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Sample records for high tc superconductivity

  1. High Tc superconducting materials and devices

    NASA Technical Reports Server (NTRS)

    Haertling, Gene H.

    1990-01-01

    The high Tc Y1Ba2Cu3O(7-x) ceramic materials, initially developed in 1987, are now being extensively investigated for a variety of engineering applications. The superconductor applications which are presently identified as of most interest to NASA-LaRC are low-noise, low thermal conductivity grounding links; large-area linear Meissner-effect bearings; and sensitive, low-noise sensors and leads. Devices designed for these applications require the development of a number of processing and fabrication technologies. Included among the technologies most specific to the present needs are tapecasting, melt texturing, magnetic field grain alignment, superconductor/polymer composite fabrication, thin film MOD (metal-organic decomposition) processing, screen printing of thick films, and photolithography of thin films. The overall objective of the program was to establish a high Tc superconductivity laboratory capability at NASA-LaRC and demonstrate this capability by fabricating superconducting 123 material via bulk and thin film processes. Specific objectives include: order equipment and set up laboratory; prepare 1 kg batches of 123 material via oxide raw material; construct tapecaster and tapecaster 123 material; fabricate 123 grounding link; fabricate 123 composite for Meissner linear bearing; develop 123 thin film processes (nitrates, acetates); establish Tc and Jc measurement capability; and set up a commercial use of space program in superconductivity at LaRC. In general, most of the objectives of the program were met. Finally, efforts to implement a commercial use of space program in superconductivity at LaRC were completed and at least two industrial companies have indicated their interest in participating.

  2. Unconventional high-Tc superconductivity in fullerides.

    PubMed

    Takabayashi, Yasuhiro; Prassides, Kosmas

    2016-09-13

    A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter-the overlap between the outer wave functions of the constituent molecules-is controlled by the C60 (3-) molecular electronic structure via the on-molecule Jahn-Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott-Jahn-Teller state through chemical or physical pressurization yields an unconventional Jahn-Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen-Cooper-Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn-Teller and Fermi liquid metal when the Jahn-Teller distortion melts.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

  3. Unconventional high-Tc superconductivity in fullerides.

    PubMed

    Takabayashi, Yasuhiro; Prassides, Kosmas

    2016-09-13

    A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter-the overlap between the outer wave functions of the constituent molecules-is controlled by the C60 (3-) molecular electronic structure via the on-molecule Jahn-Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott-Jahn-Teller state through chemical or physical pressurization yields an unconventional Jahn-Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen-Cooper-Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn-Teller and Fermi liquid metal when the Jahn-Teller distortion melts.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. PMID:27501971

  4. Research on high Tc superconducting compounds

    NASA Technical Reports Server (NTRS)

    Oliver, Frederick W. (Principal Investigator)

    1996-01-01

    Mossbauer research using the 21.54 kev resonance radiation of Eu-151 on the high temperature superconductors Bi(2)Ca(0.5)Eu(0.5)Sr(2)CU2O(x), and EuBa(2)CU(3)O(7-x) is performed. For the Bismuth compound the Mossbauer measurements gave a weak signal at room temperature but improved at lower temperatures. Experimental data indicated that europium is located at only one crystallographic site. Isomer shift measurements were .69 + 0.02 mm/s with respect to EuF(3). The linewidth at room temperature was found to be 2.54 mm/s. This value falls within the values observed by other researchers on Eu based 1,2,3 high-Tc compounds. Our results also show the Eu to be trivalent with no trace of divalent europium present. Superconducting europium based 1,2,3 compounds were prepared and measurements completed. Our results show the Eu to be trivalent with no trace of divalent europium present. These compounds had an average isomer shift of .73 mm/s +/- O.02 for all samples made. One of these was irradiated with 3.5 X 10(exp 16) neutrons and a comparison made of the Mossbauer parameters for the irradiated and non-irradiated samples. Experimental results showed no difference between linewidths but a measurable effect was seen for the isomer shift.

  5. Technical issues of a high-Tc superconducting bulk magnet

    NASA Astrophysics Data System (ADS)

    Fujimoto, Hiroyuki

    2000-06-01

    Superconducting magnets made of high-Tc superconductors are promising for industrial applications. It is well known that REBa2Cu3O7-x superconductors prepared by melt processes have a high critical current density, Jc, at 77 K and high magnetic fields. The materials are very promising for high magnetic field applications as a superconducting permanent/bulk magnet with liquid-nitrogen refrigeration. Light rare-earth (LRE) BaCuO bulks, compared with REBaCuO bulks, exhibit a larger Jc in high magnetic fields and a much improved irreversibility field, Hirr, at 77 K. In this study, we discuss technical issues of a high-Tc superconducting bulk magnet, namely the aspects of the melt processing for bulk superconductors, their characteristic superconducting properties and mechanical properties, and trapped field properties of a superconducting bulk magnet. One of the possible applications is a superconducting bulk magnet for the magnetically levitated (Maglev) train in the future.

  6. Heterogeneity: the essential ingredient to high Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Bussmann-Holder, Annette

    2005-08-01

    High temperature superconductivity (HTSC) in copper oxides appears upon doping an antiferromagnetic Mott-Hubbard insulator. While at high temperatures the dopants are randomly distributed over the host lattice, at the pseudo-gap temperature T* dynamic patterning in terms of stripe segments is observed. In this regime charge rich and charge poor regions coexist and interact dynamically with each other. It is shown here that this form of heterogeneity leads to multicomponent superconductivity with largely enhanced values of the superconducting transition temperature Tc. The special role played by the lattice is addressed and it is shown that intermediate sized polarons are formed which are the origin of unconventional isotope and strain effects.

  7. Pressure and high-Tc superconductivity in sulfur hydrides

    PubMed Central

    Gor’kov, Lev P.; Kresin, Vladimir Z.

    2016-01-01

    The paper discusses fundamentals of record-TC superconductivity discovered under high pressure in sulfur hydride. The rapid increase of TC with pressure in the vicinity of Pcr ≈ 123GPa is interpreted as the fingerprint of a first-order structural transition. Based on the cubic symmetry of the high-TC phase, it is argued that the lower-TC phase has a different periodicity, possibly related to an instability with a commensurate structural vector. In addition to the acoustic branches, the phonon spectrum of H3S contains hydrogen modes with much higher frequencies. Because of the complex spectrum, usual methods of calculating TC are here inapplicable. A modified approach is formulated and shown to provide realistic values for TC and to determine the relative contributions of optical and acoustic branches. The isotope effect (change of TC upon Deuterium for Hydrogen substitution) originates from high frequency phonons and differs in the two phases. The decrease of TC following its maximum in the high-TC phase is a sign of intermixing with pairing at hole-like pockets which arise in the energy spectrum of the cubic phase at the structural transition. On-pockets pairing leads to the appearance of a second gap and is remarkable for its non-adiabatic regime: hydrogen mode frequencies are comparable to the Fermi energy. PMID:27167334

  8. Pressure and high-Tc superconductivity in sulfur hydrides

    NASA Astrophysics Data System (ADS)

    Gor’Kov, Lev P.; Kresin, Vladimir Z.

    2016-05-01

    The paper discusses fundamentals of record-TC superconductivity discovered under high pressure in sulfur hydride. The rapid increase of TC with pressure in the vicinity of Pcr ≈ 123GPa is interpreted as the fingerprint of a first-order structural transition. Based on the cubic symmetry of the high-TC phase, it is argued that the lower-TC phase has a different periodicity, possibly related to an instability with a commensurate structural vector. In addition to the acoustic branches, the phonon spectrum of H3S contains hydrogen modes with much higher frequencies. Because of the complex spectrum, usual methods of calculating TC are here inapplicable. A modified approach is formulated and shown to provide realistic values for TC and to determine the relative contributions of optical and acoustic branches. The isotope effect (change of TC upon Deuterium for Hydrogen substitution) originates from high frequency phonons and differs in the two phases. The decrease of TC following its maximum in the high-TC phase is a sign of intermixing with pairing at hole-like pockets which arise in the energy spectrum of the cubic phase at the structural transition. On-pockets pairing leads to the appearance of a second gap and is remarkable for its non-adiabatic regime: hydrogen mode frequencies are comparable to the Fermi energy.

  9. High- Tc superconductivity via superpropagators revisited

    NASA Astrophysics Data System (ADS)

    Malik, G. P.

    2008-07-01

    We revisit our earlier paper because it was perceived in some quarters to be based on a formulation that took into account the electron-pairs (e-pairs), but not the hole-pairs (h-pairs). Through a more comprehensive study of the basic equation on which our earlier work was based, we present here temperature-generalized equations for the Bethe-Salpeter amplitudes for Cooper pairs (CPs) of the (e-e), (h-h), and (e-h/h-e) varieties (our earlier paper seemed to deal with only the first category of pairs). We then show that solution of the (e-e) or the (h-h) equation, at T = 0, yields a pair of pure imaginary binding energies (W); this result is in agreement with the one obtained long ago by Thouless, by Abrikosov et al., by Schrieffer, and others, and signifies that both the e-pairs and the h-pairs have been taken into account in our work. A salient feature of our approach is that it determines the all-important Tc and Hc in the limit of vanishing W whereas, in the BCS theory, Tc is obtained in the limit gap → 0, and Hc is determined via the condensation energy of the CPs.

  10. Predicted Mechanical Behavior of High-Tc Superconducting Ceramic Films

    NASA Astrophysics Data System (ADS)

    Suhir, Ephraim

    1990-03-01

    In potential applications, the recently discovered high transition temperature (high-Tc) ceramic superconductors (Bednorz and Muller, 1986, Wu et al., 1987, Cava et al., 1987) may experience large mechanical stresses and strains. These can be imposed by magnet fabrication, high magnetic fields, and, in the case of superconducting films, also by thermal contraction mismatch with the substrate material (see, for instance, Baynham, 1988, Severin and de With, 1988). Although mechanical strength of a superconductor may appear to be not as important a property, as, say, high superconducting transition temperature, high upper critical magnetic field or high critical current density, it may play a decisive role, when a superconducting material is used for practical purposes. Since ceramics are brittle materials, and break quite easily when stretched, bent or hit, use of ceramics as practical superconductors requires that they possess high ultimate stress and strain, sufficient fracture toughness and good shock resistance. It is also important that the actual stresses and strains arising in superconducting ceramics at low temperatures can be predicted and, if possible, minimized.

  11. High-Tc superconducting quantum interference device recordings of spontaneous brain activity: Towards high-Tc magnetoencephalography

    NASA Astrophysics Data System (ADS)

    Öisjöen, F.; Schneiderman, J. F.; Figueras, G. A.; Chukharkin, M. L.; Kalabukhov, A.; Hedström, A.; Elam, M.; Winkler, D.

    2012-03-01

    We have performed single- and two-channel high transition temperature (high-Tc) superconducting quantum interference device (SQUID) magnetoencephalography (MEG) recordings of spontaneous brain activity in two healthy human subjects. We demonstrate modulation of two well-known brain rhythms: the occipital alpha rhythm and the mu rhythm found in the motor cortex. We further show that despite higher noise-levels compared to their low-Tc counterparts, high-Tc SQUIDs can be used to detect and record physiologically relevant brain rhythms with comparable signal-to-noise ratios. These results indicate the utility of high-Tc technology in MEG recordings of a broader range of brain activity.

  12. Polytypoids in high Tc thallium based superconducting materials

    SciTech Connect

    Singh, A.K. ); Imam, M.A.; Sadananda, K.; Qadri, S.B.; Skelton, E.F.; Osofsky, M.S.; Le Tourneau, V.; Gubser, D.U. )

    1990-08-01

    Several high {Tc} compounds containing Tl (thallium) were prepared starting from different initial compositions. Superconducting properties and the structure were determined for each sample. Electron diffraction and transmission electron microscopy showed the existence of polytypic high {ital T}{sub {ital c}} compounds with the same {ital a}- and {ital b}-axes but different {ital c}-axis values. The {ital c}-axis appears to increase approximately in integral multiples of 0.15 nm with varying composition could be associated with the insertion of Cu-Ca or Cu-Tl layers in each unit cell. Several random stacking faults were also noted which give rise to diffuse streaking in the electron diffraction pattern.

  13. Terahertz imaging system using high-Tc superconducting oscillation devices

    NASA Astrophysics Data System (ADS)

    Tsujimoto, M.; Minami, H.; Delfanazari, K.; Sawamura, M.; Nakayama, R.; Kitamura, T.; Yamamoto, T.; Kashiwagi, T.; Hattori, T.; Kadowaki, K.

    2012-06-01

    Microwatt power oscillation devices at sub-terahertz frequency region between 0.3 and 1.0 terahertz (THz) were fabricated from high-Tc superconducting single crystalline Bi2Sr2CaCu2O8+δ and used as a source of the transmission terahertz imaging system. As test examples, terahertz images of coins and a razor blade placed inside the brownish paper envelopes with the spatial resolution of 1 mm are presented. The signal-to-noise ratio exceeds 130 in these images. Using a simple wedge-shaped interferometer and analysing the interference fringe pattern, the wavelength of the terahertz wave is calibrated within 0.1% accuracy. This interferometer also provides a simple method to measure the absorption coefficient of the liquid sample. Two test measurements for distilled water and ethanol are demonstrated and their absorption coefficients are obtained with 99.2% accuracy. This suggests that our terahertz imaging system can be applied to many practical applications, such as biological and biomedical imaging, environmental monitoring, microanalysis of impurities, structure and dynamical analyses of large molecules and ions in solution.

  14. High-[Tc] superconducting magnets based on thick film arrangements

    SciTech Connect

    Kirschner, I.; Zsolt, G.; Karman, T.; Porjesz, T. . Dept. for Low Temperature Physics); Leppaevuori, S.; Uusimaeki, A. . Microelectronics Lab.); Lukacs, P. )

    1993-11-01

    On the basis of the authors' earlier idea on magnetic feeding, high-[Tc] superconducting magnets can be built consisting of Y-Ba-Cu-O or Bi(Pb)-Sr-Ca-Cu-O thick films. Critical current densities of the samples prepared by an oxalate route are between 7,000 and 23,000 A/cm[sup 2] at helium temperatures depending on the details of the preparation. The self-magnetic field of the individual layer rings are 0.5--1.7 mT which can produce field strength of the magnets of 55 178 mT, corresponding to the experimental critical currents. If the specimens of oxide-nitrate reactions can provide critical current densities of 5,000--15,000 A/cm[sup 2] at nitrogen temperatures they lead to the number of ampere-turns of 550--22,500 A/cm and magnetic field intensity of 69 mT--2.82 T. Since the applicable techniques of the film preparation are very flexible concerning the shape and size of the products, magnetic field profiles of different character can be obtained for various purposes.

  15. Bosonic high-Tc superconductivity in two dimensions

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Kang, H.; Lee, Y. C.; Chen, Jin-Chang

    1994-10-01

    The mixed boson-fermion model of superconductivity of Friedburg and Lee is adapted to two dimensions. Owing to the finite correlation length l(T), Bose-Einstein (BE) condensation can prevail only for a finite, but still macroscopic system. It is shown that for T<Tc~40 K, BE condensation of charged bosons that are converted from fermion (electron or hole) pairs leads not only to a perfect Meissner effect but also an energy gap in the fermion excitation spectrum. For the temperature range Tc

  16. Magnetic forces in high-Tc superconducting bearings

    NASA Technical Reports Server (NTRS)

    Moon, F. C.

    1991-01-01

    In September 1987, researchers at Cornell levitated a small rotor on superconducting bearings at 10,000 rpm. In April 1989, a speed of 120,000 rpm was achieved in a passive bearing with no active control. The bearing material used was YBa2Cu307. There is no evidence that the rotation speed has any significant effect on the lift force. Magnetic force measurements between a permanent rare-earth magnet and high T(sub c) superconducting material versus vertical and lateral displacements were made. A large hysteresis loop results for large displacements, while minor loops result for small displacements. These minor loops seem to give a slope proportional to the magnetic stiffness, and are probably indicative of flux pinning forces. Experiments of rotary speed versus time show a linear decay in a vacuum. Measurements of magnetic dipole over a high-T(sub c) superconducting disc of YBCO show that the lateral vibrations of levitated rotors were measured which indicates that transverse flux motion in the superconductor will create dissipation. As a result of these force measurements, an optimum shape for the superconductor bearing pads which gives good lateral and axial stability was designed. Recent force measurements on melt-quench processed superconductors indicate a substantial increase in levitation force and magnetic stiffness over free sintered materials. As a result, application of high-T(sub c) superconducting bearings are beginning to show great promise at this time.

  17. Prospects and progress of high Tc superconductivity for space applications

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R.; Sokoloski, Marty M.

    1991-01-01

    Current research in the area of high temperature superconductivity is organized around four key areas: communications and data, sensors and cryogenics, propulsion and power, and space materials technology. Recently, laser ablated YBa2Cu3O(7-x) films on LaAlO3 produced far superior RF characteristics when compared to metallic films on the same substrate. The achievement has enabled a number of unique microwave device applications, such as low insertion loss phase shifters and high-Q filters. Melt texturing and melt-quenched techniques are being used to produce bulk material with optimized magnetic properties. These yttrium-enriched materials possess enhanced flux pinning characteristics and could lead to prototype cryocooler bearings. Significant progress has also occurred in bolometer and current lead technology. Studies were conducted to evaluate the effect of high temperature superconducting materials on the performance and life of high power magnetoplasma-dynamic thrusters. Extended studies were also performed to evaluate the benefit of superconducting magnetic energy storage for LEO space station, lunar, and Mars mission applications.

  18. Underlying mechanisms of pseudogap phenomena and Bose-liquid superconductivity in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Karimboev, E. X.; Djumanov, Sh. S.

    2016-06-01

    We show that the high-Tc cuprates are non-BCS superconductors exhibiting distinct pseudogap (PG) behaviors (related to real and momentum space excitations) and other anomalies above Tc, novel Bose-liquid superconductivity below Tc, and also a λ-like superconducting (SC) transition at Tc similar to the λ transition in liquid 4He. In these materials, the relevant charge carriers are polarons which are bound into bosonic Cooper pairs above Tc followed by condensing into a Bose superfluid at Tc. We found that the polaronic effects and related PG weaken with increasing of the doping level and disappear in the overdoped region, where the crossover from Bose-liquid to Fermi-liquid (BCS-type) superconductivity occurs at the quantum critical point. We identify the real phase diagrams of the cuprates, the PG and vortex-like states above Tc, the novel SC state and two distinct SC phases below Tc like two superfluid phases of 3He, and explain the rich cuprate phenomenology from lightly doped to overdoped region.

  19. Applications using high-Tc superconducting terahertz emitters

    PubMed Central

    Nakade, Kurama; Kashiwagi, Takanari; Saiwai, Yoshihiko; Minami, Hidetoshi; Yamamoto, Takashi; Klemm, Richard A.; Kadowaki, Kazuo

    2016-01-01

    Using recently-developed THz emitters constructed from single crystals of the high-Tc superconductor Bi2Sr2CaCu2O8+δ, we performed three prototype tests of the devices to demonstrate their unique characteristic properties for various practical applications. The first is a compact and simple transmission type of THz imaging system using a Stirling cryocooler. The second is a high-resolution Michelson interferometer used as a phase-sensitive reflection-type imaging system. The third is a system with precise temperature control to measure the liquid absorption coefficient. The detailed characteristics of these systems are discussed. PMID:26983905

  20. Applications using high-Tc superconducting terahertz emitters.

    PubMed

    Nakade, Kurama; Kashiwagi, Takanari; Saiwai, Yoshihiko; Minami, Hidetoshi; Yamamoto, Takashi; Klemm, Richard A; Kadowaki, Kazuo

    2016-03-17

    Using recently-developed THz emitters constructed from single crystals of the high-Tc superconductor Bi2Sr2CaCu2O8+δ, we performed three prototype tests of the devices to demonstrate their unique characteristic properties for various practical applications. The first is a compact and simple transmission type of THz imaging system using a Stirling cryocooler. The second is a high-resolution Michelson interferometer used as a phase-sensitive reflection-type imaging system. The third is a system with precise temperature control to measure the liquid absorption coefficient. The detailed characteristics of these systems are discussed.

  1. Applications using high-Tc superconducting terahertz emitters

    NASA Astrophysics Data System (ADS)

    Nakade, Kurama; Kashiwagi, Takanari; Saiwai, Yoshihiko; Minami, Hidetoshi; Yamamoto, Takashi; Klemm, Richard A.; Kadowaki, Kazuo

    2016-03-01

    Using recently-developed THz emitters constructed from single crystals of the high-Tc superconductor Bi2Sr2CaCu2O8+δ, we performed three prototype tests of the devices to demonstrate their unique characteristic properties for various practical applications. The first is a compact and simple transmission type of THz imaging system using a Stirling cryocooler. The second is a high-resolution Michelson interferometer used as a phase-sensitive reflection-type imaging system. The third is a system with precise temperature control to measure the liquid absorption coefficient. The detailed characteristics of these systems are discussed.

  2. High- Tc superconductivity: new issues from photoemission data

    NASA Astrophysics Data System (ADS)

    Margaritondo, G.; Grioni, M.; Vobornik, I.; Pavuna, D.

    2001-11-01

    Recent high-resolution photoemission results on high- Tc superconductors and other low-dimensional systems solve some critical issues but also open new fundamental questions. A recent breakthrough enabled us to clarify the interplay of conflicting periodicities in photoemission data, thus legitimizing the photoemission analysis of crystals with super-periodicities. On the other hand, results on the role of doping and of intentional disorder in Bi 2Sr 2CaCu 2O 8+ x single crystals raise questions about the origin of the pseudogap.

  3. A Simple Demonstration of High Tc Superconductive Powder.

    ERIC Educational Resources Information Center

    Baker, Roger; Thompson, James C.

    1987-01-01

    Described is a simple demonstration that provides a way to determine if a given sample contains even a small fraction of superconducting material. The repulsion of the powder from a magnetic field is indicative of superconductivity. (RH)

  4. Metal-insulator quantum critical point beneath the high Tc superconducting dome

    PubMed Central

    Sebastian, Suchitra E.; Harrison, N.; Altarawneh, M. M.; Mielke, C. H.; Liang, Ruixing; Bonn, D. A.; Lonzarich, G. G.; Hardy, W. N.

    2010-01-01

    An enduring question in correlated systems concerns whether superconductivity is favored at a quantum critical point (QCP) characterized by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high Tc cuprates and invoked to explain non-Fermi liquid transport signatures, experimental evidence is lacking for a critical divergence under the superconducting dome. We use ultrastrong magnetic fields to measure quantum oscillations in underdoped YBa2Cu3O6+x, revealing a dramatic doping-dependent upturn in quasiparticle effective mass at a critical metal-insulator transition beneath the superconducting dome. Given the location of this QCP under a plateau in Tc in addition to a postulated QCP at optimal doping, we discuss the intriguing possibility of two intersecting superconducting subdomes, each centered at a critical Fermi surface instability. PMID:20304800

  5. Optical detector prepared by high-Tc superconducting thin film

    NASA Astrophysics Data System (ADS)

    Wang, Lingjie; Zhou, Fang Q.; Zhao, Xing R.; Sun, Han D.; Yi, Xin J.

    1991-12-01

    An optical detector prepared by high T(subscript c) superconducting thin film has been discussed. The device has been made from YBaCuO superconducting thin film with zero resistance at more than 80 K on a ZrO(subscript 2) substrate. A pattern of the device with the dimension of the microbridge is formed through photolithographic process. Electrical contacts are made by evaporating gold or silver with thickness of 0.5 - 1 micrometers . The sample is then placed in a dewar with an infrared window and is cooled by liquid nitrogen. A blackbody source at 800 K is used to measure the responsivity of the detector, and the infrared radiation is chopped at frequencies between 6.3 and 2000 Hz. The detector output with the detectivity larger than 10(superscript 9) cmHz(superscript 1/2)/w and a typical responsivity value as large as 10(superscript 3) V/w is observed on both lock-in amplifier and root-mean-square voltmeter. In addition, the mechanism of optical detection and the methods to improve the sensitivity have been described.

  6. Temperature dependence of the superconducting gap in high-Tc cuprates.

    PubMed

    Fine, B V

    2005-04-22

    It is proposed that the temperature dependence of the superconducting gap Delta(T) in high-T(c) cuprates can be predicted just from the knowledge of Delta(0) and the critical temperature T(c), and, in particular, Delta(0)/T(c)>4 implies that Delta(T(c)) not equal 0, while Delta(0)/T(c)

  7. Search for high-Tc conventional superconductivity at megabar pressures in the lithium-sulfur system

    NASA Astrophysics Data System (ADS)

    Kokail, Christian; Heil, Christoph; Boeri, Lilia

    2016-08-01

    Motivated by the recent report of superconductivity above 200 K in ultra-dense hydrogen sulfide, we search for high-TC conventional superconductivity in the phase diagram of the binary Li-S system, using ab initio methods for crystal structure prediction and linear response calculations for the electron-phonon coupling. We find that at pressures higher than 20 GPa, several new compositions, besides the known Li2S , are stabilized; many exhibit electride-like interstitial charge localization observed in other alkali-metal compounds. Of all predicted phases, only an fcc phase of Li3S , metastable before 640 GPa, exhibits a sizable TC, in contrast to what is observed in sulfur and phosphorus hydrides, where several stoichiometries lead to high TC. We attribute this difference to 2 s -2 p hybridization and avoided core overlap, and predict similar behavior for other alkali-metal compounds.

  8. Theory of high-TC superconductivity: transition temperature

    NASA Astrophysics Data System (ADS)

    Harshman, Dale R.; Fiory, Anthony T.; Dow, John D.

    2010-12-01

    After reading over our published manuscript, we noticed that the discussion concerning the determination of σ for the ruthenate Ba2YRu0.9Cu0.1O6 in section 2.3.1 (3rd paragraph) is somewhat terse. Herein we provide an expanded analysis which better explains our estimate of γ (and thus σ) for this compound. All numbers, figures and conclusions remain unaltered. The ruthenate compounds A2YRu1-xCuxO6 (with A = Ba or Sr; x = 0.05-0.15) are double-perovskites containing no cuprate planes and with ν = μ = 1 [1] (reference [82] in the paper). The determination of γ follows from equation (2.5b), wherein rule 1b introduces the factor 1/2. In the lower limit, one expects a minimum of ~2 charges per Cu dopant, which are shared between two charge reservoirs of each layer type (AO and 1/2 (YRu1-xCuxO4)), producing a net factor of unity. Thus, for Ba2YRu0.9Cu0.1O6 (with TC0 ~ 30-40 K), we estimate γ = (1/2)(1) = 1/2, yielding σ = 0.05 as stated by equation (2.5c) in the paper. While one may expect an average effective charge state for Ru near +5, and that of Cu to be between +2 and +3 (post anneal) [2], the lower-limit estimation provided, which places the corresponding data point in figure 2 to the left of the line, appears sufficient to include the ruthenates with the other high-TC compounds found to follow equation (2.6) so far. Owing to the uncertainty in the experimental values for TC0, as well as the Ru and Cu valence states, however, this compound was excluded in the data analyses presented. Future research will attempt a more accurate determination of the charge per doped Cu, and thus σ. We would also like to point out a typographical correction in the definition of the corresponding ruthenate type II reservoir in the last column of table 1, which should read 1/2 (YRu0.9Cu0.1O4). An unrelated item is found in the fourth line of section 2.3.3, where Tb(O0.80F0.20)FeAs should read Tb(O0.80-yF0.20)FeAs. Additionally, reference [132] is now known and has the form

  9. High Tc superconducting bolometric and nonbolometric infrared (IR) detectors

    NASA Technical Reports Server (NTRS)

    Lakeou, Samuel; Rajeswari, M.; Goyal, Anuja

    1995-01-01

    The workplan for the period August 1994 through August 1995 includes the following: (1) expand the Applied Superconductivity Laboratory to include stand-alone optical response and noise measurement setups; (2) pursue studies of the low frequency excess electrical noise in YBCO films; and (3) enhance the academic support component of the project through increased student and faculty participation.

  10. High Tc superconducting bolometric and nonbolometric infrared (IR) detectors

    NASA Technical Reports Server (NTRS)

    Lakeou, Samuel

    1995-01-01

    Activities carried out during the reporting period are summarized. The workplan for the period August 1994 to August 1995 included the following: (1) expansion of the Applied Superconductivity Laboratory to include stand-alone optical response and noise measurement setups; (2) study the low frequency excess electrical noise in YBCO films; and (3) enhancement of the academic support component of the project through increased student and faculty participation. Abstracts of papers submitted for publication during this reporting period are included as attachments.

  11. Laser Plasma Vapour Deposition Of Photoconducting And High Tc Superconducting Films

    NASA Astrophysics Data System (ADS)

    Popescu, Mihai A.; Apostol, Ileana; Mihailescu, Ion N.; Botila, T.; Pentia, E.; Ciurea, M. L.; Dinescu, M.; Jaklovsky, J.; Aldica, Gheorghe V.; Miu, L.; Rusu, C.; Hening, Al. A.; Mihai, S.; Constantin, C.; Stoica, Mihaela; Pausescu, P.; Cruceanu, Eugen; Pompe, Wolfgang; Wuensch, R.; Richter, Asta; Scheibe, H. J.

    1989-05-01

    Device quality PbS photoconducting films were obtained by laser plasma vapour deposition on special glass substrates at room temperature and their structure was investigated by X-ray diffraction. High Tc superconducting films of composition Dy0.2Y0.8Ba2Cu3O~7 and YBa2Cu3O~7 were deposited on sapphire substrate. It was shown for laser deposited YBa2Cu3O~7 that a buffer layer of the same composition predeposited by rf sputtering allows for getting high quality superconducting films.

  12. Preparation and transport properties of high-Tc superconducting thick films

    NASA Astrophysics Data System (ADS)

    Aponte, J. M.; Octavio, M.

    1989-08-01

    We have prepared thick films of high Tc superconductors on a variety of substrates: SrTiO3, BeO, Zr(Ca)O2, alumina, and sapphire. The powder of the YBa2Cu3O7-δ compound is mixed with an organic solvent and painted on the substrates. The films are then dried and fired. We have studied the effect of the substrate and of the firing temperature on the superconducting properties of the films. We found an optimum firing temperature of 990 °C. The films prepared are superconducting with Tc (R=0) as high as 82 K. We discuss the shape of the resistance-versus-temperature curves as well as the temperature dependence of the critical currents of these films.

  13. Study of high [Tc] superconducting thin films grown by MOCVD

    SciTech Connect

    Erbil, A.

    1990-01-01

    Work is described briefly, which was carried out on development of techniques to grow metal-semiconductor superlattices (artificially layered materials) and on the copper oxide based susperconductors (naturally layered materials). The current growth technique utilized is metalorganic chemical vapor deposition (MOCVD). CdTe, PbTe, La, LaTe, and Bi[sub 2]Te[sub 3] were deposited, mostly on GaAs. Several YBa[sub 2]Cu[sub 3]O[sub 7] compounds were obtained with possible superconductivity at temperatures up to 550 K (1 part in 10[sup 4]). YBa[sub 2]Cu[sub 3]O[sub 7[minus]x] and Tl[sub 2]CaBa[sub 2]Cu[sub 2]O[sub y] thin films were deposited by MOCVD on common substrates such as glass.

  14. High Tc superconductivity; Thin films and applications; Proceedings of the Meeting, San Diego, CA, Mar. 20, 21, 1990

    NASA Astrophysics Data System (ADS)

    Chi, Cheng-Chung; van Dover, R. Bruce

    Various papers on high-Tc superconductivity in thin films and applications are presented. Individual topics addressed include: preparation of high-Tc YBa2Cu3O(7-x) thin films, study of epitaxial YBa2Cu3O(x) films, electrochemical deposition of high-Tc superconducting thin films, relative surface stoichiometry of high-Tc materials by total reflection X-ray fluorescence, preparation and properties YBa2Cu3O(7-x) thin-film SQUIDs, Si-coupled superconducting FETs using microfabrication technologies, enhanced critical currents by high-pressure impregnation of 1-2-3 systems with normal conductors. Also discussed are: YBaCuO thin films used as electrical switch or current limiter, optically triggered switching of superconducting YBa2Cu3O7 thin films, high-Tc superconducting thin films as optical radiation detectors, MBE as a path to novel high-Tc superconductors, ion-beam codeposition of HTSC films on SrTiO3 and ITO/Si, plasma luminescence spectroscopy for sputtering growth of high-Tc superconductors, barium diffusion in metalloorganic solution deposited barrier layers and Y1Ba2Cu3O(7-x) films.

  15. High-Tc superconducting rectangular microstrip patch covered with a dielectric layer

    NASA Astrophysics Data System (ADS)

    Bedra, Sami; Fortaki, Tarek

    2016-05-01

    This paper presents a full-wave method to calculate the resonant characteristics of rectangular microstrip antenna with and without dielectric cover, to explain the difference of performance with temperature between superconducting and normal conducting antenna. Especially the characteristics of high temperature superconducting (HTS) antenna were almost ideal around the critical temperature (Tc). The dyadic Green's functions of the considered structure are efficiently determined in the vector Fourier transform domain. The effect of the superconductivity of the patch is taken into account using the concept of the complex resistive boundary condition. The computed results are found to be in good agreement with results obtained using other methods. Also, the effects of the superstrate on the resonant frequency and bandwidth of rectangular microstrip patch in a substrate-superstrate configuration are investigated. This type of configuration can be used for wider bandwidth by proper selection of superstrate thickness and its dielectric constants.

  16. Effect of Van Hove singularities on high-Tc superconductivity in H3S

    NASA Astrophysics Data System (ADS)

    Sano, Wataru; Koretsune, Takashi; Tadano, Terumasa; Akashi, Ryosuke; Arita, Ryotaro

    2016-03-01

    One of the interesting open questions for the high-transition-temperature (Tc) superconductivity in sulfur hydrides is why high-pressure phases of H3S have extremely high Tc's. Recently, it has been pointed out that the presence of the Van Hove singularities (VHS) around the Fermi level is crucial. However, while there have been quantitative estimates of Tc based on the Migdal-Eliashberg theory, the energy dependence of the density of states (DOS) has been neglected to simplify the Eliashberg equation. In this study, we go beyond the constant DOS approximation and explicitly consider the electronic structure over 40 eV around the Fermi level. In contrast with the previous conventional calculations, this approach with a sufficiently large number of Matsubara frequencies enables us to calculate Tc without introducing the empirical pseudo Coulomb potential. We show that while H3S has much higher Tc than H2S for which the VHS is absent, the constant DOS approximation employed so far seriously overestimates (underestimates) Tc by ˜60 K (˜10 K) for H3S (H2S ). We then discuss the impact of the strong electron-phonon coupling on the electronic structure with and without the VHS and how it affects the superconductivity. In particular, we focus on (1) the feedback effect in the self-consistent calculation of the self-energy, (2) the effect of the energy shift due to the zero-point motion, and (3) the effect of the changes in the phonon frequencies due to strong anharmonicity. We show that the effect of (1)-(3) on Tc is about 10-30 K for both H3S and H2S . Eventually, Tc is estimated to be 181 K for H3S at 250 GPa and 34 K for H2S at 140 GPa, which explains the pressure dependence of Tc observed in the experiment. In addition, we evaluate the lowest-order vertex correction beyond the Migdal-Eliashberg theory and discuss the validity of the Migdal approximation for sulfur hydrides.

  17. Dynamic Jahn-Teller Coupling, Anharmonic Oxygen Vibrations and HIGH-Tc Superconductivity in Oxides

    NASA Astrophysics Data System (ADS)

    Johnson, K. H.; Clougherty, D. P.; McHenry, M. E.

    A universal dynamic Jahn-Teller (DJT) mechanism for superconductivity and its applications to CuO and BaBiO3 high-Tc oxides are reviewed. Dynamical interconversion between the shallow "double-well" potentials of degenerate delocalized oxygen-oxygen "pπ-bonds" at the Fermi energy (EF) induces anharmonic oxygen vibrations, lattice-electron coupling, and Cooper pairing. This mechanism yields high Tc's and small-to-vanishing isotope shifts for cuprates, where O(pπ)-O(pπ) bond overlap at EF is promoted by Cu(dπ*)-O(pπ) hybridization. It yields lower Tc's and larger isotope shifts for BaBiO3's, where O(pπ)-O(pπ) overlap is small. For vanishing bond overlap at EF, DJT coupling reduces to harmonic phonon coupling in BCS theory. Simple formulae for calculating Tc and isotope shifts for any superconductor from the "real-space" chemical bonding at EF are presented, yielding (Tc)max ≈ 230 K.

  18. Microwave surface resistance of high Tc superconducting films

    NASA Astrophysics Data System (ADS)

    Apte, Prakash R.; Pinto, R.; Kumar, Dhananjay; Vijayaraghavan, R.

    1995-09-01

    The surface resistance, Rs, at microwave frequencies has been an important qualification parameter for high temperature superconductor (HTS) thin films. HTS thin films with low Rs have been realized on many substrates, and many groups have realized Rs values in the range 300 - 400 (mu) (Omega) at 10 GHz at 77 K with YBa2Cu3O7-(delta ) (YBCO) films on <100> LaAlO3 substrates. Both microstrip resonator and parallel plate resonator techniques are being used to measure Rs values of HTS thin films. It has been observed that the value of Rs at given frequency and temperature critically depends upon the epitaxial quality and granularity of the films. For example, YBCO films grown on <100> MgO have been found to be granular and weak link limited with a significant microwave power dependence of Rs. On the other hand, YBCO films insitu grown on <100> LaAlO3 have shown better epitaxy with low Rs. This is obviously due to the much better lattice match of YBCO with <100> LaAlO3 if the targets used for laser deposition are doped with Ag. Extensive work carried out in our laboratory has shown that a Ag-doping level of around 5 wt.% in YBCO is the optimum which results in YBCO films of much improved quality. We have realized Ag-doped YBCO films with Jc values of 6 - 8 X 106 Acm-2 at 77 K and a low Rs value of 210 (mu) (Omega) at 10 GHz at 77 K on <100> LaAlO3. Both these values are the best realized on LaAlO3 to date. What is equally important is the fact that with Ag-doping the reproducibility of the epitaxial quality of the films improves significantly. This has been found to be due to the enhanced oxygenation of films during growth and the surfactant effect of Ag. Experiments have shown that even the optimum temperature for insitu growth in reduced considerably by Ag-doping. It must be mentioned, however, that the only negative aspect of Ag-doping is the higher microwave residual surface resistance, Rres, observed in these films at (very) low temperatures. This is obviously due

  19. Noise properties of high-Tc superconducting flux transformers fabricated using chemical-mechanical polishing

    NASA Astrophysics Data System (ADS)

    Chukharkin, M.; Kalabukhov, A.; Schneiderman, J. F.; Öisjöen, F.; Snigirev, O.; Lai, Z.; Winkler, D.

    2012-07-01

    Reproducible high-temperature superconducting multilayer flux transformers were fabricated using chemical mechanical polishing. The measured magnetic field noise of the flip-chip magnetometer based on one such flux transformer with a 9 × 9 mm2 pickup loop coupled to a bicrystal dc SQUID was 15 fT/Hz1/2 above 2 kHz. We present an investigation of excess 1/f noise observed at low frequencies and its relationship with the microstructure of the interlayer connections within the flux transformer. The developed high-Tc SQUID magnetometers may be advantageous in ultra-low field magnetic resonance imaging and, with improved low frequency noise, magnetoencephalography applications.

  20. Local effects of apical oxygen on superconductivity in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Mori, Michiyasu; Tohyama, Takami; Maekawa, Sadamichi

    2008-03-01

    The superconducting critical temperature (Tc) of high- Tc cuprates widely distributes among various series of crystal structures, even if the doping rate is optimized in the CuO2 planes. In addition, the Tc is enhanced by applying pressure[1]. These material- and pressure dependences have meaningful correlation with an energy difference of oxygen sites in an apical site and in the CuO2 plane (VA)[2]. On the other hand, Slezak et al. has found that locally modulated gap energy has anti-correlation with a distance between a Cu- and an apical O-sites, i.e., the larger distance is related to the smaller gap energy[3]. We study such a local effect of apical oxygen on superconductivity by calculating the Madelung potential. In particular, we focus on a local variation of VA, whose value approximately corresponds to stability of the Zhang- Rice singlet state[2]. It is found that, on neighboring sites of apical sites close to Cu sites, VA are locally enhanced compared to other sites. To estimate the gap energy, we propose a toy model like a BCS mean field Hamiltonian with an additional degree of freedom, which describes a role of apical oxygen. We will discuss an anti-correlation between the gap energy and the position of apical oxygen. [1] N. Tanahashi et al: Jpn. J. Appl. Phys. 28, L762 (1989). [2] Y. Ohta, T. Tohyama, and S. Maekawa: Phys. Rev. B 43, 2968 (1991). [3] J. Slezak, PhD thesis.

  1. Microstrip ring resonator technique for measuring microwave attenuation in high-Tc superconducting thin films

    NASA Astrophysics Data System (ADS)

    Takemoto, June H.; Oshita, Floyd K.; Fetterman, Harold R.; Kobrin, Paul; Sovero, Emilio

    1989-10-01

    Microwave attenuation of high-Tc superconducting (HTS) films sputtered on MgO and ZrO2 were measured using a microstrip ring resonator circuit. The results for Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O resonators were compared to those for gold-plated resonators of identical design. The losses of superconducting and gold-plated films were determined from unloaded Q-factor measurements. The attenuation of Y-Ba-Cu-O film on an MgO substrate is approximately 31 percent lower than that of gold films at 6.6 GHz and 33 percent lower at 19.2 GHz for temperatures below 50 K. The approach of using microstrips to characterize microwave losses shows the usefulness of HTS films in integrated circuit technology.

  2. Anomalous open-circuit voltage from a high-Tc superconducting dynamo

    NASA Astrophysics Data System (ADS)

    Bumby, C. W.; Jiang, Zhenan; Storey, J. G.; Pantoja, A. E.; Badcock, R. A.

    2016-03-01

    We report on the behavior of a high-Tc superconducting (HTS) homopolar dynamo which outputs a DC open-circuit voltage when the stator is in the superconducting state, but behaves as a conventional AC alternator when the stator is in the normal state. We observe that this time-averaged DC voltage arises from a change in the shape of the AC voltage waveform that is obtained from a normal conducting stator. The measured DC voltage is proportional to frequency, and decreases with increasing flux gap between the rotor magnet and the HTS stator wire. We observe that the DC output voltage decreases to zero at large flux gaps, although small differences between the normal-conducting and superconducting waveforms are still observed, which we attribute to screening currents in the HTS stator wire. Importantly, the normalised pulse shape is found to be a function of the rotor position angle only. Based on these observations, we suggest that the origin of this unexpected DC effect can be explained by a model first proposed by Giaever, which considers the impact of time-varying circulating eddy currents within the HTS stator wire. Such circulating currents form a superconducting shunt path which "short-circuits" the high field region directly beneath the rotor magnet, at those points in the cycle when the rotor magnet partially overlaps the superconducting stator wire. This reduces the output voltage from the device during these periods of the rotor cycle, leading to partial rectification of the output voltage waveform and hence the emergence of a time-averaged DC voltage.

  3. High-Tc Superconducting Thin- and Thick-Film-Based Coated Conductors for Energy Applications

    SciTech Connect

    Cantoni, Claudia; Goyal, Amit

    2010-01-01

    Although the first epitaxial films of YBCO with high Tc were grown nearly 20 years ago, the understanding and control of the nanostructures responsible for the dissipation-free electrical current transport in high temperature superconductors (HTS) is quite recent. In the last six to seven years, major advances have occurred in the fundamental investigation of low angle grain boundaries, flux-pinning phenomena, growth mode, and atomic-level defect structures of HTS epitaxial films. As a consequence, it has been possible to map and even engineer to some extent the performance of HTS coatings in large regions of the operating H, T, J phase space. With such progress, the future of high temperature superconducting wires looks increasingly promising despite the tremendous challenges offered by these brittle and anisotropic materials. Nevertheless, further performance improvements are necessary for the superconducting technology to become cost-competitive against copper wires and ultimately succeed in revolutionizing the transmission of electricity. This can be achieved by further diminishing the gap between theoretical and experimental values of the critical current density Jc, and/or increasing the thickness of the superconductive layer as much as possible without degrading performance. In addition, further progress in controlling extrinsic and/or intrinsic nano-sized defects within the films is necessary to significantly reduce the anisotropic response of HTS and obtain a nearly constant dependence of the critical current on the magnetic field orientation, which is considered crucial for power applications. This chapter is a review of the challenges still present in the area of superconducting film processing for HTS wires and the approaches currently employed to address them.

  4. Fabrication of single electron tunneling devices using layered structures of high- Tc superconducting materials

    NASA Astrophysics Data System (ADS)

    Kim, S.-J.; Yamashita, T.

    2006-10-01

    We have fabricated the submicron structures using high-Tc superconducting materials of Bi2Sr2CuO6+δ (Bi-2201). The stacks of layered structures are made by focused-ion-beam (FIB) etching methods. The fabricated 3D three terminal devices consist of source, drain and gate electrodes on the same chip. A gate electrode is capacitively coupled to a central island between two ultra-small tunnel junctions with in plane area S = 0.25 μm2 in series. Two stacks including an island structure show a Coulomb blockade region of 15 mV at zero gate potential. The effects are not smeared out by thermal fluctuations until temperatures greater than 150 K are reached.

  5. High Tc superconducting magnetic multivibrators for fluxgate magnetic-field sensors

    SciTech Connect

    Mohri, K.; Uchiyama, T.; Ozeki, A. . Faculty of Engineering)

    1989-09-01

    Sensitive and quick-response nonlinear inductance characteristics are found for high Tc superconducting (YBa/sub 2/Cu/sub 3/O/sub 7-chi/) disk cores at 77K in which soft magnetic BH hysteresis loops are observed. Various quick response magnetic devices such as modulators, amplifiers and sensors are built using these cores. The magnetizing frequency can be set to more than 20 MHz, which is difficult for conventional ferromagnetic bulk materials such as Permalloy amorphous alloys and ferrite. New quick-response fluxgate type magnetic-field sensors are made using ac and dc voltage sources. The former is used for second-harmonic type sensors, while the latter is for voltage-output multivibrator type sensors. Stable and quick-response sensor characteristics were obtained for two-core type multivibrators.

  6. Electrical characteristics of high- Tc superconducting mini-model cable under mechanical stresses in liquid nitrogen

    NASA Astrophysics Data System (ADS)

    Kim, H. J.; Kwag, D. S.; Kim, Y. S.; Kim, S. H.

    2005-01-01

    To develop 22.9 kV class high- Tc superconducting (HTS) cable in Korea, we have been studying electrical insulation properties of dielectric paper, such as breakdown voltage, partial discharge, which is one of the HTS cable structure elements. However, the research on the mechanical stress of dielectric paper compared to breakdown properties of dielectric paper is insufficient. A cracking and variation of the electrical insulation due to mechanical stresses during cooling and bending of HTS cables in cryogenic temperature is a serious problem. Thus, we investigated tensile stress and breakdown stress of dielectric paper under mechanical stress. Moreover, we manufactured mini-model cables investigated breakdown stress under bending stress to design a cable drum for conveyance. In the AC, impulse and partial discharge properties, all test results showed a similar tendency, and the suitable bending radius ratio R/ r was decided to be more than 25.

  7. High-Tc superconducting quantum interference filters (SQIFs) made by ion irradiation

    NASA Astrophysics Data System (ADS)

    Ouanani, S.; Kermorvant, J.; Ulysse, C.; Malnou, M.; Lemaître, Y.; Marcilhac, B.; Feuillet-Palma, C.; Bergeal, N.; Crété, D.; Lesueur, J.

    2016-09-01

    Superconducting quantum interference filters (SQIFs) are arrays of superconducting loops of different sizes including Josephson junctions (JJ). For a random distribution of sizes, they present a non-periodic response to an applied magnetic field, with a large transfer function and a magnetic field sensitivity potentially improved with respect to that of a single SQUID. Such properties make SQIFs interesting devices to detect the magnetic component of electromagnetic waves at microwave frequencies. We have used the highly scalable technique of ion irradiation to make SQUIDs and SQIFs based on commercial YBa2Cu3O7 films, and studied their properties. Both display optimal performance as a function of temperature and bias current, that can be understood in the frame of numerical simulations that we developed. The role of asymmetries and dispersion in JJ characteristics (routinely found in high Tc superconductors technologies) is also studied. We have found that none of them impede the existence of a SQIF effect but both play a role on the emergence of the optimal point. We finally present results on SQIF made with 2000 SQUIDs in series, showing a transfer function {{d}}V/{{d}}B∼ 1000V/T.

  8. Levitation performance of the magnetized bulk high- Tc superconducting magnet with different trapped fields

    NASA Astrophysics Data System (ADS)

    Liu, W.; Wang, J. S.; Liao, X. L.; Zheng, S. J.; Ma, G. T.; Zheng, J.; Wang, S. Y.

    2011-03-01

    To a high- Tc superconducting (HTS) maglev system which needs large levitation force density, the magnetized bulk high- Tc superconductor (HTSC) magnet is a good candidate because it can supply additional repulsive or attractive force above a permanent magnet guideway (PMG). Because the induced supercurrent within a magnetized bulk HTSC is the key parameter for the levitation performance, and it is sensitive to the magnetizing process and field, so the magnetized bulk HTSC magnets with different magnetizing processes had various levitation performances, not only the force magnitude, but also its force relaxation characteristics. Furthermore, the distribution and configuration of the induced supercurrent are also important factor to decide the levitation performance, especially the force relaxation characteristics. This article experimentally investigates the influences of different magnetizing processes and trapped fields on the levitation performance of a magnetized bulk HTSC magnet with smaller size than the magnetic inter-pole distance of PMG, and the obtained results are qualitatively analyzed by the Critical State Model. The test results and analyses of this article are useful for the suitable choice and optimal design of magnetized bulk HTSC magnets.

  9. Development of high Tc (greater than 100 K) Bi, Tl and Y-based materials as superconducting circuit elements

    NASA Technical Reports Server (NTRS)

    Haertling, Gene; Grabert, Gregory; Gilmour, Phillip

    1993-01-01

    Results on this project over the past three years have shown that the Bi and Tl-based superconducting materials in bulk form are noticeably different from the Y-based 123 material in that superconductivity is considerably harder to achieve, maintain and reproduce. This is due primarily to the difficulty in obtaining the higher Tc phase in pure form since it commonly co-exists with other undesirable, lower Tc phases. In particular, it has been found that long processing times for calcining and firing (20 - 200 hrs.) and close control of temperatures which are very near the melting point are required in order to obtain higher proportions of the desirable, high Tc (2223) phase.

  10. Spectroscopy of metal "superatom" nanoclusters and high-Tc superconducting pairing

    NASA Astrophysics Data System (ADS)

    Halder, Avik; Kresin, Vitaly V.

    2015-12-01

    A unique property of metal nanoclusters is the "superatom" shell structure of their delocalized electrons. The electronic shell levels are highly degenerate and therefore represent sharp peaks in the density of states. This can enable exceptionally strong electron pairing in certain clusters composed of tens to hundreds of atoms. In a finite system, such as a free nanocluster or a nucleus, pairing is observed most clearly via its effect on the energy spectrum of the constituent fermions. Accordingly, we performed a photoionization spectroscopy study of size-resolved aluminum nanoclusters and observed a rapid rise in the near-threshold density of states of several clusters (A l37 ,44 ,66 ,68 ) with decreasing temperature. The characteristics of this behavior are consistent with compression of the density of states by a pairing transition into a high-temperature superconducting state with Tc≳100 K. This value exceeds that of bulk aluminum by two orders of magnitude. These results highlight the potential of novel pairing effects in size-quantized systems and the possibility to attain even higher critical temperatures by optimizing the particles' size and composition. As a new class of high-temperature superconductors, such metal nanocluster particles are promising building blocks for high-Tc materials, devices, and networks.

  11. A high Tc superconducting terahertz emitter operated from 0.5 to 2.4 THz

    NASA Astrophysics Data System (ADS)

    Kashiwagi, T.; Sakamoto, K.; Kubo, H.; Shibano, Y.; Enomoto, T.; Kitamura, T.; Asanuma, K.; Yasui, T.; Watanabe, C.; Nakade, K.; Saiwai, Y.; Katsuragawa, T.; Tanaka, T.; Yuasa, T.; Tsujimoto, M.; Yoshizaki, R.; Yamamoto, T.; Minami, H.; Klemm, R. A.; Kadowaki, K.

    According to our previous studies, the efficiency of the THz radiation from a high Tc superconducting emitter can be improved greatly when the stand-alone mesa structure of Bi2212 single crystal is used for the emitter1). The principal reason for that lies in the heat removal from the mesa. Recently, we developed a new device structure with high heat exhaust from the stand-alone mesa structures and studied the radiation characteristics from the different shape of mesa structures. The results obtained from a cylindrical stand alone mesa show very wide the radiation frequencies ranging from 0.5 to 2.4 THz. Strong emission power peaks were observed at about 1.0 THz and 1.6 THz2). 1) T. Kitamura et al., Appl. Phys. Lett. 105, 202603 (2014) 2) T. Kashiwagi et al., Appl. Phys. Lett. 107, 082601 (2015) T. K. is supported by Futaba Electronics Memorial Foundation and JSPS KAKENHI Grant No. 15K20897. This work is in part performed in collaboration with Dr. Wai Kwok and his group in Argonne National Lab.

  12. Pressure-induced metallization of dense (H₂S)₂H₂ with high-Tc superconductivity.

    PubMed

    Duan, Defang; Liu, Yunxian; Tian, Fubo; Li, Da; Huang, Xiaoli; Zhao, Zhonglong; Yu, Hongyu; Liu, Bingbing; Tian, Wenjing; Cui, Tian

    2014-01-01

    The high pressure structures, metallization, and superconductivity of recently synthesized H2-containing compounds (H2S)2H2 are elucidated by ab initio calculations. The ordered crystal structure with P1 symmetry is determined, supported by the good agreement between theoretical and experimental X-ray diffraction data, equation of states, and Raman spectra. The Cccm structure is favorable with partial hydrogen bond symmetrization above 37 GPa. Upon further compression, H2 molecules disappear and two intriguing metallic structures with R3m and Im-3m symmetries are reconstructive above 111 and 180 GPa, respectively. The predicted metallization pressure is 111 GPa, which is approximately one-third of the currently suggested metallization pressure of bulk molecular hydrogen. Application of the Allen-Dynes-modified McMillan equation for the Im-3m structure yields high Tc values of 191 K to 204 K at 200 GPa, which is among the highest values reported for H2-rich van der Waals compounds and MH3 type hydride thus far.

  13. Development of high Tc (greater than 100 K) Bi, Tl and Y-based materials as superconducting circuit elements

    NASA Technical Reports Server (NTRS)

    Haertling, Gene; Grabert, Gregory; Gilmour, Phillip

    1994-01-01

    Experimental work on this project over the last four years has resulted in establishing processing and characterization techniques for producing both the Bi-based and Tl-based superconductors in their high temperature (2223) forms. In the bulk, dry pressed form, maximum critical temperatures (Tc) of 108.2 K and 117.8 K, respectively, were measured. Results have further shown that the Bi and Tl-based superconducting materials in bulk form are noticeably different from the Y-based 123 material in that superconductivity is considerably harder to achieve, maintain, and reproduce. This is due primarily to the difficulty in obtaining the higher Tc phase in pure form since it commonly co-exists with other undesirable, lower Tc phases. In particular, it has been found that long processing times for calcining and firing (20 - 200 hrs.) and close control of temperatures which are very near the melting point are required in order to obtain higher proportions of the desirable, high Tc (2223) phase. Thus far, the BSCCO bulk materials has been prepared in uniaxially pressed, hot pressed, and tapecast form. The uniaxially pressed material has been synthesized by the mixed oxide, coprecipitation, and melt quenching processes. The tapecast and hot pressed materials have been prepared via the mixed oxide process. In addition, thick films of BSCCO (2223 phase) have been prepared by screen printing on to yttria and magnesia stabilized zirconia with only moderate success; i.e., superconductivity was achieved in these thick films, but the highest Tc obtained in these films was 89.0 K. The Tc's of the bulk hot pressed, tapecast, and screen printed thick film materials were found to be 108.2, 102.4, and 89.0 K, respectively.

  14. HIGH-Tc Superconductivity in Electron-Doped Layer Structured Nitrides

    NASA Astrophysics Data System (ADS)

    Yamanaka, Shoji

    2000-08-01

    A new series of superconductors based on layer structured nitrides has been developed. The general compositions of the nitrides are MNX (M = Zr, Hf; X = Cl, Br, I). The beta-type polymorph consists of MN double layers sandwiched between close-packed halogen layers, which are characterized as semiconductors with a band gap of 3-4 eV. Electrons can be doped to the nitride layers by intercalation of alkali metals between the layers. Upon the intercalation, the compounds become superconductors with the transition temperatures (Tcs) as high as 13 and 25.5 K for beta-ZrNCl and beta-HfNCl systems, respectively. The Tc of the electron doped beta-HfNCl is higher than that observed in any intermetallic compound and suggests that layered nitrides may exhibit Tcs comparable to those observed in layer structured complex copper oxide superconductors. The layer structured nitrides can be variously modified by the amounts of doping, the types of alkali metals, and the interlayer separation, which can be controlled by co-intercalation of organic molecules with alkali metals. This article dicusses topics including the synthesis and structure of the transition metal nitride halides, intercalation, superconductivity, and band structures.

  15. High T(c) superconductivity in MgB2 by nonadiabatic pairing.

    PubMed

    Cappelluti, E; Ciuchi, S; Grimaldi, C; Pietronero, L; Strässler, S

    2002-03-18

    The evidence for the key role of the sigma bands in the electronic properties of MgB2 points to the possibility of nonadiabatic effects in the superconductivity of these materials. These are governed by the small value of the Fermi energy due to the vicinity of the hole doping level to the top of the sigma bands. We show that the nonadiabatic theory leads to a coherent interpretation of T(c) = 39 K and the boron isotope coefficient alphaB = 0.30 without invoking very large couplings and it naturally explains the role of the disorder on T(c). It also leads to various specific predictions for the properties of MgB2 and for the material optimization of these types of compounds.

  16. Superconductivity and chemical composition of the high-Tc phase (Tc = 111 K) in the Sb-Pb-Bi-Sr-Ca-Cu-O system

    NASA Astrophysics Data System (ADS)

    Kijima, Naota; Gronsky, Ronald; McKernan, Steffen K.; Endo, Hozumi; Oguri, Yasuo

    1991-01-01

    A superconducting phase with a critical temperature of 111 K in the Sb-Pb-Bi-Sr-Ca-Cu-O system has been synthesized by means of a long firing period. Its crystal structure is similar to the high-Tc phase (107 K) in the Pb-Bi-Sr-Ca-Cu-O system, and its average chemical composition is 4.3, 2.6, 19.2, 21.4, 15.8 and 36.9 percent for Sb, Pb, Bi, Sr, Ca, and Cu, respectively. The summation of the Sb concentration and the Ca concentration is approximately the same for all the samples of this phase, implying that Sb substitutes for Ca, and oxygen atoms are introduced to compensate the oxygen deficiency in the central Cu-O layer sandwiched by the two Ca layers in the crystal structure of the high-Tc phase.

  17. First principles Study on Transparent High-Tc Superconductivity in hole-doped Delafossite CuAlO2

    NASA Astrophysics Data System (ADS)

    Nakanishi, Akitaka; Katayama-Yoshida, Hiroshi

    2012-02-01

    The CuAlO2 is the transparent p-type conductor without any intentional doping. Transparent superdoncutivity and high thermoelectric power are suggested in p-type CuAlO2 [1]. Katayama-Yoshida et al. proposed that it may cause a strong electron-phonon interaction and a superconductivity. But, the calculation of superconducting critical temperature Tc is not performed. We performed the first principles calculation about the Tc of hole-doped CuAlO2 by shifting the Fermi level rigidly. In lightly hole-doped CuAlO2, the Fermi level is located at Cu and O anti-bonding band. The electrons of this band strongly interact with the A1L1 phonon mode because the direction of O-Cu-O dumbbell is parallel to the oscillation direction of the A1L1 phonon mode. As a result, Tc of lightly hole-doped CuAlO2 is about 50 K. We also discuss the materials design to enhance the Tc based on the charge-excitation-induced negative effective U system.[4pt] [1] H. Katayama-Yoshida, T. Koyanagi, H. Funashima, H. Harima, A. Yanase: Solid State Communication 126 (2003) 135. [0pt] [2] A. Nakanishi and H. Katayama-Yoshida: Solid State Communication, in printing. (arXiv:1107.2477v3

  18. Study on Recovery Performance of High Tc Superconducting Tapes for Resistive Type Superconducting Fault Current Limiter Applications

    NASA Astrophysics Data System (ADS)

    kar, Soumen; Kulkarni, Sandeep; Dixit, Manglesh; Singh, Kuwar Pal; Gupta, Alok; Balasubramanyam, P. V.; Sarangi, S. K.; Rao, V. V.

    Recent advances in reliable production of long length high temperature superconducting (HTS) tapes have resulted in commercial application of superconducting fault current limiters (SFCLs) in electrical utility networks. SFCL gives excellent technical performance when compared to conventional fault current limiters. The fast self-recovery from normal state to superconducting state immediately after the fault removal is an essential criterion for resistive type SFCL operation. In this paper, results on AC over-current testing of 1st generation (1G) Bi2223 tapes and 2nd generation (2G) YBCO coated conductors operating at 77 K are reported. From these results, the recovery time is estimated for different available HTS tapes in the market. The current limiting tests have also been performed to study the effective current limitation. Further, the recovery characteristics after the current limitation are quantitatively discussed for repetitive faults for different time intervals in the range of 100 ms to few seconds.

  19. Effect of superconducting fluctuations on the NMR relaxation rate of high-Tc superconductors

    SciTech Connect

    Appel, J. ); Fay, D.; Kautz, C. )

    1994-06-01

    The effect of superconducting order parameter fluctuations on the nuclear-spin relaxation rate, 1/T[sub 1], is studied for clean two-dimensional systems by calculating the three Maki-Thomson-type diagrams which represent the lowest-order fluctuation contributions to the transverse susceptibility. For Gaussian fluctuations and for temperatures near the mean field transition temperature, T[sub c0], we employ a weak-coupling theory in which the pair-fluctuation propagator can also include pair-breaking effects. We also go beyond the Gaussian theory and take into account the interactions between Cooper-pair fluctuations corresponding to the fourth-order Ginzburg Landau fluctuation terms. We compare our results with previous results in the dirty limit and in 3D. We obtain a pronounced peak in 1/T[sub 1] at Tc and briefly discuss possible reasons why this peak is not observed. 6 refs., 4 figs., 1 tab.

  20. Superconductivity in the high-Tc Bi-Ca-Sr-Cu-O system - Phase identification

    NASA Technical Reports Server (NTRS)

    Hazen, R. M.; Prewitt, C. T.; Angel, R. J.; Ross, N. L.; Finger, L. W.

    1988-01-01

    Four phases are observed in superconducting Bi-Ca-Sr-Cu-O samples. The superconducting phase, with onset temperature near 120 K, is a 15.4-A-layered compound with composition near Bi2Ca1Sr2Cu2O9 and an A-centered orthorhombic unit subcell 5.41 x 5.44 x 30.78 A. X-ray diffraction and electron microscopy data are consistent with a structure of alternating perovskite and Bi2O2 layers. High-resolution transmission electron microscopy images reveal a b-axis superstructure of 27.2 A, numerous (001) stacking faults, and other defects.

  1. Environmental testing of high Tc superconductive thermal isolators for space-borne cryogenic detector systems

    NASA Technical Reports Server (NTRS)

    Wise, Stephanie A.; Buckley, John D.; Randolf, Henry W.; Verbelyi, Darren; Haertling, Gene H.; Hooker, Matthew W.; Selim, Raouf; Caton, Randall

    1992-01-01

    Thick films of superconductive material on low thermal conductivity substrates (e.g., yttria-stabilized zirconia and fused silica) are considered as a replacement for the existing electrical connections between the detector array and data acquisition and storage electronics in the cryogenic detector systems being developed by NASA. The paper describes some of the design constraints on the superconducting device and presents results of a preliminary analysis of the effects of vibration, gamma irradiation, and long-term exposure to high vacuum and liquid nitrogen encountered in operating such a device in space.

  2. On local pairs vs. BCS: Quo vadis high-Tc superconductivity

    DOE PAGES

    Pavuna, D.; Dubuis, G.; Bollinger, A. T.; Wu, J.; He, X.; Bozovic, I.

    2016-07-28

    Since the discovery of high-temperature superconductivity in cuprates, proposals have been made that pairing may be local, in particular in underdoped samples. Furthermore, we briefly review evidence for local pairs from our experiments on thin films of La 2–xSrxCuO4, synthesized by atomic layer-by-layer molecular beam epitaxy (ALL-MBE).

  3. Collective pinning behavior of intergranular Josephson vortices and the intergranular irreversibility line of high-{Tc} superconducting ceramics

    SciTech Connect

    Miu, L.

    1995-02-01

    The supercurrent-transport properties of YBa{sub 2}Cu{sub 3}O{sub {approximately}7} (Y:123) polycrystalline bulk sintered samples with random grain orientation were thoroughly investigated. The dissipation process in these materials occurs due to intergranular flux motion, rather than by weak-link quenching. It was found that the model which takes into consideration collective creep of intergranular vortices is self-consistent in describing the low-voltage-level current-voltage characteristics and the intergranular irreversibility line of high-{Tc} superconducting ceramics.

  4. Plasma-Assisted Laser Deposition of High T(c) Oxide Superconducting Thin Films.

    NASA Astrophysics Data System (ADS)

    Witanachchi, Sarath

    1990-01-01

    Since the discovery of the high T_ {rm c} oxide superconductor YBa _2Cu_3O _7 a great deal of attention has been given to the fabrication of superconducting thin films of this material. Thin films of the new superconductor have an immense importance in scientific research, such as microwave, infrared and critical current studies, and also in applications, such as Josephson junction based digital computer circuits, SQUID (Superconducting Quantum Interference Devices), transmission lines, and interconnectors. Integration of these films with semiconductors and multilayer capabilities are important for future practical uses. For most of these applications, a low temperature in-situ fabrication process is designed to obtain smooth surfaces and sharp interfaces. Less than 500^circC growth temperatures would be compatible with the existing semiconductor technology. At the beginning of this research project, the lowest deposition temperature reported for the fabrication of in-situ superconducting films was about 650^circC. Our goal was to develop a technique that would enable us to fabricate in-situ high T_{ rm c} superconducting films at a substrate temperature lower than 650^circC. By incorporating a weak oxygen plasma in the laser evaporation zone, we have been able to develop a novel plasma assisted laser deposition (PLD) technique to grow YBaCuO films that are superconducting in the as-deposited state. Using this technique, good quality superconducting films with mirror -like surfaces have been grown at substrate temperatures as low as 500^circC. YBaCuO films were deposited on single crystal substrates, SrTiO_3, ZrO _2, MgO, sapphire and Si, and also on flexible stainless steel substrates. Films deposited on SrTiO _3 at 500^circC showed a critical temperature of 86K and a critical current of 10^5 A/cm^2 at 80K and 5 times 10^6 A/cm^2 at 4.3K. The possibility of improving the superconducting properties of the films deposited on sapphire, Si, and stainless steel by

  5. Phase Diagram and Electronic Properties of High-Tc Superconducting Oxides

    NASA Astrophysics Data System (ADS)

    Pavuna, Davor

    We firstly briefly summarize some of the most relevant recent results and open questions across rather complex electronic phase diagram of cuprates. We continue with a discussion of results on thin superconducting oxide films grown by laser ablation. Systematic studies show that BSCCO-phases and LSCO-214 exhibit conductor-like Fermi edge, whereas materials containing "chains" (like YBCO-123) are prone to very rapid surface degradation, most likely related to critical oxygen loss at the outermost layers. Recently, direct ARPES dispersion measurements on in-situ grown, strained 10UC thin LSCO-214 films (Tc = 44 K) have shown the band crossing of Fermi level well before the Brillouin zone boundary. This is in contrast to the flat band observed in unstrained single crystals — and to the band flattening predicted by band calculations for in-plane compressive strain. In spite of density of states reduction near the Fermi level, the critical temperature increases in strained films with respect to unstrained crystals; this poses further challenge to HTSC theory.

  6. Conceptual design of high Tc superconducting power cable and its economic evaluation

    NASA Astrophysics Data System (ADS)

    Suzuki, H.; Fukagawa, H.; Akita, S.

    1988-08-01

    The authors performed a conceptual design and cost evaluation of liquid nitrogen cooled superconducting power cables. They showed the results and clarified the concrete applications of high t(sub c) superconducting cables to electric power systems. They designed two types of cables, which have semi-flexible structure of three cable cores within one pipe. The optimum transmission voltage is 66kV for 2.5GVA/cct or 154kV for 5.0GVA/cct. This means an excellent economical merit of neglecting undergound power substations in the metropolitan cities. Instead of 6ccts of 275kV conventional OF cables installed in a culvert, only one circuit of 66kV liquid nitrogen cooled superconducting cable can transmit the same capacity. It was clarified that if all conventional cables in one culvert can be replaced by new cables, the transmission capacity can be increased 5 to 6 times or maximum 7.5 times.

  7. Direct angle resolved photoemission spectroscopy and superconductivity of strained high-Tc films

    NASA Astrophysics Data System (ADS)

    Pavuna, Davor; Ariosa, Daniel; Cloetta, Dominique; Cancellieri, Claudia; Abrecht, Mike

    2008-02-01

    Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (<30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-T_{c} superconductors (HTSC) under different degrees of epitaxial ({compressive vs. tensile}) strain. In overdoped and underdoped in-plane compressed (the strain is induced by the choice of substrate) ≈15 nm thin La_{2-x}Sr_{x}CuO_{4} (LSCO) films we almost double T_{c} to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES data under {tensile} strain exhibit the dispersion that is three-dimensional, yet T_{c} drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO_{2} plane, enhances the two-dimensional character of the dispersion and increases T_{c}, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual lattice of cuprates is like a `Napoleon-cake', i.e. rigid CuO_{2 } planes alternating with softer `reservoir', that distort differently under strain, our data rule out all oversimplified two-dimensional (rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced T_{c}.

  8. Twenty-GHz broadband microstrip array with electromagnetically coupled high-{Tc} superconducting feed network

    SciTech Connect

    Herd, J.S.; Poles, L.D.; Kenney, J.P.

    1996-07-01

    The use of high-temperature superconducting (HTS) feed lines and phase shifters can substantially improve the performance of microwave and millimeter-wave printed phased array antennas. A novel antenna architecture is described that provides a broadband radiating aperture to be used as a scanning array with compatible low-loss HTS phase shifters. The approach follows an earlier design demonstrated at 12 GHz, and this work extends the approach to 20 GHz. The antenna design, radiation patterns, bandwidth measurements, and thermal analysis are reported. A prototype thermal isolator design is described that reduces the heat load of coaxial interconnections between cryocooled and room temperature systems.

  9. Voltage divider operation using high-Tc superconducting interface-engineered Josephson junctions

    NASA Astrophysics Data System (ADS)

    Saitoh, Kazuo; Soutome, Yoshihisa; Fukazawa, Tokuumi; Tarutani, Yoshinobu; Takagi, Kazumasa

    2000-05-01

    A rapid-single-flux-quantum toggle-flip-flop logic gate was fabricated using high-temperature superconducting interface-engineered Josephson junctions. It was shown that the gate can operate as a voltage divider up to 155 GHz at 15 K and 19 GHz at 27 K. At the same time, the temperature dependence of the IcRn product and the maximum divided voltage was compared. As a result, it was found that the ratio of these values is 0.4-0.1 for 15 K>T>27 K. Circuit simulation with noise sources reveals this peculiar temperature dependence of the maximum divided voltage.

  10. An instrument for spatial conductivity measurements of high Tc superconducting (HTSC) materials

    NASA Technical Reports Server (NTRS)

    Vansant, T.

    1991-01-01

    High T(sub c) Superconducting (HTSC) thin films are suggested for use in a number of aerospace applications such as an IR bolometer and as electromagnetic shielding. As part of its flight assurance role, the Materials Branch of the Goddard Space Flight Center has initiated development of an instrument capable of measuring variations in conductivity for flat samples using an eddy current testing device and an X-Y positioning table. This instrument was used to examine bulk HTSC samples. System changes that would enable characterization of thin film materials are discussed.

  11. THz emission from a slice of high-Tc superconducting single crystal

    NASA Astrophysics Data System (ADS)

    Wang, Huabing

    2008-03-01

    Copper oxide superconductors possess intrinsically a layered crystalline structure, in which superconducting and non-superconducting layers interleave each other. Therefore the crystal itself consists of a number of superconducting junctions sequentially stacked along the c axis of the crystal, and these junctions are often referred to as intrinsic Josephson junctions (IJJs). In the case of Bi2Sr2CaCu2O8+δ (BSCCO), each IJJ measures approximately 1.5 nm thick. Many groups have been exploring the possibilities to develop terahertz (THz) detectors and oscillators based on IJJs, due to the high collective plasma frequencies (up to THz region), the uniformity in junction properties, the easiness to make a large junction array, and the low loss at high frequencies. Some years ago, in IJJs singled out from inside a slice of BSCCO single crystal with a double-sided process, THz response was successfully observed as sharp Shapiro steps at frequencies up to 2.5 THz, and harmonic mixings were carried out with harmonic numbers as large as 90. Recently observed have been THz oscillations in various structures of BSCCO IJJs, which can be excited by dc bias, in-plane magnetic fields, or microwave irradiations at several gigahertz. Needless to say, for practical applications, it is necessary to synchronize the emissions from IJJs, couple the THz oscillations into a finite space, guide them in a controllable way, monitor the frequencies and power levels, and preferably do the jobs using an integrated system. We have been making extensive efforts to explore these ideas, and will report our latest results at the meeting.

  12. Superconducting anisotropy in the electron-doped high-Tc superconductors Pr2-xCexCuO4-y.

    PubMed

    Wu, Guoqing; Greene, R L; Reyes, A P; Kuhns, P L; Moulton, W G; Wu, Bing; Wu, Feng; Clark, W G

    2014-10-01

    We report superconducting anisotropy measurements in the electron-doped high-Tc superconductors (HTSCs) Pr(2-x)Ce(x)C(u)O(4-y) (PCCO, x = 0.15 and 0.17) with an applied magnetic field (H0) up to 28 T. Our results show that the upper critical field [H(c2)(T)] of PCCO is highly anisotropic and as the temperature T → 0, the value of it at H0 ∥ c [H(c2,∥c)(0)] is far less than the Pauli limit. The low temperature anisotropic character of PCCO is found to be rather similar to that of hole-doped cuprate HTSCs, but apparently larger than that of typical Fe-based superconductors. This study also proves a new sensitive probe of detecting rich properties of unconventional superconductors with the use of the resonant frequency of an NMR probe circuit. PMID:25219526

  13. Superconducting anisotropy in the electron-doped high-Tc superconductors Pr2-xCexCuO4-y

    NASA Astrophysics Data System (ADS)

    Wu, Guoqing; Greene, R. L.; Reyes, A. P.; Kuhns, P. L.; Moulton, W. G.; Wu, Bing; Wu, Feng; Clark, W. G.

    2014-10-01

    We report superconducting anisotropy measurements in the electron-doped high-Tc superconductors (HTSCs) Pr2-xCexCuO4-y (PCCO, x = 0.15 and 0.17) with an applied magnetic field (H0) up to 28 T. Our results show that the upper critical field [Hc2(T)] of PCCO is highly anisotropic and as the temperature T → 0, the value of it at H0 ∥ c [Hc2,∥c(0)] is far less than the Pauli limit. The low temperature anisotropic character of PCCO is found to be rather similar to that of hole-doped cuprate HTSCs, but apparently larger than that of typical Fe-based superconductors. This study also proves a new sensitive probe of detecting rich properties of unconventional superconductors with the use of the resonant frequency of an NMR probe circuit.

  14. Series-Parallel Superconducting Quantum Interference Device Arrays Using High-TC Ion Damage Junctions

    NASA Astrophysics Data System (ADS)

    Wong, Travis; Mukhanov, Oleg

    2015-03-01

    We have fabricated several designs of three junction series-parallel DC Superconducting Quantum Interference Device (BiSQUID) arrays in YBa2Cu3O7-x using 104 ion damage Josephson Junctions on a single 1 cm2 chip. A high aspect ratio ion implantation mask (30:1 ratio) with 30 nm slits was fabricated using electron beam lithography and low pressure reactive ion etching. Samples were irradiated with 60 keV helium ions to achieve a highly uniform damaged region throughout the thickness of the YBCO thin film as confirmed with Monte Carlo ion implantation simulations. Low frequency measurements of four different BiSQUID series-parallel SQUID array devices will be presented to investigate the effect of the BiSQUID design parameters on the linearity of the SQUID array in response to magnetic fields. BiSQUID arrays could provide a promising architecture for improved linearity transimpedance amplifiers with high linearity.

  15. Imaging of local temperature distributions in mesas of high-Tc superconducting terahertz sources

    NASA Astrophysics Data System (ADS)

    Tsujimoto, M.; Kambara, H.; Maeda, Y.; Yoshioka, Y.; Nakagawa, Y.; Kakeya, I.

    2014-12-01

    Stacks of intrinsic Josephson junctions in high-Tc superconductors are a promising source of intense, continuous, and monochromatic terahertz waves. In this paer, we establish a fluorescence-based temperature imaging system to directly image the surface temperature on a Bi2Sr2CaCu2O8+δ mesa sample. Intense terahertz emissions are observed in both high- and low-bias regimes, where the mesa voltage satisfies the cavity resonance condition. In the high- bias regime, the temperature distributions are shown to be inhomogeneous with a considerable temperature rise. In contrast, in the low-bias regime, the distributions are rather uniform and the local temperature is close to the bath temperature over the entire sample.

  16. Magnetic relaxation with vortex creep observed by the magneto-optical image method for high Tc superconducting films

    NASA Astrophysics Data System (ADS)

    Lee, Wongi; Lee, Jhinhwan; Youm, Dojun; Yoo, Jaeun

    2016-06-01

    The relaxation of magnetic flux in high Tc superconducting films was investigated. After the samples were cooled in the applied magnetic fields, the magnetic field was turned off and the changes of the remaining magnetic flux distribution were observed by using the magneto-optical image method. The induced current density was examined which varies with the logarithmic-time dependence associated with the creep motions of vortices. The overall magnitude of the induced current density is observed to decrease as the external magnetic field applied during cooling is increased. The range of external fields examined was 30-50 mT. This could be explained by taking into account the formation of meandering shapes of vortices which develop during the period of transition to the creep mode. The results of the numerical simulation for this effect are in good agreement with the experimental results.

  17. Irradiation response of commercial, high-Tc superconducting tapes: Electromagnetic transport properties

    SciTech Connect

    Gapud, A. A.; Greenwood, N. T.; Alexander, J. A.; Khan, A.; Leonard, K. J.; Aytug, T.; List III, F. A.; Rupich, M. W.; Zhang, Y.

    2015-07-01

    Effects of low dose irradiation on the electrical transport current properties of commercially available high-temperature superconducting, coated-conductor tapes were investigated, in view of potential applications in the irradiative environment of fusion reactors. Three different tapes, each with unique as-grown flux-pinning structures, were irradiated with Au and Ni ions at energies that provide a range of damage effects, with accumulated damage levels near that expected for conductors in a fusion reactor environment. Measurements using transport current determined the pre- and post-irradiation resistivity, critical current density, and pinning force density, yielding critical temperatures, irreversibility lines, and inferred vortex creep rates. Results show that at the irradiation damage levels tested, any detriment to as-grown pre-irradiation properties is modest; indeed in one case already-superior pinning forces are enhanced, leading to higher critical currents.

  18. Irradiation response of commercial, high-Tc superconducting tapes: Electromagnetic transport properties

    DOE PAGES

    Gapud, A. A.; Greenwood, N. T.; Alexander, J. A.; Khan, A.; Leonard, K. J.; Aytug, T.; List III, F. A.; Rupich, M. W.; Zhang, Y.

    2015-07-01

    Effects of low dose irradiation on the electrical transport current properties of commercially available high-temperature superconducting, coated-conductor tapes were investigated, in view of potential applications in the irradiative environment of fusion reactors. Three different tapes, each with unique as-grown flux-pinning structures, were irradiated with Au and Ni ions at energies that provide a range of damage effects, with accumulated damage levels near that expected for conductors in a fusion reactor environment. Measurements using transport current determined the pre- and post-irradiation resistivity, critical current density, and pinning force density, yielding critical temperatures, irreversibility lines, and inferred vortex creep rates. Results showmore » that at the irradiation damage levels tested, any detriment to as-grown pre-irradiation properties is modest; indeed in one case already-superior pinning forces are enhanced, leading to higher critical currents.« less

  19. Irradiation response of commercial, high-Tc superconducting tapes: Electromagnetic transport properties

    NASA Astrophysics Data System (ADS)

    Gapud, A. A.; Greenwood, N. T.; Alexander, J. A.; Khan, A.; Leonard, K. J.; Aytug, T.; List, F. A.; Rupich, M. W.; Zhang, Y.

    2015-07-01

    Effects of low dose ion irradiation on the electrical transport current properties of commercially available high-temperature superconducting, coated-conductor tapes were investigated, in view of potential applications in irradiative environments. Three different tapes, each with unique and tailored as-grown flux-pinning structures, were irradiated with Au and Ni ions at energies that provide a range of damage effects, with accumulated damage levels near that expected for conductors in, for example, a fusion reactor environment. Measurements using transport current determined the pre- and post-irradiation resistivity, critical current density, and pinning force density, yielding critical temperatures, irreversibility lines, and inferred vortex creep rates. Results show that, at the irradiation damage levels tested, any detriment to as-grown pre-irradiation properties is modest; indeed in one case already-superior pinning forces are enhanced, leading to higher critical currents.

  20. Experimental and theoretical investigation on high-Tc superconducting intrinsic Josephson junctions

    NASA Astrophysics Data System (ADS)

    Grib, Alexander; Shukrinov, Yury; Schmidl, Frank; Seidel, Paul

    2010-11-01

    Within the last years many groups have realized and investigated different types of intrinsic Josephson junction (IJJ) arrays out of high-temperature superconducting single crystals or thin films. We tried to improve the synchronization between the junctions by external shunts. Mesa structures as well as microbridges on vicinal cut substrates showed multi-branch behaviour in their IV characteristics and random switching between branches. Theoretical modelling was done investigating phase dynamics and stability numerically as well as analytically. Branch structure in current voltage characteristics of IJJ is studied in the framework of different models, particularly, in capacitevely coupled Josephson junctions (CCJJ) model and CCJJ model with diffusion current. Results of modelling of return current in IV characteristics for stacks with different number of IJJ are presented. We discussed the possible mechanisms of synchronization and the ranges of stability. Conclusions with respect to application of such arrays such as radiation sources were given.

  1. Charge transfer polarisation wave in high Tc oxides and superconductive pairing

    NASA Technical Reports Server (NTRS)

    Chakraverty, B. K.

    1991-01-01

    A general formalism of quantized charge transfer polarization waves was developed. The nature of possible superconductive pairing between oxygen holes is discussed. Unlike optical phonons, these polarization fields will give rise to dielectric bipolarons or bipolaron bubbles. In the weak coupling limit, a new class of superconductivity is to be expected.

  2. High-Tc superconductivity at the interface between the CaCuO2 and SrTiO3 insulating oxides

    DOE PAGES

    Di Castro, D.; Cantoni, C.; Ridolfi, F.; Aruta, C.; Tebano, A.; Yang, N.; Balestrino, G.

    2015-09-28

    At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low Tc. We report the occurrence of high Tc superconductivity in the bilayer CaCuO2/SrTiO3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO2/SrTiO3 interface must be realized between the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this case can oxygen ions be incorporated in themore » interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO2 planes. In addition, a detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O K edge, clearly showing that the (super)conductivity is confined to about 1–2 CaCuO2 unit cells close to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3 interface can be extended to multilayered high Tc cuprates, contributing to explaining the dependence of Tc on the number of CuO2 planes in these systems.« less

  3. Pairing Mechanism for the High-TC Superconductivity: Symmetries and Thermodynamic Properties

    PubMed Central

    Szczęśniak, Radosław

    2012-01-01

    The pairing mechanism for the high- superconductors based on the electron-phonon (EPH) and electron-electron-phonon (EEPH) interactions has been presented. On the fold mean-field level, it has been proven, that the obtained s-wave model supplements the predictions based on the BCS van Hove scenario. In particular: (i) For strong EEPH coupling and the energy gap () is very weak temperature dependent; up to the critical temperature extends into the anomalous normal state to the Nernst temperature. (ii) The model explains well the experimental dependence of the ratio on doping for the reported superconductors in the terms of the few fundamental parameters. In the presented paper, the properties of the d-wave superconducting state in the two-dimensional system have been also studied. The obtained results, like for s-wave, have shown the energy gap amplitude crossover from the BCS to non-BCS behavior, as the value of the EEPH potential increases. However, for the energy gap amplitude extends into the anomalous normal state to the pseudogap temperature. Finally, it has been presented that the anisotropic model explains the dependence of the ratio on doping for the considered superconductors. PMID:22529891

  4. Enhancement of high-TC superconducting thin film devices by nanoscale polishing

    NASA Astrophysics Data System (ADS)

    Michalowski, P.; Shapoval, T.; Meier, D.; Katzer, C.; Schmidl, F.; Schultz, L.; Seidel, P.

    2012-11-01

    The effects of mechanical nanoscale polishing on the superconducting parameters of YBa2Cu3O7-δ (YBCO) thin films and bi-crystal grain boundary Josephson junctions have been investigated. We prepared samples with additional gold nanocrystallites in the YBCO film. As they are distributed throughout the whole YBCO film, they provide a low-resistance ohmic contact even if parts of the film are removed. Polishing was performed either before or after the patterning and did not change the properties of the grain boundary. However, nanopolishing reduces the film roughness in a significant way, which makes it an indispensable tool for the preparation of integrated superconducting circuits. We also succeeded in tuning the IC and RN of the Josephson junctions of direct current superconducting quantum interference devices (dc-SQUIDs) by systematically reducing the film thickness, which opens up new possibilities in the application of magnetic field sensors.

  5. A new type of superconducting journal bearing using high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Komori, M.; Kitamura, T.

    The characteristics between a set of alternating-polarity ring magnets and a superconductor are studied. The magnets have strong repulsion and attraction forces with the superconductor owing to the pinning effect. Using these characteristics a prototype of a superconducting journal bearing with a magnet shaft supported by a cylindrical housing has been developed. The superconductors (type-II superconductors) and a magnet shaft as the rotor of alternating-polarity ring magnets of the same size. The magnet shaft can be levitated in the center of the housing without contact. Levitation and drag forces of the superconducting journal bearing are investigated. The levitation force shows circular hysteresis loops depending on the displacement because of the flux pinning effect. Owing to the simple and useful structure of the superconducting journal bearing it is applicable to practical devices in the industrial field.

  6. Fabrication and chemical composition of RF magnetron sputtered Tl-Ca-Ba-Cu-O high Tc superconducting thin films

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Radpour, F.; Kapoor, V. J.; Lemon, G. H.

    1990-01-01

    The preparation of TlCaBaCuO superconducting thin films on (100) SrTiO3 substrates is described, and the results of their characterization are presented. Sintering and annealing the thin films in a Tl-rich ambient yielded superconductivity with a Tc of 107 K. The results of an XPS study support two possible mechanisms for the creation of holes in the TlCaBaCuO compound: (1) partial substitution of Ca(2+) for Tl(3+), resulting in hole creation, and (2) charge transfer from Tl(3+) to the CuO layers, resulting in a Tl valence between +3 and +1.

  7. Transport Anomalies and Possible High Tc Superconductivity in interconnected multiwall carbon nanotube sheets doped by ion implantation

    NASA Astrophysics Data System (ADS)

    Zakhidov, Anvar; Howard, Austin; Cornell, Nicholas; Goskun, Ulas; Salamon, Myron; Baughman, Ray; Bykova, Julia; Mayo, Nathanael; Wang, Xuemei; Galstyan, Eduard; Freyhardt, Herbert; Kan Chu, Wei

    2012-02-01

    Ion implantation offers an alternative doping method. In searching for superconductivity,we describe here the ion-implantation doping of MWCNT interconnected networks by boron and other dopants (phosphorous, sulfur, arsenic) and report transport anomalies in oriented networks of ion implanted MWCNT sheets as compared to cross coated (non-oriented multilayer MWCNT sheets). The strong drop of resistance R(T) with temperature decrease starting at Tc1= 50-60 K and even at higher T is reminiscent of inhomogeneous superconducting islands appearing in the non-SC matrix. An unusual anomaly of the 4-terminal resistance is observed in many samples, R(T) becoming negative at lower T< Tc2 ˜ 10-20 K, This negative resistance is found to be associated with unusual I-V curves with s-shape at low T < Tc2 and R(T) shows nonlinear dependence on excitation current and other features that are studied carefully in MWCNTs with different lengths and densities. This negative-resistance behavior gives a hint for the possible incorporation of superconducting areas and can be explained in terms of an imbalanced resistance bridge.

  8. Preparation, structure and superconductivity of high T(c) compounds: Research of high temperature superconductors in Hungary

    NASA Technical Reports Server (NTRS)

    Kirschner, I.

    1995-01-01

    In this paper the main directions, methods and results of the investigation of high-T(c) superconductors in Hungary are briefly summarized. The fundamental idea of this research is to study the effect of starting conditions on the microstructure of samples and the influence of the latter one on their superconducting parameters. The investigation concerning technical development is also mentioned.

  9. Levitation force from high-Tc superconducting thin-film disks

    NASA Astrophysics Data System (ADS)

    Riise, Anjali B.; Johansen, T. H.; Bratsberg, H.; Koblischka, M. R.; Shen, Y. Q.

    1999-10-01

    Experimental studies and theoretical modeling of the levitation force between a permanent magnet and superconducting thin film are reported. Measurements of the force Fz and magnetic stiffness κz=\\|δFz/δz\\| as functions of the magnet-superconductor separation z, show several features contrasting all previous levitation force data for bulk superconductors. In particular, the Fz(z) curves measured for decreasing and increasing separation form hysteresis loops of nearly symmetrical shape, also displaying a peak in the repulsive force branch. Recent theories for flux penetration in thin type-II superconductors in transverse magnetic fields are invoked to explain the results, which were obtained using a cylindrical Nd-Fe-B magnet and a YBa2Cu3O7-δ circular disk made by laser ablation. We derive explicit formulas for both Fz and κz, reproducing quantitatively all the features seen experimentally.

  10. Observation of two distinct components during pulsed laser deposition of high T(c) superconducting films

    NASA Astrophysics Data System (ADS)

    Venkatesan, T.; Wu, X. D.; Inam, A.; Wachtman, J. B.

    1988-04-01

    Using Rutherford backscattering technique, the angular distribution of the composition and thickness of the Y-Ba-Cu oxide film deposited by firing excimer laser (30 ns, 248 nm) pulses at a stoichiometric YBa2Cu3O(7-x) pellet was measured. The angular distribution consisted of two distinct components: one a cos theta component, a result of evaporation, and the other a highly forward directed component, a result of a secondary ejection process. The evaporated component is nonstoichiometric, as one would expect, whereas the forward-directed component has a composition close to that of the pellet. Further, the forward-directed stoichiometric component increases with the laser energy density in comparison with the evaporated component. These observations are discussed in the context of current models of laser-induced material ejection at surfaces.

  11. Passive magnetic field cancellation device by multiple high-Tc superconducting coils

    NASA Astrophysics Data System (ADS)

    Gu, C.; Zou, S.; Han, Z.; Qu, T.-M.

    2010-04-01

    A passive magnetic field cancellation device (PMFCD) is designed. The PMFCD could automatically cancel the field as an active cancellation system did; however it requires no power sources and feedback systems. The capability of the PMFCD is based on the principle that a closed loop can resist flux variation and keep the flux constant inside. The closed loop in the PMFCD is formed by connecting two pairs of high temperature superconductor Helmholtz coils with different radii in series. More important thing is that the ratio of the radius and the turn number between the coils has to satisfy a number of conditions, with which 100% cancellation can be reached. Theoretical methods to obtain the turn number ratio and radius ratio are the major part of the paper. Numerical simulation was followed, aiming to evaluate field distribution under a cancellation state and correct the theoretical values.

  12. Improved heat exhaust and the characteristics of the high Tc superconducting terahertz emitter

    NASA Astrophysics Data System (ADS)

    Kashiwagi, T.; Yamamoto, T.; Kitamura, T.; Asanuma, K.; Yasui, T.; Shibano, Y.; Watanabe, C.; Nakade, K.; Saiwai, Y.; Kubo, H.; Sakamoto, K.; Katsuragawa, T.; Tsujimoto, M.; Yoshizaki, R.; Minami, H.; Klemm, R. A.; Kadowaki, K.

    2015-03-01

    In our previous study it is known that THz emitting efficiency improves greatly when the stand-alone type of mesa structure is used for the THz emitting device. The principle reason for that lies in the heat removal from the mesa, in which a gigantic amount of heat is generated while the mesa is in the resistive state. Recently, we developed a new device structure based on the stand-alone type of mesa structure of Bi2212 single crystal in order to make high exhaust of Joule heating. The results show that although the power is comparable and is not significantly increased, very wide the radiation frequencies ranging from 0.3 to 1.6 THz were obtained. We will discuss the details of the radiation characteristics of this one. This study has been supported by CREST-JST. TK is also supported by the Matsuda grant and JST A-STEP. This work is in part performed in collaboration with Dr. Wai Kwok and his group in Argonne National Lab.

  13. Reassessment of the electronic state, magnetism, and superconductivity in high-Tc cuprates with the Nd2CuO4 structure

    NASA Astrophysics Data System (ADS)

    Naito, Michio; Krockenberger, Yoshiharu; Ikeda, Ai; Yamamoto, Hideki

    2016-04-01

    The electronic phase diagram of the cuprates remains enigmatic and is still a key ingredient to understand the mechanism of high-Tc superconductivity. It has been believed for a long time that parent compounds of cuprates were universally antiferromagnetic Mott insulators (charge-transfer insulators) and that high-Tc superconductivity would develop upon doping holes or electrons in a Mott-Hubbard insulator ("doped Mott-insulator scenario"). However, our recent discovery of superconductivity in the parent compounds of square-planar cuprates with the Nd2CuO4 (T') structure and the revised electronic phase diagram in T' cuprates urged a serious reassessment to the above scenario. In this review, we present the main results derived from our synthesis and experiments on T' cuprates in the undoped or heavily underdoped regime over 20 years, including material issues and basic physics. The key material issue is how to remove excess oxygen ions at the apical site without introducing oxygen vacancies in the CuO2 planes. In order to put this into practice, the basic knowledge of complex solid-state chemistry in T' cuprates is required, which is also included in this review.

  14. Development of high Tc (greater than 110K) Bi, Tl and Y-based materials as superconducting circuit elements

    NASA Technical Reports Server (NTRS)

    Haertling, Gene; Grabert, Gregory; Gilmour, Phillip

    1991-01-01

    Experimental work was continued on the development and characterization of bulk and hot pressed powders and tapecast materials in the Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O systems. A process for producing warp-free, sintered, superconducting tapes of Bi composition Bi1Sr2Ca2 Cu3O(x) was established. The procedure requires a triple calcination at 830 C for 24 hours and sintering at 845 C from 20 to 200 hours. Hot pressing the triple calcined powder at 845 C for 6 hours at 5000 psi yielded a dense material, which on further heat treatment at 845 C for 24 hours, exhibited a Tc of 108.2K. The Bi compositions were found to be much less oxygen sensitive than the Y compositions. This was especially noted in the case of the hot pressed materials which were superconducting as hot pressed, a condition that could not be achieved in the Y compositions. Safire-type grounding links are in the process of being fabricated from these materials.

  15. Ab initio molecular-orbital study on electron correlation effects in CuO sub 6 clusters relating to high- Tc superconductivity

    SciTech Connect

    Yamamoto, S. Faculty of Liberal Arts, Chukyo University, Kaizu-cho, Toyota 470-03 ); Yamaguchi, K. ); Nasu, K. )

    1990-07-01

    {ital Ab} {ital initio} molecular-orbital calculations for CuO{sub 6} clusters have been performed to elucidate the electronic structures of undoped and doped copper oxides, which are of current interest in relation to high-{ital T}{sub {ital c}} superconductivity. The electron correlation effects for these species are thoroughly investigated by the full-valence configuration-interaction method and the complete-active-space self-consistent-field method. The electron correlation effect is relatively simple for the {ital A}{sub {ital g}} state ({sigma} hole), whereas pair excitations and spin-flip excitations give sizable contributions to the configuration-interaction wave function for the {ital B} state (in-plane {pi} hole). Implications of these results are discussed in relation to the mechanisms of the high-{Tc} superconductivity.

  16. High temperature interface superconductivity

    DOE PAGES

    Gozar, A.; Bozovic, I.

    2016-01-20

    High-Tc superconductivity at interfaces has a history of more than a couple of decades. In this review we focus our attention on copper-oxide based heterostructures and multi-layers. We first discuss the technique, atomic layer-by-layer molecular beam epitaxy (ALL-MBE) engineering, that enabled High-Tc Interface Superconductivity (HT-IS), and the challenges associated with the realization of high quality interfaces. Then we turn our attention to the experiments which shed light on the structure and properties of interfacial layers, allowing comparison to those of single-phase films and bulk crystals. Both ‘passive’ hetero-structures as well as surface-induced effects by external gating are discussed. Here, wemore » conclude by comparing HT-IS in cuprates and in other classes of materials, especially Fe-based superconductors, and by examining the grand challenges currently laying ahead for the field.« less

  17. High temperature interface superconductivity

    NASA Astrophysics Data System (ADS)

    Gozar, A.; Bozovic, I.

    2016-02-01

    High-Tc superconductivity at interfaces has a history of more than a couple of decades. In this review we focus our attention on copper-oxide based heterostructures and multi-layers. We first discuss the technique, atomic layer-by-layer molecular beam epitaxy (ALL-MBE) engineering, that enabled High-Tc Interface Superconductivity (HT-IS), and the challenges associated with the realization of high quality interfaces. Then we turn our attention to the experiments which shed light on the structure and properties of interfacial layers, allowing comparison to those of single-phase films and bulk crystals. Both 'passive' hetero-structures as well as surface-induced effects by external gating are discussed. We conclude by comparing HT-IS in cuprates and in other classes of materials, especially Fe-based superconductors, and by examining the grand challenges currently laying ahead for the field.

  18. High-Tc superconductivity in ultrathin Bi2Sr2CaCu2O(8+x) down to half-unit-cell thickness by protection with graphene.

    PubMed

    Jiang, Da; Hu, Tao; You, Lixing; Li, Qiao; Li, Ang; Wang, Haomin; Mu, Gang; Chen, Zhiying; Zhang, Haoran; Yu, Guanghui; Zhu, Jie; Sun, Qiujuan; Lin, Chengtian; Xiao, Hong; Xie, Xiaoming; Jiang, Mianheng

    2014-01-01

    High-Tc superconductors confined to two dimension exhibit novel physical phenomena, such as superconductor-insulator transition. In the Bi2Sr2CaCu2O(8+x) (Bi2212) model system, despite extensive studies, the intrinsic superconducting properties at the thinness limit have been difficult to determine. Here, we report a method to fabricate high quality single-crystal Bi2212 films down to half-unit-cell thickness in the form of graphene/Bi2212 van der Waals heterostructure, in which sharp superconducting transitions are observed. The heterostructure also exhibits a nonlinear current-voltage characteristic due to the Dirac nature of the graphene band structure. More interestingly, although the critical temperature remains essentially the same with reduced thickness of Bi2212, the slope of the normal state T-linear resistivity varies by a factor of 4-5, and the sheet resistance increases by three orders of magnitude, indicating a surprising decoupling of the normal state resistance and superconductivity. The developed technique is versatile, applicable to investigate other two-dimensional (2D) superconducting materials. PMID:25483591

  19. Magnetic field dependence of high- Tc interface superconductivity in La1.55Sr0.45CuO4/La2CuO4 heterostructures

    DOE PAGES

    Gasparov, V. A.; Drigo, L.; Audouard, A.; He, Xi; Božović, I.

    2016-07-11

    Heterostructures made of a layer of a cuprate insulator La2CuO4 on the top of a layer of a nonsuperconducting cuprate metal La1.55Sr0.45CuO4 show high-Tc interface superconductivity confined within a single CuO2 plane. Given this extreme quasi-two-dimensional quantum confinement, it is of interest to find out how interface superconductivity behaves when exposed to an external magnetic field. With this motivation, we have performed contactless tunnel-diode-oscillator-based measurements in pulsed magnetic fields up to 56 T as well as measurements of the complex mutual inductance between a spiral coil and the film in static fields up to 3 T. Remarkably, we observe thatmore » interface superconductivity survives up to very high perpendicular fields, in excess of 40 T. Additionally, the critical magnetic field Hm(T) reveals an upward divergence with decreasing temperature, in line with vortex melting as in bulk superconducting cuprates.« less

  20. Uniform mixing of high- Tc superconductivity and antiferromagnetism on a single CuO 2 plane in five-layered cuprates

    NASA Astrophysics Data System (ADS)

    Mukuda, H.; Abe, M.; Kitaoka, Y.; Kotegawa, H.; Tokiwa, K.; Watanabe, T.; Iyo, A.; Kito, H.; Tanaka, Y.; Kodama, Y.

    2007-09-01

    We report systematic Cu-NMR studies on five-layered cuprates from under-doped HgBa2Ca4Cu5O12+δ (Hg-1245(UD)) to slightly overdoped Tl-1245(OVD), and compare with optimally-doped Hg-1245(OPT). In the under-doped Hg-1245(UD), antiferromagnetism (AFM) has been found to take place at TN = 290 K, exhibiting a large antiferromagnetic moment of 0.67-0.69 μB at three inner planes (IP's). These values are comparable to that reported for non-doped cuprates, suggesting that the IP's may be in a nearly non-doped regime. Most surprisingly, the AFM order is also detected with MAFM(OP) = 0.1 μB even at two outer planes (OP's) that are responsible for the onset of superconductivity (SC) with Tc = 72 K. The high-Tc SC at Tc = 72 K can uniformly coexist on a microscopic level with the AFM at OP's. This is the first microscopic evidence for the uniformly mixed phase of AFM and SC on a single CuO2 plane. Although, the AFM/SC mixed CuO2 planes are significantly separated by three non-doped AFM layers, the onset of AFM does not prevent the occurrence of SC with the high value of Tc = 72 K.

  1. Direct angle resolved photoelectron spectroscopy (DARPES) on high-Tc films: doping, strains, Fermi surface topology and superconductivity

    NASA Astrophysics Data System (ADS)

    Pavuna, D.; Ariosa, D.; Cancellieri, C.; Cloetta, D.; Abrecht, M.

    2008-03-01

    Since 1997 we systematically perform Direct ARPES ( = DARPES) on in-situ grown, non-cleaved, ultra-thin (<25nm) cuprate films. Specifically, we probe low energy electronic structure and properties of high-Tc films under different degree of epitaxial (compressive vs tensile) strain. In overdoped in-plane compressed La2-xSrxCuO4 (LSCO) thin films we double Tc from 20K to 40K, yet the Fermi surface (FS) remains essentially 2-dimensional (2D). In contrast, tensile strained films show 3-dimensional (3D) dispersion, while Tc is drastically reduced. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the 2D character of the dispersion and increases Tc, while the tensile strain seems to act exactly in the opposite direction and the resulting dispersion is 3D. We have the FS topology for both cases. As the actual lattice of cuprates is 'Napoleon-cake' -like i.e. rigid CuO2 planes alternate with softer 'reservoir' (that strains distort differently) our results tend to rule out 2D rigid lattice mean field models. Finally, we briefly discuss recent successful determination of the FS topology from the observed wavevector quantization by DARPES in cuprate films thinner than 18 units cells (<24nm). Such an approach is of broader interest as it can be extended to other similar confined (ultra-thin) functional oxide systems.

  2. In-situ deposition of YBCO high-Tc superconducting thin films by MOCVD and PE-MOCVD

    NASA Technical Reports Server (NTRS)

    Zhao, J.; Noh, D. W.; Chern, C.; Li, Y. Q.; Norris, P. E.; Kear, B.; Gallois, B.

    1991-01-01

    Metal-Organic Chemical Vapor Deposition (MOCVD) offers the advantages of a high degree of compositional control, adaptability for large scale production, and the potential for low temperature fabrication. The capability of operating at high oxygen partial pressure is particularly suitable for in situ formation of high temperature superconducting (HTSC) films. Yttrium barium copper oxide (YBCO) thin films having a sharp zero-resistance transition with T(sub c) greater than 90 K and J(sub c) of approximately 10(exp 4) A on YSZ have been prepared, in situ, at a substrate temperature of about 800 C. Moreover, the ability to form oxide films at low temperature is very desirable for device applications of HTSC materials. Such a process would permit the deposition of high quality HTSC films with a smooth surface on a variety of substrates. Highly c-axis oriented, dense, scratch resistant, superconducting YBCO thin films with mirror-like surfaces have been prepared, in situ, at a reduced substrate temperature as low as 570 C by a remote microwave-plasma enhanced metal-organic chemical vapor deposition (PE-MOCVD) process. Nitrous oxide was used as a reactant gas to generate active oxidizing species. This process, for the first time, allows the formation of YBCO thin films with the orthorhombic superconducting phase in the as-deposited state. The as-deposited films grown by PE-MOCVD show attainment of zero resistance at 72 K with a transition width of about 5 K. MOCVD was carried out in a commercial production scale reactor with the capability of uniform deposition over 100 sq cm per growth run. Preliminary results indicate that PE-MOCVD is a very attractive thin film deposition process for superconducting device technology.

  3. THORIUM-DOPING INDUCED HIGH-Tc SUPERCONDUCTIVITY IN Dy1-xThxFeAsO

    NASA Astrophysics Data System (ADS)

    Luo, Yongkang; Lin, Xiao; Li, Yuke; Tao, Qian; Li, Linjun; Zhu, Zengwei; Cao, Guanghan; Xu, Zhu'an

    2012-12-01

    Parent compound of DyFeAsO was successfully synthesized by solid-state reaction under ambient pressure and superconductivity was induced by partial substitution of trivalent Dy3+ ions with tetravalent Th4+ in Dy1-xThx FeAsO. In the undoped parent compound, an anomaly in the resistivity appears around 140 K which corresponds to the structural phase transition and/or antiferromagnetic (AFM) order of the magnetic moments of Fe2+ ions. At low temperature, another AFM order associated with the magnetic moments of Dy3+ ions occurs at TN of 9.55 K. The AFM order around 140 K has significant influence on the transport properties, which can be interpreted by opening of partial gap on Fermi surface. Th doping suppresses the AFM order related to the Fe2+ ions and the midpoint transition temperature Tc mid of 49.3 K is observed for x = 0.3. Our results also indicate that the [Ln2O2]2+ layer has influence on the magnetism of [Fe2As2]2- layer.

  4. Field-dependent critical state of high-Tc superconducting strip simultaneously exposed to transport current and perpendicular magnetic field

    SciTech Connect

    Xue, Cun; He, An; Yong, Huadong; Zhou, Youhe

    2013-12-15

    We present an exact analytical approach for arbitrary field-dependent critical state of high-T{sub c} superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the I{sub a}-B{sub a} plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.

  5. Computed tomography image using sub-terahertz waves generated from a high-Tc superconducting intrinsic Josephson junction oscillator

    NASA Astrophysics Data System (ADS)

    Kashiwagi, T.; Nakade, K.; Saiwai, Y.; Minami, H.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y.; Tsujimoto, M.; Yamamoto, T.; Marković, B.; Mirković, J.; Klemm, R. A.; Kadowaki, K.

    2014-02-01

    A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-Tc superconductor Bi2Sr2CaCu2O8+δ was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.

  6. A two-phase charge-density real-space-pairing model of high-Tc superconductivity.

    PubMed

    Humphreys

    1999-03-01

    It is usually assumed that high-T(c) superconductors have a periodic band structure and a periodic charge density, although amorphous low-T(c) superconductors are known. In this paper, it is suggested that the CuO(2) conduction planes of cuprate superconductors consist of regions of two different charge densities which do not normally repeat periodically. It is suggested that the pairing of holes occurs in real space in cuprate superconductors. It is proposed that the hole-pairing mechanism is magnetic exchange coupling and the pairing force is strong, the pairing energy being greater than kT at room temperature. The bound hole pair is essentially a bipolaron. A real-space model is very tentatively suggested in which the CuO(2) planes of YBa(2)Cu(3)O(7) contain nanodomains of a 3 x 3 hole lattice surrounded by interfaces one unit cell wide in which the holes are paired. In the superconducting state in this model, the existing hole pairs condense and move coherently and collectively around the insulating nanodomains, like trams running around blocks of houses, with one hole on each tramline. The hole pairs move in an elegant manner with hole pairs hopping from oxygen to oxygen via adjacent copper sites. The model explains the superconducting current being in the ab plane and it also explains the very short coherence lengths. Because the pairing force is strong, the model suggests that room-temperature superconductivity might be possible in carefully designed new oxide materials.

  7. Novel Interplay between High-Tc Superconductivity and Antiferromagnetism in Tl-Based Six-CuO2-Layered Cuprates: 205Tl- and 63Cu-NMR Probes

    NASA Astrophysics Data System (ADS)

    Mukuda, Hidekazu; Shiki, Nozomu; Kimoto, Naoki; Yashima, Mitsuharu; Kitaoka, Yoshio; Tokiwa, Kazuyasu; Iyo, Akira

    2016-08-01

    We report 63Cu- and 205Tl-NMR studies on six-layered (n = 6) high-Tc superconducting (SC) cuprate TlBa2Ca5Cu6O14+δ (Tl1256) with Tc ˜ 100 K, which reveal that antiferromagnetic (AFM) order takes place below TN ˜ 170 K. In this compound, four underdoped inner CuO2 planes [n(IP) = 4] sandwiched by two outer planes (OPs) are responsible for the onset of AFM order, whereas the nearly optimally-doped OPs responsible for the onset of bulk SC. It is pointed out that an increase in the out-of-plane magnetic interaction within an intra-unit-cell causes TN ˜ 45 K for Tl1245 with n(IP) = 3 to increase to ˜170 K for Tl1256 with n(IP) = 4. It is remarkable that the marked increase in TN and the AFM moments for the IPs does not bring about any reduction in Tc, since Tc ˜ 100 K is maintained for both compounds with nearly optimally doped OP. We highlight the fact that the SC order for n ≥ 5 is mostly dominated by the long-range in-plane SC correlation even in the multilayered structure, which is insensitive to the magnitude of TN and the AFM moments at the IPs or the AFM interaction among the IPs. These results demonstrate a novel interplay between the SC and AFM orders when the charge imbalance between the IPs and OP is significantly large.

  8. Low-energy physical properties of high- Tc superconducting Cu oxides: A comparison between the resonating valence bond and experiments

    NASA Astrophysics Data System (ADS)

    Yang, Kai-Yu; Shih, C. T.; Chou, C. P.; Huang, S. M.; Lee, T. K.; Xiang, T.; Zhang, F. C.

    2006-06-01

    In a recent review by Anderson and co-workers, it was pointed out that an early resonating valence bond (RVB) theory is able to explain a number of unusual properties of high-temperature superconducting (SC) Cu oxides. Here we extend previous calculations to study more systematically the low-energy physical properties of the plain vanilla d -wave RVB state, and to compare the results with the available experiments. We use a renormalized mean-field theory combined with variational Monte Carlo and power Lanczos methods to study the RVB state of an extended t-J model in a square lattice with parameters suitable for the hole-doped Cu oxides. The physical observable quantities we study include the specific heat, the linear residual thermal conductivity, the in-plane magnetic penetration depth, the quasiparticle energy at the antinode (π,0) , the superconducting energy gap, the quasiparticle spectra, and the Drude weights. The traits of nodes (including kF , the Fermi velocity vF , and the velocity along Fermi surface v2 ), and the SC order parameter are studied. Comparisons of the theory and the experiments in cuprates show an overall qualitative agreement, especially on their doping dependences.

  9. Ac losses for the self field of an ac transport current with a dc transport current offset in high {Tc} superconducting magnet coils for MagLev application

    SciTech Connect

    Koosh, V.F.

    1993-10-01

    Although much research has been conducted concerning the losses of high-{Tc} superconductors, very little has concentrated on the self-field losses in an actual magnet arrangement. The coils studied in this work were designed for use as actual magnets in an industrial application. Self field loss measurements were made upon tape-wound 2223 superconducting helix coils. The self-field losses were produced by an AC transport current with a DC transport current offset. Losses were taken for single, double and triple tape windings, giving essentially monofilament, dual, and three filament cases. The losses measured here were varied over a range of AC current values for several different DC values, and over a range of frequencies. The currents were all AC sinusoids with a DC offset. All measurements were made at T = 77K.

  10. Synthesis of high {Tc} superconducting coatings and patterns by melt writing and oxidation of metallic precursor alloys

    DOEpatents

    Gao, W.; Vander Sande, J.B.

    1998-07-28

    A method is provided for fabrication of superconducting oxides and superconducting oxide composites and for joining superconductors to other materials. A coating of a molten alloy containing the metallic elements of the oxide is applied to a substrate surface and oxidized to form the superconducting oxide. A material can be contacted to the molten alloy which is subsequently oxidized joining the material to the resulting superconducting oxide coating. Substrates of varied composition and shape can be coated or joined by this method. 5 figs.

  11. Voltage divider based on submicron slits in a high Tc superconducting film and two bicrystal grain boundaries

    NASA Astrophysics Data System (ADS)

    Kaplunenko, V. K.; Ivanov, Z. G.; Stepantsov, E. A.; Claeson, T.; Wikborg, E.

    1995-07-01

    Experiments on a model of rapid single flux quantum (RSFQ) flip-flop cell, based on high-Tc (HTS) Josephson junctions show that it can operate as a voltage divider at frequency up to 400 GHz. The junctions were formed in YBaCuO film, deposited on novel Y-ZrO2 bicrystals with two asymmetric 32° grain boundaries, about 10 μm apart, and allow a new design of RSFQ logic based on a single HTS layer. Small inductances (≂10 pH) were made as narrow, submicron size slits. The junction widths were between 4 and 10 μm and for ten junctions located close to the tested circuits, the linear critical current densities at T=4.4 K were 10.7 μA/μm±50% for one grain boundary and 8.3 μA/μm±50% for the other one. IcRn was about 1 mV±50%. A current density of half the expected value meant that the test circuit did not act as an ideal flip-flop down to the lowest frequency. As a voltage divider it gave a half value division up to 0.82 mV at T=4.4 K and to 0.4 mV at 30 K.

  12. A signal input coil made of superconducting thin film for improved signal-to-noise ratio in a high-Tc SQUID-based ultra-low field nuclear magnetic resonance system

    NASA Astrophysics Data System (ADS)

    Chen, Kuen-Lin; Hsu, Chin-Wei; Ku, Yue-Bai; Chen, Hsin-Hsien; Liao, Shu-Hsien; Wang, Li-Min; Horng, Herng-Er; Yang, Hong-Chang

    2013-11-01

    Resonant coupling schemes are commonly used in SQUID-based ultra-low field (ULF) nuclear magnetic resonance (NMR) systems to couple the spin relaxation signals from samples to the SQUID. Generally, in NMR systems, a resonant coupling scheme is composed of two solenoid coils which are made of enamel insulated wires and a capacitor connected in series. In this work, we tried to replace the metal solenoid input coil with a planar high-Tc superconducting spiral coil to improve the signal-to-noise ratio (SNR) of the ULF NMR signal. A measurement of the free induction decay signal of water protons was performed to demonstrate the improved performance of the system. This improvement is due to the fact that the planar superconducting spiral coil possesses a higher mutual inductance with the SQUID. Therefore, it is a promising way to enhance the SNR of high-Tc SQUID-based ULF NMR/MRI systems.

  13. Study of high {Tc} superconducting thin films grown by MOCVD. Final report, July 1, 1986--April 30, 1990

    SciTech Connect

    Erbil, A.

    1990-12-31

    Work is described briefly, which was carried out on development of techniques to grow metal-semiconductor superlattices (artificially layered materials) and on the copper oxide based susperconductors (naturally layered materials). The current growth technique utilized is metalorganic chemical vapor deposition (MOCVD). CdTe, PbTe, La, LaTe, and Bi{sub 2}Te{sub 3} were deposited, mostly on GaAs. Several YBa{sub 2}Cu{sub 3}O{sub 7} compounds were obtained with possible superconductivity at temperatures up to 550 K (1 part in 10{sup 4}). YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} and Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub y} thin films were deposited by MOCVD on common substrates such as glass.

  14. High-Tc Superconductivity near the Anion Height Instability in Fe-Based Superconductors: Analysis of LaFeAsO1-xHx

    NASA Astrophysics Data System (ADS)

    Onari, Seiichiro; Yamakawa, Youichi; Kontani, Hiroshi

    2014-05-01

    The isostructural transition in the tetragonal phase with a sizable change in the anion height, is realized in heavily H-doped LaFeAsO and (La,P) codoped CaFe2As2. In these compounds, the superconductivity with higher Tc (40-50 K) is realized near the isostructural transition. To find the origin of the anion-height instability and the role in realizing the higher-Tc state, we develop the orbital-spin fluctuation theory by including the vertex correction. We analyze LaFeAsO1-xHx and find that the non-nematic orbital fluctuations, which induce the anion-height instability, are automatically obtained at x ˜0.5, in addition to the conventional nematic orbital fluctuations at x˜0. The non-nematic orbital order triggers the isostructural transition, and its fluctuation would be a key ingredient to realize higher-Tc superconductivity of order 50 K.

  15. Growth of high {Tc} superconducting fibers using a miniaturized laser-heated float zone process. Progress report, November 6, 1990--December 31, 1991

    SciTech Connect

    Feigelson, R.S.; Route, R.K.; DeMattei, R.C.

    1991-12-31

    This report summarizes the progress made on the project ``Growth of High {Tc} Superconducting Fibers Using a Miniaturized Laser-Heated Float Zone Process`` during the 14 month period from Nov. 6, 1990 to Dec. 31, 1991. The studies during this period focused primarily on phase diagram studies, phase relations in the calcium aluminate system and on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (BSCCO). Some work was also done on the Advanced Fiber Growing Station. Because of the complicated phase relationships found in the incongruently melting BSCCO system, the incongruently melting CA{sub 3}Al{sub 2}O{sub 6} phase of the calcium oxide-aluminum oxide system was studied as a model material. The data obtained was in agreement with well known solidification theory. Fibers grown from calcium oxide rich sources contained calcium oxide nodules which transported from the melting source interface to the growth interface, while those grown from aluminum oxide rich sources contained continuous inclusions of a divorced eutectic. The melt compositions were also found to follow theoretical predictions. The agreement of this data with the phase diagram and solidification theory demonstrates that phase equilibrium information can be extracted from fiber growth experiments. BSCCO feed rods were made from 12 different compositions. Fibers were grown from these rods and the melts were abruptly quenched which preserves the as-grown 2212 fiber, a glassy frozen melt and the source. A future study of these sections will reveal the phase relationships that exist in the BSCCO system. Melt temperature gradients of 500--1,000 C/cm were measured near the interface in these experiments. During this reporting period, work continued on the mechanical components of the Advanced Fiber Growth Station.

  16. Pseudogap and superconducting phases in high TC superconductivity based on an improved slave-boson representation of t-J Hamiltonian with the inclusion of a rigorous Lagrange multiplier field

    NASA Astrophysics Data System (ADS)

    Eom, Jae-Hyeon; Kim, Ki-Suk; Salk, Sung-Ho Suck

    2002-03-01

    By overcoming the usual mean field treatment of Lagrange multiplier field which appears in the slave-boson representation of the t-J Hamiltonian, we present a derivation of an effective Lagrangian for the study of high TC phase diagram. The new Lagrangian exhibits the importance of additional spinon-spinon, holon-holon and spinon-holon coupling terms, as a result of more accurate account of single occupancy constraint beyond the mean field level. From the use of the newly derived effective Lagrangian we will explore how these additional coupling terms affect the phase diagram involving the pseudogap and superconducting temperature. In this study we will present the applications of both the holon-pair bose condensation theory of Lee and Salk[1] and the single holon-bose condensation theory of Ubbens and Lee[2] to our improved method of accounting the Lagrange multipler field. 1. S. -S. Lee and Sung-Ho Suck Salk,Phys. Rev. B 64 052501 (2001); Int. J. Mod. Phys. B 13, 3455 (1999); Physica C.353, 130 (2001) 2. M. U. Ubbens and P. A. Lee, Phys. Rev. B 46, 8434 (1992); Phys. Rev. B 49, 6853 (1994)

  17. THE 2D HEISENBERG ANTIFERROMAGNET IN HIGH-Tc SUPERCONDUCTIVITY:. A Review of Numerical Techniques and Results

    NASA Astrophysics Data System (ADS)

    Barnes, T.

    In this article we review numerical studies of the quantum Heisenberg antiferromagnet on a square lattice, which is a model of the magnetic properties of the undoped “precursor insulators” of the high temperature superconductors. We begin with a brief pedagogical introduction and then discuss zero and nonzero temperature properties and compare the numerical results to analytical calculations and to experiment where appropriate. We also review the various algorithms used to obtain these results, and discuss algorithm developments and improvements in computer technology which would be most useful for future numerical work in this area. Finally we list several outstanding problems which may merit further investigation.

  18. How Electron Spectroscopy with Synchrotron Light Can Help Us Understand High-Tc Superconductivity and Other Complex States of Matter

    SciTech Connect

    Campuzano, Juan Carlos

    2012-03-07

    All the physical, chemical, and mechanical properties of materials are controlled by electrons that occupy the highest energy levels in solids, those near the Fermi energy. Many techniques were developed to study those electrons, leading to the great successes of condensed matter physics. Newer and complex materials, such as the high-temperature superconductors, tend to exhibit very large anisotropies in their physical properties, requiring a more detailed knowledge of the behavior of electrons not only as a function of their energy, but also their momentum. Angle-resolved photoemission can contribute to our understanding by providing a great deal of information on many of the momentum-dependent properties of electrons and their interactions. In this talk, I will present a brief overview of how a long-term and focused collaboration between scientists at Argonne and other institutions has contributed to making angle-resolved photoemissions a most useful tool in the study of complex states of matter.

  19. Development of high Tc (greater than 110K) Bi, Tl and Y-based materials as superconducting circuit elements

    NASA Technical Reports Server (NTRS)

    Haertling, Gene H.; Lee, Burtrand; Grabert, Gregory; Gilmour, Phillip

    1991-01-01

    This report is presented in two parts. Part 1 deals primarily with Bi-based materials and a small amount of work on a Y-based composition while Part 2 covers work on Tl-based materials. In Part 1, a reliable and reproducible process for producing bulk bismuth-based superconductors has been developed. It is noted however, that a percentage of the tapecast material experiences curling and fracturing after a 30 hour sintering period and is thus in need of further examination. The Bi-Sr-Ca-Cu-O (BSCCO) material has been characterized by critical temperature data, X-ray diffraction data, and surface morphology. In the case of T sub c, it is not critical to anneal the material. It appears that the BSCCO material has the possibility of producing a better grounding strap than that of the 123 material. Attempts to reproduce near room temperature superconductors in the Y-Ba-Cu-O system were unsuccessful. In Part 2, several methods of processing the high temperature superconductor Tl2Ba2Ca2Cu3O10 were investigated; i.e., different precursor compositions were sintered at various sintering times and temperatures. The highest superconductig temperature was found to be 117.8K when fired at 900 C for three hours. Higher sintering temperatures produced a melted sample which was nonsuperconducting at liquid nitrogen temperature. Also, a preliminary study found Li2O substitutions for copper appeared to increase the transition temperature and create fluxing action upon sintering. It was suggested that lower sintering temperatures might be obtained with lithium additions to produce reliable Tl2Ba2Ca2Cu3O10 processing methods.

  20. Development of high Tc (greater than 110K) Bi, Tl and Y-based materials as superconducting circuit elements

    NASA Astrophysics Data System (ADS)

    Haertling, Gene H.; Lee, Burtrand; Grabert, Gregory; Gilmour, Phillip

    1991-06-01

    This report is presented in two parts. Part 1 deals primarily with Bi-based materials and a small amount of work on a Y-based composition while Part 2 covers work on Tl-based materials. In Part 1, a reliable and reproducible process for producing bulk bismuth-based superconductors has been developed. It is noted however, that a percentage of the tapecast material experiences curling and fracturing after a 30 hour sintering period and is thus in need of further examination. The Bi-Sr-Ca-Cu-O (BSCCO) material has been characterized by critical temperature data, X-ray diffraction data, and surface morphology. In the case of T sub c, it is not critical to anneal the material. It appears that the BSCCO material has the possibility of producing a better grounding strap than that of the 123 material. Attempts to reproduce near room temperature superconductors in the Y-Ba-Cu-O system were unsuccessful. In Part 2, several methods of processing the high temperature superconductor Tl2Ba2Ca2Cu3O10 were investigated; i.e., different precursor compositions were sintered at various sintering times and temperatures. The highest superconductig temperature was found to be 117.8K when fired at 900 C for three hours. Higher sintering temperatures produced a melted sample which was nonsuperconducting at liquid nitrogen temperature. Also, a preliminary study found Li2O substitutions for copper appeared to increase the transition temperature and create fluxing action upon sintering. It was suggested that lower sintering temperatures might be obtained with lithium additions to produce reliable Tl2Ba2Ca2Cu3O10 processing methods.

  1. High-Temperature Superconductivity

    NASA Astrophysics Data System (ADS)

    Tanaka, Shoji

    2006-12-01

    A general review on high-temperature superconductivity was made. After prehistoric view and the process of discovery were stated, the special features of high-temperature superconductors were explained from the materials side and the physical properties side. The present status on applications of high-temperature superconductors were explained on superconducting tapes, electric power cables, magnets for maglev trains, electric motors, superconducting quantum interference device (SQUID) and single flux quantum (SFQ) devices and circuits.

  2. Superconductivity in the metallic elements at high pressures

    NASA Astrophysics Data System (ADS)

    Hamlin, J. J.

    2015-07-01

    Although the highest superconducting critical temperature, Tc , found in an elemental solid at ambient pressure is 9.2 K (niobium), under the application of ultra-high pressures, several elements exhibit Tc values near or above 20 K. This review includes a survey of the occurrence and understanding of pressure-induced superconductivity in the subset of elements that are metallic at ambient pressure. A particular focus is directed towards those elements that display the highest superconducting critical temperatures or exhibit substantial increases in Tc with pressure. A separate article in this issue by Shimizu will cover pressure-induced superconductivity in elements that are insulating at ambient pressure.

  3. Non-invasive and high-sensitivity scanning detection of magnetic nanoparticles in animals using high-Tc scanning superconducting-quantum-interference-device biosusceptometry.

    PubMed

    Chieh, J J; Hong, C Y

    2011-08-01

    Although magnetic nanoparticles (MNPs) have been widely applied to animals in biomedicine, MNPs within animals should be examined in real time, in vivo, and without bio-damaged possibility to evaluate whether the bio-function of MNPs is valid or to further controls the biomedicinal process because of accompanying complex problems such as MNPs distribution and MNPs biodegradation. The non-invasive and high-sensitivity scanning detection of MNPs in animals using ac susceptometry based on a high-T(c) superconducting quantum interference device (SQUID) is presented. The non-invasive results and biopsy results show good agreement, and two gold-standard biomedicine methods, Prussian blue stain and inductively coupled plasma, prove the magnetic results. This confirms that the future clinical diagnosis of bio-functional MNPs could be operated by using scanning SQUID biosusceptometry as conveniently as an ultrasonic probe.

  4. High Temperature Superconducting Materials Database

    National Institute of Standards and Technology Data Gateway

    SRD 149 NIST High Temperature Superconducting Materials Database (Web, free access)   The NIST High Temperature Superconducting Materials Database (WebHTS) provides evaluated thermal, mechanical, and superconducting property data for oxides and other nonconventional superconductors.

  5. Rugged Low-Resistance Contacts To High-Tc Superconductors

    NASA Technical Reports Server (NTRS)

    Caton, Randall; Selim, Raouf; Byvik, Charles E.; Buoncristiani, A. Martin

    1992-01-01

    Newly developed technique involving use of gold makes possible to fabricate low-resistance contacts with rugged connections to high-Tc superconductors. Gold diffused into specimen of superconducting material by melting gold beads onto surface of specimen, making strong mechanical contacts. Shear strength of gold bead contacts greater than epoxy or silver paste. Practical use in high-current-carrying applications of new high-Tc materials, including superconducting magnets, long-wavelength sensors, electrical ground planes at low temperatures, and efficient transmission of power.

  6. First 13 Years of HIGH-Tc:. Brief Review and Open Questions

    NASA Astrophysics Data System (ADS)

    Pavuna, Davor

    Exactly 13 years ago, in April 1986, appeared the famous paper1 by Bednorz and Müller, that announced a striking discovery of high-Tc superconductivity in cuprates. Some 40'000 papers later, we are still struggling to understand the high-Tc superconductivity. Here I summarize some of the most relevant recent results and open questions by discussing the observed phenomena in a rather complex electronic phase diagram of high-Tc oxides.

  7. Laser surface interactions of high-(Tc) superconductors

    NASA Astrophysics Data System (ADS)

    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-(Tc) metal oxide superconductors. Although many theoretical models were proposed, there has been no general agreement on any theory to explain these materials. One of the peculiar features of these high-(Tc) materials is the noninteger number of oxygen atoms. The oxygen content is extremely critical to the superconductive properties. Our results from mass spectroscopy of laser desorbed species indicate that significant quantities of oxygen molecules are trapped in the bulk of these superconductors. It appears that these trapped oxygen molecules may play key roles in superconductive properties.

  8. Superconductivity in undoped T'-RE2CuO4 with TC > 30 K

    NASA Astrophysics Data System (ADS)

    Naito, Michio; Matsumoto, Osamu; Utsuki, Aya; Tsukada, Akio; Yamamoto, Hideki; Manabe, Takaaki

    2008-03-01

    We report the superconductivity in T'-RE2CuO4 (RE = Pr, Nd, Sm, Eu, and Gd), which have been for a long time believed as a Mott insulator. The highest Tc of undoped T'-RE2CuO4 is over 30 K, substantially higher than that of `electron-doped' analogs. Remarkably, Gd2CuO4, even the derivatives of which have not shown superconductivity so far, gets superconducting with Tc^onset as high as 20 K. Our discovery was achieved by using metal-organic decomposition (MOD), an inexpensive and easy-to-implement thin-film process. The keys to prepare the superconducting films are rather simple, namely low-PO2 firing and subsequent low-temperature reduction. One point to be emphasized is that low-PO2 phase field has been almost unexplored in the search for new superconductors because of the belief that high PO2 should be required in the synthesis of Cu^2+ compounds. Our discovery contradicts with the past results supporting undoped mother compounds, T'-RE2CuO4, to be insulating. The clue to understanding the sharp contrast between the past and our results is impurity oxygen (Oap) at the apical site, which has to be cleaned up in order to reach the `generic' electronic phase diagram.

  9. High temperature interfacial superconductivity

    SciTech Connect

    Bozovic, Ivan; Logvenov, Gennady; Gozar, Adrian Mihai

    2012-06-19

    High-temperature superconductivity confined to nanometer-scale interfaces has been a long standing goal because of potential applications in electronic devices. The spontaneous formation of a superconducting interface in bilayers consisting of an insulator (La.sub.2CuO.sub.4) and a metal (La.sub.1-xSr.sub.xCuO.sub.4), neither of which is superconducting per se, is described. Depending upon the layering sequence of the bilayers, T.sub.c may be either .about.15 K or .about.30 K. This highly robust phenomenon is confined to within 2-3 nm around the interface. After exposing the bilayer to ozone, T.sub.c exceeds 50 K and this enhanced superconductivity is also shown to originate from a 1 to 2 unit cell thick interfacial layer. The results demonstrate that engineering artificial heterostructures provides a novel, unconventional way to fabricate stable, quasi two-dimensional high T.sub.c phases and to significantly enhance superconducting properties in other superconductors. The superconducting interface may be implemented, for example, in SIS tunnel junctions or a SuFET.

  10. From Ions to Wires to the Grid: The Transformational Science of LANL Research in High-Tc Superconducting Tapes and Electric Power Applications

    SciTech Connect

    Marken, Ken

    2009-05-20

    The Department of Energy (DOE) Office of Electricity Delivery and Energy Reliability (OE) has been tasked to lead national efforts to modernize the electric grid, enhance security and reliability of the energy infrastructure, and facilitate recovery from disruptions to energy supplies. LANL has pioneered the development of coated conductors – high-temperature superconducting (HTS) tapes – which permit dramatically greater current densities than conventional copper cable, and enable new technologies to secure the national electric grid. Sustained world-class research from concept, demonstration, transfer, and ongoing industrial support has moved this idea from the laboratory to the commercial marketplace.

  11. From Ions to Wires to the Grid: The Transformational Science of LANL Research in High-Tc Superconducting Tapes and Electric Power Applications

    SciTech Connect

    Marken, Ken

    2009-05-20

    The Department of Energy (DOE) Office of Electricity Delivery and Energy Reliability (OE) has been tasked to lead national efforts to modernize the electric grid, enhance security and reliability of the energy infrastructure, and facilitate recovery from disruptions to energy supplies. LANL has pioneered the development of coated conductors - high-temperature superconducting (HTS) tapes - which permit dramatically greater current densities than conventional copper cable, and enable new technologies to secure the national electric grid. Sustained world-class research from concept, demonstration, transfer, and ongoing industrial support has moved this idea from the laboratory to the commercial marketplace.

  12. From Ions to Wires to the Grid: The Transformational Science of LANL Research in High-Tc Superconducting Tapes and Electric Power Applications

    ScienceCinema

    Marken, Ken [Superconductivity Technology Center, Los Alamos, New Mexico, United States

    2016-07-12

    The Department of Energy (DOE) Office of Electricity Delivery and Energy Reliability (OE) has been tasked to lead national efforts to modernize the electric grid, enhance security and reliability of the energy infrastructure, and facilitate recovery from disruptions to energy supplies. LANL has pioneered the development of coated conductors – high-temperature superconducting (HTS) tapes – which permit dramatically greater current densities than conventional copper cable, and enable new technologies to secure the national electric grid. Sustained world-class research from concept, demonstration, transfer, and ongoing industrial support has moved this idea from the laboratory to the commercial marketplace.

  13. High- Tc thin-film magnetometer

    SciTech Connect

    Miklich, A.H.; Wellstood, F.C.; Kingston, J.J.; Clarke, J. ); Colclough, M.S. ); Cardona, A.H.; Bourne, L.C.; Olson, W.L.; Eddy, M.M. )

    1990-09-01

    We have constructed and tested high-{Tc} magnetometers by coupling a high-{Tc} thin-film Superconducting QUantum Interference Device (SQUID) to two different high-{Tc} thin-film flux transformers. The SQUID was made from Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub 8+y} films grown on MgO, with junctions consisting of native grain boundaries. The flux transformers were made from YBa{sub 2}Cu{sub 3}O{sub 7-x}, and each had 10-turn input coils and a single-turn pickup loop. The first transformer, which was patterned with a combination of shadow masks and photolithography, yielded a magnetic field gain of about {minus}7.5, functioned up to 79 K, and gave a magnetic field sensitivity B{sub N} (10 Hz) {approx} 3.1 pT Hz{sup {minus}1/2}at 38 K. The second transformer, which was patterned entirely by photolithography, yielded a gain of about {minus}8.7, functioned up to 25 K, and had a sensitivity B{sub N} (10 Hz) {approx} 3.5 pT Hz{sup {minus}1/2} at 4.2 K. In both cases, the limiting noise arose in the SQUID. 10 refs., 5 figs., 1 tab.

  14. Spectral investigation of hot-spot and cavity resonance effects on the terahertz radiation emitted from high-Tc superconducting Bi2Sr2CaCu2O8+δ single crystal mesa structures

    NASA Astrophysics Data System (ADS)

    Kadowaki, Kazuo; Watanabe, Chiharu; Minami, Hidetoshi; Yamamoto, Takashi; Kashiwagi, Takanari; Klemm, Richard

    2014-03-01

    Terahertz (THz) electromagnetic radiation emitted from high-Tc superconducting Bi2Sr2CaCu2O8+δ mesa structures in the case of single mesa and series-connected mesas is investigated by the FTIR spectroscopic technique while observing its temperature distribution simultaneously by a SiC photoluminescence technique. Changing the bias level, sudden jumps of the hot-spot position were clearly observed. Although the radiation intensity changes drastically associated with the jump of the hot spot position, the frequency is unaffected as long as the voltage per junction is kept constant. Since the frequency of the intense radiation satisfies the cavity resonance condition, we confirmed that the cavity resonance is of primarily importance for the synchronization of whole intrinsic Josephson junctions in the mesa for high power radiation. This work was supported in part by the Grant-in-Aid for challenging Exploratory Research, the Ministry of Education, Culture, Sports, Science & Technology (MEXT).

  15. Are the high Tc superconductors d-wave?

    NASA Astrophysics Data System (ADS)

    Kallin, Catherine; Berlinsky, A. John

    1994-12-01

    Although it has been widely accepted for several years that the normal state of high Tc superconductors is anomalous, only recently has there been growing evidence for the anomalous nature of the superconducting state. A number of recent experiments show clear evidence for the existence of low-lying excitations in the superconducting state. Moreover, the observation by Bonn, Hardy and coworkers of a linear temperature dependence in the microwave surface resistance and penetration depth of YBCO at low temperatures suggests d-wave pairing with line nodes. The evidence for and against unconventional superconductivity in the high Tc oxides is reviewed. Specific topics discussed include the different behaviours observed for the penetration depth in thin films and in single crystals, what is known about the absolute value of the penetration depth, the role of disorder and inelastic scattering, the relative merits of strong vs. weak correlation theories of d-wave superconductivity in the high Tc oxides, and most important, what have we actually learned about the penetration depth of high Tc superconductors from μSR?

  16. μSR Studies on Magnetism in High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Koike, Yoji; Adachi, Tadashi

    2016-09-01

    Since the discovery of high-Tc superconductivity in cuprates, muon spin relaxation (μSR) measurements have greatly contributed to the understanding of high-Tc superconductivity. In this paper, μSR studies on the magnetism in high-Tc cuprates obtained these past three decades are reviewed. Antiferromagnetic long-range order, 1/8 anomaly, stripes of Cu spins and holes, impurity-induced magnetism, magnetic-field-induced magnetism, pseudogap, ferromagnetism in the heavily overdoped regime, and undoped superconductivity in T'-type cuprates are discussed. Moreover, the fundamentals of μSR measurements for the study of magnetism are described for μSR beginners.

  17. Pairing theory of high Tc and low Tc superconductors

    NASA Astrophysics Data System (ADS)

    Sang, Boo Nam

    1994-09-01

    New solutions for Tc, the order parameter, and the density of states are obtained, based on the fact that pairs are formed within the pairing interaction range, TD (Debye), via the BCS pairing theory (not the BCS results). They are valiid for all ify = {T D}/{πT c}, and are applicable to low Tc (LTC) and high Tc (HTS) superconductors. The order parameter variation with y is shown to account for all features of HTS. A new density of states via the zero order parameter outside the pairing interaction range is found to account for low energy states observed in HTS. For large y (LTS), the BCS results are reproduced.

  18. Photoinduced Melting of Superconductivity in the High-Tc Superconductor La2−xSrxCuO4 Probed by Time-resolved Optical and Terahertz Techniques

    SciTech Connect

    Logvenov, G.; Beyer, M.; Staedter, D.; Beck, M.; Schaefer, H.; Kabanov, V.V.; Bozovic, I.; Koren, G.; Demsar, J.

    2011-06-13

    The dynamics of depletion and recovery of a superconducting state in La{sub 2-x}Sr{sub x}CuO{sub 4} thin films is investigated utilizing optical pump-probe and optical pump-THz-probe techniques as a function of temperature and excitation fluence. The absorbed energy density required to suppress superconductivity is found to be about eight times higher than the thermodynamically determined condensation energy density and nearly temperature independent between 4 and 25 K. These findings indicate that, during the time when the superconducting state suppression takes place ({approx}0.7 ps), a large part (nearly 90%) of the energy is transferred to the phonons with energy lower than twice the maximum value of the superconducting gap and only 10% is spent on Cooper pair breaking.

  19. Magnetic and Superconducting Materials at High Pressures

    SciTech Connect

    Struzhkin, Viktor V.

    2015-03-24

    The work concentrates on few important tasks in enabling techniques for search of superconducting compressed hydrogen compounds and pure hydrogen, investigation of mechanisms of high-Tc superconductivity, and exploring new superconducting materials. Along that route we performed several challenging tasks, including discovery of new forms of polyhydrides of alkali metal Na at very high pressures. These experiments help us to establish the experimental environment that will provide important information on the high-pressure properties of hydrogen-rich compounds. Our recent progress in RIXS measurements opens a whole field of strongly correlated 3d materials. We have developed a systematic approach to measure major electronic parameters, like Hubbard energy U, and charge transfer energy Δ, as function of pressure. This technique will enable also RIXS studies of magnetic excitations in iridates and other 5d materials at the L edge, which attract a lot of interest recently. We have developed new magnetic sensing technique based on optically detected magnetic resonance from NV centers in diamond. The technique can be applied to study superconductivity in high-TC materials, to search for magnetic transitions in strongly correlated and itinerant magnetic materials under pressure. Summary of Project Activities; development of high-pressure experimentation platform for exploration of new potential superconductors, metal polyhydrides (including newly discovered alkali metal polyhydrides), and already known superconductors at the limit of static high-pressure techniques; investigation of special classes of superconducting compounds (high-Tc superconductors, new superconducting materials), that may provide new fundamental knowledge and may prove important for application as high-temperature/high-critical parameter superconductors; investigation of the pressure dependence of superconductivity and magnetic/phase transformations in 3d transition metal compounds, including

  20. 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

  1. Standard Model for Superconductivity in Graphite Intercalation Compounds: Prediction of Optimum Tc

    NASA Astrophysics Data System (ADS)

    Takada, Yasutami

    2009-03-01

    Based on the model that was successfully applied to the explanation of superconductivity with the transition temperature Tc of about 0.1K or less in the alkali- intercalated graphite compounds such as KC8, RbC8, and CsC8 in 1982 [Y. Takada, J. Phys. Soc. Jpn. 51, 63 (1982) ], we have calculated Tc for the alkaline-earth- intercalated graphite compounds including CaC6, YbC6, and SrC6 with Tc of about 10K or less to find that the same model reproduces the observed Tc in those compounds as well, indicating that it is a standard model for superconductivity in the graphite intercalation compounds with Tc ranging over three orders of magnitude. The difference in Tc by two orders between KC8 and CaC6 can be accounted for by (i) doubling Z the valency of the metal ions, which enhances Tc by one order, and (ii) tripling m^* the effective mass of the superconducting three-dimensional electrons in the interlayer band, which also enhances Tc by one order. Enhancement of Tc well beyond 10 K is also predicted in this model, if intercalant metals are judiciously chosen so that both Z and m^* are increased further.

  2. High field superconducting magnets

    NASA Technical Reports Server (NTRS)

    Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

    2011-01-01

    A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

  3. Properties of HIGH-Tc Cuprates: Some Recent Results and Open Questions

    NASA Astrophysics Data System (ADS)

    Vobornik, Ivana; Pavuna, Davor

    Thirteen years ago, late in 1986, several groups confirmed striking claims of the famous paper by Bednorz and M[Z Phys. B 64 (1986) 189] that announced the discovery of high-Tc superconductivity in cuprates. Some 60,000 papers later, we are still struggling to understand the high-Tc oxide superconductivity. Here we present some of the most relevant recent experiments and discuss some open questions across rather complex electronic phase diagram; we also note an important role of un-intentional and intentional disorder in these layered, high-Tc oxides.

  4. Optimization of the detection coil of high-Tc superconducting quantum interference device-based nuclear magnetic resonance for discriminating a minimum amount of liver tumor of rats in microtesla fields

    NASA Astrophysics Data System (ADS)

    Chen, Hsin-Hsien; Huang, Kai-Wen; Yang, Hong-Chang; Horng, Herng-Er; Liao, Shu-Hsien

    2013-08-01

    This study presents an optimization of the detection coil of high-Tc superconducting quantum interference device (SQUID)-based nuclear magnetic resonance (NMR) in microtesla fields for discriminating a minimum amount of liver tumor in rats by characterizing the longitudinal relaxation rate, T1-1, of tested samples. The detection coil, which was coupled to the SQUID through a flux transformer, was optimized by varying the copper wires' winding turns and diameters. When comparing the measured NMR signals, we found that the simulated NMR signal agrees with simulated signals. When discriminating liver tumors in rats, the averaged longitudinal relaxation rate was observed to be T1-1 = 3.3 s-1 for cancerous liver tissue and T1-1 = 6.6 s-1 for normal liver tissue. The results suggest that it can be used to successfully discriminate cancerous liver tissue from normal liver tissues in rats. The minimum amount of samples that can be detected is 0.2 g for liver tumor and 0.4 g for normal liver tissue in 100 μT fields. The specimen was not damaged; it can be used for other pathological analyses. The proposed method provides more possibilities for examining undersized specimens.

  5. Structural, electronic, superconducting and mechanical properties of ReC and TcC

    NASA Astrophysics Data System (ADS)

    Kavitha, M.; Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Santhosh, M.

    2015-06-01

    The structural, electronic, superconducting and mechanical properties of ReC and TcC are investigated using density functional theory calculations. The lattice constants, bulk modulus, and the density of states are obtained. The calculated lattice parameters are in good agreement with the available results. The density of states reveals that ReC and TcC exhibit metallic behavior at ambient condition. A pressure-induced structural phase transition is observed in both materials.

  6. Structural, electronic, superconducting and mechanical properties of ReC and TcC

    SciTech Connect

    Kavitha, M.; Priyanga, G. Sudha; Rajeswarapalanichamy, R. Santhosh, M.

    2015-06-24

    The structural, electronic, superconducting and mechanical properties of ReC and TcC are investigated using density functional theory calculations. The lattice constants, bulk modulus, and the density of states are obtained. The calculated lattice parameters are in good agreement with the available results. The density of states reveals that ReC and TcC exhibit metallic behavior at ambient condition. A pressure-induced structural phase transition is observed in both materials.

  7. Determination of concentration and distribution of (CuO) + in high- Tc superconducting La 2- xSr xCuO y pellet by flow-coulometry

    NASA Astrophysics Data System (ADS)

    Sasaki, Y.; Aoyagi, H.; Takeishi, H.; Yoshida, Z.

    1992-02-01

    The novel wet-chemical method for the analysis of the concentration and the distribution of constituent(s) at a higher oxidation state, [CuO] +, in superconducting La 2- xSr xCuO y was developed. The sample pellet was dissolved in a flow of acid solution containing Fe 2+, and the solution was introduced continuously into a flow-coulometric system composed of two-step column electrodes of glassy carbon fibers as working electrodes. Fe 3+ generated in the solution through the stoichiometric redox between [CuO] + and Fe 2+ was detected at the first column electrode, and Cu 2+ in the dissolving solution was detected at the second column. It was obvious that the [CuO] + concentration in the surface region of ca. 200 μm in depth from the surface was lower than that of the bulk pellet and the distribution of [CuO] + near the surface was dependent on such sample-preparation parameters as sintering time, annealing atmosphere and storage time of the pellets, etc.

  8. Investigations of chemical interaction between Bi-based 2212 and (RE)Ba 2Cu 3O 7 high Tc superconducting materials

    NASA Astrophysics Data System (ADS)

    Cloots, R.; Rulmont, A.; Gillet, F.; Ausloos, M.

    Composite materials have been synthesized by mixing 90% (or 95%) YBa 2Cu 3O 7 and 10% (or 5%) Bi 2Sr 2Ca 1Cu 2O 8 by weight, and firing at 900°C to promote grain growth by inducing a liquid phase (Bi 2Sr 2Ca 1Cu 2O 8) in the system. The influence of the amount of liquid phase on the X-ray diffraction data and electrical properties is reported. Energy dispersive X-ray (EDX) analyses are also reported. The YBiBa 2O 6 phase is formed during the heat treatment and introduces additional chemical heterogeneities at the grain boundaries. A previously reported 2212-related superconducting phase, Bi 2(Sr,Ba) 2(Ca,Y)Cu 2O 8+y, could also be formed during the synthesis process, and its effect on the electrical resistance versus temperature measurements is discussed. Attempts to substitute RE ions (Dy 3+, Er 3+, Ho 3+) for Y 3+ in YBiBa 2O 6 have been successful and are reported in an appendix section. X-ray diffraction data are also reported. EDX analyses have been performed specifically for a typical ErBiBa 2O 6 compound and reveal the presence of a new Er 2Ba 4O 7 phase.

  9. Organic conductor/high-Tc superconductor bilayer structures

    NASA Astrophysics Data System (ADS)

    Clevenger, Marvin B.; Jones, Christopher E.; Haupt, Steven G.; Zhao, Jianai; McDevitt, John T.

    1996-07-01

    Electrochemical techniques are exploited to fabricate conductive polymer/high Tc superconductor bilayer structures. SCanning electron microscopy and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto YBa2Cu3O7-(delta ) films. In such hybrid polymer/superconductor systems, it is found that when the polymer is oxidized to its conductive state, the transition temperatures (Tc) and critical currents (Jc) of the underlying superconductor film are suppressed. Reversible modulation of the values of the transition temperatures of up to 50K are noted for these structures. Upon reduction of the conductive polymer layer back to its non-conductive form, both Tc and Jc are found to return to values close to those acquired for the underivatized YBa2Cu3O7-(delta ) film. Moreover, measurements as a function of temperature of the polymer/superconductor interface resistance show dramatic decrease in this value at Tc. ALso, estimates of superconducting coherence lengths within the organic conductor samples suggest superconducting properties over macroscopically large distances within the organic materials can be expected. Collectively these results are consistent with the first observation of a conductive polymer proximity effect.

  10. Organic conductor/high-{Tc} superconductor bilayer structures

    SciTech Connect

    Clevenger, M.B.; Jones, C.E.; Haupt, S.G.; Zhao, J.; McDevitt, J.T.

    1996-12-31

    Electrochemical techniques are exploited to fabricate conducive polymer/high-{Tc} superconductor bilayer structures. Scanning electron microscopy and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films. In such hybrid polymer/superconductor systems, it is found that when the polymer is oxidized to its conductive state, the transition temperature ({Tc}) and critical currents (J{sub c}) of the underlying superconductor films are suppressed. Reversible modulation of the values of the transition temperatures of up to 50 K are noted for these structures. Upon reduction of the conductive polymer layer back to its non-conductive form, both {Tc} and J{sub c} are found to return to values close to those acquired for the underivatized YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films. Moreover, measurements as a function of temperature of the polymer/superconductor interface resistance show dramatic decrease in this value at {Tc}. Also, estimates of superconducting coherence lengths within the organic conductor samples suggest superconducting properties over macroscopically large distances within the organic materials can be expected. Collectively these results are consistent with the first observation of a conductive polymer proximity effect.

  11. High Tc superconductivity in the triple-perovskite La-rare earth or alkali metal-Ba-Ca-Mg or Cd-Cu-oxide system. Technical report, January-December 1996

    SciTech Connect

    Tauber, A.; Tidrow, S.C.; Pierce, D.; Eckart, D.W.

    1997-03-01

    Bulk targets of compounds in the system La(3{minus}z)Me(z)Ba3Ca(1{minus}v)Nc{sub v}Cu7O(16+v) where Me=rare earth or Na and Nc=Mg or Cd were prepared by solid state reactions. They were employed to deposit by pulse laser deposition thin films of the superconductor on single crystal substrates of LaAlO3, LSAT, and GGG. Phase relationships and orientation relationships were obtained from diffractometer scans. All compounds exhibited a (001) relationship with all substrates. Lattice parameters, transition temperatures and widths are reported for each superconducting compound. All substituted compounds were superconducting but no increase in Tc was observed for any. All thin films heated to 750 deg C desorbed little oxygen compared to YBCO.

  12. Thermodynamic critical fields in high T c superconductivity

    NASA Astrophysics Data System (ADS)

    Clougherty, Dennis P.; Johnson, Keith H.

    1988-06-01

    Using the free electron approximation, a real space mechanism of how magnetic fields of sufficient strength destroy the superconducting state is outlined. Using the resultant equation together with the molecular orbital model of superconductivity 1,2, the thermodynamic critical magnetic field is calculated and compared to experiment for type I elemental superconductors and type II superconductors, including high-Tc superconductors. The expression for critical field compares favorably with an expression derived by Schrieffer.

  13. The spin bag mechanism of high temperature superconductivity

    NASA Technical Reports Server (NTRS)

    Schrieffer, J. R.; Wen, X.-G.; Zhang, S.-C.

    1989-01-01

    In oxide superconductors the local suppression of antiferromagnetic correlations in the vicinity of a hole lowers the energy of the system. This quasi two-dimensional bag of weakened spin order follows the hole in its motion. In addition, holes prefer to share a bag, leading to a strong pairing attraction and a high Tc superconductivity. There are many experimental consequences of this mechanism for both the superconducting and normal phases.

  14. High temperature superconductivity in sulfur hydride under ultrahigh pressure: A complex superconducting phase beyond conventional BCS

    NASA Astrophysics Data System (ADS)

    Bussmann-Holder, Annette; Köhler, Jürgen; Whangbo, M.-H.; Bianconi, Antonio; Simon, Arndt

    2016-05-01

    The recent report of superconductivity under high pressure at the record transition temperature of Tc =203 K in pressurized H2S has been identified as conventional in view of the observation of an isotope effect upon deuteration. Here it is demonstrated that conventional theories of superconductivity in the sense of BCS or Eliashberg formalisms cannot account for the pressure dependence of the isotope coefficient. The only way out of the dilemma is a multi-band approach of superconductivity where already small interband coupling suffices to achieve the high values of Tc together with the anomalous pressure dependent isotope coefficient. In addition, it is shown that anharmonicity of the hydrogen bonds vanishes under pressure whereas anharmonic phonon modes related to sulfur are still active.

  15. Simulating the Euclidean time Schroedinger equations using an Intel iPSC/860 hypercube: Application to the t-J model of high-{Tc} superconductivity

    SciTech Connect

    Kovarik, M.D.; Barnes, T. |

    1993-10-01

    We describe a Monte Carlo simulation of a dynamical fermion problem in two spatial dimensions on an Intel iPSC/860 hypercube. The problem studied is the determination of the dispersion relation of a dynamical hole in the t-J model of the high temperature superconductors. Since this problem involves the motion of many fermions in more than one spatial dimensions, it is representative of the class of systems that suffer from the ``minus sign problem`` of dynamical fermions which has made Monte Carlo simulation very difficult. We demonstrate that for small values of the hole hopping parameter one can extract the entire hole dispersion relation using the GRW Monte Carlo algorithm, which is a simulation of the Euclidean time Schroedinger equation, and present results on 4 {times} 4 and 6 {times} 6 lattices. Generalization to physical hopping parameter values wig only require use of an improved trial wavefunction for importance sampling.

  16. NMR/MRI with hyperpolarized gas and high Tc SQUID

    DOEpatents

    Schlenga, Klaus; de Souza, Ricardo E.; Wong-Foy, Annjoe; Clarke, John; Pines, Alexander

    2000-01-01

    A method and apparatus for the detection of nuclear magnetic resonance (NMR) signals and production of magnetic resonance imaging (MRI) from samples combines the use of hyperpolarized inert gases to enhance the NMR signals from target nuclei in a sample and a high critical temperature (Tc) superconducting quantum interference device (SQUID) to detect the NMR signals. The system operates in static magnetic fields of 3 mT or less (down to 0.1 mT), and at temperatures from liquid nitrogen (77K) to room temperature. Sample size is limited only by the size of the magnetic field coils and not by the detector. The detector is a high Tc SQUID magnetometer designed so that the SQUID detector can be very close to the sample, which can be at room temperature.

  17. High-pressure superconducting state in hydrogen

    NASA Astrophysics Data System (ADS)

    Duda, A. M.; Szczȩśniak, R.; Sowińska, M. A.; Kosiacka, A. H.

    2016-10-01

    The paper determines the thermodynamic parameters of the superconducting state in the metallic atomic hydrogen under the pressure at 1 TPa, 1.5 TPa, and 2.5 TPa. The calculations were conducted in the framework of the Eliashberg formalism. It has been shown that the critical temperature is very high (in the range from 301.2 K to 437.3 K), as well as high are the values of the electron effective mass (from 3.43me to 6.88me), where me denotes the electron band mass. The ratio of the low-temperature energy gap to the critical temperature explicitly violates the predictions of the BCS theory: 2 Δ (0) /kB TC ∈ < 4.84 , 5.85 > . Additionally, the free energy difference between the superconducting and normal state, the thermodynamic critical field, and the specific heat of the superconducting state have been determined. Due to the significant strong-coupling and retardation effects those quantities cannot be correctly described in the framework of the BCS theory.

  18. High-Tc Superconductivity and Raman Scattering Study of the phonon properties of electron doped (transition metal, rare-earth) - Oxygen-Free CaFeAsF and compared with RFeAsO system

    NASA Astrophysics Data System (ADS)

    Sasmal, Kalyan; Hadjiev, Viktor; Chu, C. W.(Paul)

    Quaternary CaFeAsF has ZrCuSiAs-type structure,(RO)δ+ layer in RFeAsO replaced by (CaF)δ+ layer,with tetragonal (P4/nmm)-orthorhombic (Cmma) phase transition at 134K,while magnetic order,SDW sets in at 114K. Partial replacement of Fe with Co/Ni is direct electron doping to (FeAs)δ+ layer.Tc ~15K in CaFe0.9Ni0.1AsF.Substitution of rare earth metal for alkaline earth metal suppresses anomaly in resistivity & induces superconductivity.Tc ~52K in Ca0.5Pr0.5FeAsF.Characterized by resistivity, susceptibility,XRD & EDX-SEM.Upper critical field estimated from magneto resistance.Bulk superconductivity proved by DC magnetization. Hall coefficient RH revealed hole-like charge carriers in parent compound CaFeAsF, while electron-type (RH in normal state is -Ve) for Ca0.5Pr0.5FeAsF.Evolution of Raman active phonons of Ca1-xPrxFeAsF measured with polarized Raman spectroscopy at room temperature from absurfaces of impurity-free microcrystals.Spectra exhibit sharp phonon lines on very weak electronic scattering background.Frequency and symmetry of Raman phonons involving out-of-plane atomic vibrations are found at 162.5 cm-1 (A1 g, Pr), 201 cm-1 (A1 g, As), 215.5 cm-1 (B1 g, Fe), 265 cm-1 (Eg, Fe) and 334 cm-1 (B1 g, F) for Ca0.5Pr0.5FeAsF.Observations are compared with RFeAsO unconventional superconductors also possibly related to magnetic fluctuations

  19. Defect-Induced Changes in the Spectral Properties of HIGH-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Vobornik, I.; Berger, H.; Rullier-Albenque, F.; Margaritondo, G.; Pavuna, D.; Grioni, L. Forroand M.

    Superconductivity in high-Tc cuprates is particularly sensitive to disorder due to the unconventional d-wave pairing symmetry. We investigated effects of disorder on the spectral properties of Bi2Sr2CaCu2O8+x high-Tc superconductor. We found that already small defect densities suppress the characteristic spectral signature of the superconducting state. The spectral line shape clearly reflects new excitations within the gap, as expected for defect-induced pair breaking. At the lowest defect concentrations the normal state remains unaffected, while increased disorder leads to suppression of the normal quasiparticle peaks.

  20. Enlargement of the field of view and maintenance of a high signal-to-noise ratio using a two-element high-Tc superconducting array in a 3T MRI.

    PubMed

    Lin, In-Tsang; Yang, Hong-Chang; Chen, Jyh-Horng

    2012-01-01

    This study examines the enlargement of the field of view (FOV) and the maintenance of a high signal-to-noise ratio (SNR) through the use of two high-temperature superconducting (HTS) resonators in a 3T MRI. Two Bi(2)Sr(2)Ca(2)Cu(3)O(x) (Bi-2223) surface resonators, each of 4-cm diameter, were used in a 3T MRI. Professionally made copper resonators operate at 300 K, but each Bi-2223 resonator, operated at 77 K and demonstrated a 3.75 fold increase in SNR gain. For the same scanning time, the SNR of the images of a rat's brain and back, obtained using two small Bi-2223 surface resonators, was higher than that obtained using a single 8-cm surface resonator.

  1. Polaron models of high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Mott, N. F.

    1993-01-01

    A review is given of theories of high-temperature superconductors in which the current is carried by bipolarons, which form a condensed Bose gas below Tc and a non-degenerate gas above it. Such theories were first proposed by Schafroth, Alexandrov, Ranninger and de Jongh; the present author has, for the copper oxide materials, proposed spin bipolarons. Experimental work has, however, shown no magnetic moments in the superconducting and “spin glass” ranges of composition; a modification of the spin bipolaron model is proposed to take account of these observations. Other aspects of the model are discussed, particularly heat conduction and the effect of disorder. A comparison is made with the cubic bismuth materials.

  2. High Temperature Superconductivity and Cold Fusion

    NASA Astrophysics Data System (ADS)

    Rabinowitz, Mario

    There are numerous historical and scientific parallels between high temperature superconductivity (HTSC) and the newly emerging field of cold fusion (CF). Just as the charge carrier effective mass plays an important role in SC, the deuteron effective mass may play a vital role in CF. A new theory including effects of proximity, electron shielding, and decreased effective mass of the fusing nuclei can account for the reported CF results. A quantum-gas model that covers the range from low temperature to superhigh temperature SC indicates an increased Tc with reduced dimensionality. A reduced dimensionality effect may also enhance CF. A relation is shown between CF and the significant cluster-impact fusion experiments.

  3. Enhancement of Superconductivity of Beryllium at High Pressure

    NASA Astrophysics Data System (ADS)

    Shimizu, Katsuya; Kubota, Kazuhisa; Katsuoka, Takahiro; Miyake, Atsushi; Sakata, Masafumi; Nakamoto, Yuki; Ohishi, Yasuo

    2013-06-01

    Among elements shows superconductivity at high pressure, some elements show the large enhancement of the transition temperature (Tc) at higher pressures. In the case of lithium, the Tc at ambient pressure is 0.4 mK which is the lowest observed value in whole elements, however, is enhanced by pressure up to near 20 K. And calcium, which is on the same group II and not superconductive at ambient pressure, shows the highest Tc of elements at 29 K under pressure. Then we focused on beryllium which is near to them on the periodic table. At ambient pressure, Tc of beryllium is 24 mK. We measured the electrical resistance at high pressure (P < 50 GPa) and low temperature (T > 100 mK) and found that the Tc rose up to few Kelvin at pressure above 20 GPa and reached up to 3.7 K at 30 GPa. In this pressure range the hcp crystal structure is stable at room temperature. We performed a powder X-ray diffraction measurement at room temperature and low temperature in BL10XU at SPring-8 and found a discontinuous change in c/a ratio at around 25 GPa.

  4. Electric and magnetic characterization of NbSe 2 single crystals: Anisotropic superconducting fluctuations above TC

    NASA Astrophysics Data System (ADS)

    Soto, F.; Berger, H.; Cabo, L.; Carballeira, C.; Mosqueira, J.; Pavuna, D.; Toimil, P.; Vidal, F.

    2007-09-01

    Electric and magnetic characterization of NbSe 2 single crystals is first presented in detail. Then, some preliminary measurements of the fluctuation-diamagnetism (FD) above the transition temperature TC are presented. The moderate uniaxial anisotropy of this compound allowed us to observe the fluctuation effects for magnetic fields H applied in the two main crystallographic orientations. The superconducting parameters resulting from the characterization suggest that it is possible to do a reliable analysis of the FD in terms of the Ginzburg-Landau (GL) theory.

  5. Shock compaction of high- Tc superconductors

    SciTech Connect

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

    1990-09-01

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

  6. First-principles studies for understanding diverse high- Tc

    NASA Astrophysics Data System (ADS)

    Cheng, Hai-Ping

    2011-03-01

    In this talk, I survey results and insights gained from first-principles calculations on materials that exhibit superconducting behavior at temperatures higher than those characteristic of conventional BCS superconductors. These range from highly correlated cuprate Mott insulators as represented by the bismuth-strontium-calcium-copper-oxides (BSCCOs) to border-line itinerant-Mott systems such as the recently discovered 1111 and 122 pnictides. ultimate goal of our studies is to correlate Tc with specific material composition using detailed first-principles calculations in conjunction with many-body physics techniques via the critical step of constructing real-materials model Hamiltonians. By manipulating impurity doping, which plays a crucial role in the phase diagrams of high Tc materials, we hope to find guidance for designing candidate systems with Tc higher than ones currently known. BSCCO material, density functional calculations using a good generalized-gradient approximation (GGA) yield structural information that is correlated to the experimentally observed (STM) super-modulation and impurity peak in the high energy regime (~ 1 eV), even though the Kohn-Sham bands from such functionals fail to have a band gap. For FeAs-based high-Tc systems, DFT band-structure calculations provide a very good starting point for constructing model Hamiltonians for studies of spin fluctuation and electron pairing mechanisms. Fermi sheets that have been constructed using Wannier transformed Kohn-Sham states have provided critical information for understanding this family of superconducting materials. Analysis of the details of magnetic ordering, density of states, and 2D vs. 3D features in both the 1111 and 122 materials have been valuable in understanding sometimes perplexing experimental findings. Effects of Co impurities have been studied and fully analyzed as well., I will discuss persistent challenges related to calculations on the structure of the non-magnetic state Ba 1

  7. High-Temperature Superconductivity

    SciTech Connect

    Peter Johnson

    2008-11-05

    Like astronomers tweaking images to gain a more detailed glimpse of distant stars, physicists at Brookhaven National Laboratory have found ways to sharpen images of the energy spectra in high-temperature superconductors — materials that carry electrical c

  8. High-Temperature Superconductivity

    ScienceCinema

    Peter Johnson

    2016-07-12

    Like astronomers tweaking images to gain a more detailed glimpse of distant stars, physicists at Brookhaven National Laboratory have found ways to sharpen images of the energy spectra in high-temperature superconductors — materials that carry electrical c

  9. Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure

    PubMed Central

    Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi; Oda, Tatsuki; Suzuki, Naoshi

    2016-01-01

    Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30–70 K in pressure range of 100–170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system. PMID:26983593

  10. Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure

    NASA Astrophysics Data System (ADS)

    Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi; Oda, Tatsuki; Suzuki, Naoshi

    2016-03-01

    Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30–70 K in pressure range of 100–170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system.

  11. Superconductivity in highly disordered dense carbon disulfide.

    PubMed

    Dias, Ranga P; Yoo, Choong-Shik; Struzhkin, Viktor V; Kim, Minseob; Muramatsu, Takaki; Matsuoka, Takahiro; Ohishi, Yasuo; Sinogeikin, Stanislav

    2013-07-16

    High pressure plays an increasingly important role in both understanding superconductivity and the development of new superconducting materials. New superconductors were found in metallic and metal oxide systems at high pressure. However, because of the filled close-shell configuration, the superconductivity in molecular systems has been limited to charge-transferred salts and metal-doped carbon species with relatively low superconducting transition temperatures. Here, we report the low-temperature superconducting phase observed in diamagnetic carbon disulfide under high pressure. The superconductivity arises from a highly disordered extended state (CS4 phase or phase III[CS4]) at ~6.2 K over a broad pressure range from 50 to 172 GPa. Based on the X-ray scattering data, we suggest that the local structural change from a tetrahedral to an octahedral configuration is responsible for the observed superconductivity.

  12. High specific heat superconducting composite

    DOEpatents

    Steyert, Jr., William A.

    1979-01-01

    A composite superconductor formed from a high specific heat ceramic such as gadolinium oxide or gadolinium-aluminum oxide and a conventional metal conductor such as copper or aluminum which are insolubly mixed together to provide adiabatic stability in a superconducting mode of operation. The addition of a few percent of insoluble gadolinium-aluminum oxide powder or gadolinium oxide powder to copper, increases the measured specific heat of the composite by one to two orders of magnitude below the 5.degree. K. level while maintaining the high thermal and electrical conductivity of the conventional metal conductor.

  13. Charge segregation model for superconducting correlations in cuprates above T(c).

    PubMed

    de Mello, E V L; Sonier, J E

    2014-12-10

    We present a theoretical framework for understanding recent transverse field muon spin rotation (TF-µSR) experiments on cuprate superconductors in terms of localized regions of phase-coherent pairing correlations above the bulk superconducting transition temperature Tc. The local regions of phase coherence are associated with a tendency toward charge ordering, a phenomenon found recently in hole-doped cuprates. We use the Cahn-Hilliard equation as a means to phenomenologically model the inhomogeneous charge distribution of the electron system observed experimentally. For this system we perform self-consistent superconducting calculations using the Bogoliubov-deGennes method. Within this context we explore two possible scenarios: (i) the magnetic field is diamagnetically screened by the sum of varying shielding currents of isolated small-sized superconducting domains. (ii) These domains become increasingly correlated by Josephson coupling as the temperature is lowered and the main response to the applied magnetic field is from the sum of all varying tunneling currents. The results indicate that these two approaches may be used to simulate the TF-µSR data but case (ii) yields better agreement. PMID:25364008

  14. Simulations of high-Tc superconductors using the DCA+ algorithm

    NASA Astrophysics Data System (ADS)

    Staar, Peter

    2015-03-01

    For over three decades, the high Tc-cuprates have been a gigantic challenge for condensed matter theory. Even the simplest representation of these materials, i.e. the single band Hubbard model, is hard to solve quantitatively and its phase-diagram is therefore elusive. In this talk, we present the recent algorithmic and implementation advances to the Dynamical Cluster Approximation (DCA). The algorithmic advances allow us to determine self-consistently a continuous self-energy in momentum space, which in turn reduces the cluster-shape dependency of the superconducting transition temperature and thus accelerates the convergence of the latter versus cluster-size. Furthermore, the introduction of the smooth self-energy suppresses artificial correlations and thus reduces the fermionic sign-problem, allowing us to simulate larger clusters at much lower temperatures. By combining these algorithmic improvements with a very efficient GPU accelerated QMC-solver, we are now able to determine the superconducting transition temperature accurately and show that the Cooper-pairs have indeed a d-wave structure, as was predicted by Zhang and Rice.

  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. Enhancement of superconducting Tc (33 K) by entrapment of FeSe in carbon coated Au-Pd17Se15 nanoparticles.

    PubMed

    Mishra, Sukhada; Song, Kai; Ghosh, Kartik C; Nath, Manashi

    2014-03-25

    FeSe has been an interesting member of the Fe-based superconductor family ever since the discovery of superconductivity in this simple binary chalcogenide. Simplicity of composition and ease of synthesis has made FeSe, in particular, very lucrative as a test system to understand the unconventional nature of superconductivity, especially in low-dimensional models. In this article we report the synthesis of composite nanoparticles containing FeSe nanoislands entrapped within an ent-FeSe-Pd16Se15-Au nanoparticle and sharing an interface with Pd17Se15. This assembly exhibits a significant enhancement in the superconducting Tc (onset at 33 K) accompanied by a noticeable lattice compression of FeSe along the <001> and <101> directions. The Tc in FeSe is very sensitive to application of pressure and it has been shown that with increasing external pressure Tc can be increased almost 4-fold. In these composite nanoparticles reported here, immobilization of FeSe on the Pd17Se15 surface contributes to increasing the effect of interfacial pressure, thereby enhancing the Tc. The effect of interfacial pressure is also manifested in the contraction of the FeSe lattice (up to 3.8% in <001> direction) as observed through extensive high-resolution TEM imaging. The confined FeSe in these nanoparticles occupied a region of approximately 15-25 nm, where lattice compression was uniform over the entire FeSe region, thereby maximizing its effect in enhancing the Tc. The nanoparticles have been synthesized by a simple catalyst-aided vapor transport reaction at 800 °C where iron acetylacetonate and Se were used as precursors. Morphology and composition of these nanoparticles have been studied in details through extensive electron microscopy. PMID:24494773

  17. High Temperature Superconducting Underground Cable

    SciTech Connect

    Farrell, Roger, A.

    2010-02-28

    The purpose of this Project was to design, build, install and demonstrate the technical feasibility of an underground high temperature superconducting (HTS) power cable installed between two utility substations. In the first phase two HTS cables, 320 m and 30 m in length, were constructed using 1st generation BSCCO wire. The two 34.5 kV, 800 Arms, 48 MVA sections were connected together using a superconducting joint in an underground vault. In the second phase the 30 m BSCCO cable was replaced by one constructed with 2nd generation YBCO wire. 2nd generation wire is needed for commercialization because of inherent cost and performance benefits. Primary objectives of the Project were to build and operate an HTS cable system which demonstrates significant progress towards commercial progress and addresses real world utility concerns such as installation, maintenance, reliability and compatibility with the existing grid. Four key technical areas addressed were the HTS cable and terminations (where the cable connects to the grid), cryogenic refrigeration system, underground cable-to-cable joint (needed for replacement of cable sections) and cost-effective 2nd generation HTS wire. This was the world’s first installation and operation of an HTS cable underground, between two utility substations as well as the first to demonstrate a cable-to-cable joint, remote monitoring system and 2nd generation HTS.

  18. Peak Effect in High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Ling, Xinsheng

    1996-03-01

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

  19. High-temperature interface superconductivity between metallic and insulating copper oxides.

    PubMed

    Gozar, A; Logvenov, G; Kourkoutis, L Fitting; Bollinger, A T; Giannuzzi, L A; Muller, D A; Bozovic, I

    2008-10-01

    The realization of high-transition-temperature (high-T(c)) superconductivity confined to nanometre-sized interfaces has been a long-standing goal because of potential applications and the opportunity to study quantum phenomena in reduced dimensions. This has been, however, a challenging target: in conventional metals, the high electron density restricts interface effects (such as carrier depletion or accumulation) to a region much narrower than the coherence length, which is the scale necessary for superconductivity to occur. By contrast, in copper oxides the carrier density is low whereas T(c) is high and the coherence length very short, which provides an opportunity-but at a price: the interface must be atomically perfect. Here we report superconductivity in bilayers consisting of an insulator (La(2)CuO(4)) and a metal (La(1.55)Sr(0.45)CuO(4)), neither of which is superconducting in isolation. In these bilayers, T(c) is either approximately 15 K or approximately 30 K, depending on the layering sequence. This highly robust phenomenon is confined within 2-3 nm of the interface. If such a bilayer is exposed to ozone, T(c) exceeds 50 K, and this enhanced superconductivity is also shown to originate from an interface layer about 1-2 unit cells thick. Enhancement of T(c) in bilayer systems was observed previously but the essential role of the interface was not recognized at the time. PMID:18843365

  20. High-temperature interface superconductivity between metallic and insulating copper oxides.

    PubMed

    Gozar, A; Logvenov, G; Kourkoutis, L Fitting; Bollinger, A T; Giannuzzi, L A; Muller, D A; Bozovic, I

    2008-10-01

    The realization of high-transition-temperature (high-T(c)) superconductivity confined to nanometre-sized interfaces has been a long-standing goal because of potential applications and the opportunity to study quantum phenomena in reduced dimensions. This has been, however, a challenging target: in conventional metals, the high electron density restricts interface effects (such as carrier depletion or accumulation) to a region much narrower than the coherence length, which is the scale necessary for superconductivity to occur. By contrast, in copper oxides the carrier density is low whereas T(c) is high and the coherence length very short, which provides an opportunity-but at a price: the interface must be atomically perfect. Here we report superconductivity in bilayers consisting of an insulator (La(2)CuO(4)) and a metal (La(1.55)Sr(0.45)CuO(4)), neither of which is superconducting in isolation. In these bilayers, T(c) is either approximately 15 K or approximately 30 K, depending on the layering sequence. This highly robust phenomenon is confined within 2-3 nm of the interface. If such a bilayer is exposed to ozone, T(c) exceeds 50 K, and this enhanced superconductivity is also shown to originate from an interface layer about 1-2 unit cells thick. Enhancement of T(c) in bilayer systems was observed previously but the essential role of the interface was not recognized at the time.

  1. The unusually high Tc in rare-earth-doped single crystalline CaFe2As2

    NASA Astrophysics Data System (ADS)

    Wei, Fengyan; Lv, Bing; Deng, Liangzi; Meen, James K.; Xue, Yu-Yi; Chu, Ching-Wu

    2014-08-01

    In rare-earth-doped single crystalline CaFe2As2, the mysterious small volume fraction which superconducts up to 49 K, much higher than the bulk Tc ~ 30 s K, has prompted a long search for a hidden variable that could enhance the Tc by more than 30% in iron-based superconductors of the same structure. Here we report a chemical, structural and magnetic study of CaFe2As2 systematically doped with La, Ce, Pr and Nd. Coincident with the high Tc phase, we find extreme magnetic anisotropy, accompanied by an unexpected doping-independent Tc and equally unexpected superparamagnetic clusters associated with As vacancies. These observations lead us to conjecture that the tantalizing Tc enhancement may be associated with naturally occurring chemical interfaces and may thus provide a new paradigm in the search for superconductors with higher Tc.

  2. Spectroscopic evidence for a pseudogap in the normal state of underdoped high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Ding, H.; Yokoya, T.; Campuzano, J. C.; Takahashi, T.; Randeria, M.; Norman, M. R.; Mochiku, T.; Kadowaki, K.; Giapintzakis, J.

    1996-07-01

    IT is well known that BCS mean-field theory is remarkably successful in describing conventional superconductors. A central concept of BCS theory is the energy gap in the electronic excitation spectrum below the superconducting transition temperature, Tc. The gap also serves as the order parameter: quite generally, long-range phase coherence and a non-zero gap go hand-in-hand1. But in underdoped high-Tc superconductors there is considerable evidence that a pseudogap (a suppression of spectral weight) is already formed in the normal state above Tc-first, from studies of the spin excitation spectrum2-5,24, which measure a 'spin gap', and later from a variety of other probes6-10. Here we present a study of underdoped Bi2Sr2CaCu2O8+δ (Bi2212) using angle-resolved photoemission spectroscopy (ARPES), which directly measures the momentum-resolved electron excitation spectrum of the CuO2 planes. We find that a pseudogap with d-wave symmetry opens up in the normal state below a temperature T* > Tc, and develops into the d-wave superconducting gap once phase coherence is established below Tc.

  3. Electronic origin of high-temperature superconductivity in single-layer FeSe superconductor.

    PubMed

    Liu, Defa; Zhang, Wenhao; Mou, Daixiang; He, Junfeng; Ou, Yun-Bo; Wang, Qing-Yan; Li, Zhi; Wang, Lili; Zhao, Lin; He, Shaolong; Peng, Yingying; Liu, Xu; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Hu, Jiangping; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

    2012-07-03

    The recent discovery of high-temperature superconductivity in iron-based compounds has attracted much attention. How to further increase the superconducting transition temperature (T(c)) and how to understand the superconductivity mechanism are two prominent issues facing the current study of iron-based superconductors. The latest report of high-T(c) superconductivity in a single-layer FeSe is therefore both surprising and significant. Here we present investigations of the electronic structure and superconducting gap of the single-layer FeSe superconductor. Its Fermi surface is distinct from other iron-based superconductors, consisting only of electron-like pockets near the zone corner without indication of any Fermi surface around the zone centre. Nearly isotropic superconducting gap is observed in this strictly two-dimensional system. The temperature dependence of the superconducting gap gives a transition temperature T(c)~ 55 K. These results have established a clear case that such a simple electronic structure is compatible with high-T(c) superconductivity in iron-based superconductors.

  4. High critical current superconducting tapes

    DOEpatents

    Holesinger, Terry G.; Jia, Quanxi; Foltyn, Stephen R.

    2003-09-23

    Improvements in critical current capacity for superconducting film structures are disclosed and include the use of a superconducting RE-BCO layer including a mixture of rare earth metals, e.g., yttrium and europium, where the ratio of yttrium to europium in the RE-BCO layer ranges from about 3 to 1 to from about 1.5 to 1.

  5. Space applications of superconductivity - High field magnets

    NASA Technical Reports Server (NTRS)

    Fickett, F. R.

    1979-01-01

    The paper discusses developments in superconducting magnets and their applications in space technology. Superconducting magnets are characterized by high fields (to 15T and higher) and high current densities combined with low mass and small size. The superconducting materials and coil design are being improved and new high-strength composites are being used for magnet structural components. Such problems as maintaining low cooling temperatures (near 4 K) for long periods of time and degradation of existing high-field superconductors at low strain levels can be remedied by research and engineering. Some of the proposed space applications of superconducting magnets include: cosmic ray analysis with magnetic spectrometers, energy storage and conversion, energy generation by magnetohydrodynamic and thermonuclear fusion techniques, and propulsion. Several operational superconducting magnet systems are detailed.

  6. High-temperature superconductivity in potassium-coated multilayer FeSe thin films.

    PubMed

    Miyata, Y; Nakayama, K; Sugawara, K; Sato, T; Takahashi, T

    2015-08-01

    The recent discovery of possible high-temperature (T(c)) superconductivity over 65 K in a monolayer FeSe film on SrTiO3 (refs 1-6) triggered a fierce debate on how superconductivity evolves from bulk to film, because bulk FeSe crystal exhibits a T(c) of no higher than 10 K (ref. 7). However, the difficulty in controlling the carrier density and the number of FeSe layers has hindered elucidation of this problem. Here, we demonstrate that deposition of potassium onto FeSe films markedly expands the accessible doping range towards the heavily electron-doped region. Intriguingly, we have succeeded in converting non-superconducting films with various thicknesses into superconductors with T(c) as high as 48 K. We also found a marked increase in the magnitude of the superconducting gap on decreasing the FeSe film thickness, indicating that the interface plays a crucial role in realizing the high-temperature superconductivity. The results presented provide a new strategy to enhance and optimize T(c) in ultrathin films of iron-based superconductors.

  7. High-temperature superconductivity in potassium-coated multilayer FeSe thin films

    NASA Astrophysics Data System (ADS)

    Miyata, Y.; Nakayama, K.; Sugawara, K.; Sato, T.; Takahashi, T.

    2015-08-01

    The recent discovery of possible high-temperature (Tc) superconductivity over 65 K in a monolayer FeSe film on SrTiO3 (refs , , , , , ) triggered a fierce debate on how superconductivity evolves from bulk to film, because bulk FeSe crystal exhibits a Tc of no higher than 10 K (ref. ). However, the difficulty in controlling the carrier density and the number of FeSe layers has hindered elucidation of this problem. Here, we demonstrate that deposition of potassium onto FeSe films markedly expands the accessible doping range towards the heavily electron-doped region. Intriguingly, we have succeeded in converting non-superconducting films with various thicknesses into superconductors with Tc as high as 48 K. We also found a marked increase in the magnitude of the superconducting gap on decreasing the FeSe film thickness, indicating that the interface plays a crucial role in realizing the high-temperature superconductivity. The results presented provide a new strategy to enhance and optimize Tc in ultrathin films of iron-based superconductors.

  8. Highly textured oxypnictide superconducting thin films on metal substrates

    NASA Astrophysics Data System (ADS)

    Iida, Kazumasa; Kurth, Fritz; Chihara, Masashi; Sumiya, Naoki; Grinenko, Vadim; Ichinose, Ataru; Tsukada, Ichiro; Hänisch, Jens; Matias, Vladimir; Hatano, Takafumi; Holzapfel, Bernhard; Ikuta, Hiroshi

    2014-10-01

    Highly textured NdFeAs(O,F) thin films have been grown on ion beam assisted deposition-MgO/Y2O3/Hastelloy substrates by molecular beam epitaxy. The oxypnictide coated conductors showed a superconducting transition temperature (Tc) of 43 K with a self-field critical current density (Jc) of 7.0 × 10 4 A / cm 2 at 5 K, more than 20 times higher than powder-in-tube processed SmFeAs(O,F) wires. Albeit higher Tc as well as better crystalline quality than Co-doped BaFe2As2 coated conductors, in-field Jc of NdFeAs(O,F) was lower than that of Co-doped BaFe2As2. These results suggest that grain boundaries in oxypnictides reduce Jc significantly compared to that in Co-doped BaFe2As2 and, hence biaxial texture is necessary for high Jc.

  9. Electrochemical Na-intercalation-induced high-temperature superconductivity in FeSe

    NASA Astrophysics Data System (ADS)

    Kajita, Tetsuya; Kawamata, Takayuki; Noji, Takashi; Hatakeda, Takehiro; Kato, Masatsune; Koike, Yoji; Itoh, Takashi

    2015-12-01

    Iron-chalcogenide-based superconductors have attracted much attention due to their relatively high superconducting transition temperatures (Tc) and their simple layered crystal structures. We have performed electrochemical co-intercalation of Na and propylene carbonate (PC) into FeSe, and successfully synthesized a new superconductor, Nax(PC)yFe2Se2, with Tc = 43 K. The type and amount of intercalated metal, and the electrolyte used in the intercalation affected the superconductivity. Our electrochemical intercalation method should be a useful tool for discovering new superconductors by controlling the intercalation conditions.

  10. Submillimeter residual losses in high-{Tc} superconductors

    SciTech Connect

    Miller, D.

    1993-09-01

    Bolometry was used obtain accurate submillimeter residual loss data for epitaxial films of YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO), Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub 10}, Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub 8} (TCBCO), and Ba{sub 0.6}K{sub 0.4}BiO{sub 3} (BKBO). We were able to fit the absorptivity measured for Nb films to an Eliashberg strong coupling calculation; excellent agreement resulted between parameters from best fits and measured Residual Resistivity Ratio. Microwave surface resistance measurements made on the same YBCO and TCBCO films are in excellent agreement with submillimeter measurements. Absorptivities for all YBCO films studied are qualitatively similar, increasing smoothly with frequency, with no gap-like features below the well known absorption edge at 450 cm{sup {minus}1}. Losses in YBCO films were fit to a weakly coupled grain model for the a-b plane conductivity. Strong phonon structure was observed in TCBCO films between 60 and 700 cm{sup {minus}1} (2 THz and 23 THz); these losses could not be fitted to the simple weakly coupled grain model, in contrast to the case for other high-{Tc} superconductors where phonon structure observed in ceramics are is absent in epitaxial oriented films and crystals because of electronic screening due to high conductivity of a-b planes. Absorptivity data for the BKBO films all show a strong absorption onset near the BCS tunneling gap of 3.5 k{sub B}{Tc}. Comparison with strong coupling Eliashberg predictions and of a Kramers-Kronig analysis indicate that the absorption onset is consistent with a superconducting energy gap. Effects of magnetic field on residual losses in YBCO films show a resonant absorption feature in vicinity of predicted

  11. Dimensionality of high temperature superconductivity in oxides

    NASA Technical Reports Server (NTRS)

    Chu, C. W.

    1989-01-01

    Many models have been proposed to account for the high temperature superconductivity observed in oxide systems. Almost all of these models proposed are based on the uncoupled low dimensional carrier Cu-O layers of the oxides. Results of several experiments are presented and discussed. They suggest that the high temperature superconductivity observed cannot be strictly two- or one-dimensional, and that the environment between the Cu-O layers and the interlayer coupling play an important role in the occurrence of such high temperature superconductivity. A comment on the very short coherence length reported is also made.

  12. Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system.

    PubMed

    Drozdov, A P; Eremets, M I; Troyan, I A; Ksenofontov, V; Shylin, S I

    2015-09-01

    A superconductor is a material that can conduct electricity without resistance below a superconducting transition temperature, Tc. The highest Tc that has been achieved to date is in the copper oxide system: 133 kelvin at ambient pressure and 164 kelvin at high pressures. As the nature of superconductivity in these materials is still not fully understood (they are not conventional superconductors), the prospects for achieving still higher transition temperatures by this route are not clear. In contrast, the Bardeen-Cooper-Schrieffer theory of conventional superconductivity gives a guide for achieving high Tc with no theoretical upper bound--all that is needed is a favourable combination of high-frequency phonons, strong electron-phonon coupling, and a high density of states. These conditions can in principle be fulfilled for metallic hydrogen and covalent compounds dominated by hydrogen, as hydrogen atoms provide the necessary high-frequency phonon modes as well as the strong electron-phonon coupling. Numerous calculations support this idea and have predicted transition temperatures in the range 50-235 kelvin for many hydrides, but only a moderate Tc of 17 kelvin has been observed experimentally. Here we investigate sulfur hydride, where a Tc of 80 kelvin has been predicted. We find that this system transforms to a metal at a pressure of approximately 90 gigapascals. On cooling, we see signatures of superconductivity: a sharp drop of the resistivity to zero and a decrease of the transition temperature with magnetic field, with magnetic susceptibility measurements confirming a Tc of 203 kelvin. Moreover, a pronounced isotope shift of Tc in sulfur deuteride is suggestive of an electron-phonon mechanism of superconductivity that is consistent with the Bardeen-Cooper-Schrieffer scenario. We argue that the phase responsible for high-Tc superconductivity in this system is likely to be H3S, formed from H2S by decomposition under pressure. These findings raise hope for the

  13. Introduction to high-temperature superconductivity

    SciTech Connect

    Sheahen, T.P.

    1994-12-31

    The Electric Power Research Institute, as part of its program to develop high-temperature superconductivity applications for the power industry, has endevoured to educate utility engineers and executives on superconductivity. This book is a series of tutorials prepared by the Argonne National Laboratory. Part one is at an introductory level, asking and answering the question `What is superconductivity?` Part 2 is an exposition of the basic properties of the new materials - structure, phase equilibria, effects of doping, etc. with consideration of theoretical issues. Part 3 covers potential practical uses of high temperature superconductors.

  14. High-temperature superconductivity: A conventional conundrum

    DOE PAGES

    Božović, Ivan

    2016-01-07

    High-temperature superconductivity in ultrathin films of iron selenide deposited on strontium titanate has been attributed to various exotic mechanisms, and new experiments indicate that it may be conventional, with broader implications.

  15. Design of high-T[sub c] superconducting bolometers for a far infrared imaging array

    SciTech Connect

    Verghese, S.; Richards, P.L. ); Fork, D.K. ); Char, K. ); Geballe, T.H. . Dept. of Applied Physics)

    1992-08-01

    The design of high-[Tc] superconducting bolometers for use in a far infrared imaging array from wavelengths 30--100[mu]m is discussed. Measurements of the voltage noise in thin films of YBa[sub 2]CU[sub 3]O[sub 7-[var sigma

  16. Characteristic two-dimensional Fermi surface topology of high-Tc iron-based superconductors

    PubMed Central

    Sunagawa, Masanori; Ishiga, Toshihiko; Tsubota, Koji; Jabuchi, Taihei; Sonoyama, Junki; Iba, Keita; Kudo, Kazutaka; Nohara, Minoru; Ono, Kanta; Kumigashira, Hiroshi; Matsushita, Tomohiro; Arita, Masashi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki; Wakita, Takanori; Muraoka, Yuji; Yokoya, Takayoshi

    2014-01-01

    Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors. Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-Tc). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-Tc materials remains unclear. Here we demonstrate a phase of electron-doped CaFe2As2 (La and P co-doped CaFe2As2) with Tc = 45 K, which is the highest Tc found for the AEFe2As2 bulk superconductors (122-type; AE = Alkaline Earth), possesses only cylindrical hole- and electron-like FSs. This result indicates that FS topology consisting only of two-dimensional sheets is characteristic of both hole- and electron-doped 122-type high-Tc superconductors. PMID:24625746

  17. High Tc thin film and device development

    SciTech Connect

    Betts, K.; Burbank, M.B.; Cragg, A.; Fife, A.A.; Kubik, P.R.; Lee, S.; Chaklader, A.C.D.; Roemer, G.; Heinrich, B.; Chrzanowski, J.

    1989-03-01

    Thin films of the high Tc superconductor YBa/sub 2/Cu/sub 3/O/sub y/ have been deposited on various substrates by diode and magnetron sputtering using bulk sintered targets. These films have been analyzed by a variety of methods - SEM, X-rays, Electron Beam Microprobe, Mass Spectrometry and Raman Spectroscopy. The stoichiometries of the films have been measured as a function of the radial position from the centre of the sputtered beam at a fixed target-substrate distance. Patterning of the films has been carried out to form planar structures such as strip lines, microbridges and RF SQUIDs. DC current-voltage characteristics of the microbridges were measured as a function of temperature. RF SQUID behaviour has been observed for single loop devices and their properties established at 4.2 K and higher temperatures. Flux locked noise spectra with a 1/f noise power response were recorded in the frequency range 0.01 to approx.100 Hz. RF SQUID signals have been observed for temperatures up to 55 K.

  18. Normal-state nodal electronic structure in underdoped high-Tc copper oxides.

    PubMed

    Sebastian, Suchitra E; Harrison, N; Balakirev, F F; Altarawneh, M M; Goddard, P A; Liang, Ruixing; Bonn, D A; Hardy, W N; Lonzarich, G G

    2014-07-01

    An outstanding problem in the field of high-transition-temperature (high-Tc) superconductivity is the identification of the normal state out of which superconductivity emerges in the mysterious underdoped regime. The normal state uncomplicated by thermal fluctuations can be studied using applied magnetic fields that are sufficiently strong to suppress long-range superconductivity at low temperatures. Proposals in which the normal ground state is characterized by small Fermi surface pockets that exist in the absence of symmetry breaking have been superseded by models based on the existence of a superlattice that breaks the translational symmetry of the underlying lattice. Recently, a charge superlattice model that positions a small electron-like Fermi pocket in the vicinity of the nodes (where the superconducting gap is minimum) has been proposed as a replacement for the prevalent superlattice models that position the Fermi pocket in the vicinity of the pseudogap at the antinodes (where the superconducting gap is maximum). Although some ingredients of symmetry breaking have been recently revealed by crystallographic studies, their relevance to the electronic structure remains unresolved. Here we report angle-resolved quantum oscillation measurements in the underdoped copper oxide YBa2Cu3O6 + x. These measurements reveal a normal ground state comprising electron-like Fermi surface pockets located in the vicinity of the nodes, and also point to an underlying superlattice structure of low frequency and long wavelength with features in common with the charge order identified recently by complementary spectroscopic techniques. PMID:24930767

  19. A high temperature superconductivity communications flight experiment

    NASA Technical Reports Server (NTRS)

    Ngo, P.; Krishen, K.; Arndt, D.; Raffoul, G.; Karasack, V.; Bhasin, K.; Leonard, R.

    1992-01-01

    The proposed high temperature superconductivity (HTSC) millimeter-wave communications flight experiment from the payload bay of the Space Shuttle Orbiter to the Advanced Communications Technology Satellite (ACTS) in geosynchronous orbit is described. The experiment will use a Ka-band HTSC phased array antenna and front-end electronics to receive a downlink communications signal from the ACTS. The discussion covers the system configuration, a description of the ground equipment, the spacecraft receiver, link performance, thermal loading, and the superconducting antenna array.

  20. What Makes the Tc of FeSe/SrTiO3 so High?

    NASA Astrophysics Data System (ADS)

    Lee, Dung-Hai

    Raising the superconducting transition temperature to a point where applications are practical is one of the most important challenges in science. In the history of high Tcsuperconductivity there are two landmark events: the discovery of copper-oxide superconductor in 1986, and the discovery of iron-based superconductor in 2006 For the Fe-based superconductors the record of Tc was 55 K until 2012. In the interface system composed of an one unit cell thick FeSe film grown on the TiO2 terminated (001) surface of SrTiO3 an anomalously large superconducting-like energy gap was seen by scan tunneling microscopy for. Later ARPES works show the gap opening temperature can reach nearly the liquid nitrogen boiling temperature. More recently several FeSe-related bulk and thin film high Tc systems have be discovered. This talk reviews some of the recent experimental and theoretical progresses in the study of the mechanism for high temperature superconductivity in this interface system. It offers the author's personal view of why Tcis so high and how to further increase it. DHL was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Grant DE-AC02-05CH11231.

  1. Inhomogeneity of charge-density-wave order and quenched disorder in a high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Campi, G.; Bianconi, A.; Poccia, N.; Bianconi, G.; Barba, L.; Arrighetti, G.; Innocenti, D.; Karpinski, J.; Zhigadlo, N. D.; Kazakov, S. M.; Burghammer, M.; Zimmermann, M. V.; Sprung, M.; Ricci, A.

    2015-09-01

    It has recently been established that the high-transition-temperature (high-Tc) superconducting state coexists with short-range charge-density-wave order and quenched disorder arising from dopants and strain. This complex, multiscale phase separation invites the development of theories of high-temperature superconductivity that include complexity. The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mesoscale (between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both short-range charge-density-wave `puddles' (domains with only a few wavelengths) and quenched disorder in HgBa2CuO4 + y, the single-layer cuprate with the highest Tc, 95 kelvin (refs 26, 27, 28). We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of self-organization near a critical point. However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usually assumed random, uncorrelated distribution. The interstitial-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, because higher doping does not favour the stripy charge-density-wave puddles, leading to a complex emergent geometry of the spatial landscape for superconductivity.

  2. Inhomogeneity of charge-density-wave order and quenched disorder in a high-Tc superconductor.

    PubMed

    Campi, G; Bianconi, A; Poccia, N; Bianconi, G; Barba, L; Arrighetti, G; Innocenti, D; Karpinski, J; Zhigadlo, N D; Kazakov, S M; Burghammer, M; Zimmermann, M v; Sprung, M; Ricci, A

    2015-09-17

    It has recently been established that the high-transition-temperature (high-Tc) superconducting state coexists with short-range charge-density-wave order and quenched disorder arising from dopants and strain. This complex, multiscale phase separation invites the development of theories of high-temperature superconductivity that include complexity. The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mesoscale (between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both short-range charge-density-wave 'puddles' (domains with only a few wavelengths) and quenched disorder in HgBa2CuO4 + y, the single-layer cuprate with the highest Tc, 95 kelvin (refs 26-28). We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of self-organization near a critical point. However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usually assumed random, uncorrelated distribution. The interstitial-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, because higher doping does not favour the stripy charge-density-wave puddles, leading to a complex emergent geometry of the spatial landscape for superconductivity. PMID:26381983

  3. Superconducting order parameter fluctuations above Tc in polycrystalline Ho 1Ba 2Cu 3O 7-δ compounds

    NASA Astrophysics Data System (ADS)

    Vidal, Félix; Veira, J. A.; Maza, J.; Ponte, J. J.; Amador, J.; Cascales, C.; Casais, M. T.; Rasines, I.

    1988-08-01

    We report measurements of the excess electrical conductivity, Δσ, above Tc in polycrystalline HoBa 2Cu 3O 7-δ single-phase 0 (within 4%) compounds. The relative temperature resolution is of the order of 10 -2 K which, in spite of the broadening of the transition by nonintrinsic effects, should probably make accessible the whole mean-field regime for Δσ and also to penetrate inside the full critical dynamic region. The general behavior of Δσ(ɛ) in these Ho-based samples is very similar to that previously observed in our laboratory for Y-based high-temperature superconductors. In particular, when analyzed in terms of the Aslamazov-Larkin theory and by using some dynamic scaling ideas, the Δσ(ɛ) data are compatible with a superconducting order parameter of two components fluctuating in three dimensions. No influence of the magnetic Ho ions on Δσ is observed in the whole reduced-temperature range studied.

  4. Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe

    NASA Astrophysics Data System (ADS)

    Sun, J. P.; Matsuura, K.; Ye, G. Z.; Mizukami, Y.; Shimozawa, M.; Matsubayashi, K.; Yamashita, M.; Watashige, T.; Kasahara, S.; Matsuda, Y.; Yan, J.-Q.; Sales, B. C.; Uwatoko, Y.; Cheng, J.-G.; Shibauchi, T.

    2016-07-01

    The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of Tc has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ~15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ~6 GPa the sudden enhancement of superconductivity (Tc<=38.3 K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-Tc phase above 6 GPa. The obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-Tc cuprates.

  5. Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe

    DOE PAGES

    Sun, J. P.; Matsuura, K.; Ye, G. Z.; Mizukami, Y.; Shimozawa, M.; Matsubayashi, K.; Yamashita, M.; Watashige, T.; Kasahara, S.; Matsuda, Y.; et al

    2016-07-19

    The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of Tc has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ~15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ~6 GPa the sudden enhancement of superconductivity (Tc ≤ 38.3 K) accompanies a suppression of magnetic order,more » demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-Tc phase above 6 GPa. In conclusion, the obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-Tc cuprates.« less

  6. The high temperature superconductivity space experiment

    NASA Technical Reports Server (NTRS)

    Webb, Denis C.; Nisenoff, M.

    1991-01-01

    The history and the current status of the high temperature superconductivity space experiment (HTSSE) initiated in 1988 are briefly reviewed. The goal of the HTSSE program is to demonstrate the feasibility of incorporating high temperature superconductivity (HTS) technology into space systems. The anticipated payoffs include the development of high temperature superconductor devices for space systems; preparation and space qualification of a cryogenically cooled experimental package containing HTS devices and components; and acquisition of data for future space experiments using more complex HTS devices and subsystems. The principal HTSSE systems and devices are described.

  7. Kinetic inductance effects in high-Tc microstrip circuits at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Byrne, D. P.; Kwor, R.; Kalkur, T. S.

    1990-10-01

    This paper describes the fabrication of high-Tc superconducting thin films of BiCaSrCuO and the patterning of these films into integrated microstrip transmission line resonators designed to exhibit the effects of kinetic inductance. Emphasis is given to techniques to fabricate very thin, low-loss dielectric layers on BiCaSrCuO. Microwave S-parameter measurements on these resonators are reported along with functional dependence of tranmission line phase velocity and the characteristic impedance with temperature and microwave power density, especially at temperatures just below Tc. The results are used to infer high-frequency penetration depths and surface resistivities in BiCaSrCuO.

  8. On detection of the Fermi edge in in situ grown thin films of high- Tc oxides

    NASA Astrophysics Data System (ADS)

    Abrecht, M.; Ariosa, D.; Saleh, S. A.; Rast, S.; Margaritondo, G.; Onellion, M.; Pavuna, D.

    2001-11-01

    We discuss our systematic series of experiments on the photoelectric detection of the Fermi edge using a cylindrical mirror analyser on films of high- Tc oxides, grown in situ by pulsed laser ablation. The Fermi edge (comparable to the edge of the reference Ag) is very easily observed even in the two-phase BSCCO-2212 film that exhibits onsets of superconducting transitions, at 85 and 45 K. In contrast, the Fermi edge is weaker and more difficult to observe even in the state-of-the-art, highly epitaxial, monophase YBa 2Cu 3O 7- y (YBCO) and NdBa 2Cu 3O 7- y (NBCO-123) films (both with Tc=92 K). So far we could not detect the Fermi edge in the films of the double-`chain' YBCO-124.

  9. Use of high-temperature superconducting films in superconducting bearings.

    SciTech Connect

    Cansiz, A.

    1999-07-14

    We have investigated the effect of high-temperature superconductor (HTS) films deposited on substrates that are placed above bulk HTSs in an attempt to reduce rotational drag in superconducting bearings composed of a permanent magnet levitated above the film/bulk HTS combination. According to the critical state model, hysteresis energy loss is inversely proportional to critical current density, J{sub c}, and because HTS films typically have much higher J{sub c} than that of bulk HTS, the film/bulk combination was expected to reduce rotational losses by at least one order of magnitude in the coefficient of fiction, which in turn is a measure of the hysteresis losses. We measured rotational losses of a superconducting bearing in a vacuum chamber and compared the losses with and without a film present. The experimental results showed that contrary to expectation, the rotational losses are increased by the film. These results are discussed in terms of flux drag through the film, as well as of the critical state model.

  10. High temperature superconducting fault current limiter

    DOEpatents

    Hull, John R.

    1997-01-01

    A fault current limiter (10) for an electrical circuit (14). The fault current limiter (10) includes a high temperature superconductor (12) in the electrical circuit (14). The high temperature superconductor (12) is cooled below its critical temperature to maintain the superconducting electrical properties during operation as the fault current limiter (10).

  11. High temperature superconducting fault current limiter

    DOEpatents

    Hull, J.R.

    1997-02-04

    A fault current limiter for an electrical circuit is disclosed. The fault current limiter includes a high temperature superconductor in the electrical circuit. The high temperature superconductor is cooled below its critical temperature to maintain the superconducting electrical properties during operation as the fault current limiter. 15 figs.

  12. Superconductivity of high-pressure phases of S and Se to 230 GPa

    NASA Astrophysics Data System (ADS)

    Struzhkin, Viktor; Gregoryanz, Eugene; Timofeev, Yuri; Eremets, Mikhail; Mao, Ho-Kwang; Hemley, Russell

    2000-03-01

    We have investigated in detail the superconducting state of sulfur in its β-Po phase from 160 to 230 GPa. The superconducting Tc is close to 17 K from 160 to 200 GPa, and drops to 15 K at 230 GPa. Similar behavior was predicted recently [1] from ab initio LDA calculations. The high value of Tc in the β-Po phase is consistent with electon-phonon coupling mechanism with reasonably strong electron-phonon coupling (λ=0.76), and with the standard value of the Morel-Anderson pseudopotential μ^*=0.11 [1]. Our measurements in Se at high pressures indicate superconductivity from 17 to 23 GPa, which apparently has not been previously reported. We relate this behavior to the occurence of new metastable phase in Se which can be observed on decompression from 30 GPa at low temperatures. The results for Tc in Se at higher pressures will be also presented. We will also discuss the similiarities in high-pressure induced superconductivity of chalcogen family members: S, Se, and Te. ^1 Sven P. Rudin and Amy Y. Liu, Phys. Rev. Lett. 83, 3049 (1999).

  13. Techniques for Connecting Superconducting Thin Films

    NASA Technical Reports Server (NTRS)

    Mester, John; Gwo, Dz-Hung

    2006-01-01

    Several improved techniques for connecting superconducting thin films on substrates have been developed. The techniques afford some versatility for tailoring the electronic and mechanical characteristics of junctions between superconductors in experimental electronic devices. The techniques are particularly useful for making superconducting or alternatively normally conductive junctions (e.g., Josephson junctions) between patterned superconducting thin films in order to exploit electron quantum-tunneling effects. The techniques are applicable to both low-Tc and high-Tc superconductors (where Tc represents the superconducting- transition temperature of a given material), offering different advantages for each. Most low-Tc superconductors are metallic, and heretofore, connections among them have been made by spot welding. Most high-Tc superconductors are nonmetallic and cannot be spot welded. These techniques offer alternatives to spot welding of most low-Tc superconductors and additional solutions to problems of connecting most high-Tc superconductors.

  14. From quantum oscillations to charge order in high-Tc copper oxides in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Vignolle, Baptiste; Vignolles, David; Julien, Marc-Henri; Proust, Cyril

    2013-01-01

    This article constitutes an update made of numerous elements from an article by Vignolle et al. [C. R. Phys. 12 (2011) 446] published in the issue of C. R. Physique dedicated to superconductivity. By including this article to the present issue on physics in high magnetic field, we have aimed, in agreement with the editorial board of the review, offering a complete issue and also reporting on the last developments in the study of superconductors in high field. We review how experiments in very high magnetic fields over the last five years have given a new twist to the understanding of the normal state of hole-doped cuprate superconductors. The discovery of quantum oscillations in underdoped YBa2Cu3Oy and overdoped Tl2Ba2CuO6 + δ has proven the existence of a Fermi surface across the whole phase diagram, which had been a controversial issue for more than twenty years. However, the striking difference in oscillation frequency for the two compounds has revealed a very different Fermi surface topology. The observation of negative Hall and Seebeck coefficients in the underdoped materials has shown that the large hole-like Fermi surface of overdoped materials undergoes a reconstruction in the high field and low temperature limits for which quantum oscillation can be observed. This has been interpreted as evidence for a translational symmetry breaking due to some form of electronic (spin, charge, or orbital current) order. The angular dependence of the quantum oscillations has constrained the source of the Fermi-surface reconstruction to something other than a spin-density wave with moments perpendicular to the field. Finally, nuclear magnetic resonance studies have revealed that it is actually charge order, without spin order, which is induced in the copper oxide planes as soon as superconductivity is sufficiently weakened by the magnetic field. The results suggest that there is a generic competition between superconductivity and a charge-density-wave instability in high

  15. Quasiparticle mass enhancement approaching optimal doping in a high-Tc superconductor

    DOE PAGES

    Ramshaw, B. J.; Sebastian, S. E.; McDonald, R. D.; Day, J.; Tan, B. S.; Zhu, Z.; Betts, J. B.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; et al

    2015-03-26

    In the quest for superconductors with higher transition temperatures (Tc), one emerging motif is that electronic interactions favorable for superconductivity can be enhanced by fluctuations of a broken-symmetry phase. In recent experiments it is suggested that the existence of the requisite broken-symmetry phase in the high-Tc cuprates, but the impact of such a phase on the ground-state electronic interactions has remained unclear. Here, we used magnetic fields exceeding 90 tesla to access the underlying metallic state of the cuprate YBa2Cu3O6+δ over a wide range of doping, and observed magnetic quantum oscillations that reveal a strong enhancement of the quasiparticle effectivemore » mass toward optimal doping. Finally, this mass enhancement results from increasing electronic interactions approaching optimal doping, and suggests a quantum critical point at a hole doping of pcrit ≈ 0.18.« less

  16. Plaquette valence bond theory of high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Harland, Malte; Katsnelson, Mikhail I.; Lichtenstein, Alexander I.

    2016-09-01

    We present a strong-coupling approach to the theory of high-temperature superconductivity based on the observation of a quantum critical point in the plaquette within the t ,t' Hubbard model. The crossing of ground-state energies in the N =2 -4 sectors occurs for parameters close to the optimal doping. The theory predicts the maximum of the dx2-y2-wave order parameter at the border between localized and itinerant electron behaviors and gives a natural explanation for the pseudogap formation via the soft-fermion mode related to local singlet states of the plaquette in the environment. Our approach follows the general line of resonating valence-bond theory stressing a crucial role of singlets in the physics of high-Tc superconductors but focuses on the formation of local singlets, similar to phenomena observed in frustrated one-dimensional quantum spin models.

  17. High- Tc superconductor characteristics control by ion implantation

    NASA Astrophysics Data System (ADS)

    Matsui, S.; Matsutera, H.; Yoshitake, T.; Fujita, J.; Satoh, T.

    1989-03-01

    Transition temperature ( Tc) control and annealing effects of YBa 2Cu 3O x and Bi 2Sr 1.4 Ca 1.8Cu 2.2O y superconductor thin films implanted by 200 keV Ne + have been investigated. YBa 2Cu 3 O xTc end points for 0, 1 × 10 14, 1 × 10 15 and 1 × 10 16 ions/cm 2 doses are 75, 71, 62 and 16 K, respectively. On the other hand, Bi 2Sr 1.4Ca 1.8Cu 2.2O y, Tc end points for 0, 1 × 10 12 and 1 × 10 13 ions/cm 2 doses are 78, 76 and 54 K, respectively, c lattice constant increases were observed for the implanted films. It is confirmed that the superconducting characteristics for films, are recovered by anneaing in O 2 atomosphere. Moreover, microcrystal growth caused by annealing the implanted YBa 2Cu 3O x film was observed on the surface.

  18. High pressure effects on the superconductivity in rare-earth-doped CaFe2As2

    NASA Astrophysics Data System (ADS)

    Uhoya, Walter; Cargill, Daniel; Gofryk, Krzysztof; Tsoi, Georgiy M.; Vohra, Yogesh K.; Sefat, Athena S.; Weir, S. T.

    2014-01-01

    High pressure superconductivity in a rare-earth-doped Ca0.86Pr0.14Fe2As2 single-crystalline sample has been studied up to 12 GPa and temperatures down to 11 K using the designer diamond anvil cell under a quasi-hydrostatic pressure medium. The electrical resistance measurements were complemented by high pressure and low-temperature X-ray diffraction studies at a synchrotron source. The electrical resistance measurements show an intriguing observation of superconductivity under pressure, with Tc as high as ∼51 K at 1.9 GPa, presenting the highest Tc reported in the intermetallic class of 122 iron-based superconductors. The resistive transition observed suggests a possible existence of two superconducting phases at low pressures of 0.5 GPa: one phase starting at Tc1 ∼ 48 K and the other starts at Tc2 ∼ 16 K. The two superconducting transitions show distinct variations with increasing pressure. High pressure and low-temperature structural studies indicate that the superconducting phase is a collapsed tetragonal ThCr2Si2-type (122) crystal structure.

  19. Proximity Effect at Graphene - High Tc Superconductor Junctions

    NASA Astrophysics Data System (ADS)

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

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

  20. Space applications of high temperature superconductivity technology

    NASA Technical Reports Server (NTRS)

    Connolly, D. J.; Aron, P. R.; Leonard, R. F.; Wintucky, E. G.

    1991-01-01

    A review is presented of the present status of high temperature superconductivity (HTS) technology and related areas of potential space application. Attention is given to areas of application that include microwave communications, cryogenic systems, remote sensing, and space propulsion and power. Consideration is given to HTS phase shifters, miniaturization of microwave filters, far-IR bolometers, and magnetic refrigeration using flux compression.

  1. A universal order underlying the pseudogap regime of the underdoped high Tc cuprates

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    2014-03-01

    A major achievement in condensed matter physics in the last quarter century has been a step towards the understanding of the unconventional d-wave superconducting state in the copper-oxide materials. Surprisingly, the normal state out of which the superconducting state emerges remains a mystery at low charge carrier densities, i.e., in the underdoped regime. This regime is of particular interest because it is characterised by an unusual momentum dependent energy pseudogap in the excitation spectrum that has defied explanation and is key to a full understanding of the unconventional d-wave superconducting state. I will present new quantum oscillation experimental results within the pseudogap regime of the high Tc superconductors YBa2Cu3O6+x and YBa2Cu4O8 which now extend up to the optimally-doped regime. These data reveal the evolution of the Fermi surface approaching the putative quantum critical point under the superconducting dome. A comprehensive angle-resolved study of the Fermi surface enables us to unambiguously identify a specific form of order that accounts for the observed quantum oscillations as well as other spectroscopic, transport and thermodynamic probes within the pseudogap regime. The author would like to thank B. Ramshaw, S. Sebastian, F. Balakirev, C. Mielke, M. Altarawneh, P. Goddard, S. Sabok, B. Babrowski, D. Bonn, W. Hardy, R. Liang and G. Lonzarich. This work was supported by the DOE BES ``Science of 100 tesla'' project and by the NSF and Florida State.

  2. Superconducting magnets

    SciTech Connect

    Not Available

    1994-08-01

    This report discusses the following topics on superconducting magnets: D19B and -C: The next steps for a record-setting magnet; D20: The push beyond 10 T: Beyond D20: Speculations on the 16-T regime; other advanced magnets for accelerators; spinoff applications; APC materials development; cable and cabling-machine development; and high-{Tc} superconductor at low temperature.

  3. Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe.

    PubMed

    Sun, J P; Matsuura, K; Ye, G Z; Mizukami, Y; Shimozawa, M; Matsubayashi, K; Yamashita, M; Watashige, T; Kasahara, S; Matsuda, Y; Yan, J-Q; Sales, B C; Uwatoko, Y; Cheng, J-G; Shibauchi, T

    2016-01-01

    The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of Tc has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ∼15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ∼6 GPa the sudden enhancement of superconductivity (Tc≤38.3 K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-Tc phase above 6 GPa. The obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-Tc cuprates. PMID:27431724

  4. Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe.

    PubMed

    Sun, J P; Matsuura, K; Ye, G Z; Mizukami, Y; Shimozawa, M; Matsubayashi, K; Yamashita, M; Watashige, T; Kasahara, S; Matsuda, Y; Yan, J-Q; Sales, B C; Uwatoko, Y; Cheng, J-G; Shibauchi, T

    2016-07-19

    The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of Tc has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ∼15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ∼6 GPa the sudden enhancement of superconductivity (Tc≤38.3 K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-Tc phase above 6 GPa. The obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-Tc cuprates.

  5. Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe

    PubMed Central

    Sun, J. P.; Matsuura, K.; Ye, G. Z.; Mizukami, Y.; Shimozawa, M.; Matsubayashi, K.; Yamashita, M.; Watashige, T.; Kasahara, S.; Matsuda, Y.; Yan, J. -Q.; Sales, B. C.; Uwatoko, Y.; Cheng, J. -G.; Shibauchi, T.

    2016-01-01

    The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of Tc has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ∼15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ∼6 GPa the sudden enhancement of superconductivity (Tc≤38.3 K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-Tc phase above 6 GPa. The obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-Tc cuprates. PMID:27431724

  6. Magnetic and thermal properties of high Tc superconductors

    SciTech Connect

    Lee, Wonchoon.

    1990-09-21

    Measurements of the normal state magnetic susceptibility {chi}(T) of YBa{sub 2}Cu{sub 3}O{sub 7}, Bi{sub 1.8}Pb{sub 0.2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}, and Bi{sub 2{minus}x}Pb{sub x}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+{delta}} (x = 0.2 and 0.25) were carried out. All {chi}(T) data show negative curvature below {approximately}2{Tc}. The data for YBa{sub 2}Cu{sub 3}O{sub 7} are in excellent agreement with a new calculation of the superconducting fluctuation diamagnetism. From the analysis, we infer s-wave pairing and microscopic parameters are obtained. For {chi}(T) of YBa{sub 2}Cu{sub 3}O{sub 7}, part of the negative curvature is inferred to arise from the normal state background. We find a strong temperature dependent anisotropy {delta}{chi} {equivalent to} {chi}{sub c} {minus} {chi}{sub ab} and estimate the normal state spin contributions to {chi}(T). The heat capacity C(T) of YBa{sub 2}Cu{sub 3}O{sub 7} is reported for 0.4 K < T < 400 K in zero and 70 kG magnetic fields. In addition to the feature associated with the onset of the superconductivity at {Tc}, two anomalies in C(T) were observed near 74 K and 330 K, with another possible anomaly near 102 K; the temperatures at which they occur correlate with anomalies in {chi}(T) and ultransonic measurements. The occurrence of the anomaly at {approx equal} 330 K is found to be sample-dependent. The influences of a magnetic field and the thermal and/or magnetic field treatment history dependence of a pellet sample on C(T), the entropy and the influence of superconducting fluctuations on C(T) near {Tc}, and the possible source of the observed intrinsic nonzero {gamma}(0) at low T are discussed.

  7. Stable superconducting magnet. [high current levels below critical temperature

    NASA Technical Reports Server (NTRS)

    Boom, R. W. (Inventor)

    1967-01-01

    Operation of a superconducting magnet is considered. A method is described for; (1) obtaining a relatively high current in a superconducting magnet positioned in a bath of a gas refrigerant; (2) operating a superconducting magnet at a relatively high current level without training; and (3) operating a superconducting magnet containing a plurality of turns of a niobium zirconium wire at a relatively high current level without training.

  8. Laser surface interaction of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    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.

  9. High-Temperature Superconductivity in Single-Unit-Cell FeSe Films on Anatase TiO2(001 )

    NASA Astrophysics Data System (ADS)

    Ding, Hao; Lv, Yan-Feng; Zhao, Kun; Wang, Wen-Lin; Wang, Lili; Song, Can-Li; Chen, Xi; Ma, Xu-Cun; Xue, Qi-Kun

    2016-08-01

    We report on the observation of high-temperature (Tc) superconductivity and magnetic vortices in single-unit-cell FeSe films on anatase TiO2(001 ) substrate by using scanning tunneling microscopy. A systematic study and engineering of interfacial properties has clarified the essential roles of substrate in realizing the high-Tc superconductivity, probably via interface-induced electron-phonon coupling enhancement and charge transfer. By visualizing and tuning the oxygen vacancies at the interface, we find their very limited effect on the superconductivity, which excludes interfacial oxygen vacancies as the primary source for charge transfer between the substrate and FeSe films. Our findings have placed severe constraints on any microscopic model for the high-Tc superconductivity in FeSe-related heterostructures.

  10. Doping dependence of spin excitations and its correlations with high-temperature superconductivity in iron pnictides.

    PubMed

    Wang, Meng; Zhang, Chenglin; Lu, Xingye; Tan, Guotai; Luo, Huiqian; Song, Yu; Wang, Miaoyin; Zhang, Xiaotian; Goremychkin, E A; Perring, T G; Maier, T A; Yin, Zhiping; Haule, Kristjan; Kotliar, Gabriel; Dai, Pengcheng

    2013-01-01

    High-temperature superconductivity in iron pnictides occurs when electrons and holes are doped into their antiferromagnetic parent compounds. Since spin excitations may be responsible for electron pairing and superconductivity, it is important to determine their electron/hole-doping evolution and connection with superconductivity. Here we use inelastic neutron scattering to show that while electron doping to the antiferromagnetic BaFe₂As₂ parent compound modifies the low-energy spin excitations and their correlation with superconductivity (<50 meV) without affecting the high-energy spin excitations (>100 meV), hole-doping suppresses the high-energy spin excitations and shifts the magnetic spectral weight to low-energies. In addition, our absolute spin susceptibility measurements for the optimally hole-doped iron pnictide reveal that the change in magnetic exchange energy below and above T(c) can account for the superconducting condensation energy. These results suggest that high-T(c) superconductivity in iron pnictides is associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons.

  11. Phase Diagram and High-Temperature Superconductivity of Compressed Selenium Hydrides

    NASA Astrophysics Data System (ADS)

    Zhang, Shoutao; Wang, Yanchao; Zhang, Jurong; Liu, Hanyu; Zhong, Xin; Song, Hai-Feng; Yang, Guochun; Zhang, Lijun; Ma, Yanming

    2015-10-01

    Recent discovery of high-temperature superconductivity (Tc = 190 K) in sulfur hydrides at megabar pressures breaks the traditional belief on the Tc limit of 40 K for conventional superconductors, and opens up the doors in searching new high-temperature superconductors in compounds made up of light elements. Selenium is a sister and isoelectronic element of sulfur, with a larger atomic core and a weaker electronegativity. Whether selenium hydrides share similar high-temperature superconductivity remains elusive, but it is a subject of considerable interest. First-principles swarm structure predictions are performed in an effort to seek for energetically stable and metallic selenium hydrides at high pressures. We find the phase diagram of selenium hydrides is rather different from its sulfur analogy, which is indicated by the emergence of new phases and the change of relative stabilities. Three stable and metallic species with stoichiometries of HSe2, HSe and H3Se are identified above ~120 GPa and they all exhibit superconductive behaviors, of which the hydrogen-rich HSe and H3Se phases show high Tc in the range of 40-110 K. Our simulations established the high-temperature superconductive nature of selenium hydrides and provided useful route for experimental verification.

  12. Phase Diagram and High-Temperature Superconductivity of Compressed Selenium Hydrides

    PubMed Central

    Zhang, Shoutao; Wang, Yanchao; Zhang, Jurong; Liu, Hanyu; Zhong, Xin; Song, Hai-Feng; Yang, Guochun; Zhang, Lijun; Ma, Yanming

    2015-01-01

    Recent discovery of high-temperature superconductivity (Tc = 190 K) in sulfur hydrides at megabar pressures breaks the traditional belief on the Tc limit of 40 K for conventional superconductors, and opens up the doors in searching new high-temperature superconductors in compounds made up of light elements. Selenium is a sister and isoelectronic element of sulfur, with a larger atomic core and a weaker electronegativity. Whether selenium hydrides share similar high-temperature superconductivity remains elusive, but it is a subject of considerable interest. First-principles swarm structure predictions are performed in an effort to seek for energetically stable and metallic selenium hydrides at high pressures. We find the phase diagram of selenium hydrides is rather different from its sulfur analogy, which is indicated by the emergence of new phases and the change of relative stabilities. Three stable and metallic species with stoichiometries of HSe2, HSe and H3Se are identified above ~120 GPa and they all exhibit superconductive behaviors, of which the hydrogen-rich HSe and H3Se phases show high Tc in the range of 40–110 K. Our simulations established the high-temperature superconductive nature of selenium hydrides and provided useful route for experimental verification. PMID:26490223

  13. Phase Diagram and High-Temperature Superconductivity of Compressed Selenium Hydrides.

    PubMed

    Zhang, Shoutao; Wang, Yanchao; Zhang, Jurong; Liu, Hanyu; Zhong, Xin; Song, Hai-Feng; Yang, Guochun; Zhang, Lijun; Ma, Yanming

    2015-01-01

    Recent discovery of high-temperature superconductivity (Tc = 190 K) in sulfur hydrides at megabar pressures breaks the traditional belief on the Tc limit of 40 K for conventional superconductors, and opens up the doors in searching new high-temperature superconductors in compounds made up of light elements. Selenium is a sister and isoelectronic element of sulfur, with a larger atomic core and a weaker electronegativity. Whether selenium hydrides share similar high-temperature superconductivity remains elusive, but it is a subject of considerable interest. First-principles swarm structure predictions are performed in an effort to seek for energetically stable and metallic selenium hydrides at high pressures. We find the phase diagram of selenium hydrides is rather different from its sulfur analogy, which is indicated by the emergence of new phases and the change of relative stabilities. Three stable and metallic species with stoichiometries of HSe2, HSe and H3Se are identified above ~120 GPa and they all exhibit superconductive behaviors, of which the hydrogen-rich HSe and H3Se phases show high Tc in the range of 40-110 K. Our simulations established the high-temperature superconductive nature of selenium hydrides and provided useful route for experimental verification. PMID:26490223

  14. High-Tc/high-coupling relaxed PZT-based single crystal thin films

    NASA Astrophysics Data System (ADS)

    Wasa, K.; Matsushima, T.; Adachi, H.; Matsunaga, T.; Yanagitani, T.; Yamamoto, T.

    2015-03-01

    Pb(Zr,Ti)O3 (PZT)-based ferroelectric ceramics exhibit high piezoelectricity, however, their Curie temperature (Tc) values are not so high, i.e., Tc < 400 °C. PZT-based piezoelectric thin films with higher Tc would be beneficial for improved micro actuators, sensors, memories, and piezoelectric micro-electro mechanical systems. In-plane biaxial strained PZT thin films in a laminated composite structure are known to exhibit enhanced Tc; however, the thickness of PZT-based thin films is limited to below a critical thickness typically <50 nm. The Tc of relaxed PZT-based thin films with thicknesses greater than the critical thickness is the same as bulk Tc. However, a sort of relaxed PZT-based single-crystal thin films exhibit extraordinary high Tc, Tc = ˜600 °C. In addition, the films show extremely low dielectric constant, ɛ/ɛo ˜ 100 with high coupling factor, kt ˜ 0.7, and large remnant polarization, Pr ˜ 100 μC/cm2. These exotic properties would result from the single-domain/single-crystal structure. The enhanced Tc is possibly caused by the highly stable interface between the PZT-based thin films and substrates. Their ferroelectric performances are beyond those of conventional PZT. The high-Tc/high-coupling performances are demonstrated, and the possible mechanisms of the high Tc behavior in relaxed PZT-based single-crystal thin films are discussed.

  15. 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.

  16. Systematic variation of magnetic-field penetration depth in high-Tc superconductors studied by muon-spin relaxation

    NASA Technical Reports Server (NTRS)

    Uemura, Y. J.; Emery, V. J.; Moodenbaugh, A. R.; Suenaga, M.; Johnston, D. C.

    1988-01-01

    The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 SrO.15 CuO4 in transverse external magnetic fields 1 is approximately 4 kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

  17. The NASA high temperature superconductivity program

    NASA Technical Reports Server (NTRS)

    Sokoloski, Martin M.; Romanofsky, Robert R.

    1990-01-01

    It has been recognized from the onset that high temperature superconductivity held great promise for major advances across a broad range of NASA interests. The current effort is organized around four key areas: communications and data, sensors and cryogenics, propulsion and power, and space materials technology. Recently, laser ablated YBa2Cu3O(7-x) films on LaAIO produced far superior RF characteristics when compared to metallic films on the same substrate. This achievement has enabled a number of unique microwave device applications, such as low insertion loss phase shifters and high Q filters. Melt texturing and melt quenched techniques are being used to produce bulk materials with optimized magnetic properties. These yttrium enriched materials possess enhanced flux pinning characteristics and will lead to prototype cryocooler bearings. Significant progress has also occurred in bolometer and current lead technology. Studies are being conducted to evaluate the effect of high temperature superconducting materials on the performance and life of high power magneto-plasma-dynamic thrusters. Extended studies were also performed to evaluate the benefit of superconducting magnetic energy storage for LEO space station, lunar and Mars mission applications. The project direction and level of effort of the program are also described.

  18. Magnetic suspension using high temperature superconducting cores

    NASA Technical Reports Server (NTRS)

    Scurlock, R. G.

    1992-01-01

    The development of YBCO high temperature superconductors, in wire and tape forms, is rapidly approaching the point where the bulk transport current density j vs magnetic field H characteristics with liquid nitrogen cooling will enable its use in model cores. On the other hand, BSCCO high temperature superconductor in wire form has poor j-H characteristics at 77 K today, although with liquid helium or hydrogen cooling, it appears to be superior to NbTi superconductor. Since liquid nitrogen cooling is approx. 100 times cheaper than liquid helium cooling, the use of YBCO is very attractive for use in magnetic suspension. The design is discussed of a model core to accommodate lift and drag loads up to 6000 and 3000 N respectively. A comparison is made between the design performance of a liquid helium cooled NbTi (or BSCCO) superconducting core and a liquid nitrogen cooled YBCO superconducting core.

  19. Bi-Sr-Ca-Cu-O high TC superconductors (abstract)

    NASA Astrophysics Data System (ADS)

    Sherwood, R. C.; Tiefel, T. H.; Jin, S.; Davis, M. E.; Kammlott, G. W.; Fastnacht, R. A.

    1988-11-01

    A recent paper by Maeda et al.1 reported the discovery of a new 120 K superconductor based on a rare-earth-free ceramic material in the bismuth-strontium-calcium-copper-oxide system. We have confirmed the existence of the 120-K phase in the oxide system. The resistivity-temperature curve showed a fairly well-defined double-dip shape with the first dip starting at ˜120 K and the second at ˜95 K. The transition temperature, TC(R=0), was 84 K. This material appears to contain two superconducting phases with different TC's. A pellet made from this superconductor levitates well at 77 K (liquid-nitrogen temperature) above a neodynium-iron-boron magnet with a surface magnetic field of ˜3000 Oe, thus indicating a nontrivial critical field in this material. The critical current density and its magnetic field dependence will be reported. The magnetic and mechanical behavior of the new superconductor will also be discussed.

  20. Superconductivity in metastable phases of phosphorus-hydride compounds under high pressure

    NASA Astrophysics Data System (ADS)

    Flores-Livas, José A.; Amsler, Maximilian; Heil, Christoph; Sanna, Antonio; Boeri, Lilia; Profeta, Gianni; Wolverton, Chris; Goedecker, Stefan; Gross, E. K. U.

    2016-01-01

    Hydrogen-rich compounds have been extensively studied both theoretically and experimentally in the quest for novel high-temperature superconductors. Reports on sulfur hydride attaining metallicity under pressure and exhibiting superconductivity at temperatures as high as 200 K have spurred an intense search for room-temperature superconductors in hydride materials. Recently, compressed phosphine was reported to metallize at pressures above 45 GPa, reaching a superconducting transition temperature (TC) of 100 K at 200 GPa. However, neither the exact composition nor the crystal structure of the superconducting phase have been conclusively determined. In this work, the phase diagram of PHn (n =1 ,2 ,3 ,4 ,5 ,6 ) was extensively explored by means of ab initio crystal structure predictions using the minima hopping method (MHM). The results do not support the existence of thermodynamically stable PHn compounds, which exhibit a tendency for elemental decomposition at high pressure even when vibrational contributions to the free energies are taken into account. Although the lowest energy phases of PH1 ,2 ,3 display TC's comparable to experiments, it remains uncertain if the measured values of TC can be fully attributed to a phase-pure compound of PHn.

  1. Highly flexible, mechanically robust superconducting wire consisting of NbN-carbon-nanotube nanofibril composites

    NASA Astrophysics Data System (ADS)

    Kim, Jeong-Gyun; Kang, Haeyong; Kim, Joonggyu; Lee, Young Hee; Suh, Dongseok

    A flexible superconducting fiber is prepared by twisting carbon nanotube (CNT) sheets coated with sputter-deposited niobium nitride (NbN) layer to form the shape of yarn. Twisted CNT yarn, which has been extensively studied due to its high flexibility as well as excellent mechanical properties, and NbN, which is a superconducting material with high transition temperature (Tc) and critical magnetic field (Hc), are combined together by the deposition of NbN layer on free-standing CNT-sheet substrate followed by the biscrolling process. We tried many experimental conditions to investigate the superconducting properties of NbN-CNT yarn as a function of NbN thickness and number of CNT-sheet layers, and found out that the superconducting property of NbN on CNT-sheet can be comparable to that of NbN thin film on the normal solid substrate. In addition, the superconducting property survived even under the condition of severe mechanical deformation such as knotting. These results show the potential application of this technology as a large-scale fabrication method of flexible, mechanically robust, high performance superconducting wire. This work is supported by the Institute for Basic Science (IBS-R011-D1), and by the National Research Foundation (BSR-2013R1A1A1076063) funded by the Ministry of Science, ICT & Future Planning, Republic of Korea.

  2. High temperature superconducting magnetic energy storage for future NASA missions

    NASA Technical Reports Server (NTRS)

    Faymon, Karl A.; Rudnick, Stanley J.

    1988-01-01

    Several NASA sponsored studies based on 'conventional' liquid helium temperature level superconductivity technology have concluded that superconducting magnetic energy storage has considerable potential for space applications. The advent of high temperature superconductivity (HTSC) may provide additional benefits over conventional superconductivity technology, making magnetic energy storage even more attractive. The proposed NASA space station is a possible candidate for the application of HTSC energy storage. Alternative energy storage technologies for this and other low Earth orbit missions are compared.

  3. Synthesis and characterization of high-Tc superconductors in the Tl-Ca-Ba-Cu-O system

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Farrell, D. E.

    1989-01-01

    Both Tl2Ca2Ba2Cu3O10 and TlCa3BaCu3O8.5 are investigated for superconductivity as a function of the sintering temperature, time, atmosphere, and quench rate in an effort to synthesize the high-Tc superconducting phase in the thallium system. The samples are characterized by electrical resistivity measurements, X-ray diffraction, and scanning electron microscopy. Samples of starting composition Tl2Ca2Ba2Cu3O10 fired in air at 860-900 C and rapidly quenched show a Tc of 96-107 K. In contrast, specimens of starting composition TlCa3BaCu3O8.5 when baked at 900 C and slowly cooled in oxygen superconduct at 116 K and above and consist of Tl2Ca2Ba2Cu3O(10+x) as the dominant phase. The results also show that, in contrast to the case of YBa2Cu3O(7-x), doping with a small concentration of fluorine sharpens the resistive transition and produces a large Tc increase in thallium-based superconductors.

  4. Synthesis and characterization of high-Tc superconductors in the Tl-Ca-Ba-Cu-O system

    NASA Astrophysics Data System (ADS)

    Bansal, Narottam P.; Farrell, D. E.

    1989-05-01

    Both Tl2Ca2Ba2Cu3O10 and TlCa3BaCu3O8.5 are investigated for superconductivity as a function of the sintering temperature, time, atmosphere, and quench rate in an effort to synthesize the high-Tc superconducting phase in the thallium system. The samples are characterized by electrical resistivity measurements, X-ray diffraction, and scanning electron microscopy. Samples of starting composition Tl2Ca2Ba2Cu3O10 fired in air at 860-900 C and rapidly quenched show a Tc of 96-107 K. In contrast, specimens of starting composition TlCa3BaCu3O8.5 when baked at 900 C and slowly cooled in oxygen superconduct at 116 K and above and consist of Tl2Ca2Ba2Cu3O(10+x) as the dominant phase. The results also show that, in contrast to the case of YBa2Cu3O(7-x), doping with a small concentration of fluorine sharpens the resistive transition and produces a large Tc increase in thallium-based superconductors.

  5. Local fields in high- Tc materials

    NASA Astrophysics Data System (ADS)

    Tarrio, C.; Benitez, E. L.; Schnatterly, S. E.

    1992-04-01

    Most high-temperature superconductors exhibit two-dimensional conductance; therefore the conduction electrons are localized in the third dimension, and experience the local electric field rather than the macroscopic applied field in that direction. We report model calculations which indicate that the local field leads to enhanced electron-phonon coupling in these materials which may play a role in determining the high transition temperatures.

  6. CaFeAs2: A staggered intercalation of quantum spin Hall and high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Wu, Xianxin; Qin, Shengshan; Liang, Yi; Le, Congcong; Fan, Heng; Hu, Jiangping

    2015-02-01

    We predict that CaFeAs2, a newly discovered iron-based high-temperature (Tc) superconductor, is a staggered intercalation compound that integrates topological quantum spin Hall (QSH) and superconductivity (SC). CaFeAs2 has a structure with staggered CaAs and FeAs layers. While the FeAs layers are known to be responsible for high Tc superconductivity, we show that with spin orbital coupling each CaAs layer is a Z2 topologically nontrivial two-dimensional QSH insulator and the bulk is a three-dimensional weak topological insulator. In the superconducting state, the edge states in the CaAs layer are natural one-dimensional topological superconductors. The staggered intercalation of QSH and SC provides us a unique opportunity to realize and explore physics, such as Majorana modes and Majorana fermion chains.

  7. Superconducting state in bromium halide at high pressure

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, R.; Zemła, T. P.; Szczȩśniak, D.

    2016-08-01

    The thermodynamic properties of the superconducting state in bromium halide (HBr) compound have been analyzed in the framework of the Eliashberg formalism. In particular, for the range of the pressure (p) from 140 GPa to 200 GPa, it has been shown that the critical temperature increases significantly: TC(p) ∈ < 28.8 , 55.1 > K, whereas the Coulomb pseudopotential (μ⋆) is equal to 0.1. Together with the increase of p, the values of the thermodynamic parameters such as: the ratio of the energy gap at the temperature of zero Kelvin to the critical temperature (RΔ ≡ 2 Δ (0) /kB TC), the ratio of the specific heat jump at the critical temperature to the electronic specific heat of the normal state (RC ≡ ΔC (TC) /CN (TC)), and the ratio related to the thermodynamic critical field (RH ≡TC CN (TC) / HC2 (0)) increasingly deviate from the predictions of the BCS model: RΔ(p) ∈ < 3.79 , 4.05 >, RC(p) ∈ < 1.94 , 2.27 >, and RH(p) ∈ < 0.157 , 0.147 >. It should be noted that the increase of μ⋆ visibly lowers TC and significantly reduces the difference between the results of the Eliashberg and BCS theory.

  8. High-Tc superconductor coplanar waveguide filter

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  9. Possible light-induced superconductivity in K3C60 at high temperature.

    PubMed

    Mitrano, M; Cantaluppi, A; Nicoletti, D; Kaiser, S; Perucchi, A; Lupi, S; Di Pietro, P; Pontiroli, D; Riccò, M; Clark, S R; Jaksch, D; Cavalleri, A

    2016-02-25

    The non-equilibrium control of emergent phenomena in solids is an important research frontier, encompassing effects such as the optical enhancement of superconductivity. Nonlinear excitation of certain phonons in bilayer copper oxides was recently shown to induce superconducting-like optical properties at temperatures far greater than the superconducting transition temperature, Tc (refs 4-6). This effect was accompanied by the disruption of competing charge-density-wave correlations, which explained some but not all of the experimental results. Here we report a similar phenomenon in a very different compound, K3C60. By exciting metallic K3C60 with mid-infrared optical pulses, we induce a large increase in carrier mobility, accompanied by the opening of a gap in the optical conductivity. These same signatures are observed at equilibrium when cooling metallic K3C60 below Tc (20 kelvin). Although optical techniques alone cannot unequivocally identify non-equilibrium high-temperature superconductivity, we propose this as a possible explanation of our results.

  10. Possible light-induced superconductivity in K3C60 at high temperature.

    PubMed

    Mitrano, M; Cantaluppi, A; Nicoletti, D; Kaiser, S; Perucchi, A; Lupi, S; Di Pietro, P; Pontiroli, D; Riccò, M; Clark, S R; Jaksch, D; Cavalleri, A

    2016-02-25

    The non-equilibrium control of emergent phenomena in solids is an important research frontier, encompassing effects such as the optical enhancement of superconductivity. Nonlinear excitation of certain phonons in bilayer copper oxides was recently shown to induce superconducting-like optical properties at temperatures far greater than the superconducting transition temperature, Tc (refs 4-6). This effect was accompanied by the disruption of competing charge-density-wave correlations, which explained some but not all of the experimental results. Here we report a similar phenomenon in a very different compound, K3C60. By exciting metallic K3C60 with mid-infrared optical pulses, we induce a large increase in carrier mobility, accompanied by the opening of a gap in the optical conductivity. These same signatures are observed at equilibrium when cooling metallic K3C60 below Tc (20 kelvin). Although optical techniques alone cannot unequivocally identify non-equilibrium high-temperature superconductivity, we propose this as a possible explanation of our results. PMID:26855424

  11. Scanning tunneling microscopy studies of an electron-doped high-Tc superconductor, praseodymium lanthanum cerium copper oxide

    NASA Astrophysics Data System (ADS)

    Kunwar, Shankar

    It has been more than two decades since the first high temperature superconductor was discovered. In this time there has been tremendous progress in understanding these materials both theoretically and experimentally. Some important questions however remain to be answered; one of them is the temperature dependence of the superconducting gap which is in turn tied to question of the origin of the pseudogap and its connection with superconductivity. In this thesis, we present detailed Scanning Tunneling Microscopy (STM) spectroscopic studies of an electron doped superconductor, Pr0.88LaCe 0.12CuO4-delta (PLCCO). The electron doped compounds form an interesting venue for STM studies for many reasons. In the hole-doped materials, especially in the underdoped side of the phase diagram, there is mounting evidence of a second gap that survives to high temperatures (high temperature pseudogap) that may have a different origin from superconductivity. This complicates studies of the temperature dependence of the superconducting gap in these materials. In PLCCO however, there is little evidence for a high temperature pseudogap potentially allowing us to address the question of the temperature evolution of the superconducting gap without the complication of a second gap. Secondly, the low Tc of the optimally doped materials makes it easily accessible to temperature dependent STM studies. Finally, while hole-doped materials have been extensively studied by scanning tunneling microscopy (STM), there have been no detailed STM spectroscopic studies on the electron doped compounds. In the first part of the thesis, we investigate the effect of temperature on the superconducting gap of optimally doped PLCCO with Tc = 24K. STM spectroscopy data is analyzed to obtain the gap as a function of temperature from 5K to 35K. The gap is parameterized with a d-wave form and the STM spectra are fit at each temperature to extract the gap value. A plot of this gap value as a function of

  12. Aerospace applications of high temperature superconductivity

    NASA Technical Reports Server (NTRS)

    Heinen, V. O.; Connolly, D. J.

    1991-01-01

    Space application of high temperature superconducting (HTS) materials may occur before most terrestrial applications because of the passive cooling possibilities in space and because of the economic feasibility of introducing an expensive new technology which has a significant system benefit in space. NASA Lewis Research Center has an ongoing program to develop space technology capitalizing on the potential benefit of HTS materials. The applications being pursued include space communications, power and propulsion systems, and magnetic bearings. In addition, NASA Lewis is pursuing materials research to improve the performance of HTS materials for space applications.

  13. Effective carrier type and field dependence of the reduced- Tc superconducting state in SrFe2-xNixAs2

    NASA Astrophysics Data System (ADS)

    Butch, N. P.; Saha, S. R.; Zhang, X. H.; Kirshenbaum, K.; Greene, R. L.; Paglione, J.

    2010-01-01

    Measurements of the Hall effect, thermoelectric power, magnetic susceptibility, and upper and lower critical fields were performed on single crystals of SrFe2-xNixAs2 , an FeAs-based superconducting system that exhibits a reduced superconducting transition temperature Tc in comparison to most other iron-pnictide superconductors. Studies of the Hall and thermoelectric responses indicate that Ni substitution in this system results in a dominant electronlike response, consistent with electron doping in other similar systems but with a weaker change in the Hall coefficient and a more gradual change in the thermoelectric response with Ni concentration. For optimally doped samples with full superconducting volume fraction, the lower and upper critical fields were determined to be Hc1(1.8K)=0.08T and Hc2(0)=25T , respectively, with lower- Tc samples showing reduced values and indications of inhomogeneous superconductivity. Comparable to other higher- Tc FeAs-based materials, the temperature dependence of the upper critical field, ∂Hc2/∂T , is linear over a wide temperature range, and the large values of Hc2(0) greatly exceed conventional estimates of paramagnetic and orbital limits.

  14. High Tc screen-printed YBa2Cu3O(7-x) films - Effect of the substrate material

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Simons, Rainee N.; Farrell, D. E.

    1988-01-01

    Thick films of YBa2Cu3O(7-x) have been deposited on highly polished alumina, magnesia spinel, nickel aluminum titanate (Ni-Al-Ti), and barium tetratitanate (Ba-Ti) substrates by the screen printing technique. Properties of the films were found to be highly sensitive to the choice of the substrate material. The film on Ba-Ti turned green after firing, due to a reaction with the substrate and were insulating. A film on Ni-Al-Ti had a Tc (onset) of about 95 K and lost 90 percent of its resistance by about 75 K. However, even at 4 K it was not fully superconducting, possibly due to a reaction between the film and the substrate and interdiffusion of the reaction products. The film on alumina had Tc (onset) of about 96 K, Tc (zero) of about 66 K, and Delta Tc of about 10 K. The best film was obtained on spinel and had Tc (onset) of about 94 K, zero resistance at 81 K, and a transition width of about 7 K.

  15. Perspectives on high temperature superconducting electronics

    NASA Technical Reports Server (NTRS)

    Venkatesan, T.

    1990-01-01

    The major challenges in making high temperature superconducting (HTSC) electronics viable are predominantly materials problems. Unlike their predecessors the metal oxide-based superconductors are integratable with other advanced technologies such as opto-electronics and micro-electronics. The materials problems to be addressed relate to the epitaxial growth of high quality films, highly oriented films on non-lattice matched substrates, heterostructures with atomically sharp interfaces of junctions and other novel devices, and the processing of these films with negligible deterioration of the superconducting properties. These issues are illustrated with results based on films prepared in-situ by a pulsed laser deposition process. Films with zero-transition temperatures of 90 K and critical current densities of 5 x 10(exp 6) A/sq cm at 77 K have been prepared by this technique. Ultra-thin films, less than 100 A show T(sub c) is greater than 80 K, supporting the idea of two-dimensional transport in these materials. By the use of appropriate buffer layers, films with T(sub c) of 87 K and J(sub c) of 6 x 10(exp 4) A/sq cm were fabricated on silicon substrates. Submicron structures with J(sub c) is greater than 2 x 10(exp 7) at 10 K were fabricated. Results on nonlinear switching elements, IR detectors, and microwave studies will be briefly summarized.

  16. Perspectives on high temperature superconducting electronics

    NASA Technical Reports Server (NTRS)

    Venkatesan, T.

    1991-01-01

    The major challenges in making high temperature superconducting (HTSC) electronics viable are predominantly materials problems. Unlike their predecessors, the metal oxide-based superconductors are integratable with other advanced technologies such as opto-electronics and micro-electronics. The materials problems to be addressed relate to the epitaxial growth of high quality films, highly oriented films on non-lattice matched substrates, heterostructures with atomically sharp interfaces of junctions and other novel devices, and the processing of these films with negligible deterioration of the superconducting properties. These issues are illustrated with results based on films prepared in-situ by a pulsed laser deposition process. Films with zero-transition temperatures of 90 K and critical current densities of 5 x 10(exp 6) A/sq cm at 77 K have been prepared by this technique. Ultra-thin films, less than 100 A show T(sub c) is greater than 80 K, supporting the idea of two-dimensional transport in these materials. By the use of appropriate buffer layers, films with T(sub c) of 87 K and J(sub c) of 6 x 10(exp 4) A/sq cm were fabricated on silicon substrates. Submicron structures with J(sub c) is greater than 2 x 10(exp 7) at 10 K were fabricated. Results on nonlinear switching elements, IR detectors, and microwave studies will be briefly summarized.

  17. Early High Tc Activity in Japan: The Franco Rasetti Lecture

    NASA Astrophysics Data System (ADS)

    Tanaka, Shoji

    2007-03-01

    From 1960 to 1980, R&D of superconductivity in Japan was carried out mainly to improve A15 superconducting wires and magnets. Improvement of wires were made mainly in the National Institute for Metals, and improvements of superconducting magnets were made in the Japan Atomic Energy Research Institute for future nuclear fusion reactors, the National Railway Laboratory for future maglev trains and also in the Electo-Technical Laboratory for MHD generators. I began the research of BPBO in 1975 and at that time the research of oxide superconductors was limited only to my laboratory in the University of Tokyo. During the study of this new superconductor, we learned quite a lot on how to make ceramic samples, how to measure electrical conductivity and magnetic susceptibility at low temperatures. In 1982, Prof. S. Nakajima organized a rather small group for investigating ``New Superconducting Phenomena,'' and I became a member of the group. In 1985, Nakajima expanded the research group to include more than 5 experimentalists and 5 theoreticians. The title of the research was ``New Superconducting Materials'' and the funds came from the Ministry of Education of Japan. In late October, 1986, we followed the first paper of Bednorz and Muller, and immediately found the material includes high temperature superconductor and reported it to the group meeting held in early November. In early December, we confirmed La2-xBaxCuO4 is the real high temperature superconductor, the critical temperature is 28K. I sent a copy of our paper to Prof. Beasley of California and asked to inform this fact to his colleagues. Asahi Shimbun, the biggest newspaper in Japan announced this in its science section, and then many people knew the high temperature superconductor had been discovered. Then many physicists and chemists rushed to this field very quickly and many kinds of materials were synthesized. In the Government, the Ministry of Education, the Ministry of International Trade and Industry

  18. Bio-application of high-Tc SQUID magnetic sensor

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Aspanut, Zarina; Kurita, Hirofumi; Toriyabe, Chika; Hatuskade, Yoshimi; Katsura, Shinji

    2006-05-01

    We propose medical applications using ultra-small magnetic particles and a SQUID magnetic sensor. A high-Tc SQUID system for biological molecules (DNA) detection is one of that. This system is based on a hybridization process. Two strands in a DNA molecule are held together by hydrogen bonds between base pairs like a ladder. The two strands are referred to as being complementary to each other. One strand (sample DNA) was labeled with Fe 3O 4 ultra-small magnetic particles and the other (probe DNA) was anchored on a glass slide. Then they were hybridized each other on the slide. After washing the excess sample DNA, the hybridized DNA was evaluated in the presence of excitation AC field by high-Tc SQUID. The signal was initially proportional to the concentration of the sample DNA and then saturated. It means that the hybridization occurred successfully between the sample DNA and the probe DNA.

  19. Cryocooler cooled HTS current lead for a 35 kJ/7 kW-class high- Tc SMES system

    NASA Astrophysics Data System (ADS)

    Ren, L.; Tang, Y.; Shi, J.; Chen, N.; Li, J.; Cheng, S.

    2008-09-01

    Within 863 program of China, a 35 kJ/7 kW-class high- Tc superconducting magnetic energy storage system (SMES) was completed in Nov. 2005. It operates at 100 A in the cryogenic environment of 20 K and is cooled by conduction cooling. It is essential to minimize heat loss from room temperature and to optimize the ohmic heating of current leads. So, 100 A hybrid type current leads, consisting of conventional copper parts and high- Tc superconducting (HTS) parts, were designed, fabricated and tested. The HTS parts of the leads were made of Bi-2223 cylindrical bulk and the copper parts were winded into just like a sparse solenoid to prolong the path for heat transfer. The current leads were cooled directly by a two-stage cryocooler. And, a series of experiments were carried out. The experimental results show a good according with the simulation, which verify that the hybrid current lead meets the requirements of high- Tc SMES.

  20. Quantum topological transition in hyperbolic metamaterials based on high Tc superconductors.

    PubMed

    Smolyaninov, Igor I

    2014-07-30

    Hyperbolic metamaterials are known to exhibit a transition in the topology of the photon iso-frequency surface from a closed ellipsoid to an open hyperboloid, resulting in a considerable increase of the photonic density of states. This topological transition may also be described as a change of metric signature of the effective optical space. Here we demonstrate that high Tc superconductors exhibit hyperbolic metamaterial behavior in the far infrared and THz frequency ranges. In the THz range the hyperbolic behavior occurs only in the normal state, while no propagating photon modes exist in the superconducting state. Thus, a quantum topological transition may be observed for THz photons at zero temperature as a function of the external magnetic field, in which the effective Minkowski spacetime arises in the mixed state of the superconductor at some critical value of the external magnetic field. Nucleation of effective Minkowski spacetime occurs via the formation of quantized Abrikosov vortices. PMID:25001512

  1. SHMUTZ & PROTON-DIAMANT H + Irradiated/Written-Hyper/Super-conductivity(HC/SC) Precognizance/Early Experiments Connections: Wet-Graphite Room-Tc & Actualized MgB2 High-Tc: Connection to Mechanical Bulk-Moduli/Hardness: Diamond Hydrocarbon-Filaments, Disorder, Nano-Powders:C,Bi,TiB2,TiC

    NASA Astrophysics Data System (ADS)

    Wunderman, Irwin; Siegel, Edward Carl-Ludwig; Lewis, Thomas; Young, Frederic; Smith, Adolph; Dresschhoff-Zeller, Gieselle

    2013-03-01

    SHMUTZ: ``wet-graphite''Scheike-....[Adv.Mtls.(7/16/12)]hyper/super-SCHMUTZ-conductor(S!!!) = ``wet''(?)-``graphite''(?) = ``graphene''(?) = water(?) = hydrogen(?) =ultra-heavy proton-bands(???) = ...(???) claimed room/high-Tc/high-Jc superconductOR ``p''-``wave''/ BAND(!!!) superconductIVITY and actualized/ instantiated MgB2 high-Tc superconductors and their BCS- superconductivity: Tc Siegel[ICMAO(77);JMMM 7,190(78)] connection to SiegelJ.Nonxline-Sol.40,453(80)] disorder/amorphous-superconductivity in nano-powders mechanical bulk/shear(?)-moduli/hardness: proton-irradiated diamond, powders TiB2, TiC,{Siegel[Semis. & Insuls.5:39,47, 62 (79)])-...``VS''/concommitance with Siegel[Phys.Stat.Sol.(a)11,45(72)]-Dempsey [Phil.Mag. 8,86,285(63)]-Overhauser-(Little!!!)-Seitz-Smith-Zeller-Dreschoff-Antonoff-Young-...proton-``irradiated''/ implanted/ thermalized-in-(optimal: BOTH heat-capacity/heat-sink & insulator/maximal dielectric-constant) diamond: ``VS'' ``hambergite-borate-mineral transformable to Overhauser optimal-high-Tc-LiBD2 in Overhauser-(NW-periodic-table)-Land: CO2/CH4-ETERNAL-sequestration by-product: WATER!!!: physics lessons from

  2. Superconductivity applications for infrared and microwave devices; Proceedings of the Meeting, Orlando, FL, Apr. 19, 20, 1990

    NASA Technical Reports Server (NTRS)

    Bhasin, Kul B. (Editor); Heinen, Vernon O. (Editor)

    1990-01-01

    Various papers on superconductivity applications for IR and microwave devices are presented. The individual topics addressed include: pulsed laser deposition of Tl-Ca-Ba-Cu-O films, patterning of high-Tc superconducting thin films on Si substrates, IR spectra and the energy gap in thin film YBa2Cu3O(7-delta), high-temperature superconducting thin film microwave circuits, novel filter implementation utilizing HTS materials, high-temperature superconductor antenna investigations, high-Tc superconducting IR detectors, high-Tc superconducting IR detectors from Y-Ba-Cu-O thin films, Y-Ba-Cu0-O thin films as high-speed IR detectors, fabrication of a high-Tc superconducting bolometer, transition-edge microbolometer, photoresponse of YBa2Cu3O(7-delta) granular and epitaxial superconducting thin films, fast IR response of YBCO thin films, kinetic inductance effects in high-Tc microstrip circuits at microwave frequencies.

  3. Tunable high-q superconducting notch filter

    DOEpatents

    Pang, C.S.; Falco, C.M.; Kampwirth, R.T.; Schuller, I.K.

    1979-11-29

    A superconducting notch filter is made of three substrates disposed in a cryogenic environment. A superconducting material is disposed on one substrate in a pattern of a circle and an annular ring connected together. The second substrate has a corresponding pattern to form a parallel plate capacitor and the second substrate has the circle and annular ring connected by a superconducting spiral that forms an inductor. The third substrate has a superconducting spiral that is placed parallel to the first superconducting spiral to form a transformer. Relative motion of the first substrate with respect to the second is effected from outside the cryogenic environment to vary the capacitance and hence the frequency of the resonant circuit formed by the superconducting devices.

  4. Aerospace applications of high temperature superconductivity

    NASA Technical Reports Server (NTRS)

    Connolly, D. J.; Heinen, V. O.; Aron, P. R.; Lazar, J.; Romanofsky, Robert R.

    1990-01-01

    A review is presented of all the applications that are part of the NASA program to develop space technology capitalizing on the potential benefit of high temperature superconducting materials. The applications in three major areas are being pursued: sensors and cryogenic systems, space communications, and propulsion and power systems. This review places emphasis on space communications applications and the propulsion and power applications. It is concluded that the power and propulsion applications will eventually be limited by structural considerations rather than by the availability of suitable superconductors. A cursory examination of structural limitations implied by the virial theorem suggested that there is an upper limit to the size of high field magnetic systems that are feasible in space.

  5. Permanent magnet design for high-speed superconducting bearings

    DOEpatents

    Hull, John R.; Uherka, Kenneth L.; Abdoud, Robert G.

    1996-01-01

    A high temperature superconducting bearing including a permanent magnet rotor levitated by a high temperature superconducting structure. The rotor preferably includes one or more concentric permanent magnet rings coupled to permanent magnet ring structures having substantially triangular and quadrangular cross-sections. Both alternating and single direction polarity magnet structures can be used in the bearing.

  6. Permanent magnet design for high-speed superconducting bearings

    DOEpatents

    Hull, J.R.; Uherka, K.L.; Abdoud, R.G.

    1996-09-10

    A high temperature superconducting bearing including a permanent magnet rotor levitated by a high temperature superconducting structure is disclosed. The rotor preferably includes one or more concentric permanent magnet rings coupled to permanent magnet ring structures having substantially triangular and quadrangular cross-sections. Both alternating and single direction polarity magnet structures can be used in the bearing. 9 figs.

  7. Korea's developmental program for superconductivity

    NASA Technical Reports Server (NTRS)

    Hong, Gye-Won; Won, Dong-Yeon; Kuk, Il-Hyun; Park, Jong-Chul

    1995-01-01

    Superconductivity research in Korea was firstly carried out in the late 70's by a research group in Seoul National University (SNU), who fabricated a small scale superconducting magnetic energy storage system under the financial support from Korea Electric Power Company (KEPCO). But a few researchers were involved in superconductivity research until the oxide high Tc superconductor was discovered by Bednorz and Mueller. After the discovery of YBaCuO superconductor operating above the boiling point of liquid nitrogen (77 K)(exp 2), Korean Ministry of Science and Technology (MOST) sponsored a special fund for the high Tc superconductivity research to universities and national research institutes by recognizing its importance. Scientists engaged in this project organized 'High Temperature Superconductivity Research Association (HITSRA)' for effective conducting of research. Its major functions are to coordinate research activities on high Tc superconductivity and organize the workshop for active exchange of information. During last seven years the major superconductivity research has been carried out through the coordination of HITSRA. The major parts of the Korea's superconductivity research program were related to high temperature superconductor and only a few groups were carrying out research on conventional superconductor technology, and Korea Atomic Energy Research Institute (KAERI) and Korea Electrotechnology Research Institute (KERI) have led this research. In this talk, the current status and future plans of superconductivity research in Korea will be reviewed based on the results presented in interim meeting of HITSRA, April 1-2, 1994. Taejeon, as well as the research activity of KAERI.

  8. Eliashberg Theory and the High T(c) Oxides.

    NASA Astrophysics Data System (ADS)

    Marsiglio, Frank

    The Eliashberg theory of superconductivity has been very successful in accounting for properties of conventional materials. The price for this success has been a lack of understanding of exactly what features of the input parameters affect the superconducting properties in significant ways. The first part of this thesis is concerned with the identification of an important parameter in the study of thermodynamic, critical magnetic field, and electromagnetic properties of a superconductor. The Bardeen-Cooper-Schreiffer (BCS) theory of superconductivity produces laws of corresponding states, i.e., various properties are predicted to have universal values. We have studied the deviation from BCS theory due to retardation effects, which are embodied in Eliashberg theory. These deviations, or corrections to BCS, can be well understood and characterized by a single simple parameter, T_{c}/omega _{rm ln}, to be defined later. Attention has been focussed on reproducing numerical (theoretical) results, since for most conventional superconducting materials, experiment agrees with theory at the 10% level. The second half of the thesis has been largely motivated by the recent discoveries of the high-T _{c} oxide materials. We have applied Eliashberg theory almost entirely in an inverse manner. That is, with little knowledge of the microscopic parameters for these new materials, we have investigated the relationships between various macroscopically observable properties, based on model spectra. The model spectra have been of three general types, the conventional category, spectra based on a combined phonon-exciton mechanism, and thirdly those based on relatively low frequency exchange bosons. We have called this latter category the very strong coupling regime. It was hoped that measured properties could uniquely specify the type of spectrum responsible for the superconductivity in the high-T_ {c} oxides. At this point in time this goal has not really been achieved. Too many

  9. Superconducting High Resolution Fast-Neutron Spectrometers

    SciTech Connect

    Hau, Ionel Dragos

    2006-01-01

    Superconducting high resolution fast-neutron calorimetric spectrometers based on 6LiF and TiB{sub 2} absorbers have been developed. These novel cryogenic spectrometers measure the temperature rise produced in exothermal (n, α) reactions with fast neutrons in 6Li and 10B-loaded materials with heat capacity C operating at temperatures T close to 0.1 K. Temperature variations on the order of 0.5 mK are measured with a Mo/Cu thin film multilayer operated in the transition region between its superconducting and its normal state. The advantage of calorimetry for high resolution spectroscopy is due to the small phonon excitation energies kBT on the order of μeV that serve as signal carriers, resulting in an energy resolution ΔE ~ (kBT2C)1/2, which can be well below 10 keV. An energy resolution of 5.5 keV has been obtained with a Mo/Cu superconducting sensor and a TiB2 absorber using thermal neutrons from a 252Cf neutron source. This resolution is sufficient to observe the effect of recoil nuclei broadening in neutron spectra, which has been related to the lifetime of the first excited state in 7Li. Fast-neutron spectra obtained with a 6Li-enriched LiF absorber show an energy resolution of 16 keV FWHM, and a response in agreement with the 6Li(n, α)3H reaction cross section and Monte Carlo simulations for energies up to several MeV. The energy resolution of order of a few keV makes this novel instrument applicable to fast-neutron transmission spectroscopy based on the unique elemental signature provided by the neutron absorption and scattering resonances. The optimization of the energy resolution based on analytical and numerical models of the detector response is discussed in the context of these applications.

  10. Parameters of high-temperature superconducting transformers

    NASA Astrophysics Data System (ADS)

    Volkov, E. P.; Dzhafarov, E. A.

    2015-12-01

    Parameters of the high-temperature superconducting (HTSC) transformer with a core-type magnetic circuit and with coaxial and symmetrical interleaved windings made of the first-generation HTSC wire with a localized magnetic field are considered. The parameters of the most widespread core-type transformer with a coaxial HTSC winding are compared with those of a conventional transformer with a copper wire winding. Advantages of the HTSC transformers, such as reduction in the leakage inductive reactance and the HTSC winding's cross section, volume, and mass, as compared with the same parameters of conventional transformers with a copper wire winding are demonstrated. The efficiency of the HTSC transformers has proven to be determined predominantly by the core loss. In order to increase the efficiency of the HTSC transformer, it is proposed to use the amorphous electrical steel as the material of its magnetic circuit.

  11. High temperature superconductivity space experiment (HTSSE)

    NASA Technical Reports Server (NTRS)

    Ritter, J. C.; Nisenoff, M.; Price, G.; Wolf, S. A.

    1991-01-01

    An experiment dealing with high-temperature superconducting devices and components in space is discussed. A variety of devices (primarily passive microwave and millimeter-wave components) has been procured and will be integrated with a cryogenic refrigerating and data acquisition system to form the space package, which will be launched in late 1992. This space experiment is expected to demonstrate that this technology is sufficiently robust to survive the space environment and that the technology has the potential to improve the operation of space systems significantly. The devices for the initial launch have been evaluated electrically, thermally, and mechanically, and will be integrated into the final space package early in 1991. The performance of the devices is summarized, and some potential applications of this technology in space systems are outlined.

  12. Nodal bilayer-splitting controlled by spin-orbit interactions in underdoped high-Tc cuprates

    DOE PAGES

    Harrison, N.; Ramshaw, B. J.; Shekhter, A.

    2015-06-03

    The highest superconducting transition temperatures in the cuprates are achieved in bilayer and trilayer systems, highlighting the importance of interlayer interactions for high Tc. It has been argued that interlayer hybridization vanishes along the nodal directions by way of a specific pattern of orbital overlap. Recent quantum oscillation measurements in bilayer cuprates have provided evidence for a residual bilayer-splitting at the nodes that is sufficiently small to enable magnetic breakdown tunneling at the nodes. Here we show that several key features of the experimental data can be understood in terms of weak spin-orbit interactions naturally present in bilayer systems, whosemore » primary effect is to cause the magnetic breakdown to be accompanied by a spin flip. These features can now be understood to include the equidistant set of three quantum oscillation frequencies, the asymmetry of the quantum oscillation amplitudes in c-axis transport compared to ab-plane transport, and the anomalous magnetic field angle dependence of the amplitude of the side frequencies suggestive of small effective g-factors. We suggest that spin-orbit interactions in bilayer systems can further affect the structure of the nodal quasiparticle spectrum in the superconducting phase. PACS numbers: 71.45.Lr, 71.20.Ps, 71.18.+y« less

  13. High-field superconducting nested coil magnet

    NASA Technical Reports Server (NTRS)

    Laverick, C.; Lobell, G. M.

    1970-01-01

    Superconducting magnet, employed in conjunction with five types of superconducting cables in a nested solenoid configuration, produces total, central magnetic field strengths approaching 70 kG. The multiple coils permit maximum information on cable characteristics to be gathered from one test.

  14. van Hove Singularities and Spectral Smearing in High Temperature Superconducting H3S

    NASA Astrophysics Data System (ADS)

    Quan, Yundi; Pickett, Warren E.

    The superconducting phase of hydrogen sulfide at Tc=200 K observed by Drozdov and collaborators at pressures around 200 GPa is simple bcc Im 3 m H3S reopens questions about what is achievable in high Tc. The various ''extremes'' that are involved - pressure, implying extreme reduction of volume, extremely high H phonon energy scale around 1400K, extremely high temperature for a superconductor - necessitate a close look at new issues raised by these characteristics in relation to high Tc. We have applied first principles methods to analyze the H3S electronic structure, particularly the van Hove singularities (vHs) and the effect of sulfur. Focusing on the two closely spaced vHs near the Fermi level that give rise to the impressively sharp peak in the density of states, the implications of strong coupling Migdal-Eliashberg theory are assessed. The electron spectral density smearing due to virtual phonon emission and absorption, as done in earlier days for A15 superconductors, must be included explicitly to obtain accurate theoretical predictions and a correct understanding. Means for increasing Tc in H3S-like materials will be mentioned. NSF DMR Grant 1207622.

  15. Superconductivity and Critical Current of Iron-Based Superconductors in High Field

    NASA Astrophysics Data System (ADS)

    Li, Qiang

    2014-03-01

    Although high-temperature superconducting cuprates have been discovered for more than 26 years, high-field applications are still based on low-temperature superconductors (LTS), such as Nb3Sn. The high anisotropies, brittle textures and high manufacturing costs limit the applicability of the cuprates. Recently, we demonstrated that the iron superconductors, without most of the drawbacks of the cuprates, have a superior high-field performance over LTS at 4.2 K [Nat. Commun. 4:1347 (2013); Rep. Prog. Phys. 74 124510 (2011)]. In this presentation, I will discuss recent progress aimed at understanding the relationships between superconductivity, critical current, and nano-scaled structure defects in iron-based superconductors, with emphasis on the properties of superconducting iron chalcogenide films. Critical current densities Jc ~ 107 A/cm2 were observed in FeSe0.5Te0.5 films grown on CeO2 buffered single-crystalline and flexible metal substrates. These films are capable of carrying Jc exceeding 105 A/cm2 under 30 T magnetic fields. Furthermore, we found that these films have significantly higher Tc (>20K) as compared to bulk samples (bulk Tc ~ 15 K) for the entire doping regime of FeSe1-xTex. Structural analysis revealed that these films generally have significantly smaller c-axis and a-axis lattice constant than the bulk value, suggesting that the crystal structure changes have a dominating impact on the superconducting transition in iron-based superconductors. Large Jc enhancement can also be realized in iron based superconductors by irradiation with proton and heavy ions that opens a new avenue for a tailored landscape of effective vortex pinning defects.

  16. Microstructures and critical currents in high-{Tc} superconductors

    SciTech Connect

    Suenaga, Masaki

    1998-11-01

    Microstructural defects are the primary determining factors for the values of critical-current densities in a high {Tc} superconductor after the electronic anisotropy along the a-b plane and the c-direction. A review is made to assess firstly what would be the maximum achievable critical-current density in YBa{sub 2}Cu{sub 3}O{sub 7} if nearly ideal pinning sites were introduced and secondly what types of pinning defects are currently introduced or exist in YBa{sub 2}Cu{sub 3}O{sub 7} and how effective are these in pinning vortices.

  17. Structural alloys for high field superconducting magnets

    SciTech Connect

    Morris, J.W. Jr.

    1985-08-01

    Research toward structural alloys for use in high field superconducting magnets is international in scope, and has three principal objectives: the selection or development of suitable structural alloys for the magnet support structure, the identification of mechanical phenomena and failure modes that may influence service behavior, and the design of suitable testing procedures to provide engineering design data. This paper reviews recent progress toward the first two of these objectives. The structural alloy needs depend on the magnet design and superconductor type and differ between magnets that use monolithic and those that employ force-cooled or ICCS conductors. In the former case the central requirement is for high strength, high toughness, weldable alloys that are used in thick sections for the magnet case. In the latter case the need is for high strength, high toughness alloys that are used in thin welded sections for the conductor conduit. There is productive current research on both alloy types. The service behavior of these alloys is influenced by mechanical phenomena that are peculiar to the magnet environment, including cryogenic fatigue, magnetic effects, and cryogenic creep. The design of appropriate mechanical tests is complicated by the need for testing at 4/sup 0/K and by rate effects associated with adiabatic heating during the tests. 46 refs.

  18. AuBa 2(Y 1- x, Ca x)Cu 2O 7: a new superconducting gold cuprate with Tc above 80 K

    NASA Astrophysics Data System (ADS)

    Bordet, P.; LeFloch, S.; Chaillout, C.; Duc, F.; Gorius, M. F.; Perroux, M.; Capponi, J. J.; Toulemonde, P.; Tholence, J. L.

    1997-02-01

    We have synthesised by the high pressure-high temperature technique a new layered gold cuprate of chemical formula AuBa 2(Y 1- x,Ca x)Cu 2O 7 (0 ≤ × ≤ 0.4) (hereafter denoted as Au-1212). The structural properties of this compound are investigated by means of electron microscopy and powder X-ray diffraction. The average structure (orthorhombic Pmmm, a = 3.8298(5) Å, b = 3.8420(5) Å, c = 12.111(1) Å for nominal composition x = 0.4) is very similar to that of YBa 2Cu 3O 7, with Au 3+ cations in square planar coordination sharing corners to form chains running along the b axis. Electron microscopy reveals the presence of a superstructure with double b parameter, which is attributed to a long range ordered zig-zag conformation of the square chains. For x = 0, the formal copper valence is 2 + and the compound is insulating. Doping of the conducting CuO 2 planes is achieved by the partial substitution of yttrium by calcium, up to x ≈ 0.4. Upon substitution, the compound becomes superconducting with a maximum Tc at ∼ 82 K for x ≈ 0.4.

  19. Damping in high-temperature superconducting levitation systems

    DOEpatents

    Hull, John R.

    2009-12-15

    Methods and apparatuses for improved damping in high-temperature superconducting levitation systems are disclosed. A superconducting element (e.g., a stator) generating a magnetic field and a magnet (e.g. a rotor) supported by the magnetic field are provided such that the superconducting element is supported relative to a ground state with damped motion substantially perpendicular to the support of the magnetic field on the magnet. Applying this, a cryostat housing the superconducting bearing may be coupled to the ground state with high damping but low radial stiffness, such that its resonant frequency is less than that of the superconducting bearing. The damping of the cryostat may be substantially transferred to the levitated magnetic rotor, thus, providing damping without affecting the rotational loss, as can be derived applying coupled harmonic oscillator theory in rotor dynamics. Thus, damping can be provided to a levitated object, without substantially affecting the rotational loss.

  20. High Performance High-Tc Superconducting Wires

    SciTech Connect

    Kang, Sukill; Goyal, Amit; Li, Jing; Gapud, Albert Agcaoili; Martin, Patrick M; Heatherly Jr, Lee; Thompson, James R; Christen, David K; List III, Frederick Alyious; Paranthaman, Mariappan Parans; Lee, Dominic F

    2006-01-01

    We demonstrated short segments of a superconducting wire that meets or exceeds performance requirements for many large-scale applications of high-temperature superconducting materials, especially those requiring a high supercurrent and/or a high engineering critical current density in applied magnetic fields. The performance requirements for these varied applications were met in 3-micrometer-thick YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} films epitaxially grown via pulsed laser ablation on rolling assisted biaxially textured substrates. Enhancements of the critical current in self-field as well as excellent retention of this current in high applied magnetic fields were achieved in the thick films via incorporation of a periodic array of extended columnar defects, composed of self-aligned nanodots of nonsuperconducting material extending through the entire thickness of the film. These columnar defects are highly effective in pinning the superconducting vortices or flux lines, thereby resulting in the substantially enhanced performance of this wire.

  1. Preparation of high T(c) Tl-Ba-Ca-Cu-O thin films by pulsed laser evaporation and Tl2O3 vapor processing

    NASA Technical Reports Server (NTRS)

    Johs, B.; Thompson, D.; Ianno, N. J.; Woollam, John A.; Liou, S. H.

    1989-01-01

    Tl-Ba-Ca-Cu-O superconducting thin films with zero-resistance temperatures up to 115 K have been prepared using a Tl2O3 vapor process on Ba-Ca-Cu-O precursor thin films. The Ba-Ca-Cu-O thin films were made by laser deposition on Y-stabilized ZrO2 substrates. This technique minimizes problems caused by the toxicity of Tl2O3, and its subsequent decomposition to the volatile and toxic Tl2O upon heating. Therefore, it may have practical application in the fabrication of high T(c) Tl-Ba-Ca-Cu-O superconducting thin-film devices.

  2. Design of high-T{sub c} superconducting bolometers for a far infrared imaging array

    SciTech Connect

    Verghese, S.; Richards, P.L.; Fork, D.K.; Char, K.; Geballe, T.H.

    1992-08-01

    The design of high-{Tc} superconducting bolometers for use in a far infrared imaging array from wavelengths 30--100{mu}m is discussed. Measurements of the voltage noise in thin films of YBa{sub 2}CU{sub 3}O{sub 7-{var_sigma}} on yttria-stabilized zirconia buffer layers on silicon substrates are used to make performance estimates. Useful opportunities exist for imaging and spectroscopy with bolometer arrays made on micro-machined silicon membranes. A circuit on each pixel which performs some signal integration can improve the sensitivity of large two-dimensional arrays of bolometers which use multiplexed readout amplifiers.

  3. Modifications of Superconducting Properties of Niobium Caused by Nitrogen Doping Recipes for High Q Cavities

    SciTech Connect

    Vostrikov, Alexander; Checchin, Mattia; Grassellino, Anna; Kim, Young-Kee; Romanenko, Alexander

    2015-06-01

    A study is presented on the superconducting properties of niobium used for the fabrication of the SRF cavities after treating by recently discovered nitrogen doping methods. Cylindrical niobium samples have been subjected to the standard surface treatments applied to the cavities (electro-polishing, l 20°C bake) and compared with samples treated by additional nitrogen doping recipes routinely used to reach ultra-high quality factor values (>3· 1010 at 2 K, 16 MV/m). The DC magnetization curves and the complex magnetic AC susceptibility have been measured. Evidence for the lowered field of first flux penetration after nitrogen doping is found suggesting a correlation with the lowered quench fields. Superconducting critical temperatures Tc = 9.25 K are found to be in agreement with previous measurements, and no strong effect on the critical surface field (Bd) from nitrogen doping was found.

  4. Method and apparatus for connecting high voltage leads to a high temperature super-conducting transformer

    DOEpatents

    Golner, Thomas M.; Mehta, Shirish P.

    2005-07-26

    A method and apparatus for connecting high voltage leads to a super-conducting transformer is provided that includes a first super-conducting coil set, a second super-conducting coil set, and a third super-conducting coil set. The first, second and third super-conducting coil sets are connected via an insulated interconnect system that includes insulated conductors and insulated connectors that are utilized to connect the first, second, and third super-conducting coil sets to the high voltage leads.

  5. Architecture for high critical current superconducting tapes

    DOEpatents

    Jia, Quanxi; Foltyn, Stephen R.

    2002-01-01

    Improvements in critical current capacity for superconducting film structures are disclosed and include the use of, e.g., multilayer YBCO structures where individual YBCO layers are separated by a layer of an insulating material such as CeO.sub.2 and the like, a layer of a conducting material such as strontium ruthenium oxide and the like or by a second superconducting material such as SmBCO and the like.

  6. High- and Mid-temperature Superconducting Sensors for Far IR/Sub-mm Applications in Space

    NASA Technical Reports Server (NTRS)

    Lakew, Brook; Brasunas, J. C.

    2004-01-01

    In this review paper an overview of the potential applications of high Tc (approx. 90 K) superconductors (HTS) and mid-Tc (approx. 39 K) superconductors (MTS) thin films in far IR/Sub-mm thermal detectors is presented. HTSs (YBCO, GdBCO etc.) were discovered in the late 80s while superconductivity in MgB2, an MTS, was discovered in 2001. The sharp transition in transport properties of HTS has allowed the fabrication of composite infrared thermal detectors (bolometers) with better figures of merit than thermopile detectors - thermopiles are currently on board the CIRS instrument on the Cassini mission to Saturn. The potential for developing even more sensitive sensors for IR/Sub-mm applications using MgB2 thin films is assessed. Current MgB2 thin film deposition techniques and film quality are reviewed.

  7. Low-Tc direct current superconducting quantum interference device magnetometer-based 36-channel magnetocardiography system in a magnetically shielded room

    NASA Astrophysics Data System (ADS)

    Qiu, Yang; Li, Hua; Zhang, Shu-Lin; Wang, Yong-Liang; Kong, Xiang-Yan; Zhang, Chao-Xiang; Zhang, Yong-Sheng; Xu, Xiao-Feng; Yang, Kang; Xie, Xiao-Ming

    2015-07-01

    We constructed a 36-channel magnetocardiography (MCG) system based on low-Tc direct current (DC) superconducting quantum interference device (SQUID) magnetometers operated inside a magnetically shielded room (MSR). Weakly damped SQUID magnetometers with large Steward-McCumber parameter βc (βc ≈ 5), which could directly connect to the operational amplifier without any additional feedback circuit, were used to simplify the readout electronics. With a flux-to-voltage transfer coefficient ∂ V/∂ Φ larger than 420 μV/Φ 0, the SQUID magnetometers had a white noise level of about 5.5 fT·Hz-1/2 when operated in MSR. 36 sensing magnetometers and 15 reference magnetometers were employed to realize software gradiometer configurations. The coverage area of the 36 sensing magnetometers is 210×210 mm2. MCG measurements with a high signal-to-noise ratio of 40 dB were done successfully using the developed system. Project supported by “One Hundred Persons Project” of the Chinese Academy of Sciences and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB04020200).

  8. Apparatus for continuous manufacture of high temperature superconducting wires from molten superconducting oxides

    SciTech Connect

    Hed, A.Z.

    1991-09-10

    This patent describes an apparatus for making a composite high-temperature superconducting wire, comprising a refractory core having a melting point above a melt temperature of a superconducting oxide ceramic having a critical temperature T{sub c} above 23{degrees} K and a layer of the superconducting oxide ceramic on the core. It comprises means forming a controlled-atmosphere chamber; a vessel received in the chamber and formed with an opening at a bottom thereof, the vessel receiving an annular mass of the superconducting oxide ceramic in solid form surrounding a passage traversing the mass and extending upwardly from the opening; means for forming a melt of the superconductive oxide ceramic in a small pool in the mass above the passage and at a temperature slightly above a melting point of the superconducting oxide ceramic; means for drawing the refractory core through the opening, the passage and the melt in succession and depositing the melt on the core, the pool being in contact only with the mass, the core and the atmosphere; means in the chamber above the pool for cooling the melt deposited on the core by radiation and convection.

  9. Structural and magnetic phase diagram of CeFeAsO(1- x)F(x) and its relation to high-temperature superconductivity.

    PubMed

    Zhao, Jun; Huang, Q; de la Cruz, Clarina; Li, Shiliang; Lynn, J W; Chen, Y; Green, M A; Chen, G F; Li, G; Li, Z; Luo, J L; Wang, N L; Dai, Pengcheng

    2008-12-01

    Recently, high-transition-temperature (high-Tc) superconductivity was discovered in the iron pnictide RFeAsO(1-x)F(x) (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO(1-x)F(x) as the system is tuned from a semimetal to a high-Tc superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x=0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x>0.06, resulting in an electronic phase diagram remarkably similar to that of the high-Tc copper oxides. Comparison of the structural evolution of CeFeAsO(1-x)F(x) with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-Tc superconductivity in these Fe pnictides.

  10. Towards a complete Fermi surface in underdoped high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    The discovery of magnetic quantum oscillations in underdoped high Tc superconductors raised many questions, and initiated a quest to understand the origin of the Fermi surface the like of which had not been seen since the very first discovery of quantum oscillations in elemental bismuth. While studies of the Fermi surface of materials are today mostly assisted by computer codes for calculating the electronic band structure, this was not the case in the underdoped high Tc materials. The Fermi surface was shown to reconstructed into small pockets, yet there was no hint of a viable order parameter. Crucial clues to understanding the origin of the Fermi surface were provided by the small value of the observed Fermi surface cross-section, the negative Hall coefficient and the small electronic heat capacity at high magnetic fields. We also know that the magnetic fields were likely to be too weak to destroy the pseudogap and that vortex pinning effects could be seen to persist to high magnetic fields at low temperatures. I will show that the Fermi surface that appears to fit best with the experimental observations is a small electron pocket formed by connecting the nodal `Fermi arcs' seen in photoemission experiments, corresponding to a density-wave state with two different orthogonal ordering vectors. The existence of such order has subsequently been detected by x-ray scattering experiments, thereby strengthening the case for charge ordering being responsible for reconstructing the Fermi surface. I will discuss new efforts to understand the relationship between the charge ordering and the pseudogap state, discussing the fate of the quasiparticles in the antinodal region and the dimensionality of the Fermi surface. The author acknowledges contributions from Suchitra Sebastian, Brad Ramshaw, Mun Chan, Yu-Te Hsu, Mate Hartstein, Gil Lonzarich, Beng Tan, Arkady Shekhter, Fedor Balakirev, Ross McDonald, Jon Betts, Moaz Altarawneh, Zengwei Zhu, Chuck Mielke, James Day, Doug

  11. Hidden Fermi liquid: Self-consistent theory for the normal state of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Casey, Philip A.

    The anomalous "strange metal" properties of the normal, non-superconducting state of the high-Tc cuprate superconductors have been extensively studied for over two decades. The resistivity is robustly T-linear at high temperatures, while at low T it appears to maintain linearity near optimal doping and is T2 at higher doping. The inverse Hall angle is strictly T2 and hence has a distinct scattering lifetime from the resistivity. The transport scattering lifetime is highly anisotropic as directly measured by angle-dependent magnetoresistance (ADMR) and indirectly in more traditional transport experiments. The IR conductivity exhibits a non-integer power-law in frequency, which we take as a defining characteristic of the "strange metal". A phenomenological theory of the transport and spectroscopic properties at a self-consistent and predictive level has been much sought after, yet elusive. Hidden Fermi liquid theory (HFL) explicitly accounts for the effects of Gutzwiller projection in the t-J Hamiltonian, widely believed to contain the essential physics of the high-Tc superconductors. We show this theory to be the first self-consistent description for the normal state of the cuprates based on transparent, fundamental assumptions. Our well-defined formalism also serves as a guide for further experimental confirmation. Chapter 1 reviews the "strange metal" properties and the relevant aspects of competing models. Chapter 2 presents the theoretical foundations of the formalism. Chapters 3 and 4 derive expressions for the entire normal state relating many of the properties, for example: angle-resolved photoemission, IR conductivity, resistivity, Hall angle, and by generalizing the formalism to include the Fermi surface topology---ADMR. Self-consistency is demonstrated with experimental comparisons, including the most recent laser-ARPES and ADMR. Chapter 5 discusses entropy transport, as in the thermal conductivity, thermal Hall conductivity, and consequent metrics of non

  12. High-temperature superconductivity: Electron mirages in an iron salt

    NASA Astrophysics Data System (ADS)

    Zaanen, Jan

    2014-11-01

    The detection of unusual 'mirage' energy bands in photoemission spectra of single-atom layers of iron selenide reveals the probable cause of high-temperature superconductivity in these artificial structures. See Letter p.245

  13. Design considerations for high-current superconducting ion linacs

    SciTech Connect

    Delayen, J.R.; Bohn, C.L.; Micklich, B.J.; Roche, C.T.; Sagalovsky, L.

    1993-08-01

    Superconducting linacs may be a viable option for high-current applications such as fusion materials irradiation testing, spallation neutron source, transmutation of radioactive waste, tritium production, and energy production. These linacs must run reliably for many years and allow easy routine maintenance. Superconducting cavities operate efficiently with high cw gradients, properties which help to reduce operating and capital costs, respectively. However, cost-effectiveness is not the sole consideration in these applications. For example, beam impingement must be essentially eliminated to prevent unsafe radioactivation of the accelerating structures, and thus large apertures are needed through which to pass the beam. Because of their high efficiency, superconducting cavities can be designed with very large bore apertures, thereby reducing the effect of beam impingement. Key aspects of high-current cw superconducting linac designs are explored in this context.

  14. High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides

    PubMed Central

    Charnukha, A.; Evtushinsky, D. V.; Matt, C. E.; Xu, N.; Shi, M.; Büchner, B.; Zhigadlo, N. D.; Batlogg, B.; Borisenko, S. V.

    2015-01-01

    In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials. PMID:26678565

  15. Strength and flexibility of bulk high-{Tc} superconductors

    SciTech Connect

    Goretta, K.C.; Jiang, M.; Kupperman, D.S.; Lanagan, M.T.; Singh, J.P.; Vasanthamohan, N.; Hinks, D.G.; Mitchell, J.F.; Richardson, J.W. Jr.

    1996-08-01

    Strength, fracture toughness, and elastic modulus data have been gathered for bulk high-temperature superconductors, commercial 99.9% Ag, and a 1.2 at.% Mg/Ag alloy. These data have been used to calculate fracture strains for bulk conductors. The calculations indicate that the superconducting cores of clad tapes should begin to fracture at strains below 0.2%. In addition, residual strains in Ag-clad (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} tapes have been measured by neutron diffraction. An explanation is offered for why many tapes appear to be able to tolerate large strains before exhibiting a reduction in current transport.

  16. Design of a Cryogen Free Cryo-flipper using a High Tc YBCO Film

    NASA Astrophysics Data System (ADS)

    Parnell, S. R.; Kaiser, H.; Washington, A. L.; Li, F.; Wang, T.; Baxter, D. V.; Pynn, R.

    It is well-known that the Meissner effect in superconducting materials can be used to provide a well-defined non- adiabatic magnetic field transition that can be utilised to produce an efficient white beam neutron spin flipper. Typically these devices utilise niobium and hence require continuous use of liquid helium in order to maintain the device tem- perature. The use of high Tc materials removes the need for cryogens and has been explored previously and shown to provide efficient flipping of the neutron spin. Improvements in thin high Tc films over the past few years make these materials even more attractive. Here we present a design using a 350-nm-thick YBCO film capped with 100 nm of gold on a 78 x 100 x 0.5 mm sapphire substrate (Theva, Germany). The apparatus is compact (200 mm in length along the neutron beam), consisting of an oxygen-free high-conductivity copper frame, which holds the YBCO film and is mounted to the cold finger of a closed-cycle refrigerator. The part of the vacuum chamber, where the YBCO film is located, is ≈ 50 mm wide, which allows us to minimise the distance from the film to the external magnets. This distance is 26 mm on each side. The details of the guide field design are also discussed. In this design, the maximum neutron beam size that can be used is 40 × 40 mm2 and we can easily switch from a vertical to a horizontal guide field on either side of the YBCO film.

  17. Buffer layers for high-Tc thin films on sapphire

    NASA Technical Reports Server (NTRS)

    Wu, X. D.; Foltyn, S. R.; Muenchausen, R. E.; Cooke, D. W.; Pique, A.; Kalokitis, D.; Pendrick, V.; Belohoubek, E.

    1992-01-01

    Buffer layers of various oxides including CeO2 and yttrium-stabilized zirconia (YSZ) have been deposited on R-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa2Cu3O(7-delta) (YBCO) thin films. An ion beam channeling minimum yield of about 3 percent was obtained in the CeO2 layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO2 was found to be the best one for YBCO thin films on R-plane sapphire. High Tc and Jc were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were about 4 mOmega at 77 K and 25 GHz.

  18. Modeling of tunneling spectroscopy in high-TC superconductors

    NASA Astrophysics Data System (ADS)

    Shukrinov, Yu. M.; Namiranian, A.; Najafi, A.

    2001-01-01

    The tunneling density of states of high-Tc superconductors is calculated taking into account the tight-binding band structure, group velocity, and tunneling directionality for s-wave and d-wave gap symmetry. The characteristic density of states has asymmetry of the quasiparticle peaks, flat s-wave and cusplike d-wave subgap behavior, and an asymmetric background. It is assumed that the underlying asymmetry of the conductance peaks is primarily due to the features of the quasiparticle energy spectrum and that the d-wave symmetry enhances the degree of asymmetry of the peaks. Increasing the lifetime broadening factor changes the degree of asymmetry of the tunneling conductance peaks and leads to confluence of the quasiparticle and van Hove singularity peaks.

  19. Recent Progress in the Superconductivity Research Field

    NASA Astrophysics Data System (ADS)

    Ichinose, Ataru

    Major developments in the research field of superconductivity have been achieved in 2008. Since the discovery of high-Tc superconductors, their practical application has been studied by many researchers. Coated conductors consisting of an YBa2Cu3Oy superconducting layer deposited on metal tapes buffered oxide layers were developed in the NEDO project between FY2003 and FY2007. These technologies for coated conductors are expected to be applicable to electrical power equipment. A new NEDO project that started in FY2008 is focusing on the development of superconducting electric power equipment such as power cables, superconducting magnetic energy storage devices (SMES) and transformers. Furthermore, a new family of high-Tc superconductors, Fe-As-O-based superconductors, has been discovered. The highest reported critical temperature, Tc, has rapidly increased owing to the considerable effort of many researchers. A new social environment based on superconductivity technology might indeed be realized in the near future.

  20. Microwave properties of high transition temperature superconducting thin films

    NASA Technical Reports Server (NTRS)

    Gordon, W. L.

    1991-01-01

    Extensive studies of the interaction of microwaves with YBa2Cu3O(7-delta), Bi-based, and Tl-based superconducting thin films deposited in several microwave substrates were performed. The data were obtained by measuring the microwave power transmitted through the film in the normal and the superconducting state and by resonant cavity techniques. The main motives were to qualify and understand the physical parameters such as the magnetic penetration depth, the complex conductivity, and the surface impedance, of high temperature superconducting (HTS) materials at microwave frequencies. Based on these parameters, the suitability of these HTS thin films is discussed for microwave applications.

  1. Environmental considerations for application of high Tc superconductors in space

    NASA Technical Reports Server (NTRS)

    Carlberg, I. A.; Kelliher, W. C.; Wise, S. A.; Hooker, M. W.; Buckley, J. D.

    1993-01-01

    The impact of the environmental factors on the performance of the superconductive devices during spaceflight missions is reviewed. Specific factors typical of spaceflight are addressed to evaluate superconductive devices for space-based applications including preflight storage, radiation, vibration, and thermal cycling.

  2. A review of basic phenomena and techniques for sputter-deposition of high temperature superconducting films

    SciTech Connect

    Auciello, O. North Carolina State Univ., Raleigh, NC . Dept. of Materials Science and Engineering); Ameen, M.S.; Kingon, A.I.; Lichtenwalner, D.J. . Dept. of Materials Science and Engineering); Krauss, A.R. )

    1990-01-01

    The processes involved in plasma and ion beam sputter-deposition of high temperature superconducting thin films are critically reviewed. Recent advances in the development of these techniques are discussed in relation to basic physical phenomena, specific to each technique, which must be understood before high quality films can be produced. Control of film composition is a major issue in sputter-deposition of multicomponent materials. Low temperature processing of films is a common goal for each technique, particularly in relation to integrating high temperature superconducting films with the current microelectronics technology. It has been understood for some time that for Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} deposition, the most intensely studied high-{Tc} compound, incorporation of sufficient oxygen into the film during deposition is necessary to produce as-deposited superconducting films at relatively substrate temperatures. Recent results have shown that with the use of suitable buffer layers, high quality Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} sputtered films can be obtained on Si substrates without the need for post-deposition anneal processing. This review is mainly focussed on issues related to sputter-deposition of Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} thin films, although representative results concerning the bismuth and thallium based compounds are included. 143 refs., 11 figs.

  3. A microscopic two-band model for the electron-hole asymmetry in high-Tc superconductors and reentering behavior

    NASA Astrophysics Data System (ADS)

    Bru, J.-B.; Pedra, W. de Siqueira; Dömel, A.-S.

    2011-07-01

    To our knowledge there is no rigorously analyzed microscopic model explaining the electron-hole asymmetry of the critical temperature seen in high-Tc cuprate superconductors - at least no model not breaking artificially this symmetry. We present here a microscopic two-band model based on the structure of energetic levels of holes in CuO2 conducting layers of cuprates. In particular, our Hamiltonian does not contain ad hoc terms implying - explicitly - different masses for electrons and holes. We prove that two energetically near-lying interacting bands can explain the electron-hole asymmetry. Indeed, we rigorously analyze the phase diagram of the model and show that the critical temperatures for fermion densities below half-filling can manifest a very different behavior as compared to the case of densities above half-filling. This fact results from the inter-band interaction and intra-band Coulomb repulsion in interplay with thermal fluctuations between two energetic levels. So, if the energy difference between bands is too big (as compared to the energy scale defined by the critical temperatures of superconductivity) then the asymmetry disappears. Moreover, the critical temperature turns out to be a non-monotonic function of the fermion density and the phase diagram of our model shows "superconducting domes" as in high-Tc cuprate superconductors. This explains why the maximal critical temperature is attained at donor densities away from the maximal one. Outside the superconducting phase and for fermion densities near half-filling the thermodynamics governed by our Hamiltonian corresponds, as in real high-Tc materials, to a Mott-insulating phase. The nature of the inter-band interaction can be electrostatic (screened Coulomb interaction), magnetic (for instance, some Heisenberg-type one-site spin-spin interaction), or a mixture of both. If the inter-band interaction is predominately magnetic then - additionally to the electron-hole asymmetry - we observe a

  4. Mapping the Electronic Structure of Each Ingredient Oxide Layer of High-Tc Cuprate Superconductor Bi2 Sr2 CaCu2 O8 +δ

    NASA Astrophysics Data System (ADS)

    Lv, Yan-Feng; Wang, Wen-Lin; Peng, Jun-Ping; Ding, Hao; Wang, Yang; Wang, Lili; He, Ke; Ji, Shuai-Hua; Zhong, Ruidan; Schneeloch, John; Gu, Gen-Da; Song, Can-Li; Ma, Xu-Cun; Xue, Qi-Kun

    2015-12-01

    Understanding the mechanism of high transition temperature (Tc) superconductivity in cuprates has been hindered by the apparent complexity of their multilayered crystal structure. Using a cryogenic scanning tunneling microscopy (STM), we report on layer-by-layer probing of the electronic structures of all ingredient planes (BiO, SrO, CuO2 ) of Bi2 Sr2 CaCu2 O8 +δ superconductor prepared by argon-ion bombardment and annealing technique. We show that the well-known pseudogap (PG) feature observed by STM is inherently a property of the BiO planes and thus irrelevant directly to Cooper pairing. The SrO planes exhibit an unexpected van Hove singularity near the Fermi level, while the CuO2 planes are exclusively characterized by a smaller gap inside the PG. The small gap becomes invisible near Tc, which we identify as the superconducting gap. The above results constitute severe constraints on any microscopic model for high Tc superconductivity in cuprates.

  5. Evolution of High-Temperature Superconductivity from a Low-T_{c} Phase Tuned by Carrier Concentration in FeSe Thin Flakes.

    PubMed

    Lei, B; Cui, J H; Xiang, Z J; Shang, C; Wang, N Z; Ye, G J; Luo, X G; Wu, T; Sun, Z; Chen, X H

    2016-02-19

    We report the evolution of superconductivity in an FeSe thin flake with systematically regulated carrier concentrations by the liquid-gating technique. With electron doping tuned by the gate voltage, high-temperature superconductivity with an onset at 48 K can be achieved in an FeSe thin flake with T_{c} less than 10 K. This is the first time such high temperature superconductivity in FeSe is achieved without either an epitaxial interface or external pressure, and it definitely proves that the simple electron-doping process is able to induce high-temperature superconductivity with T_{c}^{onset} as high as 48 K in bulk FeSe. Intriguingly, our data also indicate that the superconductivity is suddenly changed from a low-T_{c} phase to a high-T_{c} phase with a Lifshitz transition at a certain carrier concentration. These results help to build a unified picture to understand the high-temperature superconductivity among all FeSe-derived superconductors and shed light on the further pursuit of a higher T_{c} in these materials.

  6. Resource Letter Scy-3: Superconductivity

    NASA Astrophysics Data System (ADS)

    Butch, N. P.; de Andrade, M. C.; Maple, M. B.

    2008-02-01

    This Resource Letter provides a guide to the literature on superconductivity. Since the last Resource Letter on superconductivity, Scy-2, was published in 1970, there have been dramatic advances in our basic understanding of superconductivity, discovery of new superconducting materials, and improved technological exploitation of superconductors. We review basic phenomenology, followed by concise descriptions of several main classes of superconductors recognized today. Journal articles and books are cited for the following topics: Conventional superconductors, paramagnetic impurities in superconductors, magnetically ordered superconductors, heavy fermion superconductors, high Tc superconductors, organic superconductors, applications of superconductivity, and laboratory demonstrations of superconductivity. Owing to the large volume of available literature on superconductivity, the journal articles and books we discuss constitute good starting points for further exploration of particular topics.

  7. Van Hove singularities and spectral smearing in high-temperature superconducting H3S

    NASA Astrophysics Data System (ADS)

    Quan, Yundi; Pickett, Warren E.

    2016-03-01

    The superconducting phase of hydrogen sulfide at Tc=200 K observed by Drozdov and collaborators at pressures around 200 GPa is simple bcc I m 3 ¯m H3S from a combination of theoretical and experimental confirmation. The various "extremes" that are involved—high pressure implying extreme reduction of volume, extremely high H phonon energy scale around 1400 K, extremely high temperature for a superconductor—necessitates a close look at new issues raised by these characteristics in relation to high Tc itself. First principles methods are applied to analyze the H3S electronic structure, beginning with the effect of sulfur and then focusing on the origin and implications of the two van Hove singularities (vHs) providing an impressive peak in the density of states near the Fermi energy. Implications arising from strong coupling Migdal-Eliashberg theory are studied. It becomes evident that electron spectral density smearing due to virtual phonon emission and absorption must be accounted for in a correct understanding of this unusual material and to obtain accurate theoretical predictions. Means for increasing Tc in H3S -like materials are noted.

  8. Magnetic Measurements of Superconducting KxFe2-ySe2 Single Crystals Under High Pressure

    NASA Astrophysics Data System (ADS)

    Miyoshi, K.; Kondo, M.; Morishita, K.; Takeuchi, J.

    Measurements of DC magnetization for single crystal specimens of KxFe2-ySe2 both under hydrostatic and uniaxial pressure have been performed using liquid Ar and NaCl as pressure transmitting media to generate hydrostatic and nearly uniaxial pressure, respectively. It has been found that TC is pressure independent below 2 GPa but decreases rapidly above 3 GPa under hydrostatic pressure, indicating that the bulk superconductivity disappears above 6 GPa. We have also observed a very weak diamagnetic response below ∽10 K for P≥6 GPa, suggesting that non-bulk superconductivity survives even under high pressure. On the other hand, TC is found to decrease rapidly above 1.5 GPa by the application of uniaxial pressure along c-axis, indicating that the lattice compression along c-axis suppresses the superconductivity more effectively. This suggests that c-axis lattice constant is an important factor to determine TC in KxFe2-ySe2.

  9. Effect of high pressure on the phonon spectra and superconductivity in ZrN and HfN

    NASA Astrophysics Data System (ADS)

    Maksimov, E. G.; Wang, S. Q.; Magnitskaya, M. V.; Ebert, S. V.

    2009-07-01

    We report ab initio calculations of the phonon spectra, the electron-phonon interaction, and the superconducting transition temperature Tc for zirconium and hafnium nitrides under high pressure. The calculated phonon densities of states are qualitatively similar to Raman spectra measured at various pressures up to 32 GPa. The critical temperature Tc is determined by directly solving the Eliashberg equation using our calculated Eliashberg function. The pressure derivative of Tc for ZrN is in good agreement with the low pressure experimental result. In the case of HfN, for which there are no relevant experimental data, the available phenomenological estimate of Tc is significantly different from our first-principles prediction and we discuss the reasons for such a discrepancy. The calculated dependence Tc(p) becomes nonlinear at p>10 GPa. We show that in these compounds a decrease in Tc upon compression mainly occurs because of a decrease in the electron-phonon coupling constant λ, which is, in turn, due to an increase in the phonon frequencies.

  10. High quality superconducting NbN thin films on GaAs

    NASA Astrophysics Data System (ADS)

    Marsili, Francesco; Gaggero, Alessandro; Li, Lianhe H.; Surrente, Alessandro; Leoni, Roberto; Lévy, Francis; Fiore, Andrea

    2009-09-01

    A very promising way to increase the detection efficiency of nanowire superconducting single-photon detectors (SSPDs) consists in integrating them with advanced optical structures such as distributed Bragg reflectors (DBRs) and optical waveguides. This requires transferring the challenging SSPD technology from the usual substrates, i.e. sapphire and MgO, to an optical substrate like GaAs, on which DBRs and waveguides can be easily obtained. Therefore, we optimized the deposition process of few-nm thick superconducting NbN films on GaAs and AlAs/GaAs-based DBRs at low temperatures (substrate temperature TS = 400 °C), in order to prevent As evaporation. NbN films ranging from 150 to 3 nm in thickness were then deposited on single-crystal MgO, GaAs, MgO-buffered GaAs and DBRs by current-controlled DC magnetron sputtering (planar, circular, balanced configuration) of Nb in an Ar+N2 plasma. 5.5 nm thick NbN films on GaAs exhibit TC = 10.7 K, ΔTC = 1.1 K and RRR = 0.7. The growth of such high quality thin NbN films on GaAs and DBRs has never been reported before.

  11. A Superconducting transformer system for high current cable testing

    SciTech Connect

    Godeke, A.; Dietderich, D. R.; Joseph, J. M.; Lizarazo, J.; Prestemon, S. O.; Miller, G.; Weijers, H. W.

    2010-02-15

    This article describes the development of a direct-current (dc) superconducting transformer system for the high current test of superconducting cables. The transformer consists of a core-free 10 464 turn primary solenoid which is enclosed by a 6.5 turn secondary. The transformer is designed to deliver a 50 kA dc secondary current at a dc primary current of about 50 A. The secondary current is measured inductively using two toroidal-wound Rogowski coils. The Rogowski coil signal is digitally integrated, resulting in a voltage signal that is proportional to the secondary current. This voltage signal is used to control the secondary current using a feedback loop which automatically compensates for resistive losses in the splices to the superconducting cable samples that are connected to the secondary. The system has been commissioned up to 28 kA secondary current. The reproducibility in the secondary current measurement is better than 0.05% for the relevant current range up to 25 kA. The drift in the secondary current, which results from drift in the digital integrator, is estimated to be below 0.5 A/min. The system's performance is further demonstrated through a voltage-current measurement on a superconducting cable sample at 11 T background magnetic field. The superconducting transformer system enables fast, high resolution, economic, and safe tests of the critical current of superconducting cable samples.

  12. Processing of superconductive materials and high frequency

    SciTech Connect

    Smith, J.L.

    1987-01-01

    We do not know yet if superconductivity will become useful without refrigeration. Now, the superconductors are so different from copper that it is difficult to imagine replacing copper with such a brittle material. Superconductors conduct dc with no loss, ac with small losses, and microwaves in co-axial lines with almost no loss and with no dispersion from dc to the highest frequencies. They will probably allow us to close the gap between radio frequency and infrared optical transmission. Clearly your industry should know some things about where superconductivity may lead us and must consider whether the greater risk is to develop them or to let others try it. There are no easy answers yet.

  13. High temperature superconductive flux gate magnetometer

    SciTech Connect

    Gershenson, M. )

    1991-03-01

    This paper proposes a different type of HTS superconducting magnetometer based on the non-linear magnetic behavior of bulk HTS materials. The device design is based on the generation of second harmonics which arise as a result of non-linear magnetization observed in Type-II superconductors. Even harmonics are generated from the non-linear interaction of an ac excitation signal with an external DC magnetic field which acts as a bias signal.

  14. Melt processing of bulk high Tc superconductors and their application

    NASA Astrophysics Data System (ADS)

    Murakami, M.; Oyama, T.; Fujimoto, H.; Gotoh, S.; Yamaguchi, K.

    1991-03-01

    The authors report a melt-powder-melt-growth (MPMG) process which results in high Jc for bulk Y-Ba-Cu-O superconductors. The Y-Ba-Cu-O pellets or powders are melt quenched. The quenched plates are crushed into powder and mixed well. The powder is then compacted into desired shapes, remelted, and slowly cooled in a thermal gradient. When the starting composition is changed from the 1:2:3 stoichiometry toward the Y2BaCuO5(211) rich region, the 211 inclusions can be dispersed in the YBa2Cu3O(x) matrix, which contributes to increases in both flux pinning force and fracture toughness. A Jc value exceeding 3 x 108 A/sq m has been achieved at 77 K and 1 T. Another attractive feature of the MPMG process is that other components such as fine Ag powders can be added during solid-state mixing. Fine dispersion of Ag particles can effectively reduce the amount of cracking. MPMG-processed Y-Ba-Cu-O with Ag doping can levitate a mass of 3-kg at 1-mm height using a repulsive force against a 0.4-T magnet. A noncontacting rotation device such as a magnetic bearing can be made utilizing bulk high-Jc materials. A superconducting permanent magnet is also a promising candidate for future application. MPMG-processed Y-Ba-Cu-O can generate 0.25 T at 77 K.

  15. High critical currents in iron-clad superconducting MgB2 wires.

    PubMed

    Jin, S; Mavoori, H; Bower, C; van Dover, R B

    2001-05-31

    Technically useful bulk superconductors must have high transport critical current densities, Jc, at operating temperatures. They also require a normal metal cladding to provide parallel electrical conduction, thermal stabilization, and mechanical protection of the generally brittle superconductor cores. The recent discovery of superconductivity at 39 K in magnesium diboride (MgB2) presents a new possibility for significant bulk applications, but many critical issues relevant for practical wires remain unresolved. In particular, MgB2 is mechanically hard and brittle and therefore not amenable to drawing into the desired fine-wire geometry. Even the synthesis of moderately dense, bulk MgB2 attaining 39 K superconductivity is a challenge because of the volatility and reactivity of magnesium. Here we report the successful fabrication of dense, metal-clad superconducting MgB2 wires, and demonstrate a transport Jc in excess of 85,000 A cm-2 at 4.2 K. Our iron-clad fabrication technique takes place at ambient pressure, yet produces dense MgB2 with little loss of stoichiometry. While searching for a suitable cladding material, we found that other materials dramatically reduced the critical current, showing that although MgB2 itself does not show the 'weak-link' effect characteristic of the high-Tc superconductors, contamination does result in weak-link-like behaviour.

  16. High-pressure synthesis of pure and doped superconducting MgB2 compounds

    NASA Astrophysics Data System (ADS)

    Toulemonde, P.; Musolino, N.; Flükiger, R.

    2003-02-01

    Superconducting properties of bulk, dense, pure MgB2 and doped (Mg1-xAx)B2 samples with A = Na, Ca, Cu, Ag, Zn and Al were studied for compositional ranges 0 < x leq 0.20. The effects on pinning properties and critical current were investigated, particularly for A = aluminium. The samples were sintered and/or synthesized at high pressure-high temperature in a cubic multi-anvil press (typically 3.5-6 GPa, 900-1000 °C). They were characterized by x-ray diffraction, scanning electron microscopy and their superconducting properties were investigated by ac susceptibility, magnetization (VSM and SQUID) and transport measurements under a magnetic field. Only Al really substitutes on the Mg site. The other elements form secondary phases with B or Mg which do not act as pinning centres. No positive effect is observed on the superconducting properties of the bulk MgB2 samples with these doping elements added: Tc, critical current jc, Hirr and Hc2. For Al, the effect on Hc2 remains small, and the irreversibility line does not move, thus not improving the critical current of the Al-doped MgB2 samples.

  17. Lilienfeld Prize Recipient: Numerical Computations and the Physics of the High Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Scalapino, Douglas J.

    1998-04-01

    Numerical calculations provided early evidence for d_x^2-y^2 pairing in various models believed to embody the basic physics characteristic of the high transition temperature superconducting cuperates. Here we will review this focusing on what these studies tells us about the mechanism which is responsible for high temperature superconductivity.

  18. Recent developments in the application of rf superconductivity to high-brightness and high-gradient ion beam accelerators

    SciTech Connect

    Delayen, J.R.; Bohn, C.L.; Kennedy, W.L.; Nichols, G.L.; Roche, C.T.; Sagalovsky, L.

    1991-12-31

    A development program is underway to apply rf superconductivity to the design of continuous-wave (cw) linear accelerators for high- brightness ion beams. Since the last workshop, considerable progress has been made both experimentally and theoretically toward this application. Recent tests of niobium resonators for ion acceleration have yielded average accelerating gradients as high as 18 MV/m. In an experiment with a radio-frequency quadrupole geometry, niobium was found to sustain cw peak surface electric fields as high as 128 MV/m over large (10 cm{sup 2}) surface areas. Theoretical studies of beam impingement and cumulative beam breakup have also yielded encouraging results. Consequently, a section of superconducting resonators and focusing elements has been designed for tests with high-current deuteron beams. In addition, considerable data pertaining to the rf properties of high-{Tc} superconductors has been collected at rf-field amplitudes and frequencies of interest in connection with accelerator operation. This paper summarizes the recent progress and identifies current and future work in the areas of accelerator technology and superconducting materials which will build upon it.

  19. Recent developments in the application of rf superconductivity to high-brightness and high-gradient ion beam accelerators

    SciTech Connect

    Delayen, J.R.; Bohn, C.L.; Kennedy, W.L.; Nichols, G.L.; Roche, C.T.; Sagalovsky, L.

    1991-01-01

    A development program is underway to apply rf superconductivity to the design of continuous-wave (cw) linear accelerators for high- brightness ion beams. Since the last workshop, considerable progress has been made both experimentally and theoretically toward this application. Recent tests of niobium resonators for ion acceleration have yielded average accelerating gradients as high as 18 MV/m. In an experiment with a radio-frequency quadrupole geometry, niobium was found to sustain cw peak surface electric fields as high as 128 MV/m over large (10 cm{sup 2}) surface areas. Theoretical studies of beam impingement and cumulative beam breakup have also yielded encouraging results. Consequently, a section of superconducting resonators and focusing elements has been designed for tests with high-current deuteron beams. In addition, considerable data pertaining to the rf properties of high-{Tc} superconductors has been collected at rf-field amplitudes and frequencies of interest in connection with accelerator operation. This paper summarizes the recent progress and identifies current and future work in the areas of accelerator technology and superconducting materials which will build upon it.

  20. Quantitative determination of pairing interactions for high-temperature superconductivity in cuprates

    PubMed Central

    Bok, Jin Mo; Bae, Jong Ju; Choi, Han-Yong; Varma, Chandra M.; Zhang, Wentao; He, Junfeng; Zhang, Yuxiao; Yu, Li; Zhou, X. J.

    2016-01-01

    A profound problem in modern condensed matter physics is discovering and understanding the nature of fluctuations and their coupling to fermions in cuprates, which lead to high-temperature superconductivity and the invariably associated strange metal state. We report the quantitative determination of normal and pairing self-energies, made possible by laser-based angle-resolved photoemission measurements of unprecedented accuracy and stability. Through a precise inversion procedure, both the effective interactions in the attractive d-wave symmetry and the repulsive part in the full symmetry are determined. The latter is nearly angle-independent. Near Tc, both interactions are nearly independent of frequency and have almost the same magnitude over the complete energy range of up to about 0.4 eV, except for a low-energy feature at around 50 meV that is present only in the repulsive part, which has less than 10% of the total spectral weight. Well below Tc, they both change similarly, with superconductivity-induced features at low energies. Besides finding the pairing self-energy and the attractive interactions for the first time, these results expose the central paradox of the problem of high Tc: how the same frequency-independent fluctuations can dominantly scatter at angles ±π/2 in the attractive channel to give d-wave pairing and lead to angle-independent repulsive scattering. The experimental results are compared with available theoretical calculations based on antiferromagnetic fluctuations, the Hubbard model, and quantum-critical fluctuations of the loop-current order. PMID:26973872

  1. Topological nature and the multiple Dirac cones hidden in Bismuth high-Tc superconductors.

    PubMed

    Li, Gang; Yan, Binghai; Thomale, Ronny; Hanke, Werner

    2015-05-27

    Recent theoretical studies employing density-functional theory have predicted BaBiO3 (when doped with electrons) and YBiO3 to become a topological insulator (TI) with a large topological gap (~0.7 eV). This, together with the natural stability against surface oxidation, makes the Bismuth-Oxide family of special interest for possible applications in quantum information and spintronics. The central question, we study here, is whether the hole-doped Bismuth Oxides, i.e. Ba(1-x)K(x)BiO3 and BaPb(1-x)Bi(x)O3, which are "high-Tc" bulk superconducting near 30 K, additionally display in the further vicinity of their Fermi energy EF a topological gap with a Dirac-type of topological surface state. Our electronic structure calculations predict the K-doped family to emerge as a TI, with a topological gap above EF. Thus, these compounds can become superconductors with hole-doping and potential TIs with additional electron doping. Furthermore, we predict the Bismuth-Oxide family to contain an additional Dirac cone below EF for further hole doping, which manifests these systems to be candidates for both electron- and hole-doped topological insulators.

  2. Topological nature and the multiple Dirac cones hidden in Bismuth high-Tc superconductors.

    PubMed

    Li, Gang; Yan, Binghai; Thomale, Ronny; Hanke, Werner

    2015-01-01

    Recent theoretical studies employing density-functional theory have predicted BaBiO3 (when doped with electrons) and YBiO3 to become a topological insulator (TI) with a large topological gap (~0.7 eV). This, together with the natural stability against surface oxidation, makes the Bismuth-Oxide family of special interest for possible applications in quantum information and spintronics. The central question, we study here, is whether the hole-doped Bismuth Oxides, i.e. Ba(1-x)K(x)BiO3 and BaPb(1-x)Bi(x)O3, which are "high-Tc" bulk superconducting near 30 K, additionally display in the further vicinity of their Fermi energy EF a topological gap with a Dirac-type of topological surface state. Our electronic structure calculations predict the K-doped family to emerge as a TI, with a topological gap above EF. Thus, these compounds can become superconductors with hole-doping and potential TIs with additional electron doping. Furthermore, we predict the Bismuth-Oxide family to contain an additional Dirac cone below EF for further hole doping, which manifests these systems to be candidates for both electron- and hole-doped topological insulators. PMID:26014056

  3. Emergence of Complex States in CMR Manganites and High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Dagotto, Elbio

    2005-03-01

    Recent developments in the context of theory and experiments for manganites and cuprates will be discussed. It will be argued that the presence of nanoscale phase separation is at the heart of the colossal magnetoresistance phenomenon [1]. Simulation results support this view, as well as experimental data. These effects are not limited to manganites, but they may appear in other compounds as well, such as the high-Tc cuprates. New results will be presented in this area, on the phenomenological competition between antiferromagnetism and d-wave superconductivity, suggesting the possibility of ``colossal'' effects in this context [2]. This is compatible with the recent discovery of ``giant proximity effects'' in Cu-oxides [3]. All this suggests that clustered or mixed-phase states could form a new paradigm for the understanding of compounds in condensed matter physics. Work in collaboration with G. Alvarez, M. Mayr, A. Moreo, C. Sen, and I. Sergienko, supported by NSF DMR. [1] A. Moreo et al., Science 283, 2034 (1999); E.D., T. Hotta and A. Moreo, Physics Reports 344,1 (2001); E.D., ``Nanoscale Phase Separation and Colossal Magnetoresistance'', Springer-Verlag, 2002. [2] G. Alvarez et al., cond-mat/0401474, PRB to appear. [3] I. Bozovic et al., Phys. Rev. Lett. 93, 157002 (2004)

  4. Growth of High TcYBaCuO Thin Films by Metalorganic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Kirlin, Peter S.; Binder, R.; Gardiner, R.; Brown, Duncan W.

    1990-03-01

    Thin films of YBa2Cu3O7-x were grown on MgO(100) by metalorganic chemical vapor deposition (MOCVD). Low pressure growth studies were carried out between 400 and 600°C using metal β-diketonate complexes as source reagents for Y, Ba, and Cu. As-deposited films were amorphous and a two stage annealing protocol was used in which fluorine was first removed in a Ar/H20 stream between 700 and 850°C, followed by calcination in flowing oxygen between 500 and 950°C. Scanning electron microscopy, X-ray diffraction and energy dispersive analysis indicate that good compositional and dimensional uniformity could be achieved. The temperature of the oxygen annealing step was shown to have a dramatic impact on the physical and electrical properties of the YBa2Cu307-x thin films. Annealing temperatures exceeding 910°C gave large crystallites and semiconducting resistivity above Tc; annealing temperatures below 910°C yielded films with metallic conductivity whose density and superconducting transition varied inversely with maximum annealing temperature. Optimized deposition/annealing protocols yielded films with a preferred c-axis orientation, R273/R100 ratios of 2, onsets as high as 94K and zero resistance exceeding 90K.

  5. Possible enhancements of AFM spin-fluctuations in high-TC cuprates

    NASA Astrophysics Data System (ADS)

    Jarlborg, Thomas

    2009-03-01

    Ab-initio band calculations for high-TC cuprates, together with modelling based of a free electron like band, show a strong interaction between anti-ferromagnetic (AFM) spin waves and periodic lattice distortions as for phonons, even though this type of spin-phonon coupling (SPC) is underestimated in calculations using the local density approximation. The SPC has a direct influence on the properties of the HTC cuprates and it can explain many observations. The strongest effects are seen for modulated waves in the CuO bond direction, and a band gap is formed near the X,Y points, but unusal band dispersion (like ``waterfalls'') might also be induced below the Fermi energy (EF) in the diagonal direction. The band results are used to propose different ways of increasing AFM spin-fluctuations locally, and to have a higher density-of-states (DOS) at EF. Static potential modulations, via periodic distribution of dopants or lattice distortions, can be tuned to increase the DOS. This opens for possibilities to enhance coupling for spin fluctuations (λsf) and superconductivity. The exchange enhancement is in general increased near a surface, which suggests a tendency towards static spin configurations. The sensivity of the band results to corrections of the local density potential are discussed.

  6. High-{Tc} DC SQUID and flux transformer development

    SciTech Connect

    Fife, A.A.; Angus, V.; Betts, K.

    1994-12-31

    A description is presented of the fabrication and properties of high {Tc} DC SQUIDS and flux transformers fabricated by dry processing of pulsed laser ablated YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) thin films. SQUIDs have been fabricated with either bicrystal substrate or step edge junctions. For all devices fabricated thus far, measurements indicate a similar character to the flux noise spectra with a significant 1/f noise component below 100--500 Hz. The transfer function and energy sensitivities as a function of SQUID inductances in the range 60--200 pH have been measured for bicrystal DC SQUIDs and compared with estimates. Various techniques have been employed to improve the magnetic field sensitivity of the uncoupled DC SQUID toward more practical levels including the use of large area washers, single layer magnetometers and 3-level flux transformers fabricated from trilayers of YBCO/SrTiO{sub 3}/YBCO. The properties of open input coils are presented as well as the performance of closed loop transformers coupled via flip chip geometry to the SQUID washer. A white magnetic noise level of {approx} 130 fT rms/{radical}Hz above 200 Hz has been reached with a flux transformer with a 15 turn input coil and pick-up loop area of 13 mm{sup 2}.

  7. High-Temperature Superconductivity in Single-Unit-Cell FeSe Films on Anatase TiO_{2}(001).

    PubMed

    Ding, Hao; Lv, Yan-Feng; Zhao, Kun; Wang, Wen-Lin; Wang, Lili; Song, Can-Li; Chen, Xi; Ma, Xu-Cun; Xue, Qi-Kun

    2016-08-01

    We report on the observation of high-temperature (T_{c}) superconductivity and magnetic vortices in single-unit-cell FeSe films on anatase TiO_{2}(001) substrate by using scanning tunneling microscopy. A systematic study and engineering of interfacial properties has clarified the essential roles of substrate in realizing the high-T_{c} superconductivity, probably via interface-induced electron-phonon coupling enhancement and charge transfer. By visualizing and tuning the oxygen vacancies at the interface, we find their very limited effect on the superconductivity, which excludes interfacial oxygen vacancies as the primary source for charge transfer between the substrate and FeSe films. Our findings have placed severe constraints on any microscopic model for the high-T_{c} superconductivity in FeSe-related heterostructures.

  8. High-Temperature Superconductivity in Single-Unit-Cell FeSe Films on Anatase TiO_{2}(001).

    PubMed

    Ding, Hao; Lv, Yan-Feng; Zhao, Kun; Wang, Wen-Lin; Wang, Lili; Song, Can-Li; Chen, Xi; Ma, Xu-Cun; Xue, Qi-Kun

    2016-08-01

    We report on the observation of high-temperature (T_{c}) superconductivity and magnetic vortices in single-unit-cell FeSe films on anatase TiO_{2}(001) substrate by using scanning tunneling microscopy. A systematic study and engineering of interfacial properties has clarified the essential roles of substrate in realizing the high-T_{c} superconductivity, probably via interface-induced electron-phonon coupling enhancement and charge transfer. By visualizing and tuning the oxygen vacancies at the interface, we find their very limited effect on the superconductivity, which excludes interfacial oxygen vacancies as the primary source for charge transfer between the substrate and FeSe films. Our findings have placed severe constraints on any microscopic model for the high-T_{c} superconductivity in FeSe-related heterostructures. PMID:27541474

  9. Superconductivity:

    NASA Astrophysics Data System (ADS)

    Sacchetti, N.

    In this paper a short historical account of the discovery of superconductivity and of its gradual development is given. The physical interpretation of its various aspects took about forty years (from 1911 to 1957) to reach a successful description of this phenomenon in terms of a microscopic theory At the very end it seemed that more or less everything could be reasonably interpreted even if modifications and refinements of the original theory were necessary. In 1986 the situation changed abruptly when a cautious but revolutionary paper appeared showing that superconductivity was found in certain ceramic oxides at temperatures above those up to then known. A rush of frantic experimental activity started world-wide and in less than one year it was shown that superconductivity is a much more widespread phenomenon than deemed before and can be found at temperatures well above the liquid air boiling point. The complexity and the number of the substances (mainly ceramic oxides) involved call for a sort of modern alchemy if compounds with the best superconducting properties are to be manufactured. We don't use the word alchemy in a deprecatory sense but just to emphasise that till now nobody can say why these compounds are what they are: superconductors.

  10. Material Specific Rational Design of A1B2C3O7 High-Tc Superconductors without Copper [A, B, C = Cations

    NASA Astrophysics Data System (ADS)

    Isikaku-Ironkwe, O'paul; Schaffer, Michael J.

    Soon after the discovery of YBa2Cu3O7 with Tc = 93K, a similar structured system with Ag replacing Cu was discovered with a Tc = 50K. Also, the discovery of Ba0 . 6 K0 . 4 BiO3 with Tc = 30K indicated that Cu was not indispensable for high temperature superconductivity (HTSC). Latter, the discoveries of the Pnictide and Chalcogenide high-Tc superconductors confirmed those earlier experimental indications. Using our recently developed Material Specific Characterization Dataset (MSCD) model for analysis and design of superconductors, we have computed many designs that satisfy the MSCD characteristics of YBa2Cu3O7 as a design model. Our design recognizes the valence state characteristics that make YBa2Cu3O6 a semiconductor, while YBa2Cu3O7is a superconductor. Here we present ten material specific rational design examples of potential A1B2C3O7 HTSCs without Cu, using the YBa2Cu3O7 design model. This MSCD design model opens the possibility for search and discovery of high-Tc oxide superconductor systems without copper.

  11. High-pressure superconducting phase diagram of 6Li: isotope effects in dense lithium.

    PubMed

    Schaeffer, Anne Marie; Temple, Scott R; Bishop, Jasmine K; Deemyad, Shanti

    2015-01-01

    We measured the superconducting transition temperature of (6)Li between 16 and 26 GPa, and report the lightest system to exhibit superconductivity to date. The superconducting phase diagram of (6)Li is compared with that of (7)Li through simultaneous measurement in a diamond anvil cell (DAC). Below 21 GPa, Li exhibits a direct (the superconducting coefficient, α, T(c) proportional M(-α), is positive), but unusually large isotope effect, whereas between 21 and 26 GPa, lithium shows an inverse superconducting isotope effect. The unusual dependence of the superconducting phase diagram of lithium on its atomic mass opens up the question of whether the lattice quantum dynamic effects dominate the low-temperature properties of dense lithium.

  12. Ion-channeling study of anomalous atomic displacements at the superconducting transition in high-T sub c materials

    SciTech Connect

    Rehn, L.E.; Sharma, R.P.; Baldo, P.M.

    1990-06-01

    Ion channeling along the (001) direction in high-quality single crystals of (Y/Er)Ba{sub 2}Cu{sub 3}O{sub 7-x} revealed an abrupt change in displacements in the a-b plane of the Cu and O atoms at the superconducting transition, {Tc}; normal Debye-like'' vibrations were found for the Y/Er and Ba atoms. The anomalous change in Cu-O displacements was found to shift directly with stoichiometry-induced changes in {Tc}, implying a direct link between the observed phonon anomaly and the superconducting transition. Recent measurements of ion-channeling along the (001) axis in (Bi{sub 1.7}Pb{sub 0.3})Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub x} single-crystals revealed a similar change at {Tc}, suggesting that this phonon anomaly is a general feature of high-{Tc} superconductivity. In order to identify more specifically the crystallographic directions and displacement amplitudes associated with the anomalous phonon behavior, axial channeling scans using RBS, as well as characteristic x-ray production, were taken at several temperatures between 30 and 300K along the (301) and (331) directions of YBa{sub 2}Cu{sub 3}O{sub 7-x} single crystals. Twins present in the specimens, and the existing static atomic displacements present along these directions, caused the channeling to be poorer along these axes compared to the (001) direction. Also, a much stronger dependence of the minimum yield on depth was observed. However, since only one twin variant generally dominated over sufficiently wide areas of the specimens, reasonably good ({approximately}10%) minimum yields could be obtained along the appropriate (331) axis, and detwinned crystals produced good results along (301). 22 refs., 5 figs.

  13. General Rule of Negative Effective Ueff System & Materials Design of High-Tc Superconductors by ab initio Calculations

    NASA Astrophysics Data System (ADS)

    Katayama-Yoshida, Hiroshi; Nakanishi, Akitaka; Uede, Hiroki; Takawashi, Yuki; Fukushima, Tetsuya; Sato, Kazunori

    2014-03-01

    Based upon ab initio electronic structure calculation, I will discuss the general rule of negative effective U system by (1) exchange-correlation-induced negative effective U caused by the stability of the exchange-correlation energy in Hund's rule with high-spin ground states of d5 configuration, and (2) charge-excitation-induced negative effective U caused by the stability of chemical bond in the closed-shell of s2, p6, and d10 configurations. I will show the calculated results of negative effective U systems such as hole-doped CuAlO2 and CuFeS2. Based on the total energy calculations of antiferromagnetic and ferromagnetic states, I will discuss the magnetic phase diagram and superconductivity upon hole doping. I also discuss the computational materials design method of high-Tc superconductors by ab initio calculation to go beyond LDA and multi-scale simulations.

  14. Evidence for a new excitation at the interface between a high-Tc superconductor and a topological insulator

    DOE PAGES

    Zareapour, Parisa; Hayat, Alex; Zhao, Shu Yang F.; Kreshchuk, Michael; Lee, Yong Kiat; Reijnders, Anjan A.; Jain, Achint; Xu, Zhijun; Liu, T. S.; Gu, G. D.; et al

    2014-12-09

    In this research, high-temperature superconductors exhibit a wide variety of novel excitations. If contacted with a topological insulator, the lifting of spin rotation symmetry in the surface states can lead to the emergence of unconventional superconductivity and novel particles. In pursuit of this possibility, we fabricated high critical-temperature (Tc ~ 85 K) superconductor/topological insulator (Bi₂Sr₂CaCu₂O₈₊δ/Bi₂Te₂Se) junctions. Below 75 K, a zero-bias conductance peak (ZBCP) emerges in the differential conductance spectra of this junction. The magnitude of the ZBCP is suppressed at the same rate for magnetic fields applied parallel or perpendicular to the junction. Furthermore, it can still be observedmore » and does not split up to at least 8.5 T. The temperature and magnetic field dependence of the excitation we observe appears to fall outside the known paradigms for a ZBCP.« less

  15. The characteristic electronic structure needed for high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Pyper, N. C.; Edwards, P. P.

    1991-01-01

    It is shown that the magnon mechanism proposed by Goddard and co-workers to explain high-temperature superconductivity in oxidized cuprates can also account for such superconductivity in both oxidized barium bismuthate and the electron superconductors based on neodynium cuprate. The specific and characteristic electronic structure required for the operation of the magnon mechanism naturally accounts for why only a small number of basic types of high-temperature superconductors are currently known. This mechanism can readily explain the effects of doping cuprate superconductors with both magnetic and non-magnetic ions.

  16. Superconducting spoke cavities for high-velocity applications

    SciTech Connect

    Hopper, Christopher S.; Delayen, Jean R.

    2013-10-01

    To date, superconducting spoke cavities have been designed, developed, and tested for particle velocities up to {beta}{sub 0}~0.6, but there is a growing interest in possible applications of multispoke cavities for high-velocity applications. We have explored the design parameter space for low-frequency, high-velocity, double-spoke superconducting cavities in order to determine how each design parameter affects the electromagnetic properties, in particular the surface electromagnetic fields and the shunt impedance. We present detailed design for cavities operating at 325 and 352 MHz and optimized for {beta}{sub 0}~=0.82 and 1.

  17. High-temperature superconductivity in compressed solid silane.

    PubMed

    Zhang, Huadi; Jin, Xilian; Lv, Yunzhou; Zhuang, Quan; Liu, Yunxian; Lv, Qianqian; Bao, Kuo; Li, Da; Liu, Bingbing; Cui, Tian

    2015-01-01

    Crystal structures of silane have been extensively investigated using ab initio evolutionary simulation methods at high pressures. Two metallic structures with P2₁/c and C2/m symmetries are found stable above 383 GPa. The superconductivities of metallic phases are fully explored under BCS theory, including the reported C2/c one. Perturbative linear-response calculations for C2/m silane at 610 GPa reveal a high superconducting critical temperature that beyond the order of 10(2) K.

  18. Proximity superconductivity in ballistic graphene at high magnetic fields

    NASA Astrophysics Data System (ADS)

    Prance, J. R.; Ben Shalom, M.; Zhu, M. J.; Fal'Ko, V. I.; Mishchenko, A.; Kretinin, A. V.; Novoselov, K. S.; Woods, C. R.; Watanabe, K.; Taniguchi, T.; Geim, A. K.

    We present measurements of the superconducting proximity effect in graphene-based Josephson junctions with a mean free path of several microns, which exceeds the junctions' length. The junctions exhibit low contact resistance and large supercurrents. We observe Fabry-Pérot oscillations in the normal-state resistance and the critical current of the junctions. The proximity effect is mostly suppressed in magnetic fields of <10 mT showing the conventional Fraunhofer interference pattern; however, unexpectedly, a weak proximity effect survives in magnetic fields as high as 1 T. Superconducting states randomly appear and disappear as a function of field and carrier concentration, and each exhibits a supercurrent carrying capacity close to the universal limit of e Δ/h where Δ is the superconducting gap of the contacts. We attribute the high-field supercurrent to mesoscopic Andreev states that persist near graphene edges. Our work reveals new proximity regimes that can be controlled by quantum confinement and cyclotron motion.

  19. High Tc YBCO superconductor deposited on biaxially textured Ni substrate

    DOEpatents

    Budai, John D.; Christen, David K.; Goyal, Amit; He, Qing; Kroeger, Donald M.; Lee, Dominic F.; List, III, Frederick A.; Norton, David P.; Paranthaman, Mariappan; Sales, Brian C.; Specht, Eliot D.

    1999-01-01

    A superconducting article includes a biaxially-textured Ni substrate, and epitaxial buffer layers of Pd (optional), CeO.sub.2 and YSZ, and a top layer of in-plane aligned, c-axis oriented YBCO having a critical current density (J.sub.c) in the range of at least 100,000 A/cm.sup.2 at 77 K.

  20. Ultra-sensitive sensors for weak electromagnetic fields using high-{Tc} SQUIDS for biomagnetism, NDE, and corrosion currents

    SciTech Connect

    Kraus, R.H. Jr.; Flynn, E.R.; Espy, M.; Jia, Q.X.; Wu, X.D.; Reagor, D.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The research has directly contributed to a new DOE supported project, three patents (one granted and two submitted), and several potential opportunities for new program funding at the Laboratory. The authors report significant developments extending from basic understanding of and fabrication techniques for high critical-temperature (high-{Tc}) SQUID devices to the development of high-level applications such as the SQUID Microscope. The development of ramp edge geometry and silver-doped YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) electrodes has tremendously improved the performance of high-{Tc} SQUIDS. Recent experiments have proven and quantified the LANL-patented superconducting imaging plane gradiometry concept. A SQUID microscope, developed largely under this project, has recently acquired data that demonstrated exceptional sensitivity a nd resolution. New techniques for background noise suppression, needed to use the extraordinarily sensitive SQUID sensors in unshielded environments, have also been developed. Finally, initial investigations to use SQUIDs in a basic physics experiment to measure the electric dipole moment of the neutron were very successful.

  1. Performance of a polarised neutron cryo-flipper using a high TcYBCO film

    NASA Astrophysics Data System (ADS)

    Parnell, S. R.; Washington, A. L.; Kaiser, H.; Li, F.; Wang, T.; Hamilton, W. A.; Baxter, D. V.; Pynn, R.

    2013-09-01

    It is well-known that the Meissner effect in superconducting materials can be used to provide a well-defined, non-adiabatic, magnetic-field transition. This can be utilised to produce a highly efficient neutron spin flipper that is suitable for use with neutrons of multiple wavelengths. Devices of this type using superconducting niobium have been deployed on neutron diffractometers for several decades but have required liquid helium to maintain the correct temperature. The use of high Tc materials, which removes the need for cryogens and simplifies the device, was first explored by Fitzsimmons et al. in [1]. In this communication, we describe a π flipper which uses commercially available films consisting of a 350-nm-thick YBCO film capped with 100 nm of gold on a 78×100×0.5 mm sapphire substrate. We discuss the design and performance of this device. The apparatus is compact (≈200 mm in length along the neutron beam), consisting of an oxygen-free high-conductivity copper frame, which holds the YBCO film and is mounted to the cold finger of a closed-cycle He refrigerator. The part of the vacuum chamber, where the YBCO film is located, is 5 cm wide, which allows us to minimise the distance from the film to the magnetic guide fields. Negligible small angle neutron scattering is observed from the flipper and its transmission is measured to be greater than 98.5% over a wide band of neutron wavelengths. In this design, the maximum neutron beam size that can be used is 42×42 mm2 and we can easily switch from a vertical to a horizontal guide field (both perpendicular to the neutron beam) on either side of the YBCO film. Data are reported for neutron wavelengths between 4 and 8.5 Å and flipping efficiencies under a variety of conditions are discussed. Under optimum conditions an efficiency of 99.5±0.3% was achieved for 4-8 Å neutrons on a pulsed source and 99.4±0.5% was achieved at a monochromatic source using a neutron wavelength of 4.2 Å.

  2. High intensity neutrino source superconducting solenoid cyrostat design

    SciTech Connect

    Page, T.M.; Nicol, T.H.; Feher, S.; Terechkine, I.; Tompkins, J.; /Fermilab

    2006-06-01

    Fermi National Accelerator Laboratory (FNAL) is involved in the development of a 100 MeV superconducting linac. This linac is part of the High Intensity Neutrino Source (HINS) R&D Program. The initial beam acceleration in the front end section of the linac is achieved using room temperature spoke cavities, each of which is combined with a superconducting focusing solenoid. These solenoid magnets are cooled with liquid helium at 4.5K, operate at 250 A and have a maximum magnetic field strength of 7.5 T. The solenoid cryostat will house the helium vessel, suspension system, thermal shield, multilayer insulation, power leads, instrumentation, a vacuum vessel and cryogenic distribution lines. This paper discusses the requirements and detailed design of these superconducting solenoid cryostats.

  3. Optical studies of high-temperature superconducting cuprates.

    PubMed

    Tajima, Setsuko

    2016-09-01

    The optical studies of high-temperature superconducting cuprates (HTSC) are reviewed. From the doping dependence of room temperature spectra, a dramatic change of the electronic state from a Mott (charge transfer) insulator to a Fermi liquid has been revealed. Additionally, the unusual 2D nature of the electronic state has been found. The temperature dependence of the optical spectra provided a rich source of information on the pseudogap, superconducting gap, Josephson plasmon, transverse Josephson plasma mode and precursory superconductivity. Among these issues, Josephson plasmons and transverse Josephson plasma mode were experimentally discovered by optical measurements, and thus are unique to HTSC. The effect of the spin/charge stripe order is also unique to HTSC, reflecting the conducting nature of the stripe order in this system. The pair-breaking due to the stripe order seems stronger in the out-of-plane direction than in the in-plane one. PMID:27472654

  4. High Intensity Neutrino Source Superconducting Solenoid Cryostat Design

    NASA Astrophysics Data System (ADS)

    Page, T. M.; Nicol, T. H.; Feher, S.; Terechkine, I.; Tompkins, J.

    2008-03-01

    Fermi National Accelerator Laboratory (FNAL) is involved in the development of a 100 MeV superconducting linac. This linac is part of the High Intensity Neutrino Source (HINS) R&D Program. The initial beam acceleration in the front end section of the linac is achieved using room temperature spoke cavities, each of which is combined with a superconducting focusing solenoid. These solenoid magnets are cooled with liquid helium at 4.5 K, operate at 250 A and have a maximum magnetic field strength of 7.5 T. The solenoid cryostat will house the helium vessel, suspension system, thermal shield, multilayer insulation, power leads, instrumentation, a vacuum vessel and cryogenic distribution lines. This paper discusses the requirements and detailed design of these superconducting solenoid cryostats.

  5. Multistable current states in high-temperature superconducting composites

    NASA Astrophysics Data System (ADS)

    Romanovskii, V. R.

    2016-09-01

    Conditions for current instabilities that arise in high-temperature superconducting composites with essentially nonlinear dependences of the critical current densities and resistivity on the temperature and magnetic induction have been studied. The analysis has been conducted in terms of zero-dimensional models, which has made it possible to formulate general physical mechanisms behind the formation of currents states in superconducting composites according to the external magnetic field induction, cooling conditions, and the properties of the superconductor and cladding. The possible existence of current and temperature stable steps, as well as stable steps of the electric field strength, in the absence of the superconducting-normal transition, has been demonstrated. Reasons for instabilities under multistable current states have been discussed.

  6. Optical studies of high-temperature superconducting cuprates

    NASA Astrophysics Data System (ADS)

    Tajima, Setsuko

    2016-09-01

    The optical studies of high-temperature superconducting cuprates (HTSC) are reviewed. From the doping dependence of room temperature spectra, a dramatic change of the electronic state from a Mott (charge transfer) insulator to a Fermi liquid has been revealed. Additionally, the unusual 2D nature of the electronic state has been found. The temperature dependence of the optical spectra provided a rich source of information on the pseudogap, superconducting gap, Josephson plasmon, transverse Josephson plasma mode and precursory superconductivity. Among these issues, Josephson plasmons and transverse Josephson plasma mode were experimentally discovered by optical measurements, and thus are unique to HTSC. The effect of the spin/charge stripe order is also unique to HTSC, reflecting the conducting nature of the stripe order in this system. The pair-breaking due to the stripe order seems stronger in the out-of-plane direction than in the in-plane one.

  7. Spin-bag mechanism of high-temperature superconductivity

    NASA Technical Reports Server (NTRS)

    Schrieffer, J. R.; Wen, X.-G.; Zhang, S.-C.

    1988-01-01

    A new approach to the theory of high-temperature superconductivity is proposed, based on the two-dimensional antiferromagnetic spin correlations observed in these materials over distances large compared to the lattice spacing. The spin ordering produces an electronic pseudogap which is locally suppressed by the addition of a hole. This suppression forms a bag inside which the hole is self-consistently trapped. Two holes are attracted by sharing a common bag. The resulting pairing interaction leads to a superconducting energy gap which is nodeless over the Femri surface.

  8. Fabrication of Large Bulk High Temperature Superconducting Articles

    NASA Technical Reports Server (NTRS)

    Koczor, Ronald (Inventor); Hiser, Robert A. (Inventor)

    2003-01-01

    A method of fabricating large bulk high temperature superconducting articles which comprises the steps of selecting predetermined sizes of crystalline superconducting materials and mixing these specific sizes of particles into a homogeneous mixture which is then poured into a die. The die is placed in a press and pressurized to predetermined pressure for a predetermined time and is heat treated in the furnace at predetermined temperatures for a predetermined time. The article is left in the furnace to soak at predetermined temperatures for a predetermined period of time and is oxygenated by an oxygen source during the soaking period.

  9. Fabrication and voltage divider operation of a T flip-flop using high-Tc interface-engineered Josephson junctions

    NASA Astrophysics Data System (ADS)

    Kim, Jun Ho; Hyeob Kim, Sang; Sung, Gun Yong

    2002-09-01

    We designed and fabricated a rapid-single-flux-quantum T flip-flop (TFF) with high-Tc interface-engineered Josephson junctions. Y1Ba2Cu3O7-d and Sr2AlTaO6 were deposited for the superconducting layer and the insulating layer, respectively. The Josephson junction was formed through an interface treatment process using Ar ion milling and vacuum annealing. We simulated a TFF circuit and designed a physical layout using WRspice and Xic. The fabricated TFF has a minimum junction width of 3 μm. Through the measurement of the voltage divider operation, the maximum operation frequency was estimated to be 53 GHz at 22 K and 106 GHz at 12 K.

  10. Conceptual design of a superconducting high-intensity proton linac

    SciTech Connect

    Dominic Chan, K.C.

    1996-09-01

    A SCRF (superconducting RF linac) has been developed for a high-intensity proton linac which will be used as the driver for neutron sources. This design is conservative, using current SCRF technologies. As well as lowering operating cost, the design offers performance advantages in availability, beam loss, and upgradability, which are important for the application as a neutron source.

  11. Survey of high field superconducting material for accelerator magnets

    SciTech Connect

    Scahlan, R.; Greene, A.F.; Suenaga, M.

    1986-05-01

    The high field superconductors which could be used in accelerator dipole magnets are surveyed, ranking these candidates with respect to ease of fabrication and cost as well as superconducting properties. Emphasis is on Nb/sub 3/Sn and NbTi. 27 refs., 2 figs. (LEW)

  12. Incorporation and retention of 99-Tc(IV) in magnetite under high pH conditions.

    PubMed

    Marshall, Timothy A; Morris, Katherine; Law, Gareth T W; Mosselmans, J Frederick W; Bots, Pieter; Parry, Stephen A; Shaw, Samuel

    2014-10-21

    Technetium incorporation into magnetite and its behavior during subsequent oxidation has been investigated at high pH to determine the technetium retention mechanism(s) on formation and oxidative perturbation of magnetite in systems relevant to radioactive waste disposal. Ferrihydrite was exposed to Tc(VII)(aq) containing cement leachates (pH 10.5-13.1), and crystallization of magnetite was induced via addition of Fe(II)aq. A combination of X-ray diffraction (XRD), chemical extraction, and X-ray absorption spectroscopy (XAS) techniques provided direct evidence that Tc(VII) was reduced and incorporated into the magnetite structure. Subsequent air oxidation of the magnetite particles for up to 152 days resulted in only limited remobilization of the incorporated Tc(IV). Analysis of both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data indicated that the Tc(IV) was predominantly incorporated into the magnetite octahedral site in all systems studied. On reoxidation in air, the incorporated Tc(IV) was recalcitrant to oxidative dissolution with less than 40% remobilization to solution despite significant oxidation of the magnetite to maghemite/goethite: All solid associated Tc remained as Tc(IV). The results of this study provide the first direct evidence for significant Tc(IV) incorporation into the magnetite structure and confirm that magnetite incorporated Tc(IV) is recalcitrant to oxidative dissolution. Immobilization of Tc(VII) by reduction and incorporation into magnetite at high pH and with significant stability upon reoxidation has clear and important implications for limiting technetium migration under conditions where magnetite is formed including in geological disposal of radioactive wastes. PMID:25236360

  13. High-Field Superconducting Magnets Supporting PTOLEMY

    NASA Astrophysics Data System (ADS)

    Hopkins, Ann; Luo, Audrey; Osherson, Benjamin; Gentile, Charles; Tully, Chris; Cohen, Adam

    2013-10-01

    The Princeton Tritium Observatory for Light, Early Universe, Massive Neutrino Yield (PTOLEMY) is an experiment planned to collect data on Big Bang relic neutrinos, which are predicted to be amongst the oldest and smallest particles in the universe. Currently, a proof-of-principle prototype is being developed at Princeton Plasma Physics Laboratory to test key technologies associated with the experiment. A prominent technology in the experiment is the Magnetic Adiabatic Collimation with an Electrostatic Filter (MAC-E filter), which guides tritium betas along magnetic field lines generated by superconducting magnets while deflecting those of lower energies. B field mapping is performed to ensure the magnets produce a minimum field at the midpoint of the configuration of the magnets and to verify accuracy of existing models. Preliminary tests indicate the required rapid decrease in B field strength from the bore of the more powerful 3.35 T magnet, with the field dropping to 0.18 T approximately 0.5 feet from the outermost surface of the magnet.

  14. Focus on superconducting properties of iron chalcogenides

    NASA Astrophysics Data System (ADS)

    Takano, Yoshihiko

    2012-10-01

    Since the discovery of iron-based superconductors, much attention has been given to the exploration of new superconducting compounds. Numerous superconducting iron compounds have been found and categorized into five groups: LnFeAsO (Ln = lanthanide), BaFe2As2, KFeAs, FeSe and FeAs with perovskite blocking layers. Among them, FeSe has the simplest crystal structure. Since the crystal structure is composed of only superconducting Fe layers, the FeSe family must be the best material to investigate the mechanism of iron-based superconductivity. FeSe shows very strong pressure effects. The superconducting transition temperature (Tc) of FeSe is approximately 8 K at ambient pressure. However Tc dramatically increases up to 37 K under applied pressure of 4-6 GPa. This is the third highest Tc value among binary superconductors, surpassed only by CsC60 under pressure (Tc = 38 K) and MgB2 (Tc = 39 K). On the other hand, despite FeTe having a crystal structure analogous to that of FeSe, FeTe shows antiferromagnetic properties without superconductivity. Doping of small ions, either Se or S, however, can induce superconductivity in FeTe1-xSex or FeTe1-xSx . The superconductivity is very weak for small x values, and annealing under certain conditions is required to obtain strong superconductivity, for instance annealing in oxygen or alcoholic beverages such as red wine. The following selection of papers describe many important experimental and theoretical studies on iron chalcogenide superconductors including preparation of single crystals, bulk samples and thin films; NMR measurements; photoemission spectroscopy; high-pressure studies; annealing effects and research on new BiS2-based superconductors. I hope this focus issue will help researchers understand the frontiers of iron chalcogenide superconductors and assist in the discovery of new phenomena related to iron-based superconductivity.

  15. Measurement of repulsive force of high Tc materials due to Meissner effect and its two dimensional distribution

    NASA Astrophysics Data System (ADS)

    Ishigaki, H.; Itoh, M.; Hida, A.; Endo, H.; Oya, T.

    1991-03-01

    As a basic study for magnetic bearings using high-Tc superconductors, evaluations of the materials were conducted. These evaluations included measurements of the repulsive force and lateral restoring force of various kinds of YBCO pellets. Pure air, which was supplied in the process of fabrication, and the presence of Ag in YBCO showed evidence of the effects of increasing the repulsive force. The lateral restoring force which was observed in the lateral displacement of a levitated permanent magnet over YBCO pellets was also affected by pure air and the presence of Ag. A new measuring instrument for magnetic fields was developed by using a highly sensitive force sensor. Because this instrument has the capability of measuring the repulsive force due to the Meissner effect, it was used for evaluating the two-dimensional distribution of superconducting properties. Results show that the pellets had nonuniform superconducting properties. The two-dimensional distribution of residual flux density on the pellets which had been cooled in a magnetic field (field cooling) was also observed by means of the instrument. The mechanism for generating lateral force is discussed in relation to the distribution.

  16. High Tc superconductors for plasmonics and metamaterials fabrication: A preliminary normal state optical characterisation of Nd123 and Gd1212

    NASA Astrophysics Data System (ADS)

    Gombos, M.; Romano, S.; Rendina, I.; Carapella, G.; Ciancio, R.; Mocella, V.

    2013-08-01

    The application of metamaterials and plasmonic structures in the visible and near infrared are strongly limited by the dissipative losses due to the low conductivity of the most used metals in this frequency range. High temperature superconductors are plasmonic materials at nonzero temperature that can provide a possible alternative approach to overcome this limit. Moreover, they can have zero or even negative dielectric constant, and a bipolar behavior. All these characteristics are attractive for plasmonic applications, and encourage further studies aimed at a more detailed knowledge of the parameters characterizing high temperature superconductors as possible optical materials. In this paper, Fourier Transform Infrared Spectroscopy analysis and ellipsometric measurements in the visible and infrared spectral regions on NdBa2Cu3O7-δ (Nd123) and ruthenocuprate superconductor GdSr2RuCu2O8-δ (Gd1212) are reported. As a matter of fact, Nd123 presents the highest transition temperature (Tc = 96 K) and the most interesting magnetic response properties among YBCO-like cuprate superconductors, whereas the coexistence in the same cell of superconductivity and magnetic order below Tc in Gd1212 can be an interesting feature for next metamaterial-like applications. The obtained results confirm the promising features of the considered materials.

  17. Issues in heavy fermions and in high-T c superconductive materials raised at this conference

    NASA Astrophysics Data System (ADS)

    Varma, C. M.

    1991-05-01

    In this closing session at the conference I would like, in the light of the presentations at this conference to briefly summarize the remarkable progress achieved in the heavy-fermion and heavy-fermion superconductivity problems, and point to what seem to me the principal problems remaining. The situation in the theory of high- Tc materials, on the face of it, appears much less bright. Unlike the heavy fermions, there is no agreement on what model represents the essentials of the problem. I believe, the difficulty in achieving a consensus here is only partly scientific. It is also sociological. I will paint a rather sanguine picture of the scientific developments there as well.

  18. Novel superconducting skutterudite-type phosphorus nitride at high pressure from first-principles calculations

    PubMed Central

    Raza, Zamaan; Errea, Ion; Oganov, Artem R.; Saitta, A. Marco

    2014-01-01

    State of the art variable composition structure prediction based on density functional theory demonstrates that two new stoichiometries of PN, PN3 and PN2, become viable at high pressure. PN3 has a skutterudite-like Immm structure and is metastable with positive phonon frequencies at pressures between 10 and 100 GPa. PN3 is metallic and is the first reported nitrogen-based skutterudite. Its metallicity arises from nitrogen p-states which delocalise across N4 rings characteristic of skutterudites, and it becomes a good electron-phonon superconductor at 10 GPa, with a Tc of around 18 K. The superconductivity arises from strongly enhanced electron-phonon coupling at lower pressures, originating primarily from soft collective P-N phonon modes. The PN2 phase is an insulator with P2/m symmetry and is stable at pressures in excess of 200 GPa. PMID:25074347

  19. Fabrication of an infrared bolometer with a high T sub c superconducting thermometer

    SciTech Connect

    Vergjese, S.; Richards, P.L. . Dept. of Physics Lawrence Berkeley Lab., CA ); Char, K.; Sachtjen, S.A. )

    1990-09-01

    A sensitive high {Tc} superconducting bolometer has been fabricated on a 20 {mu}m thick sapphire substrate with a YBCO thin film transition edge thermometer. Optical measurements with a He-Ne laser gave a noise equivalent power of 2.4{center dot}10{sup {minus}11} W/Hz{sup 1/2} at 10 Hz and a responsivity of 17 V/W in good agreement with electrical bolometer measurements. Gold black smoke was then deposited on the back side of the assembled bolometer as an absorber. Spectral measurements on a Fourier transform spectrometer show that the bolometer has useful sensitivity from visible wavelengths to beyond {approximately}100 {mu}m. This performance is clearly superior to that of a commercial room temperature pyroelectric detector. Some improvement appears possible. 10 refs., 5 figs.

  20. Lateral Damping in a Magnet-High T_c SC System

    NASA Astrophysics Data System (ADS)

    Brunet, Y.; Biarrotte, J. L.; Tixador, P.

    1997-03-01

    The properties shown by a magnet levitating above a high T_c superconductor pellet can lead to use them in magnetic bearings or other applications such as coupling devices or dampers. The levitation properties and the static stability are well demonstrated but it is not clear if their damping properties are sufficient for applications to avoid any active damping device. The work presented here studies the damping of the oscillations of a magnet above a superconducting pellet, in a pendulum device where displacements and forces are simultaneously measured. Magnet and superconducting pellet dimensions are of the same order. The pulsation of the harmonic motion is governed by the static lateral forces but the damping seems to be dependent on the initial amplitudes. In our configuration, even for the first oscillations, the damping is less efficient than with copper at 77 K, and the small oscillations are quite undamped. Les propriétés de lévitation entre un aimant permanent et un supraconducteur massif à haute température critique permettent d'envisager leur utilisation dans des paliers magnétiques ou dans d'autres applications (coupleurs, amortisseurs). Si leurs propriétés de lévitation et de stabilité statique sont démontrées, une des clés de leur application est leur stabilité dynamique, qui doit permettre de réaliser des dispositifs entièrement passifs performants. Ce travail présente une étude de l'amortissement à l'aide d'un dispositif permettant de mesurer en même temps les oscillations et les forces entre un aimant vibrant librement au-dessus d'une pastille supraconductrice, les deux éléments ayant des tailles analogues. La pulsation du mouvement harmonique amorti vérifie bien un comportement dans lequel les forces latérales modifient la pulsation propre, les propriétés d'amortissement paraissent non linéaires et dépendent de l'amplitude des oscillations. Dans notre configuration, même en prenant les premières oscillations, l

  1. Possible solution of the grain-boundary problem for applications of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Hammerl, G.; Herrnberger, A.; Schmehl, A.; Weber, A.; Wiedenmann, K.; Schneider, C. W.; Mannhart, J.

    2002-10-01

    It is shown that the critical current density of high-Tc wires can be greatly enhanced by using a three-fold approach, which consists of grain alignment, doping, and optimization of the grain architecture. According to model calculations, current densities of 4 x106 A/cm2 can be achieved for an average grain alignment of 10deg at 77 K. Based on this approach, a road to competitive high-Tc cables is proposed.

  2. Formation of the low-field peak in magnetization loops of high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka, M. R.; Půst, L.; Jirsa, M.; Johansen, T. H.

    1999-07-01

    The positions of the central (low-field) peak in the magnetization hysteresis loops (MHLs) are analyzed in various high- Tc superconducting samples comprising several RBa 2Cu 3O 7- δ (RBCO; R=rare earths) single crystals of different thicknesses, a laser-ablated YBa 2Cu 3O 7- δ (YBCO) thin film, Ag-sheathed (Pb,Bi) 2Sr 2Ba 2Cu 3O 10+ δ (Bi-2223) mono- and multifilamentary tapes, and a model sample designed to reproduce a layer of grains [M.R. Koblischka et al., Appl. Phys. Lett. 70 (1997) 514]. The single crystals and the thin film show the peak at zero-field or at negative applied fields on the descending field branch according to the critical state models, the Bi-2223 tapes are found to exhibit the peak anomalously in positive applied fields. In order to better understand the magnetization processes leading to the formation of the central peak in the MHLs, the local field distributions in applied fields close to zero were studied using magneto-optic (MO) flux visualization on the same samples. These flux patterns show how the vortices are rearranged when sweeping through zero-field. A large demagnetizing effect (“perpendicular geometry”) facilitates the penetration of vortices of opposite polarity, especially along structural defects, thus, forcing the central peak towards zero or even to very small positive fields. To explain the anomalous behaviour found in Bi-2223 tapes, effects of granularity have to be considered additionally. Further, we discuss the interaction of the central peak with other “peak effects” observed in MHLs.

  3. Nd, Ce(fπ)-O(pπ) Hybridization in Nd2-xCexCuO4 and Dynamic Jahn-Teller Pairing in HIGH-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Johnson, K. H.; Clougherty, D. P.; McHenry, M. E.

    Hybridization of Nd(fπ) and Ce(fπ) orbitals with composite O(pπ)-O(pπ) bonding/ Cu(dπ*)-O(pπ) antibonding orbitals at the Fermi energy (EF) is shown to promote high-Tc superconductivity in Nd2-xCexCuO4. Dynamic Jahn-Teller coupling of these hybrid molecular orbitals to the lattice leads to Cooper pairing as it does in other high-Tc superconductors, such as La2-xSrxCuO4, where O(pπ) character at EF is dominant.

  4. Quantum quenching an O(N) non linear sigma model (NLSM) and oscillation experiments of high Tc underdoped cuprate superconductor

    NASA Astrophysics Data System (ADS)

    Hung, Ling Yan

    2014-03-01

    Recent X-ray scattering experiments have provided strong evidence of the coexistence of a charge density wave order (CDW) and superconductivity (SC) in underdoped crystals of the prototypical high-Tc cuprate superconductor, YBa2Cu3O6+x. Sachdev et al have proposed a O(6) NLSM as an effective description of the competing orders, which finds excellent quantitative fit with the X-ray data. On the other hand, Hinton et al report coherent oscillations associated with CDW in these cuprates, whose phenomenology above and below Tc find qualitative match with the picture of the competing orders. Motivated by these recent results, we study the dynamical evolution of the O(6) NLSM model upon a quantum quench - a sudden disturbance of some parameters of the model to mimic the effect of the laser pulse in the oscillation experiment. As a first brush, we simplify the problem by taking the large-N limit of the O(6) NLSM. We observe a general exponentially decaying oscillations, which experiences phase shift as temperature is varied, at an extent determined by the specific choice of the parameter that is quenched. We also discuss the variation of the oscillation frequency and amplitude as various parameters are varied. The author is supported by the Croucher Foundation (Hong Kong)

  5. Hydrostatic High-Pressure Studies to 25 GPA on the Model Superconducting Pnictide LaRu2P2

    NASA Astrophysics Data System (ADS)

    Lim, Jinhyuk; Forouzani, Neda; Schilling, James; Fotovat, Roxanna; Zheng, Chong; Hoffmann, Roald

    2014-03-01

    Prior to the discovery of the Fe-pnictides in 2008, the ruthenium phosphide LaRu2P2 possessed the highest value of the su- perconducting transition temperature, Tc ~ 4 K, in the entire pnictide family. Recently, there has been renewed interest in this compound in an effort to better understand why the Fe-pnictides have much higher values of Tc. In related phosphides superconductivity appears to only be present if the separation be- tween the phosphor ions dp-p in neigh- boring Ru2P2 planes is greater than the critical value 2.8 Å, too great for a P-P covalent bond to be formed. For example, in superconducting LaRu2P2, the value of dp-p is 3.0 Å. To test these ideas directly, we have carried out hydro- static high-pressure studies on single-crystalline LaRu2P2 in a diamond-anvil cell using He pressure medium to pres- sures as high as 25 GPa and temperatures as low as 1.5 K. We find that Tc initially increases under pressure, but suddenly disappears above 2.1 GPa. Since dp-p decreases under pressure, the sudden disappearance of superconductivity is likely due to the formation of a covalent P-P bond between adjacent Ru2P2 planes and a possible structural phase transition. Work at Washington University is supported by the NSF through Grant No. DMR-1104742 and by the Carnegie/DOE through NNSA/DOE Grant No. DE-FC52-08NA28554.

  6. High speed data transmission at the Superconducting Super Collider

    SciTech Connect

    Leskovar, B.

    1990-04-01

    High speed data transmission using fiber optics in the data acquisition system of the Superconducting Super Collider has been investigated. Emphasis is placed on the high speed data transmission system overview, the local data network and on subassemblies, such as optical transmitters and receivers. Also, the performance of candidate subassemblies having a low power dissipation for the data acquisition system is discussed. 14 refs., 5 figs.

  7. A current limiter with superconducting coil for magnetic field shielding

    NASA Astrophysics Data System (ADS)

    Kaiho, K.; Yamaguchi, H.; Arai, K.; Umeda, M.; Yamaguchi, M.; Kataoka, T.

    2001-05-01

    The magnetic shield type superconducting fault current limiter have been built and successfully tested in ABB corporate research and so on. The device is essentially a transformer in which the secondary winding is the superconducting tube. However, due to the large AC losses and brittleness of the superconducting bulk tube, they have not yet entered market. A current limiter with superconducting coil for the magnetic field shielding is considered. By using the superconducting coil made by the multi-filamentary high Tc superconductor instead of the superconducting bulk tube, the AC losses can be reduced due to the reduced superconductor thickness and the brittleness of the bulk tube can be avoidable. This paper presents a preliminary consideration of the magnetic shield type superconducting fault current limiter with superconducting coil as secondary winding and their AC losses in comparison to that of superconducting bulk in 50 Hz operation.

  8. High-affinity no-carrier-added 99mTc-labeled chemotactic peptides for studies of inflammation in vivo.

    PubMed

    Baidoo, K E; Scheffel, U; Stathis, M; Finley, P; Lever, S Z; Zhan, Y; Wagner, H N

    1998-01-01

    Nalpha-for-Nle-Leu-Phe-Nle-Tyr-Lys, a chemotactic peptide that binds with high affinity to the chemoattractant receptor on granulocytes and monocytes, was labeled with 99mTc using the diaminedithiol (DADT) chelating system to coordinate the Tc. 99mTc labeling of the DADT-coupled peptide was accomplished in 84% overall yield (room temperature for 10 min) using [99mTc]glucoheptonate as the donor of prereduced Tc. HPLC analysis showed two major 99mTc-labeled peptide peaks, 99mTc-DADT-Pep-I and 99mTc-DADT-Pep-II, were obtained in a ratio of 1:0.85. Using an iodoacetamide-derivatized gel to remove unlabeled peptide from the 99mTc labeling mixtures, essentially no-carrier-added (nca) high-specific activity 99mTc-labeled chemotactic peptides were obtained. The 99Tc analogues of the peptides were synthesized (72% yield) in a similar fashion and correlated with 99mTc complexes I and II by HPLC. In vitro competitive receptor binding assays of the isolated 99Tc analogues were performed against the tritiated chemotactic peptide [3H]N-for-Met-Leu-Phe ([3H]fMLF) using isolated granulocytes. The 99Tc-derivatized peptides showed similar binding affinities to the chemoattractant receptor as the unlabeled Nalpha-for-Nle-Leu-Phe-Nle-Tyr-Lys. The nca 99mTc-labeled peptides gave high contrast images of experimental inflammation in rabbits without causing neutropenia. Thus, it is feasible to attach the Tc-DADT chelate to low-molecular weight receptor binding chemotactic peptides and retain substantial binding to the receptor. Chemotactic peptides labeled with 99mTc via the DADT ligand system have the potential for imaging focal sites of inflammation without toxic effects, an important consideration in the successful utilization of chemotactic peptide agonists.

  9. Optimization of the Processing Parameters of High Temperature Superconducting Glass-Ceramics: Center Director's Discretionary Fund Final Report

    NASA Technical Reports Server (NTRS)

    Ethridge, E. C.; Kaukler, W. F.

    1993-01-01

    A number of promising glass forming compositions of high Tc superconducting Ba-Sr-Ca-Cu-O (BSCCO) materials were evaluated for their glass-ceramic crystallization ability. The BSCCO ceramics belonging to the class of superconductors in the Ba-Sr-Ca-Cu-O system were the focus of this study. By first forming the superconducting material as a glass, subsequent devitrification into the crystalline (glass-ceramic) superconductor can be performed by thermal processing of the glass preform body. Glass formability and phase formation were determined by a variety of methods in another related study. This study focused on the nucleation and crystallization of the materials. Thermal analysis during rapid cooling aids in the evaluation of nucleation and crystallization behavior. Melt viscosity is used to predict glass formation ability.

  10. High-Tc Layered Ferrielectric Crystals by Coherent Spinodal Decomposition.

    PubMed

    Susner, Michael A; Belianinov, Alex; Borisevich, Albina; He, Qian; Chyasnavichyus, Marius; Demir, Hakan; Sholl, David S; Ganesh, Panchapakesan; Abernathy, Douglas L; McGuire, Michael A; Maksymovych, Petro

    2015-12-22

    Research in the rapidly developing field of 2D electronic materials has thus far been focused on metallic and semiconducting materials. However, complementary dielectric materials such as nonlinear dielectrics are needed to enable realistic device architectures. Candidate materials require tunable dielectric properties and pathways for heterostructure assembly. Here we report on a family of cation-deficient transition metal thiophosphates whose unique chemistry makes them a viable prospect for these applications. In these materials, naturally occurring ferrielectric heterostructures composed of centrosymmetric In4/3P2S6 and ferrielectrically active CuInP2S6 are realized by controllable chemical phase separation in van der Waals bonded single crystals. CuInP2S6 by itself is a layered ferrielectric with a ferrielectric transition temperature (Tc) just over room temperature, which rapidly decreases with homogeneous doping. Surprisingly, in our composite materials, the ferrielectric Tc of the polar CuInP2S6 phase increases. This effect is enabled by unique spinodal decomposition that retains the overall van der Waals layered morphology of the crystal, but chemically separates CuInP2S6 and In4/3P2S6 within each layer. The average spatial periodicity of the distinct chemical phases can be finely controlled by altering the composition and/or synthesis conditions. One intriguing prospect for such layered spinodal alloys is large volume synthesis of 2D in-plane heterostructures with periodically alternating polar and nonpolar phases.

  11. (Giant) Proximity Effects in high-Tc superlattices

    NASA Astrophysics Data System (ADS)

    Bozovic, Ivan

    2006-03-01

    Molecular beam epitaxy enables one to synthesize HTS thin films with rms surface roughness in the range 0.2-0.5 nm, much less than the unit cell height (1-2 nm).^1 One can also make atomically smooth multilayers and superlattices in which HTS or spacer layers can be just one unit cell thick if so desired. A detailed study of transport properties of such heterostructures has already revealed some unexpected findings.^2 In junctions where the barrier is made out of underdoped cuprate with a reduced critical temperature Tc, we observe the Giant Proximity Effect: supercurrent runs through very thick barrier layers even at temperature well above Tc (contrary to what is expected from the standard theory).^ Atomic smoothness of films and multilayers, excellent device uniformity, and reversible modulation of barrier properties by oxygen intake provided solid evidence against experimental artifacts such as pinholes and micro-shorts. Hence, the effect is real and intrinsic, and it defies the conventional explanation. Interpretation and significance of our experimental results will be discussed in the context of theoretical concepts such as the pseudogap, midgap states, electronic inhomogeneity, preformed pairs, and possibly resonant pair tunneling. The work at BNL is done in collaboration with G. Logvenov, V. Butko, A. Gozar and A. Bollinger. ^1 I. Bozovic et al., Phys. Rev. Lett. 89, 107001 (2002); P. Abbamonte et al., Science 297, 581 (2002). ^2 I. Bozovic et al., Nature 421, 873 (2003); Phys. Rev. Lett. 93, 157002 (2004).

  12. Emergence of double-dome superconductivity in ammoniated metal-doped FeSe.

    PubMed

    Izumi, Masanari; Zheng, Lu; Sakai, Yusuke; Goto, Hidenori; Sakata, Masafumi; Nakamoto, Yuki; Nguyen, Huyen L T; Kagayama, Tomoko; Shimizu, Katsuya; Araki, Shingo; Kobayashi, Tatsuo C; Kambe, Takashi; Gu, Dachun; Guo, Jing; Liu, Jing; Li, Yanchun; Sun, Liling; Prassides, Kosmas; Kubozono, Yoshihiro

    2015-04-01

    The pressure dependence of the superconducting transition temperature (Tc) and unit cell metrics of tetragonal (NH3)yCs0.4FeSe were investigated in high pressures up to 41 GPa. The Tc decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The Tc vs. c plot is compared with those of various (NH3)yMxFeSe (M: metal atoms) materials exhibiting different Tc and c, showing that the Tc is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the Tc. No superconductivity was observed down to 4.3 K in (NH3)yCs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the Tc reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, Tc slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

  13. Emergence of double-dome superconductivity in ammoniated metal-doped FeSe

    PubMed Central

    Izumi, Masanari; Zheng, Lu; Sakai, Yusuke; Goto, Hidenori; Sakata, Masafumi; Nakamoto, Yuki; Nguyen, Huyen L. T.; Kagayama, Tomoko; Shimizu, Katsuya; Araki, Shingo; Kobayashi, Tatsuo C.; Kambe, Takashi; Gu, Dachun; Guo, Jing; Liu, Jing; Li, Yanchun; Sun, Liling; Prassides, Kosmas; Kubozono, Yoshihiro

    2015-01-01

    The pressure dependence of the superconducting transition temperature (Tc) and unit cell metrics of tetragonal (NH3)yCs0.4FeSe were investigated in high pressures up to 41 GPa. The Tc decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The Tc vs. c plot is compared with those of various (NH3)yMxFeSe (M: metal atoms) materials exhibiting different Tc and c, showing that the Tc is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the Tc. No superconductivity was observed down to 4.3 K in (NH3)yCs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the Tc reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, Tc slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe. PMID:25828620

  14. High temperature superconducting composite conductor and method for manufacturing the same

    DOEpatents

    Holesinger, Terry G.; Bingert, John F.

    2002-01-01

    A high temperature superconducting composite conductor is provided including a high temperature superconducting material surrounded by a noble metal layer, the high temperature superconducting composite conductor characterized as having a fill factor of greater than about 40. Additionally, the conductor can be further characterized as containing multiple cores of high temperature superconducting material surrounded by a noble metal layer, said multiple cores characterized as having substantially uniform geometry in the cross-sectional dimensions. Processes of forming such a high temperature superconducting composite conductor are also provided.

  15. Revealing the high-energy electronic excitations underlying the onset of high-temperature superconductivity in cuprates

    PubMed Central

    Giannetti, Claudio; Cilento, Federico; Conte, Stefano Dal; Coslovich, Giacomo; Ferrini, Gabriele; Molegraaf, Hajo; Raichle, Markus; Liang, Ruixing; Eisaki, Hiroshi; Greven, Martin; Damascelli, Andrea; van der Marel, Dirk; Parmigiani, Fulvio

    2011-01-01

    In strongly correlated systems the electronic properties at the Fermi energy (EF) are intertwined with those at high-energy scales. One of the pivotal challenges in the field of high-temperature superconductivity (HTSC) is to understand whether and how the high-energy scale physics associated with Mott-like excitations (|E−EF|>1 eV) is involved in the condensate formation. Here, we report the interplay between the many-body high-energy CuO2 excitations at 1.5 and 2 eV, and the onset of HTSC. This is revealed by a novel optical pump-supercontinuum-probe technique that provides access to the dynamics of the dielectric function in Bi2Sr2Ca0.92Y0.08Cu2O8+δ over an extended energy range, after the photoinduced suppression of the superconducting pairing. These results unveil an unconventional mechanism at the base of HTSC both below and above the optimal hole concentration required to attain the maximum critical temperature (Tc). PMID:21673674

  16. Growth of high T{sub c} superconducting fibers using a minaturized laser-heated float zone process. Annual progress report, January 1, 1993--December 31, 1993

    SciTech Connect

    Feigelson, R.S.

    1993-12-01

    This report covers the research done on {open_quotes}Growth of High Tc Superconducting Fibers using a Miniaturized Laser-Heated Float Zone Process{close_quotes} during the 12 months from Jan. 1, 1993 until Dec. 31, 1993. The effort during this period were directed into two areas; the influence of growth conditions on the properties of the superconducting fibers and the construction of the advanced fiber growth station. In the first area of emphasis, studies were done on constitutional super cooling effect, the influence of processing parameters on Tc, the correlation between Tc and growth parameters and the mechanical properties of 2212 fibers. These studies showed that there are two types of interfacial breakdowns; one type that involves low temperature inclusions caused by excessive solute buildup and another involving high temperature inclusions which require two conditions to be met. These condition are: (1) significant compositional gradients in the melt and (2) an interface melt temperature near the peritectic decomposition temperature. Analysis of the experimental data lead to the hypothesis that fibers with the highest crystallinity are grown from SrO-rich 2212 melts. Evaluation of the constitutional supercooling responsible for the high temperature inclusions suggested that growth under these conditions was most vulnerable to disruption by HT inclusions. Tc increased with growth temperature for as-grown fibers. The concentration of SrO in the fibers had a parabolic relationship with temperature. The same parabolic relationship was observed between composition and Tc. The thermal history of 2212 crystals has been shown to influence their oxygen content which played a significant role in determining their Tc`s. Fiber heat treatment and the ambient gaseous atmosphere were found to dominate the Tc variations measured in this study.

  17. High T_{c} via Spin Fluctuations from Incipient Bands: Application to Monolayers and Intercalates of FeSe.

    PubMed

    Linscheid, A; Maiti, S; Wang, Y; Johnston, S; Hirschfeld, P J

    2016-08-12

    We investigate superconductivity in a two-band system with an electronlike and a holelike band, where one of the bands is away from the Fermi level (or "incipient"). We argue that the incipient band contributes significantly to spin-fluctuation pairing in the strong coupling limit where the system is close to a magnetic instability and can lead to a large T_{c}. In this case, T_{c} is limited by a competition between the frequency range of the coupling (set by an isolated paramagnon) and the coupling strength itself, such that a domelike T_{c} dependence on the incipient band position is obtained. The coupling of electrons to phonons is found to further enhance T_{c}. The results are discussed in the context of experiments on monolayers and intercalates of FeSe. PMID:27563992

  18. High Tc via Spin Fluctuations from Incipient Bands: Application to Monolayers and Intercalates of FeSe

    NASA Astrophysics Data System (ADS)

    Linscheid, A.; Maiti, S.; Wang, Y.; Johnston, S.; Hirschfeld, P. J.

    2016-08-01

    We investigate superconductivity in a two-band system with an electronlike and a holelike band, where one of the bands is away from the Fermi level (or "incipient"). We argue that the incipient band contributes significantly to spin-fluctuation pairing in the strong coupling limit where the system is close to a magnetic instability and can lead to a large Tc. In this case, Tc is limited by a competition between the frequency range of the coupling (set by an isolated paramagnon) and the coupling strength itself, such that a domelike Tc dependence on the incipient band position is obtained. The coupling of electrons to phonons is found to further enhance Tc. The results are discussed in the context of experiments on monolayers and intercalates of FeSe.

  19. A Snapshot View of High Temperature Superconductivity 2002

    SciTech Connect

    Schuller, Ivan K.; Bansil, Arun; Basov, Dimitri N.

    2002-04-05

    This report outlines the conclusions of a workshop on High Temperature Superconductivity held April 5-8, 2002 in San Diego. The purpose of this report is to outline and highlight some outstanding and interesting issues in the field of High Temperature Superconductivity. The range of activities and new ideas that arose within the context of High Temperature Superconductors is so vast and extensive that it is impossible to summarize it in a brief document. Thus this report does not pretend to be all-inclusive and cover all areas of activity. It is a restricted snapshot and it only presents a few viewpoints. The complexity and difficulties with high temperature superconductivity is well illustrated by the Buddhist parable of the blind men trying to describe “experimentally” an elephant. These very same facts clearly illustrate that this is an extremely active field, with many unanswered questions, and with a great future potential for discoveries and progress in many (sometimes unpredictable) directions. It is very important to stress that independently of any current or future applications, this is a very important area of basic research.

  20. Vitaly Ginzburg and high temperature superconductivity: Personal reminiscences

    NASA Astrophysics Data System (ADS)

    Mazin, Igor I.

    2008-01-01

    This article is an attempt to give Western readers, as well as young researchers in Russia, a glance at the atmosphere in one of the leading physics institutions in the USSR from 1977-1988, through the eye of a graduate student and later a posdoc in the theory group led by Vitaly Ginzburg, arguably the most enthusiatic proponent of high-temperature superconductivity before the discovery of Bednorz and Muller. This is a very personal narration, wherein the events of my own life and career are inevitably intertwined with scientific events and with my reminiscences of great Russian physicists whom I had the pleasure to meet with while working in the “High-Temperature Superconductivity Section” at the Lebedev Institute within the aforementioned 12 years.

  1. Theory of high Tc ferrimagnetism in a multiorbital Mott insulator.

    PubMed

    Meetei, O Nganba; Erten, Onur; Randeria, Mohit; Trivedi, Nandini; Woodward, Patrick

    2013-02-22

    We propose a model for the multiorbital material Sr(2)CrOsO(6), an insulator with remarkable magnetic properties and the highest T(c) ~/= 725 K among all perovskites with a net moment. We derive a new criterion for the Mott transition (U(1)U(2))(1/2)>2.5W by using slave-rotor mean field theory, where W is the bandwidth and U(1(2)) are the effective Coulomb interactions on Cr(Os) including Hund's coupling. We show that Sr(2)CrOsO(6) is a Mott insulator, where the large Cr U(1) compensates for the small Os U(2). The spin sector is described by a frustrated antiferromagnetic Heisenberg model that naturally explains the net moment arising from canting and also the observed nonmonotonic magnetization M(T). We predict characteristic magnetic structure factor peaks that can be probed by neutron experiments.

  2. The superconductivity at 18 K in LiFeAs system

    NASA Astrophysics Data System (ADS)

    Wang, X. C.; Liu, Q. Q.; Lv, Y. X.; Gao, W. B.; Yang, L. X.; Yu, R. C.; Li, F. Y.; Jin, C. Q.

    2008-12-01

    The recent discovery of superconductivity in iron arsenide compounds RFeAsO (R=rare earth) or AFe 2As 2 (A=alkaline earth) has attracted great attention due to the unexpected high Tc in the system containing ferromagnetic elements like Fe. Similar to high Tc cuprates, the superconductivity in iron arsenide is related to a layered structure. Searching for new superconductors with [FeAs] layer, but of simpler structure will be of scientific significance either to build up new multilayered superconductors that may reach higher Tc or to study the mysterious underlined superconducting mechanism in iron arsenide compounds. Here we report that a new superconducting iron arsenide system LiFeAs was found. The compound crystallizes into a structure containing [FeAs] conducting layer that is interlaced with Li charge reservoir. Superconductivity was observed with Tc up to 18 K in the compounds.

  3. High Tc layered ferrielectric crystals by coherent spinodal decomposition

    DOE PAGES

    Susner, Michael A.; Belianinov, Alex; Borisevich, Albina Y.; He, Qian; Chyasnavichyus, Marius; Demir, Hakan; Sholl, David; Ganesh, Panchapakesan; Abernathy, Douglas L.; McGuire, Michael A.; et al

    2015-11-13

    Research in the rapidly-developing field of 2D-electronic materials has thus far been focused on metallic and semiconducting materials. However, complementary dielectric materials such as non-linear dielectrics are needed to enable realistic device architectures. Candidate materials require tunable dielectric properties and pathways for heterostructure assembly. Here we report on a family of cation-deficient transition metal thiophosphates whose unique chemistry makes them a viable prospect for these applications. In these materials, naturally occurring ferrielectric heterostructures composed of centrosymmetric In4/3P2S6 and ferrielectrically-active CuInP2S6 are realized by controllable chemical phase separation in van-der-Waals bonded single crystals. CuInP2S6 by itself is a layered ferrielectric withmore » Tc just over room-temperature which rapidly decreases with homogenous doping. Surprisingly, in our composite materials, the ferrielectric Tc of the polar CuInP2S6 phase increases. This effect is enabled by unique spinodal decomposition that retains the overall van-der-Waals layered morphology of the crystal, but chemically separates CuInP2S6 and In4/3P2S6 within each layer. The average spatial periodicity of the distinct chemical phases can be finely controlled by altering the composition and/or synthesis conditions. One intriguing prospect for such layered spinodal alloys is large volume synthesis of 2D in-plane heterostructures with periodically alternating polar and non-polar phases.« less

  4. Superconducting properties of copper oxide high-temperature superconductors

    PubMed Central

    Chen, Guanhua; Langlois, Jean-Marc; Guo, Yuejin; Goddard, William A.

    1989-01-01

    The equations for the magnon pairing theory of high-temperature copper-oxide-based superconductors are solved and used to calculate several properties, leading to results for specific heat and critical magnetic fields consistent with experimental results. In addition, the theory suggests an explanation of why there are two sets of transition temperatures (Tc ≈ 90 K and Tc ≈ 55 K) for the Y1Ba2Cu3O6+x class of superconductors. It also provides an explanation of why La2-xSrxCuO4 is a superconductor for only a small range of x (and suggests an experiment to independently test the theory). These results provide support for the magnon pairing theory of high-temperature superconductors. On the basis of the theory, some suggestions are made for improving these materials. PMID:16594038

  5. Space applications for high temperature superconductivity - Brief review

    NASA Technical Reports Server (NTRS)

    Krishen, Kumar

    1990-01-01

    An overview is presented of materials and devices based on high-temperature superconductivity (HTS) that could have useful space-oriented applications. Of specific interest are applications of HTS technologies to mm and microwave systems, spaceborne and planet-surface sensors, and to magnetic subsystems for robotic, rescue, and docking maneuvers. HTS technologies can be used in optoelectronics, magnetic-field detectors, antennae, transmission/delay lines, and launch/payload coils.

  6. Superconducting Nb3Ge for high-field magnets

    NASA Technical Reports Server (NTRS)

    Braginski, A. I.; Daniel, M. R.; Roland, C. W.; Woollam, J. A.

    1978-01-01

    Superconducting Nb3Ge tape conductors 5 to 10 m long were fabricated by chemical vapor deposition. Such tapes could be used in high-field magnet applications. Average tape properties set the upper performance limit of a magnet at 17 teslas (4.2 K). Highest critical-current densities obtained in thin and layered films set the upper performance limit at 20 teslas (4.2 K).

  7. Antenna-coupled high T.sub.c superconducting microbolometer

    DOEpatents

    Hu, Qing

    1992-01-01

    A device is provided for measuring radiant energy, the device comprising a substrate; a bolometer formed from a high T.sub.c superconducting material disposed on the substrate in an area that is about 1.times.5 .mu.m.sup.2 and about 0.02 .mu.m in depth; and a planar antenna disposed on the substrate and coupled to receive radiation and to impart the received radiation to the bolometer.

  8. Antenna-coupled high T[sub c] superconducting microbolometer

    DOEpatents

    Hu, Q.

    1992-12-15

    A device is provided for measuring radiant energy, the device comprising a substrate; a bolometer formed from a high T[sub c] superconducting material disposed on the substrate in an area that is about 1[times]5 [mu]m[sup 2] and about 0.02 [mu]m in depth; and a planar antenna disposed on the substrate and coupled to receive radiation and to impart the received radiation to the bolometer. 5 figs.

  9. High precision tide spectroscopy. [using the superconducting gravimeter

    NASA Technical Reports Server (NTRS)

    Goodkind, J. M.

    1978-01-01

    Diurnal and long period earth tides were measured to high accuracy and precision with the superconducting gravimeter. The results provide new evidence on the geophysical questions which have been attacked through earth tide measurements in the past. In addition, they raise new questions of potential interest. Slow fluctuations in gravity of order 10 micron gal over periods of 3 to 5 months were observed and are discussed.

  10. High-field magnets using high-critical-temperature superconducting thin films

    DOEpatents

    Mitlitsky, Fred; Hoard, Ronald W.

    1994-01-01

    High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field.

  11. High-field magnets using high-critical-temperature superconducting thin films

    DOEpatents

    Mitlitsky, F.; Hoard, R.W.

    1994-05-10

    High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla are disclosed. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field. 4 figures.

  12. Materials science challenges for high-temperature superconducting wire.

    PubMed

    Foltyn, S R; Civale, L; Macmanus-Driscoll, J L; Jia, Q X; Maiorov, B; Wang, H; Maley, M

    2007-09-01

    Twenty years ago in a series of amazing discoveries it was found that a large family of ceramic cuprate materials exhibited superconductivity at temperatures above, and in some cases well above, that of liquid nitrogen. Imaginations were energized by the thought of applications for zero-resistance conductors cooled with an inexpensive and readily available cryogen. Early optimism, however, was soon tempered by the hard realities of these new materials: brittle ceramics are not easily formed into long flexible conductors; high current levels require near-perfect crystallinity; and--the downside of high transition temperature--performance drops rapidly in a magnetic field. Despite these formidable obstacles, thousands of kilometres of high-temperature superconducting wire have now been manufactured for demonstrations of transmission cables, motors and other electrical power components. The question is whether the advantages of superconducting wire, such as efficiency and compactness, can outweigh the disadvantage: cost. The remaining task for materials scientists is to return to the fundamentals and squeeze as much performance as possible from these wonderful and difficult materials.

  13. Magnetic forces in high-T(sub c) superconducting bearings

    NASA Technical Reports Server (NTRS)

    Moon, F. C.

    1990-01-01

    In September 1987 research at Cornell levitated a small rotor on superconducting bearing at 10,000 rpm. In April 1989 a speed of 120,000 rpm was achieved in a passive bearing with no active control. The bearing material used was YBa2Cu3O7. There is no evidence that the rotation speed has any significant effect on the lift force. Magnetic force measurements between a permanent rare-earth magnet and high T(sub c) superconducting material versus vertical and lateral displacements were made. A large hysteresis loop results for large displacements, while minor loops result for small displacements. These minor loops seem to give a slope proportional to the magnetic stiffness, and are probably indicative of flux pinning forces. Experiments of rotary speed versus time show a linear decay in a vacuum. Measurements of magnetic drag forces of a magnetic dipole over a high-T(sub c) superconducting disc of YBCO show that the drag force reaches a constant value, independent of the speed. Dampling of lateral vibrations of levitated rotors were measured which indicates that transverse flux motion in the superconductor will create dissipation. As a result of these force measurements, an optimum shape for the superconductor bearing pads which gives good lateral and axial stability was designed. Recent force measurements on melt-quench processed superconductors indicate a substantial increase in levitation force and magnetic stiffness over free sintered materials. As a result, application of high-T(sub c) superconducting bearings are beginning to show great promise at this time.

  14. Superconductivity in carbon nanomaterials

    NASA Astrophysics Data System (ADS)

    Dlugon, Katarzyna

    The purpose of this thesis is to explain the phenomenon of superconductivity in carbon nanomaterials such as graphene, fullerenes and carbon nanotubes. In the introductory chapter, there is a description of superconductivity and how it occurs at critical temperature (Tc) that is characteristic and different to every superconducting material. The discovery of superconductivity in mercury in 1911 by Dutch physicist Heike Kamerlingh Onnes is also mentioned. Different types of superconductors, type I and type II, low and high temperatures superconductors, as well as the BCS theory that was developed in 1957 by Bardeen, Cooper, and Schrieffer, are also described in detail. The BCS theory explains how Cooper's pairs are formed and how they are responsible for the superconducting properties of many materials. The following chapters explain superconductivity in doped fullerenes, graphene and carbon nanotubes, respectively. There is a thorough explanation followed by many examples of different types of carbon nanomaterials in which small changes in chemical structure cause significant changes in superconducting properties. The goal of this research was not only to take into consideration well known carbon based superconductors but also to search for the newest available materials such as the fullerene nanowhiskers discovered quite recently. There is also a presentation of fairly new ideas about inducing superconductivity in a monolayer of graphene which is more challenging than inducing superconductivity in graphite by simply intercalating metal atoms between its graphene sheets. An effort has been taken to look for any available information about carbon nanomaterials that have the potential to superconduct at room temperature, mainly because discovery of such materials would be a real revolution in the modern world, although no such materials have been discovered yet.

  15. Superconductivity in Opal-based superconducting nanocomposites

    NASA Astrophysics Data System (ADS)

    Lee, M. K.; Charnaya, E. V.; Chang, L. J.; Kumzerov, Yu. A.; Lin, M. F.

    2015-03-01

    In this study, we investigate superconducting nanocomposites (SCNCs) to elucidate superconductivity in nanostructured type I superconductor. In, Sn and Hg are loaded into opal matrices by high pressure up to 10kbar, in which introducing superconducting metals into templates preserves their own 3D nanostructures. The opal matrices is adopted because it is a well-developed nanoconfinement and widely used in the studies of photonic crystal due to its periodically-superlatticed nanoporous structure. The SCNCs are then measured by Quantum Design MPMS 3 under different external magnetic fields reveal the field dependences of Tc and irreversibility temperature (Tirr). Next, AC susceptibility measurements of SCNCs determine grain coupling, vortex dynamics and field dependence of activation barrier (Ua) as well as Tc. Additionally, the phase diagrams of these SCNCs are analyzed to study superconductivity for a system with similar nanogeometry. Exotic phase diagrams in the opal SCNC studies reveal an enhanced upper critical field (Hc2 (0)) and curvature crossover of upper critical field line. Additionally, according to the field dependence of Ua(H), curvature crossover of the upper critical field line can occur, owing to vortex phase transition.

  16. Spontaneous quenches of a high temperature superconducting pancake coil

    SciTech Connect

    Lue, J.W.; Lubell, M.S.; Aized, D.; Campbell, J.M.; Schwall, R.E.

    1995-09-01

    A double-pancake coil made of Bi-2223/Ag high temperature superconducting (HTS) tape was constructed with an embedded heater and graded conductors to study the stability and quench propagation in HTS coils. The experiments were performed with liquid nitrogen and gaseous helium cooling in temperatures ranging from 5 to 77 K. The coil was very stable, and no ``normal`` zone was sustained or propagated with local pulsed heating. However, spontaneous quenches of the cod were experienced. This was found to be the result of having the coil current higher than that of the lower I{sub c} sections of the coil for a long time. This quench process took minutes to develop--much longer than would be expected in a low temperature superconducting coil. The quench behaved more like a spreading and continuous heating of an increasingly larger partially resistive section of the coil than like a sequential ``normal`` front propagation.

  17. Control and data acquisition systems for high field superconducting wigglers

    NASA Astrophysics Data System (ADS)

    Batrakov, A.; Ilyin, I.; Karpov, G.; Kozak, V.; Kuzin, M.; Kuper, E.; Mamkin, V.; Mezentsev, N.; Repkov, V.; Selivanov, A.; Shkaruba, V.

    2001-07-01

    This paper describes the control and DAQ system of superconducting wigglers with magnetic field range up to 10.3 T. The first version of the system controls a 7 T superconducting wiggler prepared for installation at Bessy-II (Germany). The second one controls a 10 T wiggler which is under testing now at the SPring-8 site (Japan). Both systems are based on VME apparatus. The set of specialized VME modules is elaborated to arrange wiggler power supply control, full time wiggler monitoring, and magnetic field high accuracy measurement and field stabilization. The software for the control of the wigglers is written in C language for VxWorks operation system for a Motorola-162 VME controller. The task initialization, stops and acquisition of the data can be done from the nearest personal computer (FTP host for VME), or from the remote system as well.

  18. Predicting Unconventional High-Temperature Superconductors in Trigonal Bipyramidal Coordinations

    NASA Astrophysics Data System (ADS)

    Hu, Jiangping; Le, Congcong; Wu, Xianxin

    2015-10-01

    Cuprates and iron-based superconductors are two classes of unconventional high-Tc superconductors based on 3 d transition elements. Recently, two principles, the correspondence principle and the magnetic selective pairing rule, have emerged to unify their high-Tc superconducting mechanisms. These principles strongly regulate electronic structures that can host high-Tc superconductivity. Guided by these principles, here, we propose high-Tc superconducting candidates that are formed by cation-anion trigonal bipyramidal complexes with a d7 filling configuration on the cation ions. Their superconducting states are expected to be dominated by the dx y±i dx2-y2 pairing symmetry.

  19. Superconducting Phase in λ-(BEDT-STF)2GaCl4 at High Pressures

    NASA Astrophysics Data System (ADS)

    Minamidate, Takaaki; Oka, Yuki; Shindo, Hironori; Yamazaki, Toshitaka; Matsunaga, Noriaki; Nomura, Kazushige; Kawamoto, Atsushi

    2015-06-01

    Electrical resistivity measurements under pressure were conducted on the organic conductor λ-(BEDT-STF)2GaCl4, which is situated between λ-(ET)2GaCl4 and λ-(BETS)2GaCl4. Magnetic susceptibility was also measured at ambient pressure. A drop in resistivity, which is associated with the superconducting transition, was observed at Tc ≈ 5 K above 1.22 GPa. The superconducting phase was confirmed by pair-breaking under a magnetic field. This is the first observation of superconductivity in λ-(BEDT-STF)2GaCl4. The temperature dependence of spin susceptibility suggests a two-dimensional antiferromagnetic spin system without any magnetic ordering. The phase adjacent to the superconducting phase in λ-type systems is not the antiferromagnetic phase, unlike the case for κ-(ET)2X.

  20. Insights from the study of high-temperature interface superconductivity.

    PubMed

    Pereiro, J; Bollinger, A T; Logvenov, G; Gozar, A; Panagopoulos, C; Bozović, I

    2012-10-28

    A brief overview is given of the studies of high-temperature interface superconductivity based on atomic-layer-by-layer molecular beam epitaxy (ALL-MBE). A number of difficult materials science and physics questions have been tackled, frequently at the expense of some technical tour de force, and sometimes even by introducing new techniques. ALL-MBE is especially suitable to address questions related to surface and interface physics. Using this technique, it has been demonstrated that high-temperature superconductivity can occur in a single copper oxide layer-the thinnest superconductor known. It has been shown that interface superconductivity in cuprates is a genuine electronic effect-it arises from charge transfer (electron depletion and accumulation) across the interface driven by the difference in chemical potentials rather than from cation diffusion and mixing. We have also understood the nature of the superconductor-insulator phase transition as a function of doping. However, a few important questions, such as the mechanism of interfacial enhancement of the critical temperature, are still outstanding. PMID:22987034

  1. Nuclear Magnetic Resonance Study of High Temperature Superconductivity

    NASA Astrophysics Data System (ADS)

    Mounce, Andrew M.

    The high temperature superconductors HgBa2CuO 4+delta (Hg1201) and Bi2SrCa2Cu2O 8+delta (Bi2212) have been treated with 17O for both nuclear magnetic resonance (NMR) sensitivity and various electronic properties. Subsequently, NMR experiments were performed on Hg1201 and Bi2212 to reveal the nature of the pseudogap, in the normal state, and vortex phases, in the superconducting state. NMR has been performed on 17O in an underdoped Hg1201 crystal with a superconducting transition transition temperature of 74 K to look for circulating orbital currents proposed theoretically and inferred from neutron scattering. The measurements reveal narrow spectra which preclude static local fields in the pseudogap phase at the apical site, suggesting that the moments observed with neutrons are fluctuating or the orbital current ordering is not the correct model for the neutron scattering observation. The fine detail of the NMR frequency shifts at the apical oxygen site are consistent with a dipolar field from the Cu+2 site and diamagnetism below the superconducting transition. It has been predicted that superconducting vortices should be electrically charged and that this effect is particularly enhanced for high temperature superconductors. Here it is shown that the Abrikosov vortex lattice, characteristic of the mixed state of superconductors, will become unstable at sufficiently high magnetic field if there is charge trapped on the vortex core for highly anisotropic superconductors. NMR measurements of the magnetic fields generated by vortices in Bi2212 single crystals provide evidence for an electro-statically driven vortex lattice reconstruction with the magnitude of charge on each vortex pancake of 2x10-3e, depending on doping, in line with theoretical estimates. Competition with magnetism is at the heart of high temperature superconductivity, most intensely felt near a vortex core. To investigate vortex magnetism spatially resolved NMR has been used, finding a strongly non

  2. Abrupt onset of a second energy gap at the superconducting transition of underdoped Bi2212

    SciTech Connect

    Hussain, Zahid; Lee, W.S.; Vishik, I.M.; Tanaka, K.; Lu, D.H.; Sasagawa, T.; Nagaosa, N.; Devereaux, T.P.; Hussain, Z.; Shen, Z.-X.

    2007-05-26

    he superconducting gap--an energy scale tied to the superconducting phenomena--opens on the Fermi surface at the superconducting transition temperature (Tc) in conventional BCS superconductors. In underdoped high-Tc superconducting copper oxides, a pseudogap (whose relation to the superconducting gap remains a mystery) develops well above Tc (refs 1, 2). Whether the pseudogap is a distinct phenomenon or the incoherent continuation of the superconducting gap above Tc is one of the central questions in high-Tc research3, 4, 5, 6, 7, 8. Although some experimental evidence suggests that the two gaps are distinct9, 10, 11, 12, 13, 14, 15, 16, 17, 18, this issue is still under intense debate. A crucial piece of evidence to firmly establish this two-gap picture is still missing: a direct and unambiguous observation of a single-particle gap tied to the superconducting transition as function of temperature. Here we report the discovery of such an energy gap in underdoped Bi2Sr2CaCu2O8+delta in the momentum space region overlooked in previous measurements. Near the diagonal of Cu?O bond direction (nodal direction), we found a gap that opens at Tc and has a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasi-particles, a classical signature of superconductivity. This is in sharp contrast to the pseudogap near the Cu?O bond direction (antinodal region) measured in earlier experiments19, 20, 21.

  3. JETC (Japanese Technology Evaluation Center) Panel Report on High Temperature Superconductivity in Japan

    NASA Technical Reports Server (NTRS)

    Shelton, Duane; Gamota, George

    1989-01-01

    The Japanese regard success in R and D in high temperature superconductivity as an important national objective. The results of a detailed evaluation of the current state of Japanese high temperature superconductivity development are provided. The analysis was performed by a panel of technical experts drawn from U.S. industry and academia, and is based on reviews of the relevant literature and visits to Japanese government, academic and industrial laboratories. Detailed appraisals are presented on the following: Basic research; superconducting materials; large scale applications; processing of superconducting materials; superconducting electronics and thin films. In all cases, comparisons are made with the corresponding state-of-the-art in the United States.

  4. High temperature superconducting infrared imaging satellite

    NASA Technical Reports Server (NTRS)

    Angus, B.; Covelli, J.; Davinic, N.; Hailey, J.; Jones, E.; Ortiz, V.; Racine, J.; Satterwhite, D.; Spriesterbach, T.; Sorensen, D.

    1992-01-01

    A low earth orbiting platform for an infrared (IR) sensor payload is examined based on the requirements of a Naval Research Laboratory statement of work. The experiment payload is a 1.5-meter square by 0.5-meter high cubic structure equipped with the imaging system, radiators, and spacecraft mounting interface. The orbit is circular at 509 km (275 nmi) altitude and 70 deg. inclination. The spacecraft is three-axis stabilized with pointing accuracy of plus or minus 0.5 deg. in each axis. The experiment payload requires two 15-minute sensing periods over two contiguous orbit periods for 30 minutes of sensing time per day. The spacecraft design is presented for launch via a Delta 2 rocket. Subsystem designs include attitude control, propulsion, electric power, telemetry, tracking and command, thermal design, structure, and cost analysis.

  5. Superconductivity in anti-post-Perovskite vanadium compounds.

    PubMed

    Wang, Bosen; Ohgushi, Kenya

    2013-11-29

    Superconductivity, which is a quantum state induced by spontaneous gauge symmetry breaking, frequently emerges in low-dimensional materials. Hence, low dimensionality has long been considered as necessary to achieve high superconducting transition temperatures (TC). The recently discovered post-perovskite (ppv) MgSiO3, which constitutes the Earth's lowermost mantle (D" layer), has attracted significant research interest due to its importance in geoscience. The ppv structure has a peculiar two-dimensional character and is expected to be a good platform for superconductivity. However, hereunto, no superconductivity has been observed in isostructural materials, despite extensive investigation. Here, we report the discovery of superconductivity with a maximum TC of 5.6 K in V3PnNx (Pn = P, As) phases with the anti-ppv structure, where the anion and cation positions are reversed with respect to the ppv structure. This discovery stimulates further explorations of new superconducting materials with ppv and anti-ppv structures.

  6. Unusual isotope effects on the pseudogap in high-Tc cuprate superconductors as support for the BCS-like pairing theory of large polarons above Tc

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Baimatov, P. J.; Djumanov, Sh. S.

    2015-06-01

    The BCS-like pairing theory is extended to the intermediate coupling regime and to the cases of exotic cuprate superconductors with large and small Fermi surfaces, so as to describe the pairing correlations above Tc , the opening of a pseudogap (PG) at a mean-field temperature T∗ >Tc and the unusual isotope effects on the PG in these materials within the large polaron model and two different BCS-like approaches. We argue that unconventional electron-phonon interactions are responsible for the polaron formation and the separation between temperatures T∗ (the onset of precursor Cooper pairing) and Tc (the onset of the superconducting transition) in exotic cuprate superconductors. Using the extended BCS-like approaches, we calculate the PG formation temperature T∗ , isotope shifts ΔT∗ , oxygen and copper isotope exponents and show that isotope effects on the PG basically depend on strengths of Coulomb and electron-phonon interactions, doping levels and dielectric constants of the cuprates. The new BCS-like pairing theory of polaronic carriers predicts the existence of small and sizable positive oxygen isotope effect and very large negative oxygen and copper isotope effects on the PG in the cuprates with large Fermi surfaces. The calculated results for T∗ , isotope shifts and exponents are compared with experimental data on various cuprate superconductors. For all the considered cases, a good quantitative agreement was found between theory and experimental data. We also predict the existence of small and sizable negative isotope effects on T∗ in deeply underdoped cuprates with small Fermi surfaces. Further, we find that the isotope effects on T∗ (=Tc) in heavily overdoped cuprates just like in some metals are relatively small positive or become even negative.

  7. The high temperature superconductivity space experiment (HTSSE-II) design

    SciTech Connect

    Kawecki, T.G.; Golba, G.A.; Price, G.E.; Rose, V.S.; Meyers, W.J.

    1996-07-01

    The high temperature superconductivity space experiment (HTSSE) program, initiated by the Naval Research Laboratory (NRL) in 1988, is described. The HTSSE program focuses high temperature superconductor (HTS) technology applications on space systems. The program phases, goals, and objectives are discussed. The devices developed for the HTSSE-II phase of the program and their suppliers are enumerated. Eight space-qualified components were integrated as a cryogenic experimental payload on DOD`s ARGOS spacecraft. The payload was designed and built using a unique NRL/industry partnership and was integrated and space-qualified at NRL.

  8. Low-loss, high-speed, high-{Tc} superconducting bearings

    DOEpatents

    Hull, J.R.; Mulcahy, T.M.; Uherka, K.L.

    1997-06-24

    A flywheel energy storage device is disclosed including an iron structure disposed for rotation adjacent a stationary superconductor material structure and a stationary permanent magnet. The stationary permanent magnet levitates the iron structure while the superconductor structure can stabilize the rotating iron structure. 15 figs.

  9. Low-loss, high-speed, high-{Tc} superconducting bearings

    DOEpatents

    Hull, J.R.; Mulcahy, T.M.; Uherka, K.L.

    1996-07-30

    A flywheel energy storage device is disclosed including an iron structure disposed for rotation adjacent a stationary superconductor material structure and a stationary permanent magnet. The stationary permanent magnet levitates the iron structure while the superconductor structure can stabilize and levitate the rotating iron structure. 15 figs.

  10. Experimenting with a Superconducting Levitation Train

    ERIC Educational Resources Information Center

    Miryala, Santosh; Koblischka, M. R.

    2014-01-01

    The construction and operation of a prototype high-"Tc" superconducting train model is presented. The train is levitated by a melt-processed GdBa[subscript 2]Cu[subscript 3]O[subscript x] (Gd-123) superconducting material over a magnetic rail (track). The oval shaped track is constructed in S-N-S or PM3N configuration arranged on an iron…

  11. Dynamic Jahn-Teller coupling and high T c superconductivity

    NASA Astrophysics Data System (ADS)

    Clougherty, Dennis P.; Johnson, Keith H.; McHenry, Michael E.

    1989-12-01

    Based on the cooperative dynamic Jahn-Teller effect, a universal model of superconductivity is sketched which accounts for many aspects of conventional BCS and high T c superconductors. Within the quasi-molecular approximation, a real space vibronic coupling of degenerate (or nearly degenerate) electronic states to anharmonically mixed nuclear distortions is shown to lead to electron pairing. The crossover from electron-phonon behavior to electronic behavior as a function of Jahn-Teller coupling and anharmonic mixing is illustrated for the case of a CuO 4 cluster having D 4 h symmetry.

  12. Method of producing high T(subc) superconducting NBN films

    NASA Technical Reports Server (NTRS)

    Thakoor, Sarita (Inventor); Lamb, James L. (Inventor); Thakoor, Anilkumar P. (Inventor); Khanna, Satish K. (Inventor)

    1988-01-01

    Thin films of niobium nitride with high superconducting temperature (T sub c) of 15.7 K are deposited on substrates held at room temperature (approx 90 C) by heat sink throughout the sputtering process. Films deposited at P sub Ar 12.9 + or - 0.2 mTorr exhibit higher T sub c with increasing P sub N2,I with the highest T sub c achieved at P sub n2,I= 3.7 + or - 0.2 mTorr and total sputtering pressure P sub tot = 16.6 + or - 0.4. Further increase of N2 injection starts decreasing T sub c.

  13. Conductor requirements for high-temperature superconducting utility power transformers

    SciTech Connect

    Pleva, E. F.; Mehrotra, V.; Schwenterly, S W

    2010-01-01

    High-temperature superconducting (HTS) coated conductors in utility power transformers must satisfy a set of operating requirements that are driven by two major considerations-HTS transformers must be economically competitive with conventional units, and the conductor must be robust enough to be used in a commercial manufacturing environment. The transformer design and manufacturing process will be described in order to highlight the various requirements that it imposes on the HTS conductor. Spreadsheet estimates of HTS transformer costs allow estimates of the conductor cost required for an HTS transformer to be competitive with a similarly performing conventional unit.

  14. A novel excitonic mechanism for high temperature superconductivity

    SciTech Connect

    Tesanovic, Z.; Bishop, A.R.; Martin, R.L.

    1988-01-01

    We propose a novel mechanism for superconductivity, based on intra and interband Cu/longleftrightarrow/O charge transfer excitations in oxide superconductors. The dynamic polarizability of the environment surrounding CuO/sup 2/ planes plays an important role in enhancing T/sub c/. The ''sandwich'' structure in which CuO/sub 2/ planes are separated by a highly polarizable medium is ideally suited for this mechanism. Our proposal is consistent with a variety of available data, and suggests several new experimental directions. 9 refs., 2 figs.

  15. Shock-induced synthesis of high temperature superconducting materials

    DOEpatents

    Ginley, D.S.; Graham, R.A.; Morosin, B.; Venturini, E.L.

    1987-06-18

    It has now been determined that the unique features of the high pressure shock method, especially the shock-induced chemical synthesis technique, are fully applicable to high temperature superconducting materials. Extraordinarily high yields are achievable in accordance with this invention, e.g., generally in the range from about 20% to about 99%, often in the range from about 50% to about 90%, lower and higher yields, of course, also being possible. The method of this invention involves the application of a controlled high pressure shock compression pulse which can be produced in any conventional manner, e.g., by detonation of a high explosive material, the impact of a high speed projectile or the effect of intense pulsed radiation sources such as lasers or electron beams. Examples and a discussion are presented.

  16. Theoretical predictions of novel superconducting phases of BaGe3 stable at atmospheric and high pressures.

    PubMed

    Zurek, Eva; Yao, Yansun

    2015-03-16

    A series of new superconducting binary silicides and germanides have recently been synthesized under high-pressure high-temperature conditions. A representative member of this group, BaGe3, was theoretically investigated using evolutionary structure searches coupled with structural analogies in the pressure range from 1 atm to 250 GPa, where three new phases were discovered. At 1 atm, in addition to the synthesized P63/mmc phase, we predicted two new phases, I4/mmm and Amm2, to be dynamically stable. The Amm2 structure comprises Ge clusters and triangular prisms intercalated with Ba and Ge atoms, a unique structural motif unknown to this group. The I4/mmm structure has been previously synthesized in binary silicides and is calculated to be thermodynamically stable in BaGe3 between 15.6 and 35.4 GPa. Above 35.4 GPa, two new phases of P6̅m2 and R3̅m symmetry become the global minima and remain so up to the highest pressure considered. These two phases have very similar enthalpies, and both feature layers of double Kagome nets of Ge intercalated with Ba-Ge layers. The predicted phases are suggested to be metallic with itinerant electrons and to be potentially superconducting from the considerable electron-phonon coupling strength. Density functional perturbation calculations combined with the Allen-Dynes-modified McMillan formula were used to estimate the superconducting critical temperatures (Tc) for these new phases, which, with slight pressure variations, are comparable to the experimental Tc measured for the P63/mmc phase.

  17. Local Inhomogeneity and Filamentary Superconductivity in Pr-Doped CaFe2As2

    NASA Astrophysics Data System (ADS)

    Gofryk, Krzysztof; Pan, Minghu; Cantoni, Claudia; Saparov, Bayrammurad; Mitchell, Jonathan E.; Sefat, Athena S.

    2014-01-01

    We use multiscale techniques to determine the extent of local inhomogeneity and superconductivity in Ca0.86Pr0.14Fe2As2 single crystal. The inhomogeneity is manifested as a spatial variation of the praseodymium concentration, local density of states, and superconducting order parameter. We show that the high-Tc superconductivity emerges from cloverlike defects associated with Pr dopants. The highest Tc is observed in both the tetragonal and collapsed tetragonal phases, and its filamentary nature is a consequence of nonuniform Pr distribution that develops localized, isolated superconducting regions within the crystals.

  18. Local inhomogeneity and filamentary superconductivity in Pr-doped CaFe2As2.

    PubMed

    Gofryk, Krzysztof; Pan, Minghu; Cantoni, Claudia; Saparov, Bayrammurad; Mitchell, Jonathan E; Sefat, Athena S

    2014-01-31

    We use multiscale techniques to determine the extent of local inhomogeneity and superconductivity in Ca0.86Pr0.14Fe2As2 single crystal. The inhomogeneity is manifested as a spatial variation of the praseodymium concentration, local density of states, and superconducting order parameter. We show that the high-Tc superconductivity emerges from cloverlike defects associated with Pr dopants. The highest Tc is observed in both the tetragonal and collapsed tetragonal phases, and its filamentary nature is a consequence of nonuniform Pr distribution that develops localized, isolated superconducting regions within the crystals. PMID:24580484

  19. Rotor instrumentation study for high-temperature superconducting generators

    SciTech Connect

    Schwenterly, S.W.; Wilson, C.T.

    1996-06-01

    In FY 9195, ORNL carried out work on rotor instrumentation systems in support of the General Electric (GE) Superconductivity Partnership Initiative (SPI) on Superconducting Generator Development. The objective was to develop a system for tramsitting data from sensors in the spinning rotor to a stationary data acquisition system. Previous work at ORNL had investigated an optical method of cryogenic temperature measurement using laser-induced fluorescence in certain phosphors. Later follow-up discussions with experts in the ORNL Engineering Technology Division indicated that this method could also be extended to measure strain and magnetic field. Another optical alternative using standard fiber optic transmission modules was also investigated. The equipment is very inexpensive, but needs to be adapted for operation in a high-g-force rotating environment. An optical analog of a commutator or slip ring also needs to be developed to couple the light signals from the rotor to the stationary frame. Sealed mercury-film rotary contacts are manufactured by Meridian Laboratory. Unlike conventional slipring assemblies, these offer low noise and long lifetime, with low costs per channel. Standard units may need some upgrading for 3600-rpm or high-voltage operation. A commercial electronic telemetry system offered by Wireless Data Corporation (WDC) was identified as a viable candidate, and information on this system was presented to GE. GE has since ordered two of these systems from WDC for temperature measurements in their rotating test cryostat.

  20. Superconductivity in the Graphite Intercalation Compound BaC(6).

    PubMed

    Heguri, Satoshi; Kawade, Naoya; Fujisawa, Takumi; Yamaguchi, Akira; Sumiyama, Akihiko; Tanigaki, Katsumi; Kobayashi, Mototada

    2015-06-19

    Among many two-dimensional (2D) high T(C) superconductors, graphite intercalation compounds (GICs) are the most famous intercalation family, which are classified as typical electron-phonon mediated superconductors. We show unambiguous experimental facts that BaC(6), the superconductivity of which has been missing for many years so far among various alkaline earth metal (Ca, Sr, and Ba) intercalted GICs, exhibits superconductivity at T(C)=65  mK. By adding this finding as the additional experimental point, a complete figure displaying the relationship between T(C) and interlayer distance (d) for GICs is now provided, and their possible superconducting mechanisms raised so far are revisited. The present study settles a long-running debate between theories and experiments on the superconductivity in the first stage GICs.

  1. High Temperature Irradiation Resistant Thermocouple (HTIR-TC)

    ScienceCinema

    None

    2016-07-12

    INL researchers have created a new thermocouple that can resist high temperature and radiation. This device will improve safety and reduce costs associated with unit failures. Learn more about INL research at http://www.facebook.com/idahonationallaboratory

  2. High Temperature Irradiation Resistant Thermocouple (HTIR-TC)

    SciTech Connect

    2011-01-01

    INL researchers have created a new thermocouple that can resist high temperature and radiation. This device will improve safety and reduce costs associated with unit failures. Learn more about INL research at http://www.facebook.com/idahonationallaboratory

  3. Superfluid Stiffness and Tc Enhancement in Cuprate Heterostructures

    NASA Astrophysics Data System (ADS)

    Goren, Lilach

    The basic electronic correlations underlying the effect of high Tc superconductivity in cuprates, still elude a complete and unified theoretical description. This thesis deals with several central open questions regarding the crucial aspects that determine superconductivity in cuprates. A key question concerns the nature of the phase which is formed when superconductivity is destroyed. The origin of the 'pseudogap' in the density of states above Tc is not clear to this day. We address this question by investigating the destruction of superconductivity at T = 0 as current is applied. We design novel Gutzwiller projected variational states, that incorporate supercurrent in a d-wave BCS wave-function. We identify two different mechanisms which determine the critical current at which superconductivity is destroyed: at high hole doping [special characters omitted] it occurs when quasiparticle pockets completely destroy the gap in a BCS-like mechanism. In the underdoped regime the mechanism is bosonic, whereby the critical current is set by a maximal phase twist which destroys the superfluid stiffness with pairing still intact. This result is indicative of a pseudogapped 'normal' state which retains pairing correlations. Moreover, we find a dome shaped critical current as a function of doping, similar to Tc. A second question concerns the determination of Tc and in particular possible ways to increase it in cuprate heterostructures. We investigate two possible scenarios that are aimed at profiting from proximity between a largegap underdoped and a large carrier density overdoped cuprate material. In the first scenario we consider an underdoped-overdoped bilayer and find a possible Tc enhancement, assuming a relatively high interlayer coupling. In the second case, we investigate underdoped-overdoped in-plane inhomogeneity. There, the coupling is naturally high, and the proximity effect can be strong. For a microscopic doping inhomogeneity we find an enhancement of Tc

  4. Research & Development on Superconducting Niobium Materials via Magnetic Measurements

    SciTech Connect

    S. B. Roy, V. C. Sahni, and G. R. Myneni

    2011-03-01

    We present a study of superconducting properties of both large grain (1 mm average grain size) and small grain (50 micron average grain size) Niobium materials containing varying amounts of Tantalum impurities that have been used in the fabrication of high accelerating gradient superconducting radio frequency cavities. We found that a buffered chemical polishing of these Niobium samples causes a distinct reduction in the superconducting parameters like TC, wt- ppm to 1300 wt-ppm. Implications of these results on the performance of niobium superconducting radio frequency cavities are discussed, especially the anomalous high field RF losses that have been reported in the literature.

  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. 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.

  7. Superconductivity in compressed sulfur hydride: Dependences on pressure, composition, and crystal structure from first principles

    NASA Astrophysics Data System (ADS)

    Akashi, Ryosuke

    The recent discovery of high-temperature superconductivity in sulfur hydride under extreme pressure has broken the long-standing record of superconducting transition temperature (Tc) in the Hg-cuprate. According to the isotope effect measurement and theoretical calculations, the superconducting transition is mainly ascribed to the conventional phonon-mediated pairing interaction. It is, however, not enough for understanding the high-Tc superconductivity in the sulfur hydride. To elucidate various possible effects on Tc with accuracy, we have analyzed Tc with first-principles methods without any empirical parameters. First, for various pressures and theoretically proposed crystal structures, we calculated Tc with the density functional theory for superconductors (SCDFT) to examine which structure(s) can explain experimentally measured Tc data [Akashi et al., PRB 91, 224513 (2015)]. We next solved the Eliashberg equations without introducing the renormalized Coulomb parameter mu*, which is the Green-function-based counterpart of the SCDFT, and evaluated the effects of rapidly varying electron density of states, atomic zero-point motion, and phonon anharmonic corrections on Tc [Sano et al., in preparation]. In the talk, we review these results and discuss the dominant factors for the Tc and their relation to the experimental results. We also report some crystal structures that we recently found with first-principles calculations, which could have a key role for the pressure-induced transformation to the high-Tc phase.

  8. High Temperature Superconducting Reciprocating Magnetic Separator Final Report

    SciTech Connect

    James F. Maguire

    2008-06-05

    In 2001, under DOE's Superconductivity Partnership Initiative (SPI), E. I. du Pont de Nemours & Co. (Dupont) was awarded a cost-share contract to build a fully functional full-scale model high temperature superconducting reciprocating magnet unit specifically designed for the koalin clay industry. After competitive bidding, American Superconductor (AMSC) was selected to provide the coil for the magnet. Dupont performed the statement of work until September 2004, when it stopped work, with the concurrence of DOE, due to lack of federal funds. DOE had paid all invoices to that point, and Dupont had provided all cost share. At this same time, Dupont determined that this program did not fit with its corporate strategies and notified DOE that it was not interesting in resuming the program when funding became available. AMSC expressed interest in assuming performance of the Agreement to Dupont and DOE, and in March 2005, this project was transferred to AMSC by DOE amendment to the original contract and Novation Agreement between AMSC and Dupont. Design drawings and some hardware components and subassemblies were transferred to AMSC. However, no funding was obligated by DOE and AMSC never performed work on the project. This report contains a summary of the work performed by Dupont up to the September 04 timeframe.

  9. High-Density Superconducting Cables for Advanced ACTPol

    NASA Astrophysics Data System (ADS)

    Pappas, C. G.; Austermann, J.; Beall, J. A.; Duff, S. M.; Gallardo, P. A.; Grace, E.; Henderson, S. W.; Ho, S. P.; Koopman, B. J.; Li, D.; McMahon, J.; Nati, F.; Niemack, M. D.; Niraula, P.; Salatino, M.; Schillaci, A.; Schmitt, B. L.; Simon, S. M.; Staggs, S. T.; Stevens, J. R.; Vavagiakis, E. M.; Ward, J. T.; Wollack, E. J.

    2016-07-01

    Advanced ACTPol (AdvACT) is an upcoming Atacama Cosmology Telescope (ACT) receiver upgrade, scheduled to deploy in 2016, that will allow measurement of the cosmic microwave background polarization and temperature to the highest precision yet with ACT. The AdvACT increase in sensitivity is partly provided by an increase in the number of transition-edge sensors (TESes) per array by up to a factor of two over the current ACTPol receiver detector arrays. The high-density AdvACT TES arrays require 70 \\upmu m pitch superconducting flexible cables (flex) to connect the detector wafer to the first-stage readout electronics. Here, we present the flex fabrication process and test results. For the flex wiring layer, we use a 400-nm-thick sputtered aluminum film. In the center of the cable, the wiring is supported by a polyimide substrate, which smoothly transitions to a bare (uncoated with polyimide) silicon substrate at the ends of the cable for a robust wedge wire-bonding interface. Tests on the first batch of flex made for the first AdvACT array show that the flex will meet the requirements for AdvACT, with a superconducting critical current above 1 mA at 500 mK, resilience to mechanical and cryogenic stress, and a room temperature yield of 97 %.

  10. 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.

  11. 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. PMID:25879999

  12. Study of some superconducting and magnetic materials on high T sub c oxide superconductors

    NASA Technical Reports Server (NTRS)

    Wu, M. K.

    1987-01-01

    On the basis of existing data it appears that the high-temperature superconductivity above 77 K reported here, occurs only in compound systems consisting of a phase other than the K2NiF4 phase. A narrow superconducting transition was obtained with T sub c0 = 98 K and T sub c1 = 94 K in Y-Ba-Cu-O (YBCO). Preliminary results indicate that YBCO is rather different from the layered LaBCO, LaSCO, and LaCCO. While electron-photon interaction cannot be absent from this compound system, nonconventional enhanced superconducting interactions due to interfaces, Resonating Valence Bond (RVB) states, or even a superconducting state beyond the BCS framework, may be required to account for the high T sub c in YBCO. It is believed that study of the possible subtle correlation between magnetism and superconductivity will definitely provide important insight into the superconducting mechanism in YBCO and other oxides.

  13. Pressure-driven dome-shaped superconductivity and electronic structural evolution in tungsten ditelluride.

    PubMed

    Pan, Xing-Chen; Chen, Xuliang; Liu, Huimei; Feng, Yanqing; Wei, Zhongxia; Zhou, Yonghui; Chi, Zhenhua; Pi, Li; Yen, Fei; Song, Fengqi; Wan, Xiangang; Yang, Zhaorong; Wang, Baigeng; Wang, Guanghou; Zhang, Yuheng

    2015-07-23

    Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 T. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we boost the electronic properties by applying a high pressure, and introduce superconductivity successfully. Superconductivity sharply appears at a pressure of 2.5 GPa, rapidly reaching a maximum critical temperature (Tc) of 7 K at around 16.8 GPa, followed by a monotonic decrease in Tc with increasing pressure, thereby exhibiting the typical dome-shaped superconducting phase. From theoretical calculations, we interpret the low-pressure region of the superconducting dome to an enrichment of the density of states at the Fermi level and attribute the high-pressure decrease in Tc to possible structural instability. Thus, tungsten ditelluride may provide a new platform for our understanding of superconductivity phenomena in transition metal dichalcogenides.

  14. Pressure-driven dome-shaped superconductivity and electronic structural evolution in tungsten ditelluride

    PubMed Central

    Pan, Xing-Chen; Chen, Xuliang; Liu, Huimei; Feng, Yanqing; Wei, Zhongxia; Zhou, Yonghui; Chi, Zhenhua; Pi, Li; Yen, Fei; Song, Fengqi; Wan, Xiangang; Yang, Zhaorong; Wang, Baigeng; Wang, Guanghou; Zhang, Yuheng

    2015-01-01

    Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 T. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we boost the electronic properties by applying a high pressure, and introduce superconductivity successfully. Superconductivity sharply appears at a pressure of 2.5 GPa, rapidly reaching a maximum critical temperature (Tc) of 7 K at around 16.8 GPa, followed by a monotonic decrease in Tc with increasing pressure, thereby exhibiting the typical dome-shaped superconducting phase. From theoretical calculations, we interpret the low-pressure region of the superconducting dome to an enrichment of the density of states at the Fermi level and attribute the high-pressure decrease in Tc to possible structural instability. Thus, tungsten ditelluride may provide a new platform for our understanding of superconductivity phenomena in transition metal dichalcogenides. PMID:26203922

  15. Oxyhalides: A new class of high-TC multiferroic materials

    PubMed Central

    Zhao, Li; Fernández-Díaz, Maria Teresa; Tjeng, Liu Hao; Komarek, Alexander C.

    2016-01-01

    Magnetoelectric multiferroics have attracted enormous attention in the past years because of their high potential for applications in electronic devices, which arises from the intrinsic coupling between magnetic and ferroelectric ordering parameters. The initial finding in TbMnO3 has triggered the search for other multiferroics with higher ordering temperatures and strong magnetoelectric coupling for applications. To date, spin-driven multiferroicity is found mainly in oxides, as well as in a few halogenides. We report multiferroic properties for synthetic melanothallite Cu2OCl2, which is the first discovery of multiferroicity in a transition metal oxyhalide. Measurements of pyrocurrent and the dielectric constant in Cu2OCl2 reveal ferroelectricity below the Néel temperature of ~70 K. Thus, melanothallite belongs to a new class of multiferroic materials with an exceptionally high critical temperature. Powder neutron diffraction measurements reveal an incommensurate magnetic structure below TN, and all magnetic reflections can be indexed with a propagation vector [0.827(7), 0, 0], thus discarding the claimed pyrochlore-like “all-in–all-out” spin structure for Cu2OCl2, and indicating that this transition metal oxyhalide is, indeed, a spin-induced multiferroic material. PMID:27386552

  16. Superconducting magnets in high radiation environments: Design problems and solutions

    SciTech Connect

    St. Lorant, S.J.; Tillmann, E.

    1989-11-01

    As part of the Stanford Linear Collider Project, three high-field superconducting solenoid magnets are used to rotate the spin direction of a polarized electron beam. The magnets are installed in a high-radiation environment, where they will receive a dose of approximately 10{sup 3} rad per hour, or 10{sup 8} rad over their lifetimes. This level of radiation and the location in which the magnets are installed, some 10 meters below ground in contiguous tunnels, required careful selection of materials for the construction of the solenoids and their ancillary cryogenic equipment, as well as the development of compatible component designs. This paper describes the materials used and the design of the equipment appropriate for the application. Included are summaries of the physical and mechanical properties of the materials and how they behave when irradiated. 16 refs., 7 figs., 1 tab.

  17. Hybrid Superconducting Magnetic Bearing (HSMB) for high load devices

    NASA Technical Reports Server (NTRS)

    Mcmichael, C. K.; Ma, K. B.; Lamb, M. A.; Lin, M. W.; Chow, L.; Meng, R. L.; Hor, P. H.; Chu, W. K.

    1992-01-01

    Lifting capacities greater than 41 N/cm(exp 2) (60 psi) at 77 K have been achieved with a new type of levitation (hybrid) using a combination of permanent magnets and high quality melt-mixtured YBa2Cu3O(7-delta) (YBCO). The key concept of the hybrid superconducting magnetic bearing (HSMB) is the use of strong magnetic repulsion and attraction from permanent magnets for high levitation or suspension forces in conjunction with a superconductor's flux pinning characteristics to counteract the inherent instabilities in a system consisting of magnets only. To illustrate this concept, radial and axial forces between magnet/superconductor, magnet/magnet, and magnet/superconductor/magnet, were measured and compared for the thrust bearing configuration

  18. Hybrid Superconducting Magnetic Bearing (HSMB) for high load devices

    NASA Astrophysics Data System (ADS)

    McMichael, C. K.; Ma, K. B.; Lamb, M. A.; Lin, M. W.; Chow, L.; Meng, R. L.; Hor, P. H.; Chu, W. K.

    1992-05-01

    Lifting capacities greater than 41 N/cm(exp 2) (60 psi) at 77 K have been achieved with a new type of levitation (hybrid) using a combination of permanent magnets and high quality melt-mixtured YBa2Cu3O(7-delta) (YBCO). The key concept of the hybrid superconducting magnetic bearing (HSMB) is the use of strong magnetic repulsion and attraction from permanent magnets for high levitation or suspension forces in conjunction with a superconductor's flux pinning characteristics to counteract the inherent instabilities in a system consisting of magnets only. To illustrate this concept, radial and axial forces between magnet/superconductor, magnet/magnet, and magnet/superconductor/magnet, were measured and compared for the thrust bearing configuration

  19. Can Laser Physics Notions Explain High Temperature Superconductivity?

    NASA Astrophysics Data System (ADS)

    James, John C.

    2003-03-01

    Thinking of large excitations in superconductivity (SC) in terms of population inversions would seem to allow for phonon laser amplification while simultaneously refrigerating the environment (an obvious impossibility). Fortunately, fluctuation of the SC ground state, when the population is inverted (ns < n_e), prevents second law violation by disallowing directional control of the spontaneous coherent phonon bursts. The bursts are therefore allowed to prevent the complete collapse of the SC state by driving the excited electrons back down into the SC state. Stabilization of the SC state by spontaneous, real coherent phonon deexcitation of the population inversion circumvents the instability problems in strong coupling theories bound together through virtual exchange of phonons. EXTERNAL (REAL PHONON) STABILIZATION OF STRONG COUPLED SC EXPLAINS HIGH TEMPERATURE SC ITSELF. Allowing the use of laser physics notions in high temperature SC theory dramatically simplifies understanding of an enormous number of experiments.

  20. Superconducting magnets in high-radiation environment at supercolliders

    SciTech Connect

    Mokhov, N.V.; Chichili, D.R.; Gourlay, S.A.; Van Sciver, S.; Zeller, A.

    2006-07-01

    The principal challenges arising from beam-induced energy deposition in superconducting (SC) magnets at high-energy high-luminosity hadron and lepton colliders are described. Radiation constraints are analyzed that include quench stability, dynamic heat loads on the cryogenic system, radiation damage limiting the component lifetime, and residual dose rates related to hands-on maintenance. These issues are especially challenging for the interaction regions (IR), particularly for the considered upgrade layouts of the Large Hadron Collider. Up to a few kW of beam power can dissipate in a single SC magnet, and a local peak power density can substantially exceed the quench levels. Just formally, the magnet lifetime is limited to a few months under these conditions. Possible solutions and the ways to mitigate these problems are described in this paper along with R&D needed.

  1. High-gradient, pulsed operation of superconducting niobium cavities

    SciTech Connect

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

    1984-02-01

    Tests performed on several Niobium TM/sub 010/ cavities at frequencies of about 2856 MHz using a high-power, pulsed method indicate that, at the end of the charging pulse, peak surface magnetic fields of up to approx. 1300 Oe, corresponding to a peak surface electric field of approx. 68 MV/m, can be reached at 4.2/sup 0/K without appreciable average losses. Further studies of the properties of superconductors under pulsed operation might shed light on fundamental properties of rf superconductivity, as well as lead to the possibility of applying the pulse method to the operation of high-gradient linear colliders. 7 references, 30 figures, 2 tables.

  2. Flux-motion related ac losses in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Chen, Q. Y.

    1993-03-01

    The ac losses of high-temperature superconductors in the flux-depinned mixed-state have been treated using the classical magnetic diffusion equation in conjunction with various models of flux-motion. With the imaginary part representing the ac losses, the field- and frequency-dependent ac susceptibilities were investigated. The imaginary component was found to obey a scaling rule with a characteristic frequency, estimated to be about 10 exp 5-10 exp 9 Hz, that depended on the sample size and normal state resistivity. This frequency range agrees with earlier experimental results, which could not be accounted for previously based upon the notion of thermally activated hopping of vortices. The frequency scaling behaviors using flux-creep and flux-flow models are presented.

  3. Formation of High-Order Oligomers by a Hyperthemostable Fe-Superoxide Dismutase (tcSOD)

    PubMed Central

    Wang, Sha; Dong, Zhi-Yang; Yan, Yong-Bin

    2014-01-01

    Hyperthermostable proteins are highly resistant to various extreme conditions. Many factors have been proposed to contribute to their ultrahigh structural stability. Some thermostable proteins have larger oligomeric size when compared to their mesophilic homologues. The formation of compact oligomers can minimize the solvent accessible surface area and increase the changes of Gibbs free energy for unfolding. Similar to mesophilic proteins, hyperthermostable proteins also face the problem of unproductive aggregation. In this research, we investigated the role of high-order oligomerization in the fight against aggregation by a hyperthermostable superoxide dismutase identified from Tengchong, China (tcSOD). Besides the predominant tetramers, tcSOD could also form active high-order oligomers containing at least eight subunits. The dynamic equilibrium between tetramers and high-order oligomers was not significantly affected by pH, salt concentration or moderate temperature. The secondary and tertiary structures of tcSOD remained unchanged during heating, while cross-linking experiments showed that there were conformational changes or structural fluctuations at high temperatures. Mutational analysis indicated that the last helix at the C-terminus was involved in the formation of high-order oligomers, probably via domain swapping. Based on these results, we proposed that the reversible conversion between the active tetramers and high-order oligomers might provide a buffering system for tcSOD to fight against the irreversible protein aggregation pathway. The formation of active high-order oligomers not only increases the energy barrier between the native state and unfolded/aggregated state, but also provides the enzyme the ability to reproduce the predominant oligomers from the active high-order oligomers. PMID:25313557

  4. Damping and support in high-temperature superconducting levitation systems

    DOEpatents

    Hull, John R.; McIver, Carl R.; Mittleider, John A.

    2009-12-15

    Methods and apparatuses to provide improved auxiliary damping for superconducting bearings in superconducting levitation systems are disclosed. In a superconducting bearing, a cryostat housing the superconductors is connected to a ground state with a combination of a damping strip of material, a set of linkage arms to provide vertical support, and spring washers to provide stiffness. Alternately, the superconducting bearing may be supported by a cryostat connected to a ground state by posts constructed from a mesh of fibers, with the damping and stiffness controlled by the fiber composition, size, and mesh geometry.

  5. Low-Cost Superconducting Wire for Wind Generators: High Performance, Low Cost Superconducting Wires and Coils for High Power Wind Generators

    SciTech Connect

    2012-01-01

    REACT Project: The University of Houston will develop a low-cost, high-current superconducting wire that could be used in high-power wind generators. Superconducting wire currently transports 600 times more electric current than a similarly sized copper wire, but is significantly more expensive. The University of Houston’s innovation is based on engineering nanoscale defects in the superconducting film. This could quadruple the current relative to today’s superconducting wires, supporting the same amount of current using 25% of the material. This would make wind generators lighter, more powerful and more efficient. The design could result in a several-fold reduction in wire costs and enable their commercial viability of high-power wind generators for use in offshore applications.

  6. Downsized superconducting magnetic energy storage systems

    NASA Astrophysics Data System (ADS)

    Palmer, David N.

    Scaled-down superconductive magnetic energy storage systems (DSMES) and superconductive magnetic energy power sources (SMEPS) are proposed for residential, commercial/retail, industrial off-peak and critical services, telephone and other communication systems, computer operations, power back-up/energy storages, power sources for space stations, and in-field military logistics/communication systems. Recent advances in high-Tc superconducting materials technology are analyzed. DSMES/SMEPS concepts are presented, and design, materials, and systems requirements are discussed. Problems ar identified, and possible solutions are offered. Comparisons are made with mechanical and primary and secondary energy storage and conversion systems.

  7. Exotic Superconductivity in Correlated Electron Systems

    DOE PAGES

    Mu, Gang; Sandu, Viorel; Li, Wei; Shen, Bing

    2015-05-25

    Over the past decades, the search for high-Tc superconductivity (SC) and its novel superconducting mechanisms is one of the most challenging tasks of condensed matter physicists and material scientists, wherein the most striking achievement is the discovery of high-c and unconventional superconductivity in strongly correlated 3d-electron systems, such as cuprates and iron pnictides/chalcogenides. Those exotic superconductors display the behaviors beyond the scope of the BCS theory (in the SC states) and the Landau-Fermi liquid theory (in the normal states). In general, such exotic superconductivity can be seen as correlated electron systems, where there are strong interplays among charge, spin, orbital,more » and lattice degrees of freedom. Thus, we focus on the exotic superconductivity in materials with correlated electrons in the present special issue.« less

  8. High temperature superconductivity in sulfur and selenium hydrides at high pressure

    NASA Astrophysics Data System (ADS)

    Flores-Livas, José A.; Sanna, Antonio; Gross, E. K. U.

    2016-03-01

    Due to its low atomic mass, hydrogen is the most promising element to search for high-temperature phononic superconductors. However, metallic phases of hydrogen are only expected at extreme pressures (400 GPa or higher). The measurement of the record superconducting critical temperature of 203 K in a hydrogen-sulfur compound at 160 GPa of pressure [A.P. Drozdov, M.I. Eremets, I.A. Troyan, arXiv:1412.0460; [cond-mat.supr-con] (2014); A.P. Drozdov, M.I. Eremets, I.A. Troyan, V. Ksenofontov, S.I. Shylin, Nature 525, 73 (2015)], shows that metallization of hydrogen can be reached at significantly lower pressure by inserting it in the matrix of other elements. In this work we investigate the phase diagram and the superconducting properties of the H-S systems by means of minima hopping method for structure prediction and density functional theory for superconductors. We also show that Se-H has a similar phase diagram as its sulfur counterpart as well as high superconducting critical temperature. We predict H3Se to exceed 120 K superconductivity at 100 GPa. We show that both H3Se and H3S, due to the critical temperature and peculiar electronic structure, present rather unusual superconducting properties. Supplementary material in the form of one pdf file available from the Journal web page at: http://dx.doi.org/10.1140/epjb/e2016-70020-0

  9. Superconducting Tunnel Junctions for High-Precision EUV Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ponce, F.; Carpenter, M. H.; Cantor, R.; Friedrich, S.

    2016-08-01

    We have characterized the photon response of superconducting tunnel junctions in the extreme ultraviolet energy range below 100 eV with a pulsed 355 nm laser. The detectors are operated at rates up to 5000 counts/s, are very linear in energy and have an energy resolution between 0.9 and 2 eV. We observe multiple peaks that correspond to an integer number of photons with a Poissonian probability distribution and that can be used for high-accuracy energy calibration. The uncertainty of the centroid depends on the detector resolution and the counting statistics and can be as low as 1 meV for well-separated peaks with >10^5 counts. We discuss the precision of the peak centroid as a function of detector resolution and total number of counts and the accuracy of the energy calibration.

  10. High Temperature Superconducting Bearings for Lunar Telescope Mounts

    NASA Technical Reports Server (NTRS)

    Lamb, Mark; BuiMa, Ki; Cooley, Rodger; Mackey, Daniel; Meng, Ruling; Chu, Ching Wu; Chu, Wei Kan; Chen, Peter C.; Wilson, Thomas

    1995-01-01

    A telescope to be installed on the lunar surface in the near future must work in a cold and dusty vacuum environment for long periods without on site human maintenance. To track stars, the drive mechanism must be capable of exceedingly fine steps and repeatability. Further, the use of lightweight telescopes for obvious economic benefits burdens the requirement for stable support and rotation. Conventional contact bearings and gear drives have numerous failure modes under such a restrictive and harsh environment. However, hybrid superconducting magnetic bearings (HSMB) fit in naturally. These bearings are stable, light, passive, and essentially frictionless, allowing high precision electronic positioning control. By passive levitation, the HSMB does not wear out and requires neither maintenance nor power. A prototype illustrating the feasibility of this application is presented.

  11. Improved capacitive stress transducers for high-field superconducting magnets

    NASA Astrophysics Data System (ADS)

    Benson, Christopher Pete; Holik, Eddie Frank, III; Jaisle, Andrew; McInturff, A.; McIntyre, P.

    2012-06-01

    High-field (12-18 Tesla) superconducting magnets are required to enable an increase in the energy of future colliders. Such field strength requires the use of Nb3Sn superconductor, which has limited tolerance for compressive and shear strain. A strategy for stress management has been developed at Texas A&M University and is being implemented in TAMU3, a short-model 14 Tesla stress-managed Nb3Sn block dipole. The strategy includes the use of laminar capacitive stress transducers to monitor the stresses within the coil package. We have developed fabrication techniques and fixtures, which improve the reproducibility of the transducer response both at room temperature and during cryogenic operation. This is a report of the status of transducer development.

  12. Voltage spike detection in high field superconducting accelerator magnets

    SciTech Connect

    Orris, D.F.; Carcagno, R.; Feher, S.; Makulski, A.; Pischalnikov, Y.M.; /Fermilab

    2004-12-01

    A measurement system for the detection of small magnetic flux changes in superconducting magnets, which are due to either mechanical motion of the conductor or flux jump, has been developed at Fermilab. These flux changes are detected as small amplitude, short duration voltage spikes, which are {approx}15mV in magnitude and lasts for {approx}30 {micro}sec. The detection system combines an analog circuit for the signal conditioning of two coil segments and a fast data acquisition system for digitizing the results, performing threshold detection, and storing the resultant data. The design of the spike detection system along with the modeling results and noise analysis will be presented. Data from tests of high field Nb{sub 3}Sn magnets at currents up to {approx}20KA will also be shown.

  13. The fabrication and characterization of high temperature superconducting magnetic shields

    SciTech Connect

    Purpura, J.W.; Clem, T.R.

    1989-03-01

    Tubes fabricated of polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-x/ are characterized and details of the fabrication procedure are discussed. The microstructure of the tubes determined by scanning electron microscopy and x-ray diffractometry is described. Resistive measurements of T/sub c/ and /Delta/T/sub c/ have been made. The tubes have also been characterized by means of SQUID magnetometry. The temperature dependence of magnetic fields trapped axially in the tubes has been measured and estimates of penetration depth are given. Moreover, measurements of transverse shielding effectiveness of the tubes have been made and are compared with theoretical predictions. Studies on flux penetration into the tubes are described. Findings from the microstructure studies are correlated with the observed superconductivity properties. The results on the high temperature materials are compared to results obtained previously on tubes made from conventional superconductors.

  14. Exploration of Anomalous Gravity Effects by rf-Pumped Magnetized High-T(c) Superconducting Oxides

    NASA Technical Reports Server (NTRS)

    Robertson, Tony; Litchford, Ron; Peters, Randall; Thompson, Byran; Rodgers, Stephen L. (Technical Monitor)

    2001-01-01

    A number of anomalous gravitational effects have been reported in the scientific literature during recent years, but there has been no independent confirmation with regard to any of these claims. Therefore, the NASA Marshall Space Flight Center, in response to the propulsion challenges specified by NASA's Breakthrough Propulsion Physics (BPP) program, proposed to explore the possibility of observing anomalous gravitation behavior through the manipulation of Josephson junction effects in magnetized high-Tc superconducting oxides. The technical goal was to critically test this revolutionary physical claim and provide a rigorous, independent, empirical confirmation (or refutation) of anomalous effects related to the manipulation of gravity by radio frequency (rf)-pumped magnetized type-2 superconductors. Because the current empirical evidence for gravity modification is anecdotal, our objective was to design, construct, and meticulously implement a discriminating experiment, which would put these observations on a more firm footing within the scientific community. Our approach is unique in that we advocate the construction of an extremely sensitive torsion balance with which to measure gravity modification effects by rf-pumped type-2 superconductor test masses. This paper reviews the anecdotal evidence for anomalous gravity effects, describes the design and development of a simplified torsion balance experiment for empirically investigating these claims, and presents the results of preliminary experiments.

  15. Discovery of a superconducting high-entropy alloy.

    PubMed

    Koželj, P; Vrtnik, S; Jelen, A; Jazbec, S; Jagličić, Z; Maiti, S; Feuerbacher, M; Steurer, W; Dolinšek, J

    2014-09-01

    High-entropy alloys (HEAs) are multicomponent mixtures of elements in similar concentrations, where the high entropy of mixing can stabilize disordered solid-solution phases with simple structures like a body-centered cubic or a face-centered cubic, in competition with ordered crystalline intermetallic phases. We have synthesized an HEA with the composition Ta34Nb33Hf8Zr14Ti11 (in at. %), which possesses an average body-centered cubic structure of lattice parameter a=3.36  Å. The measurements of the electrical resistivity, the magnetization and magnetic susceptibility, and the specific heat revealed that the Ta34Nb33Hf8Zr14Ti11 HEA is a type II superconductor with a transition temperature Tc≈7.3  K, an upper critical field μ0H_c2≈8.2  T, a lower critical field μ0Hc1≈32  mT, and an energy gap in the electronic density of states (DOS) at the Fermi level of 2Δ≈2.2  meV. The investigated HEA is close to a BCS-type phonon-mediated superconductor in the weak electron-phonon coupling limit, classifying it as a "dirty" superconductor. We show that the lattice degrees of freedom obey Vegard's rule of mixtures, indicating completely random mixing of the elements on the HEA lattice, whereas the electronic degrees of freedom do not obey this rule even approximately so that the electronic properties of a HEA are not a "cocktail" of properties of the constituent elements. The formation of a superconducting gap contributes to the electronic stabilization of the HEA state at low temperatures, where the entropic stabilization is ineffective, but the electronic energy gain due to the superconducting transition is too small for the global stabilization of the disordered state, which remains metastable. PMID:25238377

  16. Anisotropy Effect on Levitation Performance of Bulk High-Tc Superconductors Above a Permanent Magnet Guideway

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Liao, Xinglin; Jing, Hailian; Lin, Qunxu; Ma, Guangtong; Yen, Fei; Wang, Suyu; Wang, Jiasu

    The anisotropy properties of bulk high-temperature superconductors (HTSCs) are taken into consideration for the application of high-temperature superconducting (HTS) Maglev systems, which are especially based on the different flux-trapping capabilities as well as critical current density, Jc, values between the growth section boundary (GSB) and the growth sections (GS) in bulk superconductors. By adjusting the angle between the GSB of bulk HTSCs and the strongest magnetic field position of a permanent magnet guideway (PMG), the levitation force and its relaxation processes are compared at different field-cooling conditions. Experimental results show that the levitation capability and the suppression of levitation force decay can be enhanced by optimizing the GS/GSB alignment of every bulk HTSC above the PMG. Meanwhile, our conclusions may provide references to other HTS maglev systems with small levitation gaps, i.e., superconducting magnetic bearings.

  17. Large low-symmetry polarons of the high-Tc, copper oxides: Formation, mobility and ordering

    NASA Astrophysics Data System (ADS)

    Bersuker, Gennadi I.; Goodenough, John B.

    1997-02-01

    A microscopic model of the evolution from antiferromagnetic insulator to superconductor on oxidation of the parent-phase (CuO 2) 2- sheets of a cuprate superconductor starts with the assumption that strong electron-lattice interactions are dominant and give a heterogeneous electronic distribution. Introduction of pseudo-Jahn-Teller vibronic coupling associated with the δ holes in the (CuO 2) (2-δ) - sheets is shown to stabilize, below a critical temperature Tp ≈ 850 K, large non-adiabatic polarons containing 5 to 7 copper centers; cooperative low-symmetry in-plane vibrations also stabilize an elastic attractive force between polarons that can overcome the longer-range Coulomb repulsion between polarons. Utilizing established parameters for isolated CuO 6 complexes gives a calculated polaron size of 5 to 7 copper centers, which compares with a measured mean size of 5.3 copper centers in underdoped samples 0 < δ ≤ 0.10. A large polaron is shown to move by a piece-wise tunneling of a fraction of itself across a peripheral CuO vibronic bond rather than by an activated hopping. This type of motion, which is not described by conventional transport theories, gives a linear increase of the resistivity with temperature above a temperature Tϱ due to scattering of the polaron at its own border, which separates regions inside and outside the polaron of slightly different mean CuO bond length. At lower temperatures, the polaron mobility becomes activated, but at higher concentrations this change is obscured because the elastic interpolaron attractive force causes the polarons to condense into a “polaron liquid,” and below some critical temperature Td ≥ Tc the polarons undergo long-range ordering into one-dimensional <110> polaronic stripes separated by stripes of the parent phase, which support antiferromagnetic spin fluctuations. The zig-zag polaron stripes consist of polaron pairs oriented alternately along [100] and [010] axes of a CuO 2 sheet. Formation

  18. Shielded high-Tc bscco tapes or wires for high field applications

    DOEpatents

    Balachandran, Uthamalingam; Lelovic, Milan; Eror, Nicholas G.

    2002-01-01

    A composite superconductor having an interior component of multiple filaments of superconducting Bi-2223 sheathed in a Ag or Ag alloy material, and a RE, TI or Hg based superconductor surrounding the interior component.

  19. Shielded high-TC BSCCO tapes or wires for high field applications

    DOEpatents

    Balachandran, Uthamalingam; Lelovic, Milan; Eror, Nicholas G.

    2001-01-01

    A composite superconductor having an interior component of multiple filaments of superconducting Bi-2223 sheathed in a Ag or Ag alloy material, and a RE, TI or Hg based superconductor surrounding the interior component.

  20. Numerical solution of High-kappa model of superconductivity

    SciTech Connect

    Karamikhova, R.

    1996-12-31

    We present formulation and finite element approximations of High-kappa model of superconductivity which is valid in the high {kappa}, high magnetic field setting and accounts for applied magnetic field and current. Major part of this work deals with steady-state and dynamic computational experiments which illustrate our theoretical results numerically. In our experiments we use Galerkin discretization in space along with Backward-Euler and Crank-Nicolson schemes in time. We show that for moderate values of {kappa}, steady states of the model system, computed using the High-kappa model, are virtually identical with results computed using the full Ginzburg-Landau (G-L) equations. We illustrate numerically optimal rates of convergence in space and time for the L{sup 2} and H{sup 1} norms of the error in the High-kappa solution. Finally, our numerical approximations demonstrate some well-known experimentally observed properties of high-temperature superconductors, such as appearance of vortices, effects of increasing the applied magnetic field and the sample size, and the effect of applied constant current.

  1. Scanning instrumentation for measuring magnetic field trapping in high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Sisk, R. C.; Helton, A. J.

    1993-01-01

    Computerized scanning instrumentation measures and displays trapped magnetic fields across the surface of high Tc superconductors at 77 K. Data are acquired in the form of a raster scan image utilizing stepping motor stages for positioning and a cryogenic Hall probe for magnetic field readout. Flat areas up to 45 mm in diameter are scanned with 0.5-mm resolution and displayed as false color images.

  2. Preparing Teachers to Discuss Superconductivity at High School Level: A Didactical Approach

    ERIC Educational Resources Information Center

    Ostermann, Fernanda; Ferreira, Leticie Mendonca

    2006-01-01

    We present an introduction to superconductivity that is intended to support the teaching and learning of this subject at a high school level. As a first step we propose to focus on the main properties of superconducting materials, i.e. zero electrical resistivity and the Meissner effect. Physics teachers and students will thereby be enabled to…

  3. Reflection and transmission measurements on high-T{sub c} superconducting films in the MM-wave region

    SciTech Connect

    Gallerano, G.P.; Doria, P.; Giovenale, E.

    1995-12-31

    The characterization of high-Tc superconducting films is in progress at the Frascati FEL Facility, F-CUBE. The experiment is aimed at obtaining the complex conductivity of YBCO films deposited on a LaAlO3 substrate by measuring the reflection and transmission coefficients. Similar experiments have been performed by other groups at far infrared wavelengths. The continues tunability and the high peak power, up to 10 kW, of F-CUBE make this experiment possible also at millimeter wavelengths even in very lossy samples with transmission of less than 1%. Such an experiment is important for the study of high-Tc superconductors, because it provides additional spectral information and a better comprehension of the internal structure of these materials. The experimental technique utilized will be discussed together with the issues related to the detection process and to the stability of the FEL source. Results in the spectral range between 2 and 3.5 mm will be presented and compared with the characteristics at shorter wavelengths.

  4. Superconductivity in CVD Diamond Films

    NASA Astrophysics Data System (ADS)

    Takano, Yoshihiko

    2005-03-01

    The recent news of superconductivity 2.3K in heavily boron-doped diamond synthesized by high pressure sintering was received with considerable surprise (1). Opening up new possibilities for diamond-based electrical devices, a systematic investigation of these phenomena clearly needs to be achieved. Application of diamond to actual devices requires it to be made into the form of wafers or thin films. We show unambiguous evidence for superconductivity in a heavily boron-doped diamond thin film deposited by the microwave plasma assisted chemical vapor deposition (MPCVD) method (2). An advantage of the MPCVD deposited diamond is that it can control boron concentration in its wider range, particularly in (111) oriented films. The temperature dependence of resistivity for (111) and (100) homoepitaxial thin films were measured under several magnetic fields. Superconducting transition temperatures of (111) homoepitaxial film are determined to be 11.4K for Tc onset and 7.2K for zero resistivity. And the upper critical field is estimated to be about 8T. These values are 2-3 times higher than these ever reported (1,3). On other hand, for (100) homoepitaxial film, Tc onset and Tc zero resistivity were estimated to be 6.3 and 3.2K respectively. The superconductivity in (100) film was strongly suppressed even at the same boron concentration. These differences of superconductivity in film orientation will be discussed. These findings established the superconductivity as a universal property of boron-doped diamond, demonstrating that device application is indeed a feasible challenge. 1. E. A. Ekimov et al. Nature, 428, 542 (2004). 2. Y. Takano et al., Appl. Phys. Lett. 85, 2851 (2004). 3. E. Bustarret et al., ond-mat 0408517.

  5. A technique to measure the thermal diffusivity of high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Powers, Charles E.

    1991-01-01

    High T(sub c) superconducting electrical current leads and ground straps will be used in cryogenic coolers in future NASA Goddard Space Flight Center missions. These superconducting samples are long, thin leads with a typical diameter of two millimeters. A longitudinal method is developed to measure the thermal diffusivity of candidate materials for this application. This technique uses a peltier junction to supply an oscillatory heat wave into one end of a sample and will use low mass thermocouples to follow the heat wave along the sample. The thermal diffusivity is calculated using both the exponential decay of the heat wave and the phase shift to the wave. Measurements are performed in a cryostat between 10 K and room temperature.

  6. Disentangling the electronic and phononic glue in a high-Tc superconductor.

    PubMed

    Dal Conte, S; Giannetti, C; Coslovich, G; Cilento, F; Bossini, D; Abebaw, T; Banfi, F; Ferrini, G; Eisaki, H; Greven, M; Damascelli, A; van der Marel, D; Parmigiani, F

    2012-03-30

    Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamental step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (Ω)-dependent bosonic function, Π(Ω). We performed optical spectroscopy on Bi(2)Sr(2)Ca(0.92)Y(0.08)Cu(2)O(8+δ) crystals with simultaneous time and frequency resolution; this technique allowed us to disentangle the electronic and phononic contributions by their different temporal evolution. The spectral distribution of the electronic excitations and the strength of their interaction with fermionic quasiparticles fully account for the high critical temperature of the superconducting phase transition.

  7. Compensated electron and hole pickets in an underdoped high Tc superconductor

    SciTech Connect

    Harrison, Neil; Altarawneh, Moaz M; Mielke, Charles H; Sebastian, Suchitra E; Goddard, P A; Liang, Ruixing; Bonn, D A; Hardy, W N; Andersen, O K; Lonzarich, G G

    2010-01-01

    Important to the question of high temperature superconductivity is whether bound fermionic pairs with zero or finite momentum - exhibiting bosonic physics - are involved. Here we use angle-dependent magnetic quantum oscillation measurements in underdoped YBa{sub 2}Cu{sub 3}O{sub 6+x} to reveal two significantly differently corrugated small sections of Fermi surface, identifying them as comprising opposite carriers located at different locations of the Brillouin zone. The surprising finding that these disproportionately heavy small pockets are equal in size indicates they are prone to a finite momentum excitonic insulator instability. We discuss the possibility that reducing the doping drives YBa{sub 2}Cu{sub 3}O{sub 6+x} closer to an instability of this nature, its ultimate realization occuring at the metal-insulator quantum critical point, accompanied by a potential enhancement of superconducting transition temperatures.

  8. Fracture behavior of an inclined crack interacting with a circular inclusion in a high-TC superconductor under an electromagnetic force

    NASA Astrophysics Data System (ADS)

    Xue, Feng; Zhang, Zhaoxia; Gou, Xiaofan

    2015-11-01

    A simple model is proposed to investigate the interaction problem for a circular nonsuperconducting inclusion embedded in a high-TC superconducting matrix which contains an inclined crack, oriented at an arbitrary angle from the direction of the critical currents. The electromagnetic behavior is described by the critical state, the original Bean model. The perturbation brought upon by the circular inclusion and the crack on the critical current density is assumed to be negligible and not considered in this model. The distribution dislocation technology is applied to formulate the current problem. The stress intensity factors (SIFs) are obtained by solving the formulated singular integral equations. The effects of the crack angle, the elastic modulus, the inclusion-crack distance and the inclusion-crack size on the stress intensity factors are discussed in detail.

  9. Miniaturized high-temperature superconducting multiplexer with cascaded quadruplet structure

    NASA Astrophysics Data System (ADS)

    Xu, Zhang; Jingping, Liu; Shaolin, Yan; Lan, Fang; Bo, Zhang; Xinjie, Zhao

    2015-06-01

    In this paper, compact high temperature superconducting (HTS) multiplexers are presented for satellite communication applications. The first multiplexer consists of an input coupling node and three high-order bandpass filters, which is named triplexer. The node is realized by a loop microstrip line instead of conventional T-junction to eliminate the redundant susceptance due to combination of three filters. There are two eight-pole band-pass filters and one ten-pole band-pass filter with cascaded quadruplet structure for realizing high isolation. Moreover, the triplexer is extended to a multiplexer with six channels so as to verify the expansibility of the suggested approach. The triplexer is fabricated using double-sided YBa2Cu3O7 thin films on a 38 × 25 mm2 LaAlO3 substrate. The experimental results, when compared with those ones from the T-junction multiplexer, show that our multiplexer has lower insertion loss, smaller sizes and higher isolation between any two channels. Also, good agreement has been achieved between simulations and measurements, which illustrate the effectiveness of our methods for the design of high performance HTS multiplexers.

  10. Twenty years of talking past each other: The theory of high Tc

    NASA Astrophysics Data System (ADS)

    Anderson, Philip W.

    2007-09-01

    In 1988, the outline of an essentially correct theory of the high Tc cuprates was published by two groups, Zhang et al. in Zurich and Kotliar et al. in the US, based on earlier suggestions. The rather startling experimental predictions: that the gap would be real d-wave with nodes; that the gap would greatly increase with underdoping; that Tc would exhibit a dome terminating linearly around x = 30%; were so bizarre that these papers gathered little attention from others, including myself and at least 8 other Nobel prize-winners, and as they came to be substantiated one by one nobody much noticed that fact until the method was revived a dozen years later by Paramekanti et al. and Sorella et al. I will discuss some recent achievements and generalizations of these methods.

  11. Superconductivity in an Organic Insulator at Very High Magnetic Fields

    SciTech Connect

    Balicas, L.; Brooks, J. S.; Storr, K.; Uji, S.; Tokumoto, M.; Tanaka, H.; Kobayashi, H.; Kobayashi, A.; Barzykin, V.; Gor'kov, L. P.

    2001-08-06

    We investigate by electrical transport the field-induced superconducting state (FISC) in the organic conductor {lambda}-(BETS){sub 2}FeCl{sub 4} . Below 4K, antiferromagnetic-insulator, metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. The FISC state survives between 18 and 41T and can be interpreted in terms of the Jaccarino-Peter effect, where the external magnetic field compensates the exchange field of aligned Fe{sup 3+} ions. We further argue that the Fe{sup 3+} moments are essential to stabilize the resulting singlet, two-dimensional superconducting state.

  12. Electron-phonon coupling and exchange-correlation effects in superconducting H3S under high pressure

    NASA Astrophysics Data System (ADS)

    Komelj, Matej; Krakauer, Henry

    2015-11-01

    We investigate the H3S phase of sulfur hydride under high pressure ≃200 GPa by means of ab initio calculations within the framework of the density-functional theory with the PBE0 hybrid exchange-correlation (Exc) approximation. The choice of Exc has the largest effect on the calculated electron-phonon coupling (EPC) matrix elements; the high-pressure equation of state and phonon frequencies are only slightly modified. Mode-dependent EPC correction factors are determined from PBE0 using a frozen-phonon supercell approach, while standard density-functional perturbation theory is used to determine the EPC with PBE generalized-gradient approximation Exc. Our principle finding is that the calculated PBE 0 Tc is enhanced by 25% compared to PBE. This is similar in magnitude, but in opposite direction, to the proposed suppression of Tc by anharmonic effects [I. Errea et al., Phys. Rev. Lett. 114, 157004 (2015), 10.1103/PhysRevLett.114.157004]. Our calculations demonstrate the importance of considering exchange-correlation approximations for calculations of superconducting properties for this class of materials.

  13. CoBi3-the first binary compound of cobalt with bismuth: high-pressure synthesis and superconductivity

    NASA Astrophysics Data System (ADS)

    Tencé, S.; Janson, O.; Krellner, C.; Rosner, H.; Schwarz, U.; Grin, Y.; Steglich, F.

    2014-10-01

    The first compound in the cobalt bismuth system was synthesized by high-pressure high-temperature synthesis at 5 GPa and 450 °C. CoBi3 crystallizes in space group Pnma (no. 62) with lattice parameters of a = 8.8464(7) Å, b = 4.0697(4) Å and c = 11.5604(9) Å adopting a NiBi3-type crystal structure. CoBi3 undergoes a superconducting transition at Tc = 0.48(3) K as evidenced by electrical-resistivity and specific-heat measurements. Based on the anomaly of the specific heat at Tc and considering the estimated electron-phonon coupling, the new Bi-rich compound can be classified as a Bardeen-Cooper-Schrieffer-type superconductor with weak electron-phonon coupling. Density-functional theory calculations disclose a sizable influence of the spin-orbit coupling to the valence states and proximity to a magnetic instability, which accounts for a significantly enhanced Sommerfeld coefficient.

  14. Singularity in the positive Hall coeffcient near pre-onset temperatures in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Vezzoli, G. C.; Chen, M. F.; Craver, F.; Moon, B. M.; Safari, A.; Burke, T.; Stanley, W.

    1990-10-01

    Hall measurements using continuous extremely slow cooling and reheating rates as well as employing eqiulibrium point-by-point conventional techniques reveals a clear anomally in RH at pre-onset temperatures near Tc in polycrystalline samples Y1Ba2Cu3O7 and Bi2Sr2Ca2Cu3O10. The anomaly has the appearance of a singularity of Dirac-delta function which parallels earlier work on La1-xSrxCuO4. Recent single crystal work on the Bi-containing high-Tc superconductor is in accord with a clearcut anomaly. The singularity is tentatively interpreted to be associated (upon cooling) with initially the removal of positive holes from the hopping conduction system of the normal state such as from the increased concentration of bound virtual excitons due to increased exciton and hole lifetimes at low temperature. Subsequently the formation of Cooper pairs by mediation from these centers (bound-holes) and/or bound excitons) may cause an ionization of these bound virtual excitons thereby re-introducing holes and electrons into the conduction system at Tc.

  15. High temperature superconducting FeSe films on SrTiO3 substrates

    PubMed Central

    Sun, Yi; Zhang, Wenhao; Xing, Ying; Li, Fangsen; Zhao, Yanfei; Xia, Zhengcai; Wang, Lili; Ma, Xucun; Xue, Qi-Kun; Wang, Jian

    2014-01-01

    Interface enhanced superconductivity at two dimensional limit has become one of most intriguing research directions in condensed matter physics. Here, we report the superconducting properties of ultra-thin FeSe films with the thickness of one unit cell (1-UC) grown on conductive and insulating SrTiO3 (STO) substrates. For the 1-UC FeSe on conductive STO substrate (Nb-STO), the magnetization versus temperature (M-T) measurement shows a drop crossover around 85 K. For the FeSe films on insulating STO substrate, systematic transport measurements were carried out and the sheet resistance of FeSe films exhibits Arrhenius TAFF behavior with a crossover from a single-vortex pinning region to a collective creep region. More intriguing, sign reversal of Hall resistance with temperature is observed, demonstrating a crossover from hole conduction to electron conduction above TC in 1-UC FeSe films. PMID:25113391

  16. Fabrication and characterization of scanning tunneling microscopy superconducting Nb tips having highly enhanced critical fields

    NASA Astrophysics Data System (ADS)

    Kohen, A.; Noat, Y.; Proslier, T.; Lacaze, E.; Aprili, M.; Sacks, W.; Roditchev, D.

    2005-02-01

    We report a simple method for the fabrication of Niobium superconducting (SC) tips for scanning tunneling microscopy which allow atomic resolution. The tips, formed in situ by the mechanical breaking of a niobium wire, reveal a clear SC gap of 1.5 meV and a critical temperature Tc = 9.2 ± 0.3 K, as deduced from Superconductor Insulator Normal metal (SIN) and Superconductor Insulator Superconductor (SIS) spectra. These match the values of bulk Nb samples. We systematically find an enhanced value of the critical magnetic field in which superconductivity in the tip is destroyed (around 1 T for some tips) up to five times larger than the critical field of bulk Nb (0.21 T). Such enhancement is attributed to a size effect at the tip apex.

  17. An overview of recent developments in high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Falicov, L. M.

    1987-10-01

    The BCS theory, in all probability, will explain the properties of new superconducting oxide materials. However, a detailed account of why they have such an unusually high transition temperature will require much more work. The key to the answer to the theoretical questions may be found in the fact that all these materials are ceramics, i.e., bad conductors in their normal phase. In fact, they are 'almost insulators', with strange and varied magnetic properties. And although the lattice polarization will certainly play a role (as shown by the isotope effect), the detailed motion of the electrons and the short-range Coulomb repulsion may give the unusual characteristics which result in high transition temperatures. From the point of view of practical applications and their implications in our everyday life, much can be speculated: transmission lines without any power losses, levitated trains, super-super-computers, new and not-yet-invented devices. But all these innovations will require the solution of complicated (and expensive to solve) materials problems (brittle, hard to handle ceramics; unstable phases; low critical currents) as well as a cool-headed economic analysis which this author is unable to provide.

  18. High temperature superconductivity technology for advanced space power systems

    NASA Technical Reports Server (NTRS)

    Faymon, Karl A.; Myers, Ira T.; Connolly, Denis J.

    1990-01-01

    In 1987, the Lewis Research center of the NASA and the Argonne National Laboratory of the Department of Energy joined in a cooperative program to identify and assess high payoff space and aeronautical applications of high temperature superconductivity (HTSC). The initial emphasis of this effort was limited, and those space power related applications which were considered included microwave power transmission and magnetic energy storage. The results of these initial studies were encouraging and indicated the need of further studies. A continuing collaborative program with Argonne National Laboratory has been formulated and the Lewis Research Center is presently structuring a program to further evaluate HTSC, identify applications and define the requisite technology development programs for space power systems. This paper discusses some preliminary results of the previous evaluations in the area of space power applications of HTSC which were carried out under the joint NASA-DOE program, the future NASA-Lewis proposed program, its thrusts, and its intended outputs and give general insights on the anticipated impact of HTSC for space power applications of the future.

  19. Transient analysis and burnout of high temperature superconducting current leads

    NASA Astrophysics Data System (ADS)

    Seol, S. Y.; Hull, J. R.

    The transient behaviour of high-temperature superconductor (HTS) current leads operated between liquid helium and liquid nitrogen temperatures is analysed for burnout conditions upon transition of the HTS into the normal state. Leads composed of HTS only and of HTS sheathed by pure silver or silver alloy are investigated numerically for temperature-dependent properties and analytically for temperature-independent properties. For lower values of shape factor (current density times length), the lead can be operated indefinitely without burnout. At higher values of shape factor, the lead reaches burnout in a finite time. With high current densities, the leads heat adiabatically. For a fixed shape factor, low current densities are desired to achieve long burnout times. To achieve a low helium boil-off rate in the superconducting state without danger of burnout, there is a preferred temperature dependence for thermal conductivity, and silver alloy sheaths are preferred to pure silver sheaths. However, for a given current density, pure silver sheaths take longer to burn out.

  20. Highly textured oxypnictide superconducting thin films on metal substrates

    SciTech Connect

    Iida, Kazumasa Kurth, Fritz; Grinenko, Vadim; Hänisch, Jens; Chihara, Masashi; Sumiya, Naoki; Hatano, Takafumi; Ikuta, Hiroshi; Ichinose, Ataru; Tsukada, Ichiro; Matias, Vladimir; Holzapfel, Bernhard

    2014-10-27

    Highly textured NdFeAs(O,F) thin films have been grown on ion beam assisted deposition-MgO/Y{sub 2}O{sub 3}/Hastelloy substrates by molecular beam epitaxy. The oxypnictide coated conductors showed a superconducting transition temperature (T{sub c}) of 43 K with a self-field critical current density (J{sub c}) of 7.0×10{sup 4} A/cm{sup 2} at 5 K, more than 20 times higher than powder-in-tube processed SmFeAs(O,F) wires. Albeit higher T{sub c} as well as better crystalline quality than Co-doped BaFe{sub 2}As{sub 2} coated conductors, in-field J{sub c} of NdFeAs(O,F) was lower than that of Co-doped BaFe{sub 2}As{sub 2}. These results suggest that grain boundaries in oxypnictides reduce J{sub c} significantly compared to that in Co-doped BaFe{sub 2}As{sub 2} and, hence biaxial texture is necessary for high J{sub c.}.

  1. Recovery time of high temperature superconducting tapes exposed in liquid nitrogen

    NASA Astrophysics Data System (ADS)

    Sheng, Jie; Zeng, Weina; Yao, Zhihao; Zhao, Anfeng; Hu, Daoyu; Hong, Zhiyong

    2016-08-01

    The recovery time is a crucial parameter to high temperature superconducting tapes, especially in power applications. The cooperation between the reclosing device and the superconducting facilities mostly relies on the recovery time of the superconducting tapes. In this paper, a novel method is presented to measure the recovery time of several different superconducting samples. In this method criterion used to judge whether the sample has recovered is the liquid nitrogen temperature, instead of the critical temperature. An interesting phenomenon is observed during the testing of superconducting samples exposed in the liquid nitrogen. Theoretical explanations of this phenomenon are presented from the aspect of heat transfer. Optimization strategy of recovery characteristics based on this phenomenon is also briefly discussed.

  2. Submicron-scale high- Tc superconducting Bi-2212 stack fabrication for single-Cooper-pair tunneling

    NASA Astrophysics Data System (ADS)

    Kim, S.-J.; Latyshev, Yu. I.; Yamashita, T.; Sato, N.; Kishida, S.

    2000-07-01

    We report the characteristics of Bi-2212 intrinsic Josephson junctions (IJJ) showing single-Cooper-pair tunneling effect with a decrease of their in-plane area, S, smaller than a micron scale. The junctions show the typical slope of critical current and current peak-like structure up to 37 K.

  3. TlCaBaCuO high Tc superconducting microstrip ring resonators designed for 12 GHz

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Kapoor, V. J.; Chorey, C. M.; Bhasin, K. B.

    1993-01-01

    Microwave properties of sputtered Tl-Ca-Ba-Cu-O thin films were investigated by designing, fabricating, and testing microstrip ring resonators. Ring resonators designed for 12 GHz fundamental resonance frequency, were fabricated and tested. From the unloaded Q values for the resonators, the surface resistance was calculated by separating the conductor losses from the total losses. The penetration depth was obtained from the temperature dependence of resonance frequency, assuming that the shift in resonance frequency is mainly due to the temperature dependence of penetration depth. The effective surface resistance at 12 GHz and 77 K was determined to be between 1.5 and 2.75 mOmega, almost an order lower than Cu at the same temperature and frequency. The effective penetration depth at 0 K is approximately 7000 A.

  4. Infrared detection with high-[Tc] bolometers and response of Nb tunnel junctions to picosecond voltage pulses

    SciTech Connect

    Verghese, S.

    1993-05-01

    Oxide superconductors with high critical temperature [Tc] make sensitive thermometers for several types of infrared bolometers. The authors built composite bolometers with YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta

  5. New k-phase materials, k-(ET) sub 2 Cu(N(CN) sub 2 )X: X = Cl, Br and I: The synthesis, structure and superconductivity above 11 K in the Cl ( Tc = 12. 8 K, 0. 3 kbar) and Br( Tc = 11. 6 K) salts

    SciTech Connect

    Wang, H.H.; Carlson, K.D.; Geiser, U.; Kini, A.M.; Schultz, A.J.; Williams, J.M.; Montgomery, L.K.; Kwok, W.K.; Welp, U.; Vandervoort, K.G.; Boryschuk, S.J.; Strieby Crouch, A.V.; Kommers, J.M.; Watkins, D.M. ); Schirber, J.E.; Overmyer, D.L. ); Jung, D.; Novoa, J.J.; Whangbo, M.H. )

    1990-01-01

    The syntheses, structures, selected physical properties, and band electronic structures of three copper (I) dicyanamide halide salts of bis(ethylenedithio)tetrathiafulvalene ({kappa}-(ET){sub 2}Cu(N(CN){sub 2})X, where X = Cl, Br, and I) are discussed. X-ray crystallographic studies demonstrate that the three derivatives are isostructural. The bromide salt is an ambient pressure superconductor with an inductive onset at 11.6 K and a resistive onset at 12.5 K. {kappa}-(ET){sub 2}Cu(N(CN){sub 2})Cl exhibits the highest reported superconducting transition temperature ({Tc} = 12.8 K, 0.3 kbar) for an organic superconductor, once a semiconductor-semiconductor transition (42 K) is suppressed. The application of GE varnish or Apiezon N grease to crystals of {kappa}-(ET){sub 2}Cu(N(CN){sub 2})Cl provides sufficient stress to induce superconductivity at ambient pressure.'' Crystals of the iodide remain metallic to {approximately}150 K, where they become weakly semiconductive. No sign of superconductivity was detected at pressures (hydrostatic and shearing) up to 5.2 kbar and at temperatures as low as 1.1 K. The band electronic structures of the three salts are essentially identical. The differences in superconducting properties are explained in terms of differences in lattice softness, which are strongly influenced by short C-H{hor ellipsis}donor and C-H{hor ellipsis}anion contacts. 17 refs., 2 figs.

  6. Cryocooled superconducting magnets for high magnetic fields at the HFLSM and future collaboration with the TML

    NASA Astrophysics Data System (ADS)

    Watanabe, K.; Nishijima, G.; Awaji, S.; Koyama, K.; Takahashi, K.; Kobayashi, N.; Kiyoshi, T.

    2006-11-01

    A hybrid magnet needs a large amount of liquid helium for operation. In order to make an easy-to-operate hybrid magnet system, we constructed a cryocooled 28 T hybrid magnet, consisting of an outer cryocooled 10 T superconducting magnet and an inner traditional water-cooled 19 T resistive magnet. As a performance test, the cryocooled hybrid magnet generated 27.5 T in a 32 mm room temperature experimental bore. As long as Nb3Sn superconducting wires are employed, the expected maximum high field generation in the cryocooled superconducting magnet will be 17 T at 5 K. We adopted the high temperature superconducting insert coil, employing Ag-sheathed Bi2Sr2Ca2Cu3O10superconducting tape. In combination with the low temperature 16.5 T back-up coil with a 174 mm cold bore, the cryocooled high temperature superconducting magnet successfully generated the total central field of 18.1 T in a 52 mm room temperature bore. As a next step, we start the collaboration with the National Institute for Materials Science for the new developmental works of a 30 T high temperature superconducting magnet and a 50 T-class hybrid magnet.

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

    SciTech Connect

    Green, M.A.

    1988-02-01

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

  8. High temperature superconducting axial field magnetic coupler: realization and test

    NASA Astrophysics Data System (ADS)

    Belguerras, L.; Mezani, S.; Lubin, T.; Lévêque, J.; Rezzoug, A.

    2015-09-01

    Contactless torque transmission through a large airgap is required in some industrial applications in which hermetic isolation is necessary. This torque transmission usually uses magnetic couplers, whose dimension strongly depends on the airgap flux density. The use of high temperature superconducting (HTS) coils to create a strong magnetic field may constitute a solution to reduce the size of the coupler. It is also possible to use this coupler to replace a torque tube in transmitting the torque produced by a HTS motor to its load. This paper presents the detailed construction and tests of an axial field HTS magnetic coupler. Pancake coils have been manufactured from BSCCO tape and used in one rotor of the coupler. The second rotor is mainly composed of NdFeB permanent magnets. Several tests have been carried out showing that the constructed coupler is working properly. A 3D finite element (FE) model of the studied coupler has been developed. Airgap magnetic field and torque measurements have been carried out and compared to the FE results. It has been shown that the measured and the computed quantities are in satisfactory agreement.

  9. First-principles prediction of MgB2-like NaBC: A more promising high-temperature superconducting material than LiBC

    NASA Astrophysics Data System (ADS)

    Miao, Rende; Huang, Guiqin; Yang, Jun

    2016-05-01

    Crystal structure, lattice dynamics, and superconducting properties for sodium borocarbides NaB1+xC1-x are investigated with first-principles calculations. Based on crystal structure analysis by particle swarm optimization methodology, NaBC is predicted to crystallize in the layered P63 / mmc crystal structure as LiBC. However, it is different from LiBC, in that Na atoms are effectively ionized, with no longitudinal covalence exist between Na and B-C layers, just as in the case of MgB2. Therefore, Na1-xBC is more similar to MgB2 than Li1-xBC as a potential high-temperature superconductor. Further more, we suggest that the slight hole doping of NaBC through partial substitution of C by B atoms can also produce cause superconductivity. The phonon spectra for NaBC and NaB1.1C0.9 are obtained within the virtual-crystal approximation treatment. There is a remarkable softening of the in-plane B-C bond-stretching modes for NaB1.1C0.9 in certain regions of the Brillouin zone, while other phonon bands show no obvious softening behavior. This conspicuous softening of the in-plane B-C bond-stretching modes indicates a strong electron-phonon coupling for them. The obtained total electron-phonon coupling strength λ for NaB1.1C0.9 is 0.73, and superconducting transition temperature TC is predicted to be 35 K (μ* = 0.1). This indicates that NaB1+xC1-x is potentially high-temperature superconducting and hole doping of NaBC could produce high-temperature superconductivity. In addition, we conjecture that, to design a MgB2-like high TC superconducting material, the longitudinal covalent bonds between the metal cations and graphite-like layers need be excluded.

  10. Effects of post-annealing and cobalt co-doping on superconducting properties of (Ca,Pr)Fe2As2 single crystals

    NASA Astrophysics Data System (ADS)

    Okada, T.; Ogino, H.; Yakita, H.; Yamamoto, A.; Kishio, K.; Shimoyama, J.

    2014-10-01

    In order to clarify the origin of anomalous superconductivity in (Ca,RE)Fe2As2 system, Pr doped and Pr,Co co-doped CaFe2As2 single crystals were grown by the FeAs flux method. These samples showed two-step superconducting transition with Tc1 = 25-42 K, and Tc2 < 16 K, suggesting that (Ca,RE)Fe2As2 system has two superconducting components. Post-annealing performed for these crystals in evacuated quartz ampoules at various temperatures revealed that post-annealing at ∼400 °C increased the c-axis length for all samples. This indicates that as-grown crystals have a certain level of strain, which is released by post-annealing at ∼400 °C. Superconducting properties also changed dramatically by post-annealing. After annealing at 400 °C, some of the co-doped samples showed large superconducting volume fraction corresponding to the perfect diamagnetism below Tc2 and high Jc values of 104-105 A cm-2 at 2 K in low field, indicating the bulk superconductivity of (Ca,RE)Fe2As2 phase occurred below Tc2. On the contrary, the superconducting volume fraction above Tc2 was always very small, suggesting that 40 K-class superconductivity observed in this system is originating in the local superconductivity in the crystal.

  11. Products of pertechnetate radiolysis in highly alkaline solution: structure of TcO2 x xH2O.

    PubMed

    Lukens, Wayne W; Bucher, Jerome I; Edelstein, Norman M; Shuh, David K

    2002-03-01

    The chemistry of technetium in certain high-level nuclear waste (HLW) tanks at the Hanford Site complicates the treatment and vitrification of HLW. A major problem is the presence, in certain tanks, of unidentified, lower-valent technetium species, which are difficult to remove from the waste by current separation processes. Radiolytic reduction of TcO4- in alkaline solutions containing selected organic compounds, approximating the conditions in HLW, was investigated to determine the classes of compounds that can be formed under these conditions. Insoluble TcO2 x xH2O is the primary radiolysis product with the majority of organic compounds investigated, including citrate, dibutyl phosphate, and aminopolycarboxylates. X-ray absorption fine structure (XAFS) measurements show that TcO2 x xH2O has a one-dimensional chain structure consisting of edge-sharing TcO6 octahedra with bridging oxide and trans water ligands. When diols, such as ethylene glycol, are present, only soluble, Tc(IV) alkoxide compounds are produced. The XAFS and UV-visible spectra of these compounds provide evidence for a binuclear structure similar to (H2EDTA)2Tc2(mu-O)2. The properties of the Tc(IV) alkoxide complexes were determined and are consistent with those observed for the soluble, lower-valent technetium complexes that complicate the treatment of HLW at the Hanford site.

  12. Products of pertechnetate radiolysis in highly alkaline solution: structure of TcO2 x xH2O.

    PubMed

    Lukens, Wayne W; Bucher, Jerome I; Edelstein, Norman M; Shuh, David K

    2002-03-01

    The chemistry of technetium in certain high-level nuclear waste (HLW) tanks at the Hanford Site complicates the treatment and vitrification of HLW. A major problem is the presence, in certain tanks, of unidentified, lower-valent technetium species, which are difficult to remove from the waste by current separation processes. Radiolytic reduction of TcO4- in alkaline solutions containing selected organic compounds, approximating the conditions in HLW, was investigated to determine the classes of compounds that can be formed under these conditions. Insoluble TcO2 x xH2O is the primary radiolysis product with the majority of organic compounds investigated, including citrate, dibutyl phosphate, and aminopolycarboxylates. X-ray absorption fine structure (XAFS) measurements show that TcO2 x xH2O has a one-dimensional chain structure consisting of edge-sharing TcO6 octahedra with bridging oxide and trans water ligands. When diols, such as ethylene glycol, are present, only soluble, Tc(IV) alkoxide compounds are produced. The XAFS and UV-visible spectra of these compounds provide evidence for a binuclear structure similar to (H2EDTA)2Tc2(mu-O)2. The properties of the Tc(IV) alkoxide complexes were determined and are consistent with those observed for the soluble, lower-valent technetium complexes that complicate the treatment of HLW at the Hanford site. PMID:11918000

  13. Pair correlation and dynamic Jahn-Teller effect: High-Tc in nanoclusters

    NASA Astrophysics Data System (ADS)

    Kresin, Vladimir; Ovchinnikov, Yurii; Friedel, Jacques

    2014-11-01

    Electronic states in metallic nanoclusters form energy shells and degree of their filling depends on the number of delocalized electrons. In the region close to half-filling the cluster's geometry oscillates between the prolate and oblate configurations (dynamic Jahn-Teller effect). For large clusters (N > 102 N is the number of delocalized electrons) this effect competes with pair correlation and, as a result, it is perfectly realistic to observe the transition to the superconducting state. For some clusters (e.g., for Zn76, Al70) the value of the critical temperature is rather high (≳ 140 \\text{K}) .

  14. High performance superconducting radio frequency ingot niobium technology for continuous wave applications

    SciTech Connect

    Dhakal, Pashupati Ciovati, Gianluigi Myneni, Ganapati R.

    2015-12-04

    Future continuous wave (CW) accelerators require the superconducting radio frequency cavities with high quality factor and medium accelerating gradients (≤20 MV/m). Ingot niobium cavities with medium purity fulfill the specifications of both accelerating gradient and high quality factor with simple processing techniques and potential reduction in cost. This contribution reviews the current superconducting radiofrequency research and development and outlines the potential benefits of using ingot niobium technology for CW applications.

  15. High field superconductivity in alkali metal intercalates of MoS2

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.; Flood, D. J.; Wagoner, D. E.; Somoano, R. B.; Rembaum, A.

    1973-01-01

    In the search for better high temperature, high critical field superconductors, a class of materials was found which have layered structures and can be intercalated with various elements and compounds. Since a large number of compounds can be formed, intercalation provides a method of control of superconducting properties. They also provide the possible medium for excitonic superconductivity. Results of magnetic field studies are presented on alkali metal (Na, K, Rb, and Cs) intercalated MoS2 (2H polymorph).

  16. Preisach-type modeling of high-temperature superconducting hysteresis

    NASA Astrophysics Data System (ADS)

    ElBidweihy, Hatem

    2016-05-01

    Even though Isaak Mayergoyz described it as: "much more accurate for the description of superconducting hysteresis than for the description of hysteresis of magnetic materials", Preisach modeling of superconducting hysteresis is not a popular investigative tool. This might be due to the complexity of identifying the Preisach distribution function or due to lack of convincing physical reasoning behind pure phenomenological versions. In this paper, a two-component Preisach-type model is presented which is computationally-efficient and physically-sound. The change in the slope of the minor hysteresis loops is incorporated in the model and is attributed to reversible fluxoid motion. The model presented is clearly capable of simulating various shapes of superconducting hysteresis loops and could be easily coupled with finite element method (FEM) numerical software.

  17. Terahertz applications of integrated circuits based on intrinsic Josephson junctions in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Huabing; Wu, Peiheng; Yamashita, Tsutomu

    2001-10-01

    Using a newly developed double-side fabrication method, an IJJ stack plus a bow-tie antenna and chokes were integrated in a slice 200 nm thick and singled out from inside a bulk Bi2Sr2CaCu2O8+x (BSCCO) single crystal. The junctions in the fabricated stack were very uniform, and the number of junctions involved was rather controllable. In addition to this method, which can be used to fabricate integrated circuits based on intrinsic Josephson junctions in high temperature (Tc) superconductors, also reported will be terahertz responses of IJJs, and the possible applications in quantum voltage standard, spectroscopy, and so on.

  18. Inelastic electron scattering in the high-Tc compound YBa2Cu3O7-x

    NASA Astrophysics Data System (ADS)

    Tarrio, C.; Schnatterly, S. E.

    1988-07-01

    We have carried out inelastic electron scattering transmission measurements on the high-Tc compound YBa2Cu3O7-x in the energy range 1-100 eV. We have directly observed the free-electron plasma peak at 1.1 eV in addition to the bound electron plasmon at 25.5 eV. The interband threshold is at 2.1 eV, above which the material behaves as a typical oxide insulator.

  19. Tunneling Spectral Dip Feature in High Tc Cuprates: Experiment and Analysis

    NASA Astrophysics Data System (ADS)

    Zasadzinski, John; Coffey, Liam; Kurter, Cihan; Gray, Ken

    2009-03-01

    A fully self-consistent Eliashberg analysis is presented to analyze the spectral dip feature observed in tunnel junctions on Bi2212. Methods include SIS break junctions, intrinsic Josephson junctions in mesas and SIN junctions from STM. This analysis is presented for a variety of doping levels and the resulting electron-boson spectral function and self-energy is compared with other spectroscopic probes. Evidence of spectral dip features in other high Tc cuprates is presented including Tl2212 to demonstrate the universality of the spectral dip and its relation to the mechanism of pairing.

  20. High duty factor plasma generator for CERN's Superconducting Proton Linac.

    PubMed

    Lettry, J; Kronberger, M; Scrivens, R; Chaudet, E; Faircloth, D; Favre, G; Geisser, J-M; Küchler, D; Mathot, S; Midttun, O; Paoluzzi, M; Schmitzer, C; Steyaert, D

    2010-02-01

    CERN's Linac4 is a 160 MeV linear accelerator currently under construction. It will inject negatively charged hydrogen ions into CERN's PS-Booster. Its ion source is a noncesiated rf driven H(-) volume source directly inspired from the one of DESY and is aimed to deliver pulses of 80 mA of H(-) during 0.4 ms at a 2 Hz repetition rate. The Superconducting Proton Linac (SPL) project is part of the luminosity upgrade of the Large Hadron Collider. It consists of an extension of Linac4 up to 5 GeV and is foreseen to deliver protons to a future 50 GeV synchrotron (PS2). For the SPL high power option (HP-SPL), the ion source would deliver pulses of 80 mA of H(-) during 1.2 ms and operate at a 50 Hz repetition rate. This significant upgrade motivates the design of the new water cooled plasma generator presented in this paper. Its engineering is based on the results of a finite element thermal study of the Linac4 H(-) plasma generator that identified critical components and thermal barriers. A cooling system is proposed which achieves the required heat dissipation and maintains the original functionality. Materials with higher thermal conductivity are selected and, wherever possible, thermal barriers resulting from low pressure contacts are removed by brazing metals on insulators. The AlN plasma chamber cooling circuit is inspired from the approach chosen for the cesiated high duty factor rf H(-) source operating at SNS. PMID:20192392