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Sample records for superconducting energy gaps

  1. Abrupt onset of a second energy gap at the superconducting transition of underdoped Bi2212

    SciTech Connect

    Hussain, Zahid; Lee, W.S.; Vishik, I.M.; Tanaka, K.; Lu, D.H.; Sasagawa, T.; Nagaosa, N.; Devereaux, T.P.; Hussain, Z.; Shen, Z.-X.

    2007-05-26

    he superconducting gap--an energy scale tied to the superconducting phenomena--opens on the Fermi surface at the superconducting transition temperature (Tc) in conventional BCS superconductors. In underdoped high-Tc superconducting copper oxides, a pseudogap (whose relation to the superconducting gap remains a mystery) develops well above Tc (refs 1, 2). Whether the pseudogap is a distinct phenomenon or the incoherent continuation of the superconducting gap above Tc is one of the central questions in high-Tc research3, 4, 5, 6, 7, 8. Although some experimental evidence suggests that the two gaps are distinct9, 10, 11, 12, 13, 14, 15, 16, 17, 18, this issue is still under intense debate. A crucial piece of evidence to firmly establish this two-gap picture is still missing: a direct and unambiguous observation of a single-particle gap tied to the superconducting transition as function of temperature. Here we report the discovery of such an energy gap in underdoped Bi2Sr2CaCu2O8+delta in the momentum space region overlooked in previous measurements. Near the diagonal of Cu?O bond direction (nodal direction), we found a gap that opens at Tc and has a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasi-particles, a classical signature of superconductivity. This is in sharp contrast to the pseudogap near the Cu?O bond direction (antinodal region) measured in earlier experiments19, 20, 21.

  2. Abrupt Onset of a Second Energy Gap at the Superconducting Transition of Underdoped Bi2212

    SciTech Connect

    Lee, W.S.; Vishik, I.M.; Tanaka, K.; Lu, D.H.; Sasagawa, T.; Nagaosa, N.; Devereaux, T.P.; Hussain, Z.; Shen, Z.X.; /Stanford U., Appl. Phys. Dept. /SLAC, SSRL

    2007-11-21

    The superconducting gap--an energy scale tied to the superconducting phenomena--opens on the Fermi surface at the superconducting transition temperature ({Tc}) in conventional BCS superconductors. In underdoped high-{Tc} superconducting copper oxides, a pseudogap (whose relation to the superconducting gap remains a mystery) develops well above {Tc}. Whether the pseudogap is a distinct phenomenon or the incoherent continuation of the superconducting gap above {Tc} is one of the central questions in high-{Tc} research. Although some experimental evidence suggests that the two gaps are distinct, this issue is still under intense debate. A crucial piece of evidence to firmly establish this two-gap picture is still missing: a direct and unambiguous observation of a single-particle gap tied to the superconducting transition as function of temperature. Here we report the discovery of such an energy gap in underdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} in the momentum space region overlooked in previous measurements. Near the diagonal of Cu-O bond direction (nodal direction), we found a gap that opens at {Tc} and has a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasi-particles, a classical signature of superconductivity. This is in sharp contrast to the pseudogap near the Cu-O bond direction (antinodal region) measured in earlier experiments

  3. Protection of excited spin states by a superconducting energy gap

    NASA Astrophysics Data System (ADS)

    Heinrich, B. W.; Braun, L.; Pascual, J. I.; Franke, K. J.

    2013-12-01

    The latest concepts for quantum computing and data storage rely on the addressing and manipulation of single spins. A limitation for single atoms or molecules in contact with a metal surface is the short lifetime of excited spin states, typically picoseconds, due to the exchange of energy and angular momentum with the itinerant electrons of the substrate. Here we show that paramagnetic molecules on a superconducting substrate exhibit excited spin states with a lifetime of ?~10ns. We ascribe this increase in lifetime by orders of magnitude to the depletion of electronic states around the Fermi level in the superconductor. This prohibits pathways of energy relaxation into the substrate and allows the magnetic molecule to be electrically pumped into higher spin states, making superconducting substrates prime candidates for spin manipulation. We further show that the proximity of the scanning tunnelling microscope tip modifies the magnetic anisotropy.

  4. Search for Superconducting Energy Gap in UPt3 by Point-Contact Spectroscopy

    NASA Astrophysics Data System (ADS)

    Gouchi, Jun; Sumiyama, Akihiko; Yamaguchi, Akira; Motoyama, Gaku; Kimura, Noriaki; Yamamoto, Etsuji; Haga, Yoshinori; ?nuki, Yoshichika

    2015-03-01

    We have investigated the differential resistance of the point contacts between heavy-fermion superconductor UPt3 and a normal metal Pt, which were fabricated using a commercial piezo-electric actuator, and retried the observation of the energy gap of UPt3. A V-shaped dip is observed in both normal and superconducting states and disappeared around TK ~ 20 K, suggesting that it is related to the Kondo effect. Below the superconducting transition temperature, a shallow double-minimum structure, which indicates the energy gap, has been observed for the contacts on the faces perpendicular to the a-, b- and c-axes of UPt3.

  5. Quantization of the superconducting energy gap in an intense microwave field

    NASA Astrophysics Data System (ADS)

    Boris, A. A.; Krasnov, V. M.

    2015-11-01

    We study experimentally photon-assisted tunneling in Nb /AlOx/Nb Josephson junctions. We perform a quantitative calibration of the microwave field inside the junction. This allows direct verification of the quantum efficiency of microwave photon detection, which corresponds to tunneling of one electron per one absorbed microwave photon. We observe that voltages of photon-assisted tunneling steps vary both with the microwave power and the tunneling current. However, this variation is not monotonous but staircaselike. The phenomenon is caused by mutual locking of positive and negative step series. A similar locking is observed with Shapiro steps. As a result, the superconducting gap assumes quantized values equal to multiples of the quarter of the photon energy. The quantization is a manifestation of nonequilibrium tuning (suppression or enhancement) of superconductivity by the microwave field.

  6. Point contact Andreev reflection spectroscopy of superconducting energy gaps in 122-type family of iron pnictides

    NASA Astrophysics Data System (ADS)

    Samuely, P.; Pribulov, Z.; Szab, P.; Prist, G.; Bud'ko, S. L.; Canfield, P. C.

    2009-05-01

    A brief overview of the superconducting energy gap studies on 122-type family of iron pnictides is given. It seems that the situation in the hole doped Ba 1-xK xFe 2As 2 is well resolved. Most of the measurements including the presented here point contact Andreev reflection spectra agree on existence of multiple nodeless gaps in the excitation spectrum of this multiband system. The gaps have basically two sizes - the small one with a strength up to the BCS weak coupling limit and the large one with a very strong coupling with 2 ? L/ kT c > 6-8. In the electron doped Ba(Fe 1-xCo x) 2As 2 the most of the experiments including our point contact measurements reveal in quite broadened spectra only a single gap with a strong coupling strength. The high precision ARPES measurements on this system identified two gaps but very close to each other, both showing a strong coupling with 2 ?/ kT c ? 5 and 6, respectively.

  7. Temperature dependence of the energy gap in superconducting single crystalline Bi 2Sr 2CaCu 2O 8+? from threshold photoemission

    NASA Astrophysics Data System (ADS)

    Nepijko, S. A.; Park, W. G.; Fanelsa, A.; Kisker, E.; Winkeler, L.; Gntherodt, G.

    1997-02-01

    From threshold photoemission measurements on Bi 2Sr 2CaCu 2O 8+? single crystals taken at temperatures above and below Tc we derive the temperature dependence of the width of the superconducting energy gap. By different methods of data analysis, we obtain the relative and absolute values of the gap energy width.

  8. Doping and temperature dependence of the superconducting energy gap in the electron-doped cuprate Pr 2- xCe xCuO 4- ?

    NASA Astrophysics Data System (ADS)

    Diamant, I.; Greene, R. L.; Dagan, Y.

    In hole-doped cuprate superconductors at low carrier concentrations two energy scales are identified: the superconducting energy gap and the pseudogap. The relation between these energy scales is still a puzzle. In these compounds a measurement of the energy gap is not necessarily a probe of the order parameter. In the electron-doped cuprates the pseudogap does not obscure the superconducting state. Consequently, the superconducting gap can be studied directly in a tunneling experiment. Here we show that by studying superconductor/insulator/superconductor planar tunnel junctions we are able to map the behavior of the gap amplitude for the entire (doping-temperature) phase diagram of the electron-doped cuprate superconductor Pr2-xCuO. The superconducting gap, ?, shows a BCS-like temperature dependence even for extremely low carrier concentrations. Moreover, ? follows the doping dependence of planes where d-wave superconductivity takes place [8]. In addition there are changes in the shape of the Fermi surface with doping [9-12]. On the other hand, there are several differences between these compounds, including the temperature dependence of the resistivity above (PCCO) with lead as a counter electrode. We measured the differential conductance at different temperatures and magnetic fields for the entire doping range where superconductivity exists. Fig. 1 presents the normalized (by the conductance at ?0H=10 T) differential conductance at various temperatures of the extremely underdoped x = 0.125. For each temperature we fit the data using a modified BTK model for a non-monotonic d-wave as described elsewhere [17]. From our fit we found that ? goes to zero at the critical temperature in a BCS way for the entire doping range, this is seen in Fig. 2. We made use of the absence of the pseudogap and the accessible upper critical field to measure the low temperature limit of the gap amplitude as a function of doping for the entire superconducting regime [18]. Our results are shown in Fig. 3. For the overdoped and optimally doped regions the gap follows the doping dependence of Tc as found for hole-doped cuprates. Surprisingly, this behavior persists for underdoped samples. For this doping regime, the gap amplitude decreases with decreasing doping, in strong contrast with the celebrated tunneling measurements on hole-doped cuprates [19]. In summary, we present the tunneling spectra of lead/insulator/PCCO junctions over the entire doping range where superconductivity is observed. We found that the gap amplitude follows the BCS-type temperature dependence. In addition, we show that for this cuprate the gap amplitude follows the critical temperature as a function of doping, even for underdoped samples. Our results are therefore consistent with a single superconducting energy scale, in contrast with the hole-doped cuprates. We note that for hole-doped cuprates probed by node sensitive spectroscopies and Andreev-Saint-James reflections one finds an energy scale which decreases with doping in the underdoped regime. This behavior resembles our findings reported here. Assuming that the hole-doped and the electron-doped cuprates share the same mechanism for superconductivity, we can conclude that for hole-doped cuprates the Andreev-Saint-James (and nodal) gap is the superconducting gap, while the pseudogap is a competing order to superconductivity.We are indebted to G. Deutscher, S. Hacohen-Gourgy for fruitful discussions, to M. Karpovski for evaporating lead electrodes. This research was partially supported by the Binational Science Foundation Grant Number 2006385, the Israel Science Foundation Grant Number 1421/08 and by the Wolfson Family Charitable Trust. RLG is partially supported by the NSF DMR0653535.

  9. Model Evidence of a Superconducting State with a Full Energy Gap in Small Cuprate Islands

    NASA Astrophysics Data System (ADS)

    Black-Schaffer, Annica M.; Golubev, Dmitri S.; Bauch, Thilo; Lombardi, Floriana; Fogelstrm, Mikael

    2013-05-01

    We investigate subdominant order parameters stabilizing at low temperatures in nanoscale high-Tc cuprate islands, motivated by the recent observation of a fully gapped state in nanosized YBa2Cu3O7-? [D. Gustafsson et al., Nature Nanotech. 8, 25 (2013)]. Using complementary quasiclassical and tight-binding Bogoliubov-de Gennes methods, we show on distinctly different properties dependent on the symmetry being dx2-y2+is or dx2-y2+idxy. We find that a surface-induced dx2-y2+is phase creates a global spectroscopic gap which increases with an applied magnetic field, consistent with experimental observation.

  10. Phonon-induced enhancements of the energy gap and critical current in superconducting aluminum

    SciTech Connect

    Seligson, D.

    1983-05-01

    8 to 10 GHz phonons were generated by piezoelectric transduction of a microwave and by means of a quartz delay line, were allowed to enter the aluminum only after the microwaves had long since disappeared. The maximum enhancements detected were (deltaT/T/sub c/) = -0.07, for i/sub c/ and (deltaT/T/sub c/) = -0.03 for ..delta... The power- and temperature-dependence (0.82 less than or equal to T/T/sub c/ less than or equal to 0.994) of the enhancements were compared with the prediction of a theory given by Eliashberg. The gap-enhancement was in good agreement with the theory only for low input lower. The critical current measurements are predicted to be in rough agreement with the ..delta.. measurements but this was not observed. The magnitude of the critical current enhancements was typically more than twice the observed gap enhancements. The measured critical current enhancement was relatively independent of temperature whereas the gap enhancement decreased rapidly as the temperature was lowered.

  11. Development of Tunneling Spectroscopy Apparatus for Kelvin and Sub-Kelvin Measurements of Superconducting Energy Gaps by Multi-disciplinary students at a Liberal Arts University

    NASA Astrophysics Data System (ADS)

    Eckhardt, Matt

    2014-03-01

    Tunneling spectroscopy is an important technique used to measure the superconducting energy gap, a feature that is at the heart of the nature of superconductivity in various materials. In this presentation, we report the progress and results in developing high-resolution tunneling spectroscopy experimental platforms in a helium three cryostat, a 3 Kelvin cryocooler and a helium dip-tester. The experimental team working in a liberal arts university is a multi-disciplinary group consisting of one physics major, chemisty majors and a biology major. Students including non-physics majors learned and implemented current-voltage measurement techniques, vacuum system engineering, built electronic boxes and amplifier circuits from scratch, built custom multi-conductor cables for thermometry and current-voltage measurements, and performed conductance measurements. We report preliminary results. Acknowledgments: We acknowledge support from National Science Foundation Grant # DMR-1206561.

  12. ARPES measurements of superconducting gaps in iron-chalcogenide superconductors

    NASA Astrophysics Data System (ADS)

    Richard, Pierre; Miao, H.; Qian, T.; Shi, Y.-B.; Xu, N.; Wang, X.-P.; Zhang, P.; Ding, H.; Dai, X.; Hu, J.-P.; Xu, Y.-M.; Tanaka, Y.; Nakayama, K.; Umezawa, K.; Sato, T.; Takahashi, T.; Yang, H.-B.; Xu, Z.-J.; Wen, J.-S.; Gu, G.-D.

    2012-02-01

    The size and momentum dependence of the superconducting gap are crucial to the determination of the mechanism leading to Cooper pairing. Previous ARPES results on iron-pnictides superconductors reveal nearly-isotropic superconducting gaps with size varying from one Fermi surface to another. Here we show that this scheme is also valid in the iron-chalcogenide superconductors. We demonstrate that the superconducting gaps can be fitted by a single function derived from local pairing scenarios. Our finding of an apparent universality in iron-based superconductivity is a serious challenge to weak coupling approaches and rather favors pairing from local antiferromagnetic exchange interactions.

  13. Superconducting energy gap and antiferromagnetic spin fluctuations in the superconductor YNi2B2C: An NMR study

    NASA Astrophysics Data System (ADS)

    Kohara, T.; Oda, T.; Ueda, K.; Yamada, Y.; Mahajan, A.; Elankumaran, K.; Hossian, Zakir; Gupta, L. C.; Nagarajan, R.; Vijayaraghavan, R.; Mazumdar, Chandan

    1995-02-01

    Pulsed NMR studies of 11B and 89Y have been carried out in the recently discovered quaternary borocarbide superconductor YNi2B2C (Tc=15.5 K). These results are as follows: (a) Superconducting state: Though there is only one crystallographic B site in this structure, we have observed two 11B resonances in the superconducting state. One signal comes from a superconducting region, and the other from a normal-metal region. As for the former signal, the nuclear relaxation rate, T-11 decreases drastically with further decrease of temperature with no appreciable enhancement just below Tc, and it starts to saturate below 6 K. (b) Normal state: (T1T)-1 increases as temperature decreases. We interpret this temperature dependence as arising due to two-dimensional or three-dimensional antiferromagnetic spin fluctuations (structure of YNi2B2C is tetragonal and highly anisotropic).

  14. Heat Transport as a Probe of Superconducting Gap Structure

    SciTech Connect

    Petrovic, C.; Shakeripour, H.; Taillefer, L.

    2009-05-29

    The structure of the superconducting gap provides important clues on the symmetry of the order parameter and the pairing mechanism. The presence of nodes in the gap function imposed by symmetry implies an unconventional order parameter, other than s-wave. Here we show how measurements of the thermal conductivity at very low temperature can be used to determine whether such nodes are present in a particular superconductor, and shed light on their nature and location. We focus on the residual linear term at T {yields} 0. A finite value in zero magnetic field is strong evidence for symmetry-imposed nodes, and the dependence on impurity scattering can distinguish between a line of nodes or point nodes. Application of a magnetic field probes the low-energy quasiparticle excitations, whether associated with nodes or with a small value of the gap on some part of the Fermi surface, as in a multi-band superconductor. We frame our discussion around archetypal materials: Nb for s-wave, Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} for d-wave, Sr{sub 2}RuO{sub 4} for p-wave, and NbSe{sub 2} for multi-band superconductivity. In that framework, we discuss three heavy-fermion superconductors: CeIrIn{sub 5}, CeCoIn{sub 5} and UPt{sub 3}.

  15. Temperature dependence of superconducting gap and penetration depth for MgB2

    NASA Astrophysics Data System (ADS)

    Karakaya, Seniye; Ozbas, Omer

    2012-09-01

    In this study, we have investigated both the temperature dependence of magnetic penetration depth and superconducting energy gap for magnesium diboride (MgB2) by considering several models such as Bardeen-Cooper-Schrieffer (BCS), two fluids and two band Eliashberg model. These models are compared with each others and available literature results. Several studies reported that MgB2 has two different superconducting gaps. That is, the multi-band superconductor MgB2 exhibits two dimensional (2D) ?-band and three-dimensional (3D) ?-band superconductivity and have the remarkably high critical temperature (Tc= 39K) all of the metallic superconductors. So, recently it has attracted great attention. The superconductivity in MgB2 has been analyzed by using two band Eliashberg model. We also have calculated the temperature dependence of the superconducting gaps (?? and ??) and compared them with the available experimental data and the other theoretical predictions.

  16. Nodal to Nodeless Superconducting Energy-Gap Structure Change Concomitant with Fermi-Surface Reconstruction in the Heavy-Fermion Compound CeCoIn5

    NASA Astrophysics Data System (ADS)

    Kim, Hyunsoo; Tanatar, M. A.; Flint, R.; Petrovic, C.; 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 -xRxCoIn5 , R =La , Nd, and Yb down to Tmin?50 mK (Tc/Tmin50 ) using a tunnel-diode resonator. In the cleanest samples ? ? (T ) is best described by the power law ? ? (T )?Tn, with n 1 , consistent with the existence of line nodes in the superconducting gap. 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 substitution leads to an increase in the exponent n and saturation at n 2 , as expected for a dirty nodal superconductor, Yb substitution 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.

  17. The effects of Coulomb interactions on the superconducting gaps in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Leong, Zhidong; Phillips, Philip

    2015-03-01

    Recent ARPES measurements on Co-doped LiFeAs report a large and robust superconducting gap on a band below the chemical potential. We will show that, unlike a conventional BCS theory, a multiband system with strong interband Coulomb interactions can explain the observations. We use a two-band model consisting of a superconducting electron band and a hole band that is below the chemical potential. The two bands are coupled via interband Coulomb interactions. Using Eliashberg theory, we found that superconductivity in the electron band induces a large superconducting gap in the hole band. Furthermore, the repulsive nature of the Coulomb interactions gives the induced gap an opposite sign, corresponding to an s+/- gap symmetry. Unlike other families of iron pnictides, the gap symmetry of LiFeAs has not been ascertained experimentally. The implications for the superconducting mechanism in iron pnictides will be discussed. Z. Leong is supported by a scholarship from the Agency of Science, Technology and Research. P. Phillips is supported by the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center, Grant No. DE-AC0298CH1088.

  18. 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 ?07 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.

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

    DOE PAGESBeta

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

    2015-06-29

    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 σ bands follows a BCS-like variation with temperature with Δ0 ~ 7meV. Furthermore, the value of the gap is isotropic within experimental uncertainty and in agreement with a pure s-wave pairing symmetry. We observe in-gap states confined to kF of the σ band that occur at some locations of the sample surface. As a result, the energy of thismore » excitation, ~ 3 meV, was found to be somewhat larger than the previously reported gap on π Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin.« less

  20. Effects of large induced superconducting gap on semiconductor Majorana nanowires

    NASA Astrophysics Data System (ADS)

    Cole, William S.; Das Sarma, S.; Stanescu, Tudor D.

    2015-11-01

    With the recent achievement of extremely high-quality epitaxial interfaces between InAs nanowires and superconducting Al shells with strong superconductor-semiconductor tunnel coupling, a new regime of proximity-induced superconductivity in semiconductors can be explored where the induced gap may be similar in value to the bulk Al gap (large gap) with negligible subgap conductance (hard gap). We propose several experimentally relevant consequences of this large-gap strong-coupling regime for tunneling experiments, and we comment on the prospects of this regime for topological superconductivity. In particular, we show that the advantages of having a strong spin-orbit coupling and a large spin g factor in the semiconductor nanowire may both be compromised in this strongly coupled limit, and somewhat weaker interface tunneling may be necessary for achieving optimal proximity superconductivity in the semiconductor nanowire. We derive a minimal, generic theory for the strong-coupling hard-gap regime obtaining good qualitative agreement with the experiment and pointing out future directions for further progress toward Majorana nanowires in hybrid semiconductor-superconductor structures.

  1. Superconducting dark energy

    NASA Astrophysics Data System (ADS)

    Liang, Shi-Dong; Harko, Tiberiu

    2015-04-01

    Based on the analogy with superconductor physics we consider a scalar-vector-tensor gravitational model, in which the dark energy action is described by a gauge invariant electromagnetic type functional. By assuming that the ground state of the dark energy is in a form of a condensate with the U(1) symmetry spontaneously broken, the gauge invariant electromagnetic dark energy can be described in terms of the combination of a vector and of a scalar field (corresponding to the Goldstone boson), respectively. The gravitational field equations are obtained by also assuming the possibility of a nonminimal coupling between the cosmological mass current and the superconducting dark energy. The cosmological implications of the dark energy model are investigated for a Friedmann-Robertson-Walker homogeneous and isotropic geometry for two particular choices of the electromagnetic type potential, corresponding to a pure electric type field, and to a pure magnetic field, respectively. The time evolutions of the scale factor, matter energy density and deceleration parameter are obtained for both cases, and it is shown that in the presence of the superconducting dark energy the Universe ends its evolution in an exponentially accelerating vacuum de Sitter state. By using the formalism of the irreversible thermodynamic processes for open systems we interpret the generalized conservation equations in the superconducting dark energy model as describing matter creation. The particle production rates, the creation pressure and the entropy evolution are explicitly obtained.

  2. Measurement of an enhanced superconducting phase and a pronounced anisotropy of the energy gap of a strained FeSe single layer in FeSe/Nb:SrTiO3/KTaO3 heterostructures using photoemission spectroscopy.

    PubMed

    Peng, R; Shen, X P; Xie, X; Xu, H C; Tan, S Y; Xia, M; Zhang, T; Cao, H Y; Gong, X G; Hu, J P; Xie, B P; Feng, D L

    2014-03-14

    Single-layer FeSe films with an extremely expanded in-plane lattice constant of 3.990.02?? are fabricated by epitaxially growing FeSe/Nb:SrTiO3/KTaO3 heterostructures and studied by insitu angle-resolved photoemission spectroscopy. Two elliptical electron pockets at the Brillouin zone corner are resolved with negligible hybridization between them, indicating that the symmetry of the low-energy electronic structure remains intact as a freestanding single-layer FeSe, although it is on a substrate. The superconducting gap closes at a record high temperature of 70K for the iron-based superconductors. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results place strong constraints on current theories. PMID:24679321

  3. Measurement of an Enhanced Superconducting Phase and a Pronounced Anisotropy of the Energy Gap of a Strained FeSe Single Layer in FeSe /Nb:SrTiO3/KTaO3 Heterostructures Using Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Peng, R.; Shen, X. P.; Xie, X.; Xu, H. C.; Tan, S. Y.; Xia, M.; Zhang, T.; Cao, H. Y.; Gong, X. G.; Hu, J. P.; Xie, B. P.; Feng, D. L.

    2014-03-01

    Single-layer FeSe films with an extremely expanded in-plane lattice constant of 3.990.02 are fabricated by epitaxially growing FeSe /Nb:SrTiO3/KTaO3 heterostructures and studied by in situ angle-resolved photoemission spectroscopy. Two elliptical electron pockets at the Brillouin zone corner are resolved with negligible hybridization between them, indicating that the symmetry of the low-energy electronic structure remains intact as a freestanding single-layer FeSe, although it is on a substrate. The superconducting gap closes at a record high temperature of 70 K for the iron-based superconductors. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results place strong constraints on current theories.

  4. 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

  5. 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.

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

    DOE PAGESBeta

    Prozorov, R.; Cho, K.; Kim, H.; Tanatar, M. A.

    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 »As a result, this trend is not related to the presence of the long-range magnetic order in the underdoped state.« less

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

    SciTech Connect

    Prozorov, R.; Cho, K.; Kim, H.; Tanatar, M. A.

    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''. As a result, this trend is not related to the presence of the long-range magnetic order in the underdoped state.

  8. Far-infrared Optical Conductivity Gap in Superconducting MgB2 Films

    NASA Astrophysics Data System (ADS)

    Carnahan, M. A.; Kaindl, R. A.; Chemla, D. S.; Christen, H. M.; Zhai, H. Y.; Paranthaman, M.; Lowndes, D. H.

    2002-03-01

    The prospect of unconventional coupling in the superconductor MgB2 motivates experiments which probe the density of states around the superconducting gap. The frequency and temperature dependent optical conductivity contains important spectroscopic information about the fundamental gap excitations as well as providing a contactless measure of the superconducting condensate. Here we present the first measurements of the far-infrared conductivity of MgB2 over a broad frequency range which spans excitations across its lowest-energy superconducting gap [1]. Thin films of MgB2 are grown on Al_2O3 substrates through e-beam evaporation and subsequent ex-situ annealing [2]. Both the real and imaginary parts of the conductivity are obtained - without recourse to Kramers-Kronig transformations - from terahertz time-domain spectroscopy. Below Tc we observe a depletion of oscillator strength due to the opening of a superconducting gap. We find a gap size of 2? ? 5 meV. This result, a value which is only half that expected in weak-coupling BCS theory, disfavors a conventional isotropic single-gap scenario. [1] R. Kaindl et al., Phys. Rev. Lett. (to appear). [2] M. Paranthaman et al., Appl. Phys. Lett. 78, 3669 (2001).

  9. Perfect switching of the spin polarization in a ferromagnetic gapless graphene/superconducting gapped graphene junction

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

    With the fabrication of gapped graphene, interest in the tunneling spectroscopy in graphene-based FG/SG junctions in which one side consists of a gapless ferro-magnetic graphene (FG) and the other side, of a gapped superconducting graphene (SG) has arisen. The carriers in the gapless (gapped) graphene are 2D relativistic particles having an energy spectrum given by E=?{?2vF2k2+(mvF2)2} (where mvF2 is the gap and v F is the Fermi velocity). The spin currents in this FG/SG junction are obtained within the framework of the extended Blonder-Tinkham-Klapwijk (BTK) formalism. The effects of the superconducting energy gap in SG, of the gap mvF2 which opened in the superconducting graphene, of the exchange field in FG, of the spin-dependent specular Andreev reflection, of the effective Fermi energy ( E FF) of FG and of the bias voltage across the junction ( V) are simulated. It is seen that by adjusting EFF or V, the spin polarization (defined as SP(%) = 100% ( G? - G?)/( G? + G?)) can be switched from a pure spin up (SP = +100%) state to pure spin down (SP = -100%) state.

  10. Nodal to nodeless superconducting energy-gap structure change concomitant with Fermi-surface reconstruction in the heavy-fermion compound CeCoIn5

    DOE PAGESBeta

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

    2015-01-15

    The London penetration depth λ(T) was measured in single crystals of Ce1–xRxCoIn₅, R=La, Nd, and Yb down to Tmin ≈ 50 mK (Tc/Tmin ~50) using a tunnel-diode resonator. In the cleanest samples Δλ(T) is best described by the power law, Δλ(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 Δλ(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 leadsmore » to n > 3, suggesting a change from nodal to nodeless superconductivity. As a result, 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

  11. Smeared gap equations in crystalline color superconductivity

    SciTech Connect

    Ruggieri, M.

    2006-01-12

    In the framework of HDET, we discuss an averaging procedure of the NJL quark-quark interaction lagrangian, treated in the mean field approximation, for the two flavor LOFF phase of QCD. This procedure gives results which are valid in domains where Ginzburg-Landau results may be questionable. We compute and compare the free energy for different LOFF crystalline structures.

  12. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  14. Laser pumped superconductive energy storage system

    SciTech Connect

    Wolf, A.A.

    1983-11-08

    A superconductive energy storage system comprising a magnetic field surrounding a superconducting coil having large currents circulating therein, cooling said coil to superconducting temperatures, starting said circulating current in said superconducting coil inductively by a small primer coil, transmitting additional energy into said energy storage system utilizing a laser beam, and retaining said energy in said energy storage system until needed.

  15. 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.

  16. Propagating photonic modes below the gap in a superconducting composite

    SciTech Connect

    Lee, W.M.; Hui, P.M.; Stroud, D.

    1995-04-01

    We show that there are propagating modes for electromagnetic waves in a periodic array of superconductor and insulator with two-dimensional symmetry. For waves polarized perpendicular to the array, the vector Maxwell equations reduce to a scalar wave equation for the nonvanishing component of electric field. This reduction is still valid if the superconducting component has an anisotropic dielectric tensor, as in the high-{ital T}{sub {ital c}} CuO-based materials. Using the Mattis-Bardeen form for the finite-frequency conductivity of a superconductor below its gap, the wave equation becomes formally identical to a Schroedinger equation. We give numerical examples for the case of a two-dimensional array of air cylinders embedded in a superconducting host. The results suggest that these modes may be observable in a highly anisotropic high-{ital T}{sub {ital c}} superconductor with {ital c} axis parallel to the direction of wave polarization.

  17. Energy gaps in high-transition-temperature cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Hashimoto, Makoto; Vishik, Inna M.; He, Rui-Hua; Devereaux, Thomas P.; Shen, Zhi-Xun

    2014-07-01

    The spectral energy gap is an important signature that defines states of quantum matter: insulators, density waves and superconductors have very different gap structures. The momentum-resolved nature of angle-resolved photoemission spectroscopy (ARPES) makes it a powerful tool to characterize spectral gaps. ARPES has been instrumental in establishing the anisotropic d-wave structure of the superconducting gap in high-transition-temperature (Tc) cuprates, which is different from the conventional isotropic s-wave superconducting gap. Shortly afterwards, ARPES demonstrated that an anomalous gap above Tc, often termed the pseudogap, follows a similar anisotropy. The nature of this poorly understood pseudogap and its relationship with superconductivity has since become the focal point of research in the field. To address this issue, the momentum, temperature, doping and materials dependence of spectral gaps have been extensively examined with significantly improved instrumentation and carefully matched experiments in recent years. This article overviews the current understanding and unresolved issues of the basic phenomenology of gap hierarchy. We show how ARPES has been sensitive to phase transitions, has distinguished between orders having distinct broken electronic symmetries, and has uncovered rich momentum- and temperature-dependent fingerprints reflecting an intertwined and competing relationship between the ordered states and superconductivity that results in multiple phenomenologically distinct ground states inside the superconducting dome. These results provide us with microscopic insights into the cuprate phase diagram.

  18. Nonequilibrium superconducting thin films with sub-gap and pair-breaking photon illumination

    NASA Astrophysics Data System (ADS)

    Guruswamy, T.; Goldie, D. J.; Withington, S.

    2015-05-01

    We calculate nonequilibrium quasiparticle and phonon distributions for a number of widely-used low transition temperature thin-film superconductors under constant, uniform illumination by sub-gap probe and pair-breaking signal photons simultaneously. From these distributions we calculate material-characteristic parameters that allow rapid evaluation of an effective quasiparticle temperature using a simple analytical expression, for all materials studied (Mo, Al, Ta, Nb, and NbN) for all photon energies. We also explore the temperature and energy-dependence of the low-energy quasiparticle generation efficiency ? by pair-breaking signal photons finding ? ? 0.6 in the limit of thick films at low bath temperatures that is material-independent. Taking the energy distribution of excess quasiparticles into account, we find ? \\to 1 as the bath temperature approaches the transition temperature in agreement with the assumption of the two-temperature model of the nonequilibrium response that is appropriate in that regime. The behaviour of ? with signal frequency scaled by the superconducting energy gap is also shown to be material-independent, and is in qualitative agreement with recent experimental results. An enhancement of ? in the presence of sub-gap (probe) photons is shown to be most significant at signal frequencies near the superconducting gap frequency and arises due to multiple photon absorption events that increase the average energy of excess quasiparticles above that in the absence of the probe.

  19. 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.

  20. 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; Nygrd, 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.

  1. Disorder-induced topological change of the superconducting gap structure in iron pnictides.

    PubMed

    Mizukami, Y; Konczykowski, M; Kawamoto, Y; Kurata, S; Kasahara, S; Hashimoto, K; Mishra, V; Kreisel, A; Wang, Y; Hirschfeld, P J; Matsuda, Y; Shibauchi, T

    2014-01-01

    In superconductors with unconventional pairing mechanisms, the energy gap in the excitation spectrum often has nodes, which allow quasiparticle excitations at low energies. In many cases, such as in d-wave cuprate superconductors, the position and topology of nodes are imposed by the symmetry, and thus the presence of gapless excitations is protected against disorder. Here we report on the observation of distinct changes in the gap structure of iron-pnictide superconductors with increasing impurity scattering. By the successive introduction of nonmagnetic point defects into BaFe2(As(1-x)P(x))(2) crystals via electron irradiation, we find from the low-temperature penetration depth measurements that the nodal state changes to a nodeless state with fully gapped excitations. Moreover, under further irradiation the gapped state evolves into another gapless state, providing bulk evidence of unconventional sign-changing s-wave superconductivity. This demonstrates that the topology of the superconducting gap can be controlled by disorder, which is a strikingly unique feature of iron pnictides. PMID:25430419

  2. Vacuum-Gap Capacitors for Low-Loss Superconducting Resonant Circuits

    NASA Astrophysics Data System (ADS)

    Cicak, Katarina; Allman, Michael S.; Strong, Joshua A.; Osborn, Kevin D.; Simmonds, Raymond W.

    2009-06-01

    Low-loss microwave components are used in many superconducting resonant circuits from multiplexed readouts of low-temperature detector arrays to quantum bits. Two-level system defects in amorphous dielectric materials cause excess energy loss. In an effort to improve capacitor components, we have used optical lithography and micromachining techniques to develop superconducting parallel-plate capacitors in which lossy dielectrics are replaced by vacuum gaps. Resonance measurements at 50 mK on lumped LC circuits that incorporate these vacuum-gap capacitors (VGCs) reveal loss tangents at low powers as low as 4x10^{-5}, significantly lower than with capacitors using amorphous dielectrics. VGCs are structurally robust, small, and easily scaled to capacitance values above 100 pF.

  3. Design Tool for Liquid-Nitrogen Gaps in Superconducting Apparatus

    SciTech Connect

    Pace, Marshall O; Sauers, Isidor; James, David Randy; Tuncer, Enis; Polyzos, Georgios

    2011-01-01

    For designers of high temperature superconducting equipment with liquid nitrogen as a dielectric, an expedient universal curve is sought that provides breakdown strength for a specified class of electrode shapes, with any practical sizes of electrodes and gap; thus the universal curve fills in missing experimental data. Universal breakdown strength curves at pressures of or slightly above 100 kPa, are being developed for AC, DC or impulse stress for the class with sphere-sphere, plane-plane and sphere-plane gaps, with three independent parameters: the size of each electrode and gap. A user can normalize his parameters and find the corresponding breakdown strength, even though no data were available for his exact dimensions. For AC and DC stresses the geometrical effects of stressed area/volume are incorporated from most published AC and DC experimental data of the last 50 years, by plotting breakdown field versus new geometrical quantities, such that all data fall approximately on or near one normalized universal curve. This avoids the usual difficult task of calculating stressed area and volume effects on the breakdown values for the graph ordinate. For impulse stress a more traditional plot suffices to produce a universal curve. This suggests that area/volume effects might not be so important with impulse stress. If the method proves reliable, it may be possible to determine design parameters for a broad range of geometries, help unify seemingly disparate breakdown data in the literature, and provide easily used, practical guidance for designers.

  4. Superconducting transistor

    DOEpatents

    Gray, Kenneth E.

    1979-01-01

    A superconducting transistor is formed by disposing three thin films of superconducting material in a planar parallel arrangement and insulating the films from each other by layers of insulating oxides to form two tunnel junctions. One junction is biased above twice the superconducting energy gap and the other is biased at less than twice the superconducting energy gap. Injection of quasiparticles into the center film by one junction provides a current gain in the second junction.

  5. Energy gaps in ?-graphdiyne nanoribbons

    SciTech Connect

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

    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.

  6. Soft superconducting gap in semiconductor-based Majorana nanowires

    NASA Astrophysics Data System (ADS)

    Stanescu, Tudor D.; Lutchyn, Roman M.; Das Sarma, S.

    2014-08-01

    We develop a theory for the proximity effect in superconductor-semiconductor-normal-metal tunneling structures, which have recently been extensively studied experimentally, leading to the observation of transport signatures consistent with the predicted zero-energy Majorana bound states. We show that our model for the semiconductor nanowire having multiple occupied subbands with different transmission probabilities through the barrier reproduces the observed "soft-gap" behavior associated with substantial subgap tunneling conductance. We study the manifestations of the soft-gap phenomenon both in the tunneling conductance and in local density of states measurements and discuss the correlations between these two quantities. We emphasize that the proximity effect associated with the hybridization between low-lying states in the multiband semiconductor and the normal-metal states in the lead is an intrinsic effect leading to the soft-gap problem. In addition to the intrinsic contribution, there may be extrinsic effects, such as, for example, interface disorder, exacerbating the soft-gap problem. Our work establishes the generic possibility of an ubiquitous presence of an intrinsic soft gap in the superconductor-semiconductor-normal-metal tunneling transport conductance induced by the inverse proximity effect of the normal metal.

  7. Andreev spectroscopy of FeSe: Evidence for two-gap superconductivity

    NASA Astrophysics Data System (ADS)

    Ponomarev, Ya. G.; Kuzmichev, S. A.; Mikheev, M. G.; Sudakova, M. V.; Tchesnokov, S. N.; Shanygina, T. E.; Volkova, O. S.; Vasiliev, A. N.; Wolf, Th.

    2011-09-01

    Current-voltage characteristics (CVCs) of Andreev superconductor-constriction-superconductor (ScS) contacts in polycrystalline samples of FeSe with the critical temperature T C = (12 1) K have been measured using the break-junction technique. In Sharvin-type nanocontacts, two sets of subharmonic gap structures were detected due to multiple Andreev reflections, indicating the existence of two nodeless superconducting gaps ? L = (2.75 0.3) meV and ? S = (0.8 0.2) meV. Well-shaped CVCs for stacks of Andreev contacts with up to five contacts were observed due to the layered structure of FeSe (the intrinsic multiple Andreev reflections effect). An additional fine structure in the CVCs of Andreev ScS nanocontacts is attributed to the existence of a Leggett mode. A linear relation between the superconducting gap ? L and the magnetic resonance energy E magres ? 2? L is found to be valid for layered iron pnictides.

  8. Andreev spectroscopy of FeSe: Evidence for two-gap superconductivity

    SciTech Connect

    Ponomarev, Ya. G.; Kuzmichev, S. A.; Mikheev, M. G.; Sudakova, M. V.; Tchesnokov, S. N.; Shanygina, T. E.; Volkova, O. S.; Vasiliev, A. N.; Wolf, Th.

    2011-09-15

    Current-voltage characteristics (CVCs) of Andreev superconductor-constriction-superconductor (ScS) contacts in polycrystalline samples of FeSe with the critical temperature T{sub C} = (12 {+-} 1) K have been measured using the break-junction technique. In Sharvin-type nanocontacts, two sets of subharmonic gap structures were detected due to multiple Andreev reflections, indicating the existence of two nodeless superconducting gaps {Delta}{sub L} = (2.75 {+-} 0.3) meV and {Delta}{sub S} = (0.8 {+-} 0.2) meV. Well-shaped CVCs for stacks of Andreev contacts with up to five contacts were observed due to the layered structure of FeSe (the intrinsic multiple Andreev reflections effect). An additional fine structure in the CVCs of Andreev ScS nanocontacts is attributed to the existence of a Leggett mode. A linear relation between the superconducting gap {Delta}{sub L} and the magnetic resonance energy E{sub magres} Almost-Equal-To 2{Delta}{sub L} is found to be valid for layered iron pnictides.

  9. Momentum dependence of the superconducting gap in Ba1-xKxFe2As2

    NASA Astrophysics Data System (ADS)

    Evtushinsky, D. V.; Inosov, D. S.; Zabolotnyy, V. B.; Koitzsch, A.; Knupfer, M.; Bchner, B.; Viazovska, M. S.; Sun, G. L.; Hinkov, V.; Boris, A. V.; Lin, C. T.; Keimer, B.; Varykhalov, A.; Kordyuk, A. A.; Borisenko, S. V.

    2009-02-01

    The precise momentum dependence of the superconducting gap in the iron-arsenide superconductor Ba1-xKxFe2As2 (BKFA) with Tc=32K was determined from angle-resolved photoemission spectroscopy (ARPES) via fitting the distribution of the quasiparticle density to a model. The model incorporates finite lifetime and experimental resolution effects, as well as accounts for peculiarities of BKFA electronic structure. We have found that the value of the superconducting gap is practically the same for the inner ? barrel, X pocket, and blade pocket, and equals 9 meV, while the gap on the outer ? barrel is estimated to be less than 4 meV, resulting in 2?/kBTc=6.8 for the large gap and 2?/kBTc<3 for the small gap. A large (773%) nonsuperconducting component in the photoemission signal is observed below Tc . Details of gap extraction from ARPES data are discussed in Appendixes .

  10. Review of new energy. Superconductivity

    NASA Astrophysics Data System (ADS)

    1989-03-01

    An summary is given of the research and development on high temperature superconductivity. It begins with a description of superconducting state and enumerates chemical elements, in particular oxides, associated with high temperature superconductivity. A brief account is next given on the progress of research and development on the present subject. Some of well known topics associated with superconductivity are described shortly, namely Meissner effect, quenching (transition to normal conducting state from superconducting one), Perovskite structure, positive hole earrier, Josephson effect, SQUID (superconducting quantum interference device) and so on. Various devices or technology are enumerated, to which superconductivity, in particular high temperature one, is proposed to apply, namely electromagnet, MRI (magnetic resonance imaging), particle accelerator, linear motor car, electric power storage and so on. The summary is finished with a future outlook.

  11. 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.

  12. Kinetic-energy-driven superconductivity in cuprate superconductors

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Superconductivity in cuprate superconductors occurs upon charge-carrier doping Mott insulators, where a central question is what mechanism causes the loss of electrical resistance below the superconducting (SC) transition temperature? In this paper, we attempt to summarize the basic idea of the kinetic-energy-driven SC mechanism in the description of superconductivity in cuprate superconductors. The mechanism of the kinetic-energy-driven superconductivity is purely electronic without phonons, where the charge-carrier pairing interaction in the particle-particle channel arises directly from the kinetic energy by the exchange of spin excitations in the higher powers of the doping concentration. This kinetic-energy-driven d-wave SC-state is controlled by both the SC gap and quasiparticle coherence, which leads to that the maximal SC transition temperature occurs around the optimal doping, and then decreases in both the underdoped and overdoped regimes. In particular, the same charge-carrier interaction mediated by spin excitations that induces the SC-state in the particle-particle channel also generates the normal-state pseudogap state in the particle-hole channel. The normal-state pseudogap crossover temperature is much larger than the SC transition temperature in the underdoped and optimally doped regimes, and then monotonically decreases upon the increase of doping, eventually disappearing together with superconductivity at the end of the SC dome. This kinetic-energy-driven SC mechanism also indicates that the strong electron correlation favors superconductivity, since the main ingredient is identified into a charge-carrier pairing mechanism not from the external degree of freedom such as the phonon but rather solely from the internal spin degree of freedom of the electron. The typical properties of cuprate superconductors discussed within the framework of the kinetic-energy-driven SC mechanism are also reviewed.

  13. Superconducting gap in BaFe2(As1 -xPx )2 from temperature-dependent transient optical reflectivity

    NASA Astrophysics Data System (ADS)

    Pogrebna, A.; Mertelj, T.; Ye, Z. R.; Feng, D. L.; Mihailovic, D.

    2015-10-01

    Temperature and fluence dependence of the 1.55-eV optical transient reflectivity in BaFe2(As1 -xPx )2 was measured and analyzed in the low and high excitation density limit. The effective magnitude of the superconducting gap of ˜5 meV obtained from the low-fluence-data bottleneck model fit is consistent with the angle-resolved photoemission spectroscopy results for the γ - and β -hole Fermi surfaces. The superconducting state nonthermal optical destruction energy was determined from the fluence dependent data. The planar optical destruction energy density scales well with Tc2 and is found to be similar in a number of different layered superconductors.

  14. Nodeless superconducting gaps in noncentrosymmetric superconductor PbTaSe2 with topological bulk nodal lines

    NASA Astrophysics Data System (ADS)

    Wang, M. X.; Xu, Y.; He, L. P.; Zhang, J.; Hong, X. C.; Cai, P. L.; Wang, Z. B.; Dong, J. K.; Li, S. Y.

    2016-01-01

    Low-temperature thermal conductivity measurements were performed on single crystal of PbTaSe2, a noncentrosymmetric superconductor with topological bulk nodal lines in the electronic band structure. It is found that the residual linear term ?0/T is negligible in zero magnetic field. Furthermore, the field dependence of ?0/T exhibits an S -shaped curve. These results suggest that PbTaSe2 has multiple nodeless superconducting gaps. Therefore, the spin-triplet state with gap nodes does not play an important role in this noncentrosymmetric superconductor with strong spin-orbital coupling. The fully gapped superconducting state also meets the requirement of a topological superconductor, if PbTaSe2 is indeed the case.

  15. Doping-induced evolution of superconducting gap in iron-based superconductors: a point-contact Andreev reflection study of BaNi-122 single crystals

    NASA Astrophysics Data System (ADS)

    Ren, Cong; Wang, Zhaosheng; Shen, Bing; Luo, Huiqian; Lu, Xingye; Wang, Zhenyu; Zhu, Jun; Gong, Jun; Hou, Xingyuan; Li, Chunhong; Shan, Lei; Yang, Huan; Wen, Haihu

    2012-02-01

    We report a systematic investigation on c-axis point-contact Andreev reflection (PCAR) in superconducting BaFe2-xNixAs2 single crystals from underdoped to overdoped regions (0.075 < x < 0.15). At optimal doping (x = 0.1) the PCAR spectrum feature a dip-hump structure at the edge of the conductance gap, which corresponds to electron-boson coupling mode in energy scale. Two-superconducting-gap structure is resolved in the PCAR spectroscopy. In the s scenario, quantitative analysis using a generalized Blonder-Tinkham-Klapwijk (BTK) formalism with two gaps: one isotropic and another angle dependent, suggest a nodeless state in strong-coupling limit with gap minima on the Fermi surfaces. Upon crossing above the optimal doping (x > 0.1), the PCAR spectrum show an in-gap sharp narrow peak at low bias, in contrast to the case of underdoped samples (x < 0.1), signaling the onset of deepened gap minima or nodes in the superconducting gap. This result provides evidence of the modulation of the gap amplitude with doping concentration, consistent with the calculations for the orbital dependent pair interaction mediated by the antiferromagne

  16. Fully gapped superconductivity in In-doped topological crystalline insulator Pb0.5Sn0.5Te

    DOE PAGESBeta

    Du, Guan; Gu, G. D.; Du, Zengyi; Fang, Delong; Yang, Huan; Zhong, R. D.; Schneeloch, J.; Wen, Hai -Hu

    2015-07-27

    In this study, superconductors derived from topological insulators and topological crystalline insulators by chemical doping have long been considered to be candidates as topological superconductors. Pb0.5Sn0.5Te is a topological crystalline insulator with mirror symmetry protected surface states on (001)-, (011)-, and (111)-oriented surfaces. The superconductor (Pb0.5Sn0.5)0.7In0.3Te is produced by In doping in Pb0.5Sn0.5Te, and is thought to be a topological superconductor. Here we report scanning tunneling spectroscopy measurements of the superconducting state as well as the superconducting energy gap in (Pb0.5Sn0.5)0.7In0.3Te on a (001)-oriented surface. The spectrum can be well fitted by an anisotropic s-wave gap function of Δ =more » 0.72 + 0.18cos4θ meV using Dynes model. The results show that the superconductor seems to be a fully gapped one without any in-gap states, in contradiction with the expectation of a topological superconductor.« less

  17. 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.

  18. Two-gap superconductivity in heavily n-doped graphene: Ab initio Migdal-Eliashberg theory

    NASA Astrophysics Data System (ADS)

    Margine, E. R.; Giustino, Feliciano

    2014-07-01

    Graphene is the only member of the carbon family from zero- to three-dimensional materials for which superconductivity has not been observed yet. At this time, it is not clear whether the quest for superconducting graphene is hindered by technical challenges, or else by the fluctuation of the order parameter in two dimensions. In this area, ab initio calculations are useful to guide experimental efforts by narrowing down the search space. In this spirit, we investigate from first principles the possibility of inducing superconductivity in doped graphene using the fully anisotropic Migdal-Eliashberg theory powered by Wannier-Fourier interpolation. To address a best-case scenario, we consider both electron and hole doping at high carrier densities so as to align the Fermi level to a van Hove singularity. In these conditions, we find superconducting gaps of s-wave symmetry, with a slight anisotropy induced by the trigonal warping, and, in the case of n-doped graphene, an unexpected two-gap structure reminiscent of MgB2. Our Migdal-Eliashberg calculations suggest that the observation of superconductivity at low temperature should be possible for n-doped graphene at carrier densities exceeding 1015cm-2.

  19. Observation of multiple superconducting gaps in Fe1+yTe1-xSex via a nanoscale approach to point-contact spectroscopy

    NASA Astrophysics Data System (ADS)

    Peng, Haibing; De, Debtanu; Wu, Zheng; Diaz-Pinto, Carlos

    2012-11-01

    We report a novel experimental approach to point-contact Andreev reflection spectroscopy with diagnostic capability via a unique design for nanoscale normal metal/superconductor devices with excellent thermomechanical stability, and have employed this method to unveil the existence of two superconducting energy gaps in iron chalcogenide Fe1+yTe1-xSex, which is crucial for understanding its pairing mechanism. This work opens up new opportunities to study gap structures in superconductors and elemental excitations in solids.

  20. Non-Fermi liquid behavior and non-universal superconducting gap structure in Fe-pnictides

    NASA Astrophysics Data System (ADS)

    Matsuda, Yuji

    2010-03-01

    The discovery of Fe-pnictide superconductors with Tc exceeding 55 K raises fundamental questions about origin of high-Tc superconductivity. Here we report the systematic studies of the normal-state charge transport, Fermi surface structure and superconducting gap structure in high-quality single crystals of BaFe2(As1-xPx)2 (0 <=x <=0.71), ranging from the SDW state to overdoped Fermi liquid state. Near the SDW boundary, the transport coefficients, including resistivity, Hall coefficient and magnetoresistance, exhibit striking deviations from the Fermi liquid properties [1]. The Fermi surface structure determined by the dHvA effect shows that in the superconducting dome the volume of the electron and hole sheets shrink linearly and the effective masses become strongly enhanced with decreasing x [2]. It is likely that these trends originate from the many-body interaction which gives rise to superconductivity. The penetration depth, thermal conductivity and NMR data for BaFe2(As0.67P0.33)2 (Tc=30 K) provide unambiguous evidence for line nodes in the superconducting gap function [3], in sharp contrast to the other Fe-based compounds with fully gapped structure. This indicates that the gap structure of Fe-based high-Tc superconductors is not universal.[1] S. Kasahara et al., arXiv:0905.4427 [2] H. Shishido et al., arXiv:0910.3634 [3] K. Hashimoto et al., arXiv:0907.4399 [4] K. Hashimoto et al., Phys. Rev. Lett. 102, 017002 (2009), ibid 102, 207001 (2009).

  1. ARPES measurements of the superconducting gap of Fe-based superconductors and their implications to the pairing mechanism

    NASA Astrophysics Data System (ADS)

    Richard, P.; Qian, T.; Ding, H.

    2015-07-01

    Its direct momentum sensitivity confers to angle-resolved photoemission spectroscopy (ARPES) a unique perspective in investigating the superconducting gap of multi-band systems. In this review we discuss ARPES studies on the superconducting gap of high-temperature Fe-based superconductors. We show that while Fermi-surface-driven pairing mechanisms fail to provide a universal scheme for the Fe-based superconductors, theoretical approaches based on short-range interactions lead to a more robust and universal description of superconductivity in these materials. Our findings are also discussed in the broader context of unconventional superconductivity.

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

    SciTech Connect

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

    2015-06-29

    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 σ bands follows a BCS-like variation with temperature with Δ0 ~ 7meV. Furthermore, the value of the gap is isotropic within experimental uncertainty and in agreement with a pure s-wave pairing symmetry. We observe in-gap states confined to kF of the σ band that occur at some locations of the sample surface. As a result, the energy of this excitation, ~ 3 meV, was found to be somewhat larger than the previously reported gap on π Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin.

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

    SciTech Connect

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

    2014-06-16

    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.

  4. Superconductivity:

    NASA Astrophysics Data System (ADS)

    Zimmerman, George O.

    The discovery of superconductivity brought with it the promise of a miracle solution to many technological problems encountered by the electrical power industry. That discovery was at Leiden in 1911. Since then, engineering designs and prototypes have been developed for the use of superconductive materials in electric power transmission, transformers, and machinery. The development of superconducting magnetic energy storage systems also held great promise. Superconductivity was even used to build marine propulsion systems and levitated track vehicles. Despite that, and despite the financial support of governments for prototype developments, the only commercial application of the technology, outside of laboratories, is for MRI magnets. Similar experience is encountered in superconducting applications to electronics, although some success has been achieved in the communication industry. The discovery of high temperature superconductivity, despite its promise, did not significantly change the situation. The developments will be reviewed, and some of the reasons why superconductivity is still mainly confined to the laboratory will be given with the view of what we, as scientists, can do in order to enhance and hasten the commercial adoption of superconducting technology.

  5. 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

  6. Molecular Pairing and Fully Gapped Superconductivity in Yb-doped CeCoIn5

    NASA Astrophysics Data System (ADS)

    Erten, Onur; Flint, Rebecca; Coleman, Piers

    2015-01-01

    The recent observation of fully gapped superconductivity in Yb doped CeCoIn5 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 T4 dependence of the penetration depth associated with the sound mode of this condensate is in accordance with observation.

  7. 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.

  8. Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high temperature superconductor La2-x(Sr;Ba)xCuO4

    DOE PAGESBeta

    Wagman, J. J.; Carlo, Jeremy P.; Gaudet, J.; Van Gastel, G. J.; Abernathy, Douglas L.; Stone, Matthew B.; Granroth, Garrett E.; Kolesnikov, Alexander I.; Savici, Andrei T.; Kim, Young -June; et al

    2016-03-14

    We present time-of- ight neutron-scattering measurements on single crystals of La2-xBaxCuO4 (LBCO) with 0 ≤ x ≤ 0.095 and La2-xSrxCuO4 (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high temperature cuprate superconductivity, ranging from insulating, three dimensional commensurate long range antiferromagnetic order for x ≤ 0.02 to two dimensional (2D) incommensurate antiferromagnetism co-existing with superconductivity for x ≥ 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear resonant enhancement of the inelastic scattering coincident with the low energy crossings of the highly dispersive spinmore » excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore we show that the low temperature, low energy magnetic spectral weight is substantially larger for samples with non-superconducting ground states relative to any of the samples with superconducting ground states. Lastly spin gaps, suppression of low energy magnetic spectral weight, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO« less

  9. 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.

  10. Fermi surface dichotomy of superconducting gap and pseudogap in underdoped pnictides

    NASA Astrophysics Data System (ADS)

    Xu, Y.-M.; Richard, P.; Nakayama, K.; Kawahara, T.; Sekiba, Y.; Qian, T.; Neupane, M.; Souma, S.; Sato, T.; Takahashi, T.; Luo, H.; Wen, H.-H.; Chen, G.-F.; Wang, N.-L.; Wang, Z.; Fang, Z.; Dai, X.; Ding, H.

    2010-03-01

    A systematic angle-resolved photoemission spectroscopy (ARPES) study has been performed on the hole-doped 122-phase (Ba1-xKxFe2As2) in the underdoped (UD) region. We observe that the superconducting (SC) gap of the UD pnictides scales linearly with the transition temperature, and a distinct pseudogap develops upon underdoping and coexists with the SC gap. Remarkably, this pseudogap occurs mainly on the FS sheets that are connected by the AF wave vector, where the SC pairing is stronger as well. The observed dichotomic behaviour of the pseudogap and the SC gap on different FS sheets in the UD pnictides shares many similarities with those observed in the UD copper oxide superconductors, providing a unifying picture for both families of high- temperature superconductors.

  11. Superconductivity at 9 K in Mo5PB2 with evidence for multiple gaps

    NASA Astrophysics Data System (ADS)

    McGuire, Michael A.; Parker, David S.

    2016-02-01

    Superconductivity is observed with critical temperatures near 9 K in the tetragonal compound Mo5PB2 . This material adopts the Cr5B3 structure type common to superconducting Nb5Si3 -xBx ,Mo5SiB2 , and W5SiB2 , which have critical temperatures of 5.8 -7.8 K. We have synthesized polycrystalline samples of the compound, made measurements of electrical resistivity, magnetic susceptibility, and heat capacity, and performed first-principles electronic structure calculations. The highest Tc value (9.2 K) occurs in slightly phosphorus rich samples, with composition near Mo5P1.1B1.9 , and the upper critical field Hc 2 at T =0 is estimated to be ≈17 kOe. Together, the measurements and band-structure calculations indicate intermediate coupling (λ =1.0 ), phonon mediated superconductivity. The temperature dependence of the heat capacity and upper critical field Hc 2 below Tc suggest multiple superconducting gaps may be present.

  12. Energy loss in spark gap switches

    SciTech Connect

    Oreshkin, V. I. Lavrinovich, I. V.

    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.

  13. Superconducting gap and vortex lattice of the heavy-fermion compound CeCu2Si2

    NASA Astrophysics Data System (ADS)

    Enayat, Mostafa; Sun, Zhixiang; Maldonado, Ana; Suderow, Hermann; Seiro, Silvia; Geibel, Christoph; Wirth, Steffen; Steglich, Frank; Wahl, Peter

    2016-01-01

    The order parameter and pairing mechanism for superconductivity in heavy-fermion compounds are still poorly understood. Scanning tunneling microscopy and spectroscopy at ultralow temperatures can yield important information about the superconducting order parameter and the gap structure. Here, we study the first heavy-fermion superconductor, CeCu2Si2 . Our data show the superconducting gap which is not fully formed and exhibits features that point to a multigap order parameter. Spatial mapping of the zero-bias conductance in magnetic field reveals the vortex lattice, which allows us to unequivocally link the observed conductance gap to superconductivity in CeCu2Si2 . The vortex lattice is found to be predominantly triangular with distortions at fields close to 0.7 Hc 2 .

  14. Isotropic multi-gap superconductivity in BaFe1.9Pt0.1As2 from thermal transport and spectroscopic measurements

    NASA Astrophysics Data System (ADS)

    Ziemak, Steven; Kirshenbaum, K.; Saha, S. R.; Hu, R.; Reid, J.-Ph; Gordon, R.; Taillefer, L.; Evtushinsky, D.; Thirupathaiah, S.; Büchner, B.; Borisenko, S. V.; Ignatov, A.; Kolchmeyer, D.; Blumberg, G.; Paglione, J.

    2015-01-01

    Thermal conductivity, point contact spectroscopy, angle-resolved photoemission and Raman spectroscopy measurements were performed on BaFe1.9Pt0.1As2 single crystals obtained from the same synthesis batch in order to investigate the superconducting energy gap structure using multiple techniques. Low temperature thermal conductivity was measured in the superconducting state as a function of temperature and magnetic field, revealing an absence of quasiparticle excitations in the T\\to 0 limit up to 15 T applied magnetic fields. Point-contact Andreev reflection spectroscopy measurements were performed as a function of temperature using the needle-anvil technique, yielding features in the conductance spectra at both 2.5 meV and 7.0 meV scales consistent with a multi-gap scenario. Angle-resolved photoemission spectroscopy probed the electronic band structure above and below the superconducting transition temperature of Tc = 23 K, revealing an isotropic gap of magnitude ˜ 3 meV on both electron and hole pockets. Finally, Raman spectroscopy was used to probe quasiparticle excitations in multiple channels, showing a threshold energy scale of 3 meV below Tc. Overall, we find strong evidence for an isotropic gap structure with no nodes or deep minima in this system, with a 3 meV magnitude gap consistently observed and a second, larger gap suggested by point-contact spectroscopy measurements. We discuss the implications that the combination of these results reveal about the superconducting order parameter in the BaFe2-xPtxAs2 doping system and how this relates to similar substituted iron pnictides.

  15. 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.

  16. Cosmological constraints on superconducting dark energy models

    NASA Astrophysics Data System (ADS)

    Keresztes, Zoltán; Gergely, László Á.; Harko, Tiberiu; Liang, Shi-Dong

    2015-12-01

    We consider cosmological tests of a scalar-vector-tensor gravitational model, in which the dark energy is included in the total action through a gauge-invariant, electromagnetic type contribution. The ground state of dark energy, corresponding to a constant potential V , is a Bose-Einstein type condensate with spontaneously broken U(1) symmetry. In other words, dark energy appears as a massive vector field emerging from a superposition of a massless vector and a scalar field, the latter corresponding to the Goldstone boson. Two particular cosmological models, corresponding to pure electric and pure magnetic type potentials, respectively, are confronted with type IA supernovae and Hubble parameter data. In the electric case, a good fit is obtained along a narrow inclined stripe in the Ωm-ΩV parameter plane, which includes the Λ cold dark matter limit as the best fit. The other points on this admissible region represent superconducting dark energy as a sum of a cosmological constant and a time-evolving contribution. In the magnetic case the cosmological test selects either (i) parameter ranges of the superconducting dark energy allowing for the standard baryonic sector plus dark matter or (ii) a unified superconducting dark matter and dark energy model, additionally including only the baryonic sector.

  17. ARPES observation of isotropic superconducting gaps in isovalent Ru-substituted Ba(Fe0.75Ru0.25)2As2

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoping; Xu, N.; Richard, P.; Shi, X.; Roekeghem, A. Van; Qian, T.; Ding, H.; Nakayama, K.; Sato, T.; Ieki, E.; Takahashi, T.; Xing, J.; Wen, H.-H.; Shi, M.; Rienks, E.; Thirupathaiah, S.

    2014-03-01

    We used high-energy resolution angle-resolved photoemission spectroscopy to extract the momentum dependence of the superconducting gap of Ru-substituted Ba(Fe0.75Ru0.25)2As2(Tc = 15 K). Despite a strong out-of-plane warping of the Fermi surface, the magnitude of the superconducting gap observed experimentally is nearly isotropic and independent of the out-of-plane momentum. More precisely, we respectively observed 5.7 meV and 4.5 meV superconducting gaps on the inner and outer ?-centered hole Fermi surface pockets, whereas a 4.8 meV gap is recorded on the M-centered electron Fermi surface pockets. Our results are consistent with the J1 -J2 model with a dominant antiferromagnetic exchange interaction between the next-nearest Fe neighbors. This work was supported by grants from CAS (2010Y1JB6), MOST (2010CB923000 and 2011CBA001000, 2011CBA00102, 2012CB821403) and NSFC (10974175, 11004232 and 11034011/A0402) from China, JSPS, TRiP-JST, CREST-JST and MEXT of Japan.

  18. Impact of the Spin Density Wave Order on the Superconducting Gap of Ba(Fe1-x Cox)2 As2

    NASA Astrophysics Data System (ADS)

    Chauviere, Ludivine; Gallais, Yann; Cazayous, Maximilien; Measson, Marie-Aude; Sacuto, Alain; Colson, Dorothee; Forget, Anne; Squap Team; Spec Collaboration

    2011-03-01

    We report a doping dependent electronic Raman scattering measurements on iron-pnictide superconductor Ba(Fe1-x Cox)2 As 2 single crystals. The B2g Raman spectrum at optimal doping is consistent with a strongly anisotropic gap on the electron pocket. Upon entering the coexistence region between superconducting (SC) and spin-density-wave (SDW) orders, the effective pairing energy scale is strongly reduced. Our results are interpreted in terms of a competition between SC and SDW orders for electronic states at the Fermi level. Our findings advocate for a strong connection between the SC and SDW gaps anisotropies which are both linked to interband interactions.

  19. Impact of the spin-density-wave order on the superconducting gap of Ba(Fe1-xCox)2As2

    NASA Astrophysics Data System (ADS)

    Chauvire, L.; Gallais, Y.; Cazayous, M.; Masson, M. A.; Sacuto, A.; Colson, D.; Forget, A.

    2010-11-01

    We report a doping-dependent electronic Raman-scattering measurements on iron-pnictide superconductor Ba(Fe1-xCox)2As2 single crystals. The B2g Raman spectrum at optimal doping is consistent with a strongly anisotropic gap on the electron pocket. Upon entering the coexistence region between superconducting (SC) and spin-density-wave (SDW) orders, the effective pairing energy scale is strongly reduced. Our results are interpreted in terms of a competition between SC and SDW orders for electronic states at the Fermi level. Our findings advocate for a strong connection between the SC and SDW gaps anisotropies which are both linked to interband interactions.

  20. NMR Study of the Superconducting Gap Variation near the Mott Transition in Cs3C60

    NASA Astrophysics Data System (ADS)

    Wzietek, P.; Mito, T.; Alloul, H.; Pontiroli, D.; Aramini, M.; Ricc, M.

    2014-02-01

    Former extensive studies of superconductivity in the A3C60 compounds, where A is an alkali metal, have led one to consider that Bardeen-Cooper-Schrieffer electron-phonon pairing prevails in those compounds, though the incidence of electronic Coulomb repulsion has been highly debated. The discovery of two isomeric fulleride compounds Cs3C60 which exhibit a transition with pressure from a Mott insulator (MI) to a superconducting (SC) state clearly reopens that question. Using pressure (p) as a single control parameter of the C60 balls lattice spacing, one can now study the progressive evolution of the SC properties when the electronic correlations are increased towards the critical pressure pc of the Mott transition. We have used C13 and Cs133 NMR measurements on the cubic phase A15-Cs3C60 just above pc=5.0(3) kbar, where the SC transition temperature Tc displays a dome shape with decreasing cell volume. From the T dependence below Tc of the nuclear spin lattice relaxation rate (T1)-1 we determine the electronic excitations in the SC state, that is 2?, the gap value. The latter is found to be largely enhanced with respect to the Bardeen-Cooper-Schrieffer value established in the case of dense A3C60 compounds. It even increases slightly with decreasing p towards pc, where Tc decreases on the SC dome, so that 2? /kBTc increases regularly upon approaching the Mott transition. These results bring clear evidence that the increasing correlations near the Mott transition are not significantly detrimental to superconductivity. They rather suggest that repulsive electron interactions might even reinforce elecron-phonon superconductivity, being then partly responsible for the large Tc values, as proposed by theoretical models taking the electronic correlations as a key ingredient.

  1. Distinct Fermi Surface Topology and Nodeless Superconducting Gap in a (Tl0.58Rb0.42)Fe1.72Se2 Superconductor

    NASA Astrophysics Data System (ADS)

    Mou, Daixiang; Liu, Shanyu; Jia, Xiaowen; He, Junfeng; Peng, Yingying; Zhao, Lin; Yu, Li; Liu, Guodong; He, Shaolong; Dong, Xiaoli; Zhang, Jun; Wang, Hangdong; Dong, Chiheng; Fang, Minghu; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Xu, Zuyan; Chen, Chuangtian; Zhou, X. J.

    2011-03-01

    High resolution angle-resolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the (Tl0.58Rb0.42)Fe1.72Se2 superconductor with a Tc=32K. The Fermi surface topology consists of two electronlike Fermi surface sheets around the ? point which is distinct from that in all other iron-based superconductors reported so far. The Fermi surface around the M point shows a nearly isotropic superconducting gap of 12meV. The large Fermi surface near the ? point also shows a nearly isotropic superconducting gap of 15meV, while no superconducting gap opening is clearly observed for the inner tiny Fermi surface. Our observed new Fermi surface topology and its associated superconducting gap will provide key insights and constraints into the understanding of the superconductivity mechanism in iron-based superconductors.

  2. Energy gaps in a spacetime crystal

    NASA Astrophysics Data System (ADS)

    Horwitz, L. P.; Engelberg, E. Z.

    2009-12-01

    This Letter presents an analysis of the band structure of a spacetime potential lattice created by a standing electromagnetic wave. We show that there are energy band gaps. We estimate the effect, and propose a measurement that could confirm the existence of such phenomena.

  3. Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor.

    PubMed

    Guguchia, Z; Amato, A; Kang, J; Luetkens, H; Biswas, P K; Prando, G; von Rohr, F; Bukowski, Z; Shengelaya, A; Keller, H; Morenzoni, E; Fernandes, Rafael M; Khasanov, R

    2015-01-01

    The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap. PMID:26548650

  4. Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

    DOE PAGESBeta

    Guguchia, Z.; Amato, A.; Kang, J.; Luetkens, H.; Biswas, P. K.; Prando, G.; von Rohr, F.; Bukowski, Z.; Shengelaya, A.; Keller, H.; et al

    2015-11-09

    The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. Contrasting with other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperaturemore » behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap.« less

  5. Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

    NASA Astrophysics Data System (ADS)

    Guguchia, Z.; Amato, A.; Kang, J.; Luetkens, H.; Biswas, P. K.; Prando, G.; von Rohr, F.; Bukowski, Z.; Shengelaya, A.; Keller, H.; Morenzoni, E.; Fernandes, Rafael M.; Khasanov, R.

    2015-11-01

    The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap.

  6. Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

    PubMed Central

    Guguchia, Z.; Amato, A.; Kang, J.; Luetkens, H.; Biswas, P. K.; Prando, G.; von Rohr, F.; Bukowski, Z.; Shengelaya, A.; Keller, H.; Morenzoni, E.; Fernandes, Rafael M.; Khasanov, R.

    2015-01-01

    The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap. PMID:26548650

  7. Competition between superconductivity and magnetic/nematic order as a source of anisotropic superconducting gap in underdoped Ba1-xKxFe2As2

    SciTech Connect

    Kim, H; Tanatar, M A; Straszheim, W E; Cho, K; Murphy, J; Spyrison, N; Reid, J -Ph; Shen, Bing; Wen, Hai-Hu; Fernandes, R M; Prozorov, R

    2014-07-01

    The in-plane London penetration depth Δλ(T) was measured using a tunnel diode resonator technique in single crystals of Ba1-xKxFe2As2 with doping levels x ranging from heavily underdoped, x=0.16 (Tc=7K), to nearly optimally doped, x=0.34 (Tc=39K). Exponential saturation of Δλ(T) in the T→0 limit is found in optimally doped samples, with the superfluid density ρs(T)≡[λ(0)/λ(T)]2 quantitatively described by a self-consistent γ model with two nodeless isotropic superconducting gaps. As the doping level is decreased towards the extreme end of the superconducting dome at x=0.16, the low-temperature behavior of Δλ(T) becomes nonexponential and is best described by the power law Δλ(T)∝T2, characteristic of strongly anisotropic gaps. The change between the two regimes happens within the range of coexisting magnetic/nematic order and superconductivity, x<0.25, and is accompanied by a rapid rise in the absolute value of Δλ(T) with underdoping. This effect, characteristic of the competition between superconductivity and other ordered states, is very similar to but of significantly smaller magnitude than what is observed in the electron-doped Ba(Fe1-xCox)2As2 compounds. Our study suggests that the competition between superconductivity and magnetic/nematic order in hole-doped compounds is weaker than in electron-doped compounds, and that the anisotropy of the superconducting state in the underdoped iron pnictides is a consequence of the anisotropic changes in the pairing interaction and in the gap function promoted by both magnetic and nematic long-range orders.

  8. Operation of a test bed axial-gap brushless dc rotor with a superconducting stator

    SciTech Connect

    McKeever, J.W.; Sohns, C.W.; Schwenterly, S.W.; Young, R.W. Sr.; Campbell, V.W.; Hickey, M.H.; Ott, G.W.; Bailey, J.M.

    1993-08-01

    A variable-speed axial-gap motor with a stator consisting of four liquid helium cooled superconducting electromagnets (two pole pairs) was built and proof tested up to 608 rpm in November 1990 as a tool for joint industry-laboratory evaluation of coils fabricated from high-temperature oxide superconductors. A second rotor was fabricated with improved materia winding configuration, and wire type, and the drive system was modified to eliminate current spiking. The modified motor was characterized to design speed, 188 rad/s (1800 rpm), to acquire a performance baseline for future comparison with that of high-temperature superconducting (HIS) wire. As it becomes commercially available, HTS wire will replace the low-temperature electromagnet wire in a stator modified to control wire temperatures between 4 K and 77 K. Measurements of the superconducting electromagnetic field and locked rotor torque as functions of cryocurrent and dc current through two phases of the rotor, respectively, provided data to estimate power that could be developed by the rotor. Back emf and parasitic mechanical and electromagnetic drag torques were measured as functions of angular velocity to calculate actual rotor power developed and to quantify losses, which reduce the motor`s efficiency. A detailed measurement of motor power at design speed confirmed the developed power equation. When subsequently operated at the 33-A maximum available rotor current, the motor delivered 15.3 kill (20.5 hp) to the load. In a final test, the cryostat was operated at 2500 A, 200 A below its critical current. At rotor design current of 60 A and 2500 A stator current, the extrapolated developed power would be 44.2 kill (59.2 hp) with 94% efficiency.

  9. Multiband superconductivity in Ta4Pd3Te16 with anisotropic gap structure.

    PubMed

    Jiao, Wen-He; Liu, Yi; Li, Yu-Ke; Xu, Xiao-Feng; Bao, Jin-Ke; Feng, Chun-Mu; Li, S Y; Xu, Zhu-An; Cao, Guang-Han

    2015-08-19

    We carried out measurements of the magnetoresistance, magnetic susceptibility and specific heat on crystals of the low-dimensional transition metal telluride Ta4Pd3Te16. Our results indicate that Ta4Pd3Te16 is an anisotropic type-II superconductor in the clean limit with the extracted Ginzburg-Landau parameter KGL = 84. The upper critical field Hc2(T) shows an anomalous temperature dependence at low temperatures and the anisotropy of Hc2(T) is strongly T-dependent, both of which indicate a multiband scenario. The electronic specific heat Cel(T) can be consistently described by a two-gap (s???+???d waves) model from the base temperature T/Tc ~ 0.12 up to Tc. Our results suggest nodal and multiband superconductivity in Ta4Pd3Te16. PMID:26214563

  10. Multiband superconductivity in Ta4Pd3Te16 with anisotropic gap structure

    NASA Astrophysics Data System (ADS)

    Jiao, Wen-He; Liu, Yi; Li, Yu-Ke; Xu, Xiao-Feng; Bao, Jin-Ke; Feng, Chun-Mu; Li, S. Y.; Xu, Zhu-An; Cao, Guang-Han

    2015-08-01

    We carried out measurements of the magnetoresistance, magnetic susceptibility and specific heat on crystals of the low-dimensional transition metal telluride Ta4Pd3Te16. Our results indicate that Ta4Pd3Te16 is an anisotropic type-II superconductor in the clean limit with the extracted Ginzburg-Landau parameter {?\\text{GL}}= 84. The upper critical field Hc2(T) shows an anomalous temperature dependence at low temperatures and the anisotropy of Hc2(T) is strongly T-dependent, both of which indicate a multiband scenario. The electronic specific heat {{C}\\text{el}} (T) can be consistently described by a two-gap (s???+???d waves) model from the base temperature T/{{T}\\text{c}} 0.12 up to {{T}\\text{c}} . Our results suggest nodal and multiband superconductivity in Ta4Pd3Te16.

  11. Anomalous Inner-Gap Structure in Transport Characteristics of Superconducting Junctions with Degraded Interfaces.

    PubMed

    Zhitlukhina, E; Devyatov, I; Egorov, O; Belogolovskii, M; Seidel, P

    2016-12-01

    Quantitative description of charge transport across tunneling and break-junction devices with novel superconductors encounters some problems not present or not as severe for traditional superconducting materials. In this work, we explain unexpected features in related transport characteristics as an effect of a degraded nanoscaled sheath at the superconductor surface. A model capturing the main aspects of the ballistic charge transport across hybrid superconducting structures with normally conducting nanometer-thick interlayers is proposed. The calculations are based on a scattering formalism taking into account Andreev electron-into-hole (and inverse) reflections at normal metal-superconductor interfaces as well as transmission and backscattering events in insulating barriers between the electrodes. Current-voltage characteristics of such devices exhibit a rich diversity of anomalous (from the viewpoint of the standard theory) features, in particular shift of differential-conductance maxima at gap voltages to lower positions and appearance of well-defined dips instead expected coherence peaks. We compare our results with related experimental data. PMID:26842791

  12. Anomalous Inner-Gap Structure in Transport Characteristics of Superconducting Junctions with Degraded Interfaces

    NASA Astrophysics Data System (ADS)

    Zhitlukhina, E.; Devyatov, I.; Egorov, O.; Belogolovskii, M.; Seidel, P.

    2016-02-01

    Quantitative description of charge transport across tunneling and break-junction devices with novel superconductors encounters some problems not present or not as severe for traditional superconducting materials. In this work, we explain unexpected features in related transport characteristics as an effect of a degraded nanoscaled sheath at the superconductor surface. A model capturing the main aspects of the ballistic charge transport across hybrid superconducting structures with normally conducting nanometer-thick interlayers is proposed. The calculations are based on a scattering formalism taking into account Andreev electron-into-hole (and inverse) reflections at normal metal-superconductor interfaces as well as transmission and backscattering events in insulating barriers between the electrodes. Current-voltage characteristics of such devices exhibit a rich diversity of anomalous (from the viewpoint of the standard theory) features, in particular shift of differential-conductance maxima at gap voltages to lower positions and appearance of well-defined dips instead expected coherence peaks. We compare our results with related experimental data.

  13. A Superconducting Linac for the Energy Amplifier

    NASA Astrophysics Data System (ADS)

    Ruggiero, A. G.

    1997-05-01

    Because of the safer and more reliable mode of operation, a Superconducting Linac is proposed here as the proton beam accelerator which drives a nuclear plant based on the concept of the Energy Amplifier. The accelerator has also high electric power efficiency, estimated around 40%. An example based on the net generation of 400 MW (electric) is described here. 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. The study compares the cost and performance of several rf cavity frequencies, namely 350 versus 800 MHz. Higher power values can be obtained with larger beam energy and intensity. A re-circulation configuration mode of the Linac is also proposed and studied.

  14. Coexistence of a pseudogap and a superconducting gap for the high-Tc superconductor La2 -xSrxCuO4 studied by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Yoshida, T.; Malaeb, W.; Ideta, S.; Lu, D. H.; Moor, R. G.; Shen, Z.-X.; Okawa, M.; Kiss, T.; Ishizaka, K.; Shin, S.; Komiya, Seiki; Ando, Yoichi; Eisaki, H.; Uchida, S.; Fujimori, A.

    2016-01-01

    The relationship between the superconducting gap and the pseudogap has been the subject of controversies. In order to clarify this issue, we have studied the superconducting gap and pseudogap of the high-Tc superconductor La2 -xSrxCuO4 (x =0.10 ,14 ) by angle-resolved photoemission spectroscopy (ARPES). Through the analysis of the ARPES spectra above and below Tc, we have identified a superconducting coherence peak even in the antinodal region on top of the pseudogap of a larger energy scale. The superconducting peak energy nearly follows the pure d -wave form. The d -wave order parameter ?0 [defined by ? (k ) =?0(coskxa -coskya ) ] for x =0.10 and 0.14 are nearly the same, ?012 -14 meV , leading to strong coupling 2 ?0/kBTc10 . The present result indicates that the pseudogap and the superconducting gap are distinct phenomena and can be described by the "two-gap" scenario.

  15. Superconducting magnetic energy storage for asynchronous electrical systems

    DOEpatents

    Boenig, H.J.

    1984-05-16

    It is an object of the present invention to provide superconducting magnetic energy storage for a plurality of asynchronous electrical systems. It is a further object of the present invention to provide load leveling and stability improvement in a plurality of independent ac systems using a single superconducting magnetic energy storage coil.

  16. Energy gaps measured by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Wang, Chen; Giambattista, B.; Slough, C. G.; Coleman, R. V.; Subramanian, M. A.

    1990-11-01

    A scanning tunneling microscope (STM) has been used to measure energy gaps in the charge-density-wave (CDW) phases of the layer-structure dichalcogenides and in the high-temperature superconductor Bi2Sr2CaCu2O8. Measured values of ?CDW at 4.2 K for 2H-TaSe2, 2H-TaS2, and 2H-NbSe2 are 80, 50, and 34 meV giving values of 2?CDW/kBTc equal to 15.2, 15.4, and 23.9, indicating strong coupling in these CDW systems. Measured values of ?CDW at 4.2 K in 1T-TaSe2 and 1T-TaS2 are ~150 meV for both materials giving 2?CDW/kBTc~=5.8. STM scans of Bi2Sr2CaCu2O8 at 4.2 K resolve atoms on the BiOx layer and show possible variations in electronic structure. The energy gap determined from I versus V and dI/dV versus V curves is in the range 30-35 meV giving values of 2?/kBTc~=8. Spectroscopy measurements with the STM can exhibit large zero-bias anomalies which complicate the analysis of the energy-gap structure, but adequate separation has been accomplished.

  17. 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 ...

  18. Fully gapped superconductivity in In-doped topological crystalline insulator Pb0.5Sn0.5Te

    SciTech Connect

    Du, Guan; Gu, G. D.; Du, Zengyi; Fang, Delong; Yang, Huan; Zhong, R. D.; Schneeloch, J.; Wen, Hai -Hu

    2015-07-27

    In this study, superconductors derived from topological insulators and topological crystalline insulators by chemical doping have long been considered to be candidates as topological superconductors. Pb0.5Sn0.5Te is a topological crystalline insulator with mirror symmetry protected surface states on (001)-, (011)-, and (111)-oriented surfaces. The superconductor (Pb0.5Sn0.5)0.7In0.3Te is produced by In doping in Pb0.5Sn0.5Te, and is thought to be a topological superconductor. Here we report scanning tunneling spectroscopy measurements of the superconducting state as well as the superconducting energy gap in (Pb0.5Sn0.5)0.7In0.3Te on a (001)-oriented surface. The spectrum can be well fitted by an anisotropic s-wave gap function of Δ = 0.72 + 0.18cos4θ meV using Dynes model. The results show that the superconductor seems to be a fully gapped one without any in-gap states, in contradiction with the expectation of a topological superconductor.

  19. Hydrocarbon deposition in gaps of tungsten and graphite tiles in Experimental Advanced Superconducting Tokamak edge plasma parameters

    NASA Astrophysics Data System (ADS)

    Xu, Qian; Yang, Zhongshi; Luo, Guang-Nan

    2015-09-01

    The three-dimensional (3D) Monte Carlo code PIC-EDDY has been utilized to investigate the mechanism of hydrocarbon deposition in gaps of tungsten tiles in the Experimental Advanced Superconducting Tokamak (EAST), where the sheath potential is calculated by the 2D in space and 3D in velocity particle-in-cell method. The calculated results for graphite tiles using the same method are also presented for comparison. Calculation results show that the amount of carbon deposited in the gaps of carbon tiles is three times larger than that in the gaps of tungsten tiles when the carbon particles from re-erosion on the top surface of monoblocks are taken into account. However, the deposition amount is found to be larger in the gaps of tungsten tiles at the same CH4 flux. When chemical sputtering becomes significant as carbon coverage on tungsten increases with exposure time, the deposition inside the gaps of tungsten tiles would be considerable.

  20. 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.

  1. Flywheel energy storage using superconducting magnetic bearings

    SciTech Connect

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

    1994-04-01

    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 a demonstration project to advance the state of the art in high temperature superconductor (HTS) bearing performance and the overall demonstration of efficient Flywheel Energy Storage. Currently, electricity must be used simultaneously with its generation as electrical energy storage is not available for most utilities. Existing storage methods either are dependent on special geography, are too expensive, or are too inefficient. Without energy storage, electric utilities, such as Commonwealth Edison Company, are forced to cycle base load power plants to meet load swings in hourly customer demand. Demand can change by as much as 30% over a 12-hour period and result in significant costs to utilities as power plant output is adjusted to meet these changes. HTS FES systems can reduce demand-based power plant cycling by storing unused nighttime capacity until it is needed to meet daytime demand.

  2. Average kinetic energy of the superconducting state

    NASA Astrophysics Data System (ADS)

    Doria, Mauro M.; Salem-Sugui, S.; de Oliveira, I. G.; Ghivelder, L.; Brandt, E. H.

    2002-04-01

    Isothermal magnetization curves are plotted as the magnetization times the magnetic induction, 4?M.B, versus the applied field H. We show here that this curve is the average kinetic energy of the superconducting state versus the applied field, for type-II superconductors with a high Ginzburg-Landau parameter ?. The maximum of 4?M.B occurs at a field H*, directly related to the upper critical field Hc2, suggesting that Hc2(T) may be extracted from such plots even in cases when it is too high for direct measurement. We obtain these plots both theoretically, from the Ginzburg-Landau theory, and experimentally, using a Niobium sample with Tc=8.5 K, and compare them.

  3. 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.

  4. Energy band gaps in periodic bent graphene

    NASA Astrophysics Data System (ADS)

    Xie, Wenze; Li, Zhongyao

    2016-01-01

    Based on the first-principles calculations, we studied the energy bandgaps of the two kinds of periodic bent graphenes: smooth-bent graphene and stepped graphene. In the smooth-bent graphene, the sinusoidal type of graphene superlattice is a gapless semiconductor as the flattened graphene. The periodic smooth bending is unable to open the bandgap of graphene. Although the bandgap can be larger than 100 meV in stepped graphene, it is sensitively dependent on the details of structure. Band gap can only be opened in a certain range of tilt angle. The localized states greatly influence the bandgap opening in stepped graphene.

  5. The role of engineered materials in superconducting tunnel junction X-ray detectors - Suppression of quasiparticle recombination losses via a phononic band gap

    NASA Technical Reports Server (NTRS)

    Rippert, Edward D.; Ketterson, John B.; Chen, Jun; Song, Shenian; Lomatch, Susanne; Maglic, Stevan R.; Thomas, Christopher; Cheida, M. A.; Ulmer, Melville P.

    1992-01-01

    An engineered structure is proposed that can alleviate quasi-particle recombination losses via the existence of a phononic band gap that overlaps the 2-Delta energy of phonons produced during recombination of quasi-particles. Attention is given to a 1D Kronig-Penny model for phonons normally incident to the layers of a multilayered superconducting tunnel junction as an idealized example. A device with a high density of Bragg resonances is identified as desirable; both Nb/Si and NbN/SiN superlattices have been produced, with the latter having generally superior performance.

  6. The role of engineered materials in superconducting tunnel junction X-ray detectors - Suppression of quasiparticle recombination losses via a phononic band gap

    NASA Astrophysics Data System (ADS)

    Rippert, Edward D.; Ketterson, John B.; Chen, Jun; Song, Shenian; Lomatch, Susanne; Maglic, Stevan R.; Thomas, Christopher; Cheida, M. A.; Ulmer, Melville P.

    1992-10-01

    An engineered structure is proposed that can alleviate quasi-particle recombination losses via the existence of a phononic band gap that overlaps the 2-Delta energy of phonons produced during recombination of quasi-particles. Attention is given to a 1D Kronig-Penny model for phonons normally incident to the layers of a multilayered superconducting tunnel junction as an idealized example. A device with a high density of Bragg resonances is identified as desirable; both Nb/Si and NbN/SiN superlattices have been produced, with the latter having generally superior performance.

  7. 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.

  8. 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.

  9. Optical study of BaFe2As2 under pressure: Coexistence of spin-density-wave gap and superconductivity

    NASA Astrophysics Data System (ADS)

    Uykur, E.; Kobayashi, T.; Hirata, W.; Miyasaka, S.; Tajima, S.; Kuntscher, C. A.

    2015-12-01

    Temperature-dependent reflectivity measurements in the frequency range 85 -7000 cm-1 were performed on BaFe2As2 single crystals under pressure up to ˜5 GPa. The corresponding pressure- and temperature-dependent optical conductivity was analyzed with the Drude-Lorentz model to extract the coherent and incoherent contributions. The gradual suppression of the spin-density-wave (SDW) state with increasing pressure and the appearance of the superconducting phase coexisting with the SDW phase at 3.6 GPa were observed. At 3.6 GPa, the reflectivity reaches unity below ˜95 cm-1 indicating the opening of the superconducting gap and shows a full gap tendency at 6 K.

  10. Scrutinizing the double superconducting gaps and strong coupling pairing in (Li1−xFex)OHFeSe

    PubMed Central

    Du, Zengyi; Yang, Xiong; Lin, Hai; Fang, Delong; Du, Guan; Xing, Jie; Yang, Huan; Zhu, Xiyu; Wen, Hai-Hu

    2016-01-01

    In the field of iron-based superconductors, one of the frontier studies is about the pairing mechanism. The recently discovered (Li1−xFex)OHFeSe superconductor with the transition temperature of about 40 K provides a good platform to check the origin of double superconducting gaps and high transition temperature in the monolayer FeSe thin film. Here we report a scanning tunnelling spectroscopy study on the (Li1−xFex)OHFeSe single crystals. The tunnelling spectrum mimics that of the monolayer FeSe thin film and shows double gaps at about 14.3 and 8.6 meV. Further analysis based on the quasiparticle interference allows us to rule out the d-wave gap, and for the first time assign the larger (smaller) gap to the outer (inner) Fermi pockets (after folding) associating with the dxy (dxz/dyz) orbitals, respectively. The gap ratio amounts to 8.7, which demonstrates the strong coupling mechanism in the present superconducting system. PMID:26822281

  11. Scrutinizing the double superconducting gaps and strong coupling pairing in (Li1-xFex)OHFeSe

    NASA Astrophysics Data System (ADS)

    Du, Zengyi; Yang, Xiong; Lin, Hai; Fang, Delong; Du, Guan; Xing, Jie; Yang, Huan; Zhu, Xiyu; Wen, Hai-Hu

    2016-01-01

    In the field of iron-based superconductors, one of the frontier studies is about the pairing mechanism. The recently discovered (Li1-xFex)OHFeSe superconductor with the transition temperature of about 40 K provides a good platform to check the origin of double superconducting gaps and high transition temperature in the monolayer FeSe thin film. Here we report a scanning tunnelling spectroscopy study on the (Li1-xFex)OHFeSe single crystals. The tunnelling spectrum mimics that of the monolayer FeSe thin film and shows double gaps at about 14.3 and 8.6 meV. Further analysis based on the quasiparticle interference allows us to rule out the d-wave gap, and for the first time assign the larger (smaller) gap to the outer (inner) Fermi pockets (after folding) associating with the dxy (dxz/dyz) orbitals, respectively. The gap ratio amounts to 8.7, which demonstrates the strong coupling mechanism in the present superconducting system.

  12. Scrutinizing the double superconducting gaps and strong coupling pairing in (Li1-xFex)OHFeSe.

    PubMed

    Du, Zengyi; Yang, Xiong; Lin, Hai; Fang, Delong; Du, Guan; Xing, Jie; Yang, Huan; Zhu, Xiyu; Wen, Hai-Hu

    2016-01-01

    In the field of iron-based superconductors, one of the frontier studies is about the pairing mechanism. The recently discovered (Li1-xFex)OHFeSe superconductor with the transition temperature of about 40 K provides a good platform to check the origin of double superconducting gaps and high transition temperature in the monolayer FeSe thin film. Here we report a scanning tunnelling spectroscopy study on the (Li1-xFex)OHFeSe single crystals. The tunnelling spectrum mimics that of the monolayer FeSe thin film and shows double gaps at about 14.3 and 8.6 meV. Further analysis based on the quasiparticle interference allows us to rule out the d-wave gap, and for the first time assign the larger (smaller) gap to the outer (inner) Fermi pockets (after folding) associating with the dxy (dxz/dyz) orbitals, respectively. The gap ratio amounts to 8.7, which demonstrates the strong coupling mechanism in the present superconducting system. PMID:26822281

  13. Method for making mirrored surfaces comprising superconducting material

    DOEpatents

    Early, James T. (Livermore, CA); Hargrove, R. Steven (Danville, CA)

    1989-01-01

    Superconducting mirror surfaces are provided by forming a mirror surface from a material which is superconductive at a temperature above about 40.degree. K. and adjusting the temperature of the surface to that temperature at which the material is superconducting. The mirror surfaces are essentially perfect reflectors for electromagnetic radiation with photon energy less than the superconducting band gap.

  14. Method for making mirrored surfaces comprising superconducting material

    DOEpatents

    Early, J.T.; Hargrove, R.S.

    1989-12-12

    Superconducting mirror surfaces are provided by forming a mirror surface from a material which is superconductive at a temperature above about 40 K and adjusting the temperature of the surface to that temperature at which the material is superconducting. The mirror surfaces are essentially perfect reflectors for electromagnetic radiation with photon energy less than the superconducting band gap.

  15. Evaluation of superconducting magnetic energy storage systems

    NASA Astrophysics Data System (ADS)

    Lee, S. T.; Albert, R. S.; Imamura, D. T.

    1983-02-01

    The breakeven capital cost of Superconducting Magnetic Energy Storage (SMES) and its highest possible value were studied. The results are compared by EPRI to the capital cost of SMES being estimated by Bechtel in a related study. The best and most reasonable estimate of the SMES breakeven capital cost is 1080 $/kW in 1981 dollars. The highest possible value for an ideal SMES with perfect availability, zero refrigeration load and 100% incremental cycle efficiency is 1510 $/kW when installed in a utility approximately one third of the US in size. Two methods of analysis are used. A single year analysis that assigns an energy credit and a capacity credit to SMES provides the method for parametric and sensitivity analyses. A thirty year life cycle analysis comparing SMES to a coal fired generation alternative recognizes fuel cost escalation effects. The value of SMES to each of the six EPRI Regional Systems is computed. In comparison with pumped storage, SMES is worth 14% more to a utility.

  16. A rotating superconducting solenoid for 100 kWh energy storage. [in space

    NASA Technical Reports Server (NTRS)

    Waynert, J.; Eyssa, Y. M.; Mcintosh, G. E.; Feng, Z.

    1985-01-01

    Two concentric superconducting solenoids, one rotating, the other stationary are analyzed for energy storage in space. Energy is transferred from the rotating mass through a shaft coupled to a motor-generator. The inner windings interact with the magnetic field of the outer solenoid to cancel the centrifugal and self-field forces of the flywheel rim. Current is induced in the inner solenoid thus requiring no separate power supply, while the current in the outer solenoid must vary with the angular velocity of the flywheel. The effect of the gap and scaling laws are developed. The efficiency in energy per unit mass is marginally attractive.

  17. Upper critical field of KFe2As2 under pressure: A test for the change in the superconducting gap structure

    SciTech Connect

    Taufour, Valentin; Foroozani, Neda; Tanatar, Makariy A.; Lim, Jinhyuk; Kaluarachchi, Udhara; Kim, Stella K.; Liu, Yong; Lograsso, Thomas A.; Kogan, Vladimir G.; Prozorov, Ruslan; Bud'ko, Sergey L.; Schilling, James S.; Canfield, Paul C.

    2014-06-01

    We report measurements of electrical resistivity under pressure to 5.8 GPa, magnetization to 6.7 GPa, and ac susceptibility to 7.1 GPa in KFe2As2. The previously reported change of slope in the pressure dependence of the superconducting transition temperature Tc(p) at a pressure p??1.8 GPa is confirmed, and Tc(p) is found to be nearly constant above p? up to 7.1 GPa. The T?p phase diagram is very sensitive to the pressure conditions as a consequence of the anisotropic uniaxial pressure dependence of Tc. Across p?, a change in the behavior of the upper critical field is revealed through a scaling analysis of the slope of Hc2 with the effective mass as determined from the A coefficient of the T2 term of the temperature-dependent resistivity. We show that this scaling provides a quantitative test for the changes of the superconducting gap structure and suggests the development of a kz modulation of the superconducting gap above p? as a most likely explanation.

  18. Upper critical field of KFe2As2 under pressure: A test for the change in the superconducting gap structure

    NASA Astrophysics Data System (ADS)

    Taufour, Valentin; Foroozani, Neda; Tanatar, Makariy A.; Lim, Jinhyuk; Kaluarachchi, Udhara; Kim, Stella K.; Liu, Yong; Lograsso, Thomas A.; Kogan, Vladimir G.; Prozorov, Ruslan; Bud'ko, Sergey L.; Schilling, James S.; Canfield, Paul C.

    2014-06-01

    We report measurements of electrical resistivity under pressure to 5.8 GPa, magnetization to 6.7 GPa, and ac susceptibility to 7.1 GPa in KFe2As2. The previously reported change of slope in the pressure dependence of the superconducting transition temperature Tc(p) at a pressure p*1.8 GPa is confirmed, and Tc(p) is found to be nearly constant above p* up to 7.1 GPa. The T-p phase diagram is very sensitive to the pressure conditions as a consequence of the anisotropic uniaxial pressure dependence of Tc. Across p*, a change in the behavior of the upper critical field is revealed through a scaling analysis of the slope of Hc_2 with the effective mass as determined from the A coefficient of the T2 term of the temperature-dependent resistivity. We show that this scaling provides a quantitative test for the changes of the superconducting gap structure and suggests the development of a kz modulation of the superconducting gap above p* as a most likely explanation.

  19. Toroidal constant-tension superconducting magnetic energy storage units

    DOEpatents

    Herring, J. Stephen

    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.

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

    DOE PAGESBeta

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

    2015-06-18

    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 γr=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 α model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of Δ₀~5.3 me V, corresponding to Δ₀/kBTc ~ 2.2. Increasing the phosphorus concentration x, the main gap reduces tillmore » a value of Δ₀ ~ 1.9 meV for x = 0.55 and a second weaker gap becomes evident. From the magnetic field effect on γr, all samples however show similar behavior [γr(H) - γr (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

  1. 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 γr=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 α model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of Δ0˜5.3 meV , corresponding to Δ0/kBTc˜2.2 . Increasing the phosphorus concentration x , the main gap reduces till a value of Δ0˜1.9 meV for x =0.55 and a second weaker gap becomes evident. From the magnetic field effect on γr, all samples however show similar behavior [γr(H ) -γr(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.

  2. 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.

  3. Superconductivity

    NASA Astrophysics Data System (ADS)

    Cyrot, Michel

    Superconductiviy is a quantum phenomenon. It shows up through strange physical properties which arouse curiosity but also lead to interesting applications. The presence of superconductivity in a book on magnetism is justified: first, because superconductor substances are generally strongly diamagnetic, but also because superconductors are used both to generate relatively intense magnetic fields (superconducting magnets), and to detect very weak magnetic inductions (SQUIDs).

  4. Application of magnetic atom induced bound states in superconducting gap for chemical identification of single magnetic atoms

    NASA Astrophysics Data System (ADS)

    Ji, Shuai-Hua; Zhang, Tong; Fu, Ying-Shuang; Chen, Xi; Jia, Jin-Feng; Xue, Qi-Kun; Ma, Xu-Cun

    2010-02-01

    Elemental identification at single atom level has been achieved with a low temperature scanning tunneling microscope. Magnetic atoms (Mn or Cr) adsorbed on a superconducting Pb substrate induce a set of well-defined resonance states inside the superconductor gap in scanning tunneling spectroscopy. We show that these localized characteristic bound states could serve as fingerprint for chemical identification of the corresponding atoms, similar to atomic/molecular spectra widely used in optical spectrometry. The experiment demonstrates a technique for element-resolved spectroscopy with simultaneous atomic-level spatial resolution. The influence of magnetic impurity concentration on the bound states has also been investigated.

  5. Probing hybridization of a single energy level coupled to superconducting leads

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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 leads 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.

  6. Nodeless superconducting gap in the caged-type superconductors Y5Rh6Sn18 and Lu5Rh6Sn18

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Xu, Y.; Kuo, C. N.; Hong, X. C.; Wang, M. X.; Cai, P. L.; Dong, J. K.; Lue, C. S.; Li, S. Y.

    2015-10-01

    Low-temperature thermal conductivity measurements were performed on the single crystal of caged-type superconductors Y5Rh6Sn18 and Lu5Rh6Sn18 down to 80 mK. In zero magnetic field, no residual linear term {? }0/T is found for either superconductor. At low field, the {? }0/T of these two superconductors shows weak field dependence. These results exclude the nodal superconducting gap in Y5Rh6Sn18 as revealed by recent specific heat measurements, and suggest that the caged-type superconductors R5Rh6Sn18 (R = Y and Lu) may have a common nodeless superconducting gap.

  7. 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.

  8. Research and development of superconductivity for energy technology in electrotechnical laboratory

    SciTech Connect

    Koyama, K.

    1984-10-01

    Superconductivity is a physical effect wherein the electrical resistivity disappears at cryogenic temperatures. Superconductivity has the advantage of following large current densities and high magnetic fields, which are stable and homogeneous. There are many applications of superconductivity which take advantage of these merits. It is of special importance to apply superconductors to alternative energy and energy saving technology. This paper presents briefly some of the research and development efforts to apply superconductivity to energy technology in the Electrotechnical Laboratory (ETL).

  9. 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.

  10. Nodal to nodeless superconducting energy-gap structure change concomitant with Fermi-surface reconstruction in the heavy-fermion compound CeCoIn5

    SciTech Connect

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

    2015-01-15

    The London penetration depth λ(T) was measured in single crystals of Ce1–xRxCoIn₅, R=La, Nd, and Yb down to Tmin ≈ 50 mK (Tc/Tmin ~50) using a tunnel-diode resonator. In the cleanest samples Δλ(T) is best described by the power law, Δλ(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 Δλ(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. As a result, 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.

  11. Nodal to nodeless superconducting energy-gap structure change concomitant with Fermi-surface reconstruction in the heavy-fermion compound CeCoIn5

    SciTech Connect

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

    2015-01-15

    The London penetration depth ?(T) was measured in single crystals of Ce1xRxCoIn?, 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. As a result, 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.

  12. Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

    SciTech Connect

    Guguchia, Z.; Amato, A.; Kang, J.; Luetkens, H.; Biswas, P. K.; Prando, G.; von Rohr, F.; Bukowski, Z.; Shengelaya, A.; Keller, H.; Morenzoni, E.; Fernandes, Rafael M.; Khasanov, R.

    2015-11-09

    The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. Contrasting with other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap.

  13. Superconductivity:

    NASA Astrophysics Data System (ADS)

    Sacchetti, N.

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

  14. Multifrequency modes in superconducting resonators: Bridging frequency gaps in off-resonant couplings

    NASA Astrophysics Data System (ADS)

    Andersen, Christian Kraglund; Mlmer, Klaus

    2015-02-01

    A superconducting quantum interference device (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 sidebands. In this work we calculate the multifrequency eigenmodes of resonators coupled to periodically driven SQUIDs and we use the Lagrange formalism to propose a theory for their quantization. The elementary excitations of a multifrequency mode 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 of our multifrequency modes, we determine their coupling to transmon qubits with different frequencies and we present a bichromatic scheme for entanglement and gate operations.

  15. Energy of magnetic moment of superconducting current in magnetic field

    NASA Astrophysics Data System (ADS)

    Gurtovoi, V. L.; Nikulov, A. V.

    2015-09-01

    The energy of magnetic moment of the persistent current circulating in superconducting loop in an externally produced magnetic field is not taken into account in the theory of quantization effects because of identification of the Hamiltonian with the energy. This identification misleads if, in accordance with the conservation law, the energy of a state is the energy expended for its creation. The energy of magnetic moment is deduced from a creation history of the current state in magnetic field both in the classical and quantum case. But taking this energy into account demolishes the agreement between theory and experiment. Impartial consideration of this problem discovers the contradiction both in theory and experiment.

  16. Langmuir vacuum and superconductivity

    SciTech Connect

    Veklenko, B. A.

    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.

  17. ESR spectrometer with a loop-gap resonator for cw and time resolved studies in a superconducting magnet.

    PubMed

    Simon, Ferenc; Murnyi, Ferenc

    2005-04-01

    The design and performance of an electron spin resonance spectrometer operating at 3 and 9 GHz microwave frequencies combined with a 9-T superconducting magnet are described. The probehead contains a compact two-loop, one gap resonator, and is inside the variable temperature insert of the magnet enabling measurements in the 0-9T magnetic field and 1.5-400 K temperature range. The spectrometer allows studies on systems where resonance occurs at fields far above the g approximately 2 paramagnetic condition such as in antiferromagnets. The low quality factor of the resonator allows time resolved experiments such as, e.g., longitudinally detected ESR. We demonstrate the performance of the spectrometer on the NaNiO2 antiferromagnet, the MgB2 superconductor, and the RbC60 conducting alkaline fulleride polymer. PMID:15780920

  18. 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.

  19. Numerical analysis of magnetic field in superconducting magnetic energy storage

    SciTech Connect

    Kanamaru, Y. ); Amemiya, Y. )

    1991-09-01

    This paper reports that the superconducting magnetic energy storage (SMES) is more useful than the other systems of electric energy storage because of larger stored energy and higher efficiency. The other systems are the battery, the flywheel, the pumped-storage power station. Some models of solenoid type SMES are designed in U.S.A. and Japan. But a high magnetic field happens by the large scale SMES in the living environment, and makes the erroneous operations of the computer display, the pacemaker of the heart and the electronic equipments. We study some fit designs of magnetic shielding of the solenoidal type SMES for reduction of the magnetic field in living environment. When some superconducting shielding coils are over the main storage coil, magnetic field reduces remarkably than the case of non shielding coil. The calculated results of the magnetic field are obtained y the finite element method.

  20. Anisotropic rectifying characteristics induced by the superconducting gap of YBa2Cu3O7-δ/Nb-doped SrTiO3 heterojunctions

    NASA Astrophysics Data System (ADS)

    Zhang, M. J.; Hao, F. X.; Zhang, C.; Liu, X.; Li, X. G.

    2015-11-01

    In this paper, we investigated the anisotropic rectifying characteristics of a YBa2Cu3O7-δ (YBCO)/Nb-doped SrTiO3 heterojunction in magnetic fields of up to 9 T by rotating the junction from H//c to H//ab of the YBCO film. From the temperature and field dependencies of the diffusion potential Vd, we found that the angle-resolved reductions of Vd from its original value, δVd, were induced by the anisotropic superconducting gap Δ of the YBCO. The anisotropic parameter obtained from Δ was close to that obtained from the angular-dependent upper critical fields of the YBCO. This heterojunction is helpful both in investigating the superconducting gap and in designing sensitive superconducting devices.

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

    NASA Astrophysics Data System (ADS)

    Andersen, Christian Kraglund; Mlmer, 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.

  2. Universality of superconducting gaps in overdoped Ba0.3K0.7Fe2As2 observed by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Nakayama, K.; Sato, T.; Richard, P.; Xu, Y.-M.; Kawahara, T.; Umezawa, K.; Qian, T.; Neupane, M.; Chen, G. F.; Ding, H.; Takahashi, T.

    2011-01-01

    We have performed angle-resolved photoemission spectroscopy on the overdoped Ba0.3K0.7Fe2As2 superconductor (Tc=22 K). We demonstrate that the superconducting (SC) gap on each Fermi surface (FS) is nearly isotropic whereas the gap value varies from 4.4 to 7.9 meV on different FSs. By comparing with under- and optimally doped Ba1-xKxFe2As2, we find that the gap value on each FS nearly scales with Tc over a wide doping range (0.25?x?0.7). Although the FS volume and the SC gap magnitude are strongly doping dependent, the multiple nodeless gaps can be commonly fitted by a single gap function assuming pairing up to the second nearest neighbor, suggesting the universality of the short-range pairing states with the s-wave symmetry.

  3. Which Way to the Energy Gap?

    ERIC Educational Resources Information Center

    Loftas, Tony

    1973-01-01

    The higher cost of energy in the future might well dampen the current ardour for industrialization. Cheap sources are the ones most likely to disappear, pointing to a further disparity between industrialized and nonindustrialized societies. (BL)

  4. 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 ?0.55W, 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.

  5. Superconducting magnetic energy storage apparatus structural support system

    DOEpatents

    Withers, Gregory J.; Meier, Stephen W.; Walter, Robert J.; Child, Michael D.; DeGraaf, Douglas W.

    1992-01-01

    A superconducting magnetic energy storage apparatus comprising a cylindrical superconducting coil; a cylindrical coil containment vessel enclosing the coil and adapted to hold a liquid, such as liquefied helium; and a cylindrical vacuum vessel enclosing the coil containment vessel and located in a restraining structure having inner and outer circumferential walls and a floor; the apparatus being provided with horizontal compression members between (1) the coil and the coil containment vessel and (2) between the coil containment vessel and the vacuum vessel, compression bearing members between the vacuum vessel and the restraining structure inner and outer walls, vertical support members (1) between the coil bottom and the coil containment vessel bottom and (2) between the coil containment vessel bottom and the vacuum vessel bottom, and external supports between the vacuum vessel bottom and the restraining structure floor, whereby the loads developed by thermal and magnetic energy changes in the apparatus can be accommodated and the structural integrity of the apparatus be maintained.

  6. Doping Dependence on Two Sizes of Superconducting Gaps on Tl1223 by Tunneling Spectroscopy at 4.2 K

    NASA Astrophysics Data System (ADS)

    Sekine, R.; Kawashima, S.; Minematsu, M.; Inose, T.; Mikusu, S.; Tokiwa, K.; Watanabe, T.; Tsukada, A.; Miyakawa, N.

    We present tunneling results on tri-layered cuprate superconductors TlBa2Ca2Cu3O8.5+? (Tl1223) with two different hole concentration, which are an over-doped Tl1223 with TC ? 112 K (OD-112K) and a slightly over-doped Tl1223 with TC ? 126 K (SOD-126K). The tunneling conductances on both samples exhibited two sizes of gaps originated from outer (OP) and inner (IP) CuO2 planes. The superconducting gap at each planes, ?(OP)/e ? Vp(OP) and ?(IP)/e ? Vp(IP) on OD-112K are observed that Vp(OP) is 22 2 mV and Vp(IP) is 37 4 mV. Similarly, Vp(OP) is 26 2 mV and Vp(IP) is 39 3 mV on SOD-126K. Although both Vp(OP) and Vp(IP) decrease with increasing oxygen contents, ?Vp(OP) = Vp(OP)(SOD-126K) - Vp(OP)(OD-112K) is larger than ?Vp(IP) for IP. Moreover, ?Vp(plane) tbnd6 Vp(IP) - Vp(OP) increases with overdoping. These results as a function of doping implies the OP might control the variation of TC dominantly.

  7. Magnetic Field Effect on the Superconducting Magnetic Gap of Nd1.85Ce0.15CuO4

    NASA Astrophysics Data System (ADS)

    Motoyama, E. M.; Mang, P. K.; Petitgrand, D.; Yu, G.; Vajk, O. P.; Vishik, I. M.; Greven, M.

    2006-04-01

    Inelastic neutron-scattering measurements on the archetypical electron-doped material Nd1.85Ce0.15CuO4 up to a high relative magnetic-field strength, H/Hc250%, reveal a simple linear magnetic-field effect on the superconducting magnetic gap and the absence of field-induced in-gap states. The extrapolated gap-closing field value is consistent with the upper critical field Hc2, and the high-field response resembles that of the paramagnetic normal state.

  8. STRIPES AND SUPERCONDUCTIVITY IN CUPRATE SUPERCONDUCTORS

    SciTech Connect

    TRANQUADA, J.M.

    2005-08-22

    One type of order that has been observed to compete with superconductivity in cuprates involves alternating charge and antiferromagnetic stripes. Recent neutron scattering studies indicate that the magnetic excitation spectrum of a stripe-ordered sample is very similar to that observed in superconducting samples. In fact, it now appears that there may be a universal magnetic spectrum for the cuprates. One likely implication of this universal spectrum is that stripes of a dynamic form are present in the superconducting samples. On cooling through the superconducting transition temperature, a gap opens in the magnetic spectrum, and the weight lost at low energy piles up above the gap; the transition temperature is correlated with the size of the spin gap. Depending on the magnitude of the spin gap with respect to the magnetic spectrum, the enhanced magnetic scattering at low temperature can be either commensurate or incommensurate. Connections between stripe correlations and superconductivity are discussed.

  9. Absence of a spin gap in the superconducting ladder compound Sr{sub 2}Ca{sub 12}Cu{sub 24}O{sub 41}

    SciTech Connect

    Mayaffre, H.; Auban-Senzier, P.; Nardone, M.

    1998-01-16

    Transport and copper-63 nuclear magnetic resonance measurements of the Knight shift and relaxation time T{sub 1} performed on the two-leg spin ladders of Sr{sub 2}Ca{sub 12}Cu{sub 24}O{sub 41} single crystals as a function of pressure show a collapse of the gap in ladder spin excitations when superconductivity is stabilized at 31 kilobars. This result suggests that the superconducting phase in these materials may be connected to this transition and the collapse of the spin gap, and support the prediction made with exact diagonalization techniques in two-leg isotropic t - J ladder models of a transition between a low-doping spin gap phase and a gapless regime.

  10. 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.

  11. Development and operation of the JAERI superconducting energy recovery linacs

    NASA Astrophysics Data System (ADS)

    Minehara, Eisuke J.

    2006-02-01

    The Japan Atomic Energy Research Institute free-electron laser (JAERI FEL) group at Tokai, Ibaraki, Japan has successfully developed one of the most advanced and newest accelerator technologies named "superconducting energy recovery linacs (ERLs)" and some applications in near future using the ERLs. In the text, the current operation and high power JAERI ERL-FEL 10 kW upgrading program, ERL-light source design studies, prevention of the stainless-steel cold-worked stress-corrosion cracking failures and decommissioning of nuclear power plants in nuclear energy industries were reported and discussed briefly as a typical application of the ERL-FEL.

  12. Remarkable magneto-optical properties of europium selenide nanoparticles with wide energy gaps.

    PubMed

    Hasegawa, Yasuchika; Adachi, Taka-aki; Tanaka, Atsushi; Afzaal, Mohammad; O'Brien, Paul; Doi, Takahiro; Hinatsu, Yukio; Fujita, Koji; Tanaka, Katsuhisa; Kawai, Tsuyoshi

    2008-04-30

    The enhanced magneto-optical properties of nanoscaled lanthanide chalogenide semiconductors which have a wide energy gap were observed at around 500 nm for the first time. The nanoscaled semiconductors, Eu(1-x)Se nanoparticles 1 (cubic shapes) and 2 (spherical shapes), were synthesized by the thermal reduction of Eu(III) ion with organic ligands containing Se atoms. The resulting Eu(1-x)Se nanoparticles were characterized by X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, superconducting quantum interference devices magnetometer, and microwave induced plasma atomic emission spectroscopy measurements. The particle grain sizes of 1 and 2 were estimated to be 11 and 20 nm, respectively. The concentration-normalized Veldet constants (the magnitude of the Faraday effect) of Eu(1-x)Se nanoparticles were much larger than those of corresponding bulk EuSe and EuS nanoparticles. PMID:18396873

  13. Scaling of the energy gap in pattern-hydrogenated graphene.

    PubMed

    Grassi, Roberto; Low, Tony; Lundstrom, Mark

    2011-11-01

    Recent experiments show that a substantial energy gap in graphene can be induced via patterned hydrogenation on an iridium substrate. Here, we show that the energy gap is roughly proportional to N(H)(1/2)/N(C) when disorder is accounted for, where N(H) and N(C) denote concentrations of hydrogen and carbon atoms, respectively. The dispersion relation, obtained through calculation of the momentum-energy resolved density of states, is shown to agree with previous angle-resolved photoemission spectroscopy results. Simulations of electronic transport in finite size samples also reveal a similar transport gap, up to 1 eV within experimentally achievable N(H)(1/2)/N(C) values. PMID:21999430

  14. 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.

  15. The role of gap analyses in energy assurance planning.

    PubMed

    Shea, Katherine

    2013-01-01

    Energy-related emergencies, such as power outages or interruptions to other energy supplies, can arise from a number of factors. Common causes include severe weather events--such as snowstorms, hurricanes, or summer storms with strong winds--as well as energy infrastructure that is overburdened, aging, or in need of repair. As past experience indicates, jurisdictions will continue to experience severe weather events, as well as confront infrastructure issues that make future power outages likely. As a result, state and local governments have turned to energy assurance planning, an energy-specific form of planning that helps jurisdictions prepare for and recover from energy emergencies. Energy assurance recognizes that power loss/disruption cannot be eradicated completely, but jurisdictions can mitigate the impact of power loss through effective planning. This article discusses the role of energy assurance planning and provides a description of what energy assurance means and why developing such plans at the state and local levels is important. In addition, this article discusses the role of statutory gap analyses in energy assurance planning and discusses how a gap analysis can be used by planners to identify trends and gaps in energy assurance. To provide context, a recently conducted statutory gap analysis analyzing national emergency backup power trends is provided as a case study. A summary of this project and key findings is included. Finally, this article briefly touches on legislation as an alternative to energy assurance planning, and provides summaries of recent legislative proposals introduced in the aftermath of Hurricane Sandy. PMID:24180061

  16. Design optimization of superconducting magnetic energy storage coil

    NASA Astrophysics Data System (ADS)

    Bhunia, Uttam; Saha, Subimal; Chakrabarti, Alok

    2014-05-01

    An optimization formulation has been developed for a superconducting magnetic energy storage (SMES) solenoid-type coil with niobium titanium (Nb-Ti) based Rutherford-type cable that minimizes the cryogenic refrigeration load into the cryostat. Minimization of refrigeration load reduces the operating cost and opens up the possibility to adopt helium re-condensing system using cryo-cooler especially for small-scale SMES system. Dynamic refrigeration load during charging or discharging operational mode of the coil dominates over steady state load. The paper outlines design optimization with practical design constraints like actual critical characteristics of the superconducting cable, maximum allowable hoop stress on winding, etc., with the objective to minimize refrigeration load into the SMES cryostat. Effect of design parameters on refrigeration load is also investigated.

  17. 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

  18. Fractal superconductivity near localization threshold

    SciTech Connect

    Feigel'man, M.V.; Ioffe, L.B.; Kravtsov, V.E.; Cuevas, E.

    2010-07-15

    We develop a semi-quantitative theory of electron pairing and resulting superconductivity in bulk 'poor conductors' in which Fermi energy E{sub F} is located in the region of localized states not so far from the Anderson mobility edge E{sub c}. We assume attractive interaction between electrons near the Fermi surface. We review the existing theories and experimental data and argue that a large class of disordered films is described by this model. Our theoretical analysis is based on analytical treatment of pairing correlations, described in the basis of the exact single-particle eigenstates of the 3D Anderson model, which we combine with numerical data on eigenfunction correlations. Fractal nature of critical wavefunction's correlations is shown to be crucial for the physics of these systems. We identify three distinct phases: 'critical' superconductive state formed at E{sub F} = E{sub c}, superconducting state with a strong pseudo-gap, realized due to pairing of weakly localized electrons and insulating state realized at E{sub F} still deeper inside a localized band. The 'critical' superconducting phase is characterized by the enhancement of the transition temperature with respect to BCS result, by the inhomogeneous spatial distribution of superconductive order parameter and local density of states. The major new feature of the pseudo-gapped state is the presence of two independent energy scales: superconducting gap {Delta}, that is due to many-body correlations and a new 'pseudo-gap' energy scale {Delta}{sub P} which characterizes typical binding energy of localized electron pairs and leads to the insulating behavior of the resistivity as a function of temperature above superconductive T{sub c}. Two gap nature of the pseudo-gapped superconductor is shown to lead to specific features seen in scanning tunneling spectroscopy and point-contact Andreev spectroscopy. We predict that pseudo-gapped superconducting state demonstrates anomalous behavior of the optical spectral weight. The insulating state is realized due to the presence of local pairing gap but without superconducting correlations; it is characterized by a hard insulating gap in the density of single electrons and by purely activated low-temperature resistivity ln R(T) {approx} 1/T. Based on these results we propose a new 'pseudo-spin' scenario of superconductor-insulator transition and argue that it is realized in a particular class of disordered superconducting films. We conclude by the discussion of the experimental predictions of the theory and the theoretical issues that remain unsolved.

  19. A superconducting linac as the driver of the energy amplifier

    SciTech Connect

    Ruggiero, A.G.

    1996-10-11

    Because of the safer and more reliable mode of operation, a Superconducting Linac is proposed here as the proton beam accelerator which drives a nuclear plant based on the concept of the Energy Amplifier. The accelerator has also high electric power efficiency. An example based on the net generation of 400 MW (electric) is described here. 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.

  20. Controllable generation of two-mode-entangled states in two-resonator circuit QED with a single gap-tunable superconducting qubit

    NASA Astrophysics Data System (ADS)

    Ma, Sheng-Li; Li, Zhen; Fang, Ai-Ping; Li, Peng-Bo; Gao, Shao-Yan; Li, Fu-Li

    2014-12-01

    We study controllable generation of two-mode-entangled states in a circuit QED setup, which consists of two spatially separated superconducting transmission line resonators and a single gap-tunable superconducting qubit. Two sharp coupling sidebands are induced when the artificial atom is suitably driven by a bichromatic microwave field. The two resonators can have squeezing-type interactions with the qubit via the coupling sidebands. If the two resonators are not degenerate, we show that the two resonators can be cooled down into the two-mode squeezed vacuum via dissipation of the qubit. The generation of the two-mode squeezed state is based on a dissipative state-engineering process, which explores the energy relaxation of the qubit as a resource. Moreover, the scheme does not need both the specific preparation of the initial state and the designed special dynamical process of the system. If the resonators are degenerate, we show that entangled coherent states of the resonators can be generated by use of the unitary dynamical evolution process of the system and the state-projection measurement. Moreover, macro entangled coherent states of the resonators with huge photons can in principle be created if the resonators and the qubit have sufficiently long lifetimes. The present scheme has two remarkable features: (1) only a single qubit is used in the generation of the two-mode squeezed state; and (2) the ultrastrong coupling condition and initializing the resonators in coherent states are not required. These make the present scheme more simple and feasible in experimental implementation.

  1. A universal theorem of energy discretization - its implication in a promising mechanism of all superconductivities[1

    NASA Astrophysics Data System (ADS)

    Zheng-Johansson, J. X.; Johansson, P.-I.

    2000-03-01

    We report on a theorem stating that discretization of wavevector hence energy would universally result, if the motion of a quantum particle is spatially prohibited. The prohibition to electrons in a metal can be effectuated by such as a tight binding effect or a large resistivity. On identification of the resultant energy quanta as the superconducting gap, and, in combining this with the simple theory of metals, we correctly predict that good "normal conductors" such as Cu are not superconductors, or vice verse; and the estimated T_c's for the superconductors fall within the right magnitudes. Work supported by the Swedish Natural Science Research Council. With thanks to Prof B Johansson, Prof V Heine, Prof K-F Berggren, Prof M Springford, Dr B Sernulius for useful discussions. [1] Paper presented at The XXII Int Conf on Low Temp Phys (1999) Finland; also: Abst, pp307.

  2. 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.

  3. Energy Gaps in the Failed High-Tc Superconductor La1.875Ba0.125CuO4

    SciTech Connect

    Not Available

    2011-08-11

    A central issue in 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, although 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 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-waev 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 that involves a possible precursor-pairing energy scale around the node and another of different but unknown origin near the antinode.

  4. Energy Gaps in the Failed High-Tc Superconductor La_1.875Ba_0.125Cu_O4

    SciTech Connect

    Tanaka, K.

    2011-08-19

    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.

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

    SciTech Connect

    Wang, Yan; Berlijn, Tom; Hirschfeld, Peter J.; Scalapino, Douglas J.; Maier, Thomas A.

    2015-03-10

    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 propose that so-called ?-pairing states with nonzero total momentum can be realized and possess such exotic properties as odd parity spin singlet symmetry and time-reversal symmetry breaking. Here we show that when there is orbital weight at the Fermi level from orbitals with even and odd mirror reflection symmetry in z, ? pairing is inevitable; however, we conclude from explicit calculation that the gap function appearing in observable quantities is identical to that found in earlier pseudocrystal momentum calculations with 1 Fe per unit cell.

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

    DOE PAGESBeta

    Wang, Yan; Berlijn, Tom; Hirschfeld, Peter J.; Scalapino, Douglas J.; Maier, Thomas A.

    2015-03-10

    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 propose that so-called ?-pairing states with nonzero total momentum can be realized and possess such exotic properties as odd parity spin singlet symmetry and time-reversal symmetry breaking. Here we show that when there is orbital weight at the Fermi level from orbitals with even and odd mirror reflection symmetry in z, ? pairing is inevitable; however, we conclude from explicit calculation that the gap function appearing in observable quantities is identical to that found in earlier pseudocrystal momentummorecalculations with 1 Fe per unit cell.less

  7. Superconductivity in graphite intercalation compounds

    DOE PAGESBeta

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

    2015-02-26

    This study examines the field of superconductivity in the class of materials known as graphite intercalation compounds which has a history dating back to the 1960s. 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 this relates to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic statesmore » 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.« less

  8. Superconductivity in graphite intercalation compounds

    SciTech Connect

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

    2015-02-26

    This study examines the field of superconductivity in the class of materials known as graphite intercalation compounds which 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.

  9. Superconductivity in graphite intercalation compounds

    SciTech Connect

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

    2015-02-26

    This study examines the field of superconductivity in the class of materials known as graphite intercalation compounds which has a history dating back to the 1960s. 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 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.

  10. 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.

  11. Effective low-energy theory for superconducting topological insulators.

    PubMed

    Hao, Lei; Lee, Ting-Kuo

    2015-03-18

    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. PMID:25705794

  12. Anisotropic Superconducting Gap and Elongated Vortices with Caroli-De Gennes-Matricon States in the New Superconductor Ta4Pd3Te16

    PubMed Central

    Du, Zengyi; Fang, Delong; Wang, Zhenyu; Li, Yufeng; Du, Guan; Yang, Huan; Zhu, Xiyu; Wen, Hai-Hu

    2015-01-01

    The superconducting state is formed by the condensation of a large number of Cooper pairs. The normal state electronic properties can give significant influence on the superconducting state. For usual type-II superconductors, the vortices are cylinder like with a round cross-section. For many two dimensional superconductors, such as Cuprates, albeit the in-plane anisotropy, the vortices generally have a round shape. In this paper we report results based on the scanning tunnelling microscopy/spectroscopy measurements on a newly discovered superconductor Ta4Pd3Te16. The chain-like conducting channels of PdTe2 in Ta4Pd3Te16 make a significant anisotropy of the in-plane Fermi velocity. We suggest at least one anisotropic superconducting gap with gap minima or possible node exists in this multiband system. In addition, elongated vortices are observed with an anisotropy of ?||b/?&bottom?b ? 2.5. Clear Caroli-de Gennes-Matricon states are also observed within the vortex cores. Our results will initiate the study on the elongated vortices and superconducting mechanism in the new superconductor Ta4Pd3Te16. PMID:25797138

  13. 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.

  14. ORNL Superconducting Technology Program for Electric Energy Systems

    SciTech Connect

    Hawsey, R.A.

    1993-02-01

    The Oak Ridge National Laboratory (ORNL) Superconducting Technology Program is conducted as part of a national effort by the US Department of Energy's (DOE's) Office of Conservation and Renewable Energy to develop the technology base needed by US industry for commercial development of electric power applications of high-temperature superconductivity. The two major elements of this program are wire development and systems development. This document describes the major research and development activities for this program together with related accomplishments. The technical progress reported was summarized from information prepared for the FY 1992 Peer Review of Projects, conducted by DOE's Office of Program Analysis, Office of Energy Research. This ORNL program is highly leveraged by the staff and other resources of US industry and universities. Interlaboratory teams are also in place on a number of industry-driven projects. Patent disclosures, working group meetings, staff exchanges, and joint publications and presentations ensure that there is technology transfer to US industry. Working together, the collaborative teams are making tremendous progress in solving the scientific and technical issues necessary for the commercialization of long lengths of practical high-temperature superconductor wire and wire products.

  15. Parameter-dependences of superconducting condensation energy of 2D Hubbard model

    NASA Astrophysics Data System (ADS)

    Yamaji, K.; Koike, S.; Miyazaki, M.; Yanagisawa, T.

    2003-10-01

    By calculating the superconducting and spin density wave (SDW) condensation energies for the two-dimensional Hubbard model by the variational Monte Carlo method on the 10 10 and 12 12 lattices, we have searched for the parameter region where superconductivity overcomes SDW in the ground state. This model leads to a reasonable superconducting region as a function of electron density ? when on-site Coulomb energy U=6 in units of nearest-neighbor transfer energy t which was suggested from recent neutron diffraction data of the spin wave energy. When we fix U=6 and ?=0.84 (hole density 0.16), the superconducting phase wins in a relatively narrow range of -0.10? t??0.05, where t? is the second-neighbor transfer energy. In this region the superconducting condensation energy sharply increases with decreasing t?, which is considered to give the basis for clarifying the family dependence of the maximum Tc in the cuprate superconductors.

  16. Optical and electronic properties of some semiconductors from energy gaps

    NASA Astrophysics Data System (ADS)

    Tripathy, Sunil K.; Pattanaik, Anup

    2016-03-01

    II-VI and III-V tetrahedral semiconductors have significant potential for novel optoelectronic applications. In the present work, some of the optical and electronic properties of these groups of semiconductors have been studied using a recently proposed empirical relationship for refractive index from energy gap. The calculated values of these properties are also compared with those calculated from some well known relationships. From an analysis of the calculated electronic polarisability of these tetrahedral binary semiconductors from different formulations, we have proposed an empirical relation for its calculation. The predicted values of electronic polarisability of these semiconductors agree fairly well with the known values over a wide range of energy gap. The proposed empirical relation has also been used to calculate the electronic polarisability of some ternary compounds.

  17. Public perceptions and information gaps in solar energy in Texas

    NASA Astrophysics Data System (ADS)

    Rai, Varun; Beck, Ariane L.

    2015-07-01

    Studying the behavioral aspects of the individual decision-making process is important in identifying and addressing barriers in the adoption of residential solar photovoltaic (PV). However, there is little systematic research focusing on these aspects of residential PV in Texas, an important, large, populous state, with a range of challenges in the electricity sector including increasing demand, shrinking reserve margins, constrained water supply, and challenging emissions reduction targets under proposed federal regulations. This paper aims to address this gap through an empirical investigation of a new survey-based dataset collected in Texas on solar energy perceptions and behavior. The results of this analysis offer insights into the perceptions and motivations influencing intentions and behavior toward solar energy in a relatively untapped market and help identify information gaps that could be targeted to alleviate key barriers to adopting solar, thereby enabling significant emissions reductions in the residential sector in Texas.

  18. Spectral Gap Energy Transfer in Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Bhushan, S.; Walters, K.; Barros, A. P.; Nogueira, M.

    2012-12-01

    Experimental measurements of atmospheric turbulence energy spectra show E(k) ~ k-3 slopes at synoptic scales (~ 600 km - 2000 km) and k-5/3 slopes at the mesoscales (< 400 km). The -5/3 spectra is presumably related to 3D turbulence which is dominated by the classical Kolmogrov energy cascade. The -3 spectra is related to 2D turbulence, which is dominated by strong forward scatter of enstrophy and weak forward scatter of energy. In classical 2D turbulence theory, it is expected that a strong backward energy cascade would develop at the synoptic scale, and that circulation would grow infinitely. To limit this backward transfer, energy arrest at macroscales must be introduced. The most commonly used turbulence models developed to mimic the above energy transfer include the energy backscatter model for 2D turbulence in the horizontal plane via Large Eddy Simulation (LES) models, dissipative URANS models in the vertical plane, and Ekman friction for the energy arrest. One of the controversial issues surrounding the atmospheric turbulence spectra is the explanation of the generation of the 2D and 3D spectra and transition between them, for energy injection at the synoptic scales. Lilly (1989) proposed that the existence of 2D and 3D spectra can only be explained by the presence of an additional energy injection in the meso-scale region. A second issue is related to the observations of dual peak spectra with small variance in meso-scale, suggesting that the energy transfer occurs across a spectral gap (Van Der Hoven, 1957). Several studies have confirmed the spectral gap for the meso-scale circulations, and have suggested that they are enhanced by smaller scale vertical convection rather than by the synoptic scales. Further, the widely accepted energy arrest mechanism by boundary layer friction is closely related to the spectral gap transfer. This study proposes an energy transfer mechanism for atmospheric turbulence with synoptic scale injection, wherein the generation of 2D and 3D spectra is explained using spectral gap energy transfer. The existence of the spectral gap energy transfer is validated by performing LES for the interaction of large scale circulation with a wall, and studying the evolution of the energy spectra both near to and far from the wall. Simulations are also performed using the Advanced Weather and Research Forecasting (WRF-ARW) for moist zonal flow over Gaussian ridge, and the energy spectra close and away from the ground are studied. The energy spectra predicted by WRF-ARW are qualitatively compared with LES results to emphasize the limitations of the currently used turbulence parameterizations. Ongoing validation efforts include: (1) extending the interaction of large scale circulation with wall simulations to finer grids to capture a wider range of wavenumbers; and (2) a coupled 2D-3D simulation is planned to predict the entire atmospheric turbulence spectra at a very low computational expense. The overarching objective of this study to develop turbulence modeling capability based on the energy transfer mechanisms proposed in this study. Such a model will be implemented in WRF-ARW, and applied to atmospheric simulations, for example the prediction of moisture convergence patterns at the meso-scale in the southeast United States (Tao & Barros, 2008).

  19. Photonic Band Gap resonators for high energy accelerators

    SciTech Connect

    Schultz, S.; Smith, D.R.; Kroll, N. |

    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.

  20. Parametric investigation of nano-gap thermophotovoltaic energy conversion

    NASA Astrophysics Data System (ADS)

    Lau, Japheth Z.-J.; Bong, Victor N.-S.; Wong, Basil T.

    2016-03-01

    Nano-gap thermophotovoltaic energy converters have the potential to be excellent generators of electrical power due to the near-field radiative effect which enhances the transfer of energy from one medium to another. However, there is still much to learn about this new form of energy converter. This paper seeks to investigate three parameters that affect the performance of nano-gap thermophotovoltaic devices: the emitter material, the thermophotovoltaic cell material, and the cell thickness. Furthermore, the temperature profiles in insulated thin films (cells exposed to below-band gap near-field radiation) are analysed. It was discovered that an effective emitter material is one that has a high generalised emissivity value and is also able to couple with the TPV cell material through surface polaritons while a cell material's electrical properties and its thickness has heavy bearing on its internal quantum efficiency. In regards to the temperature profile, the heat-flux absorbed causes a rise in temperature across the thin film, but is insufficient to generate a temperature gradient across the film.

  1. Design of a 4.5 MJ/1 MW sectored toroidal superconducting energy storage magnet

    NASA Astrophysics Data System (ADS)

    Bhunia, Uttam; Akhter, Javed; Nandi, Chinmay; Pal, Gautam; Saha, Subimal

    2014-09-01

    A 4.5 MJ/1 MW superconducting magnetic energy storage (SMES) system is being developed at VECC centre, Kolkata. The magnet system consists of the cryostat and coil assembly comprising eight superconducting solenoid coils made of custom-made NbTi based Rutherford-type cable and arranged in toroidal fashion with finite inter-sector gap. Since the strong electromagnetic force distributed to the coil is asymmetric and non-uniform in nature, a precise 3-D finite element analysis (FEA) has been carried out to design a mechanically stable coil and support structure under various operational scenarios. The results reveal that maximum stress developed on coil and its support structure is below allowable stress limit. Extensive transient analysis has also been carried out to evaluate transient loss and assess the feasibility of using helium re-condensation technology with commercially available cryo-refrigerators. Finally, quench protection scenario has also been discussed suitable for this toroidal-type SMES system. The article investigates the design concept of the cryostat and coil assembly.

  2. Survey of domestic research on superconducting magnetic energy storage

    SciTech Connect

    Dresner, L.

    1991-09-01

    This report documents the results of a survey of domestic research on superconducting magnetic energy storage (SMES) undertaken with the support of the Oak Ridge National Laboratory (ORNL) Superconductivity Pilot Center. Each survey entry includes the following: Name, address, and other telephone and facsimile numbers of the principal investigator and other staff members; funding for fiscal year 1991, 1992, 1993; brief descriptions of the program, the technical progress to date, and the expected technical progress; a note on any other collaboration. Included with the survey are recommendations intended to help DOE decide how best to support SMES research and development (R&D). To summarize, I would say that important elements of a well-rounded SMES research program for DOE are as follows. (1) Construction of a large ETM. (2) Development of SMES as an enabling technology for solar and wind generation, especially in conjunction with the ETM program, if possible. (3) Development of small SMES units for electric networks, for rapid transit, and as noninterruptible power supplies [uses (2), (3), and (4) above]. In this connection, lightweight, fiber-reinforced polymer structures, which would be especially advantageous for space and transportation applications, should be developed. (4) Continued study of the potential impacts of high-temperature superconductors on SMES, with construction as soon as feasible of small SMES units using high-temperature superconductors (HTSs).

  3. Survey of domestic research on superconducting magnetic energy storage

    SciTech Connect

    Dresner, L.

    1991-09-01

    This report documents the results of a survey of domestic research on superconducting magnetic energy storage (SMES) undertaken with the support of the Oak Ridge National Laboratory (ORNL) Superconductivity Pilot Center. Each survey entry includes the following: Name, address, and other telephone and facsimile numbers of the principal investigator and other staff members; funding for fiscal year 1991, 1992, 1993; brief descriptions of the program, the technical progress to date, and the expected technical progress; a note on any other collaboration. Included with the survey are recommendations intended to help DOE decide how best to support SMES research and development (R D). To summarize, I would say that important elements of a well-rounded SMES research program for DOE are as follows. (1) Construction of a large ETM. (2) Development of SMES as an enabling technology for solar and wind generation, especially in conjunction with the ETM program, if possible. (3) Development of small SMES units for electric networks, for rapid transit, and as noninterruptible power supplies (uses (2), (3), and (4) above). In this connection, lightweight, fiber-reinforced polymer structures, which would be especially advantageous for space and transportation applications, should be developed. (4) Continued study of the potential impacts of high-temperature superconductors on SMES, with construction as soon as feasible of small SMES units using high-temperature superconductors (HTSs).

  4. Superconductivity and transport properties of narrow-gap semiconductor Pb(Tl)Te film by HWE growth

    NASA Astrophysics Data System (ADS)

    Murakami, Hironaru; Hattori, Wataru; Aoki, Ryozo

    1996-02-01

    The IV-VI semiconductor PbTe doped with a small amount of Tl shows superconductivity of Tc max ? 1.4 K in spite of the small hole carrier densities of p?10 20 cm -3. The superconducting generating mechanism has received much attention from the viewpoint of carrier resonance scattering with a Tl quasi-localized state. In order to investigate the superconductivity on well-defined film samples, we prepared high-quality Pb(Tl)Te films by the HWE method, and carried out the observation of superconductivity and electrical-transport properties. Furthermore, in the experiment with the coordinated system of Pb(Tl,Na)Te film, the results show for the first time the possible existence of two quasi-localized states of Tl causing strong scattering of carriers accompanied by reduction in Hall mobility ?, which play an important role in the superconductivity of this Pb(Tl)Te system.

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

    SciTech Connect

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

    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.

  6. Superconducting gap symmetry of Ba0.6K0.4Fe2As2 studied by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Nakayama, K.; Sato, T.; Richard, P.; Xu, Y.-M.; Sekiba, Y.; Souma, S.; Chen, G. F.; Luo, J. L.; Wang, N. L.; Ding, H.; Takahashi, T.

    2009-03-01

    We have performed high-resolution angle-resolved photoemission spectroscopy on the optimally doped Ba0.6K0.4Fe2As2 compound and determined the accurate momentum dependence of the superconducting (SC) gap in four Fermi-surface sheets including a newly discovered outer electron pocket at the M-point. The SC gap on this pocket is nearly isotropic and its magnitude is comparable (?~11 meV) to that of the inner electron and hole pockets (~12 meV), although it is substantially larger than that of the outer hole pocket (~6 meV). The Fermi-surface dependence of the SC gap value is basically consistent with the ?(k)=?0 cos kx cos ky formula expected for the extended s-wave symmetry. The observed finite deviation from the simple formula suggests the importance of multi-orbital effects.

  7. Magnetic Resonant Mode in the Low-Energy Spin-Excitation Spectrum of Superconducting Rb2Fe4Se5 Single Crystals

    NASA Astrophysics Data System (ADS)

    Park, J. T.; Friemel, G.; Li, Yuan; Kim, J.-H.; Tsurkan, V.; Deisenhofer, J.; Krug von Nidda, H.-A.; Loidl, A.; Ivanov, A.; Keimer, B.; Inosov, D. S.

    2011-10-01

    We have studied the low-energy spin-excitation spectrum of the single-crystalline Rb2Fe4Se5 superconductor (Tc=32K) by means of inelastic neutron scattering. In the superconducting state, we observe a magnetic resonant mode centered at an energy of ??res=14meV and at the (0.5 0.25 0.5) wave vector (unfolded Fe-sublattice notation), which differs from the ones characterizing magnetic resonant modes in other iron-based superconductors. Our finding suggests that the 245-iron selenides are unconventional superconductors with a sign-changing order parameter, in which bulk superconductivity coexists with the 55 magnetic superstructure. The estimated ratios of ??res/kBTc?5.10.4 and ??res/2??0.70.1, where ? is the superconducting gap, indicate moderate pairing strength in this compound, similar to that in optimally doped 1111 and 122 pnictides.

  8. Superconducting magnetic energy storage (SMES) program, January 1-December 31, 1981

    SciTech Connect

    Rogers, J.D.

    1982-02-01

    Work reported is on the development of a 30 MJ superconducting magnetic energy storage (SMES) unit for use by the Bonneville Power Administration (BPA) to stabilize power oscillations on their Pacific AC Intertie. The 30 MJ superconducting coil manufacture was completed. Design of the seismic mounting of the coil to the nonconducting dewar lid and a concrete foundation is complete. The superconducting application VAR (SAVAR) control study indicated a low economic advantage and the SAVAR program was terminated. An economic and technological evaluation of superconducting fault current limiter (SFCL) was completed and the results are reported.

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

    SciTech Connect

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

    2015-06-18

    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 γr=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 α model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of Δ₀~5.3 me V, corresponding to Δ₀/kBTc ~ 2.2. Increasing the phosphorus concentration x, the main gap reduces till a value of Δ₀ ~ 1.9 meV for x = 0.55 and a second weaker gap becomes evident. From the magnetic field effect on γr, all samples however show similar behavior [γr(H) - γr (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.

  10. The energy gap of the compound FeSe0.5Te0.5 determined by specific heat and Point Contact Spectroscopy

    NASA Astrophysics Data System (ADS)

    Escudero, Roberto; Lpez-Romero, Rodolfo E.

    2015-10-01

    The superconductor FeSe0.5Te0.5 was studied with Point Contact spectroscopy and specific heat in polycrystalline samples. The transition temperature determined by magnetic measurement was TC=14.5 K. The size of the energy gap measured by junctions is ? = 1.9 meV, whereas the gap determined by the specific heat measurements was ? = 2.3 meV. The gap evolution with temperature follows BCS, the ratio 2?/KBTC has values between 2.88 ? 2 ? /KBTC ? 3.04. The compound was grown by solid state synthesis in quartz ampoules under vacuum at 950 C. Crystal structure was characterized by X-ray diffraction. The superconducting properties were characterized by magnetization, resistivity and specific heat. This superconductor shows an isotropic energy gap as observed with the fitting of the specific heat at low temperature.

  11. New Insights into High-Tc Superconductivity from Angle-Resolved Photoemission at Low Photon Energies

    NASA Astrophysics Data System (ADS)

    Plumb, Nicholas Clark

    Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct and powerful probes for studying the physics of solids. ARPES takes a "snapshot" of electrons in momentum space (k-space) to reveal details of the dispersion relation E( k), as well as information about the lifetimes of interacting quasiparticles. From this we learn not only where the electrons live, but also, if we are crafty, what they are doing. Beginning with work by our group in 2006 using a 6-eV laser, ARPES experiments have begun to make use of a new, low photon energy regime (roughly hnu = 6--9 eV). These low photon energies give drastic improvements in momentum resolution, photoelectron escape depths, and overall spectral sharpness. This has led to several important new findings in the intensively-studied problem of high-temperature superconductivity. This thesis will focus on two of the latest results from our group using low-energy ARPES (LE-ARPES) to study the cuprate high-Tc superconductor Bi2Sr2CaCu2O8+delta (Bi2212). The first of these is an investigation into the nature of many-body interactions at a well-known energy scale ( 60--70 meV) where the dispersion shows a large bend, or "kink". Using LE-ARPES measurements, the k-dependence of this kink is investigated in unprecedented detail. An attempt is then made to map the feature's k evolution into the scattering q-space of boson dispersions. In our analysis, the q-dispersion of the kink bears more resemblance to dispersive spin excitations than phonons --- a surprising finding in light of previous evidence that the the kink originates from interactions with phonons. However, phonons cannot be ruled out, and the results may hint that both types of interactions contribute to the main nodal kink. A second result is the discovery of a new ultralow (< 10 meV) energy scale for electron interactions, corresponding to a distinct, smaller kink in the electron dispersion. The temperature and doping dependence of this feature show not only that it turns on near Tc --- signalling a possible relation to the mechanism of high-T c superconductivity --- but also that it leads to a subtle breakdown of the so-called "universal" Fermi velocity vF along nodes of the anisotropic superconducting gap. Moreover, vF is found to depend quite strongly on temperature, which may be an important factor in the physics of cuprates.

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

    NASA Astrophysics Data System (ADS)

    Rix, Craig; McColskey, David; Acree, Robert

    1994-07-01

    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 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.

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

    SciTech Connect

    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.

  14. A diffusional alternative to the Marcus free energy gap law.

    PubMed

    Burshtein, Anatoly I; Ivanov, Anatoly I

    2007-01-21

    The results of the precise kinetic fitting of the highly exergonic electron transfer from excited perylene to tetracyanoethylene in acetonitrile were used to estimate the Stern-Volmer constant of perylene quenching by double channel electron transfer (to the ground and excited states of the radical ion pair). It appears that the Stern-Volmer constant is exactly the same as the diffusional height of the Rehm-Weller plateau, substituting the exergonic wing of the Marcus free energy gap law. Even the single channel transfer is shown to be fast enough that the quenching should be under true diffusional control at the highest available exergonicity. PMID:17199156

  15. Optimization of HTS superconducting magnetic energy storage magnet volume

    NASA Astrophysics Data System (ADS)

    Korpela, Aki; Lehtonen, Jorma; Mikkonen, Risto

    2003-08-01

    Nonlinear optimization problems in the field of electromagnetics have been successfully solved by means of sequential quadratic programming (SQP) and the finite element method (FEM). For example, the combination of SQP and FEM has been proven to be an efficient tool in the optimization of low temperature superconductors (LTS) superconducting magnetic energy storage (SMES) magnets. The procedure can also be applied for the optimization of HTS magnets. However, due to a strongly anisotropic material and a slanted electric field, current density characteristic high temperature superconductors HTS optimization is quite different from that of the LTS. In this paper the volumes of solenoidal conduction-cooled Bi-2223/Ag SMES magnets have been optimized at the operation temperature of 20 K. In addition to the electromagnetic constraints the stress caused by the tape bending has also been taken into account. Several optimization runs with different initial geometries were performed in order to find the best possible solution for a certain energy requirement. The optimization constraints describe the steady-state operation, thus the presented coil geometries are designed for slow ramping rates. Different energy requirements were investigated in order to find the energy dependence of the design parameters of optimized solenoidal HTS coils. According to the results, these dependences can be described with polynomial expressions.

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

    SciTech Connect

    2010-10-01

    GRIDS Project: ABB is developing an advanced energy storage system using superconducting magnets that could store significantly more energy than todays 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 durationsgenerally less than a few minutes. ABBs 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.

  17. 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.

  18. Analytical design of a superconducting magnetic energy storage for pulsed power peak

    SciTech Connect

    Netter, D.; Leveque, J.; Rezzoug, A.; Caron, J.P.; Sargos, F.M.

    1996-09-01

    A Superconducting Magnetic Energy Storage can be used to produce very high pulsed power peak. A superconducting coil is magnetically coupled with another coil linked to the load. During the storage phase, the current is constant. In order to transfer the energy to the load, the authors cause the quench of the superconducting coil. It is very important to know the efficiency of the transfer and how much energy is discharged in the Helium vessel. In this paper, they propose an analytical method which enables to calculate very quickly the electrical parameters of such a device.

  19. Doping Evolution of the Superconducting Gap Structure in Heavily Hole-Doped Ba1‑xKxFe2As2: a Heat Transport Study

    NASA Astrophysics Data System (ADS)

    Hong, Xiao-Chen; Wang, Ai-Feng; Zhang, Zhen; Pan, Jian; He, Lan-Po; Luo, Xi-Gang; Chen, Xian-Hui; Li, Shi-Yan

    2015-12-01

    We performed systematic thermal conductivity measurements on heavily hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ single crystals with 0.747 $\\leq x \\leq$ 0.974. At $x$ = 0.747, the $\\kappa_0/T$ is negligible, indicating nodeless superconducting gap. A small residual linear term $\\kappa_0/T$ ($\\approx$ 0.035 mW/K$^2$ cm) appears at $x$ = 0.826, and it increases slowly up to $x$ = 0.974, followed by a drastic increase of more than 20 times to the pure KFe$_2$As$_2$ ($x$ = 1.0). This doping dependence of $\\kappa_0/T$ clearly shows that the nodal gap appears near $x = 0.8$, likely associated with the change of Fermi surface topology. The small values of $\\kappa_0/T$ from $x$ = 0.826 to 0.974 support a "$\\curlyvee$"-shaped nodal $s$-wave gap recently revealed by angle-resolved photoemission spectroscopy experiments at $x$ = 0.9. Furthermore, the drastic increase of $\\kappa_0/T$ from $x$ = 0.974 to 1.0 is inconsistent with a symmetry-imposed $d$-wave gap in KFe$_2$As$_2$, and the possible nodal gap structure in KFe$_2$As$_2$ is discussed.

  20. Gap anisotropy and phonon self-energy effects in single-crystal YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/

    SciTech Connect

    Cooper, S.L.; Slakey, F.; Klein, M.V.; Rice, J.P.; Bukowski, E.D.; Ginsberg, D.M.

    1988-12-01

    We report a Raman scattering investigation of superconducting gap anisotropy in single-crystal YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/. Gap anisotropy is investigated by studying the peak in the low-temperature Raman continuum in various symmetries. Roughly, a 35% difference in the energy of this peak is observed between different symmetries, suggesting the presence of substantial gap anisotropy. Anisotropy is further evidenced by the damping behavior of the 340 cm/sup -1/ Raman-active phonon below T/sub c/, which displays increased attenuation due to phonon-induced pair breaking. The temperature dependence of this attenuation is consistent with a T = 0 gap which is much larger than the 340 cm/sup -1/ phonon in certain regions of the Fermi surface.

  1. Revisiting orbital-fluctuation-mediated superconductivity in LiFeAs: Nontrivial spin-orbit interaction effects on the band structure and superconducting gap function

    NASA Astrophysics Data System (ADS)

    Saito, Tetsuro; Yamakawa, Youichi; Onari, Seiichiro; Kontani, Hiroshi

    2015-10-01

    The precise gap structure in LiFeAs (Tc=18 K) given by ARPES studies offers significant information that helps us understand the pairing mechanism in iron-based superconductors. The most remarkable characteristic in the LiFeAs gap structure would be that "the largest gap emerges on the tiny hole-pockets around the Z point." This result has been naturally explained in terms of the orbital-fluctuation scenario [T. Saito et al., Phys. Rev. B 90, 035104 (2014)], 10.1103/PhysRevB.90.035104, whereas the opposite result is obtained by the spin-fluctuation scenario. In this paper, we study the gap structure in LiFeAs by taking the spin-orbit interaction (SOI) into account, motivated by the recent ARPES studies that revealed a significant SOI-induced modification of the Fermi surface topology. For this purpose, we construct two possible tight-binding models with finite SOI by referring the band structures given by different ARPES groups. In addition, we extend the gap equation for multiorbital systems with finite SOI, and calculate the gap functions by applying the orbital-spin fluctuation theory. On the basis of both SOI-induced band structures, the main characteristics of the gap structure in LiFeAs are naturally reproduced only in the presence of strong interorbital interactions between (dx z /y z-dx y) orbitals. Thus the experimental gap structure in LiFeAs is a strong evidence for the orbital-fluctuation pairing mechanism.

  2. Superconducting cascade electron refrigerator

    SciTech Connect

    Camarasa-Gómez, M.; Giazotto, F.; Di Marco, A.; Hekking, F. W. J.; Winkelmann, C. B.; Courtois, H.

    2014-05-12

    The design and operation of an electronic cooler based on a combination of superconducting tunnel junctions is described. The cascade extraction of hot-quasiparticles, which stems from the energy gaps of two different superconductors, allows for a normal metal to be cooled down to about 100 mK starting from a bath temperature of 0.5 K. We discuss the practical implementation, potential performance, and limitations of such a device.

  3. Superconducting cascade electron refrigerator

    NASA Astrophysics Data System (ADS)

    Camarasa-Gmez, M.; Di Marco, A.; Hekking, F. W. J.; Winkelmann, C. B.; Courtois, H.; Giazotto, F.

    2014-05-01

    The design and operation of an electronic cooler based on a combination of superconducting tunnel junctions is described. The cascade extraction of hot-quasiparticles, which stems from the energy gaps of two different superconductors, allows for a normal metal to be cooled down to about 100 mK starting from a bath temperature of 0.5 K. We discuss the practical implementation, potential performance, and limitations of such a device.

  4. 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.

  5. Topological superconductivity induced by ferromagnetic metal chains

    NASA Astrophysics Data System (ADS)

    Li, Jian; Chen, Hua; Drozdov, Ilya K.; Yazdani, A.; Bernevig, B. Andrei; MacDonald, A. H.

    2014-12-01

    Recent experiments have provided evidence that one-dimensional (1D) topological superconductivity can be realized experimentally by placing transition-metal atoms that form a ferromagnetic chain on a superconducting substrate. We address some properties of this type of system by using a Slater-Koster tight-binding model to account for important features of the electronic structure of the transition-metal chains on the superconducting substrate. We predict that topological superconductivity is nearly universal when ferromagnetic transition-metal chains form straight lines on superconducting substrates and that it is possible for more complex chain structures. When the chain is weakly coupled to the substrate and is longer than superconducting coherence lengths, its proximity-induced superconducting gap is ? ESO/J where ? is the s -wave pair potential on the chain, ESO is the spin-orbit splitting energy induced in the normal chain state bands by hybridization with the superconducting substrate, and J is the exchange splitting of the ferromagnetic chain d bands. Because of the topological character of the 1D superconducting state, Majorana end modes appear within the gaps of finite length chains. We find, in agreement with the experiment, that when the chain and substrate orbitals are strongly hybridized, Majorana end modes are substantially reduced in amplitude when separated from the chain end by less than the coherence length defined by the p -wave superconducting gap. We conclude that Pb is a particularly favorable substrate material for ferromagnetic chain topological superconductivity because it provides both strong s -wave pairing and strong Rashba spin-orbit coupling, but that there is an opportunity to optimize properties by varying the atomic composition and structure of the chain. Finally, we note that in the absence of disorder, a new chain magnetic symmetry, one that is also present in the crystalline topological insulators, can stabilize multiple Majorana modes at the end of a single chain.

  6. Superconductivity, cohesive energy density, and electron-atom ratio in metals

    NASA Technical Reports Server (NTRS)

    England, C.; Lawson, D. D.; Hrubes, J. D.

    1981-01-01

    It is shown that superconductivity above 8 K occurs in alloys and metallic compounds within relatively narrow regions of cohesive energy density with a sharp peak which includes Nb3Ge, SiV3, Nb3Ga, and NbN. When cross-correlated with the electron-atom ratio, high-temperature superconductivity can be observed in only a few regions. This suggests a search for superconductors with high-transition temperatures and critical fields within these regions.

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

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

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

  8. The effects of hybridization on Cooper-pair binding energy in an intra-band model of superconductivity

    NASA Astrophysics Data System (ADS)

    Dinla Neto, F.; Dinla, I. S.; Neto, M. A.; Padilha, I. T.; Rowley, S. E.; Continentino, M. A.

    2015-10-01

    In this paper we analyze the effects of electron band hybridization in a superconducting material studying the effects on the binding energy of the Cooper pairs and on their size. We adopt a multi-band model that provides the intra-band pairing correlation functions. The hybridization can be tuned by an externally applied pressure or doping, and couple both bands acting to suppress the superconducting gap amplitude. Our analysis extends for all ranges of interactions coming from the usual BCS limit (weak coupling) going to the BEC limit of Cooper pairs (strong coupling) where these pairs become an effective bosonic particle. Our results show the dependence of the Cooper-pair binding energy and size as a function of the hybridization for T = 0. We propose a theoretical description for the intra-band binding-energy of the effective bosons in the BEC limit as a function of the hybridization. We also propose a description for the dependence of doping parameter as a function of the hybridization for the La2 - xSrxCuO4 compound.

  9. Tunneling spectra and superconducting gaps observed by scanning tunneling microscopy near the grain boundaries of FeSe0.3Te0.7 films

    NASA Astrophysics Data System (ADS)

    Lin, K. C.; Li, Y. S.; Shen, Y. T.; Wu, M. K.; Chi, C. C.

    2013-12-01

    We used scanning tunneling microscopy (STM) to study the tunneling spectra of FeSe0.3Te0.7 films with two orientations of the ab-planes and a connection ramp between them. We discovered that by pulsed laser deposition (PLD) method, the a- and b-axis of the FeSe0.3Te0.7 film deposited on an Ar-ion-milled magnesium oxide (MgO) substrate were rotated 45 with respect to those of MgO, whereas the a- and b-axis of the film grown on a pristine MgO substrate were parallel to those of MgO. With photolithography and this technique, we can prepare FeSe0.3Te0.7 films with two orientations on the same MgO substrate so that the connection between them forms a ramp at an angle of about 25 to the substrate plane. In the planar region, for either the 0 or 45 orientation, we observed tunneling spectra with a superconducting gap of about 5 meV and 1.78 meV, respectively. However, a much larger gap at about 18 meV was observed in the ramp region. Furthermore, we observed a small zero-bias conductance peak (ZBCP) inside the large gap at T = 4.3 K. The ZBCP becomes smaller with increasing temperature and disappeared at temperature above 7 K.

  10. Scanning tunneling spectroscopy of proximity superconductivity in epitaxial multilayer graphene

    NASA Astrophysics Data System (ADS)

    Natterer, Fabian D.; Ha, Jeonghoon; Baek, Hongwoo; Zhang, Duming; Cullen, William G.; Zhitenev, Nikolai B.; Kuk, Young; Stroscio, Joseph A.

    2016-01-01

    We report on spatial measurements of the superconducting proximity effect in epitaxial graphene induced by a graphene-superconductor interface. Superconducting aluminum films were grown on epitaxial multilayer graphene on SiC. The aluminum films were discontinuous, with networks of trenches in the film morphology reaching down to exposed graphene terraces. Scanning tunneling spectra measured on the graphene terraces show a clear decay of the superconducting energy gap with increasing separation from the graphene-aluminum edges. The spectra were well described by BCS theory. The decay length for the superconducting energy gap in graphene was determined to be greater than 400 nm. Deviations in the exponentially decaying energy gap were also observed on a much smaller length scale of tens of nanometers.

  11. 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.

  12. 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.

  13. Conductance spectrum and superconducting gap structures observed in c-axis FeSe0.46Te0.54/Au junctions

    NASA Astrophysics Data System (ADS)

    Shen, Y. T.; Li, Y. S.; Lin, K. C.; Wu, M. K.; Chi, C. C.

    2013-09-01

    The electric transport properties of superconducting c-axis FeSe0.46Te0.54/Au (S/N) junctions, fabricated using pulsed laser deposition, have been investigated in the temperature range of 2 K to the superconducting transition temperature Tc ( 13.5 K) and in the presence of applied magnetic fields from 0 to 9 T. A large zero bias conductance peak has always been observed in every conductance spectrum of several batches of junctions. In addition, we have found several gap-like features. Using the extended BTK theory with the currently favored nodeless S-wave symmetry, our conductance spectrum can be reproduced quite well in the low bias range with ?1 = 4 meV and ?2 = 6 meV at 2 K. However, the experimental conductance spectrum is substantially below the one calculated in the high bias range. Furthermore, there is a conductance minimum at approximately 20 meV, which may be the reason for the discrepancy.

  14. Localization of Metal-Induced Gap States at the Metal-Insulator Interface: Origin of Flux Noise in SQUIDs and Superconducting Qubits

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    The origin of magnetic flux noise in dc Superconducting Quantum Interference Devices (SQUIDs) with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 25 years. This noise limits both the low frequency performance of SQUIDs and the decoherence time of flux-sensitive superconducting qubits, making scaling-up for quantum computing problematic. Recent calculations and experiments indicate that the noise is generated by electrons that randomly reverse their spin directions. Their areal density of 5 x 10^17 m-2 is relatively insensitive to the nature of the superconductor and substrate. Here, we propose that the local magnetic moments originate in metal-induced gap states (MIGSs) localized by potential disorder at the metal-insulator interface. MIGSs are particularly sensitive to such disorder, so that the localized states have a Coulomb repulsion sufficiently large to make them singly occupied. Our calculations demonstrate that a modest level of disorder generates the required areal density of localized moments. This result suggests that magnetic flux noise could be reduced by fabricating superconductor-insulator interfaces with less disorder. Support: NSF DMR07-05941, US DOE De-AC02-05CH11231, Samsung Foundation, Teragrid, NERSC.

  15. 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.

  16. Electron tunneling into superconducting filaments using mechanically adjustable barriers

    SciTech Connect

    Moreland, J.; Ekin, J.W.

    1985-07-15

    A new type of squeezable electron tunneling (SET) junction has been developed for tunneling into superconducting filaments. Stable, mechanically adjustable tunneling barriers between the native surfaces of sputtered Nb films and 30-..mu..m-diam Nb filaments were established in liquid helium at 4 K. The current versus voltage characteristics of these SET junctions were used to determine the superconducting energy gap at the surface of the filaments. Since the filaments were etched from commercial superconducting magnet wire, this type of tunnel junction shows promise as a diagnostic probe of superconducting materials for high-field magnets.

  17. Liquid helium dump concept for a large scale superconducting magnetic energy storage plant

    NASA Astrophysics Data System (ADS)

    Schoenung, S. M.; Loyd, R. J.; Nakamura, T.; Rogers, J. D.; Purcell, J. R.

    Superconducting Magnetic Energy Storage (SMES) is a potentially cost effective technology for electric utility load leveling. Design concepts and cost estimates of SMES plants capable of delivering 5000 MWh daily have been previously identified. An important feature of a large commercial plant is a system that will reliably shut down the magnet by thermally dissipating the stored energy in the event of an imminent or actual loss of superconductivity. To prevent damage to the coil during such a protective energy dump, the entire coil must be driven normal, i.e., resistive rather than superconducting, in a short period of time. This requires rapid removal of the liquid helium coolant surrounding the coil. A simple system that has been developed to rapidly remove the liquid helium from the helium vessel is described. The system requires only a small number of active components, no external helium storage, and is practical to reset and maintain.

  18. Superconducting gap measurements on Co-doped SrFe2As2 single crystals by point contact spectroscopy

    NASA Astrophysics Data System (ADS)

    Hunt, Cassandra R.; Arham, H. Z.; Park, W. K.; Greene, L. H.; Gillett, J.; Sebastian, S.

    2011-03-01

    We present point contact spectroscopy results on single crystal Co-doped SrFe 2 As 2 . Two sets of Andreev-like enhancements in conductance are seen with nominally c -axis contacts. For temperatures up to Tc = 14.5 K, the conductance is fit to a Blonder-Tinkham-Klapwijk (BTK) model extended to two independent bands with lifetime broadening. We also consider recently proposed s+/- -wave extensions to BTK [2,3]. Many recent reports claim multiple gaps in the 122 compounds, however care must be taken to distinguish the presence of Andreev peaks from other excitation modes. We find robust evidence of an SC gap at 6 meV and evidence of another conductance enhancement at 12 mV that tracks the inner gap. The origin of this feature, and of multi-gap features as measured by PCS, are discussed. Work at UIUC supported by U.S. DOE under Award No.DE-AC02-98CH10886. Work at Cambridge supported by the EPSRC, Trinity College, the Royal Society and the Commonwealth Trust.

  19. Capacitor energy needed to induce transitions from the superconducting to the normal state

    NASA Astrophysics Data System (ADS)

    Eberhard, P. H.; Ross, R. R.

    1985-08-01

    A technique is described to turn a long length of superconducting wire normal by dumping a charged capacitor into it and justify some formulae needed in the design. The physical phenomenon is described. A formula for the energy to be stored in the capacitor is given. There are circumstances where the dc in an electrical circuit containing superconducting elements has to be turned off quickly and where the most convenient way to switch the current off is to turn a large portion or all of the superconducting wire normal. Such was the case of the Time Projection Chamber (TPC) superconducting magnet as soon as a quench was detected. The technique used was the discharge of a capacitor into the coil center tap. It turned the magnet winding normal in ten milliseconds or so and provided an adequate quench protection. The technique of discharging a capacitor into a superconducting wire should have many other applications whenever a substantial resistance in a superconducting circuit has to be generated in that kind of time scale.

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

    SciTech Connect

    Bianchi, Marcus 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.

  1. 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

  2. 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…

  3. In-plane electrodynamics of the superconductivity in Bi2Sr2CaCu2O8+? : ? Energy scales and spectral weight distribution

    NASA Astrophysics Data System (ADS)

    Santander-Syro, A. F.; Lobo, R. P. S. M.; Bontemps, N.; Lopera, W.; Girat, D.; Konstantinovic, Z.; Li, Z. Z.; Raffy, H.

    2004-10-01

    The in-plane infrared and visible (3meV-3eV) reflectivity of Bi2Sr2CaCu2O8+? (Bi-2212) thin films is measured between 300K and 10K for different doping levels with unprecedented accuracy. The optical conductivity is derived through an accurate fitting procedure. We study the transfer of spectral weight from finite energy into the superfluid as the system becomes superconducting. In the overdoped regime, the superfluid develops at the expense of states lying below 60meV , which is a conventional energy of the order of a few times the superconducting gap. In the underdoped regime, spectral weight is removed from up to 2eV , far beyond any conventional scale. The intraband spectral weight change between the normal and superconducting state, if analyzed in terms of a change of kinetic energy, is 1meV . Compared to the condensation energy, this figure addresses the issue of a kinetic-energy driven mechanism.

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

    SciTech Connect

    Xia, Zule; Ma, Ki; Chen, Quark

    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.

  5. Two-Gap Superconductivity in Ba1-xKxFe2As2: A Complementary Study of the Magnetic Penetration Depth by Muon-Spin Rotation and Angle-Resolved Photoemission

    NASA Astrophysics Data System (ADS)

    Khasanov, R.; Evtushinsky, D. V.; Amato, A.; Klauss, H.-H.; Luetkens, H.; Niedermayer, Ch.; Bchner, B.; Sun, G. L.; Lin, C. T.; Park, J. T.; Inosov, D. S.; Hinkov, V.

    2009-05-01

    We investigate the magnetic penetration depth ? in superconducting Ba1-xKxFe2As2 (Tc?32K) with muon-spin rotation (?SR) and angle-resolved photoemission (ARPES). Using ?SR, we find the penetration-depth anisotropy ??=?c/?ab and the second-critical-field anisotropy ?Hc2 to show an opposite T evolution below Tc. This dichotomy resembles the situation in the two-gap superconductor MgB2. A two-gap scenario is also suggested by an inflection point in the in-plane penetration depth ?ab around 7 K. The complementarity of ?SR and ARPES allows us to pinpoint the values of the two gaps and to arrive to a remarkable agreement between the two techniques concerning the full T evolution of ?ab. This provides further support for the described scenario and establishes ARPES as a tool to assess macroscopic properties of the superconducting condensate.

  6. 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

  7. 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 γ (≡Cel/T) at T = 0 K, γ0, is enhanced under the magnetic field H applied along the c axis. The increment of γ0, Δγ0, follows the Volovik relation Δγ0 = 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 γ0-value in the Cel/T versus T curve increases with increasing Ni concentrations. Interestingly, as the SC part of Cel/T, Cel/T - γ0 ≡ γs, decreases in LSCNO, Tc is reduced in proportion to the decrease of γs. 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.

  8. Rugged superconducting detector for monitoring infrared energy sources in harsh environments

    NASA Astrophysics Data System (ADS)

    Laviano, F.; Gerbaldo, R.; Ghigo, G.; Gozzelino, L.; Minetti, B.; Rovelli, A.; Mezzetti, E.

    2010-12-01

    Broadband electromagnetic characterization of hot plasmas, such as in nuclear fusion reactors and related experiments, requires detecting systems that must withstand high flux of particles and electromagnetic radiations. We propose a rugged layout of a high temperature superconducting detector aimed at 3 THz collective Thomson scattering (CTS) spectroscopy in hot fusion plasma. The YBa2Cu3O7 - x superconducting film is patterned by standard photolithography and the sensing area of the device is created by means of high-energy heavy ion irradiation, in order to modify the crystal structure both of the superconducting film and of the substrate. This method diminishes process costs and resulting device fragility due to membrane or air-bridge structures that are commonly needed for MIR and FIR radiation detection. Moreover the sensing area of the device is wired by the same superconducting material and thus excellent mechanical strength is exhibited by the whole device, due to the oxide substrate. Continuous wave operation of prototype devices is demonstrated at liquid nitrogen temperature, for selected infrared spectra of broadband thermal energy sources. Several solutions, which exploit the advantages coming from the robustness of this layout in terms of intrinsic radiation hardness of the superconducting material and of the needed optical components, are analysed with reference to applications of infrared electromagnetic detectors in a tokamak machine environment.

  9. Theory of Topological Superconductivity in Ferromagnetic Metal Chains on Superconducting Substrates

    NASA Astrophysics Data System (ADS)

    Chen, Hua

    2015-03-01

    Recent experiments have provided evidence that one-dimensional (1D) topological superconductivity based on transition metal atom chains formed on a superconducting substrate can be realized experimentally when the chain behaves like a ferromagnetic macrospin. In this talk I will address the structural and bonding considerations which determine whether or not a particular atom chain will have magnetic and electronic properties favorable for topological superconductivity. By using a Slater-Koster tight-binding model to account for important features of transition metal electronic structure, I conclude that topological states are common for ferromagnetic chains on superconductors and that they are nearly universal when ferromagnetic transition metal chains form straight lines on superconducting substrates. The proximity induced superconducting gap on the chain is ~ ?Eso / J where ? is the s-wave pair-potential on the chain, Eso is the spin-orbit splitting energy induced in the normal chain state bands by hybridization with the superconducting substrate, and J is the exchange-splitting of the ferromagnetic chain d-bands. Because of the topological character of the 1D superconducting state, Majorana end modes appear within the gaps of finite length chains. I will specifically discuss the spatial decay length of the Majorana end modes which can be much shorter than the coherence length from the induced p-wave gap on the chain due to its strong coupling to the three-dimensional superconducting substrate, in agreement with experimental results. Pb is a particularly favorable substrate material for ferromagnetic chain topological superconductivity because it provides both strong s - wave pairing and strong Rashba spin-orbit coupling, but there seems to be considerable scope to optimize the 1D topological superconductivity by varying the atomic composition and structure of the chain. The authors acknowledge support from the Office of Naval Research under Grant ONR-N00014-14-1-0330.

  10. Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra

    NASA Astrophysics Data System (ADS)

    Vos, M.; Marmitt, G. G.; Finkelstein, Y.; Moreh, R.

    2015-09-01

    Reflection electron energy loss spectra from some insulating materials (CaCO3, Li2CO3, and SiO2) taken at relatively high incoming electron energies (5-40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO2, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E - Egap)1.5. For CaCO3, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li2CO3 (7.5 eV) is the first experimental estimate.

  11. Generation of full polarization in ferromagnetic graphene with spin energy gap

    SciTech Connect

    Wu, Qing-Ping; Liu, Zheng-Fang E-mail: aixichen@ecjtu.edu.cn; Liu, Zhi-Min; Chen, Ai-Xi E-mail: aixichen@ecjtu.edu.cn; Xiao, Xian-Bo

    2014-12-22

    We propose a workable scheme for the generation of full spin polarization in ferromagnetic graphene system with strain or Rashba spin-orbit interaction. A spin energy gap can be opened in ferromagnetic graphene system in the presence of strain or Rashba spin-orbit interaction, leading to the full polarization in the spin energy gap. In addition, under the combined modulation of strain and Rashba spin-orbit interaction, the ferromagnetic graphene system can generate significantly large spin-polarized current with a full polarization in the spin energy gap. It is anticipated to apply such a phenomenon to design the electron spin devices based on the graphene.

  12. Evidence of a nodeless superconducting gap in PrCeCuO from magnetic penetration depth measurements

    NASA Astrophysics Data System (ADS)

    Lemberger, Thomas

    2005-03-01

    We have measured the inverse-squared magnetic penetration depth, ?-2(T), at 50 kHz of films of the electron-doped cuprate superconductor Pr2-xCexCuO4-? over a range of Ce dopings, 0.124 <= x <= 0.144, that extends from underdoped to overdoped. The maximum TC was 24 K at x = 0.131. The films were grown by mbe on SrTiO3 substrates that had been buffered with a thin layer of the insulating parent compound, Pr2CuO4-?, to obtain the cleanest possible films. Resistivity decreased smoothly and monotonically with doping. We used a two-coil mutual inductance technique to determine the film conductivity ? down to about 0.5 K, and we obtained ?-2 from ?2 in the usual fashion. We found that ?-2(T) was flat at low temperatures. That is, ?-2(T)/?-2(0) changed by less than the experimental noise of 0.15% over a factor of 3 or more change in T. Fits to the low-T data yield minimum a gap value, ?min(0)/kBTC, that is unity near optimal doping and decreases with over- and underdoping. This talk will compare our results with other penetration depth measurements that find quadratic behavior at low T, consistent with a d-wave gap and with phase sensitive measurements.

  13. 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.

  14. Beauty physics at the ultrahigh energies of the ELOISATRON (Euroasiatic Long Intersecting Superconducting Accelerator Synchrotron)

    SciTech Connect

    Cox, B.

    1988-02-01

    The potential for experimentally studying B physics at the proposed INFN 100 TeV ELOISATRON (Euroasiatic Long Intersecting Superconducting Accelerator Synchrotron) is compared with possibilities at 40 TeV at the Superconducting Super Collider. The effect of the increase in center of mass energy on the production and decay of B mesons has been investigated, particularly with respect to the accummulation of large samples of B hadron decays necessary for the detection of CP violating effects. 13 refs., 7 figs., 1 tab.

  15. Cryogenic system for production testing and measurement of Fermilab energy saver superconducting magnets

    SciTech Connect

    Cooper, W.E.; Bianchi, A.J.; Barger, R.K.; Johnson, F.B.; McGuire, K.J.; Pinyan, K.D.; Wilson, F.R.

    1983-03-01

    The cryogenic system of the Fermilab Magnet Test Facility has been used to provide cooling for the testing of approximately 1200 Energy Saver superconducting magnets. The system provides liquid helium, liquid nitrogen, gas purification, and vacuum support for six magnet test stands. It provides for simultaneous high current testing of two superconducting magnets and non-high current cold testing of two additional magnets. The cryogenic system has been in operation for about 32000 hours. The 1200 magnets have taken slightly more than three years to test.

  16. On the Equivalence of the Binding Energy of a Cooper Pair and the BCS Energy Gap:. a Framework for Dealing with Composite Superconductors

    NASA Astrophysics Data System (ADS)

    Malik, G. P.

    Employing the Bethe-Salpeter equation (BSE) and the Matsubara recipe, and invoking both the electron-electron and the hole-hole scattering channels, we establish that the binding energy (W) of a Cooper pair (CP) is real, and equals the BCS energy gap (?) for all T ? Tc for a one-component superconductor. Given that the BCS theory is a generalization of the Hartree-Fock theory (generalized to allow for particle number fluctuations), the cognescenti would expect this result as a direct consequence of Koopman's theorem, proved for and well-known in the latter theory. However, this theorem is seldom mentioned in the literature on superconductivity; on the contrary, there is the statement in well-known texts that the binding energy of a CP becomes imaginary when the above-stated scattering channels are invoked for their formation. The importance of |W| = |?| for high-Tc superconductors is brought out by replacing the one-particle propagator in the BSE by a superpropagator a field-theoretic construct apt for dealing with composite superconductors (CSs). A set of generalized BCS equations is thus obtained which, with the input of the multiple gaps of a CS, enables one to calculate its Tc uniquely. Applications of these equations will be taken up in a subsequent paper.

  17. Graphene field effect transistor without an energy gap

    PubMed Central

    Jang, Min Seok; Kim, Hyungjun; Son, Young-Woo; Atwater, Harry A.; Goddard, William A.

    2013-01-01

    Graphene is a room temperature ballistic electron conductor and also a very good thermal conductor. Thus, it has been regarded as an ideal material for postsilicon electronic applications. A major complication is that the relativistic massless electrons in pristine graphene exhibit unimpeded Klein tunneling penetration through gate potential barriers. Thus, previous efforts to realize a field effect transistor for logic applications have assumed that introduction of a band gap in graphene is a prerequisite. Unfortunately, extrinsic treatments designed to open a band gap seriously degrade device quality, yielding very low mobility and uncontrolled on/off current ratios. To solve this dilemma, we propose a gating mechanism that leads to a hundredfold enhancement in on/off transmittance ratio for normally incident electrons without any band gap engineering. Thus, our saw-shaped geometry gate potential (in place of the conventional bar-shaped geometry) leads to switching to an off state while retaining the ultrahigh electron mobility in the on state. In particular, we report that an on/off transmittance ratio of 130 is achievable for a sawtooth gate with a gate length of 80 nm. Our switching mechanism demonstrates that intrinsic graphene can be used in designing logic devices without serious alteration of the conventional field effect transistor architecture. This suggests a new variable for the optimization of the graphene-based devicegeometry of the gate electrode. PMID:23671093

  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. 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.

  20. Space applications of superconductivity

    NASA Technical Reports Server (NTRS)

    Sullivan, D. B.; Vorreiter, J. W.

    1979-01-01

    Some potential applications of superconductivity in space are summarized, e.g., the use of high field magnets for cosmic ray analysis or energy storage and generation, space applications of digital superconducting devices, such as the Josephson switch and, in the future, a superconducting computer. Other superconducting instrumentation which could be used in space includes: low frequency superconducting sensors, microwave and infrared detectors, instruments for gravitational studies, and high-Q cavities for use as stabilizing elements in clocks and oscillators.

  1. 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.

  2. Parton-parton elastic scattering and rapidity gaps at SSC and LHC energies

    SciTech Connect

    Duca, V.D.

    1993-08-01

    The theory of the perturbative pomeron, due to Lipatov and collaborators, is used to compute the probability of observing parton-parton elastic scattering and rapidity gaps between jets in hadron collisions at SSC and LHC energies.

  3. Photoluminescence-tunable carbon nanodots: surface-state energy-gap tuning.

    PubMed

    Bao, Lei; Liu, Cui; Zhang, Zhi-Ling; Pang, Dai-Wen

    2015-03-11

    The photoluminescence of carbon nanodots (C-dots) can be tuned by changing their surface chemistry or size because the photoluminescence is a function of the surface-state electronic transitions. Increasing the degree of surface oxidation leads to a narrowing of the energy gap of the surface; meanwhile, larger C-dots with an extensive ?-electron system, which can couple with surface electronic states, can also lead to a narrowing of the energy gap of the surface states. PMID:25589141

  4. 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.

  5. 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.

  6. Energy Transfer with Hydrogen and Superconductivity - The Review of the First Experimental Results

    NASA Astrophysics Data System (ADS)

    Vysotsky, V. S.; Antyukhov, I. V.; Firsov, V. P.; Blagov, E. V.; Kostyuk, V. V.; Nosov, A. A.; Fetisov, S. S.; Zanegin, S. Yu.; Rachuk, V. S.; Katorgin, B. I.

    The transfer of massive amounts of both electrical and chemical power over long distances will present a major challenge for the global energy enterprise in future. Attraction of hydrogen is apparent as a chemical energy agent, possessing among the highest energy density content of various common fuels, whose combustive "waste" is simply water. The usage of "gratis" cold to cool a superconducting cable made of proper superconductor permits to deliver extra electrical power with the same line. This, rather old theoretical idea recently found its experimental realization. The team of Russian institutes and organizations with using Italian-produced MgB2 wire has made and successfully tested two hybrid energy transfer lines with liquid hydrogen as a chemical source of power and superconducting cable as a source of electricity. The first line has been tested in 2011. It has length ∼10 m, maximum liquid hydrogen flow ∼250 g/s and maximum current of MgB2 superconducting cable 2600 A @ 20K. This test was the first experimental proof of conception of the hybrid energy transfer line. The second line has been tested in October 2013. It has length ∼30 m. The new MgB2 cable has critical current at 21 K ∼3500 A and successfully passed high voltage DC test of 50 kV. New hydrogen cryostat has three sections with different types of thermal insulation in each section. The idea of hybrid energy transfer is formulated and details of first experiments are reviewed.

  7. Dirac-Hartree-Bogoliubov calculation for spherical and deformed hot nuclei: Temperature dependence of the pairing energy and gaps, nuclear deformation, nuclear radii, excitation energy, and entropy

    NASA Astrophysics Data System (ADS)

    Lisboa, R.; Malheiro, M.; Carlson, B. V.

    2016-02-01

    Background: Unbound single-particle states become important in determining the properties of a hot nucleus as its temperature increases. We present relativistic mean field (RMF) for hot nuclei considering not only the self-consistent temperature and density dependence of the self-consistent relativistic mean fields but also the vapor phase that takes into account the unbound nucleon states. Purpose: The temperature dependence of the pairing gaps, nuclear deformation, radii, binding energies, entropy, and caloric curves of spherical and deformed nuclei are obtained in self-consistent RMF calculations up to the limit of existence of the nucleus. Method: We perform Dirac-Hartree-Bogoliubov (DHB) calculations for hot nuclei using a zero-range approximation to the relativistic pairing interaction to calculate proton-proton and neutron-neutron pairing energies and gaps. A vapor subtraction procedure is used to account for unbound states and to remove long range Coulomb repulsion between the hot nucleus and the gas as well as the contribution of the external nucleon gas. Results: We show that p -p and n -n pairing gaps in the S10 channel vanish for low critical temperatures in the range Tcp≈0.6 -1.1 MeV for spherical nuclei such as 90Zr, 124Sn, and 140Ce and for both deformed nuclei 150Sm and 168Er. We found that superconducting phase transition occurs at Tcp=1.03 Δp p(0 ) for 90Zr, Tcp=1.16 Δp p(0 ) for 140Ce, Tcp=0.92 Δp p(0 ) for 150Sm, and Tcp=0.97 Δp p(0 ) for 168Er. The superfluidity phase transition occurs at Tcp=0.72 Δn n(0 ) for 124Sn, Tcp=1.22 Δn n(0 ) for 150Sm, and Tcp=1.13 Δn n(0 ) for 168Er. Thus, the nuclear superfluidity phase—at least for this channel—can only survive at very low nuclear temperatures and this phase transition (when the neutron gap vanishes) always occurs before the superconducting one, where the proton gap is zero. For deformed nuclei the nuclear deformation disappear at temperatures of about Tcs=2.0 -4.0 MeV , well above the critical temperatures for pairing, Tcp. If we associate the melting of hot nuclei into the surrounding vapor with the liquid-gas phase transition our results indicate that it occurs at temperatures around T =8.0 -10.0 MeV , somewhat higher than observed in many experimental results. Conclusions: The change of the pairing fields with the temperature is important and must be taken into account in order to define the superfluidity and superconducting phase transitions. We obtain a Hamiltonian form of the pairing field calibrated by an overall constant cpair to compensate for deficiencies of the interaction parameters and of the numerical calculation. When the pairing is not zero, the states close to the Fermi energy make the principal contribution to the anomalous density that appears in the pairing field. By including temperature through the use of the Matsubara formalism, the normal and anomalous densities are multiplied by a Fermi occupation factor. This leads to a reduction in the anomalous density and in the pairing as the temperature increases. When the temperature increases (T ≥4 MeV ), the effects of the vapor phase that take into account the unbound nucleon states become important, allowing the study of nuclear properties of finite nuclei from zero to high temperatures.

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

    SciTech Connect

    none,

    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.

  9. 93Nb and63Cu NMR studies of superconducting Nb/Cu multilayers

    NASA Astrophysics Data System (ADS)

    Kohori, Yoh; Kohara, Takao; Oda, Yasukage; Nishikawa, Masakazu; Kita, Eiji; Tasaki, Akira

    1996-02-01

    We have carried out93Nb and63Cu NMR measurements in Nb/Cu superconducting multilayered thin film down to 0.1K, and measured nuclear spin lattice relaxation rate (1/ T 1) in zero field using the field cycling method. The temperature dependence of 1/ T 1 has shown the existence of the superconducting energy gap with the magnitude of 3.5 k B T C in Nb layers and a smaller energy gap in Cu layers induced by the superconducting proximity effect.

  10. Energy band gap and optical transition of metal ion modified double crossover DNA lattices.

    PubMed

    Dugasani, Sreekantha Reddy; Ha, Taewoo; Gnapareddy, Bramaramba; Choi, Kyujin; Lee, Junwye; Kim, Byeonghoon; Kim, Jae Hoon; Park, Sung Ha

    2014-10-22

    We report on the energy band gap and optical transition of a series of divalent metal ion (Cu(2+), Ni(2+), Zn(2+), and Co(2+)) modified DNA (M-DNA) double crossover (DX) lattices fabricated on fused silica by the substrate-assisted growth (SAG) method. We demonstrate how the degree of coverage of the DX lattices is influenced by the DX monomer concentration and also analyze the band gaps of the M-DNA lattices. The energy band gap of the M-DNA, between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), ranges from 4.67 to 4.98 eV as judged by optical transitions. Relative to the band gap of a pristine DNA molecule (4.69 eV), the band gap of the M-DNA lattices increases with metal ion doping up to a critical concentration and then decreases with further doping. Interestingly, except for the case of Ni(2+), the onset of the second absorption band shifts to a lower energy until a critical concentration and then shifts to a higher energy with further increasing the metal ion concentration, which is consistent with the evolution of electrical transport characteristics. Our results show that controllable metal ion doping is an effective method to tune the band gap energy of DNA-based nanostructures. PMID:25247447

  11. Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1xCox)?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.

    2012-07-13

    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 ? ? H0.50.1, 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 ? ? H0.30.4, followed by an inflection point, followed at higher fields by ? ? H. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.

  12. Tunneling spectroscopy of a La-Sr-Cu-O break junction: Evidence for strong-coupling superconductivity

    SciTech Connect

    Moreland, J.; Clark, A.F.; Goodrich, L.F.; Ku, H.C.; Shelton, R.N.

    1987-06-01

    Detailed structure in the quasiparticle tunneling has been observed in La-Sr-Cu-O superconductive tunneling junctions using the break-junction technique. Variability in the energy gap and associated structure in the current-voltage curves is observed indicating significant inhomogeneity in the superconducting properties. Large energy gaps (7.0 meV) and deep structure in the conductance derivatives are evidence for a strong-coupling mechanism.

  13. 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

  14. Distinct Fermi-Momentum-Dependent Energy Gaps in Deeply UnderdopedBi2212

    SciTech Connect

    Tanaka, Kiyohisa; Lee, W.S.; Lu, D.H.; Fujimori, A.; Fujii, T.; Risdiana, ???; Terasaki, I.; Scalapino, D.J.; Devereaux, T.P.; Hussain,Z.; Shen, Z.-X.

    2006-11-16

    We used angle-resolved photoemission spectroscopy applied todeeply underdoped cuprate superconductors Bi2Sr2Ca(1-x)YxCu2O8 (Bi2212)to reveal the presence of two distinct energy gaps exhibiting differentdoping dependence. One gap, associated with the antinodal region where nocoherent peak is observed, increased with underdoping, a behavior knownfor more than a decade and considered as the general gap behavior in theunderdoped regime. The other gap, associated with the near-nodal regimewhere a coherent peak in the spectrum can be observed, did not increasewith less doping, a behavior not previously observed in the singleparticle spectra. We propose a two-gap scenario in momentum space that isconsistent with other experiments and may contain important informationon the mechanism of high-transition temperaturesuperconductivity.

  15. Topological Superconductivity in Bilayer Rashba System

    NASA Astrophysics Data System (ADS)

    Nakosai, Sho; Tanaka, Yukio; Nagaosa, Naoto

    2012-04-01

    We theoretically study a possible topological superconductivity in the interacting two layers of Rashba systems, which can be fabricated by the heterostructures of semiconductors and oxides. The hybridization, which induces the gap in the single particle dispersion, and the electron-electron interaction between the two layers leads to the novel phase diagram of the superconductivity. It is found that the topological superconductivity without breaking time-reversal symmetry is realized when (i) the Fermi energy is within the hybridization gap, and (ii) the interlayer interaction is repulsive, both of which can be satisfied in realistic systems. Edge channels are studied in a tight-binding model numerically, and the several predictions on experiments are also given.

  16. Charge fluctuations on a superconducting island

    NASA Astrophysics Data System (ADS)

    Neumann, Frank; Grabert, Hermann

    1995-12-01

    The charge on a superconducting island coupled to a superconducting electrode by a Josephson junction is determined in the region where the gap energy and the single-electron charging energy of the island are of comparable magnitude. The Coulomb staircase describing the incremental charging of the island in response to a biasing voltage is studied. The rounding of the staircase corners due to thermal and quantum fluctuations is found to depend on the parity of the island charge in the adjacent tread. This should allow for an experimental disentanglement of the effects of quantum charge fluctuations from thermal fluctuations.

  17. CW Superconducting RF Photoinjector Development for Energy Recovery Linacs

    SciTech Connect

    Neumann A.; Rao T.; Anders, W.; Dirsat, M.; Frahm, A. Jankowiak, A.; Kamps, T.; Knobloch, J.; Kugeler, O.; Quast, T.; Rudolph, J.; Schenk, M.; Schuster, M.; Smedley, J.; Sekutowicz, J.; Kneisel, P.; Nietubyc, R.; Will, I.

    2010-10-31

    ERLs have the powerful potential to provide very high current beams with exceptional and tailored parameters for many applications, from next-generation light sources to electron coolers. However, the demands placed on the electron source are severe. It must operate CW, generating a current of 100 mA or more with a normalized emittance of order 1 {micro}m rad. Beyond these requirements, issues such as dark current and long-term reliability are critical to the success of ERL facilities. As part of the BERLinPro project, Helmholtz Zentrum Berlin (HZB) is developing a CWSRF photoinjector in three stages, the first of which is currently being installed at HZB's HoBiCaT facility. It consists of an SRF-cavity with a Pb cathode and a superconducting solenoid. Subsequent development stages include the integration of a high-quantum-efficiency cathode and RF components for high-current operation. This paper discusses the first stage towards an ERL-suitable SRF photoinjector, the present status of the facility and first cavity tests.

  18. Superconducting transport in single and parallel double InAs quantum dot Josephson junctions with Nb-based superconducting electrodes

    NASA Astrophysics Data System (ADS)

    Baba, Shoji; Sailer, Juergen; Deacon, Russell S.; Oiwa, Akira; Shibata, Kenji; Hirakawa, Kazuhiko; Tarucha, Seigo

    2015-11-01

    We report conductance and supercurrent measurements for InAs single and parallel double quantum dot Josephson junctions contacted with Nb or NbTiN superconducting electrodes. Large superconducting gap energy, high critical field, and large switching current are observed, all reflecting the features of Nb-based electrodes. For the parallel double dots, we observe an enhanced supercurrent when both dots are on resonance, which may reflect split Cooper pair tunneling.

  19. Photoemission and density functional theory study of Ir(111); energy band gap mapping

    NASA Astrophysics Data System (ADS)

    Pletikosi?, I.; Kralj, M.; ok?evi?, D.; Brako, R.; Lazi?, P.; Pervan, P.

    2010-04-01

    We have performed combined angle-resolved photoemission spectroscopy (ARPES) experiments and density functional theory (DFT) calculations of the electronic structure of the Ir(111) surface, with the focus on the existence of energy band gaps. The investigation was motivated by the experimental results suggesting Ir(111) as an ideal support for the growth of weakly bonded graphene. Therefore, our prime interest was electronic structure around the \\bar {\\mathrm {K}} symmetry point. In accordance with DFT calculations, ARPES has shown a wide energy band gap with the shape of a parallelogram centred around the \\bar {\\mathrm {K}} point. Within the gap three surface states were identified; one just below the Fermi level and two spin-orbit split surface states at the bottom of the gap.

  20. Point contact spectroscopy in oriented La[sub 2-x]Sr[sub x]CuO[sub 4] superconductors; energy gap and Fermi velocity

    SciTech Connect

    Hass, N. ); Deutscher, G. ); Revcolevschi, A.; Dhalenne, G. )

    1994-08-01

    Point contact measurements in oriented La[sub 2-x]Sr[sub x]CuO[sub 4] samples were performed using metal tips. The current-voltage curves measured along the CuO plane direction (ab) are characteristic of the Andreev reflection phenomenon. The superconducting energy gap in the ab plane is determined, [Delta][sub ab] = 6 [+-] 1 meV, with a possibility for the existence of a lower subgap in the plane. A lower limit for the Fermi velocity in the CuO planes is also set by the measurements; V[sub F] [ge] 6 [times] 10[sup 7] cm/sec, which is significantly higher than the average velocity obtained by band calculations. The results are discussed in the context of different models for superconductivity in the layered oxides. In particular, the authors raise the possibility of an anisotropic gap parameter which may indicate a nonstandard s-wave pairing in La[sub 2-x]Sr[sub x]CuO[sub 4]. A comparison with previous results obtained on YBa[sub 2]Cu[sub 3]O[sub 7-[delta

  1. First-principle study on energy gap of CNT superlattice structure

    NASA Astrophysics Data System (ADS)

    Zhonghua, Yang; Guili, Liu; Yingdong, Qu; Rongde, Li

    2015-10-01

    By using the CASTEP modules based on density functional theory, the electronic structures of B/N pair co-doping (5, 5) CNT rings superlattice have been investigated. The calculation results show that the formation energies of B/N pair co-doping CNT rings are negative, indicating that the new type construction will probably be stable. The band structure and state density of the new type construction show that the energy gap is opened by B/N co-doping in (5, 5) metallic CNT and the metallic CNT is changed into a semiconductor. The energy gap of pure CNT is strongly sensitive to the changes of CNT diameter but the energy gap of B/N co-doping CNT rings remains stable when the diameters are in a reasonable scope, which means that the requirements for the production of CNT have been reduced. The compressive deformation effects mean that the energy gaps are narrowed, which is equivalent to enhancing the doping volume concentration. However, the changes of the energy gap under the tensile deformation effect are opposite. Achieving control of the electrical conductivity of CNT has an important significance for electron devices. Project supported by the National Natural Science Foundation of China (Nos. 51274142, 50671069).

  2. Energy Flow for a Variable-Gap Capacitor

    NASA Astrophysics Data System (ADS)

    Greene, Nathaniel R.

    2005-09-01

    When capacitor plates are separated, the capacitor's electrostatic energy either increases or decreases, depending upon whether the charge or the voltage is held constant. For the constant-voltage case, an interesting puzzle can be posed to students: How is it possible that an external agent does positive work on the capacitor while at the same time the capacitor's stored energy decreases? An energy flow diagram, as suggested by Art Hobson's TPT article, helps to visualize the movements of energy among different parts of the system. What Richard Feynman calls a "surprising factor of one-half" in the expression for the force between capacitor plates confronts students with an additional puzzle to decipher.2

  3. Energy-resolved detection of single infrared photons with ? = 8 ?m using a superconducting microbolometer

    NASA Astrophysics Data System (ADS)

    Karasik, Boris S.; Pereverzev, Sergey V.; Soibel, Alexander; Santavicca, Daniel F.; Prober, Daniel E.; Olaya, David; Gershenson, Michael E.

    2012-07-01

    We report on the detection of single photons with ? = 8 ?m using a superconducting hot-electron microbolometer. The sensing element is a titanium transition-edge sensor with a volume 0.1 ?m3 fabricated on a silicon substrate. Poisson photon counting statistics including simultaneous detection of 3 photons was observed. The width of the photon-number peaks was 0.11 eV, 70% of the photon energy, at 50-100 mK. This achieved energy resolution is one of the best figures reported so far for superconducting devices. Such devices can be suitable for single-photon calorimetric spectroscopy throughout the mid-infrared and even the far-infrared.

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

    SciTech Connect

    Rogers, J.D.

    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.

  5. 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. )

    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.

  6. Limiting efficiencies of ideal single and multiple energy gap terrestrial solar cells

    SciTech Connect

    Henry, C.H.

    1980-08-01

    The maximum efficiencies of ideal solar cells are calculated for both single and multiple energy gap cells using a standard air mass 1.5 terrestrial solar spectrum. The calculations of efficiency are made by a simple graphical method, which clearly exhibits the contributions of the various intrinsic losses. The maximum efficiency, at a concentration of 1 sun, is 31%. At a concentration of 1000 suns with the cell at 300 K, the maximum efficiencies are 37, 50, 56, and 72% for cells with 1, 2, 3, and 36 energy gaps, respectively. The value of 72% is less than the limit of 93% imposed by thermodynamics for the conversion of direct solar radiation into work. Ideal multiple energy gap solar cells fall below the thermodynamic limit because of emission of light from the forward-biased p-n junctions. The light is radiated at all angles and causes an entropy increase as well as an energy loss.

  7. Electronic energy gap correlation function and spectral density of anharmonic molecules at low temperatures I: Theory

    NASA Astrophysics Data System (ADS)

    Toutounji, Mohamad

    2015-01-01

    A closed-form expression for the electronic energy gap correlation function of anharmonic molecules weighed by their coupling strengths to the electronic transition is derived. These undamped anharmonic vibrations may be viewed as only linearly coupled phonons. The spectral density derived herein may be viewed as a spectrum of Franck-Condon factors for the phonons coupled linearly to the electronic transition in the low temperature limit. A formula for Morse oscillator reorganizational energy is derived. An approximate form for anharmonic energy gap correlation function is also provided, from which the spectral density of intramolecular vibrations is derived.

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

    SciTech Connect

    Mitani, Y.; Uranaka, T.; Tsuji, K.

    1995-08-01

    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 independent of the location of controller in a long distance bulk power transmission system.

  9. Anomalous behavior of the energy gap in the one-dimensional quantum X Y model

    NASA Astrophysics Data System (ADS)

    Okuyama, Manaka; Yamanaka, Yuuki; Nishimori, Hidetoshi; Rams, Marek M.

    2015-11-01

    We reexamine the well-studied one-dimensional spin-1 /2 X Y model to reveal its nontrivial energy spectrum, in particular the energy gap between the ground state and the first excited state. In the case of the isotropic X Y model, the X X model, the gap behaves very irregularly as a function of the system size at a second order transition point. This is in stark contrast to the usual power-law decay of the gap and is reminiscent of the similar behavior at the first order phase transition in the infinite-range quantum X Y model. The gap also shows nontrivial oscillatory behavior for the phase transitions in the anisotropic model in the incommensurate phase. We observe a close relation between this anomalous behavior of the gap and the correlation functions. These results, those for the isotropic case in particular, are important from the viewpoint of quantum annealing where the efficiency of computation is strongly affected by the size dependence of the energy gap.

  10. Functionals of the ground-state energy and the band gaps of semiconductors and insulators

    SciTech Connect

    Rasolt, M.

    1987-09-15

    We argue that the functional density for the energy of a semiconductor is nonanalytic in the density. Formal expansions in powers of the density, which are at the core of the local-density and gradient-expansion approximations, cannot be rigorously valid for macroscopic systems with energy gaps in the excitation spectrum.

  11. Phase competition in trisected superconducting dome.

    PubMed

    Vishik, I M; Hashimoto, M; He, Rui-Hua; Lee, Wei-Sheng; Schmitt, Felix; Lu, Donghui; Moore, R G; Zhang, C; Meevasana, W; Sasagawa, T; Uchida, S; Fujita, Kazuhiro; Ishida, S; Ishikado, M; Yoshida, Yoshiyuki; Eisaki, Hiroshi; Hussain, Zahid; Devereaux, Thomas P; Shen, Zhi-Xun

    2012-11-01

    A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials, such as the cuprate high-temperature superconductors. Because of its unique momentum-space discrimination, angle-resolved photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates, where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping- and temperature-dependence ARPES study of spectral gaps in Bi(2)Sr(2)CaCu(2)O(8+δ), covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p = 0.19 for the pseudogap phase and p = 0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below T(c) and exists p > 0.19 at higher temperatures. Our data imply a revised phase diagram that reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome. PMID:23093670

  12. A promising way to open an energy gap in bilayer graphene

    NASA Astrophysics Data System (ADS)

    Hao, Jialei; Huang, Chengxi; Wu, Haiping; Qiu, Yuhao; Gao, Qian; Hu, Zhenpeng; Kan, Erjun; Zhang, Lixin

    2015-10-01

    There has been huge research interest in the energy gap problem of monolayer and bilayer graphene due to their great potential in practical applications. Herein, based on first-principles calculations, we report a promising way to open a large band gap in bilayer graphene (BLG) by sandwiching it between two substrates, although this is not usually expected to occur due to the weak interlayer interactions dominated by van der Waals forces. Taking surface-functionalized boron-nitrides as substrates, we predict from first-principles calculations that BLG can have energy gaps ranging from 0.35 eV to 0.55 eV, depending on the substrates and stacking order. Compared to other methods of band-gap manipulation in BLG, the structural integrity of BLG is well-preserved in our study, and the predicted energy gap is suitable for electric devices. Since the proposed method is easily realized in experiments, our results will hopefully accelerate the application of graphene in semiconductor devices and promote the development of graphene technology.There has been huge research interest in the energy gap problem of monolayer and bilayer graphene due to their great potential in practical applications. Herein, based on first-principles calculations, we report a promising way to open a large band gap in bilayer graphene (BLG) by sandwiching it between two substrates, although this is not usually expected to occur due to the weak interlayer interactions dominated by van der Waals forces. Taking surface-functionalized boron-nitrides as substrates, we predict from first-principles calculations that BLG can have energy gaps ranging from 0.35 eV to 0.55 eV, depending on the substrates and stacking order. Compared to other methods of band-gap manipulation in BLG, the structural integrity of BLG is well-preserved in our study, and the predicted energy gap is suitable for electric devices. Since the proposed method is easily realized in experiments, our results will hopefully accelerate the application of graphene in semiconductor devices and promote the development of graphene technology. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04554a

  13. The energy trilogy: An integrated sustainability model to bridge wastewater treatment plant energy and emissions gaps

    NASA Astrophysics Data System (ADS)

    Al-Talibi, A. Adhim

    An estimated 4% of national energy consumption is used for drinking water and wastewater services. Despite the awareness and optimization initiatives for energy conservation, energy consumption is on the rise owing to population and urbanization expansion and to commercial and industrial business advancement. The principal concern is since energy consumption grows, the higher will be the energy production demand, leading to an increase in CO2 footprints and the contribution to global warming potential. This research is in the area of energy-water nexus, focusing on wastewater treatment plant (WWTP) energy trilogy -- the group of three related entities, which includes processes: (1) consuming energy, (2) producing energy, and (3) the resulting -- CO2 equivalents. Detailed and measurable energy information is not readily obtained for wastewater facilities, specifically during facility preliminary design phases. These limitations call for data-intensive research approach on GHG emissions quantification, plant efficiencies and source reduction techniques. To achieve these goals, this research introduced a model integrating all plant processes and their pertinent energy sources. In a comprehensive and "Energy Source-to-Effluent Discharge" pattern, this model is capable of bridging the gaps of WWTP energy, facilitating plant designers' decision-making for meeting energy assessment, sustainability and the environmental regulatory compliance. Protocols for estimating common emissions sources are available such as for fuels, whereas, site-specific emissions for other sources have to be developed and are captured in this research. The dissertation objectives were met through an extensive study of the relevant literature, models and tools, originating comprehensive lists of processes and energy sources for WWTPs, locating estimation formulas for each source, identifying site specific emissions factors, and linking the sources in a mathematical model for site specific CO2 e determination. The model was verified and showed a good agreement with billed and measured data from a base case study. In a next phase, a supplemental computational tool can be created for conducting plant energy design comparisons and plant energy and emissions parameters assessments. The main conclusions drawn from this research is that current approaches are severely limited, not covering plant's design phase and not fully considering the balance of energy consumed (EC), energy produced (EP) and the resulting CO2 e emission integration. Finally their results are not representative. This makes reported governmental and institutional national energy consumption figures incomplete and/or misleading, since they are mainly considering energy consumptions from electricity and some fuels or certain processes only. The distinction of the energy trilogy model over existing approaches is based on the following: (1) the ET energy model is unprecedented, prepared to fit WWTP energy assessment during the design and rehabilitation phases, (2) links the energy trilogy eliminating the need for using several models or tools, (3) removes the need for on-site expensive energy measurements or audits, (4) offers alternatives for energy optimization during plant's life-cycle, and (5) ensures reliable GHG emissions inventory reporting for permitting and regulatory compliance.

  14. Two-gap superconducting properties of alkaline-earth intercalated {{\\rm{A}}}_{x}({{\\rm{NH}}}_{3}){{\\rm{Fe}}}_{2}{{\\rm{Se}}}_{2} (A = Ba or Sr)

    NASA Astrophysics Data System (ADS)

    Hsu, Yung-Yuan; Li, Yu-Bo; Jian, Shou-Ting; Li, Gu-Kuei; Yang, Ming-Cheng

    2016-03-01

    Superconducting properties were studied on high quality superconductors {{{Ba}}}x({{{NH}}}3){{{Fe}}}2{{{Se}}}2 (T c = 39 K) and {{{Sr}}}x({{{NH}}}3){{{Fe}}}2{{{Se}}}2 (T c = 44 K) prepared by intercalating Ba/Sr atoms into tetragonal β-FeSe by liquid ammonia. The elongated c-axis and almost unchanged a-axis of {{{Ba}}}x({{{NH}}}3){{{Fe}}}2{{{Se}}}2, compared with β-FeSe, suggests an unchanged intra-{{{Fe}}}2{{{Se}}}2-layer structure and the T c enhancement is due to a 3D to 2D-like Fermi surface transformation. The superconducting coherent lengths ξ(0), the Ginzburg–Landau parameters κ and penetration depths λ(0) obtained from the extrapolated lower and upper critical fields B c1(0) and B c2(0) indicate that both compounds are typical type-II superconductors. The temperature dependence of 1/{λ }2(T) of {{{Ba}}}x({{{NH}}}3){{{Fe}}}2{{{Se}}}2 deduced from the low-field magnetic susceptibility shows a two-gap s-wave behavior with superconducting gaps of {{{Δ }}}1 = 6.47 meV and {{{Δ }}}2 = 1.06 meV.

  15. Energy-gap reduction in heavily doped silicon: Causes and consequences

    NASA Astrophysics Data System (ADS)

    Pantelides, Sokrates T.; Selloni, Annabella; Car, Roberto

    1985-02-01

    The authors review briefly the existing theoretical treatments of the various effects that contribute to the reduction of the energy gap in heavily doped Si, namely electron-electron and electron-impurity interactions and the effect of disorder in the impurity distribution. They then turn to the longstanding question why energy-gap reductions extracted from three different types of experiments have persistently produced values with substantial discrepancies, making it impossible to compare with theoretical values. First, they demonstrate that a meaningful comparison between theory and experiment can indeed be made if theoretical calculations are carried out for actual quantities that experiments measure, e.g. luminescence spectra, as recently done by Selloni and Pantelides. Then, they demonstrate that, independent of any theoretical calculations, the optical absorption spectra are fully consistent with the luminescence spectra and that the discrepancies in the energy-gap reductions extracted from the two sets of spectra are caused entirely by the curve-fitting procedures used in analyzing optical-absorption data. Finally, they show explicitly that, as already believed by many authors, energy-gap reductions extracted from electrical measurements on transistors do not correspond to true gap reductions. They identify two corrections that must be added to the values extracted from the electrical data in order to arrive at the true gap reductions and show that the resulting values are in good overall agreement with luminescence and absorption data. They, therefore, demonstrate that the observed reduction in emitter injection efficiency in bipolar transistors is not strictly due to a gap reduction, as generally believed, but to three very different effects.

  16. Rotochemical heating with a density-dependent superfluid energy gap in neutron stars

    SciTech Connect

    Gonzalez-Jimenez, Nicolas; Petrovich, Cristobal; Reisenegger, Andreas

    2010-08-04

    When a rotating neutron star loses angular momentum, the 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 Fernandez and Reisenegger for neutron stars of non-superfluid matter and by Petrovich and Reisenegger for superfluid matter, finding that the system in both cases reaches a quasi-steady state, corresponding to a partial equilibration between compression, due to the loss of angular momentum, and reactions that try to restore the equilibrium. However, Petrovich and Reisenegger assumes a constant value of the superfluid energy gap, whereas theoretical models predict density-dependent gap amplitudes, and therefore gaps that depend on the location in the star. In this work, we try to discriminate between several proposed gap models, comparing predicted surface temperatures to the value measured for the nearest millisecond pulsar, J0437-4715.

  17. 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.

  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. Modeling US Adult Obesity Trends: A System Dynamics Model for Estimating Energy Imbalance Gap

    PubMed Central

    Rahmandad, Hazhir; Huang, Terry T.-K.; Bures, Regina M.; Glass, Thomas A.

    2014-01-01

    Objectives. We present a system dynamics model that quantifies the energy imbalance gap responsible for the US adult obesity epidemic among gender and racial subpopulations. Methods. We divided the adult population into gender–race/ethnicity subpopulations and body mass index (BMI) classes. We defined transition rates between classes as a function of metabolic dynamics of individuals within each class. We estimated energy intake in each BMI class within the past 4 decades as a multiplication of the equilibrium energy intake of individuals in that class. Through calibration, we estimated the energy gap multiplier for each gender–race–BMI group by matching simulated BMI distributions for each subpopulation against national data with maximum likelihood estimation. Results. No subpopulation showed a negative or zero energy gap, suggesting that the obesity epidemic continues to worsen, albeit at a slower rate. In the past decade the epidemic has slowed for non-Hispanic Whites, is starting to slow for non-Hispanic Blacks, but continues to accelerate among Mexican Americans. Conclusions. The differential energy balance gap across subpopulations and over time suggests that interventions should be tailored to subpopulations’ needs. PMID:24832405

  20. 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.

  1. 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.

  2. Preparation of Nb3Al by high-energy ball milling and superconductivity

    NASA Astrophysics Data System (ADS)

    Chen, Yongliang; Liu, Zhao; Li, Pingyuan; Zhang, Xiaolan; Yang, Suhua; Yang, Dawei; Du, Lupeng; Cui, Yajing; Pan, Xifeng; Yan, Guo; Zhao, Yong

    2014-05-01

    The A15 phase superconductor Nb3Al has been considered as an alternative to Nb3Sn for high field and large scale applications. However, to prepare a stoichiometric Nb3Al with fine grain structures is very difficult. High-energy ball milling is a solid state powder processing technique and is a very useful for preparing Nb-Al alloys (Nb3Al). The effects of ball milling time and annealing temperature on the formation of Nb3Al superconducting phase have been studied. Pure Nb and Al powders with stoichiometric ratio of Nb3Al were mixed and milled, and the charging and milling were performed in an inert atmosphere. Phase formation and structural evolution during high-energy ball milling have been examined by X-ray diffraction. Al disappeared and Nb peaks broadened after about one hour of milling. With increasing milling time, the peaks of Nb became considerably broader and intensities decreased, the Nb-Al solid solution phase was extensive when milled about 3 hours. In order to obtain Nb3Al superconducting phase, a subsequent anneal was required. We have annealed the as-milled powders at 800-900C for different times to prepared Nb3Al superconducting alloy. The results indicated that Nb3Al with small amount of impurity phase can be obtained on annealing the Nb-Al solid solution phase and the superconducting transition temperature was about 15K, but it is difficult to obtain a homogeneous Nb3Al phase by annealing the amorphous powder.

  3. A promising way to open an energy gap in bilayer graphene.

    PubMed

    Hao, Jialei; Huang, Chengxi; Wu, Haiping; Qiu, Yuhao; Gao, Qian; Hu, Zhenpeng; Kan, Erjun; Zhang, Lixin

    2015-10-28

    There has been huge research interest in the energy gap problem of monolayer and bilayer graphene due to their great potential in practical applications. Herein, based on first-principles calculations, we report a promising way to open a large band gap in bilayer graphene (BLG) by sandwiching it between two substrates, although this is not usually expected to occur due to the weak interlayer interactions dominated by van der Waals forces. Taking surface-functionalized boron-nitrides as substrates, we predict from first-principles calculations that BLG can have energy gaps ranging from 0.35 eV to 0.55 eV, depending on the substrates and stacking order. Compared to other methods of band-gap manipulation in BLG, the structural integrity of BLG is well-preserved in our study, and the predicted energy gap is suitable for electric devices. Since the proposed method is easily realized in experiments, our results will hopefully accelerate the application of graphene in semiconductor devices and promote the development of graphene technology. PMID:26420470

  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. Coil protection for a utility scale superconducting magnetic energy storage plant

    SciTech Connect

    Loyd, R.J.; Schoenung, S.M.; Hassenzahl, W.V.; Rogers, J.D.; Purcell, J.R.

    1986-01-01

    Superconducting Magnetic Energy Storage (SMES) is proposed for electric utility load leveling. Attractive costs, high diurnal energy efficiency (greater than or equal to 92%), and rapid response are advantages relative to other energy storage technologies. Recent industry-led efforts have produced a conceptual design for a 5000 MWh/1000 MW energy storage plant which is technically feasible at commercially attractive estimated costs. The SMES plant design includes a protection system which prevents damage to the magnetic coil if events require a rapid discharge of stored energy. This paper describes the design and operation of the coil protection system, which is primarily passive and uses the thermal capacity of the coil itself to absorb the stored electromagnetic energy.

  6. Energy gap in the aetiology of body weight gain and obesity: a challenging concept with a complex evaluation and pitfalls.

    PubMed

    Schutz, Yves; Byrne, Nuala M; Dulloo, Abdul; Hills, Andrew P

    2014-01-01

    The concept of energy gap(s) is useful for understanding the consequence of a small daily, weekly, or monthly positive energy balance and the inconspicuous shift in weight gain ultimately leading to overweight and obesity. Energy gap is a dynamic concept: an initial positive energy gap incurred via an increase in energy intake (or a decrease in physical activity) is not constant, may fade out with time if the initial conditions are maintained, and depends on the 'efficiency' with which the readjustment of the energy imbalance gap occurs with time. The metabolic response to an energy imbalance gap and the magnitude of the energy gap(s) can be estimated by at least two methods, i.e. i) assessment by longitudinal overfeeding studies, imposing (by design) an initial positive energy imbalance gap; ii) retrospective assessment based on epidemiological surveys, whereby the accumulated endogenous energy storage per unit of time is calculated from the change in body weight and body composition. In order to illustrate the difficulty of accurately assessing an energy gap we have used, as an illustrative example, a recent epidemiological study which tracked changes in total energy intake (estimated by gross food availability) and body weight over 3 decades in the US, combined with total energy expenditure prediction from body weight using doubly labelled water data. At the population level, the study attempted to assess the cause of the energy gap purported to be entirely due to increased food intake. Based on an estimate of change in energy intake judged to be more reliable (i.e. in the same study population) and together with calculations of simple energetic indices, our analysis suggests that conclusions about the fundamental causes of obesity development in a population (excess intake vs. low physical activity or both) is clouded by a high level of uncertainty. PMID:24457473

  7. 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.

  8. Strain energy minimization in SSC (Superconducting Super Collider) magnet winding

    SciTech Connect

    Cook, J.M.

    1990-09-24

    Differential geometry provides a natural family of coordinate systems, the Frenet frame, in which to specify the geometric properties of magnet winding. By a modification of the Euler-Bernoulli thin rod model, the strain energy is defined with respect to this frame. Then it is minimized by a direct method from the calculus of variations. The mathematics, its implementation in a computer program, and some analysis of an SSC dipole by the program will be described. 16 refs.

  9. A bi-annular-gap magnetorheological energy absorber for shock and vibration mitigation

    NASA Astrophysics Data System (ADS)

    Bai, Xian-Xu; Wereley, Norman M.; Choi, Young-Tai; Wang, Dai-Hua

    2012-04-01

    For semi-active shock and vibration mitigation systems using magnetorheological energy absorbers (MREAs), the minimization of the field-off damper force of the MREA at high speed is of particular significance because the damper force due to the viscous damping at high speed becomes too excessive and thus the controllable dynamic force range that is defined by the ratio of the field-on damper force to the field-off damper force is significantly reduced. In this paper, a bi-annular-gap MREA with an inner-set permanent magnet is proposed to decrease the field-off damper force at high speed while keeping appropriate dynamic force range for improving shock and vibration mitigation performance. In the bi-annular-gap MREA, two concentric annular gaps are configured in parallel so as to decrease the baseline damper force and both magnetic activation methods using the electromagnetic coil winding and the permanent magnet are used to keep holding appropriate magnetic intensity in these two concentric annular gaps in the consideration of failure of the electric power supply. An initial field-on damper force is produced by the magnetic field bias generated from the inner-set permanent magnet. The initial damper force of the MREA can be increased (or decreased) through applying positive (or negative) current to the electromagnetic coil winding inside the bi-annular-gap MREA. After establishing the analytical damper force model of the bi-annular-gap MREA using a Bingham-plastic nonlinear fluid model, the principle and magnetic properties of the MREA are analytically validated and analyzed via electromagnetic finite element analysis (FEA). The performance of the bi-annular-gap MREA is also theoretically compared with that of a traditional single-annular- gap MREA with the constraints of an identical volume by the performance matrix, such as the damper force, dynamic force range, and Bingham number with respect to different excitation velocities.

  10. Electron energy loss spectroscopy study of superconducting Nb and its native oxides

    NASA Astrophysics Data System (ADS)

    Tao, Runzhe; Todorovic, R.; Liu, J.; Meyer, R.; Arnold, A.; Walkosz, W.; Zapol, P.; Romanenko, A.; Cooley, L.; Klie, Robert

    2012-02-01

    Niobium has attracted increasing attention in recent years due to its usage in superconducting RF-cavities in next generation particle accelerators. In particular, the possible role of oxidation or the presence of oxygen vacancies on the superconducting properties of niobium metals used in superconducting RF cavities has been the focus on many recent studies. Here, we present a series of electron energy-loss spectroscopy (EELS) studies on niobium (Nb) and its oxides (NbO, NbO2, Nb2O5) to develop a reliable method for quantifying the oxidation state in mixed niobium oxide thin films. Our approach utilizes a combination of transmission electron microscopy and EELS experiments with density functional theory calculations to distinguish between metallic niobium and the different niobium oxides. Based on these observed changes in the core-loss edges, we propose a linear relationship that correlates the peak positions in the Nb M- and O K-edges with the Nb valence state. The methods developed in this paper will then be applied to ultrathin niobium oxide films to examine the effects of low-temperature baking on the films' oxidation states. In addition to oxides, Niobium hydrides are considered as one of the main reasons for Q-decrease under high field. The different phases of Nb hydride can be identified directly using electron diffraction and EELS, which allows for the local hydrogen concentration to be examined at room temperature as well as 95 K.

  11. Enhancing the design of a superconducting coil for magnetic energy storage systems

    NASA Astrophysics Data System (ADS)

    Indira, Gomathinayagam; UmaMaheswaraRao, Theru; Chandramohan, Sankaralingam

    2015-01-01

    Study and analysis of a coil for Superconducting Magnetic Energy Storage (SMES) system is presented in this paper. Generally, high magnetic flux density is adapted in the design of superconducting coil of SMES to reduce the size of the coil and to increase its energy density. With high magnetic flux density, critical current density of the coil is degraded and so the coil is wound with High Temperature Superconductors (HTS) made of different materials. A comparative study is made to emphasize the relationship between the energy storage and length of the coil wound by Bi2223, SF12100, SCS12100 and YBCO tapes. Recently for the construction of HTS magnets, YBCO tapes have been used. Simulation models for various designs have been developed to analyze the magnetic field distribution for the optimum design of energy storage. The design which gives the maximum stored energy in the coil has been used with a certain length of second-generation HTS. The performance analysis and the results of comparative study are done.

  12. An outer gap model of high-energy emission from rotation-powered pulsars

    NASA Technical Reports Server (NTRS)

    Chiang, James; Romani, Roger W.

    1994-01-01

    We describe a refined calculation of high-energy emission from rotation-powered pulsars based on the outer gap model of Cheng, Ho, & Ruderman (1986 a, b). In this calculation, vacuum gaps form in regions near the speed-of-light cylinder of the pulsar magnetosphere along the boundary between the closed and open field line zones. We have improved upon previous efforts to model the spectra from these pulsars (e.g., Cheng et al. 1986b; Ho 1989) by following the variation in particle production and radiation properties with position in the outer gap. Curvature, synchotron, and inverse-Compton scattering fluxes vary significantly over the gap, and their interactions via photon-photon pair production build up the radiating charge populations at varying rates. We have also incorporated an approximate treatment of the transport particle and photon fluxes between gap emission zones. These effects, along with improved computations of the particle and photon distribution, provide very important modifications of the model gamma-ray flux. In paticular, we attempt to make specific predictions of pulse profile shapes and spectral variations as a function of pulse phase and suggest further extensions to the model which may provide accurate computations of the observed high-energy emissions.

  13. Concentration and temperature dependence of the energy gap in some binary and alloy semiconductors

    NASA Astrophysics Data System (ADS)

    Kumar, V.; Sinha, Anita; Farooque, U.

    2015-03-01

    Concentration dependence of the energy gap Eg(x) of In1-xGaxAs, InP1-xAsx, GaxAl1-xAs, GaPxAs1-x and AgGaxIn1-xSe2 alloy semiconductors, and temperature dependence of the energy gap Eg(T) of GaS, GaSe, GaTe, SnS and SnSe2 binary semiconductors have been studied. Both the concentration and temperature dependence of the energy gap Eg(x, T) of AlxGa1-xN ternary alloy, and concentrations dependence of the energy gap Eg(x, y) of In1-xGaxAs1-yPy quaternary alloy semiconductor have also been investigated. Simple relations have been proposed for the calculation of Eg(x), Eg(T), Eg(x, T) and Eg(x, y) for various binary and alloys semiconductors. The average percentage deviation of all proposed relations has been estimated and found to be better than the earlier correlations. The calculated values are compared with the available experimental values and the values reported by different workers. A fairly good agreement has been obtained between them.

  14. Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)₂As₂

    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.

    2012-07-13

    Low-temperature specific heat, C, in magnetic fields up to Hc2 is reported for underdoped Ba(Fe₀.₉₅₅Co₀.₀₄₅)₂As₂ (Tc = 8 K) and for three overdoped samples Ba(Fe₁₋xCox)₂As₂ (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 γ (∝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 γ ∝ 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 γ ∝ H0.3–0.4, followed by an inflection point, followed at higher fields by γ ∝ H¹. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.« less

  15. 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.

  16. A pressure dependence model for the band gap energy of the dilute nitride GaNP

    NASA Astrophysics Data System (ADS)

    Zhao, Chuan-Zhen; Wei, Tong; Li, Na-Na; Wang, Sha-Sha; Lu, Ke-Qing

    2014-08-01

    The pressure dependence of the band gap energy of the dilute nitride GaNP is analyzed. It is found that the pressure dependence of the ? conduction band minimum (CBM) is stronger than that of the X CBM. We also find that the energy difference between the X CBM and the ? CBM in GaNP becomes large with increasing N content. In order to describe the pressure dependence of the band gap energy of the dilute nitride GaNP, a model is developed. Based on the model, we obtain the energy difference between the X CBM and the ? CBM in GaNP at standard atmospheric pressure. It agrees well with the results obtained by other method.

  17. 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.

  18. Hermetically sealed superconducting magnet motor

    DOEpatents

    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.

  19. ORNL Superconducting Technology Program for Electric Energy Systems. Annual report for FY 1992

    SciTech Connect

    Hawsey, R.A.

    1993-02-01

    The Oak Ridge National Laboratory (ORNL) Superconducting Technology Program is conducted as part of a national effort by the US Department of Energy`s (DOE`s) Office of Conservation and Renewable Energy to develop the technology base needed by US industry for commercial development of electric power applications of high-temperature superconductivity. The two major elements of this program are wire development and systems development. This document describes the major research and development activities for this program together with related accomplishments. The technical progress reported was summarized from information prepared for the FY 1992 Peer Review of Projects, conducted by DOE`s Office of Program Analysis, Office of Energy Research. This ORNL program is highly leveraged by the staff and other resources of US industry and universities. Interlaboratory teams are also in place on a number of industry-driven projects. Patent disclosures, working group meetings, staff exchanges, and joint publications and presentations ensure that there is technology transfer to US industry. Working together, the collaborative teams are making tremendous progress in solving the scientific and technical issues necessary for the commercialization of long lengths of practical high-temperature superconductor wire and wire products.

  20. 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.

  1. Development of NbTi Superconducting Strands and Cables for the Field Winding of 200MW Class High Energy Density Type Superconducting Generator

    NASA Astrophysics Data System (ADS)

    Miyashita, Katsumi; Sato, Hiroyuki; Arika, Mitsuhiro; Takahashi, Ryukichi

    The NbTi superconducting strands and cables for the field winding of 200MW class high energy density type superconducting generator are developed. They are composed of Cu/Cu-10wt%Ni/Nb-46.5wt%Ti superconducting strands and the 10kA (at 5T) class 9-strand compacted cables. The diameter of strands is 1.33mm, and the 9-strand compacted cables are 2.4mm thick and 6.0mm wide. In order to produce high current density NbTi strands, we made strands under the controlled aging heat treatments, the total and final strains, and the strains between heat treatments, by using large scale extruder. Moreover, in order to produce high stability and low A. C. loss NbTi strands and cables, the matrix ratio of strands and the cross sections of strands are optimized. The current density of NbTi filaments for the 4 times aging manufactured 1.33mm dia. strands was Jc = 3150A/mm2 at 5T, 1150A/mm2 at 8T. The critical current of the class 9-strand compacted cable is 10.7kA at 5T. The A. C. losses of the final compacted cables are less than 100kW/m3 at 5T, 5T/s, they are decreased to less than half of the target of the A. C. loss value (< 200kW/m3 at 5T, 5T/s). Compared with the strand (Cu ratio: 1.77), the minimum quench energy (MQE) of the strand (Cu ratio > 2) increased about 40% at the operation mode current of the superconducting generator.

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

    NASA Astrophysics Data System (ADS)

    Hickling, Andrew; Wiseman, Toby

    2016-02-01

    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 minimized 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 to that of the scalar fluctuations—the ratio of CFT energy to a power of entropy for the states dual to black holes in the ‘small’ limit is bounded from below when appropriately normalized by the minimum Ricci scalar of the boundary space. Again the bound is saturated for a sphere.

  3. Performance of Small-Gap Undulators at the SLS Intermediate Energy Storage Ring

    SciTech Connect

    Ingold, G.; Boege, M.; Bulgheroni, W.; Keller, A.; Krempaski, J.; Schulze-Briese, C.; Schulz, L.; Schmidt, T.; Zimoch, D.; Hara, T.; Tanaka, T.; Kitamura, H.

    2007-01-19

    The Swiss Light Source (SLS) at the Paul Scherrer Institut (PSI) became the first medium energy synchrotron user facility to rely on the high harmonic operation of small gap, short period undulators to extend high brightness radiation into a regime (3-18 keV) otherwise only accessible using lower brightness wigglers or operation at higher electron beam energy. Today several facilities with beam energy 2-3 GeV follow a similar route. A PSI/SPring-8 collaboration was formed to install and operate the first in-vacuum undulator shortly after commissioning of the SLS storage ring (2.4 GeV) in 2001. The goal of the joint project was to prove that high harmonic operation of small period undulators at small gaps is a valid concept to operate the PX-I beamline at 1 Aa under user operation conditions. The performance of the PX-I beamline proved to be excellent and launched the installation of meanwhile 4 new in-vacuum undulators. Having routinely operated such devices for 5 years, our experience confirms that (1) the concept of operating short period undulators (19-24 mm) on higher harmonics (11./13.) is valid, (2) reliable small gap (5-6 mm) undulator operation is feasible in the presence of top-up injection, and (3) during gap scans the photon beam can be stabilized to sub-{mu}rad precision using non-intercepting photon beam monitors.

  4. Eddy Current Analysis and Optimization for Superconducting Magnetic Bearing of Flywheel Energy Storage System

    NASA Astrophysics Data System (ADS)

    Arai, Yuuki; Yamashita, Tomohisa; Hasegawa, Hitoshi; Matsuoka, Taro; Kaimori, Hiroyuki; Ishihara, Terumasa

    Levitation and guidance force is electromagnetic generated between a superconducting coil and zero field cooled bulk superconductors used in our flywheel energy storage system (FESS). Because the magnetic field depends on the configuration of the coil and the bulks, the eccentricity and the vibration of a rotor cause fluctuation in the magnetic field which induces eddy current and consequent Joule heat on electric conductors such as cooling plates. Heat generation in the cryogenic region critically reduces the efficiency of the FESS. In this paper, we will report the result of the electromagnetic analysis of the SMB and propose an optimal divided cooling plate for reducing the eddy current and Joule heat.

  5. Coherence and decay of higher energy levels of a superconducting transmon qubit.

    PubMed

    Peterer, Michael J; Bader, Samuel J; Jin, Xiaoyue; Yan, Fei; Kamal, Archana; Gudmundsen, Theodore J; Leek, Peter J; Orlando, Terry P; Oliver, William D; Gustavsson, Simon

    2015-01-01

    We present measurements of coherence and successive decay dynamics of higher energy levels of a superconducting transmon qubit. By applying consecutive ? pulses for each sequential transition frequency, we excite the qubit from the ground state up to its fourth excited level and characterize the decay and coherence of each state. We find the decay to proceed mainly sequentially, with relaxation times in excess of 20???s for all transitions. We also provide a direct measurement of the charge dispersion of these levels by analyzing beating patterns in Ramsey fringes. The results demonstrate the feasibility of using higher levels in transmon qubits for encoding quantum information. PMID:25615454

  6. 30 MJ superconducting magnetic energy storage stabilizing coil. Final report for construction

    SciTech Connect

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  8. Tuning the energy gap of bilayer α-graphyne by applying strain and electric field

    NASA Astrophysics Data System (ADS)

    Yang, Hang; Wu, Wen-Zhi; Jin, Yu; Wan-Lin, Guo

    2016-02-01

    Our density functional theory calculations show that the energy gap of bilayer α-graphyne can be modulated by a vertically applied electric field and interlayer strain. Like bilayer graphene, the bilayer α-graphyne has electronic properties that are hardly changed under purely mechanical strain, while an external electric field can open the gap up to 120 meV. It is of special interest that compressive strain can further enlarge the field induced gap up to 160 meV, while tensile strain reduces the gap. We attribute the gap variation to the novel interlayer charge redistribution between bilayer α-graphynes. These findings shed light on the modulation of Dirac cone structures and potential applications of graphyne in mechanical-electric devices. Project supported by the National Key Basic Research Program of China (Grant Nos. 2013CB932604 and 2012CB933403), the National Natural Science Foundation of China (Grant Nos. 51472117 and 51535005), the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures, China (Grant No. 0414K01), the Nanjing University of Aeronautics and Astronautics (NUAA) Fundamental Research Funds, China (Grant No. NP2015203), and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

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

    SciTech Connect

    Snead, C.L. Jr.; Hanson, A.; Greene, G.A.

    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.

  10. Optimized use of superconducting magnetic energy storage for electromagnetic rail launcher powering

    NASA Astrophysics Data System (ADS)

    Badel, Arnaud; Tixador, Pascal; Arniet, Michel

    2012-01-01

    Electromagnetic rail launchers (EMRLs) require very high currents, from hundreds of kA to several MA. They are usually powered by capacitors. The use of superconducting magnetic energy storage (SMES) in the supply chain of an EMRL is investigated, as an energy buffer and as direct powering source. Simulations of direct powering are conducted to quantify the benefits of this method in terms of required primary energy. In order to enhance further the benefits of SMES powering, a novel integration concept is proposed, the superconducting self-supplied electromagnetic launcher (S3EL). In the S3EL, the SMES is used as a power supply for the EMRL but its coil serves also as an additional source of magnetic flux density, in order to increase the thrust (or reduce the required current for a given thrust). Optimization principles for this new concept are presented. Simulations based on the characteristics of an existing launcher demonstrate that the required current could be reduced by a factor of seven. Realizing such devices with HTS cables should be possible in the near future, especially if the S3EL concept is used in combination with the XRAM principle, allowing current multiplication.

  11. 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.

  12. Temperature dependence of the energy gap and spin-orbit splitting in a narrow-gap InGaAsSb solid solution

    NASA Astrophysics Data System (ADS)

    Motyka, M.; Janiak, F.; Sek, G.; Misiewicz, J.; Moiseev, K. D.

    2012-05-01

    Temperature dependence of the energy gap and the spin-orbit split off transition in a thick layer of narrow-gap InGaAsSb material with high In content has been determined by a combination of photoluminescence and photoreflectance. The respective temperature coefficients have been found to be equal for both the transitions and determined to be ? = -0.41 meV/K. For the investigated In0.86Ga0.14As0.83Sb0.17 alloy, the separation energy of the split-off band has been obtained to be ?so = 0.460 eV and experimentally evidenced to be independent on temperature, which opens broad application prospects for these multinary (multicomponent) narrow gap compounds and their heterostructures.

  13. 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.

  14. 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.

  15. High temperature superconductivity with repulsive pairing interactions

    NASA Astrophysics Data System (ADS)

    Fink, Herman J.; Haley, Stephen B.

    2015-10-01

    A pairing Hamiltonian H (?) with an interaction kernel ? characterized by [ -?0, -?0 ] , where ?0 denotes the separable part and ?0 the degree of non-separability, produces high temperature superconductivity for both attractive ?0 > 0 and repulsive ?0 < 0 when ?0 > 0 . For ?0 > 0 , typical HTS properties, e.g. cuprate, are produced. Repulsive ?0 < 0 produces a distinct difference in the kinetic energy dependence of the SC gap, significantly altering thermodynamic properties.

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

    NASA Astrophysics Data System (ADS)

    Muslimov, Alex G.; Harding, Alice K.

    2003-05-01

    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 & Scharlemann 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 that 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 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, which 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 γ-ray pulsars. We illustrate the results of our modeling of the pair cascades and γ-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.

  17. 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.

  18. 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.

  19. 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.

  20. Magnetic Properties of Iron Chalcogenide Superconducting Materials for Energy Storage Applications

    NASA Astrophysics Data System (ADS)

    Knock, Destenie; Pough, Korey; Kebede, Abebe; Seifu, Dereje

    2013-03-01

    A superconductor is characterized by its ability to conduct electricity without loss and expel magnetic flux when exposed to an external magnetic field. Additionally, the smaller the relaxation rate (S = dM/dt), the better the material for energy storage. This research focuses on the recently discovered high-quality, single-crystalline Iron-based superconductors of FeTe1-xSex (x =0.5), with a transition temperature at Tc = 14.5K. Standard creep models are used to analyze the data and determine the effective pinning potential. The magnetization relaxation were measured the Superconducting Quantum Interference Device (SQUID). The relaxation rate appears to be independent of field and temperature for fields below 3T and temperatures below 7K. This result shows that the thermally activated flux motion is not as significant as in other high temperature superconductors, hence FeTe1-xSex, can be a candidate for wire development to be used in Superconducting Magnetic Energy Storage systems.

  1. 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.

  2. Secondary "smile"-gap in the density of states of a diffusive Josephson junction for a wide range of contact types

    NASA Astrophysics Data System (ADS)

    Reutlinger, J.; Glazman, L.; Nazarov, Yu. V.; Belzig, W.

    2014-07-01

    The superconducting proximity effect leads to strong modifications of the local density of states in diffusive or chaotic cavity Josephson junctions, which displays a phase-dependent energy gap around the Fermi energy. The so-called minigap of the order of the Thouless energy ETh is related to the inverse dwell time in the diffusive region in the limit ETh??, where ? is the superconducting energy gap. In the opposite limit of a large Thouless energy ETh??, a small new feature has recently attracted attention, namely, the appearance of a further secondary gap, which is around two orders of magnitude smaller compared to the usual superconducting gap. It appears in a chaotic cavity just below the superconducting gap edge ? and vanishes for some value of the phase difference between the superconductors. We extend previous theory restricted to a normal cavity connected to two superconductors through ballistic contacts to a wider range of contact types. We show that the existence of the secondary gap is not limited to ballistic contacts, but is a more general property of such systems. Furthermore, we derive a criterion which directly relates the existence of a secondary gap to the presence of small transmission eigenvalues of the contacts. For generic continuous distributions of transmission eigenvalues of the contacts, no secondary gap exists, although we observe a singular behavior of the density of states at ?. Finally, we provide a simple one-dimensional scattering model which is able to explain the characteristic "smile" shape of the secondary gap.

  3. Localized description of surface energy gap effects in the resonant charge exchange between atoms and surfaces.

    PubMed

    Iglesias-Garca, A; Garca, Evelina A; Goldberg, E C

    2011-02-01

    The resonant charge exchange between atoms and surfaces is described by considering a localized atomistic view of the solid within the Anderson model. The presence of a surface energy gap is treated within a simplified tight-binding model of the solid, and a proper calculation of the Hamiltonian terms based on a LCAO expansion of the solid eigenstates is performed. It is found that interference terms jointly with a surface projected gap maximum at the ? point and the Fermi level inside it, lead to hybridization widths negligible around the Fermi level. This result can explain experimental observations related to long-lived adsorbate states and anomalous neutral fractions of low energy ions in alkali/Cu(111) systems. PMID:21406877

  4. Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle

    NASA Technical Reports Server (NTRS)

    Elkadi, Asmaa; Decrossas, Emmanuel; El-Ghazaly, Samir

    2013-01-01

    The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of the electron density for an individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closest neighbours reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%.

  5. Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle

    NASA Technical Reports Server (NTRS)

    Elkadi, Asmaa; Decrossas, Emmanuel; El-Ghazaly, Samir

    2013-01-01

    The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of electron density for na individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closet neighbors reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%.

  6. Availability analysis of a 100 kWh superconducting magnetic energy storage

    NASA Astrophysics Data System (ADS)

    Maekinen, H.; Mikkonen, R.

    Superconducting Magnetic Energy Storage (SMES) is one of the possible and useful applications of modern superconducting technology. It is known that some loads on electricity distribution networks are particularly sensitive to short power interruptions and voltage sags. Different ranges of SMES applications have been widely discussed for large scale units (1 MWh - 1 GWh) as well as for small and medium scale units (1 kWh - 1 MWh). The major components of a SMES system are the superconducting magnet winding, the cryogenic refrigeration system and the power conditioning system, which interfaces the coil to the utility grid and applied load. The SMES winding is cooled by a cryogenic coolant: liquid helium for LTS (low temperature superconductor) wires; gaseous helium, liquid hydrogen or liquid nitrogen for HTS (high temperature superconductor) wires. In addition the higher operating temperature of HTS materials also means higher refrigeration efficiencies, greater reliability and easier acceptance within the utility community. It has been estimated that applying HTS materials in a SMES system will reduce the capital costs some 14-26 %. In this calculation it has been assumed that the price of HTS material is equivalent to that of LTS material. This report deals with the availability aspects of a 100 kWh SMES. A conceptual design of a reference unit has been used as a basis of the study. Therefore the lack of the detailed design leads to uncertainty in evaluating the failure data for single components. The failure rate data are mainly adopted from fusion data sources. This extrapolation is problematic, but in most cases the only way to get results at all. The method used is based on the failure modes, effects and criticality analysis, FMECA. Fault trees describe the outage logic based on the functional analysis. Event trees clarify the consequences of the primary events and the criticality of these consequences are expressed as system down times.

  7. Neutron Scattering Studies On Stoner Gap In The Superconducting Ferromagnet UGe2 By Using A Small Piston-Cylinder-Type Clamp Cell

    NASA Astrophysics Data System (ADS)

    Aso, N.; Uwatoko, Y.; Fujiwara, T.; Motoyama, G.; Ban, S.; Homma, Y.; Shiokawa, Y.; Hirota, K.; Sato, N. K.

    2006-09-01

    The design and fundamental properties of a small copper-beryllium (CuBe) based piston-cylinder-type clamp cell for low-temperature (LT) neutron diffraction (ND) measurements are reported. The results obtained for the superconducting ferromagnet UGe2 showed that the perfectly polarized ferromagnetic state is realized below Px.

  8. The Effect of Carbon Nanotube on Band Gap Energy of TiO2 Nanoparticles

    NASA Astrophysics Data System (ADS)

    Taleshi, F.

    2015-05-01

    A composite of TiO2-carbon nanotubes (CNTs) was synthesized via a sol-gel method. The structure and morphology of the nanocomposite samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optical properties of the samples were studied using UV-Vis spectroscopy. The results show that CNTs can decrease the value of band gap energy of TiO2 nanoparticles considerably.

  9. 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.

  10. Large gap magnetic suspension system

    NASA Technical Reports Server (NTRS)

    Abdelsalam, Moustafa K.; Eyssa, Y. M.

    1991-01-01

    The design of a large gap magnetic suspension system is discussed. Some of the topics covered include: the system configuration, permanent magnet material, levitation magnet system, superconducting magnets, resistive magnets, superconducting levitation coils, resistive levitation coils, levitation magnet system, and the nitrogen cooled magnet system.

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

    SciTech Connect

    Markin, S. N.; Primetzhofer, D.; Bauer, P.

    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.

  12. In situ electrical transport measurementof superconductive ultrathin films

    NASA Astrophysics Data System (ADS)

    Liu, Can-Hua; Jia, Jin-Feng

    2015-11-01

    The discovery of an extraordinarily superconductive large energy gap in SrTiO3 supported single-layer FeSe films has recently initiated a great deal of research interests in surface-enhanced superconductivity and superconductive ultrathin films fabricated on crystal surfaces. On account of the instability of ultra-thin films in air, it is desirable to perform electrical transport measurement in ultra-high vaccum (UHV). Here we review the experimental techniques of in situ electrical transport measurement and their applications on superconductive ultrathin films. The work in SJTU was supported by the National Basic Research Program of China (Grant Nos. 2013CB921902 and 2011CB922200) and the National Natural Science Foundation of China (Grant Nos. 11227404, 11274228, 11521404, 11174199, and 11134008).

  13. The Čerenkov limit of Si, GaAs and GaP in electron energy loss spectrometry.

    PubMed

    Horák, Michal; Stöger-Pollach, Michael

    2015-10-01

    Since the advent of monochromated electron energy loss spectrometry (EELS) the experimental detection of band gaps in semiconducting materials is of great importance. In the non-relativistic limit of this technique the onset of the inelastic signal represents the band gap. But due to relativistic energy losses, like Čerenkov losses and the corresponding light guiding modes, appearing at high beam energies the band gap is usually hidden. The highest beam energy, which does not excite relativistic losses in a certain material, is called the Čerenkov limit of the material. In this work the low loss EELS signals of Si, GaAs and GaP are measured at various beam energies and the calculated Čerenkov limits are experimentally confirmed. PMID:26094202

  14. 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..

  15. Proximity-induced superconducting transition temperature

    SciTech Connect

    Farrell, M.E. , U.S. Naval Air Development Center, Warminster, Pennsylvania 18974-5000 ); Bishop, M.F. )

    1989-12-01

    We have calculated the proximity-induced superconducting transition temperature for a thin weak-coupling normal metal in contact with an infinitely thick strong-coupling superconductor. The model considered is that of aluminum in perfect contact with superconducting lead, where both metals are clean. The energy-dependent gap is calculated numerically as a function of temperature for the strong-coupling Pb superconductor with the Eliashberg equations, and this is used to calculate the induced energy-dependent gap in the weak-coupling Al metal through the modified Eliashberg equations for the normal-metal-superconductor configuration. In this latter calculation the presence of the Al metal is assumed to have a negligible effect on the energy gap of the Pb. We find the transition temperature of Al to be enhanced to 4.5 K, compared with its bulk transition temperature of 1.2 K. In addition, we find that the magnitude of the zero-temperature Al gap is enhanced from 0.17 to 0.68 meV.

  16. Generalized Gradient Approximation Correlation Energy Functionals Based on the Uniform Electron Gas with Gap Model.

    PubMed

    Fabiano, Eduardo; Trevisanutto, Paolo E; Terentjevs, Aleksandrs; Constantin, Lucian A

    2014-05-13

    We studied uniform electron gas with a gap model in the context of density functional theory. On the basis of this analysis, we constructed two local gap models that are used in generalized gradient approximation (GGA) correlation functionals that satisfy numerous exact constraints for correlation energy. The first one, named GAPc, fulfills the full second-order correlation gradient expansion at any density regime and is very accurate for jellium surfaces, comparable to state-of-the-art GGAs for atomic systems and molecular systems, and is well compatible with known semilocal exchanges. The second functional, named GAPloc, satisfies the same exact conditions, except that the second-order gradient expansion is sacrificed for a better behavior under the Thomas-Fermi scaling and a more realistic correlation energy density of the helium atom. The GAPloc functional displays a high accuracy for atomic correlation energies, still preserving a reasonable behavior for jellium surfaces. Moreover, it shows a higher compatibility with the Hartree-Fock exchange than other semilocal correlation functionals. This feature is explained in terms of the real-space analysis of the GAPloc correlation energy. PMID:26580528

  17. Caffeine-Containing Energy Drinks: Beginning to Address the Gaps in What We Know1234

    PubMed Central

    Sorkin, Barbara C.; Coates, Paul M.

    2014-01-01

    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 mat, 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 20102012 timeframe report discrepant prevalence of CCED use by teenagers, ranging from 10.3% in 1317 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

  18. Progress with High-Field Superconducting Magnets for High-Energy Colliders

    NASA Astrophysics Data System (ADS)

    Apollinari, Giorgio; Prestemon, Soren; Zlobin, Alexander V.

    2015-10-01

    One of the possible next steps for high-energy physics research relies on a high-energy hadron or muon collider. The energy of a circular collider is limited by the strength of bending dipoles, and its maximum luminosity is determined by the strength of final focus quadrupoles. For this reason, the high-energy physics and accelerator communities have shown much interest in higher-field and higher-gradient superconducting accelerator magnets. The maximum field of NbTi magnets used in all present high-energy machines, including the LHC, is limited to 10 T at 1.9 K. Fields above 10 T became possible with the use of Nb3Sn superconductors. Nb3Sn accelerator magnets can provide operating fields up to 15 T and can significantly increase the coil temperature margin. Accelerator magnets with operating fields above 15 T require high-temperature superconductors. This review discusses the status and main results of Nb3Sn accelerator magnet research and development and work toward 20-T magnets.

  19. Solving LFC problem in an interconnected power system using superconducting magnetic energy storage

    NASA Astrophysics Data System (ADS)

    Farahani, Mohsen; Ganjefar, Soheil

    2013-04-01

    This paper proposes the combination of a load frequency control (LFC) with superconducting magnetic energy storage (SMES) to solve the LFC problem in interconnected power systems. By using this combination, the speed damping of frequency and tie-line power flow deviations is considerably increased. A new control strategy of SMES is proposed in this paper. The problem of determining optimal parameters of PID and SMES control loop is considered as an optimization problem and a pattern search algorithm (PS) optimization is employed to solve it. The simulation results show that if an SMES unit is installed in an interconnected power system, in addition to eliminating oscillations and deviations, the settling time in the frequency and tie-line power flow responses is considerably reduced.

  20. SUPERCONDUCTING PHOTOCATHODES.

    SciTech Connect

    SMEDLEY, J.; RAO, T.; WARREN, J.; SEKUTOWICZ, LANGNER, J.; STRZYZEWSKI, P.; LEFFERS, R.; LIPSKI, A.

    2005-10-09

    We present the results of our investigation of lead and niobium as suitable photocathode materials for superconducting RF injectors. Quantum efficiencies (QE) have been measured for a range of incident photon energies and a variety of cathode preparation methods, including various lead plating techniques on a niobium substrate. The effects of operating at ambient and cryogenic temperatures and different vacuum levels on the cathode QE have also been studied.

  1. Point-contact Andreev reflection tunneling spectroscopy (PCARTS) of the superconducting gap structure in LuNi2B2C

    NASA Astrophysics Data System (ADS)

    Lu, Xin; Park, W. K.; Greene, L. H.; Yeo, Sunmog; Oh, Kyu-Hwan; Lee, Sung-Ik; Bud'Ko, Sergey L.; Canfield, Paul C.

    2008-03-01

    The PCARTS technique is employed to investigate the gap anisotropy and proposed existence of point-nodes in LuNi2B2C (TC 16 K). Differential conductance spectra are taken from two different sets of single crystal samples along three major orientations: [001], [110], and [100]. Analyzing using the single-gap Blonder-Tinkham-Klapwijk (BTK) model reproducibly shows the gaps along these directions are 2.4, 2.6, and 2.3 meV, respectively, for one set of samples and 2.4, 2.8, and 2.7 meV, respectively, for the other set. This is smaller than the gap anisotropy reported by other groups[1]. At low temperatures, the single-gap BTK model does not satisfactorily fit our data. Models employing an anisotropic gap are being investigated, as are experiments parameterizing the tunneling cone effect.[1] Y.G. Naidyuk, et al,condmat/0609769(2006); N.L.Bobrov, et al,PRB 71, 014512 (2005); S. Mukhopadhyay, et al,PRB 72, 014545 (2005).

  2. Conceptual design study of superconducting magnetic energy storage using high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Schoenung, S. M.; Meier, W. R.; Fagaly, R. L.; Heiberger, M.; Stephens, R. B.; Leuer, J. A.; Guzman, R. A.; Johnson, E. R.; Purcell, J.; Creedon, L.

    1992-02-01

    Since the discovery of high critical temperature superconductors (HTS), many predictions have been made for savings in the cost or performance of superconducting technologies for electric utility systems, such as superconducting magnetic energy storage (SMES). The higher operating temperature of HTS materials could mean the use of less expensive cryogens, such as liquid nitrogen, higher refrigeration efficiencies, greater reliability, and easier acceptance within the utility community. While all of these developments may occur, the significance of the improvements depends on the application and other characteristics of the system. Also, today's HTS materials have some negative features, including lower critical current density and greater brittleness, compared to conventional metallic superconductors. A conceptual design for SMES using HTS has been analyzed to determine configuration parameters, refrigeration requirements, and estimated costs of major components. The study covered the energy storage range from 2 to 200 MWh at power levels from 4 to 400 MW. This range includes utility applications from transient and power stabilization to spinning reserve and load leveling. The present assessment has been carried out for cold-supported modular torus and for comparison, a cold-supported modular solenoid. The toroidal configuration was chosen for analysis because it has minimal magnetic field, which could be an advantage in locating a small unit near a utility or customer load. The comparison shows that for all cases, the solenoid is comparable in price or less expensive. However, the solenoid has a varying external magnetic field which must be accommodated. The modular approach was selected primarily as a way to wind the coil and keep the brittle oxide superconductor under compression at all operating conditions to avoid breakage.

  3. 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.

  4. Number theory, periodic orbits, and superconductivity in nanocubes

    NASA Astrophysics Data System (ADS)

    Mayoh, James; Garca-Garca, Antonio M.

    2014-07-01

    We study superconductivity in isolated superconducting nanocubes and nanosquares of size L in the limit of negligible disorder ? /?0?1 and kFL?1 for which mean-field theory and semiclassical techniques are applicable, with kF the Fermi wave vector, ? the mean level spacing, and ?0 the bulk gap. By using periodic orbit theory and number theory we find explicit analytical expressions for the size dependence of the superconducting order parameter. Our formalism takes into account contributions from both the spectral density and the interaction matrix elements in a basis of one-body eigenstates. The leading size dependence of the energy gap in three dimensions seems to be universal as it agrees with the result for chaotic grains. In the region of parameters corresponding to conventional metallic superconductors, and for sizes L ?10 nm, the contribution to the superconducting gap from the matrix elements is substantial (20%). Deviations from the bulk limit are still clearly observed even for comparatively large grains L 50 nm. These analytical results are in excellent agreement with the numerical solution of the mean-field gap equation.

  5. 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.

  6. Determination of composition and energy gaps of GaInNAsSb layers grown by MBE

    NASA Astrophysics Data System (ADS)

    Aho, A.; Korpijärvi, V.-M.; Isoaho, R.; Malinen, P.; Tukiainen, A.; Honkanen, M.; Guina, M.

    2016-03-01

    We present a method to accurately determine the composition of GaInNAsSb heterostructures and a modified band anti-crossing model to calculate the corresponding bandgaps. The composition determination method is based on combining x-ray diffractometry and energy dispersive x-ray spectroscopy measurements. The modified band anti-crossing model was derived from the model known for GaInNAs and using band-gap composition relations for GaInAs, GaInSb, InAsSb and GaAsSb. The model parameters were defined by fitting with experimental bandgap data retrieved from photoluminescence. For validation and data fitting we used experimental samples with N composition in the range of 0-0.06, In composition from 0 to 0.17, and Sb composition in the range of 0-0.08. All samples were thermally annealed to minimize the band gap shift caused by the short range ordering effects in GaInNAsSb crystal. The modified model yields an excellent fit to the experimental band gap data with an accuracy of ~20 meV, and is a practical tool for designing, fabricating and analyzing optoelectronics devices.

  7. The Energy Band Gap of AlxGa1-xN

    NASA Astrophysics Data System (ADS)

    Paduano, Qing S.; Weyburne, David W.; Bouthillette, Lionel O.; Wang, Shen-Qi; Alexander, Michael N.

    2002-04-01

    Combining experimental measurements with an analysis of sample strain, we have determined the unstrained energy band gap, Eg, of AlxGa1-xN for 0 ? x ? 1. Care was taken to grow films with narrow (00.2) and (10.2) X-ray diffraction rocking curve widths, to insure low residual strain in the samples. This is significant because, even for our high quality AlxGa1-xN thin films, residual strain shifts the fitted band gap bowing parameter significantly. For AlxGa1-xN random alloys on GaN films deposited on sapphire, the strain-corrected band gap dependence on alloy composition is fit well by a bowing parameter of b = 0.70 0.05. In contrast, AlxGa1-xN films deposited directly on sapphire had much higher X-ray line-widths and their Egs are not fit well by one value of the bowing parameter. This suggests that material quality may be a significant reason for the large range of bowing parameters reported in the literature.

  8. The effect of cluster size on the optical band gap energy of Zn-based metal-organic frameworks.

    PubMed

    Ghosh, Raja; Pedicini, Anthony F; Rao, Purna Chandra; Asha, K S; Reber, Arthur C; Mandal, Sukhendu

    2015-08-14

    We have synthesized three Metal-Organic Frameworks (MOFs) in which Zn metal ions form the secondary building unit, and 4,4'-sulfonyldibenzoic acid (SDB) serves as the ligand: [[Zn(DMF)(SDB)](DMF), 1, [Zn(3)(DMF)(3)(SDB)(3)](DMF), 2 and [Zn(3)(OH)(2)(SDB)(2)] (DMF)(2), 3, where DMF = dimethyl formamide]. Compound contains a paddle-wheel type Zn dimer, compound contains a Zn trimer motif, and contains a one-dimensional Zn-OH-Zn chain. These building units may be considered to be Zn clusters. We have measured and theoretically calculated the band gap energy and by theoretical investigations we found that the cluster size plays an important role in the band gap energy, however additional effects are observed. The larger cluster size corresponds to a larger band gap energy, however the cavity of the trimer based compound (2) traps a solvent molecule that decreases the band gap energy. PMID:26151648

  9. The role of solvents in framework dimensionality and their effect on band gap energy.

    PubMed

    Asha, K S; Kavyasree, P R; George, Anu; Mandal, Sukhendu

    2015-01-21

    The crystal growth rate and morphology can be modulated by tuning the ratio of the solvent in mixed solvents during synthesis. We present here a solvothermal method to synthesize a Cd-FDC based metal-organic framework with different morphologies by tuning the ratio of water in the DMF-water mixed solvent system without adding any other additives. With the increasing water volume ratio a series of crystals with different morphologies were synthesized. Among these we have isolated two single crystal structures, [Cd3(FDC)3(DMF)4(H2O)], and [DMA]2[Cd3(FDC)4]·2H2O, . Compound was synthesized from DMF with small amounts of water while was formed from 25 vol% of water in the DMF-water mixed solvent. Compound contains trimer clusters as building units, which are linked by the furan dicarboxylate ligand to form a two-dimensional structure. Compound also contains trimer clusters which are linked to each other to form a one-dimensional chain with the Cd-O-Cd linkage. This one-dimensional chain in turn is connected by the furan dicarboxylate ligand to form a three-dimensional structure. All these structures are characterized by SEM, XRD, TGA and IR. We have measured the band gap energy and measurements show that the values are decreasing from to . The lower band gap energy of may be due to the presence of infinite Cd-O-Cd linkages which split the states of the conduction band and reduces the band gap energy. PMID:25408115

  10. Analysis of superconducting magnetic energy storage applications at a proposed wind farm site near Browning, Montana

    NASA Astrophysics Data System (ADS)

    Gaustad, K. L.; Desteese, J. G.

    1993-07-01

    A computer program was developed to analyze the viability of integrating superconducting magnetic energy storage (SMES) with proposed wind farm scenarios at a site near Browning, Montana. The program simulated an hour-by-hour account of the charge/discharge history of a SMES unit for a representative wind-speed year. Effects of power output, storage capacity, and power conditioning capability on SMES performance characteristics were analyzed on a seasonal, diurnal, and hourly basis. The SMES unit was assumed to be charged during periods when power output of the wind resource exceeded its average value. Energy was discharged from the SMES unit into the grid during periods of low wind speed to compensate for below-average output of the wind resource. The option of using SMES to provide power continuity for a wind farm supplemented by combustion turbines was also investigated. Levelizing the annual output of large wind energy systems operating in the Blackfeet area of Montana was found to require a storage capacity too large to be economically viable. However, it appears that intermediate-sized SMES economically levelize the wind energy output on a seasonal basis.

  11. 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.

  12. The resummation of inter-jet energy flow for gaps-between-jets processes at HERA

    NASA Astrophysics Data System (ADS)

    Appleby, R. B.; Seymour, M. H.

    2003-09-01

    We calculate resummed perturbative predictions for gaps-between-jets processes and compare to HERA data. Our calculation of this non-global observable needs to include the effects of primary gluon emission (global logarithms) and secondary gluon emission (non-global logarithms) to be correct at the leading logarithm (LL) level. We include primary emission by calculating anomalous dimension matrices for the geometry of the specific event definitions and estimate the effect of non-global logarithms in the large Nc limit. The resulting predictions for energy flow observables are consistent with experimental data.

  13. A Spin Chern pump with fully gapped energy and spin spectra

    NASA Astrophysics Data System (ADS)

    Chen, M. N.; Su, W.; Sheng, L.; Xing, D. Y.

    2015-10-01

    We propose a topological spin Chern pump using a two-dimensional topological insulator subject to electromagnetic radiations. In each cycle, spin can be continuously pumped into leads, which is attributed to the nonzero spin Chern numbers. In comparison to a previous model (Chen M. N. et al., Phys. Rev. B, 91 (2015) 125117), this system can have a much larger spin pumping conductivity. Moreover, the energy and spin spectra are always gapped in the present system, which makes the spin pumping more stable to perturbations. The spin pumping is an observable effect of the topological invariant spin Chern numbers, which may be useful in spintronic applications.

  14. 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.

  15. 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.

  16. Electron-phonon interaction and pairing mechanism in superconducting Ca-intercalated bilayer graphene

    PubMed Central

    Margine, E. R.; Lambert, Henry; Giustino, Feliciano

    2016-01-01

    Using the ab initio anisotropic Eliashberg theory including Coulomb interactions, we investigate the electron-phonon interaction and the pairing mechanism in the recently-reported superconducting Ca-intercalated bilayer graphene. We find that C6CaC6 can support phonon-mediated superconductivity with a critical temperature Tc = 6.8–8.1 K, in good agreement with experimental data. Our calculations indicate that the low-energy Caxy vibrations are critical to the pairing, and that it should be possible to resolve two distinct superconducting gaps on the electron and hole Fermi surface pockets. PMID:26892805

  17. Electron-phonon interaction and pairing mechanism in superconducting Ca-intercalated bilayer graphene

    NASA Astrophysics Data System (ADS)

    Margine, E. R.; Lambert, Henry; Giustino, Feliciano

    2016-02-01

    Using the ab initio anisotropic Eliashberg theory including Coulomb interactions, we investigate the electron-phonon interaction and the pairing mechanism in the recently-reported superconducting Ca-intercalated bilayer graphene. We find that C6CaC6 can support phonon-mediated superconductivity with a critical temperature Tc = 6.8–8.1 K, in good agreement with experimental data. Our calculations indicate that the low-energy Caxy vibrations are critical to the pairing, and that it should be possible to resolve two distinct superconducting gaps on the electron and hole Fermi surface pockets.

  18. Electron-phonon interaction and pairing mechanism in superconducting Ca-intercalated bilayer graphene.

    PubMed

    Margine, E R; Lambert, Henry; Giustino, Feliciano

    2016-01-01

    Using the ab initio anisotropic Eliashberg theory including Coulomb interactions, we investigate the electron-phonon interaction and the pairing mechanism in the recently-reported superconducting Ca-intercalated bilayer graphene. We find that C6CaC6 can support phonon-mediated superconductivity with a critical temperature Tc = 6.8-8.1 K, in good agreement with experimental data. Our calculations indicate that the low-energy Caxy vibrations are critical to the pairing, and that it should be possible to resolve two distinct superconducting gaps on the electron and hole Fermi surface pockets. PMID:26892805

  19. Large dust gaps in the transitional disks of HD 100453 and HD 34282. Connecting the gap size to the spectral energy distribution and mid-infrared imaging

    NASA Astrophysics Data System (ADS)

    Khalafinejad, S.; Maaskant, K. M.; Mariñas, N.; Tielens, A. G. G. M.

    2016-03-01

    Context. The formation of dust gaps in protoplanetary disks is one of the most important signs of disk evolution and might indicate the formation of planets. Aims: We aim to characterize the flaring disk structure around the Herbig Ae/Be stars HD 100453 and HD 34282. Their spectral energy distributions (SEDs) show an emission excess between 15-40 μm, but very weak (HD 100453) and no (HD 34282) signs of the 10 and 20 μm amorphous silicate features. We investigate whether this implies the presence of large dust gaps. Methods: We investigated spatially resolved mid-infrared Q-band images taken with Gemini North/MICHELLE. We performed radiative transfer modeling and examined the radial distribution of dust. We simultaneously fit the Q-band images and SEDs of HD 100453 and HD 34282. Results: Our solutions require that the inner halos and outer disks be separated by large dust gaps that are depleted with respect to the outer disk by a factor of 1000 or more. The inner edges of the outer disks of HD 100453 and HD 34282 have temperatures of ~160 ± 10 K and ~60 ± 5 K, respectively. Because of the high surface brightness of these walls, they dominate the emission in the Q band. Their radii are constrained at 20-2+2 AU and 92-17+31 AU, respectively. Conclusions: HD 100453 and HD 34282 most likely have disk dust gaps. The upper limit of the dust mass in each gap is estimated to be about 10-7 M⊙. We find that the locations and sizes of disk dust gaps are connected to the SED, as traced by the mid-infrared flux ratio F30/F13.5. We propose a new classification scheme for the Meeus groups based on the F30/F13.5 ratio. The absence of amorphous silicate features in the observed SEDs is caused by the depletion of small (≲1 μm) silicate dust at temperatures above ≳160 K, which could be related to the presence of a dust gap in that region of the disk.

  20. Raman scattering from superconducting gap excitations in single-crystal YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/

    SciTech Connect

    Cooper, S.L.; Klein, M.V.; Pazol, B.G.; Rice, J.P.; Ginsberg, D.M.

    1988-04-01

    The results of a polarized light scattering study of single-crystal YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ are presented. Strong interband electronic scattering in YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ is observed through interference effects with certain phonons. Below T/sub c/, this electronic scattering undergoes a redistribution due to gap formation, which is monitored by a rapid change in the damping rates of the strongly coupled phonons. Our lowest temperature data further indicates the presence of residual electronic scattering well below the expected 2..delta.. gap onset, suggesting that a continuum of electronic states exists inside the gap.

  1. Superconductivity in noncentrosymmetric SrAuSi3

    NASA Astrophysics Data System (ADS)

    Isobe, Masaaki; Arai, Masao; Shirakawa, Naoki

    2016-02-01

    Superconductivity in the noncentrosymmetric compound SrAuSi3 [BaNiS n3 type, I 4 m m ,a =4.4024 (9 )Å , and c =9.942 (2 )Å ] was studied by electrical resistivity, magnetic susceptibility, and specific heat measurements using single-phase polycrystalline samples, and ab initio band calculation. These measurements of the physical properties confirmed that the SrAuSi3 phase shows bulk superconductivity with a critical temperature of TC˜1.6 K and an upper critical field of HC 2˜1.8 kOe . In the superconducting state, the electronic specific heat exhibits a thermal-activation-type temperature dependence and the Sommerfeld constant γ linearly responds to magnetic fields for low-energy excitation. These results clearly indicate that SrAuSi3 is a full-gap s -wave superconductor without a gap node in the superconducting order parameter. The density functional theory ab initio band calculation revealed that the electron system is composed of three kinds of Fermi surface: a cylindrical shape, a dumbbell shape, and a peculiar-shaped hole pocket. Fermi-surface splitting due to spin-orbit coupling exists only along limited directions in the Brillouin zone. Overall, the splitting energy size is small, insufficient to realize unconventional anisotropic superconductivity attributed to space-inversion symmetry breaking.

  2. Closing data gaps for LCA of food products: estimating the energy demand of food processing.

    PubMed

    Sanjun, Neus; Stoessel, Franziska; Hellweg, Stefanie

    2014-01-21

    Food is one of the most energy and CO2-intensive consumer goods. While environmental data on primary agricultural products are increasingly becoming available, there are large data gaps concerning food processing. Bridging these gaps is important; for example, the food industry can use such data to optimize processes from an environmental perspective, and retailers may use this information for purchasing decisions. Producers and retailers can then market sustainable products and deliver the information demanded by governments and consumers. Finally, consumers are increasingly interested in the environmental information of foods in order to lower their consumption impacts. This study provides estimation tools for the energy demand of a representative set of food process unit operations such as dehydration, evaporation, or pasteurization. These operations are used to manufacture a variety of foods and can be combined, according to the product recipe, to quantify the heat and electricity demand during processing. In combination with inventory data on the production of the primary ingredients, this toolbox will be a basis to perform life cycle assessment studies of a large number of processed food products and to provide decision support to the stakeholders. Furthermore, a case study is performed to illustrate the application of the tools. PMID:24344613

  3. Effect of band gap energy on the electrical conductivity in doped ZnO thin film

    NASA Astrophysics Data System (ADS)

    Benramache, Said; Belahssen, Okba; Ben Temam, Hachemi

    2014-07-01

    The transparent conductive pure and doped zinc oxide thin films with aluminum, cobalt and indium were deposited by ultrasonic spray technique on glass substrate at 350 °C. This paper is to present a new approach to the description of correlation between electrical conductivity and optical gap energy with dopants' concentration of Al, Co and In. The correlation between the electrical and optical properties with doping level suggests that the electrical conductivity of the films is predominantly estimated by the band gap energy and the concentrations of Al, Co and In. The measurement in the electrical conductivity of doped films with correlation is equal to the experimental value, the error of this correlation is smaller than 13%. The minimum error value was estimated in the cobalt-doped ZnO thin films. This result indicates that such Co-doped ZnO thin films are chemically purer and have far fewer defects and less disorder owing to an almost complete chemical decomposition.

  4. Fast superconducting storage systems

    SciTech Connect

    Mawardi, O.K.

    1982-01-01

    A review of the requirements for a fast superconducting inductive pulsed storage system is presented. The discussion includes the important characteristics of the components of the pulse source: the high current source, the switch and the energy transfer scheme. A proposed superconducting pulsed source incorporating some of these characteristics is described. 23 refs.

  5. Spin-bag mechanism of high-temperature superconductivity

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    A new approach to the theory of high-temperature superconductivity is proposed, based on the two-dimensional antiferromagnetic spin correlations observed in these materials over distances large compared to the lattice spacing. The spin ordering produces an electronic pseudogap which is locally suppressed by the addition of a hole. This suppression forms a bag inside which the hole is self-consistently trapped. Two holes are attracted by sharing a common bag. The resulting pairing interaction leads to a superconducting energy gap which is nodeless over the Femri surface.

  6. Break-junction Tunneling Spectroscopy of Superconducting FeSexTe1-x

    NASA Astrophysics Data System (ADS)

    Ekino, Toshikazu; Nagasaka, Kouhei; Sakai, Yuta; Sugimoto, Akira; Gabovich, Alexander M.

    The energy gap ofFeSexTe1-x(x = 0.4-0.5) was investigated by break-junctiontunneling spectroscopy. We found two main kinds of the gap. The predominant one is aBardeen-Cooper-Schrieffersuperconducting gap structure with 4? (4 K) = 5 - 13 meV, corresponding to the SIS (superconductor-insulator-superconductor) junction, where 2? stands for the superconducting gap. The observed gap distribution is naturally attributed to local inhomogeneity in the tested crystalpatch. Another gap-likestructure appears as broadened gap peaks of Vp-p(4 K) ? 80 mV, which is consistent with the local large gapdetected by our scanning-tunneling-spectroscopy measurements using the same crystal batch. The possible origin of the gap is discussed bearing in mind the structural phase transitions occurring in FeSexTe1-x.

  7. Low-frequency Excitation in the Optical Properties of Superconducting CeCoIn5

    SciTech Connect

    Petrovic, C.; Sudhakar Rao, G.V.; Ocadlik, S.; Reedyk, M.

    2009-08-20

    The far-infrared optical response of CeCoIn{sub 5}, a superconducting heavy fermion metal with a T{sub C} of 2.3 K, was investigated from 5-40 cm{sup -1} at temperatures from 0.5-2.5 K using a polarizing interferometer and a He{sup 3} cryostat. A strong absorption feature is revealed at low temperatures which appears to be a gap in the density of states, reminiscent of the energy gap seen in the hidden order state in URu{sub 2}Si{sub 2}. The depth of the spectral structure decreases with increasing temperature from 0.5 to 2.5 K indicating that the characteristic temperature for this behavior is close to the superconducting T{sub C}. A peak in the superconducting state Kramers-Kronig-derived optical conductivity occurs just above the gap at 1.5 meV.

  8. Three energy scales in the superconducting state of hole-doped cuprates detected by electronic Raman scattering

    SciTech Connect

    Benhabib, S.; Gu, G. D.; Gallais, Y.; Cazayous, M.; Measson, M. -A.; Zhong, R. D.; Schneeloch, J.; Forget, A.; Colson, D.; Sacuto, A.

    2015-10-06

    We explore by electronic Raman scattering the superconducting state of the Bi2Sr2CaCu2O8+δ (Bi-2212) crystal by performing a fine-tuned doping study. We find three distinct energy scales in A1g, B1g, and B2g symmetries which show three distinct doping dependencies. Above p=0.22, the three energies merge; below p=0.12, the A1g scale is no longer detectable, while the B1g and B2g scales become constant in energy. In between, the A1g and B1g scales increase monotonically with underdoping, while the B2g one exhibits a maximum at p=0.16. The three superconducting energy scales appear to be a universal feature of hole-doped cuprates. Furthermore, we propose that the nontrivial doping dependencies of the three scales originate from the Fermi-surface changes and reveal competing orders inside the superconducting dome.

  9. Three energy scales in the superconducting state of hole-doped cuprates detected by electronic Raman scattering

    DOE PAGESBeta

    Benhabib, S.; Gu, G. D.; Gallais, Y.; Cazayous, M.; Measson, M. -A.; Zhong, R. D.; Schneeloch, J.; Forget, A.; Colson, D.; Sacuto, A.

    2015-10-06

    We explore by electronic Raman scattering the superconducting state of the Bi2Sr2CaCu2O8+δ (Bi-2212) crystal by performing a fine-tuned doping study. We find three distinct energy scales in A1g, B1g, and B2g symmetries which show three distinct doping dependencies. Above p=0.22, the three energies merge; below p=0.12, the A1g scale is no longer detectable, while the B1g and B2g scales become constant in energy. In between, the A1g and B1g scales increase monotonically with underdoping, while the B2g one exhibits a maximum at p=0.16. The three superconducting energy scales appear to be a universal feature of hole-doped cuprates. Furthermore, we proposemore » that the nontrivial doping dependencies of the three scales originate from the Fermi-surface changes and reveal competing orders inside the superconducting dome.« less

  10. Frustrated Heisenberg antiferromagnet on the honeycomb lattice: Spin gap and low-energy parameters

    NASA Astrophysics Data System (ADS)

    Bishop, R. F.; Li, P. H. Y.; Gtze, O.; Richter, J.; Campbell, C. E.

    2015-12-01

    We use the coupled cluster method implemented to high orders of approximation to investigate the frustrated spin-1/2 J1-J2-J3 antiferromagnet on the honeycomb lattice with isotropic Heisenberg interactions of strength J1>0 between nearest-neighbor pairs, J2>0 between next-nearest neighbor pairs, and J3>0 between next-next-nearest-neighbor pairs of spins. In particular, we study both the ground-state (GS) and lowest-lying triplet excited-state properties in the case J3=J2?? J1 , in the window 0 ?? ?1 of the frustration parameter, which includes the (tricritical) point of maximum classical frustration at ?cl=1/2 . We present GS results for the spin stiffness ?s and the zero-field uniform magnetic susceptibility ? , which complement our earlier results for the GS energy per spin E /N and staggered magnetization M to yield a complete set of accurate low-energy parameters for the model. Our results all point towards a phase diagram containing two quasiclassical antiferromagnetic phases, one with Nel order for ? ?c 2 . The results for both ? and the spin gap ? provide compelling evidence for a disordered quantum paramagnetic phase that is gapped over a considerable portion of the intermediate region ?c1energy parameters is consistent with the values ?c1=0.450.02 and ?c 2=0.60 0.02 , and with the transition at ?c1being of continuous (and hence probably of the deconfined) type and that at ?c 2 being of first-order type.

  11. Fabrication of Nb/A1 Superconducting Tunnel Junction

    NASA Astrophysics Data System (ADS)

    Cho, Sung-Ik; Park, Young-Sik; Park, Jang-Hyun; Lee, Yong-Ho; Lee, Sang-Kil; Kim, Sug-Whan; Han, Won-Yong

    2004-12-01

    We report the successful fabrication and I--V curve superconductivity test results of the Nb/Al-based superconducting tunnel junctions. STJs with side-lengths of 20, 40, 60 and 80 ?m were fabricated by deposition of polycrystalline Nb/Al/AlOx/Al/Nb 5-layer thin films incorporated on a 3-inch Si wafer. STJ was designed by TannerTM L-Edit 8.3 program, and fabricated in SQUID fabrication facility, KRISS. 5-layer STJ thin-films were fabricated using UV photolithography, DC magnetron sputtering, Reactive ion etching, and CVD(Chemical Vapor Deposition) techniques. Superconducting state test for STJ was succeeded in 4K with liquid helium cooling system. Their performance indicators such as energy gap, normal resistance, normal resistivity, dynamic resistance, dynamic resistivity, and quality factor were measured from I--V curve. Fabricated Nb/Al STJ shows 11% higher FWHM energy resolution than genuine Nb STJ.

  12. First-principles study of energy band gap of single-layer Mo1?xCrxS2

    NASA Astrophysics Data System (ADS)

    Ueda, Akiko; Honda, Syuta; Imamura, Hiroshi

    2016-02-01

    The electronic structures of single-layer Mo1?xCrxS2 are calculated by the spin-polarized density functional method. Single-layer Mo1?xCrxS2 exhibits a direct band gap for any Cr concentration (x). The energy band gap monotonically decreases as a function of x and takes an ideal value for photovoltaic applications at x ? 0.23.

  13. Esaki Diodes in van der Waals Heterojunctions with Broken-Gap Energy Band Alignment.

    PubMed

    Yan, Rusen; Fathipour, Sara; Han, Yimo; Song, Bo; Xiao, Shudong; Li, Mingda; Ma, Nan; Protasenko, Vladimir; Muller, David A; Jena, Debdeep; Xing, Huili Grace

    2015-09-01

    van der Waals (vdW) heterojunctions composed of two-dimensional (2D) layered materials are emerging as a solid-state materials family that exhibits novel physics phenomena that can power a range of electronic and photonic applications. Here, we present the first demonstration of an important building block in vdW solids: room temperature Esaki tunnel diodes. The Esaki diodes were realized in vdW heterostructures made of black phosphorus (BP) and tin diselenide (SnSe2), two layered semiconductors that possess a broken-gap energy band offset. The presence of a thin insulating barrier between BP and SnSe2 enabled the observation of a prominent negative differential resistance (NDR) region in the forward-bias current-voltage characteristics, with a peak to valley ratio of 1.8 at 300 K and 2.8 at 80 K. A weak temperature dependence of the NDR indicates electron tunneling being the dominant transport mechanism, and a theoretical model shows excellent agreement with the experimental results. Furthermore, the broken-gap band alignment is confirmed by the junction photoresponse, and the phosphorus double planes in a single layer of BP are resolved in transmission electron microscopy (TEM) for the first time. Our results represent a significant advance in the fundamental understanding of vdW heterojunctions and broaden the potential applications of 2D layered materials. PMID:26226296

  14. Determining the Energy Gap Between the sd-pf Neutron Shells in 25O

    NASA Astrophysics Data System (ADS)

    Jones, Michael; Frank, Nathan; Deyoung, Paul; Baumann, Thomas; Kohley, Zach; Smith, Jenna; Spyrou, Artemis; Stiefel, Krystin; Kuchera, Anthony; Thoennessen, Michael; MoNA Collaboration

    2014-09-01

    The excited states of 25O, particularly those of negative parity, are of great interest for determining the evolution of the sd-pf shell gap in and around the ``island of inversion.'' Shell Model (WBBS) calculations tuned to nearby 27Ne predict the 3/2- state in 25O to be only 500 keV above the ground state, implying the sd-pf shell gap to be small. Hence it is likely for nuclei beyond N = 16 to have mixing between the 0d3/2 and 1p3/2 orbitals. A recent experiment, performed at the NSCL, populated 25O through use of a (d , p) reaction. Using the Ursinus College Liquid Hydrogen Target, an 24O beam impinged on a deuterium target cell with a thickness of 400 mg/cm2 at a rate of approximately 30 pps to produce 25O, which decayed immediately by neutron emission. The resulting charged fragments were bent by the Sweeper magnet into a suite of charged particle detectors, while the neutrons traveled unimpeded towards MoNA (Modular Neutron Array) and LISA (Large multi-Institutional Scintillator Array). Together, MoNA-LISA and the Sweeper provide a full kinematic measurement from which the decay energy of the 2-body system can be determined. Preliminary results will be discussed.

  15. A quantum galvanometer with high-energy resolution based on a superconducting interferometer circuit

    SciTech Connect

    Bakhtin, P.A.; Makhov, V.I.; Masalov, V.V.; Sretenskii, V.N.; Tyablikov, A.V.; Vasenkov, A.A.

    1985-07-01

    The authors make a comprehensive analysis of principles of constructing measurement systems based on the superconducting quantum interferometer (SQUID) implemented in integrated form. They note trends of promising applications for galvanometric measurement systems. They describe the two types of SQUID, one-junction and two junction. They analyze the processing and formation of superconducting ion chemical signals and structures. And they present their results in a series of charts and diagrams. They conclude that quantum galvanometry using superconducting microcircuits allows one to propose new experimental studies in microelectronics, the techniques of high-precision measurements, and equipment for metrological work.

  16. Exponential vanishing of the ground-state gap of the quantum random energy model via adiabatic quantum computing

    NASA Astrophysics Data System (ADS)

    Adame, J.; Warzel, S.

    2015-11-01

    In this note, we use ideas of Farhi et al. [Int. J. Quantum. Inf. 6, 503 (2008) and Quantum Inf. Comput. 11, 840 (2011)] who link a lower bound on the run time of their quantum adiabatic search algorithm to an upper bound on the energy gap above the ground-state of the generators of this algorithm. We apply these ideas to the quantum random energy model (QREM). Our main result is a simple proof of the conjectured exponential vanishing of the energy gap of the QREM.

  17. 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

  18. Electronic properties of graphene nano-flakes: Energy gap, permanent dipole, termination effect, and Raman spectroscopy

    SciTech Connect

    Singh, Sandeep Kumar Peeters, F. M.; Neek-Amal, M.

    2014-02-21

    The electronic properties of graphene nano-flakes (GNFs) with different edge passivation are investigated by using density functional theory. Passivation with F and H atoms is considered: C{sub N{sub c}} X{sub N{sub x}} (X = F or H). We studied GNFs with 10 < N{sub c} < 56 and limit ourselves to the lowest energy configurations. We found that: (i) the energy difference Δ between the highest occupied molecular orbital and the lowest unoccupied molecular orbital decreases with N{sub c}, (ii) topological defects (pentagon and heptagon) break the symmetry of the GNFs and enhance the electric polarization, (iii) the mutual interaction of bilayer GNFs can be understood by dipole-dipole interaction which were found sensitive to the relative orientation of the GNFs, (iv) the permanent dipoles depend on the edge terminated atom, while the energy gap is independent of it, and (v) the presence of heptagon and pentagon defects in the GNFs results in the largest difference between the energy of the spin-up and spin-down electrons which is larger for the H-passivated GNFs as compared to F-passivated GNFs. Our study shows clearly the effect of geometry, size, termination, and bilayer on the electronic properties of small GNFs. This study reveals important features of graphene nano-flakes which can be detected using Raman spectroscopy.

  19. Cryogenic Tests of 30 m Flexible Hybrid Energy Transfer Line with Liquid Hydrogen and Superconducting MgB2 Cable

    NASA Astrophysics Data System (ADS)

    Vysotsky, V. S.; Antyukhov, I. V.; Firsov, V. P.; Blagov, E. V.; Kostyuk, V. V.; Nosov, A. A.; Fetisov, S. S.; Zanegin, S. Yu.; Rachuk, V. S.; Katorgin, B. I.

    Recently we reported about first in the world test of 10 m hybrid energy transfer line with liquid hydrogen and MgB2 superconducting cable. In this paper we present the new development of our second hybrid energy transfer line with 30 m length. The flexible 30 m hydrogen cryostat has three sections with different types of thermal insulation in each section: simple vacuum superinsulation, vacuum superinsulation with liquid nitrogen shield and active evaporating cryostatting (AEC) system. We performed thermo-hydraulic tests of the cryostat to compare three thermo-insulating methods. The tests were performed at temperatures from 20 to 26 K, hydrogen flow from 100 to 450 g/s and pressure from 0.25 to 0.5 MPa. It was found that AEC thermal insulation practically eliminated completely heat transfer from room temperature to liquid hydrogen in the 10 m section. AEC thermal insulation method can be used for long superconducting power cables. High voltage current leads were developed as well. The current leads and superconducting MgB2 cable have been passed high voltage DC test up to 50 kV DC. Critical current of the cable at ∼21 K was ∼3500 A. The 30 m hybrid energy system developed is able to deliver up to 135 MW of chemical and electrical power in total.

  20. 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

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

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2006-01-01

    Thirty-five years after the discovery of rotation-powered pulsars, we still do not understand the fundamentals of their pulsed emission at any wavelength. I will review 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 the next generation of gamma-ray detectors, AGILE and GLAST, will test prediction of these models.

  2. Edge multi-energy soft x-ray diagnostic in Experimental Advanced Superconducting Tokamak.

    PubMed

    Li, Y L; Xu, G S; Tritz, K; Zhu, Y B; Wan, B N; Lan, H; Liu, Y L; Wei, J; Zhang, W; Hu, G H; Wang, H Q; Duan, Y M; Zhao, J L; Wang, L; Liu, S C; Ye, Y; Li, J; Lin, X; Li, X L

    2015-12-01

    A multi-energy soft x-ray (ME-SXR) diagnostic has been built for electron temperature profile in the edge plasma region in Experimental Advanced Superconducting Tokamak (EAST) after two rounds of campaigns. Originally, five preamplifiers were mounted inside the EAST vacuum vessel chamber attached to five vertically stacked compact diode arrays. A custom mechanical structure was designed to protect the detectors and electronics under constraints of the tangential field of view for plasma edge and the allocation of space. In the next experiment, the mechanical structure was redesigned with a barrel structure to absolutely isolate it from the vacuum vessel. Multiple shielding structures were mounted at the pinhole head to protect the metal foils from lithium coating. The pre-amplifiers were moved to the outside of the vacuum chamber to avoid introducing interference. Twisted copper cooling tube was embedded into the back-shell near the diode to limit the temperature of the preamplifiers and diode arrays during vacuum vessel baking when the temperature reached 150 °C. Electron temperature profiles were reconstructed from ME-SXR measurements using neural networks. PMID:26724032

  3. An Action Dependent Heuristic Dynamic Programming-controlled Superconducting Magnetic Energy Storage for Transient Stability Augmentation

    NASA Astrophysics Data System (ADS)

    Wang, Xinpu; Yang, Jun; Zhang, Xiaodong; Yu, Xiaopeng

    To enhance the stability of power system, the active power and reactive power can be absorbed from or released to Superconducting magnetic energy storage (SMES) unit according to system power requirements. This paper proposes a control strategy based on action dependent heuristic dynamic programing (ADHDP) which can control SMES to improve the stability of electric power system with on-line learning ability. Based on back propagation (BP) neural network, ADHDP approximates the optimal control solution of nonlinear system through iteration step by step. This on-line learning ability improves its performance by learning from its own mistakes through reinforcement signal from external environment, so that it can adjust the neural network weights according to the back propagation error to achieve optimal control performance. To investigate the effectiveness of the proposed control strategy, simulation tests are carried out in Matlab/Simulink. And a conventional Proportional-Integral (PI) controlled method is used to compare the performance of ADHDP. Simulation results show that the proposed controller demonstrates superior damping performance on power system oscillation caused by three-phase fault and wind power fluctuation over the PI controller.

  4. 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.

  5. Edge multi-energy soft x-ray diagnostic in Experimental Advanced Superconducting Tokamak

    NASA Astrophysics Data System (ADS)

    Li, Y. L.; Xu, G. S.; Tritz, K.; Zhu, Y. B.; Wan, B. N.; Lan, H.; Liu, Y. L.; Wei, J.; Zhang, W.; Hu, G. H.; Wang, H. Q.; Duan, Y. M.; Zhao, J. L.; Wang, L.; Liu, S. C.; Ye, Y.; Li, J.; Lin, X.; Li, X. L.

    2015-12-01

    A multi-energy soft x-ray (ME-SXR) diagnostic has been built for electron temperature profile in the edge plasma region in Experimental Advanced Superconducting Tokamak (EAST) after two rounds of campaigns. Originally, five preamplifiers were mounted inside the EAST vacuum vessel chamber attached to five vertically stacked compact diode arrays. A custom mechanical structure was designed to protect the detectors and electronics under constraints of the tangential field of view for plasma edge and the allocation of space. In the next experiment, the mechanical structure was redesigned with a barrel structure to absolutely isolate it from the vacuum vessel. Multiple shielding structures were mounted at the pinhole head to protect the metal foils from lithium coating. The pre-amplifiers were moved to the outside of the vacuum chamber to avoid introducing interference. Twisted copper cooling tube was embedded into the back-shell near the diode to limit the temperature of the preamplifiers and diode arrays during vacuum vessel baking when the temperature reached 150 °C. Electron temperature profiles were reconstructed from ME-SXR measurements using neural networks.

  6. Micro superconducting magnetic energy storage (SMES) system for protection of critical industrial and military loads

    SciTech Connect

    Kalafala, A.K.; Bascunan, J.; Bell, D.D.; Blecher, L.; Murray, F.S.; Parizh, M.B.; Sampson, M.W.; Wilcox, R.E.

    1996-07-01

    A 6 MJ, 750 kVA Micro SMES system has been designed to protect critical loads against voltage sags and interruptions, as well as to provide continuous power conditioning. Life-cycle costs have been minimized through the use of energy efficient refrigeration units. Maintenance is simplified through the use of Line Replaceable Units (LRU). Availability is maximized through a design approach which allows the magnet to continue protecting the load even in the case of refrigeration degradation or total failure. Reliability is maximized by the use of proven commercial-off-the-shelf (COTS) items. The system provides ride-through capability for {approximately}9 seconds at a power level of 454 kW. The system comprises a niobium titanium superconducting magnet, permanent conduction cooled hybrid current leads, a low loss cryostat, a closed-loop refrigeration subsystem, an off-the-shelf uninterruptible power supply (UPS), a magnet interface unit to connect the magnet to the UPS, and an off-the-shelf monitoring unit providing both local and remote monitoring capability of system parameters.

  7. Superconducting magnetic energy storage (SMES) program. Progress report, January 1-December 31, 1984

    SciTech Connect

    Rogers, J.D.

    1985-05-01

    The 30 MJ, 10 MW superconducting magnetic energy storage (SMES) system was devised to interact in the Western US Power System as an alternate means to damp unstable oscillations at 0.35 Hz on the Pacific HVAC Intertie. The SMES unit was installed at the Tacoma Substation of the Bonneville Power Administration (BPA). The operating limits of the 30 MJ SMES unit were established, and different means of controlling real and reactive power were tested. The unit can follow a sinusoidal power demand signal with an amplitude of up to 8.6 MW with the converter working in a 12 pulse mode. When the converter operates in the constant VAR mode, a time varying real power demand signal of up to 5 MW can be met. Experiments showed that the Pacific ac Intertie has current and reactive power variations of the same frequency as the modulating frequency of the SMES device. Endurance tests were run to assess the reliability of the SMES subsystems with a narrow band noise input, which is characteristic of the modulation signal for stabilizer operation. During the endurance tests, parameters of the ac power system were determined. Converter short circuit tests, load tests under various control conditions, dc breaker tests for coil current interruption, and converter failure mode tests were conducted. The experimental operation of the SMES system was concluded and the operation was terminated in early 1984.

  8. 30-MJ superconducting magnetic-energy-storage stabilizing system: an overview

    SciTech Connect

    Roger, J.D.; Boenig, H.J.; Dean, J.W.; Schermer, R.I.; Annestrand, S.A.; Hauer, J.F.; Miller, B.L.

    1983-01-01

    The 30-MJ superconducting magnetic-energy-storage (SMES) system was devised as an alternate means to modulate the Bonneville Power Administration (BPA) Pacific AC Intertie, a part of the Western US Power System, to prevent undamped power oscillations at 0.35 Hz that were observed to be associated with high power transmission. The SMES system was installed at the BPA Tacoma Substation and successfully operated as an experimental device to initiate tests to determine power system dynamics, to investigate their variability, to assess system response to SMES modulation with a major variable load, and to use SMES to develop stability-control techniques. The system has been operated at frequencies of 0.1 to 1.0 Hz at power levels of +- 8.3 MW with a parallel modulation of the converter bridges and up to 9.5 MW reactive power together with +- 4.5 MW real power in constant VAR mode with buck-boost modulation of the bridges. The coil has been charged at a maximum rate of 11.8 MW. Operation of the SMES system is now under BPA jurisdiction, and all hardware has been transferred to BPA.

  9. Air gap optimization for output power and band width in out-of-plane vibration energy harvesters employing electrets

    NASA Astrophysics Data System (ADS)

    Asanuma, H.; Hara, M.; Oguchi, H.; Kuwano, H.

    2015-10-01

    We investigated the dependence of output power, frequency band width, and resonance frequency on the initial air gap for electret-based out-of-plane vibration energy harvesters, both numerically and experimentally. In this investigation, the external acceleration and surface charge densities of the electret were held constant. The numerical investigation predicted the following results: (1) an optimum value exists in the initial air gap to maximize the output power; and (2) enhanced electrostatic forces with decreasing the initial air gap emphasize the soft spring effect, which widens the frequency band width and lowers the resonance frequency. The experimental results showed behaviour consistent with the numerical predictions. The maximum output power in experiment was 4.0??W at the optimum initial air gap of 0.43?mm when the external acceleration and the frequency were 4.9?m?s-2 and 102?Hz, respectively. With reducing the initial air gap to 0.28?mm, the frequency band width increased to 17?Hz, a 2.6-fold increase over the optimum initial air gap. The peak output power at the initial air gap of 0.28?mm was 2.7??W, when the external acceleration and frequency were 4.9?m?s-2 and 96?Hz, respectively.

  10. Band Gap Engineering in a 2D Material for Solar-to-Chemical Energy Conversion.

    PubMed

    Hu, Jun; Guo, Zhenkun; Mcwilliams, Peter E; Darges, John E; Druffel, Daniel L; Moran, Andrew M; Warren, Scott C

    2016-01-13

    The electronic structure of 2D semiconductors depends on their thickness, providing new opportunities to engineer semiconductors for energy conversion, electronics, and catalysis. Here we show how a 3D semiconductor, black phosphorus, becomes active for solar-to-chemical energy conversion when it is thinned to a 2D material. The increase in its band gap, from 0.3 eV (3D) to 2.1 eV (2D monolayer), is accompanied by a 40-fold enhancement in the formation of chemical products. Despite this enhancement, smaller flakes also have shorter excited state lifetimes. We deduce a mechanism in which recombination occurs at flake edges, while the "van der Waals" surface of black phosphorus bonds to chemical intermediates and facilitates electron transfer. The unique properties of black phosphorus highlight its potential as a customizable material for solar energy conversion and catalysis, while also allowing us to identify design rules for 2D photocatalysts that will enable further improvements in these materials. PMID:26651872

  11. Linear Scaling of the Exciton Binding Energy versus the Band Gap of Two-Dimensional Materials

    NASA Astrophysics Data System (ADS)

    Choi, Jin-Ho; Cui, Ping; Lan, Haiping; Zhang, Zhenyu

    2015-08-01

    The exciton is one of the most crucial physical entities in the performance of optoelectronic and photonic devices, and widely varying exciton binding energies have been reported in different classes of materials. Using first-principles calculations within the G W -Bethe-Salpeter equation approach, here we investigate the excitonic properties of two recently discovered layered materials: phosphorene and graphene fluoride. We first confirm large exciton binding energies of, respectively, 0.85 and 2.03 eV in these systems. Next, by comparing these systems with several other representative two-dimensional materials, we discover a striking linear relationship between the exciton binding energy and the band gap and interpret the existence of the linear scaling law within a simple hydrogenic picture. The broad applicability of this novel scaling law is further demonstrated by using strained graphene fluoride. These findings are expected to stimulate related studies in higher and lower dimensions, potentially resulting in a deeper understanding of excitonic effects in materials of all dimensionalities.

  12. Linear Scaling of the Exciton Binding Energy versus the Band Gap of Two-Dimensional Materials.

    PubMed

    Choi, Jin-Ho; Cui, Ping; Lan, Haiping; Zhang, Zhenyu

    2015-08-01

    The exciton is one of the most crucial physical entities in the performance of optoelectronic and photonic devices, and widely varying exciton binding energies have been reported in different classes of materials. Using first-principles calculations within the GW-Bethe-Salpeter equation approach, here we investigate the excitonic properties of two recently discovered layered materials: phosphorene and graphene fluoride. We first confirm large exciton binding energies of, respectively, 0.85 and 2.03eV in these systems. Next, by comparing these systems with several other representative two-dimensional materials, we discover a striking linear relationship between the exciton binding energy and the band gap and interpret the existence of the linear scaling law within a simple hydrogenic picture. The broad applicability of this novel scaling law is further demonstrated by using strained graphene fluoride. These findings are expected to stimulate related studies in higher and lower dimensions, potentially resulting in a deeper understanding of excitonic effects in materials of all dimensionalities. PMID:26296125

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

    PubMed Central

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

    2013-01-01

    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. PMID:24345869

  14. Narrow energy gap between triplet and singlet excited states of Sn2+ in borate glass.

    PubMed

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

    2013-01-01

    Transparent inorganic luminescent materials have attracted considerable scientific and industrial attention recently because of their high chemical durability and formability. However, photoluminescence dynamics of ns(2)-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 Sn(2+)-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. PMID:24345869

  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. Superconductivity in the system of p electrons

    SciTech Connect

    Zaitsev, R. O.

    2012-10-15

    The problem of superconductivity in an electron system with partly filled sp shell is studied. The scattering amplitudes are determined and the equations of superconductivity are derived from the assumption that the Hubbard energy is the largest energy parameter.

  17. Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

    NASA Astrophysics Data System (ADS)

    Gao, Weiwei; Gao, Xiang; Abtew, Tesfaye A.; Sun, Yi-Yang; Zhang, Shengbai; Zhang, Peihong

    2016-02-01

    The quasiparticle band gap is one of the most important materials properties for photovoltaic applications. Often the band gap of a photovoltaic material is determined (and can be controlled) by various factors, complicating predictive materials optimization. An in-depth understanding of how these factors affect the size of the gap will provide valuable guidance for new materials discovery. Here we report a comprehensive investigation on the band gap formation mechanism in organic-inorganic hybrid perovskites by decoupling various contributing factors which ultimately determine their electronic structure and quasiparticle band gap. Major factors, namely, quasiparticle self-energy, spin-orbit coupling, and structural distortions due to the presence of organic molecules, and their influences on the quasiparticle band structure of organic-inorganic hybrid perovskites are illustrated. We find that although methylammonium cations do not contribute directly to the electronic states near band edges, they play an important role in defining the band gap by introducing structural distortions and controlling the overall lattice constants. The spin-orbit coupling effects drastically reduce the electron and hole effective masses in these systems, which is beneficial for high carrier mobilities and small exciton binding energies.

  18. Raman-scattering studies of coupled modes and superconducting gap excitations in single-crystal YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/

    SciTech Connect

    Cooper, S.L.; Slakey, F.; Klein, M.V.; Rice, J.P.; Bukowski, E.D.; Ginsberg, D.M.

    1989-03-01

    The results of polarized light-scattering studies of single-crystal YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ are presented. In the normal state, strong electronic scattering is observed both directly and through interference effects with certain phonons. Below T/sub c/ this electronic scattering undergoes a redistribution that is due to gap formation. The redistribution of the continuum below T/sub c/ has a strong symmetry dependence, suggesting possible gap anisotropy in YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/. Phonon self-energy effects are also shown to be consistent with gap anisotropy. Finally, studies of untwinned single crystals illustrate striking optical anisotropy of the Raman spectra in the a--b plane.

  19. 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.

  20. High temperature superconductivity: A joint feasibility study for a power application with HTS cable by PECO Energy Company. Final report

    SciTech Connect

    1998-11-01

    High temperature superconductivity (HTS) cables have the potential to revolutionize the power delivery industry by reducing costs and maximizing the use of existing conduits for underground transmission. In 1986 a class of ceramic materials showing superconductivity slightly below the temperature of liquid nitrogen was discovered and, when used in cables, can carry two to five times more current than conventional cables of comparable size. In October of 1996, EPRI, Pirelli Cable Corporation, and PECO Energy Company performed a joint study to assess the technical and economic feasibility of installing a HTS cable system in downtown Philadelphia. The project team concluded that HTS system could be designed to meet the requirements of a standard underground transmission cable at distribution voltages, and be more advantageous than a conventional system because of better utilization of the existing duct system.

  1. 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.

    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.

  2. Superconductivity, magnetism, and pairing symmetry in Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Eremin, Ilya

    2009-03-01

    We analyze antiferromagnetism and superconductivity within the renormalization group(RG) technique in novel Fe-based superconductors using the itinerant model of small electron and hole pockets near (0; 0) and (?,?), respectively, originating from the two strongly hybridized orbitals. We find that, for this model, the bare interactions in the Cooper channel are repulsive, and superconductivity does not occur at the mean-field level. However, under RG the effective interaction in the superconducting channel changes sign and becomes attractive. Furthermore, the effective interactions in antiferromagnetic and superconducting channels logarithmically flow towards the same absolute values at low energies, i.e., both must be treated on equal footings. The magnetic instability comes first for equal sizes of the two pockets, but looses to superconductivity upon doping. The superconducting gap has no nodes, but changes sign between the two Fermi surfaces (extended s-wave symmetry). We argue that the T dependencies of the spin susceptibility and NMR relaxation rate for such state are exponential only at very low T, and can be well fitted by power-laws over a wide T range below Tc. We further show that below Tc excitonic resonance appears in the spin excitations spectrum. [4pt] [1] M. Korshunov, and I. Eremin, Phys. Rev. B 78, 140509(R) (2008) [0pt] [2] A.V. Chubukov, D. Efremov, I. Eremin, Phys. Rev. B 78, 134512 (2008). [0pt] [3] M.M. Korshunov and I. Eremin, Europhys. Lett. 83, 67003 (2008).

  3. Superconducting Graphene Nanoelectronic Devices

    NASA Astrophysics Data System (ADS)

    Wang, Joel; Zaffalon, Michele; Jarillo-Herrero, Pablo

    2010-03-01

    Graphene, a single atom-thick sheet of graphite discovered in recent years, has attracted tremendous attention due to its exotic electronic properties. At low energy, its gapless linear band structure results in transport properties described by the Dirac equation, making it an ideal system for the study of exotic quantum phenomena and other new physics. Graphene may also exhibit many novel transport characteristics in the superconducting regime. New phenomena, such as pseudo-diffusive dynamics of ballistic electrons, the relativistic Josephson effect, and specular Andreev reflection are predicted by theoretical models combining relativistic quantum mechanics and superconductivity. We study these phenomena experimentally with superconductor-graphene-superconductor junctions. The supercurrent in graphene is induced by the superconducting contacts through proximity effect. Various superconducting materials are considered for different explorations. Preliminary tests indicate clean electrical contact with graphene and superconducting properties as expected.

  4. Enhanced spin polarization in graphene with spin energy gap induced by spin-orbit coupling and strain

    SciTech Connect

    Liu, Zheng-Fang; Wu, Qing-Ping E-mail: aixichen@ecjtu.jx.cn; Chen, Ai-Xi E-mail: aixichen@ecjtu.jx.cn; Xiao, Xian-Bo; Liu, Nian-Hua

    2014-05-28

    We investigate the possibility of spin polarization in graphene. The result shows that a spin energy gap can be opened in the presence of both spin-orbit coupling and strain. We find that high spin polarization with large spin-polarized current is achieved in the spin energy gap. However, only one of the two modulations is present, no spin polarization can be generated. So the combination of the two modulations provides a way to design tunable spin polarization without need for a magnetic element or an external magnetic field.

  5. Broadband illumination of superconducting pair breaking photon detectors

    NASA Astrophysics Data System (ADS)

    Guruswamy, T.; Goldie, D. J.; Withington, S.

    2016-04-01

    Understanding the detailed behaviour of superconducting pair breaking photon detectors such as Kinetic Inductance Detectors (KIDs) requires knowledge of the nonequilibrium quasiparticle energy distributions. We have previously calculated the steady state distributions resulting from uniform absorption of monochromatic sub gap and above gap frequency radiation by thin films. In this work, we use the same methods to calculate the effect of illumination by broadband sources, such as thermal radiation from astrophysical phenomena or from the readout system. Absorption of photons at multiple above gap frequencies is shown to leave unchanged the structure of the quasiparticle energy distribution close to the superconducting gap. Hence for typical absorbed powers, we find the effects of absorption of broadband pair breaking radiation can simply be considered as the sum of the effects of absorption of many monochromatic sources. Distribution averaged quantities, like quasiparticle generation efficiency η, match exactly a weighted average over the bandwidth of the source of calculations assuming a monochromatic source. For sub gap frequencies, however, distributing the absorbed power across multiple frequencies does change the low energy quasiparticle distribution. For moderate and high absorbed powers, this results in a significantly larger η–a higher number of excess quasiparticles for a broadband source compared to a monochromatic source of equal total absorbed power. Typically in KIDs the microwave power absorbed has a very narrow bandwidth, but in devices with broad resonance characteristics (low quality factors), this increase in η may be measurable.

  6. Superconductivity and ferromagnetism in topological insulators

    NASA Astrophysics Data System (ADS)

    Zhang, Duming

    Topological insulators, a new state of matter discovered recently, have attracted great interest due to their novel properties. They are insulating inside the bulk, but conducting at the surface or edges. This peculiar behavior is characterized by an insulating bulk energy gap and gapless surface or edge states, which originate from strong spin-orbit coupling and time-reversal symmetry. The spin and momentum locked surface states not only provide a model system to study fundamental physics, but can also lead to applications in spintronics and dissipationless electronics. While topological insulators are interesting by themselves, more exotic behaviors are predicted when an energy gap is induced at the surface. This dissertation explores two types of surface state gap in topological insulators, a superconducting gap induced by proximity effect and a magnetic gap induced by chemical doping. The first three chapters provide introductory theory and experimental details of my research. Chapter 1 provides a brief introduction to the theoretical background of topological insulators. Chapter 2 is dedicated to material synthesis principles and techniques. I will focus on two major synthesis methods: molecular beam epitaxy for the growth of Bi2Se3 thin films and chemical vapor deposition for the growth of Bi2Se3 nanoribbons and nanowires. Material characterization is discussed in Chapter 3. I will describe structural, morphological, magnetic, electrical, and electronic characterization techniques used to study topological insulators. Chapter 4 discusses the experiments on proximity-induced superconductivity in topological insulator (Bi2Se3) nanoribbons. This work is motivated by the search for the elusive Majorana fermions, which act as their own antiparticles. They were proposed by Ettore Majorara in 1937, but have remained undiscovered. Recently, Majorana's concept has been revived in condensed matter physics: a condensed matter analog of Majorana fermions is predicted to exist when topological insulators are interfaced with superconductors. The observation of Majorana fermions would not only be fundamentally important, but would also lead to applications in fault-tolerant topological quantum computation. By interfacing topological insulator nanoribbons with superconducting electrodes, we observe distinct signatures of proximity-induced superconductivity, which is found to be present in devices with channel lengths that are much longer than the normal transport characteristic lengths. This might suggest preferential coupling of the proximity effect to a ballistic surface channel of the topological insulator. In addition, when the electrodes are in the superconducting state, we observe periodic magnetoresistance oscillations which suggest the formation of vortices in the proximity-induced region of the nanoribbons. Our results demonstrate that proximity-induced superconductivity and vortices can be realized in our nanoribbon geometry, which accomplishes a first important step towards the search for Majorana fermions in condensed matter. In Chapter 5, I will discuss experiments on a magnetically-doped topological insulator (Mn-doped Bi2Se3) to induce a surface state gap. The metallic Dirac cone surface states of a topological insulator are expected to be protected against small perturbations by time-reversal symmetry. However, these surface states can be dramatically modified and a finite energy gap can be opened at the Dirac point by breaking the time-reversal symmetry via magnetic doping. The interplay between magnetism and topological surface states is predicted to yield novel phenomena of fundamental interest such as a topological magneto-electric effect, a quantized anomalous Hall effect, and the induction of magnetic monopoles. Our systematic measurements reveal a close correlation between the onset of ferromagnetism and quantum corrections to diffusive transport, which crosses over from the symplectic (weak anti-localization) to the unitary (weak localization) class. A comprehensive interpretation of data obtained from elec

  7. Size dependence in hexagonal mesoporous germanium: pore wall thickness versus energy gap and photoluminescence.

    PubMed

    Armatas, Gerasimos S; Kanatzidis, Mercouri G

    2010-09-01

    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(2)/g. The porous Ge framework of these materials is assembled from the templated oxidative self-polymerization of (Ge(9))(4-) Zintl clusters. Total X-ray scattering analysis supports a model of interconnected deltahedral (Ge(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. PMID:20698483

  8. 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.

  9. Ultrasonic investigation of the superconducting properties of the Nb-Mo system

    NASA Technical Reports Server (NTRS)

    Lacy, L. L.

    1972-01-01

    The superconducting properties of single crystals of Nb and two alloys of Nb with Mo were investigated by ultrasonic techniques. The results of measurements of the ultrasonic attenuation and velocities as a function of temperature, Mo composition, crystallographic direction, and ultrasonic frequency are reported. The attenuation and small velocity changes associated with the superconductivity of the samples are shown to be dependent on the sample resistivity ratio which varied from 4.3 for Nb-9% Mo to 6500 for pure Nb. The ultrasonic attenuation data are analyzed in terms of the superconducting energy gap term of the BCS theory. A new model is proposed for the analysis of ultrasonic attenuation in pure superconductors with two partially decoupled energy bands. To analyze the attenuation in pure superconducting Nb, the existence of two energy gaps was assumed to be associated with the two partially decoupled energy bands. One of the gaps was found to have the normal BCS value of 3.4 and the other gap was found to have the anomalously large value of 10. No experimental evidence was found to suggest that the second energy gap had a different transition temperature. The interpretation of the results for the Nb-Mo alloys is shown to be complicated by the possible existence of a second superconducting phase in Nb-Mo alloys with a transition temperature of 0.35 of the transition temperature of the first phase. The elastic constants of Nb and Nb-Mo alloys are shown to be approximately independent of Mo composition to nine atomic percent Mo. These results do not agree with the current microscopic theory of transition temperature for the transition elements.

  10. Single-particle density of states of a superconductor with a spatially varying gap and phase fluctuations

    NASA Astrophysics Data System (ADS)

    Valdez-Balderas, Daniel; Stroud, David

    2006-11-01

    Recent experiments have shown that the superconducting energy gap in some cuprates is spatially inhomogeneous. Motivated by these experiments, and using exact diagonalization of a model d -wave Hamiltonian, combined with Monte Carlo simulations of a Ginzburg-Landau free energy functional, we have calculated the single-particle local density of states LDOS (?,r) of a model high- Tc superconductor as a function of temperature. Our calculations include both quenched disorder in the pairing potential and thermal fluctuations in both phase and amplitude of the superconducting gap. Most of our calculations assume two types of superconducting regions: ? with a small gap and large superfluid density, and ? with the opposite. If the ? regions are randomly embedded in an ? host, the LDOS on the ? sites still has a sharp coherence peak at T=0 , but the ? component does not, in agreement with experiment. An ordered arrangement of ? regions leads to oscillations in the LDOS as a function of energy. The model leads to a superconducting transition temperature Tc well below the pseudogap temperature Tc0 and has a spatially varying gap at very low T , both consistent with experiments in underdoped Bi2212. Our calculated LDOS (?,r) shows coherence peaks for TTc , in agreement with previous work considering phase but not amplitude fluctuations in a homogeneous superconductor. Well above Tc , the gap in the LDOS disappears.

  11. Superconductive wire

    DOEpatents

    Korzekwa, D.A.; Bingert, J.F.; Peterson, D.E.; Sheinberg, H.

    1995-07-18

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity. 2 figs.

  12. Superconductive wire

    DOEpatents

    Korzekwa, David A.; Bingert, John F.; Peterson, Dean E.; Sheinberg, Haskell

    1995-01-01

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity.

  13. 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

  14. Superconductive energy storage. Volume IV. Final technical report revision, January 1976-September 1981

    SciTech Connect

    Hartwig, K.T. Jr.

    1983-07-01

    The design history of Inductor-Converter (I-C) superconductive energy storage units includes first a solenoid in one deep tunnel, then segmented deep solenoids and finally a fifteen tunnel hour-glass system. Conductor research includes NbTi studies, welding of high purity and high strength aluminum components, moderate strength aluminum alloy development, conductor cruciform alloys and overall conductor fabrication studies. Cryogenic tests of boundary layers are undertaken. Structure research includes the analytical structural design of the conductor, the rippled dewar system and the fiberglass composite struts. Experimental structural work includes property tests of fiberglass composites emphasizing polyester products. The tests are for compressive strengths, cyclic compression, shear strength, fracture toughness, bonding, tensile strength, and creep. Rock mechanics research includes experimental site studies of granite, quartzite, rhyolite, and sedimentary locations. Topics include in situ and laboratory measurements of rock stresses, ground water characteristics, joints, and basic rock sample properties. Design studies cover a three tunnel model, a five tunnel model and a low aspect ratio system. Some attention is given to earth quake analysis. This cryogenics effort includes refrigeration design, cool-down analysis, conductor cooling comparisons, heat transfer from bedrock, and conductor stability. Experimentally there are several He II heat transfer and transport experiments, a He I two phase flow void fraction study, and dielectric breakdown in helium. The electric studies cover converter-inverter technology with both analytical and experimental circuitry. System design and electrical use for diurnal storage and pulsed storage cover primarily three phase Graetz bridge circuitry with some attention to a flying capacitor system.

  15. A kinetic analysis of the primary charge separation in bacterial photosynthesis. Energy gaps and static heterogeneity

    NASA Astrophysics Data System (ADS)

    Bixon, M.; Jortner, Joshua; Michel-Beyerle, M. E.

    1995-08-01

    We consider the energetics, the mechanism and the implications of static heterogeneity for the primary electron transfer (ET) from the electronically excited singlet state of the bacteriochlorophyll dimer ( 1O ?) in the bacterial photosynthetic reaction center (RC) and some of its mutants. The energetics of the primary ET was inferred from an analysis of the experimental free energy relation (at T = 300 K) between the short-time decay rates of 1P ? and the oxidation potentials of the dimer (P) for a series of single site "good" mutants, for which geometrical changes are minimized and perturbations of the prosthetic groups of the accessory bacteriochlorophyll (B) and of the bacteriopheophytin (H) by the mutants are minor. This analysis resulted in the reasonable value of ?1 = 800 250 cm -1 for the (mutant invariant) medium reorganization energy and ?G10(N) = -480 180 cm -1 for the energy gap for the native (N) RC. The low value of ?G10(N) implies that the dominant room temperature ET mechanism for the native RC involves sequential ET. Next, we have explored the effects of heterogeneity on the primary ET by model calculations for the parallel sequential-superexchange mechanism, which is subjected to Gaussian energy distributions of the energies of the P +B -H and P +BH - ion pair states (with a width parameter of ? = 400 cm -1). The modelling of the heterogeneous kinetics by varying the (mean) energy gap ?G1 between P +B -H and 1P ? was performed to elucidate the temporal decay of 1P ? and the ET quantum yield in "good" mutants, to explore the gross feature of primary ET in a triple hydrogen bonded mutant and to characterize some of the temperature dependence of the primary ET. The most pronounced manifestations of heterogeneity within the native RC and its single site mutants ( ?G1 = -900 to 300 cm -1) are the nonexponential temporal decay probabilities for 1P ?, which exhibit long-time tails, with heterogeneity effects being marked (in the classical limit) when ?( ?G1 + ?1) > ?1kBT. When ?G1 ? ? (i.e., ?G1 ? 1000 cm -1), the relaxation rate of 1P ? is slow, being dominated by the dimer internal conversion rate, with the effects of heterogeneity being less marked, as is the case for the triple hydrogen bond mutant. Regarding mechanistic issues, our kinetic modelling implies that at room temperature, primary ET in the native RC and its single site mutants is dominated by the sequential route and only the triple mutant exhibits a marked contribution of the superexchange route. At low temperature ( T = 20 K), ET in the native RC is still dominated by the sequential route (with a small (i.e., 10%) superexchange contribution being manifested in its long-time decay), for single site mutants there is an interplay between sequential and superexchange routes, while superexchange dominates ET in the triple mutant. The heterogeneous parallel sequential-superexchange mechanism is of intrinsic significance to insure the stability of primary photosynthetic ET for different native and mutagenetically modified RCs over a broad temperature domain.

  16. Formation of quantum spin Hall state on Si surface and energy gap scaling with strength of spin orbit coupling

    PubMed Central

    Zhou, Miao; Ming, Wenmei; Liu, Zheng; Wang, Zhengfei; Yao, Yugui; Liu, Feng

    2014-01-01

    For potential applications in spintronics and quantum computing, it is desirable to place a quantum spin Hall insulator [i.e., a 2D topological insulator (TI)] on a substrate while maintaining a large energy gap. Here, we demonstrate a unique approach to create the large-gap 2D TI state on a semiconductor surface, based on first-principles calculations and effective Hamiltonian analysis. We show that when heavy elements with strong spin orbit coupling (SOC) such as Bi and Pb atoms are deposited on a patterned H-Si(111) surface into a hexagonal lattice, they exhibit a 2D TI state with a large energy gap of ?0.5?eV. The TI state arises from an intriguing substrate orbital filtering effect that selects a suitable orbital composition around the Fermi level, so that the system can be matched onto a four-band effective model Hamiltonian. Furthermore, it is found that within this model, the SOC gap does not increase monotonically with the increasing strength of SOC. These interesting results may shed new light in future design and fabrication of large-gap topological quantum states. PMID:25407432

  17. Formation of quantum spin Hall state on Si surface and energy gap scaling with strength of spin orbit coupling

    DOE PAGESBeta

    Zhou, Miao; Ming, Wenmei; Liu, Zheng; Wang, Zhengfei; Yao, Yugui; Liu, Feng

    2014-11-19

    For potential applications in spintronics and quantum computing, it is desirable to place a quantum spin Hall insulator [i.e., a 2D topological insulator (TI)] on a substrate while maintaining a large energy gap. Here, we demonstrate a unique approach to create the large-gap 2D TI state on a semiconductor surface, based on first-principles calculations and effective Hamiltonian analysis. We show that when heavy elements with strong spin orbit coupling (SOC) such as Bi and Pb atoms are deposited on a patterned H-Si(111) surface into a hexagonal lattice, they exhibit a 2D TI state with a large energy gap of ≥0.5more » eV. The TI state arises from an intriguing substrate orbital filtering effect that selects a suitable orbital composition around the Fermi level, so that the system can be matched onto a four-band effective model Hamiltonian. Furthermore, it is found that within this model, the SOC gap does not increase monotonically with the increasing strength of SOC. These interesting results may shed new light in future design and fabrication of large-gap topological quantum states.« less

  18. Formation of quantum spin Hall state on Si surface and energy gap scaling with strength of spin orbit coupling

    SciTech Connect

    Zhou, Miao; Ming, Wenmei; Liu, Zheng; Wang, Zhengfei; Yao, Yugui; Liu, Feng

    2014-11-19

    For potential applications in spintronics and quantum computing, it is desirable to place a quantum spin Hall insulator [i.e., a 2D topological insulator (TI)] on a substrate while maintaining a large energy gap. Here, we demonstrate a unique approach to create the large-gap 2D TI state on a semiconductor surface, based on first-principles calculations and effective Hamiltonian analysis. We show that when heavy elements with strong spin orbit coupling (SOC) such as Bi and Pb atoms are deposited on a patterned H-Si(111) surface into a hexagonal lattice, they exhibit a 2D TI state with a large energy gap of ≥0.5 eV. The TI state arises from an intriguing substrate orbital filtering effect that selects a suitable orbital composition around the Fermi level, so that the system can be matched onto a four-band effective model Hamiltonian. Furthermore, it is found that within this model, the SOC gap does not increase monotonically with the increasing strength of SOC. These interesting results may shed new light in future design and fabrication of large-gap topological quantum states.

  19. Tuning the superconductivity in single-layer FeSe/oxides by interface engineering

    NASA Astrophysics Data System (ADS)

    Peng, Rui

    2015-03-01

    The discovery of high Tc in single-layer FeSe films has enormous implications for both searching new high Tc superconductors and exploring the important factors for high temperature superconductivity. In this talk, I will show our recent angle-resolved photoemission studies on various FeSe-based heterostructures grown by molecular beam epitaxy. We systematically studied the electronic structures and superconducting properties of FeSe with varied strain, different interfacial oxide materials and different thicknesses, and uncover that electronic correlations and superconducting gap-closing temperatures are tuned by interfacial effects. We exclude the direct relation between superconductivity and tensile strain, or the energy of an interfacial phonon mode, and demonstrate the crucial and non-trivial role of FeSe/oxide interface on the high pairing temperature. By tuning the interface, superconducting pairing temperature reaches up to 75K in FeSe/Nb:BaTiO3/KTaO3 with the in-plane lattice of 3.99 , which sets a new superconducting-gap-closing temperature record for iron-based superconductors, and may paves the way to more cost-effective applications of ultra-thin superconductors. Besides, in extremely tensile-strained single-layer FeSe films, we found that the Fermi surfaces consist of two elliptical electron pockets at the zone corner, without detectable hybridization. The lifting of degeneracy is clearly observed for the first time for the iron-based superconductors with only electron Fermi surfaces. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results provide important experimental foundations for understanding the interfacial superconductivity and the pairing symmetry puzzle of iron-based superconductors, and also provide clues for further enhancing Tc through interface engineering.

  20. Superconducting wire fabrication

    NASA Astrophysics Data System (ADS)

    Glad, W. E.; Chase, G. G.

    1990-05-01

    Experiments were done leading to the fabrication of high-temperature superconducting composite wire. Bulk superconductor was characterized by using optical microscopy, scanning electron microscopy, and energy-dispersive x ray spectroscopy. The chemical compatibility of superconducting materials with a number of metal sheathing candidates was tested, with silver offering the best compatibility. Wire was fabricated by drawing 0.250-inch-diameter silver tubing packed with superconducting powder. Single core wires were drawn to 0.037-inch diameter. The best critical current performance (660 A/sq cm) for leaded bismuth 2-2-2-3 material was achieved by flattening single-core wire before heat treatment.

  1. Band gap and defect states of MgO thin films investigated using reflection electron energy loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Heo, Sung; Cho, Eunseog; Lee, Hyung-Ik; Park, Gyeong Su; Kang, Hee Jae; Nagatomi, T.; Choi, Pyungho; Choi, Byoung-Deog

    2015-07-01

    The band gap and defect states of MgO thin films were investigated by using reflection electron energy loss spectroscopy (REELS) and high-energy resolution REELS (HR-REELS). HR-REELS with a primary electron energy of 0.3 keV revealed that the surface F center (FS) energy was located at approximately 4.2 eV above the valence band maximum (VBM) and the surface band gap width (EgS) was approximately 6.3 eV. The bulk F center (FB) energy was located approximately 4.9 eV above the VBM and the bulk band gap width was about 7.8 eV, when measured by REELS with 3 keV primary electrons. From a first-principles calculation, we confirmed that the 4.2 eV and 4.9 eV peaks were FS and FB, induced by oxygen vacancies. We also experimentally demonstrated that the HR-REELS peak height increases with increasing number of oxygen vacancies. Finally, we calculated the secondary electron emission yields (?) for various noble gases. He and Ne were not influenced by the defect states owing to their higher ionization energies, but Ar, Kr, and Xe exhibited a stronger dependence on the defect states owing to their small ionization energies.

  2. Evidence for Intertwining of Superconductivity and Antiferromagnetism in a Cuprate

    NASA Astrophysics Data System (ADS)

    Tranquada, John; Xu, Zhijun; Stock, C.; Chi, S. X.; Kolesnikov, A. I.; Xu, G. Y.; Gu, G. D.

    2014-03-01

    We have used inelastic neutron scattering to measure the low-energy, incommensurate antiferromagnetic spin excitations both above and below the superconducting transition temperature (Tc = 32 K) of La1.905Ba0.095CuO4. While the magnetic excitations in optimally-doped cuprates typically show the development of a spin gap and magnetic resonance below Tc, our sample shows no such effect. Instead strong, gapless spin excitations coexist with bulk superconductivity. To understand this, we note that previous transport measurements have shown that the superconducting layers are decoupled by a magnetic field applied along the c-axis, resulting in a state with frustrated interlayer Josephson coupling, similar to LBCO with x = 1 / 8 , where it has been proposed that pair-density-wave superconductivity occurs. This suggests that, in a similar fashion, the spatially modulated antiferromagnetic correlations (which we see directly in the x = 0 . 095 sample) are intertwined with a spatially modulated superconducting pair wave function. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.

  3. Synthesis, characterization and band gap energy of poly(ɛ-caprolactone)/Sr-MSA nano-composite

    NASA Astrophysics Data System (ADS)

    Kannammal, L.; Palanikumar, S.; Meenarathi, B.; Yelilarasi, A.; Anbarasan, R.

    2014-04-01

    A mercaptosuccinic acid (MSA) decorated Sr nano-particle (NP) was prepared and characterized by using various analytical techniques and was used as a chemical initiator for the ring opening polymerization (ROP) of ɛ-caprolactone (CL). The ROP of CL was carried out at various experimental conditions under N2 atmosphere with mild stirring. The initiating efficiency of MSA-decorated Sr NP was tested in terms of Fourier transform infrared-relative intensity, melting temperature (Tm), degradation temperature (Td) and molecular weight (Mw) of poly(ɛ-caprolactone) (PCL), differential scanning calorimetry, UV-visible spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis and gel permeation chromatography analytical techniques. The nuclear magnetic resonance spectrum confirms the chemical structure of PCL. While increasing the [M/I] ratio, the Mw of PCL was linearly increased. The band gap energy of Sr was determined from the UV-visible spectrum. The reflectance study proves the hydrophobic nature of the Sr-hybrid and its nano-composite formation with PCL.

  4. 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.

  5. Quasiparticle properties of the superconducting state of the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Gull, E.; Millis, A. J.

    2015-02-01

    Cluster dynamical mean field methods are used to calculate the normal and anomalous components of the electron self-energy of the two-dimensional Hubbard model. Issues associated with the analytical continuation of the normal and anomalous parts of the gap function are discussed. Methods of minimizing the uncertainties associated with the pseudogap-related pole in the self-energy are discussed. From these the evolution of the superconducting gap and the momentum-dependent electron spectral function across the phase diagram are determined. In the pseudogap regime, decreasing the temperature into the superconducting state leads to a decrease in the energy gap and the formation of a "peak-dip-hump" structure in the electronic density of states. The peak feature disperses very weakly. The calculated spectral functions are in good qualitative agreement with published data. The mathematical origin of the behavior is found to be the effect of the superconductivity on the pole structure giving rise to the normal state pseudogap. In particular the "hump" feature is found to arise from a zero crossing of the real part of the electron self-energy rather than from an onset of scattering. The effect of superconductivity on the zone diagonal spectra is presented.

  6. Energy Impacts of Wide Band Gap Semiconductors in U.S. Light-Duty Electric Vehicle Fleet.

    PubMed

    Warren, Joshua A; Riddle, Matthew E; Graziano, Diane J; Das, Sujit; Upadhyayula, Venkata K K; Masanet, Eric; Cresko, Joe

    2015-09-01

    Silicon carbide and gallium nitride, two leading wide band gap semiconductors with significant potential in electric vehicle power electronics, are examined from a life cycle energy perspective and compared with incumbent silicon in U.S. light-duty electric vehicle fleet. Cradle-to-gate, silicon carbide is estimated to require more than twice the energy as silicon. However, the magnitude of vehicle use phase fuel savings potential is comparatively several orders of magnitude higher than the marginal increase in cradle-to-gate energy. Gallium nitride cradle-to-gate energy requirements are estimated to be similar to silicon, with use phase savings potential similar to or exceeding that of silicon carbide. Potential energy reductions in the United States vehicle fleet are examined through several scenarios that consider the market adoption potential of electric vehicles themselves, as well as the market adoption potential of wide band gap semiconductors in electric vehicles. For the 2015-2050 time frame, cumulative energy savings associated with the deployment of wide band gap semiconductors are estimated to range from 2-20 billion GJ depending on market adoption dynamics. PMID:26247853

  7. Nodal superconductivity and superconducting dome in the layered superconductor Ta4Pd3Te16

    NASA Astrophysics Data System (ADS)

    Pan, J.; Jiao, W. H.; Hong, X. C.; Zhang, Z.; He, L. P.; Cai, P. L.; Zhang, J.; Cao, G. H.; Li, S. Y.

    2015-11-01

    We measured the low-temperature thermal conductivity of a layered superconductor with quasi-one-dimensional characteristics, the ternary telluride Ta4Pd3Te16 with a transition temperature Tc?4.3 K. The significant residual linear term of thermal conductivity in zero magnetic field and its rapid field dependence provide evidence for nodes in the superconducting gap. By measuring resistivity under pressure, we reveal a superconducting dome in the temperature-pressure phase diagram. The existence of gap nodes and a superconducting dome suggest unconventional superconductivity in Ta4Pd3Te16 , which may relate to a charge-density-wave instability in this low-dimensional compound.

  8. Noncentrosymmetric superconductivity in a clean crystal of type II superconductor Bi-Pd

    NASA Astrophysics Data System (ADS)

    Ramakrishnan, Srinivasan; Pratap, Bhanu; Thamizhavel, A.

    2016-02-01

    In this work, we present the bulk superconductivity of a high-quality single crystal of monoclinic BiPd (α-BiPd, space group P21) below 3.8 K by studying its electrical resistivity, magnetic susceptibility, and heat capacity. This is the cleanest noncentrosymmetric superconductor (NCS) that display anisotropy due to spin-orbit scattering and also exhibits unusual superconducting properties due to s and p wave mixing as evidenced by the observation of Andreev bound state and multiple energy gaps via point contact measurements. In addition, Fermi surface studies suggest multiband superconductivity in this compound. Penetration depth studies and NQR investigations support mixing of s and p wave Copper paring in this crystal. Moroever, Muon spin rotation measurements indicate strong field dependence of the Ginzburg- Landau coefficient of this superconductor. Unusual pairing and multiband superconductivity are extremely sensitive to disorder and they can be observed only in cleanest (RRR > 170) single crystals.

  9. Origin of matching effect in anti-dot array of superconducting NbN thin films

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjeev; Kumar, Chandan; Jesudasan, John; Bagwe, Vivas; Parab, Pradnya; Raychaudhuri, Pratap; Bose, Sangita

    2015-05-01

    We investigate the origin of the matching effect observed in disordered superconducting NbN thin films with a periodic array of holes. In addition to the periodic variation in electrical resistance just above the superconducting transition temperature Tc0, we find pronounced periodic variations with magnetic field in all dynamical quantities that can be influenced by flux-line motion under an external drive, including the magnetic shielding response and the critical current, which survives in some samples down to temperatures as low as 0.09Tc0. In contrast, the superconducting energy gap ?, which is a true thermodynamic quantity, does not show any periodic variation with magnetic field for the same films. Our results show that commensurate pinning of the flux-line lattice driven by vortex-vortex interaction is the dominant mechanism for the matching effects observed in these superconducting anti-dot films, rather than a Little-Parks-like quantum interference effect.

  10. 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.

  11. Dominant superconducting fluctuations in the one-dimensional extended Holstein-extended Hubbard model

    NASA Astrophysics Data System (ADS)

    Tam, Ka-Ming; Tsai, Shan-Wen; Campbell, David K.

    2014-01-01

    The search for realistic one-dimensional (1D) models that exhibit dominant superconducting (SC) fluctuations effects has a long history. In these 1D systems, the effects of commensurate band fillingsstrongest at half-fillingand electronic repulsions typically lead to a finite charge gap and the favoring of insulating density wave ordering over superconductivity. Accordingly, recent proposals suggesting a gapless metallic state in the Holstein-Hubbard (HH) model, possibly superconducting, have generated considerable interest and controversy, with the most recent work demonstrating that the putative dominant superconducting state likely does not exist. In this paper we study a model with nonlocal electron-phonon interactions, in addition to electron-electron interactions. This model unambiguously possesses dominant superconducting fluctuations at half filling in a large region of parameter space. Using both the numerical multi-scale functional renormalization group (MFRG) for the full model and an analytic conventional renormalization group for a bosonized version of the model, we demonstrate the existence of these dominant SC fluctuations and show that they arise because the spin-charge coupling at high energies is weakened by the nonlocal electron-phonon interaction and the charge gap is destroyed by the resultant suppression of the Umklapp process. The existence of the dominant SC pairing instability in this half-filled 1D system suggests that nonlocal boson-mediated interactions may be important in the superconductivity observed in the organic superconductors.

  12. Prospects for the medium- and long-term development of China`s electric power industry and analysis of the potential market for superconductivity technology

    SciTech Connect

    Li, Z.

    1998-05-01

    First of all, overall economic growth objectives in China are concisely and succinctly specified in this report. Secondly, this report presents a forecast of energy supply and demand for China`s economic growth for 2000--2050. In comparison with the capability of energy construction in China in the future, a gap between supply and demand is one of the important factors hindering the sustainable development of Chain`s economy. The electric power industry is one of China`s most important industries. To adopt energy efficiency through high technology and utilizing energy adequately is an important technological policy for the development of China`s electric power industry in the future. After briefly describing the achievements of China`s electric power industry, this report defines the target areas and policies for the development of hydroelectricity and nuclear electricity in the 2000s in China, presents the strategic position of China`s electric power industry as well as objectives and relevant plans of development for 2000--2050. This report finds that with the discovery of superconducting electricity, the discovery of new high-temperature superconducting (HTS) materials, and progress in materials techniques, the 21st century will be an era of superconductivity. Applications of superconductivity in the energy field, such as superconducting storage, superconducting transmission, superconducting transformers, superconducting motors, its application in Magneto-Hydro-Dynamics (MHD), as well as in nuclear fusion, has unique advantages. Its market prospects are quite promising. 12 figs.

  13. Ultrafast Photoemission Spectroscopy of the Uranium Dioxide UO2 Mott Insulator: Evidence for a Robust Energy Gap Structure

    NASA Astrophysics Data System (ADS)

    Gilbertson, Steve M.; Durakiewicz, Tomasz; Dakovski, Georgi L.; Li, Yinwan; Zhu, Jian-Xin; Conradson, Steven D.; Trugman, Stuart A.; Rodriguez, George

    2014-02-01

    Time-resolved photoemission spectroscopy utilizing a probe energy of 32.55 eV and a pump energy of 3.1 and 4.65 eV with 30 fs temporal resolution is used to study the carrier dynamics in the 5f Mott insulator uranium dioxide (UO2). The Mott gap and on-site Coulomb interaction energies are measured directly as Egap=2.5 eV and UC=5 eV, respectively, and the dynamics of the upper Hubbard band is mapped. The f-fMott-Hubbard dynamics involves subpicosecond fluence-dependent relaxation, followed by decay via coupling to the lattice upon formation of excitonic polarons. Instead of an expected metallic transition, we observe a robust Mott gap structure, even at high pump fluences.

  14. Phenomenological theory of the superconducting state inside the hidden-order phase of URu2Si2

    NASA Astrophysics Data System (ADS)

    Kang, Jian; Fernandes, Rafael M.

    2015-08-01

    Recent experiments have unveiled important properties of the ground state of the elusive heavy fermion URu2Si2 . While tetragonal symmetry-breaking was reported below the hidden-order (HO) transition at THO?17.5 K , time-reversal symmetry breaking was observed below the superconducting transition temperature Tcsuperconducting state, such an order parameter is incompatible with broken tetragonal symmetry. Here, we employ a phenomenological model to investigate the properties of a chiral superconducting state that develops inside the hidden-order phase. In this case, there are actually two superconducting transition temperatures: while Tc marks a normal-state to superconducting transition, Tc*superconducting-to-superconducting transition in which time-reversal symmetry is broken. In the phase Tc*energy density of states ? (? ) is enhanced due to the crossing of two nodal lines, giving rise to an unusual ? ln(? ) dependence of ? (? ) , which is manifested in several thermodynamic properties. We also investigate the emergence of a soft amplitude gap mode near Tc*. In contrast to the usual amplitude mode near a regular normal-state to superconducting transition, this mode becomes soft near a superconducting-to-superconducting transition, which in principle allows for its detection by Raman spectroscopy. Finally, we investigate the impact of twin domains on the anisotropic properties of the superconducting state, and propose experiments in mechanically strained samples to explore the interplay between hidden order and superconductivity in URu2Si2 .

  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. Superconducting thermoelectric generator

    DOEpatents

    Metzger, J.D.; El-Genk, M.S.

    1998-05-05

    An apparatus and method for producing electricity from heat is disclosed. 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. 4 figs.

  18. 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.

  19. Superconducting thermoelectric generator

    DOEpatents

    Metzger, John D.; El-Genk, Mohamed S.

    1998-01-01

    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.

  20. Enhancement of magnetic flux distribution in a DC superconducting electric motor

    NASA Astrophysics Data System (ADS)

    Hamid, N. A.; Ewe, L. S.; Chin, K. M.

    2013-06-01

    Most motor designs require an air gap between the rotor and stator to enable the armature to rotate freely. The interaction of magnetic flux from rotor and stator within the air gap will provide the thrust for rotational motion. Thus, the understanding of magnetic flux in the vicinity of the air gap is very important to mathematically calculate the magnetic flux generated in the area. In this work, a finite element analysis was employed to study the behavior of the magnetic flux in view of designing a synchronous DC superconducting electric motor. The analysis provides an ideal magnetic flux distribution within the components of the motor. From the flux plot analysis, it indicates that flux losses are mainly in the forms of leakage and fringe effect. The analysis also shows that the flux density is high at the area around the air gap and the rotor. The high flux density will provide a high force area that enables the rotor to rotate. In contrast, the other parts of the motor body do not show high flux density indicating low distribution of flux. Consequently, a bench top model of a DC superconducting motor was developed where by motor with a 2-pole type winding was chosen. Each field coil was designed with a racetrack-shaped double pancake wound using DI-BSCCO Bi-2223 superconducting tapes. The performance and energy efficiency of the superconducting motor was superior when compared to the conventional motor with similar capacity.

  1. 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.

  2. Superconductivity in ultra-thin FeSe films

    NASA Astrophysics Data System (ADS)

    Deng, L. Z.; Xue, Y. Y.; Lv, B.; Wu, Z.; Wang, L. L.; Ma, X. C.; Xue, Q. K.; Chu, C. W.

    2014-03-01

    The recent discovery of a high Tc above 50 K in FeSe unit-cell film in comparison with the 8 K in bulk FeSe has attracted much attention, which is proposed to be related to interface superconductivity. Meissner effect and zero resistivity are two critical evidence for the existence of superconductivity. Unfortunately, the Tc has mostly indirectly obtained from the energy gap measurements, and preliminary resistive and magnetic measurements. There has not been report of the observation of Meissner effect to provide the sufficient proof of superconductivity to date. This motivates our systematic magnetic investigation here. We have observed in the 1-4 unit-cell FeSe-films: 1) Meissner effect with extensive weak-links up to ~ 20 K; 2) unconnected small superconducting patches up to ~ 40 K; and 3) an unusual relaxation of the diamagnetic signal of unknown nature up to 80 K, all are consistent with our resistance results. Their implications on the high Tc superconductivity and the film growth will be discussed. Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720.

  3. Superconducting electronics

    SciTech Connect

    Weinstock, H.; Nisenoff, M.

    1989-01-01

    The book provides an in-depth understanding of the fundamentals of superconducting electronics and the practical considerations for the fabrication of superconducting electronic structures. Additionally, it covers in detail the opportunities afforded by superconductivity for uniquely sensitive electronic devices and illustrates how these devices (in some cases employing high-temperature, ceramic superconductors) can be applied in analog and digital signal processing, laboratory instruments, biomagnetism, geophysics, nondestructive evaluation and radioastronomy. Improvements in cryocooler technology for application to cryoelectronics are also covered.

  4. Electronic Density of States of a Superconductor with a Spatially Varying Gap and Phase Fluctuations: A Monte Carlo Simulation

    NASA Astrophysics Data System (ADS)

    Valdez-Balderas, Daniel; Stroud, David

    2006-03-01

    Recent experiments have shown that the superconducting energy gap in some high-Tc superconductors is spatially inhomogeneous. Motivated by these experiments, and using exact diagonalization of a model d-wave Hamiltonian (T. Eckl et al. PRB 66 140510), combined with Monte Carlo simulations of a Ginzburg-Landau free energy functional, we have calculated the electronic density of states n(E) of a model high-Tc superconductor with an inhomogeneous gap. The free energy functional incorporates both phase and amplitude fluctuations together with quenched disorder. It leads to a superconducting transition temperature Tc well below the pseudogap temperature Tc0, and has a spatially varying gap at very low T, both consistent with experiments in underdoped Bi2212. Our calculated n(E) shows coherence peaks for T < Tc, which disappear for T > Tc. We will also present calculated results for both the global and local n(E) as a function of temperature and disorder.

  5. 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.

  6. Valence band gaps and plasma energies for galena, sphalerite, and chalcopyrite natural minerals using differential optical reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Todoran, R.; Todoran, D.; Szakacs, Zs.

    2015-12-01

    The paper presents the determinations of the valence band gaps and plasma energies of the galena, sphalerite and chalcopyrite natural minerals. The work was carried out using differential optical reflectance spectroscopy of the clean mineral surfaces. The determination of the optical properties such as refractive index, real part of the complex dielectric constant and the location of certain van Hove singularities, was carried out using the Kramers-Kronig formalism.

  7. Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te)

    PubMed Central

    Massee, Freek; Sprau, Peter Oliver; Wang, Yong-Lei; Davis, J. C. Samus; Ghigo, Gianluca; Gu, Genda D.; Kwok, Wai-Kwong

    2015-01-01

    Maximizing the sustainable supercurrent density, JC, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because JC amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSexTe1?x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or columnar defects, plus a higher density of single atomic site point defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields. PMID:26601180

  8. Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te).

    PubMed

    Massee, Freek; Sprau, Peter Oliver; Wang, Yong-Lei; Davis, J C Samus; Ghigo, Gianluca; Gu, Genda D; Kwok, Wai-Kwong

    2015-05-01

    Maximizing the sustainable supercurrent density, J C, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because J C amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSe x Te1-x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or "columnar defects," plus a higher density of single atomic site "point" defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields. PMID:26601180

  9. X-ray energy spectrum measurements by an annular superconducting tunnel junction with trapped magnetic flux quanta

    NASA Astrophysics Data System (ADS)

    Lisitskiy, M. P.; Nappi, C.; Ejrnaes, M.; Cristiano, R.; Huber, M.; Rottler, K.; Jochum, J.; von Feilitzsch, F.; Barone, A.

    2004-06-01

    We report on the Fe55 x-ray pulse height spectrum of an annular superconducting tunnel junction (STJ) collected without an external magnetic field. An energy resolution of 100eV was obtained for the K? line of the top electrode. The Josephson critical current and Fiske resonances were suppressed by the presence of trapped magnetic flux quanta which created a persistent current and self-generated magnetic field. The obtained energy resolution and the stability of the trapped magnetic flux under irradiation demonstrate the capability of an annular STJ device with trapped flux quanta to detect radiation without using the external magnetic field that is required in the conventional detection scheme.

  10. 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.

  11. 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.

  12. Lifshitz transitions and zero point lattice fluctuations in sulfur hydride showing near room temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Bianconi, Antonio; Jarlborg, Thomas

    2015-11-01

    Emerets's experiments on pressurized sulfur hydride have shown that H3S metal has the highest known superconducting critical temperature Tc = 203 K. The Emerets data show pressure induced changes of the isotope coefficient between 0.25 and 0.5, in disagreement with Eliashberg theory which predicts a nearly constant isotope coefficient.We assign the pressure dependent isotope coefficient to Lifshitz transitions induced by pressure and zero point lattice fluctuations. It is known that pressure could induce changes of the topology of the Fermi surface, called Lifshitz transitions, but were neglected in previous papers on the H3S superconductivity issue. Here we propose thatH3S is a multi-gap superconductor with a first condensate in the BCS regime (located in the large Fermi surface with high Fermi energy) which coexists with second condensates in the BCS-BEC crossover regime (located on the Fermi surface spots with small Fermi energy) near the and Mpoints.We discuss the Bianconi-Perali-Valletta (BPV) superconductivity theory to understand superconductivity in H3S since the BPV theory includes the corrections of the chemical potential due to pairing and the configuration interaction between different condensates, neglected by the Eliashberg theory. These two terms in the BPV theory give the shape resonance in superconducting gaps, similar to Feshbach resonance in ultracold fermionic gases, which is known to amplify the critical temperature. Therefore this work provides some key tools useful in the search for new room temperature superconductors.

  13. Theory of superconductivity in a three-orbital model of Sr2RuO4

    NASA Astrophysics Data System (ADS)

    Wang, Q. H.; Platt, C.; Yang, Y.; Honerkamp, C.; Zhang, F. C.; Hanke, W.; Rice, T. M.; Thomale, R.

    2013-10-01

    In conventional and high transition temperature copper oxide and iron pnictide superconductors, the Cooper pairs all have even parity. As a rare exception, Sr2RuO4 is the first prime candidate for topological chiral p-wave superconductivity, which has time-reversal breaking odd-parity Cooper pairs known to exist before only in the neutral superfluid 3He. However, there are several key unresolved issues hampering the microscopic description of the unconventional superconductivity. Spin fluctuations at both large and small wave vectors are present in experiments, but how they arise and drive superconductivity is not yet clear. Spontaneous edge current is expected but not observed conclusively. Specific experiments point to highly band- and/or momentum-dependent energy gaps for quasiparticle excitations in the superconducting state. Here, by comprehensive functional renormalization group calculations with all relevant bands, we disentangle the various competing possibilities. In particular, we show the small wave vector spin fluctuations, driven by a single two-dimensional band, trigger p-wave superconductivity with quasi-nodal energy gaps.

  14. Thermoelectric effects in triple quantum dots coupled to a normal and a superconducting leads

    NASA Astrophysics Data System (ADS)

    Xu, Wei-Ping; Zhang, Yu-Ying; Wang, Qiang; Li, Zhi-Jian; Nie, Yi-Hang

    2016-02-01

    The thermoelectric transport properties through laterally coupled triple quantum dots attached to a metal and a superconducting electrodes are investigated theoretically in the linear response regime. We calculate thermoelectric quantities by means of non-equilibrium Green's function, analyze their dependence on the energy gap, interdot coupling and Coulomb interaction, and discuss the effects of quantum interference, Coulomb blockade, Andreev reflection and bipolar effect on these quantities in transport process. Our results show that at low temperature the superconducting electrode suppresses the thermal conductance and enhances the thermopower outside the gap, which favors the improvement of figure of merit. In particular, the enhancement function of tunneling coupling between quantum dots and Coulomb blockade on figure of merit, compared with the system with two normal metal electrodes, is greatly increased due to the existence of the gap.

  15. Korea's developmental program for superconductivity

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  16. 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

    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.

  17. 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

  18. Electron pairing without superconductivity

    NASA Astrophysics Data System (ADS)

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P.; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C. Stephen; Levy, Jeremy

    2015-05-01

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). 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 a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity.

  19. Electron pairing without superconductivity.

    PubMed

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C Stephen; Levy, Jeremy

    2015-05-14

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances-paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). 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 a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. PMID:25971511

  20. Superconducting Microelectronics.

    ERIC Educational Resources Information Center

    Henry, Richard W.

    1984-01-01

    Discusses superconducting microelectronics based on the Josephson effect and its advantages over conventional integrated circuits in speed and sensitivity. Considers present uses in standards laboratories (voltage) and in measuring weak magnetic fields. Also considers future applications in superfast computer circuitry using Superconducting

  1. Dependence of mobility on density of gap states in organics by GAMEaS-gate modulated activation energy spectroscopy

    NASA Astrophysics Data System (ADS)

    So, Woo-young; Lang, David V.; Butko, Vladimir Y.; Chi, Xiaoliu; Lashley, Jason C.; Ramirez, Arthur P.

    2008-09-01

    We develop a broadly applicable transport-based technique, gate modulated activation energy spectroscopy (GAMEaS), for determining the density of states (DOS) in an energy gap. GAMEaS is applied to field-effect transistors (FETs) made from different single crystal oligomer semiconductors. We find that there are two distinct types of band tails, deep and shallow, depending on the crystallization process. The exponential band tails of the localized DOS are characterized by their slope with the highest mobility FETs having a value of 29 eV-1 close to 1/kBT at 300 K.

  2. Superconducting Structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2005-09-13

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  3. Superconducting structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2003-04-01

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  4. Coexistence of antiferromagnetism and d+id superconducting correlations in the graphene bilayer

    NASA Astrophysics Data System (ADS)

    Milovanovi?, M. V.; Predin, S.

    2012-11-01

    We discuss the t-J-U model on a honeycomb monolayer that has the same low-energy description of the kinetic term as the graphene bilayer, and in particular study coexistence of antiferromagnetism and superconducting correlations that originate from Cooper pairs without phase coherence. We show that the model is relevant for the description of the graphene bilayer and that the presence of the d+id superconducting correlations with antiferromagnetism can lead to quadratic dependence in small magnetic fields of the gap of the effective monolayer consistent with the transport measurements of Velasco on the graphene bilayer.

  5. s- AND d-WAVE SYMMETRIES IN NONADIABATIC THEORY OF SUPERCONDUCTIVITY

    NASA Astrophysics Data System (ADS)

    Paci, Paola; Grimaldi, Claudio; Pietronero, Luciano; Cappelluti, Emmanuele

    High-Tc superconductors have Fermi energies EF much smaller than conventional metals comparable to phonon frequencies. In such a situation nonadiabatic effects are important. A generalization of Eliashberg theory in the nonadiabatic regime has previously been shown to reproduce some anomalous features of the high-Tc superconductors as for instance the enhancement of Tc or the isotopic effects on Tc and m*. In this contribution we address the issue of the symmetry of the gap in the context of nonadiabatic superconductivity. We show that vertex corrections have a momentum structure which favours d-wave superconductivity when forward scattering is predominant. An additional increase of Tc is also found.

  6. 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.

  7. HOM damping properties of fundamental power couplers in the superconducting electron gun of the energy recovery LINAC at Brookhaven National Laboratory

    SciTech Connect

    Hammons, L.; Hahn, H.

    2011-03-28

    Among the accelerator projects under construction at the Relativistic Heavy Ion Collider (RHIC) is an R and D energy recovery LINAC (ERL) test facility. The ERL includes both a five-cell superconducting cavity as well as a superconducting, photoinjector electron gun. Because of the high-charge and high-current demands, effective higher-order mode (HOM) damping is essential, and several strategies are being pursued. Among these is the use of the fundamental power couplers as a means for damping some HOMs. Simulation studies have shown that the power couplers can play a substantial role in damping certain HOMs, and this presentation discusses these studies along with measurements.

  8. 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

  9. Executive summary of NIH workshop on the Use and Biology of Energy Drinks: Current Knowledge and Critical Gaps

    PubMed Central

    Sorkin, Barbara C; Camp, Kathryn M; Haggans, Carol J; Deuster, Patricia A; Haverkos, Lynne; Maruvada, Padma; Witt, Ellen; Coates, Paul M

    2014-01-01

    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

  10. Perturbation theory of a superconducting 0 - ? impurity quantum phase transition

    NASA Astrophysics Data System (ADS)

    onda, M.; Pokorn, V.; Jani, V.; Novotn, 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.

  11. Computing the band structure and energy gap of penta-graphene by using DFT and G0W0 approximations

    NASA Astrophysics Data System (ADS)

    Einollahzadeh, H.; Dariani, R. S.; Fazeli, S. M.

    2016-03-01

    In this paper, we consider the optimum coordinate of the penta-graphene. Penta-graphene is a new stable carbon allotrope which is stronger than graphene. Here, we compare the band gap of penta-graphene with various density functional theory (DFT) methods. We plot the band structure of penta-graphene which calculated with the generalized gradient approximation functional HTCH407, about Fermi energy. Then, one-shot GW (G0W0) correction for precise computations of band structure is applied. Quasi-direct band gap of penta-graphene is obtained around 4.1-4.3 eV by G0W0 correction. Penta-graphene is an insulator and can be expected to have broad applications in future, especially in nanoelectronics and nanomechanics.

  12. Self-Consistent Calculation of the correct Band-Gap and Low Energy Conduction Bands in Gallium-Nitride

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bagayoko, D.; Fan, J. D.

    1998-03-01

    The III-V nitrides are viewed as new semiconductors for optoelectronic applications in the blue and UV wavelengths and, more recently, as high-power, high-temperature electronic devices. However, a reliable prediction of the band gap and the low energy conduction bands had, until now, remained a problem in ab initio computations. A spurious effect of the variational procedure and of basis sets is shown to be a source of this problem. We present first principle computational steps that avoid this effect. We applied our new approach to calculate the electronic structure of III-V gallium-nitride using a local density approximation (LDA) for the exchange-correlation potential. Our calculated electronic structure and band gap, for an optimum basis set, agree qualitatively and quantitatively with experiment. *Work supported in part by funding from the Department of the Navy, Office of Naval Research (ONR), and from the Physics Graduate Program at Southern University and A & M College.

  13. 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.

  14. Superconducting magnet development in Japan

    SciTech Connect

    Yasukochi, K.

    1983-05-01

    The present state of R and D works on the superconducting magnet and its applications in Japan are presented. On electrical rotating machines, 30 MVA superconducting synchronous rotary condenser (Mitsubishi and Fuji) and 50 MVA generator are under construction. Two ways of ship propulsion by superconducting magnets are developing. A superconducting magnetically levitated and linear motor propelled train ''MAGLEV'' was developed by the Japan National Railways (JNR). The superconducting magnet development for fusion is the most active field in Japan. The Cluster Test program has been demonstrated on a 10 T Nb/sub 3/Sn coil and the first coil of Large Coil Task in IEA collaboration has been constructed and the domestic test was completed in JAERI. These works are for the development of toroidal coils of the next generation tokamak machine. R and D works on superconducting ohmic heating coil are in progress in JAERI and ETL. The latter group has constructed 3.8 MJ pulsed coil. A high ramp rate of changing field in pulsed magnet, 200 T/s, has been tested successfully. High Energy Physics Laboratory (KEK) are conducting active works. The superconducting ..mu.. meson channel and ..pi.. meson channel have been constructed and are operating successfully. KEK has also a project of big accelerator named ''TRISTAN'', which is similar to ISABELLE project of BNL. Superconducting synchrotron magnets are developed for this project. The development of superconducting three thin wall solenoid has been started. One of them, CDF, is progressing under USA-Japan collaboration.

  15. Fermionic scenario for the destruction of superconductivity in ultrathin MoC films evidenced by STM measurements

    NASA Astrophysics Data System (ADS)

    Szabó, P.; Samuely, T.; Hašková, V.; Kačmarčík, J.; Žemlička, M.; Grajcar, M.; Rodrigo, J. G.; Samuely, P.

    2016-01-01

    We use sub-Kelvin scanning tunneling spectroscopy to investigate the suppression of superconductivity in homogeneously disordered ultrathin MoC films. We observe that the superconducting state remains spatially homogeneous even on the films of 3-nm thickness. The vortex imaging suggests the global phase coherence in our films. Upon decreasing thickness, when the superconducting transition drops from 8.5 to 1.2 K, the superconducting energy gap Δ follows Tc perfectly. All this is pointing to a two-stage fermionic scenario of the superconductor-insulator transition (SIT) via a metallic state as an alternative to the direct bosonic SIT scenario with a Cooper-pair insulating state evidenced by the past decade STM experiments.

  16. Xenon-plasma light ultrahigh-resolution ARPES study of low-energy single-particle excitation gap in (Bi,Pb)2Sr2CuO6

    NASA Astrophysics Data System (ADS)

    Nakayama, K.; Sato, T.; Sekiba, Y.; Terashima, K.; Richard, P.; Kudo, K.; Okumura, N.; Sasaki, T.; Kobayashi, N.; Takahashi, T.

    2010-12-01

    We have performed ultrahigh-resolution angle-resolved photoemission spectroscopy of (Bi,Pb)2Sr2CuO6 by using a newly developed xenon-plasma light source to clarify the origin of the pseudogap (PG). We determined the comprehensive momentum and temperature dependences of the superconducting (SC) gap and the PG, and revealed a smooth evolution of the PG from the SC gap. We also found a linear scaling behavior of the characteristic PG temperature with the SC gap size regardless of the momentum location. These experimental results strongly suggest that the observed PG is caused by the precursor pairing.

  17. Superconducting terahertz metamaterials

    SciTech Connect

    Chen, Hou-tong; Singh, Ranjan; O' Hara, John F; Azad, Abul K; Trugman, Stuart A; Jia, Quanxi; Taylor, Antoinette J

    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.

  18. First-principles data-driven discovery of new low-band-gap oxides for solar energy capture and conversion

    NASA Astrophysics Data System (ADS)

    Yan, Qimin; Chen, Wei; Jain, Anubhav; Persson, Kristin; Neaton, Jeffery B.

    2014-03-01

    We develop first-principles data driven discovery approach to explore experimentally-known oxide compounds with low band gaps. Cr-based oxide compounds comprise a nice test bed for assessing high throughput discovery of light absorbers and photocatalysts. An interesting subclass with promising band gaps, this Cr oxide testbed spans a range of electronic and magnetic properties; predicting trends across such a range can challenge for standard density functional theory and many-body perturbation theory. We focus on this set and implement a broadly-applicable high-throughput workflow for calculation of band gaps, adsorption spectra, and band edges, initially using semi-local and hybrid functionals. We develop best practices for analysis of these data, and successfully identify several promising new compounds for solar energy capture and conversion applications, which we then apply more rigorous many-body perturbation theory including GW method and beyond to further study their optical and electronic properties. This work was supported by DOE through the Materials Project; computational resources provided by NERSC.

  19. Energy band gap, intrinsic carrier concentration, and Fermi level of CdTe bulk crystal between 304 and 1067 K

    NASA Astrophysics Data System (ADS)

    Su, Ching-Hua

    2008-04-01

    Optical transmission measurements were performed on CdTe bulk single crystals. It was found that when sliced and polished CdTe wafers were used, a white film started to develop on the sample surface and the wafer became opaque when it was heated above 530K. Therefore, a bulk crystal of CdTe was first grown in the window area by physical vapor transport. The optical transmission was then measured between 304 and 1067K and from which the energy band gap was derived. The band gaps of CdTe can fit well as a function of temperature by the Varshni expression. Using the band gap data, the high temperature electron-hole equilibrium was numerically calculated by assuming Kane's conduction band structure and a light-hole and a heavy-hole parabolic valence bands. The calculated intrinsic carrier concentrations agree well with the experimental data previously reported. The calculated intrinsic Fermi levels between 200 and 1200K were also presented.

  20. Inhomogeneous superconductivity

    NASA Astrophysics Data System (ADS)

    Covaci, Lucian

    We have studied the effects of inhomogeneities like surfaces, interfaces and disorder on the properties of s-wave and d-wave superconductors. The description of such inhomogeneous scenarios is very important, as they have a big influence on experimental observations. Tunneling experiments on the surface of superconductors will have a direct look into these peculiar surface states, like the zero bias conductance peak and the Andreev bound states. Using the tight-binding Extended Hubbard Hamiltonian, we numerically solve the discretized Bogoliubov-de Gennes equations applied to various inhomogeneous problems. We use simplifications due to the symmetries of surfaces, to solve problems like superconductivity near a surface, the giant proximity effect and the formation of Andreev bound states. Full two-dimensional calculations are employed to describe rough surfaces, finite size systems and the localization of the Andreev bound states in finite size samples. We find that the order parameter near surfaces exhibits Friedel-like oscillations on the order of the Fermi wavelength, and that interference effects occur in finite size systems. Major differences between the properties of d-wave superconductors near the (100) surface as compared to the (110) surface are uncovered. Zero energy bound states are present not only at the (110) surface of a d-wave superconductor, but also in a normal metal layer sitting on top of a d-wave superconductor. We demonstrate that rough surfaces of d-wave superconductors will acquire zero energy bound states at any surface orientation. We observe that Andreev bound states form in a normal metal when it is in proximity to a superconductor, and we show that in the case of finite size systems these states are localized in different locations depending on their energy.

  1. Multi-Functional Current Multiplier by High Temperature Superconducting Magnet Energy Storage

    NASA Astrophysics Data System (ADS)

    Yamada, S.; Hishinuma, Y.; Aso, Y.

    We had been developing a current multiplier by inductive storage (CMIS). The prototype of CMIS consists of 12 storage copper coil with switching units. Coils and feeders are cooled by the liquid nitrogen to reduce the resistivity. Output current pulse with 480 A could be generated, by charging the coils to 40 A. The continuous current pulses of 666 pulses per minute were obtained owing to the fast switching of coil currents by using IGBTs. Two types of the multi-functional CMIS were designed conceptually; one is for mega ampere and the other is for long pulse. The system consists of the superconducting (SC) magnet section with a temperature of 20 K and the IGBT control switch section with a temperature of 77 K. The SC coil is cooled down from 77 to 20 K by a G-M refrigerator. The IGBT control switches are soaked in liquid nitrogen to reduce the total resistance from CMIS coils to the load.

  2. 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.

  3. NLO vertex for a forward jet plus a rapidity gap at high energies

    SciTech Connect

    Hentschinski, Martin; Madrigal Martnez, Jos Daniel; Murdaca, Beatrice; Vera, Agustn Sabio

    2015-04-10

    We present the calculation of the forward jet vertex associated to a rapidity gap (coupling of a hard pomeron to the jet) in the BFKL formalism at next-to-leading order (NLO). Real emission contributions are computed via Lipatovs effective action. The NLO jet vertex turns out to be finite within collinear factorization and allows, together with the NLO non-forward gluon Greens function, to perform NLO studies of jet production in diffractive events (e.g. Mueller-Tang dijets)

  4. 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.

  5. Energy Gap and Electron Effective Mass in Chlorine Halide Superconductor at High Pressure

    NASA Astrophysics Data System (ADS)

    Szcz??niak, R.; Szcz??niak, D.

    2014-11-01

    Dependences of the order parameter (?) and the electron effective mass (me*) on the temperature for the chlorine halide superconductor are determined in the present work. The high values of the pressure (p1 = 320 GPa andp2 = 360 GPa), for which the critical temperature is equal to [TC]p1 = 30.6 K and [TC]p2 = 41.5 K, are taken into consideration. It is found that the dependence of the order parameter on the temperature deviates from the predictions of the classical BardeenCooperSchrieffer theory, due to the existence of the significant strong-coupling and retardation effects. The values of the order parameter, for the temperature close to zero Kelvin, are equal to [?(0)]p1 = 4.89 meV and [?(0)]p2 = 6.82 meV. The obtained results allowed next to calculate the dimensionless ratio R? ? 2?(0)/kBTC, which is equal to 3.71 and 3.81 in respect to p1 and p2. In the last step, it is proven that the electron effective mass is weakly dependent on the temperature in the area of the existence of the superconducting state and reaches its maximum at the critical temperature. For the considered values of the pressure, we obtain [me*]maxp1 = 1.69me and [me*]maxp2 = 1.78me, where the symbol me denotes the electron band mass.

  6. A relation between kinetic-energy density and the band gap in alkali and alkaline-earth oxides.

    PubMed

    Seriani, Nicola

    2010-06-30

    Alkali and alkaline-earth oxides are analysed by means of Bader's atom-in-molecule theory and density functional theory. Particular attention is devoted to the analysis of properties of the bond critical points. A linear relation is found between the kinetic-energy density at the bond critical point between cation and anion and the electronic band gap. This result might shed new light on the relationship between ground-state density, the nature of the bonds and insulating behaviour. Its generality is discussed. PMID:21393801

  7. Generalized thermoelastic wave band gaps in phononic crystals without energy dissipation

    NASA Astrophysics Data System (ADS)

    Wu, Ying; Yu, Kaiping; Li, Xiao; Zhou, Haotian

    2016-01-01

    We present a theoretical investigation of the thermoelastic wave propagation in the phononic crystals in the context of Green–Nagdhi theory by taking thermoelastic coupling into account. The thermal field is assumed to be steady. Thermoelastic wave band structures of 3D and 2D are derived by using the plane wave expansion method. For the 2D problem, the anti-plane shear mode is not affected by the temperature difference. Thermoelastic wave bands of the in-plane x–y mode are calculated for lead/silicone rubber, aluminium/silicone rubber, and aurum/silicone rubber phononic crystals. The new findings in the numerical results indicate that the thermoelastic wave bands are composed of the pure elastic wave bands and the thermal wave bands, and that the thermal wave bands can serve as the low boundary of the first band gap when the filling ratio is low. In addition, for the lead/silicone rubber phononic crystals the effects of lattice type (square, rectangle, regular triangle, and hexagon) and inclusion shape (circle, oval, and square) on the normalized thermoelastic bandwidth and the upper/lower gap boundaries are analysed and discussed. It is concluded that their effects on the thermoelastic wave band structure are remarkable.

  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. Time-reversal invariant topological superconductivity in doped Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Hosur, Pavan; Dai, Xi; Fang, Zhong; Qi, Xiao-Liang

    2015-03-01

    Time-reversal invariant topological superconductors are a new state of matter which have a bulk superconducting gap and robust Majorana fermion surface states. These have not yet been realized in solid state systems. In this paper, we propose that this state can be realized in doped Weyl semimetals or Weyl metals. The Fermi surfaces of a Weyl metal carry Chern numbers, which is a required ingredient for such a topological superconductor. By applying the fluctuation-exchange approach to a generic model of time-reversal invariant Dirac and Weyl semimetals, we investigate what microscopic interactions can supply the other ingredient, viz., sign changing of the superconducting gap function between Fermi surfaces with opposite Chern numbers. We find that if the normal state is inversion symmetric, onsite repulsive and exchange interactions induce various nodal phases as well as a small region of topological superconductivity on the phase diagram. Unlike the He3B topological superconductor, the phase here does not rely on any special momentum dependence of the pairing amplitude. Breaking inversion symmetry precludes some of the nodal phases and the topological superconductor becomes much more prominent, especially at large ferromagnetic interaction. We acknowledge support from the David and Lucile Packard Foundation, the Department of Energy Office of Basic Sciences, National Science Foundation, National Science Foundation of China and 973 Program of China for financial support.

  10. Optical absorption of divalent metal tungstates: Correlation between the band-gap energy and the cation ionic radius

    NASA Astrophysics Data System (ADS)

    Lacomba-Perales, R.; Ruiz-Fuertes, J.; Errandonea, D.; Martínez-García, D.; Segura, A.

    2008-08-01

    We have carried out optical-absorption and reflectance measurements at room temperature in single crystals of AWO4 tungstates (A=Ba, Ca, Cd, Cu, Pb, Sr, and Zn). From the experimental results their band-gap energy has been determined to be 5.26 eV (BaWO4), 5.08 eV (SrWO4), 4.94 eV (CaWO4), 4.15 eV (CdWO4), 3.9-4.4 eV (ZnWO4), 3.8-4.2 eV (PbWO4), and 2.3 eV (CuWO4). The results are discussed in terms of the electronic structure of the studied tungstates. It has been found that those compounds where only the s electron states of the A2+ cation hybridize with the O 2p and W 5d states (e.g., BaWO4) have larger band-gap energies than those where also p, d, and f states of the A2+ cation contribute to the top of the valence band and the bottom of the conduction band (e.g., PbWO4). The results are of importance in view of the large discrepancies existent in prevoiusly published data.

  11. Anomalous Energy Gaps of the Odd Denominator Fractional Quantum Hall States in Different Spin Branches of the Second Landau Level

    NASA Astrophysics Data System (ADS)

    Kleinbaum, Ethan; Kumar, Ashwani; Manfra, Michael; Pfeiffer, Loren; West, Ken; Csathy, Gabor

    2013-03-01

    The nature of the fractional quantum Hall states forming in the second Landau level, including those with odd denominator Landau level filling factors, remain unknown. Conjectures of nonconventional origins have lead to the investigation of several odd denominator states in the lower spin branch of the second Landau level, such as the ones at ?=2+1/3 and 2+2/3. We report first measurements of the energy gaps in the upper spin branch of the second Landau level at ?=3+1/3, 3+2/3, 3+1/5 and 3+4/5. A comparison of the energy gaps of these states to those of their counterparts in the lower spin branch reveals a surprising reversal in the relative magnitudes of the states at partial filling factors 1/3 and 1/5. We explore possible explanations of this unusual observation. The work at Purdue was supported by the DOE BES contract no. DE-SC0006671. K.K. West and L.N. Pfeiffer acknowledge the support of the Princeton NSF-MRSEC and the Moore Foundation.

  12. Effect of Al Doping on Optical Band Gap Energy of Al-TiO2 Thin Films.

    PubMed

    Song, Yo-Seung; Kim, Bae-Yeon; Cho, Nam-Ihn; Lee, Deuk Yong

    2015-07-01

    Al-TiO2 thin films were prepared using a sol-gel derived spin coating by varying the Al/Ti molar ratio from 0 to 0.73 to investigate the effect of Al doping on the optical band gap energy (Eg) of the films. GAXRD results indicated that Al-TiO2 is composed of anatase and FTO phases when the Al/Ti molar ratio was less than 0.18. Above 0.38, no other peaks except FTO were found and transparency of the films was severely deteriorated. Eg of Al-TiO2 decreased from 3.20 eV to 2.07 eV when the Al/Ti ratio was raised from 0 to 0.38. Eg of 2.59 eV was found for the anatase Al-TiO2 films having the Al/Ti ratio of 0.18. The absorption band of Al-TiO2 coatings shifted dramatically from the UV region to the visible region with increasing the amount of Al dopant. The Al doping was mainly attributed to the optical band gap energy of Al-TiO2. PMID:26373112

  13. 4. MESOSCOPIC SUPERCONDUCTIVITY: Scanning tunneling spectroscopy on superconducting proximity nanostructures

    NASA Astrophysics Data System (ADS)

    Chapelier, C.; Vinet, M.; Lefloch, F.

    2001-10-01

    We investigated the local density of states (LDOS) of a normal metal (N) in good electrical contact with a superconductor (S) as a function of the distance x to the NS interface. The sample consists of a pattern of alternate L = 1 mm wide strips of Au and Nb made by UV lithography. We used a low temperature scanning tunneling microscope and a lock-in detection technique to record simultaneously dI/dV(V,x) curves and the topographic profile z(x) at 1.5 K. We scanned along lines perpendicular to the strips. All the spectra show a dip near the Fermi energy, which spectral extension decreases from the superconducting gap ? at the NS interface to zero at distances x gg ?N where ?N simeq ?hslashDN/2? simeq 53nm is the coherence length in the normal metal. Our measurements are correctly described in the framework of the quasi-classical Green's function formalism. We numerically solved the 1D Usadel equation and extracted a decoherence time in gold of 4 ps. We also investigated the LDOS of small ridges of Au deposited on the top of the Nb lines. In this case, L <= ?N and the spatial variations of the spectra depend on the exact shape of the Au ridge. However, our results are consistent with a predicted minigap related to the Thouless energy.

  14. Hierarchy of gaps and magnetic minibands in graphene in the presence of the Abrikosov vortex lattice

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Fal'ko, Vladimir I.

    2016-01-01

    We determine the bands and gaps in graphene subjected to the magnetic field of an Abrikosov lattice of vortices in the underlying superconducting film. The spectrum features one nondispersive magnetic miniband at zero energy, separated by the largest gaps in the miniband spectrum from a pair of minibands resembling a slightly broadened first Landau level in graphene, suggesting the persistence of ? =2 and 6 quantum Hall effect states. Also, we identify an occasional merging point of magnetic minibands with a Dirac-type dispersion at the miniband edges.

  15. Making Superconducting Welds between Superconducting Wires

    NASA Technical Reports Server (NTRS)

    Penanen, Konstantin I.; Eom, Byeong Ho

    2008-01-01

    A technique for making superconducting joints between wires made of dissimilar superconducting metals has been devised. The technique is especially suitable for fabrication of superconducting circuits needed to support persistent electric currents in electromagnets in diverse cryogenic applications. Examples of such electromagnets include those in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems and in superconducting quantum interference devices (SQUIDs). Sometimes, it is desirable to fabricate different parts of a persistent-current-supporting superconducting loop from different metals. For example, a sensory coil in a SQUID might be made of Pb, a Pb/Sn alloy, or a Cu wire plated with Pb/Sn, while the connections to the sensory coil might be made via Nb or Nb/Ti wires. Conventional wire-bonding techniques, including resistance spot welding and pressed contact, are not workable because of large differences between the hardnesses and melting temperatures of the different metals. The present technique is not subject to this limitation. The present technique involves the use (1) of a cheap, miniature, easy-to-operate, capacitor-discharging welding apparatus that has an Nb or Nb/Ti tip and operates with a continuous local flow of gaseous helium and (2) preparation of a joint in a special spark-discharge welding geometry. In a typical application, a piece of Nb foil about 25 m thick is rolled to form a tube, into which is inserted a wire that one seeks to weld to the tube (see figure). The tube can be slightly crimped for mechanical stability. Then a spark weld is made by use of the aforementioned apparatus with energy and time settings chosen to melt a small section of the niobium foil. The energy setting corresponds to the setting of a voltage to which the capacitor is charged. In an experiment, the technique was used to weld an Nb foil to a copper wire coated with a Pb/Sn soft solder, which is superconducting. The joint was evaluated as part of a persistent-current circuit having an inductance of 1 mH. A current was induced in a loop, and no attenuation of the current after a time interval 1,000 s was discernible in a measurement having a fractional accuracy of 10(exp -4): This observation supports the conclusion that the weld had an electrical resistance <10(exp -10) omega.

  16. Visualizing the Atomic-scale Influence on Superconductivity and Vortex Pinning of High-Energy Ion Irradiation in FeSeTe

    NASA Astrophysics Data System (ADS)

    Sprau, Peter; Massee, Freek; Wang, Yonglei; Davis, J. C. Seamus; Gu, Genda; Kwok, Wai-Kwong

    2015-03-01

    The maximum sustainable supercurrent density, JC, may be greatly enhanced by preventing dissipative motion of quantized vortices. Irradiation of superconductors with heavy ions is often used to create nanoscale defects with deep pinning potential for the vortices and this approach holds great promise for high current applications of iron-based superconductivity. However, for these compounds virtually nothing is known directly about the atomic-scale interplay between the crystal damage from high-energy ions, the superconducting order parameter, and the vortex pinning processes. Here, we visualize the atomic-scale effects of irradiating FeSe0.45Te0.55 with 249 MeV Au ions and find two distinct forms of damage: compact regions of crystal disruption ascribable to the actual ion trajectory along with single atomic-site `point' defects. We show directly that the superconducting order is virtually annihilated within the former while it is strongly altered by the latter. Simultaneous atomically-resolved images of the crystal defects, the superconducting density-of-states, and the vortex cores, then reveal how the vortex pinning evolves with increasing field in irradiating FeSe0.45Te0.55.

  17. Investigation of superconducting and normal-state properties of the filled-skutterudite system PrPt4Ge12-xSbx

    NASA Astrophysics Data System (ADS)

    Jeon, I.; Huang, K.; Yazici, D.; Kanchanavatee, N.; White, B. D.; Ho, P.-C.; Jang, S.; Pouse, N.; Maple, M. B.

    2016-03-01

    We report a study of the superconducting and normal-state properties of the filled-skutterudite system PrPt4Ge12 -xSbx . Polycrystalline samples with Sb concentrations up to x =5 were synthesized and investigated by means of x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements. We observed a suppression of superconductivity with increasing Sb substitution up to x =4 , above which no signature of superconductivity was observed down to 140 mK. The Sommerfeld coefficient, γ , of superconducting specimens decreases with increasing x up to x =3 , suggesting that superconductivity may depend on the density of electronic states in this system. The specific heat for x =0.5 exhibits an exponential temperature dependence in the superconducting state, reminiscent of a nodeless superconducting energy gap. We observed evidence for a weak "rattling" mode associated with the Pr ions, characterized by an Einstein temperature ΘE˜60 K for 0 ≤x ≤5 ; however, the rattling mode may not play any role in suppressing superconductivity.

  18. Fabrication and evaluation of superconducting magnetic bearing for 10 kW h-class flywheel energy storage system

    NASA Astrophysics Data System (ADS)

    Ichihara, T.; Matsunaga, K.; Kita, M.; Hirabayashi, I.; Isono, M.; Hirose, M.; Yoshii, K.; Kurihara, K.; Saito, O.; Saito, S.; Murakami, M.; Takabayashi, H.; Natsumeda, M.; Koshizuka, N.

    2005-10-01

    Radial-type superconducting magnetic bearings (SMB) have been developed for a 10 kW h-class flywheel energy storage system. The bearings consist of an inner-cylindrical stator composed of YBCO bulk superconductors and an outer-rotor composed of permanent magnets. The rotor is suspended without contact using the pinning forces of the bulk superconductors. After construction of the whole system, various tests on both static and dynamic characteristics of the SMB were carried out to confirm that the SMB has sufficient performance for 10 kW h-class flywheel systems. Besides, the bearing rotation loss was measured. In this paper, we describe the implementation of the stator part and report the SMB test results, namely that the rotor was successfully suspended up to 7500 rpm. Thus we succeeded in the energy storage of 2.24 kW h. The rotation loss of the SMB was estimated as 40 W at 7500 rpm, which was mainly caused by the inhomogeneous magnetic field of the bulk superconductors.

  19. Attempting to bridge the gap between laboratory and seismic estimates of fracture energy

    USGS Publications Warehouse

    McGarr, A.; Fletcher, Joe B.; Beeler, N.M.

    2004-01-01

    To investigate the behavior of the fracture energy associated with expanding the rupture zone of an earthquake, we have used the results of a large-scale, biaxial stick-slip friction experiment to set the parameters of an equivalent dynamic rupture model. This model is determined by matching the fault slip, the static stress drop and the apparent stress. After confirming that the fracture energy associated with this model earthquake is in reasonable agreement with corresponding laboratory values, we can use it to determine fracture energies for earthquakes as functions of stress drop, rupture velocity and fault slip. If we take account of the state of stress at seismogenic depths, the model extrapolation to larger fault slips yields fracture energies that agree with independent estimates by others based on dynamic rupture models for large earthquakes. For fixed stress drop and rupture speed, the fracture energy scales linearly with fault slip.

  20. Surface electronic state of superconducting topological crystalline insulator

    NASA Astrophysics Data System (ADS)

    Hashimoto, Tatsuki; Yada, Keiji; Sato, Masatoshi; Tanaka, Yukio

    2015-11-01

    We study the surface state of a doped topological crystalline insulator in the superconducting state. Motivated by Sn1 -xInxTe , we consider fully gapped pair potentials and calculate the surface spectral function. It is found that mirror-protected zero-energy surface Andreev bound states (SABSs) appear at the (001) surface. The gapless points of these SABSs appear on the mirror-symmetric line on the surface Brillouin zone while the positions of the gapless points depend on the chemical potential. In addition, due to the presence of the Dirac surface states in the normal state, the dispersion of the SABSs drastically changes with the chemical potential.