Sample records for superconducting energy gaps

  1. The superconductive energy gap of UPt3 investigated by point-contact spectroscopy

    NASA Astrophysics Data System (ADS)

    Löhneysen, H. V.; Goll, G.

    1994-04-01

    Point-contact spectroscopy, via the mechanism of Andreev reflection between a normal metal and a superconductor, can be employed to obtain information about the superconductive energy gap. In the present work, point-contacts between the heavy-fermion superconductor UPt3 and Pt have been studied down to 36 mK and in magnetic fields up to 6 T. Andreev reflection is observed only in the low-field, low-temperature superconducting phase. The unusual temperature and magneticfield dependence together with the gap anisotropy give direct experimental evidence that the different superconductive phases in UPt3 have distinctly different order parameters.

  2. Effect of Magnetic Field on Thermal Conductivity and Energy Gap of Superconducting Films

    Microsoft Academic Search

    D. E. Morris; M. Tinkham

    1964-01-01

    We have measured the change in the thermal conductivity of superconducting tin, indium, and lead films upon application of a magnetic field in the plane of the film. These experiments were undertaken to explore the dependence of the energy gap upon magnetic field and to determine the thermodynamic order of the field-induced transition in films. Within the range of temperatures

  3. Calculation of the cyclotron mass and superconducting energy gap as a function of Fermi surface position in zinc

    Microsoft Academic Search

    Philip G. Tomlinson; J. C. Swihart

    1979-01-01

    The anisotropic mass enhancement and anisotropic superconducting energy gap are calculated for zinc using pseudopotential theory. The phonon frequencies and polarization vectors are obtained from a model developed here which uses Shaw's optimized model potential with three force-constant terms adjusted to obtain agreement with neutron scattering data. A realistic Fermi-surface geometry is used and the electron wave functions are made

  4. Anisotropy of the Fermi surface, Fermi velocity, many-body enhancement, and superconducting energy gap in Nb

    NASA Astrophysics Data System (ADS)

    Crabtree, G. W.; Dye, D. H.; Karim, D. P.; Campbell, S. A.; Ketterson, J. B.

    1987-02-01

    The detailed angular dependence of the Fermi radius kF, the Fermi velocity vF(k), the many-body enhancement factor ?(k), and the superconducting energy gap ?(k), for electrons on the Fermi surface of Nb are derived with use of the de Haas-van Alphen (dHvA) data of Karim, Ketterson, and Crabtree [J. Low Temp. Phys. 30, 389 (1978)], a Korringa-Kohn-Rostoker parametrization scheme, and an empirically adjusted band-structure calculation of Koelling. The parametrization is a nonrelativistic five-parameter fit allowing for cubic rather than spherical symmetry inside the muffin-tin spheres. The parametrized Fermi surface gives a detailed interpretation of the previously unexplained ?, ?', and ?'' orbits in the dHvA data. Comparison of the parametrized Fermi velocities with those of the empirically adjusted band calculation allow the anisotropic many-body enhancement factor ?(k) to be determined. Theoretical calculations of the electron-phonon interaction based on the tight-binding model agree with our derived values of ?(k) much better than those based on the rigid-muffin-tin approximation. The anisotropy in the superconducting energy gap ?(k) is estimated from our results for ?(k), assuming weak anisotropy.

  5. Superconducting-gap-node spectroscopy using nonlinear electrodynamics

    Microsoft Academic Search

    Igor Zutic; Oriol T. Valls

    1997-01-01

    We present a method to determine the nodal structure of the energy gap of unconventional superconductors such as high-Tc materials. We show how nonlinear electrodynamics phenomena in the Meissner regime, arising from the presence of lines on the Fermi surface where the superconducting energy gap is very small or zero, can be used to perform ``node spectroscopy,'' that is, as

  6. Magnetic-Field Dependence of Microwave Absorption and Energy Gap in Superconducting Films

    Microsoft Academic Search

    R. H. White; M. Tinkham

    1964-01-01

    We have measured the change in absorption of microwave radiation by superconducting indium, tin, and lead films as a function of magnetic field. Experiments have been conducted on films 145-700 Å thick using 8-mm- and 4-mm-wavelength microwave radiation, primarily with the magnetic field parallel to the plane of the film, but also as a function of angle between the magnetic

  7. Superconducting-gap-node spectroscopy using nonlinear electrodynamics

    Microsoft Academic Search

    I. Zutic; Oriol T. Valls

    1997-01-01

    We present a method to determine the nodal structure of the energy gap of unconventional superconductors such as high-T{sub c} materials. We show how nonlinear electrodynamics phenomena in the Meissner regime, arising from the presence of lines on the Fermi surface where the superconducting energy gap is very small or zero, can be used to perform {open_quotes}node spectroscopy,{close_quotes} that is,

  8. Energy-Gap Dynamics of Superconducting NbN Thin Films Studied by Time-Resolved Terahertz Spectroscopy

    Microsoft Academic Search

    M. Beck; M. Klammer; S. Lang; P. Leiderer; V. V. Kabanov; G. N. Gol'Tsman; J. Demsar

    2011-01-01

    Using time-domain terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparticle recombination rate, the Cooper pair-breaking rate

  9. Extended Supersymmetry in Gapped and Superconducting Graphene

    E-print Network

    V. K. Oikonomou

    2014-11-30

    In view of the many quantum field theoretical descriptions of graphene in $2+1$ dimensions, we present another field theoretical feature of graphene, in the presence of defects. Particularly, we shall be interested in gapped graphene in the presence of a domain wall and also for superconducting graphene in the presence of a vortex. As we explicitly demonstrate, the gapped graphene electrons that are localized on the domain wall are associated with four $N=2$ one dimensional supersymmetries, with each pair combining to form an extended $N=4$ supersymmetry with non-trivial topological charges. The case of superconducting graphene is more involved, with the electrons localized on the vortex being associated with $n$ one dimensional supersymmetries, which in turn combine to form an $N=2n$ extended supersymmetry with no-trivial topological charges. As we shall prove, all supersymmetries are unbroken, a feature closely related to the number of the localized fermions and also to the exact form of the associated operators. In addition, the corresponding Witten index is invariant under compact and odd perturbations.

  10. Extended Supersymmetry in Gapped and Superconducting Graphene

    E-print Network

    V. K. Oikonomou

    2015-06-27

    In view of the many quantum field theoretical descriptions of graphene in $2+1$ dimensions, we present another field theoretical feature of graphene, in the presence of defects. Particularly, we shall be interested in gapped graphene in the presence of a domain wall and also for superconducting graphene in the presence of a vortex. As we explicitly demonstrate, the gapped graphene electrons that are localized on the domain wall are associated with four $N=2$ one dimensional supersymmetries, with each pair combining to form an extended $N=4$ supersymmetry with non-trivial topological charges. The case of superconducting graphene is more involved, with the electrons localized on the vortex being associated with $n$ one dimensional supersymmetries, which in turn combine to form an $N=2n$ extended supersymmetry with no-trivial topological charges. As we shall prove, all supersymmetries are unbroken, a feature closely related to the number of the localized fermions and also to the exact form of the associated operators. In addition, the corresponding Witten index is invariant under compact and odd perturbations.

  11. A Proposed New Measurement of the Superconducting Gap in YBa2Cu3O7

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bagayoko, D.

    2007-03-01

    The superconducting energy gap of YBa2Cu3O7 (YBCO) varies strongly with kand from a sheet of the Fermi surface to another. The strong anisotropic superconducting gap in high Tc materials such as YBCO has led to conflicting d-wave and s-wave interpretations. We have utilized electronic wave functions from the ab-initio density functional calculation and the related electron-phonon interaction matrix elements for the calculation of the superconducting gap values of YBCO. For three pieces of the Fermi surfaces, the calculated superconducting gaps exhibit a strong anisotropy. In contrast, we have found that the superconducting gap on one sheet of the Fermi surface around S-point only shows a minor variation from about 18 meV to 25 meV. Especially, there is no node on this sheet of the Fermi surface. We propose a new test measurement of the superconducting gap of YBCO on this sheet of the Fermi surface around the S-point. This measurement is expected to shed light on the gap symmetry properties of high Tc superconductors. This work was funded in part by NSF (Award No. 0508245) and ONR (Grant No: N00014-05-1-0009).

  12. Superconducting-gap-node spectroscopy using nonlinear electrodynamics

    SciTech Connect

    Zutic, I.; Valls, O.T. [School of Physics and Astronomy and Minnesota Supercomputer Institute, University of Minnesota, Minneapolis, Minnesota 55455-0149 (United States)

    1997-11-01

    We present a method to determine the nodal structure of the energy gap of unconventional superconductors such as high-T{sub c} materials. We show how nonlinear electrodynamics phenomena in the Meissner regime, arising from the presence of lines on the Fermi surface where the superconducting energy gap is very small or zero, can be used to perform {open_quotes}node spectroscopy,{close_quotes} that is, as a sensitive bulk probe to locate the angular position of those lines. In calculating the nonlinear supercurrent response, we include the effects of orthorhombic distortion and a-b plane anisotropy. Analytic results presented demonstrate a systematic way to experimentally distinguish order parameters of different symmetries, including cases with mixed symmetry (for example, d+s and s+id). We consider, as suggested by various experiments, order parameters with predominantly d-wave character, and describe how to determine the possible presence of other symmetries. The nonlinear magnetic moment displays a distinct behavior if nodes in the gap are absent but regions with small finite values of the energy gap exist. {copyright} {ital 1997} {ital The American Physical Society}

  13. Momentum dependence of the superconducting gap and in-gap states in MgB2 multiband superconductor

    NASA Astrophysics Data System (ADS)

    Mou, Daixiang; Jiang, Rui; Taufour, Valentin; Bud'ko, S. L.; Canfield, P. C.; Kaminski, Adam

    2015-06-01

    We use tunable laser-based angle-resolved photoemission spectroscopy to study the electronic structure of the multiband superconductor MgB2. These results form the baseline for detailed studies of superconductivity in multiband systems. We find that the magnitude of the superconducting gap on both ? bands follows a BCS-like variation with temperature with ?0˜7 meV . The value of the gap is isotropic within experimental uncertainty and in agreement with a pure s -wave pairing symmetry. We also observe in-gap states confined to kF of the ? band that occur at some locations of the sample surface. The energy of this excitation, ˜3 meV, is somewhat larger than the previously reported gap on ? Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin.

  14. a Proposed New Measurement of the Superconducting Gap in YBa2Cu3O7

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bagayoko, D.

    The superconducting energy gap of YBa2Cu3O7 (YBCO) varies strongly with ?c{k} and from a sheet of the Fermi surface to another. The strong anisotropic superconducting gap in high Tc materials such as YBCO has led to conflicting d-wave and s-wave interpretations. We have utilized electronic wave functions from the ab-initio density functional calculation and the related electron-phonon interaction matrix elements for the calculation of the superconducting gap values of YBCO. We have found that the superconducting gap on one sheet of the Fermi surface around S-point only shows a minor variation from about 18 meV to 25 meV. Especially, there is no node on this sheet of the Fermi surface around the S-point. We propose a new test measurement of the superconducting gap of YBCO on this sheet of the Fermi surface around the S-point in the Brillouin zone. This measurement is expected to shed light on the gap symmetry properties of high Tc superconductors.

  15. Superconducting energy gap and normal state conductivity of a single domain Y sub 1 Ba sub 2 Cu sub 3 O sub 7 crystal

    SciTech Connect

    Schlesinger, Z.; Collins, R.T.; Holtzberg, F.; Feild, C.; Blanton, S.H. (International Business Machines Corp., Yorktown Heights, NY (USA). Thomas J. Watson Research Center); Welp, U. (Science and Technology Center for Superconductivity (USA) Argonne National Lab., IL (USA)); Crabtree, G.W.; Fang, Y. (Argonne National Lab., IL (USA)); Liu, J.Z. (California Univ., Davis, CA (USA). Dept. of Physics)

    1990-09-01

    Using polarized reflectivity measurements of single domain crystals, we are able to distinguish chain and plane contributions to the infrared conductivity of Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7}. A substantial chain contribution to {sigma}({omega}) persisting to low frequency and temperature is observed. For the intrinsic conductivity of the CuO{sub 2} planes a superconducting energy gap of 500 cm{sup {minus}1} (2{Delta}/k{Tc} {approx equal} 8) is evident in the infrared data, while the normal state conductivity drops much more slowly with {omega} than the ordinary Drude form, and can be described in terms of a scattering rate {Dirac h}/{tau}* {approximately} kT + {Dirac h}{omega} at low frequency. The former result (2{Delta}/k{Tc} {approx equal} 8) suggests substantial suppression of {Tc}; the latter, that Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} is not ordinary Fermi liquid. 26 refs., 4 figs.

  16. Relation between the nodal and antinodal gap and critical temperature in superconducting Bi2212

    PubMed Central

    Anzai, H.; Ino, A.; Arita, M.; Namatame, H.; Taniguchi, M.; Ishikado, M.; Fujita, K.; Ishida, S.; Uchida, S.

    2013-01-01

    An energy gap is, in principle, a dominant parameter in superconductivity. However, this view has been challenged for the case of high-Tc cuprates, because anisotropic evolution of a d-wave-like superconducting gap with underdoping has been difficult to formulate along with a critical temperature Tc. Here we show that a nodal-gap energy 2?N closely follows 8.5 kBTc with underdoping and is also proportional to the product of an antinodal gap energy ?* and a square-root superfluid density ?Ps for Bi2Sr2CaCu2O8+?, using low-energy synchrotron-radiation angle-resolved photoemission. The quantitative relations imply that the distinction between the nodal and antinodal gaps stems from the separation of the condensation and formation of electron pairs, and that the nodal-gap suppression represents the substantial phase incoherence inherent in a strong-coupling superconducting state. These simple gap-based formulae reasonably describe a crucial part of the unconventional mechanism governing Tc. PMID:23652003

  17. Nodal to nodeless superconducting energy gap structure change concomitant with Fermi surface reconstruction in the heavy-fermion CeCoIn?

    DOE PAGESBeta

    Kim, Hyunsoo; Petrovic, C.; Tanatar, M. A.; Flint, R.; Hu, Rongwei; White, B. D.; Lum, I. K.; Maple, M. B.; Prozorov, R.

    2015-01-01

    The London penetration depth ?(T) was measured in single crystals of Ce1?xRxCoIn?, R=La, Nd, and Yb down to Tmin ? 50??mK (Tc/Tmin ~50) using a tunnel-diode resonator. In the cleanest samples ??(T) is best described by the power law, ??(T) ? Tn, with n ~ 1, consistent with line nodes. Substitutions of Ce with La, Nd, and Yb lead to similar monotonic suppressions of Tc, however, the effects on ??(T) differ. While La and Nd dopings lead to increase of the exponent n and saturation at n ~ 2, as expected for a dirty nodal superconductor, Yb doping leads tomore »n > 3, suggesting a change from nodal to nodeless superconductivity. This superconducting gap structure change happens in the same doping range where changes of the Fermi surface topology were reported, implying that the nodal structure and Fermi surface topology are closely linked.« less

  18. Dome-like variation of the superconducting gap anisotropy in Fe-based superconductors

    DOE PAGESBeta

    Prozorov, Ruslan; Cho, Kyuil; Kim, Hyong June; Tanatar, Makariy

    2013-07-17

    Experiments performed on different iron-based superconductors suggest a variety of possible structures of the superconducting energy gap, both nodeless and nodal. To understand the pairing mechanisms, it is important to identify common features in the behavior of different materials. Measurements of the temperature - dependent London penetration depth provide important information on the structure of the superconducting gap. We show that despite significant differences between different iron - based superconductors, there is a universal trend: the gap is least anisotropic at the optimal doping and its anisotropy increases upon the departure towards underdoped and overdoped ends of the ''superconducting dome''.more »This trend is not related to the presence of the long-range magnetic order in the underdoped state.« less

  19. Dome-like variation of the superconducting gap anisotropy in Fe-based superconductors

    DOE PAGESBeta

    Prozorov, Ruslan [Ames Lab., Ames, IA (United States); Cho, Kyuil [Ames Lab., Ames, IA (United States); Kim, Hyong June [Ames Lab., Ames, IA (United States); Tanatar, Makariy [Ames Lab., Ames, IA (United States)

    2013-07-17

    Experiments performed on different iron-based superconductors suggest a variety of possible structures of the superconducting energy gap, both nodeless and nodal. To understand the pairing mechanisms, it is important to identify common features in the behavior of different materials. Measurements of the temperature - dependent London penetration depth provide important information on the structure of the superconducting gap. We show that despite significant differences between different iron - based superconductors, there is a universal trend: the gap is least anisotropic at the optimal doping and its anisotropy increases upon the departure towards underdoped and overdoped ends of the ''superconducting dome''. This trend is not related to the presence of the long-range magnetic order in the underdoped state.

  20. Noise and Bandwidth Measurements of Diffusion-Cooled Nb Hot-Electron Bolometer Mixers at Frequencies Above the Superconductive Energy Gap

    NASA Technical Reports Server (NTRS)

    Wyss, R. A.; Karasik, B. S.; McGrath, W. R.; Bumble, B.; LeDuc, H.

    1999-01-01

    Diffusion-cooled Nb hot-electron bolometer (HEB) mixers have the potential to simultaneously achieve high intermediate frequency (IF) bandwidths and low mixer noise temperatures for operation at THz frequencies (above the superconductive gap energy). We have measured the IF signal bandwidth at 630 GHz of Nb devices with lengths L = 0.3, 0.2, and 0.1 micrometer in a quasioptical mixer configuration employing twin-slot antennas. The 3-dB EF bandwidth increased from 1.2 GHz for the 0.3 gm long device to 9.2 GHz for the 0.1 gm long device. These results demonstrate the expected 1/L squared dependence of the IF bandwidth at submillimeter wave frequencies for the first time, as well as the largest EF bandwidth obtained to date. For the 0.1 gm device, which had the largest bandwidth, the double sideband (DSB) noise temperature of the receiver was 320-470 K at 630 GHz with an absorbed LO power of 35 nW, estimated using the isothermal method. A version of this mixer with the antenna length scaled for operation at 2.5 THz has also been tested. A DSB receiver noise temperature of 1800 plus or minus 100 K was achieved, which is about 1,000 K lower than our previously reported results. These results demonstrate that large EF bandwidth and low-noise operation of a diffusion-cooled HEB mixer is possible at THz frequencies with the same device geometry.

  1. Nodal to nodeless superconducting energy gap structure change concomitant with Fermi surface reconstruction in the heavy-fermion CeCoIn?

    SciTech Connect

    Kim, Hyunsoo [Iowa State Univ., Ames, IA (United States); Petrovic, C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Tanatar, M. A. [Iowa State Univ., Ames, IA (United States); Flint, R. [Iowa State Univ., Ames, IA (United States); Hu, Rongwei [Brookhaven National Lab. (BNL), Upton, NY (United States); White, B. D. [Univ. of California, San Diego, La Jolla, CA (United States); Lum, I. K. [Univ. of California, San Diego, La Jolla, CA (United States); Maple, M. B. [Univ. of California, San Diego, La Jolla, CA (United States); Prozorov, R. [Iowa State Univ., Ames, IA (United States)

    2015-01-01

    The London penetration depth ?(T) was measured in single crystals of Ce1?xRxCoIn?, R=La, Nd, and Yb down to Tmin ? 50??mK (Tc/Tmin ~50) using a tunnel-diode resonator. In the cleanest samples ??(T) is best described by the power law, ??(T) ? Tn, with n ~ 1, consistent with line nodes. Substitutions of Ce with La, Nd, and Yb lead to similar monotonic suppressions of Tc, however, the effects on ??(T) differ. While La and Nd dopings lead to increase of the exponent n and saturation at n ~ 2, as expected for a dirty nodal superconductor, Yb doping leads to n > 3, suggesting a change from nodal to nodeless superconductivity. This superconducting gap structure change happens in the same doping range where changes of the Fermi surface topology were reported, implying that the nodal structure and Fermi surface topology are closely linked.

  2. Superconducting magnetic energy storage

    SciTech Connect

    Hassenzahl, W.

    1988-08-01

    Recent programmatic developments in Superconducting Magnetic Energy Storage (SMES) have prompted renewed and widespread interest in this field. In mid 1987 the Defense Nuclear Agency, acting for the Strategic Defense Initiative Office, issued a request for proposals for the design and construction of SMES Engineering Test Model (ETM). Two teams, one led by Bechtel and the other by Ebasco, are now engaged in the first phase of the development of a 10 to 20 MWhr ETM. This report presents the rationale for energy storage on utility systems, describes the general technology of SMES, and explains the chronological development of the technology. The present ETM program is outlined; details of the two projects for ETM development are described in other papers in these proceedings. The impact of high T/sub c/ materials on SMES is discussed. 69 refs., 3 figs., 3 tabs.

  3. Evidence for fully gapped strong coupling s-wave superconductivity in Bi4O4S3.

    PubMed

    Shruti; Srivastava, P; Patnaik, S

    2013-08-01

    We report on the superconducting gap and pairing symmetry in the layered superconductor Bi4O4S3. The measurement of temperature dependence of magnetic penetration depth was carried out using the tunnel diode oscillator technique. It is observed that Bi4O4S3 is a conventional s-wave type superconductor with a fully developed gap. The zero-temperature value of the superconducting energy gap ?0 was found to be 1.54 meV, corresponding to the ratio 2?0/k(B)T(c) = 7.2 which is much higher than the BCS value of 3.53. In the superconducting range, superfluid density is very well described by the single gap s-wave model. PMID:23838210

  4. Superconducting energy storage

    SciTech Connect

    Giese, R.F.

    1993-10-01

    This report describes the status of energy storage involving superconductors and assesses what impact the recently discovered ceramic superconductors may have on the design of these devices. Our description is intended for R&D managers in government, electric utilities, firms, and national laboratories who wish an overview of what has been done and what remains to be done. It is assumed that the reader is acquainted with superconductivity, but not an expert on the topics discussed here. Indeed, it is the author`s aim to enable the reader to better understand the experts who may ask for the reader`s attention, support, or funding. This report may also inform scientists and engineers who, though expert in related areas, wish to have an introduction to our topic.

  5. Hard proximity induced superconducting gap in semiconductor - superconductor epitaxial hybrids

    NASA Astrophysics Data System (ADS)

    Jespersen, Thomas; Krogstrup, Peter; Ziino, Nino; Albrecht, Sven; Chang, Willy; Madsen, Morten; Johnson, Erik; Kuemmeth, Ferdinand; Nygård, Jesper; Marcus, Charles

    2015-03-01

    We present molecular beam epitaxy grown InAs semiconductor nanowires capped with a shell of aluminum (superconductor). The hybrid wires are grown without breaking vacuum, resulting in an epitaxial interface between the two materials as demonstrated by detailed transmission electron microscopy and simulations. The domain matching at the interface is discussed. Incorporating the epitaxial nanowire hybrids in electrical devices we performed detailed tunneling spectroscopy of the proximity induced superconducting gap in the InAs core at 20 mK. We find the sub-gap conductance being at least a factor 200 smaller than the normal state value (gap hardness). This is a significant improvement compared to devices fabricated by conventional lithographic methods and metal evaporation showing no more than a factor of ~ 5 . The epitaxial hybrids seem to solve the soft gap problem associated with the use of nanowire hybrids for future applications in topological quantum information based on Majorana zero modes. Research supported by Microsoft Station Q, Danish National Research Foundation, Villum Foundation, Lundbeck Foundation, and the European Commission.

  6. Energy gaps in ?-graphdiyne nanoribbons

    NASA Astrophysics Data System (ADS)

    Niu, X. N.; Yang, D. Z.; Si, M. S.; Xue, D. S.

    2014-04-01

    ?-graphdiyne is a novel predicted Dirac cone material, which is similar to graphene. But the absence of a band gap significantly limits its practical applications. In order to extend this limitation, an opening of energy gap is needed. To this end, we resort to the nanoribbon structure of ?-graphdiyne. This is a conventional proposal to open up the energy gaps in nanomaterials. The results show that both the armchair and the zigzag ?-graphdiyne nanoribbons do generate energy gaps, which are width-dependent. In addition, the underlying mechanism of this opening is explored. The former is ascribed to the combination of quantum confinement and edges' effect, while the latter arises from the edge magnetic ordering. These novel nanoribbons with opening energy gaps would be potentially used in electronic devices.

  7. Energy gaps in ?-graphdiyne nanoribbons

    SciTech Connect

    Niu, X. N.; Yang, D. Z.; Si, M. S., E-mail: sims@lzu.edu.cn; Xue, D. S., E-mail: xueds@lzu.edu.cn [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

    2014-04-14

    ?-graphdiyne is a novel predicted Dirac cone material, which is similar to graphene. But the absence of a band gap significantly limits its practical applications. In order to extend this limitation, an opening of energy gap is needed. To this end, we resort to the nanoribbon structure of ?-graphdiyne. This is a conventional proposal to open up the energy gaps in nanomaterials. The results show that both the armchair and the zigzag ?-graphdiyne nanoribbons do generate energy gaps, which are width-dependent. In addition, the underlying mechanism of this opening is explored. The former is ascribed to the combination of quantum confinement and edges' effect, while the latter arises from the edge magnetic ordering. These novel nanoribbons with opening energy gaps would be potentially used in electronic devices.

  8. Superconducting energy storage magnet

    NASA Technical Reports Server (NTRS)

    Boom, Roger W. (Inventor); Eyssa, Yehia M. (Inventor); Abdelsalam, Mostafa K. (Inventor); Huang, Xianrui (Inventor)

    1993-01-01

    A superconducting magnet is formed having composite conductors arrayed in coils having turns which lie on a surface defining substantially a frustum of a cone. The conical angle with respect to the central axis is preferably selected such that the magnetic pressure on the coil at the widest portion of the cone is substantially zero. The magnet structure is adapted for use as an energy storage magnet mounted in an earthen trench or tunnel where the strength the surrounding soil is lower at the top of the trench or tunnel than at the bottom. The composite conductor may be formed having a ripple shape to minimize stresses during charge up and discharge and has a shape for each ripple selected such that the conductor undergoes a minimum amount of bending during the charge and discharge cycle. By minimizing bending, the working of the normal conductor in the composite conductor is minimized, thereby reducing the increase in resistance of the normal conductor that occurs over time as the conductor undergoes bending during numerous charge and discharge cycles.

  9. Properties of High Temperature Superconducting Magnet With Optimized Air Gap Between Pancake Windings

    Microsoft Academic Search

    Youngmin Kim; Myunghwan Ku; Gueesoo Cha

    2011-01-01

    In a magnet with pancake windings, inserting a gap between the pancake windings can increase the central magnetic field. This paper shows the optimized length of each gap is able to maximize the central magnetic field. Inserting a gap also im- proves field uniformity because the pancake windings are spread across a wider area. A high temperature superconducting (HTS) magnet

  10. Energy gaps in graphene nanoribbons.

    PubMed

    Son, Young-Woo; Cohen, Marvin L; Louie, Steven G

    2006-11-24

    Based on a first-principles approach, we present scaling rules for the band gaps of graphene nanoribbons (GNRs) as a function of their widths. The GNRs considered have either armchair or zigzag shaped edges on both sides with hydrogen passivation. Both varieties of ribbons are shown to have band gaps. This differs from the results of simple tight-binding calculations or solutions of the Dirac's equation based on them. Our ab initio calculations show that the origin of energy gaps for GNRs with armchair shaped edges arises from both quantum confinement and the crucial effect of the edges. For GNRs with zigzag shaped edges, gaps appear because of a staggered sublattice potential on the hexagonal lattice due to edge magnetization. The rich gap structure for ribbons with armchair shaped edges is further obtained analytically including edge effects. These results reproduce our ab initio calculation results very well. PMID:17155765

  11. Penetration depth study of superconducting gap structure of 2H-NbSe2.

    PubMed

    Fletcher, J D; Carrington, A; Diener, P; Rodière, P; Brison, J P; Prozorov, R; Olheiser, T; Giannetta, R W

    2007-02-01

    We report measurements of the temperature dependence of both in-plane and out-of-plane penetration depths (lambda(a) and lambda(c), respectively) in 2H-NbSe2. Measurements were made with a radio-frequency tunnel diode oscillator circuit at temperatures down to 100 mK. Analysis of the anisotropic superfluid density shows that a reduced energy gap is located on one or more of the quasi-two-dimensional Nb Fermi surface sheets rather than on the Se sheet, in contrast with some previous reports. This result suggests that the gap structure is not simply related to the weak electron-phonon coupling on the Se sheet and is therefore important for microscopic models of anisotropic superconductivity in this compound. PMID:17358886

  12. Signature of superconductivity in UBe13 as seen by neutron scattering: Superconducting and magnetic energy scales

    NASA Astrophysics Data System (ADS)

    Hiess, A.; Schneidewind, A.; Stockert, O.; Fisk, Z.

    2014-06-01

    We here present inelastic neutron scattering results on the strongly correlated cubic superconductor UBe13 (Tc = 0.85 K) obtained on a large single crystal by high-resolution cold neutron three-axis spectroscopy. We observed spin dynamics at a unique momentum space position building up below T ˜50 K and changing significantly on entering the superconducting state. The observed short-range longitudinal character of the correlations can be understood as a result of competing magnetic interactions. The energy dependence in the normal state reflects the energy scales determined from specific heat, whereas the low-temperature data suggest the opening of a superconducting gap. Our findings are consistent with a superconducting order parameter exhibiting s ± or d-wave symmetry and placing pure UBe13 in the strong coupling regime.

  13. Doping - dependent anisotropy of the superconducting gap in underdoped pnictide superconductors

    NASA Astrophysics Data System (ADS)

    Prozorov, Ruslan

    2012-02-01

    The in-plane London penetration depth, ??(T), was studied in single crystals of Ba1-xKxFe2As2 (``Ba122") and Ca10(Pt3As8)[(Fe1-xPtx)2As2]5 (``10-3-8"). Whereas in Ba122 magnetism and superconductivity coexist in the underdoped regime, the 10-3-8 compound exhibits a clear separation of two order parameters. By comparing the results obtained in these two systems, we could study general features of the superconducting gap structure as function of doping in the underdoped regime. Similar to all other pnictides, the low-temperature variation of London penetration depth exhibits a power-law behavior, ??(T)= AT^n, in both systems. Moving towards the underdoped edge of the superconducting dome, the exponent n decreases well below scattering - limited value of n=2 and, at the same time, the pre-factor A increases. Both trends indicate an increasing anisotropy of the superconducting gap in more underdoped compounds. These and previous results suggest that the development of the superconducting gap anisotropy towards the underdoped edge of the superconducting dome is an intrinsic property of iron pnictides, similar to the known tendency on the overdoped side where magnetism and superconductivity do not interfere.[4pt] In collboration with M.A. Tanatar, H. Kim, The Ames Laboratory; Bing Shen, Hai-Hu Wen, Nanjing University; and N. Ni, R.J. Cava, Princeton University.

  14. Pseudogap from ARPES experiment: Three gaps in cuprates and topological superconductivity (Review Article)

    NASA Astrophysics Data System (ADS)

    Kordyuk, A. A.

    2015-05-01

    A term first coined by Mott back in 1968 a "pseudogap" is the depletion of the electronic density of states at the Fermi level, and pseudogaps have been observed in many systems. However, since the discovery of the high-temperature superconductors (HTSC) in 1986, the central role attributed to the pseudogap in these systems has meant that by many researchers now associate the term pseudogap exclusively with the HTSC phenomenon. Recently, the problem has got a lot of new attention with the rediscovery of two distinct energy scales ("two-gap scenario") and charge density waves patterns in the cuprates. Despite many excellent reviews on the pseudogap phenomenon in HTSC, published from its very discovery up to now, the mechanism of the pseudogap and its relation to superconductivity are still open questions. The present review represents a contribution dealing with the pseudogap, focusing on results from angle resolved photoemission spectroscopy (ARPES) and ends up with the conclusion that the pseudogap in cuprates is a complex phenomenon which includes at least three different "intertwined" orders: spin and charge density waves and preformed pairs, which appears in different parts of the phase diagram. The density waves in cuprates are competing to superconductivity for the electronic states but, on the other hand, should drive the electronic structure to vicinity of Lifshitz transition, that could be a key similarity between the superconducting cuprates and iron-based superconductors. One may also note that since the pseudogap in cuprates has multiple origins there is no need to recoin the term suggested by Mott.

  15. Observation of a ubiquitous three-dimensional superconducting gap function in optimally doped Ba0.6K0.4Fe2As2

    NASA Astrophysics Data System (ADS)

    Xu, Y.-M.; Huang, Y.-B.; Cui, X.-Y.; Razzoli, E.; Radovic, M.; Shi, M.; Chen, G.-F.; Zheng, P.; Wang, N.-L.; Zhang, C.-L.; Dai, P.-C.; Hu, J.-P.; Wang, Z.; Ding, H.

    2011-03-01

    The iron-pnictide superconductors have a layered structureformed by stacks of FeAs planes from which the superconductivity originates. Given the multiband and quasi three-dimensional (3D) electronic structure of these high-temperature superconductors, knowledge of the quasi-3D superconducting (SC) gap is essential for understanding the superconducting mechanism. By using the kz capability of angle-resolved photoemission, we completely determined the SC gap on all five Fermi surfaces (FSs) in three dimensions on Ba0.6K0.4Fe2As2 samples. We found a marked kz dispersion of the SC gap, which can derive only from interlayer pairing. Remarkably, the SC energy gaps can be described by a single 3D gap function with two energy scales characterizing the strengths of intralayer ?1 and interlayer ?2 pairing. The anisotropy ratio ?1/?2, determined from the gap function, is close to the c-axis anisotropy ratio of the magnetic exchange coupling Jc/Jab in the parent compound. The ubiquitous gap function for all the 3D FSs reveals that pairing is short-ranged and strongly constrains the possible pairing force in the pnictides. A suitable candidate could arise from short-range antiferromagnetic fluctuations.

  16. Effect of external magnetic field on superconducting and spin density wave gaps of high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Pradhan, B.; Raj, B. K.; Rout, G. C.

    2009-07-01

    A theoretical model is addressed here to study the interplay of the superconductivity (SC) and the spin density wave (SDW) long range orders in underdoped region in the vicinity of on-set of superconductivity in presence of an external magnetic field. The order parameters are calculated by using Zubarev’s technique of Green’s functions and determined numerically self-consistently. The gap parameters are found to be strongly coupled to each other through their coupling constants. The interplay displays BCS type two gaps in the quasi-particle density of states (DOS) which resemble the tunneling conductance of STM experiments. The gap edges in the DOS appear at ±(z+z1) and ±(z-z1). The applied magnetic field further induces Zeeman splitting which is explained on the basis of spin-filter effect of tunneling experiment.

  17. Point-contact spectroscopy investigation of superconducting-gap anisotropy in the nickel borocarbide compound LuNi2B2C 

    E-print Network

    Bobrov, NL; Beloborod'ko, SI; Tyutrina, LV; Yanson, IK; Naugle, Donald G.; Rathnayaka, KDD.

    2005-01-01

    Point contacts are used to investigate the anisotropy of the superconducting energy gap in LuNi2B2C in the ab plane and along the c axis. It is shown that the experimental curves should be described assuming that the ...

  18. Superconductivity: Phenomenology

    SciTech Connect

    Falicov, L.M.

    1988-08-01

    This document discusses first the following topics: (a) The superconducting transition temperature; (b) Zero resistivity; (c) The Meissner effect; (d) The isotope effect; (e) Microwave and optical properties; and (f) The superconducting energy gap. Part II of this document investigates the Ginzburg-Landau equations by discussing: (a) The coherence length; (b) The penetration depth; (c) Flux quantization; (d) Magnetic-field dependence of the energy gap; (e) Quantum interference phenomena; and (f) The Josephson effect.

  19. Tantalum nitride superconducting single-photon detectors with low cut-off energy

    NASA Astrophysics Data System (ADS)

    Engel, A.; Aeschbacher, A.; Inderbitzin, K.; Schilling, A.; Il'in, K.; Hofherr, M.; Siegel, M.; Semenov, A.; Hübers, H.-W.

    2012-02-01

    Materials with a small superconducting energy gap are expected to favor a high detection efficiency of low-energy photons in superconducting nanowire single-photon detectors. We developed a TaN detector with smaller gap and lower density of states at the Fermi energy than in comparable NbN devices, while other relevant parameters remain essentially unchanged. The observed reduction of the minimum photon energy required for direct detection is in line with model predictions of ?1/3 as compared to NbN.

  20. Raising gradient limitations in 2.1?GHz superconducting photonic band gap accelerator cavities

    SciTech Connect

    Simakov, Evgenya I., E-mail: smirnova@lanl.gov; Arsenyev, Sergey A.; Haynes, W. Brian; Shchegolkov, Dmitry Yu.; Suvorova, Natalya A.; Tajima, Tsuyoshi [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545 (United States); Boulware, Chase H.; Grimm, Terry L. [Niowave, Inc., 1012 North Walnut Street, Lansing, Michigan 48906 (United States)

    2014-06-16

    We report results from recent 2.1?GHz superconducting radio frequency (SRF) photonic band gap (PBG) resonator experiments at Los Alamos. Two 2.1?GHz PBG cells with elliptical rods were fabricated and tested at high power in a liquid helium bath at the temperatures of 4?K and below 2?K. The described SRF PBG cells were designed with a particular emphasis on changing the shape of the PBG rods to reduce peak surface magnetic fields and at the same time to preserve its effectiveness at damping higher-order-modes. The superconducting PBG cavities have great potential for damping long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. The cells performed in accordance with simulation's predictions and the maximum achieved accelerating gradient was 18.3 MV/m. This represents a 30% increase over gradients previously demonstrated in superconducting PBG cavities with round rods.

  1. Raising gradient limitations in 2.1 GHz superconducting photonic band gap accelerator cavities

    NASA Astrophysics Data System (ADS)

    Simakov, Evgenya I.; Arsenyev, Sergey A.; Haynes, W. Brian; Shchegolkov, Dmitry Yu.; Suvorova, Natalya A.; Tajima, Tsuyoshi; Boulware, Chase H.; Grimm, Terry L.

    2014-06-01

    We report results from recent 2.1 GHz superconducting radio frequency (SRF) photonic band gap (PBG) resonator experiments at Los Alamos. Two 2.1 GHz PBG cells with elliptical rods were fabricated and tested at high power in a liquid helium bath at the temperatures of 4 K and below 2 K. The described SRF PBG cells were designed with a particular emphasis on changing the shape of the PBG rods to reduce peak surface magnetic fields and at the same time to preserve its effectiveness at damping higher-order-modes. The superconducting PBG cavities have great potential for damping long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. The cells performed in accordance with simulation's predictions and the maximum achieved accelerating gradient was 18.3 MV/m. This represents a 30% increase over gradients previously demonstrated in superconducting PBG cavities with round rods.

  2. The effect of magnetic order on the superconducting gap in the co-existence phase of Fe-pnictides

    NASA Astrophysics Data System (ADS)

    Hinojosa Alvarado, Alberto; Chubukov, Andrey

    2014-03-01

    We study the structure and symmetry of the superconducting gap in the presence of spin density wave (SDW) order in iron-based superconductors. We show that SDW order generally induces a spin-triplet component of the gap, in addition to the conventional spin singlet. We further show that, in some range of temperatures below Tc, the phases of superconducting order parameters on different reconstructed Fermi surfaces differ by an amount other than 0 or ?, i.e., superconductivity directly reflects the breaking of time-reversal symmetry by SDW order. We specifically consider co-existing SDW and superconducting orders in a model with circular hole pockets and elliptic electronic pockets and present analytical results for the phase diagram and the structure of the superconducting gap at various temperatures.

  3. Molecular pairing and fully gapped superconductivity in Yb-doped CeCoIn(5).

    PubMed

    Erten, Onur; Flint, Rebecca; Coleman, Piers

    2015-01-16

    The recent observation of fully gapped superconductivity in Yb doped CeCoIn_{5} poses a paradox, for the disappearance of nodes suggests that they are accidental, yet d-wave symmetry with protected nodes is well established by experiment. Here, we show that composite pairing provides a natural resolution: in this scenario, Yb doping drives a Lifshitz transition of the nodal Fermi surface, forming a fully gapped d-wave molecular superfluid of composite pairs. The T^{4} dependence of the penetration depth associated with the sound mode of this condensate is in accordance with observation. PMID:25635559

  4. Observation of a ubiquitous three-dimensional superconducting gap function in optimally-doped Ba0.6 K 0.4 Fe 2 As 2

    NASA Astrophysics Data System (ADS)

    Xu, Y.-M.; Huang, Y.-B.; Cui, X.-Y.; Razzoli, E.; Radovic, M.; Shi, M.; Chen, G.-F.; Zheng, P.; Wang, N.-L.; Zhang, C.-L.; Dai, P.-C.; Hu, J.-P.; Wang, Z.; Ding, H.

    2011-03-01

    The knowledge of the quasi-three-dimensional (3D) superconducting (SC) gap is essential for understanding the superconducting mechanism of the iron-pnictides highlighted by their multiband and quasi-3D electronic structure. By using the kz -capability of angle-resolved photoemission, we completely determined the SC gap on all five FSs in 3D on Ba 0.6 K0.4 Fe 2 As 2 samples. We found a significant kz dispersion of the SC gap which can only derive from interlayer pairing. Remarkably, the SC energy gaps can be described by a single 3D gap function with two energy scales characterizing the strengths of intra-layer (?1) and interlayer (?2) pairing. The anisotropy ratio ?2 /?1 , determined from the gap function, is close to the c -axis anisotropy ratio of the magnetic exchange coupling Jc /Jab in the parent compound. The ubiquitous gap function for all the 3D FSs reveals that pairing is short-ranged and strongly constrain the possible pairing force in the pnictides.

  5. Field dependence of the superconducting gap in YPd2Sn: A ?SR and NMR study

    NASA Astrophysics Data System (ADS)

    Morenzoni, E.; Saadaoui, H.; Amato, A.; Baines, C.; Luetkens, H.; Pomjakushina, E.; Pikulski, M.; Shiroka, T.

    2014-12-01

    We have performed muon spin rotation/relaxation and 119Sn nuclear magnetic resonance (NMR) measurements to study the vortex state of polycrystalline samples of YPd2Sn (Tc = 5.4 K), over a wide range of applied magnetic fields up to Bc2(T). Measurements in the vortex state provide the temperature dependence of the effective magnetic penetration depth ?(T) and the field dependence of the superconducting gap ?(0). The results are consistent with a very dirty s-wave BCS superconductor with ?(0) = 212(1) nm, a gap ?(0) = 0.85(3) meV, and a Ginzburg-Landau coherence length ?GL(0) ? 23 nm. The ?SR data in a broad range of applied fields are well reproduced by taking into account a field-related reduction of the effective superconducting gap. Interestingly, the ratio 2?(0)/(kBTc) appears to a good approximation to be field-independent, with a value at low field of 3.85(9), implying a field dependence of the gap . We discuss the significance of this result.

  6. Energy Gaps in Graphene Nanoribbons

    Microsoft Academic Search

    Young-Woo Son; Marvin L. Cohen; Steven G. Louie

    2006-01-01

    Based on a first-principles approach, we present scaling rules for the band\\u000agaps of graphene nanoribbons (GNRs) as a function of their widths. The GNRs\\u000aconsidered have either armchair or zigzag shaped edges on both sides with\\u000ahydrogen passivation. Both varieties of ribbons are shown to have band gaps.\\u000aThis differs from the results of simple tight-binding calculations or solutions

  7. Energy loss in spark gap switches

    SciTech Connect

    Oreshkin, V. I., E-mail: oreshkin@ovpe.hcei.tsc.ru; Lavrinovich, I. V. [Institute of High Current Electronics SB RAS, Akademichesky Ave. 2/3, 634055 Tomsk (Russian Federation) [Institute of High Current Electronics SB RAS, Akademichesky Ave. 2/3, 634055 Tomsk (Russian Federation); National Research Tomsk Polytechnic University, Lenin Avenue 30, 634050 Tomsk (Russian Federation)

    2014-04-15

    The paper reports on numerical study of the energy loss in spark gap switches. The operation of the switches is analyzed using the Braginsky model which allows calculation of the time dependence of the spark channel resistance. The Braginsky equation is solved simultaneously with generator circuit equations for different load types. Based on the numerical solutions, expressions which determine both the energy released in a spark gap switch and the switching time are derived.

  8. Flywheel energy storage using superconducting magnetic bearings

    Microsoft Academic Search

    R. G. Abboud; K. Uherka; J. Hull; T. Mulcahy; R ABBOUD

    1994-01-01

    Storage of electrical energy on a utility scale is currently not practicable for most utilities, preventing the full utilization of existing base-load capacity. A potential solution to this problem is Flywheel Energy Storage (FES), made possible by technological developments in high-temperature superconducting materials. Commonwealth Research Corporation (CRC), the research arm of Commonwealth Edison Company, and Argonne National Laboratory are implementing

  9. Spin-singlet superconductivity with a full gap in locally noncentrosymmetric SrPtAs

    NASA Astrophysics Data System (ADS)

    Matano, K.; Arima, K.; Maeda, S.; Nishikubo, Y.; Kudo, K.; Nohara, M.; Zheng, Guo-qing

    2014-04-01

    We report Pt-NMR195 and As75 nuclear quadrupole resonance measurements for the locally noncentrosymmetric superconductor SrPtAs where the As-Pt layer breaks inversion symmetry while globally the compound is centrosymmetric. The nuclear spin-lattice relaxation rate 1/T1 shows a well-defined coherence peak below Tc and decreases exponentially at low temperatures. The spin susceptibility measured by the Knight shift also decreases below Tc down to T superconducting state with a full gap. Our results suggest that the spin-orbit coupling due to the local inversion-symmetry breaking is not large enough to bring about an exotic superconducting state, or the interlayer hopping interaction is larger than the spin-orbit coupling.

  10. 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.

  11. Far-infrared conductivity and anomalous below-gap absorption in superconducting granular NbN

    Microsoft Academic Search

    D. R. Karecki; G. L. Carr; S. Perkowitz; D. U. Gubser; S. A. Wolf

    1983-01-01

    The far-infrared (10--100 cm⁻¹) complex conductivity of superconducting granular NbN films has been determined from reflection and transmission data. Moderately granular films, with R\\/sub D'Alembertian\\/ = 150 and 200 ..cap omega..\\/D'Alembertian, followed Leplae-modified Bardeen-Cooper-Schrieffer-- theory predictions with no absorption below the gap frequency ..omega..\\/sub g\\/. The derived values of 2..delta..\\/kT\\/sub c\\/ were 3.8 and 4.0, slightly below the results for

  12. Far-infrared conductivity and anomalous below-gap absorption in superconducting granular NbN

    Microsoft Academic Search

    D. R. Karecki; G. L. Carr; S. Perkowitz; D. U. Gubser; S. A. Wolf

    1983-01-01

    The far-infrared (10-100 cm-1) complex conductivity of superconducting granular NbN films has been determined from reflection and transmission data. Moderately granular films, with R□=150 and 200 Omega□, followed Leplae-modified Bardeen-Cooper-Schrieffer-theory predictions with no absorption below the gap frequency omegag. The derived values of 2DeltakTc were 3.8 and 4.0, slightly below the results for homogeneous films. Highly granular films, with R□>=500

  13. Point-Contact Study of the Superconducting Gap in the Magnetic Rare-Earth Nickel-Borocarbide RNi2B2C (R = Dy, Ho, Er, Tm) Compounds

    Microsoft Academic Search

    Yu. G. Naidyuk; N. L. Bobrov; V. N. Chernobay; S.-L. Drechsler; G. Fuchs; O. E. Kvitnitskaya; D. G. Naugle; K. D. D. Rathnayaka; L. V. Tyutrina; I. K. Yanson

    2009-01-01

    We present an overview of the efforts in point-contact (PC) study of the superconducting (SC) gap in the antiferromagnetic (AF) nickel-borocarbide compounds RNi2B2C (R = Dy, Ho, Er, Tm), for which the energy scales of AF and SC order, measured by the Neel temperature T N and the critical temperature T c, respectively, can be varied over a wide range.

  14. London penetration depth as a sensitive tool for determining the superconducting gap structure in iron-pnictide superconductors

    NASA Astrophysics Data System (ADS)

    Gordon, Ryan

    2011-03-01

    In the high -Tc cuprates, experiments and theories have relied on a single-band picture that is essentially two- dimensional with a single superconducting gap, which provided a simple way to understand the angular dependence of the superconducting order parameter. In iron-based superconductors, the experimental mapping of the superconducting gap structure is complicated by the doping- dependent, multi-band electronic structure with three- dimensional character and the existence of at least two distinct superconducting gaps. Focusing on precision measurements of the London penetration depth, ? (T) , in ``122'' Ba(Fe 1-x Tx)2 As 2 (T=Co,Ni,Ru,Pt,Pd,Co+Cu) single crystals, I will discuss the systematics of the ubiquitous power law temperature variation of the in-plane penetration depth, ?ab (T) =?ab (0) + ?Tn , and of the absolute value, ?ab (0) , with the doping level, x . To understand the role of disorder and pairbreaking scattering, the effect of heavy ion irradiation has been systematically studied and the results are compared with other systems, most notably stoichiometric LiFeAs. Together with the doping dependence of the out-of- plane London penetration depth, ?c (T) , and comparisons to thermal conductivity and specific heat data, these results strongly suggest the development of a significant in-plane anisotropy of the superconducting gap(s) and are also consistent with the appearance of accidental c-axis nodes (not imposed by symmetry) for concentrations moving away from optimal doping. By taking pairbreaking scattering into account, the data for the optimally doped compounds are well described by weak-coupling superconductivity with two nodeless superconducting gaps having amplitudes that differ by about a factor of two. I conclude by emphasizing the significant role of three-dimensionality and scattering in determining the electrodynamics of iron-based superconductors.

  15. Superconducting gap in MgB(2): electronic Raman scattering measurements of single crystals.

    PubMed

    Quilty, J W; Lee, S; Yamamoto, A; Tajima, S

    2002-02-25

    Polarization-resolved Raman scattering measurements were performed on MgB(2) single crystals to determine the magnitude, symmetry, and temperature dependence of the superconducting gap. A single sharp peak due to Cooper pair breaking appears in the electronic continuum below T(c), reaching a maximum Raman shift of 105 +/- 1 cm(-1) [2 Delta(0)/k(B)T(c) = 3.96 +/- 0.09] and showing up to 5 cm(-1) anisotropy between polarized and depolarized spectra. The temperature dependence of 2 Delta follows that predicted from BCS theory, while the anisotropy decreases with decreasing temperature. It is concluded that the Raman results are consistent with a slightly anisotropic s-wave gap in a conventional BCS superconductor. PMID:11863969

  16. Raman scattering investigation of the superconducting gap anisotropy in La{sub 2-x}Sr{sub x}CuO{sub 4}

    SciTech Connect

    Irwin, J.C.; Chen, X.K. [Simon Fraser Univ., British Columbia (Canada); Trodahl, H.J. [Univ. of Wellington (New Zealand)] [and others

    1995-08-01

    The low energy electronic Raman continua of a La1.83Sr0.17CuO4 single crystal have been obtained in several different scattering geometries, and for temperatures above and below Tc. Based upon the polarization dependence of the spectra obtained for T{le}Tc it is concluded that the superconducting gap is anisotropic with nodes located near the ({+-}1,{+-}1) directions in reciprocal space and maxima close to the kx and ky axes. The results are compared to spectra obtained from other high-Tc compounds and the possible compatibility of the results with particular gap functions is discussed.

  17. Indication of Both d- and s-Wave like Superconducting Gaps in YBa2Cu3O7

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bagayoko, D.

    2008-03-01

    Both of the d- and s- wave interpretations of the superconducting gaps in high Tc superconductors are separately supported by experiments, leading sometimes to conflicting views. In an effort to resolve this conflict, we performed first-principle quantum calculations as follows. We utilized self-consistent, electronic wave functions and electron-phonon interaction matrix elements, and we solved four-dimensional Eliashberg gap equations. Our results showed that on three sheets of the Fermi surfaces, the calculated superconducting gap exhibits a strong anisotropy and can lend itself to a d-wave interpretation. In contrast, the calculated superconducting gap on the small sheet of the Fermi surface around the S-Point only shows a relatively small variation from about 18 meV to 25 meV and there is no node on this sheet, leading to s-wave interpretation. Our findings point to the need for measurements of the superconducting gap on this sheet of the Fermi surface around the S-point. Such measurements are expected to shed light on the gap symmetry properties of high Tc superconductors. Work funded in part by the Department of the Navy, Office of Naval Research (ONR, Grant No. N00014-4-1-0587) and by the National Science Foundation (Award No. HRD 0503362)

  18. Evidence of double-gap superconductivity in noncentrosymmetric Nb0.18Re0.82 single crystals

    NASA Astrophysics Data System (ADS)

    Cirillo, C.; Fittipaldi, R.; Smidman, M.; Carapella, G.; Attanasio, C.; Vecchione, A.; Singh, R. P.; Lees, M. R.; Balakrishnan, G.; Cuoco, M.

    2015-04-01

    We combine point contact spectroscopy with specific heat measurements to probe the superconducting state in noncentrosymmetric Nb0.18Re0.82 single crystals. The conductance spectra clearly exhibit a two-peak structure that is well reproduced within a two-band model with isotropic gaps in the spectrum. Such an observation is confirmed by distinct features of the specific heat both at low temperatures and in the range approaching the transition to the normal state. The analyses provide convincing evidence that the two-gap superconducting pairing is a robust feature of Nb0.18Re0.82 .

  19. Study of the superconducting gap in RNi2B2C,,RY, Lu... single crystals by inelastic light scattering

    E-print Network

    Yang, In-Sang

    Study of the superconducting gap in RNi2B2C,,RÄY, Lu... single crystals by inelastic light Raman-scattering response were observed for the RNi2B2C (R Y, Lu system in different scattering, for both YNi2B2C and LuNi2B2C systems, there exists reproducible scattering strength below the 2 gap which

  20. Pushing the Gradient Limitations of Superconducting Photonic Band Gap Structure Cells

    SciTech Connect

    Simakov, Evgenya I. [Los Alamos National Laboratory; Haynes, William B. [Los Alamos National Laboratory; Kurennoy, Sergey S. [Los Alamos National Laboratory; Shchegolkov, Dmitry [Los Alamos National Laboratory; O'Hara, James F. [Los Alamos National Laboratory; Olivas, Eric R. [Los Alamos National Laboratory

    2012-06-07

    Superconducting photonic band gap resonators present us with unique means to place higher order mode couples in an accelerating cavity and efficiently extract HOMs. An SRF PBG resonator with round rods was successfully tested at LANL demonstrating operation at 15 MV/m. Gradient in the SRF PBG resonator was limited by magnetic quench. To increase the quench threshold in PBG resonators one must design the new geometry with lower surface magnetic fields and preserve the resonator's effectiveness for HOM suppression. The main objective of this research is to push the limits for the high-gradient operation of SRF PBG cavities. A NCRF PBG cavity technology is established. The proof-of-principle operation of SRF PBG cavities is demonstrated. SRF PBG resonators are effective for outcoupling HOMs. PBG technology can significantly reduce the size of SRF accelerators and increase brightness for future FELs.

  1. A superconducting linac for the energy amplifier

    SciTech Connect

    Ruggiero, A.G.

    1997-07-01

    Because of the safer and more reliable mode of operation, a Superconducting Linac has been proposed as the proton beam accelerator which drives a nuclear plant based on the concept of the Energy Amplifier. An example based on the net generation of 400 MW (electric) is described. This requires a proton beam energy of 1 GeV with a continuous beam current of 10 mA, corresponding to a beam power of 10 MW. Two frequency cases, 360 and 805 MHz, have been considered for the Linac design. Performance and cost comparison for the two cases are given.

  2. Closing the energy gap through passive energy expenditure

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Development of obesity is a gradual process occurring when daily energy intake persistently exceeds energy expenditure (EE). Typical daily weight gain is attributed to an energy gap or excess of stored energy of 15 to 50 kcal/day. Sedentary jobs likely promote weight gain. Standing may be a passive ...

  3. Superconducting gap structure of spin-triplet superconductor Sr2RuO4 studied by thermal conductivity.

    PubMed

    Izawa, K; Takahashi, H; Yamaguchi, H; Matsuda, Y; Suzuki, M; Sasaki, T; Fukase, T; Yoshida, Y; Settai, R; Onuki, Y

    2001-03-19

    To clarify the superconducting gap structure of the spin-triplet superconductor Sr2RuO4, the in-plane thermal conductivity has been measured as a function of relative orientations of the thermal flow, the crystal axes, and a magnetic field rotating within the 2D RuO2 planes. The in-plane variation of the thermal conductivity is incompatible with any model with line nodes vertical to the 2D planes and indicates the existence of horizontal nodes. These results place strong constraints on models that attempt to explain the mechanism of the triplet superconductivity. PMID:11290003

  4. Tracing the evolution of the two energy gaps in magnesium diboride under pressure

    NASA Astrophysics Data System (ADS)

    Kononenko, V.; Tarenkov, V.; Belogolovskii, M.; Döring, S.; Schmidt, S.; Seidel, P.

    2015-04-01

    We have studied transport characteristics of mesoscopic multiple-mode superconducting contacts formed between two grains in bulk two-gap magnesium diboride. The experimental setup was realized by driving a normal-metal tip into MgB2 polycrystalline sample and proved to be extremely stable, providing possibility to perform pressure experiments at low temperatures. It is argued that in our procedure a small piece of the superconducting electrode is captured by the tip apex and, as a result, two junctions in series are formed: a junction between a tip and MgB2 grain and a mesoscopic disordered contact between two superconducting pellets. Although the relative weight of the first junction resistance was considerably less, its contribution is shown to be important for the comparison of measured data with expected gap values. Two hallmarks of multiple Andreev reflections inside the MgB2-c-MgB2 contact (c stands for a high-transparent constriction), a zero-bias 1/ ?{|V | } -like singularity of the dc differential conductance and peaks connected to the two gap values, have been revealed. Finally, we report results of a hydrostatic compression experiment showing the evolution of the MgB2 gap values with pressure. In contrast to the theoretical expectations, we have observed an increase of the smaller gap ?? whereas the larger gap ?? decreased with increasing pressure as it should be for the electron-phonon pairing mechanism. We argue that the so-called separable model of anisotropy effects is insufficient to describe such changes and only improved two-band versions are capable to reproduce the pressure effect on the energy gaps in magnesium diboride.

  5. Point-Contact Study of the Superconducting Gap in the Magnetic Rare-Earth Nickel-Borocarbide RNi2B2C (R = Dy, Ho, Er, Tm) Compounds

    NASA Astrophysics Data System (ADS)

    Naidyuk, Yu. G.; Bobrov, N. L.; Chernobay, V. N.; Drechsler, S.-L.; Fuchs, G.; Kvitnitskaya, O. E.; Naugle, D. G.; Rathnayaka, K. D. D.; Tyutrina, L. V.; Yanson, I. K.

    We present an overview of the efforts in point-contact (PC) study of the superconducting (SC) gap in the antiferromagnetic (AF) nickel-borocarbide compounds RNi2B2C (R = Dy, Ho, Er, Tm), for which the energy scales of AF and SC order, measured by the Neel temperature T N and the critical temperature T c, respectively, can be varied over a wide range. The SC gap was determined from the experimental dV / dI curves of PCs employing the well-known BTK theory of conductivity for normal metal-superconductor PCs accounting Andreev reflection. Additionally, the mentioned theory including pair-breaking effect due to magnetic impurities was employed and a multiband structure of the title compounds was taken into consideration. Recent directional PC study of the SC gaps gives evidence for the anisotropic two-band (two-gap) nature of SC-ty in R = Er (T N ? 6 K < T c ? 11 K). Additionally, a distinct decrease of both gaps in this compound in the AF state is observed. The SC gap in R = Ho (T N ? 5. 2 K < T c ? 8. 5 K) exhibits below T ? ? 5. 6 K a standard single-band BCS-like dependence vanishing above T ?, where a specific magnetic ordering starts to play a role. For R = Tm (T N ? 1. 5 K < T c ? 10. 5 K) a decrease of the SC gap is observed below ˜ 5 K, while for R = Dy (T N ? 10. 5 K > T c ? 6. 5 K) the SC gap has BCS-like dependence in the AF state. Distinct features of the SC gap behavior in the mentioned magnetic superconductors are discussed.

  6. A superconducting high-speed flywheel energy storage system

    Microsoft Academic Search

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

    2004-01-01

    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

  7. Superconducting Gap and Pseudogap in Iron-Based Layered Superconductor La(O1-xFx)FeAs

    Microsoft Academic Search

    Takafumi Sato; Seigo Souma; Kosuke Nakayama; Kensei Terashima; Katsuaki Sugawara; Takashi Takahashi; Yoichi Kamihara; Masahiro Hirano; Hideo Hosono

    2008-01-01

    We report high-resolution photoemission spectroscopy of newly-discovered iron-based layered superconductor La(O0.93F0.07)FeAs (Tc = 24 K). We found that the superconducting gap shows a marked deviation from the isotropic s-wave symmetry. The estimated gap size at 5 K is 3.6 meV in the s- or axial p-wave case, while it is 4.1 meV in the polar p- or d-wave case. We

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  9. New power-conditioning systems for superconducting magnetic energy storage

    Microsoft Academic Search

    Byung Moon Han

    1992-01-01

    This dissertation presents the development of new power-conditioning systems for superconducting magnetic energy storage (SMES), which can regulate fast and independently the active and reactive powers demanded in the ac network. Three new power-conditioning systems were developed through a systematic approach to match the requirements of the superconducting coil and the ac power network. Each of these new systems is

  10. Superconducting magnetic energy storage for asynchronous electrical systems

    DOEpatents

    Boenig, Heinrich J. (Los Alamos, NM)

    1986-01-01

    A superconducting magnetic energy storage coil connected in parallel between converters of two or more ac power systems provides load leveling and stability improvement to any or all of the ac systems. Control is provided to direct the charging and independently the discharging of the superconducting coil to at least a selected one of the ac power systems.

  11. Voltage sags compensation using a superconducting flywheel energy storage system

    Microsoft Academic Search

    Antonio C. Ferreira; Guilherme G. Sotelo; José L. Silva Neto; Luiz G. B. Rolim; Walter I. Suemitsu; Márcio F. Bessa; Richard M. Stephan; Roberto Nicolsky

    2005-01-01

    This paper presents a voltage sag compensator, which uses a flywheel energy storage system with superconducting magnetic axial thrust bearing (SMB) and a permanent magnet radial bearing (PMB). The SMB was built with Nd-Fe-B magnet and YBCO superconducting blocks, refrigerated with liquid Nitrogen. The magnets are assembled with magnetic flux shapers in order to increase the levitation force and the

  12. Superconductivity

    SciTech Connect

    Langone, J.

    1989-01-01

    This book explains the theoretical background of superconductivity. Includes discussion of electricity, material fabrication, maglev trains, the superconducting supercollider, and Japanese-US competition. The authors reports the latest discoveries.

  13. Superconducting gap evolution in overdoped BaFe2(As1-xPx) 2 single crystals through nanocalorimetry

    NASA Astrophysics Data System (ADS)

    Campanini, D.; Diao, Z.; Fang, L.; Kwok, W.-K.; Welp, U.; Rydh, A.

    2015-06-01

    We report on specific heat measurements on clean overdoped BaFe2(As1-xPx)2 single crystals performed with a high resolution membrane-based nanocalorimeter. A nonzero residual electronic specific heat coefficient at zero temperature ?r=C/T | T ?0 is seen for all doping compositions, indicating a considerable fraction of the Fermi surface ungapped or having very deep minima. The remaining superconducting electronic specific heat is analyzed through a two-band s -wave ? model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of ?0˜5.3 meV , corresponding to ?0/kBTc˜2.2 . Increasing the phosphorus concentration x , the main gap reduces till a value of ?0˜1.9 meV for x =0.55 and a second weaker gap becomes evident. From the magnetic field effect on ?r, all samples however show similar behavior [?r(H ) -?r(H =0 ) ?Hn , with n between 0.6 and 0.7]. This indicates that, despite a considerable redistribution of the gap weights, the total degree of gap anisotropy does not change drastically with doping.

  14. Superconducting gap evolution in overdoped BaFe?(As1-xPx)? single crystals through nanocalorimetry

    DOE PAGESBeta

    Campanini, D.; Diao, Z.; Fang, L.; Kwok, W.-K.; Welp, U.; Rydh, A.

    2015-06-01

    We report on specific heat measurements on clean overdoped BaFe?(As1?xPx)? single crystals performed with a high resolution membrane-based nanocalorimeter. A nonzero residual electronic specific heat coefficient at zero temperature ?r=C/T|T?0 is seen for all doping compositions, indicating a considerable fraction of the Fermi surface ungapped or having very deep minima. The remaining superconducting electronic specific heat is analyzed through a two-band s-wave ? model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of ??~5.3 me V, corresponding to ??/kBTc ~ 2.2. Increasing the phosphorus concentration x, the main gap reduces till a value of ?? ~ 1.9 meV for x = 0.55 and a second weaker gap becomes evident. From the magnetic field effect on ?r, all samples however show similar behavior [?r(H) ? ?r (H = 0)? Hn, with n between 0.6 and 0.7]. This indicates that, despite a considerable redistribution of the gap weights, the total degree of gap anisotropy does not change drastically with doping.

  15. Superconducting gap evolution in overdoped BaFe?(As1-xPx)? single crystals through nanocalorimetry

    DOE PAGESBeta

    Campanini, D.; Diao, Z.; Fang, L.; Kwok, W.-K.; Welp, U.; Rydh, A.

    2015-06-01

    We report on specific heat measurements on clean overdoped BaFe?(As1-xPx)? single crystals performed with a high resolution membrane-based nanocalorimeter. A nonzero residual electronic specific heat coefficient at zero temperature ?r=C/T|T?0 is seen for all doping compositions, indicating a considerable fraction of the Fermi surface ungapped or having very deep minima. The remaining superconducting electronic specific heat is analyzed through a two-band s-wave ? model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of ??~5.3 me V, corresponding to ??/kBTc ~ 2.2. Increasing the phosphorus concentration x, the main gap reduces tillmore »a value of ?? ~ 1.9 meV for x = 0.55 and a second weaker gap becomes evident. From the magnetic field effect on ?r, all samples however show similar behavior [?r(H) - ?r (H = 0)? Hn, with n between 0.6 and 0.7]. This indicates that, despite a considerable redistribution of the gap weights, the total degree of gap anisotropy does not change drastically with doping.« less

  16. Superconductivity and fusion energy—the inseparable companions

    NASA Astrophysics Data System (ADS)

    Bruzzone, Pierluigi

    2015-02-01

    Although superconductivity will never produce energy by itself, it plays an important role in energy-related applications both because of its saving potential (e.g., power transmission lines and generators), and its role as an enabling technology (e.g., for nuclear fusion energy). The superconducting magnet’s need for plasma confinement has been recognized since the early development of fusion devices. As long as the research and development of plasma burning was carried out on pulsed devices, the technology of superconducting fusion magnets was aimed at demonstrations of feasibility. In the latest generation of plasma devices, which are larger and have longer confinement times, the superconducting coils are a key enabling technology. The cost of a superconducting magnet system is a major portion of the overall cost of a fusion plant and deserves significant attention in the long-term planning of electricity supply; only cheap superconducting magnets will help fusion get to the energy market. In this paper, the technology challenges and design approaches for fusion magnets are briefly reviewed for past, present, and future projects, from the early superconducting tokamaks in the 1970s, to the current ITER (International Thermonuclear Experimental Reactor) and W7-X projects and future DEMO (Demonstration Reactor) projects. The associated cryogenic technology is also reviewed: 4.2 K helium baths, superfluid baths, forced-flow supercritical helium, and helium-free designs. Open issues and risk mitigation are discussed in terms of reliability, technology, and cost.

  17. Optimizing the configuration of a superconducting photonic band gap accelerator cavity to increase the maximum achievable gradients

    NASA Astrophysics Data System (ADS)

    Simakov, Evgenya I.; Kurennoy, Sergey S.; O'Hara, James F.; Olivas, Eric R.; Shchegolkov, Dmitry Yu.

    2014-02-01

    We present a design of a superconducting rf photonic band gap (SRF PBG) accelerator cell with specially shaped rods in order to reduce peak surface magnetic fields and improve the effectiveness of the PBG structure for suppression of higher order modes (HOMs). The ability of PBG structures to suppress long-range wakefields is especially beneficial for superconducting electron accelerators for high power free-electron lasers (FELs), which are designed to provide high current continuous duty electron beams. Using PBG structures to reduce the prominent beam-breakup phenomena due to HOMs will allow significantly increased beam-breakup thresholds. As a result, there will be possibilities for increasing the operation frequency of SRF accelerators and for the development of novel compact high-current accelerator modules for the FELs.

  18. Superconducting magnetic energy storage for electric utilities and fusion systems

    Microsoft Academic Search

    J. D. Rogers; H. J. Boenig; W. V. Hassenzahl

    1978-01-01

    Energy storage inductors, under development for load leveling and transmission line stabilization in electric utility systems and for driving magnetic confinement and plasma heating coils in fusion energy system are described. Superconducting magnetic energy storage (SMES) systems, which will store and deliver electrical energy for load leveling, peak shaving, and the stabilization of electric utility network are discussed. In the

  19. Point-Contact Study of the Superconducting Gap in the Magnetic Rare-Earth Nickel-Borocarbide R Ni 2 B 2 C ( R = Dy, Ho, Er, Tm) Compounds

    Microsoft Academic Search

    Yu. G. Naidyuk; N. L. Bobrov; V. N. Chernobay; S.-L. Drechsler; G. Fuchs; O. E. Kvitnitskaya; D. G. Naugle; K. D. D. Rathnayaka; L. V. Tyutrina; I. K. Yanson

    We present an overview of the efforts in point-contact (PC) study of the superconducting (SC) gap in the antiferromagnetic\\u000a (AF) nickel-borocarbide compounds RNi2B2C (R = Dy, Ho, Er, Tm), for which the energy scales of AF and SC order, measured by the Neel temperature T\\u000a N and the critical temperature T\\u000a c, respectively, can be varied over a wide range.

  20. Superconducting magnetis in spectrometers of high-energy particles

    Microsoft Academic Search

    Yu. A. Shishov

    2006-01-01

    This is a retrospective review of superconducting magnets for spectrometers of high-energy particles. The magnets are grouped\\u000a according to the purpose of the spectrometers and the shape of coils. Data on the thermostatting and electrical protection\\u000a of the coils are presented. Design features of various-type magnets are described. The first large superconducting solenoids\\u000a were constructed for hydrogen bubble chambers. Further

  1. Toroidal constant-tension superconducting magnetic energy storage units

    DOEpatents

    Herring, J. Stephen (Idaho Falls, ID)

    1992-01-01

    A superconducting magnetic energy storage unit is provided in which the magnet is wound in a toroidal fashion such that the magnetic field produced is contained only within the bore of the magnet, and thus producing a very low external field. The superconducting magnet includes a coolant channel disposed through the wire. The bore of the magnet comprises a storage volume in which cryogenic coolant is stored, and this volume supplies the coolant to be delivered to the coolant channel in the magnet.

  2. High energy ion linacs based on superconducting spoke cavities

    Microsoft Academic Search

    K. W. Shepard; P. N. Ostroumov; J. R. Delayen

    2003-01-01

    The applicability of superconducting TEM-class spoke cavities to high-energy ion linacs is discussed, and detailed designs for two TEM-class, triple-spoke-loaded superconducting niobium resonant cavities are presented. The 345 MHz cavities have a velocity range of 0.4<<0.75 and a beam aperture of 4 cm. Spoke-loaded cavities offer several advantages compared with the higher-frequency elliptical-cell cavities that are currently being developed for

  3. Nodal and multi-gap superconductivity in Ta4Pd3Te16 with weakly ferromagnetic normal state

    NASA Astrophysics Data System (ADS)

    Cao, Guang-Han; Jiao, Wen-He; Feng, Chun-Mu; Xu, Zhu-An; Institute of condensed matter physics Team

    2015-03-01

    We recently discovered bulk superconductivity at Tc = 4.6 K in a transition metal telluride Ta4Pd3Te16 [W. H. Jiao et al., J. Am. Chem. Soc. 136, 1284 (2014)]. This material has a layered structure with one-dimensional PdTe2 chains. Significant electron correlations are indicated by the enhanced Sommerfeld coefficient. Here we report the measurements of magnetoresistance, Hall effect, magnetization and specific heat using high-quality crystals. Our results show that Ta4Pd3Te16 is an anisotropic type-II superconductor. The anisotropy of upper critical fields Hc 2 (T) is strongly T-dependent, resulted from the multi-band effect. The zero-field electronic specific heat Ce (T) far below the Tc is found to be proportional to T3, suggestive of presence of point nodes in at least one of the superconducting gaps, which is further supported by a nonlinear (~H 1 / 2) field dependence of Sommerfeld coefficient in the mixed state. Notably, the material shows anisotropic weak-ferromagnetism above Tc, implying that spin-triplet superconductivity is likely in this material. Work supported by National Basic Research Program of China (No.2011CBA00103) and National Science Foundation of China (No.11190023).

  4. Superconducting magnetic bearing for a flywheel energy storage system using superconducting coils and bulk superconductors

    NASA Astrophysics Data System (ADS)

    Nagashima, K.; Seino, H.; Sakai, N.; Murakami, M.

    2009-10-01

    Stable levitation or suspension of a heavy object in mid-air can be realized using a combination of a permanent magnet and a bulk superconductor with high critical current density, in that the force density has reached 100 kN/m 2. The superconducting flywheel system for energy storage is attractive due to a great reduction in the rotational loss of the bearings. So long as a permanent magnet is used as a magnetic source, however, the electromagnetic force (EMF) is essentially limited by its field strength. In order to overcome such a limitation, we employed a superconducting coil/magnet as a magnetic source and studied the EMF characteristics of bulk superconductors in high-magnetic fields. We also measured the EMF between a bulk superconductor and a specially designed superconducting coil having a high field gradient, and confirmed that the EMF reached 9450 N (force density: 2507 kN/m 2).

  5. Tests of the nuclear equation of state and superfluid and superconducting gaps using the Cassiopeia A neutron star

    E-print Network

    Wynn C. G. Ho; Khaled G. Elshamouty; Craig O. Heinke; Alexander Y. Potekhin

    2015-01-15

    The observed rapid cooling of the Cassiopeia A neutron star can be interpreted as being caused by neutron and proton transitions from normal to superfluid and superconducting states in the stellar core. Here we present two new Chandra ACIS-S Graded observations of this neutron star and measurements of the neutron star mass M and radius R found from consistent fitting of both the X-ray spectra and cooling behavior. This comparison is only possible for individual nuclear equations of state. We test phenomenological superfluid and superconducting gap models which mimic many of the known theoretical models against the cooling behavior. Our best-fit solution to the Cassiopeia A data is one in which the (M,R) = (1.44 Msun,12.6 km) neutron star is built with the BSk21 equation of state, strong proton superconductor and moderate neutron triplet superfluid gap models, and a pure iron envelope or a thin carbon layer on top of an iron envelope, although there are still large observational and theoretical uncertainties.

  6. Optimal emitter-collector gap for thermionic energy converters

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Hyung; Bargatin, Igor; Melosh, Nicholas A.; Howe, Roger T.

    2012-04-01

    In this letter, we calculate numerically the emitter-collector gaps that maximize the power conversion efficiency of vacuum thermionic energy converters (TECs). The optimum arises because efficiency drops both at very large gaps, due to space-charge limitations on the TEC current, and at very small gaps, due to the increased parasitic heat loss via near-field radiative heat transfer. For typical TECs made with cesiated tungsten electrodes, the optimal gaps range from 900 nm to 3 ?m and are approximately equal to the characteristic wavelength of the emitter thermal radiation, as given by Wien's displacement law.

  7. Doping dependence of low-energy quasiparticle excitations in superconducting Bi2212

    PubMed Central

    2013-01-01

    The doping-dependent evolution of the d-wave superconducting state is studied from the perspective of the angle-resolved photoemission spectra of a high-Tc cuprate, Bi2Sr2CaCu2 O8+? (Bi2212). The anisotropic evolution of the energy gap for Bogoliubov quasiparticles is parametrized by critical temperature and superfluid density. The renormalization of nodal quasiparticles is evaluated in terms of mass enhancement spectra. These quantities shed light on the strong coupling nature of electron pairing and the impact of forward elastic or inelastic scatterings. We suggest that the quasiparticle excitations in the superconducting cuprates are profoundly affected by doping-dependent screening. PMID:24314035

  8. Superconductivity

    SciTech Connect

    Mayo, J.L.

    1988-01-01

    The author presents treatment of the field of superconductivity, from its inception in 1911 to the present day. Its discussions range from scientific aspects to applications in business, medicine, etc. This book provides definitions and a selective bibliography.

  9. Probing Hybridization of a Single Energy Level Coupled to Superconducting Leads

    E-print Network

    D. M. T. van Zanten; H. Courtois; C. B. Winkelmann

    2015-06-25

    Electron transport through a quantum dot coupled to superconducting leads shows a sharp conductance onset when a quantum dot orbital level crosses the superconducting coherence peak of one lead. We study superconducting single electron transistors in the weak coupling limit by connecting individual gold nanoparticles with aluminum junctions formed by electromigration. We show that the transport features close to the conductance onset threshold can be accurately described by the quantum dot levels' hybridization with the leads, which is strongly enhanced by the divergent density of states at the superconducting gap edge. This highlights the importance of electron cotunneling effects in spectroscopies with superconducting probes.

  10. Langmuir vacuum and superconductivity

    SciTech Connect

    Veklenko, B. A. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

    2012-06-15

    It is shown that, in the 'jelly' model of cold electron-ion plasma, the interaction between electrons and the quantum electromagnetic vacuum of Langmuir waves involves plasma superconductivity with an energy gap proportional to the energy of the Langmuir quantum.

  11. Distinct Fermi Surface Topology and nearly Isotropic Superconducting Gap in AxFe2-y Se2 (A=K, Tl, Rb) Superconductors

    NASA Astrophysics Data System (ADS)

    Zhou, Xingjiang

    2012-02-01

    High resolution angle-resolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the newly discovered AxFe2-ySe2 [A=K, (Tl,K) and (Tl,Rb)] superconductors[1,2,3] 1. Distinct Fermi surface topology, consisting of two electron-like Fermi surface sheets around the ?(0,0) point and an electron-like Fermi surface sheet near the M(?,?) point, was revealed in all these samples. This is in strong contrast to the Fermi surface topology of other Fe-based superconductors where hole-like Fermi surface sheets are present near the ?(0,0) point. 2. Both the electron-like Fermi surface sheet near M point and the large electron-like Fermi surface sheet near ? point show nearly isotropic superconducting gap without nodes 3. The doping evolution of the electronic structure from insulating samples to the superconducting samples is consistent with a phase separation picture. The information on the Fermi surface topology and superconducting gap of this new AxFe2-ySe2 superconductor will provide key insights and constraints to understand the superconductivity mechanism in iron-based superconductors. [4pt] [1]. D. X. Mou, X. J. Zhou et. al, Phys. Rev. Lett. 106, 107001 (2011). [0pt] [2]. L. Zhao, X. J. Zhou et. al, Phys. Rev. B 83, 140508(R) (2011). [0pt] [3]. L. Yu, X. J. Zhou et al., unpublished.

  12. Thermal conductivity and gap structure of the superconducting phases of UPt{sub 3}

    SciTech Connect

    Suderow, H.; Huxley, A.; Flouquet, J. [CEA, Grenoble (France); Brison, J.P. [CNRS, Grenoble (France)

    1997-07-01

    We present new measurements of the thermal conductivity ({kappa}) of Upt{sub 3} down to very low temperatures (16 mK) and under magnetic fields (up to 4 T) which cover all the superconducting phases of Upt{sub 3}. The measurements in zero field are compared with recent theoretical predictions for the thermal conductivity, which is dominated by impurity states at the lowest temperatures studied. The measurements under magnetic field at low temperatures are surprising since they don`t show the expected low field square root dependence, {kappa} {proportional_to} {radical}B. The discontinuity of d{kappa}/dT at T{sub c} changes drastically when passing from the high field low temperature C phase to the low field high temperature A phase: this is related to the change of the symmetry of the superconducting order parameter when crossing the A {yields} C phase transition.

  13. Power applications of high-temperature superconductivity: Variable speed motors, current switches, and energy storage for end use

    SciTech Connect

    Hawsey, R.A. [Oak Ridge National Lab., TN (United States); Banerjee, B.B.; Grant, P.M. [Electric Power Research Inst., Palo Alto, CA (United States)

    1996-08-01

    The objective of this project is to conduct joint research and development activities related to certain electric power applications of high-temperature superconductivity (HTS). The new superconductors may allow development of an energy-efficient switch to control current to variable speed motors, superconducting magnetic energy storage (SMES) systems, and other power conversion equipment. Motor types that were considered include induction, permanent magnet, and superconducting ac motors. Because it is impractical to experimentally alter certain key design elements in radial-gap motors, experiments were conducted on an axial field superconducting motor prototype using 4 NbTi magnets. Superconducting magnetic energy storage technology with 0.25--5 kWh stored energy was studied as a viable solution to short duration voltage sag problems on the customer side of the electric meter. The technical performance characteristics of the device wee assembled, along with competing technologies such as active power line conditioners with storage, battery-based uninterruptible power supplies, and supercapacitors, and the market potential for SMES was defined. Four reports were prepared summarizing the results of the project.

  14. Energy BandGap Engineering of Graphene Nanoribbons

    Microsoft Academic Search

    Melinda Y. Han; Barbaros Ozyilmaz; Yuanbo Zhang; Philip Kim

    2007-01-01

    We investigate electronic transport in lithographically patterned graphene\\u000aribbon structures where the lateral confinement of charge carriers creates an\\u000aenergy gap near the charge neutrality point. Individual graphene layers are\\u000acontacted with metal electrodes and patterned into ribbons of varying widths\\u000aand different crystallographic orientations. The temperature dependent\\u000aconductance measurements show larger energy gaps opening for narrower ribbons.\\u000aThe sizes

  15. Effective-mass superlattice: surface states and zero energy gaps

    Microsoft Academic Search

    R Kucharczyk; M St??licka

    1997-01-01

    The electronic structure of a terminated effective-mass superlattice (EMSL) is investigated taking into account the effect of the EMSL surface (i.e. the EMSL\\/substrate interface). Special attention is paid to the conditions under which two neighbouring miniband edges cross each other, which results in the vanishing of a corresponding mini-gap for certain EMSL bulk parameters (the so-called zero energy gap conditions).

  16. Electric utility benefits of superconducting magnetic energy storage

    Microsoft Academic Search

    J. G. De Steese; J. E. Dagle

    1990-01-01

    This paper summarizes a preliminary scoping analysis to illustrate examples of the benefits electric utilities might derive from Superconducting Magnetic Energy Storage (SMES). A major objective of the study was to show that, even though SMES technology is at an early stage of development, available data permit the assessment of SMES benefits and costs in specific system applications. The purpose

  17. Low cost composite structures for superconducting magnetic energy storage systems

    Microsoft Academic Search

    Craig Rix; David McColskey; Robert Acree

    1994-01-01

    As part of the Superconducting Magnetic Energy Storage\\/Engineering Test Model (SMES-ETM) program, design, analysis, fabrication and test programs were conducted to evaluate the low cost manufacturing of fiberglass reinforced plastic (FRP) beams for usage as major components of the structural and electrical insulation systems. These studies utilized pultrusion process technologies and vinylester resins to produce large net sections at costs

  18. Increased electricity use must handle energy gap

    Microsoft Academic Search

    Bueche

    1977-01-01

    Growth in electricity use is seen to be part of the solution to resolving the country's energy problem because its flexibility allows shifts to be made according to the availability of fuels. Energy demand based on energy-to-GNP ratio, has been projected to increase from a present 73 to 170 quads by the year 2000, much more than can be gained

  19. Toroidal constant-tension superconducting magnetic energy storage units

    DOEpatents

    Herring, J.S.

    1992-11-03

    A superconducting magnetic energy storage unit is provided in which the magnet is wound in a toroidal fashion such that the magnetic field produced is contained only within the bore of the magnet, and thus producing a very low external field. The superconducting magnet includes a coolant channel disposed through the wire. The bore of the magnet comprises a storage volume in which cryogenic coolant is stored, and this volume supplies the coolant to be delivered to the coolant channel in the magnet. 6 figs.

  20. Battery energy storage and superconducting magnetic energy storage for utility applications: A qualitative analysis

    SciTech Connect

    Akhil, A.A.; Butler, P.; Bickel, T.C.

    1993-11-01

    This report was prepared at the request of the US Department of Energy`s Office of Energy Management for an objective comparison of the merits of battery energy storage with superconducting magnetic energy storage technology for utility applications. Conclusions are drawn regarding the best match of each technology with these utility application requirements. Staff from the Utility Battery Storage Systems Program and the superconductivity Programs at Sandia National contributed to this effort.

  1. Energy gap in graphene nanoribbons with structured external electric potentials

    NASA Astrophysics Data System (ADS)

    Apel, W.; Pal, G.; Schweitzer, L.

    2011-03-01

    The electronic properties of graphene zigzag nanoribbons with electrostatic potentials along the edges are investigated. Using the Dirac-fermion approach, we calculate the energy spectrum of an infinitely long nanoribbon of finite width w, terminated by Dirichlet boundary conditions in the transverse direction. We show that a structured external potential that acts within the edge regions of the ribbon can induce a spectral gap and thus switch the nanoribbon from metallic to insulating behavior. The basic mechanism of this effect is the selective influence of the external potentials on the spinorial wave functions that are topological in nature and localized along the boundary of the graphene nanoribbon. Within this single-particle description, the maximal obtainable energy gap is Emax???vF/w, i.e., ?0.12 eV for w=15 nm. The stability of the spectral gap against edge disorder and the effect of disorder on the two-terminal conductance is studied numerically within a tight-binding lattice model. We find that the energy gap persists as long as the applied external effective potential is larger than ?0.55×W, where W is a measure of the disorder strength. We argue that there is a transport gap due to localization effects even in the absence of a spectral gap.

  2. Nuclear energy in Malaysia - closing the gaps

    NASA Astrophysics Data System (ADS)

    >Malaysian Nuclear Society (Mns,

    2013-06-01

    This article is prepared by the Malaysian Nuclear Society (MNS) to present the views of the Malaysian scientific community on the need for Malaysia to urgently upgrade its technical know-how and expertise to support the nuclear energy industry for future sustainable economic development of the country. It also present scientific views that nuclear energy will bring economic growth as well as technically sound industry, capable of supporting nuclear energy industry needs in the country, and recommend action items for timely technical upgrading of Malaysian expertise related to nuclear energy industry.

  3. Field-induced Energy Gaps in Bilayer Graphene under Shear

    NASA Astrophysics Data System (ADS)

    Choi, Seon-Myeong; Son, Young-Woo

    2013-03-01

    Using the first-principles calculations method, we study the effects of shear on field-induced insulating states of bilayer graphene (BLG). It is shown that the low energy bands near the charge neutral point of BLG change significantly upon application of shear. We also find that the energy gap of BLG under transverse electric field sensitively depend on both direction and amount of shear. Generally, the field-induced energy gap decreases as the sliding increases under shear. For BLG with the specific direction of shear, the shear can quench the energy gap to zero completely even in the presence of electric field thus realizing insulator-to-metal transition just by sliding. We discuss origins of these interesting phenomena and suggest some experimental methods to detect the transition. Using the first-principles calculations method, we study the effects of shear on field-induced insulating states of bilayer graphene (BLG). It is shown that the low energy bands near the charge neutral point of BLG change significantly upon application of shear. We also find that the energy gap of BLG under transverse electric field sensitively depend on both direction and amount of shear. Generally, the field-induced energy gap decreases as the sliding increases under shear. For BLG with the specific direction of shear, the shear can quench the energy gap to zero completely even in the presence of electric field thus realizing insulator-to-metal transition just by sliding. We discuss origins of these interesting phenomena and suggest some experimental methods to detect the transition. Computational resources have been provided by KISTI Supercomputing Center (Project No. KSC-2011-C1-21) and the CAS of KIAS.

  4. Momentum Dependence of Superconducting Gap, Strong-Coupling Dispersion Kink, And Tightly Bound Cooper Pairs in the High-T(C)(Sr,Ba)(1-X)(K,Na)(X)Fe(2) As(2) Superconductors

    SciTech Connect

    Wray, L.; Qian, D.; Hsieh, D.; Xia, Y.; Li, L.; Checkelsky, J.G.; Pasupathy, A.; Gomes, K.K.; Parker, C.V.; Fedorov, A.V.; Chen, G.F.; Luo, J.L.; Yazdani, A.; Ong, N.P.; Wang, N.L.; Hasan, M.Z.

    2009-05-28

    We present a systematic angle-resolved photoemission spectroscopic study of the high-T{sub c} superconductor class (Sr/Ba){sub 1-x}K{sub x}Fe{sub 2}As{sub 2}. By utilizing a photon-energy-modulation contrast and scattering geometry we report the Fermi surface and the momentum dependence of the superconducting gap, {triangle}(k{open_square}). A prominent quasiparticle dispersion kink reflecting strong scattering processes is observed in a binding-energy range of 25--55 meV in the superconducting state, and the coherence length or the extent of the Cooper pair wave function is found to be about 20 {angstrom}, which is uncharacteristic of a superconducting phase realized by the BCS-phonon-retardation mechanism. The observed 40{+-}15 meV kink likely reflects contributions from the frustrated spin excitations in a J{sub 1}-J{sub 2} magnetic background and scattering from the soft phonons. Results taken collectively provide direct clues to the nature of the pairing potential including an internal phase-shift factor in the superconducting order parameter which leads to a Brillouin zone node in a strong-coupling setting.

  5. Multi-frequency modes in superconducting resonators: Bridging frequency gaps in off-resonant couplings

    NASA Astrophysics Data System (ADS)

    Andersen, Christian Kraglund; Mølmer, Klaus

    2015-03-01

    A SQUID inserted in a superconducting waveguide resonator imposes current and voltage boundary conditions that makes it suitable as a tuning element for the resonator modes. If such a SQUID element is subject to a periodically varying magnetic flux, the resonator modes acquire frequency side bands. We calculate the multi-frequency eigenmodes and these can couple resonantly to physical systems with different transition frequencies and this makes the resonator an efficient quantum bus for state transfer and coherent quantum operations in hybrid quantum systems. As an example of the application, we determine their coupling to transmon qubits with different frequencies and we present a bi-chromatic scheme for entanglement and gate operations. In this calculation, we obtain a maximally entangled state with a fidelity F = 95 % . Our proposal is competitive with the achievements of other entanglement-gates with superconducting devices and it may offer some advantages: (i) There is no need for additional control lines and dephasing associated with the conventional frequency tuning of qubits. (ii) When our qubits are idle, they are far detuned with respect to each other and to the resonator, and hence they are immune to cross talk and Purcell-enhanced decay.

  6. The Coulomb gap and low energy statistics for Coulomb glasses

    Microsoft Academic Search

    Andreas Glatz; Valerii M. Vinokur; Joakim Bergli; Martin Kirkengen; Yuri M. Galperin

    2008-01-01

    We study the statistics of local energy minima in the configuration space of two-dimensional lattice Coulomb glasses with site disorder and the behavior of the Coulomb gap depending on the strength of random site energies. At intermediate disorder, i.e., when the typical strength of the disorder is of the same order as the nearest-neighbor Coulomb energy, the high energy tail

  7. Superconducting energy storage development for electric utility systems

    Microsoft Academic Search

    R. D. Turner; H. J. Boenig; W. V. Hassenzahl

    1977-01-01

    High load factors are desirable goals for all electric utilities to reduce the total power generation cost. Superconducting Magnetic Energy Storage (SMES) technology has progressed to the point where it shows promise as an alternate energy-storage method to pumped hydrostorage for improving electric-utility load factors. Experiments indicate that a SMES system responds quickly (i.e., in milliseconds) to power-system demand and

  8. Optimal current distribution for energy storage in superconducting magnets

    SciTech Connect

    Salingaros, N.A. (Division of Mathematics, University of Texas, San Antonio, Texas 78285 (US) Center for Fusion Engineering, University of Texas, Austin, Texas 78712)

    1991-01-01

    The magnetic energy stored in a cylinder or torus is optimized by adopting a special current distribution with helical windings. A cylindrical cable wound following a Bessel-function distribution that reverses on the surface has greatly reduced self-force and self-stresses. This result applies to energy storage in large-scale superconducting magnets, and is also of importance in plasma physics and astrophysics.

  9. Heat transport in RbFe2As2 single crystals: Evidence for nodal superconducting gap

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Wang, A. F.; Hong, X. C.; Zhang, J.; Pan, B. Y.; Pan, J.; Xu, Y.; Luo, X. G.; Chen, X. H.; Li, S. Y.

    2015-01-01

    The in-plane thermal conductivity of iron-based superconductor RbFe2As2 single crystal (Tc? 2.1 K) was measured down to 100 mK. In zero field, the observation of a significant residual linear term ?0/T = 0.65 mW K-2 cm-1 provides clear evidence for nodal superdonducting gap. The field dependence of ?0/T is similar to that of its sister compound CsFe2As2 with comparable residual resistivity ?0 and lies between the dirty and clean KFe2As2 . These results suggest that the (K, Rb, Cs)Fe2As2 serial superconductors have a common nodal gap structure.

  10. Evaluation of a Tunnel Barrier in Superconducting NbN Junctions With Subharmonic Gap Structures

    Microsoft Academic Search

    Yoshinori Uzawa; Zhen Wang; Masanori Takeda; Matthias Kroug

    2007-01-01

    We have investigated the current density dependence of subharmonic gap structures in NbN tunnel junctions. Using multiple Andreev reflection theory for a homogeneous barrier, we evaluated barrier transparency for junctions with various current densities ranging from 4 to 20 kA\\/cm2 by observing the current step height at a voltage of 2Delta\\/ne for n = 1, 2, and 3. The results

  11. The calculation of band gap energy in zinc oxide films

    NASA Astrophysics Data System (ADS)

    Arif, Ali; Belahssen, Okba; Gareh, Salim; Benramache, Said

    2015-01-01

    We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor; the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques. The thin films were deposited at different substrate temperatures ranging between 200 and 500 °C. In this paper, we present a new approach to control the optical gap energy of ZnO thin films by concentration of the ZnO solution and substrate temperatures from experimental data, which were published in international journals. The model proposed to calculate the band gap energy with the Urbach energy was investigated. The relation between the experimental data and theoretical calculation suggests that the band gap energies are predominantly estimated by the Urbach energies, film transparency, and concentration of the ZnO solution and substrate temperatures. The measurements by these proposal models are in qualitative agreements with the experimental data; the correlation coefficient values were varied in the range 0.96–0.99999, indicating high quality representation of data based on Equation (2), so that the relative errors of all calculation are smaller than 4%. Thus, one can suppose that the undoped ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition and contained higher optical band gap energy.

  12. Localization of metal-induced gap states at the metal-insulator interface: Origin of flux noise in SQUIDs and superconducting qubits

    SciTech Connect

    Choi, SangKook; Lee, Dung-Hai; Louie, Steven G.; Clarke, John

    2009-10-10

    The origin of magnetic flux noise in Superconducting Quantum Interference Devices with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 20 years. This noise limits the decoherence time of superconducting qubits. A consensus has emerged that the noise arises from fluctuating spins of localized electrons with an areal density of 5 x 10(17)m(-2). We show that, in the presence of potential disorder at the metal-insulator interface, some of the metal-induced gap states become localized and produce local moments. A modest level of disorder yields the observed areal density.

  13. Energy Gaps in the Failed High-Tc Superconductor La_1.875Ba_0.125CuO_4

    SciTech Connect

    He, R.

    2010-05-04

    A central issue on high-T{sub c} superconductivity is the nature of the normal-state gap (pseudogap) in the underdoped regime and its relationship with superconductivity. Despite persistent efforts, theoretical ideas for the pseudogap evolve around fluctuating superconductivity, competing order and spectral weight suppression due to many-body effects. Recently, while some experiments in the superconducting state indicate a distinction between the superconducting gap and pseudogap, others in the normal state, either by extrapolation from high-temperature data or directly from La{sub 1.875}Ba{sub 0.125}CuO{sub 4} (LBCO-1/8) at low temperature, suggest the ground-state pseudogap is a single gap of d-wave form. Here we report angle-resolved photoemission (ARPES) data from LBCO-1/8, collected with improved experimental conditions, that reveal the ground-state pseudogap has a pronounced deviation from the simple d-wave form. It contains two distinct components: a d-wave component within an extended region around the node and the other abruptly enhanced close to the antinode, pointing to a dual nature of the pseudogap in this failed high-T{sub c} superconductor which involves a possible precursor pairing energy scale around the node and another of different but unknown origin near the antinode.

  14. Development of Low Energy Gap and Fully Regioregular Polythienylenevinylene Derivative

    DOE PAGESBeta

    David, Tanya M. S.; Zhang, Cheng; Sun, Sam-Shajing

    2014-01-01

    Low energy gap and fully regioregular conjugated polymers find its wide use in solar energy conversion applications. This paper will first briefly review this type of polymers and also report synthesis and characterization of a specific example new polymer, a low energy gap, fully regioregular, terminal functionalized, and processable conjugated polymer poly-(3-dodecyloxy-2,5-thienylene vinylene) or PDDTV. The polymer exhibited an optical energy gap of 1.46?eV based on the UV-vis-NIR absorption spectrum. The electrochemically measured highest occupied molecular orbital (HOMO) level is ?4.79?eV, resulting in the lowest unoccupied molecular orbital (LUMO) level of ?3.33?eV based on optical energy gap. The polymer wasmore »synthesized via Horner-Emmons condensation and is fairly soluble in common organic solvents such as tetrahydrofuran and chloroform with gentle heating. DSC showed two endothermic peaks at 67°C and 227°C that can be attributed to transitions between crystalline and liquid states. The polymer is thermally stable up to about 300°C. This polymer appears very promising for cost-effective solar cell applications.« less

  15. Energy gaps in Bi2Sr2CaCu2O8+? cuprate superconductors

    PubMed Central

    Ren, J. K.; Zhu, X. B.; Yu, H. F.; Tian, Ye; Yang, H. F.; Gu, C. Z.; Wang, N. L.; Ren, Y. F.; Zhao, S. P.

    2012-01-01

    The relationship between the cuprate pseudogap (?p) and superconducting gap (?s) remains an unsolved mystery. Here, we present a temperature- and doping-dependent tunneling study of submicron Bi2Sr2CaCu2O8+? intrinsic Josephson junctions, which provides a clear evidence that ?s closes at a temperature Tc0 well above the superconducting transition temperature Tc but far below the pseudogap opening temperature T*. We show that the superconducting pairing first occurs predominantly on a limited Fermi surface near the node below Tc0, accompanied by a Fermi arc due to the lifetime effects of quasiparticles and Cooper pairs. The arc length has a linear temperature dependence, and as temperature decreases below Tc it reduces to zero while pairing spreads to the antinodal region of the pseudogap leading to a d-wave superconducting gap on the entire Fermi surface at lower temperatures. PMID:22355760

  16. A High-Energy Graphite Spark Gap Switch

    Microsoft Academic Search

    He Meng-bing; Liu Ning; Hu Guan; Li Tao; Pan Yuan

    2009-01-01

    High-energy switch and trigger systems are required for a range of capacitor bank applications such as for electromagnetic rail, coil, and electro-thermal guns. Spark gaps can be made from brass copper or other metallic electrodes. Under high current and high charge transfer the metal may vaporize and create some deviations in trigger performance. A new approach using graphite electrodes avoids

  17. Energy gap of some alkaline halate crystals by optical methods

    NASA Astrophysics Data System (ADS)

    Koralewski, M.; Szafra?ski, M.

    1986-03-01

    Applying four optical methods i.e. Faraday rotation, optical absorption, diffuse reflection and refractive index dispersion the energy gap was calculated for LiIO 3, NaBrO 3 and NaClO 3 crystals. Preliminary discussion of electronic band structure of the crystals studied is given.

  18. Optical and electrical properties of thin superconducting films

    NASA Technical Reports Server (NTRS)

    Covington, Billy C.; Jing, Feng Chen

    1990-01-01

    Infrared spectroscopic techniques can provide a vital probe of the superconducting energy gap which is one of the most fundamental physical properties of superconductors. Currently, the central questions regarding the optical properties of superconductors are how the energy gap can be measured by infrared techniques and at which frequency the gap exists. An effective infrared spectroscopic method to investigate the superconducting energy gap, Eg, was developed by using the Bomem DA 3.01 Fourier Transformation Spectrophotometer. The reflectivity of a superconducting thin film of YBaCuO deposited on SrTiO3 was measured. A shoulder was observed in the superconducting state reflectance R(sub S) at 480/cm. This gives a value of Eg/kT(sub c) = 7.83, where k is the Boltzmann constant and T(sub c) is the superconducting transition temperature, from which, it is suggested that YBaCuO is a very strong coupling superconductor.

  19. Superconducting magnetic energy storage for BPA transmission line stabilization

    Microsoft Academic Search

    J. Rogers; M. Barron; H. Boenig; A. Criscuolo; J. Dean; R. Schermer

    1983-01-01

    The Bonneville Power Administration (BPA) operates the electrical transmission system that joins the Pacific Northwest with southern California. A 30 MJ (8.4 kWh) Superconducting Magnetic Energy Storage (SMES) unit with a 10 MW converter is being installed at the Tacoma Substation to provide system damping for low frequency oscillations of 0.35 Hz. The integrated system status is described and reviewed.

  20. New power-conditioning systems for superconducting magnetic energy storage

    NASA Astrophysics Data System (ADS)

    Han, Byung Moon

    1992-06-01

    This dissertation presents the development of new power-conditioning systems for superconducting magnetic energy storage (SMES), which can regulate fast and independently the active and reactive powers demanded in the ac network. Three new power-conditioning systems were developed through a systematic approach to match the requirements of the superconducting coil and the ac power network. Each of these new systems is composed of ten 100-MW modules connected in parallel to handle the large current through the superconducting coil. The first system, which was published in the IEEE Transactions on Energy Conversion, consists of line-commutated 24-pulse converter, a thyristor-switched tap-changing transformer, and a thyristor-switched capacitor bank. The second system, which was accepted for publication in the IEEE Transactions on Energy Conversion, consists of a 12-pulse GTO (gate turn-off thyristor) converter and a thyristor-switched tap-changing transformer. The third system, which was submitted to the International Journal of Energy System, consists of a dc chopper and a voltage-source PWM (pulse width modulation) converter. The operational concept of each new system is verified through mathematical analyses and computer simulations. The dynamic interaction of each new system with the ac network and the superconducting coil is analyzed using a simulation model with EMTP (electro-magnetic transients program). The analysis results prove that each new system is feasible and realizable. Each system can regulate the active and reactive powers of the utility network rapidly and independently, and each offer a significant reduction of the system rating by reducing the reactive power demand in the converter. Feasible design for each new system was introduced using a modular design approach based on the 1000 MW/5000 MWH plant, incorporating commercially available components and proven technologies.

  1. New power-conditioning systems for superconducting magnetic energy storage

    SciTech Connect

    Han, B.M.

    1992-01-01

    This dissertation presents the development of new power-conditioning systems for superconducting magnetic energy storage (SMES), which can regulate fast and independently the active and reactive powers demanded in the ac network. Three new power-conditioning systems were developed through a systematic approach to match the requirements of the superconducting coil and the ac power network. Each of these new systems is composed of ten 100-MW modules connected in parallel to handle the large current through the superconducting coil. The first system, which was published in the IEEE Transactions on EnergyConversion, consists of line-commutated 24-pulse converter, a thyristor-switched tap-changing transformer, and a thyristor-switched capacitor bank. The second system, which was accepted for publication in the IEEE Transactions on Energy Conversion, consists of a 12-pulse GTO (gate turn-off thyristor) converter and a thyristor-switched tap-changing transformer. The third system, which was submitted to the International Journal of Energy System, consists of a dc chopper and a voltage-source PWM (pulse width modulation) converter. The operational concept of each new system is verified through mathematical analyses and computer simulations. The dynamic interaction of each new system with the ac network and the superconducting coil is analyzed using a simulation model with EMTP (electro-magnetic transients program). The analysis results prove that each new system is feasible and realizable. Each system can regulate the active and reactive powers of the utility network rapidly and independently, and each offer a significant reduction of the system rating by reducing the reactive power demand in the converter. Feasible design for each new system was introduced using a modular design approach based on the 1000 MW/5000 MWH plant, incorporating commercially available components and proven technologies.

  2. Microcomputer control for the superconducting magnetic energy storage system

    SciTech Connect

    Seamons, M.J.; Criscuolo, A.L.

    1981-01-01

    The microcomputer-based, automatic control and data acquisition system for the Superconducting Magnetic Energy Storage system is described. A brief discussion of the function of SMES and identification of its major systems is followed by a detailed discussion of the control and data acquisition system. The distributed control and data acquisition architecture, interprocessor timing and communications, task scheduler, master-slave relationship, and man/machine interface are some of the topics discussed.

  3. Superconductivity in graphite intercalation compounds

    DOE PAGESBeta

    Smith, Robert P.; Dean, Mark P. M.; Weller, Thomas E.; Howard, Christopher A.; Rahnejat, Kaveh C.; Saxena, Siddharth S.; Ellerby, Mark

    2015-07-01

    The field of superconductivity in the class of materials known as graphite intercalation compounds has a history dating back to the 1960s This paper recontextualizes the field in light of the discovery of superconductivity in CaC? and YbC? in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how this relates to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes aremore »most important for superconductivity and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.« less

  4. Superconductivity in graphite intercalation compounds

    NASA Astrophysics Data System (ADS)

    Smith, Robert P.; Weller, Thomas E.; Howard, Christopher A.; Dean, Mark P. M.; Rahnejat, Kaveh C.; Saxena, Siddharth S.; Ellerby, Mark

    2015-07-01

    The field of superconductivity in the class of materials known as graphite intercalation compounds has a history dating back to the 1960s (Dresselhaus and Dresselhaus, 1981; Enoki et al., 2003). This paper recontextualizes the field in light of the discovery of superconductivity in CaC6 and YbC6 in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how these relate to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity, and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.

  5. Superconductivity in graphite intercalation compounds

    DOE PAGESBeta

    Smith, Robert P. [Univ. of Cambridge (United Kingdom); Dean, Mark P. M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Weller, Thomas E. [Univ. College of London (United Kingdom); Howard, Christopher A. [Univ. College of London (United Kingdom); Rahnejat, Kaveh C. [Univ. College of London (United Kingdom); Saxena, Siddharth S. [Univ. of Cambridge (United Kingdom); Ellerby, Mark [Univ. College of London (United Kingdom)

    2015-07-01

    The field of superconductivity in the class of materials known as graphite intercalation compounds has a history dating back to the 1960s This paper recontextualizes the field in light of the discovery of superconductivity in CaC? and YbC? in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how this relates to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.

  6. Glide-plane symmetry and superconducting gap structure of iron-based superconductors.

    PubMed

    Wang, Y; Berlijn, T; Hirschfeld, P J; Scalapino, D J; Maier, T A

    2015-03-13

    We consider the effect of glide-plane symmetry of the Fe-pnictogen/chalcogen layer in Fe-based superconductors on pairing in spin fluctuation models. Recent theories have proposed that so-called ?-pairing states with nonzero total momentum can be realized and possess exotic properties such as odd parity spin singlet symmetry and time-reversal symmetry breaking. Here we show that ? pairing is inevitable when there is orbital weight at the Fermi level from orbitals with even and odd mirror reflection symmetry in z; however, by explicit calculation, we conclude that the gap function that appears in observable quantities is identical to that found in earlier, 1 Fe per unit cell pseudocrystal momentum calculations. PMID:25815960

  7. Glide-Plane Symmetry and Superconducting Gap Structure of Iron-Based Superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Berlijn, T.; Hirschfeld, P. J.; Scalapino, D. J.; Maier, T. A.

    2015-03-01

    We consider the effect of glide-plane symmetry of the Fe-pnictogen/chalcogen layer in Fe-based superconductors on pairing in spin fluctuation models. Recent theories have proposed that so-called ? -pairing states with nonzero total momentum can be realized and possess exotic properties such as odd parity spin singlet symmetry and time-reversal symmetry breaking. Here we show that ? pairing is inevitable when there is orbital weight at the Fermi level from orbitals with even and odd mirror reflection symmetry in z ; however, by explicit calculation, we conclude that the gap function that appears in observable quantities is identical to that found in earlier, 1 Fe per unit cell pseudocrystal momentum calculations.

  8. Concept of Cold Energy Storage for Superconducting Flywheel Energy Storage System

    Microsoft Academic Search

    Jisung Lee; Sangkwon Jeong; Young Hee Han; Byung Jun Park

    2011-01-01

    A superconducting flywheel energy storage (SFES) system is an energy storage device with unprecedented small kinetic energy loss by utilizing diamagnetic levitation property of superconductor. The system, therefore, is expected to be one of the most promising candidates in the application of renewable energy field such as PV (photovoltaic) or wind energy development where the power generation is intermittent. An

  9. The role of Higher-Harmonics in the Superconducting Gap on the Magnetic Susceptibility of High-Tc Materials

    NASA Astrophysics Data System (ADS)

    Bill, Andreas; Schnyder, Andreas; Mudry, Christopher; Gilardi, Raffaele; Mesot, Joël

    2004-03-01

    Angle Resolved Photoemission Spectroscopy performed on high-temperature superconductors has established the increasing importance of long-range pairing interactions with underdoping [1]: higher harmonics beyond ?(k) ˜ s(k_x)-s(k_y) and consistent with d-wave symmetry have to be considered to account for the experimental findings. We show with a simple phenomenological model how the presence of these higher harmonics significantly affect the magnetic susceptibility in the superconducting state as observed by means of Inelastic Neutron Scattering [2]. In particular, we show that the contribution of higher harmonics renormalizes the spin-gap. This fact is traced back to Fermi surface nesting effects. We discuss several other features of the magnetic susceptibility that are yet to be verified experimentally. begindescription [1] J. Mesot, M.R. Norman, H. Ding, M. Randeria, J.C. Campuzano, A. Paramekanti, H.M. Fretwell, A. Kaminski, T. Takeuchi, T. Yokoya, T. Sato, T. Takahashi, T. Mochiku, and K. Kadowaki, Phys. Rev. Lett. 83, 840 (1999). [2] C.H. Lee, K. Yamada, Y. Endoh, G. Shirane, R.J. Birgeneau, M.A. Kastner, M. Greven, and Y.-J. Kim, J. Phys. Soc. Jap. 69, 1170 (2000); P. Dai, H.A. Mook, R.D. Hunt, F. Dobrevegan, Phys. Rev. B 63, 054525 (2001). description

  10. Superconducting magnetic energy storage for BPA transmission-line stabilization

    SciTech Connect

    Rogers, J.D.; Barron, M.H.; Boenig, H.J.; Criscuolo, A.L.; Dean, J.W.; Schermer, R.I.

    1982-01-01

    The Bonneville Power Administration (BPA) operates the electrical transmission system that joins the Pacific Northwest with southern California. A 30 MJ (8.4 kWh) Superconducting Magnetic Energy Storage (SMES) unit with a 10 MW converter is being installed at the Tacoma Substation to provide system damping for low frequency oscillations of 0.35 Hz. The integrated system status is described and reviewed. Components included in the system are the superconducting coil, seismically mounted in an epoxy fiberglass nonconducting dewar; a helium refrigerator; a heat rejection subsystem; a high pressure gas recovery subsystem; a liquid nitrogen trailer; the converter with power transformers and switchgear; and a computer system for remote microwave link operation of the SMES unit.

  11. The Slot Gap Model for Pulsar High-Energy Emission

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Muslimov, Alexander

    2004-01-01

    A new picture of pulsar high-energy emission is proposed that is different from both the traditional polar cap and outer gap models, but combines elements of each. The slot gap model is based on electron acceleration along the edge of the open field region from the neutron star surface to near the light cylinder. Along the last open field line, the pair formation front rises to very high altitude forming a slot gap, where the accelerating electric field is unscreened by pairs. Electrons continue to accelerate to high altitudes in the slot gap, reaching a radiation reaction-limited energy of several TeV. The resulting radiation pattern features sharp caustics on the trailing edge of the open field region, allowing for the possibility of double-peaked pulse profiles very similar to those observed in gamma-ray pulsars. Since emission from a large range of altitudes arrives in phase, this model very naturally explains the phase alignment of radiation at all wavelengths from the Crab pulsar.

  12. Semiconductor switched capacitive circuit for energy transfer between superconducting magnets

    SciTech Connect

    Baker, J.R.; Walters, J.D. [Naval Surface Warfare Center, Annapolis, MD (United States)

    1994-12-31

    A solid-state IGBT switched capacitive circuit capable of transferring energy between two 0.94 henry NbTi superconducting magnets storing 5.0 kJ has been developed. Maximum operating current in the magnets and switching circuit is 100A. Energy transfer between magnets is step-wise requiring the coupling capacitor to store only a small fraction of a magnet`s total stored energy. Energy transfer time is directly proportional to magnet current and inductance, and is inversely proportional to the maximum voltage across the coupling capacitor. Initial energy transfer rate goal is 5.0 kW; equating to a time rate of change in the magnetic field of 1.7 Tesla/sec. Only a small power supply is required to provide the initial charge to one coil, replace dissipated energy due to resistive heating in the semiconductor switches and connecting cables, and A.C. losses in the superconducting magnets. Test results from operating this energy transfer circuit are presented and discussed.

  13. Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)?As?

    DOE PAGESBeta

    Kim, J. S.; Faeth, B. D.; Wang, Y.; Hirschfeld, P. J.; Stewart, G. R.; Gofryk, K.; Ronning, F.; Sefat, A. S.; Choi, K. Y.; Kim, K. H.

    2012-07-01

    Low-temperature specific heat, C, in magnetic fields up to Hc2 is reported for underdoped Ba(Fe?.???Co?.???)?As? (Tc = 8 K) and for three overdoped samples Ba(Fe??xCox)?As? (x = 0.103, 0.13, and 0.15; Tc = 17.2, 16.5, and 11.7 K, respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable-composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials, respectively. The present work shows that the measured behavior of the specific heat ? (?C/T as T ? 0, i.e., a measure of the electronic density of states at the Fermi energy) as a function of field approximately obeys ? ? H0.5±0.1, similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions x = 0.103 and 0.13, the low-field (H ? 10 T) data show a Volovik-like behavior of ? ? H0.3–0.4, followed by an inflection point, followed at higher fields by ? ? H¹. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.

  14. Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)?As?

    DOE PAGESBeta

    Kim, J. S.; Faeth, B. D.; Wang, Y.; Hirschfeld, P. J.; Stewart, G. R.; Gofryk, K.; Ronning, F.; Sefat, A. S.; Choi, K. Y.; Kim, K. H.

    2012-07-01

    Low-temperature specific heat, C, in magnetic fields up to Hc2 is reported for underdoped Ba(Fe?.???Co?.???)?As? (Tc = 8 K) and for three overdoped samples Ba(Fe??xCox)?As? (x = 0.103, 0.13, and 0.15; Tc = 17.2, 16.5, and 11.7 K, respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable-composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials, respectively. The present work shows that the measured behavior of the specific heat ? (?C/T as T ? 0, i.e., a measure of the electronic density of statesmore »at the Fermi energy) as a function of field approximately obeys ? ? H0.5±0.1, similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions x = 0.103 and 0.13, the low-field (H ? 10 T) data show a Volovik-like behavior of ? ? H0.3–0.4, followed by an inflection point, followed at higher fields by ? ? H¹. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.« less

  15. Superconducting magnetic bearings for energy storage flywheels

    Microsoft Academic Search

    T. Coombs; A. M. Campbell; R. Storey; R. Weller

    1999-01-01

    We are investigating the use of flywheels for energy storage. Flywheel devices need to be of high efficiency and an important source of losses is the bearings. In addition, the requirement is for the devices to have long lifetimes with minimal or no maintenance. Conventional rolling element bearings can and have been used, but a noncontact bearing, such as a

  16. Photonic Band Gap resonators for high energy accelerators

    SciTech Connect

    Schultz, S.; Smith, D.R. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics; Kroll, N. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics]|[Stanford Linear Accelerator Center, Menlo Park, CA (United States)

    1993-12-31

    We have proposed that a new type of microwave resonator, based on Photonic Band Gap (PBG) structures, may be particularly useful for high energy accelerators. We provide an explanation of the PBG concept and present data which illustrate some of the special properties associated with such structures. Further evaluation of the utility of PBG resonators requires laboratory testing of model structures at cryogenic temperatures, and at high fields. We provide a brief discussion of our test program, which is currently in progress.

  17. Power-law-like correlation between condensation energy and superconducting transition temperatures in iron pnictide/chalcogenide superconductors: Beyond the BCS understanding

    NASA Astrophysics Data System (ADS)

    Xing, Jie; Li, Sheng; Zeng, Bin; Mu, Gang; Shen, Bing; Schneeloch, J.; Zhong, R. D.; Liu, T. S.; Gu, G. D.; Wen, Hai-Hu

    2015-03-01

    Superconducting condensation energy U0int has been determined by integrating the electronic entropy in various iron pnictide/chalcogenide superconducting systems. It is found that U0int ~Tcn with n = 3 to 4, which is in sharp contrast to the simple BCS prediction U0BCS = 1 / 2NF?s2 , with NF the quasiparticle density of states at the Fermi energy and ?s the superconducting gap. A similar correlation holds if we compute the condensation energy through U0cal = 3?neff ?s2 / 4?2kB2 , with ?neff the effective normal state electronic specific heat coefficient. This indicates a general relationship ?neff ~Tcm with m = 1 to 2, which is not predicted by the BCS scheme. A picture based on quantum criticality is proposed to explain this phenomenon.

  18. Effective low-energy theory for superconducting topological insulators

    NASA Astrophysics Data System (ADS)

    Hao, Lei; Lee, Ting-Kuo

    2015-03-01

    Candidate pairings of superconducting topological insulators support interesting surface Andreev bound states (SABSs) known as Majorana fermions. As these materials are described by a two-orbital Bernevig–Hughes–Zhang type model, a general understanding of the low-energy physics such as the possible kinds of SABSs are difficult. By virtue of an analogy between a topological insulator and a time reversal invariant topological superconductor, we propose a simple and intuitive method of constructing the low-energy effective models for superconducting topological insulators like CuxBi2Se3. Depending on the value of the chemical potential and for experimentally relevant model parameters, the low-energy properties of these superconductors are shown to be determined by one copy or two copies of single-orbital effective models. If the effective pairing potential shows sign reversal upon reflection by the surface, one Kramers' pair or two Kramers' pairs of SABSs are expected to appear. Explicit analytical calculations in terms of the effective low energy model reproduce the dispersions of the numerically confirmed two pairs of SABSs for a commonly studied pairing.

  19. Superconductive tunneling in junctions containing lead-gold layered films

    Microsoft Academic Search

    S. Basavaiah; S. K. Lahiri

    1974-01-01

    Tunneling between lead-gold layered films separated by an oxide barrier has been investigated. From these results, the superconducting transition temperature and the energy gap of the compound, AuPb3, present in these films have been deduced.

  20. Hybridization and superconducting gaps in heavy-fermion superconductor PuCoGa5 probed via the dynamics of photoinduced quasiparticles

    SciTech Connect

    Talbayev, Diyar [Los Alamos National Laboratory; Trugman, Stuart A [Los Alamos National Laboratory; Zhu, Jian - Xin [Los Alamos National Laboratory; Bauer, Eric D [Los Alamos National Laboratory; Kennison, John A [Los Alamos National Laboratory; Mitchell, Jeremy N [Los Alamos National Laboratory; Thompson, Joe D [Los Alamos National Laboratory; Sarrao, John L [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory; Burch, Kenneth S [CANADA; Chia, Elbert E. M. [CANADA

    2009-01-01

    We have examined the relaxation of photoinduced quasiparticles in the heavy-fermion superconductor PuCoGa{sub 5}. The deduced electron-phonon coupling constant is incompatible with the measured superconducting transition temperature T{sub c}, which speaks against phonon-mediated superconducting pairing. Upon lowering the temperature, we observe an order-of-magnitude increase of the quasiparticle relaxation time in agreement with the phonon bottleneck scenario - evidence for the presence of a hybridization gap in the electronic density of states. The modification of photoinduced reflectance in the superconducting state is consistent with the heavy character of the quasiparticles that participate in Cooper pairing. The discovery of relatively high-temperature superconductivity in the Pu-based compounds PuCoGa{sub 5} (T{sub c} = 18.5 K) and PuRhGa{sub 5} (T{sub c} = 8.7 K) has renewed the interest in actinide materials research. The Pu-based superconductors share the HoCoGa{sub 5}-type tetragonal lattice stucture with the Ce-based series of compounds (CeRhIn{sub 5}, CeCoIn{sub 5}, and CeIrIn{sub 5}) commonly referred to as '115' materials. In the Ce-based 115 compounds, CeIrIn{sub 5} (T{sub c} = 0.4 K) and CeCoIn{sub 5} (T{sub c} = 2.3 K), display superconductivity at ambient pressure. Both Ce- and Pu-based 115 compounds display the heavy fermion behavior resulting from the influence of 4f (Ce) and 5f (Pu) electrons. The most intriguing question concerns the origin of superconductivity (SC) in the 115 materials. In the Ce series, the d-wave symmetry of the SC order parameter and the proximity of SC order to magnetism have lead to a widespread belief that the unconventional SC is induced by antiferromagnetic spin fluctuations. In the Pu compounds, two possible scenarios regarding the SC mechanism have been considered: one approach favors a magnetically mediated unconventional SC similar to that in CeCoIn{sub 5}. In the other scenario, the conventional SC is mediated by phonons, where the strength of the electron-phonon (e-ph) coupling {lambda} is the crucial parameter that sets the superconducting transition temperature T{sub c}. In this Letter, we present a measurement of the e-ph coupling constant {lambda} via the pump-probe optical study of the room-temperature relaxation time of photoinduced reflectance. We find that e-ph coupling ({lambda} = 0.2-0.26) is too weak to explain the high T{sub c} of PuCoGa{sub 5} and that phonon-mediated superconductivity is unlikely in this material. Upon lowering the temperature in the normal state (T > T{sub c}), we find an order-of-magnitude increase in the relaxation time consistent with a phonon bottleneck, similar to other heavy-fermion materials, which provides the first optical evidence of the presence of a hybridization gap in the electronic density of states (DOS). Below T{sub c}, the photoinduced response exhibits dramatic changes that we ascribe to the opening of the superconducting (SC) gap at the Fermi level. The observed dynamics confirms that the same quasiparticles detected in the normal state, i.e., the heavy quasiparticles, also participate in the SC pairing. Our study is the first to directly probe the electronic structure of PuCoGa{sub 5} in the SC state and corroborate that fact. Our results are consistent with the theoretical investigations, which find that the electronic structure is dominated by cylindrical sheets of Fermi surfaces with large 5f electron character, suggesting that the delocalized 5f electrons of Pu playa key role in the superconducting pairing.

  1. Effects of Out-of-Plane Disorder on the Nodal Quasiparticle and Superconducting Gap in Single-Layer Bi_2Sr_1.6Ln_0.4CuO_6 delta (Ln = La, Nd, Gd)

    SciTech Connect

    Hashimoto, M.

    2011-01-04

    How out-of-plane disorder affects the electronic structure has been investigated for the single-layer cuprates Bi{sub 2}Sr{sub 1.6}Ln{sub 0.4}CuO{sub 6+{delta}} (Ln = La, Nd, Gd) by angle-resolved photoemission spectroscopy. We have observed that, with increasing disorder, while the Fermi surface shape and band dispersions are not affected, the quasi-particle width increases, the anti-nodal gap is enhanced and the superconducting gap in the nodal region is depressed. The results indicate that the superconductivity is significantly depressed by out-of-plane disorder through the enhancement of the anti-nodal gap and the depression of the superconducting gap in the nodal region.

  2. Infrared Study of Superconductivity: Grating Coupled Plasmons in Yttrium BARIUM(2) COPPER(3) OXYGEN(7) and Gap Features in BARIUM(1-X) Potassium(x) Bismuth OXYGEN(3)

    NASA Astrophysics Data System (ADS)

    Dunmore, Franklin John

    1995-01-01

    The electrodynamic properties of two different superconductors, Barium Potassium Bismuth Oxide (BKBO) and Yttrium Barium Copper Oxide (YBCO) have been studied using the technique of transmission Fourier transform spectroscopy with liquid helium temperature bolometric detection. Plasmon resonances have been observed in far infrared transmission measurements on superconducting YBCO films. An Aluminum/Nichrome grating is used to couple infrared radiation to collective two-dimensional plasma modes. The plasmon dispersion is measured by using different grating periods. The strength of the plasma resonances weaken, then disappear as the temperature approaches the critical temperature. The results are analyzed using a grating coupler theory that includes the hybridization of the plasmons with the diffraction modes. Data taken in a magnetic field of up to 12 Tesla are characteristic of the real part of the conductivity of the YBCO film increasing with field, behavior similar to that with increasing of temperature. These results are consistent with the inducement of vortices in the YBCO film. The far infrared transmission of BKBO thin films, grown on Magnesium Oxide (MgO) substrates, was measured in the frequency range from 15 to 200 wavenumbers, and temperature range from 9 to 100 Kelvin. There is a BCS -like peak in the transmission spectrum. The strong coupling Eliashberg theory gives a better description of the optical data than the weak coupling Mattis-Bardeen theory. For an 18 Kelvin critical temperature (T_{c }) sample the Eliashberg model extrapolated to zero temperature gives a London penetration depth of 5500+/-100A and an energy gap of 6.2 meV (50.1 wavenumbers, or 4.0 kT_{c }). Because BKBO is in the dirty limit, the strong coupling characteristics in the optical conductivity is adequately described by the Allen-Dynes parameter only, as opposed to the full Holstein structure due to the electron -phonon interaction alpha^2F(omega). .

  3. Energy gap of the spin density wave at the Cr(110) surface

    NASA Astrophysics Data System (ADS)

    Schäfer, J.; Rotenberg, Eli; Kevan, S. D.; Blaha, P.

    2000-05-01

    Angle resolved photoemission is used to directly monitor the energy gap of the spin density wave of Cr at a (110) surface. Density functional calculations, including a Fermi surface contour, predict an energy gap in the surface proximity. Surface states are identified, and a near-surface gap of ˜200 meV at room temperature is found, using spectroscopy, extending above the Fermi level. The gap exhibits an increased critical temperature of ˜440 K and extends isotropically around the ? point.

  4. Low cost composite structures for superconducting magnetic energy storage systems

    SciTech Connect

    Rix, C. (General Dynamics Space Magnetics, San Diego, CA (United States)); McColskey, D. (National Inst. of Standards and Technology, Boulder, CO (United States)); Acree, R. (Phillips Lab., Edwards Air Force Base, CA (United States))

    1994-07-01

    As part of the Superconducting Magnetic Energy Storage/Engineering Test Model (SMES-ETM) programs, design, analysis, fabrication and test programs were conducted to evaluate the low cost manufacturing of Fiberglass Reinforced Plastic (FRP) beams for usage as major components of the structural and electrical insulation systems. These studies utilized pultrusion process technologies and vinylester resins to produce large net sections at costs significantly below that of conventional materials. Demonstration articles incorporating laminate architectures and design details representative of SMES-ETM components were fabricated using the pultrusion process and epoxy, vinylester, and polyester resin systems. The mechanical and thermal properties of these articles were measured over the temperature range from 4 K to 300 K. The results of these tests showed that the pultruded, vinylester components have properties comparable to those of currently used materials, such as G-10, and are capable of meeting the design requirements for the SMES-ETM system.

  5. Ni-impurity effects on the superconducting gap of La2-xSrxCuO4 studied from the magnetic field and temperature dependence of the electronic specific heat

    NASA Astrophysics Data System (ADS)

    Kurosawa, T.; Momono, N.; Oda, M.; Ido, M.

    2012-04-01

    The magnetic field and temperature dependence of the electronic specific heat Cel have been systematically investigated in La2-xSrxCu1-yNiyO4 (LSCNO) in order to study Ni-impurity effects on the superconducting (SC) gap. In LSCNO with x = 0.15 and y = 0.015, the value of ? (?Cel/T) at T = 0 K, ?0, is enhanced under the magnetic field H applied along the c axis. The increment of ?0, ??0, follows the Volovik relation ??0 = AH, characteristic of the SC gap with line nodes, with prefactor A similar to that of a pure sample. The Cel/T versus T curve under H = 0 shows a d-wave-like SC anomaly with an abrupt increase at Tc and T-linear dependence at T ? Tc, although the ?0-value in the Cel/T versus T curve increases with increasing Ni concentrations. Interestingly, as the SC part of Cel/T, Cel/T - ?0 ? ?s, decreases in LSCNO, Tc is reduced in proportion to the decrease of ?s. These findings can be explained phenomenologically by a simple model in which Ni impurities bring about strong pair breaking at the edges of the coherent nodal part of the Fermi surface but in the vicinity of the nodes of the SC gap. The reduction of the SC condensation energy U0 in LSCNO, evaluated from Cel at T?Tc, is also understood by the same model.

  6. Energy resolution of superconducting tunnel diodes in low-energy radiation detection

    Microsoft Academic Search

    V. V. Samedov

    1998-01-01

    In this paper, we obtain an expression for the energy resolution of superconducting tunnel diodes for detection of low-energy\\u000a x-rays. We show that the major contribution to the energy resolution comes from the relative variance of the probability that\\u000a a quasielectron tunnels from one layer to another, which is due to the spatial dependence of the probability of interaction\\u000a between

  7. Department of Energy`s Wire Development Workshop - Superconductivity program for electric systems

    SciTech Connect

    NONE

    1996-06-01

    The 1996 High-Temperature Superconducting Wire Development Workshop was held on January 31--February 1 at the Crown Plaza Tampa Westshore in Tampa, Florida. The meeting was hosted by Tampa Electric Company and sponsored by the Department of Energy`s Superconductivity Program for Electric Systems. The meeting focused on recent high-temperature superconducting wire development activities in the Department of Energy`s Superconductivity Systems program. Tampa Electric`s Greg Ramon began the meeting by giving a perspective on the changes now occurring in the utility sector. Major program wire development accomplishments during the past year were then highlighted, particularly the world record achievements at Los Alamos and Oak Ridge National Laboratories. The meeting then focussed on three priority technical issues: thallium conductors; AC losses in HTS conductors; and coated conductors on textured substrates. Following in-depth presentations, working groups were formed in each technology area to discuss and critique the most important current research and development issues. The working groups identified research areas that have the potential for greatly enhancing the wire development effort. These areas are discussed in the summary reports from each of the working groups. This document is a compilation of the workshop proceedings including all general session presentations and summary reports from the working groups.

  8. Magnetic Energy Storage System: Superconducting Magnet Energy Storage System with Direct Power Electronics Interface

    SciTech Connect

    None

    2010-10-01

    GRIDS Project: ABB is developing an advanced energy storage system using superconducting magnets that could store significantly more energy than today’s best magnetic storage technologies at a fraction of the cost. This system could provide enough storage capacity to encourage more widespread use of renewable power like wind and solar. Superconducting magnetic energy storage systems have been in development for almost 3 decades; however, past devices were designed to supply power only for short durations—generally less than a few minutes. ABB’s system would deliver the stored energy at very low cost, making it ideal for eventual use in the electricity grid as a costeffective competitor to batteries and other energy storage technologies. The device could potentially cost even less, on a per kilowatt basis, than traditional lead-acid batteries.

  9. Length and energy gap dependences of thermoelectricity in nanostructured junctions.

    PubMed

    Asai, Yoshihiro

    2013-04-17

    The possibilities of an enhanced thermoelectric figure of merit value, ZT, in a nanostructured junction are examined for a wide range of parameter values in a theoretical model. Our research shows that the figure of merit can take a very large maximum, which depends both on the length and the energy gap values. The maximum of ZT is achieved when the Fermi level of the electrodes is aligned to the edge of the electronic transmission function of the junction, where both the conductance and the Seebeck constant are significantly enhanced. On the basis of our results, we conclude that nanowires and molecular junctions form a special class of systems where a large ZT can be expected in some cases. PMID:23528878

  10. Electrode Erosion of a High Energy Impulse Spark Gap Switch

    NASA Astrophysics Data System (ADS)

    Yao, Xueling; Zeng, Zhengzhong; Chen, Jinliang

    2005-12-01

    Based on the principle of thermal conduction, three metal alloys (stainless steel, copper-tungsten and graphite) were chosen as the material of the high impulse current discharging switch. Experimental results indicate that the mass loss and surface erosion morphology of the electrode are related with the electrode material (conductivity ?, melting point Tm, density ? and thermal capacity c) and the impulse transferred charge (or energy) per impulse for the same total impulse transferred charge. The experimental results indicate that the mass loss of stainless steel, copper-tungsten and graphite are 380.10 ?g/C, 118.10 ?g/C and 81.90 ?g/C respectively under the condition of a total impulse transferred charge of 525 C and a transferred charge per impulse of 10.5 C. Under the same impulse transferred charge, the mass loss of copper-tungsten (118.10 ?g/C) with the transferred charge per impulse at 10.5 C is far larger than the mass loss (38.61 ?g/C) at a 1.48 C transferred charge per impulse. The electrode erosion mechanism under high energy impulse arcs is analyzed briefly and it is suggested that by selecting high conductive metal or metal alloy as the electrode material of a high energy impulse spark gap switch and setting high erosion resistance material at the top of the electrode, the mass loss of the electrode can be reduced and the life of the switch prolonged.

  11. Energy gap induced by the surface optical polaron in graphene on polar substrates

    NASA Astrophysics Data System (ADS)

    Wang, Zi-Wu; Liu, Lei; Li, Zhi-Qing

    2015-03-01

    The polaron effects are investigated in the presence of a magnetic field based on the carrier-surface optical phonon coupling induced by the polar substrates under the graphene. We find that the energy gap is opened in the zero-energy Landau level due to the polaron effect. The magnitude of energy gap is consistent with recent experimental measurements. Moreover, the gap can be tuned by choosing the polarization of substrates and controlling the distance between graphene and polar substrate. The results obtained provide a possible explanation for the origin of energy gap opening and highlight the bandgap engineering of graphene on polar substrates.

  12. Effect of anisotropy on the magnon energy gap in a two-layer ferromagnetic superlattice

    Microsoft Academic Search

    Rong-Ke Qiu; Jing Liang; Qing-Feng Li; Zhi-Dong Zhang; Pan-Pan Song; Xiao-Min Hong

    2009-01-01

    The magnon energy bands or spectra in a two-layer ferromagnetic superlattice are studied. It is found that a modulated energy gap exists in the magnon energy band along Kx direction perpendicular to the superlattice plane, which is different from the optical magnon gap at Kx=0. The anisotropy, the spin quantum numbers and the interlayer exchange couplings all affect the magnon

  13. Superconductive Magnetic Energy Storage (SMES) System Studies for Electrical Utility at Wisconsin 

    E-print Network

    Boom, R. W.; Eyssa, Y. M.; Abdelsalem, M. K.; Huang, X.

    1988-01-01

    Two-layer low aspect ratio rippled and non-rippled solenoids mounted in surface trenches are described for superconductive magnetic energy storage utility applications. Open pool cooling in superfluid helium provides extended time cryogenic...

  14. Breakdown of the energy gap law in molecular lanthanoid luminescence: the smallest energy gap is not universally relevant for nonradiative deactivation.

    PubMed

    Doffek, Christine; Wahsner, Jessica; Kreidt, Elisabeth; Seitz, Michael

    2014-04-01

    For several decades, the energy gap law has been the prevalent theoretical framework for the discussion of nonradiative deactivation of lanthanoid luminescence in molecular coordination chemistry. Here we show experimentally on samarium and dysprosium model complexes that the size of the energy gap ?E between a lanthanoid emitting state and the next-lower electronic state cannot be considered a reliable and accurate predictor of the quantitative extent of nonradiative deactivation by aromatic C-H and C-D oscillator overtones. Because the energy gap is the central pillar for the entire conceptual framework of the energy gap law, this finding amounts to largely invalidating this theory for the quantitative description of molecular multiphonon relaxation. PMID:24665884

  15. Design and operation of a superconducting high energy beam line at the Argonne National Laboratory zero gradient synchrotron

    Microsoft Academic Search

    J. Bywater; C. Brzegowy; J. Dvorak; R. Fuja; H. Ludwig; K. Mataya; R. Moffett; R. Niemann; S. Wang; J. Purcell

    1977-01-01

    A superconducting high energy physics beam line 60 meters long is now operating at the Argonne National Laboratory Zero Gradient Synchrotron (ZGS). The line transports 12 GeV\\/c polarized protons to a large particle spectrometer. It consists of ten superconducting dipoles, two superconducting quadrupoles, and several conventional magnets. The superconducting magnets are contained in four cryostats; three 3-dipole cryostats, each 3.5

  16. InN{x}As{1-x} band gap energy and band bowing coefficient calculation

    NASA Astrophysics Data System (ADS)

    Sentosa, D.; Tang, X.; Chua, S. J.

    2007-12-01

    The band gap energies of zinc-blende InN{x}As{1-x} alloy as a function of its nitrogen composition have been calculated using the density functional theory. The results agree well with those obtained from experimental results. The minimum band gap energy of InN{x}As{1-x} alloy obtained is 70 meV at its N composition of 0.45. The band gap bowing coefficient of InN{x}As{1-x} alloy is obtained from the curve fitting of the simulated band gap energy versus the nitrogen composition, x. The band gap bowing coefficient of zinc-blende InN{x}As{1-x} alloy is found to be 2.072 ± 0.236 eV. The energy band gap for InN is also correctly predicted from this calculation.

  17. High Energy Emission from Rotation-Powered Pulsars: Outer-gap vs. Slot-gap Models

    E-print Network

    Kouichi Hirotani

    2008-09-08

    We explore particle accelerator electrodynamics in the magnetosphere of a rapidly rotating neutron star (NS). We address the importance of a self-consistent treatment of pair production, solving the Poisson equation describing the acceleration electric field, the Boltzmann equations for produced electrons and positrons, and the radiative transfer equation simultaneously. It is demonstrated that the accelerator solution is obtained if we only specify the NS spin period, magnetic dipole moment, magnetic inclination angle with respect to the rotation axis, and the NS surface temperature, and that the solution corresponds to a quantitative extension of previous outer-gap models. We apply the scheme to the Crab pulsar and show that the predicted pulse profiles and phase-resolved spectrum are roughly consistent with observations. Applying the same scheme to the slot-gap model, we show that this alternative model predicts too small photon flux to reproduce observations, because the gap trans-field thickness is significantly restricted by its pair-free condition.

  18. Superconducting gamma and fast-neutron spectrometers with high energy resolution

    DOEpatents

    Friedrich, Stephan (San Jose, CA); , Niedermayr, Thomas R. (Oakland, CA); Labov, Simon E. (Berkeley, CA)

    2008-11-04

    Superconducting Gamma-ray and fast-neutron spectrometers with very high energy resolution operated at very low temperatures are provided. The sensor consists of a bulk absorber and a superconducting thermometer weakly coupled to a cold reservoir, and determines the energy of the incident particle from the rise in temperature upon absorption. A superconducting film operated at the transition between its superconducting and its normal state is used as the thermometer, and sensor operation at reservoir temperatures around 0.1 K reduces thermal fluctuations and thus enables very high energy resolution. Depending on the choice of absorber material, the spectrometer can be configured either as a Gamma-spectrometer or as a fast-neutron spectrometer.

  19. Superconducting Cable Development for Future High Energy Physics Detector Magnets

    NASA Astrophysics Data System (ADS)

    Horvath, I. L.

    1995-11-01

    Under the leadership of the Swiss Federal Institute of Technology (ETHZ) an international ad hoc collaboration for superconducting cables developed an aluminium stabilised superconducting cable for future detector magnets. With the financial support of the Swiss government, this R&D work was carried out for the European Organisation for Nuclear Research (CERN). In this report the manufacturing process is described and results of the quality control measurements are summarised. These tests showed that the industrial manufacturing of an aluminium stabilised superconducting cable is feasible.

  20. A possible mechanism of the pseudo-gap in organic superconductor on the basis of the superconducting fluctuation

    Microsoft Academic Search

    Takanobu Jujo; Kosaku Yamada

    2000-01-01

    The explanation of the anomalous behavior which was revealed by the nuclear magnetic resonance experiments in ?-type (BEDT-TTF)2X is presented. We calculate the electronic properties by using the one-loop approximation for the superconducting fluctuation. The decrease of the density of states due to the large damping effect is obtained and the one-particle spectrum has a pseudogap structure around the Fermi

  1. Experimental and analytical study of the DC breakdown characteristics of polypropylene laminated paper with a butt gap condition considering the insulation design of superconducting cable

    NASA Astrophysics Data System (ADS)

    Seo, In-jin; Choi, Won; Seong, Jae-gyu; Lee, Bang-wook; Koo, Ja-yoon

    2014-08-01

    It has been reported that the insulation design under DC stress is considered as one of the critical factors in determining the performance of high-voltage direct current (HVDC) superconducting cable. Therefore, it is fundamentally necessary to investigate the DC breakdown characteristics of the composite insulation system consisting of liquid nitrogen (LN2)/polypropylene-laminated-paper (PPLP). In particular, the insulation characteristics under DC polarity reversal condition should be verified to understand the polarity effect of the DC voltage considering the unexpected incidents taking place at line-commutated-converters (LCC) under service at a DC power grid. In this study, to examine the variation of DC electric field strength, the step voltage and polarity reversal breakdown tests are performed under DC stress. Also, we investigate the electric field distributions in a butt gap of the LN2/PPLP condition considering the DC polarity reversal by using simulation software.

  2. Neutron spin resonance as a probe of superconducting gap anisotropy in partially detwinned electron underdoped NaFe0.985Co0.015As

    NASA Astrophysics Data System (ADS)

    Zhang, Chenglin; Park, J. T.; Lu, Xingye; Yu, Rong; Li, Yu; Zhang, Wenliang; Zhao, Yang; Lynn, J. W.; Si, Qimiao; Dai, Pengcheng

    2015-03-01

    We use inelastic neutron scattering (INS) to study the spin excitations in partially detwinned NaFe0.985Co0.015As which has coexisting static antiferromagnetic (AF) order and superconductivity (Tc=15 K, TN=30 K). In previous INS work on a twinned sample, spin excitations formed a dispersive sharp resonance near Er 1=3.25 meV and a broad dispersionless mode at Er 1=6 meV at the AF ordering wave vector QAF=Q1=(1 ,0 ) and its twinned domain Q2=(0 ,1 ) . For partially detwinned NaFe0.985Co0.015As with the static AF order mostly occurring at QAF=(1 ,0 ) , we still find a double resonance at both wave vectors with similar intensity. Since Q1=(1 ,0 ) characterizes the explicit breaking of the spin rotational symmetry associated with the AF order, these results indicate that the double resonance cannot be due to the static and fluctuating AF orders but originate from the superconducting gap anisotropy.

  3. High frequency resonant inverter for contactless energy transmission over large air gap

    Microsoft Academic Search

    R. Mecke; C. Rathge

    2004-01-01

    The paper investigates the influence of geometrical and electrical parameters on energy transmission through air gaps of several hundred millimetres. The transferable electric power and the efficiency of magnetic assemblies with large air gaps can be considerably improved by using higher transmission frequencies in the range of several hundred kilohertz. Contactless energy transmission systems operate at resonance. With a proper

  4. R&D of superconducting bearing technologies for flywheel energy storage systems

    Microsoft Academic Search

    N. Koshizuka

    2006-01-01

    Recent advances on superconducting magnetic bearing (SMB) technologies for flywheel energies storage systems (FESSs) are reviewed based on the results of NEDO flywheel project (2000–2004). We constructed a radial-type SMB model for 100kWh class FESSs and evaluated the bearing characteristics. The SMB model consists of a superconducting stator of YBCO bulks and a NdFeB permanent magnet circuit. The levitation force

  5. High-field studies of superconducting fluctuations in high-Tc cuprates: Evidence for a small gap distinct from the large pseudogap

    NASA Astrophysics Data System (ADS)

    Rullier-Albenque, F.; Alloul, H.; Rikken, G.

    2011-07-01

    We have used large pulsed magnetic fields up to 60 T to suppress the contribution of superconducting fluctuations (SCFs) to the ab-plane conductivity above Tc in a series of YBa2Cu3O6+x from the deep pseudogapped state to slight overdoping. Accurate determinations of the SCF contribution to the conductivity versus temperature and magnetic field have been achieved. Their joint quantitative analyses with respect to Nernst data allow us to establish that thermal fluctuations following the Ginzburg-Landau scheme are dominant for nearly optimally doped samples. The deduced coherence length ?(T) is in perfect agreement with a Gaussian (Aslamazov-Larkin) contribution for 1.01Tc?T?1.2Tc. A phase-fluctuation contribution might be invoked for the most underdoped samples in a T range which increases when controlled disorder is introduced by electron irradiation. For all dopings we evidence that the fluctuations are highly damped when increasing T or H. This behavior does not follow the Ginzburg-Landau approach, which should be independent of the microscopic specificities of the superconducting state. The data permits us to define a field Hc'(T) and a temperature Tc' above which the SCFs are fully suppressed. The analysis of the fluctuation magnetoconductance in the Ginzburg-Landau approach allows us to determine the critical field Hc2(0). The actual values of Hc'(0) and Hc2(0) are found to be quite similar and both increase with hole doping. These depairing fields, which are directly connected to the magnitude of the superconducting gap, do therefore follow the Tc variation which is at odds with the sharp decrease of the pseudogap T* with increasing hole doping. This is on line with our previous evidence that T* is not the onset of pairing. So the large gap seen by spectroscopic experiments in the underdoped regime has to be associated with the pseudogap. We finally propose here a three-dimensional phase diagram including a disorder axis, which makes it possible to explain most peculiar observations done so far on the diverse cuprate families.

  6. Superconductivity from insulating elements under high pressure

    NASA Astrophysics Data System (ADS)

    Shimizu, Katsuya

    2015-07-01

    The insulating and superconducting states would seem to have very different characteristics. Can any insulator become a superconductor? One proven method, doping an insulating material with carriers, can create itinerant states inside the gap between the conduction and valence bands. Another method is to squeeze the structure by applying pressure. Pressure can expand the bandwidth and also narrow the energy band gap. So the first step to turn an insulator into a superconductor is to make it metallic. Here we review our experimental research and results on superconductivity induced by applying pressure to insulating molecular systems such as elemental molecules.

  7. Simple Experimental Verification of the Relation between the Band-Gap Energy and the Energy of Photons Emitted by LEDs

    ERIC Educational Resources Information Center

    Precker, Jurgen W.

    2007-01-01

    The wavelength of the light emitted by a light-emitting diode (LED) is intimately related to the band-gap energy of the semiconductor from which the LED is made. We experimentally estimate the band-gap energies of several types of LEDs, and compare them with the energies of the emitted light, which ranges from infrared to white. In spite of…

  8. Hybrid fuel cell and energy storage systems using superconducting coil or batteries for clean electricity generation

    Microsoft Academic Search

    Darmawan Sutanto; Kai Ding

    2009-01-01

    This paper described a novel design of a hybrid fuel cell and energy storage system using high temperature superconducting energy storage system (HT-SMES) or batteries to meet fast changing load. The power electronic switches in the converter of the energy storage system are controlled in such a way that the amplitude and waveform of the inverter output current from the

  9. Theorem on the existence of a nonzero energy gap in adiabatic quantum computation

    E-print Network

    Da-Jian Zhang; Xiao-Dong Yu; D. M. Tong

    2014-10-14

    Adiabatic quantum computation, based on the adiabatic theorem, is a promising alternative to conventional quantum computation. The validity of an adiabatic algorithm depends on the existence of a nonzero energy gap between the ground and excited states. However, it is difficult to ascertain the exact value of the energy gap. In this paper, we put forward a theorem on the existence of nonzero energy gap for the Hamiltonians used in adiabatic quantum computation. It can help to effectively identify a large class of the Hamiltonians without energy-level crossing between the ground and excited states.

  10. Superconducting magnetic energy storage inductor and method of manufacture

    SciTech Connect

    Heyne, C.J.; Repp, J.R.; Hackworth, D.T.

    1990-03-27

    This patent describes a conductor for a superconducting coil. The conductor comprising a plurality of strands twisted together to form a cylindrical structure. Each strand comprising: a core composed of a plurality of parallel filaments of a material capable of exhibiting superconductivity; a sheath of metal surrounding, and intimately contacting, the core and forming a matrix in which at least some of the filaments are embedded; and a tubular member of high purity aluminum enclosing the sheath so as to be in intimate electrical contact with the sheath and support the core.

  11. Basic Research Needs for Superconductivity. Report of the Basic Energy Sciences Workshop on Superconductivity, May 8-11, 2006

    SciTech Connect

    Sarrao, J.; Kwok, W-K; Bozovic, I.; Mazin, I.; Seamus, J. C.; Civale, L.; Christen, D.; Horwitz, J.; Kellogg, G.; Finnemore, D.; Crabtree, G.; Welp, U.; Ashton, C.; Herndon, B.; Shapard, L.; Nault, R. M.

    2006-05-11

    As an energy carrier, electricity has no rival with regard to its environmental cleanliness, flexibility in interfacing with multiple production sources and end uses, and efficiency of delivery. In fact, the electric power grid was named ?the greatest engineering achievement of the 20th century? by the National Academy of Engineering. This grid, a technological marvel ingeniously knitted together from local networks growing out from cities and rural centers, may be the biggest and most complex artificial system ever built. However, the growing demand for electricity will soon challenge the grid beyond its capability, compromising its reliability through voltage fluctuations that crash digital electronics, brownouts that disable industrial processes and harm electrical equipment, and power failures like the North American blackout in 2003 and subsequent blackouts in London, Scandinavia, and Italy in the same year. The North American blackout affected 50 million people and caused approximately $6 billion in economic damage over the four days of its duration. Superconductivity offers powerful new opportunities for restoring the reliability of the power grid and increasing its capacity and efficiency. Superconductors are capable of carrying current without loss, making the parts of the grid they replace dramatically more efficient. Superconducting wires carry up to five times the current carried by copper wires that have the same cross section, thereby providing ample capacity for future expansion while requiring no increase in the number of overhead access lines or underground conduits. Their use is especially attractive in urban areas, where replacing copper with superconductors in power-saturated underground conduits avoids expensive new underground construction. Superconducting transformers cut the volume, weight, and losses of conventional transformers by a factor of two and do not require the contaminating and flammable transformer oils that violate urban safety codes. Unlike traditional grid technology, superconducting fault current limiters are smart. They increase their resistance abruptly in response to overcurrents from faults in the system, thus limiting the overcurrents and protecting the grid from damage. They react fast in both triggering and automatically resetting after the overload is cleared, providing a new, self-healing feature that enhances grid reliability. Superconducting reactive power regulators further enhance reliability by instantaneously adjusting reactive power for maximum efficiency and stability in a compact and economic package that is easily sited in urban grids. Not only do superconducting motors and generators cut losses, weight, and volume by a factor of two, but they are also much more tolerant of voltage sag, frequency instabilities, and reactive power fluctuations than their conventional counterparts. The challenge facing the electricity grid to provide abundant, reliable power will soon grow to crisis proportions. Continuing urbanization remains the dominant historic demographic trend in the United States and in the world. By 2030, nearly 90% of the U.S. population will reside in cities and suburbs, where increasingly strict permitting requirements preclude bringing in additional overhead access lines, underground cables are saturated, and growth in power demand is highest. The power grid has never faced a challenge so great or so critical to our future productivity, economic growth, and quality of life. Incremental advances in existing grid technology are not capable of solving the urban power bottleneck. Revolutionary new solutions are needed ? the kind that come only from superconductivity.

  12. Sensing with Superconducting Point Contacts

    PubMed Central

    Nurbawono, Argo; Zhang, Chun

    2012-01-01

    Superconducting point contacts have been used for measuring magnetic polarizations, identifying magnetic impurities, electronic structures, and even the vibrational modes of small molecules. Due to intrinsically small energy scale in the subgap structures of the supercurrent determined by the size of the superconducting energy gap, superconductors provide ultrahigh sensitivities for high resolution spectroscopies. The so-called Andreev reflection process between normal metal and superconductor carries complex and rich information which can be utilized as powerful sensor when fully exploited. In this review, we would discuss recent experimental and theoretical developments in the supercurrent transport through superconducting point contacts and their relevance to sensing applications, and we would highlight their current issues and potentials. A true utilization of the method based on Andreev reflection analysis opens up possibilities for a new class of ultrasensitive sensors. PMID:22778630

  13. Physical origin of photonic energy gaps in the propagation of surface plasmons on gratings

    Microsoft Academic Search

    W. L. Barnes; T. W. Preist; S. C. Kitson; J. R. Sambles

    1996-01-01

    We present an analytic model to describe the existence of photonic energy gaps in the propagation of surface plasmon polaritons on corrugated surfaces. We concentrate on elucidating the physical origin of the band gap, and accordingly we place strong emphasis on the physical reasoning and assumptions that we use. Our model is designed to give direct access to expressions for

  14. Minimum Quench Energy and Early Quench Development in NbTi Superconducting Strands

    E-print Network

    Breschi, M; Boselli, M; Bottura, Luca; Devred, Arnaud; Ribani, P L; Trillaud, F

    2007-01-01

    The stability of superconducting wires is a crucial task in the design of safe and reliable superconducting magnets. These magnets are prone to premature quenches due to local releases of energy. In order to simulate these energy disturbances, various heater technologies have been developed, such as coated tips, graphite pastes, and inductive coils. The experiments studied in the present work have been performed using a single-mode diode laser with an optical fiber to illuminate the superconducting strand surface. Minimum quench energies and voltage traces at different magnetic flux densities and transport currents have been measured on an LHC-type, Cu/NbTi wire bathed in pool boiling helium I. This paper deals with the numerical analysis of the experimental data. In particular, a coupled electromagnetic and thermal model has been developed to study quench development and propagation, focusing on the influence of heat exchange with liquid helium.

  15. Procedures for Filling Short Gaps in Energy Use and Weather Data 

    E-print Network

    Chen, H.; Claridge, D. E.

    2000-01-01

    Filling short gaps (a few hours) in hourly energy use and weather data can be useful for (i) retrofit savings analysis and calculation, and for (ii) diagnostic purposes. The paper evaluates four methods for rehabilitating short periods of missing...

  16. Hybrid superconducting magnetic bearing for kinetic energy storage applications and its frictional energy loss

    SciTech Connect

    Xia, Zule; Ma, Ki; Chen, Quark [Univ. of Houston, TX (United States)] [and others

    1996-12-31

    A hybrid superconducting magnetic bearing (HSMB) has been designed, constructed and implemented in a flywheel energy storage (FES) prototype. The HSMB design uses magnetic forces from permanent magnets for levitation and high temperature superconductor YBCO in between the magnets for stabilization. A 19 kg (42 lb.) flywheel currently can rotate up to 6,000 RPM with kinetic energy of 8 Wh stored. To identify the factors of frictional energy loss in the bearings, the authors have conducted a series of spin-down experiments in different operational conditions. The result from the recent test under the air pressure of 10{sup {minus}5} torr indicates an average frictional energy loss <2% per hour, with the imperfect system alignment and an unbalanced rotor.

  17. Resonant energy transfer between two defects in a photonic-band-gap system

    Microsoft Academic Search

    Yui Chow; Lie-Ming Li; Zhao-Qing Zhang; C. T. Chan

    1999-01-01

    The wave interference behaviors between two interacting defects in a two-dimensional photonic-band-gap system are studied by using the multiple-scattering method. By injecting electromagnetic wave energy at one defect, we find oscillatory resonant energy transfer between two defects when both defect mode frequencies lie inside a full gap. When one of the defect mode frequency merges with the pass band forming

  18. System modeling for Superconducting Magnetic Energy Storage (SMES)

    E-print Network

    Phadke, Nayana

    1992-01-01

    . The superconducting coils carry direct current. SMES has a rapid response time that permits going from full charging power to full discharging power in two cycles. This property makes its prospects look very bright for incorporating it in a, power system... For Improving System Stability This section describes the application of SMES in the area, of power system stability. The first prototype of SMES built was tested to see its ability to improve the dynamic stability of the Bonneville Power Administration...

  19. A correlation between ionization energies and critical temperatures in superconducting A3C60 fullerides

    NASA Astrophysics Data System (ADS)

    Hetfleisch, Florian; Stepper, Marco; Roeser, Hans-Peter; Bohr, Artur; Lopez, Juan Santiago; Mashmool, Mojtaba; Roth, Susanne

    2015-06-01

    Buckminster A3C60 fullerides (A = alkali metal) are usually superconductors with critical temperatures Tc in the range 2.5-40 K. Although they are very similar in size, structure and many other aspects, the effect of the alkali atoms on Tc has generally been understood in terms of the variation of the lattice constant. Here we show that there seems to be a direct correlation between the sum of the ionization energies of the three alkali atoms in the superconducting A3C60 compounds and the corresponding critical temperatures. A linear fit of the correlation implies a certain limit for the sum, below which superconductivity should not occur. Ionization energies have so far not been connected to superconductivity.

  20. Carrier relaxation in colloidal nanocrystals: Bridging large electronic energy gaps by low-energy vibrations

    NASA Astrophysics Data System (ADS)

    Han, Peng; Bester, Gabriel

    2015-02-01

    The three-dimensional confinement characterizing a nanocrystal (NC) leads to the formation of discrete electronic states. The energy gap between these states in colloidal NCs can be up to an order of magnitude larger than the vibrational energy of the host material. This large energetic mismatch (not given in self-assembled quantum dots) leads to the expectation that an electron occupying an excited state would be unable to release its energy to vibrations and a "phonon bottleneck" should finally be observed. Using large-scale ab initio calculations and a time-dependent formalism, we show that on the contrary, a phonon bottleneck can be observed only in a narrow window of diameters for CdSe and InAs NCs and should not occur at all in Si NCs. Two relaxation pathways enable fast carrier relaxation. For smaller structures (below 20-Å radius), the coupling strength and energy detuning are such that quantum mechanics allows us to effectively bridge electronic gaps much larger than the vibronic energy. For larger structures, the coupling to passivant modes, although very weak, leads to an efficient picosecond carrier relaxation. This work provides insight into the nature of carrier relaxation in colloidal nanostructures and highlights that defects, of any kind, are not necessary to explain the observed fast carrier relaxation.

  1. Development of an abort gap monitor for high-energy proton rings

    SciTech Connect

    Beche, Jean-Francois; Byrd, John; De Santis, Stefano; Denes, Peter; Placidi, Massimo; Turner, William; Zolotorev, Max

    2004-05-03

    The fill pattern in proton synchrotrons usually features an empty gap, longer than the abort kicker raise time, for machine protection. This gap is referred to as the ''abort gap'' and any particles, which may accumulate in it due to injection errors and diffusion between RF buckets, would be lost inside the ring, rather than in the beam dump, during the kicker firing. In large proton rings, due to the high energies involved, it is vital to monitor the build up of charges in the abort gap with a high sensitivity. We present a study of an abort gap monitor based on a photomultiplier with a gated microchannel plate, which would allow for detecting low charge densities by monitoring the synchrotron radiation emitted. We show results of beam test experiments at the Advanced Light Source using a Hamamatsu 5916U MCP-PMT and compare them to the specifications for the Large Hadron Collider

  2. Summary of Gaps and Barriers for Implementing Residential Building Energy Efficiency Strategies

    SciTech Connect

    Not Available

    2010-08-01

    This report presents the key gaps and barriers to implementing residential energy efficiency strategies in the U.S. market, as identified in sessions at the U.S. Department of Energy's Building America 2010 Residential Energy Efficiency Meeting held in Denver, Colorado, on July 20-22, 2010.

  3. Double Moral Hazard and the Energy Efficiency Gap Louis-Gatan Giraudet1

    E-print Network

    Boyer, Edmond

    Double Moral Hazard and the Energy Efficiency Gap Louis-Gaëtan Giraudet1 , Sébastien Houde2. Abstract (23 words) Moral hazard issues can deter profitable investments in energy efficiency. Energy literature. This article summarizes early results, focusing on moral hazard issues and policy solutions

  4. Double Moral Hazard and the Energy Efficiency Gap Louis-Gaetan Giraudet

    E-print Network

    Paris-Sud XI, Université de

    Double Moral Hazard and the Energy Efficiency Gap Louis-Ga¨etan Giraudet , S´ebastien Houde June 21, 2014 Abstract We investigate how moral hazard problems can cause sub-optimal investment in energy formalize the double moral haz- ard problem described above and examine how the resulting energy efficiency

  5. Excitation of Superconducting Qubits from Hot Nonequilibrium Quasiparticles

    NASA Astrophysics Data System (ADS)

    Wenner, J.; Yin, Yi; Lucero, Erik; Barends, R.; Chen, Yu; Chiaro, B.; Kelly, J.; Lenander, M.; Mariantoni, Matteo; Megrant, A.; Neill, C.; O'Malley, P. J. J.; Sank, D.; Vainsencher, A.; Wang, H.; White, T. C.; Cleland, A. N.; Martinis, John M.

    2013-04-01

    Superconducting qubits probe environmental defects such as nonequilibrium quasiparticles, an important source of decoherence. We show that “hot” nonequilibrium quasiparticles, with energies above the superconducting gap, affect qubits differently from quasiparticles at the gap, implying qubits can probe the dynamic quasiparticle energy distribution. For hot quasiparticles, we predict a non-negligible increase in the qubit excited state probability Pe. By injecting hot quasiparticles into a qubit, we experimentally measure an increase of Pe in semiquantitative agreement with the model and rule out the typically assumed thermal distribution.

  6. Superconducting Tunnel Junction Array Development for High-Resolution Energy-Dispersive X-ray Spectroscopy

    Microsoft Academic Search

    S. Friedrich; C. A. Mears; B. Nideröst; L. J. Hiller; M. Frank; S. E. Labov; A. T. Barfknecht; S. P. Cramer

    1998-01-01

    : Cryogenic energy-dispersive X-ray detectors are being developed because of their superior energy resolution (10 eV FWHM for keV X-rays) compared to that achieved in semiconductor energy-dispersive spectrometry (EDS) systems. So far, their range of application is limited because of their comparably small size and low count rate. We present data on the development of superconducting tunnel junction (STJ) detector

  7. Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)?As?

    SciTech Connect

    Kim, J. S.; Faeth, B. D.; Wang, Y.; Hirschfeld, P. J.; Stewart, G. R.; Gofryk, K.; Ronning, F.; Sefat, A. S.; Choi, K. Y.; Kim, K. H.

    2012-07-01

    Low-temperature specific heat, C, in magnetic fields up to Hc2 is reported for underdoped Ba(Fe?.???Co?.???)?As? (Tc = 8 K) and for three overdoped samples Ba(Fe??xCox)?As? (x = 0.103, 0.13, and 0.15; Tc = 17.2, 16.5, and 11.7 K, respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable-composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials, respectively. The present work shows that the measured behavior of the specific heat ? (?C/T as T ? 0, i.e., a measure of the electronic density of states at the Fermi energy) as a function of field approximately obeys ? ? H0.5±0.1, similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions x = 0.103 and 0.13, the low-field (H ? 10 T) data show a Volovik-like behavior of ? ? H0.3–0.4, followed by an inflection point, followed at higher fields by ? ? H¹. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.

  8. Preliminary investigation of small scale superconducting magnetic energy storage (SMES) systems. Final report

    Microsoft Academic Search

    J. Schwartz; E. E. Burkhardt; W. R. Taylor

    1996-01-01

    Most Army installations purchase electricity from local utilities and pay an additional charge for peak demand. If the peak demand can be reduced, installations can realize significant cost savings. This research investigated the technical and economic issues associated with constructing a small scale superconducting magnetic energy storage (SMES) system for reducing peak demand at Army installations. Analyses included magnetic design

  9. 30 MJ superconducting magnetic energy storage for BPA transmission line stabilizer

    Microsoft Academic Search

    R. I. Schermer; H. J. Boenig; J. Dean

    1981-01-01

    The development of a 30 MJ (8.4 kWh) superconducting magnetic energy storage (SMES) unit with a 10 MW converter which can provide system damping for low frequency oscillations is described. The coil is complete and all major components of the electrical and cryogenic systems were received and are tested. Computer control hardware is in place and software development is proceeding.

  10. Performance of a power conversion system for superconducting magnetic energy storage (SMES)

    Microsoft Academic Search

    James J. Skiles; Robert L. Kustom; Ka-Pui Ko; V. Wong; Ka-Shu Ko; F. Vong; K. Klontz

    1996-01-01

    This paper presents the results of laboratory tests of a power conversion system (PCS) for superconducting magnetic energy storage (SMES) applications. The PCS uses a two-quadrant chopper and a voltage-source power converter. Operating modes of the chopper are discussed. Operation of SMES to provide independent control of real and reactive power, operation as a static VAr compensator, low frequency modulation

  11. Improving the dynamics of a flywheel energy storage system with superconducting magnetic bearings

    Microsoft Academic Search

    Mochimitsu Komori; Toru Kawashima

    2004-01-01

    This paper describes a new method for improving the dynamics of a flywheel energy storage system using superconducting magnetic bearings (SMBs). The SMBs are composed of a ring-shaped superconductor and some permanent magnets (PM). Changes in stiffness and damping coefficient of the SMBs were investigated. Forced displacements are given to the SMBs to improve the stiffness and the damping coefficient.

  12. Design of superconducting magnetic bearings with high levitating force for flywheel energy storage systems

    Microsoft Academic Search

    Z. Xia; Q. Y. Chen; K. B. Ma; C. K. McMichael; M. Lamb; R. S. Cooley; P. C. Fowler; W. K. Chu

    1995-01-01

    Hybrid superconducting magnetic bearing (SMB), using YBCO high temperature superconductors (HTS) coupled with permanent magnets, has been implemented into a flywheel energy storage (FES) system prototype. The hybrid SMB design uses permanent magnets to levitate the rotor weighing 19 kg and superconductors to stabilize the inherently unstable magnet-magnet interactions. The SMB bearings are brought into action under convenient field-cooled conditions.

  13. Halbach array superconducting magnetic bearing for a flywheel energy storage system

    Microsoft Academic Search

    Guilherme G. Sotelo; Antonio C. Ferreira

    2005-01-01

    In order to develop a new magnetic bearing set for a flywheel energy storage prototype, it was designed and simulated some configurations of Permanent Magnetic Bearings (PMB) and Superconducting Magnetic Bearings (SMB). The bearings were assembled with Nd-Fe-B permanent magnets and the simulations were carried out with the Finite Element Method (FEM). The PMB was designed to reduce the load

  14. Power system stabilization by superconducting magnetic energy storage with solid-state phase shifter

    Microsoft Academic Search

    Y. Mitani; T. Uranaka; K. Tsuji

    1995-01-01

    In this paper, a new configuration of power system controller with a combination of superconducting magnetic energy storage and phase shifter, is proposed to improve the stability of a long distance bulk power transmission system. A power system stabilizing control scheme is also proposed. A related simulation shows that the proposed controller is effective for enhancement of power system stability

  15. Development towards ultra-thin superconducting solenoid magnets for high energy particle detectors

    Microsoft Academic Search

    Akira Yamamoto; Yasuhiro Makida; Ken-Ichi Tanaka; Yoshikuni Doi; Takahiko Kondo; Katsunori Wada; Shin-Ichiro Meguro

    1999-01-01

    Development towards ultra-thin superconducting solenoid magnets for high energy particle detector has been carried out by focusing on aluminum stabilized superconductor mechanically reinforced while keeping electrical resistivity as low as possible. It has been realized by using combined technologies of “micro-alloying” and “cold-work hardening”. Further general efforts to realize transparent solenoids are also discussed.

  16. Concepts of flywheels for energy storage using autostable high-T(sub c) superconducting magnetic bearings

    NASA Technical Reports Server (NTRS)

    Bornemann, Hans J.; Zabka, R.; Boegler, P.; Urban, C.; Rietschel, H.

    1994-01-01

    A flywheel for energy storage using autostable high-T(sub c) superconducting magnetic bearings has been built. The rotating disk has a total weight of 2.8 kg. The maximum speed is 9240 rpm. A process that allows accelerated, reliable and reproducible production of melt-textured superconducting material used for the bearings has been developed. In order to define optimum configurations for radial and axial bearings, interaction forces in three dimensions and vertical and horizontal stiffness have been measured between superconductors and permanent magnets in different geometries and various shapes. Static as well as dynamic measurements have been performed. Results are being reported and compared to theoretical models.

  17. The potential energy of a superconducting ring system locking magnetic flows in a gravity field

    NASA Astrophysics Data System (ADS)

    Bishaev, A. M.; Bush, A. A.; Gavrikov, M. B.; Kamentsev, K. E.; Kozintseva, M. V.; Saveliev, V. V.; Sigov, A. S.

    2012-10-01

    The possibility of creating a magnetic system of a plasma trap with levitating magnetic coils is under consideration. For this purpose, the analytical function of the potential energy of the system of several superconducting rings, which lock the required flows (at that, the one ring is fixed), versus the coordinates of free rings in the homogeneous gravity field under approximation of thin rings. Using calculations in the Mathcad medium, it is shown that, under definite values of parameters, there are equilibrium states of such a system. In the positions that corresponded to the calculated values, stable levitation states of the superconducting ring are observed experimentally in the field of another superconducting ring. The obtained results prove that a magnetic system can be created on the basis of a levitating quadrupole.

  18. 30-MJ superconducting magnetic energy storage for electric-transmission stabilization

    SciTech Connect

    Turner, R.D.; Rogers, J.D.

    1981-01-01

    The Bonneville Power Administration operates the electric power transmission system that connects the Pacific Northwest and southern California. The HVAC interties develop 0.35 Hz oscillations when the lines are heavily loaded. A 30 MJ (8.4 kWh) Superconducting Magnetic Energy Storage (SMES) unit with a 10 MW converter can provide system damping for the oscillation. The unit is scheduled for installation in 1982 and operation in 1982-83. Status of the project is described. The conductor has been fully tested electrically and mechanically and the 5 kA superconducting cable has been produced. The 30 MJ superconducting coil is essentially complete. All major components of the electrical and cryogenic systems except the nonconducting dewar have been completed. The refrigerator and converter are undergoing tests. The system is to be located at the BPA Tacoma Substation and operated by microwave link from Portland, OR.

  19. Distinct Fermi-momentum dependent energy gaps in deeply underdoped Bi2212.

    NASA Astrophysics Data System (ADS)

    Tanaka, K.; Lee, W. S.; Lu, D. H.; Fujimori, A.; Fujii, T.; Risdiana; Terasaki, I.; Fujita, K.; Ishikado, M.; Uchida, S.; Scalapino, D. J.; Devereaux, T. P.; Hussain, Z.; Shen, Z.-X.

    2007-03-01

    Our recent angle-resolved photoemission spectroscopy study of deeply underdoped cuprate superconductors Bi2Sr2(Ca,R)Cu2O8 (R = Y or Dy) (Bi2212) suggested the presence of two distinct energy gaps exhibiting different doping dependences [1]. One gap, associated with the antinodal region where no coherent peak is observed, increases with underdoping - a behavior known for more than a decade and considered as the general behavior of the gap in the underdoped regime. The other gap, associated with the near nodal regime where a coherent peak can be observed in energy distribution curves (EDCs), does not increase with less doping - a behavior not seen in the single particle spectra before. The theoretical implications of these findings and temperature dependence of the spectra will be discussed. [1] Science, in press. (http://www.sciencemag.org/cgi/content/abstract/1133411)

  20. Magnetic and Superconducting Properties of Vanadium Nanoconstrictions

    NASA Astrophysics Data System (ADS)

    Takata, Hiroki; Inagaki, Yuji; Kawae, Tatsuya; Ienaga, Koichiro; Tsujii, Hiroyuki

    2015-03-01

    We study the magnetic and superconducting properties in a paramagnetic vanadium (V) nanoconstriction with changing its size using a mechanically controllable break junction technique. In the normal state the magnetoresistance effect is observed below the diameter d ~ 8 nm. Moreover, a Fano resonance appears around zero-bias voltage in the differential conductance for the atomic-size contacts and changes shape as the size of the constriction changes. On the other hand, below the superconducting critical temperature the superconducting gap features in V contacts are largely different from those in Pb contacts which exhibit typical features expected in superconducting point contacts. Only a single Andreev anomaly at 2?, where ? is the superconducting energy gap, is observed in the spectra of the V contacts, while two anomalies at ? and 2? appear in the case of the Pb contacts. In the tunnel conductance regime, the structure of the superconducting quasiparticle tunneling density of states is not seen in the V spectra in contrast to the Pb spectra. The origin of these features is discussed.

  1. Study of superconducting magnetic bearing applicable to the flywheel energy storage system that consist of HTS-bulks and superconducting-coils

    NASA Astrophysics Data System (ADS)

    Seino, Hiroshi; Nagashima, Ken; Tanaka, Yoshichika; Nakauchi, Masahiko

    2010-06-01

    The Railway Technical Research Institute conducted a study to develop a superconducting magnetic bearing applicable to the flywheel energy-storage system for railways. In the first step of the study, the thrust rolling bearing was selected for application, and adopted liquid-nitrogen-cooled HTS-bulk as a rotor, and adopted superconducting coil as a stator for the superconducting magnetic bearing. Load capacity of superconducting magnetic bearing was verified up to 10 kN in the static load test. After that, rotation test of that approximately 5 kN thrust load added was performed with maximum rotation of 3000rpm. In the results of bearing rotation test, it was confirmed that position in levitation is able to maintain with stability during the rotation. Heat transfer properties by radiation in vacuum and conductivity by tenuous gas were basically studied by experiment by the reason of confirmation of rotor cooling method. The experimental result demonstrates that the optimal gas pressure is able to obtain without generating windage drag. In the second stage of the development, thrust load capacity of the bearing will be improved aiming at the achievement of the energy capacity of a practical scale. In the static load test of the new superconducting magnetic bearing, stable 20kN-levitation force was obtained.

  2. Superconducting Pairing through the Spin Resonance Mode in High-Temperature Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Onufrieva, F.; Pfeuty, P.

    2009-05-01

    We find that the spin resonance mode mediator scenario can explain important anomalies observed in the superconducting (SC) high-Tc cuprates: the famous low energy nodal kink with its doping dependence, the U-shaped form of the SC gap angular dependence, the anomalous form of electron density of states, the high absolute value of the SC gap, and some other unconventional properties.

  3. Effect of temperature, energy gap, and distortion of potential surfaces on photoinduced intramolecular electron transfer

    SciTech Connect

    Islampour, R.; Alden, R.G.; Wu, G.Y.C.; Lin, S.H. (Arizona State Univ., Tempe, AZ (United States))

    1993-07-01

    We report the quantitative examination of the effect of distortion of potential energy surfaces and the temperature effect on photoinduced intramolecular electron transfer (PIET) as a function of electronic energy gap. The results demonstrate the importance of distorted oscillators in determining the dependence of the rate of PIET on the energy gap. This phenomenon may in some cases lead to misinterpretations of experimental data, when undistorted oscillators are assumed to be involved in the PIET process. The condition for observing the linear (rather than parabolic) dependence of the ET rate will be determined using the multimode model. The inclusion of multivibrational modes in the nuclear factors results in energy gap behavior, which is markedly different from the single mode case. Finally, a comparison between PIET and internal conversion is discussed. 25 refs., 5 figs., 3 tabs.

  4. Fermi Surfaces and Energy Gaps in Sn/Ge(111)

    NASA Astrophysics Data System (ADS)

    Chiang, T.-C.

    2001-03-01

    The recent discovery of a charge-density-wave (CDW) transition in 1/3-monolayer Sn on Ge(111) has stimulated much interest. An intriguing aspect of this transition is the coexistence of phases over a wide temperature range, which is a basic hallmark for a broad class of complex functional materials, including high temperature superconductors, relaxor ferroelectrics, and colossal magnetoresistive materials. The Sn/Ge surface exhibits a (root 3)x(root 3)R30 reconstruction at room temperature. Each Sn adatom is three-fold coordinated. This leaves an electron in a dangling bond, giving rise to a half-filled surface band. As the temperature is lowered below 210 K, the system transforms gradually and becomes a fully developed (3x3) CDW phase below 100 K. Such CDW transitions are usually driven by electron-phonon coupling enhanced by Fermi surface nesting, but calculations for Sn/Ge have indicated no nesting. Alternative models that have been put forth include rehybridization, order-disorder transition, dynamic fluctuation, and strong electron correlation. Related to this debate is the question whether the (3x3) surface is metallic, semiconducting, or insulating with a correlation gap. A key issue often neglected in previous studies is that the system inevitably contains defects that are Ge atoms substituting for Sn atoms in the top layer. As revealed by STM, they induce a CDW phase in surrounding areas in an otherwise (root 3)x(root 3)R30 surface at room temperature. We have performed angle-resolved photoemission measurements of the valence structure, with a focus on the (3x3) zone boundary. Despite the lack of nesting as noted above, a gap opening is seen all around the (3x3) zone boundary. Taking into account the mixed phase at room temperature, the results yield band dispersions in excellent agreement with theory. A highly sensitive electronic response to doping by intrinsic surface defects is the cause for this unusual behavior, and a detailed calculation illustrates the origin of the (3x3) symmetry.

  5. Study on high temperature superconducting magnetic bearing for 10 kWh flywheel energy storage system

    Microsoft Academic Search

    Shigeo Nagaya; N. Kashima; M. Minami; H. Kawashima; S. Unisuga

    2001-01-01

    Flywheel energy storage systems with high temperature superconducting magnetic bearings are expected for load leveling use. A 1 kWh flywheel of 600 mm diameter was developed and the maximum energy storage of 1.4 kWh at 20,000 RPM was attained. For the development of a large capacity flywheel system, it is necessary to sophisticate the cooling system and improve the performance

  6. Introduction to progress and promise of superconductivity for energy storage in the electric power sector

    SciTech Connect

    Wolsky, A.M.

    1998-05-01

    Around the world, many groups conduct research, development and demonstration (RD and D) to make storage an economic option for the electric power sector. The progress and prospects for the application of superconductivity, with emphasis on high-temperature superconductivity, to the electric power sector has been the topic of an IEA Implementing Agreement, begun in 1990. The present Task members are Canada, Denmark, Finland, Germany, Israel, Italy, Japan, Korea, the Netherlands, Norway, Sweden, Switzerland, Turkey, the United Kingdom and the US. As a result of the Implementing Agreement, work has been done by the Operating Agent with the full participation of all the member countries. This work has facilitated the exchange of informtion among experts in all countries and has documented relevant assessments. Further, this work has reviewed the status of SMES and is now updating same, as well as investigating the progress on and prospects for flywheels with superconducting bearings. The Operating Agent and Task members find a substantially different set of opportunities for and alternatives to storage than was the case before the 1987 discovery of high-temperature superconductivity. Beside the need to level generation, there is also the need to level the load on transmission lines, increase transmission stability, and increase power quality. These needs could be addressed by high power storage that could be brought in and out of the grid in fractions of a second. Superconducting Magnetic Energy Storage and flywheels with superconducting bearings are devices that deserve continued RD and D because they promise to be the needed storage devices.

  7. Anomalous behavior of the energy gap in the one-dimensional quantum XY model

    E-print Network

    Yuuki Yamanaka; Hidetoshi Nishimori

    2015-01-13

    We show for the one-dimensional quantum $XY$ model with $s=1/2$ that the energy gap between the ground and first excited states behaves anomalously as a function of the system size at the first-order quantum phase transition. Although it is generally the case that the energy gap closes exponentially at a quantum first-order transition, the gap in the present model behaves non-monotonically as a function of the system size, apparently very irregularly in some cases. This property of the gap is similar to that of the infinite-range quantum $XY$ model, in which the gap closes polynomially, exponentially, or even factorially fast depending on the choice of the series of system sizes toward the thermodynamic limit. This observation is surprising in consideration of the apparent maturity of our understanding of the one-dimensional quantum $XY$ model. Our result is also important from the viewpoint of quantum annealing, where the rate of gap closing determines the efficiency of computation.

  8. Peak power reduction and energy efficiency improvement with the superconducting flywheel energy storage in electric railway system

    NASA Astrophysics Data System (ADS)

    Lee, Hansang; Jung, Seungmin; Cho, Yoonsung; Yoon, Donghee; Jang, Gilsoo

    2013-11-01

    This paper proposes an application of the 100 kWh superconducting flywheel energy storage systems to reduce the peak power of the electric railway system. The electric railway systems have high-power characteristics and large amount of regenerative energy during vehicles’ braking. The high-power characteristic makes operating cost high as the system should guarantee the secure capacity of electrical equipment and the low utilization rate of regenerative energy limits the significant energy efficiency improvement. In this paper, it had been proved that the peak power reduction and energy efficiency improvement can be achieved by using 100 kWh superconducting flywheel energy storage systems with the optimally controlled charging or discharging operations. Also, economic benefits had been assessed.

  9. Fermi arc in the superconducting state of impurity-doped Bi2Sr2CaCu2O8

    Microsoft Academic Search

    T. Sato; K. Terashima; K. Nakayama; S. Souma; T. Takahashi; T. Yamamoto; K. Kadowaki

    2008-01-01

    We have performed ultrahigh energy- and momentum-resolved angle-resolved photoemission spectroscopy of impurity-doped Bi2Sr2CaCu2O8 . We found that the point node of the superconducting gap near the (pi\\/2,pi\\/2) point in a pristine sample gradually evolves into a small gapless Fermi arc upon Zn or Ni doping. The shape of impurity-induced density of states inside the superconducting gap shows a marked difference

  10. Commissioning tests of the Bonneville Power Administration 30 MJ superconducting magnetic energy storage unit

    NASA Astrophysics Data System (ADS)

    Boening, H. J.; Hauer, J. F.

    A 30 MJ (8.4 kWh) Superconducting Magnetic Energy Storage (SMES) unit with a 10 MW converter was installed and commissioned at the Bonneville Power Administration (BPA) substation in Tacoma, Washington. This is the first large-scale application in the US of superconductivity in an electric utility system. The unit, which is capable of absorbing and releasing up to 10 MJ of energy at a frequency of 0.35 Hz, was designed to damp the dominant power swing mode of the Pacific AC Intertie. The electrical characteristics of the magnetic energy storage unit, its modes of operation, results of device tests, means for controlling real and reactive power, and some initial power system response tests are described. A short summary of the operating history of the unit over the first eleven months is also presented.

  11. 1GWh diurnal load-leveling superconducting magnetic energy storage system reference design. Appendix A: energy storage coil and superconductor

    Microsoft Academic Search

    Schermer

    1979-01-01

    The technical aspects of a 1-GWh Superconducting Magnetic Energy Storage (SMES) coil for use as a diurnal load-leveling device in an electric utility system are presented. The superconductor for the coil is analyzed, and costs for the entire coil are developed.

  12. Manipulating the magnetic state of a carbon nanotube Josephson junction using the superconducting phase

    NASA Astrophysics Data System (ADS)

    Delagrange, R.; Luitz, D. J.; Weil, R.; Kasumov, A.; Meden, V.; Bouchiat, H.; Deblock, R.

    2015-06-01

    The magnetic state of a quantum dot attached to superconducting leads is experimentally shown to be controlled by the superconducting phase difference across the dot. This is done by probing the relation between the Josephson current and the superconducting phase difference of a carbon nanotube junction whose Kondo energy and superconducting gap are of comparable size. It exhibits distinctively anharmonic behavior, revealing a phase-mediated singlet-to-doublet transition. We obtain an excellent quantitative agreement with numerically exact quantum Monte Carlo calculations. This provides strong support that we indeed observed the finite-temperature signatures of the phase-controlled zero temperature level crossing transition originating from strong local electronic correlations.

  13. Manipulating the magnetic state of a carbon nanotube Josephson junction using the superconducting phase

    E-print Network

    R. Delagrange; D. J. Luitz; R. Weil; A. Kasumov; V. Meden; H. Bouchiat; R. Deblock

    2015-06-10

    The magnetic state of a quantum dot attached to superconducting leads is experimentally shown to be controlled by the superconducting phase difference across the dot. This is done by probing the relation between the Josephson current and the superconducting phase difference of a carbon nanotube junction whose Kondo energy and superconducting gap are of comparable size. It exhibits distinctively anharmonic behavior, revealing a phase mediated singlet to doublet transition. We obtain an excellent quantitative agreement with numerically exact quantum Monte Carlo calculations. This provides strong support that we indeed observed the finite temperature signatures of the phase controlled zero temperature level-crossing transition originating from strong local electronic correlations.

  14. Controlling of optical energy gap of Co-ferrite quantum dots in poly (methyl methacrylate) matrix

    NASA Astrophysics Data System (ADS)

    El-Sayed, H. M.; Agami, W. R.

    2015-07-01

    Different crystallite sizes of Co-ferrite nanoparticles were prepared and dispersed in the matrix of poly (methyl methacrylate) (PMMA) polymer. The effect of crystallite size on the structure and optical energy gap of Co-nanoferrite/PMMA composite has been studied. The optical energy gap of Co-ferrite was greatly affected by the crystallite size. This result was discussed in terms of the formation of electron-hole exciton using particle in a box model. The effective mass and the Bohr radius of the formed exciton have been calculated from the spectroscopic measurements.

  15. Direct observation of the superconducting energy gap developing in the conductivity spectra of niobium 

    E-print Network

    Pronin, AV; Dressel, M.; Pimenov, A.; Loidl, A.; Roshchin, Igor V.; Greene, LH.

    1998-01-01

    This project explores the grain growth characteristics and grain morphology of bulk niobium (Nb) processed by severe plastic deformation (SPD). This report deals with factors affecting grain growth and recrystallization: ...

  16. Extracting the Mott gap from energy measurements in trapped atomic gases

    SciTech Connect

    Carrasquilla, Juan [International School for Advanced Studies (SISSA), Via Beirut 2, I-34151, Trieste (Italy); Becca, Federico [International School for Advanced Studies (SISSA), Via Beirut 2, I-34151, Trieste (Italy); Democritos Simulation Center, Istituto Officina dei Materiali (CNR-IOM), Trieste (Italy)

    2010-11-15

    We show that the measure of the so-called release energy, which is an experimentally accessible quantity, makes it possible to assess the value of the Mott gap in the presence of the unavoidable confinement potential in the actual experimental setup. Indeed, the curve of the release energy as a function of the total number of particles shows kinks that are directly related to the existence of excitation gaps. Calculations are presented within the Gutzwiller approach, but the final results go beyond this simple approximation and represent a genuine feature of the real system. In the case of harmonic confinement, the Mott gaps may be renormalized with respect to the uniform case. On the other hand, in the case of the recently proposed off-diagonal confinement, our results show good agreement with the homogeneous case.

  17. Superconducting magnetic energy storage (SMES) program. Progress report, January 1-December 31, 1980

    SciTech Connect

    Rogers, J.D. (comp.)

    1981-03-01

    Work is reported on the development of two superconducting magnetic energy storage (SMES) units. One is a 30-MJ unit for use by the Bonneville Power Administration (BPA) to stabilize power oscillations on their Pacific AC Intertie, and the second is a 1- to 10-GWh unit for use as a diurnal load leveling device. Emphasis has been on the stabilizing system. The manufacturing phase of the 30-MJ superconducting coil was initiated and the coil fabrication has advanced rapidly. The two converter power transformers were manufactured, successfully factory tested, and shipped. One transformer reached the Tacoma Substation in good condition; the other was dropped enroute and has been returned to the factory for rebuilding. Insulation of the 30-MJ coil has been examined for high voltage effects apt to be caused by transients such as inductive voltage spikes from the protective dump circuit. The stabilizing system converter and protective energy dump system were completed, factory tested, and delivered.

  18. Auger-Electron-Stimulated Organic Electroluminescence at Ultralow Voltages Below the Energy Gap

    NASA Astrophysics Data System (ADS)

    He, Shou-Jie; Wang, Deng-Ke; Jiang, Nan; Zhang, Jin; Lu, Zheng-Hong

    2015-05-01

    In typical organic light-emitting diodes (OLEDs), the device turn-on voltages are above the HOMO-LUMO energy gaps of emitters. This paper reports that various combinations of active materials can be strategically selected to construct OLEDs with device working voltages below the HOMO-LUMO energy gaps of emitters; i.e., emitted photon energies are higher than applied electrical energies. The operation mechanism of this type of OLED is found to be related to ballistic Auger-electron injection at organic heterojunctions. This Auger-electron injection acts as a built-in voltage booster. The Auger-electron process predicts that the turn-on voltage scales linearly with the energy difference between an acceptor's LUMO and a donor's HOMO. This prediction is in excellent agreement with experimental data.

  19. Superconductivity-induced optical anomaly in an iron arsenide

    PubMed Central

    Charnukha, A.; Popovich, P.; Matiks, Y.; Sun, D. L.; Lin, C. T.; Yaresko, A. N.; Keimer, B.; Boris, A. V.

    2011-01-01

    One of the central tenets of conventional theories of superconductivity, including most models proposed for the recently discovered iron-pnictide superconductors, is the notion that only electronic excitations with energies comparable to the superconducting energy gap are affected by the transition. Here, we report the results of a comprehensive spectroscopic ellipsometry study of a high-quality crystal of superconducting Ba0.68K0.32Fe2As2 that challenges this notion. We observe a superconductivity-induced suppression of an absorption band at an energy of 2.5 eV, two orders of magnitude above the superconducting gap energy 2??20 meV. On the basis of density functional calculations, this band can be assigned to transitions from As-p to Fe-d orbitals crossing the Fermi level. We identify a related effect at the spin-density wave transition in parent compounds of the 122 family. This suggests that As-p states deep below the Fermi level contribute to the formation of the superconducting and spin-density wave states in the iron arsenides. PMID:21364558

  20. The 30-MJ superconducting magnetic energy storage for BPA transmission-line stabilizer

    NASA Astrophysics Data System (ADS)

    Schermer, R. I.

    The development of a 30 MJ (8.4 kWh) superconducting magnetic energy storage (SMES) unit with a 10 MW converter which can provide system damping for low frequency oscillations is described. The coil is complete and all major components of the electrical and cryogenic systems were received and are tested. Computer control hardware is in place and software development is proceeding. Support system components and dewar lid are fabricated and foundation design is complete.

  1. Design of a superconducting linac cavity for high-current energy recovery linac operation

    Microsoft Academic Search

    Dong Wang; Yongxiang Zhao; Ilan Ben-Zvi; Xiangyun Chang; J. Kewisch; C. Montag; J. Sekutowicz; C. Pagani; P. Pierini

    2003-01-01

    The RHIC electron cooler as well as other applications (such as a linac-ring version of eRHIC) requires a very high average current CW electron linac in an energy recovery mode. In this paper we present the design of a 5-cell superconducting linac cavity for velocity of light particles. This cavity will operate at 703.75 MHz with a large beam pipe

  2. Present status of R&D on superconducting magnetic bearing technologies for flywheel energy storage system

    Microsoft Academic Search

    N. Koshizuka; F. Ishikawa; H. Nasu; M. Murakami; K. Matsunaga; S. Saito; O. Saito; Y. Nakamura; H. Yamamoto; R. Takahata; T. Oka; H. Ikezawa; M. Tomita

    2002-01-01

    We report on the NEDO project of superconducting magnetic bearing (SMB) technologies for flywheel energy storage system. We fabricated SMB modules which consist of a stator of roof-tile shape YBaCuO bulks and a NdFeB permanent magnet circuit. The levitation force density of the bearings was 9 N\\/cm2. It was confirmed that pre-loading and excess cooling methods are both effective for

  3. Application of superconducting magnetic bearings to a 10 kWh-class flywheel energy storage system

    Microsoft Academic Search

    Takumi Ichihara; Koji Matsunaga; Makoto Kita; Izumi Hirabayashi; Masayuki Isono; Makoto Hirose; Keiji Yoshii; Kazuaki Kurihara; Osamu Saito; Shinobu Saito; Masato Murakami; Hirohumi Takabayashi; Mitsutoshi Natsumeda; Naoki Koshizuka

    2005-01-01

    Radial type superconducting magnetic bearings have been developed for a 10 kWh-class flywheel energy storage system. The bearings consist of an inner-cylindrical stator of YBCO bulk superconductors and an outer-rotor of permanent magnets. The rotor is suspended without contact via the pinning forces of the bulk superconductors that are arranged such that the c-axis of each superconductor is aligned parallel

  4. Engineering prototype of a superconducting flywheel for long term energy storage

    Microsoft Academic Search

    H. J. Bornemann; Andrea Tonoli; Tobias Ritter; Claus Urban; Oleg Zaitsev; Klaus Weber; Hennann Rietschel

    1995-01-01

    We built a flywheel system with superconducting magnetic bearings. The bearing consists of six melt-textured YBCO pellets mounted inside a continuous flow LN2 cryostat. A disk measuring ? 190 mm×30 mm was safely rotated at speeds up to 15000 rpm. The disk was driven by a high speed three phase synchronous homopolar motor\\/generator. Maximum energy capacity was 4.8 Wh, maximum

  5. Distribution of time-energy entanglement over 100 km fiber using superconducting single-photon detectors.

    PubMed

    Zhang, Qiang; Takesue, Hiroki; Nam, Sae Woo; Langrock, Carsten; Xie, Xiuping; Baek, Burm; Fejer, M M; Yamamoto, Yoshihisa

    2008-04-14

    In this letter, we report an experimental realization of distributing entangled photon pairs over 100 km of dispersion-shifted fiber. In the experiment, we used a periodically poled lithium niobate waveguide to generate the time-energy entanglement and superconducting single-photon detectors to detect the photon pairs after 100 km. We also demonstrate that the distributed photon pairs can still be useful for quantum key distribution and other quantum communication tasks. PMID:18542687

  6. Hermetically sealed superconducting magnet motor

    DOEpatents

    DeVault, R.C.; McConnell, B.W.; Phillips, B.A.

    1996-07-02

    A hermetically sealed superconducting magnet motor includes a rotor separated from a stator by either a radial gap, an axial gap, or a combined axial and radial gap. Dual conically shaped stators are used in one embodiment to levitate a disc-shaped rotor made of superconducting material within a conduit for moving cryogenic fluid. As the rotor is caused to rotate when the field stator is energized, the fluid is pumped through the conduit. 6 figs.

  7. Hermetically sealed superconducting magnet motor

    SciTech Connect

    DeVault, Robert C. (Knoxville, TN); McConnell, Benjamin W. (Knoxville, TN); Phillips, Benjamin A. (Benton Harbor, MI)

    1996-01-01

    A hermetically sealed superconducting magnet motor includes a rotor separated from a stator by either a radial gap, an axial gap, or a combined axial and radial gap. Dual conically shaped stators are used in one embodiment to levitate a disc-shaped rotor made of superconducting material within a conduit for moving cryogenic fluid. As the rotor is caused to rotate when the field stator is energized, the fluid is pumped through the conduit.

  8. Gaps, barriers and conceptual chasms: theories of technology transfer and energy in buildings

    Microsoft Academic Search

    Elizabeth Shove

    1998-01-01

    Having shown how much energy might be saved through the use of economically worthwhile measures and technologies, researchers and policy makers then find themselves trying to close the gap between current practice and recognised technical potential. The ensuing process of technology transfer is often seen as a process of overcoming ‘non technical barriers’ which inhibit the realisation of proven technical

  9. The optical band gap and surface free energy of polyethylene modified by electron beam irradiations

    NASA Astrophysics Data System (ADS)

    Abdul-Kader, A. M.

    2013-04-01

    In this study, investigations have been carried out on electron beam irradiated ultra high molecular weight polyethylene (UHMWPE). Polyethylene samples were irradiated with 1.5 MeV electron beam at doses ranging from 50 to 500 kGy. Modifications in optical properties and photoluminescence behavior of the polymer were evaluated by UV-vis and photoluminescence techniques. Changes of surface layer composition of UHMWPE produced by electron irradiations were studied by Rutherford back scattering spectrometry (RBS). The change in wettability and surface free energy induced by irradiations was also investigated. The optical absorption studies reveal that both optical band gap and Urbach's energy decreases with increasing electron dose. A correlation between energy gap and the number of carbon atoms in clusters is discussed. Photoluminescence spectra were reveal remarkable decrease in the integrated luminescence intensity with increasing irradiation dose. Contact angle measurements showed that wettability and surface free energy increases with increasing the irradiation dose.

  10. Influence of the gap energy on phononic and low-energy electronic excitations in Y_1-x(Pr,Ca)_xBa_2Cu_3O_6+y films

    NASA Astrophysics Data System (ADS)

    Bock, A.; Ostertun, S.; Das Sharma, R.; Rübhausen, M.; Subke, K.-O.

    1998-03-01

    The superconducting gap of cuprate superconductors shows up in low-temperature Raman spectra via, e.g. the redistribution of low-energy electronic excitations or the renormalization of phonon self-energies. In Y-123 compounds the B_1g mode at 340 cm-1 exhibits the strongest self-energy effect resulting from a large electron-phonon coupling leading to a pronounced Fano profile. By varying the doping in Y_1-x(Pr,Ca)_xBa_2Cu_3O_6+y films, which are prepared with pulsed laser deposition, we obtain gap energies below, near, and above the energy of the B_1g mode causing corresponding redistributions of the low-energy electronic excitations. We have extended the Greens-function model of Chen et al.(X.K. Chen et al.), Phys. Rev. B 48, 10530 (1993). to describe the Fano profile and to study the phononic and electronic excitations in the entire doping regime separately. We compare the results of our model with those of conventional ones and show that it allows us a more detailed interpretation of the temperature dependence of the phonon self-energy effects as well as of the low-energy electronic excitations, especially, in the presence of high phonon intensities.

  11. Superconducting tunnel junctions

    Microsoft Academic Search

    Didier D. E. Martin; Peter Verhoeve

    2010-01-01

    Superconducting tunnel junctions (STJ) are a class of cryogenic detectors that rely on the generation of free charge carriers by breaking Cooper pairs in a superconducting material with the use of absorbed photon energy. In an STJ, consisting of two superconducting films separated by a thin insulating barrier, the charge carriers can be detected through the tunnel-current pulse they produce

  12. Evaluation of the extrinsic and intrinsic stacking-fault energies of GaP

    Microsoft Academic Search

    Dov Cohen; C. Barry Carter

    1999-01-01

    Stacking-fault double ribbons have been observed by transmission electron microscopy in undoped GaP films grown on Si. Values of the extrinsic and intrinsic stacking-fault energies of 40.5_3mJm-2 and 43.4_2mJm-2, respectively, were obtained from measurements of the widths of the individual ribbons. The ratio of the intrinsic to extrinsic stacking-fault energy was found to be 1.07 0.05.

  13. GAPS - Dark matter search with low-energy cosmic-ray antideuterons and antiprotons

    E-print Network

    von Doetinchem, P; Boggs, S; Fuke, H; Hailey, C J; Mognet, S I; Ong, R A; Perez, K; Zweerink, J

    2015-01-01

    The GAPS experiment is foreseen to carry out a dark matter search by measuring low-energy cosmic-ray antideuterons and antiprotons with a novel detection approach. It will provide a new avenue to access a wide range of different dark matter models and masses from about 10GeV to 1TeV. The theoretically predicted antideuteron flux resulting from secondary interactions of primary cosmic rays is very low. Well-motivated theories beyond the Standard Model contain viable dark matter candidates, which could lead to a significant enhancement of the antideuteron flux due to annihilation or decay of dark matter particles. This flux contribution is believed to be especially large at low energies, which leads to a high discovery potential for GAPS. The GAPS low-energy antiproton search will provide some of the most stringent constraints on ~30GeV dark matter, will provide the best limits on primordial black hole evaporation on galactic length scales, and explore new discovery space in cosmic-ray physics. GAPS is designed...

  14. Observation of a ubiquitous three-dimensional superconducting gap function in optimally-doped Ba1-xKxFe2As2

    E-print Network

    Hu, Jiangping

    that map out the planar band dispersion as a function of kx and ky. Thus far, four Fermi-surface sheets around the M (, 0) point in the unfolded two-dimensional (2D) Bril- louin zone. Below the superconducting

  15. Point-contact spectroscopy investigation of superconducting-gap anisotropy in the nickel borocarbide compound LuNi2B2C

    E-print Network

    Bobrov, NL; Beloborod'ko, SI; Tyutrina, LV; Yanson, IK; Naugle, Donald G.; Rathnayaka, KDD.

    2005-01-01

    , in the ab plane by a larger gap. The deviation from the one-gap BCS model is pronounced in the temperature dependence of the gap in both directions. The temperature range, where the deviation occurs, is for the c direction approximately 1.5 times more than...

  16. Performance of Variable Energy Cyclotron Centre superconducting cyclotron liquid nitrogen distribution system.

    PubMed

    Pal, Gautam; Nandi, Chinmay; Bhattacharyya, Tamal Kumar; Chakrabarti, Alok

    2014-01-01

    The liquid nitrogen distribution at Variable Energy Cyclotron Centre, Kolkata, India K500 superconducting cyclotron uses parallel branches to cool the thermal shield of helium vessel housing the superconducting coil and the cryopanels. Liquid nitrogen is supplied to the thermal shields from a pressurised liquid nitrogen dewar. Direct measurement of flow is quite difficult and seldom used in an operational cryogenic system. The total flow and heat load of the liquid nitrogen system was estimated indirectly by continuous measurement of level in the liquid nitrogen tanks. A mathematical model was developed to evaluate liquid nitrogen flow in the parallel branches. The model was used to generate flow distribution for different settings and the total flow was compared with measured data. PMID:24517753

  17. Technical Barriers, Gaps, and Opportunities Related to Home Energy Upgrade Market Delivery

    SciTech Connect

    Bianchi, M. V. A.

    2011-11-01

    This report outlines the technical barriers, gaps, and opportunities that arise in executing home energy upgrade market delivery approaches, as identified through research conducted by the U.S. Department of Energy's Building America program. The objective of this report is to outline the technical1 barriers, gaps, and opportunities that arise in executing home energy upgrade market delivery approaches, as identified through research conducted by the U.S. Department of Energy's (DOE) Building America program. This information will be used to provide guidance for new research necessary to enable the success of the approaches. Investigation for this report was conducted via publications related to home energy upgrade market delivery approaches, and a series of interviews with subject matter experts (contractors, consultants, program managers, manufacturers, trade organization representatives, and real estate agents). These experts specified technical barriers and gaps, and offered suggestions for how the technical community might address them. The potential benefits of home energy upgrades are many and varied: reduced energy use and costs; improved comfort, durability, and safety; increased property value; and job creation. Nevertheless, home energy upgrades do not comprise a large part of the overall home improvement market. Residential energy efficiency is the most complex climate intervention option to deliver because the market failures are many and transaction costs are high (Climate Change Capital 2009). The key reasons that energy efficiency investment is not being delivered are: (1) The opportunity is highly fragmented; and (2) The energy efficiency assets are nonstatus, low-visibility investments that are not properly valued. There are significant barriers to mobilizing the investment in home energy upgrades, including the 'hassle factor' (the time and effort required to identify and secure improvement works), access to financing, and the opportunity cost of capital and split incentives.

  18. Ion Desorption Stability in Superconducting High Energy Physics Proton Colliders

    SciTech Connect

    Turner, W.C.

    1995-05-29

    In this paper we extend our previous analysis of cold beam tube vacuum in a superconducting proton collider to include ion desorption in addition to thermal desorption and synchrotron radiation induced photodesorption. The new ion desorption terms introduce the possibility of vacuum instability. This is similar to the classical room temperature case but now modified by the inclusion of ion desorption coefficients for cryosorbed (physisorbed) molecules which can greatly exceed the coefficients for tightly bound molecules. The sojourn time concept for physisorbed H{sub 2} is generalized to include photodesorption and ion desorption as well as the usually considered thermal desorption. The ion desorption rate is density dependent and divergent so at the onset of instability the sojourn time goes to zero. Experimental data are used to evaluate the H{sub 2} sojourn time for the conditions of the Large Hadron Collider (LHC) and the situation is found to be stable. The sojourn time is dominated by photodesorption for surface density s(H{sub 2}) less than a monolayer and by thermal deposition for s(H{sub 2}) greater than a monolayer. For a few percent of a monolayer, characteristic of a beam screen, the photodesorption rate exceeds ion desorption rate by more than two orders of magnitude. The photodesorption rate corresponds to a sojourn time of approximately 100 sec. The paper next turns to the evaluation of stability margins and inclusion of gases heavier than H{sub 2} (CO, CO{sub 2} and CH{sub 4}), where ion desorption introduces coupling between molecular species. Stability conditions are worked out for a simple cold beam tube, a cold beam tube pumped from the ends and a cold beam tube with a co-axial perforated beam screen. In each case a simple inequality for stability of a single component is replaced by a determinant that must be greater than zero for a gas mixture. The connection with the general theory of feedback stability is made and it is shown that the gains of the diagonal uncoupled feedback loops are first order in the ion desorption coefficients whereas the gains of the off diagonal coupled feedback loops are second and higher order. For this reason it turns out that in practical cases stability is dominated by the uncoupled diagonal elements and the inverse of the largest first order closed loop gain is a useful estimate of the margin of stability. In contrast to the case of a simple cold beam tube, the stability condition for a beam screen does not contain the desorption coefficient for physisorbed molecules, even when the screen temperature is low enough that there is a finite surface density of them on the screen surface. Consequently there does not appear to be any particular advantage to operating the beam screen at high enough temperature to avoid physisorption. Numerical estimates of ion desorption stability are given for a number of cases relevant to LHC and all of the ones likely to be encountered were found to be stable. The most important case, a I % transparency beam screen at {approx}4.2 K, was found to have a stability safety margin of approximately thirty determined by ion desorption of CO. Ion desorption of H{sub 2} is about a factor of eighty less stringent than CO. For these estimates the beam tube surface was assumed to be solvent cleaned but otherwise untreated, for example by a very high temperature vacuum bakeout or by glow discharge cleaning.

  19. Free energy surfaces in the superconducting mixed state

    NASA Technical Reports Server (NTRS)

    Finnemore, D. K.; Fang, M. M.; Bansal, N. P.; Farrell, D. E.

    1989-01-01

    The free energy surface for Tl2Ba2Ca2Cu3O1O has been measured as a function of temperature and magnetic field to determine the fundamental thermodynamic properties of the mixed state. The change in free energy, G(H)-G(O), is found to be linear in temperature over a wide range indicating that the specific heat is independent of field.

  20. On the massless gap'' adjustment of detected energy for passive material in front of a calorimeter

    SciTech Connect

    Trost, H.J.

    1992-01-31

    I have designed a correction scheme for energy losses in passive material in front of a calorimeter based on the massless gap'' idea. I use a flexible geometry model of a calorimeter design for SDC outside of a solenoidal coil made of aluminium cylinders of adjustable thickness. The signal from the first radiation length of active calorimetry is scaled dependent on the incoming and observed energies of the shower. A reasonable recovery of the resolution of an unobstructed calorimeter is achieved using correction factors that depend only upon the total thickness of passive material. Thus a useful correction may be built into the hardware by increasing the amount of scintillator in the first radiation length of the active calorimeter. The distribution of correction factors determined event-by-event indicate that an additional dependence on the observed signal in the massless gap and total incident energy is clearly present.

  1. On the ``massless gap`` adjustment of detected energy for passive material in front of a calorimeter

    SciTech Connect

    Trost, H.J.

    1992-01-31

    I have designed a correction scheme for energy losses in passive material in front of a calorimeter based on the ``massless gap`` idea. I use a flexible geometry model of a calorimeter design for SDC outside of a solenoidal coil made of aluminium cylinders of adjustable thickness. The signal from the first radiation length of active calorimetry is scaled dependent on the incoming and observed energies of the shower. A reasonable recovery of the resolution of an unobstructed calorimeter is achieved using correction factors that depend only upon the total thickness of passive material. Thus a useful correction may be built into the hardware by increasing the amount of scintillator in the first radiation length of the active calorimeter. The distribution of correction factors determined event-by-event indicate that an additional dependence on the observed signal in the massless gap and total incident energy is clearly present.

  2. Extended Acceleration in Slot Gaps and Pulsar High-Energy Emission

    NASA Technical Reports Server (NTRS)

    White, Nicholas E. (Technical Monitor); Muslimov, Alex G.; Harding, Alice K.

    2003-01-01

    We revise the physics of primary electron acceleration in the "slot gap" (SG) above the pulsar polar caps (PCs), a regime originally proposed by Arons and Scharlemann (1979) in their electrodynamic model of pulsar PCs. We employ the standard definition of the SG as a pair-free space between the last open field lines and the boundary of the pair plasma column which is expected to develop above the bulk of the PC. The rationale for our revision is that the proper treatment of primary acceleration within the pulsar SGs should take into account the effect of the narrow geometry of the gap on the electrodynamics within the gap and also to include the effect of inertial frame dragging on the particle acceleration. We show that the accelerating electric field within the gap, being significantly boosted by the effect of frame dragging, becomes reduced because of the gap geometry by a factor proportional to the square of the SG width. The combination of the effects of frame dragging and geometrical screening in the gap region naturally gives rise to a regime of extended acceleration, that is not limited to favorably curved field lines as in earlier models, and the possibility of multiple-pair production by curvature photons at very high altitudes, up to several stellar radii. We present our estimates of the characteristic SG thickness across the PC, energetics of primaries accelerated within the gap, high-energy bolometric luminosities emitted from the high altitudes in the gaps, and maximum heating luminosities produced by positrons returning from the elevated pair fronts. The estimated theoretical high-energy luminosities are in good agreement with the corresponding empirical relationships for gamma-ray pulsars. We illustrate the results of our modeling of the pair cascades and gamma-ray emission from the high altitudes in the SG for the Crab pulsar. The combination of the frame-dragging field and high-altitude SG emission enables both acceleration at the smaller inclination angles and a larger emission beam, both necessary to produce widely-spaced double-peaked profiles.

  3. AdS/CFT and the geometry of an energy gap

    E-print Network

    Hickling, Andrew

    2015-01-01

    We consider a CFT defined on a static metric that is the product of time with a smooth closed space of positive scalar curvature. We expect the theory to exhibit an energy gap and our aim is to investigate how that gap depends on the geometry of the space. For a free conformal scalar it is straightforward to show the gap normalised by the minimum value of the Ricci scalar of the space is minimised when the space is a sphere. Our main result is then to show using geometric arguments that precisely the same result holds for fluctuations of a scalar operator in any holographic CFT. We prove this under the assumption that the dual vacuum geometry is a smooth Einstein metric ending only on the conformal boundary, and then consider fluctuations of a minimally coupled massive scalar field about this. We also argue the holographic CFT will have states dual to small bulk black holes whose existence is related to the energy gap. We show the thermodynamic properties of these black holes obey a bound of a similar nature ...

  4. FLYWHEEL ENERGY STORAGE SYSTEMS WITH SUPERCONDUCTING BEARINGS FOR UTILITY APPLICATIONS

    SciTech Connect

    Dr. Michael Strasik; Mr. Arthur Day; Mr. Philip Johnson; Dr. John Hull

    2007-10-26

    This project’s mission was to achieve significant advances in the practical application of bulk high-temperature superconductor (HTS) materials to energy-storage systems. The ultimate product was planned as an operational prototype of a flywheel system on an HTS suspension. While the final prototype flywheel did not complete the final offsite demonstration phase of the program, invaluable lessons learned were captured on the laboratory demonstration units that will lead to the successful deployment of a future HTS-stabilized, composite-flywheel energy-storage system (FESS).

  5. Higgsless superconductivity from topological defects in compact BF terms

    NASA Astrophysics Data System (ADS)

    Diamantini, M. Cristina; Trugenberger, Carlo A.

    2015-02-01

    We present a new Higgsless model of superconductivity, inspired from anyon superconductivity but P- and T-invariant and generalisable to any dimension. While the original anyon superconductivity mechanism was based on incompressible quantum Hall fluids as average field states, our mechanism involves topological insulators as average field states. In D space dimensions it involves a (D - 1)-form fictitious pseudovector gauge field which originates from the condensation of topological defects in compact low-energy effective BF theories. In the average field approximation, the corresponding uniform emergent charge creates a gap for the (D - 2)-dimensional branes via the Magnus force, the dual of the Lorentz force. One particular combination of intrinsic and emergent charge fluctuations that leaves the total charge distribution invariant constitutes an isolated gapless mode leading to superfluidity. The remaining massive modes organise themselves into a D-dimensional charged, massive vector. There is no massive Higgs scalar as there is no local order parameter. When electromagnetism is switched on, the photon acquires mass by the topological BF mechanism. Although the charge of the gapless mode (2) and the topological order (4) are the same as those of the standard Higgs model, the two models of superconductivity are clearly different since the origins of the gap, reflected in the high-energy sectors are totally different. In 2D this type of superconductivity is explicitly realised as global superconductivity in Josephson junction arrays. In 3D this model predicts a possible phase transition from topological insulators to Higgsless superconductors.

  6. Superconducting electronics requirements for single-photon, energy resolving detectors

    Microsoft Academic Search

    Armen M. Gulian; Gilbert G. Fritz; Kent S. Wood; Deborah Van Vechten

    2001-01-01

    Development of single photon sensors capable of determining the energy (“color”) of each photon incident on a pixelated focal plane in real time is a central activity of many groups worldwide developing state-of-the-art hardware for the space astrophysics community. Terrestrial applications in materials analysis are also being targeted. The most successful class of approaches uses “hot-electron” microbolometers in which the

  7. Structural stability and energy-gap modulation through atomic protrusion in freestanding bilayer silicene

    NASA Astrophysics Data System (ADS)

    Sakai, Yuki; Oshiyama, Atsushi

    2015-05-01

    We report on first-principles total-energy and phonon calculations that clarify structural stability and electronic properties of freestanding bilayer silicene. By extensive structural exploration, we reach all the stable structures reported before and find four additional dynamically stable structures, including the structure with the largest cohesive energy. We find that atomic protrusion from the layer is the principal relaxation pattern which stabilizes bilayer silicene and determines the lateral periodicity. The hybrid-functional calculation shows that the most stable bilayer silicene is a semiconductor with the energy gap of 1.3 eV.

  8. Evolution of the N=50 shell gap energy towards $^{78}$Ni

    E-print Network

    J. Hakala; S. Rahaman; V. -V. Elomaa; T. Eronen; U. Hager; A. Jokinen; A. Kankainen; I. D. Moore; H. Penttilä; S. Rinta-Antila; J. Rissanen; A. Saastamoinen; T. Sonoda; C. Weber; J. Äystö

    2008-06-27

    Atomic masses of the neutron-rich isotopes $^{76-80}$Zn, $^{78-83}$Ga, $^{80-85}Ge, $^{81-87}$As and $^{84-89}$Se have been measured with high precision using the Penning trap mass spectrometer JYFLTRAP at the IGISOL facility. The masses of $^{82,83}$Ga, $^{83-85}$Ge, $^{84-87}$As and $^{89}$Se were measured for the first time. These new data represent a major improvement in the knowledge of the masses in this neutron-rich region. Two-neutron separation energies provide evidence for the reduction of the N=50 shell gap energy towards germanium Z=32 and a subsequent increase at gallium (Z=31). The data are compared with a number of theoretical models. An indication of the persistent rigidity of the shell gap towards nickel (Z=28) is obtained.

  9. Energy-gap opening in a Bi110 nanoribbon induced by edge reconstruction.

    PubMed

    Sun, Jia-Tao; Huang, Han; Wong, Swee Liang; Gao, H-J; Feng, Yuan Ping; Wee, Andrew Thye Shen

    2012-12-14

    Scanning tunnelling microscopy and spectroscopy experiments complemented by first-principles calculations have been conducted to study the electronic structure of 4 monolayer Bi(110) nanoribbons on epitaxial graphene on silicon carbide [4H-SiC(0001)]. In contrast with the semimetal property of elemental bismuth, an energy gap of 0.4 eV is measured at the centre of the Bi(110) nanoribbons. Edge reconstructions, which can facilitate the edge strain energy release, are found to be responsible for the band gap opening. The calculated density of states around the Fermi level are decreased quickly to zero from the terrace edge to the middle of a Bi(110) nanoribbon potentially signifying a spatial metal-to-semiconductor transition. This study opens new avenues for room-temperature bismuth nanoribbon-based electronic devices. PMID:23368363

  10. Nonlinear behavior of the energy gap in Ge1-xSnx alloys at 4 K

    NASA Astrophysics Data System (ADS)

    Pérez Ladrón de Guevara, H.; Rodríguez, A. G.; Navarro-Contreras, H.; Vidal, M. A.

    2007-10-01

    The optical energy gap of Ge1-xSnx alloys (x?0.14) grown on Ge substrates has been determined by performing transmittance measurements at 4K using a fast fourier transform infrared interferometer. The direct energy gap transitions in Ge1-xSnx alloys behave following a nonlinear dependence on the Sn concentration, expressed by a quadratic equation, with a so called bowing parameter b0 that describes the deviation from a simple linear dependence. Our observations resulted in b0RT=2.30±0.10eV and b04K=2.84±0.15eV, at room temperature and 4K, respectively. The validity of our fit is limited for Sn concentrations lower than 15%.

  11. Development Of A Compact, High-energy Spark Gap Switch And Trigger Generator System

    Microsoft Academic Search

    D. Bhasavanich; S. S. Hitchcock; P. M. Creely; R. S. Shaw; H. G. Hammon; J. T. Naff

    1991-01-01

    High-energy switches and trigger generators are required for a range of capacitor banks in electric gun applications. We have developed a compact, long-lived spark gap and a matched series-injection trigger generator. The switch is of a two-electrode design using high density graphite electrodes. The demonstrated peak current capability is near 300 kA, with a charge transfer of 700 Cb, and

  12. Electronic energy gap of molecular hydrogen from electrical conductivity measurements at high shock pressures

    NASA Technical Reports Server (NTRS)

    Nellis, W. J.; Mitchell, A. C.; Mccandless, P. C.; Erskine, D. J.; Weir, S. T.

    1992-01-01

    Electrical conductivities were measured for liquid D2 and H2 shock compressed to pressures of 10-20 GPa (100-200 kbar), molar volumes near 8 cu cm/mol, and calculated temperatures of 2900-4600 K. The semiconducting energy gap derived from the conductivities is 12 eV, in good agreement with recent quasi-particle calculations and with oscillator frequencies measured in diamond-anvil cells.

  13. Non-Uniform Absorption of Terahertz Radiation in Superconducting Hot Electron Bolometer Mixers

    NASA Astrophysics Data System (ADS)

    Miao, W.; Zhang, W.; Delorme, Y.; Lefevre, R.; Feret, A.; Shi, S. C.

    We present an improved hot spot model that includes the non-uniform absorption of terahertz radiation on a superconducting HEB microbridge. We propose that the terahertz radiation is indeed absorbed mainly in the region of the superconducting microbridge with its energy gap (2?), in connection with the local electron temperature, less than the photon energy of the incoming radiation. With this improved hot spot model, we can precisely model LO (Local Oscillator)-pumped current-voltage and LO-pumped resistance-temperature characteristics of superconducting HEB mixers.

  14. Coexistence of ferromagnetism and superconductivity in normal mental/superconductor/ferromagnet structures

    NASA Astrophysics Data System (ADS)

    Yu, Hua-Ling; Peng, Ju; Jin, Ben-Xi

    2010-08-01

    We extend the Blonder, Tinkham and Klapwijk theory to the study of the inverse proximity effects in the normal mental/superconductor/ferromagnet structures. In the superconducting film, there are the gapless superconductivity and the spin-dependent density of states both within and without the energy gap. It indicates an appearance of the inverse-proximity-effect-induced ferromagnetism and a coexistence of ferromagnetism and superconductivity near the interface. The influence of exchange energy in the ferromagnet and barrier strength at the superconductor/ferromagnet interface on the inverse proximity effects is discussed.

  15. Superconducting magnets

    SciTech Connect

    Willen, E.

    1996-12-31

    Superconducting dipole magnets for high energy colliders are discussed. As an example, the magnets recently built for the Relativistic Heavy Ion Collider at Brookhaven are reviewed. Their technical performance and the cost for the industry-built production dipoles are given. The cost data is generalized in order to extrapolate the cost of magnets for a new machine.

  16. Superconducting Memristors

    NASA Astrophysics Data System (ADS)

    Peotta, Sebastiano; Di Ventra, Massimiliano

    2014-09-01

    In his original work, Josephson predicted that a phase-dependent conductance should be present in superconducting tunnel junctions, an effect difficult to detect, mainly because it is hard to single it out from the usual nondissipative Josephson current. We propose a solution for this problem that consists of using different superconducting materials to realize the two junctions of a superconducting interferometer. According to the Ambegaokar-Baratoff relation the two junctions have different conductances if the critical currents are equal, thus the Josephson current can be suppressed by fixing the magnetic flux in the loop at half of a flux quantum without canceling the phase-dependent conductance. Our proposal can be used to study the phase-dependent conductance, an effect present in principle in all superconducting weak links. From the standpoint of nonlinear circuit theory, such a device is in fact an ideal memristor with possible applications to memories and neuromorphic computing in the framework of ultrafast and low-energy-consumption superconducting digital circuits.

  17. Renewable and non-renewable energy status in Iran: Art of know-how and technology-gaps

    Microsoft Academic Search

    Amir Hossein Ghorashi; Abdulrahim Rahimi

    2011-01-01

    This paper reviews the present energy status in Islamic Republic of Iran with an emphasis on utilization of environmentally friendly energy resources. The paper reveals the huge energy losses due to technological gaps and absence of relevant art of know-how in conventional energy industries. It also includes some critical issues effecting the efficient operation of Renewable Energy Converting Systems (RECS)

  18. Effect of a Quartic Anisotropy Energy on the Spiral Magnetic Coexistence State of Superconductivity and Ferromagnetism 

    E-print Network

    ROSE, GH; Hu, Chia-Ren.

    1988-01-01

    PHYSICAL REVIE% 8 VOLUME 37, NUMBER 4 1 FEBRUARY 1988 Effect of a quartic anisotropy energy on the "spiral magnetic" coexistence state of superconductivity and ferromagnetism Gregory H. Rose and Chia-Ren Hu Center for Theoretical Physics... polarization transition can be induced by a mere change of temperature, and for ErRh484 and HoMo6SS the coexistence state only occurs in a very nar- row temperature range anyway. In Ref. 10 an investiga- GREGORY H. ROSE AND CHIA-REN HU tion was also made...

  19. 30-MJ superconducting magnetic-energy storage for BPA transmission-line stabilizer

    SciTech Connect

    Schermer, R.I.

    1981-01-01

    The Bonneville Power Administration operates the transmission system that joins the Pacific Northwest and southern California. A 30 MJ (8.4 kWh) Superconducting Magnetic Energy Storage (SMES) unit with a 10 MW converter can provide system damping for low frequency oscillations. The unit is scheduled to operate in 1982. Progress during FY 81 is described. The coil is complete. All major components of the electrical and cryogenic systems have been received and testing has begun. Computer control hardware is in place and software development is proceeding. Support system components and dewar lid are being fabricated and foundation design is complete. A contract for dewar fabrication is being negotiated.

  20. 30 MJ superconducting magnetic energy storage stabilizing coil. Final report for construction

    SciTech Connect

    NONE

    1983-03-01

    This report covers Phase II, Fabrication and Delivery of the 30 MJ Superconducting Magnetic Energy Storage Stabilizing Coil. A history of the manufacturing and assembly phase of the magnet is presented. Major problems and solutions are summarized, and illustrations of the major operations are provided. The Quality Assurance program is described with a listing of all nonconformance reports. Design documentation is provided, including a Design Document Index, monthly progress reports, and a list of papers given on the project. Appendices to the report contain copies of released and revised design calculations, test reports, assembly procedure, and nonconformance reports and engineering dispositions.

  1. Resistivity changes in superconducting-cavity-grade Nb following high-energy proton irradiation

    SciTech Connect

    Snead, C.L. Jr.; Hanson, A.; Greene, G.A. [and others

    1997-12-01

    Niobium superconducting rf cavities are proposed for use in the proton LINAC accelerators for spallation-neutron applications. Because of accidental beam loss and continual halo losses along the accelerator path, concern for the degradation of the superconducting properties of the cavities with accumulating damage arises. Residual-resistivity-ratio (RRR) specimens of Nb, with a range of initial RRR`s were irradiated at room temperature with protons at energies from 200 to 2000 MeV. Four-probe resistance measurements were made at room temperature and at 4.2 K both prior to and after irradiation. Nonlinear increases in resistivity simulate expected behavior in cavity material after extended irradiation, followed by periodic anneals to room temperature: For RRR = 316 material, irradiations to (2 - 3) x 10{sup 15} p/cm{sup 2} produce degradations up to the 10% level, a change that is deemed operationally acceptable. Without. periodic warming to room temperature, the accumulated damage energy would be up to a factor of ten greater, resulting in unacceptable degradations. Likewise, should higher-RRR material be used, for the same damage energy imparted, relatively larger percentage changes in the RRR will result.

  2. Infrared Study of Superconductivity: Grating Coupled Plasmons in Yttrium BARIUM(2) COPPER(3) OXYGEN(7) and Gap Features in BARIUM(1-X) Potassium(x) Bismuth OXYGEN(3)

    Microsoft Academic Search

    Franklin John Dunmore

    1995-01-01

    The electrodynamic properties of two different superconductors, Barium Potassium Bismuth Oxide (BKBO) and Yttrium Barium Copper Oxide (YBCO) have been studied using the technique of transmission Fourier transform spectroscopy with liquid helium temperature bolometric detection. Plasmon resonances have been observed in far infrared transmission measurements on superconducting YBCO films. An Aluminum\\/Nichrome grating is used to couple infrared radiation to collective

  3. Vanishing Electronic Energy Loss of Very Slow Light Ions in Insulators with Large Band Gaps

    SciTech Connect

    Markin, S. N.; Primetzhofer, D.; Bauer, P. [Institut fuer Experimentalphysik, Johannes-Kepler Universitaet Linz, A-4040 Linz (Austria)

    2009-09-11

    Electronic energy loss of light ions in nanometer films of materials with large band gaps has been studied for very low velocities. For LiF, a threshold velocity is observed at 0.1 a.u. (250 eV/u), below which the ions move without transferring energy to the electronic system. For KCl, a lower (extrapolated) threshold velocity is found, identical for H and He ions. For SiO{sub 2}, no clear velocity threshold is observed for He particles. For protons and deuterons, electronic stopping is found to perfectly fulfill velocity scaling, as expected for binary ion-electron interaction.

  4. Bowing parameter of the band-gap energy of GaNxAs1 - x

    NASA Astrophysics Data System (ADS)

    Bi, W. G.; Tu, C. W.

    1997-03-01

    We report a study of nitrogen incorporation in GaAs using a N rf plasma source. The N composition can be increased by lowering the growth temperature. X-ray diffraction shows no phase separation. Optical absorption measurements indicate that GaNxAs1-x is a direct band-gap material in the N composition range studied (x?14.8%), rather than a semimetal, contrary to theoretical predictions based on Van Vechten's model. Analyzing the N composition dependence of the band-gap energy of the alloy indicates a composition-dependent bowing parameter, consistent with the first-principles supercell calculations [L. Bellaiche, S. H. Wei, and A. Zunger, Phys. Rev. B 54, 17 568 (1996)].

  5. Manifestation of a gap due to the exchange energy in a spinor condensate

    NASA Astrophysics Data System (ADS)

    Navez, Patrick

    2008-07-01

    We investigate the dynamic response of population transfer between two components of a finite temperature spinor Bose condensed gas to a time-dependent coupling potential. Comparison between the results obtained in the Bogoliubov-Popov approximation (BPA) and in the generalized random phase approximation (GRPA) shows noticeable discrepancies. In particular, the inter-component current response function calculated in the GRPA displays a gapped spectrum due to the exchange interaction energy whereas the corresponding density response function is gapless. We verify that, contrary to the BPA, the GRPA preserves the SU(2) symmetry and the f-sum rule associated to the spinor gas. In order to validate the approximation, we propose an experimental setup that allows the observation of the predicted gap.

  6. Superconducting tunnel junction array development for high-resolution energy-dispersive x-ray spectroscopy

    SciTech Connect

    Barfknecht, A. T.; Cramer, S. P; Frank, M.; Friedrich, S.; Hiller, L. J.; Labov, S. E.; Mears, C. A.; Niderost, B.

    1998-07-01

    Cryogenic energy-dispersive x-ray detectors are being developed because of their superior energy resolution ((less than or equal to) 10 eV FWHM for keV x rays) compared to semiconductor EDS systems. So far, their range of application is limited due to their comparably small size and low count rate. We present data on the development of superconducting tunnel junction (STJ) detector arrays to address both of these issues. A single STJ detector has a resolution around 10 eV below 1 keV and can be operated at count rates of order 10,000 counts/s. We show that the simultaneous operation of several STJ detectors does not diminish their energy resolution significantly, while increasing the detector area and the maximum count rate by a factor given by the total number of independent channels.

  7. Ground state energy and scaling behaviour of spin gap in the XXZ spin-12 antiferromagnetic chain in longitudinal staggered field

    NASA Astrophysics Data System (ADS)

    Paul, Susobhan; Ghosh, Asim Kumar

    2014-08-01

    The ground state energy and the spin gap of a spin-12 Heisenberg antiferromagnetic XXZ chain in the presence of longitudinal staggered field (hz) have been estimated by using Jordan-Wigner representation, exact diagonalization and perturbative analysis. All those quantities have been obtained for a region of anisotropic parameter (?) defined by 0???1. For ?=0, the exact value of ground state energy is found for finite values of hz. The spin gap is found to develop as soon as the staggered field is switched on. The magnitude of spin gap is compared with the field induced gap measured in magnetic compounds CuBenzoate and Yb4As3 when ?=1. The dependence of spin gap on both ? and hz has been found which gives rise to scaling laws associated with hz. Scaling exponents obtained in two different cases show excellent agreements with the previously determined values. The variation of scaling exponents with ? can be fitted with a regular function.

  8. Influence of hole doping on the superconducting state in graphane

    NASA Astrophysics Data System (ADS)

    Durajski, A. P.

    2015-03-01

    The unique properties of two-dimensional materials have recently been attracting a huge amount of interest from researchers. From the point of view of potential applications in nanoelectronics, fully hydrogenated graphene (graphane) seems to be of particular interest. In the present paper, we analyze theoretically the possible superconductivity in hole-doped graphane. In particular, within the framework of the strong-coupling Eliashberg theory of superconductivity, we determine the superconducting transition temperature, the energy gap, the free energy and entropy differences between the superconducting and normal states, the thermodynamic critical field and the specific heat. The results obtained suggest that hole-doped graphane could potentially be a superconductor with a high transition temperature, {{T}C}\\in < 76,108> K, and with a large value of the superconducting energy gap, 2? (0)\\in < 27,42> meV. Moreover, it was shown that the thermodynamic properties of hole-doped graphane cannot be correctly described using the BCS (Bardeen–Cooper–Schrieffer) theory due to the strong-coupling and retardation effects.

  9. Roles of superconducting magnetic bearings and active magnetic bearings in attitude control and energy storage flywheel

    NASA Astrophysics Data System (ADS)

    Tang, Jiqiang; Fang, Jiancheng; Ge, Shuzhi Sam

    2012-12-01

    Compared with conventional energy storage flywheel, the rotor of attitude control and energy storage flywheel (ACESF) used in space not only has high speed, but also is required to have precise and stable direction. For the presented superconducting magnetic bearing (SMB) and active magnetic bearing (AMB) suspended ACESF, the rotor model including gyroscopic couples is established originally by taking the properties of SMB and AMB into account, the forces of SMB and AMB are simplified by linearization within their own neighbors of equilibrium points. For the high-speed rigid discal rotor with large inertia, the negative effect of gyroscopic effect of rotor is prominent, the radial translation and tilting movement of rotor suspended by only SMB, SMB with equivalent PMB, or SMB together with PD controlled AMB are researched individually. These analysis results proved originally that SMB together with AMB can make the rotor be stable and make the radial amplitude of the vibration of rotor be small while the translation of rotor suspended by only SMB or SMB and PM is not stable and the amplitude of this vibration is large. For the stability of the high-speed rotor in superconducting ACESF, the AMB can suppress the nutation and precession of rotor effectively by cross-feedback control based on the separated PD type control or by other modern control methods.

  10. COMMERCIALIZATION DEMONSTRATION OF MID-SIZED SUPERCONDUCTING MAGNETIC ENERGY STORAGE TECHNOLOGY FOR ELECTRIC UTILITYAPPLICATIONS

    SciTech Connect

    CHARLES M. WEBER

    2008-06-24

    As an outgrowth of the Technology Reinvestment Program of the 1990’s, an Agreement was formed between BWXT and the DOE to promote the commercialization of Superconducting Magnetic Energy Storage (SMES) technology. Business and marketing studies showed that the performance of electric transmission lines could be improved with this SMES technology by stabilizing the line thereby allowing the reserved stability margin to be used. One main benefit sought was to double the capacity and the amount of energy flow on an existing transmission line by enabling the use of the reserved stability margin, thereby doubling revenue. Also, electrical disturbances, power swings, oscillations, cascading disturbances and brown/black-outs could be mitigated and rendered innocuous; thereby improving power quality and reliability. Additionally, construction of new transmission lines needed for increased capacity could be delayed or perhaps avoided (with significant savings) by enabling the use of the reserved stability margin of the existing lines. Two crucial technical aspects were required; first, a large, powerful, dynamic, economic and reliable superconducting magnet, capable of oscillating power flow was needed; and second, an electrical power interface and control to a transmission line for testing, demonstrating and verifying the benefits and features of the SMES system was needed. A project was formed with the goals of commercializing the technology by demonstrating SMES technology for utility applications and to establish a domestic capability for manufacturing large superconducting magnets for both commercial and defense applications. The magnet had very low AC losses to support the dynamic and oscillating nature of the stabilizing power flow. Moreover, to economically interface to the transmission line, the magnet had the largest operating voltage ever made. The manufacturing of that design was achieved by establishing a factory with newly designed and acquired equipment, tooling, methods and skilled personnel. The final magnet system measured 14 feet in diameter, 10 feet in height, and weighed about 35 tons. The superconducting magnet and design technology was successfully implemented and demonstrated. The project was not successfully concluded however; as the critical planned final demonstration was not achieved. The utilities could not understand or clarify their future business needs and the regulatory requirements, because of the deregulation policies and practices of the country. Much uncertainty existed which prevented utilities from defining business plans, including asset allocation and cost recovery. Despite the technical successes and achievements, the commercial development could not be implemented and achieved. Thus, the demonstration of this enhancement to the utility’s transmission system and to the reliability of the nation’s electrical grid was not achieved. The factory was ultimately discontinued and the technology, equipment and product were placed in storage.

  11. A New Insight into Energy Distribution of Electrons in Fuel-Rod Gap in VVER-1000 Nuclear Reactor

    NASA Astrophysics Data System (ADS)

    Fereshteh, Golian; Ali, Pazirandeh; Saeed, Mohammadi

    2015-06-01

    In order to calculate the electron energy distribution in the fuel rod gap of a VVER-1000 nuclear reactor, the Fokker-Planck equation (FPE) governing the non-equilibrium behavior of electrons passing through the fuel-rod gap as an absorber has been solved in this paper. Besides, the Monte Carlo Geant4 code was employed to simulate the electron migration in the fuel-rod gap and the energy distribution of electrons was found. As for the results, the accuracy of the FPE was compared to the Geant4 code outcomes and a satisfactory agreement was found. Also, different percentage of the volatile and noble gas fission fragments produced in fission reactions in fuel rod, i.e. Krypton, Xenon, Iodine, Bromine, Rubidium and Cesium were employed so as to investigate their effects on the electrons' energy distribution. The present results show that most of the electrons in the fuel rod's gap were within the thermal energy limitation and the tail of the electron energy distribution was far from a Maxwellian distribution. The interesting outcome was that the electron energy distribution is slightly increased due to the accumulation of fission fragments in the gap. It should be noted that solving the FPE for the energy straggling electrons that are penetrating into the fuel-rod gap in the VVER-1000 nuclear reactor has been carried out for the first time using an analytical approach.

  12. Caffeine-containing energy drinks: beginning to address the gaps in what we know.

    PubMed

    Sorkin, Barbara C; Coates, Paul M

    2014-09-01

    Energy drinks are relatively new to the United States but are the fastest growing segment of the beverage market. Humans have a long history of consuming caffeine in traditional beverages, such as cocoa, coffee, tea, and yerba maté, but 2 workshops held at the Institute of Medicine (http://www.iom.edu/Activities/Nutrition/PotentialHazardsCaffeineSupplements/2013-AUG-05.aspx) and the NIH (http://ods.od.nih.gov/News/EnergyDrinksWorkshop2013.aspx) in 2013 highlighted many critical gaps in understanding the biologic and behavioral effects of the mixtures of caffeine, vitamins, herbs, sugar or other sweeteners, and other ingredients that typify caffeine-containing energy drinks (CCEDs). For example, different surveys over the same 2010–2012 timeframe report discrepant prevalence of CCED use by teenagers, ranging from 10.3% in 13–17 y olds to >30% of those in grades 10 and 12. Understanding of functional interactions between CCED ingredients, drivers of use, and biologic and behavioral effects is limited. The 4 speakers in the Experimental Biology 2014 symposium titled “Energy Drinks: Current Knowledge and Critical Research Gaps” described recent progress by their groups in extending our understanding of prevalence of CCED use, sources of caffeine in the United States, drivers of CCED use, and behavioral correlations and effects of CCEDs, including effects on attractiveness of both alcoholic and non-alcoholic beverages. PMID:25469387

  13. Competition between the pseudogap and superconductivity in the high-Tc copper oxides

    SciTech Connect

    Kondo, T.; Khasanov, R.; Takeuchi, T.; Schmalian, J.; Kaminski, A.

    2009-01-15

    In a classical Bardeen-Cooper-Schrieffer superconductor, pairing and coherence of electrons are established simultaneously below the critical transition temperature (T{sub c}), giving rise to a gap in the electronic energy spectrum. In the high-T{sub c} copper oxide superconductors, however, a pseudogap extends above T{sub 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.

  14. Energy band-gap bowing parameter in an AlxGa1 - x N alloy

    NASA Astrophysics Data System (ADS)

    Koide, Y.; Itoh, H.; Khan, M. R. H.; Hiramatu, K.; Sawaki, N.; Akasaki, I.

    1987-05-01

    Optical measurements are performed near the fundamental absorption edge for single-crystal AlxGa1-x N epitaxial layers in the composition range of 0?x?0.4. The dependence of the energy band gap on composition is found to deviate downwards from linearity, the bowing parameter being b=1.0±0.3 eV. The origin of the large bowing is discussed in terms of the pseudopotential of Al and Ga based on the pseudopotential of the Heine-Abarenkov type. With increasing x the absorption edges broaden, which is attributed to the increase of the compositional nonuniformity.

  15. Wave equations for determining energy-level gaps of quantum systems

    E-print Network

    Zeqian Chen

    2006-09-10

    An differential equation for wave functions is proposed, which is equivalent to Schr\\"{o}dinger's wave equation and can be used to determine energy-level gaps of quantum systems. Contrary to Schr\\"{o}dinger's wave equation, this equation is on `bipartite' wave functions. It is shown that those `bipartite' wave functions satisfy all the basic properties of Schr\\"{o}dinger's wave functions. Further, it is argued that `bipartite' wave functions can present a mathematical expression of wave-particle duality. This provides an alternative approach to the mathematical formalism of quantum mechanics.

  16. Theoretical study of some bis-verdazyl diradicals: singlet triplet energy gap

    NASA Astrophysics Data System (ADS)

    Chung, Gyusung; Lee, Duckhwan

    2001-12-01

    The bis-verdazyl diradical (BVD) system is closely examined by using the multiconfiguration wavefunctions as well as the density functional theory (DFT). The totally symmetric singlet ground state turns out to have strong multiconfiguration character at all levels of theory. The singlet ground state takes on the planar structure while the most stable triplet state corresponds to the twisted form. The MCSCF+MCQDPT2 calculations are shown to be sufficient to predict the singlet-triplet energy gap which is insensitive to the electronic characters of the ring substituents.

  17. The effects of the magnetopolaron on the energy gap opening in graphene.

    PubMed

    Li, Wei-Ping; Wang, Zi-Wu; Yin, Ji-Wen; Yu, Yi-Fu

    2012-04-01

    The magnetopolaron is formed via electron-acoustic deformation phonon coupling in the presence of a magnetic field in monolayer graphene. We find that an energy gap (EG) is opened due to the electron-phonon coupling. Both linear and square-root forms for the dependence of the EG on the magnetic field are obtained, which are in agreement with experimental measurements. Furthermore, we suggest that the EG can be estimated through observing the variation of Fermi velocity in cyclotron resonance experiments. The relation of the EG with the Debye cut-off wavenumber is also discussed. PMID:22392819

  18. Mono-parametric charge pumping through a quantum dot coupled with energy-gapped leads

    NASA Astrophysics Data System (ADS)

    Kwapi?ski, Tomasz; Taranko, Ryszard

    2015-06-01

    We present a proposal for a single-parametric electron pump composed of a quantum dot between two unbiased leads with energy-gapped electron density of states (DOS). The model tight-binding Hamiltonian and the evolution operator technique are used in the calculations. The quantum dot is driven by the external harmonic field which leads to the pumping current flowing from the left or right electrode depending on the system parameters. We show that the net pumping current appears in the system if (i) there are at least two sideband states: one of them lying below and the second lying above the Fermi energy; (ii) the left and right lead DOS in the vicinity of these sideband states are different. Moreover, the energy-gapped structure of DOS is visible on the average quantum dot charge and the pumped current curves as well as on the transconductance characteristics. Thus mono-parametric pumping provides useful information about the system parameters, in particular about the lead DOS structure.

  19. SUPERCONDUCTING PHOTOINJECTOR

    SciTech Connect

    BEN-ZVI,I.; BURRILL, A.; CALAGA, R.; CHANG, X.; GROVER, R.; GUPTA, R.; HAHN, H.; HAMMONS, L.; KAYRAN, D.; KEWISCH, J.; LAMBIASE, R.; LITVINENKO, V.; MCINTYRE, G.; NAIK, D.; PATE, D.; PHILLIPS, D.; POZDEYEV, E.; RAO, T.; SMEDLEY, J.; THAN, R.; TODD, R.; WEISS, D.; WU, Q.; ZALTSMAN, A.; ET AL.

    2007-08-26

    One of the frontiers in FEL science is that of high power. In order to reach power in the megawatt range, one requires a current of the order of one ampere with a reasonably good emittance. The superconducting laser-photocathode RF gun with a high quantum efficiency photocathode is the most natural candidate to provide this performance. The development of a 1/2 cell superconducting photoinjector designed to operate at up to a current of 0.5 amperes and beam energy of 2 MeV and its photocathode system are the subjects covered in this paper. The main issues are the photocathode and its insertion mechanism, the power coupling and High Order Mode damping. This technology is being developed at BNL for DOE nuclear physics applications such as electron cooling at high energy and electron ion colliders..

  20. Measurement of groove features and dimensions of the vertical test cathode and the choke joint of the superconducting electron gun cavity of the Energy Recovery LINAC

    Microsoft Academic Search

    L. Hammons; M. Ke

    2011-01-01

    A testing program for the superconducting electron gun cavity that has been designed for the Energy Recovery LINAC is being planned. The goal of the testing program is to characterize the RF properties of the gun cavity at superconducting temperatures and, in particular, to study multipacting that is suspected to be occurring in the choke joint of the cavity where

  1. Superconducting transmission line particle detector

    DOEpatents

    Gray, Kenneth E. (Naperville, IL)

    1989-01-01

    A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non-superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propogating in a superconducting transmission line are used to resolve N.sup.2 ambiguity of charged particle events.

  2. Superconducting transmission line particle detector

    DOEpatents

    Gray, K.E.

    1988-07-28

    A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non- superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propagating in a superconducting transmission line are used to resolve N/sup 2/ ambiguity of charged particle events. 6 figs.

  3. Design of an accelerating cavity for the Superconducting Super Collider Low-Energy Booster

    SciTech Connect

    Friedrichs, C.C.; Walling, L. (Los Alamos National Lab., NM (USA)); Campbell, B.M. (Superconducting Super Collider Lab., Dallas, TX (USA))

    1991-01-01

    This paper presents the history and current status of the design of the accelerator cavity to be incorporated into the Low-Energy Booster (LEB) of the Superconducting Super Collider (SSC). The LEB is a proton synchrotron, 540 meters in circumference, and having 108 buckets around the ring. Acceleration programs, each 50 msec long, take place at a rate of 10 per second. The beta change of the particles from injection to extraction is from 0.8 to 0.997. Since the rf excitation frequency must track beta, the rf frequency must shift from 47.5 to 60 MHz over the 50-msec acceleration program. The cavity will use ferrite in a perpendicular control bias mode to effect the require tuning. 4 refs., 1 fig.

  4. Superconducting pairing through the spin resonance mode in high-temperature cuprate superconductors.

    PubMed

    Onufrieva, F; Pfeuty, P

    2009-05-22

    We find that the spin resonance mode mediator scenario can explain important anomalies observed in the superconducting (SC) high-T_{c} cuprates: the famous low energy nodal kink with its doping dependence, the U-shaped form of the SC gap angular dependence, the anomalous form of electron density of states, the high absolute value of the SC gap, and some other unconventional properties. PMID:19519064

  5. Energy gaps in quantum first-order mean-field-like transitions: The problems that quantum annealing cannot solve

    NASA Astrophysics Data System (ADS)

    Jörg, T.; Krzakala, F.; Kurchan, J.; Maggs, A. C.; Pujos, J.

    2010-02-01

    We study first-order quantum phase transitions in models where the mean-field treatment is exact, and in particular the exponentially fast closure of the energy gap with the system size at the transition. We consider exactly solvable ferromagnetic models, and show that they reduce to the Grover problem in a particular limit. We compute the coefficient in the exponential closure of the gap using an instantonic approach, and discuss the (dire) consequences for quantum annealing.

  6. Non-invasive measurements of mesoscopic superconductors by superconducting single electron transistors

    Microsoft Academic Search

    Hideki Sato; Shingo Katsumoto; Yasuhiro Iye

    1998-01-01

    We have applied single-electron transistors (SETs) for the measurement of the energy gap of a quasiparticle as a function of magnetic field in mesoscopic superconductors. Through the measurements, it turned out that the randomness results in the pinning force of vortices, though the configuration of the order parameter is dominated by the edge nucleation of the superconductivity. The pinning of

  7. Coherent suppression of electromagnetic dissipation due to superconducting quasiparticles

    NASA Astrophysics Data System (ADS)

    Pop, Ioan M.; Geerlings, Kurtis; Catelani, Gianluigi; Schoelkopf, Robert J.; Glazman, Leonid I.; Devoret, Michel H.

    2014-04-01

    Owing to the low-loss propagation of electromagnetic signals in superconductors, Josephson junctions constitute ideal building blocks for quantum memories, amplifiers, detectors and high-speed processing units, operating over a wide band of microwave frequencies. Nevertheless, although transport in superconducting wires is perfectly lossless for direct current, transport of radio-frequency signals can be dissipative in the presence of quasiparticle excitations above the superconducting gap. Moreover, the exact mechanism of this dissipation in Josephson junctions has never been fully resolved experimentally. In particular, Josephson's key theoretical prediction that quasiparticle dissipation should vanish in transport through a junction when the phase difference across the junction is ? (ref. 2) has never been observed. This subtle effect can be understood as resulting from the destructive interference of two separate dissipative channels involving electron-like and hole-like quasiparticles. Here we report the experimental observation of this quantum coherent suppression of quasiparticle dissipation across a Josephson junction. As the average phase bias across the junction is swept through ?, we measure an increase of more than one order of magnitude in the energy relaxation time of a superconducting artificial atom. This striking suppression of dissipation, despite the presence of lossy quasiparticle excitations above the superconducting gap, provides a powerful tool for minimizing decoherence in quantum electronic systems and could be directly exploited in quantum information experiments with superconducting quantum bits.

  8. Illusory Continuity without Sufficient Sound Energy to Fill a Temporal Gap: Examples of Crossing Glide Tones

    ERIC Educational Resources Information Center

    Kuroda, Tsuyoshi; Nakajima, Yoshitaka; Eguchi, Shuntarou

    2012-01-01

    The gap transfer illusion is an auditory illusion where a temporal gap inserted in a longer glide tone is perceived as if it were in a crossing shorter glide tone. Psychophysical and phenomenological experiments were conducted to examine the effects of sound-pressure-level (SPL) differences between crossing glides on the occurrence of the gap…

  9. Pulsar High-Energy Emission From the Polar Cap and Slot Gap

    E-print Network

    Alice K. Harding

    2007-10-18

    Forty years after the discovery of rotation-powered pulsars, we still do not understand many aspects of their pulsed emission. In the last few years there have been some fundamental developments in acceleration and emission models. I will review both the basic physics of the models as well as the latest developments in understanding the high-energy emission of rotation-powered pulsars, with particular emphasis on the polar-cap and slot-gap models. Special and general relativistic effects play important roles in pulsar emission, from inertial frame-dragging near the stellar surface to aberration, time-of-flight and retardation of the magnetic field near the light cylinder. Understanding how these effects determine what we observe at different wavelengths is critical to unraveling the emission physics. I will discuss how current and future X-ray and gamma-ray detectors can test the predictions of these models.

  10. Surprisingly High Conductivity and Efficient Exciton Blocking in Fullerene/Wide-Energy-Gap Small Molecule Mixtures.

    PubMed

    Bergemann, Kevin J; Amonoo, Jojo A; Song, Byeongseop; Green, Peter F; Forrest, Stephen R

    2015-06-10

    We find that mixtures of C60 with the wide energy gap, small molecular weight semiconductor bathophenanthroline (BPhen) exhibit a combination of surprisingly high electron conductivity and efficient exciton blocking when employed as buffer layers in organic photovoltaic cells. Photoluminescence quenching measurements show that a 1:1 BPhen/C60 mixed layer has an exciton blocking efficiency of 84 ± 5% compared to that of 100% for a neat BPhen layer. This high blocking efficiency is accompanied by a 100-fold increase in electron conductivity compared with neat BPhen. Transient photocurrent measurements show that charge transport through a neat BPhen buffer is dispersive, in contrast to nondispersive transport in the compound buffer. Interestingly, although the conductivity is high, there is no clearly defined insulating-to-conducting phase transition with increased insulating BPhen fraction. Thus, we infer that C60 undergoes nanoscale (<10 nm domain size) phase segregation even at very high (>80%) BPhen fractions. PMID:25942074

  11. Singlet-triplet energy gaps for diradicals from particle-particle random phase approximation.

    PubMed

    Yang, Yang; Peng, Degao; Davidson, Ernest R; Yang, Weitao

    2015-05-21

    The particle-particle random phase approximation (pp-RPA) for calculating excitation energies has been applied to diradical systems. With pp-RPA, the two nonbonding electrons are treated in a subspace configuration interaction fashion while the remaining part is described by density functional theory (DFT). The vertical or adiabatic singlet-triplet energy gaps for a variety of categories of diradicals, including diatomic diradicals, carbene-like diradicals, disjoint diradicals, four-?-electron diradicals, and benzynes are calculated. Except for some excitations in four-?-electron diradicals, where four-electron correlation may play an important role, the singlet-triplet gaps are generally well predicted by pp-RPA. With a relatively low O(r(4)) scaling, the pp-RPA with DFT references outperforms spin-flip configuration interaction singles. It is similar to or better than the (variational) fractional-spin method. For small diradicals such as diatomic and carbene-like ones, the error of pp-RPA is slightly larger than noncollinear spin-flip time-dependent density functional theory (NC-SF-TDDFT) with LDA or PBE functional. However, for disjoint diradicals and benzynes, the pp-RPA performs much better and is comparable to NC-SF-TDDFT with long-range corrected ?PBEh functional and spin-flip configuration interaction singles with perturbative doubles (SF-CIS(D)). In particular, with a correct asymptotic behavior and being almost free from static correlation error, the pp-RPA with DFT references can well describe the challenging ground state and charge transfer excitations of disjoint diradicals in which almost all other DFT-based methods fail. Therefore, the pp-RPA could be a promising theoretical method for general diradical problems. PMID:25891638

  12. Superconductivity of vapour quenched beryllium and beryllium-based alloys

    Microsoft Academic Search

    C. G. Granqvist; T. Claeson

    1975-01-01

    The properties of Be films, quench-condensed upon a3He cooled substrate, have been investigated by resistance and tunneling measurements. The superconducting transition temperature,Tc, of Be films increased with thickness and a thick film limit of 9.95 K could be estimated. Alloying with Al or Pb decreasedTc. The ratios between energy gaps andTc's indicated that Be is a weak coupling superconductor, and

  13. Probing the gap feature in high Tc superconductors using resonance electronic Raman scattering

    NASA Astrophysics Data System (ADS)

    Klein, M.; Rubhausen, M.; Budelmann, D.; Schulz, B.; Guptasarma, P.; Bonn, D.; Liang, R.; Hardy, W.

    2004-03-01

    We present resonance electronic Raman scattering (RERS) results from the near to optimally doped HTCs Bi-2212 and Y-123 for incident photon energies from 1.96 to 4.5 eV. In RERS the k-space and symmetry dependent Raman amplitude A is tuned by varying the incident photon energy. The local pair susceptibility is multiplied by A^2, "illuminating" those regions of k-space where strong interband transitions occur at the incident photon energy. The resonance behavior of the superconducting gap feature in B_1g symmtery shows changes in shape and peak position as well as an asymmetric resonance profile, approximately 1.5 eV wide. The gap feature shows several components at different energies, which resonate differently with incident photon energy, revealing the composite nature of the gap excitations. Moreover, no superconductivity-induced gap features are visible with photon energies above 3.8 eV, sufficient to excite optical transitions into the buffer layers, suggesting that these buffer layer states do not contribute to superconductivity.

  14. Texture improvements in the high-temperature superconducting Bi?Sr?Ca?Cu?Ox̳/Ag system via surface energy driven grain alignment

    E-print Network

    Vodhanel, Mark E

    2005-01-01

    The relation between processing, microstructure, and material property was investigated in the high-temperature superconducting Bi?Sr?Ca?Cu?Ox̳/Ag system. Experiments were based on a theoretical surface energy model ...

  15. Narrow Energy Gap between Triplet and Singlet Excited States of Sn2+ in Borate Glass

    NASA Astrophysics Data System (ADS)

    Masai, Hirokazu; Yamada, Yasuhiro; Suzuki, Yuto; Teramura, Kentaro; Kanemitsu, Yoshihiko; Yoko, Toshinobu

    2013-12-01

    Transparent inorganic luminescent materials have attracted considerable scientific and industrial attention recently because of their high chemical durability and formability. However, photoluminescence dynamics of ns2-type ions in oxide glasses has not been well examined, even though they can exhibit high quantum efficiency. We report on the emission property of Sn2+-doped strontium borate glasses. Photoluminescence dynamics studies show that the peak energy of the emission spectrum changes with time because of site distribution of emission centre in glass. It is also found that the emission decay of the present glass consists of two processes: a faster S1-S0 transition and a slower T1-S0 relaxation, and also that the energy difference between T1 and S1 states was found to be much smaller than that of (Sn, Sr)B6O10 crystals. We emphasize that the narrow energy gap between the S1 and T1 states provides the glass phosphor a high quantum efficiency, comparable to commercial crystalline phosphors.

  16. Tests of the 30-MJ superconducting magnetic-energy storage unit

    SciTech Connect

    Boenig, H.J.; Dean, J.W.; Rogers, J.D.; Schermer, R.I.; Hauer, J.F.

    1983-01-01

    A 30-MJ (8.4 kWh) superconducting magnetic energy storage (SMES) unit with a 10-MW converter was installed during the later months of 1982 at the Bonneville Power Administration (BPA) Tacoma substation in Tacoma, Washington. The unit, which is capable of absorbing and releasing up to 10 MJ of energy at a frequency of 0.35 Hz, was designed to damp the dominant power swing mode of the Pacific AC Intertie. Extensive tests were performed with the unit during the first half of 1983. This paper will review the major components of the storage unit and describe the startup and steady state operating experience with the coil, dewar, refrigerator and converter. The unit has absorbed power up to a level of 11.8 Mw. Real power was modulated following a sinusoidal power demand with frequencies from 0.1 to 1.2 Hz and a power level up to +- 8.3 MW. The unit has performed in accordance with design expectations and no major problems have developed.

  17. An overview of Boeing flywheel energy storage systems with high-temperature superconducting bearings

    NASA Astrophysics Data System (ADS)

    Strasik, M.; Hull, J. R.; Mittleider, J. A.; Gonder, J. F.; Johnson, P. E.; McCrary, K. E.; McIver, C. R.

    2010-03-01

    An overview summary of recent Boeing work on high-temperature superconducting (HTS) bearings is presented. A design is presented for a small flywheel energy storage system that is deployable in a field installation. The flywheel is suspended by a HTS bearing whose stator is conduction cooled by connection to a cryocooler. At full speed, the flywheel has 5 kW h of kinetic energy, and it can deliver 3 kW of three-phase 208 V power to an electrical load. The entire system, which includes a containment structure, is compatible with transportation by forklift or crane. Laboratory measurements of the bearing loss are combined with the parasitic loads to estimate the efficiency of the system. Improvements in structural composites are expected to enable the operation of flywheels with very high rim velocities. Small versions of such flywheels will be capable of very high rotational rates and will likely require the low loss inherent in HTS bearings to achieve these speeds. We present results of experiments with small-diameter rotors that use HTS bearings for levitation and rotate in vacuum at kHz rates. Bearing losses are presented as a function of rotor speed.

  18. Reply to ``Comment on `High-field studies of superconducting fluctuations in high-Tc cuprates: Evidence for a small gap distinct from the large pseudogap'''

    NASA Astrophysics Data System (ADS)

    Rullier-Albenque, F.; Alloul, H.; Rikken, G.

    2012-03-01

    The experimental investigations done in our paper [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.84.014522 84, 014522 (2011)] allowed us to establish that the superconducting fluctuations (SCF) always die out sharply with increasing T. But contrary to the claim in the Comment of Ramallo , this sharp cutoff of SCF measured in YBa2Cu2O6+x depends on hole doping and/or disorder. So our data cannot be used to claim a universality of the extended Gaussian Ginzburg-Landau theory proposed by Ramallo Furthermore, to explain quantitatively our data near optimal doping using this model they need to consider that fluctuations in the two CuO2 planes of a bilayer are totally decoupled, which is not physically well justified. On the contrary, a consistent interpretation of all our data (paraconductivity, Nernst effect, and magnetoresistance) has been done by considering that the coupling between the two layers of the unit cell is dominant at least up to 1.1Tc.

  19. Operation of the 30 MJ superconducting magnetic energy storage system in the Bonneville Power Administration Electrical Grid

    SciTech Connect

    Rogers, J.D.; Boenig, H.J.; Schermer, R.I.; Hauer, J.F.

    1984-01-01

    The 30 MJ superconducting magnetic energy storage (SMES) system was installed in the Bonneville Power Administration (BPA) Tacoma Substation in 1982 to 1983. Operation of the unit since that time has been for over 1200 hours. Specific tests to explore the SMES system's thermal and electrical characteristics and the control functions were conducted. The coil heat load with current modulation was determined. A converter with two 6-pulse bridges interfaces the superconducting coil to the power bus. Equal bridge voltage amplitude and constant reactive power modes of operation of the system were run with computer control of the SCR bridge firing angles. Coil energy dump tests were performed. Electrical grid system response to SMES modulation was observed, and full power SMES modulation was undertaken.

  20. Conceptual system design of a 5 MWh\\/100 MW superconducting flywheel energy storage plant for power utility applications

    Microsoft Academic Search

    H. J. Bornemann; M. Sander

    1997-01-01

    The authors have designed a 5 MWh\\/100 MW superconducting flywheel energy storage plant. The plant consists of 10 flywheel modules rated at 0.5 MWh\\/10 MW each. Module weight is 30 t, size is ? 3.5 m×6.5 m high. A synchronous type motor-generator is used for power input\\/output. Each flywheel system consists of four disk modules made from a carbon fibre

  1. Scanning Tunneling Spectroscopy of Transition Metal Dichalcogenides: Quasiparticle Gap, Critical Point Energies and Heterojunction Band Offsets

    NASA Astrophysics Data System (ADS)

    Shih, Chih-Kang

    2015-03-01

    As an emergent atomically thin electronic and photonic materials material, transition metal dichalcogenides (TMDs) has triggered intensive research activities toward understanding of their electronic structures. Here I will introduce a comprehensive form of scanning tunneling spectroscopy (STS) which allows us to probe details quasi-particle electronic structures of TMDs. More specifically, we show that not only the quasi-particle band gaps but also the critical point energy locations and their origins in the Brillouin Zone (BZ) can be revealed using this comprehensive form of STS. By using this new method, we unravel the systematic trend of the critical point energies for TMDs due to atomic orbital couplings, spin-orbital coupling and the interlayer coupling. Moreover, by combining the micro-beam X-ray photoelectron spectroscopy (micro-XPS) and STS, we determine the band offsets in planar heterostructures formed between dissimilar single layer TMDs (MoS2, WSe2, and WS2). We show that both commutativity and transitivity of heterojunction band offset hold within the experimental uncertainty. Other Contributors: (i) Chendong Zhang, Yuxuan Chen, and Amber Johnson at the University of Texas at Austin; (ii) Ming-Yang Li, Jing-Kai Huang, Lain-Jong Li, Chih-Piao Chuu and Mei-Yin Chou at the Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan.

  2. Size dependence in hexagonal mesoporous germanium : pore wall thickness versus energy gap and photoluinescence.

    SciTech Connect

    Armatas, G. S.; Kanatzidis, M. G.; Materials Science Division; Northwestern Univ.; Univ. of Crete

    2010-08-10

    A series of hexagonal mesoporous germanium semiconductors with tunable wall thickness is reported. These nanostructures possess uniform pores of 3.1-3.2 nm, wall thicknesses from 1.3 to 2.2 nm, and large internal BET surface area in the range of 404-451 m{sup 2}/g. The porous Ge framework of these materials is assembled from the templated oxidative self-polymerization of (Ge{sub 9}){sup 4-} Zintl clusters. Total X-ray scattering analysis supports a model of interconnected deltahedral (Ge{sub 9})-cluster forming the framework and X-ray photoelectron spectroscopy indicates nearly zero-valence Ge atoms. We show the controllable tuning of the pore wall thickness and its impact on the energy band gap which increases systematically with diminishing wall thickness. Furthermore, there is room temperature photoluminescence emission which shifts correspondingly from 672 to 640 nm. The emission signal can be quenched via energy transfer with organic molecules such as pyridine diffusing into the pores.

  3. Biological effects of magnetic fields from superconducting magnetic energy storage systems

    SciTech Connect

    Tenforde, T.S.

    1989-12-01

    Physical interaction mechanisms and potential biological effects of static and slowly time-varying magnetic fields are summarized. The results of laboratory and human health studies on this topic are related to the fringe magnetic field levels anticipated to occur in the proximity of superconducting magnetic energy storage (SMES) systems. The observed biological effects of magnetic fields include: (1) magnetic induction of electrical potentials in the circulatory system and other tissues, (2) magneto-orientation of macromolecules and membranes in strong magnetic fields, and (3) Zeeman interactions with electronic spin states in certain classes of charge transfer reactions. In general, only the first of these interactions is relevant to the establishment of occupational exposure guidelines. Physical hazards posed by the interactions of magnetic fields with cardiac pacemakers and other implanted medical devices, e.g., aneurysm clips and prostheses, are important factors that must also be considered in establishing exposure guidelines. Proposed guidelines for limiting magnetic field exposure are discussed. 50 refs., 1 fig.

  4. Large-bore, superconducting magnets for high-energy density propellant storage

    Microsoft Academic Search

    M. S. Lubell; J. W. Lue; B. Palaszewski

    1997-01-01

    A study has been conducted on the design of large-bore, superconducting solenoid magnets in an effort to determine how weight and cost scales with field and size. The fields considered ranged from 0.5 to 20 T and bore sizes from 3 to 10 m. The designs are based on light-weight, high-performance superconducting magnet designs using cable-in-conduit niobium-titanium and niobium-tin conductors.

  5. Scanning Josephson Tunneling Microscopy of Single Crystal Bi2Sr2CaCu2O8+delta with a Conventional Superconducting Tip

    SciTech Connect

    Kimura, H.; Barber Jr., R. P.; Ono, S.; Ando, Yoichi; Dynes, Robert C.

    2009-10-28

    We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed between a conventional superconducting scanning tunneling microscope tip and overdoped Bi2Sr2CaCu2O8+ single crystals. A Josephson current is observed with a peak centered at a small finite voltage due to the thermal-fluctuation-dominated superconducting phase dynamics. Josephson measurements at different surface locations yield local values for the Josephson ICRN product. Corresponding energy gap measurements were also performed and a surprising inverse correlation was observed between the local ICRN product and the local energy gap.

  6. Determination of the optical energy gap of Ge1-xSnx alloys with 0

    NASA Astrophysics Data System (ADS)

    Ladrón de Guevara, H. Pérez; Rodríguez, A. G.; Navarro-Contreras, H.; Vidal, M. A.

    2004-05-01

    The optical energy gap of Ge1-xSnx alloys has been determined from transmittance measurements, using a fast-Fourier-transform infrared interferometer. Our results show that the change from indirect to direct band gap occurs at a lower critical Sn concentration (xc) than the value predicted from the virtual crystal approximation, tight binding, and pseudopotential models. However, a close agreement between the experimental results and the predictions with deformation potential theory is observed. The concentration xc, which is theoretically expected to be 0.09, actually it is observed to lie between 0.10

  7. Ga-rich GaP(001)(2×4) surface structure studied by low-energy ion scattering spectroscopy

    Microsoft Academic Search

    M. Naitoh; A Konishi; H Inenaga; S Nishigaki; N Oishi; F Shoji

    1998-01-01

    We report the results of low-energy He+-ion scattering spectroscopy investigation of a Ga-rich GaP(001)(2×4) surface prepared by Ne+-ion bombardment and annealing. The incidence-angle ? dependence of the scattered ion intensity was obtained along the [11?0] two-fold direction and the [110] four-fold direction. Our results suggest that this Ga-rich GaP(001) surface contains a Ga double-layer consisting of a (2×4)-arrangement of two

  8. Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata

    SciTech Connect

    Som, Sumit; Ghosh, Surajit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Roy, Suprakash [Variable Energy Cyclotron Centre, Kolkata (India)] [Variable Energy Cyclotron Centre, Kolkata (India)

    2013-11-15

    Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A and M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9–27 MHz with amplitude and phase stability of 100 ppm and ±0.1°, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ±0.1° during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase/Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata.

  9. Superconductivity-Induced Self-Energy Evolution of the Nodal Electron in Optimally-Doped Bi2212

    SciTech Connect

    Lee, W.S.

    2010-05-03

    The temperature dependent evolution of the renormalization effect in optimally-doped Bi2212 along the nodal direction has been studied via angle-resolved photoemission spectroscopy. Fine structure is observed in the real part of the self-energy (Re{Sigma}), including a subkink and maximum, suggesting that electrons couple to a spectrum of bosonic modes, instead of just one mode. Upon cooling through the superconducting phase transition, the fine structures of the extracted Re{Sigma} exhibit a two-processes evolution demonstrating an interplay between kink renormalization and superconductivity. We show that this two-process evolution can be qualitatively explained by a simple Holstein model in which a spectrum of bosonic modes is considered.

  10. Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata.

    PubMed

    Som, Sumit; Ghosh, Surajit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Roy, Suprakash

    2013-11-01

    Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A&M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.1°, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ±0.1° during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase?Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata. PMID:24289392

  11. Design and construction of the main linac module for the superconducting energy recovery linac project at Cornell

    NASA Astrophysics Data System (ADS)

    Eichhorn, R.; Bullock, B.; He, Y.; Hoffstaetter, G.; Liepe, M.; O'Connell, T.; Quigley, P.; Sabol, D.; Sears, J.; Smith, E.; Veshcherevich, V.

    2014-01-01

    Cornell University has been designing and building superconducting accelerators for various applications for more than 50 years. Currently, an energy-recovery linac (ERL) based synchrotron-light facility is proposed making use of the existing CESR facility. As part of the phase 1 R&D program funded by the NSF, critical challenges in the design were addressed, one of them being a full linac cryo-module. It houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode - with individual HOM absorbers and one magnet/ BPM section. Pushing the limits, a high quality factor of the cavities (2?1010) and high beam currents (100 mA accelerated plus 100 mA decelerated) are targeted. We will present the design of the main linac cryo-module (MLC) being finalized recently, its cryogenic features and report on the status of the fabrication which started in late 2012.

  12. Design and construction of the main linac module for the superconducting energy recovery linac project at Cornell

    SciTech Connect

    Eichhorn, R.; Bullock, B.; He, Y.; Hoffstaetter, G.; Liepe, M.; O'Connell, T.; Quigley, P.; Sabol, D.; Sears, J.; Smith, E.; Veshcherevich, V. [Cornell Laboratory for Accelerator-based Science and Education (CLASSE), Cornell University, 161 Synchrotron Drive, Ithaca, NY 14853 (United States)

    2014-01-29

    Cornell University has been designing and building superconducting accelerators for various applications for more than 50 years. Currently, an energy-recovery linac (ERL) based synchrotron-light facility is proposed making use of the existing CESR facility. As part of the phase 1 R and D program funded by the NSF, critical challenges in the design were addressed, one of them being a full linac cryo-module. It houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode - with individual HOM absorbers and one magnet/ BPM section. Pushing the limits, a high quality factor of the cavities (2?10{sup 10}) and high beam currents (100 mA accelerated plus 100 mA decelerated) are targeted. We will present the design of the main linac cryo-module (MLC) being finalized recently, its cryogenic features and report on the status of the fabrication which started in late 2012.

  13. Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata

    NASA Astrophysics Data System (ADS)

    Som, Sumit; Ghosh, Surajit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Roy, Suprakash

    2013-11-01

    Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A&M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.1°, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ±0.1° during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase/Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata.

  14. Superconducting PM undiffused machines with stationary superconducting coils

    DOEpatents

    Hsu, John S.; Schwenterly, S. William

    2004-03-02

    A superconducting PM machine has a stator, a rotor and a stationary excitation source without the need of a ferromagnetic frame which is cryogenically cooled for operation in the superconducting state. PM material is placed between poles on the rotor to prevent leakage or diffusion of secondary flux before reaching the main air gap, or to divert PM flux where it is desired to weaken flux in the main air gap. The PM material provides hop-along capability for the machine in the event of a fault condition.

  15. Dust filtration at gap edges: Implications for the spectral energy distributions of discs with embedded planets

    E-print Network

    W. K. M. Rice; Philip J. Armitage; Kenneth Wood; Giuseppe Lodato

    2006-09-29

    The spectral energy distributions (SEDs) of some T Tauri stars display a deficit of near-IR flux that could be a consequence of an embedded Jupiter-mass planet partially clearing an inner hole in the circumstellar disc. Here, we use two-dimensional numerical simulations of the planet-disc interaction, in concert with simple models for the dust dynamics, to quantify how a planet influences the dust at different radii within the disc. We show that pressure gradients at the outer edge of the gap cleared by the planet act as a filter - letting particles smaller than a critical size through to the inner disc while holding back larger particles in the outer disc. The critical particle size depends upon the disc properties, but is typically of the order of 10 microns. This filtration process will lead to discontinuous grain populations across the planet's orbital radius, with small grains in the inner disc and an outer population of larger grains. We show that this type of dust population is qualitatively consistent with SED modelling of systems that have optically thin inner holes in their circumstellar discs. This process can also produce a very large gas-to-dust ratio in the inner disc, potentially explaining those systems with optically thin inner cavities that still have relatively high accretion rates.

  16. Energy gaps in disordered systems: II. Alloys This article has been downloaded from IOPscience. Please scroll down to see the full text article.

    E-print Network

    Taylor, Philip L.

    Energy gaps in disordered systems: II. Alloys This article has been downloaded from IOPscience. SOC., 1967,VOL. 90. PRINTED I N GREAT BRITAIN Energy gaps in disordered systems 11. Alloys P. L in another, then no state exists in the region of overlap in any alloy of the two, provided only

  17. Band gap energy and bowing parameter of In-rich InAlN films grown by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    He, Hong; Cao, Yongge; Fu, Renli; Guo, Wang; Huang, Zhi; Wang, Meili; Huang, Changgang; Huang, Jiquan; Wang, Hai

    2010-01-01

    The crystal structure, band gap energy and bowing parameter of In-rich In xAl 1- xN (0.7 < x < 1.0) films grown by magnetron sputtering were investigated. Band gap energies of In xAl 1- xN films were obtained from absorption spectra. Band gap tailing due to compositional fluctuation in the films was observed. The band gap of the as-grown InN measured by optical absorption method is 1.34 eV, which is larger than the reported 0.7 eV for pure InN prepared by molecular beam epitaxy (MBE) method. This could be explained by the Burstein-Moss effect under carrier concentration of 10 20 cm -3 of our sputtered films. The bowing parameter of 3.68 eV is obtained for our In xAl 1- xN film which is consistent with the previous experimental reports and theoretical calculations.

  18. Effects of Ca and Sr chemical doping on the average superconducting kinetic energy of YBa2Cu3O7-?

    NASA Astrophysics Data System (ADS)

    Vieira, V. N.; Mendonça, A. P. A.; Dias, F. T.; Hneda, M. L.; Pureur, P.; Schaf, J.; Mesquita, F.

    2015-03-01

    In this brief communication we applied the MZFC(T) and MFCC(T) reversible dc magnetizations to get the average superconducting kinetic energy density, kS(T,B) of YBa2Cu3O7-?, Y0.95Ca0.05Ba2Cu3O7-? and YBa1.75Sr0.25Cu3O7-? ceramic samples with the aim of study the effects of Ca and Sr doping on the kS(T,B). The MZFC(T) and MFCC(T) measurements were performed with a SQUID magnetometer from quantum design to dc magnetic fields up to 50kOe. The determination of the kS(T,B) from reversible dc magnetization is supported by virial theorem of superconductivity [kS(T,B) = – MB]. The kS(T,B) results show an common temperature profile for all the samples which is smoothly affected by the magnetic field. On the other hand the kS(T,B) results to T > Tc could not be associated to the pseudogap phenomenon. The Ca doping affects more effectively the kS(T,B) behaviour then Sr doping. A possible explanation to this feature could be associated to the fact that the hole doping promoted by Ca doping depress more considerably the superconducting state and enhances the granular character of the YBa2Cu3O7-? superconductor than the chemical pressure effect promoted by Sr doping.

  19. Electronic Raman scattering on out-of-plane disordered Bi2Sr2CaCu2O8 +? : How the pseudogap affects the superconducting Raman response

    NASA Astrophysics Data System (ADS)

    Murai, N.; Masui, T.; Ishikado, M.; Ishida, S.; Eisaki, H.; Uchida, S.; Tajima, S.

    2015-06-01

    We report Raman scattering measurements on Bi2Sr2CaCu2O8 +? single crystals with a different degree of out-of-plane disorder to examine the effect of Tc change on the the electronic Raman response at the optimal doping level. The B1 g peak energies for lower Tc disordered samples are essentially independent of Tc. However, a further increase of Tc by minimizing the degree of out-of-plane disorder leads to a high-energy shift of the B1 g peak. Interestingly, abrupt change of the B1 g peak energy occurs when the the superconducting gap energy exceeds the pseudogap energy, which results in the recovery of superconductivity-dominated Raman response in B1 g symmetry. It suggests that these anomalous properties of the antinodal electrons are a consequence of the unconventional superconducting state of the cuprates where superconductivity coexists with the pseudogap in the ground state.

  20. Revealing the high-energy electronic excitations underlying the onset of high-temperature superconductivity in cuprates

    PubMed Central

    Giannetti, Claudio; Cilento, Federico; Conte, Stefano Dal; Coslovich, Giacomo; Ferrini, Gabriele; Molegraaf, Hajo; Raichle, Markus; Liang, Ruixing; Eisaki, Hiroshi; Greven, Martin; Damascelli, Andrea; van der Marel, Dirk; Parmigiani, Fulvio

    2011-01-01

    In strongly correlated systems the electronic properties at the Fermi energy (EF) are intertwined with those at high-energy scales. One of the pivotal challenges in the field of high-temperature superconductivity (HTSC) is to understand whether and how the high-energy scale physics associated with Mott-like excitations (|E?EF|>1 eV) is involved in the condensate formation. Here, we report the interplay between the many-body high-energy CuO2 excitations at 1.5 and 2 eV, and the onset of HTSC. This is revealed by a novel optical pump-supercontinuum-probe technique that provides access to the dynamics of the dielectric function in Bi2Sr2Ca0.92Y0.08Cu2O8+? over an extended energy range, after the photoinduced suppression of the superconducting pairing. These results unveil an unconventional mechanism at the base of HTSC both below and above the optimal hole concentration required to attain the maximum critical temperature (Tc). PMID:21673674

  1. Control of Superconducting Magnetic Energy Storage Units in Multi-Machine Power Systems

    NASA Astrophysics Data System (ADS)

    Ranaweera, Aruna

    A new scheme, in which a synchronous generator connected to the SMES busbar is used as a feedback generator, is proposed to control superconducting magnetic energy storage (SMES) units in multi-machine power systems, in this dissertation. The speed and the load angle changes of the feedback generator are used to calculate the necessary real power transfers to the SMES, while the necessary reactive power transfers are calculated from the voltage changes of the common busbar. Expressions are derived for the direct and quadrature axis components of the current drawn by the SMES, for unequal firing angles in the converter bridge, and the relationships of the two currents to the total real and reactive power transfers to the SMES are shown. The expressions derived are valid for small or large systems, under steady state or transient conditions, and it is shown through computer simulations in a small power system that, the proposed scheme is quite effective in stabilizing electromechanical oscillations caused by small as well as large disturbances. It is also shown that, the SMES can improve the power output of wind turbine induction generators, and also stabilize the oscillations caused by wind power losses in a steam turbine generator system, and thereby eliminate the need to use diesel turbine generators for the same purpose. Finally, equations are derived to represent the synchronous machine in terms of its d-q circuits, while it is connected to the network which is described by complex quantities, and the formulations done for the proposed scheme are extended to study the use of SMES units with proposed control in power systems of large and complex configurations. The proposed scheme of control is simple, and does not call for a special design of a controller requiring simplifying assumptions such as the presence of an infinite busbar or steady state operating conditions on the system, and therefore, would help in the widespread use of SMES units in electric utilities.

  2. Energy gap and proximity effect in MgB2 superconducting wires R. Prozorov* and R. W. Giannetta

    E-print Network

    Prozorov, Ruslan

    of the penetration depth (T,H) in the presence of a dc magnetic field were performed in MgB2 wires. In as-prepared wires (T,H 130 Oe) shows a strong diamagnetic downturn below 10 K. A dc magnetic field of 130 Oe in a box furnace at 950 °C for approxi- mately 2 h. The reaction ampoule was then removed from the furnace

  3. ARPES Studies of Cuprate Fermiology: Superconductivity, Pseudogap and Quasiparticle Dynamics

    SciTech Connect

    Vishik, Inna

    2011-06-23

    We present angle-resolved photoemission spectroscopy (ARPES) studies of the cuprate high-temperature superconductors which elucidate the relation between superconductivity and the pseudogap and highlight low-energy quasiparticle dynamics in the superconducting state. Our experiments suggest that the pseudogap and superconducting gap represent distinct states, which coexist below T{sub c}. Studies on Bi-2212 demonstrate that the near-nodal and near-antinodal regions behave differently as a function of temperature and doping, implying that different orders dominate in different momentum-space regions. However, the ubiquity of sharp quasiparticles all around the Fermi surface in Bi-2212 indicates that superconductivity extends into the momentum-space region dominated by the pseudogap, revealing subtlety in this dichotomy. In Bi-2201, the temperature dependence of antinodal spectra reveals particle-hole asymmetry and anomalous spectral broadening, which may constrain the explanation for the pseudogap. Recognizing that electron-boson coupling is an important aspect of cuprate physics, we close with a discussion of the multiple 'kinks' in the nodal dispersion. Understanding these may be important to establishing which excitations are important to superconductivity.

  4. Effect of electron divergence in air gaps on the measurement of the energy of cascades in emulsion chambers

    NASA Technical Reports Server (NTRS)

    Apanasenko, A. V.; Baradzey, L. T.; Kanevskaya, Y. A.; Smorodin, Y. A.

    1975-01-01

    The effect of an increase in electron density in the vicinity of the cascade axis caused by an avalanche passing through the gap between lead filters of the emulsion chamber was investigated experimentally. Optical densities were measured in three X-ray films spaced at 400, 800 and 1200 micrometer from the filter surface having a thickness of 6 cascade units. The optical densities of blackening spots caused by electron photon cascades of 1 to 2, 2 to 7 and greater than 7 BeV energies were measured. The results prove the presence of a gap between the filter and the nuclear emulsion which results in the underestimation of energy by several tenths of a percent.

  5. Spin Dynamics and Magnetic Coherence in the Superconducting State of High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Morr, Dirk K.

    2000-03-01

    Recent inelastic neutron scattering (INS) experiments(T. Mason et al.), Phys. Rev. Lett 77, 1604 (1996); B. Lake et al., Nature 400, 43 (1999). on La_2-xSr_xCuO4 have observed dramatic changes in the incommensurate magnetic response, \\chi'', upon entering the superconducting state (magnetic coherence effect). In particular, they observed a sharpening of the incommensurate peaks which is accompanied by a transfer of spectral weight to higher energies, and an only weakly momentum dependent spin-gap. In this talk I propose a scenario in which the magnetic coherence effect arises from an interplay of incommensurate spin structure, d-wave symmetry of the superconducting gap and the form of the Fermi surface in La_2-xSr_xCuO_4. This scenario is based on the idea that incommensurate spin excitations are a relaxational mode whose frequency dependence is solely determined by its coupling to fermionic quasiparticles. Within the spin-fermion model I show that the opening of the superconducting gap in the electronic spectrum gives rise to the observed transfer of spectral weight, and simultaneously, to a sharpening of the incommensurate peaks. This scenario provides a quantitative explanation for the momentum and frequency dependence of \\chi'' in the superconducting state, as well as for the weak momentum dependence of the spin-gap. I thus argue that magnetic coherence is simply a reflection of electronic coherence in the superconducting phase. Moreover, I demonstrate that INS data in the superconducting state provide insight into the form of the Fermi surface and thus complement angle-resolved photoemission experiments. For La_2-xSr_xCuO_4, the analysis of INS data within the presented scenario suggests a Fermi surface which is closed around (?,?). Finally, I discuss several predictions for the appearance of a similar magnetic coherence effect in other cuprate superconductors which exhibit an incommensurate magnetic response.

  6. T(z) phase diagram and optical energy gaps in CuGa(Se z Te1- z )2 alloys

    Microsoft Academic Search

    Miguel Quintero; Tibaire Tinoco; Carlos Rincón

    1991-01-01

    The T(z) phase diagram of the system CuGa(Se z Te1- z )2 was obtained from x-ray diffraction and differencial thermal analysis (DTA) measurements. DTA measurements were carried out on each sample and the transition temperatures were plotted as a function of alloy composition. Values of lattice parameter were determined in all cases. Values of the optical energy gap at 300

  7. Edge effects on band gap energy in bilayer 2H-MoS2 under uniaxial strain

    NASA Astrophysics Data System (ADS)

    Dong, Liang; Wang, Jin; Namburu, Raju; O'Regan, Terrance P.; Dubey, Madan; Dongare, Avinash M.

    2015-06-01

    The potential of ultrathin MoS2 nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS2 film. In this study, a bilayer MoS2 supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS2 film under uniaxial mechanical deformations. The supercell contains an MoS2 bottom layer and a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS2 flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS2 films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.

  8. Energy gap of a molecularly doped polymer measured by a new method of electron spectroscopy: Measurement of charge transfer force

    Microsoft Academic Search

    Chikara Manabe; Taishi Shigematsu; Hiroyuki Watanabe; Masaaki Shimizu

    2001-01-01

    We have proposed a new method of electron spectroscopy which is measuring charge transfer (CT) force by atomic force microscopy. We have applied this new method to a typical molecularly doped polymer system [N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4' diamine (TPD) and polycarbonate] to elucidate the electronic structure of the system. CT force spectra obtained show that the energy gap (Eg) continuously decreases with increasing

  9. Measurement of energy gaps of integer and fractional quantum Hall states in suspended bilayer graphene devices

    NASA Astrophysics Data System (ADS)

    Shi, Yanmeng; Lee, Yongjin; Che, Shi; Pi, Ziqi; Espiritu, Tim; Myhro, Kevin; Stepanov, Petr; Gillgreen, Nathanial; Smirnov, Dmitry; Lau, Chun Ning

    2015-03-01

    Single- and few-layer graphene have emerged as interesting 2D systems for the investigation of novel integer and quantum Hall states. Recently clear fractional quantum Hall states in bi-layer graphene have been observed, though studies of the magnitudes of the gaps and their dependence on electric field are very limited. Here, using dual-gated suspended bilayer graphene device, we measure the Landau level gaps for the nu =1 and nu =2/3 states, and explore their dependence on electric field.

  10. Dependence of global superconductivity on inter-island coupling in arrays of long SNS junctions.

    PubMed

    Eley, Serena; Gopalakrishnan, Sarang; Goldbart, Paul M; Mason, Nadya

    2013-11-01

    We present measurements of the superconducting transition temperature, Tc, for arrays of mesoscopic Nb islands patterned on Au films, for large island spacings d. We show that Tc ? 1/d(2), and explain this dependence in terms of the quasiclassical prediction that the Thouless energy, rather than the superconducting gap, governs the inter-island coupling at large spacings. We also find that the temperature dependence of the critical current, Ic(T), in our arrays is similar to that of single SNS junctions. However, our results deviate from the quasiclassical theory in that Tc is sensitive to island height, because the islands are mesoscopic. PMID:24113354

  11. Direct band gap measurement of Cu(In,Ga)(Se,S)2 thin films using high-resolution reflection electron energy loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Heo, Sung; Lee, Hyung-Ik; Song, Taewon; Park, Jong-Bong; Ko, Dong-Su; Chung, JaeGwan; Kim, KiHong; Kim, Seong Heon; Yun, Dong-Jin; Ham, YongNam; Park, Gyeong Su; Lee, Dongho; Nam, Junggyu; Kang, Hee Jae; Choi, Pyung-Ho; Choi, Byoung-Deog

    2015-06-01

    To investigate the band gap profile of Cu(In1-x,Gax)(Se1-ySy)2 of various compositions, we measured the band gap profile directly as a function of in-depth using high-resolution reflection energy loss spectroscopy (HR-REELS), which was compared with the band gap profile calculated based on the auger depth profile. The band gap profile is a double-graded band gap as a function of in-depth. The calculated band gap obtained from the auger depth profile seems to be larger than that by HR-REELS. Calculated band gaps are to measure the average band gap of the spatially different varying compositions with respect to considering its void fraction. But, the results obtained using HR-REELS are to be affected by the low band gap (i.e., out of void) rather than large one (i.e., near void). Our findings suggest an analytical method to directly determine the band gap profile as function of in-depth.

  12. Conductance Measurements of Magnesium Diboride-based Josephson Junctions Below 1 Kelvin: Beyond the 2-Gap Model

    NASA Astrophysics Data System (ADS)

    Carabello, Steven; Lambert, Joseph; Mlack, Jerome; Dai, Wenqing; Li, Qi; Chen, Ke; Cunnane, Daniel; Zhuang, C. G.; Xi, X. X.; Ramos, Roberto

    2014-03-01

    Theoretical and experimental studies have probed the nature of magnesium diboride's two superconducting energy gaps ?? and ??. Several theoretical analyses have predicted fine structures within each energy gap, with recent experiments revealing similar structures. We have performed high-resolution tunneling measurements of low-transparency Josephson junctions using ``terraced,'' ``columnar,'' and c-axis MgB2 films separated by its native oxide from either lead (Pb) or tin (Sn) counter-electrodes. Using high-resolution I-V data at T as low as 23mK, we observe sub-structures within both energy gaps. We also observe sharp peaks in the subgap that identify, to high precision, the energy gap values of the junction counter-electrodes (Pb and Sn). These lead us to conclude that the substructures seen in the gaps are due to MgB2. We then fit the data using simplified two-gap and four-gap models with variable weights and broadening factors. By demonstrating the inadequacy of a simple two-gap model in fitting the data, we illustrate that some distinctions between theoretical models of energy gap substructures are experimentally observable. R.C.R. acknowledges partial support from National Science Foundation Grant # DMR-1206561.

  13. BSCCO superconductors : hole-like fermi surface and doping dependence of the gap function.

    SciTech Connect

    Campuzano, J. C.; Ding, H.; Fretwell, H. M.; Kadowaki, K.; Kaminski, A.; Mesot, J.; Mochiku, T.; Norman, M. R.; Paramekanti, A.; Randeria, M.; Sato, T.; Takahashi, T.; Takeuchi, T.; Yokoya, T.

    1999-08-18

    We use the gradient of the energy-integrated angle resolved photoemission (ARPES) intensity in order to define precisely the Fermi surface (FS) in BSCCO superconductors. We show that, independent of the photon energy, the FS is a hole barrel centered at ({pi},{pi}), Then, the superconducting gap along the FS is precisely determined from ARPES measurements on over-doped and underdoped samples of Bi2212. As the doping decreases, the maximum gap increases, but the slope of the gap near the nodes decreases. Though consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple cos(k{sub x})-cos(k{sub y}) form. A comparison of our ARPES results with available penetration depth data indicates that the renormalization of the linear T suppression of the superfluid density at low temperatures due to quasiparticle excitations around the d-wave nodes is large and doping dependent.

  14. Superconducting thermoelectric generator

    DOEpatents

    Metzger, J.D.; El-Genk, M.S.

    1996-01-01

    An apparatus and method for producing electricity from heat. The present invention is a thermoelectric generator that uses materials with substantially no electrical resistance, often called superconductors, to efficiently convert heat into electrical energy without resistive losses. Preferably, an array of superconducting elements is encased within a second material with a high thermal conductivity. The second material is preferably a semiconductor. Alternatively, the superconducting material can be doped on a base semiconducting material, or the superconducting material and the semiconducting material can exist as alternating, interleaved layers of waferlike materials. A temperature gradient imposed across the boundary of the two materials establishes an electrical potential related to the magnitude of the temperature gradient. The superconducting material carries the resulting electrical current at zero resistivity, thereby eliminating resistive losses. The elimination of resistive losses significantly increases the conversion efficiency of the thermoelectric device.

  15. Superconducting Cable

    DOEpatents

    Hughey, Raburn L. (Franklin, GA); Sinha, Uday K. (Carrollton, GA); Reece, David S. (Carrollton, GA); Muller, Albert C. (Eidson, TN)

    2005-07-22

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  16. Superconducting Cable

    DOEpatents

    Hughey, Raburn L. (Franklin, GA); Sinha, Uday K. (Carrollton, GA); Reece, David S. (Carrollton, GA); Muller, Albert C. (Eidson, TN)

    2005-03-08

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  17. Executive summary of NIH workshop on the Use and Biology of Energy Drinks: Current Knowledge and Critical Gaps.

    PubMed

    Sorkin, Barbara C; Camp, Kathryn M; Haggans, Carol J; Deuster, Patricia A; Haverkos, Lynne; Maruvada, Padma; Witt, Ellen; Coates, Paul M

    2014-10-01

    Sales of energy drinks in the United States reached $12.5 billion in 2012. Emergency department visits related to consumption of these products have increased sharply, and while these numbers remain small relative to product sales, they raise important questions regarding biological and behavioral effects. Although some common ingredients of energy drinks have been extensively studied (e.g., caffeine, B vitamins, sugars, inositol), data on other ingredients (e.g., taurine) are limited. Summarized here are data presented elsewhere in this issue on the prevalence and patterns of caffeine-containing energy drink use, the effects of these products on alertness, fatigue, cognitive functions, sleep, mood, homeostasis, as well as on exercise physiology and metabolism, and the biological mechanisms mediating the observed effects. There are substantial data on the effects of some energy drink ingredients, such as caffeine and sugars, on many of these outcomes; however, even for these ingredients many controversies and gaps remain, and data on other ingredients in caffeine-containing energy drinks, and on ingredient interactions, are sparse. This summary concludes with a discussion of critical gaps in the data and potential next steps. PMID:25293538

  18. Perturbation theory of a superconducting 0 - ? impurity quantum phase transition

    NASA Astrophysics Data System (ADS)

    Žonda, M.; Pokorný, V.; Janiš, V.; Novotný, T.

    2015-03-01

    A single-level quantum dot with Coulomb repulsion attached to two superconducting leads is studied via the perturbation expansion in the interaction strength. We use the Nambu formalism and the standard many-body diagrammatic representation of the impurity Green functions to formulate the Matsubara self-consistent perturbation expansion. We show that at zero temperature second order of the expansion in its spin-symmetric version yields a nearly perfect agreement with the numerically exact calculations for the position of the 0 - ? phase boundary at which the Andreev bound states reach the Fermi energy as well as for the values of single-particle quantities in the 0-phase. We present results for phase diagrams, level occupation, induced local superconducting gap, Josephson current, and energy of the Andreev bound states with the precision surpassing any (semi)analytical approaches employed thus far.

  19. Electronic Characterization of Defects in Narrow Gap Semiconductors-Comparison of Electronic Energy Levels and Formation Energies in Mercury Cadmium Telluride, Mercury Zinc Telluride, and Mercury Zinc Selenide

    NASA Technical Reports Server (NTRS)

    Patterson, James D.

    1996-01-01

    We have used a Green's function technique to calculate the energy levels and formation energy of deep defects in the narrow gap semiconductors mercury cadmium telluride (MCT), mercury zinc telluride (MZT) and mercury zinc selenide (MZS). The formation energy is calculated from the difference between the total energy with an impurity cluster and the total energy for the perfect crystal. Substitutional (including antisite), interstitial (self and foreign), and vacancy deep defects are considered. Relaxation effects are calculated (with molecular dynamics). By use of a pseudopotential, we generalize the ideal vacancy model so as to be able to consider relaxation for vacancies. Different charge states are considered and the charged state energy shift (as computed by a modified Haldane-Anderson model) can be twice that due to relaxation. Different charged states for vacancies were not calculated to have much effect on the formation energy. For all cases we find deep defects in the energy gap only for cation site s-like orbitals or anion site p-like orbitals, and for the substitutional case only the latter are appreciably effected by relaxation. For most cases for MCT, MZT, MZS, we consider x (the concentration of Cd or Zn) in the range appropriate for a band gap of 0.1 eV. For defect energy levels, the absolute accuracy of our results is limited, but the precision is good, and hence chemical trends are accurately predicted. For the same reason, defect formation energies are more accurately predicted than energy level position. We attempt, in Appendix B, to calculate vacancy formation energies using relatively simple chemical bonding ideas due to Harrison. However, these results are only marginally accurate for estimating vacancy binding energies. Appendix C lists all written reports and publications produced for the grant. We include abstracts and a complete paper that summarizes our work which is not yet available.

  20. Design of high-energy high-current linac with focusing by superconducting solenoids

    Microsoft Academic Search

    Guennady I. Batskikh; Vladimir M. Belugin; Boris I. Bondarev; Arkady P. Fedotov; Alexander P. Durkin; Yury D. Ivanov; Vladimir N. Mikhailov; Boris P. Murin; Kharis Kh. Mustafin; Igor V. Shumakov; Nikolay I. Uksusov

    1995-01-01

    The advancement of MRTI design for 1.5 GeV and 250 mA ion CW linac is presented in the report. In new linac version all the way from input to output the ions are focused by magnetic fields of superconducting solenoids. The ion limit current is far beyond the needed value. The linac focusing channel offers major advantages over the more

  1. Singlet-Triplet Energy Gaps for Diradicals from Fractional-Spin Density-Functional Theory

    SciTech Connect

    Ess, Daniel H.; Johnson, E R; Hu, Xiangqian; Yang, W T

    2011-01-01

    Open-shell singlet diradicals are difficult to model accurately within conventional Kohn?Sham (KS) density-functional theory (DFT). These methods are hampered by spin contamination because the KS determinant wave function is neither a pure spin state nor an eigenfunction of the S2 operator. Here we present a theoretical foray for using single-reference closed-shell ground states to describe diradicals by fractional-spin DFT (FS-DFT). This approach allows direct, self-consistent calculation of electronic properties using the electron density corresponding to the proper spin eigenfunction. The resulting FS-DFT approach is benchmarked against diradical singlet?triplet gaps for atoms and small molecules. We have also applied FS-DFT to the singlet?triplet gaps of hydrocarbon polyacenes.

  2. Potential for precision measurement of low-energy antiprotons with GAPS for dark matter and primordial black hole physics

    NASA Astrophysics Data System (ADS)

    Aramaki, T.; Boggs, S. E.; von Doetinchem, P.; Fuke, H.; Hailey, C. J.; Mognet, S. A. I.; Ong, R. A.; Perez, K.; Zweerink, J.

    2014-07-01

    The general antiparticle spectrometer (GAPS) experiment is a proposed indirect dark matter search focusing on antiparticles produced by WIMP (weakly interacting massive particle) annihilation and decay in the Galactic halo. In addition to the very powerful search channel provided by antideuterons (Donato et al., 2000, 2008) [1,2], (Vittino et al.) [3], (Fornengo, 2013) [4], GAPS has a strong capability to measure low-energy antiprotons (0.07?E?0.25 GeV) as dark matter signatures. This is an especially effective means for probing light dark matter, whose existence has been hinted at in the direct dark matter searches, including the recent result from the CDMS-II experiment (Agnese, 2013) [5]. While severely constrained by LUX and other direct dark matter searches (Akerib et al.) [6], light dark matter candidates are still viable in an isospin-violating dark matter scenario and halo-independent analysis (Del Nobile et al.) [7,8]. Along with the excellent antideuteron sensitivity, GAPS will be able to detect an order of magnitude more low-energy antiprotons, compared to BESS (Abe et al., 2012) [9], (Orito et al., 2000) [10], PAMELA (Adriani et al., 2010) [11] and AMS-02 (Casaus, 2009) [12], providing a precision measurement of low-energy antiproton flux and a unique channel for probing light dark matter models. Additionally, dark matter signatures from gravitinos and Kaluza-Klein right-handed neutrinos as well as evidence of primordial black hole evaporation can be observed through low-energy antiproton search.

  3. Coexistence of the spini-density-wave and superconductivity in the Ba1-xKxFe2As2

    SciTech Connect

    Bao, Wei [Los Alamos National Laboratory; Chen, H [HEFEI NAT. LAB; Ren, Y [ANL; Qiu, Y [NIST CENTER FOR NEUTRON; Liu, R [HEFEI NAT. LAB.; Wu, G H [HEFEI NAT. LAB; Wu, T [HEFEI NAT. LAB.; Xie, Y L [HEFEI NAT. LAB; Wang, F [HEFEI NAT. LAB.; Huang, Q [NIST CENTER FOR NEUTRON; Chen, X H [HEFEI NAT. LAB

    2008-01-01

    The relation between the spin-density-wave (SDW) and superconducting order is a central topic in current research on the FeAs-based high T{sub c} superconductors. Conflicting results exist in the LaFeAs(O,F)-class of materials, for which whether the SDW and superconductivity are mutually exclusive or they can coexist has not been settled. Here we show that for the (Ba,K)Fe{sub 2}As{sub 2} system, the SDW and superconductivity can coexist in an extended range of compositions. The availability of single crystalline samples and high value of the energy gaps would make the materials a model system to investigate the high T{sub c} ferropnictide superconductivity.

  4. Superconducting bearings in flywheels

    Microsoft Academic Search

    T. A. Coombs; A. M. Campbell; I. Ganney; W. Lo; T. Twardowski; B. Dawson

    1998-01-01

    Investigations are being carried out into the use of superconducting magnetic bearings to levitate Energy storage flywheels. In a planned program of work, Cambridge University are aiming to produce a practical bearing system for Pirouette™. The Pirouette™ system is designed to provide 5 kWh of recoverable energy which is currently recoverable at a rate of 5 kW (future revisions will

  5. Crossover from a pseudogap state to a superconducting state

    E-print Network

    Tian De Cao

    2011-02-10

    On the basis of our calculation we deduce that the particular electronic structure of cuprate superconductors confines Cooper pairs to be firstly formed in the antinodal region which is far from the Fermi surface, and these pairs are incoherent and result in the pseudogap state. With the change of doping or temperature, some pairs are formed in the nodal region which locates the Fermi surface, and these pairs are coherent and lead to superconductivity. Thus the coexistence of the pseudogap and the superconducting gap is explained when the two kinds of gaps are not all on the Fermi surface. It is also shown that the symmetry of the pseudogap and the superconducting gap are determined by the electronic structure, and non-s wave symmetry gap favors the high-temperature superconductivity. Why the high-temperature superconductivity occurs in the metal region near the Mott metal-insulator transition is also explained.

  6. Low-energy excitations of the correlation-gap insulator SmB{sub 6}: A light-scattering study

    SciTech Connect

    Nyhus, P.; Cooper, S.L. [Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana-Champaign, Urbana, Illinois 61801 (United States); Fisk, Z.; Sarrao, J. [Department of Physics and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306 (United States)] [Department of Physics and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306 (United States)

    1997-05-01

    We present the results of Raman scattering studies of single-crystal SmB{sub 6} for temperatures down to 4 K and in magnetic fields up to 8 T. At temperatures below T{sup {asterisk}}{approximately}50K the electronic Raman continuum exhibits an abrupt redistribution of scattering intensity around a temperature-independent ({open_quotes}isobestic{close_quotes}) energy, {Delta}{sub c}{approximately}290cm{sup {minus}1}, reflecting the opening of a pseudogap which is larger than previously suggested by transport measurements. Additionally, the Raman response exhibits at least four well-defined excitations within the gap below T{sup {asterisk}}. The field dependencies of some of these in-gap states are consistent with the expected g factor (g{sub eff}=2/7) for the Sm{sup 3+} {Gamma}{sub 8} level, suggesting that these gap edge states are crystal-electric-field excitations of the Sm{sup 3+} ion split by magnetoelastic coupling. {copyright} {ital 1997} {ital The American Physical Society}

  7. Restoration of the Derivative Discontinuity in Kohn-Sham Density Functional Theory: An Efficient Scheme for Energy Gap Correction

    E-print Network

    Jeng-Da Chai; Po-Ta Chen

    2012-12-20

    From the perspective of perturbation theory, we propose a systematic procedure for the evaluation of the derivative discontinuity (DD) of the exchange-correlation energy functional in Kohn-Sham density functional theory (KS-DFT), wherein the exact DD can in principle be obtained by summing up all the perturbation corrections to infinite order. Truncation of the perturbation series at low order yields an efficient scheme for obtaining the approximate DD. While the zeroth-order theory yields a vanishing DD, the first-order correction to the DD can be expressed as an explicit universal functional of the ground-state density and the KS lowest unoccupied molecular orbital density, allowing the direct evaluation of the DD in the standard KS method without extra computational cost. The fundamental gap can be predicted by adding the estimated DD to the KS gap. This scheme is shown to be accurate in the prediction of the fundamental gaps for a wide variety of atoms and molecules.

  8. The Cost of Superconducting Magnets as a Function of Stored Energy and Design Magnetic Induction Times the Field Volume

    SciTech Connect

    Green, Mike; Green, M.A.; Strauss, B.P.

    2007-08-27

    By various theorems one can relate the capital cost of superconducting magnets to the magnetic energy stored within that magnet. This is particularly true for magnet where the cost is dominated by the structure needed to carry the magnetic forces. One can also relate the cost of the magnet to the product of the magnetic induction and the field volume. The relationship used to estimate the cost the magnet is a function of the type of magnet it is. This paper updates the cost functions given in two papers that were published in the early 1990 s. The costs (escalated to 2007 dollars) of large numbers of LTS magnets are plotted against stored energy and magnetic field time field volume. Escalated costs for magnets built since the early 1990 s are added to the plots.

  9. Mechanical Design of a High Energy Beam Absorber for the Advanced Superconducting Test Accelerator (ASTA) at Fermilab

    SciTech Connect

    Baffes, C.; Church, M.; Leibfritz, J.; Oplt, S.; Rakhno, I.; /Fermilab

    2012-05-10

    A high energy beam absorber has been built for the Advanced Superconducting Test Accelerator (ASTA) at Fermilab. In the facility's initial configuration, an electron beam will be accelerated through 3 TTF-type or ILC-type SRF cryomodules to an energy of 750MeV. The electron beam will be directed to one of multiple downstream experimental and diagnostic beam lines and then deposited in one of two beam absorbers. The facility is designed to accommodate up to 6 cryomodules, which would produce a 75kW beam at 1.5GeV; this is the driving design condition for the beam absorbers. The beam absorbers consist of water-cooled graphite, aluminum and copper layers contained in a helium-filled enclosure. This paper describes the mechanical implementation of the beam absorbers, with a focus on thermal design and analysis. The potential for radiation-induced degradation of the graphite is discussed.

  10. Interface superconductivity

    NASA Astrophysics Data System (ADS)

    Gariglio, S.; Gabay, M.; Mannhart, J.; Triscone, J.-M.

    2015-07-01

    Low dimensional superconducting systems have been the subject of numerous studies for many years. In this article, we focus our attention on interfacial superconductivity, a field that has been boosted by the discovery of superconductivity at the interface between the two band insulators LaAlO3 and SrTiO3. We explore the properties of this amazing system that allows the electric field control and on/off switching of superconductivity. We discuss the similarities and differences between bulk doped SrTiO3 and the interface system and the possible role of the interfacially induced Rashba type spin-orbit. We also, more briefly, discuss interface superconductivity in cuprates, in electrical double layer transistor field effect experiments, and the recent observation of a high Tc in a monolayer of FeSe deposited on SrTiO3.

  11. Gap and sub-gap structures of intrinsic Josephson tunnel junctions in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} single crystals

    SciTech Connect

    Yurgens, A.; Winkler, D.; Zavaritsky, N.; Claeson, T. [Chalmers Univ. of Technology, Goeteborg (Sweden); [P.L. Kapitza Inst., Moscow (Russian Federation)

    1996-12-31

    Stacked series arrays of intrinsic Josephson (IJ) tunnel junctions fabricated on the surfaces of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} (BI2212) single crystals by photolithography have been studied. Advanced technology with in-situ control of stack heights allows one to make a specified number (3--200) of junctions in the stack. The quasi-particle branch of an individual IJ junction has a well-developed gap structure. The gap value is {approximately} 12--13 meV at low temperature, which is approximately two times smaller than reported elsewhere. The temperature dependence of the gap deviates strongly from the BCS one. Proximity induced superconductivity of the Bi-O layers is one probable explanation for the reduced gap observed in the experiments. True superconducting contact obtained between the outermost Bi-O layer of a freshly cleaved Bi2212 single crystal and a Pb thin film is a supporting evidence for the Bi-O layers being superconducting. Multiple peaks are seen in the first derivative of the current-voltage characteristics at sub-gap voltages for all samples studied. The peak positions in voltage do not change with temperature and do not depend on the dimensions of the stack. Dynamic modulation of the tunnel density of states by low energy optical phonons and/or resonant tunneling through localized electronic states of the Bi-O and Sr-O layers are possible reasons for these observations.

  12. Superconducting terahertz metamaterials

    SciTech Connect

    Chen, Hou-tong [Los Alamos National Laboratory; Singh, Ranjan [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Azad, Abul K [Los Alamos National Laboratory; Trugman, Stuart A [Los Alamos National Laboratory; Jia, Quanxi [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory

    2010-01-01

    During the past ten years subwavelength metallic structures have enabled metamaterials exhibiting exotic physical properties that are not possible or difficult to realize using naturally occurring materials, This bottom-up metamaterial approach is particularly attractive in the terahertz (THz) frequency range, where the THz gap is inherently associated with the lack of materials with appropriate reponse. In fact THz metamaterial devices have accomplished unprecedented performance towards practical applications. In these devices, the key is to incorporate natural materials, e,g, semiconductors, as the metamaterial substrates or integration parts of metamaterial structures. The active or dynamic tunability of metamaterials is through the application of external stimuli such as temperature, photoexcitation, or electric field. to modify the capacitive gaps in split-ring resonators (SRRs), It becomes clear that we would not be able to do much on the metallic SRRs, i.e. the metal conductivity and therefore the inductance largely remain constant not affected by external stimuli. Recently, there has been increasing interest in superconducting metamaterials towards loss reduction. Significant Joule losses have often prevented resonant metal metamaterials from achieving proposed applications. particularly in the optical frequency range. At low temperatures, superconducting materials possess superior conductivity than metals at frequencies up to THz. and therefore it is expected that superconducting melamaterials will have a lower loss than metal metamatetials, More interestingly, superconductors exhibit tunable complex conductivity over a wide range of values through change of temperature and application of photoexcitation, electrical currents and magnetic fields. Therefore, we would expect correspondingly tunable metamaterials. which originate from the superconducting materials composing the metamaterial, in contrast to tuning the metamaterial embedded environment.

  13. Two-dimensional p-wave superconducting states with magnetic moments on a conventional s-wave superconductor

    NASA Astrophysics Data System (ADS)

    Nakosai, Sho; Tanaka, Yukio; Nagaosa, Naoto

    2013-11-01

    Unconventional superconductivity induced by the magnetic moments in a conventional spin-singlet s-wave superconductor is theoretically studied. By choosing the spin directions of these moments, one can design spinless pairing states appearing within the s-wave superconducting energy gap. It is found that the helix spins produce a px+py-wave state while the skyrmion crystal configuration a px+ipy-wave-like state. Nodes in the energy gap and the zero-energy flat band of Majorana edge states exist in the former case, while the chiral Majorana channels along edges of the sample and the zero-energy Majorana bound state at the core of the vortex appear in the latter case.

  14. Far-infrared optical absorption and reflectivity of a superconducting NbN film

    Microsoft Academic Search

    K. E. Kornelsen; M. Dressel; J. E. Eldridge; M. J. Brett; K. L. Westra

    1991-01-01

    We report measurements of bolometric absorption and absolute reflectivity of a thin film of NbN on a silicon substrate, above and below the superconducting transition temperature of 13.3 K. The opening of the gap at an energy of 3.9 kBTc is seen clearly in both types of measurement. The data are compared with the predictions of the Mattis-Bardeen theory. The

  15. Strained graphene Josephson junction with anisotropic d-wave superconductivity

    NASA Astrophysics Data System (ADS)

    Goudarzi, H.; Khezerlou, M.; Kamalipour, H.

    2015-07-01

    Effect of proximity-induced superconductivity in the new two-dimensional structures, as graphene and topological insulator on the Andreev bound states (ABSs) and Josephson supercurrent has attracted much efforts. Motivated by this subject, we study, in particular, the influence of anisotropic Fermi velocity and unconventional d-wave pairing in a strained graphene-based superconductor/normal/ superconductor junction. Strain is applied in the zigzag direction of graphene sheet. In this process, effect of zero energy states and Fermi wavevector mismatch are investigated. It is shown, that strain up to 22% in graphene lattice differently affects Josephson currents in parallel and perpendicular directions of strain. Strain causes to exponentially decrease the supercurrent in the strain direction, whereas increase for other direction. We find that, in one hand, the ABSs strongly depend on strain and, on the other hand, a gap opens in the states with respect to non-zero incidence angle of quasiparticles, where a period of 2 ? is obtained for Andreev states. Moreover, we observe no gap for ?s ? 0 , when the zero energy states (ZESs) occur in ? = ? / 4 due to anisotropic superconducting gap. In this case, ABSs have a period of 4 ? .S

  16. Sensitivity of a 3D fully-gapped topological superconductor to non-magnetic impurities

    NASA Astrophysics Data System (ADS)

    Ota, Yukihiro; Nagai, Yuki; Machida, Masahiko

    2015-03-01

    Topological superconductors (TSC) are notable materials, owing to the mathematical curiosity and the application potential. The bulk TSC can emerge by copper intercalation into topological insulator Bi2Se3. In this paper, we theoretically study the non-magnetic impurity effects in the mean-field model of CuxBi2Se3, focusing on the odd-parity fully-gapped superconducting state. Calculating the density of states with a self-consistent T-matrix approach, we test the presence of mid-gap states, leading to pair-breaking effects. Remarkably, the sensitivity to non-magnetic impurities strongly depend on a normal-state dispersion character, i.e., either non-relativistic or relativistic dispersion relations. We show unification picture for understanding this intriguing result, deriving a low-energy effective superconducting theory.

  17. Superconducting accelerating structures for very low velocity ion beams

    NASA Astrophysics Data System (ADS)

    Xu, J.; Shepard, K. W.; Ostroumov, P. N.; Fuerst, J. D.; Waldschmidt, G.; Gonin, I. V.

    2008-03-01

    This paper presents designs for four types of very-low-velocity superconducting (SC) accelerating cavity capable of providing several MV of accelerating potential per cavity, and suitable for particle velocities in the range 0.006Superconducting TEM-class cavities have been widely applied to cw acceleration of ion beams. SC linacs can be formed as an array of independently phased cavities, enabling a variable velocity profile to maximize the output energy for each of a number of different ion species. Several laboratories in the U.S. and Europe are planning exotic beam facilities based on SC linacs. The cavity designs presented here are intended for the front end of such linacs, particularly for the postacceleration of rare isotopes of low charge state. Several types of SC cavities have been developed recently to cover particle velocities above 0.06c. Superconducting four-gap quarter-wave resonators for velocities 0.008gap quarter-wave resonator for exotic beam facilities and other low-velocity applications.

  18. Energy band gaps and lattice parameters evaluated with the Heyd-Scuseria-Ernzerhof screened hybrid functional.

    PubMed

    Heyd, Jochen; Peralta, Juan E; Scuseria, Gustavo E; Martin, Richard L

    2005-11-01

    This work assesses the Heyd-Scuseria-Ernzerhof (HSE) screened Coulomb hybrid density functional for the prediction of lattice constants and band gaps using a set of 40 simple and binary semiconductors. An extensive analysis of both basis set and relativistic effects is given. Results are compared with established pure density functionals. For lattice constants, HSE outperforms local spin-density approximation (LSDA) with a mean absolute error (MAE) of 0.037 A for HSE vs 0.047 A for LSDA. For this specific test set, all pure functionals tested produce MAEs for band gaps of 1.0-1.3 eV, consistent with the very well-known fact that pure functionals severely underestimate this property. On the other hand, HSE yields a MAE smaller than 0.3 eV. Importantly, HSE correctly predicts semiconducting behavior in systems where pure functionals erroneously predict a metal, such as, for instance, Ge. The short-range nature of the exchange integrals involved in HSE calculations makes their computation notably faster than regular hybrid functionals. The current results, paired with earlier work, suggest that HSE is a fast and accurate alternative to established density functionals, especially for solid state calculations. PMID:16375511

  19. Superconducting septum magnet design for Jefferson Lab Hall A

    SciTech Connect

    Brindza, Paul; Gavalya, Alan; Lassiter, Steven; LeRose, John; Cisbani, Evaristo; Frullani, Salvatore; Garibaldi, Franco; Iodice, Mauro; Urciuoli, Guido; Nilles, Michael

    2001-03-01

    A pair of superconducting septum magnets are required to permit hypernuclear physics experiments at JLAB's Hall A at angles to the incident beam as small as 6 degrees. A cold iron superconducting zCz magnet design has been selected. This magnet has a central field of 4.23 Tesla at a current density of 25,000 Amp/cm2, the stored energy is 0.22 Megajoules and the inductance is 1.0 Henries. The magnet has an effective field length of 0.67 meters, an average gap of 0.25 meters and an average pole width of 0.15 meters. The magnet is currently being fabricated by BWXT Inc. under contract to INFN

  20. The effects of potting on training and quench propagation in a large stored energy superconducting dipole coil

    NASA Astrophysics Data System (ADS)

    Cox, B.; Garbincius, P. H.; Guerra, J.; Mazur, P. O.; Satti, J. A.; Tilles, E. B.

    1981-01-01

    The training and quench behavior of a superconducting racetrack dipole coil were compared in potted and non-potted coils. The coil stored energy was 175 KJoules at the conductor's short sample limit of 238 amp with a peak field of 7.6 Tesla. Steel and aluminum rods were tested with helium flow provided by fiberglass cable tape channels permitting direct access to the He supply to 1/4 of the conductor surface. The coil was trained to 90% of the short sample limit, the tie rods were relaxed, and the whole coil was impregnated with a standard clear magnet epoxy. The tests showed that fully impregnated coils of this design are not suitable for thermally cycled magnets operating above 80% of the short sample limit.

  1. Ultrasonic attenuation in superconducting molybdenum-rhenium alloys.

    NASA Technical Reports Server (NTRS)

    Ashkin, M.; Deis, D. W.; Gottlieb, M.; Jones, C. K.

    1971-01-01

    Investigation of longitudinal sound attenuation in superconducting Mo-Re alloys as a function of temperature, magnetic field, and frequency. Evaporated thin film CdS transducers were used for the measurements at frequencies up to 3 GHz. The normal state attenuation coefficient was found to be proportional to the square of frequency over this frequency range. Measurements in zero magnetic field yielded a value of the energy gap parameter close to the threshold value of 3.56 kTc, appropriate to a weakly coupled dirty limit superconductor.

  2. Kinetics of thermal-assisted delayed fluorescence in blue organic emitters with large singlet-triplet energy gap.

    PubMed

    Dias, Fernando B

    2015-06-28

    The kinetics of thermally activated delayed fluorescence (TADF) is investigated in dilute solutions of organic materials with application in blue light-emitting diodes (OLEDs). A method to accurately determine the energy barrier (?Ea) and the rate of reverse intersystem crossing (kRisc) in TADF emitters is developed, and applied to investigate the triplet-harvesting mechanism in blue-emitting materials with large singlet-triplet energy gap (?EST). In these materials, triplet-triplet annihilation (TTA) is the dominant mechanism for triplet harvesting; however, above a threshold temperature TADF is able to compete with TTA and give enhanced delayed fluorescence. Evidence is obtained for the interplay between the TTA and the TADF mechanisms in these materials. PMID:25987577

  3. Controlling superconductivity

    NASA Astrophysics Data System (ADS)

    2011-08-01

    The use of intense ultrafast terahertz pulses to gate superconductivity not only provides insights into charge transport in such materials but may also lead to new forms of data switching, explains Andrea Cavalleri.

  4. Superconducting Memristors

    NASA Astrophysics Data System (ADS)

    di Ventra, Massimiliano; Peotta, Sebastiano

    2014-03-01

    In his original work Josephson [Phys. Lett. 1, 251 (1962)] predicted that a phase-dependent conductance should be present in superconductor tunnel junctions. This effect attracted considerable attention in the past but is difficult to detect, mainly because it is hard to single it out from the background pair current. Here, we propose to isolate it by using a two-junction interferometer where the junctions have the same critical currents but different conductances. The pair current is completely suppressed when the magnetic flux in the loop is half of a flux quantum and the device is characterized by a pure phase-dependent conductance. According to the theory of nonlinear circuit elements this is in fact an ideal voltage-controlled memristor. Possible applications of this memristive device are memories and neuromorphic computing within the framework of ultrafast and low-energy superconducting digital circuits. This work has been supported by DOE under Grant No. DE-FG02-05ER46204.

  5. APS/123-QED Evidence for nodeless energy gaps in hole-doped Ba0.68K0.32Fe2As2

    E-print Network

    Hu, Jiangping

    , 17]. It has been shown that the s± -wave or a multiple-gap d-wave model can fit quite well the spinREV IEW CO PY N O T FO R D ISTRIBU TIO N APS/123-QED Evidence for nodeless energy gaps in hole.5 K). The spin-lattice relaxation rate 1/T1 shows an exponential decrease below T 0.45Tc down to T 0

  6. Gap Winds

    NSDL National Science Digital Library

    2014-09-14

    This module provides a basic understanding of why gap winds occur, their typical structures, and how gap wind strength and extent are controlled by larger-scale, or synoptic, conditions. You will learn about a number of important gap flows in coastal regions around the world, with special attention given to comprehensively documented gap wind cases in the Strait of Juan de Fuca and the Columbia River Gorge. Basic techniques for evaluating and predicting gap flows are presented. The module reviews the capabilities and limitations of the current generation of mesoscale models in producing realistic gap winds. By the end of this module, you should have sufficient background to diagnose and forecast gap flows around the world, and to use this knowledge to understand their implications for operational decisions. Other features in this module include a concise summary for quick reference and a final exam to test your knowledge. Like other modules in the Mesoscale Meteorology Primer, this module comes with audio narration, rich graphics, and a companion print version.

  7. Gap Junctions

    PubMed Central

    Nielsen, Morten Schak; Axelsen, Lene Nygaard; Sorgen, Paul L.; Verma, Vandana; Delmar, Mario; Holstein-Rathlou, Niels-Henrik

    2013-01-01

    Gap junctions are essential to the function of multicellular animals, which require a high degree of coordination between cells. In vertebrates, gap junctions comprise connexins and currently 21 connexins are known in humans. The functions of gap junctions are highly diverse and include exchange of metabolites and electrical signals between cells, as well as functions, which are apparently unrelated to intercellular communication. Given the diversity of gap junction physiology, regulation of gap junction activity is complex. The structure of the various connexins is known to some extent; and structural rearrangements and intramolecular interactions are important for regulation of channel function. Intercellular coupling is further regulated by the number and activity of channels present in gap junctional plaques. The number of connexins in cell-cell channels is regulated by controlling transcription, translation, trafficking, and degradation; and all of these processes are under strict control. Once in the membrane, channel activity is determined by the conductive properties of the connexin involved, which can be regulated by voltage and chemical gating, as well as a large number of posttranslational modifications. The aim of the present article is to review our current knowledge on the structure, regulation, function, and pharmacology of gap junctions. This will be supported by examples of how different connexins and their regulation act in concert to achieve appropriate physiological control, and how disturbances of connexin function can lead to disease. © 2012 American Physiological Society. Compr Physiol 2:1981-2035, 2012. PMID:23723031

  8. Electron Pairing Without Superconductivity

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy; Cheng, G.; Tomczyk, M.; Lu, S.; Veazey, J. P.; Huang, M.; Irvin, P.; Ryu, S.; Lee, H.; Eom, C.-B.; Hellberg, C. S.

    2015-03-01

    Strontium titanate (SrTiO3) exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. We describe transport experiments with nanowire-based quantum dots localized at the interface between SrTiO3 and LaAlO3. Electrostatic gating of the quantum dot reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical magnetic field Bp 1-4 Tesla, an order of magnitude larger than the superconducting critical magnetic field. For B Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as T = 900 mK, far above the superconducting transition temperature (Tc 300 mK). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by an attractive-U Hubbard model that describes real-space electron pairing as a precursor to superconductivity. This work was supported by ARO MURI W911NF-08-1-0317 (J.L.), AFOSR MURI FA9550-10-1-0524 (C.-B.E., J.L.) and FA9550-12-1-0342 (C.-B.E.), and grants from the National Science Foundation DMR-1104191 (J.L.), DMR.

  9. Electronic characterization of defects in narrow gap semiconductors: Comparison of electronic energy levels and formation energies in mercury cadmium telluride, mercury zinc telluride, and mercury zinc selenide

    NASA Technical Reports Server (NTRS)

    Patterson, James D.; Li, Wei-Gang

    1995-01-01

    The project has evolved to that of using Green's functions to predict properties of deep defects in narrow gap materials. Deep defects are now defined as originating from short range potentials and are often located near the middle of the energy gap. They are important because they affect the lifetime of charge carriers and hence the switching time of transistors. We are now moving into the arena of predicting formation energies of deep defects. This will also allow us to make predictions about the relative concentrations of the defects that could be expected at a given temperature. The narrow gap materials mercury cadmium telluride (MCT), mercury zinc telluride (MZT), and mercury zinc selenide (MZS) are of interest to NASA because they have commercial value for infrared detecting materials, and because there is a good possibility that they can be grown better in a microgravity environment. The uniform growth of these crystals on earth is difficult because of convection (caused by solute depletion just ahead of the growing interface, and also due to thermal gradients). In general it is very difficult to grow crystals with both radial and axial homogeneity.

  10. Thermodynamic properties of superconducting nuclear matter

    Microsoft Academic Search

    M. F. Jiang; T. T. S. Kuo

    1988-01-01

    Phase diagrams of superconducting nuclear matter are calculated by solving a set of finite temperature gap equations, using several Skyrme effective interactions. Our results indicate that nuclear matter may have a superconducting phase in a small region with density near one half of the normal nuclear matter density and temperature kBT <~ 1.4 MeV. Our calculation is based on a

  11. Superconducting states of an extended Hubbard model

    SciTech Connect

    Coppersmith, S.N. (AT T Bell Laboratories, Murray Hill, NJ (USA))

    1990-08-01

    The variational Monte Carlo method is used to study possible superconducting states of a two-dimensional extended Hubbard model on a copper-oxygen lattice. It is found that {ital d}-wave and extended {ital s}-wave superconducting variational wave functions can have lower energy than the corresponding normal state for different parameter regions, while simple {ital s}-wave superconductivity is never favored. Increasing the nearest-neighbor repulsion and decreasing the copper-oxygen level separation can promote extended {ital s}-wave superconductivity and inhibit {ital d}-wave superconductivity.

  12. Effect of surface viscosity, anchoring energy, and cell gap on the response time of nematic liquid crystals

    SciTech Connect

    Souza, R.F. de [Departamento de Física, Universidade Estadual de Maringá, Avenida Colombo 5790, 87020 - 900 Maring᠖PR (Brazil); Yang, D.-Ke [Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH 44242 (United States); Lenzi, E.K.; Evangelista, L.R. [Departamento de Física, Universidade Estadual de Maringá, Avenida Colombo 5790, 87020 - 900 Maring᠖PR (Brazil); Zola, R.S., E-mail: rzola@utfpr.edu.br [Departamento de Física, Universidade Estadual de Maringá, Avenida Colombo 5790, 87020 - 900 Maring᠖PR (Brazil); Universidade Tecnologica Federal do Paraná, Rua Marcilio Dias 635, 86812-460 Apucarana, Paraná (Brazil)

    2014-07-15

    An analytical expression for the relaxation time of a nematic liquid crystal is obtained for the first time by considering the influence of surface viscosity, anchoring energy strength and cell gap, validated numerically by using the so-called relaxation method. This general equation for the molecular response time (?{sub 0}) was derived for a vertical aligned cell and by solving an eigenvalue equation coming from the usual balance of torque equation in the Derzhanskii and Petrov formulation, recovering the usual equations in the appropriate limit. The results show that ??d{sup b}, where b=2 is observed only for strongly anchored cells, while for moderate to weak anchored cells, the exponent lies between 1 and 2, depending on both, surface viscosity and anchoring strength. We found that the surface viscosity is important when calculating the response time, specially for thin cells, critical for liquid crystal devices. The surface viscosity’s effect on the optical response time with pretilt is also explored. Our results bring new insights about the role of surface viscosity and its effects in applied physics. - Highlights: • The relaxation of nematic liquid crystals is calculated by taking the surface viscosity into account. • An analytical expression for the relaxation time depending on surface viscosity, anchoring strength and cell gap is obtained. • The results are numerically verified. • Surface viscosity is crucial for thin and weak anchored cells. • The effect on optical time and pretilt angle is also studied.

  13. Pairing gaps and Fermi energies at scission for 296Lv alpha-decay

    E-print Network

    M. Mirea

    2014-11-12

    The pairing corrections, the single particle occupation numbers, are investigated within density-dependent delta interaction formalism for pairing residual interactions. The potential barrier is computed in the framework of the macroscopic-microscopic model. The microscopic part is based on the Woods-Saxon two center shell model. The alpha-decay of a superheavy element is treated, by paying a special attention to the region of the scission configurations. The sequence of nuclear shapes follows the superasymmetric fission path for alpha decay. It was found that the pairing gaps of the states that reach asymptotically the potential well of the alpha particle have large values at scission but become zero after scission. The 1s1/2 single particle levels of the nascent alpha particle are fully occupied while the superior levels are empties in the scission region and remains in the same states during the penetration of the Coulomb barrier. The projection of the numbers of particle on the two fragments are obtained naturally. At scission, the nascent alpha particle forms a very bound cluster.

  14. Building and Testing a Superconductivity Measurement Platform for a Helium Cryostat

    NASA Astrophysics Data System (ADS)

    Rose, Heath; Ostrander, Joshua; Wu, Jim; Ramos, Roberto

    2013-03-01

    Superconductivity experiments using Josephson junctions are an excellent environment to study quantum mechanics and materials science. A standard electrical transport technique uses filtered four wire measurement of these superconducting devices. We report our experience as undergraduates in a liberal arts college in building and testing an experimental platform anchored on the cold-finger of a helium cryostat and designed for performing differential conductance measurements in Josephson junctions. To filter out RF, we design, build and test cryogenic filters using ceramic capacitors and inductors and thermocoax cables. We also use fixed attenuators for thermal anchoring and use miniature connectors to connect wires and coax to a sample box. We report on progress in our diagnostic measurements as well as low-temperature tunneling experiments to probe the structure of the energy gap in both single- and multi-gapped superconductors. Superconductivity experiments using Josephson junctions are an excellent environment to study quantum mechanics and materials science. A standard electrical transport technique uses filtered four wire measurement of these superconducting devices. We report our experience as undergraduates in a liberal arts college in building and testing an experimental platform anchored on the cold-finger of a helium cryostat and designed for performing differential conductance measurements in Josephson junctions. To filter out RF, we design, build and test cryogenic filters using ceramic capacitors and inductors and thermocoax cables. We also use fixed attenuators for thermal anchoring and use miniature connectors to connect wires and coax to a sample box. We report on progress in our diagnostic measurements as well as low-temperature tunneling experiments to probe the structure of the energy gap in both single- and multi-gapped superconductors. We acknowledge the support of the National Science Foundation through NSF Grant DMR-1206561.

  15. Superconducting Storage Cavity for RHIC

    SciTech Connect

    Ben-Zvi,I.

    2009-01-02

    This document provides a top-level description of a superconducting cavity designed to store hadron beams in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. It refers to more detailed documents covering the various issues in designing, constructing and operating this cavity. The superconducting storage cavity is designed to operate at a harmonic of the bunch frequency of RHIC at a relatively low frequency of 56 MHz. The current storage cavities of RHIC operate at 197 MHz and are normal-conducting. The use of a superconducting cavity allows for a high gap voltage, over 2 MV. The combination of a high voltage and low frequency provides various advantages stemming from the resulting large longitudinal acceptance bucket.

  16. Superconductivity deep inside the hidden-order phase of URu2Si2: a phenomenological model

    NASA Astrophysics Data System (ADS)

    Kang, Jian; Fernandes, Rafael

    2015-03-01

    Recent magnetic torque and x-ray experiments have revealed that the tetragonal symmetry is broken in the hidden-order phase of URu2Si2. An important issue is how this symmetry breaking affects the superconducting state that develops deep inside the hidden-order state. Here we investigate this problem using a phenomenological model for both the ``nematic'' (i.e. tetragonal symmetry-broken) and superconducting phases. Based on recent field-angle-dependent heat capacity and thermal conductivity data, as well as Kerr effect measurements, we consider a chiral d + id superconducting state that also breaks time-reversal symmetry. We find that in the presence of an orthorhombic/nematic order parameter, the system displays two sequential superconducting transitions: in the first, at Tc, the system enters a superconducting phase whereas in the second, at T* gap amplitude fluctuations emerges, which could be manifested in Raman scattering data. Between these two transitions, we find an unusual ?log (?) dependence of the low-energy density of states, and show how it impacts the properties of several thermodynamic quantities in the T* < T Energy under Award Number DE-SC0012336.

  17. Development of large high current density superconducting solenoid magnets for use in high energy physics experiments. [Thesis

    Microsoft Academic Search

    1977-01-01

    The development of a unique type of large superconducting solenoid magnet, characterized by very high current density windings and a two-phase helium tubular cooling system is described. The development of the magnet's conceptual design and the construction of two test solenoids are described. The successful test of the superconducting coil and its tubular cooling refrigeration system is presented. The safety,

  18. On the critical temperature and the energy gap in dense SiH4(H2)2 at 250 GPa

    NASA Astrophysics Data System (ADS)

    Szcze&?acute; niak, R.; Durajski, A. P.

    2013-01-01

    The critical temperature (TC) and the energy gap (2?(T)) for the superconductor SiH4(H2)2 at 250 GPa have been calculated. The wide range of the Coulomb pseudopotential's values has been considered: ???<0.1,0.3>. It has been stated that TC decreases together with the increase of ?? from 129.83 K to 81.40 K. The low-temperature energy gap (T˜0 K) decreases together with the increase of the Coulomb pseudopotential from 50.96 meV to 30.12 meV. The high values of 2?(0) mean that the dimensionless ratio R??2?(0)/kBTC significantly exceeds the value predicted by the classical BCS theory. In the considered case: R??<4.55,4.29>. Due to the unusual dependence of the critical temperature and the energy gap on ??, the analytical expressions for TC(??) and ?(??) have been given.

  19. Quantum Tunneling and Heterodyne Detection in Superconducting Tunnel Junctions

    Microsoft Academic Search

    Nuray George Ugras

    1993-01-01

    The quasiparticle susceptance and conductance of a superconducting tunnel junction was measured including the singularity in the quasiparticle susceptance at the gap voltage. Results are compared to existing theories of superconductive tunneling, and the results agree well with theory. An analogy to a two-level atomic system is developed to explain the photon assisted tunneling process and its dependence on the

  20. Investigation of joint operation of a superconducting kinetic energy storage (flywheel) and solar cells

    Microsoft Academic Search

    I. Vajda; Z. Kohari; L. Benko; V. Meerovich; W. Gawalek

    2003-01-01

    Superconductors provide unique possibilities for storage of electricity, which is especially important for the reliability of networks supplied by renewable energy sources such as solar energy and wind energy. A system consisting of an HTS-based levitated flywheel as the energy storage unit and solar cells as the power supply was installed and investigated as a model of a viable variant

  1. Superconductive articles

    SciTech Connect

    Wu, X.D.; Muenchausen, R.E.

    1991-12-31

    An article of manufacture including a substrate, a patterned interlayer of magnesium oxide, barium-titanium oxide or barium-zirconium oxide, the patterned interlayer material overcoated with a secondary interlayer material of yttria-stabilized zirconia or magnesium-aluminum oxide, upon the surface of the substrate whereby an intermediate article with an exposed surface of both the overcoated patterned interlayer and the substrate is formed, a coating of a buffer layer selected from the group consisting of oxides of Ce, Y, Cm, Dy, Er, Eu, Fe, Gd, Ho, In, La, Mn, Lu, Nd, Pr, Pu, Sm, Tb, Tl, Tm, Y, and Yb over the entire exposed surface of the intermediate article, and, a ceramic superconductive material layer as an overcoat upon the buffer layer whereby the ceramic superconductive material situated directly above the substrate has a crystal structure substantially different than the ceramic superconductive material situated above the overcoated patterned interlayer.

  2. Superconducting thermoelectric generator

    DOEpatents

    Metzger, J.D.; El-Genk, M.S.

    1994-01-01

    Thermoelectricity is produced by applying a temperature differential to dissimilar electrically conducting or semiconducting materials, thereby producing a voltage that is proportional to the temperature difference. Thermoelectric generators use this effect to directly convert heat into electricity; however, presently-known generators have low efficiencies due to the production of high currents which in turn cause large resistive heating losses. Some thermoelectric generators operate at efficiencies between 4% and 7% in the 800{degrees} to 1200{degrees}C range. According to its major aspects and bradly stated, the present invention is an apparatus and method for producing electricity from heat. In particular, the invention is a thermoelectric generator that juxtaposes a superconducting material and a semiconducting material - so that the superconducting and the semiconducting materials touch - to convert heat energy into electrical energy without resistive losses in the temperature range below the critical temperature of the superconducting material. Preferably, an array of superconducting material is encased in one of several possible configurations within a second material having a high thermal conductivity, preferably a semiconductor, to form a thermoelectric generator.

  3. Superconducting superferric dipole magnet with cold iron core for the VLHC

    Microsoft Academic Search

    Vladimir Kashikhin G. William Foster

    2001-01-01

    The magnet system of the Very Large Hadron Collider (VLHC) Stage I is based on a superconducting 2 Tesla magnetic field combined function magnets. These magnets will have a room temperature iron core with two 20 mm air gaps. Magnetic field in both horizontally separated air gaps is excited by a single turn 100 kA superconducting transmission line. The alternative

  4. Superconducting superferric dipole magnet with cold iron core for the VLHC

    Microsoft Academic Search

    G. W. Foster; V. S. Kashikhin

    2002-01-01

    Magnetic system of the stage I Very Large Hadron Collider (VLHC) is based on 2 Tesla superconducting magnets with combined functions. These magnets have a room temperature iron yoke with two 20 mm air gaps. Magnetic field in both horizontally separated air gaps is generated by a single, 100 kA superconducting transmission line. An alternative design with a cold iron

  5. Topological superconducting states with magnetic moments on a conventional s-wave superconductor

    NASA Astrophysics Data System (ADS)

    Nakosai, Sho; Tanaka, Yukio; Nagaosa, Naoto

    2014-03-01

    The search for topological properties in superconductors has been one of the most highlighted topics in nearly a decade. Especially Majorana fermions, appearing as topologically protected boundary modes associated with nontrivial features of superconductors, provide a promising platform for quantum computations. Therefore there is a real need for designing adapted superconductivity with ordinary materials. In this talk, we will present theoretical calculations on unconventional superconductivity induced by the magnetic moments in a conventional spin-singlet s-wave superconductor. By choosing the spin directions of these moments, one can design spinless pairing states appearing within the s-wave superconducting energy gap. It is found that the helix spins produce a px +py -wave state while the skyrmion crystal configuration a px + ipy -wave-like state. Nodes in the energy gap and the zero-energy flat band of Majorana edge states exist in the former case, while the chiral Majorana channels along edges of the sample and the zero-energy Majorana bound state at the core of the vortex appear in the latter case.

  6. PREFACE: Superconducting materials Superconducting materials

    NASA Astrophysics Data System (ADS)

    Charfi Kaddour, Samia; Singleton, John; Haddad, Sonia

    2011-11-01

    The discovery of superconductivity in 1911 was a great milestone in condensed matter physics. This discovery has resulted in an enormous amount of research activity. Collaboration among chemists and physicists, as well as experimentalists and theoreticians has given rise to very rich physics with significant potential applications ranging from electric power transmission to quantum information. Several superconducting materials have been synthesized. Crucial progress was made in 1987 with the discovery of high temperature superconductivity in copper-based compounds (cuprates) which have revealed new fascinating properties. Innovative theoretical tools have been developed to understand the striking features of cuprates which have remained for three decades the 'blue-eyed boy' for researchers in superconductor physics. The history of superconducting materials has been notably marked by the discovery of other compounds, particularly organic superconductors which despite their low critical temperature continue to attract great interest regarding their exotic properties. Last but not least, the recent observation of superconductivity in iron-based materials (pnictides) has renewed hope in reaching room temperature superconductivity. However, despite intense worldwide studies, several features related to this phenomenon remain unveiled. One of the fundamental key questions is the mechanism by which superconductivity takes place. Superconductors continue to hide their 'secret garden'. The new trends in the physics of superconductivity have been one of the two basic topics of the International Conference on Conducting Materials (ICoCoM2010) held in Sousse,Tunisia on 3-7 November 2010 and organized by the Tunisian Physical Society. The conference was a nice opportunity to bring together participants from multidisciplinary domains in the physics of superconductivity. This special section contains papers submitted by participants who gave an oral contribution at ICoCoM2010 and by invited authors selected by the editor. We are grateful to IUPAP, ICTP and the European Office of Aerospace Research and Development, Air Force Office of Scientific Research, United States Air Force Laboratory. We would like to acknowledge the authors for their careful work, and finally we thank Dr L Smith the publisher of Journal of Physics: Condensed Matter for her patience and help. Superconducting materials contents Raman spectrum in the pseudogap phase of the underdoped cuprates: effect of phase coherence and the signature of the KT-type superconducting transitionTao Li and Haijun Liao Pressure effects on Dirac fermions in ?-(BEDT-TTF)2I3Takahiro Himura, Takao Morinari and Takami Tohyama Effect of Zn doping in hole-type 1111 phase (Pr, Sr)FeAsOXiao Lin, Chenyi Shen, Chen Lv, Jianjian Miao, Hao Tan, Guanghan Cao and Zhu-An Xu Superconductivity and ferromagnetism in EuFe2(As1 - xPx)2*Guanghan Cao, Shenggao Xu, Zhi Ren, Shuai Jiang, Chunmu Feng and Zhu'an Xu OInhomogeneous superconductivity in organic conductors: the role of disorder and magnetic fieldS Haddad, S Charfi-Kaddour and J-P Pouget

  7. American Institute of Aeronautics and Astronautics Energy Coupling Through the Small Gap in Optical

    E-print Network

    Guo, Zhixiong "James"

    -gallery modes on energy coupling, resonance quality and frequency. Photon tunneling between an optical resonator reflection losses inside the cavity. The resonant quality is described by the cavity Q factor that is defined that the resonant frequencies are more sparsely distributed throughout the cavity size-dependent resonant optical

  8. Invariant Eigen-Operator Method for Solving Energy Gap for Some Hamiltonians in Molecular Physics

    Microsoft Academic Search

    Hong-Yi Fan; Tong-Tong Wang

    2007-01-01

    We show that the recently proposed invariant eigen-operator method is particularly applicable to solving the energy levels for some Hamiltonians in molecular physics. These are tri-atom molecules, the identical d-dimensional coupled harmonic oscillators and the dissipative linear-chain molecular model etc. The calculation is more direct and simpler than the usual diagonalization method for dynamic Hamiltonians.

  9. Physica E 32 (2006) 1416 Tuning the cross-gap transition energy of a quantum dot

    E-print Network

    Ludwig-Maximilians-Universität, München

    2006-01-01

    optics and quantum information processing [1­3]. QDs have been embedded in cavities to improve energy by using uniaxial strain. The strain is applied by glueing the sample to a piezoelectric actuator (piezo) as shown in Fig. 1 [9]. This enables a continuous and in situ change of the applied strain

  10. Electron Energy Distribution in Hotspots of Cygnus A:Filling the Gap with Spitzer Space Telescope

    SciTech Connect

    Stawarz, L.; Cheung, C.C.; Harris, D.E.; Ostrowski, M.

    2007-03-06

    Here we present Spitzer Space Telescope imaging of Cyg A with the Infrared Array Camera at 4.5 {micro}m and 8.0 {micro}m, resulting in the detection of the high-energy tails or cut-offs in the synchrotron spectra for all four hotspots of this archetype radio galaxy. When combined with the other data collected (and re-analyzed) from the literature, our observations allow for detailed modeling of the broad-band (radio-to-X-ray) emission for the brightest spots A and D. We confirm that the X-ray flux detected previously from these features is consistent with the synchrotron self-Compton radiation for the magnetic field intensity B {approx} 170 {micro}G in spot A, and B {approx} 270 {micro}G in spot D. We also find that the energy density of the emitting electrons is most likely larger by a factor of a few than the energy density of the hotspots magnetic field. We construct energy spectra of the radiating ultrarelativistic electrons. We find that for both hotspots A and D these spectra are consistent with a broken power-law extending from at least 100MeV up to {approx} 100GeV, and that the spectral break corresponds almost exactly to the proton rest energy of {approx} 1GeV. We argue that the shape of the electron continuum most likely reflects two different regimes of the electron acceleration process taking place at mildly relativistic shocks, rather than resulting from radiative cooling and/or absorption e.ects. In this picture the protons inertia defines the critical energy for the hotspot electrons above which Fermi-type acceleration processes may play a major role, but below which the operating acceleration mechanism has to be of a different type. At energies {approx}> 100 GeV, the electron spectra cut-off/steepen again, most likely as a result of spectral aging due to radiative loss effects. We discuss several implications of the presented analysis for the physics of extragalactic jets.

  11. Harmonics suppression of vacuum chamber eddy current induced fields with application to the Superconducting Super Collider (SSC) Low Energy Booster (LEB) Magnets

    SciTech Connect

    Schlueter, R.D.; Halbach, K.

    1991-12-04

    This memo presents the formulation of an expression for eddy currents induced in a thin-walled conductor due to a time-dependent electromagnet field excitation. Then follows an analytical development for prediction of vacuum chamber eddy current induced field harmonics in iron-core electromagnets. A passive technique for harmonics suppression is presented with specific application to the design of the Superconducting Super Collider (SSC) Low Energy B (LEB) Magnets.

  12. Design, Fabrication, and Test of a 5kWh\\/100kW Flywheel Energy Storage Utilizing a High-Temperature Superconducting Bearing

    Microsoft Academic Search

    M. Strasik; P. E. Johnson; A. C. Day; J. Mittleider; M. D. Higgins; J. Edwards; J. R. Schindler; K. E. McCrary; C. R. McIver; D. Carlson; J. F. Gonder; J. R. Hull

    2007-01-01

    The Boeing team has designed, fabricated, and is currently testing a 5-kWh\\/100-kW flywheel energy-storage system (FESS) utilizing a high-temperature superconducting (HTS) bearing suspension\\/damping system. Primary design features include: a robust rotor design utilizing a composite rim combined with a metallic hub to create a 164-kg rotor assembly without critical resonances within the normal operating range, a closed-loop passive HTS bearing

  13. On the energy growth of some periodically driven quantum systems with shrinking gaps in the spectrum

    E-print Network

    Pierre Duclos; Ondra Lev; Pavel Stovicek

    2007-10-11

    We consider quantum Hamiltonians of the form H(t)=H+V(t) where the spectrum of H is semibounded and discrete, and the eigenvalues behave as E_n~n^\\alpha, with 00, p>=1 and \\gamma=(1-\\alpha)/2. We show that the energy diffusion exponent can be arbitrarily small provided p is sufficiently large and \\epsilon is small enough. More precisely, for any initial condition \\Psi\\in Dom(H^{1/2}), the diffusion of energy is bounded from above as _\\Psi(t)=O(t^\\sigma) where \\sigma=\\alpha/(2\\ceil{p-1}\\gamma-1/2). As an application we consider the Hamiltonian H(t)=|p|^\\alpha+\\epsilon*v(\\theta,t) on L^2(S^1,d\\theta) which was discussed earlier in the literature by Howland.

  14. A Study of Higher-Order Mode Damping in the Superconducting Energy Recovery LINAC at Brookhaven National Laboratory

    NASA Astrophysics Data System (ADS)

    Hammons, Lee Reginald, III

    An energy recovery LINAC (ERL) is being constructed at Brookhaven National Laboratory that will involve a superconducting LINAC along with a superconducting electron gun, all operating at 703.75 MHz. The ERL will serve as a testbed for the concepts and technologies required to implement future upgrades in the Relativistic Heavy Ion Collider (RHIC). Because of the high current and high charge requirements of the ERL, effective higher-order mode (HOM) damping is an essential component of the ERL research and development program. This thesis focuses on three areas of HOM characterization and damping development: damping of HOMs in the five-cell LINAC, use of the electron gun fundamental power couplers (FPCs) to damp HOMs, and the development of a ceramic/ferrite damper for the electron gun. The five-cell LINAC uses an HOM load lined with ferrite and attached to the beampipe on either side of the cavity. These studies characterized the frequency-dependent nature of the ferrite absorbing material and derived a set of "portable" ferrite parameters that simplified simulation work. Using these "portable" parameters, it was determined that the ferrite absorber is effective in damping the HOMs of the five-cell cavity over a range of frequencies. In addition, higher-order mode damping in the electron gun was studied using the fundamental power couplers. The gun cavity is a superconducting half-cell structure designed to accelerate electrons to an energy of 2.5 MeV and features dual fundamental power couplers. The HOMs of the gun cavity were studied along with the damping capabilities of the FPCs. Simulation studies determined that the FPCs couple strongly to many of the HOMs studied. However, the transition between the coaxial FPCs and the waveguide that feeds power to the FPCs is a "doorknob" type transition, and it was found that this component shows the best transmission qualities between 1 and 2 GHz, thus limiting the damping capabilities of the FPCs to this bandwidth. It remains to be seen how the FPCs will perform under actual conditions. Finally, the development of a ceramic/ferrite damper was described for the electron gun. The damper features a lossless alumina ceramic break surrounded by a ferrite load and was designed to isolate the vacuum chamber from the ferrite tiles. Various studies were conducted using simulation and prototype designs, and it was determined that the ceramic/ferrite load can be effective in damping higher-order modes of the gun cavity. Analytical calculations along with simulation show that the ceramic tends to alter the field distribution of higher-order modes and change the damping qualities depending on the frequency. The effectiveness of the damping for a given mode depends on a variety of factors including the thickness of the ceramic, the spacing between the ceramic and ferrite layers, and the diameter of the inner ceramic surface.

  15. Suppression of activation energy and superconductivity by the addition of Al{sub 2}O{sub 3} nanoparticles in CuTl-1223 matrix

    SciTech Connect

    Jabbar, Abdul; Qasim, Irfan; Mumtaz, M.; Zubair, M.; Nadeem, K. [Materials Research Laboratory, Department of Physics, FBAS, International Islamic University (IIU) Islamabad, Islamabad 44000 (Pakistan); Khurram, A. A. [Experimental Physics Labs, National Centre for Physics, Islamabad (Pakistan)

    2014-05-28

    Low anisotropic (Cu{sub 0.5}Tl{sub 0.5})Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10??} (CuTl-1223) high T{sub c} superconducting matrix was synthesized by solid-state reaction and Al{sub 2}O{sub 3} nanoparticles were prepared separately by co-precipitation method. Al{sub 2}O{sub 3} nanoparticles were added with different concentrations during the final sintering cycle of CuTl-1223 superconducting matrix to get the required (Al{sub 2}O{sub 3}){sub y}/CuTl-1223, y?=?0.0, 0.5, 0.7, 1.0, and 1.5?wt.?%, composites. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray, and dc-resistivity (?) measurements. The activation energy and superconductivity were suppressed with increasing concentration of Al{sub 2}O{sub 3} nanoparticles in (CuTl-1223) matrix. The XRD analysis showed that the addition of Al{sub 2}O{sub 3} nanoparticles did not affect the crystal structure of the parent CuTl-1223 superconducting phase. The suppression of activation energy and superconducting properties is most probably due to weak flux pinning in the samples. The possible reason of weak flux pinning is reduction of weak links and enhanced inter-grain coupling due to the presence of Al{sub 2}O{sub 3} nanoparticles at the grain boundaries. The presence of Al{sub 2}O{sub 3} nanoparticles at the grain boundaries possibly reduced the number of flux pinning centers, which were present in the form of weak links in the pure CuTl-1223 superconducting matrix. The increase in the values of inter-grain coupling (?) deduced from the fluctuation induced conductivity analysis with the increased concentration of Al{sub 2}O{sub 3} nanoparticles is a theoretical evidence of improved inter-grain coupling.

  16. Superconductivity above 100 K in single-layer FeSe films on doped SrTiO3.

    PubMed

    Ge, Jian-Feng; Liu, Zhi-Long; Liu, Canhua; Gao, Chun-Lei; Qian, Dong; Xue, Qi-Kun; Liu, Ying; Jia, Jin-Feng

    2015-03-01

    Recent experiments on FeSe films grown on SrTiO3 (STO) suggest that interface effects can be used as a means to reach superconducting critical temperatures (Tc) of up to 80 K (ref. ). This is nearly ten times the Tc of bulk FeSe and higher than the record value of 56 K for known bulk Fe-based superconductors. Together with recent studies of superconductivity at oxide heterostructure interfaces, these results rekindle the long-standing idea that electron pairing at interfaces between two different materials can be tailored to achieve high-temperature superconductivity. Subsequent angle-resolved photoemission spectroscopy measurements of the FeSe/STO system revealed an electronic structure distinct from bulk FeSe (refs , ), with an energy gap vanishing at around 65 K. However, ex situ electrical transport measurements have so far detected zero resistance-the key experimental signature of superconductivity-only below 30 K. Here, we report the observation of superconductivity with Tc above 100 K in the FeSe/STO system by means of in situ four-point probe electrical transport measurements. This finding confirms FeSe/STO as an ideal material for studying high-Tc superconductivity. PMID:25419814

  17. Superconductivity above 100 K in single-layer FeSe films on doped SrTiO3

    NASA Astrophysics Data System (ADS)

    Ge, Jian-Feng; Liu, Zhi-Long; Liu, Canhua; Gao, Chun-Lei; Qian, Dong; Xue, Qi-Kun; Liu, Ying; Jia, Jin-Feng

    2015-03-01

    Recent experiments on FeSe films grown on SrTiO3 (STO) suggest that interface effects can be used as a means to reach superconducting critical temperatures (Tc) of up to 80 K (ref. ). This is nearly ten times the Tc of bulk FeSe and higher than the record value of 56 K for known bulk Fe-based superconductors. Together with recent studies of superconductivity at oxide heterostructure interfaces, these results rekindle the long-standing idea that electron pairing at interfaces between two different materials can be tailored to achieve high-temperature superconductivity. Subsequent angle-resolved photoemission spectroscopy measurements of the FeSe/STO system revealed an electronic structure distinct from bulk FeSe (refs , ), with an energy gap vanishing at around 65 K. However, ex situ electrical transport measurements have so far detected zero resistance—the key experimental signature of superconductivity—only below 30 K. Here, we report the observation of superconductivity with Tc above 100 K in the FeSe/STO system by means of in situ four-point probe electrical transport measurements. This finding confirms FeSe/STO as an ideal material for studying high-Tc superconductivity.

  18. Fields and forces in flywheel energy storage with high-temperature superconducting bearings

    SciTech Connect

    Turner, L.R. [Argonne National Lab., IL (United States). Energy Technology Div.] [Argonne National Lab., IL (United States). Energy Technology Div.

    1997-03-01

    The development of low-loss bearings employing high-temperature superconductors has brought closer the advent of practical flywheel energy storage systems. These systems require magnetic fields and forces for levitation, stabilization, and energy transfer. This paper describes the status of experiments on flywheel energy storage at Argonne National Laboratory and computations in support of that project, in particular computations for the permanent-magnet rotor of the motor-generator that transfers energy to and from the flywheel, for other energy-transfer systems under consideration, and for the levitation and stability subsystems.

  19. Fields and forces in flywheel energy storage with high-temperature superconducting bearings

    SciTech Connect

    Turner, L.R. [Argonne National Lab., IL (United States). Energy Technology Div.

    1996-05-01

    The development of low-loss bearings employing high-temperature superconductors has brought closer the advent of practical flywheel energy storage systems. These systems require magnetic fields and forces for levitation, stabilization, and energy transfer. This paper describes the status of experiments on flywheel energy storage at Argonne National Laboratory and computations in support of that project, in particular computations for the permanent-magnet rotor of the motor-generator that transfers energy to and from the flywheel, for other energy-transfer systems under consideration, and for the levitation and stabilization subsystem.

  20. Superconducting Radio-Frequency Cavities

    NASA Astrophysics Data System (ADS)

    Padamsee, Hasan S.

    2014-10-01

    Superconducting cavities have been operating routinely in a variety of accelerators with a range of demanding applications. With the success of completed projects, niobium cavities have become an enabling technology, offering upgrade paths for existing facilities and pushing frontier accelerators for nuclear physics, high-energy physics, materials science, and the life sciences. With continued progress in basic understanding of radio-frequency superconductivity, the performance of cavities has steadily improved to approach theoretical capabilities.

  1. Imaging the impact on cuprate superconductivity of varying the interatomic distances within individual crystal unit cells.

    PubMed

    Slezak, J A; Lee, Jinho; Wang, M; McElroy, K; Fujita, K; Andersen, B M; Hirschfeld, P J; Eisaki, H; Uchida, S; Davis, J C

    2008-03-01

    Many theoretical models of high-temperature superconductivity focus only on the doping dependence of the CuO(2)-plane electronic structure. However, such models are manifestly insufficient to explain the strong variations in superconducting critical temperature, T(c), among cuprates that have identical hole density but are crystallographically different outside of the CuO(2) plane. A key challenge, therefore, has been to identify a predominant out-of-plane influence controlling the superconductivity, with much attention focusing on the distance d(A) between the apical oxygen and the planar copper atom. Here we report direct determination of how variations in interatomic distances within individual crystalline unit cells affect the superconducting energy-gap maximum Delta of Bi(2)Sr(2)CaCu(2)O(8+delta). In this material, quasiperiodic variations of unit cell geometry occur in the form of a bulk crystalline "supermodulation." Within each supermodulation period, we find approximately 9 +/- 1% cosinusoidal variation in local Delta that is anticorrelated with the associated d(A) variations. Furthermore, we show that phenomenological consistency would exist between these effects and the random Delta variations found near dopant atoms if the primary effect of the interstitial dopant atom is to displace the apical oxygen so as to diminish d(A) or tilt the CuO(5) pyramid. Thus, we reveal a strong, nonrandom out-of-plane effect on cuprate superconductivity at atomic scale. PMID:18287001

  2. Band Gap, Excitons, Thermal Conductance, and Energy Applications of Few-Layer Black Phosphorus

    NASA Astrophysics Data System (ADS)

    Yang, Li

    2015-03-01

    We investigated anisotropic polarization dependence of light scattering in black phosphorus by optical microscopy and Raman spectroscopy. Due to a high carrier mobility (~ 300 V cm2/s) and a high on/off ratio (~ 105) , black phosphorus is attracting interest as a promising candidate for a field effect transistor. Black phosphorus has an anisotropic crystal structure, which leads to directional dependence of the mobility and infrared light absorption. We prepared samples on SiO2/Si substrates by mechanical exfoliation. We chose a few-hundred-nanometer thick sample with well-defined edges. By using a polarized optical microscope, we found that the optical contrast depends on the crystal direction. By comparing results with TEM measurements, we can determine the crystallographic orientation of the sample. We also performed polarized Raman measurements with several excitation energies. The intensity of each mode is largely dependent on the incident polarization direction. Furthermore, these polarization dependences vary with the excitation energy. From the polarization dependence of the Raman intensity one can determine the crystallographic orientation of the sample. We investigated anisotropic polarization dependence of light scattering in black phosphorus by optical microscopy and Raman spectroscopy. Due to a high carrier mobility (~ 300 V cm2/s) and a high on/off ratio (~ 105) , black phosphorus is attracting interest as a promising candidate for a field effect transistor. Black phosphorus has an anisotropic crystal structure, which leads to directional dependence of the mobility and infrared light absorption. We prepared samples on SiO2/Si substrates by mechanical exfoliation. We chose a few-hundred-nanometer thick sample with well-defined edges. By using a polarized optical microscope, we found that the optical contrast depends on the crystal direction. By comparing results with TEM measurements, we can determine the crystallographic orientation of the sample. We also performed polarized Raman measurements with several excitation energies. The intensity of each mode is largely dependent on the incident polarization direction. Furthermore, these polarization dependences vary with the excitation energy. From the polarization dependence of the Raman intensity one can determine the crystallographic orientation of the sample. SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University.

  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. Design of single-winding energy-storage reactors for dc-to-dc converters using air-gapped magnetic-core structures

    NASA Technical Reports Server (NTRS)

    Ohri, A. K.; Wilson, T. G.; Owen, H. A., Jr.

    1977-01-01

    A procedure is presented for designing air-gapped energy-storage reactors for nine different dc-to-dc converters resulting from combinations of three single-winding power stages for voltage stepup, current stepup and voltage stepup/current stepup and three controllers with control laws that impose constant-frequency, constant transistor on-time and constant transistor off-time operation. The analysis, based on the energy-transfer requirement of the reactor, leads to a simple relationship for the required minimum volume of the air gap. Determination of this minimum air gap volume then permits the selection of either an air gap or a cross-sectional core area. Having picked one parameter, the minimum value of the other immediately leads to selection of the physical magnetic structure. Other analytically derived equations are used to obtain values for the required turns, the inductance, and the maximum rms winding current. The design procedure is applicable to a wide range of magnetic material characteristics and physical configurations for the air-gapped magnetic structure.

  5. Gap structure in Fe-based superconductors with accidental nodes: The role of hybridization

    NASA Astrophysics Data System (ADS)

    Hinojosa, Alberto; Chubukov, Andrey V.

    2015-06-01

    We study the effects of hybridization between the two electron pockets in Fe-based superconductors with s -wave gap with accidental nodes. We argue that hybridization reconstructs the Fermi surfaces and also induces an additional interpocket pairing component. We analyze how these two effects modify the gap structure by tracing the position of the nodal points of the energy dispersions in the superconducting state. We find three possible outcomes. In the first, the nodes simply shift their positions in the Brillouin zone; in the second, the nodes merge and disappear, in which case the gap function has either equal or opposite signs on the electron pockets; in the third, a new set of nodal points emerges, doubling the original number of nodes.

  6. SrPt3P : A two-band single-gap superconductor

    NASA Astrophysics Data System (ADS)

    Khasanov, R.; Amato, A.; Biswas, P. K.; Luetkens, H.; Zhigadlo, N. D.; Batlogg, B.

    2014-10-01

    The magnetic penetration depth (? ) as a function of applied magnetic field and temperature in SrPt3P (Tc?8.4 K) was studied by means of muon-spin rotation (? SR ). The dependence of ?-2 on temperature suggests the existence of a single s -wave energy gap with the zero-temperature value ?0=1.55 (2 ) meV. At the same time ? was found to be strongly field dependent which is the characteristic feature of the nodal gap and/or multiband systems. The multiband nature of the superconducting state is further suggested by the upward curvature of the upper critical field. This apparent contradiction is resolved by SrPt3P being a particular two-band superconductor with equal gaps but different coherence lengths within the two Fermi surface sheets.

  7. Properties of Superconducting Mo, Mo2n and Trilayer Mo2n-Mo-Mo2n Thin Films

    NASA Technical Reports Server (NTRS)

    Barrentine, E. M.; Stevenson, T. R.; Brown, A. D.; Lowitz, A. E.; Noroozian, O.; U-Yen, K.; Eshan, N.; Hsieh, W. T.; Moseley, S. H.; Wollack, E. J.

    2014-01-01

    We present measurements of the properties of thin film superconducting Mo, Mo2N and Mo2N/Mo/Mo2N trilayers of interest for microwave kinetic inductance detector (MKID) applications. Using microwave resonator devices, we investigate the transition temperature, energy gaps, kinetic inductance, and internal quality factors of these materials. We present an Usadel-based interpretation of the trilayer transition temperature as a function of trilayer thicknesses, and a 2-gap interpretation to understand the change in kinetic inductance and internal resonance quality factor (Q) as a function of temperature.

  8. Fast-cycling superconducting synchrotrons and possible path to the future of US experimental high-energy particle physics

    SciTech Connect

    Piekarz, Henryk; /Fermilab

    2008-02-01

    The authors outline primary physics motivation, present proposed new arrangement for Fermilab accelerator complex, and then discuss possible long-range application of fast-cycling superconducting synchrotrons at Fermilab.

  9. Vacuum low-temperature superconductivity is the essence of superconductivity - Atomic New Theory

    NASA Astrophysics Data System (ADS)

    Yongquan, Han

    2010-10-01

    The universe when the temperature closest to the Big Bang the temperature should be nuclear. Because, after the big bang, instant formation of atoms, nuclei and electrons between the absolute vacuum, the nucleus can not emit energy. (Radioactive elements, except in fact, radiation Yuan Su limited power emitted) which causes atomic nuclei and external temperature difference are so enormous that a large temperature difference reasons, all external particles became closer to the nucleus, affect the motion of electrons. When the conductor conductivity and thus affect the conductivity, the formation of resistance. Assumption that no particles affect the motion of electrons (except outside the nucleus) to form a potential difference will not change after the vector form, is now talking about the phenomenon of superconductivity, and then to introduce general, the gap between atoms in molecules or between small, valence electron number of high temperature superconducting conductors. This theory of atomic nuclei, but also explain the atomic and hydrogen bombs can remain after an explosion Why can release enormous energy reasons. Can also explain the ``super flow'' phenomenon. natural world. Tel 13241375685

  10. Fields and forces in flywheel energy storage with high-temperature superconducting bearings

    Microsoft Academic Search

    Larry R. Turner

    1997-01-01

    The development of low-loss bearings employing high-temperature superconductors has brought closer the advent of practical flywheel energy storage systems. These systems require magnetic fields and forces for levitation, stabilization, and energy transfer. This paper describes the status of experiments on flywheel energy storage at Argonne National Laboratory and computations in support of that project, in particular computations for the permanent-magnet

  11. Two-dimensional macroscopic quantum tunneling in multi-gap superconductor Josephson junctions

    E-print Network

    Hidehiro Asai; Shiro Kawabata; Yukihiro Ota; Masahiko Machida

    2014-12-17

    Low-temperature characters of superconducting devices yield definite probes for different superconducting phenomena. We study the macroscopic quantum tunneling (MQT) in a Josephson junction, composed of a single-gap superconductor and a two-gap superconductor. Since this junction has two kinds to the superconducting phase differences, calculating the MQT escape rate requires the analysis of quantum tunneling in a multi-dimensional configuration space. Our approach is the semi-classical approximation along a 1D curve in a 2D potential- energy landscape, connecting two adjacent potential (local) minimums through a saddle point. We find that this system has two plausible tunneling paths; an in-phase path and an out-of-phase path. The former is characterized by the Josephson-plasma frequency, whereas the latter is by the frequency of the characteristic collective mode in a two-band superconductor, Josephson- Leggett mode. Depending on external bias current and inter-band Josephson-coupling energy, one of them mainly contributes to the MQT. Our numerical calculations show that the difference between the in-phase path and the out-of-phase path is manifest, with respect to the bias- current-dependence of the MQT escape rate. This result suggests that our MQT setting be an indicator of the Josephson-Leggett mode.

  12. Nonequilibrium transport in superconducting tunneling structures.

    SciTech Connect

    Chtchelkatchev, N. M.; Vinokur, V. M.; Baturina, T. I. (Materials Science Division); (Moscow Inst. Physics and Technology); (Inst. Semiconductor Physics)

    2010-12-01

    We derive the current-voltage (I-V) characteristics of far from equilibrium superconducting tunneling arrays and find that the energy relaxation ensuring the charge transfer occurs in two stages: (i) the energy exchange between charge carriers and the intermediate bosonic agent, environment, and (ii) relaxing the energy further to the (phonon) thermostat, the bath, provided the rate of the environmental modes-phonon interactions is slower than their energy exchange rate with the tunneling junction. For a single junction we find I {proportional_to} (V/R)ln({Lambda}/V), where R is the bare tunnel resistance of the junction and {Lambda} is the high energy cut-off of the electron-environment interaction. In large tunneling arrays comprised of macroscopic number of junctions, low-temperature transport is governed by the cotunneling processes losing energy to the electron-hole environment. Below some critical temperature, T*, the Coulomb interactions open a finite gap in the environment excitations spectrum blocking simultaneously Cooper pair and normal excitations currents through the array; this is the microscopic mechanism of the insulator-to-superinsulator transition.

  13. Estimating the energy of electric breakdown in air gap between electrolyte and metal electrode

    NASA Astrophysics Data System (ADS)

    Orlov, A. M.; Yavtushenko, I. O.; Churilov, M. V.

    2010-07-01

    The influence of induced electric charge (localized on the surface of a suspended copper rod) on the formation of a protrusion (Taylor cone) on the inducing liquid (aqueous solution) surface is considered. At an applied voltage of U ? 12 kV, the protrusion height in the interval of pre-breakdown voltages ( U < U P) is limited by the electric field strength. At U > U P, the growth of protrusion is terminated by an electric discharge, which drives the liquid to oscillate in a broad range of applied voltages U at almost constant multiple frequencies f = f 0 n, which are resonantly switched at certain fixed U values. By measuring the amount of evaporated liquid, the energy (27.8 × 10-3 J) and current (64.9 A) of single discharge were evaluated and the electric capacitance (7.6 × 10-10 F) of a system comprising the water surface and suspended copper electrode was estimated. Serial connection of an additional capacitor (100 ?F) to the copper electrode with induced electric charge leads to a threefold increase in these parameters.

  14. Superconductivity Engineering and Its Application for Fusion 3.Superconducting Technology as a Gateway to Future Technology

    Microsoft Academic Search

    Katsuhiko Asano

    2005-01-01

    Hopes for achieving a new source of energy through nuclear fusion rest on the development of superconducting technology that is needed to make future equipments more energy efficient as well as increase their performance. Superconducting technology has made progress in a wide variety of fields, such as energy, life science, electronics, industrial use and environmental improvement. It enables the actualization

  15. Superconducting magnetic system of the detector KEDR

    Microsoft Academic Search

    V. V. Anashin; L. M. Barkov; G. A. Blinov; G. M. Kolachev; S. G. Pivovarov; V. P. Smakhtin; S. V. Sukhanov

    1992-01-01

    The detector KEDR will be used in high-energy physics experiments on the storage ring VEPP-4M. The authors describe the KEDR magnetic system, which consists of a main superconducting coil, compensating superconducting solenoids, and an iron yoke closing the magnetic flux. The main superconducting coil is a one-layer solenoid of 3-m diameter and 3-m length with an inductance of 1.2 H,

  16. Transition radiation effects in superconducting granules

    NASA Technical Reports Server (NTRS)

    Drukier, A. K.; Valette, C.; Waysand, G.; Peters, F.; Yuan, L. C. L.

    1975-01-01

    The paper examines the use of a superheated superconducting suspension as a transition radiation detector of relativistic charged particles. The suspensions would also be used for detecting low-energy X-ray photons. The DESY experiment for developing such a superconducting detector has been carried out at a 7 GeV electron synchrotron. The detection is shown to be based on the recordable flipping of the state of a single superconducting grain.

  17. Static forces in a superconducting magnet bearing

    SciTech Connect

    Stoye, P.; Fuchs, G. [Institut fuer Festkoerper- und Werkstofforschung, Dresden (Germany)] [Institut fuer Festkoerper- und Werkstofforschung, Dresden (Germany); Gawalek, W.; Goernert, P. [Institut fuer Physikalische Hochtechnologie, Jena (Germany)] [Institut fuer Physikalische Hochtechnologie, Jena (Germany); Gladun, A. [Technische Univ., Dresden (Germany)] [Technische Univ., Dresden (Germany)

    1995-11-01

    Static levitation forces and stiffnesses in a superconducting bearing consisting of concentric ring magnets and a superconducting YBaCuO ring are investigated. In the field-cooled mode a levitation force of 20 N has been achieved. The axial and radial stiffnesses have values of 15 N/mm and 10 N/mm, respectively. An arrangement with two bearings supporting a high speed shaft is now under development. A possible application of superconducting magnetic bearings is flywheels for energy storage.

  18. Athermal Energy Loss from X-rays Deposited in Thin Superconducting Films on Solid Substrates

    NASA Technical Reports Server (NTRS)

    Kozorezov, Alexander G.; Lambert, Colin J.; Bandler, Simon R.; Balvin, Manuel A.; Busch, Sarah E.; Sagler, Peter N.; Porst, Jan-Patrick; Smith, Stephen J.; Stevenson, Thomas R.; Sadleir, John E.

    2013-01-01

    When energy is deposited in a thin-film cryogenic detector, such as from the absorption of an X-ray, an important feature that determines the energy resolution is the amount of athermal energy that can be lost to the heat bath prior to the elementary excitation systems coming into thermal equilibrium. This form of energy loss will be position-dependent and therefore can limit the detector energy resolution. An understanding of the physical processes that occur when elementary excitations are generated in metal films on dielectric substrates is important for the design and optimization of a number of different types of low temperature detector. We have measured the total energy loss in one relatively simple geometry that allows us to study these processes and compare measurements with calculation based upon a model for the various di.erent processes. We have modeled the athermal phonon energy loss in this device by finding an evolving phonon distribution function that solves the system of kinetic equations for the interacting system of electrons and phonons. Using measurements of device parameters such as the Debye energy and the thermal di.usivity we have calculated the expected energy loss from this detector geometry, and also the position-dependent variation of this loss. We have also calculated the predicted impact on measured spectral line-shapes, and shown that they agree well with measurements. In addition, we have tested this model by using it to predict the performance of a number of other types of detector with di.erent geometries, where good agreement is also found.

  19. Theory of spin-fluctuation induced superconductivity in iron-based superconductors

    SciTech Connect

    Zhang, Junhua

    2011-08-15

    In this dissertation we focus on the investigation of the pairing mechanism in the recently discovered high-temperature superconductor, iron pnictides. Due to the proximity to magnetic instability of the system, we considered short-range spin fluctuations as the major mediating source to induce superconductivity. Our calculation supports the magnetic fluctuations as a strong candidate that drives Cooper-pair formation in this material. We find the corresponding order parameter to be of the so-called ss-wave type and show its evolution with temperature as well as the capability of supporting high transition temperature up to several tens of Kelvin. On the other hand, our itinerant model calculation shows pronounced spin correlation at the observed antiferromagnetic ordering wave vector, indicating the underlying electronic structure in favor of antiferromagnetic state. Therefore, the electronic degrees of freedom could participate both in the magnetic and in the superconducting properties. Our work shows that the interplay between magnetism and superconductivity plays an important role to the understanding of the rich physics in this material. The magnetic-excitation spectrum carries important information on the nature of magnetism and the characteristics of superconductivity. We analyze the spin excitation spectrum in the normal and superconducting states of iron pnictides in the magnetic scenario. As a consequence of the sign-reversed gap structure obtained in the above, a spin resonance mode appears below the superconducting transition temperature. The calculated resonance energy, scaled with the gap magnitude and the magnetic correlation length, agrees well with the inelastic neutron scattering (INS) measurements. More interestingly, we find a common feature of those short-range spin fluctuations that are capable of inducing a fully gapped ss state is the momentum anisotropy with elongated span along the direction transverse to the antiferromagnetic momentum transfer. This calculated intrinsic anisotropy exists both in the normal and in the superconducting state, which naturally explains the elliptically shaped magnetic responses observed in INS experiments. Our detailed calculation further shows that the magnetic resonance mode exhibits an upward dispersion-relation pattern but anisotropic along the transverse and longitudinal directions. We also perform a qualitative analysis on the relationship between the anisotropic momentum structure of the magnetic fluctuations and the stability of superconducting phase by intraorbital but interband pair scattering to show the consistency of the magnetic mechanism for superconductivity. As discussed for cuprates, an important identification of the mediating boson is from the fermionic spectrum. We study the spectral function in the normal and superconducting state. Not only do we extract the gap magnitude on the electron- and hole-pockets to show the momentum structure of the gap, but also find a peak-dip-hump feature in the electron spectrum, which reflects the feedback from the spin excitations on fermions. This serves as an interpretation of the kink structure observed in ARPES measurements.

  20. Key features for high- T c -superconductivity phenomenon: antiferromagnetic exchange as attractrive interaction and a saddle-point singularity close to Fermi level

    NASA Astrophysics Data System (ADS)

    Onufrieva, F.; Petit, S.; Sidis, Y.

    1996-11-01

    A new mechanism for high-Tc superconductivity of magnetic origin is proposed, different from exchange by spin waves. A superconducting pairing of the d-wave symmetry with high amplitude of the SC gap is found.

  1. Computer simulation of the energy gap in ZnO- and TiO{sub 2}-based semiconductor photocatalysts

    SciTech Connect

    Skorikov, N. A., E-mail: nskorikov@gmail.com; Korotin, M. A.; Kurmaev, E. Z. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation); Cholakh, S. O. [Ural Federal University (Russian Federation)

    2012-12-15

    Ab initio calculations of the electronic structures of binary ZnO- and TiO{sub 2}-based oxides are performed to search for optimum dopants for efficient absorption of the visible part of solar radiation. Light elements B, C, and N are chosen for anion substitution. Cation substitution is simulated by 3d elements (Cr, Mn, Fe, Co) and heavy metals (Sn, Sb, Pb, Bi). The electronic structures are calculated by the full-potential linearized augmented plane wave method using the modified Becke-Johnson exchange-correlation potential. Doping is simulated by calculating supercells Zn{sub 15}D{sub 1}O{sub 16}, Zn{sub 16}O{sub 15}D{sub 1}, Ti{sub 15}D{sub 1}O{sub 32}, and Ti{sub 8}O{sub 15}D{sub 1}, where one-sixteenth of the metal (Ti, Zn) or oxygen atoms is replaced by dopant atoms. Carbon and antimony are found to be most effective dopants for ZnO: they form an energy gap {Delta}E = 1.78 and 1.67 eV, respectively. For TiO{sub 2}, nitrogen is the most effective dopant ({Delta}E = 1.76 eV).

  2. The collective emission of electromagnetic waves from astrophysical jets - Luminosity gaps, BL Lacertae objects, and efficient energy transport

    NASA Technical Reports Server (NTRS)

    Baker, D. N.; Borovsky, Joseph E.; Benford, Gregory; Eilek, Jean A.

    1988-01-01

    A model of the inner portions of astrophysical jets is constructed in which a relativistic electron beam is injected from the central engine into the jet plasma. This beam drives electrostatic plasma wave turbulence, which leads to the collective emission of electromagnetic waves. The emitted waves are beamed in the direction of the jet axis, so that end-on viewing of the jet yields an extremely bright source (BL Lacertae object). The relativistic electron beam may also drive long-wavelength electromagnetic plasma instabilities (firehose and Kelvin-Helmholtz) that jumble the jet magnetic field lines. After a sufficient distance from the core source, these instabilities will cause the beamed emission to point in random directions and the jet emission can then be observed from any direction relative to the jet axis. This combination of effects may lead to the gap turn-on of astrophysical jets. The collective emission model leads to different estimates for energy transport and the interpretation of radio spectra than the conventional incoherent synchrotron theory.

  3. Charging energy and superconducting reentrant behavior of zero point fluctuated arrays of Josephson Junctions

    SciTech Connect

    Liengme, O.

    1986-05-07

    High sheet resistance coplanar arrays with very high densities of small Josephson Junctions (JJs) have been measured. They present a reentrance of the critical current with an exponential behavior. This suggests a thermal activation in the number of Cooper pairs tunneling across the barrier, in which tunneling is reduced by charging energy, an effect partially compensated by the thermal bath. In addition, a sample of intermediate sheet resistance also presents a new regime at low temperatures, where the critical current raises again, but remains much below the expected unfluctuated critical current. Sample parameters indicate that, in this regime, the Josephson coupling energy might become larger than the otherwise dominating charging energy. 20 refs., 5 figs.

  4. Effect of a Quartic Anisotropy Energy on the Spiral Magnetic Coexistence State of Superconductivity and Ferromagnetism

    E-print Network

    ROSE, GH; Hu, Chia-Ren.

    1988-01-01

    , Department of Physics, Texas A&M University, College Station, Texas ??843 (Received 26 June 1987} The effect of three types of "quartic" anisotropy energy (i.e., in the M term of the magnetic Ginzburg-Landau free energy} on the polarization of the "spiral... the principal axes in the basal plane. This last case studied provides a plausible explanation for the linear polarization observed in the coexistence state of ErRh484. I. INTRODUCTION AND SUMMARY Using an isotropic Ginzburg-Landau theory to investi- gate...

  5. Superconducting and magnetic properties of Sr?Ir?Sn??

    DOE PAGESBeta

    Biswas, P. K.; Wang, Kefeng; Amato, A.; Khasanov, R.; Luetkens, H.; Petrovic, C.; Cook, R. M.; Lees, M. R.; Morenzoni, E.

    2014-10-01

    Magnetization and muon spin relaxation or rotation (µSR) measurements have been performed to study the superconducting and magnetic properties of Sr?Ir?Sn??. From magnetization measurements the lower and upper critical fields of Sr?Ir?Sn?? are found to be 81(1) Oe and 14.4(2) kOe, respectively. Zero-field µSR data show no sign of any magnetic ordering or weak magnetism in Sr?Ir?Sn??. Transverse-field µSR measurements in the vortex state provided the temperature dependence of the magnetic penetration depth ?. The dependence of ??² with temperature is consistent with the existence of single s-wave energy gap in the superconducting state of Sr?Ir?Sn?? with a gap valuemore »of 0.82(2) meV at absolute zero temperature. The magnetic penetration depth at zero temperature ?(0) is 291(3) nm. The ratio ?(0)/kBTc = 2.1(1) indicates that Sr?Ir?Sn?? should be considered as a strong-coupling superconductor.« less

  6. Superconducting and magnetic properties of Sr?Ir?Sn??

    SciTech Connect

    Biswas, P. K. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Wang, Kefeng [Brookhaven National Lab. (BNL), Upton, NY (United States); Amato, A. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Khasanov, R. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Luetkens, H. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Petrovic, C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Cook, R. M. [Univ. of Warwick, Coventry (United Kingdom); Lees, M. R. [Univ. of Warwick, Coventry (United Kingdom); Morenzoni, E. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    2014-10-01

    Magnetization and muon spin relaxation or rotation (µSR) measurements have been performed to study the superconducting and magnetic properties of Sr?Ir?Sn??. From magnetization measurements the lower and upper critical fields of Sr?Ir?Sn?? are found to be 81(1) Oe and 14.4(2) kOe, respectively. Zero-field µSR data show no sign of any magnetic ordering or weak magnetism in Sr?Ir?Sn??. Transverse-field µSR measurements in the vortex state provided the temperature dependence of the magnetic penetration depth ?. The dependence of ??² with temperature is consistent with the existence of single s-wave energy gap in the superconducting state of Sr?Ir?Sn?? with a gap value of 0.82(2) meV at absolute zero temperature. The magnetic penetration depth at zero temperature ?(0) is 291(3) nm. The ratio ?(0)/kBTc = 2.1(1) indicates that Sr?Ir?Sn?? should be considered as a strong-coupling superconductor.

  7. Superconducting and magnetic properties of Sr?Ir?Sn??

    DOE PAGESBeta

    Biswas, P. K. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Wang, Kefeng [Brookhaven National Lab. (BNL), Upton, NY (United States); Amato, A. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Khasanov, R. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Luetkens, H. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Petrovic, C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Cook, R. M. [Univ. of Warwick, Coventry (United Kingdom); Lees, M. R. [Univ. of Warwick, Coventry (United Kingdom); Morenzoni, E. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    2014-10-01

    Magnetization and muon spin relaxation or rotation (µSR) measurements have been performed to study the superconducting and magnetic properties of Sr?Ir?Sn??. From magnetization measurements the lower and upper critical fields of Sr?Ir?Sn?? are found to be 81(1) Oe and 14.4(2) kOe, respectively. Zero-field µSR data show no sign of any magnetic ordering or weak magnetism in Sr?Ir?Sn??. Transverse-field µSR measurements in the vortex state provided the temperature dependence of the magnetic penetration depth ?. The dependence of ??² with temperature is consistent with the existence of single s-wave energy gap in the superconducting state of Sr?Ir?Sn?? with a gap value of 0.82(2) meV at absolute zero temperature. The magnetic penetration depth at zero temperature ?(0) is 291(3) nm. The ratio ?(0)/kBTc = 2.1(1) indicates that Sr?Ir?Sn?? should be considered as a strong-coupling superconductor.

  8. A superconducting thrust-bearing system for an energy storage flywheel

    Microsoft Academic Search

    T. A. Coombs; A. Cansiz; A. M. Campbell

    2002-01-01

    We have constructed a bearing system for an energy storage flywheel. This bearing system uses a combination of permanent magnets and superconductors in an arrangement commonly termed as an Evershed bearing. In an Evershed system there are in fact two bearings which act in concert. In our system we have one bearing constructed entirely out of permanent magnets acting in

  9. Understanding Superconducting Magnetic Energy Storage (SMES) technology, applications, and economics, for end-use workshop

    SciTech Connect

    Ferraro, R.J. [Ferraro, Oliver, and Associates, Inc., Knoxville, TN (United States); McConnell, B.W. [Oak Ridge National Lab., TN (United States)

    1993-06-01

    The overall objective of this project was to determine the state-of-the-art and to what extent existing SMES is a viable option in meeting the needs of utilities and their customers for improving electric service power quality. By defining and analyzing SMES electrical/mechanical performance characteristics, and comparing SMES application benefits with competitive stored energy systems, industry will be able to determine SMES unique applications and potential market penetration. Building on this information base, it would also be possible to evaluate the impact of high temperature superconductors (77 K and 20-35 K) on SMES technology applications. The authors of this report constructed a network of industry contacts and research consultants that were used to collect, update, and analyze ongoing SMES R&D and marketing activities in industries, utilities, and equipment manufacturers. These key resources were utilized to assemble performance characteristics on existing SMES, battery, capacitor, flywheel, and high temperature superconductor (HTS) stored energy technologies. From this information, preliminary stored energy system comparisons were accomplished. In this way, the electric load needs would be readily comparable to the potential solutions and applications offered by each aforementioned energy storage technology.

  10. Rotochemical heating of millisecond and classical pulsars with anisotropic and density-dependent superfluid gap models

    NASA Astrophysics Data System (ADS)

    González-Jiménez, Nicolás; Petrovich, Cristobal; Reisenegger, Andreas

    2015-03-01

    When a rotating neutron star loses angular momentum, the progressive reduction of the centrifugal force makes it contract. This perturbs each fluid element, raising the local pressure and originating deviations from beta equilibrium, inducing reactions that release heat (`rotochemical heating'). This effect has previously been studied by Fernández & Reisenegger for non-superfluid neutron stars and by Petrovich & Reisenegger for superfluid millisecond pulsars. Both studies found that pulsars reach a quasi-steady state in which the compression driving the matter out of beta equilibrium is balanced by the reactions trying to restore the equilibrium. We extend previous studies by considering the effect of density-dependence and anisotropy of the superfluid energy gaps, for the case in which the dominant reactions are the modified Urca processes, the protons are non-superconducting, and the neutron superfluidity is parametrized by models proposed in the literature. By comparing our predictions with the surface temperature of the millisecond pulsar PSR J0437-4715 and upper limits for 21 classical pulsars, we find the millisecond pulsar can be only explained by the models with the effectively largest energy gaps (type B models), the classical pulsars require with the gap models that vanish for some angle (type C) and two different envelope compositions. Thus, no single model for neutron superfluidity can simultaneously account for the thermal emission of all available observations of non-accreting neutron stars, possibly due to our neglect of proton superconductivity.

  11. Uncertainties in Gapped Graphene

    E-print Network

    Eylee Jung; Kwang S. Kim; DaeKil Park

    2012-03-20

    Motivated by graphene-based quantum computer we examine the time-dependence of the position-momentum and position-velocity uncertainties in the monolayer gapped graphene. The effect of the energy gap to the uncertainties is shown to appear via the Compton-like wavelength $\\lambda_c$. The uncertainties in the graphene are mainly contributed by two phenomena, spreading and zitterbewegung. While the former determines the uncertainties in the long-range of time, the latter gives the highly oscillation to the uncertainties in the short-range of time. The uncertainties in the graphene are compared with the corresponding values for the usual free Hamiltonian $\\hat{H}_{free} = (p_1^2 + p_2^2) / 2 M$. It is shown that the uncertainties can be under control within the quantum mechanical law if one can choose the gap parameter $\\lambda_c$ freely.

  12. Effects of alloying and magnetic field on the stability of the energy gaps in the compounds CeNiSn and CeRhSb

    NASA Astrophysics Data System (ADS)

    Adroja, D. T.; Rainford, B. D.

    1994-08-01

    CeRhSb and CeNiSn are valence fluctuating compounds which develop energy gaps in the electronic density of states at the Fermi level at temperatures below 10 K. Electrical transport and magnetic measurements on the alloys Ce 1- xLa xRhSb, CeRh 1- xPd xSb, Ce 1- xR xNiSn (R = La, Y) and CeNi 1- xT xSn (T = Pd, P t) have been used to compare and contrast the effects of alloying and lattice coherence in these two compounds. Magnetoresistance measurements show that the gaps decrease with increasing applied magnetic fields up to 12 T. Disruption of the Ce lattice coherence by alloying with La or Y rapidly eliminates the energy gaps. The substitution of 15% Pd for Rh in CeRhSb, and of 15% Pd and Pt for Ni in CeNiSn also suppresses the low temperature gap and drives the systems into a Kondo lattice regime. The resistivity of CeRh 0.85Pd 0.15Sb shows the presence of Kondo and crystalline field effects. The magnetic susceptibility results for CeRhSb, Ce 0.8La 0.2RhSb and Ce 0.8La 0.2NiSn have been analyzed on the basis of the Coqblin-Schrieffer model.

  13. Superconductivity of Ba1-xKxFe2As2 with and without artificial disorder over the entire doping range

    NASA Astrophysics Data System (ADS)

    Teknowijoyo, Serafim; Cho, Kyuil; Tanatar, Makariy A.; Prozorov, Ruslan; Liu, Yong; Lograsso, Thomas; Konczykowski, Marcin

    2015-03-01

    Effects of electron irradiation on superconducting transition temperature and in-plane London penetration depth were studied in single crystals of Ba1-xKxFe2As2 (x= 0.22, 0.34, 0.47, 0.56, 0.65, 0.80, 0.82, 0. 90, 0.92, 1.0). Electron irradiation introduces point - like disorder that gives insight into the superconducting gap structure by studying the effects of increasing scattering. We studied the entire superconducting ``dome'' and find distinctly different behaviours in underdoped, optimal, and overdoped compositions and unusual behaviour near x = 0.7 - 0.8. This work was supported by the Department of Energy Office of Science, Basic Energy Sciences under Contract No. DE-AC02-O7CH11358.

  14. Molecular viewpoint on high-temperature superconductivity Importance of orbital degeneracy

    NASA Astrophysics Data System (ADS)

    Mestechkin, M.; Whyman, G.; Klimko, G.

    It is shown that the antisymmetrized geminal power wavefunction (AGP) in the macroscopic limit and the Bardeen-Cooper-Schrieffer (BCS) supercon-ductivity model with fixed mean number of electrons coincide to arbitrary order in deviations from the extreme-type function which is considered as the carrier of the superconductivity property. Variational equations for the AGP in the macroscopic limit are formulated in terms of two sets of parameters, ?i and ?i, which under simplifying assumptions reduce to eigenvalues of the open-shell Roothaan one-electron Hamiltonian and to the BCS energy gap parameter, respectively. The superconducting state is shown to be stable for the solution of these equations with a macroscopic number of non-zero ?i and of degenerate ?i=?F at the Fermi level ?F. The macroscopic contribution to the maximal pair occupation number which is responsible for the superconductivity is expressed as a mean value of ?i2/[(?i-?F)2+?i2]. The formulated non-zero temperature version of the equations for ?i, ?i is able to describe the superconducting phase transition. On this ground the necessary condition of stabilization of the superconducting state is formulated that is the existence of the macroscopic-fold near-degenerate and almost half-filled level. As is shown it is realized in the energy band structure of doped fullerides, copper oxide ceramics and perovskite-type crystals, e.g. BaBiO3. The additional requirement of negativity of exchange interelectron-interaction integrals may be satisfied not only by the known vibronic mechanism but also, as is demonstrated, by the polarization potential of an environment in a plane layer of stratum structures.

  15. The 30 MJ superconducting magnetic energy storage for BPA transmission line stabilizer

    NASA Astrophysics Data System (ADS)

    Rogers, J. D.

    1982-12-01

    The stability of the Western U.S. Power System is affected by the relative weakness of the electric transmission system connecting the Pacific Northwest and southern California. A 30 MJ (8.4 kWh) superconnecting magnetic energy storage unit with a 10 MW converter to provide system damping for low frequency oscillations is being installed to provide system damping for low frequency oscillations. The seismic mounting of the 30 MJ coil to the dewar lid is complete. Computer operation of the heat rejection trailer, high pressure gas recovery trailer, and converter is accomplished. The converter was operated with an inductive load with energy discharge through the protective dump circuit. Partial computer operation of the refrigerator was performed. The nonconducting dewar was built and tested.

  16. First-principles prediction of superconductivity in LiBSi1-xAlx

    NASA Astrophysics Data System (ADS)

    Miao, Rende; Yang, Jun; Bai, Zhong; Can, Dan; Zhang, Xi; Jiang, Min; Liu, Cuicui; Wu, Fangping; Ma, Shuyun

    2015-02-01

    Electronic structure, lattice dynamics and superconducting properties for theoretically devised superconductor LiBSi1-x Alx are obtained by first-principles calculations. We assume that Lithium Boron Silicon (LiBSi) has the same crystal structure as that of Lithium borocarbide (LiBC). The pristine LiBSi is predicted to be a zero-gap semiconductor. Hole doping of LiBSi through partial substitution of Si by SiAl atoms can produce a semiconductor-metal transition and develop superconductivity. To assess the thermodynamic stability of LiBSi1-xAlx, the formation energies are calculated using the supercell method. For LiBSi0.75 Al0.25 and LiBSi0.875Al0.125, the obtained formation energies are -5.9 and -6.1 eV, respectively, indicating that LiBSi1-xAlx is energetically favorable at least in the range of 0 ? x ? 0.25. Phonon spectra and superconducting properties are obtained within the virtual-crystal approximation (VCA) treatment. The results show that LiBSi1-xAlx is dynamically stable approximately in the range of 0 ? x ? 0.35. For LiBSi0.8Al0.2, the obtained electron-phonon coupling constant ? is 0.86 and superconducting transition temperature TC is predicted to be in the range of 11-13 K (0.14 ? ?* ? 0.1).

  17. Modulating Sub-THz Radiation with Current in Superconducting Metamaterial V. Savinov,1,* V. A. Fedotov,1

    E-print Network

    Gruner, Daniel S.

    Modulating Sub-THz Radiation with Current in Superconducting Metamaterial V. Savinov,1,* V. A at frequencies below the superconducting gap in the THz and subterahertz bands. DOI: 10.1103/PhysRevLett.109 show how superconducting metamaterials can be used to create agile radiation modu- lators in the THz

  18. Air force applications of lightweight superconducting machinery

    Microsoft Academic Search

    C. Oberly

    1977-01-01

    The U.S. Air Force has actively developed superconductor technology since 1961. Early Air Force involvement was disappointing due to the primitive technological state of superconductivity in the mid- 1960's. Following the successful application of stability theories, programs in the areas of superconducting alternators, magnetohydrodynamic (MHD) generator coils and inductive energy storage coils have been productive. The universal Air Force requirement

  19. Superconductivity in the surface states of a Bi2X3 topological insulator: effects of a realistic model

    NASA Astrophysics Data System (ADS)

    Hao, Lei; Wang, Jun

    2015-06-01

    Superconductivity in the topological surface states is essential to both the surface spectrum of bulk superconducting state and the proximity-induced superconductivity of \\text{B}{{\\text{i}}2}{{\\text{X}}3} (X is Se or Te) topological insulators. While previous theories were mostly based on simplified models for the bulk topological insulator and the surface states, the accumulating experiments stimulate us to make an analysis using realistic model for the normal state electronic structures, incorporating terms responsible for particle–hole asymmetry and hexagonal warping. An effective low-energy model for the topological surface states is derived first. Then we identify all the bulk time-reversal-invariant superconducting pairings in the topological insulator that can open a gap in the topological surface states. Many more pairings are found to be able to gap the topological surface states as compared to conclusions based on simplified models. The number of proximity-induced pairing channels in the topological surface states increases by one as a result of the hexagonal warping term, but is not changed by the particle–hole asymmetry term.

  20. Advanced superconducting power conditioning system with SMES for effective use of renewable energy

    NASA Astrophysics Data System (ADS)

    Hamajima, T.; Tsuda, M.; Miyagi, D.; Amata, H.; Iwasaki, T.; Son, K.; Atomura, N.; Shintomi, T.; Makida, Y.; Takao, T.; Munakata, K.; Kajiwara, M.

    Since it is an urgent issue to reduce the global Carbon-dioxide in the world, renewable energy should be supplied as a large amount of the electric power. However, if a large amount of fluctuating renewable energy becomes more than adjustable amount of a utility grid capacity, instabilities such as frequency deviation might occur. We propose a system that is composed of SMES and FC-H2-Electrolyzer and also installed adjacent to Liquid Hydrogen station to cool down the SMES. Since the SMES has potentials of quick response and large I/O power, and Fuel Cell has potentials of slow response and steady power supplied from a large amount of hydrogen, we combine both storage devices and apply them to suppress the fluctuating power. We convert the fluctuating power to the constant power by using a developed prediction technology of Kalman filter to predict a trend of the fluctuating power. While the trend power should be supplied by FC or absorbed by the electrolyzer to produce hydrogen, the power difference between the renewable power and the trend power should be stored by the SMES. We simulate the power balance and analyze the required SMES capacity, design the concept of the SMES, and propose an operation algorithm for the SMES to estimate the electric efficiency of the system. It is found that the electric efficiency of the ASPCS can become greater than that of a pumped hydro-machine.

  1. Determination of the first satellite valley energy in the conduction band of wurtzite GaN by near-band-gap photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Piccardo, Marco; Martinelli, Lucio; Iveland, Justin; Young, Nathan; DenBaars, Steven P.; Nakamura, Shuji; Speck, James S.; Weisbuch, Claude; Peretti, Jacques

    2014-06-01

    The position of the first satellite valley in wurtzite GaN is directly determined by near-band-gap photoemission spectroscopy of p-doped GaN activated to negative electron affinity. The photoemission spectra exhibit two structures, with fixed energy position, which originate from electrons accumulated in the conduction band valleys of the bulk material. We assigned the two observed features respectively to ? and L valleys and obtain an intervalley energy separation of 0.90±0.08 eV, well below the theoretical values of the lowest subsidiary valley energy provided by ab initio calculations.

  2. Ground-state energy and spin gap of spin-(1)/(2) Kagomé-Heisenberg antiferromagnetic clusters: Large-scale exact diagonalization results

    NASA Astrophysics Data System (ADS)

    Läuchli, Andreas M.; Sudan, Julien; Sørensen, Erik S.

    2011-06-01

    We present a comprehensive list of the ground-state energies and the spin gaps of finite Kagomé clusters with up to 42 spins obtained using large-scale exact diagonalization techniques. This represents the current limit of this exact approach. For a fixed number of spins N, we study several cluster shapes under periodic boundary conditions in both directions resulting in a toroidal geometry. The clusters are characterized by their side length and diagonal as well as the shortest “Manhattan” diameter of the torii. A finite-size scaling analysis of the ground-state energy as well as the spin gap is then performed in terms of the shortest toroidal diameter as well as the shortest “Manhattan” diameter. The structure of the spin-spin correlations further supports the importance of short loops wrapping around the torii.

  3. A 0.5 kWh flywheel energy storage system using a high-Tc superconducting magnetic bearing

    Microsoft Academic Search

    Y. Miyagawa; H. Kameno; R. Takahata; H. Ueyama

    1999-01-01

    A flywheel rotor having a main shaft, two flywheel disks and one permanent magnet for a SMB (superconducting magnetic bearing) was designed and manufactured. The flywheel was made of CFRP material which is light weight and has high tensile strength. The permanent magnet was hooped by CPRP in order to prevent centrifugal bursting. The rotor was levitated by a SMB

  4. A comparative study of suppression of the energy gap with La substitution in the Kondo insulators: CeNiSn and CeRhSb

    Microsoft Academic Search

    D. T. Adroja; B. D. Rainford; A. J. Neville; P. Mandal; A. G. M. Jansen

    1996-01-01

    We report structural, transport and magnetic measurements on the solid solutions of Ce1?xLaxNiSn and Ce1?xLaxRhSb (x = 0 to 1). The results have been used to compare and contrast the effect of La substitution on the ground state properties of the Kondo insulators CeNiSn and CeRhSb. The resistivity measurements reveal that the energy gap in CeNiSn and CeRhSb decreases with

  5. A comparative study of suppression of the energy gap with La substitution in the Kondo insulators: CeNiSn and CeRhSb

    Microsoft Academic Search

    D. T. Adroja; B. D. Rainford; A. J. Neville; P. Mandal; A. G. M. Jansen

    1996-01-01

    We report structural, transport acid magnetic measurements on the solid solutions of Ce1-xLaxNiSn and Ce1-xLaxRhSb (x = 0 to 1). The results have been used to compare and contrast the effect of La substitution on the ground state properties of the Kondo insulators CeNiSn and CeRhSb. The resistivity measurements reveal that the energy gap in CeNiSn and CeRhSb decreases with

  6. Significant reduction in NiO band gap upon formation of Lix Ni1-x O alloys: applications to solar energy conversion.

    PubMed

    Alidoust, Nima; Toroker, Maytal Caspary; Keith, John A; Carter, Emily A

    2014-01-01

    Long-term sustainable solar energy conversion relies on identifying economical and versatile semiconductor materials with appropriate band structures for photovoltaic and photocatalytic applications (e.g., band gaps of ? 1.5-2.0 eV). Nickel oxide (NiO) is an inexpensive yet highly promising candidate. Its charge-transfer character may lead to longer carrier lifetimes needed for higher efficiencies, and its conduction band edge is suitable for driving hydrogen evolution via water-splitting. However, NiO's large band gap (? 4 eV) severely limits its use in practical applications. Our first-principles quantum mechanics calculations show band gaps dramatically decrease to ? 2.0 eV when NiO is alloyed with Li2O. We show that Lix Ni1-x O alloys (with x=0.125 and 0.25) are p-type semiconductors, contain states with no impurity levels in the gap and maintain NiO's desirable charge-transfer character. Lastly, we show that the alloys have potential for photoelectrochemical applications, with band edges well-placed for photocatalytic hydrogen production and CO2 reduction, as well as in tandem dye-sensitized solar cells as a photocathode. PMID:24265209

  7. Significant Reduction in NiO Band Gap upon Formation of LixNi1?xO Alloys: Applications to Solar Energy Conversion

    SciTech Connect

    Alidoust, Nima; Toroker, Maytal; Keith, John A.; Carter, Emily A.

    2014-01-01

    Long-term sustainable solar energy conversion relies on identifying economical and versatile semiconductor materials with appropriate band structures for photovoltaic and photocatalytic applications (e.g., band gaps of ?1.5–2.0 eV). Nickel oxide (NiO) is an inexpensive yet highly promising candidate. Its charge-transfer character may lead to longer carrier lifetimes needed for higher efficiencies, and its conduction band edge is suitable for driving hydrogen evolution via water-splitting. However, NiO’s large band gap (?4 eV) severely limits its use in practical applications. Our first-principles quantum mechanics calculations show band gaps dramatically decrease to ?2.0 eV when NiO is alloyed with Li2O. We show that LixNi1?xO alloys (with x=0.125 and 0.25) are p-type semiconductors, contain states with no impurity levels in the gap and maintain NiO’s desirable charge-transfer character. Lastly, we show that the alloys have potential for photoelectrochemical applications, with band edges well-placed for photocatalytic hydrogen production and CO2 reduction, as well as in tandem dye-sensitized solar cells as a photocathode.

  8. Superconducting states in graphene

    NASA Astrophysics Data System (ADS)

    Uchoa, Bruno

    2013-03-01

    In spite of the remarkable electronic properties of graphene, which include the existence of massless Dirac quasiparticles, the low density of states near the Dirac points seems to conspire against the formation of new many body ground states. In this context, the search for intriscic superconductivity in graphene has involved either combining graphene with other materials, or else exploring ways to modify the electronic density of states at the Fermi level. In this talk, after discussing the classification of symmetry states in the honeycomb lattice and analysing the general thermodynamic properties for Dirac fermion superconductors, I will describe a few promissing mechanisms to induce superconductivity in graphene. In particular, I will show that in the situation where strain effects lead to a reconstruction of the vacuum into a discrete spectrum of Landau levels due to pseudo magnetic fields, which preserve overall time reversal symmetry, superconductivity is quantum critical at integer filling of the Landau levels, when the system is incompressible. At partial filling, the quenching of the kinetic energy due to the Landau levels leads to a crossover to a non-Fermi liquid regime, where the critical temperature scales linearly with the coupling in the weak coupling limit. I will show that the critical temperature can be orders of magnitude larger than in conventional weak coupling superconductors, and may be triggered by phonons.

  9. Self-consistent Eliashberg theory and the gap function in electron-doped cuprates

    NASA Astrophysics Data System (ADS)

    Dhokarh, Dhananjay

    In this thesis, I consider normal state properties, the pairing instability temperature, and the structure of the pairing gap in electron-doped cuprates. I assume that the pairing is mediated by collective spin excitations, with antiferromagnetism emerging with the appearance of hot spots. I use a low-energy spin-fermion model and Eliashberg theory up to two-loop order. I justify ignoring vertex corrections by extending the model to N >> 1 fermionic flavors, with 1/N playing the role of a small Eliashberg parameter. I argue, however, that it is still necessary to solve coupled integral equations for the frequency dependent fermionic and bosonic self-energies, both in the normal and superconducting state. Using the solution of the coupled equations, I find an onset of d-wave pairing at Tc ˜ 30 K, roughly three times larger than the one obtained previously [P. Krotkov and A. Chubukov, Phys. Rev. B 74, 014509 (2006)], where it was assumed that the equations for fermionic and bosonic self-energies decouple in the normal state. To obtain the momentum and frequency dependent d-wave superconducting gap, ?( k?F , ?n), I derive and solve the non-linear gap equation together with the modified equation for the bosonic self energy which below Tc also depends on ?( k?F , ?n). I find that ?( k?F , ?n) is a non-monotonic function of momentum along the Fermi surface, with its node along the zone diagonal and its maximum some distance away from it. I obtain 2?max( T ? 0)/Tc ˜ 4. I argue that the value of Tc, the non-monotonicity of the gap, and 2?max/Tc ratio are all in good agreement with the experimental data on electron-doped cuprates.

  10. Band-gap energy of heteropoly compounds containing Keggin polyanion-[PVxMo12-xO40]-(3+x) relates to counter-cations and temperature studied by UV-VIS diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Sasca, Viorel; Popa, Alexandru

    2013-10-01

    The band gap energy (absorption edge energies) of the pure H3[PMo12O40].13H2O and H4[PVMo11O40].13H2O, respectively, supported on SiO2 and SiC and some of its NH4+ and Cs+ salts were determined by different methods. The influence of the counter-cations and the temperature on band gap energy was studied. In this purpose, the diffuse reflectance spectra of above mentioned compounds were registered at different temperatures, and it were transposed in the curves of the Kubelka-Munk function vs. wavelength. The band gap energies were determined by processing of low field energy of the ligand-metal charge transfer band (O2- ? Mo6+ and O2- ? V5+) usually observed between 200 and 400 nm on these curves. In this aim, the Tauc's relation was adapted for Kubelka-Munk function use and it was plotted for n = 1/2 (direct transition) and 2 (indirect transition) vs. wave energy (photon energy). The intersection of the curves' tangent drawn to their point of inflection with horizontal axis gives the band gap energy. The other method for calculation of band gap energy was the differential calculus on the Kubelka-Munk function vs. wave energy curve where the x value corresponding to curves' maximum is the found value. The comparison between experimental band gap values and literature data showed their partial fit. The higher temperature produces the band gap energy diminution as a result of a stronger interaction between Keggin Units, which occurs especially by the crystallization water loss. The Keggin Units isolation one from another by voluminous counter-ion or their spreading on a support leads to a weaker interaction between them and as a consequence, the increasing of absorption edge energy. A linear correlation of the crystallites size with band gap energy was observed.

  11. Argonne is a partner in the Argonne-Northwestern Solar Energy Research Center led by Northwestern University. Argonne is a partner in the Center for Emergent Superconductivity led by Brookhaven National Laboratory.

    E-print Network

    Kemner, Ken

    Argonne is a partner in the Argonne-Northwestern Solar Energy Research Center led by Northwestern University. Argonne is a partner in the Center for Emergent Superconductivity led by Brookhaven National Conductivity (CES) W. Kwok (MSD) Argonne-Northwestern Solar Energy Research (ANSER) M. Pellin (MSD) #12;

  12. Pairing gaps near ferromagnetic quantum critical points

    NASA Astrophysics Data System (ADS)

    Einenkel, M.; Meier, H.; Pépin, C.; Efetov, K. B.

    2015-02-01

    We address the quantum-critical behavior of two-dimensional itinerant ferromagnetic systems described by spin-fermion models in which fermions interact with close-to-critical bosonic modes. We consider Heisenberg ferromagnets, Ising ferromagnets, and the Ising nematic transition. Mean-field theory close to the quantum critical point predicts a superconducting gap with spin-triplet symmetry for the ferromagnetic systems and a singlet gap for the nematic scenario. Studying fluctuations in this ordered phase using a nonlinear sigma model, we find that these fluctuations are not suppressed by any small parameter. As a result, we find that a superconducting quasi-long-range order is still possible in the Ising-like models but long-range order is destroyed in Heisenberg ferromagnets.

  13. Superconductivity in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Maiti, Saurabh

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

  14. Designing focusing solenoids for superconducting RF accelerators

    SciTech Connect

    Davis, G.; Kashikhin, V.V.; Page, T.; Terechkine, I.; Tompkins, J.; Wokas, T.; /Fermilab

    2006-08-01

    The design of a focusing solenoid for use in a superconducting RF linac requires resolving a range of problems with conflicting requirements. Providing the required focusing strength contradicts the goal of minimizing the stray field on the surfaces of adjacent superconducting RF cavities. The requirement of a compact solenoid, able to fit into a gap between cavities, contradicts the need of mechanical support necessary to restrain electromagnetic forces that can result in coil motion and subsequent quenching. In this report we will attempt to address these and other issues arising during the development of focusing solenoids. Some relevant test data will also be presented.

  15. Visualizing nodal superconductivity and heavy fermion formation in CeCoIn5

    NASA Astrophysics Data System (ADS)

    Zhou, Brian

    2014-03-01

    In solids containing elements with f - orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy excitations with heavy effective mass. Previously, we used the scanning tunneling microscope (STM) to visualize the scattering of quasiparticles and detect their mass enhancement with the lowering of temperature in the prototypical Ce-115 heavy fermion family. Tunneling into different surface terminations revealed the composite nature of these heavy excitations, arising from the entanglement of conduction and f electrons. Here, by extending our techniques to milli-Kelvin temperature and high magnetic field, we first observe a spectroscopic pseudogap in the tunneling density of states of the heavy quasiparticles both prior to superconductivity and also above the critical field, indicating the development of further correlations from which the unconventional superconducting state arises. Quasiparticle interference (QPI) measurements in the superconducting and normal states demonstrate the onset of strong particle-hole asymmetry in the superconducting state, dissimilar from previous STM QPI studies of gap symmetry. Nevertheless, we can directly pinpoint the d-wave nature of Cooper pairing through visualizing the spatial symmetry of quasi-particle bound states in the vicinity of atomic scale defects. Work done in the collaboration with R. E. Baumbach, J. D. Thompson, E. D. Bauer, and A. Yazdani. Primary financial support from DOE-BES.

  16. Bridging the gap by shaking superfluid matter

    E-print Network

    Mark G. Alford; Sanjay Reddy; Kai Schwenzer

    2011-10-27

    In cold compact stars, Cooper pairing between fermions in dense matter leads to the formation of a gap in their excitation spectrum and typically exponentially suppresses transport properties. However, we show here that weak Urca reactions become strongly enhanced and approach their ungapped level when the star undergoes density oscillations of sufficiently large amplitude. We study both the neutrino emissivity and the bulk viscosity due to direct Urca processes in hadronic, hyperonic and quark matter and discuss different superfluid and superconducting pairing patterns.

  17. PUBLISHED ONLINE: 22 SEPTEMBER 2013 | DOI: 10.1038/NPHYS2762 A large-energy-gap oxide topological insulator

    E-print Network

    Loss, Daniel

    topological insulator based on the superconductor BaBiO3 Binghai Yan1,2,3 *, Martin Jansen1 and Claudia Felser1,3 Topological insulators are a new class of quantum materials that are characterized by robust topological surface states (TSSs) inside the bulk insulating gap1,2 , which hold great po- tential

  18. Superconductivity in oxygen doped iron telluride by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zheng, Mao

    Iron base superconductor have gained much attention in the research community. They offer great potentials to improve our understanding of the subject of superconductivity by having another family of high temperature superconductors to compare and contrast to the cuprates. Practically, the iron based superconductors seems to be even better candidates for applications in power generation and power transmission. Iron telluride is regarded as the parent compound of the "11" family, the family of iron chalcogenide that has the simplest structure. Iron telluride itself is not a superconductor, by can become one when doped with oxygen. In this investigation, we developed the growth recipe of thin film iron telluride by Molecular Beam Epitaxy (MBE). We found the growth to be self-regulated, similar to that of GaAs. The initial layers of growth seem to experience a spontaneous crystallization, as the film quickly go from the initial polycrystalline phase to highly crystalline in just a few unit cells. We studied oxygen doping to the iron telluride thin films and the resultant superconductivity. We characterized the sample with AFM, XRD, transport, and STEM-EELS, and we found that interfacial strain is not an essential ingredient of superconductivity in this particular case. We investigated the doping conditions for two candidate oxygen doping modes: substitution and interstitial. We found that substitution occurs when the film grown in oxygen, while interstitial oxygen is primarily incorporated during annealing after growth. The substitutional oxygen are concentrated in small local regions where substitution is around 100%, but does not contribute to superconductivity. We estimated substitutional oxygen to be about 5%, and is the proximate cause of superconductivity. Hall experiment on our sample showed a shift of dominant carrier type from holes to electrons around 35 K, but the transition was set in motion as early as the structural phase transition around 70 K. We believe the shift is a result of enhanced mobility of electrons at low temperatures. Using the capability of MBE to make pristine and abrupt interfaces, we grow two film structures: FeTe:Ox/AlO x/Au and FeTe:Ox/Al/AlO x/Au. We explored processing recipes to fabricate these films into tunel junctions devices. FeTe:Ox/AlO x/Au type of devices turned out to be suffering from nanoshorts and exhibit point contact spectroscopy junction behaviors. We observed evolution of enhanced conduction peaks around 20mV, consistent with published literature. FeTe:Ox/Al/AlOx/Au junctions behave differently, showing a evolving energy gap around 3mV. The fact that the energy gap evolved together with the superconducting transition, and the close match of gap size to these of the other iron chalcogenide superconductors, gives evidence of proximity coupling between the iron telluride layer and the aluminum layer.

  19. Absence of a {open_quote}{open_quote}Threshold Effect{close_quote}{close_quote} in the Energy Loss of Slow Protons Traversing Large-Band-Gap Insulators

    SciTech Connect

    Eder, K.; Semrad, D.; Bauer, P. [Institut fuer Experimentalphysik, Johannes-Kepler Universitaet Linz, A-4040 Linz (Austria)] [Institut fuer Experimentalphysik, Johannes-Kepler Universitaet Linz, A-4040 Linz (Austria); Golser, R. [Institut fuer Radiumforschung und Kernphysik, Universitaet Wien, A-1090 Wien (Austria)] [Institut fuer Radiumforschung und Kernphysik, Universitaet Wien, A-1090 Wien (Austria); Maier-Komor, P. [Target Laboratory, Technical University Munich, D-85748 Garching (Germany)] [Target Laboratory, Technical University Munich, D-85748 Garching (Germany); Aumayr, F. [Institut fuer Allgemeine Physik, Technische Universitaet Wien, A-1040 Wien (Austria)] [Institut fuer Allgemeine Physik, Technische Universitaet Wien, A-1040 Wien (Austria); Penalba, M. [Departamento de Fisica Aplicada I, E.T.S.I.I. y T., Universidad del Pais Vasco, Bilbao (Spain)] [Departamento de Fisica Aplicada I, E.T.S.I.I. y T., Universidad del Pais Vasco, Bilbao (Spain); Arnau, A.; Ugalde, J.M.; Echenique, P.M. [Departamento de Fisica de Materiales, Universidad del Pais Vasco, Apartado 1072, San Sebastian 20080 (Spain)] [Departamento de Fisica de Materiales, Universidad del Pais Vasco, Apartado 1072, San Sebastian 20080 (Spain)

    1997-11-01

    The electronic stopping cross section {var_epsilon} of slow hydrogen projectiles in large-band-gap insulators has been measured at energies of a few keV. Even at velocities as low as v{sub 0}/3 (v{sub 0}=c/137) , we find no influence of the band gap on the velocity dependence of {var_epsilon} , contrary to the case of gaseous targets with similar minimum excitation energy. The magnitude of {var_epsilon} and its essentially linear velocity dependence allow us to arrive at the following conclusion: Electron promotion processes contribute substantially to stopping due to formation of molecular orbitals. This points towards the existence of a bound electron state at a proton that moves slowly in an insulator. A simple model based on the calculation of molecular orbital correlation diagrams for the H/LiF collision system supports the idea of local reduction of the band gap of an insulating target. {copyright} {ital 1997} {ital The American Physical Society}

  20. Cryogenic design and test results of 30-m flexible hybrid energy transfer line with liquid hydrogen and superconducting MgB2 cable

    NASA Astrophysics Data System (ADS)

    Kostyuk, V. V.; Blagov, E. V.; Antyukhov, I. V.; Firsov, V. P.; Vysotsky, V. S.; Nosov, A. A.; Fetisov, S. S.; Zanegin, S. Yu.; Svalov, G. G.; Rachuk, V. S.; Katorgin, B. I.

    2015-03-01

    In this paper we present the development of a new hybrid energy transfer line with 30 m length. The line is essentially a flexible 30 m hydrogen cryostat that has three sections with different types of thermal insulation in each section: simple vacuum superinsulation, vacuum superinsulation with liquid nitrogen precooling and active evaporating cryostatting (AEC) system. We performed thermo-hydraulic tests of the cryostat to compare three thermo-insulating methods. The tests were made at temperatures from 20 to 26 K, hydrogen flow from 70 to 450 g/s and pressure from 0.25 to 0.5 MPa. It was found that AEC thermal insulation was the most effective in reducing heat transfer from room temperature to liquid hydrogen in ?10 m section of the cryostat, indicating that it can be used for long superconducting power cables. High voltage current leads were developed as well. The current leads and superconducting MgB2 cable passed high voltage DC test up to 50 kV DC. Critical current of the cable at ?21 K was 3500 A. It means that the 30 m hybrid energy system developed is able to deliver ?50-60 MW of chemical power and ?50-75 MW of electrical power, i.e. up to ?135 MW in total.

  1. Field-Angle-Dependent Low-Energy Excitations around a Vortex in the Superconducting Topological Insulator CuxBi2Se3

    NASA Astrophysics Data System (ADS)

    Nagai, Yuki

    2014-06-01

    We study the quasiparticle excitations around a single vortex in the superconducting topological insulator CuxBi2Se3, focusing on a superconducting state with point nodes. Inspired by the recent Knight shift measurements, we propose two ways to detect the positions of point nodes, using an explicit formula of the density of states with Kramer–Pesch approximation in the quasiclassical treatment. The zero-energy local density of states around a vortex parallel to the c-axis has a twofold shape and splits along the nodal direction with increasing energy; these behaviors can be detected by the scanning tunneling microscopy. An angular dependence of the density of states with a rotating magnetic field on the a–b plane has deep minima when the magnetic field is parallel to the directions of point nodes, which can be detected by angular-resolved heat capacity and thermal conductivity measurements. All the theoretical predictions are detectable via standard experimental techniques in magnetic fields.

  2. GAP FILLING CERAMIC INSULATING PUTTY FOR HIGH FIELD MAGNETS

    SciTech Connect

    Rice, J. A.; Rice, H. M. [MultiPhase Composites, LLC Longmont, CO, 80501 (United States)

    2008-03-03

    Gaps between the A15 superconducting cable and its supports can sometimes occur requiring expensive rework of the support or filling with a non-optimal material. Recently, a new ceramic putty has been developed that can fill these gaps to fully support the superconducting cable. This ceramic material can withstand the extreme temperature differences between the high temperature heat treatment and the cryogenic operation. Significant performance improvements have been made that will enable the insulating putty to be used in some accelerator magnet systems. Processing methods will be discussed as well as strength and thermal data.

  3. computational group theory with GAP 1 GAP in Sage

    E-print Network

    Verschelde, Jan

    computational group theory with GAP 1 GAP in Sage the GAP system combinatorics and list 2013 1 / 44 #12;computational group theory with GAP 1 GAP in Sage the GAP system combinatorics and list explicitly in Sage via 1 the class Gap, do help(gap); or 2 opening a Terminal Session with GAP, type gap

  4. The temperature and magnetic effect in d-wave superconductivity with the competing antiferromagnetism

    NASA Astrophysics Data System (ADS)

    Chen, Hong-Yi

    The interplay between superconductivity and antiferromagnetism has been investigated by using a phenomenological t-t'-U-V model defined in a two dimensional lattice. The Coulomb repulsion U is responsible for the antiferromagnetism and the nearest neighbor attraction V is responsible for the d-wave pairing. The ratio of U/V determines the competition between superconductivity and an antiferromagnetic order. In intermediate U/V, superconductivity and antiferromagnetism coexist to a certain extent. At high temperatures, antiferromagnetism emerges and coexists with superconductivity. When the antiferromagnetism appears, both local density of states (LDOS) and local differential tunneling conductance (LDTC) exhibit the same charge density wave (CDW)-like modulations along the x-axis with the average periodicity of 4.8a. The LDTC at higher temperatures shows that the "gap" of the quasiparticles obtained directly from STM experiments does not correspond to the real gap of the system in cuprate superconductors. Under an applied magnetic field, LDOS maps show stripe-like modulations along the x-axis with the periodicity of 4a. At low energies, the modulation appears inside the vortex core. At vortex core states, the modulation spreads away from the vortex core. At high energies, the modulation is the same as those at vortex core states, but the intensities inside the vortex core are lower than those outside the vortex core. The superposition of the degenerate eigenfunctions that describe the stripe modulations along the x- and y-directions is able to explain the checkerboard pattern observed by STM experiments.

  5. Superconducting states study in electron-overdoped BaFe1.8Co0.2As2 using terahertz and far-infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Ahmad, D.; Min, B. H.; Seo, Y. I.; Choi, W. J.; Kimura, Shin-Ichi; Seo, Jungpil; Kwon, Yong Seung

    2015-07-01

    Terahertz and far-infrared spectroscopy in the temperature range, 4–300 K were used to study the normal and superconducting states of superconductor BaFe1.8Co0.2As2 with Tc = 22.5 K. At T < Tc, the vanishing of optical conductivity caused by the unity approach and flat behavior in reflectivity were observed below 45 cm?1. This feature indicates the formation of a superconducting energy gap due to the formation of Cooper pairs. The introduction of the two Drudes model well reproduced the normal state optical conductivity, indicating the multiband nature of this superconductor. Two superconducting energy gaps were estimated as {{? }1} = 2.90 meV and {{? }2} = 6.75 meV by the BCS model. Using the sum rule and dielectric function, the superconducting plasma frequency ({{? }p,s}) can be estimated as 5170 ± 270 cm?1, yielding that the magnetic penetration depth (?) is 3090 ± 160 Å. This material was observed to fall on the universal scaling line, Nc ? 4.4 {{? }dc}{{T}c}.

  6. 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.

  7. Picosecond laser generation of Ag-TiO2 nanoparticles with reduced energy gap by ablation in ice water and their antibacterial activities

    NASA Astrophysics Data System (ADS)

    Hamad, Abubaker; Li, Lin; Liu, Zhu; Zhong, Xiang Li; Wang, Tao

    2015-06-01

    Ag-TiO2 nanoparticles were synthesised in ice water using a picosecond laser with a 1064-nm wavelength, at a 200-kHz repetition rate, a laser pulse energy of 42-43.79 µJ, and laser fluences of 0.342-0.357 J/cm2, by ablation of solid Ag and Ti targets. The absorption spectra and size distribution of the colloidal nanoparticles were obtained by UV-Vis spectroscopy and transmission electron microscopy, respectively. The morphology and chemical composition of the nanoparticles were characterised using high-angle annular dark-field-scanning transmission electron microscope and energy-dispersive X-ray spectroscopy. The results show that the sizes of the Ag-TiO2 nanoparticles range from less than 10-130 nm, with some large particles above 130 nm, of which the predominant size is 20 nm. A significant reduction in the energy gap of TiO2 nanoparticles was obtained to 1.75 eV after the modification with Ag nanoparticles during co-ablation. The role of Ag nanoparticles in the reduction in the energy band gap of the TiO2 nanoparticles can only be seen during laser ablation in an ice environment but not in deionised water at room temperature. Furthermore, the TiO2 nanoparticles were produced in ice and deionised water under the same laser and experimental conditions; the results show that the nanoparticles in both media have the same energy gap (about 2.4 eV). The antibacterial activity of the Ag-TiO2 nanoparticles generated was then tested against E. coli bacteria under standard laboratory light conditions. The results show that the nanoparticles can effectively kill E. coli bacteria much more effectively than laser-generated TiO2 nanoparticles.

  8. Space Radiation Superconducting Shields

    NASA Astrophysics Data System (ADS)

    R-Musenich; Calvelli, V.; Farinon, S.; Burger, W. J.; Battiston, R.

    2014-05-01

    The interest on shields to protect astronauts I long term missions against GCR has recently grown and several projects have been funded. Due to their large mass, passive shields for large volume habitable modules are no longer an option and the attention is focused on the more complex, technologically challenging active systems. Among the possible solutions, the most promising is based on huge superconducting coils having a bending power sufficient to deflect out of the habitat charged particles with kinetic energy in the order of 1 GeV. Toroidal magnet systems based wound with Ti clad MgB2 conductor is proposed and described.

  9. Dual fast-cycling superconducting synchrotron at Fermilab and a possible path to the future of high energy particle physics

    SciTech Connect

    Piekarz, H.; /Fermilab

    2009-01-01

    We briefly outline shorter and longer term physics motivation for constructing a dual, fast-cycling superconducting synchrotron accelerator (DSFMR - Dual Super-Ferric Main Ring) in the Tevatron tunnel at Fermilab. We discuss using this accelerator as a high-intensity dual neutrino beam source for the long-baseline neutrino oscillation search experiments, and also as a fast, dual pre-injector accelerator for the VLHC (Very Large Hadron Collider).

  10. Design and operating experience of an ac-dc power converter for a superconducting magnetic energy storage unit

    SciTech Connect

    Boenig, H.J.; Nielsen, R.G.; Sueker, K.H.

    1984-01-01

    The design philosophy and the operating behavior of a 5.5 kA, +-2.5 kV converter, being the electrical interface between a high voltage transmission system and a 30 MJ superconducting coil, are documented in this paper. Converter short circuit tests, load tests under various control conditions, dc breaker tests for magnet current interruption, and converter failure modes are described.

  11. Dual fast-cycling superconducting synchrotron at Fermilab and a possible path to the future of high energy particle physics

    NASA Astrophysics Data System (ADS)

    Piekarz, H.

    2009-08-01

    We briefly outline shorter and longer term physics motivation for constructing a dual, fast-cycling superconducting synchrotron accelerator (DSFMR — Dual Super-Ferric Main Ring) in the Tevatron tunnel at Fermilab. We discuss using this accelerator as a high-intensity dual neutrino beam source for the long-baseline neutrino oscillation search experiments, and also as a fast, dual pre-injector accelerator for the VLHC (Very Large Hadron Collider).

  12. Dual fast-cycling superconducting synchrotron at Fermilab and a possible path to the future of high energy particle physics

    E-print Network

    Piekarz, H

    2010-01-01

    We briefly outline shorter and longer term physics motivation for constructing a dual, fast-cycling superconducting synchrotron accelerator (DSFMR - Dual Super-Ferric Main Ring) in the Tevatron tunnel at Fermilab. We discuss using this accelerator as a high-intensity dual neutrino beam source for the long-baseline neutrino oscillation search experiments, and also as a fast, dual pre-injector accelerator for the VLHC (Very Large Hadron Collider).

  13. Effects of hole doping and chemical pressure on the average superconducting kinetic energy of YBa2Cu3O7-? single crystals

    NASA Astrophysics Data System (ADS)

    Vieira, V. N.; Mendonça, A. P. A.; Dias, F. T.; da Silva, D. L.; Pureur, P.; Schaf, J.; Hneda, M. L.; Mesquita, F.

    2014-12-01

    We reported on MZFC(T) and MFCC(T) reversible dc magnetizations of YBa2Cu3O7-?, Y0.99Ca0.01Ba2Cu3O7-? and YBa1.75Sra0.25Cu3O7-? single crystals with a strong focus on the effects of Ca and Sr doping on the average superconducting kinetic energy density, k(T) of the YBa2Cu3O7-? The k(T) is used as a relevant tool to provide physical information about the HTSC paring mechanism. The determination of the k(T) from MZFC(T) and MFCC(T) data is supported by virial theorem of superconductivity [k(T) = – MB]. The MZFC(T) and MFCC(T) measurements were performed with a SQUID magnetometer to H <= 50kOe applied parallel to the c axis of the samples. The results show that the samples present a common k(T) behavior that is characterized by a maximum value for T <= Tc that gradually decreases as the temperature rises towards to the Tc, becoming null to T <= Tc. The magnetic field affects smoothly the k(T) data behavior. The k(T) results contrasting of our samples shows that the Ca and Sr doping promotes a reduction of its amplitude. A possible explanation to this feature could be associated to the fact that the hole doping character promoted by Ca doping and the chemical pressure effect motivated by Sr doping affects considerably the superconducting paring mechanism of the YBa2Cu3O7-?.

  14. Phonon self-energy effects due to superconductivity in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}

    SciTech Connect

    Martin, A.A.; Sanjurjo, J.A. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, 13083-970 Campinas, Sao Paulo (Brazil)] [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, 13083-970 Campinas, Sao Paulo (Brazil); Hewitt, K.C.; Wang, X.; Irwin, J.C. [Simon Fraser University, Department of Physics, British Columbia, V5A 1S6 (CANADA)] [Simon Fraser University, Department of Physics, British Columbia, V5A 1S6 (CANADA); Lee, M.J. [Department of Physics and Scarborough College, University of Toronto, Toronto, Ontario, M5S 1A7 (CANADA)] [Department of Physics and Scarborough College, University of Toronto, Toronto, Ontario, M5S 1A7 (CANADA)

    1997-10-01

    Raman scattering of A{sub 1g} phonons in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals ({delta}=0.13, T{sub c}=86thinspK) has been measured as a function of temperature. We report an anomalous softening in the frequency and a decrease in the linewidth of the A{sub 1g} phonon at 290thinspcm{sup {minus}1} (O{sub 1,2} c-axis in-phase vibration) below T{sub c}. We also confirm a smaller anomalous softening in the frequency of the A{sub 1g} phonon at 465thinspcm{sup {minus}1} (O{sub 3} c-axis vibration), but for this phonon mode no linewidth anomaly has been found. We compare the anomalous softening and linewidth behavior in the superconducting state with theoretical calculations for isotropic s-wave, planar d-wave, and d{sub x{sup 2}{minus}y{sup 2}} gap symmetries and as for a layered superconductor model. thinsp {copyright} {ital 1997} {ital The American Physical Society}

  15. Near-zero modes in superconducting graphene

    E-print Network

    Ghaemi, Pouyan

    Vortices in the simplest superconducting state of graphene contain very-low-energy excitations whose existence is connected to an index theorem that applies strictly to an approximate form of the relevant Bogoliubov–de ...

  16. Magnetic fluctuations and heavy electron superconductivity

    SciTech Connect

    Norman, M.R.

    1988-01-01

    A magnetic fluctuation self-energy based on neutron scattering data is used to calculate mass renormalizations, and superconducting critical temperatures and order parameters, for various heavy electron metals.

  17. [A quest for a new superconducting state

    SciTech Connect

    Collman, J.P.; Little, W.A.

    1993-12-31

    The authors report on progress of work for the past twelve months, and the work which is planned for the coming year. They have been working on the theory of the long range proximity effect discovered experimentally on Bi-Ag-Tl(2223) sandwiches during the period of the previous grant. This has led to the prediction of a novel effect which they refer to as a ``pair echo`` which occurs in these sandwiches and is analogous to the familiar ``spin echo`` seen in certain NMR experiments. Experimentally, they have extended the measurements of the proximity effect to lower temperatures and to other superconductors. They have completed high resolution studies of the thermal difference optical reflectance of the high {Tc} superconductor Tl(2223), for temperatures both above and below the transition temperature, over a photon energy range from 0.3 eV to 5.3 eV. A striking anomaly in this thermal difference spectrum has been found near 1.6 eV, which appears below {Tc} and scales in magnitude with temperature like {Delta}(T){sup 2} where {Delta}(T) is a BCS gap. This is precisely the kind of effect which they had hoped to find, based on a Holstein-like mechanism in these materials, and which they had predicted in a paper on ``Gap Modulation``. The proper interpretation of the effect observed should reveal the mechanism responsible for the superconductivity of the cuprates. They have completed a search for the, so-called Zhang-modes in the above high {Tc} superconductor, Tl(2223) over the same energy range, 0.3 eV to 5.3 eV. These modes are predicted to exist if the proper description of the ground state of the system is that of a Hubbard model.

  18. Spin fluctuation dynamics and multiband superconductivity in iron pnictides

    NASA Astrophysics Data System (ADS)

    Stanev, Valentin; Kang, Jian; Tesanovic, Zlatko

    2008-11-01

    Multiband superconductivity, involving resonant pair scattering between different bands, has emerged as a possible explanation of some of the main characteristics of the recently discovered iron pnictides. A key feature of such interband pairing mechanism is that it can generate or enhance superconductivity irrespective of whether it is attractive or repulsive. The latter case typically leads to the superconducting gap switching its sign among different sections of the Fermi surface. In iron pnictides, the natural scenario is that the gap changes sign between the hole and the electron Fermi surfaces. However, the macroscopic symmetry of such an extended s' -wave state still belongs to the general s -wave category, raising the question of how to distinguish it from an ordinary s wave. In such a quest, it is essential to use experimental techniques that have a momentum space resolution and can probe momenta of order (?,?) : the wave vector that separates the hole and the electron Fermi surfaces in the Brillouin zone. Here we study experimental signatures in the spin fluctuation dynamics of the fully gapped s - and s' -wave superconducting states, as well as those of the nodal d and p wave states. The coupling between spin fluctuations of the incipient nearly nested spin-density wave (SDW) and the Bogoliubov-de Gennes quasiparticles of the superconducting state leads to the Landau-type damping of the former. The intrinsic structure of the superconducting gap leaves a distinctive signature in the form of this damping, allowing it to be used to diagnose the nature of iron-based superconductivity in neutron scattering and other experiments sensitive to spin fluctuations in momentum space. We also discuss the coexistence between superconductivity and SDW order.

  19. Free-standing oxide superconducting articles

    DOEpatents

    Wu, Xin D. (Greenbelt, MD); Muenchausen, Ross E. (Espanola, NM)

    1993-01-01

    A substrate-free, free-standing epitaxially oriented superconductive film including a layer of a template material and a layer of a ceramic superconducting material is provided together with a method of making such a substrate-free ceramic superconductive film by coating an etchable material with a template layer, coating the template layer with a layer of a ceramic superconductive material, coating the layer of ceramic superconductive material with a protective material, removing the etchable material by an appropriate means so that the etchable material is separated from a composite structure including the template lay This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).

  20. The Nature of the Superconductivity of Tl5Te3

    NASA Astrophysics Data System (ADS)

    Arpino, Kathryn; Wallace, David; Koohpayeh, Seyed; Wen, Jiajia; Page, Katharine; Chen, Tingyong; Chien, C. L.; McQueen, Tyrel

    2013-03-01

    The search for topologically non-trivial states of matter, such as topological insulators, has sparked significant interest in the impact of spin-orbit coupling on strongly correlated electronic behaviors, such as superconductivity. The known compound Tl5Te3 exhibits a superconducting transition at Tc = 2.4 K, and contains heavy elements, making it an ideal compound in which to look for new physics at the intersection between superconductivity and strong spin-orbit coupling. In 1973, Haemmerle et al. conjectured that two-gap superconductivity might explain previous anomalous superconducting volume fractions observed in their polycrystalline samples. We have reinvestigated the superconductivity of Tl5Te3 using magnetic susceptibility, heat capacity, and point contact measurements on powder and single crystal samples, and resolved these previous discrepancies. Further, we report on long-range and local structure determination of superconducting and non-superconducting Tl5Te3 samples, as well as the relationship between structural details and the observed superconductivity.

  1. Approximate tight-binding sum rule for the superconductivity-related change of c-axis kinetic energy in multilayer cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Munzar, Dominik; Holden, Todd; Bernhard, Christian

    2003-01-01

    We present an extension of the c-axis tight-binding sum rule discussed by Chakravarty, Kee, and Abrahams [Phys. Rev. Lett. 82, 2366 (1999)] that applies to multilayer high-Tc cuprate superconductors (HTCS) and use it to estimate—from available infrared data—the change below Tc of the c-axis kinetic energy, , in YBa2Cu3O7-? (??0.45,0.25,0.07), Bi2Sr2CaCu2O8, and Bi2Sr2Ca2Cu3O10. In all these compounds decreases below Tc and except for Bi2Sr2CaCu2O8 the change of is of the same order of magnitude as the condensation energy. This observation supports the hypothesis that in multilayer HTCS superconductivity is considerably amplified by the interlayer tunneling mechanism.

  2. Energy Band Gap, Intrinsic Carrier Concentration and Fermi Level of CdTe Bulk Crystal between 304 K and 1067 K

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua

    2007-01-01

    Optical transmission measurements were performed on CdTe bulk single crystal. It was found that when a sliced and polished CdTe wafer was used, a white film started to develop when the sample was heated above 530 K and the sample became opaque. Therefore, a bulk crystal of CdTe was first grown in the window area by physical vapor transport; the optical transmission was then measured and from which the energy band gap was derived between 304 and 1067 K. The band gaps of CdTe can be fit well as a function of temperature using the Varshini expression: Eg (e V) = 1.5860 - 5.9117xl0(exp -4) T(sup 2)/(T + 160). Using the band gap data, the high temperature electron-hole equilibrium was calculated numerically by assuming the Kane's conduction band structure and a heavy-hole parabolic valance band. The calculated intrinsic carrier concentrations agree well with the experimental data reported previously. The calculated intrinsic Fermi levels between 270 and 1200 K were also presented.

  3. Optimization of the AGS superconducting helical partial snake strength.

    SciTech Connect

    Lin,F.; Huang, H.; Luccio, A.U.; Roser, T.

    2008-06-23

    Two helical partial snakes, one super-conducting (a.k.a cold snake) and one normal conducting (a.k.a warm snake), have preserved the polarization of proton beam up to 65% in the Brookhaven Alternating Gradient Synchrotron (AGS) at the extraction energy from 85% at injection. In order to overcome spin resonances, stronger partial snakes would be required. However, the stronger the partial snake, the more the stable spin direction tilted producing a stronger horizontal intrinsic resonance. The balance between increasing the spin tune gap generated by the snakes and reducing the tilted stable spin direction has to be considered to maintain the polarization. Because the magnetic field of the warm snake has to be a constant, only the cold snake with a maximum 3T magnetic field can be varied to find out the optimum snake strength. This paper presents simulation results by spin tracking with different cold snake magnetic fields. Some experimental data are also analyzed.

  4. Temperature-dependent transformation of the magnetic excitation spectrum on approaching superconductivity in Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5).

    PubMed

    Xu, Zhijun; Wen, Jinsheng; Zhao, Yang; Matsuda, Masaaki; Ku, Wei; Liu, Xuerong; Gu, Genda; Lee, D-H; Birgeneau, R J; Tranquada, J M; Xu, Guangyong

    2012-11-30

    Spin excitations are one of the top candidates for mediating electron pairing in unconventional superconductors. Their coupling to superconductivity is evident in a large number of systems, by the observation of an abrupt redistribution of magnetic spectral weight at the superconducting transition temperature, T(c), for energies comparable to the superconducting gap. Here we report inelastic neutron scattering measurements on Fe-based superconductors, Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5) that emphasize an additional signature. The overall shape of the low energy magnetic dispersion changes from two incommensurate vertical columns at T?T(c) to a distinctly different U-shaped dispersion at low temperature. Importantly, this spectral reconstruction is apparent for temperatures up to ~3T(c). If the magnetic excitations are involved in the pairing mechanism, their surprising modification on the approach to T(c) demonstrates that strong interactions are involved. PMID:23368150

  5. High-temperature superconductivity at the FeSe/SrTiO[subscript 3] interface

    E-print Network

    Wang, Fa

    In several recent experiments the superconducting gap of a single-unit-cell-thick FeSe film on SrTiO[subscript 3] substrate has been observed by scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy. ...

  6. Suppressed Critical Current in Superconducting Nanowire Single-Photon Detectors With High Fill-Factors

    E-print Network

    Yang, Joel K. W.

    In this work we present a new fabrication process that enabled the fabrication of superconducting nanowire single photon detectors SNSPD with fill-factors as high as 88% with gaps between nanowires as small as 12 nm. This ...

  7. Superconducting microfabricated ion traps

    E-print Network

    Wang, Shannon Xuanyue

    We fabricate superconducting ion traps with niobium and niobium nitride and trap single [superscript 88]Sr ions at cryogenic temperatures. The superconducting transition is verified and characterized by measuring the ...

  8. Superconducting magnet

    DOEpatents

    Satti, John A. (Naperville, IL)

    1980-01-01

    A superconducting magnet designed to produce magnetic flux densities of the order of 4 to 5 Webers per square meter is constructed by first forming a cable of a plurality of matrixed superconductor wires with each wire of the plurality insulated from each other one. The cable is shaped into a rectangular cross-section and is wound with tape in an open spiral to create cooling channels. Coils are wound in a calculated pattern in saddle shapes to produce desired fields, such as dipoles, quadrupoles, and the like. Wedges are inserted between adjacent cables as needed to maintain substantially radial placement of the long dimensions of cross sections of the cables. After winding, individual strands in each of the cables are brought out to terminals and are interconnected to place all of the strands in series and to maximize the propagation of a quench by alternating conduction from an inner layer to an outer layer and from top half to bottom half as often as possible. Individual layers are separated from others by spiraled aluminum spacers to facilitate cooling. The wound coil is wrapped with an epoxy tape that is cured by heat and then machined to an interference fit with an outer aluminum pipe which is then affixed securely to the assembled coil by heating it to make a shrink fit. In an alternate embodiment, one wire of the cable is made of copper or the like to be heated externally to propagate a quench.

  9. Effects of disorder on superconductivity of systems with coexisting itinerant electrons and local pairs

    NASA Astrophysics Data System (ADS)

    Paw?owski, G.; Micnas, R.; Robaszkiewicz, S.

    2010-02-01

    We study the influence of diagonal disorder (random site energy) of local pair (LP) site energies on the superconducting properties of a system of coexisting local pairs and itinerant electrons described by the (hardcore) boson-fermion model. Our analysis shows that the properties of such a model with s -wave pairing can be very strongly affected by the diagonal disorder in LP subsystem (the randomness of the LP site energies). This is in contrast with the conventional s -wave BCS superconductors, which according to the Anderson’s theorem are rather insensitive to the diagonal disorder (i.e., to nonmagnetic impurities). It has been found that the disorder effects depend in a crucial way on the total particle concentration n and the LP level position ?o and depending on the parameters the system can exhibit various types of superconducting behavior, including the LP-like, intermediate (MIXED), and the “BCS”-like. In the extended range of {n,?o} the superconducting ordering is suppressed by the randomness of the LP site energies and the increasing disorder induces a changeover from the MIXED-like behavior to the BCS-like one, connected with abrupt reduction in Tc and energy gap to zero. However, there also exists a definite range of {n,?o} in which the increasing disorder has a quite different effect: namely, it can substantially enhance Tc or even lead to the phenomenon which can be called disorder-induced superconductivity. Another interesting effect is a possibility of a disorder-induced bound pair formation of itinerant electrons, connected with the changeover to the LP-like regime.

  10. Optical conductivity evidence of clean-limit superconductivity in LiFeAs

    NASA Astrophysics Data System (ADS)

    Lobo, R. P. S. M.; Chanda, G.; Pronin, A. V.; Wosnitza, J.; Kasahara, S.; Shibauchi, T.; Matsuda, Y.

    2015-05-01

    We measured the optical conductivity of superconducting LiFeAs. In the superconducting state, the formation of the condensate leads to a spectral-weight loss and yields a penetration depth of 225 nm. No sharp signature of the superconducting gap is observed. This suggests that the system is likely in the clean limit. A Drude-Lorentz parametrization of the data in the normal state reveals a quasiparticle scattering rate supportive of spin fluctuations and proximity to a quantum critical point.

  11. Design and construction of a low temperature scanning tunneling microscope for studying high temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Jayasundara, Dilushan R.

    2008-10-01

    The complexities associated with high temperature superconductivity (HTS) have challenged scientists for over two decades, and as a result, the need for microscopic measurements has grown steadily. The scanning tunneling microscope's (STM) ability to image both the surface structure, and the local density of states (LDOS) with subatomic resolution has therefore made it a valuable technique to study HTS. In this thesis, I will present the design and construction of our state-of-the-art cryogenic scanning tunneling microscope, from which we were able to obtain both topographic and spectroscopic data with high spatial and energy resolution. The STM experiments on Yittrium-Bi2212, with a doping concentration close to the critical doping, revealed a checkerboard like modulations in its LDOS maps. Evaluation of these modulations for their energy dependence was carried out using Fourier transform mapping technique. We found a continuous dispersion of the modulation wave vector with energy. Whereas the dispersion was substantial at lower energies, it became continuously smaller with increasing energy. In this thesis, I will also present the STM investigation of the newly discovered pnictide superconductors. For this we studied the Co-BaFe 2As2 superconductor, which has a Tc of 22K. The cleaved surface of Co-BaFe2As2 showed a 2a0 stripe modulation along the As-As bond direction and the differential conductance spectra obtained on this surface revealed a 6meV gap opening at the Fermi energy. The Value of the BCS reduced gap and the shape of the gap reveals that the superconductivity is unconventional.

  12. Discovery of a superconducting high-entropy alloy.

    PubMed

    Koželj, P; Vrtnik, S; Jelen, A; Jazbec, S; Jagli?i?, Z; Maiti, S; Feuerbacher, M; Steurer, W; Dolinšek, J

    2014-09-01

    High-entropy alloys (HEAs) are multicomponent mixtures of elements in similar concentrations, where the high entropy of mixing can stabilize disordered solid-solution phases with simple structures like a body-centered cubic or a face-centered cubic, in competition with ordered crystalline intermetallic phases. We have synthesized an HEA with the composition Ta34Nb33Hf8Zr14Ti11 (in at.?%), which possesses an average body-centered cubic structure of lattice parameter a=3.36??Å. The measurements of the electrical resistivity, the magnetization and magnetic susceptibility, and the specific heat revealed that the Ta34Nb33Hf8Zr14Ti11 HEA is a type II superconductor with a transition temperature Tc?7.3??K, an upper critical field ?0H_c2?8.2??T, a lower critical field ?0Hc1?32??mT, and an energy gap in the electronic density of states (DOS) at the Fermi level of 2??2.2??meV. The investigated HEA is close to a BCS-type phonon-mediated superconductor in the weak electron-phonon coupling limit, classifying it as a "dirty" superconductor. We show that the lattice degrees of freedom obey Vegard's rule of mixtures, indicating completely random mixing of the elements on the HEA lattice, whereas the electronic degrees of freedom do not obey this rule even approximately so that the electronic properties of a HEA are not a "cocktail" of properties of the constituent elements. The formation of a superconducting gap contributes to the electronic stabilization of the HEA state at low temperatures, where the entropic stabilization is ineffective, but the electronic energy gain due to the superconducting transition is too small for the global stabilization of the disordered state, which remains metastable. PMID:25238377

  13. Discovery of a Superconducting High-Entropy Alloy

    NASA Astrophysics Data System (ADS)

    Koželj, P.; Vrtnik, S.; Jelen, A.; Jazbec, S.; Jagli?i?, Z.; Maiti, S.; Feuerbacher, M.; Steurer, W.; Dolinšek, J.

    2014-09-01

    High-entropy alloys (HEAs) are multicomponent mixtures of elements in similar concentrations, where the high entropy of mixing can stabilize disordered solid-solution phases with simple structures like a body-centered cubic or a face-centered cubic, in competition with ordered crystalline intermetallic phases. We have synthesized an HEA with the composition Ta34Nb33Hf8Zr14Ti11 (in at. %), which possesses an average body-centered cubic structure of lattice parameter a =3.36 Å. The measurements of the electrical resistivity, the magnetization and magnetic susceptibility, and the specific heat revealed that the Ta34Nb33Hf8Zr14Ti11 HEA is a type II superconductor with a transition temperature Tc?7.3 K, an upper critical field ?0Hc2?8.2 T, a lower critical field ?0Hc1?32 mT, and an energy gap in the electronic density of states (DOS) at the Fermi level of 2? ?2.2 meV. The investigated HEA is close to a BCS-type phonon-mediated superconductor in the weak electron-phonon coupling limit, classifying it as a "dirty" superconductor. We show that the lattice degrees of freedom obey Vegard's rule of mixtures, indicating completely random mixing of the elements on the HEA lattice, whereas the electronic degrees of freedom do not obey this rule even approximately so that the electronic properties of a HEA are not a "cocktail" of properties of the constituent elements. The formation of a superconducting gap contributes to the electronic stabilization of the HEA state at low temperatures, where the entropic stabilization is ineffective, but the electronic energy gain due to the superconducting transition is too small for the global stabilization of the disordered state, which remains metastable.

  14. Luttinger-liquid behavior and superconducting correlations in {ital t}-{ital J} ladders

    SciTech Connect

    Hayward, C.A.; Poilblanc, D. [Laboratoire de Physique Quantique, Universite Paul Sabatier, 31062 Toulouse (France)] [Laboratoire de Physique Quantique, Universite Paul Sabatier, 31062 Toulouse (France)

    1996-05-01

    The low-energy behavior of the isotropic {ital t}-{ital J} ladder system is investigated using exact diagonalization techniques, specifically finding the Drude weight, the charge velocity, and the compressibility. By applying the ideas of Luttinger-liquid theory, we determine the correlation exponent {ital K}{sub {rho}} which defines the behavior of the long-range correlations in the system. The boundary to phase separation is determined and a phase diagram is presented. At low electron density, a Tomonaga-Luttinger-like phase is stabilized while at higher electron densities a gapped phase with power law pairing correlations is stabilized: A large region of this gapped phase is found to exhibit dominant superconducting correlations. {copyright} {ital 1996 The American Physical Society.}

  15. Ground-state properties of a triangular triple quantum dot connected to superconducting leads

    NASA Astrophysics Data System (ADS)

    Oguri, Akira; Sato, Izumi; Shimamoto, Masashi; Tanaka, Yoichi

    2015-03-01

    We study ground-state properties of a triangular triple quantum dot connected to two superconducting (SC) leads. In this system orbital motion along the triangular configuration causes various types of quantum phases, such as the SU(4) Kondo state and the Nagaoka ferromagnetic mechanism, depending on the electron filling. The ground state also evolves as the Cooper pairs penetrate from the SC leads. We describe the phase diagram in a wide range of the parameter space, varying the gate voltage, the couplings between the dots and leads, and also the Josephson phase between the SC gaps. The results are obtained in the limit of large SC gap, carrying out exact diagonalization of an effective Hamiltonian. We also discuss in detail a classification of the quantum states according to the fixed point of the Wilson numerical renormalization group (NRG). Furthermore, we show that the Bogoliubov zero-energy excitation determines the ground state of a ? Josephson junction at small electron fillings.

  16. Nb-Pb Superconducting RF Gun

    SciTech Connect

    Sekutowicz, J.; Iversen, J.; Kreps, G.; Moller, W.D.; Singer, W.; Singer, X.; /DESY; Ben-Zvi, I.; Burrill, A.; Smedley, J.; Rao, T.; /Brookhaven; Ferrario, M.; /Frascati; Kneisel, P.; /Jefferson Lab; Langner, J.; Strzyzewski, P.; /Warsaw, Inst. Nucl. Studies; Lefferts, R.; Lipski, A.; /SUNY, Stony Brook; Szalowski, K.; /Lodz U.; Ko, K.; Xiao, L.; /SLAC

    2006-03-29

    We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.

  17. Nb-Pb superconducting RF gun

    SciTech Connect

    J. Sekutowicz; J. Iversen; G. Kreps; W.D. Moller; W. Singer; X. Singer; I. Ben-Zvi; A. Burrill; J. Smedley; T. Rao; M. Ferrario; P. Kneisel; J. Langner; P. Strzyzewski; R. Lefferts; A. Lipski; K. Szalowski; K. Ko; L. Xiao

    2006-04-14

    We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.

  18. Photonic band gap materials

    NASA Astrophysics Data System (ADS)

    Cassagne, D.

    Photonic band gap materials Photonic band gap materials are periodic dielectric structures that control the propagation of electromagnetic waves. We describe the plane wave method, which allows to calculate the band structures of photonic crystals. By symmetry analysis and a perturbative approach, we predict the appearance of the low energy photonic band gaps of hexagonal structures. We propose new two-dimensional structures called graphite and boron nitride. Using a transfer matrix method, we calculate the transmission of the graphite structure and we show the crucial role of the coupling with external modes. We study the appearance of allowed modes in the photonic band gap by the introduction of localized defects in the periodicity. Finally, we discuss the properties of opals formed by self-organized silica microspheres, which are very promising for the fabrication of three-dimensional photonic crystals. Les matériaux à bandes interdites photoniques sont des structures diélectriques périodiques qui contrôlent la propagation des ondes électromagnétiques. Nous décrivons la méthode des ondes planes qui permet de calculer les structures de bandes des cristaux photoniques. Par une analyse de la symétrie et une approche perturbative, nous précisons les conditions d'existence des bandes interdites de basse énergie. Nous proposons de nouvelles structures bidimensionnelles appelées graphite et nitrure de bore. Grâce à une méthode de matrices de transfert, nous calculons la transmission de la structure graphite et nous mettons en évidence le rôle fondamental du couplage avec les modes extérieurs. Nous étudions l'apparition de modes permis dans la bande interdite grâce à l'introduction de défauts dans la périodicité. Enfin, nous discutons les propriétés des opales constituées de micro-billes de silice auto-organisées, qui sont très prometteuses pour la fabrication de cristaux photoniques tridimensionnels.

  19. Coupling spin ensembles via superconducting flux qubits

    E-print Network

    Yueyin Qiu; Wei Xiong; Lin Tian; J. Q. You

    2014-09-10

    We study a hybrid quantum system consisting of spin ensembles and superconducting flux qubits, where each spin ensemble is realized using the nitrogen-vacancy centers in a diamond crystal and the nearest-neighbor spin ensembles are effectively coupled via a flux qubit.We show that the coupling strengths between flux qubits and spin ensembles can reach the strong and even ultrastrong coupling regimes by either engineering the hybrid structure in advance or tuning the excitation frequencies of spin ensembles via external magnetic fields. When extending the hybrid structure to an array with equal coupling strengths, we find that in the strong-coupling regime, the hybrid array is reduced to a tight-binding model of a one-dimensional bosonic lattice. In the ultrastrong-coupling regime, it exhibits quasiparticle excitations separated from the ground state by an energy gap. Moreover, these quasiparticle excitations and the ground state are stable under a certain condition that is tunable via the external magnetic field. This may provide an experimentally accessible method to probe the instability of the system.

  20. Coupled superconducting and magnetic order in CeCoIn5

    SciTech Connect

    Movshovich, Roman [Los Alamos National Laboratory; Bauer, Eric D [Los Alamos National Laboratory; Sarrao, J D [Los Alamos National Laboratory; Thompson, Joe D [Los Alamos National Laboratory; Kenselmann, M [PAUL SCHERRER INST.; Strassle, Th. [ETH ZURICH; Niedermayer, C [ETH ZURICH; Sigrist, M [ETH ZURICH; Padmanabhan, B [ETH ZURICH; Zolliker, M [PAUL SCHERRER INST.; Bianchi, A D [U. DE MONTREAL

    2008-01-01

    Strong magnetic fluctuations can provide a coupling mechanism for electrons that leads to unconventional superconductivity. Magnetic order and superconductivity have been found to coexist in a number of magnetically-mediated superconductors, but these order parameters generally compete. We report that close to the upper critical field, CeCoIn{sub 5} adopts a multi-component ground state that simultaneously carries cooperating magnetic and superconducting order. Suppressing superconductivity in a first-order transition at the upper critical field leads to the simultaneous collapse of the magnetic order, showing that superconductivity is necessary for the magnetic order. A symmetry analysis of the coupling between the magnetic order and the superconducting gap function suggests a form of superconductivity that is associated with a non-vanishing momentum.