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Sample records for high tc superconductivity

  1. Gauge Model of High-Tc Superconductivity

    NASA Astrophysics Data System (ADS)

    Kui Ng, Sze

    2012-12-01

    A simple gauge model of superconductivity is presented. The seagull vertex term of this gauge model gives an attractive potential between electrons for the forming of Cooper pairs of superconductivity. This gauge model gives a unified description of superconductivity and magnetism including antiferromagnetism, pseudogap phenomenon, stripes phenomenon, paramagnetic Meissner effect, Type I and Type II supeconductivity and high-Tc superconductivity. The doping mechanism of superconductivity is found. It is shown that the critical temperature Tc is related to the ionization energies of elements and can be computed by a formula of Tc. For the high-Tc superconductors such as La2-xSrxCuO4, Y Ba2Cu3O7, and MgB2, the computational results of Tc agree with the experimental results.

  2. Theory of High-TC Superconductivity: Accurate Predictions of TC

    NASA Astrophysics Data System (ADS)

    Harshman, Dale; Fiory, Anthony

    2012-02-01

    The superconducting transition temperatures of high-TC compounds based on copper, iron, ruthenium and certain organic molecules is discovered to be dependent on bond lengths, ionic valences, and Coulomb coupling between electronic bands in adjacent, spatially separated layers [1]. Optimal transition temperature, denoted as TC0, is given by the universal expression kBTC0 = e^2λ/lζ; l is the spacing between interacting charges within the layers, ζ is the distance between interacting layers and λ is a universal constant, equal to about twice the reduced electron Compton wavelength (suggesting that Compton scattering plays a role in pairing). Non-optimum compounds in which sample degradation is evident typically exhibit TC < TC0. For the 31+ optimum compounds tested, the theoretical and experimental TC0 agree statistically to within ± 1.4 K. The elemental high-TC building block comprises two adjacent and spatially separated charge layers; the factor e^2/ζ arises from Coulomb forces between them. The theoretical charge structure representing a room-temperature superconductor is also presented. * 1. doi:10.1088/0953-8984/23/29/295701

  3. 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.

  4. High Tc superconducting materials and devices

    NASA Astrophysics Data System (ADS)

    Haertling, Gene H.

    1990-09-01

    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.

  5. High-{Tc} superconducting superlattices

    SciTech Connect

    Wood, R.F.

    1993-06-01

    Superlattices composed of YBa{sub 2}CU{sub 3}O{sub 7} and PrBa{sub 2}Cu{sub 3}O{sub 7} have been studied extensively experimentally and several theoretical attempts to correlate the resistivity as a function of temperature with the superlattice structure have appeared in the literature. The theoretical interest in such structures comes about primarily because of insight into dimensionality effects, interlayer coupling, and interlayer charge redistribution in high-T {sub c}, superconductors. On the experimental side, there are possibilities for device applications that are just now beginning to be explored. After an overview of the experimental work and a discussion of charge transfer calculations, a description of how the experimental data can be explained using a model that incorporates Kosterlitz-Thouless (vortex-antivortex unbinding) and Azlamazov-Larkin (fluctuation-enhanced conductivity) theories in the resistive transition region and charge-transfer effects, variable-range hopping, etc. in the normal state. Difficulty in disentangling charge transfer and dimensionality effects in determining the nominal transition temperature is pointed out and other mechanisms that influence the width of the resistive transition are considered.

  6. Superconducting bolometers: high-Tc and low-Tc

    NASA Astrophysics Data System (ADS)

    Richards, Paul L.

    1991-07-01

    A description is given of recent work at Berkeley on superconducting detectors and mixers for infrared and millimeter wavelengths. The first report is a review article which summarizes the status of development of superconducting components for infrared and millimeter wave receivers. Next, a report is given on measurements and theoretical modeling of the absorptivity (surface resistance) of high quality epitaxial films of the high-Tc superconductor YBCO from 750 GHz to 21 THz. The next report describes measurements of the thermal boundary resistance between YBCO films and various substrates. This resistance is much larger than expected from the acoustic impedance mismatch model and gives a thermal time constant in the nanosecond range for typical YBCO films. Reports are also included on the design and experimental performance of two different types of high-Tc bolometric detectors. One is a conventional bolometer with a gold-black absorber. The other is an antenna coupled microbolometer. The properties of a low-Tc microbolometer are also described. The last reports describe accurate measurements and also theoretical modeling of an SIS quasi-particle waveguide mixer for W-band which uses very high quality Ta junctions. The best mixer noise is only 1.3 times the quantum limit. Both the mixer gain and the noise are in quantitative agreement with the quantum theory.

  7. 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'.

  8. 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.

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

    NASA Technical Reports Server (NTRS)

    Lakeou, Samuel

    1994-01-01

    The original workplan for the first year of the project includes the following: establishment of a pilot superconductivity application laboratory at UDC to support the research component of the project; research on the source of electrical noise in High Tc superconducting films in order to optimize the film microstructure and lower the NEP; and lay the foundation of an academic support for exposing UDC students to the theory and application of High Tc superconductivity. Attached to this status report are abstracts and the course description for Introduction to Applications of Superconductivity.

  10. How to optimize high-Tc superconductive cuprates

    NASA Astrophysics Data System (ADS)

    Raveau, B.; Michel, C.; Hervieu, M.; Groult, D.; Maignan, A.; Provost, J.

    1992-06-01

    Several examples are used here to illustrate the way that modifying the structure of high-Tc superconductive cuprates (HTSCs) allows their superconducting properties to be significantly improved. It is shown that energetic heavy ions can be used as projectiles to modify and tailor superconducting properties. In particular, the creation of columnar defects with dimensions of Xi(ab) or more can act as efficient pinning centers for flux lines and can be used to extend the operating field range of HTSCs to substantially higher fields near Tc's. The crucial role of radiation-induced defects in controlling the magnetic hysteresis shape and therefore the critical current density is demonstrated.

  11. Prospects for high-Tc superconducting optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1992-04-01

    Two possible approaches for the development of a complete optoelectronic system with the elements based on high-temperature superconducting (HTS) films are discussed. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. In this latter case, a laser writing process is implemented to define superconducting and nonsuperconducting regions in the same, epitaxial HTS film Several practical devices, such as high-speed interconnects, high-frequency traveling-wave optical modulators, picosecond electrical pulse generators, sensitive photodetectors, and a novel HTS charging-effect transistor are proposed. All the devices can operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting (e.g., GaAs) devices are optimal.

  12. High {Tc} superconductivity: Symmetries and reflections

    SciTech Connect

    Zhang, S.C.

    1999-12-30

    This is a talk given at the Symposium Symmetries and Reflections, dedicated to Prof. C.N. Yang's retirement. In this talk, the author reflects on his personal interaction with Prof. Yang since his graduate career at SUNY Stony Brook, and his profound impact on his understanding of theoretical physics. He also reviews the SO(5) theory of high T{sub c} superconductivity and shows how his collaboration with Prof. Yang in 1990 lead to the foundation of this idea.

  13. Ultrafast Broadband Photodetectors for High-Tc Superconductive Optoelectronics

    DTIC Science & Technology

    1997-01-01

    TITLE AND SUBTITLE Ultrafast Broadband Photodetectors for High-Tc Supercondcutive Optoelectronics 6. AUTHOR(S) Dr. Roman Sobolewski (PI) Dr...The rapid suppression of the Maki-Thompson process for the oxygen-deficient YBCO films, indicated an unconventional symmetry of the superconducting

  14. 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

  15. 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.

  16. Bec Model of HIGH-Tc Superconductivity in Layered Cuprates

    NASA Astrophysics Data System (ADS)

    Lomnitz, M.; Villarreal, C.; de Llano, M.

    2013-11-01

    High-Tc superconductivity in layered cuprates is described in a BCS-BEC formalism with linearly-dispersive s- and d-wave Cooper pairs moving in quasi-2D finite-width layers around the CuO2 planes. This yields a closed formula for Tc involving the layer width, the Debye frequency, the pairing energy and the in-plane penetration depth. The new formula has no free parameters and reasonably reproduces empirical values of superconducting Tcs for 11 different layered superconductors over a wide doping regime including YBCO itself as well as other compounds like LSCO, BSCCO and TBCCO. In agreement with the London formalism, the formula also yields a fair description of the Tc dependence of the lower critical magnetic field in highly underdoped YBCO.

  17. High- Tc superconductivity: phenomenology and microscopics

    NASA Astrophysics Data System (ADS)

    Eliashberg, G. M.

    1993-11-01

    The Luttinger-Wart sum rule is used as the start-point of a consistent semi-phenomenological description of the one-electron spectrum in solids. For normal metals it is essentially the Fermi-liquid theory but the effects of the Coulomb correlations are explicitly included. It is shown that the BCS theory can be formulated for strongly correlated metals, although the accuracy of this description decreases along with enhancement of Tc.

  18. Fabrication Of High-Tc Superconducting Integrated Circuits

    NASA Technical Reports Server (NTRS)

    Bhasin, Kul B.; Warner, Joseph D.

    1992-01-01

    Microwave ring resonator fabricated to demonstrate process for fabrication of passive integrated circuits containing high-transition-temperature superconductors. Superconductors increase efficiencies of communication systems, particularly microwave communication systems, by reducing ohmic losses and dispersion of signals. Used to reduce sizes and masses and increase aiming accuracies and tracking speeds of millimeter-wavelength, electronically steerable antennas. High-Tc superconductors preferable for such applications because they operate at higher temperatures than low-Tc superconductors do, therefore, refrigeration systems needed to maintain superconductivity designed smaller and lighter and to consume less power.

  19. Dynamic resistance of a high-Tc superconducting flux pump

    NASA Astrophysics Data System (ADS)

    Jiang, Zhenan; Hamilton, K.; Amemiya, Naoyuki; Badcock, R. A.; Bumby, C. W.

    2014-09-01

    Superconducting flux pumps enable large currents to be injected into a superconducting circuit, without the requirement for thermally conducting current leads which bridge between the cryogenic environment and room temperature. In this work, we have built and studied a mechanically rotating flux pump which employs a coated conductor high-Tc superconducting (HTS) stator. This flux pump has been used to excite an HTS double pancake coil at 77 K. Operation of the flux pump causes the current within the superconducting circuit to increase over time, before saturating at a limiting value. Interestingly, the superconducting flux pump is found to possess an effective internal resistance, Reff, which varies linearly with frequency, and is two orders of magnitude larger than the measured series resistance of the soldered contacts within the circuit. This internal resistance sets a limit for the maximum achievable output current from the flux pump, which is independent of the operating frequency. We attribute this effect to dynamic resistance within the superconducting stator wire which is caused by the interaction between the DC transport current and the imposed alternating magnetic field. We provide an analytical expression describing the output characteristics of our rotating flux pump in the high frequency limit, and demonstrate that it describes the time-dependent behavior of our experimental circuit. Dynamic resistance is highlighted as a generic issue that must be considered when optimizing the design of an HTS flux pump.

  20. High-Tc superconducting quantum interference devices: Status and perspectives

    NASA Astrophysics Data System (ADS)

    Yang, Hong-Chang; Chen, Ji-Chen; Chen, Kuen-Lin; Wu, Chiu-Hsien; Horng, Herng-Er; Yang, S. Y.

    2008-07-01

    In this paper, an overview of the current status of high-Tc superconducting quantum interference devices (SQUIDs), from device engineering to biomagnetic applications, is given. The authors offer a description of the current status of SQUID sensors, challenges encountered, and the solution of fabricating SQUID sensors with low flux noises. The current challenge that we face is to fabricate high-Tc SQUIDs that are not only more reproducible than the current technology but also capable of providing a high IcRn product and fabricating SQUID with high yield. Improvement of flux noises and fabrication yield in the integrated multichoices directly coupled SQUID magnetometer or gradiometer with series SQUID array are presented. High-Tc SQUID magnetometers exhibiting magnetic field sensitivity of ˜30-50fT/Hz1/2 or better at 100Hz was demonstrated by incorporating serial SQUID into the pickup loop of the magnetometers. New technologies currently being developed and applications for high-Tc SQUIDs are addressed.

  1. The superconducting gap ratio, isotope-shift exponent and pressure coefficient of Tc for high- Tc systems

    NASA Astrophysics Data System (ADS)

    Das, A. N.; Sarkar, Sujit

    1996-02-01

    The superconducting gap ratio, isotope-shift exponent and the pressure co-efficient of the superconducting transition temperature are studied within different models proposed for high- Tc cuprate oxide systems. A comparison with the experimental results of high- Tc oxide systems is made.

  2. Photoemission studies of high-tc superconductors: the superconducting gap.

    PubMed

    Shen, Z X; Spicer, W E; King, D M; Dessau, D S; Wells, B O

    1995-01-20

    Over the last several years there have been great improvements in the energy resolution and detection efficiency of angle-resolved photoemission spectroscopy. These improvements have made it possible to discover a number of fascinating features in the electronic structure of the high transition temperature (T(c)) superconductors: apparently bandlike Fermi surfaces, flat-band saddle points, and nested Fermi surface sections. Recent work suggests that these features, previously thought explainable only by one-electron band theory, may be better understood with a many-body approach. Furthermore, other properties of the high-T(c) superconductors, which are difficult to understand with band theory, are well described using a many-body picture. Angle-resolved photoemission spectroscopy has also been used to investigate the nature of the superconducting pairing state, revealing an anisotropic gap consistent with a d-wave order parameter and fueling the current debate over s-wave versus d-wave superconductivity.

  3. Five Possible Reasons why HIGH-Tc Superconductivity is Stalled

    NASA Astrophysics Data System (ADS)

    Grether, M.; de Llano, M.

    Five commonly held premises considered questionable assumptions in the microscopic theory of superconductivity are discussed as possible reasons why the search appears to be stalled for a theoretical framework, admittedly ambitious, capable of predicting materials with critical temperatures Tc higher than the 1993 record of 164K in HgTlBaCaCuO (under pressure). We focus the dilemma as a whole in terms of a generalized Bose-Einstein condensation (GBEC) interpretation that includes and further extends BCS theory, as well as substantially enhancing its predicted Tcs within the electron-phonon mechanism producing pairing. The new GBEC model is an extension of the Friedberg-T.D. Lee 1989 boson-fermion BEC theory of high-Tc superconductors in that it includes hole pairs as well as electron pairs.

  4. Five Possible Reasons why HIGH-Tc Superconductivity is Stalled

    NASA Astrophysics Data System (ADS)

    Grether, M.; de Llano, M.

    2007-09-01

    Five commonly held premises considered questionable assumptions in the microscopic theory of superconductivity are discussed as possible reasons why the search appears to be stalled for a theoretical framework, admittedly ambitious, capable of predicting materials with critical temperatures Tc higher than the 1993 record of 164K in HgTlBaCaCuO (under pressure). We focus the dilemma as a whole in terms of a generalized Bose-Einstein condensation (GBEC) interpretation that includes and further extends BCS theory, as well as substantially enhancing its predicted Tcs within the electron-phonon mechanism producing pairing. The new GBEC model is an extension of the Friedberg-T.D. Lee 1989 boson-fermion BEC theory of high-Tc superconductors in that it includes hole pairs as well as electron pairs.

  5. 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.

  6. Deformation processing of high-Tc superconducting oxides

    NASA Astrophysics Data System (ADS)

    Rajan, K.; German, R. M.; Knorr, D. B.; Maccrone, R. K.; Misiolek, W.; Wright, R. N.

    1989-04-01

    Plastic deformation and texture development in polycrystalline YBa2Cu3O7- δ has been studied to expedite the process development of high-critical-temperature (high-Tc) superconducting wires and tapes. It is anticipated that deformation texture will be a major processing consideration in terms of maximizing critical current density, assessing conductor-fabrication options in light of critical current density, and developing such mechanical properties as strength, toughness and thermal fatigue. The intrinsic texture development in YBa2Cu3O7- δ deformation processing should be highly beneficial, insofar as the c axes of the crystals tend to become oriented along the compression axis. This means that conducting tapes and wires formed by rolling, extrusion and drawing can develop textures with the c axis in the transverse or radial direction, thus maximizing the flow of current along the length of the conductor.

  7. The first five years of high- Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Müller, K. Alex

    1991-12-01

    After the 1986 discovery and confirmation of superconductivity in doped La 2CuO 4, a “gold rush” occurred in the following year when the transition temperature in YBa 2Cu 3O 7-δ exceeded the boiling point of liquid nitrogen. In 1988, even higher Tc's were reported in new compounds without rare-earth ions. The preparation techniques started to be improved substantially and results on scholarly conducted experiments became available. Since then, the data obtained with different techniques fitted together like pieces of a puzzle, and continue to do so. Early in 1987, high critical magnetic fields and currents were reported in epitaxial films and single crystals. This opened the way for application-oriented research and has led to first true successes in 1990/91. The following is a near verbal transcript of my presentation.

  8. Theory of Superconductivity in the High tc Materials

    NASA Astrophysics Data System (ADS)

    Anderson, P. W.

    The following sections are included: * INTRODUCTION * CONFINEMENT AND ITS CONSEQUENCES * PERTURBATION TREATMENT OF Tc; GREEN'S FUNCTIONS OF THE SUPERCONDUCTING STATE * HEURISTIC GAP EQUATION FOR THE INTERLAYER MECHANISM * A ROUGH PICTURE OF SOLUTIONS OF THE NEW GAP EQUATION * SURVEY OF THE EXPERIMENTAL PICTURE AND CORRELATION WITH THEORY * REFERENCES

  9. Analysis and characterization of high- Tc superconducting planar transmission lines for microwave circuit components

    SciTech Connect

    Kong Keonshik.

    1991-01-01

    A loss modeling of high {Tc} superconducting planar transmission lines is presented in this dissertation. Transmission structures such as microstrip lines, coplanar waveguides and conductor backed coplanar waveguides are investigated for implementation of a high-{Tc} superconductor. Also, short pulse propagation in the superconducting coplanar stripline is characterized. The motivation for this work is to provide an analytical basis for the effective application of a high {Tc} superconductor to planar transmission lines for microwave components. First, a loss characterization of the various high {Tc} superconducting microstrip line structures is presented in which either the strip or the ground plane is a high {Tc} superconductor. In the analysis, the internal impedances in the strip and the ground plane are separately calculated, and the total internal impedance is obtained by the superposition of the internal impedances. Next, the characteristic of a superconducting coplanar waveguide is investigated and compared with a superconducting microstrip line.

  10. Optimal High-TC Superconductivity in Cs3C60

    NASA Astrophysics Data System (ADS)

    Harshman, Dale; Fiory, Anthony

    The highest superconducting transition temperatures in the (A1-xBx)3C60 superconducting family are seen in the A15 and FCC structural phases of Cs3C60 (optimized under hydrostatic pressure), exhibiting measured values for near-stoichiometric samples of TC0 meas . = 37.8 K and 35.7 K, respectively. It is argued these two Cs-intercalated C60 compounds represent the optimal materials of their respective structures, with superconductivity originating from Coulombic e- h interactions between the C60 molecules, which host the n-type superconductivity, and mediating holes associated with the Cs cations. A variation of the interlayer Coulombic pairing model [Harshman and Fiory, J. Supercond. Nov. Magn. 28 ̲, 2967 (2015), and references therein] is introduced in which TC0 calc . ~ 1 / lζ , where l relates to the mean spacing between interacting charges on surfaces of the C60 molecules, and ζ is the average radial distance between the surface of the C60 molecules and the neighboring Cs cations. For stoichiometric Cs3C60, TC0 calc . = 38.08 K and 35.67 K for the A15 and FCC macrostructures, respectively; the dichotomy is attributable to differences in ζ.

  11. 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.

  12. A novel propulsion method for high- Tc superconducting maglev vehicle

    NASA Astrophysics Data System (ADS)

    Ma, Guangtong; Wang, Jiasu; Wang, Suyu; Liu, Minxian; Jing, Hua; Lu, Yiyun; Lin, Qunxu

    2008-01-01

    High-Tc superconducting (HTS) maglev is considered as a perfect transportation type because of its unique inherent stability. A direct current (DC) linear motor using the permanent magnet guideway (PMG) as the stator and the on-board coil as the rotor instead of the present inductive or synchronous alternate current (AC) linear motor which has an economic disadvantage due to the necessity to lay primary coil along the guideway is proposed in this paper. In order to modulate the magnetic field under the PMG, an inverse E shape ferromagnetic device (IESFD) core is designed. The possible winding method for the on-board coil is listed, and the analytical result shows that a considerable net ampere force and thus the propulsion force can be generated by this special structure. The influence of the concentrated effect of the IESFD on the maglev performance of HTS bulk is studied by a numerical program, and the results show that the levitation force with the IESFD is 90% of that without. It is also indicated that the load capability and lateral performance of the maglev vehicle combined this propulsion method can be improved thanks to the attractive effect between the IESFD and PMG. The cost of the HTS maglev vehicle will be remarkably reduced and then shorten the distance to practical application with this propulsion method.

  13. Mechanical resonance characteristics of a high-{Tc} superconducting levitation system

    SciTech Connect

    Sugiura, Toshihiko; Fujimori, Hideki

    1996-05-01

    This research deals with dynamic response of a permanent magnet freely levitated above an excited high-{Tc} superconductor. Evaluation of dynamic characteristics is required in mechanical design of high-{Tc} superconducting levitation systems. Their dynamics is coupled with Type-II superconducting phenomena. By a numerical approach based on some macroscopic models they evaluate mechanical resonance characteristics of a superconducting levitation system. Numerical results show some nonlinear properties and effect of the flux flow in Type-II superconductor, which are observed in experiments or predicted by analyses.

  14. Development of Elements of a High Tc Superconducting Cable

    DTIC Science & Technology

    1989-03-31

    0 0O DTIC N ELECTE MA 61989D N00014-88-C-000681 DEVELOPMENT OF ELEMENTS OF A HIGH T SUPERCONDUCTING CABLE C Dr. Kenneth W. Lay 518-387-6147 FAX 518... superconducting coating on a supporting fiber. The composite will also include a barrier layer between the fiber and the superconductor and a protective layer...is the development of textured polycrystalline YBa 2Cu3Oy (Y-123) with improved critical current carrying capacity. Phase II is the development of

  15. 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.

  16. High-Tc Superconductivity and Antiferromagnetism in Multilayered Copper Oxides ---A New Paradigm of Superconducting Mechanism---

    NASA Astrophysics Data System (ADS)

    Mukuda, Hidekazu; Shimizu, Sunao; Iyo, Akira; Kitaoka, Yoshio

    2012-01-01

    High-temperature superconductivity (HTSC) in copper oxides emerges on a layered CuO2 plane when an antiferromagnetic Mott insulator is doped with mobile hole carriers. We review extensive studies of multilayered copper oxides by site-selective nuclear magnetic resonance (NMR), which have uncovered the intrinsic phase diagram of antiferromagnetism (AFM) and HTSC for a disorder-free CuO2 plane with hole carriers. We present our experimental findings such as the existence of the AFM metallic state in doped Mott insulators, the uniformly mixed phase of AFM and HTSC, and the emergence of d-wave SC with a maximum Tc just outside a critical carrier density, at which the AFM moment on a CuO2 plane disappears. These results can be accounted for by the Mott physics based on the t--J model. The superexchange interaction Jin among spins plays a vital role as a glue for Cooper pairs or mobile spin-singlet pairs, in contrast to the phonon-mediated attractive interaction among electrons established in the Bardeen--Cooper--Schrieffer (BCS) theory. We remark that the attractive interaction for raising the Tc of HTSC up to temperatures as high as 160 K is the large Jin (˜ 0.12 eV), which binds electrons of opposite spins to be on neighboring sites, and that there are no bosonic glues. It is the Coulomb repulsive interaction U (> 6 eV) among Cu-3d electrons that plays a central role in the physics behind high-Tc phenomena. A new paradigm of the SC mechanism opens to strongly correlated electron matter.

  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. High-Tc superconducting materials for electric power applications.

    PubMed

    Larbalestier, D; Gurevich, A; Feldmann, D M; Polyanskii, A

    2001-11-15

    Large-scale superconducting electric devices for power industry depend critically on wires with high critical current densities at temperatures where cryogenic losses are tolerable. This restricts choice to two high-temperature cuprate superconductors, (Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Ox, and possibly to MgB2, recently discovered to superconduct at 39 K. Crystal structure and material anisotropy place fundamental restrictions on their properties, especially in polycrystalline form. So far, power applications have followed a largely empirical, twin-track approach of conductor development and construction of prototype devices. The feasibility of superconducting power cables, magnetic energy-storage devices, transformers, fault current limiters and motors, largely using (Bi,Pb)2Sr2Ca2Cu3Ox conductor, is proven. Widespread applications now depend significantly on cost-effective resolution of fundamental materials and fabrication issues, which control the production of low-cost, high-performance conductors of these remarkable compounds.

  19. 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)

  20. 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)

  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. 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

  3. Light-induced superconductivity in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Kaiser, Stefan

    2017-10-01

    Ultrashort laser pulses allow for optical control of superconductivity on picosecond timescales. Intriguing experiments at mid-IR and THz frequencies using tailored excitation pulses tuned resonantly to specific phonon modes have been shown to induce transient superconducting states even far above the equilibrium transition temperature (T c). So far, experiments with light-induced superconductivity can be roughly divided into two classes: on the one hand the light pulses trigger the interplay of competing order parameters in favor of superconductivity, while in the second class of experiments a transient superconducting coherence is induced and dynamically stabilized.

  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. A New Piece in the High Tc Superconductivity Puzzle: Fe based Superconductors

    NASA Astrophysics Data System (ADS)

    Moreo, Adriana

    2011-10-01

    An overview of the historic and current developments in superconductivity will be be presented. The phenomenon of superconductivity was discovered almost 100 hundred years ago and it is still one of the hottest research topics providing fascinating puzzles and challenges to both theoreticians and experimentalists. There was a lag of almost 50 years between the experimental discovery of (low Tc) superconductivity and the development of the BCS theory which explained the phenomenon in terms of pairs of electrons held together by the interaction with the phonons in the material. The quest to discover superconducting materials with higher Tc's continued quietly for many years until huge progress occurred in the 1980' when Tc's higher than 77K were observed in copper-oxide based materials. The study of these new materials generated tremendous advances in both experimental and theoretical methods and much is now known about their properties; but the mechanism, i.e., the ``glue,'' that binds the electrons together is still unknown; it appears that phonons are unable to do the job and there is controversy on whether the magnetism present in these materials helps or hurts. Very recently, in 2008, high Tc was discovered in a new family of iron based materials. While they are similar to the cuprates in some ways, i.e., magnetism is present, there are many differences as well. This discovery provides a new chance to unveil the high-Tc mystery and the condensed matter community is intensely working on the subject.

  6. Note: A hand-held high-Tc superconducting quantum interference device operating without shielding.

    PubMed

    He, D F

    2011-02-01

    By improving the compensation circuit, a hand-held high-Tc rf superconducting quantum interference devices (SQUID) system was developed. It could operate well when moving in unshielded environment. To check the operation, it was used to do eddy-current testing by hand moving the SQUID, and the artificial defect under 6 mm aluminum plate could be successfully detected in shielded environment.

  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 Superconductivity in Superhard Diamondlike BC5

    NASA Astrophysics Data System (ADS)

    Calandra, Matteo; Mauri, Francesco

    2008-07-01

    Using density functional theory calculations we show that the recently synthesized superhard diamondlike BC5 is superconducting with a critical temperature of the same order as that of MgB2. The average electron-phonon coupling is λ=0.89, the phonon-frequency logarithmic average is ⟨ω⟩log⁡=67.4meV, and the isotope coefficients are α(C)=0.3 and α(B)=0.2. In BC5, superconductivity is mostly sustained by concerted vibrations of the B atom and its C neighbors.

  10. 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.

  11. 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.

  12. A study of high {Tc} superconducting ceramic/metal alloy composites

    SciTech Connect

    Stevens, M.G.; Du, J.; Lee, R.M; Unsworth, J.; Hely, J.; Hodges, J.

    1995-09-01

    High-{Tc} superconducting ceramic YBa{sub 2}Cu{sub 3}O{sub 7{minus}x}/metal alloy composites were fabricated. The metal matrix was a low melting point alloy of bismuth, lead, tin, cadmium and indium. The structure, DC electrical resistivity, AC magnetic susceptibility, levitation and mechanical strength of the composites were investigated. The influence of filler content on these properties was also studied. The composites behaved as a typical metal with the resistivity increasing with temperature increase and, further, did not undergo the characteristic superconducting transition to zero resistance that is obtained with the ceramic superconductor. On the other hand, the diamagnetic properties of the superconducting ceramic were preserved in the composites. The values of diamagnetic susceptibility and levitation force increase with the volume fraction of the superconducting material. The flexural strength of the composites is improved significantly in comparison with the ceramic superconductor.

  13. New Trend in THz Detection: High Tc Superconducting Hot Electron Bolometer Technology May Exhibit Advantage vs Low Tc Devices

    NASA Astrophysics Data System (ADS)

    Kreisler, A. J.; Degardin, A. F.; Aurino, M.; Peroz, C.; Villegier, J.-C.; Beaudin, G.; Delorme, Y.; Redon, M.; Sentz, A.

    2007-07-01

    Superconducting hot electron bolometer (HEB) mixers are a competitive alternative to conventional mixer technologies in the terahertz range because of their ultrawide bandwidth, high conversion gain, and low intrinsic noise level, even at 77 K. A technological process to realize HEBs based on high-Tc YBa2Cu3O7-zeta (YBCO) materials is described. Ultrathin 12 to 40 nm layers were sputtered on MgO (100) substrates, sub-micrometer constrictions (0.5 micrometer x 0.5 micrometer) were etched on these and log-periodic gold antennas were then integrated. Good superconducting properties were measured after the whole process. Electrical transport characteristics of the device are discussed, ageing effects are considered and regular bolometric THz response results are given.

  14. High- Tc Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

    DOE PAGES

    Sun, J. P.; Ye, G. Z.; Shahi, P.; ...

    2017-04-07

    The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (Tc). However, high-Tc superconductivity without hole carriers has been suggested in FeSe single-layer films and intercalated iron-selenides, raising a fundamental question whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in another high-Tc phase induced by pressure in bulk FeSe from magneto-transport measurements and first-principles calculations. With increasing pressure, the low-Tc superconducting phase transforms into high-Tc phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstrating dominant hole carriers in strikingmore » contrast to other FeSe-derived high-Tc systems. Moreover, the Hall coefficient is remarkably enlarged and the magnetoresistance exhibits anomalous scaling behaviours, evidencing strongly enhanced interband spin fluctuations in the high-Tc phase. These results in FeSe highlight similarities with high-Tc phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.« less

  15. High-Tc superconductivity in weakly electron-doped HfNCl

    NASA Astrophysics Data System (ADS)

    Pamuk, Betül; Mauri, Francesco; Calandra, Matteo

    2017-07-01

    We investigate the magnetic and superconducting properties in electron-doped LixHfNCl . HfNCl is a band insulator that undergoes an insulator to superconductor transition upon doping at x ≈0.13 . The persistence of the insulating state for x <0.13 is due to an Anderson transition probably related to Li disorder. In the metallic and superconducting phase, LixHfNCl is a prototype two-dimensional two-valley electron gas with parabolic bands. By performing a model random phase approximation approach as well as first-principles range-separated Heyd-Scuseria-Ernzerhof (HSE06) calculations, we find that the spin susceptibility χs is strongly enhanced in the low-doping regime by the electron-electron interaction. Furthermore, in the low-doping limit, the exchange interaction renormalizes the intervalley electron-phonon coupling and results in a strong increase of the superconducting critical temperature for x <0.15 . On the contrary, for x >0.15 , Tc is approximately constant, in agreement with experiments. At x =0.055 we found that Tc can be as large as 40 K, suggesting that the synthesis of cleaner samples of LixHfNCl could remove the Anderson insulating state competing with superconductivity and generate a high-Tc superconductor.

  16. BaO Planes, not CuO2 Planes, Contain HIGH-TC Superconductivity

    NASA Astrophysics Data System (ADS)

    Dow, John D.; Harshman, Dale R.

    Muon spin rotation (μ+SR) measurements conducted on crystalline YBa2Cu3O7 are consistent with s-wave pairing, not d-wave, suggesting that the superconducting hole condensate resides in the BaO layers, not in the cuprate-planes. The specific heat and thermal conductivity data are explained by the superconducting BaO layers alone, unlike the failed interpretation based on CuO2-plane superconductivity. The layer charges of the CuO2 planes are almost -2 |e|, indicating that those planes are primarily carriers of electrons, not holes. The cuprate-planes are not the dominant hole-carriers of high-TC superconductivity, as demonstrated by doped YBa2RuO6, which has no such CuO2 lanes, yet superconducts at ~ 93 K. Moreover the trio of related compounds, YSr2RuO6 (doped with Cu on Ru sites), undoped GdSr2Cu2RuO8, and undoped Gd2-zCezSr2Cu2RuO10 all start superconducting near 49 K in their SrO layers, not in the cuprate planes of the two compounds that have such planes, because those planes are either antiferromagnetic or weakly ferromagnetic and so do not superconduct. In PrBa2Cu3O7, a Pr-on-Ba-site (PrBa) defect kills the superconductivity, but Pr-on-Pr-site (PrPr) does not. Both defects are approximately equidistant from the intervening cuprate plane, suggesting that the cuprate plane does not carry significant superconductivity. In GdBa2Cu3O7, Gd-on-a-Gd-site (GdGd) does not break Cooper pairs, but Gd-on-a-Ba-site (GdBa) does, indicating that the superconductivity is in the BaO layers, and not in the cuprate-planes. In HgBa2Can-1CunO2n+2, the BaO layers, not the cuprate-planes, gain positive charge as TC, pressure, and the number of layers n increase. The reason that theories based on holes in the cuprate-planes have done so poorly is that those planes were incorrectly identified as the source of high-temperature superconductivity on the basis of a single datum by Cava et al., that was first contradicted by Jorgensen et al., and then endorsed by Jorgensen alone on the

  17. Review of the state of the art of high-Tc superconducting technology. Final report

    SciTech Connect

    Tauritz, J.L.

    1990-06-01

    Phenomenological aspects of superconductivity are summarized, particularly with respect to use at microwave frequencies. Bulk and thin-film methods of fabrication of high T(c) materials are described, and recent experimental results are reported. Applicability to microwave component design is considered, and a number of device demonstrators are reviewed. Representative European and non-European activities of relevance to future space vehicle borne microwave systems are discussed.

  18. Truncated Hilbert space approach to models of high-{Tc} superconductivity

    SciTech Connect

    Riera, J.

    1995-07-01

    In this talk the author introduces a method of diagonalization in a systematically expanded Hilbert space. The author shows some applications of this procedure to several models of relevance to high-Tc superconductivity like the t-J, the t-J{sub z} and Hubbard models. Finally, the author discusses the relation of this method of diagonalization in a reduced Hilbert space with perturbation theory and with variational methods.

  19. Potential high-Tc superconducting lanthanum and yttrium hydrides at high pressure

    NASA Astrophysics Data System (ADS)

    Liu, Hanyu; Naumov, Ivan I.; Hoffmann, Roald; Ashcroft, N. W.; Hemley, Russell J.

    2017-07-01

    A systematic structure search in the La-H and Y-H systems under pressure reveals some hydrogen-rich structures with intriguing electronic properties. For example, LaH10 is found to adopt a sodalite-like face-centered cubic (fcc) structure, stable above 200 GPa, and LaH8 a C2/m space group structure. Phonon calculations indicate both are dynamically stable; electron phonon calculations coupled to Bardeen-Cooper-Schrieffer (BCS) arguments indicate they might be high-Tc superconductors. In particular, the superconducting transition temperature Tc calculated for LaH10 is 274-286 K at 210 GPa. Similar calculations for the Y-H system predict stability of the sodalite-like fcc YH10 and a Tc above room temperature, reaching 305-326 K at 250 GPa. The study suggests that dense hydrides consisting of these and related hydrogen polyhedral networks may represent new classes of potential very high-temperature superconductors.

  20. High-Tc Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

    NASA Astrophysics Data System (ADS)

    Sun, J. P.; Ye, G. Z.; Shahi, P.; Yan, J.-Q.; Matsuura, K.; Kontani, H.; Zhang, G. M.; Zhou, Q.; Sales, B. C.; Shibauchi, T.; Uwatoko, Y.; Singh, D. J.; Cheng, J.-G.

    2017-04-01

    The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (Tc ). However, the absence of hole pockets near the Fermi level of the iron-selenide (FeSe) derived high-Tc superconductors raises a fundamental question of whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in the high-Tc phase induced by pressure in bulk FeSe from magnetotransport measurements and first-principles calculations. With increasing pressure, the low-Tc superconducting phase transforms into the high-Tc phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstrating dominant hole carriers in contrast to other FeSe-derived high-Tc systems. Moreover, the Hall coefficient is enlarged and the magnetoresistance exhibits anomalous scaling behaviors, evidencing strongly enhanced interband spin fluctuations in the high-Tc phase. These results in FeSe highlight similarities with high-Tc phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.

  1. Developments of high- Tc superconducting current feeders for a large-scale superconducting coil system

    NASA Astrophysics Data System (ADS)

    Mito, T.; Maehata, K.; Mizokami, M.; Ishibashi, K.; Takeo, M.; Iwamoto, A.; Hirano, N.; Shintomi, T.; Kimura, K.; Sawamura, M.; Yamada, S.; Satoh, S.; Motojima, O.

    1998-10-01

    A large-scale superconducting coil system, which is an essential technology for a fusion reactor, requires large capacity and high performance current feeders from the power supplies at the room temperature to the superconducting coils at the operating temperature, which is usually liquid helium temperature at present. The superconducting current feeders are being considered as a promising application of a high temperature superconductor (HTS), which can satisfy the requirements of a large current capacity and a low heat in-leak, simultaneously. To study the feasibility of the HTS current feeders, a melt-textured YBCO bulk superconductor was selected as a candidate material because of its high current transport characteristics. The YBCO disk fabricated by quench and melt growth process was cut into a short sample with the cross section of 7 mm × 7 mm and the length of 40 mm and was mounted on the copper bars to perform the actual large current transport tests. The sample could be successfully excited up to 20 kA at 4.2 K and 10 kA at 77 K. These performance test results and the further R&D items for the HTS current feeders are discussed.

  2. Pulsed Laser Deposition of High Tc Superconducting Thin Films

    DTIC Science & Technology

    1992-04-15

    de- temperature thermal detectors such as the pyroelectric ec sign of imaging arrays of high-T, bolometers for wave- tector, the thermopile , or the... concepts to discuss materials and fabrication considerations. The thermal con- the sensitivity of imaging arrays of high-T, bolometers as a ductance G to...any conceived IR detector . In addition, flux motion studies have been made by this group using our films of YBCO grown on 0.003" thick silicon wafers

  3. 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.

  4. Superfluid inhomogeneity and microwave absorption in a model for thin high- Tc superconducting films

    NASA Astrophysics Data System (ADS)

    Barabash, Sergey V.; Stroud, David

    2003-10-01

    We investigate the microwave absorption arising from inhomogeneity in the superfluid density of thin high- Tc superconducting films. Such inhomogeneities may arise from a wide variety of sources, including quenched random disorder and static charge density waves such as stripes. We show that both mechanisms will inevitably produce additional absorption at finite frequencies. We present simple model calculations for this extra absorption, and discuss applications to other transport properties in high- Tc materials. Finally, we discuss the connection of these predictions to recent measurements by Corson et al. (Nature (London) 398 (1999) 221) of absorption by the high-temperature superconductor Bi 2Sr 2CaCu 2O 8+δ in the THz frequency regime.

  5. 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.

  6. Finding new superconductors: the spin-fluctuation gateway to high Tc and possible room temperature superconductivity.

    PubMed

    Pines, David

    2013-10-24

    We propose an experiment-based strategy for finding new high transition temperature superconductors that is based on the well-established spin fluctuation magnetic gateway to superconductivity in which the attractive quasiparticle interaction needed for superconductivity comes from their coupling to dynamical spin fluctuations originating in the proximity of the material to an antiferromagnetic state. We show how lessons learned by combining the results of almost three decades of intensive experimental and theoretical study of the cuprates with those found in the decade-long study of a strikingly similar family of unconventional heavy electron superconductors, the 115 materials, can prove helpful in carrying out that search. We conclude that, since Tc in these materials scales approximately with the strength of the interaction, J, between the nearest neighbor local moments in their parent antiferromagnetic state, there may not be a magnetic ceiling that would prevent one from discovering a room temperature superconductor.

  7. Search for Very High-Tc Superconductivity in Modified Compositions of Strontium Ruthenates

    NASA Astrophysics Data System (ADS)

    Gulian, Armen; Nikoghosyan, Vahan

    2013-03-01

    In 2004-2007 we discovered unusual properties in laser-processed crystals of strontium ruthenates (including resistive and magnetic transitions) pointing towards superconductivity at 200K and higher. Being interested in understanding and reproducing their properties we explored their composition further. We obtained, via Auger-analysis, the presence of sulfur in the explored sample. The appearance of iron-based superconductors further enhanced our interest, since compositionally our materials turned out to be close to some of these new materials. If our reported observations have been caused by superconductivity that may mean that one can get Tc as high as 200-250K or even higher with these materials at proper processing. We undertook systematic research of ceramic materials Sr2RuO4 with sulfur and other dopants. Data on resistive, magnetic and other physical properties, as well as preparation techniques are reported. This work is supported by ONR Grants N000141210768 and N000141210244

  8. Analysis of a high Tc superconducting levitation system with vibration isolation control

    SciTech Connect

    Nagaya, Kosuke

    1996-03-01

    This paper presents a method for controlling vibrations of a levitated high Tc superconducting body subjected to base disturbances. To have the control forces, an actuator consisting of a permanent magnet with an electromagnet was presented. The analytical solution for calculating levitation forces due to the permanent magnet and the control currents in the electromagnet was obtained. The levitation forces obtained coincide with the previously published results. The equation of motion of the levitated body subjected to base disturbances under the control was presented. Nonlinear vibrations of the body were first discussed; then the method of vibration isolation control using the direct disturbance cancellation combining the velocity feedback control was investigated. Numerical calculations were carried out for the levitation forces, with respect to the levitated body subjected to harmonic or pulse base excitations. It was clarified that the present method is valid for controlling nonlinear systems like the magnetic levitated superconducting body.

  9. Strong correlations and the search for high-Tc superconductivity in chromium pnictides and chalcogenides

    NASA Astrophysics Data System (ADS)

    Pizarro, J. M.; Calderón, M. J.; Liu, J.; Muñoz, M. C.; Bascones, E.

    2017-02-01

    Undoped iron superconductors accommodate n =6 electrons in five d orbitals. Experimental and theoretical evidence shows that the strength of correlations increases with hole doping, as the electronic filling approaches half filling with n =5 electrons. This evidence delineates a scenario in which the parent compound of iron superconductors is the half-filled system, in analogy to cuprate superconductors. In cuprates the superconductivity can be induced upon electron or hole doping. In this work we propose to search for high-Tc superconductivity and strong correlations in chromium pnictides and chalcogenides with n <5 electrons. By means of ab initio slave-spin and multiorbital random-phase-approximation calculations we analyze the strength of the correlations and the superconducting and magnetic instabilities in these systems with the main focus on LaCrAsO. We find that electron-doped LaCrAsO is a strongly correlated system with competing magnetic interactions, with (π ,π ) antiferromagnetism and nodal d -wave pairing being the most plausible magnetic and superconducting instabilities, respectively.

  10. Electron scattering from interacting tunneling units: A model for high-Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Simanovsky, Sergey B.; Klein, Michael W.

    1996-09-01

    We consider the existence of high-Tc superconductivity and the symmetry of the gap function when electrons are scattered from tunneling units that interact via an elastic strainlike potential. We examine the consequences of conduction electron scattering for the specific case of tunneling units found in experiments on the high-Tc superconductors YBa2Cu3O6+x, Bi2CaSr2Cu2O8, Tl2CaBa2Cu2O8, Tl2Ca2Ba2Cu3O10, and Tl2CaBa2CuO6. Our calculations give (i) a strongly anisotropic scattering of the conduction electrons, (ii) a strongly anisotropic superconducting gap in k space, (iii) an isotope effect different from that associated with phonon scattering in the BCS theory, (iv) a high transition temperature, and (v) a gap function with nodes and a combination of an s-wave and a dx2-y2-wave symmetry. The dx2-y2 symmetry arises from the directionally dependent scattering of electrons by the tunneling units which have a well-defined orientation with respect to the crystal axis.

  11. High-Tc superconductivity and antiferromagnetism on self-doped high-Tc cuprate Ba2Ca3Cu4O8F2

    NASA Astrophysics Data System (ADS)

    Shimizu, Sunao; Mukuda, Hidekazu; Kitaoka, Yoshio; Iyo, Akira; Kodama, Yasuharu; Kito, Hijiri; Tokiwa, Kazuyasu; Watanabe, Tsuneo

    2007-03-01

    We report on the antiferromagnetism and high-Tc superconductivity in a F-substituted four-layered cuprate, composed of two outer and inner CuO2 planes in a unit cell, Ba2Ca3Cu4O8F2. Although a formal Cu valence is expected to be just +2.0 in the nominal composition, this is not a half-filled Mott insulator but a superconductor with Tc = 55K. Recently, it has been suggested that the origin of the superconductivity in this compound is self-doping by ARPES measurement [1] and band calculation [2], which means either outer or inner CuO2 planes are hole-doped, and the others are electron-doped. From F-NMR study, we have confirmed magnetic order with TN = 100K, concluding the uniform mixing of superconductivity and magnetic order in a single CuO2 plane. In addition, we have compared a three-layered compound Ba2Ca2Cu3O6F2, which is also superconductor with Tc = 76K. We will introduce the unique magntic and superconducting phenomena in F-substituted cuprates from microscopic points of view. [1]Y. Chen, et al., cond-mat/0611291 (2006) [2] W. Xie, et al., cond-mat/0607198 (2006)

  12. 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.

  13. Investigation of high-Tc superconducting tunnel junction after laser radiation processing

    NASA Astrophysics Data System (ADS)

    Broslavez, U. U.; Fomitchev, A. A.; Yakshin, Mikhail A.

    1995-03-01

    We investigate dynamic resistance (dV/dI) of high-Tc superconducting thin films and tunnel junction after laser radiation processing. The films of YBaCuO were prepared by laser and magnetron ablation on Al2O3 substrates. The tunnel junctions were made by fine silver wires attached to the processing surfaces. The resistance (dV/dI) was determined by a four-probe measurement. The YAG laser operating in Q-switched mode was used to interact with superconductors. The anomaly is observed in the current-voltage curve of the junction after radiation interaction. We observe hysteresis in the shape of V(I) curve. These effects are not observed without laser radiation interaction and in this case the behavior of tunnel junction is described for the standard BCS theory.

  14. Detectors of Infrared Radiation Based on High T(c) Superconducting YBCO Films

    DTIC Science & Technology

    1991-06-01

    d4 . mvuAT.OATS 3. AIPOST ’l ’ TE ’OEE FINAL REPORT 1 Dec 87-30 Apr 90 Detectors of Infrared Radiation Based on High T(c) Superconducting YBCO Films...YBa2CU3O7 film on LaAlO3 at 6.8 K biased with 20.6 mA. > .11 --- . I’ M e nsq FW m.. E\\pe of th .5.i.=nl 3(0wnN n UA*. ). l=btototpte vCV ra. dt mdm lenmo ,5,25 ind 9W nj/pu- 4=5mAT=8s’

  15. Development of a Compact Moving-Sample Magnetometer Using High-Tc Superconducting Quantum Interference Device

    NASA Astrophysics Data System (ADS)

    Mawardi Saari, Mohd; Sakai, Kenji; Kiwa, Toshihiko; Tsukamoto, Akira; Adachi, Seiji; Tanabe, Keiichi; Kandori, Akihiko; Tsukada, Keiji

    2012-04-01

    We developed a compact moving-sample magnetometer that uses a high-temperature superconductor-superconducting quantum interference device (high-Tc SQUID) to directly measure the flux coupled to a normal detection coil from a sample's magnetic moment in the presence of an external DC magnetic field. The moving-sample method is employed by inserting the sample between the poles of a DC electromagnet and vibrating the sample along the axis perpendicular to the external field axis using an actuator at a frequency of 2.693 Hz. First, the magnetic field of the sample is transferred by a first-order differential normal Cu coil to a SQUID for detection. Then, the SQUID output is fed to a lock-in amplifier for detection. The critical feature of the system design is the use of high-Tc SQUID, which enables the realization of a compact system. The basic characteristics of the developed system are presented, and the current system exhibited a detection limit of 1×10-7 emu.

  16. Development of a Compact Moving-Sample Magnetometer Using High-Tc Superconducting Quantum Interference Device

    NASA Astrophysics Data System (ADS)

    Saari, Mohd Mawardi; Sakai, Kenji; Kiwa, Toshihiko; Tsukamoto, Akira; Adachi, Seiji; Tanabe, Keiichi; Kandori, Akihiko; Tsukada, Keiji

    2012-04-01

    We developed a compact moving-sample magnetometer that uses a high-temperature superconductor--superconducting quantum interference device (high-Tc SQUID) to directly measure the flux coupled to a normal detection coil from a sample's magnetic moment in the presence of an external DC magnetic field. The moving-sample method is employed by inserting the sample between the poles of a DC electromagnet and vibrating the sample along the axis perpendicular to the external field axis using an actuator at a frequency of 2.693 Hz. First, the magnetic field of the sample is transferred by a first-order differential normal Cu coil to a SQUID for detection. Then, the SQUID output is fed to a lock-in amplifier for detection. The critical feature of the system design is the use of high-Tc SQUID, which enables the realization of a compact system. The basic characteristics of the developed system are presented, and the current system exhibited a detection limit of 1× 10-7 emu.

  17. 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.

  18. Vibration reduction using autoparametric resonance in a high-Tc superconducting levitation system

    NASA Astrophysics Data System (ADS)

    Yamasaki, Hiroshi; Takazakura, Toyoki; Sakaguchi, Ryunosuke; Sugiura, Toshihiko

    2014-05-01

    High-Tc superconducting levitation systems have very small damping and enable stable levitation without control. Therefore, they can be applied to various kinds of application. However, there are some problems that small damping produces large vibration and nonlinearity of magnetic force can generate complicated phenomena. Accordingly, analysis of these phenomena and reduction of vibration occurring in the system are important. In this study, we examined reduction of vibration without using any absorbers, but utilizing autoparametric resonance caused by nonlinear coupling between vertical oscillation and horizontal oscillation. We conducted numerical analysis and experiments in order to investigate motions of a rigid bar levitated by the electromagnetic force from high-Tc superconductors. As a result, if the ratio of the natural frequency of vertical oscillation and that of horizontal oscillation is two to one, the vertical oscillation decreases while the horizontal oscillation is excited. Thus, it was confirmed that the amplitude of a primary resonance can be reduced by occurrence of autoparametric resonance without using any absorbers.

  19. High-Tc superconductivity in entirely end-bonded carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Haruyama, Junji; Takesue, Izumi; Kobayashi, Naoki; Chiashi, Shohei; Maruyama, Shigeo; Sugai, Toshiki; Shinohara, Hisanori

    2006-03-01

    One-dimensional (1D) systems face some obstructions that may prevent the emergence of superconductivity(SC), e.g., a Tomonaga-Luttinger liquid (TLL) and Peierls transition. A carbon nanotube (CN) is one of the best candidates for investigating a possibility of 1D SC and its interplay with such obstructions. Only two groups have experimentally reported SC in ropes of single-walled CNs (SWNTs) and very thin SWNTs [1] to date. In addition, those interplay with 1D phenomena have never been clarified. Some theoretical papers also predicted strong correlation between TLL states and SC for SWNT ropes and importance of electron-phonon interaction for thin SWNTs [2]. Here, we report that entirely end-bonded multi-walled CNs (MWNTs) can show SC with the Tc as high as 12K [3] (about 50-times larger than Tc in former of [1]). We find that emergence of this SC and its interplay with TLL states are highly sensitive to junction structures of Au electrode/MWNTs. Only MWNTs with optimal numbers of electrically activated shells realized by the entire end-bonding can allow the SC due to intershell effects. Refs. 1.M. Kociak, et al., PRL 86, 2416 (2001); Z. K. Tang, et al., Science 292, 2462 (2001), 2.J.Gonzalez, PRL 88, 076403 (2002); R.Barnett, et al., PRB 71, 035429 (2005), 3.J.Haruyama et al., PRL Accepted

  20. The Discovery of High-Tc Superconductivity and the Countdown to the Rally

    NASA Astrophysics Data System (ADS)

    Bednorz, J. Georg

    2007-03-01

    The guiding ideas on our road towards high-Tc superconductivity and the early work at the IBM Zurich Research Laboratory are briefly addressed. I will shed some light onto the environment and the decisive circumstances that in January 1986 led to the breakthrough with the discovery of superconductivity in the cuprates. The pre-``Woodstock'' period, which lasted less than a year, covers the time in which the Zurich team tested different La2CuO4-based compounds, confirmed the Meissner effect, and studied flux trapping in these new materials. It was also the time in which the news of the discovery started to spread and in which we experienced mixed reactions ranging from silent skepticism to polite (cautious) congratulations. This changed dramatically into excitement with the confirmation of the Zurich results by the Tokyo (S. Tanaka) and the Houston ( C.W. Chu) group, and cumulated in the take-off of the new field at the famous ``Woodstock Meeting of Physics'' after the discovery of the 90 K superconductor.

  1. 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.

  2. 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.

  3. 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

    2014-11-10

    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.

  4. 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.

  5. A DFT study of rocksalt proxy copper monochalcogenide structures - Implications for possible high-Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Grant, P. M.; Hammond, R. H.; W2AGZ Technologies/GLAM, Stanford University Collaboration

    2014-03-01

    We report findings derived from a series of DFT calculations on the structural stability and paramagnetic ground states of four idealized copper monochalcogenide (CuO, CuS, CuSe, CuTe) rocksalt structures. Note that none of these target compounds occur naturally, but can possibly be fabricated using ``forced epitaxy'' MBE methods, as has been done to grow CuO tetragonal rocksalt films 5-6 monolayers thick.[1,2] Therefore, we treat all examples we report herein as proxies intended to explore candidate implications for possible future high-TC materials. In particular, we find, as might be expected from the long accepted Van Vleck-Anderson-Hubbard formalism describing antiferromagnetic insulators, the Neel temperature scales upward roughly as the width of the spin-carrying bands near or adjacent to the Fermi level or energy gap. We conclude such trend might result in higher superconducting transition temperatures should this be mediated by carrier-spin excitation/fluctuation driven pairing scaled by TN. Finally, we briefly discuss synthetic paths to realizing actual embodiments of our proxy exercises.

  6. 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.

  7. High-Tc Nodeless s±-wave Superconductivity in (Y,La)FeAsO1-y with Tc=50K:As75-NMR Study

    NASA Astrophysics Data System (ADS)

    Mukuda, H.; Furukawa, S.; Kinouchi, H.; Yashima, M.; Kitaoka, Y.; Shirage, P. M.; Eisaki, H.; Iyo, A.

    2012-10-01

    We report on an As75-NMR study on the Fe-pnictide high-Tc superconductor Y0.95La0.05FeAsO1-y (Y0.95La0.051111) with Tc=50K that includes no magnetic rare-earth elements. The measurement of the nuclear-spin lattice-relaxation rate (751/T1) has revealed that the nodeless bulk superconductivity takes place at Tc=50K while antiferromagnetic spin fluctuations develop moderately in the normal state. These features are consistently described by the multiple fully gapped s±-wave model based on the Fermi-surface nesting. Incorporating the theory based on band calculations, we propose that the reason that Tc=50K in Y0.95La0.051111 is larger than Tc=28K in La1111 is that the Fermi-surface multiplicity is maximized, and hence the Fermi-surface nesting condition is better than that in La1111.

  8. TOPICAL REVIEW: Impurity band Mott insulators: a new route to high Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Baskaran, Ganapathy

    2008-10-01

    Last century witnessed the birth of semiconductor electronics and nanotechnology. The physics behind these revolutionary developments is certain quantum mechanical behaviour of 'impurity state electrons' in crystalline 'band insulators', such as Si, Ge, GaAs and GaN, arising from intentionally added (doped) impurities. The present article proposes that certain collective quantum behaviour of these impurity state electrons, arising from Coulomb repulsions, could lead to superconductivity in a parent band insulator, in a way not suspected before. Impurity band resonating valence bond theory of superconductivity in boron doped diamond, recently proposed by us, suggests possibility of superconductivity emerging from impurity band Mott insulators. We use certain key ideas and insights from the field of high-temperature superconductivity in cuprates and organics. Our suggestion also offers new possibilities in the field of semiconductor electronics and nanotechnology. The current level of sophistication in solid state technology and combinatorial materials science is very well capable of realizing our proposal and discover new superconductors.

  9. High-Tc nodeless s±-wave superconductivity in (Y,La)FeAsO(1-y) with Tc=50 K:75As-NMR study.

    PubMed

    Mukuda, H; Furukawa, S; Kinouchi, H; Yashima, M; Kitaoka, Y; Shirage, P M; Eisaki, H; Iyo, A

    2012-10-12

    We report on an (75)As-NMR study on the Fe-pnictide high-T(c) superconductor Y(0.95)La(0.05)FeAsO(1-y) (Y(0.95)La(0.05)1111) with T(c)=50 K that includes no magnetic rare-earth elements. The measurement of the nuclear-spin lattice-relaxation rate (75)(1/T(1)) has revealed that the nodeless bulk superconductivity takes place at T(c)=50 K while antiferromagnetic spin fluctuations develop moderately in the normal state. These features are consistently described by the multiple fully gapped s(±)-wave model based on the Fermi-surface nesting. Incorporating the theory based on band calculations, we propose that the reason that T(c)=50 K in Y(0.95)La(0.05)1111 is larger than T(c)=28 K in La1111 is that the Fermi-surface multiplicity is maximized, and hence the Fermi-surface nesting condition is better than that in La1111.

  10. Fabrication of high-Tc superconducting hot electron bolometers for terahertz mixer applications

    NASA Astrophysics Data System (ADS)

    Villegier, Jean-Claude; Degardin, Annick F.; Guillet, Bruno; Houze, Frederic; Kreisler, Alain J.; Chaubet, Michel

    2005-03-01

    Superconducting Hot Electron Bolometer (HEB) mixers are a competitive alternative to Schottky diode mixers or other conventional superconducting receiver technologies in the terahertz frequency range because of their ultrawide bandwidth (from millimeter waves to the visible), high conversion gain, and low intrinsic noise level, even at 77 K. A new technological process has been developed to realize HEB mixers based on high temperature superconducting materials, using 15 to 40 nm thick layers of YBa2Cu3O7-δ (YBCO), sputtered on MgO (100) substrates by hollow cathode magnetron sputtering. Critical temperature values of YBCO films were found in the 85 to 91 K range. Sub-micron HEB bridges (0.8 μm x 0.8 μm) were obtained by combining electronic and UV lithography followed by selective etching techniques. Realization of YBCO HEB coupling to planar integrated gold antennas was also considered.

  11. 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.

  12. Oxygen stabilization induced enhancement in superconducting characteristics of high-Tc oxides

    NASA Technical Reports Server (NTRS)

    Wu, M. K.; Chen, J. T.; Huang, C. Y.

    1991-01-01

    In an attempt to enhance the electrical and mechanical properties of the high temperature superconducting oxides, high T(sub c) composites were prepared composed of the 123 compounds and AgO. The presence of extra oxygen due to the decomposition of AgO at high temperature is found to stabilize the superconducting 123 phase. Ag is found to serve as clean flux for grain growth and precipitates as pinning center. Consequently, almost two orders of magnitude enhancement in critical current densities were also observed in these composites. In addition, these composites also show much improvement in workability and shape formation. On the other hand, proper oxygen treatment of Y5Ba6Cu11Oy was found to possibly stabilize superconducting phase with T(sub c) near 250 K. I-V, ac susceptibility, and electrical resistivity measurements indicate the existence of this ultra high T(sub c) phase in this compound. Detailed structure, microstructure, electrical, magnetic and thermal studies of the superconducting composites and the ultra high T(sub c) compound are presented and discussed.

  13. Enhancement in low field nuclear magnetic resonance with a high-Tc superconducting quantum interference device and hyperpolarized 3He

    NASA Astrophysics Data System (ADS)

    Liao, Shu-Hsien; Yang, Hong-Chang; Horng, Herng-Er; Chen, Hsin-Hsien; Yang, Shieh-Yueh; Chen, Ming-Jye; Yang, Chang-Hau

    2008-09-01

    In this work, we present a design that improves signals produced by nuclear magnetic resonance (NMR) and magnetic resonance imaging by using optical pumping and a high-Tc superconducting quantum interference device (SQUID) magnetometer. In our design for a NMR detection system, a pickup coil is coupled to the spin procession of a H3e nucleus; the input coil is coupled to a high-Tc SQUID magnetometer; and the capacitor is connected in series to form a tank circuit resonating at the Larmor frequency of the H3e nucleus in the measuring field. A signal-to-noise ratio gain of 2.67 over a conventional Faraday detection coil was obtained with the high-Tc SQUID detection system in a measuring magnetic field equaling 0.1128 mT, at which the central frequency was 3.66 kHz for H3e nucleus. The improvement in the NMR signal for large-size, hyperpolarized H3e coupled to a high-Tc SQUID-based spectrometer in low magnetic fields at room temperature is significant compared to that without flux coupling. This result may be of interest given its potential for use in a low field imager.

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

    DOE PAGES

    Pavuna, D.; Dubuis, G.; Bollinger, A. T.; ...

    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).

  15. Systematic Modification of Electrical and Superconducting Properties of YBCO and Nano-Patterning of High-Tc Superconducting Thin Films by Light-Ion Irradiation

    NASA Astrophysics Data System (ADS)

    Pedarnig, J. D.; Bodea, M. A.; Steiger, B.; Markowitsch, W.; Lang, W.

    Irradiation of high-temperature superconducting (HTS) YBa2Cu3O7-d (YBCO) thin films with 75 keV He+ ions leads to a quasi-exponential increase of the in-plane (ρab) and the out-of-plane (ρc) resistivity in the normal state and to a non-linear decrease of the critical temperature Tc with ion dose. In situ electrical measurements at room temperature reveal an irradiation-induced reduction of resistivity anisotropy ρc/ρab and a slight relaxation of film resistivity after the ion irradiation is stopped. Ex situ measurements show a stretched-exponential relaxation of Tc and normal state resistivity that continues for several weeks after the ion irradiation. Irradiation of YBCO thin films by low-energy He+ ions through stencil masks results in local modification of the electrical and superconducting properties of the HTS material. We demonstrate that masked ion-beam lithography enables to produce structures smaller than 100 nm in size that have potential for applications in future superconducting nano-electronics.

  16. Evolution of High-Temperature Superconductivity from a Low-Tc Phase Tuned by Carrier Concentration in FeSe Thin Flakes

    NASA Astrophysics Data System (ADS)

    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.

    2016-02-01

    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 Tc 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 Tconset as high as 48 K in bulk FeSe. Intriguingly, our data also indicate that the superconductivity is suddenly changed from a low-Tc phase to a high-Tc 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 Tc in these materials.

  17. IN-SITU Diagnostics For Deposition And Processing Of High Tc Superconducting Thin Films

    NASA Astrophysics Data System (ADS)

    Venkatesan, T.

    1990-02-01

    The deposition of high quality superconducting thin films based on the metal oxides has given rise to a variety of needs for diagnostic techniques. These needs are primarily for monitoring, 1. the material ejection process from the target, 2. the ejected vapor interaction with the background oxygen, 3. the crystallization dynamics at the substrate and 4. post deposition analysis and processing of the film. This paper summarizes some of the recent work in this direction

  18. Design aspects and comparison between high Tc superconducting coplanar waveguide and microstrip line

    NASA Technical Reports Server (NTRS)

    Kong, K. S.; Bhasin, K. B.; Itoh, T.

    1991-01-01

    The high T sub c superconducting microstrip line and coplanar waveguide are compared in terms of the loss characteristics and the design aspects. The quality factor Q values for each structure are compared in respect to the same characteristic impedance with the comparable dimensions of the center conductor of the coplanar waveguide and the strip of the microstrip line. Also, the advantages and disadvantages for each structure are discussed in respect to passive microwave circuit applications.

  19. Antiferromagnetism and high- Tc superconductivity in F-substituted four-layered cuprates probed by Cu-NMR

    NASA Astrophysics Data System (ADS)

    Shimizu, S.; Mukuda, H.; Matoba, K.; Kitaoka, Y.; Tokiwa, K.; Watanabe, T.; Iyo, A.; Tanaka, Y.; Kito, H.

    2007-03-01

    We report on the onset of antiferromagnetism in F-substituted four-layered high- Tc compounds Ba2Ca3Cu4O8(O1-yFy)2 ( 2y=1.2,1.4,1.6 and 2.0) which are composed of two types of CuO2 planes in a unit cell; three inner planes (IPs) and two outer planes (OPs). The Cu-NMR study has revealed that the hole density at the OPs are slightly larger than that at the IPs, and a total carrier density decreases as F content increases. The observation of zero-field Cu-NMR spectra over a broad frequency range has demonstrated that antiferromagnetically ordered phases emerges at low temperatures for all compounds. This result is similar to the case for the five-layered cuprates HgBa2Ca4Cu5Oy where the optimally doped OP undergoes a superconducting (SC) transition, whereas the three underdoped IPs do an antiferromagnetic (AFM) transition [H. Kotegawa, et al., Phys. Rev. B 64 (2001) 064515; H. Mukuda, et al., Phys. Rev. Lett. 96 (2006) 087001]. The present result gives evidence for a coexistence of antiferromagnetism and superconductivity in four-layered high- Tc cuprates.

  20. Voltage-biased high-{Tc} superconducting infrared bolometers with strong electrothermal feedback

    SciTech Connect

    Lee, A.T.; Gildemeister, J.M.; Lee, Shih-Fu; Richards, P.L.

    1996-08-01

    In the current generation of high-{Tc} bolometers the thermal conductance is often chosen for a short time-constant rather than for optimal sensitivity. We describe a novel bolometer bias and readout scheme that promises to relax this constraint. Voltage bias of the superconductor results in strong negative electrothermal feedback that greatly reduces the time-constant of the bolometer. We estimate that a decrease of more than one order of magnitude in time-constant should be possible with existing high-Tc thermometers. We give theoretical estimates of the performance gain with voltage bias for several bolometers that have been reported in the literature. We find cases where the sensitivity can be greatly improved (by changing the thermal conductance) while holding the time constant fixed and others where the bolometer can be made much faster while maintaining the sensitivity.

  1. Nonlinear Harmonic Responses of Live Cells Using High-Tc Superconducting Quantum Interference Devices

    NASA Astrophysics Data System (ADS)

    Miller, J. H.; Nawarathna, D.; Sanabria, H.; Vajrala, V.; Claycomb, J. R.

    2006-09-01

    We report on a novel application of high-Tc SQUIDs, in which harmonics produced by live cells in response to a sinusoidal electric field are measured. The use of SQUIDs to probe induced currents without contacts reduces spurious harmonics generated at electrode interfaces, and enables one to noninvasively probe metabolic activity manifested by changes in conformational states of protein complexes in the plasma membrane and internal organelles. The method can also potentially be developed for clinical applications.

  2. 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}.

  3. 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.

  4. 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.

  5. Correlation of normal and superconducting properties and unified approach to the description of high Tc oxides

    NASA Technical Reports Server (NTRS)

    Kresin, V. Z.; Wolf, S. A.

    1991-01-01

    We present a unified approach based on the Fermi liquid picture which allows us to describe the normal as well as the superconducting properties of the doped cuprates. The theory that is presented is for the doped compounds which are metallic. One can distinguish two interrelated, but nevertheless, different directions in the physics of high T(sub c): one involving the problem of carrier doping and the transition to the metallic state, and the second being the description of the metallic state. It is important that this metallic phase undergoes the transition into the superconducting state; as a result, our analysis is directly related to the origin of high T(sub c). We are using a quasi-2D Fermi liquid model to estimate the fundamental parameters of these very interesting materials. We find that this description is able to describe these materials and also that phonons and plasmons play a major role in the mechanism of high T(sub c).

  6. Enhancement of nuclear magnetic resonance in microtesla magnetic field with prepolarization field detected with high-Tc superconducting quantum interference device

    NASA Astrophysics Data System (ADS)

    Yang, Hong-Chang; Liao, Shu-Hsien; Horng, Herng-Er; Kuo, Shing-Ling; Chen, Hsin-Hsien; Yang, S. Y.

    2006-06-01

    We applied prepolarization field and high-Tc superconducting quantum interference device (SQUID) detector to enhance nuclear magnetic resonance signal in a microtesla magnetic field. The minimum measuring magnetic field is 8.9μT at which the proton resonance frequency is 380Hz. The specificity instrumentation and the difficulty of using a high-Tc SQUID with prepolarization field were investigated. We applied gradient field to perform one-dimensional proton imaging in a microtesla magnetic field. Additionally, low field high-Tc SQUID-based NMR systems are promising in biomagnetic research due to its use, for example, in imaging with hyperpolarized noble gas.

  7. 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.

  8. Sensitive J-coupling spectroscopy using high-Tc superconducting quantum interference devices in magnetic fields as low as microteslas

    NASA Astrophysics Data System (ADS)

    Liao, Shu-Hsien; Yang, Hong-Chang; Horng, Herng-Er; Yang, S. Y.; Chen, H. H.; Hwang, Dennis W.; Hwang, Lian-Pin

    2009-04-01

    In this work we present a sensitive J-coupling spectroscopy in one shot using high-Tc superconducting quantum interference devices and a flux transformer in microtesla fields. In the proposed NMR detection scheme the precession of proton spin was inductively coupled to the SQUID magnetometer. We enhanced the SNR signal and the spectral resolution significantly by applying a pre-polarization field of 0.045 T. In microtesla fields where chemical shifts are absent, we demonstrate proton-phosphate coupling J3[H,P] = (10.94 ± 0.08) Hz in trimethyl phosphate. The sensitive NMR spectrometer will be of great interest for diagnosis information of molecular structure and biological applications.

  9. 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.

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

    DOE PAGES

    Gapud, A. A.; Greenwood, N. T.; Alexander, J. A.; ...

    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

  11. 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.

  12. High- Tc superconductivity due to coexisting wide and narrow bands: A fluctuation exchange study of the Hubbard ladder as a test case

    NASA Astrophysics Data System (ADS)

    Kuroki, Kazuhiko; Higashida, Takafumi; Arita, Ryotaro

    2005-12-01

    We propose that when the Fermi level lies within a wide band and also lies close to but not within a coexisting narrow band, high- Tc superconductivity may take place due to the large number of interband pair scattering channels and the small renormalization of the quasiparticles. We show using the fluctuation exchange method that this mechanism works for the Hubbard model on a ladder lattice with diagonal hoppings. From this viewpoint, we give a possible explanation for the low Tc for the actual hole-doped ladder compound, and further predict a higher Tc for the case of electron doping.

  13. Conceptual design of 275 kV class high-Tc superconducting cable

    NASA Astrophysics Data System (ADS)

    Mukoyama, S.; Yagi, M.; Fujiwara, N.; Ichikawa, H.

    2010-11-01

    High-temperature superconducting (HTS) cables are expected to be next generation transmission line because of the compact, lightweight, large capacity, and low loss features. Especially, since the YBa2Cu3Ox (YBCO) tape has a high critical current, high magnetic-field property, low AC loss, and low cost, using YBCO tapes for a HTS cable seems to be one of the most promising ways to make the HTS cable attractive. Therefore, YBCO HTS cables have been studied extensively in Japan, the United States, Korea, and many other countries. We now believe that 275 kV class HTS cables will be used for future large capacity lines based on the needs of Japanese transmission networks for bulk transmission power in overhead transmission lines or gas insulated transmission lines (GIL). We started to develop the 275 kV class HTS cable for the new energy and industrial technology development organization (NEDO) project at 2008, and we have studied the applicability and the environmental and economic advantages of the 275 kV cable. This paper will introduce advantages and a conceptual design of the 275 kV HTS cable.

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

    DOE PAGES

    Di Castro, D.; Cantoni, C.; Ridolfi, F.; ...

    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

  15. Fast neutron irradiation of high- Tc superconducting materials engineered for magnetic field and THz photon detection

    NASA Astrophysics Data System (ADS)

    Gozzelino, Laura; Gerbaldo, Roberto; Ghigo, Gianluca; Laviano, Francesco; Mezzetti, Enrica; Cherubini, Roberto; Minetti, Bruno

    2012-02-01

    Radiation-hard sensors are at present time highly requested for applications in environments with potential radiation hazard such as space, accelerators and fusion machines. We developed device prototypes for magnetic field and THz photon detection, both based on YBa 2Cu 3O 7-x (YBCO) superconducting films locally nanostructured by means of 0.25 GeV Au-ion lithography. This micro-collimated implantation of high-density columnar defects in YBCO films allows localizing external electromagnetic excitations by means of dissipative signals only induced into the nanostructured regions. The radiation hardness of detector prototypes was checked under fast neutron radiation. It turns out that, up to a neutron fluence comparable with those expected for 10 years long permanence in the space, no significant change was detected in superconductor characteristics such as zero-field resistance-temperature or magneto-resistance, whose variations could dramatically affect device figures of merit as responsivity or noise equivalent power. Fluences and energy spectrum of the neutrons impinging on the sensor prototypes were determined by a Monte-Carlo code implemented "ad hoc".

  16. The role of selected f ions in the suppression of high-Tc superconductivity.

    SciTech Connect

    Soderholm, L.

    1998-09-25

    The initial observations of superconductivity at temperatures above 77 K in copper-oxide based materials was surprising from a variety of different perspectives. Among the unexpected findings were reports of superconductivity for the series RBa{sub 2}Cu{sub 3}O{sub 7} where R is a rare earth (Y, Nd-Tm), which may carry a large, local magnetic moment. Superconductivity was subsequently demonstrated for all 4f analogs in this series except Ce, Pr, and Tb. In addition to the RBa{sub 2}Cu{sub 3}O{sub 7} series, there are several other CuO based series of superconductors that are formed by substituting R ions. The most studied of these are listed in Table 1, together with the f ions that form isostructural compounds and their superconducting critical temperatures (T{sub c}). The presence of an R ion with a large magnetic moment does not significantly influence the superconductivity. In contrast, even the presence of small concentrations of magnetic impurity ions in a conventional superconductor inhibits superconductivity by interfering with the formation of Cooper pairs. Most R ions substitute into an isostructural series with no observable effect on the superconducting properties of the material. As can be seen from Table 1, there are notable exceptions to this observation. In particular, the rare-earth ions Ce, Pr, and Tb, together with the 5f-actinide ions Am and Cm, sometimes behave anomalously. These ions either do not form an isostructural phase, or if the phase forms it may not be superconducting. The fact that an f-ion can suppress superconductivity is clearly demonstrated in the isostructural series Y{sub 1{minus}x}Pr{sub x}Ba{sub 2}Cu{sub 3}O{sub 7} (0 < x < 1){sup 3}, in which the critical temperature decreases with increasing x, such that for concentrations of Pr greater than x {approx} 0.5, the samples no longer superconduct.

  17. 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

  18. Nonlinear vibration behaviors of high-Tc superconducting bulks in an applied permanent magnetic array field

    NASA Astrophysics Data System (ADS)

    Li, Jipeng; Li, Haitao; Zheng, Jun; Zheng, Botian; Huang, Huan; Deng, Zigang

    2017-06-01

    The nonlinear vibration of high temperature superconducting (HTS) bulks in an applied permanent magnetic array (Halbach array) field, as a precondition for commercial application to HTS maglev train and HTS bearing, is systematically investigated. This article reports the actual vibration rules of HTS bulks from three aspects. First, we propose a new numerical model to simplify the calculation of levitation force. This model could provide precise simulations, especially the estimation of eigenfrequency. Second, an approximate analytic solution of the vibration of the HTS bulks is obtained by using the method of harmonic balance. Finally, to verify the results mentioned above, we measure the vertical vibration acceleration signals of an HTS maglev model, consisting of eight YBaCuO bulks, oscillating freely above a Halbach array with large displacement excitation. Higher order harmonic components, which indicate the nonlinear vibration phenomenon, are detected in the responses. All the three results are compared and agreed well with each other. This study combines the experimental and theoretical analyses and provides a deep understanding of the physical phenomenon of the nonlinear vibration and is meaningful for the vibration control of the relevant applications.

  19. A magnetic levitation rotating plate model based on high-Tc superconducting technology

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Li, Jipeng; Sun, Ruixue; Qian, Nan; Deng, Zigang

    2017-09-01

    With the wide requirements of the training aids and display models of science, technology and even industrial products for the public like schools, museums and pleasure grounds, a simple-structure and long-term stable-levitation technology is needed for these exhibitions. Opportunely, high temperature superconducting (HTS) technology using bulk superconductors indeed has prominent advantages on magnetic levitation and suspension for its self-stable characteristic in an applied magnetic field without any external power or control. This paper explores the feasibility of designing a rotatable magnetic levitation (maglev) plate model with HTS bulks placed beneath a permanent magnet (PM) plate. The model is featured with HTS bulks together with their essential cryogenic equipment above and PMs below, therefore it eliminates the unclear visual effects by spray due to the low temperature coolant such as liquid nitrogen (LN2) and additional levitation weight of the cryogenic equipment. Besides that, a matched LN2 automation filling system is adopted to help achieving a long-term working state of the rotatable maglev plate. The key low-temperature working condition for HTS bulks is maintained by repeatedly opening a solenoid valve and automatically filling LN2 under the monitoring of a temperature sensor inside the cryostat. With the support of the cryogenic devices, the HTS maglev system can meet all requirements of the levitating display model for exhibitions, and may enlighten the research work on HTS maglev applications.

  20. 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.

  1. 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.

  2. Observation of high Tc one dimensional superconductivity in 4 angstrom carbon nanotube arrays

    NASA Astrophysics Data System (ADS)

    Zhang, Bing; Liu, Yang; Chen, Qihong; Lai, Zhiping; Sheng, Ping

    2017-02-01

    The only known approach to fabricate large, uniform arrays of 4-Å single wall carbon nanotubes (SWNTs) is by using zeolite crystals as the template, in which the nanotubes are formed by chemical vapor deposition inside the linear channels of the AlPO4-5 (AFI for short) zeolite. However, up to now the pore filling factor has been very low, as evidenced by the weight percentage of carbon in thermal gravimetric analysis (TGA) measurements. In this work, we show that by using a new, micro-platelet AFI crystals as the template, combined with the use of a new CVD process, we can increase the TGA result to 22.5wt%, which translates to a pore filling factor of 91%. We have observed one dimensional (1D) superconductivity in such samples. The temperature dependence of resistance shows a smooth decreasing trend below 60 K, and the differential resistance displays a gap that disappears above the 1D superconducting initiation temperature. The observed behaviour is shown to agree very well with the theoretical predictions of 1D superconductivity.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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.

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

    PubMed Central

    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. PMID:25382349

  6. Magnetic levitation force measurement on high [Tc] superconducting ceramic/polymer composites

    SciTech Connect

    Unsworth, J.; Du, Jia; Crosby, B.J. ); Macfarlane, J.C. )

    1993-01-01

    An experimental study of magnetic levitation force for 0--3 and 3--3 superconducting ceramic/polymer composites is presented. A simple, inexpensive force versus distance measurement technique is described. The measurements of force against distance or magnetic field show strong hysteretic behavior, which is similar to the sintered superconductor ceramics and is consistent with the hysteresis in magnetization of superconductor. The volume fraction dependence and sample thickness dependence of the levitation forces are also studied for 0--3 composites. Results suggest that the new composite materials are most suitable for levitation applications.

  7. Correlation between the superconducting transition temperature and crystal structure of high- Tc cuprate compounds

    NASA Astrophysics Data System (ADS)

    de Leeuw, D. M.; Groen, W. A.; Feiner, L. F.; Havinga, E. E.

    1990-03-01

    For the various p-type cuprate superconductors we have calculated the formal valence for the copper and the oxygen ions in the central CuO 2 planes from bond lengths according to Zachariasen rules. It is shown that in all structures these values correlate remarkably well with the maximum critical temperature. The correlation found shows that Tc, max increases the more the holes in the CuO 2 planes prefer the oxygen sites over the copper sites. In a correlated electron picture this implies a higher value for U - Δ + {W}/{2}.

  8. Detectors of Infrared Radiation Based on High T(c) Superconducting YBCO Films

    DTIC Science & Technology

    1988-02-23

    of the YBCO films. Second, the best (epitaxial) super- conducting YBCO films are grown on the SrTiO3 substrates, which may be disadvantageous for...sintered pellets, thin films, single crystals and fibers. We have grown thin BCSCO films on SrTiO3 substrates( 3 ); they showed zero resistance at Tc...is a "line" .., compound - i.e. it forms at nearly exact stoichiometry composition. As it grows epitaxially on the (001) face of SrTiO3 substrate, it

  9. Theoretical analysis of NMR experiments in normal and superconducting states of high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Mack, Frank; Kulić, Miodrag L.; Mehring, Michael

    1998-01-01

    The Knight shift and T1- and T2-rates of YBa 2Cu 3O 6+ x in the normal and superconducting state are modeled by calculating the magnetic susceptibility in the bi-layer Hubbard model within various approximations. An optimal set of parameters (OSP) is found in the RPA approximation which fits experiments on YBCO for optimal and nearly optimal doping. The analysis of the self-consistent FLEX approximation for the particle self-energy and susceptibility shows that the latter is renormalized quantitatively but not qualitatively. The differences in the oxygen and copper T1-rates are explained by using the OSP parameters and assuming the finite hyperfine coupling C‧ between 17O and next-nearest neighboring Cu spins. The numerical analysis of T1-1 and T2-1 and the ratio 63T1 ab-1/ 63T1 c-1 in the superconducting state supports strongly the idea of d-wave pairing in YBa 2Cu 3O 7 with much stronger intraplane rather than interplane pairing. It is also shown that the simple RPA or FLEX approximations are inadequate in explaining NMR data in underdoped YBCO systems, where antiferromagnetic fluctuations are very pronounced.

  10. High-temperature conventional superconductivity

    NASA Astrophysics Data System (ADS)

    Eremets, M. I.; Drozdov, A. P.

    2017-02-01

    Conventional superconductors are described well by the Bardeen – Cooper – Schrieffer (BCS) theory (1957) and its related theories, all of which importantly put no explicit limit on transition temperature Tc. While this allows, in principle, room-temperature superconductivity, no such phenomenon has been observed. Since the discovery of superconductivity in 1911, the measured critical temperature of BCS superconductors has not until recently exceeded 39 K. In 2014, hydrogen sulfide under high pressure was experimentally found to exhibit superconductivity at Tc = 200 K, a record high value which greatly exceeds that of the previous class of high-temperature superconductors, the cuprates. The superconductivity mechanism in cuprates has not yet been explained. Over a period of 25 years, the critical temperature of cuprates has not been increased above 164 K. The paper reviews research on record-high Tc superconductivity in hydrogen sulphide and other hydrides. Prospects for increasing Tc to room temperature are also discussed.

  11. High-temperature conventional superconductivity

    NASA Astrophysics Data System (ADS)

    Eremets, M. I.; Drozdov, A. P.

    2016-11-01

    Conventional superconductors are described well by the Bardeen - Cooper - Schrieffer (BCS) theory (1957) and its related theories, all of which importantly put no explicit limit on transition temperature T_c. While this allows, in principle, room-temperature superconductivity, no such phenomenon has been observed. Since the discovery of superconductivity in 1911, the measured critical temperature of BCS superconductors has not until recently exceeded 39 K. In 2014, hydrogen sulfide under high pressure was experimentally found to exhibit superconductivity at T_c=200 K, a record high value which greatly exceeds that of the previous class of high-temperature superconductors, the cuprates. The superconductivity mechanism in cuprates has not yet been explained. Over a period of 25 years, the critical temperature of cuprates has not been increased above 164 K. The paper reviews research on record-high T_c superconductivity in hydrogen sulphide and other hydrides. Prospects for increasing T_c to room temperature are also discussed.

  12. Recent high-magnetic-field experiments on the 'high Tc' cuprates: Fermi-surface instabilities as a driver for superconductivity

    SciTech Connect

    Singleton, John; Mc Donald, Ross D; Cox, Susan

    2008-01-01

    The authors give a brief review of high-magnetic-field quantum-oscillation measurements on cuprate superconductors. In the case of the underdoped cuprates, a number of small Fermi-surface pockets are observed, probably due to the incommensurate nesting of the predicted (large) hole Fermi surface. The Fermi-surface instabilities that drive this nesting are also likely to result in the incommensurate spin fluctuations observed in inelastic neutron-scattering measurements. They suggest that the unusually high superconducting transitions in the cuprates are driven by an exact mapping of these incommensurate spin fluctuations onto the d{sub x{sup 2}-y{sup 2}} Cooper-pair wavefunction. The maximum energy of the fluctuations {approx} 100s of Kelvin gives an appropriate energy scale for the superconducting transition temperature.

  13. Citrate sol-gel route to high Tc superconducting YBaCuO fiber

    NASA Astrophysics Data System (ADS)

    Choy, Jin-Ho; Yoo, Jong-Seok; Park, Jung-Chul; Kang, Seong-Gu; Kim, Whan; Kang, Sang-Gu

    1991-12-01

    Drawing of the citrate gel fiber (diameter: 0.1∼2mm, length: ∞) was carried out within the pH range of 4.7∼6.1, which was theoretically estimated by considering the formation of ammine complexes in the solution. Single phase of YBa 2Cu 3O 7-δ(Tc off-set ≅ 85K) could only be obtained if the gel fiber was treated at 900°C, but the special care should be made because of the significant weight loss at 200°C and 300°C due to the decomposition of nitrates and organic constituents. Therefore, the heating rate should be lower than 1°C/min in these temperature range. From the SEM data, it was found that the fiber consisted of polycrystalline with very round graines(ø ∼ 1μm). The chemical composition was estimated as Y:Ba:Cu=1:2:3 by EPMA and the ratio of trivalent to divalent copper and the oxygen deficiency were determined as YBa 2Cu 3+0.62Cu 2+2.38O 6.81 by the redox titration.

  14. Graphoepitaxial high-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Faley, M. I.; Meertens, D.; Poppe, U.; Dunin-Borkowski, R. E.

    2014-05-01

    The fabrication process and physical properties of graphoepitaxially engineered high-Tc direct current superconducting quantum interferometer devices (DC SQUIDs) are studied. Double buffer layers, each comprising a graphoepitaxial seed layer of YBa2Cu3O7-x and an epitaxial blocking layer of SrTiO3, were deposited over textured step edges on (001) surfaces of MgO substrates. Scanning electron microscopy and high-resolution transmission electron microscopy were used to investigate the microstructural properties of DC SQUIDs with graphoepitaxial Josephson junctions. Both direct coupled and inductively coupled high-Tc DC SQUIDs with graphoepitaxial step edge junctions and flux transformers were studied.

  15. Analysis of a High-Tc Hot-Electron Superconducting Mixer for Terahertz Applications

    NASA Technical Reports Server (NTRS)

    Karasik, B. S.; McGrath, W. R.; Gaidis, M. C.

    1996-01-01

    The prospects of a YBa2Cu3O7(delta)(YBCO) hot-electron bolometer (HEB) mixer for a THz heterodyne receiver is discussed. The modeled device is a submicron bridge made from a 10 nm thick film on a high thermal conductance substrate.

  16. Undoped high-Tc superconductivity in T'-La1.8Eu0.2CuO4+δ revealed by 63,65Cu and 139La NMR: Bulk superconductivity and antiferromagnetic fluctuations

    NASA Astrophysics Data System (ADS)

    Fukazawa, Hideto; Ishiyama, Seiya; Goto, Masato; Kanamaru, Shuhei; Ohashi, Kohki; Kawamata, Takayuki; Adachi, Tadashi; Hirata, Michihiro; Sasaki, Takahiko; Koike, Yoji; Kohori, Yoh

    2017-10-01

    We performed 63,65Cu and 139La NMR measurements of T'-La1.8Eu0.2CuO4+δ (T'-LECO) with the Nd2CuO4-type structure (so-called T'-structure). As a result, we detected the 63,65Cu NMR signal under finite magnetic fields and found superconductivity without antiferromagnetic (AF) order only in the reduced T'-LECO, where excess apical oxygen atoms are properly removed. This indicates that the intrinsic ground state of the ideal T'-LECO is a paramagnetic and superconducting (SC) state. Below Tc, the Knight shift was found to rapidly decrease, which indicates the emergence of bulk superconductivity due to spin-singlet Cooper pairs in the reduced T'-LECO. In the SC state of the reduced T'-LECO, moreover, a characteristic temperature dependence of the spin-lattice relaxation rate 1/T1 was observed, which implies the existence of nodal lines in the SC gap. These findings suggest that the superconductivity in the reduced T'-LECO probably has d-wave symmetry. In the normal state of the reduced T'-LECO, on the other hand, AF fluctuations were found to exist from the temperature dependence of 1/T1T, though no clear pseudogap behavior was observed. This suggests that the AF correlation plays a key role in the superconductivity of undoped high-Tc cuprate superconductors with the T'-structure.

  17. 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.

  18. Modeling and Optimization of a High-Tc Hot-Electron Superconducting Mixer for Terahertz Applicaitons

    NASA Technical Reports Server (NTRS)

    Karasik, B. S.; McGrath, W. R.; Gaidis, M. C.; Burns, M. J.; Kleinsasser, A. W.; Delin, K. A.; Vasquez, R. P.

    1996-01-01

    The development of a YBa(sub 2)Cu(sub 3)O(sub 7-(kronecker delta))(YBCO) hot-electron bolometer (HEB) quasioptical mixer for a 2.5 heterodyne receiver is discussed. The modeled device is a submicron bridge made from a 10 nm thick film on a high thermal conductance substrate. The mixer performance expected for this device is analyzed in the framework of a two-temperature model which includes heating both of the electrons and the lattice. Also, the contribution of heat diffusion from the film through the substrate and from the film to the normal metal contacts is evaluated....a single sideband temperature of less than 2000k is predicted.

  19. Fabrication and Microwave Properties of Asymmetric Dual-band High-Tc Superconducting Filter

    NASA Astrophysics Data System (ADS)

    Wang, Li-Min; Lin, Shyue-Han; Chang, Ying-Shyuan; Liu, Jer-Wei

    An asymmetric dual-band band-pass filter (DBPF) is proposed for the applications of IEEE 802.11b/g (2.4 GHz ∼ 2.48 GHz) on the multimode wireless local area networks (WLAN). The high temperature superconducing (HTS) filter was fabricated by pattering YBa2Cu3Oy (YBCO) films double-sided deposited on 20 × 20 mm2 LaAlO3 substrates with an RF sputtering technique and by putting them in copper housings. The simulation results show the asymmetric dual-band feature of two passbands at 2.45 and 2.48 GHz, each with a minimum in-band insertion loss of about 0.3 dB and bandwidths of 20 and 23 MHz, respectively. The realized HTS DBPF shows two passbands at 2.47 and 2.49 GHz with maximum insertion losses of 1.75 and 3.17 dB at 77 K, respectively. The measured results show a good HTS DBPF performance. Moreover, the temperature-dependent frequency responses can be well described by the modified two-fluid model based formulas, indicating that the frequency shift in HTS DBPFs is dominated by the temperature dependence of the magnetic penetration depth.

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

    NASA Astrophysics Data System (ADS)

    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-Tc 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.

  1. 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.

  2. An experimental study of high Tc superconducting microstrip transmission lines at 35 GHz and the effect of film morphology

    NASA Technical Reports Server (NTRS)

    Chorey, C. M.; Bhasin, K. B.; Warner, J. D.; Josefowicz, J. Y.; Rensch, D. B.

    1991-01-01

    Microstrip transmission lines in the form of ring resonators were fabricated from a number of in-situ grown laser ablated films and post-annealed co-sputtered YBa2Cu3O(7-x) films. The properties of these resonators were measured at 35 GHz and the observed performance is examined in light of the critical temperature (Tc) and film thickness, and also the film morphology, which is different for the two deposition techniques. It is found that Tc is a major indicator of the film performance for each growth type, with film thickness becoming important as it decreases towards 1000 A. It is also found that the films with a mixed grain orientation (both a-axis and c-axis oriented grains) have poorer microwave properties as compared with the primarily c-axis oriented material. This is probably due to the significant number of grain boundaries between the different crystallites, which may act as superconducting weak links and contribute to the surface resistance.

  3. An experimental study of high Tc superconducting microstrip transmission lines at 35 GHz and the effect of film morphology

    NASA Technical Reports Server (NTRS)

    Chorey, C. M.; Bhasin, K. B.; Warner, J. D.; Josefowicz, J. Y.; Rensch, D. B.; Nieh, C. W.

    1990-01-01

    Microstrip transmission lines in the form of ring resonators were fabricated from a number of in-situ grown laser ablated films and post-annealed co-sputtered YBa2Cu3O(7-x) films. The properties of these resonators were measured at 35 GHz and the observed performance is examined in light of the critical temperature (Tc) and film thickness and also the film morphology which is different for the two deposition techniques. It is found that Tc is a major indicator of the film performance for each growth type with film thickness becoming important as it decreases towards 100 A. It is also found that the films with a mixed grain orientation (both a axis and c axis oriented grains) have poorer microwave properties as compared with the primarily c axis oriented material. This is probably due to the significant number of grain boundaries between the different crystallites, which may act as superconducting weak links and contribute to the surface resistance.

  4. Characterization of magnetic nanoparticles as contrast agents in magnetic resonance imaging using high-Tc superconducting quantum interference devices in microtesla magnetic fields

    NASA Astrophysics Data System (ADS)

    Liao, Shu-Hsien; Yang, Hong-Chang; Horng, Herng-Er; Yang, S. Y.

    2009-02-01

    In this paper, we characterize the spin-lattice relaxation T1, spin-spin relaxation T2, and effective relaxation rate ΓMF of magnetic fluids for magnetic resonance imaging using a high-Tc superconducting quantum interference device (SQUID) in microtesla magnetic fields. When the magnetic susceptibility of the magnetic fluid was increased, a broadening of proton nuclear magnetic resonance spectra and a growing spin-lattice relaxation T1 as well as spin-spin relaxation T2 were observed. The effective relaxation rate ΓMF increased monotonically from 0 to 13 s-1 when the magnetic susceptibility of the magnetic fluids, relative to tap water, was increased from 0 to 0.0015 emu g-1. We demonstrate the magnetic fluid as an image contrast via a high-Tc SQUID in microtesla magnetic fields.

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

    PubMed

    Choy; Kwon; Park

    1998-06-05

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

  6. High-Tc SQUID biomagnetometers

    NASA Astrophysics Data System (ADS)

    Faley, M. I.; Dammers, J.; Maslennikov, Y. V.; Schneiderman, J. F.; Winkler, D.; Koshelets, V. P.; Shah, N. J.; Dunin-Borkowski, R. E.

    2017-08-01

    In this paper, we review the preparation technology, integration in measurement systems and tests of high-Tc superconducting quantum interference devices (SQUIDs) intended for biomagnetic applications. A focus is on developments specific to Forschungszentrum Jülich GmbH, Chalmers University of Technology, MedTech West, and the University of Gothenburg, while placing these results in the perspective of those achieved elsewhere. Sensor fabrication, including the deposition and structuring of epitaxial oxide heterostructures, materials for substrates, epitaxial bilayer buffers, bicrystal and step-edge Josephson junctions, and multilayer flux transformers are detailed. The properties of the epitaxial multilayer high-Tc direct current SQUID sensors, including their integration in measurement systems with special electronics and liquid nitrogen cryostats, are presented in the context of biomagnetic recording. Applications that include magnetic nanoparticle based molecular diagnostics, magnetocardiography, and magnetoencephalography are presented as showcases of high-Tc biomagnetic systems. We conclude by outlining future challenges.

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

    DOE PAGES

    Gasparov, V. A.; Drigo, L.; Audouard, A.; ...

    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

  8. Minimization of noise-induced bit error rate in a high Tc superconducting dc/single flux quantum converter

    NASA Astrophysics Data System (ADS)

    Ortlepp, Thomas; Toepfer, Hannes; Uhlmann, Hermann F.

    2001-02-01

    The thermally induced bit error rate of a rapid single flux quantum logic circuit is theoretically examined using the Fokker-Planck equation. The error rate versus design parameters of a high Tc dc/single flux quantum converter is derived. In comparison with other design methodologies, a vanishingly small error rate at optimal parameters can be achieved.

  9. NEUTRON SCATTERING STUDY OF THE HIGH-Tc SUPERCONDUCTING SYSTEM YBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Rossat-Mignod, J.; Regnault, L. P.; Bourges, P.; Burlet, P.; Vettier, C.; Henry, J. Y.

    The following sections are included: * Introduction * The neutron scattering technique * Phase diagrams of high-Tc superconductors * The undoped AF-doped * The doped AF-state * The weakly-doped metallic state * The heavily-doped metallic state * The overdoped metallic state * Discussion and concluding remarks * Acknowledgements * References

  10. 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.

  11. Uniform mixing of high-Tc superconductivity and antiferromagnetism on a single CuO2 plane of a Hg-based five-layered cuprate.

    PubMed

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

    2006-03-03

    We report a site selective Cu-NMR study on underdoped Hg-based five-layered high-Tc cuprate HgBa2Ca4CU5O(12+delta) with a Tc = 72 K. Antiferromagnetism (AFM) has been found to take place at T(N) = 290 K, exhibiting a large antiferromagnetic moment of 0.67-0.69 microB at three inner planes (IP). This value is comparable to the values reported for nondoped cuprates, suggesting that the IP may be in a nearly nondoped regime. Most surprisingly, the AFM order is also detected with M(AFM)(OP) = 0.1 microB even at two outer planes (OP) that are responsible for the onset of superconductivity (SC). 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 uniform mixed phase of AFM and SC on a single CuO2 plane in a simple environment without any vortex lattice and/or stripe order.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. Influence of disorder on the local density of states in high- T(c) superconducting thin films

    PubMed

    Cren; Roditchev; Sacks; Klein; Moussy; Deville-Cavellin; Lagues

    2000-01-03

    Using a low temperature scanning tunneling microscope in the spectroscopic mode, we find that the disorder in a Bi(2)Sr(2)CaCu(2)O(8+delta) thin film modifies dramatically the quasiparticle local density of states. Small, but well-defined superconducting regions, coexisting with dominating semiconducting areas, show well-pronounced gap structures, similar to those observed previously in high-quality single crystals. Surprisingly, between these two regions, the detailed shape of the quasiparticle spectrum is virtually identical to the pseudogap previously observed at temperatures T>T(c), or in the vortex core, at 4.2 K. Thus, the role of the disorder in destroying the superconducting phase is comparable to that of the magnetic field or thermal fluctuations.

  17. 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.

  18. High-Tc Superconductivity with Tc = 52 K under Antiferromagnetic Order in Five-Layered Cuprate Ba2Ca4Cu5O10(F,O)2 with TN = 175 K: 19F- and Cu-NMR Studies

    NASA Astrophysics Data System (ADS)

    Shimizu, Sunao; Tabata, Shin-ichiro; Mukuda, Hidekazu; Kitaoka, Yoshio; Shirage, Parasharam M.; Kito, Hijiri; Iyo, Akira

    2011-04-01

    We report on the observation of high-Tc superconductivity (SC) emerging with the background of an antiferro magnetic (AFM) order in the five-layered cuprate Ba2Ca4Cu5O10(F,O)2 through 19F-NMR and zero-field Cu-NMR studies. The measurements of spectrum and nuclear spin--lattice relaxation rates 19 of 19F-NMR give convincing evidence for the AFM order taking place below TN = 175 K and for the onset of SC below Tc = 52 K, hence both coexisting. The zero-field Cu-NMR study has revealed that AFM moments at Cu sites are 0.14 μB at outer CuO2 layers and 0.20 μB at inner ones. We remark that an intimate coupling exists between the AFM state and the SC order parameter below Tc = 52 K; the spin alignment in the AFM state is presumably changed in the SC-AFM mixed state.

  19. 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.

  20. Simulation of Field Dependence of Critical Current Densities of Bulk High Tc Superconducting Materials regarding Thermally Activated Flux Motion

    NASA Astrophysics Data System (ADS)

    Santosh, M.; Naik, S. Pavan Kumar; Koblischka, M. R.

    2017-07-01

    In the upcoming generation, bulk high temperature superconductors (HTS) will play a crucial and a promising role in numerous industrial applications ranging from Maglev trains to magnetic resonance imaging, etc. Especially, the bulk HTS as permanent magnets are suitable due to the fact that they can trap magnetic fields being several orders of magnitude higher than those of the best hard ferromagnets. The bulk HTS LREBa2Cu3O7-δ (LREBCO or LRE-123, LRE: Y, Gd, etc.,) materials could obtain very powerful compact superconducting super-magnets, which can be operated at the cheaper liquid nitrogen temperature or below due to higher critical temperatures (i.e., ∼90 K). As a result, the new advanced technology can be utilized in a more attractive manner for a variety of technological and medical applications which have the capacity to revolutionize the field. An understanding of the magnetic field dependence of the critical current density (J c(H)) is important to develop better adapted materials. To achieve this goal, a variety of Jc (H) behaviours of bulk LREBCO samples were modelled regarding thermally activated flux motion. In essence, the Jc (H) curves follows a certain criterion where an exponential model is applied. However, to fit the complete Jc (H) curve of the LRE-123 samples an unique model is necessary to explain the behavior at low and high fields. The modelling of the various superconducting materials could be understood in terms of the pinning mechanisms.

  1. Superconducting fluctuations and large diamagnetism of low-Tc nanoparticles

    NASA Astrophysics Data System (ADS)

    Imry, Yoseph

    2015-03-01

    It is shown that nanoparticles made of very low-Tc superconductors have a large diamagnetic response at temperatures several orders of magnitude above Tc. Most of the features of the recently observed giant diamagnetism of Au nanorods are explained in terms of superconducting fluctuations, except for the huge magnitude of the effect.

  2. 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.

  3. 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.

  4. The performance improvement calculation of corrugated quantum well infrared photodetector (C-QWIP) with a high critical temperature (Tc) superconducting electron filter

    NASA Astrophysics Data System (ADS)

    Sun, Jason; Choi, K. K.

    2011-10-01

    The Corrugated Quantum Well Infrared Photodetector (C-QWIP) holds significant performance and other advantages over other infrared (IR) detectors. However, one disadvantage of the detector is the relatively low operating temperature needed to suppress the dark current. By coating two additional layers (thin insulator and high critical temperature (Tc) superconductor) on the top contact layer of a C-QWIP wafer, the top three layers of the detector form a high-Tc superconducting single electron tunneling junction. It could act as an electron filter because of the presence of an energy gap in superconductors. For QWIPs, the photo electrons and dark electrons are well separated in energy, most dark current is conducting below the quantum well (QW) barrier height and most photo current is conducting above the barrier height. Most dark electrons thus could be blocked by the junction while most photo electrons pass the junction by applying an appropriate voltage. Therefore, both the sensitivity and the operating temperature of the detector could be improved. Our calculation shows that the filter could provide 40% or 70% improvement in Noise Equivalent Temperature Difference (NETD) of detector focal plane arrays (FPAs) at normal operating temperature, depending on whether the detector emitter photocurrent to dark current ratio is = 1 (Emitter is background limited BLIP) or = 0.1 (Emitter is far from BLIP). For both cases, the filter could increase the detector FPAs operating temperatures up to 90K (30K improvement) with 15% to 25% NETD improvement respectively.

  5. Epitaxial thick film high-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Faley, M. I.; Mi, S. B.; Jia, C. L.; Poppe, U.; Urban, K.; Fagaly, R. L.

    2008-02-01

    Low-noise operation of superconducting quantum interference devices (SQUIDs) in magnetic fields requires high critical current and strong pinning of vortices in the superconducting electrodes and in the flux transformer. Crack-free epitaxial high-Tc dc-SQUID structures with a total thickness ?5 μm and a surface roughness determined by 30 nm high growth spirals were prepared with YBa2Cu3O7-x (YBCO) films on MgO substrates buffered by a SrTiO3/BaZrO3-bilayer. HRTEM demonstrated a high quality epitaxial growth of the films. The YBCO films and SQUID structures deposited on the buffered MgO substrates had a superconducting transition temperature Tc exceeding 91 K and critical current densities Jc > 3 MA/cm2 at 77 K up to a thickness ~5 μm. The application of thicker superconducting and insulator films helped us to increase the critical current and dynamic range of the multilayer high-Tc flux transformer and improve the insulation between the superconducting layers. An optimization of SQUID inductance allowed us to fabricate 8 mm SQUID magnetometers with SQUID voltage swings of ~60 μV and a field resolution of ~30 fT/√Hz at 77 K.

  6. Magnetic properties of a high Tc superconductivity related system Y1 - xPrxBa2Fe3O8

    NASA Astrophysics Data System (ADS)

    Yuen, T.; Seyedahmadian, M.; Salomon, R. E.; Myer, G. H.; Cao, G.

    1996-04-01

    We studied Pr substitution for Y in a 123 high Tc superconductor related system, Y1-xPrxBa2Fe3O8 using of x-ray diffraction, magnetization, and 57Fe transmission Mössbauer spectroscopy. The Fe sublattices are magnetically ordered through the whole system. The Pr substitution, however, suppressed the Fe ordering temperature. The low temperature susceptibility across the system increases with increased Pr concentration x, and an additional antiferromagnetic ordering at 24 K is observed for x=1, indicating a possible Pr ordering. The averaged magnetic hyperfine field at Fe sites measured at 15 K is also reduced as x increases. The dramatic effect of Pr substitution for Y in this system, which is not observed in studies of Y substitution by other rare-earth elements, is interpreted as the effect of the hybridization between the Pr 4-f electrons and the electrons in the Fe(2)O2 layers, similar to the Pr hybridization in Y1-xPrxBa2Cu3O7-y system.

  7. COMPARISON BETWEEN DISCRETE AND SEMI-CONTINUOUS LAYERED MODELS OF SUPERCONDUCTING VORTICES IN HIGH TC MATERIALS FOR TEM OBSERVATIONS.

    SciTech Connect

    BELEGGIA,M.; POZZI,G.; TONOMURA,A.

    2004-08-01

    In order to interpret Transmission Electron Microscopy observations of superconducting vortices in anisotropic or layered materials we have found the analytical solution for the Fourier transform of the electron optical phase shift for the case of a straight vortex piercing the specimen at arbitrary angle. The layered case suffered from the shortcoming that only a limited number of pancakes; up to 7, is allowed by the discrete approach followed. Seven layers, however, are scarcely representative of the real stack of pancake vortices, especially when the core pierces the specimen at large angles with respect to the specimen normal. In fact, in these conditions, the pancake discrete structure may no longer be buried in the diffraction fringes of the Fresnel image. Moreover, a small number of layers is a limiting factor when more exotic vortex structures with no straight cores are investigated. This drawback has been overcome by a semi-continuous approach, where each pancake layer is considered singularly, and the discrete structure of the other pancakes is substituted by a superconducting continuous medium that carries supercurrent only parallel to the layers, as proposed by Clem and further developed by Coffey and Phipps. The solution for the vector potential has been found by Fourier methods, connecting the general solutions in the vacuum with those in the superconducting regions. The presence of a vortex in the layer is taken into account by considering the layer as an additional superconducting region of negligible thickness. Once the vector potential is found, the electron optical phase shift can be calculated by integrating the vector potential along a straight trajectory suitably chosen in order to take correctly into account the overall geometry of the experimental set-up, including a tilt of the specimen with respect to the electron beam.

  8. Inverse correlation between quasiparticle mass and Tc in a cuprate high-Tc superconductor

    PubMed Central

    Putzke, Carsten; Malone, Liam; Badoux, Sven; Vignolle, Baptiste; Vignolles, David; Tabis, Wojciech; Walmsley, Philip; Bird, Matthew; Hussey, Nigel E.; Proust, Cyril; Carrington, Antony

    2016-01-01

    Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature Tc is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-Tc superconductivity. We have tested the robustness of this correlation between m* and Tc by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as Tc increases under pressure. This inverse correlation between m* and Tc suggests that quantum fluctuations of the charge order enhance m* but do not enhance Tc. PMID:27034989

  9. 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.

  10. 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.

  11. 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.

  12. High-Tc superconductivity near the anion height instability in Fe-based superconductors: analysis of LaFeAsO(1-x)H(x).

    PubMed

    Onari, Seiichiro; Yamakawa, Youichi; Kontani, Hiroshi

    2014-05-09

    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 LaFeAsO(1-x)H(x) 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.

  13. High temperature superconducting compounds

    NASA Astrophysics Data System (ADS)

    Goldman, Allen M.

    1992-11-01

    The major accomplishment of this grant has been to develop techniques for the in situ preparation of high-Tc superconducting films involving the use of ozone-assisted molecular beam epitaxy. The techniques are generalizable to the growth of trilayer and multilayer structures. Films of both the DyBa2Cu3O(7-x) and YBa2Cu3O(7-x) compounds as well as the La(2-x)Sr(x)CuO4 compound have been grown on the usual substrates, SrTiO3, YSZ, MgO, and LaAlO3, as well as on Si substrates without any buffer layer. A bolometer has been fabricated on a thermally isolated SiN substrate coated with YSZ, an effort carried out in collaboration with Honeywell Inc. The deposition process facilitates the fabrication of very thin and transparent films creating new opportunities for the study of superconductor-insulator transitions and the investigation of photo-doping with carriers of high temperature superconductors. In addition to a thin film technology, a patterning technology has been developed. Trilayer structures have been developed for FET devices and tunneling junctions. Other work includes the measurement of the magnetic properties of bulk single crystal high temperature superconductors, and in collaboration with Argonne National Laboratory, measurement of electric transport properties of T1-based high-Tc films.

  14. Superconductivity

    DTIC Science & Technology

    1989-07-01

    SUPERCONDUCTIVITY HIGH-POWER APPLICATIONS Electric power generation/transmission Energy storage Acoustic projectors Weapon launchers Catapult Ship propulsion • • • Stabilized...temperature superconductive shields could be substantially enhanced by use of high-Tc materials. 27 28 NRAC SUPERCONDUCTIVITY SHIP PROPULSION APPLICATIONS...motor shown in the photograph. As a next step in the evolution of electric-drive ship propulsion technology, DTRC has proposed to scale up the design

  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. 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.

  17. 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.

  18. On the coherent quasiparticle weight in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Zheng, Yong; Zhang, Xiaowei; Zhou, Wulei; Liu, Xiaochun; Zhao, Hua

    2017-09-01

    The anomalous temperature dependence of the coherent quasiparticle weight below the superconducting transition temperature Tc in high-Tc cuprates, as has been extensively revealed by angle-resolved photoemission measurements, has been addressed theoretically. We find that this puzzling phenomenon universally appears along the whole Fermi surface, from the nodal to antinodal regions, in momentum space, and can be well comprehended in a mean-field slave-boson picture. The ordinary deduction that the coherent quasiparticle peak is a superconducting one, just from such temperature dependence of the coherent quasiparticle weight below Tc, is found to be questionable, and it could correspond to a competing order, especially in the antinodal region.

  19. 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.

  20. 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.

  1. Structural and superconducting properties of co-doped YBa2-xLaxCu3-xMxOz and La-free YBa2Cu3-xMxOz (M = Al, Zn) high-TC superconductors

    NASA Astrophysics Data System (ADS)

    Hao, S. J.; Jin, W. T.; Guo, C. Q.; Zhang, H.

    2012-05-01

    Two co-doped high-Tc superconducting systems, YBa2-xLaxCu3-xAlxOz and YBa2-xLaxCu3-xZnxOz (0 ⩽ x ⩽ 0.3), both of which have not been reported up to the present, were synthesized. The structural and superconducting properties have been investigated by X-ray diffraction (XRD) and DC magnetization measurement. Comparing the properties of these co-doped systems with single-doped systems YBa2Cu3-xAlxOz and YBa2Cu3-xZnxOz, it shows that in the Al-single-doped YBCO system, the depression of the critical temperature (Tc) with doping is stronger than that in (La, Al)-co-doped system, however, in the Zn-single-doped system, the Tc descends slower than that in (La, Zn)-co-doped system. This is possibly due to the opposite change of the distance between the Ba site and the CuO2 plane induced by the La doping. Besides, the La doping has another effect of improving the solid solubility compared with the Al- or Zn-single-doped system.

  2. 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.

  3. 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.

  4. 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.

  5. Processing for both high-{Tc} and high-J{sub c} (Tl,Pb,Bi)(Sr,Ba){sub 2}Ca{sub 2}Cu{sub 3}O{sub 9} superconducting tapes

    SciTech Connect

    Liu, R.S.; Wu, S.F.; Tai, C.H.; Shy, D.S.

    1994-12-31

    The authors have found an efficient and highly reproducible method for the preparation of the homogeneous Tl-1223 powders by the partial substitution of Ba{sup 2+} into the Sr{sup 2+} sites in the (Tl{sub 0.6}Pb{sub 0.2}Bi{sub 0.2})(Sr{sub 2{minus}x}Ba{sub x})Ca{sub 2}Cu{sub 3}O{sub 9} system. Superconducting tapes (sheathed in silver) based on the titled system have been fabricated by using the powder-in-tube (PIT) method. Typical critical temperatures ({Tc}) of around 120 K and transport critical current densities (J{sub c}) of about 1.05 {times} 10{sup 4} A/cm{sup 2} at 77 K in a zero magnetic field have been routinely obtained on short lengths ({approximately}3 cm) of the sintered Tl-1223 tapes after rolling. Moreover, a prototype superconducting (Tl,Pb,Bi)(Sr,Ba){sub 2}Ca{sub 2}Cu3O{sub 9} magnet (with three pancake coils, each containing four 3 m lengths of rolled tapes) generated field of 240 G at 77 K was obtained.

  6. High-Tc SQUID magnetocardiography imaging system.

    PubMed

    Yang, H C; Hung, S Y; Wu, C H; Chen, J C; Hsu, S J; Liao, S H; Horng, H E

    2004-11-30

    We set up a high-Tc SQUID system for magnetocardiography (MCG) in a moderately magnetically shielded room. The electronically balanced gradiometer consists of superconducting quantum interference device (SQUID) magnetometer. One reference SQUID was mounted above the sensing SQUID while the sensing SQUID is seated at the bottom of the cryostat. The baseline of the gradiometer is varied from 5 cm to 7 cm. The output of the MCG signal was filtered with the band pass filter (0.5 - 40 Hz) and the power-line filter. The MCG system was used to detect the magnetic signal of the human heart. Equivalent current sources were used to study the inverse problem.

  7. First 13 years of high-{Tc}: Brief review and open questions

    SciTech Connect

    Pavuna, D.

    1999-12-20

    Exactly 13 years ago, in April 1986, appeared the famous paper by Bednorz and Mueller, that announced a striking discovery of high-{Tc} superconductivity in cuprates. Some 40,000 papers later, scientists are still struggling to understand the high-{Tc} superconductivity. Here the author summarizes 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.

  8. Spin-spin relaxation of protons in ferrofluids characterized with a high-Tc superconducting quantum interference device-detected magnetometer in microtesla fields

    NASA Astrophysics Data System (ADS)

    Liao, Shu-Hsien; Liu, Chieh-Wen; Yang, Hong-Chang; Chen, Hsin-Hsien; Chen, Ming-Jye; Chen, Kuen-Lin; Horng, Herng-Er; Wang, Li-Min; Yang, Shieh-Yueh

    2012-06-01

    In this work, the spin-spin relaxation of protons in ferrofluids is characterized using a high-Tc SQUID-based detector in microtesla fields. We found that spin-spin relaxation rate is enhanced in the presence of superparamagnetic nanoparticles. The enhanced relaxation rates are attributed to the microscopic field gradients from magnetic nanoparticles that dephase protons' spins nearby. The relaxation rates decrease when temperatures increase. Additionally, the alternating current magnetic susceptibility was inversely proportional to temperature. Those characteristics explained the enhanced Brownian motion of nanoparticles at high temperatures. Characterizing the relaxation will be helpful for assaying bio-molecules and magnetic resonance imaging in microtesla fields.

  9. High-temperature superconductivity

    SciTech Connect

    Burns, G.

    1992-01-01

    Review of conventional superconductors. Structures. Normal-state properties. Superconducting properties. Vortex behavior, J[sub c], and applications. Index. An introductory presentation of high-temperature superconductivity, with emphasis on the experimental approach. Intended as a supplementary text for undergraduate solid state physics courses, assumes some background in physics and applicable technologies. Chapters contain unsolved problems. Bibliography and chapter notes appear at end of text.

  10. 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.

  11. 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.

  12. 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).

  13. High-Tc and low-Tc dc SQUID electronics

    NASA Astrophysics Data System (ADS)

    Drung, Dietmar

    2003-12-01

    Superconducting quantum interference devices (SQUIDs) are commonly operated in a flux-locked loop (FLL). The SQUID electronics amplifies the small SQUID signal to an acceptable level without adding noise, and it linearizes the transfer function of the SQUID in order to provide sufficient dynamic range. In this paper, the fundamentals of SQUID readout are reviewed including a discussion of preamplifier noise. The basic FLL concepts, direct readout and flux modulation readout, are discussed both with dc bias and bias reversal. Alternative readout concepts such as additional positive feedback (APF), two-stage SQUIDs, SQUID series arrays, relaxation oscillation SQUIDs and digital SQUIDs are briefly described. The FLL dynamics are discussed on the basis of a simple model with finite loop delay. It is shown that with optimized SQUID electronics a system bandwidth of ap18 MHz and a corresponding slew rate of ap8 PHgr0 µs-1 are possible. A novel FLL scheme involving a Smith predictor is presented which allows one to increase the FLL bandwidth to about 100 MHz. The theoretical predictions are experimentally checked using a high-speed SQUID electronics prototype with a small-signal bandwidth of 300 MHz. Methods for increasing the dynamic range of SQUID systems are described: flux-quanta counting and dynamic field compensation (DFC). With DFC, the residual magnetic field at the SQUID can be kept close to zero even if the device is moved in the Earth's field. Therefore, the noise level of a high-Tc magnetometer measured inside a magnetically shielded room (60 fT Hz-1/2 with a 1/f corner at 2 Hz) remained unchanged after moving the device in the magnetic field outside the room (60 µT dc plus 0.8 µT peak-to-peak power line interference).

  14. Gossamer high-temperature bulk superconductivity in FeSe

    NASA Astrophysics Data System (ADS)

    Sinchenko, A. A.; Grigoriev, P. D.; Orlov, A. P.; Frolov, A. V.; Shakin, A.; Chareev, D. A.; Volkova, O. S.; Vasiliev, A. N.

    2017-04-01

    Using the anisotropic electron transport and susceptibility measurements we demonstrate the appearance of inhomogeneous gossamer superconductivity in FeSe single crystals at ambient pressure and at temperature five times higher than its zero resistance Tc. We also find and quantitatively describe a general property: If inhomogeneous superconductivity in a anisotropic conductor first appears in the form of isolated superconducting islands, it reduces electric resistivity anisotropically with maximal effect along the least conducting axis. This gives a simple tool to study inhomogeneous superconductivity in various anisotropic compounds, which helps to investigate the onset of high-temperature superconductivity.

  15. Effects of non-magnetic doping on high- Tc cuprates

    NASA Astrophysics Data System (ADS)

    Ming-wen, Xiao; Zheng-zhong, Li; Da-ning, Shi

    1992-11-01

    The Anderson lattice model (ALM) is adopted to study the substitution effects of non-magnetic impurities at Cu-sites on the properties of high- Tc superconductors by the slave-boson technique. We found that they can weaken the effective strength of Cu O hybridization and lower the characteristic temperature Tk of the normal state. The ability of these effects to depress superconductivity is proved to be important and not negligible. Non-magnetic impurities turn out to be pair-breaking and responsible for the quick decreasing of Tc because of the energy dependence of the superconducting order parameter in ALM. Particularly, the linear relationship between Tc and doping concentration in the dilute case is obtained analytically, which is in good agreement with experiment.

  16. 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.

  17. Raman Scattering in HIGH-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Thomsen, Christian; Cardona, Manuel

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

  18. High Tc composite silver/oxide superconductors

    NASA Technical Reports Server (NTRS)

    Curreri, P. A.; Peters, P. N.; Sisk, R. C.; Wu, M. K.; Huang, C. Y.

    1990-01-01

    Factors involved in the strong flux pinning effect of high-Tc YBa2Cu3O7/AgO (Y-123/AgO) composite and other REE-123/AgO composites were investigated. Samples of superconducting REE-123 and REE-123/AgO (where REE was Nd, Sm, Eu, Gd, Dy, Ho, Er, or Y) were prepared and used to obtain magnetic moments, critical field, and microstructure data. The optimum heat treatment conditions for the formation of strong flux-pinning REE-123/AgO composites were found to be different for different REE-123 compounds. It was found that the annealing temperature depends on the ionic size of the REE, with larger rare-earth ions requiring higher temperature. It was also found that strong flux-pinning REE-123/AgO composites form only in a narrow annealing temperature range.

  19. High Tc composite silver/oxide superconductors

    NASA Technical Reports Server (NTRS)

    Curreri, P. A.; Peters, P. N.; Sisk, R. C.; Wu, M. K.; Huang, C. Y.

    1990-01-01

    Factors involved in the strong flux pinning effect of high-Tc YBa2Cu3O7/AgO (Y-123/AgO) composite and other REE-123/AgO composites were investigated. Samples of superconducting REE-123 and REE-123/AgO (where REE was Nd, Sm, Eu, Gd, Dy, Ho, Er, or Y) were prepared and used to obtain magnetic moments, critical field, and microstructure data. The optimum heat treatment conditions for the formation of strong flux-pinning REE-123/AgO composites were found to be different for different REE-123 compounds. It was found that the annealing temperature depends on the ionic size of the REE, with larger rare-earth ions requiring higher temperature. It was also found that strong flux-pinning REE-123/AgO composites form only in a narrow annealing temperature range.

  20. Metallic and superconducting gallane under high pressure

    NASA Astrophysics Data System (ADS)

    Gao, Guoying; Wang, Hui; Bergara, Aitor; Li, Yinwei; Liu, Guangtao; Ma, Yanming

    2011-08-01

    Using our newly developed particle swarm optimization algorithm on crystal structural prediction, we characterized the pressure-induced structural transition sequence of gallane (GaH3). As has been observed in alane (AlH3), enthalpy calculations reveal that the Pm3¯n structure of GaH3 becomes stable above 160 GPa, below which it is unstable with respect to elemental decomposition. Interestingly, the Pm3¯n structure is metallic, and the application of the Allen-Dynes modified McMillan equation reveals a high superconducting transition temperature (Tc), which reaches 86 K at 160 GPa and increases with decreasing pressure (Tc = 102 K at 120 GPa). Our band structure calculations demonstrate that GaH3 within the Pm3¯n structure is a highly ionic solid, where the ionicity of H atoms plays an important role in the predicted high temperature superconductivity.

  1. Characteristics of high-stiffness superconducting bearing

    SciTech Connect

    Okano, M.; Tamada, N.; Fuchino, S.; Ishii, I.

    1996-07-01

    Magnetic bearings using a high-Tc superconductor have been studied. Generally the bearing makes use of the pinning effects to get the levitation force. The stiffness of the bearing, however, is extremely low as compared with industrial-scale conventional one. To improve the bearing stiffness the authors propose a disc-type repulsive superconducting thrust bearing with a slit for the restraint of the flux. Both theoretical and experimental evaluation on the load performance was carried out, and it is clarified that the proposed superconducting bearing has higher stiffness.

  2. 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

  3. Phase Transformations in the High-Tc Superconducting Compounds, Ba2RCu3O7-δ (R = Nd, Sm, Gd, Y, Ho, and Er).

    PubMed

    Wong-Ng, W; Cook, L P; Su, H B; Vaudin, M D; Chiang, C K; Welch, D R; Fuller, E R; Yang, Z; Bennett, L H

    2006-01-01

    The phase transformation between the orthorhombic and tetragonal structures of six high-T c superconductors, Ba2RCu3O7- δ , where R = Nd, Sm, Gd, Y, Ho, and Er, and δ = 0 to 1, has been investigated using techniques of x-ray diffraction, differential thermal analysis/thermogravimetric analysis (DTA/TGA) and electron diffraction. The transformation from the oxygen-rich orthorhombic phase to the oxygen-deficient tetragonal phase involves two orthorhombic phases. A superlattice cell caused by oxygen ordering, with a' = 2a, was observed for materials with smaller ionic radius (Y, Ho, and Er). For the larger lanthanide samples (Nd, Sm, and Gd), the a' = 2a type superlattice cell was not observed. The structural phase transition temperatures, oxygen stoichiometry and characteristics of the T c plateaus appear to correlate with the ionic radius, which varies based on the number of f electrons. Lanthanide elements with a smaller ionic radius stabilize the orthorhombic phase to higher temperatures and lower oxygen content. Also, the superconducting temperature is less sensitive to the oxygen content for materials with smaller ionic radius. The trend of dependence of the phase transformation temperature on ionic radius across the lanthanide series can be explained using a quasi-chemical approximation (QCA) whereby the strain effect plays an important role on the order-disorder transition due to the effect of oxygen content on the CuO chain sites.

  4. 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

  5. High temperature interface superconductivity

    SciTech Connect

    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, 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.

  6. Interface high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Wang, Lili; Ma, Xucun; Xue, Qi-Kun

    2016-12-01

    Cuprate high-temperature superconductors consist of two quasi-two-dimensional (2D) substructures: CuO2 superconducting layers and charge reservoir layers. The superconductivity is realized by charge transfer from the charge reservoir layers into the superconducting layers without chemical dopants and defects being introduced into the latter, similar to modulation-doping in the semiconductor superlattices of AlGaAs/GaAs. Inspired by this scheme, we have been searching for high-temperature superconductivity in ultra-thin films of superconductors epitaxially grown on semiconductor/oxide substrates since 2008. We have observed interface-enhanced superconductivity in both conventional and unconventional superconducting films, including single atomic layer films of Pb and In on Si substrates and single unit cell (UC) films of FeSe on SrTiO3 (STO) substrates. The discovery of high-temperature superconductivity with a superconducting gap of ∼20 meV in 1UC-FeSe/STO has stimulated tremendous interest in the superconductivity community, for it opens a new avenue for both raising superconducting transition temperature and understanding the pairing mechanism of unconventional high-temperature superconductivity. Here, we review mainly the experimental progress on interface-enhanced superconductivity in the three systems mentioned above with emphasis on 1UC-FeSe/STO, studied by scanning tunneling microscopy/spectroscopy, angle-resolved photoemission spectroscopy and transport experiments. We discuss the roles of interfaces and a possible pairing mechanism inferred from these studies.

  7. An Economical Magnetocardiogram System Based on High-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Li, Zhuo; Zhu, Xue-Min; Zhang, Li-Hua; Huang, Xu-Guang; Ren, Yu-Feng; Chen, Geng-Hua; Yang, Qian-Sheng; Feng, Ji

    2006-08-01

    An economical magnetocardiogram (MCG) system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-Tc superconducting quantum interference device (SQUID) magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements.

  8. Side-suspended High-Tc Superconducting Maglev Prototype Vehicle Running at a High Speed in an Evacuated Circular Test Track

    NASA Astrophysics Data System (ADS)

    Zhou, Dajin; Zhao, Lifeng; Cui, Chenyu; Zhang, Yong; Guo, Jianqiang; Zhao, Yong

    2017-07-01

    High-T c superconductor (HTS) and permanent magnetic guideway (PMG) based maglev train is intensively studied in China, Japan, Germany and Brazil, mainly through static or vibration test. Amongst these studies, only a few of reports are available for the direct and effective assessment on the dynamic performance of the HTS maglev vehicle by running on a straight or circular PMG track. The highest running speed of these experiments is lower than 50 km/h. In this paper, a side-suspended HTS permanent magnetic guideway maglev system was proposed and constructed in order to increase the running speed in a circular track. By optimizing the arrangement of YBCO bulks besides the PMG, the side-suspended HTS maglev prototype vehicle was successfully running stably at a speed as high as 150 km/h in a circular test track with 6.5 m in diameter, and in an evacuated tube environment, in which the pressure is 5 × 103 Pa.

  9. 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.

  10. Superconductivity and magnetism in niobium doped YBa{sub 2}Cu{sub 3}O{sub 7} related high-{Tc} ceramics

    SciTech Connect

    Bennahmias, M. |; Radousky, H.B. |; Goodwin, T.J.; Shelton, R.N.

    1993-02-01

    Magnetic characterization has been performed on the members of the cuprate-niobate RBa{sub 2}Cu{sub 2}NbO{sub 8} (R = Pr, Nd, and La) series and R{sub l.5}Ce{sub 0.5}Sr{sub 2}Cu{sub 2}NbO{sub 10} (R = Pr, Eu, Nd, and Sm) series. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12 K. The PrCSCNO sample is non-superconducting and shows two distinct orderings at 17 and 53 K. No such magnetic phase transition is observed down to 2 K in the Nd and La based RBCNO materials or the Nd, Sm, and Eu based RCSCNO materials. Measurements of the lower critical field curve, dc irreversibility line, and critical current densities are reported for each of the superconducting NdCSCNO, SmCSCNO, and EuCSCNO compounds.

  11. High Tc SQUID Detector for Magnetic Metallic Particles in Products

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Akai, Tomonori; Hatsukade, Yoshimi; Suzuki, Shuichi

    High-Tc superconducting quantum interference device (SQUID) is an ultra-sensitive magnetic sensor. After the discovery of the high-Tc superconducting materials, the performance of the high-Tc SQUID has been improved and stabilized. One strong candidate for application is a detection system of magnetic foreign matters in industrial products. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. If this happens, the manufacturer of the product suffers a great loss recalling products. The outer dimension of metallic particles less than 100 micron cannot be detected using X-ray imaging, which is commonly used for the inspection. Therefore a highly sensitive system for small foreign matters is required. We developed detection systems based on high-Tc SQUID for industrial products. We could successfully detect small iron particles of less than 50 micron on a belt conveyer. These detection levels were hard to be achieved using conventional X-ray detection or other methods.

  12. 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.

  13. 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.

  14. Approximate boundary conditions in a circular conductor and their application to nonlinear vibration analyses of high-Tc superconducting levitation system

    SciTech Connect

    Nagaya, Kosuke; Shuto, Syunsuke

    1996-05-01

    When a levitated superconductor vibrates, the levitation force has nonlinear relationship among an air gap, amplitude, and frequency, so the usual static analysis for levitation forces is invalid. There are two phenomena of a flux creep and flux flow when the conductor vibrates in a magnetic field. The present article provides an analytical result for the levitation forces of a thick superconducting disc with consideration of the phenomena and effects of flux variations on the critical current. It is significantly difficult to have the analytical result of levitation force by using the exact boundary conditions. This paper presents approximate boundary conditions which give an appropriate result. To validate the proposed boundary conditions, eddy currents in a conductor are first discussed, then the superconductor is discussed. Numerical results for the levitation forces were obtained and compared with the previously published experimental data. The levitation force becomes a restoring force having the nonlinear relationship, so it is difficult to solve vibrations. The present article gives a simplified method for solving nonlinear vibration problems for the levitated conductor. Numerical calculations were carried out for some typical examples.

  15. 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.

  16. High-pressure studies on Tc and crystal structure of iron chalcogenide superconductors

    PubMed Central

    Takahashi, Hiroki; Tomita, Takahiro; Takahashi, Hiroyuki; Mizuguchi, Yoshikazu; Takano, Yoshihiko; Nakano, Satoshi; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya

    2012-01-01

    The superconducting transition temperature, Tc, in iron-based solids can be enhanced by applied pressure: Tc increases from 8 to 37 K for the 11-type FeSe when the pressure is raised from 0 to 4 GPa. High-pressure studies can elucidate the mechanism of superconductivity in such novel materials. In this paper, we present a high-pressure study of Fe(Se1−xTex) and Fe(Se1−xSx). In the case of Fe(Se1−xTex), the maximum Tc under high pressure did not exceed the Tc of FeSe, which can be attributed to the structural transition to the monoclinic phase. For Fe(Se1−xSx) (0 < x < 0.3), Tc exhibited a significant increase with pressure; however, the maximum Tc under high pressure did not exceed the Tc of FeSe. This may be due to the disorder induced by substituting S for Se, which is similar to the pressure effect on Tc for the 1111-type superconductor Ca(Fe1−xCox)AsF. The Tc of Fe(Se1−xSx) showed a complex behavior below 1 GPa, first decreasing and then increasing with increasing pressure. From high-pressure x-ray diffraction measurements, the Tc (P) curve was correlated with the local structural parameter. PMID:27877519

  17. Evidence for intrinsic superconductivity at Tc1 in PrOs4Sb12

    NASA Astrophysics Data System (ADS)

    Andraka, B.; Pocsy, K.

    2012-04-01

    Superconductivity in PrOs4Sb12 shows unusual sample size dependence. Large good quality crystals exhibit two superconducting transitions at Tc1 (˜1.85 K) and Tc2 (˜1.74 K). The upper temperature transition is manifested by the change of slope in C/T. It is shown that this transition is suppressed when the crystal is polished to a thickness smaller than 50 μm. At the same time the polishing enhances the transition at Tc2. This behavior is independent on whether material studied is removed from the interior or contains the original surface of the as-cast crystal. The effect of sample polishing is similar to that of powdering, which clearly induces a large number of defects.

  18. Nonsuperconducting Micron Size Particle as Effective Pinning Centre for Enhanced Jc in High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Roul, B. K.

    2008-10-01

    Understanding the real mechanism responsible for achieving high transport critical current density (Jc) in the high temperature (high-Tc) cuprate superconductors has been one of the primary goal. The only promising way is to tailor the high-Tc cuprate material during preparation stage incorporating suitable non-superconducting particles within superconducting matrix, which are known to serve as effective pining centers. Incorporation of non-superconducting particle like silver with dimension down to micron/submicron size in the superconducting matrix is very stable and form a homogenous solid solution matrix, which has got the better stability on aging and found to be effective in enhancing flux pining in high-Tc superconducting system. In this paper, studies have been made to investigate and review the effect of non-superconducting micron size Ag particle in to the matrix of RE-Ba-Cu-O (RE = Sm, Gd & Y) 123 high-Tc ceramic superconducting system. XRD, SEM, magnetization, magnetotransport and microwave induce DC voltage measurements were carried out to study the effect of Ag into 123-superconducting system. It is observed that controlled addition of Ag into Sm-Ba-Cu-O (SBCO), Gd-Ba-Cu-O (GBCO) and Y-Ba-Cu-O (YBCO) ceramic superconductor do not react with the decomposed phases but remains in the metallic form. This brings about a lowering of the normal-state resistivity. The increase of magnetic critical current density (Jmc), transport critical current density (Jtc), and, hence pinning force density (Fp) with Ag addition into above three systems suggest the creation of an SNS-type proximity junction at the intergranular region and stronger Josephson current paths between the superconducting intergrains. This is attributed to the physical densification and consequent reduction of the total number of weak links by Ag addition into the above mentioned ceramic superconducting system.

  19. Width Dependence of Tc for Photoinduced Superconducting Wires in Underdoped YBCO

    NASA Astrophysics Data System (ADS)

    Palmer, B. S.; Drew, H. D.; Mairov, B.; Osquiguil, E.; Hughes, R. A.; Preston, J. S.

    2003-03-01

    A near-field scanning optical microscope (NSOM) has been used to photogenerate superconducting wires in underdoped YBa_2Cu_3Ox (x ˜6.4) thin films ( ˜100 nm). After the wires are generated at room temperature, the sample is cooled to low temperatures where I-V measurements are performed. We have found that the superconducting transition temperature (T_c) is strongly suppressed for narrow wires (< 500 nm) compared with when the film is photogenerated with the same integrated photon density using far field light to generate a wide (10 μm) wire which produces an enhancement of the superconducting state with an increase in Tc of approximately 10K. We interpret these results in terms of the proximity effect between the superconducting and surrounding non-superconducting material that suppresses the superconducting transition temperature of the narrow wires. The experiment gives a measure of the characteristic length for the proximity effect, which is approximately 1 μm for the underdoped material.

  20. Synthesis and transport properties of superconducting thin films of K0.33WO3: Tc reduction due to disorder

    NASA Astrophysics Data System (ADS)

    Wu, Phillip M.; Hart, Chris; Luna, Katherine; Munakata, Ko; Tsukada, Akio; Risbud, Subhash H.; Geballe, T. H.; Beasley, M. R.

    2014-05-01

    Via a two-step deposition and post-annealing procedure, K-doped WO3 thin films with reproducible transport properties are obtained. We observe a larger critical field Hc2 along the c axis, consistent with the picture of the Fermi surface containing one-dimensional bands along this direction. Reducing the film thickness results in a superconductor to insulator transition. Scanning electron microscopy (SEM) images show that KWO3 crystallites become less connected as the deposition time is reduced, providing a microscopic explanation for the transport behavior. In the superconducting films, a resistive anomaly is observed similar to bulk crystals, with a characteristic temperature that shifts lower with decreasing film thickness. The competing electronic effects manifest as a suppression of the density of states at the Fermi level, observed using point contact tunneling spectroscopy, demonstrating that disorder-induced increased Coulomb interactions are present. Using the theory of Belitz for the reduction of Tc due to disorder, we can infer that the film with the highest observed Tc has a relatively large disorder dependent electron-phonon interaction parameter ˜1.2. Understanding microscopically why certain films display higher Tc will aid in the search for the trace high-Tc superconducting anomalies observed in lightly surface doped bronzes.

  1. Magnetically-related properties of bismuth containing high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Vezzoli, Gary C.; Chen, M. F.; Craver, F.; Safari, A.; Moon, B. M.; Lalevic, B.; Burke, Terence; Shoga, M.

    1990-08-01

    The effect of magnetic fields to 15 T on electrical resistance has been measured for the BiSrCaCuO superconductor at precise temperatures during the transition to the superconducting state from pre-onset conditions to essentially zero resistance conditions. The results show that the temperature at which the magnetic field causes a divergence in the resistance versus 1000/ T curve is approximately the same temperature as the value at which, during cooling, the positive Hall coefficient begins its abrupt descent to zero. This temperature gives the best measure of Tc. It is also shown that small oscillations of low frequency start near onset conditions, the amplitude of which at a given temperature is B-field dependent. Additionally, Hall effect studies as a function of temperature at 4 T in three separate experiments (including high Tc BiSrCaCu PbO of > 90% theoretical density) show that sharp delta-function-like peaks in + RH are observed near Tc and are superimposed on a broader maximum. The Hall data are explicable in terms of exciton formation and ionization. The bound holes associated with these excitons are believed to be the mediators producing Cooper-pairing, and scale very well with Tc for all the known high Tc oxides.

  2. High Temperature Superconducting Compounds.

    DTIC Science & Technology

    1999-04-02

    addition to superconducting films, non-superconducting mixed-valence manganite perovskites, which exhibit so-called colossal magnetoresistance were grown...The manganites are unique in that their charge carriers are believed to be almost 100% spin polarized. These materials were combined with the...brought about by the injection of spin polarized carriers from the manganite into the curate. This work may make possible new classes of devices based on

  3. Weak Coupling Electron-Phonon for High Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Labbe, J.

    1989-01-01

    Our opinion is that, in the high Tc copper oxides, the electronic correlations are not large enough to allow the localization of the electrons of the half-filled d-p sub-band. Thus, we treat them as itinerant electrons, in a bidimensional structure. And we show that, contrary to a widely held opinion, the electron-phonon interaction can induce high Tc superconductivity in these compounds, even in the weak coupling limit. This is due to the fact that, because of the bidimensionality, the electronic density of states is sharply peaked in the neighbourhood of the Fermi energy. A small coupling between nearest neighbouring CuO2 planes is sufficient to prevent a very large reduction of Tc by the critical fluctuations. The calculated isotope effect is much smaller than usually in the BCS theory. And, in our weak coupling theory, the antiferromagnetic (AF) phase is much more rapidly destabilized by dopping or internal charge transfer than the superconducting phase, which takes place when the AF phase has vanished.

  4. 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.

  5. 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.

  6. One-dimensional model for BiS2 superconductivity: analyzing the pressure effect over Tc

    NASA Astrophysics Data System (ADS)

    Griffith, M. A.; Foyevtsova, K.; Continentino, M. A.; Martins, G. B.

    2016-02-01

    The recently synthesized compound SrFBiS2 [Lei H et al. 2013 Inorg. Chem. 52 106851] has been shown to become superconducting [Lin X et al. 2013 Phys. Rev. B 87 020504] through the substitution of Sr2+ by La3+. In addition, application of moderate hydrostatic pressure in Sr0.5RE0.5FBiS2 (RE=Ce, Nd, Pr, and Sm) [Jha R et al. 2015 J. Appl. Phys. 117 013901] has shown a dramatic increase in the superconducting transition temperature Tc. In this work, using a recently proposed one-dimensional model for BiS2-based superconductors [Griffith M A et al. 2015 submitted to Phys. Rev. B], the authors analyze the effect of pressure over Tc.

  7. Doping dependence of fluctuation diamagnetism in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Sarkar, Kingshuk; Banerjee, Sumilan; Mukerjee, Subroto; Ramakrishnan, T. V.

    2016-02-01

    Using a recently proposed Ginzburg-Landau-like lattice free energy functional due to Banerjee et al. (2011) we calculate the fluctuation diamagnetism of high-Tc superconductors as a function of doping, magnetic field and temperature. We analyse the pairing fluctuations above the superconducting transition temperature in the cuprates, ranging from the strong phase fluctuation dominated underdoped limit to the more conventional amplitude fluctuation dominated overdoped regime. We show that a model where the pairing scale increases and the superfluid density decreases with underdoping produces features of the observed magnetization in the pseudogap region, in good qualitative and reasonable quantitative agreement with the experimental data. In particular, we explicitly show that even when the pseudogap has a pairing origin the magnetization actually tracks the superconducting dome instead of the pseudogap temperature, as seen in experiment. We discuss the doping dependence of the 'onset' temperature for fluctuation diamagnetism and comment on the role of vortex core-energy in our model.

  8. 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

  9. Preparation of the High-Tc Phase of Bi-Sr-Ca-Cu-O Superconductor

    NASA Astrophysics Data System (ADS)

    Endo, Utako; Koyama, Satoshi; Kawai, Tomoji

    1988-08-01

    Co-decomposition of mixed nitrates of Bi, Pb, Sr, Ca and Cu around 830°C under low oxygen pressure led to the formation of a high-Tc superconducting phase of Bi(Pb)-Sr-Ca-Cu-O with Tc(zero) at 107.5 K. A sample prepared by a conventional solid state reaction method under low oxygen pressure also showed the superconducting transition at 107.5 K. X-ray powder diffraction and magnetic susceptibility measurements on these samples revealed the high-Tc phase without 80 K or semiconducting phase. The reaction under low oxygen pressure has an effect to lower the temperature with broad ranges to render the high-Tc phase of the Bi-Sr-Ca-Cu-O.

  10. Realization of High-Temperature Superconductivity in Nano-Carbon Materials and Its Power Application

    DTIC Science & Technology

    2012-08-12

    1 Final Report for AOARD Grant: FA2386-11-1-4093 “Realization of high-temperature superconductivity in nano-carbon materials and its power...particular, they have possibility for realization of high- transition temperature (Tc) superconductivity (SC) (e.g., Tc > 40K). In the present work, I have...walled CNTs (MWNTs), (2) Arrays of boron-doped MWNTs synthesized on SiC substrate. We find that the former exhibits Meissner effect with the highest

  11. 14N nuclear quadrupole resonance of p-nitrotoluene using a high-Tc rf SQUID

    NASA Astrophysics Data System (ADS)

    He, D. F.; Tachiki, M.; Itozaki, H.

    2007-03-01

    Using a high-Tc radio-frequency superconducting quantum interference device (rf SQUID), we successfully detected nuclear quadrupole resonance (NQR) at about 887 kHz for 14N in p-nitrotoluene (PNT). A normal metal transformer made of copper wire was used to improve the sensitivity of the high-Tc rf SQUID and pulse-controlled rf switches and cross diodes were inserted in the transformer to reduce the influence of the strong excitation field. The preliminary results for NQR detection using the high-Tc SQUID had a similar signal-to-noise ratio to that of using a low noise preamplifier.

  12. Induction magnetometer using a high-Tc superconductor coil

    NASA Astrophysics Data System (ADS)

    Sasada, Ichiro

    2010-05-01

    An induction magnetometer consisting of a search coil and an inverting operational amplifier is simple in structure and in signal transferring mechanism from the magnetic field input to the voltage output. Because this magnetometer is based on Faraday's law of induction, it has a lower cutoff frequency r/(2πL), where r is the resistance of the coil and L is its inductance. An attempt has been made to lower the cutoff frequency of the induction magnetometer by using a high-Tc superconductor coil. With a pancake coil (inner diameter ≈18 cm and outer diameter ≈23 cm, 92 turns, 3.23 mH) made of a Bismuth strontium calcium copper oxide (BSCCO) superconductor tape of 5 mm in width and 0.23 mm in thickness, the cutoff frequency achieved was 1.7 Hz which is much lower than that obtained with a bulky copper search coil which is typically in the range of 10-20 Hz. In the experiment, an inverting amplifier was made with a complementary metal-oxide semiconductor operational amplifier and was immersed in liquid nitrogen together with a BSCCO high-Tc superconducting coil. Discussion is made on the resolution of the induction magnetometer using a high-Tc superconductor search coil.

  13. High-temperature superconductivity in perspective

    NASA Astrophysics Data System (ADS)

    1990-04-01

    The technology of superconductivity and its potential applications are discussed; it is warned that U.S companies are investing less than their main foreign competitors in both low- and high-temperature superconductivity R and D. This is by far the most critical issue affecting the future U.S. competitive position in superconductivity, and in many other emerging technologies. The major areas covered include: Executive summary; High-temperature superconductivity - A progress report; Applications of superconductivity; The U.S. response to high-temperature superconductivity; High-temperature superconductivity programs in other countries; Comparison of industrial superconductivity R and D efforts in the United States and Japan - An OTA survey; Policy issues and options.

  14. Ultrasonic study on Bi-based high-Tc superconductors with preferred orientations

    NASA Astrophysics Data System (ADS)

    Dong, Jian; Deng, Tingzhang; Li, Fengying; Yao, Yushu

    1990-07-01

    Ultrasonic experimental studies on Bi-based ceramic superconductors are reported. The specimens used in our experiments were hot pressed after sintering in air; therefore, a preferred orientation of the granules was obtained. The frequencies of ultrasound were about 10 MHz, both for longitudinal and for transverse waves. It has been found that anomalies in the attenuation coefficient and sound velocity occur near 220 K, in the range between 10 and 50 K above Tc, and at Tc, respectively. The investigation shows that the pretransition in the range between 10 and 50 K above Tc leads to a tendency of softness and instability in crystal lattice, and the superconducting transition is present on the background of a rapid decrease in attenuation with the decrease in temperature. It is believed that a strong superconducting fluctuation exists above Tc. The deformation-potential model for acoustic-phonon-electron interaction, which is the basis of BCS theory, may be unsuitable for the high-Tc superconductors. A model of superconductivity due to optical-phonon-electron coupling is suggested.

  15. Phase diagram and isotopic effect in high-Tc pnictide superconductors

    NASA Astrophysics Data System (ADS)

    Chen, Xianhui

    2010-03-01

    We will talk about the discovery of superconductivity with Tc higher than 40 K in Fe-based superconductors SmFeAsO1-xF. Tc higher than McMillan limit of 39 K definitely proves pnictide superconductors high-Tc superconductivity^1,2. In this talk, we present the transport properties: resistivity, Hall coefficient and transport properties under high magnetic field. These results suggest a quantum phase transition around x=0.14 in SmFeAsO1-xFx system. A electronic phase diagram is proposed, and coexistence of superconductivity and spin-density-wave is observed in Sm-1111 and Ba-122 system. We discuss the effect of isotopic effect on TC and TSDW in SmFeAsO1-xFx and Ba1-xKxFe2As2 systems. Our results show that oxygen isotope effect on TC and TSDW is very little, while the iron isotope exponent is about 0.35. Surprisingly, the iron isotope exchange shows the same effect on SDW transition as on superconductivity. Our results indicate that electron-phonon interaction plays some role in the superconducting mechanism, but simple electron-phonon coupling mechanism seems to be rather unlikely because a strong magnon-phonon coupling is included^3. 1. Chen, X. H. et al. Nature 453, 761-762 (2008). 2. Liu, R. H. et al. Phys. Rev. Lett. 101, 087001 (2008). 3. R. H. Liu et al., Nature 459, 64-67(2009).

  16. High Tc superconductors - Composite wire fabrication

    NASA Astrophysics Data System (ADS)

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

    1987-07-01

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

  17. 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.

  18. 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

  19. 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

  20. 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

  1. 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.

  2. Aerospace Applications Of High Temperature Superconductivity

    NASA Astrophysics Data System (ADS)

    Anderson, W. W.

    1988-05-01

    The existence of superconductors with TcOOK (which implies device operating temper-atures the order of Top ≍45K) opens up a variety of potential applications within the aerospace/defense industry. This is partly due to the existence of well developed cooler technologies to reach this temperature regime and partly due to the present operation of some specialized components at cryogenic temperatures. In particular, LWIR focal planes may operate at 10K with some of the signal processing electronics at an intermediate temperature of 40K. Addition of high Tc superconducting components in the latter system may be "free" in the sense of additional system complexity required. The established techniques for cooling in the 20K to 50K temperature regime are either open cycle, expendable material (stored gas with Joule-Thomson expansion, liquid cryogen or solid cryogen) or mechanical refrigerators (Stirling cycle, Brayton cycle or closed cycle Joule-Thomson). The high Tc materials may also contribute to the development of coolers through magnetically levitated bearings or providing the field for a stage of magnetic refrigeration. The discovery of materials with Tc, 90K has generated a veritable shopping list of applications. The superconductor properties which are of interest for applications are (1) zero resistance, (2) Meissner effect, (3) phase coherence and (4) existence of an energy gap. The zero resistance property is significant in the development of high field magnets requiring neglible power to maintain the field. In addition to the publicized applications to rail guns and electromagnetic launcher, we can think of space born magnets for charged particle shielding or whistler mode propagation through a plasma sheath. Conductor losses dominate attenuation and dispersion in microstrip transmission lines. While the surface impedance of a superconductor is non vanishing, significant improvements in signal transmission may be obtained. The Meissner effect may be utilized

  3. High Temperature Superconducting Compounds

    DTIC Science & Technology

    1990-10-01

    usual substrates, SrTiO3 , YSZ, MgO, and LaA103, it has been possible to deposit films on Si substrates without any buffer layer. A bolometer has been...new opportunities for the study of superconductor-insulator transitions and the investigation of photo- doping with carriers of high temperature super... SrTiO3 (00), SrTiO3 (l 10), LaA103 (100), MgO(100), and yttria stabilized zirconia (YSZ). The surfaces of these films could be imaged with a scanning

  4. 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.

  5. 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.

  6. 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.

  7. High-temperature processing of oxide superconductors and superconducting oxide-silver oxide composite

    NASA Technical Reports Server (NTRS)

    Wu, M. K.; Loo, B. H.; Peters, P. N.; Huang, C. Y.

    1988-01-01

    High temperature processing was found to partially convert the green 211 phase oxide to 123 phase. High Tc superconductivity was observed in Bi-Sr-Cu-O and Y-Sr-Cu-O systems prepared using the same heat treatment process. High temperature processing presents an alternative synthetic route in the search for new high Tc superconductors. An unusual magnetic suspension with enhancement in critical current density was observed in the 123 and AgO composite.

  8. Th-substituted SmFeAsO: Structural details and superconductivity with Tc above 50 K

    NASA Astrophysics Data System (ADS)

    Zhigadlo, N. D.; Katrych, S.; Weyeneth, S.; Puzniak, R.; Moll, P. J. W.; Bukowski, Z.; Karpinski, J.; Keller, H.; Batlogg, B.

    2010-08-01

    We report structural, magnetic, and transport properties of polycrystalline samples and single crystals of superconducting Sm1-xThxFeAsO with maximal Tc above 50 K, prepared under high pressure. Bulk superconducting samples do not undergo a structural phase transition from tetragonal to orthorhombic symmetry at low temperatures. The unit-cell parameters a and c shrink with Th substitution and the fractional atomic coordinate of the As site zAs remains almost unchanged while that of Sm/Th zSm/Th increases. Upon warming from 5 to 295 K the increase in the FeAs layer thickness is dominant, while the changes in the other structural building blocks are minor, and they compensate each other, since the As-Sm/Th distance contracts by about the same amount as the O-Sm/Th expands. The polycrystalline and single-crystalline samples are characterized by a full diamagnetic response in low magnetic field, by a high intergrain critical current density for polycrystalline samples, and by a critical current density on the order of 8×105A/cm2 for single crystals at 2 K in fields up to 7 T. The magnetic penetration depth anisotropy γλ increases with decreasing temperature, in a similar way to that of SmFeAsO1-xFy single crystals. The upper critical field estimated from resistance measurements is anisotropic with slopes of ˜5.4T/K ( H∥ab plane) and ˜2.7T/K ( H∥c axis), at temperatures sufficiently far below Tc . The low-temperature upper critical field anisotropy γH is in the range of ˜2 , consistent with the tendency of a decreasing γH with decreasing temperature, previously reported for SmFeAsO1-xFy single crystals.

  9. Uniform mixing of antiferromagnetism and high- Tc superconductivity in multilayer copper oxides Ba2Can-1CunO2nF2 (n=2,3,4) with apical fluorines: C63u-NMR/NQR and F19-NMR studies

    NASA Astrophysics Data System (ADS)

    Shimizu, S.; Sakaguchi, T.; Mukuda, H.; Kitaoka, Y.; Shirage, P. M.; Kodama, Y.; Iyo, A.

    2009-02-01

    We report C63u-NMR/NQR and F19-NMR studies on the multilayered high- Tc copper oxides Ba2Can-1CunO2nF2 with n=2,3,4 , where n is the number of CuO2 planes. It is revealed that bilayered Ba2CaCu2O4F2 is an underdoped superconductor with hole carriers, which are introduced into CuO2 planes by an unexpected deviation from the nominal content of apical fluorines. In a previous paper, we proposed a self-doping mechanism as the origin of carrier doping in n=3 and n=4 ; in the mechanism, electrons are transferred from the inner CuO2 plane (IP) to the outer one (OP). However, since it has been found that the bilayered compound is hole doped, we have re-examined the superconducting and magnetic properties in n=3 and n=4 by C63u-NMR/NQR and F19-NMR . The extensive NMR studies have confirmed that the apical-fluorine compounds are not self-doped but hole doped and that antiferromagnetism (AFM) and superconductivity (SC) coexist in a single CuO2 plane. In n=4 , the AFM ordering occurs at TN=80K well above Tc=55K , where the respective AFM moments are MAFM=0.11μB and 0.18μB at the OP and the IP. In n=3 , on the other hand, the underdoped single IP exhibits a spontaneous moment MAFM=0.12μB at low temperatures and a peak in the nuclear-spin-lattice relaxation rate 1/T1 of F19 at TN=23K much lower than Tc=76K . We note that the increase in the number of IPs from one to two results in the strengthening of the interlayer coupling; TN increases as the interlayer coupling becomes stronger, although the doping levels for both compounds are comparable. Consequently, we conclude that the uniform mixing of AFM and SC is a general property inherent to a single CuO2 plane in an underdoped regime for hole doping. This conclusion incorporates the angle-resolved photoemission spectroscopy results on the n=4 compound [Chen , Phys. Rev. Lett. 97, 236401 (2006)]; it was found that the two Fermi sheets of the IP and OP are observed and that the SC gap opens at the IP and OP below Tc=55K .

  10. 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.

  11. Enhancement of Tc in Pb-based cuprate superconductors prepared at high-oxygen-pressure

    NASA Astrophysics Data System (ADS)

    Ohta, M.; Tsutsumi, M.; Yoshimoto, J.; Okai, B.

    1991-12-01

    Samples of nominal compositions, In 0.3Pb 0.7Sr 2Y 0.2Ca 0.6Cu 2O y and Pb 0.5Sr 2.0Y 0.1Ca 0.8Cu 2O y were heat-treated under high oxygen pressure of 6 GPa at 1150°C. The recovered specimens showed superconductivity above 85 K, in the former Tc being nearly 90 K. The content of Indium incorporated in the superconducting phase was found to be less than about 2 atomic% of the total constituting cations.

  12. 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.

  13. Tunneling studies of pseudogap in high-Tc superconductor Bi2212

    NASA Astrophysics Data System (ADS)

    Gupta, Anjan Kumar

    2001-11-01

    The BCS theory predicts an energy gap in superconductors below their critical temperature Tc. This gap has been observed in conventional as well as high-Tc cuprate superconductors. However, in underdoped cuprates an energy gap has been found to exist even above Tc from several experiments. In this dissertation a study of this normal state gap, called the pseudogap, is presented using ab-plane tunneling spectroscopy of a high-Tc superconductor Bi2Sr2CaCu2O8+delta (Bi2212) at different dopings delta. Temperature and magnetic field dependent ab-plane tunneling spectra of Bi2212 crystals were studied using a home built low temperature scanning tunneling microscope (STM). Single crystals of Bi2212 were grown using self flux method, which were than underdoped by annealing in vacuum or in Argon atmosphere at 500--700°C. Resistivity, magnetic susceptibility and X-ray measurements were used for characterization. The Tc of Bi2212 decreases with underdoping while the superconducting energy gap, 2Delta, increases. The energy gap, near the maximum gap direction, at 42K is found to be 30 mV for slightly overdoped (Tc = 85K) and 38 mV for the underdoped (Tc = 70K) crystals giving a 2Delta/ kTc value of 8.2 and 12.6 for the two compounds, respectively. An energy gap is found to exist above T c for underdoped Bi2212 while it gets very weak for the overdoped compound. A dip-hump feature at energies ˜2Delta-3Delta is also seen for both the compounds. The tunneling spectra are analyzed with an interpretation that the pseudogap and the superconducting gaps coexist at low temperatures and that the superconducting gap disappears at Tc. The conservation of states rule is violated but it is recovered if the low temperature spectra are normalized with those above Tc. This normalization also removes the dip-hump and other background features. Such coexistence of two gaps can rule out a scenario that the pre-formed Cooper pairs are responsible for the pseudogap. A new low temperature STM

  14. High-pressure superconductivity in yttrium: The strong-coupling approach

    NASA Astrophysics Data System (ADS)

    Jarosik, Marcin W.; Wrona, Izabela A.; Duda, Anna M.

    2015-10-01

    In the framework of the Eliashberg formalism, the properties of the superconducting state inducing in yttrium for the pressure at p1 ≡ 26 GPa and p2 ≡ 31 GPa([TC]p1 = 7.9 K and[TC]p2 = 9.27 K) have been determined. It has been proven that the value of the Coulomb pseudopotential is high and increases with the increasing pressure: [μ⋆]p1 = 0.181 and [μ⋆]p2 = 0.251. Next, the order parameter (Δ(T)), the thermodynamic critical field (HC(T)), the specific heat in the superconducting state (CS(T)), and the specific heat in the normal state (CN(T)) have been calculated. It has been proven that the values of the dimensionless parameters RΔ ≡ 2 Δ(0)/kBTC, RC ≡ CS(TC) -CN(TC)/CN(TC), and RH ≡ TC/CN(TC) HC2 (0) significantly deviate from the predictions of the classical BCS theory: RΔ ∈ { 3.97 , 4.13 } ,RC ∈ { 2.16 , 2.41 }, and RH ∈ { 0.153 , 0.152 }. The electron effective mass is high for both pressures [me⋆] p1 T =TC = 2.16me and [me⋆ ] p2 T =TC = 2.64me, where the symbol me denotes the electron band mass.

  15. High-{Tc} rf SQUID magnetometers

    SciTech Connect

    Mueck, M.

    1994-12-31

    The discovery of high temperature superconductors has revived the interest in rf SQUIDS, which, in the case of conventional superconductors had been surpassed in performance by the dc SQUID. Several advantages are offered by the rf SQUID, like the requirement for only a single weak link and a low 1/f noise. With high bias frequencies (> 100 MHz) it is possible to obtain flux noise values comparable to dc SQUIDS. At present, HTS rf SQUIDs offer a field sensitivity of less than 100 fT/{radical}Hz ({at} 1 Hz). This is already sufficient for a number of serious applications. This paper reviews recent developments towards practical rf SQUIDs made of high-{Tc} superconductors.

  16. 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

    2008-10-09

    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.

  17. High-temperature superconductivity in FeSe monolayers

    NASA Astrophysics Data System (ADS)

    Sadovskii, M. V.

    2016-10-01

    This paper reviews the basic experimental and theoretical aspects of high-temperature superconductivity in intercalated FeSe compounds and FeSe monolayer films on SrTiO_3 and similar substrates. The paper examines in detail the electronic structure of these systems, how it is calculated, and how the calculated results compare with ARPES experiments. It is emphasized that the reviewed systems have qualitatively different electronic spectra from the typical pattern of well-studied FeAs superconductors and explores the implications of these differences for a theoretical description of how these spectra form. Possible mechanisms of Cooper pairing in FeSe monolayers are discussed and the associated problems are examined. Because FeSe monolayer films on SrTiO_3 are typical Ginzburg 'sandwiches', the possibility of increasing their T_c via 'excitonic' superconductivity mechanisms is considered. It is shown that, while the classical version of this mechanism (as proposed for such systems by Allender, Bray, and Bardeen) fails to explain the observed values of T_c, the situation changes when optical phonons in SrTiO_3 (with energy of about 100 meV) are considered to be 'excitons'. Both the simplest possible model of T_c enhancement due to interaction with such phonons and more complex ones with dominant 'forward' scattering that explain successfully the increase in T_c compared to bulk FeSe and intercalated FeSe systems are verified. Problems related to the antiadiabatic nature of this superconductivity mechanism are also discussed.

  18. High-pressure behavior of superconducting boron-doped diamond

    NASA Astrophysics Data System (ADS)

    Abdel-Hafiez, Mahmoud; Kumar, Dinesh; Thiyagarajan, R.; Zhang, Q.; Howie, R. T.; Sethupathi, K.; Volkova, O.; Vasiliev, A.; Yang, W.; Mao, H. K.; Rao, M. S. Ramachandra

    2017-05-01

    This work investigates the high-pressure structure of freestanding superconducting (Tc=4.3 K) boron-doped diamond (BDD) and how it affects the electronic and vibrational properties using Raman spectroscopy and x-ray diffraction in the 0-30 GPa range. High-pressure Raman scattering experiments revealed an abrupt change in the linear pressure coefficients, and the grain boundary components undergo an irreversible phase change at 14 GPa. We show that the blueshift in the pressure-dependent vibrational modes correlates with the negative pressure coefficient of Tc in BDD. The analysis of x-ray diffraction data determines the equation of state of the BDD film, revealing a high bulk modulus of B0=510 ±28 GPa. The comparative analysis of high-pressure data clarified that the s p2 carbons in the grain boundaries transform into hexagonal diamond.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Quantum and superconducting fluctuations effects in disordered Nb 1- xTa x thin films above Tc

    NASA Astrophysics Data System (ADS)

    Giannouri, M.; Papastaikoudis, C.

    1999-05-01

    Disordered Nb 1- xTa x thin films are prepared with e-gun coevaporation. The influence of the β-phase of tantalum in the critical temperature Tc is observed as a function of the substrate temperature. The measurements of transverse magnetoresistance at various isothermals are interpreted in terms of weak-localization and superconducting fluctuations. From the fitting procedure, the phase breaking rate τφ-1 and the Larkin parameter βL are estimated as a function of temperature. Conclusions about the dominant inelastic scattering mechanisms at various temperature regions as well as for the dominant mechanism of superconducting fluctuations near the transition temperature are extracted.

  5. Short electrical pulse generation using light-induced switching in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Balevicius, Saulius

    2001-03-01

    This report demonstrates that optically triggered switches based on high Tc superconductor thin films can be used for the generation of sub-nanosecond rise time high-power pulses. Presented in this article are the experimental investigations of the light-induced switching dynamics in YBCO thin films biased by high-current nanosecond duration pulses. This research indicates that a high-power superconducting opto-electronic opening switch can operate in several regimes. The following transitions between the various states of the film are realized: superconducting to normal (S-N), super-conducting to mixed (S-M), low resistance mixed to high resistance mixed (MLR-MHR) and mixed to normal (M-N). When the superconductor is biased with a high current, the value of the light intensity needed for triggering the switch decreases by several times. The explanation of the main light-induced switching characteristics and their behavior is based on a model, which takes into account the simultaneous action of the light and the bias current on the superconducting film. The report also includes a discussion f the ultra-fast film damaging phenomenon which appears as a result of the dissipation of intense power during switching. Discussed is also how this process limits the highest amplitude of the generated pulse. The possible application of high-power superconducting opto-electronic switches for the creation of jitter free radar is also discussed.

  6. High-Temperature Superconductivity and Lattice Relaxation in Lithium-Deposited FeSe on SrTiO3

    NASA Astrophysics Data System (ADS)

    Phan, Giao N.; Nakayama, Kosuke; Kanayama, Shota; Kuno, Masato; Sugawara, Katsuaki; Sato, Takafumi; Takahashi, Takashi

    2017-03-01

    We studied the effect of strain, interface, and electron doping on the superconductivity in thin FeSe film on SrTiO3 by angle-resolved photoemission spectroscopy (ARPES). We observed the superconductivity with Tc as high as 43 K in a lithium (Li) deposited heavily electron-doped multilayer FeSe film. We found a significant relaxation of tensile strain at the surface in contrast to the case of potassium (K) deposition, although the high-Tc superconductivity is commonly observed in both cases. We discuss the interplay among carrier doping, tensile strain, and high-Tc superconductivity by comparing ARPES results on Li- and K-deposited FeSe films.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    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

  9. 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

    2015-09-03

    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

  10. High temperature superconducting magnetic refrigeration

    NASA Astrophysics Data System (ADS)

    Blumenfeld, P. E.; Prenger, F. C.; Sternberg, A.; Zimm, C.

    2002-05-01

    A near-room temperature active magnetic regenerative refrigerator (AMRR) was designed and built using a high-temperature superconducting (HTS) magnet in a charge-discharge cycle and a gadolinium-packed regenerative bed as the magnetocaloric component. Current to the HTS magnet was ramped periodically from zero to 100 amperes, which generated a ramp in field strength from zero to 1.7 tesla. Water was moved periodically through the bed and through hot and cold heat exchangers to accomplish a continuous refrigeration cycle. Cycle periods as short as 30 seconds were realized. Refrigerator performance was measured in terms of cooling capacity as a function of temperature span and in terms of efficiency expressed as a percentage of maximum obtainable (Carnot) efficiency. A three-watt cooling capacity was measured over a temperature span of 15 degrees C between hot and cold end temperatures of 25 degrees C and 10 degrees C. This experiment is directed to two possible applications for magnetic refrigeration: a no-moving part cryogenic refrigerator for space applications, and a compact permanent magnet refrigerator for commercial and consumer applications.

  11. 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.

  12. High-temperature superconductivity: A conventional conundrum

    SciTech Connect

    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.

  13. High-Tc SQUID gradiometer system for immunoassays

    NASA Astrophysics Data System (ADS)

    Öisjöen, F.; Magnelind, P.; Kalabukhov, A.; Winkler, D.

    2008-03-01

    A high-Tc dc SQUID (superconducting quantum interference device) gradiometer was developed for magnetic immunoassays where magnetic nanoparticles are used as markers to detect biological reactions. The gradiometer was fabricated on a 5 × 10 mm2 SrTiO3 bicrystal substrate and has a gradiometer resolution of 2.1 pT cm-1 Hz-1/2. A magnetic signal was detected from a sample of 1 µl of Fe3O4 nanoparticles in a 40 mg ml-1 solution kept in a microcavity fabricated on Si wafers with Si3N4 membranes using MEMS (micro-electro-mechanical-systems) technology. It was found that volumes as small as 0.3 nl in principle would be detectable with our present device. This corresponds to a total number of particles of 2.2 × 107. The estimated average dipole moment per particle is 4.8 × 10-22 A m2. We are aiming at reading out immunoassays by detecting the Brownian relaxation of magnetic nanoparticles, and we also intend to integrate MEMS technology into our system.

  14. 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

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

    PubMed

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

    2014-03-14

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

  16. Superconductivity

    NASA Astrophysics Data System (ADS)

    Yeo, Yung K.

    Many potential high-temperature superconductivity (HTS) military applications have been demonstrated by low-temperature superconductivity systems; they encompass high efficiency electric drives for naval vessels, airborne electric generators, energy storage systems for directed-energy weapons, electromechanical launchers, magnetic and electromagnetic shields, and cavity resonators for microwave and mm-wave generation. Further HST applications in militarily relevant fields include EM sensors, IR focal plane arrays, SQUIDs, magnetic gradiometers, high-power sonar sources, and superconducting antennas and inertial navigation systems. The development of SQUID sensors will furnish novel magnetic anomaly detection methods for ASW.

  17. Thermal instability induced by high current densities in high-Tc coated conductors

    NASA Astrophysics Data System (ADS)

    Maza, J.; Ferro, G.; Veira, J. A.; Vidal, F.

    2013-10-01

    By using a 1 ms pulse technique, the current-voltage curves (CVC) under zero-applied magnetic field have been measured in practical high-Tc superconducting wires based on coated (RE)BCO. The measurements extend up to the so-called supercritical current intensity, I*, at which superconductivity disappears accompanied by an abrupt jump in the voltage. The resulting CVC, including the temperature dependence of I*, were analysed at a quantitative level in terms of a thermal instability model proposed recently. An attractive aspect of our thermal instability approach is that in spite of the complexity of the coated layered structure, in its simpler formulation all the geometric and thermal variables are encapsulated into a single characteristic parameter r with units of thermal resistance. All the experimental results for I* from 76 to 86 K are quantitatively, within 2%, accounted for by the thermal instability analysis. Furthermore, the best-fit value of r is found to be quite consistent with the inner geometry and composition of the wires. Another remarkable result of our analysis is that the temperature T* reached by the wire at I*, i.e., the temperature triggering the thermal runaway, is less than one kelvin above the bath temperature. These results further support the universality of the thermal instability mechanism of superconductivity quenching by high current densities.

  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

    2014-07-03

    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.

  19. Progress of research of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Tanaka, Shoji

    1991-01-01

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

  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. 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.

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

    PubMed Central

    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 Tc can account for the superconducting condensation energy. These results suggest that high-Tc 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. PMID:24301219

  3. High-Tc SQUID Magnetometers for Industrial Applications

    NASA Astrophysics Data System (ADS)

    Diiorio, Mark; Yang, Kai-Yueh; Yoshizumi, Shozo; Haupt, Steven; Haran, Don; Koch, Roger; Lathrop, Dan; Trammel, Hoke

    1998-03-01

    We have developed high-Tc SQUID magnetometers for use in a variety of industrial applications. Relatively inexpensive direct-coupled magnetometers have been developed for low-frequency applications including fetal-magnetocardiography. A manufacturable process has been developed to reproducibly fabricate high-resistance (up to 6 Ω) SNS step-edge junctions with YBa_2Cu_3O_7-x as the superconductor and Ag-Au alloy as the normal metal. Magnetic field sensitivities at 77K of 22 ft/Hz^1/2 at 1 KHz and 32 ft/Hz^1/2 at 1 Hz have been achieved in a well-shielded laboratory environment. Current effort is focused on operation in an unshielded environment using flux dams(Milliken et al. Appl. Phys. Lett. 71 1857 (1997)) in conjunction with narrow superconducting pickup coils placed in parallel. An integrated magnetometer process has also been optimized for use in high-frequency applications. The integrated megnetometer utilizes two layers of YBa_2Cu_3O_7-x and one layer of deposited SrTiO_3, all on the same 24 mm x 5 mm substrate. The applications under development include the detection of the explosive material in non-metallic land mines using nuclear quadrupole resonance as well as the non-destructive evaluation of non-metallic composites using nuclear magnetic resonance. For operation in the MHz regime, these applications demand a high quality insulator layer and a robust SQUID that can withstand high current transients.

  4. Quasiparticle tunneling spectroscopy of high {Tc} cuprates

    SciTech Connect

    Zasadzinski, J.; Ozyuzer, L.; Yusof, Z.; Chen, J.; Gray, K.E.; Mogilevsky, R.; Hinks, D.G.; Cobb, J.L.; Markert, J.T.

    1996-04-01

    Superconductor-insulator-normal metal (SIN) and superconductor-insulator-superconductor (SIS) tunnel junctions provide important information on pairing state symmetry and mechanism. Measurements of such junctions on high {Tc} superconductors (HTS) are reported using mechanical point contacts, which generally display the optimum characteristics that can be obtained from HTS native-surface tunnel barriers. New tunneling data on the infinite-layer cuprate, Sr{sub 1{minus}x}Nd{sub x}CuO{sub 2} are reported which show a remarkable similarity to another electron-doped cuprate, Nd{sub 1.85}Ce{sub 0.85}CuO{sub 4}. In particular, there is a strong, asymmetric linear background conductance that is indicative of inelastic tunneling from a continuum of states. A discussion is given of the anomalous dip feature found in the tunneling and photoemission data on BSCCO 2212. It is shown that a similar feature is found in many cuprate junctions and that this dip scales with the gap energy over a wide range. New data on the single-layer, tetragonal cuprate, Tl{sub 2}Ba{sub 2}CuO{sub 6} (Tl2201) are presented and discussed in light of recent published results on the similar compound HgBa{sub 2}CuO{sub 4} (Hg1201). The HG1201 data display a low, flat sub-gap tunneling conductance which is consistent with a BCS density of states whereas the T12201 data display a cusp-like feature at zero bias which is more consistent with d{sub x}2-{sub y}2 symmetry.

  5. Measurements of the rf surface resistance of high- Tc superconductors

    SciTech Connect

    Delayen, J.R.; Bohn, C.L.; Roche, C.T.

    1990-01-01

    An experimental program is being conducted to assess the applicability of high-{Tc} superconductors for use in high power rf and microwave devices. The program involves the measurement of the rf surface resistance of high-{Tc} samples at frequencies between 0.15 and 40 GHz and rf surface magnetic fields as high as 640 gauss. Polycrystalline samples were found to have surface resistances which increase monotonically with rf-field amplitude, saturating at high field at a few percent of the normal-state surface resistance just above {Tc}. 13 refs., 2 figs., 1 tab.

  6. Search for and Study of Novel Superconductor with Higher Tc and Jc

    DTIC Science & Technology

    2015-12-22

    low Tc but with novel structure-types for new discoveries; to realize new superconducting mechanism for higher Tc; to unravel new physics important...to high Tc and Jc; to discover new physics and phenomena in non-superconducting but related compounds for HTS development and devices; to develop...New physics and phenomena were discovered in both superconducting and non-superconducting compounds including cuprates, other Fe-based

  7. Superconductive sodalite-like clathrate calcium hydride at high pressures

    PubMed Central

    Wang, Hui; Tse, John S.; Tanaka, Kaori; Iitaka, Toshiaki; Ma, Yanming

    2012-01-01

    Hydrogen-rich compounds hold promise as high-temperature superconductors under high pressures. Recent theoretical hydride structures on achieving high-pressure superconductivity are composed mainly of H2 fragments. Through a systematic investigation of Ca hydrides with different hydrogen contents using particle-swam optimization structural search, we show that in the stoichiometry CaH6 a body-centered cubic structure with hydrogen that forms unusual “sodalite” cages containing enclathrated Ca stabilizes above pressure 150 GPa. The stability of this structure is derived from the acceptance by two H2 of electrons donated by Ca forming an “H4” unit as the building block in the construction of the three-dimensional sodalite cage. This unique structure has a partial occupation of the degenerated orbitals at the zone center. The resultant dynamic Jahn–Teller effect helps to enhance electron–phonon coupling and leads to superconductivity of CaH6. A superconducting critical temperature (Tc) of 220–235 K at 150 GPa obtained from the solution of the Eliashberg equations is the highest among all hydrides studied thus far. PMID:22492976

  8. Superconductive sodalite-like clathrate calcium hydride at high pressures.

    PubMed

    Wang, Hui; Tse, John S; Tanaka, Kaori; Iitaka, Toshiaki; Ma, Yanming

    2012-04-24

    Hydrogen-rich compounds hold promise as high-temperature superconductors under high pressures. Recent theoretical hydride structures on achieving high-pressure superconductivity are composed mainly of H(2) fragments. Through a systematic investigation of Ca hydrides with different hydrogen contents using particle-swam optimization structural search, we show that in the stoichiometry CaH(6) a body-centered cubic structure with hydrogen that forms unusual "sodalite" cages containing enclathrated Ca stabilizes above pressure 150 GPa. The stability of this structure is derived from the acceptance by two H(2) of electrons donated by Ca forming an "H(4)" unit as the building block in the construction of the three-dimensional sodalite cage. This unique structure has a partial occupation of the degenerated orbitals at the zone center. The resultant dynamic Jahn-Teller effect helps to enhance electron-phonon coupling and leads to superconductivity of CaH(6). A superconducting critical temperature (T(c)) of 220-235 K at 150 GPa obtained from the solution of the Eliashberg equations is the highest among all hydrides studied thus far.

  9. A New Mechanism for High-Tc:. Electron Scattering from Interacting Tunneling Units

    NASA Astrophysics Data System (ADS)

    Klein, Michael W.; Simanovsky, Sergey B.

    A theoretical model for high-Tc superconductivity is presented based on electron pairing due to their interaction with two-level or multi-level tunneling units (TU's) present in high-Tc materials. TU's were found experimentally in YBa2Cu3O7-δ, Bi2CaSr2Cu2O8, Tl2CaBa2Cu2O8 and in Tl2CaBa2CuO6. The TU's have specific directions of orientation with respect to the crystal axis and hence cause a strongly anisotropic scattering of the conduction electrons and a strongly anisotropic gap function Δ(k) with wave vector k. For the weak coupling case we obtain, (i) an analytically derived Δ(k) which has a linear combination of s-wave and dx2-y2-wave symmetry with nodes in Δ(k), (ii) a high-Tc determined by the elastic interaction potential between the TU's, (iii) an isotope effect consistent with experiment, (iv) a large uniaxial pressure p dependence of Tc for YBa2Cu3O7-δ close to optimal oxygen doping and (dTc/dpa) ≈ -(dTc/dpb) where Pa and Pb are the pressures in the a and b directions, (v) a quantitative agreement with experiment for dTc/dPi (i = a, b) when we use the elastic constant. The recently observed d ± s wave pairing in twinned YBa2Cu3O7-δ, with a reversal of the sign of s-wave component across the twin boundary, is also in agreement with our model.

  10. STM tunneling spectroscopy on high Tc superconductors

    SciTech Connect

    Hasegawa, T.; Nantoh, M.; Ogino, M.

    1995-08-01

    STM tunneling spectroscopy has been performed on the bulk single crystals of BiSrCaCuO (BSCCO) and the epitaxial thin films of YBaCuO (YBCO) at cryogenic temperatures. The STM images and tunneling spectra observed on the (001) surfaces can be classified into three cases; (1) Atomic image is visible. However, the tunneling spectrum shows semiconducting or smeared superconducting gap structures, depending on the tip-sample distance. (2) Clear atomic image can be obtained. But, the tunneling spectrum shows flat bottom region with quite low zero bias conductance. (3) Tunneling spectra demonstrate gapless behavior, independent of the tip-sample separation. These observations support the quasi-2D electronic picture in which s-wave like 2D superconducting layers are coupled with each other through the Josephson effect.

  11. Risk Mitigation for High Temperature Superconducting Generators

    DTIC Science & Technology

    2009-01-01

    and Technology Division Background: High temperature superconduct- ing (HTS) motors and generators will enable high- efficiency , high power density...naval propulsion, and compact electrical generators for weapons and ship systems. The second-generation high temperature superconductors (2G-HTS...manufacturability of long lengths of these materials, sufficient for demonstrations of large motors and generators. Ensuring superior fatigue prop- erties

  12. Some consequences of the breakdown of Migdal's theorem in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Ummarino, G. A.; Gonnelli, R. S.

    1999-05-01

    In order to reproduce the experimental Tc and tunneling data of high- Tc superconductors in the framework of the Eliashberg theory for strong electron-boson interaction, it is necessary to use large values of the coupling constant. In this work, we investigate whether this fact is a possible consequence of the breakdown of Migdal's theorem that certainly occurs in the cuprates due to their very low value of Fermi energy as compared to the characteristic phonon energy. In order to numerically quantify the consequences of the violation of the Migdal's approximation, we use the theoretical approach developed by Pietronero et al. [L. Pietronero, S. Strässler, C. Grimaldi, Phys. Rev. B 52, 10516 (1995)] and Grimaldi et al. [C. Grimaldi, L. Pietronero, S. Strässler, Phys. Rev. B 52, 10530 (1995)] on experimental data taken from the literature. The effects on the electron-phonon coupling constant λ, on the critical temperature Tc and on the superconducting gap Δ are calculated also by means of a direct solution of the standard Eliashberg equations and discussed in different kinds of superconducting materials both with low and high critical temperature.

  13. Metallic Contaminant Detection System for Industrial Products by High TC SQUID Magnetic Sensor

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Fujita, Hiroyoshi; Hatsukade, Yoshimi; Otani, Takeyoshi; Suzuki, Shuichi

    High-Tc superconducting quantum interference device (SQUID) system for detection of magnetic foreign matter in industrial products was developed. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products, such as lithium ion batteries. The outer dimension of metallic particles less than 100 microns cannot be detected by conventional X-ray imaging. Therefore, we developed a detection system based on high-Tc SQUID microscopes with a high-performance magnetic shield. Using SQUID microscopes with a 0.5 mm-thick vacuum window was proposed. This design enables the SQUID to approach an object to be measured as close as 1 mm and enhances the sensitivity. A new magnetic shield with sleeves was carefully designed and built. As a result, we could successfully measure a small iron particle with 100 μm. This detection level was hard to achieve by conventional X-ray detection methods.

  14. 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.

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

    DOE PAGES

    Sun, J. P.; Matsuura, K.; Ye, G. Z.; ...

    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

  16. Superconducting correlations above Tc in the pseudogap state of Bi2Sr2CaCu2O8 +δ cuprates revealed by angular-dependent magnetotunneling

    NASA Astrophysics Data System (ADS)

    Jacobs, Th.; Katterwe, S. O.; Krasnov, V. M.

    2016-12-01

    We present an angular-dependent magnetotunneling technique, which facilitates unambiguous separation of superconducting (supporting circulating screening currents) and nonsuperconducting (not supporting screening currents) contributions to the pseudogap phenomenon in layered Bi2Sr2CaCu2O8 +δ cuprates. Our data indicate persistence of superconducting correlations at temperatures up to 1.5 Tc in a form of both phase and amplitude fluctuations of the superconducting order parameter. However, despite a profound fluctuations region, only a small fraction of the pseudogap spectrum is caused by superconducting correlations, while the dominating part comes from a competing nonsuperconducting order, which does not support circulating orbital currents.

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

    NASA Astrophysics Data System (ADS)

    Flores Livas, Jose; Amsler, Maximilian; Sanna, Antonio; Heil, Christoph; Boeri, Lilia; Profeta, Gianni; Wolverton, Crhis; Goedecker, Stefan; Gross, E. K. U.

    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 prediction methods. 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 questionable if the measured values of Tc can be fully attributed to a phase-pure compound of PHn. This work was done within the NCCR MARVEL project.

  18. Superconducting phase fluctuations in SmFeAsO0.8F0.2 from diamagnetism at a low magnetic field above Tc

    NASA Astrophysics Data System (ADS)

    Prando, G.; Lascialfari, A.; Rigamonti, A.; Romanó, L.; Sanna, S.; Putti, M.; Tropeano, M.

    2011-08-01

    Superconducting fluctuations (SFs) in SmFeAsO0.8F0.2 (characterized by superconducting transition temperature Tc≃52.3 K) are investigated by means of isothermal high-resolution dc magnetization measurements. The diamagnetic response above Tc to magnetic fields up to 1 T is similar to that previously reported for underdoped cuprate superconductors and justified in terms of metastable superconducting islands of nonzero order parameter lacking long-range coherence because of strong phase fluctuations. In the high-field regime (H≳1.5 T) scaling arguments predicted on the basis of the Ginzburg-Landau theory for conventional SFs are confirmed, at variance with what is observed in the low-field regime. This fact shows that two different phenomena are simultaneously present in the fluctuating diamagnetism, namely the phase SFs of novel character and the conventional SFs. High magnetic fields (1.5 T ≲H≪Hc2) are found to suppress the former while leaving unaltered the latter.

  19. Neutron depolarization effects in a high-Tc superconductor (abstract)

    NASA Astrophysics Data System (ADS)

    Nunes, A. C.; Pickart, S. J.; Crow, L.; Goyette, R.; McGuire, T. R.; Shinde, S.; Shaw, T. M.

    1988-11-01

    Using the polarized beam small-angle neutron scattering spectrometer at the Rhode Island Nuclear Science Center Reactor, we have observed significant depolarization of a neutron beam by passage through polycrystalline high-Tc superconductors, specifically 123 Y-Ba-Cu-O prepared and characterized at the IBM Watson Research Center. We believe that this technique will prove useful in studying aspects of these materials, such as the penetration depth of shielding currents, the presence and structure of trapped flux vortices, and grain size effects on the supercurrent distribution in polycrystalline samples. The two samples showed sharp transitions at 87 and 89 K, and have been studied at temperatures of 77 K; the second sample has also been studied at 4 K. The transition to the superconducting state was monitored by the shift in resonant frequency of a coil surrounding the sample. No measurable depolarization was observed in either sample at 77 K in both the field-cooled and zero-field-cooled states, using applied fields of 0 (nominal), 54, and 1400 Oe. This negative result may be connected with the fact that the material is still in the reversible region as indicated by susceptibility measurements, but it allows an estimate of the upper bound of possible inhomogeneous internal fields, assuming a distance scale for the superconducting regions. For the 10-μm grain size suggested by photomicrographs, this upper bound for the field turns out to be 1.2 kOe, which seems reasonable. At 4 K a significant depolarization was observed when the sample was cooled in low fields and a field of 1400 Oe was subsequently applied. This result suggests that flux lines are penetrating the sample. Further investigations are being carried out to determine the field and temperature dependence of the depolarization, and attempts will be made to model it quantitatively in terms of possible internal field distributions. We are also searching for possible diffraction effects from ordered vortex

  20. Fundamental operation of single-flux-quantum circuits using coplanar-type high-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Fuke, Hiroyuki; Saitoh, Kazuo; Utagawa, Tadashi; Enomoto, Youichi

    1996-11-01

    We have fabricated coplanar type dc SQUIDs using NdBa2Cu3Oy superconducting thin films and operated fundamental single-flux-quantum (SFQ) circuits. The Josephson junctions were made by the narrow-focused ion beam irradiation technique. For a 145 μm wide and 10 μm long logic SQUID having a critical current of 105 μA and an inductive parameter (βL) of 28, a store and a restore of the flux quantum have been demonstrated at temperatures of 4.2-30 K. These operations were performed with an input pulsewidth of 5 ns (5 ns was the shortest input pulse width available from our function generating equipment). These results show experimentally the possibility of high speed operation in all high-Tc superconducting digital circuits.

  1. The self-energies and bosonic spectrum of high Tc cuprate from laser-based ARPES

    NASA Astrophysics Data System (ADS)

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

    While phonon mediated conventional superconductors are revealed by comparing tunneling and neutron scattering experiment, high Tc cuprate which has d-wave symmetry is still in debate. Laser-based AREPS can provide both momentum and energy dependence of spectral function that enables self-energy extraction using one particle Green's function. It is well known that anisotropy of electronic structure and d-wave superconducting gap on ARPES experiments. We analyzed high resolution APRES data of under and overdoped Bi2212 and extracted both normal and pairing self-energy. Here we report the extracted normal and pairing self-energy in supercondcuting state. Also we obtained bosonic spectrum from both self-energies by performing maximum entropy method. Implications of these results for understanding the superconductivity mechanism will be discussed.

  2. 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.

  3. Ab-initio studies of thermal and superconducting properties of HfX2 alloys (X = Tc, Re, and Os)

    NASA Astrophysics Data System (ADS)

    Sathyakumari, V. S.; Sankar, S.; Mahalakshmi, K.

    2014-09-01

    A systematic study of thermal properties such as the Debye temperature, specific heat coefficient, Grüneisen constant, electron-phonon coupling constant and transition temperature have been carried out using the results of electronic band structure and related characteristics, for hafnium superconducting alloys, namely, HfTc2, HfRe2 and HfOs2. Computation of the electronic band structure and associated properties has been carried out using the tight-binding-linear-muffin-tin-orbital (TBLMTO) method within atomic sphere approximation (ASA). The calculated values have been compared with the available results of literature data.

  4. 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.

  5. Antiferromagnetism, superconductivity, and pseudogap in three-layered high-Tc cuprates Ba2Ca2Cu3O6(F,O)2 probed by Cu-NMR

    NASA Astrophysics Data System (ADS)

    Shimizu, Sunao; Tabata, Shin-Ichiro; Mukuda, Hidekazu; Kitaoka, Yoshio; Shirage, Parasharam M.; Kito, Hijiri; Iyo, Akira

    2011-06-01

    We report on the phase diagram of antiferromagnetism (AFM) and superconductivity (SC) in three-layered Ba2Ca2Cu3O6(F,O)2 by means of Cu-NMR measurements. It is demonstrated that AFM and SC coexist uniformly in three-layered compounds as well as in four- and five-layered ones. The critical hole density pc for the long-range AFM order is determined as pc≃ 0.075, which is larger than pc≃ 0.02 and 0.055 in single- and bilayered compounds, and smaller than pc≃0.08-0.09 and 0.10-0.11 in four- and five-layered compounds, respectively. This variation of pc is attributed to the magnetic interlayer coupling, which becomes stronger as the stacking number of CuO2 layers increases; that is, the uniform coexistence of AFM and SC is a universal phenomenon in underdoped regions when a magnetic interlayer coupling is strong enough to stabilize an AFM ordering. In addition, we highlight an unusual pseudogap behavior in three-layered compounds—the gap behavior in low-energy magnetic excitations collapses in an underdoped region where the ground state is the AFM-SC mixed phase.

  6. Superconductivity of lithium-doped hydrogen under high pressure.

    PubMed

    Xie, Yu; Li, Quan; Oganov, Artem R; Wang, Hui

    2014-02-01

    The high-pressure lattice dynamics and superconductivity of newly proposed lithium hydrides (LiH2, LiH6 and LiH8) have been extensively studied using density functional theory. The application of the Allen-Dynes modified McMillan equation and electron-phonon coupling calculations show that LiH6 and LiH8 are superconductors with critical temperatures (T(c)) of 38 K at 150 GPa for LiH6 and 31 K at 100 GPa for LiH8, while LiH2 is not a superconductor. The T(c) of LiH6 increases rapidly with pressure and reaches 82 K at 300 GPa due to enhancement of the electron-phonon coupling and the increased density of states at the Fermi level, while the T(c) of LiH8 remains almost constant.

  7. Competition between the pseudogap and superconductivity in the high-T(c) copper oxides.

    PubMed

    Kondo, Takeshi; Khasanov, Rustem; Takeuchi, Tsunehiro; Schmalian, Jörg; Kaminski, Adam

    2009-01-15

    In a classical Bardeen-Cooper-Schrieffer superconductor, pairing and coherence of electrons are established simultaneously below the critical transition temperature (T(c)), giving rise to a gap in the electronic energy spectrum. In the high-T(c) copper oxide superconductors, however, a pseudogap extends above T(c). The relationship between the pseudogap and superconductivity is one of the central issues in this field. Spectral gaps arising from pairing precursors are qualitatively similar to those caused by competing electronic states, rendering a standard approach to their analysis inconclusive. The issue can be settled, however, by studying the correlation between the weights associated with the pseudogap and superconductivity spectral features. Here we report a study of two spectral weights using angle-resolved photoemission spectroscopy. The weight of the superconducting coherent peak increases away from the node following the trend of the superconducting gap, but starts to decrease in the antinodal region. This striking non-monotonicity reveals the presence of a competing state. We demonstrate a direct correlation, for different values of momenta and doping, between the loss in the low-energy spectral weight arising from the opening of the pseudogap and a decrease in the spectral weight associated with superconductivity. We therefore conclude that the pseudogap competes with the superconductivity by depleting the spectral weight available for pairing.

  8. Detection of the Cracks using High-Tc SQUID

    NASA Astrophysics Data System (ADS)

    Fujii, Tatsuhiko; Hyun-Sung, Tae; Takamatsu, Tsuyoshi; Sakuta, Ken; Itozaki, Hideo

    Eddy current non-distractive evaluation (NDE) is very useful technique for detection of cracks. We use the high-Tc SQUID in this system. First, we respect the result of this measurement by the finite element method. We can detect of the signal from the hole by NDE system with high-Tc SQUID. This result is reasonable to compare with the result of simulation. Finaly, we can detect of the hidden defect under 5mm depth from the sample surface.

  9. 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.

  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. Development of a High-Tc SQUID-Based System for Neurophysiology Studies In-Vitro

    NASA Astrophysics Data System (ADS)

    Magnelind, Per; Tarte, Ed; Winkler, Dag; Hanse, Eric

    2006-06-01

    In this paper we report on the development of a system based on a high-Tc SQUID (HTS) sensor for measurements of the neuromagnetic field generated by neurons inside tissue slices. SQUIDs have successfully been measured inside the system. The system white noise level is lower than 7 pT/Hz{1/2}, which is only slightly higher than previously reported 4.5 pT/Hz{1/2} for the same kind of SQUID measured inside a superconducting shield.

  12. On infrared and terahertz imaging of surface plasmons in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Stinson, H. T.; Fei, Z.; Rodin, A. S.; McLeod, A. S.; Fogler, M. M.; Basov, D. N.

    2013-03-01

    Recent scattering-mode scanning near-field optical microscopy (s-SNOM) experiments have imaged surface plasmons in graphene at infrared frequencies.[1] The scanning probe launches surface plasmons and detects their standing-wave interference pattern upon reflection from the sample edge. The surface plasmon dispersion relation directly relates the standing wave fringe separation and amplitude decay to the optical constants of the sample. We have modeled surface plasmon s-SNOM imaging for high-Tc superconductor (HTSC) thin films. Our results indicate that surface plasmons can be imaged in HTSCs at frequencies near or below the superconducting gap. This would allow for a direct measurement of HTSC optical constants below the gap. For known HTSCs such as YBCO, this is in the far-IR or terahertz range. Our simulations show that this method can also distinguish between superconducting and normal states at the nanoscale.

  13. Anomalous effect of doping on the superconducting state of CeCoIn5 in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Tokiwa, Y.; Movshovich, R.; Ronning, F.; Bauer, E. D.; Bianchi, A. D.; Fisk, Z.; Thompson, J. D.

    2010-12-01

    We investigated the effect of electron and hole doping on the high-field low-temperature superconducting state in CeCoIn5 by measuring specific heat of CeCo(In1-xMx)5 with M=Sn , Cd, and Hg and x up to 0.33% at temperatures down to 0.1 K and fields up to 14 T. Although both Cd and Hg doping (hole doping) suppresses the zero-field Tc monotonically, Hc2 increases with small amounts of doping and has a maximum around x=0.2% (M=Cd) . On the other hand, with Sn doping (electron doping) both zero-field Tc and Hc2 decrease monotonically. The critical temperature for the high-field low-temperature superconducting state correlates with Hc2 and Tc , which we interpret in support of the superconducting origin of this state.

  14. 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).

  15. 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.

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

    DOE PAGES

    Ramshaw, B. J.; Sebastian, S. E.; McDonald, R. D.; ...

    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

  17. Scattering rates and specific heat jumps in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Storey, James

    Inspired by recent ARPES and tunneling studies on high-Tc cuprates, we examine the effect of a pair-breaking term in the self-energy on the shape of the electronic specific heat jump. It is found that the observed specific heat jump can be described in terms of a superconducting gap, that persists above the observed Tc, in the presence of a strongly temperature dependent pair-breaking scattering rate. An increase in the scattering rate is found to explain the non-BCS-like suppression of the specific heat jump with magnetic field. A discussion of these results in the context of other properties such as the superfluid density and Raman spectra will also be presented. Supported by the Marsden Fund Council from Government funding, administered by the Royal Society of New Zealand.

  18. Phase diagrams for high Tc superconductors

    SciTech Connect

    Whitler, J.D.; Roth, R.S. NIST, Gaithersburg, MD )

    1991-01-01

    The phase diagrams of ternary and quaternary systems containing superconducting phases are presented, as are the phase diagrams of the associated binary systems. The diagrams are divided into two large groups: (1) alkaline earth-rare earth-copper-oxygen diagrams, and (2) alkaline earth-bismuth/lead-copper-oxygen diagrams. The first group includes BaO-REO-CuO systems followed by SrO-REO-CuO or Nd2O3-CeO-CuO systems. The second group includes systems related to the AE-Bi2O3-CuO and AE-PbO-CuO systems. The phase diagrams are accompanied by notes relating procedures used in the studies, results obtained, and comparisons with the results in the literature for the same system.

  19. 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.

  20. 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.

  1. 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.

  2. Thermodynamic investigations of high-pressure superconducting state in CaLi2 at 45 GPa

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, R.; Szczȩśniak, D.

    2012-05-01

    The thermodynamic properties of the high-pressure superconducting phase in CaLi2 have been studied. A pressure value of 45 GPa has been chosen, at which the critical temperature reaches the maximum (TC=12.9 K). The following results have been obtained. (i) The critical temperature cannot be calculated using the classical analytical formulas (McMillan or Allen-Dynes). (ii) The critical value of the Coulomb pseudopotential is high: μC⋆=0.23. Generalizing the results, the function μC⋆(p) has a high value (μC⋆(p)>0.15) in practically the entire pressure range from 28 to 60 GPa. (iii) The remaining fundamental thermodynamic parameters differ from the Bardeen, Cooper, and Schrieffer (BCS) values. In particular, the zero-temperature energy gap to the critical temperature: R1≡2Δ(0)/kBTC=3.95; the ratio of the specific heat for superconducting (CS) and the normal (CN) state: R2≡(CS(TC)-CN(TC))/CN(TC)=2.01; and the parameter connected with the zero-temperature thermodynamic critical field: R3=TCCN(TC)/HC2(0)=0.158. Finally, it has been shown that the value of the electronic effective mass is high: me⋆/me>2.

  3. 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.

  4. 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.

  5. Laser surface interaction of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  6. 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

  7. 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.

  8. A high-Tc SQUID micro-detector with a high performance magnetic shield for contaminant detection in industrial products

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Fujita, H.; Hatsukade, Y.; Otani, T.; Suzuki, S.; Nagaishi, T.

    2007-11-01

    A high-Tc superconducting quantum interference device (SQUID) system for the detection of magnetic foreign matter in industrial products was developed. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. Metallic particles with outer dimensions less than 100 µm cannot be detected by conventional x-ray imaging. Therefore we developed a detection system based on a high-Tc SQUID microscope with a high performance magnetic shield. The use of SQUID microscopes with a 0.5 mm thick vacuum window was proposed. This design enables the SQUID to approach the object to be measured as close as 1 mm and enhances the sensitivity. A new magnetic shield with sleeves was carefully designed and built. As a result, we could successfully measure small particles sized 100 µm. This detection level was hard to achieve using a conventional x-ray detection method.

  9. 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.

  10. High-Pressure Structures of Disilane and Their Superconducting Properties

    NASA Astrophysics Data System (ADS)

    Flores-Livas, José A.; Amsler, Maximilian; Lenosky, Thomas J.; Lehtovaara, Lauri; Botti, Silvana; Marques, Miguel A. L.; Goedecker, Stefan

    2012-03-01

    A systematic ab initio search for low-enthalpy phases of disilane (Si2H6) at high pressures was performed based on the minima hopping method. We found a novel metallic phase of disilane with Cmcm symmetry, which is enthalpically more favorable than the recently proposed structures of disilane up to 280 GPa, but revealing compositional instability below 190 GPa. The Cmcm phase has a moderate electron-phonon coupling yielding a superconducting transition temperature Tc of around 20 K at 100 GPa, decreasing to 13 K at 220 GPa. These values are significantly smaller than previously predicted Tc’s for disilane at equivalent pressure. This shows that similar but different crystalline structures of a material can result in dramatically different Tc’s and stresses the need for a systematic search for a crystalline ground state.

  11. A 63Cu-NMR study on four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2

    NASA Astrophysics Data System (ADS)

    Shimizu, S.; Mukuda, H.; Kitaoka, Y.; Kito, H.; Kodama, Y.; Shirage, P. M.; Iyo, A.

    2010-01-01

    We report on superconducting and magnetic characteristics in four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2 with apical fluorine through 63Cu-NMR measurements. The temperature dependence of the Knight shift shows that the substitution of oxygen for fluorine at the apical site increases carrier density (Nh) and Tc from 55 up to 102 K. The 63Cu-NMR spectra suggest that antiferromagnetic (AFM) order takes place in underdoped CuO2 layers; especially, the AFM order coexists with superconductivity in a single CuO2 plane at y=1.0.

  12. Diamagnetie Shielding and Meissner Effect in the High Tc Superconductor SrxLa2-xCuO4-y

    NASA Astrophysics Data System (ADS)

    Tokumoto, Madoka; Ihara, Hideo; Murata, Keizo; Hirabayashi, Masayuki; Terada, Norio; Senzaki, Kiyoshi; Kimura, Yoichi

    1987-04-01

    Static magnetization measurements of the high Tc superconductor SrxLa2-xCuO4-y, with the layered perovskite K2NiF4 structure and a 43 K resistive onset, are reported. Diamagnetic susceptivility was observed below 37 K indicating a bulk superconductivity. The magnetization measurement revealed a characteristic nature of type-II superconductor with Hc1(0)≈500 Oe and Hc2(0)>100 kOe.

  13. 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.

  14. 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.

  15. Improving the sensitivity of a high-Tc SQUID at MHz frequency using a normal metal transformer

    NASA Astrophysics Data System (ADS)

    He, D. F.; Itozaki, H.; Tachiki, M.

    2006-05-01

    Superconducting quantum interference devices (SQUIDs) can be used to detect the signals of nuclear quadrupole resonance (NQR). The NQR frequencies of some interesting materials are in the order of MHz. However, the sensitivity of a high-Tc SQUID is normally not enough to detect the weak NQR signals. To improve the sensitivity of a high-Tc SQUID at MHz frequency, we used a transformer made of normal copper wire. The transformer was composed of a pickup coil, an input coil and a capacitor. The pickup coil was used to detect the magnetic field; the input coil was used to couple the field to the SQUID; and the capacitor was used to create a resonant frequency. By using the normal metal transformer, the magnetic field resolution of the high-Tc dc SQUID was improved by about 38.8 times (from 220 to 5.67 fT Hz-1/2) at 954 kHz.

  16. High-temperature superconducting phase of HBr under pressure predicted by first-principles calculations

    NASA Astrophysics Data System (ADS)

    Gu, Qinyan; Lu, Pengchao; Xia, Kang; Sun, Jian; Xing, Dingyu

    2017-08-01

    The high pressure phases of HBr are explored with an ab initio crystal structure search. By taking into account the contribution of zero-point energy (ZPE), we find that the P 4 /n m m phase of HBr is thermodynamically stable in the pressure range from 150 to 200 GPa. The superconducting critical temperature (Tc) of P 4 /n m m HBr is evaluated to be around 73 K at 170 GPa, which is the highest record so far among binary halogen hydrides. Its Tc can be further raised to around 95K under 170 GPa if half of the bromine atoms in the P 4 /n m m HBr are substituted by the lighter chlorine atoms. Our study shows that, in addition to lower mass, higher coordination number, shorter bonds, and more highly symmetric environment for the hydrogen atoms are important factors to enhance the superconductivity in hydrides.

  17. 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

  18. 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

    2015-10-22

    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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. The NASA high temperature superconductivity program

    NASA Astrophysics Data System (ADS)

    Sokoloski, Martin M.; Romanofsky, Robert R.

    1990-04-01

    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.

  5. 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.

  6. 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.

  7. High-temperature superconductivity: the explanation

    NASA Astrophysics Data System (ADS)

    Alexandrov, A. S.

    2011-03-01

    Soon after the discovery of the first high-temperature superconductor by Georg Bednorz and Alex Müller in 1986, the late Sir Nevill Mott in answering his own question 'Is there an explanation?' (1987 Nature 327 185) expressed the view that the Bose-Einstein condensation (BEC) of small bipolarons, predicted by us in 1981, could be the one. Several authors then contemplated BEC of real-space tightly bound pairs, but with a purely electronic mechanism of pairing rather than with an electron-phonon interaction (EPI). However, a number of other researchers criticized the bipolaron (or any real-space pairing) scenario as incompatible with some angle-resolved photoemission spectra, with experimentally determined effective masses of carriers and unconventional symmetry of the superconducting order parameter in cuprates. Since then, the controversial issue of whether EPI is crucial for high-temperature superconductivity or is weak and inessential has been one of the most challenging problems of contemporary condensed matter physics. Here I outline some developments in the bipolaron theory suggesting that the true origin of high-temperature superconductivity is found in a proper combination of strong electron-electron correlations with a significant finite-range (Fröhlich) EPI, and that the theory is fully compatible with key experiments.

  8. 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.

  9. Cuprate High Temperature Superconductors and the Vision for Room Temperature Superconductivity

    NASA Astrophysics Data System (ADS)

    Newns, Dennis M.; Martyna, Glenn J.; Tsuei, Chang C.

    Superconducting transition temperatures of 164 K in cuprate high temperature superconductors (HTS) and recently 200 K in H3S under high pressure encourage us to believe that room temperature superconductivity (RTS) might be possible. In considering paths to RTS, we contrast conventional (BCS) SC, such as probably manifested by H3S, with the unconventional superconductivity (SC) in the cuprate HTS family. Turning to SC models, we show that in the presence of one or more van Hove singularities (vHs) near the Fermi level, SC mediated by classical phonons (kBTc>ℏ×phonon frequency) can occur. The phonon frequency in the standard Tc formula is replaced by an electronic cutoff, enabling a much higher Tc independent of phonon frequency. The resulting Tc and isotope shift plot versus doping strongly resembles that seen experimentally in HTS. A more detailed theory of HTS, which involves mediation by classical phonons, satisfactorily reproduces the chief anomalous features characteristic of these materials. We propose that, while a path to RTS through an H3S-like scenario via strongly-coupled ultra-high frequency phonons is attractive, features perhaps unavailable at ordinary pressures, a route involving SC mediated by classical phonons which can be low frequency may be found.

  10. Investigation of High-Tc Superconductivity in Carbon Nanotubes

    DTIC Science & Technology

    2011-05-03

    previous conditions. However, diamagnetism in zero-field-cooled and field-cooled regimes in raw data was not observed owing to positive background...observation of appearance of diamagnetism in both zero-field cooling (ZFC) and FC regimes for temperature dependence of magnetization, and also observation of...ZFC regime. Unfortunately, diamagnetism doesn’t appear even at T = 2K in both figures. However, the critical temperatures of 8K and 10K for

  11. Angular momentum blockade in nanoscale high-Tc superconducting grains

    NASA Astrophysics Data System (ADS)

    Mancarella, Francesco; Balatsky, Alexander; Wallin, Mats; Rosengren, Anders; Nordita-Condensed Matter Collaboration; KTH-Theoretical Physics Collaboration

    2014-03-01

    We discuss the angular momentum blockade in small d-wave SC grains in an external magnetic field. We find abrupt changes in angular momentum state of the condensate (''angular momentum blockade'') as a result of the variation of the external field. The effect represents a direct analog of the Coulomb blockade. We use the Ginzburg-Landau theory to illustrate how the field turns a d-wave order parameter (OP) into a(dx2 -y2 + idxy)-OP. We derive the volume magnetic susceptibility as a function of the field, and corresponding small jumps in magnetization at critical values of the field that should be experimentally observable in SC grains. The observation of these jumps requires a small grain, since their extent is inversely proportional to the number of Cooper pairs in the sample. The general source of instability of the pure d-wave gap is the presence of gap nodes, completely lifted by the secondary OP component. A d + id' -state is chiral and hence has an orbital moment carried by Cooper pairs. We consider fields H <

  12. 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.

  13. Theoretical study of stability and superconductivity of ScHn (n =4 -8 ) at high pressure

    NASA Astrophysics Data System (ADS)

    Qian, Shifeng; Sheng, Xiaowei; Yan, Xiaozhen; Chen, Yangmei; Song, Bo

    2017-09-01

    The synthesis of hydrogen sulfides, with the potential of high-temperature superconductivity, was recently proposed at high Tc = 203 K. It motivated us to employ an ab initio approach for the predictions of crystal structures to find the stable scandium hydrides. In addition to the earlier predicted three stoichiometries of ScH, ScH2, and ScH3, we identify three other metallic stoichiometries of ScH4, ScH6, and ScH8, which show superconductivity at significantly higher temperatures. The phases of ScH4 and ScH6, whose stability does not require extremely high pressures (<150 GPa with ZPE), are primarily ionic compounds containing exotic quasimolecular H2 arrangements. The present electron-phonon calculations revealed the superconductive potential of ScH4 and ScH6 with estimated Tc of 98 K and 129 K at 200 GPa and 130 GPa, respectively. The superconductivity of ScHn stems from the large electron-phonon coupling associated with the wagging, bending, and intermediate-frequency modes attributed mainly to the hydrogen atoms.

  14. Superconductivity-related insulating behavior.

    PubMed

    Sambandamurthy, G; Engel, L W; Johansson, A; Shahar, D

    2004-03-12

    We present the results of an experimental study of superconducting, disordered, thin films of amorphous indium oxide. These films can be driven from the superconducting phase to a reentrant insulating state by the application of a perpendicular magnetic field (B). We find that the high-B insulator exhibits activated transport with a characteristic temperature, TI. TI has a maximum value (TpI) that is close to the superconducting transition temperature (Tc) at B=0, suggesting a possible relation between the conduction mechanisms in the superconducting and insulating phases. Tp(I) and Tc display opposite dependences on the disorder strength.

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

    NASA Astrophysics Data System (ADS)

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

    1991-04-01

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

  16. High-temperature superconducting undulator magnets

    NASA Astrophysics Data System (ADS)

    Kesgin, Ibrahim; Kasa, Matthew; Ivanyushenkov, Yury; Welp, Ulrich

    2017-04-01

    This paper presents test results on a prototype superconducting undulator magnet fabricated using 15% Zr-doped rare-earth barium copper oxide high temperature superconducting (HTS) tapes. On an 11-pole magnet we demonstrate an engineering current density, J e, of more than 2.1 kA mm-2 at 4.2 K, a value that is 40% higher than reached in comparable devices wound with NbTi-wire, which is used in all currently operating superconducting undulators. A novel winding scheme enabling the continuous winding of tape-shaped conductors into the intricate undulator magnets as well as a partial interlayer insulation procedure were essential in reaching this advance in performance. Currently, there are rapid advances in the performance of HTS; therefore, achieving even higher current densities in an undulator structure or/and operating it at temperatures higher than 4.2 K will be possible, which would substantially simplify the cryogenic design and reduce overall costs.

  17. High-temperature superconducting undulator magnets

    DOE PAGES

    Kesgin, Ibrahim; Kasa, Matthew; Ivanyushenkov, Yury; ...

    2017-02-13

    Here, this paper presents test results on a prototype superconducting undulator magnet fabricated using 15% Zr-doped rare-earth barium copper oxide high temperature superconducting (HTS) tapes. On an 11-pole magnet we demonstrate an engineering current density, Je, of more than 2.1 kA mm-2 at 4.2 K, a value that is 40% higher than reached in comparable devices wound with NbTi-wire, which is used in all currently operating superconducting undulators. A novel winding scheme enabling the continuous winding of tape-shaped conductors into the intricate undulator magnets as well as a partial interlayer insulation procedure were essential in reaching this advance in performance.more » Currently, there are rapid advances in the performance of HTS; therefore, achieving even higher current densities in an undulator structure or/and operating it at temperatures higher than 4.2 K will be possible, which would substantially simplify the cryogenic design and reduce overall costs.« less

  18. High-Temperature Superconductivity in Boron-Doped Q-Carbon.

    PubMed

    Bhaumik, Anagh; Sachan, Ritesh; Narayan, Jagdish

    2017-06-27

    We report high-temperature superconductivity in B-doped amorphous quenched carbon (Q-carbon). This phase is formed after nanosecond laser melting of B-doped amorphous carbon films in a super-undercooled state and followed by rapid quenching. Magnetic susceptibility measurements show the characteristics of type-II Bardeen-Cooper-Schrieffer superconductivity with a superconducting transition temperature (Tc) of 36.0 ± 0.5 K for 17.0 ± 1.0 atom % boron concentration. This value is significantly higher than the best experimentally reported Tc of 11 K for crystalline B-doped diamond. We argue that the quenching from metallic carbon liquid leads to a stronger electron-phonon coupling due to close packing of carbon atoms with higher density of states at the Fermi level. With these results, we propose that the non-equilibrium undercooling-assisted synthesis method can be used to fabricate highly doped materials that provide greatly enhanced superconducting properties.

  19. Fabrication of sensitive high Tc bolometers

    NASA Technical Reports Server (NTRS)

    Nahum, Michael; Verghese, S.; Hu, Qing; Richards, Paul L.; Char, K.; Newman, N.; Sachtjen, Scott A.

    1990-01-01

    The rapid change of resistance with temperature of high quality films of high T sub c superconductors can be used to make resistance thermometers with very low temperature noise. Measurements on c-axis yttrium barium copper oxide (YBCO) films have given a spectral intensity of temperature noise less than 4 times 10(exp -8) K/Hz(exp 1/2) at 10 Hz. Consequently, the opportunity exists to make useful bolometric infrared detectors that operate near 90 K which can be cooled with liquid nitrogen. The fabrication and measurement of two bolometer architectures are discussed. The first is a conventional bolometer which consists of a 3000 A thick YBCO film deposited in situ by laser ablation on top of a 500 A thick SrTiO3 thickness and diced into 1x1 mm(exp 2) bolometer chips. Gold black smoke was used as the radiation absorber. The voltage noise was less than the amplifier noise when the film was current biased. Optical measurements gave an NEP of 5 times 10(exp -11) W/Hz(exp 1/2) at 10 Hz. The second architecture is that of an antenna-coupled microbolometer which consists of a small (5x10 cubic microns) YBCO film deposited directly on a bulk substrate with a low thermal conductance (YSZ) and an impedance matched planar lithographed spiral or log-periodic antenna. This structure is produced by standard photolithographic techniques. Measurements gave an electrical NEP of 4.7 times 10(exp -12) W/Hz(exp 1/2) at 10 kHz. Measurements of the optical efficiency are in progress. The measured performance of both bolometers will be compared to other detectors operating at or above liquid nitrogen temperatures so as to identify potential applications.

  20. HIGH CURRENT SUPERCONDUCTING CAVITIES AT RHIC.

    SciTech Connect

    CALAGA,R.BEN-ZVI,I.ZHAO,Y.ET AL.

    2004-07-05

    A five-cell high current superconducting cavity for the electron cooling project at RHIC is under fabrication. Higher order modes (HOMs), one of main limiting factors for high current energy-recovery operation, are under investigation. Calculations of HOMs using time-domain methods in Mafia will be discussed and compared to calculations in the frequency domain. Beam breakup thresholds determined from numerical codes for the five-cell cavity will be presented. A possible motivation towards a 2 x 2 superstructure using the current five-cell design will also be discussed.

  1. High temperature superconducting digital circuits and subsystems

    SciTech Connect

    Martens, J.S.; Pance, A.; Whiteley, S.R.; Char, K.; Johansson, M.F.; Lee, L.; Hietala, V.M.; Wendt, J.R.; Hou, S.Y.; Phillips, J.

    1993-10-01

    The advances in the fabrication of high temperature superconducting devices have enabled the demonstration of high performance and useful digital circuits and subsystems. The yield and uniformity of the devices is sufficient for circuit fabrication at the medium scale integration (MSI) level with performance not seen before at 77 K. The circuits demonstrated to date include simple gates, counters, analog to digital converters, and shift registers. All of these are mid-sized building blocks for potential applications in commercial and military systems. The processes used for these circuits and blocks will be discussed along with observed performance data.

  2. 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.

  3. High-temperature superconducting conductors and cables

    SciTech Connect

    Peterson, D.E.; Maley, M.P.; Boulaevskii, L.; Willis, J.O.; Coulter, J.Y.; Ullmann, J.L.; Cho, Jin; Fleshler, S.

    1996-09-01

    This is the final report of a 3-year LDRD project at LANL. High-temperature superconductivity (HTS) promises more efficient and powerful electrical devices such as motors, generators, and power transmission cables; however this depends on developing HTS conductors that sustain high current densities J{sub c} in high magnetic fields at temperatures near liq. N2`s bp. Our early work concentrated on Cu oxides but at present, long wire and tape conductors can be best made from BSCCO compounds with high J{sub c} at low temperatures, but which are degraded severely at temperatures of interest. This problem is associated with thermally activated motion of magnetic flux lines in BSCCO. Reducing these dc losses at higher temperatures will require a high density of microscopic defects that will pin flux lines and inhibit their motion. Recently it was shown that optimum defects can be produced by small tracks formed by passage of energetic heavy ions. Such defects result when Bi is bombarded with high energy protons. The longer range of protons in matter suggests the possibility of application to tape conductors. AC losses are a major limitation in many applications of superconductivity such as power transmission. The improved pinning of flux lines reduces ac losses, but optimization also involves other factors. Measuring and characterizing these losses with respect to material parameters and conductor design is essential to successful development of ac devices.

  4. Superconducting specific-heat jump ΔCel∝Tcβ(β ≈2) for K1-xNaxFe2As2

    NASA Astrophysics Data System (ADS)

    Grinenko, V.; Efremov, D. V.; Drechsler, S.-L.; Aswartham, S.; Gruner, D.; Roslova, M.; Morozov, I.; Nenkov, K.; Wurmehl, S.; Wolter, A. U. B.; Holzapfel, B.; Büchner, B.

    2014-02-01

    We present a systematic study of the electronic specific-heat jump (ΔCel) at the superconducting transition temperature Tc of K1-xNaxFe2As2. Both Tc and ΔCel monotonously decrease with increasing x. The specific heat jump scales approximately with a power law, ΔCel∝Tcβ, with β ≈2 determined by the impurity scattering rate, in contrast to most iron-pnictide superconductors, where the remarkable Bud'ko-Ni-Canfield (BNC) scaling ΔCel∝T3 has been found. Both the T dependence of Cel(T ) in the superconducting state and the nearly quadratic scaling of ΔCel at Tc are well described by the Eliashberg theory for a two-band d-wave superconductor with weak pair breaking due to nonmagnetic impurities. The disorder induced by the Na substitution significantly suppresses the small gaps, leading to gapless states in the slightly disordered superconductor, which results in a large observed residual Sommerfeld coefficient in the superconducting state for x >0.

  5. 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.

  6. Relaxation of the transport critical current in high-Tc polycrystals

    NASA Astrophysics Data System (ADS)

    Altshuler, E.; Cobas, R.; Batista-Leyva, A. J.; Noda, C.; Flores, L. E.; Martínez, C.; Orlando, M. T. D.

    1999-08-01

    We perform a systematic study of the time evolution of the transport critical current in polycrystalline samples of the high temperature superconducting system (Hg1-xRex)Ba2Ca2Cu3O8+δ and YBa2Cu3O7-δ after application and removal of an external magnetic field Hm. Within our time, temperature, and remanent field windows, the transport critical current increases logarithmically in time. The relaxation rates in the range 80-115 K decrease with increasing temperature at a fixed Hm, while temperature-dependent maxima are observed in the relaxation rate versus Hm plots. These experimental results are reproduced by a phenomenological model applicable to any high-Tc polycrystals. In the model, the time increase of the transport current is determined by the effective field at the intergrain junctions, which relaxes in time due to the flux creep of the intragrain magnetization.

  7. 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

  8. High-temperature superconducting transformer evaluation

    SciTech Connect

    DeSteese, J.G.; Dagle, J.E.; Dirks, J.A.

    1995-04-01

    The advancing development of high-temperature superconducting (HTS) materials is encouraging the evaluation of many practical applications. This paper summarizes a study that examined the future potential of HTS power transformers in the 30-MVA to 1000-MVA capacity range. Transformer performance was characterized on the basis of potentially achievable HTS materials capabilities and dominant transformer design parameters. Life-cycle costs were estimated and compared with those of conventional transformers to evaluate the economic viability and market potential of HTS designs. HTS transformers are projected to have both capital and energy cost advantages attributable to their ability to be intrinsically smaller and lighter than conventional transformers of comparable capacity.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1988-08-01

    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.

  11. The t J model for the oxide high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Ogata, Masao; Fukuyama, Hidetoshi

    2008-03-01

    A theoretical review is given on high temperature superconductivity in copper oxides (cuprates) by focusing on the hole doping cases based on the view that it is realized in carrier doped Mott insulators, as noted by Anderson in the initial stage. From the detailed knowledge of electronic states deduced from experiments that showed the undoped parent case is Mott insulators (charge transfer type insulators, to be precise) and that the hole doping is mainly on oxygen sites, the t-J model, as derived by Zhang and Rice, is shown to be a canonical model for hole doped cuprates and values of various parameters of the model have been assessed. Results of many different numerical methods so far obtained for this t-J model, especially the variational Monte Carlo method, have clearly indicated the stability of the \\rmd_{x^2-y^2} -wave superconductivity at absolute zero for the parameter region of actual experimental interest and the particular doping dependences of the condensation energy of superconductivity reflecting particular features of doped Mott insulators. For finite temperatures, on the other hand, the field theoretical slave-boson approximation based on the spin (spinons) and charge (holons) separations and the gauge fields as a glue combining them predicts qualitatively particular features of the existence of characteristic crossover temperatures of the spin singlet of the resonating valence bond (RVB) state, TRVB and the onset of Bose condensation of holons, TB, triggering coherent motion of electrons as convoluted particles of spinons and holons. The considerations based on the gauge field indicate that the onset temperature of superconductivity, Tc, is the lower one of these two, i.e. either TB (overdoped cases) or TRVB (underdoped cases), respectively. These characteristic features of the 'phase diagram' at finite temperatures are in overall agreement with various experimental observations, especially with the existence of spin-gap or pseudo-gap phases. In

  12. 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.

  13. Direct observation of the influence of the As-Fe-As angle on the Tc of superconducting SmFeAsO1-xFx

    NASA Astrophysics Data System (ADS)

    Garbarino, G.; Weht, R.; Sow, A.; Sulpice, A.; Toulemonde, P.; Álvarez-Murga, M.; Strobel, P.; Bouvier, P.; Mezouar, M.; Núñez-Regueiro, M.

    2011-07-01

    The electrical resistivity, crystalline structure, and electronic properties calculated from the experimentally measured atomic positions of the compound SmFeAsO0.81F0.19 have been studied up to pressures ˜20 GPa. The correlation between the pressure dependence of the superconducting transition temperature (Tc) and crystallographic parameters on the same sample shows clearly that a regular FeAs4 tetrahedron maximizes Tc through optimization of carrier transfer to the FeAs planes as indicated by the evolution of the electronic band structures.

  14. Novel all-high Tc epitaxial Josephson junction

    NASA Astrophysics Data System (ADS)

    Chin, D. K.; van Duzer, T.

    1991-02-01

    Josephson junctions are essential components in high-temperature superconductive integrated circuits. YBaCuO/Nb-doped SrTiO3/YBaCuO epitaxial Josephson junctions have been designed, fabricated, and tested. The YBaCuO and Nb-doped SrTiO3 films were deposited by off-axis sputtering. Both dc and ac Josephson effects have been observed and the supercurrent persists up to 80 K. The critical current density is an exponential function of the barrier layer thickness. The product of critical current and normal resistance is between one and three millivolts. A superconducting quantum interference device made of the junctions displays magnetic field modulation of critical current.

  15. Superfluid and quasiparticle behavior below Tc of strain introduced high-quality epitaxial thin films of Fe(Se,Te)

    NASA Astrophysics Data System (ADS)

    Maeda, Atsutaka; Nabeshima, Fuyuki; Imai, Yoshnori; Hanawa, Masafumi; Ichinose, Ataru; Tsukada, Ichiro

    2014-03-01

    We succeeded in introducing compressive strain in epitaxial films of FeSe and Fe(Te,Se), leading to high Tcs' (1.5 times higher that in bulk crystals for FeSe). It is of great interest how the effect of strain shows up in properties in the superconducting state of these thin-film samples. We investigated superfluid- and quaiparticle response at THz frequencies. Structures characteristic of superconductivity was found clearly both in real part and imaginary part of the conductivity spectrum. Increase of quasiparticle scattering time below Tc was observed even in THz frequencies, which is connected with microwave data measured in bulk crystals consistently. Even in these high-quality, high Tc films, development of superfluid density with decreasing temperature is rather gradual, keeping a ``dirty'' feature. This might be related to possible excess Fe characteristic of this material, and further improvement of Tc is expected by additional heat treatment. Alternatively, the contribution of Legget mode is also considered. At present, any anomalous features related to strain have not been observed in these properties. The data at microwave frequencies taken by a dielectric resonator will also be discussed. This work is partially supported by Japan Science and Technology Agency as the IRON-SEA program.

  16. High-spin states in the 96Tc nucleus

    NASA Astrophysics Data System (ADS)

    Bucurescu, D.; Căta-Danil, Gh.; Căta-Danil, I.; Ivaşcu, M.; Mărginean, N.; Rusu, C.; Stroe, L.; Ur, C. A.; Gizon, A.; Gizon, J.; Nyakó, B.; Timár, J.; Zolnai, L.; Boston, A. J.; Joss, D. T.; Paul, E. S.; Semple, A. T.; Parry, C. M.

    High-spin states in the 96Tc nucleus have been studied with the reactions 82Se(19F,5nγ) at 68 MeV and Zn(36S,αpxn) at 130 MeV. Two γ-ray cascades (irregular bandlike structures) have been observed up to an excitation energy of about 10 MeV and spin 21-22?.

  17. High-spin states in the 97Tc nucleus

    NASA Astrophysics Data System (ADS)

    Bucurescu, D.; Gadea, A.; Căta-Danil, Ghe.; Căta-Danil, I.; Ivaşcu, M.; Mărginean, N.; Rusu, C.; Stroe, L.; Ur, C. A.

    High-spin states in the 97Tc nucleus have been studied by in-beam γ-ray spectroscopy with the reaction 82Se(19F,4nγ) at 68 MeV incident energy. Excited states have been observed up to about 8 MeV excitation and spin 43/2ℎ. The observed level scheme is compared with results of shell model calculations.

  18. New type of second-order high- Tc SQUID planar gradiometer

    NASA Astrophysics Data System (ADS)

    Lang, P. L.; Zheng, D. N.; Zhang, M. J.; Chen, K.; Qi, H. H.; Zhao, Z. X.

    2004-09-01

    We have proposed a novel type of high- Tc superconducting quantum interference device (SQUID) planar gradiometer that could measure the mixed partial derivative of magnetic fields ∂2Bz/ ∂x ∂y . The device consists of two parts, one is the signal pickup antenna formed by four square pickup loops, and another one is a SQUID directly coupled to the common line which separates the antenna loops. The four pickup loops were arranged to a two-dimensional array. The loops in the diagonal direction are connected in series. The total current in the common line in this configuration is directly proportional to the mixed partial derivative of the magnetic field. We have made a device of such design on a STO bicrystal substrate and tested the device in gradient field.

  19. Research on high-Tc SQUID based non-destructive evaluation

    NASA Astrophysics Data System (ADS)

    Wang, Hui-Wu; Kong, Xiang-Yan; Ren, Yu-Feng; Yu, Hong-Wei; Ding, Hong-Sheng; Zhao, Shi-Ping; Chen, Geng-Hua; Zhou, Yue-Liang; Zhang, Li-Hua; He, Yu-Sheng; Yang, Qian-Sheng

    2004-01-01

    A non-destructive evaluation system based on high-Tc dc-SQUID (superconducting quantum interference device) incorporating a gradient field excitation has been built. By using this system a 1mm-diameter hole at a depth of 2mm inside an aluminium plate at room temperature can be easily detected and imaged in an unshielded environment. The relation between the spatial resolution, or the smallest detectable flaw size and experimental parameters is briefly analysed in terms of a simple metal ring model. The result shows that the spatial resolution depends strongly on the sensor-sample separation as well as on some other parameters, such as signal-to-noise ratio of excitation, excitation frequency and material conductivity.

  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.

  1. Phase diagram of high- Tc superconductor: Cu-NMR studies on multi-layered cuprates

    NASA Astrophysics Data System (ADS)

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

    2008-04-01

    A new phase diagram is presented for an ideally flat CuO2 plane through the Cu-NMR studies on five-layered cuprates MBa2Ca4Cu5Oy(M-1245) (M=Hg,Tl,Cu), which includes an antiferromagnetic (AFM) metal phase and a uniform mixing phase of AFM metal and high- Tc superconductivity (HTSC) in an under-doped region. It has been found that a disorder causes a quantum-phase transition from an AFM metal to an insulating state in an under-doped regime in the Cu-1245 where a disorder is introduced via an oxygen-reduced process. This finding reinforces that an AFM metallic phase exists between the AFM insulating phase and the SC phase for the ideally flat CuO2 plane provided that a disorder is absent.

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

    SciTech Connect

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

    1991-04-01

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

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

    SciTech Connect

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

    1991-04-01

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

  4. Temperature dependence of thermal and electrical conductivity of Bi-based high- Tc (2 2 2 3) superconductor

    NASA Astrophysics Data System (ADS)

    Gul, I. H.; Anis-ur-Rehman, M.; Maqsood, A.

    2006-12-01

    Superconducting samples with nominal composition Bi 1.6Pb 0.4Sr 2Ca 2Cu 3O δ were prepared by the conventional solid-state reaction technique. The samples have been characterized by X-ray diffraction, dc electrical resistivity, ac magnetic susceptibility and thermal conductivity. The X-ray diffraction studies were done at room temperature and the lattice constants of the material were determined by indexing all the peaks. All the above measurements show that, there exists two phases i.e. high- Tc (2 2 2 3) and low- Tc (2 2 1 2). The information obtained from dc electrical resistivity data agrees with ac magnetic susceptibility measurements. The onset temperature Tc (onset) and zero resistivity temperature Tc ( R = 0) of the samples remains within the temperature 120 ± 1 K and 103 ± 1 K. Thermal conductivity has been measured with a transient plane source (TPS) technique in the temperature range 77-300 K. The estimation of the electrical resistivity change due to scattering by phonons and impurities has been discussed. An increase in thermal conductivity is observed above and below Tc ( R = 0). The electron-phonon scattering time, phonon-limited mobility and the size of the electron-phonon constant are also calculated. Wiedemann-Franz law is applied to gain prediction about the magnitude of electronic and phonon contribution to the total thermal conductivity of the samples. It is observed that heat is mainly conducted by the phonons in this system.

  5. 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

  6. NMR initiatives on understanding high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

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

    2007-03-01

    We review a recent progress of NMR studies [H. Mukuda, et al., Phys. Rev. Lett 96 (2006) 087001; S. Shimizu, et al., submitted for publication.] on multi-layered cuprates. This work has shed new light to a generic phase diagram of high-temperature superconductivity (HTSC) which suggests a competition between antiferromagnetism (AFM) and superconductivity (SC). The multi-layered cuprates include two types of CuO2 planes, an outer CuO2 plane (OP) in a pyramidal coordination and an inner CuO2 plane (IP) in a square one with no apical oxygen. Remarkable feature of the multi-layered systems is the presence of ideally flat CuO2 planes that are homogeneously doped. Systematic Cu-NMR studies on the optimally-doped five-layered HgBa2Ca4Cu5O(Hg-1245(OPT)) and slightly overdoped Tl-1245(OVD) have revealed the coexistent phase of SC and AFM in a unit cell [H. Kotegawa, et al., Phys. Rev. B 64 (2001) 064515; H. Kotegawa, et al., Phys. Rev. B 69 (2004) 014501.]. The optimally doped two OPs are predominantly superconducting with Tc=108 and 100 K, whereas the under-doped three IPs show the AFM order below TN=60 and 45 K for Hg-1245(OPT) and Tl-1245(OVD), respectively. Recently exciting is the finding of the uniform mixing of AFM and HTSC in a single CuO2 layer in the under-doped Hg-1245(UD) and the heavily underdoped four-layered Ba2Ca3Cu4O8F2 (0234F(2.0)) that has fluorine ions (F) as apical ions [H. Mukuda, et al., Phys. Rev. Lett 96 (2006) 087001; S. Shimizu, et al., submitted for publication.]. In Hg-1245(UD) with Tc=72 K and TN=290 K, the OPs exhibit the uniform mixing of AFM and HTSC with AFM moment of MAFM(OP)=0.1 μB, whereas the IPs are possibly AFM insulators with a small doping [H. Mukuda, et al., Phys. Rev. Lett 96 (2006) 087001.]. In 0234F(2.0) with Tc=55 K and TN=100 K, the uniform mixing of AFM and HTSC is demonstrated to take place in electron (n)- doped IPs [S. Shimizu, et al., submitted for publication.], thanks to insight from recent ARPES results [Y. Chen, et

  7. Superconducting bolometers: High-T(sub c) and low-T(sub c)

    NASA Astrophysics Data System (ADS)

    Richards, P. L.

    1991-04-01

    A description is given of recent work at Berkeley on superconducting detectors and mixers for infrared and millimeter wavelengths. The first report is a review article which summarizes the status of development of superconducting components for infrared and millimeter wave receivers. Next, a report is given on measurements and theoretical modeling of the absorptivity (surface resistance) of high quality epitaxial films of the high-(Tc) superconductor YBCO from 750 GHz to 21 THz. The next report describes measurements of the thermal boundary resistance between YBCO films and various substrates. This resistance is much larger than expected from the acoustic impedance mismatch model and gives a thermal time constant in the nanosecond range for typical YBCO films. Then, there are reports on the design and experimental performance of two different types of high-(Tc) bolometric detectors. One is a conventional bolometer with a gold-black absorber. The other is an antenna coupled microbolometer. The properties of a low-(Tc) microbolometer are also described. The last reports describe accurate measurements and also theoretical modeling of an SIS quasiparticle waveguide mixer for W-band which uses very high quality Ta junctions. The best mixer noise is only 1.3 times the quantum limit. Both the mixer gain and the noise are in quantitative agreement with the quantum theory.

  8. 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.

  9. Superconductivity in aromatic hydrocarbons

    NASA Astrophysics Data System (ADS)

    Kubozono, Yoshihiro; Goto, Hidenori; Jabuchi, Taihei; Yokoya, Takayoshi; Kambe, Takashi; Sakai, Yusuke; Izumi, Masanari; Zheng, Lu; Hamao, Shino; Nguyen, Huyen L. T.; Sakata, Masafumi; Kagayama, Tomoko; Shimizu, Katsuya

    2015-07-01

    'Aromatic hydrocarbon' implies an organic molecule that satisfies the (4n + 2) π-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (Kxpicene, five benzene rings). Its superconducting transition temperatures (Tc's) were 7 and 18 K. Recently, we found a new superconducting Kxpicene phase with a Tc as high as 14 K, so we now know that Kxpicene possesses multiple superconducting phases. Besides Kxpicene, we discovered new superconductors such as Rbxpicene and Caxpicene. A most serious problem is that the shielding fraction is ⩽15% for Kxpicene and Rbxpicene, and it is often ∼1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metal-doped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of Tc that is clearly observed in some phases of aromatic hydrocarbon superconductors, suggesting behavior not explained by the standard BCS picture of superconductivity. In this article, we describe the present status of this research field, and discuss its future prospects.

  10. A simple figure of merit for high temperature superconducting switches

    SciTech Connect

    Honig, E.M.

    1989-01-01

    The discovery of the new high temperature superconductors has revived interest in many special applications, including superconducting switches. For comparison of switch types, a simple figure of merit based in switch performance is proposed, derived for superconducting switches, and then calculated for thyristors and vacuum switches. The figure of merit is then used to show what critical current density would be needed for superconducting switches to compete with more conventional switches. 46 refs., 1 fig.

  11. Strong periodic flux pinning in oxygen-ion-irradiated high-TC superconductors

    NASA Astrophysics Data System (ADS)

    Villegas, Javier; Swiecicki, I.; Briatico, J.; Bernard, R.; Crassous, A.; Wolf, T.; Bergeal, N.; Lesueur, J.; Ulysse, C.; Faini, G.; Hallet, X.; Piraux, L.

    2012-02-01

    We used oxygen ion irradiation to transfer into high-TC superconducting thin films the nanoscale pattern of different types of masks (alumina [1] and [2] PMMA templates with ordered arrays of holes). This causes a nanoscale spatial modulation of superconductivity, and strongly affects the magneto-transport in the mixed-state. By tuning the irradiation dose and the array parameters, it is possible to engineer vortex energy landscapes sufficiently strong to govern flux dynamics. This is evidenced by a periodic series of strong magneto-resistance oscillations, the well-known fingerprint of periodic flux pinning. Interestingly, this irradiation technique allows tuning the geometry and the strength of the pinning potential wells at the nanoscale. This allows the observation of unusually strong matching effects at relatively high fields (up to several kOe). We show that the amplitude of the magneto-resistance oscillations is intimately connected with vortex channeling effects. [1] J.E. Villegas et al. Nanotechnology 22 075302 (2011). [2] I. Swiecicki et al. submitted

  12. 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.

  13. 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.

  14. Clocking the onset of bilayer coherence in a high-Tc cuprate

    NASA Astrophysics Data System (ADS)

    Baldini, Edoardo; Mann, Andreas; Mallett, Benjamin P. P.; Arrell, Christopher; van Mourik, Frank; Wolf, Thomas; Mihailovic, Dragan; Tallon, Jeffrey L.; Bernhard, Christian; Lorenzana, José; Carbone, Fabrizio

    2017-01-01

    In cuprates, a precursor state of superconductivity is speculated to exist above the critical temperature TC. Here we show via a combination of far-infrared ellipsometry and ultrafast broadband optical spectroscopy that signatures of such a state can be obtained via three independent observables in an underdoped sample of NdBa2Cu3O6 +δ . The pseudogap correlations were disentangled from the response of laser-broken pairs by clocking their characteristic time scales. The onset of a superconducting precursor state was found at a temperature TONS>TC , consistent with the temperature scale identified via static optical spectroscopy. Furthermore, the temperature evolution of the coherent vibration of the Ba ion, strongly renormalized by the onset of superconductivity, revealed a pronounced anomaly at the same temperature TONS. The microscopic nature of such a precursor state is discussed in terms of preformed pairs and enhanced bilayer coherence.

  15. Overlap junctions for high coherence superconducting qubits

    NASA Astrophysics Data System (ADS)

    Wu, X.; Long, J. L.; Ku, H. S.; Lake, R. E.; Bal, M.; Pappas, D. P.

    2017-07-01

    Fabrication of sub-micron Josephson junctions is demonstrated using standard processing techniques for high-coherence, superconducting qubits. These junctions are made in two separate lithography steps with normal-angle evaporation. Most significantly, this work demonstrates that it is possible to achieve high coherence with junctions formed on aluminum surfaces cleaned in situ by Ar plasma before junction oxidation. This method eliminates the angle-dependent shadow masks typically used for small junctions. Therefore, this is conducive to the implementation of typical methods for improving margins and yield using conventional CMOS processing. The current method uses electron-beam lithography and an additive process to define the top and bottom electrodes. Extension of this work to optical lithography and subtractive processes is discussed.

  16. 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.

  17. Fabrication and measurement of high T sub c superconducting microbolometers

    SciTech Connect

    Nahum, M.; Hu, Qing; Richards, P.L. ); Sachtjen, S.A.; Newman, N.; Cole, B.F. )

    1990-09-01

    We have fabricated and measured the performance of antenna-coupled microbolometers based on the resistive transition of a high {Tc} superconducting film for use as detectors of far-infrared and millimeter waves. A planar lithographed antenna (log-periodic or log-spiral) is used to couple the radiation to a thin YBCO film with dimensions ({approx}6 {times} 13 {mu}m{sup 2}) which are smaller than the wavelength to be measured. This film acts both as the resistor to thermalize the rf currents and as a transition edge thermometer to measure the resulting temperature rise. Because of its small size, both the thermal conductance from the film into the bulk of the substrate and the heat capacity of the thermally active region are small. Consequently, the microbolometer has low noise, fast response and a high voltage responsivity. We have measured a phonon limited electrical NEP of 4.5 {times} 10{sup {minus}12} WHz{sup {minus}{1/2}} at 10 kHz modulation frequency and a responsivity of 478 V/W at a bias of 550 {mu}A. Measurements of the optical efficiency are in progress and will be discussed. 12 refs., 6 figs.

  18. 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.

  19. 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.

  20. Superconducting (Li,Fe)OHFeSe Film of High Quality and High Critical Parameters

    NASA Astrophysics Data System (ADS)

    Huang, Yulong; Feng, Zhongpei; Ni, Shunli; Li, Jun; Hu, Wei; Liu, Shaobo; Mao, Yiyuan; Zhou, Huaxue; Zhou, Fang; Jin, Kui; Wang, Huabing; Yuan, Jie; Dong, Xiaoli; Zhao, Zhongxian

    2017-06-01

    A superconducting film of (Li1-x Fe x )OHFeSe is reported for the first time. The thin film exhibits a small in-plane crystal mosaic of 0.22°, in terms of the full width at half maximum of the x-ray rocking curve, and an excellent out-of-plane orientation by x-ray φ-scan. Its bulk superconducting transition temperature {T}{{c}} of 42.4 K is characterized by both zero electrical resistance and diamagnetization measurements. The upper critical field {H}{{c}2} is estimated to be 79.5 T and 443 T for the magnetic field perpendicular and parallel to the ab plane, respectively. Moreover, a large critical current density {J}{{c}} of a value over 0.5 MA/cm2 is achieved at ˜20 K. Such a (Li1-x Fe x )OHFeSe film is therefore not only important to the fundamental research for understanding the high-{T}{{c}} mechanism, but also promising in the field of high-{T}{{c}} superconductivity application, especially in high-performance electronic devices and large scientific facilities such as superconducting accelerator. Supported by the National Basic Research Program of China under Grant No 2017YFA0303000, the National Natural Science Foundation of China under Grant Nos 11574370, 11234006 and 61501220, the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences under Grant Nos QYZDY-SSW-SLH001, QYZDY-SSW-SLH008 and XDB07020100.

  1. 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.

  2. Implications of charge ordering in high Tc cuprate superconductors in far-infrared spectroscopy.

    PubMed

    Kim, Y H; Hor, P H

    2013-09-04

    We addressed the issue of the absence of far-infrared signatures pertaining to charge ordering in the published far-infrared reflectivity data of La2-xSrxCuO4 single crystals while other experimental probes reveal that charge ordering is a hallmark of superconducting cuprates. Through direct comparison of the far-infrared data reported by various groups side by side and also with the Raman scattering data, we found that the inconsistencies stem from the failure in capturing delicate spectral features embedded in the close-to-perfect ab-plane far-infrared reflectivity of La2-xSrxCuO4 single crystals by misidentifying the reflectivity as the Drude-like metallic reflectivity. The analysis of the close-to-true reflectivity data reveals that only a small fraction (<3%) of the total doping-induced charge carriers (electrons) are itinerant on the electron lattice made up with the rest of the electrons (>97%) at all doping levels up to 16%. We conclude that the far-infrared reflectivity study is far from being ready to construct a coherent picture of the ubiquitous charge ordering phenomenon and its relationship with the high Tc superconductivity.

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

    PubMed Central

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

    2015-01-01

    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, whose 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 PMID:26039222

  4. 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

  5. High temperature superconductivity space experiment (HTSSE)

    SciTech Connect

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

    1991-03-01

    The Naval Research Laboratory (NRL) is developing an experiment to deploy high temperature superconducting (HTS) devices and components in space. 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 late in 1992. This space experiment will demonstrate that this technology is sufficiently robust to survive the space environment and that has the potential to improve the operation of space systems significantly. The devices for the initial launch (HTSSE-I) have been received by NRL and evaluated electrically, thermally and mechanically and will be integrated into the final space package early in 1991. In this paper, the performance of the devices is summarized and some potential applications of HTS technology in space systems is outlined.

  6. 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.

  7. High- Tc superconductors with antiferromagnetic order: limitations on spin-fluctuation pairing mechanism

    NASA Astrophysics Data System (ADS)

    Kulić, Miodrag L.; Kulić, Igor M.

    2003-08-01

    The antagonistic interplay of antiferromagnetism (AF) and superconductivity (SC), recently discovered in high-temperature superconductors, is studied in the framework of a microscopic theory. We explain the surprisingly large increase of the magnetic Bragg peak intensity IQ at Q∼( π, π) in the magnetic field H≪ Hc2 at low temperatures 0< T≪ Tc, TAF in La 2- xSr xCuO 4. Good agreement with experimental results is found. The theory predicts large anisotropy of the relative intensity RQ( H)=( IQ( H)- IQ(0))/ IQ(0), i.e. R Q( H∥c -axis)≫R Q( H⊥c -axis) . The quantum ( T=0) phase diagram at H=0 is constructed. The theory also predicts: (i) that the magnetic field can induce the AF order in the SC state; (ii) that the spin-fluctuation (SF) effective coupling constant g<0.1 eV is small, which gives small SC critical temperature Tc (≪40 K)--thus questioning the SF mechanism of pairing in HTS oxides.

  8. Genuine Phase Diagram of Homogeneously Doped CuO2 Plane in High-Tc Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Mukuda, Hidekazu; Yamaguchi, Yuhei; Shimizu, Sunao; Kitaoka, Yoshio; Shirage, Parasharam; Iyo, Akira

    2008-12-01

    We report a genuine phase diagram for a disorder-free CuO2 plane based on the precise evaluation of the local hole density (Nh) by site-selective Cu-NMR studies on five-layered high-Tc cuprates. It has been unraveled that (1) the antiferromagnetic metallic state (AFMM) is robust up to Nh≈ 0.17, (2) the uniformly mixed phase of superconductivity (SC) and AFMM is realized at Nh≤ 0.17, (3) the tetracritical point for the AFMM/(AFMM+SC)/SC/PM (paramagnetism) phases may be present at Nh≈ 0.15 and T≈ 75 K, (4) Tc is maximum close to a quantum critical point (QCP) at which the AFM order collapses, suggesting the intimate relationship between the high-Tc SC and the AFM order. The results presented here strongly suggest that the AFM interaction plays the vital role as the glue for the Cooper pairs, which will lead us to a genuine understanding of why the Tc of cuprate superconductors is so high.

  9. 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.

  10. Low cost, formable, high T(sub c) superconducting wire

    NASA Technical Reports Server (NTRS)

    Smialek, James L. (Inventor)

    1991-01-01

    A ceramic superconductivity part such as a wire is produced through the partial oxidation of a specially formulated copper alloy in the core. The alloys contain low level quantities of rare earth and alkaline earth dopant elements. Upon oxidation at high temperature, superconducting oxide phases are formed as a thin film.

  11. Detecting defect in cast iron using high- TC SQUID

    NASA Astrophysics Data System (ADS)

    He, D. F.; Yoshizawa, M.; Oyama, Y.; Nakamura, M.

    2004-10-01

    For eddy-current NDE, due to the big permeability of ferromagnetic material, low testing frequency is needed to detect defects in it. SQUID has advantages in low frequency eddy current NDE. But the large magnetic field produced by ferromagnetic material often exceeds the dynamic range of general SQUID system. We developed a mobile high- TC SQUID system, with which, the dc and low-frequency magnetic field could be compensated well. Using our mobile SQUID system, the magnetic field produced by the cast iron could be compensated well and the defect in it could be successfully detected.

  12. Scanning high-Tc SQUID imaging system for magnetocardiography

    NASA Astrophysics Data System (ADS)

    Yang, Hong-Chang; Wu, Tsung-Yeh; Horng, Herng-Er; Wu, Chau-Chung; Yang, S. Y.; Liao, Shu-Hsien; Wu, Chiu-Hsien; Jeng, J. T.; Chen, J. C.; Chen, Kuen-Lin; Chen, M. J.

    2006-05-01

    A scanning magnetocardiography (MCG) system constructed from SQUID sensors offers potential to basic or clinical research in biomagnetism. In this work, we study a first order scanning electronic high-Tc (HTS) SQUID MCG system for biomagnetic signals. The scanning MCG system was equipped with an x-y translation bed powered by step motors. Using noise cancellation and μ-metal shielding, we reduced the noise level substantially. The established scanning HTS MCG system was used to study the magnetophysiology of hypercholesterolaemic (HC) rabbits. The MCG data of HC rabbits were analysed. The MCG contour map of HC rabbits provides experimental models for the interpretation of human cardiac patterns.

  13. Thermodynamics of the magnetic-field-induced "normal" state in an underdoped high Tc superconductor

    NASA Astrophysics Data System (ADS)

    Riggs, Scott Chandler

    High magnetic fields are used to kill superconductivity and probe what happens to system when it cannot reach the ideal ground state, i.e. what is the normal-state ground state? Early work in High-Tc, where the application of magnetic field destroyed the zero resistance state and recovered a resistivity value that connected continuously with the zero field curve, lead people to believe this magnetic-field-induced-state had fully driven the system normal, revealing the true underlying ground state, without any vestige of superconductivity. Many experiments done in this region of phase space have results interpreted as coming from the low energy ground state excitations. With the emergence of ultra-clean crystals in a unique family of hole doped high-Tc superconductors, YBa2Cu3O 7-delta, YBCO, a new and highly unexpected phenomena of quantum oscillations were discovered, and they followed the standard Liftshitz-Kosevich (LK) theory for a normal metal. The results suddenly made the problem of high-T c appear to be analogous to superconductivity in the organics, which is brought about by a wave-vector nesting and Fermi surface reconstruction. The only problem, it appeared, that needed to be reconciled was with Angle Resolved Photo-Emission Spectroscopy (ARPES) and Scanning Tunneling Microscopy (STM) data that claimed to see no such Fermi surface, instead only "arcs", a set of disconnected segments in the Brillouin zone which quasiparticle peaks are observed at the Fermi energy, which in a mean field description does not allow for a continuous Fermi surface contour. These two discrepancies led to the "arc vs pocket" debate, which is still unresolved. The other kink in the quantum oscillation armor is that, to this date, quantum oscillations in the hole-doped cuprates have only been seen in YBCO, the only cuprate structure to have CuO chains, which conduct and are located in between two CuO2 superconducting planes in the unit cell. In an attempt to reconcile the "arc vs

  14. 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.

  15. 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.

  16. Incoherent superconductivity well above {T}_{{\\rm{c}}} in high-{T}_{{\\rm{c}}} cuprates—harmonizing the spectroscopic and thermodynamic data

    NASA Astrophysics Data System (ADS)

    Storey, J. G.

    2017-07-01

    Cuprate superconductors have long been known to exhibit an energy gap that persists high above the superconducting transition temperature ({T}{{c}}). Debate has continued now for decades as to whether it is a precursor superconducting gap or a pseudogap arising from some competing correlation. Failure to resolve this has arguably delayed explaining the origins of superconductivity in these highly complex materials. Here we effectively settle the question by calculating a variety of thermodynamic and spectroscopic properties, exploring the effect of a temperature-dependent pair-breaking term in the self-energy in the presence of pairing interactions that persist well above {T}{{c}}. We start by fitting the detailed temperature-dependence of the electronic specific heat and immediately can explain its hitherto puzzling field dependence. Taking this same combination of pairing temperature and pair-breaking scattering we are then able to simultaneously describe in detail the unusual temperature and field dependence of the superfluid density, tunneling, Raman and optical spectra, which otherwise defy explanation in terms a superconducting gap that closes conventionally at {T}{{c}}. These findings demonstrate that the gap above {T}{{c}} in the overdoped regime likely originates from incoherent superconducting correlations, and is distinct from the competing-order ‘pseudogap’ that appears at lower doping.

  17. 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.

  18. 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.

  19. Can doping graphite trigger room temperature superconductivity? Evidence for granular high-temperature superconductivity in water-treated graphite powder.

    PubMed

    Scheike, T; Böhlmann, W; Esquinazi, P; Barzola-Quiquia, J; Ballestar, A; Setzer, A

    2012-11-14

    Granular superconductivity in powders of small graphite grains (several tens of micrometers) is demonstrated after treatment with pure water. The temperature, magnetic field and time dependence of the magnetic moment of the treated graphite powder provides evidence for the existence of superconducting vortices with some similarities to high-temperature granular superconducting oxides but even at temperatures above 300 K. Room temperature superconductivity in doped graphite or at its interfaces appears to be possible.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Anomalous Behavior of High Quality Factor Planar Superconducting Resonators

    NASA Astrophysics Data System (ADS)

    Megrant, Anthony; Chen, Zijun; Chiaro, Ben; Dunsworth, Andrew; Quintana, Chris; Campbell, Brooks; Kelly, Julian; Barends, Rami; Chen, Yu; Jeffrey, Evan; Mutus, Josh; Neill, Charles; O'Malley, Peter; Sank, Daniel; Vainsencher, Amit; Wenner, Jim; White, Ted; Bochmann, Jorg; Hoi, Iochun; Palmstrom, Christopher; Martinis, John; Cleland, Andrew

    2014-03-01

    Superconducting coplanar waveguide resonators have proven to be invaluable tools in studying some of the decoherence mechanisms found in superconducting qubits. Surface two-level states tend to dominate decoherence at temperatures below Tc/10 and at very low microwave powers, assuming loss through other channels (e.g. quasiparticles, vortices, and radiation loss) has been mitigated through proper shielding and design. I will present recent measurements of resonators whose behavior diverges significantly from the standard two-level state model at low temperatures and low excitation energies, resulting in startling behavior of the internal quality factor. This research was funded by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), through the Army Research Office grant W911NF-09-1-0375.

  5. Progress in Nanoengineered Microstructures for Tunable High-Current, High-Temperature Superconducting Wires

    SciTech Connect

    Holesinger, T. G.; Civale, L.; Maiorov, B.; Feldmann, D. M.; Coulter, Yates; Miller, D. J.; Maroni, Victor A.; Chen, Zhijun; Larbalestier, D. C.; Feenstra, Roeland; Li, Xiaoping; Huang, Y.; Kodenkandath, Thomas; Zhang, W.; Rupich, Marty; Malozemoff, Alex

    2008-01-01

    High critical current densities (J{sub c}) in thick films of the Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO, {Tc}{approx}92 K) superconductor directly depend upon the types of nanoscale defects and their densities within the films. A major challenge for developing a viable wire technology is to introduce nanoscale defect structures into the YBCO grains of the thick film suitable for flux pinning and the tailoring of the superconducting properties to specific, application-dependent, temperature and magnetic field conditions. Concurrently, the YBCO film needs to be integrated into a macroscopically defect-free conductor in which the grain-to-grain connectivity maintains levels of inter-grain J{sub c} that are comparable to the intra-grain J{sub c}. That is, high critical current (I{sub c}) YBCO coated conductors must contain engineered in homogeneities on the nanoscale, while being homogeneous on the macroscale. An analysis is presented of the advances in high-performance YBCO coated-conductors using chemical solution deposition (CSD) based on metal trifluoroacetates and the subsequent processing to nano-engineer the microstructure for tunable superconducting wires. Multi-scale structural, chemical, and electrical investigations of the CSD film processes, thick film development, key microstructural features, and wire properties are presented. Prospects for further development of much higher I{sub c} wires for large-scale, commercial application are discussed within the context of these recent advances.

  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. Superconducting high-pressure phases composed of hydrogen and iodine

    DOE PAGES

    Shamp, Andrew; Zurek, Eva

    2015-09-25

    Evolutionary structure searches predict three new phases of iodine polyhydrides stable under pressure. Insulating P1-H5I, consisting of zigzag chains of (HI) δ+ and H 2 molecules, is stable between 30-90 GPa. Cmcm-H2I and P6/mmm-H4I are found on the 100, 150 and 200 GPa convex hulls. These two phases are good metals, even at 1 atm, because they consist of monoatomic lattices of iodine. At 100 GPa the superconducting transition temperature, Tc, of H2I and H4I are estimated to be 7.8 and 17.5 K, respectively. Lastly, the increase in Tc relative to elemental iodine results from a larger ωlog from themore » light mass of hydrogen, and an enhanced from modes containing H/I and H/H vibrations.« less

  8. Phenomenological study of the normal state angle resolved photoelectron spectroscopy line shapes of high temperature superconducting cuprates

    NASA Astrophysics Data System (ADS)

    Matsuyama, Kazue; Dilip, Rohit; Gweon, G.-H.

    2015-03-01

    Understanding the normal state properties of high temperature (high-Tc) superconducting cuprates remains a central mystery in the high-Tc problem. Standing out among those mysterious properties are the anomalous angle resolved photoelectron spectroscopy (ARPES) line shapes. The extremely correlated Fermi liquid (ECFL) theory recently introduced by Shastry has renewed interest in quantitatively understanding ARPES line shapes. In this talk, we combine certain phenomenological considerations with the ECFL framework in order to describe the ARPES data. Our phenomenological models have the property of preserving the universal property of the original ECFL theory, while introducing phenomenological changes in a non-universal property. Our models describe, with unprecedented fidelity, the key aspects of the dichotomy between momentum distribution curves (MDCs) and energy distribution curves (EDCs) of high-Tc ARPES data. Therefore, our study goes well beyond the prevailing studies that discuss only MDCs and EDCs.

  9. A silver-bearing, High-Temperature, Superconducting (HTS) paint

    NASA Astrophysics Data System (ADS)

    Ferrando, William A.

    1990-02-01

    A substantial set of device applications awaits development of a workable, durable, high-temperature superconducting (HTS) paint. Such a paint should be truly superconducting with its critical temperature T sub c greater than 77K. For most of these applications, a high critical current (J sub c) is not required, although probably desirable. A process is described which can be used to produce silver-bearing HTS paint coatings on many engineering materials. Preliminary tests have shown good adherence to several ceramics and the ability to meet the superconducting criteria. Moreover, the coatings withstand multiple thermal cycling and stability under laboratory ambient storage conditions for periods of at least several months.

  10. Effect of weak inhomogeneities in high temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Doluweera, D. G. Sumith P.

    We present results of three studies done using a dynamical cluster quantum Monte Carlo approximation. First, we investigate the d-wave superconducting transition temperature Tc in the doped 2D repulsive Hubbard model with a weak inhomogeneity in hopping in the form of checkerboard pattern or a lattice of 2 x 2 plaquettes. Near neighbor hoppings within a plaquette is t and that of between the plaquettes is t'. We investigate T c in the weak inhomogeneous limit 0.8t < t' < 1.2t. We find inhomogeneity (t' ≠ t) suppresses Tc. The characteristic spin excitation energy (effective exchange energy) and the strength of d-wave pairing interaction decrease with decreasing T c. The latter observations suggest a strong correlation among effective exchange interaction, Tc and the d-wave pairing interaction of the system. Second1, we further find that enhancement of effective exchange interaction causes a slight increase in Tc of a weakly disordered system with low impurity concentration, compared to the homogeneous system. Here the disorder is introduced to homogeneous repulsive 2D Hubbard model as a weak local potential disorder. Third, we present an improved maximum entropy method to analytically continue quantum Monte Carlo data with a severe sign problem. 1A result from a collaborative study done with A. Kemper of Florida State University.

  11. Mesoscopic superconductivity and high spin polarization coexisting at metallic point contacts on Weyl semimetal TaAs.

    PubMed

    Aggarwal, Leena; Gayen, Sirshendu; Das, Shekhar; Kumar, Ritesh; Süß, Vicky; Felser, Claudia; Shekhar, Chandra; Sheet, Goutam

    2017-01-10

    A Weyl semimetal is a topologically non-trivial phase of matter that hosts mass-less Weyl fermions, the particles that remained elusive for more than 80 years since their theoretical discovery. The Weyl semimetals exhibit unique transport properties and remarkably high surface spin polarization. Here we show that a mesoscopic superconducting phase with critical temperature Tc=7 K can be realized by forming metallic point contacts with silver (Ag) on single crystals of TaAs, while neither Ag nor TaAs are superconductors. Andreev reflection spectroscopy of such point contacts reveals a superconducting gap of 1.2 meV that coexists with a high transport spin polarization of 60% indicating a highly spin-polarized supercurrent flowing through the point contacts on TaAs. Therefore, apart from the discovery of a novel mesoscopic superconducting phase, our results also show that the point contacts on Weyl semimetals are potentially important for applications in spintronics.

  12. Mesoscopic superconductivity and high spin polarization coexisting at metallic point contacts on Weyl semimetal TaAs

    NASA Astrophysics Data System (ADS)

    Aggarwal, Leena; Gayen, Sirshendu; Das, Shekhar; Kumar, Ritesh; Süß, Vicky; Felser, Claudia; Shekhar, Chandra; Sheet, Goutam

    2017-01-01

    A Weyl semimetal is a topologically non-trivial phase of matter that hosts mass-less Weyl fermions, the particles that remained elusive for more than 80 years since their theoretical discovery. The Weyl semimetals exhibit unique transport properties and remarkably high surface spin polarization. Here we show that a mesoscopic superconducting phase with critical temperature Tc=7 K can be realized by forming metallic point contacts with silver (Ag) on single crystals of TaAs, while neither Ag nor TaAs are superconductors. Andreev reflection spectroscopy of such point contacts reveals a superconducting gap of 1.2 meV that coexists with a high transport spin polarization of 60% indicating a highly spin-polarized supercurrent flowing through the point contacts on TaAs. Therefore, apart from the discovery of a novel mesoscopic superconducting phase, our results also show that the point contacts on Weyl semimetals are potentially important for applications in spintronics.

  13. 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

  14. 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

  15. 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.

  16. Separation of charge-order and magnetic QCPs in heavy fermions and high Tc cuprates

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    2010-03-01

    The Fermi surface topology of high temperature superconductors inferred from magnetic quantum oscillation measurements provides clues for the origin of unconventional pairing thus previously not accessed by other spectroscopy techniques. While the overdoped regime of the high Tc phase diagram has a large Fermi surface consistent with bandstructure calculations, the underdoped regime of YBa2Cu2O6+x is found to be composed of small pockets. There is considerable debate as to whether the small observed ``pocket'' is hole-like or electron-like- whether the Fermi surface is best described by a t-J model or a conventional band folding picture- whether or not a Fermi liquid description applies- or- whether bilayer coupling splits the degeneracy of the observed pockets. We (myself and collaborators) have now collected an extensive body of experimental data that brings this debate to rest, but raises new questions about the nature of itinerant magnetism in underdoped high Tc cuprates. Quantum oscillation measurements are performed on multiple samples in magnetic fields extending to 85 T, temperatures between 30 mK (dilution fridge in dc fields to 45 T) and 18 K, over a range of hole dopings and with samples rotated in-situ about multiple axes with respect to the magnetic field. We perform a topographical map of the Fermi surface, enabling the in-plane shape of one of the pockets to be determined- imposing stringent constraints on the origin of the Fermi surface. While quantum oscillations measurements are consistent with a topological Fermi surface change associated with magnetism near optimal doping, they also point to a secondary instability deep within the underdoped regime beneath a high Tc superconducting sub-dome. An steep upturn in the quasiparticle effective mass is observed on underdoping, suggestive of a quantum critical point near x= 0.46 separating the metallic regime (composed of small pockets) from a more underdoped insulating charge-ordered regime (earlier

  17. 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

  18. Transmission Level High Temperature Superconducting Fault Current Limiter

    SciTech Connect

    Stewart, Gary

    2016-10-05

    The primary objective of this project was to demonstrate the feasibility and reliability of utilizing high-temperature superconducting (HTS) materials in a Transmission Level Superconducting Fault Current Limiter (SFCL) application. During the project, the type of high-temperature superconducting material used evolved from 1st generation (1G) BSCCO-2212 melt cast bulk high-temperature superconductors to 2nd generation (2G) YBCO-based high-temperature superconducting tape. The SFCL employed SuperPower's “Matrix” technology, that offers modular features to enable scale up to transmission voltage levels. The SFCL consists of individual modules that contain elements and parallel inductors that assist in carrying the current during the fault. A number of these modules are arranged in an m x n array to form the current-limiting matrix.

  19. Cryogenic deformation of high temperature superconductive composite structures

    DOEpatents

    Roberts, Peter R.; Michels, William; Bingert, John F.

    2001-01-01

    An improvement in a process of preparing a composite high temperature oxide superconductive wire is provided and involves conducting at least one cross-sectional reduction step in the processing preparation of the wire at sub-ambient temperatures.

  20. 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.

  1. Exploratory Research for a High Temperature Superconducting Integrated Circuit

    DTIC Science & Technology

    1993-09-01

    of monolithic integration of the subsystems in a compact package which can be efficiently cryocooled. In addressing this issue, the goal of this...AD-A275 798 WL-TR-93-5031 EXPLORATORY RESEARCH FOR A HIGH TEMPERATURE SUPERCONDUCTING INTEGRATED CIRCUIT E. K. Track & 0. Mukhanov Hypres Inc., 175...RESEARCH FOR A HIGH C F33615-90-C-1456 TEMPERATURE SUPERCONDUCTING PE 65502 INTEGRATED CIRCUIT PR 3005 o 0. MUKHANOV, J.N. ECKSTEIN, TA 65 I. BOZOVIC

  2. 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.

  3. Vortex Pinning in the High-Tc Superconductor YBa2Cu3O6+x

    DTIC Science & Technology

    2009-09-24

    vortex pinning and dissipation in high-Tc superconductors with potential for DOD applications (e.g. for use in efficient filters for high-frequency...Final Performance Report 3. DATES COVERED (From - To) 15-05-2005 to 31-12-2008 4. TITLE AND SUBTITLE Vortex Pinning in the High-Tc Superconductor ...optimized for the study of superconductors . The microscope was first used to study the vortex liquid state in the cuprate high-Tc superconductor

  4. 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.

  5. 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.

  6. Activation of high- Tc superconductors due to neutron irradiation

    NASA Astrophysics Data System (ADS)

    Shitamichi, T.; Nakano, M.; Terai, T.; Yamawaki, M.; Hoshiya, T.

    2003-10-01

    For actual application of high- Tc superconductors (HTSC), the improvement of Jc is required. It has been reported that pinning centers in the HTSC increase Jc. Particle beam irradiation is one of the most effective methods to introduce strong pinning centers into HTSC for Jc enhancement. In particular, neutron irradiation is very effective for bulk materials, although the activation might be an important problem. In this study, activation of HTSCs was analysed by using the computer code, ORIGEN-II. The contribution of impurities in Bi 2Sr 2CaCu 2O 8+ x (Bi-2212) to 1 cm dose equivalent occupies about 15%. In RE-123 family, Y, La, Nd, Sm. Gd, Dy, Ho and Yb gave low activation. In the case of U-doped Y-123, about 75% of the activity is from the contribution of the fission products.

  7. 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.

  8. Moderately shielded high-Tc SQUID system for rat MCG

    NASA Astrophysics Data System (ADS)

    Bechstein, S.; Kim, I.-S.; Drung, D.; Novikov, I.; Schurig, Th

    2010-06-01

    Recently, we have developed a 5-channel high-Tc SQUID system with one signal channel intended for rat magnetocardiography (MCG) in moderately shielded or "quiet" real environment. This system is an adapted version of a human MCG system which has been improved with respect to user-friendliness and stability. A dewar with a cold-warm distance of 7 mm and a refill cycle time of up to one week is utilized. The implemented high-Tc SQUIDs are single-layer devices with grain boundary junctions fabricated at KRISS with laser ablation on 10 mm × 10 mm STO substrates. In order to cancel environmental magnetic noise, three of the five SQUIDs are arranged to build an axial software first-order or second-order gradiometer with a base line of 35 mm. The other two SQUIDs are used for balancing. To overcome previous system instabilities, we have implemented an Earth field compensation for each SQUID. For this, the SQUIDs were mounted in capsules containing integrated field compensation coils. The three Earth field components are measured with an additional triaxial fluxgate, and compensated at the SQUID locations using the low-noise current source of the SQUID readout electronics. This way, the SQUIDs can be cooled and operated in a low residual field that improves system stability and reduces low-frequency SQUID noise. It is even possible to slowly move the dewar in the Earth field (dynamic field compensation). Different noise cancellation procedures were optimized and compared employing a periodic signal source.

  9. Interplay between magnetism and superconductivity and the appearance of a second superconducting transition in α-FeSe at high pressure.

    PubMed

    Sidorov, V A; Tsvyashchenko, A V; Sadykov, R A

    2009-10-14

    We synthesized tetragonal α-FeSe by melting a powder mixture of iron and selenium at high pressure. Subsequent annealing at normal pressure results in removing traces of hexagonal β-FeSe, formation of a rather sharp transition to a superconducting state at T(c)∼7 K, and the appearance of a magnetic transition near T(M) = 120 K. Resistivity and ac-susceptibility were measured on the annealed sample at hydrostatic pressure up to 4.5 GPa. A magnetic transition visible in ac-susceptibility shifts down under pressure and a resistive anomaly typical for a spin density wave (SDW) antiferromagnetic transition develops near the susceptibility anomaly. T(c), determined by the appearance of a diamagnetic response in susceptibility, increases linearly under pressure at a rate dT(c)/dP = 3.5 K GPa(-1). Below 1.5 GPa, the resistive superconducting transition is sharp, the width of transition does not change with pressure and, T(c), determined by a peak in dρ/dT, increases at a rate ∼3.5 K GPa(-1). At higher pressure, a giant broadening of the resistive transition develops. This effect cannot be explained by possible pressure gradients in the sample and is inherent to α-FeSe. The dependences dρ(T)/dT show a signature for a second peak above 3 GPa which is indicative of the appearance of another superconducting state in α-FeSe at high pressure. We argue that this second superconducting phase coexists with SDW antiferromagnetism in a partial volume fraction and originates from pairing of charge carriers from other sheets of the Fermi surface.

  10. High-Tc and high-Jc SmFeAs(O,F) films on fluoride substrates grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ueda, Shinya; Takeda, Soichiro; Takano, Shiro; Yamamoto, Akiyasu; Naito, Michio

    2011-12-01

    Superconducting thin films of SmFeAs(O,F) were prepared by molecular beam epitaxy on fluoride substrates. In our process, F-free SmFeAsO films were grown first, and F was subsequently introduced to the films by diffusion from an overlayer of SmF3. By this simple process, record high Tc, namely, Tcon (Tcend) = 57.8 K (56.4 K) was obtained in a film on CaF2. Furthermore, the films on CaF2 showed high critical current density over 1 MA/cm2 in the self-field at 5 K. The correlation between superconductivity and epitaxial strain in SmFeAs(O,F) films is discussed.

  11. Large-moment antiferromagnetic order in overdoped high-Tc superconductor (154)SmFeAsO1-x D x.

    PubMed

    Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C; Otomo, Toshiya; Hosono, Hideo

    2017-05-30

    In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of (154)SmFeAsO1-x D x , and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.

  12. Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-xDx

    NASA Astrophysics Data System (ADS)

    Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C.; Otomo, Toshiya; Hosono, Hideo

    2017-05-01

    In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154SmFeAsO1-xDx, and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.

  13. Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1−xDx

    PubMed Central

    Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C.; Otomo, Toshiya; Hosono, Hideo

    2017-01-01

    In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154SmFeAsO1−xDx, and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity. PMID:28507123

  14. Lattice dynamics of high-Tc superconductors: Optical modes of the thallium-based compounds

    NASA Astrophysics Data System (ADS)

    Kulkarni, A. D.; de Wette, F. W.; Prade, J.; Schröder, U.; Kress, W.

    1990-04-01

    We present a lattice-dynamical calculation of the Raman- and infrared-active modes of the following six thallium-based high-Tc superconductors: Tl2Ba2CuO6, Tl2CaBa2Cu2O8, and Tl2Ca2Ba2Cu3O10 (body-centered-tetragonal structures) and TlCaBa2Cu2O7, TlCa2Ba2Cu3O9, and TlCa3Ba2Cu4O11 (simple-tetragonal structures). Our calculations are based on a shell model that incorporates short-range overlap potentials, long-range Coulomb potentials, and ionic polarizabilities. We also require that the shell models for different high-Tc superconducting compounds be mutually compatible, namely that the short-range potentials for given ion pairs in equivalent environments be transferable from one compound to the other. The model presented here does in fact utilize a common set of short-range potentials that apply to the entire series of thallium-based superconductors as well as to YBa2Cu3O7 and Bi2CaSr2Cu2O8, studied earlier. The model reproduces the available experimental infrared and Raman data of all these compounds quite well and is thus supported by a broad database, albeit only of optical modes. We expect that our model, which is based on realistic interaction potentials, reproduces eigenvalues and eigenvectors to the same approximation. Thus we conclude from the satisfactory agreement between calculated and measured eigenfrequencies that the calculated eigenvectors provide a realistic description of the displacement patterns of the optical modes.

  15. 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.

  16. Surface superconductivity as the primary cause of broadening of superconducting transition in Nb films at high magnetic fields

    NASA Astrophysics Data System (ADS)

    Zeinali, A.; Golod, T.; Krasnov, V. M.

    2016-12-01

    We study the origin of broadening of superconducting transition in sputtered Nb films at high magnetic fields. From simultaneous tunneling and transport measurements we conclude that the upper critical field Hc 2 always corresponds to the bottom of transition R ˜0 , while the top R ˜Rn occurs close to the critical field for destruction of surface superconductivity Hc 3≃1.7 Hc 2 . The two-dimensional nature of superconductivity at H >Hc 2 is confirmed by cusplike angular dependence of magnetoresistance. Our data indicates that surface superconductivity is remarkably robust even in disordered polycrystalline films and, surprisingly, even in perpendicular magnetic fields. We conclude that surface superconductivity, rather than flux-flow phenomenon, inhomogeneity, or superconducting fluctuations, is the primary cause of broadening of superconducting transition in magnetic field.

  17. Nanoscale Structures and Pseudogap in Under-doped High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Saarela, M.; Kusmartsev, F. V.

    We show that superconductor-insulator transitions in oxides and FeAs-based high Tc superconducting multilayers may arise due to a charge density wave instability induced by charged impurities and the over-screening of the long-ranged part of the Coulomb interaction, which is enhanced due to decreasing carrier density [1]. When the carrier density is low enough, impurities begin to trap particles and form bound states of clusters of charge carriers, which we call Coulomb bubbles. These bubbles are embedded inside the superconductor and form nuclei of the new insulating state. The growth of a bubble is terminated by the Coulomb force and each of them has a quantized charge and a fluctuating phase. When clusters first appear, they are covered by superfluid liquid due to the proximity effect and invisible. However, when the carrier density decreases the size of bubbles increases and the superconducting proximity inside them vanishes. The insulating state arises via a percolation of these insulating islands, which form a giant percolating cluster that prevents the flow of the electrical supercurrent through the system. We also show the formation of two groups of charge carriers in these compounds associated with free and localized states. The localized component arises due to the Coulomb bubbles. Our results are consistent with the two-component picture for cuprates deducted earlier by Gorkov and Teitelbaum [2] from the analysis of the Hall effect data and ARPES spectra. The Coulomb clusters induce nanoscale superstructures observed in scanning tunneling microscope (STM) experiments [3] and are responsible for the pseudogap [4].

  18. Cavity phenomena in mesas of cuprate high- Tc superconductors under voltage bias

    NASA Astrophysics Data System (ADS)

    Hu, Xiao; Lin, Shizeng

    2009-08-01

    Modeling a single crystal of cuprate high- Tc superconductor, such as Bi2Sr2CaCu2O8+δ , as a stack of intrinsic Josephson junctions, we formulate explicitly the cavity phenomenon of plasma oscillations and electromagnetic (EM) waves in mesas of cylindrical and annular shapes. The phase differences of the junctions are governed by the inductively coupled sine-Gordon equations, with the Neumann-type boundary condition for sample thickness much smaller than the EM wavelength, which renders the superconductor single crystal a cavity. Biasing a dc voltage in the c direction, a state with ±π kinks in the superconductivity phase difference piled up alternatively along the c axis is stabilized. The ±π phase kinks provide interlock between superconductivity phases in adjacent junctions, taking the advantage of huge inductive couplings inherent in the cuprate superconductors, which establishes the coherence across the whole system of more than ˜600 junctions. They also permit a strong coupling between the lateral cavity mode of the transverse Josephson plasma and the c -axis bias, and enhance the plasma oscillation significantly at the cavity modes which radiates EM waves in the terahertz band when the lateral size of mesa is set to tens of micrometers. It is discussed that the cavity mode realized in a very recent experiment using a cylindrical mesa can be explained by the present theory. In order to overcome the heating effect, we propose to use annular geometry. The dependence of frequency on the radius ratio is analyzed, which reveals that the shape tailor is quite promising for improving the present technique of terahertz excitation. The annular geometry may be developed as a waveguide resonator, mimicking the fiber lasers for visible lights.

  19. High-Pressure Study of the Ground- and Superconducting-State Properties of CeAu2Si2

    NASA Astrophysics Data System (ADS)

    Scheerer, Gernot W.; Giriat, Gaétan; Ren, Zhi; Lapertot, Gérard; Jaccard, Didier

    2017-06-01

    The pressure-temperature phase diagram of the new heavy-fermion superconductor CeAu2Si2 is markedly different from those studied previously. Indeed, superconductivity emerges not on the verge but deep inside the magnetic phase, and mysteriously Tc increases with the strengthening of magnetism. In this context, we have carried out ac calorimetry, resistivity, and thermoelectric power measurements on a CeAu2Si2 single crystal under high pressure. We uncover a strong link between the enhancement of superconductivity and quantum-critical-like features in the normal-state resistivity. Non-Fermi-liquid behavior is observed around the maximum of superconductivity and enhanced scattering rates are observed close to both the emergence and the maximum of superconductivity. Furthermore we observe signatures of pressure- and temperature-driven modifications of the magnetic structure inside the antiferromagnetic phase. A comparison of the features of CeAu2Si2 and its parent compounds CeCu2Si2 and CeCu2Ge2 plotted as function of the unit-cell volume leads us to propose that critical fluctuations of a valence crossover play a crucial role in the superconducting pairing mechanism. Our study illustrates the complex interplay between magnetism, valence fluctuations, and superconductivity.

  20. High-T(c) Superconductivity at the Interface between the CaCuO2 and SrTiO3 Insulating Oxides.

    PubMed

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

    2015-10-02

    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 T(c). We report the occurrence of high T(c) superconductivity in the bilayer CaCuO(2)/SrTiO(3), where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO(2)/SrTiO(3) interface must be realized between the Ca plane of CaCuO(2) and the TiO(2) plane of SrTiO(3). Only in this case can oxygen ions be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO(2) planes. 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 CaCuO(2) unit cells close to the interface with SrTiO(3). The results obtained for the CaCuO(2)/SrTiO(3) interface can be extended to multilayered high T(c) cuprates, contributing to explaining the dependence of T(c) on the number of CuO(2) planes in these systems.

  1. Antiferromagnetic Phase Transition in Four-Layered High-Tc Superconductors Ba2Ca3Cu4O8(FyO1-y)2 with Tc=55--102 K: 63Cu- and 19F-NMR Studies

    NASA Astrophysics Data System (ADS)

    Shimizu, Sunao; Mukuda, Hidekazu; Kitaoka, Yoshio; Kito, Hijiri; Kodama, Yasuharu; Shirage, Parasharam M.; Iyo, Akira

    2009-06-01

    We report on the magnetic characteristics of four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2 with apical fluorine through 63Cu- and 19F-NMR measurements. The substitution of oxygen for fluorine at the apical site increases carrier density (Nh) and Tc from 55 up to 102 K. The NMR measurements reveal that antiferromagnetic order, which can uniformly coexist with superconductivity, exists up to Nh ≃ 0.15, which is somewhat smaller than Nh ≃ 0.17, the quantum critical point (QCP) for five-layered compounds. The fact that the QCP for the four-layered compounds moves to a region of lower carrier density than for five-layered ones ensures that a decrease in the number of CuO2 layers makes an interlayer magnetic coupling weaker.

  2. Towards a better understanding of superconductivity at high transition temperatures

    NASA Astrophysics Data System (ADS)

    Hackl, R.; Hanke, W.

    2010-10-01

    We provide an overview over the following eleven contributions on superconductivity in copper-oxygen and iron-based compounds. The main objective of this volume is an improved general understanding of superconductivity at high transition temperatures. The key questions on the way towards understanding superconducting pairing beyond electron-phonon coupling are spelled out, and the present status of theoretical reasoning is summarized. The crucial experiments, their results and interrelations are discussed. The central result is that fluctuations of spin and charge contribute substantially to superconductivity and also to other ordering phenomena. Methodically, the simultaneous analysis of results obtained from different experimental techniques such as photoelectron spectroscopy and neutron scattering, on one and the same sample, turned out to be of pivotal importance.

  3. 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.

  4. A superconducting transformer system for high current cable testing.

    PubMed

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

    2010-03-01

    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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2001-05-01

    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 39K 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 39K 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 85,000Acm-2 at 4.2K. 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.

  7. A study of superconductivity in Y-Ba-Cu-F-O system

    NASA Astrophysics Data System (ADS)

    J, H. Jia; J, Y. Jiang; G, R. Liu; Y, M. Gao; Q, Q. Zheng; J, J. Du; W, G. Yao

    1988-02-01

    High temperature superconductivity, up to 258K, was observed in the Y1Ba2Cu3F2xO7-x-δ(0.2 leqq x leqq 1) bulk materials prepared by means of conventional ceramic-technique. X-ray diffraction analysis shows that these materials are multiphase. It is believed that to obtain a high Tc superconducting material with Tc near room temperature is possible. though the high Tc state of samples is now very unstable.

  8. Macroscopic character of composite high-temperature superconducting wires

    NASA Astrophysics Data System (ADS)

    Kivelson, S. A.; Spivak, B.

    2015-11-01

    The "d -wave" symmetry of the superconducting order in the cuprate high temperature superconductors is a well established fact [J. Tsuei and J. R. Kirtley, Rev. Mod. Phys. 72, 969 (2000), 10.1103/RevModPhys.72.969 and D. J. Vanharlingen, Rev. Mod. Phys. 67, 515 (1995), 10.1103/RevModPhys.67.515], and one which identifies them as "unconventional." However, in macroscopic contexts—including many potential applications (i.e., superconducting "wires")—the material is a composite of randomly oriented superconducting grains in a metallic matrix, in which Josephson coupling between grains mediates the onset of long-range phase coherence. [See, e.g., D. C. Larbalestier et al., Nat. Mater. 13, 375 (2014), 10.1038/nmat3887, A. P. Malozemoff, MRS Bull. 36, 601 (2011), 10.1557/mrs.2011.160, and K. Heine et al., Appl. Phys. Lett. 55, 2441 (1989), 10.1063/1.102295] Here we analyze the physics at length scales that are large compared to the size of such grains, and in particular the macroscopic character of the long-range order that emerges. While X Y -superconducting glass order and macroscopic d -wave superconductivity may be possible, we show that under many circumstances—especially when the d -wave superconducting grains are embedded in a metallic matrix—the most likely order has global s -wave symmetry.

  9. Interface induced high temperature superconductivity in single unit-cell FeSe on SrTiO3(110)

    NASA Astrophysics Data System (ADS)

    Zhou, Guanyu; Zhang, Ding; Liu, Chong; Tang, Chenjia; Wang, Xiaoxiao; Li, Zheng; Song, Canli; Ji, Shuaihua; He, Ke; Wang, Lili; Ma, Xucun; Xue, Qi-Kun

    2016-05-01

    We report high temperature superconductivity in one unit-cell (1-UC) FeSe films grown on SrTiO3 (STO)(110) substrate by molecular beam epitaxy. By in-situ scanning tunneling microscopy measurement, we observe a superconducting gap as large as 17 meV on the 1-UC FeSe films. Transport measurements on 1-UC FeSe/STO(110) capped with FeTe layers reveal superconductivity with an onset transition temperature (TC) of 31.6 K and an upper critical magnetic field of 30.2 T. We also find that TC can be further increased by external electric field although the effect is weaker than that on STO(001) substrate.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. Heat treatment of wires on the basis of the high Tc superconductor YBa2Cu3Ox

    NASA Astrophysics Data System (ADS)

    Müller, P.; Schubert, M.; Rodig, Ch.; Fuchs, G.; Fischer, K.

    1989-08-01

    Ag-sheathed powder-in-tube wires on the basis of the high Tc superconductor YBa2Cu3Ox are produced by a drawing process. After cold working, the wires are not superconducting. By heat treatment at temperatures >900 °C, lattice defects are healed and the contact between the grains is improved. After this heat treatment the wires are slowly cooled in an O2 atmosphere in order to adjust the optimum O2 stoichiometry. The annealing temperature has a strong influence on the attainable critical current density. By annealing a wire with 420 ppm carbon content at 950 °C, jc values of 5020 A/cm2 at 4.2 K and 1130 A/cm2 at 77 K were achieved. Drastically reduced critical current densities in wires with high carbon content demonstrate the importance of a low carbon content for achieving high critical current densities in YBa2Cu3Ox .

  15. Bosonization Theorem and a Model of High-Tc Superconductor.

    NASA Astrophysics Data System (ADS)

    Ren, Hai-Cang

    1996-03-01

    For a purely fermionic system on a lattice, there exists a different, but well defined system on the same lattice, consisting both of bona fide fermions and bosons with an interaction depending on a parameter G characterizing on-site repulsion between particles(R. Friedberg, T. D. Lee and H. C. Ren, Phys. Rev. B50, 10190 (1994).). The energy spectrum and the scattering matrix of the former are identical to those in the finite-energy sector of the latter in the hard-core limit, G→∞. This theorem is particularly useful for the description of a fermionic system whose low-lying spectrum consists of bosonic resonances. We argue that the high-Tc superconductors belong to this category and the long-range order in the superphase can be identified with the condensation of resonance bosons. A short coherence length, results from μSR experiments, measurements of the Hall number and the anomalous behavior of H_c2 near T=0 can be understood in terms of this resonance-boson model(R. Friedberg, T. D. Lee and H. C. Ren, Phys. Rev. B42, 4122 (1990).). We have also examined the possibility of a bosonic d-wave resonance(O.Tchernyshyov, A.S.Blaer and H.Ren, in the current Proceedings.). In this case, the bosonization theorem predicts coexistence of an s-wave bosonic condensate and a d-wave gap parameter for fermions.

  16. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-10-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enable definition of superconducting and nonsuperconducting regions in the same epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel monolithic devices. Recent experiments are discussed which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronics devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors are presented.

  17. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-10-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis on the laser-writing method, which enables definition of superconducting and nonsuperconducting regions in the same epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3optical modulator is introduced. The second, more futuristic, approach is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments are discussed which reveal intriguing optical properties of HTS films and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors, are presented.

  18. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-09-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enables definition of superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments are discussed, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors will be presented.

  19. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-09-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications are given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method. These techniques make it possible to define superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches are presented for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid-nitrogen temperatures. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y- on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTs phases to fabricate novel, monolithic devices. We discuss recent experiments, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors are presented.

  20. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-08-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro- optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optical. A review of the substrate materials and deposition techniques suitable for fabrication of high-quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enables the definition of superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid-nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro- optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices are discussed. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors will be presented.

  1. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-08-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro- optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high-quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enables the definition of superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid-nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro- optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3/$O(subscript 7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices are discussed. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors will be presented.

  2. 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

    2016-08-05

    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.

  3. Analysis of Magnetic Critical Fields in Iron-Based SmFeAsO0.85 HIGH-Tc Superconductor

    NASA Astrophysics Data System (ADS)

    Ahmad, Dawood; Song, Tae Kwon; Park, In Suk; Kim, G. C.; Ren, Zhi-An; Kim, Y. C.

    The magnetic properties of the newly discovered iron-oxypnictide SmFeAsO0.85 high-Tc superconductor with a Tc of around 55 K were investigated. Bulk SmFeAsO0.85 was prepared by a method for high-pressure synthesis. The lower critical field Hc1 was estimated from the magnetization at low fields; Hc1(0) was measured to be 212 Oe. A linear temperature dependence instead of saturation at low temperatures in Hc1(T) revealed unconventional superconductivity with a nodal gap structure in our SmFeAsO0.85 superconductor. The results showed that the well-known secondary peak in the temperature dependence of the critical current density Jc is absent in the SmFeAsO0.85 high-Tc superconductor. The irreversibility line Birr was fitted well by the power law dependence (1 - T/Tc)n with n ~ 1.5. This is indicative of the flux creep phenomena in the SmFeAsO0.85 high-Tc superconductor. In addition, within the range of measurement temperatures in this study, no crossover was observed in the temperature dependence of the irreversibility line Birr which may be due to low anisotropy in our SmFeAsO0.85 superconductor.

  4. The High Pressure Superconductivity of CaLi2 Compound: The Thermodynamic Properties

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, R.; Durajski, A. P.; Pach, P. W.

    2013-06-01

    The thermodynamic properties of the superconducting state in CaLi2 at 60 GPa have been described in the paper. The numerical analysis has been carried out in the framework of the Eliashberg formalism. It has been shown that: (i) the critical value of the Coulomb pseudopotential is equal to 0.20, which corresponds to the value of 1795 meV for the Coulomb potential; (ii) the critical temperature ( T C ) cannot be correctly calculated by using the Allen-Dynes (AD) formula; (iii) the dimensionless ratios: TCCN (TC )/H2C (0 ), ( C S ( T C )- C N ( T C ))/ C N ( T C ) and 2Δ(0)/ k B T C take the non-BCS values: 0.157, 1.78 and 3.85, respectively. The symbol C N represents the specific heat in the normal state, C S denotes the specific heat in the superconducting state, H C (0) is the thermodynamic critical field near the temperature of zero Kelvin, and Δ(0) is the order parameter; (iv) the ratio of the electron effective mass (m^{star}e) to the electron band mass ( m e ) assumes a high value, in the whole range of the temperature, where the superconducting state exists. The maximum of m^{star}e/me is equal to 2.15 for T= T C .

  5. Nernst effect in the electron-doped cuprate superconductor Pr2-xCexCuO4: Superconducting fluctuations, upper critical field Hc2, and the origin of the Tc dome

    NASA Astrophysics Data System (ADS)

    Tafti, F. F.; Laliberté, F.; Dion, M.; Gaudet, J.; Fournier, P.; Taillefer, Louis

    2014-07-01

    The Nernst effect was measured in the electron-doped cuprate superconductor Pr2-xCexCuO4 (PCCO) at four concentrations, from underdoped (x =0.13) to overdoped (x=0.17), for a wide range of temperatures above the critical temperature Tc. A magnetic field H up to 15 T was used to reliably access the normal-state quasiparticle contribution to the Nernst signal Nqp, which is subtracted from the total signal N, to obtain the superconducting contribution Nsc. As a function of H, Nsc peaks at a field H whose temperature dependence obeys Hc2ln(T /Tc), as it does in a conventional superconductor such as NbxSi1-x. The doping dependence of the characteristic field scale Hc2, shown to be closely related to the upper critical field Hc2, tracks the domelike dependence of Tc, showing that superconductivity is weakened below the quantum critical point where the Fermi surface is reconstructed, presumably by the onset of antiferromagnetic order. Our data at all dopings are quantitatively consistent with the theory of Gaussian superconducting fluctuations, eliminating the need to invoke unusual vortexlike excitations above Tc, and ruling out phase fluctuations as the mechanism for the fall of Tc with underdoping. We compare the properties of PCCO with those of hole-doped cuprates and conclude that the domes of Tc and Hc2 versus doping in the latter materials are also controlled predominantly by phase competition rather than phase fluctuations.

  6. Alloying effects of Y on Tc in superconducting (La 1- xY x)NiC 2

    NASA Astrophysics Data System (ADS)

    Liao, T. F.; Sung, H. H.; Syu, K. J.; Lee, W. H.

    2009-03-01

    As revealed in the powder X-ray diffraction and crystallographic data, the partial substitution of La with Y in (La 1- xY x)NiC 2 could be systematic up to the solubility limit near x=0.35. The variation of room temperature lattice parameters, a, b, c and v of these substitute compounds are consistent with what one would expect from a chemical pressure effect. Magnetic, electrical and heat capacity measurements indicate that the change in Tc with x is similar to the change in the lattice parameter. It is found that the Tc change rate is dTc/dx=-7.0 K and dTc/dv=0.46 K/Å3. According to the BCS theory, the stiffening of the lattice under pressure may change both the electron-phonon coupling strength V and the electron density of states at the Fermi level, N(0), which will lead to the change of Tc. Analysis of the electron density of states at Fermi level N(0) from the specific heat data indicates that the effect of N(0) on Tc dominates in the (La 1- xY x)NiC 2 system.

  7. 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.; ...

    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

  8. 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.

  9. 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.

  10. High-temperature Superconductivity in compressed Solid Silane

    PubMed Central

    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 102 K. PMID:25746861

  11. A superconducting high-speed flywheel energy storage system

    NASA Astrophysics Data System (ADS)

    de Andrade, R.; Ferreira, A. C.; Sotelo, G. G.; Suemitsu, W. I.; Rolim, L. G. B.; Silva Neto, J. L.; Neves, M. A.; dos Santos, V. A.; da Costa, G. C.; Rosario, M.; Stephan, R.; Nicolsky, R.

    2004-08-01

    High-speed flywheel systems have been studied as compensators of voltage sags and momentary interruptions of energy. Besides the complexity of these systems, the main concerns are bearing losses. This work is part of the development of a superconducting high-speed flywheel energy storage prototype. In order to minimize the bearing losses, this system uses a superconducting axial thrust magnetic bearing in a vacuum chamber, which guarantees low friction losses, and a switched reluctance motor-generator to drive the flywheel system. Dynamic simulations made for this prototype, connected to the electric power network, show the viability of use it as a compensator.

  12. Publisher's Note: High-temperature superconductivity stabilized by electron-hole interband coupling in collapsed tetragonal phase of KFe2As2 under high pressure [Phys. Rev. B 91 , 060508(R) (2015)

    DOE PAGES

    Nakajima, Yasuyuki; Wang, Renxiong; Metz, Tristin; ...

    2015-03-09

    Here, we report a high-pressure study of simultaneous low-temperature electrical resistivity and Hall effect measurements on high quality single-crystalline KFe2As2 using designer diamond anvil cell techniques with applied pressures up to 33 GPa. In the low pressure regime, we show that the superconducting transition temperature Tc finds a maximum onset value of 7 K near 2 GPa, in contrast to previous reports that find a minimum Tc and reversal of pressure dependence at this pressure. Upon applying higher pressures, this Tc is diminished until a sudden drastic enhancement occurs coincident with a first-order structural phase transition into a collapsed tetragonalmore » phase. The appearance of a distinct superconducting phase above 13 GPa is also accompanied by a sudden reversal of dominant charge carrier sign, from hole- to electron-like, which agrees with our band calculations predicting the emergence of an electron pocket and diminishment of hole pockets upon Fermi surface reconstruction. Our results suggest the high-temperature superconducting phase in KFe2As2 is substantially enhanced by the presence of nested electron and hole pockets, providing the key ingredient of high-Tc superconductivity in iron pnictide superconductors.« less

  13. A zero-field Cu-NMR study on antiferromagnetic ordered state in four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2

    NASA Astrophysics Data System (ADS)

    Shimizu, S.; Mukuda, H.; Kitaoka, Y.; Kito, H.; Kodama, Y.; Shirage, P. M.; Iyo, A.

    2010-12-01

    We report on superconducting and magnetic characteristics in four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2 with apical fluorine through zero-field Cu-NMR measurements. The zero-field NMR spectra shows that the internal magnetic field, induced by antiferromagnetic (AFM) ordered moments, decreases with increasing the local carrier density (Nh). The AFM phase expands up to Nh˜0.15, which is the magnetic critical point where the AFM order collapses. Moreover, for y=1.0, the AFM order is observed at all CuO2 layers, although superconducting transition takes place at Tc=55K. This result suggests that the AFM order uniformly coexists with superconductivity in a single CuO2 plane in an underdoped region.

  14. Anomalous optical conductivity in the normal state of high Tc oxides

    NASA Astrophysics Data System (ADS)

    Moriya, Toru; Takahashi, Yoshinori

    1991-03-01

    The optical resistivity due to antiferromagnetic spin fluctuations in two-dimensional metals, as a possible model for high Tc oxides, is calculated within the Born approximation and the self-consistent renormalization (SCR) theory for the spin fluctuations. The result is shown to explain the observed anomalous behavior of optical conductivity in YBa2Cu3O7 above Tc quantitatively.

  15. The spin polaron theory as a mechanism for high temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Yanga, Danilo M.

    2017-08-01

    I summarize in this paper our previous works on the spin polaron theory as a mechanism for high temperature superconductivity in the finite temperature (Matsubara) Green's function method. In this formulation, some bulk thermodynamic properties of high-Tc materials like entropy and specific heat are treated. The hole spectral function is likewise derived. Single-particle tunneling current is calculated for normal metal-superconductor and superconductor-superconductor junctions. With an effective Hamiltonian derived from this theory, the Josephson tunneling current between two high temperature superconductors is obtained. Current problems like mobility of holes, calculation of energy gap function, the triplet pairing mechanism, among others, are also discussed in this paper, all using the spin polaron formulation.

  16. Fermi surface reconstruction in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Taillefer, Louis

    2009-03-01

    The recent observation of quantum oscillations in underdoped high-Tc superconductors (1), combined with their negative Hall coefficient at low temperature (2), reveals that the Fermi surface of hole-doped cuprates includes a small electron pocket. This strongly suggests that the large hole Fermi surface characteristic of the overdoped regime undergoes a reconstruction caused by the onset of some order which breaks translational symmetry. Here we consider the possibility that this order is ``stripe'' order, a form of combined charge / spin modulation observed most clearly in materials like Eu- doped and Nd-doped LSCO. In these materials, the onset of stripe order coincides with major changes in transport properties (3), providing strong evidence that stripe order is indeed the cause of Fermi-surface reconstruction. We identify the critical doping where this reconstruction occurs and show that the temperature dependence of transport coefficients at that doping is typical of metals at a quantum critical point (4). We discuss an interpretation of the pseudogap as a fluctuating precursor of the stripe-ordered phase.This work was performed in collaboration with L. Balicas, D.A. Bonn, J. Chang, O. Cyr-Choinière, R. Daou, N. Doiron- Leyraud, W.N. Hardy, N.E. Hussey, F. Lalibert'e, D. LeBoeuf, S.Y. Li, R. Liang, C. Proust, H. Takagi, and J.S. Zhou.(1) N. Doiron-Leyraud et al., Nature 447, 565 (2007).(2) D. LeBoeuf et al., Nature 450, 533 (2007).(3) R. Daou et al., Nature Physics, in press (DOI 10.1038/nphys1109); http://arXiv.org/abs/0806.2881.(4) R. Daou et al., to be published; http://arXiv.org/abs/0810.4280.

  17. Magnetoplasma waves in thin high-temperature-superconducting layers

    NASA Astrophysics Data System (ADS)

    Mishonov, T. M.

    1990-10-01

    It is shown that, in thin Bi2Sr2CaCu2O8 layers with thickness d much lower than the London penetration depth λ, two-dimensional magnetoplasma waves can propagate. These collective excitations are analogous to the well-known excitations of the two-dimensional electron gas. The propagation of these plasma waves is possible in both normal and superconducting phases if their frequency ω is lower than the superconducting gap 2Δ(0) at zero temperature. In the case of the magnetic field H perpendicular to the layer, the plasma frequency receives a shift connected with the cyclotron frequency. A magnetoplasma-wave frequency shift like that is possible for a superconducting phase only in the flux-flow regime for very large wave amplitudes. A measurement of the magnetoplasma shift created by the hybridization between plasma and cyclotron waves will give a new direct method for determining both the cyclotron mass of the holes mh in the normal phase and the cyclotron mass of the Cooper pairs m* in the superconducting phase. The checking of the BCS clean-limit relation m*=2mh can be an important tool for understanding the mechanism of high-temperature superconductivity.

  18. 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.

  19. 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.

  20. 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.