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Sample records for electron-doped high-tc superconductors

  1. Spin correlations in electron-doped high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Fujita, M.

    2007-11-01

    Spin correlations in the electron-doped Pr1-xLaCexCuO4 have been investigated by neutron-scattering and muon rotation/relaxation measurements. The low-enegy spin correlations were found to be in commensurate with the wide superconducting phase, unlike the incommensurate ones in the hole-doped La2-xSrxCuO4. No enhancement of the magnetic order by impurity-doping and applying magnetic fields was observed, although the superconductivity is effectively suppressed, compared to that in the hole-doped system. Distinct impurity and magnetic field effects between the static spin correlation in the electron-doped system and those in the hole-doped systems suggest the different magnetic ground state in the two systems.

  2. Effect of Strong Correlations on the High Energy Anomaly in Hole- and Electron-Doped High-Tc Superconductors

    SciTech Connect

    Moritz, B.; Schmitt, F.; Meevasana, W.; Johnston, S.; Motoyama, E.M.; Greven, M.; Lu, D.H.; Kim, C.; Scalettar, R.T.; Shen, Z.-X.; Devereaux, T.P.; /SLAC, SIMES

    2010-02-15

    Recently, angle-resolved photoemission spectroscopy (ARPES) has been used to highlight an anomalously large band renormalization at high binding energies in cuprate superconductors: the high energy 'waterfall' or high energy anomaly (HEA). This paper demonstrates, using a combination of new ARPES measurements and quantum Monte Carlo simulations, that the HEA is not simply the byproduct of matrix element effects, but rather represents a cross-over from a quasi-particle band at low binding energies near the Fermi level to valence bands at higher binding energy, assumed to be of strong oxygen character, in both hole- and electron-doped cuprates. While photoemission matrix elements clearly play a role in changing the aesthetic appearance of the band dispersion, i.e. the 'waterfall'-like behavior, they provide an inadequate description for the physics that underlies the strong band renormalization giving rise to the HEA. Model calculations of the single-band Hubbard Hamiltonian showcase the role played by correlations in the formation of the HEA and uncover significant differences in the HEA energy scale for hole- and electron-doped cuprates. In addition, this approach properly captures the transfer of spectral weight accompanying both hole and electron doping in a correlated material and provides a unifying description of the HEA across both sides of the cuprate phase diagram.

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

    NASA Astrophysics Data System (ADS)

    Kunwar, Shankar

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

  4. Correlation between Fermi surface transformations and superconductivity in the electron-doped high-Tc superconductor Nd2 -xCexCuO4

    NASA Astrophysics Data System (ADS)

    Helm, T.; Kartsovnik, M. V.; Proust, C.; Vignolle, B.; Putzke, C.; Kampert, E.; Sheikin, I.; Choi, E.-S.; Brooks, J. S.; Bittner, N.; Biberacher, W.; Erb, A.; Wosnitza, J.; Gross, R.

    2015-09-01

    Two critical points have been revealed in the normal-state phase diagram of the electron-doped cuprate superconductor Nd2 -xCexCuO4 by exploring the Fermi surface properties of high-quality single crystals by high-field magnetotransport. First, the quantitative analysis of the Shubnikov-de Haas effect shows that the weak superlattice potential responsible for the Fermi surface reconstruction in the overdoped regime extrapolates to zero at the doping level xc=0.175 corresponding to the onset of superconductivity. Second, the high-field Hall coefficient exhibits a sharp drop right below optimal doping xopt=0.145 where the superconducting transition temperature is maximum. This drop is most likely caused by the onset of long-range antiferromagnetic ordering. Thus the superconducting dome appears to be pinned by two critical points to the normal state phase diagram.

  5. Spin Dynamics in the electron-doped high-Tc superconductors Pr0.88LaCe0.12CuO4-δ

    NASA Astrophysics Data System (ADS)

    Dai, Pengcheng

    2007-03-01

    We briefly review results of recent neutron scattering experiments designed to probe the evolution of antiferromagnetic (AF) order and spin dynamics in the electron- doped Pr0.88LaCe0.12CuO4-δ (PLCCO) as the system is tuned from its as-grown non-superconducting AF state into an optimally doped superconductor (Tc = 27.5 K) without static AF order [1-3]. For under doped materials, a quasi-two- dimensional spin-density wave was found to coexist with three- dimensional AF order and superconductivity. In addition, the low-energy spin excitations follow Bose statistics. In the case of optimally doped material, we have discovered a magnetic resonance intimately related to superconductivity analogous to the resonance in hole-doped materials. On the other hand, the low energy spin excitations have very weak temperature dependence and do not follow Bose statistics, in sharp contrast to the as-grown nonsuperconducting materials. 1 Stephen D. Wilson, Pengcheng Dai, Shiliang Li, Songxue Chi, H. J. Kang, and J. W. Lynn, Nature (London) 442, 59 (2006). 2 Stephen D. Wilson, Shiliang Li, Hyungje Woo, Pengcheng Dai, H. A. Mook, C. D. Frost, S. Komiya, and Y. Ando, Phys. Rev. Lett. 96, 157001 (2006). 3. Stephen D. Wilson, Shiliang Li, Pengcheng Dai, Wei Bao, J. H. Chung, H. J. Kang, S.-H. Lee, S. Komiya, and Y. Ando, Phys. Rev. B 74, 144514 (2006).

  6. Muon spin relaxation study of the Cu spin dynamics in electron-doped high- Tc superconductor Pr0.86LaCe0.14Cu1-yZnyO4

    NASA Astrophysics Data System (ADS)

    Risdiana; Adachi, T.; Oki, N.; Koike, Y.; Suzuki, T.; Watanabe, I.

    2010-07-01

    Muon-spin-relaxation (μSR) measurements have been performed for the partially Zn-substituted electron-doped high- Tc superconductor Pr0.86LaCe0.14Cu1-yZnyO4+α-δ with y=0-0.05 and the reduced oxygen content δ=0-0.09 , in order to investigate nonmagnetic Zn-impurity effects on the Cu-spin dynamics. For all the measured samples with 0.01≤δ≤0.09 , it has been found that a fast depolarization of muon spins is observed below 100 K due to the effect of Pr3+ moments and that the μSR time spectrum in the long-time region above 5μsec increases with decreasing temperature at low temperatures below 30 K possibly due to slowing down of the Cu-spin fluctuations assisted by Pr3+ moments. No Zn-induced slowing down of the Cu-spin fluctuations has been observed for moderately oxygen-reduced samples with 0.04≤δ≤0.09 , which is very different from the μSR results of La2-xSrxCu1-yZnyO4 . The possible reason may be that there are no dynamical stripe correlations of spins and electrons in the electron-doped high- Tc cuprates or that the effect of Pr3+ moments on the μSR spectra is stronger than that of a small amount of Zn impurities.

  7. Internal static electric and magnetic field at the copper cite in a single crystal of the electron-doped high-Tc superconductor Pr1.85Ce0.15CuO4 -y

    NASA Astrophysics Data System (ADS)

    Wu, Guoqing; Zamborszky, F.; Reyes, A. P.; Kuhns, P. L.; Greene, R. L.; Clark, W. G.

    2014-12-01

    We report 63 ,65Cu -NMR spectroscopy and Knight shift measurements on a single crystal of the electron-doped high-Tc superconductor Pr1.85Ce0.15CuO4 -y with an applied magnetic field (H ) up to 26.42 T. A very small NQR frequency is obtained with the observation of the spectrum, which shows an extremely wide continuous distribution of it that becomes significantly narrower below 20 K at H ∥c where the superconductivity is completely suppressed, indicating a significant change in the charge distribution at the Cu site, while the corresponding change at H ⊥c is negligible when the superconductivity is present or not fully suppressed. The Knight shift and central linewidth are proportional to the applied magnetic field with a high anisotropy. We find that the magnitude of the internal static magnetic field at the copper is dominated by the anisotropic Cu2 + 3 d orbital contributions, while its weak temperature dependence is mainly determined by the isotropic contact hyperfine coupling to the paramagnetic Pr3 + spins, which also gives rise to the full distribution of the internal static magnetic field at the copper for H ⊥c . This internal static electric and magnetic field environment at the copper is very different from that in the hole-doped cuprates, and may provide new insight into the understanding of high-Tc superconductivity. Other experimental techniques are needed to verify whether the observed significant narrowing of the charge distribution at the Cu site with H ∥c is caused by the charge ordering [E. H. da Silva Neto et al., Science (to be published, 2014)] or a new type of charge modulation.

  8. Ultrasonic attenuation studies in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Shen, Zhong Cheng; Jiang, Zuo

    2005-04-01

    In this paper a great number of mechanical relaxation spectrum experiment results in the mixed state of high Tc superconductors have been summarized. A new low frequency mechanical relaxation spectrum apparatus have been shown. We pointed out that the mechanical relaxation peaks are attributed to anelastic relaxation processes and the transition of rigidly pinned FLL into a depinned state.

  9. Shock compaction of high- Tc superconductors

    SciTech Connect

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

    1990-09-01

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

  10. Peak Effect in High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Ling, Xinsheng

    1996-03-01

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

  11. High -Tc superlight bipolarons in novel superconductors

    NASA Astrophysics Data System (ADS)

    Alexandrov, Sasha

    2003-03-01

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

  12. Quaternary borocarbides: Relatively high Tc intermetallic superconductors and magnetic superconductors

    NASA Astrophysics Data System (ADS)

    Mazumdar, Chandan; Nagarajan, R.

    2015-07-01

    Discovery of superconductivity in Y-Ni-B-C (Tc ∼ 13 K) gave rise to the class of quaternary rare earth transition metal borocarbide superconductors. Before the discovery of Fe-based arsenide superconductors, this was the only class of materials containing a magnetic element, viz., Ni, yet exhibiting Tcs > 5 K. Many members of this class have high Tc (>10 K). Tc of ∼23 K in Y-Pd-B-C system equaled the record Tc known then, for intermetallics. Another feature that sets this class apart, is the occurrence of the exotic phenomenon of coexistence of superconductivity and magnetism at temperatures >5 K. Availability of large and electronically 'clean' single crystals and large Ginzburg-Landau (G-L) parameter, κ, have enabled detailed investigation of nonlocal effects of superconductivity. Intermediate value of upper critical field Hc2, has enabled detailed investigation of superconductivity in this class, over the complete H-T plane. This has revealed details of anisotropy of superconductivity (e.g., a fourfold symmetry in the square a-b plane is found) and raised questions on the symmetry of order parameter. After a brief outline of the discovery, this article gives a summary of the materials and highlights of superconducting properties of this class of materials. Interesting results from studies, using various techniques, on YNi2B2C (Tc ∼ 15 K) and LuNi2B2C (Tc ∼ 16 K) are presented, including observation of unusual square vortex lattice and its structural transformation with H and T. With conduction electrons involved in the magnetic order of this class of superconductors, the interplay of superconductivity and magnetism is intimate in these magnetic superconductors. With Tc (∼11 K) > TN (∼6 K) in ErNi2B2C, Tc (∼8 K) = TN (∼8 K) in HoNi2B2C and Tc (∼6 K) < TN (∼11 K) in DyNi2B2C, and with other parameters being favorable as mentioned earlier, this class of magnetic superconductors have become ideal materials to investigate the coexistence

  13. High Tc superconductors - Composite wire fabrication

    NASA Astrophysics Data System (ADS)

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

    1987-07-01

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

  14. High-Tc superconductor coplanar waveguide filter

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  15. Fluxoid motion and resistive transition in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, T.; Ni, B.

    1990-07-01

    Significantly broad resistive transition has been observed in high-Tc superconductors under a magnetic field. A similar broad transition was observed by French et al. (1967) in resistance versus magnetic field characteristics in low-temperature superconductors for various current densities. In this case, the critical current density and the flow resistivity completely determine the overall resistive characteristics. This suggests that the resistive characteristics in high-Tc superconductors may also be determined by these two quantities alone. In fact, the procedure outlined reproduces the commonly observed resistive characteristics. A notable feature determined from this procedure is that a knee exists in the resistance versus temperature curve. This projection corresponds to the irreversibility point; i.e. the temperature at which the critical current density is reduced to zero.

  16. Isotope coefficient in high Tc superconductors

    SciTech Connect

    Kishore, R.

    1995-10-01

    An exact expression for the isotope coefficient ({alpha}), within the conventional BCS theory, has been derived for any arbitrary electronic density of states and the mass dependence of carrier concentration. It is shown that the effect of the mass dependence of the carrier concentration within the van-Hove scenario (VHS) can explain some anomalous features of {alpha} for La{sub 2}CuO{sub 4} based superconductors, not explained by earlier theories based on VHS. These anomalous features are the asymmetry of {alpha} about the optimum concentration (n{sub m}) corresponding to the maximum critical temperature, minimum in {alpha} above n{sub m}, and the value of {alpha} less than 0.5 below n{sub m}.

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

    SciTech Connect

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

    1990-01-01

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

  18. Proximity Effect at Graphene - High Tc Superconductor Junctions

    NASA Astrophysics Data System (ADS)

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

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

  19. Raman scattering in high-{Tc} superconductors: Electronic excitations

    SciTech Connect

    Cardona, M.; Strohm, T.; Kircher, J.

    1996-12-31

    Since the discovery of the high {Tc} superconductors Raman scattering has proven to be an excellent technique to characterize them and to investigate basic physical properties relevant to the elusive mechanism responsible for their superconductivity. The authors discuss here several aspects of the technique as applied to superconductivity, including scattering by lattice vibrations, magnetic excitations, and electronic excitations, with particular emphasis on the latter, both in the normal and the superconducting state. 47 refs., 8 figs., 1 tab.

  20. The unconventional electrodynamics of high {Tc} and organic superconductors

    SciTech Connect

    Timusk, T.; Cao, N.; Basov, D.N.; Homes, C.C.

    1996-12-31

    The combination of lowered dimensionality and electron-electron correlations are responsible for the unusual temperature and frequency dependence of the electrical conductivity of the new superconductors. The authors first review the electrodynamics of two systems, U{sub 2}Ru{sub 2}Si{sub 2} and Sr{sub 2}RuO{sub 4} where conventional Fermi liquid ideas seem to work. Here transport is by free carriers with strongly renormalized masses. On the other hand the electrodynamics of the high {Tc} cuprates and the organic charge transfer salts is unconventional. The high {Tc}`s show a Drude peak with an anomalous temperature and frequency dependent scattering rate for the in-plane conductivity, while normal to the planes they are almost insulating. In the organics, the transport currents are carried by a narrow collective mode coupled to phonons. 44 refs., 7 figs.

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

    SciTech Connect

    Suenaga, Masaki

    1998-11-01

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

  2. Electronic excitations in electron-doped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Unger, P.; Fulde, P.

    1995-04-01

    We calculate the electronic single-particle spectrum of an electron-doped cuprate superconductor such as Nd2-xCexCuO4-y. The dynamics of holes in the Cu-O planes is described by the extended Hubbard or Emery model. We consider the system at half-filling (one hole per unit cell, nh=1) and in the case of electron doping where the ground state is paramagnetic. The projection technique of Mori and Zwanzig is applied to derive the equations of motion for the Green's functions of Cu and O holes. These equations are solved self-consistently as in a previous calculation, where we considered the case of hole doping. At half-filling the system exhibits a charge-transfer gap bounded by Zhang-Rice singlet states and the upper Hubbard band. Upon electron doping the upper Hubbard band crosses the Fermi level and the system becomes metallic. With increasing electron doping the singlet band loses intensity and finally vanishes for nh=0. The corresponding spectral weight is transferred to the upper Hubbard band, which becomes a usual tight-binding band for zero hole concentration. The shape of the flat band crossing the Fermi level fits well to angle-resolved photoemission spectra of Nd2-xCexCuO4-y for x=0.15 and 0.22. Furthermore, our findings are in excellent agreement with exact diagonalization studies of 2×2 CuO2 cluster with periodic boundary conditions.

  3. Aspects of nodal quasiparticle transport in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Smith, Michael F.

    Various low-temperature thermodynamic and transport properties of high TC superconductors at temperatures well below TC are studied theoretically under the assumption that the low-energy excited states can be regarded as independent Bogolubov quasiparticles near the nodes of the superconducting order parameter. In the limiting case of temperatures well above that corresponding to the impurity scattering rate, a Boltzmann-equation description of the quasiparticle distribution is used to study thermal and electrical transport for several scattering mechanisms. In particular, the dominant scattering mechanism for the relaxation of microwave electrical currents well below TC is identified, and the observed temperature dependence of the microwave conductivity data in optimally-doped YBa2Cu3O7-delta thus explained. The Knight shift and nuclear spin relaxation rate at temperatures well above the impurity scattering rate are also calculated and compared with available data. In the opposite limiting case of temperatures well below that corresponding to the impurity scattering rate, the sound attenuation and electron-phonon heat transfer rate are calculated. A model for the electron-phonon interaction in square-lattice tight-binding materials is developed and used to explain the huge measured anisotropy of the normal-state sound attenuation in the unconventional superconductor Sr2RuO4 and to rule out certain candidates for the order parameter symmetry of this material. A calculation of the electron-phonon heat transfer rate for d-wave superconductors gives the dependence of this quantity on various material parameters. Finally, the result for the electron-phonon heat transfer rate is used to explain the origin of the anomalous downturns in the thermal conductivity that have been observed in both the normal and superconducting state of cuprate superconductors, most notably in Pr2-xCe xCuO7-delta.

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

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

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

  5. Liquid-gated superconductor-insulator transition in an electron-doped cuprate

    NASA Astrophysics Data System (ADS)

    Zeng, Shengwei; Huang, Zhen; Bao, Nina; Lv, Weiming; Liu, Zhiqi; Herng, T. S.; Gopinadhan, K.; Jian, Linke; Ding, J.; Venkatesan, T.; Ariando, Ariando

    2014-03-01

    Doping charge carriers will causes the change of cuprates from antiferromagnetic Mott insulators to high-Tc superconductors. Continuous changing of carrier density is necessary to understand the nature of such phase transition, and thus, further our understanding of cuprate superconductors. Electric field-effect doping, especially with electronic double layer transistors (EDLT) configuration which use ionic liquids (ILs) and polymer electrolyte as the gate dielectrics, is a potential avenue for this investigation and it has been shown its effectiveness in inducing phase transition in strongly correlated electron system. Owing to EDLT, superconductor-to-insulator transition (SIT) has been observed in hole-doped cuprates La2-xSrxCuO4 and YBa2Cu3Oy. Here we use EDLT to tune the carrier density in electron-doped cuprates Pr2-xCexCuO4 ultrathin films and cause the sample evolves from a superconducting state to an insulating state. This present results could be helpful to study SIT between electron- and hole-doped cuprates.

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

    SciTech Connect

    Miller, D.

    1993-09-01

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

  7. Silver sheathing of high-Tc superconductor wires

    NASA Astrophysics Data System (ADS)

    Wu, C. T.; Risch, G. A.; Poeppel, R. B.; Goretta, K. C.; Danyluk, S.; Herro, H. M.

    1990-10-01

    The properties of Ag sheaths on high-temperature super-conductors are examined. Ag is chemically compatible with YBa2Cu3O(x) and Bi-based superconductors can be safely coprocessed with them. Residual stresses created by differences in thermal expansion coefficients are favorable and can be controlled by proper annealing. Although Ag forms low-resistance contact with high temperature superconductors, it is not certain that effective cryogenic stabilization by Ag can occur at 77 K and above.

  8. Gap anisotropy and van Hove singularities in high {Tc} superconductors

    SciTech Connect

    Bok, J.; Bouvier, J.

    1996-12-31

    The authors compute the superconducting gap {Delta}{sub {rvec k}} using a simple band structure of the CuO{sub 2} planes in the high Tc materials. They suppose that for materials with doping corresponding to maximum {Tc}, the van Hove singularities lie close to the Fermi level as is confirmed by many photoemission experiments. They use a electron-photon interaction with weak screening, they find a strong gap anisotropy. For Bi 2212, {Delta} is maximum along the 100 and 010 directions with values between 20 and 30 meV and minimum along 110 with values between 0 and 10 meV. They use this anisotropic gap to compute the quasi-particle excitations density of states and the tunneling current-voltage I(V) characteristic for N-I-S and S-I-S junctions. This model agrees remarkably well with recent experiments of tunneling spectroscopy in high {Tc} cuprates.

  9. Numerical analyses of levitation force and flux creep on high [Tc] superconductor

    SciTech Connect

    Tsuchimoto, M.; Kojima, T.; Takeuchi, H.; Honma, T. . Dept. of Electrical Engineering)

    1993-11-01

    Large levitation force and a stable equilibrium are obtained with a permanent magnet and a bulk high [Tc] superconductor (HTSC). Evaluation of the levitation force is important for many applications, such as magnetically levitated vehicles, magnetic bearing, flywheel and linear drive. Levitation force between a permanent magnet and a high [Tc] superconductor is examined by using two numerical methods. The levitation force to vertical direction is calculated by using the critical state model. Stiffness of restoring force to horizontal direction is calculated by using a frozen-in field model. Numerical solutions agree well with experimental results. Dynamic properties of the levitation force are also analyzed by combining the two methods.

  10. Measuring Thermal Diffusivity Of A High-Tc Superconductor

    NASA Technical Reports Server (NTRS)

    Powers, Charles E.; Oh, Gloria; Leidecker, Henning

    1992-01-01

    Technique for measuring thermal diffusivity of superconductor of high critical temperature based on Angstrom's temperature-wave method. Peltier junction generates temperature oscillations, which propagate with attenuation up specimen. Thermal diffusivity of specimen calculated from distance between thermocouples and amplitudes and phases of oscillatory components of thermocouple readings.

  11. Laser surface interaction of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  12. Flux lattice melting in the high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Bishop, D. J.; Gammel, P. L.; Schneemeyer, L. F.

    1989-01-01

    One of the important issues for technological application of the high temperature superconductors is their behavior in a magnetic field. A variety of experiments including electrical transport, mechanical oscillators, and magnetic decoration have suggested that these magnetic properties will make applications more difficult than originally anticipated. These experiments and their results are briefly discussed.

  13. Transport anomalies and quantum criticality in electron-doped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Yu, Heshan; He, Ge; Hu, Wei; Yuan, Jie; Zhu, Beiyi; Jin, Kui

    2016-06-01

    Superconductivity research is like running a marathon. Three decades after the discovery of high-Tc cuprates, there have been mass data generated from transport measurements, which bring fruitful information. In this review, we give a brief summary of the intriguing phenomena reported in electron-doped cuprates from the aspect of electrical transport as well as the complementary thermal transport. We attempt to sort out common features of the electron-doped family, e.g. the strange metal, negative magnetoresistance, multiple sign reversals of Hall in mixed state, abnormal Nernst signal, complex quantum criticality. Most of them have been challenging the existing theories, nevertheless, a unified diagram certainly helps to approach the nature of electron-doped cuprates.

  14. Flux flow and flux dynamics in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Bennett, L. H.; Turchinskaya, M.; Swartzendruber, L. J.; Roitburd, A.; Lundy, D.; Ritter, J.; Kaiser, D. L.

    1991-01-01

    Because high temperature superconductors, including BYCO and BSSCO, are type 2 superconductors with relatively low H(sub c 1) values and high H(sub c 2) values, they will be in a critical state for many of their applications. In the critical state, with the applied field between H(sub c 1) and H(sub c 2), flux lines have penetrated the material and can form a flux lattice and can be pinned by structural defects, chemical inhomogeneities, and impurities. A detailed knowledge of how flux penetrates the material and its behavior under the influence of applied fields and current flow, and the effect of material processing on these properties, is required in order to apply, and to improve the properties of these superconductors. When the applied field is changed rapidly, the time dependence of flux change can be divided into three regions, an initial region which occurs very rapidly, a second region in which the magnetization has a 1n(t) behavior, and a saturation region at very long times. A critical field is defined for depinning, H(sub c,p) as that field at which the hysteresis loop changes from irreversible to reversible. As a function of temperature, it is found that H(sub c,p) is well described by a power law with an exponent between 1.5 and 2.5. The behavior of H(sub c,p) for various materials and its relationship to flux flow and flux dynamics are discussed.

  15. Vortices and charge order in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Einenkel, Matthias; Meier, Hendrik; Pépin, Catherine; Efetov, Konstantin B.

    2015-03-01

    We theoretically investigate the vortex state of the cuprate high-temperature superconductors in the presence of magnetic fields. Assuming the recently derived nonlinear σ-model for fluctuations in the pseudogap phase, we find that the vortex cores consist of two crossed regions of elliptic shape, in which a static charge order emerges. Charge density wave order manifests itself as satellites to the ordinary Bragg peaks directed along the axes of the reciprocal copper lattice. Quadrupole density wave (bond order) satellites, if seen, are predicted to be along the diagonals. The intensity of the satellites should grow linearly with the magnetic field, in agreement with the result of recent experiments.

  16. Vortices and charge order in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Einenkel, M.; Meier, H.; Pépin, C.; Efetov, K. B.

    2014-08-01

    We theoretically investigate the vortex state of the cuprate high-temperature superconductors in the presence of magnetic fields. Assuming the recently derived nonlinear σ-model for fluctuations in the pseudogap phase, we find that the vortex cores consist of two crossed regions of elliptic shape, in which a static charge order emerges. Charge density wave order manifests itself as satellites to the ordinary Bragg peaks directed along the axes of the reciprocal copper lattice. Quadrupole density wave (bond order) satellites, if seen, are predicted to be along the diagonals. The intensity of the satellites should grow linearly with the magnetic field, in agreement with the result of recent experiments.

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

    SciTech Connect

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

    1996-08-01

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

  18. High- Tc superconductor characteristics control by ion implantation

    NASA Astrophysics Data System (ADS)

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

    1989-03-01

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

  19. Predicted midgap states in unconventional superconductors and their numerous implications for high-[Tc] superconductors

    SciTech Connect

    Hu, C.R. . Dept. of Physics)

    1998-12-20

    A fundamental topological consequence of the unconventional (i.e., non-s-wave) pairing symmetry of high-[Tc] superconductors (HTSC's) is the existence of midgap (quasi-particle) states (MS's) bound to surface,m interfaces and other locations. This prediction by the author has most-likely solved a decade-old puzzle, viz., the ubiquitous observation of a zero-bias conductance peak (ZBCP) in tunneling experiments performed on HTSC's. There are also numerous other novel consequences of these MS's, predicted by various researchers, including a new Josephson critical current term; an (already observed) low-temperature splitting of the ZBCP due possibly to a spontaneous breaking of the time-reversal symmetry at a sample surface; a new explanation of the paramagnetic Meissner effect; and a giant magnetic moment, etc. Here the author will review the physical origin of the MS's, the several extensions of the original idea and the many novel consequences of these MS's, some of which have been investigated quantitatively and some others only deduced in qualitative terms so far.

  20. Feasibility of far-infrared radiation modulators using high-{Tc} superconductors

    SciTech Connect

    Zhang, Z.M.

    1996-12-31

    The potential of using high-{Tc} superconductors as intensity modulators for far-infrared radiation is investigated in this work. Reflectance and transmittance for several design structures are computed using the published optical constants of the superconductor YBa{sub 2}Cu{sub 3}O{sub 7} and substrate materials. Notable differences in the reflectance and transmittance between the superconducting state and the normal state are illustrated. The best results are obtained based on the reflectance of thin films (10 nm--50 nm thick) on thin substrates (less than 100 {micro}m thick) and for radiation incident on the substrate. This study demonstrates that high-{Tc} superconductive thin films can be used to build far-infrared radiation modulators. Future experimental study is recommended in order to materialize this promising thermooptical device.

  1. Theoretical Analysis on the Band Structure Variance of the Electron Doped 1111 Iron-based Superconductors

    NASA Astrophysics Data System (ADS)

    Suzuki, K.; Usui, H.; Iimura, S.; Sato, Y.; Matsuishi, S.; Hosono, H.; Kuroki, K.

    We perform first principles band calculation of electron doped iron-based superconductors adopting the virtual crystal approximation. We find that when electrons are doped by element substitution in the blocking layer, the band structure near the Fermi level is affected due to the increase of the positive charge in the layer. On the other hand, when Fe in the conducting layer is substituted by Co, the band structure is barely affected. This difference should be a key factor in understanding the phase diagram of the heavily doped electron doped systems LnFeAsO1-xHx.

  2. Scanning instrumentation for measuring magnetic field trapping in high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Sisk, R. C.; Helton, A. J.

    1993-01-01

    Computerized scanning instrumentation measures and displays trapped magnetic fields across the surface of high Tc superconductors at 77 K. Data are acquired in the form of a raster scan image utilizing stepping motor stages for positioning and a cryogenic Hall probe for magnetic field readout. Flat areas up to 45 mm in diameter are scanned with 0.5-mm resolution and displayed as false color images.

  3. Designs and analyses of flywheel energy storage systems using high- Tc superconductor bearings

    NASA Astrophysics Data System (ADS)

    Sung, T. H.; Han, S. C.; Han, Y. H.; Lee, J. S.; Jeong, N. H.; Hwang, S. D.; Choi, S. K.

    2002-06-01

    A horizontal axle-type flywheel energy storage system was manufactured using high- Tc superconductor bearings. The system running in a vacuum chamber mainly consists of a composite flywheel rotor, superconductor bearings, a motor/generator and its controller. The present system was designed to have an energy storage capacity of 440 W h at its operating speed of 40,000 rpm, which is way above two rigid body mode critical speeds. Rotordynamic analysis was performed on this system. Another flywheel system with vertical axis was conceptualized, which uses a hybrid superconductor bearing set to carry the wheel part load. The models for permanent magnet parts of the bearing set were designed using numerical magnetostatic analysis tool. The vertical magnetic force characteristics of the bearing set were experimentally measured. These results were discussed in regard of application to the flywheel system with a passive hybrid superconductor bearing set.

  4. Electronic structure Fermi liquid theory of high Tc superconductors: Comparison of predictions with experiments

    NASA Technical Reports Server (NTRS)

    Yu, Jaejun; Freeman, A. J.

    1991-01-01

    Predictions of local density functional (LDF) calculations of the electronic structure and transport properties of high T(sub c) superconductors are presented. As evidenced by the excellent agreement with both photoemission and positron annihilation experiments, a Fermi liquid nature of the 'normal' state of the high T(sub c) superconductors become clear for the metallic phase of these oxides. In addition, LDF predictions on the normal state transport properties are qualitatively in agreement with experiments on single crystals. It is emphasized that the signs of the Hall coefficients for the high T(sub c) superconductors are not consistent with the types of dopants (e.g., electron-doped or hole-doped) but are determined by the topology of the Fermi surfaces obtained from the LDF calculations.

  5. Development and study of high-Tc superconductor conductive polymer assemblies

    NASA Astrophysics Data System (ADS)

    Schougaard, Steen Brian

    2002-01-01

    This dissertation presents the development and study of organic polymeric conductor/High-Tc superconductor bilayers, for exploration of the superconductor proximity effect. A major obstacle to this research is the instability of the High-Tc superconductor towards H2O and CO2 as it is necessary to create hybrid structures where the two conductors have intimate contact. For this reason, a study of the corrosion characteristics of the RBa2Cu3O 7 (R=Y, Eu, Nd) series was undertaken. In this study, R=Nd was shown to have enhanced corrosion resistance. In an effort to develop chemical processing methods that allow for the production of intimate contact between the cuprate superconductor and the conductive polymer systems, a study of alkyl amine adsorbed onto the surface of the superconductor is presented. In the electrochemical part of the study, alkyl amine ferrocene adsorbed onto the surface revealed that the amines are strongly adhered to the superconductor while still allowing electrons to pass from the superconductor to the ferrocene moiety. The self-assembled monolayer (SAM) structure of CF3(CF2)3(CH2) 11NH2 atop the superconductor was elucidated by employing several techniques, including atomic scale atomic force microscopy (AFM). A novel multistep bilayer sample preparation protocol is presented involving thin film fabrication by pulsed laser deposition (PLD), patterning by shadow mask ablation, sample thinning by scanning probe and electropolymerization of the polymer. Scanning probe thinning yields a smooth superconductor surface, a known superconductor thickness, and if a blocking layer is employed prior to thinning, the localization of polymer growth. Studies of the response of a bilayer structure of Y0.6Ca 0.4Ba1.6La0.4 Cu3O7/poly pyrrole to polymer redox cycling showed a semi-reversible suppression of transition temperature qualitatively consistent with a combination of corrosion and superconductor proximity effect. Quantitative analysis in the framework of

  6. Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-Tc Superconductor

    SciTech Connect

    Chen, Y.

    2010-05-03

    We report the discovery of a self-doped multi-layer high T{sub c} superconductor Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub 8}F{sub 2} (F0234) which contains distinctly different superconducting gap magnitudes along its two Fermi surface(FS) sheets. While formal valence counting would imply this material to be an undoped insulator, it is a self-doped superconductor with a T{sub c} of 60K, possessing simultaneously both electron- and hole-doped FS sheets. Intriguingly, the FS sheet characterized by the much larger gap is the electron-doped one, which has a shape disfavoring two electronic features considered to be important for the pairing mechanism: the van Hove singularity and the antiferromagnetic ({pi}/a, {pi}/a) scattering.

  7. X-ray diffuse scattering experiments on bismuth based high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Comes, R.; Izquierdo, M.; Megtert, S.; Albouy, P. A.; Avila, J.; Valbuena, M. A.; Gu, G.; Abell, J. S.; Asensio, M. C.

    2007-09-01

    A detailed X-ray diffuse scattering study of the recently found two dimensional (2D) displacive short range order (SRO) superstructure, with doubled periodicity along the orthorhombic a direction from the high Tc superconductors Bi 2Sr 2CaCu 2O 8+ δ (BISCO-2212) is reported. The investigation has been extended to high and low temperatures for optimally doped crystals, to crystals with different doping levels and to the one layer compound Bi 2Sr 2CuO 6+ δ (BISCO-2201). The most striking feature is that both, the intensity of the diffuse scattering and the extent of the 2DSRO vary with doping as the critical temperature, Tc. These findings show that these short range ordering features are of importance for a better understanding of high Tc materials, at least those from the BISCO family.

  8. X-ray diffuse scattering experiments from bismuth based high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Izquierdo, M.; Megtert, S.; Albouy, P. A.; Avila, J.; Valbuena, M. A.; Gu, G.; Abell, J. S.; Yang, G.; Asensio, M. C.; Comes, R.

    2007-03-01

    A detailed X-ray diffuse scattering study of the recently found two dimensional (2D) displacive short range order (SRO) superstructure, with doubled periodicity along the orthorhombic a direction from the high Tc superconductors Bi2Sr2CaCu2O8+δ(BISCO-2212) is reported. The investigation has been extended to high and low temperatures for optimally doped crystals, to crystals with different doping levels and to the one layer compound Bi2Sr2CaCuO6+δ (Bi-2201). The most striking feature is that both, the intensity of the diffuse scattering and the extent of the 2DSRO vary with doping as the critical temperature, Tc. These findings show that these short range ordering features are of importance for a better understanding of high Tc materials, at least those from the BISCO family.

  9. The Electronic Structure of the HighTc Superconductors Obtained by Angle-Resolved Photoemission

    NASA Astrophysics Data System (ADS)

    Campuzano, Juan-Carlos; Randeria, Mohit; Norman, Michael; Ding, Hong

    In conclusion, we hope that we have been able to convey to the readers the exciting new physics that has come out of ARPES studies of the high Tc superconductors. What is really astonishing is the range of issues on which ARPES has given new insights: from non-Fermi liquid behavior with a Fermi surface, to the symmetry of the superconducting order parameter, to the development of a Fermi surface in a doped Mott-insulator and the pseudo-gap phenomena in the underdoped cuprates.

  10. Emergence of superconductivity in HighTc copper oxide superconductors via two crossovers

    NASA Astrophysics Data System (ADS)

    Chatterjee, Utpal; Norman, Mike; Randeria, Mohit; Rosenkranz, Stephan; Campuzano, Juan Carlos

    2011-03-01

    From our detailed ARPES measurements on BISCO 2212 High Tc Superconductors we found that unlike in conventional superconductors, where there is a single temperature scale Tc separating the normal from the superconducting state, HTSCs exhibit with two additional temperature scales. One is T*, below which electronic excitations are gapped. And the other one is Tcoh, below which electronic states are long-lived. We observed that T* and Tcoh change strongly with doping. They cross each other near optimal doping. There is a region in the normal state where the single particle excitations are gapped as well as coherent. Quite remarkably, this is the region from which superconductivity with highest Tc emerges. Our experimental finding that the two crossover lines intersect is not consistent with a ``single quantum critical'' point near optimal doping, rather it is more naturally consistent with theories of superconductivity for doped Mott insulators.

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

    SciTech Connect

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

    1991-04-01

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

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

    SciTech Connect

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

    1991-04-01

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

  13. Dynamical scaling exponents in Josephson networks of high-{Tc} superconductors

    SciTech Connect

    Prester, M.

    1996-12-31

    Universal aspects of inhomogeneous transport was studied in natural Josephson junction networks. The weak link networks of polycrystalline high-{Tc} superconductors were found perfectly suitable for quantitative investigation of cluster growth phenomena in percolation (or fractal) networks. The authors report the experimental results of their studies of I-V (or I-dV/dI) characteristics of the two high-{Tc} families, YBCO and BSCCO. The onset of dissipation, represented by these characteristics, is interpreted as a critical phenomenon, i.e., as a current-induced phase transition. The cluster growth which underlies this phase transition is analyzed by the use of an appropriate model. The model links the non-Ohmic weak link network with classical Ohmic percolation networks (e.g., random resistor network). As a result, they were able to determine the values of appropriate dynamical exponents (exponent t with high precision, t = 2 {+-} 0.1, and exponent s approximately, s {approx} 0.7), as well as to assign the dissipative ranges inside which the corresponding cluster dynamics takes place. It is therefore concluded that the high-{Tc} weak link networks represent a natural mesoscopic-scale system convenient for systematic investigation of the transport critical phenomena.

  14. Microstructure of RABiTS-type high-Tc superconductor coated conductors

    NASA Astrophysics Data System (ADS)

    Yang, Chau-Yun

    2000-11-01

    The objective of this dissertation was to characterize quantitatively the microstructure of the high Tc superconductor and buffer layer materials in prototype superconducting coated conductor tapes with the goal of understanding the microstructure-property relationships that determine their suitability for large scale applications of high Tc superconductivity. The coated conductor materials were fabricated by the rolling-assisted biaxially-textured substrates (RABiTS) approach at Oak Ridge National Laboratory. YBa2Cu 3O7-δ (YBCO), a high Tc superconductor, was deposited on various combinations of oxide buffer layers on RABiT metal tape substrates. Scanning and transmission electron microscopy, x-ray diffraction, atomic force microscopy, and Auger electron spectroscopy were used in combination to study the microstructure in the superconductor and buffer layers. The electromagnetic properties of the samples were determined in collaborations with researchers in the UW Applied Superconductivity Center and Oak Ridge National Laboratory. Buffer layers deposited by both physical vapor deposition and chemical solution deposition methods showed a wide range of microstructures and surface topographies. Electron-beam evaporated yttia stabilized-zirconia (YSZ) buffer layers were composed of loosely packed, slab- shaped columnar grains with rectangular cross sections and average dimensions of 10nm by 50nm by the film thickness. Magnetron sputtered YSZ had a smooth and featureless surface and a 50nm diameter cell structure defined by the threading dislocations. Solution deposited buffer layers were locally dense, but showed larger scale surface roughness of ~50 nm in some cases. The YBCO films grown epitaxially on these buffer layers had similar microstructures and properties, however. With one exception, the YBCO layers possessed island structures. The average misorientation angles of the boundaries that defined the islands were largely between 2 and 4° in the high critical

  15. Two-dimensional superconductor-insulator quantum phase transitions in an electron-doped cuprate

    NASA Astrophysics Data System (ADS)

    Zeng, S. W.; Huang, Z.; Lv, W. M.; Bao, N. N.; Gopinadhan, K.; Jian, L. K.; Herng, T. S.; Liu, Z. Q.; Zhao, Y. L.; Li, C. J.; Harsan Ma, H. J.; Yang, P.; Ding, J.; Venkatesan, T.; Ariando

    2015-07-01

    We use an ionic liquid-assisted electric-field effect to tune the carrier density in an electron-doped cuprate ultrathin film and cause a two-dimensional superconductor-insulator transition (SIT). The low upper critical field in this system allows us to perform magnetic-field (B)-induced SIT in the liquid-gated superconducting film. Finite-size scaling analysis indicates that SITs induced both by electric and by magnetic fields are quantum phase transitions and the transitions are governed by percolation effects—quantum mechanical in the former and classical in the latter cases. Compared to the hole-doped cuprates, the SITs in the electron-doped system occur at critical sheet resistances (Rc) much lower than the pair quantum resistance RQ=h /(2e ) 2=6.45 k Ω , suggesting the possible existence of fermionic excitations at finite temperatures at the insulating phase near the SITs.

  16. Composite Fermions and Quartets in Optical Traps and in High-Tc Superconductors

    SciTech Connect

    Kagan, M. Yu.; Brodsky, I. V.; Klaptsov, A. V.; Efremov, D. V.; Combescot, R.; Leyronas, X.

    2006-09-07

    We consider a possibility of the creation of composite fermions in optical traps and in high-Tc superconductors. For optical traps we study a model of Fermi-Bose mixture with resonant attraction between particles of different sorts. In this case a pairing between fermion and boson of the type bf is possible. This pairing corresponds to creation of composite fermions. At low temperatures and equal densities of fermions and bosons composite fermions are further paired in quartets. In the 2D case we exactly solve Skorniakov-Ter-Martirosian type of integral equations and find the binding energies of two bosons plus one fermion fbb and two bosons plus two fermions fbfb. For high-Tc superconductors we consider a quartet -- a bound state of two composite holes {delta} =< hh >, where each composite hole h = fb consists of a spinon and a holon bound by the stringlike potential. Our investigations are important for recent experiments on the observation of weakly bound composite fermions and bosons in optical traps in the regime of Feshbach resonance.

  17. NMR investigation of iron-selenide and iron-arsenide high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Imai, Takashi

    2012-02-01

    We have investigated the electronic, magnetic, and superconducting properties of the iron-selenide high Tc superconductor KxFe2-ySez (Tc=33 K) with ^77Se NMR [1]. We will compare the results with those observed for FeSe in ambient and applied pressures (Tc>9 K) [2], and with iron-arsenides [3]. Similarities and dissimilarities will be pointed out, with primary focus on the anomalous normal state properties. Our latest work on KxFe2-ySez was carried out in collaboration with D. Torchetti, M. Fu, D. Christensen, K. Nelson (McMaster), H. Lei, and C. Petrovic (Brookhaven National Lab).[4pt] [1] D. Torchetti et al., PR B83, 104508 (2011).[0pt] [2] T. Imai et al. PRL 102, 177005 (2009).[0pt] [3] F.L. Ning et al., PRL 104, 037001 (2010); JPSJ 78, 103711 (2009).

  18. Critical current measurements of high Tc superconductors in a scanning low temperature cryostat

    SciTech Connect

    Telschow, K.L.; O'Brien, T.K.

    1991-01-01

    Maintaining uniformity of properties over long distances is one of the fabrication problems encountered with the new high {Tc} superconductors. Uniform properties are crucial in long tapes or wires with high critical current since local nonuniformities can limit the current carrying capacity of the whole piece. Transport critical currents in high {Tc} superconductors are conventionally measured with the contact 4-point probe DC current-voltage technique. This technique requires contact with the sample and and spatially averages over the region between the two voltage contacts. Two techniques have been used to infer the critical state model. The first uses the net magnetization of a suitably shaped sample in an external magnetic field. The second combines a DC magnetic field with AC induced currents to infer spatial flux profiles. The AC magnetization technique offers an advantage in that it is noncontacting; however, it also averages the measurement over a large area and requires that the sample be shaped and positioned such that it exhibits zero demagnetizing factor. This paper describes a measurement technique and a scanning cryostat assembly that are capable of determining local critical current in a tape or wire with high resolution and without any direct sample electrical contact. A small compensated coil was used to induce AC currents in slab-shaped samples. The coil was situated near the surface on one side of the slab. With this method, the AC probe can be used as a noncontacting dissipation probe, replacing the voltage probe in the 4-point contact method, when an externally driven transport current is used, or by itself as a local critical state generator and dissipation detector. The results are shown to be meaningful even when the internal magnetic field is not uniform due to shape demagnetizing effects. 10 refs., 5 figs.

  19. Charge ordering in the electron-doped superconductor Nd(2-x)Ce(x)CuO₄.

    PubMed

    da Silva Neto, Eduardo H; Comin, Riccardo; He, Feizhou; Sutarto, Ronny; Jiang, Yeping; Greene, Richard L; Sawatzky, George A; Damascelli, Andrea

    2015-01-16

    In cuprate high-temperature superconductors, an antiferromagnetic Mott insulating state can be destabilized toward unconventional superconductivity by either hole or electron doping. In hole-doped (p-type) cuprates, a charge ordering (CO) instability competes with superconductivity inside the pseudogap state. We report resonant x-ray scattering measurements that demonstrate the presence of charge ordering in the n-type cuprate Nd(2-x)Ce(x)CuO4 near optimal doping. We find that the CO in Nd(2-x)Ce(x)CuO4 occurs with similar periodicity, and along the same direction, as in p-type cuprates. However, in contrast to the latter, the CO onset in Nd(2-x)Ce(x)CuO4 is higher than the pseudogap temperature, and is in the temperature range where antiferromagnetic fluctuations are first detected. Our discovery opens a parallel path to the study of CO and its relationship to antiferromagnetism and superconductivity. PMID:25593186

  20. Synthesis of high-Tc superconductors at Uppsala University: ceramics and crystal growth

    NASA Astrophysics Data System (ADS)

    Lundström, Torsten; Lönnberg, Bertil; Tergenius, Lars-Erik

    1991-07-01

    Synthetic and process studies of the new high-Tc super-conductors are carried out using the methods of powder technology. The equipment for these studies at the Institute of Chemistry, University of Uppsala is described. The laboratory is equipped with jaw crusher, various mills, powder mixer, spray dryer and several sintering furnaces. The laboratory has excellent facilities for powder characterization, such as a semi-automatic image analyzer, a system for X-ray line broadening analysis, BET apparatus, sample divider and a sieving machine. Single-crystal growth experiments are also reported. Single crystals of YBa2Cu3O7 and Bi2Sr2CaCu2O8 were grown by the off-stoichiometric method. The largest crystals of YBa2Cu3O7 were obtained with the soaking temperature of 980°C and a cooling rate of 2°C h-1. A soaking temperature of 925°C and a cooling rate of 40°C h-1 produced the largest Bi2Sr2CaCu2O8 single crystals. A single crystal examination showed that the structure of Bi2Sr2CaCu2O8 is incommensurate along the b axis. The lattice parameters were a = 5.40 Å, b = 25.25 Å, c = 30.62 Å.

  1. Unconventional charge order in a co-doped high-Tc superconductor.

    PubMed

    Pelc, D; Vučković, M; Grafe, H-J; Baek, S-H; Požek, M

    2016-01-01

    Charge-stripe order has recently been established as an important aspect of cuprate high-Tc superconductors. However, owing to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent high-temperature state. Here we report on the discovery of an unconventional ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La1.8-xEu0.2SrxCuO4. We use three complementary experiments-nuclear quadrupole resonance, nonlinear conductivity and specific heat-to demonstrate that the order appears through a sharp phase transition and exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is a state, which preserves translational symmetry: a charge nematic. We thus resolve the process of charge-stripe development in cuprates, show that this nematic phase is distinct from high-temperature pseudogap and establish a link with other strongly correlated electronic materials with prominent nematic order. PMID:27605152

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

    PubMed Central

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

    2016-01-01

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

  3. Electron pockets in the Fermi surface of hole-doped high-Tc superconductors.

    PubMed

    LeBoeuf, David; Doiron-Leyraud, Nicolas; Levallois, Julien; Daou, R; Bonnemaison, J-B; Hussey, N E; Balicas, L; Ramshaw, B J; Liang, Ruixing; Bonn, D A; Hardy, W N; Adachi, S; Proust, Cyril; Taillefer, Louis

    2007-11-22

    High-temperature superconductivity in copper oxides occurs when the materials are chemically tuned to have a carrier concentration intermediate between their metallic state at high doping and their insulating state at zero doping. The underlying evolution of the electron system in the absence of superconductivity is still unclear, and a question of central importance is whether it involves any intermediate phase with broken symmetry. The Fermi surface of the electronic states in the underdoped 'YBCO' materials YBa2Cu3O(y) and YBa2Cu4O8 was recently shown to include small pockets, in contrast with the large cylinder that characterizes the overdoped regime, pointing to a topological change in the Fermi surface. Here we report the observation of a negative Hall resistance in the magnetic-field-induced normal state of YBa2Cu3O(y) and YBa2Cu4O8, which reveals that these pockets are electron-like rather than hole-like. We propose that these electron pockets most probably arise from a reconstruction of the Fermi surface caused by the onset of a density-wave phase, as is thought to occur in the electron-doped copper oxides near the onset of antiferromagnetic order. Comparison with materials of the La2CuO4 family that exhibit spin/charge density-wave order suggests that a Fermi surface reconstruction also occurs in those materials, pointing to a generic property of high-transition-temperature (T(c)) superconductors. PMID:18033293

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

    NASA Astrophysics Data System (ADS)

    Riggs, Scott Chandler

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

  5. Rigid levitation, flux pinning, thermal depinning and fluctuation in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Brandt, E. H.

    1991-01-01

    Here, the author shows that the strong velocity-independent frictional force on a levitating superconductor and on any type-II superconductor moving in a homogeneous magnetic field is caused by pinning and depinning of the magnetic flux lines in its interior. Levitation may thus be used to investigate the pinning properties of a superconductor, and friction in a superconductor bearing may be minimized by choosing appropriate materials and geometries.

  6. Phase transition between two kinds of flux-line lattice in high- Tc superconductors in a tilted field

    NASA Astrophysics Data System (ADS)

    Nonomura, Y.; Hu, X.

    2004-10-01

    Structures of flux-line lattices (FLL) in vortex states of high- Tc superconductors in a tilted field are directly studied by Monte Carlo simulations of the three-dimensional anisotropic XY model, where only Josephson couplings are considered between superconducting layers. A nontrivial structural transition between the Josephson-dominant and Abrikosov-dominant FLL phases occurs as the tilting angle of the external field is increased at low enough temperatures. A similar phase transition is observed by varying the anisotropy parameter with a fixed external field. A finite latent heat at the transition point indicates that this phase transition is of first order.

  7. Electron-Doped Sr2IrO4 : An Analogue of Hole-Doped Cuprate Superconductors Demonstrated by Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Yan, Y. J.; Ren, M. Q.; Xu, H. C.; Xie, B. P.; Tao, R.; Choi, H. Y.; Lee, N.; Choi, Y. J.; Zhang, T.; Feng, D. L.

    2015-10-01

    Sr2Ir O4 was predicted to be a high-temperature superconductor upon electron doping since it highly resembles the cuprates in crystal structure, electronic structure, and magnetic coupling constants. Here, we report a scanning tunneling microscopy/spectroscopy (STM/STS) study of Sr2Ir O4 with surface electron doping by depositing potassium (K) atoms. We find that as the electron doping increases, the system gradually evolves from an insulating state to a normal metallic state, via a pseudogaplike phase, and a phase with a sharp, V-shaped low-energy gap with about 95% loss of density of state (DOS) at EF . At certain K coverage (0.5-0.6 monolayer), the magnitude of the low-energy gap is 25-30 meV, and it closes at around 50 K. Our observations show that the electron-doped Sr2Ir O4 remarkably resembles hole-doped cuprate superconductors.

  8. Sintering of bulk high- Tc superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B. ); Nash, A.S. )

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  9. Sintering of bulk high-{Tc} superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B.; Nash, A.S.

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  10. Bearing design for flywheel energy storage using high-TC superconductors

    DOEpatents

    Hull, John R.; Mulcahy, Thomas M.

    2000-01-01

    A high temperature superconductor material bearing system (38) This system (38) includes a rotor (50) having a ring permanent magnet (60), a plurality of permanent magnets (16, 20 and 70) for interacting to generate levitation forces for the system (38). This group of magnets are a push/pull bearing (75). A high temperature superconductor structure (30) interacts with the ting permanent magnet (60) to provide stabilizing forces for the system (38).

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

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

  12. Influence of lateral displacement on the levitation performance of a magnetized bulk high-Tc superconductor magnet

    NASA Astrophysics Data System (ADS)

    Liu, W.; Wang, J. S.; Ma, G. T.; Zheng, J.; Tuo, X. G.; Li, L. L.; Ye, C. Q.; Liao, X. L.; Wang, S. Y.

    2012-03-01

    Compared with the permanent magnet, the magnetized bulk high-Tc superconductor magnet (MBSCM) can trap higher magnetic field due to its strong flux pinning ability, so it is a good candidate to improve the levitation performance of high-Tc superconductive (HTS) maglev system. The trapped magnetic flux of a MBSCM is sustained by the inductive superconducting current produced by the magnetizing process and is susceptible to the current intensity as well as configuration. In the HTS maglev system, the lateral displacement is an important process to change the superconducting current within a MBSCM and then affects its levitation performance, which is essential for the traffic ability in curve-way, the loading capacity of lateral impact and so on. The research about influence of lateral displacement on the levitation performance of MBSCM is necessary when MBSCM is applied on the HTS maglev vehicle. The experimental investigations about the influence of lateral displacement on the levitation performance of a MBSCM with different trapped fluxes and applied fields are processed in this article. The analyses and conclusions of this article are useful for the practical application of MBSCM in HTS maglev system.

  13. Momentum-Resolved Electronic Structure of the High-Tc Superconductor Parent Compound BaBiO3

    NASA Astrophysics Data System (ADS)

    Plumb, N. C.; Gawryluk, D. J.; Wang, Y.; Ristić, Z.; Park, J.; Lv, B. Q.; Wang, Z.; Matt, C. E.; Xu, N.; Shang, T.; Conder, K.; Mesot, J.; Johnston, S.; Shi, M.; Radović, M.

    2016-07-01

    We investigate the band structure of BaBiO3 , an insulating parent compound of doped high-Tc superconductors, using in situ angle-resolved photoemission spectroscopy on thin films. The data compare favorably overall with density functional theory calculations within the local density approximation, demonstrating that electron correlations are weak. The bands exhibit Brillouin zone folding consistent with known BiO6 breathing distortions. Though the distortions are often thought to coincide with Bi3 +/Bi5 + charge ordering, core level spectra show that bismuth is monovalent. We further demonstrate that the bands closest to the Fermi level are primarily oxygen derived, while the bismuth 6 s states mostly contribute to dispersive bands at deeper binding energy. The results support a model of Bi-O charge transfer in which hole pairs are localized on combinations of the O 2 p orbitals.

  14. Magneto-optical studies of magnetization processes in high-Tc superconductors structure.

    SciTech Connect

    Vlasko-Vlasox, V. K.

    1998-12-02

    Magneto-optical imaging is a powerful tool for nondestructive quality control and scientific research through visualization of magnetic fields around any magnetic flux or current carrying sample. It allows real time observations of domain structures and their transformations in magnetics, static and dynamic field patterns due to inhomogeneous currents in electric circuits and superconductors, and reveals distortions of the fields due to defects. In addition to qualitative pictures showing different details in the intensities of the magneto-optical images, one can obtain quantitative maps of field distributions and retrieve values of the underlying currents or magnetization variations. In this review we discuss the advantages of magneto-optics for studies of superconductors, show its place among other techniques, and report recent results in magneto-optical investigations of high temperature superconductors (HTS).

  15. Experimental study of electrical conduction across high-Tc superconductor-graphene interfaces

    NASA Astrophysics Data System (ADS)

    Perconte, David; Cuellar, Fabian; Martin, Marie-Blandine; Dlubak, Bruno; Piquemal-Banci, Maelis; Bernard, Rozenn; Trastoy, Juan; Moreau-Luchaire, Constance; Seneor, Pierre; Villegas, Javier; Kidambi, Piran; Robertson, John; Hofmann, Stephan

    Proximity-induced superconductivity presents unusual features in graphene (i.e. specular Andreev reflection) due to its particular electronic structure. It has been theoretically discussed that, if a d-wave superconductor is put contact with graphene, the latter will sustain d-wave superconductivity, and further unusual features (such as oscillatory behavior) should be observed in the superconductor-graphene junction conductance. Motivated by these prospects, we experimentally investigate YBCO-graphene junctions. We will show differential conductance measurements as a function of temperature, magnetic field, and graphene doping. The observed behavior will be discussed in the frame of the theory developed in. Work supported by Labex Nanosaclay.

  16. 3D modeling of high-Tc superconductors by finite element software

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Coombs, T. A.

    2012-01-01

    A three-dimensional (3D) numerical model is proposed to solve the electromagnetic problems involving transport current and background field of a high-Tc superconducting (HTS) system. The model is characterized by the E-J power law and H-formulation, and is successfully implemented using finite element software. We first discuss the model in detail, including the mesh methods, boundary conditions and computing time. To validate the 3D model, we calculate the ac loss and trapped field solution for a bulk material and compare the results with the previously verified 2D solutions and an analytical solution. We then apply our model to test some typical problems such as superconducting bulk array and twisted conductors, which cannot be tackled by the 2D models. The new 3D model could be a powerful tool for researchers and engineers to investigate problems with a greater level of complicity.

  17. Investigation of low-energy electronic response in high-{Tc} superconductor by Raman spectroscopy

    SciTech Connect

    Yamanaka, Akio; Asayama, Nobuo; Furutani, Takashi; Inoue, Kuon; Takekawa, Shunji

    1996-12-31

    Low-energy electronic response due to single-particle excitations has been investigated in high-{Tc} copper-oxide Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single-crystals by Raman scattering spectroscopy. The authors find that the low-energy electronic response in the superconducting phase depends significantly on polarization configuration. For tetragonal B{sub 1g} the suppression of the low-energy spectral weight of the electronic continuum due to an opening of the superconducting gap occurs abruptly below {Tc}, whereas that of the B{sub 2g}-response shows a gradual temperature dependence. The symmetry-dependent superconducting response is basically consistent with the superconducting order parameter having a nodal structure with X{sup 2}-Y{sup 2} symmetry.

  18. Critical currents and flux creep in melt processed high Tc oxide superconductors

    NASA Astrophysics Data System (ADS)

    Murakami, M.; Gotoh, S.; Koshizuka, N.; Tanaka, S.; Matsushita, T.; Kambe, S.; Kitazawa, K.

    YBa 2Cu 3O 7 crystals fabricated by a quench and melt growth process contain fine Y 2BaCuO 5 particles. These fine precipitates are considered to have three beneficial effects: they suppress crack formation; they promote oxygen diffusion; and they act as pinning centres. Such crystals exhibit larger flux pinning than single crystals and their magnetic behaviour can be understood in terms of the critical state model which has been developed for conventional type II superconductors. Both transport and magnetization measurements gave Jc values exceeding 30 000 A cm -2 at 77 K and 1 T. Flux creep rate is also much smaller than that of single crystals and a value of pinning energy, U, comparable to that of conventional superconductors was obtained. A theoretical estimation of the contribution of 211 precipitates to flux pinning is also presented.

  19. Anisotropy Effect on Levitation Performance of Bulk High-Tc Superconductors Above a Permanent Magnet Guideway

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Liao, Xinglin; Jing, Hailian; Lin, Qunxu; Ma, Guangtong; Yen, Fei; Wang, Suyu; Wang, Jiasu

    The anisotropy properties of bulk high-temperature superconductors (HTSCs) are taken into consideration for the application of high-temperature superconducting (HTS) Maglev systems, which are especially based on the different flux-trapping capabilities as well as critical current density, Jc, values between the growth section boundary (GSB) and the growth sections (GS) in bulk superconductors. By adjusting the angle between the GSB of bulk HTSCs and the strongest magnetic field position of a permanent magnet guideway (PMG), the levitation force and its relaxation processes are compared at different field-cooling conditions. Experimental results show that the levitation capability and the suppression of levitation force decay can be enhanced by optimizing the GS/GSB alignment of every bulk HTSC above the PMG. Meanwhile, our conclusions may provide references to other HTS maglev systems with small levitation gaps, i.e., superconducting magnetic bearings.

  20. Infrared optical spectra of high-{Tc} superconductors: Assignment and implications

    SciTech Connect

    Georgiev, M.; Borissov, M.; Mihailov, L.

    1996-12-31

    An overview is presented of experimental and theoretical work that has so far been done to study and understand the optical spectra of high-temperature superconductors. Emphasis is laid on experiments involving single crystals and good textured ceramic samples. The theory has offered a few main suggestions but they have failed to produce the magic formula for understanding the optical response. Further comments are made as regards experimental, theoretical, and practical developments. 75 refs.

  1. p-Orbital Density Wave with d Symmetry in High-Tc Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Tsuchiizu, Masahisa; Yamakawa, Youichi; Kontani, Hiroshi

    Emergence of the nematic density wave is a fundamental unsolved problem in cuprate superconductors. To understand the origin of the nematicity, we employ the recently-developed functional renormalization-group method with high numerical accuracy, and discover the critical development of the p-orbital-density-wave (p-ODW) instability in the strong-spin-fluctuation region. The obtained p-ODW state possesses the key characteristics of the charge ordering pattern in Bi- and Y-based superconductors, such as the wavevector parallel to the nearest Cu-Cu direction, and the d-symmetry form factor with the antiphase correlation between px and py orbitals in the same unit cell. From the beautiful scaling relation between the spin susceptibility and the p-ODW susceptibility, we conclude that the p-ODW is driven by the strong interference between spin and charge fluctuations. It is clarified that the strong charge-spin interference, which is the origin of the nematicity, is the hidden but significant characteristics of the electronic states in cuprate superconductors.

  2. Analysis of the renormalization of the quasiparticle dispersion in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Li, Jian-Xin; Wang, Z. D.

    2005-03-01

    Based on the slave-boson approach to the bilayer t-t^'- J model, the renormalization of the quasiparticle dispersion in high-Tc cuprates is investigated by examining both interactions of fermions with spin fluctuations and phonons. It is shown that both interactions can give rise to a kink in the dispersion around the antinodes of the d-wave gap (near (,) and (0,π)). However, three remarkable differences caused by these interactions are found, namely the peak/dip/hump structure in the quasiparticle lineshape, the doping dependence of the quasiparticle weight, and the role played by the interlayer coupling on the formation of the antinodal kink. These differences are suggested to serve as a discriminance to single out the main residual interaction in the superconducting state. A comparison to the recent angle-resolved photoemission (ARPES) experiments shows that the coupling to the spin resonance dominates for quasiparticles around the antinodes. ^1National Laboratory of Solid State of Microstructure and Department of Physics, Nanjing University, Nanjing 210093, China^2Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China^3The Interdisciplinary Center of Theoretical Studies, Chinese Academy of Science, Beijing 100080, China.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    PubMed

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

    2015-09-17

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

  5. Tunneling spectroscopy into high-Tc superconductors: Goals and open questions

    NASA Astrophysics Data System (ADS)

    Cucolo, Anna Maria

    1996-07-01

    Josephson currents, implying Cooper pairs tunneling, and quasi-particle currents, implying single electron tunneling, are discussed in terms of HTS superconducting and normal state properties, respectively. Two examples of Josephson measurements reported in the literature give contradictory indication about the symmetry of the superconducting state in the YBaCuO compound. On the other hand, normal state tunneling characteristics measured both in bismuth oxides and cuprate superconductors, indicate an universal relationship between the slope of the linear DOS and the value of the conductance at zero bias in these materials.

  6. Positron annihilation studies of the electronic structure and fermiology of the high-{Tc} superconductors

    SciTech Connect

    Smedskjaer, L.C.; Bansil, A.

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T{sub c} superconductors, with focus on the YBa{sub 2}Cu{sub 3}O{sub 7} system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  7. Positron annihilation studies of the electronic structure and fermiology of the high-[Tc] superconductors

    SciTech Connect

    Smedskjaer, L.C. ); Bansil, A. . Dept. of Physics)

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T[sub c] superconductors, with focus on the YBa[sub 2]Cu[sub 3]O[sub 7] system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  8. Terahertz applications of integrated circuits based on intrinsic Josephson junctions in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Huabing; Wu, Peiheng; Yamashita, Tsutomu

    2001-10-01

    Using a newly developed double-side fabrication method, an IJJ stack plus a bow-tie antenna and chokes were integrated in a slice 200 nm thick and singled out from inside a bulk Bi2Sr2CaCu2O8+x (BSCCO) single crystal. The junctions in the fabricated stack were very uniform, and the number of junctions involved was rather controllable. In addition to this method, which can be used to fabricate integrated circuits based on intrinsic Josephson junctions in high temperature (Tc) superconductors, also reported will be terahertz responses of IJJs, and the possible applications in quantum voltage standard, spectroscopy, and so on.

  9. Microwave (EPR) measurements of the penetration depth measurements of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Dalal, N. S.; Rakvin, B.; Mahl, T. A.; Bhalla, A. S.; Sheng, Z. Z.

    1991-01-01

    The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T sub c superconductors. The method uses the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T sub c is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, neutron scattering, and magnetic susceptibility.

  10. Phonon characteristics of high {Tc} superconductors from neutron Doppler broadening measurements

    SciTech Connect

    Trela, W.J.; Kwei, G.H.; Lynn, J.E.; Meggers, K.

    1994-12-01

    Statistical information on the phonon frequency spectrum of materials can be measured by neutron transmission techniques if they contain nuclei with low energy resonances, narrow enough to be Doppler-broadened, in their neutron cross sections. The authors have carried out some measurements using this technique for materials of the lanthanum barium cuprate class, La{sub 2{minus}x}Ba{sub x}CuO{sub 4}. Two samples with slightly different concentrations of oxygen, one being superconductive, the other not, were examined. Pure lanthanum cuprate was also measured. Lanthanum, barium and copper all have relatively low energy narrow resonances. Thus it should be possible to detect differences in the phonons carried by different kinds of atom in the lattice. Neutron cross section measurements have been made with high energy resolution and statistical precision on the 59m flight path of LANSCE, the pulsed spallation neutron source at Los Alamos National Laboratory. Measurements on all three materials were made over a range of temperatures from 15K to 300K, with small steps through the critical temperature region near 27K. No significant changes in the mean phonon energy of the lanthanum atoms were observed near the critical temperature of the super-conducting material. It appears however that the mean phonon energy of lanthanum in the superconductor is considerably higher than that in the non-superconductors. The samples used in this series of experiments were too thin in barium and copper to determine anything significant about their phonon spectra.

  11. Flux Creep and Giant Flux Creep in High Tc Hg,Pb-based Superconductors

    NASA Astrophysics Data System (ADS)

    Kirven, Douglas; Owens, Frank; Iqbal, Z.; Bleiweiss, M.; Lungu, A.; Datta, T.

    1996-03-01

    Dynamic behavior of the trapped flux in fields of up to 17.5 T was studied in a set of Hg-Pb based superconductors with a Tc in excess of 130 K. Depending on the experimental conditions, both creep and giant flux creep dynamics were observed. Results were analyzed using to standard models such as Anderson-Kim and giant-flux creep models (GFC). The plots of relaxation rate of remnant magnetization versus temperature show a peak below Tc. These results were compared with other Cu-O compounds. A distribution of activation energies was found from the magnetization rate. The activation energy distribution shows a peak around 50 K. The peak determines the temperature where the flux flow rate is a maximum. A universal relation of the resistive behavior was also found as a function of temperature and field. The zero-field/field-cooled results gave a reversibility curve that also obeyed a universal power relation.

  12. Grain orientation in high Tc superconductors by molten salt powder synthesis

    NASA Technical Reports Server (NTRS)

    Gopalakrishnan, Sudhakar; Schulze, Walter A.

    1991-01-01

    The molten salt or the flux method is used to fabricate a grain oriented YBa2Cu3O(7-x) (123) superconductor. Here we suggest a two-stage approach in using the 'green phase', Y2BaCuO5 (211), as seed crystals in the formation of YBa2Cu3O(7-x). The process uses Y2BaCuO5 formed by molten salt synthesis. The Y2BaCuO5 phase was observed to be stable in water and in most of the salt systems. Salt processing can form a small quantity of anisotropic particles of Y2BaCuO5. This material can form the 123 phase when tape cast and sintered in the presence of the required levels of Ba and Cu.

  13. Electron energy spectrum and magnetic interactions in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Turshevski, S. A.; Liechtenstein, A. I.; Antropov, V. P.; Gubanov, V. A.

    1991-01-01

    The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T(sub N1) and T(sub N2). The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T(sub N2) reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T(sub N1) and T(sub N2) which depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg Hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J(sub ij) parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors.

  14. Band Structure of the Heavily-Electron-Doped FeAs-Based Ba(Fe,​Co)2As2 Superconductor Suppresses Antiferromagnetic Correlations

    NASA Astrophysics Data System (ADS)

    Sudayama, T.; Wakisaka, Y.; Takubo, K.; Morinaga, R.; Sato, T. J.; Arita, M.; Namatame, H.; Taniguchi, M.; Mizokawa, T.

    2010-04-01

    In the heavily-electron-doped regime of the Ba(Fe,​Co)2As2 superconductor, three hole bands at the zone center are observed and two of them reach the Fermi level. The larger hole pocket at the zone center is apparently nested with the smaller electron pocket around the zone corner. However, the (π,​0) Fermi surface reconstruction reported for the hole-doped case is absent in the heavily-electron-doped case. This observation shows that the apparent Fermi surface nesting alone is not enough to enhance the antiferromagnetic correlation as well as the superconducting transition temperature.

  15. Coupled bipolarons and optical phonons as a model for high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Kasperczyk, J.

    1991-01-01

    The coherence length of the new high-temperature superconductors reaches a small value which is comparable to the dimensions of the unit cell of the compound. This means that a pair consists of two holes occupying the same site or two adjacent sites. Such a situation is described by a model of the local-pairs (bipolarons). The origin of local-pairs may come not only from strong enough electron or hole-phonon interaction but also from other interactions. Independent of the specific nature of such local-pairs, they can undergo a Bose-like condensation to the superconducting state at a critical temperature which is usually much lower than the temperature of the pair formation. An interplay of ferroelectric and superconducting properties is considered within the model of hole-like local-pairs interacting with optical phonons. Therefore, researchers extend the usual local-pair Hamiltonian by including a direct interaction between the local-pairs and the optical phonons. These optical phonons are known to play an important role in the ferroelectric transition and they transform into an additional pseudo-acoustic branch at the ferroelectric critical temperature. (This is associated with nonzero electric polarization due to the existence of two separate lattices composed of negative and positive ions, respectively.)

  16. Stabilization of high Tc phase in bismuth cuprate superconductor by lead doping

    NASA Technical Reports Server (NTRS)

    Gupta, Ram. P.; Pachauri, J. P.; Khokle, W. S.; Nagpal, K. C.; Date, S. K.

    1991-01-01

    It has been widely ascertained that doping of lead in Bi-Sr-Ca-Cu-O systems promotes the growth of high T sub c (110 K) phase, improves critical current density, and lowers processing temperature. A systematic study was undertaken to determine optimum lead content and processing conditions to achieve these properties. A large number of samples with cationic compositions of Bi(2-x)Pb(x)Sr2Ca2Cu3 (x = 0.2 to 2.0) were prepared by conventional solid state reaction technique. Samples of all compositions were annealed together at a temperature and characterized through resistance temperature (R-T) measurements and x ray diffraction to determine the zero resistance temperature, T sub c(0) and to identify presence of phases, respectively. The annealing temperature was varied between 790 and 880 C to optimize processing parameters. Results are given. In brief, an optimum process is reported along with composition of leaded bismuth cuprate superconductor which yields nearly a high T sub c single phase with highly stable superconducting properties.

  17. Emission of terahertz electromagnetic waves by vortex flow in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Tachiki, Masashi; Iizuka, Mikio; Minami, Kazuo; Tejima, Shogo; Nakamura, Hisashi

    2006-05-01

    Continuous terahertz electromagnetic waves have new applications in scientific and industrial fields such as medicine and information technology. Cuprate high-temperature superconductors have a layer structure, and form a naturally multi-connected Josephson junction system called intrinsic Josephson junction (IJJ). In IJJ, there appears a new excitation called the Josephson plasma. Its frequency is in the region of terahertz inside the superconducting energy gap. The excited plasma wave is converted into an electromagnetic wave at sample surfaces. Therefore the IJJ has a great potential to generate terahertz continuous wave. Here we report the results of simulations to find the optimum condition for obtaining the strongest emission power of the terahertz waves. The simulations were carried out using our theory. Since the simulation uses very large-sized coupled nonlinear equations therefore difficult to compute, we used the fastest supercomputer named as Earth Simulator. We found that the quite intense continuous terahertz coherent wave is emitted from a small sample with high-energy efficiency.

  18. Ultrafast momentum-dependent quasiparticle dynamics in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Bovensiepen, Uwe

    2013-03-01

    Femtosecond time- and angle-resolved photoelectron spectroscopy trARPES facilitates insight into electronic relaxation and electronic structure of non-equilibrium states of matter. Hot electrons and holes relax in metals on ultrafast time scales due to the screened Coulomb interaction. In superconductors the relaxation rates of quasiparticles at energies close to the superconducting gap edge are reduced because of the loss of quasiparticle states near EF. Since in the superconducting state the relaxation of optically excited carriers proceeds partly by Cooper pair reformation, the study of the quasiparticle dynamics bears the potential to analyze the interaction responsible for Cooper pair formation. Results of trARPES will be discussed for optimally doped Bi2Sr2CaCu2O8+δ in the superconducting state and on EuFe2As2 in the antiferromagnetic state. In the cuprate system we find a predominant excitation of quasiparticles at momenta near the antinode. We show furthermore, that at excitation densities of several 10 μJ/cm2 quasiparticle relaxation is dominated by Cooper pair reformation, which again proceeds near the antinode. In the Fe-pnictide material we monitor a difference in the relaxation rate for electrons and holes near the Fermi momentum, which disappears above the Neel temperature. We conclude that this anisotropic relaxation of electrons and holes is a consequence of the optical modification of the antiferromagnetic order. Analysis of energy transfer from electrons to phonons allows to determine the momentum averaged electron-phonon coupling constant λ. We find values below 0.25 for Bi2Sr2CaCu2O8+δ and below 0.15 for EuFe2As2. We acknowledge funding through the Deutsche Forschungsgemeinschaft through BO 1823/2, SPP 1458 and the Alexander von Humboldt foundation.

  19. MAGLEV: the double benefits of high-Tc superconductors and its development as an aerospace technology

    SciTech Connect

    Johnson, L.R.; Giese, R.F.

    1988-01-01

    The potential for magnetically levitated (MAGLEV) vehicles is discussed as a means of both inter-city travel and a technology option to relieve the growing problem of air traffic congestion. A brief summary is presented of the two primary maglev concepts: (1) the attractive-force, electromagnetic system (EMS) and (2) the repulsive-force, electrodynamic system (EDS), and continues with a discussion of the advantages, potential for reduced costs and higher reliability, that the newly-discovered, high-temperature superconductors offer for EDS maglev vehicles. A summary of the current status of worldwide maglev research is presented, followed by a discussion of the resurgence of US interest in maglev. An analysis of air-traffic congestion suggests that maglev can substitute for short-to-medium distance air travel. By promoting maglev as an airline technology, airlines can retain their familiar hub-and-spoke systems with maglevs an integral part of the spoke portion. A preliminary analysis suggests that maglev capital costs are likely to be comparable to those of interstate highways, and use of maglevs can declay the need for new airport and construction. For each short-to-medium flight diverted to maglev, an airline can substitute a longer flight. The short-haul flights use an inordinate amount of fuel, which is a major component of airline operating costs. Maglev energy consumption would be significantly less and would not have the emissions associated with petroleum fuel. Finally, passengers should benefit from maglev technology: travel options will be extended, delays will be reduced, and costs for inter-city travel will be reduced.

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

    NASA Astrophysics Data System (ADS)

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

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

  1. Chemistry of electron doped Ln{sub 2-x}Ce{sub x}CuO{sub 4} superconductors

    SciTech Connect

    Manthiram, A.; Zhu, Y.T.

    1993-10-01

    The electron doped Ln{sub 2{minus}x}Ce{sub x}CuO{sub 4} (Ln = lanthanide) oxides have intergrowth structures consisting of superconductively active CuO{sub 2} sheets alternating with inactive (Ln, Ce){sub 2}O{sub 2} fluorite layers along the c-axis. Stabilization of such intergrowth structures requires bond length matching across the intergrowth interface. The bond length matching criterion causes a monotonic decrease in the Ce solubility limit from x = 0.24 to x = 0.15 as the size of Ln{sup 3+} decreased from Ln=La{sub 0.5}Nd{sub 0.5} to Ln=Gd. Annealing in N{sub 2} atm of Ln{sub 2{minus}x}Ce{sub x}CuO{sub 4} at temperatures above 900 degrees C creates oxygen vacancies and the number of vacancies decreases with increasing Ce content. The value of x at which a semiconductor to superconductor transition occurs in Ln{sub 2{minus}x}Ce{sub x}CuO{sub 4} increases with decreasing size of Ln{sup 3+} due to an increasing Madelung energy caused by a decreasing Cu-O bond length.

  2. Determination of the phase diagram of the electron doped superconductor Ba(Fe1-xCox)2As2

    SciTech Connect

    Chu, Jiun-Haw; Analytis, James G.; Kucharczyk, Chris; Fisher, Ian R.; /Stanford U., Geballe Lab.

    2010-02-15

    Systematic measurements of the resistivity, heat capacity, susceptibility and Hall coefficient are presented for single crystal samples of the electron-doped superconductor Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2}. These data delineate an x-T phase diagram in which the single magnetic/structural phase transition that is observed for undoped BaFe{sub 2}As{sub 2} at 134 K apparently splits into two distinct phase transitions, both of which are rapidly suppressed with increasing Co concentration. Superconductivity emerges for Co concentrations above x {approx}0.025, and appears to coexist with the broken symmetry state for an appreciable range of doping, up to x {approx} 0.06. The optimal superconducting transition temperature appears to coincide with the Co concentration at which the magnetic/structural phase transitions are totally suppressed, at least within the resolution provided by the finite step size between crystals prepared with different doping levels. Superconductivity is observed for a further range of Co concentrations, before being completely suppressed for x {approx} 0.018 and above. The form of this x-T phase diagram is suggestive of an association between superconductivity and a quantum critical point arising from suppression of the magnetic and/or structural phase transitions.

  3. SPECIAL ISSUE DEVOTED TO THE 80TH ANNIVERSARY OF ACADEMICIAN N G BASOV'S BIRTH: Interlayer electrodynamics of high-Tc superconductors: an experimental overview

    NASA Astrophysics Data System (ADS)

    Basov, Dmitrii N.

    2002-12-01

    An astonishing feature of underdoped high-Tc superconductors is that the energy scale associated with the formation of superconducting condensate dramatically exceeds the energy gap and appears to be of the interband caliber. This effect can be interpreted in terms of lowering of the electronic kinetic energy at T < Tc and thus points to a mechanism of superconductivity radically departing from the Bardeen — Cooper — Schrieffer (BCS) theory. This nontrivial superconducting state electrodynamics appears to be directly connected to anomalies of cuprates observed in the normal state, including the pseudogap, and to the lack of well-defined quasiparticles.

  4. Quantum-limit linkage of ‘strange’ and conventional metal states of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Krusin-Elbaum, L.; Shibauchi, T.; Kasahara, Y.; Okazaki, R.; Matsuda, Y.; McDonald, R. D.; Mielke, C. H.; Hasegawa, M.

    2013-10-01

    The key to the nature of superconducting pairing in high-Tc cuprates lies in understanding the transition to a conventional behavior when they are heavily doped. By using high magnetic fields, we show that the pseudogapped Tl2Ba2CuO6+x becomes a conventional metal at heavy doping in a quantum phase transition, where the pseudogap boundary develops a thermodynamic divergence corresponding to a zero entropy jump. The critical doping point downshifts with magnetic field in unison with the suppression of Tc. This implies that quantum critical fluctuations and magnetic degrees that destabilize the pseudogap are linked to the superconductivity with high Tc.

  5. Inhibition of aqueous degradation of Y1Ba2Cu3O7 - x high-Tc superconductor by nitrogen ion implantation

    NASA Astrophysics Data System (ADS)

    Chaudhari, S. M.; Viswanathan, R.; Bendre, S. T.; Nawale, P. P.; Kanetkar, S. M.; Ogale, S. B.

    1989-11-01

    The influence of 60-keV N+2 ion implantation on the aqueous degradation of the Y1Ba2Cu3O7-x high-Tc superconductor is studied by the small-angle x-ray diffraction technique. Structural depth profiling is performed by registering the x-ray data at several small angles of incidence between 0.3° and 10.0° within Seeman-Bohlin geometry. Examination of samples implanted at a dose value of 3×1017 ions/cm2 and subjected to different aqueous treatments reveals that implantation arrests the degradation process and imparts structural stability to the superconductor. Resistivity temperature data are also provided for specific cases of interest.

  6. Magnetic fluctuations in n-type high-Tc superconductors reveal breakdown of fermiology:Experiments and Fermi-liquid/RPA calculations

    SciTech Connect

    Krueger, S.D.

    2010-03-02

    By combining experimental measurements of the quasiparticle and dynamical magnetic properties of optimally electron-doped Pr{sub 0.88}LaCe{sub 0.12}CuO{sub 4} with theoretical calculations, we demonstrate that the conventional fermiology approach cannot possibly account for the magnetic fluctuations in these materials. In particular, we perform tunneling experiments on the very same sample for which a dynamical magnetic resonance has been reported recently and use photoemission data by others on a similar sample to characterize the fermionic quasiparticle excitations in great detail. We subsequently use this information to calculate the magnetic response within the conventional fermiology framework as applied in a large body of work for the hole-doped superconductors to find a profound disagreement between the theoretical expectations and the measurements: this approach predicts a steplike feature rather than a sharp resonance peak, it underestimates the intensity of the resonance by an order of magnitude, it suggests an unreasonable temperature dependence of the resonance, and most severely, it predicts that most of the spectral weight resides in incommensurate wings which are a key feature of the hole-doped cuprates but have never been observed in the electron-doped counterparts. Our findings strongly suggest that the magnetic fluctuations reflect the quantum-mechanical competition between antiferromagnetic and superconducting orders.

  7. Quasiparticle tunneling spectroscopy of high {Tc} cuprates

    SciTech Connect

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

    1996-04-01

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

  8. NMR characterization of sulphur substitution effects in the KxFe2-ySe2-zSz high-Tc superconductor

    DOE PAGESBeta

    Torchetti, D. A.; Imai, T.; Lei, H. C.; Petrovic, C.

    2012-04-17

    We present a⁷⁷ Se NMR study of the effect of S substitution in the high-Tc superconductor KxFe2-ySe2-zSz in a temperature range up to 250 K. We examine two S concentrations, with z=0.8 (Tc~ 26 K) and z=1.6 (nonsuperconducting). The samples containing sulphur exhibit broader NMR line shapes than the KxFe₂Se₂ sample due to local disorder in the Se environment. Our Knight shift ⁷⁷K data indicate that in all samples, uniform spin susceptibility decreases with temperature, and that the magnitude of the Knight shift itself decreases with increased S concentration. In addition, S substitution progressively suppresses low-frequency spin fluctuations. None ofmore » the samples exhibit an enhancement of low-frequency antiferromagnetic spin fluctuations near Tc in 1/T₁T, as seen in FeSe.« less

  9. Feasibility of introducing ferromagnetic materials to onboard bulk high-Tc superconductors to enhance the performance of present maglev systems

    NASA Astrophysics Data System (ADS)

    Deng, Zigang; Wang, Jiasu; Zheng, Jun; Zhang, Ya; Wang, Suyu

    2013-02-01

    Performance improvement is a long-term research task for the promotion of practical application of promising high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle technologies. We studied the feasibility to enhance the performance of present HTS Maglev systems by introducing ferromagnetic materials to onboard bulk superconductors. The principle here is to make use of the high magnetic permeability of ferromagnetic materials to alter the flux distribution of the permanent magnet guideway for the enhancement of magnetic field density at the position of the bulk superconductors. Ferromagnetic iron plates were added to the upper surface of bulk superconductors and their geometric and positioning effects on the maglev performance were investigated experimentally. Results show that the guidance performance (stability) was enhanced greatly for a particular setup when compared to the present maglev system which is helpful in the application where large guidance forces are needed such as maglev tracks with high degrees of curves.

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

    DOE PAGESBeta

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

    2014-12-09

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

  11. p -orbital density wave with d symmetry in high-Tc cuprate superconductors predicted by renormalization-group + constrained RPA theory

    NASA Astrophysics Data System (ADS)

    Tsuchiizu, Masahisa; Yamakawa, Youichi; Kontani, Hiroshi

    2016-04-01

    The discovery of the charge-density-wave formation in the high-Tc cuprate superconductors has activated intensive theoretical studies for the pseudogap states. However, the microscopic origin of the charge-density-wave state has been unknown so far since the many-body effects beyond the mean-field-level approximations, called the vertex corrections, are essential. Toward solving this problem, we employ the recently developed functional renormalization group method, by which we can calculate the higher-order vertex corrections in a systematic and unbiased way with high numerical accuracy. We discover the critical development of the p -orbital-density-wave (p -ODW) instability in the strong-spin-fluctuation region. The obtained p -ODW state possesses the key characteristics of the charge-ordering pattern in Bi- and Y-based superconductors, such as the wave vector parallel to the nearest Cu-Cu direction, and the d -symmetry form factor with the antiphase correlation between px and py orbitals in the same unit cell. In addition, from the observation of the beautiful scaling relation between the spin susceptibility and the p -ODW susceptibility, we conclude that the main driving force of the density wave is the Aslamazov-Larkin vertex correction that becomes very singular near the magnetic quantum-critical point.

  12. Crystallography, chemistry and structural disorder in the new high-Tc Bi-Ca-Sr-Cu-O superconductor

    NASA Technical Reports Server (NTRS)

    Veblen, D. R.; Heaney, P. J.; Angel, R. J.; Finger, L. W.; Hazen, R. M.

    1988-01-01

    Diffraction experiments are reported which indicate that the new Bi-Ca-Sr-Cu-O layer-structure superconductor possesses a primitive orthorhombic unit cell with probable space group Pnnn. The material exhibits severe structural disorder which is primarily related to stacking within the layers. The apparent orthorhombic structure is an average resulting from orthorhombic material mixed with monoclinic domains in two twinned orientations. Two distinct types of structural disorder that are common in materials synthesized to date are also described. This disorder complicates the crystallographic analysis and suggests that X-ray and neutron diffraction methods may yield only an average structure.

  13. Thallium 2223 high Tc superconductor in a silver matrix and its magnetic shielding, hermal cycle and time aging properties

    SciTech Connect

    Fei, X.; He, W.S.; Havenhill, A.

    1994-12-31

    Superconducting Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} (Tl2223) was ground to powder. Mixture with silver powder (0--80% weight) and press to desired shape. After proper annealing, one can get good silver-content Tl2223 bulk superconductor. It is time-stable and has good superconducting property as same as pure Tl2223. It also has better mechanical property and far better thermal cycle property than pure Tl2223.

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  15. Signatures of the electronic nature of pairing in high-Tc superconductors obtained by non-equilibrium boson spectroscopy

    PubMed Central

    Krasnov, Vladimir M.; Katterwe, Sven-Olof; Rydh, Andreas

    2013-01-01

    Understanding the pairing mechanism that gives rise to high-temperature superconductivity is one of the longest-standing problems of condensed-matter physics. Almost three decades after its discovery, even the question of whether or not phonons are involved remains a point of contention to some. Here we describe a technique for determining the spectra of bosons generated during the formation of Cooper pairs on recombination of hot electrons as they tunnel between the layers of a cuprate superconductor. The results obtained indicate that the bosons that mediate pairing decay over micrometre-scale distances and picosecond timescales, implying that they propagate at a speed of around 106 m s−1. This value is more than two orders of magnitude greater than the phonon propagation speed but close to Fermi velocity for electrons, suggesting that the pairing mechanism is mediated by unconventional repulsive electron–electron, rather than attractive electron–phonon, interactions. PMID:24336159

  16. Nd, Ce(fπ)-O(pπ) Hybridization in Nd2-xCexCuO4 and Dynamic Jahn-Teller Pairing in HIGH-Tc Superconductors

    NASA Astrophysics Data System (ADS)

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

    Hybridization of Nd(fπ) and Ce(fπ) orbitals with composite O(pπ)-O(pπ) bonding/ Cu(dπ*)-O(pπ) antibonding orbitals at the Fermi energy (EF) is shown to promote high-Tc superconductivity in Nd2-xCexCuO4. Dynamic Jahn-Teller coupling of these hybrid molecular orbitals to the lattice leads to Cooper pairing as it does in other high-Tc superconductors, such as La2-xSrxCuO4, where O(pπ) character at EF is dominant.

  17. Suppression of the antiferromagnetic pseudogap in the electron-doped high-temperature superconductor by protect annealing

    PubMed Central

    Horio, M.; Adachi, T.; Mori, Y.; Takahashi, A.; Yoshida, T.; Suzuki, H.; Ambolode, L. C. C.; Okazaki, K.; Ono, K.; Kumigashira, H.; Anzai, H.; Arita, M.; Namatame, H.; Taniguchi, M.; Ootsuki, D.; Sawada, K.; Takahashi, M.; Mizokawa, T.; Koike, Y.; Fujimori, A.

    2016-01-01

    In the hole-doped cuprates, a small number of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only in a narrow window of high-doped Ce concentration after reduction annealing, and strong antiferromagnetic correlation persists in the superconducting phase. Recently, Pr1.3−xLa0.7CexCuO4 (PLCCO) bulk single crystals annealed by a protect annealing method showed a high critical temperature of around 27 K for small Ce content down to 0.05. Here, by angle-resolved photoemission spectroscopy measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an antiferromagnetic pseudogap unlike all the previous work, indicating a dramatic reduction of antiferromagnetic correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present results fundamentally challenge the long-standing picture on the electronic structure in the electron-doped regime. PMID:26843063

  18. Suppression of the antiferromagnetic pseudogap in the electron-doped high-temperature superconductor by protect annealing.

    PubMed

    Horio, M; Adachi, T; Mori, Y; Takahashi, A; Yoshida, T; Suzuki, H; Ambolode, L C C; Okazaki, K; Ono, K; Kumigashira, H; Anzai, H; Arita, M; Namatame, H; Taniguchi, M; Ootsuki, D; Sawada, K; Takahashi, M; Mizokawa, T; Koike, Y; Fujimori, A

    2016-01-01

    In the hole-doped cuprates, a small number of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only in a narrow window of high-doped Ce concentration after reduction annealing, and strong antiferromagnetic correlation persists in the superconducting phase. Recently, Pr1.3-xLa0.7CexCuO4 (PLCCO) bulk single crystals annealed by a protect annealing method showed a high critical temperature of around 27 K for small Ce content down to 0.05. Here, by angle-resolved photoemission spectroscopy measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an antiferromagnetic pseudogap unlike all the previous work, indicating a dramatic reduction of antiferromagnetic correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present results fundamentally challenge the long-standing picture on the electronic structure in the electron-doped regime. PMID:26843063

  19. Rare Earth Ion Effects on the Pseudo-Gap in Electron-Doped Superconductors And Possible Nodeless D-Wave Gap

    SciTech Connect

    Park, S.R.; Leem, C.S.; Roh, Y.S.; Choi, K.J.; Kim, J.H.; Kim, B.J.; Koh, H.; Eisaki, H.; Lu, D.H.; Shen, Z.-X.; Armitage, N.P.; Kim, C.

    2009-05-21

    We report angle resolved photoemission (ARPES) studies on electron-doped cuprate superconductor Sm{sub 2-x}Ce{sub x}CuO{sub 4} (x = 0.14 and 0.18). A wide energy range scan shows clear 'waterfall' effect at an energy scale close to 500 meV which is consistent with the value found in Nd{sub 2-x}Ce{sub x}CuO{sub 4} (NCCO) but larger than that from hole-doped superconductors. High resolution results from both dopings show pseudo-gap effects that were observed in NCCO. However, the effects are found to be stronger than that observed in optimally doped NCCO. The overall electronic structure is well understood within a simple model in which a {radical}2 x {radical}2 static order is assumed. Both ARPES and optical measurements give the coupling strengths to the Q = ({pi}/2,{pi}/2) (due to the {radical}2 x {radical}2 order) to be about 0.1 eV, compatible with each other. The effect is strong enough to push the band near the nodal region below the Fermi energy, resulting in possible nodeless d-wave superconductivity where zero energy quasi-particle excitation is inhibited.

  20. Fabrication and characterization of high-{Tc} tapes and coils made from Ag-clad Bi-2223 superconductors

    SciTech Connect

    Balachandran, U.; Iyer, A.N.; Youngdahl, C.A.; Motowidlo, L.R.; Hoehn, J.G. Jr.; Haldar, P.

    1993-07-01

    Prereacted Pb-doped Bi-Sr-Ca-Cu-0 powders were packed into Ag tubes, drawn, rolled, and given intermediate heat treatment to prepare long lengths of Ag-clad Bi-2223 superconductor tapes. With the use of improved process conditions, transport critical current density (J{sub c}) values exceeding 10{sup 5} A/cm{sup 2} at 4.2 K and 27 K, and greater than 4 {times} 10{sup 4} A/cm{sup 2} at 77 K, were obtained in zero applied field with short tape samples. Detailed microstructural analysis and J{sub c} measurements in applied fields up to 20 T are reported. Rolled tapes were cut into lengths of up to 10 m, and several such tapes were used in parallel to fabricate small superconducting pancake coils by the ``wind-and-react`` technique. Recently, we fabricated a test magnet with six pancake coils, each containing three 10-m lengths of rolled tapes and tested at 4.2, 27, and 77 K as a function of applied fields up to 14.5 T. A maximum generated field of 1.25 T was measured in zero applied field at 4.2 T. Detailed measurements made on the pancake coils and test magnets are reported in this paper.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  2. Primary Phase Field of the Pb-Doped 2223 High-Tc Superconductor in the (Bi, Pb)-Sr-Ca-Cu-O System

    PubMed Central

    Wong-Ng, W.; Cook, L. P.; Kearsley, A.; Greenwood, W.

    1999-01-01

    Both liquidus and subsolidus phase equilibrium data are of central importance for applications of high temperature superconductors in the (Bi, Pb)-Sr-Ca-Cu-O system, including material synthesis, melt processing and single crystal growth. The subsolidus equilibria of the 110 K high-Tc Pb-doped 2223 ([Bi, Pb], Sr, Ca, Cu) phase and the location of the primary phase field (crystallization field) have been determined in this study. For the quantitative determination of liquidus data, a wicking technique was developed to capture the melt for quantitative microchemical analysis. A total of 29 five-phase volumes that include the 2223 phase as a component was obtained. The initial melt compositions of these volumes range from a mole fraction of 7.3 % to 28.0 % for Bi, 11.3 % to 27.8 % for Sr, 1.2 % to 19.4 % for Pb, 9.8 % to 30.8 % for Ca, and 17.1 % to 47.0 % for Cu. Based on these data, the crystallization field for the 2223 phase was constructed using the convex hull technique. A section of this “volume” was obtained by holding two components of the composition at the median value, allowing projection on the other three axes to show the extent of the field.

  3. Emergent nesting of the Fermi surface from local-moment description of iron-pnictide high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Rodriguez, Jose P.; Araujo, Miguel A. N.; Sacramento, Pedro D.

    2014-07-01

    We uncover the low-energy spectrum of a t-J model for electrons on a square lattice of spin-1 iron atoms with 3dxz and 3dyz orbital character by applying Schwinger-boson-slave-fermion mean-field theory and by exact diagonalization of one hole roaming over a 4 × 4 × 2 lattice. Hopping matrix elements are set to produce hole bands centered at zero two-dimensional (2D) momentum in the free-electron limit. Holes can propagate coherently in the t-J model below a threshold Hund coupling when long-range antiferromagnetic order across the d + = 3d(x + iy)z and d - = 3d(x - iy)z orbitals is established by magnetic frustration that is off-diagonal in the orbital indices. This leads to two hole-pocket Fermi surfaces centered at zero 2D momentum. Proximity to a commensurate spin-density wave (cSDW) that exists above the threshold Hund coupling results in emergent Fermi surface pockets about cSDW momenta at a quantum critical point (QCP). This motivates the introduction of a new Gutzwiller wavefunction for a cSDW metal state. Study of the spin-fluctuation spectrum at cSDW momenta indicates that the dispersion of the nested band of one-particle states that emerges is electron-type. Increasing Hund coupling past the QCP can push the hole-pocket Fermi surfaces centered at zero 2D momentum below the Fermi energy level, in agreement with recent determinations of the electronic structure of mono-layer iron-selenide superconductors.

  4. Synthesis and Structural/microstructural Characteristics of Zn-DOPED Tl-BASED HIGH-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Yadav, B. S.; Verma, G. D.; Phase, D. M.; Lalla, N. P.; Das, B.

    Bulk superconducting samples of type Tl2Ba2Can-1Cun-xZnxO8 (where n = 2, 3 and x = 0, 0.1, 0.25, 0.50) were prepared by standard ceramic method. The gross structural characteristics/phase identification of the as synthesized samples were carried out by powder X-ray diffraction technique. The microstructural characteristics of these samples were explored by scanning electron microscopic and transmission electron microscopic techniques. The chemical compositions of these samples were determined by energy dispersive analysis of X-rays technique. The powder X-ray diffraction patterns indicate that the lattice parameter "c" vary and "a" showed no regular variation but the gross structure of Tl-2212 and Tl-2223 remain tetragonal with Zn substitution upto 0.50. The transition temperature (Tc) measured by standard four-probe method decreases as x increases from 0 to 0.50. The transport critical density (Jc) values were also measured by standard four-probe method as potential difference of 1 μV/cm appears across the sample by increasing current. The electron microscopic explorations exhibit various structural features (stacking faults and uniform distribution of ZnO nanoparticles) which improve the physical properties (e.g., transport critical current density "Jc") of these superconductors. The observed enhancement in transport critical current densities (Jc) of at least one order of magnitude (from 102 to 103 A/cm2) is due to the uniform distribution of ZnO nanoparticles which act as flux pinning centres.

  5. Exact diagonalization study of the effects of Zn and Ni impurities on the pseudogap of underdoped cuprate high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Vašátko, Jiří; Munzar, Dominik

    2016-03-01

    The influence of Zn and Ni impurities on the normal-state pseudogap of underdoped high-Tc cuprate superconductors is studied using exact diagonalization of effective t -J -like Hamiltonians describing low energy electronic excitations of the CuO2 plane with some of the copper ions replaced with Zn/Ni. The Ni case Hamiltonian has been obtained by a sequence of approximations from a more complete model involving Cu 3 d , Ni 3 d , and O 2 p orbitals. Our main findings are: (i) The width ΩPG of the pseudogap occurring in the many body density of states, and manifesting itself also in the c -axis infrared conductivity, decreases with increasing Zn concentration as a consequence of a suppression of short range spin correlations. (ii) In the case of one hole and one Ni impurity, the hole is—for realistic values of the model parameters—weakly bound to the Ni site. This causes a slight increase of ΩPG with respect to the pure case. (iii) Based on this result and further results for 1-2 holes and 1-2 Ni impurities, we suggest that in the real Ni substituted CuO2 plane ΩPG is larger than in the pure case due to the binding of the doped holes to the Ni sites and effective underdoping. Our findings clarify the trends observed in the c -axis infrared conductivity data of Zn and Ni substituted (Sm,Nd)Ba2Cu3O7 -δ crystals.

  6. Conditions for observing Shapiro steps in a Bi2Sr2CaCu2O8+δ high- Tc superconductor intrinsic Josephson junction: Numerical calculations

    NASA Astrophysics Data System (ADS)

    Kitamura, Michihide; Irie, Akinobu; Oya, Gin-Ichiro

    2007-08-01

    Conditions to observe Shapiro steps clearly and stably are studied for an intrinsic Josephson junction (IJJ) in Bi2Sr2CaCu2O8+δ high- Tc superconductors. The current equation normalized by the critical current Ic(T) is solved fully numerically. In the calculations, the quasiparticle tunneling current is evaluated by using the normalized I-V characteristics obtained within the d -wave symmetry superconducting gap, while the Cooper-pair (CP) one is calculated on the basis of the general way in which the coherent and incoherent CP tunneling currents can be correctly calculated within the d -wave treatment and the current due to thermal noises is also simulated by using normal random numbers. It is found that the product SRshunt of the junction cross section S and the shunt resistance Rshunt , and the critical current density Jc are important junction parameters, and moreover, that the current equation of the IJJ with no shunt resistance depends on only a universal curve μ(i0) as a function of the normalized external dc current i0 . Furthermore, the effects of the noise, the normalized CP tunneling currents, the SRshunt product, the normalized amplitude ir of external ac modulation, and the Jc on observing the Shapiro steps are studied. When the IJJ is operated under the condition that the shunt resistance is added and the external ac modulation frequency fr is higher than the plasma frequency fp , it is found that (1) clear and stable Shapiro steps with good responses are obtained within the wide range of ir , (2) the response does not so largely depend on the value of SRshunt , and (3) the response for the high Jc junction is much better than that for the low one.

  7. Se77 NMR investigation of the KxFe2-ySe2 high-Tc superconductor (Tc=33 K)

    NASA Astrophysics Data System (ADS)

    Torchetti, D. A.; Fu, M.; Christensen, D. C.; Nelson, K. J.; Imai, T.; Lei, H. C.; Petrovic, C.

    2011-03-01

    We report comprehensive Se77 NMR measurements on a single crystalline sample of the recently discovered FeSe-based high-temperature superconductor KxFe2-ySe2 (Tc=33 K) in a broad temperature range up to 290 K. Despite deviations from the stoichiometric KFe2Se2 composition, we observed Se77 NMR line shapes as narrow as 4.5 kHz under a magnetic field applied along the crystal c axis, and found no evidence for co-existence of magnetic order with superconductivity. On the other hand, the Se77 NMR line shape splits into two peaks with equal intensities at all temperatures when we apply the magnetic field along the ab plane. This suggests that K vacancies may have a superstructure and that the local symmetry of the Se sites is lower than the tetragonal fourfold symmetry of the average structure. This effect might be a prerequisite for stabilizing the s± symmetry of superconductivity in the absence of the hole bands at the Brillouin zone center. From the increase of NMR linewidth below Tc induced by the Abrikosov lattice of superconducting vortices, we estimate the in-plane penetration depth λab~290 nm and the carrier concentration ne~1×10+21 cm-3. Our Knight shift 77K data indicate that the uniform spin susceptibility decreases progressively with temperature, in analogy with the case of FeSe (Tc~9 K) as well as other FeAs high-Tc systems. The strong suppression of 77K observed immediately below Tc for all crystal orientations is consistent with a singlet pairing of Cooper pairs. We do not however observe the Hebel-Slichter coherence peak of the nuclear spin-lattice relaxation rate 1/T1 immediately below Tc, expected for conventional BCS s-wave superconductors. In contrast with the case of FeSe, we do not observe evidence for an enhancement of low-frequency antiferromagnetic spin fluctuations near Tc in 1/T1T. Instead, 1/T1T exhibits qualitatively the same behavior as overdoped non-superconducting Ba(Fe1-xCox)2As2 with x~0.14 or greater, where hole bands are missing in

  8. EDITORIAL: PLASMA 2006: The 5th International Conference on the Intrinsic Josephson Effect and Plasma Oscillations in High-TC Superconductors

    NASA Astrophysics Data System (ADS)

    Warburton, Paul; Yurgens, August

    2007-02-01

    The 5th International Conference on the Intrinsic Josephson Effect and Plasma Oscillations in High-TC Superconductors (known as `PLASMA' for short) took place in London from July 17th to 19th 2006. The meeting was organised jointly by the Superconductivity Group of the Institute of Physics and the European Science Foundation network `Arrays of Quantum Dots and Josephson Junctions' (AQDJJ). It was sponsored by the UK Engineering and Physical Sciences Research Council, AQDJJ, the Japan Society for the Promotion of Physics and the National Institute of Materials Science (NIMS). The meeting was chaired by Paul Warburton of University College London who wishes to put on record his thanks to the conference sponsors for their generosity, without which the conference could not have taken place. Since the previous PLASMA conference in Tsukuba in 2004 the most significant advance in intrinsic Josephson junction (IJJ) research has arguably been the observation of macroscopic quantum tunnelling in IJJs. At the time of the conference this had been observed by both the RIEC/NIMS/AIST collaboration in Japan and by Paul M\\"uller's group in Erlangen. We therefore felt that the conference presented an ideal and timely opportunity for the IJJ community to learn from the more established community of researchers on macroscopic quantum phenomena in low-TC superconductors---and indeed vice versa. As a result a number of leading researchers from the field of low-TC Josephson qubit devices gave several illuminating presentations. Other sessions included those on Josephson vortex dynamics in layered systems and terahertz oscillations in IJJs, in addition to a lively poster session on the first evening. The conference was rounded off by an excellent summary of the highlights of the meeting given by Professor Hu-Jong Lee. The conference organisers would like to thank all those who made the meeting possible and contributed to its smooth running. In addition to the international organising

  9. From high-Tc superconductors to highly correlated Mott insulators—25 years of pulsed laser deposition of functional oxides in Leipzig

    NASA Astrophysics Data System (ADS)

    Lorenz, Michael; Hochmuth, Holger; Kneiß, Max; Bonholzer, Michael; Jenderka, Marcus; Grundmann, Marius

    2015-02-01

    Pulsed laser deposition (PLD) in Leipzig started in 1989 with Bi2Sr2Ca1Cu2O8 high-Tc superconducting thin films grown in a laser-ionization mass spectrometer. Here, we briefly review 25 years of development of advanced PLD processes in Leipzig and their application to high-Tc superconducting, wide-bandgap semiconducting and multiferroic thin films, nanostructures and composites. The first two decades were devoted to large-area and double-sided YBa2Cu3O7-δ thin films and hetero- and homoepitaxial ZnO-based films and nanowires, respectively. Based on that, transparent, oxide-based electronic devices are processed with epitaxial n-ZnO:Mg, Ga2O3, In2O3, or TiO2 films. Amorphous oxide films of p-ZnCo2O4 and p-NiO provide p-type counterparts in highly rectifying pn-junction devices and are an environmentally friendly alternative. Magnetoelectric multiferroic composites, and highly correlated iridate thin films are other current hot research topics. PLD appears as one of the most flexible growth techniques for functional oxides on research and demonstrator level.

  10. Quantum skyrmions and the destruction of long-range antiferromagnetic order in the high-Tc superconductors La2-xSrxCuO4 and YBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Marino, Eduardo C.; Silva Neto, Marcello B.

    2001-09-01

    We study the destruction of long-range antiferromagnetic order in the high-Tc superconductors La2-xSrxCuO4 and YBa2Cu3O6+x. The CP1-nonlinear sigma model formulation of the two-dimensional quantum Heisenberg antiferromagnet is used for describing the pure system. Dopants are introduced as independent fermions with an appropriate dispersion relation determined by the shape of the Fermi surface. Skyrmion topological defects are shown to be introduced by doping and their energy is used as an order parameter for the antiferromagnetic order. We obtain analytic expressions for the skyrmion energy as a function of doping that allow us to plot, without adjustable parameters, the curves TN(xc)×xc and M(x)×x, for the two compounds, in good quantitative agreement with the experimental data.

  11. Trends in orthorhombic crystal field parameters for trivalent rare-earth ions in high-Tc superconductors REBa2Cu3O7-δ - Correct interpretation based on standardization

    NASA Astrophysics Data System (ADS)

    Rudowicz, Czesław; Lewandowska, Monika

    2013-02-01

    Trends in orthorhombic crystal field parameters (CFPs) reported for RE3+ ions in high-Tc superconductors REBa2Cu3O7-δ are considered. The cases of trends based on the CFP sets belonging to different regions of CF parameter space are identified and clarified. The crucial feature of such correlated alternative CFP sets is their intrinsic incompatibility. This makes meaningless direct comparisons of such CFP sets and thus presentations of CFP trends involving a mixture of alternative CFP sets. The aim of this paper is to ascertain that correct interpretation of trends in orthorhombic CFPs must be based on standardization. Examples of graphs inappropriately representing trends in orthorhombic CFPs reported for REBa2Cu3O7-δ compounds are considered and the corrected graphs based on the standardized CFP sets are provided.

  12. Resistivity tensor correlations in the mixed state of electron-doped superconductor Nd2-xCexCuO4+δ

    NASA Astrophysics Data System (ADS)

    Charikova, T. B.; Shelushinina, N. G.; Harus, G. I.; Petukhov, D. S.; Petukhova, O. E.; Ivanov, A. A.

    2016-06-01

    The magnetic-field dependencies of the longitudinal and Hall resistance of the electron-doped compounds Nd2-xCexCuO4+δ in underdoped region with x = 0.14 and with varying degrees of disorder (δ) were investigated. It was established experimentally that the correlation between the longitudinal electrical resistivity and the Hall resistivity can be analyzed on the basis of scaling relationships: ρxy(B) ∼ [ρxx(B)]β. For the totality of the investigated single-crystal films of Nd2-xCexCuO4+δ/SrTiO3 the values of β from 0.8 to 1.55 is found. The observed feature in the electron-doped two-dimensional systems can be associated both with a displaying of anisotropic s - wave or d - wave pairing symmetry and with a pinning due to an essential degree of disorder in the samples under study.

  13. Fracture behavior of an inclined crack interacting with a circular inclusion in a high-TC superconductor under an electromagnetic force

    NASA Astrophysics Data System (ADS)

    Xue, Feng; Zhang, Zhaoxia; Gou, Xiaofan

    2015-11-01

    A simple model is proposed to investigate the interaction problem for a circular nonsuperconducting inclusion embedded in a high-TC superconducting matrix which contains an inclined crack, oriented at an arbitrary angle from the direction of the critical currents. The electromagnetic behavior is described by the critical state, the original Bean model. The perturbation brought upon by the circular inclusion and the crack on the critical current density is assumed to be negligible and not considered in this model. The distribution dislocation technology is applied to formulate the current problem. The stress intensity factors (SIFs) are obtained by solving the formulated singular integral equations. The effects of the crack angle, the elastic modulus, the inclusion-crack distance and the inclusion-crack size on the stress intensity factors are discussed in detail.

  14. Trends in orthorhombic crystal field parameters for trivalent rare-earth ions in high-Tc superconductors REBa₂Cu₃O₇-δ - correct interpretation based on standardization.

    PubMed

    Rudowicz, Czesław; Lewandowska, Monika

    2013-02-15

    Trends in orthorhombic crystal field parameters (CFPs) reported for RE(3+) ions in high-T(c) superconductors REBa(2)Cu(3)O(7-)(δ) are considered. The cases of trends based on the CFP sets belonging to different regions of CF parameter space are identified and clarified. The crucial feature of such correlated alternative CFP sets is their intrinsic incompatibility. This makes meaningless direct comparisons of such CFP sets and thus presentations of CFP trends involving a mixture of alternative CFP sets. The aim of this paper is to ascertain that correct interpretation of trends in orthorhombic CFPs must be based on standardization. Examples of graphs inappropriately representing trends in orthorhombic CFPs reported for REBa(2)Cu(3)O(7-)(δ) compounds are considered and the corrected graphs based on the standardized CFP sets are provided. PMID:23261624

  15. High Tc superconductors: The scaling of Tc with the number of bound holes associated with charge transfer neutralizing the multivalence cations

    NASA Technical Reports Server (NTRS)

    Vezzoli, G. C.; Chen, M. F.; Craver, F.

    1991-01-01

    It is observed that for the known high-T(sub c) Cu-, Tl-, and Bi-based superconductors, T(sub c) scales consistently with the number of bound holes per unit cell which arise from charge transfer excitations of frequency approximately = 3 x 10(exp 13) that neutralized the multivalence cations into diamagnetic states. The resulting holes are established on the oxygens. Extrapolation of this empirical fit in the up-temperature direction suggests a T(sub c) of about 220-230 K at a value of 25 holes/unit cell (approximately the maximum that can be materials-engineered into a high-T(sub c) K2MnF4 or triple Perovskite structure). In the down-temperature direction, the extrapolation gives a T(sub c) in the vicinity of 235 K for the Y-Ba-Cu-O system as well as the known maximum temperature of 23 K for low-T(sub c) materials shown by Nb3Ge. The approach is also consistent with the experimental findings that only multivalence ions which are diamagnetic in their atomic state (Cu, Tl, Bi, Pb, and Sb) associate with high-T(sub c) compounds.

  16. NMR Characterization of Sulphur Substitution Effects in the KxFe2−ySe2−zSz High-Tc Superconductor

    SciTech Connect

    Petrovic C.; Torchetti, D.A.; Imai, T.; Lei, H.C.

    2012-04-17

    We present a {sup 77}Se NMR study of the effect of S substitution in the high-T{sub c} superconductor K{sub x}Fe{sub 2-y}Se{sub 2-z}S{sub z} in a temperature range up to 250 K. We examine two S concentrations, with z = 0.8 (T{sub c} {approx} 26 K) and z = 1.6 (nonsuperconducting). The samples containing sulphur exhibit broader NMR line shapes than the K{sub x}Fe{sub 2}Se{sub 2} sample due to local disorder in the Se environment. Our Knight shift {sup 77}K data indicate that in all samples, uniform spin susceptibility decreases with temperature, and that the magnitude of the Knight shift itself decreases with increased S concentration. In addition, S substitution progressively suppresses low-frequency spin fluctuations. None of the samples exhibit an enhancement of low-frequency antiferromagnetic spin fluctuations near T{sub c} in 1/T{sub 1}T, as seen in FeSe.

  17. 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.

  18. Effect of particle size and particle size distribution on physical characteristics, morphology and crystal strucutre of explosively compacted high-Tc superconductors

    SciTech Connect

    Kotsis, I.; Enisz, M.; Oravetz, D.

    1994-12-31

    A superconductor, of composition Y(Ba,K,Na){sub 2}Cu{sub 3}O{sub x}/F{sub y} and a composite, of composition Y(Ba,K,Na){sub 2}Cu{sub 3}O{sub x}/F{sub y}+Ag, with changing K, Na and F content, but a constant silver content (Ag=10 mass per cent) was prepared using a single heat treatment. The resulting material was ground in a corundum lined mill, separated to particle size fractions of 0-40 {mu}m, 0-63 {mu}m and 63-900 {mu}m and explosively compacted, using an explosive pressure of 10{sup 4} MPa and a subsequent heat treatment. Best results were obtained with the 63-900 {mu}m fraction of composition Y(Ba{sub 1,95}K{sub 0,01})Cu{sub 3}O{sub x}F{sub 0,05}/Ag: porosity <0.01 cm{sup 3}/g and current density 2800 A/cm{sup 2} at 77 K.

  19. Imaging studies of hole-electron asymmetry observed in a lightly-doped high-Tc superconductor Ca2-xNaxCuO2Cl2

    NASA Astrophysics Data System (ADS)

    Kohsaka, Yuhki; Hanaguri, Tetsuo; Azuma, Masaki; Takagi, Hidenori; Davis, Seamus

    2005-03-01

    We have reported spectroscopic imaging on the electronic state intervening between the Mott insulator and the d-wave superconductor [1]. The electronic state with |E|<100 meV shows complex spatial modulations with 4a0x4a0 (a0: in-plane lattice constant) correlations. Moreover, the tunneling spectra show characteristic hole-electron asymmetry, which is thought to be related to the approach of the Mott insulator [2]. Here we report on new studies of imaging the 'Mottness' through mapping the asymmetry in tunneling spectra associated with high energies |E|>100 meV. Spectroscopic mapping of the asymmetry reveals strong 4a0x4a0 periodic modulation up to several hundreds meV. However the 4a0/3x4a0/3 component, which appears in the Fourier transform of the checkerboard pattern observed at |E|<100 meV, is negligle. This spatial modulation of the 'Mottness' may indicate that hole density is modulated with the 4a0x4a0 periodicity. This would imply that the 4a0/3x4a0/3 periodicity observed at lower energies may arise from umklapp scattering due to the hole density modulation. [1] T. Hanaguri et al., Nature 430, 1001 (2004). [2] P. W. Anderson and N. P. Ong, cond-mat/0405518.

  20. Resonance in the Electron-doped High-Tc Superconductor Pr0.88LaCe0.12CuO4-?

    SciTech Connect

    Wilson, Stephen D.; Dai, Pengcheng; Li, Shiliang; Chi, Songxue; Kang, H. J.; Lynn, J. W.

    2006-01-01

    In conventional superconductors, the interaction that pairs the electrons to form the superconducting state is mediated by lattice vibrations (phonons). In high-transition-temperature (high-T{sub c}) copper oxides, it is generally believed that magnetic excitations might play a fundamental role in the superconducting mechanism because superconductivity occurs when mobile 'electrons' or 'holes' are doped into the antiferromagnetic parent compounds. Indeed, a sharp magnetic excitation termed 'resonance' has been observed by neutron scattering in a number of hole-doped materials. The resonance is intimately related to superconductivity, and its interaction with charged quasi-particles observed by photoemission, optical conductivity, and tunnelling suggests that it might play a part similar to that of phonons in conventional superconductors. The relevance of the resonance to high-T{sub c} superconductivity, however, has been in doubt because so far it has been found only in hole-doped materials. Here we report the discovery of the resonance in electron-doped superconducting Pr{sub 0.88}LaCe{sub 0.12}CuO{sub 4-{delta}} (T{sub c} = 24 K). We find that the resonance energy (E{sub r}) is proportional to T{sub c} via E{sub r} {approx} 5.8k{sub B}T{sub c} for all high-T{sub c} superconductors irrespective of electron- or hole-doping. Our results demonstrate that the resonance is a fundamental property of the superconducting copper oxides and therefore must be essential in the mechanism of superconductivity.

  1. Finite gap behaviour in the superconductivity of the 'infinite layer' n-doped high-Tc superconductor Sr0.9La0.1CuO2

    NASA Astrophysics Data System (ADS)

    White, J. S.; Forgan, E. M.; Laver, M.; Häfliger, P. S.; Khasanov, R.; Cubitt, R.; Dewhurst, C. D.; Park, M.-S.; Jang, D.-J.; Lee, H.-G.; Lee, S.-I.

    2008-03-01

    We report on the first small-angle neutron scattering measurements from the flux line lattice (FLL) in the high-Tc cuprate superconductor Sr0.9La0.1CuO2. Using a polycrystalline sample, the scattered intensity decreases monotonically with scattering angle away from the undiffracted beam, independently of the azimuthal angle around the beam. The absence of clear peaks in the intensity suggests the establishment of a highly disordered FLL within the grains. We find that the intensity distribution may be represented by the form factor for a single flux line in the London approximation, with some contribution from crystal anisotropy. Most interestingly however, we find that, over the observed field range, the temperature dependence of the diffracted intensity is best represented by s-wave pairing, with lower limits of the gap values being very similar to the Bardeen-Cooper-Schrieffer value of Δ(0) = 1.76 kBTc. However, a qualitative consideration of corrections to the observed intensity suggests that these gap values are likely to be higher, implying strong-coupling behaviour.

  2. Numerical Study of a Multiorbital Hubbard Model for the Two-Leg Ladder BaFe2S3 High-Tc Superconductor Using the Density Matrix Renormalization Group

    NASA Astrophysics Data System (ADS)

    Patel, Niravkumar; Nocera, Alberto; Alvarez, Gonzalo; Arita, Ryotaro; Dagotto, Elbio

    Iron based high-Tc superconductors have attracted considerable attention because of its unconventional superconducting properties. Here, we analyze the magnetic and pairing characteristics of the recently discovered two-leg ladder material BaFe2S3 that becomes superconducting by applying pressure, using a two-orbital Hubbard model studied via the Density Matrix Renormalization Group technique. The hopping parameters, which spans up-to the 2nd nearest-neighbor rungs, were obtained from the ab-initio downfolded band structure at ambient and high pressures. The magnetic phase diagram at a realistic Hund coupling J / U = 0 . 25 is presented varying the Hubbard U, at select values of the electronic fillings. At half-filling, we find a robust magnetic order in excellent agreement with experiments i.e. antiferromagnetic (ferromagnetic) along the leg (rung) directions. We also discuss a possible tendency for this system to form a paired bound state of holes in a small but finite window of Hubbard U. The symmetries of this tentative paired ground state will be discussed.

  3. Role of the upper branch of the hour-glass magnetic spectrum in the formation of the main kink in the electronic dispersion of high-Tc cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Geffroy, Dominique; Chaloupka, Jiří; Dahm, Thomas; Munzar, Dominik

    2016-04-01

    We investigate the electronic dispersion of the high-Tc cuprate superconductors using the fully self-consistent version of the phenomenological model, where charge planar quasiparticles are coupled to spin fluctuations. The inputs we use, the underlying (bare) band structure and the spin susceptibility χ , are extracted from fits of angle-resolved photoemission and inelastic neutron scattering data of underdoped YBa2Cu3O6.6 by T. Dahm and coworkers [Nat. Phys. 5, 217 (2009), 10.1038/nphys1180]. Our main results are as follows: (i) We have confirmed the finding by Dahm and coworkers that the main nodal kink is, for the present values of the input parameters, determined by the upper branch of the hourglass of χ . We demonstrate that the properties of the kink depend qualitatively on the strength of the charge-spin coupling. (ii) The effect of the resonance mode of χ on the electronic dispersion strongly depends on its kurtosis in the quasimomentum space. A low (high) kurtosis implies a negligible (considerable) effect of the mode on the dispersion in the near-nodal region. (iii) The energy of the kink decreases as a function of the angle θ between the Fermi surface cut and the nodal direction, in qualitative agreement with recent experimental observations. We clarify the trend and make a specific prediction concerning the angular dependence of the kink energy in underdoped YBa2Cu3O6.6 .

  4. 77Se NMR Investigation of the KxFe2−ySe2 high-Tc Superconductor (Tc = 33 K)

    SciTech Connect

    Petrovic, C.; Torchetti, D.A. Fu, M.; Christensen, D.C.; Nelson, K.J.; Imai, T.; Lei, H.C.

    2011-03-18

    We report comprehensive {sup 77}Se NMR measurements on a single crystalline sample of the recently discovered FeSe-based high-temperature superconductor K{sub x}Fe{sub 2-y}Se{sub 2} (T{sub c} = 33 K) in a broad temperature range up to 290 K. Despite deviations from the stoichiometric KFe{sub 2}Se{sub 2} composition, we observed {sup 77}Se NMR line shapes as narrow as 4.5 kHz under a magnetic field applied along the crystal c axis, and found no evidence for co-existence of magnetic order with superconductivity. On the other hand, the {sup 77}Se NMR line shape splits into two peaks with equal intensities at all temperatures when we apply the magnetic field along the ab plane. This suggests that K vacancies may have a superstructure and that the local symmetry of the Se sites is lower than the tetragonal fourfold symmetry of the average structure. This effect might be a prerequisite for stabilizing the s{sub {+-}} symmetry of superconductivity in the absence of the hole bands at the Brillouin zone center. From the increase of NMR linewidth below T{sub c} induced by the Abrikosov lattice of superconducting vortices, we estimate the in-plane penetration depth {lambda}{sub ab} {approx} 290 nm and the carrier concentration n{sub e} {approx} 1 x 10{sup +21} cm{sup -3}. Our Knight shift {sup 77}K data indicate that the uniform spin susceptibility decreases progressively with temperature, in analogy with the case of FeSe (T{sub c} {approx} 9 K) as well as other FeAs high-T{sub c} systems. The strong suppression of {sup 77}K observed immediately below T{sub c} for all crystal orientations is consistent with a singlet pairing of Cooper pairs. We do not however observe the Hebel-Slichter coherence peak of the nuclear spin-lattice relaxation rate 1/T1 immediately below T{sub c}, expected for conventional BCS s-wave superconductors. In contrast with the case of FeSe, we do not observe evidence for an enhancement of low-frequency antiferromagnetic spin fluctuations near T{sub c

  5. Nuclear magnetic resonance: Its role as a microscopic probe of the electronic and magnetic properties of High-{Tc} superconductors and related materials

    SciTech Connect

    Suh, Byoung Jin

    1995-12-27

    NMR experiments are reported for Sr{sub 2}CuO{sub 2}Cl{sub 2}, HgBa{sub 2}CuO{sub 4+d}, YNi{sub 2}B{sub 2}C and YBa{sub 2}Cu{sub 3}O{sub 7}. NMR studies typify three different aspects of microscopic properties of HTSC. In non-superconducting antiferromagnetic (AF) prototype Sr{sub 2}CuO{sub 2}Cl{sub 2}, we used NMR to investigate Cu{sup 2+} correlated spin dynamics and AF phase transition in CuO2 layers. In the superconductors, we used NMR both to investigate the electronic properties of the Fermi-liquid in normal and superconducting states and to investigate flux lattice and flux-line dynamics in the superconducting state in presence of magnetic field. A summary of each study is given: {sup 35}Cl NMR was measured in Sr{sub 2}CuO{sub 2}Cl{sub 2} single crystals with T{sub N}=257K. {sub 35}Cl NMR relaxation rates showed crossover of Cu{sup 2+} spin dynamics from Heisenberg to XY-like correlation at 290 K well above T{sub N}. A field-dependent T{sub N} for H{perpendicular}c was observed and explained by a field-induced Ising-like anisotropy in ab plane. {sup 199}Hg NMR was measured in HgBa{sub 2}CuO{sub 4+d}. Properties of the Fermi-liquid are characterized by a single-spin fluid picture and opening of a spin pseudo-gap at q=0 above {Tc}. Below {Tc}, spin component of Knight shift decreases rapidly in agreement with prediction for d-wave pairing scheme. {sup 11}B and {sup 89}Y NMR/magnetization were measured in YNi{sub 2}B{sub 2}C. Temperature dependence of {sup 11}B Knight shift and of the NSLR gave a normal state which agrees with the Korringa relation, indicating that the AF fluctuations on the Ni sublattice are negligible. Opening of the superconducting gap obeys BCS. A NMR approach to investigate vortex thermal motion in HTSC is presented, based on contribution of thermal flux-lines motion to both T{sub 2}{sup {minus}1} and T{sub 1}{sup {minus}1}. Effects are demonstrated in YBa{sub 2}Cu{sub 3}O{sub 7} and HgBa{sub 2}CuO{sub 4+d}.

  6. Gauge Model of High-Tc Superconductivity

    NASA Astrophysics Data System (ADS)

    Kui Ng, Sze

    2012-12-01

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

  7. Heavy electron doping induced antiferromagnetic phase as the parent for the iron oxypnictide superconductor LaFeAs O1 -xHx

    NASA Astrophysics Data System (ADS)

    Iimura, Soshi; Matsuishi, Satoru; Hosono, Hideo

    2016-07-01

    We perform transport measurements and band structure calculations of electron-doped LaFeAs O1 -xHx over a wide range of x from 0.01 to 0.66. The T2 and √ T dependency of the resistivity are observed at x ˜0.17 and 0.41, respectively. The sign change of RH without opening of the spin-density-wave gap for 0.45 ≤x ≤0.58 and T

  8. Quantum spin correlations through the superconducting-to-normal phase transition in electron-doped superconducting Pr0.88LaCe0.12CuO4-δ

    PubMed Central

    Wilson, Stephen D.; Li, Shiliang; Zhao, Jun; Mu, Gang; Wen, Hai-Hu; Lynn, Jeffrey W.; Freeman, Paul G.; Regnault, Louis-Pierre; Habicht, Klaus; Dai, Pengcheng

    2007-01-01

    The quantum spin fluctuations of the S = 1/2 Cu ions are important in determining the physical properties of high-transition-temperature (high Tc) copper oxide superconductors, but their possible role in the electron pairing of superconductivity remains an open question. The principal feature of the spin fluctuations in optimally doped high-Tc superconductors is a well defined magnetic resonance whose energy (ER) tracks Tc (as the composition is varied) and whose intensity develops like an order parameter in the superconducting state. We show that the suppression of superconductivity and its associated condensation energy by a magnetic field in the electron-doped high-Tc superconductor Pr0.88LaCe0.12CuO4-δ (Tc = 24 K), is accompanied by the complete suppression of the resonance and the concomitant emergence of static antiferromagnetic order. Our results demonstrate that the resonance is intimately related to the superconducting condensation energy, and thus suggest that it plays a role in the electron pairing and superconductivity. PMID:17884981

  9. Fabrication Of High-Tc Superconducting Integrated Circuits

    NASA Technical Reports Server (NTRS)

    Bhasin, Kul B.; Warner, Joseph D.

    1992-01-01

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

  10. Gate-tuned superconductor-insulator transition in (Li,Fe)OHFeSe

    NASA Astrophysics Data System (ADS)

    Lei, B.; Xiang, Z. J.; Lu, X. F.; Wang, N. Z.; Chang, J. R.; Shang, C.; Zhang, A. M.; Zhang, Q. M.; Luo, X. G.; Wu, T.; Sun, Z.; Chen, X. H.

    2016-02-01

    The antiferromagnetic (AFM) insulator-superconductor transition has always been a center of interest in the underlying physics of unconventional superconductors. However, in the family of iron-based high-Tc superconductors, no intrinsic superconductor-insulator transition has been confirmed so far. Here, we report a first-order transition from superconductor to AFM insulator with a strong charge doping induced by ionic gating in the thin flakes of single crystal (Li,Fe)OHFeSe. The superconducting transition temperature (Tc) is continuously enhanced with electron doping by ionic gating up to a maximum Tc of 43 K, and a striking superconductor-insulator transition occurs just at the verge of optimal doping with highest Tc. A phase diagram of temperature-gating voltage with the superconductor-insulator transition is mapped out, indicating that the superconductor-insulator transition is a common feature for unconventional superconductivity. These results help to uncover the underlying physics of iron-based superconductivity as well as the universal mechanism of high-Tc superconductivity. Our finding also suggests that the gate-controlled strong charge doping makes it possible to explore novel states of matter in a way beyond traditional methods.

  11. Anisotropy of the Electron-Doped Infinite-Layer Superconductor Sr0.9La0.1CuO2

    NASA Astrophysics Data System (ADS)

    Kim, Heon-Jung; Park, Min-Seok; Jung, C. U.; Lee, Sung-Ik; Kim, Mun-Seog

    Anisotropy of a c-axis aligned Sr0.9La0.1CuO2 infinite-layer superconductor was studied by measuring the magnetization in different temperature (M(T)) and angle (M(θ)). The M(θ) and the critical temperature as a function of the angle (Tc2(θ)) deduced from M(T) was well described by the anisotropic Ginzburg-Landua theory with a moderate anisotropy value γ≈9. This low value, which is comparable to that of YBa2Cu3O7-δ implied strong interlayer coupling between CuO2 planes. In this compound, the strong interlayer coupling was thought to solely result from the crystal structure without charge reservoir blocks.

  12. Optoelectronic device applications of high [Tc] superconductors

    SciTech Connect

    Shi, Lei.

    1993-01-01

    Material processing and optoelectronic device applications of high T[sub c] materials are the main topic of this work. This dissertation is organized into three parts. Part I describes the material processing aspects of the HTSCs, YBCO thin films in particular. Pulsed laser deposition and device fabrication processes of high T[sub c] superconducting thin films are studied. 1/f noise measurement of HTSC thin films is also discussed. The deposition of CdS thin films onto YBCO superconducting films are studied. It is the author's effort to hybridize the semiconductor technology into HTSCs. High quality CdS/YBCO heterostructure is obtained. Part II concentrates on the construction of a femtosecond dye laser system and on the introduction of the femtosecond laser spectroscopy. Femtosecond colliding pulse mode-locking (CPM) dye laser has been built and is used to study the femtosecond transient reflectivity of high T[sub c] YBCO thin films and n-type GaAs samples. Part III describes in full detail both theory and experimental results of the optical response measurements on ultrathin YBCO thin films. Several important topics such as thermal diffusion, thermal boundary resistance and optical response in YBCO thin films are addressed. Single laser pulse duractions of 400 ps, 40 ps and 500 fs and a 40 ps pulse train are used in the experiments. A Double-bridge Voltage Correlation Technique is proposed and applied to measure the superconductivity recovery time in ultrathin YBCO films. Ultrafast voltage pulses faster than 40 ps are generated. A quasiparticle generation and recombination mechanism is further supported by two experimental evidences: (1) thickness dependence of the superconductivity recovery time; (2) the relaxation time scale <40ps.

  13. Quantized massive collective modes and massive spin fluctuations in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Kanazawa, I.; Sasaki, T.

    2015-10-01

    We have analyzed angle-resolved photoemission spectra of the single- and double-layered Bi-family high-Tc superconductors by using quantized massive gauge fields, which might contain effects of spin fluctuations, charge fluctuations, and phonons. It is suggested strongly that the quantized massive gauge fields might be mediating Cooper pairing in high-Tc cuprates.

  14. Microwave Absorption Studies on HIGH-Tc Superconductors and Related Materials Iv:. Esr as a Probe of Flux Pinning in Y-Ba-Cu-O Superconductors Prepared by the "mpmg" Method

    NASA Astrophysics Data System (ADS)

    Sugawara, K.; Baar, D. J.; Murakami, M.; Kondoh, A.; Yamaguchi, K.; Shiohara, Y.; Tanaka, S.

    The electron spin resonances of both DPPH surface coatings and Y2Ba1Cu1O5 ("211" phase) non-superconducting inclusions have been used to probe the flux pinning in high critical current density Y-Ba-Cu-O bulk superconductors prepared by the "MPMG" (Melt-Powder-Melt-Growth) method. The ESR lineshapes for both the surface coatings and the 211 inclusions were observed to broaden when the MPMG samples entered the superconducting state. The excess ESR linewidth for the DPPH coatings was found to increase monotonically with decreasing temperature, as the result of increasing field gradients due to pinned flux. The ESR linewidth of the 211 inclusions had a complicated temperature dependence. This linewidth was less than that of isolated Y2Ba1Cu1O5 below 20 K, possibly due to a lower magnetic ordering temperature, mechanical stress, and/or different composition of the inclusions as compared to isolated Y2Ba1Cu1O5. Strong hysteresis in the ESR linewidths due to flux trapping was observed at low temperatures. Comparisons with the ESR linewidth of DPPH coated on the surface of the samples suggest that this flux trapping is due to strong pinning in the neighborhood of the 211 inclusions.

  15. High Tc superconducting materials and devices

    NASA Technical Reports Server (NTRS)

    Haertling, Gene H.

    1990-01-01

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

  16. Epitaxial stabilization of ultra thin films of electron doped manganites

    NASA Astrophysics Data System (ADS)

    Middey, S.; Kareev, M.; Meyers, D.; Liu, X.; Cao, Y.; Tripathi, S.; Yazici, D.; Maple, M. B.; Ryan, P. J.; Freeland, J. W.; Chakhalian, J.

    2014-05-01

    Ultra-thin films of the electron doped manganite La0.8Ce0.2MnO3 were grown in a layer-by-layer growth mode on SrTiO3 (001) substrates by pulsed laser interval deposition. High structural quality and surface morphology were confirmed by a combination of synchrotron based x-ray diffraction and atomic force microscopy. Resonant X-ray absorption spectroscopy measurements confirm the presence of Ce4+ and Mn2+ ions. In addition, the electron doping signature was corroborated by Hall effect measurements. All grown films show a ferromagnetic ground state as revealed by both dc magnetization and x-ray magnetic circular dichroism measurements and remain insulating contrary to earlier reports of a metal-insulator transition. Our results hint at the possibility of electron-hole asymmetry in the colossal magnetoresistive manganite phase diagram akin to the high-Tc cuprates.

  17. The effect of a large amount of Ag introduced into the Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10+δ (110 K phase) high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Song, Ki Young; Lee, Min Soo

    2006-12-01

    We synthesized a 50 wt% Ag-doped Bi-110 K phase high-Tc superconductor by a solid state reaction method. The nominal composition of the 110 K phase was Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10+δ, which was prepared from powders of Bi2O3 (99.99%), PbO (99.99%), SrCO3 (99.99%), CaCO3 (99.99%) and CuO (99.99%). The synthesized Bi single-phase high-Tc superconductor was pulverized and mixed with Ag powder amounting to 50 wt%. Then the 50 wt% Ag-doped composition was sintered between 830 and 850 °C, and the superconducting properties, such as the structural characteristics, critical temperature (Tc), grain size and the mapping image of the surface were investigated. The critical temperature was about 99 K, independent of the sintering temperature in the range from 830 to 850 °C, and most superconducting grains were sintered in the layer near the surface, while Ag particles were aggregated and sintered as clusters and mostly distributed over an inside layer during the sintering process.

  18. Multiple sign reversal of the Hall effect in electron-doped superconductor Pr0.9LaCe0.1CuO4+/-δ thin films

    NASA Astrophysics Data System (ADS)

    Zhu, Beiyi

    We have investigated the temperature and field dependence of the Hall resistivity of the electron-doped Pr0.9LaCe0.1CuO4+/-δ(PLCCO) superconducting thin films(Tc 0 =22 K). In the low magnetic field region (0.03 ~ 0.1 T), a concrete triple sign reversal of the Hall resistivity ρxy has been observed in the ρxy (T) curve. With the increase of the magnetic field, the Hall resistivity ρxy (T) suffers triple, double, single sign reversal transitions and it will be completely disappear around 4.5 T. We contribute the triple sign reversal to the competition between the hole and the electron carriers in our electron-doped samples and a fourth sign reversal may be expected in the regime of the two-band system.

  19. Direct Pen Writing of High-Tc, Flexible Magnesium Diboride Superconducting Arrays.

    PubMed

    Xue, Mianqi; Chen, Dong; Long, Yujia; Wang, Peipei; Zhao, Lingxiao; Chen, Genfu

    2015-06-24

    High-Tc , flexible MgB2 -nanowire-based superconducting arrays are fabricated via a direct pen writing method on both copper foils and poly(dimethylsiloxane) (PDMS) substrates. Such superconducting arrays constitute a new approach for fabricating superconducting devices. The realization of a PDMS-based device demonstrates the potential for expanding this material into other high-Tc superconductor systems, which may lead to novel ways of driving the development of "real-life" applications. PMID:25974155

  20. Research on high Tc superconducting compounds

    NASA Technical Reports Server (NTRS)

    Oliver, Frederick W. (Principal Investigator)

    1996-01-01

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

  1. Direct observation of intrinsic Josephson junction characteristics in electron-doped Sm2-xCexCuO4-δ

    NASA Astrophysics Data System (ADS)

    Kawakami, Tsuyoshi; Suzuki, Minoru

    2007-10-01

    We have investigated the current-voltage (CV) characteristics of the intrinsic Josephson junctions (IJJs) in the electron-doped high- Tc superconductor Sm2-xCexCuO4-δ by using a small mesa structure fabricated on a single crystal surface. It is found that multiple resistive branches, i.e., typical IJJ characteristics, are observed in the CV characteristics when the junction area of a mesa is 10μm2 or less. It is also found that a typical Josephson critical current density Jc is 7.5kA/cm2 at 4.2K for Tc=20.7K . The Josephson penetration depth is experimentally estimated to be 1.0-1.6μm from the size dependence of Jc . Both Jc and Tc are found to decrease with the carrier doping level, as is found for hole-doped Bi2Sr2CaCu2O8+δ in the heavily overdoped region. These results are discussed in relation to the current locking in terms of the coupled Josephson junction stack model.

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

    SciTech Connect

    Sugiura, Toshihiko; Fujimori, Hideki

    1996-05-01

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

  3. Applications using high-Tc superconducting terahertz emitters

    PubMed Central

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

    2016-01-01

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

  4. Applications using high-Tc superconducting terahertz emitters

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  5. Effects of La-doping on crystallinity and dielectric properties of SrAl 0.5Ta 0.5O 3 thin films for high- Tc superconductor multilayer structure

    NASA Astrophysics Data System (ADS)

    Takahashi, Yoshihiro; Wakana, Hironori; Ogawa, Akihiro; Morishita, Tadataka; Tanabe, Keiichi

    2003-10-01

    La xSr 1- xAl 0.5Ta 0.5O 3 (La-SAT) thin films were prepared to examine the effects of La-doping to SrAl 0.5Ta 0.5O 3 (SAT) as intermediate insulating films for high- Tc devices. 300-nm-thick La-SAT films were grown on approximately 10-μm-thick YBa 2Cu 3O 7- δ (YBCO) films by metalorganic chemical vapor deposition with the La-doping ratio x of 0-0.2. The La-SAT films with x⩽0.1 exhibited good crystallinity and monotonic lattice contraction with increasing x. 300-nm-thick La 0.2Y 0.9Ba 1.9Cu 3O 7- δ (La-YBCO) films deposited on these La-SAT films had good Tc and Jc values comparable to those for the SAT films without La-doping. On the other hand, the La-SAT film with x≅0.2 changed to have random orientation and a La-YBCO film on the La-SAT film showed much poorer Tc and Jc values. These results suggest that the La solubility limit to SAT exists in the range of x=0.1-0.2, although a monotonic decrease in the dielectric constant with increasing x was observed for all the La-SAT films in the x range of 0-0.2 and low conductance less than 10 -6 S.

  6. Metallic alloy targets for high Tc superconducting film deposition

    NASA Astrophysics Data System (ADS)

    Manini, P.; Nigro, A.; Romano, P.; Vaglio, R.

    1989-02-01

    Many experiments are nowadays conducting worldwide on superconducting films based on the recently developed high Tc superconductor materials (YBCO, BISCO, etc). There are different ways to produce these films, among which sputtering and evaporation are most popular. Normally, use is made of oxides, pure metals or compounds as material sources. In the present paper we describe the fabrication process and the physico-chemical characteristics of various metallic alloy components for both sputtering and evaporation processes which show various advantages in terms of stability, easiness of use, purity, flexibility in composition and shape and allow good process control. Deposition techniques and experimental results obtained on thin films of the new superconductors realized starting from these alloys are also reported.

  7. Modulation effect of interlayer spacing on the superconductivity of electron-doped FeSe-based intercalates.

    PubMed

    Hayashi, Fumitaka; Lei, Hechang; Guo, Jiangang; Hosono, Hideo

    2015-04-01

    FeSe-based intercalates are regarded as promising candidates for high-critical temperature (Tc) superconductors. Here we present new Na- and Sr-intercalated FeSe superconductors with embedded linear diamines (H2N)CnH2n(NH2) (abbreviated as DA; n = 0, 2, 3, or 6) prepared using a low-temperature ammonothermal method to investigate the effect of interlayer spacing on the superconductivity of electron-doped FeSes. The embedded DA formed a monolayer or bilayer in the interlayer of FeSe. The interlayer spacing between nearest FeSe layers could be tuned from 0.87 to 1.14 nm without significant change in the Na/Sr content or the ratio of Fe to Se. Importantly, bilayer phases Na/ethylenediamine- and Sr/hydrazine-FeSe show improved structural stability compared to that of Na/NH3-FeSe. The series of Na- and Sr-intercalated FeSe samples exhibited nearly the same high Tc values of 41-46 and 34-38 K, respectively, irrespective of rather different interlayer spacing d. The peculiar insensitivity for both series can be ascribed to the negligible dispersions of bands along the c axis; i.e., Fermi surfaces are nearly two-dimensional when d is larger than a certain threshold value (dsat) of ∼0.9 nm. The Fermi surface shape is already optimal for Tc, and a larger d will not enhance Tc further. On the other hand, the difference in Tc between two series may be explained by the higher carrier doping level in Na/DA-FeSes compared to that in Sr/DA-FeSes, resulting in the increased density of states at the Fermi level and superconducting pairing strength. PMID:25768303

  8. Role of hydrogen in the electronic properties of CaFeAsH-based superconductors

    NASA Astrophysics Data System (ADS)

    Huang, Y. N.; Liu, D. Y.; Zou, L. J.; Pickett, W. E.

    2016-05-01

    The electronic and magnetic properties of the hydride superconductor CaFeAsH, which superconducts up to 47 K when electron doped with La, and the isovalent alloy system CaFeAsH1 -xFx are investigated using density functional based methods. The Q ⃗=(π ,π ,0 ) peak of the nesting function ξ (q ⃗) is found to be extremely strong and sharp, and the additional structure in ξ (q ⃗) associated with the near-circular Fermi surfaces (FSs) that may impact low energy excitations is quantified. The unusual band introduced by H, which shows strong dispersion perpendicular to the FeAs layers, is shown to be connected to a peculiar van Hove singularity just below the Fermi level. This band provides a three-dimensional electron ellipsoid Fermi surface not present in other Fe-based superconducting materials nor in CaFeAsF. Electron doping by 25% La or Co has a minor effect on this ellipsoid Fermi surface, but suppresses FS nesting strongly, consistent with the viewpoint that eliminating strong nesting and the associated magnetic order allows high Tc superconductivity to emerge. Various aspects of the isovalent alloy system CaFeAsH1 -xFx and means of electron doping are discussed in terms of influence of incipient bands.

  9. Vortex movement and magnetization of high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Roytburd, A. L.; Turchinskaya, M. J.

    1991-01-01

    The basic characteristics of the thermoactivated vortex mobility in Y1Ba2Cu3O7 are determined by measurement of the kinetics of magnetization in two time regimes. The analysis of the kinetics of the approach of the equilibrium results in the activation energy, while the measurement of the log-creep rate allows determination of the activated moment. It is shown that the movement of vortices can be regarded as the diffusion process.

  10. Dipolar clusters and ferroelectricity in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Kusmartsev, F. V.; Saarela, M.

    2015-08-01

    In this paper, we show that doping of hole charge carriers induces formation of resonance plaquettes (RPs) having electric dipolar moments and fluctuating stripes in cuprates. A single RP is created by many-body interactions between the dopant ion or a charge fluctuation outside and holes inside the CuO plane. In such a process, Coulomb interacting holes in the CuO plane are self-organized into four-particles resonance valence bond plaquettes bound with dopants or polarons located in the spacer layer between CuO planes. Such RPs have ordered and disordered phases. They are ordered into charge density waves (CDW) or stripes only at certain conditions. The lowest energy of the ordered phase corresponds to a local antiferroelectric ordering. The RPs mobility is very low at low temperatures and they are bound into dipole-dipole pairs. Electromagnetic radiation interacts strongly with RPs electric dipoles and when the sample is subjected to it, the mobility changes significantly. This leads to a fractal growth of dipolar RP clusters. The existence of electric dipoles and CDW reveal a series of new phenomena such as ferroelectricity, strong light and microwave absorption and the field induced superconductivity.

  11. Magnetism and electron pairing in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Tsang, T.

    1990-01-01

    Correlated wave functions are used for YBa2Cu3O(7-y) where epsilon(d)-epsilon(p) is about 0 for Cu3d- and 02p-electrons. The electrons are delocalized (metallic) for y less than 0.5 with weak and temperature-independent paramagnetism. In contrast, the systems are conventional antiferromagnetic insulators for y greater than 0.6 with a narrow y between 0.5 and 0.6 transition region. These results are in agreement with magnetic and neutron diffraction data.

  12. Magnetic and thermal properties of high Tc superconductors

    SciTech Connect

    Lee, Wonchoon.

    1990-09-21

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

  13. Grain boundary dissipation in high-{Tc} superconductors

    SciTech Connect

    Gray, K. E.; Miller, D. J.; Field, M. B.; Kim, D. H.; Berghuis, P.

    2000-04-03

    Thin-film and bulk [001] tilt bicrystal grain boundaries (GBs) in YBa{sub 2}Cu{sub 3}O{sub 7} exhibit a strong dependence of critical current density, J{sub c} on misorientation angle. What was initially difficult to understand was the 30x smaller J{sub c} in bulk GBs which are microscopically more perfect. The authors review an explanation of this zero-field data, which is based on the pinning of Josephson vortices by the meandering found in thin-film GBs. In addition, there is evidence that J{sub c} of GBs does not drop as quickly with applied magnetic field as expected by simple Josephson junction models. The long-wavelength pinning potential due to meandering is less effective at high fields, but Gurevich and Cooley (GC) proposed a new mechanism for an enhanced GB J{sub c} arising from pinned Abrikosov vortices in the banks of a GB which present a static, quasiperiodic pinning potential to pin GB vortices. They find a peak in J{sub c} and an unusual hysteresis which give considerable support to the GC concept. In low fields, the GBs exhibit a larger J{sub c} for field cooling, which is opposite to the usual hysteresis but agrees with GC due to the larger Abrikosov vortex density in the banks. Magnetization data on the same sample are consistent including the identification of the irreversibility field.

  14. Flux pinning and percolation in high-Tc oxide superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, Teruo; Ni, Baorong; Yamafuji, Kaoru

    Critical current characteristics in quench and melt growth (QMG) processed Y-Ba-Cu-O are investigated by ac inductive measurements. The critical current in these samples is percolative as is observed in sintered materials. However, this percolative behavior is not caused by weak-link grain boundaries but seems to be mainly attributed to layers of nonsuperconducting solidified melt. The experimental result of magnetization critical current density is compared with the theoretical estimate from the effective medium theory. It is also found that the shielding current with very high density flows locally inside the sample. Candidates for the dominant pinning centers in QMG processed samples are also discussed.

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

    DOEpatents

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

    1999-01-01

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

  16. High- Tc thin-film magnetometer

    SciTech Connect

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

    1990-09-01

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

  17. Direct observation of a Fermi liquid-like normal state in an iron-pnictide superconductor.

    PubMed

    Tytarenko, Alona; Huang, Yingkai; de Visser, Anne; Johnston, Steve; van Heumen, Erik

    2015-01-01

    There are two prerequisites for understanding high-temperature (high-Tc) superconductivity: identifying the pairing interaction and obtaining a correct description of the normal state from which superconductivity emerges. The nature of the normal state of iron-pnictide superconductors, and the role played by correlations arising from partially screened interactions, are still under debate. Here we show that the normal state of carefully annealed electron-doped BaFe(2-x)Co(x)As2 at low temperatures has all the hallmark properties of a local Fermi liquid, with a more incoherent state emerging at elevated temperatures, an identification made possible using bulk-sensitive optical spectroscopy with high frequency and temperature resolution. The frequency dependent scattering rate extracted from the optical conductivity deviates from the expected scaling M2 (ω, T) ∝ (ħω)(2) + (pπkBT)(2) with p ≈ 1.47 rather than p = 2, indicative of the presence of residual elastic resonant scattering. Excellent agreement between the experimental results and theoretical modeling allows us to extract the characteristic Fermi liquid scale T0 ≈ 1700 K. Our results show that the electron-doped iron-pnictides should be regarded as weakly correlated Fermi liquids with a weak mass enhancement resulting from residual electron-electron scattering from thermally excited quasi-particles. PMID:26201499

  18. Subgap Structures in High-Tc Intrinsic Josephson Junctions

    NASA Astrophysics Data System (ADS)

    Müller, Paul

    1998-03-01

    Due to their extremely short coherence length many high-Tc superconductors form natural superconducting multilayers. Adjacent superconducting layers are weakly coupled by the Josephson effect. As a result single crystals act intrinsically as vertical stacks of hundreds of Josephson junctions. We start by summarizing our present state of knowledge, including recent observations of Cherenkov radiation from moving fluxons (G. Hechtfischer, R. Kleiner, A.V. Ustinov, P. Müller, Phys. Rev. Lett. 79, 1365 (1997), and this conference.), and the direct measurement of the (collective) Josephson plasma frequency. We then report on pronounced structures in the current-voltage characteristics of Bi_2Sr_2CaCu_2O8 single crystals, and of Tl_2Ba_2Ca_2Cu_3O_10 thin films. These structures appear well below the superconducting gap, independent on magnetic field and temperatures up to 0.5 T_c(K. Schlenga, G. Hechtfischer, R. Kleiner, W. Walkenhorst, P. Müller, Phys. Rev. Lett. 76, 4943 (1996).). We explain these features by coupling between c-axis phonons and Josephson oscillations(Ch. Helm, Ch. Preis, F. Forsthofer, J. Keller, K. Schlenga, R. Kleiner, P. Müller, Phys. Rev. Lett. 79, 737 (1997).). C-axis lattice vibrations between adjacent superconducting layers are exited by the rf Josephson currents in the resistive state. Our results correspond well to the frequencies of longitudinal c-axis phonons.

  19. Anomalous correlation effects and unique phase diagram of electron-doped FeSe revealed by photoemission spectroscopy

    PubMed Central

    Wen, C. H. P.; Xu, H. C.; Chen, C.; Huang, Z. C.; Lou, X.; Pu, Y. J.; Song, Q.; Xie, B. P.; Abdel-Hafiez, Mahmoud; Chareev, D. A.; Vasiliev, A. N.; Peng, R.; Feng, D. L.

    2016-01-01

    FeSe layer-based superconductors exhibit exotic and distinctive properties. The undoped FeSe shows nematicity and superconductivity, while the heavily electron-doped KxFe2−ySe2 and single-layer FeSe/SrTiO3 possess high superconducting transition temperatures that pose theoretical challenges. However, a comprehensive study on the doping dependence of an FeSe layer-based superconductor is still lacking due to the lack of a clean means of doping control. Through angle-resolved photoemission spectroscopy studies on K-dosed thick FeSe films and FeSe0.93S0.07 bulk crystals, here we reveal the internal connections between these two types of FeSe-based superconductors, and obtain superconductivity below ∼46 K in an FeSe layer under electron doping without interfacial effects. Moreover, we discover an exotic phase diagram of FeSe with electron doping, including a nematic phase, a superconducting dome, a correlation-driven insulating phase and a metallic phase. Such an anomalous phase diagram unveils the remarkable complexity, and highlights the importance of correlations in FeSe layer-based superconductors. PMID:26952215

  20. Anomalous correlation effects and unique phase diagram of electron-doped FeSe revealed by photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Wen, C. H. P.; Xu, H. C.; Chen, C.; Huang, Z. C.; Lou, X.; Pu, Y. J.; Song, Q.; Xie, B. P.; Abdel-Hafiez, Mahmoud; Chareev, D. A.; Vasiliev, A. N.; Peng, R.; Feng, D. L.

    2016-03-01

    FeSe layer-based superconductors exhibit exotic and distinctive properties. The undoped FeSe shows nematicity and superconductivity, while the heavily electron-doped KxFe2-ySe2 and single-layer FeSe/SrTiO3 possess high superconducting transition temperatures that pose theoretical challenges. However, a comprehensive study on the doping dependence of an FeSe layer-based superconductor is still lacking due to the lack of a clean means of doping control. Through angle-resolved photoemission spectroscopy studies on K-dosed thick FeSe films and FeSe0.93S0.07 bulk crystals, here we reveal the internal connections between these two types of FeSe-based superconductors, and obtain superconductivity below ~46 K in an FeSe layer under electron doping without interfacial effects. Moreover, we discover an exotic phase diagram of FeSe with electron doping, including a nematic phase, a superconducting dome, a correlation-driven insulating phase and a metallic phase. Such an anomalous phase diagram unveils the remarkable complexity, and highlights the importance of correlations in FeSe layer-based superconductors.

  1. Anomalous correlation effects and unique phase diagram of electron-doped FeSe revealed by photoemission spectroscopy.

    PubMed

    Wen, C H P; Xu, H C; Chen, C; Huang, Z C; Lou, X; Pu, Y J; Song, Q; Xie, B P; Abdel-Hafiez, Mahmoud; Chareev, D A; Vasiliev, A N; Peng, R; Feng, D L

    2016-01-01

    FeSe layer-based superconductors exhibit exotic and distinctive properties. The undoped FeSe shows nematicity and superconductivity, while the heavily electron-doped KxFe2-ySe2 and single-layer FeSe/SrTiO3 possess high superconducting transition temperatures that pose theoretical challenges. However, a comprehensive study on the doping dependence of an FeSe layer-based superconductor is still lacking due to the lack of a clean means of doping control. Through angle-resolved photoemission spectroscopy studies on K-dosed thick FeSe films and FeSe0.93S0.07 bulk crystals, here we reveal the internal connections between these two types of FeSe-based superconductors, and obtain superconductivity below ∼46 K in an FeSe layer under electron doping without interfacial effects. Moreover, we discover an exotic phase diagram of FeSe with electron doping, including a nematic phase, a superconducting dome, a correlation-driven insulating phase and a metallic phase. Such an anomalous phase diagram unveils the remarkable complexity, and highlights the importance of correlations in FeSe layer-based superconductors. PMID:26952215

  2. Tunneling spectroscopy of anisotropic superconductors

    SciTech Connect

    Kashiwaya, Satoshi; Koyanagi, Masao; Kajimura, Koji; Tanaka, Yukio

    1996-12-31

    Tunneling spectroscopy of normal-insulator-superconductor junction is investigated theoretically. In anisotropic superconductors, differently from the case of isotropic superconductor, the effective pair potentials felt by quasiparticles depend on the direction of their motion. By taking this effect into account, it is shown that the conductance spectra strongly depend on the crystal orientation. Using Green`s function method, local density of states (LDOS) in superconductor is also calculated. The close relation between conductance spectra and LDOS is presented. The calculation is compared with experimental spectra of high-{Tc} superconductors.

  3. Generalized statistics and high- Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Uys, H.; Miller, H. G.; Khanna, F. C.

    2001-10-01

    Introducing the generalized, non-extensive statistics proposed by Tsallis (J. Stat. Phys. 52 (1/2) (1988) 479) into the standard s-wave pairing BCS theory of superconductivity in 2D yields a reasonable description of many of the main properties of high temperature superconductors, provided some allowance is made for non-phonon mediated interactions.

  4. Superconductor as movie star

    SciTech Connect

    Pool, R.

    1993-12-03

    Japanese researchers have succeeded in producing a movie of changes in the magnetic flux lattice of a high-Tc superconductor as it is warmed. They used a technique called electron holography, in which electrons are passed through a superconductor, and flux lines are visualized as interference patterns induced by the electrons as they undergo a phase change as they pass to one side or another of the flux lines. The technique will have application in designing superconductors so that they do not lose their superconductivity when exposed to magnetic fields.

  5. Unconventional high-Tc superconductivity in fullerides.

    PubMed

    Takabayashi, Yasuhiro; Prassides, Kosmas

    2016-09-13

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

  6. EDITORIAL: Focus on Iron-Based Superconductors FOCUS ON IRON-BASED SUPERCONDUCTORS

    NASA Astrophysics Data System (ADS)

    Hosono, Hideo; Ren, Zhi-An

    2009-02-01

    Superconductivity is the most dramatic and clear cut phenomenon in condensed matter physics. Realization of room temperature superconductors, which would lead to the revolution of our society, is an ultimate goal for researchers. The discovery of high Tc cuprate superconductors in 1986 by Bednorz and Müller triggered intensive research worldwide and the maximum critical temperature has been raised above 100 K. Scientific research on this break-through material clarified a new route to high Tc materials, carrier doping to a Mott insulator with anti-ferromagnetic ordering. High superconductivity occurs in the neighborhood of Mott-insulators and Fermi-metals. Such a view, which was completely new, now stands as a guiding principle for exploring new high Tc materials. Many theoretical approaches to the mechanism for cuprate superconductors have been carried out to understand this unexpected material and to predict new high Tc materials. In 2006 a new superconductor based on iron, LaFeOP, was discovered by a group at Tokyo Institute of Technology, Japan. Iron, as a ferromagnet, was believed to be the last element for the realization of superconductivity because of the way ferromagnetism competes against Cooper pair formation. Unexpectedly, however, the critical temperature remained at 4-6 K irrespective of hole/electron-doping. A large increase in the Tc to 26 K was then found in LaFe[O1-xFx]As by the same group (and was published on 23 February 2008, in the Journal of the American Chemical Society). The Tc of this material was further raised to 43 K under a pressure of 2 GPa and scientists in China then achieved a Tc of 56 K at ambient pressure by replacing La with other rare earth ions with smaller radius—a critical temperature that is second only to the high Tc cuprates. This fast progress has revitalized research within superconductivity and in 2008 there were more than seven international symposia specifically on Fe(Ni)-based superconductors. Through the rapid

  7. High-Tc SQUID Magnetometers for Industrial Applications

    NASA Astrophysics Data System (ADS)

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

    1998-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  9. High Tc: The Discovery of RBCO

    NASA Astrophysics Data System (ADS)

    Chu, C. W.

    2007-03-01

    It was said by Emerson that ``there is no history; there is only biography.'' This is especially true when the events are recounted by a person who, himself, has been heavily involved and the line between history and autobiography can become blurred. However, it is reasonable to say that discovery itself is not a series of accidents but an inevitable product of each development stage of scientific knowledge as was also pointed out by Holden et al. (1) The discovery of RBCO (2,3) with R = Y, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu is no exception. In this presentation, I will briefly recount several events that were crucial to the discovery of RBCO: those before 1986 (4) that sowed the seeds in our group important to our later high temperature superconductivity effort; those in 1986 (5) that were critical to our discovery of the 93 K RBCO soon after the discovery of the 35 K high temperature superconductor by M"uller and Bednorz (6); and those in 1987 when the barrier of the liquid nitrogen boiling temperature of 77 K was finally conquered. 1. G. J. Holton et al., American Scientist 84, 364 (1996). 2. M. K. Wu et al., Phys. Rev. Lett. 58, 908 (1987). 3. P. H. Hor et al., Phys. Rev. Lett. 58, 1891 (1987). 4. C. W. Chu et al., S. S. Comm. 18, 977 (1976); C. W. Chu and V. Diatchenko, Phys. Rev. Lett. 41, 572 (1978); T. H. Lin et al., Phys. Rev. B(RC) 29, 1493 (1984); J. H. Lin et al., J. Low Temp. Phys. 58, 363 (1985). 5. C. W. Chu et al., Phys. Rev. Lett. 58, 405 (1987); C. W. Chu et al., Science 235, 567 (1987). 6. J. G. Bednorz and K. A. M"uller, Z. Phys. B64, 189 (1986).

  10. Fabrication of sensitive high Tc bolometers

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  11. Link between spin fluctuations and Cooper pairing in copper oxide superconductors

    NASA Astrophysics Data System (ADS)

    Jin, Kui

    2012-02-01

    Although it is generally accepted that superconductivity is unconventional in the high-Tc cuprates, the relative importance of phenomena such as spin and charge (strip) order, superconductivity fluctuations, proximity to Mott insulator, a pseudogap phase and quantum criticality are still a matter of debate. In electron-doped cuprates, the absence of ``anomalousphase in the underdoped region of the phase diagram and weaker electron correlations suggest that Mott physics and other unidentified competing orders are less relevant and that antiferromagnetic (AFM) spin fluctuations are the dominant feature. In this talk, I will report results of low temperature magnetotransport experiments in optimal to overdoped (non-superconducting) thin films of the electron-doped cuprate La2-xCexCuO4 (LCCO). We find that a linear-in-T scattering rate is correlated with the superconductivity (Tc). Our results show that an envelope of such scattering surrounds the superconducting phase, surviving to 20 mK (the limit of our experiments) when superconductivity is suppressed by magnetic fields [1]. Comparison with similar behavior found in organic superconductors [2] strongly suggests that the linear-in-T resistivity in the electron-doped cuprates is caused by spin-fluctuation scattering. Because linear-in-T scattering has also been linked to T% c in some hole-doped cuprates [2], our results suggest a fundamental connection between AFM spin fluctuations and the pairing mechanism of high temperature superconductivity in all cuprates. In addition, I will discuss how quantum criticality plays a significant role in shaping the anomalous properties of the electron-doped cuprate phase diagram. We identify quantum critical scaling in LCCO with a line of quantum critical points that surrounds the superconducting phase as a function of magnetic field and charge doping [3]. [4pt] [1] K. Jin, N.P. Butch, K. Kirshenbaum, J. Paglione, and R.L. Greene, Nature 476, 73 (2011).[0pt] [2] L. Taillefer, Annu

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  14. Doping-dependent charge order correlations in electron-doped cuprates.

    PubMed

    da Silva Neto, Eduardo H; Yu, Biqiong; Minola, Matteo; Sutarto, Ronny; Schierle, Enrico; Boschini, Fabio; Zonno, Marta; Bluschke, Martin; Higgins, Joshua; Li, Yangmu; Yu, Guichuan; Weschke, Eugen; He, Feizhou; Le Tacon, Mathieu; Greene, Richard L; Greven, Martin; Sawatzky, George A; Keimer, Bernhard; Damascelli, Andrea

    2016-08-01

    Understanding the interplay between charge order (CO) and other phenomena (for example, pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. We use resonant x-ray scattering to measure the CO correlations in electron-doped cuprates (La2-x Ce x CuO4 and Nd2-x Ce x CuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2-x Ce x CuO4 show that CO is present in the x = 0.059 to 0.166 range and that its doping-dependent wave vector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166 but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wave vector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall, these findings indicate that, although verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates. PMID:27536726

  15. Doping-dependent charge order correlations in electron-doped cuprates

    PubMed Central

    da Silva Neto, Eduardo H.; Yu, Biqiong; Minola, Matteo; Sutarto, Ronny; Schierle, Enrico; Boschini, Fabio; Zonno, Marta; Bluschke, Martin; Higgins, Joshua; Li, Yangmu; Yu, Guichuan; Weschke, Eugen; He, Feizhou; Le Tacon, Mathieu; Greene, Richard L.; Greven, Martin; Sawatzky, George A.; Keimer, Bernhard; Damascelli, Andrea

    2016-01-01

    Understanding the interplay between charge order (CO) and other phenomena (for example, pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. We use resonant x-ray scattering to measure the CO correlations in electron-doped cuprates (La2−xCexCuO4 and Nd2−xCexCuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2−xCexCuO4 show that CO is present in the x = 0.059 to 0.166 range and that its doping-dependent wave vector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166 but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wave vector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall, these findings indicate that, although verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates. PMID:27536726

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  18. Identification of Liquids by High-Tc Josephson THz Detectors

    NASA Astrophysics Data System (ADS)

    Divin, Y.; Lyatti, M.; Poppe, U.; Urban, K.

    Fast and reliable detection of liquids will be required for future checkpoint screening techniques. Recently, a new electromagnetic-wave concept based on our high-Tc Josephson detectors and Hilbert spectroscopy has been suggested to distinguish between liquids. This technology covers a spectral range of main dispersions of liquids, from a few GHz to a few THz, and thus significantly enhances reliability of identification. The high-Tc detectors, due to a power dynamic range of more than five orders, might guarantee short identification times. Several demonstration set-ups of liquid identifiers, consisting of high-Tc Josephson detectors, integrated in Stirling coolers, and polychromatic radiation sources, have been developed and characterized. Reflection polychromatic spectra of various liquids in plastic containers have been measured at the spectral range of 15-500 GHz with total scanning time down to 0.2 second. Reliable identification of liquids, both benign and threat, within an accuracy of 0.3% was demonstrated using water as a reflectance reference. The reflectance values for 30%H2O2/H2O solution at frequencies of 30 and 100 GHz were practically undistinguishable from that of for pure water, but an increase of the relative reflectance from 1.017 at 282 GHz to 1.033 at 434 GHz has been found. Last circumstance will be used for optimization of the identifiers.

  19. High-Tc SQUID magnetometer system with active cancellation

    NASA Astrophysics Data System (ADS)

    Kuriki, S.; Oyama, H.; Hayashi, A.; Washio, T.; Fujita, M.; Hirata, Y.

    2002-05-01

    Recent developments of high-Tc SQUIDs have enabled high sensitivity magnetometers to be used in wide range of places, such as laboratory and outdoor fields. At the early stage of developing multichannel system for measurement of magnetocardiogram (MCG) in clinical application, we have fabricated a single channel high-Tc SQUID magnetometer system. The system includes a direct-coupled SQUID with slot structure, a simple magnetically shielded room (MSR), and some active compensation electronics for the purpose of reducing various environmental field noises. A novel active noise cancellation was made by using a combination of a normal conducting detection coil that was horizontally wound in the middle height of the MSR, and two compensation coils that were wound at the top and bottom of the MSR. In addition, adaptive noise cancellation was supplemented by means of adaptive digital filter that was implemented in a digital signal processor. A total noise field attenuation of 50-60 dB was attained at 0.5-100 Hz. Low noise signals from the human heart were measured with a high-Tc SQUID in the noise reduced space in the MSR.

  20. The phase diagram of electron-doped La2-xCexCuO4-δ

    NASA Astrophysics Data System (ADS)

    Saadaoui, H.; Salman, Z.; Luetkens, H.; Prokscha, T.; Suter, A.; Macfarlane, W. A.; Jiang, Y.; Jin, K.; Greene, R. L.; Morenzoni, E.; Kiefl, R. F.

    2015-01-01

    Superconductivity is a striking example of a quantum phenomenon in which electrons move coherently over macroscopic distances without scattering. The high-temperature superconducting oxides (cuprates) are the most studied class of superconductors, composed of two-dimensional CuO2 planes separated by other layers that control the electron concentration in the planes. A key unresolved issue in cuprates is the relationship between superconductivity and magnetism. Here we report a sharp phase boundary of static three-dimensional magnetic order in the electron-doped superconductor La2-xCexCuO4-δ, where small changes in doping or depth from the surface switch the material from superconducting to magnetic. Using low-energy spin-polarized muons, we find that static magnetism disappears close to where superconductivity begins and well below the doping level at which dramatic changes in the transport properties are reported. These results indicate a higher degree of symmetry between the electron and hole-doped cuprates than previously thought.

  1. EDITORIAL: Focus on Iron-Based Superconductors FOCUS ON IRON-BASED SUPERCONDUCTORS

    NASA Astrophysics Data System (ADS)

    Hosono, Hideo; Ren, Zhi-An

    2009-02-01

    Superconductivity is the most dramatic and clear cut phenomenon in condensed matter physics. Realization of room temperature superconductors, which would lead to the revolution of our society, is an ultimate goal for researchers. The discovery of high Tc cuprate superconductors in 1986 by Bednorz and Müller triggered intensive research worldwide and the maximum critical temperature has been raised above 100 K. Scientific research on this break-through material clarified a new route to high Tc materials, carrier doping to a Mott insulator with anti-ferromagnetic ordering. High superconductivity occurs in the neighborhood of Mott-insulators and Fermi-metals. Such a view, which was completely new, now stands as a guiding principle for exploring new high Tc materials. Many theoretical approaches to the mechanism for cuprate superconductors have been carried out to understand this unexpected material and to predict new high Tc materials. In 2006 a new superconductor based on iron, LaFeOP, was discovered by a group at Tokyo Institute of Technology, Japan. Iron, as a ferromagnet, was believed to be the last element for the realization of superconductivity because of the way ferromagnetism competes against Cooper pair formation. Unexpectedly, however, the critical temperature remained at 4-6 K irrespective of hole/electron-doping. A large increase in the Tc to 26 K was then found in LaFe[O1-xFx]As by the same group (and was published on 23 February 2008, in the Journal of the American Chemical Society). The Tc of this material was further raised to 43 K under a pressure of 2 GPa and scientists in China then achieved a Tc of 56 K at ambient pressure by replacing La with other rare earth ions with smaller radius—a critical temperature that is second only to the high Tc cuprates. This fast progress has revitalized research within superconductivity and in 2008 there were more than seven international symposia specifically on Fe(Ni)-based superconductors. Through the rapid

  2. Infrared detection with high-{Tc} bolometers and response of Nb tunnel junctions to picosecond voltage pulses

    SciTech Connect

    Verghese, S.

    1993-05-01

    Oxide superconductors with high critical temperature {Tc} make sensitive thermometers for several types of infrared bolometers. The authors built composite bolometers with YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thermometers on sapphire substrates which have higher sensitivity than competing thermal detectors which operate at temperatures above 77 K. A 1 x 1 mm bolometer with gold black serving as the radiation absorber has useful sensitivity for wavelengths 20--100 {mu}m. A 3 x 3 mm bolometer with a bismuth film as the absorber operates from 20--100 {mu}m. High-{Tc} bolometers which are fabricated with micromachining techniques on membranes of Si or Si{sub 3}N{sub 4} have potential application to large-format arrays which are used for infrared imaging. A nonisothermal high-{Tc} bolometer can be fabricated on a membrane of yttria-stabilized zirconia (YSZ) which is in thermal contact with the heat sink along the perimeter of the membrane. A thermal analysis indicates that the YSZ membrane bolometer can have improved sensitivity compared to the sapphire bolometer for spectrometer applications. The quasiparticle tunneling current in a superconductor-insulator-superconductor (SIS) junction is highly nonlinear in the applied voltage. The authors have made the first measurement of the linear response of the quasiparticle current in a Nb/AlO{sub x}/Nb junction over a broad bandwidth from 75--200 GHz. Nonlinear measurements made with these pulses may provide information about the quasiparticle lifetime. Preliminary data from such measurements are presented.

  3. Ultrafast IR detector response in high Tc superconducting thin films

    NASA Technical Reports Server (NTRS)

    Lindgren, Mikael; Ahlberg, Henrik; Danerud, Martin; Larsson, Anders; Eng, Sverre T.

    1991-01-01

    The response from a high Tc superconducting multielement optical detector made of a laser deposited Y-Ba-Cu-O thin film has been evaluated. Several microscopic and spectroscopic techniques were used to establish the presence of the correct phase of the thin film. Optical pulses from a laser diode at 830 nm and from a Q-switched CO2-laser at 10.6 microns were used. The detector responded to 50 ps (FWHM) pulses. A comparison between dR/dT of the film and the response amplitude as a function of temperature indicated a bolometric response.

  4. Complementary Variational Theorems for inhomogeneous superconductors

    NASA Astrophysics Data System (ADS)

    Choy, T. C.

    1997-03-01

    Complementary variational theorems are derived for an inhomogeneous London (local) superconductor in which both the magnetic permeability μ(r) and the London penetration length λ_L(r) vary randomly in space (T.C. Choy, Physical Review B (1997) (to appear)). An essential feature is the close coupling between magnetic and supercurrent polarisation effects, developed self-consistently in this work. Using these theorems and a suitable ansatz for the single particle polarisabilities, we obtained complementary bounds for a composite superconductor near Tc and T=0^circ K. Our results may be important for the empirical study of systems containing magnetic (normal) and superconducting mixtures, including the high Tc oxide superconductors.

  5. Practical superconductor development for electrical power applications

    SciTech Connect

    Goretta, K.C.

    1991-10-01

    Development of useful high-critical-temperature (high-{Tc}) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes technical progress of research and development efforts aimed at producing superconducting components based on the Y-Ba-Cu, Bi-Sr-Ca-Cu, Bi-Pb-Sr-Ca-Cu, and Tl-Ba-Ca-Cu oxides systems. Topics discussed are synthesis and heat treatment of high-{Tc} superconductors, formation of monolithic and composite wires and tapes, superconductor/metal connectors, characterization of structures and superconducting and mechanical properties, and fabrication and properties of thin films. Collaborations with industry and academia are also documented. 10 figs.

  6. Practical superconductor development for electrical power applications

    SciTech Connect

    Goretta, K.C.

    1992-10-01

    Development of useful high-critical-temperature (high-[Tc]) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes the technical progress of research and development efforts aimed at producing superconducting components that are based on the Y-Ba-Cu, Bi-Sr-Ca-Cu, Bi-Pb-Sr-Ca-Cu, and (TI,Pb)-(Ba,Sr)-Ca-Cu oxide systems. Topics discussed are synthesis and heat treatment of high-[Tc] superconductors, formation of monolithic and composite wires and tapes, superconductor/metal connectors, characterization of structures and superconducting and mechanical properties, fabrication and properties of thin films, and development of prototype components. Collaborations with industry and academia are documented.

  7. Pressure and high-Tc superconductivity in sulfur hydrides

    PubMed Central

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

    2016-01-01

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

  8. Pressure and high-Tc superconductivity in sulfur hydrides.

    PubMed

    Gor'kov, Lev P; Kresin, Vladimir Z

    2016-01-01

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

  9. Pressure and high-Tc superconductivity in sulfur hydrides

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  10. Tunable topological states in electron-doped HTT-Pt

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoming; Wang, Zhenhai; Zhao, Mingwen; Liu, Feng

    2016-04-01

    Modulating topologically nontrivial states in trivial materials is of both scientific and technological interest. Using first-principles calculations, we propose a demonstration of electron-doping- (or gate-voltage-) induced multiple quantum states; namely, quantum spin Hall (QSH) and quantum anomalous Hall (QAH) states, in a single material of the organometallic framework (HTT-Pt) synthesized from triphenylene hexathiol molecules (HTT) and PtC l2 . At a low doping level, the trivial HTT-Pt converts to a QSH insulator protected by time-reversal symmetry (TRS). When the electronic doping concentration is further increased, TRS will be broken, making the HTT-Pt a QAH insulator. The band gaps of these topologically nontrivial states can be as large as 42.5 meV, suggesting robustness at high temperatures. The possibility of switching between the QSH and QAH states offers an intriguing platform for a different device paradigm by interfacing between QSH and QAH states.

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

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    2010-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Halder, Avik; Kresin, Vitaly V.

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  15. Electron-doping of graphene-based devices by hydrazine

    SciTech Connect

    Feng, Tingting; Xie, Dan; Wang, Dongxia; Wen, Lang; Wu, Mengqiang

    2014-12-14

    A facile and effective technique to tune the electronic properties of graphene is essential to facilitate the flexibility of graphene-based device performances. Here, the use of hydrazine as a solution-processable and effective n-type dopant for graphene is described. By dropping hydrazine solutions at different concentrations on a graphene surface, the Dirac point of graphene can be remarkably tuned. The transport behavior of graphene can be changed from p-type to n-type accordingly, demonstrating the controllable and adjustable doping effect of the hydrazine solutions. Accompanying the Dirac point shift is an enhanced hysteretic behavior of the graphene conductance, indicating an increasing trap state density induced by the hydrazine adsorbates. The electron-doping of graphene by the hydrazine solutions can be additionally confirmed with graphene/p-type silicon heterojunctions. The decrease of the junction current after the hydrazine treatment demonstrates an increase of the junction barrier between graphene and silicon, which is essentially due to the electron-doping of graphene and the resultant upshift of the Fermi level. Finally, partially doped graphene is realized and its electrical property is studied to demonstrate the potential of the hydrazine solutions to selectively electron-doping graphene for future electronic applications.

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

    DOEpatents

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

    2000-01-01

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

  17. Global Phase Diagram of the High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Chen, Han-Dong; Zhang, Shou-Cheng

    2006-02-01

    We propose a bosonic effective quantum Hamiltonian based on the projected SO(5) model with extended interactions, which can be derived from the microscopic models of the cuprates. The global phase diagram of this model is obtained using mean-field theory and the quantum Monte Carlo simulation. We show that this single quantum model can account for most salient features observed in the high-Tc cuprates, with different families of the cuprates attributed to different traces in the global phase diagram. A particular prediction of this theory is the checkerboard state of the d-wave hole pairs formed at certain magic filling fractions. We shall describe various properties of this state and present evidence that this novel state has been detected in recent STM and transport experiments.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  19. Study of Cu-wound Flux transformer for High-Tc SQUID Ultra-Low Field MRI

    NASA Astrophysics Data System (ADS)

    Tanaka, S.; Murata, H.; Imamura, K.; Hatsukade, Y.

    2014-05-01

    We constructed a ultra-low field (ULF) nuclear magnetic resonance (NMR) / magnetic resonance imaging (MRI) system employing a high-temperature superconductor (High Tc) SQUID with a separated Cu-wound flux transformer. The pickup coil consisted of two single solenoid coils and each coil was differentially connected each other. The flux transformer consisted of a pickup coil at room temperature and an input coil, which was put in liquid nitrogen and was magnetically coupled with a high-Tc SQUID. The ratio of the transformer was considered and optimized. A water phantom of 10 mL was located in the one side of pickup coil. In the system, we applied polarizing field Bp perpendicular to the measurement field Bm before measurements. Bp was 0.8 T and permanent magnet was used. By using this system, free induction decay (FID) signals of 2H were measured at Bm of 30 μT to evaluate the system. The longitudinal relaxation times T1 of water were also estimated by changing the polarizing time of Bp.

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

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

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

  1. Dielectric resonator for measuring the magnetic penetration depth at low temperature in high-Tc superconducting thin films

    NASA Astrophysics Data System (ADS)

    Mourachkine, A. P.

    1995-11-01

    Knowledge of magnetic penetration depth λ(T) at low temperatures allows one to determine the pairing state in the superconductors. A simple method for the evaluation of λ(T) of small (˜1 cmט1 cm), flat, high-Tc superconductive samples at low T is discussed. The resolution of the method is a few Å. In addition to high resolution, the method has several advantages including nondestructive analysis, flexibility in sample size, and minimal requirements on the dielectric resonator. The current distribution within the sample being tested can also be accurately calculated, the experimental setup is convenient, and the procedure is comparatively rapid and can be performed in the necktube of a liquid-helium storage Dewar. The measurements for YBCO thin films have been performed at 14.4 GHz.

  2. A technique to measure the thermal diffusivity of high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Powers, Charles E.

    1991-01-01

    High T(sub c) superconducting electrical current leads and ground straps will be used in cryogenic coolers in future NASA Goddard Space Flight Center missions. These superconducting samples are long, thin leads with a typical diameter of two millimeters. A longitudinal method is developed to measure the thermal diffusivity of candidate materials for this application. This technique uses a peltier junction to supply an oscillatory heat wave into one end of a sample and will use low mass thermocouples to follow the heat wave along the sample. The thermal diffusivity is calculated using both the exponential decay of the heat wave and the phase shift to the wave. Measurements are performed in a cryostat between 10 K and room temperature.

  3. Reactive nanophase oxide additions to melt-processed high-{Tc} superconductors

    SciTech Connect

    Goretta, K.C.; Brandel, B.P.; Lanagan, M.T.; Hu, J.; Miller, D.J.; Sengupta, S.; Parker, J.C.; Ali, M.N.; Chen, Nan

    1994-10-01

    Nanophase TiO{sub 2} and Al{sub 2}O{sub 3} powders were synthesized by a vapor-phase process and mechanically mixed with stoichiometric YBa{sub 2}Cu{sub 3}O{sub x} and TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} powders in 20 mole % concentrations. Pellets produced from powders with and without nanophase oxides were heated in air or O{sub 2} above the peritectic melt temperature and slow-cooled. At 4.2 K, the intragranular critical current density (J{sub c}) increased dramatically with the oxide additions. At 35--50 K, effects of the oxide additions were positive, but less pronounced. At 77 K, the additions decreased J{sub c}, probably because of inducing a depresion of the transition temperature.

  4. Probing the local structure of high-{Tc} superconductors using XAFS spectroscopy

    SciTech Connect

    Bridges, F.; Booth, C.H.; Li, G.G.; Bauer, E.D.; Boyce, J.; Claeson, T.

    1996-12-31

    X-ray Absorption Fine-Structure (XAFS) is a local structural probe that is complementary to diffraction techniques. The authors discuss the types of information that can be obtained using this probe and then consider several examples, including the distortion about Co in YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO), an unusual negative correlation of atom pair displacements in HgBa{sub 2}CuO{sub 4+{delta}}, and the distortions about the O(4) atom in thin films and single crystals of YBCO.

  5. The nature of long range order in the vortex lattice of high {Tc} superconductors

    SciTech Connect

    Ryu, S.; Doniach, S.; Kapitulnik, A.

    1994-12-31

    Recent neutron data on the disappearance of long-range order in the vortex lattice of BSCCO at fields of order 1 kGauss is interpreted in terms of the results of a Monte Carlo simulation of the thermodynamics of the vortex lattice in a pure system. The authors show that the neutron data is consistent with a disorder-driven phase transition from a vortex crystal at low fields to a vortex glass at higher fields.

  6. Low-frequency noise in high-{Tc} superconductor Josephson junctions, SQUIDs, and magnetometers

    SciTech Connect

    Miklich, A.H.

    1994-05-01

    Design and performance of high-T{sub c} dc superconducting quantum interference devices (SQUEDs), junctions that comprise them, and magnetometers made from them are described, with attention to sources of 1/f noise. Biepitaxial junctions are found to have large levels of critical current fluctuations which make them unsuitable for low-noise SQUIDS; this suggests a poorly connected interface at the grain boundary junction. SQUIDs from bicrystal junctions have levels of critical current noise controllable using bias current reversal techniques which leave the noise white down to frequencies of a few Hz. A SQUID with an energy resolution of 1.5{times}10{sup {minus}30} J Hz{sup {minus}1} at 1 Hz is reported. Magnetometers in which a (9 mm){sup 2} pickup loop is directly coupled to a SQUID body have achieved field resolutions of 93 fT Hz{sup {minus}1/2} down to frequencies below I Hz, improving to 39 fT Hz{sup {minus}1/2} at 1 Hz with the addition of a 50mm-diameter single-turn flux transformer. Poor coupling to pickup loop makes it difficult to satisfy competing goals of high field resolution and small detector size necessary for multichannel biomagnetic imaging. Improved coupling is demonstrated by the use of multiturn-input-coil flux transformers, and a resolution of 35 fT Hz{sup {minus}1/2} in the white noise region is reported with a (10 mm){sup 2} pickup loop. However, additional 1/f noise from processed multilayer structures in the transformer limits the resolution at 1 Hz to 114 fT Hz{sup {minus}1/2}. High-T{sub c} SQUIDs exhibit additional 1/f noise when cooled in a nonzero static magnetic field because of additional flux vortices trapped in the film, with the noise power at 1 Hz typically increasing by a factor of 10--20 in a field of 0.05mT (0.5 G). Finally, a SQUID-based voltmeter with a resolution of 9.2 pV.Hz{sup {minus}1/2} at 10 Hz (24 pV Hz{sup {minus}1/2} at 1 Hz) is described.

  7. Experimental evidence for flux-lattice melting. [in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.

    1991-01-01

    A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal of YBa2Cu3O(7-delta). The damping of the oscillator was measured as a function of temperature, for applied magnetic fields in the range H = 0.1-2.3 T. A remarkably sharp damping peak has been located. It is suggested that the temperature of the peak corresponds to the melting point of the Abrikosov flux lattice.

  8. Impurity effects in quasiparticle spectrum of high-Tc superconductors (Review Article)

    NASA Astrophysics Data System (ADS)

    Pogorelov, Yu. G.; Santos, M. C.; Loktev, V. M.

    2011-08-01

    The revision is made of Green function methods that describe the dynamics of electronic quasiparticles in disordered superconducting systems with d-wave symmetry of order parameter. Various types of impurity perturbations are analyzed within the simplest T-matrix approximation. The extension of the common self-consistent T-matrix approximation (SCTMA) to the so-called group expansions in clusters of interacting impurity centers is discussed and hence the validity criteria for SCTMA are established. A special attention is paid to the formation of impurity resonance states and localized states near the characteristic points of energy spectrum, corresponding to nodal points on the Fermi surface.

  9. Future prospects of high Tc superconductors-coated conductors and their applications

    NASA Astrophysics Data System (ADS)

    Shiohara, Yuh; Yoshizumi, Masateru; Takagi, Yuji; Izumi, Teruo

    2013-01-01

    The research and development of high-temperature superconducting wires, especially yttrium-based coated conductors (CCs), and their energy applications have been expected to reduce CO2 emissions. This article reviews recent progress in this area, mainly focusing on the results obtained by national projects in Japan. The Ic (critical current) × L (wire length) value of CCs has been improved to reach 466,752 A m (572 A/cm-W, 816 m), which exceeds that of Bi-system wires. CCs have also been improved in terms of in-field performance and AC loss reduction to meet market requirements. Power applications such as superconducting magnetic energy storage (SMES) systems, power cables and transformers have been developed using CCs in the current project. Because of fundamental research on high-capacity power cables, a low AC loss of 0.8 W/m-ph at 3 kA and 73.7 K was achieved. System design and fundamental research were performed on a 2GJ-class SMES system and a 20 MVA-class transformer. Based on the technologies developed by the end of the current project (FY2012), the innovation process of those applications will reach the implementation stage, where the long-term reliability tests will be performed. The process is expected to reach the penetration and propagation stage around 2020.

  10. Novel magnetic excitations in a model cuprate high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Li, Yuan

    2011-03-01

    Magnetic fluctuations might be essential to the mechanism of high-temperature superconductivity in the cuprates. For a long time, such fluctuations have been theoretically regarded as arising from the antiferromagnetic correlations within the copper-oxygen layers, and experimental studies of magnetic excitation spectrum have mainly been carried out near the corresponding wave vector (1/2,~1/2). Following neutron diffraction experiments which demonstrated the universal existence of a `` q ~=~0 antiferromagnetic order'' in the pseudogap phase of three different cuprates [1-3], our recent inelastic neutron scattering experiments on the model compound HgBa 2 Cu O4 + δ (Hg1201) revealed the existence of unusual magnetic excitations that weakly disperse throughout the entire Brillouin zone [4,5]. Like the q ~=~0 antiferromagnetic order, the new excitations are observed in the pseudogap phase and therefore appear to be associated with the order. The excitations possess very large spectral weights at well-defined characteristic energies that are comparable to the resonance energy and to those of electron-boson-coupling features observed in a wide range of cuprates, highlighting their possible influence on the electronic structure. These findings demonstrate that the pseudogap state is a distinct phase of matter rather than a mere crossover. They furthermore cast doubt on the presumed predominant importance of the wave vector (1/2,~1/2) in the magnetic excitation spectrum, and have the profound implication that a single-band description of the cuprates is insufficient. Project was funded by DOE and NSF grants. The author achnowledges the Alexander von Humboldt Foundation.

  11. Compensated electron and hole pickets in an underdoped high Tc superconductor

    SciTech Connect

    Harrison, Neil; Altarawneh, Moaz M; Mielke, Charles H; Sebastian, Suchitra E; Goddard, P A; Liang, Ruixing; Bonn, D A; Hardy, W N; Andersen, O K; Lonzarich, G G

    2010-01-01

    Important to the question of high temperature superconductivity is whether bound fermionic pairs with zero or finite momentum - exhibiting bosonic physics - are involved. Here we use angle-dependent magnetic quantum oscillation measurements in underdoped YBa{sub 2}Cu{sub 3}O{sub 6+x} to reveal two significantly differently corrugated small sections of Fermi surface, identifying them as comprising opposite carriers located at different locations of the Brillouin zone. The surprising finding that these disproportionately heavy small pockets are equal in size indicates they are prone to a finite momentum excitonic insulator instability. We discuss the possibility that reducing the doping drives YBa{sub 2}Cu{sub 3}O{sub 6+x} closer to an instability of this nature, its ultimate realization occuring at the metal-insulator quantum critical point, accompanied by a potential enhancement of superconducting transition temperatures.

  12. Low-frequency noise in high-(Tc) superconductor Josephson junctions, SQUIDs, and magnetometers

    NASA Astrophysics Data System (ADS)

    Miklich, A. H.

    1994-05-01

    Design and performance of high-T(sub c) dc superconducting quantum interference devices (SQUID's), junctions that comprise them, and magnetometers made from them are described, with attention to sources of 1/f noise. Biepitaxial junctions are found to have large levels of critical current fluctuations which make them unsuitable for low-noise SQUID's; this suggests a poorly connected interface at the grain boundary junction. SQUID's from bicrystal junctions have levels of critical current noise controllable using bias current reversal techniques which leave the noise white down to frequencies of a few Hz. A SQUID with an energy resolution of 1.5 x 10(exp -30) J Hz(exp -1) at 1 Hz is reported. Magnetometers in which a (9 mm)(exp 2) pickup loop is directly coupled to a SQUID body have achieved field resolutions of 93 fT Hz(exp -1/2) down to frequencies below 1 Hz, improving to 39 fT Hz(exp -1/2) at 1 Hz with the addition of a 50mm-diameter single-turn flux transformer. Poor coupling to pickup loop makes it difficult to satisfy competing goals of high field resolution and small detector size necessary for multichannel biomagnetic imaging. Improved coupling is demonstrated by the use of multiturn-input-coil flux transformers, and a resolution of 35 fT Hz(exp -1/2) in the white noise region is reported with a (10 mm)(exp 2) pickup loop. However, additional 1/f noise from processed multilayer structures in the transformer limits the resolution at 1 Hz to 114 fT Hz(exp -1/2). High-T(sub c) SQUID's exhibit additional 1/f noise when cooled in a nonzero static magnetic field because of additional flux vortices trapped in the film, with the noise power at 1 Hz typically increasing by a factor of 10-20 in a field of 0.05mT (0.5 G). Finally, a SQUID-based voltmeter with a resolution of 9.2 pV Hz(exp -1/2) at 10 Hz (24 pV Hz(exp -1/2) at 1 Hz) is described.

  13. Terahertz wave emission from intrinsic Josephson junctions in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Ozyuzer, L.; Simsek, Y.; Koseoglu, H.; Turkoglu, F.; Kurter, C.; Welp, U.; Koshelev, A. E.; Gray, K. E.; Kwok, W. K.; Yamamoto, T.; Kadowaki, K.; Koval, Y.; Wang, H. B.; Müller, P.

    2009-11-01

    Recently, we experimentally demonstrated that rectangular mesa structures of intrinsic Josephson junctions (IJJ) in Bi2Sr2CaCu2O8+d (Bi2212) can be used as a compact solid-state generator of continuous, coherent and polarized terahertz (THz) radiation. In the present work, we will exhibit tall mesas (over 600 junctions) which were fabricated using UV lithography, e-beam lithography with photoresist and e-beam lithography with a Ti selective etching technique. We will present measurements of the c-axis resistance as a function of temperature and of current-voltage characteristics of THz emitting mesas with lateral sizes ranging from 30 × 300 to 100 × 300 µm2. Furthermore, we will discuss the dependence of the characteristics of the mesa structures on the oxygen doping level of the Bi2212 crystals. We will also experimentally show that the voltage-frequency relation of the ac Josephson effect has to match the cavity resonance for successful emission.

  14. Design and performance of a high-Tc superconductor coplanar waveguide filter

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    The design of a coplanar waveguide low-pass filter made of YBa2Cu3O(7-delta) (YBCO) on an LaAlO3 substrate is described. Measurements were incorporated into simple models for microwave CAD analysis to develop a final design. The patterned and packaged coplanar waveguide low-pass filter of YBCO, with dimensions suited for integrated circuits, exhibited measured insertion losses when cooled in liquid nitrogen superior to those of a similarly cooled thin-film copper filter throughout the 0 to 9.5 GHz passband. Coplanar waveguide models for use with thin-film normal metal (with thickness either greater or less than the skin depth) and YBCO are discussed and used to compare the losses of the measured YBCO and copper circuits.

  15. Torque magnetometry in unconventional superconductors

    NASA Astrophysics Data System (ADS)

    Li, Lu

    This thesis describes torque magnetometry studies on unconventional superconductors. Torque magnetometry measures the anisotropic magnetization of samples by recording their torque signals in a tilted magnetic field. Applied to superconductors, this method provides a reliable way to measure the field dependence of magnetization with high resolution under extreme conditions: DC magnetic fields from zero to 45.2 T, and temperature from 300 mK to 300K. The results can be used to determine many important parameters, such as the upper critical field H c2, the superconducting condensation energy, the onset temperature of diamagnetic signals, and so on. We carried out the torque magnetometry measurements on unconventional superconductors---high Tc superconductors and the p-wave superconductor Sr2RuO4---and uncovered new features that do not exist in conventional BCS superconductors. In high Tc superconductors, our torque magnetometry studies focus on the properties of the vortex liquid state. First, by comparing the observed magnetization curves with the Nernst effect results in Bi 2Sr2CaCu2O8+delta, we confirm that the unusually large Nernst effect signals originate from the surviving vortex liquid state above Tc. Second, the M-H curves near the critical temperature Tc suggest that the nature of the transition is the Kosterlitz-Thouless transition. Near Tc, the magnetization response at low field is strongly nonlinear, and the T dependence of the magnetic susceptibility in the low-field limit approaches the predicted curve from the Kosterlitz-Thouless transition. Third, the measurements in intense magnetic field up to 45 T reveal the unusual, weak T-dependence of Hc2. These observations strongly support the existence of the vortex liquid state above Tc. The superconducting state is destroyed by the phase fluctuation of the pair condensate, while the pair condensate keeps its amplitude above T c. Further studies in single-layered high Tc superconductors reveal more

  16. Analysis of microstrip lines with alternative implementation of conductors and superconductors

    NASA Technical Reports Server (NTRS)

    Kong, K.-S.; Lee, H.-Y.; Itoh, T.; Chorey, C. M.; Bhasin, K. B.

    1990-01-01

    An analysis of microstrip line structures in which either the strip or the ground plane or both are made of a high Tc superconductor is presented. The effect of implementation of a superconductor to the strip and the ground plane is explained with the calculation of a conductor loss of the structure by the Phenomenological Loss Equivalence Method (PEM). The theoretical values are compared with the experimental results from a ring resonator which is made of a gold ground plane and a high Tc superconductor, YBa2Cu3O(7-x), strip.

  17. Magnetic forces in high-Tc superconducting bearings

    NASA Technical Reports Server (NTRS)

    Moon, F. C.

    1991-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Tanaka, Shoji

    2007-03-01

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

  19. Characteristics of an electromagnetic levitation system using a bulk superconductor

    SciTech Connect

    Senba, A.; Kitahara, H.; Ohsaki, H.; Masada, E.

    1996-09-01

    It is beneficial to apply a high-Tc bulk superconductor as a large flux source to an electromagnetic levitation system, which needs large amounts of levitation force. The authors made an attractive-type electromagnetic levitation system using a hybrid magnet that mainly consisted of bulk superconductor and control coils to confirm the principle of the levitation, and obtained characteristics of its system by both experiment and numerical analysis with magnetic circuit calculation. This is applicable to maglev transportation systems.

  20. X-ray photoemission study of the infinite-layer cuprate superconductor Sr(0.9) La (0.1) CuO(2)

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Jung, C. U.; Kim, J. Y.; Kim, M. S.; Lee, S. Y.; Lee, S. I.

    2001-01-01

    The electron-doped infinite-layer superconductor Sr(0.9)La(0.1) CuO(2) is studied with x-ray photoemission spectroscopy (XPS). A nonaqueous chemical etchant is shown to effectively remove contaminants and to yield surfaces from which signals intrinsic to the superconductor dominate.

  1. Epitaxial stabilization of ultra thin films of electron doped manganites

    SciTech Connect

    Middey, S. Kareev, M.; Meyers, D.; Liu, X.; Cao, Y.; Tripathi, S.; Chakhalian, J.; Yazici, D.; Maple, M. B.; Ryan, P. J.; Freeland, J. W.

    2014-05-19

    Ultra-thin films of the electron doped manganite La{sub 0.8}Ce{sub 0.2}MnO{sub 3} were grown in a layer-by-layer growth mode on SrTiO{sub 3} (001) substrates by pulsed laser interval deposition. High structural quality and surface morphology were confirmed by a combination of synchrotron based x-ray diffraction and atomic force microscopy. Resonant X-ray absorption spectroscopy measurements confirm the presence of Ce{sup 4+} and Mn{sup 2+} ions. In addition, the electron doping signature was corroborated by Hall effect measurements. All grown films show a ferromagnetic ground state as revealed by both dc magnetization and x-ray magnetic circular dichroism measurements and remain insulating contrary to earlier reports of a metal-insulator transition. Our results hint at the possibility of electron-hole asymmetry in the colossal magnetoresistive manganite phase diagram akin to the high-T{sub c} cuprates.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  3. Compact spherical neutron polarimeter using high-Tc YBCO films

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    We describe a simple, compact device for spherical neutron polarimetry measurements at small neutron scattering angles. The device consists of a sample chamber with very low (<0.01 G) magnetic field flanked by regions within which the neutron polarization can be manipulated in a controlled manner. This allows any selected initial and final polarization direction of the neutrons to be obtained. We have constructed a prototype device using high-Tc superconducting films and mu-metal to isolate regions with different magnetic fields and tested device performance in transmission geometry. Finite-element methods were used to simulate the device's field profile and these have been verified by experiment using a small solenoid as a test sample. Measurements are reported using both monochromatic and polychromatic neutron sources. The results show that the device is capable of extracting sample information and distinguishing small angular variations of the sample magnetic field. As a more realistic test, we present results on the characterization of a 10 μm thick Permalloy film in zero magnetic field, as well as its response to an external magnetic field.

  4. The spin-polaron theory of high-Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Mott, N. F.

    1990-01-01

    An outline is given of the model for some high-temperature superconductors which assumes that the carriers are holes in the (hybridized) oxygen 2p band and form ‘spin polarons’ with the moments on the copper atoms. A comparison is made with observations of spin polarons in Gd3-xvxS4 and with the properties of La1-xSrxVO3 in relation to those of La2-xSrxCuO4. It is assumed, following several authors, that in the superconductors the polarons form bipolarons, which are bosons, and a comparison is made with some other treatments of this hypothesis. It is proposed that in many such superconductors the boson, essentially a pair of these holes, moves in an impurity band, and that normally all the polarons (fermions) form bipolarons; the fermions repel each other on the same site (positive Hubbard U) but attract when on adjacent sites; the critical temperature Tc is then that at which the Bose gas becomes non-degenerate. In such materials a non-degenerate gas of bosons would carry the current above Tc as first suggested by Alexandrov et al. (1986). The linear increase in the resistivity above Tc is explained on this hypothesis. The effective mass of the bipolaron is, we believe, large (˜20 30me). The copper 3d9 moments in the superconducting range resonate between their two orientations as a consequence of the motion of the carriers, as they do in the description by Brinkman and Rice (1970) of highly correlated metals. Spin polarons, we believe, form only when this is so, but not in the antiferromagnetic range of x. A discussion is given of the resistivity above Tc, thermopower above Tc, and of the nature of the superconducting gap as shown by tunnelling. We confine our discussion to the materials containing copper, excluding for instance cubic Ba1-xKxBiO3, and possibly any superconductor containing bismuth, where the bosons may be Bi3+.

  5. The specific heat of the 2201 BISCO high-T c superconductor

    NASA Astrophysics Data System (ADS)

    Yu, M. K.; Franck, J. P.

    1994-04-01

    The specific heat of two samples of the single-plane 2201 bismuth superconductor was measured. No linear term in Cp was observed at low temperatures. The lattice molar specific heat below 14 K exceeds that of the 2221 and 2223 bismuth superconductors considerably. As a consequence no peak in Cp/ T3 is observed in this superconductor, in contrast to other high- Tc cuprates. The specific-heat anomaly near Tc could not be resolved.

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

    SciTech Connect

    Cantoni, Claudia; Goyal, Amit

    2010-01-01

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

  7. Mechanism of a high-Tc superconducting flux pump: Using alternating magnetic field to trigger flux flow

    NASA Astrophysics Data System (ADS)

    Geng, Jianzhao; Coombs, T. A.

    2015-10-01

    High-Tc Superconducting (HTS) magnets operating in persistent current mode suffer a current decay due to flux creep of superconductor and joint resistance. Flux pumps are able to inject direct current into superconducting circuit to compensate the current decay, without the thermal loss caused by current leads. In this work, we proposed a flux pumping mechanism for HTS coils, with an experimental verification and an analytical model. The basic principle we have used is that flux flow can be triggered when the superconductor carrying a direct current is subjected to a perpendicular AC magnetic field. Low frequency alternating current is induced in a loop of YBCO tape using an AC field. A portion of the tape which we refer to as the "bridge" shorts a superconducting coil. A high frequency AC field is applied perpendicular to the bridge tape when alternating current in the tape reaches one polarity. This triggers a net flux flow and results in a current increase in the coil. The proposed flux pump has clear physics and is easily controllable, which may make it promising in practical use.

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

    NASA Astrophysics Data System (ADS)

    Drung, Dietmar

    2003-12-01

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

  9. Antiferromagnetic superconducting state in the electron-doped cuprates?

    NASA Astrophysics Data System (ADS)

    Das, Tanmoy; Markiewicz, Robert S.; Bansil, Arun

    2006-03-01

    Recent angle-resolved photoemission (ARPES) studies of the electron-doped cuprate Nd2-xCexCuO4 (NCCO)[1] have been interpreted in terms of a uniform antiferromagnetic (AF) metal, with doping into the upper magnetic band and gap collapse close to optimal doping[2]. An open question is whether the system remains uniform in the simultaneous presence of AF and (d- wave) superconducting (SC) order. Here, we explore the properties of a uniform AF-SC model for NCCO, to ascertain to what extent we can explain anomalous features, such as the nonmonotonic angle dependence of the superconducting gap[3]. Work supported by the USDOE. [1] N.P. Armitage, et al., PRL 87, 147003 (2002). [2] C. Kusko, et al., PRB66, 140513 (2002); A.-M.S. Tremblay, et al., cond-mat/0511334. [3] H. Matsui, et al., PRL 95, 017003 (2005).

  10. Self-limited kinetics of electron doping in correlated oxides

    SciTech Connect

    Chen, Jikun Zhou, You; Jiang, Jun; Shi, Jian; Ramanathan, Shriram; Middey, Srimanta; Chakhalian, Jak; Chen, Nuofu; Chen, Lidong; Shi, Xun; Döbeli, Max

    2015-07-20

    Electron doping by hydrogenation can reversibly modify the electrical properties of complex oxides. We show that in order to realize large, fast, and reversible response to hydrogen, it is important to consider both the electron configuration on the transition metal 3d orbitals, as well as the thermodynamic stability in nickelates. Specifically, large doping-induced resistivity modulations ranging several orders of magnitude change are only observed for rare earth nickelates with small ionic radii on the A-site, in which case both electron correlation effects and the meta-stability of Ni{sup 3+} are important considerations. Charge doping via metastable incorporation of ionic dopants is of relevance to correlated oxide-based devices where advancing approaches to modify the ground state electronic properties is an important problem.

  11. Detecting magnetic flux distributions in superconductors with polarized x rays

    NASA Astrophysics Data System (ADS)

    Stahl, Claudia; Audehm, Patrick; Gräfe, Joachim; Ruoß, Stephen; Weigand, Markus; Schmidt, Mathias; Treiber, Sebastian; Bechtel, Michael; Goering, Eberhard; Schütz, Gisela; Albrecht, Joachim

    2014-09-01

    The magnetic flux distribution arising from a high-Tc superconductor is detected and visualized using polarized x rays. Therefore, we introduce a sensor layer, namely, an amorphous, soft-magnetic Co40Fe40B20 cover layer, providing a large x-ray magnetic circular dichroism (XMCD). Temperature-dependent XMCD spectroscopy on the magnetic layer has been performed. Exploiting the temperature dependence of the critical current density of the superconductor we find a quantitative correlation between the XMCD signal and the in-plane stray field of the superconductor. Magneto-optical Kerr effect experiments on the sensor layer can simulate the stray field of the superconductor and hence verify the correlation. We show that the XMCD contrast in the sensor layer corresponds to the in-plane magnetic flux distribution of the superconductor and can hence be used to image magnetic structures in superconductors.

  12. Arsenic-75 and cobalt-59 NMR study of the electron doped barium iron cobalt arsenide

    NASA Astrophysics Data System (ADS)

    Ning, Fanlong

    We report a systematic investigation of the local electronic, magnetic, and superconducting properties of the new iron-based high temperature superconductor Ba(Fe1-xCox) 2As2 (x = 0, 0.02, 0.04, 0.082) through the measurement of 75As and 59Co NMR (Nuclear Magnetic Resonance) lineshapes, Knight shift (K), and spin-lattice relaxation rate (1/T1). The 75As NMR lineshape of the undoped parent compound splits into two sets due to discrete values of hyperfine magnetic field Bchf = +/- 1.32 Tesla below the magnetic ordering temperature to the SDW (Spin Density Wave) state, TSDW. In contrast, for lightly Co doped samples with x = 0.02 and 0.04, the 75As and 59Co lineshapes become broad and featureless below TSDW, indicating that the ground state is no longer the commensurate SDW ordered state. The observed lineshape is consistent with an incommensurate SDW ordered state, or a commensurate state with large distribution of hyperfine field Bhf. In the optimally doped superconductor with x = 0.082 (T c = 22 K), we observe two types of As sites and three types of Co sites, respectively, as expected from a binomial distribution of Co dopants. We found no evidence for induced localized moments in the vicinity of Co dopants. This finding is in remarkable contrast with the case of Zn or Ni doped high Tc cuprates, and suggests that the fundamental physics of iron-based superconductors is different from that of cuprates. The temperature dependences of 75,59K and 75,59(1/ T1T) at both 75As and 59Co sites show that Ba(Fe1-xCo x)2As2 exhibits spin pseudo-gap like behavior down to ˜ 100 K for a broad Co concentration range. Below ˜ 100 K, we observe the enhancement of residual antiferromagnetic spin fluctuations associated with inter-band spin excitations between the hole and electron Fermi surfaces even for x = 0.082. This effect is suppressed in the overdoped sample with x = 0.099, and T c decreases. Therefore, we suggest that antiferromagnetic spin fluctuations play a crucial role

  13. Electronic correlations in hole- and electron-doped Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Hardy, Frederic; Boehmer, Anna; Schweiss, Peter; Wolf, Thomas; Heid, Rolf; Eder, Robert; Fisher, Robert A.; Meingast, Christoph

    2015-03-01

    High-temperature superconductivity in the cuprates occurs at the crossover from a highly-correlated Mott insulating state to a weaker correlated Fermi liquid as a function of hole doping. The iron pnictides were initially thought to be fairly weakly correlated. However, we have recently shown using transport and thermodynamic measurements that KFe2As2 is strongly correlated. Both the Sommerfeld coefficient and the Pauli susceptibility are strongly enhanced with respect to their bare DFT values. These correlations are even further enhanced in RbFe2As2andCsFe2As2. The temperature dependence of both the susceptibility and the thermal expansion provides strong experimental evidence for the existence of a coherence-incoherence crossover; similar to what is found in heavy-fermion compounds. Whereas the correlations in the cuprates result from a large value of the Hubbard U, recent works have stressed the particular relevance of Hund's coupling in the pnictides. Our data may be interpreted in terms of a close proximity of KFe2As2 to an orbital-selective Mott transition. We now have good thermodynamic data covering both the hole and electron sides of the BaFe2As2 system and we will discuss how these correlations are modified by doping.

  14. μSR Studies on Magnetism in High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Koike, Yoji; Adachi, Tadashi

    2016-09-01

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

  15. High-Tc superconducting materials for electric power applications.

    PubMed

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

    2001-11-15

    Large-scale superconducting electric devices for power industry depend critically on wires with high critical current densities at temperatures where cryogenic losses are tolerable. This restricts choice to two high-temperature cuprate superconductors, (Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Ox, and possibly to MgB2, recently discovered to superconduct at 39 K. Crystal structure and material anisotropy place fundamental restrictions on their properties, especially in polycrystalline form. So far, power applications have followed a largely empirical, twin-track approach of conductor development and construction of prototype devices. The feasibility of superconducting power cables, magnetic energy-storage devices, transformers, fault current limiters and motors, largely using (Bi,Pb)2Sr2Ca2Cu3Ox conductor, is proven. Widespread applications now depend significantly on cost-effective resolution of fundamental materials and fabrication issues, which control the production of low-cost, high-performance conductors of these remarkable compounds. PMID:11713544

  16. Theory of high-TC superconductivity: transition temperature

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  17. First order vortex phase transition in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}

    SciTech Connect

    Inada, M.; Sasaki, T.; Nishizaki, T.; Kobayashi, N.; Yamada, S.; Fukase, T.

    1999-12-01

    The local magnetic induction is measured in the quasi-two dimensional organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} by using a micro Hall probe. The small step is observed on the temperature dependence of the local magnetic induction. This result implies the existence of the first-order phase transition of the vortex system in this organic superconductor as is already reported in high-{Tc} oxide and other organic superconductors.

  18. Plasma oscillations in layered superconductors

    SciTech Connect

    Pokrovsky, V.L.

    1996-12-31

    Very soon after publication of the famous BCS work explaining the puzzle of the superconductivity, N.N. Bogolyubov and coworkers have proposed their version of the theory. One of the new results they obtained was the discovery of a collective mode--an oscillation of the Cooper pair density with the energy smaller than 2{Delta}. P.W. Anderson has indicated that this collective mode can not be found experimentally since the Coulomb forces neglected in the above mentioned work shift its energy to the plasma frequency, i.e., to the high-ultraviolet range in which the superconductivity is unessential. The interest for plasmons in superconductors revived a little in the search for the mechanism of the High-{Tc} superconductivity. However, a real surge of interest to this problem occurred after experimental observations of the plasma edge in the reflectivity of High-{Tc} superconductors La{sub 2{minus}x}Sr{sub x}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub 8{minus}y}. It is worthwhile to mention that a theoretical prediction had preceded the experiment. For external reasons, the paper was published a long time after its completion. Here the author presents a brief review of the experiments and theoretical developments in the field. The theoretical works will be presented in more detail, given the author`s specialization.

  19. Photochemical electronic doping of colloidal CdSe nanocrystals.

    PubMed

    Rinehart, Jeffrey D; Schimpf, Alina M; Weaver, Amanda L; Cohn, Alicia W; Gamelin, Daniel R

    2013-12-18

    A method for electronic doping of colloidal CdSe nanocrystals (NCs) is reported. Anaerobic photoexcitation of CdSe NCs in the presence of a borohydride hole quencher, Li[Et3BH], yields colloidal n-type CdSe NCs possessing extra conduction-band electrons compensated by cations deposited by the hydride hole quencher. The photodoped NCs possess excellent optical quality and display the key spectroscopic signatures associated with NC n-doping, including a bleach at the absorption edge, appearance of a new IR absorption band, and Auger quenching of the excitonic photoluminescence. Although stable under anaerobic conditions, these spectroscopic changes are all reversed completely upon exposure of the n-doped NCs to air. Chemical titration of the added electrons confirms previous correlations between absorption bleach and electron accumulation and provides a means of quantifying the extent of electron trapping in some NCs. The generality of this photodoping method is demonstrated by initial results on colloidal CdE (E = S, Te) NCs as well as on CdSe quantum dot films. PMID:24289732

  20. Normal state incoherent pseudogap in FeSe superconductor

    NASA Astrophysics Data System (ADS)

    Craco, Luis; Laad, Mukul S.

    2016-05-01

    The normal state of Iron chalcogenide superconductors show a range of unconventional features. Bad-metallic resistivity and proximity to insulating state manifest themselves in spectral and transport responses. In particular, obervation of low-energy pseudogap feature in the normal state raises the issue of the nature of processes underpinning its emergence as well as its relation to unconventional superconductivity. Here, using the LDA+DMFT method, we show how correlation-induced orbital-selective pseudogap-like physics underpin these incoherent features in stoichimetric and electron-doped FeSe superconductor. We discuss the pseudogap regime microscopically, along with implications for the superconductive instability.

  1. Layered superconductors as one-dimensional Josephson arrays

    SciTech Connect

    Mueller, P.

    1996-12-31

    The large anisotropy and the extremely short coherence lengths of the high-{Tc} superconductors suggest that the layered crystal structure is mapped onto a periodic modulation of the superconducting order parameter. Even ideal high-{Tc} single crystals consist of a stacked series of superconducting and non-superconducting layers. As the typical interlayer distance is approximately 15 {angstrom}, a single crystal of 3 {micro}m thickness should behave like a stack of 2000 Josephson junctions. In order to access these atomic scale devices, vertical structures on single crystal surfaces and epitaxial thin films were fabricated. The authors present results of mesa structures and vertical step-edges.

  2. Dynamical Mean-Field Theory Study of Correlated Electronic Structures and the Phase Diagram of Hydrocarbon Superconductors

    NASA Astrophysics Data System (ADS)

    Kim, Minjae; Choi, Hong Chul; Shim, Ji Hoon; Min, B. I.

    2014-03-01

    We have studied correlated electronic structures and the phase diagram of electron-doped hydrocarbon molecular solids, based on the dynamical mean-field theory. We have determined the phase diagram of hydrocarbon molecular solids as functions of doping and energy parameters including the Coulomb correlation, the Hund coupling, and the molecular-orbital (MO) energy level splitting. We have found that the hydrocarbon superconductors (electron-doped picene and coronene) belong to the multi-band Fermi liquid state, while non-superconducting electron-doped pentacene belongs to the single-band state in the proximity of the metal-insulator transition. The size of the MO energy level splitting plays an important role in deriving the superconductivity of electron-doped hydrocarbon solids. The multi-band nature of hydrocarbon solids from the small MO energy level splitting boosts the superconductivity through the enhanced density of states at the Fermi level.

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

    SciTech Connect

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

    2012-07-13

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

  4. Spin-polaron theory of high-{Tc} superconductivity: 2, electronic structure of the CuO{sub 2} planes

    SciTech Connect

    Wood, R.F.

    1993-06-01

    After an introductory discussion of electronic structure calculations for the CuO{sub 2} planes in the copper-oxide based high-{Tc} superconductors, the method suggested by Slater for studying antiferromagnetic (AF) metals is described. In this method, as applied here, the chemical unit cell is doubled to form a magnetic unit cell which contains one Cu ion with predominantly up spin and one with predominantly down spin. Down spins are kept off up-spin sites, and conversely, by the introduction of a Hubbard U term. As a result, the band structure obtained is typical of that for a Mott-Hubbard (M-H) or, more generally, a charge transfer insulator. Conductivity in the a-b plane results when holes are introduced into the M-H valence band. The band structure as a function of the parameters in Koster-Slater type calculations is discussed and the Fermi surface is described. A calculation of the delocalization energy for spin-polaron formation is carried out within the context of the band calculations.

  5. Shielded high-Tc bscco tapes or wires for high field applications

    DOEpatents

    Balachandran, Uthamalingam; Lelovic, Milan; Eror, Nicholas G.

    2002-01-01

    A composite superconductor having an interior component of multiple filaments of superconducting Bi-2223 sheathed in a Ag or Ag alloy material, and a RE, TI or Hg based superconductor surrounding the interior component.

  6. Shielded high-TC BSCCO tapes or wires for high field applications

    DOEpatents

    Balachandran, Uthamalingam; Lelovic, Milan; Eror, Nicholas G.

    2001-01-01

    A composite superconductor having an interior component of multiple filaments of superconducting Bi-2223 sheathed in a Ag or Ag alloy material, and a RE, TI or Hg based superconductor surrounding the interior component.

  7. High-Tc SNS Junctions: A New Generation of Proximity-Coupled Josephson Devices

    NASA Technical Reports Server (NTRS)

    Kleinsasser, A. W.

    1997-01-01

    This paper reviews this evolution of proximity - coupled Josephson jucntion from the early investigations on low temperature superconductor-normal -superconductor junctions through the introduction of hybrid superconductor-semiconductor devices and the resulting interest in mesoscopic Josephson junctions, to the recent development of high temperature devices.

  8. A close look at antiferromagnetic phase boundary in multidimensional phase diagram of electron-doped copper oxide

    NASA Astrophysics Data System (ADS)

    Yu, Heshan; He, Ge; Lin, Ziquan; Yuan, Jie; Zhu, Beiyi; Yang, Yi-Feng; Xiang, Tao; Kusmartsev, Feo. V.; Li, Liang; Wang, Junfeng; Jin, Kui

    In copper-oxide superconductors, spin fluctuations play a predominant role in electron pairing with electron dopants yet composite orders veil the nature of superconductivity for hole-doped family. However, in electron-doped ones the ending point of AFM is still in controversy for different probes or its sensitivity to oxygen content. Here, by carefully tuning the oxygen content, a systematic study of Hall signal and magnetoresistivity up to 58 Tesla on optimally doped La2-xCexCuO4+/-δ (x = 0.10) thin films identifies two characteristic temperatures at 62.5 K (error is 7.5 K) and 25 K (error is 5 K). The former is quite robust whereas the latter becomes flexible with increasing magnetic field, thereby linked to two- and three-dimensional AFM, evident from the multidimensional phase diagram as a function of oxygen as well as Ce dopants. Consequently, the observation of extended AFM phase in contrast to μSR probe corroborates an elevated critical doping in field, providing an unambiguous picture to understand the interactions between AFM and superconductivity.

  9. Long-range two-dimensional superstructure in the superconducting electron-doped cuprate Pr0.88LaCe0.12CuO4

    NASA Astrophysics Data System (ADS)

    Campbell, B. J.; Rosenkranz, S.; Kang, H. J.; Stokes, H. T.; Chupas, P. J.; Komiya, S.; Ando, Y.; Li, Shiliang; Dai, Pengcheng

    2015-07-01

    Utilizing single-crystal synchrotron x-ray scattering, we observe distorted CuO2 planes in the electron-doped superconductor Pr1 -xLaCexCuO4 +δ , x = 0.12. Resolution-limited rods of scattering are indicative of a long-range two-dimensional 2 √{2 }×2 √{2 } superstructure in the a -b plane, adhering to planar space-group symmetry p 4 g m , which is subject to stacking disorder perpendicular to the planes. This superstructure is present only in annealed, superconducting samples, but not in the as-grown, nonsuperconducting samples. These long-range distortions of the CuO2 planes, which are generally considered to be detrimental to superconductivity, have avoided detection to date due to the challenges of observing and interpreting subtle diffuse-scattering features.

  10. James C. McGroddy Prize Lecutre: Iron-Based Superconductors: Discovery and Progress

    NASA Astrophysics Data System (ADS)

    Hosono, Hideo

    2015-03-01

    The largest breakthrough in the history is the discovery of high Tc Cuprates by G.Bednorz and A.Muller in 1986 and the maximum Tc exceeded 77K, boiling temperature of liquid nitrogen in 1987. However, no new superconductors with high Tc had been reported since then except MgB2 (Tc =39K) discovered by J.Akimitsu in 2001.We found LaFePO superconductor with Tc =3K in 2006 and LaFeAsO1-xFx with Tc =26K (42K at under high pressure of 5GPa) in early 2008. The latter discovery rekindled the extensive superconductivity research globally, and more than 10,000 papers have been published to now. This excitement originates from disprovement of a widely accepted belief that iron with a large magnetic moment is harmful for emergence of superconductivity and relatively high Tc. Extensive research on iron-based superconductors pushed up the maximal Tc to 56K, which is next to high Tc cuprates and has led to the discovery of more than 50 new iron-based superconducting materials to date. Seen are so many advances in elucidation of superconducting properties and pairing mechanism. In this talk, I introduce a tale to the discovery and show the current status by reviewing progresses in materials, properties, mechanism and the application covering the recent hot topics. Emphases are placed on the unique characteristics arising from multi-orbital nature which totally differs from high Tc cuprates.

  11. Organic Superconductors

    SciTech Connect

    Charles Mielke

    2009-02-27

    Intense magnetic fields are an essential tool for understanding layered superconductors. Fundamental electronic properties of organic superconductors are revealed in intense (60 tesla) magnetic fields. Properties such as the topology of the Fermi surface and the nature of the superconducting order parameter are revealed. With modest maximum critical temperatures~13K the charge transfer salt organic superconductors prove to be incredibly valuable materials as their electronically clean nature and layered (highly anisotropic) structures yield insights to the high temperature superconductors. Observation of de Haas-van Alphen and Shubnikov-de Haas quantum oscillatory phenomena, magnetic field induced superconductivity and re-entrant superconductivity are some of the physical phenomena observed in the charge transfer organic superconductors. In this talk, I will discuss the nature of organic superconductors and give an overview of the generation of intense magnetic fields; from the 60 tesla millisecond duration to the extreme 1000 tesla microsecond pulsed magnetic fields.

  12. Magnetic field generated by shielding current in high Tc superconducting coils for NMR magnets

    NASA Astrophysics Data System (ADS)

    Amemiya, Naoyuki; Akachi, Ken

    2008-09-01

    Numerical electromagnetic field analyses of high Tc superconducting tape in coils were carried out to calculate the magnetic field generated by the shielding (magnetization) current in superconducting tape. The numerical model employs the power law electric field-current density characteristic and the thin strip approximation, in which the current component normal to the wide face of the tape is neglected. The shielding (magnetization) currents lead to non-uniform current distributions in the superconducting tape in the coils. The magnetic field generated by the shielding (magnetization) current can deteriorate the field quality and could be a concern in insert coils for NMR magnets using high Tc superconducting tape.

  13. Avoided valence transition in a plutonium superconductor

    PubMed Central

    Ramshaw, B. J.; Shekhter, Arkady; McDonald, Ross D.; Betts, Jon B.; Mitchell, J. N.; Tobash, P. H.; Mielke, C. H.; Bauer, E. D.; Migliori, Albert

    2015-01-01

    The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5—the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)—and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability—therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5. PMID:25737548

  14. Avoided valence transition in a plutonium superconductor.

    PubMed

    Ramshaw, B J; Shekhter, Arkady; McDonald, Ross D; Betts, Jon B; Mitchell, J N; Tobash, P H; Mielke, C H; Bauer, E D; Migliori, Albert

    2015-03-17

    The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5--the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)--and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability--therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5. PMID:25737548

  15. Practical superconductor development for electrical power applications. Quarterly report for the period ending June 30, 2000

    SciTech Connect

    2000-07-21

    This is a multiyear experimental research program focused on improving relevant material properties of high-{Tc} superconductors (HTSs) and on development of fabrication methods that can be transferred to industry for production of commercial conductors. The development of teaming relationships through agreements with industrial partners is a key element of the Argonne (ANL) program.

  16. Nernst effect in high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Yayu

    This thesis presents a study of the Nernst effect in high temperature superconductors. The vortex Nernst measurements have been carried out on various high Tc cuprates to high magnetic fields. These results provide vital information about the properties and relations of the pseudogap phase and superconducting phase in high Tc superconductors. Our first finding is the existence of vortex-like excitations at temperatures much higher than Tc0, the zero filed transition temperature, in the underdoped cuprates. This result suggests that in the putative normal state of cuprates, although bulk Meissner effect is absent and resistivity looks normal, the amplitude of the Cooper pairing is still sizable. The transition at Tc0 is driven by the loss of long range phase coherence rather than the disappearance of superconducting condensate. The high field Nernst effect offers a reliable way to determine the upper critical field Hc2 of high Tc cuprates and many unusual properties are uncovered. For cuprates with relatively large hole density (x > 0.15), we found that H c2 is almost temperature independent for T < Tc0. This is in strong contrast to the Hc2 - T relation of conventional superconductors. Moreover, using a scaling analysis, we have demonstrated that H c2 increases with decreasing hole density x in this doping range, implying a stronger pairing potential at lower doping. In the severely underdoped regime (x < 0.12), some new features become apparent and they imply that the vortex Nernst signal is comprised of two distinct contributions. The first is from coherent regions with long range phase coherence and relatively low upper critical field, more like the superconducting phase; the second is from phase incoherent regions with much larger field scales, indicative of the pseudogap phase. As temperature rises, the superconducting phase gives weight to the pseudogap phase. Moreover, the upper critical field Hc2 of the superconducting phase scales with the onset

  17. Melting of the Abrikosov flux lattice in anisotropic superconductors

    NASA Technical Reports Server (NTRS)

    Beck, R. G.; Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.; Kogan, V. G.

    1992-01-01

    It has been proposed that the Abrikosov flux lattice in high-Tc superconductors is melted over a significant fraction of the phase diagram. A thermodynamic argument is provided which establishes that the angular dependence of the melting temperature is controlled by the superconducting mass anisotropy. Using a low-frequency torsional-oscillator technique, this relationship has been tested in untwinned single-crystal YBa2Cu3O(7-delta). The results offer decisive support for the melting proposal.

  18. Tests of a GM Cryocooler and high Tc leads for use on the ALS superbend magnets

    SciTech Connect

    Zbasnik, J.; Green, M.A.; Hoyer, E.H.; Taylor, C.E.; Chen, J.Y.; Wang, S.T.

    1999-07-09

    A 1.5 W (at the second stage) Gifford McMahon (GM) cryocooler was selected for cooling the superconducting SuperBend dipoles for the Advanced Light Source (ALS) at Berkeley. A GM cryocooler is a reasonable choice if conduction cooled leads are used to provide current to the superconducting magnet. The expected parasitic heat leaks are expected to range from 0.1 to 0.5 W at 4.2 K depending on the temperature of the shield and the cold mass support intercepts. Heat flow to 4 K down the SuperBend 350 A high Tc superconducting leads is expected to vary from 0.11 to 0.35 W depending on the intercept temperature and the current in the leads. The high Tc leads are designed to carry 350 A without significant resistive heating when the upper end of the lead is at 80 K. The 1.5 W cryocooler is expected to provide 45 to 50 W of refrigeration at the first stage at 50 K. The parasitic beat load into the first stage of the cryocooler will be about 8 W. The heat flow from 300 K down the upper copper leads is expected to be around 30 W. The cryocooler and high Tc lead test will measure the penormance of the cryocooler and the high Tc leads. The heat leak down the cryocooler, when it is not operating, is also of interest.

  19. Theoretical models of flux pinning and flux motion in high-{Tc} superconducting oxides

    SciTech Connect

    Welch, D.O.

    1991-12-31

    Various issues involved in the development of phenomenological models of flux pinning and motion in high-{Tc} oxides are discussed. A simplified model is presented for the critical current density and is used to examine the question of whether flux flow results from an instability due to plasticity of the flux-line array or from pin breaking.

  20. Theoretical models of flux pinning and flux motion in high- Tc superconducting oxides

    SciTech Connect

    Welch, D.O.

    1991-01-01

    Various issues involved in the development of phenomenological models of flux pinning and motion in high-{Tc} oxides are discussed. A simplified model is presented for the critical current density and is used to examine the question of whether flux flow results from an instability due to plasticity of the flux-line array or from pin breaking.

  1. Phase engineering of monolayer transition-metal dichalcogenide through coupled electron doping and lattice deformation

    SciTech Connect

    Ouyang, Bin; Lan, Guoqiang; Song, Jun; Guo, Yinsheng; Mi, Zetian

    2015-11-09

    First-principles calculations were performed to investigate the phase stability and transition within four monolayer transition-metal dichalcogenide (TMD) systems, i.e., MX{sub 2} (M = Mo or W and X = S or Se) under coupled electron doping and lattice deformation. With the lattice distortion and electron doping density treated as state variables, the energy surfaces of different phases were computed, and the diagrams of energetically preferred phases were constructed. These diagrams assess the competition between different phases and predict conditions of phase transitions for the TMDs considered. The interplay between lattice deformation and electron doping was identified as originating from the deformation induced band shifting and band bending. Based on our findings, a potential design strategy combining an efficient electrolytic gating and a lattice straining to achieve controllable phase engineering in TMD monolayers was demonstrated.

  2. Phase engineering of monolayer transition-metal dichalcogenide through coupled electron doping and lattice deformation

    NASA Astrophysics Data System (ADS)

    Ouyang, Bin; Lan, Guoqiang; Guo, Yinsheng; Mi, Zetian; Song, Jun

    2015-11-01

    First-principles calculations were performed to investigate the phase stability and transition within four monolayer transition-metal dichalcogenide (TMD) systems, i.e., MX2 (M = Mo or W and X = S or Se) under coupled electron doping and lattice deformation. With the lattice distortion and electron doping density treated as state variables, the energy surfaces of different phases were computed, and the diagrams of energetically preferred phases were constructed. These diagrams assess the competition between different phases and predict conditions of phase transitions for the TMDs considered. The interplay between lattice deformation and electron doping was identified as originating from the deformation induced band shifting and band bending. Based on our findings, a potential design strategy combining an efficient electrolytic gating and a lattice straining to achieve controllable phase engineering in TMD monolayers was demonstrated.

  3. Potentials of iron-based superconductors for practical future materials

    NASA Astrophysics Data System (ADS)

    Shimoyama, Jun-ichi

    2014-04-01

    Since the discovery of high-Tc superconductivity in the REFeAs(O, F) system in 2008, studies on the development of superconducting materials using iron-based superconductors has been undertaken because of their high Hc2 and relatively high Tc. Although the cuprate superconductors exhibit much higher Tc and similar high Hc2, the small degree of electromagnetic anisotropy between the c-axis and ab-plane directions confirmed in 11, 122 and 1111 systems encouraged us to develop more versatile conductors. Single crystals and thin films deposited on single-crystalline and metal substrates have proved that the potentials of the iron-based superconductors are high enough for designing superconducting materials for high field generation. In addition, critical current properties of powder-in-tube processed tapes have been greatly improved in the past two years and are reaching the application level at 4.2 K in high magnetic field. However, the pinning mechanism and determining factors of the critical current properties of the iron-based superconductors have not been well understood. Characteristics and potentials of iron-based superconductors are discussed from various viewpoints in this paper in an effort to understand the current status and future prospects.

  4. EDITORIAL: Focus on Superconductors with Exotic Symmetries FOCUS ON SUPERCONDUCTORS WITH EXOTIC SYMMETRIES

    NASA Astrophysics Data System (ADS)

    Rice, T. Maurice; Sigrist, Manfred; Maeno, Yoshiteru

    2009-05-01

    Superconductors can usefully be divided into two classes, those that are well described by the classic Bardeen-Cooper-Schrieffer (BCS) theory and its extensions and those which require a different microscopic description. The BCS theory of superconductivity solved the long standing mystery of this spectacular phenomenon and described all superconductors that were known when it was formulated in the 1950s. The key ingredient is an attractive interaction generated by the exchange of phonons between electrons which overcomes a Coulomb repulsion weakened by screening, to give a net attractive force on the low energy scale. In this case the simplest s-wave pairing always maximises the energy gain. There were speculations a little later that other types of electron pairing could be possible, but it took a quarter of a century until the first signs of superconductors with different and exotic pairing appeared. In the intervening thirty years many superconductors with exotic pairing have been and continue to be discovered and the study of their superconductivity has grown into a major subfield of condensed matter physics today. The importance of these exotic superconductors with unconventional symmetry is that their pairing is of electronic origin. As a result they are freed from the restrictions of low transition temperatures that go along with the phonon driven conventional superconductors. However in two of the main classes of the exotic superconductors, namely heavy fermion and organic superconductors, the intrinsic energy scales are very small leading to low temperature scales. The third class contains the small number of superconducting transition metal compounds with exotic pairing symmetry. The most studied of these are the high-Tc cuprates, the newly discovered iron pnictides and strontium ruthenate which is closely related to superfluid 3He. Although the basic electronic structure of these materials is well understood, the origin of the pairing is more complex

  5. Fermi Arcs vs. Fermi Pockets in Electron-doped Perovskite Iridates

    PubMed Central

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; Hogan, T.; Dhital, C.; Chen, X.; Lin, Qisen; Hashimoto, M.; Lu, D. H.; Zhang, Y.; Markiewicz, R. S.; Bansil, A.; Wilson, S. D.; He, Rui-Hua

    2015-01-01

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1−xLax)3Ir2O7. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr2IrO4. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system. PMID:25704850

  6. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    DOE PAGESBeta

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; Hogan, T.; Dhital, C.; Chen, X.; Lin, Qisen; Hashimoto, M.; Lu, D. H.; Zhang, Y.; et al

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  7. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    SciTech Connect

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; Hogan, T.; Dhital, C.; Chen, X.; Lin, Qisen; Hashimoto, M.; Lu, D. H.; Zhang, Y.; Markiewicz, R. S.; Bansil, A.; Wilson, S. D.; He, Rui -Hua

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

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

    NASA Astrophysics Data System (ADS)

    Haertling, Gene; Grabert, Gregory; Gilmour, Phillip

    1994-07-01

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

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

    NASA Technical Reports Server (NTRS)

    Haertling, Gene; Grabert, Gregory; Gilmour, Phillip

    1994-01-01

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

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

    PubMed

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

    2014-01-01

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

  11. Recent Advances in Layered Metal Chalcogenides as Superconductors and Thermoelectric Materials: Fe-Based and Bi-Based Chalcogenides.

    PubMed

    Mizuguchi, Yoshikazu

    2016-04-01

    Recent advances in layered (Fe-based and Bi-based) chalcogenides as superconductors or functional materials are reviewed. The Fe-chalcogenide (FeCh) family are the simplest Fe-based high-Tc superconductors. The superconductivity in the FeCh family is sensitive to external or chemical pressure, and high Tc is attained when the local structure (anion height) is optimized. The Bi-chalcogenide (BiCh2 ) family are a new group of layered superconductors with a wide variety of stacking structures. Their physical properties are also sensitive to external or chemical pressure. Recently, we revealed that the emergence of superconductivity and the Tc in this family correlate with the in-plane chemical pressure. Since the flexibility of crystal structure and electronic states are an advantage of the BiCh2 family for designing functionalities, I briefly review recent developments in this family as not only superconductors but also other functional materials. PMID:26821763

  12. Low-loss, high-speed, high-{Tc} superconducting bearings

    DOEpatents

    Hull, J.R.; Mulcahy, T.M.; Uherka, K.L.

    1996-07-30

    A flywheel energy storage device is disclosed including an iron structure disposed for rotation adjacent a stationary superconductor material structure and a stationary permanent magnet. The stationary permanent magnet levitates the iron structure while the superconductor structure can stabilize and levitate the rotating iron structure. 15 figs.

  13. Low-loss, high-speed, high-{Tc} superconducting bearings

    DOEpatents

    Hull, J.R.; Mulcahy, T.M.; Uherka, K.L.

    1997-06-24

    A flywheel energy storage device is disclosed including an iron structure disposed for rotation adjacent a stationary superconductor material structure and a stationary permanent magnet. The stationary permanent magnet levitates the iron structure while the superconductor structure can stabilize the rotating iron structure. 15 figs.

  14. Cooper Pairs with Broken Parity and Spin-Rotational Symmetries in d-Wave Superconductors

    NASA Astrophysics Data System (ADS)

    Lebed, A. G.

    2006-01-01

    Paramagnetic effects are shown to result in the appearance of a triplet component of order parameter in a vortex phase of a d-wave superconductor in the absence of impurities. This component, which breaks parity and spin-rotational symmetries of Cooper pairs, is expected to be of the order of unity in a number of modern superconductors such as organic, high Tc, and some others. A generic phase diagram of such type-IV superconductors, which are singlet ones at H=0 and in the Meissner phase, and characterized by singlet-triplet mixed Copper pairs Δs+iΔt with broken symmetries in a vortex phase, is discussed.

  15. Paramagnetic intrinsic Meissner effect in layered superconductors

    NASA Astrophysics Data System (ADS)

    Lebed, A. G.

    2008-07-01

    Free energy of a layered superconductor with ξ⊥high- Tc superconductors, as well as in superconducting superlattices.

  16. Paramagnetic Intrinsic Meissner Effect in Layered Superconductors

    NASA Astrophysics Data System (ADS)

    Lebed, Andrei

    2008-03-01

    Free energy of a quasi-two-dimensional superconductor with a coherence length perpendicular to the conducting layers being less than an inter-layer distance is calculated. The free energy is shown to differ from that in the textbook Lawerence-Doniach model at high fields, where the Meissner currents are found to create an unexpected positive magnetic moment due to shrinking of the Cooper pairs ``sizes'' by a magnetic field. This unique phenomenon - paramagnetic intrinsic Meissner effect (PIME) in a bulk [1] - is suggested to detect by measuring in-plane magnetization and torque in layered organic and high-Tc superconductors as well as in superconducting superlattices. [1] A.G. Lebed, Physical Review Letters, submitted.

  17. Superconductor Composite

    DOEpatents

    Dorris, Stephen E.; Burlone, Dominick A.; Morgan; Carol W.

    1999-02-02

    A superconducting conductor fabricated from a plurality of wires, e.g., fine silver wires, coated with a superconducting powder. A process of applying superconducting powders to such wires, to the resulting coated wires and superconductors produced therefrom.

  18. Practical superconductor development for electrical power applications. Annual report for FY 1992

    SciTech Connect

    Goretta, K.C.

    1992-10-01

    Development of useful high-critical-temperature (high-{Tc}) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes the technical progress of research and development efforts aimed at producing superconducting components that are based on the Y-Ba-Cu, Bi-Sr-Ca-Cu, Bi-Pb-Sr-Ca-Cu, and (TI,Pb)-(Ba,Sr)-Ca-Cu oxide systems. Topics discussed are synthesis and heat treatment of high-{Tc} superconductors, formation of monolithic and composite wires and tapes, superconductor/metal connectors, characterization of structures and superconducting and mechanical properties, fabrication and properties of thin films, and development of prototype components. Collaborations with industry and academia are documented.

  19. Novel design of rapid single flux quantum logic based on a single layer of a high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Kaplunenko, V. K.; Ivanov, Z. G.; Stepantsov, E. A.; Claeson, T.; Holst, T.; Sun, Z. J.; Kromann, R.; Shen, Y. Q.; Vase, P.; Freltoft, T.; Wikborg, E.

    1995-07-01

    We suggest a new design of rapid single flux quantum (RSFQ) logic circuits which is based on a single superconducting layer and does not require a superconducting ground plane. Small inductances of about 10 pH, obligatory for RSFQ circuits, are formed as narrow slits of widths comparable to the London penetration depth (≂0.15 μm). The design allows us to decrease the geometric size of the RSFQ cell. Test circuits with YBaCuO grain boundary junctions on asymmetric 32° Y- ZrO2 bicrystals were used to measure the slit inductance per unit length and the mutual inductance of neighboring slits. A typical inductance of a 0.4 μm slit was found to be 0.7-0.8 pH/μm.

  20. Correlation between fabrication factor and superconducting properties of the Tl-and-Bi-based high-Tc superconductor

    NASA Technical Reports Server (NTRS)

    Maki, Naoki; Okada, Michiya; Doi, Toshiya J.; Kanai, Tsuneyuki; Sato, Junichi; Higashiyama, Kazutoshi

    1995-01-01

    Large critical current densities (J(sub c)) were obtained in c axis oriented Tl-1 223/Ag composite tapes fabricated by spraying methods without a vacuum. Transport measurements at 77K under a zero field indicated a J(sub c) of 9 x 10(exp 4) A/sq cm and 7 x 10(exp 3) A/sq cm at 1T for the tapes fabricated by spray pyrolysis. The novel GPM method was also applied for Bi-2212/Ag PIT composite wire, and found to be very effective for improving the distribution of voids, which caused from the melt-solidifying process. The GPM showed a marked effect for obtaining homogeneous long wire. A 1 T class coil was successfully fabricated with monocore wire.

  1. Soft-x-ray emission spectroscopy study of La2CuO4 and three high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Barnole, V.; Mariot, J.-M.; Hague, C. F.; Michel, C.; Raveau, B.

    1990-03-01

    High-resolution x-ray emission spectroscopy measurements have been performed on sintered samples of La2CuO4, La1.85Sr0.15CuO4-δ, YBa2Cu3O7-δ (δ<0.1), and compressed polycrystalline Bi2Sr2CaCu2O8+δ. The Cu Lα and O Kα emission bands, which reflect the local partial Cu 3d and O 2p states, respectively, are compared to photoelectron spectra and ground-state local-density-approximation (LDA) densities-of-states (DOS) calculations. Our results show that solid-state effects are dominant. In particular, the differences in shape of the O Kα emission bands follow the trends predicted by LDA, although it must be stressed that they mainly arise from O 2p states at oxygen sites not directly involved in the Cu-O planes. The Cu-side 3d states, on the other hand, vary little from one cuprate to the next and are more strongly localized than expected from LDA predictions. The Anderson-impurity model calculations of Kotani and co-workers are discussed, and it is concluded that they provide a satisfactory explanation of the Cu Lα emission data, which reflect strong on-site Coulomb interaction. We conclude that the apparently good agreement between LDA-calculated DOS and low-energy photoemission experiments recently reported results from the high sensitivity of the latter to O 2p states. Discrepancies are to be expected in excitation spectra that involve mainly 3d electrons.

  2. Apparatus for nonresonant rf power absorption studies in high Tc superconductors and CMR materials using rf oscillators

    NASA Astrophysics Data System (ADS)

    Sarangi, S.; Bhat, S. V.

    2005-02-01

    The design, fabication, and performance of an apparatus for measurement of nonresonant rf power absorption (NRRA) in superconducting and CMR samples are described. The system consists of an effective self-resonant LC tank circuit driven by a NOT gate (Logic gate). The samples under investigation are placed in the core of an inductive coil and nonresonant power absorption is determined from the measured shift in total current supplies to the whole oscillator circuit. A customized low temperature insert is used to integrate the experiment with a commercial oxford cryostat and temperature controller. The system makes use of a sensitive digital multimeter (Keithley 2002 model) and is capable of measuring NRRA in superconducting and colossal magnetoresistance samples of volume as small as 1×10-3cm3 with a signal to noise ratio of 10. Further increase in the sensitivity of the experimental setup can be obtained by summing the results of repeated measurements obtained in the same temperature interval. The system has been tested for an IC 74LS04 oscillator at frequencies between 1MHz and 25MHz in the temperature range from 4.2Kto400K and in magnetic field from 0to1.4T. The system performance is evaluated by measuring the NRRA in YBa2Cu3O7 (YBCO) superconducting sample and La0.7Sr0.3MnO3 (LSMO) colossal magnetoresistive (CMR) manganite samples at different rf frequencies. During a measurement all operation are controlled automatically by computer from a menu-driven software system, with user input required only on initiation of measurement sequence.

  3. In situ observation of oxygen deficiency occurring during electron irradiation in high Tc superconductor YBa2Cu3Oy.

    PubMed

    Akase, Z; Tomokiyo, Y; Watanabe, M

    2001-07-01

    The decreasing process of oxygen in YBa2Cu3Oy is investigated through high resolution electron microscopy (HREM) and convergent beam electron diffraction (CBED). Measurements of the axial length in HREM images show that oxygen content y decreases faster near a twin boundary than at the inner part of a twin lamella. The transformation from an orthorhombic to a tetragonal phase starts at a twin boundary and the transformed region propagates to an inner region of lamella. Lattice strains are observed near boundaries between transformed and non-transformed regions. The transformation is almost complete within 30 s during observation of HREM images at 400 kV and at room temperature. A value of y was quantitatively measured by analysing observed intensities of energy-filtered CBED patterns with the dynamical theory. The value of y decreases from 6.9 to 6.5 when 200 kV electrons are irradiated for 160 s in a microscope at 108 K. More precise analysis of the intensities provides information on charge distribution along the c-axis as well as local oxygen content at a spatial resolution of several nanometres. PMID:11454148

  4. “Nodal Gap” induced by the incommensurate diagonal spin density modulation in underdoped high- Tc superconductors

    DOE PAGESBeta

    Zhou, Tao; Gao, Yi; Zhu, Jian -Xin

    2015-03-07

    Recenmore » tly it was revealed that the whole Fermi surface is fully gapped for several families of underdoped cuprates. The existence of the finite energy gap along the d-wave nodal lines (nodal gap) contrasts the common understanding of the d-wave pairing symmetry, which challenges the present theories for the high-Tcsuperconductors. Here we propose that the incommensurate diagonal spin-density-wave order can account for the above experimental observation. The Fermi surface and the local density of states are also studied. Our results are in good agreement with many important experiments in high-Tcsuperconductors.« less

  5. Superconductor consolidation

    NASA Astrophysics Data System (ADS)

    Staudhammer, K. P.

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

  6. Superconductor consolidation

    SciTech Connect

    Staudhammer, K.P.

    1988-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Kokail, Christian; Heil, Christoph; Boeri, Lilia

    2016-08-01

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

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

    PubMed

    He, D F

    2011-02-01

    By improving the compensation circuit, a hand-held high-Tc rf superconducting quantum interference devices (SQUID) system was developed. It could operate well when moving in unshielded environment. To check the operation, it was used to do eddy-current testing by hand moving the SQUID, and the artificial defect under 6 mm aluminum plate could be successfully detected in shielded environment. PMID:21361649

  9. Electronic transport in unconventional superconductors

    SciTech Connect

    Graf, M.J.

    1998-12-31

    The author investigates the electron transport coefficients in unconventional superconductors at low temperatures, where charge and heat transport are dominated by electron scattering from random lattice defects. He discusses the features of the pairing symmetry, Fermi surface, and excitation spectrum which are reflected in the low temperature heat transport. For temperatures {kappa}{sub B}T {approx_lt} {gamma} {much_lt} {Delta}{sub 0}, where {gamma} is the bandwidth of impurity induced Andreev states, certain eigenvalues become universal, i.e., independent of the impurity concentration and phase shift. Deep in the superconducting phase ({kappa}{sub B}T {approx_lt} {gamma}) the Wiedemann-Franz law, with Sommerfeld`s value of the Lorenz number, is recovered. He compares the results for theoretical models of unconventional superconductivity in high-{Tc} and heavy fermion superconductors with experiment. The findings show that impurities are a sensitive probe of the low-energy excitation spectrum, and that the zero-temperature limit of the transport coefficients provides an important test of the order parameter symmetry.

  10. Lateral restoring force on a magnet levitated above a superconductor

    NASA Astrophysics Data System (ADS)

    Davis, L. C.

    1990-03-01

    The lateral restoring force on a magnet levitated above a superconductor is calculated as a function of displacement from its original position at rest using Bean's critical-state model to describe flux pinning. The force is linear for small displacements and saturates at large displacements. In the absence of edge effects the force always attracts the magnet to its original position. Thus it is a restoring force that contributes to the stability of the levitated magnet. In the case of a thick superconductor slab, the origin of the force is a magnetic dipole layer consisting of positive and negative supercurrents induced on the trailing side of the magnet. The qualitative behavior is consistent with experiments reported to date. Effects due to the finite thickness of the superconductor slab and the granular nature of high-Tc materials are also considered.

  11. ARPES of K-doped iron selenide superconductor

    NASA Astrophysics Data System (ADS)

    Yokoya, Takayoshi; Sunagawa, Masanori; Terashima, Kensei; Hamada, Takahiro; Fujiwara, Hirokazu; Tanaka, Masashi; Takeya, Hiroyuki; Takano, Yoshihiko; Arita, Masashi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki; Suzuki, Katsuhiro; Usui, Hidetomo; Kuroki, Kazuhiko; Wakita, Takanori; Muraoka, Yuji

    2015-03-01

    In iron pnictide superconductors, the characteristic Fermi surface(FS) topology, namely nesting of hole-like FS at the zone center and electron-like FS at the zone corner, is considered to induce spin/orbital fluctuation leading to high-Tc superconductivity. In K-doped iron selenide superconductors, however, ARPES studies reported absence of hole-like FS at the zone center, which is different from that observed in iron pnictides. So far, proposed models for the superconductivity based on the FS topology appear to fail to explain available experimental results. In this talk, we present our recent ARPES studies on a K-doped iron selenide superconductor performed with careful tuning of experimental conditions, which show a hole-like FS around the zone center.

  12. Lateral restoring force on a magnet levitated above a superconductor

    NASA Technical Reports Server (NTRS)

    Davis, L. C.

    1990-01-01

    The lateral restoring force on a magnet levitated above a superconductor is calculated as a function of displacement from its original position at rest using Bean's critical-state model to describe flux pinning. The force is linear for small displacements and saturates at large displacements. In the absence of edge effects the force always attracts the magnet to its original position. Thus it is a restoring force that contributes to the stability of the levitated magnet. In the case of a thick superconductor slab, the origin of the force is a magnetic dipole layer consisting of positive and negative supercurrents induced on the trailing side of the magnet. The qualitative behavior is consistent with experiments reported to date. Effects due to the finite thickness of the superconductor slab and the granular nature of high-Tc materials are also considered.

  13. Anisotropic softening of magnetic excitations in lightly electron-doped Sr2IrO4

    DOE PAGESBeta

    Liu, X.; Dean, M. P. M.; Meng, Z. Y.; Upton, M. H.; Qi, T.; Gog, T.; Cao, Y.; Lin, J. Q.; Meyers, D.; Ding, H.; et al

    2016-06-10

    The magnetic excitations in electron doped (Sr1-xLax)2IrO4 with x = 0:03 were measured using resonant inelastic X-ray scattering at the Ir L3-edge. Although much broadened, well defined dispersive magnetic excitations were observed. Comparing with the magnetic dispersion from the undoped compound, the evolution of the magnetic excitations upon doping is highly anisotropic. Along the anti-nodal direction, the dispersion is almost intact. On the other hand, the magnetic excitations along the nodal direction show significant softening. These results establish the presence of strong magnetic correlations in electron doped (Sr1-xLax)2IrO4 with close analogies to the hole doped cuprates, further motivating the searchmore » for high temperature superconductivity in this system.« less

  14. Electron doping through lithium intercalation to interstitial channels in tetrahedrally bonded SiC

    SciTech Connect

    Sakai, Yuki; Oshiyama, Atsushi

    2015-11-07

    We report on first-principles calculations that clarify the effect of lithium atom intercalation into zinc blende 3C-silicon carbide (3C-SiC) on electronic and structural properties. Lithium atoms inside 3C-SiC are found to donate electrons to 3C-SiC that is an indication of a new way of electron doping through the intercalation. The electrons doped into the conduction band interact with lithium cations and reduce the band spacing between the original valence and conduction bands. We have also found that a silicon monovacancy in 3C-SiC promotes the lithium intercalation, showing that the vacancy generation makes SiC as a possible anode material for lithium-ion battery.

  15. Electron-doping-enhanced trion formation in monolayer molybdenum disulfide functionalized with cesium carbonate.

    PubMed

    Lin, Jia Dan; Han, Cheng; Wang, Fei; Wang, Rui; Xiang, Du; Qin, Shiqiao; Zhang, Xue-Ao; Wang, Li; Zhang, Hua; Wee, Andrew Thye Shen; Chen, Wei

    2014-05-27

    We report effective and stable electron doping of monolayer molybdenum disulfide (MoS2) by cesium carbonate (Cs2CO3) surface functionalization. The electron charge carrier concentration in exfoliated monolayer MoS2 can be increased by about 9 times after Cs2CO3 functionalization. The n-type doping effect was evaluated by in situ transport measurements of MoS2 field-effect transistors (FETs) and further corroborated by in situ ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering measurements. The electron doping enhances the formation of negative trions (i.e., a quasiparticle comprising two electrons and one hole) in monolayer MoS2 under light irradiation and significantly reduces the charge recombination of photoexcited electron-hole pairs. This results in large photoluminescence suppression and an obvious photocurrent enhancement in monolayer MoS2 FETs. PMID:24785254

  16. Anisotropic softening of magnetic excitations in lightly electron-doped Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Liu, X.; Dean, M. P. M.; Meng, Z. Y.; Upton, M. H.; Qi, T.; Gog, T.; Cao, Y.; Lin, J. Q.; Meyers, D.; Ding, H.; Cao, G.; Hill, J. P.

    2016-06-01

    The magnetic excitations in electron-doped (Sr1 -xLax )2IrO4 with x =0.03 were measured using resonant inelastic x-ray scattering at the Ir L3 edge. Although much broadened, well defined dispersive magnetic excitations were observed. Comparing with the magnetic dispersion from the undoped compound, the evolution of the magnetic excitations upon doping is highly anisotropic. Along the antinodal direction, the dispersion is almost intact. On the other hand, the magnetic excitations along the nodal direction show significant softening. These results establish the presence of strong magnetic correlations in electron-doped (Sr1 -xLax )2IrO4 with close analogies to the hole-doped cuprates, further motivating the search for high temperature superconductivity in this system.

  17. Electron doping through lithium intercalation to interstitial channels in tetrahedrally bonded SiC

    NASA Astrophysics Data System (ADS)

    Sakai, Yuki; Oshiyama, Atsushi

    2015-11-01

    We report on first-principles calculations that clarify the effect of lithium atom intercalation into zinc blende 3C-silicon carbide (3C-SiC) on electronic and structural properties. Lithium atoms inside 3C-SiC are found to donate electrons to 3C-SiC that is an indication of a new way of electron doping through the intercalation. The electrons doped into the conduction band interact with lithium cations and reduce the band spacing between the original valence and conduction bands. We have also found that a silicon monovacancy in 3C-SiC promotes the lithium intercalation, showing that the vacancy generation makes SiC as a possible anode material for lithium-ion battery.

  18. High Tc superconducting IR detectors from Y-Ba-Cu-O thin films

    NASA Technical Reports Server (NTRS)

    Lindgren, M.; Ahlberg, H.; Danerud, M.; Larsson, A.; Eng, M.

    1990-01-01

    A thin-film high-Tc superconducting multielement optical detector made of Y-Ba-Cu-O has been designed and evaluated using optical pulses from a diode laser (830 nm) and a Q-switched CO2-laser (10.6 microns). Different thin films have been tested. A laser deposited film showed the strongest response amplitude for short pulses and responded to an ultrafast, 50 ps wide pulse. Comparisons between dR/dT and response as a function of temperature indicated, however, a bolometric response.

  19. Position determine system for lymph node relating breast cancer using a high- Tc SQUID

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Ota, Hajime; Kondo, Yoichi; Tamaki, Yasuhiro; Noguchi, Shinzaburo; Hasegawa, Masakatsu

    2002-03-01

    The performance of a lymph-node detection system used with a high- Tc superconducting quantum interference device was investigated. Ultra-small iron oxide particles containing 360 pg in weight of iron could be detected at a distance of 1 mm using Helmholtz coils. When a pair of angled field coils, which were of a more practical design, were used this value was increased to 2.8 ng. This value is still large enough to apply the technique for sentinel-node biopsy and lymphatic mapping.

  20. Coherently coupling distinct spin ensembles through a high-Tc superconducting resonator

    NASA Astrophysics Data System (ADS)

    Ghirri, A.; Bonizzoni, C.; Troiani, F.; Buccheri, N.; Beverina, L.; Cassinese, A.; Affronte, M.

    2016-06-01

    The problem of coupling multiple spin ensembles through cavity photons is revisited by using (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl (PyBTM) organic radicals and a high-Tc superconducting coplanar resonator. An exceptionally strong coupling is obtained and up to three spin ensembles are simultaneously coupled. The ensembles are made physically distinguishable by chemically varying the g factor and by exploiting the inhomogeneities of the applied magnetic field. The coherent mixing of the spin and field modes is demonstrated by the observed multiple anticrossing, along with the simulations performed within the input-output formalism, and quantified by suitable entropic measures.

  1. Superconductor cable

    DOEpatents

    Allais, Arnaud; Schmidt, Frank; Marzahn, Erik

    2010-05-04

    A superconductor cable is described, having a superconductive flexible cable core (1) , which is laid in a cryostat (2, 3, 4), in which the cable core (1) runs in the cryostat (2, 3, 4) in the form of a wave or helix at room temperature.

  2. Electron-Phonon Interaction in Oxide Superconductors - Proceedings of the First Cinvestav Superconductivity Symposium

    NASA Astrophysics Data System (ADS)

    Matsumoto, Koichi; Hashimoto, Takasu

    1991-12-01

    The Table of Contents for the book is as follows: * List of Invited Speakers * Preface * PHONONS * Lattice Vibrations of the Cuprate Superconductors * INFRARED * Evidence of Strong Electron-Phonon Interaction from the Infrared Spectra of YBa2Cu3O7 * Electron-Phonon Interaction and Infrared Spectra of High Temperature Superconductors * TUNNELING * Tunneling Studies of Bismuthate and Cuprate Superconductors * Phonon Mechanism of the High Tc Superconductivity Based on the Tunneling Structure * LATTICE INSTABILITIES * Lattice Instabilities in High Temperature Superconductors: The X Point Tilt Energy Surface for La2-xBaxCuO4 * Structural Instability and Strong Coupling in Oxide Superconductors * ISOTOPE EFFECT * On the Isotope Effect * Electron-Phonon Coupling, Oxygen Isotope Effect and Superconductivity in Ba1-xKxBio3 * BCJ AND ELIASHBERG THEORY * Weak Coupling Theory of the High Tc Superconductors Based on the Electron-Phonon Interaction * Phonon Self-Energy Effects in Migdal-Eliashberg Theory * OTHER TOPICS * Electron-Phonon Interaction and Superconductivity in BaxK1-xBio3 * The Effect of Strong Coulomb Correlations on Electron-Phonon Interactions in the Copper Oxides: Implications for Transport * EXPERIMENT (OTHER TOPICS) * Zinc Substitution Effects on the Superconducting Properties of Nd1.85Ce0.15CuO4-δ * SUMMARY * Manifestations of the e-ph Interaction: A Summary * Author Index

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  4. Metallic contaminant detection system using multi-channel high Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Kitamura, Yoshihiro; Hatsukade, Yoshimi; Ohtani, Takeyoshi; Suzuki, Shuichi

    2012-10-01

    We have developed the magnetic metallic contaminant detectors using multiple high Tc SQUID gradiometers for industrial products. Finding ultra-small metallic contaminants is a big issue for manufacturers producing commercial products. The quality of industrial products such as lithium ion batteries can deteriorate by the inclusion of tiny metallic contaminants. When the contamination does occur, the manufacturer of the product suffers a great loss to recall the tainted products. Metallic particles with outer dimension less than 50 μm cannot be detected by a conventional X-ray imaging. Therefore a high sensitive detection system for small foreign matters is required. However, in most of the cases, the matrix of an active material coated sheet electrode is magnetized and the magnetic signal from the matrix is large enough to mask the signal from contaminants. Thus we have developed a detection system based on a SQUID gradiometer and a horizontal magnetization to date. For practical use, we should increase the detection width of the system by employing multiple sensors. We successfully realized an eight-channel high-Tc SQUID gradiometer system for inspection of sheet electrodes of a lithium ion battery with width of at least 60 to 70 mm. Eight planar SQUID gradiometers were mounted with a separation of 9.0 mm. As a result, small iron particles of less than 50 μm were successfully measured. This result suggests that the system is a promising tool for the detection of contaminants in a lithium ion battery.

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

    PubMed Central

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

    2006-01-01

    The phase transformation between the orthorhombic and tetragonal structures of six high-Tc superconductors, Ba2RCu3O7−δ, where R = Nd, Sm, Gd, Y, Ho, and Er, and δ = 0 to 1, has been investigated using techniques of x-ray diffraction, differential thermal analysis/thermogravimetric analysis (DTA/TGA) and electron diffraction. The transformation from the oxygen-rich orthorhombic phase to the oxygen-deficient tetragonal phase involves two orthorhombic phases. A superlattice cell caused by oxygen ordering, with a′ = 2a, was observed for materials with smaller ionic radius (Y, Ho, and Er). For the larger lanthanide samples (Nd, Sm, and Gd), the a′ = 2a type superlattice cell was not observed. The structural phase transition temperatures, oxygen stoichiometry and characteristics of the Tc plateaus appear to correlate with the ionic radius, which varies based on the number of f electrons. Lanthanide elements with a smaller ionic radius stabilize the orthorhombic phase to higher temperatures and lower oxygen content. Also, the superconducting temperature is less sensitive to the oxygen content for materials with smaller ionic radius. The trend of dependence of the phase transformation temperature on ionic radius across the lanthanide series can be explained using a quasi-chemical approximation (QCA) whereby the strain effect plays an important role on the order-disorder transition due to the effect of oxygen content on the CuO chain sites. PMID:27274916

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  7. Quantum oscillation signatures of spin-orbit interactions controlling the residual nodal bilayer-splitting in underdoped high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Harrison, Neil; Shekhter, Arkady

    2015-03-01

    We investigate the origin of the small residual nodal bilayer-splitting in the underdoped high-Tc superconductor YBa2Cu3O6+x using the results of recently published angle-resolved quantum oscillation data [Sebastian et al., Nature 511, 61 (2014)]. A crucial clue to the origin of the residual bilayer-splitting is found to be provided by the anomalously small Zeeman-splitting of some of the observed cyclotron orbits. We show that such an anomalously Zeeman-splitting (or small effective g-factor) for a subset of orbits can be explained by spin-orbit interactions, which become significant in the nodal regions as a result of the vanishing bilayer coupling. The primary effect of spin-orbit interactions is to cause quasiparticles traversing the nodal region of the Brillouin zone to undergo a spin flip. We suggest that the Rashba-like spin-orbit interactions, naturally present in bilayer systems, have the right symmetry and magnitude to give rise to a network of coupled orbits consistent with experimental observations in underdoped YBa2Cu3O6+x. This work is supported by the DOEm BES proposal LANLF100, while the magnet lab is supported by the NSF and Florida State.

  8. Superconductor cable

    DOEpatents

    Smith, Jr., Darrell F.; Lake, Bill L.; Ballinger, Ronald G.

    1988-01-01

    A superconducting cable comprising an in-situ-formed type II superconductor, e.g. Nb.sub.3 Sn, in association with a stabilizing conductor both in heat transfer relationship with at least one passage adapted to carry liquified gaseous refrigerant. The conductor and said at least one passage are enclosed by a sheath comprising an alloy consisting essentially of about 49% nickel, about 4% chromium, about 3% niobium, about 1.4% titanium, about 1% aluminum, balance essentially iron.

  9. Chiral superconductors.

    PubMed

    Kallin, Catherine; Berlinsky, John

    2016-05-01

    Chiral superconductivity is a striking quantum phenomenon in which an unconventional superconductor spontaneously develops an angular momentum and lowers its free energy by eliminating nodes in the gap. It is a topologically non-trivial state and, as such, exhibits distinctive topological modes at surfaces and defects. In this paper we discuss the current theory and experimental results on chiral superconductors, focusing on two of the best-studied systems, Sr2RuO4, which is thought to be a chiral triplet p-wave superconductor, and UPt3, which has two low-temperature superconducting phases (in zero magnetic field), the lower of which is believed to be chiral triplet f-wave. Other systems that may exhibit chiral superconductivity are also discussed. Key signatures of chiral superconductivity are surface currents and chiral Majorana modes, Majorana states in vortex cores, and the possibility of half-flux quantum vortices in the case of triplet pairing. Experimental evidence for chiral superconductivity from μSR, NMR, strain, polar Kerr effect and Josephson tunneling experiments are discussed. PMID:27088452

  10. Chiral superconductors

    NASA Astrophysics Data System (ADS)

    Kallin, Catherine; Berlinsky, John

    2016-05-01

    Chiral superconductivity is a striking quantum phenomenon in which an unconventional superconductor spontaneously develops an angular momentum and lowers its free energy by eliminating nodes in the gap. It is a topologically non-trivial state and, as such, exhibits distinctive topological modes at surfaces and defects. In this paper we discuss the current theory and experimental results on chiral superconductors, focusing on two of the best-studied systems, Sr2RuO4, which is thought to be a chiral triplet p-wave superconductor, and UPt3, which has two low-temperature superconducting phases (in zero magnetic field), the lower of which is believed to be chiral triplet f-wave. Other systems that may exhibit chiral superconductivity are also discussed. Key signatures of chiral superconductivity are surface currents and chiral Majorana modes, Majorana states in vortex cores, and the possibility of half-flux quantum vortices in the case of triplet pairing. Experimental evidence for chiral superconductivity from μSR, NMR, strain, polar Kerr effect and Josephson tunneling experiments are discussed.

  11. Electron Doping by Charge Transfer at LaFeO 3 /Sm 2 CuO 4 Epitaxial Interfaces

    SciTech Connect

    Bruno, Flavio Y.; Schmidt, R; Varela, Maria; Garcia-Barriocanal, Javier; Rivera-Calzada, Alberto; Cuellar, F.; Leon, Carlos; Thakur, P.; Cezar, J. C.; Brookes, N. B.; Garcia-Hernandez, M; Dagotto, Elbio R; Pennycook, Stephen J; Santamaria, J.

    2013-01-01

    The breakdown of the lattice translational invariance symmetry that occurs at complex oxide interfaces may profoundly modify their electronic structure, leading to interfacial states with properties drastically different from those of the superlattice individual components. The appearance of a conducting two dimensional (2D) electron gas at the interface between two insulating oxides and induced magnetism in a non-magnetic material are just two among many fascinating examples. [ 1 8 ] One of the key factors underlying novel properties is the modifi cation of the doping and orbital occupancy near those interfaces, which may result from charge transfer processes. [ 3 , 9 11 ] If materials used in heterostructures have different work functions, a non-equilibrium situation will be created at the interface and charge will be transferred until the chemical potential levels off. [ 12 ] The use of such phenomena to modify doping in heterostructures has been proposed theoretically as a new route to avoid the quenched disorder that inevitably accompanies the chemical doping. At the interface between a Mott insulating parent compound of the high critical temperature superconductor (HTSC) family and a suitable material that would act as the charge donor, electron doped phases could be stabilized which would eventually turn metallic and perhaps superconducting. [ 12 , 13 ] Such charge transfer processes have been observed at interfaces involving copper oxides such as La 0.7 Ca 0.3 MnO 3 / YBa 2 Cu 3 O 7 , [ 14 ] La 2 x Sr x CuO 4 /La 2 CuO 4 [ 15 ] and SrTi 1 x Nb x O 3 / Sm 2 CuO 4 . [ 16 ] While a novel 2D superconducting state was found at the La 2-x Sr x CuO 4 /La 2 CuO 4 interface, [ 17 ] the effect of doping by charge transfer could not be examined in the other two cases due to the detrimental effect on the YBa 2 Cu 3 O 7 superconductivity of the spin polarized electrons from La 0.7 Ca 0.3 MnO 3 in one case and due to the conducting nature of the SrTi 1 x Nb x O 3 in the

  12. Importance of the Fermi-surface topology to the superconducting state of the electron-doped pnictide Ba(Fe1-xCox)₂As₂

    DOE PAGESBeta

    Liu, Chang; Palczewski, A. D.; Dhaka, R. S.; Kondo, Takeshi; Fernandes, R. M.; Mun, E. D.; Hodovanets, H.; Thaler, A. N.; Schmalian, J.; Bud’ko, S. L.; et al

    2011-07-25

    We used angle-resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe1-xCox)₂As₂ high-temperature superconductor. Our data demonstrate that several Lifshitz transitions—topological changes of the Fermi surface—occur for large x. The central hole barrel changes to ellipsoids that are centered at Z at x~0.11 and subsequently disappear around x~0.2; changes in thermoelectric power occur at similar x values. Tc decreases and goes to zero around x~0.15—between the two Lifshitz transitions. Beyond x=0.2 the central pocket becomes electron-like and superconductivity does not exist. Our observations reveal the importance of the underlying Fermiologymore » in electron-doped iron arsenides. We speculate that a likely necessary condition for superconductivity in these materials is the presence of the central hole pockets rather than nesting between central and corner pockets.« less

  13. Nuclear spin-lattice relaxation rate in electron-doped Pr 0.91 LaCe 0.09 CuO 4 - y : Constraint on the gap symmetry

    NASA Astrophysics Data System (ADS)

    Zhao, Guo-meng

    2011-09-01

    We present numerical calculations of the nuclear spin-lattice relaxation (R) rate in the superconducting state of pure indium and slightly underdoped n-type cuprate Pr 0.91LaCe 0.09CuO 4 - y. By properly taking into account electron-phonon coupling, our calculated R for the conventional s-wave superconductor, indium, is in quantitative agreement the experimental data with a clear Hebel-Slichter peak. In contrast, the absence of the Hebel-Slichter peak in the R data of Pr 0.91LaCe 0.09CuO 4 - y can be explained by either d-wave or highly anisotropic s-wave gap symmetry. Thus, the absence of the Hebel-Slichter peak does not necessarily argue against an s-wave gap symmetry in this electron-doped cuprate.

  14. Practical superconductor development for electrical power applications. Annual report for FY 1995

    SciTech Connect

    Balachandran, U.

    1995-10-01

    Development of useful high-critical-temperature (high-{Tc}) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds: production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes the technical progress of research and development efforts aimed at producing superconducting components in the (Bi,Pb)-Sr-Ca-Cu, (Tl,Pb,Bi,V)-(Ba,Sr)-Ca-Cu, and Y-Ba-Cu oxide systems. The topics that are discussed are synthesis and heat treatment of high-{Tc} superconductors, formation of monolithic and composite conductors, characterization of structures and superconducting and mechanical properties, and fabrication and testing of prototype components. Collaboration with industry and academia is documented.

  15. Electronic Raman Response in Disordered Unconventional Superconductors

    NASA Astrophysics Data System (ADS)

    Devereaux, Thomas

    1998-03-01

    Due to the strong symmetry dependence of the observed Raman spectra in all high Tc compounds, i.e., the characteristic features of light scattering for different incident and scattered polarization orientations, electronic Raman scattering in unconventional superconductors has grown to be of considerable interest in light of identifying the symmetry of the energy gap and ultimately, the mechanism of superconductivity in high temperature superconductors. I review the theory of the effects of impurities on the Raman response of unconventional superconductors with a view towards understanding the role polarization plays in determining the order parameter symmetry in the cuprates.(T. P. Devereaux, Phys. Rev. Lett. 74), 4313 (1995) (T. P. Devereaux and A. P. Kampf, Int. Journ. Mod. Phys. B 11), 2093 (1997) Signatures of the effects of disorder on the low frequency and low temperature behavior of the Raman spectra obtained for different polarizations will be discussed in relation to the magnitude and phase of the energy gap. Extensions of the theory to include anisotropic impurity scattering and inelastic spin fluctuation scattering will be discussed. Good agreement of the theory with the data on optimally- and overdoped-samples will be shown, although discrepancies remain.

  16. High-Tc superconductivity at 40 K emerged in ultrathin FeSe electric-double-layer transistors

    NASA Astrophysics Data System (ADS)

    Junichi, Shiogai; Ito, Yukihiro; Mitsuhashi, Toshiki; Nojima, Tsutomu; Tsukazaki, Atsushi

    A few unit-cell (UC) FeSe films on SrTiO3 substrates have recently attracted much attentions owing to emergence of high temperature superconductivity (high-Tc) about 65 K compared to the bulk value of 8 K. Modulation of electronic structure, charge transfer from SrTiO3, and electron-phonon coupling between the film and substrate are proposed as possible origins for high-Tc. Although the in-situ scanning tunneling and photoemission spectroscopies have been intensively studied, systematic thickness, carrier density and substrate material dependences of electrical measurements have been limited so far. Here we report on high-Tc in FeSe films on SrTiO3 and MgO in electric-double-layer transistor (EDLT). Both the film thickness and electric field can be tuned by electrochemical etching and electrostatic doping in EDLT. The systematic thickness dependences reveal that the onset Tc of 40 K appears from around 10 nm to 1 UC under the electric field while the initial 18-nm-thick FeSe shows no high-Tc. Our results point out the importance of electron accumulation or electronic band modulation for high-Tc in FeSe rather than electron-phonon coupling.

  17. High- Tc dc SQUID readout electronics with low noise and high bandwidth

    NASA Astrophysics Data System (ADS)

    He, D. F.; Itozaki, H.

    2006-10-01

    Using AD797 low noise op amps and 2SA1048 low noise transistors, we have developed a composite preamplifier for use in dc SQUID readout electronics. This preamplifier has a small dc drift and super low noise at high frequencies. The equivalent input voltage noise of the preamplifier is about 0.35 nV/√Hz from 100 kHz to 10 MHz. Using this preamplifier, we developed dc SQUID readout electronics having low noise and high bandwidth. Used with a 3 mm2 high-Tc dc SQUID, the white flux noise was about 18 μΦ0/√Hz above 100 kHz and the FLL bandwidth was about 2 MHz. This readout electronics can be used for the applications of SQUID-based NDE and SQUID-based NQR.

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

    SciTech Connect

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

    1989-09-01

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

  19. High-energy anomalies in covalent high-Tc cuprates with large Hubbard Ud on copper

    NASA Astrophysics Data System (ADS)

    Barišić, O. S.; Barišić, S.

    2015-03-01

    A large Ud theory is constructed for the metallic state of high-Tc cuprates. The Emery three-band model, extended with Ox-Oy hopping tpp, and with Ud → ∞, is mapped on slave fermions. The Dyson time-dependent diagrammatic theory in terms of the Cu-O hopping tpd, starting from the nondegenerate unperturbed ground state, is translationally and asymptotically locally gauge invariant. The small parameter of the theory is the average hole occupation of Cu sites nd. The lowest order of the theory generates the single particle propagators of the hybridized pdp- and dpd-fermions with the exact covalent three band structure. The leading many-body effect is band narrowing, accompanied by Landau-like damping of the single particle propagation, due to incoherent local charge Cu-O fluctuations. The corresponding continuum is found below and above the Fermi level.

  20. Interlayer tunneling mechanism of high- Tc superconductivity: Nonuniversal discontinuity in specific heat

    NASA Astrophysics Data System (ADS)

    Sudbø, A.

    1994-12-01

    Interlayer tunneling mechanism of high- Tc superconductivity is considered with emphasis on the thermodynamics close to T = Tc. For a k-independent interlayer Josephson coupling TJ, we find that, for | T - Tc|/ Tc ≪ 1, the gap on the Fermi surface is Δ( T) = Tcη( Tc; TJ)(1 - T/ Tc) α, with mean-field exponent α = {1}/{2}. The nonuniversal prefactor η( Tc; TJ) drops rapidly from the BCS-value π( {8}/{7}ς(3)) {1}/{2} ≈ 3.06 , as a function of TJ. The nor malized. specific heat discontinuity at T = Tc, ΔCv/ Nn(0) Tc = η2( Tc; TJ)/[1 - TJ/4 Tc] 2, increases initiall y rapidly as a function of TJ, while lim TJ → 0 ΔCv/ Nn(0) Tc = 8 π2/7 ς(3) ≈ 9.4.

  1. High {Tc} trilayer tunneling and Josephson junction structures made using atomic layer by layer growth

    SciTech Connect

    Eckstein, J.N.; Bozovic, I.; Virshup, G.F.

    1994-12-31

    Very precise artificial structuring of high {Tc} heterostructures is possible using atomic layer-by-layer molecular beam epitaxy (ALL-MBE). Cuprates are combined with other oxides, such as titanates, to make atomically precise heterostructures for studying transport and interfacial effects. Titanate slabs as thin as one unit cell thick can be grown without pinholes and provide tunneling barriers for c-axis transport. Single doped unit cells of BSCCO-2212 can also be used as barriers. These give SNS Josephson junctions at temperatures as high as 65 K. Since the crystallographic structure of the barrier is identical to the structure of the 2212 electrode material, it is easily possible to stack more than junction in close proximity. This results in phase-locked operation of two junctions together.

  2. A high- Tc SQUID-based sensor head cooled by a Joule-Thomson cryocooler

    NASA Astrophysics Data System (ADS)

    Rijpma, A. P.; ter Brake, H. J. M.; de Vries, E.; Nijhof, N.; Holland, H. J.; Rogalla, H.

    2002-08-01

    The goal of the so-called FHARMON project is to develop a high- Tc SQUID-based magnetometer system for the measurement of fetal heart activity in standard clinical environments. To lower the threshold for the application of this fetal heart monitor, it should be simple to operate. It is, therefore, advantageous to replace the liquid cryogen bath by a closed-cycle refrigerator. For this purpose, we selected a mixed-gas Joule-Thomson cooler; the APD Cryotiger ©. Because of its magnetic interference, the compressor of this closed-cycle cooler will be placed at a distance of ≈2 m from the actual sensor, which is an axial second order gradiometer. The gradiometer is formed by three magnetometers placed on an alumina cylinder, which is connected to the cold head of the cooler. This paper describes the sensor head in detail and reports on test experiments.

  3. Development of a rat biomagnetic measurement system using a high-TC SQUID magnetometer

    NASA Astrophysics Data System (ADS)

    Kim, In-Seon; Lee, Chul-Ho; Lee, Yong-Ho

    2010-08-01

    We have developed a rat magnetocardiograph (MCG) system employing a high-TC SQUID magnetometer and a tabletop magnetic shield. We obtained clear MCG signals from a healthy Wistar Kyoto rat with a relatively high peak amplitude of 50 pT by virtue of the small gap cryostat developed in this study. Well defined P-, QRS- and T-waves were observed on the MCG of the healthy rat. In the case of a spontaneously hypertensive rat measurement, the MCG showed quite a disturbed wave pattern thought to be caused by the hypertensive heart abnormality. The results suggest that the rat biomagnetic measurement system has a strong potential for monitoring the progress of the heart disease model.

  4. Fabrication of Monolithic Sapphire Membranes for High Tc Bolometer Array Development

    NASA Technical Reports Server (NTRS)

    Pugel, D. E.; Lakew, B.; Aslam, S.; Wang, L.

    2003-01-01

    This paper examines the effectiveness of Pt/Cr thin film masks for the architecture of monolithic membrane structures in r-plane sapphire. The development of a pinhole-free Pt/Cr composite mask that is resistant to hot H2SO4:H3PO4 etchant, will lead to the fabrication of smooth sapphire membranes whose surfaces are well-suited for the growth of low-noise high Tc films. In particular, the relationship of thermal annealing conditions on the Pt/Cr composite mask system to: (1) changes in the surface morphology and elemental concentration of the Pt/Cr thin film layers and (2) etch pit formation on the sapphire surface will be presented.

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

    PubMed Central

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

    2010-01-01

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

  6. Twenty years of talking past each other: The theory of high Tc

    NASA Astrophysics Data System (ADS)

    Anderson, Philip W.

    2007-09-01

    In 1988, the outline of an essentially correct theory of the high Tc cuprates was published by two groups, Zhang et al. in Zurich and Kotliar et al. in the US, based on earlier suggestions. The rather startling experimental predictions: that the gap would be real d-wave with nodes; that the gap would greatly increase with underdoping; that Tc would exhibit a dome terminating linearly around x = 30%; were so bizarre that these papers gathered little attention from others, including myself and at least 8 other Nobel prize-winners, and as they came to be substantiated one by one nobody much noticed that fact until the method was revived a dozen years later by Paramekanti et al. and Sorella et al. I will discuss some recent achievements and generalizations of these methods.

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

    SciTech Connect

    Nagaya, Kosuke

    1996-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Storey, James

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-10-01

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

  10. Magnetic frustration in the three-band Anderson lattice model for high-temperature superconductors

    SciTech Connect

    Ihle, D.; Kasner, M. )

    1990-09-01

    The three-band Anderson lattice model for the CuO{sub 2} planes in high-{Tc} superconductors is established. Treating this model by perturbation theory, the effective spin interactions are derived. The antiferromagnetic superexchange integrals are calculated as functions of the direct oxygen transfer and the hole concentration. It is found that frustration in the superexchange occurs, even in the undoped case, which increases with oxygen trnasfer and decreases with hole concentration.

  11. Current induced decomposition of Abrikosov vortices in p-n layered superconductors and heterostructures.

    PubMed

    Rakhmanov, A L; Savel'ev, Sergey; Kusmartsev, F V

    2008-11-01

    We describe the decomposition of Abrikosov vortices into decoupled pancake vortices in superconductors having both electron and hole charge carriers. We estimate the critical current of such a decomposition, at which a superconducting-normal state transition occurs, and find that it is very sensitive to the magnetic field and temperature. The effect can be observed in recently synthesized self-doped high-Tc layered superconductors with electrons and holes coexisting in different Cu-O planes and in artificial p-n superconductor heterostructures. The sensitivity of the critical current to a magnetic field may be used for sensors and detectors of a magnetic field, which can be built up from the superconductor heterostructures. PMID:19113298

  12. Superconductivity and ceramic superconductors II; Proceedings of the Symposium, Orlando, FL, Nov. 12-15, 1990

    NASA Astrophysics Data System (ADS)

    Nair, K. M.; Balachandran, U.; Chiang, Y.-M.; Bhalla, A. S.

    The present symposium on superconductivity and ceramic superconductors discusses fundamentals and general principles, powder processing and properties, fabrication and properties, and device reliability and applications. Attention is given to phase formation in the Tl-Ca-Ba-Cu-O system, comparative defect studies in La2CuO4 and La2NiO4, solid solution and defect behavior in high Tc oxides, oxygen ion transport and disorder in cuprates, and Sr-free Bi-Ln-Ca-Cu-O superconductors. Topics addressed include the preparation of superconductor Y-Ba-Cu-O powder by single-step calcining in air, low-temperature synthesis of YBa2Cu3O(7-x), synthesis of high-phase purity ceramic oxide superconductors by the xerogel method, and the preparation and characterization of the BYa2Cu4O8 superconductor. Also discussed are optical studies of humidity-based corrosion effects on thin film and bulk ceramic YBa2Cu3O(7-delta), thermomechanical processing of YBa2Cu3O(x)/Ag sheathed wires, and the expansion of high-Tc superconducting ceramics.

  13. Electronic structure, irreversibility line and magnetoresistance of Cu0.3Bi2Se3 superconductor

    DOE PAGESBeta

    Hemian, Yi; Gu, Genda; Chen, Chao -Yu; Sun, Xuan; Xie, Zhuo -Jin; Feng, Ya; Liang, Ai -Ji; Peng, Ying -Ying; He, Shao -Long; Zhao, Lin; et al

    2015-06-01

    CuxBi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ~4000 Oe formore » the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.9K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu0.3Bi2Se3 superconductors up to room temperature. As a result, these observations provide useful information for further study of this possible candidate for topological superconductors.« less

  14. Search for spontaneous magnetization in noncentrosymmetric superconductors

    NASA Astrophysics Data System (ADS)

    Sumiyama, A.; Kawakatsu, D.; Gouchi, J.; Kawasaki, I.; Yamaguchi, A.; Motoyama, G.; Hirose, Y.; Settai, R.; Ōnuki, Y.

    2016-02-01

    We have measured the magnetization of two noncentrosymmetric superconductors: Ir2Ga9 and CePt3Si using a SQUID magnetometer, neither of which has been tested for the time-reversal symmetry in the superconducting state. For Ir2Ga9, the magnetization change ΔM below the superconducting transition temperature Tc ˜ 2.2 K was smaller than 10-5 G in zero magnetic field, suggesting that ΔM originates in the Meissner effect induced by the possible residual field. When CePt3Si was cooled in zero magnetic field, ΔM along the c axis first decreased below Tc+ ˜ 0.75 K (high-Tc phase) and then increased below Tc- ˜ 0.45 K (bulk superconducting phase). Since this behavior cannot be explained by the Meissner effect, it may be a sign of a spontaneous magnetization.

  15. Nematic Resonance in the Raman Response of Iron-Based Superconductors.

    PubMed

    Gallais, Yann; Paul, Indranil; Chauvière, Ludivine; Schmalian, Jörg

    2016-01-01

    In a fully gapped superconductor the electronic Raman response has a pair-breaking peak at twice the superconducting gap Δ, if the Bogoliubov excitations are uncorrelated. Motivated by the iron based superconductors, we study how this peak is modified if the superconducting phase hosts a nematic-structural quantum critical point. We show that, upon approaching this point by tuning, e.g., doping, the growth of nematic correlations between the quasiparticles transforms the pair-breaking peak into a nematic resonance. The mode energy is below 2Δ, and stays finite at the quantum critical point, where its spectral weight is sharply enhanced. The latter is consistent with recent experiments on electron-doped iron based superconductors and provides direct evidence of nematic correlations in their superconducting phases. PMID:26799039

  16. Present status of the theory of the high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Anderson, P. W.

    2006-04-01

    The Gutzwiller-projected mean-field theory, also called plain vanilla or renormalized mean-field theory, is explained, and its successes and possible extensions in describing the phenomenology of the cuprate superconductors are discussed. Throughout, we emphasize that while this is a Hartree-Fock-based BCS theory, it embodies fundamental differences from conventional perturbative many-body theory which may be characterized by calling it a theory of the doped Mott insulator.

  17. Spin-state blockade in Te6+-substituted electron-doped LaCoO3

    NASA Astrophysics Data System (ADS)

    Tomiyasu, Keisuke; Koyama, Shun-Ichi; Watahiki, Masanori; Sato, Mika; Nishihara, Kazuki; Onodera, Mitsugi; Iwasa, Kazuaki; Nojima, Tsutomu; Yamasaki, Yuuichi; Nakao, Hironori; Murakami, Youichi

    2015-03-01

    Perovskite-type LaCoO3 (Co3+: d6) is a rare inorganic material with sensitive and characteristic responses among low, intermediate, and high spin states. For example, in insulating nonmagnetic low-spin states below about 20 K, light hole doping (Ni substitution) induces much larger magnetization than expected; over net 10μB/hole (5μB/Ni) for 1μB/hole (1μB/Ni), in which the nearly isolated dopants locally change the surrounding Co low-spin states to magnetic ones and form spin molecules with larger total spin. Further, the former is isotropic, whereas the latter exhibits characteristic anisotropy probably because of Jahn-Teller distortion. In contrast, for electron doping, relatively insensitive spin-state responses were reported, as in LaCo(Ti4+) O3, but are not clarified, and are somewhat controversial. Here, we present macroscopic measurement data of another electron-doped system LaCo(Te6+) O3 and discuss the spin-state responses. This study was financially supported by Grants-in-Aid for Young Scientists (B) (No. 22740209 and 26800174) from the MEXT of Japan.

  18. Electron-doped organics: Charge-disproportionate insulators and Hubbard-Fröhlich metals

    NASA Astrophysics Data System (ADS)

    Naghavi, S. Shahab; Fabrizio, Michele; Qin, Tao; Tosatti, Erio

    2013-09-01

    Several examples of metallic electron-doped polycyclic aromatic hydrocarbons (PAHs) molecular crystals have recently been experimentally proposed. Some of them have superconducting components, but most other details are still unknown beginning with structure and the nature of metallicity. We carried out ab initio density functional calculations for La-Phenanthrene (La-PA), here meant to represent a generic case of three-electron doping, to investigate structure and properties of a conceptually simple case. To our surprise we found first of all that the lowest energy state is not metallic but band insulating, with a disproportionation of two inequivalent PA molecular ions and a low P1 symmetry, questioning the common assumption that three electrons will automatically metallize a PAH crystal. Our best metallic structure is metastable and slightly higher in energy, and retains equivalent PA ions and a higher P21 symmetry—the same generally claimed for metallic PAHs. We show that a “dimerizing” periodic distortion opens very effectively a gap in place of a symmetry related degeneracy of all P21 structures near the Fermi level, foreshadowing a possible role of that special intermolecular phonon in superconductivity of metallic PAHs. A Hubbard-Fröhlich model describing that situation is formulated for future studies.

  19. Electron doping evolution of the magnetic excitations in NaFe1 xCoxAs

    DOE PAGESBeta

    Carr, Scott V.; Zhang, Chenglin; Song, Yu; Tan, Guotai; Li, Yu; Abernathy, Douglas L.; Stone, Matthew B.; Granroth, Garrett E.; Perring, T. G.; Dai, Pengcheng

    2016-06-13

    We use time-of-flight (TOF) inelastic neutron scattering (INS) spectroscopy to investigate the doping dependence of magnetic excitations across the phase diagram of NaFe1-xCoxAs with x = 0, 0.0175, 0.0215, 0.05, and 0.11. The effect of electron-doping by partially substituting Fe by Co is to form resonances that couple with superconductivity, broaden and suppress low energy (E 80 meV) spin excitations compared with spin waves in undoped NaFeAs. However, high energy (E > 80 meV) spin excitations are weakly Co-doping dependent. Integration of the local spin dynamic susceptibility "(!) of NaFe1-xCoxAs reveals a total fluctuating moment of 3.6 μ2 B/Fe andmore » a small but systematic reduction with electron doping. The presence of a large spin gap in the Cooverdoped nonsuperconducting NaFe0.89Co0.11As suggests that Fermi surface nesting is responsible for low-energy spin excitations. These results parallel Ni-doping evolution of spin excitations in BaFe2-xNixAs2, confirming the notion that low-energy spin excitations coupling with itinerant electrons are important for superconductivity, while weakly doping dependent high-energy spin excitations result from localized moments.« less

  20. Influence of Electron Doping on Magnetic Order in CeRu2Al10

    DOE PAGESBeta

    Kobayashi, Riki; Kaneko, Koji; Saito, Kotaro; Mignot, Jean-Michel; André, Gilles; Robert, Julien; Wakimoto, Shuichi; Matsuda, Masaaki; Chi, Songxue; Haga, Yoshinori; et al

    2014-09-17

    The effect of electron doping by the substitution of Rh for Ru on unconventional magnetic order in CeRu2Al10 was investigated via neutron powder diffraction. In Ce(Ru1-xRhx)2Al10 with x = 0.05, 0.12, and 0.2, reorientation of the ordered moment from the c- to the a-axis takes place in all samples, while the ordering vector q=(0 1 0) remains unchanged within this concentration range. The moment reorientation is accompanied by an enhancement in its size by a factor of ~2.4, from μ=0.43 μB at x=0 to μ =1.06, 1.04, and 1.02 μB for x=0.05, 0.12 and 0.2, respectively. The continuous decrease inmore » N´eel temperature T0(TN), despite an abrupt increase in μ , underlines the strong anisotropy in the exchange interaction in CeRu2Al10, and the fact that this anisotropy is easily suppressed by electron doping.« less

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

    PubMed Central

    Szczęśniak, Radosław

    2012-01-01

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

  2. Verification of electron doping in single-layer graphene due to H{sub 2} exposure with thermoelectric power

    SciTech Connect

    Hong, Sung Ju; Kang, Hojin; Soler-Delgado, David; Kim, Kyung Ho; Park, Yung Woo E-mail: kbh37@incheon.ac.kr; Park, Min; Lee, Minwoo; Jeong, Dae Hong; Shin, Dong Seok; Kim, Byung Hoon E-mail: kbh37@incheon.ac.kr; Kubatkin, Sergey

    2015-04-06

    We report the electron doping of single-layer graphene (SLG) grown by chemical vapor deposition (CVD) by means of dissociative hydrogen adsorption. The transfer characteristic showed n-type doping behavior similar to that of mechanically exfoliated graphene. Furthermore, we studied the thermoelectric power (TEP) of CVD-grown SLG before and after exposure to high-pressure H{sub 2} molecules. From the TEP results, which indicate the intrinsic electrical properties, we observed that the CVD-grown SLG is n-type doped without degradation of the quality after hydrogen adsorption. Finally, the electron doping was also verified by Raman spectroscopy.

  3. Verification of electron doping in single-layer graphene due to H2 exposure with thermoelectric power

    NASA Astrophysics Data System (ADS)

    Hong, Sung Ju; Park, Min; Kang, Hojin; Lee, Minwoo; Soler-Delgado, David; Shin, Dong Seok; Kim, Kyung Ho; Kubatkin, Sergey; Jeong, Dae Hong; Park, Yung Woo; Kim, Byung Hoon

    2015-04-01

    We report the electron doping of single-layer graphene (SLG) grown by chemical vapor deposition (CVD) by means of dissociative hydrogen adsorption. The transfer characteristic showed n-type doping behavior similar to that of mechanically exfoliated graphene. Furthermore, we studied the thermoelectric power (TEP) of CVD-grown SLG before and after exposure to high-pressure H2 molecules. From the TEP results, which indicate the intrinsic electrical properties, we observed that the CVD-grown SLG is n-type doped without degradation of the quality after hydrogen adsorption. Finally, the electron doping was also verified by Raman spectroscopy.

  4. Beyond the simple hexagonal Abrikosov vortex lattice in layered superconductors

    NASA Astrophysics Data System (ADS)

    Feinberg, D.; Ettouhami, A. M.

    1993-01-01

    In layered superconductors as high-Tc materials but also organic superconductors, chalcogenides and superlattices, the simple concept of an distorted hexagonal lattice of straight vortices becomes unsufficient. Due to anisotropy and short coherence lengths, quite new vortex structures may arise. Some of them, as staircase vortices, simply add a modulation in the direction of vortex lines. This phenomenon is reviewed, together with the resulting lock-in transition, especially when the effects of the layered structure are weak. More exotic structures like a decomposed vortex lattice can also occur in specific situations: they involve two perpendicular sublattices, one parallel and one normal to the layers. We propose that extended defects as twin boundaries or irradiation tracks can trigger such a structure even in moderately anisotropic compounds as Y:123.

  5. Spectroscopic studies of superconductors. Part A: Infrared and Raman spectra

    SciTech Connect

    Bozovic, I.; Marel, D. van der

    1996-12-31

    During the ten years that followed the discovery of superconductivity above 30 K in lanthanum barium cuprate by Bednorz and Mueller, the condensed matter physics community has been engaged in an unprecedented worldwide effort in materials processing, characterization of physical properties, and theoretical modeling of superconductors. The present conference has brought together a group of researchers who are actively involved in the experimental determination of the physical properties of high-{Tc} superconductors, the quest for the microscopic mechanism (or mechanisms) of superconductivity, the search for new physical phenomena in these materials, or the search for new classes of superconducting materials. The distinguishing feature and the unifying theme of this conference was the use of spectroscopic techniques as the primary tools in pursuing these goals. Separate abstracts were prepared for 32 papers in this conference.

  6. Andreev-Bragg reflection from an Amperian superconductor

    NASA Astrophysics Data System (ADS)

    Baireuther, Paul; Hyart, Timo; Tarasinski, Brian; Beenakker, Carlo

    2015-03-01

    We show how an electrical measurement can detect the pairing of electrons on the same side of the Fermi surface (Amperian pairing), recently proposed by Patrick Lee for the pseudogap phase of high-Tc cuprate superconductors. Bragg scattering from the pair-density wave introduces odd multiples of 2kF momentum shifts when an electron incident from a normal metal is Andreev-reflected as a hole. These Andreev-Bragg reflections can be detected in a three-terminal device, containing a ballistic Y-junction between normal leads (1 , 2) and the superconductor. The cross-conductance dI1 / dV2 has the opposite sign for Amperian pairing than it has either in the normal state or for the usual BCS pairing.

  7. Andreev-Bragg Reflection from an Amperian Superconductor

    NASA Astrophysics Data System (ADS)

    Baireuther, P.; Hyart, T.; Tarasinski, B.; Beenakker, C. W. J.

    2015-08-01

    We show how an electrical measurement can detect the pairing of electrons on the same side of the Fermi surface (Amperian pairing), recently proposed by Patrick Lee for the pseudogap phase of high-Tc cuprate superconductors. Bragg scattering from the pair-density wave introduces odd multiples of 2 kF momentum shifts when an electron incident from a normal metal is Andreev reflected as a hole. These Andreev-Bragg reflections can be detected in a three-terminal device, containing a ballistic Y junction between normal leads (1, 2) and the superconductor. The cross-conductance d I1/d V2 has the opposite sign for Amperian pairing than it has either in the normal state or for the usual BCS pairing.

  8. Andreev-Bragg Reflection from an Amperian Superconductor.

    PubMed

    Baireuther, P; Hyart, T; Tarasinski, B; Beenakker, C W J

    2015-08-28

    We show how an electrical measurement can detect the pairing of electrons on the same side of the Fermi surface (Amperian pairing), recently proposed by Patrick Lee for the pseudogap phase of high-Tc cuprate superconductors. Bragg scattering from the pair-density wave introduces odd multiples of 2k(F) momentum shifts when an electron incident from a normal metal is Andreev reflected as a hole. These Andreev-Bragg reflections can be detected in a three-terminal device, containing a ballistic Y junction between normal leads (1, 2) and the superconductor. The cross-conductance dI1/dV2 has the opposite sign for Amperian pairing than it has either in the normal state or for the usual BCS pairing. PMID:26371674

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

    PubMed Central

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

    2015-01-01

    The highest superconducting transition temperatures in the cuprates are achieved in bilayer and trilayer systems, highlighting the importance of interlayer interactions for high Tc. It has been argued that interlayer hybridization vanishes along the nodal directions by way of a specific pattern of orbital overlap. Recent quantum oscillation measurements in bilayer cuprates have provided evidence for a residual bilayer-splitting at the nodes that is sufficiently small to enable magnetic breakdown tunneling at the nodes. Here we show that several key features of the experimental data can be understood in terms of weak spin-orbit interactions naturally present in bilayer systems, whose primary effect is to cause the magnetic breakdown to be accompanied by a spin flip. These features can now be understood to include the equidistant set of three quantum oscillation frequencies, the asymmetry of the quantum oscillation amplitudes in c-axis transport compared to ab-plane transport, and the anomalous magnetic field angle dependence of the amplitude of the side frequencies suggestive of small effective g-factors. We suggest that spin-orbit interactions in bilayer systems can further affect the structure of the nodal quasiparticle spectrum in the superconducting phase. PACS numbers: 71.45.Lr, 71.20.Ps, 71.18.+y PMID:26039222

  10. High-Tc superconductivity in nanostructured NaxWO3-y: Sol-gel route

    NASA Astrophysics Data System (ADS)

    Aliev, Ali

    2009-03-01

    Tungsten trioxide, WO3-y infiltrated into various nanoporous matrix structures such as carbon inverse opal, carbon nanotubes paper, or platinum sponge and then intercalated with alkaline ions (Li^+, Na^+) exhibits a pronounced diamagnetic onset in ZFC magnetization in a wide range of temperatures, 125-132 K. Resistivity measurements show non zero jump and intensive fluctuations of electrical resistance below observed transition points. The observed magnetic and electrical anomalies in nanostructured tungsten bronzes (LixWO3-y, NaxWO3-y) suggest the possibility of localized non-percolated superconductivity. The direct evidence of polaron formation from temperature dependence of EPR and photoemission spectra and formation of bipolarons in weakly reduced to WO3-y, with 3-y typically in the order of 2.95 suggest bipolarons mechanism of a Bose-Einstein condensation of trapped electron pairs in doped WO3-y. On the other hand the strong lattice instabilities in 2D systems like layered cuprates and tungsten bronzes place the upper limit on Tc. Than, the percolative self-organized mechanism on the metal/insulator interface like Na/WO3 and NaWO3/nanostructured matrix can facilitate the high Tc obtained in sodium bronzes infiltrated into inverted carbon opal or carbon nanotube matricies.

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

    NASA Astrophysics Data System (ADS)

    Dagotto, Elbio

    2005-03-01

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

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

    PubMed

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

    2014-07-01

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

  13. Effect of van Hove singularities on high-Tc superconductivity in H3 S

    NASA Astrophysics Data System (ADS)

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

    One of interesting open questions for the high-Tc superconductivity in sulfur hydrides is why some of the H3S phases under high pressures are so special. Recently, it has been pointed out that the presence of the van Hove singularities (vHs) around the Fermi level is crucial. Interestingly, such vHs are always absent in H2S, for which Tc is estimated to be much lower. Although there have been quantitative calculations of Tc based on the Migdal-Eliashberg theory, the effect of the vHs on the superconductivity is yet to be fully understood. This is because the energy dependence of the density of states (DOS) has been neglected to simplify the Eliashberg equation. In this study, we perform a calculation beyond the constant DOS approximation. In contrast with the conventional calculations, this approach with a sufficiently large number of Matsubara frequencies enables us to calculate Tc self-consistently without introducing the empirical pseudo Coulomb potential. We show that the constant DOS approximation seriously overestimates (underestimates) Tc by ~60 K (~10 K) for H3S (H2S). We then consider the effect of the anharmonicity of the phonon and the energy shift due to the zero-point motion. Eventually, Tc is estimated to be 180 K for H3S and 35 K for H2S, which successfully explains the pressure dependence of Tc observed in the experiment.

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

    NASA Astrophysics Data System (ADS)

    Jarlborg, Thomas

    2009-03-01

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

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

    DOE PAGESBeta

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

    2015-06-03

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

  16. Interplay of 3 d-5 d interactions in high-TC osmium-based double perovskites

    NASA Astrophysics Data System (ADS)

    Taylor, A. E.; Calder, S.; Morrow, R.; Woodward, P. M.; Yan, J. Q.; Winn, B.; Lumsden, M. D.; Christianson, A. D.

    2015-03-01

    In 3d-5d systems the strongly magnetic 3d orbitals and extended 5d orbitals with enhanced spin-orbit coupling lead to a range of high TC magnetic states and novel behavior not present in systems consisting solely of 3d or 5d ions. The two distinct octahedral sites in double perovskites A2 BB 'O6 allow an ordered 3d-5d structure to form, providing a variety of systems to be investigated. Unravelling the interactions controlling these systems, however, is an open challenge. The highest known TC in such a system, 725K, is found in insulator Sr2CrOsO6. This questions the theory for high-TCs in systems such as TC=400K Sr2FeReO6 which relies on half-metallic behavior. To unravel the nature of the interactions in 3d-5d systems, we have studied the series of compounds Sr2 X OsO6. We have utilized elastic and inelastic neutron scattering to probe the spin states in the systems, and therefore test predictions that the magnetic interactions are controlled by a frustrated AFM Heisenberg model. By studying the series, we are able to relate changes in the spin wave spectrum to dramatic changes in the magnetic order from TN = 95 K antiferromagnetism to TC = 725 K ferrimagnetism.

  17. A novel buffered high-Tc superconducting step-edge Josephson junction

    NASA Astrophysics Data System (ADS)

    van Staden, W. F.; Büttner, U.; Srinivasu, V. V.; Perold, W. J.

    2007-11-01

    A novel high-Tc superconducting (HTS) buffered step-edge Josephson junction is fabricated. A 250 nm PrBa2Cu3O7 (PBCO) layer was epitaxially grown on a (001) MgO substrate by PLD, which acts as a buffered template for a step-edge. Argon-ion milling was used to obtain a step-edge with a step angle of 25°. The step-edge is analysed in terms of an extended Wu and Chen model (Wu and Chen 2006 Rev. Sci. Instrum. 77 1). The model validity is confirmed by the correspondence between the theoretically proposed and experimentally observed step angles. A 150 nm YBa2Cu3O7-δ (YBCO) thin film was accordingly grown over the PBCO step-edge and patterned by standard photolithography. I-V characteristics were obtained by DC and AC excitation of the patterned junctions. The IcRn product values are of the order of 1.6 mV and 0.36 mV at 53 K and 77 K, respectively. These values are higher than typical values found in the literature. The observation of Shapiro steps confirms the presence of the Josephson effect in this novel junction topology.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  19. Orbital order and spin nematicity in the tetragonal phase of the electron-doped iron pnictides NaFe1 -xCoxAs

    NASA Astrophysics Data System (ADS)

    Zhou, R.; Xing, L. Y.; Wang, X. C.; Jin, C. Q.; Zheng, Guo-qing

    2016-02-01

    In copper-oxide and iron-based high-temperature (high-Tc) superconductors, many physical properties exhibit in-plane anisotropy, which is believed to be caused by a rotational symmetry-breaking nematic order, whose origin and its relationship to superconductivity remain elusive. In many iron pnictides, a tetragonal-to-orthorhombic structural transition temperature Ts coincides with the magnetic transition temperature TN, making the orbital and spin degrees of freedom highly entangled. NaFeAs is a system where Ts=54 K is well separated from TN=42 K, which helps simplify the experimental situation. Here we report nuclear magnetic resonance (NMR) measurements on NaFe1 -xCoxAs (0 ≤x ≤0.042 ) that revealed orbital and spin nematicity occurring at a temperature T* far above Ts in the tetragonal phase. We show that the NMR spectra splitting and its evolution can be explained by an incommensurate orbital order that sets in below T* and becomes commensurate below Ts, which brings about the observed spin nematicity.

  20. Superconductor cable

    DOEpatents

    Allais, Arnaud; Schmidt, Frank (Langenhagen, DE

    2009-12-15

    A superconductor cable includes a superconductive cable core (1) and a cryostat (2) enclosing the same. The cable core (1) has a superconductive conductor (3), an insulation (4) surrounding the same and a shielding (5) surrounding the insulation (4). A layer (3b) of a dielectric or semiconducting material is applied to a central element (3a) formed from a normally conducting material as a strand or tube and a layer (3c) of at least one wire or strip of superconductive material is placed helically on top. The central element (3a) and the layer (3c) are connected to each other in an electrically conducting manner at the ends of the cable core (1).

  1. Impact of lattice distortion and electron doping on α-MoO3 electronic structure

    PubMed Central

    Huang, Peng-Ru; He, Yao; Cao, Chao; Lu, Zheng-Hong

    2014-01-01

    Band structure of transition metal oxides plays a critical role in many applications such as photo-catalysis, photovoltaics, and electroluminescent devices. In this work we report findings that the band structure of MoO3 can be significantly altered by a distortion in the octahedral coordination structure. We discovered that, in addition to epitaxial type of structural strain, chemical force such as hydrogen inclusion can also cause extended lattice distortion. The lattice distortion in hydrogenated MoO3 led to a significant reduction of the energy gap, overshadowing the Moss-Burstein effect of band filling. Charge doping simulations revealed that filling of conduction band drives the lattice distortion. This suggests that any charge transfer or n-type electron doping could lead to lattice distortion and consequentially a reduction in energy gap. PMID:25410814

  2. Tunability of Band Gap in Multilayer Phosphorene by External Electric Fields and Electron Dopings

    NASA Astrophysics Data System (ADS)

    Baik, Seung Su; Choi, Hyoung Joon

    2015-03-01

    Black phosphorus (BP) and its two-dimensional derivative phosphorene are rapidly emerging nanoelectronic materials with potential applicability to field effect transistors and optoelectronic devices. Unlike the gapless semiconductor graphene, multilayer BP has a substantial band gap of ~ 0.2 eV and the band-gap size is reportedly varied by external electric fields. To explore the extensibility of such band-gap modulation, we have investigated electronic band structures of multilayer BP by using the first-principles density-functional method as implemented in the SIESTA code. By controlling the electron doping concentrations and the resultant electric fields therefrom, we examine the manageability of the band-gap size and the anisotropic carrier mobility. This work was supported by NRF of Korea (Grant No. 2011-0018306) and KISTI supercomputing center (Project No. KSC-2013-C3-062).

  3. Electron doping evolution of the magnetic excitations in NaFe1 -xCoxAs

    NASA Astrophysics Data System (ADS)

    Carr, Scott V.; Zhang, Chenglin; Song, Yu; Tan, Guotai; Li, Yu; Abernathy, D. L.; Stone, M. B.; Granroth, G. E.; Perring, T. G.; Dai, Pengcheng

    2016-06-01

    We use time-of-flight (TOF) inelastic-neutron-scattering (INS) spectroscopy to investigate the doping dependence of magnetic excitations across the phase diagram of NaFe1 -xCoxAs with x =0 , 0.0175, 0.0215, 0.05, and 0.11 . The effect of electron doping by partially substituting Fe by Co is to form resonances that couple with superconductivity, broaden, and suppress low-energy (E ≤80 meV) spin excitations compared with spin waves in undoped NaFeAs. However, high-energy (E >80 meV) spin excitations are weakly Co-doping-dependent. Integration of the local spin dynamic susceptibility χ''(ω ) of NaFe1 -xCoxAs reveals a total fluctuating moment of 3.6 μB2/Fe and a small but systematic reduction with electron doping. The presence of a large spin gap in Co-overdoped nonsuperconducting NaFe0.89Co0.11As suggests that Fermi surface nesting is responsible for low-energy spin excitations. These results parallel the Ni-doping evolution of spin excitations in BaFe2 -xNixAs2 in spite of the differences in crystal structures and Fermi surface evolution in these two families of iron pnictides, thus confirming the notion that low-energy spin excitations coupling with itinerant electrons are important for superconductivity, while weakly doping-dependent high-energy spin excitations result from localized moments.

  4. Effective single-band models for the high-Tc cuprates. I. Coulomb interactions

    NASA Astrophysics Data System (ADS)

    Feiner, L. F.; Jefferson, J. H.; Raimondi, R.

    1996-04-01

    Starting with the three-band extended Hubbard model (or d-p model) widely used to represent the CuO2 planes in the high-Tc cuprates, we make a systematic reduction to an effective single-band model using a previously developed cell-perturbation method. The range of parameters for which this mapping is a good approximation is explored in the full Zaanen-Sawatzky-Allen diagram (copper Coulomb repulsion Ud versus charge-transfer energy ɛ), together with an investigation of the validity of a further mapping to an effective charge-spin (t-J-V) model. The variation of the effective single-band parameters with the parameters of the underlying multi-band model is investigated in detail, and the parameter regime where the model represents the high-Tc cuprates is examined for specific features that might distinguish it from the general case. In particular, we consider the effect of Coulomb repulsions on oxygen (Up) and between copper and oxygen (Vpd). We find that the reduction to an effective single-band model is generally valid for describing the low-energy physics, and that Vpd and Up (unless unrealistically large) actually slightly improve the convergence of the cell-perturbation method. Unlike in the usual single-band Hubbard model, the effective intercell hopping and Coulomb interactions are different for electrons and holes. We find that this asymmetry, which vanishes in the extreme Mott-Hubbard regime (Ud<<ɛ), is quite appreciable in the charge-transfer regime (Ud>~ɛ), particularly for the effective Coulomb interactions. We show that for doped holes (forming Zhang-Rice singlets) on neighboring cells the interaction induced by Vpd can even be attractive due to locally enhanced pd hybridization, while this cannot occur for electrons. The Coulomb interaction induced by Up is always repulsive; in addition Up gives rise to a ferromagnetic spin-spin interaction which opposes antiferromagnetic superexchange. We show that for hole-doped systems this leads to a subtle

  5. Phase Separation in Cuprate Superconductors - Proceedings of the Workshop

    NASA Astrophysics Data System (ADS)

    Müller, K. A.; Benedek, G.

    1993-01-01

    The Table of Contents for the full book PDF is as follows: * Preface and Scope * Frustrated Phase Separation and High Temperature Superconductivity * Phase Separation and Photo-Induced High Tc Superconductivity in the Cuprates * Neutron Scattering Studies of the Spin Dynamics in La2-xSrxCuO4 * Percolative Phase Separation and High Tc Superconductivity * Phase Separation in Cuprate Superconductors from NMR and Microwave Absorption Measurements * Electronic Structure and Phase Separation in Superconducting Cuprates * The Virtual Exciton Mechanism of Superconductivity * Linear Arrays of Non Homogeneous Cu Sites in the CuO2 Plane: A New Scenario for Pairing Mechanisms in a Corrugated-Iron-Like Plane * Phase Separation, Structure and Superconductivity in Oxygen-Annealed La2CuO4+δ * Phase Separation in La2-xSrxCuO4 and YBa2Cu3Ox Studied by Mössbauer Spectroscopy * Phase Diagram and Transport Studies on La2-xSrxCuO4 * Static and Dynamic Transport Aspects of Phase Separation * Phase Separation in the Superconducting La2Cu4+δ Phases (0 < δ < 0.09) Prepared by Electrochemical Oxidation * Neutron Scattering Study of the YBa2Cu3O6+x System * NMR Investigation of Low Energy Excitations in YBa2Cu3O6+x Single Crystals * Aspects of the Spin Dynamics in the Cuprate Superconductors * Oxygen Order and Spin Structure in YBa2Cu3Ox Deduced from Copper NMR and NQR * Static and Dynamic Magnetic Properties of Ba, Cu and O in YBa2Cu4O8 and Y2Ba4Cu7O15.1 * Positional Splitting of Apex Oxygen and Nonlinear Excitations in Cuprates * Cooper Pair Formation by Distortive Electron-Lattice Coupling * Bipolaronic Charge Density Waves, Polaronic Spin Density Waves, and High Tc Superconductivity * Phase Separation as Result of a Thermodynamical Variational Method for the Emery Model * General Discussion led by G. Benedek and K. A. Müller

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  7. Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

    DOE PAGESBeta

    Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

    2015-09-21

    The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (xz,yz,xy) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. Moreover, in this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly,more » our Monte Carlo simulations reveal that the fast reduction with doping of the N eel TN and the structural TS transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Finally, our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. Our study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped

  8. Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

    SciTech Connect

    Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

    2015-09-21

    The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (xz,yz,xy) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. Moreover, in this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly, our Monte Carlo simulations reveal that the fast reduction with doping of the N eel TN and the structural TS transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Finally, our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. Our study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found

  9. Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

    SciTech Connect

    Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio R

    2015-01-01

    The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (xz,yz,xy) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. In this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly, our Monte Carlo simulations reveal that the fast reduction with doping of the N eel TN and the structural TS transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. This study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped 122 compounds.

  10. Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

    NASA Astrophysics Data System (ADS)

    Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

    2015-09-01

    The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (x z ,y z ,x y ) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. In this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly, our Monte Carlo simulations reveal that the fast reduction with doping of the Néel TN and the structural TS transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. This study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped 122 compounds.

  11. Pristine and intercalated transition metal dichalcogenide superconductors

    NASA Astrophysics Data System (ADS)

    Klemm, Richard A.

    2015-07-01

    Transition metal dichalcogenides (TMDs) are quasi-two-dimensional layered compounds that exhibit strongly competing effects of charge-density wave (CDW) formation and superconductivity (SC). The weak van der Waals interlayer bonding between hexagonal layers of octahedral or trigonal prismatic TMD building blocks allows many polytypes to form. In the single layer 1 T polytype materials, one or more CDW states can form, but the pristine TMDs are not superconducting. The 2 H polytypes have two or more Fermi surfaces and saddle bands, allowing for dual orderings, which can be coexisting CDW and SC orderings, two SC gaps as in MgB2, two CDW gaps, and possibly even pseudogaps above the onset TCDW s of CDW orderings. Higher order polytypes allow for multiple CDW gaps and at least one superconducting gap. The CDW transitions TCDW s usually greatly exceed the superconducting transitions at their low Tc values, their orbital order parameters (OPs) are generally highly anisotropic and can even contain nodes, and the SC OPs can be greatly affected by their simultaneous presence. The properties of the CDWs ubiquitously seen in TMDs are remarkably similar to those of the pseudogaps seen in the high-Tc cuprates. In 2H-NbSe2, for example, the CDW renders its general s-wave SC OP orbital symmetry to be highly anisotropic and strongly reduces its Josephson coupling strength (IcRn) with the conventional SC, Pb. Hence, the pristine TMDs are highly "unconventional" in comparison with Pb, but are much more "conventional" than are the ferromagnetic superconductors such as URhGe. Applied pressure and intercalation generally suppress the TMD CDWs, allowing for enhanced SC formation, even in the 1 T polytype materials. The misfit intercalation compound (LaSe)1.14(NbSe2) and many 2 H -TMDs intercalated with organic Lewis base molecules, such as TaS2(pyridine)1/2, have completely incoherent c-axis transport, dimensional-crossover effects, and behave as stacks of intrinsic Josephson junctions

  12. Superconductor/Semiconductor Hybrid Analog-to-Digital Converter

    NASA Astrophysics Data System (ADS)

    Furuta, Futoshi; Saitoh, Kazuo; Yoshida, Akira; Suzuki, Hideo

    We have designed a superconductor-semiconductor hybrid analog-to-digital (A/D) converter and experimentally evaluated its performance at sampling frequencies up to 18.6GHz. The A/D converter consists of a superconductor front-end circuit and a semiconductor back-end circuit. The front-end circuit includes a sigma-delta modulator and an interface circuit, which is for transmitting data signal to the semiconductor back-end circuit. The semiconductor back-end circuit performs decimation filtering. The design of the modulator was modified to reduce effects of integrator leak and thermal noise on signal-to-noise ratio (SNR). Using the improved modulator design, we achieved a bit-accuracy close to the ideal value. The hybrid architecture enabled us to reduce the integration scale of the front-end circuit to fewer than 500 junctions. This simplicity makes feasible a circuit based on a high TC superconductor as well as on a low TC superconductor. The experimental results show that the hybrid A/D converter operated perfectly and that SNR was 84.8dB (bit accuracy-13.8bit) at a band width of 9.1MHz. This converter has the highest pertormance of all sigma-delta A/D converters.

  13. Fabrication and testing of long length high-{Tc} composite conductors. Final report

    SciTech Connect

    Fisher, L.M.

    1997-12-31

    Presently some methods of HTS-conductors processing are under study in the authors laboratory. ``Powder-in-tube`` (PIT), ``Jelly-roll``, electrophorethis are among them. PIT process has developed predominantly both in a view of the achieved J{sub c} values Bi-2223 phase was used as a core material for these tapes. Since the main purpose of the task order was to enhance the development of long length high temperature superconductor tapes, the authors have considered reasonable to lay the perfection idea of the PIT process step by step or tape by tape. To realize it they have assumed, keeping stable the basic scheme of PIT process, to vary some technological parameters which are as follows: (1) type of initial powder; (2) sheath material; (3) tape construction (filaments number, cross section e.a.); and (4) processing regimes. This report covers the fabrication process and characteristics of the produced conductors.

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

    NASA Astrophysics Data System (ADS)

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

    2008-09-01

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

  15. Fragile surface zero-energy flat bands in three-dimensional chiral superconductors

    NASA Astrophysics Data System (ADS)

    Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

    2015-12-01

    We study surface zero-energy flat bands in three-dimensional chiral superconductors with pz(px+i py) ν -wave pairing symmetry (ν is a nonzero integer), based on topological arguments and tunneling conductance. It is shown that the surface flat bands are fragile against (i) the surface misorientation and (ii) the surface Rashba spin-orbit interaction. The fragility of (i) is specific to chiral SCs, whereas that of (ii) happens for general odd-parity SCs. We demonstrate that these flat-band instabilities vanish or suppress a zero-bias conductance peak in a normal/insulator/superconductor junction, which behavior is clearly different from high-Tc cuprates and noncentrosymmetric superconductors. By calculating the angle-resolved conductance, we also discuss a topological surface state associated with the coexistence of line and point nodes.

  16. Magnetic x-ray microscopy at low temperatures - Visualization of flux distributions in superconductors

    NASA Astrophysics Data System (ADS)

    Stahl, Claudia; Ruoß, Stephen; Weigand, Markus; Bechtel, Michael; Schütz, Gisela; Albrecht, Joachim

    2016-01-01

    X-ray Magnetic Circular Dichroism (XMCD) microscopy at liquid nitrogen temperature has been performed on bilayers of high-Tc superconducting YBCO (YBa2Cu3O7-δ) and soft-magnetic Co40Fe40B20. This should allow us to map the magnetic flux density distribution in the current-carrying state of the superconductor with high spatial resolution. For that purpose the UHV scanning X-ray microscope MAXYMUS has been upgraded by a MMR Micro Miniature Joule-Thompson cryostat capable of temperatures between 75 K and 580 K. Resulting XMCD images of the magnetic flux density in the superconductor with a field of view ranging from millimeters to micrometers are presented. The microscope's unique combination of total electron yield (TEY) measurements together with low temperatures offers novel possibilities concerning the current transport in superconductors on small length scales.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  18. Enhanced s +/- pairing due to prioritized diagonal motion of electrons in the iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Kuroki, Kazuhiko; Suzuki, Katsuhiro; Usui, Hidetomo

    2015-03-01

    In the itinerant spin picture of the iron-based superconductors, the nesting between electron and hole Fermi surfaces is usually considered to be the origin of the spin fluctuation. However, there are now some experimental results suggesting that the nesting is not important for superconductivity. An example is the 1111 materials LnFeAsO1-xHx (Ln=La,Sm etc.), where over 50% of electron doping can be accomplished. Superconductivity not only survives, but is even enhanced in the largely electron doped regime, in contradition to the expectation from the bad nesting. In LaFeAsO1-xHx in particular, the x vs. Tc phase diagram exhibits a double dome feature, suggesting a possible difference in the pairing mechanism between the lightly doped and the heavily doped regimes. In the present study, we analyze the five orbital model of this system, and show that a peculiar relation among the real space hoppings is realized in the largely electron doped regime, namely, the next nearest neighbor hopping dominates over the nearest one within the dxy orbitals. We argue that this enhances the s +/- pairing, which is a next nearest neighbor pairing in real space, despite the degraded nesting. We also discuss about some other materials having similar real space hoppings.

  19. The Doping Dependence of the Ground State in the Electron-doped Cuprates

    NASA Astrophysics Data System (ADS)

    Greene, Richard L.

    2004-03-01

    The mechanism behind high-temperature superconductivity in the cuprates is not yet determined. Understanding the nature of the normal ground state at various dopings is important for the ultimate determination of the mechanism. Some theories suggest that excitations associated with a doping-dependent quantum phase transition (QPT) are an essential ingredient. So far the evidence for a QPT in the cuprates has been indirect and inconclusive. The electron-doped cuprates offer a distinct advantage over their hole-doped counterparts because the maximum critical magnetic field (H_c2) necessary to access the T=0 normal state is less than 10T. Here, I will present comprehensive measurements of the low-temperature (0.35K to 20K) ab-plane resistivity and Hall effect in the normal state (H>H_c2) of the electron-doped cuprate Pr_2-xCe_xCuO4 (PCCO) as a function of Ce doping. These measurements [1] strongly suggest a quantum critical point at x_c=0.165±0.005 with an associated quantum fluctuation regime at higher temperatures and at nearby dopings. I will also present tunneling results which show that a normal state pseudogap, of unknown origin, disappears near the same doping [2]. The nature of the QPT cannot be determined from our measurements but other results [3] on PCCO suggest an antiferromagnetic-metal to paramagnetic- metal phase transition. I will also report low-temperature specific heat and Raman scattering data in the superconducting state, which show that the superconducting gap anisotropy changes near the critical doping x_c. [1] Y. Dagan et al., cond-mat/0310475. [2] A. Biswas et al., Phys. Rev. B64, 104519 (2001); L. Alff et al., Nature 422, 698 (2003. [3] J. Sonier et al., Phys. Rev. Lett. 91, 147002 (2003); M. Fujita et al., cond-mat/0311269. In collaboration with Y. Dagan, H. Balci, G. Blumberg, C. Kendziora, and M.M.Qazilbash. Support from the NSF under DMR-0102350.

  20. Recrystallization of high temperature superconductors

    SciTech Connect

    Kouzoudis, D.

    1996-05-09

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

  1. Infrared detection with high-[Tc] bolometers and response of Nb tunnel junctions to picosecond voltage pulses

    SciTech Connect

    Verghese, S.

    1993-05-01

    Oxide superconductors with high critical temperature [Tc] make sensitive thermometers for several types of infrared bolometers. The authors built composite bolometers with YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta

  2. Effects of the Electronic Doping In the Stability of the Metal Hydride NaH

    NASA Astrophysics Data System (ADS)

    Olea-Amezcua, Monica-Araceli; Rivas-Silva, Juan-Francisco; de La Peña-Seaman, Omar; Heid, Rolf; Bohnen, Klaus-Peter

    2015-03-01

    Despite metal hydrides light weight and high hydrogen volumetric densities, the Hydrogen desorption process requires excessively high temperatures due to their high stability. Attempts for improvement the hydrogenation properties have been focus on the introduction of defects, impurities and doping on the metal hydride. We present a systematic study of the electronic doping effects on the stability of a model system, NaH doped with magnesium, forming the alloying system Na1-xMgxH. We use the density functional theory (DFT) and the self-consistent version of the virtual crystal approximation (VCA) to model the doping of NaH with Mg. The evolution of the ground state structural and electronic properties is analyzed as a function of Mg-content. The full-phonon dispersion, calculated by the linear response theory (LRT) and density functional perturbation theory (DFPT), is analyzed for several Mg-concentrations, paying special attention to the crystal stability and the correlations with the electronic structure. Applying the quasiharmonic approximation (QHA), the free energy from zero-point motion is obtained, and its influence on the properties under study is analyzed. This work is partially supported by the VIEP-BUAP (OMPS-EXC14-I) and CONACYT-Mexico (No. 221807) projects.

  3. Stabilization of Ferromagnetic States by Electron Doping in ZnO-Based Diluted Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2001-03-01

    In order to investigate functionality of ZnO as a diluted magnetic semiconductor (DMS), we had studied the magnetism in ZnO doped with 3d transition metal atoms (TM) and showed that it was also a candidate for a new functional magnetic material [1]. In this paper, we develop our previous work and give detailed materials design with ZnO-based DMS based on ab initio calculations. The electronic structure of a TM-doped ZnO was calculated within the local density approximation by the Korringa-Kohn-Rostoker method combined with the coherent potential approximation. Total energies of Zn_1-xTM^\\uparrow_xO and Zn_1-xTM^\\uparrow_x/2TM^downarrow_x/2O, where up and down arrows mean the directions of respective atomic magnetic moments, were compared and appearance of the ferromagnetism was discussed. Effects of carrier doping to these systems were also considered. It was found that their magnetic states were controllable by changing the carrier density. In particular, ferromagnetic states were stabilized by electron doping in the case of Fe, Co or Ni doped ZnO. From the point of practical applications, it is favorable feature to realize high Curie temperature ferromagnet, because n-type ZnO is easily available. [1] K. Sato and H. Katayama-Yoshida, Jpn. J. Appl. Phys. 39 (2000) L555.

  4. A 16-channel high-Tc SQUID-magnetometer system for magnetocardiogram mapping

    NASA Astrophysics Data System (ADS)

    Yokosawa, Koichi; Tsukamoto, Akira; Suzuki, Daisuke; Kandori, Akihiko; Miyashita, Tsuyoshi; Ogata, Kuniomi; Seki, Yusuke; Tsukada, Keiji

    2003-12-01

    A compact, light and easy-to-handle magnetocardiograph (MCG) has been developed. The MCG consists of a sensor array with superconducting-quantum-interference-device magnetometers made of a high-critical temperature superconductor, arranged in a 4 × 4 matrix, and operated in a vertical magnetically shielding cylinder (1.7 m high and 1 m in diameter). Each magnetometer is paired with each of its adjacent magnetometers, and the difference between the respective outputs provides us with a measure of magnetic gradient. This configuration for the electronic gradiometers cancels out the environmental magnetic field noise within the shielding cylinder. We use the data from the multiple gradiometers to construct a current arrow map that describes the distribution of original current vectors in the area being measured. We used the fabricated MCG to record magnetocardiograms of healthy volunteers. The smallest signals, i.e., the P-waves, were clearly detected without averaging. The current arrow maps obtained from the single-beat magnetocardiograms indicate the feasibility of clinical application of this MCG.

  5. Photo-enhanced antinodal conductivity in the pseudogap state of high-Tc cuprates

    PubMed Central

    Cilento, F.; Dal Conte, S.; Coslovich, G.; Peli, S.; Nembrini, N.; Mor, S.; Banfi, F.; Ferrini, G.; Eisaki, H.; Chan, M. K.; Dorow, C. J.; Veit, M. J.; Greven, M.; van der Marel, D.; Comin, R.; Damascelli, A.; Rettig, L.; Bovensiepen, U.; Capone, M.; Giannetti, C.; Parmigiani, F.

    2014-01-01

    A major challenge in understanding the cuprate superconductors is to clarify the nature of the fundamental electronic correlations that lead to the pseudogap phenomenon. Here we use ultrashort light pulses to prepare a non-thermal distribution of excitations and capture novel properties that are hidden at equilibrium. Using a broadband (0.5–2 eV) probe, we are able to track the dynamics of the dielectric function and unveil an anomalous decrease in the scattering rate of the charge carriers in a pseudogap-like region of the temperature (T) and hole-doping (p) phase diagram. In this region, delimited by a well-defined T*neq(p) line, the photoexcitation process triggers the evolution of antinodal excitations from gapped (localized) to delocalized quasiparticles characterized by a longer lifetime. The novel concept of photo-enhanced antinodal conductivity is naturally explained within the single-band Hubbard model, in which the short-range Coulomb repulsion leads to a k-space differentiation between nodal quasiparticles and antinodal excitations. PMID:25014895

  6. Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR

    NASA Astrophysics Data System (ADS)

    Wiecki, P.; Roy, B.; Johnston, D. C.; Bud'ko, S. L.; Canfield, P. C.; Furukawa, Y.

    2015-09-01

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. These FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting dome in these and other iron-pnictide families.

  7. Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-T(c) Superconductor

    SciTech Connect

    Chen, Yulin; Iyo, Akira; Yang, Wanli; Zhou, Xingjiang; Lu, Donghui; Eisaki, Hiroshi; Devereaux, Thomas P.; Hussain, Zahid; Shen, Z.-X.; /Stanford U., Phys. Dept. /SLAC, SSRL /AIST, Tsukuba /Waterloo U. /LBNL, ALS

    2007-02-12

    We report the discovery of a self-doped multilayer high T{sub c} superconductor Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub 8}F{sub 2} (F0234) which contains distinctly different superconducting gap magnitudes along its two Fermi-surface sheets. While formal valence counting would imply this material to be an undoped insulator, it is a self-doped superconductor with a T{sub c} of 60 K, possessing simultaneously both electron- and hole-doped Fermi-surface sheets. Intriguingly, the Fermi-surface sheet characterized by the much larger gap is the electron-doped one, which has a shape disfavoring two electronic features considered to be important for the pairing mechanism: the van Hove singularity and the antiferromagnetic ({pi}/{alpha}, {pi}/{alpha}) scattering.

  8. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    SciTech Connect

    Wiecki, P.; Roy, B.; Johnston, D. C.; Bud’ko, S. L.; Canfield, P. C.; Furukawa, Y.

    2015-09-22

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. Furthermore, these FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting dome in these and other iron-pnictide families.

  9. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    DOE PAGESBeta

    Wiecki, P.; Roy, B.; Johnston, D. C.; Bud’ko, S. L.; Canfield, P. C.; Furukawa, Y.

    2015-09-22

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. Furthermore, these FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting domemore » in these and other iron-pnictide families.« less

  10. Fine uniform filament superconductors

    DOEpatents

    Riley, Jr., Gilbert N.; Li, Qi; Roberts, Peter R.; Antaya, Peter D.; Seuntjens, Jeffrey M.; Hancock, Steven; DeMoranville, Kenneth L.; Christopherson, Craig J.; Garrant, Jennifer H.; Craven, Christopher A.

    2002-01-01

    A multifilamentary superconductor composite having a high fill factor is formed from a plurality of stacked monofilament precursor elements, each of which includes a low density superconductor precursor monofilament. The precursor elements all have substantially the same dimensions and characteristics, and are stacked in a rectilinear configuration and consolidated to provide a multifilamentary precursor composite. The composite is thereafter thermomechanically processed to provide a superconductor composite in which each monofilament is less than about 50 microns thick.

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

    NASA Astrophysics Data System (ADS)

    Wang, Huabing

    2008-03-01

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

  12. Superconductor rotor cooling system

    DOEpatents

    Gamble, Bruce B.; Sidi-Yekhlef, Ahmed; Schwall, Robert E.; Driscoll, David I.; Shoykhet, Boris A.

    2002-01-01

    A system for cooling a superconductor device includes a cryocooler located in a stationary reference frame and a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with a rotating reference frame in which the superconductor device is located. A method of cooling a superconductor device includes locating a cryocooler in a stationary reference frame, and transferring heat from a superconductor device located in a rotating reference frame to the cryocooler through a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with the rotating reference frame.

  13. Superconductor rotor cooling system

    DOEpatents

    Gamble, Bruce B.; Sidi-Yekhlef, Ahmed; Schwall, Robert E.; Driscoll, David I.; Shoykhet, Boris A.

    2004-11-02

    A system for cooling a superconductor device includes a cryocooler located in a stationary reference frame and a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with a rotating reference frame in which the superconductor device is located. A method of cooling a superconductor device includes locating a cryocooler in a stationary reference frame, and transferring heat from a superconductor device located in a rotating reference frame to the cryocooler through a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with the rotating reference frame.

  14. Photothermal measurements of superconductors

    SciTech Connect

    Kino, G.S.; Studenmund, W.R.; Fishman, I.M.

    1996-12-31

    A photothermal technique has been used to measure diffusion and critical temperature in high temperature superconductors. The technique is particularly suitable for determining material quality and inhomogeneity.

  15. Oxides and oxide superconductors: Elastic and related properties

    SciTech Connect

    Ming Lei.

    1991-01-01

    Using both measurements and modeling, the elastic and related properties of some oxides and oxide superconductors were studied. The polycrystal elastic constants were measured using a MHz-frequency pulse-echo method between 295 and 4 K and corrected to the void-free state by using a model for a composite material containing spherical particles. The elastic moduli of the high-{Tc} superconductor YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) were compared with that of oxides, especially the perovskites BaTiO{sub 3} and SrTiO{sub 3}, which are crystal-structure building blocks for the YBCO superconductor. The bulk moduli were also calculated using a Born ionic model with two energy terms: electrostatic (Madelung) and ion-core-repulsion. The calculated bulk modulus of YBCO, 98 GPa, agrees well with measurement, 101 GPa. Based on monocrystal measurements combined with analysis-theory, elastic stiffnesses C{sub ij} for orthorhombic YBCO were estimated. The bulk modulus obtained from the estimated C{sub ij} by the Voigt-Reuss-Hill averaging method agrees with the monocrystal measurement.

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

    SciTech Connect

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

    1998-11-01

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

  17. Designing with superconductors

    SciTech Connect

    Hammond, R.B.; Hey-Shipton, G.L. ); Matthaei, G.L. )

    1993-04-01

    This article examines the basics of designing with superconducting microwave ICs. The topics of this article include high-temperature superconductors of copper-oxide compounds, the shortcomings of designing ICs with CAD, building small, high-Q bandpass or bandstop filters, combining high-temperature superconductors and conventional components, oscillator stability, tuning, digital interconnects, and cryogenic cooling options.

  18. Oxygen ordering in the high-Tc superconductor HgBa2CaCu2O6+δ as revealed by perturbed angular correlation

    NASA Astrophysics Data System (ADS)

    Mendonça, T. M.; Correia, J. G.; Haas, H.; Odier, P.; Tavares, P. B.; da Silva, M. R.; Lopes, A. M. L.; Pereira, A. M.; Gonçalves, J. N.; Amaral, J. S.; Darie, C.; Araujo, J. P.

    2011-09-01

    Lattice sites and collective ordering of oxygen atoms in HgBa2CaCu2O6+δ were studied using the perturbed angular correlation (PAC) technique at ISOLDE/CERN. The electric field gradients (EFG) at 199mHg nuclei have been measured as functions of oxygen doping on the Hg planes, above and below Tc. In comparison with the results obtained for oxygen and fluorine doping in Hg-1201, the analysis shows a different oxygen ordering exhibited by Hg-1212. Moreover, for all studied cases, the experimental results show that at a local scale there is non uniform oxygen distribution. A series of ab initio EFG calculations allowed to infer that at low concentrations, regions without oxygen coexist with regions where O2δ dumbbell molecules are located at the center of the Hg mesh. On the other side, at high concentrations, O2δ dumbbell molecules coexist with single Oδ atoms occupying the center of the Hg mesh. The present results suggest that oxygen sits on the Hg planes in the form of a molecule and not as a single atom.

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

    SciTech Connect

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

    2011-06-13

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

  20. Deviations from Fermi-liquid behavior in (2+1)-dimensional quantum electrodynamics and the normal phase of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Aitchison, I. J. R.; Mavromatos, N. E.

    1996-04-01

    We argue that the gauge-fermion interaction in multiflavor quantum electrodynamics in (2+1) dimensions is responsible for non-Fermi-liquid behavior in the infrared, in the sense of leading to the existence of a nontrivial (quasi)fixed point that lies between the trivial fixed point (at infinite momenta) and the region where dynamical symmetry breaking and mass generation occurs. This quasifixed-point structure implies slowly varying, rather than fixed, couplings in the intermediate regime of momenta, a situation which resembles that of (four-dimensional) ``walking technicolor'' models of particle physics. The inclusion of wave-function renormalization yields marginal O(1/N) corrections to the ``bulk'' non-Fermi-liquid behavior caused by the gauge interaction in the limit of infinite flavor number. Such corrections lead to the appearance of modified critical exponents. In particular, at low temperatures there appear to be logarithmic scaling violations of the linear resistivity of the system of order O(1/N). The connection with the anomalous normal-state properties of certain condensed-matter systems relevant for high-temperature superconductivity is briefly discussed. The relevance of the large (flavor) N expansion to the Fermi-liquid problem is emphasized. As a partial result of our analysis, we point out the absence of charge-density-wave instabilities from the effective low-energy theory, as a consequence of gauge invariance.

  1. High-resolution angle-resolved photoemission studies of high Tc superconductor Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8

    SciTech Connect

    Liu, Rong.

    1990-09-21

    An angle-resolved photoemission study of the normal and superconducting states in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} was performed. Measurements in the normal state show bands dispersing through the Fermi level from at least 350 meV below E{sub F}. The Fermi level crossings are consistant with local-density band calculation, including a point calculated to be of Bi-O character. Additional measurements were made where bands crossed the Fermi level between 100 and 250K, along with measurements on an adjacent Pt foil. The Fermi edges of both materials agree to within the noise. Below the Fermi level, the spectra show correlation effects on the form of an increased effective mass. The shape of the spectra can be explained by a lifetime-broadened photohole and secondary electrons. The effective inverse photohole lifetime is linear in energy. A superconducting gap has been measured at a number of points where there is density at the Fermi level in the normal state. By proper modeling, a gap of 24 meV was obtained for all these points, including points of Cu-O and Bi-O character respectively, according to band calculation. The lack of gap anisotropy in the basal plane suggests that pinning in this material is not d-wave pairing.

  2. Matching field effects at tesla-level magnetic fields in critical current density in high-Tc superconductors containing self-assembled columnar defects

    SciTech Connect

    Sinclair, J.; Zuev, Yuri L; Cantoni, Claudia; Wee, Sung Hun; Varanasi, C. V.; Thompson, James R; Christen, David K

    2012-01-01

    We have investigated the superconductive transport properties of YBa2Cu3O7 films containing self-assembled columnar arrays of second phase SrZrO3 or BaSnO3 precipitates. A matching condition between columnar pinning sites (aligned at or near the c axis) and external magnetic flux, tilted with respect to them, is identified in the critical current JC.H/ data. The results for the material containing SrZrO3-based pins are analyzed within a simple intuitive model. At matching, the critical current is enhanced above the model prediction. In complementary contact-free investigations of BaSnO3-doped material, matching effects are observed over a wide range of temperatures in the field dependence of JC.H/. The deduced matching fields agree reasonably well with the densities of columnar pins directly observed by scanning electron microscopy.

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

    NASA Astrophysics Data System (ADS)

    Onari, Seiichiro; Yamakawa, Youichi; Kontani, Hiroshi

    2014-05-01

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

  4. High resolution polarized Cu L3 XAS of high temperature superconductors: correlations between the symmetry of d holes and the critical temperature

    NASA Astrophysics Data System (ADS)

    Flank, A. M.; Lagarde, P.; Bianconi, A.; Castrucci, P.; Fabrizi, A.; Pompa, M.; Katayama-Yoshida, H.; Calestani, G.

    1990-06-01

    High resolution polarized Cu L3 X-ray absorption spectra of single crystals and of highly oriented pellets of high Tc superconductors of the bismuth kind have been measured by using synchrotron radiation at Super-ACO. We have investigated the energy splitting Δ between the in-plane and out-of-plane 2p → 3d transition. We find that the splitting Δ as well as the intensity of the Eparallelz component is correlated with the critical temperature of the superconducting systems for each class of superconductors.

  5. Single parameter analysis of hysteretic magnetic flux trapping in high T[sub c] superconductor ribbon

    SciTech Connect

    Telschow, K.L.

    1992-01-01

    This paper described the application of an AC surface probe, similar to presently used eddy current probes, to the measurement of DC transport critical currents and critical state dissipation in high [Tc] superconductors. It has been shown that the probe can provide quantitative measurement of the full field penetration in superconducting samples by measuring the response of AC induced screening currents for superconducting materials in the form of tapes with overlayers of silver. In this manner, the AC probe can be used to replace the contact DC probe for determining critical currents in a noncontacting and local manner suitable for scanning over or along the sample.

  6. Single parameter analysis of hysteretic magnetic flux trapping in high T{sub c} superconductor ribbon

    SciTech Connect

    Telschow, K.L.

    1992-10-01

    This paper described the application of an AC surface probe, similar to presently used eddy current probes, to the measurement of DC transport critical currents and critical state dissipation in high {Tc} superconductors. It has been shown that the probe can provide quantitative measurement of the full field penetration in superconducting samples by measuring the response of AC induced screening currents for superconducting materials in the form of tapes with overlayers of silver. In this manner, the AC probe can be used to replace the contact DC probe for determining critical currents in a noncontacting and local manner suitable for scanning over or along the sample.

  7. Simulation of magnetization process of Pure-type superconductor magnet undulator based on T-method

    NASA Astrophysics Data System (ADS)

    Deri, Yi; Kawaguchi, Hideki; Tsuchimoto, Masanori; Tanaka, Takashi

    2015-11-01

    For the next generation Free Electron Laser, Pure-type undulator made of high Tc superconductors (HTSs) was considered to achieve a small size and high intensity magnetic field undulator. In general, it is very difficult to adjust the undulator magnet alignment after the HTS magnetization since the entire undulator is installed inside a cryostat. The appropriate HTS alignment has to be determined in the design stage. This paper presents the development of a numerical simulation code for magnetization process of the Pure-type HTS undulator to assist the design of the optimal size and alignment of the HTS magnets.

  8. Vortex-Core Charging Due to the Lorentz Force in a d-Wave Superconductor

    NASA Astrophysics Data System (ADS)

    Ueki, Hikaru; Kohno, Wataru; Kita, Takafumi

    2016-06-01

    We derive augmented quasiclassical equations of superconductivity with the Lorentz force in the Matsubara formalism so that the charge redistribution due to supercurrent can be calculated quantitatively. Using it, we obtain an analytic expression for the vortex-core charge of an isolated vortex in extreme type-II materials given in terms of the London penetration depth and the equilibrium Hall coefficient. It depends strongly on the Fermi surface curvature and gap anisotropy, and may change sign even as a function of temperature due to the variation in the excitation curvature under the growing energy gap. This is also confirmed in our numerical study of high-Tc superconductors.

  9. Electronic structure, irreversibility line and magnetoresistance of Cu0.3Bi2Se3 superconductor

    SciTech Connect

    Hemian, Yi; Gu, Genda; Chen, Chao -Yu; Sun, Xuan; Xie, Zhuo -Jin; Feng, Ya; Liang, Ai -Ji; Peng, Ying -Ying; He, Shao -Long; Zhao, Lin; Liu, Guo -Dong; Dong, Xiao -Li; Zhang, Jun; Chen, Chuang -Tian; Xu, Zu -Yan; Zhou, X. -J.

    2015-06-01

    CuxBi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ~4000 Oe for the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.9K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu0.3Bi2Se3 superconductors up to room temperature. As a result, these observations provide useful information for further study of this possible candidate for topological superconductors.

  10. Fabrication of high temperature superconductors

    DOEpatents

    Balachandran, Uthamalingam; Dorris, Stephen E.; Ma, Beihai; Li, Meiya

    2003-06-17

    A method of forming a biaxially aligned superconductor on a non-biaxially aligned substrate substantially chemically inert to the biaxially aligned superconductor comprising is disclosed. A non-biaxially aligned substrate chemically inert to the superconductor is provided and a biaxially aligned superconductor material is deposited directly on the non-biaxially aligned substrate. A method forming a plume of superconductor material and contacting the plume and the non-biaxially aligned substrate at an angle greater than 0.degree. and less than 90.degree. to deposit a biaxially aligned superconductor on the non-biaxially aligned substrate is also disclosed. Various superconductors and substrates are illustrated.

  11. Divergent nematic susceptibility of optimally doped Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Chu, Jiun-Haw; Kuo, Hsueh-Hui; Fisher, Ian

    2015-03-01

    By performing differential elastoresistivity measurements on a wider range of iron based superconductors, including electron doped (Ba(Fe1-xCox)2As2, Ba(Fe1-xNix)2As2),holedoped(Ba1-xKxFe2As2), isovalent substituted pnictides (BaFe2(As1-xPx)2) and chalcogenides (FeTe1-xSex), we show that a divergent nematic susceptibility in the B2g symmetry channel appears to be a generic feature of optimally doped compositions. For the specific case of optimally ``doped'' BaFe2(As1-xPx)2, the nematic susceptibility can be well fitted by a Curie-Weiss temperature dependence with critical temperature close to zero, consistent with expectations of quantum critical behavior in the absence of disorder. However for all the other optimal doped iron based superconductors, the nematic susceptibility exhibits a downward deviation from Curie-Weiss behavior, suggestive of an important role played by disorder.

  12. Tellurium Hydrides at High Pressures: High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    Observation of high-temperature superconductivity in compressed sulfur hydrides has generated an irresistible wave of searches for new hydrogen-containing superconductors. We herein report the prediction of high-Tc superconductivity in tellurium hydrides stabilized at megabar pressures identified by first-principles calculations in combination with a swarm structure search. Although tellurium is isoelectronic to sulfur or selenium, its heavier atomic mass and weaker electronegativity makes tellurium hydrides fundamentally distinct from sulfur or selenium hydrides in stoichiometries, structures, and chemical bondings. We identify three metallic stoichiometries of H4Te , H5Te2 , and HTe3 , which are not predicted or known stable structures for sulfur or selenium hydrides. The two hydrogen-rich H4Te and H5Te2 phases are primarily ionic and contain exotic quasimolecular H2 and linear H3 units, respectively. Their high-Tc (e.g., 104 K for H4Te at 170 GPa) superconductivity originates from the strong electron-phonon couplings associated with intermediate-frequency H-derived wagging and bending modes, a superconducting mechanism which differs substantially with those in sulfur or selenium hydrides where the high-frequency H-stretching vibrations make considerable contributions.

  13. A spectroscopic fingerprint of electron correlation in high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Gweon, Gey-Hong; Matsuyama, Kazue; Gu, G.-D.; Schneeloch, J.; Zhong, R. D.; Liu, T. S.

    2014-03-01

    The so-called ``strange metal phase'' of high temperature (high Tc) superconductors remains at the heart of the high Tc mystery. Better experimental data and insightful theoretical work would improve our understanding of this enigmatic phase. In particular, the recent advance in angle resolved photoelectron spectroscopy (ARPES), incorporating low photon energies (~ 7 eV), has given a much more refined view of the many body interaction in these materials. Here, we report a new ARPES feature of Bi2Sr2CaCu2O8+δ that we demonstrate to have the key ability to distinguish between different classes of theories of the normal state. This feature-the anomaly in the nodal many body density of states (nMBDOS)-is clearly observed in the low energy ARPES data, but also observed in more conventional high energy ARPES data, when a sufficient temperature range is covered. We show that key characteristics of this anomaly are explained by a strong electron correlation model; the electron-hole asymmetry and the momentum dependent self energy emerge as key required ingredients. In particular, we find that, among many theories available for comparison, the phenomenological extremely correlated Fermi liquid (ECFL) model scores the best in terms of explaining the new anomaly feature.

  14. A Novel Large Moment Antiferromagnetic Order in K0.8Fe1.6Se2 Superconductor

    NASA Astrophysics Data System (ADS)

    Bao, Wei; Huang, Qing-Zhen; Chen, Gen-Fu; A. Green, M.; Wang, Du-Ming; He, Jun-Bao; Qiu, Yi-Ming

    2011-08-01

    The discovery of cuprate high TC superconductors has inspired the search for unconventional superconductors in magnetic materials. A successful recipe has been to suppress long-range order in a magnetic parent compound by doping or high pressure to drive the material towards a quantum critical point. We report an exception to this rule in the recently discovered potassium iron selenide. The superconducting composition is identified as the iron vacancy ordered K0.83(2)Fe1.64(1)Se2 with TC above 30 K. A novel large moment 3.31 μB/Fe antiferromagnetic order that conforms to the tetragonal crystal symmetry has an unprecedentedly high ordering temperature TN ≈ 559 K for a bulk superconductor. Staggeringly polarized electronic density of states is thus suspected, which would stimulate further investigation into superconductivity in a strong spin-exchange field under new circumstances.

  15. Cluster calculations of the electronic structure of copper oxide superconductors

    SciTech Connect

    Wang Yujuin.

    1990-01-01

    A semiempirical INDO model suitable for examination of the transition metal complexes is used to study the electronic structure of various clusters representing the La-Sr-Cu-O and Nd-Ce-Cu-O types of the high-{Tc} superconductors. The clusters are stabilized by embedding in an appropriate Madelung field. The results show a convergent picture independent of the cluster sizes. In the undoped clusters, all copper sites have a {approximately} d{sup 9} configuration with one unpaired spin coupled antiferromagnetically to the spin of adjacent Cu sites. Fitting the resulting energies to the Heisenberg spin Hamiltonian, the superexchange J values obtained were in excellent agreement with experiments. The hole carriers are mainly of planar O character, while the electron carriers are of Cu character.

  16. Test Status for Proposed Coupling of a Gravitational Force to Extreme Type II YBCO Ceramic Superconductors

    NASA Technical Reports Server (NTRS)

    Noever, David; Li, Ning; Robertson, Tony; Koczor, Ron; Brantley, Whitt

    1999-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair electron density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (about 10-6 g/cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with the percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10(exp 4) was reported above a stationary (non-rotating) superconductor. In the present experiments reported using a sensitive gravimeter (resolution <10(exp -9) unit gravity or variation of 10(exp -6) cm/sq s in accelerations), bulk YBCO superconductors were stably levitated in a DC magnetic field (0.6 Tesla) subject to lateral AC fields (60 Gauss at 60 Hz) and rotation. With magnetic shielding, thermal control and buoyancy compensation, changes in acceleration were measured to be less than 2 parts in 10(exp 8) of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between high-Tc superconductors and gravity. Latest test results will be reported, along with status for future improvements and prospects.

  17. Critical Current Test of Liquid Hydrogen Cooled HTC Superconductors under External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Shirai, Yasuyuki; Shiotsu, Masahiro; Tatsumoto, Hideki; Kobayashi, Hiroaki; Naruo, Yoshihiro; Nonaka, Satoshi; Inatani, Yoshifumi

    High-Tc (HTC) superconductors including MgB2 will show excellent properties under temperature of Liquid Hydrogen (LH2:20K), which has large latent heat and low viscosity coefficient. In order to design and fabricate the LH2 cooled superconducting energy devices, we must clear the cooling property of LH2 for superconductors, the cooling system and safety design of LH2 cooled superconducting devices and electro-magnetic property evaluation of superconductors (BSCCO, REBCO and MgB2) and their magnets cooled by LH2. As the first step of the study, an experimental setup which can be used for investigating heat transfer characteristics of LH2 in a pool and also in forced flow (circulation loop with a pump), and also for evaluation of electro-magnetic properties of LH2 cooled superconductors under external magnetic field (up to 7 T). In this paper, we will show a short sketch of the experimental set-up, practical experiences in safety operation of liquid hydrogen cooling system and example test results of critical current evaluation of HTC superconductors cooled by LH2.

  18. Optical spectra of high temperature superconductors

    SciTech Connect

    Ruvalds, J.

    1996-12-31

    The concept of free electrons which yields the Drude description of the conductivity works surprisingly well in conventional metals. By contrast, the infrared reflectivity of the cuprate superconductors deviates dramatically from Drude behavior and thus challenges theory to explain the origin of the anomalous electron damping and the related mass divergence which has implications for the existence of a Fermi surface. The controversial key issue of the carrier concentration in cuprates needs to be resolved by a conserving analysis of the puzzling conductivity. Raman spectra of cuprates also exhibit unconventional electronic contributions over a wide frequency range up to 1 eV, and recent data provide evidence for the symmetry of the superconducting energy gap. A microscopic theory for both the optical conductivity and the Raman anomalies in cuprates derives a linear frequency variation of the damping from electron-electron collisions on a nested Fermi surface that refers to nearly parallel segments of an electron trajectory. Thus the nesting theory links the cuprate anomalies to phenomena in chromium and rare earth metals. Nesting also yields a novel mechanism for d-wave superconductivity that requires a Coulomb repulsion of intermediate strength and key nesting features that distinguish high {Tc} cuprates from other materials. 41 refs., 7 figs.

  19. Direct readout flux locked loop circuit with automatic tuning of bias current and bias flux for high-Tc SQUID

    NASA Astrophysics Data System (ADS)

    Hirano, T.; Nagaishi, T.; Itozaki, H.

    1999-11-01

    Measurement of high-frequency magnetic signals has been required from some SQUID applications. We fabricated a high-Tc SQUID magnetic sensor system that can treat high-frequency signals. This system is composed of a SQUID, a preamplifier circuit, a flux locked loop (FLL) circuit with I/O and a personal computer and a PC card. We used the FLL circuit with no modulation to treat the high-frequency signal and to simplify the circuit. This system can treat a signal from dc to 1 MHz. All the sequence from tuning the SQUID to data acquisition can be done by a personal computer. This system successfully realized easy operation of SQUID measurement.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    NASA Technical Reports Server (NTRS)

    Haertling, Gene; Grabert, Gregory; Gilmour, Phillip

    1993-01-01

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

  2. TOPICAL REVIEW: Theory of extrinsic and intrinsic tunnelling in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Beanland, J.; Alexandrov, A. S.

    2010-10-01

    There has been a huge theoretical and experimental push to try to illuminate the mechanism behind the high-temperature superconductivity of copper oxides. Cuprates are distinguishable from conventional metallic superconductors in originating from the doping of the parent charge-transfer insulators. The superconducting parts are weakly coupled two-dimensional doped layers held together by the parent lattice. Apart from their high-Tc they have other characteristic features including the 'superconducting' gap (SG) which develops below the superconducting critical temperature and can be seen in extrinsic and intrinsic tunnelling experiments as well as using high-resolution angle-resolved photoemission (ARPES); there also exists another energy gap, the 'pseudogap' (PG), which is a large anomalous gap that exists well above Tc. We present a brief review of recent theories behind the pseudogap and discuss in detail one specific (polaronic) approach which explains the SG, PG and unusual tunnelling characteristics of cuprate superconductors.

  3. High field paramagnetic Meissner effect in Mo100-xRex alloy superconductors

    NASA Astrophysics Data System (ADS)

    Sundar, Shyam; Chattopadhyay, M. K.; Sharath Chandra, L. S.; Roy, S. B.

    2015-07-01

    We have performed an experimental study on the temperature and field dependence of magnetization of a series of superconducting Mo100-xRex alloys. Our studies reveal the presence of high field paramagnetic effect (HFPME) in these low temperature superconductors. The results of our studies indicate that the HFPME in the Mo100-xRex alloys is related to the inhomogeneous distribution of strong and weak flux-line pinning centres, and the flux-compression resulting due to the same while cooling down the samples in the presence of high magnetic fields. The results are complemented by the studies on the temperature dependence of the electrical resistivity and heat capacity of these alloys in different constant magnetic fields. We compare our findings with the studies reported in literature on both low TC and high TC superconductors.

  4. Momentum-resolved electronic structure of the superconductor parent compound BaBiO3

    NASA Astrophysics Data System (ADS)

    Plumb, N. C.; Ristic, Z.; Park, J.; Wang, Z.; Matt, C. E.; Xu, N.; Lv, B. Q.; Gawryluk, D.; Pomjakushina, E.; Conder, K.; Wang, Y.; Johnston, S.; Mesot, J.; Shi, M.; Radovic, M.

    We use in situ angle-resolved photoemission to study thin films of BaBiO3, a parent compound of bismuthate superconductors with Tc up to 30 K. By simple electron counting, BaBiO3 should be metallic. However, in analogy with many unconventional and high-Tc superconductor families, it is instead insulating, and superconductivity emerges with doping. Our experiments reveal a folded band structure consistent with known BiO6 breathing distortions. However, charge ordering often thought to accompany the distortions is virtually nonexistent. The data combined with DFT calculations indicate that states near EF are primarily oxygen-derived. Hence BaBiO3 appears to be characterized by negative charge transfer energy. This can account for the seeming discrepancy between the atomic structure and ''missing'' charge order. It should also be relevant for understanding the doping evolution and superconductivity in bismuthates.

  5. Practical superconductor development for electrical power applications, annual report for FY 1994

    SciTech Connect

    Balachandran, U.

    1994-10-01

    Development of useful high-critical-temperature superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes technical progress of research and development efforts aimed at producing superconducting components in the Y-Ba-Cu, (Bi,Pb)-Sr-Ca-Cu, (Tl,Pb,Bt)-(Ba,Sr)-Ca-Cu. and Hg-Ba-Ca-Cu-0 oxide systems. Topics discussed are synthesis and heat treatment of high-Tc superconductors, formation of monolithic and composite conductors. characterization of structures and superconducting and mechanical properties, and fabrication and testing of prototype components. Collaborations with industry and academia are documented.

  6. Scaling relation for the superfluid density of cuprate superconductors: Origins and limits

    NASA Astrophysics Data System (ADS)

    Tallon, J. L.; Cooper, J. R.; Naqib, S. H.; Loram, J. W.

    2006-05-01

    A universal scaling relation, ρs∝σ(Tc)×Tc has been reported by Homes [Nature (London) 430, 539 (2004)] where ρs is the superfluid density and σ(T) is the dc conductivity. The relation was shown to apply to both c -axis and in-plane dynamics for high- Tc superconductors as well as to the more conventional superconductors Nb and Pb, suggesting common physics in these systems. We show quantitatively that the scaling behavior has several possible origins, including marginal Fermi-liquid behavior, Josephson coupling, dirty-limit superconductivity, and unitary impurity scattering for a d -wave order parameter. However, the relation breaks down seriously in overdoped cuprates, and possibly even at lower doping.

  7. The refrigeration of high temperature superconductors between 25K and 65K

    SciTech Connect

    Richardson, R.N.; Scurlock, R.G.; Tavner, A.C.R.

    1996-12-31

    The present state of the art indicates that acceptable j - H characteristics for power applications of the new high Tc superconductors will only be achieved using materials at temperatures below liquid nitrogen temperature. A boiling point of 27.1K and high specific cooling capacity make neon an eminently suitable choice of refrigerant at these temperatures. A cryostat has been constructed which employs a two stage Gifford-McMahon cooler to liquefy neon gas. The cryostat contains up to 5 litres of liquid neon which can be used for {open_quote}in-situ{close_quote} experiments or transfer to another cryostat. Another set of cryostats are being used with liquid nitrogen/oxygen mixtures at reduced pressure for temperatures down to 50K. All these cryostats provide a core facility for characterising and operating high T{sub c} superconductors at Southampton.

  8. Influence of electron doping on the ground state of (Sr1-xLax)2IrO4

    DOE PAGESBeta

    Chen, Xiang; Hogan, Tom; Walkup, D.; Zhou, Wenwen; Pokharel, M.; Yao, Mengliang; Tian, Wei; Ward, Thomas Zac; Zhao, Y.; Parshall, Dr. D.; et al

    2015-08-17

    The evolution of the electronic properties of electron-doped (Sr1-xLax)2IrO4 is experimentally explored as the doping limit of La is approached. As electrons are introduced, the electronic ground state transitions from a spin-orbit Mott phase into an electronically phase separated state, where long-range magnetic order vanishes beyond x = 0:02 and charge transport remains percolative up to the limit of La substitution (x =0:06). In particular, the electronic ground state remains inhomogeneous even beyond the collapse of the parent state's long-range antiferromagnetic order, while persistent short-range magnetism survives up to the highest La-substitution levels. Furthermore, as electrons are doped into Sr2IrO4,more » we observe the appearance of a low temperature magnetic glass-like state intermediate to the complete suppression of antiferromagnetic order. Universalities and di erences in the electron-doped phase diagrams of single layer and bilayer Ruddlesden-Popper strontium iridates are discussed.« less

  9. Influence of Electron Doping on Magnetic Order in CeRu2Al10

    SciTech Connect

    Kobayashi, Riki; Kaneko, Koji; Saito, Kotaro; Mignot, Jean-Michel; André, Gilles; Robert, Julien; Wakimoto, Shuichi; Matsuda, Masaaki; Chi, Songxue; Haga, Yoshinori; Matsuda, Tatsuma D.; Yamamoto, Etsuji; Nishioka, Takashi; Matsumura, Masahiro; Tanida, Hiroshi; Sera, Masafumi

    2014-09-17

    The effect of electron doping by the substitution of Rh for Ru on unconventional magnetic order in CeRu2Al10 was investigated via neutron powder diffraction. In Ce(Ru1-xRhx)2Al10 with x = 0.05, 0.12, and 0.2, reorientation of the ordered moment from the c- to the a-axis takes place in all samples, while the ordering vector q=(0 1 0) remains unchanged within this concentration range. The moment reorientation is accompanied by an enhancement in its size by a factor of ~2.4, from μ=0.43 μB at x=0 to μ =1.06, 1.04, and 1.02 μB for x=0.05, 0.12 and 0.2, respectively. The continuous decrease in N´eel temperature T0(TN), despite an abrupt increase in μ , underlines the strong anisotropy in the exchange interaction in CeRu2Al10, and the fact that this anisotropy is easily suppressed by electron doping.

  10. Observation of a d-wave gap in electron-doped Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Kim, Y. K.; Sung, N. H.; Denlinger, J. D.; Kim, B. J.

    2016-01-01

    High-temperature superconductivity in cuprates emerges out of a highly enigmatic `pseudogap' metal phase. The mechanism of high-temperature superconductivity is probably encrypted in the elusive relationship between the two phases, which spectroscopically is manifested as Fermi arcs--disconnected segments of zero-energy states--collapsing into d-wave point nodes upon entering the superconducting phase. Here, we reproduce this distinct cuprate phenomenology in the 5d transition-metal oxide Sr2IrO4. Using angle-resolved photoemission, we show that the clean, low-temperature phase of 6-8% electron-doped Sr2IrO4 has gapless excitations only at four isolated points in the Brillouin zone, with a predominant d-wave symmetry of the gap. Our work thus establishes a connection between the low-temperature d-wave instability and the previously reported high-temperature Fermi arcs in electron-doped Sr2IrO4 (ref. ). Although the physical origin of the d-wave gap remains to be understood, Sr2IrO4 is the first non-cuprate material to spectroscopically reproduce the complete phenomenology of the cuprates, thus offering a new material platform to investigate the relationship between the pseudogap and the d-wave gap.

  11. Influence of electron doping on the ground state of (Sr1 -xLax)2IrO4

    NASA Astrophysics Data System (ADS)

    Chen, Xiang; Hogan, Tom; Walkup, D.; Zhou, Wenwen; Pokharel, M.; Yao, Mengliang; Tian, Wei; Ward, Thomas Z.; Zhao, Y.; Parshall, D.; Opeil, C.; Lynn, J. W.; Madhavan, Vidya; Wilson, Stephen D.

    2015-08-01

    The evolution of the electronic properties of electron-doped (Sr1 -xLax)2IrO4 is experimentally explored as the doping limit of La is approached. As electrons are introduced, the electronic ground-state transitions from a spin-orbit Mott phase into an electronically phase separated state, where long-range magnetic order vanishes beyond x =0.02 and charge transport remains percolative up to the limit of La substitution (x ≈0.06 ). In particular, the electronic ground state remains inhomogeneous even beyond the collapse of the parent state's long-range antiferromagnetic order, while persistent short-range magnetism survives up to the highest La-substitution levels. Furthermore, as electrons are doped into Sr2IrO4 , we observe the appearance of a low-temperature magnetic glasslike state intermediate to the complete suppression of antiferromagnetic order. Universalities and differences in the electron-doped phase diagrams of single-layer and bilayer Ruddlesden-Popper strontium iridates are discussed.

  12. SU(2) symmetry in a realistic spin-fermion model for cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Kloss, T.; Montiel, X.; Pépin, C.

    2015-05-01

    We consider the pseudogap (PG) state of high-Tc superconductors in the form of a composite order parameter fluctuating between 2 pF -charge ordering and superconducting (SC) pairing. In the limit of linear dispersion and at the hot spots, both order parameters are related by a SU(2) symmetry, and the eight-hot-spot model of Efetov et al. [Nat. Phys. 9, 442 (2013), 10.1038/nphys2641] is recovered. In the general case, however, curvature terms of the dispersion will break this symmetry, and the degeneracy between both states is lifted. Taking the full momentum dependence of the order parameter into account, we measure the strength of this SU(2) symmetry breaking over the full Brillouin zone. For realistic dispersion relations including curvature we find generically that the SU(2) symmetry breaking is small and robust to the fermiology and that the symmetric situation is restored in the large paramagnon mass and coupling limit. Comparing the level splitting for different materials, we propose a scenario that could account for the competition between the PG and SC states in the phase diagram of high-Tc superconductors.

  13. Reduction in bearing size due to superconductors in magnetic bearings

    NASA Technical Reports Server (NTRS)

    Rao, Dantam K.; Lewis, Paul; Dill, James F.

    1991-01-01

    A design concept that reduces the size of magnetic bearings is assessed. The small size will enable magnetic bearings to fit into limited available bearing volume of cryogenic machinery. The design concept, called SUPERC, uses (high Tc) superconductors or high-purity aluminum conductors in windings instead of copper. The relatively high-current density of these conductors reduces the slot radial thickness for windings, which reduces the size of the bearings. MTI developed a sizing program called SUPERC that translates the high-current density of these conductors into smaller sized bearings. This program was used to size a superconducting bearing to carry a 500 lb. load. The sizes of magnetic bearings needed by various design concepts are as follows: SUPERC design concept = 3.75 in.; magnet-bias design concept = 5.25 in.; and all electromagnet design concept = 7.0 in. These results indicate that the SUPERC design concept can significantly reduce the size of the bearing. This reduction, in turn, reduces the weight and yields a lighter bearing. Since the superconductors have inherently near-zero resistance, they are also expected to save power needed for operation considerably.

  14. Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Hoffman, Jennifer E.

    2011-12-01

    In the first three years since the discovery of Fe-based high Tc superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed light on three important questions. First, STM has demonstrated the complexity of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle interference (QPI) imaging and low temperature spectroscopy have shown that the pairing order parameter varies from nodal to nodeless s± within a single family, FeTe1-xSex. Second, STM has imaged C4 → C2 symmetry breaking in the electronic states of both parent and superconducting materials. As a local probe, STM is in a strong position to understand the interactions between these broken symmetry states and superconductivity. Finally, STM has been used to image the vortex state, giving insights into the technical problem of vortex pinning, and the fundamental problem of the competing states introduced when superconductivity is locally quenched by a magnetic field. Here we give a pedagogical introduction to STM and QPI imaging, discuss the specific challenges associated with extracting bulk properties from the study of surfaces, and report on progress made in understanding Fe-based superconductors using STM techniques.

  15. On-site attractive multiorbital Hamiltonian for d -wave superconductors

    NASA Astrophysics Data System (ADS)

    Bishop, Christopher B.; Liu, Guangkun; Dagotto, Elbio; Moreo, Adriana

    2016-06-01

    We introduce a two-orbital Hamiltonian on a square lattice that contains on-site attractive interactions involving the two eg orbitals. Via a canonical mean-field procedure similar to the one applied to the well-known negative-U Hubbard model, it is shown that the model develops d -wave (B1 g) superconductivity with nodes along the diagonal directions of the square Brillouin zone. This result is also supported by exact diagonalization of the model in a small cluster. The expectation is that this relatively simple attractive model could be used to address the properties of multiorbital d -wave superconductors in the same manner that the negative-U Hubbard model is widely applied to the study of the properties of s -wave single-orbital superconductors. In particular, we show that by splitting the eg orbitals and working at three-quarters filling, such that the x2-y2 orbital dominates at the Fermi level but the 3 z2-r2 orbital contribution is nonzero, the d -wave pairing state found here phenomenologically reproduces several properties of the superconducting state of the high Tc cuprates.

  16. Effect of granularity and annealing conditions on the magneto-resistance of the electron doped superconductor Nd1.85Ce0.15CuO4

    NASA Astrophysics Data System (ADS)

    Raveendran, N. Radhikesh; Amaladass, E. P.; Janaki, J.; Mani, Awadhesh

    2016-05-01

    A single phase polycrystalline sample of Nd1.85Ce0.15CuO4 has been synthesized and well characterized. Detailed studies on electrical resistivity behavior of this system as a function of temperature and magnetic field reveal interesting features attributable to the granularity effects. These features have been qualitatively understood based on the interplay of Josephson junction coupling and quasi particle tunneling which dictates the evolution of the observed temperature and field dependent resistivity behavior of Nd1.85Ce0.15CuO4 system. The studies also reveal significant changes with respect to annealing conditions, indicating that such compounds are very sensitive to annealing conditions. It has been observed that prolonged annealing in Argon atmosphere leads to a decrease in normal state resistivity. This is associated with a decrease in the S-I-S type Josephson tunnel junctions perhaps due to improved inter-granular coupling, nevertheless they could not be completely eliminated.

  17. Magnetic susceptibility of electron-doped superconductor (Nd 0.92Ce 0.08) 2CuO 4-δ

    NASA Astrophysics Data System (ADS)

    Suzuki, Masayuki; Ami, Takaaki; Isobe, Masaaki; Tanaka, Masahiro

    1991-12-01

    Magnetic susceptibility and the Tc of (Nd 0.92Ce 0.08) 2CuO 4-δ synthesized by an oxygen partial pressure controllable heat treatment system were investigated. The Tc started to increase at about 1%-Po 2 and saturated below 100ppm-Po 2. Oxygen deficiency reduced both the effective Bohr magnetons and the magnetic susceptibility, suggesting that the oxygen deficiency induced a magnetic interaction between Nd 3+ and Cu 2+. As the oxygen partial pressure moved to 0.1%, the magnetic correlation changed from positive to negative.

  18. Granular Superconductors and Gravity

    NASA Technical Reports Server (NTRS)

    Noever, David; Koczor, Ron

    1999-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

  19. Theory of nodal s ± -wave pairing symmetry in the Pu-based 115 superconductor family.

    PubMed

    Das, Tanmoy; Zhu, Jian-Xin; Graf, Matthias J

    2015-01-01

    The spin-fluctuation mechanism of superconductivity usually results in the presence of gapless or nodal quasiparticle states in the excitation spectrum. Nodal quasiparticle states are well established in copper-oxide, and heavy-fermion superconductors, but not in iron-based superconductors. Here, we study the pairing symmetry and mechanism of a new class of plutonium-based high-Tc superconductors and predict the presence of a nodal s(±) wave pairing symmetry in this family. Starting from a density-functional theory (DFT) based electronic structure calculation we predict several three-dimensional (3D) Fermi surfaces in this 115 superconductor family. We identify the dominant Fermi surface "hot-spots" in the inter-band scattering channel, which are aligned along the wavevector Q = (π, π, π), where degeneracy could induce sign-reversal of the pairing symmetry. Our calculation demonstrates that the s(±) wave pairing strength is stronger than the previously thought d-wave pairing; and more importantly, this pairing state allows for the existence of nodal quasiparticles. Finally, we predict the shape of the momentum- and energy-dependent magnetic resonance spectrum for the identification of this pairing symmetry. PMID:25721375

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1995-07-01

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

  2. Discriminating Hepatocellular Carcinoma in Rats Using a High-Tc SQUID Detected Nuclear Resonance Spectrometer in a Magnetic Shielding Box

    PubMed Central

    Huang, Kai-Wen; Chen, Hsin-Hsien; Yang, Hong-Chang; Horng, Herng-Er; Liao, Shu-Hsien; Yang, Shieh Yueh; Chieh, Jen-Jie; Wang, Li-Ming

    2012-01-01

    In this study, we report the spin-lattice relaxation rate of hepatocellular carcinoma (HCC) and normal liver tissue in rats using a high-Tc superconducting quantum interference device (SQUID) based nuclear magnetic resonance (NMR) spectrometer. The resonance spectrometer used for discriminating liver tumors in rats via the difference in longitudinal relaxation time in low magnetic fields was set up in a compact and portable magnetic shielding box. The frequency-domain NMR signals of HCC tissues and normal liver tissues were analyzed to study their respective longitudinal relaxation rate T1−1. The T1−1 of liver tissues for ten normal rats and ten cancerous rats were investigated respectively. The averaged T1−1 value of normal liver tissue was (6.41±0.66) s−1, and the averaged T1−1 value of cancerous tissue was (3.38±0.15) s−1. The ratio of T1−1 for normal liver tissues and cancerous liver tissues of the rats investigated is estimated to be 1.9. Since this significant statistical difference, the T1−1 value can be used to distinguish the HCC tissues from normal liver tissues. This method of examining liver and tumor tissues has the advantages of being convenient, easy to operate, and stable. PMID:23071710

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

    PubMed Central

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

    2014-01-01

    The high pressure structures, metallization, and superconductivity of recently synthesized H2-containing compounds (H2S)2H2 are elucidated by ab initio calculations. The ordered crystal structure with P1 symmetry is determined, supported by the good agreement between theoretical and experimental X-ray diffraction data, equation of states, and Raman spectra. The Cccm structure is favorable with partial hydrogen bond symmetrization above 37 GPa. Upon further compression, H2 molecules disappear and two intriguing metallic structures with R3m and Im-3m symmetries are reconstructive above 111 and 180 GPa, respectively. The predicted metallization pressure is 111 GPa, which is approximately one-third of the currently suggested metallization pressure of bulk molecular hydrogen. Application of the Allen-Dynes-modified McMillan equation for the Im-3m structure yields high Tc values of 191 K to 204 K at 200 GPa, which is among the highest values reported for H2-rich van der Waals compounds and MH3 type hydride thus far. PMID:25382349

  4. Doping dependence of spin dynamics in electron-doped Ba(Fe1-xCox)2As2

    SciTech Connect

    Matan, K.; Lynn, J W; Christianson, Andrew D; Lumsden, Mark D; Sato, T. J.

    2010-01-01

    The spin dynamics in single crystal, electron-doped Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} has been investigated by inelastic neutron scattering over the full range from undoped to the overdoped regime. We observe damped magnetic fluctuations in the normal state of the optimally doped compound (x=0.06) that share a remarkable similarity with those in the paramagnetic state of the parent compound (x=0). In the overdoped superconducting compound (x=0.14), magnetic excitations show a gaplike behavior, possibly related to a topological change in the hole Fermi surface (Lifshitz transition) while the imaginary part of the spin susceptibility {chi}' prominently resembles that of the overdoped cuprates. For the heavily overdoped, nonsuperconducting compound (x=0.24) the magnetic scattering disappears, which could be attributed to the absence of a hole Fermi-surface pocket observed by photoemission.

  5. Decoupling of the superconducting and magnetic/structural phase transitions in electron-doped BaFe2As2

    SciTech Connect

    Canfield, P.C.; Bud'ko, S.L.; Ni, Ni; Yan, J.Q.; Kracher, A.

    2009-08-03

    Study and comparison of over 30 examples of electron-doped BaFe{sub 2}As{sub 2} for transition metal (TM) = Co, Ni, Cu, and (Co/Cu mixtures) have led to an understanding that the suppression of the structural/antiferromagnetic phase transition to low-enough temperature in these compounds is a necessary condition for superconductivity but not a sufficient one. Whereas the structural/antiferromagnetic transitions are suppressed by the number of TM dopant ions (or changes in the c axis) the superconducting dome exists over a limited range of values of the number of valence electrons added by doping (or values of the a/c ratio). By choosing which combination of dopants is used we can change the relative positions of the upper phase lines and the superconducting dome, even to the extreme limit of suppressing the upper structural and magnetic phase transitions without the stabilization of a lower-temperature superconducting dome.

  6. Microscopic Examinations of Co Valences and Spin States in Electron-Doped LaCoO3

    NASA Astrophysics Data System (ADS)

    Tomiyasu, Keisuke; Koyama, Syun-Ichi; Watahiki, Masanori; Sato, Mika; Nishihara, Kazuki; Takahashi, Yuki; Onodera, Mitsugi; Iwasa, Kazuaki; Nojima, Tsutomu; Nojiri, Hiroyuki; Okamoto, Jun; Huang, Di-Jing; Yamasaki, Yuuichi; Nakao, Hironori; Murakami, Youichi

    2016-09-01

    We studied the Co valences and spin states in electron-doped LaCo1-yTeyO3 by measuring X-ray absorption spectra and electron spin resonance. The low-temperature insulating state involves the low-spin Co3+ state (S = 0) and the high-spin Co2+ state, where the latter is described by g = 3.8 and jeff = 1/2. The results, in concurrence with the electron-hole asymmetry confirmed in the electrical resistivity, coincide with the spin-blockade phenomenon in this system. Furthermore, we discuss the g factor in terms of the strong covalent-bonding nature and consider multiple origins of this phenomenon.

  7. Effect of electron doping on thermoelectric properties for narrow-bandgap intermetallic compound RuGa2

    NASA Astrophysics Data System (ADS)

    Takagiwa, Y.; Kitahara, K.; Kimura, K.

    2013-01-01

    The maximum dimensionless figure of merit, ZTmax, as a function of the chemical potential of the narrow-bandgap intermetallic compound RuGa2 was calculated by using the Boltzmann transport equation with a simple rigid band approach under the constant relaxation time assumption. The calculation, including the effect of the group velocity, indicates that ZTmax over unity would be achieved by electron doping rather than hole doping. Based on this calculation, the effects of Ir substitution for Ru on the thermoelectric properties for RuGa2 have been investigated in the temperature range from 373 K to 973 K. Indeed, a relatively large ZT value of 0.31 for n-type material was obtained in the nominal composition of Ir3.0Ru30.4Ga66.6. The discussion includes the validity of the rigid band approximation and further enhancement of ZT from theoretical and experimental aspects.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  9. Lightning in superconductors

    PubMed Central

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

    2012-01-01

    Crucially important for application of type-II superconductor films is the stability of the vortex matter – magnetic flux lines penetrating the material. If some vortices get detached from pinning centres, the energy dissipated by their motion will facilitate further depinning, and may trigger a massive electromagnetic breakdown. Up to now, the time-resolved behaviour of these ultra-fast events was essentially unknown. We report numerical simulation results revealing the detailed dynamics during breakdown as within nanoseconds it develops branching structures in the electromagnetic fields and temperature, with striking resemblance of atmospheric lightning. During a dendritic avalanche the superconductor is locally heated above its critical temperature, while electrical fields rise to several kV/m as the front propagates at instant speeds near up to 100 km/s. The numerical approach provides an efficient framework for understanding the ultra-fast coupled non-local dynamics of electromagnetic fields and dissipation in superconductor films. PMID:23185691

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

    SciTech Connect

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

    1998-07-28

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

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

    NASA Astrophysics Data System (ADS)

    Barnes, T.

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

  12. Co-existence of spin fluctuation and superconductivity in electron doped cuprate Pr1-xLaCexCuO4

    NASA Astrophysics Data System (ADS)

    Song, Dongjoon; Park, S. R.; Kim, Chul; Choi, S. K.; Jung, W. S.; Koh, Y. Y.; Kim, Y. K.; Eisaki, H.; Yoshida, Y.; Kim, C.

    2012-02-01

    Even though spin fluctuation has been proposed to be as the pairing glue in the cuprate high temperature superconductivity, there is lack of a clear evidence for its coupling to electron. One of the reasons is that, for hole doped cuprates, both anti-ferromagnetism (AFM) and recently proposed charge ordering effects due to Fermi surface nesting occur in the same region of the momentum space (anti-nodal region). On the other hand, electron doped cuprates are known to have the pseudo gap effect at hot spots from AFM band renormalization. This fact makes it advantageous to investigate electron doped cuprates for the spin fluctuation issue. We performed ARPES studies on superconducting electron doped cuprates PLCCO (x=0.1, 0.15, 0.18) to investigate the relation between the spin fluctuation and superconductivity. We observe pseudo gap for all the dopings, which indicates that the short range AFM ordering survives far away from the AFM phase boundary. This coincidence of the short range AFM and superconductivity even in the over doped state may support the spin fluctuation scenarios at least in the electron doped side.

  13. Superconductor materials engineering

    NASA Astrophysics Data System (ADS)

    Shumay, William C., Jr.

    1988-11-01

    The development status of the most promising high-temperature superconducting oxides is discussed with a view to the diversity of the compounds being investigated and the difficulties yet to be surmounted in their fabrication into commercially applicable products such as cables and thin films. Attention is given to R&D expenditures, laser processing methods for novel material phases, optimization methods for bulk superconductors, wire and filament production methods for large systems, explosive processing for matrix compatibility, the use of binders in tape casting and wire-forming, screen-printing of superconductor patterns, and thallium oxide-containing compositions promising higher transition temperatures.

  14. Type-IV Superconductivity Phenomenon: Cooper Pairs with Broken Parity and Spin-Rotational Symmetries in D- and S-wave Singlet Superconductors

    NASA Astrophysics Data System (ADS)

    Lebed, Andrei

    2006-03-01

    Paramagnetic effects are shown to result in the appearance of a triplet component of order parameter in vortex phases of d- and s-wave singlet superconductors in the absence of impurities. This component, which breaks both parity and spin-rotational symmetries of Cooper pairs, is expected to be of the order of unity in a number of modern superconductors such as high-Tc, organic, MgB2, and some others. A generic phase diagram of such type-IV superconductors [1], which are singlet ones at H=0 and in the Meissner phase and characterized by singlet-triplet mixed Copper pairs, δs+iδt, in a vortex phase, is suggested. [1] A.G. Lebed, Physical Review Letters, accepted (2006).

  15. Phase diagram of the Cu-O model in the oxide superconductors: Variational Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Takashi; Koike, Soh; Yamaji, Kunihiko

    2000-07-01

    A variational Monte Carlo method is formulated to study the ground state of the model for the Cu-O plane in the oxide superconductors. The possibility of superconductivity is investigated employing the Gutzwiller-projected BCS and SDW wave functions with respect to dependences on electron density ρ and transfer tpp between neighboring oxygen orbitals. Near half-filling the SDW state is most stable for both the hole and electron doping cases. Away from half-filling when hole doping ratio δ∼0.2, the d-wave superconducting state turns out to be more favorable than the SDW state. The superconducting condensation energy is in reasonable agreement with the experimental value obtained from the critical magnetic field Hc.

  16. Doping Dependent Charge Transfer Gap and Realistic Electronic Model of n-type Cuprate Superconductors

    SciTech Connect

    Xiang, T.

    2010-05-03

    Based on the analysis of the measurement data of angle-resolved photoemission spectroscopy (ARPES) and optics, we show that the charge transfer gap is significantly smaller than the optical one and is reduced by doping in electron doped cuprate superconductors. This leads to a strong charge fluctuation between the Zhang-Rice singlet and the upper Hubbard bands. The basic model for describing this system is a hybridized two-band t-J model. In the symmetric limit where the corresponding intra- and inter-band hopping integrals are equal to each other, this two-band model is equivalent to the Hubbard model with an antiferromagnetic exchange interaction (i.e. the t-U-J model). The mean-field result of the t-U-J model gives a good account for the doping evolution of the Fermi surface and the staggered magnetization.

  17. Quantum phenomena in superconductors

    SciTech Connect

    Clarke, J.

    1987-08-01

    This paper contains remarks by the author on aspects of macroscopic quantum phenomena in superconductors. Some topics discussed are: Superconducting low-inductance undulatory galvanometer (SLUGS), charge imbalance, cylindrical dc superconducting quantum interference device (SQUIDS), Geophysics, noise theory, magnetic resonance with SQUIDS, and macroscopic quantum tunneling. 23 refs., 4 figs. (LSP)

  18. Method for preparing superconductors

    DOEpatents

    Dahlgren, Shelley D.

    1976-01-01

    A superconductor having an equiaxed fine grain beta-tungsten crystalline structure found to have improved high field critical current densities is prepared by sputter-depositing superconductive material onto a substrate cooled to below 200.degree. C. and heat-treating the deposited material.

  19. Paramagnetic Meissner effect of high-temperature granular superconductors: Interpretation by anisotropic and isotropic models

    SciTech Connect

    Chen, F.H. |; Horng, W.C.; Hsu, H.T.; Tseng, T.Y.

    1995-02-01

    The field-cooled magnetization of high-{Tc} superconducting ceramics measured in low magnetic field exhibits the paramagnetic Meissner effect (PME), i.e., the diamagnetic signal initially increases with decrease in temperature but reaches a maximum at temperature T{sub d} and later decreases with decrease in temperature. Even in some samples the signal is ultimately able to transform inversely into a paramagnetic regime once the sample is cooled below a temperature T{sub p} as long as the applied field is sufficiently small. This PME has been observed in various high-{Tc} cuprates and is explained by disparate aspects. An anisotropic model, in which the granular superconductors are assumed to be ideally anisotropic, was first alternatively proposed in the present work so as to theoretically account for this effect. On the other hand, an isotropic model, suitable for granular superconductors with randomly oriented grains, was proposed to deal with the samples prepared by a conventional solid-state reaction method. The anomalous magnetization behavior in the present model was demonstrated to be the superposition of the diamagnetic signal, which occurs as a result of the intragranular shielding currents, over the paramagnetic one due to the induction of the intergranular component induced by these currents where the intergranular one behaved as the effective pinning centers. The PME was demonstrated by this model to exist parasitically in granular superconductors. This intergranular effect is therefore worthy of remark when evaluating the volume fraction of superconductivity for the samples from the Meissner signal, in particular, at a low magnetic field.

  20. Theoretical study of large proximity-induced s -wave-like pairing from a d -wave superconductor

    NASA Astrophysics Data System (ADS)

    Li, Wan-Ju; Chao, Sung-Po; Lee, Ting-Kuo

    2016-01-01

    We use the proximity effect to generate effective topological superconductors by placing metals with strong spin-orbit coupling in contact with a superconductor, aiming to produce Majorana zero modes useful for topologically protected quantum computation. In recent experiments, several quintuple layers of Bi2Se3 were epitaxially grown on the high-Tc material Bi2Sr2CaCu2O8+δ , and conflicting experimental results were reported. We use the standard mean-field approach to study this heterostructure and find it is unlikely to have a large proximity-induced superconducting gap. Despite the seemingly correct temperature dependence, the s -wave gap claimed to be observed may not be purely superconducting in origin. Future work on the proximity-induced bulk superconducting gap and the interfacial band structure should shed light on this issue.

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

    SciTech Connect

    Campuzano, Juan Carlos

    2012-03-07

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

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

    SciTech Connect

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

    2008-01-01

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

  3. Platform for engineering topological superconductors: Superlattices on Rashba superconductors

    NASA Astrophysics Data System (ADS)

    Lu, Yao; He, Wen-Yu; Xu, Dong-Hui; Lin, Nian; Law, K. T.

    2016-07-01

    The search for topological superconductors which support Majorana fermion excitations has been an important topic in condensed matter physics. In this work, we propose an experimental scheme for engineering topological superconductors. In this scheme, by manipulating the superlattice structure of organic molecules placed on top of a superconductor with Rashba spin-orbit coupling, topological superconducting phases can be achieved without or with little fine tuning of the chemical potential. Moreover, superconductors with different Chern numbers can be obtained by changing the superlattice structure of the organic molecules.

  4. Nanostructured organic light-emitting diodes with electronic doping, transparent carbon nanotube charge injectors, and quantum dots

    NASA Astrophysics Data System (ADS)

    Williams, Christopher D.

    Organic light-emitting diodes (OLEDs) and polymeric light-emitting diodes (PLEDs) are rapidly-emerging technologies which are being studied extensively in industrial, academic, and government laboratories for applications in displays and solid-state lighting. Their thin film structure (with total thickness of active layers less than a micron) and the inherent flexibility of the constituent materials give them promise in the flat panel display industry as well as open new areas of possible applications for flexible transparent displays and even textile displays. The materials also show high electroluminescence efficiency, and with proper device engineering these devices demonstrate efficiencies and lifetimes which surpass current methods of lighting such at incandescent bulbs, which average approximately 1% efficiency. Lastly, the materials offer easy processing through well studied and developed methods such as thermal evaporation, solution spin-casting and ink jet printing. Ink jet printing of polymeric layers in PLEDs offers many advantages when considering mass production of display and lighting panels, as it allows uniform films to be produced on large area substrates using a simple roll-to-roll method. In this dissertation, we discuss several new methods and procedures which we have developed and used to produce OLEDs and PLEDs. More specifically these are electronic doping of transport layers, fluorescent doping of emissive layers by semiconductor nanocrystals (NC) (also known as quantum dots (QD)), and electrode engineering, namely by the use of transparent carbon nanotube sheets as charge injectors. We expand on the existing field of molecular doping and introduce a doped device with a very thick hole transport layer. Such a device is more resistant to failure due to excessive current density. We also investigate the effects of the presence of dopant molecules in the emissive layer of a multilayer OLED. This portion of the work introduces the negative

  5. "Fluctuoscopy" of Superconductors

    NASA Astrophysics Data System (ADS)

    Varlamov, A. A.

    Study of fluctuation phenomena in superconductors (SCs) is the subject of great fundamental and practical importance. Understanding of their physics allowed to clear up the fundamental properties of SC state. Being predicted in 1968, one of the fluctuation effects, namely paraconductivity, was experimentally observed almost simultaneously. Since this time, fluctuations became a noticeable part of research in the field of superconductivity, and a variety of fluctuation effects have been discovered. The new wave of interest to fluctuations (FL) in superconductors was generated by the discovery of cuprate oxide superconductors (high-temperature superconductors, HTS), where, due to extremely short coherence length and low effective dimensionality of the electron system, superconductive fluctuations manifest themselves in a wide range of temperatures. Moreover, anomalous properties of the normal state of HTS were attributed by many theorists to strong FL in these systems. Being studied in the framework of the phenomenological Ginzburg-Landau theory and, more extensively, in diagrammatic microscopic approach, SC FLs side by side with other quantum corrections (weak localization, etc.) became a new tool for investigation and characterization of such new systems as HTS, disordered electron systems, granular metals, Josephson structures, artificial super-lattices, etc. The characteristic feature of SC FL is their strong dependence on temperature and magnetic fields in the vicinity of phase transition. This allows one to definitely separate the fluctuation effects from other contributions and to use them as the source of information about the microscopic parameters of a material. By their origin, SC FLs are very sensitive to relaxation processes, which break phase coherence. This allows using them for versatile characterization of SC. Today, one can speak about the " fluctuoscopy" of superconductive systems. In review, we present the qualitative picture both of thermodynamic

  6. Superconductor stability 90: A review

    SciTech Connect

    Dresner, L.

    1990-01-01

    This paper reviews some recent developments in the field of stability of superconductors. The main topics dealt with are hydrodynamic phenomena in cable-in-conduit superconductors, namely, multiple stability, quench pressure, thermal expulsion, and thermal hydraulic quenchback, traveling normal zones in large, composite conductors, such as those intended for SMES, and the stability of vapor-cooled leads made of high-temperature superconductors. 31 refs., 5 figs.

  7. Ambient-pressure organic superconductor

    DOEpatents

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

    1986-01-01

    A new class of organic superconductors having the formula (ET).sub.2 MX.sub.2 wherein ET represents bis(ethylenedithio)-tetrathiafulvalene, M is a metal such as Au, Ag, In, Tl, Rb, Pd and the like and X is a halide. The superconductor (ET).sub.2 AuI.sub.2 exhibits a transition temperature of 5 K which is high for organic superconductors.

  8. Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca0.9La0.1FeAs2

    NASA Astrophysics Data System (ADS)

    Liu, Z. T.; Xing, X. Z.; Li, M. Y.; Zhou, W.; Sun, Y.; Fan, C. C.; Yang, H. F.; Liu, J. S.; Yao, Q.; Li, W.; Shi, Z. X.; Shen, D. W.; Wang, Z.

    2016-07-01

    CaFeAs2 is a parent compound of recently discovered 112-type iron-based superconductors. It is predicted to be a staggered intercalation compound that naturally integrates both quantum spin Hall insulating and superconducting layers and an ideal system for the realization of Majorana modes. We performed a systematical angle-resolved photoemission spectroscopy and first-principles calculation study of the slightly electron-doped CaFeAs2. We found that the zigzag As chain of 112-type iron-based superconductors play a considerable role in the low-energy electronic structure, resulting in the characteristic Dirac-cone like band dispersion as the prediction. Our experimental results further confirm that these Dirac cones only exist around the X but not Y points in the Brillouin zone, breaking the S4 symmetry at iron sites. Our findings present the compelling support to the theoretical prediction that the 112-type iron-based superconductors might host the topological nontrivial edge states. The slightly electron doped CaFeAs2 would provide us a unique opportunity to realize and explore Majorana fermion physics.

  9. Vortex cutting in superconductors

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  10. Overview of organic superconductors

    SciTech Connect

    Mori, Hatsumi . Nagoya Division)

    1994-01-10

    Organic materials which are usually used for insulators, were shown to be an electrical conductor by H. Akamatsu, H. Inokuchi, and Y. Matsunaga in 1954. Moreover, J.P. Ferraris et al. showed that TTF [center dot] TCNQ was stably metallic down to around 60 K in 1973. Because of a low dimensionality of organic compound, however, a stabilization of an electronic state and a destabilization of a periodic lattice constructed a charge density wave which led a metal-insulator transition (a Peierls transition). After overcoming this low dimensionality, D. Jerome et al. discovered the first organic superconductor, (TMTSF)[sub 2] PF[sub 6] ([Tc] = 0.9 K (12kbar)) in 1980. Then with the resisting up of [Tc] constantly, the superconductor [kappa]-(BEDT-TTF)[sub 2](NCS)[sub 2] ([Tc] = 10.4 K) was found in 1987 and the [Tc] of [kappa]-(BEDT-TTF)[sub 2]Cu[N(CN)[sub 2

  11. Probing Topological Superconductors

    NASA Astrophysics Data System (ADS)

    Schmeltzer, David

    2015-03-01

    The presence of attractive interaction on the surface of a 3D topological insulator which is characterized by spinors carrying a Berry phase of π gives rise to superconductivity that support space time half vortices (Majorana zero modes). We construct the effective dual action for the superconductor with the vortices, and show that the 2 n Majorana fermions are localized and can be replaced with n spinless fermions. The effect of the Majorana zero modes can be observed trough the the Andreev cross reflection when metallic leads are attached to the superconductor. The presence of the Majorana fermions can be detected with transverse sound waves. We have computed the effect of elastic strain fields and obtain an anomalous response indicating the presence of the Majorana fermions.

  12. Analytic holographic superconductor

    NASA Astrophysics Data System (ADS)

    Herzog, Christopher P.

    2010-06-01

    We investigate a holographic superconductor that admits an analytic treatment near the phase transition. In the dual 3+1-dimensional field theory, the phase transition occurs when a scalar operator of scaling dimension two gets a vacuum expectation value. We calculate current-current correlation functions along with the speed of second sound near the critical temperature. We also make some remarks about critical exponents. An analytic treatment is possible because an underlying Heun equation describing the zero mode of the phase transition has a polynomial solution. Amusingly, the treatment here may generalize for an order parameter with any integer spin, and we propose a Lagrangian for a spin-two holographic superconductor.

  13. Electron doping evolution of structural and antiferromagnetic phase transitions in NaFe1 -xCoxAs iron pnictides

    NASA Astrophysics Data System (ADS)

    Tan, Guotai; Song, Yu; Zhang, Chenglin; Lin, Lifang; Xu, Zhuang; Hou, Tingting; Tian, Wei; Cao, Huibo; Li, Shiliang; Feng, Shiping; Dai, Pengcheng

    2016-07-01

    We use transport and neutron diffraction to study the electronic phase diagram of NaFe1 -xCoxAs . In the undoped state, NaFeAs exhibits a tetragonal-to-orthorhombic structural transition below Ts followed by a collinear antiferromagnetic (AF) order below TN. Upon codoping to form NaFe1 -xCoxAs ,Ts and TN are gradually suppressed, leading to optimal superconductivity near Co-doping x =0.025 . While transport experiments on these materials reveal an anomalous behavior suggesting the presence of a quantum critical point (QCP) near optimal superconductivity, our neutron diffraction results indicate that commensurate AF order becomes transversely incommensurate with TN>Tc before vanishing abruptly at optimal superconductivity. These results are remarkably similar to electron-doping and isovalent-doping evolution of the AF order in BaFe2 -xNixAs2 and BaFe2(As1 -xPx)2 , thus suggesting a universal behavior in the suppression of the magnetic order in iron pnictides as superconductivity is induced.

  14. On the character of the coherent and incoherent excitations of electron-doped SrTiO3

    NASA Astrophysics Data System (ADS)

    Ishida, Yukiaki; Eguchi, Ritsuko; Matsunami, Masaharu; Horiba, Koji; Taguchi, Munetaka; Chainani, Ashishi; Senba, Yasunori; Ohashi, Haruhiko; Ohta, Hiromichi; Shin, Shik

    2007-03-01

    Lightly-electron-doped SrTiO3 shows little sign of electron correlation effects in the transport and thermodynamic properties, but photoemission spectra show not only coherent excitations from the Fermi level but also broad incoherent excitations positioned ˜1.5 eV below the Fermi level [1]. We have investigated the near-EF electronic structures of Nb-doped SrTiO3 thin film [2] by performing resonant photoemission at the Ti 2p and O 1s absorption edges. Both the coherent and incoherent excitations showed giant resonances at the Ti 2p edge, while at the O 1s edge, resonance occurred mainly in the incoherent excitations. This indicates that the coherent excitations have mainly Ti 3d character, while the incoherent excitations have mixed character of Ti 3d and O 2p states. We attribute the incoherent and coherent excitations to locally and non-locally screened final states, respectively, similar to that argued in Ca1-xSrxVO3 [3]. [1] A. Fujimori et al., Phys. Rev. B 46, 9841 (1992). [2] S. Ohta, H. Ohta et al., Appl. Phys. Lett. 87, 092108 (2006). [3] R.J.O. Mossanek, M. Abbate, and A. Fujimori, cond-mat/0606253.

  15. Superconductivity below 20 K in heavily electron-doped surface layer of FeSe bulk crystal.

    PubMed

    Seo, J J; Kim, B Y; Kim, B S; Jeong, J K; Ok, J M; Kim, Jun Sung; Denlinger, J D; Mo, S-K; Kim, C; Kim, Y K

    2016-01-01

    A superconducting transition temperature (Tc) as high as 100 K was recently discovered in one monolayer FeSe grown on SrTiO3. The discovery ignited efforts to identify the mechanism for the markedly enhanced Tc from its bulk value of 8 K. There are two main views about the origin of the Tc enhancement: interfacial effects and/or excess electrons with strong electron correlation. Here, we report the observation of superconductivity below 20 K in surface electron-doped bulk FeSe. The doped surface layer possesses all the key spectroscopic aspects of the monolayer FeSe on SrTiO3. Without interfacial effects, the surface layer state has a moderate Tc of 20 K with a smaller gap opening of 4.2 meV. Our results show that excess electrons with strong correlation cannot induce the maximum Tc, which in turn reveals the need for interfacial effects to achieve the highest Tc in one monolayer FeSe on SrTiO3. PMID:27050161

  16. Enhanced carrier collection efficiency and reduced quantum state absorption by electron doping in self-assembled quantum dot solar cells

    SciTech Connect

    Li, Tian E-mail: dage@ece.umd.edu; Dagenais, Mario E-mail: dage@ece.umd.edu; Lu, Haofeng; Fu, Lan; Tan, Hark Hoe; Jagadish, Chennupati

    2015-02-02

    Reduced quantum dot (QD) absorption due to state filling effects and enhanced electron transport in doped QDs are demonstrated to play a key role in solar energy conversion. Reduced QD state absorption with increased n-doping is observed in the self-assembled In{sub 0.5}Ga{sub 0.5}As/GaAs QDs from high resolution below-bandgap external quantum efficiency (EQE) measurement, which is a direct consequence of the Pauli exclusion principle. We also show that besides partial filling of the quantum states, electron-doping produces negatively charged QDs that exert a repulsive Coulomb force on the mobile electrons, thus altering the electron trajectory and reducing the probability of electron capture, leading to an improved collection efficiency of photo-generated carriers, as indicated by an absolute above-bandgap EQE measurement. The resulting redistribution of the mobile electron in the planar direction is further validated by the observed photoluminescence intensity dependence on doping.

  17. Superconductivity below 20 K in heavily electron-doped surface layer of FeSe bulk crystal

    PubMed Central

    Seo, J. J.; Kim, B. Y.; Kim, B. S.; Jeong, J. K.; Ok, J. M.; Kim, Jun Sung; Denlinger, J. D.; Mo, S. -K.; Kim, C.; Kim, Y. K.

    2016-01-01

    A superconducting transition temperature (Tc) as high as 100 K was recently discovered in one monolayer FeSe grown on SrTiO3. The discovery ignited efforts to identify the mechanism for the markedly enhanced Tc from its bulk value of 8 K. There are two main views about the origin of the Tc enhancement: interfacial effects and/or excess electrons with strong electron correlation. Here, we report the observation of superconductivity below 20 K in surface electron-doped bulk FeSe. The doped surface layer possesses all the key spectroscopic aspects of the monolayer FeSe on SrTiO3. Without interfacial effects, the surface layer state has a moderate Tc of 20 K with a smaller gap opening of 4.2 meV. Our results show that excess electrons with strong correlation cannot induce the maximum Tc, which in turn reveals the need for interfacial effects to achieve the highest Tc in one monolayer FeSe on SrTiO3. PMID:27050161

  18. Superconductivity below 20 K in heavily electron-doped surface layer of FeSe bulk crystal

    NASA Astrophysics Data System (ADS)

    Seo, J. J.; Kim, B. Y.; Kim, B. S.; Jeong, J. K.; Ok, J. M.; Kim, Jun Sung; Denlinger, J. D.; Mo, S.-K.; Kim, C.; Kim, Y. K.

    2016-04-01

    A superconducting transition temperature (Tc) as high as 100 K was recently discovered in one monolayer FeSe grown on SrTiO3. The discovery ignited efforts to identify the mechanism for the markedly enhanced Tc from its bulk value of 8 K. There are two main views about the origin of the Tc enhancement: interfacial effects and/or excess electrons with strong electron correlation. Here, we report the observation of superconductivity below 20 K in surface electron-doped bulk FeSe. The doped surface layer possesses all the key spectroscopic aspects of the monolayer FeSe on SrTiO3. Without interfacial effects, the surface layer state has a moderate Tc of 20 K with a smaller gap opening of 4.2 meV. Our results show that excess electrons with strong correlation cannot induce the maximum Tc, which in turn reveals the need for interfacial effects to achieve the highest Tc in one monolayer FeSe on SrTiO3.

  19. Holographic Superconductor Vortices

    SciTech Connect

    Montull, Marc; Pomarol, Alex; Silva, Pedro J.

    2009-08-28

    A gravity dual of a superconductor at finite temperature has been recently proposed. We present the vortex configuration of this model and study its properties. In particular, we calculate the free energy as a function of an external magnetic field, the magnetization, and the superconducting density. We also find the two critical magnetic fields that define the region in which the vortex configurations are energetically favorable.

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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