluxons, while a new type of dark fluxon with peculiar shape is found.

  13. Shock compaction of high- Tc superconductors

    SciTech Connect

    Weir, S.T.; Nellis, W.J.; McCandless, P.C.; Brocious, W.F. ); Seaman, C.L.; Early, E.A.; Maple, M.B. . Dept. of Physics); Kramer, M.J. ); Syono, Y.; Kikuchi, M. )

    1990-09-01

    We present the results of shock compaction experiments on high-{Tc} superconductors and describe the way in which shock consolidation addresses critical problems concerning the fabrication of high J{sub c} bulk superconductors. In particular, shock compaction experiments on YBa{sub 2}Cu{sub 3}O{sub 7} show that shock-induced defects can greatly increase intragranular critical current densities. The fabrication of crystallographically aligned Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} samples by shock-compaction is also described. These experiments demonstrate the potential of the shock consolidation method as a means for fabricating bulk high-{Tc} superconductors having high critical current densities.

  14. The superconducting state parameters of glassy superconductors

    NASA Astrophysics Data System (ADS)

    Vora, Aditya M.

    2011-11-01

    We present theoretical investigations of the superconducting state parameters (SSPs), i.e. the electron-phonon coupling strength, λ, Coulomb pseudopotential, μ*, transition temperature, Tc, isotope effect exponent, α, and effective interaction strength, N0V, of glassy superconductors by employing Ashcroft's well know empty core model potential for the first time using five screening functions proposed by Hartree (H), Taylor, Ichimaru-Utsumi (IU), Farid et al and Sarkar et al. The Tc obtained from the H and IU screening functions is found to be in excellent agreement with available experimental data. Also, the present results confirm the superconducting phase in bulk metallic glass superconductors. A strong dependency of the SSPs of the glassy superconductors on the 'Z' valence is found.

  15. 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.

  16. Lifshitz transition in d-wave superconductors

    SciTech Connect

    Botelho, S.S.; Sa de Melo, C.A.R.

    2005-04-01

    The BCS-to-BEC evolution has been recently the focus of studies in superconductors and cold atomic gases. For a d-wave system, we show that a Lifshitz transition occurs at a critical particle density which separates two topologically distinct phases according to their quasiparticle excitation energies: a BCS-like gapless superconductor in the higher-density limit and a BEC-like fully gapped superconductor in the lower-density limit. This transition is second-order according to Ehrenfest's classification, but it occurs without a change in the symmetry of the order parameter and thus cannot be classified under Landau's scheme. To illustrate the nature of the transition, we compute the compressibility and the superfluid density as functions of particle density.

  17. 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].

  18. 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.

  19. 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

  20. Giant paramagnetic Meissner effect in multiband superconductors.

    PubMed

    da Silva, R M; Milošević, M V; Shanenko, A A; Peeters, F M; Aguiar, J Albino

    2015-01-01

    Superconductors, ideally diamagnetic when in the Meissner state, can also exhibit paramagnetic behavior due to trapped magnetic flux. In the absence of pinning such paramagnetic response is weak, and ceases with increasing sample thickness. Here we show that in multiband superconductors paramagnetic response can be observed even in slab geometries, and can be far larger than any previous estimate - even multiply larger than the diamagnetic Meissner response for the same applied magnetic field. We link the appearance of this giant paramagnetic response to the broad crossover between conventional Type-I and Type-II superconductors, where Abrikosov vortices interact non-monotonically and multibody effects become important, causing unique flux configurations and their locking in the presence of surfaces. PMID:26244936

  1. Giant paramagnetic Meissner effect in multiband superconductors

    PubMed Central

    da Silva, R. M.; Milošević, M. V.; Shanenko, A. A.; Peeters, F. M.; Aguiar, J. Albino

    2015-01-01

    Superconductors, ideally diamagnetic when in the Meissner state, can also exhibit paramagnetic behavior due to trapped magnetic flux. In the absence of pinning such paramagnetic response is weak, and ceases with increasing sample thickness. Here we show that in multiband superconductors paramagnetic response can be observed even in slab geometries, and can be far larger than any previous estimate - even multiply larger than the diamagnetic Meissner response for the same applied magnetic field. We link the appearance of this giant paramagnetic response to the broad crossover between conventional Type-I and Type-II superconductors, where Abrikosov vortices interact non-monotonically and multibody effects become important, causing unique flux configurations and their locking in the presence of surfaces. PMID:26244936

  2. Giant paramagnetic Meissner effect in multiband superconductors

    NASA Astrophysics Data System (ADS)

    da Silva, R. M.; Milošević, M. V.; Shanenko, A. A.; Peeters, F. M.; Aguiar, J. Albino

    2015-08-01

    Superconductors, ideally diamagnetic when in the Meissner state, can also exhibit paramagnetic behavior due to trapped magnetic flux. In the absence of pinning such paramagnetic response is weak, and ceases with increasing sample thickness. Here we show that in multiband superconductors paramagnetic response can be observed even in slab geometries, and can be far larger than any previous estimate - even multiply larger than the diamagnetic Meissner response for the same applied magnetic field. We link the appearance of this giant paramagnetic response to the broad crossover between conventional Type-I and Type-II superconductors, where Abrikosov vortices interact non-monotonically and multibody effects become important, causing unique flux configurations and their locking in the presence of surfaces.

  3. 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.

  4. 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

  5. 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.

  6. Anomalous Hall effect in Weyl superconductors

    NASA Astrophysics Data System (ADS)

    Bednik, G.; Zyuzin, A. A.; Burkov, A. A.

    2016-08-01

    We present a theory of the anomalous Hall effect in a topological Weyl superconductor with broken time reversal symmetry. Specifically, we consider a ferromagnetic Weyl metal with two Weyl nodes of opposite chirality near the Fermi energy. In the presence of inversion symmetry, such a metal experiences a weak-coupling Bardeen–Cooper–Schrieffer instability, with pairing of parity-related eigenstates. Due to the nonzero topological charge, carried by the Weyl nodes, such a superconductor is necessarily topologically nontrivial, with Majorana surface states coexisting with the Fermi arcs of the normal Weyl metal. We demonstrate that, surprisingly, the anomalous Hall conductivity of such a superconducting Weyl metal coincides with that of a nonsuperconducting one, under certain conditions, in spite of the nonconservation of charge in a superconductor. We relate this to the existence of an extra (nearly) conserved quantity in a Weyl metal, the chiral charge.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Topological state engineering by potential impurities on chiral superconductors

    NASA Astrophysics Data System (ADS)

    Kaladzhyan, Vardan; Röntynen, Joel; Simon, Pascal; Ojanen, Teemu

    2016-08-01

    In this work we consider the influence of potential impurities deposited on top of two-dimensional chiral superconductors. As discovered recently, magnetic impurity lattices on an s -wave superconductor may give rise to a rich topological phase diagram. We show that a similar mechanism takes place in chiral superconductors decorated by nonmagnetic impurities, thus avoiding the delicate issue of magnetic ordering of adatoms. We illustrate the method by presenting the theory of potential impurity lattices embedded on chiral p -wave superconductors. While a prerequisite for the topological state engineering is a chiral superconductor, the proposed procedure results in vistas of nontrivial descendant phases with different Chern numbers.

  12. Building blocks for correlated superconductors and magnets

    SciTech Connect

    Sarrao, J. L.; Ronning, F.; Bauer, E. D.; Batista, C. D.; Zhu, J. -X.; Thompson, J. 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.

  13. NbTi superconductors with aluminium matrix

    SciTech Connect

    Buryak, V.P.; Dugadko, A.B.; Mironova, O.N.; Petrusenko, A.I. ); Bliznyuk, V.A.; Dolbinov, J.D.; Lykhin, V.A. )

    1992-01-01

    This paper reports that the authors designed, produced and studied NbTi composite superconductors with Al, or Al-alloy, or combined Al and Cu matrix, which have reduced weight. Wires of different design with 0.5-2.0 mm diameter were manufactured using hydrostatic extrusion. The weight reduction in comparison with the same filling factor copper matrix superconductor achieves 20-40%. The overall critical current density at 5 T magnetic field is (1.6-2.8) {center dot} 10{sup 9} A/cm{sup 2}.

  14. 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.

  15. Holographic superconductors from the massive gravity

    NASA Astrophysics Data System (ADS)

    Zeng, Hua Bi; Wu, Jian-Pin

    2014-08-01

    A holographic superconductor is constructed in the background of a massive gravity theory. In the normal state without condensation, the conductivity exhibits a Drude peak that approaches a delta function in the massless gravity limit as studied by David Vegh. In the superconducting state, besides the infinite dc conductivity, the ac conductivity has Drude behavior at low frequency followed by a power-law fall. These results are in agreement with that found earlier by Horowitz and Santos, who studied a holographic superconductor with an implicit periodic potential beyond the probe limit. The results also agree with measurements on some cuprates.

  16. 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.

  17. Electrical connection structure for a superconductor element

    SciTech Connect

    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.

  18. 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.

  19. Recrystallization of high temperature superconductors

    SciTech Connect

    Kouzoudis, D.

    1996-05-09

    Currently one of the most widely used high {Tc} superconductors is the Bi-based compounds Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub z} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub z} (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. 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.

  1. Converting a topologically trivial superconductor into a chiral topological superconductor via diluted magnetic doping

    NASA Astrophysics Data System (ADS)

    Qin, Wei; Xiao, Di; Chang, Kai; Shen, Shun-Qing; Zhang, Zhenyu

    We employ two complementary theoretical approaches to explore the feasibility of altering the topological properties of two-dimensional Rashba spin-orbit coupled superconductors by proper introduction of magnetic disorders. First, using the self-consistent Born approximation, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorders, which gradually narrow, close, and reopen the quasi-particle gap of the paired electrons in a nontrivial manner. Such a topological phase transition is further characterized by the change in the corresponding topological invariant. The central predictions made here are then confirmed using the complementary numerical approach by solving the Bogoliubov-de Gennes equations self-consistently within a tight-binding model. We also discuss the validity of the present model studies in connection with existing experimental findings. Collectively, the present study offers appealing new schemes for potential experimental realization of topological superconductors. Supported by NSF of China.

  2. Crystal chemistry of anhydrous Li uranyl phosphates and arsenates. I. Polymorphism and structure topology: Synthesis and crystal structures of α-Li[(UO 2)(PO 4)], α-Li[(UO 2)(AsO 4)], β-Li[(UO 2)(AsO 4)] and Li 2[(UO 2) 3(P 2O 7) 2

    NASA Astrophysics Data System (ADS)

    Alekseev, Evgeny V.; Krivovichev, Sergey V.; Malcherek, Thomas; Depmeier, Wulf

    2008-11-01

    Four new Li uranyl phosphates and arsenates have been prepared by high-temperature solid-state reactions: α-Li[(UO 2)(PO 4)] ( 1), α-Li[(UO 2)(AsO 4)] ( 2), β-Li[(UO 2)(AsO 4)] ( 3) and Li 2[(UO 2) 3(P 2O 7) 2] ( 4). The structures of the compounds have been solved by direct methods: 1—triclinic, P1¯, a=5.0271(1) Å, b=9.8799(2) Å, c=10.8920(2) Å, α=108.282(9)°, β=102.993(8)°, γ=104.13(1)°, V=470.69(2) Å 3, Z=4, R1=0.0415 for 2786 unique reflections with | F0|⩾4 σ F; 2—triclinic, P1¯, a=5.129(2) Å, b=10.105(3) Å, c=11.080(3) Å, α=107.70(2)°, β=102.53(3)°, γ=104.74(3)°, V=501.4(3) Å 3, Z=4, R1=0.055 for 1431 unique reflections with | F0|⩾4 σF; 3—triclinic, P1¯, a=5.051(1) Å, b=5.303(1) Å, c=10.101(1) Å, α=90.31(1)°, β=97.49(1)°, γ=105.08(1)°, V=258.80(8) Å 3, Z=2, R1=0.0339 for 2055 unique reflections with | F0|⩾4 σF; 4—triclinic, P1¯, a=5.312(1) Å, b=6.696(1) Å, c=12.542(1) Å, α=94.532(9)°, β=99.059(8)°, γ=110.189(7)°, V=409.17(10) Å 3, Z=2, R1=0.0565 for 1355 unique reflections with | F0|⩾4 σF. The structures of all four compounds are based upon 3-D frameworks of U and T polyhedra ( T=P, As). Phases 1 and 2 are isostructural and consist of U 2O 12 dimers and UO 6 square bipyramids linked by single TO 4 tetrahedra. The structure of 3 consists of 3-D framework of corner-sharing UO 6 bipyramids and AsO 4 tetrahedra. In the structure of 4, the framework is composed of U 2O 12 dimers, UO 6 bipyramids and P 2O 7 dimers. In all the compounds, Li + cations reside in framework cavities. The topologies of the 3-D frameworks can be described as derivatives of the PtS (cooperite) network.

  3. Disorder-Driven Superconductor-Insulator Transition in d-Wave Superconductors

    NASA Astrophysics Data System (ADS)

    Song, Yun; He, Long

    2014-03-01

    We study the superconductor-insulator transition (SIT) in d-wave superconductors. By means of the kernel polynomial method, the Bogoliubov-de Gennes equations are solved self-consistently, making it possible to observe fully the nanoscale spatial fluctuations of the superconducting order parameters. It is shown that Anderson localization can not entirely inhibit the occurrence of the local superconductivity in strongly-disordered d-wave superconductors. Separated by an insulating ``sea'' completely, a few isolated superconducting ``islands'' with significant enhancement of the local superconducting order parameters can survive across the SIT. The disorder-driven SIT, therefore, is a transition from a d-wave superconductor to a boson insulator which consists of localized Cooper pairs. Unlike an s-wave superconductor which presents a robust single-particle gap across the SIT, the optical conductivity of a d-wave superconductor reveals a gapless insulating phase, where the SIT can be detected by observing the disappearance of the Drude weight with the increasing disorder. The National Basic Research Program of China (Grant Nos. 2011CBA00108).

  4. 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.

  5. 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

  6. Ultrasonic attenuation studies in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Shen, Zhong Cheng; Jiang, Zuo

    2005-04-01

    In this paper a great number of mechanical relaxation spectrum experiment results in the mixed state of high Tc superconductors have been summarized. A new low frequency mechanical relaxation spectrum apparatus have been shown. We pointed out that the mechanical relaxation peaks are attributed to anelastic relaxation processes and the transition of rigidly pinned FLL into a depinned state.

  7. Development of standards for superconductors, FY 1980

    NASA Astrophysics Data System (ADS)

    Fickett, F. R.; Goodrich, L. F.; Clark, A. F.

    1980-12-01

    The critical current standard for superconductors was investigated through a survey of manufacturers. Experimental determinations of the effect of various parameters on the measurement were made by NBS and by the wire manufacturers. Significant progress was made in the preparation of the actual critical current measurement standard and the definition standard.

  8. 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.

  9. Structural and vibrational study and superprotonic behavior of the new solid acid: K0.47(NH4)0.53H2(PO4)0.52(AsO4)0.48

    NASA Astrophysics Data System (ADS)

    Chouchene, Samia; Jaouadi, Khaled; Mhiri, Tahar; Zouari, Nabil

    2016-12-01

    The new compound K0.47(NH4)0.53H2(PO4)0.52(AsO4)0.48 crystallizes in the tetragonal system I 4 bar 2d with lattice parameters a = 7.606(5) Å and c = 7.401(5) Å. This material has a unit cell volume of 428.16 Å3 and four formula units per cell. The main feature of the structure is the coexistence of two groups with a motive (NH4/K)+-H2(P/As)O4-. In this structure, there are two types of hydrogen bonding (Osbnd H⋯O and Nsbnd H⋯O) which contributes to their stability. The infrared spectra of K0.47(NH4)0.53H2(PO4)0.52(AsO4)0.48 recorded at room temperature in the frequency range 4000-400 cm-1 confirm the presence of two different anions (AsO43- and PO43-) in the same crystal. A calorimetric study of the title compound shows two distinct endothermal peaks which are detected at 248 and 490 K. Samples were examined by impedance and modulus spectroscopy techniques. The first transition (248 K) is attributed to a antiferroelectric-paraelectric type. A high temperature phase transition (490 K) leading to a superionic-protonic phase was found, characterized by an unusual high conductivity. The conductivity relaxation parameters associated with the high-disorder protonic conduction have been determined from analysis of the M″/M″max spectrum measured in a wide temperature range. Transport properties of this material appear to be due to the proton hopping mechanism.

  10. Fluorite-related one-dimensional units in natural bismuth oxysulfates: the crystal structures of Bi14O16(SO4)5 and Bi30O33(SO4)9(AsO4)2.

    PubMed

    Pinto, Daniela; Garavelli, Anna; Bindi, Luca

    2015-10-01

    The crystal structures of two new natural Bi oxysulfates with the formula Bi14O16(SO4)5 [labelled new phase I; monoclinic, space group C2, a = 21.658 (4), b = 5.6648 (9), c = 15.092 (3) Å, β = 119.433 (11)° and Z = 2] and Bi30O33(SO4)9(AsO4)2 [labelled new phase II; triclinic, space group P1, a = 5.670 (3), b = 13.9408 (9), c = 22.7908 (18) Å, α = 80.903 (5), β = 82.854 (14), γ = 78.27 (2)° and Z = 1] from the high-temperature fumarole deposit of the La Fossa crater at Vulcano (Aeolian Islands, Italy) are reported. The structures are built up by a combination of fluorite-related Bi-O units and isolated (SO4)(2-) tetrahedra (new phase I) or both (SO4)(2-) and (AsO4)(3-) tetrahedra (new phase II). Owing to the effect of stereoactive lone pairs of Bi(3+), Bi-O units in both the structures can be suitably described in terms of oxo-centered OBi4 tetrahedra. The structure of Bi14O16(SO4)5 is based upon one-dimensional [O16Bi14](10+) ribbons formed by six chains of edge-sharing OBi4 tetrahedra extending along [010]. In the structure of Bi30O33(SO4)9(AsO4)2 the same ribbon type coexists with another one-dimensional ribbon formed by seven chains of edge-sharing OBi4 tetrahedra and with the composition [O17Bi16](14+). Ribbons of the same type are joined by (SO4)(2-) and (AsO4)(3-) tetrahedra along [010] – if a reduced triclinic unit-cell setting is considered – so forming two different (001) slabs which alternate to each other along [001] and are joined by additional (SO4)(2-) tetrahedra. New phase I represents the natural analogues of synthetic Bi14O16(SO4)5, but with an ordered structure model. PMID:26428401

  11. Auriacusite, Fe3+Cu2+AsO4O, the first M 3+ member of the olivenite group, from the Black Pine mine, Montana, USA

    NASA Astrophysics Data System (ADS)

    Mills, Stuart J.; Kampf, Anthony R.; Poirier, Glenn; Raudsepp, Mati; Steele, Ian M.

    2010-05-01

    Auriacusite, ideally Fe3+Cu2+AsO4O, is a new arsenate mineral (IMA2009-037) and the Fe3+ analogue of olivenite, from the Black Pine mine, 14.5 km NW of Philipsburg, Granite Co., Montana, USA. It occurs lining quartz vughs and coating quartz crystals and is associated with segnitite, brochantite, malachite, tetrahedrite and pyrite. Auriacusite forms fibrous crystals up to about 5 µm in width and up to about 100 µm in length, which are intergrown to form fibrous mats. Individual crystals are a brownish golden yellow, whilst the fibrous mats are ochreous yellow. The crystals have a silky lustre and a brownish yellow streak. Mohs hardness is about 3 (estimated). The fracture is irregular and the tenacity is brittle. Auriacusite crystals are biaxial (+), with α = 1.830(5), β = 1.865(5) and γ = 1.910(5), measured using white light, and with 2 V meas. = 83(3)º and 2 V calc. = 84.6º. Orientation: X = a, Y = c, Z = b. Crystals are nonpleochroic or too weakly so to be observed. The empirical formula (based on 5 O atoms) is (Fe{1.33/3+}Cu0.85Zn0.03)Σ2.21(As0.51Sb0.27Si0.04 S0.02Te0.01)Σ0.85O5. Auriacusite is orthorhombic, space group Pnnm, a = 8.6235(7), b = 8.2757(7), c = 5.9501(5) Å, V = 424.63(6) Å3, Z = 4. The five strongest lines in the powder X-ray diffraction pattern are [ d obs in Å / ( I) / hkl]: 4.884 / (100) / 101, 001; 2.991 / (92) / 220; 2.476 / (85) / 311; 2.416 / (83) / 022; 2.669 / (74) / 221. The crystal structure was solved from single-crystal X-ray diffraction data utilising synchrotron radiation and refined to R 1 = 0.1010 on the basis of 951 unique reflections with F o > 4σ F. Auriacusite is identified as a member of the olivenite group with Fe3+ replacing Zn2+ or Cu2+ in trigonal bipyramidal coordination. Evidence suggests that auriacusite is an intermediate member between olivenite and an as yet undescribed Fe3+Fe3+-dominant member. The name is derived from the Latin auri (golden yellow) and acus (needle), in reference to its colour and

  12. Nambu-Goldstone-Leggett modes in multi-condensate superconductors

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Takashi

    2015-12-01

    Multi-gap superconductors exhibit interesting properties. In an N-gap superconductor, we have in general U(1)N phase invariance. This multiple-phase invariance is partially or totally spontaneously broken in a superconductor. The Nambu-Goldstone modes, as well as Higgs modes, are important and will play an important role in multi-condensate superconductors. The additional phase invariance leads to a new quantum phase, with help of frustrated Josephson effects, such as the time-reversal symmetry breaking, the emergence of massless modes and fractionally quantized-flux vortices. There is a possibility that half-flux vortices exist in two-component superconductors in a magnetic field. The half-quantum flux vortex can be interpreted as a monopole, and two half-flux vortices form a bound state connected by a domain wall. There is an interesting analogy between quarks and fractionally quantized-flux vortices in superconductors.

  13. Detecting magnetic flux distributions in superconductors with polarized x rays

    NASA Astrophysics Data System (ADS)

    Stahl, Claudia; Audehm, Patrick; Gräfe, Joachim; Ruoß, Stephen; Weigand, Markus; Schmidt, Mathias; Treiber, Sebastian; Bechtel, Michael; Goering, Eberhard; Schütz, Gisela; Albrecht, Joachim

    2014-09-01

    The magnetic flux distribution arising from a high-Tc superconductor is detected and visualized using polarized x rays. Therefore, we introduce a sensor layer, namely, an amorphous, soft-magnetic Co40Fe40B20 cover layer, providing a large x-ray magnetic circular dichroism (XMCD). Temperature-dependent XMCD spectroscopy on the magnetic layer has been performed. Exploiting the temperature dependence of the critical current density of the superconductor we find a quantitative correlation between the XMCD signal and the in-plane stray field of the superconductor. Magneto-optical Kerr effect experiments on the sensor layer can simulate the stray field of the superconductor and hence verify the correlation. We show that the XMCD contrast in the sensor layer corresponds to the in-plane magnetic flux distribution of the superconductor and can hence be used to image magnetic structures in superconductors.

  14. 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.

  15. Low resistivity contact to iron-pnictide superconductors

    SciTech Connect

    Tanatar, Makariy; Prozorov, Ruslan; Ni, Ni; Bud'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.

  16. Silver sheathing of high-Tc superconductor wires

    NASA Astrophysics Data System (ADS)

    Wu, C. T.; Risch, G. A.; Poeppel, R. B.; Goretta, K. C.; Danyluk, S.; Herro, H. M.

    1990-10-01

    The properties of Ag sheaths on high-temperature super-conductors are examined. Ag is chemically compatible with YBa2Cu3O(x) and Bi-based superconductors can be safely coprocessed with them. Residual stresses created by differences in thermal expansion coefficients are favorable and can be controlled by proper annealing. Although Ag forms low-resistance contact with high temperature superconductors, it is not certain that effective cryogenic stabilization by Ag can occur at 77 K and above.

  17. The structure of the mineral leogangite Cu 10(OH) 6(SO 4)(AsO 4) 4·8H 2O—Implications for arsenic accumulation and removal

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; Xi, Yunfei; Palmer, Sara J.

    2011-11-01

    The objective of this research is to determine the molecular structure of the mineral leogangite. The formation of the types of arsenosulphate minerals offers a mechanism for arsenate removal from soils and mine dumps. Raman and infrared spectroscopy have been used to characterise the mineral. Observed bands are assigned to the stretching and bending vibrations of (SO 4) 2- and (AsO 4) 3- units, stretching and bending vibrations of hydrogen bonded (OH) - ions and Cu 2+-(O,OH) units. The approximate range of O-H⋯O hydrogen bond lengths is inferred from the Raman spectra. Raman spectra of leogangite from different origins differ in that some spectra are more complex, where bands are sharp and the degenerate bands of (SO 4) 2- and (AsO 4) 3- are split and more intense. Lower wavenumbers of δ H 2O bending vibration in the spectrum may indicate the presence of weaker hydrogen bonds compared with those in different leogangite samples. The formation of leogangite offers a mechanism for the removal of arsenic from the environment.

  18. Temperature and concentration dependences of acoustic velocity and damping in Rb1-x(ND4)xD2AsO4 mixed crystals by Brillouin backscattering

    NASA Astrophysics Data System (ADS)

    Tu, Chi-Shun; Schmidt, V. Hugo

    1994-12-01

    The LA[100] (a-axis) Brillouin backscattering phonon spectra have been measured as a function of temperature (20-370 K) in the mixed ferroelectric (FE)-antiferroelectric (AFE) system Rb1-x(ND4)xD2AsO4 (DRADA-x) for ammonium concentrations x=0, 0.10, and 0.28. The Brillouin frequency shift with decreasing temperature shows hardening (positive coupling) whose steepness decreases with higher ND4 content. For RbD2AsO4 (DRDA), a Landau-Khalatnikov-like maximum (which persists in weaker form for x=0.10) was observed and the polarization relaxation time is estimated to be τ~3.8×10-12/(Tc-T) s, where Tc is the ferroelectric transition temperature. For both x=0.10 and 0.28, a broad damping peak anomaly which is stronger in x=0.28 was observed and can be connected with the dynamic order parameter fluctuations. Taking into account earlier NMR and dielectric results, we conclude that the local structure competition between FE ordering and AFE ordering is the origin of these broad damping anomalies.

  19. Noncommutative extension of AdS-CFT and holographic superconductors

    NASA Astrophysics Data System (ADS)

    Pramanik, Souvik; Das, Sudipta; Ghosh, Subir

    2015-03-01

    In this Letter, we consider a Non-Commutative (NC) extension of AdS-CFT correspondence and its effects on holographic superconductors. NC corrections are incorporated via the NC generalization of Schwarzschild black hole metric in AdS with the probe limit. We study NC effects on the relations connecting the charge density and the critical temperature of the Holographic Superconductors. Furthermore, condensation operator of the superconductor has been analyzed. Our results suggest that generically, NC effects increase the critical temperature of the holographic superconductor.

  20. 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.

  1. 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.

  2. Enhanced heat transfer computations for internally cooled cable superconductor

    NASA Astrophysics Data System (ADS)

    Rogers, J. D.

    1985-03-01

    Superconducting magnets are built with conductors that are pool bath cooled, internally cooled with the superconductor cable and contained within a conduit, or conduction cooled. The first two embody superconductors are in direct contact with liquid helium. Practical designs of internally cooled cable superconductor (ICCS) are not cryostable. Such superconductors have shown multiple regions of stability and instability. A computational method of adjusting the heat transfer coefficient of a one dimensional system of equations to enhance joule heat removal, primarily in the central region of a pulse heated model of ICCS, has been used to attempt simulation of the multiple stability/instability experiment.

  3. 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.

  4. Search for Magnesium Diboride like Binary Superconductors

    NASA Astrophysics Data System (ADS)

    Isikaku-Ironkwe, O. Paul

    2008-03-01

    Efforts to create compounds iso-electronic and iso-structural with magnesium diboride and also superconducting have so far met with limited success. Doping the Mg-site or the B-site have also not yielded higher transition temperatures. They have either been non-superconducting or have lower transition temperatures, Tc. Searching for magnesium diboride-like compounds using the electronegativity of MgB2 (1.7333) has yielded a rich family of potential superconductors. The search has been facilitated using the recently designed ElectroNegativity Spectrum Maps [ENSMaps] of binary systems AxBy. Here we display the potential families. Using the relationship between Tc and atomic mass, we estimate the transition temperatures of the most likely MgB2-like binary superconductors. We also suggest materials that can be doped to give an electronegativity of 1.7333.

  5. Paramagnetic intrinsic Meissner effect in layered superconductors

    NASA Astrophysics Data System (ADS)

    Lebed, A. G.

    2008-07-01

    Free energy of a layered superconductor with ξ⊥superconductors, as well as in superconducting superlattices.

  6. Paramagnetic Intrinsic Meissner Effect in Layered Superconductors

    NASA Astrophysics Data System (ADS)

    Lebed, Andrei

    2008-03-01

    Free energy of a quasi-two-dimensional superconductor with a coherence length perpendicular to the conducting layers being less than an inter-layer distance is calculated. The free energy is shown to differ from that in the textbook Lawerence-Doniach model at high fields, where the Meissner currents are found to create an unexpected positive magnetic moment due to shrinking of the Cooper pairs ``sizes'' by a magnetic field. This unique phenomenon - paramagnetic intrinsic Meissner effect (PIME) in a bulk [1] - is suggested to detect by measuring in-plane magnetization and torque in layered organic and high-Tc superconductors as well as in superconducting superlattices. [1] A.G. Lebed, Physical Review Letters, submitted.

  7. Very general holographic superconductors and entanglement thermodynamics

    NASA Astrophysics Data System (ADS)

    Dey, Anshuman; Mahapatra, Subhash; Sarkar, Tapobrata

    2014-12-01

    We construct and analyze holographic superconductors with generalized higher derivative couplings, in single R-charged black hole backgrounds in four and five dimensions. These systems, which we call very general holographic superconductors, have multiple tuning parameters and are shown to exhibit a rich phase structure. We establish the phase diagram numerically as well as by computing the free energy, and then validated the results by calculating the entanglement entropy for these systems. The entanglement entropy is shown to be a perfect indicator of the phase diagram. The differences in the nature of the entanglement entropy in R-charged backgrounds compared to the AdS-Schwarzschild cases are pointed out. We also compute the analogue of the entangling temperature for a subclass of these systems and compare the results with non-hairy backgrounds.

  8. 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.

  9. 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.

  10. 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.

  11. Light amplification in semiconductor-superconductor structures

    NASA Astrophysics Data System (ADS)

    Marjieh, Raja; Sabag, Evyatar; Hayat, Alex

    2016-02-01

    We study a new effect of Cooper-pair-based two-photon gain in semiconductor-superconductor structures, showing broadband enhancement of ultrafast two-photon amplification. We further show that with the superconducting enhancement, at moderately high seed intensities, the two-photon gain contribution approaches that of the one-photon gain. A full quantum-optical model of singly- and fully-stimulated two-photon emission is developed. Our results provide new insights on nonlinear light-matter interaction in the superconducting state, including the possibility of coherent control in two-photon semiconductor-superconductor devices. The theoretically-demonstrated effects can have important implications in optoelectronics and in coherent-control applications.

  12. Superconductors with Staggered Non-centrosymmetricity

    NASA Astrophysics Data System (ADS)

    Sigrist, Manfred; Agterberg, Daniel F.; Fischer, Mark H.; Goryo, Jun; Loder, Florian; Rhim, Sung-Hyon; Maruyama, Daisuke; Yanase, Youichi; Yoshida, Tomohiro; Youn, Suk Joo

    2014-06-01

    Non-centrosymmetric superconductors have attracted much interest in the context of heavy Fermion and interface superconductivity. Here we show that a sublattice structure of staggered subunits without inversion center can have important implications for superconductivity even in a globally centrosymmetric system. After discussing general aspects of systems with alternating non-centrosymmetric layers, two concrete examples are studied: (1) the artificially grown superlattices of CeCoIn5/YbCoIn5 and (2) the pnictide superconductor SrPtAs. For example (1) implications on the upper critical field are analysed and novel phases in a magnetic field are explored. Example (2) realizes likely a chiral d-wave phase for which a few implications of staggered non-centrosymmetricity are discussed.

  13. High Tc superconductors - Composite wire fabrication

    NASA Astrophysics Data System (ADS)

    Jin, S.; Sherwood, R. C.; van Dover, R. B.; Tiefel, T. H.; Johnson, D. W., Jr.

    1987-07-01

    The fabrication of fine-wire, composite superconductors consisting of a high-conductivity normal metal shell, such as Ag or Cu/Ni/Au, and a superconducting core of Ba2YCu3O oxide is described. The functions of the normal metal shell and the importance of using the proper diffusion barrier metals are discussed. A resistivity-temperature curve for the composite wire Ag/Ba2YCu3O7 is examined, and the compound inside the finished wire is analyzed using X-ray diffraction. It is observed that the zero-field critical current density of the wire at 77 K is about 175 A/sq cm and the superconducting core is continuous and retains phase composition after wire drawing and heat treatment. The supplying of oxygen to the core of the long wire during heat treatments is studied. The data reveal that it is possible to process ceramic superconductors into a desirable composite wire form.

  14. Persistent superconductor currents in holographic lattices.

    PubMed

    Iizuka, Norihiro; Ishibashi, Akihiro; Maeda, Kengo

    2014-07-01

    We consider a persistent superconductor current along the direction with no translational symmetry in a holographic gravity model. Incorporating a lattice structure into the model, we numerically construct novel solutions of hairy charged stationary black branes with momentum or rotation along the latticed direction. The lattice structure prevents the horizon from rotating, and the total momentum is only carried by matter fields outside the black brane horizon. This is consistent with the black hole rigidity theorem, and it suggests that in dual field theory with lattices, superconductor currents are made up of "composite" fields, rather than "fractionalized" degrees of freedom. We also show that our solutions are consistent with the superfluid hydrodynamics. PMID:25032917

  15. Magnetic chains on a triplet superconductor.

    PubMed

    Sacramento, P D

    2015-11-11

    The topological state of a two-dimensional triplet superconductor may be changed by an appropriate addition of magnetic impurities. A ferromagnetic magnetic chain at the surface of a superconductor with spin-orbit coupling may eliminate the edge states of a finite system giving rise to localized zero modes at the edges of the chain. The coexistence/competition between the two types of zero modes is considered. The reduction of the system to an effective 1d system gives partial information on the topological properties but the study of the two sets of zero modes requires a two-dimensional treatment. Increasing the impurity density from a magnetic chain to magnetic islands leads to a finite Chern number. At half-filling small concentrations are enough to induce chiral modes. PMID:26459719

  16. Search for Majorana Fermions in Superconductors

    NASA Astrophysics Data System (ADS)

    Beenakker, C. W. J.

    2013-04-01

    Majorana fermions (particles that are their own antiparticle) may or may not exist in nature as elementary building blocks, but in condensed matter they can be constructed out of electron and hole excitations. What is needed is a superconductor to hide the charge difference and a topological (Berry) phase to eliminate the energy difference from zero-point motion. A pair of widely separated Majorana fermions, bound to magnetic or electrostatic defects, has non-Abelian exchange statistics. A qubit encoded in this Majorana pair is expected to have an unusually long coherence time. I discuss strategies to detect Majorana fermions in a topological superconductor, as well as possible applications in a quantum computer. The status of the experimental search is reviewed.

  17. 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

  18. 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

  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. Superconductivity in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Maiti, Saurabh

    Iron based superconductors(FeSC) are a new class of high temperature superconductors with very intriguing properties. These materials cannot be explained using the 'conventional' logic of the 'conventional' superconductors, and is also different from the Cuprates-the other popular class of high temperature superconductors. A complete description of the superconducting state in these materials requires a thorough understanding of its superconducting order parameter and the mechanism that leads to superconductivity-both of which are unsettled issues. In this thesis, we attempt to tackle some aspects of these issues. We first discuss, keeping the wisdom of Fermi-liquid theory in mind, the criteria for the superconducting instability in FeSC which is a lattice based system. Superconductivity in lattice based systems is different from well known BCS superconductivity. We make the point that the presence of electron and hole like carriers are crucial for the manifestations of such properties in the FeSCs. We then present a prescription to analyze the symmetries and structure of the superconducting order parameter (the gap) in generic lattice based systems where only the interaction amongst fermions close to the Fermi surface is important. We demonstrate the effectiveness of this prescription by applying it to the case of FeSCs where we study the evolution of the gap with injecting of carriers (of both hole and electron like). This prescription avoids use of heavy numerical studies and still gives results in excellent agreement with numerical and experimental studies. Elaborating more on the intriguing nature of FeSCs, we also point to the possibility of a new time reversal symmetry breaking s+is state that is unique to systems like these (due to presence of multiple Fermi pockets of the carriers) and discuss its experimental consequences.

  1. Low angle resistivity anomaly in layered superconductors

    SciTech Connect

    Koshelev, A.E. |; Vinokur, V.M.

    1993-01-01

    The pinning effect of vortex lines by the layered structure (intrinsic pinning) on resistivity of high-T{sub c}, superconductors in the mixed state is investigated by means of perturbation theory. A sharp drop in the resistivity at small angles for which vortex lines are almost aligned with the ab-planes is shown to occur even in a high-temperature region where the pinning potential is reduced by thermal fluctuations.

  2. Phase diagram of superconductor-ferromagnet superlattices

    SciTech Connect

    Radovic, Z.; Dobrosavljevic-Grujic, L.

    1994-12-31

    Recent progress in the proximity effect theory of superconductor-ferromagnet superlattices is reviewed. The phase diagram calculations, transition temperature {Tc} and upper critical fields H{sub c2}, are presented. Characteristic features in {Tc} and H{sub c2}(T) dependence on layers thicknesses, including the predicted unusual oscillatory variations and new inhomogeneous superconducting state with nontrivial phase difference between neighboring superconducting layers, are discussed and compared with experimental data for V/Fe and Nb/Gd superlattices.

  3. Soft wall model for a holographic superconductor

    NASA Astrophysics Data System (ADS)

    Afonin, S. S.; Pusenkov, I. V.

    2016-06-01

    We consider the soft wall holographic approach for description of the high-T_c superconductivity. In comparison with the existing bottom-up holographic superconductors, the proposed approach is more phenomenological and does not describe the superconducting phase transition. On the other hand, technically it is simpler and has more freedom for fitting the conductivity properties of the real high-T_c materials in the superconducting phase. Some examples of emerging models are analyzed.

  4. 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

  5. Electromagnetic phenomena and hysteresis losses in superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, T.

    Hysteresis losses in superconductors are caused by irreversible motion of fluxoids. This motion is, in most cases, described by the critical state model. In this article, various electromagnetic phenomena due to flux pinning effects are reviewed and explanations of these phenomena are given using the critical state model. The phenomena which cannot be well described by the present model, such as reversible fluxoid motion and the longitudinal field effect, are also introduced.

  6. 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.

  7. 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.

  8. Guided design of copper oxysulfide superconductors

    NASA Astrophysics Data System (ADS)

    Yee, Chuck-Hou; Birol, Turan; Kotliar, Gabriel

    2015-03-01

    Using the framework of chemical intuition introduced by Antipov, et. al., in his synthesis of the Hg-based high-temperature superconductors, supplemented with modern first-principles electronic structure tools, materials databases, and evolutionary algorithms capable of exploring large configurational spaces, we design a novel family of copper oxysulfides. We explore the predictions of theories based on charge-transfer energies, orbital distillation and uniaxial strain on the superconducting transition temperatures of these oxysulfides.

  9. An Integrated Balanced Superconductor-Insulator-Superconductor Heterodyne Mixer on a Silicon Membrane

    NASA Astrophysics Data System (ADS)

    Westig, M. P.; Jacobs, K.; Schultz, M.; Justen, M.; Stutzki, J.; Honingh, C. E.

    2011-03-01

    We have designed and fabricated a 380-520 GHz integrated balanced NbAlAlOxNb superconductor-insulator-superconductor (SIS) heterodyne waveguide mixer for submillimeter astrophysics. The response of the mixer measured with a Fourier transform spectrometer shows excellent agreement with the design. The novelty of our device is that we deposit the complete superconducting mixer circuit (tapered slotline antennas, hybrid coupler, MIM capacitors, SIS junctions, tuning circuits and blocking filters) on top of a 9 μ m silicon membrane. The membrane is held suspended in a waveguide by 2.5 μ m thick gold plated beamleads. We will show that silicon membrane technology and a thorough device design render the integration of SIS devices with larger circuits feasible. This is an important step towards large arrays of mixers. When using an appropriate superconductor technology, these devices are scalable to higher frequencies. We will present the design, fabrication results and first results of heterodyne measurements.

  10. 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.

  11. Superconductor Digital-RF Receiver Systems

    NASA Astrophysics Data System (ADS)

    Mukhanov, Oleg A.; Kirichenko, Dmitri; Vernik, Igor V.; Filippov, Timur V.; Kirichenko, Alexander; Webber, Robert; Dotsenko, Vladimir; Talalaevskii, Andrei; Tang, Jia Cao; Sahu, Anubhav; Shevchenko, Pavel; Miller, Robert; Kaplan, Steven B.; Sarwana, Saad; Gupta, Deepnarayan

    Digital superconductor electronics has been experiencing rapid maturation with the emergence of smaller-scale, lower-cost communications applications which became the major technology drivers. These applications are primarily in the area of wireless communications, radar, and surveillance as well as in imaging and sensor systems. In these areas, the fundamental advantages of superconductivity translate into system benefits through novel Digital-RF architectures with direct digitization of wide band, high frequency radio frequency (RF) signals. At the same time the availability of relatively small 4K cryocoolers has lowered the foremost market barrier for cryogenically-cooled digital electronic systems. Recently, we have achieved a major breakthrough in the development, demonstration, and successful delivery of the cryocooled superconductor digital-RF receivers directly digitizing signals in a broad range from kilohertz to gigahertz. These essentially hybrid-technology systems combine a variety of superconductor and semiconductor technologies packaged with two-stage commercial cryocoolers: cryogenic Nb mixed-signal and digital circuits based on Rapid Single Flux Quantum (RSFQ) technology, room-temperature amplifiers, FPGA processing and control circuitry. The demonstrated cryocooled digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals in X-band and performing signal acquisition in HF to L-band at ˜30GHz clock frequencies.

  12. Electronic Raman Response in Disordered Unconventional Superconductors

    NASA Astrophysics Data System (ADS)

    Devereaux, Thomas

    1998-03-01

    Due to the strong symmetry dependence of the observed Raman spectra in all high Tc compounds, i.e., the characteristic features of light scattering for different incident and scattered polarization orientations, electronic Raman scattering in unconventional superconductors has grown to be of considerable interest in light of identifying the symmetry of the energy gap and ultimately, the mechanism of superconductivity in high temperature superconductors. I review the theory of the effects of impurities on the Raman response of unconventional superconductors with a view towards understanding the role polarization plays in determining the order parameter symmetry in the cuprates.(T. P. Devereaux, Phys. Rev. Lett. 74), 4313 (1995) (T. P. Devereaux and A. P. Kampf, Int. Journ. Mod. Phys. B 11), 2093 (1997) Signatures of the effects of disorder on the low frequency and low temperature behavior of the Raman spectra obtained for different polarizations will be discussed in relation to the magnitude and phase of the energy gap. Extensions of the theory to include anisotropic impurity scattering and inelastic spin fluctuation scattering will be discussed. Good agreement of the theory with the data on optimally- and overdoped-samples will be shown, although discrepancies remain.

  13. Peak Effect in High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Ling, Xinsheng

    1996-03-01

    Like many low-Tc superconductors, high-quality YBCO single crystals are found(X.S. Ling and J.I. Budnick, in Magnetic Susceptibility of Superconductors and Other Spin Systems), edited by R.A. Hein, T.L. Francavilla, and D.H. Liebenberg (Plenum Press, New York, 1991), p.377. to exhibit a striking peak effect. In a magnetic field, the temperature dependence of the critical current has a pronounced peak below T_c(H). Pippard(A.B. Pippard, Phil. Mag. 19), 217 (1969)., and subsequently Larkin and Ovchinnikov(A.I. Larkin and Yu.N. Ovchinnikov, J. Low Temp. Phys. 34), 409 (1979)., attributed the onset of the peak effect to a softening of the vortex lattice. In this talk, the experimental discovery^1 of the peak effect in high-Tc superconductors will be described, followed by a brief historical perspective of the understanding of this phenomenon and a discussion of a new model(X.S. Ling, C. Tang, S. Bhattacharya, and P.M. Chaikin, cond-mat/9504109, (NEC Preprint 1995).) for the peak effect. In this model, the peak effect is an interesting manifestation of the vortex-lattice melting in the presence of weak random pinning potentials. The rise of critical current with increasing temperature is a signature of the ``melting'' of the Larkin domains. This work is done in collaboration with Joe Budnick, Chao Tang, Shobo Bhattacharya, Paul Chaikin, and Boyd Veal.

  14. 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.

  15. Nanomaterials for superconductors from the energy prospective

    SciTech Connect

    Cantoni, Claudia; Goyal, Amit

    2010-01-01

    High Temperature Superconductors (HTS) wires or coated conductors (CC) are expected to revolutionize the transmission of electricity enabling the present electric grid to meet the world s growing energy needs. Although superconducting wires can carry 150 times more power than copper wires of the same cross section, further performance improvements are necessary for the superconducting technology to become cost-competitive. This objective can be achieved by introducing and controlling nano-sized defects and non-superconducting phases within the superconducting film s matrix. Such nanostructures, when carefully engineered, significantly increase the loss-free current sustained by the superconductor through a mechanism known as flux pinning. This chapter is a review of the various types of nanostructures that are artificially introduced in superconducting films to enhance the superconductor s performance. Different approaches, materials, and techniques are discussed and the most recent results in this field compared. The last section of this chapter discusses an additional example of nanotechnology employment in superconducting wires. This nanotechnology can be regarded as an atomic surface treatment designed to enable the right crystallographic orientation of the superconducting film deposited on the metal template.

  16. 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. PMID:26831071

  17. 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

  18. The missing angular momentum of superconductors.

    PubMed

    Hirsch, J E

    2008-06-11

    We point out that the Meissner effect, the process by which a superconductor expels magnetic field from its interior, represents an unsolved puzzle within the London-Bardeen-Cooper-Schrieffer theoretical framework used to describe the physics of conventional superconductors, because it appears to give rise to non-conservation of angular momentum. Possible ways to avoid this inconsistency within the conventional theory of superconductivity are argued to be far-fetched. Consequently, we argue that unless/until a consistent explanation is put forth, the existence of the Meissner effect represents an anomaly that casts doubt on the validity of the conventional framework. Instead, we point out that three elements of the unconventional theory of hole superconductivity (that are not part of the conventional theory) allow for a consistent explanation of the Meissner effect, namely: (i) that the charge distribution in superconductors is macroscopically inhomogeneous, (ii) that superconducting electrons reside in mesoscopic orbits of radius 2λ(L) (λ(L) = London penetration depth), and (iii) that spin-orbit coupling plays an essential role in superconductivity. PMID:21694324

  19. 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.

  20. Equivalence of topological insulators and superconductors

    NASA Astrophysics Data System (ADS)

    Cobanera, Emilio; Ortiz, Gerardo

    2015-10-01

    Systems of free fermions are classified by symmetry, space dimensionality, and topological properties described by K homology. Those systems belonging to different classes are inequivalent. In contrast, we show that by taking a many-body/Fock-space viewpoint it becomes possible to establish equivalences of topological insulators and superconductors in terms of duality transformations. These mappings connect topologically inequivalent systems of fermions, jumping across entries in existent classification tables, because of the phenomenon of symmetry transmutation by which a symmetry and its dual partner have identical algebraic properties but very different physical interpretations. To constrain our study to established classification tables, we define and characterize mathematically Gaussian dualities as dualities mapping free fermions to free fermions (and interacting to interacting). By introducing a large, flexible class of Gaussian dualities we show that any insulator is dual to a superconductor, and that fermionic edge modes are dual to Majorana edge modes, that is, the Gaussian dualities of this paper preserve the bulk-boundary correspondence. Transmutation of relevant symmetries, particle number, translation, and time reversal is also investigated in detail. As illustrative examples, we show the duality equivalence of the dimerized Peierls chain and the Majorana chain of Kitaev, and a two-dimensional Kekulé-type topological insulator, including graphene as a special instance in coupling space, dual to a p -wave superconductor. Since our analysis extends to interacting fermion systems, we also briefly discuss some such applications.

  1. A simple holographic superconductor with momentum relaxation

    NASA Astrophysics Data System (ADS)

    Kim, Keun-Young; Kim, Kyung Kiu; Park, Miok

    2015-04-01

    We study a holographic superconductor model with momentum relaxation due to massless scalar fields linear to spatial coordinates( ψ I = βδ Ii x i ), where β is the strength of momentum relaxation. In addition to the original superconductor induced by the chemical potential( μ) at β = 0, there exists a new type of superconductor induced by β even at μ = 0. It may imply a new `pairing' mechanism of particles and antiparticles interacting with β, which may be interpreted as `impurity'. Two parameters μ and β compete in forming superconducting phase. As a result, the critical temperature behaves differently depending on β/μ. It decreases when β/μ is small and increases when β/μ is large, which is a novel feature compared to other models. After analysing ground states and phase diagrams for various β/μ, we study optical electric( σ), thermoelectric( α), and thermal() conductivities. When the system undergoes a phase transition from normal to a superconducting phase, 1 /ω pole appears in the imaginary part of the electric conductivity, implying infinite DC conductivity. If β/μ < 1, at small ω, a two-fluid model with an imaginary 1 /ω pole and the Drude peak works for σ, α, and , but If β/μ > 1 a non-Drude peak replaces the Drude peak. It is consistent with the coherent/incoherent metal transition in its metal phase. The Ferrell-Glover-Tinkham (FGT) sum rule is satisfied for all cases even when μ = 0.

  2. 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. PMID:25737548

  3. 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).

  4. Meissner holes in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Tamegai, Tsuyoshi; Mohan, Shyam; Tsuchiya, Yuji; Nakajima, Yasuyuki

    2012-02-01

    Magnetic flux penetrates into a superconductor in the form of quantized vortices. This process is usually described by the Bean model, and the flux front forms a regular pattern reflecting the shape of the sample. However, a novel form of flux penetration accompanying wiggling fronts between vortices and antivortices has been observed in YBa2Cu3O7-δ upon remagnetization [1]. Such a phenomenon is ascribed to the presence of special arrangements of vortices at the front accompanying flux free regions and excess current around it. The flux free region is called as `Mesissner hole'. We have performed extensive magneto-optical imagings of iron-based superconductor single crystals and found similar anomalous features for the first time in superconductors other than 123-type cuprates [2]. Implications of this finding will be discussed with possible origins of the anomalous vortex arrangements. [1] V. K. Vlasko-Vlasov et al., Phys. Rev. B 56, 5622 (1997). [2] S. Mohan, Y. Tsuchiya, Y. Nakajima, and T. Tamegai, Phys. Rev. B 84, 18050X (2011).

  5. 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.

  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. Attikaite, Ca3Cu2Al2(AsO4)4(OH)4 · 2H2O, a new mineral species

    NASA Astrophysics Data System (ADS)

    Chukanov, N. V.; Pekov, I. V.; Zadov, A. E.

    2007-12-01

    Attikaite, a new mineral species, has been found together with arsenocrandalite, arsenogoyazite, conichalcite, olivenite, philipsbornite, azurite, malachite, carminite, beudantite, goethite, quartz, and allophane at the Christina Mine No. 132, Kamareza, Lavrion District, Attiki Prefecture (Attika), Greece. The mineral is named after the type locality. It forms spheroidal segregations (up to 0.3 mm in diameter) consisting of thin flexible crystals up to 3 × 20 × 80 μm in size. Its color is light blue to greenish blue, with a pale blue streak. The Mohs’ hardness is 2 to 2.5. The cleavage is eminent mica-like parallel to {001}. The density is 3.2(2) g/cm3 (measured in heavy liquids) and 3.356 g/cm3 (calculated). The wave numbers of the absorption bands in the infrared spectrum of attikaite are (cm-1; sh is shoulder; w is a weak band): 3525 sh, 3425, 3180, 1642, 1120 w, 1070 w, 1035 w, 900 sh, 874, 833, 820, 690 w, 645 w, 600 sh, 555, 486, 458, and 397. Attikaite is optically biaxial, negative, α = 1.642(2), β = γ = 1.644(2) ( X = c) 2 V means = 10(8)°, and 2 V calc = 0°. The new mineral is microscopically colorless and nonpleochroic. The chemical composition (electron microprobe, average over 4 point analyses, wt %) is: 0.17 MgO, 17.48 CaO, 0.12 FeO, 16.28 CuO, 10.61 Al2O3, 0.89 P2O5, 45.45 As2O5, 1.39 SO3, and H2O (by difference) 7.61, where the total is 100.00. The empirical formula calculated on the basis of (O,OH,H2O)22 is: Ca2.94Cu{1.93/2+} Al1.97Mg0.04Fe{0.02/2+} [(As3.74S0.16P0.12)Σ4.02O16.08](OH)3.87 · 2.05H2 O. The simplified formula is Ca3Cu2Al2(AsO4)4(OH)4 · 2H2O. Attikaite is orthorhombic, space group Pban, Pbam or Pba2; the unit-cell dimensions are a = 10.01(1), b = 8.199(5), c = 22.78(1) Å, V = 1870(3) Å3, and Z = 4. In the result of the ignition of attikaite for 30 to 35 min at 128 140°, the H2O bands in the IR spectrum disappear, while the OH-group band is not modified; the weight loss is 4.3%, which approximately corresponds to two H2O

  8. 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.

  9. Interface superconductor with gap behaviour like a high-temperature superconductor.

    PubMed

    Richter, C; Boschker, H; Dietsche, W; Fillis-Tsirakis, E; Jany, R; Loder, F; Kourkoutis, L F; Muller, D A; Kirtley, J R; Schneider, C W; Mannhart, J

    2013-10-24

    The physics of the superconducting state in two-dimensional (2D) electron systems is relevant to understanding the high-transition-temperature copper oxide superconductors and for the development of future superconductors based on interface electron systems. But it is not yet understood how fundamental superconducting parameters, such as the spectral density of states, change when these superconducting electron systems are depleted of charge carriers. Here we use tunnel spectroscopy with planar junctions to measure the behaviour of the electronic spectral density of states as a function of carrier density, clarifying this issue experimentally. We chose the conducting LaAlO3-SrTiO3 interface as the 2D superconductor, because this electron system can be tuned continuously with an electric gate field. We observed an energy gap of the order of 40 microelectronvolts in the density of states, whose shape is well described by the Bardeen-Cooper-Schrieffer superconducting gap function. In contrast to the dome-shaped dependence of the critical temperature, the gap increases with charge carrier depletion in both the underdoped region and the overdoped region. These results are analogous to the pseudogap behaviour of the high-transition-temperature copper oxide superconductors and imply that the smooth continuation of the superconducting gap into pseudogap-like behaviour could be a general property of 2D superconductivity. PMID:24097347

  10. Effect of exciton pairing on the stationary Josephson current in superconductor-semimetal-superconductor junctions

    SciTech Connect

    Itskovich, I.F.; Shekhter, R.I.

    1983-01-01

    The effect of exciton pairing of charge carriers in a semimetal on the stationary Josephson current in superconductor-semimetal-superconductor junctions is considered. It is shown that the phase transition of the semimetal interlayer into an exciton dielectric state for T/sub ..gamma../superconductor-semimetal-superconductor junction is exponentially smaller than the current in the absence of exciton pairing.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  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 and apparatus for dissipating remanent fields and preserving diamagnetism of ceramic superconductors

    SciTech Connect

    Youngdahl, C.A.

    1993-12-31

    A method for dissipating a remanent field, created when a magnetic field is brought into contact with a superconductor, while preserving the diamagnetism of a superconductor comprises the steps of (1) providing a ceramic superconductor; (2) continuously or intermittently generating an AC current to the ceramic superconductor; and (3) gradually decreasing the AC current until the undesired remanent field is dissipated.

  18. Exploring intertwined orders in cuprate superconductors

    DOE PAGESBeta

    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

  19. 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.

  20. 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

  1. 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.

  2. Gapless topological superconductors: Model Hamiltonian and realization

    NASA Astrophysics Data System (ADS)

    Baum, Yuval; Posske, Thore; Fulga, Ion Cosma; Trauzettel, Björn; Stern, Ady

    2015-07-01

    The existence of an excitation gap in the bulk spectrum is one of the most prominent fingerprints of topological phases of matter. In this paper, we propose a family of two-dimensional Hamiltonians that yield an unusual class D topological superconductor with a gapless bulk spectrum but well-localized Majorana edge states. We perform a numerical analysis for a representative model of this phase and suggest a concrete physical realization by analyzing the effect of magnetic impurities on the surface of a strong topological insulator.

  3. Quasiparticles near domain walls in hexagonal superconductors

    NASA Astrophysics Data System (ADS)

    Mukherjee, S. P.; Samokhin, K. V.

    2016-02-01

    We calculate the energy spectrum of quasiparticles trapped by a domain wall separating different time-reversal symmetry-breaking ground states in a hexagonal superconductor, such as UPt3. The bound-state energy is found to be strongly dependent on the gap symmetry, the domain-wall orientation, the quasiparticle's direction of semiclassical propagation, and the phase difference between the domains. We calculate the corresponding density of states and show how one can use its prominent features, in particular, the zero-energy singularity, to distinguish between different pairing symmetries.

  4. 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.

  5. 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.

  6. 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.

  7. Superconductor-Diamond Hybrid Quantum System

    NASA Astrophysics Data System (ADS)

    Semba, Kouichi; Yoshihara, Fumiki; Johansson, Jan E. S.; Zhu, Xiaobo; Mizuochi, Norikazu; Munro, William J.; Saito, Shiro; Kakuyanagi, Kosuke; Matsuzaki, Yuichiro

    This chapter describes recent progress on research into superconducting flux qubit, NV diamond, and superconductor-diamond hybrid quantum systems. First, we describe important physical properties of superconducting macroscopic artificial atoms i.e., the tunability of the qubit energy level spacing, the coherence property, an example of strong coupling to another quantum system such as an LC harmonic oscillator, and qubit state readout through a Josephson bifurcation amplifier. We then introduce the NV center in diamond as an intriguing candidate for quantum information processing, which offers excellent multiple accessibility via visible light, microwaves and magnetic fields. Finally, we describe the superconducting flux qubit - NV centers in a diamond hybrid quantum system.

  8. Stimulated quasiparticles in spin-split superconductors

    NASA Astrophysics Data System (ADS)

    Virtanen, P.; Heikkilä, T. T.; Bergeret, F. S.

    2016-01-01

    In superconductors spin split by an exchange field, thermal effects are coupled to spin transport. We show how an oscillating electromagnetic field in such systems creates spin imbalance, that can be detected with a spin-polarized probe. The sign and magnitude of the probe signal result from a competition between processes converting field-induced spin energy imbalance to spin imbalance, dominant at low frequencies, and microwave-driven pair breaking at high frequencies. In the presence of spin-flip scattering, we show that ac excitation also leads to multistabilities in the superconducting state.

  9. Vortex induced strain effects in anisotropic superconductors

    SciTech Connect

    Miranovic, P.; Dobrosavljevic-Grujic, L.; Kogan, V.G.

    1996-12-31

    Strain in a superconductor, produced by the normal vortex core, can affect both static and dynamic properties of vortices. It causes an additional vortex-vortex interaction which is long-ranged ({approximately} 1/r{sup 2}) as compared with finite but much stronger London interaction in the fields far below H{sub c2}. The energy of this magneto-elastic interaction is calculated within London model. The role of strain effects in forming vortex lattice structure is demonstrated for YBa{sub 2}Cu{sub 3}O{sub 7}.

  10. Giant proximity effect in cuprate superconductors.

    PubMed

    Bozovic, I; Logvenov, G; Verhoeven, M A J; Caputo, P; Goldobin, E; Beasley, M R

    2004-10-01

    Using an advanced molecular beam epitaxy system, we have reproducibly synthesized atomically smooth films of high-temperature superconductors and uniform trilayer junctions with virtually perfect interfaces. We found that supercurrent runs through very thick barriers. We can rule out pinholes and microshorts; this "giant proximity effect" (GPE) is intrinsic. It defies the conventional explanation; it might originate in resonant tunneling through pair states in an almost-superconducting barrier. GPE may also be significant for superconducting electronics, since thick barriers are easier to fabricate. PMID:15524925

  11. Quasiparticles near domain walls in hexagonal superconductors

    NASA Astrophysics Data System (ADS)

    Mukherjee, Soumya; Samokhin, Kirill

    We calculate the energy spectrum of quasiparticles trapped by a domain wall separating different time reversal symmetry-breaking ground states in a hexagonal superconductor, such as UPt3. The bound state energy is found to be strongly dependent on the gap symmetry, the domain wall orientation, the quasiparticle's direction of semiclassical propagation, and the phase difference between the domains. We calculate the corresponding density of states and show how one can use its prominent features, in particular, the zero-energy singularity, to distinguish between different pairing symmetries. Discovery Grant from the Natural Sciences and Engineering Research Council of Canada.

  12. Analytic Treatment on Stimulated Holographic Superconductors

    NASA Astrophysics Data System (ADS)

    Zeng, Xiao-Xiong; Liu, Xian-Ming; Liu, Wen-Biao

    Using the classical time-average approximation to deal with equation of motion for scalar field, holographic superconductor with a time-dependent chemical potential is studied analytically in probe limit. On the basis of the minimum eigenvalue of Sturm-Liouville equation, concrete values of the phase transition temperature and critical frequency are obtained. The condensed solution in high frequency regime is also calculated. It is shown that the phase transition temperature enhances and the superconductivity can be got easier as the frequency of the time-dependent chemical potential, which should be larger than the critical frequency, rises.

  13. Modeling forces in high-temperature superconductors

    SciTech Connect

    Turner, L. R.; Foster, M. W.

    1997-11-18

    We have developed a simple model that uses computed shielding currents to determine the forces acting on a high-temperature superconductor (HTS). The model has been applied to measurements of the force between HTS and permanent magnets (PM). Results show the expected hysteretic variation of force as the HTS moves first toward and then away from a permanent magnet, including the reversal of the sign of the force. Optimization of the shielding currents is carried out through a simulated annealing algorithm in a C++ program that repeatedly calls a commercial electromagnetic software code. Agreement with measured forces is encouraging.

  14. Potential aerospace applications of high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Selim, Raouf

    1994-12-01

    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

  15. Inversion symmetry protected topological insulators and superconductors

    NASA Astrophysics Data System (ADS)

    Lee, Dung-Hai; Lu, Yuan-Ming

    2015-03-01

    Three dimensional topological insulator represents a class of novel quantum phases hosting robust gapless boundary excitations, which is protected by global symmetries such as time reversal, charge conservation and spin rotational symmetry. In this work we systematically study another class of topological phases of weakly interacting electrons protected by spatial inversion symmetry, which generally don't support stable gapless boundary states. We classify these inversion-symmetric topological insulators and superconductors in the framework of K-theory, and construct their lattice models. We also discuss quantized response functions of these inversion-protected topological phases, which serve as their experimental signatures.

  16. 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

  17. Guided design of copper oxysulfide superconductors

    NASA Astrophysics Data System (ADS)

    Yee, Chuck-Hou; Birol, Turan; Kotliar, Gabriel

    2015-07-01

    We describe a framework for designing novel materials, combining modern first-principles electronic-structure tools, materials databases, and evolutionary algorithms capable of exploring large configurational spaces. Guided by the chemical principles introduced by Antipov et al., for the design and synthesis of the Hg-based high-temperature superconductors, we apply our framework to screen 333 proposed compositions to design a new layered copper oxysulfide, Hg(CaS)2CuO2. We evaluate the prospects of superconductivity in this oxysulfide using theories based on charge-transfer energies, orbital distillation and uniaxial strain.

  18. 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.

  19. High-Tc superconductor coplanar waveguide filter

    NASA Technical Reports Server (NTRS)

    Chew, Wilbert; Bajuk, Louis J.; Cooley, Thomas W.; Foote, Marc C.; Hunt, Brian D.; Rascoe, Daniel L.; Riley, A. L.

    1991-01-01

    Coplanar waveguide (CPW) low-pass filters made of YBa2Cu3O(7-delta) (YBCO) on LaAlO3 substrates, with dimensions suited for integrated circuits, were fabricated and packaged. A complete filter gives a true idea of the advantages and difficulties in replacing thin-film metal with a high-temperature superconductor in a practical circuit. Measured insertion losses in liquid nitrogen were superior to the loss of a similar thin-film copper filter throughout the 0- to 9.5-GHz passband. These results demonstrate the performance of fully patterned YBCO in a practical CPW structure after sealing in a hermetic package.

  20. Magnetic exchange coupling through superconductors: A trilayer study

    NASA Astrophysics Data System (ADS)

    Sá de Melo, C. A.

    2000-11-01

    The possibility of magnetic exchange coupling between two ferromagnets (F) separated by a superconductor (S) spacer is analyzed using the functional integral method. For this coupling to occur three prima facie conditions need to be satisfied. First, an indirect exchange coupling between the ferromagnets must exist when the superconductor is in its normal state. Second, superconductivity must not be destroyed due to the proximity to ferromagnetic boundaries. Third, roughness of the F/S interfaces must be small. Under these conditions, when the superconductor is cooled to below its critical temperature, the magnetic coupling changes. The appearance of the superconducting gap introduces a new length scale (the coherence length of the superconductor) and modifies the temperature dependence of the indirect exchange coupling existent in the normal state. The magnetic coupling is oscillatory both above and below the the critical temperature of the superconductor, as well as strongly temperature-dependent. However, at low temperatures the indirect exchange coupling decay length is controlled by the coherence length of the superconductor, while at temperatures close to and above the critical temperature of the superconductor the magnetic coupling decay length is controlled by the thermal length.

  1. Pinning Loss Power Density in Superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, Teruo

    2015-03-01

    The pinning loss power density is theoretically derived based on the resistive energy dissipation when the flux lines are driven by the Lorentz force in a superconductor. The obtained loss power density does not depend on the viscosity or flow resistivity, but is proportional to the pinning force density only, and it possesses the nature of hysteresis loss, as commonly measured in experiments. These features are predicted by the critical state model, which was recently proved theoretically. The obtained pinning force density is consistent with the prediction of the coherent potential approximation theory, a kind of statistical summation theory, for flux pinning. Thus, the irreversible properties associated with the flux pinning can be comprehensively described by these flux pinning theories. The irreversible flux pinning in the superconductor is compared with similar irreversible phenomena such as the motion of magnetic domain walls in ferromagnetic materials and the friction in mechanical systems. The possibility is also discussed for a general theoretical description of these irreversible phenomena in which the hysteresis loss occurs.

  2. Superfluid density through 2D superconductor junctions

    NASA Astrophysics Data System (ADS)

    Nam, Hyoungdo; Shih, Chih-Kang

    As S. Qin et al. reported, two monolayer (2 ML) lead film on a silicon (111) substrate has one of two different atomic structures on the silicon substrate: the unstrained 1x1 and the psedumorphically strained √3x √3 (i.e. the same lattice constant as the Si √3x √3 lattice). Most interestingly, although these two different regions show the same quantum well state features, they have different Tc's (5 K and 4 K). These two different regions of 2 ML film naturally form superconductor-superconductor (SS or SS') junctions along silicon step edges. Physical connection of the junction is only 1 ML thickness because of the step height difference of substrate. We will present this study of SS (or SS') junction system using scanning tunneling microscopy/spectroscopy and in-situ double-coil mutual inductance measurement. The transition of superconducting gaps across either SS or SS' junctions should show how to locally affect each other. Double coil measurement show a global Tc close to the lower Tc region with sizable superfluid density. We will discuss the phase rigidity and its relationship to the superfluid density in this ultra-thin Pb film that is only 2 ML thick.

  3. Meissner effect of odd-frequency superconductors

    NASA Astrophysics Data System (ADS)

    Hashimoto, Katsufumi

    2001-10-01

    We present theoretical results on the Meissner effect of odd-frequency superconductors with the order parameter of the form, sgn(ωn)φ(k,iωn), where φ(k,iωn) is even in the Matsubara frequency ωn as in the conventional case. It is shown that the spectral function of the anomalous Green's function is given in the form of the Hilbert transformation of the one for the even-frequency part, and the anomalous contribution to the paramagnetic kernel consists of the conventional term but with the opposite sign and a term expressed by the digamma function. In the static limit the latter term reduces to twice the former one with the opposite sign so that the net contribution becomes the same as the conventional one. This indicates the presence of the Meissner effect for this class of the odd-frequency superconductors. A model interaction is discussed that leads to the order parameter mentioned above.

  4. Abrikosov Gluon Vortices in Color Superconductors

    NASA Astrophysics Data System (ADS)

    Ferrer, Efrain J.

    2011-09-01

    In this talk I will discuss how the in-medium magnetic field can influence the gluon dynamics in a three-flavor color superconductor. It will be shown how at field strengths comparable to the charged gluon Meissner mass a new phase can be realized, giving rise to Abrikosov's vortices of charged gluons. In that phase, the inhomogeneous gluon condensate anti-screens the magnetic field due to the anomalous magnetic moment of these spin-1 particles. This paramagnetic effect can be of interest for astrophysics, since due to the gluon vortex antiscreening mechanism, compact stars with color superconducting cores could have larger magnetic fields than neutron stars made up entirely of nuclear matter. I will also discuss a second gluon condensation phenomenon connected to the Meissner instability attained at moderate densities by two-flavor color superconductors. In this situation, an inhomogeneous condensate of charged gluons emerges to remove the chromomagnetic instability created by the pairing mismatch, and as a consequence, the charged gluonic currents induce a magnetic field. Finally, I will point out a possible relation between glitches in neutron stars and the existence of the gluon vortices.

  5. Charge of a quasiparticle in a superconductor

    PubMed Central

    Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas

    2016-01-01

    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. PMID:26831071

  6. Method for fabrication of high temperature superconductors

    SciTech Connect

    Balachandran, Uthamalingam; Ma, Beihai; Miller, Dean

    2006-03-14

    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 Y2O3 and then a layer of CeO2 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 CeO2 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. Insulation system for high temperature superconductor cables

    NASA Astrophysics Data System (ADS)

    Michael, P. C.; Haight, A. E.; Bromberg, L.; Kano, K.

    2015-12-01

    Large-scale superconductor applications, like fusion magnets, require high-current capacity conductors to limit system inductance and peak operating voltage. Several cabling methods using high temperature superconductor (HTS) tapes are presently under development so that the unique high-field, high-current-density, high operating temperature characteristics of 2nd generation REBCO coated conductors can be utilized in next generation fusion devices. Large-scale magnets are generally epoxy impregnated to support and distribute electromagnetic stresses through the magnet volume. However, the present generation of REBCO coated conductors are prone to delamination when tensile stresses are applied to the broad surface of REBCO tapes; this can occur during epoxy cure, cooldown, or magnet energization. We present the development of an insulation system which effectively insulates HTS cabled conductors at high withstand voltage while simultaneously preventing the intrusion of the epoxy impregnant into the cable, eliminating degradation due to conductor delamination. We also describe a small-scale coil test program to demonstrate the cable insulation scheme and present preliminary test results.

  8. Percolation effect in thick film superconductors

    SciTech Connect

    Sali, R.; Harsanyi, G.

    1994-12-31

    A thick film superconductor paste has been developed to study the properties of granulated superconductor materials, to observe the percolation effect and to confirm the theory of the conducting mechanism in the superconducting thick films. This paste was also applied to make a superconducting planar transformer. Due to high T{sub c} and advantageous current density properties the base of the paste was chosen to be of Bi(Pb)SrCaCuO system. For contacts a conventional Ag/Pt paste was used. The critical temperature of the samples were between 110 K and 115 K depending on the printed layer thickness. The critical current density at the boiling temperature of the liquid He- was between 200-300 A/cm{sup 2}. The R(T) and V(I) functions were measured with different parameters. The results of the measurements have confirmed the theory of conducting mechanism in the material. The percolation structure model has been built and described. As an application, a superconducting planar thick film transformer was planned and produced. Ten windings of the transformer were printed on one side of the alumina substrate and one winding was printed on the other side. The coupling between the two sides was possible through the substrate. The samples did not need special drying and firing parameters. After the preparation, the properties of the transformer were measured. The efficiency and the losses were determined. Finally, some fundamental advantages and problems of the process were discussed.

  9. Advantageous grain boundaries in iron pnictide superconductors

    PubMed Central

    Katase, Takayoshi; Ishimaru, Yoshihiro; Tsukamoto, Akira; Hiramatsu, Hidenori; Kamiya, Toshio; Tanabe, Keiichi; Hosono, Hideo

    2011-01-01

    High critical temperature superconductors have zero power consumption and could be used to produce ideal electric power lines. The principal obstacle in fabricating superconducting wires and tapes is grain boundaries—the misalignment of crystalline orientations at grain boundaries, which is unavoidable for polycrystals, largely deteriorates critical current density. Here we report that high critical temperature iron pnictide superconductors have advantages over cuprates with respect to these grain boundary issues. The transport properties through well-defined bicrystal grain boundary junctions with various misorientation angles (θGB) were systematically investigated for cobalt-doped BaFe2As2 (BaFe2As2:Co) epitaxial films fabricated on bicrystal substrates. The critical current density through bicrystal grain boundary (JcBGB) remained high (>1 MA cm−2) and nearly constant up to a critical angle θc of ∼9°, which is substantially larger than the θc of ∼5° for YBa2Cu3O7–δ. Even at θGB>θc, the decay of JcBGB was much slower than that of YBa2Cu3O7–δ. PMID:21811238

  10. 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.

  11. Superconductor disorder and strong proximity coupling effects in Majorana nanowires

    NASA Astrophysics Data System (ADS)

    Cole, William; Sau, Jay

    Topological superconductivity induced by proximity to a conventional superconductor is only robust against moderate disorder in the parent superconductor, and only when the energy scale of the interface coupling is much smaller than the parent gap. I present detailed calculations of proximity-induced superconductivity in one-dimensional, spin-orbit coupled, semiconductor nanowires when the parent superconductor disorder and interface coupling exceed this limit. This parameter regime is characterized by unique spectroscopic signatures on both sides of the external field tuned topological phase transition. This work is supported by LPS-MPO-CMTC, Microsoft Q, and JQI-NSF-PFC.

  12. Rotordynamic Characterization of a Hybrid Superconductor Magnet Bearing

    NASA Technical Reports Server (NTRS)

    Ma, Ki B.; Xia, Zule H.; Cooley, Rodger; Fowler, Clay; Chu, Wei-Kan

    1996-01-01

    A hybrid superconductor magnet bearing uses magnetic forces between permanent magnets to provide lift and the flux pinning force between permanent magnets and superconductors to stabilize against instabilities intrinsic to the magnetic force between magnets. We have constructed a prototype kinetic energy storage system, using a hybrid superconductor magnet bearing to support a 42 lb. flywheel at the center. With five sensors on the periphery of the flywheel, we have monitored the position and attitude of the flywheel during its spin down. The results indicate low values of stiffnesses for the bearing. The implications of this and other consequences will be discussed.

  13. Levitation of a magnet over a flat type II superconductor

    SciTech Connect

    Hellman, F.; Gyorgy, E.M.; Johnson D.W. Jr.; O'Bryan, H.M.; Sherwood, R.C.

    1988-01-15

    Levitation of a magnet over a type II superconductor where the field at the superconductor exceeds H/sub c//sub 1/ is described and shown. The penetration and pinning of the flux lines in the superconductor cause the position of the magnet to be stable over a flat disk; a complete Meissner effect would make this position unstable. Furthermore, the observed dependence of the height of levitation on such variables as the thickness of the superconducting disk and the size of the magnet are consistent with a model described in this paper based on the energy cost of flux penetration through vortices and inconsistent with a Meissner effect model.

  14. Flux-flow resistivity of three high-temperature superconductors

    SciTech Connect

    Cha, Y.S.; Evans, D.J.; Hull, J.R.; Seol, S.Y.

    1996-10-01

    Results of experiments on flux-flow resistivity (the relationship of voltage to current) of three high-temperature superconductors are described. The superconductors are a melt-cast BSCCO 2212 rod, a single filament BSCCO powder-in-tube (PIT) tape, and a multifilament PIT tape. The flux-flow resistivity of these superconductors was measured at three temperatures: 77 K (saturated liquid nitrogen), 87 K (saturated liquid argon), and 67 K (subcooled liquid nitrogen). Implications of the present results for practical applications are discussed.

  15. Low-voltage current noise in long quantum superconductor/insulator/normal-metal/insulator/superconductor junctions.

    SciTech Connect

    Kopnin, N. B.; Galperin, Y. M.; Vinokur, V.; Materials Science Division; Helsinki Univ. Tech.; L.D. Landau Inst. for Theoretical Physics; Univ. Oslo; A.F. Ioffe Physico-Tech. Inst. of Russian Academy of Sciences

    2007-01-01

    The current noise in long superconductor/insulator/normal-metal/insulator/superconductor junctions at low temperatures is sensitive to the population of the subgap states, which is far from equilibrium even at low bias voltages. A nonequilibrium distribution is established due to an interplay between voltage-driven interlevel Landau-Zener transitions and intralevel inelastic relaxation. The Fano factor (the ratio of the zero-frequency noise to the dc current) is enhanced drastically, being proportional to the number of times which a particle flies along the Andreev trajectory before it escapes from the level due to inelastic scattering. For weak Landau-Zener transitions, the enhancement is even larger due to a smaller dc current.

  16. 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

  17. Josephson current in a normal-metal nanowire coupled to a superconductor/ferromagnet/superconductor junction

    NASA Astrophysics Data System (ADS)

    Ebisu, Hiromi; Lu, Bo; Taguchi, Katsuhisa; Golubov, Alexander A.; Tanaka, Yukio

    2016-01-01

    We consider a superconducting nanowire proximity coupled to a superconductor/ferromagnet/superconductor (S/F/S) junction, where the magnetization penetrates into a superconducting segment in a nanowire decaying as ˜exp[-∣n/∣ ξ ] , where n is the site index and the ξ is the decay length. We tune chemical potential and spin-orbit coupling so that the topological superconducting regime hosting the Majorana fermion is realized for long ξ . We find that when ξ becomes shorter, zero energy state at the interface between a superconductor and a ferromagnet splits into two states at nonzero energy. Accordingly, the behavior of the Josephson current is drastically changed due to this "zero mode-nonzero mode crossover." By tuning the model parameters, we find an almost second-harmonic current-phase relation sin2 φ , where φ is the phase difference of the junction. Based on the analysis of Andreev bound state (ABS), we clarify that the current-phase relation is determined by coupling of the states within the energy gap. We find that the emergence of crossing points of ABS is a key ingredient to generate sin2 φ dependence in the current-phase relation. We further study both the energy and φ dependence of pair amplitudes in the ferromagnetic region. For large ξ , an odd-frequency spin-triplet s -wave component is dominant. The magnitude of the odd-frequency pair amplitude is enhanced at the energy level of ABS.

  18. Pristine and intercalated transition metal dichalcogenide superconductors

    NASA Astrophysics Data System (ADS)

    Klemm, Richard A.

    2015-07-01

    Transition metal dichalcogenides (TMDs) are quasi-two-dimensional layered compounds that exhibit strongly competing effects of charge-density wave (CDW) formation and superconductivity (SC). The weak van der Waals interlayer bonding between hexagonal layers of octahedral or trigonal prismatic TMD building blocks allows many polytypes to form. In the single layer 1 T polytype materials, one or more CDW states can form, but the pristine TMDs are not superconducting. The 2 H polytypes have two or more Fermi surfaces and saddle bands, allowing for dual orderings, which can be coexisting CDW and SC orderings, two SC gaps as in MgB2, two CDW gaps, and possibly even pseudogaps above the onset TCDW s of CDW orderings. Higher order polytypes allow for multiple CDW gaps and at least one superconducting gap. The CDW transitions TCDW s usually greatly exceed the superconducting transitions at their low Tc values, their orbital order parameters (OPs) are generally highly anisotropic and can even contain nodes, and the SC OPs can be greatly affected by their simultaneous presence. The properties of the CDWs ubiquitously seen in TMDs are remarkably similar to those of the pseudogaps seen in the high-Tc cuprates. In 2H-NbSe2, for example, the CDW renders its general s-wave SC OP orbital symmetry to be highly anisotropic and strongly reduces its Josephson coupling strength (IcRn) with the conventional SC, Pb. Hence, the pristine TMDs are highly "unconventional" in comparison with Pb, but are much more "conventional" than are the ferromagnetic superconductors such as URhGe. Applied pressure and intercalation generally suppress the TMD CDWs, allowing for enhanced SC formation, even in the 1 T polytype materials. The misfit intercalation compound (LaSe)1.14(NbSe2) and many 2 H -TMDs intercalated with organic Lewis base molecules, such as TaS2(pyridine)1/2, have completely incoherent c-axis transport, dimensional-crossover effects, and behave as stacks of intrinsic Josephson junctions

  19. Nonlinear electrodynamics of vortex matter in hard superconductors (Review)

    NASA Astrophysics Data System (ADS)

    Voloshin, I. F.; Fisher, L. M.; Yampol'Skiĭ, V. A.

    2010-01-01

    Nontrivial electrodynamic properties of vortex matter, which are due to a specific nonlinearity of the material equations, in hard superconductors are discussed: collapse of the transport current and the static magnetization of superconductors by an external orthogonal ac magnetic field; appearance of jumps in the time dependence of the electric field at the boundary of a sample as a result of nonlinear interaction of waves having different frequencies; specific staged penetration of an electromagnetic field into anisotropic superconductors. Nonlocal effects resulting in a large modification of nonlinear phenomena are also examined. Special attention is given to a discussion of the unique phenomenon of macroturbulent instability, associated with the flow of Abrikosov vortices, in hard superconductors. Most results presented are based on original experimental and theoretical investigations performed with the participation of the present authors.

  20. The Discovery of a Class of High-Temperature Superconductors.

    ERIC Educational Resources Information Center

    Muller, K. Alex; Bednorz, J. Georg

    1987-01-01

    Describes the new class of oxide superconductors, the importance of these materials, and the concepts that led to its discovery. Summarizes the discovery itself and its early confirmation. Discusses the observation of a superconductive glass state in percolative samples. (TW)

  1. 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.

  2. Kinetics of vortex formation in superconductors with d pairing

    NASA Astrophysics Data System (ADS)

    Filippov, A. E.; Radievsky, A. V.; Zeltser, A. S.

    1996-08-01

    We study the kinetics of vortex formation in superconductors with d pairing. We find order-parameter peculiarities and associated magnetic field maxima at intermediate stages of the evolution from the disordered to the ordered state.

  3. Scaling rules for critical current density in anisotropic biaxial superconductors

    NASA Astrophysics Data System (ADS)

    Li, Yingxu; Kang, Guozheng; Gao, Yuanwen

    2016-06-01

    Recent researches highlight the additional anisotropic crystallographic axis within the superconducting plane of high temperature superconductors (HTS), demonstrating the superconducting anisotropy of HTS is better understood in the biaxial frame than the previous uniaxial coordinates within the superconducting layer. To quantitatively evaluate the anisotropy of flux pinning and critical current density in HTS, we extend the scaling rule for single-vortex collective pinning in uniaxial superconductors to account for flux-bundle collective pinning in biaxial superconductors. The scaling results show that in a system of random uncorrected point defects, the field dependence of the critical current density is described by a unified function with the scaled magnetic field of the isotropic superconductor. The obtained angular dependence of the critical current density depicts the main features of experimental observations, considering possible corrections due to the strong-pinning interaction.

  4. Inhomogeneities in single crystals of cuprate oxide superconductors

    NASA Technical Reports Server (NTRS)

    Moorjani, K.; Bohandy, J.; Kim, B. F.; Adrian, F. J.

    1991-01-01

    The next stage in the evolution of experimental research on the high temperature superconductors will require high quality single crystals and epitaxially grown crystalline films. However, inhomogeneities and other defects are not uncommon in single crystals of cuprate oxide superconductors, so a corollary requirement will be a reliable method for judging the quality of these materials. The application of magnetically modulated resistance methods in this task is briefly described and illustrated.

  5. Magneto-optical imaging of transport current densities in superconductors

    SciTech Connect

    Crabtree, G.W.; Welp, U.; Gunter, D.O.; Zhong, W.; Balachandran, U.; Haldar, P.; Sokolowski, R.S.; Vlasko-Vlasov, V.K.; Nikitenko, V.I.

    1995-12-31

    Direct imaging of the paths of transport currents in superconductors creates many new possibilities for exploring the basic features of vortex pinning mechanisms and for improving the performance of superconducting materials. A technique for imaging the path and magnitude of the transport current density flowing in superconductors is described. Results are given for a 37-filament BSCCO 2223 powder-in-tube wire, showing a highly inhomogeneous current path within the filaments.

  6. Flux periodicities and quantum hair on holographic superconductors.

    PubMed

    Montull, Marc; Pujolàs, Oriol; Salvio, Alberto; Silva, Pedro J

    2011-10-28

    Superconductors in a cylindrical geometry respond periodically to a cylinder-threading magnetic flux, with the period changing from hc/2e to hc/e depending on whether the Aharonov-Bohm effects are suppressed. We show that holographic superconductors present a similar phenomenon, and that the different periodicities follow from classical no-hair theorems. We also give the Ginzburg-Landau description of the period-doubling phenomenon. PMID:22107621

  7. On the electrodynamics of Josephson effect in anisotropic superconductors

    SciTech Connect

    Mints, R.G.

    1989-01-01

    Specificities of Josephson effect electrodynamics in anisotropic superconductors are of considerable interest for the study of high temperature superconductors with strongly anisotropic layered structure. In this paper the authors give the calculation for the tunnel Josephson contact of an isolated vortex, the law of dispersion of its low-amplitude oscillations, the critical field H/sub cl/ for the penetration of magnetic flux, and the maximum current across a rectangular contact.

  8. Josephson effect and quasiparticle states in d-wave superconductors

    SciTech Connect

    Tanaka, Yukio; Kashiwaya, Satoshi

    1996-12-31

    A general formula for the Josephson current in a d-wave/insulator/d-wave-superconductor junction is presented by taking account of the zero-energy states formed around the interfaces. For a fixed phase difference between the two superconductors, the current component becomes either positive or negative depending on the injection angle of the quasiparticle. Anomalous temperature dependences are predicted in the maximum Josephson current and in the free energy minima.

  9. Superconductivity in nonclassical superconductors as a periodical (oscillating) redox reaction

    SciTech Connect

    Kostikova, G.P.; Korol`kov, D.V.; Kostikov, Yu.P.

    1995-10-20

    Comparison of the properties of high-temperature superconductors with those of chemical systems where a periodical (oscillating) redox reaction is realized suggests that the high-temperature superconducting of nonclassical superconductors (in particular, ternary oxides) results from activation of a periodical redox reaction within a single compounds containing heterovalent forms of each of two dissimilar elements. In this redox reaction, reversible converison of the corresponding heterovalent forms occur. 37 refs., 1 fig., 1 tab.

  10. 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.

  11. Stability of magnetic tip/superconductor levitation systems

    NASA Astrophysics Data System (ADS)

    K. Alqadi, M.

    2015-11-01

    The vertical stability of a magnetic tip over a superconducting material is investigated by using the critical state and the frozen image models. The analytical expressions of the stiffness and the vibration frequency about the equilibrium position are derived in term of the geometrical parameters of the magnet/superconductor system. It is found that the stability of the system depends on the shape of the superconductor as well as its thickness.

  12. Hairy balls and flux lines in superconductors

    NASA Astrophysics Data System (ADS)

    Laver, Mark; Forgan, Ted

    2011-03-01

    Many physical phenomena originate from geometrical effects rather than from local physics. For example, the hairy ball theorem --- a hairy sphere cannot be combed --- is fulfilled by the atmospheric circulation with the existence of stratospheric polar vortices, and the fact that there is always at least one place on Earth where the horizontal wind is still. We examine the consequences of the hairy ball theorem for the flux line lattice (FLL). We find that discontinuities must exist in lattice shape as a function of field direction relative to the crystal. The remarkable ways in which the hairy ball theorem is fulfilled are demonstrated for FLL's in superconducting niobium. We show that extraordinary, unconventional flux line lattice shapes that spontaneously break the underlying crystal symmetry are surprisingly likely across all Type-II superconductors, both conventional and unconventional.

  13. A hydroxycarbonate route to superconductor precursor powders

    NASA Astrophysics Data System (ADS)

    Voigt, J. A.; Bunker, B. C.; Doughty, D. H.; Lamppa, D. L.; Kimball, K. M.

    A precipitation process is described for the preparation of powders that can be thermally decomposed to form high critical temperature superconductors such as YBa2Cu3O7. In the process, a cationic solution (a concentrated chloride or nitrate solution) is instantaneously mixed with an anionic solution (a mixture of tetramethylammonium hydroxide and carbonate) to produce a metal-hydroxycarbonate precipitate having the metal stoichiometry of the desired superconducting oxide. The calcining and sintering of the precipitates is critical in controlling the structural integrity and morphology of the superconducting ceramics made from the chem-prep powders, as well as controlling superconducting properties. Under appropriate conditions, high density (greater than 95 percent) materials that exhibit good superconducting characteristics can be prepared with the chem-prep powders.

  14. Vertical Transport in Ferroelectric/Superconductor Heterostructures

    NASA Astrophysics Data System (ADS)

    Begon-Lours, Laura; Trastoy, Juan; Bernard, Rozenn; Jacquet, Eric; Carretero, Cecile; Bouzehouane, Karim; Fusil, Stephane; Garcia, Vincent; Xavier, Stephane; Girod, Stephanie; Deranlot, Cyrile; Bibes, Manuel; Barthelemy, Agnes; Villegas, Javier E.

    2015-03-01

    We study electric field-effects in superconducting films by measuring vertical transport in ferroelectric/superconductor heterostructures. These are based on ultrathin (4 to 8 nm thick) BiFeO3-Mn grown on YBa2Cu3O7 by pulsed laser deposition. Nanoscale contacts are defined on the BiFeO3 via a series of nanofabrication steps which include e-beam lithography, metal deposition (Nb or Co capped with Pt) and lift-off. Conductive-tip atomic force microscopy and piezoresponse force microscopy are used to characterize the transport across the ferroelectric barrier as a function of its polarization (up/down). The observed electro-resistance, measured at various temperatures, allows studying the different electric-field screening in the normal and superconducting states. Work supported by DIM Oxymore.

  15. Search for spontaneous magnetization in noncentrosymmetric superconductors

    NASA Astrophysics Data System (ADS)

    Sumiyama, A.; Kawakatsu, D.; Gouchi, J.; Kawasaki, I.; Yamaguchi, A.; Motoyama, G.; Hirose, Y.; Settai, R.; Ōnuki, Y.

    2016-02-01

    We have measured the magnetization of two noncentrosymmetric superconductors: Ir2Ga9 and CePt3Si using a SQUID magnetometer, neither of which has been tested for the time-reversal symmetry in the superconducting state. For Ir2Ga9, the magnetization change ΔM below the superconducting transition temperature Tc ˜ 2.2 K was smaller than 10-5 G in zero magnetic field, suggesting that ΔM originates in the Meissner effect induced by the possible residual field. When CePt3Si was cooled in zero magnetic field, ΔM along the c axis first decreased below Tc+ ˜ 0.75 K (high-Tc phase) and then increased below Tc- ˜ 0.45 K (bulk superconducting phase). Since this behavior cannot be explained by the Meissner effect, it may be a sign of a spontaneous magnetization.

  16. Dynamics of Josephson pancakes in layered superconductors

    SciTech Connect

    Mints, R.G.; Snapiro, I.B.

    1994-03-01

    We consider a pointlike vortex in a layered superconductor with linear defects in the superconducting layers. We treat these defects as Josephson junctions with high critical current density. We consider the electrodynamics of these junctions within the framework of nonlocal Josephson electrodynamics. We show that Josephson current through a linear defect in a superconducting layer results in a pointlike vortex with a superconducting core residing in this layer (Josephson pancake). We find the mobility of a Josephson pancake. We consider a small amplitude wave in a Josephson junction with nonlocal electrodynamics. We treat a bending wave for an infinite stack of Josephson pancakes. We find the dispersion relation for these waves. We show that their velocities tend to a certain finite limit when the wavelength tends to infinity.

  17. Current-carrying capacity of composite superconductors

    SciTech Connect

    Andrianov, V.; Baeu, V.; Ivanov, S.; Mints, R.; Rakhmanov, A.

    1983-05-01

    The maximum transport current I /SUB m/ of the composite superconductors is investigated both theoretically and experimentally. It is shown that the high values of the transport current observed in these materials is due to the non-linear part of the current-voltage characteristic in the range of low electric fields (E less than or equal to 10/sup -6/ Vcm/sup -1/). The conductors of rather different structure with Nb-Ti superconducting filaments were tested in a wide range of the external parameters. It is shown that in the external magnetic fields B /SUB a/ greater than or equal to 1T the ratio I /SUB m/ /I /SUB c/ (where I /SUB c/ is the critical current) is the universal function of the single dimensionless parameter which depends on the sample properties and the external conditions. The theory and experiment are in a good agreement.

  18. Holographic p-wave superconductor with disorder

    NASA Astrophysics Data System (ADS)

    Areán, D.; Farahi, A.; Pando Zayas, L. A.; Salazar Landea, I.; Scardicchio, A.

    2015-07-01

    We implement the effects of disorder on a holographic p-wave superconductor by introducing a random chemical potential which defines the local energy of the charge carriers. Since there are various possibilities for the orientation of the vector order parameter, we explore the behavior of the condensate in the parallel and perpendicular directions to the introduced disorder. We clarify the nature of various branches representing competing solutions and construct the disordered phase diagram. We find that moderate disorder enhances superconductivity as determined by the value of the condensate. Though we mostly focus on uncorrelated noise, we also consider a disorder characterized by its spectral properties and study in detail its influence on the spectral properties of the condensate and charge density. We find fairly universal responses of the resulting power spectra characterized by linear functions of the disorder power spectrum.

  19. Isotope coefficient in high Tc superconductors

    SciTech Connect

    Kishore, R.

    1995-10-01

    An exact expression for the isotope coefficient ({alpha}), within the conventional BCS theory, has been derived for any arbitrary electronic density of states and the mass dependence of carrier concentration. It is shown that the effect of the mass dependence of the carrier concentration within the van-Hove scenario (VHS) can explain some anomalous features of {alpha} for La{sub 2}CuO{sub 4} based superconductors, not explained by earlier theories based on VHS. These anomalous features are the asymmetry of {alpha} about the optimum concentration (n{sub m}) corresponding to the maximum critical temperature, minimum in {alpha} above n{sub m}, and the value of {alpha} less than 0.5 below n{sub m}.

  20. Paramagnetic Meissner effect in conventional Nb superconductors

    SciTech Connect

    Thompson, D.J.; Wenger, L.E.; Chen, J.T.

    1996-11-01

    The paramagnetic Meissner effect (PME), in which the field-cooled-magnetization (FCM) of superconducting samples is positive below the superconducting transition temperature T{sub c}, has been observed in certain ceramic and single-crystal samples of the high-T{sub c} cuprate superconductors and more recently in disk-shaped Nb samples. Through systematic investigations of the conditions for observing the PME in Nb disks, various surface treatments to the Nb disks were found to change both the zero-field-cooled-magnetization (ZFCM) and the FCM, including the appearance of a positive FCM in samples previously not exhibiting the PME as well as the elimination of the PME through surface abrasion. These results suggest that the PME arises from the field distributions created by the flux pinning associated with microstructural defects on the surface layer of the disk.

  1. High temperature superconductor materials and applications

    NASA Technical Reports Server (NTRS)

    Doane, George B., III. (Editor); Banks, Curtis; Golben, John

    1991-01-01

    One of the areas concerned itself with the investigation of the phenomena involved in formulating and making in the laboratory new and better superconductor material with enhanced values of critical current and temperature. Of special interest were the chemistry, physical processes, and environment required to attain these enhanced desirable characteristics. The other area concerned itself with producing high temperature superconducting thin films by pulsed laser deposition techniques. Such films are potentially very useful in the detection of very low power signals. To perform this research high vacuum is required. In the course of this effort, older vacuum chambers were maintained and used. In addition, a new facility is being brought on line. This latter activity has been replete with the usual problems of bringing a new facility into service. Some of the problems are covered in the main body of this report.

  2. Vortex flow for a holographic superconductor

    SciTech Connect

    Maeda, Kengo; Okamura, Takashi

    2011-03-15

    We investigate energy dissipation associated with the motion of the scalar condensate in a holographic superconductor model constructed from the charged scalar field coupled to the Maxwell field. Upon application of constant magnetic and electric fields, we analytically construct the vortex-flow solution and find the vortex-flow resistance near the second-order phase transition where the scalar condensate begins. The characteristic feature of the nonequilibrium state agrees with the one predicted by the time-dependent Ginzburg-Landau (TDGL) theory. We evaluate the kinetic coefficient in the TDGL equation along the line of the second-order phase transition. At zero magnetic field, the other coefficients in the TDGL equation are also evaluated just below the critical temperature.

  3. Noncommutative effects of spacetime on holographic superconductors

    NASA Astrophysics Data System (ADS)

    Ghorai, Debabrata; Gangopadhyay, Sunandan

    2016-07-01

    The Sturm-Liouville eigenvalue method is employed to analytically investigate the properties of holographic superconductors in higher dimensions in the framework of Born-Infeld electrodynamics incorporating the effects of noncommutative spacetime. In the background of pure Einstein gravity in noncommutative spacetime, we obtain the relation between the critical temperature and the charge density. We also obtain the value of the condensation operator and the critical exponent. Our findings suggest that the higher value of noncommutative parameter and Born-Infeld parameter make the condensate harder to form. We also observe that the noncommutative structure of spacetime makes the critical temperature depend on the mass of the black hole and higher value of black hole mass is favourable for the formation of the condensate.

  4. Organic superconductors: The Bechgaard salts and relatives

    NASA Astrophysics Data System (ADS)

    Brown, S. E.

    2015-07-01

    Organic conductors were originally considered a route to achieving high temperature superconductivity. While that goal could not be met, what came to be was a class of materials in which the interplay between correlations and dimensionality, and sometimes geometric frustration, lead to a spectacular diversity of phases and phenomena that are tuned by magnetic field, pressure, and temperature. Highlighted here are the physical properties of the superconducting and normal states of the first family of organic superconductors, the quasi-one dimensional Bechgaard salts (TMTSF)2X, as well as the quasi-two dimensional compounds κ -(BEDT-TTF)2X. In both cases, the preponderance of experiments indicate that the superconductivity is nodal. As well, the importance of correlations is evident in the temperature/pressure phase diagrams, and the influence of low-energy magnetic fluctuations over the normal state properties above the superconducting transition temperature is substantial.

  5. High temperature superconductors for magnetic suspension applications

    NASA Technical Reports Server (NTRS)

    Mcmichael, C. K.; Cooley, R. S.; Chen, Q. Y.; Ma, K. B.; Lamb, M. A.; Meng, R. L.; Chu, C. W.; Chu, W. K.

    1994-01-01

    High temperature superconductors (HTS) hold the promise for applications in magnetic levitation bearings, vibration damping, and torque coupling. Traditional magnetic suspension systems require active feedback and vibration controls in which power consumption and low frequency vibration are among the major engineering concerns. HTS materials have been demonstrated to be an enabling approach towards such problems due to their flux trapping properties. In our laboratory at TCSUH, we have been conducting a series of experiments to explore various mechanical applications using HTS. We have constructed a 30 lb. model flywheel levitated by a hybrid superconducting magnetic bearing (HSMB). We are also developing a levitated and vibration-dampled platform for high precision instrumentation. These applications would be ideal for space usages where ambient temperature is adequate for HTS to operate properly under greatly reduced cryogenic requirements. We will give a general overview of these potential applications and discuss the operating principles of the HTS devices we have developed.

  6. (Thermochemistry of phases related to oxide superconductors)

    SciTech Connect

    Not Available

    1991-01-01

    The aim of this project has been to understand the crystal-chemical and energetic constraints on the stability of phases related to oxide superconductors, using high temperature reaction calorimetry, the unique expertise of this laboratory, coupled with synthesis and structural studies. The YBCO (Y{sub 2}O{sub 3}-BaO-Cu-O) system has been studied in detail by Zhou for his Ph.D. thesis, while DiCarlo has been studying alkaline earth doped lanthanium cuprates of the series La{sub 2-x}A{sub x}CuO{sub 4-y} having structures related to K{sub 2}NiF{sub 4}.

  7. Fabrication and wire extrusion of ceramic superconductors

    SciTech Connect

    Poeppel, R.B.; Balachandran, U.; Singh, J.P.; Dusek, J.T.; Picciolo, J.J.; Dorris, S.E.; Lanagan, M.T.; Goretta, K.C.; Youngdahl, C.A.; Hull, J.R.

    1991-05-01

    Many applications of high-temperature superconductors (HTSs) will depend on the ability to fabricate these materials into long lengths with suitable electrical and mechanical properties maintained over the entire length. The program described in this paper is focused on improvement of the relevant material properties of HTSs and on development of fabrication methods that can be transferred to industry for production of commercial conductors. Our research has resulted in advances in fabrication methods that improve the performance of long lengths of polycrystalline HTS wires and tapes. We have examined the Y-Ba-Cu-O (YBCO), Bi-Sr-Ca-Cu-O (BSCCO), and Tl- Ba-Ca-Cu-O (TBCCO) classes of HTSs. Significant results from our research and work by contemporaries are reported in the various sections of the paper. 28 refs.

  8. Magneto-optical imaging of exotic superconductors

    NASA Astrophysics Data System (ADS)

    van der Beek, C. J.; Losco, J.; Konczykowski, M.; Pari, P.; Shibauchi, T.; Shishido, H.; Matsuda, Y.

    2009-02-01

    We have constructed a novel compact cryostat for optical measurements at temperatures below 2 K. The desktop cryostat, small enough to be placed under the objective of a standard commercial polarized light microscope, functions in a single shot mode, with a five hour autonomy at 1.5 K. Central to its conception are four charcoal pumps for adsorption and desorption of He contained in a closed circuit, and novel thermal switches allowing for thermalization of the pumps and of the two 1 K pots. The latter are connected to the 1" diameter sample holder through braids. Sample access is immediate, through the simple removal of the optical windows. In this contribution, we shall present first results on magneto-optical imaging of flux penetration in the heavy-fermion superconductor CeCoIn5.

  9. ''Soft'' Anharmonic Vortex Glass in Ferromagnetic Superconductors

    SciTech Connect

    Radzihovsky, Leo; Ettouhami, A. M.; Saunders, Karl; Toner, John

    2001-07-09

    Ferromagnetic order in superconductors can induce a spontaneous vortex (SV) state. For external field H=0 , rotational symmetry guarantees a vanishing tilt modulus of the SV solid, leading to drastically different behavior than that of a conventional, external-field-induced vortex solid. We show that quenched disorder and anharmoinc effects lead to elastic moduli that are wave-vector dependent out to arbitrarily long length scales, and non-Hookean elasticity. The latter implies that for weak external fields H , the magnetic induction scales universally like B(H){approx}B(0)+cH{sup {alpha}} , with {alpha}{approx}0.72 . For weak disorder, we predict the SV solid is a topologically ordered glass, in the ''columnar elastic glass'' universality class.

  10. Magnetic interactions in iron superconductors: A review

    NASA Astrophysics Data System (ADS)

    Bascones, Elena; Valenzuela, Belén; Calderón, Maria José

    2016-01-01

    High-temperature superconductivity in iron pnictides and chalcogenides emerges when a magnetic phase is suppressed. The multi-orbital character and the strength of correlations underlie this complex phenomenology, involving magnetic softness and anisotropies, with Hund's coupling playing an important role. We review here the different theoretical approaches used to describe the magnetic interactions in these systems. We show that taking into account the orbital degree of freedom allows us to unify in a single phase diagram the main mechanisms proposed to explain the (π , 0) order in iron pnictides: nesting-driven superconductivity, exchange between localised spins, and Hund-induced magnetic state with orbital differentiation. Comparison of theoretical estimates and experimental results helps locate the Fe superconductors in the phase diagram. In addition, orbital physics is crucial to address the magnetic softness, the doping-dependent properties, and the anisotropies.

  11. Gravimeter using high-temperature superconductor bearing.

    SciTech Connect

    Hull, J. R.

    1998-09-11

    We have developed a sensitive gravimeter concept that uses an extremely low-friction bearing based on a permanent magnet (PM) levitated over a high-temperature superconductor (HTS). A mass is attached to the PM by means of a cantilevered beam, and the combination of PM and HTS forms a bearing platform that has low resistance to rotational motion but high resistance to horizontal, vertical, or tilting motion. The combination acts as a low-loss torsional pendulum that can be operated in any orientation. Gravity acts on the cantilevered beam and attached mass, accelerating them. Variations in gravity can be detected by time-of-flight acceleration, or by a control coil or electrode that would keep the mass stationary. Calculations suggest that the HTS gravimeter would be as sensitive as present-day superconducting gravimeters that need cooling to liquid helium temperatures, but the HTS gravimeter needs cooling only to liquid nitrogen temperatures.

  12. Designing heterostructures -- a route towards new superconductors

    NASA Astrophysics Data System (ADS)

    Kopp, Thilo

    2013-03-01

    By now it has become technologically feasible to grow controllably transition metal oxides layer by layer. In effect, the achieved progress allows to design heterostructures with optimized electronic properties. The talk will specifically address scenarios for interface superconductivity and the possibility to raise the transition temperature of bulk superconductors by layer design. Heterostructures offer a complexity beyond that of bulk materials. The nature of the superconducting states formed in layered materials and at interfaces is a fascinating topic of recent research which will be in the focus of this presentation. This work was supported by the DFG (TRR 80). I thankfully acknowledge the collaboration with Natalia Pavlenko, Peter Hirschfeld, Cyril Stephanos, Florian Loder, Arno Kampf, and Jochen Mannhart.

  13. Thermodynamic Properties in Triangular-Lattice Superconductors

    NASA Astrophysics Data System (ADS)

    Ma, Xixiao; Qin, Ling; Zhao, Huaisong; Lan, Yu; Feng, Shiping

    2016-06-01

    The study of superconductivity arising from doping a Mott insulator has become a central issue in the area of superconductivity. Within the framework of the kinetic-energy-driven superconducting (SC) mechanism, we discuss the thermodynamic properties in the triangular-lattice cobaltate superconductors. It is shown that a sharp peak in the specific heat appears at the SC transition temperature T_c, and then the specific heat varies exponentially as a function of temperature for temperatures T

  14. Equivalence of topological insulators and superconductors

    NASA Astrophysics Data System (ADS)

    Ortiz, Gerardo; Cobanera, Emilio

    Systems of free fermions are classified by symmetry, space dimensionality, and topological properties described by K-homology. We show that by taking a many-body/Fock space viewpoint it becomes possible to establish equivalences of topological insulators and superconductors in terms of duality transformations. These mappings connect topologically inequivalent systems of fermions, jumping across entries in existent classification tables, because of the phenomenon of symmetry transmutation by which a symmetry and its dual partner have identical algebraic properties but very different physical interpretations and electromagnetic response. Since our analysis extends to interacting fermion systems we also briefly discuss some such applications. To illustrate main concepts we will present dual superconducting partners of paradigmatic models, such as the Haldane Chern insulator as well as a quantum spin Hall effect graphene model.

  15. Conductance Anomalies for Normal- Insulator- Superconductor Contacts

    NASA Astrophysics Data System (ADS)

    Yip, Sungkit

    1996-03-01

    I shall present a theoretical study of the conductance through a dirty junction between a normal conductor and a superconductor with an insulating barrier. It is shown that for large barrier resistances there is a relative enhancement of the conductance near zero voltage, whereas for low barrier resistance this anomaly appears at finite voltage. (S. K. Yip, Phys. Rev. B, to appear) The results here, obtained by numerical solution of the Usadel equations, will be compared with those obtained via the transmission matrix approaches reported by the others in the literature. (e.g. ( I. K. Marmorkos , C. W. J. Beenakker and R. A. Jalabert, Phys. Rev.) B 48, 2811 (1993); Y. Takane and H. Ebisawa, J. Phys. Soc. Jpn 62, 1844 (1993). )

  16. Contact characteristics for YBCO bulk superconductors

    NASA Astrophysics Data System (ADS)

    Yamamoto, Naoki; Sakai, Tomokazu; Sawa, Koichiro; Tomita, Masaru; Murakami, Masato

    2003-10-01

    We have studied the contact characteristics of two resin-impregnated YBCO (a composite of YBa 2Cu 3O y and Y 2BaCuO 5) bulk superconductors in mechanical contact. A switching phenomenon could be observed at a threshold current or a transfer current value in the V- I curves of the YBCO contact. The transfer current exceeded the previous value of 13.5 A at 77 K in the contact when the sample surfaces were carefully polished. The present results suggest that a pair of YBCO blocks might be applicable to the mechanical persistent current switch for superconducting magnetic energy storage and other superconducting systems run in a persistent current mode.

  17. A hydroxycarbonate route to superconductor precursor powders

    SciTech Connect

    Voigt, J.A.; Bunker, B.C.; Doughty, D.H.; Lamppa, D.L.; Kimball, K.M.

    1987-01-01

    A precipitation process is described for the preparation of powders that can be thermally decomposed to form high critical temperature superconductors such as YBa/sub 2/Cu/sub 3/O/sub 7/. In the process, a cationic solution (a concentrated chloride or nitrate solution) is instantaneously mixed with an anionic solution (a mixture of tetramethylammonium hydroxide and carbonate) to produce a metal-hydroxycarbonate precipitate having the metal stoichiometry of the desired superconducting oxide. The calcining and sintering of the precipitates is critical in controlling the structural integrity and morphology of the superconducting cermaics made from the chem-prep powders, as well as controlling superconducting properties. Under appropriate conditions, high density (>95%) materials that exhibit good superconducting characteristics can be prepared with the chem-prep powders. 6 refs., 3 figs.

  18. Hole-doped cuprate high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Chu, C. W.; Deng, L. Z.; Lv, B.

    2015-07-01

    Hole-doped cuprate high temperature superconductors have ushered in the modern era of high temperature superconductivity (HTS) and have continued to be at center stage in the field. Extensive studies have been made, many compounds discovered, voluminous data compiled, numerous models proposed, many review articles written, and various prototype devices made and tested with better performance than their nonsuperconducting counterparts. The field is indeed vast. We have therefore decided to focus on the major cuprate materials systems that have laid the foundation of HTS science and technology and present several simple scaling laws that show the systematic and universal simplicity amid the complexity of these material systems, while referring readers interested in the HTS physics and devices to the review articles. Developments in the field are mostly presented in chronological order, sometimes with anecdotes, in an attempt to share some of the moments of excitement and despair in the history of HTS with readers, especially the younger ones.

  19. Correction of magnetization sextupole and decapole in a 5 centimeter bore SSC dipole using passive superconductor

    SciTech Connect

    Green, M.A.

    1991-05-01

    Higher multipoles due to magnetization of the superconductor in four and five centimeter bore Superconducting Super Collider (SSC) superconducting dipole magnets have been observed. The use of passive superconductor to correct out the magnetization sextupole has been demonstrated on two dipoles built by the Lawrence Berkeley Laboratory (LBL). This reports shows how passive correction can be applied to the five centimeter SSC dipoles to remove sextupole and decapole caused by magnetization of the dipole superconductor. Two passive superconductor corrector options will be presented. The change in magnetization sextupole and decapole due to flux creep decay of the superconductor during injection can be partially compensated for using the passive superconductor. 9 refs; 5 figs.

  20. System and method for quench and over-current protection of superconductor

    DOEpatents

    Huang, Xianrui; Laskaris, Evangelos Trifon; Sivasubramaniam, Kiruba Haran; Bray, James William; Ryan, David Thomas; Fogarty, James Michael; Steinbach, Albert Eugene

    2005-05-31

    A system and method for protecting a superconductor. The system may comprise a current sensor operable to detect a current flowing through the superconductor. The system may comprise a coolant temperature sensor operable to detect the temperature of a cryogenic coolant used to cool the superconductor to a superconductive state. The control circuit is operable to estimate the superconductor temperature based on the current flow and the coolant temperature. The system may also be operable to compare the estimated superconductor temperature to at least one threshold temperature and to initiate a corrective action when the superconductor temperature exceeds the at least one threshold temperature.

  1. Superconducting state parameters of ternary amorphous superconductors

    NASA Astrophysics Data System (ADS)

    Vora, Aditya M.

    2008-11-01

    The theoretical investigations of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ∗, transition temperature TC, isotope effect exponent α and effective interaction strength N0V of five Nb xTa yMo z ( x = 0.15, 0.30, 0.30, 0.40, 0.45; y = 0.15, 0.30, 0.30, 0.40, 0.45 and z = 0.10, 0.30, 0.30, 0.40, 0.70) ternary amorphous superconductors viz. Nb 0.45Ta 0.45Mo 0.10, Nb 0.30Ta 0.40Mo 0.30, Nb 0.40Ta 0.30Mo 0.30, Nb 0.30Ta 0.30Mo 0.40 and Nb 0.15Ta 0.15Mo 0.70 have been reported for the first time using Ashcroft’s empty core (EMC) model potential. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. The TC obtained from Hartree (H) local field correction function are found an excellent agreement with available theoretical data. Quadratic TC equation has been proposed, which provide successfully the TC values of ternary amorphous alloys under consideration. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the superconductors.

  2. Superconductors Enable Lower Cost MRI Systems

    NASA Technical Reports Server (NTRS)

    2013-01-01

    The future looks bright, light, and green, especially where aircraft are concerned. The division of NASA s Fundamental Aeronautics Program called the Subsonic Fixed Wing Project is aiming to reach new heights by 2025-2035, improving the efficiency and environmental impact of air travel by developing new capabilities for cleaner, quieter, and more fuel efficient aircraft. One of the many ways NASA plans to reach its aviation goals is by combining new aircraft configurations with an advanced turboelectric distributed propulsion (TeDP) system. Jeff Trudell, an engineer at Glenn Research Center, says, "The TeDP system consists of gas turbines generating electricity to power a large number of distributed motor-driven fans embedded into the airframe." The combined effect increases the effective bypass ratio and reduces drag to meet future goals. "While room temperature components may help reduce emissions and noise in a TeDP system, cryogenic superconducting electric motors and generators are essential to reduce fuel burn," says Trudell. Superconductors provide significantly higher current densities and smaller and lighter designs than room temperature equivalents. Superconductors are also able to conduct direct current without resistance (loss of energy) below a critical temperature and applied field. Unfortunately, alternating current (AC) losses represent the major part of the heat load and depend on the frequency of the current and applied field. A refrigeration system is necessary to remove the losses and its weight increases with decreasing temperature. In 2001, a material called magnesium diboride (MgB2) was discovered to be superconducting. The challenge, however, has been learning to manufacture MgB2 inexpensively and in long lengths to wind into large coils while meeting the application requirements.

  3. Universality in Transport Processes of Unconventional Superconductors

    NASA Astrophysics Data System (ADS)

    Sauls, J. A.

    1997-03-01

    I will review recent work on the theory of charge and energy transport in unconventional superconductors, with applications to d-wave models for the cuprates and the heavy fermion superconductors.(M.J. Graf, S.-K. Yip, D. Rainer and J.A. Sauls, Phys. Rev. B,53), 15147 (1996). Comparisons with recent experiments will be presented.(L. Taillefer, this conference.) I will discuss the key features of the pairing symmetry, Fermi surface and excitation spectrum that are reflected in the electrical, thermal and acoustic response functions at very low temperatures, where transport is limited by electron scattering from random defects. Certain eigenvalues of the thermal conductivity and acoustic attenuation tensors are shown to be universal at low temperature, kB T<< γ, where γ is the bandwidth of impurity-induced bound states in the superconducting phase. The components of the electrical and thermal conductivity also obey a Wiedemann-Franz law with the Lorenz ratio, L(T)=κ/σ T, given by the Sommerfeld value of L_S=(π^2/3)(k_B/e)^2 for k_BT<<γ. For intermediate temperatures the Lorenz ratio deviates significantly from L_S, and is strongly dependent on the scattering cross section, and qualitatively different for resonant vs. nonresonant scattering. Nonuniversal results for the acoustic response, arising from nonvanishing impurity scattering vertex corrections, are shown to be direct tests of spontaneously broken time-reversal symmetry by the pairing state.(M.J. Graf, et al., this conference.)

  4. Proximity Effect at Graphene - High Tc Superconductor Junctions

    NASA Astrophysics Data System (ADS)

    Wang, Da; Shih, En-Min; Arefe, Ghidewon; Kim, Youngduck; Edelberg, Drew; Andrade, Erick; Wang, Dennis; Hone, James; Dean, Cory; Pasupathy, Abhay; Department of Physics, Columbia University, New York, NY 10027, USA Collaboration

    The proximity effect is a well-known mesoscopic phenomenon where Cooper pairs from a superconductor (S) enter into a normal metal (N) that is well coupled to it. Since graphene was discovered a decade ago, the proximity effect at superconductor-graphene junctions has been extensively studied and interesting phenomena such as specular Andreev reflection and ballistic transport at graphene Josephson junctions have been observed. However, superconductors used in these experiments to date are of conventional low Tc, such as aluminum(Tc=1.2K), NbSe2(Tc=7K), and MoRe(Tc=8K). Understanding how the proximity effect works between high-Tc superconductors (pnictides and cuprates) and the Dirac Fermions of graphene remains largely unexplored. The chief technical challenge here is to create high-quality junctions between high-Tc superconductors and graphene. In this work, we will introduce a home-made setup that allows us to exfoliate, transfer and encapsulate superconductor-graphene junctions in a well controlled inert atmosphere. Transport measurements of the proximity effect at graphene-iron pnictide(FeSe, FeTeSe) and graphene-cuprate(BSCCO) junctions will be described.

  5. EDITORIAL: Focus on Iron-Based Superconductors FOCUS ON IRON-BASED SUPERCONDUCTORS

    NASA Astrophysics Data System (ADS)

    Hosono, Hideo; Ren, Zhi-An

    2009-02-01

    Superconductivity is the most dramatic and clear cut phenomenon in condensed matter physics. Realization of room temperature superconductors, which would lead to the revolution of our society, is an ultimate goal for researchers. The discovery of high Tc cuprate superconductors in 1986 by Bednorz and Müller triggered intensive research worldwide and the maximum critical temperature has been raised above 100 K. Scientific research on this break-through material clarified a new route to high Tc materials, carrier doping to a Mott insulator with anti-ferromagnetic ordering. High superconductivity occurs in the neighborhood of Mott-insulators and Fermi-metals. Such a view, which was completely new, now stands as a guiding principle for exploring new high Tc materials. Many theoretical approaches to the mechanism for cuprate superconductors have been carried out to understand this unexpected material and to predict new high Tc materials. In 2006 a new superconductor based on iron, LaFeOP, was discovered by a group at Tokyo Institute of Technology, Japan. Iron, as a ferromagnet, was believed to be the last element for the realization of superconductivity because of the way ferromagnetism competes against Cooper pair formation. Unexpectedly, however, the critical temperature remained at 4-6 K irrespective of hole/electron-doping. A large increase in the Tc to 26 K was then found in LaFe[O1-xFx]As by the same group (and was published on 23 February 2008, in the Journal of the American Chemical Society). The Tc of this material was further raised to 43 K under a pressure of 2 GPa and scientists in China then achieved a Tc of 56 K at ambient pressure by replacing La with other rare earth ions with smaller radius—a critical temperature that is second only to the high Tc cuprates. This fast progress has revitalized research within superconductivity and in 2008 there were more than seven international symposia specifically on Fe(Ni)-based superconductors. Through the rapid

  6. Hydrogen bonding system in euchroite, Cu2(AsO4)(OH)(H2O)3: low-temperature crystal-structure refinement and solid-state density functional theory modeling

    NASA Astrophysics Data System (ADS)

    Krivovichev, Sergey V.; Zolotarev, Andrey A.; Pekov, Igor V.

    2016-06-01

    Hydrogen bonding in euchroite has been studied by means of low-temperature single-crystal X-ray diffraction (XRD) and solid-state density functional theory (DFT) calculations. The mineral is orthorhombic, P212121, a = 10.0350(8), b = 10.4794(8), c = 6.1075(5) Å, V = 642.27(9) Å3, and Z = 4. The structure has been refined to R 1 = 0.036 for 2436 unique observed reflections with |F o| ≥ 4σ F . DFT calculations were performed with the CRYSTAL14 software package. The basic features of the crystal structure of euchroite are the same as described by previous authors. There are two symmetrically-independent Cu sites octahedrally coordinated by O atoms. The CuO6 octahedra are strongly distorted containing four short (1.927-2.012 Å) and two long (2.360-2.797 Å) bonds each, in agreement with the expected Jahn-Teller distortion of an octahedrally-coordinated Cu2+ cation. There is one symmetrically-independent As site that is tetrahedrally coordinated by four O atoms to form an arsenate oxyanion, AsO4 3-. The structure is based upon chains of edge-sharing CuO6 octahedra running parallel to [001]. The chains are linked by AsO4 tetrahedra into a three-dimensional framework, which is stabilized by hydrogen bonds formed from OH and H2O groups. The coordinates of H atoms determined by single-crystal X-ray diffraction and those calculated using DFT are very similar. The distance Δ between experimental and theoretical H positions does not exceed 0.250 Å, except for the H72 site, for which Δ = 0.609 Å. The hydrogen bonding scheme in euchroite is rather complex and involves a combination of relatively strong two-center hydrogen bonds as well as few three-center (bifurcated) hydrogen bonds. The largest difference between the XRD and DFT results involves the H72 atom of the H2O7 molecule and can be assigned to the effect of temperature, which favors a strong linear hydrogen bond at 0 K (calculated) and a bifurcated three-center bond at 100 K (measured). The Cu-H2O

  7. Engineered flux-pinning centers in BSCCO TBCCO and YBCO superconductors

    DOEpatents

    Goretta, Kenneth C.; Lanagan, Michael T.; Miller, Dean J.; Sengupta, Suvankar; Parker, John C.; Hu, Jieguang; Balachandran, Uthamalingam; Siegel, Richard W.; Shi, Donglu

    1999-01-01

    A method of preparing a high temperature superconductor. A method of preparing a superconductor includes providing a powdered high temperature superconductor and a nanophase material. These components are combined to form a solid compacted mass with the material disposed in the polycrystalline high temperature superconductor. This combined mixture is rapidly heated, forming a dispersion of nanophase size particles without a eutectic reaction. These nanophase particles can have a flat plate or columnar type morphology.

  8. Engineered flux-pinning centers in BSCCO TBCCO and YBCO superconductors

    DOEpatents

    Goretta, K.C.; Lanagan, M.T.; Miller, D.J.; Sengupta, S.; Parker, J.C.; Hu, J.; Balachandran, U.; Siegel, R.W.; Shi, D.

    1999-07-27

    A method of preparing a high temperature superconductor is disclosed. A method of preparing a superconductor includes providing a powdered high temperature superconductor and a nanophase material. These components are combined to form a solid compacted mass with the material disposed in the polycrystalline high temperature superconductor. This combined mixture is rapidly heated, forming a dispersion of nanophase size particles without a eutectic reaction. These nanophase particles can have a flat plate or columnar type morphology. 4 figs.

  9. Rigid levitation, flux pinning, thermal depinning and fluctuation in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Brandt, E. H.

    1991-01-01

    Here, the author shows that the strong velocity-independent frictional force on a levitating superconductor and on any type-II superconductor moving in a homogeneous magnetic field is caused by pinning and depinning of the magnetic flux lines in its interior. Levitation may thus be used to investigate the pinning properties of a superconductor, and friction in a superconductor bearing may be minimized by choosing appropriate materials and geometries.

  10. Vortex Dynamics Studies in Type II Superconductors

    NASA Astrophysics Data System (ADS)

    Xu, Zhigang

    1993-03-01

    Vibrating reed, ac susceptibility and resistance measurements have been used to study the dynamics of vortices in type II superconductors. In Nb measurements, in spite of the low T _{c}'s and long coherence lengths compared to the high T_{c} superconductors, we find an extended region of temperature and field over which reversible flux line motion occurs when the Nb reed is oriented with its long dimension perpendicular to the applied field. We observe a strong, frequency-independent depression of the "irreversibility temperature" T _{Q}(H) below the resistively determined critical temperature T_{R}. The results of the ac susceptibility measurements also support these results. We concluded that observation of an extended region of magnetic reversibility is not restricted to high T_{c} or extremely anisotropic materials, and depends upon the geometry of samples with respect to the applied field direction. In NbSe_2 measurements, vibrating reed measurements were performed with the hexagonal c-axis approximately parallel or perpendicular to an applied magnetic field. Field-cooling data revealed an unusual peak in the frequency shift of the reed, accompanied by two peaks in reed dissipation. The upper peak occurs near the temperature where R~ 0, and the lower peak is very sample and amplitude dependent and hysteretic. The ac susceptibility results also show that corresponding features. The interplay of superconductivity and density waves were investigated by comparing data for NbSe _2 with the results for NbS_2 , which has a comparable superconducting T _{c } and crystal structure. In NbS_2 measurements, we did not see such a peak in the frequency shift nor the double peak feature in the dissipation in either vibrating reed measurements or ac susceptibility measurements. We have also studied the (Ba,K)BiO_3 system. It is cubic at its superconducting composition, but exhibits a moderately high T_{c }=30 K that is intermediate between conventional and high T_{rm c

  11. Materials and Physics in Pnictide Superconductors

    NASA Astrophysics Data System (ADS)

    Wen, Hai-Hu

    2009-03-01

    Superconductivity in the pnictides has shown itself to be very interesting and attractive. Some experimental results have revealed that the superconducting mechanism could be unconventional. In this talk I will survey our recent progress of both material synthesizing and physical properties of this rich family. We have made several major contributions to the synthesizing of new pnictide superconductors. (1) Fabrication of the hole doped RE1-xSrxFeAsO samples (RE=La and Pr); (2) Fabrication of a series of new parent compounds DvFeAsF (Dv=divalent metals: Sr, Ca, Eu etc.) and many new superconductors with Tc beyond 50 K by doping electrons into the system; (3) Invention of the new material (Sr3Sc2O5)Fe2As2 with rather large spacing distance between the FeAs planes. We have successfully grown the NdFeAsO1-xFx and Ba1-xKxFe2As2 single crystals. It is found that the anomalous electron scattering in the normal state cannot be simply attributed to the multiband effect. The influence given by the magnetic correlation may play an important role. Specific heat, lower critical field and point contact tunneling all indicate the unconventional superconductivity and multigap features, while the paring symmetry of the superconducting gap may be a non-trivial issue. In the 1111 phase, the superfluid density is rather low and contains probably a nodal feature. While in the 122 phase, both the superfluid density and the quasiparticle density of states is about 5-10 times higher than that in the 1111 phase. An s-wave component was found in the 122 phase. I will also report the measurements on anisotropy, critical current density, critical fields and vortex phase diagram. Small anisotropy, high upper critical field and fish-tail effect (in 122) were observed. All these suggest very good potential applications. In collaboration with Gang Mu, Zhaosheng Wang, Huiqian Luo, Huan Yang, Xiyu Zhu, Ying Jia, Yonglei Wang, Fei Han, Bing Zeng, Bing Shen, Cong Ren, Lei Shan.

  12. Electronic and magnetic properties of a new 2D diluted magnetic semiconductor La1 - x Ba x Zn1 - x Mn x AsO from Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Bannikov, V. V.; Ivanovskii, A. L.

    2013-12-01

    Very recently, on the example of hole- and spin-doped semiconductor LaZnAsO, quite an unexpected area of potential applications of quasi-two-dimensional 1111-like phases was proposed (C. Ding et al., Phys. Rev. B 88, 041102R (2013)) as a promising platform for searching for new diluted magnetic semiconductors (DMSs). In this work, by means of the ab initio calculations, we have examined in detail the electronic and magnetic properties of LaZnAsO alloyed with Ba and Mn. Our results demonstrate that Ba or Mn doping transforms the parent non-magnetic semiconductor LaZnAsO into a non-magnetic metal or a magnetic semiconductor, respectively. On the other hand, the joint effect of these dopants (i.e., co-doping Ba + Mn) leads to transition of La0.89Ba0.11Zn0.89Mn0.11AsO into the state of magnetic metal, which is formed by alternately stacked semiconducting non-magnetic blocks [La0.89Ba0.11O] and metallic-like magnetic blocks [Zn0.89Mn0.11As].

  13. Method and apparatus for dissipating remanent fields and preserving diamagnetism of ceramic superconductors

    SciTech Connect

    Youngdahl, C.A.

    1991-12-31

    A method for dissipating a remanent field, created when a magnetic field is brought into contact with a superconductor, comprising the steps of (1) providing a ceramic superconductor; (2) continuously or intermittently applying an AC current to the ceramic superconductor; (3) gradually removing the AC current until the undesired remanent field is dissipated.

  14. Anomalous scaling of the penetration depth in nodal superconductors

    NASA Astrophysics Data System (ADS)

    She, Jian-Huang; Lawler, Michael J.; Kim, Eun-Ah

    2015-07-01

    Recent findings of anomalous superlinear scaling of low-temperature (T ) penetration depth (PD) in several nodal superconductors near putative quantum critical points suggest that the low-temperature PD can be a useful probe of quantum critical fluctuations in a superconductor. On the other hand, cuprates, which are poster child nodal superconductors, have not shown any such anomalous scaling of PD, despite growing evidence of quantum critical points (QCP). Then it is natural to ask when and how can quantum critical fluctuations cause anomalous scaling of PD? Carrying out the renormalization group calculation for the problem of two-dimensional superconductors with point nodes, we show that quantum critical fluctuations associated with a point group symmetry reduction result in nonuniversal logarithmic corrections to the T dependence of the PD. The resulting apparent power law depends on the bare velocity anisotropy ratio. We then compare our results to data sets from two distinct nodal superconductors: YBa2Cu3O6.95 and CeCoIn5. Considering all symmetry-lowering possibilities of the point group of interest, C4 v, we find our results to be remarkably consistent with YBa2Cu3O6.95 being near a vertical nematic QCP and CeCoIn5 being near a diagonal nematic QCP. Our results motivate a search for diagonal nematic fluctuations in CeCoIn5.

  15. Coherent Two Photon Production in Superconductor-Semiconductor Heterostructures

    NASA Astrophysics Data System (ADS)

    Baireuther, Paul; Vekhter, Ilya; Schmalian, Jörg

    2012-02-01

    Connecting a thin (direct band gap) p-n junction to a superconductor allows Cooper pairs to tunnel into the junction. This leads to an enhancement of the luminescence at the junction via Cooper pair based radiative recombination[1,2], an effect that has recently been observed experimentally[3]. Due to the proximity-induced Cooper pairs in the junction, anomalous photon production related to coherent two photon processes becomes allowed. Using a simple model for direct band gap luminescence we study a superconductor-p-n-superconductor heterostructure where the two photon state depends on the relative phase between the two superconductors. We investigate to what extend the production rate of entangled photons is controlled by the phase difference between the attached superconductors. [1] E. Hanamura, Phys. Stat. Sol. (b) 234, 166 (2002). [2] Y. Asano, I. Suemune, H. Takayanagi, and E. Hanamura, Phys. Rev. Lett. 103, 187001 (2009). [3] I. Suemune, T. Akazaki, K. Tanaka, M. Jo, K. Uesugi, M. Endo1, H. Kumano, E. Hanamura, H. Takayanagi, M. Yamanishi and H. Kan, Jpn. Journ. of Appl. Phys. 45, 9264 (2006).

  16. Potentials of iron-based superconductors for practical future materials

    NASA Astrophysics Data System (ADS)

    Shimoyama, Jun-ichi

    2014-04-01

    Since the discovery of high-Tc superconductivity in the REFeAs(O, F) system in 2008, studies on the development of superconducting materials using iron-based superconductors has been undertaken because of their high Hc2 and relatively high Tc. Although the cuprate superconductors exhibit much higher Tc and similar high Hc2, the small degree of electromagnetic anisotropy between the c-axis and ab-plane directions confirmed in 11, 122 and 1111 systems encouraged us to develop more versatile conductors. Single crystals and thin films deposited on single-crystalline and metal substrates have proved that the potentials of the iron-based superconductors are high enough for designing superconducting materials for high field generation. In addition, critical current properties of powder-in-tube processed tapes have been greatly improved in the past two years and are reaching the application level at 4.2 K in high magnetic field. However, the pinning mechanism and determining factors of the critical current properties of the iron-based superconductors have not been well understood. Characteristics and potentials of iron-based superconductors are discussed from various viewpoints in this paper in an effort to understand the current status and future prospects.

  17. Superconductor digital electronics: Scalability and energy efficiency issues (Review Article)

    NASA Astrophysics Data System (ADS)

    Tolpygo, Sergey K.

    2016-05-01

    Superconductor digital electronics using Josephson junctions as ultrafast switches and magnetic-flux encoding of information was proposed over 30 years ago as a sub-terahertz clock frequency alternative to semiconductor electronics based on complementary metal-oxide-semiconductor (CMOS) transistors. Recently, interest in developing superconductor electronics has been renewed due to a search for energy saving solutions in applications related to high-performance computing. The current state of superconductor electronics and fabrication processes are reviewed in order to evaluate whether this electronics is scalable to a very large scale integration (VLSI) required to achieve computation complexities comparable to CMOS processors. A fully planarized process at MIT Lincoln Laboratory, perhaps the most advanced process developed so far for superconductor electronics, is used as an example. The process has nine superconducting layers: eight Nb wiring layers with the minimum feature size of 350 nm, and a thin superconducting layer for making compact high-kinetic-inductance bias inductors. All circuit layers are fully planarized using chemical mechanical planarization (CMP) of SiO2 interlayer dielectric. The physical limitations imposed on the circuit density by Josephson junctions, circuit inductors, shunt and bias resistors, etc., are discussed. Energy dissipation in superconducting circuits is also reviewed in order to estimate whether this technology, which requires cryogenic refrigeration, can be energy efficient. Fabrication process development required for increasing the density of superconductor digital circuits by a factor of ten and achieving densities above 107 Josephson junctions per cm2 is described.

  18. Production of superconductor/carbon bicomponent fibers

    NASA Technical Reports Server (NTRS)

    Wise, S. A.; Fain, C. C.; Leigh, H. D.

    1991-01-01

    Certain materials are unable to be drawn or spun into fiber form due to their improper melting characteristics or brittleness. However, fibrous samples of such materials are often necessary for the fabrication of intricate shapes and composites. In response to this problem, a unique process, referred to as the piggyback process, was developed to prepare fibrous samples of a variety of nonspinnable ceramics. In this technique, specially produced C shaped carbon fibers serve as micromolds to hold the desired materials prior to sintering. Depending on the sintering atmosphere used, bicomponent or single component fibers result. While much has been shown worldwide concerning the YBa2Cu3O(7-x) superconductor, fabrication into unique forms has proven quite difficult. However, a variety of intricate shapes are necessary for rapid commercialization of the superconducting materials. The potential for producing fibrous samples of the YBa2Cu3O(7-x) compound by the piggyback process is being studied. Various organic and acrylic materials were studied to determine suspending ability, reactivity with the YBa2Cu3O(7-x) compound during long term storage, and burn out characteristics. While many questions were answered with respect to the interfacial reactions between YBa2Cu3O(7-x) and carbon, much work is still necessary to improve the quality of the sintered material if the fibers produced are to be incorporated into useful composite or cables.

  19. Twin Boundaries in d-wave Superconductors

    NASA Astrophysics Data System (ADS)

    Feder, D. L.; Beardsall, A. J.; Berlinsky, A. J.; Kallin, C.

    1997-03-01

    Twin boundaries in orthorhombic d-wave superconductors are investigated numerically within the Bogoliubov-De Gennes formalism. When the d-wave order parameter is strongly perturbed by the twin boundary, we find that the induced s-wave component may break time-reversal symmetry at low temperatures. This gives rise to local supercurrents in the direction parallel to the twin boundary. The characteristics of the low-lying quasiparticle states are investigated, with particular emphasis on the role of Andreev reflections and the possible existence of bound states. The results are compared with recent c-axis tunneling,(A.G. Sun, A. Truscott, A.S. Katz, R.C. Dynes, B.W. Veal, and C. Gu, Phys. Rev. B54), 6734 (1996). SQUID,(K.A. Moler, J.R. Kirtley, R. Liang, D. Bonn, and W. Hardy, unpublished.) and transport(C. Villard, G. Koren, D. Cohen, E. Polturak, B. Thrane, and D. Chateignier, Phys. Rev. Lett. 77), 3913 (1996) measurements.

  20. Phase diagram of the lattice superconductor

    SciTech Connect

    Shenoy, S.R.; Gupte, N.

    1988-08-01

    In a mean-field approximation the phase transition of a lattice superconductor is understood in terms of an orientation of its topological excitations (vortex loops and magnetic field loops). The loops are obtained through a duality transformation of the original variables. The phase boundary T/sub c/(e/sup 2/,b/sup -1/) is found as a function of the charge e and a Ginzburg-Landau quartic term coefficient b. Second-order behavior is found for a region b>b/sub c/(e/sup 2/) and a tricritical point with first-order behavior appears for bT/sub c/(e/sup 2/, b/sup -1/) is also found, consistent with the early continuum results of Halperin, Lubensky, and Ma (HLM). T/sub HLM/(e/sup 2/,b/sup -1/) is associated with ordering within a superconducting grain, while T/sub c/(e/sup 2/,b/sup -1/) involves phase locking between grains.

  1. Topology of crystalline insulators and superconductors

    NASA Astrophysics Data System (ADS)

    Shiozaki, Ken; Sato, Masatoshi

    2014-10-01

    We complete a classification of topological phases and their topological defects in crystalline insulators and superconductors. We consider topological phases and defects described by noninteracting Bloch and Bogoliubov-de Gennes Hamiltonians that support additional order-two spatial symmetry, besides any of 10 classes of symmetries defined by time-reversal symmetry and particle-hole symmetry. The additional order-two spatial symmetry we consider is general and it includes Z2 global symmetry, mirror reflection, twofold rotation, inversion, and their magnetic point group symmetries. We find that the topological periodic table shows a periodicity in the number of flipped coordinates under the order-two spatial symmetry, in addition to the Bott periodicity in the space dimensions. Various symmetry-protected topological phases and gapless modes will be identified and discussed in a unified framework. We also present topological classification of symmetry-protected Fermi points. The bulk classification and the surface Fermi point classification provide a realization of the bulk-boundary correspondence in terms of the K theory.

  2. Optical spectra of high temperature superconductors

    SciTech Connect

    Ruvalds, J.

    1996-12-31

    The concept of free electrons which yields the Drude description of the conductivity works surprisingly well in conventional metals. By contrast, the infrared reflectivity of the cuprate superconductors deviates dramatically from Drude behavior and thus challenges theory to explain the origin of the anomalous electron damping and the related mass divergence which has implications for the existence of a Fermi surface. The controversial key issue of the carrier concentration in cuprates needs to be resolved by a conserving analysis of the puzzling conductivity. Raman spectra of cuprates also exhibit unconventional electronic contributions over a wide frequency range up to 1 eV, and recent data provide evidence for the symmetry of the superconducting energy gap. A microscopic theory for both the optical conductivity and the Raman anomalies in cuprates derives a linear frequency variation of the damping from electron-electron collisions on a nested Fermi surface that refers to nearly parallel segments of an electron trajectory. Thus the nesting theory links the cuprate anomalies to phenomena in chromium and rare earth metals. Nesting also yields a novel mechanism for d-wave superconductivity that requires a Coulomb repulsion of intermediate strength and key nesting features that distinguish high {Tc} cuprates from other materials. 41 refs., 7 figs.

  3. Studies of anisotropy of iron based superconductors

    SciTech Connect

    Murphy, Jason A.

    2013-01-01

    To study the electronic anisotropy in iron based superconductors, the temperature dependent London penetration depth, Δλ(T), have been measured in several compounds, along with the angular dependent upper critical field, Hc2(T). Study was undertaken on single crystals of Ba(Fe1-xCox)2As2 with x=0.108 and x=0.127, in the overdoped range of the doping phase diagram, characterized by notable modulation of the superconducting gap. Heavy ion irradiation with matching field doses of 6 T and 6.5 T respectively, were used to create columnar defects and to study their effect on the temperature Δλ(T). The variation of the low-temperature penetration depth in both pristine and irradiated samples was fitted with a power-law function Δλ(T) = ATn. Irradiation increases the magnitude of the pre-factor A and decreases the exponent n, similar to the effect on the optimally doped samples. This finding supports the universal s ± scenario for the whole doping range.

  4. Topological transitions in multi-band superconductors

    SciTech Connect

    Continentino, Mucio A.; Deus, Fernanda; Padilha, Igor T.; Caldas, Heron

    2014-09-15

    The search for Majorana fermions has been concentrated in topological insulators or superconductors. In general, the existence of these modes requires the presence of spin–orbit interactions and of an external magnetic field. The former implies in having systems with broken inversion symmetry, while the latter breaks time reversal invariance. In a recent paper, we have shown that a two-band metal with an attractive inter-band interaction has non-trivial superconducting properties, if the k-dependent hybridization is anti-symmetric in the wave-vector. This is the case, if the crystalline potential mixes states with different parities as for orbitals with angular momentum l and l+1. In this paper we take into account the effect of an external magnetic field, not considered in the previous investigation, in a two-band metal and show how it modifies the topological properties of its superconducting state. We also discuss the conditions for the appearance of Majorana fermions in this system.

  5. Josephson current between topological and conventional superconductors

    NASA Astrophysics Data System (ADS)

    Ioselevich, P. A.; Ostrovsky, P. M.; Feigel'man, M. V.

    2016-03-01

    We study the stationary Josephson current in a junction between a topological and an ordinary (topologically trivial) superconductor. Such an S-TS junction hosts a Majorana zero mode that significantly influences the current-phase relation. The presence of the Majorana state is intimately related with the breaking of the time-reversal symmetry in the system. We derive a general expression for the supercurrent for a class of short topological junctions in terms of the normal-state scattering matrix. The result is strongly asymmetric with respect to the superconducting gaps in the ordinary (Δ0) and topological (Δtop) leads. We apply the general result to a simple model of a nanowire setup with strong spin-orbit coupling in an external magnetic field and proximity-induced superconductivity. The system shows parametrically strong suppression of the critical current Ic∝Δtop/RN2 in the tunneling limit (RN is the normal-state resistance). This is in strong contrast with the Ambegaokar-Baratoff relation applicable to junctions with preserved time-reversal symmetry. We also consider the case of a generic junction with a random scattering matrix and obtain a more conventional scaling law Ic∝Δtop/RN .

  6. Epitaxy of semiconductor-superconductor nanowires.

    PubMed

    Krogstrup, P; Ziino, N L B; Chang, W; Albrecht, S M; Madsen, M H; Johnson, E; Nygård, J; Marcus, C M; Jespersen, T S

    2015-04-01

    Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are discussed. We formulate the grain growth kinetics of the metal phase in general terms of continuum parameters and bicrystal symmetries. The method realizes the ultimate limit of uniform interfaces and seems to solve the soft-gap problem in superconducting hybrid structures. PMID:25581626

  7. Mm-wave components - SIS (superconductor-insulator-superconductor) mixers. Final report, November 1986-December 1988

    SciTech Connect

    Whiteley, S.R.

    1989-04-26

    Superconductor-Insulator-Superconductor (SIS) tunnel-junction mixers are known to provide ultra-high sensitivity receiver applications above 30 GHz. In this two year (Phase II) program, HYPRES, in collaboration with the National Radio Astronomy Observatory, have developed novel fully integrated SIS mixer circuits, and demonstrated a unique high efficiency cooling system. The integrated SIS mixer chip contains, aside from the actual mixer elements, passive tuning components, an IF filter, a coplanar transmission line, and a waveguide coupler, necessary components heretofore realized off-chip. Fabrication of the integrated mixer required development of a nine-level process and optimization of the process dependent electrical parameters of the SIS devices. The device performs efficiently in the range of 75-115 GHz. A novel dewar-based cooler, which makes use of the extremely low thermal conductivity of the fused silica chip substrate to achieve an incremental thermal load of 25 mW, was fabricated and demonstrated. Such a cryostat allows relatively long-term unattended operation of SIS, or other, cryogenic devices.

  8. EDITORIAL: Focus on Iron-Based Superconductors FOCUS ON IRON-BASED SUPERCONDUCTORS

    NASA Astrophysics Data System (ADS)

    Hosono, Hideo; Ren, Zhi-An

    2009-02-01

    Superconductivity is the most dramatic and clear cut phenomenon in condensed matter physics. Realization of room temperature superconductors, which would lead to the revolution of our society, is an ultimate goal for researchers. The discovery of high Tc cuprate superconductors in 1986 by Bednorz and Müller triggered intensive research worldwide and the maximum critical temperature has been raised above 100 K. Scientific research on this break-through material clarified a new route to high Tc materials, carrier doping to a Mott insulator with anti-ferromagnetic ordering. High superconductivity occurs in the neighborhood of Mott-insulators and Fermi-metals. Such a view, which was completely new, now stands as a guiding principle for exploring new high Tc materials. Many theoretical approaches to the mechanism for cuprate superconductors have been carried out to understand this unexpected material and to predict new high Tc materials. In 2006 a new superconductor based on iron, LaFeOP, was discovered by a group at Tokyo Institute of Technology, Japan. Iron, as a ferromagnet, was believed to be the last element for the realization of superconductivity because of the way ferromagnetism competes against Cooper pair formation. Unexpectedly, however, the critical temperature remained at 4-6 K irrespective of hole/electron-doping. A large increase in the Tc to 26 K was then found in LaFe[O1-xFx]As by the same group (and was published on 23 February 2008, in the Journal of the American Chemical Society). The Tc of this material was further raised to 43 K under a pressure of 2 GPa and scientists in China then achieved a Tc of 56 K at ambient pressure by replacing La with other rare earth ions with smaller radius—a critical temperature that is second only to the high Tc cuprates. This fast progress has revitalized research within superconductivity and in 2008 there were more than seven international symposia specifically on Fe(Ni)-based superconductors. Through the rapid

  9. Dynamical conductivity across the superconductor-insulator transition

    NASA Astrophysics Data System (ADS)

    Swanson, Mason; Loh, Yen Lee; Randeria, Mohit; Trivedi, Nandini

    2013-03-01

    Thin superconducting films can exhibit a quantum phase transition from a superconductor to an insulator with increasing disorder. While the exact mechanism of the transition is not completely understood, there is strong evidence that it is bosonic in nature in some models and materials, with disorder acting to localize the superconducting pairs. Previous studies of bosonic models of the superconductor-insulator transition (SIT) have focused almost entirely on criticality and dc properties at the transition. We go beyond these studies by calculating the dynamical conductivity of a disordered (2 +1)D XY model using quantum Monte Carlo simulations that capture the phase fluctuations driving the SIT. Our results obey standard sum rule constraints for the longitudinal and transverse current correlation functions and show a build-up of integrated spectral weight near the transition. We will discuss the low frequency spectral weight in terms of a possible intermediate bose-metal phase between the superconductor and insulator.

  10. Flux-line tilt moduli in anisotropic superconductors

    SciTech Connect

    Sudbo, A.; Brandt, E.H. )

    1991-04-01

    A general expression for the elastic energy of the flux-line lattice (FLL) in anisotropic superconductors is given. From this we derive three tilt moduli {ital c}{sub 44}({bold k}) for the FLL in uniaxial superconductors with induction {ital B}{parallel} and {perpendicular} to the basal plane. The discreteness of the FLL leads to a logarithmically dispersive isolated-vortex term, which at {ital B}{much lt}{ital B}{sub {ital c}2} in a large part of the Brillouin-zone area exceeds the usual Lorentzian-dispersive {ital c}{sub 44}({bold k}) originating from the overlapping vortex fields. The difference between vortex self-energy, line tension, and tilt modulus in an anisotropic superconductor is discussed.

  11. Recent advantages in processing and fabrication of ceramic superconductors

    NASA Astrophysics Data System (ADS)

    Balachandran, U.; Poeppel, R. B.; Ferrando, W. A.; Karmarkar, S. D.; Kerr, J.; Hess, P. W.; Divecha, A. P.

    1991-08-01

    The properties of ceramic superconductors are greatly influenced by the temperature, heating rate, pressure, and gas atmosphere used during processing and fabrication. For example, transport critical current density decreases drastically in the presence of trace amounts of CO2 in the sintering atmosphere. The grain boundaries of samples sintered in O2 atmospheres containing various levels of CO2 have been thoroughly characterized by high-resolution electron microscopy. Reduced total pressure during binder removal and sintering was found to prevent decomposition of the superconductor. We have developed a low-oxygen-pressure technique for calcining precursors and sintering long lengths of wires and coils. Other advances include the improvement of critical current density and levitation force through melt-growth processing, incorporating of insulating coatings, and powder-in-tube processing of superconductors.

  12. Pseudogap in a thin film of a conventional superconductor.

    SciTech Connect

    Sacepe, B.; Chapelier, C.; Baturina, T. I.; Vinokur, V. M.; Baklanov, M. R.; Sanquer, M.

    2010-12-01

    A superconducting state is characterized by the gap in the electronic density of states, which vanishes at the superconducting transition temperature T{sub c}. It was discovered that in high-temperature superconductors, a noticeable depression in the density of states, the pseudogap, still remains even at temperatures above T{sub c}. Here, we show that a pseudogap exists in a conventional superconductor, ultrathin titanium nitride films, over a wide range of temperatures above T{sub c}. Our study reveals that this pseudogap state is induced by superconducting fluctuations and favoured by two-dimensionality and by the proximity to the transition to the insulating state. A general character of the observed phenomenon provides a powerful tool to discriminate between fluctuations as the origin of the pseudogap state and other contributions in the layered high-temperature superconductor compounds.

  13. 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.

  14. Upper critical field of the noncentrosymmetric superconductor BiPd

    NASA Astrophysics Data System (ADS)

    Peets, Darren C.; Maldonado, Ana; Enayat, Mostafa; Sun, Zhixiang; Wahl, Peter; Schnyder, Andreas P.

    2016-05-01

    The superconducting parameters and upper critical field of the noncentrosymmetric superconductor BiPd have proven contentious. This material is of particular interest because it is a rare example of a 4 f -electron-free noncentrosymmetric superconductor of which crystals may be grown and cleaved, enabling surface-sensitive spectroscopies. Here, using bulk probes augmented by tunneling data on defects, we establish that the lower of the previously reported upper critical fields corresponds to the bulk transition. The material behaves as a nearly weak-coupled BCS s -wave superconductor, and we report its superconducting parameters as drawn from the bulk upper critical field. Possible reasons behind the order-of-magnitude discrepancy in the reported upper critical fields are discussed.

  15. Unified Picture for Magnetic Correlations in Iron-Based Superconductors

    SciTech Connect

    Yin, W.G.; Lee, E.-C.; Ku, W.

    2010-09-02

    The varying metallic antiferromagnetic correlations observed in iron-based superconductors are unified in a model consisting of both itinerant electrons and localized spins. The decisive factor is found to be the sensitive competition between the superexchange antiferromagnetism and the orbital-degenerate double-exchange ferromagnetism. Our results reveal the crucial role of Hund's rule coupling for the strongly correlated nature of the system and suggest that the iron-based superconductors are closer kin to manganites than cuprates in terms of their diverse magnetism and incoherent normal-state electron transport. This unified picture would be instrumental for exploring other exotic properties and the mechanism of superconductivity in this new class of superconductors.

  16. 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. PMID:27482621

  17. Mean-field description of topological charge 4e superconductors

    NASA Astrophysics Data System (ADS)

    Gabriele, Victoria; Luo, Jing; Teo, Jeffrey C. Y.

    BCS superconductors can be understood by a mean-field approximation of two-body interacting Hamiltonians, whose ground states break charge conservation spontaneously by allowing non-vanishing expectation values of charge 2e Cooper pairs. Topological superconductors, such as one-dimensional p-wave wires, have non-trivial ground states that support robust gapless boundary excitations. We construct a four-body Hamiltonian in one dimension and perform a mean-field analysis. The mean-field Hamiltonian is now quartic in fermions but is still exactly solvable. The ground state exhibits 4-fermion expectation values instead of Cooper pair ones. There also exists a topological phase, where the charge 4e superconductor carries exotic zero energy boundary excitations.

  18. Does the electric power grid need a room temperature superconductor?

    NASA Astrophysics Data System (ADS)

    Malozemoff, A. P.

    2013-11-01

    Superconductivity can revolutionize electric power grids, for example with high power underground cables to open urban power bottlenecks and fault current limiters to solve growing fault currents problems. Technology based on high temperature superconductor (HTS) wire is beginning to meet these critical needs. Wire performance is continually improving. For example, American Superconductor has recently demonstrated long wires with up to 500 A/cm-width at 77 K, almost doubling its previous production performance. But refrigeration, even at 77 K, is a complication, driving interest in discovering room temperature superconductors (RTS). Unfortunately, short coherence lengths and accelerated flux creep will make RTS applications unlikely. Existing HTS technology, in fact, offers a good compromise of relatively high operating temperature but not so high as to incur coherence-length and flux-creep limitations. So - no, power grids do not need RTS; existing HTS wire is proving to be what grids really need.

  19. Fluxoid motion and resistive transition in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, T.; Ni, B.

    1990-07-01

    Significantly broad resistive transition has been observed in high-Tc superconductors under a magnetic field. A similar broad transition was observed by French et al. (1967) in resistance versus magnetic field characteristics in low-temperature superconductors for various current densities. In this case, the critical current density and the flow resistivity completely determine the overall resistive characteristics. This suggests that the resistive characteristics in high-Tc superconductors may also be determined by these two quantities alone. In fact, the procedure outlined reproduces the commonly observed resistive characteristics. A notable feature determined from this procedure is that a knee exists in the resistance versus temperature curve. This projection corresponds to the irreversibility point; i.e. the temperature at which the critical current density is reduced to zero.

  20. Lateral restoring force on a magnet levitated above a superconductor

    NASA Astrophysics Data System (ADS)

    Davis, L. C.

    1990-03-01

    The lateral restoring force on a magnet levitated above a superconductor is calculated as a function of displacement from its original position at rest using Bean's critical-state model to describe flux pinning. The force is linear for small displacements and saturates at large displacements. In the absence of edge effects the force always attracts the magnet to its original position. Thus it is a restoring force that contributes to the stability of the levitated magnet. In the case of a thick superconductor slab, the origin of the force is a magnetic dipole layer consisting of positive and negative supercurrents induced on the trailing side of the magnet. The qualitative behavior is consistent with experiments reported to date. Effects due to the finite thickness of the superconductor slab and the granular nature of high-Tc materials are also considered.

  1. Supercurrent in a p-wave holographic superconductor

    SciTech Connect

    Zeng Huabi; Sun Weimin; Zong Hongshi

    2011-02-15

    The p-wave and p+ip-wave holographic superconductors with fixed DC supercurrent are studied by introducing a nonvanishing vector potential. We find that close to the critical temperature T{sub c} of zero current, the numerical results of both the p-wave model and the p+ip model are the same as those of Ginzburg-Landau (GL) theory; for example, the critical current is j{sub c}{approx}(T{sub c}-T){sup 3/2} and the phase transition in the presence of a DC current is a first-order transition. Beside the similar results between both models, the p+ip superconductor shows isotropic behavior for the supercurrent, while the p-wave superconductor shows anisotropic behavior for the supercurrent.

  2. Neutron and Synchrotron X-Ray Scattering Studies of Superconductors

    SciTech Connect

    Tranquada,J.M.

    2008-09-01

    Superconductors hold the promise for a more stable and efficient electrical grid, but new isotropic, high-temperature superconductors are needed in order to reduce cable manufacturing costs. The effort to understand high-temperature superconductivity, especially in the layered cuprates, provides guidance to the search for new superconductors. Neutron scattering has long provided an important probe of the collective excitations that are involved in the pairing mechanism. For the cuprates, neutron and x-ray diffraction techniques also provide information on competing types of order, such as charge and spin stripes, that appear to be closely connected to the superconductivity. Recently, inelastic x-ray scattering has become competitive for studying phonons and may soon provide valuable information on electronic excitations. Examples of how these techniques contribute to our understanding of superconductivity are presented.

  3. Topological Blount's theorem of odd-parity superconductors

    NASA Astrophysics Data System (ADS)

    Kobayshi, Shingo; Shiozaki, Ken; Sato, Masatoshi; Tanaka, Yukio

    2014-03-01

    Nontrivial nodal structures are one of the most salient features of gap functions of the unconventional superconductors. In a system with spin-orbit coupling and crystal field, the group theory plays a key role to determine the node of the gap function. From the group theoretical ground, Blount proved that the line node is ``vanishingly improbable'' in spin-triplet superconductors. Namely, it is impossible to create a stable line node in odd-parity superconductors. Our motivation is to compare the group theoretical result with topological stability of nodes by K-theory As a result, we found that K-theory not only rebuilds the original Blount's argument but also exhibits counterexamples with the stable line node. In this talk, we will show the physical interpretation of them.

  4. ARPES of K-doped iron selenide superconductor

    NASA Astrophysics Data System (ADS)

    Yokoya, Takayoshi; Sunagawa, Masanori; Terashima, Kensei; Hamada, Takahiro; Fujiwara, Hirokazu; Tanaka, Masashi; Takeya, Hiroyuki; Takano, Yoshihiko; Arita, Masashi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki; Suzuki, Katsuhiro; Usui, Hidetomo; Kuroki, Kazuhiko; Wakita, Takanori; Muraoka, Yuji

    2015-03-01

    In iron pnictide superconductors, the characteristic Fermi surface(FS) topology, namely nesting of hole-like FS at the zone center and electron-like FS at the zone corner, is considered to induce spin/orbital fluctuation leading to high-Tc superconductivity. In K-doped iron selenide superconductors, however, ARPES studies reported absence of hole-like FS at the zone center, which is different from that observed in iron pnictides. So far, proposed models for the superconductivity based on the FS topology appear to fail to explain available experimental results. In this talk, we present our recent ARPES studies on a K-doped iron selenide superconductor performed with careful tuning of experimental conditions, which show a hole-like FS around the zone center.

  5. Lateral restoring force on a magnet levitated above a superconductor

    NASA Technical Reports Server (NTRS)

    Davis, L. C.

    1990-01-01

    The lateral restoring force on a magnet levitated above a superconductor is calculated as a function of displacement from its original position at rest using Bean's critical-state model to describe flux pinning. The force is linear for small displacements and saturates at large displacements. In the absence of edge effects the force always attracts the magnet to its original position. Thus it is a restoring force that contributes to the stability of the levitated magnet. In the case of a thick superconductor slab, the origin of the force is a magnetic dipole layer consisting of positive and negative supercurrents induced on the trailing side of the magnet. The qualitative behavior is consistent with experiments reported to date. Effects due to the finite thickness of the superconductor slab and the granular nature of high-Tc materials are also considered.

  6. The Born-Mayer-Huggins potential in high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Singh, Hempal; Singh, Anu; Indu, B. D.

    2016-07-01

    The Born-Mayer-Huggins potential which has been found the best suitable potential to study the YBa2Cu3O7‑δ type high temperature superconductors is revisited in a new framework. A deeper insight in it reveals that the Born-Mayer parameters for different interactions in high temperature superconductor are not simple quantities but several thermodynamic and spatial functions enter the problem. Based on the new theory, the expressions for pressure, bulk modulus and Born-Mayer parameters have been derived and it is established that these quantities depend upon Gruneisen parameter which is the measure of the strength of anharmonic effects in high temperature superconductors. This theory has been applied to a specific model YBa2Cu3O7‑δ crystal for the purpose of numerical estimates to justify the new results.

  7. Josephson supercurrent in a graphene-superconductor junction

    NASA Astrophysics Data System (ADS)

    Sarvestani, E.; Jafari, S. A.

    2012-01-01

    Within the tunneling Hamiltonian formulation for the eight-component spinors, the Josephson critical supercurrent has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intravalley and intervalley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical supercurrent are completely separable. Therefore, it is possible to consider the effect of the intervalley tunnelings in the critical supercurrent. The incorporation of these type of processes into the tunneling Hamiltonian exposes a special feature of the graphene Josephson junctions. The effect of intervalley tunneling appears in the length dependence plot of critical current in the form of oscillations. We also present the results for temperature dependence of critical supercurrent and compare with experimental results and other theoretical calculations.

  8. Electron teleportation via Majorana bound states in a mesoscopic superconductor.

    PubMed

    Fu, Liang

    2010-02-01

    Zero-energy Majorana bound states in superconductors have been proposed to be potential building blocks of a topological quantum computer, because quantum information can be encoded nonlocally in the fermion occupation of a pair of spatially separated Majorana bound states. However, despite intensive efforts, nonlocal signatures of Majorana bound states have not been found in charge transport. In this work, we predict a striking nonlocal phase-coherent electron transfer process by virtue of tunneling in and out of a pair of Majorana bound states. This teleportation phenomenon only exists in a mesoscopic superconductor because of an all-important but previously overlooked charging energy. We propose an experimental setup to detect this phenomenon in a superconductor-quantum-spin-Hall-insulator-magnetic-insulator hybrid system. PMID:20366777

  9. Time-resolved study of Higgs mode in superconductors

    NASA Astrophysics Data System (ADS)

    Shimano, Ryo

    The behavior of superconductors far from equilibrium has been intensively studied over decades. Goals of these studies are the elucidation of bosonic fluctuations essential for the pairing mechanisms, the manifestation of competing orders or hidden phases, and the optical manipulation of superconductivity. The study of collective modes is crucially important for these perspectives as it provides the information on the dynamics of order parameters in non-equilibirium states. Generally, collective modes in ordered phases associated with spontaneous symmetry breaking are classified into 1) gapless phase modes and 2) gapped amplitude modes. In superconductors, the phase mode is eaten by gauge field, according to the Anderson-Higgs mechanism. The remaining amplitude mode is recently termed as Higgs mode from its analogy to the Higgs boson in particle physics. Despite its long history of investigation, unambiguous observation of Higgs mode has remained elusive. This is because the Higgs mode does not have a charge nor electric dipole and therefore it does not couple directly to the electromagnetic field. Here we report on our recent observation of Higgs mode in s-wave superconductors by using THz-pump and THz-probe spectroscopy technique. After nonadiabatic excitation near the superconducting gap energy with monocycle THz pulses, Higgs mode was observed as oscillations in the transmission of THz probe pulse. The resonant nonlinear coupling between the Higgs mode and coherent radiation field was also discovered, resulting in an efficient third order harmonic generation of the incident THz radiation. The extension of experiments to multiband superconductors and unconventional superconductors will be discussed. Time-resolved study of Higgs mode in superconductors.

  10. The search for superconductors through solid state chemistry

    NASA Astrophysics Data System (ADS)

    Schoop, Leslie Mareike

    Despite intensive research in the field of superconductivity, there exists no "recipe" for finding new materials that superconduct. Although the most fundamental type of superconductivity is understood, we do not understand all the condition in which the phenomenon occurs. Therefore finding routes for discovering new superconductors is of high interest. This thesis discusses a systematic search for new superconductors. This is done by comparing known superconductors and finding common similarities. Chapter 1 explains the most famous families of superconductors and explain common features appearing in most superconducting materials. Two different routes for searching for new superconductors are discussed. Chapter 2 focuses on crystal structure families that are commonly adopted by superconducting materials. In particular the XYZ family, a family of intermetallic phases with 1:1:1 stoichiometry will be investigated. Chapter 2 discusses the discovery of a new XYZ compound, HfCuGe2, the investigation of superconducting NaAlSi under pressure, and the discovery of a new high pressure phase of CaAuBi. The structural chemistry of XYZ phases is also discussed along with its relation to ionic and metallic radii. Chapter 3 focuses on the idea that superconductivity often appears close to a structural, magnetic, or electronic instability. In this Chapter I predict superconductivity in Tl halide Perovskites, with the help of density functional theory. This is done by drawing an analogy to BaBiO3based superconductors. Furthermore the discovery of a new Hollandite phase, Rb0.17IrO 2 is reported. Lastly, the magnetic instabilities and the newly discovered quantum phase transition in Fe doped Cr2B is presented.

  11. New Fe-based superconductors: properties relevant for applications

    SciTech Connect

    Putti, M; Pallecchi, I; Bellingeri, E; Cimberle, M R; Tropeano, M; Ferdeghini, C; Palenzona, A; Tarantini, C; Yamamoto, A.; Jiang, J; Jaroszynski, J; Kametani, F; Abraimov, D; Polyanskii, A. A.; Weiss, J. D.; Hellstrom, E. E.; Gurevich, A.; Larbalestier, D. C.; Jin, Rongying; Sales, Brian C; Safa-Sefat, Athena; McGuire, Michael A; Mandrus, David; Cheng, P.; Jia, Y.; Wen, H. H.; Lee, S; Eom, C. B.

    2009-01-01

    Less than two years after the discovery of high temperature superconductivity in oxypnictide LaFeAs(O, F) several families of superconductors based on Fe layers (1111, 122, 11, 111) are available. They share several characteristics with cuprate superconductors that compromise easy applications, such as the layered structure, the small coherence length and unconventional pairing. On the other hand, the Fe-based superconductors have metallic parent compounds and their electronic anisotropy is generally smaller and does not strongly depend on the level of doping, and the supposed order parameter symmetry is s-wave, thus in principle not so detrimental to current transmission across grain boundaries. From the application point of view, the main efforts are still devoted to investigate the superconducting properties, to distinguish intrinsic from extrinsic behaviors and to compare the different families in order to identify which one is the fittest for the quest for better and more practical superconductors. The 1111 family shows the highest T{sub c}, huge but also the most anisotropic upper critical field and in-field, fan-shaped resistive transitions reminiscent of those of cuprates. On the other hand, the 122 family is much less anisotropic with sharper resistive transitions as in low temperature superconductors, but with about half the T{sub c} of the 1111 compounds. An overview of the main superconducting properties relevant to applications will be presented. Upper critical field, electronic anisotropy parameter, and intragranular and intergranular critical current density will be discussed and compared, where possible, across the Fe-based superconductor families.

  12. Electric field effect in superconductor-ferroelectric structures

    NASA Technical Reports Server (NTRS)

    Lemanov, V. V.

    1995-01-01

    Electric field effect (the E-effect) in superconductors has been studied since 1960 when Glover and Sherill published their results on a shift of the critical temperature T(sub c) about 0.1 mK in Sn and In thin films under the action Off the field E=300 kV/cm. Stadler was the first to study the effect or spontaneous polarization of ferroelectric substrate on the electric properties of superconductors. He observed that the reversal of polarization of TGS substrate under action of external electric field in Sn-TGS structures induced the T(sub c) shift in Sn about 1.3 mK. Since in this case the effect is determined not by the electric field but by the spontaneous polarization, we may call this effect the P-effect. High-T(sub c) superconductors opened the new possibilities to study the E- and P-effects due to low charge carrier density, as compared to conventional superconductors, and to anomalously small coherence length. Experiments in this field began in many laboratories but a breakthrough was made where a shift in T(sub c) by 50 mK was observed in YBCO thin films. Much higher effects were observed in subsequent studies. The first experiments on the P-effect in high-T(sub c) superconductors were reported elsewhere. In this report we shall give a short description of study on the P-effect in high-T(sub c) superconductors.

  13. Electromechanical properties of superconductors for DOE/OFE applications. Final report

    SciTech Connect

    Ekin, J.W.; Bray, S.L.

    1998-09-01

    In many superconductor applications, especially large magnets, the superconductor is required to perform while under the influence of strong mechanical forces. These forces are commonly due to residual fabrication stress, differential thermal contraction of dissimilar materials, and electromagnetic forces generated within an energized magnet coil. Thorough knowledge of a superconductor`s electrical performance under the influence of these forces (electromechanical properties) is required for successful magnet engineering. This report presents results of research conducted during the period from august 1993 through March 1997 on the electromechanical properties of superconductors for DOE/OFE fusion applications.

  14. Aluminum-stabilized Nb[sub 3]Sn superconductor

    DOEpatents

    Scanlan, R.M.

    1988-05-10

    Disclosed are 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. 4 figs.

  15. Three dimensional reflectance properties of superconductor-dielectric photonic crystal

    NASA Astrophysics Data System (ADS)

    Pandey, G. N.; Pandey, J. P.; Pandey, U. K.; Sancheti, Bhagyashree; Ojha, S. P.

    2016-05-01

    In this present communication, we have studied the optical properties of Photonics Crystals with super conducting constituent using the TMM method for a stratified medium. We also studied the three dimensional reflectance property of superconductor-dielectric photonic crystal at different temperature and thickness. From above study we show that the superconductor-dielectric photonic crystal may be used as broad band reflector and omnidirectional reflector at low temperature below to the critical temperature. Such property may be applied to make of the reflector which can be used in low temperature region.

  16. Magnetic response of holographic Lifshitz superconductors: Vortex and Droplet solutions

    NASA Astrophysics Data System (ADS)

    Lala, Arindam

    2014-07-01

    In this paper a holographic model of s-wave superconductor with anisotropic Lifshitz scaling has been considered. In the presence of an external magnetic field our holographic model exhibits both vortex and droplet solutions. Based on analytic methods we have shown that the anisotropy has no effect on the vortex and droplet solutions whereas it may affect the condensation. Our vortex solution closely resembles the Ginzburg-Landau theory and a relation between the upper critical magnetic field and superconducting coherence length has been speculated from this comparison. Using Sturm-Liouville method, the effect of anisotropy on the critical parameters in insulator/superconductor phase transitions has been analyzed.

  17. Tail states in clean superconductors with magnetic impurities.

    SciTech Connect

    Vekhter, I.; Shytov, A. V.; Gruzberg, I. A.; Balatsky, A. V.

    2002-01-01

    We analyse the behavior of the density of states in a singlet s-wave superconductor with weak magnetic impurities in the clean limit. By using the method of optimal fluctuation and treating the order parameter self-consistently we show that the density of states is finite everywhere in the superconducting gap, and that it varies as in N(E) {proportional_to} -|E-{Delta}{sub 0}|{sup (7-d)/4} the mean field gap edge {Delta}{sub 0} in a d-dimensional superconductor. In contrast to most studied cases the optimal fluctuation is strongly anisotropic.

  18. Space-time formulation for finite element modeling of superconductors

    SciTech Connect

    Ashworth, Stephen P; Grilli, Francesco; Sirois, Frederic; Laforest, Marc

    2008-01-01

    In this paper we present a new model for computing the current density and field distributions in superconductors by means of a periodic space-time formulation for finite elements (FE). By considering a space dimension as time, we can use a static model to solve a time dependent problem. This allows overcoming one of the major problems of FE modeling of superconductors: the length of simulations, even for relatively simple cases. We present our first results and compare them to those obtained with a 'standard' time-dependent method and with analytical solutions.

  19. Normal state incoherent pseudogap in FeSe superconductor

    NASA Astrophysics Data System (ADS)

    Craco, Luis; Laad, Mukul S.

    2016-05-01

    The normal state of Iron chalcogenide superconductors show a range of unconventional features. Bad-metallic resistivity and proximity to insulating state manifest themselves in spectral and transport responses. In particular, obervation of low-energy pseudogap feature in the normal state raises the issue of the nature of processes underpinning its emergence as well as its relation to unconventional superconductivity. Here, using the LDA+DMFT method, we show how correlation-induced orbital-selective pseudogap-like physics underpin these incoherent features in stoichimetric and electron-doped FeSe superconductor. We discuss the pseudogap regime microscopically, along with implications for the superconductive instability.

  20. Thermomagnetic effects above and below {Tc} in the cuprate superconductors

    SciTech Connect

    Clayhold, J.A.; Xue, Y.Y.; Chu, C.W.; Eckstein, J.N.; Bozovic, I.

    1996-12-31

    Two different thermomagnetic transport quantities, the electrothermal conductivity and the Nernst effect are shown to be powerful probes of high-temperature superconductors. In the vortex state below {Tc}, the electrothermal conductivity is independent of both the magnetic field and the vortex viscosity because it is sensitive only to the properties of the vortex normal cores. Some new data from cuprate superconductors show a surprising, low-field anomaly in the dilute vortex limit. Above {Tc} in the normal state, it is shown how the Nernst effect is a probe of transport anisotropy around the Fermi surface.

  1. Aluminum-stabilized Nb/sub 3/Sn superconductor

    DOEpatents

    Scanlan, R.M.

    1984-02-10

    This patent discloses 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.

  2. Critical field measurements in superconductors using ac inductive techniques

    NASA Astrophysics Data System (ADS)

    Campbell, S. A.; Ketterson, J. B.; Crabtree, G. W.

    1983-09-01

    The ac in-phase and out-of-phase response of type II superconductors is discussed in terms of dc magnetization curves. Hysteresis in the dc magnetization is shown to lead to a dependence of the ac response on the rate at which an external field is swept. This effect allows both Hc1 and Hc2 to be measured by ac techniques. A relatively simple mutual inductance bridge for making such measurements is described in the text, and factors affecting bridge sensitivity are discussed in the Appendix. Data for the magnetic superconductor ErRh4B4 obtained using this bridge are reported.

  3. Interaction of ultrasound with vortices in type-II superconductors

    SciTech Connect

    Sonin, E.B.

    1996-04-01

    The theory of ultrasound in the mixed state of type-II superconductors is suggested which takes into account the Magnus force on vortices, the anti-Magnus force on ions, and diamagnetism of the mixed state. The acoustic Faraday effect (rotation of polarization of the transverse ultrasonic wave propagating along vortices) is linear in the Magnus force in any regime of the flux flow for wavelengths now used in the ultrasound experiments. Therefore, in contrast to previous predictions, the Faraday effect should be looked for only in clean superconductors with a strong Magnus force. {copyright} {ital 1996 The American Physical Society.}

  4. Method of making V.sub.3 Ga superconductors

    DOEpatents

    Dew-Hughes, David

    1980-01-01

    An improved method for producing a vanadium-gallium superconductor wire having aluminum as a component thereof is disclosed, said wire being encased in a gallium bearing copper sheath. The superconductors disclosed herein may be fabricated under normal atmospheres and room temperatures by forming a tubular shaped billet having a core composed of an alloy of vanadium and aluminum and an outer sheath composed of an alloy of copper, gallium and aluminum. Thereafter the entire billet is swage reduced to form a wire therefrom and heat treated to form a layer of V.sub.3 Ga in the interior of the wire.

  5. Chemistry and Electronic Structure of Iron-Based Superconductors

    SciTech Connect

    Safa-Sefat, Athena; Singh, David J

    2011-01-01

    The solid state provides a richly varied fabric for intertwining chemical bonding, electronic structure, and magnetism. The discovery of superconductivity in iron pnictides and chalcogenides has revealed new aspects of this interplay, especially involving magnetism and superconductivity. Moreover, it has challenged prior thinking about high-temperature superconductivity by providing a set of materials that differ in many crucial aspects from the previously known cuprate superconductors. Here we review some of what is known about the superconductivity and its interplay with magnetism, chemistry, and electronic structure in Fe-based superconductors.

  6. Vortex in holographic two-band superfluid/superconductor

    NASA Astrophysics Data System (ADS)

    Wu, Mu-Sheng; Wu, Shang-Yu; Zhang, Hai-Qing

    2016-05-01

    We construct numerically static vortex solutions in a holographic model of two-band superconductor with an interband Josephson coupling in both the superfluid and superconductor regime. We investigate the effects of the interband coupling on the order parameter of each superconducting band in the vortex solution, and we find that it is different for each of the two bands. We compute also the free energy, critical magnetic field, magnetic penetration length and coherence lengths for the two bands, and we study their dependence on the interband coupling and temperature. Interestingly, we find that the coherence lengths of the two bands are close to identical.

  7. Energy-gap spectroscopy of superconductors using a tunneling microscope

    NASA Technical Reports Server (NTRS)

    Le Duc, H. G.; Kaiser, W. J.; Stern, J. A.

    1987-01-01

    A unique scanning tunneling microscope (STM) system has been developed for spectroscopy of the superconducting energy gap. High-resolution control of tunnel current and voltage allows for measurement of superconducting properties at tunnel resistance levels 100-1000 greater than that achieved in prior work. The previously used STM methods for superconductor spectroscopy are compared to those developed for the work reported here. Superconducting energy-gap spectra are reported for three superconductors, Pb, PbBi, and NbN, over a range of tunnel resistance. The measured spectra are compared directly to theory.

  8. Superconductor-insulator transition in the presence of Coulomb disorder

    NASA Astrophysics Data System (ADS)

    Shklovskii, B. I.

    2007-12-01

    Superconductor-insulator transition driven by the decreasing concentration of electrons n is studied in the case of the disorder potential created by randomly positioned charged impurities. Electrons and Cooper pairs (formed by a non-Coulomb attraction) nonlinearly screen the random potential of impurities. Both electrons and Cooper pairs can be delocalized or localized in the resulting self-consistent potential. The border separating the superconductor and insulator phases in the plane of the concentration of electrons and the length of the Cooper pair is found. For a strong disorder, the central segment of this border follows the Bose-Einstein-Condensation-BCS crossover line defined for a clean sample.

  9. Phase coherence and pairing amplitude in photo-excited superconductors

    NASA Astrophysics Data System (ADS)

    Perfetti, Luca; Piovera, Christian; Zhang, Zailan

    2016-05-01

    New data on Bi2Sr2CaCu2O8+δ (Bi2212) reveal interesting aspects of photoexcited superconductors. The electrons dynamics show that inelastic scattering by nodal quasiparticles decreases when the temperature is lowered below the critical value of the superconducting phase transition. This drop of electronic dissipation is astonishingly robust and survives to photoexcitation densities much larger than the value sustained by long-range superconductivity. The unconventional behavior of quasiparticle scattering is ascribed to superconducting correlations extending on a length scale comparable to the inelastic mean-free path. Our measurements indicate that strongly driven superconductors enter in a regime without phase coherence but finite pairing amplitude.

  10. Coherent Excited States in Superconductors due to a Microwave Field.

    PubMed

    Semenov, A V; Devyatov, I A; de Visser, P J; Klapwijk, T M

    2016-07-22

    We describe theoretically the depairing effect of a microwave field on diffusive s-wave superconductors. The ground state of the superconductor is altered qualitatively in analogy to the depairing due to a dc current. In contrast to dc depairing, the density of states acquires, for microwaves with frequency ω_{0}, steps at multiples of the photon energy Δ±nℏω_{0} and shows an exponential-like tail in the subgap regime. We show that this ac depairing explains the measured frequency shift of a superconducting resonator with microwave power at low temperatures. PMID:27494495

  11. High-T/sub c/ superconductor and its use in superconducting magnets

    SciTech Connect

    Green, M.A.

    1988-02-01

    Many of the proposed uses for the high-T/sub c/ superconductor involve the creation of a magnetic field using superconducting coils. This report will assess what is known about the high-T/sub c/ superconductors and take a realistic look at their potential use in various kinds of superconducting magnets. Based on what is known about the high-T/sub c/ superconductors, one can make a ''wish list'' of things that will make such materials useful for magnets. Then, the following question is asked. If one had a high-T/sub c/ superconductor with the same properties as modern niobium-titanium superconductor, how would the superconductor work in a magnet environment. Finally, this report will show the potential impact of the ideal high-T/sub c/ superconductor on: 1) accelerator dipole and quadrupole magnets, 2) superconducting magnets for use in space, and 3) superconducting solenoids for magnetic resonance imaging. 78 refs., 11 tabs.

  12. Production of superconductor/carbon bicomponent fibers

    NASA Technical Reports Server (NTRS)

    Wise, S. A.; Fain, C. C.; Leigh, H. D.; Sherrill, M.

    1990-01-01

    Certain materials are unable to be drawn or spun into fiber form due to their improper melting characteristics or brittleness. However, fibrous samples of such materials are often necessary for the fabrication of intricate shapes and composites. In response to this problem, a unique process, referred to as the piggyback process, was developed to prepare fibrous samples of a variety of nonspinnable ceramics. In this technique, specially produced C-shaped carbon fibers serve as micromolds to hold the desired materials prior to sintering. Depending on the sintering atmosphere used, bicomponent or single component fibers result. While much has been demonstrated worldwide concerning the YBa2Cu3O(7-x) superconductor, fabrication into unique forms has proven quite difficult. However, a variety of intricate shapes are necessary for rapid commercialization of the superconducting materials. The potential for producing fibrous samples of the YBa2Cu3O(7-x) compound by the piggyback process is being investigated. Various organic and acrylic materials were investigated to determine suspending ability, reactivity with the YBa2Cu3O(7-x) compound during long term storage, and burn out characteristics. While many questions were answered with respect to the interfacial reactions between YBa2Cu3O(7-x) and carbon, much work is still necessary to improve the quality of the sintered material if the fibers produced are to be incorporated into useful composites or cables. Additional research is necessary to evaluate quality of the barrier layer during long soakings at the peak temperature; adjust the firing schedule to avoid microcracking and improve densification; and increase the solids loading in the superconductive suspension to decrease porosity.

  13. Effect of the characteristics of a superconductor on the levitation properties of the magnet-superconductor system

    SciTech Connect

    Rudnev, I. A. Ermolaev, Yu. S.

    2007-07-15

    The results of the experimental and theoretical investigations of the magnetic levitation force appearing at the interaction of the multilayer superconducting block of the YBa{sub 2}Cu{sub 3}O{sub 7-x} melted textured ceramic and a permanent magnet are presented. The maximum repulsive force and maximum attractive force are determined as functions of the thickness of the superconducting block in the superconductor cooling regime in both zero and nonzero magnetic fields. The dependence of the levitation force on the geometric parameters and critical current of the superconductor is found.

  14. Superconducting proximity effect in superconductor / semiconducting-carbon-nanotube / superconductor junctions.

    NASA Astrophysics Data System (ADS)

    Barbara, Paola

    2005-03-01

    We measure the proximity effect in devices made of two superconducting electrodes bridged by a 3-micrometer long semiconducting carbon nanotube. The electrodes are made of a Pd/Nb bilayer and the junctions are fabricated by using standard photolithography [1]. The superconducting proximity effect manifests itself with a peak in the low-bias differential conductance due to Andreev reflection at the superconductor/carbon nanotube interfaces. Application of a gate voltage allows the transparency of the junction to be tuned from high (Andreev reflection) to low (tunneling) [2]. We have studied the temperature dependence of the features in each regime. This work is supported by the NSF (DMR-0239721) and by the Research Corporation. [1] A. Tselev, K. Hatton, M. S. Fuhrer, M. Paranjape and P. Barbara, Nanotechnology 15, 1475 (2004). [2] A. F. Morpurgo, J. Kong, C. M. Marcus, and H. Dai, Science 286, 263 (1999).

  15. Method of producing Pb-stabilized superconductor precursors and method of producing superconductor articles therefrom

    DOEpatents

    Kroeger, D.M.; Hsu, H.S.; Brynestad, J.

    1995-03-07

    Metal oxide superconductor powder precursors are prepared in an aerosol pyrolysis process. A solution of the metal cations is introduced into a furnace at 600--1,000 C for 0.1 to 60 seconds. The process produces micron to submicron size powders without the usual loss of the lead stabilizer. The resulting powders have a narrow particle size distribution, a small grain size, and are readily converted to a superconducting composition upon subsequent heat treatment. The precursors are placed in a metal body deformed to form a wire or tape and heated to form a superconducting article. The fine powders permit a substantial reduction in heat treatment time, thus enabling a continuous processing of the powders into superconducting wire, tape or multifilamentary articles by the powder-in-tube process. 3 figs.

  16. Method of producing Pb-stabilized superconductor precursors and method of producing superconductor articles therefrom

    DOEpatents

    Kroeger, Donald M.; Hsu, Huey S.; Brynestad, Jorulf

    1995-01-01

    Metal oxide superconductor powder precursors are prepared in an aerosol pyrolysis process. A solution of the metal cations is introduced into a furnace at 600.degree.-1000.degree. C. for 0.1 to 60 seconds. The process produces micron to submicron size powders without the usual loss of the lead stabilizer. The resulting powders have a narrow particle size distribution, a small grain size, and are readily converted to a superconducting composition upon subsequent heat treatment. The precursors are placed in a metal body deformed to form a wire or tape and heated to form a superconducting article. The fine powders permit a substantial reduction in heat treatment time, thus enabling a continuous processing of the powders into superconducting wire, tape or multifilamentary articles by the powder-in-tube process.

  17. Measuring Thermal Diffusivity Of A High-Tc Superconductor

    NASA Technical Reports Server (NTRS)

    Powers, Charles E.; Oh, Gloria; Leidecker, Henning

    1992-01-01

    Technique for measuring thermal diffusivity of superconductor of high critical temperature based on Angstrom's temperature-wave method. Peltier junction generates temperature oscillations, which propagate with attenuation up specimen. Thermal diffusivity of specimen calculated from distance between thermocouples and amplitudes and phases of oscillatory components of thermocouple readings.

  18. Global critical temperature in disordered superconductors with weak multifractality

    NASA Astrophysics Data System (ADS)

    Mayoh, James; García-García, Antonio M.

    2015-11-01

    There is growing evidence that a key feature of sufficiently disordered superconductors is the spatial inhomogeneity of the order parameter. However, not much is known analytically about the impact of the inhomogeneity on the global critical temperature that signals the onset of resistance in the superconductor. Here we address this problem in the experimentally relevant case of disordered conventional superconductors characterized by weak multifractality such as quasi-two-dimensional thin films. We compute analytically the superconducting energy gap, the temperature at which it vanishes, and the energy dependence and spatial distribution of the order parameter. The latter is found to be log normal. The global critical temperature, computed by percolation techniques, is much smaller than the temperature at which the energy gap vanishes. We show that disorder might enhance superconductivity but only for very weakly coupled superconductors, such as Al, and for relatively weak phase fluctuations. These results are consistent with experiments where enhancement of the critical temperature is observed in Al thin films but not in more strongly coupled materials.

  19. Antiferromagnetic topological superconductor and electrically controllable Majorana fermions.

    PubMed

    Ezawa, Motohiko

    2015-02-01

    We investigate the realization of a topological superconductor in a generic bucked honeycomb system equipped with four types of mass-generating terms, where the superconductor gap is introduced by attaching the honeycomb system to an s-wave superconductor. Constructing the topological phase diagram, we show that Majorana modes are formed in the phase boundary. In particular, we analyze the honeycomb system with antiferromagnetic order in the presence of perpendicular electric field E(z). It becomes topological for |E(z)|>E(z)(cr) and trivial for |E(z)|superconductor by controlling applied electric field. One Majorana zero-energy bound state appears at the phase boundary. We can arbitrarily control the position of the Majorana fermion by moving the spot of applied electric field, which will be made possible by a scanning tunneling microscope probe. PMID:25699460

  20. The anisotropic properties of high temperature superconductors - an ARPES study

    NASA Astrophysics Data System (ADS)

    Kaminski, Adam; Fretwell, Helen; Mesot, Joel; Rozenkrantz, Stephan; Djendjinovic, Marin; Campuzano, Juan; Randeria, Mohit; Norman, Michael; Sato, Takafumi; Takahashi, Takashi; Kadowaki, Kazuo; Hinks, David; Raffy, Helen

    2001-03-01

    It is now well established that cuprates are d-wave superconductors. Natural question arises concerning the symmetry of other electronic properties in these materials and their relation to anisotropic order parameter. We present our recent ARPES measurements of these properties performed on a the same sample of single cristal BISCO 2212.

  1. Process for the production of superconductor containing filaments

    DOEpatents

    Tuominen, Olli P.; Hoyt, Matthew B.; Mitchell, David F.; Morgan, Carol W.; Roberts, Clyde Gordon; Tyler, Robert A.

    2002-01-01

    Superconductor containing filaments having embedments of superconducting material surrounded by a rayon matrix are formed by preparing a liquid suspension which contains at least 10 weight percent superconducting material; forming a multicomponent filament having a core of the suspension and a viscose sheath which contains cellulose xanthate; and thereafter, regenerating cellulose from the cellulose xanthate to form a rayon matrix.

  2. 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.

  3. Numerical analysis of thermally actuated magnets for magnetization of superconductors

    NASA Astrophysics Data System (ADS)

    Li, Quan; Yan, Yu; Rawlings, Colin; Coombs, Tim

    2010-06-01

    Superconductors, such as YBCO bulks, have extremely high potential magnetic flux densities, comparing to rare earth magnets. Therefore, the magnetization of superconductors has attracted broad attention and contribution from both academic research and industry. In this paper, a novel technique is proposed to magnetize superconductors. Unusually, instead of using high magnetic fields and pulses, repeatedly magnetic waves with strength of as low as rare earth magnets are applied. These magnetic waves, generated by thermally controlling a Gadolinium (Gd) bulk with a rare earth magnet underneath, travel over the flat surface of a YBCO bulk and get trapped little by little. Thus, a very small magnetic field can be used to build up a very large magnetic field. In this paper, the modelling results of thermally actuated magnetic waves are presented showing how to transfer sequentially applied thermal pulses into magnetic waves. The experiment results of the magnetization of YBCO bulk are also presented to demonstrate how superconductors are progressively magnetized by small magnetic field

  4. Laser-ARPES studies of BSCCO-BASED cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Douglas, J. F.; Koralek, J. D.; Sun, Z.; Plumb, N. C.; Wang, Q.; Reber, T. J.; Griffith, J. D.; Aiura, Y.; Oka, K.; Eisaki, H.; Dessau, D. S.; Devereaux, T. P.; Johnson, S. S.

    2007-03-01

    Utilizing 6 eV and 7 eV laser light, we have performed high-resolution ANGLE RESOLVED PHOTOEMISSION studies of the BSCCO family of superconductors. This higher resolution, in both energy and momentum, has allowed the observation of interesting new doping- and temperature-dependent features in the nodal and near nodal dispersions in these materials.

  5. Some aspects of the theory of high temperature superconductors

    SciTech Connect

    Emery, V.J.

    1990-01-01

    A qualitative survey of the theory of high temperature superconductors as strongly correlated electron systems is presented. Various microscopic models and their implications for the theory of the normal state are described. Constraints on the mechanism and many body theory of the superconducting state are discussed.

  6. The formation and analysis of thin film high temperature superconductors

    SciTech Connect

    Nastasi, M.; Muenchausen, R.E.; Arendt, P.N.

    1989-01-01

    Thin films of high temperature superconductors have been fabricated using a variety of physical vapor deposition techniques. Recent results of HTS thin films produced by coevaporation, sputtering and laser deposition will be briefly reviewed. In addition some examples of the utility of high energy ion backscattering for the analysis of film stoichiometry will be given. 34 refs., 6 figs.

  7. The formation and analysis of thin film high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Nastasi, Michael; Muenchausen, Ross E.; Arendt, Paul N.

    Thin films of high temperature superconductors have been fabricated using a variety of physical vapor deposition techniques. Recent results of HTS thin films produced by coevaporation, sputtering and laser deposition will be briefly reviewed. In addition some examples of the utility of high energy ion backscattering for the analysis of film stoichiometry will be given.

  8. Hybrid crystals of cuprates and iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Xia, Dai; Cong-Cong, Le; Xian-Xin, Wu; Jiang-Ping, Hu

    2016-07-01

    We propose two possible new compounds, Ba2CuO2Fe2As2 and K2CuO2Fe2Se2, which hybridize the building blocks of two high temperature superconductors, cuprates and iron-based superconductors. These compounds consist of square CuO2 layers and antifluorite-type Fe2 X 2 (X = As, Se) layers separated by Ba/K. The calculations of binding energies and phonon spectra indicate that they are dynamically stable, which ensures that they may be experimentally synthesized. The Fermi surfaces and electronic structures of the two compounds inherit the characteristics of both cuprates and iron-based superconductors. These compounds can be superconductors with intriguing physical properties to help to determine the pairing mechanisms of high T c superconductivity. Project supported by the National Basic Research Program of China (Grant No. 2015CB921300), the National Natural Science Foundation of China (Grant Nos. 1190020 and 11334012), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB07000000).

  9. Nonlinear response of superconductors to alternating fields and currents

    SciTech Connect

    McDonald, J.

    1997-10-08

    This report discusses the following topics on superconductivity: nonlinearities in hard superconductors such as surface impedance of a type II superconductimg half space and harmonic generation and intermodulation due to alternating transport currents; and nonlinearities in superconducting weak links such as harmonic generation by a long Josephson Junction in a superconducting slab.

  10. Paramagnetic Meissner effect in high-temperature superconductors

    SciTech Connect

    Braunisch, W.; Knauf, N.; Bauer, G.; Kock, A.; Becker, A.; Freitag, B.; Gruetz, A.; Kataev, V.; Neuhausen, S.; Roden, B.; Khomskii, D.; Wohlleben, D. ); Bock, J.; Preisler, E. )

    1993-08-01

    We have studied the low-field Meissner effect of polycrystalline Bi high-temperature superconductors using a special superconducting-quantum-interference-device magnetometer. In certain samples a surprising feature was observed: Instead of the usual diamagnetic moment a paramagnetic moment develops in the field cooling mode below [ital T][sub [ital c

  11. Fermi surfaces and energy gaps of high-temperature superconductors

    SciTech Connect

    Shen, Z.X.; Dessau, D.S.

    1994-12-31

    In this short paper, the authors describe their recent experimental results from high-temperature superconductors. In the normal state, the data reveals interesting features of the Fermi surfaces and low energy excitations near the Fermi level. In the superconducting state, the data shows a very strong anisotropy in the superconducting gap.

  12. Hard gap in a normal layer coupled to a superconductor

    NASA Astrophysics Data System (ADS)

    Reeg, Christopher R.; Maslov, Dmitrii L.

    2016-07-01

    The ability to induce a sizable gap in the excitation spectrum of a normal layer placed in contact with a conventional superconductor has become increasingly important in recent years in the context of engineering a topological superconductor. The quasiclassical theory of the proximity effect shows that Andreev reflection at the superconductor/normal interface induces a nonzero pairing amplitude in the metal but does not endow it with a gap. Conversely, when the normal layer is atomically thin, the tunneling of Cooper pairs induces an excitation gap that can be as large as the bulk gap of the superconductor. We study how these two seemingly different views of the proximity effect evolve into one another as the thickness of the normal layer is changed. We show that a fully quantum-mechanical treatment of the problem predicts that the induced gap is always finite but falls off with the thickness of the normal layer d . If d is less than a certain crossover scale, which is much larger than the Fermi wavelength, the induced gap is comparable to the bulk gap. As a result, a sizable excitation gap can be induced in normal layers that are much thicker than the Fermi wavelength.

  13. Superconductor/Semiconductor Hybrid Analog-to-Digital Converter

    NASA Astrophysics Data System (ADS)

    Furuta, Futoshi; Saitoh, Kazuo; Yoshida, Akira; Suzuki, Hideo

    We have designed a superconductor-semiconductor hybrid analog-to-digital (A/D) converter and experimentally evaluated its performance at sampling frequencies up to 18.6GHz. The A/D converter consists of a superconductor front-end circuit and a semiconductor back-end circuit. The front-end circuit includes a sigma-delta modulator and an interface circuit, which is for transmitting data signal to the semiconductor back-end circuit. The semiconductor back-end circuit performs decimation filtering. The design of the modulator was modified to reduce effects of integrator leak and thermal noise on signal-to-noise ratio (SNR). Using the improved modulator design, we achieved a bit-accuracy close to the ideal value. The hybrid architecture enabled us to reduce the integration scale of the front-end circuit to fewer than 500 junctions. This simplicity makes feasible a circuit based on a high TC superconductor as well as on a low TC superconductor. The experimental results show that the hybrid A/D converter operated perfectly and that SNR was 84.8dB (bit accuracy-13.8bit) at a band width of 9.1MHz. This converter has the highest pertormance of all sigma-delta A/D converters.

  14. Controlling the flux dynamics in superconductors by nanostructured magnetic arrays

    NASA Astrophysics Data System (ADS)

    Kapra, Andrey

    In this thesis we investigate theoretically how the critical current jc of nano-engineered mesoscopic superconducting film can be improved and how one can control the dynamics of the magnetic flux, e.g., the transition from flux-pinned to flux-flow regime, using arrays of magnetic nanostructures. In particularly we investigate: (1) Vortex transport phenomena in superconductors with deposited ferromagnetic structures on top, and the influence of the sample geometry on the critical parameters and on the vortex configurations. Changing geometry of the magnetic bars and magnetization of the bars will affect the critical current jc of the superconducting film. Such nanostructured ferromagnets strongly alter the vortex structure in its neighborhood. The influence of geometry, position and magnetization of the ferromagnet (single bar or regular lattice of the bars) on the critical parameters of the superconductor is investigated. (2) Effect of flux confinement in narrow superconducting channels with zigzag-shaped banks: the flux motion is confined in the transverse (perpendicular) direction of a diamond-cell-shape channel. The matching effect for the magnetic flux is found in the system relevantless of boundary condition. We discuss the dynamics of vortices in the samples and vortex pattern formation in the channel. We show how the inclusion of higher-Tc superconductor into the sample can lead to enhanced properties of the system. By adding an external driving force, we study the vortex dynamics. The different dynamic regimes are discussed. They allowed an effective control of magnetic flux in superconductors.

  15. Flux lattice melting in the high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Bishop, D. J.; Gammel, P. L.; Schneemeyer, L. F.

    1989-01-01

    One of the important issues for technological application of the high temperature superconductors is their behavior in a magnetic field. A variety of experiments including electrical transport, mechanical oscillators, and magnetic decoration have suggested that these magnetic properties will make applications more difficult than originally anticipated. These experiments and their results are briefly discussed.

  16. Research On Bi-Based High-Temperature Superconductors

    NASA Technical Reports Server (NTRS)

    Banks, Curtis; Doane, George B., III; Golben, John

    1993-01-01

    Brief report describes effects of melt sintering on Bi-based high-temperature superconductor system, as well as use of vibrating-sample magnetometer to determine hysteresis curves at 77 K for partially melt-sintered samples. Also discussed is production of high-temperature superconducting thin films by laser ablation: such films potentially useful in detection of signals of very low power.

  17. Designed 3D architectures of high-temperature superconductors.

    PubMed

    Green, David C; Lees, Martin R; Hall, Simon R

    2013-04-14

    Self-supporting superconducting replicas of pasta shapes are reported, yielding products of differing 3D architectures. Functioning high-temperature superconductor wires are developed and refined from replicas of spaghetti, demonstrating a unique sol-gel processing technique for the design and synthesis of novel macroscopic morphologies of complex functional materials. PMID:23388857

  18. Quantum creep in a highly crystalline two-dimensional superconductor

    NASA Astrophysics Data System (ADS)

    Saito, Yu; Kasahara, Yuichi; Ye, Jianting; Iwasa, Yoshihiro; Nojima, Tsutomu

    Conventional studies on quantum phase transitions, especially on superconductor-insulator or superconductor-metal-insulator transitions have been performed in deposited metallic thin films such as Bismuth or MoGe. Although the techniques of thin films deposition have been considerably improved, unintentional disorder such as impurities and deficiencies, generating the pinning centers, seems to still exist in such systems. The mechanical exfoliated highly crystalline two-dimensional material can be a good candidate to realize a less-disordered 2D superconductor with extremely weak pinning, combined with transfer method or ionic-liquid gating. We report on the quantum metal, namely, magnetic-field-induced metallic state observed in an ion-gated two-dimensional superconductor based on an ultra-highly crystalline layered band insulator, ZrNCl. We found that the superconducting state is extremely fragile against external magnetic fields; that is, zero resistance state immediately disappears, once an external magnetic field switches on. This is because the present system is relatively clean and the pinning potential is extremely weak, which cause quantum tunneling and flux flow of vortices, resulting in metallic ground state.

  19. Quasiclassical description of a superconductor with a spin density wave

    NASA Astrophysics Data System (ADS)

    Moor, A.; Volkov, A. F.; Efetov, K. B.

    2011-04-01

    We derive equations for the quasiclassical Green’s functions ǧ within a simple model of a two-band superconductor with a spin density wave (SDW). The elements of the matrix ǧ are the retarded, advanced, and Keldysh functions, each of which is an 8×8 matrix in the Gor’kov-Nambu, the spin, and the band space. In equilibrium, these equations are a generalization of the Eilenberger equation. On the basis of the derived equations, we analyze the Knight shift, the proximity, and the dc Josephson effects in the superconductors under consideration. The Knight shift is shown to depend on the orientation of the external magnetic field with respect to the direction of the vector of the magnetization of the SDW. The proximity effect is analyzed for an interface between a superconductor with the SDW and a normal metal. The function describing both superconducting and magnetic correlations is shown to penetrate the normal metal or a metal with the SDW due to the proximity effect. The dc Josephson current in an SSDW/N/SSDW junction is also calculated as a function of the phase difference φ. It is shown that in our model, the Josephson current does not depend on the mutual orientation of the magnetic moments in the superconductors SSDW and is proportional to sinφ. The dissipationless spin current jsp depends on the angle α between the magnetization vectors in the same way (jsp~sinα) and is not zero above the superconducting transition temperature.

  20. Controlled Manipulation of Individual Vortices in a Superconductor

    SciTech Connect

    Straver, E.W.J.

    2010-04-05

    We report controlled local manipulation of single vortices by low temperature magnetic force microscope (MFM) in a thin film of superconducting Nb. We are able to position the vortices in arbitrary configurations and to measure the distribution of local depinning forces. This technique opens up new possibilities for the characterization and use of vortices in superconductors.