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Sample records for ndfe1-xrhx aso superconductor

  1. Effect of hydrostatic pressure on the superconducting transition temperature and superfluid density of SmFeAsO0.85 and PrFe0.925Co0.075AsO superconductors

    NASA Astrophysics Data System (ADS)

    Dong, X. L.; Lu, W.; Yang, J.; Yi, W.; Li, Z. C.; Zhang, C.; Ren, Z. A.; Che, G. C.; Sun, L. L.; Zhou, F.; Zhou, X. J.; Zhao, Z. X.

    2010-12-01

    We have measured magnetic susceptibility of iron pnictide superconductors SmFeAsO0.85 and PrFe0.925Co0.075AsO under hydrostatic pressure up to 1.15 GPa. The superconducting transition temperature (TC) deceases linearly and the Meissner signal size also decreases with increasing pressure for SmFeAsO0.85 . In contrast, the TC of PrFe0.925Co0.075AsO initially increases with pressure then saturates above ˜0.8GPa . Meanwhile its Meissner signal exhibits the similar pressure dependence. Our results indicate that the pressure dependences of TC and superfluid density in both systems are positively correlated which suggests that these quaternary iron-based superconductors are not conventional BCS ones.

  2. 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

  3. The Lyman-α Solar Telescope (LST) for the ASO-S mission

    NASA Astrophysics Data System (ADS)

    Li, Hui

    The Lyman-α (Lyα) 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 R⊙ (R⊙ = solar radius), a Solar Corona Imager (SCI) with an FOV of 1.1 - 2.5 R⊙, and a full-disk White-light Solar Telescope (WST) with the same FOV as the SDI, which also serves as the guiding telescope. The SCI is designed to work in the Lyα (121.6 nm) waveband and white-light (for polarization brightness observation), while the SDI will work in the Lyα waveband only. The WST works in both visible (for guide) and ultraviolet (for science) broadband. The LST will observe the Sun from disk-center up to 2.5 R⊙ for both solar flares and coronal mass ejections with high tempo-spatial resolution

  4. 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.

  5. Coexistence of magnetic fluctuations and superconductivity in SmFe0.95Co0.05AsO seen in 57Fe Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Long, G.; Demarco, M.; Chudyk, M.; Steiner, J.; Coffey, D.; Zeng, H.; Li, Y. K.; Cao, G. H.; Xu, Z. A.

    2011-08-01

    The Mössbauer spectra (MS) of powder samples of SmFe1-xCoxAsO (x = 0.0, 0.05, and 0.1) were measured in applied fields up to 9 T and at temperatures up to 298 K. SmFeAsO is magnetically ordered with TN = 137 K and has a hyperfine magnetic field of (4.98 ± 0.18) T at 4.2 K. In applied magnetic fields, the MS is consistent with a distribution of hyperfine magnetic fields of width Happlied+Hhyperfine. This arises because the angles between the direction of the ordered field in the crystallites making up the sample are randomly distributed about the direction of the applied field. The MS of the superconductors SmFe0.95Co0.05AsO (TC≃5 K) and SmFe0.9Co0.1AsO (TC≃17 K) are well described by a single peak from room temperature to 4.2 K indicating the absence of static magnetic order. However, the half width at half maximum, Γ, of the peak in SmFe0.95Co0.05AsO increases with decreasing temperature from its high temperature value, 0.13 mm/s at 25 K, to 0.25 mm/s at 10 K. No such temperature dependence is seen in SmFe0.9Co0.1AsO. We analyze this temperature dependence in terms of a fluctuating hyperfine magnetic field model whose frequency at 4.2 K is found to be ˜5-10 MHz, giving direct evidence of coexisting magnetic fluctuations and superconductivity at the interface in the phase diagram between the regions with magnetic and superconducting order. In a 5 T applied field, SmFe0.95Co0.05AsO is no longer superconducting; however, the temperature-dependent fluctuating magnetic field is still present and largely unchanged. The absence of fluctuations in superconducting SmFe0.9Co0.1AsO and their presence in superconducting SmFe0.95Co0.05AsO in zero applied field and in nonsuperconducting SmFe0.95Co0.05AsO at 5 T suggests that magnetic order is in competition with superconductivity in SmFe1-xCoxAsO.

  6. Superconductor developments

    SciTech Connect

    Larbalestier, D.

    1989-04-05

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

  7. Organic superconductors.

    PubMed

    Saito, Gunzi; Yoshida, Yukihiro

    2011-06-01

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

  8. 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.

  9. 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.

  10. 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.

  11. Superconductor consolidation

    SciTech Connect

    Staudhammer, K.P.

    1988-01-01

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

  12. Superconductor consolidation

    NASA Astrophysics Data System (ADS)

    Staudhammer, K. P.

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

  13. Coseismic rupturing stopped by Aso volcano during the 2016 Mw 7.1 Kumamoto earthquake, Japan.

    PubMed

    Lin, A; Satsukawa, T; Wang, M; Mohammadi Asl, Z; Fueta, R; Nakajima, F

    2016-11-18

    Field investigations and seismic data show that the 16 April 2016 moment magnitude (Mw) 7.1 Kumamoto earthquake produced a ~40-kilometer-long surface rupture zone along the northeast-southwest-striking Hinagu-Futagawa strike-slip fault zone and newly identified faults on the western side of Aso caldera, Kyushu Island, Japan. The coseismic surface ruptures cut Aso caldera, including two volcanic cones inside it, but terminate therein. The data show that northeastward propagation of coseismic rupturing terminated in Aso caldera because of the presence of magma beneath the Aso volcanic cluster. The seismogenic faults of the 2016 Kumamoto earthquake may require reassessment of the volcanic hazard in the vicinity of Aso volcano.

  14. Coseismic rupturing stopped by Aso volcano during the 2016 Mw 7.1 Kumamoto earthquake, Japan

    NASA Astrophysics Data System (ADS)

    Lin, A.; Satsukawa, T.; Wang, M.; Mohammadi Asl, Z.; Fueta, R.; Nakajima, F.

    2016-11-01

    Field investigations and seismic data show that the 16 April 2016 moment magnitude (Mw) 7.1 Kumamoto earthquake produced a ~40-kilometer-long surface rupture zone along the northeast-southwest-striking Hinagu-Futagawa strike-slip fault zone and newly identified faults on the western side of Aso caldera, Kyushu Island, Japan. The coseismic surface ruptures cut Aso caldera, including two volcanic cones inside it, but terminate therein. The data show that northeastward propagation of coseismic rupturing terminated in Aso caldera because of the presence of magma beneath the Aso volcanic cluster. The seismogenic faults of the 2016 Kumamoto earthquake may require reassessment of the volcanic hazard in the vicinity of Aso volcano.

  15. Organic superconductors

    NASA Astrophysics Data System (ADS)

    Jérome, D.

    1994-10-01

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

  16. 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.

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. 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).

  2. La variété β-NaMoO2(AsO4)

    PubMed Central

    Ben Hlila, Soumaya; Zid, Mohamed Faouzi; Driss, Ahmed

    2009-01-01

    The title compound, sodium dioxidomolybdenum(VI) arsenate(V), β-NaMoO2AsO4, was prepared by solid-state reaction at 953 K. In the crystal structure, the AsO4 tetra­hedra and MoO6 octa­hedra (both with m symmetry) share corner atoms to form a three-dimensional framework that delimits cavities parallel to [010] where disordered six-coordinated sodium cations (half-occupation) are located. Structural relationships between the different orthoarsenates of the AMoO2AsO4 series (A = Ag, Li, Na, K and Rb) are discussed. PMID:21581739

  3. 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...

  4. 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

  5. Gaia17aso and Gaia17asp transients confirmed by Euler imaging

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    We report confirmation of Gaia Science Alerts transients Gaia17aso and Gaia17asp. Images were obtained through modified Gunn R band filter of the ECAM instrument installed on the Swiss 1.2m Euler telescope at La Silla, on 2017 March 21st - 22nd.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. K2V2O2(AsO4)2

    PubMed Central

    Belkhiri, Sabrina; Mezaoui, Djillali; Roisnel, Thierry

    2012-01-01

    The vanadium oxide arsenate with formula K2V2O2(AsO4)2, dipotassium divanadium(IV) dioxide diarsenate, has been synthesized by solid-state reaction in an evacuated silica ampoule. Its structure is isotypic with K2V2O2(PO4)2. The framework is built up from corner-sharing VO6 octa­hedra and AsO4 tetra­hedra, creating an infinite [VAsO8]∞ chain running along the a- and c-axis directions. The K+ cations are located in hexa­gonal tunnels, which are delimited by the connection of the [VAsO8]∞ chains. PMID:22807696

  12. Structural features of two novel alluaudite-like arsenates Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5

    PubMed Central

    Stojanović, Jovica; Đorđević, Tamara; Karanović, Ljiljana

    2012-01-01

    Two new compounds, Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 (1) and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5 (2), have been prepared hydrothermally. Their crystal structures consist of chains of edge-sharing M1O4(OH0.5)2, M1aO4(OH0.5)2, M2O5(OH0.5), and M2aO5(OH0.5) octahedra (M1, M1a = Zn, Cd; M2, M2a = Zn for 1, and M1, M1a = Mg, Cd; M2, M2a = Mg for 2) that are stacked parallel to (1 0 1) and are connected by the [(AsO4)0.5(AsO3(OH))0.5]2.5− and [(AsO4)0.5(AsO2(OH)2)0.5]2− tetrahedra. These chains produce two types of channels parallel to the c-axis. Cd atoms are located in channels 2, while in channels 1 are situated hydrogen atoms of OH groups. The infrared spectra clearly show the presence of broad O—H stretching and bending vibrations centred at 3236, 2392 1575 and 1396 cm−1 in (1), and 3210, 2379 1602 and 1310 cm−1 in (2). The O—H stretching frequency is in good agreement with O⋯O distances. Furthermore, structural characteristics of compounds with similar alluaudite-like structures were discussed. PMID:23471556

  13. Structural features of two novel alluaudite-like arsenates Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5.

    PubMed

    Stojanović, Jovica; Dorđević, Tamara; Karanović, Ljiljana

    2012-04-15

    Two new compounds, Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 (1) and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5 (2), have been prepared hydrothermally. Their crystal structures consist of chains of edge-sharing M1O4(OH0.5)2, M1aO4(OH0.5)2, M2O5(OH0.5), and M2aO5(OH0.5) octahedra (M1, M1a = Zn, Cd; M2, M2a = Zn for 1, and M1, M1a = Mg, Cd; M2, M2a = Mg for 2) that are stacked parallel to (1 0 1) and are connected by the [(AsO4)0.5(AsO3(OH))0.5](2.5-) and [(AsO4)0.5(AsO2(OH)2)0.5](2-) tetrahedra. These chains produce two types of channels parallel to the c-axis. Cd atoms are located in channels 2, while in channels 1 are situated hydrogen atoms of OH groups. The infrared spectra clearly show the presence of broad O-H stretching and bending vibrations centred at 3236, 2392 1575 and 1396 cm(-1) in (1), and 3210, 2379 1602 and 1310 cm(-1) in (2). The O-H stretching frequency is in good agreement with O⋯O distances. Furthermore, structural characteristics of compounds with similar alluaudite-like structures were discussed.

  14. K0.8Ag0.2Nb4O9AsO4

    PubMed Central

    Ben Amor, Rym; Zid, Mohamed Faouzi; Driss, Ahmed

    2008-01-01

    The title compound, potassium silver tetra­niobium nona­oxide arsenate, K0.8Ag0.2Nb4O9AsO4, was prepared by a solid-state reaction at 1183 K. The structure consists of infinite (Nb2AsO14)n chains parallel to the b axis and cross-linked by corner sharing via pairs of edge-sharing octa­hedra. Each pair links together four infinite chains to form a three-dimensional framework. The K+ and Ag+ ions partially occupy several independent close positions in the inter­connected cavities delimited by the framework. K0.8Ag0.2Nb4O9AsO4 is likely to exhibit fast alkali-ion mobility and ion-exchange properties. The Wyckoff symbols of special positions are as follows: one Nb 8e, one Nb 8g, As 4c, two K 8f, one Ag 8f, one Ag 4c, one O 8g, one O 4c. PMID:21202442

  15. NaAg2Mo3O9AsO4

    PubMed Central

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

    2010-01-01

    The title compound, sodium disilver arsenatotrimolybdate, Na0.93 (1)Ag2.07 (1)Mo3AsO13, was prepared by a solid-state reaction. In the crystal structure, isolated AsO4 tetra­hedra share corners with groups of three edge-sharing MoO6 octa­hedra. This arrangement leads to the formation of anionic 1 ∞[Mo3AsO13]n ribbons extending parallel to [100]. The three metal sites show occupational disorder by AgI and NaI 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 MO7 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

  16. K0.78Na0.22MoO2AsO4

    PubMed Central

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

    2013-01-01

    The title compound, potassium sodium dioxidomolybden­um(VI) arsenate, K0.78Na0.22MoO2AsO4, was synthesized by a solid-state reaction route. The structure is built up from corner-sharing MoO6 octa­hedra and AsO4 tetra­hedra, creating infinite [MoAsO8]∞ chains running along the b-axis direction. As, Mo and all but one O atom are on special positions (4c) with m symmetry and K (occupancy 0.78) is on a position (4a) of -1 in the tunnels. The possible motion of the alkali cations has been investigated by means of the bond-valance sum (BVS) model. The simulation shows that the Na+ motion appears to be easier mainly along the b-axis direction. Structural relationships between the different compounds of the AMoO2AsO4 (A = Ag, Li, Na, K, Rb) series and MXO8 (M = V; X = P, As) chains are discussed. PMID:24109253

  17. 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.

  18. Large area bulk superconductors

    DOEpatents

    Miller, Dean J.; Field, Michael B.

    2002-01-01

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

  19. Soil carbon stocks and carbon sequestration rates in seminatural grassland in Aso region, Kumamoto, Southern Japan.

    PubMed

    Toma, Yo; Clifton-Brown, John; Sugiyama, Shinji; Nakaboh, Makoto; Hatano, Ryusuke; Fernández, Fabián G; Ryan Stewart, J; Nishiwaki, Aya; Yamada, Toshihiko

    2013-06-01

    Global soil carbon (C) stocks account for approximately three times that found in the atmosphere. In the Aso mountain region of Southern Japan, seminatural grasslands have been maintained by annual harvests and/or burning for more than 1000 years. Quantification of soil C stocks and C sequestration rates in Aso mountain ecosystem is needed to make well-informed, land-use decisions to maximize C sinks while minimizing C emissions. Soil cores were collected from six sites within 200 km(2) (767-937 m asl.) from the surface down to the k-Ah layer established 7300 years ago by a volcanic eruption. The biological sources of the C stored in the Aso mountain ecosystem were investigated by combining C content at a number of sampling depths with age (using (14) C dating) and δ(13) C isotopic fractionation. Quantification of plant phytoliths at several depths was used to make basic reconstructions of past vegetation and was linked with C-sequestration rates. The mean total C stock of all six sites was 232 Mg C ha(-1) (28-417 Mg C ha(-1) ), which equates to a soil C sequestration rate of 32 kg C ha(-1)  yr(-1) over 7300 years. Mean soil C sequestration rates over 34, 50 and 100 years were estimated by an equation regressing soil C sequestration rate against soil C accumulation interval, which was modeled to be 618, 483 and 332 kg C ha(-1)  yr(-1) , respectively. Such data allows for a deeper understanding in how much C could be sequestered in Miscanthus grasslands at different time scales. In Aso, tribe Andropogoneae (especially Miscanthus and Schizoachyrium genera) and tribe Paniceae contributed between 64% and 100% of soil C based on δ(13) C abundance. We conclude that the seminatural, C4 -dominated grassland system serves as an important C sink, and worthy of future conservation.

  20. Topological nonsymmorphic crystalline superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Qing-Ze; Liu, Chao-Xing

    2016-01-01

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

  1. Topological Nonsymmorphic Crystalline Superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Qing-Ze; Liu, Chao-Xing

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

  2. Electrocaloric Refrigeration for Superconductors

    DTIC Science & Technology

    1977-02-01

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

  3. Topological superconductors: a review.

    PubMed

    Sato, Masatoshi; Ando, Yoichi

    2017-04-03

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

  4. Layered nickel based superconductors

    SciTech Connect

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

    2009-01-01

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

  5. Continuous lengths of oxide superconductors

    DOEpatents

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

    2000-01-01

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

  6. 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

  7. The NASA Airborne Snow Observatory: Demonstration Mission-3 and the Path Forward to a Broader ASO Program

    NASA Astrophysics Data System (ADS)

    Painter, T. H.

    2015-12-01

    The NASA Airborne Snow Observatory (ASO), an imaging spectrometer and imaging LiDAR system, to quantify snow water equivalent and snow albedo, provide unprecedented knowledge of snow properties, and provide complete, robust inputs to snowmelt runoff models, water management models, and systems of the future. This talk presents results from the third Demonstration Mission that occurred during the intense California drought of spring 2015, a snow year far worse than the previously worst snow year on record of 2014, and an overview of the various analyses that are finally available due to the uniqueness of the ASO data. In 2015, ASO provided complete basin coverage for the Tuolumne, Merced, Lakes, Rush Creek, and Middle+South Forks of Kings River Basins in the California Sierra Nevada and the Upper Rio Grande, Conejos, and Uncompahgre Basins in the Colorado Rocky Mountains. ASO performed its first wintertime acquisitions in the Tuolumne Basin in response to water managers' needs to quantify SWE volume in what was already realized as dire conditions. Analyses show that with ASO data, river flows and reservoir inflows from the ASO acquisition date to 1 July can be estimated with uncertainties of less than 2%. These results provide enormous value in management operational flexibility for the diversity of needs, and provide strong scientific constraints on the physical processes controlling snowmelt runoff. Snowmelt runoff models are markedly better constrained due to the now accurate knowledge of the distribution of snow water equivalent. With the ASO high-resolution spectrometer and lidar data for a snow-free acquisition, we can determine surface classifications, vegetation heights, and river networks. These data allow runoff models to be accurately and rapidly developed with unprecedented accuracy. These data are now being used to constrain models of varying complexity. Finally, we discuss the path forward on expanding ASO to cover the entire Sierra Nevada and the

  8. Theoretical and experimental study of the vibrational spectra of sarkinite Mn2(AsO4)(OH) and adamite Zn2(AsO4)(OH)

    NASA Astrophysics Data System (ADS)

    Makreski, Petre; Jovanovski, Stefan; Pejov, Ljupco; Kloess, Gert; Hoebler, Hans-Joachim; Jovanovski, Gligor

    2013-09-01

    The arsenate hydroxyl-bearing minerals sarkinite and adamite were studied with vibrational spectroscopic (IR and Raman) and quantum theoretical methods. The observed IR bands in the higher (1100-600 cm-1) and especially lower (600-450 cm-1) frequency region of AsO4 vibrations could clearly discriminate between the studied analogues. The differences between their crystal structures are much pronounced in both IR and Raman OH-stretching regions. Namely, a single strong band is found in the case of orthorhombic adamite compared to four weaker bands observed in corresponding IR and Raman spectral regions of monoclinic sarkinite. Essentially all bands in the experimental spectra, collected at both room and liquid nitrogen temperature, were tentatively assigned. To support the tentative assignment of bands in the vibrational spectra of the mentioned minerals, periodic pseudopotential plane wave density functional theory calculations were carried out. Geometry optimizations of the 3D periodic systems included both optimizations of the atomic positions within the unit cell and of the unit cell itself. In most cases, the assignments were either supported or implied by the obtained theoretical data. It is worth mentioning that this is the first experimental and theoretical study of the vibrational spectra of the very-rare sarkinite mineral.

  9. 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.

  10. Lightning in superconductors.

    PubMed

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

    2012-01-01

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

  11. 75 FR 59695 - Foreign-Trade Zone 169-Manatee County, Florida; Extension of Subzone; Aso LLC (Adhesive Bandage...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-28

    ... (Adhesive Bandage Manufacturing); Sarasota County, FL An application has been submitted to the Foreign-Trade... strips per year) was approved by the Board in 2000 for the manufacture of adhesive bandages under FTZ... has at times instead used various duty suspension provisions on adhesive tape. Aso is now...

  12. Crustal magma pathway beneath Aso caldera inferred from three-dimensional electrical resistivity structure

    NASA Astrophysics Data System (ADS)

    Hata, Maki; Takakura, Shinichi; Matsushima, Nobuo; Hashimoto, Takeshi; Utsugi, Mitsuru

    2016-10-01

    At Naka-dake cone, Aso caldera, Japan, volcanic activity is raised cyclically, an example of which was a phreatomagmatic eruption in September 2015. Using a three-dimensional model of electrical resistivity, we identify a magma pathway from a series of northward dipping conductive anomalies in the upper crust beneath the caldera. Our resistivity model was created from magnetotelluric measurements conducted in November-December 2015; thus, it provides the latest information about magma reservoir geometry beneath the caldera. The center of the conductive anomalies shifts from the north of Naka-dake at depths >10 km toward Naka-dake, along with a decrease in anomaly depths. The melt fraction is estimated at 13-15% at 2 km depth. Moreover, these anomalies are spatially correlated with the locations of earthquake clusters, which are distributed within resistive blocks on the conductive anomalies in the northwest of Naka-dake but distributed at the resistive sides of resistivity boundaries in the northeast.

  13. 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.

  14. 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

  15. Electrocaloric Refrigeration for Superconductors

    DTIC Science & Technology

    1974-12-31

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

  16. 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)

  17. 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.

  18. 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.

  19. Vortex cutting in superconductors

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  20. Experimental and theoretical characterization of arsenite in water: insights into the coordination environment of As-O.

    PubMed

    Ramírez-Solís, Alejandro; Mukopadhyay, Rita; Rosen, Barry P; Stemmler, Timothy L

    2004-05-03

    Long-term exposure to arsenic in drinking water has been linked to cancer of the bladder, lungs, skin, kidney, nasal passages, liver, and prostate in humans. It is therefore important to understand the structural aspects of arsenic in water, as hydrated arsenic is most likely the initial form of the metalloid absorbed by cells. We present a detailed experimental and theoretical characterization of the coordination environment of hydrated arsenite. XANES analysis confirms As(III) is a stable redox form of the metalloid in solution. EXAFS analysis indicate, at neutral pH, arsenite has a nearest-neighbor coordination geometry of approximately 3 As-O bonds at an average bond length of 1.77 A, while at basic pH the nearest-neighbor coordination geometry shifts to a single short As-O bond at 1.69 A and two longer As-O bonds at 1.82 A. Long-range ligand scattering is present in all EXAFS samples; however, these data could not be fit with any degree of certainty. There is no XAS detectable interaction between As and antimony, suggesting they are not imported into cells as a multinuclear complex. XAS results were compared to a structural database of arsenite compounds to confirm that a 3 coordinate As-O complex for hydrated arsenite is the predominate species in solution. Finally, quantum chemical studies indicate arsenite in solution is solvated by 3 water molecules. These results indicate As(OH)3 as the most stable structure existing in solution at neutral pH; thus, ionic As transport does not appear to be involved in the cellular uptake process.

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

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

    PubMed

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

    2009-06-12

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

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

    PubMed Central

    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

  4. Volcanic magma reservoir imaged as a low-density body beneath Aso volcano that terminated the 2016 Kumamoto earthquake rupture

    NASA Astrophysics Data System (ADS)

    Miyakawa, Ayumu; Sumita, Tatsuya; Okubo, Yasukuni; Okuwaki, Ryo; Otsubo, Makoto; Uesawa, Shimpei; Yagi, Yuji

    2016-12-01

    We resolve the density structure of a possible magma reservoir beneath Aso, an active volcano on Kyushu Island, Japan, by inverting gravity data. In the context of the resolved structure, we discuss the relationship between the fault rupture of the 2016 Kumamoto earthquake and Aso volcano. Low-density bodies were resolved beneath central Aso volcano using a three-dimensional inversion with an assumed density contrast of ±0.3 g/cm3. The resultant location of the southern low-density body is consistent with a magma reservoir reported in previous studies. No Kumamoto aftershocks occur in the southern low-density body; this aseismic anomaly may indicate a ductile feature due to high temperatures and/or the presence of partial melt. Comparisons of the location of the southern low-density body with rupture models of the mainshock, obtained from teleseismic waveform and InSAR data, suggest that the rupture terminus overlaps the southern low-density body. The ductile features of a magma reservoir could have terminated rupture propagation. On the other hand, a northern low-density body is resolved in the Asodani area, where evidence of current volcanic activity is scarce and aftershock activity is high. The northern low-density body might, therefore, be derived from a thick caldera fill in the Asodani area, or correspond to mush magma or a high-crystallinity magma reservoir that could be the remnant of an ancient intrusion.[Figure not available: see fulltext.

  5. Helical phases in superconductors

    NASA Astrophysics Data System (ADS)

    Sandhu, Raminder P. Kaur

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

  6. Antenna applications of superconductors

    NASA Astrophysics Data System (ADS)

    Hansen, R. C.

    1991-09-01

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

  7. 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.

  8. Vortex cutting in superconductors

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  9. Conventional magnetic superconductors

    DOE PAGES

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

    2015-07-01

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

  10. 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.

  11. 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.

  12. 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.

  13. Superconductors (History & Advanced Research)

    NASA Astrophysics Data System (ADS)

    Khorrami, Mona

    2012-02-01

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

  14. 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.

  15. 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.

  16. 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.}

  17. Superconductor and magnet levitation devices

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

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

  18. 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.

  19. 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

    2015-05-21

    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.

  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. Experiments on Nanoscale Disordered Superconductor-Normal-Superconductor Arrays

    NASA Astrophysics Data System (ADS)

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

    2003-03-01

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

  2. Crustal deformation associated with the 2016 Kumamoto Earthquake and its effect on the magma system of Aso volcano

    NASA Astrophysics Data System (ADS)

    Ozawa, Taku; Fujita, Eisuke; Ueda, Hideki

    2016-11-01

    An MJMA6.5 earthquake (foreshock) and MJMA7.3 earthquake (mainshock) struck Kumamoto Prefecture on April 14, 2016, and April 16, 2016. To evaluate the effect of crustal deformation due to the earthquake on the Aso magma system, we detected crustal deformation using InSAR and GNSS. From InSAR analysis, we detected large crustal deformations along the Hinagu Fault, the Futagawa Fault, and the northeast extension of the latter fault. It extended to more than 50 km, and the maximum slant-range change exceeded 1 m. Although the obtained crustal deformation was approximately explained by the right-lateral strike-slip on the fault, its details could not be explained by such simple faulting. Additionally, we found complex surface deformation west of the Aso caldera rim, suggesting that shallow fault slips occurred in many known and unknown faults associated with the earthquake. Most of the crustal deformation could be reasonably explained by four rectangle faults located along the Futagawa Fault, in the northeast extension of the Futagawa Fault, alongside the Hinagu Fault, and in the eastern part of the Futagawa Fault. The first three of faults have high dip angles and right-lateral slip. The other was a fault with a low dip angle that branched from the shallow depth of the fault along the Futagawa Fault. The normal-dip right-lateral slip was estimated for this segment. Based on the estimated fault model, we calculated the displacement and stress field around the Aso volcano by the finite-element method (FEM) to evaluate the effects on the Aso magma system. In this calculation, we assumed a spherical soft medium located at a 6-km depth beneath the area south of the Kusasenri region as the magma system and considered only static effects. The result shows complex distributions of displacements and stresses, but we can notice the following significant points. (1) The spherical magma system deformed to an ellipsoid, and the total volume was slightly increased, less than 1%. (2

  3. Crystal growth and crystal structures of six novel phases in the Mn/As/O/Cl(Br) system, as well as magnetic properties of α-Mn3(AsO4)2

    NASA Astrophysics Data System (ADS)

    Weil, Matthias; Kremer, Reinhard K.

    2017-01-01

    Chemical vapour transport reactions (900 °C → 820 °C, Cl2 or Br2 as transport agent) of in situ formed Mn3(AsO4)2 yielded the orthoarsenates(V) α-Mn3(AsO4)2 and β-Mn3(AsO4)2 as well as the oxoarsenate(V) halide compounds Mn7(AsO4)4Cl2, Mn11(AsO4)7Cl, Mn11(AsO4)7Br and Mn5(AsO4)3Cl. The crystal structures of all six phases were determined from single crystal X-ray diffraction data. The crystal structures of α-and β-Mn3(AsO4)2 are isotypic with the corresponding phosphate phases γ- and α-Mn3(PO4)2, respectively, and are reported here for the first time. A comparative discussion with other structures of general composition M3(AsO4)2 (М = Mg; divalent first-row transition metal) is given. The unique crystal structures of Mn7(AsO4)4Cl2 and that of the two isotypic Mn11(AsO4)7X (X = Cl, Br) structures are composed of two [MnO5] polyhedra, two [MnO4Cl2] polyhedra (one with site symmetry 1 bar), two AsO4 tetrahedra, and one [MnO5] polyhedron, three [MnO6] octahedra (one with site symmetry.m.), one [MnO4X], one [MnO5X] polyhedron and four AsO4 tetrahedra, respectively. The various polyhedra of the three arsenate(V) halides are condensed into three-dimensional framework structures by corner- and edge-sharing. Mn5(AsO4)3Cl adopts the chloroapatite structure. The magnetic and thermal properties of pure polycrystalline samples of a-Mn3(AsO4)2 were investigated in more detail. The magnetic susceptibility proves all Mn atoms to be in the oxidation state +2 yielding an effective magnetic moment per Mn atom of 5.9 μB. Long-range antiferromagnetic ordering is observed below 8.2 K consistent with the negative Curie-Weiss temperature of -50 K derived from the high temperature susceptibility data. Chemical vapour transport reactions of in situ formed Mn3(AsO4)2 using Cl2 or Br2 as transport agents led to crystal growth of six phases structurally determined for the first time: α-Mn3(AsO4)2, β-Mn3(AsO4)2, Mn7(AsO4)4Cl2, Mn11(AsO4)7Cl, Mn11(AsO4)7Br and Mn5(AsO4)3Cl.

  4. 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.

  5. 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)

  6. Processing of Mixed Oxide Superconductors

    DTIC Science & Technology

    1990-07-01

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

  7. Fluidized landslides induced by extreme rainfall along basaltic caldera cliff of Mt. Aso in July 2012

    NASA Astrophysics Data System (ADS)

    Fukuoka, Hiroshi; Matsushi, Yuki; Furuya, Gen; Saito, Hitoshi

    2013-04-01

    In the end of the rainy season of 2012, a extreme rainfall affected western Japan in July and induced hundreds of fluidized landslides claiming casualties of more than 20. Measured trigger precipitation was recorded by the nearby ground-based station of the AMeDAS network (Automated Meteorological Data Acquisition System)as about 80 mm/h for consecutive 4 hours. Analysis of Radar-Raingauge Analyzed Precipitation-operated by the Japan Meteorological Agency showed landslide affected area almost coincided with the ones of heavier precipitation. Most of the landslides took place along the outer caldera rim and flank of the central cone of Mt. Aso, a basaltic active volcano. Most of the landslides slid on the boundary of strongly weathered soils, which used to be new volcanic accretion materials. Outstanding features of these landslides are: (1) This area had been affected by similar heavy rainfall decades ago, however, again a number of landslides took place in the nearby past scars; (2) Many of the soil slide bodies are shallow less than 5 meters deep and possibly immediately transformed into debris flows or mud flows and traveled long distance to reach the downslope communities; (3) Visual observation of the sources showed the high possibility that some of the slides were apparently induced by liquefaction. Similar cases were reported of past 2 landslide disasters in Japan. This strongly suggests that excessive rainfall can trigger numerous mud flows of unexpected reach. We conducted close field study at a typical soil slide - mud flow site. It originally initiated as debris or soil slide on a thin steep bedding plane of about 34 degrees consisting of coarser accretion materials. Needle penetration test showed comparatively weaker strength in the layer. It is underlain by a layer of finer materials. Such a higher permeability contrast could contribute to higher susceptibility of excess pore pressure generation. We took soil samples from the vicinity of sliding

  8. Superconductivity in SmFe1-xMxASO (M = Co, Rh, Ir)

    NASA Astrophysics Data System (ADS)

    Qi, Yan-Peng; Wang, Lei; Gao, Zhao-Shun; Wang, Don-Liang; Zhang, Xian-Ping; Zhang, Zhi-Yu; Ma, Yan-Wei

    2010-03-01

    In this paper we report the comparative study of superconductivity by 3d (Co), 4d (Rh), 5d (Ir) element doping in SmFeAsO. X-ray diffraction patterns indicate that the material has formed the ZrCuSiAs-type structure with a space group P4/nmm. It is found that the antiferromagnetic spin-density-wave (SDW) order in the parent compounds is rapidly suppressed by Co, Rh, and Ir doping, and superconductivity emerges. The diamagnetism, consistent with the R-T data, conforms to the bulk superconductivity in our SmFe1-xMxAsO (M=Co, Rh, Ir) samples. Co, Rh and Ir locate in the same column in the periodic table of the elements but have different electronic band structure, so a comparative study would add more ingredients to the underlying physics of iron-based superconductors.

  9. 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

  10. Stability of holographic superconductors

    SciTech Connect

    Kanno, Sugumi; Soda, Jiro

    2010-10-15

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

  11. Stability of holographic superconductors

    NASA Astrophysics Data System (ADS)

    Kanno, Sugumi; Soda, Jiro

    2010-10-01

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

  12. 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

  13. Na3Co2(AsO4)(As2O7): a new sodium cobalt arsenate

    PubMed Central

    Guesmi, Abderrahmen; Driss, Ahmed

    2012-01-01

    In the title compound, tris­odium dicobalt arsenate diarsenate, Na3Co2AsO4As2O7, the two Co atoms, one of the two As and three of the seven O atoms lie on special positions, with site symmetries 2 and m for the Co, m for the As, and 2 and twice m for the O atoms. The two Na atoms are disordered over two general and special positions [occupancies 0.72 (3):0.28 (3) and 0.940 (6):0.060 (6), respectively]. The main structural feature is the association of the CoO6 octa­hedra in the ab plane, forming Co4O20 units, which are corner- and edge-connected via AsO4 and As2O7 arsenate groups, giving rise to a complex polyhedral connectivity with small tunnels, such as those running along the b- and c-axis directions, in which the Na+ ions reside. The structural model is validated by both bond-valence-sum and charge-distribution methods, and the distortion of the coordination polyhedra is analyzed by means of the effective coordination number. PMID:22807699

  14. Wyllieite-type Ag1.09Mn3.46(AsO4)3

    PubMed Central

    Frigui, Wafa; Zid, Mohamed Faouzi; Driss, Ahmed

    2012-01-01

    Single crystals of wyllieite-type silver(I) manganese(II) tris­orthoarsenate(V), Ag1.09Mn3.46(AsO4)3, were grown by a solid-state reaction. The three-dimensional framework is made up from four Mn2+/Mn3+ cations surrounded octa­hedrally by O atoms. The MnO6 octa­hedra are linked through edge- and corner-sharing. Three independent AsO4 tetra­hedra are linked to the framework through common corners, delimiting channels along [100] in which two partly occupied Ag+ sites reside, one on an inversion centre and with an occupancy of 0.631 (4), the other on a general site and with an occupancy of 0.774 (3), both within distorted tetra­hedral environments. One of the Mn sites is also located on an inversion centre and is partly occupied, with an occupancy of 0.916 (5). Related compounds with alluaudite-type or rosemaryite-type structures are compared and discussed. PMID:22719272

  15. 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.

  16. 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

  17. Physics and chemistry of layered chalcogenide superconductors

    PubMed Central

    Deguchi, Keita; Takano, Yoshihiko; Mizuguchi, Yoshikazu

    2012-01-01

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

  18. 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.

  19. Tunneling in Superconductors

    NASA Astrophysics Data System (ADS)

    Giaever, Ivar

    2002-03-01

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

  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. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Topological surface states in nodal superconductors.

    PubMed

    Schnyder, Andreas P; Brydon, Philip M R

    2015-06-24

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

  7. 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.

  8. 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.

  9. Nekodake stratovolcano formed at the edge of caldera before the huge pyroclastic eruptions of Aso, Japan: petrological constraints on magma supply system

    NASA Astrophysics Data System (ADS)

    Ueda, Y.; Hasenaka, T.; Mori, Y.

    2011-12-01

    Volcanic activities prior to caldera-forming eruptions give important constraints on the magma supply system leading to catastrophic eruptions. Nekodake volcano located in the eastern end of Aso Caldera, Central Kyushu, Japan, was considered to have been active during the post-caldera period. However, the stratigraphic relations and radiometric ages suggest that the Nekodake volcano was active during the caldera forming periods, Aso-1, Aso-2, Aso-3 and Aso-4 pyroclastic flows. In the history of the activities of the Aso volcano, there are some parasitic eruptive activities between pyroclastic flows. However, the relationship between those activities and the pyroclastic flow eruptions is not clear. The purpose of this study is to clarify the petrological relation between magmas of the Nekodake volcano and those of Aso pyroclastic flows. We investigated geological features of the Nekodake volcano, and conducted whole rock chemical analysis and the petrographical description of the volcanic products of Nekodake. We classified the Nekodake volcanic products into four groups from phenocryst assemblage, and two groups from the chemical composition. We found a correlation between petrographical groups and compositional groups. For example, incompatible elements are abundant in olivine group (olivine + 2 pyroxene + plagioclases). Nekodake volcanic products and the caldera-forming products show contrasting differentiation trends on the Harker diagrams. MgO, Al2O3, and CaO contents are high and TiO2, P2O5, and Fe2O3 are low in Nekodake products compared with those in caldera-forming products. Incompatible elements of Nekodake volcanic products show characteristically lower values (K20:0. 6 wt.% - 1.5 wt.%, Rb: 14.2 - 50.0 ppm, Zr: 90.7 ppm -129.2 ppm) than those of caldera-forming products (K20: 1.2 wt.%- 5.0 wt.%, Rb: 21.2 - 165.0 ppm, Zr: 93.76 ppm -321.0 ppm). These data show that the magma reservoir of Nekodake volcano and that of the gigantic pyroclastic eruptions are

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. K0.12Na0.54Ag0.34Nb4O9AsO4

    PubMed Central

    Chérif, Saïda Fatma; Zid, Mohamed Faouzi; Driss, Ahmed

    2011-01-01

    Potassium sodium silver tetra­niobium nona­oxide arsenate, K0.12Na0.54Ag0.34Nb4AsO13, synthesized by solid-state reaction at 1123 K, adopts a three-dimensional framework delimiting tunnels running along [001] in which occupationally disordered sodium, silver, and potassium ions are located. Of the 11 atoms in the asymmetric unit (two Nb, one As, one Ag, one K, one Na and fiveO), nine are located on special positions: one Nb and the K, Ag, Na and two O atoms are situated on mirror planes, the other Nb is on a twofold rotation axis, and the As atom and one O atom are on sites of m2m symmetry. PMID:21522808

  15. 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.

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

    PubMed

    Dubi, Yonatan; Meir, Yigal; Avishai, Yshai

    2007-10-18

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

  17. 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.

  18. 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.

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

    SciTech Connect

    Ionov, A. I.

    2013-05-15

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

  20. Current status of iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Kamihara, Yoichi

    2012-03-01

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

  1. A Road Towards High Temperature Superconductors

    DTIC Science & Technology

    2013-08-01

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

  2. 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.

  3. Suppression of superconductivity in mesoscopic superconductors.

    PubMed

    Sobnack, M B; Kusmartsev, F V

    2001-01-22

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

  4. Recent status of superconductors for accelerator magnets

    SciTech Connect

    Greene, A.F.

    1992-01-01

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

  5. Recent status of superconductors for accelerator magnets

    SciTech Connect

    Greene, A.F.

    1992-10-01

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

  6. 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.

  7. 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.

  8. Topological properties of ferromagnetic superconductors

    DOE PAGES

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

    2016-04-27

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

  9. Topological properties of ferromagnetic superconductors

    SciTech Connect

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

    2016-04-27

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

  10. Growth of superconducting NdFe0.88Co0.12AsO films by metal-organic chemical vapor deposition and post arsenic diffusion

    NASA Astrophysics Data System (ADS)

    Corrales-Mendoza, I.; Bartolo-Pèrez, P.; Sánchez-Reséndiz, V. M.; Gallardo-Hernández, S.; Conde-Gallardo, A.

    2015-01-01

    Metal-organic chemical vapor deposition (MOCVD) and post-deposition arsenic diffusion processes were successfully employed to grow superconducting NdFe0.88Co0.12AsO thin films. First, by employing iron, cobalt and neodymium metal-organic precursors, a precursor film is grown by MOCVD on (001)-oriented LaAlO3 substrates. Subsequently, the arsenic is incorporated during an annealing of these precursor films in the presence of a NdFe0.9Co0.1AsO pellet. The chemical composition and crystallographic results indicate the formation of the cobalt-doped NdFeAsO polycrystalline phase. The secondary ion mass spectroscopy indicates a homogeneous arsenic diffusion process. The resistance and magnetization measurements as a function of temperature indicate a superconducting transition ˜15 \\text{K} .

  11. High-Temperature Ceramic Superconductors

    DTIC Science & Technology

    1991-12-15

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

  12. 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.

  13. 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.

  14. Fault current limiters using superconductors

    NASA Astrophysics Data System (ADS)

    Norris, W. T.; Power, A.

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

  15. 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.

  16. In silico and in vitro evaluation of exonic and intronic off-target effects form a critical element of therapeutic ASO gapmer optimization

    PubMed Central

    Kamola, Piotr J.; Kitson, Jeremy D. A.; Turner, Gemma; Maratou, Klio; Eriksson, Sofie; Panjwani, Aliza; Warnock, Linda C.; Douillard Guilloux, Gaelle A.; Moores, Kitty; Koppe, Emma L.; Wixted, William E.; Wilson, Paul A.; Gooderham, Nigel J.; Gant, Timothy W.; Clark, Kenneth L.; Hughes, Stephen A.; Edbrooke, Mark R.; Parry, Joel D.

    2015-01-01

    With many safety and technical limitations partly mitigated through chemical modifications, antisense oligonucleotides (ASOs) are gaining recognition as therapeutic entities. The increase in potency realized by ‘third generation chemistries’ may, however, simultaneously increase affinity to unintended targets with partial sequence complementarity. However, putative hybridization-dependent off-target effects (OTEs), a risk historically regarded as low, are not being adequately investigated. Here we show an unexpectedly high OTEs confirmation rate during screening of fully phosphorothioated (PS)-LNA gapmer ASOs designed against the BACH1 transcript. We demonstrate in vitro mRNA and protein knockdown of off-targets with a wide range of mismatch (MM) and gap patterns. Furthermore, with RNase H1 activity residing within the nucleus, hybridization predicted against intronic regions of pre-mRNAs was tested and confirmed. This dramatically increased ASO-binding landscape together with relatively high potency of such interactions translates into a considerable safety concern. We show here that with base pairing-driven target recognition it is possible to predict the putative off-targets and address the liability during lead design and optimization phases. Moreover, in silico analysis performed against both primary as well as spliced transcripts will be invaluable in elucidating the mechanism behind the hepatoxicity observed with some LNA-modified gapmers. PMID:26338776

  17. 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.

  18. Redetermination of the cubic struvite analogue Cs[Mg(OH2)6](AsO4)

    PubMed Central

    Weil, Matthias

    2009-01-01

    In contrast to the previous refinement from photographic data [Ferrari et al. (1955 ▶). Gazz. Chim. Ital. 84, 169–174], the present redetermination of the title compound, caesium hexa­aqua­magnesium arsenate(V), revealed the Cs atom to be on Wyckoff position 4d instead of Wyckoff position 4b of space group F 3m. The structure can be derived from the halite structure. The centres of the complex [Mg(OH2)6] octa­hedra and the AsO4 tetra­hedra (both with 3m symmetry) are on the respective Na and Cl positions. The building units are connected to each other by O—H⋯O hydrogen bonds. The Cs+ cations (3m symmetry) are located in the voids of this arrangement and exhibit a regular cubocta­hedral 12-coordination to the O atoms of the water mol­ecules. The O atom bonded to As has 2mm site symmetry (Wyckoff position 24f) and the water-mol­ecule O atom has m site symmetry (Wyckoff position 48h). PMID:21581464

  19. High temperature superconductors: A technological revolution

    NASA Technical Reports Server (NTRS)

    1990-01-01

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

  20. Enhancement of mechanical properties of 123 superconductors

    DOEpatents

    Balachandran, Uthamalingam

    1995-01-01

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

  1. Enhancement of mechanical properties of 123 superconductors

    DOEpatents

    Balachandran, U.

    1995-04-25

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

  2. 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.

  3. Magnetization of anisotropic Type II superconductors

    SciTech Connect

    Mints, R.G.

    1989-04-10

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

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

    DTIC Science & Technology

    1980-07-21

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

  5. 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.

  6. 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.

  7. Pressure effects in the isoelectronic REFe0.85Ir0.15AsO system.

    PubMed

    Maroni, Beatrice; Di Castro, Daniele; Hanfland, Michael; Boby, Joseph; Vercesi, Cristiano; Mozzati, M Cristina; Weyeneth, Stephen; Keller, Hugo; Khasanov, Rustem; Drathen, Christina; Dore, Paolo; Postorino, Paolo; Malavasi, Lorenzo

    2011-03-16

    The effect of chemical and hydrostatic pressure has been studied systematically in a selected system belonging to the 1111 family of iron pnictide high-temperature superconductors. The results show a surprising similarity between the trend of critical temperature vs hydrostatic pressure for isoelectronic samples with different rare earths (RE) on the RE site and samples of the SmFeAsO(1-x)F(x) series with different doping levels. These results open new questions about the underlying mechanism for superconductivity in iron pnictides.

  8. Superconductor lunar telescopes --Abstract only

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  9. 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.

  10. 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.

  11. Passivation of high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Vasquez, Richard P. (Inventor)

    1991-01-01

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

  12. Noncentrosymmetric superconductors in one dimension

    NASA Astrophysics Data System (ADS)

    Samokhin, K. V.

    2017-02-01

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

  13. Holographic superconductors with hyperscaling violation

    NASA Astrophysics Data System (ADS)

    Fan, ZhongYing

    2013-09-01

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

  14. 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.

  15. Losses of Superconductor Journal Bearing

    NASA Astrophysics Data System (ADS)

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

    2004-06-01

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

  16. 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.

  17. Highly crystalline 2D superconductors

    NASA Astrophysics Data System (ADS)

    Saito, Yu; Nojima, Tsutomu; Iwasa, Yoshihiro

    2016-12-01

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

  18. 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.

  19. Position-sensitive superconductor detectors

    NASA Astrophysics Data System (ADS)

    Kurakado, M.; Taniguchi, K.

    2016-12-01

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

  20. 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.

  1. Aeronautical applications of high-temperature superconductors

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  2. Circuit Theory of Unconventional Superconductor Junctions

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

  3. Aeronautical applications of high-temperature superconductors

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  4. 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.

  5. 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.

  6. Clinical significance of miR-155 expression in breast cancer and effects of miR-155 ASO on cell viability and apoptosis.

    PubMed

    Zheng, Shu-Rong; Guo, Gui-Long; Zhang, Wei; Huang, Guan-Li; Hu, Xiao-Qu; Zhu, Jin; Huang, Qi-Di; You, Jie; Zhang, Xiao-Hua

    2012-04-01

    Accumulating evidence shows that mircroRNAs (miRNAs) play a vital role in tumorigenesis. miR-155 is one of the most multifunctional miRNAs whose overexpression has been found to be associated with different types of cancer including breast cancer. To further determine the potential involvement of miR-155 in breast cancer, we evaluated the expression levels of miR-155 by real-time PCR and correlated the results with clinicopathological features. Matched non-tumor and tumor tissues of 42 infiltrating ductal carcinomas and 3 infiltrating lobular carcinomas were analyzed for miR-155 expression by real-time PCR. Further, we used an antisense technique to inhibit miR-155 expression in vitro. WST-8 test was performed to evaluate cell viability and apoptosis assay was used to investigate the effect of the miR-155 antisense oligonucleotide (miR-155 ASO) on HS578T cell death. The expression levels of miR-155 were significantly higher in tumor tissues than the levels in matched non-tumor tissues (P<0.001). Up-regulated miR-155 expression was associated with lymph node positivity (P=0.034), higher proliferation index (Ki-67 >10%) (P=0.019) and advanced breast cancer TNM clinical stage (P=0.002). Interestingly, we next found that miR-155 expression levels had close relations with ER status (P=0.041) and PR status (P=0.029). Transfection efficiency detected by flow cytometry was higher than 70%, the WST-8 test showed that viability of HS578T cells was greatly reduced after transfection with miR-155 ASO compared with the scramble (SCR) group or the liposome group. The Annexin V-FITC/PI assay also indicated that transfection with miR-155 ASO promoted apoptosis.

  7. 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.

  8. 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.

  9. NEW APPROACHES: High temperature superconductor levitation motor

    NASA Astrophysics Data System (ADS)

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

    1998-01-01

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

  10. Fracturing during ductile-brittle transition and development of flow banding in the Takanoobane Rhyolite lava of Aso volcano, Japan

    NASA Astrophysics Data System (ADS)

    Furukawa, K.; Uno, K.

    2014-12-01

    Flow banding, which is characterized by deformation of highly vesicular part, is ubiquitously observed in rhyolite lavas. To explore the origin of the highly vesicular part, we examined Takanoobane rhyolite lava (TR lava) in Aso caldera, Japan, which effused at 51+/-5 ka (Matsumoto et al., 1991). The highly vesicular parts characterized by ductile deformation are well developed in the central crystalline layer, at which the parts tend to be flattened with an increasing of distance from the source. The part develops into flow bands. The highly vesicular parts are also recognized around fractures that developed perpendicular to the flow direction, and adjacent to phenocrysts. The highly vesicular part is composed of cavities with mainly <100 μm in diameter. Microscopic observation and the SEM image show that the cavities have ragged walls characterized by the protrusion of groundmass crystals and phenocrysts. Smith et al. (2001) described such cavities in detail using three silicic lavas in Japan, and proposed that the cavities were formed by failure of the magma by flow during ductile-brittle transition. The authors described the fracturing mechanism as cavitation, and considered that groundmass adjacent to phenocryst also appears to act as a site of strong cavitation because of the steep strain gradient between deforming matrix and non-deforming phenocrysts. The similarity of the textures means that the highly vesicular part in TR lava was also formed by cavitation during ductile-brittle transition. The part would be deformed and flattened with progression of lava deformation. We analyzed the anisotropy of magnetic susceptibility (AMS) to estimate the deformation style of TR lava. The results show that the highly vesicular part was deformed by pure shear strain. We established the following model for the development of flow banding. In TR lava, the highly vesicular parts were formed by failure of the magma during ductile-brittle transition during and/or after lava

  11. 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.

  12. Superconductors for pulsed rf accelerators

    SciTech Connect

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

    1985-04-01

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

  13. 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.

  14. 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).

  15. 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).

  16. ASO: Antistreptolysin O titer

    MedlinePlus

    ... or glomerulonephritis , a form of kidney disease Caused rheumatic fever in a person with signs and symptoms The ... and/or go untreated, however, complications ( sequelae ), namely rheumatic fever and glomerulonephritis, can develop in some people, especially ...

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  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. Electron tunneling and point contact Andreev reflection studies of superconductors

    NASA Astrophysics Data System (ADS)

    Dai, Wenqing

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

  4. Stop of magnetic flux movement in levitating superconductor

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

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

    DOEpatents

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

    1978-01-01

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

  6. 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. Quantum interference in an interfacial superconductor

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  8. Quantum interference in an interfacial superconductor.

    PubMed

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

    2016-10-01

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

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    Green, Michael A.

    1988-07-01

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

  13. 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.

  14. 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

  15. High-temperature superconductor antenna investigations

    NASA Astrophysics Data System (ADS)

    Karasack, Vincent G.

    1990-10-01

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

  16. High-temperature superconductor antenna investigations

    NASA Technical Reports Server (NTRS)

    Karasack, Vincent G.

    1990-01-01

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

  17. 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.

  18. Chemistry of high-temperature superconductors.

    PubMed

    Sleight, A W

    1988-12-23

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

  19. 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.

  20. 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.

  1. 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.

  2. 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].

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. Vortex core size in unconventional superconductors

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

  8. Order parameter fluctuations in the holographic superconductor

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  9. Iron chalcogenide superconductors at high magnetic fields

    PubMed Central

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

    2012-01-01

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

  10. Electrical connection structure for a superconductor element

    DOEpatents

    Lallouet, Nicolas; Maguire, James

    2010-05-04

    The invention relates to an electrical connection structure for a superconductor element cooled by a cryogenic fluid and connected to an electrical bushing, which bushing passes successively through an enclosure at an intermediate temperature between ambient temperature and the temperature of the cryogenic fluid, and an enclosure at ambient temperature, said bushing projecting outside the ambient temperature enclosure. According to the invention, said intermediate enclosure is filled at least in part with a solid material of low thermal conductivity, such as a polyurethane foam or a cellular glass foam. The invention is applicable to connecting a superconductor cable at cryogenic temperature to a device for equipment at ambient temperature.

  11. 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.

  12. Building blocks for correlated superconductors and magnets

    DOE PAGES

    Sarrao, J. L.; Ronning, F.; Bauer, E. D.; ...

    2015-04-01

    Recent efforts at Los Alamos to discover strongly correlated superconductors and hard ferromagnets are reviewed. While serendipity remains a principal engine of materials discovery, design principles and structural building blocks are beginning to emerge that hold potential for predictive discovery. Successes over the last decade with the so-called “115” strongly correlated superconductors are summarized, and more recent efforts to translate these insights and principles to novel hard magnets are discussed. While true “materials by design” remains a distant aspiration, progress is being made in coupling empirical design principles to electronic structure simulation to accelerate and guide materials design and synthesis.

  13. 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.

  14. [The arsenate Na3Fe2(AsO4) 3: structural study at low temperature and simulation of conduction properties of alkaline cations].

    PubMed

    Ouerfelli, Najoua; Guesmi, Abderrahmen; Mazza, Daniele; Zid, Mohamed Faouzi; Driss, Ahmed

    2008-05-01

    The crystal structure of the low-temperature garnet-like form of trisodium diiron(III) triarsenate, Na(3)Fe(2)(AsO(4))(3), exhibits a three-dimensional framework with small tunnels running along the [111] direction, in which the Na(+) cations are located. This study demonstrates the structural origins of the different ionic conductivities of the low- and high-temperature forms. Sodium conduction properties are simulated by means of the bond-valence-sum (BVS) model; the correlations between the low- and high-temperature crystal structures are discussed. The As, Fe and Na atoms lie on special positions (Wyckoff symbols 24d, 16a and 24c, respectively).

  15. Effect of glycine substitution on the ferroelectric phase of betaine arsenate [(CH 3) 3NCH 2COO·H 3AsO 4

    NASA Astrophysics Data System (ADS)

    Dekola, T.; Ribeiro, J. L.; Klöpperpieper, A.

    2011-09-01

    The present work reports an experimental investigation on the influence of glycine (NH 2CH 2COOH) substitution in the polar properties and the critical dynamics of the molecular ferroelectric betaine arsenate, (CH 3) 3NCH 2COO·H 3AsO 4. The dielectric dispersion (20 Hz<ν<3 MHz) and the thermally induced displacement currents are investigated in detail over the extended Curie region of the system (130 K< T<100 K). The results obtained for a single crystal with nominal glycine content of 20% are analyzed, compared with those obtained for pure betaine arsenate and discussed within the scope of a phenomenological Landau model previously used to describe a system with competing ferroelectric and structural instabilities.

  16. 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.

  17. Dynamics of interfaces in superconductors

    SciTech Connect

    Dorsey, A.T. )

    1994-08-01

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

  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. 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.

  20. 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

  1. 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.

  2. Stripe phases in high-temperature superconductors

    PubMed Central

    Emery, V. J.; Kivelson, S. A.; Tranquada, J. M.

    1999-01-01

    Stripe phases are predicted and observed to occur in a class of strongly correlated materials describable as doped antiferromagnets, of which the copper-oxide superconductors are the most prominent representatives. The existence of stripe correlations necessitates the development of new principles for describing charge transport and especially superconductivity in these materials. PMID:10430848

  3. Stripe Phases in High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Emery, V. J.; Kivelson, S. A.; Tranquada, J. M.

    1999-08-01

    Stripe phases are predicted and observed to occur in a class of strongly correlated materials describable as doped antiferromagnets, of which the copper-oxide superconductors are the most prominent representatives. The existence of stripe correlations necessitates the development of new principles for describing charge transport and especially superconductivity in these materials.

  4. Stripe phases in high-temperature superconductors.

    PubMed

    Emery, V J; Kivelson, S A; Tranquada, J M

    1999-08-03

    Stripe phases are predicted and observed to occur in a class of strongly correlated materials describable as doped antiferromagnets, of which the copper-oxide superconductors are the most prominent representatives. The existence of stripe correlations necessitates the development of new principles for describing charge transport and especially superconductivity in these materials.

  5. Mg6.75(OH)3(H0.166AsO4)3(HAsO4), a member of the M 1- xM′6(OH)3(H2x/3AsO4)3(HAsO4) family (M,M′ = Co; Ni)

    PubMed Central

    Weil, Matthias

    2013-01-01

    In the structure of the title compound, magnesium hydroxide hydrogenarsenate (6.75/3/4), two different Mg2+ ions, one located on a site with symmetry 3m. (occupancy 3/4) and one on a general position, as well as two different AsO3(OH) tetra­hedra (symmetry .m. with partial occupancy for the H atom for one, and symmetry 3m. with full occupancy for the H atom for the other) and one OH− ion (site symmetry .m.) are present. Both Mg2+ ions are octa­hedrally surrounded by O atoms. The MgO6 octa­hedra belonging to the partially occupied Mg2+ sites share faces, forming chains along [001]. The other type of MgO6 octa­hedra share corners and faces under formation of strands parallel to [001] whereby individual strands are linked through common corner atoms. The two types of AsO3(OH) tetra­hedra inter­link the strands and the chains, building up a three-dimensional framework resembling that of the mineral dumortierite. The OH groups were assigned on basis of bond-valence calculations and crystal chemical considerations. PMID:23723752

  6. Isotope and multiband effects in layered superconductors.

    PubMed

    Bussmann-Holder, Annette; Keller, Hugo

    2012-06-13

    In this review we consider three classes of superconductors, namely cuprate superconductors, MgB(2) and the new Fe based superconductors. All of these three systems are layered materials and multiband compounds. Their pairing mechanisms are under discussion with the exception of MgB(2), which is widely accepted to be a 'conventional' electron-phonon interaction mediated superconductor, but extending the Bardeen-Cooper-Schrieffer (BCS) theory to account for multiband effects. Cuprates and Fe based superconductors have higher superconducting transition temperatures and more complex structures. Superconductivity is doping dependent in these material classes unlike in MgB(2) which, as a pure compound, has the highest values of T(c) and a rapid suppression of superconductivity with doping takes place. In all three material classes isotope effects have been observed, including exotic ones in the cuprates, and controversial ones in the Fe based materials. Before the area of high-temperature superconductivity, isotope effects on T(c) were the signature for phonon mediated superconductivity-even when deviations from the BCS value to smaller values were observed. Since the discovery of high T(c) materials this is no longer evident since competing mechanisms might exist and other mediating pairing interactions are discussed which are of purely electronic origin. In this work we will compare the three different material classes and especially discuss the experimentally observed isotope effects of all three systems and present a rather general analysis of them. Furthermore, we will concentrate on multiband signatures which are not generally accepted in cuprates even though they are manifest in various experiments, the evidence for those in MgB(2), and indications for them in the Fe based compounds. Mostly we will consider experimental data, but when possible also discuss theoretical models which are suited to explain the data.

  7. Recrystallization of high temperature superconductors

    SciTech Connect

    Kouzoudis, Dimitris

    1996-05-09

    Currently one of the most widely used high Tc superconductors is the Bi-based compounds Bi2Sr2CaCu2Oz and Bi2Sr2Ca2Cu3Oz (known as BSCCO 2212 and 2223 compounds) with Tc values of about 85 K and 110 K respectively. Lengths of high performance conductors ranging from 100 to 1000 m long are routinely fabricated and some test magnets have been wound. An additional difficulty here is that although Bi-2212 and Bi-2223 phases exist over a wide range of stoichiometries, neither has been prepared in phase-pure form. So far the most successful method of constructing reliable and robust wires or tapes is the so called powder-in-tube (PIT) technique [1, 2, 3, 4, 5, 6, 7] in which oxide powder of the appropriate stoichiometry and phase content is placed inside a metal tube, deformed into the desired geometry (round wire or flat tape), and annealed to produce the desired superconducting properties. Intermediate anneals are often incorporated between successive deformation steps. Silver is the metal used in this process because it is the most compatible with the reacting phase. In all of the commercial processes for BSCCO, Ag seems to play a special catalytic role promoting the growth of high performance aligned grains that grow in the first few micrometers near the Ag/BSCCO interface. Adjacent to the Ag, the grain alignment is more perfect and the current density is higher than in the center of the tape. It is known that Ag lowers the melting point of several of the phases but the detailed mechanism for growth of these high performance grains is not clearly understood. The purpose of this work is to study the nucleation and growth of the high performance material at this interface.

  8. 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

  9. 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.

  10. Theoretical study of pair density wave superconductors

    NASA Astrophysics Data System (ADS)

    Zheng, Zhichao

    In conventional superconductors, the Cooper pairs are formed from quasiparticles. We explore another type of superconducting state, a pair density wave (PDW) order, which spontaneously breaks some of the translational and point group symmetries. In a PDW superconductor, the order parameter is a periodic function of the center-of-mass coordinate, and the spatial average value of the superconducting order parameter vanishes. In the early 1960s, following the success of the BCS theory of superconductivity, Fulde and Ferrell and Larkin and Ovchinnikov (FFLO) developed theories of inhomogeneous superconducting states. Because of this Zeeman splitting in a magnetic field, the Cooper pairs having a nonzero center-of-mass momentum are more stable than the normal pairing, leading to the FFLO state. Experiments suggest possible occurrence of the FFLO state in the heavy-fermion compound CeCoIn5, and in quasi-low-dimensional organic superconductors. FFLO phases have also been argued to be of importance in understanding ultracold atomic Fermi gases and in the formation of color superconductivity in high density quark matter. In all Fermi superfluids known at the present time, Cooper pairs are composed of particles with spin 1/2. The spin component of a pair wave function can be characterized by its total spin S = 0 (singlet) and S = 1 (triplet). In the discovered broken inversion superconductors CePt3Si, Li2Pt3B, and Li2Pd3B, the magnetic field leads to novel inhomogeneous superconducting states, namely the helical phase and the multiple-q phase. Its order parameter exhibits periodicity similar to FFLO phase, and the consequences of both phases are same: the enhancement of transition temperature as a function of magnetic field. We have studied the PDW phases in broken parity superconductors with vortices included. By studying PDW vortex states, we find the usual Abrikosov vortex solution is unstable against a new solution with fractional vortex pairs. We have also studied the

  11. Low resistivity contact to iron-pnictide superconductors

    DOEpatents

    Tanatar, Makariy; Prozorov, Ruslan; Ni, Ni; Bud& #x27; ko, Sergey; Canfield, Paul

    2013-05-28

    Method of making a low resistivity electrical connection between an electrical conductor and an iron pnictide superconductor involves connecting the electrical conductor and superconductor using a tin or tin-based material therebetween, such as using a tin or tin-based solder. The superconductor can be based on doped AFe.sub.2As.sub.2, where A can be Ca, Sr, Ba, Eu or combinations thereof for purposes of illustration only.

  12. 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

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

    NASA Astrophysics Data System (ADS)

    Pesin, Dmytro; Andreev, Anton; Spivak, Boris

    2008-03-01

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

  14. Ferrite-superconductor devices for advanced microwave applications

    SciTech Connect

    Dionne, G.F.; Oates, D.E.; Temme, D.H.; Weiss, J.A.

    1996-07-01

    Microwave devices comprising magnetized ferrite in contact with superconductor circuits designed to eliminate magnetic field penetration of the superconductor have demonstrated phase shift without significant conduction losses. The device structures are adaptable to low- or high-{Tc} superconductors. A nonoptimized design of a ferrite phase shifter that employs niobium or YBCO meanderlines has produced over 1,000 degrees of differential phase shift with a figure of merit exceeding 1,000 degrees/dB at X band. By combining superconductor meanderline sections with alternating T junctions on a ferrite substrate in a configuration with three-fold symmetry, a low-loss three-port switching circulator has been demonstrated.

  15. 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.

  16. 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.

  17. 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.

  18. Surface superconductivity of short coherence length superconductors

    NASA Astrophysics Data System (ADS)

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

    1994-09-01

    Based on the theory of Valls et al. for short coherence length superconductors, de Gennes' boundary theory for conventional superconductors with ξ 0≫ K-1F may be modified. We solve the G-L equation exactly under zero magnetic field for various temperatures. The order parameter Ψ( x) is not depleted but enhanced near the surface. We also obtain some interesting results: Tc will be enhanced by contracting of the thickness of a superconducting film. The nucleation field Hc3 ( T)∝( Tcb- T) near Tcb; and H c3(T)∝(T c-T) {1}/{2} near Tc. The critical current in SIS Josephson junctions Jc( T)∝( Tc- T)+√ 2 τ0( T0- T) for T< Tcb; and Jc( T)∝( Tc- T) for Tcb≤ T< Tc.

  19. Proximity effects in ferromagnet-superconductor structures

    NASA Astrophysics Data System (ADS)

    Halterman, Klaus Byron

    I present an extensive theoretical investigation of the proximity effects that occur in ferromagnet/superconductor systems. I use a numerical method to solve self consistently the Bogoliubov-de Gennes equations in the continuum. I obtain the pair amplitude and the local density of states (DOS), and use these results to extract the relevant lengths characterizing both the leakage of superconductivity into the magnet and to study spin splitting induced in the superconductor. These phenomena are investigated as a function of parameters such as temperature, magnet polarization, interfacial scattering, sample size and Fermi wave vector mismatch, all of which turn out to have an important influence on the results. These comprehensive results should help characterize and analyze future data, and are shown to be in agreement with existing experiments.

  20. Unconventional Disorder Effects in Correlated Superconductors

    NASA Astrophysics Data System (ADS)

    Gastiasoro, Maria N.; Bernardini, Fabio; Andersen, Brian M.

    2016-12-01

    We study the effects of disorder on unconventional superconductors in the presence of correlations, and explore a novel correlated disorder paradigm dominated by strong deviations from standard Abrikosov-Gor'kov theory due to generation of local bound states and cooperative impurity behavior driven by Coulomb interactions. Specifically we explain under which circumstances magnetic disorder acts as a strong poison destroying high-Tc superconductivity at the sub-1% level, and when nonmagnetic disorder, counterintuitively, hardly affects the unconventional superconducting state while concomitantly inducing an inhomogeneous full-volume magnetic phase. Recent experimental studies of Fe-based superconductors have discovered that such unusual disorder behavior seems to be indeed present in those systems.

  1. 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.

  2. Neutron stars as type-I superconductors.

    PubMed

    Buckley, Kirk B W; Metlitski, Max A; Zhitnitsky, Ariel R

    2004-04-16

    In a recent paper by Link, it was pointed out that the standard picture of the neutron star core composed of a mixture of a neutron superfluid and a proton type-II superconductor is inconsistent with observations of a long period precession in isolated pulsars. In the following we will show that an appropriate treatment of the interacting two-component superfluid (made of neutron and proton Cooper pairs), when the structure of proton vortices is strongly modified, may dramatically change the standard picture, resulting in a type-I superconductor. In this case the magnetic field is expelled from the superconducting regions of the neutron star, leading to the formation of the intermediate state when alternating domains of superconducting matter and normal matter coexist.

  3. A Fifth Force: Generalized through Superconductors

    NASA Technical Reports Server (NTRS)

    Robertson, Glen A.

    1999-01-01

    The connection between the Biefield-Brown Effect, the recent repeat of the 1902 Trouton-Noble (TN) experiments, and the gravity shielding experiments was explored. This connection is visualized through high capacitive electron concentrations. From this connection, a theory is proposed that connects mass energy to gravity and a fifth force. The theory called the Gravi-Atomic Energy theory presents two new terms: Gravi-atomic energy and quantum vacuum pressure (QVP). Gravi-atomic energy is defined as the radiated mass energy, which acts on vacuum energy to create a QVP about a mass, resulting in gravity and the fifth force. The QVP emission from a superconductor was discussed followed by the description of a test for QVP from a superconductor using a Cavendish balance.

  4. Unconventional Disorder Effects in Correlated Superconductors.

    PubMed

    Gastiasoro, Maria N; Bernardini, Fabio; Andersen, Brian M

    2016-12-16

    We study the effects of disorder on unconventional superconductors in the presence of correlations, and explore a novel correlated disorder paradigm dominated by strong deviations from standard Abrikosov-Gor'kov theory due to generation of local bound states and cooperative impurity behavior driven by Coulomb interactions. Specifically we explain under which circumstances magnetic disorder acts as a strong poison destroying high-T_{c} superconductivity at the sub-1% level, and when nonmagnetic disorder, counterintuitively, hardly affects the unconventional superconducting state while concomitantly inducing an inhomogeneous full-volume magnetic phase. Recent experimental studies of Fe-based superconductors have discovered that such unusual disorder behavior seems to be indeed present in those systems.

  5. Ordering dynamics in type-II superconductors.

    PubMed

    Guttenberg, Nicholas; Goldenfeld, Nigel

    2006-12-01

    We use analytic and numerical methods to analyze the dynamics of vortices following the quench of a type-II superconductor under the application of an external magnetic field. In three dimensions, in the absence of a field, the spacing between vortices scales with time t with an exponent phi=0.414+/-0.01, in a thin sheet of a superconductor, the scaling exponent is phi=0.294+/-0.01. When an external magnetic field h is applied, the vortices are confined with respect to the length scale of the Abrikosov lattice, leading to a crossover between the power-law scaling length scale and the lattice length scale. From this we suggest a one-parameter scaling of r with h and r that is consistent with numerical data.

  6. 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.

  7. Energy gap structure of layered superconductors

    SciTech Connect

    Liu, S.H.; Klemm, R.A.

    1993-11-01

    We report the energy gap structure and density-of-states (DOS) of a model layered superconductor with one superconducting layer and one normal layer in a unit cell along the c-axis. In the physically interesting parameter range where the interlayer hopping strengths of the quasiparticles are comparable to the critical temperature, the peaks in the DOS curve do not correspond to the order parameter (OP) of the superconducting layer, but depend on the OP and the band dispersion in the c-direction in a complex manner. In contrast to a BCS superconductor, the DOS of layered systems have logarithmic singularities. Our simulated tunneling characteristics bear close resemblance to experimental results.

  8. Transport in ferromagnet/superconductor spin valves

    NASA Astrophysics Data System (ADS)

    Moen, Evan; Valls, Oriol T.

    2017-02-01

    We consider charge transport properties in realistic, fabricable, ferromagnet/superconductor spin valves having a layered structure F1/N /F2/S , where F1 and F2 denote the ferromagnets, S the superconductor, and N the normal-metal spacer usually inserted in actual devices. Our calculation is fully self-consistent, as required to ensure that conservation laws are satisfied. We include the effects of scattering at all the interfaces. We obtain results for the device conductance G , as a function of bias voltage, for all values of the angle ϕ between the magnetizations of the F1 and F2 layers and a range of realistic values for the material and geometrical parameters in the sample. We discuss, in the context of our results for G , the relative influence of all parameters on the spin valve properties. We also study the spin current and the corresponding spin-transfer torque in F1/F2/S structures.

  9. 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

  10. Asymmetric Ferromagnet-Superconductor-Ferromagnet Switch

    SciTech Connect

    Cadden-Zimansky, P.; Bazaliy, Ya.B.; Litvak, L.M.; Jiang, J.S.; Pearson, J.; Gu, J.Y.; You, Chun-Yeol; Beasley, M.R.; Bader, S.D.

    2011-11-04

    In layered ferromagnet-superconductor-ferromagnet F{sub 1} /S/F{sub 2} structures, the critical temperature T{sub c} of the superconductors depends on the magnetic orientation of the ferromagnetic layers F{sub 1} and F{sub 2} relative to each other. So far, the experimentally observed magnitude of change in T{sub c} for structures utilizing weak ferromagnets has been 2 orders of magnitude smaller than is expected from calculations. We theoretically show that such a discrepancy can result from the asymmetry of F/S boundaries, and we test this possibility by performing experiments on structures where F{sub 1} and F{sub 2} are independently varied. Our experimental results indicate that asymmetric boundaries are not the source of the discrepancy. If boundary asymmetry is causing the suppressed magnitude of T{sub c} changes, it may only be possible to detect in structures with thinner ferromagnetic layers.

  11. 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.

  12. 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}.

  13. 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

  14. 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.

  15. Semiconductor/High-Tc-Superconductor Hybrid ICs

    NASA Technical Reports Server (NTRS)

    Burns, Michael J.

    1995-01-01

    Hybrid integrated circuits (ICs) containing both Si-based semiconducting and YBa(2)Cu(3)O(7-x) superconducting circuit elements on sapphire substrates developed. Help to prevent diffusion of Cu from superconductors into semiconductors. These hybrid ICs combine superconducting and semiconducting features unavailable in superconducting or semiconducting circuitry alone. For example, complementary metal oxide/semiconductor (CMOS) readout and memory devices integrated with fast-switching Josephson-junction super-conducting logic devices and zero-resistance interconnections.

  16. Substrates For High-Temperature Superconductors

    NASA Technical Reports Server (NTRS)

    Shlichta, Paul J.

    1988-01-01

    Proposed hot-dipping process prepares materials well suited to serve as substrates for high-temperature superconductors. Makes it possible to produce substrates combining properties needed for given application, such as flexibility, strength, long grains, and <001> crystal orientation. Properties favor growth of superconductive films carrying high current and fabricated in variety of useful shapes. Used in making solar cells, described in "Hot-Dipped Metal Films as Epitaxial Substrates" (NPO-15904).

  17. Protection considerations for force-cooled superconductors

    SciTech Connect

    Dresner, L.

    1985-01-01

    This paper treats some hydrodynamic aspects of protecting magnets wound with force-cooled superconductors, namely, the rise in internal pressure and the forceful expulsion of helium during a quench. Two initial conditions are considered: an entire hydraulic path going normal all at once, and an initially small but nonrecovering normal zone. Formulas are given for the quench pressure and expulsion velocity in both cases and are compared with available experimental data.

  18. Electronic Properties of High-Temperature Superconductors

    DTIC Science & Technology

    1989-08-01

    presented at the International Superconductor Applications Convention, San Francisco, 1989 (unpublished). SJ. %I. Tranquada , S. 2M. Heald, A. R. Moodenbaugh...Lett. 62, 102 (1989). 151 J. M. Tranquada , D. E. Cox, WV. Kunnmann, H. Moudden, G. Shirane, %I. Suenaga, P. Zolliker, D. Vaknin, S. K. Sinha, M. S...Alvarez, A. J. Jacobson, and D. C. Johnston, Phys. Rev. Lett. 60, 136 (1988); J. M. Tranquada , A. H. Nioudden, A. 1. Goldman, P. Zolliker, D. E. Cox, G

  19. Spray-Deposited Superconductor/Polymer Coatings

    NASA Technical Reports Server (NTRS)

    Wise, Stephanie A.; Tran, Sang Q.; Hooker, Matthew W.

    1993-01-01

    Coatings that exhibit the Meissner effect formed at relatively low temperature. High-temperature-superconductor/polymer coatings that exhibit Meissner effect deposited onto components in variety of shapes and materials. Simple, readily available equipment needed in coating process, mean coatings produced economically. Coatings used to keep magnetic fields away from electronic circuits in such cryogenic applications as magnetic resonance imaging and detection of infrared, and in magnetic suspensions to provide levitation and/or damping of vibrations.

  20. 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.

  1. Magnetic impurities in spin-split superconductors

    NASA Astrophysics Data System (ADS)

    van Gerven Oei, W.-V.; Tanasković, D.; Žitko, R.

    2017-02-01

    Hybrid semiconductor-superconductor quantum dot devices are tunable physical realizations of quantum impurity models for a magnetic impurity in a superconducting host. The binding energy of the localized subgap Shiba states is set by the gate voltages and external magnetic field. In this work we discuss the effects of the Zeeman spin splitting, which is generically present both in the quantum dot and in the (thin-film) superconductor. The unequal g factors in semiconductor and superconductor materials result in respective Zeeman splittings of different magnitude. We consider both classical and quantum impurities. In the first case we analytically study the spectral function and the subgap states. The energy of bound states depends on the spin-splitting of the Bogoliubov quasiparticle bands as a simple rigid shift. For the case of collinear magnetization of impurity and host, the Shiba resonance of a given spin polarization remains unperturbed when it overlaps with the branch of the quasiparticle excitations of the opposite spin polarization. In the quantum case, we employ numerical renormalization group calculations to study the effect of the Zeeman field for different values of the g factors of the impurity and of the superconductor. We find that in general the critical magnetic field for the singlet-doublet transition changes nonmonotonically as a function of the superconducting gap, demonstrating the existence of two different transition mechanisms: Zeeman splitting of Shiba states or gap closure due to Zeeman splitting of Bogoliubov states. We also study how in the presence of spin-orbit coupling, modeled as an additional noncollinear component of the magnetic field at the impurity site, the Shiba resonance overlapping with the quasiparticle continuum of the opposite spin gradually broadens and then merges with the continuum.

  2. 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

  3. Holographic disorder driven superconductor-metal transition

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    We implement the effects of disorder on a holographic superconductor by introducing a random chemical potential on the boundary. We demonstrate explicitly that increasing disorder leads to the formation of islands where the superconducting order is enhanced and subsequently to the transition to a metal. We study the behavior of the superfluid density and of the conductivity as a function of the strength of disorder. We find explanations for various marked features in the conductivities in terms of hydrodynamic quasinormal modes of the holographic superconductors. These identifications plus a particular disorder-dependent spectral weight shift in the conductivity point to a signature of the Higgs mode in the context of disordered holographic superconductors. We observe that the behavior of the order parameter close to the transition is not mean-field type as in the clean case; rather we find robust agreement with exp (-A |T -Tc|-ν), with ν =1.03 ±0.02 for this disorder-driven smeared transition.

  4. 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

  5. Characterization of bulk superconductors through EBSD methods

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

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

  6. 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.

  7. 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.

  8. Anomalous critical fields in quantum critical superconductors

    PubMed Central

    Putzke, C.; Walmsley, P.; Fletcher, J. D.; Malone, L.; Vignolles, D.; Proust, C.; Badoux, S.; See, P.; Beere, H. E.; Ritchie, D. A.; Kasahara, S.; Mizukami, Y.; Shibauchi, T.; Matsuda, Y.; Carrington, A.

    2014-01-01

    Fluctuations around an antiferromagnetic quantum critical point (QCP) are believed to lead to unconventional superconductivity and in some cases to high-temperature superconductivity. However, the exact mechanism by which this occurs remains poorly understood. The iron-pnictide superconductor BaFe2(As1−xPx)2 is perhaps the clearest example to date of a high-temperature quantum critical superconductor, and so it is a particularly suitable system to study how the quantum critical fluctuations affect the superconducting state. Here we show that the proximity of the QCP yields unexpected anomalies in the superconducting critical fields. We find that both the lower and upper critical fields do not follow the behaviour, predicted by conventional theory, resulting from the observed mass enhancement near the QCP. Our results imply that the energy of superconducting vortices is enhanced, possibly due to a microscopic mixing of antiferromagnetism and superconductivity, suggesting that a highly unusual vortex state is realized in quantum critical superconductors. PMID:25477044

  9. 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).

  10. 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.

  11. 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.

  12. 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.

  13. McMillan-Rowell like oscillations in a superconductor-InAs/GaSb-superconductor junction

    NASA Astrophysics Data System (ADS)

    Shi, Xiaoyan; Yu, Wenlong; Hawkins, S. D.; Klem, J. F.; Pan, W.

    2015-08-01

    We have fabricated a superconductor (Ta)-InAs/GaSb bilayer-superconductor (Ta) junction device that has a long mean free path and can preserve the wavelike properties of particles (electrons and holes) inside the junction. Differential conductance measurements were carried out at low temperatures in this device, and McMillan-Rowell like oscillations (MROs) were observed. Surprisingly, a much larger Fermi velocity, compared to that from Shubnikov-de Haas oscillations, was obtained from the frequency of MROs. Possible mechanisms are discussed for this discrepancy.

  14. 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.

  15. 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.

  16. 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

    2017-01-05

    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.

  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

    NASA Astrophysics Data System (ADS)

    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 905 cm- 1 are assigned to the antisymmetric stretching vibrations of AsO43 -. The IR bands at 1021, 1086 and 1136 cm- 1 correspond to the possible antisymmetric and symmetric stretching vibrations of SO42 -. The Raman bands at 807, 843 and 875 cm- 1 clearly show that arsenate components in the mineral structure, which are assigned to the symmetric stretching vibrations (ν1) of AsO43 - (807 and 843 cm- 1) and the antisymmetric vibration (ν3) (875 cm- 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.

  18. Deuteron NMR study of dynamics and of coexistence of paraelectric and ferroelectric phases in Rb0.90(ND4)0.10D2AsO4

    NASA Astrophysics Data System (ADS)

    Pinto, Nicholas J.; Howell, Francis L.; Schmidt, V. Hugo

    1993-09-01

    The deuteron glass Rb1-x(ND4)xD2AsO4 (DRADA) is a mixed crystal of RbD2AsO4 (DRDA) and ND4D2AsO4 (DADA). Deuteron nuclear magnetic resonance has been performed on the acid and ammonium deuterons. The crystal studied has an ammonium concentration (x=0.10) that puts it in the coexistence region of the phase diagram. Line-shape measurements of the ammonium deuterons show the coexistence of the ferroelectric (FE) and paraelectric (PE) phases as the temperature is lowered below the ferroelectric-phase-transition temperature Tc. The acid deuteron line shape on the other hand is found to broaden as the temperature is reduced but is unaffected by the ferroelectric transition. Spin-lattice-relaxation measurements have been performed and the activation energies for the relaxation processes have been computed. The relaxation-rate anomaly for acid deuterons in the ferroelectric-transition range indicates a short correlation length for the FE phase in the coexistence region of the phase diagram.

  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. Magnetic excitations in iron chalcogenide superconductors.

    PubMed

    Kotegawa, Hisashi; Fujita, Masaki

    2012-10-01

    Nuclear magnetic resonance and neutron scattering experiments in iron chalcogenide superconductors are reviewed to make a survey of the magnetic excitations in FeSe, FeSe1-x Te x and alkali-metal-doped Ax Fe2-y Se2 (A = K, Rb, Cs, etc). In FeSe, the intimate relationship between the spin fluctuations and superconductivity can be seen universally for the variations in the off-stoichiometry, the Co-substitution and applied pressure. The isovalent compound FeTe has a magnetic ordering with different wave vector from that of other Fe-based magnetic materials. The transition temperature Tc of FeSe increases with Te substitution in FeSe1-x Te x with small x, and decreases in the vicinity of the end member FeTe. The spin fluctuations are drastically modified by the Te substitution. In the vicinity of the end member FeTe, the low-energy part of the spin fluctuation is dominated by the wave vector of the ordered phase of FeTe; however, the reduction of Tc shows that it does not support superconductivity. The presence of same wave vector as that of other Fe-based superconductors in FeSe1-x Te x and the observation of the resonance mode demonstrate that FeSe1-x Te x belongs to the same group as most of other Fe-based superconductors in the entire range of x, where superconductivity is mediated by the spin fluctuations whose wave vector is the same as the nesting vector between the hole pockets and the electron pockets. On the other hand, the spin fluctuations differ for alkali-metal-doped Ax Fe2-y Se2 and FeSe or other Fe-based superconductors in their wave vector and strength in the low-energy part, most likely because of the different Fermi surfaces. The resonance mode with different wave vector suggests that Ax Fe2-y Se2 has an exceptional superconducting symmetry among Fe-based superconductors.

  1. Proceedings of high-T sub c superconductors: Magnetic interactions

    SciTech Connect

    Bennett, L.H.; Flom, Y.; Vezzoli, G.C.

    1989-01-01

    This book contains the proceedings of the 1988 meeting on High-T{sub c} superconductors. Included are the following papers: Mechanism in high-T{sub c} superconductivity, Analysis of microwave surface resistance in high-T{sub c} superconductors, Patents and superconductivity.

  2. 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.

  3. Peltier effect in the mixed state of high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Logvenov, G. Yu.; Ryazanov, V. V.; Ustinov, A. V.; Huebener, R. P.

    1991-04-01

    The Peltier and Seebeck effects in the mixed state of high- Tc superconductors are proportional to the resistivity due to flux motion. Therefore, both effects also show the broadening of the transition regime characteristic for these superconductors. The origin of the Peltier effect is discussed in detail, and the validity of the Thomson relation is confirmed, as expected.

  4. 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…

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Disappearance of nodal gap across the insulator-superconductor transition in a copper-oxide superconductor.

    PubMed

    Peng, Yingying; Meng, Jianqiao; Mou, Daixiang; He, Junfeng; Zhao, Lin; Wu, Yue; Liu, Guodong; Dong, Xiaoli; He, Shaolong; Zhang, Jun; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Lee, T K; Zhou, X J

    2013-01-01

    The parent compound of the copper-oxide high-temperature superconductors is a Mott insulator. Superconductivity is realized by doping an appropriate amount of charge carriers. How a Mott insulator transforms into a superconductor is crucial in understanding the unusual physical properties of high-temperature superconductors and the superconductivity mechanism. Here we report high-resolution angle-resolved photoemission measurement on heavily underdoped Bi₂Sr₂-xLaxCuO(₆+δ) system. The electronic structure of the lightly doped samples exhibit a number of characteristics: existence of an energy gap along the nodal direction, d-wave-like anisotropic energy gap along the underlying Fermi surface, and coexistence of a coherence peak and a broad hump in the photoemission spectra. Our results reveal a clear insulator-superconductor transition at a critical doping level of ~0.10 where the nodal energy gap approaches zero, the three-dimensional antiferromagnetic order disappears, and superconductivity starts to emerge. These observations clearly signal a close connection between the nodal gap, antiferromagnetism and superconductivity.

  11. 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

  12. Exploring intertwined orders in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Tranquada, John M.

    2015-03-01

    The concept of intertwined orders has been introduced to describe the cooperative relationship between antiferromagnetic spin correlations and electron (or hole) pair correlations that develop in copper-oxide superconductors. This contrasts with systems in which, for example, charge-density-wave (CDW) order competes for Fermi surface area with superconductivity. La2-xBaxCuO4 with x=0.125 provides an example in which the ordering of spin stripes coincides with the onset of two-dimensional superconducting correlations. The apparent frustration of the interlayer Josephson coupling has motivated the concept of the pair-density-wave superconductor, a state that theoretical calculations show to be energetically competitive with the uniform d-wave superconductor. Even at x=0.095, where there is robust superconductivity below 32 K in zero field, the coexistence of strong, low-energy, incommensurate spin excitations implies a spatially modulated and intertwined pair wave function. Recent observations of CDW order in YBa2Cu3O6+x and other cuprate families have raised interesting questions regarding the general role of charge modulations and the relation to superconductivity. While there are differences in the doping dependence of the modulation wave vectors in YBa2Cu3O6+x and La2-xBaxCuO4, the maximum ordering strength is peaked at the hole concentration of 1/8 in both cases. There are also possible connections with the quantum oscillations that have been detected about the same hole concentration but at high magnetic fields. Resolving these relationships remains a research challenge.

  13. Exploring intertwined orders in cuprate superconductors

    DOE PAGES

    Tranquada, John M.

    2014-11-22

    In this study, the concept of intertwined orders has been introduced to describe the cooperative relationship between antiferromagnetic spin correlations and electron (or hole) pair correlations that develop in copper-oxide superconductors. This contrasts with systems in which, for example, charge-density-wave (CDW) order competes for Fermi surface area with superconductivity. La2-xBaxCuO4 with x = 0.125 provides an example in which the ordering of spin stripes coincides with the onset of two-dimensional superconducting correlations. The apparent frustration of the interlayer Josephson coupling has motivated the concept of the pair-density-wave superconductor, a state that theoretical calculations show to be energetically competitive with themore » uniform d-wave superconductor. Even at x = 0.095, where there is robust superconductivity below 32 K in zero field, the coexistence of strong, low-energy, incommensurate spin excitations implies a spatially modulated and intertwined pair wave function. Recent observations of CDW order in YBa2Cu3O6+x and other cuprate families have raised interesting questions regarding the general role of charge modulations and the relation to superconductivity. While there are differences in the doping dependence of the modulation wave vectors in YBa2Cu3O6+x and La2-xBaxCuO4, the maximum ordering strength is peaked at the hole concentration of 1/8 in both cases. There are also possible connections with the quantum oscillations that have been detected about the same hole concentration but at high magnetic fields. Resolving these relationships remains a research challenge.« less

  14. 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.

  15. Paramagnetic excited vortex states in superconductors

    NASA Astrophysics Data System (ADS)

    Gomes, Rodolpho Ribeiro; Doria, Mauro M.; Romaguera, Antonio R. de C.

    2016-06-01

    We consider excited vortex states, which are vortex states left inside a superconductor once the external applied magnetic field is switched off and whose energy is lower than of the normal state. We show that this state is paramagnetic and develop here a general method to obtain its Gibbs free energy through conformal mapping. The solution for any number of vortices in any cross-section geometry can be read off from the Schwarz-Christoffel mapping. The method is based on the first-order equations used by Abrikosov to discover vortices.

  16. 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.

  17. Applications of bulk high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Hull, J. R.

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

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. Vortex Core Structure in Multilayered Rashba Superconductors

    NASA Astrophysics Data System (ADS)

    Higashi, Y.; Nagai, Y.; Yoshida, T.; Yanase, Y.

    2014-12-01

    We numerically study the electronic structure of a single vortex in two dimensional superconducting bilayer systems within the range of the mean-field theory. The lack of local inversion symmetry in the system is taken into account through the layer dependent Rashba spin-orbit coupling. The spatial profiles of the pair potential and the local quasiparticle density of states are calculated in the clean spin-singlet superconductor on the basis of the quasiclassical theory. In particular, we discuss the characteristic core structure in the pair-density wave state, which is spatially modulated exotic superconducting phase in a high magnetic field.

  3. Fermi-liquid theory for unconventional superconductors

    SciTech Connect

    Sauls, J.A.

    1994-12-31

    Fermi liquid theory is used to generate the Ginzburg-Landau free energy functionals for unconventional superconductors belonging to various representations. The parameters defining the GL functional depend on Fermi surface anisotropy, impurity scattering and the symmetry class of the pairing interaction. As applications the author considers the basic models for the multiple superconducting phases of UPt{sub 3}. An important prediction of the leading order Fermi liquid theory for the two-dimensional representations of the hexagonal symmetry group is that the zero-field equilibrium state exhibits spontaneously broken time-reversal symmetry.

  4. Edge current in a small chiral superconductor

    NASA Astrophysics Data System (ADS)

    Suzuki, Shu-Ichiro; Asano, Yasuhiro

    2016-10-01

    We discuss a theoretical description of the edge current in a chiral superconductor. On the basis of the quasiclassical Green function formalism, we derive a useful expression of the chiral edge current which enable us to understand how Cooper pairs contribute to the electric current. We will show that the chiral edge current is carried by the combinations of two Cooper pairs belonging to different pairing symmetries. One Cooper pair belongs to the usual even-frequency pairing symmetry class. However, the other belongs to the odd-frequency symmetry class.

  5. 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.

  6. Quantum oscillations in superconductors in magnetic field

    NASA Astrophysics Data System (ADS)

    Gvozdikov, Vladimir M.; Gvozdikova, Mariya V.

    2000-07-01

    The Aharonov-Bohm oscillations (ABO) of the free energy, the critical temperature, and the magnetic susceptibility in a stack of hollow mesoscopic cylinders are calculated. It is shown that sinusoidal (in flux) ABO crosses over to the parabolic Little-Parks oscillations (LPO) when the diameter of cylinders exceeds the coherence length. The exponential temperature behaviour of the magnetic susceptibility is like that found in Ag cylinders with thin Nb coating [Czech. J. Physics 46 (1996) 2317]. The formal analogy between oscillations of the free energy in the Aharonov-Bohm system in question and the de Haas-van Alphen oscillations (dHvAO) in layered superconductors is discussed.

  7. Characterizing long-term radon concentration changes in a geothermal area for correlation with volcanic earthquakes and reservoir temperatures: A case study from Mt. Aso, southwestern Japan

    NASA Astrophysics Data System (ADS)

    Koike, Katsuaki; Yoshinaga, Tohru; Asaue, Hisafumi

    2014-04-01

    The purpose of this study is to characterize in detail the temporal changes in Rn (radon-222) concentration in soil gases near fumaroles and clarify its correlation with volcanic earthquakes and temperatures in two geothermal reservoirs. Mt. Aso crater in southwest Japan, which has two reservoirs on its western side estimated by magnetotelluric survey to be at about 2 km in depth, was selected for this study. For the long-term survey, the α scintillation counter method was used weekly for 12.5 years at the three hot springs within a 2-km range. Rn concentrations were calculated using the CRAS method, a calculation method that considers radioactive equilibrium or nonequilibrium state of the soil gas. Rn concentrations generally showed similar fluctuation patterns among the sites. CRAS was used as a new indicator for evaluating the age of the soil gas. This age corresponds to the elapsed time determined from the generation of Rn based on the measurement of the numbers of atoms of Rn and its daughter 218Po at the start of measurement. In comparing the Rn data with the history of earthquakes in the Aso caldera, volcanic seismicity was identified as a major controlling factor in the sudden increase and decrease in Rn concentration as a function of age. For more precise detections of change, Rn concentrations were measured continuously at one site by pumping soil gas from a borehole and using an ionization chamber over 2.5 years. Five chemical components (He, H2, N2, CH4, and CO2) were then measured by gas chromatography at 1-week intervals. Because Rn concentrations are affected strongly by atmospheric temperatures, the residual components were obtained by subtracting the trend of the components from the original data. Chemical component data were used to estimate the temperature and pressure in the reservoir at the site; temperatures ranged from 229 to 280 °C, (average 265 °C, average pressure 80 MPa). Residual Rn concentrations showed a clear correlation with

  8. Antiferromagnetic order and spin dynamics in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Dai, Pengcheng

    2015-07-01

    High-transition temperature (high-Tc) superconductivity in the iron pnictides or chalcogenides emerges from the suppression of the static antiferromagnetic order in their parent compounds, similar to copper oxide superconductors. This raises a fundamental question concerning the role of magnetism in the superconductivity of these materials. Neutron scattering, a powerful probe to study the magnetic order and spin dynamics, plays an essential role in determining the relationship between magnetism and superconductivity in high-Tc superconductors. The rapid development of modern neutron time-of-flight spectrometers allows a direct determination of the spin dynamical properties of iron-based superconductors throughout the entire Brillouin zone. In this paper, an overview is presented of the neutron scattering results on iron-based superconductors, focusing on the evolution of spin-excitation spectra as a function of electron and hole doping and isoelectronic substitution. Spin dynamical properties of iron-based superconductors are compared with those of copper oxide and heavy fermion superconductors and the common features of spin excitations in these three families of unconventional superconductors and their relationship with superconductivity are discussed.

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

    PubMed

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

    2015-05-13

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

  10. Method for fabrication of high temperature superconductors

    DOEpatents

    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.

  11. Demagnetisation by crossed fields in superconductors

    NASA Astrophysics Data System (ADS)

    Campbell, Archie; Baghdadi, Mehdi; Patel, Anup; Zhou, Difan; Huang, K. Y.; Shi, Yunhua; Coombs, Tim

    2017-03-01

    A study has been made of the decay of the trapped magnetisation in superconductors when exposed to a crossed field. Numerical results have been compared with the theory of Brandt and Mikitik (2002 Phys. Rev. Lett. 89 027002) which solves the problem for a thin strip superconductor. FlexPDE with the A formulation and COMSOL with the H formulation were both used. Simulations of a strip with a cross section aspect ratio of 20 showed good agreement with theory both for the case of a transverse field larger than the transverse penetration field and for one smaller. In the latter case the magnetisation saturates as predicted, however the simulations show a slow decay after many cycles. In the case of stacked YBCO tapes the movement of flux lines is very small and the effects of the reversible motion were investigated. This can decrease the decay initially for very thin decoupled tapes, but cause a steady decay after very large numbers of cycles. Simulations on stacked strips showed that the decay constant increased approximately linearly with the number of strips. When combined with the theory for one tape this can explain the very slow decay observed in previous experiments. Experimental results were qualitatively in agreement with theory and simulations but showed some discrepancies. However there are a number of differences between the experimental situation and theory so good agreement is not expected.

  12. 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

  13. 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.

  14. Kohn anomaly in phonon driven superconductors

    NASA Astrophysics Data System (ADS)

    Das, M. P.; Chaudhury, R.

    2014-08-01

    Anomalies often occur in the physical world. Sometimes quite unexpectedly anomalies may give rise to new insight to an unrecognized phenomenon. In this paper we shall discuss about Kohn anomaly in a conventional phonon-driven superconductor by using a microscopic approach. Recently Aynajian et al.'s experiment showed a striking feature; the energy of phonon at a particular wave-vector is almost exactly equal to twice the energy of the superconducting gap. Although the phonon mechanism of superconductivity is well known for many conventional superconductors, as has been noted by Scalapino, the new experimental results reveal a genuine puzzle. In our recent work we have presented a detailed theoretical analysis with the help of microscopic calculations to unravel this mystery. We probe this aspect of phonon behaviour from the properties of electronic polarizability function in the superconducting phase of a Fermi liquid metal, leading to the appearance of a Kohn singularity. We show the crossover to the standard Kohn anomaly of the normal phase for temperatures above the transition temperature. Our analysis provides a nearly complete explanation of this new experimentally discovered phenomenon. This report is a shorter version of our recent work in JPCM.

  15. 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.

  16. Mesoscopic superconductor as a ballistic quantum switch.

    SciTech Connect

    Melnikov, A. S.; Vinokur, V. M.; Materials Science Division; Russian Academy of Sciences

    2002-01-03

    Several key experiments have revealed a rich variety of vortex structures in mesoscopic superconductors in which only a few quanta of magnetic flux are trapped: these structures are polygon-like vortex 'molecules' and multi-quanta giant vortices. Ginzburg-Landau calculations confirmed second-order phase transitions between the giant vortex states and stable molecule-like configurations. Here we study theoretically the electronic structure and the related phase-coherent transport properties of such mesoscopic superconductor systems. The quasiparticle excitations in the vortices form coherent quantum-mechanical states that offer the possibility of controlling the phase-coherent transport through the sample by changing the number of trapped flux quanta and their configuration. The sample conductance measured in the direction of the applied magnetic field is determined by the transparency of multi-vortex configurations, which form a set of quantum channels. The transmission coefficient for each channel is controlled by multiple Andreev reflections within the vortex cores and at the sample edge. These interference phenomena result in a stepwise behaviour of the conductance as a function of the applied magnetic field, and we propose to exploit this effect to realize a vortex-based quantum switch where the magnetic field plays the role of the gate voltage.

  17. Fluctuations and disorder in high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Blatter, Gianni; Ivlev, Boris

    1994-02-01

    The special material parameters of the oxide superconductors lead to a dramatic increase of the importance of thermal and quantum fluctuations. The latter can be quantified by the Ginzburg number Gi = {[T c/ }/{H 2c(0)ɛξ 3(0)] 2/2 } and the quantum resistance Q u = {(e 2/ }/{h̵}) {[ϱN/}/{ɛξ(0)]}, where H c(0), ξ(0), and ϱ N denote the thermodynamic critical field, the planar coherence length (both linearly extrapolated to zero), and the planar normal resistivity. ɛ 2 = {m/}/{M} < 1 is the anisotropy parameter. In the high Tc's (specifically for YBCO) we have Gi ≅ 10 -2 and Qu ≅ 1 and thus these parameters are by orders of magnitude larger than in conventional low- Tc superconductors. The large fluctuations lead to the melting of the vortex lattice well below the upper critical field line. The inclusion of quenched disorder as parametrized by the critical current density ratio jc/ jo drastically changes the dynamic behavior of the vortex system ( jc and jo denote the depinning and depairing current densities). We discuss the equilibrium statistical mechanics (vortex lattice melting) and the dynamic behavior (creep) of the vortex system with a particular emphasis on the role of quantum fluctuations.

  18. Magnetic Excitations from Stripes in Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Tranquada, J. M.; Woo, H.; Perring, T. G.; Goka, H.; Gu, G. D.; Xu, G.; Fujita, M.; Yamada, K.

    2004-03-01

    While it is generally believed that antiferromagnetic spin excitations play a significant role in the pairing mechanism of copper-oxide superconductors [1], the nature of the magnetic excitations themselves remains a matter of controversy. Recent measurements of the dispersion of spin excitations in superconducting YBa_2Cu_3O_6+x (YBCO) have attracted much attention. Here we present the results of comprehensive inelastic neutron scattering measurements of the momentum- and energy-dependent spectra of the magnetic fluctuations in La_0.875Ba_0.125CuO_4, which exhibits inhomogeneous, charge-stripe order. We will also point out universalities and differences in the magnetic excitation spectra compared to related charge-stripe ordered compounds and high-temperature superconductors, including La_2-xSr_xNiO4 and YBCO. JMT, HW, GDG and GX are supported by U.S. Department of Energy contract # DE-AC02-98CH1088 [1] J. Orenstein and A. J. Millis, Science 288, 468 (2000).

  19. Thermal fluctuations in superconductor/ferromagnet nanostripes

    NASA Astrophysics Data System (ADS)

    Nasti, U.; Parlato, L.; Ejrnaes, M.; Cristiano, R.; Taino, T.; Myoren, H.; Sobolewski, Roman; Pepe, G.

    2015-07-01

    Thermal fluctuations in hybrid superconductor/ferromagnetic NbN /NiCu bilayers, as well as in pure superconducting NbN, two-dimensional (2D), nanostripes, have been investigated in order to understand the origin of dark counts in superconducting nanostripes when operated as single-photon detectors in the temperature range from 4.2 to 8 K . In 2D superconductors, the dynamics of vortex motion play a significant role in the formation of a transient normal state, leading to dark-count events in current-biased nanostripes. By introducing a weak ferromagnetic overlayer on top of pure NbN, we managed to control the vortex dynamics, which subsequently enabled us to differentiate between several proposed theoretical models. In particular, a 6 -nm-thick NiCu film grown on top of 8 -nm-thick NbN nanostripes led to an enhanced critical current density in the resulting nanostructure, as well as significantly lowered fluctuation rates, as compared to pure NbN structures, leading to reduced dark counts. The enhancement of pinning in NbN /NiCu bilayers provided evidence that thermal excitations of single vortices (vortex hopping) near the edge of a 2D nanostripe were the dominant mechanism of the observed dark-count transients. On the other hand, in pure NbN the leading source of thermal fluctuations was the current-assisted thermal unbinding of vortex-antivortex pairs.

  20. Effects of chiral helimagnets on vortex states in a superconductor

    NASA Astrophysics Data System (ADS)

    Fukui, Saoto; Kato, Masaru; Togawa, Yoshihiko

    2016-12-01

    We have investigated vortex states in chiral helimagnet/superconductor bilayer systems under an applied external magnetic field {H}{appl}, using the Ginzburg-Landau equations. Effect of the chiral helimagnet on the superconductor is taken as a magnetic field {H}{CHM}, which is perpendicular to the superconductor and oscillates spatially. For {H}{appl}=0 and weak {H}{CHM}, there appear pairs of up- and down-vortices. Increasing {H}{appl}, down-vortices gradually disappear, and the number of up-vortices increases in the large magnetic field region. Then, up-vortices form parallel, triangular, or square structures.

  1. Microwave surface resistance of superconductors with grain boundaries

    NASA Astrophysics Data System (ADS)

    Mawatari, Yasunori

    2005-02-01

    Microwave-field distribution, dissipation, and surface impedance are theoretically investigated for superconductors with laminar grain boundaries (GBs). In the present theory we adopt the two-fluid model for intragrain transport current in the grains, and the Josephson-junction model for intergrain tunneling current across GBs. Results show that the surface resistance Rs nonmonotonically depends on the critical current density Jcj at GB junctions, and Rs for superconductors with GBs can be smaller than the surface resistance Rs0 for ideal homogeneous superconductors without GBs.

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

    NASA Technical Reports Server (NTRS)

    Brown, Beth A.

    1992-01-01

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

  3. 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.

  4. Spectroscopy of magnetic excitations in magnetic superconductors using vortex motion.

    PubMed

    Bulaevskii, L N; Hruska, M; Maley, M P

    2005-11-11

    In magnetic superconductors a moving vortex lattice is accompanied by an ac magnetic field which leads to the generation of spin waves. At resonance conditions the dynamics of vortices in magnetic superconductors changes drastically, resulting in strong peaks in the dc I-V characteristics at voltages at which the washboard frequency of the vortex lattice matches the spin wave frequency omegaS(g), where g are the reciprocal vortex lattice vectors. We show that if the washboard frequency lies above the magnetic gap, measurement of the I-V characteristics provides a new method to obtain information on the spectrum of magnetic excitations in borocarbides and cuprate layered magnetic superconductors.

  5. Observability of surface currents in p-wave superconductors

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  6. 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.

  7. 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.

  8. Electric field induced by vortex transport in percolation superconductors

    NASA Astrophysics Data System (ADS)

    Kuz'min, Yu. I.

    2016-10-01

    The influence of fractal normal phase clusters on the electric field induced by the flow and creep of the magnetic flux in percolation superconductors has been considered. The current-voltage characteristics of such superconductors with allowance for the influence of the fractal dimension of cluster boundaries and the pinning barrier height have been obtained. The vortex dynamics in percolation superconductors with a fractal cluster structure in a viscous flow of the magnetic flux, the Anderson-Kim creep, and the collective flux creep has been analyzed. It has been discovered that the fractality of normal phase clusters reduces the electric field arising in the initial stage of the resistive transition.

  9. 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.

  10. Andreev Reflection Study of the Superconductor Mo3Sb7

    NASA Astrophysics Data System (ADS)

    Dmitriev, V. M.; Rybaltchenko, L. F.; Khristenko, E. V.; Ishchenko, L. A.; Bukowski, Z.; Troć, R.

    2008-07-01

    The point-contact Andreev-reflection measurements on the new paramagnetic superconductor Mo3Sb7 were carried out. It was found that the order parameter Δ is strongly anisotropic varying over a very wide range depending on the contact orientation when the maximum Δmax exceeds at least 40 times the minimum Δmin in spite of the invariable Tc that cannot be typical of conventional superconductors. For these and other reasons we suggest that Mo3Sb7 is not a trivial BCS (s-wave) superconductor but rather has some unconventional pairing symmetry.

  11. Effects of electron irradiation on high temperature superconductors and contacts to high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Caton, Randall

    1988-01-01

    The discovery of a new class of ceramic superconductors with transition temperatures above liquid nitrogen has opened the doors for exciting space applications. Energy storage, pointing maneuvers, magnetic shielding, and sensitive detection of electromagnetic radiation are some of the longer term possible applications. One near term application involves low electrical resistance, high thermal resistance connections between a detector operating at approximatly or equal to 4 and the electronics operating at approximatly or equal to 77 K. The new high temperature superconductors could accomplish this providing the necessary electrical connections to the ground plane while isolating the system thermally, thus prolonging the life of the mission. With such possibilities it is clearly of value to study the effects of radiation that would be experienced during a typical space mission. In this work we focused specifically on the effects of the electron radiation environment.

  12. Observation of giant supercurrent states in a superconductor-InAs/GaSb-superconductor junction

    NASA Astrophysics Data System (ADS)

    Shi, Xiaoyan; Yu, Wenlong; Jiang, Zhigang; Bernevig, B. Andrei; Pan, W.; Hawkins, S. D.; Klem, J. F.

    2015-03-01

    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. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  13. 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.

  14. 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.

  15. Experiments on non-equilibrium superconductor-normal metal-superconductor Josephson junctions

    NASA Astrophysics Data System (ADS)

    Crosser, Michael S.

    By controlling the distribution function within the normal metal of a superconductor/normal metal/superconductor (SNS) Josephson junction, one can reverse the supercurrent-phase relation in the normal wire, creating a pi-junction. This manipulation is done by injecting normal quasiparticle current into the wire, via one or more leads attached at the middle of the junction. Two experiments evolve from this concept. First, in a sample of four reservoirs, two normal and two superconducting, all connected by a wire cross of normal metal, one may inject current either antisymmetrically (AS) or symmetrically (S). In the AS case, current is injected into one normal lead and extracted from the other, creating normal current flow that does not interact with the supercurrent except at the junction. In the S case, current is injected into both normal leads and extracted from the superconductors. Theory predicts that, in the absence of electron energy relaxation in the normal part of the junction, these two situations should result in identical behavior of the Josephson junction. However, due to Joule heating, the S case shows a slightly larger maximum pi-current than the AS case. The second experiment considers a more subtle effect resulting from normal current being injected symmetrically into a SNS Josephson junction. One side of the SNS junction has both normal current and supercurrent flowing in the same direction while the other side has opposing current flows. This situation creates an effective energy gradient across the SNS junction that can appear in the distribution function of the normal wire. Using superconductor/insulator/normal metal tunnelling spectroscopy, it is possible to extract these changes to the distribution function.

  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. Large Tunable Thermophase in Superconductor – Quantum Dot – Superconductor Josephson Junctions

    PubMed Central

    Kleeorin, Yaakov; Meir, Yigal; Giazotto, Francesco; Dubi, Yonatan

    2016-01-01

    In spite of extended efforts, detecting thermoelectric effects in superconductors has proven to be a challenging task, due to the inherent superconducting particle-hole symmetry. Here we present a theoretical study of an experimentally attainable Superconductor – Quantum Dot – Superconductor (SC-QD-SC) Josephson Junction. Using Keldysh Green’s functions we derive the exact thermo-phase and thermal response of the junction, and demonstrate that such a junction has highly tunable thermoelectric properties and a significant thermal response. The origin of these effects is the QD energy level placed between the SCs, which breaks particle-hole symmetry in a gradual manner, allowing, in the presence of a temperature gradient, for gate controlled appearance of a superconducting thermo-phase. This thermo-phase increases up to a maximal value of ±π/2 after which thermovoltage is expected to develop. Our calculations are performed in realistic parameter regimes, and we suggest an experimental setup which could be used to verify our predictions. PMID:27734919

  18. 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.

  19. 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.

  20. 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

  1. High-temperature superconductor applications development at Argonne National Laboratory

    NASA Astrophysics Data System (ADS)

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

    1992-02-01

    Developments at Argonne National Laboratory of near and intermediate term applications using high-temperature superconductors are discussed. Near-term applications of liquid-nitrogen depth sensors, current leads, and magnetic bearings are discussed in detail.

  2. Proceedings of the physics and chemistry of oxide superconductors

    SciTech Connect

    Iye, Y.; Yasuoka, H.

    1992-01-01

    This book contains the proceedings of the physics and chemistry of oxide superconductors. Topics covered include: materials; electronic states; spectroscopy; lattice properties; pressure effects; carrier dynamics; doping effects; spin dynamics; magnetism; strong correlation, and superconducting properties.

  3. 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)

  4. High-temperature superconductor applications development at Argonne National Laboratory

    SciTech Connect

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

    1992-02-09

    Developments at Argonne National Laboratory of near and intermediate term applications using high-temperature superconductors are discussed. Near-term applications of liquid-nitrogen depth sensors, current leads, and magnetic bearings are discussed in detail.

  5. 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.

  6. Chiral CP2 skyrmions in three-band superconductors

    NASA Astrophysics Data System (ADS)

    Garaud, Julien; Carlström, Johan; Babaev, Egor; Speight, Martin

    2013-01-01

    It is shown that under certain conditions, three-component superconductors (and, in particular, three-band systems) allow stable topological defects different from vortices. We demonstrate the existence of these excitations, characterized by a CP2 topological invariant, in models for three-component superconductors with broken time-reversal symmetry. We term these topological defects “chiral GL(3) skyrmions,” where “chiral” refers to the fact that due to broken time-reversal symmetry, these defects come in inequivalent left- and right-handed versions. In certain cases, these objects are energetically cheaper than vortices and should be induced by an applied magnetic field. In other situations, these skyrmions are metastable states, which can be produced by a quench. Observation of these defects can signal broken time-reversal symmetry in three-band superconductors or in Josephson-coupled bilayers of s± and s-wave superconductors.

  7. Broad-Based Search for New and Practical Superconductors

    DTIC Science & Technology

    2014-10-31

    grant. Many new superconductors were discovered, most with transition temperatures (Tc) below 10K. One noteworthy discovery was the superconductivity ...Collaboration with the Smithsonian Museum was established to search for superconductivity in their collection of over 300,000 minerals. To date, about 50...compounds have been measured with one superconductor (Tc ~4K) found at high pressure. Superconductivity was found to be enhanced in a nanocrystalline

  8. 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.

  9. 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.

  10. Holographic superconductor developed in BTZ black hole background with backreactions

    NASA Astrophysics Data System (ADS)

    Liu, Yunqi; Pan, Qiyuan; Wang, Bin

    2011-08-01

    We develop a holographic superconductor in BTZ black hole background with backreactions. We investigate the influence of the backreaction on the condensation of the scalar hair and the dynamics of perturbation in the background spacetime. When the Breitenlohner-Freedman bound is approached, we argue that only one of two possible operators can reflect the real property of the condensation in the holographic superconductor. This argument is supported by the investigation in dynamics.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Surface superconductivity of short coherence length superconductors

    NASA Astrophysics Data System (ADS)

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

    1994-12-01

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

  16. Surface superconductivity of short coherence length superconductors

    NASA Astrophysics Data System (ADS)

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

    1994-12-01

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

  17. Correlations between Majorana Fermions Through a Superconductor

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  18. Theory of surface spectroscopy for noncentrosymmetric superconductors

    NASA Astrophysics Data System (ADS)

    Wennerdal, Niclas; Eschrig, Matthias

    2017-01-01

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

  19. Underdoped superconducting cuprates as topological superconductors

    NASA Astrophysics Data System (ADS)

    Lu, Yuan-Ming; Xiang, Tao; Lee, Dung-Hai

    2014-09-01

    Superconductivity in copper oxide (cuprate) high-transition-temperature superconductors follows from the chemical doping of an antiferromagnetic insulating state. The consensus that the wavefunction of the superconducting carrier, the Cooper pair, has dx2-y2 symmetry has long been reached. This pairing symmetry implies the existence of nodes in the superconducting energy gap. Recently, a series of angle-resolved photoemission spectroscopy experiments have revealed that deeply underdoped cuprates exhibit a particle-hole symmetric superconducting-like energy gap at the momentum-space locations where the dx2-y2 gap nodes are expected. Here we discuss the possibility that this phenomenon is caused by a fully gapped topological superconducting state that coexists with the antiferromagnetic order. If experimentally confirmed, this result will completely change our view of how exactly the high-temperature superconductivity state evolves from the insulating antiferromagnet.

  20. 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.

  1. 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.

  2. 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.

  3. Raman Scattering in HIGH-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Thomsen, Christian; Cardona, Manuel

    The following sections are included: * INTRODUCTION * Theory * Light scattering by phonons * Electronic scattering * Instrumentation * VIBRATIONAL ANALYSIS AND LATTICE DYNAMICS * Optical Modes of RBa2Cu3O7-δ * Symmetry analysis of the ěc{k} = 0 modes * Lattice dynamical calculation for RBa2Cu3O7 and RBa2Cu3O6 * The Bismuth and Thallium Compounds * The Zurich Superconductors * EXPERIMENTAL RESULTS ON RBa2Cu3O7-δ * Raman Scattering by Phonons * Single crystals of YBa2Cu3O7-δ * Ceramic materials, impurity phases, and thin films * Oxygen deficiency * Isotope effect * Electronic scattering and the gap problem * Scattering by magnons * Bismuth and CuO2-Based Materials: Single-Crystal Spectra and Phonon Assignments * Thallium and CuO2 Based Materials * The Zurich Oxides * BRIEF COMPARISON WITH IR DATA * CONSEQUENCES CONCERNING THE MECHANISM OF HIGH-TC SUPERCONDUCTIVITY AND CONCLUSIONS * ACKNOWLEDGEMENTS * REFERENCES

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. ''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.

  9. Fermi Surface of the Most Dilute Superconductor

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  10. Searching for the Genes of Unconventional High Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Hu, Jiangping

    In the past, both curates and iron-based superconductors were discovered accidentally. Lacking of successful predictions on new high Tc materials is one of major obstacles to reach a consensus on the high Tc mechanism. In this talk, we discuss two emergent principles, which are called as the correspondence principle and the selective magnetic pairing rule, to unify the understanding of both cuprates and iron-based superconductors. These two principles provide an unified explanation why the d-wave pairing symmetry and the s-wave pairing symmetry are robust respectively in cuprates and iron-based superconductors. In the meanwhile, the above two principles explain the rareness of unconventional high Tc superconductivity, identify necessary electronic environments required for high Tc superconductivity and finally serve as direct guiding rules to search new high Tc materials. We predict that the third family of unconventional high Tc superconductors exist in the compounds which carry two dimensional hexagonal lattices formed by cation-anion trigonal bipyramidal complexes with a d filling configuration on the cation ions. Their superconducting states are expected to be dominated by the d+id pairing symmetry and their maximum Tc should be higher than those of iron-based superconductors. Verifying the prediction can convincingly establish the high Tc superconducting mechanism and pave a way to design new high Tc superconductors

  11. Simulators of Superconductor Critical Current: Design, Characteristics, and Applications

    PubMed Central

    Goodrich, L. F.; Srivastava, A. N.; Stauffer, T. C.

    1991-01-01

    The superconductor simulator is an electronic circuit that emulates the extremely nonlinear voltage-current characteristic (the basis of a critical-current measurement) of a superconductor along with its other major electrical properties. Three different types of simulators have been constructed: the passive, active, and hybrid simulator. The passive simulator has the fewest circuit components and offers the least amount of versatility, while the active and hybrid simulators offer more versatility and consequently have more components. Design, characteristics, and applications of the superconductor simulator along with a summary of features are presented. These simulators are high precision instruments, and are thus useful for establishing the integrity of part of a superconductor measurement system. They are potentially useful for testing the measurement method and data acquisition and analysis routines. The 50 A simulator provides critical-current precision of 0.1% at a 1 μV signal. This is significantly higher than the precision of a superconducting standard reference material. The superconductor simulator could significantly benefit superconductor measurement applications that require high-precision quality assurance. PMID:28184143

  12. High Temperature Superconductors for the Electric Power Grid

    NASA Astrophysics Data System (ADS)

    Malozemoff, Alexis P.

    2011-03-01

    High Temperature Superconductor power equipment is positioned to play a key role in addressing our national and global energy challenges. While the most obvious benefit is efficiency by using the superconductor's lossless current flow to cut the 10% power lost in the grid, other benefits are likely to be even more impactful. These benefits arise from the high current density of superconductor wire which enables design of highly power-dense and compact equipment including high capacity cables and rotating machinery -- generators and motors. Vast and dense urban areas are becoming home to an increasingly large proportion of world population, and high capacity ac superconductor cables offer a non-interfering and easily installed solution to increasing urban power needs. Longer term, the ultra-low loss of long-distance dc superconductor cables offers strengthened links and power sharing across wide geographical areas. Compact superconductor generators are the key to high power off-shore wind turbines, a major source of renewable energy. Some of these applications have reached a sophisticated level of demonstration, initiating commercial use.

  13. 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.

  14. K1+2x Ni1-x Fe2(AsO4)3 (x = 0,125): un nouvel arséniate à structure de type α-CrPO4.

    PubMed

    Ben Smail, Ridha; Zid, Mohamed Faouzi

    2017-02-01

    A new arsenate K1+2x Ni1-x Fe2(AsO4)3 (x = 1/8) {potassium nickel diiron(III) tris-[arsenate(V)]} was synthesized using a flux method and its crystal structure was determined from single-crystal X-ray diffraction data. This material was also characterized by qualitative energy dispersive X-ray spectroscopy (EDS) analysis. The crystal structure belongs to the α-CrPO4-structure type, space group Imma. It consists of a three-dimensional-framework built up from FeO6 and Ni0.875□1.25O6-octa-hedra and AsO4-tetra-hedra that are sharing corners and/or edges, generating tunnels running along the [010] and [001] directions in which the potassium cations are located. The proposed structural model was validated by bond-valence-sum calculations, charge-distribution (CHARDI) and Madelung energy analyses.

  15. K1+2xNi1−xFe2(AsO4)3 (x = 0,125): un nouvel arséniate à structure de type α-CrPO4

    PubMed Central

    Zid, Mohamed Faouzi

    2017-01-01

    A new arsenate K1+2xNi1−xFe2(AsO4)3 (x = 1/8) {potassium nickel diiron(III) tris­[arsenate(V)]} was synthesized using a flux method and its crystal structure was determined from single-crystal X-ray diffraction data. This material was also characterized by qualitative energy dispersive X-ray spectroscopy (EDS) analysis. The crystal structure belongs to the α-CrPO4-structure type, space group Imma. It consists of a three-dimensional-framework built up from FeO6 and Ni0.875□1.25O6-octa­hedra and AsO4-tetra­hedra that are sharing corners and/or edges, generating tunnels running along the [010] and [001] directions in which the potassium cations are located. The proposed structural model was validated by bond-valence-sum calculations, charge-distribution (CHARDI) and Madelung energy analyses. PMID:28217351

  16. Spectroscopic characterization and solubility investigation on the effects of As(V) on mineral structure tooeleite (Fe6(AsO3)4SO4(OH)4·H2O)

    NASA Astrophysics Data System (ADS)

    Liu, Jing; Deng, Shiming; Zhao, Fenghua; Cheng, Hongfei; Frost, Ray L.

    2015-01-01

    Tooeleite is an unique ferric arsenite sulfate mineral, which has the potential significance of directly fixing As(III) as mineral trap. The tooeleite and various precipitates were hydrothermally synthesized under the different of initial As(III)/As(V) molar ratios and characterized by XRD, FTIR, XPS and SEM. The crystallinity of tooeleite decreases with the amount of As(V). The precipitate is free of any crystalline tooeleite at the level of that XRD could detect when the ratio of As(III)/As(V) of 7:3 and more. The characteristic bands of tooeleite are observed in 772, 340, 696 and 304 cm-1, which are assigned to the ν1, ν2, ν3 and ν4 vibrations of AsO33-. These intensities of bands gradually decreases with the presence of As(V) and its increasing. An obviously wide band is observed in 830 cm-1, which is the ν1 vibration of AsO4. The result of XPS reveals that the binding energies of As3d increase from 44.0 eV to 45.5 eV, which indicates that the amount of As(V) in the precipitates increases. The concentrations of arsenic released of these precipitates are 350-650 mg/L. The stability of tooeleite decreases by comparison when the presence of coexisting As(V) ions.

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

    NASA Astrophysics Data System (ADS)

    Leng, Xiang

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

  18. 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.

  19. 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.

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

    SciTech Connect

    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.

  1. Nonlinear electrodynamics of high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Zutic, Igor

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

  2. Structure, stoichiometry and spectroscopy of oxide superconductors

    NASA Astrophysics Data System (ADS)

    Rao, C. N. R.

    In the new oxide superconductors, structure and oxygen stoichiometry play the most crucial role. Thus, all the high-temperature oxide superconductors are orthorhombic perovskites with low-dimensional features. Oxygen stoichiometry in YBa2Cu3O7-δ has an important bearing on the structure as well as superconductivity. This is equally true in the La3-xBa3+xCu 6O14+δ system of which only the 123 oxide (x = 1) with the orthorhombic structure shows high Tc. Orthorhombicity though not essential, is generally found ; it is necessary for the formation of twins. The nature of oxygen and copper in the cuprates has been examined by electron spectroscopy. Copper in these cuprates is only in 1 + and 2 + states. It seems likely that oxygen holes are responsible for superconductivity of the cuprates as well as Ba(Bi, Pb)O3. High Tc superconductivity is also found in oxides of the Bi-(Ca, Sr)-Cu-O and related oxides possessing Cu-O sheets. Dans les nouveaux oxydes supraconducteurs, la structure et la stoechiométrie de l'oxygène jouent un rôle absolument crucial. Ainsi, tous les oxydes supraconducteurs à haute température critique sont des pérovskites orthorhombiques possédant des propriétés de basse dimensionnalité. La stoechiométrie de l'oxygène dans YBa2Cu3O7- δ a une influence importante tant sur la structure que sur la supraconductibilité. Ceci est également valable pour les composés du type La3 -xBa3 + xCu 6O14 + δ parmi lesquels seul l'oxyde 123 (x = 1) à structure orthorhombique présente un grand T. Bien que ce ne soit pas essentiel, cette orthorhombicité est fréquente ; elle est nécessaire à la formation de macles. La nature de l'oxygène et du cuivre a été observée par spectroscopie électronique... Dans ces cuprates, le cuivre est dans les seuls états de valence + 1 et + 2. Vraisemblablement, les trous logés sur l'oxygène sont responsables de la supraconductibilité des cuprates comme de Ba(Bi, Pb)O3. La supraconductibilité existe aussi

  3. Vortices in high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Blatter, G.; Feigel'Man, M. V.; Geshkenbein, V. B.; Larkin, A. I.; Vinokur, V. M.

    1994-10-01

    With the high-temperature superconductors a qualitatively new regime in the phenomenology of type-II superconductivity can be accessed. The key elements governing the statistical mechanics and the dynamics of the vortex system are (dynamic) thermal and quantum fluctuations and (static) quenched disorder. The importance of these three sources of disorder can be quantified by the Ginzburg number Gi=(TcH2cɛξ3)22, the quantum resistance Qu=(e2ℏ)(ρnɛξ), and the critical current-density ratio jcjo, with jc and jo denoting the depinning and depairing current densities, respectively (ρn is the normal-state resistivity and ɛ2=mM<1 denotes the anisotropy parameter). The material parameters of the oxides conspire to produce a large Ginzburg number Gi~10-2 and a large quantum resistance Qu~10-1, values which are by orders of magnitude larger than in conventional superconductors, leading to interesting effects such as the melting of the vortex lattice, the creation of new vortex-liquid phases, and the appearance of macroscopic quantum phenomena. Introducing quenched disorder into the system turns the Abrikosov lattice into a vortex glass, whereas the vortex liquid remains a liquid. The terms "glass" and "liquid" are defined in a dynamic sense, with a sublinear response ρ=∂E∂j|j-->0 characterizing the truly superconducting vortex glass and a finite resistivity ρ(j-->0)>0 being the signature of the liquid phase. The smallness of jcjo allows one to discuss the influence of quenched disorder in terms of the weak collective pinning theory. Supplementing the traditional theory of weak collective pinning to take into account thermal and quantum fluctuations, as well as the new scaling concepts for elastic media subject to a random potential, this modern version of the weak collective pinning theory consistently accounts for a large number of novel phenomena, such as the broad resistive transition, thermally assisted flux flow, giant and quantum creep, and the glassiness

  4. 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.

  5. (HBCU) Doped Graphene and Graphite as a Potential High Temperature Superconductor

    DTIC Science & Technology

    2013-07-23

    AFRL-OSR-VA-TR-2013-0420 (HBCU) DOPED GRAPHENE AND GRAPHITE AS A POTENTIAL HIGH TEMPERATURE SUPERCONDUCTOR Grover L. Larkins Jr...POTENTIAL HIGH TEMPERATURE SUPERCONDUCTOR Grover Larkins larkinsg@fiu.edu Florida International University Miami, Fl. 33199...onset temperatures in un- damaged doped graphite existed. This work was published in Superconductor Science and Technology as a rapid communication

  6. Anatomy of a Periodically Driven p-Wave Superconductor

    NASA Astrophysics Data System (ADS)

    Zhao, Erhai

    2016-10-01

    The topological properties of periodically driven many-body systems often have no static analogs and defy a simple description based on the effective Hamiltonian. To explore the emergent edge modes in driven p-wave superconductors in two dimensions, we analysed a toy model of Kitaev chains (one-dimensional spinless p-wave superconductors with Majorana edge states) coupled by time-periodic hopping. We showed that with proper driving, the coupled Kitaev chains can turn into a fully gapped superconductor, which is analogous to the px+ipy state but has two, rather than one, chiral edge modes. A different driving protocol turns it into a gapless superconductor with isolated point nodes and completely flat edge states at quasienergy ω=0 or π/T, with T as the driving period. The time evolution operator U(kx, ky, t) of the toy model is computed exactly to yield the phase bands. And the "topological singularities" of the phase bands are exhausted and compared to those of a periodically driven Hofstadter model, which features counter-propagating chiral edge modes. These examples demonstrate the unique edge states in driven superconducting systems and suggest driving as a potentially fruitful route to engineer new topological superconductors.

  7. 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.

  8. 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.

  9. Magnetoanisotropic Josephson effect due to interfacial spin-orbit fields in superconductor/ferromagnet/superconductor junctions

    NASA Astrophysics Data System (ADS)

    Costa, Andreas; Högl, Petra; Fabian, Jaroslav

    2017-01-01

    We study theoretically the effects of interfacial Rashba and Dresselhaus spin-orbit coupling in superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions—with allowing for tunneling barriers between the ferromagnetic and superconducting layers—by solving the Bogoljubov-de Gennes equation for realistic heterostructures and applying the Furusaki-Tsukada technique to calculate the electric current at a finite temperature. The presence of spin-orbit couplings leads to out-of-plane and in-plane magnetoanisotropies of the Josephson current, which are giant in comparison to current magnetoanisotropies in similar normal-state ferromagnet/normal metal (F/N) junctions. Especially huge anisotropies appear in the vicinity of 0 -π transitions, caused by the exchange-split bands in the ferromagnetic metal layer. We also show that the direction of the Josephson critical current can be controlled (inducing 0 -π transitions) by the strength of the spin-orbit coupling and, more crucial, by the orientation of the magnetization. Such a control can bring new functionalities into Josephson junction devices.

  10. The improved damping of superconductor bearings for 35 kWh superconductor flywheel energy storage system

    NASA Astrophysics Data System (ADS)

    Han, Y. H.; Park, B. J.; Jung, S. Y.; Han, S. C.; Lee, W. R.; Bae, Y. C.

    2013-02-01

    A 35 kWh Superconductor Flywheel Energy Storage system (SFES) using hybrid bearing sets, which is composed of a high temperature superconductor (HTS) bearing and an active magnet damper (AMD), has been developed at KEPCO Research Institute (KEPRI). Damping is a source of energy loss but necessary for the stability of the flywheel system. We found that the damping of HTS bearings can be improved by thermal insulating bolts, which play a role of passive type external damper. To investigate the source of the increased damping, damping coefficients were measured with HTS bearings using insulating bolts made of three kinds of polymer materials. The damping coefficient was raised over 3000 N s/m in the case of PEEK bolts. The value was almost a quarter of the AMD. In this study, thermoelastic and Coulomb friction damping mechanisms are discussed. The main damping mechanism was the thermoelastic damping of the bolts themselves. And interfacial gap between the insulating bolt and metal chamber, which increased during the cooling process, was considered to be the cause of the anisotropic damping coefficients. Finally, the effects of the HTS bearings on the first critical speed are shown.

  11. Antiferromagnetic phase diagram of the cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Nunes, L. H. C. M.; Teixeira, A. W.; Marino, E. C.

    2017-02-01

    Taking the spin-fermion model as the starting point for describing the cuprate superconductors, we obtain an effective nonlinear sigma-field hamiltonian, which takes into account the effect of doping in the system. We obtain an expression for the spin-wave velocity as a function of the chemical potential. For appropriate values of the parameters we determine the antiferromagnetic phase diagram for the YBa2Cu3O6+x compound as a function of the dopant concentration in good agreement with the experimental data. Furthermore, our approach provides a unified description for the phase diagrams of the hole-doped and the electron doped compounds, which is consistent with the remarkable similarity between the phase diagrams of these compounds, since we have obtained the suppression of the antiferromagnetic phase as the modulus of the chemical potential increases. The aforementioned result then follows by considering positive values of the chemical potential related to the addition of holes to the system, while negative values correspond to the addition of electrons.

  12. Artificially engineered superlattices of pnictide superconductors.

    PubMed

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

    2013-05-01

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

  13. 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.

  14. Terahertz Generation & Vortex Motion Control in Superconductors

    NASA Astrophysics Data System (ADS)

    Nori, Franco

    2005-03-01

    A grand challenge is to controllably generate electromagnetic waves in layered superconducting compounds because of its Terahertz frequency range. We propose [1] four experimentally realizable devices for generating continuous and pulsed THz radiation in a controllable frequency range. We also describe [2-4] several novel devices for controlling the motion of vortices in superconductors, including a reversible rectifier made of a magnetic-superconducting hybrid structure [4]. Finally, we summarize a study [5] of the friction force felt by moving vortices. 1) S. Savel'ev, V. Yampol'skii, A. Rakhmanov, F. Nori, Tunable Terahertz radiation from Josephson vortices, preprint 2) S. Savel'ev and F. Nori, Experimentally realizable devices for controlling the motion of magnetic flux quanta, Nature Mat. 1, 179 (2002) 3) S. Savel'ev, F. Marchesoni, F. Nori, Manipulating small particles, PRL 92, 160602 (2004); B. Zhu, F. Marchesoni, F. Nori, Controlling the motion of magnetic flux quanta, PRL 92, 180602 (2004) 4) J.E. Villegas, et al., Reversible Rectifier that Controls the Motion of Magnetic Flux Quanta, Science 302, 1188 (2003) 5) A. Maeda, et al., Nano-scale friction: kinetic friction of magnetic flux quanta and charge density waves, preprint

  15. 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.

  16. 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

  17. Upper critical fields and critical current densities of Fe-based superconductors as compared to those of other technical superconductors

    NASA Astrophysics Data System (ADS)

    Pallecchi, I.; Tropeano, M.; Lamura, G.; Pani, M.; Palombo, M.; Palenzona, A.; Putti, M.

    2012-11-01

    Three years since the discovery by the Hosono's group of Fe-based superconductors, an enormous number of compounds, belonging to several different families have been discovered and fundamental properties have been deeply investigated in order to clarify the interplay between magnetisms and superconductivity in these compounds. Indeed, the actual potential of these compounds for practical applications remains still unclear. Fe-based superconductors are midway between high temperature superconductors (HTSCs) and MgB2. In Fe-based superconductors the critical current is rather independent of the field, similarly to HTSCs, as a consequence of the exceptionally high upper critical field and strong pinning associated with nm-scale local modulations of the order parameter. They exhibit low anisotropy of the critical current with respect to the crystalline directions, as in the case of MgB2, which allows current flow along the c-axis. However, Fe-based superconductor polycrystalline materials currently available still exhibit electromagnetic granularity, like the HTSCs, which suppresses superconducting current flow over long length. Whether the nature of such granularity is extrinsic, as due to spurious phases or cracks between grains or intrinsic, as related to misalignment of adjacent grains, is under debate. These aspects will be reviewed in the light of the recent literature.

  18. 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.

  19. 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.

  20. 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.

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

    PubMed

    Fu, Liang

    2010-02-05

    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.

  2. Vortices in high-performance high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Kwok, Wai-Kwong; Welp, Ulrich; Glatz, Andreas; Koshelev, Alexei E.; Kihlstrom, Karen J.; Crabtree, George W.

    2016-11-01

    The behavior of vortex matter in high-temperature superconductors (HTS) controls the entire electromagnetic response of the material, including its current carrying capacity. Here, we review the basic concepts of vortex pinning and its application to a complex mixed pinning landscape to enhance the critical current and to reduce its anisotropy. We focus on recent scientific advances that have resulted in large enhancements of the in-field critical current in state-of-the-art second generation (2G) YBCO coated conductors and on the prospect of an isotropic, high-critical current superconductor in the iron-based superconductors. Lastly, we discuss an emerging new paradigm of critical current by design—a drive to achieve a quantitative correlation between the observed critical current density and mesoscale mixed pinning landscapes by using realistic input parameters in an innovative and powerful large-scale time dependent Ginzburg-Landau approach to simulating vortex dynamics.

  3. 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.

  4. Anisotropy of strong pinning in multi-band superconductors

    NASA Astrophysics Data System (ADS)

    van der Beek, C. J.; Konczykowski, M.; Prozorov, R.

    2012-08-01

    The field-angular dependence and anisotropy of the critical current density in iron-based superconductors is evaluated using a phenomenological approach featuring distinct anisotropy factors for the penetration depth and the coherence length. Both the weak collective pinning limit and the strong pinning limit relevant for iron-based superconductors at low magnetic fields are considered. It is found that in the more anisotropic materials, such as SmFeAsO and NdFeAsO, the field-angular dependence is completely dominated by the coherence length (upper critical field) anisotropy, thereby explaining recent results on the critical current in these materials. In less anisotropic superconductors, strong pinning can lead to an apparent inversion of the anisotropy. Finally, it is shown that, under all circumstances, the ratio of the c-axis and ab-plane critical current densities for the magnetic field along the ab-plane directly yields the coherence length anisotropy factor ɛξ.

  5. Unified picture for magnetic correlations in iron-based superconductors.

    PubMed

    Yin, Wei-Guo; Lee, Chi-Cheng; Ku, Wei

    2010-09-03

    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.

  6. Flux pinning characteristics and irreversibility line in high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Matsushita, T.; Ihara, N.; Kiuchi, M.

    1995-01-01

    The flux pinning properties in high temperature superconductors are strongly influenced by thermally activated flux motion. The scaling relation of the pinning force density and the irreversibility line in various high temperature superconductors are numerically analyzed in terms of the flux creep model. The effect of two factors, i.e., the flux pinning strength and the dimensionality of the material, on these properties are investigated. It is speculated that the irreversibility line in Bi-2212 superconductors is one order of magnitude smaller than that in Y-123, even if the flux pinning strength in Bi-2212 is improved up to the level of Y-123. It is concluded that these two factors are equally important in determination of the flux pinning characteristics at high temperatures.

  7. Vortices in high-performance high-temperature superconductors.

    PubMed

    Kwok, Wai-Kwong; Welp, Ulrich; Glatz, Andreas; Koshelev, Alexei E; Kihlstrom, Karen J; Crabtree, George W

    2016-11-01

    The behavior of vortex matter in high-temperature superconductors (HTS) controls the entire electromagnetic response of the material, including its current carrying capacity. Here, we review the basic concepts of vortex pinning and its application to a complex mixed pinning landscape to enhance the critical current and to reduce its anisotropy. We focus on recent scientific advances that have resulted in large enhancements of the in-field critical current in state-of-the-art second generation (2G) YBCO coated conductors and on the prospect of an isotropic, high-critical current superconductor in the iron-based superconductors. Lastly, we discuss an emerging new paradigm of critical current by design-a drive to achieve a quantitative correlation between the observed critical current density and mesoscale mixed pinning landscapes by using realistic input parameters in an innovative and powerful large-scale time dependent Ginzburg-Landau approach to simulating vortex dynamics.

  8. Spin injection from a normal metal into a mesoscopic superconductor

    NASA Astrophysics Data System (ADS)

    Wolf, M. J.; Hübler, F.; Kolenda, S.; v. Löhneysen, H.; Beckmann, D.

    2013-01-01

    We report on nonlocal transport in superconductor hybrid structures, with ferromagnetic as well as normal-metal tunnel junctions attached to the superconductor. In the presence of a strong Zeeman splitting of the density of states, both charge and spin imbalance is injected into the superconductor. While previous experiments demonstrated spin injection from ferromagnetic electrodes, we show that spin imbalance is also created for normal-metal injector contacts. Using the combination of ferromagnetic and normal-metal detectors allows us to directly discriminate between charge and spin injection, and demonstrate a complete separation of charge and spin imbalance. The relaxation length of the spin imbalance is of the order of several μm and is found to increase with a magnetic field, but is independent of temperature. We further discuss possible relaxation mechanisms for the explanation of the spin relaxation length.

  9. Amplitude or Higgs modes in d-wave superconductors

    NASA Astrophysics Data System (ADS)

    Barlas, Yafis; Varma, C. M.

    2013-02-01

    In Lorentz-invariant systems spontaneously broken gauge symmetry results in three types of fundamental excitations: density excitations, Higgs bosons (amplitude modes), and Goldstone bosons (phase modes). The density and phase modes are coupled by electromagnetic interactions while the amplitude modes are not. In s-wave superconductors, the Higgs mode, which can be observed only under special conditions, has been detected. We show that unconventional d-wave superconductors, such as the high-temperature cuprate superconductors, should have a rich assortment of Higgs bosons, each in a different irreducible representation of the point-group symmetry of the lattice. We also show that these modes have a characteristic singular spectral structure and discuss conditions for their observability.

  10. Consistent two-lifetime model for spectral functions of superconductors

    NASA Astrophysics Data System (ADS)

    Herman, František; Hlubina, Richard

    2017-03-01

    Recently it has been found that models with at least two lifetimes have to be considered when analyzing the angle-resolved photoemission data in the nodal region of the cuprates [Kondo et al., Nat. Commun. 6, 7699 (2015), 10.1038/ncomms8699]. In this paper we compare two such models. First we show that the phenomenological model used by Kondo et al. violates the sum rule for the occupation number. Next we consider the recently proposed model of the so-called Dynes superconductors, wherein the two lifetimes measure the strengths of pair-conserving and pair-breaking processes. We demonstrate that the model of the Dynes superconductors is fully consistent with known exact results, and we study in detail the resulting spectral functions. Finally, we show that the spectral functions in the nodal region of the cuprates can be fitted well by the model of the Dynes superconductors.

  11. 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.

  12. Symmetry analysis of transport properties in helical superconductor junctions

    NASA Astrophysics Data System (ADS)

    Cheng, Qiang; Zhang, Yinhan; Zhang, Kunhua; Jin, Biao; Zhang, Changlian

    2017-03-01

    We study the discrete symmetries satisfied by helical p-wave superconductors with the d-vectors {{k}x}\\hat{x}+/- {{k}y}\\hat{y} or {{k}y}\\hat{x}+/- {{k}x}\\hat{y} and the transformations brought by symmetry operations to ferromagnet and spin-singlet superconductors, which show intimate associations with the transport properties in heterojunctions, including helical superconductors. In particular, the partial symmetries of the Hamiltonian under spin-rotation and gauge-rotation operations are responsible for the novel invariances of the conductance in tunnel junctions and the new selection rules for the lowest current and peculiar phase diagrams in Josephson junctions, which were reported recently. The symmetries of constructed free energies for Josephson junctions are also analyzed, and are consistent with the results from the Hamiltonian.

  13. 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.

  14. 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.

  15. Unified picture of the oxygen isotope effect in cuprate superconductors.

    PubMed

    Chen, Xiao-Jia; Struzhkin, Viktor V; Wu, Zhigang; Lin, Hai-Qing; Hemley, Russell J; Mao, Ho-kwang

    2007-03-06

    High-temperature superconductivity in cuprates was discovered almost exactly 20 years ago, but a satisfactory theoretical explanation for this phenomenon is still lacking. The isotope effect has played an important role in establishing electron-phonon interaction as the dominant interaction in conventional superconductors. Here we present a unified picture of the oxygen isotope effect in cuprate superconductors based on a phonon-mediated d-wave pairing model within the Bardeen-Cooper-Schrieffer theory. We show that this model accounts for the magnitude of the isotope exponent as functions of the doping level as well as the variation between different cuprate superconductors. The isotope effect on the superconducting transition is also found to resemble the effect of pressure on the transition. These results indicate that the role of phonons should not be overlooked for explaining the superconductivity in cuprates.

  16. Symmetry analysis of transport properties in helical superconductor junctions.

    PubMed

    Cheng, Qiang; Zhang, Yinhan; Zhang, Kunhua; Jin, Biao; Zhang, Changlian

    2017-03-01

    We study the discrete symmetries satisfied by helical p-wave superconductors with the d-vectors [Formula: see text] or [Formula: see text] and the transformations brought by symmetry operations to ferromagnet and spin-singlet superconductors, which show intimate associations with the transport properties in heterojunctions, including helical superconductors. In particular, the partial symmetries of the Hamiltonian under spin-rotation and gauge-rotation operations are responsible for the novel invariances of the conductance in tunnel junctions and the new selection rules for the lowest current and peculiar phase diagrams in Josephson junctions, which were reported recently. The symmetries of constructed free energies for Josephson junctions are also analyzed, and are consistent with the results from the Hamiltonian.

  17. Temperature Dependent Anisotropy of Oxypnictide Superconductors Studied by Torque Magnetometry

    NASA Astrophysics Data System (ADS)

    Weyeneth, Stephen; Puzniak, Roman; Zhigadlo, Nikolai D.; Katrych, Sergiy; Bukowski, Zbigniew; Karpinski, Janusz; Mosele, Urs; Kohout, Stefan; Roos, Josef; Keller, Hugo

    2009-03-01

    Single crystals of different oxypnictide superconductors of the family ReFeAsO1-xFy (Re = Sm, Nd, Pr) with various carrier dopings and with masses m˜100 ng have been investigated by means of torque magnetometry. We present most recent data, obtained by using highly sensitive piezoresistive torque sensors from which the superconducting anisotropy parameter γ and the in-plane magnetic penetration depth λab were extracted. As an important result γ was found to increase strongly as the temperature is decreased from Tc down to low temperatures. This unconventional temperature dependence of γ is similar to that observed in the two-band superconductor MgB2 and cannot be explained within the classical Ginzburg-Landau model. This scenario strongly suggests a new multi-band mechanism in the novel class of oxypnictide high-temperature superconductors.

  18. Anisotropy of strong pinning in multi-band superconductors

    SciTech Connect

    van der Beek, C.J.; Konczykowski, M.; Prozorov, Ruslan

    2012-07-17

    The field-angular dependence and anisotropy of the critical current density in iron-based superconductors is evaluated using a phenomenological approach featuring distinct anisotropy factors for the penetration depth and the coherence length. Both the weak collective pinning limit and the strong pinning limit relevant for iron-based superconductors at low magnetic fields are considered. It is found that in the more anisotropic materials, such as SmFeAsO and NdFeAsO, the field-angular dependence is completely dominated by the coherence length (upper critical field) anisotropy, thereby explaining recent results on the critical current in these materials. In less anisotropic superconductors, strong pinning can lead to an apparent inversion of the anisotropy. Finally, it is shown that, under all circumstances, the ratio of the c-axis and ab-plane critical current densities for the magnetic field along the ab-plane directly yields the coherence length anisotropy factor εξ.

  19. 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.

  20. 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.

  1. 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.

  2. Model for large arrays of Josephson junctions with unconventional superconductors

    NASA Astrophysics Data System (ADS)

    Khveshchenko, D. V.; Crooks, R.

    2011-10-01

    We study large arrays of mesoscopic junctions made out of gapless unconventional superconductors where the tunneling processes of both particle-hole and Cooper pairs give rise to a strongly retarded effective action which, contrary to the standard case, cannot be readily characterized in terms of a local Josephson energy. This action can be relevant, for example, to grain boundary and c-axis junctions in layered high-Tc superconductors. By using a particular functional representation, we describe emergent collective phenomena in this system, ascertain its phase diagram, and compute electrical conductivity.

  3. 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.

  4. Vortex liquid crystals in anisotropic type II superconductors.

    PubMed

    Carlson, E W; Castro Neto, A H; Campbell, D K

    2003-02-28

    In an isotropic type II superconductor in a moderate magnetic field, the transition to the normal state occurs by vortex lattice melting. In certain anisotropic cases, the vortices acquire elongated cross sections and interactions. Systems of anisotropic, interacting constituents generally exhibit liquid crystalline phases. We examine the possibility of a two step melting in homogeneous type II superconductors with anisotropic superfluid stiffness from a vortex lattice into first a vortex smectic and then a vortex nematic at high temperature and magnetic field. We find that fluctuations of the ordered phase favor an instability to an intermediate smectic-A in the absence of intrinsic pinning.

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

    PubMed

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

    2014-03-14

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

  6. Exotic magnetic states in Pauli-limited superconductors.

    PubMed

    Kenzelmann, M

    2017-03-01

    Magnetism and superconductivity compete or interact in complex and intricate ways. Here we review the special case where novel magnetic phenomena appear due to superconductivity, but do not exist without it. Such states have recently been identified in unconventional superconductors. They are different from the mere coexistence of magnetic order and superconductivity in conventional superconductors, or from competing magnetic and superconducting phases in many materials. We describe the recent progress in the study of such exotic magnetic phases, and articulate the many open questions in this field.

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

    NASA Technical Reports Server (NTRS)

    Tanaka, Shoji

    1990-01-01

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

  8. High-Tc superconductors in the two-dimensional limit:

    PubMed

    Choy; Kwon; Park

    1998-06-05

    The free modulation of interlayer distance in a layered high-transition temperature (high-Tc) superconductor is of crucial importance not only for the study of the superconducting mechanism but also for the practical application of high-Tc superconducting materials. Two-dimensional (2D) superconductors were achieved by intercalating a long-chain organic compound into bismuth-based high-Tc cuprates. Although the intercalation of the organic chain increased the interlayer distance remarkably, to tens of angstroms, the superconducting transition temperature of the intercalate was nearly the same as that of the pristine material, suggesting the 2D nature of the high-Tc superconductivity.

  9. Exotic magnetic states in Pauli-limited superconductors

    NASA Astrophysics Data System (ADS)

    Kenzelmann, M.

    2017-03-01

    Magnetism and superconductivity compete or interact in complex and intricate ways. Here we review the special case where novel magnetic phenomena appear due to superconductivity, but do not exist without it. Such states have recently been identified in unconventional superconductors. They are different from the mere coexistence of magnetic order and superconductivity in conventional superconductors, or from competing magnetic and superconducting phases in many materials. We describe the recent progress in the study of such exotic magnetic phases, and articulate the many open questions in this field.

  10. 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.

  11. 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.

  12. Theoretical modeling and properties of class DIII topological superconductors

    NASA Astrophysics Data System (ADS)

    Nakosai, Sho; Tanaka, Yukio; Nagaosa, Naoto

    2014-01-01

    We theoretically study topological superconductors (TSCs) with time-reversal (TR) symmetry in one- and two-dimensions (1D and 2D). In 2D, we introduce bilayer system with Rashba spin-orbit interaction (SOI), and find that the interplay between SOI and degrees of freedom of layers induces unconventional pairing states, which are topologically nontrivial and have the helical Majorana edge channels. We also find that a usual quantum nanowire on unconventional superconductor becomes a 1D TSC by means of the proximity effect. Majorana fermions at the ends of the wire offer a unique opportunity to relate fermion parity and non-local spin correlations.

  13. Energy gap structure and tunneling characteristics of layered superconductors

    SciTech Connect

    Liu, S.H.; Klemm, R.A.

    1993-06-01

    The authors have analyzed the energy gaps and density-of-states (DOS) of layered superconductors with two inequivalent layers in a unit cell along the c-axis. In the physically interesting parameter range where the interlayer hopping strengths of the quasiparticles are comparable to the critical temperature, the peaks in the DOS curve do not correspond to the order parameters (OP`s) of each layer, but depend on the OP`s and the interlayer hopping strengths in a complex manner. In contrast to a BCS superconductor, the DOS of layered systems have logarithmic singularities. The simulated tunneling characteristics bear close resemblance to experimental results.

  14. 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.

  15. Progress of research of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Tanaka, Shoji

    1991-01-01

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

  16. 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.}

  17. Voltages induced in superconductors in the absence of transport currents.

    NASA Technical Reports Server (NTRS)

    Ohmer, M. C.; Joiner, W. C. H.

    1972-01-01

    Experimental observations of the production of dc and harmonic voltages are described in superconductors subjected to superimposed dc and oscillatory magnetic fields. The attempt is made to account for these observations in a qualitative manner by relating them to the asymmetric flux flow induced by the magnetic fields in the superconductor samples. The observed effects are quite complex and depend on the values of the many parameters in the experiment. Regarding some of the observed phenomena, for which no satisfactory explanation is as yet available, further understanding is expected to come from detailed work on samples with asymmetric surfaces produced in a controlled fashion.

  18. Correlated spin currents generated by resonant-crossed Andreev reflections in topological superconductors.

    PubMed

    He, James J; Wu, Jiansheng; Choy, Ting-Pong; Liu, Xiong-Jun; Tanaka, Y; Law, K T

    2014-01-01

    Topological superconductors, which support Majorana fermion excitations, have been the subject of intense studies due to their novel transport properties and their potential applications in fault-tolerant quantum computations. Here we propose a new type of topological superconductors that can be used as a novel source of correlated spin currents. We show that inducing superconductivity on a AIII class topological insulator wire, which respects a chiral symmetry and supports protected fermionic end states, will result in a topological superconductor. This topological superconductor supports two topological phases with one or two Majorana fermion end states, respectively. In the phase with two Majorana fermions, the superconductor can split Cooper pairs efficiently into electrons in two spatially separated leads due to Majorana-induced resonant-crossed Andreev reflections. The resulting currents in the leads are correlated and spin-polarized. Importantly, the proposed topological superconductors can be realized using quantum anomalous Hall insulators in proximity to superconductors.

  19. Disorder-induced topological phase transitions in two-dimensional spin-orbit coupled superconductors

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Normal superconductors with Rashba spin-orbit coupling have been explored as candidate systems of topological superconductors. Here we present a comparative theoretical study of the effects of different types of disorder on the topological phases of two-dimensional Rashba spin-orbit coupled superconductors. First, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorder, which close and reopen the quasiparticle gap of the paired electrons in a nontrivial manner. Secondly, the superconducting nature of a topological superconductor is found to be robust against Anderson disorder, but the topological nature is not, converting the system into a topologically trivial state even in the weak scattering limit. These topological phase transitions are distinctly characterized by variations in the topological invariant. We discuss the central findings in connection with existing experiments, and provide new schemes towards eventual realization of topological superconductors.

  20. Disorder-induced topological phase transitions in two-dimensional spin-orbit coupled superconductors

    PubMed Central

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

    2016-01-01

    Normal superconductors with Rashba spin-orbit coupling have been explored as candidate systems of topological superconductors. Here we present a comparative theoretical study of the effects of different types of disorder on the topological phases of two-dimensional Rashba spin-orbit coupled superconductors. First, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorder, which close and reopen the quasiparticle gap of the paired electrons in a nontrivial manner. Secondly, the superconducting nature of a topological superconductor is found to be robust against Anderson disorder, but the topological nature is not, converting the system into a topologically trivial state even in the weak scattering limit. These topological phase transitions are distinctly characterized by variations in the topological invariant. We discuss the central findings in connection with existing experiments, and provide new schemes towards eventual realization of topological superconductors. PMID:27991541

  1. Raman spectroscopy of selected tsumcorite Pb(Zn,Fe3+)2(AsO4)2(OH,H2O) minerals--implications for arsenate accumulation.

    PubMed

    Frost, Ray L; Xi, Yunfei

    2012-02-01

    The presence of arsenic in the environment is a hazard. The accumulation of arsenate by a range of cations in the formation of minerals provides a mechanism for the accumulation of arsenate. The formation of the tsumcorite minerals is an example of a series of minerals which accumulate arsenate. There are about twelve examples in this mineral group. Raman spectroscopy offers a method for the analysis of these minerals. The structure of selected tsumcorite minerals with arsenate and sulphate anions were analysed by Raman spectroscopy. Isomorphic substitution of sulphate for arsenate is observed for gartrellite and thometzekite. A comparison is made with the sulphate bearing mineral natrochalcite. The position of the hydroxyl and water stretching vibrations are related to the strength of the hydrogen bond formed between the OH unit and the AsO(4)(3-) anion. Characteristic Raman spectra of the minerals enable the assignment of the bands to specific vibrational modes.

  2. Resistivity scaling 1111 iron-pnictide superconductors

    NASA Astrophysics Data System (ADS)

    Arushanov, E.; Levcenko, S.; Fuchs, G.; Drechsler, S.-L.

    2011-09-01

    We show that the zero field normal-state resistivity above T c for various levels of electron doping-both for LaO 1-xF xFeAs (La-1111) and underdoped SmO 1-xF xFeAs (Sm-1111) members of the 1111-iron-pnictide superconductor family-can be scaled in a broad temperature range from 20 to 300 K onto a single curve for underdoped La-1111 ( x = 0.05-0.075), for optimally and overdoped La-1111 ( x = 0.1-0.2) and for underdoped Sm-1111 ( x = 0.06-0.1). It is found that the ρ( T) dependences can be reproduced by the formulas ρ(T)=ρ0+cTexp-2Δ/T and ρ(T)=ρ0+(c/T)exp-2Δ/T in the case of LaO 1-xF xFeAs and SmO 1-xF xFeAs, respectively. The scaling was performed using the energy scale 2 Δ, c and the residual resistivity ρ0 as scaling parameters as well as applying a recently proposed model-independent scaling method [H.G. Luo, Y.H. Su, T. Xiang, Phys. Rev. B 77 (2008) 014529]. The scaling parameters have been calculated and the compositional variation of 2 Δ has been determined. The observed scaling behavior for ρ( T) is interpreted as an indication of a common mechanism which dominates the scattering of the charge carriers in underdoped La-1111, in optimally and overdoped La-1111 and in underdoped Sm-1111.

  3. 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.

  4. Pairing symmetry of the hydrated cobaltate superconductor

    NASA Astrophysics Data System (ADS)

    Zheng, Guo-Qing

    2008-03-01

    We report NMR/NQR measurements on the hydrated cobaltate superconductor NaxCoO2*1.3H2O at elevated pressures. The spin-lattice relaxation rate (1/T1) decreases below Tc with no coherence peak [1], and is in proportion to T^3 down to T˜Tc/10, which provides compelling evidence for the existence of line nodes in the gap function [2,3]. The spin susceptibility obtained from the Knight shift measurement in a single crystal decreases below Tc along all crystal-axis directions [4]. These results indicate anisotropic, spin-singlet pairing, and are most consistent with a d-wave gap. The electron correlations in the normal state are antiferromagnetic-like, which increases with decreasing Na-content [1,2]. The phase diagrams of Tc and various physical properties as functions of Na-content [2], and pressure [3] will be presented, and the inter-relation between the superconductivity and the spin correlations will be discussed. References: [1] T. Fujimoto, G. - q. Zheng, Y. Kitaoka, R.L. Meng, J. Cmaidalka, and C.W. Chu, Phys. Rev. Lett. 92, 047004 (2004). [2] G. - q. Zheng, K. Matano, R.L. Meng, J. Cmaidalka, and C.W. Chu, J. Phys.: Condens. Matter 18, L63 (2006). [3] E. Kusano, S. Kawasaki, K. Matano, G. - q. Zheng, R.L. Meng, J. Cmaidalka, and C.W. Chu, Phys. Rev. B 76, 100506 (R) (2007). [4] G. - q. Zheng, K. Matano, D.P. Chen and C.T. Lin, Phys. Rev. B73, 180503 (R) (2006).

  5. 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.

  6. 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.

  7. Study of superconductor bearings for a 35 kWh superconductor flywheel energy storage system

    NASA Astrophysics Data System (ADS)

    Han, Y. H.; Park, B. J.; Jung, S. Y.; Han, S. C.

    2012-12-01

    A Superconductor Flywheel Energy Storage system (SFES) is used as an electro-mechanical battery which transforms electrical energy into mechanical energy and vice versa. A 35 kWh SFES using hybrid bearing sets was developed in KEPRI. Mechanical properties of HTS bearings are the critical factors for stability of the flywheel and the main parameter in designing the system. The properties of the HTS bearing were studied. The stiffness and the damping coefficient of the HTS bearing were 346.6 ± 6.7 kN/m and 1255 ± 102 N s/m, respectively. The damping coefficient was twelve times bigger than the estimate value. Therefore, we concluded that there were some external damping mechanisms. Finally, the 35 kWh SFES was test operated up to 4000 rpm. After passing two predicted critical speeds, the amplitude of vibration decreased and reached a stable rotation state.

  8. 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.

  9. Superconductor-Insulator-Superconductor Mixers for the 2 mm Band (129-174 GHz)

    NASA Astrophysics Data System (ADS)

    Navarrini, Alessandro; Fontana, Anne Laure; Maier, Doris; Serres, Patrice; Billon-Pierron, Dominique

    2014-07-01

    We present the design, construction and performance of backshort-tuned Single Side Band (SSB) and of fixed-tuned Double Side Band (DSB) Superconductor-Insulator-Superconductor (SIS) mixers covering the frequency range of 129-174 GHz (2 mm band). Receivers employing these SSB mixers have been continuously operated for astronomical observations on the six antennas of the IRAM Plateau de Bure Intereferometer (PdBI) since 2007 and on the IRAM 30 m Pico Veleta (PV) radio telescope since 2009. The DSB version of the mixer was employed in a prototype of a four-element focal plane array that was tested on the IRAM 30 m radio telescope. Both SSB and DSB mixers employ the same chip and are based on a wideband single ended probe transition from WR6 full-height waveguide to thin-film microstrip line and on a series array of two Nb/Al-AlOx/Nb junctions. The measured receiver noise for the four-element DSB mixer array pumped by a Gunn oscillator cascaded with a frequency doubler was in the range 25-35 K across the 135-168 GHz LO band. The PdBI and PV receivers equipped with the SSB mixers have measured noise temperatures in the range of 30 K to 60 K and an image sideband rejection below -10 dB over the 129-174 GHz RF band. The measurement results agree well with the predictions obtained through detailed simulations of the SIS receivers based on the standard theory of quantum mixing.

  10. Non-Minimal RF2-TYPE Corrections to Holographic Superconductor

    NASA Astrophysics Data System (ADS)

    Sert, Özcan; Adak, Muzaffer

    2013-12-01

    We study (2+1)-dimensional holographic superconductors in the presence of non-minimally coupled electromagnetic field to gravity by considering an arbitrary linear combination of RF2-type invariants with three parameters. Our analytical analysis shows that the non-minimal couplings affect the condensate and the critical temperature.

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  12. p-Wave superconductors in D-brane systems

    NASA Astrophysics Data System (ADS)

    Bu, Yanyan

    2012-11-01

    In this work we take the intersecting D-brane models to explore some properties of p-wave superconductor at strong coupling. Our studies are focused on four-dimensional spacetime, which is not completely researched as in planar case. Optimistically, the AdS/CFT approach to superconductor, or more precisely superconducting-like phase transition, can give us some intuitions about mysterious high Tc superconductors. Concretely, we use defect D4/D6 and D4/D4 (noncritical) models to carry out comparative investigations. To make the system in the finite temperature bath, we assume that the superconducting phase is in the deconfined and chiral symmetry restoring phase for black D4-brane geometry. For the background fields, we use both analytical and numerical methods to solve the coupled nonlinear equations of motion. Near the phase transition, both methods give the mean filed behavior for the superconducting condensate. We then study gauge field perturbations of the systems to probe the AC conductivity. Similar to previous results, there comes out a gap in low frequency regime and the conductivity gets exponentially small as the condensation is enhanced. In contrast to previous investigations, we also compute the AC conductivity along the x direction, which needs to study a coupled sets of fluctuation modes. This shows us the anisotropic feature of p-wave superconductors.

  13. [Raman spectra of YBCO superconductor with hot ultrapressing treatment].

    PubMed

    Yang, Hai-feng; Wei, Le-han; Cao, Xiao-wei

    2002-02-01

    Laser Raman spectra of YBCO oxide superconductor with hot ultrapressing and annealing treatment are reported. In addition to improving physical properties, the spectra data show that the processing can also perfect orthorhombie phase and enhance lattice on orientation trend as well as is good for formation of two dimension CuO2 net. The relation between structure and the superconductivity has been discussed.

  14. Cuprate-titanate superconductor and method for making

    DOEpatents

    Toreki, R.; Poeppelmeier, K.; Dabrowski, B.

    1995-05-23

    A new copper oxide superconductor of the formula Ln{sub 1{minus}x}M{sub x}Sr{sub 2}Cu{sub 3{minus}y}Ti{sub y}O{sub 7+{delta}} is disclosed, and exhibits a {Tc} of 60 K with deviations from linear metallic behavior as high as 130 K. 2 Figs.

  15. Cuprate-titanate superconductor and method for making

    DOEpatents

    Toreki, Robert; Poeppelmeier, Kenneth; Dabrowski, Bogdan

    1995-01-01

    A new copper oxide superconductor of the formula Ln.sub.1-x M.sub.x Sr.sub.2 Cu.sub.3-y Ti.sub.y O.sub.7+.delta. is disclosed, and exhibits a Tc of 60.degree. K. with deviations from linear metallic behavior as high as 130.degree. K.

  16. Transport across a junction of topological insulators and a superconductor

    NASA Astrophysics Data System (ADS)

    Soori, Abhiram; Deb, Oindrila; Sengupta, K.; Sen, Diptiman

    2013-06-01

    We study transport across a line junction lying between two orthogonal topological insulator surfaces and a superconductor which can have either s-wave (spin-singlet) or p-wave (spin-triplet) pairing symmetry. The junction can have three time-reversal invariant barriers on three sides. We compute the charge and the spin conductance across such a junction and study their behaviors as a function of the bias voltage applied across the junction and the three parameters used to characterize the barrier. We find that the presence of topological insulators and a superconductor leads to both Dirac- and Schrödinger-like features in charge and spin conductances. We discuss the effect of bound states on the superconducting side of the barrier on the conductance; in particular, we show that for triplet p-wave superconductors, such a junction may be used to determine the spin state of its Cooper pairs. Our study reveals that there is a nonzero spin conductance for some particular spin states of the triplet Cooper pairs; this is an effect of the topological insulators which break the spin rotation symmetry. Finally, we find an unusual satellite peak (in addition to the usual zero bias peak) in the spin conductance for p-wave symmetry of the superconductor order parameter.

  17. Final Report. Novel Behavior of Ferromagnet/Superconductor Hybrid Systems

    SciTech Connect

    Birge, Norman

    2016-09-26

    Final report for grant DE-FG02-06ER46341. This work has produced a most convincing experimental demonstration that spin-triplet supercurrent can appear in Josephson junctions containing ferromagnetic materials, even when the superconducting electrodes are conventional, spin-singlet superconductors.

  18. Using high-temperature superconductors for levitation applications

    NASA Astrophysics Data System (ADS)

    Hull, John R.

    1999-07-01

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

  19. New application of superconductors: High sensitivity cryogenic light detectors

    NASA Astrophysics Data System (ADS)

    Cardani, L.; Bellini, F.; Casali, N.; Castellano, M. G.; Colantoni, I.; Coppolecchia, A.; Cosmelli, C.; Cruciani, A.; D'Addabbo, A.; Di Domizio, S.; Martinez, M.; Tomei, C.; Vignati, M.

    2017-02-01

    In this paper we describe the current status of the CALDER project, which is developing ultra-sensitive light detectors based on superconductors for cryogenic applications. When we apply an AC current to a superconductor, the Cooper pairs oscillate and acquire kinetic inductance, that can be measured by inserting the superconductor in a LC circuit with high merit factor. Interactions in the superconductor can break the Cooper pairs, causing sizable variations in the kinetic inductance and, thus, in the response of the LC circuit. The continuous monitoring of the amplitude and frequency modulation allows to reconstruct the incident energy with excellent sensitivity. This concept is at the basis of Kinetic Inductance Detectors (KIDs) that are characterized by natural aptitude to multiplexed read-out (several sensors can be tuned to different resonant frequencies and coupled to the same line), resolution of few eV, stable behavior over a wide temperature range, and ease in fabrication. We present the results obtained by the CALDER collaboration with 2×2 cm2 substrates sampled by 1 or 4 Aluminum KIDs. We show that the performances of the first prototypes are already competitive with those of other commonly used light detectors, and we discuss the strategies for a further improvement.

  20. 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.

  1. Three-dimensional Majorana fermions in chiral superconductors.

    PubMed

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

    2016-12-01

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

  2. High T(c) superconductors: Technical and commercial challenge

    NASA Technical Reports Server (NTRS)

    Kirschner, I.; Horvath, E.; Vajda, I.; Bencze, L.; Goebl, N.

    1995-01-01

    Some basic questions of the way which leads from the discovery of high-T(c) superconductors to their applications is surveyed. The influence of high-T(c) superconducting technology on the industrial and social development is also briefly analyzed.

  3. Identifying the genes of unconventional high temperature superconductors.

    PubMed

    Hu, Jiangping

    We elucidate a recently emergent framework in unifying the two families of high temperature (high [Formula: see text]) superconductors, cuprates and iron-based superconductors. The unification suggests that the latter is simply the counterpart of the former to realize robust extended s-wave pairing symmetries in a square lattice. The unification identifies that the key ingredients (gene) of high [Formula: see text] superconductors is a quasi two dimensional electronic environment in which the d-orbitals of cations that participate in strong in-plane couplings to the p-orbitals of anions are isolated near Fermi energy. With this gene, the superexchange magnetic interactions mediated by anions could maximize their contributions to superconductivity. Creating the gene requires special arrangements between local electronic structures and crystal lattice structures. The speciality explains why high [Formula: see text] superconductors are so rare. An explicit prediction is made to realize high [Formula: see text] superconductivity in Co/Ni-based materials with a quasi two dimensional hexagonal lattice structure formed by trigonal bipyramidal complexes.

  4. Hall probe response to a distribution of vortices in superconductor

    NASA Astrophysics Data System (ADS)

    Reiderman, A.; Wolfus, Y.; Abulafia, Y.; Yeshurun, Y.

    1993-04-01

    Based on an analytical approach, an approximation of the Hall probe local sensitivity function by the square uniformly sensitive region w×w, where w is the distance between the Hall electrodes, is given. A simple formula for the Hall probe response to a distribution of vortices in superconductors is proposed.

  5. 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.

  6. Universal lower limit on vortex creep in superconductors.

    PubMed

    Eley, S; Miura, M; Maiorov, B; Civale, L

    2017-02-13

    Superconductors are excellent testbeds for studying vortices, topological excitations that also appear in superfluids, liquid crystals and Bose-Einstein condensates. Vortex motion can be disruptive; it can cause phase transitions, glitches in pulsars, and losses in superconducting microwave circuits, and it limits the current-carrying capacity of superconductors. Understanding vortex dynamics is fundamentally and technologically important, and the competition between thermal energy and energy barriers defined by material disorder is not completely understood. Specifically, early measurements of thermally activated vortex motion (creep) in iron-based superconductors unveiled fast rates (S) comparable to measurements of YBa 2Cu3O7-δ (refs ,,,,,). This was puzzling because S is thought to somehow correlate with the Ginzburg number (Gi), and Gi is significantly lower in most iron-based superconductors than in YBa 2Cu3O7-δ. Here, we report very slow creep in BaFe 2(As0.67P0.33)2 films, and propose the existence of a universal minimum realizable S ∼ Gi(1/2)(T/Tc) (Tc is the superconducting transition temperature) that has been achieved in our films and few other materials, and is violated by none. This limitation provides new clues about designing materials with slow creep and the interplay between material parameters and vortex dynamics.

  7. 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.

  8. Modulated spin and charge densities in cuprate superconductors

    SciTech Connect

    Tranquada, J.M.

    1997-08-01

    Neutron scattering experiments have played a crucial role in characterizing the spin and charge correlations in copper-oxide superconductors. While the data are often interpreted with respect to specific theories of the cuprates, an attempt is made here to distinguish those facts that can be extracted empirically, and the connections that can be made with minimal assumptions.

  9. 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.

  10. Supercold technique duplicates magnetic field in second superconductor

    NASA Technical Reports Server (NTRS)

    Hildebrandt, A. F.

    1964-01-01

    A superconductor cylinder, charged with a high magnetic field, can be used to create a similar field in a larger cylinder. The uncharged cylinder is precooled, lowered into a helium dewar system, and fitted around the cylinder with the magnetic field. Magnetic flux lines pass through the two cylinders.

  11. Process for the production of superconductor containing filaments

    SciTech Connect

    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.

  12. Three-dimensional Majorana fermions in chiral superconductors

    PubMed Central

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

    2016-01-01

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

  13. 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.

  14. Using high-temperature superconductors for levitation applications.

    SciTech Connect

    Hull, J. R.; Energy Technology

    1999-07-01

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

  15. Time-frequency Analyses of AE Signals in YBCO Superconductors

    NASA Astrophysics Data System (ADS)

    Nanato, N.; Takemoto, N.

    AE (Acoustic Emission) measurements are well known methods to detect mechanical signals from superconducting coil The mechanical signals could be generated by micro cracks of epoxy resins, the motion of superconductors and the thermal expansion of superconductors, which were generated before and/or after a quench. We have presented a time-frequency visualization of AE signals as a method to detect the quench. We can detect very small AE signals regardless of lectromagnetic noises and can find the time of the AE occurrence and the frequency bands of AE signals by using this method. Recently it has been presented that YBCO superconductors are delaminated and degraded by a transverse tensile stress. The delamination is accompanied with AE signals. Also, it is known that amplitudes and frequency bands of AE signals vary with causes of AE occurrence. In this paper, we present time-frequency analyses of AE signa s caused by the delamination of a YBCO superconductor and the micro of epoxy resins.

  16. Cryocoolers for the new high-temperature superconductors

    SciTech Connect

    Walker, G.; Ellison, W.; Zylstra, S.

    1988-06-01

    Compact, reliable, low-cost cryocoolers operated simply by closing a switch are an essential requirement for the coming age of superconductivity and cold electronic systems. The advent of high-temperature superconductors has substantially eased the task of those seeking to fill the above need. This article reviews some recent developments in cryocooler systems and examined some prospects for the future.

  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. A stoichiometry criterion for high T c superconductors

    NASA Astrophysics Data System (ADS)

    Veljković, V.; Lalović, D.

    1989-12-01

    We consider high Tc superconducting materials from point of view of the famous Matthias empirical rules for superconductivity. We point out that for all recently discovered high Tc superconductors the average number of electrons outside of the closed shells per atom is close to 7. We offer a possible explanation of this fact and point to its practical implications.

  19. Nonlinear response of superconductors to alternating fields and currents

    SciTech Connect

    McDonald, Jason

    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.

  20. High Temperature Superconductor/Semiconductor Hybrid Microwave Devices and Circuits

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R.; Miranda, Felix A.

    1999-01-01

    Contents include following: film deposition technique; laser ablation; magnetron sputtering; sequential evaporation; microwave substrates; film characterization at microwave frequencies; complex conductivity; magnetic penetration depth; surface impedance; planar single-mode filters; small antennas; antenna arrays phase noise; tunable oscillations; hybrid superconductor/semiconductor receiver front ends; and noise modeling.

  1. Ground state, collective mode, phase soliton and vortex in multiband superconductors.

    PubMed

    Lin, Shi-Zeng

    2014-12-10

    This article reviews theoretical and experimental work on the novel physics in multiband superconductors. Multiband superconductors are characterized by multiple superconducting energy gaps in different bands with interaction between Cooper pairs in these bands. The discovery of prominent multiband superconductors MgB2 and later iron-based superconductors, has triggered enormous interest in multiband superconductors. The most recently discovered superconductors exhibit multiband features. The multiband superconductors possess novel properties that are not shared with their single-band counterpart. Examples include: the time-reversal symmetry broken state in multiband superconductors with frustrated interband couplings; the collective oscillation of number of Cooper pairs between different bands, known as the Leggett mode; and the phase soliton and fractional vortex, which are the main focus of this review. This review presents a survey of a wide range of theoretical exploratory and experimental investigations of novel physics in multiband superconductors. A vast amount of information derived from these studies is shown to highlight unusual and unique properties of multiband superconductors and to reveal the challenges and opportunities in the research on the multiband superconductivity.

  2. Development of high temperature superconductors for electric power applications

    SciTech Connect

    Schiff, N.

    1995-09-01

    The Nobel Prize-winning discovery in 1986 of a new family of superconductors that exhibited the property of no resistance at temperatures more than ten times greater than the traditional low temperature superconductors (LTS) currently used in MRI and high field magnets, made it possible to foresee a new era for the production, transmission and distribution of electrical power. Smaller, more efficient motors, generators, power cables, transformers, inductors, and superconducting magnetic energy storage (SMES) for power quality were applications immediately envisioned for these high temperature superconductors (HTS), promising enhanced capabilities and lower costs. Work also began on new product concepts, such as more effective fault current limiters for both transmission and distribution systems that could protect expensive hardware and avoid the cost of upgrading circuit breakers as system capacity is increased. The interest of industry and utilities has been increased by successful demonstrations of small-scale prototypes. Recent demonstrations include a one meter conductor for an underground transmission cable produced by American Superconductor which carried over 4,200 amps, a 5 hp synchronous motor produced by Reliance Electric Company, magnet systems which generated over 2 Tesla at temperatures over 20 Kelvin (K) by both American Superconductor Corporation (ASC) and Sumitomo Electric Industries. The Department of Energy, under the Superconductivity Partnership Initiative Program (SPI), recently funded four application development projects: a 100 hp HTS motor demonstration, design of a generator rotor, a fault current limiter for distribution systems, and a 30 meter HTS power transmission cable. This paper will review the progress in application development of HTS products. The specific benefits and costs associated with this technology in power applications will be examined.

  3. High -Tc superlight bipolarons in novel superconductors

    NASA Astrophysics Data System (ADS)

    Alexandrov, Sasha

    2003-03-01

    Over the last decade, several competing models of high-temperature superconductivity (HTSC) have been proposed, none of which have succeeded to explain high values of the superconducting critical temperature Tc without adjustable parameters. Most of the proposed models are based on the short-range electron-electron correlations or/and on a short-range electron-phonon interaction. However, in the cuprates the screening is poor due to the low carrier density, layered crystal structure, and high ionicity of the lattice. Here we develop further a model of HTSC, which explicitly takes into account the long-range origin of both types of interaction [1]. The long-range electron-phonon (Froehlich) interaction binds carriers into real space pairs-small bipolarons with surprisingly low mass but sufficient binding energy, while the long-range Coulomb repulsion keeps them from forming larger clusters. We analytically solve this multi-polaron "Froelich-Coulomb" model of oxides for a zigzag ladder and a perovskite layer [2]. The model numerically explains high Tc values in the cuprates without any fitting parameters. It describes other key features of the cuprates such as the isotope effect on the effective mass, pseudogap, the normal state diamagnetism, anomalous upper critical field, and spectral functions measured in tunnelling and photoemission. We argue that strong coupling of carriers with high-frequency phonons and low Fermi energies is the cause of high critical temperatures of novel superconductors. [1] A.S. Alexandrov, in Models and Phenomenology for Conventional and High-temperature Superconductivity (Course CXXXVI of the International School of Physics`Enrico Fermi'), eds. G. Iadonisi, J.R. Schrieffer and M.L. Chiofalo, (IOS Press, Amsterdam), p. 309 (1998). [2] A.S. Alexandrov and P.E. Kornilovitch, J. Phys.: Condens. Matter 14 (2002) 5337. * Mailing address: Department of Physics, Loughborough University, Loughborough LE11 3TU, United Kingdom; E-mail: a

  4. Quaternary borocarbides: New class of intermetallic superconductors

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  5. Vibronic dispersion in the copper oxide superconductors

    NASA Astrophysics Data System (ADS)

    Goodenough, J. B.; Zhou, J.-S.

    1994-02-01

    Attempts to describe the normal-state electronic behavior of the copper oxide superconductors have been unable to reconcile the following observations: (i) a well-defined Fermi surface with a locus predicted by band theory, but having charge carriers of a sign predicted for a Mott-Hubbard splitting of the band; (ii) a change in sign of the carriers to that predicted by band theory, but without a significant change in the locus of the Fermi surface, on overdoping beyond the narrow superconductive compositional range; (iii) a remarkable stability of the narrow range of superconductive charge-carrier concentrations in the CuO2 sheets even in the presence of charge transfer from nonsuperconductive intergrowth layers; (iv) a dramatic sensitivity of the Néel temperature of the parent compound to oxidation of the CuO2 sheets, but the persistence of antiferromagnetic spin fluctuations into the superconductive compositions; and (v) unusual transport properties that cannot be treated within the Migdal approximation and are insensitive to high magnetic fields. To address this impasse, we propose a phenomenological polaron model based on the observation that the system must accommodate to the coexistence of ``ionic'' and ``covalent'' Cu-O bonding having different equilibrium Cu-O bond lengths. We designate this entity a correlation polaron. Covalent Cu-O bonding with molecular-orbital formation occurs within the polaron, which moves in a background of ionic Cu-O bonding. Vibronic coupling at the ``avoided crossover'' from ionic to covalent bonding allows diffusional motion of uncoupled polarons without any motional enthalpy in the mobility. At temperatures T>Tl>~300 K the polarons are uncoupled and move randomly; in the narrow superconductive compositional range they condense below Tl to form a distinguishable thermodynamic phase consisting of extended vibronic states. In this ``polaron liquid,'' a distinction between bonding and antibonding states within the polarons opens a

  6. High field superconductor development and understanding

    SciTech Connect

    Larbalestier, David C.; Lee, Peter J.; Tarantini, Chiara

    2014-09-28

    All present circular accelerators use superconducting magnets to bend and to focus the particle beams. The most powerful of these machines is the large hadron collider (LHC) at CERN. The main ring dipole magnets of the LHC are made from Nb-Ti but, as the machine is upgraded to higher luminosity, more powerful magnets made of Nb3Sn will be required. Our work addresses how to make the Nb3Sn conductors more effective and more suitable for use in the LHC. The most important property of the superconducting conductor used for an accelerator magnet is that it must have very high critical current density, the property that allows the generation of high magnetic fields in small spaces. Nb3Sn is the original high field superconductor, the material which was discovered in 1960 to allow a high current density in the field of about 9 T. For the high luminosity upgrade of the LHC, much higher current densities in fields of about 12 Tesla will be required. The critical value of the current density is of order 2600 A/mm2 in a field of 12 Tesla. But there are very important secondary factors that complicate the attainment of this critical current density. The first is that the effective filament diameter must be no larger than about 40 µm. The second factor is that 50% of the cross-section of the Nb3Sn conductor that is pure copper must be protected from any poisoning by any Sn leakage through the diffusion barrier that protects the package of niobium and tin from which the Nb3Sn is formed by a high temperature reaction. These three, somewhat conflicting requirements, mean that optimization of the conductor is complex. The work described in this contract report addresses these conflicting requirements. They show that very sophisticated characterizations can uncover the way to satisfy all 3 requirements and they also suggest that the ultimate optimization of Nb3Sn is still not yet in sight

  7. Multiple Andreev reflections in s -wave superconductor-quantum dot-topological superconductor tunnel junctions and Majorana bound states

    NASA Astrophysics Data System (ADS)

    Golub, Anatoly

    2015-05-01

    We calculate the current as a function of applied voltage in a nontopological s -wave superconductor-quantum dot-topological superconductor (TS) tunnel junction. We consider the type of TS which hosts two Majorana bound states (MBSs) at the ends of a semiconductor quantum wire or of a chain of magnetic atoms in the proximity with an s -wave superconductor. We find that the I -V characteristic of such a system in the regime of big voltages has a typical two-dot shape and is ornamented by peaks of multiple Andreev reflections. We also consider the other options when the zero-energy states are created by disorder (hereby Shiba states) or by Andreev zero-energy bound states at the surface of a quantum dot and a superconductor. The later are obtained by tuning the magnetic field to a specific value. Unlike the last two cases the MBS I -V curves are robust to change the magnetic field. Therefore, the magnetic-field dependence of the tunneling current can serve as a unique signature for the presence of a MBS.

  8. High-T(sub c) Superconductor-Normal-Superconductor Junctions with Polyimide-Passivated Ambient Temperature Edge Formation

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

    The ability to controllably fabricate High-Temperature Superconductor (HTS) S-Normal-S (SNS) Josephson Juntions (JJ's) enhances the possibilities fro many applications, including digital circuits, SQUID's, and mixers. A wide variety of approaches to fabricating SNS-like junctions has been tried and analyzed in terms of proximity effect behavior.

  9. Tunneling study based on the circuit theory in d-wave superconductors

    NASA Astrophysics Data System (ADS)

    Shigeta, Iduru; Asano, Yasuhiro; Tanaka, Yukio; Ichikawa, Fusao; Kashiwaya, Satoshi

    2006-01-01

    We propose a new interpretation about zero-bias conductance peak (ZBCP) behaviours in high-Tc superconductors. The ZBCP has been frequently observed in many tunneling spectroscopic experiments for unconventional superconductors. The ZBCP mechanism was well understood by the Andreev bound states theory for unconventional superconductors. On the other hand, the circuit theory has been recently developed from conventional superconductors to unconventional superconductors. The ZBCP often appears in this theory as well. Therefore, we have analyzed experimental spectra with the ZBCP of Bi2Sr2CaCu2O8+δ planar tunnel junctions by using both theories for d-wave paring symmetry. The experimental spectra are consistent with those of recent studies on the circuit theory for d-wave superconductors.

  10. Studies of anisotropy of iron based superconductors

    SciTech Connect

    Murphy, Jason

    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. Knowing that the s± gap symmetry exists across the superconducting dome for the electron doped systems, we next looked at λ (T), in optimally - doped, SrFe2(As1-xPx)2, x =0.35. Both, as-grown (Tc ~ 25 K) and annealed (Tc ~ 35 K) single crystals of SrFe2(As1-xPx)2 were measured. Annealing decreases the absolute value of the London penetration depth from λ(0) = 300 ± 10 nm in as-grown samples to λ (0) = 275±10 nm. At low temperatures, λ (T) ~ T indicates a superconducting gap with line nodes. Analysis of the full-temperature range superfluid density is consistent with the line nodes, but differs from the simple single-gap d-wave. The observed behavior is very similar to that of BaFe2(As1-xPx)2, showing that isovalently substituted pnictides are inherently different from

  11. Ambient-temperature superconductor symetrical metal-dihalide bis-(ethylenedithio)-tetrathiafulvalene compounds

    DOEpatents

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

    1987-01-01

    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.

  12. Improved ambient-pressure organic superconductor. [Bis(ethylenedithio)TTF-MX/sub 2/

    DOEpatents

    Williams, J.M.; Wang, Hsien-Hau; Beno, M.A.

    1985-05-29

    Disclosed is 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/sup 0/K which is high for organic superconductors.

  13. Vibration suppression of a disk-shaped superconductor with PD control

    NASA Astrophysics Data System (ADS)

    Komori, M.; Ide, T.; Fukata, S.; Matsushita, T.

    In order to investigate superconducting magnetic bearings (SMBs) using repulsion forces between superconductors and electromagnets, an experimental setup for a thrust SMB able to move in one direction has been made. The experimental setup is composed of a high Tc superconductor, permanent magnets, electromagnets and a Hall sensor. The superconductor used in this paper is supported by the permanent magnets in the radial direction. The vibration of the superconductor is suppressed by an analog PD (proportional and derivative) controller. From the experiments, it is found that suppressing the vibration is well performed by the PD controller. Also, it is found that the controller needs more resistance against disturbance caused by the pinning effect.

  14. Superconductors and Complex Transition Metal Oxides for Tunable THz Plasmonic Metamaterials

    SciTech Connect

    Singh, Ranjan; Xiong, Jie; Azad, Md A.; Yang, Hao; Trugman, Stuart A.; Jia, Quanxi; Taylor, Antoinette; Chen, Houtong

    2012-07-13

    The outline of this presentation are: (1) Motivation - Non-tunability of metal metamaterials; (2) Superconductors for temperature tunable metamaterials; (3) Ultrafast optical switching in superconductor metamaterials; (4) Controlling the conductivity with infrared pump beam; (5) Complex metal oxides as active substrates - Strontium Titanate; and (6) Conclusion. Conclusions are: (1) High Tc superconductors good for tunable and ultrafast metamaterials; (2) Large frequency and amplitude tunability in ultrathin superconductor films; (3) Such tunable properties cannot be accessed using metals; (4) Complex metal oxides can be used as active substrates - large tunability; (5) Complex oxides fail to address the issue of radiation losses in THz metamaterials.

  15. Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Vasquez, Richard P. (Inventor); Hunt, Brian D. (Inventor); Foote, Marc C. (Inventor)

    1994-01-01

    Epitaxial heterojunctions formed between high temperature superconductors and metallic or semiconducting oxide barrier layers are provided. Metallic perovskites such as LaTiO3, CaVO3, and SrVO3 are grown on electron-type high temperature superconductors such as Nd(1.85)Ce(0.15)CuO(4-x). Alternatively, transition metal bronzes of the form A(x)MO(3) are epitaxially grown on electron-type high temperature superconductors. Also, semiconducting oxides of perovskite-related crystal structures such as WO3 are grown on either hole-type or electron-type high temperature superconductors.

  16. Status of high temperature superconductor cable and fault current limiter projects at American Superconductor

    NASA Astrophysics Data System (ADS)

    Maguire, J. F.; Yuan, J.

    2009-10-01

    This paper will describe the status of three key programs currently underway at American Superconductor Corp. The first program is the LIPA project which is a transmission voltage high temperature superconducting cable program, with funding support from the US Department of Energy. The 600 m cable, capable of carrying 574 MVA, was successfully installed and commissioned in LIPA grid on April 22, 2008. An overview of the project, system level design details and operational data will be provided. In addition, the status of the newly awarded LIPA II project will be described. The second program is Project Hydra, with funding support from the US Department of Homeland Security, to design, develop and demonstrate an HTS cable with fault current limiting functionality. The cable is 300 m long and is being designed to carry 96 MVA at a distribution level voltage of 13.8 kV. The cable will be permanently installed and energized in Manhattan, New York in 2010. The initial status of Project Hydra will be presented. The final program to be discussed is a transmission voltage, high temperature superconducting fault current limiter funded by the US DOE. The project encompasses the design, construction and test of a 115 kV FCL for power transmission within a time frame of 4-5 years. Installation and testing are planned for a Southern California Edison substation. A project overview and progress under the first phase will be reported.

  17. 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.

    2016-12-01

    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

  18. Reverse process of usual optical analysis of boson-exchange superconductors: impurity effects on s- and d-wave superconductors.

    PubMed

    Hwang, Jungseek

    2015-03-04

    We performed a reverse process of the usual optical data analysis of boson-exchange superconductors. We calculated the optical self-energy from two (MMP and MMP+peak) input model electron-boson spectral density functions using Allen's formula for one normal and two (s- and d-wave) superconducting cases. We obtained the optical constants including the optical conductivity and the dynamic dielectric function from the optical self-energy using an extended Drude model, and finally calculated the reflectance spectrum. Furthermore, to investigate impurity effects on optical quantities we added various levels of impurities (from the clean to the dirty limit) in the optical self-energy and performed the same reverse process to obtain the optical conductivity, the dielectric function, and reflectance. From these optical constants obtained from the reverse process we extracted the impurity-dependent superfluid densities for two superconducting cases using two independent methods (the Ferrel-Glover-Tinkham sum rule and the extrapolation to zero frequency of -ϵ1(ω)ω(2)); we found that a certain level of impurities is necessary to get a good agreement on results obtained by the two methods. We observed that impurities give similar effects on various optical constants of s- and d-wave superconductors; the greater the impurities the more distinct the gap feature and the lower the superfluid density. However, the s-wave superconductor gives the superconducting gap feature more clearly than the d-wave superconductor because in the d-wave superconductors the optical quantities are averaged over the anisotropic Fermi surface. Our results supply helpful information to see how characteristic features of the electron-boson spectral function and the s- and d-wave superconducting gaps appear in various optical constants including raw reflectance spectrum. Our study may help with a thorough understanding of the usual optical analysis process. Further systematic study of experimental

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

    PubMed Central

    Grosfeld, Eytan; Stern, Ady

    2011-01-01

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

  20. Phase diagram of superconductors from nonperturbative flow equations

    SciTech Connect

    Bergerhoff, B.; Freire, F.; Litim, D.F.; Lola, S.; Wetterich, C.

    1996-03-01

    The universal behavior of superconductors near the phase transition is described by the three-dimensional field theory of scalar quantum electrodynamics. We approximately solve the model with the help of nonperturbative flow equations. A first- or second-order phase transition is found depending on the relative strength of the scalar versus the gauge coupling. The region of a second-order phase transition is governed by a fixed point of the flow equations with associated critical exponents. We also give an approximate description of the tricritical behavior and briefly discuss the crossover relevant for the onset of scaling near the critical temperature. Final confirmation of a second-order transition for strong type-II superconductors requires further analysis with extended truncations of the flow equations. {copyright} {ital 1996 The American Physical Society.}