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Sample records for enhanced superconducting pairing

  1. Enhanced superconducting pairing interaction in indium-doped tin telluride

    SciTech Connect

    Erickson, A.S.; Chu, J.-H.; Toney, M.F.; Geballe, T.H.; Fisher, I.R.; /SLAC, SSRL /Stanford U., Appl. Phys. Dept. /Stanford U., Geballe Lab.

    2010-02-15

    The ferroelectric degenerate semiconductor Sn{sub 1-{delta}}Te exhibits superconductivity with critical temperatures, T{sub c}, of up to 0.3 K for hole densities of order 10{sup 21} cm{sup -3}. When doped on the tin site with greater than x{sub c} = 1.7(3)% indium atoms, however, superconductivity is observed up to 2 K, though the carrier density does not change significantly. We present specific heat data showing that a stronger pairing interaction is present for x > x{sub c} than for x < x{sub c}. By examining the effect of In dopant atoms on both T{sub c} and the temperature of the ferroelectric structural phase transition, T{sub SPT}, we show that phonon modes related to this transition are not responsible for this T{sub c} enhancement, and discuss a plausible candidate based on the unique properties of the indium impurities.

  2. Enhanced superconducting pairing interaction in indium-doped tin telluride

    SciTech Connect

    Erickson, A.S.

    2010-05-03

    The ferroelectric degenerate semiconductor Sn{sub 1-{delta}}Te exhibits superconductivity with critical temperatures, T{sub c}, of up to 0.3 K for hole densities of order 10{sup 21} cm{sup -3}. When doped on the tin site with greater than x{sub c} = 1.7(3)% indium atoms, however, superconductivity is observed up to 2 K, though the carrier density does not change significantly. We present specific heat data showing that a stronger pairing interaction is present for x > x{sub c} than for x < x{sub c}. By examining the effect of In dopant atoms on both T{sub c} and the temperature of the ferroelectric structural phase transition, T{sub SPT}, we show that phonon modes related to this transition are not responsible for this T{sub c} enhancement, and discuss a plausible candidate based on the unique properties of the indium impurities.

  3. Superconducting-state enhancement of thermal conductivity in the cuprates: Correlation with the pair density

    SciTech Connect

    Cohn, J.L.

    1996-02-01

    The systematics of the superconducting-state enhancements of in-plane thermal conductivity for YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}} (Y-123), Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}, Tl{sub 2}Ba{sub 2}CuO{sub 6}, and La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4} single crystals are examined. For Y-123 the enhancements are shown to correlate with specific-heat jumps, a measure of the superconducting pair density. The substantially larger enhancements observed for Y-123 are attributed to the condensate arising from oxygen-filled CuO chains. We discuss the constraints imposed by measurements of microwave conductivity on the electronic contribution to this phenomenon.

  4. Electron pairing without superconductivity.

    PubMed

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C Stephen; Levy, Jeremy

    2015-05-14

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances-paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. PMID:25971511

  5. Electron pairing without superconductivity

    NASA Astrophysics Data System (ADS)

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P.; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C. Stephen; Levy, Jeremy

    2015-05-01

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity.

  6. Electron pairing without superconductivity

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. Support from AFOSR, ONR, ARO, NSF, DOE and NSSEFF is gratefully acknowledged.

  7. Electron Pairing Without Superconductivity

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy; Cheng, G.; Tomczyk, M.; Lu, S.; Veazey, J. P.; Huang, M.; Irvin, P.; Ryu, S.; Lee, H.; Eom, C.-B.; Hellberg, C. S.

    2015-03-01

    Strontium titanate (SrTiO3) exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. We describe transport experiments with nanowire-based quantum dots localized at the interface between SrTiO3 and LaAlO3. Electrostatic gating of the quantum dot reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical magnetic field Bp 1-4 Tesla, an order of magnitude larger than the superconducting critical magnetic field. For B Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as T = 900 mK, far above the superconducting transition temperature (Tc 300 mK). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by an attractive-U Hubbard model that describes real-space electron pairing as a precursor to superconductivity. This work was supported by ARO MURI W911NF-08-1-0317 (J.L.), AFOSR MURI FA9550-10-1-0524 (C.-B.E., J.L.) and FA9550-12-1-0342 (C.-B.E.), and grants from the National Science Foundation DMR-1104191 (J.L.), DMR.

  8. Coulomb enhancement of superconducting pair-pair correlations in a 3/4 -filled model for κ -(BEDT-TTF)2X

    NASA Astrophysics Data System (ADS)

    De Silva, W. Wasanthi; Gomes, N.; Mazumdar, S.; Clay, R. T.

    2016-05-01

    We present the results of precise correlated-electron calculations on the monomer lattices of the organic charge-transfer solids κ -(BEDT-TTF) 2X for 32 and 64 molecular sites. Our calculations are for band parameters corresponding to X =Cu[N (CN) 2]Cl and Cu2(CN) 3, which are semiconducting antiferromagnetic and quantum spin liquid, respectively, at ambient pressure. We have performed our calculations for variable electron densities ρ per BEDT-TTF molecule, with ρ ranging from 1 to 2. We find that d -wave superconducting pair-pair correlations are enhanced by electron-electron interactions only for a narrow carrier concentration about ρ =1.5 , which is precisely the carrier concentration where superconductivity in the charge-transfer solids occurs. Our results indicate that the enhancement in pair-pair correlations is not related to antiferromagnetic order, but to a proximate hidden spin-singlet state that manifests itself as a charge-ordered state in other charge-transfer solids. Long-range superconducting order does not appear to be present in the purely electronic model, suggesting that electron-phonon interactions also must play a role in a complete theory of superconductivity.

  9. Enhanced Cooper pairing versus suppressed phase coherence shaping the superconducting dome in coupled aluminum nanograins

    NASA Astrophysics Data System (ADS)

    Pracht, Uwe S.; Bachar, Nimrod; Benfatto, Lara; Deutscher, Guy; Farber, Eli; Dressel, Martin; Scheffler, Marc

    2016-03-01

    The development of the fundamental superconducting (SC) energy scales—the SC energy gap Δ and the superfluid stiffness J —of granular aluminum, i.e., thin films composed of coupled nanograins, is studied by means of optical THz spectroscopy. Starting from well-coupled grains, Δ grows as the grains are progressively decoupled, causing the unconventional increase of Tc with sample resistivity. When the grain coupling is suppressed further, Δ saturates while the critical temperature Tc decreases, concomitantly with a sharp decline of J , delimiting a SC dome in the phase diagram. This crossover to a phase-driven SC transition is accompanied by an optical gap surviving into the normal state above Tc. We demonstrate that granular aluminum is an ideal testbed to understand the interplay between quantum confinement and global SC phase coherence due to nanoinhomogeneity.

  10. Superconductivity: A celebration of pairs

    NASA Astrophysics Data System (ADS)

    Norman, Michael R.

    2007-12-01

    It is fifty years since John Bardeen, Leon Cooper and Bob Schrieffer presented the microscopic theory of superconductivity. At a wonderful conference in Urbana the 'good old days' were remembered, and the challenges ahead surveyed.

  11. Charge Aspects of Composite Pair Superconductivity

    NASA Astrophysics Data System (ADS)

    Flint, Rebecca

    2014-03-01

    Conventional Cooper pairs form from well-defined electronic quasiparticles, making the internal structure of the pair irrelevant. However, in the 115 family of superconductors, the heavy electrons are forming as they pair and the internal pair structure becomes as important as the pairing mechanism. Conventional spin fluctuation mediated pairing cannot capture the direct transition from incoherent local moments to heavy fermion superconductivity, but the formation of composite pairs favored by the two channel Kondo effect can. These composite pairs are local d-wave pairs formed by two conduction electrons in orthogonal Kondo channels screening the same local moment. Composite pairing shares the same symmetries as magnetically mediated pairing, however, only composite pairing necessarily involves a redistribution of charge within the unit cell originating from the internal pair structure, both as a monopole (valence change) and a quadrupole effect. This redistribution will onset sharply at the superconducting transition temperature. A smoking gun test for composite pairing is therefore a sharp signature at Tc - for example, a cusp in the Mossbauer isomer shift in NpPd5Al2 or in the NQR shift in (Ce,Pu)CoIn5.

  12. Superconductivity in CuCl/Si superlattices: excitonic pairing?

    NASA Astrophysics Data System (ADS)

    Rhim, S. H.; Saniz, Rolando; Weinert, Michael; Freeman, A. J.

    2013-03-01

    Two-dimensional (2D) hetero-bonded semiconductor interfaces have been suggested as candidate geometries where excitonic superconductivity [2] - and the greatly enhanced where TC compared to phonon mechanisms mediation - can be realized. Among experimental efforts, epitaxially grown CuCl on Si (111) has reportedly exhibited excitonic superconductivity at 60 ~150 K. Our first-principles calculations confirm 2D metallicity at the interfaces due to charge transfer by valence mismatch. [3] The excitonic mechanism is investigated by calculating the kernel function, K (ω) , for the average of the electronic contributions to the effective interaction.[4] The attractive interaction found in the CuCl/Si superlattice indicates the feasibility of excitonic pairing for a certain frequency range. US Department of Energy (DE-FG02-05ER45372)

  13. Topological superconductivity and unconventional pairing in oxide interfaces

    NASA Astrophysics Data System (ADS)

    Scheurer, Mathias S.; Schmalian, Jörg

    2015-01-01

    Pinpointing the microscopic mechanism for superconductivity has proven to be one of the most outstanding challenges in the physics of correlated quantum matter. Thus far, the most direct evidence for an electronic pairing mechanism is the observation of a new symmetry of the order parameter, as done in the cuprate high-temperature superconductors. Alternatively, global, topological invariants allow for a sharp discrimination between states of matter that cannot be transformed into each other adiabatically. Here we propose an unconventional pairing state for the electron fluid in two-dimensional oxide interfaces and establish a direct link to the emergence of non-trivial topological invariants. Topological signatures, in particular Majorana edge states, can then be used to detect the microscopic origin of superconductivity. In addition, we show that also the density wave states that compete with superconductivity sensitively depend on the nature of the pairing interaction.

  14. Topological superconductivity and unconventional pairing in oxide interfaces.

    PubMed

    Scheurer, Mathias S; Schmalian, Jörg

    2015-01-01

    Pinpointing the microscopic mechanism for superconductivity has proven to be one of the most outstanding challenges in the physics of correlated quantum matter. Thus far, the most direct evidence for an electronic pairing mechanism is the observation of a new symmetry of the order parameter, as done in the cuprate high-temperature superconductors. Alternatively, global, topological invariants allow for a sharp discrimination between states of matter that cannot be transformed into each other adiabatically. Here we propose an unconventional pairing state for the electron fluid in two-dimensional oxide interfaces and establish a direct link to the emergence of non-trivial topological invariants. Topological signatures, in particular Majorana edge states, can then be used to detect the microscopic origin of superconductivity. In addition, we show that also the density wave states that compete with superconductivity sensitively depend on the nature of the pairing interaction. PMID:25629433

  15. Nonequilibrium enhancement of Cooper pairing in cold fermion systems

    SciTech Connect

    Robertson, Andrew; Galitski, Victor M.

    2009-12-15

    Nonequilibrium stimulation of superfluidity in trapped Fermi gases is discussed by analogy to the work of Eliashberg [Nonequilibrium Superconductivity, edited by D. N. Langenberg and A. I. Larkin (North-Holland, New York, 1986)] on the microwave enhancement of superconductivity. Optical excitation of the fermions balanced by heat loss due to thermal contact with a boson bath and/or evaporative cooling enables stationary nonequilibrium states to exist. Such a state manifests as a shift of the quasiparticle spectrum to higher energies and this effectively raises the pairing transition temperature. As an illustration, we calculate the effective enhancement of Cooper pairing and superfluidity in both the normal and superfluid phases for a mixture of {sup 87}Rb and {sup 6}Li in the limit of small departure from equilibrium. It is argued that in experiment the desirable effect is not limited to such small perturbations and the effective enhancement of the pairing temperature may be quite large.

  16. Signature of Cooper pairs in the non-superconducting phases of amorphous superconducting tantalum films

    NASA Astrophysics Data System (ADS)

    Li, Yize Stephanie

    2015-02-01

    We have studied the magnetic field or disorder induced insulating and metallic phases in amorphous Ta superconducting thin films. The evolution of the nonlinear transport in the insulating phase exhibits a non-monotonic behavior as the magnetic field is increased. We suggest that this observation could be evidence of the presence of localized Cooper pairs in the insulating phase. As the metallic phase intervenes the superconducting and insulating states in Ta films, this result further reveals that Cooper pairs also exist in the metallic ground state.

  17. Cooper-pair propagation and superconducting correlations in graphene

    NASA Astrophysics Data System (ADS)

    González, J.; Perfetto, E.

    2007-10-01

    We investigate the Cooper-pair propagation and the Josephson effect in graphene under conditions in which the distance L between superconducting electrodes is much larger than the width W of the contacts. In the case of undoped graphene, we show that supercurrents may exist with a spatial decay proportional to W2/L3 , reminiscent of the behavior of the critical current in disordered normal metals. We observe that there is in general a crossover temperature T*˜vF/kBL that marks the onset of the strong decay of the supercurrent and that corresponds to the scale above which the Cooper pairs are disrupted by thermal effects during their propagation. We also show that the spatial decay of the critical current changes upon doping into a 1/L2 behavior, opening the possibility to observe a supercurrent over length scales above 1μm at suitable doping levels.

  18. Broadband illumination of superconducting pair breaking photon detectors

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Understanding the detailed behaviour of superconducting pair breaking photon detectors such as Kinetic Inductance Detectors (KIDs) requires knowledge of the nonequilibrium quasiparticle energy distributions. We have previously calculated the steady state distributions resulting from uniform absorption of monochromatic sub gap and above gap frequency radiation by thin films. In this work, we use the same methods to calculate the effect of illumination by broadband sources, such as thermal radiation from astrophysical phenomena or from the readout system. Absorption of photons at multiple above gap frequencies is shown to leave unchanged the structure of the quasiparticle energy distribution close to the superconducting gap. Hence for typical absorbed powers, we find the effects of absorption of broadband pair breaking radiation can simply be considered as the sum of the effects of absorption of many monochromatic sources. Distribution averaged quantities, like quasiparticle generation efficiency η, match exactly a weighted average over the bandwidth of the source of calculations assuming a monochromatic source. For sub gap frequencies, however, distributing the absorbed power across multiple frequencies does change the low energy quasiparticle distribution. For moderate and high absorbed powers, this results in a significantly larger η-a higher number of excess quasiparticles for a broadband source compared to a monochromatic source of equal total absorbed power. Typically in KIDs the microwave power absorbed has a very narrow bandwidth, but in devices with broad resonance characteristics (low quality factors), this increase in η may be measurable.

  19. Pair density wave superconducting states and statistical mechanics of dimers

    NASA Astrophysics Data System (ADS)

    Soto Garrido, Rodrigo Andres

    The following thesis is divided in two main parts. Chapters 2, 3 and 4 are devoted to the study of the so called pair-density-wave (PDW) superconducting state and some of its connections to electronic liquid crystal (ELC) phases, its topological aspects in a one dimensional model and its appearance in a quasi-one dimensional system. On the other hand, chapter 5 is focused on the investigation of the classical statistical mechanics properties of dimers, in particular, the dimer model on the Aztec diamond graph and its relation with the octahedron equation. In chapter 2 we present a theory of superconducting states where the Cooper pairs have a nonzero center-of-mass momentum, inhomogeneous superconducting states known as a pair-density-waves (PDWs) states. We show that in a system of spin-1/2 fermions in two dimensions in an electronic nematic spin-triplet phase where rotational symmetry is broken in both real and spin space PDW phases arise naturally in a theory that can be analysed using controlled approximations. We show that several superfluid phases that may arise in this phase can be treated within a controlled BCS mean field theory, with the strength of the spin-triplet nematic order parameter playing the role of the small parameter of this theory. We find that in a spin-triplet nematic phase, in addition to a triplet p-wave and spin-singlet d-wave (or s depending on the nematic phase) uniform superconducting states, it is also possible to have a d-wave (or s) PDW superconductor. The PDW phases found here can be either unidirectional, bidirectional, or tridirectional depending on the spin-triplet nematic phase and which superconducting channel is dominant. In addition, a triple-helix state is found in a particular channel. We show that these PDW phases are present in the weak-coupling limit, in contrast to the usual Fulde-Ferrell-Larkin-Ovchinnikov phases, which require strong coupling physics in addition to a large magnetic field (and often both). In chapter

  20. Ising pairing in superconducting NbSe2 atomic layers

    NASA Astrophysics Data System (ADS)

    Xi, Xiaoxiang; Wang, Zefang; Zhao, Weiwei; Park, Ju-Hyun; Law, Kam Tuen; Berger, Helmuth; Forró, László; Shan, Jie; Mak, Kin Fai

    2016-02-01

    The properties of two-dimensional transition metal dichalcogenides arising from strong spin-orbit interactions and valley-dependent Berry curvature effects have recently attracted considerable interest. Although single-particle and excitonic phenomena related to spin-valley coupling have been extensively studied, the effects of spin-valley coupling on collective quantum phenomena remain less well understood. Here we report the observation of superconducting monolayer NbSe2 with an in-plane upper critical field of more than six times the Pauli paramagnetic limit, by means of magnetotransport measurements. The effect can be interpreted in terms of the competing Zeeman effect and large intrinsic spin-orbit interactions in non-centrosymmetric NbSe2 monolayers, where the electron spin is locked to the out-of-plane direction. Our results provide strong evidence of unconventional Ising pairing protected by spin-momentum locking, and suggest further studies of non-centrosymmetric superconductivity with unique spin and valley degrees of freedom in the two-dimensional limit.

  1. Enhancing superconducting critical current by randomness

    NASA Astrophysics Data System (ADS)

    Wang, Y. L.; Thoutam, L. R.; Xiao, Z. L.; Shen, B.; Pearson, J. E.; Divan, R.; Ocola, L. E.; Crabtree, G. W.; Kwok, W. K.

    2016-01-01

    The key ingredient of high critical currents in a type-II superconductor is defect sites that pin vortices. Contrary to earlier understanding on nanopatterned artificial pinning, here we show unequivocally the advantages of a random pinscape over an ordered array in a wide magnetic field range. We reveal that the better performance of a random pinscape is due to the variation of its local density of pinning sites (LDOPS), which mitigates the motion of vortices. This is confirmed by achieving even higher enhancement of the critical current through a conformally mapped random pinscape, where the distribution of the LDOPS is further enlarged. The demonstrated key role of LDOPS in enhancing superconducting critical currents gets at the heart of random versus commensurate pinning. Our findings highlight the importance of random pinscapes in enhancing the superconducting critical currents of applied superconductors.

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

    NASA Technical Reports Server (NTRS)

    Chakraverty, B. K.

    1991-01-01

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

  3. Local and nonlocal conductance enhancement due to Cooper pair splitting

    NASA Astrophysics Data System (ADS)

    Wei, Jian; Chandrasekhar, V.

    2012-12-01

    Enhanced local conductance due to Andreev reflection is well known for high transparency Normal metal-Superconductor (NS) interface. For low transparency NS junctions, observation of two-electron tunneling contribution (enhanced Andreev reflection) to current was also reported previously. In our recent work [J Wei and V Chandrasekhar, Nat. Phys. 6, 494 (2010)], for a three-terminal Cooper pair splitter geometry, i.e., with two closely placed NS junctions sharing the same S terminal, we were able do a 2D scan of both local and nonlocal differential resistance, since for our ideal tunneling junctions there is little current redistribution (flow from one normal-metal lead to the other via the superconducting lead). In contrast to previous 1D nonlocal resistance measurements, 2D scans clearly show regime with pronounced contribution of the nonlocal processes to both local and nonlocal conductance enhancement. The enhanced local conductance and negative nonlocal resistance are consistent with enhanced Cooper pair splitting, and dynamical Coulomb blockade could be the origin of this enhancement.

  4. The η-Pairing Superconductivity in Spin-Density Wave Background

    NASA Astrophysics Data System (ADS)

    X, M. Qiu; Z, J. Wang

    1993-10-01

    In this letter, we propose a modified attractive Hubbard model at half filling that can exhibit superconductivity through η-pairing mechanism in spin-density wave representation and derive a concise relationship between the energy disparity and the single-particle energy spectrum. This relationship, in the two limits of U, clearly shows that the system does not display superconductivity for very low doping concentration. but demonstrates superconductivity when the doping concentration exceeds a certain critical value. This conclusion is in qualitative agreement with the familiar experiments on high-Tc superconductivity.

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

    PubMed

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

    2016-01-01

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

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Eremin, Ilya

    2009-03-01

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

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

    DOE PAGESBeta

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

    2016-07-28

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

  10. Separating pairing from quantum phase coherence dynamics above the superconducting transition by femtosecond spectroscopy

    PubMed Central

    Madan, I.; Kurosawa, T.; Toda, Y.; Oda, M.; Mertelj, T.; Kusar, P.; Mihailovic, D.

    2014-01-01

    In classical superconductors an energy gap and phase coherence appear simultaneously with pairing at the transition to the superconducting state. In high-temperature superconductors, the possibility that pairing and phase coherence are distinct and independent processes has led to intense experimental search of their separate manifestations. Using femtosecond spectroscopy methods we now show that it is possible to clearly separate fluctuation dynamics of the superconducting pairing amplitude from the phase relaxation above the critical transition temperature. Empirically establishing a close correspondence between the superfluid density measured by THz spectroscopy and superconducting optical pump-probe response over a wide region of temperature, we find that in differently doped Bi2Sr2CaCu2O8+δ crystals the pairing gap amplitude monotonically extends well beyond Tc, while the phase coherence shows a pronounced power-law divergence as T → Tc, thus showing that phase coherence and gap formation are distinct processes which occur on different timescales. PMID:25014162

  11. Enhancing bulk superconductivity by engineering granular materials

    NASA Astrophysics Data System (ADS)

    Mayoh, James; García García, Antonio

    2014-03-01

    The quest for higher critical temperatures is one of the main driving forces in the field of superconductivity. Recent theoretical and experimental results indicate that quantum size effects in isolated nano-grains can boost superconductivity with respect to the bulk limit. Here we explore the optimal range of parameters that lead to an enhancement of the critical temperature in a large three dimensional array of these superconducting nano-grains by combining mean-field, semiclassical and percolation techniques. We identify a broad range of parameters for which the array critical temperature, TcArray, can be up to a few times greater than the non-granular bulk limit, Tc 0. This prediction, valid only for conventional superconductors, takes into account an experimentally realistic distribution of grain sizes in the array, charging effects, dissipation by quasiparticles and limitations related to the proliferation of thermal fluctuations for sufficiently small grains. For small resistances we find the transition is percolation driven. Whereas at larger resistances the transition occurs above the percolation threshold due to phase fluctuations. JM acknowledes support from an EPSRC Ph.D studentship, AMG acknowledges support from EPSRC, grant No. EP/I004637/1, FCT, grant PTDC/FIS/111348/2009 and a Marie Curie International Reintegration Grant PIRG07-GA-2010-268172.

  12. Enhanced Superconductivity in Superlattices of high-$T_c$ Cuprates

    SciTech Connect

    Okamoto, Satoshi; Maier, Thomas A

    2008-01-01

    The electronic properties of multilayers of strongly-correlated models for cuprate superconductors are investigated using cluster dynamical mean-field techniques. We focus on combinations of under-doped and over-doped layers and find that the superconducting order parameter in the over-doped layers is enhanced by the proximity effect of the strong pairing scale originating from the under-doped layers. The enhanced order parameter can even exceed the maximum value in uniform systems. This behavior is well reproduced in slave-boson mean-field calculations which also find higher transition temperatures than in the uniform system. These results indicate the possibility for higher critical temperatures in artificial cuprate multilayer systems.

  13. Signature of Cooper pairs in the Metallic and Insulating Phases of Homogeneously Disordered Superconducting Ta Films

    NASA Astrophysics Data System (ADS)

    Li, Yize Stephanie

    With the increase of magnetic field or the decrease of sample thickness, homogeneously disordered superconducting Ta films undergo a superconductor-metal-insulator phase transition. Each phase displays remarkably different nonlinear current-voltage (I-V) characteristics. The evolution of the nonlinear transport in the insulating phase exhibits a non-monotonic behavior as the magnetic field is increased, which could be evidence of the presence of localized Cooper pairs in the insulating phase. As the metallic phase intervenes the superconducting and insulating states in Ta films, we further suggest that Cooper pairs also exist in the metallic ground state. Data acquisition for this work was completed at the University of Virginia.

  14. Pairing symmetry and vortex zero mode for superconducting Dirac fermions

    SciTech Connect

    Lu, C.-K.; Herbut, Igor F.

    2010-10-01

    We study vortex zero-energy bound states in presence of pairing between low-energy Dirac fermions on the surface of a topological insulator. The pairing symmetries considered include the s-wave, p-wave, and, in particular, the mixed-parity symmetry, which arises in absence of the inversion symmetry on the surface. The zero mode is analyzed within the generalized Jackiw-Rossi-Dirac Hamiltonian that contains a momentum-dependent mass term, and includes the effects of the electromagnetic gauge field and the Zeeman coupling as well. At a finite chemical potential, as long as the spectrum without the vortex is fully gapped, the presence of a single Fermi surface with a definite helicity always leads to one Majorana zero mode, in which both electron's spin projections participate. In particular, the critical effects of the Zeeman coupling on the zero mode are discussed.

  15. Non-separable pairing interaction kernels applied to superconducting cuprates

    NASA Astrophysics Data System (ADS)

    Haley, Stephen B.; Fink, Herman J.

    2014-05-01

    A pairing Hamiltonian H(Γ) with a non-separable interaction kernel Γ produces HTS for relatively weak interactions. The doping and temperature dependence of Γ(x,T) and the chemical potential μ(x) is determined by a probabilistic filling of the electronic states in the cuprate unit cell. A diverse set of HTS and normal state properties is examined, including the SC phase transition boundary TC(x), SC gap Δ(x,T), entropy S(x,T), specific heat C(x,T), and spin susceptibility χs(x,T). Detailed x,T agreement with cuprate experiment is obtained for all properties.

  16. Shrinking of the Cooper Pair Insulator Phase in Thin Films with Ultrasmall Superconducting Islands

    NASA Astrophysics Data System (ADS)

    Joy, J. C.; Zhang, X.; Zhao, C.; Valles, J. M., Jr.; Fernandes, G.; Xu, J. M.

    The ubiquity of the bosonic Cooper Pair Insulator (CPI) phase near the two-dimensional superconductor to insulator transition (SIT) is a long standing question. While a number of two dimensional materials exhibit bosonic insulating phases similar to the Mott Insulator in arrays of ultrasmall, Josephson coupled superconducting islands, others show behaviors consistent with a fermionic insulating phase. Utilizing specially prepared anodized aluminum oxide substrates, we are able to fabricate films reminiscent of arrays of superconducting islands whose properties are tunable by varying the substrate morphology. Our recent work has focused on arrays of islands which possess an energy level spacing comparable to the mean field superconducting gap, where one expects pair breaking followed by fermionic Anderson Localization as the dominant mechanism by which superconductivity is destroyed. Early results show that the paradigmatic bosonic insulator exists only very near the disorder tuned SIT, while films only marginally deeper in the insulating phase exhibit transport distinct from the CPI's reentrant, activated transport. We are grateful for the support of NSF Grant No. DMR-1307290, the AFOSR, and the AOARD. Currently at Northwestern Polytechnical University, Xian, China.

  17. Topological Dirac surface states and superconducting pairing correlations in PbTaSe2

    NASA Astrophysics Data System (ADS)

    Chang, Tay-Rong; Chen, Peng-Jen; Bian, Guang; Huang, Shin-Ming; Zheng, Hao; Neupert, Titus; Sankar, Raman; Xu, Su-Yang; Belopolski, Ilya; Chang, Guoqing; Wang, BaoKai; Chou, Fangcheng; Bansil, Arun; Jeng, Horng-Tay; Lin, Hsin; Hasan, M. Zahid

    2016-06-01

    Superconductivity in topological band structures is a platform for realizing Majorana bound states and other exotic physical phenomena such as emergent supersymmetry. This potential nourishes the search for topological materials with intrinsic superconducting instabilities, in which Cooper pairing is introduced to electrons with helical spin texture such as the Dirac surface states of topological insulators, forming a time-reversal symmetric topological superconductor on the surface. We employ first-principles calculations and angle-resolved photoemission spectroscopy experiments to reveal that PbTaSe2, a noncentrosymmetric superconductor, possesses a nonzero Z2 topological invariant and fully spin-polarized Dirac surface states. Moreover, we analyze the phonon spectrum of PbTaSe2 to show how superconductivity emerges in this compound due to a stiffening of phonons by the Pb intercalation, which diminishes a competing charge-density-wave instability. By combining our findings on the topological band structure and the superconducting electron pairing, our work establishes PbTaSe2 as a stoichiometric superconductor with topological Dirac surface states. This type of intrinsic topological Dirac superconductors holds great promise for studying aspects of topological superconductors such as Majorana zero modes.

  18. Ferromagnetism and superconductivity with possible p +i p pairing symmetry in partially hydrogenated graphene

    NASA Astrophysics Data System (ADS)

    Lu, Hong-Yan; Hao, Lei; Wang, Rui; Ting, C. S.

    2016-06-01

    By means of first-principles calculations, we predict two new types of partially hydrogenated graphene systems: C6H1 and C6H5 , which are shown to be a ferromagnetic (FM) semimetal and a FM narrow-gap semiconductor, respectively. When properly doped, the Fermi surface of the two systems consists of an electron pocket or six hole patches in the first Brillouin zone with completely spin-polarized charge carriers. If superconductivity exists in these systems, the stable pairing symmetries are shown to be p +i p for both electron- and hole-doped cases. The predicted systems may provide fascinating platforms for studying the novel properties of the coexistence of ferromagnetism and triplet-pairing superconductivity.

  19. Breakdown of electron-pairs in the presence of an electric field of a superconducting ring.

    PubMed

    Pandey, Bradraj; Dutta, Sudipta; Pati, Swapan K

    2016-05-18

    The quantum dynamics of quasi-one-dimensional ring with varying electron filling factors is investigated in the presence of an external electric field. The system is modeled within a Hubbard Hamiltonian with attractive Coulomb correlation, which results in a superconducting ground state when away from half-filling. The electric field is induced by applying time-dependent Aharonov-Bohm flux in the perpendicular direction. To explore the non-equilibrium phenomena arising from the field, we adopt exact diagonalization and the Crank-Nicolson numerical method. With an increase in electric field strength, the electron pairs, a signature of the superconducting phase, start breaking and the system enters into a metallic phase. However, the strength of the electric field for this quantum phase transition depends on the electronic correlation. This phenomenon has been confirmed by flux-quantization of time-dependent current and pair correlation functions. PMID:27089910

  20. Breakdown of electron-pairs in the presence of an electric field of a superconducting ring

    NASA Astrophysics Data System (ADS)

    Pandey, Bradraj; Dutta, Sudipta; Pati, Swapan K.

    2016-05-01

    The quantum dynamics of quasi-one-dimensional ring with varying electron filling factors is investigated in the presence of an external electric field. The system is modeled within a Hubbard Hamiltonian with attractive Coulomb correlation, which results in a superconducting ground state when away from half-filling. The electric field is induced by applying time-dependent Aharonov–Bohm flux in the perpendicular direction. To explore the non-equilibrium phenomena arising from the field, we adopt exact diagonalization and the Crank–Nicolson numerical method. With an increase in electric field strength, the electron pairs, a signature of the superconducting phase, start breaking and the system enters into a metallic phase. However, the strength of the electric field for this quantum phase transition depends on the electronic correlation. This phenomenon has been confirmed by flux-quantization of time-dependent current and pair correlation functions.

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

    NASA Astrophysics Data System (ADS)

    Erten, Onur; Flint, Rebecca; Coleman, Piers

    2015-01-01

    The recent observation of fully gapped superconductivity in Yb doped CeCoIn5 poses a paradox, for the disappearance of nodes suggests that they are accidental, yet d -wave symmetry with protected nodes is well established by experiment. Here, we show that composite pairing provides a natural resolution: in this scenario, Yb doping drives a Lifshitz transition of the nodal Fermi surface, forming a fully gapped d -wave molecular superfluid of composite pairs. The T4 dependence of the penetration depth associated with the sound mode of this condensate is in accordance with observation.

  2. Spin and Time-Reversal Symmetries of Superconducting Electron Pairs Probed by the Muon Spin Rotation and Relaxation Technique

    NASA Astrophysics Data System (ADS)

    Higemoto, Wataru; Aoki, Yuji; MacLaughlin, Douglas E.

    2016-09-01

    Unconventional superconductivity based on the strong correlation of electrons is one of the central issues of solid-state physics. Although many experimental techniques are appropriate for investigating unconventional superconductivity, a complete perspective has not been established yet. The symmetries of electron pairs are crucial properties for understanding the essential state of unconventional superconductivity. In this review, we discuss the investigation of the time-reversal and spin symmetries of superconducting electron pairs using the muon spin rotation and relaxation technique. By detecting a spontaneous magnetic field under zero field and/or the temperature dependence of the muon Knight shift in the superconducting phase, the time-reversal symmetry and spin parity of electron pairs have been determined for several unconventional superconductors.

  3. Enhancing triplet superconductivity by the proximity to a singlet superconductor in oxide heterostructures

    NASA Astrophysics Data System (ADS)

    Horsdal, Mats; Khaliullin, Giniyat; Hyart, Timo; Rosenow, Bernd

    2016-06-01

    We show how in principle a coherent coupling between two superconductors of opposite parity can be realized in a three-layer oxide heterostructure. Due to strong intraionic spin-orbit coupling in the middle layer, singlet Cooper pairs are converted into triplet ones and vice versa. This results in a large enhancement of the triplet superconductivity, persisting well above the native triplet critical temperature.

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

    PubMed

    Richard, P; Qian, T; Ding, H

    2015-07-29

    Its direct momentum sensitivity confers to angle-resolved photoemission spectroscopy (ARPES) a unique perspective in investigating the superconducting gap of multi-band systems. In this review we discuss ARPES studies on the superconducting gap of high-temperature Fe-based superconductors. We show that while Fermi-surface-driven pairing mechanisms fail to provide a universal scheme for the Fe-based superconductors, theoretical approaches based on short-range interactions lead to a more robust and universal description of superconductivity in these materials. Our findings are also discussed in the broader context of unconventional superconductivity. PMID:26153847

  5. Real-time study of light-enhanced superconductivity

    NASA Astrophysics Data System (ADS)

    Sentef, Michael; Kemper, Alexander; Georges, Antoine; Kollath, Corinna

    Resonant pumping of IR-active phonons with lasers enables the ultrafast control of the crystal lattice in solids. It has been shown that transient states with significantly modified electronic properties can be created on picosecond time scales, such as a light-induced state at elevated temperatures with optical properties in close resemblance to those of a superconductor. In our work, we investigate theoretically a situation in which a change of the electronic hopping leads to a modified density of states in real time. This modification, together with electron-phonon coupling, enhances superconductivity if the system is at thermal equilibrium. Our study monitors the out-of-equilibrium time evolution of the electronic momentum distribution and the superconducting order parameter. We show that the condensate dynamics dominates the initial enhancement of superconducting order, and that energy dissipation through electron-phonon scattering helps this enhancement.

  6. Anisotropic pairing in superconducting Sr{sub 2}RuO{sub 4}: Ru NMR and NQR studies

    SciTech Connect

    Ishida, K.; Kitaoka, Y.; Asayama, K.; Ikeda, S.; Nishizaki, S.; Maeno, Y.; Yoshida, K.; Fujita, T.

    1997-07-01

    Ru NMR and nuclear quadrupole resonance studies are reported on single-crystal Sr{sub 2}RuO{sub 4} (T{sub c}=0.7 K) with the same layered perovskite structure as La{sub 2}CuO{sub 4}. The Pauli spin susceptibility deduced from the Ru Knight shift is found to be largely enhanced by a factor of {approximately}5.4 as compared with the value from the band calculation. In the superconducting state, the nuclear spin-lattice relaxation rate 1/T{sub 1} exhibits a sharp decrease with no coherence peak just below T{sub c} and the T{sub 1}T=constant behavior well below T{sub c}, suggesting that the anisotropic pairing state is realized as in heavy-fermion and high-T{sub c} superconductors. {copyright} {ital 1997} {ital The American Physical Society}

  7. Theory of light-enhanced phonon-mediated superconductivity

    NASA Astrophysics Data System (ADS)

    Sentef, M. A.; Kemper, A. F.; Georges, A.; Kollath, C.

    2016-04-01

    We investigate the dynamics of a phonon-mediated superconductor driven out of equilibrium. The electronic hopping amplitude is ramped down in time, resulting in an increased electronic density of states. The dynamics of the coupled electron-phonon model is investigated by solving Migdal-Eliashberg equations for the double-time Keldysh Green's functions. The increase of the density of states near the Fermi level leads to an enhancement of superconductivity when the system thermalizes to the new state at the same temperature. We provide a time- and momentum-resolved view on this thermalization process and show that it involves fast processes associated with single-particle scattering and much slower dynamics associated with the superconducting order parameter. The importance of electron-phonon coupling for the rapid enhancement and the efficient thermalization of superconductivity is demonstrated, and the results are compared to a BCS time-dependent mean-field approximation.

  8. High-temperature superconductivity in two-band materials with interband pairing

    SciTech Connect

    Mazur, E. A. Dubovik, V. M.

    2015-07-15

    The Eliashberg theory generalized using peculiar properties of two-band electron–phonon (EP) systems is employed for studying T{sub c} in two-band materials (in particular, pnictides). In view of probably strong EP coupling, we take into account pairing within the entire width of the electron band, not only in a narrow layer at the Fermi surface. It is found that the effect of pairing of electrons belonging to different bands is a decisive factor for manifestation of the effect of high T{sub c} in these materials. It is shown that in materials analogous to pnictides, high T{sub c} values are reproduced by the two-band spectral function of electron–phonon interaction. The existence of one more family of two-band high-temperature materials with a superconducting transition temperature T{sub c} comparable to that in cuprates is predicted.

  9. Superconductivity of electron-hole pairs in a bilayer graphene system in a quantizing magnetic field

    NASA Astrophysics Data System (ADS)

    Fil', D. V.; Kravchenko, L. Yu.

    2009-08-01

    A state with spontaneous interlayer phase coherence in a bilayer quantum Hall system based on graphene is studied. This state can be regarded as a gas of superfluid electron-hole pairs whose components belong to different layers. A superfluid flow of such pairs is equivalent to two electric supercurrents in the layers. It is shown that in a graphene system a state with interlayer phase coherence arises if a definite unbalance of the filling factors of the Landau levels in neighboring layers is created. The temperature of the transition into a superfluid state, the maximum interlayer distance for which phase coherence is possible, and the critical values of the supercurrent are found. The advantages of using graphene systems instead of GaAs heterostructures to realize bilayer electron-hole superconductivity are discussed.

  10. Enhanced localized superconductivity in Sr2RuO4 thin film by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Cao, J.; Massarotti, D.; Vickers, M. E.; Kursumovic, A.; Di Bernardo, A.; Robinson, J. W. A.; Tafuri, F.; MacManus-Driscoll, J. L.; Blamire, M. G.

    2016-09-01

    Superconducting c-axis-oriented Sr2RuO4 thin film has been fabricated using pulsed laser deposition. Although the superconductivity is localized, the onset critical temperature is enhanced over the bulk value. X-ray microstructural analysis of Sr2RuO4 superconducting and non-superconducting thin films suggests the existence of the localized stacking faults and an overall c-axis lattice expansion which may account for the locally enhanced superconductivity.

  11. Checking for odd-triplet pairing using novel superconducting spin valves

    NASA Astrophysics Data System (ADS)

    Lapa, Pavel N.; Khaire, Trupti; Ding, Junjia; Pearson, John E.; Novosad, Valentyn; Hoffmann, Axel; Jiang, J. S.

    An excitation of odd-triplet pairing in a superconducting spin valve can be revealed by measuring the dependence of the superconducting critical temperature Tc with increasing non-collinearity of the magnetizations in adjacent ferromagnetic layers. A standard approach to create such a non-collinear magnetization configuration is to pin one ferromagnetic layers and control the magnetization in another layer by rotating the multilayer in a small magnetic field. Unfortunately, the rotation can modify the vortex current which also strongly affects the critical temperature. To exclude such spurious effects, we designed and fabricated a novel superconducting spin valve which allows us to create non-collinear magnetization configurations without using a sample rotator. The valve's operational principle is based on pinning of a synthetic antiferromagnet (SAF) by exchange coupling it to FeMn layer. The ability to imprint non-collinear magnetization configurations in the spin valve was confirmed using giant magneto resistance (GMR) measurements. The response of the magnetizations on an external magnetic field was simulated based on a coherent rotation model. The dependence of the Nb layer Tc on imprinted magnetization configuration will be presented. Work was supported by The Department of Energy Office of Science, Material Science and Engineering Division.

  12. Superconducting proximity effect in graphene: Injecting Cooper pairs in quantum Hall edge states

    NASA Astrophysics Data System (ADS)

    Komatsu, Katsuyoshi; Li, Chuan; Autier-Laurent, Sandrine; Kasumov, Alik; Bouchiat, Helene; Gueron, Sophie

    2012-02-01

    A superconductor-graphene(SG) hybrid system, such as an SGS junction or an SG interface, provides an ideal platform to investigate the relativistic nature of Dirac fermions combined with superconductivity. Instead of the retro-reflection of carriers in an ordinary superconductor-normal metal interface, an SG interface is theoretically predicted to show the specular reflection of quasiparticle carriers. We show that a supercurrent flows through a SGS junction with Nb electrodes even through a very long graphene distance of 1.2μm, more than 3 times the length previously reported. This supercurrent disappears in the vicinity of the Dirac point, indicating a strong sensitivity of the transmission of Andreev pairs to the formation of charge puddles with size greater than the superconducting coherence length. We also present data on similar size graphene samples with superconducting electrodes with a high critical field (more than 7Tesla) for which the properties of the normal state are dominated by quantum Hall physics. Whereas the behavior of the supercurrent is similar to the Nb/Graphene/Nb system in zero field, new features are observed in the high field quantum Hall regime.

  13. 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.

  14. Isosuperconductivity: A nonlocal-nonhamiltonian theory of pairing in high-T{sub c} superconductivity

    SciTech Connect

    Animalu, A.O.E. |

    1994-08-01

    The author presents a review and reformulation of the author`s recent nonlocal-nonhamiltonian generalization of the standard BCS (Bardeen-Cooper-Schrieffer) theory of electron pairing in superconductors, here called iso-superconductivity or iso-standard model for short, by drawing two analogies. The first analogy is a geometrical (relativistic) one between the internal (isominkowskian) structures of the neutral pion and the Cooper pair envisaged in the generalization; and the second analogy is a dynamical (fluid mechanics) one between the classical Hamilton-Santilli limit of the generalization and its apparent local/nonlocal two-dimensional (London) superfluid mechanics realizations for flows in the CuO{sub 2} planes of the high-T{sub c} cuprate superconductors. By using the analogies and physical considerations, the author elucidates the origins of the interactions responsible for the fluctuations in the iso-characteristics of the electron within the pair due to the mutual overlapping of the paired electron wavefunctions. The fluctuations are defined in terms of a single quantity, namely an integral operator or {open_quotes}iso unit{close_quotes}. 33 refs., 5 figs., 4 tabs.

  15. 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.

  16. Enhancement of Superconductivity of Lanthanum and Yttrium Sesquicarbide

    DOEpatents

    Krupka, M. C.; Giorgi, A. L.; Krikorian, N. H.; Szklarz, E. G.

    1972-06-22

    A method of enhancing the superconductivity of body-centered cubic lanthanum and yttrium sesquicarbide through formation of the sesquicarbides from ternary alloys of novel composition (N/sub x/M/sub 1-x/)C/sub z/, where N is yttrium or lanthanum, M is thorium, any of the Group IV and VI transition metals, or gold, germanium or silicon, and z is approximately 1.2 to 1.6. These ternary sesquicarbides have superconducting transition temperatures as high as 17.0/sup 0/K.

  17. Enhancement of superconductivity of lanthanum and yttrium sesquicarbide

    DOEpatents

    Krupka, M.C.; Giorgi, A.L.; Krikorian, N.H.; Szklarz, E.G.

    1971-06-22

    A method of enhancing the superconductivity of body-centered cubic lanthanum and yttrium sesquicarbide through formation of the sesquicarbides from ternary alloys of novel composition (N/sub x/M/sub 1-x/)C/sub z/, where N is yttrium or lanthanum, M is thorium, any of the Group IV and VI transition metals, or gold, germanium or silicon, and z is approximately 1.2 to 1.6. These ternary sesquicarbides have superconducting transition temperatures as high as 17.0/sup 0/K.

  18. Superconductivity in the single-band Hubbard model: Mean-field treatment of slave-boson pairing

    SciTech Connect

    Kopp, T.; Seco, F.J.; Schiller, S.; Woelfle, P.

    1988-12-01

    We investigate the possibility of superconductivity in the large-U limit of the Hubbard model near half filling, using a slave-boson representation. The local constraint is treated in a novel way, incorporating short-range fluctuations in addition to the global constraint. We find slave-boson pairing and a superconducting extended s-wave phase at hole concentrations delta above 4% and below 32%.

  19. Two-Gap Superconductivity in LaNiGa_{2} with Nonunitary Triplet Pairing and Even Parity Gap Symmetry.

    PubMed

    Weng, Z F; Zhang, J L; Smidman, M; Shang, T; Quintanilla, J; Annett, J F; Nicklas, M; Pang, G M; Jiao, L; Jiang, W B; Chen, Y; Steglich, F; Yuan, H Q

    2016-07-01

    The nature of the pairing states of superconducting LaNiC_{2} and LaNiGa_{2} has to date remained a puzzling question. Broken time reversal symmetry has been observed in both compounds and a group theoretical analysis implies a nonunitary triplet pairing state. However, all the allowed nonunitary triplet states have nodal gap functions but most thermodynamic and NMR measurements indicate fully gapped superconductivity in LaNiC_{2}. Here we probe the gap symmetry of LaNiGa_{2} by measuring the London penetration depth, specific heat, and upper critical field. These measurements demonstrate two-gap nodeless superconductivity in LaNiGa_{2}, suggesting that this is a common feature of both compounds. These results allow us to propose a novel triplet superconducting state, where the pairing occurs between electrons of the same spin, but on different orbitals. In this case the superconducting wave function has a triplet spin component but isotropic even parity gap symmetry, yet the overall wave function remains antisymmetric under particle exchange. This model leads to a nodeless two-gap superconducting state which breaks time reversal symmetry, and therefore accounts well for the seemingly contradictory experimental results. PMID:27447519

  20. Two-Gap Superconductivity in LaNiGa2 with Nonunitary Triplet Pairing and Even Parity Gap Symmetry

    NASA Astrophysics Data System (ADS)

    Weng, Z. F.; Zhang, J. L.; Smidman, M.; Shang, T.; Quintanilla, J.; Annett, J. F.; Nicklas, M.; Pang, G. M.; Jiao, L.; Jiang, W. B.; Chen, Y.; Steglich, F.; Yuan, H. Q.

    2016-07-01

    The nature of the pairing states of superconducting LaNiC2 and LaNiGa2 has to date remained a puzzling question. Broken time reversal symmetry has been observed in both compounds and a group theoretical analysis implies a nonunitary triplet pairing state. However, all the allowed nonunitary triplet states have nodal gap functions but most thermodynamic and NMR measurements indicate fully gapped superconductivity in LaNiC2 . Here we probe the gap symmetry of LaNiGa2 by measuring the London penetration depth, specific heat, and upper critical field. These measurements demonstrate two-gap nodeless superconductivity in LaNiGa2 , suggesting that this is a common feature of both compounds. These results allow us to propose a novel triplet superconducting state, where the pairing occurs between electrons of the same spin, but on different orbitals. In this case the superconducting wave function has a triplet spin component but isotropic even parity gap symmetry, yet the overall wave function remains antisymmetric under particle exchange. This model leads to a nodeless two-gap superconducting state which breaks time reversal symmetry, and therefore accounts well for the seemingly contradictory experimental results.

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

    PubMed

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

    2016-03-01

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

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

    PubMed Central

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

    2016-01-01

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

  3. Origin of dz2 orbital suppression of d-wave superconductive pairs in cuprate

    NASA Astrophysics Data System (ADS)

    Tang, Huai Bao; Li, Guang; Zhang, Hai Jun; Zuo, Xue Qin; Meng, Fan Ming; Liu, Da Yong

    2015-07-01

    Compared to Hg-cuprate, the origin that the dz2 orbital suppresses the d-wave superconductive (SC) pairs in La-cuprate is studied based on an effective two-orbital t-J-U model by using the Kotliar-Ruckenstein (KR) slave-boson technique. By analyzing the orbital-dependent electron distribution, it is elaborated that the double occupancy of dx2-y2 orbital, caused by the dz2 orbital mixture, should be responsible for the suppression of the d-wave SC pairs in La-cuprate. When the Coulomb interaction U increases, the ground state hosting the large double occupancy of dx2-y2 orbital in La-cuprate is stabilized by the localization of the carriers due to the Coulomb-blocking instead of reducing the double occupancy by the way of lowering of Coulomb potential energy. Therefore, it could be concluded that the mechanism that the double occupancy destructs against d-wave SC pairs is robust even if the strong Coulomb interaction exists in the La-based compounds.

  4. Precise determination of the mass of a Cooper pair of electrons in superconducting niobium

    SciTech Connect

    Tate, J.

    1988-01-01

    A superconducting, thin-film niobium ring deposited on the equator of a precision quartz hemispherical rotor was used to measure the ratio of Planck's constant to the mass of a Cooper pair of electrons, h/m*. A precision of 5 ppm (statistical) and an accuracy of 30 ppm (systematic) were obtained for a combined, root sum of squares error of 30 ppm. As a result of two macroscopic quantum phenomena-flux quantization and the London moment, the flux through a rotating, superconducting ring is a multivalued function of its rotation frequency. The flux goes to zero at certain equally spaced frequencies. The ratio h/m* is proportional to this frequency spacing. It is also proportional to the cross sectional area of the niobium ring. Using the values for Planck's constant and the rest mass of the electron recommended in the most recent fundamental constants revision, the mass measured in this experiment is larger than twice the free electron mass by 84 +/- 30 ppm. The result disagrees with theoretical predictions that this experiment would observe a mass smaller than twice the free electron mass by 8 ppm.

  5. Phase fluctuation in overdoped cuprates? Superconducting dome due to Mott-ness of the tightly bound preformed pairs

    NASA Astrophysics Data System (ADS)

    Ku, Wei; Yang, Fan

    2015-03-01

    In contrast to the current lore, we demonstrate that even the overdoped cuprates suffer from superconducting phase fluctuation in the strong binding limit. Specifically, the Mott-ness of the underlying doped holes dictates naturally a generic optimal doping around 15% and nearly complete loss of phase coherence around 25%, giving rise to a dome shape of superconducting transition temperature in excellent agreement with experimental observations of the cuprates. We verify this effect with a simple estimation using Gutzwiller approximation of the preformed pairs, obtained through variational Monte Carlo calculation. This realization suggests strongly the interesting possibility that the high-temperature superconductivity in the cuprates might be mostly described by Bose-Einstein condensation, without crossing over to amplitude fluctuating Cooper pairs. Supported by Department of Energy, Office of Basic Energy Science DE-AC02-98CH10886.

  6. Resonantly Enhanced Pair Production in a Simple Diatomic Model

    NASA Astrophysics Data System (ADS)

    Fillion-Gourdeau, François; Lorin, Emmanuel; Bandrauk, André D.

    2013-01-01

    A new mechanism for the production of electron-positron pairs from the interaction of a laser field and a fully ionized diatomic molecule in the tunneling regime is presented. When the laser field is turned off, the Dirac operator has resonances in both the positive and the negative energy continua while bound states are in the mass gap. When this system is immersed in a strong laser field, the resonances move in the complex energy plane: the negative energy resonances are pushed to higher energies while the bound states are Stark shifted [F. Fillion-Gourdeau , J. Phys. A 45, 215304 (2012)JPHAC50305-4470]. It is argued here that there is a pair production enhancement at the crossing of resonances by looking at a simple one-dimensional model: the nuclei are modeled simply by Dirac delta potential wells while the laser field is assumed to be static and of finite spatial extent. The average rate for the number of electron-positron pairs produced is evaluated and the results are compared to the one and zero nucleus cases. It is shown that positrons are produced by the resonantly enhanced pair production mechanism, which is analogous to the resonantly enhanced ionization of molecular physics. This phenomenon could be used to increase the number of pairs produced at low field strength, allowing the study of the Dirac vacuum.

  7. Coupled k-space structure of d -wave superconducting and magnetic orders induced by paramagnetic pair-breaking effect

    NASA Astrophysics Data System (ADS)

    Hatakeyama, Yuhki; Ikeda, Ryusuke

    2016-03-01

    We theoretically investigate k-space structures of dx2-y2-wave superconducting (SC) and spin-density-wave (SDW) orders in their coexistent phase induced by a paramagnetic pair-breaking (PPB) effect in relation to the high-field and low-temperature SC phase in CeCoIn5. It is shown that, in k space, the SDW order develops near the gap nodes where the SC order is suppressed by PPB, and the nesting condition for the SDW ordering is satisfied. By comparing the results in the dx2-y2-wave SC model and those in an artificial model with no sign change of the gap function in k space with each other, it is shown that the dx2-y2-wave SC and SDW orders are enhanced altogether in k space due to the sign change of the dx2-y2-wave gap function there, and that this mutual enhancement largely stabilizes the coexistence of these orders in real space. It is also discussed that the field dependence of a SDW moment can be affected by the k-space structure of these orders, which is dependent on the curvature of the Fermi surface.

  8. Studying temperature dependence of pairing gap parameter in a nucleus as a small superconducting system

    NASA Astrophysics Data System (ADS)

    Rahmatinejad, A.; Razavi, R.; Kakavand, T.

    2016-07-01

    In this paper, we have taken the effect of small size of nucleus and static fluctuations into account in the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity calculations of 45Ti nucleus. Thermodynamic quantities of 45Ti have been extracted within the BCS model with the inclusion of the average value of the pairing gap square, extracted by the modified Ginzburg-Landau (MGL) method for small systems. Calculated values of the excitation energy and entropy within the MGL+BCS method improve the extracted results within the usual BCS model and show a smooth behavior around the critical temperature with a very good agreement with the semi-empirical values. The result of using MGL+BCS method for the heat capacity of 45Ti is compared with the corresponding semi-empirical values and the calculated values within the BCS, static path approximation (SPA) and Modified Pairing gap BCS (MPBCS) which is a method that was proposed in our previous publications. Both MGL+BCS and MPBCS avoid the discontinuity of the heat capacity curve, which is observed in the usual BCS method, and lead to an S-shaped curve with a good agreement with the semi-empirical results.

  9. Paired Courses: An Instructional Model Designed To Enhance Academic Success.

    ERIC Educational Resources Information Center

    Rauch, Margaret; Fillenworth, Ceil

    1987-01-01

    The paired course instructional model can help high risk students succeed by enabling them to become aware of themselves as independent learners and to enhance transfer of learning from a reading course to a general education course. In order to examine the effectiveness of this model, and focus on a reading center's participation in the paired…

  10. Enhanced superconductivity in atomically thin TaS2

    NASA Astrophysics Data System (ADS)

    Navarro-Moratalla, Efrén; Island, Joshua O.; Mañas-Valero, Samuel; Pinilla-Cienfuegos, Elena; Castellanos-Gomez, Andres; Quereda, Jorge; Rubio-Bollinger, Gabino; Chirolli, Luca; Silva-Guillén, Jose Angel; Agraït, Nicolás; Steele, Gary A.; Guinea, Francisco; van der Zant, Herre S. J.; Coronado, Eugenio

    2016-03-01

    The ability to exfoliate layered materials down to the single layer limit has presented the opportunity to understand how a gradual reduction in dimensionality affects the properties of bulk materials. Here we use this top-down approach to address the problem of superconductivity in the two-dimensional limit. The transport properties of electronic devices based on 2H tantalum disulfide flakes of different thicknesses are presented. We observe that superconductivity persists down to the thinnest layer investigated (3.5 nm), and interestingly, we find a pronounced enhancement in the critical temperature from 0.5 to 2.2 K as the layers are thinned down. In addition, we propose a tight-binding model, which allows us to attribute this phenomenon to an enhancement of the effective electron-phonon coupling constant. This work provides evidence that reducing the dimensionality can strengthen superconductivity as opposed to the weakening effect that has been reported in other 2D materials so far.

  11. Enhanced superconductivity in atomically thin TaS2.

    PubMed

    Navarro-Moratalla, Efrén; Island, Joshua O; Mañas-Valero, Samuel; Pinilla-Cienfuegos, Elena; Castellanos-Gomez, Andres; Quereda, Jorge; Rubio-Bollinger, Gabino; Chirolli, Luca; Silva-Guillén, Jose Angel; Agraït, Nicolás; Steele, Gary A; Guinea, Francisco; van der Zant, Herre S J; Coronado, Eugenio

    2016-01-01

    The ability to exfoliate layered materials down to the single layer limit has presented the opportunity to understand how a gradual reduction in dimensionality affects the properties of bulk materials. Here we use this top-down approach to address the problem of superconductivity in the two-dimensional limit. The transport properties of electronic devices based on 2H tantalum disulfide flakes of different thicknesses are presented. We observe that superconductivity persists down to the thinnest layer investigated (3.5 nm), and interestingly, we find a pronounced enhancement in the critical temperature from 0.5 to 2.2 K as the layers are thinned down. In addition, we propose a tight-binding model, which allows us to attribute this phenomenon to an enhancement of the effective electron-phonon coupling constant. This work provides evidence that reducing the dimensionality can strengthen superconductivity as opposed to the weakening effect that has been reported in other 2D materials so far. PMID:26984768

  12. Superconductivity pairing mechanism from cobalt impurity doping in FeSe: Spin (s±) or orbital (s++) fluctuation

    NASA Astrophysics Data System (ADS)

    Urata, T.; Tanabe, Y.; Huynh, K. K.; Yamakawa, Y.; Kontani, H.; Tanigaki, K.

    2016-01-01

    In high-superconducting transition temperature (Tc) iron-based superconductors, interband sign reversal (s±) and sign preserving (s++) s -wave superconducting states have been primarily discussed as the plausible superconducting mechanism. We study Co impurity scattering effects on the superconductivity in order to achieve an important clue on the pairing mechanism using single-crystal Fe1 -xCoxSe and depict a phase diagram of a FeSe system. Both superconductivity and structural transition/orbital order are suppressed by the Co replacement on the Fe sites and disappear above x = 0.036. These correlated suppressions represent a common background physics behind these physical phenomena in the multiband Fermi surfaces of FeSe. By comparing experimental data and theories so far proposed, the suppression of Tc against the residual resistivity is shown to be much weaker than that predicted in the case of general sign reversal and full gap s± models. The origin of the superconducting paring in FeSe is discussed in terms of its multiband electronic structure.

  13. Cooper pairing protected by spin-valley locking in two-dimensional superconductivity on MoS2

    NASA Astrophysics Data System (ADS)

    Saito, Yu; Nakamura, Yasuharu; Bahramy, Mohammad; Kohama, Yoshimitsu; Ye, Jianting; Kasahara, Yuichi; Tokunaga, Masashi; Nojima, Tsutomu; Yanase, Youichi; Iwasa, Yoshihiro

    MoS2 is an archetypal layered semiconductor; monolayer shows out-of-plane spin polarization at the K-points due to intrinsic Zeeman-type spin-orbit coupling (SOC) derived from its in-plane broken inversion symmetry. By ionic-liquid gating, almost all carriers are confined only to topmost layer, realizing two-dimensional superconductivity in this system. We reported the first observation of a huge in-plane upper critical field of about 52 T and a clear saturating behaviour in the low temperatures using pulsed magnetic fields up to 55 T. From first-principles-based tight binding supercell calculations followed by realistic numerical calculations of Hc 2 based on the subband structure, we revealed that this unusual behavior is due to the moderately large Zeeman-type spin splitting of 13 meV at the Fermi level (vicinity of the K points). This forces Cooper pairs to be completely aligned to out-of-plane direction by spin-valley locking effect, thereby causing the dramatic enhancement of the Pauli limit Our calculation also indicates that even if the carrier density and then spin splitting (9-15 meV) at the Fermi level changes, the Pauli limit is predominantly controlled by both the Zeeman-type SOI and Tc, and the contribution of Rashba-type SOI is negligibly small.

  14. Stoner enhanced paramagnetic influence on superconductivity in a superconductor/metallic heterostructure

    NASA Astrophysics Data System (ADS)

    Ray, S. J.; Lister, S. J.; Lee, S. L.; Hellwig, Olav; Stahn, J.

    2013-04-01

    The unusual magnetic behaviour of a Pd/Nb67Ti33/Pd heterostructure was investigated using polarised neutron reflectivity technique. On application of a large in-plane magnetic field, Stoner enhanced paramagnet Pd was found to influence the magnetic state of the Nb67Ti33 layer both above and below the superconducting transition temperature Tc significantly. Unlike the case of a conventional proximity effect for a superconductor/metallic heterostructure, the pair correlation in the superconducting state has been found to be more stable in the higher field limit compared to its low field counterpart, possibly signaturing a ‘novel’ coupled state in the system. The superconducting state in Nb67Ti33 has been found to be diamagnetic in nature at all the fields that can be fitted using a Meissner kind of behaviour in the high field limit. The magnetic properties of Pd and Nb67Ti33 are in excellent agreement with those measured using bulk magnetisation measurements.

  15. Strongly Enhanced Superconductivity in Coupled t -J Segments

    NASA Astrophysics Data System (ADS)

    Reja, Sahinur; van den Brink, Jeroen; Nishimoto, Satoshi

    2016-02-01

    The t -J Hamiltonian is one of the cornerstones in the theoretical study of strongly correlated copper-oxide based materials. Using the density-matrix renormalization group method we obtain the phase diagram of the one-dimensional t -J chain in the presence of a periodic hopping modulation, as a prototype of coupled-segment models. While in the uniform 1D t -J model the near half-filling superconducting state dominates only at unphysically large values of the exchange coupling constant J /t >3 ; we show that a small hopping and exchange modulation very strongly reduces the critical coupling to be as low as J /t ˜1 /3 —well within the physical regime. The phase diagram as a function of the electron filling also exhibits metallic, insulating line phases and regions of phase separation. We suggest that a superconducting state is easily stabilized if t -J segments creating local spin-singlet pairing are coupled to each other—another example is the ladder system.

  16. Nematic versus ferromagnetic spin filtering of triplet Cooper pairs in superconducting spintronics

    NASA Astrophysics Data System (ADS)

    Moor, Andreas; Volkov, Anatoly F.; Efetov, Konstantin B.

    2015-11-01

    We consider two types of magnetic Josephson junctions (JJ). They are formed by two singlet superconductors S and magnetic layers between them so that the JJ is a heterostructure of the Sm/n /Sm type, where Sm includes two magnetic layers with noncollinear magnetization vectors. One layer is represented by a weak ferromagnet and another one—the spin filter—is either conducting strong ferromagnet (nematic or N -type JJ) or magnetic tunnel barrier with spin-dependent transparency (magnetic or M -type JJ). Due to spin filtering only a fully polarized triplet component penetrates the normal n wire and provides the Josephson coupling between the superconductors S. Although both filters let to pass triplet Cooper pairs with total spin S parallel to the filter axes, the behavior of nematic and magnetic JJs is completely different. Whereas in the nematic case the charge and spin currents, IQ and Isp, do not depend on mutual orientation of the filter axes, both currents vanish in magnetic JJ in the case of antiparallel filter axes, and change sign with reversal of the filter direction. The obtained expressions for IQ and Isp clearly show a duality between the superconducting phase φ and the angle α between the exchange fields in the weak magnetic layers.

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

    PubMed Central

    Szczęśniak, Radosław

    2012-01-01

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

  18. Superconductivity

    SciTech Connect

    Langone, J.

    1989-01-01

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

  19. High-fidelity frequency down-conversion of visible entangled photon pairs with superconducting single-photon detectors

    SciTech Connect

    Ikuta, Rikizo; Kato, Hiroshi; Kusaka, Yoshiaki; Yamamoto, Takashi; Imoto, Nobuyuki; Miki, Shigehito; Yamashita, Taro; Terai, Hirotaka; Wang, Zhen; Fujiwara, Mikio; Sasaki, Masahide; Koashi, Masato

    2014-12-04

    We experimentally demonstrate a high-fidelity visible-to-telecommunicationwavelength conversion of a photon by using a solid-state-based difference frequency generation. In the experiment, one half of a pico-second visible entangled photon pair at 780 nm is converted to a 1522-nm photon. Using superconducting single-photon detectors with low dark count rates and small timing jitters, we observed a fidelity of 0.93±0.04 after the wavelength conversion.

  20. PRIMUS: Enhanced Specific Star Formation Rates in Close Galaxy Pairs

    NASA Astrophysics Data System (ADS)

    Wong, Kenneth C.; Blanton, Michael R.; Burles, Scott M.; Coil, Alison L.; Cool, Richard J.; Eisenstein, Daniel J.; Moustakas, John; Zhu, Guangtun; Arnouts, Stéphane

    2011-02-01

    Tidal interactions between galaxies can trigger star formation, which contributes to the global star formation rate (SFR) density of the universe and could be a factor in the transformation of blue, star-forming galaxies to red, quiescent galaxies over cosmic time. We investigate tidally triggered star formation in isolated close galaxy pairs drawn from the Prism Multi-Object Survey (PRIMUS), a low-dispersion prism redshift survey that has measured ~120,000 robust galaxy redshifts over 9.1 deg2 out to z ~ 1. We select a sample of galaxies in isolated galaxy pairs at redshifts 0.25 <= z <= 0.75, with no other objects within a projected separation of 300 h -1 kpc and Δz/(1 + z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their rest-frame FUV - r and NUV - r colors as a proxy for relative specific star formation rates (SSFRs). We find that galaxies in rp <= 50 h -1 kpc pairs have bluer dust-corrected UV - r colors on average than the control galaxies by -0.134 ± 0.045 mag in FUV - r and -0.075 ± 0.038 mag in NUV - r, corresponding to an ~15%-20% increase in SSFR. This indicates an enhancement in SSFR due to tidal interactions. We also find that this relative enhancement is greater for a subset of rp <= 30 h -1 kpc pair galaxies, for which the average color offsets are -0.193 ± 0.065 mag in FUV - r and -0.159 ± 0.048 mag in NUV - r, corresponding to an ~25%-30% increase in SSFR. We test for evolution in the enhancement of tidally triggered star formation with redshift across our sample redshift range and find marginal evidence for a decrease in SSFR enhancement from 0.25 <= z <= 0.5 to 0.5 <= z <= 0.75. This indicates that a change in enhanced star formation triggered by tidal interactions in low-density environments is not a contributor to the decline in the global SFR density across this redshift range.

  1. Light-induced enhancement of superconductivity via melting of competing bond-density wave order in underdoped cuprates

    NASA Astrophysics Data System (ADS)

    Patel, Aavishkar A.; Eberlein, Andreas

    2016-05-01

    We develop a theory for light-induced superconductivity in underdoped cuprates in which the competing bond-density wave order is suppressed by driving phonons with light. Close to a bond-density wave instability in a system with a small Fermi surface, such as a fractionalized Fermi liquid, we show that the coupling of electrons to phonons is strongly enhanced at the bond-density wave ordering wave vectors, leading to a strong softening of phonons at these wave vectors. For a model of classical phonons with anharmonic couplings, we show that the combination of strong softening and driving can lead to large phonon oscillations. When coupled to a phenomenological model describing the competition between bond-density wave order and superconductivity, these phonon oscillations melt bond-density wave order, thereby enhancing pairing correlations.

  2. Enhancement of superconductivity by pressure-driven phase competition in electronic order

    SciTech Connect

    Chen, Xiao-Jia; Struzhkin, Viktor V.; Yu, Yong; Goncharov, Alexander F.; Lin, Cheng-Tian; Mao, Ho-kwang; Hemley, Russell J.

    2010-08-19

    Finding ways to achieve higher values of the transition temperature, Tc, in superconductors remains a great challenge. The superconducting phase is often one of several competing types of electronic order, including antiferromagnetism and charge density waves. An emerging trend documented in heavy-fermion and organic conductors is that the maximum Tc for superconductivity occurs under external conditions that cause the critical temperature for a competing order to go to zero. Recently, such competition has been found in multilayer copper oxide high-temperature superconductors (HTSCs) that possess two crystallographically inequivalent CuO2 planes in the unit cell. However, whether the competing electronic state can be suppressed to enhance Tc in HTSCs remains an open question. Here we show that pressure-driven phase competition leads to an unusual two-step enhancement of c in optimally doped trilayer Bi2Sr2Ca2Cu3O10+δ (Bi2223). We find that Tc first increases with pressure and then decreases after passing through a maximum. Unexpectedly, Tc increases again when the pressure is further raised above a critical value of around 24 GPa, surpassing the first maximum. The presence of this critical pressure is a manifestation of the crossover from the competing order to superconductivity in the inner of the three CuO2 planes. We suggest that the increase at higher pressures occurs as a result of competition between pairing and phase ordering in different CuO2 planes.

  3. Spin-polaron theory of high-{Tc} superconductivity: I, spin polarons and high-{Tc} pairing

    SciTech Connect

    Wood, R.F.

    1993-06-01

    The concept of a spin polaron is introduced and contrasted with the more familiar ionic polaron picture. A brief review of aspects of ionic bipolaronic superconductivity is given with particular emphasis on the real-space pairing and true Bose condensation characteristics. The formation energy of spin polarons is then calculated in analogy with ionic polarons. The spin-flip energy of a Cu spin in an antiferromagnetically aligned CuO{sub 2} plane is discussed. It is shown that the introduction of holes into the CuO{sub 2} planes will always lead to the destruction of long-range AF ordering due to the formation of spin polarons. The pairing of two spin polarons can be expected because of the reestablishment of local (short-range) AF ordering; the magnitude of the pairing energy is estimated using a simplified model. The paper closes with a brief discussion of the formal theory of spin polarons.

  4. Strong enhancement of bulk superconductivity by engineered nanogranularity

    NASA Astrophysics Data System (ADS)

    Mayoh, J.; García-García, A. M.

    2014-10-01

    It is now well established, both theoretically and experimentally, that very small changes in the size of isolated nanograins lead to substantial nonmonotonic variations, and sometimes enhancement, of the mean-field spectroscopic gap of conventional superconductors. A natural question to ask, of broad relevance for the theory and applications of superconductivity, is whether these size effects can also enhance the critical temperature of a bulk granular material composed of such nanograins. Here we answer this question affirmatively. We combine mean-field, semiclassical, and percolation techniques to show that engineered nanoscale granularity in conventional superconductors can enhance the critical temperature by up to a few times compared to the nongranular bulk limit. This prediction is valid for three-dimensional and also quasi-two-dimensional samples, provided the thickness is much larger than the grain size. Our model takes into account an experimentally realistic distribution of grain sizes in the array, charging effects, tunneling by quasiparticles, and limitations related to the proliferation of thermal fluctuations for sufficiently small grains.

  5. Superconductivity

    NASA Astrophysics Data System (ADS)

    Yeo, Yung K.

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

  6. Enhanced spin fluctuations and s +/- pairing by diagonal electron hopping in Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Kuroki, Kazuhiko

    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 and thus the pairing glue. However, there have appeared some experimental observations suggesting absence of Fermi surface nesting. For instance, in the 1111 materials Ln FeAsO1-xHx (Ln =La,Sm, etc.), electron doping rate x reaches up to 50%, which in a rigid band picture would wipe out the hole Fermi surfaces. Still, superconductivity not only survives, but is even enhanced in the largely doped regime, in contradiction to the expectation from the bad nesting. Another example is KxFe2-ySe2, where the ARPES experiments show the absence of hole Fermi surfaces. In the present talk, we first focus on Ln FeAsO1-xHx, where the band structure is actually not rigid against doping, and the hole Fermi surface originating from the dxy orbital remains nearly unchanged. The origin of this can be traced back to real space, where the nearest neighbor hopping t1 within the dxy orbital is found to be strongly suppressed with doping. Although the nesting itself is degraded, the spin fluctuation in the largely electron doped regime is enhanced due to t2 >t1 , where t2 is the 2nd neighbor diagonal hopping. This re-enhances s +/- pairing superconductivity, and explains the double dome x-Tc phase diagram of LaFeAsO1-xHx. From this viewpoint, it is also interesting to look into the relation between t1 and t2 in other materials. For instance, our first principles estimation for KFe2Se2givest1 = - 0 . 008 eV and t2 = 0 . 056 eV, and from this strong reduction of t1, both electron and hole Fermi surfaces are expected to be present around the Γ point, in contradiction to previous experimental observations. Results of a recent ARPES experiment will be discussed from this viewpoint.

  7. Strong enhancement of s -wave superconductivity near a quantum critical point of Ca3Ir4Sn13

    DOE PAGESBeta

    Biswas, P. K.; Guguchia, Z.; Khasanov, R.; Chinotti, M.; Li, L.; Wang, Kefeng; Petrovic, C.; Morenzoni, E.

    2015-11-11

    We repormore » t microscopic studies by muon spin rotation/relaxation as a function of pressure of the Ca3Ir4Sn13 and Sr3Ir4Sn13 system displaying superconductivity and a structural phase transition associated with the formation of a charge density wave (CDW). Our findings show a strong enhancement of the superfluid density and a dramatic increase of the pairing strength above a pressure of ≈ 1.6 GPa giving direct evidence of the presence of a quantum critical point separating a superconducting phase coexisting with CDW from a pure superconducting phase. The superconducting order parameter in both phases has the same s-wave symmetry. In spite of the conventional phonon-mediated BCS character of the weakly correlated (Ca1-xSrx)3Ir4Sn13 system the dependence of the effective superfluid density on the critical temperature puts this compound in the “Uemura” plot close to unconventional superconductors. This system exemplifies that conventional BCS superconductors in the presence of competing orders or multi-band structure can also display characteristics of unconventional superconductors.« less

  8. Direct evidence for a magnetic f-electron–mediated pairing mechanism of heavy-fermion superconductivity in CeCoIn5

    PubMed Central

    Van Dyke, John S.; Massee, Freek; Allan, Milan P.; Davis, J. C. Séamus; Petrovic, Cedomir; Morr, Dirk K.

    2014-01-01

    To identify the microscopic mechanism of heavy-fermion Cooper pairing is an unresolved challenge in quantum matter studies; it may also relate closely to finding the pairing mechanism of high-temperature superconductivity. Magnetically mediated Cooper pairing has long been the conjectured basis of heavy-fermion superconductivity but no direct verification of this hypothesis was achievable. Here, we use a novel approach based on precision measurements of the heavy-fermion band structure using quasiparticle interference imaging to reveal quantitatively the momentum space (k-space) structure of the f-electron magnetic interactions of CeCoIn5. Then, by solving the superconducting gap equations on the two heavy-fermion bands Ekα,β with these magnetic interactions as mediators of the Cooper pairing, we derive a series of quantitative predictions about the superconductive state. The agreement found between these diverse predictions and the measured characteristics of superconducting CeCoIn5 then provides direct evidence that the heavy-fermion Cooper pairing is indeed mediated by f-electron magnetism. PMID:25062692

  9. Superconducting fluctuations in organic molecular metals enhanced by Mott criticality

    PubMed Central

    Nam, Moon-Sun; Mézière, Cécile; Batail, Patrick; Zorina, Leokadiya; Simonov, Sergey; Ardavan, Arzhang

    2013-01-01

    Unconventional superconductivity typically occurs in materials in which a small change of a parameter such as bandwidth or doping leads to antiferromagnetic or Mott insulating phases. As such competing phases are approached, the properties of the superconductor often become increasingly exotic. For example, in organic superconductors and underdoped high-Tc cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above Tc. By studying alloys of quasi-two-dimensional organic molecular metals in the κ-(BEDT-TTF)2X family, we reveal how the Nernst effect, a sensitive probe of superconducting phase fluctuations, evolves in the regime of extreme Mott criticality. We find strong evidence that, as the phase diagram is traversed through superconductivity towards the Mott state, the temperature scale for superconducting fluctuations increases dramatically, eventually approaching the temperature at which quasiparticles become identifiable at all. PMID:24292063

  10. Transport spectroscopy on trapped superconducting nano-islands of Pb: signature of unconventional pairing.

    PubMed

    Sirohi, Anshu; Saha, Preetha; Gayen, Sirshendu; Singh, Avtar; Sheet, Goutam

    2016-07-15

    Elemental bulk lead (Pb) is a conventional type I, spin-singlet (s-wave) superconductor with a critical temperature T c = 7.2 K and a critical magnetic field H c = 800 Oe. However, it is known that at mesoscopic length scales, like in point-contact geometries, Pb shows significantly higher critical field, sometimes up to several Tesla. We have used this property to trap a small superconducting nano-droplet of Pb by forming a metallic point contact on Pb and then applying a magnetic field larger than 800 Oe that drives the bulk of the material non-superconducting. From systematic magnetic field dependent behaviour of the point-contact spectra measured across such a trapped island of Pb we show that the superconducting order parameter of mesoscopic Pb mixes non-trivially with magnetic field possibly due to the emergence of a local spin-triplet component at such length scales. From comparative studies with Nb-based point contacts we surmise that the strong spin-orbit coupling in Pb leads to the emergence of the unconventional component in the order parameter of mesoscopic Pb. PMID:27251201

  11. Transport spectroscopy on trapped superconducting nano-islands of Pb: signature of unconventional pairing

    NASA Astrophysics Data System (ADS)

    Sirohi, Anshu; Saha, Preetha; Gayen, Sirshendu; Singh, Avtar; Sheet, Goutam

    2016-07-01

    Elemental bulk lead (Pb) is a conventional type I, spin-singlet (s-wave) superconductor with a critical temperature T c = 7.2 K and a critical magnetic field H c = 800 Oe. However, it is known that at mesoscopic length scales, like in point-contact geometries, Pb shows significantly higher critical field, sometimes up to several Tesla. We have used this property to trap a small superconducting nano-droplet of Pb by forming a metallic point contact on Pb and then applying a magnetic field larger than 800 Oe that drives the bulk of the material non-superconducting. From systematic magnetic field dependent behaviour of the point-contact spectra measured across such a trapped island of Pb we show that the superconducting order parameter of mesoscopic Pb mixes non-trivially with magnetic field possibly due to the emergence of a local spin-triplet component at such length scales. From comparative studies with Nb-based point contacts we surmise that the strong spin–orbit coupling in Pb leads to the emergence of the unconventional component in the order parameter of mesoscopic Pb.

  12. Enhancing the Higgs associated production with a top quark pair

    NASA Astrophysics Data System (ADS)

    Badziak, Marcin; Wagner, Carlos E. M.

    2016-05-01

    It is pointed out that in a wide class of models reminiscent of type-II Two-Higgs-Doublet Models (2HDM) the signal of the Higgs produced in association with a top-antitop quark pair ( tth) and decaying into gauge bosons can be significantly larger than the Standard Model (SM) prediction without violating any experimental constraints. The crucial feature of these models is enhanced (suppressed) Higgs coupling to top (bottom) quarks and existence of light colored particles that give negative contribution to the effective Higgs coupling to gluons resulting in the gluon fusion rates in the gauge boson decay channels close to SM predictions. We demonstrate this mechanism in NMSSM with light stops and show that tth signal in the W W decay channel can be two times larger than the SM prediction, as suggested by the excesses observed by ATLAS and CMS, provided that the Higgs-singlet superpotential coupling λ ≳ 0 .8 and the MSSM-like Higgs boson masses are in the range of 160 to 300 GeV.

  13. Enhanced scanning agility using a double pair of Risley prisms.

    PubMed

    Roy, Gilles; Cao, Xiaoying; Bernier, Robert; Roy, Simon

    2015-12-01

    Scanners with one pair of Risley prisms are robust and precise and they can be operated continuously. In this paper, we present a new scanner based on the use of two pairs of Risley prisms. The concept was driven by the need to add flexibility to Risley prism scanners used for lidar 3D mapping applications, while maintaining compactness and robustness. The first pair covers a FOV narrower than the second pair. The second pair is used to position the first Risley pair scan pattern anywhere within its own, larger, FOV. Doing so, it becomes possible, without additional scanner components, to increase the sampling point density at a specific location, to increase the sampling uniformity of the scanned area, and, while in motion, to maintain the sampling of a specific area of interest. PMID:26836680

  14. Superconductivity:

    NASA Astrophysics Data System (ADS)

    Sacchetti, N.

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

  15. Cooper pair of superconductivity in the coordinate representation and q-deformed harmonic oscillator

    NASA Astrophysics Data System (ADS)

    Van Ngu, Man; Gia Vinh, Ngo; Lan, Nguyen Tri; Thanh, Luu Thi Kim; Viet, Nguyen Ai

    2016-06-01

    In this work we study the similarity between the wave functions of q -deformed harmonic oscillator and wave functions of Cooper pair. The wave functions of Cooper pairs in coordinate-space have an “onion-like” layered structure with exponent decay (Boltzmann) envelope modulation. The ground state wave function of q -deform harmonic oscillator has the form of oscillate functions with Gaussian decay envelope modulation. The corresponding between Boltzmann and Gaussian forms of envelope functions and their quantum similarity are discussed.

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

    PubMed Central

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

    2016-01-01

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

  17. Distinguishing S-plus-minus and S-plus-plus electron pairing symmetries by neutron spin resonances in superconducting Sodium-Iron-Cobalt-Arsenic (transitional temperature = 18 Kelvin)

    SciTech Connect

    Das, Tanmoy; Balatsky, Alexander V.; Zhang, Chenglin; Li, Haifeng; Su, Yiki; Nethertom, Tucker; Redding, Caleb; Carr, Scott; Schneidewind, Astrid; Faulhaber, Enrico; Li, Shiliang; Yao, Daoxin; Bruckel, Thomas; Dai, Pengchen; Sobolev, Oleg

    2012-06-05

    A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechansim for superconductivity. For iron pnictide superconductors, the s{sup {+-}}-pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies (E {le} 2{Delta}). Although the resonances have been observed for various iron pnictide superconductors, they are broad in energy and can also be interpreted as arising from the s{sup ++}-pairing symmetry with E {ge} 2{Delta}. Here we use inelastic neutron scattering to reveal a sharp resonance at E = 7 meV in the SC NaFe{sub 0.935}Co{sub 0.045}As (T{sub c} = 18 K). By comparing our experiments with calculated spin-excitations spectra within the s{sup {+-}} and s{sup ++}-pairing symmetries, we conclude that the resonance in NaFe{sub 0.935}Co{sub 0.045}As is consistent with the s{sup {+-}}-pairing symmetry, thus eliminating s{sup ++}-pairing symmetry as a candidate for superconductivity.

  18. Submicron-scale high- Tc superconducting Bi-2212 stack fabrication for single-Cooper-pair tunneling

    NASA Astrophysics Data System (ADS)

    Kim, S.-J.; Latyshev, Yu. I.; Yamashita, T.; Sato, N.; Kishida, S.

    2000-07-01

    We report the characteristics of Bi-2212 intrinsic Josephson junctions (IJJ) showing single-Cooper-pair tunneling effect with a decrease of their in-plane area, S, smaller than a micron scale. The junctions show the typical slope of critical current and current peak-like structure up to 37 K.

  19. Microscopic analysis of the superconducting quantum critical point: Finite-temperature crossovers in transport near a pair-breaking quantum phase transition

    NASA Astrophysics Data System (ADS)

    Shah, Nayana; Lopatin, Andrei

    2007-09-01

    A microscopic analysis of the superconducting quantum critical point realized via a pair-breaking quantum phase transition is presented. Finite-temperature crossovers are derived for the electrical conductivity, which is a key probe of superconducting fluctuations. By using the diagrammatic formalism for disordered systems, we are able to incorporate the interplay between fluctuating Cooper pairs and electrons, that is outside the scope of a time-dependent Ginzburg-Landau or effective bosonic action formalism. It is essential to go beyond the standard approximation in order to capture the zero-temperature correction which results purely from the (dynamic) quantum fluctuations and dictates the behavior of the conductivity in an entire low-temperature quantum regime. All dynamic contributions are of the same order and conspire to add up to a negative total, thereby inhibiting the conductivity as a result of superconducting fluctuations. On the contrary, the classical and the intermediate regimes are dominated by the positive bosonic channel. Our theory is applicable in one, two, and three dimensions and is relevant for experiments on superconducting nanowires, doubly connected cylinders, thin films, and bulk in the presence of magnetic impurities, magnetic field, or other pair breakers. A window of nonmonotonic behavior is predicted to exist as either the temperature or the pair-breaking parameter is swept.

  20. Superconductivity enhancement in the S-doped Weyl semimetal candidate MoTe2

    NASA Astrophysics Data System (ADS)

    Chen, F. C.; Luo, X.; Xiao, R. C.; Lu, W. J.; Zhang, B.; Yang, H. X.; Li, J. Q.; Pei, Q. L.; Shao, D. F.; Zhang, R. R.; Ling, L. S.; Xi, C. Y.; Song, W. H.; Sun, Y. P.

    2016-04-01

    Two-dimensional transition-metal dichalcogenide (TMDs) MoTe2 has attracted much attention due to its predicted Weyl semimetal state and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that the superconductivity in MoTe2 single crystal can be greatly enhanced by the partial substitution of the Te ions by the S ones. The maximum superconducting temperature TC of MoTe1.8S0.2 single crystal is about 1.3 K. Compared with the parent MoTe2 single crystal (TC = 0.1 K), nearly 13-fold in TC is improved in the MoTe1.8S0.2 one. The superconductivity has been investigated through the resistivity and magnetization measurements. MoTe2-xSx single crystals belong to weak coupling superconductors and the improvement of the superconductivity may be related to the enhanced electron-phonon coupling induced by the S-ion substitution. A dome-shaped superconducting phase diagram is obtained in the S-doped MoTe2 single crystals. MoTe2-xSx materials may provide a new platform for our understanding of superconductivity phenomena and topological physics in TMDs.

  1. Strongly enhanced superconductivity in doped monolayer MoS2 by strain

    NASA Astrophysics Data System (ADS)

    Zeng, Shuming; Zhao, Yinchang; Li, Geng; Ni, Jun

    2016-07-01

    The effects of strain on the stability, electron-phonon coupling, and superconductivity of doped monolayer MoS2 are investigated systematically using first-principles calculations. We find that most of the electron-phonon coupling in doped monolayer MoS2 is attributed to the in-plane vibrations of Mo atoms, which can be further tuned by strain. By applying biaxial compressive strain, we find a large enhancement in the superconducting transition temperature (Tc) and we obtain a Tc of 22 K at the optimal hole doping concentration, while the electron-phonon coupling of electron-doped structure is reduced due to the direct-indirect band-gap insulator transition. Our results reveal that the Fermi surface nesting-driven mechanism is mainly responsible for phonon softening and superconductivity in monolayer MoS2, suggesting that doping combined with strain is efficient at tuning electron-phonon coupling and superconductivity.

  2. Enhanced Antiferromagnetic Exchange between Magnetic Impurities in a Superconducting Host

    NASA Astrophysics Data System (ADS)

    Yao, N. Y.; Glazman, L. I.; Demler, E. A.; Lukin, M. D.; Sau, J. D.

    2014-08-01

    It is generally believed that superconductivity only weakly affects the indirect exchange between magnetic impurities. If the distance r between impurities is smaller than the superconducting coherence length (r≲ξ), this exchange is thought to be dominated by Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, identical to the those in a normal metallic host. This perception is based on a perturbative treatment of the exchange interaction. Here, we provide a nonperturbative analysis and demonstrate that the presence of Yu-Shiba-Rusinov bound states induces a strong 1/r2 antiferromagnetic interaction that can dominate over conventional RKKY even at distances significantly smaller than the coherence length (r≪ξ). Experimental signatures, implications, and applications are discussed.

  3. Cosmic Evolution of Star Formation Enhancement in Close Major-merger Galaxy Pairs Since z = 1

    NASA Astrophysics Data System (ADS)

    Xu, C. K.; Shupe, D. L.; Béthermin, M.; Aussel, H.; Berta, S.; Bock, J.; Bridge, C.; Conley, A.; Cooray, A.; Elbaz, D.; Franceschini, A.; Le Floc'h, E.; Lu, N.; Lutz, D.; Magnelli, B.; Marsden, G.; Oliver, S. J.; Pozzi, F.; Riguccini, L.; Schulz, B.; Scoville, N.; Vaccari, M.; Vieira, J. D.; Wang, L.; Zemcov, M.

    2012-11-01

    The infrared (IR) emission of "M * galaxies" (1010.4 <= M star <= 1011.0 M ⊙) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single-disk galaxies in well-matched control samples to study the cosmic evolution of the star formation enhancement induced by galaxy-galaxy interaction. Both the mean IR spectral energy distribution and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star formation enhancement in S+S pairs to decrease with increasing redshift. Between z = 0 and z = 1, this decline of interaction-induced star formation enhancement occurs in parallel with the dramatic increase (by a factor of ~10) of the sSFR of single SFGs, both of which can be explained by the higher gas fraction in higher-z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the intergalactic medium (IGM) in the dark matter halos hosting these pairs. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  4. COSMIC EVOLUTION OF STAR FORMATION ENHANCEMENT IN CLOSE MAJOR-MERGER GALAXY PAIRS SINCE z = 1

    SciTech Connect

    Xu, C. K.; Shupe, D. L.; Bock, J.; Bridge, C.; Cooray, A.; Lu, N.; Schulz, B.; Bethermin, M.; Aussel, H.; Elbaz, D.; Le Floc'h, E.; Riguccini, L.; Conley, A.; Franceschini, A.; Marsden, G.; Oliver, S. J.; Pozzi, F.; and others

    2012-11-20

    The infrared (IR) emission of 'M {sub *} galaxies' (10{sup 10.4} {<=} M {sub star} {<=} 10{sup 11.0} M {sub Sun }) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single-disk galaxies in well-matched control samples to study the cosmic evolution of the star formation enhancement induced by galaxy-galaxy interaction. Both the mean IR spectral energy distribution and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star formation enhancement in S+S pairs to decrease with increasing redshift. Between z = 0 and z = 1, this decline of interaction-induced star formation enhancement occurs in parallel with the dramatic increase (by a factor of {approx}10) of the sSFR of single SFGs, both of which can be explained by the higher gas fraction in higher-z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the intergalactic medium (IGM) in the dark matter halos hosting these pairs.

  5. Enhancement of superconductivity via periodic modulation in a three-dimensional model of cuprates

    NASA Astrophysics Data System (ADS)

    Raines, Zachary M.; Stanev, Valentin; Galitski, Victor M.

    2015-05-01

    Recent experiments in the cuprates have seen evidence of a transient superconducting state upon optical excitation polarized along the c axis [R. Mankowsky et al., Nature (London) 516, 71 (2014), 10.1038/nature13875]. Motivated by these experiments, we propose an extension of the single-layer t -J -V model of cuprates to three dimensions in order to study the effects of interplane tunneling on the competition between superconductivity and bond density wave order. We find that an optical pump can suppress the charge order and simultaneously enhance superconductivity, due to the inherent competition between the two. We also provide an intuitive picture of the physical mechanism underlying this effect. Furthermore, based on a simple Floquet theory, we estimate the magnitude of the enhancement.

  6. Nonlocal Intuition: Replication and Paired-subjects Enhancement Effects.

    PubMed

    Rezaei, Saeed; Mirzaei, Maryam; Zali, Mohammad Reza

    2014-03-01

    This article reports the results of a study of repeat entrepreneurs in Tehran, Iran, in which nonlocal intuition was investigated in a replication and extension of experiment using measures of heart rate variability (HRV). Nonlocal intuition is the perception of information about a distant or future event by the body's psychophysiological systems, which is not based on reason or memories of prior experience. This study follows up on the McCraty, Radin, and Bradley studies, which found evidence of nonlocal intuition. We used Radin's experimental protocol, with the addition of HRV measures as in the McCraty studies involving computer administration of a random sequence of calm and emotional pictures as the stimulus, and conducted two experiments on mutually exclusive samples-the first on a group of single participants (N=15) and the second on a group of co-participant pairs (N=30)-to investigate the question of the "amplification" of intuition effects by social connection. Each experiment was conducted over 45 trials while heart rate rhythm activity was recorded continuously. Results, using random permutation analysis, a statistically conservative procedure, show significant pre-stimulus results-that is, for the period before the computer had randomly selected the picture stimulus-for both experiments. Moreover, while significant separation between the emotional and calm HRV curves was observed in the single-participant experiment, an even larger separation was apparent for the experiment on co-participant pairs; the difference between the two groups was also significant. Overall, the results of the single-participant experiment confirm previous finding: that electrophysiological measures, especially changes in the heart rhythm, can detect intuitive foreknowledge. This result is notable because it constitutes cross-cultural corroboration in a non-Western context-namely, Iran. In addition, the results for co-participant pairs offer new evidence on the amplification of

  7. Nonlocal Intuition: Replication and Paired-subjects Enhancement Effects

    PubMed Central

    Mirzaei, Maryam; Zali, Mohammad Reza

    2014-01-01

    This article reports the results of a study of repeat entrepreneurs in Tehran, Iran, in which nonlocal intuition was investigated in a replication and extension of experiment using measures of heart rate variability (HRV). Nonlocal intuition is the perception of information about a distant or future event by the body's psychophysiological systems, which is not based on reason or memories of prior experience. This study follows up on the McCraty, Radin, and Bradley studies, which found evidence of nonlocal intuition. We used Radin's experimental protocol, with the addition of HRV measures as in the McCraty studies involving computer administration of a random sequence of calm and emotional pictures as the stimulus, and conducted two experiments on mutually exclusive samples—the first on a group of single participants (N=15) and the second on a group of co-participant pairs (N=30)—to investigate the question of the “amplification” of intuition effects by social connection. Each experiment was conducted over 45 trials while heart rate rhythm activity was recorded continuously. Results, using random permutation analysis, a statistically conservative procedure, show significant pre-stimulus results—that is, for the period before the computer had randomly selected the picture stimulus—for both experiments. Moreover, while significant separation between the emotional and calm HRV curves was observed in the single-participant experiment, an even larger separation was apparent for the experiment on co-participant pairs; the difference between the two groups was also significant. Overall, the results of the single-participant experiment confirm previous finding: that electrophysiological measures, especially changes in the heart rhythm, can detect intuitive foreknowledge. This result is notable because it constitutes cross-cultural corroboration in a non-Western context—namely, Iran. In addition, the results for co-participant pairs offer new evidence on the

  8. Interplay between quantum fluctuations and reentrant superconductivity with a highly enhanced upper critical field in URhGe

    NASA Astrophysics Data System (ADS)

    Tokunaga, Y.; Aoki, D.; Mayaffre, H.; Krämer, S.; Julien, M.-H.; Berthier, C.; Horvatić, M.; Sakai, H.; Hattori, T.; Kambe, S.; Araki, S.

    2016-05-01

    The ferromagnetic superconductor URhGe has been known to exhibit an extremely large enhancement of the upper critical field when the field is confined and rotated in the (a b ) crystal plane. Our high-field 59Co NMR measurements on 10% Co-doped URhGe up to 30 T prove that this unconventional behavior of the superconductivity (SC) is associated with a strong anisotropy of field-dependent quantum fluctuations near a tricritical point. These fluctuations are rapidly suppressed by the field component along the c axis, while being unaffected by any field component along the a axis. The observed close interplay between the SC and quantum fluctuations strongly supports a pairing mechanism mediated by these fluctuations in URhGe.

  9. Spin polarization enhanced by spin-triplet pairing in Sr2RuO4 probed by NMR

    NASA Astrophysics Data System (ADS)

    Ishida, K.; Manago, M.; Yamanaka, T.; Fukazawa, H.; Mao, Z. Q.; Maeno, Y.; Miyake, K.

    2015-09-01

    We report a phenomenon intimately related to the spin-triplet superconductivity. It is well known that the spin susceptibility decreases below the superconducting transition temperature in almost all superconductors because of spin-singlet pair formation, while it may remain unchanged in a handful of spin-triplet exceptions. Here we report the observation in Sr2RuO4 with nuclear magnetic resonance that the spin susceptibility originating from the Ru-4 d electron slightly i n c r e a s e s by ˜2 % of the total and becomes inhomogeneous in the superconducting state. These are reasonably explained if the electron pairs form the equal-spin pairing in the mixed state. A similar phenomenon was predicted for superfluid 3He40 years ago, but had never been demonstrated in any superconductor.

  10. Heavy ion irradiation of Bi-2223 silver-clad tapes for superconducting current density enhancement

    SciTech Connect

    Malozcnoff, A.P.; Carter, W.L.; Riley, G.N. Jr.; Wheeler, R. IV; Kirk, M.A.; Civale, L.; Marwick, A.D.

    1993-07-01

    Silver-clad composite tapes of Bi(Pb)SrCaCuO-2223 were irradiated with 1 GeV Au{sup 23+} ions perpendicular to the tape plane, creating columnar tracks with 10 nm diameter. Detailed transmission electron microscopy shows continuous columns, but with variations in the track thickness of +/{minus}2 nm. Magnetic hystersis measurements show substantial enhancement of superconducting current density at most temperatures and fields. Granular and nongranular models for the origin of the magnetic signals are discussed. The results indicate the potential for further performance improvement in high temperature superconducting wire technology, as well as limits in the high-field performance at 77 K.

  11. Scientific Affairs Division of NATO Advanced Study Institute: abstracts for nonequilibrium superconductivity, phonons and Kapitza boundaries

    SciTech Connect

    1980-05-01

    Abstracts of papers presented at the meeting are given. Topics covered include: Kapitza resistance; superconducting tunneling; energy gap enhancement in superconductors; instabilities in nonequilibrium superconducting states; exchange of charge between superconducting pairs and quasiparticles; motion of magnetic flux (flux flow); and other new phenomena. (GHT)

  12. Enhanced Surface Superconductivity in Single Crystal La2-xBaxCuO4

    NASA Astrophysics Data System (ADS)

    Martin, Ivar; Tee, Xian Yang; Ito, Toshimitsu; Ushiyama, Tomoharu; Tomioka, Yasuhide; Panagopoulos, Christos

    Surfaces of materials often possess properties which are distinctly different from their bulk. The atomic structure can develop intricate new patterns due to surface reconstruction and the electronic properties can be very distinct, as most dramatically manifested in topological insulators. However, more subtle collective phenomena such as superconductivity are not as strongly affected by the presence of surfaces. Here, we report an unprecedented finding of enhanced superconductivity at the ab-plane surface of high-Tc cuprate La2-xBaxCuO4. Spatially-resolved electrical and thermoelectric transport measurements detect a superconducting surface below the transition temperature Tcs which is considerably higher than the bulk Tc. The effect is pronounced in the region of charge carrier doping (x) with strong spin-charge stripe correlations. Notably, for x = 0 . 12 , Tcs reaches 36 K, exceeding even the highest reported bulk Tc in this material for any doping. Possible interpretations for the novel effect are discussed.

  13. Increased extra-pair paternity in broods of aging males and enhanced recruitment of extra-pair young in a migratory bird

    PubMed Central

    Bowers, E. Keith; Forsman, Anna M.; Masters, Brian S.; Johnson, Bonnie G. P.; Johnson, L. Scott; Sakaluk, Scott K.; Thompson, Charles F.

    2015-01-01

    Despite keen interest in extra-pair mating in birds, its adaptive significance remains unresolved. Here, we use a multi-year dataset to test whether traits of a female’s social mate influence her propensity to produce extra-pair offspring in a population of house wrens, and whether producing extra-pair young has consequences for a female’s fitness through effects on offspring survival. Females were most likely to produce extra-pair offspring when paired with old males and when paired with males on poor-quality territories, although this latter effect was marginally non-significant. Among offspring, the cutaneous immunity of within-pair young decreased as the age of their sires increased, but cutaneous immunity of extra-pair young was not affected by the age of their extra-pair sires or by the age of the males rearing them. Extra-pair offspring were more likely than within-pair offspring to return as breeding adults to the local population, with extra-pair sons being more likely to return as a breeder for multiple years. Our findings support the hypothesis that females produce extra-pair offspring to enhance their inclusive fitness beyond what they are capable of given the male with which they are socially paired. PMID:26258950

  14. Interface-enhanced electron-phonon coupling and high-temperature superconductivity in potassium-coated ultrathin FeSe films on SrTiO3

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    Alkali-metal (potassium) adsorption on FeSe thin films with thickness from 2 unit cells (UC) to 4 UC on SrTi O3 grown by molecular beam epitaxy is investigated with a low-temperature scanning tunneling microscope. At appropriate potassium coverage (0.20-0.25 monolayer), the tunneling spectra of the films all exhibit a superconductinglike gap which is overall larger than 11 meV (five times the gap value of bulk FeSe) and decreases with increasing thickness, and two distinct features of characteristic phonon modes at ˜11 and ˜21 meV. The results reveal the critical role of the interface-enhanced electron-phonon coupling for possible high-temperature superconductivity in ultrathin FeSe films on SrTi O3 and is consistent with recent theories. Our study provides compelling evidence for the conventional pairing mechanism for this type of heterostructure superconducting system.

  15. CHARGE-IMBALANCE RELAXATION IN THE PRESENCE OF A PAIR-BREAKING INTERACTION IN SUPERCONDUCTING AlEr FILMS

    SciTech Connect

    Lemberger, T.R.; Clarke, J.

    1980-07-01

    The charge-imbalance relaxation rate, 1/F*{sub T{sub Q*}}, has been measured in dirty superconducting AlEr films in which Er is a pair-breaking magnetic impurity that induces charge relaxation through elastic exchange scattering. Measurements were made in the range 0.1 {approx}< {Delta}(T)/k{sub B}T{sub c} {approx}< 1.4 for Er concentrations varying from 21 to 1660 at. ppm that produced estimated exchange scattering rates, {tau}{sub S}{sup -1}, from about 10{sup 9} sec{sup -1} to 5 x 10{sup 10} sec{sup -1}. Measured values of 1/F*{sub T{sub Q*}} were in good agreement with the Schmid-Schoen expression, 1/F*{sub T{sub Q*}}=({pi}{Delta}/4k{sub B}T{sub c}{tau}{sub E}) x (1+2{tau}{sub E}/{tau}{sub S}){sup 1/2}, for {Delta}/k{sub B}T{sub c} {approx}< 0.8, where {tau}{sub E}{sup -1} is the electron-phonon scattering rate estimated from the measured transition temperature. For larger values of {Delta}/k{sub B}T{sub c}, the relaxation rate increased less rapidly with {Delta}. The appropriate Boltzmann equation was solved on a computer to obtain values for 1/F*{sub T{sub Q*}} in the range 0.5 {approx}< T/T{sub c} {approx}< 0.999999. The computed values of 1/F*{sub T{sub Q*}} agreed with several analytic expressions valid for {Delta}/k{sub B}T{sub c} << 1, but not with the experimental data: The computed curves increased more rapidly than linearly with {Delta}/k{sub B}T{sub c} near T{sub c}, and the shape of the 1/F*{sub T{sub Q*}} vs {Delta}/k{sub B}T{sub c} curves was qualitatively different. This discrepancy suggests that either the generally accepted expression for exchange charge relaxation is incorrect, or that the Boltzmann equation is inappropriate for these calculations.

  16. Pressure Induced Enhancement of Superconductivity in LaRu2P2

    PubMed Central

    Li, Baoxuan; Liu, Jianzhong; Sun, Jian; Li, Sheng; Zhu, Xiyu; Wen, Hai-Hu

    2016-01-01

    To explore new superconductors beyond the copper-based and iron-based systems is very important. The Ru element locates just below the Fe in the periodic table and behaves like the Fe in many ways. One of the common thread to induce high temperature superconductivity is to introduce moderate correlation into the system. In this paper, we report the significant enhancement of superconducting transition temperature from 3.8 K to 5.8 K by using a pressure only of 1.74 ± 0.05 GPa in LaRu2P2 which has an iso-structure of the iron-based 122 superconductors. The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan’s theory with strong electron-phonon coupling. However, it is difficult to interpret the enhancement of Tc versus pressure within this picture. Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction. This suggests that the Ru-based system has some commonality as the Fe-based superconductors. PMID:27086696

  17. Pressure Induced Enhancement of Superconductivity in LaRu2P2

    NASA Astrophysics Data System (ADS)

    Li, Baoxuan; Lu, Pengchao; Liu, Jianzhong; Sun, Jian; Li, Sheng; Zhu, Xiyu; Wen, Hai-Hu

    2016-04-01

    To explore new superconductors beyond the copper-based and iron-based systems is very important. The Ru element locates just below the Fe in the periodic table and behaves like the Fe in many ways. One of the common thread to induce high temperature superconductivity is to introduce moderate correlation into the system. In this paper, we report the significant enhancement of superconducting transition temperature from 3.8 K to 5.8 K by using a pressure only of 1.74 ± 0.05 GPa in LaRu2P2 which has an iso-structure of the iron-based 122 superconductors. The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan’s theory with strong electron-phonon coupling. However, it is difficult to interpret the enhancement of Tc versus pressure within this picture. Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction. This suggests that the Ru-based system has some commonality as the Fe-based superconductors.

  18. Pressure Induced Enhancement of Superconductivity in LaRu2P2.

    PubMed

    Li, Baoxuan; Lu, Pengchao; Liu, Jianzhong; Sun, Jian; Li, Sheng; Zhu, Xiyu; Wen, Hai-Hu

    2016-01-01

    To explore new superconductors beyond the copper-based and iron-based systems is very important. The Ru element locates just below the Fe in the periodic table and behaves like the Fe in many ways. One of the common thread to induce high temperature superconductivity is to introduce moderate correlation into the system. In this paper, we report the significant enhancement of superconducting transition temperature from 3.8 K to 5.8 K by using a pressure only of 1.74 ± 0.05 GPa in LaRu2P2 which has an iso-structure of the iron-based 122 superconductors. The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan's theory with strong electron-phonon coupling. However, it is difficult to interpret the enhancement of Tc versus pressure within this picture. Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction. This suggests that the Ru-based system has some commonality as the Fe-based superconductors. PMID:27086696

  19. Strain-enhanced superconductivity of Mo X2(X =S or Se) bilayers with Na intercalation

    NASA Astrophysics Data System (ADS)

    Zhang, Jun-Jie; Gao, Bin; Dong, Shuai

    2016-04-01

    Mo X2(X =S or Se) is a semiconductor family with two-dimensional structure. And a recent calculation predicted the superconductivity in the electron-doped MoS2 monolayer. In this work, the electronic structure and lattice dynamics of Mo X2 bilayers with monolayer Na intercalated have been calculated. According to the electron-phonon interaction, it is predicted that these bilayers can be transformed from indirect-gap semiconductors to superconductors by Na intercalation. More interestingly, the biaxial tensile strain can significantly enhance the superconducting temperature up to ˜10 K in Na-intercalated MoS2. In addition, the phonon mean free path at room temperature is also greatly improved in Na-intercalated MoSe2, which is advantageous for related applications.

  20. Superconductivity enhanced by Se doping in Eu3Bi2(S,Se)4F4

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Zhai, H. F.; Tang, Z. J.; Li, L.; Li, Y. K.; Chen, Q.; Chen, J.; Wang, Z.; Feng, C. M.; Cao, G. H.; Xu, Z. A.

    2015-07-01

    We investigated the negative-chemical-pressure effect of Eu3Bi2S4-x Se x F4 (0 ≤ x ≤ 2.0) by the partial substitution of S with Se. The crystalline lattice substantially expands as Se is doped, suggesting an effective negative chemical pressure. With Se/S doping, the charge-density-wave-like anomaly is suppressed, and meanwhile the superconducting transition temperature (T_c) is enhanced. For x = 2.0 , T c reaches 3.35 K and bulk superconductivity is confirmed by the strong diamagnetic signal, with shielding volume fraction over 90%. Magnetic-susceptibility, specific-heat and Hall-effect measurements reveal that the Se/S doping increases the carrier density, corresponding to the increase of the average Eu valence. Our work provides a rare paradigm of negative-chemical-pressure effect.

  1. The fatty acids as penetration enhancers of amino acids by ion pairing.

    PubMed

    Arct, J; Chelkowska, M; Kasiura, K; Pietrzykowski, P

    2002-12-01

    The influence of palmitic acid on n-octanol/water partition coefficient (log P) of selected amino acids, alanine, glycine, proline, hydroxyproline, seine, valine, threonine and lysine, was measured at a wide range of pH. A parabolic shape curve was obtained in every case (pH vs. Deltalog P), with maximum depending on the amino acid. In each case in the presence of palmitic acid, the apparent partition coefficient increased. To check the possible mechanism of extraction of amino acids into n-octanol phase in the presence of palmitate additionally, the influence of an amount of counter ion on partition coefficient of lysine was investigated. The results suggest that the enhanced partitioning of lysine results from the ion pair formation with palmitate. The ion pair stratum corneum-lipid membrane transport of the amino acids was investigated as well, using palmitate as a counter ion. The apparent permeability coefficients were enhanced significantly by palmitic acid at pH 7.4. As many substances (e.g. organic solvents, unsaturated fatty acids, etc.) are penetration enhancers which change the structure of intercellular lipid, the influence of palmitic acid on membrane was investigated. After pretreatment of membrane with palmitic acid, no changes in permeation of alanine were observed. Investigations suggest the enhanced permeation of amino acids via ion pairing. The method for prediction of pH in which the possibility of ion pairing is the highest was developed as well. PMID:18494885

  2. Pressure-enhanced superconductivity in Eu3Bi2S4F4

    NASA Astrophysics Data System (ADS)

    Luo, Yongkang; Zhai, Hui-Fei; Zhang, Pan; Xu, Zhu-An; Cao, Guang-Han; Thompson, J. D.

    2014-12-01

    The pressure effect on the newly discovered charge-transferred BiS2-based superconductor, Eu3Bi2S4F4 , with a Tc of 1.5 K at ambient pressure, is investigated by transport and magnetic measurements. Accompanied with the enhancement of metallicity under pressures, the onset superconducting transition temperature increases abruptly around 1.0 GPa, reaching ˜10.0 K at 2.26 GPa. Alternating current magnetic susceptibility measurements indicate that a new superconducting phase with a higher Tc emerges and dominates at high pressures. In the broad pressure window of 0.68 GPa≤p ≤2.00 GPa, the high-Tc phase coexists with the low-Tc phase. Hall effect measurements reveal a significant difference in electronic structures between the two superconducting phases. Our work devotes the effort to establish the commonality of pressure effect on the BiS2-based superconductors, and also uncovers the importance of electron carrier density in the high-Tc phase.

  3. Pressure-enhanced superconductivity in Eu3Bi2S4F4

    DOE PAGESBeta

    Luo, Yongkang; Zhai, Hui -Fei; Zhang, Pan; Xu, Zhu -An; Cao, Guang -Han; Thompson, J. D.

    2014-12-17

    The pressure effect on the newly discovered charge-transferred BiS2-based superconductor, Eu3Bi2S4F4, with a Tc of 1.5 K at ambient pressure, is investigated by transport and magnetic measurements. Accompanied with the enhancement of metallicity under pressures, the onset superconducting transition temperature increases abruptly around 1.0 GPa, reaching ~10.0 K at 2.26 GPa. Alternating current magnetic susceptibility measurements indicate that a new superconducting phase with a higher Tc emerges and dominates at high pressures. In the broad pressure window of 0.68GPa≤p≤2.00 GPa, the high-Tc phase coexists with the low-Tc phase. Hall effect measurements reveal a significant difference in electronic structures between themore » two superconducting phases. As a result, our work devotes the effort to establish the commonality of pressure effect on the BiS2-based superconductors, and also uncovers the importance of electron carrier density in the high-Tc phase.« less

  4. Enhancement of superconductivity at the onset of charge-density-wave order in a metal

    NASA Astrophysics Data System (ADS)

    Wang, Yuxuan; Chubukov, Andrey V.

    2015-09-01

    We analyze superconductivity in the cuprates near the onset of an incommensurate charge-density-wave (CDW) order with momentum Q =(Q ,0 )/(0 ,Q ) , as observed in experiments. We first consider a semiphenomenological charge-fermion model in which hot fermions, separated by Q , attract each other by exchanging soft CDW fluctuations. We find that in a quantum-critical region near the CDW transition, Tc=A g¯c , where g¯c is charge-fermion coupling and A is the prefactor, which we explicitly compute. We then consider the particular microscopic scenario in which the CDW order parameter emerges as a composite field made of primary spin-density-wave fields. We show that charge-fermion coupling g¯c is of the order of spin-fermion coupling g¯s. As a consequence, superconducting Tc is substantially enhanced near the onset of CDW order. Finally, we analyze the effect of an external magnetic field H . We show that, as H increases, the optimal Tc decreases and the superconducting dome becomes progressively more confined to the CDW quantum-critical point. These results are consistent with experiments.

  5. Method of enhancing the upper critical field (HC sub 2 ) in high temperature superconducting ceramic copper oxide perovskites

    SciTech Connect

    Rosen, C.Z.

    1992-03-03

    This patent describes a method of increasing the current carrying capacity and enhancing the upper critical (H{sub c2}) in a Type II superconducting material. It comprises providing a sample of a Type II superconducting material; exposing the sample to gamma radiation ranging in dosage level from about ten million rads to about one hundred million rads at a dose rate of about three million rads per hour.

  6. Enhanced electromechanical coupling of a nanomechanical resonator to coupled superconducting cavities

    PubMed Central

    Li, Peng-Bo; Li, Hong-Rong; Li, Fu-Li

    2016-01-01

    We investigate the electromechanical coupling between a nanomechanical resonator and two parametrically coupled superconducting coplanar waveguide cavities that are driven by a two-mode squeezed microwave source. We show that, with the selective coupling of the resonator to the cavity Bogoliubov modes, the radiation-pressure type coupling can be greatly enhanced by several orders of magnitude, enabling the single photon strong coupling to be reached. This allows the investigation of a number of interesting phenomena such as photon blockade effects and the generation of nonclassical quantum states with electromechanical systems. PMID:26753744

  7. A hybrid superconducting fault current limiter for enhancing transient stability in Korean power systems

    NASA Astrophysics Data System (ADS)

    Seo, Sangsoo; Kim, Seog-Joo; Moon, Young-Hwan; Lee, Byongjun

    2013-11-01

    Additional power generation sites have been limited in Korea, despite the fact load demands are gradually increasing. In order to meet these increasing demands, Korea’s power system company has begun constructing new generators at existing sites. Thus, multi-unit plants can create problems in terms of transient stability when a large disturbance occurs. This paper proposes a hybrid superconducting fault current limiter (SFCL) application to enhance the transient stability of multi-unit power plants. SFCLs reduce fault currents, and limitation currents decrease the imbalance of the mechanical and electrical torque of the generators, resulting in an improvement in transient stability.

  8. Superconductivity. Quasiparticle mass enhancement approaching optimal doping in a high-T(c) superconductor.

    PubMed

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

    2015-04-17

    In the quest for superconductors with higher transition temperatures (T(c)), one emerging motif is that electronic interactions favorable for superconductivity can be enhanced by fluctuations of a broken-symmetry phase. Recent experiments have suggested the existence of the requisite broken-symmetry phase in the high-T(c) cuprates, but the impact of such a phase on the ground-state electronic interactions has remained unclear. We used magnetic fields exceeding 90 tesla to access the underlying metallic state of the cuprate YBa2Cu3O(6+δ) over a wide range of doping, and observed magnetic quantum oscillations that reveal a strong enhancement of the quasiparticle effective mass toward optimal doping. This mass enhancement results from increasing electronic interactions approaching optimal doping, and suggests a quantum critical point at a hole doping of p(crit) ≈ 0.18. PMID:25814065

  9. Electronic disorder and magnetic-field-induced superconductivity enhancement in Fe1+y(Te1-xSex)

    NASA Astrophysics Data System (ADS)

    Hu, Jin; Liu, Tijiang; Qian, Bin; Mao, Zhiqiang

    2012-02-01

    The iron chalcogenide Fe1+y(Te1-xSex) superconductor system exhibits a unique electronic and magnetic phase diagram distinct from those seen in iron pnictides: bulk superconductivity does not appear immediately following the suppression of long-range (π,0) AFM order. Instead, an intermediate phase with weak charge carrier localization appears between AFM order and bulk superconductivity (Liu et al., Nat. Mater. 9, 719 (2010)). In this talk, we report our recent studies on the relationship between the normal state and superconducting properties in Fe1+y(Te1-xSex). We show that the superconducting volume fraction VSC and normal state metallicity significantly increase while the normal state Sommerfeld coefficient γ and Hall coefficient RH drop drastically with increasing Se content in the underdoped superconducting region. Additionally, VSC is surprisingly enhanced by magnetic field in heavily underdoped superconducting samples. The implications of these results will be discussed. Our analyses suggest that the suppression of superconductivity in the underdoped region is associated with electronic disorder caused by incoherent magnetic scattering arising from (π,0) magnetic fluctuations.

  10. Concomitant enhancement of spin susceptibility and pairing interaction in the reduced carrier-density regime of LixZrNCl superconductor

    NASA Astrophysics Data System (ADS)

    Kasahara, Yuichi; Kishiume, Tsukasa; Takano, Takumi; Kobayashi, Katsuki; Iwasa, Yoshihiro; Matsuoka, Eiichi; Onodera, Hideya; Taguchi, Yasujiro

    2009-03-01

    Li-intercalated layered nitrides LixZrNCl are novel superconductors, in which superconductivity emerges at relatively high transition temperature Tc˜12 - 15 K with very low carrier density ˜10^21 cm-3. The pristine β-ZrNCl is a simple band insulator, and electron doping is achieved by Li intercalation. Insulator-to-superconductor (IS) transition takes place at x˜0.05 with maximum Tc value of ˜15 K and Tc decreases with further doping, which is opposite trend to the other superconductors in doped band insulators. Here we show the results of magnetic susceptibility measurements on LixZrNCl with systematically controlled x. Estimated spin susceptibility χs is almost temperature-independent without substantial anisotropy. With decreasing x, χs evolves strongly, same as Tc. On the other hand, specific heat study revealed that the density of states is reduced but the pairing interaction is enhanced on the verge of IS transition. Therefore, our results may indicate that magnetic fluctuations are enhanced toward a band-insulator and that they are possibly responsible to superconductivity even in the present small carrier-density system.

  11. Fractal superconductivity near localization threshold

    SciTech Connect

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

    2010-07-15

    We develop a semi-quantitative theory of electron pairing and resulting superconductivity in bulk 'poor conductors' in which Fermi energy E{sub F} is located in the region of localized states not so far from the Anderson mobility edge E{sub c}. We assume attractive interaction between electrons near the Fermi surface. We review the existing theories and experimental data and argue that a large class of disordered films is described by this model. Our theoretical analysis is based on analytical treatment of pairing correlations, described in the basis of the exact single-particle eigenstates of the 3D Anderson model, which we combine with numerical data on eigenfunction correlations. Fractal nature of critical wavefunction's correlations is shown to be crucial for the physics of these systems. We identify three distinct phases: 'critical' superconductive state formed at E{sub F} = E{sub c}, superconducting state with a strong pseudo-gap, realized due to pairing of weakly localized electrons and insulating state realized at E{sub F} still deeper inside a localized band. The 'critical' superconducting phase is characterized by the enhancement of the transition temperature with respect to BCS result, by the inhomogeneous spatial distribution of superconductive order parameter and local density of states. The major new feature of the pseudo-gapped state is the presence of two independent energy scales: superconducting gap {Delta}, that is due to many-body correlations and a new 'pseudo-gap' energy scale {Delta}{sub P} which characterizes typical binding energy of localized electron pairs and leads to the insulating behavior of the resistivity as a function of temperature above superconductive T{sub c}. Two gap nature of the pseudo-gapped superconductor is shown to lead to specific features seen in scanning tunneling spectroscopy and point-contact Andreev spectroscopy. We predict that pseudo-gapped superconducting state demonstrates anomalous behavior of the optical

  12. Nanoelectromechanics of superconducting weak links (Review Article)

    NASA Astrophysics Data System (ADS)

    Parafilo, A. V.; Krive, I. V.; Shekhter, R. I.; Jonson, M.

    2012-04-01

    Nanoelectromechanical effects in superconducting weak links are considered. Three different superconducting devices are studied: (i) a single-Cooper-pair transistor, (ii) a transparent SNS junction, and (iii) a single-level quantum dot coupled to superconducting electrodes. The electromechanical coupling is due to electrostatic or magnetomotive forces acting on a movable part of the device. It is demonstrated that depending on the frequency of mechanical vibrations the electromechanical coupling could either suppress or enhance the Josephson current. Nonequilibrium effects associated with cooling of the vibrational subsystem or pumping energy into it at low bias voltages are discussed.

  13. Exposure to pairs of Aeromonas strains enhances virulence in the Caenorhabditis elegans infection model

    PubMed Central

    Mosser, Thomas; Talagrand-Reboul, Emilie; Colston, Sophie M.; Graf, Joerg; Figueras, Maria J.; Jumas-Bilak, Estelle; Lamy, Brigitte

    2015-01-01

    Aeromonad virulence remains poorly understood, and is difficult to predict from strain characteristics. In addition, infections are often polymicrobial (i.e., are mixed infections), and 5–10% of such infections include two distinct aeromonads, which has an unknown impact on virulence. In this work, we studied the virulence of aeromonads recovered from human mixed infections. We tested them individually and in association with other strains with the aim of improving our understanding of aeromonosis. Twelve strains that were recovered in pairs from six mixed infections were tested in a virulence model of the worm Caenorhabditis elegans. Nine isolates were weak worm killers (median time to death, TD50, ≥7 days) when administered alone. Two pairs showed enhanced virulence, as indicated by a significantly shortened TD50 after co-infection vs. infection with a single strain. Enhanced virulence was also observed for five of the 14 additional experimental pairs, and each of these pairs included one strain from a natural synergistic pair. These experiments indicated that synergistic effects were frequent and were limited to pairs that were composed of strains belonging to different species. The genome content of virulence-associated genes failed to explain virulence synergy, although some virulence-associated genes that were present in some strains were absent from their companion strain (e.g., T3SS). The synergy observed in virulence when two Aeromonas isolates were co-infected stresses the idea that consideration should be given to the fact that infection does not depend only on single strain virulence but is instead the result of a more complex interaction between the microbes involved, the host and the environment. These results are of interest for other diseases in which mixed infections are likely and in particular for water-borne diseases (e.g., legionellosis, vibriosis), in which pathogens may display enhanced virulence in the presence of the right partner. This

  14. Exposure to pairs of Aeromonas strains enhances virulence in the Caenorhabditis elegans infection model.

    PubMed

    Mosser, Thomas; Talagrand-Reboul, Emilie; Colston, Sophie M; Graf, Joerg; Figueras, Maria J; Jumas-Bilak, Estelle; Lamy, Brigitte

    2015-01-01

    Aeromonad virulence remains poorly understood, and is difficult to predict from strain characteristics. In addition, infections are often polymicrobial (i.e., are mixed infections), and 5-10% of such infections include two distinct aeromonads, which has an unknown impact on virulence. In this work, we studied the virulence of aeromonads recovered from human mixed infections. We tested them individually and in association with other strains with the aim of improving our understanding of aeromonosis. Twelve strains that were recovered in pairs from six mixed infections were tested in a virulence model of the worm Caenorhabditis elegans. Nine isolates were weak worm killers (median time to death, TD50, ≥7 days) when administered alone. Two pairs showed enhanced virulence, as indicated by a significantly shortened TD50 after co-infection vs. infection with a single strain. Enhanced virulence was also observed for five of the 14 additional experimental pairs, and each of these pairs included one strain from a natural synergistic pair. These experiments indicated that synergistic effects were frequent and were limited to pairs that were composed of strains belonging to different species. The genome content of virulence-associated genes failed to explain virulence synergy, although some virulence-associated genes that were present in some strains were absent from their companion strain (e.g., T3SS). The synergy observed in virulence when two Aeromonas isolates were co-infected stresses the idea that consideration should be given to the fact that infection does not depend only on single strain virulence but is instead the result of a more complex interaction between the microbes involved, the host and the environment. These results are of interest for other diseases in which mixed infections are likely and in particular for water-borne diseases (e.g., legionellosis, vibriosis), in which pathogens may display enhanced virulence in the presence of the right partner. This

  15. The road to superconducting spintronics

    NASA Astrophysics Data System (ADS)

    Eschrig, Matthias

    Energy efficient computing has become a major challenge, with the increasing importance of large data centres across the world, which already today have a power consumption comparable to that of Spain, with steeply increasing trend. Superconducting computing is progressively becoming an alternative for large-scale applications, with the costs for cooling being largely outweighed by the gain in energy efficiency. The combination of superconductivity and spintronics - ``superspintronics'' - has the potential and flexibility to develop into such a green technology. This young field is based on the observation that new phenomena emerge at interfaces between superconducting and other, competing, phases. The past 15 years have seen a series of pivotal predictions and experimental discoveries relating to the interplay between superconductivity and ferromagnetism. The building blocks of superspintronics are equal-spin Cooper pairs, which are generated at the interface between superconducting and a ferromagnetic materials in the presence of non-collinear magnetism. Such novel, spin-polarised Cooper pairs carry spin-supercurrents in ferromagnets and thus contribute to spin-transport and spin-control. Geometric Berry phases appear during the singlet-triplet conversion process in structures with non-coplanar magnetisation, enhancing functionality of devices, and non-locality introduced by superconducting order leads to long-range effects. With the successful generation and control of equal-spin Cooper pairs the hitherto notorious incompatibility of superconductivity and ferromagnetism has been not only overcome, but turned synergistic. I will discuss these developments and their extraordinary potential. I also will present open questions posed by recent experiments and point out implications for theory. This work is supported by the Engineering and Physical Science Research Council (EPSRC Grant No. EP/J010618/1).

  16. Ultrafast Synchrotron-Enhanced Thermalization of Laser-Driven Colliding Pair Plasmas

    NASA Astrophysics Data System (ADS)

    Lobet, M.; Ruyer, C.; Debayle, A.; d'Humières, E.; Grech, M.; Lemoine, M.; Gremillet, L.

    2015-11-01

    We report on the first self-consistent numerical study of the feasibility of laser-driven relativistic pair shocks of prime interest for high-energy astrophysics. Using a QED-particle-in-cell code, we simulate the collective interaction between two counterstreaming electron-positron jets driven from solid foils by short-pulse (˜60 fs ), high-energy (˜100 kJ ) lasers. We show that the dissipation caused by self-induced, ultrastrong (>1 06 T ) electromagnetic fluctuations is amplified by intense synchrotron emission, which enhances the magnetic confinement and compression of the colliding jets.

  17. Ultrafast Synchrotron-Enhanced Thermalization of Laser-Driven Colliding Pair Plasmas.

    PubMed

    Lobet, M; Ruyer, C; Debayle, A; d'Humières, E; Grech, M; Lemoine, M; Gremillet, L

    2015-11-20

    We report on the first self-consistent numerical study of the feasibility of laser-driven relativistic pair shocks of prime interest for high-energy astrophysics. Using a QED-particle-in-cell code, we simulate the collective interaction between two counterstreaming electron-positron jets driven from solid foils by short-pulse (~60 fs), high-energy (~100 kJ) lasers. We show that the dissipation caused by self-induced, ultrastrong (>10^{6} T) electromagnetic fluctuations is amplified by intense synchrotron emission, which enhances the magnetic confinement and compression of the colliding jets. PMID:26636856

  18. Resonantly enhanced electron-positron pair production in ultra-intense laser-matter interaction

    NASA Astrophysics Data System (ADS)

    Fillion-Gourdeai, Francois; Lorin, Emmanuel; Bandrauk, Andre

    2013-05-01

    A new mechanism for pair production from the interaction of a laser with two nuclei is presented. The latter takes advantage of the Stark effect in diatomic molecules and the presence of molecular resonances in the negative and positive energy continua. Both move in the complex energy plane as the interatomic distance and the electric field strength are varied. We demonstrate that there is an enhancement of pair production at the crossing of these resonances. This mechanism is studied in a very simple one-dimensional model where the nuclei are modelled by delta function potential wells and the laser by a constant electric field. The position of resonances is evaluated by using the Weyl-Titchmarch-Kodaira theory, which allows to treat singular boundary value problems and to compute the spectral density. The rate of producing pairs is also computed. It is shown that this process yields a positron production rate which is approximately an order of magnitude higher than in the single nucleus case and a few orders of magnitudes higher than Schwinger's tunnelling result in a static field.

  19. Silver-mediated base pairings: towards dynamic DNA nanostructures with enhanced chemical and thermal stability

    NASA Astrophysics Data System (ADS)

    Swasey, Steven M.; Gwinn, Elisabeth G.

    2016-04-01

    The thermal and chemical fragility of DNA nanomaterials assembled by Watson–Crick (WC) pairing constrain the settings in which these materials can be used and how they can be functionalized. Here we investigate use of the silver cation, Ag+, as an agent for more robust, metal-mediated self-assembly, focusing on the simplest duplex building blocks that would be required for more elaborate Ag+–DNA nanostructures. Our studies of Ag+-induced assembly of non-complementary DNA oligomers employ strands of 2–24 bases, with varied base compositions, and use electrospray ionization mass spectrometry to determine product compositions. High yields of duplex products containing narrowly distributed numbers of Ag+ can be achieved by optimizing solution conditions. These Ag+-mediated duplexes are stable to at least 60 mM Mg2+, higher than is necessary for WC nanotechnology schemes such as tile assemblies and DNA origami, indicating that sequential stages of Ag+-mediated and WC-mediated assembly may be feasible. Circular dichroism spectroscopy suggests simple helical structures for Ag+-mediated duplexes with lengths to at least 20 base pairs, and further indicates that the structure of cytosine-rich duplexes is preserved at high urea concentrations. We therefore propose an approach towards dynamic DNA nanomaterials with enhanced thermal and chemical stability through designs that combine sturdy silver-mediated ‘frames’ with WC paired ‘pictures’.

  20. Mapping IR Enhancements in Closely Interacting Spiral-Spiral Pairs: I. ISO CAM and ISO SWS Observations

    NASA Technical Reports Server (NTRS)

    Xu, C.; Gao, Y.; Mazzarella, J.; Lu, N.; Sulentic, J.; Domingue, D.

    2000-01-01

    Mid-infrared (MIR) imaging and spectroscopic observations are presented for a well defined sample of eight closely interacting (CLO) pairs of spiral galaxies that have overlapping disks and show enhanced far-infrared (FIR) emission.

  1. Magnetic properties and pairing tendencies of the iron-based superconducting ladder BaFe2S3 : Combined ab initio and density matrix renormalization group study

    NASA Astrophysics Data System (ADS)

    Patel, Niravkumar D.; Nocera, Alberto; Alvarez, Gonzalo; Arita, Ryotaro; Moreo, Adriana; Dagotto, Elbio

    2016-08-01

    The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3 [H. Takahashi et al., Nat. Mater. 14, 1008 (2015), 10.1038/nmat4351] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasi-one-dimensional iron-based high-critical-temperature superconductor. Similarly, as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In this publication, we derive a two-orbital Hubbard model from first principles that describes individual ladders of BaFe2S3 . The model is studied with the density matrix renormalization group. These first reported results are exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; and (ii) with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system. In addition, orbital selective Mott phase characteristics develop with doping, with only one Wannier orbital receiving the hole carriers while the other remains half-filled. These results suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies and other exotic properties of iron-based high-critical-temperature superconductors in general.

  2. Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi3 (A = Sr and Ba)

    PubMed Central

    Shao, D. F.; Luo, X.; Lu, W. J.; Hu, L.; Zhu, X. D.; Song, W. H.; Zhu, X. B.; Sun, Y. P.

    2016-01-01

    Recently, Bi-based compounds have attracted attentions because of the strong spin-orbit coupling (SOC). In this work, we figured out the role of SOC in ABi3 (A = Sr and Ba) by theoretical investigation of the band structures, phonon properties, and electron-phonon coupling. Without SOC, strong Fermi surface nesting leads to phonon instabilities in ABi3. SOC suppresses the nesting and stabilizes the structure. Moreover, without SOC the calculation largely underestimates the superconducting transition temperatures (Tc), while with SOC the calculated Tc are very close to those determined by measurements on single crystal samples. The SOC enhanced superconductivity in ABi3 is due to not only the SOC induced phonon softening, but also the SOC related increase of electron-phonon coupling matrix elements. ABi3 can be potential platforms to construct heterostructure of superconductor/topological insulator to realize topological superconductivity. PMID:26892681

  3. Interface enhanced superconductivity in single unit-cell FeSe films on SrTiO3(110)

    NASA Astrophysics Data System (ADS)

    Wang, Lili

    The advent of enhanced superconductivity in FeSe/STO(001) has instigated great interests in other interfacial systems both experimentally and theoretically. To figure out the key role of substrate, STO(110) substrate is of great interest because it resembles STO(001) in high density subsurface oxygen vacancies but distinguishes itself by anisotropic in-plane lattice constants and dielectric constant. Here, we investigated molecular beam epitaxy growth of 1-UC FeSe films on STO(110) substrates and studied the superconducting properties by combined in-situ scanning tunneling spectroscopy (STS) and ex-situ transport measurement. By STS we observed a superconducting gap as large as 17 meV. Transport measurements on 1-UC FeSe/STO(110) capped with FeTe layers reveal superconductivity with an onset transition temperature (TC) of 31.6 K and an upper critical magnetic field of 30.2 T. We also find that TC can be further increased by an external electric field, but the effect is weaker than that on STO(001) substrate. Our study highlights the important roles of interface related charge transfer and electron-phonon coupling in the high temperature superconductivity of FeSe/STO. References: [1] Q. Y. Wang, et al., Chin. Phys. Lett., 29, 037402 (2012). [2] J. J. Lee, Nature 515, 245 (2014).

  4. Rattling-enhanced superconductivity in M V2A l20(M =Sc ,Lu ,Y ) intermetallic cage compounds

    NASA Astrophysics Data System (ADS)

    Winiarski, M. J.; Wiendlocha, B.; Sternik, M.; Wiśniewski, P.; O'Brien, J. R.; Kaczorowski, D.; Klimczuk, T.

    2016-04-01

    Polycrystalline samples of four intermetallic compounds: M V2A l20 (M =Sc , Y, La, and Lu) were synthesized using an arc-melting technique. The crystal structures were analyzed by means of powder x-ray diffraction and Rietveld analysis, and the physical properties were studied by means of heat capacity, electrical resistivity, and magnetic susceptibility measurements down to 0.4 K. For Sc V2A l20 , Lu V2A l20 , and Y V2A l20 , superconductivity was observed with critical temperatures Tc=1.00 , 0.57, and 0.60 K, respectively. Superconductivity for the Lu compound is reported. Theoretical calculations of the electronic and phonon structures were conducted in order to analyze the superconductivity and dynamics in Sc V2A l20 , Y V2A l20 , and Lu V2A l20 and to explain the lack of a superconducting transition in La V2A l20 down to 0.4 K. The results of the experimental and theoretical studies show that all the compounds are weakly coupled type-II BCS superconductors, and reveal the importance of the M -atom anharmonic "rattling" modes for the superconductivity in these materials, which seem to enhance Tc, especially for Sc V2A l20 .

  5. From Electrons Paired to Electric Power Delivered- A Personal Journey in Research and Applications of Superconductivity at IBM, EPRI, and Beyond

    NASA Astrophysics Data System (ADS)

    Grant, Paul

    2014-03-01

    This talk will reprise a personal journey by the speaker in industrial and applied physics, commencing with his employment by IBM at age 17 in the early 1950s, and continuing through his corporate sponsored undergraduate and graduate years at Clarkson and Harvard Universities, resulting in 1965 in a doctorate in applied physics from the latter. He was subsequently assigned by IBM to its research division in San Jose (now Almaden), where he initially carried out both pure and applied theoretical and experimental investigations encompassing a broad range of company-related product technologies...storage, display, printer and data acquisition hardware and software. In 1973, he undertook performing DFT and quantum Monte Carlo calculations in support of group research in the then emerging field of organic and polymer superconductors, a very esoteric pursuit at the time. Following upon several corporate staff assignments involving various product development and sales strategies, in 1982 he was appointed manager of the cooperative phenomena group in the Almaden Research Center, which beginning in early 1987, made significant contributions to both the basic science and applications of high temperature superconductivity (HTSC). In 1993, after a 40-year career, he retired from IBM to accept a Science Fellow position at the Electric Power Research Institute (EPRI) where he funded power application development of superconductivity. In 2004, he retired from his EPRI career to undertake ``due diligence'' consulting services in support of the venture capital community in Silicon Valley. As a ``hobby,'' he currently pursues and publishes DFT studies in hope of discovering the pairing mechanism of HTSC. In summary, the speaker's career in industrial and applied physics demonstrates one can combine publishing a record three PRLs in one month with crawling around underground in substations with utility lineman helping install superconducting cables, along the way publishing 10

  6. Unconventional Superconductivity in La7Ir3 Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry

    NASA Astrophysics Data System (ADS)

    Barker, J. A. T.; Singh, D.; Thamizhavel, A.; Hillier, A. D.; Lees, M. R.; Balakrishnan, G.; Paul, D. McK.; Singh, R. P.

    2015-12-01

    The superconductivity of the noncentrosymmetric compound La7 Ir3 is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature Tc=2.25 K —a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La7 Ir3 may be unconventional and paves the way for further studies of this family of materials.

  7. Enhancement of critical current through oxygen irradiation in optimized 2G superconducting coated conductors

    NASA Astrophysics Data System (ADS)

    Kihlstrom, Karen; Leroux, M.; Welp, U.; Kwok, W.-K.; Koshelev, A. E.; Crabtree, G. W.; Rupich, M. W.; Fleshler, S.; Malozemoff, A. P.; Kayani, A.; CES Collaboration

    2015-03-01

    We demonstrate the strong enhancement of the critical current density, Jc, of commercial coated conductors (CC) in high magnetic fields using 3 MeV oxygen irradiation. The rapid suppression of Jc of coated conductors in magnetic fields remains a barrier for application of CCs in motors, generators, transformers, solenoids, and MRI systems. Using TRIM simulations, we determined that 3-MeV O-ions produce an essentially uniform defect distribution in bare CC at a rate that is ~ 2500 faster than that achieved with proton irradiation. Irradiating with 3 MeV O-ions to a dose of 1x1013 O-ions/cm2 generates a near doubling of the critical current at low temperatures: at 5K, 5T, we enhanced the critical current from 6.4 MA/cm2 to 12.2 MA/cm2. This dose can be achieved in a couple of seconds, thus this irradiation technique could be incorporated into a viable reel-to-reel production process. This work supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. D.O.E., Office of Science, Office of Basic Energy Sciences (K.K, M.L.,A.K) and by the D.O.E, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 (U.W., W.K.).

  8. Pharmacological Mechanisms of Cortical Enhancement Induced by the Repetitive Pairing of Visual/Cholinergic Stimulation

    PubMed Central

    Kang, Jun-Il; Huppé-Gourgues, Frédéric; Vaucher, Elvire

    2015-01-01

    Repetitive visual training paired with electrical activation of cholinergic projections to the primary visual cortex (V1) induces long-term enhancement of cortical processing in response to the visual training stimulus. To better determine the receptor subtypes mediating this effect the selective pharmacological blockade of V1 nicotinic (nAChR), M1 and M2 muscarinic (mAChR) or GABAergic A (GABAAR) receptors was performed during the training session and visual evoked potentials (VEPs) were recorded before and after training. The training session consisted of the exposure of awake, adult rats to an orientation-specific 0.12 CPD grating paired with an electrical stimulation of the basal forebrain for a duration of 1 week for 10 minutes per day. Pharmacological agents were infused intracortically during this period. The post-training VEP amplitude was significantly increased compared to the pre-training values for the trained spatial frequency and to adjacent spatial frequencies up to 0.3 CPD, suggesting a long-term increase of V1 sensitivity. This increase was totally blocked by the nAChR antagonist as well as by an M2 mAChR subtype and GABAAR antagonist. Moreover, administration of the M2 mAChR antagonist also significantly decreased the amplitude of the control VEPs, suggesting a suppressive effect on cortical responsiveness. However, the M1 mAChR antagonist blocked the increase of the VEP amplitude only for the high spatial frequency (0.3 CPD), suggesting that M1 role was limited to the spread of the enhancement effect to a higher spatial frequency. More generally, all the drugs used did block the VEP increase at 0.3 CPD. Further, use of each of the aforementioned receptor antagonists blocked training-induced changes in gamma and beta band oscillations. These findings demonstrate that visual training coupled with cholinergic stimulation improved perceptual sensitivity by enhancing cortical responsiveness in V1. This enhancement is mainly mediated by nAChRs, M2 m

  9. Does plasticity enhance or dampen phenotypic parallelism? A test with three lake-stream stickleback pairs.

    PubMed

    Oke, K B; Bukhari, M; Kaeuffer, R; Rolshausen, G; Räsänen, K; Bolnick, D I; Peichel, C L; Hendry, A P

    2016-01-01

    Parallel (and convergent) phenotypic variation is most often studied in the wild, where it is difficult to disentangle genetic vs. environmentally induced effects. As a result, the potential contributions of phenotypic plasticity to parallelism (and nonparallelism) are rarely evaluated in a formal sense. Phenotypic parallelism could be enhanced by plasticity that causes stronger parallelism across populations in the wild than would be expected from genetic differences alone. Phenotypic parallelism could be dampened if site-specific plasticity induced differences between otherwise genetically parallel populations. We used a common-garden study of three independent lake-stream stickleback population pairs to evaluate the extent to which adaptive divergence has a genetic or plastic basis, and to investigate the enhancing vs. dampening effects of plasticity on phenotypic parallelism. We found that lake-stream differences in most traits had a genetic basis, but that several traits also showed contributions from plasticity. Moreover, plasticity was much more prevalent in one watershed than in the other two. In most cases, plasticity enhanced phenotypic parallelism, whereas in a few cases, plasticity had a dampening effect. Genetic and plastic contributions to divergence seem to play a complimentary, likely adaptive, role in phenotypic parallelism of lake-stream stickleback. These findings highlight the value of formally comparing wild-caught and laboratory-reared individuals in the study of phenotypic parallelism. PMID:26411538

  10. Strong enhancement of s-wave superconductivity near a quantum critical point of (Ca1-xSrx)3Ir4Sn13 and (Ca1-xSrx)3Rh4Sn13

    NASA Astrophysics Data System (ADS)

    Morenzoni, Elvezio; Biswas, Pabitra; Guguchia, Zurab; Khasanov, Rustem; Chinotti, Manuel; Krieger, Jonas; Li, L.; Wang, Kefeng; Petrovic, Cedomir; Pomjakushina, Ekaterina

    We report microscopic studies by muon spin rotation as a function of pressure of the (Ca1-xSrx)3Ir4Sn13 and (Ca1-xSrx)3Rh4Sn13 cubic compounds, which display superconductivity and a structural phase transition associated with the formation of a charge density wave (CDW). In Ca3Ir4Sn13 we find a strong enhancement of the superfluid density and a dramatic increase of the pairing strength above a pressure of ~ 1 . 6 GPa giving direct evidence of the presence of a quantum critical point separating a superconducting phase coexisting with CDW from a pure superconducting phase. The superconducting order parameter in both phases has the same s-wave symmetry. Similar behavior is found in the other family. In spite of the conventional phonon-mediated BCS character of these weakly correlated 3-4-13 systems, the dependence of the effective superfluid density on the critical temperature put these compounds in the ``Uemura'' plot close to unconventional superconductors. These systems exemplify that conventional BCS superconductors can also display characteristics of unconventional superconductors. Supported by the Swiss National Science Foundation and by the U.S. DOE under Contract No. DE-SC00112704.

  11. Stimulation of a Singlet Superconductivity in SFS Weak Links by Spin–Exchange Scattering of Cooper Pairs

    PubMed Central

    Samokhvalov, A. V.; Shekhter, R. I.; Buzdin, A. I.

    2014-01-01

    Josephson junctions with a ferromagnetic metal weak link reveal a very strong decrease of the critical current compared to a normal metal weak link. We demonstrate that in the ballistic regime the presence of a small region with a non-collinear magnetization near the center of a ferromagnetic weak link restores the critical current inherent to the normal metal. The above effect can be stimulated by additional electrical bias of the magnetic gate which induces a local electron depletion of ferromagnetic barrier. The underlying physics of the effect is the interference phenomena due to the magnetic scattering of the Cooper pair, which reverses its total momentum in the ferromagnet and thus compensates the phase gain before and after the spin–reversed scattering. In contrast with the widely discussed triplet long ranged proximity effect we elucidate a new singlet long ranged proximity effect. This phenomenon opens a way to easily control the properties of SFS junctions and inversely to manipulate the magnetic moment via the Josephson current. PMID:25011929

  12. Volatile anaesthetic enhancement of paired-pulse depression investigated in the rat hippocampus in vitro.

    PubMed Central

    Pearce, R A

    1996-01-01

    -mediated IPSC, with no effect on the amplitude. However, enflurane markedly reduced the amplitude of the fast component of the GABAA IPSC, so that only a small slow current remained in response to a selective stimulus. 5. It is concluded that the effects of halothane on IAHP and on GABAB responses cannot account for its effects on paired-pulse depression, but that volatile anaesthetics enhance paired-pulse depression by prolonging the decay of the slow dendritic GABAA response. Furthermore, it is speculated that the proconvulsant property of enflurane is related to its depression of the fast somatic component of GABAA inhibition. PMID:8734993

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

    SciTech Connect

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

    2015-11-30

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

  14. Enhanced Field Emission Studies on Niobium Surfaces Relevant to High Field Superconducting Radio-Frequency Devices

    SciTech Connect

    Tong Wang

    2002-09-18

    Enhanced field emission (EFE) presents the main impediment to higher acceleration gradients in superconducting niobium (Nb) radiofrequency cavities for particle accelerators. The strength, number and sources of EFE sites strongly depend on surface preparation and handling. The main objective of this thesis project is to systematically investigate the sources of EFE from Nb, to evaluate the best available surface preparation techniques with respect to resulting field emission, and to establish an optimized process to minimize or eliminate EFE. To achieve these goals, a scanning field emission microscope (SFEM) was designed and built as an extension to an existing commercial scanning electron microscope (SEM). In the SFEM chamber of ultra high vacuum, a sample is moved laterally in a raster pattern under a high voltage anode tip for EFE detection and localization. The sample is then transferred under vacuum to the SEM chamber equipped with an energy-dispersive x-ray spectrometer for individual emitting site characterization. Compared to other systems built for similar purposes, this apparatus has low cost and maintenance, high operational flexibility, considerably bigger scan area, as well as reliable performance. EFE sources from planar Nb have been studied after various surface preparation, including chemical etching and electropolishing, combined with ultrasonic or high-pressure water rinse. Emitters have been identified, analyzed and the preparation process has been examined and improved based on EFE results. As a result, field-emission-free or near field-emission-free surfaces at ~140 MV/m have been consistently achieved with the above techniques. Characterization on the remaining emitters leads to the conclusion that no evidence of intrinsic emitters, i.e., no fundamental electric field limit induced by EFE, has been observed up to ~140 MV/m. Chemically etched and electropolished Nb are compared and no significant difference is observed up to ~140 MV/m. To

  15. New mechanism for the generation of electron-positron pairs in Laser-Matter Interaction: Resonantly Enhanced Pair Production in a molecular system

    NASA Astrophysics Data System (ADS)

    Fillion-Gourdeau, François; Lorin, Emmanuel; Bandrauk, André D.

    2013-02-01

    A new mechanism for pair production from the interaction of a laser with two nuclei is presented. The latter takes advantage of the Stark effect in diatomic molecules and the presence of molecular resonances in the negative and positive energy continua. Both move in the complex energy plane as the interatomic distance and the electric field strength are varied. We demonstrate that there is an enhancement of pair production at the crossing of these resonances. This mechanism is studied in a very simple one-dimensional model where the nuclei are modeled by delta function potential wells and the laser by a constant electric field. The position of resonances is evaluated by using the Weyl-Titchmarch-Kodaira theory, which allows to treat singular boundary value problems and to compute the spectral density. The rate of producing pairs is also computed. It is shown that this process yields a positron production rate which is approximately an order of magnitude higher than in the single nucleus case and a few orders of magnitudes higher than Schwinger's tunneling result in a static field.

  16. Superconducting properties and pseudogap from preformed Cooper pairs in the triclinic (CaFe1-xPtxAs ) 10Pt3As8

    NASA Astrophysics Data System (ADS)

    Surmach, M. A.; Brückner, F.; Kamusella, S.; Sarkar, R.; Portnichenko, P. Y.; Park, J. T.; Ghambashidze, G.; Luetkens, H.; Biswas, P. K.; Choi, W. J.; Seo, Y. I.; Kwon, Y. S.; Klauss, H.-H.; Inosov, D. S.

    2015-03-01

    Using a combination of muon-spin relaxation (μ SR ) , inelastic neutron scattering (INS), and nuclear magnetic resonance (NMR), we investigated the novel iron-based superconductor with a triclinic crystal structure (CaFe1-xPtxAs ) 10Pt3As8 (Tc=13 K), containing platinum-arsenide intermediary layers. The temperature dependence of the superfluid density obtained from the μ SR relaxation-rate measurements indicates the presence of two superconducting gaps, Δ1≫Δ2 . According to our INS measurements, commensurate spin fluctuations are centered at the (π ,0 ) wave vector, like in most other iron arsenides. Their intensity remains unchanged across Tc, indicating the absence of a spin resonance typical for many Fe-based superconductors. Instead, we observed a peak in the spin-excitation spectrum around ℏ ω0=7 meV at the same wave vector, which persists above Tc and is characterized by the ratio ℏ ω0/kBTc≈6.2 , which is significantly higher than typical values for the magnetic resonant modes in iron pnictides (˜4.3 ) . The temperature dependence of magnetic intensity at 7 meV revealed an anomaly around T*=45 K related to the disappearance of this new mode. A suppression of the spin-lattice relaxation rate, 1 /T1T , observed by NMR immediately below T* without any notable subsequent anomaly at Tc, indicates that T* could mark the onset of a pseudogap in (CaFe1-xPtxAs ) 10Pt3As8 , which is likely associated with the emergence of preformed Cooper pairs.

  17. Superconductivity in the ferromagnetic semiconductor samarium nitride

    NASA Astrophysics Data System (ADS)

    Anton, E.-M.; Granville, S.; Engel, A.; Chong, S. V.; Governale, M.; Zülicke, U.; Moghaddam, A. G.; Trodahl, H. J.; Natali, F.; Vézian, S.; Ruck, B. J.

    2016-07-01

    Conventional wisdom expects that making semiconductors ferromagnetic requires doping with magnetic ions and that superconductivity cannot coexist with magnetism. However, recent concerted efforts exploring new classes of materials have established that intrinsic ferromagnetic semiconductors exist and that certain types of strongly correlated metals can be ferromagnetic and superconducting at the same time. Here we show that the trifecta of semiconducting behavior, ferromagnetism, and superconductivity can be achieved in a single material. Samarium nitride (SmN) is a well-characterized intrinsic ferromagnetic semiconductor, hosting strongly spin-ordered 4 f electrons below a Curie temperature of 27 K. We have now observed that it also hosts a superconducting phase below 4 K when doped to electron concentrations above 1021cm-3 . The large exchange splitting of the conduction band in SmN favors equal-spin triplet pairing with p -wave symmetry. Significantly, superconductivity is enhanced in superlattices of gadolinium nitride (GdN) and SmN. An analysis of the robustness of such a superconducting phase against disorder leads to the conclusion that the 4 f bands are crucial for superconductivity, making SmN a heavy-fermion-type superconductor.

  18. Enhanced selectivity and efficiency of coherent population transfer via a train of pulse pairs

    SciTech Connect

    Yang Xihua; Zhang Zhenhua; Yan Xiaona; Li Chunfang

    2010-09-15

    We propose a way to significantly enhance selectivity and efficiency of coherent population transfer in a {Lambda}-type four-level system with a closely spaced doublet in the final state by using a train of counterintuitively ordered pump-Stokes pulse pairs. Due to temporal constructive and destructive quantum interference between the sequential transitions and subsequent coherent accumulation and annihilation in the time domain, the spectral resolution of selective and perfect population transfer to either of the final states can be improved by more than one order of magnitude as compared to the conventionally widely used stimulated Raman adiabatic passage and chirped adiabatic passage techniques, which can also be well understood as a result of the formation of a comblike structure of the pulse train spectrum in the frequency domain. Moreover, an arbitrary coherent superposition between the closely separated doublet can be achieved by suitably tuning the repetition period and detuning of the laser fields. This method has potential applications in control of chemical reactions and quantum information processing.

  19. Sensitivity Enhancement of Strain Sensing Utilizing a Differential Pair of Fiber Bragg Gratings

    PubMed Central

    Zhang, Zhiyong; Yan, Lianshan; Pan, Wei; Luo, Bin; Wang, Ping; Guo, Likang; Zhou, Wei

    2012-01-01

    In strain measurement applications, the matched fiber Bragg gratings (FBG) method is generally used to reduce temperature dependence effects. The FBG parameters have to be designed to meet the requirements by the particular application. The bandwidth and slope of the FBG has to be balanced well, according to the measurement range, accuracy and sensitivity. A sensitivity enhanced strain demodulation method without sacrificing the measurement range for FBG sensing systems is proposed and demonstrated utilizing a pair of reference FBGs. One of the reference FBGs and the sensing FBG have almost the same Bragg wavelength, while the other reference FBGs has a Bragg wavelength offset relative to the sensing FBG. Reflected optical signals from the sensing FBG pass through two reference FBGs, and subtract from each other after the detection. Doubled strain measurement sensitivity is obtained by static rail load experiments compared to the general matched grating approach, and further verified in dynamic load experiments. Experimental results indicate that such a method could be used for real-time rail strain monitoring applications. PMID:22666008

  20. Enhanced superconducting properties of rare-earth oxides and graphene oxide added MgB2

    NASA Astrophysics Data System (ADS)

    Sudesh; Das, S.; Bernhard, C.; Varma, G. D.

    2014-10-01

    In this paper, the effects of addition of (i) graphene oxide (GO), (ii) a series of rare-earth (RE, RE = La, Sm, Eu, Gd, Tb and Ho) oxides (REO) and (iii) a mixture of GO and rare-earth oxides (GO + REO) on the superconducting properties of MgB2, have been studied with the help of electrical transport and magnetic measurements. All the samples have been prepared following the standard solid-state reaction route. We have used an optimum value of 1 wt% REO and 3 wt% GO for addition on the basis of previous studies. X-ray diffraction studies confirm the formation of hexagonal crystal structure (space group P6/mmm) of MgB2 with small amounts of REBx (x = 4 and 6) and MgO impurity phases in all the synthesized samples. We observe that the critical current density, Jc and upper critical field Hc2(0) improve significantly in the REO-added and GO-added samples with no significant change in critical temperature, Tc. A substantial enhancement in Jc(H) and Hc2(0) is observed with the GO + REO addition in MgB2. The different flux pinning mechanisms in all the samples are studied and it is found that the point pinning is the dominant mechanism in the GO-added samples and grain boundary pinning is the dominant one in the REO added samples. We have seen the combined effect of both types of flux pinning mechanisms in GO + REO added MgB2.

  1. Enhanced superconducting transition temperature in hyper-interlayer-expanded FeSe despite the suppressed electronic nematic order and spin fluctuations

    NASA Astrophysics Data System (ADS)

    Hrovat, Matevž Majcen; Jeglič, Peter; Klanjšek, Martin; Hatakeda, Takehiro; Noji, Takashi; Tanabe, Yoichi; Urata, Takahiro; Huynh, Khuong K.; Koike, Yoji; Tanigaki, Katsumi; Arčon, Denis

    2015-09-01

    The superconducting critical temperature, Tc, of FeSe can be dramatically enhanced by intercalation of a molecular spacer layer. Here we report on a 77Se,7Li , and 1H nuclear magnetic resonance (NMR) study of the powdered hyper-interlayer-expanded Lix(C2H8N2) yFe2 -zSe2 with a nearly optimal Tc=45 K. The absence of any shift in the 7Li and 1H NMR spectra indicates a complete decoupling of interlayer units from the conduction electrons in FeSe layers, whereas nearly temperature-independent 7Li and 1H spin-lattice relaxation rates are consistent with the non-negligible concentration of Fe impurities present in the insulating interlayer space. On the other hand, the strong temperature dependence of 77Se NMR shift and spin-lattice relaxation rate, 1 /77T1 , is attributed to the holelike bands close to the Fermi energy. 1 /77T1 shows no additional anisotropy that would account for the onset of electronic nematic order down to Tc. Similarly, no enhancement in 1 /77T1 due to the spin fluctuations could be found in the normal state. Yet, a characteristic power-law dependence 1 /77T1∝T4.5 still complies with the Cooper pairing mediated by spin fluctuations.

  2. Toward a Mediation Model of Employability Enhancement: A Study of Employee-Supervisor Pairs in the Building Sector

    ERIC Educational Resources Information Center

    van der Heijden, Beatrice I. J. M.; Bakker, Arnold B.

    2011-01-01

    This study examines whether jobs that enable competence development and a constructive leadership style enhance workers' employability or career potential through their assumed positive relationship with work-related flow (absorption, work enjoyment, and intrinsic work motivation). The authors conducted an explorative study with 303 pairs of…

  3. Think Pair Share: A Teaching Learning Strategy to Enhance Students' Critical Thinking

    ERIC Educational Resources Information Center

    Kaddoura, Mahmoud

    2013-01-01

    This study investigated the change in critical thinking (CT) skills of baccalaureate nursing students who were educated using a Think-Pair-Share (TPS) or an equivalent Non-Think-Pair-Share (Non-TPS) teaching method. Critical thinking has been an essential outcome of nursing students to prepare them to provide effective and safe quality care for…

  4. Too Much Matching: A Social Relations Model Enhancement of the Pairing Game

    ERIC Educational Resources Information Center

    Eastwick, Paul W.; Buck, April A.

    2014-01-01

    The Pairing Game is a popular classroom demonstration that illustrates how people select romantic partners who approximate their own desirability. However, this game produces matching correlations that greatly exceed the correlations that characterize actual romantic pairings, perhaps because the game does not incorporate the social relations…

  5. Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5.

    PubMed

    Mankowsky, R; Subedi, A; Först, M; Mariager, S O; Chollet, M; Lemke, H T; Robinson, J S; Glownia, J M; Minitti, M P; Frano, A; Fechner, M; Spaldin, N A; Loew, T; Keimer, B; Georges, A; Cavalleri, A

    2014-12-01

    Terahertz-frequency optical pulses can resonantly drive selected vibrational modes in solids and deform their crystal structures. In complex oxides, this method has been used to melt electronic order, drive insulator-to-metal transitions and induce superconductivity. Strikingly, coherent interlayer transport strongly reminiscent of superconductivity can be transiently induced up to room temperature (300 kelvin) in YBa2Cu3O6+x (refs 9, 10). Here we report the crystal structure of this exotic non-equilibrium state, determined by femtosecond X-ray diffraction and ab initio density functional theory calculations. We find that nonlinear lattice excitation in normal-state YBa2Cu3O6+x at above the transition temperature of 52 kelvin causes a simultaneous increase and decrease in the Cu-O2 intra-bilayer and, respectively, inter-bilayer distances, accompanied by anisotropic changes in the in-plane O-Cu-O bond buckling. Density functional theory calculations indicate that these motions cause drastic changes in the electronic structure. Among these, the enhancement in the character of the in-plane electronic structure is likely to favour superconductivity. PMID:25471882

  6. Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5

    NASA Astrophysics Data System (ADS)

    Mankowsky, R.; Subedi, A.; Först, M.; Mariager, S. O.; Chollet, M.; Lemke, H. T.; Robinson, J. S.; Glownia, J. M.; Minitti, M. P.; Frano, A.; Fechner, M.; Spaldin, N. A.; Loew, T.; Keimer, B.; Georges, A.; Cavalleri, A.

    2014-12-01

    Terahertz-frequency optical pulses can resonantly drive selected vibrational modes in solids and deform their crystal structures. In complex oxides, this method has been used to melt electronic order, drive insulator-to-metal transitions and induce superconductivity. Strikingly, coherent interlayer transport strongly reminiscent of superconductivity can be transiently induced up to room temperature (300 kelvin) in YBa2Cu3O6+x (refs 9, 10). Here we report the crystal structure of this exotic non-equilibrium state, determined by femtosecond X-ray diffraction and ab initio density functional theory calculations. We find that nonlinear lattice excitation in normal-state YBa2Cu3O6+x at above the transition temperature of 52 kelvin causes a simultaneous increase and decrease in the Cu-O2 intra-bilayer and, respectively, inter-bilayer distances, accompanied by anisotropic changes in the in-plane O-Cu-O bond buckling. Density functional theory calculations indicate that these motions cause drastic changes in the electronic structure. Among these, the enhancement in the character of the in-plane electronic structure is likely to favour superconductivity.

  7. Non-hysteretic superconducting quantum interference proximity transistor with enhanced responsivity

    SciTech Connect

    Jabdaraghi, R. N.; Meschke, M.; Pekola, J. P.

    2014-02-24

    This Letter presents fabrication and characterization of an optimized superconducting quantum interference proximity transistor. The present device, characterized by reduced tunnel junction area and shortened normal-metal section, demonstrates no hysteresis at low temperatures as we increased the Josephson inductance of the weak link by decreasing its cross section. It has consequently almost an order of magnitude improved magnetic field responsivity as compared to the earlier design. The modulation of both the current and the voltage across the junction have been measured as a function of magnetic flux piercing the superconducting loop.

  8. Photofragmentation, state interaction, and energetics of Rydberg and ion-pair states: Resonance enhanced multiphoton ionization of HI

    SciTech Connect

    Hróðmarsson, Helgi Rafn; Wang, Huasheng; Kvaran, Ágúst

    2014-06-28

    Mass resolved resonance enhanced multiphoton ionization data for hydrogen iodide (HI), for two-photon resonance excitation to Rydberg and ion-pair states in the 69 600–72 400 cm{sup −1} region were recorded and analyzed. Spectral perturbations due to homogeneous and heterogeneous interactions between Rydberg and ion-pair states, showing as deformations in line-positions, line-intensities, and line-widths, were focused on. Parameters relevant to photodissociation processes, state interaction strengths and spectroscopic parameters for deperturbed states were derived. Overall interaction and dynamical schemes to describe the observations are proposed.

  9. Design of a magnetic shielding system for the time of flight enhanced diagnostics neutron spectrometer at Experimental Advanced Superconducting Tokamak

    SciTech Connect

    Cui, Z. Q.; Chen, Z. J.; Xie, X. F.; Peng, X. Y.; Hu, Z. M.; Du, T. F.; Ge, L. J.; Zhang, X.; Yuan, X.; Fan, T. S.; Chen, J. X.; Li, X. Q. E-mail: guohuizhang@pku.edu.cn; Zhang, G. H. E-mail: guohuizhang@pku.edu.cn; Xia, Z. W.; Hu, L. Q.; Zhong, G. Q.; Lin, S. Y.; Wan, B. N.

    2014-11-15

    The novel neutron spectrometer TOFED (Time of Flight Enhanced Diagnostics), comprising 90 individual photomultiplier tubes coupled with 85 plastic scintillation detectors through light guides, has been constructed and installed at Experimental Advanced Superconducting Tokamak. A dedicated magnetic shielding system has been constructed for TOFED, and is designed to guarantee the normal operation of photomultiplier tubes in the stray magnetic field leaking from the tokamak device. Experimental measurements and numerical simulations carried out employing the finite element method are combined to optimize the design of the magnetic shielding system. The system allows detectors to work properly in an external magnetic field of 200 G.

  10. Design of a magnetic shielding system for the time of flight enhanced diagnostics neutron spectrometer at Experimental Advanced Superconducting Tokamak.

    PubMed

    Cui, Z Q; Chen, Z J; Xie, X F; Peng, X Y; Hu, Z M; Du, T F; Ge, L J; Zhang, X; Yuan, X; Xia, Z W; Hu, L Q; Zhong, G Q; Lin, S Y; Wan, B N; Fan, T S; Chen, J X; Li, X Q; Zhang, G H

    2014-11-01

    The novel neutron spectrometer TOFED (Time of Flight Enhanced Diagnostics), comprising 90 individual photomultiplier tubes coupled with 85 plastic scintillation detectors through light guides, has been constructed and installed at Experimental Advanced Superconducting Tokamak. A dedicated magnetic shielding system has been constructed for TOFED, and is designed to guarantee the normal operation of photomultiplier tubes in the stray magnetic field leaking from the tokamak device. Experimental measurements and numerical simulations carried out employing the finite element method are combined to optimize the design of the magnetic shielding system. The system allows detectors to work properly in an external magnetic field of 200 G. PMID:25430242

  11. Design of a magnetic shielding system for the time of flight enhanced diagnostics neutron spectrometer at Experimental Advanced Superconducting Tokamak

    NASA Astrophysics Data System (ADS)

    Cui, Z. Q.; Chen, Z. J.; Xie, X. F.; Peng, X. Y.; Hu, Z. M.; Du, T. F.; Ge, L. J.; Zhang, X.; Yuan, X.; Xia, Z. W.; Hu, L. Q.; Zhong, G. Q.; Lin, S. Y.; Wan, B. N.; Fan, T. S.; Chen, J. X.; Li, X. Q.; Zhang, G. H.

    2014-11-01

    The novel neutron spectrometer TOFED (Time of Flight Enhanced Diagnostics), comprising 90 individual photomultiplier tubes coupled with 85 plastic scintillation detectors through light guides, has been constructed and installed at Experimental Advanced Superconducting Tokamak. A dedicated magnetic shielding system has been constructed for TOFED, and is designed to guarantee the normal operation of photomultiplier tubes in the stray magnetic field leaking from the tokamak device. Experimental measurements and numerical simulations carried out employing the finite element method are combined to optimize the design of the magnetic shielding system. The system allows detectors to work properly in an external magnetic field of 200 G.

  12. Enhancement of magnetic flux distribution in a DC superconducting electric motor

    NASA Astrophysics Data System (ADS)

    Hamid, N. A.; Ewe, L. S.; Chin, K. M.

    2013-06-01

    Most motor designs require an air gap between the rotor and stator to enable the armature to rotate freely. The interaction of magnetic flux from rotor and stator within the air gap will provide the thrust for rotational motion. Thus, the understanding of magnetic flux in the vicinity of the air gap is very important to mathematically calculate the magnetic flux generated in the area. In this work, a finite element analysis was employed to study the behavior of the magnetic flux in view of designing a synchronous DC superconducting electric motor. The analysis provides an ideal magnetic flux distribution within the components of the motor. From the flux plot analysis, it indicates that flux losses are mainly in the forms of leakage and fringe effect. The analysis also shows that the flux density is high at the area around the air gap and the rotor. The high flux density will provide a high force area that enables the rotor to rotate. In contrast, the other parts of the motor body do not show high flux density indicating low distribution of flux. Consequently, a bench top model of a DC superconducting motor was developed where by motor with a 2-pole type winding was chosen. Each field coil was designed with a racetrack-shaped double pancake wound using DI-BSCCO Bi-2223 superconducting tapes. The performance and energy efficiency of the superconducting motor was superior when compared to the conventional motor with similar capacity.

  13. Coherent growth of superconducting TiN thin films by plasma enhanced molecular beam epitaxy

    SciTech Connect

    Krockenberger, Yoshiharu; Karimoto, Shin-ichi; Yamamoto, Hideki; Semba, Kouich

    2012-10-15

    We have investigated the formation of titanium nitride (TiN) thin films on (001) MgO substrates by molecular beam epitaxy and radio frequency acitvated nitrogen plasma. Although cubic TiN is stabile over a wide temperature range, superconducting TiN films are exclusively obtained when the substrate temperature exceeds 710 Degree-Sign C. TiN films grown at 720 Degree-Sign C show a high residual resistivity ratio of approximately 11 and the superconducting transition temperature (T{sub c}) is well above 5 K. Superconductivity has been confirmed also by magnetiztion measurements. In addition, we determined the upper critical magnetic field ({mu}{sub 0}H{sub c2}) as well as the corresponding coherence length ({xi}{sub GL}) by transport measurements under high magnetic fields. High-resolution transmission electron microscopy data revealed full in plane coherency to the substrate as well as a low defect density in the film, in agreement with a mean-free path length Script-Small-L Almost-Equal-To 106 nm, which is estimated from the residual resistivity value. The observations of reflection high energy electron diffraction intensity oscillations during the growth, distinct Laue fringes around the main Bragg peaks, and higher order diffraction spots in the reciprocal space map suggest the full controlability of the thickness of high quality superconducting TiN thin films.

  14. Strong enhancement of Penning ionization for asymmetric atom pairs in cold Rydberg gases: the Tom and Jerry effect

    NASA Astrophysics Data System (ADS)

    Efimov, D. K.; Miculis, K.; Bezuglov, N. N.; Ekers, A.

    2016-06-01

    We consider Penning ionization of Rydberg atom pairs as an Auger-type process induced by the dipole–dipole interaction and employ semiclassical formulae for dipole transitions to calculate the autoionization width as a function of the principal quantum numbers, n d , n i , of both atoms. While for symmetric atom pairs with {n}d={n}i={n}0 the well-known increase of the autoionization width with increasing n 0 is obtained, the result for asymmetric pairs is counterintuitive—for a fixed n i of the ionizing atom of the pair, the autoionization width strongly increases with decreasing n d of the de-excited atom. For H Rydberg atoms this increase reaches two orders of magnitude at the maximum of the n d dependence, and the same type of counterintuitive behavior is exhibited also by Na, Rb and Cs atoms. This is a purely quantum-mechanical effect, which points towards existence of optimal (we call them ‘Tom’ and ‘Jerry’ for ‘big’ and ‘small’) pairs of Rydberg atoms with respect to autoionization efficiency. Building on the model of population redistribution in cold Rydberg gases proposed in [1], we demonstrate that population evolution following the initial laser excitation of Rydberg atoms in state n 0 would eventually lead to the formation of such Tom–Jerry pairs with {n}i\\gt {n}0\\gt {n}d which feature autoionization widths that are enhanced by several orders of magnitude compared to that of two atoms in the initial laser-excited state n 0. We also show that in the high-density regime of cold Rydberg gas experiments the ionization rate of Tom–Jerry pairs can be substantially larger than the blackbody radiation-induced photoionization rate.

  15. Quarter-filled systems with frustration: Candidate for correlated electron superconductivity

    NASA Astrophysics Data System (ADS)

    Gomes, Niladri; de Silva, W. Wasanthi; Dutta, Tirthankar; Clay, R. Torsten; Mazumdar, Sumit

    A necessary condition for superconductivity (SC) driven by electron correlation is that electron electron (e-e) interactions enhance superconducting pair-pair correlations, relative to the non-interacting limit. We present the results of high-precision calculations of superconducting pair-pair correlations on four different frustrated lattices over the complete range of carrier density 0 < ρ < 1 in each case. We find that pair correlations are enhanced relative to the noninteracting limit only for density ρ equal to or close to 0 . 5 (1 / 4 filling). At all other ρ pair correlations are suppressed by interactions. This enhancement is due to the proximity to a spin-gapped paired-electron crystal (PEC) state that occurs at ρ = 0 . 5 . Our theory explains the pseudogap observed at high temperatures in many organic superconductors. The remarkable bandfilling specificity is an essential ingredient to understanding the mechanism of superconductivity in the two-dimensional organic charge-transfer solids as well as the many different families of other unconventional superconductors that share this bandfilling. Supported by DOE Grant DE-FG02-06ER46315 and NSF-CHE-151475.

  16. Galaxy pairs in the Sloan Digital Sky Survey - X. Does gas content alter star formation rate enhancement in galaxy interactions?

    NASA Astrophysics Data System (ADS)

    Scudder, Jillian M.; Ellison, Sara L.; Momjian, Emmanuel; Rosenberg, Jessica L.; Torrey, Paul; Patton, David R.; Fertig, Derek; Mendel, J. Trevor

    2015-06-01

    New spectral line observations, obtained with the Jansky Very Large Array (VLA), of a sample of 34 galaxies in 17 close pairs are presented in this paper. The sample of galaxy pairs is selected to contain galaxies in close, major interactions (i.e. projected separations <30 h_{70}^{-1} kpc, and mass ratios less extreme than 4:1), while still having a sufficiently large angular separation that the VLA can spatially resolve both galaxies in the pair. Of the 34 galaxies, 17 are detected at >3σ. We compare the H I gas fraction of the galaxies with the triggered star formation present in that galaxy. When compared to the star formation rates (SFRs) of non-pair galaxies matched in mass, redshift, and local environment, we find that the star formation enhancement is weakly positively correlated (˜2.5σ) with H I gas fraction. In order to help understand the physical mechanisms driving this weak correlation, we also present results from a small suite of binary galaxy merger simulations with varying gas fractions. The simulated galaxies indicate that larger initial gas fractions are associated with lower levels of interaction-triggered star formation (relative to an identical galaxy in isolation), but also show that high gas fraction galaxies have higher absolute SFRs prior to an interaction. We show that when interaction-driven SFR enhancements are calculated relative to a galaxy with an average gas fraction for its stellar mass, the relationship between SFR and initial gas fraction dominates over the SFR enhancements driven by the interaction. Simulated galaxy interactions that are matched in stellar mass but not in gas fraction, like our VLA sample, yield the same general positive correlation between SFR enhancement and gas fraction that we observe.

  17. Application of a combined superconducting fault current limiter and STATCOM to enhancement of power system transient stability

    NASA Astrophysics Data System (ADS)

    Mahdad, Belkacem; Srairi, K.

    2013-12-01

    Stable and reliable operation of the power system network is dependent on the dynamic equilibrium between energy production and power demand under large disturbance such as short circuit or important line tripping. This paper investigates the use of combined model based superconducting fault current limiter (SFCL) and shunt FACTS Controller (STATCOM) for assessing the transient stability of a power system considering the automatic voltage regulator. The combined model located at a specified branch based on voltage stability index using continuation power flow. The main role of the proposed combined model is to achieve simultaneously a flexible control of reactive power using STATCOM Controller and to reduce fault current using superconducting technology based SFCL. The proposed combined model has been successfully adapted within the transient stability program and applied to enhance the transient power system stability of the WSCC9-Bus system. Critical clearing time (CCT) has been used as an index to evaluate and validate the contribution of the proposed coordinated Controller. Simulation results confirm the effectiveness and perspective of this combined Controller to enhance the dynamic power system performances.

  18. Wavelength-dependent optical enhancement of superconducting interlayer coupling in La1.885Ba0.115CuO4

    DOE PAGESBeta

    Casandruc, E.; Nicoletti, D.; Rajasekaran, S.; Laplace, Y.; Khanna, V.; Gu, G.; Hill, J. P.; Cavalleri, A.

    2015-05-05

    We analyze the pump wavelength dependence for the photo-induced enhancement of interlayer coupling in La1.885Ba0.115CuO4, which is promoted by optical melting of the stripe order. In the equilibrium superconducting state (T < TC = 13 K), in which stripes and superconductivity coexist, time-domain THz spectroscopy reveals a photo-induced blue-shift of the Josephson Plasma Resonance after excitation with optical pulses polarized perpendicular to the CuO2 planes. In the striped, non-superconducting state (TC < T < TSO ≃ 40 K) a transient plasma resonance similar to that seen below TC appears from a featureless equilibrium reflectivity. Most strikingly, both these effects becomemore » stronger upon tuning of the pump wavelength from the mid-infrared to the visible, underscoring an unconventional competition between stripe order and superconductivity, which occurs on energy scales far above the ordering temperature.« less

  19. Tunable cavity-enhanced photon pairs source in Hermite-Gaussian mode

    NASA Astrophysics Data System (ADS)

    Zhou, Zhi-Yuan; Li, Yan; Ding, Dong-Sheng; Zhang, Wei; Shi, Shuai; Shi, Bao-Sen; Guo, Guang-Can

    2016-02-01

    The spatial modes of light have grasped great research interests because of its great potentials in optical communications, optical manipulation and trapping, optical metrology and quantum information processing. Here we report on generating of photon pairs in Hermite-Gaussian (HG) mode in a type-I optical parametric oscillator operated far below threshold. The bandwidths of the photon pairs are 11.4 MHz and 20.8MHz for two different HG modes respectively, therefore the photons can be stored in cold Rubidium atomic ensembles. The non-classical properties of HG modes are clearly verified by the violation of Cauchy-Schwarz inequality. Our study provides an effective way to generate photon pairs with narrow bandwidth in high order spatial modes for high dimensional quantum communication.

  20. Strand pairing by Rad54 and Rad51 is enhanced by chromatin.

    PubMed

    Alexiadis, Vassilios; Kadonaga, James T

    2002-11-01

    We investigated the role of chromatin in the catalysis of homologous strand pairing by Rad54 and Rad51. Rad54 is related to the ATPase subunits of chromatin-remodeling factors, whereas Rad51 is related to bacterial RecA. In the absence of superhelical tension, we found that the efficiency of strand pairing with chromatin is >100-fold higher than that with naked DNA. In addition, we observed that Rad54 and Rad51 function cooperatively in the ATP-dependent remodeling of chromatin. These findings indicate that Rad54 and Rad51 have evolved to function with chromatin, the natural substrate, rather than with naked DNA. PMID:12414729

  1. Enhancement of superconductivity under pressure and the magnetic phase diagram of tantalum disulfide single crystals

    PubMed Central

    Abdel-Hafiez, M.; Zhao, X.-M.; Kordyuk, A. A.; Fang, Y.-W.; Pan, B.; He, Z.; Duan, C.-G.; Zhao, J.; Chen, X.-J.

    2016-01-01

    In low-dimensional electron systems, charge density waves (CDW) and superconductivity are two of the most fundamental collective quantum phenomena. For all known quasi-two-dimensional superconductors, the origin and exact boundary of the electronic orderings and superconductivity are still attractive problems. Through transport and thermodynamic measurements, we report on the field-temperature phase diagram in 2H-TaS2 single crystals. We show that the superconducting transition temperature (Tc) increases by one order of magnitude from temperatures at 0.98 K up to 9.15 K at 8.7 GPa when the Tc becomes very sharp. Additionally, the effects of 8.7 GPa illustrate a suppression of the CDW ground state, with critically small Fermi surfaces. Below the Tc the lattice of magnetic flux lines melts from a solid-like state to a broad vortex liquid phase region. Our measurements indicate an unconventional s-wave-like picture with two energy gaps evidencing its multi-band nature. PMID:27534898

  2. Enhancement of superconductivity under pressure and the magnetic phase diagram of tantalum disulfide single crystals.

    PubMed

    Abdel-Hafiez, M; Zhao, X-M; Kordyuk, A A; Fang, Y-W; Pan, B; He, Z; Duan, C-G; Zhao, J; Chen, X-J

    2016-01-01

    In low-dimensional electron systems, charge density waves (CDW) and superconductivity are two of the most fundamental collective quantum phenomena. For all known quasi-two-dimensional superconductors, the origin and exact boundary of the electronic orderings and superconductivity are still attractive problems. Through transport and thermodynamic measurements, we report on the field-temperature phase diagram in 2H-TaS2 single crystals. We show that the superconducting transition temperature (Tc) increases by one order of magnitude from temperatures at 0.98 K up to 9.15 K at 8.7 GPa when the Tc becomes very sharp. Additionally, the effects of 8.7 GPa illustrate a suppression of the CDW ground state, with critically small Fermi surfaces. Below the Tc the lattice of magnetic flux lines melts from a solid-like state to a broad vortex liquid phase region. Our measurements indicate an unconventional s-wave-like picture with two energy gaps evidencing its multi-band nature. PMID:27534898

  3. Pressure-enhanced superconductivity in A15-type Nb3 Ge via increased Fermi surface nesting

    NASA Astrophysics Data System (ADS)

    Stillwell, Ryan; Jeffries, Jason; McCall, Scott; Jenei, Zsolt; Weir, Sam; Vohra, Yogesh

    The A15-type superconductors are the most widely used superconductors in industrial applications yet the physics behind maximizing the superconducting transition temperature is still not completely understood. The highest transition temperatures found to date have recently been reported for high-pressure hydride materials and it is believed that they too are BCS-type phonon-mediated superconductors, just like the A15-type superconductors. Understanding the electron-phonon coupling has therefore been brought front stage in the search to understand the mechanisms for optimizing high-temperature superconductors. Using a multi-faceted suite of high-pressure techniques we found that Nb3Ge has an isostructural phase transition at high pressure that correlates directly with a bandstructure change seen in high-pressure magnetotransport measurements. Our results suggest that A15-type superconductivity is not only phonon-mediated but that the degree of Fermi surface nesting is a controlling parameter for maximizing the superconducting transition temperature. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.

  4. Ising superconductivity and Majorana fermions in transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Zhou, Benjamin T.; Yuan, Noah F. Q.; Jiang, Hong-Liang; Law, K. T.

    2016-05-01

    In monolayer transition-metal dichalcogenides (TMDs), electrons in opposite K valleys are subject to opposite effective Zeeman fields, which are referred to as Ising spin-orbit coupling (SOC) fields. The Ising SOC, originating from in-plane mirror symmetry breaking, pins the electron spins to the out-of-plane directions, and results in Ising superconducting states with strongly enhanced upper critical fields. Here, we show that the Ising SOC generates equal-spin-triplet Cooper pairs with spin polarized in the in-plane directions. Importantly, the spin-triplet Cooper pairs can induce superconducting pairings in a half-metal wire placed on top of the TMD and result in a topological superconductor with Majorana end states. Direct ways to detect equal-spin triplet Cooper pairs and the differences between Ising superconductors and Rashba superconductors are discussed.

  5. Loss of Feedback Inhibition via D2 Autoreceptors Enhances Acquisition of Cocaine Taking and Reactivity to Drug-Paired Cues

    PubMed Central

    Holroyd, Kathryn B; Adrover, Martin F; Fuino, Robert L; Bock, Roland; Kaplan, Alanna R; Gremel, Christina M; Rubinstein, Marcelo; Alvarez, Veronica A

    2015-01-01

    A prominent aspect of drug addiction is the ability of drug-associated cues to elicit craving and facilitate relapse. Understanding the factors that regulate cue reactivity will be vital for improving treatment of addictive disorders. Low availability of dopamine (DA) D2 receptors (D2Rs) in the striatum is associated with high cocaine intake and compulsive use. However, the role of D2Rs of nonstriatal origin in cocaine seeking and taking behavior and cue reactivity is less understood and possibly underestimated. D2Rs expressed by midbrain DA neurons function as autoreceptors, exerting inhibitory feedback on DA synthesis and release. Here, we show that selective loss of D2 autoreceptors impairs the feedback inhibition of DA release and amplifies the effect of cocaine on DA transmission in the nucleus accumbens (NAc) in vitro. Mice lacking D2 autoreceptors acquire a cued-operant self-administration task for cocaine faster than littermate control mice but acquire similarly for a natural reward. Furthermore, although mice lacking D2 autoreceptors were able to extinguish self-administration behavior in the absence of cocaine and paired cues, they exhibited perseverative responding when cocaine-paired cues were present. This enhanced cue reactivity was selective for cocaine and was not seen during extinction of sucrose self-administration. We conclude that low levels of D2 autoreceptors enhance the salience of cocaine-paired cues and can contribute to the vulnerability for cocaine use and relapse. PMID:25547712

  6. Loss of feedback inhibition via D2 autoreceptors enhances acquisition of cocaine taking and reactivity to drug-paired cues.

    PubMed

    Holroyd, Kathryn B; Adrover, Martin F; Fuino, Robert L; Bock, Roland; Kaplan, Alanna R; Gremel, Christina M; Rubinstein, Marcelo; Alvarez, Veronica A

    2015-05-01

    A prominent aspect of drug addiction is the ability of drug-associated cues to elicit craving and facilitate relapse. Understanding the factors that regulate cue reactivity will be vital for improving treatment of addictive disorders. Low availability of dopamine (DA) D2 receptors (D2Rs) in the striatum is associated with high cocaine intake and compulsive use. However, the role of D2Rs of nonstriatal origin in cocaine seeking and taking behavior and cue reactivity is less understood and possibly underestimated. D2Rs expressed by midbrain DA neurons function as autoreceptors, exerting inhibitory feedback on DA synthesis and release. Here, we show that selective loss of D2 autoreceptors impairs the feedback inhibition of DA release and amplifies the effect of cocaine on DA transmission in the nucleus accumbens (NAc) in vitro. Mice lacking D2 autoreceptors acquire a cued-operant self-administration task for cocaine faster than littermate control mice but acquire similarly for a natural reward. Furthermore, although mice lacking D2 autoreceptors were able to extinguish self-administration behavior in the absence of cocaine and paired cues, they exhibited perseverative responding when cocaine-paired cues were present. This enhanced cue reactivity was selective for cocaine and was not seen during extinction of sucrose self-administration. We conclude that low levels of D2 autoreceptors enhance the salience of cocaine-paired cues and can contribute to the vulnerability for cocaine use and relapse. PMID:25547712

  7. Non-thermal enhancement of electron-positron pair creation in burning thermonuclear laboratory plasmas

    NASA Astrophysics Data System (ADS)

    Hill, E. G.; Rose, S. J.

    2014-12-01

    We estimate the number of electron-positron pairs which will be produced during the burning of a Deuterium-Tritium (DT) plasma in conditions that are anticipated will be achieved at the National Ignition Facility. In particular we consider, for the first time, the effect of including the gamma photons produced in a low probability channel of the DT reaction. It is found that non-thermal effects driven by the fusion products are the dominant method of pair production, and lead to a number density of positrons within the capsule in excess of 3 × 1017 cm-3. The positrons are predominately produced by the Bethe-Heitler process and destroyed by two photon annihilation.

  8. Enhancement of the superconducting critical temperature in Nb/Py/Nb trilayers

    NASA Astrophysics Data System (ADS)

    Ilyina, E. A.; Hernàndez, J. M.; García-Santiago, A.; Cirillo, C.; Attanasio, C.

    2012-09-01

    Superconducting critical temperature, Tc, have been measured in a series of Nb/Py/Nb (here Py = Ni80Fe20) trilayers having constant Py thickness, dPy = 432 nm, and variable Nb thickness, dNb, in the range 20-30 nm. We have observed that, for dNb between 23 and 27 nm, resistive transitions shift towards higher temperature if stripe domains are present in the Py layer. We relate those observations to the non-homogeneous magnetization in the Py layer due to the presence of stripe domain structures.

  9. Superconducting T/sub c/ enhancement in weakly disordered Ge-covered tin films

    SciTech Connect

    Parashar, R.S.; Srivastava, V.

    1985-11-01

    We report on the variation of the superconducting transition temperature with the electrical resistance ratio in weakly disordered Ge-covered tin films deposited at room temperature. The normal-state sheet resistance R/sub N//sup D'Alembertian/ varied between 0.2

  10. Sequential Coherence in Sentence Pairs Enhances Imagery during Comprehension: An Individual Differences Study

    PubMed Central

    Dominey, Peter Ford; Ventre-Dominey, Jocelyne

    2015-01-01

    The present study investigates how sequential coherence in sentence pairs (events in sequence vs. unrelated events) affects the perceived ability to form a mental image of the sentences for both auditory and visual presentations. In addition, we investigated how the ease of event imagery affected online comprehension (word reading times) in the case of sequentially coherent and incoherent sentence pairs. Two groups of comprehenders were identified based on their self-reported ability to form vivid mental images of described events. Imageability ratings were higher and faster for pairs of sentences that described events in coherent sequences rather than non-sequential events, especially for high imagers. Furthermore, reading times on individual words suggested different comprehension patterns with respect to sequence coherence for the two groups of imagers, with high imagers activating richer mental images earlier than low imagers. The present results offer a novel link between research on imagery and discourse coherence, with specific contributions to our understanding of comprehension patterns for high and low imagers. PMID:26383115

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

    NASA Astrophysics Data System (ADS)

    Indira, Gomathinayagam; UmaMaheswaraRao, Theru; Chandramohan, Sankaralingam

    2015-01-01

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

  12. Superconductivity and Applications - Proceedings of the Taiwan International Symposium on Superconductivity

    NASA Astrophysics Data System (ADS)

    Ku, H. C.; Wu, P. T.; Lee, W. H.; Liu, R. S.

    1989-11-01

    The Table of Contents for the full book PDF is as follows: * Preface * Microstructural and Electron-Structural Anomalies, and High Temperature Superconductivity * Substitutional Chemistry and the Metal-Insulator Transition in Cuprates and Bismuthates * Processing of High Tc Superconductor/Metal-Oxide Composites * Electron Microscope Characterisation of the Structure of High-Tc Superconductors * Mechanism of Broadened Superconducting Transition in Oxides * Magnetic, Microstructure, and High-Field Studies of Superconducting 123-AgO Composites * Superconductivity Enhancement and Pairing Strength in the (Tl, Pb, Bi)m(Sr, Ba)2CuOm+4(m = 1,2) Systems * Bulk Superconductivity in a New Family of Tl-containing Septenary Oxides * Several Suggested Mechanisms for High-Temperature Superconductivity * Calculation of Isotope Effects in High Tc Superconductivity * The Evidences of Unconventional Pairing in Heavy Fermion Superconductors and High Tc Superconductors * Superconductive Energy Storage (SMES) for Electrical Utility Use * Energy Storage Study for Power System Stabilisation * Spin Fluctuation Near Zero and High Field for Pure and Impure High Tc Superconductors * Magnetisation Study of the Unconventional Type II Superconductor (Gd0.2Ca0.8)Sr2(Tl0.5Pb0.5)Cu2Oy * Superconductivity and High Temperature Resistivity of High-Tc Oxide Compounds * Superconducting and Normal State Properties of BiSrCaCuO with Ag and Pb Doping * Effects of Substitution of Fe, Zn and A1 for Cu in Bi2Ca1Sr2Cu2Oy * Electrical and Magnetic Properties of Y1-xCdxBa2Cu3O7-δ and Gd1-xBa2Cu3O7-δ * YBaCuO Thin Films: Epitaxial Growth, Properties and the Influence of Ion Irradiation * Epitaxial Growth of High-Tc Superconducting Films by Liquid Phase Epitaxy Method * Superconducting Thin Films in Tl-Ba-Ca-Cu-O System * The Kinetics of Solid State Formation of the YBa2Cu3O6.5+x Phase * Phase Relations of Equilibrium Compounds in the Bi-Ca-Sr-Cu-O System * Preparation of Tl2CaBa2Cu2O8 by a Low-Temperature Solid

  13. Design and Evaluation of a Novel Felbinac Transdermal Patch: Combining Ion-Pair and Chemical Enhancer Strategy.

    PubMed

    Liu, Nannan; Song, Wenting; Song, Tian; Fang, Liang

    2016-04-01

    The aim of this study was to design a novel felbinac (FEL) patch with significantly higher (P < 0.05) skin permeation amount than the commercial product SELTOUCH® using ion-pair and chemical enhancer strategy, overcoming the disadvantage of the large application area of SELTOUCH®. Six complexes of FEL with organic amines diethylamine (DEA), triethylamine (TEA), N-(2'-hydroxy-ethanol)-piperdine (HEPP), monoethanolamine (MEtA), diethanolamine (DEtA), and triethanolamine (TEtA) were prepared by ion-pair interaction, and their formation were confirmed by differential scanning calorimetry (DSC), powder X-ray diffraction (pXRD), infared spectroscopy (IR), and proton nuclear magnetic resonance spectroscopy ((1)H-NMR). Subsequently, the effect of ion-pair complexes and chemical enhancers were investigated through in vitro and in vivo experiments using rabbit abdominal skin. Results showed that FEL-TEA was the most potential candidate both in isopropyl palmitate (IPP) solution and transdermal patches. Combining use of 10% N-dodecylazepan-2-one (Azone), the optimized FEL-TEA patch achieved a flux of 18.29 ± 2.59 μg/cm(2)/h, which was twice the amount of the product SELTOUCH® (J = 9.18 ± 1.26 μg/cm(2)/h). Similarly, the area under the concentration curve from time 0 to time t (AUC0-t ) in FEL-TEA patch group (15.94 ± 3.58 h.μg/mL) was also twice as that in SELTOUCH® group (7.31 ± 1.16 h.μg/mL). Furthermore, the in vitro skin permeation results of FEL-TEA patch was found to have a good correlation with the in vivo absorption results in rabbit. These findings indicated that a combination of ion-pair and chemical enhancer strategy could be useful in developing a novel transdermal patch of FEL. PMID:26070544

  14. Synergistic enhancement of cellulase pairs linked by consensus ankyrin repeats: Determination of the roles of spacing, orientation, and enzyme identity.

    PubMed

    Cunha, Eva S; Hatem, Christine L; Barrick, Doug

    2016-08-01

    Biomass deconstruction to small simple sugars is a potential approach to biofuels production; however, the highly recalcitrant nature of biomass limits the economic viability of this approach. Thus, research on efficient biomass degradation is necessary to achieve large-scale production of biofuels. Enhancement of cellulolytic activity by increasing synergism between cellulase enzymes holds promise in achieving high-yield biofuels production. Here we have inserted cellulase pairs from extremophiles into hyperstable α-helical consensus ankyrin repeat domain scaffolds. Such chimeric constructs allowed us to optimize arrays of enzyme pairs against a variety of cellulolytic substrates. We found that endocellulolytic domains CelA (CA) and Cel12A (C12A) act synergistically in the context of ankyrin repeats, with both three and four repeat spacing. The extent of synergy differs for different substrates. Also, having C12A N-terminal to CA provides greater synergy than the reverse construct, especially against filter paper. In contrast, we do not see synergy for these enzymes in tandem with CelK (CK) catalytic domain, a larger exocellulase, demonstrating the importance of enzyme identity in synergistic enhancement. Furthermore, we found endocellulases CelD and CA with three repeat spacing to act synergistically against filter paper. Importantly, connecting CA and C12A with a disordered linker of similar contour length shows no synergistic enhancement, indicating that synergism results from connecting these domains with folded ankyrin repeats. These results show that ankyrin arrays can be used to vary spacing and orientation between enzymes, helping to design and optimize artificial cellulosomes, providing a novel architecture for synergistic enhancement of enzymatic cellulose degradation. Proteins 2016; 84:1043-1054. © 2016 Wiley Periodicals, Inc. PMID:27071357

  15. Evidence for two-dimensional Ising superconductivity in gated MoS₂.

    PubMed

    Lu, J M; Zheliuk, O; Leermakers, I; Yuan, N F Q; Zeitler, U; Law, K T; Ye, J T

    2015-12-11

    The Zeeman effect, which is usually detrimental to superconductivity, can be strongly protective when an effective Zeeman field from intrinsic spin-orbit coupling locks the spins of Cooper pairs in a direction orthogonal to an external magnetic field. We performed magnetotransport experiments with ionic-gated molybdenum disulfide transistors, in which gating prepared individual superconducting states with different carrier dopings, and measured an in-plane critical field B(c2) far beyond the Pauli paramagnetic limit, consistent with Zeeman-protected superconductivity. The gating-enhanced B(c2) is more than an order of magnitude larger than it is in the bulk superconducting phases, where the effective Zeeman field is weakened by interlayer coupling. Our study provides experimental evidence of an Ising superconductor, in which spins of the pairing electrons are strongly pinned by an effective Zeeman field. PMID:26563134

  16. Evidence for two-dimensional Ising superconductivity in gated MoS2

    NASA Astrophysics Data System (ADS)

    Lu, J. M.; Zheliuk, O.; Leermakers, I.; Yuan, N. F. Q.; Zeitler, U.; Law, K. T.; Ye, J. T.

    2015-12-01

    The Zeeman effect, which is usually detrimental to superconductivity, can be strongly protective when an effective Zeeman field from intrinsic spin-orbit coupling locks the spins of Cooper pairs in a direction orthogonal to an external magnetic field. We performed magnetotransport experiments with ionic-gated molybdenum disulfide transistors, in which gating prepared individual superconducting states with different carrier dopings, and measured an in-plane critical field Bc2 far beyond the Pauli paramagnetic limit, consistent with Zeeman-protected superconductivity. The gating-enhanced Bc2 is more than an order of magnitude larger than it is in the bulk superconducting phases, where the effective Zeeman field is weakened by interlayer coupling. Our study provides experimental evidence of an Ising superconductor, in which spins of the pairing electrons are strongly pinned by an effective Zeeman field.

  17. Hidden Fermionic Excitation Boosting High-Temperature Superconductivity in Cuprates.

    PubMed

    Sakai, Shiro; Civelli, Marcello; Imada, Masatoshi

    2016-02-01

    The dynamics of a microscopic cuprate model, namely, the two-dimensional Hubbard model, is studied with a cluster extension of the dynamical mean-field theory. We find a nontrivial structure of the frequency-dependent self-energies, which describes an unprecedented interplay between the pseudogap and superconductivity. We show that these properties are well described by quasiparticles hybridizing with (hidden) fermionic excitations, emergent from the strong electronic correlations. The hidden fermion enhances superconductivity via a mechanism distinct from a conventional boson-mediated pairing, and originates the normal-state pseudogap. Though the hidden fermion is elusive in experiments, it can solve many experimental puzzles. PMID:26894730

  18. Hidden Fermionic Excitation Boosting High-Temperature Superconductivity in Cuprates

    NASA Astrophysics Data System (ADS)

    Sakai, Shiro; Civelli, Marcello; Imada, Masatoshi

    2016-02-01

    The dynamics of a microscopic cuprate model, namely, the two-dimensional Hubbard model, is studied with a cluster extension of the dynamical mean-field theory. We find a nontrivial structure of the frequency-dependent self-energies, which describes an unprecedented interplay between the pseudogap and superconductivity. We show that these properties are well described by quasiparticles hybridizing with (hidden) fermionic excitations, emergent from the strong electronic correlations. The hidden fermion enhances superconductivity via a mechanism distinct from a conventional boson-mediated pairing, and originates the normal-state pseudogap. Though the hidden fermion is elusive in experiments, it can solve many experimental puzzles.

  19. Enhancements to a Superconducting Quantum Interference Device (SQUID) Multiplexer Readout and Control System

    NASA Technical Reports Server (NTRS)

    Forgione, J.; Benford, D. J.; Buchanan, E. D.; Moseley, S. H.; Rebar, J.; Shafer, R. A.

    2004-01-01

    Far-infrared detector arrays such as the 16x32 superconducting bolometer array for the SAFIRE instrument (flying on the SOFIA airborne observatory) require systems of readout and control electronics to provide translation between a user-driven, digital PC and the cold, analog world of the cryogenic detector. In 2001, the National Institute of Standards and Technology (NIST) developed their Mark III electronics for purposes of control and readout of their 1x32 SQUID Multiplexer chips. We at NASA s Goddard Space Flight Center acquired a Mark 111 system and subsequently designed upgrades to suit our and our collaborators purposes. We developed an arbitrary, programmable multiplexing system that allows the user to cycle through rows in a SQUID array in an infinite number of combinations. We provided hooks in the Mark III system to allow readout of signals from outside the Mark 111 system, such as telescope status information. Finally, we augmented the heart of the system with a new feedback algorithm implementation, flexible diagnostic tools, and informative telemetry.

  20. Enhanced critical currents of commercial 2G superconducting coated conductors through proton irradiation

    NASA Astrophysics Data System (ADS)

    Welp, Ulrich; Leroux, M.; Kihlstrom, K. J.; Kwok, W.-K.; Koshelev, A. E.; Miller, D. J.; Rupich, M. W.; Fleshler, S.; Malozemoff, A. P.; Kayani, A.

    2015-03-01

    We report on magnetization and transport measurements of the critical current density, Jc, of commercial 2G YBCO coated conductors before and after proton irradiation. The samples were irradiated along the c-axis with 4 MeV protons. Proton irradiation produces a mixed pinning landscape composed of pre-existing rare earth particles and a uniform distribution of irradiation induced nm-sized defects. This pinning landscape strongly reduces the suppression of Jc in magnetic fields resulting in a doubling of Jc in a field of ~ 4T. The irradiation dose-dependence of Jc is characterized by a temperature and field dependent sweat spot that at 5 K and 6 T occurs around 20x1016 p/cm2. Large-scale time dependent Ginzburg-Landau simulations yield a good description of our results. This work supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. D.O.E., Office of Science, Office of Basic Energy Sciences (KK, ML, AEK) and by the D.O.E, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 (UW, WKK).

  1. Enhancements to a superconducting quantum interference device (SQUID) multiplexer readout and control system

    NASA Astrophysics Data System (ADS)

    Forgione, Joshua B.; Benford, Dominic J.; Buchanan, Ernest D.; Moseley, S. H., Jr.; Rebar, Joyce; Shafer, Richard A.

    2004-10-01

    Far-infrared detector arrays such as the 16x32 superconducting bolometer array for the SAFIRE instrument (flying on the SOFIA airborne observatory) require systems of readout and control electronics to provide translation between a user-driven, digital PC and the cold, analog world of the cryogenic detector. In 2001, the National Institute of Standards and Technology (NIST) developed their Mark III electronics for purposes of control and readout of their 1x32 SQUID Multiplexer chips. We at NASA's Goddard Space Flight Center acquired a Mark III system and subsequently designed upgrades to suit our and our collaborators' purposes. We developed an arbitrary, programmable multiplexing system that allows the user to cycle through rows in a SQUID array in an infinite number of combinations. We provided 'hooks' in the Mark III system to allow readout of signals from outside the Mark III system, such as telescope status information. Finally, we augmented the heart of the system with a new feedback algorithm implementation, flexible diagnostic tools, and informative telemetry.

  2. Application of a modified flux-coupling type superconducting fault current limiter to transient performance enhancement of micro-grid

    NASA Astrophysics Data System (ADS)

    Chen, Lei; Zheng, Feng; Deng, Changhong; Li, Shichun; Li, Miao; Liu, Hui; Zhu, Lin; Guo, Fang

    2015-11-01

    Concerning the application and development of a micro-grid system which is designed to accommodate high penetration of intermittent renewable resources, one of the main issues is related to an increase in the fault-current level. It is crucial to ensure the micro-grid's operational stability and service reliability when a fault occurs in the main network. In this paper, our research group suggests a modified flux-coupling type superconducting fault current limiter (SFCL) to enhance the transient performance of a typical micro-grid system. The SFCL is installed at the point of common coupling (PCC) between the main network and the micro-grid, and it is expected to actively improve the micro-grid's fault ride-through capability. And for some specific faults, the micro-grid should disconnect from the main network, and the SFCL's contribution is to make the micro-grid carry out a smooth transition between its grid-connected and islanded modes. Related theory derivation, technical discussion and simulation analysis are performed. From the demonstrated results, applying the SFCL can effectively limit the fault current, maintain the power balance, and enhance the voltage and frequency stability of the micro-grid.

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

    SciTech Connect

    Seligson, D.

    1983-05-01

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

  4. Interplay between superconductivity and magnetism in iron-based superconductors

    SciTech Connect

    Chubukov, Andrey V

    2015-06-10

    This proposal is for theoretical work on strongly correlated electron systems, which are at the center of experimental and theoretical activities in condensed-matter physics. The interest to this field is driven fascinating variety of observed effects, universality of underlying theoretical ideas, and practical applications. I propose to do research on Iron-based superconductors (FeSCs), which currently attract high attention in the physics community. My goal is to understand superconductivity and magnetism in these materials at various dopings, the interplay between the two, and the physics in the phase in which magnetism and superconductivity co-exist. A related goal is to understand the origin of the observed pseudogap-like behavior in the normal state. My research explores the idea that superconductivity is of electronic origin and is caused by the exchange of spin-fluctuations, enhanced due to close proximity to antiferromagnetism. The multi-orbital/multi-band nature of FeSCs opens routes for qualitatively new superconducting states, particularly the ones which break time-reversal symmetry. By all accounts, the coupling in pnictdes is below the threshold for Mott physics and I intend to analyze these systems within the itinerant approach. My plan is to do research in two stages. I first plan to address several problems within weak-coupling approach. Among them: (i) what sets stripe magnetic order at small doping, (ii) is there a preemptive instability into a spin-nematic state, and how stripe order affects fermions; (iii) is there a co-existence between magnetism and superconductivity and what are the system properties in the co-existence state; (iv) how superconductivity emerges despite strong Coulomb repulsion and can the gap be s-wave but with nodes along electron FSs, (v) are there complex superconducting states, like s+id, which break time reversal symmetry. My second goal is to go beyond weak coupling and derive spin-mediated, dynamic interaction between

  5. Designing heterostructures with higher-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Le Hur, Karyn; Chung, Chung-Hou; Paul, I.

    2011-07-01

    We propose to increase the superconducting transition temperature Tc of strongly correlated materials by designing heterostructures which exhibit a high pairing energy as a result of magnetic fluctuations. More precisely, applying an effective theory of the doped Mott insulator, we envisage a bilayer Hubbard system where both layers exhibit intrinsic intralayer (intraband) d-wave superconducting correlations. Introducing a finite asymmetry between the hole densities of the two layers such that one layer becomes slightly more underdoped and the other more overdoped, we show a visible enhancement of Tc compared to the optimally doped isolated layer. Using the bonding and antibonding band basis, we show that the mechanism behind this enhancement of Tc is the interband pairing correlation mediated by the hole asymmetry which strives to decrease the paramagnetic nodal contribution to the superfluid stiffness. For two identical layers, Tc remains comparable to that of the isolated layer until moderate values of the interlayer single-particle tunneling term. These heterostructures shed new light on fundamental questions related to superconductivity.

  6. Superconducting magnet

    NASA Technical Reports Server (NTRS)

    1985-01-01

    Extensive computer based engineering design effort resulted in optimization of a superconducting magnet design with an average bulk current density of approximately 12KA/cm(2). Twisted, stranded 0.0045 inch diameter NbTi superconductor in a copper matrix was selected. Winding the coil from this bundle facilitated uniform winding of the small diameter wire. Test coils were wound using a first lot of the wire. The actual packing density was measured from these. Interwinding voltage break down tests on the test coils indicated the need for adjustment of the wire insulation on the lot of wire subsequently ordered for construction of the delivered superconducting magnet. Using the actual packing densities from the test coils, a final magnet design, with the required enhancement and field profile, was generated. All mechanical and thermal design parameters were then also fixed. The superconducting magnet was then fabricated and tested. The first test was made with the magnet immersed in liquid helium at 4.2K. The second test was conducted at 2K in vacuum. In the latter test, the magnet was conduction cooled from the mounting flange end.

  7. Time-resolved measurements of Cooper-pair radiative recombination in InAs quantum dots

    SciTech Connect

    Mou, S. S.; Nakajima, H.; Kumano, H.; Suemune, I.; Irie, H.; Asano, Y.; Akahane, K.; Sasaki, M.; Murayama, A.

    2015-08-21

    We studied InAs quantum dots (QDs) where electron Cooper pairs penetrate from an adjacent niobium (Nb) superconductor with the proximity effect. With time-resolved luminescence measurements at the wavelength around 1550 nm, we observed luminescence enhancement and reduction of luminescence decay time constants at temperature below the superconducting critical temperature (T{sub C}) of Nb. On the basis of these measurements, we propose a method to determine the contribution of Cooper-pair recombination in InAs QDs. We show that the luminescence enhancement measured below T{sub C} is well explained with our theory including Cooper-pair recombination.

  8. Intrinsic Paramagnetic Meissner Effect Due to s -Wave Odd-Frequency Superconductivity

    NASA Astrophysics Data System (ADS)

    Di Bernardo, A.; Salman, Z.; Wang, X. L.; Amado, M.; Egilmez, M.; Flokstra, M. G.; Suter, A.; Lee, S. L.; Zhao, J. H.; Prokscha, T.; Morenzoni, E.; Blamire, M. G.; Linder, J.; Robinson, J. W. A.

    2015-10-01

    In 1933, Meissner and Ochsenfeld reported the expulsion of magnetic flux—the diamagnetic Meissner effect—from the interior of superconducting lead. This discovery was crucial in formulating the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity. In exotic superconducting systems BCS theory does not strictly apply. A classical example is a superconductor-magnet hybrid system where magnetic ordering breaks time-reversal symmetry of the superconducting condensate and results in the stabilization of an odd-frequency superconducting state. It has been predicted that under appropriate conditions, odd-frequency superconductivity should manifest in the Meissner state as fluctuations in the sign of the magnetic susceptibility, meaning that the superconductivity can either repel (diamagnetic) or attract (paramagnetic) external magnetic flux. Here, we report local probe measurements of faint magnetic fields in a Au /Ho /Nb trilayer system using low-energy muons, where antiferromagnetic Ho (4.5 nm) breaks time-reversal symmetry of the proximity-induced pair correlations in Au. From depth-resolved measurements below the superconducting transition of Nb, we observe a local enhancement of the magnetic field in Au that exceeds the externally applied field, thus proving the existence of an intrinsic paramagnetic Meissner effect arising from an odd-frequency superconducting state.

  9. Strong enhancement of s -wave superconductivity near a quantum critical point of Ca3Ir4Sn13

    SciTech Connect

    Biswas, P. K.; Guguchia, Z.; Khasanov, R.; Chinotti, M.; Li, L.; Wang, Kefeng; Petrovic, C.; Morenzoni, E.

    2015-11-11

    We report microscopic studies by muon spin rotation/relaxation as a function of pressure of the Ca3Ir4Sn13 and Sr3Ir4Sn13 system displaying superconductivity and a structural phase transition associated with the formation of a charge density wave (CDW). Our findings show a strong enhancement of the superfluid density and a dramatic increase of the pairing strength above a pressure of ≈ 1.6 GPa giving direct evidence of the presence of a quantum critical point separating a superconducting phase coexisting with CDW from a pure superconducting phase. The superconducting order parameter in both phases has the same s-wave symmetry. In spite of the conventional phonon-mediated BCS character of the weakly correlated (Ca1-xSrx)3Ir4Sn13 system the dependence of the effective superfluid density on the critical temperature puts this compound in the “Uemura” plot close to unconventional superconductors. This system exemplifies that conventional BCS superconductors in the presence of competing orders or multi-band structure can also display characteristics of unconventional superconductors.

  10. Enhanced flux-pinning properties in superconducting YBa2Cu3O(7-delta) thin films with nanoengineering

    NASA Astrophysics Data System (ADS)

    Tsai, Chen-Fong

    into the YBCO matrix as artificial pinning centers. Results suggest that all nanoinclusions showed significant enhancement in the superconducting properties of YBCO. The ferromagnetic pinning centers dominate at high field and low temperature regimes, however, the defect pinning centers dominate at low field and high temperature regimes. The uniquely arranged VAN structure of alternating magnetic and non-magnetic nanophases, which incorporates both high defect density and tunable distribution of magnetic dopants, is believed to be an ideal solution for flux-pinning enhancement.

  11. Correlation-enhanced odd-parity inter-orbital singlet pairing in the iron-pnictide superconductor LiFeAs

    NASA Astrophysics Data System (ADS)

    Nourafkan, Reza; Kotliar, Gabriel; Tremblay, A.-M. S.

    The rich variety of iron-based superconductors and their complex electronic structure lead to a wide range of possibilities for gap symmetry and pairing components. Here we solve in the 2-Fe Brillouin zone the full frequency-dependent linearized Eliashberg equations for LiFeAs with spin-fluctuation mediated pairing interactions. The magnetic excitations are calculated with the random phase approximation on a correlated electronic structure obtained with density functional theory and dynamical mean field theory. Correlations induce long-lived local moments with orbital-dependent dynamics. The interaction between electrons through Hund's coupling promotes both the intra-orbital dxz (yz) and the inter-orbital magnetic susceptibility. As a consequence, the leading pairing channel acquires sizeable inter-orbital dxy-dxz (yz) singlet pairing with odd parity under glide-plane symmetry. These components reduce the superconducting gap magnitude induced by the intra-orbital components of the gap function at the electron pockets intersection where the Fe-d t2 g orbitals strongly mix. The combination of intra- and inter-orbital components makes the results consistent with available experiments on the angular dependence of the gaps observed on the different Fermi surfaces. Supported by NSERC, CIFAR and the Tier I Canada Research Chair Program.

  12. Superconductivity in carbon nanomaterials

    NASA Astrophysics Data System (ADS)

    Dlugon, Katarzyna

    The purpose of this thesis is to explain the phenomenon of superconductivity in carbon nanomaterials such as graphene, fullerenes and carbon nanotubes. In the introductory chapter, there is a description of superconductivity and how it occurs at critical temperature (Tc) that is characteristic and different to every superconducting material. The discovery of superconductivity in mercury in 1911 by Dutch physicist Heike Kamerlingh Onnes is also mentioned. Different types of superconductors, type I and type II, low and high temperatures superconductors, as well as the BCS theory that was developed in 1957 by Bardeen, Cooper, and Schrieffer, are also described in detail. The BCS theory explains how Cooper's pairs are formed and how they are responsible for the superconducting properties of many materials. The following chapters explain superconductivity in doped fullerenes, graphene and carbon nanotubes, respectively. There is a thorough explanation followed by many examples of different types of carbon nanomaterials in which small changes in chemical structure cause significant changes in superconducting properties. The goal of this research was not only to take into consideration well known carbon based superconductors but also to search for the newest available materials such as the fullerene nanowhiskers discovered quite recently. There is also a presentation of fairly new ideas about inducing superconductivity in a monolayer of graphene which is more challenging than inducing superconductivity in graphite by simply intercalating metal atoms between its graphene sheets. An effort has been taken to look for any available information about carbon nanomaterials that have the potential to superconduct at room temperature, mainly because discovery of such materials would be a real revolution in the modern world, although no such materials have been discovered yet.

  13. 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).

  14. Significant enhancement of compositional and superconducting homogeneity in Ti rather than Ta-doped Nb3Sn

    NASA Astrophysics Data System (ADS)

    Tarantini, C.; Sung, Z.-H.; Lee, P. J.; Ghosh, A. K.; Larbalestier, D. C.

    2016-01-01

    Nb3Sn wire is now very close to its final optimization, but despite its classical nature, a detailed understanding of the role of Ta and Ti doping in the A15 is not fully developed. Long thought to be essentially equivalent in their influence on Hc2, they were interchangeably applied. Here, we show that Ti produces significantly more homogeneous chemical and superconducting properties. Despite Ta-doped samples having a slightly higher Tc onset in zero-field, they always have a wider Tc-distribution. In particular, whereas the Ta-doped A15 has a Tc-distribution extending from 18 down to 5-6 K (the lowest expected Tc for the binary A15 phase), the Ti-doped samples have no A15 phase with Tc below ˜12 K. The much narrower Tc distribution in the Ti-doped samples has a positive effect on their in-field Tc-distribution too, leading to an extrapolated μ0Hc2(0) 2 T larger than the Ta-doped wire. Ti-doping also appears to be very homogeneous even when the Sn content is reduced in order to inhibit breakdown of the diffusion barriers in very high Jc conductors. The enhanced homogeneity of the Ti-doped samples appears to result from its assistance of rapid diffusion of Sn into the filaments and by its incorporation into the A15 phase interchangeably with Sn on the Sn sites of the A15 phase.

  15. Evolution of quasiparticle excitations with enhanced electron correlations in superconducting A Fe2As2 (A =K , Rb, and Cs)

    NASA Astrophysics Data System (ADS)

    Mizukami, Y.; Kawamoto, Y.; Shimoyama, Y.; Kurata, S.; Ikeda, H.; Wolf, T.; Zocco, D. A.; Grube, K.; Löhneysen, H. v.; Matsuda, Y.; Shibauchi, T.

    2016-07-01

    In the heavily hole-doped iron-based superconductors A Fe2As2 (A =K , Rb, and Cs), the electron effective mass increases rapidly with alkali-ion radius. To study the superconducting gap structure in this series, we measure the in-plane London penetration depth λa b(T ) in clean crystals of A Fe2As2 down to low temperature T ˜0.1 K. In KFe2As2 , the superfluid stiffness ρsa b(T ) =λab 2(0 ) /λab 2(T ) at low temperatures can be accounted for by the strongly band-dependent multiple gaps reported recently. Although the λa b(T ) in all systems exhibits similar nonexponential temperature dependence indicating nodes or small minima in the gap, we find that the quasiparticle excitations at low temperatures show a systematic suppression with increasing alkali-ion radius. A possible origin of such evolution of low-energy excitations is discussed in terms of the momentum-dependent effect of enhanced quasiparticle mass near a quantum critical point.

  16. Cooper Pairs in Insulators?!

    ScienceCinema

    James Valles

    2010-01-08

    Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions. 

  17. Two Dimensional Ising Superconductivity in Gated MoS2

    NASA Astrophysics Data System (ADS)

    Yuan, Noah; Lu, Jianming; Law, Kam Tuen; Zheliuk, Oleksandr; Leermakers, Inge; Zeitler, Ulrich; Ye, Jianting

    The Zeeman effect, which is usually considered to be detrimental to superconductivity, can surprisingly protect the superconducting states created by gating a layered transition metal dichalcogenide. This effective Zeeman field, which is originated from intrinsic spin orbit coupling induced by breaking in-plane inversion symmetry, can reach nearly a hundred Tesla in magnitude. It strongly pins the spin orientation of the electrons to the out-of-plane directions and protects the superconductivity from being destroyed by an in-plane external magnetic field. In magnetotransport experiments of ionic-gate MoS2 transistors, where gating prepares individual superconducting state with different carrier doping, we indeed observe a spin-protected superconductivity by measuring an in-plane critical field Bc 2 far beyond the Pauli paramagnetic limit. The gating-enhanced Bc 2 is more than an order of magnitude larger compared to the bulk superconducting phases where the effective Zeeman field is weakened by interlayer coupling. Our study gives the first experimental evidence of an Ising superconductor, in which spins of the pairing electrons are strongly pinned by an effective Zeeman field.

  18. Pairing forces in nuclei

    SciTech Connect

    Chasman, R.R.

    1996-12-31

    In this contribution, the author mentions some features of pairing forces that are unique to nuclei and cover some areas of major interest in nuclear structure research, that involve pairing. At the level of most nuclear structure studies, nuclei are treated as consisting of two kinds of fermions (protons and neutrons) in a valence space with rather few levels. These features give rise to unique aspects of pairing forces in nuclei: (1) n-p pairing in T = 0 as well as the usual T = 1 pairing that is characteristic of like fermions; (2) a need to correct pairing calculations for the (1/N) effects that can typically be neglected in superconducting solids. An issue of current concern is the nature of the pairing interaction: several recent studies suggest a need for a density dependent form of the pairing interaction. There is a good deal of feedback between the questions of accurate calculations of pairing interactions and the form and magnitude of the pairing interaction. Finally, the authors discuss some many-body wave functions that are a generalization of the BCS wave function form, and apply them to a calculation of energy level spacings in superdeformed rotational bands.

  19. Unconventional Superconductivity in La(7)Ir(3) Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry.

    PubMed

    Barker, J A T; Singh, D; Thamizhavel, A; Hillier, A D; Lees, M R; Balakrishnan, G; Paul, D McK; Singh, R P

    2015-12-31

    The superconductivity of the noncentrosymmetric compound La(7)Ir(3) is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature T(c)=2.25  K-a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La(7)Ir(3) may be unconventional and paves the way for further studies of this family of materials. PMID:26765016

  20. Ferromagnetic/Superconducting Multilayers

    NASA Astrophysics Data System (ADS)

    Bader, S. D.

    1998-03-01

    Although it is well known that magnetism influences superconductivity, the converse issue has been less well explored. Recent theoretical predictions for ferromagnetic/ superconducting/ ferromagnetic trilayers exhibiting interlayer magnetic coupling in the normal state indicate that the coupling should be suppressed below the superconducting transition temperature.(C.A. R. Sá de Melo, Phys. Rev. Lett. 79), 1933 (1997); O. Sipr, B.L. Györffy, J. Phys. Cond. Matt. 7, 5239 (1995). To realize such a situation, a requirement (when the magnetic layers are thick) is that the superconducting layer thickness must simultaneously be less than the range over which the magnetic interlayer coupling decays, but greater than the superconducting coherence length. This introduces serious materials constraints. The present work describes initial explorations of three sputtered multilayer systems in an attempt to observe coupling of the ferromagnetic layers across a superconducting spacer:((a) J.E. Mattson, R.M. Osgood III, C.D. Potter, C.H. Sowers, and S.D. Bader, J. Vac. Sci. Technol. A 15), 1774 (1997); (b) J.E. Mattson, C.D. Potter, M.J. Conover, C.H. Sowers, and S.D. Bader, Phys. Rev. B 55, 70 (1997), and (c) R.M. Osgood III, J.E. Pearson, C.H. Sowers, and S.D. Bader, submitted (1997). (a) Ni/Nb, (b) Fe_4N/NbN, and (c) GdN/NbN. In these systems we have retained thinner superconducting layers than had been achieved previously, but interlayer magnetic coupling is not observed even in the normal state. For Ni/Nb the interfacial Ni loses its moment, which also reduces the superconducting pair-breaking. GdN is an insulating ferromagnet, so itinerancy is sacrificed, and, probably as a result of this, no coupling is observed. Each system gives rise to interesting and anisotropic superconducting properties. Thus, although the goal remains elusive, our search highlights the challenges and opportunities.

  1. Possible Electric-Field-Induced Superconducting States in Doped Silicene

    PubMed Central

    Zhang, Li-Da; Yang, Fan; Yao, Yugui

    2015-01-01

    Silicene has been synthesized recently, with experimental evidence showing possible superconductivity in the doped case. The noncoplanar low-buckled structure of this material inspires us to study the pairing symmetry of the doped system under a perpendicular external electric field. Our study reveals that the electric field induces an interesting quantum phase transition from the singlet chiral d + id′-wave superconducting phase to the triplet f-wave one. The emergence of the f-wave pairing results from the sublattice-symmetry-breaking caused by the electric field and the ferromagnetic-like intra-sublattice spin correlations at low dopings. Due to the enhanced density of states, the superconducting critical temperature of the system is enhanced by the electric field remarkably. Furthermore, we design a particular dc SQUID experiment to detect the quantum phase transition predicted here. Our results, if confirmed, will inject a new vitality to the familiar Si-based industry through adopting doped silicene as a tunable platform to study different types of exotic unconventional superconductivities. PMID:25644143

  2. Enhancement of the superconducting transition temperature of FeSe by intercalation of a molecular spacer layer

    NASA Astrophysics Data System (ADS)

    Burrard-Lucas, Matthew; Free, David G.; Sedlmaier, Stefan J.; Wright, Jack D.; Cassidy, Simon J.; Hara, Yoshiaki; Corkett, Alex J.; Lancaster, Tom; Baker, Peter J.; Blundell, Stephen J.; Clarke, Simon J.

    2013-01-01

    The discovery of high-temperature superconductivity in a layered iron arsenide has led to an intensive search to optimize the superconducting properties of iron-based superconductors by changing the chemical composition of the spacer layer between adjacent anionic iron arsenide layers. Superconductivity has been found in iron arsenides with cationic spacer layers consisting of metal ions (for example, Li+, Na+, K+, Ba2+) or PbO- or perovskite-type oxide layers, and also in Fe1.01Se (ref. ) with neutral layers similar in structure to those found in the iron arsenides and no spacer layer. Here we demonstrate the synthesis of Lix(NH2)y(NH3)1-yFe2Se2 (x~0.6 y~0.2), with lithium ions, lithium amide and ammonia acting as the spacer layer between FeSe layers, which exhibits superconductivity at 43(1) K, higher than in any FeSe-derived compound reported so far. We have determined the crystal structure using neutron powder diffraction and used magnetometry and muon-spin rotation data to determine the superconducting properties. This new synthetic route opens up the possibility of further exploitation of related molecular intercalations in this and other systems to greatly optimize the superconducting properties in this family.

  3. Significant enhancement of compositional and superconducting homogeneity in Ti rather than Ta-doped Nb3Sn

    DOE PAGESBeta

    Tarantini, C.; Sung, Z. -H.; Lee, P. J.; Ghosh, A. K.; Larbalestier, D. C.

    2016-01-25

    Nb3Sn wires are now very close to their final optimization but despite its classical nature, detailed understanding of the role of Ta and Ti doping in the A15 is not fully understood. Long thought to be essentially equivalent in their influence on Hc2, they were interchangeably applied. Here we show that Ti produces significantly more homogeneous chemical and superconducting properties. Despite Ta-doped samples having a slightly higher Tc onset in zero-field, they always have a wider Tc-distribution. In particular, whereas the Ta-doped A15 has a Tc-distribution extending from 18 down to 5-6 K (the lowest expected Tc for the binarymore » A15 phase), the Ti-doped samples have no A15 phase with Tc below ~12 K. The much narrower Tc distribution in the Ti-doped samples has a positive effect on their in-field Tc-distribution too, leading to an extrapolated μ0Hc2(0) 2 Tesla larger than the Ta-doped one. Ti-doping also appears to be very homogeneous even when the Sn content is reduced in order to inhibit breakdown of the diffusion barriers in very high Jc conductors. As a result, the enhanced homogeneity of the Ti-doped samples appears to result from its assistance of rapid diffusion of Sn into the filaments and by its incorporation into the A15 phase interchangeably with Sn on the Sn sites of the A15 phase.« less

  4. Constructive influence of the induced electron pairing on the Kondo state

    NASA Astrophysics Data System (ADS)

    Domański, T.; Weymann, I.; Barańska, M.; Górski, G.

    2016-03-01

    Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon.

  5. Constructive influence of the induced electron pairing on the Kondo state.

    PubMed

    Domański, T; Weymann, I; Barańska, M; Górski, G

    2016-01-01

    Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon. PMID:27009681

  6. Constructive influence of the induced electron pairing on the Kondo state

    PubMed Central

    Domański, T.; Weymann, I.; Barańska, M.; Górski, G.

    2016-01-01

    Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon. PMID:27009681

  7. Superconductivity in doped semiconductors

    NASA Astrophysics Data System (ADS)

    Bustarret, E.

    2015-07-01

    A historical survey of the main normal and superconducting state properties of several semiconductors doped into superconductivity is proposed. This class of materials includes selenides, tellurides, oxides and column-IV semiconductors. Most of the experimental data point to a weak coupling pairing mechanism, probably phonon-mediated in the case of diamond, but probably not in the case of strontium titanate, these being the most intensively studied materials over the last decade. Despite promising theoretical predictions based on a conventional mechanism, the occurrence of critical temperatures significantly higher than 10 K has not been yet verified. However, the class provides an enticing playground for testing theories and devices alike.

  8. Non-Equilibrium Superconductivity and Magnetic Pair Breaking in Perovskite Half-Metallic Ferromagnet-Insulator-Superconductor (F-I-S) Heterostructures

    NASA Technical Reports Server (NTRS)

    Fu, C.-C.; Yeh, N.-C.; Samoilov, A. V.; Vakili, K.; Li, Y.; Vasquez, R. P.

    1999-01-01

    The effect of spin-polarized quasiparticle currents on the critical current density (J-c) of cuprate superconductors is studied in perovskite F-I-S heterostructures as a function of insulator thickness and of underlying magnetic materials. A pulsed current technique is employed to minimize extraneous Joule heating on the superconductor. At temperatures near T-c, F-I-S samples with insulator thicknesses\\1e2nm show precipitous decrease in J_c as current injection (I_m) is increased. In contrast, J_c in a controlled sample with a substituted non-magnetic material (N-I-S) exhibit no dependence on I_m. Similarly, a F-I-S sample with a 10 mn insulating barrier also show little J_c effect versus I_m. At low temperatures with I_m = 0, significant suppression of J-c is observed only in the thin barrier F-I-S samples, although T_c and the normal-state resistivity of all samples are comparable. These phenomena can be attributed to the Cooper pair breaking induced by externally-injected and internally-reflected spin-polarized quasiparticle currents. We estimate an order of magnitude range for the spin diffusion length of 100 nm to 100\\ mum.

  9. Design considerations of a pair of power leads for fast-cycling superconducting accelerator magnets operating at 2 Tesla and 100 kA

    SciTech Connect

    Huang, Yuenian; Hays, Steven; Piekarz, Henryk; de Rijk, Gijsbert; Rossi, L.; /Fermilab /CERN

    2007-08-01

    Recently proposed injector accelerator, Low Energy Ring (LER) for the LHC and fast cycling accelerators for the proton drivers (SF-SPS at CERN and DSF-MR at Fermilab) require that a new magnet technology be developed. In support of this accelerator program, a pair of power leads needs to be developed to close the loop between the power supply and accelerator system. The magnet proposed to be used will be a modified transmission line magnet technology that would allow for accelerator quality magnetic field sweep of 2 T/s. The transmission line conductor will be using HTS technology and cooled with supercritical helium at 5 K. The power leads consist of two sections; upper one is a copper and lower section will be using HTS tapes. The accelerator magnet will be ramped to 100 kA in a second and almost immediately ramped down to zero in one second. This paper outlines the design considerations for the power leads to meet the operational requirements for the accelerator system. The power leads thermal analysis during the magnet powering cycle will be included.

  10. Superconductive wire

    DOEpatents

    Korzekwa, David A.; Bingert, John F.; Peterson, Dean E.; Sheinberg, Haskell

    1995-01-01

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity.

  11. Superconductive wire

    DOEpatents

    Korzekwa, D.A.; Bingert, J.F.; Peterson, D.E.; Sheinberg, H.

    1995-07-18

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity. 2 figs.

  12. Superconducting transistor

    DOEpatents

    Gray, Kenneth E.

    1979-01-01

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

  13. Tuning the superconductivity in single-layer FeSe/oxides by interface engineering

    NASA Astrophysics Data System (ADS)

    Peng, Rui

    2015-03-01

    The discovery of high Tc in single-layer FeSe films has enormous implications for both searching new high Tc superconductors and exploring the important factors for high temperature superconductivity. In this talk, I will show our recent angle-resolved photoemission studies on various FeSe-based heterostructures grown by molecular beam epitaxy. We systematically studied the electronic structures and superconducting properties of FeSe with varied strain, different interfacial oxide materials and different thicknesses, and uncover that electronic correlations and superconducting gap-closing temperatures are tuned by interfacial effects. We exclude the direct relation between superconductivity and tensile strain, or the energy of an interfacial phonon mode, and demonstrate the crucial and non-trivial role of FeSe/oxide interface on the high pairing temperature. By tuning the interface, superconducting pairing temperature reaches up to 75K in FeSe/Nb:BaTiO3/KTaO3 with the in-plane lattice of 3.99 Å, which sets a new superconducting-gap-closing temperature record for iron-based superconductors, and may paves the way to more cost-effective applications of ultra-thin superconductors. Besides, in extremely tensile-strained single-layer FeSe films, we found that the Fermi surfaces consist of two elliptical electron pockets at the zone corner, without detectable hybridization. The lifting of degeneracy is clearly observed for the first time for the iron-based superconductors with only electron Fermi surfaces. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results provide important experimental foundations for understanding the interfacial superconductivity and the pairing symmetry puzzle of iron-based superconductors, and also provide clues for further enhancing Tc through interface engineering.

  14. Giant phonon anomaly associated with superconducting fluctuations in the pseudogap phase of cuprates

    PubMed Central

    Liu, Ye-Hua; Konik, Robert M.; Rice, T. M.; Zhang, Fu-Chun

    2016-01-01

    The pseudogap in underdoped cuprates leads to significant changes in the electronic structure, and was later found to be accompanied by anomalous fluctuations of superconductivity and certain lattice phonons. Here we propose that the Fermi surface breakup due to the pseudogap, leads to a breakup of the pairing order into two weakly coupled sub-band amplitudes, and a concomitant low energy Leggett mode due to phase fluctuations between them. This increases the temperature range of superconducting fluctuations containing an overdamped Leggett mode. In this range inter-sub-band phonons show strong damping due to resonant scattering into an intermediate state with a pair of overdamped Leggett modes. In the ordered state, the Leggett mode develops a finite energy, changing the anomalous phonon damping into an anomaly in the dispersion. This proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra. PMID:26785835

  15. A Study of Power Systems Stability Enhancement Effects by Excitation Control of Superconducting Generator with High Response Excitation based on Detailed Excitation Circuit Model

    NASA Astrophysics Data System (ADS)

    Wu, Guohong; Shirato, Hideyuki

    SCG (Superconducting Generator) has a superconducting field winding, which leads to many advantages such as small size, high generation efficiency, low impedance, and so on, and be considered as one of the candidates to meet the needs of high stability and high efficiency in the future power system networks. SCG with high response excitation is especially expected to be able to enhance the transient stability of power system by its SMES (Superconducting Magnetic Energy System) effect. The SMES effect of SCG is recognized that its behaviors are dominated by the structures and controls of its excitation system. For this reason, in order to verify exactly how the SMES effect of SCG influences on the power system stability, the electrical circuits of SCG high response excitation are modeled in detail for conducting digital simulation, and its influence on excitation voltage and active power output of SCG are discussed as well. The simulation results with a typical one machine - infinite bus power system model shows that the SMES effect can be certainly obtained when its exciting power is supplied from SCG terminal bus and may considerably lead to an improvement of power system transient stability.

  16. Using Stimulus Pairing to Enhance Observational Learning of Peer Initiations for a Child with Autism in a Community Play Group

    ERIC Educational Resources Information Center

    Silla, Vanessa A.; Vesloski, Mary J.

    2008-01-01

    The importance of play in child development and the barriers that individuals with autism face regarding play skills requires us to identify specific interventions which can assist in the development of such skills. Stimulus pairing, which has been documented as a procedure by which an event comes to elicit a response by being paired with an event…

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

    PubMed

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

    2014-03-25

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

  18. Superconductivity from Emerging Magnetic Moments.

    PubMed

    Hoshino, Shintaro; Werner, Philipp

    2015-12-11

    Multiorbital Hubbard models are shown to exhibit a spatially isotropic spin-triplet superconducting phase, where equal-spin electrons in different local orbitals are paired. This superconducting state is stabilized in the spin-freezing crossover regime, where local moments emerge in the metal phase, and the pairing is substantially assisted by spin anisotropy. The phase diagram features a superconducting dome below a non-Fermi-liquid metallic region and next to a magnetically ordered phase. We suggest that this type of fluctuating-moment-induced superconductivity, which is not originating from fluctuations near a quantum critical point, may be realized in spin-triplet superconductors such as strontium ruthenates and uranium compounds. PMID:26705649

  19. Superconductivity from Emerging Magnetic Moments

    NASA Astrophysics Data System (ADS)

    Hoshino, Shintaro; Werner, Philipp

    2015-12-01

    Multiorbital Hubbard models are shown to exhibit a spatially isotropic spin-triplet superconducting phase, where equal-spin electrons in different local orbitals are paired. This superconducting state is stabilized in the spin-freezing crossover regime, where local moments emerge in the metal phase, and the pairing is substantially assisted by spin anisotropy. The phase diagram features a superconducting dome below a non-Fermi-liquid metallic region and next to a magnetically ordered phase. We suggest that this type of fluctuating-moment-induced superconductivity, which is not originating from fluctuations near a quantum critical point, may be realized in spin-triplet superconductors such as strontium ruthenates and uranium compounds.

  20. Low-temperature in situ formation of Y-Ba-Cu-O high T sub c superconducting thin films by plasma-enhanced metalorganic chemical vapor deposition

    SciTech Connect

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

    1990-06-04

    Highly textured, highly dense, superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} thin films with mirror-like surfaces have been prepared, {ital in} {ital situ}, at a reduced substrate temperature as low as 570 {degree}C by a remote microwave plasma-enhanced metalorganic chemical vapor deposition process (PE-MOCVD). Nitrous oxide was used as the oxidizer gas. The as-deposited films grown by PE-MOCVD show attainment of zero resistance at 72 K. PE-MOCVD was carried out in a commercial scale MOCVD reactor.

  1. Effect of microwave-enhanced superconductivity in YBa2Cu3O7 Bi-crystalline grain bounda ry weak-links

    NASA Technical Reports Server (NTRS)

    Fu, C. M.; Chen, C. M.; Lin, H. C.; Wu, K. H.; Juang, J. Y.; Uen, T. M.; Gou, Y. S.

    1995-01-01

    We have studied systematically the effect of microwave irradiation on the temperature dependent resistivity (R(I) and the current-voltage (I-V) characteristics of YBa2Gu3O(7 - x) (YBCO) bicrystalline grain boundary weak-links (GBWL's), with grain boundary of three different tilt angles. The superconducting transition temperature, T(sub c), has significant enhancement upon microwave irradiation. The microwave enhanced T(sub c) is increased as a function of incident microwave power, but limited to an optimum power level. The GBWL's of 45 deg tilt boundary has shown to be most sensitive to the microwave irradiation power, and the GBWL's of 36.8 deg tilt boundary has displayed a moderate response. In contrast, no enhancement of T(sub c) was observed in the GBWL's of 24 deg tilt boundary, as well as in the uniform films. Under the microwave irradiation, the R(T) dependent is hystertic as the transition taken from superconducting state to normal state and vice versa. Mechanisms associated with the redistribution of nonequilibrium quasiparticles under microwave irradiation are discussed.

  2. Effect of microwave-enhanced superconductivity in YBa{sub 2}Cu{sub 3}O{sub 7} bi-crystalline grain boundary weak-links

    SciTech Connect

    Fu, C.M.; Chen, C.M.; Lin, H.C.

    1994-12-31

    We have studied systematically the effect of microwave irradiation on the temperature dependent resistivity R(T) and the current-voltage (I-V) characteristics of YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) bicrystalline grain boundary weak-links (GBWLs), with grain boundary of three different tilt angles. The superconducting transition temperature, T{sub c}, has significant enhancement upon microwave irradiation. The microwave enhanced T{sub c} is increased as a function of incidence microwave power, but limited to an optimum power level. The GBWLs of 45{degrees} tilt boundary has shown to be most sensitive to the microwave irradiation power, and the GBWLs of 36.8{degrees} tilt boundary has displayed a moderate response. In contrast, no enhancement of T{sub c} was observed in the GBWLs of 24{degrees} tilt boundary, as well as in the uniform films. Under the microwave irradiation, the R(T) dependence is hysteretic as the transition taken from superconducting state to normal state and vice versa. Mechanisms associated with the redistribution of nonequilibrium quasiparticles under microwave irradiation are discussed.

  3. High temperature interfacial superconductivity

    SciTech Connect

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

    2012-06-19

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

  4. Multiband theory of superconductivity at the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Mohanta, N.; Taraphder, A.

    2015-11-01

    We present a multiband model for superconductivity at the metallic interface between insulating oxides LaAlO3 and SrTiO3 (001). Using a self-consistent Bogoliubov-de Gennes theory, formulated with the realistic bands at the interface, we investigate the spin-singlet and spin-triplet pairings in intraband and interband channels. We find that the Rashba and atomic spin-orbit interactions at the interface induce singlet pairing in the interband channel and triplet pairing in both the intraband and interband channels when the pairing amplitude in the singlet intraband channel is finite. The gate-voltage variation of superconductivity is resolved in different pairing channels, compared with experimental results, and found to match quite well. Interestingly, an enhancement of the superconducting transition temperature by external in-plane magnetic field is found, revealing the existence of a hidden superconducting state above the observed one. As the interface is known to possess a high level of inhomogeneity, we explore the role of nonmagnetic disorder incorporating thermal phase fluctuations by using a Monte Carlo method. We show that even after the transition to the nonsuperconducting phase, driven by temperature or magnetic field, the interface possesses localized Cooper pairs whose signature was observed in previous experiments.

  5. Evidence for superconductivity in Li-decorated monolayer graphene

    PubMed Central

    Ludbrook, B. M.; Levy, G.; Nigge, P.; Zonno, M.; Schneider, M.; Dvorak, D. J.; Veenstra, C. N.; Zhdanovich, S.; Wong, D.; Dosanjh, P.; Straßer, C.; Stöhr, A.; Forti, S.; Ast, C. R.; Starke, U.; Damascelli, A.

    2015-01-01

    Monolayer graphene exhibits many spectacular electronic properties, with superconductivity being arguably the most notable exception. It was theoretically proposed that superconductivity might be induced by enhancing the electron–phonon coupling through the decoration of graphene with an alkali adatom superlattice [Profeta G, Calandra M, Mauri F (2012) Nat Phys 8(2):131–134]. Although experiments have shown an adatom-induced enhancement of the electron–phonon coupling, superconductivity has never been observed. Using angle-resolved photoemission spectroscopy (ARPES), we show that lithium deposited on graphene at low temperature strongly modifies the phonon density of states, leading to an enhancement of the electron–phonon coupling of up to λ≃0.58. On part of the graphene-derived π∗-band Fermi surface, we then observe the opening of a Δ≃0.9-meV temperature-dependent pairing gap. This result suggests for the first time, to our knowledge, that Li-decorated monolayer graphene is indeed superconducting, with Tc≃5.9 K. PMID:26351697

  6. ACTIVE GALACTIC NUCLEUS PAIRS FROM THE SLOAN DIGITAL SKY SURVEY. II. EVIDENCE FOR TIDALLY ENHANCED STAR FORMATION AND BLACK HOLE ACCRETION

    SciTech Connect

    Liu Xin; Shen Yue; Strauss, Michael A.

    2012-01-20

    Active galactic nuclei (AGNs) are occasionally seen in pairs, suggesting that tidal encounters are responsible for the accretion of material by both central supermassive black holes (BHs). In Paper I of this series, we selected a sample of AGN pairs with projected separations r{sub p} < 100 h{sup -1}{sub 70} kpc and velocity offsets <600 km s{sup -1} from the Seventh Data Release of the Sloan Digital Sky Survey and quantified their frequency. In this paper, we address the BH accretion and recent star formation properties in their host galaxies. AGN pairs experience stronger BH accretion, as measured by their [O III] {lambda}5007 luminosities (corrected for contribution from star formation) and Eddington ratios, than do control samples of single AGNs matched in redshift and host-galaxy stellar mass. Their host galaxies have stronger post-starburst activity and younger mean stellar ages, as indicated by stronger H{delta} absorption and smaller 4000 A break in their spectra. The BH accretion and recent star formation in the host galaxies both increase with decreasing projected separation in AGN pairs, for r{sub p} {approx}< 10-30 h{sup -1}{sub 70} kpc. The intensity of BH accretion, the post-starburst strength, and the mean stellar ages are correlated between the two AGNs in a pair. The luminosities and Eddington ratios of AGN pairs are correlated with recent star formation in their host galaxies, with a scaling relation consistent with that observed in single AGNs. Our results suggest that galaxy tidal interactions enhance both BH accretion and host-galaxy star formation in close AGN pairs, even though the majority of low-redshift AGNs are not coincident with on-going interactions.

  7. Topological confinement and superconductivity

    SciTech Connect

    Al-hassanieh, Dhaled A; Batista, Cristian D

    2008-01-01

    We derive a Kondo Lattice model with a correlated conduction band from a two-band Hubbard Hamiltonian. This mapping allows us to describe the emergence of a robust pairing mechanism in a model that only contains repulsive interactions. The mechanism is due to topological confinement and results from the interplay between antiferromagnetism and delocalization. By using Density-Matrix-Renormalization-Group (DMRG) we demonstrate that this mechanism leads to dominant superconducting correlations in aID-system.

  8. Supercurrent in superconducting graphene

    NASA Astrophysics Data System (ADS)

    Kopnin, N. B.; Sonin, E. B.

    2010-07-01

    The problem of supercurrent in superconducting graphene is revisited and the supercurrent is calculated within the mean-field model employing the two-component wave functions on a honeycomb lattice with pairing between different valleys in the Brillouin zone. We show that the supercurrent within the linear approximation in the order-parameter-phase gradient is always finite even if the doping level is exactly zero.

  9. Wavelength-dependent optical enhancement of superconducting interlayer coupling in La1.885Ba0.115CuO4

    SciTech Connect

    Casandruc, E.; Nicoletti, D.; Rajasekaran, S.; Laplace, Y.; Khanna, V.; Gu, G.; Hill, J. P.; Cavalleri, A.

    2015-05-05

    We analyze the pump wavelength dependence for the photo-induced enhancement of interlayer coupling in La1.885Ba0.115CuO4, which is promoted by optical melting of the stripe order. In the equilibrium superconducting state (T < TC = 13 K), in which stripes and superconductivity coexist, time-domain THz spectroscopy reveals a photo-induced blue-shift of the Josephson Plasma Resonance after excitation with optical pulses polarized perpendicular to the CuO2 planes. In the striped, non-superconducting state (TC < T < TSO ≃ 40 K) a transient plasma resonance similar to that seen below TC appears from a featureless equilibrium reflectivity. Most strikingly, both these effects become stronger upon tuning of the pump wavelength from the mid-infrared to the visible, underscoring an unconventional competition between stripe order and superconductivity, which occurs on energy scales far above the ordering temperature.

  10. Quantum fluctuations of the superconducting cosmic string

    NASA Technical Reports Server (NTRS)

    Zhang, Shoucheng

    1987-01-01

    Quantum fluctuations of the proposed superconducting string with Bose charge carriers are studied in terms of the vortices on the string world sheet. In the thermodynamical limit, it is found that they appear in the form of free vortices rather than as bound pairs. This fluctuation mode violates the topological conservation law on which superconductivity is based. However, this limit may not be reached. The critical size of the superconducting string is estimated as a function of the coupling constants involved.

  11. Superconducting Cable

    DOEpatents

    Hughey, Raburn L.; Sinha, Uday K.; Reece, David S.; Muller, Albert C.

    2005-03-08

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  12. Superconducting Cable

    DOEpatents

    Hughey, Raburn L.; Sinha, Uday K.; Reece, David S.; Muller, Albert C.

    2005-07-22

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  13. Enhancement of the finite-frequency superfluid response in the pseudogap regime of strongly disordered superconducting films

    PubMed Central

    Mondal, Mintu; Kamlapure, Anand; Ganguli, Somesh Chandra; Jesudasan, John; Bagwe, Vivas; Benfatto, Lara; Raychaudhuri, Pratap

    2013-01-01

    The persistence of a soft gap in the density of states above the superconducting transition temperature Tc, the pseudogap, has long been thought to be a hallmark of unconventional high-temperature superconductors. However, in the last few years this paradigm has been strongly revised by increasing experimental evidence for the emergence of a pseudogap state in strongly-disordered conventional superconductors. Nonetheless, the nature of this state, probed primarily through scanning tunneling spectroscopy (STS) measurements, remains partly elusive. Here we show that the dynamic response above Tc, obtained from the complex ac conductivity, is highly modified in the pseudogap regime of strongly disordered NbN films. Below the pseudogap temperature, T*, the superfluid stiffness acquires a strong frequency dependence associated with a marked slowing down of critical fluctuations. When translated into the length-scale of fluctuations, our results suggest a scenario of thermal phase fluctuations between superconducting domains in a strongly disordered s-wave superconductor. PMID:23446946

  14. 2D superconductivity by ionic gating

    NASA Astrophysics Data System (ADS)

    Iwasa, Yoshi

    2D superconductivity is attracting a renewed interest due to the discoveries of new highly crystalline 2D superconductors in the past decade. Superconductivity at the oxide interfaces triggered by LaAlO3/SrTiO3 has become one of the promising routes for creation of new 2D superconductors. Also, the MBE grown metallic monolayers including FeSe are also offering a new platform of 2D superconductors. In the last two years, there appear a variety of monolayer/bilayer superconductors fabricated by CVD or mechanical exfoliation. Among these, electric field induced superconductivity by electric double layer transistor (EDLT) is a unique platform of 2D superconductivity, because of its ability of high density charge accumulation, and also because of the versatility in terms of materials, stemming from oxides to organics and layered chalcogenides. In this presentation, the following issues of electric filed induced superconductivity will be addressed; (1) Tunable carrier density, (2) Weak pinning, (3) Absence of inversion symmetry. (1) Since the sheet carrier density is quasi-continuously tunable from 0 to the order of 1014 cm-2, one is able to establish an electronic phase diagram of superconductivity, which will be compared with that of bulk superconductors. (2) The thickness of superconductivity can be estimated as 2 - 10 nm, dependent on materials, and is much smaller than the in-plane coherence length. Such a thin but low resistance at normal state results in extremely weak pinning beyond the dirty Boson model in the amorphous metallic films. (3) Due to the electric filed, the inversion symmetry is inherently broken in EDLT. This feature appears in the enhancement of Pauli limit of the upper critical field for the in-plane magnetic fields. In transition metal dichalcogenide with a substantial spin-orbit interactions, we were able to confirm the stabilization of Cooper pair due to its spin-valley locking. This work has been supported by Grant-in-Aid for Specially

  15. Photoresponse mechanism of superconducting magnesium diboride

    NASA Astrophysics Data System (ADS)

    Khafizov, Marat

    The recent discovery of superconductivity in MgB2, with its BCS-like Cooper pairing mechanism and the 40-K critical temperature, and the demonstration of efficient single-optical-photon detection in superconducting NbN nanowire meanders inspired an interest in the development of superconducting radiation detectors based on MgB2. We report the results of our experimental and theoretical studies of a photoresponse mechanism in superconducting MgB2 thin films and microbridges. We demonstrate that despite the two-gap nature of this material, the nonequilibrium superconducting recovery dynamics in MgB2 is similar to conventional one-gap, both low- and high-temperature superconductors and is governed by quasiparticle recombination, limited by the phonon bottleneck mechanism. Our measured 100-ps-wide responses in MgB2 superconducting microbridges, operated at temperatures above 20 K, make this material promising for superconducting photodetector applications.

  16. Base pairing enhances fluorescence and favors cyclobutane dimer formation induced upon absorption of UVA radiation by DNA.

    PubMed

    Banyasz, Akos; Vayá, Ignacio; Changenet-Barret, Pascale; Gustavsson, Thomas; Douki, Thierry; Markovitsi, Dimitra

    2011-04-13

    The photochemical properties of the DNA duplex (dA)(20)·(dT)(20) are compared with those of the parent single strands. It is shown that base pairing increases the probability of absorbing UVA photons, probably due to the formation of charge-transfer states. UVA excitation induces fluorescence peaking at ∼420 nm and decaying on the nanosecond time scale. The fluorescence quantum yield, the fluorescence lifetime, and the quantum yield for cyclobutane dimer formation increase upon base pairing. Such behavior contrasts with that of the UVC-induced processes. PMID:21417388

  17. Dynamic Cluster Quantum Monte Carlo Simulations of a Two-Dimensional Hubbard Model with Stripelike Charge-Density-Wave Modulations: Interplay between Inhomogeneities and the Superconducting State

    SciTech Connect

    Maier, Thomas A; Alvarez, Gonzalo; Summers, Michael Stuart; Schulthess, Thomas C

    2010-01-01

    Using dynamic cluster quantum Monte Carlo simulations, we study the superconducting behavior of a 1=8 doped two-dimensional Hubbard model with imposed unidirectional stripelike charge-density-wave modulation. We find a significant increase of the pairing correlations and critical temperature relative to the homogeneous system when the modulation length scale is sufficiently large. With a separable form of the irreducible particle-particle vertex, we show that optimized superconductivity is obtained for a moderate modulation strength due to a delicate balance between the modulation enhanced pairing interaction, and a concomitant suppression of the bare particle-particle excitations by a modulation reduction of the quasiparticle weight.

  18. PREFACE: Superconductivity in ultrathin films and nanoscale systems Superconductivity in ultrathin films and nanoscale systems

    NASA Astrophysics Data System (ADS)

    Bianconi, Antonio; Bose, Sangita; Garcia-Garcia, Antonio Miguel

    2012-12-01

    systems. In addition, the role of thermodynamic fluctuations on superconducting properties has been extensively studied in the context of nanoparticles and nanowires both experimentally and theoretically. In the past decade, a lot of work has been initiated in the area of interface superconductivity where different techniques have been demonstrated to tune Tc. Although the progress in this field has deepened our understanding of nanoscale superconductors, there are several open and key questions which need to be addressed. Some of these are: (1) can superconductivity be enhanced and Tc increased in nanostructures with respect to the bulk limit and if so, how can it be controlled? (2) What are the theoretical and experimental limits for the enhancement and control of superconductivity? (3) Can the phenomena identified in conventional nanostructures shed light on phenomena in high Tc superconductors and vice versa? (4) How will the new fundamental physics of superconductivity at the nanoscale promote advances in nanotechnology applications and vice versa? The papers in this focus section reflect the advances made in this field, in particular in nanowires and nanofilms, but also attempt to answer some of the key open questions outlined above. The theoretical papers explore unconventional quantum phenomena such as the role of confinement in the dynamics of single Cooper pairs in isolated grains [1] and Fano resonances in superconducting gaps in multi-condensate superconductors near a 2.5 Lifshitz transition [2]. Here a new emerging class of quantum phenomena of fundamental physics appear at the Bose-BCS crossover in multi-condensate superconductors [2]. Nanosize effects can now be manipulated by controlling defects in layered oxides [3]. A new approach is provided by controlling the self-organization of oxygen interstitials in layered copper oxides that show an intrinsic nanoscale phase separation [4]. In this case a non-trivial distribution of superconducting nanograins

  19. Evaluation of an Enhanced Stimulus-Stimulus Pairing Procedure to Increase Early Vocalizations of Children with Autism

    ERIC Educational Resources Information Center

    Esch, Barbara E.; Carr, James E.; Grow, Laura L.

    2009-01-01

    Evidence to support stimulus-stimulus pairing (SSP) in speech acquisition is less than robust, calling into question the ability of SSP to reliably establish automatically reinforcing properties of speech and limiting the procedure's clinical utility for increasing vocalizations. We evaluated the effects of a modified SSP procedure on…

  20. Superconductivity in alkali-doped C60

    NASA Astrophysics Data System (ADS)

    Ramirez, Arthur P.

    2015-07-01

    Superconductivity in alkali-doped C60 (A3C60, A = an alkali atom) is well described by an s-wave state produced by phonon mediated pairing. Moderate coupling of electrons to high-frequency shape-changing intra-molecular vibrational modes produces transition temperatures (Tc) up to 33 K in single-phase material. The good understanding of pairing in A3C60 offers a paradigm for the development of new superconducting materials.

  1. Graphene/Lead (Pb)-based Cooper -pair splitter

    NASA Astrophysics Data System (ADS)

    Borzenets, Ivan; Shimazaki, Yuya; Jones, Gareth; Russo, Saverio; Yamamoto, Michihisa; Tarucha, Seigo

    2015-03-01

    We have fabricated a Cooper-pair splitter device based on a superconductor- two normal leads, ``Y'' shaped junction with graphene as the base material. (Compared to nanowire-based devices, the two dimensional nature of graphene allows for the normal leads to be placed arbitrarily close together and in a non-parallel arrangement.) The superconducting lead is created by contacting graphene with lead (Pb), thus inducing a supercurrent via the proximity effect. The normal metal leads are patterned into quantum dots by etching nano-constrictions with self-aligned side gates. Quantum dots strongly suppress two electron processes, allowing only one electron to pass at a time. Thus, the Cooper-pair splitting efficiency is enhanced as the split electrons must necessarily tunnel through different quantum dots. Using a DC measurement we have demonstrated enhanced currents though both normal leads when both quantum dots are in resonance and the input lead is in the superconducting regime: demonstrating Cooper-pair splitting. (This is contrary to the classical regime of currents though a three resistor junction.) Shot noise measurements would demonstrate that the split electrons tunnel at the same time. Demonstrating that the split electrons have opposite spin would show that such a device could be used as a source of quantum entangled electrons.

  2. Enhancement and in vitro evaluation of amifostine permeation through artificial membrane (PAMPA) via ion pairing approach and mechanistic selection of its optimal counter ion.

    PubMed

    Samiei, N; Shafaati, A; Zarghi, A; Moghimi, H R; Foroutan, S M

    2014-01-23

    This study presents the results of in vitro evaluation of a series of organic counter ions that form ion pairs with amifostine. The selected counter ions have different lipophilicity, shape and flexibility. Intrinsic octanol buffer partition coefficient and binding constant of the ion pairs were calculated using quasi-equilibrium analysis. Permeation through hydrophobic PAMPA membranes of amifostine and its ion pairs with different counter ions was studied. Three counter ions, succinic acid, benzoic acid and phthalic acid demonstrated an increase in the apparent partition coefficient of amifostine in n-octanol. These counter ions were selected for permeability experiments in PAMPA membranes and an increase of the apparent permeability value Papp (cm/s) was also observed as a function of the counter ion concentration. Phthalic acid produced 1.6-fold increase of log PAB while for benzoic acid and succinic acid the values were 1.2 and 0.75-fold respectively. PAMPA permeability of amifostine significantly increased in the presence of phthalic acid (42-fold), benzoic acid (37-fold) and succinic acid (10.5-fold). This study showed that the permeability of amifostine across a lipophilic membrane was enhanced in the presence of counter-ions resulting ion pair formation. PMID:24161609

  3. Suppression of phase separation and giant enhancement of superconducting transition temperature in FeSe1−xTex thin films

    PubMed Central

    Imai, Yoshinori; Sawada, Yuichi; Nabeshima, Fuyuki; Maeda, Atsutaka

    2015-01-01

    We demonstrate the successful fabrication on CaF2 substrates of FeSe1−xTex films with 0≤x≤1, including the region of 0.1≤x≤0.4, which is well known to be the “phase-separation region,” via pulsed laser deposition that is a thermodynamically nonequilibrium method. In the resulting films, we observe a giant enhancement of the superconducting transition temperature, Tc, in the region of 0.1≤x≤0.4: The maximum value reaches 23 K, which is ∼1.5 times as large as the values reported for bulk samples of FeSe1−xTex. We present a complete phase diagram of FeSe1−xTex films. Surprisingly, a sudden suppression of Tc is observed at 0.1superconductivity realized in x=0−0.1 and in x≥0.2. To obtain a film of FeSe1−xTex with high Tc, the controls of the Te content x and the in-plane lattice strain are found to be key factors. PMID:25646450

  4. Superconducting Structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2005-09-13

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  5. Superconducting structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2003-04-01

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  6. EVALUATION OF AN ENHANCED STIMULUS–STIMULUS PAIRING PROCEDURE TO INCREASE EARLY VOCALIZATIONS OF CHILDREN WITH AUTISM

    PubMed Central

    Esch, Barbara E; Carr, James E; Grow, Laura L

    2009-01-01

    Evidence to support stimulus–stimulus pairing (SSP) in speech acquisition is less than robust, calling into question the ability of SSP to reliably establish automatically reinforcing properties of speech and limiting the procedure's clinical utility for increasing vocalizations. We evaluated the effects of a modified SSP procedure on low-frequency within-session vocalizations that were further strengthened through programmed reinforcement. Procedural modifications (e.g., interspersed paired and unpaired trials) were designed to increase stimulus salience during SSP. All 3 participants, preschoolers with autism, showed differential increases of target over nontarget vocal responses during SSP. Results suggested an automatic reinforcement effect of SSP, although alternative interpretations are discussed, and suggestions are made for future research to determine the utility of SSP as a clinical intervention for speech-delayed children. PMID:19949511

  7. Enhanced production of low-mass electron pairs in 200 GeV/nucleon S-Au collisions at the CERN super proton synchrotron

    SciTech Connect

    Agakichiev, G.; Baur, R.; Breskin, A.; Chechik, R.; Drees, A.; Jacob, C.; Faschingbauer, U.; Fischer, P.; Fraenkel, Z.; Fuchs, C.; Gatti, E.; Glaessel, P.; Guenzel, T.; de los Heros, C.P.; Hess, F.; Irmscher, D.; Lenkeit, B.; Olsen, L.H.; Panebrattsev, Y.; Pfeiffer, A.; Ravinovich, I.; Rehak, P.; Schoen, A.; Schukraft, J.; Sampietro, M.; Shimansky, S.; Shor, A.; Specht, H.J.; Steiner, V.; Tapprogge, S.; Tel-Zur, G.; Tserruya, I.; Ullrich, T.; Wurm, J.P.; Yurevich, V. |||||

    1995-08-14

    We report on measurements of low-mass electron pairs in 450 GeV {ital p}-Be, {ital p}-Au, and 200 GeV/nucleon S-Au collisions at central rapidities. For the proton induced interactions, the low-mass spectra are, within the systematic errors, satisfactorily explained by electron pairs from hadron decays, whereas in the S-Au system an enhancement over the hadronic contributions by a factor of 5.0{plus_minus}0.7(stat){plus_minus}2.0(syst) in the invariant mass range 0.2{lt}{ital m}{lt}1.5 GeV/{ital c}{sup 2} is observed. The properties of the excess suggest that it arises from two-pion annihilation {pi}{pi}{r_arrow}{ital e}{sup +}{ital e}{sup {minus}}.

  8. Strongly enhanced current densities in Sr0.6K0.4Fe2As2 + Sn superconducting tapes

    PubMed Central

    Lin, He; Yao, Chao; Zhang, Xianping; Zhang, Haitao; Wang, Dongliang; Zhang, Qianjun; Ma, Yanwei; Awaji, Satoshi; Watanabe, Kazuo

    2014-01-01

    Improving transport current has been the primary topic for practical application of superconducting wires and tapes. However, the porous nature of powder-in-tube (PIT) processed iron-based tapes is one of the important reasons for low critical current density (Jc) values. In this work, the superconducting core density of ex-situ Sr0.6K0.4Fe2As2 + Sn tapes, prepared from optimized precursors, was significantly improved by employing a simple hot pressing as an alternative route for final sintering. The resulting samples exhibited optimal critical temperature (Tc), sharp resistive transition, small resistivity and high Vickers hardness (Hv) value. Consequently, the transport Jc reached excellent values of 5.1 × 104 A/cm2 in 10 T and 4.3 × 104 A/cm2 in 14 T at 4.2 K, respectively. Our tapes also exhibited high upper critical field Hc2 and almost field-independent Jc. These results clearly demonstrate that PIT pnictide wire conductors are very promising for high-field magnet applications. PMID:24663054

  9. Fermi surface of superconducting LaFePO determined by quantum oscillations

    SciTech Connect

    Mcdonald, Ross D; Coldea, A I; Fletcher, J D; Carrington, A; Bangura, A F; Hussey, N E; Analytis, J G; Chu, J-h; Erickson, A S; Fisher, I R

    2008-01-01

    The recent discovery of superconductivity in ferrooxypnictides, which have a maximum transition temperature intermediate between the two other known high temperature superconductors MgB{sub 2} and the cuprate family, has generated huge interest and excitement. The most critical issue is the origin of the pairing mechanism. Whereas superconductivity in MgB{sub 2} has been shown to arise from strong electron-phonon coupling, the pairing glue in cuprate superconductors is thought by many to have a magnetic origin. The oxypnictides are highly susceptible to magnetic instabilities, prompting analogies with cuprate superconductivity. Progress on formulating the correct theory of superconductivity in these materials will be greatly aided by a detailed knowledge of the Fermi surface parameters. Here we report for the first time extensive measurements of quantum oscillations in a Fe-based superconductor, LaFePO, that provide a precise calliper of the size and shape of the Fermi surface and the effective masses of the relevant charge carriers. Our results show that the Fermi surface is composed of nearly-nested electron and hole pockets in broad agreement with the band-structure predictions but with significant enhancement of the quasiparticle masses. The correspondence in the electron and hole Fermi surface areas provides firm experimental evidence that LaFePO, whilst unreconstructed, lies extremely close to a spin-density-wave instability, thus favoring models that invoke such a magnetic origin for high-temperature superconductivity in oxypnictides.

  10. Superconducting YBa sub 2 Cu sub 3 O sub 7 minus x thin films on silver substrates by in situ plasma-enhanced metalorganic chemical vapor deposition

    SciTech Connect

    Zhao, J.; Li, Y.Q.; Chern, C.S.; Norris, P.; Gallois, B.; Kear, B.; Wessels, B.W. )

    1991-01-07

    An {ital in} {ital situ} microwave plasma-enhanced metalorganic chemical vapor deposition process was used to fabricate highly {ital c}-axis oriented YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} superconducting thin films on metallic Ag substrates. The films were deposited at a reduced substrate temperature of 740 {degree}C in about 270 Pa of N{sub 2}O ambient. Magnetic susceptibilities versus temperature of the as-deposited films show attainment of zero resistance of 85 K and composition of single (high {ital T}{sub {ital c}}) phase. X-ray diffraction measurements reveal that the films deposited at 740 {degree}C have highly preferential orientation of the crystallite {ital c} axes perpendicular to the substrate surface.

  11. Strongly enhanced current densities in superconducting coated conductors of YBa2Cu3O7-x + BaZrO3.

    PubMed

    MacManus-Driscoll, J L; Foltyn, S R; Jia, Q X; Wang, H; Serquis, A; Civale, L; Maiorov, B; Hawley, M E; Maley, M P; Peterson, D E

    2004-07-01

    There are numerous potential applications for superconducting tapes based on YBa(2)Cu(3)O(7-x) (YBCO) films coated onto metallic substrates. A long-established goal of more than 15 years has been to understand the magnetic-flux pinning mechanisms that allow films to maintain high current densities out to high magnetic fields. In fact, films carry one to two orders of magnitude higher current densities than any other form of the material. For this reason, the idea of further improving pinning has received little attention. Now that commercialization of YBCO-tape conductors is much closer, an important goal for both better performance and lower fabrication costs is to achieve enhanced pinning in a practical way. In this work, we demonstrate a simple and industrially scaleable route that yields a 1.5-5-fold improvement in the in-magnetic-field current densities of conductors that are already of high quality. PMID:15170180

  12. Superconductivity in doped Dirac semimetals

    NASA Astrophysics Data System (ADS)

    Hashimoto, Tatsuki; Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

    2016-07-01

    We theoretically study intrinsic superconductivity in doped Dirac semimetals. Dirac semimetals host bulk Dirac points, which are formed by doubly degenerate bands, so the Hamiltonian is described by a 4 ×4 matrix and six types of k -independent pair potentials are allowed by the Fermi-Dirac statistics. We show that the unique spin-orbit coupling leads to characteristic superconducting gap structures and d vectors on the Fermi surface and the electron-electron interaction between intra and interorbitals gives a novel phase diagram of superconductivity. It is found that when the interorbital attraction is dominant, an unconventional superconducting state with point nodes appears. To verify the experimental signature of possible superconducting states, we calculate the temperature dependence of bulk physical properties such as electronic specific heat and spin susceptibility and surface state. In the unconventional superconducting phase, either dispersive or flat Andreev bound states appear between point nodes, which leads to double peaks or a single peak in the surface density of states, respectively. As a result, possible superconducting states can be distinguished by combining bulk and surface measurements.

  13. A 190 base pair, TGF-β responsive tooth and fin enhancer is required for stickleback Bmp6 expression.

    PubMed

    Erickson, Priscilla A; Cleves, Phillip A; Ellis, Nicholas A; Schwalbach, Kevin T; Hart, James C; Miller, Craig T

    2015-05-15

    The ligands of the Bone Morphogenetic Protein (BMP) family of developmental signaling molecules are often under the control of complex cis-regulatory modules and play diverse roles in vertebrate development and evolution. Here, we investigated the cis-regulatory control of stickleback Bmp6. We identified a 190bp enhancer ~2.5 kilobases 5' of the Bmp6 gene that recapitulates expression in developing teeth and fins, with a core 72bp sequence that is sufficient for both domains. By testing orthologous enhancers with varying degrees of sequence conservation from outgroup teleosts in transgenic reporter gene assays in sticklebacks and zebrafish, we found that the function of this regulatory element appears to have been conserved for over 250 million years of teleost evolution. We show that a predicted binding site for the TGFβ effector Smad3 in this enhancer is required for enhancer function and that pharmacological inhibition of TGFβ signaling abolishes enhancer activity and severely reduces endogenous Bmp6 expression. Finally, we used TALENs to disrupt the enhancer in vivo and find that Bmp6 expression is dramatically reduced in teeth and fins, suggesting this enhancer is necessary for expression of the Bmp6 locus. This work identifies a relatively short regulatory sequence that is required for expression in multiple tissues and, combined with previous work, suggests that shared regulatory networks control limb and tooth development. PMID:25732776

  14. A 190 base pair, TGF-β responsive tooth and fin enhancer is required for stickleback Bmp6 expression

    PubMed Central

    Erickson, Priscilla A.; Cleves, Phillip A.; Ellis, Nicholas A.; Schwalbach, Kevin T.; Hart, James C.; Miller, Craig T.

    2015-01-01

    The ligands of the Bone Morphogenetic Protein (BMP) family of developmental signaling molecules are often under the control of complex cis-regulatory modules and play diverse roles in vertebrate development and evolution. Here, we investigated the cis-regulatory control of stickleback Bmp6. We identified a 190 bp enhancer ~2.5 kilobases 5’ of the Bmp6 gene that recapitulates expression in developing teeth and fins, with a core 72 bp sequence that is sufficient for both domains. By testing orthologous enhancers with varying degrees of sequence conservation from outgroup teleosts in transgenic reporter gene assays in sticklebacks and zebrafish, we found that the function of this regulatory element appears to have been conserved for over 250 million years of teleost evolution. We show that a predicted binding site for the TGFβ effector Smad3 in this enhancer is required for enhancer function and that pharmacological inhibition of TGFβ signaling abolishes enhancer activity and severely reduces endogenous Bmp6 expression. Finally, we used TALENs to disrupt the enhancer in vivo and find that Bmp6 expression is dramatically reduced in teeth and fins, suggesting this enhancer is necessary for expression of the Bmp6 locus. This work identifies a relatively short regulatory sequence that is required for expression in multiple tissues and, combined with previous work, suggests that shared regulatory networks control limb and tooth development. PMID:25732776

  15. Pair condensation in a spin-imbalanced two-dimensional Fermi gas

    NASA Astrophysics Data System (ADS)

    Brown, Peter; Mitra, Debayan; Schauss, Peter; Kondov, Stanimir; Bakr, Waseem

    2016-05-01

    We study the phase diagram of the strongly-interacting spin-imbalanced Fermi gas in two dimensions, where the low dimensionality enhances correlations and phase fluctuations. Our interest is motivated by the connection of this system with superconductivity in the presence of a large Zeeman field. We observe pair condensation for a range of spin imbalance and interaction strengths. The measurement of the phase diagram opens the door for a detailed investigation of exotic phases such as the Sarma/broken pair phase and the elusive FFLO phase.

  16. Pair condensation in a spin-imbalanced 2D Fermi gas

    NASA Astrophysics Data System (ADS)

    Mitra, Debayan; Brown, Peter; Schauss, Peter; Kondov, Stanimir; Bakr, Waseem

    2016-05-01

    We study the phase diagram of the strongly-interacting spin-imbalanced Fermi gas in two dimensions, where the low dimensionality enhances correlations and phase fluctuations. Our interest is motivated by the connection of this system with superconductivity in the presence of a large Zeeman field. We observe pair condensation for a range of spin imbalance and interaction strengths. The measurement of the phase diagram opens the door for a detailed investigation of exotic phases such as the Sarma/broken pair phase and the elusive FFLO phase.

  17. Photophysics of the geminate polaron-pair state in copper phthalocyanine organic photovoltaic blends: evidence for enhanced intersystem crossing.

    PubMed

    Snedden, Edward W; Monkman, Andrew P; Dias, Fernando B

    2013-04-01

    Geminate polaron-pair recombination directly to the triplet state of the small dye molecule copper(II) 1,4,8,11,15,18,22,25-octabutoxy-29H,31H- phthalocyanine (CuPC) and exciton trapping in CuPC domains, combine to reduce the internal quantum efficiency of free polaron formation in the bulk-heterojunction blends of CuPC doped with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor. PMID:22933249

  18. Enhanced keV peak power and yield using twisted pair 'cables' in a z-pinch

    SciTech Connect

    Hoyt, C. L.; Knapp, P. F.; Pikuz, S. A.; Shelkovenko, T. A.; Cahill, A. D.; Gourdain, P.-A.; Greenly, J. B.; Kusse, B. R.; Hammer, D. A.

    2012-06-11

    Individual wires in a z-pinch were replaced with twisted pair 'cables' of similar linear mass on the COBRA pulsed power generator, resulting in peak power and yield increases in radiation above 1 keV. A cable is defined here as two or more fine wires twisted together to form a continuous strand with a wavelength ({lambda}{sub t}) dependent on the twists per unit length. The magnitude of {lambda}{sub t} appears to play a strong role in these increases, with the largest gains found for a {lambda}{sub t} of Almost-Equal-To 0.75 mm.

  19. PREFACE: Superconductivity in ultrathin films and nanoscale systems Superconductivity in ultrathin films and nanoscale systems

    NASA Astrophysics Data System (ADS)

    Bianconi, Antonio; Bose, Sangita; Garcia-Garcia, Antonio Miguel

    2012-12-01

    systems. In addition, the role of thermodynamic fluctuations on superconducting properties has been extensively studied in the context of nanoparticles and nanowires both experimentally and theoretically. In the past decade, a lot of work has been initiated in the area of interface superconductivity where different techniques have been demonstrated to tune Tc. Although the progress in this field has deepened our understanding of nanoscale superconductors, there are several open and key questions which need to be addressed. Some of these are: (1) can superconductivity be enhanced and Tc increased in nanostructures with respect to the bulk limit and if so, how can it be controlled? (2) What are the theoretical and experimental limits for the enhancement and control of superconductivity? (3) Can the phenomena identified in conventional nanostructures shed light on phenomena in high Tc superconductors and vice versa? (4) How will the new fundamental physics of superconductivity at the nanoscale promote advances in nanotechnology applications and vice versa? The papers in this focus section reflect the advances made in this field, in particular in nanowires and nanofilms, but also attempt to answer some of the key open questions outlined above. The theoretical papers explore unconventional quantum phenomena such as the role of confinement in the dynamics of single Cooper pairs in isolated grains [1] and Fano resonances in superconducting gaps in multi-condensate superconductors near a 2.5 Lifshitz transition [2]. Here a new emerging class of quantum phenomena of fundamental physics appear at the Bose-BCS crossover in multi-condensate superconductors [2]. Nanosize effects can now be manipulated by controlling defects in layered oxides [3]. A new approach is provided by controlling the self-organization of oxygen interstitials in layered copper oxides that show an intrinsic nanoscale phase separation [4]. In this case a non-trivial distribution of superconducting nanograins

  20. Early annihilation and diffuse backgrounds in models of weakly interacting massive particles in which the cross section for pair annihilation is enhanced by 1/upsilon.

    PubMed

    Kamionkowski, Marc; Profumo, Stefano

    2008-12-31

    Recent studies have considered modifications to the standard weakly interacting massive particle scenario in which the pair annihilation cross section (times relative velocity v) is enhanced by a factor 1/upsilon to approximately 10(-3) in the Galaxy, enough to explain several puzzling Galactic radiation signals. We show that in these scenarios a burst of weakly interacting massive particle annihilation occurs in the first collapsed dark-matter halos. We show that severe constraints to the annihilation cross section derive from measurements of the diffuse extragalactic radiation and from ionization and heating of the intergalactic medium. PMID:19437633

  1. Crystallization and preliminary X-ray diffraction analysis of the Pax9 paired domain bound to a DC5 enhancer DNA element.

    PubMed

    Narasimhan, Kamesh; Hilbig, Antonia; Udayasuryan, Barath; Jayabal, Sriram; Kolatkar, Prasanna R; Jauch, Ralf

    2014-10-01

    Pax genes belong to a family of metazoan transcription factors that are known to play a critical role in eye, ear, kidney and neural development. The mammalian Pax family of transcription factors is characterized by a ∼128-amino-acid DNA-binding paired domain that makes sequence-specific contacts with DNA. The diversity in Pax gene activities emerges from complex modes of interaction with enhancer regions and heterodimerization with multiple interaction partners. Based on in vitro optimal binding-site selection studies and enhancer identification assays, it has been suggested that Pax proteins may recognize and bind their target DNA elements with different binding modes/topologies, however this hypothesis has not yet been structurally explored. One of the most extensively studied DNA target elements of the Pax6 paired domain is the eye-lens specific DC5 (δ-crystallin) enhancer element. In order to shed light on Pax6-DC5 DNA interactions, the related paired-domain prototype Pax9 was crystallized with the minimal δ-crystallin DC5 enhancer element and preliminary X-ray diffraction analysis was attempted. A 3.0 Å resolution native data set was collected at the National Synchrotron Light Source (NSLS), Brookhaven from crystals grown in a solution consisting of 10%(w/v) PEG 20K, 20%(v/v) PEG 550 MME, 0.03 M NaNO3, 0.03 M Na2HPO4, 0.03 M NH2SO4, 0.1 M MES/imidazole pH 6.5. The data set was indexed and merged in space group C2221, with unit-cell parameters a = 75.74, b = 165.59, c = 70.14 Å, α = β = γ = 90°. The solvent content in the unit cell is consistent with the presence of one Pax9 paired domain bound to duplex DNA in the asymmetric unit. PMID:25286939

  2. Note: Magnetic targeting for enhancement of the activation efficiency of G protein-coupled receptor with a two-pair coil system

    NASA Astrophysics Data System (ADS)

    Cao, Quanliang; Han, Xiaotao; Chun, Lei; Liu, Jianfeng; Li, Liang

    2016-01-01

    Insufficient contact of drug with target cells is a primary reason for limited efficiency of G protein-coupled receptor activation. To overcome this limitation, a simple approach based on magnetic targeting for enhancing drug delivery towards the cell surfaces using magnetic nanoparticles and a two-pair coil system consisting of Helmholtz and Maxwell coils was reported. As a proof of the concept, comparative experiments on G protein-coupled receptor activation process were carried out and results show that the efficiency of G protein-coupled receptor activation can be increased about 6 times in the experiments with the aid of the proposed magnetic targeting system.

  3. Enhancement of the London Penetration Depth in Pnictides at the Onset of Spin-Density-Wave Order under Superconducting Dome

    NASA Astrophysics Data System (ADS)

    Levchenko, A.; Vavilov, M. G.; Khodas, M.; Chubukov, A. V.

    2013-04-01

    Recent measurements of the doping dependence of the London penetration depth λ(x) at low T in clean samples of isovalent BaFe2(As1-xPx)2 at T≪Tc [Hashimoto et al., Science 336, 1554 (2012)SCIEAS0036-8075] revealed a peak in λ(x) near optimal doping x=0.3. The observation of the peak at T≪Tc, points to the existence of a quantum critical point beneath the superconducting dome. We associate such a quantum critical point with the onset of a spin-density-wave order and show that the renormalization of λ(x) by critical magnetic fluctuations gives rise to the observed feature. We argue that the case of pnictides is conceptually different from a one-component Galilean invariant Fermi liquid, for which correlation effects do not cause the renormalization of the London penetration depth at T=0.

  4. Weak-coupling superconductivity in a strongly correlated iron pnictide

    PubMed Central

    Charnukha, A.; Post, K. W.; Thirupathaiah, S.; Pröpper, D.; Wurmehl, S.; Roslova, M.; Morozov, I.; Büchner, B.; Yaresko, A. N.; Boris, A. V.; Borisenko, S. V.; Basov, D. N.

    2016-01-01

    Iron-based superconductors have been found to exhibit an intimate interplay of orbital, spin, and lattice degrees of freedom, dramatically affecting their low-energy electronic properties, including superconductivity. Albeit the precise pairing mechanism remains unidentified, several candidate interactions have been suggested to mediate the superconducting pairing, both in the orbital and in the spin channel. Here, we employ optical spectroscopy (OS), angle-resolved photoemission spectroscopy (ARPES), ab initio band-structure, and Eliashberg calculations to show that nearly optimally doped NaFe0.978Co0.022As exhibits some of the strongest orbitally selective electronic correlations in the family of iron pnictides. Unexpectedly, we find that the mass enhancement of itinerant charge carriers in the strongly correlated band is dramatically reduced near the Γ point and attribute this effect to orbital mixing induced by pronounced spin-orbit coupling. Embracing the true band structure allows us to describe all low-energy electronic properties obtained in our experiments with remarkable consistency and demonstrate that superconductivity in this material is rather weak and mediated by spin fluctuations. PMID:26729630

  5. Weak-coupling superconductivity in a strongly correlated iron pnictide

    NASA Astrophysics Data System (ADS)

    Charnukha, Aliaksei

    Iron-based superconductors have been found to exhibit an intimate interplay of orbital, spin, and lattice degrees of freedom, dramatically affecting their low-energy electronic properties, including superconductivity. Albeit the precise pairing mechanism remains unidentified, several candidate interactions have been suggested to mediate the superconducting pairing, both in the orbital and in the spin channel. Here, we employ optical spectroscopy (OS), angle-resolved photoemission spectroscopy, ab initio band-structure, and Eliashberg calculations to show that nearly optimally doped NaFe0.978Co0.022As exhibits some of the strongest orbitally selective electronic correlations in the family of iron pnictides. Unexpectedly, we find that the mass enhancement of itinerant charge carriers in the strongly correlated band is dramatically reduced near the Γ point and attribute this effect to orbital mixing induced by pronounced spin-orbit coupling. Embracing the true band structure allows us to describe all low-energy electronic properties obtained in our experiments with remarkable consistency and demonstrate that superconductivity in this material is rather weak and mediated by spin fluctuations. A. Charnukha acknowledges financial support by the Alexander von Humboldt foundation.

  6. Weak-coupling superconductivity in a strongly correlated iron pnictide

    NASA Astrophysics Data System (ADS)

    Charnukha, A.; Post, K. W.; Thirupathaiah, S.; Pröpper, D.; Wurmehl, S.; Roslova, M.; Morozov, I.; Büchner, B.; Yaresko, A. N.; Boris, A. V.; Borisenko, S. V.; Basov, D. N.

    2016-01-01

    Iron-based superconductors have been found to exhibit an intimate interplay of orbital, spin, and lattice degrees of freedom, dramatically affecting their low-energy electronic properties, including superconductivity. Albeit the precise pairing mechanism remains unidentified, several candidate interactions have been suggested to mediate the superconducting pairing, both in the orbital and in the spin channel. Here, we employ optical spectroscopy (OS), angle-resolved photoemission spectroscopy (ARPES), ab initio band-structure, and Eliashberg calculations to show that nearly optimally doped NaFe0.978Co0.022As exhibits some of the strongest orbitally selective electronic correlations in the family of iron pnictides. Unexpectedly, we find that the mass enhancement of itinerant charge carriers in the strongly correlated band is dramatically reduced near the Γ point and attribute this effect to orbital mixing induced by pronounced spin-orbit coupling. Embracing the true band structure allows us to describe all low-energy electronic properties obtained in our experiments with remarkable consistency and demonstrate that superconductivity in this material is rather weak and mediated by spin fluctuations.

  7. First-Order 0-π Quantum Phase Transition in the Kondo Regime of a Superconducting Carbon-Nanotube Quantum Dot

    NASA Astrophysics Data System (ADS)

    Maurand, Romain; Meng, Tobias; Bonet, Edgar; Florens, Serge; Marty, Laëtitia; Wernsdorfer, Wolfgang

    2012-01-01

    We study a carbon-nanotube quantum dot embedded in a superconducting-quantum-interference-device loop in order to investigate the competition of strong electron correlations with a proximity effect. Depending on whether local pairing or local magnetism prevails, a superconducting quantum dot will exhibit a positive or a negative supercurrent, referred to as a 0 or π Josephson junction, respectively. In the regime of a strong Coulomb blockade, the 0-to-π transition is typically controlled by a change in the discrete charge state of the dot, from even to odd. In contrast, at a larger tunneling amplitude, the Kondo effect develops for an odd-charge (magnetic) dot in the normal state, and quenches magnetism. In this situation, we find that a first-order 0-to-π quantum phase transition can be triggered at a fixed valence when superconductivity is brought in, due to the competition of the superconducting gap and the Kondo temperature. The superconducting-quantum-interference-device geometry together with the tunability of our device allows the exploration of the associated phase diagram predicted by recent theories. We also report on the observation of anharmonic behavior of the current-phase relation in the transition regime, which we associate with the two accessible superconducting states. Our results finally demonstrate that the spin-singlet nature of the Kondo state helps to enhance the stability of the 0 phase far from the mixed-valence regime in odd-charge superconducting quantum dots.

  8. Giant phonon anomaly associated with superconducting fluctuations in the pseudogap phase of cuprates

    DOE PAGESBeta

    Liu, Ye-Hua; Konik, Robert M.; Rice, T. M.; Zhang, Fu-Chun

    2016-01-20

    The pseudogap in underdoped cuprates leads to significant changes in the electronic structure, and was later found to be accompanied by anomalous fluctuations of superconductivity and certain lattice phonons. Here we propose that the Fermi surface breakup due to the pseudogap, leads to a breakup of the pairing order into two weakly coupled sub-band amplitudes, and a concomitant low energy Leggett mode due to phase fluctuations between them. This increases the temperature range of superconducting fluctuations containing an overdamped Leggett mode. In this range inter-sub-band phonons show strong damping due to resonant scattering into an intermediate state with a pairmore » of overdamped Leggett modes. In the ordered state, the Leggett mode develops a finite energy, changing the anomalous phonon damping into an anomaly in the dispersion. Finally, this proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra.« less

  9. Paired Cut-Wire Arrays for Enhanced Transmission of Transverse-Electric Fields Through Subwavelength Slits in a Thin Metallic Screen

    NASA Astrophysics Data System (ADS)

    Gallina, Ilaria; Castaldi, Giuseppe; Galdi, Vincenzo; Di Gennaro, Emiliano; Andreone, Antonello

    It has recently been shown that the transmission of electromagnetic fields through sub-wavelength slits (parallel to the electric field direction) in a thin metallic screen can be greatly enhanced by covering one side of the screen with a metallic cut-wire array laid on a dielectric layer. In this Letter, we show that a richer phenomenology (which involves both electric- and magnetic-type resonances) can be attained by pairing a second cut-wire array at the other side of the screen. Via a full-wave comprehensive parametric study, we illustrate the underlying mechanisms and explore the additional degrees of freedom endowed, as well as their possible implications in the engineering of enhanced transmission phenomena.

  10. Superstructures and superconductivity

    SciTech Connect

    Fisk, Z.; Aeppli, G.

    1993-04-02

    Heavy fermion materials - so named because their conduction electrons behave as though they had extra mass - are like the cuprates in that they exhibit unusual superconducting properties. By the time the cuprates had been discovered, a good understanding of these materials was in hand. Unlike theories of high-[Tc] superconductivity, however, ideas about heavy fermions have not been the subject of great controversy. Thus, most of the effort in this backwater of condensed matter physics has focused on certain details of the behavior of one particularly well-studied compounds, UPt[sub 3]. The cause for sustained interest was that the process of developing ever more elaborate explanations for ever more elaborate experiments did not seem to converage. A recent paper by Midgley et al. reporting modulations in the crystal lattice of UPt[sub 3] suggests that theory and experiment might finally converge in a way that, while it does not threaten the broad understanding of heavy fermion systems, involves a degree of freedom ignored until now even in the face of past experience with elemental metallic uranium. Their transmission electron micrograph evidence for the existence of an incommensurate lattice modulation in UPt[sub 3] implicates this modulation as a probable source of the double superconducting transitions. Remarkably, the superconducting and magnetic coherence lengths, and the now discovered modulation period, are all of the same magnitude. For some time people have felt that stacking faults might be relevant to the properties of UPt[sub 3], but these new results are distinct from this. What Midgley et al. suggest is that the complicated superconducting phase diagram of UPt[sub 3] derives from the internal strain field caused by the modulation, and that this strain field lifts the degeneracy associated with unconventional pairing.

  11. Interplay Between Ferromagnetism and Superconductivity

    NASA Astrophysics Data System (ADS)

    Linder, Jacob; Sudbø, Asle

    This chapter presents results on transport properties of hybrid structures where the interplay between ferromagnetism and superconductivity plays a central role. In particular, the appearance of so-called odd-frequency pairing in such structures is investigated in detail. The basic physics of superconductivity in such structures is presented, and the quasiclassical theory of Greens functions with appropriate boundary conditions is given. Results for superconductor∣ferromagnet bilayers as well as magnetic Josephson junctions and spin valves are presented. Further phenomena that are studied include transport in the presence of inhomogenous magnetic textures, spin-Josephon effect, and crossed Andreev reflection. We also investigate the possibility of intrinsic coexistence of ferromagnetism and superconductivity, as reported in a series of uranium-based heavy-fermion compounds. The nature of such a coexistence and the resulting superconducting order parameter is discussed along with relevant experimental results. We present a thermodynamic treatment for a model of a ferromagnetic supercondcutor and moreover suggest ways to experimentally determine the pairing symmetry of the superconducting gap, in particular by means of conductance spectroscopy.

  12. Towards building artificial light harvesting complexes: enhanced singlet-singlet energy transfer between donor and acceptor pairs bound to albumins.

    PubMed

    Kumar, Challa V; Duff, Michael R

    2008-12-01

    Specific donor and acceptor pairs have been assembled in bovine serum albumin (BSA), at neutral pH and room temperature, and these dye-protein complexes indicated efficient donor to acceptor singlet-singlet energy transfer. For example, pyrene-1-butyric acid served as the donor and Coumarin 540A served as the acceptor. Both the donor and the acceptor bind to BSA with affinity constants in excess of 2x10(5) M(-1), as measured in absorption and circular dichroism (CD) spectral titrations. Simultaneous binding of both the donor and the acceptor chromophores was supported by CD spectra and one chromophore did not displace the other from the protein host, even when limited concentrations of the host were used. For example, a 1:1:1 complex between the donor, acceptor and the host can be readily formed, and spectral data clearly show that the binding sites are mutually exclusive. The ternary complexes (two different ligands bound to the same protein molecule) provided opportunities to examine singlet-singlet energy transfer between the protein-bound chromophores. Donor emission was quenched by the addition of the acceptor, in the presence of limited amounts of BSA, while no energy transfer was observed in the absence of the protein host, under the same conditions. The excitation spectra of the donor-acceptor-host complexes clearly show the sensitization of acceptor emission by the donor. Protein denaturation, as induced by the addition of urea or increasing the temperature to 360 K, inhibited energy transfer, which indicate that protein structure plays an important role. Sensitization also proceeded at low temperature (77 K) and diffusion of the donor or the acceptor is not required for energy transfer. Stern-Volmer quenching plots show that the quenching constant is (3.1+/-0.2)x10(4) M(-1), at low acceptor concentrations (<35 microM). Other albumins such as human and porcine proteins also served as good hosts for the above experiments. For the first time, non

  13. Enhancement of the London penetration depth in pnictides at the onset of SDW order under superconducting dome

    NASA Astrophysics Data System (ADS)

    Levchenko, Alex; Vavilov, Maxim; Kuzmanovski, Dushko; Khodas, Maxim; Chubukov, Andrey

    2013-03-01

    Recent measurements of the doping dependence of the London penetration depth λ (x) in clean samples of isovalent BaFe2(As1-xPx)2 at T <superconducting dome. We show that quantum magnetic fluctuations, associated with the emerging spin-density-wave order give rise to the observed feature. The effect comes from the dynamic renormalization of the effective mass m*, which is related to λ as λ √{m*} . We show that the effective mass has a maximum at the onset of the spin-density-wave order. We argue that the case of pnictides is conceptually different from a one-component Galilean invariant Fermi liquid, for which correlation effects do not cause the renormalization of the London penetration depth at T = 0 .

  14. Large enhancement of superconducting transition temperature of SrBi3 induced by Na substitution for Sr

    PubMed Central

    Iyo, Akira; Yanagi, Yousuke; Kinjo, Tatsuya; Nishio, Taichiro; Hase, Izumi; Yanagisawa, Takashi; Ishida, Shigeyuki; Kito, Hijiri; Takeshita, Nao; Oka, Kunihiko; Yoshida, Yoshiyuki; Eisaki, Hiroshi

    2015-01-01

    The Matthias rule, which is an empirical correlation between the superconducting transition temperature (Tc) and the average number of valence electrons per atom (n) in alloys and intermetallic compounds, has been used in the past as a guiding principle to search for new superconductors with higher Tc. The intermetallic compound SrBi3 (AuCu3 structure) exhibits a Tc of 5.6 K. An ab-initio electronic band structure calculation for SrBi3 predicted that Tc increases on decreasing the Fermi energy, i.e., on decreasing n, because of a steep increase in the density of states. In this study, we demonstrated that high-pressure (~ 3 GPa) and low-temperature ( < 350 °C) synthesis conditions enables the substitution of Na for about 40 at.% of Sr. With a consequent decrease in n, the Tc of (Sr,Na)Bi3 increases to 9.0 K. A new high-Tc peak is observed in the oscillatory dependence of Tc on n in compounds with the AuCu3 structure. We have shown that the oscillatory dependence of Tc is in good agreement with the band structure calculation. Our experiments reaffirm the importance of controlling the number of electrons in intermetallic compounds. PMID:25965162

  15. Observation of plasmon-induced optical field enhancement near a pair of partially metal covered dielectric spheres manipulated by optical tweezers

    NASA Astrophysics Data System (ADS)

    Zhdanov, Alexander G.; Fedyanin, Andrey A.; Rao, Satish; Kreuzer, Mark; Ballint, Stefan; Petrov, Dmitri

    2009-05-01

    Optical tweezers technique combined with local confocal luminescence spectroscopy is suggested as a tool for investigation of local optical fields. Utilizing this method plasmon-enhanced optical fields inside a pair of dielectric 2 μm spheres partially covered by 70 nm silver nanoparticles are visualized via field enhanced luminescence of rhodamine dye solution. Positions of the particles are controlled with submicrometer accuracy by two optical traps formed by strongly focused laser beams with λ=980nm. A supplementary beam from CW laser with λ=532nm provided for luminescence excitation is also focused into the sample cavity just to the trapping area. In order to obtain spatial filtering of the signal and separate luminescence signal from an area near the spheres pin-hole based confocal system is designed. The focal volume available for luminescence signal collection turns out to be approximately 3μm x 3 μm x 5 μm. Since optical field is enhanced in the region near plasmon-active 2 μm spheres the enhancement of luminescence intensity is observed. Collective plasmonic effects in two-particle measurements are also considered.

  16. Pairing Cholinergic Enhancement with Perceptual Training Promotes Recovery of Age-Related Changes in Rat Primary Auditory Cortex

    PubMed Central

    Voss, Patrice; Thomas, Maryse; Chou, You Chien; Cisneros-Franco, José Miguel; Ouellet, Lydia; de Villers-Sidani, Etienne

    2016-01-01

    We used the rat primary auditory cortex (A1) as a model to probe the effects of cholinergic enhancement on perceptual learning and auditory processing mechanisms in both young and old animals. Rats learned to perform a two-tone frequency discrimination task over the course of two weeks, combined with either the administration of a cholinesterase inhibitor or saline. We found that while both age groups learned the task more quickly through cholinergic enhancement, the young did so by improving target detection, whereas the old did so by inhibiting erroneous responses to nontarget stimuli. We also found that cholinergic enhancement led to marked functional and structural changes within A1 in both young and old rats. Importantly, we found that several functional changes observed in the old rats, particularly those relating to the processing and inhibition of nontargets, produced cortical processing features that resembled those of young untrained rats more so than those of older adult rats. Overall, these findings demonstrate that combining auditory training with neuromodulation of the cholinergic system can restore many of the auditory cortical functional deficits observed as a result of normal aging and add to the growing body of evidence demonstrating that many age-related perceptual and neuroplastic changes are reversible. PMID:27057359

  17. Pairing Cholinergic Enhancement with Perceptual Training Promotes Recovery of Age-Related Changes in Rat Primary Auditory Cortex.

    PubMed

    Voss, Patrice; Thomas, Maryse; Chou, You Chien; Cisneros-Franco, José Miguel; Ouellet, Lydia; de Villers-Sidani, Etienne

    2016-01-01

    We used the rat primary auditory cortex (A1) as a model to probe the effects of cholinergic enhancement on perceptual learning and auditory processing mechanisms in both young and old animals. Rats learned to perform a two-tone frequency discrimination task over the course of two weeks, combined with either the administration of a cholinesterase inhibitor or saline. We found that while both age groups learned the task more quickly through cholinergic enhancement, the young did so by improving target detection, whereas the old did so by inhibiting erroneous responses to nontarget stimuli. We also found that cholinergic enhancement led to marked functional and structural changes within A1 in both young and old rats. Importantly, we found that several functional changes observed in the old rats, particularly those relating to the processing and inhibition of nontargets, produced cortical processing features that resembled those of young untrained rats more so than those of older adult rats. Overall, these findings demonstrate that combining auditory training with neuromodulation of the cholinergic system can restore many of the auditory cortical functional deficits observed as a result of normal aging and add to the growing body of evidence demonstrating that many age-related perceptual and neuroplastic changes are reversible. PMID:27057359

  18. Superconducting Memristors

    NASA Astrophysics Data System (ADS)

    Peotta, Sebastiano; Di Ventra, Massimiliano

    2014-09-01

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

  19. Superconductive articles

    SciTech Connect

    Wu, X.D.; Muenchausen, R.E.

    1991-12-31

    An article of manufacture including a substrate, a patterned interlayer of magnesium oxide, barium-titanium oxide or barium-zirconium oxide, the patterned interlayer material overcoated with a secondary interlayer material of yttria-stabilized zirconia or magnesium-aluminum oxide, upon the surface of the substrate whereby an intermediate article with an exposed surface of both the overcoated patterned interlayer and the substrate is formed, a coating of a buffer layer selected from the group consisting of oxides of Ce, Y, Cm, Dy, Er, Eu, Fe, Gd, Ho, In, La, Mn, Lu, Nd, Pr, Pu, Sm, Tb, Tl, Tm, Y, and Yb over the entire exposed surface of the intermediate article, and, a ceramic superconductive material layer as an overcoat upon the buffer layer whereby the ceramic superconductive material situated directly above the substrate has a crystal structure substantially different than the ceramic superconductive material situated above the overcoated patterned interlayer.

  20. Superconducting magnets

    SciTech Connect

    Willen, E.; Dahl, P.; Herrera, J.

    1985-01-01

    This report provides a self-consistent description of a magnetic field in the aperture of a superconducting magnet and details how this field can be calculated in a magnet with cos theta current distribution in the coils. A description of an apparatus that can be used to measure the field uniformity in the aperture has been given. Finally, a detailed description of the magnet being developed for use in the Superconducting Super Collider is given. When this machine is built, it will be by far the largest application of superconductivity to date and promises to make possible the experimental discoveries needed to understand the basic laws of nature governing the world in which we live.

  1. Pick a Pair. Pancake Pairs

    ERIC Educational Resources Information Center

    Miller, Pat

    2005-01-01

    Cold February weather and pancakes are a traditional pairing. Pancake Day began as a way to eat up the foods that were abstained from in Lent--traditionally meat, fat, eggs and dairy products. The best-known pancake event is The Pancake Day Race in Buckinghamshire, England, which has been run since 1445. This column describes pairs of books that…

  2. Superconductivity in uranium compounds

    NASA Astrophysics Data System (ADS)

    Mineev, V. P.

    2014-08-01

    On the basis of microscopic theory it is demonstrated how the coupling between the electrons by means of magnetization fluctuations in ferromagnetic metals with orthorhombic symmetry gives rise to an equal-spin pairing superconducting state with the general form of the order parameter dictated by symmetry. The strong upturn of the upper critical field along the b direction above 5 T in UCoGe is explained by the increase of the pairing interaction caused by the suppression of the Curie temperature by a magnetic field parallel to the b axis. It is proposed that a similar phenomenon at a much higher field must take place also for a field directed along the magnetically hardest a direction.

  3. Superconducting proximity effect in graphene under inhomogeneous strain

    NASA Astrophysics Data System (ADS)

    Covaci, L.; Peeters, F. M.

    2011-12-01

    The interplay between quantum Hall states and Cooper pairs is usually hindered by the suppression of the superconducting state due to the strong magnetic fields needed to observe the quantum Hall effect. From this point of view, graphene is special since it allows the creation of strong pseudomagnetic fields due to strain. We show that in a Josephson junction made of strained graphene, Cooper pairs will diffuse into the strained region. The pair correlation function will be sublattice polarized due to the polarization of the local density of states in the zero pseudo-Landau level. We uncover two regimes: (1) one in which the cyclotron radius is larger than the junction length, in which case the supercurrent will be enhanced, and (2) the long junction regime where the supercurrent is strongly suppressed because the junction becomes an insulator. In the latter case quantized Hall states form and Andreev scattering at the normal/superconducting interface will induce edge states. Our numerical calculation has become possible due to an extension of the Chebyshev-Bogoliubov-de Gennes method to computations on video cards (GPUs).

  4. PREFACE: Superconducting materials Superconducting materials

    NASA Astrophysics Data System (ADS)

    Charfi Kaddour, Samia; Singleton, John; Haddad, Sonia

    2011-11-01

    The discovery of superconductivity in 1911 was a great milestone in condensed matter physics. This discovery has resulted in an enormous amount of research activity. Collaboration among chemists and physicists, as well as experimentalists and theoreticians has given rise to very rich physics with significant potential applications ranging from electric power transmission to quantum information. Several superconducting materials have been synthesized. Crucial progress was made in 1987 with the discovery of high temperature superconductivity in copper-based compounds (cuprates) which have revealed new fascinating properties. Innovative theoretical tools have been developed to understand the striking features of cuprates which have remained for three decades the 'blue-eyed boy' for researchers in superconductor physics. The history of superconducting materials has been notably marked by the discovery of other compounds, particularly organic superconductors which despite their low critical temperature continue to attract great interest regarding their exotic properties. Last but not least, the recent observation of superconductivity in iron-based materials (pnictides) has renewed hope in reaching room temperature superconductivity. However, despite intense worldwide studies, several features related to this phenomenon remain unveiled. One of the fundamental key questions is the mechanism by which superconductivity takes place. Superconductors continue to hide their 'secret garden'. The new trends in the physics of superconductivity have been one of the two basic topics of the International Conference on Conducting Materials (ICoCoM2010) held in Sousse,Tunisia on 3-7 November 2010 and organized by the Tunisian Physical Society. The conference was a nice opportunity to bring together participants from multidisciplinary domains in the physics of superconductivity. This special section contains papers submitted by participants who gave an oral contribution at ICoCoM2010

  5. Rapid prefrontal cortex activation towards aversively paired faces and enhanced contingency detection are observed in highly trait-anxious women under challenging conditions

    PubMed Central

    Rehbein, Maimu Alissa; Wessing, Ida; Zwitserlood, Pienie; Steinberg, Christian; Eden, Annuschka Salima; Dobel, Christian; Junghöfer, Markus

    2015-01-01

    Relative to healthy controls, anxiety-disorder patients show anomalies in classical conditioning that may either result from, or provide a risk factor for, clinically relevant anxiety. Here, we investigated whether healthy participants with enhanced anxiety vulnerability show abnormalities in a challenging affective-conditioning paradigm, in which many stimulus-reinforcer associations had to be acquired with only few learning trials. Forty-seven high and low trait-anxious females underwent MultiCS conditioning, in which 52 different neutral faces (CS+) were paired with an aversive noise (US), while further 52 faces (CS−) remained unpaired. Emotional learning was assessed by evaluative (rating), behavioral (dot-probe, contingency report), and neurophysiological (magnetoencephalography) measures before, during, and after learning. High and low trait-anxious groups did not differ in evaluative ratings or response priming before or after conditioning. High trait-anxious women, however, were better than low trait-anxious women at reporting CS+/US contingencies after conditioning, and showed an enhanced prefrontal cortex (PFC) activation towards CS+ in the M1 (i.e., 80–117 ms) and M170 time intervals (i.e., 140–160 ms) during acquisition. These effects in MultiCS conditioning observed in individuals with elevated trait anxiety are consistent with theories of enhanced conditionability in anxiety vulnerability. Furthermore, they point towards increased threat monitoring and detection in highly trait-anxious females, possibly mediated by alterations in visual working memory. PMID:26113814

  6. Three orders of magnitude enhancement of proton conductivity of porous coordination polymers by incorporating ion-pairs into a framework.

    PubMed

    You, Ya-Wen; Xue, Chen; Tian, Zheng-Fang; Liu, Shao-Xian; Ren, Xiao-Ming

    2016-05-01

    A clathrate NH4Br@HKUST-1 has been prepared by means of soaking the metal-organic-framework, HKUST-1, in ammonium bromide saturated ethanol solution at ambient temperature. Both NH4Br@HKUST-1 and HKUST-1 show the same framework structure. The formula of the clathrate is approximately expressed as Cu3(BTC)2(NH4Br)1.15. The thermal stability of the metal-organic framework is not affected by incorporating ammonium bromide into its pores. The impedance spectra measurements were performed for both NH4Br@HKUST-1 and HKUST-1 in anhydrous and selected relative humidity environments, disclosing that the conductivity of NH4Br@HKUST-1 is enhanced by three/four orders of magnitude under the same conditions with respect to HKUST-1. This study provided an efficient strategy to achieve new high conductivity proton transport materials. PMID:27067243

  7. Superconductivity in magnetic multipole states

    NASA Astrophysics Data System (ADS)

    Sumita, Shuntaro; Yanase, Youichi

    2016-06-01

    Stimulated by recent studies of superconductivity and magnetism with local and global broken inversion symmetry, we investigate the superconductivity in magnetic multipole states in locally noncentrosymmetric metals. We consider a one-dimensional zigzag chain with sublattice-dependent antisymmetric spin-orbit coupling and suppose three magnetic multipole orders: monopole order, dipole order, and quadrupole order. It is demonstrated that the Bardeen-Cooper-Schrieffer state, the pair-density wave (PDW) state, and the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state are stabilized by these multipole orders, respectively. We show that the PDW state is a topological superconducting state specified by the nontrivial Z2 number and winding number. The origin of the FFLO state without macroscopic magnetic moment is attributed to the asymmetric band structure induced by the magnetic quadrupole order and spin-orbit coupling.

  8. Superconducting Microelectronics.

    ERIC Educational Resources Information Center

    Henry, Richard W.

    1984-01-01

    Discusses superconducting microelectronics based on the Josephson effect and its advantages over conventional integrated circuits in speed and sensitivity. Considers present uses in standards laboratories (voltage) and in measuring weak magnetic fields. Also considers future applications in superfast computer circuitry using Superconducting…

  9. Superconductivity by means of the subquantum medium coherence

    SciTech Connect

    Agop, M.; Ioannou, P.D.; Nica, P.

    2005-06-01

    In the hydrodynamic formulation of the scale relativity theory one shows that a stable vortices distribution of bipolaron type induces superconducting pairs by means of the quantum potential. Then, usual mechanisms (as, for example, the exchange interaction used in the bipolaron theory) are reduced to the coherence on the subquantum medium, the superconducting pairs resulting as a one-dimensional projection of a fractal. The temperature dependences of the superconducting parameters (coherence length, critical speed, pair breaking time, carriers concentration, penetration depth, critical field, critical current) and the concordance with the experimental data and other theories are analyzed.

  10. 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.

  11. A 24-base-pair sequence 3' to the human erythropoietin gene contains a hypoxia-responsive transcriptional enhancer.

    PubMed Central

    Madan, A; Curtin, P T

    1993-01-01

    Erythropoietin (Epo) synthesis increases in response to hypoxia. The hepatoma cell line Hep 3B produces low basal levels of Epo mRNA which increase markedly with hypoxia. To define the sequences necessary for this response, we linked fragments of the human Epo gene to a luciferase vector, introduced these plasmids into Hep 3B cells and assayed for luciferase activity after growth in 1% or 21% oxygen. A 621-bp Epo promoter fragment resulted in a 2.4-fold increase in luciferase activity with hypoxia. We tested several Epo gene fragments upstream of this Epo promoter fragment and found that a 613-bp Bgl II-Pvu II 3' fragment had a 10-fold increase in activity with hypoxia regardless of orientation. This fragment had a similar level of activity when linked to a simian virus 40 promoter. Portions of this fragment retained activity, including a 38-bp Apa I-Taq I fragment that had a 17-fold increase in activity with hypoxia. Deletion of nt 4-13 or 19-28 from this 38-bp fragment resulted in a loss of activity. The 24-bp upstream portion of the 38-bp fragment showed an 8-fold increase in activity with hypoxia. However, deletion of nt 19-24 or mutagenesis of nt 21 or 22 in this 24-bp fragment resulted in loss of activity. Our studies indicate that the transcriptional response of the human Epo gene to hypoxia is mediated in part by promoter sequences and to a greater degree by an enhancer element located in a 24-bp portion of the 3' flanking sequence of the gene. PMID:8387202

  12. Tuning the band structure and superconductivity in single-layer FeSe by interface engineering.

    PubMed

    Peng, R; Xu, H C; Tan, S Y; Cao, H Y; Xia, M; Shen, X P; Huang, Z C; Wen, C H P; Song, Q; Zhang, T; Xie, B P; Gong, X G; Feng, D L

    2014-01-01

    The interface between transition metal compounds provides a rich playground for emergent phenomena. Recently, significantly enhanced superconductivity has been reported for single-layer FeSe on Nb-doped SrTiO3 substrate. Yet it remains mysterious how the interface affects the superconductivity. Here we use in situ angle-resolved photoemission spectroscopy to investigate various FeSe-based heterostructures grown by molecular beam epitaxy, and uncover that electronic correlations and superconducting gap-closing temperature (Tg) are tuned by interfacial effects. Tg up to 75 K is observed in extremely tensile-strained single-layer FeSe on Nb-doped BaTiO3, which sets a record high pairing temperature for both Fe-based superconductor and monolayer-thick films, providing a promising prospect on realizing more cost-effective superconducting device. Moreover, our results exclude the direct correlation between superconductivity and tensile strain or the energy of an interfacial phonon mode, and highlight the critical and non-trivial role of FeSe/oxide interface on the high Tg, which provides new clues for understanding its origin. PMID:25256736

  13. Nb-Pb Superconducting RF Gun

    SciTech Connect

    Sekutowicz, J.; Iversen, J.; Kreps, G.; Moller, W.D.; Singer, W.; Singer, X.; Ben-Zvi, I.; Burrill, A.; Smedley, J.; Rao, T.; Ferrario, M.; Kneisel, P.; Langner, J.; Strzyzewski, P.; Lefferts, R.; Lipski, A.; Szalowski, K.; Ko, K.; Xiao, L.; /SLAC

    2006-03-29

    We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.

  14. Nb-Pb superconducting RF gun

    SciTech Connect

    J. Sekutowicz; J. Iversen; G. Kreps; W.D. Moller; W. Singer; X. Singer; I. Ben-Zvi; A. Burrill; J. Smedley; T. Rao; M. Ferrario; P. Kneisel; J. Langner; P. Strzyzewski; R. Lefferts; A. Lipski; K. Szalowski; K. Ko; L. Xiao

    2006-04-14

    We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.

  15. High-temperature superconductivity in iron pnictides and chalcogenides

    NASA Astrophysics Data System (ADS)

    Si, Qimiao; Yu, Rong; Abrahams, Elihu

    2016-04-01

    Superconductivity develops in metals upon the formation of a coherent macroscopic quantum state of electron pairs. Iron pnictides and chalcogenides are materials that have high superconducting transition temperatures. In this Review, we describe the advances in the field that have led to higher superconducting transition temperatures in iron-based superconductors and the wide range of materials that are used to form these superconductors. We summarize the essential aspects of the normal state and the mechanism for superconductivity. We emphasize the degree of electron–electron correlations and their manifestation in properties of the normal state. We examine the nature of magnetism, analyse its role in driving the electronic nematicity and discuss quantum criticality at the border of magnetism in the phase diagram. Finally, we review the amplitude and structure of the superconducting pairing, and survey the potential material settings for optimizing superconductivity.

  16. Giant enhancement of the n-type conductivity in single phase p-type ZnO:N thin films by intentionally created defect clusters and pairs

    NASA Astrophysics Data System (ADS)

    Gautam, Subodh K.; Singh, R. G.; Siva Kumar, V. V.; Singh, Fouran

    2015-09-01

    The p-type conductivity with very high transparency in visible region of electromagnetic spectrum from nitrogen doped zinc oxide (ZnO:N) thin films is reported and the origin of p-type conductivity is attributed to the formation of complex zinc interstitial-nitrogen substituted oxygen (Zni-NO) centers. The films are irradiated using energetic ions for inducing the high density of defects/defect clusters in the lattice for increasing the conductivity of the films. A systematic change in nature of charge carriers from p- to n-type and about four orders of magnitude enhancement of n-type conductivity is observed with increase in the fluence of irradiation. The intentionally induced complex defects such as VO/Zni clusters and VZn-VO defects pairs are mainly ascribed to the donor defects. These induced defects also act as the compensatory defects for the p-type charge carriers at low fluences and give rise to the giant enhancement in the n-type conductivity of films at higher fluence of irradiation.

  17. Design of the radiation shielding for the time of flight enhanced diagnostics neutron spectrometer at Experimental Advanced Superconducting Tokamak

    SciTech Connect

    Du, T. F.; Chen, Z. J.; Peng, X. Y.; Yuan, X.; Zhang, X.; Hu, Z. M.; Cui, Z. Q.; Xie, X. F.; Ge, L. J.; Li, X. Q.; Zhang, G. H.; Chen, J. X.; Fan, T. S.; Gorini, G.; Nocente, M.; Tardocchi, M.; Hu, L. Q.; Zhong, G. Q.; Lin, S. Y.; Wan, B. N.

    2014-11-15

    A radiation shielding has been designed to reduce scattered neutrons and background gamma-rays for the new double-ring Time Of Flight Enhanced Diagnostics (TOFED). The shielding was designed based on simulation with the Monte Carlo code MCNP5. Dedicated model of the EAST tokamak has been developed together with the emission neutron source profile and spectrum; the latter were simulated with the Nubeam and GENESIS codes. Significant reduction of background radiation at the detector can be achieved and this satisfies the requirement of TOFED. The intensities of the scattered and direct neutrons in the line of sight of the TOFED neutron spectrometer at EAST are studied for future data interpretation.

  18. The Effect of Enhanced Spin-Orbit Scattering on the Superconducting - Nonsuperconducting Transition and the Metal-Insulator Transition in Granular Aluminum.

    NASA Astrophysics Data System (ADS)

    Miller, Theodore A.

    A small amount of bismuth was added to a set of granular aluminum samples to increase the spin-orbit scattering rate. This set is compared with a second set with no bismuth added. With the addition of bismuth, both the metal-insulator transition and the threshold for the presence of superconductivity were shifted a similar amount to higher values of resistivity. The shift of the metal-insulator transition can be explained as a result of the effect of increased spin -orbit scattering at an Anderson transiton. The fact that the superconducting threshold also shifts indicates that it is the proximity to the metal-insulator transition that depresses superconductivity.

  19. Superconductivity and disorder in the potential topological superconductor (Sn,In)Te

    NASA Astrophysics Data System (ADS)

    Smylie, Matthew; Shen, Bing; Claus, Helmut; Snezhko, Alexey; Welp, Ulrich; Kwok, Wai-Kwong; Eskildsen, Morten; de Waard, Elizabeth; Susner, Michael; Sefat, Athena

    In-doped SnTe has been proposed as a candidate topological superconductor. It has been suggested that the superconducting critical temperature (Tc) is strongly enhanced with impurity scattering in this material, with the pairing mechanism perhaps changing with doping. To access information on the paring symmetry of the superconducting order parameter, ultra-sensitive magnetic field penetration measurements have been conducted by means of a Tunnel-Diode-Oscilator (TDO) technique. Particle irradiation with low MeV protons was used as a controllable source of disorder, but no enhancement of Tc was observed in cubic-phase material as scattering increased. Detailed characterization measurements and analysis were performed before and after irradiation of the samples. Tunnel diode oscillator and magnetization measurements were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

  20. Surface superconductivity in thin cylindrical Bi nanowire.

    PubMed

    Tian, Mingliang; Wang, Jian; Ning, Wei; Mallouk, Thomas E; Chan, Moses H W

    2015-03-11

    The physical origin and the nature of superconductivity in nanostructured Bi remains puzzling. Here, we report transport measurements of individual cylindrical single-crystal Bi nanowires, 20 and 32 nm in diameter. In contrast to nonsuperconducting Bi nanoribbons with two flat surfaces, cylindrical Bi nanowires show superconductivity below 1.3 K. However, their superconducting critical magnetic fields decrease with their diameter, which is the opposite of the expected behavior for thin superconducting wires. Quasiperiodic oscillations of magnetoresistance were observed in perpendicular fields but were not seen in the parallel orientation. These results can be understood by a model of surface superconductivity with an enhanced surface-to-bulk volume in small diameter wires, where the superconductivity originates from the strained surface states of the nanowires due to the surface curvature-induced stress. PMID:25658139

  1. Detection of a Spin-Triplet Superconducting Phase in Oriented Polycrystalline U2PtC2 Samples Using 195Pt Nuclear Magnetic Resonance

    NASA Astrophysics Data System (ADS)

    Mounce, A. M.; Yasuoka, H.; Koutroulakis, G.; Ni, N.; Bauer, E. D.; Ronning, F.; Thompson, J. D.

    2015-03-01

    Nuclear magnetic resonance (NMR) measurements on the 195Pt nucleus in an aligned powder of the moderately heavy-fermion material U2PtC2 are consistent with spin-triplet pairing in its superconducting state. Across the superconducting transition temperature and to much lower temperatures, the NMR Knight shift is temperature independent for field both parallel and perpendicular to the tetragonal c axis, expected for triplet equal-spin pairing superconductivity. The NMR spin-lattice relaxation rate 1 /T1, in the normal state, exhibits characteristics of ferromagnetic fluctuations, compatible with an enhanced Wilson ratio. In the superconducting state, 1 /T1 follows a power law with temperature without a coherence peak giving additional support that U2PtC2 is an unconventional superconductor. Bulk measurements of the ac susceptibility and resistivity indicate that the upper critical field exceeds the Pauli limiting field for spin-singlet pairing and is near the orbital limiting field, an additional indication for spin-triplet pairing.

  2. Enhanced critical currents in (Gd,Y)Ba2Cu3Ox superconducting tapes with high levels of Zr addition

    NASA Astrophysics Data System (ADS)

    Selvamanickam, V.; Chen, Y.; Shi, T.; Liu, Y.; Khatri, N. D.; Liu, J.; Yao, Y.; Xiong, X.; Lei, C.; Soloveichik, S.; Galstyan, E.; Majkic, G.

    2013-03-01

    The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba2Cu3Ox film. By a modified MOCVD process, enhanced critical current densities have been achieved with high levels of Zr addition, including 3.83 MA cm-2 in 15 at.% Zr-added 1.1 μm thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/12 mm have been reached in (Gd,Y)BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape, corresponding to a pinning force value of 268 GN m-3. The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second-phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met.

  3. Enhanced critical currents in (Gd,Y)Ba2Cu3Ox superconducting tapes with high levels of Zr addition

    SciTech Connect

    Selvamanickam, V; Chen, Y; Shi, T; Liu, Y; Khatri, ND; Liu, J; Yao, Y; Xiong, X; Lei, C; Soloveichik, S; Galstyan, E; Majkic, G

    2013-01-21

    The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba2Cu3Ox film. By a modified MOCVD process,enhanced critical current densities have been achieved with high levels of Zr addition,including 3.83 MA cm(-2) in 15 at.% Zr- added 1.1 mu m thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/ 12 mm have been reached in (Gd,Y) BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape,corresponding to a pinning force value of 268 GN m(-3). The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second- phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met.

  4. Robustness of quantum critical pairing against disorder

    NASA Astrophysics Data System (ADS)

    Kang, Jian; Fernandes, Rafael M.

    2016-06-01

    The remarkable robustness of high-temperature superconductors against disorder remains a controversial obstacle towards the elucidation of their pairing state. Indeed, experiments report a weak suppression rate of the transition temperature Tc with disorder, significantly smaller than the universal value predicted by extensions of the conventional theory of dirty superconductors. However, in many high-Tc compounds, superconductivity appears near a putative magnetic quantum critical point, suggesting that quantum fluctuations, which suppress coherent electronic spectral weight, may also promote unconventional pairing. Here we investigate theoretically the impact of disorder on such a quantum critical pairing state, considering the coupling of impurities both to the low-energy electronic states and to the pairing interaction itself. We find a significant reduction in the suppression rate of Tc with disorder near the magnetic quantum critical point, shedding new light on the nature of unconventional superconductivity in correlated materials.

  5. Drive system employing frictionless bearings including superconducting matter

    SciTech Connect

    Weeks, D.E.

    1991-10-29

    This patent describes an apparatus. It comprises a rotatable support member; a pair of first magnets positioned at opposite ends of the support member, the magnets having axes of symmetry and being rotatable about the axes; a mass of a superconducting material positioned adjacent each first magnet so that based on current understanding each magnet is levitated from the mass of superconducting material by means of persistent currents induced in the mass of superconducting material by the first magnets.

  6. Color superconductivity

    SciTech Connect

    Wilczek, F.

    1997-09-22

    The asymptotic freedom of QCD suggests that at high density - where one forms a Fermi surface at very high momenta - weak coupling methods apply. These methods suggest that chiral symmetry is restored and that an instability toward color triplet condensation (color superconductivity) sets in. Here I attempt, using variational methods, to estimate these effects more precisely. Highlights include demonstration of a negative pressure in the uniform density chiral broken phase for any non-zero condensation, which we take as evidence for the philosophy of the MIT bag model; and demonstration that the color gap is substantial - several tens of MeV - even at modest densities. Since the superconductivity is in a pseudoscalar channel, parity is spontaneously broken.

  7. SUPERCONDUCTING PHOTOINJECTOR

    SciTech Connect

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

    2007-08-26

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

  8. Coulomb-induced pairing in a quarter-filled band model for κ-(BEDT-TTF)2X

    NASA Astrophysics Data System (ADS)

    de Silva, W. Wasanthi; Gomes, Niladri; Mazumdar, Sumit; Clay, R. Torsten

    κ -(BEDT-TTF)2X is a two dimensional organic charge transfer solid superconductor with a hole density of one half per (BEDT-TTF) molecule. With one hole per dimer of molecules, the material is frequently described using an effective 1 / 2 -filled band Hubbard model on an anisotropic triangular lattice. Within this effective model a metal to antiferromagnetic (AFM) semiconductor phase transition is found. Calculations beyond the mean field level, however, have shown absence of superconductivity within the model. We present the results of correlated-electron calculations on the κ-lattice for up to 64 BEDT-TTF molecules using the Constrained Path Monte Carlo (CPMC) and Path Integral Renormalization Group (PIRG) methods over a wide range of carrier density. We show that superconducting pair-pair correlations in this model are enhanced by electron-electron (e-e) interactions for d-wave pairing symmetry uniquely for hole density close to quarter-filling. Our results indicate that this enhancement of superconductivity is not related to the presence of AFM order, but to the strong tendency to spin-singlet formation in the quarter-filled band. Supported by DOE Grant DE-FG02-06ER46315 and NSF-CHE-151475.

  9. Neutron-scattering evidence for a periodically modulated superconducting phase in the underdoped cuprate La1.905Ba0.095CuO4

    DOE PAGESBeta

    Xu, Zhijun; Stock, C.; Chi, Songxue; Kolesnikov, A. I.; Xu, Guangyong I.; Gu, Genda; Tranquada, J. M.

    2014-10-01

    The role of antiferromagnetic spin correlations in high-temperature superconductors remains a matter of debate. We present inelastic neutron-scattering evidence that gapless spin fluctuations coexist with superconductivity in La1.905Ba0.095CuO4. Furthermore, we observe that both the low-energy magnetic spectral weight and the spin incommensurability are enhanced with the onset of superconducting correlations. We propose that the coexistence occurs through intertwining of spatial modulations of the pair wave function and the antiferromagnetic correlations. This proposal is also directly relevant to sufficiently underdoped La2-xSrxCuO4 and YBa2Cu3O6+x.

  10. Winning Pairs.

    ERIC Educational Resources Information Center

    Monsour, Florence

    2000-01-01

    Mentoring programs that pair experienced and first-time teachers are gaining prominence in supporting, developing, and retaining new teachers. The successful Beginning Teacher Assistance program at University of Wisconsin-River Falls was designed to give new K-12 teachers the opportunity for yearlong, structured support from mentor teachers. (MLH)

  11. Double-arm three-dimensional ion imaging apparatus for the study of ion pair channels in resonance enhanced multiphoton ionization

    NASA Astrophysics Data System (ADS)

    Poretskiy, M. S.; Chichinin, A. I.; Maul, C.; Gericke, K.-H.

    2016-02-01

    We present a novel experimental configuration for the full quantitative characterization of the multichannel resonance enhanced multiphoton ionization (REMPI) of small molecules in cases when the ion-pair dissociation channel is important. For this purpose, a double-arm time-of-flight mass spectrometer with three-dimensional (3D) ion imaging detectors at both arms is constructed. The REMPI of HCl molecules is used to examine the constructed setup. The apparatus allows us to perform simultaneous measurements of the 3D velocity vector distributions of positive (H+, HCl+, and Cl+) and negative (Cl-) photoions. The characterization consists of the determination of "two-photon absorption cross sections" for the process HCl(X)+2hν → HCl∗, one-photon absorption cross sections for subsequent processes HCl∗ + hν → HCl∗∗, and the probability of the subsequent non-adiabatic transition HCl∗∗ → HCl(B) → H+ + Cl-, which leads to ionic pairs. All these data should be obtained from the analysis of the dependencies of the number of ions on the laser energy. The full characterization of the laser beam and the knowledge of the ion detection probability are necessary parts of the analysis. Detailed knowledge of losses of produced ions in the mass spectrometer before detection requires understanding and characterization of such processes like electron emission from metallic grids under ion bombardment or charge transfer between positive ions and the metal surface of the grids, like Cl+ + (grid) → Cl-. These important phenomena from surface science are rarely discussed in the imaging literature, and here, we try to compensate for this shortcoming.

  12. Double-arm three-dimensional ion imaging apparatus for the study of ion pair channels in resonance enhanced multiphoton ionization.

    PubMed

    Poretskiy, M S; Chichinin, A I; Maul, C; Gericke, K-H

    2016-02-01

    We present a novel experimental configuration for the full quantitative characterization of the multichannel resonance enhanced multiphoton ionization (REMPI) of small molecules in cases when the ion-pair dissociation channel is important. For this purpose, a double-arm time-of-flight mass spectrometer with three-dimensional (3D) ion imaging detectors at both arms is constructed. The REMPI of HCl molecules is used to examine the constructed setup. The apparatus allows us to perform simultaneous measurements of the 3D velocity vector distributions of positive (H(+), HCl(+), and Cl(+)) and negative (Cl(-)) photoions. The characterization consists of the determination of "two-photon absorption cross sections" for the process HCl(X)+2hν → HCl*, one-photon absorption cross sections for subsequent processes HCl* + hν → HCl*, and the probability of the subsequent non-adiabatic transition HCl* → HCl(B) → H(+) + Cl(-), which leads to ionic pairs. All these data should be obtained from the analysis of the dependencies of the number of ions on the laser energy. The full characterization of the laser beam and the knowledge of the ion detection probability are necessary parts of the analysis. Detailed knowledge of losses of produced ions in the mass spectrometer before detection requires understanding and characterization of such processes like electron emission from metallic grids under ion bombardment or charge transfer between positive ions and the metal surface of the grids, like Cl(+) + (grid) → Cl(-). These important phenomena from surface science are rarely discussed in the imaging literature, and here, we try to compensate for this shortcoming. PMID:26931834

  13. Enhanced superconductivity due to forward scattering in FeSe thin films on SrTiO3 substrates

    DOE PAGESBeta

    Rademaker, Louk; Wang, Yan; Berlijn, Tom; Johnston, Steve

    2016-02-10

    In this paper, we study the consequences of an electron–phonon (e–ph) interaction that is strongly peaked in the forward scattering (more » $${\\bf{q}}=0$$) direction in a two-dimensional superconductor using Migdal–Eliashberg theory. We find that strong forward scattering results in an enhanced T c that is linearly proportional to the strength of the dimensionless e–ph coupling constant $${\\lambda }_{m}$$ in the weak coupling limit. This interaction also produces distinct replica bands in the single-particle spectral function, similar to those observed in recent angle-resolved photoemission experiments on FeSe monolayers on SrTiO3 and BaTiO3 substrates. Finally, by comparing our model to photoemission experiments, we infer an e–ph coupling strength that can provide a significant portion of the observed high T c in these systems.« less

  14. Superconductivity in Bismuth. A New Look at an Old Problem

    PubMed Central

    2016-01-01

    To investigate the relationship between atomic topology, vibrational and electronic properties and superconductivity of bismuth, a 216-atom amorphous structure (a-Bi216) was computer-generated using our undermelt-quench approach. Its pair distribution function compares well with experiment. The calculated electronic and vibrational densities of states (eDOS and vDOS, respectively) show that the amorphous eDOS is about 4 times the crystalline at the Fermi energy, whereas for the vDOS the energy range of the amorphous is roughly the same as the crystalline but the shapes are quite different. A simple BCS estimate of the possible crystalline superconducting transition temperature gives an upper limit of 1.3 mK. The e-ph coupling is more preponderant in a-Bi than in crystalline bismuth (x-Bi) as indicated by the λ obtained via McMillan’s formula, λc = 0.24 and experiment λa = 2.46. Therefore with respect to x-Bi, superconductivity in a-Bi is enhanced by the higher values of λ and of eDOS at the Fermi energy. PMID:26815431

  15. Superconductivity in Bismuth. A New Look at an Old Problem.

    PubMed

    Mata-Pinzón, Zaahel; Valladares, Ariel A; Valladares, Renela M; Valladares, Alexander

    2016-01-01

    To investigate the relationship between atomic topology, vibrational and electronic properties and superconductivity of bismuth, a 216-atom amorphous structure (a-Bi216) was computer-generated using our undermelt-quench approach. Its pair distribution function compares well with experiment. The calculated electronic and vibrational densities of states (eDOS and vDOS, respectively) show that the amorphous eDOS is about 4 times the crystalline at the Fermi energy, whereas for the vDOS the energy range of the amorphous is roughly the same as the crystalline but the shapes are quite different. A simple BCS estimate of the possible crystalline superconducting transition temperature gives an upper limit of 1.3 mK. The e-ph coupling is more preponderant in a-Bi than in crystalline bismuth (x-Bi) as indicated by the λ obtained via McMillan's formula, λc = 0.24 and experiment λa = 2.46. Therefore with respect to x-Bi, superconductivity in a-Bi is enhanced by the higher values of λ and of eDOS at the Fermi energy. PMID:26815431

  16. High pressure studies of superconductivity

    NASA Astrophysics Data System (ADS)

    Hillier, Narelle Jayne

    Superconductivity has been studied extensively since it was first discovered over 100 years ago. High pressure studies, in particular, have been vital in furthering our understanding of the superconducting state. Pressure allows researchers to enhance the properties of existing superconductors, to find new superconductors, and to test the validity of theoretical models. This thesis presents a series of high pressure measurements performed in both He-gas and diamond anvil cell systems on various superconductors and on materials in which pressure-induced superconductivity has been predicted. Under pressure the alkali metals undergo a radical departure from the nearly-free electron model. In Li this leads to a superconducting transition temperature that is among the highest of the elements. All alkali metals have been predicted to become superconducting under pressure. Pursuant to this, a search for superconductivity has been conducted in the alkali metals Na and K. In addition, the effect of increasing electron concentration on Li1-xMgx alloys has been studied. Metallic hydrogen and hydrogen-rich compounds are believed to be good candidates for high temperature superconductivity. High pressure optical studies of benzene (C6H6) have been performed to 2 Mbar to search for pressure-induced metallization. Finally, cuprate and iron-based materials are considered high-Tc superconductors. These layered compounds exhibit anisotropic behavior under pressure. Precise hydrostatic measurements of dTc/dP on HgBa2CuO 4+delta have been carried out in conjunction with uniaxial pressure experiments by another group. The results obtained provide insight into the effect of each of the lattice parameters on Tc. Finally, a series of hydrostatic and non-hydrostatic measurements on LnFePO (Ln = La, Pr, Nd) reveal startling evidence that the superconducting state in the iron-based superconductors is highly sensitive to lattice strain.

  17. Resonant tunneling of fluctuation Cooper pairs

    SciTech Connect

    Galda, Alexey; Mel'nikov, A. S.; Vinokur, V. M.

    2015-02-09

    Superconducting fluctuations have proved to be an irreplaceable source of information about microscopic and macroscopic material parameters that could be inferred from the experiment. According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, Tc, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at Tc. Here we report the current spikes due to radiation-induced resonant tunneling of fluctuation Cooper pairs between two superconductors which grow even sharper and more pronounced upon approach to Tc. This striking effect offers an unprecedented tool for direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors. Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.

  18. Resonant tunneling of fluctuation Cooper pairs

    DOE PAGESBeta

    Galda, Alexey; Mel'nikov, A. S.; Vinokur, V. M.

    2015-02-09

    Superconducting fluctuations have proved to be an irreplaceable source of information about microscopic and macroscopic material parameters that could be inferred from the experiment. According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, Tc, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at Tc. Here we report the current spikes due to radiation-induced resonant tunneling of fluctuation Cooper pairs between two superconductors which grow even sharper and more pronounced upon approach to Tc. This striking effect offers an unprecedented tool formore » direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors. Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.« less

  19. Long-range Cooper pair splitter with high entanglement production rate

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Shi, D. N.; Xing, D. Y.

    2015-01-01

    Cooper pairs in the superconductor are a natural source of spin entanglement. The existing proposals of the Cooper pair splitter can only realize a low efficiency of entanglement production, and its size is constrained by the superconducting coherence length. Here we show that a long-range Cooper pair splitter can be implemented in a normal metal-superconductor-normal metal (NSN) junction by driving a supercurrent in the S. The supercurrent results in a band gap modification of the S, which significantly enhances the crossed Andreev reflection (CAR) of the NSN junction and simultaneously quenches its elastic cotunneling. Therefore, a high entanglement production rate close to its saturation value can be achieved by the inverse CAR. Interestingly, in addition to the conventional entangled electron states between opposite energy levels, novel entangled states with equal energy can also be induced in our proposal.

  20. In situ growth of YBa sub 2 Cu sub 3 O sub 7 minus x high Tc superconducting thin films directly on sapphire by plasma-enhanced metalorganic chemical vapor deposition

    SciTech Connect

    Chern, C.S.; Zhao, J.; Li, Y.Q.; Norris, P.; Kear, B.; Gallois, B. )

    1990-08-13

    Highly {ital c}-axis oriented YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} superconducting thin films have been, {ital in} {ital situ}, deposited directly on sapphire substrate by a remote microwave plasma-enhanced metalorganic chemical vapor deposition process (PE-MOCVD). The films were deposited at a substrate temperature of 730 {degree}C followed by a fast cooling. The as-deposited films show attainment of zero resistance at 82 K and have critical current density of 10{sup 4} A/cm{sup 2} at 70 K. ac susceptibility measurement indicated that the films contain a single superconducting phase. PE-MOCVD was carried out in a commercial-scale MOCVD reactor with capability of uniform deposition over 100 cm{sup 2} per growth run.

  1. Electron pairing in the presence of incipient bands in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Chen, Xiao; Maiti, S.; Linscheid, A.; Hirschfeld, P. J.

    2015-12-01

    Recent experiments on certain Fe-based superconductors have hinted at a role for paired electrons in "incipient" bands that are close to, but do not cross, the Fermi level. Related theoretical works disagree on whether or not strong-coupling superconductivity is required to explain such effects, and whether a critical interaction strength exists. In this work, we consider various versions of the model problem of pairing of electrons in the presence of an incipient band, within a simple multiband weak-coupling BCS approximation. We categorize the problem into two cases: case (i), where superconductivity arises from the "incipient band pairing" alone, and case (ii), where it is induced on an incipient band by pairing due to Fermi-surface-based interactions. Negative conclusions regarding the importance of incipient bands have been drawn so far largely based on case (i), but we show explicitly that models under case (ii) are qualitatively different, and can explain the nonexponential suppression of Tc, as well as robust large gaps on an incipient band. In the latter situation, large gaps on the incipient band do not require a critical interaction strength. We also model the interplay between phonon and spin fluctuation driven superconductivity and describe situations in which they can enhance each other rather than compete. Finally, we discuss the effect of the dimensionality of the incipient band on our results. We argue that pairing on incipient bands may be significant and important in several Fe-based materials, including LiFeAs, FeSe intercalates, and FeSe monolayers on strontium titanate, and indeed may contribute to high critical temperatures in some cases.

  2. Characterization of anomalous pair currents in Josephson junction networks.

    PubMed

    Ottaviani, I; Lucci, M; Menditto, R; Merlo, V; Salvato, M; Cirillo, M; Müller, F; Weimann, T; Castellano, M G; Chiarello, F; Torrioli, G; Russo, R

    2014-05-28

    Measurements performed on superconductive networks shaped in the form of planar graphs display anomalously large currents when specific branches are biased. The temperature dependences of these currents evidence that their origin is due to Cooper pair hopping through the Josephson junctions connecting the superconductive islands of the array. The experimental data are discussed in terms of theoretical models which predict, for the system under consideration, an inhomogeneous Cooper pair distribution on the superconductive islands of the network as a consequence of a Bose-Einstein condensation phenomenon. PMID:24787550

  3. Influence of exchange field on d-wave superconductivity

    SciTech Connect

    Dobrosavljevic-Grujic, L.; Radovic, Z.

    1996-12-31

    Exchange field effects and d-wave pairing in superconductors may have similar manifestations, as for example {pi}-phase states and spontaneous currents in Josephson devices. Influence of exchange field on the Josephson tunneling between d-wave superconducting electrodes through a ferromagnetic barrier is studied theoretically. Implications of combined exchange field and d-wave pairing effects are discussed in the context of the experimental verification of d-wave superconductivity.

  4. Valence Bond Theory of Correlated-Electron Superconductivity

    NASA Astrophysics Data System (ADS)

    Dutta, Tirthankar; Mazumdar, Sumit; Clay, Torsten

    Whether or not the weakly doped Mott-Hubbard semiconductor is superconducting remains controversial. We present a new valence bond theory of correlated-electron superconductivity, that has overlap with the original RVB approach, and yet is substantively different. Superconductivity within the theory emerges from a correlated-electron state in which there is a strong tendency to spin-singlet formation, and where the bandwidth due to pair-tunneling is very large. We show that such a situation occurs far away from the 1/2-filled band, at or near banfilling of 1/4. In the presence of electron-phonon interactions the 1/4-filled band can form a spin-paired CDW state that we have called a paired-electron crystal, and that is a Wigner crystal of pairs. In the presence of frustration the spin-paired bonds become mobile to give a paired-electron liquid, which is a precursor to superconductivity. The superconducting state here is reached from a co-operative effect between electron-electron and electron-phonon interactions, and the theory thus has overlap also with the bipolaron theory of superconductivity. We will present exact numerical calculations on a 4x4 lattice using the valence bond basis to substantiate our conjectures. Supported by DOE Grant DE-FG02-06ER46315 and NSF-CHE-151475.

  5. Stimulated emission of Cooper pairs in a high-temperature cuprate superconductor

    PubMed Central

    Zhang, Wentao; Miller, Tristan; Smallwood, Christopher L.; Yoshida, Yoshiyuki; Eisaki, Hiroshi; Kaindl, R. A.; Lee, Dung-Hai; Lanzara, Alessandra

    2016-01-01

    The concept of stimulated emission of bosons has played an important role in modern science and technology, and constitutes the working principle for lasers. In a stimulated emission process, an incoming photon enhances the probability that an excited atomic state will transition to a lower energy state and generate a second photon of the same energy. It is expected, but not experimentally shown, that stimulated emission contributes significantly to the zero resistance current in a superconductor by enhancing the probability that scattered Cooper pairs will return to the macroscopically occupied condensate instead of entering any other state. Here, we use time- and angle-resolved photoemission spectroscopy to study the initial rise of the non-equilibrium quasiparticle population in a Bi2Sr2CaCu2O8+δ cuprate superconductor induced by an ultrashort laser pulse. Our finding reveals significantly slower buildup of quasiparticles in the superconducting state than in the normal state. The slower buildup only occurs when the pump pulse is too weak to deplete the superconducting condensate, and for cuts inside the Fermi arc region. We propose this is a manifestation of stimulated recombination of broken Cooper pairs, and signals an important momentum space dichotomy in the formation of Cooper pairs inside and outside the Fermi arc region. PMID:27364682

  6. Stimulated emission of Cooper pairs in a high-temperature cuprate superconductor.

    PubMed

    Zhang, Wentao; Miller, Tristan; Smallwood, Christopher L; Yoshida, Yoshiyuki; Eisaki, Hiroshi; Kaindl, R A; Lee, Dung-Hai; Lanzara, Alessandra

    2016-01-01

    The concept of stimulated emission of bosons has played an important role in modern science and technology, and constitutes the working principle for lasers. In a stimulated emission process, an incoming photon enhances the probability that an excited atomic state will transition to a lower energy state and generate a second photon of the same energy. It is expected, but not experimentally shown, that stimulated emission contributes significantly to the zero resistance current in a superconductor by enhancing the probability that scattered Cooper pairs will return to the macroscopically occupied condensate instead of entering any other state. Here, we use time- and angle-resolved photoemission spectroscopy to study the initial rise of the non-equilibrium quasiparticle population in a Bi2Sr2CaCu2O8+δ cuprate superconductor induced by an ultrashort laser pulse. Our finding reveals significantly slower buildup of quasiparticles in the superconducting state than in the normal state. The slower buildup only occurs when the pump pulse is too weak to deplete the superconducting condensate, and for cuts inside the Fermi arc region. We propose this is a manifestation of stimulated recombination of broken Cooper pairs, and signals an important momentum space dichotomy in the formation of Cooper pairs inside and outside the Fermi arc region. PMID:27364682

  7. Stimulated emission of Cooper pairs in a high-temperature cuprate superconductor

    NASA Astrophysics Data System (ADS)

    Zhang, Wentao; Miller, Tristan; Smallwood, Christopher L.; Yoshida, Yoshiyuki; Eisaki, Hiroshi; Kaindl, R. A.; Lee, Dung-Hai; Lanzara, Alessandra

    2016-07-01

    The concept of stimulated emission of bosons has played an important role in modern science and technology, and constitutes the working principle for lasers. In a stimulated emission process, an incoming photon enhances the probability that an excited atomic state will transition to a lower energy state and generate a second photon of the same energy. It is expected, but not experimentally shown, that stimulated emission contributes significantly to the zero resistance current in a superconductor by enhancing the probability that scattered Cooper pairs will return to the macroscopically occupied condensate instead of entering any other state. Here, we use time- and angle-resolved photoemission spectroscopy to study the initial rise of the non-equilibrium quasiparticle population in a Bi2Sr2CaCu2O8+δ cuprate superconductor induced by an ultrashort laser pulse. Our finding reveals significantly slower buildup of quasiparticles in the superconducting state than in the normal state. The slower buildup only occurs when the pump pulse is too weak to deplete the superconducting condensate, and for cuts inside the Fermi arc region. We propose this is a manifestation of stimulated recombination of broken Cooper pairs, and signals an important momentum space dichotomy in the formation of Cooper pairs inside and outside the Fermi arc region.

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

    NASA Astrophysics Data System (ADS)

    Chen, Hua

    2015-03-01

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

  9. Excitonic superconductivity in copper oxides

    SciTech Connect

    Tesanovic, Z.; Bishop, A.R.; Martin, R.L.; Harris, C.

    1988-01-01

    We discuss the possibility of excitonic superconductivity in high T/sub c/ copper oxides. The Hamiltonians describing CuO/sub 2/ planes supports both antiferromagnetism and low-lying Cu /longleftrightarrow/ O intra- and interband charge fluctuations. One crosses from one regime to another as the number of holes per unit cell increases. The high T/sub c/ superconductivity takes place at hole concentrations most favorable for intraband charge transfer excitations. The dynamic polarizability of the environment surrounding CuO/sub 2/ planes plays an important role in enhancing T/sub c/. 15 refs., 4 figs.

  10. 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.

  11. Space applications of superconductivity

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

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

  12. A Model Approach to Flux-Pinning Properties of YBa2Cu 3O7-delta Thin Film Vortex States via Non-Superconducting Impurities

    NASA Astrophysics Data System (ADS)

    Gamble, Ronald S., Jr.

    Thin film YBa2Cu3O7--delta (YBCO) samples with added non-superconducting nanodot defects of CeO 2 and BaSnO2 are the focus of recent high-temperature superconductor studies. These nanodots allow magnetic flux to penetrate at these sites of the superconducting lattice thus creating a magnetic flux vortex state. Examining the structure shows that these quantized magnetic flux vortices arrange themselves in a self-assembled lattice. The nanodots, with non-superconducting properties, serve to present structural properties to restrict motion of these vorticies under a pinning-force and to enhance the critical current density. A formulation of a new model for the system by a variation in the electron pair velocity via the virtual work from the nanodot defects in accordance to the well-known Superconductivity theories is tested. A solution to the expression for the magnetic flux, zero net force and pair velocity will generate a setting for the optimal deposition parameters of number density, growth geometry and mass density of these nanodot structures. With a calculation of pair velocities from a similar work, a comparison is made between experimental and theoretical velocity calculations using growth geometry and chemical potential. This will yield insight into how the current density for a doped high-temperature superconductor will be modified and tuned based on the dynamics and density of the nanodots themselves.

  13. Anomalous Enhancement of the Superconducting Transition Temperature of Electron-doped La2-xCexCuO4 and Pr2-xCexCuO4 Cuprate Heterostructures

    SciTech Connect

    K Jin; P Vach; X Zhang; U Grupel; E Zohar; I Diamant; Y Dagan; S Smadici; P Abbamonte; R Greene

    2011-12-31

    The superconducting transition temperature T{sub c} of multilayers of electron-doped cuprates, composed of underdoped (or undoped) and overdoped La{sub 2-x}Ce{sub x}CuO{sub 4} (LCCO) and Pr{sub 2-x}Ce{sub x}CuO{sub 4} (PCCO) thin films, is found to increase significantly with respect to the T{sub c} of the corresponding single-phase films. By investigating the critical current density of superlattices with different doping levels and layer thicknesses, we find that the T{sub c} enhancement is caused by a redistribution of charge over an anomalously large distance.

  14. Graphene Superconducting Quantum Interference Device

    NASA Astrophysics Data System (ADS)

    Girit, Çaǧlar; Bouchiat, Vincent; Naaman, Ofer; Zhang, Yuanbo; Crommie, Michael; Zettl, Alex; Siddiqi, Irfan

    2010-03-01

    Graphene can support Cooper pair transport when contacted with two superconducting electrodes, resulting in the well-known Josephson effect. By depositing aluminum/palladium electrodes in the geometry of a loop onto a single graphene sheet, we fabricate a two junction dc superconducting quantum interference device (SQUID). Not only an the supercurrent in this device be increased by moving the electrostatic gate away from the Dirac point, but it can also be modulated periodically by an applied magnetic field---a potentially powerful probe of electronic transport in graphene. We analyze the magnetic field modulation of the critical current with the asymmetric/inductive SQUID model of Fulton and Dynes and discuss the variation of the fitting parameters with gate voltage.

  15. 119Sn-NMR investigations on superconducting Ca3Ir4Sn13: Evidence for multigap superconductivity

    DOE PAGESBeta

    Sarkar, R.; Petrovic, C.; Bruckner, F.; Gunther, M.; Wang, Kefeng; Biswas, P. K.; Luetkens, H.; Morenzoni, E.; Amato, A.; Klauss, H. -H.

    2015-09-25

    In this study, we report bulk superconductivity (SC) in Ca3Ir4Sn13 by means of 119Sn nuclear magnetic resonance (NMR) experiments. Two classical signatures of BCS superconductivity in spin-lattice relaxation rate (1/T1), namely the Hebel–Slichter coherence peak just below the Tc, and the exponential decay in the superconducting phase, are evident. The noticeable decrease of 119Sn Knight shift below Tc indicates spin-singlet superconductivity. The temperature dependence of the spin-lattice relaxation rate 119(1/T1) is convincingly described by the multigap isotropic superconducting gap. NMR experiments do not witness any sign of enhanced spin fluctuations.

  16. 119Sn-NMR investigations on superconducting Ca3Ir4Sn13: Evidence for multigap superconductivity

    NASA Astrophysics Data System (ADS)

    Sarkar, R.; Brückner, F.; Günther, M.; Wang, Kefeng; Petrovic, C.; Biswas, P. K.; Luetkens, H.; Morenzoni, E.; Amato, A.; Klauss, H.-H.

    2015-12-01

    We report bulk superconductivity (SC) in Ca3Ir4Sn13 by means of 119Sn nuclear magnetic resonance (NMR) experiments. Two classical signatures of BCS superconductivity in spin-lattice relaxation rate (1/T1), namely the Hebel-Slichter coherence peak just below the Tc, and the exponential decay in the superconducting phase, are evident. The noticeable decrease of 119Sn Knight shift below Tc indicates spin-singlet superconductivity. The temperature dependence of the spin-lattice relaxation rate 119(1/T1) is convincingly described by the multigap isotropic superconducting gap. NMR experiments do not witness any sign of enhanced spin fluctuations.

  17. The p-wave superconductivity in the presence of Rashba interaction in 2DEG.

    PubMed

    Weng, Ke-Chuan; Hu, C D

    2016-01-01

    We investigate the effect of the Rashba interaction on two dimensional superconductivity. The presence of the Rashba interaction lifts the spin degeneracy and gives rise to the spectrum of two bands. There are intraband and interband pairs scattering which result in the coupled gap equations. We find that there are isotropic and anisotropic components in the gap function. The latter has the form of cos φk where . The former is suppressed because the intraband and the interband scatterings nearly cancel each other. Hence, -the system should exhibit the p-wave superconductivity. We perform a detailed study of electron-phonon interaction for 2DEG and find that, if only normal processes are considered, the effective coupling strength constant of this new superconductivity is about one-half of the s-wave case in the ordinary 2DEG because of the angular average of the additional in the anisotropic gap function. By taking into account of Umklapp processes, we find they are the major contribution in the electron-phonon coupling in superconductivity and enhance the transition temperature Tc. PMID:27459677

  18. The p-wave superconductivity in the presence of Rashba interaction in 2DEG

    NASA Astrophysics Data System (ADS)

    Weng, Ke-Chuan; Hu, C. D.

    2016-07-01

    We investigate the effect of the Rashba interaction on two dimensional superconductivity. The presence of the Rashba interaction lifts the spin degeneracy and gives rise to the spectrum of two bands. There are intraband and interband pairs scattering which result in the coupled gap equations. We find that there are isotropic and anisotropic components in the gap function. The latter has the form of cos φk where . The former is suppressed because the intraband and the interband scatterings nearly cancel each other. Hence, ‑the system should exhibit the p-wave superconductivity. We perform a detailed study of electron-phonon interaction for 2DEG and find that, if only normal processes are considered, the effective coupling strength constant of this new superconductivity is about one-half of the s-wave case in the ordinary 2DEG because of the angular average of the additional in the anisotropic gap function. By taking into account of Umklapp processes, we find they are the major contribution in the electron-phonon coupling in superconductivity and enhance the transition temperature Tc.

  19. The p-wave superconductivity in the presence of Rashba interaction in 2DEG

    PubMed Central

    Weng, Ke-Chuan; Hu, C. D.

    2016-01-01

    We investigate the effect of the Rashba interaction on two dimensional superconductivity. The presence of the Rashba interaction lifts the spin degeneracy and gives rise to the spectrum of two bands. There are intraband and interband pairs scattering which result in the coupled gap equations. We find that there are isotropic and anisotropic components in the gap function. The latter has the form of cos φk where . The former is suppressed because the intraband and the interband scatterings nearly cancel each other. Hence, −the system should exhibit the p-wave superconductivity. We perform a detailed study of electron-phonon interaction for 2DEG and find that, if only normal processes are considered, the effective coupling strength constant of this new superconductivity is about one-half of the s-wave case in the ordinary 2DEG because of the angular average of the additional in the anisotropic gap function. By taking into account of Umklapp processes, we find they are the major contribution in the electron-phonon coupling in superconductivity and enhance the transition temperature Tc. PMID:27459677

  20. Unified picture of the doping dependence of superconducting transition temperatures in alkali metal/ammonia intercalated FeSe

    NASA Astrophysics Data System (ADS)

    Guterding, Daniel; Jeschke, Harald O.; Hirschfeld, P. J.; Valentí, Roser

    2015-01-01

    In the recently synthesized Lix(NH2)y(NH3)zFe2Se2 family of iron chalcogenides, a molecular spacer consisting of lithium ions, lithium amide, and ammonia separates the layers of FeSe. It has been shown that upon variation of the chemical composition of the spacer layer, superconducting transition temperatures can reach Tc˜44 K , but the relative importance of the layer separation and effective doping to the Tc enhancement is currently unclear. Using state of the art band structure unfolding techniques, we construct eight-orbital models from ab initio density functional theory calculations for these materials. Within an RPA spin-fluctuation approach, we show that the electron doping enhances the superconducting pairing, which is of s± symmetry and explain the experimentally observed limit to Tc in the molecular spacer intercalated FeSe class of materials.

  1. Pairing in a dry Fermi sea.

    PubMed

    Maier, T A; Staar, P; Mishra, V; Chatterjee, U; Campuzano, J C; Scalapino, D J

    2016-01-01

    In the traditional Bardeen-Cooper-Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin-fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability. PMID:27312569

  2. Pairing in a dry Fermi sea

    NASA Astrophysics Data System (ADS)

    Maier, T. A.; Staar, P.; Mishra, V.; Chatterjee, U.; Campuzano, J. C.; Scalapino, D. J.

    2016-06-01

    In the traditional Bardeen-Cooper-Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin-fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.

  3. High field superconducting magnets

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  4. Superconducting nanowire networks formed on nanoporous membrane substrates

    NASA Astrophysics Data System (ADS)

    Luo, Qiong

    Introducing a regular array of holes into superconducting thin films has been actively pursued to stabilize and pin the vortex lattice against external driving forces, enabling higher current capabilities. If the width of the sections between neighboring holes is comparable to the superconducting coherence length, the circulation of the Cooper pairs in around the holes in the presence of a magnetic field can also produce the Little-Parks effect, i.e. periodic oscillation of the critical temperature. These two mechanisms, commensurate vortex pinning enhancement by the hole-array and the critical temperature oscillations of a wire network due to Little-Parks effect can induce similar experimental observations such as magnetoresistance oscillation and enhancement of the critical current at specific magnetic fields. This dissertation work investigates the effect of a hole-array on the properties of superconducting films deposited onto nanoporous substrates. Experiments on anisotropies of the critical temperature for niobium films on anodic aluminum oxide membrane substrates containing a regular hole-array reveal that the critical temperature exhibits two strong anisotropic effects: Little-Parks oscillations whose period varies with field direction superimposed on a smooth background arising from one dimensional confinement by the finite lateral space between neighboring holes. The two components of the anisotropy are intrinsically linked and appear in concert. That is, the hole-array changes the dimensionality of a two-dimensional (2D) film to a network of 1D nanowire network. Network of superconducting nanowires with transverse dimensions as small as few nanometers were achieved by coating molybdenum germanium (MoGe) layer onto commercially available filtration membranes which have extremely dense nanopores. The magnetoresistance, magnetic field dependence of the critical temperature and the anisotropies of the synthesized MoGe nanowire networks can be consistently

  5. Superconductivity in Pd, Ir, and Pt chalcogenide

    NASA Astrophysics Data System (ADS)

    Oh, Yoon Seok; Yang, Junjie; Choi, Y. J.; Hogan, A.; Horibe, Y.; Cheong, S.-W.

    2012-02-01

    Large spin-orbit coupling in materials with heavy chalcogens can result in unique quantum states or functional properties such as topological insulator, giant thermoelectric power, and superconductivity. When materials contain heavy cations in addition to heavy chalcogens, spin-orbit coupling can be further enhanced. For these reasons, we have studied the superconductivity of Pd, Ir, and Pt tellurides and selenides. In the exploration of these chalcogenides, we have focused on the competition between superconductivity and charge density wave that is associated with superlattice reflections.

  6. Accelerator magnet designs using superconducting magnetic shields

    SciTech Connect

    Brown, B.C.

    1990-10-01

    Superconducting dipoles and quadrupoles for existing accelerators have a coil surrounded by an iron shield. The shield limits the fringe field of the magnet while having minimal effect on the field shape and providing a small enhancement of the field strength. Shields using superconducting materials can be thinner and lighter and will not experience the potential of a large de-centering force. Boundary conditions for these materials, material properties, mechanical force considerations, cryostat considerations and some possible geometrical configurations for superconducting shields will be described. 7 refs., 3 figs., 3 tabs.

  7. Experiments on a Cooper pair insulator

    NASA Astrophysics Data System (ADS)

    Nguyen, Hung Q.

    At temperatures below 1K, nm thick a-Bi/Sb films, patterned with a nanohoneycomb array of holes, exhibit a novel electronic state consisting of localized Cooper pairs[1]. The Superconductor Insulator Transition (SIT), a phenomenon where the ground state of electrons is tuned from a superconducting to an insulating state, on this patterned homogeneous system shows a clear bosonic nature with activated transport on the insulating side. To date, this homogeneous system is the only one that shows clear evidence for the localization of Cooper pairs. Experiments are described that were performed to further characterize the properties of the localized Cooper pair state and its superconductor to insulator transitions. We show that: (i) The shape of the magnetoresistance (MR) oscillations, which indicate the presence of Cooper pairs in these multiply connected systems, depends on the geometry of the underlying substrates, but not on parameters like the temperature or thickness of the films. The magnetic field tuned SITs of films that are just thick enough to superconduct at zero magnetic field exhibit a common critical sheet resistance separating the superconducting and insulating phases in the range of 3.5 to 5kO. We also report a new type of SIT, an incommensurability driven SIT, which occurs due to the interplay of magnetic field and disorder in the arrangement of the honeycomb array of holes. (ii) The Cooper pair insulator state exhibits a giant positive MR, which peaks at a field estimated to be sufficient to break the pairs. The electrical transport on the low field side of the peak is activated. At the highest fields, it resembles G ˜ log(T), which is consistent with the behavior expected for weakly localized electrons rather than strongly localized Cooper pairs. We discuss this MR peak, compare it to that observed in other amorphous systems and propose a zero temperature phase diagram for these films.

  8. Waiting times of entangled electrons in normal-superconducting junctions

    NASA Astrophysics Data System (ADS)

    Albert, M.; Chevallier, D.; Devillard, P.

    2016-02-01

    We consider a normal-superconducting junction in order to investigate the effect of new physical ingredients on waiting times. First, we study the interplay between Andreev and specular scattering at the interface on the distribution of waiting times of electrons or holes separately. In that case the distribution is not altered dramatically compared to the case of a single quantum channel with a quantum point contact since the interface acts as an Andreev mirror for holes. We then consider a fully entangled state originating from splitting of Cooper pairs at the interface and demonstrate a significant enhancement of the probability to detect two consecutive electrons in a short time interval. Finally, we discuss the electronic waiting time distribution in the more realistic situation of partial entanglement.

  9. Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2 H -TaS2 and 2 H -TaSe2

    NASA Astrophysics Data System (ADS)

    Freitas, D. C.; Rodière, P.; Osorio, M. R.; Navarro-Moratalla, E.; Nemes, N. M.; Tissen, V. G.; Cario, L.; Coronado, E.; García-Hernández, M.; Vieira, S.; Núñez-Regueiro, M.; Suderow, H.

    2016-05-01

    We present measurements of the superconducting and charge-density-wave (CDW) critical temperatures (Tc and TCDW) as a function of pressure in the transition metal dichalchogenides 2 H -TaSe2 and 2 H -TaS2 . Resistance and susceptibility measurements show that Tc increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2 H -TaS2 and 8.2 K at 23 GPa in 2 H -TaSe2 . We observe a kink in the pressure dependence of TCDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases, coexisting with superconductivity within our full pressure range.

  10. Superconducting magnet

    DOEpatents

    Satti, John A.

    1980-01-01

    A superconducting magnet designed to produce magnetic flux densities of the order of 4 to 5 Webers per square meter is constructed by first forming a cable of a plurality of matrixed superconductor wires with each wire of the plurality insulated from each other one. The cable is shaped into a rectangular cross-section and is wound with tape in an open spiral to create cooling channels. Coils are wound in a calculated pattern in saddle shapes to produce desired fields, such as dipoles, quadrupoles, and the like. Wedges are inserted between adjacent cables as needed to maintain substantially radial placement of the long dimensions of cross sections of the cables. After winding, individual strands in each of the cables are brought out to terminals and are interconnected to place all of the strands in series and to maximize the propagation of a quench by alternating conduction from an inner layer to an outer layer and from top half to bottom half as often as possible. Individual layers are separated from others by spiraled aluminum spacers to facilitate cooling. The wound coil is wrapped with an epoxy tape that is cured by heat and then machined to an interference fit with an outer aluminum pipe which is then affixed securely to the assembled coil by heating it to make a shrink fit. In an alternate embodiment, one wire of the cable is made of copper or the like to be heated externally to propagate a quench.

  11. Controlling superconductivity by tunable quantum critical points.

    PubMed

    Seo, S; Park, E; Bauer, E D; Ronning, F; Kim, J N; Shim, J-H; Thompson, J D; Park, Tuson

    2015-01-01

    The heavy fermion compound CeRhIn5 is a rare example where a quantum critical point, hidden by a dome of superconductivity, has been explicitly revealed and found to have a local nature. The lack of additional examples of local types of quantum critical points associated with superconductivity, however, has made it difficult to unravel the role of quantum fluctuations in forming Cooper pairs. Here, we show the precise control of superconductivity by tunable quantum critical points in CeRhIn5. Slight tin-substitution for indium in CeRhIn5 shifts its antiferromagnetic quantum critical point from 2.3 GPa to 1.3 GPa and induces a residual impurity scattering 300 times larger than that of pure CeRhIn5, which should be sufficient to preclude superconductivity. Nevertheless, superconductivity occurs at the quantum critical point of the tin-doped metal. These results underline that fluctuations from the antiferromagnetic quantum criticality promote unconventional superconductivity in CeRhIn5. PMID:25737108

  12. Tunable graphene dc superconducting quantum interference device.

    PubMed

    Girit, Caglar; Bouchiat, V; Naaman, O; Zhang, Y; Crommie, M F; Zettl, A; Siddiqi, I

    2009-01-01

    Graphene exhibits unique electrical properties on account of its reduced dimensionality and "relativistic" band structure. When contacted with two superconducting electrodes, graphene can support Cooper pair transport, resulting in the well-known Josephson effect. We report here the fabrication and operation of a two junction dc superconducting quantum interference device (SQUID) formed by a single graphene sheet contacted with aluminum/palladium electrodes in the geometry of a loop. The supercurrent in this device can be modulated not only via an electrostatic gate but also by an applied magnetic fielda potentially powerful probe of electronic transport in graphene and an ultrasensitive platform for nanomagnetometry. PMID:19090696

  13. Effects of the arrangement of triangle-winglet-pair vortex generators on heat transfer performance of the shell side of a double-pipe heat exchanger enhanced by helical fins

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Shang, Bojun; Meng, Huibo; Li, Yaxia; Wang, Cuihua; Gong, Bin; Wu, Jianhua

    2016-04-01

    To improve heat transfer performance of the shell side of a double-pipe heat exchanger enhanced by helical fins, triangle-winglet-pair vortex generators (VG) were installed along the centerline of the helical channel with rectangular cross section. The effects of the arrangement of the triangle-winglet-pair VG, such as the geometry, the angle of attack and the quantity on heat transfer performance and pressure drop characteristics have been investigated experimentally to find out the optimal design of the VG. Air was used as working fluid within the range of Re from 680 to 16,000. The results show that, the heat exchange effectiveness of the shell side with VG is 16.6 % higher than that without VG. The vortices and the unsteadiness of the flow introduced by the VG make a great contribution to the increase. Under identical pressure drop condition, the angle of attack of 30° is the best choice compared with 45° and 60°. Under the three constraints, i.e., identical mass flow rate, identical pressure drop and identical pumping power, the largest VG size can achieve the best enhancement effect. Installation of three pairs of VG within one pitch is an optimal design for the shell side used in the present experiments. The enhancement effect of isosceles right triangle is better than that of right triangle in which one acute angle is 30°.

  14. Theory of dirty Rashba superconductivity in ultrathin Pb films

    NASA Astrophysics Data System (ADS)

    Chen, Hua; Nam, Hyoungdo; Shih, Chih-Kang; MacDonald, Allan

    Pb is a typical s-wave superconductor and also has strong atomic spin-orbit coupling. In Pb thin films inversion symmetry breaking combined with the large atomic spin-orbit coupling will split the otherwise spin-degenerate bands of Pb, an effect which can be roughly accounted for by Rashba spin-orbit coupling. Motivated by a recent experiment, we used a 2D model involving Rashba spin-orbit coupling and s-wave pairing to study the influence of the former on the superfluid density, parallel critical field, and the resistive transition to the superconducting phase. We found that in both the clean and the dirty limits, Rashba spin-orbit coupling has little influence on the superfluid density and the Kosterlitz-Thouless transition temperature. However, in the dirty limit the Rashba spin-orbit coupling can significantly enhance the parallel critical field, making the Clogston-Chandrasekhar limit inapplicable. The strong suppression of the spin pair-breaking effect of a parallel magnetic field by the Rashba spin-orbit coupling and impurity scattering can make the orbital pair-breaking effect dominant again even in ultrathin films. Finally, we propose and examine a number of mechanisms that can lead to a smeared resistive transition under parallel magnetic fields. Supported by ONR-N00014-14-1-0330.

  15. FOREWORD: Focus on Superconductivity in Semiconductors Focus on Superconductivity in Semiconductors

    NASA Astrophysics Data System (ADS)

    Takano, Yoshihiko

    2008-12-01

    Since the discovery of superconductivity in diamond, much attention has been given to the issue of superconductivity in semiconductors. Because diamond has a large band gap of 5.5 eV, it is called a wide-gap semiconductor. Upon heavy boron doping over 3×1020 cm-3, diamond becomes metallic and demonstrates superconductivity at temperatures below 11.4 K. This discovery implies that a semiconductor can become a superconductor upon carrier doping. Recently, superconductivity was also discovered in boron-doped silicon and SiC semiconductors. The number of superconducting semiconductors has increased. In 2008 an Fe-based superconductor was discovered in a research project on carrier doping in a LaCuSeO wide-gap semiconductor. This discovery enhanced research activities in the field of superconductivity, where many scientists place particular importance on superconductivity in semiconductors. This focus issue features a variety of topics on superconductivity in semiconductors selected from the 2nd International Workshop on Superconductivity in Diamond and Related Materials (IWSDRM2008), which was held at the National Institute for Materials Science (NIMS), Tsukuba, Japan in July 2008. The 1st workshop was held in 2005 and was published as a special issue in Science and Technology of Advanced Materials (STAM) in 2006 (Takano 2006 Sci. Technol. Adv. Mater. 7 S1). The selection of papers describe many important experimental and theoretical studies on superconductivity in semiconductors. Topics on boron-doped diamond include isotope effects (Ekimov et al) and the detailed structure of boron sites, and the relation between superconductivity and disorder induced by boron doping. Regarding other semiconductors, the superconducting properties of silicon and SiC (Kriener et al, Muranaka et al and Yanase et al) are discussed, and In2O3 (Makise et al) is presented as a new superconducting semiconductor. Iron-based superconductors are presented as a new series of high

  16. Stimulated Superconductivity at Strong Coupling

    SciTech Connect

    Bao, Ning; Dong, Xi; Silverstein, Eva; Torroba, Gonzalo; /Stanford U., ITP /Stanford U., Phys. Dept. /SLAC

    2011-08-12

    Stimulating a system with time dependent sources can enhance instabilities, thus increasing the critical temperature at which the system transitions to interesting low-temperature phases such as superconductivity or superfluidity. After reviewing this phenomenon in non-equilibrium BCS theory (and its marginal fermi liquid generalization) we analyze the effect in holographic superconductors. We exhibit a simple regime in which the transition temperature increases parametrically as we increase the frequency of the time-dependent source.

  17. Simple Superconducting "Permanent" Electromagnet

    NASA Technical Reports Server (NTRS)

    Israelson, Ulf E.; Strayer, Donald M.

    1992-01-01

    Proposed short tube of high-temperature-superconducting material like YBa2Cu3O7 acts as strong electromagnet that flows as long as magnetic field remains below critical value and temperature of cylinder maintained sufficiently below superconducting-transition temperature. Design exploits maximally anisotropy of high-temperature-superconducting material.

  18. Coexistence of ferromagnetism and superconductivity in YBCO nanoparticles.

    PubMed

    Zhu, Zhonghua; Gao, Daqiang; Dong, Chunhui; Yang, Guijin; Zhang, Jing; Zhang, Jinlin; Shi, Zhenhua; Gao, Hua; Luo, Honggang; Xue, Desheng

    2012-03-21

    Nanoparticles of superconducting YBa(2)Cu(3)O(7-δ) were synthesized via a citrate pyrolysis technique. Room temperature ferromagnetism was revealed in the samples by a vibrating sample magnetometer. Electron spin resonance spectra at selected temperatures indicated that there is a transition from the normal to the superconducting state at temperatures below 100 K. The M-T curves with various applied magnetic fields showed that the superconducting transition temperatures are 92 K and 55 K for the air-annealed and the post-annealed samples, respectively. Compared to the air-annealed sample, the saturation magnetization of the sample by reheating the air-annealed one in argon atmosphere is enhanced but its superconductivity is weakened, which implies that the ferromagnetism maybe originates from the surface oxygen defects. By superconducting quantum interference device measurements, we further confirmed the ferromagnetic behavior at high temperatures and interesting upturns in field cooling magnetization curves within the superconducting region are found. We attributed the upturn phenomena to the coexistence of ferromagnetism and superconductivity at low temperatures. Room temperature ferromagnetism of superconducting YBa(2)Cu(3)O(7-δ) nanoparticles has been observed in some previous related studies, but the issue of the coexistence of ferromagnetism and superconductivity within the superconducting region is still unclear. In the present work, it will be addressed in detail. The cooperation phenomena found in the spin-singlet superconductors will help us to understand the nature of superconductivity and ferromagnetism in more depth. PMID:22327377

  19. Development of high magnetic field superconducting magnet technology and applications in China

    NASA Astrophysics Data System (ADS)

    Wang, Qiuliang; Dai, Yingming; Zhao, Baozhi; Song, Shouseng; Lei, Yuanzhong; Wang, Houseng; Ye, Bai; Hu, Xinning; Huang, Tianbing; Wang, Hui; He, Chu; Shang, Muxi; Wang, Chao; Cui, Chunyan; Zhao, Shangwu; Zhang, Quan; Diao, Yanhua; Peng, Yan; Xu, Guoxin; Deng, Fanping; Weng, Peide; Kuang, Guangli; Gao, Bingjun; Lin, Liangzhen; Yan, Luguang

    2007-07-01

    High magnetic field superconducting magnet technology has been developed in the recent years for all kinds of applications in China. The superconducting magnets on the basis of the conduction-cooled high (HTS) and lower temperature superconductor (LTS) through GM cryocooler are designed, fabricated and operated for the magnetic separator, superconducting magnet energy storage system (SMES), material processing, gyrotron, electromagnetic launcher, space anti-matter detection, magnetic surgery system (MSS), heavy ion accelerator dipole magnet and test bed for characteristics of superconducting material in Institute of Electrical Engineering, Chinese Academy of Sciences (IEECAS). The EAST superconducting Tokamak is being fabricated in Institute of Plasma Physics, Chinese Academy of Sciences. In the paper, we report the successful development of high magnetic field superconducting magnet technology in China. Some new research projects, such as 40 T hybrid magnet, 25 T high magnetic field superconducting magnet, split-pair magnets for the pallation Neutron Source, high temperature superconducting coils for MSS and MRI are introduced.

  20. Superconducting electron and hole lenses

    NASA Astrophysics Data System (ADS)

    Cheraghchi, H.; Esmailzadeh, H.; Moghaddam, A. G.

    2016-06-01

    We show how a superconducting region (S), sandwiched between two normal leads (N), in the presence of barriers, can act as a lens for propagating electron and hole waves by virtue of the so-called crossed Andreev reflection (CAR). The CAR process, which is equivalent to Cooper pair splitting into two N electrodes, provides a unique possibility of constructing entangled electrons in solid state systems. When electrons are locally injected from an N lead, due to the CAR and normal reflection of quasiparticles by the insulating barriers at the interfaces, sequences of electron and hole focuses are established inside another N electrode. This behavior originates from the change of momentum during electron-hole conversion beside the successive normal reflections of electrons and holes due to the barriers. The focusing phenomena studied here are fundamentally different from the electron focusing in other systems, such as graphene p-n junctions. In particular, due to the electron-hole symmetry of the superconducting state, the focusing of electrons and holes is robust against thermal excitations. Furthermore, the effects of the superconducting layer width, the injection point position, and barrier strength are investigated on the focusing behavior of the junction. Very intriguingly, it is shown that by varying the barrier strength, one can separately control the density of electrons or holes at the focuses.

  1. Phase coherence and pairing amplitude in photo-excited superconductors

    NASA Astrophysics Data System (ADS)

    Perfetti, Luca; Piovera, Christian; Zhang, Zailan

    2016-05-01

    New data on Bi2Sr2CaCu2O8+δ (Bi2212) reveal interesting aspects of photoexcited superconductors. The electrons dynamics show that inelastic scattering by nodal quasiparticles decreases when the temperature is lowered below the critical value of the superconducting phase transition. This drop of electronic dissipation is astonishingly robust and survives to photoexcitation densities much larger than the value sustained by long-range superconductivity. The unconventional behavior of quasiparticle scattering is ascribed to superconducting correlations extending on a length scale comparable to the inelastic mean-free path. Our measurements indicate that strongly driven superconductors enter in a regime without phase coherence but finite pairing amplitude.

  2. Metal-insulator transition near a superconducting state

    NASA Astrophysics Data System (ADS)

    Kaveh, M.; Mott, N. F.

    1992-03-01

    We show that when the metal-insulation transition occurs near a superconducting state it results in a different critical behavior from that of amorphous metals or uncompensated doped semiconductors. This difference results from the enhancement of the effective electron-electron interaction caused by fluctuations to the superconducting state. This explains the recent experiments of Micklitz and co-workers on amorphous superconducting mixtures Ga-Ar and Bi-Kr.

  3. Magnetic Fluctuations in Pair-Density-Wave Superconductors.

    PubMed

    Christensen, Morten H; Jacobsen, Henrik; Maier, Thomas A; Andersen, Brian M

    2016-04-22

    Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d-wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La_{1.905}Ba_{0.095}CuO_{4} [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)]. PMID:27152819

  4. Magnetic Fluctuations in Pair-Density-Wave Superconductors

    NASA Astrophysics Data System (ADS)

    Christensen, Morten H.; Jacobsen, Henrik; Maier, Thomas A.; Andersen, Brian M.

    2016-04-01

    Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d -wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La1.905 Ba0.095 CuO4 [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)].

  5. Cooper-pair splitter: towards an efficient source of spin-entangled EPR pairs

    NASA Astrophysics Data System (ADS)

    Schonenberger, Christian

    2011-03-01

    In quantum mechanics the properties of two and more particles can be entangled. In basic science pairs of entangled particles, so called Einstein-Podolsky-Rosen (EPR) pairs, play a special role as toy objects for fundamental studies. They provide such things as ``spooky interaction at distance,'' but they also enable secure encoding and teleportation and are thus important for applications in quantum information technology. Whereas EPR pairs of photons can be generated by parametric down conversion (PDC) in a crystal, a similar source for EPR pairs of electrons does not exists yet. In several theory papers, it has been suggested to use a superconductor for this purpose. The superconducting ground state is formed by a condensate of Cooper-pairs which are electron pairs in a spin-singlet state. Since there are many Cooper pairs in a metallic superconductor like Al, the main tasks are to extract Cooper pairs one by one and to split them into different arms. A controlled and efficient splitting is possible if one makes use of Coulomb interaction. This has recently be demonstrated by two groups [2-4] using hybrid quantum-dot devices with both superconducting and normal metal contacts. In the present talk, I will discuss the Cooper-pair splitter results from the Basel-Budapest-Copenhagen team and compare with the other experiments. As an outlook we discuss approaches that aim at entanglement detection. The Cooper pair splitter holds great promises because very large splitting efficiencies approaching 100% and large pair current rates appear feasible. This work has been done by L. Hofstetter, S. Csonka, A. Geresdi, M. Aagesen, J. Nygard and C. Schönenberger

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

    PubMed Central

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

    2015-01-01

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

  7. Anomalous independence of interface superconductivity from carrier density.

    PubMed

    Wu, J; Pelleg, O; Logvenov, G; Bollinger, A T; Sun, Y-J; Boebinger, G S; Vanević, M; Radović, Z; Božović, I

    2013-10-01

    The recent discovery of superconductivity at the interface of two non-superconducting materials has received much attention. In cuprate bilayers, the critical temperature (Tc) can be significantly enhanced compared with single-phase samples. Several explanations have been proposed, invoking Sr interdiffusion, accumulation and depletion of mobile charge carriers, elongation of the copper-to-apical-oxygen bond length, or a beneficial crosstalk between a material with a high pairing energy and another with a large phase stiffness. From each of these models, one would predict Tc to depend strongly on the carrier density in the constituent materials. Here, we study combinatorial libraries of La(2-x)Sr(x)CuO4-La2CuO4 bilayer samples--an unprecedentedly large set of more than 800 different compositions. The doping level x spans a wide range, 0.15 < x < 0.47, and the measured Hall coefficient varies by one order of magnitude. Nevertheless, across the entire sample set, Tc stays essentially constant at about 40 K. We infer that doping up to the optimum level does not shift the chemical potential, unlike in ordinary Fermi liquids. This result poses a new challenge to theory--cuprate superconductors have not run out of surprises. PMID:23913171

  8. Angular Dependence of Superconductivity in Superconductor / Spin Valve Heterostructures

    NASA Astrophysics Data System (ADS)

    Jara, Alejandro; Safranski, Christopher; Krivorotov, Ilya; Wu, Chien-Te; Valls, Oriol

    2014-03-01

    The superconducting condensate in superconductor / ferromagnet (S/F) multilayers consists of singlet and triplet components. For a non-collinear state of magnetization of the multilayer, all three spin components Sz =(0 , +/- 1) of the triplet condensate are generally non-zero, which can result in a long range proximity effect in S/F multilayers. Indeed, the Sz = +/- 1 triplet components of the condensate are immune to pair breaking by the exchange field and, unlike the singlet and the Sz = 0 triplet components, they can penetrate deep into the ferromagnetic layers. Here we report measurements demonstrating magnetic control of the triplet component amplitude in Nb/Co/Cu/Co/CoOx superconducting spin valves. We find that for all values of the layer thicknesses employed in the experiment, Tc shows non-monotonic angular dependence with a minimum near perpendicular orientation of the Co layers. This drop in Tc is evidence of the enhanced long-range triplet amplitude in the maximally non-collinear configuration of the spin valve. We will present detailed measurements of the magnitude of this effect as a function of thicknesses of both Co and Cu layers of the spin valve. We will also compare our data to theoretical predictions of the angular dependence of Tc for this system.

  9. Luminescence and squeezing of a superconducting light-emitting diode

    NASA Astrophysics Data System (ADS)

    Hlobil, Patrik; Orth, Peter P.

    2015-05-01

    We investigate a semiconductor p -n junction in contact with superconducting leads that is operated under forward bias as a light-emitting diode. The presence of superconductivity results in a significant increase of the electroluminescence in a sharp frequency window. We demonstrate that the tunneling of Cooper pairs induces an additional luminescence peak on resonance. There is a transfer of superconducting to photonic coherence that results in the emission of entangled photon pairs and squeezing of the fluctuations in the quadrature amplitudes of the emitted light. We show that the squeezing angle can be electrically manipulated by changing the relative phase of the order parameters in the superconductors. We finally derive the conditions for lasing in the system and show that the laser threshold is reduced due to superconductivity. This reveals how the macroscopic coherence of a superconductor can be used to control the properties of light.

  10. Protective link for superconducting coil

    DOEpatents

    Umans, Stephen D.

    2009-12-08

    A superconducting coil system includes a superconducting coil and a protective link of superconducting material coupled to the superconducting coil. A rotating machine includes first and second coils and a protective link of superconducting material. The second coil is operable to rotate with respect to the first coil. One of the first and second coils is a superconducting coil. The protective link is coupled to the superconducting coil.

  11. Phonon limited superconducting correlations in metallic nanograins

    NASA Astrophysics Data System (ADS)

    Croitoru, M. D.; Shanenko, A. A.; Vagov, A.; Milošević, M. V.; Axt, V. M.; Peeters, F. M.

    2015-11-01

    Conventional superconductivity is inevitably suppressed in ultra-small metallic grains for characteristic sizes smaller than the Anderson limit. Experiments have shown that above the Anderson limit the critical temperature may be either enhanced or reduced when decreasing the particle size, depending on the superconducting material. In addition, there is experimental evidence that whether an enhancement or a reduction is found depends on the strength of the electron-phonon interaction in the bulk. We reveal how the strength of the e-ph interaction interplays with the quantum-size effect and theoretically obtain the critical temperature of the superconducting nanograins in excellent agreement with experimental data. We demonstrate that strong e-ph scattering smears the peak structure in the electronic density-of-states of a metallic grain and enhances the electron mass, and thereby limits the highest Tc achievable by quantum confinement.

  12. Phonon limited superconducting correlations in metallic nanograins

    PubMed Central

    Croitoru, M. D.; Shanenko, A. A.; Vagov, A.; Milošević, M. V.; Axt, V. M.; Peeters, F. M.

    2015-01-01

    Conventional superconductivity is inevitably suppressed in ultra-small metallic grains for characteristic sizes smaller than the Anderson limit. Experiments have shown that above the Anderson limit the critical temperature may be either enhanced or reduced when decreasing the particle size, depending on the superconducting material. In addition, there is experimental evidence that whether an enhancement or a reduction is found depends on the strength of the electron-phonon interaction in the bulk. We reveal how the strength of the e-ph interaction interplays with the quantum-size effect and theoretically obtain the critical temperature of the superconducting nanograins in excellent agreement with experimental data. We demonstrate that strong e-ph scattering smears the peak structure in the electronic density-of-states of a metallic grain and enhances the electron mass, and thereby limits the highest Tc achievable by quantum confinement. PMID:26565073

  13. Superconductivity in transition metals.

    PubMed

    Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified. PMID:25666075

  14. Pairing, pseudogap and Fermi arcs in cuprates

    SciTech Connect

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; Gu, Genda

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scattering creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.

  15. Demons and superconductivity

    SciTech Connect

    Ihm, J.; Cohen, M.L.; Tuan, S.F.

    1981-04-01

    Model calculations are used to explore the role of demons (acoustic plasmons involving light and heavy mass carriers) in superconductivity. Heavy d electrons and light s and p electrons in a transition metal are used for discussion, but the calculation presented is more general, and the results can be applied to other systems. The analysis is based on the dielectric-function approach and the Bardeen-Cooper-Schrieffer theory. The dielectric function includes intraband and interband s-d scattering, and a tight-binding model is used to examine the role of s-d hybridization. The demon contribution generally reduces the Coulomb interaction between the electrons. Under suitable conditions, the model calculations indicate that the electron-electron interaction via demons can be attractive, but the results also suggest that this mechanism is probably not dominant in transition metals and transition-metal compounds. An attractive interband contribution is found, and it is proposed that this effect may lead to pairing in suitable systems.

  16. The spin bag mechanism of high temperature superconductivity

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  17. 2D barrier in a superconducting niobium square

    SciTech Connect

    Joya, Miryam R. Barba-ortega, J.; Sardella, Edson

    2014-11-05

    The presence of barriers changes the vortex structure in superconducting Nb square in presence of a uniform applied magnetic field. The Cooper pair configurations in a mesoscopics superconducting square of Nb with a barrier are calculated within the nonlinear Ginzburg Landau equations. We predict the nucleation of multi-vortex states into the sample and a soft entry of the magnetic field inside and around into the barrier. A novel and non-conventional vortex configurations occurs at determined magnetic field.

  18. Emergent vortices at a ferromagnetic superconducting oxide interface

    NASA Astrophysics Data System (ADS)

    Petrović, A. P.; Paré, A.; Paudel, T. R.; Lee, K.; Holmes, S.; Barnes, C. H. W.; David, A.; Wu, T.; Tsymbal, E. Y.; Panagopoulos, C.

    2014-10-01

    Understanding the cohabitation arrangements of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface remains an open challenge. Probing this coexistence with sub-Kelvin magnetotransport experiments, we demonstrate that a hysteretic in-plane magnetoresistance develops below the superconducting transition for ≤ft| {{H}//} \\right| \\lt 0.15 T, independently of the carrier density or oxygen annealing. This hysteresis is argued to arise from vortex depinning within a thin (\\lt 20 nm) superconducting layer, mediated by discrete ferromagnetic dipoles located solely above the layer. The pinning strength may be modified by varying the superconducting channel thickness via electric field-effect doping. No evidence is found for bulk magnetism or finite-momentum pairing, and we conclude that ferromagnetism is strictly confined to the interface, where it competes with superconductivity. Our work indicates that oxide interfaces are ideal candidate materials for the growth and analysis of nanoscale superconductor/ferromagnet hybrids.

  19. Exact Results on Superconductivity due to Interband Coupling

    NASA Astrophysics Data System (ADS)

    Morita, Yoshifumi; Hatsugai, Yasuhiro; Kohmoto, Mahito

    1996-03-01

    We have constructed exactly solvable models at arbitrary filling in any dimensions which exhibit novel superconductivity with interband pairing. By the use of the hidden SU algebra the Hamiltonians are diagonalized explicitly. The zero-temperature phase diagrams and the thermodynamic properties are obtained. Several new properties are revealed which are totally different from those of the BCS-type superconductors. For example, superconductivity without a Fermi surface, which was proposed by Kohmoto and Takada footnote M. Kohmoto and Y. Takada, J. Phys. Soc. Jpn. 59, 1541 (1990)., is realized and a finite strength of attraction is needed to produce the superconductivity.

  20. Intra-versus interlayer pairing in the copper oxide superdonductors: Response to a magnetic field

    SciTech Connect

    Klemm, R.A.; Liu, Samuel H.

    1994-01-01

    We have investigated the response of layered- superconductors to an external magnetic field using the semiclassical phase approximation. The linearized-gap equations have been derived, and solved numerically to calculate the upper critical field H{sub c2}(T) for layered superconductors with one or two layers per unit cell for both s-wave and interlayer BCS-like pairing mechanisms. In the weak-hopping limit the equations reduce to the Lawrence-Doniach form, and for general hopping the appropriate gap equations are derived and numerically analyzed. One encounters the familiar dimensional crossover in the H{sub c2}{parallel}(T) curve for weak hopping. A different type of dimensional crossover can occur in the two-layer case with unequal intralayer or interlayer coupling strengths, such that at the dimensional crossover temperature, the magnetic field suppresses the superconductivity in the weakly coupled layers while leaving the strongly coupled layers superconducting. The effect is enhanced by unequal hopping strengths. The flux lattice consists of alternating superconducting and normal layers.

  1. Increased superconducting transition temperature of a niobium thin film proximity coupled to gold nanoparticles using linking organic molecules.

    PubMed

    Katzir, Eran; Yochelis, Shira; Zeides, Felix; Katz, Nadav; Kalcheim, Yaov; Millo, Oded; Leitus, Gregory; Myasodeyov, Yuri; Shapiro, Boris Ya; Naaman, Ron; Paltiel, Yossi

    2012-03-01

    The superconducting critical temperature, T(C), of thin Nb films is significantly modified when gold nanoparticles (NPs) are chemically linked to the Nb film, with a consistent enhancement when using 3 nm long disilane linker molecules. The T(C) increases by up to 10% for certain linker length and NP size. No change is observed when the nanoparticles are physisorbed with nonlinking molecules. Electron tunneling spectra acquired on the linked NPs below T(C) typically exhibit zero-bias peaks. We attribute these results to a pairing mechanism coupling electrons in the Nb and the NPs, mediated by the organic linkers. PMID:22463444

  2. Increased Superconducting Transition Temperature of a Niobium Thin Film Proximity Coupled to Gold Nanoparticles Using Linking Organic Molecules

    NASA Astrophysics Data System (ADS)

    Katzir, Eran; Yochelis, Shira; Zeides, Felix; Katz, Nadav; Kalcheim, Yaov; Millo, Oded; Leitus, Gregory; Myasodeyov, Yuri; Shapiro, Boris Ya.; Naaman, Ron; Paltiel, Yossi

    2012-03-01

    The superconducting critical temperature, TC, of thin Nb films is significantly modified when gold nanoparticles (NPs) are chemically linked to the Nb film, with a consistent enhancement when using 3 nm long disilane linker molecules. The TC increases by up to 10% for certain linker length and NP size. No change is observed when the nanoparticles are physisorbed with nonlinking molecules. Electron tunneling spectra acquired on the linked NPs below TC typically exhibit zero-bias peaks. We attribute these results to a pairing mechanism coupling electrons in the Nb and the NPs, mediated by the organic linkers.

  3. Understanding the reentrant superconducting phase diagram of the iron pnictide Ca4Al2O6Fe2(As1-xPx)2: First-principles calculations

    NASA Astrophysics Data System (ADS)

    Usui, Hidetomo; Suzuki, Katsuhiro; Kuroki, Kazuhiko; Takeshita, Nao; Shirage, Parasharam Maruti; Eisaki, Hiroshi; Iyo, Akira

    2013-05-01

    Recently, a very rich phase diagram has been obtained for an iron-based superconductor Ca4Al2O6Fe2(As1-xPx)2. It has been revealed that nodeless (x˜0) and nodal (x=1) superconductivity are separated by an antiferromagnetic phase. Here we study the origin of this peculiar phase diagram using a five orbital model constructed from first-principles band calculation, and applying the fluctuation exchange approximation assuming spin-fluctuation-mediated pairing. At x=1, there are three hole Fermi surfaces, but the most inner one around the wave vector (0,0) has strong dX2-Y2 orbital character, unlike in LaFeAsO, where the most inner Fermi surface has dXZ/YZ character. Since the Fermi surfaces around (0,0), (π,0), and (π,π) all have dX2-Y2 orbital character, the repulsive pairing interaction mediated by the spin fluctuations gives rise to a frustration in momentum space, thereby degrading superconductivity despite the bond angle being close to the regular tetrahedron angle. As x decreases and the bond angle is reduced, the inner hole Fermi surface disappears, but the frustration effect still remains because the top of the band with dX2-Y2 character lies close to the Fermi level. On the other hand, the loss of the Fermi surface itself gives rise to a very good nesting of the Fermi surface because the number of electron and hole Fermi surfaces are now the same. The pairing interaction frustration and the good nesting combined favors antiferromagnetism over superconductivity. Finally for x close to 0, the band sinks far below the Fermi level, reducing the frustration effect, so that superconductivity is enhanced. There, the Fermi surface nesting is also lost to some extent, once again favoring superconductivity over antiferromagnetism. To see whether the present theoretical scenario is consistent with the actual nature of the competition between superconductivity and antiferromagnetism, we also perform hydrostatic pressure experiment for Ca4Al2O6Fe2(As1-xPx)2. In the

  4. Superconducting circuitry for quantum electromechanical systems

    NASA Astrophysics Data System (ADS)

    LaHaye, Matthew D.; Rouxinol, Francisco; Hao, Yu; Shim, Seung-Bo; Irish, Elinor K.

    2015-05-01

    Superconducting systems have a long history of use in experiments that push the frontiers of mechanical sensing. This includes both applied and fundamental research, which at present day ranges from quantum computing research and e orts to explore Planck-scale physics to fundamental studies on the nature of motion and the quantum limits on our ability to measure it. In this paper, we first provide a short history of the role of superconducting circuitry and devices in mechanical sensing, focusing primarily on efforts in the last decade to push the study of quantum mechanics to include motion on the scale of human-made structures. This background sets the stage for the remainder of the paper, which focuses on the development of quantum electromechanical systems (QEMS) that incorporate superconducting quantum bits (qubits), superconducting transmission line resonators and flexural nanomechanical elements. In addition to providing the motivation and relevant background on the physical behavior of these systems, we discuss our recent efforts to develop a particular type of QEMS that is based upon the Cooper-pair box (CPB) and superconducting coplanar waveguide (CPW) cavities, a system which has the potential to serve as a testbed for studying the quantum properties of motion in engineered systems.

  5. On the conditions for enhanced transport through molecular junctions based on metal centres ligated by pairs of pyridazino-derived ligands

    SciTech Connect

    Ding, Bei; Washington, Victoria; Dunietz, Barry D

    2010-10-10

    Transport properties of a Ni bis-η{sup 2} complex ligated by a pair of bi-pyridazino derivative are considered. This complex provides the opportunity to avoid perpendicular alignment of the ligand π planes. We study the effects of π-bonding and of intramolecular hydrogen bonding between the ligands as mediated by the metal centre on electron transport. The complicated effect of the electronic structure equilibration with the electrodes on the transport is discussed. The analysis at the electronic structure level provides guidelines to design a molecular bridge that is based on metal complexation with effective electronic transport.

  6. Mesoscopic superconductivity in ultrasmall metallic grains

    SciTech Connect

    Alhassid, Y.; Nesterov, K. N.

    2014-10-15

    A nano-scale metallic grain (nanoparticle) with irregular boundaries in which the single-particle dynamics are chaotic is a zero-dimensional system described by the so-called universal Hamiltonian in the limit of a large number of electrons. The interaction part of this Hamiltonian includes a superconducting pairing term and a ferromagnetic exchange term. Spin-orbit scattering breaks spin symmetry and suppresses the exchange interaction term. Of particular interest is the fluctuation-dominated regime, typical of the smallest grains in the experiments, in which the bulk pairing gap is comparable to or smaller than the single-particle mean-level spacing, and the Bardeen-Cooper-Schrieffer (BCS) mean-field theory of superconductivity is no longer valid. Here we study the crossover between the BCS and fluctuation-dominated regimes in two limits. In the absence of spin-orbit scattering, the pairing and exchange interaction terms compete with each other. We describe the signatures of this competition in thermodynamic observables, the heat capacity and spin susceptibility. In the presence of strong spin-orbit scattering, the exchange interaction term can be ignored. We discuss how the magnetic-field response of discrete energy levels in such a nanoparticle is affected by pairing correlations. We identify signatures of pairing correlations in this response, which are detectable even in the fluctuation-dominated regime.

  7. Casimir effect mechanism of pairing between fermions in the vicinity of a magnetic quantum critical point

    NASA Astrophysics Data System (ADS)

    Kharkov, Yaroslav; Oleg P Sushkov Team

    We consider two spin 1 / 2 fermions in a two-dimensional magnetic system that is close to the O (3) magnetic quantum critical point (QCP) which separates magnetically ordered and disordered phases. Focusing on the disordered phase in the vicinity of the QCP, we demonstrate that the criticality results in a strong long range attraction between the fermions, with potential V (r) ~ - 1 /rα , α ~ 0 . 75 , where r is separation between the fermions. The mechanism of the enhanced attraction is similar to Casimir effect and corresponds to multi-magnon exchange processes between the fermions. While we consider a model system, the problem is originally motivated by recent experimental establishment of magnetic QCP in hole doped cuprates under the superconducting dome at doping of about 10%. We suggest the mechanism of magnetic critical enhancement of pairing in cuprates.

  8. Disorder-induced inhomogeneities of the superconducting state close to the superconductor-insulator transition.

    SciTech Connect

    Sacepe, B.; Chapelier, C.; Baturina, T. I.; Vinokur, V. M.; Baklanov, M. R.; Sanquer, M.; Materials Science Division; CEA, INAC; Inst. Semiconductor Physics; IMEC

    2008-01-01

    Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconducting titanium nitride thin films reveals strong spatial inhomogeneities of the superconducting gap {Delta} in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature T{sub c} towards zero, enhancement of spatial fluctuations in {Delta}, and growth of the {Delta}/T{sub c} ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.

  9. Superconducting levitating bearing

    NASA Technical Reports Server (NTRS)

    Moon, Francis C. (Inventor)

    1996-01-01

    A superconducting bearing assembly includes a coil field source that may be superconducting and a superconducting structure. The coil field source assembly and superconducting structure are positioned so as to enable relative rotary movement therebetween. The structure and coil field source are brought to a supercooled temperature before a power supply induces a current in the coil field source. A Meissner-like effect is thereby obtained and little or no penetration of the field lines is seen in the superconducting structure. Also, the field that can be obtained from the superconducting coil is 2-8 times higher than that of permanent magnets. Since the magnetic pressure is proportioned to the square of the field, magnetic pressures from 4 to 64 times higher are achieved.

  10. Superconducting radiofrequency window assembly

    DOEpatents

    Phillips, H.L.; Elliott, T.S.

    1997-03-11

    The present invention is a superconducting radiofrequency window assembly for use in an electron beam accelerator. The srf window assembly has a superconducting metal-ceramic design. The srf window assembly comprises a superconducting frame, a ceramic plate having a superconducting metallized area, and a superconducting eyelet for sealing plate into frame. The plate is brazed to eyelet which is then electron beam welded to frame. A method for providing a ceramic object mounted in a metal member to withstand cryogenic temperatures is also provided. The method involves a new metallization process for coating a selected area of a ceramic object with a thin film of a superconducting material. Finally, a method for assembling an electron beam accelerator cavity utilizing the srf window assembly is provided. The procedure is carried out within an ultra clean room to minimize exposure to particulates which adversely affect the performance of the cavity within the electron beam accelerator. 11 figs.

  11. Superconductive radiofrequency window assembly

    DOEpatents

    Phillips, H.L.; Elliott, T.S.

    1998-05-19

    The present invention is a superconducting radiofrequency window assembly for use in an electron beam accelerator. The SRF window assembly has a superconducting metal-ceramic design. The SRF window assembly comprises a superconducting frame, a ceramic plate having a superconducting metallized area, and a superconducting eyelet for sealing plate into frame. The plate is brazed to eyelet which is then electron beam welded to frame. A method for providing a ceramic object mounted in a metal member to withstand cryogenic temperatures is also provided. The method involves a new metallization process for coating a selected area of a ceramic object with a thin film of a superconducting material. Finally, a method for assembling an electron beam accelerator cavity utilizing the SRF window assembly is provided. The procedure is carried out within an ultra clean room to minimize exposure to particulates which adversely affect the performance of the cavity within the electron beam accelerator. 11 figs.

  12. High-Temperature Superconductivity

    NASA Astrophysics Data System (ADS)

    Tanaka, Shoji

    2006-12-01

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

  13. High Temperature Superconducting Materials Database

    National Institute of Standards and Technology Data Gateway

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

  14. Superconductive imaging surface magnetometer

    DOEpatents

    Overton, Jr., William C.; van Hulsteyn, David B.; Flynn, Edward R.

    1991-01-01

    An improved pick-up coil system for use with Superconducting Quantum Interference Device gradiometers and magnetometers involving the use of superconducting plates near conventional pick-up coil arrangements to provide imaging of nearby dipole sources and to deflect environmental magnetic noise away from the pick-up coils. This allows the practice of gradiometry and magnetometry in magnetically unshielded environments. One embodiment uses a hemispherically shaped superconducting plate with interior pick-up coils, allowing brain wave measurements to be made on human patients. another embodiment using flat superconducting plates could be used in non-destructive evaluation of materials.

  15. Multiband effects on the superconductivity in doped C[sub 60

    SciTech Connect

    Choi, H. ); Rice, M.J. )

    1994-03-01

    We consider multiband effects on the superconductivity in the alkali-doped fullerenes. It is shown that the multiband superconducting gap is reduced to the well-known Bardeen-Cooper-Schrieffer expression due to a cyclic symmetry in the orientationally ordered phases, thereby justifying many previous works assuming single-band [ital s]-wave pairing without considering several conduction bands explicitly.

  16. Nuclear Magnetic Resonance in the Superconducting States of Two Heavy Fermion Superconductors, Cerium Dicopper - and URANIUM-BERYLLIUM(13)

    NASA Astrophysics Data System (ADS)

    Tien, Cheng

    Nuclear magnetic resonance (NMR) experiments have been carried out in two heavy fermion superconductors, CeCu(,2)Si(,2) and U(,1-x)Th(,x)Be(,13) (x = 0, 0.0331). The unusual normal-state and superconducting state behavior of CeCu(,2)SDi(,2) and UBe(,13) has recently been discovered. Both compounds exhibit enormous values of the normal-state low -temperature magnetic susceptibility (chi) and the linear specific heat coefficient (gamma). Standard analyses of (chi) and (gamma) result in a two order of magnitude enhancement of the conduction-electron mass, but the ratio (chi)/(gamma) retains a value appropriate to a free-electron gas. It is of interest to obtain as much microscopic information as possible. In one of our CeCu(,2)Si(,2) superconducting specimens, the observed temperature dependence of the spin-lattice relaxation rate 1/T(,1) (T) is consistent with a conventional quasiparticle excitation spectrum below the superconducting transition temperature T(,c). In the other superconducting CeCu(,2)Si(,2) sample, the nuclear spin-lattice relaxation rate decreases drastically just below T(,c) without the apparent enhancement observed in the first sample. This lack of enhancement in 1/T(,1) (T) suggests that the superconductivity in CeCu(,2)Si(,2) is not due to a conventional mechanism. Some unusual features in 1/T(,1) (T) between T(,c) and 1.2 K appear to signal a phase transition, possibly structural in nature. NQR measurements of the nonsuperconducting CeCu(,2)Si(,2) sample are consistent with extensive disorder in the Cu site occupation. The spin-lattice relaxation rate in UBe(,13) varies approximately as T('3) well below the transition temperature T(,c). This behavior is consistent with a class of anisotropic pairing models for which the superconducting gap vanishes along lines on the Fermi surface. Two phase transitions have been observed in the specific heat measurements of U(,0.9669)Th(,0.0331)Be(,13) at T(,c1) and T(,c2). For T(,c2) < T < T(,c1), 1/T(,1

  17. Laboratory evolution of Geobacter sulfurreducens for enhanced growth on lactate via a single-base-pair substitution in a transcriptional regulator

    PubMed Central

    Summers, Zarath M; Ueki, Toshiyuki; Ismail, Wael; Haveman, Shelley A; Lovley, Derek R

    2012-01-01

    The addition of organic compounds to groundwater in order to promote bioremediation may represent a new selective pressure on subsurface microorganisms. The ability of Geobacter sulfurreducens, which serves as a model for the Geobacter species that are important in various types of anaerobic groundwater bioremediation, to adapt for rapid metabolism of lactate, a common bioremediation amendment, was evaluated. Serial transfer of five parallel cultures in a medium with lactate as the sole electron donor yielded five strains that could metabolize lactate faster than the wild-type strain. Genome sequencing revealed that all five strains had non-synonymous single-nucleotide polymorphisms in the same gene, GSU0514, a putative transcriptional regulator. Introducing the single-base-pair mutation from one of the five strains into the wild-type strain conferred rapid growth on lactate. This strain and the five adaptively evolved strains had four to eight-fold higher transcript abundance than wild-type cells for genes for the two subunits of succinyl-CoA synthase, an enzyme required for growth on lactate. DNA-binding assays demonstrated that the protein encoded by GSU0514 bound to the putative promoter of the succinyl-CoA synthase operon. The binding sequence was not apparent elsewhere in the genome. These results demonstrate that a single-base-pair mutation in a transcriptional regulator can have a significant impact on the capacity for substrate utilization and suggest that adaptive evolution should be considered as a potential response of microorganisms to environmental change(s) imposed during bioremediation. PMID:22113376

  18. On magnon mediated Cooper pair formation in ferromagnetic superconductors

    SciTech Connect

    Kar, Rakesh; Paul, Bikash Chandra; Goswami, Tamal; Misra, Anirban

    2014-08-15

    Identification of pairing mechanism leading to ferromagnetic superconductivity is one of the most challenging issues in condensed matter physics. Although different models have been proposed to explain this phenomenon, a quantitative understanding about this pairing is yet to be achieved. Using the localized-itinerant model, we find that in ferromagnetic superconducting materials both triplet pairing and singlet pairing of electrons are possible through magnon exchange depending upon whether the Debye cut off frequency of magnons is greater or lesser than the Hund's coupling (J) multiplied by average spin (S) per site. Taking into account the repulsive interaction due to the existence of paramagnons, we also find an expression for effective interaction potential between a pair of electrons with opposite spins. We apply the developed formalism in case of UGe{sub 2} and URhGe. The condition of singlet pairing is found to be fulfilled in these cases, as was previously envisaged by Suhl [Suhl, Phys. Rev. Lett. 87, 167007 (2001)]. We compute the critical temperatures of URhGe at ambient pressure and of UGe{sub 2} under different pressures for the first time through BCS equation. Thus, this work outlines a very simple way to evaluate critical temperature in case of a superconducting system. A close match with the available experimental results strongly supports our theoretical treatment.

  19. Tuning Locality of Pair Coherence in Graphene-based Andreev Interferometers

    PubMed Central

    Kim, Minsoo; Jeong, Dongchan; Lee, Gil-Ho; Shin, Yun-Sok; Lee, Hyun-Woo; Lee, Hu-Jong

    2015-01-01

    We report on gate-tuned locality of superconductivity-induced phase-coherent magnetoconductance oscillations in a graphene-based Andreev interferometer, consisting of a T-shaped graphene bar in contact with a superconducting Al loop. The conductance oscillations arose from the flux change through the superconducting Al loop, with gate-dependent Fraunhofer-type modulation of the envelope. We confirm a transitional change in the character of the pair coherence, between local and nonlocal, in the same device as the effective length-to-width ratio of the device was modulated by tuning the pair-coherence length ξT in the graphene layer. PMID:25737106

  20. Fingerprints of the superconducting pairing glue via inelastic tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    Hlobil, Patrik; Schmalian, Jörg; Jandke, Jasmin; Wulfhekel, Wulf

    In the past, tunneling spectroscopy has been interpreted as a direct probe of the fermionic density of states in superconductors. However, in this talk we discuss the impact of inelastic tunneling on tunnel spectra and show that depending on the actual system these interpretations have to be revisited. We show how such inelastic tunneling processes can occur in bulk systems and how they affect the analysis of the experimental data. Considering the spin-gap for spin excitations in the high-Tc superconductors we can trace back the peak-dip-hump features observed in many unconventional superconductors to the shift of the spin spectral weight to higher energies below the critical temperature Tc .

  1. Strongly Correlated Superconductivity close to a Mott transition in orbitally degenerate models

    NASA Astrophysics Data System (ADS)

    Capone, Massimo; Fabrizio, Michele; Castellani, Claudio; Tosatti, Erio

    2004-03-01

    Recently a novel strongly correlated superconductivity (SCS) scenario has been proposed [1] which deals with the question whether and under which conditions Cooper-pairing may get enhanced by strong electron repulsion close to a Mott transition. The core of the SCS proposal is that the effective repulsion between quasiparticles vanishes close to the Mott transition, whereas any pairing attraction will remain unrenormalized if it acts inside the spin channel. This scenario was originally demonstrated through a Dynamical Mean Field Theory (DMFT) solution of a model for doped fullerenes, but it is believed to be far more general. Very recently, a twofold orbitally degenerate model with inverted Hund rule exchange has been proposed as a new candidate for SCS [2]. We report fresh DMFT work that fully confirms this expectation, and provides an extremely appealing phase diagram, where superconductivity arises by doping the Mott insulator, out of an unstable a pseudogapped metal, very much as it happens in cuprates. [1] M. Capone, M. Fabrizio, C. Castellani, and E. Tosatti, Science 296, 2364 (2002). [2] M. Fabrizio, A.F. Ho, L. De Leo, and G. Santoro, Phys. Rev. Lett., to appear; L. De Leo and M. Fabrizio, unpublished.

  2. Unconventional Superconductivity in the Vicinity of the Local Quantum Critical Point

    NASA Astrophysics Data System (ADS)

    Si, Qimiao; Pixley, Jedediah; Deng, Lili; Ingersent, Kevin

    2015-03-01

    Unconventional superconductivity and its relationship with quantum criticality remains a central question in strongly correlated electron systems. In the case of heavy fermion metals, the existence of antiferromagnetic quantum critical points (QCPs) is well established. Theoretical work has identified the existence of a local QCP where the Kondo effect is driven critical concomitant with the vanishing of the magnetic order parameter. Experiments on the heavy fermion compound CeRhIn5 and other materials have provided strong evidence that such a QCP drives unconventional superconductivity. With this in mind we solve the periodic Anderson model using a cluster extended dynamical mean field theory. We show that the Kondo energy scale is continuously suppressed at the antiferromagnetic QCP, and we determine the scaling form of the order parameter susceptibility and find remarkable agreement with well-established experiments in the related heavy fermion system CeCu6-xAux. Most importantly, we find that the singlet pairing susceptibility is strongly enhanced at the QCP, which points towards a new pairing mechanism associated with both magnetic and local critical fluctuations.

  3. Rashba Splitting of Cooper Pairs

    NASA Astrophysics Data System (ADS)

    Shekhter, R. I.; Entin-Wohlman, O.; Jonson, M.; Aharony, A.

    2016-05-01

    We investigate theoretically the properties of a weak link between two superconducting leads, which has the form of a nonsuperconducting nanowire with a strong Rashba spin-orbit coupling caused by an electric field. In the Coulomb-blockade regime of single-electron tunneling, we find that such a weak link acts as a "spin splitter" of the spin states of Cooper pairs tunneling through the link, to an extent that depends on the direction of the electric field. We show that the Josephson current is sensitive to interference between the resulting two transmission channels, one where the spins of both members of a Cooper pair are preserved and one where they are both flipped. As a result, the current is a periodic function of the strength of the spin-orbit interaction and of the bending angle of the nanowire (when mechanically bent); an identical effect appears due to strain-induced spin-orbit coupling. In contrast, no spin-orbit induced interference effect can influence the current through a single weak link connecting two normal metals.

  4. Rashba Splitting of Cooper Pairs.

    PubMed

    Shekhter, R I; Entin-Wohlman, O; Jonson, M; Aharony, A

    2016-05-27

    We investigate theoretically the properties of a weak link between two superconducting leads, which has the form of a nonsuperconducting nanowire with a strong Rashba spin-orbit coupling caused by an electric field. In the Coulomb-blockade regime of single-electron tunneling, we find that such a weak link acts as a "spin splitter" of the spin states of Cooper pairs tunneling through the link, to an extent that depends on the direction of the electric field. We show that the Josephson current is sensitive to interference between the resulting two transmission channels, one where the spins of both members of a Cooper pair are preserved and one where they are both flipped. As a result, the current is a periodic function of the strength of the spin-orbit interaction and of the bending angle of the nanowire (when mechanically bent); an identical effect appears due to strain-induced spin-orbit coupling. In contrast, no spin-orbit induced interference effect can influence the current through a single weak link connecting two normal metals. PMID:27284669

  5. Superconductivity of magnesium diboride

    SciTech Connect

    Bud’ko, Sergey L.; Canfield, Paul C.

    2015-07-15

    Over the past 14 years MgB2 has gone from a startling discovery to a promising, applied superconductor. In our article we present a brief overview of the synthesis and the basic superconducting properties of this remarkable compound. Specifically, the effect of pressure, substitutions and neutron irradiation on superconducting properties are discussed.

  6. Superconductivity of magnesium diboride

    NASA Astrophysics Data System (ADS)

    Bud'ko, Sergey L.; Canfield, Paul C.

    2015-07-01

    Over the past 14 years MgB2 has gone from a startling discovery to a promising, applied superconductor. In this article we present a brief overview of the synthesis and the basic superconducting properties of this remarkable compound. In particular, the effect of pressure, substitutions and neutron irradiation on superconducting properties are discussed.

  7. Superconductivity in bad metals

    SciTech Connect

    Emery, V.J.; Kivelson, S.A.

    1995-12-31

    It is argued that many synthetic metals, including high temperature superconductors are ``bad metals`` with such a poor conductivity that the usual mean-field theory of superconductivity breaks down because of anomalously large classical and quantum fluctuations of the phase of the superconducting order parameter. Some consequences for high temperature superconductors are described.

  8. Superconducting gyroscope research

    NASA Technical Reports Server (NTRS)

    Hendricks, J. B.; Karr, G. R.

    1985-01-01

    Four basic areas of research and development of superconducting gyroscopes are studied. Chapter 1 studies the analysis of a SQUID readout for a superconducting gyroscope. Chapter 2 studies the dependence of spin-up torque on channel and gas properties. Chapter 3 studies the theory of super fluid plug operation. And chapter 4 studies the gyro rotor and housing manufacture.

  9. Superconducting properties of protactinium.

    PubMed

    Smith, J L; Spirlet, J C; Müller, W

    1979-07-13

    The superconducting transition temperature and upper critical magnetic field of protactinium were measured by alternating-current susceptibility techniques. Since the superconducting behavior of protactinium is affected by its 5f electron character, it is clear now that protactinium is a true actinide element. PMID:17750320

  10. Rapid cycling superconducting magnets

    NASA Astrophysics Data System (ADS)

    Fabbricatore, P.; Farinon, S.; Gambardella, U.; Greco, M.; Volpini, G.

    2006-04-01

    The paper deals with the general problematic related to the development of fast cycled superconducting magnets for application in particle accelerator machines. Starting from the requirements of SIS300 synchrotron under design at GSI and an envisaged future Super-SPS injector at CERN, it is shown which developments are mandatory in the superconducting wire technology and in the magnet design field.

  11. Development of superconductive magnets

    NASA Technical Reports Server (NTRS)

    Laurence, J. C.

    1970-01-01

    Survey of superconductive magnets considers - stabilization problems, advances in materials and their uses, and design evolution. Uses of superconducting magnets in particle accelerators and bubble chambers, as well as possible applications in magnetohydrodynamic and thermonuclear power generation and levitation are discussed.

  12. Superconductivity of magnesium diboride

    DOE PAGESBeta

    Bud’ko, Sergey L.; Canfield, Paul C.

    2015-07-15

    Over the past 14 years MgB2 has gone from a startling discovery to a promising, applied superconductor. In our article we present a brief overview of the synthesis and the basic superconducting properties of this remarkable compound. Specifically, the effect of pressure, substitutions and neutron irradiation on superconducting properties are discussed.

  13. Quantification of proteins using enhanced etching of Ag coated Au nanorods by the Cu2+/bicinchoninic acid pair with improved sensitivity

    NASA Astrophysics Data System (ADS)

    Liu, Wenqi; Hou, Shuai; Yan, Jiao; Zhang, Hui; Ji, Yinglu; Wu, Xiaochun

    2015-12-01

    Plasmonic nanosensors show great potential in ultrasensitive detection, especially with the plasmon peak position as the detection modality. Herein, a new sensitive but simple total protein quantification method termed the SPR-BCA assay is demonstrated by combining plasmonic nanosensors with protein oxidation by Cu2+. The easy tuning of localized surface plasmon resonance (LSPR) features of plasmonic nanostructures makes them ideal sensing platforms. We found that the Cu2+/bicinchoninic acid (BCA) pair exhibits accelerated etching of Au@Ag nanorods and results in the LSPR peak shift. A linear relationship between Cu2+ and the LSPR shift is found in a double logarithmic coordinate. Such double logarithm relationship is transferred to the concentration of proteins. Theoretical simulation shows that Au nanorods with large aspect ratios and small core sizes show high detection sensitivity. Via optimized sensor design, we achieved an increased sensitivity (the limit of detection was 3.4 ng ml-1) and a wide working range (0.5 to 1000 μg ml-1) compared with the traditional BCA assay. The universal applicability of our method to various proteins further proves its potential in practical applications.Plasmonic nanosensors show great potential in ultrasensitive detection, especially with the plasmon peak position as the detection modality. Herein, a new sensitive but simple total protein quantification method termed the SPR-BCA assay is demonstrated by combining plasmonic nanosensors with protein oxidation by Cu2+. The easy tuning of localized surface plasmon resonance (LSPR) features of plasmonic nanostructures makes them ideal sensing platforms. We found that the Cu2+/bicinchoninic acid (BCA) pair exhibits accelerated etching of Au@Ag nanorods and results in the LSPR peak shift. A linear relationship between Cu2+ and the LSPR shift is found in a double logarithmic coordinate. Such double logarithm relationship is transferred to the concentration of proteins. Theoretical

  14. The SNS Superconducting Linac System

    SciTech Connect

    Claus Rode

    2001-07-01

    The SNS has adopted superconducting RF technology for the high-energy end of its linac. The design uses cavities of {beta} = 0.61 and 0.81 to span the energy region from 186 MeV up to a maximum of 1.3 GeV. Thirty-three of the lower {beta} cavities are contained in 11 cryomodules, and there could be as many as 21 additional cryomodules, each containing four of the higher {beta} cavities, to reach the maximum energy. The design uses a peak surface gradient of 35 MV/m. Each cavity will be driven by a 550 kW klystron. Cryomodules will be connected to the refrigerator by a pair of ''tee'' shape transfer lines. The refrigerator will produce 120 g/sec of refrigeration at 2.1 K, 15 g/sec of liquefaction at 4.5 K, and 8,300 W of 50 K shield refrigeration.

  15. Superconducting Graphene Nanoelectronic Devices

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

  16. Quantification of proteins using enhanced etching of Ag coated Au nanorods by the Cu(2+)/bicinchoninic acid pair with improved sensitivity.

    PubMed

    Liu, Wenqi; Hou, Shuai; Yan, Jiao; Zhang, Hui; Ji, Yinglu; Wu, Xiaochun

    2016-01-14

    Plasmonic nanosensors show great potential in ultrasensitive detection, especially with the plasmon peak position as the detection modality. Herein, a new sensitive but simple total protein quantification method termed the SPR-BCA assay is demonstrated by combining plasmonic nanosensors with protein oxidation by Cu(2+). The easy tuning of localized surface plasmon resonance (LSPR) features of plasmonic nanostructures makes them ideal sensing platforms. We found that the Cu(2+)/bicinchoninic acid (BCA) pair exhibits accelerated etching of Au@Ag nanorods and results in the LSPR peak shift. A linear relationship between Cu(2+) and the LSPR shift is found in a double logarithmic coordinate. Such double logarithm relationship is transferred to the concentration of proteins. Theoretical simulation shows that Au nanorods with large aspect ratios and small core sizes show high detection sensitivity. Via optimized sensor design, we achieved an increased sensitivity (the limit of detection was 3.4 ng ml(-1)) and a wide working range (0.5 to 1000 μg ml(-1)) compared with the traditional BCA assay. The universal applicability of our method to various proteins further proves its potential in practical applications. PMID:26669539

  17. Strain-induced time-reversal odd superconductivity in graphene

    NASA Astrophysics Data System (ADS)

    Juricic, Vladimir; Roy, Bitan

    2014-03-01

    I will discuss the possibility of realizing a time-reversal-symmetry breaking superconducting state that exhibits an f + is pairing symmetry in strained graphene. Although the underlying attractive interactions need to be sufficiently strong and comparable in pristine graphene to support such pairing state, I will argue that strain can be conducive for its formation even for weak interactions. I will show that quantum-critical behavior near the transition is controlled by a fermionic multicritical point, characterized by various critical exponents computed in the framework of an ɛ-expansion near four spacetime dimensions. I will then discuss the scaling of the superconducting gap with the strain-induced axial pseudo-magnetic field. Furthermore, a vortex in this mixed superconducting state hosts a pair of Majorana fermions supporting a quartet of insulating and superconducting orders, among which quantum spin Hall topological insulator. Finally, I will mention some experimental signatures of this f + is time-reversal odd superconductor. These findings suggest that strained graphene could provide a platform for the realization of exotic superconducting states of Dirac fermions. VJ is supported by the Netherlands Organization for Scientific Research (NWO).

  18. The selective dopamine D3 receptor antagonist SB-277011A reduces nicotine-enhanced brain reward and nicotine-paired environmental cue functions.

    PubMed

    Pak, Arlene C; Ashby, Charles R; Heidbreder, Christian A; Pilla, Maria; Gilbert, Jeremy; Xi, Zheng-Xiong; Gardner, Eliot L

    2006-10-01

    Increasing evidence suggests that enhanced dopamine (DA) neurotransmission in the nucleus accumbens (NAc) may play a role in mediating the reward and reinforcement produced by addictive drugs and in the attentional processing of drug-associated environmental cues. The meso-accumbens DA system is selectively enriched with DA D3 receptors, a DA receptor subtype increasingly implicated in reward-related brain and behavioural processes. From a variety of evidence, it has been suggested that selective DA D3 receptor antagonism may be a useful pharmacotherapeutic approach for treating addiction. The present experiments tested the efficacy of SB-277011A, a selective DA D3 receptor antagonist, in rat models of nicotine-enhanced electrical brain-stimulation reward (BSR), nicotine-induced conditioned locomotor activity (LMA), and nicotine-induced conditioned place preference (CPP). Nicotine was given subcutaneously within the dose range of 0.25-0.6 mg/kg (nicotine-free base). SB-277011A, given intraperitoneally within the dose range of 1-12 mg/kg, dose-dependently reduced nicotine-enhanced BSR, nicotine-induced conditioned LMA, and nicotine-induced CPP. The results suggest that selective D3 receptor antagonism constitutes a new and promising pharmacotherapeutic approach to the treatment of nicotine dependence. PMID:16942635

  19. Cooper pairing in the insulating valence band in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Hu, Lun-Hui; Chen, Wei-Qiang; Zhang, Fu-Chun

    2015-04-01

    Conventional Cooper pairing arises from attractive interaction of electrons in the metallic bands. A recent experiment on Co-doped LiFeAs shows superconductivity in the insulating valence band, which is evolved from a metallic hole band upon doping. Here we examine this phenomenon by studying superconductivity in a three-orbital Hamiltonian relevant to the doped LiFeAs. We show explicitly that Cooper pairing of the insulating hole band requires a finite pairing interaction strength. For strong coupling, the superconductivity in the hole band is robust against the sink of the hole band below the Fermi level. Our theory predicts a substantial upward shift of the chemical potential in the superconducting transition for Co-doped LiFeAs.

  20. Optical mirror coated with organic superconducting material

    NASA Astrophysics Data System (ADS)

    Lake, John A.; Heath, William B.

    1988-08-01

    An optical mirror has enhanced reflectivity and reduced thermal distortions when it is composed of a substrate coated with a reflective coating made of an organic superconducting material. The substrate is best constructed of materials which have the most favorable thermal expansion and thermal conduction characteristics at temperatures near 0 K. such as: silicon, diamond, copper, and sapphire. The reflective coating is only a few microns thick and composed of organometallic compounds and is cooled to superconducting or cryogenic temperatures of less than 100 K.

  1. Cooper pairing in non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Metlitski, Max A.; Mross, David F.; Sachdev, Subir; Senthil, T.

    2015-03-01

    States of matter with a sharp Fermi surface but no well-defined Landau quasiparticles arise in a number of physical systems. Examples include (i) quantum critical points associated with the onset of order in metals; (ii) spinon Fermi-surface [U(1) spin-liquid] state of a Mott insulator; (iii) Halperin-Lee-Read composite fermion charge liquid state of a half-filled Landau level. In this work, we use renormalization group techniques to investigate possible instabilities of such non-Fermi liquids in two spatial dimensions to Cooper pairing. We consider the Ising-nematic quantum critical point as an example of an ordering phase transition in a metal, and demonstrate that the attractive interaction mediated by the order-parameter fluctuations always leads to a superconducting instability. Moreover, in the regime where our calculation is controlled, superconductivity preempts the destruction of electronic quasiparticles. On the other hand, the spinon Fermi surface and the Halperin-Lee-Read states are stable against Cooper pairing for a sufficiently weak attractive short-range interaction; however, once the strength of attraction exceeds a critical value, pairing sets in. We describe the ensuing quantum phase transition between (i) U(1 ) and Z2 spin-liquid states; (ii) Halperin-Lee-Read and Moore-Read states.

  2. Merging Problem-Based Learning with Simulation-Based Learning in the Medical Undergraduate Curriculum: The PAIRED Framework for Enhancing Lifelong Learning

    PubMed Central

    Koh, Jansen

    2016-01-01

    Lifelong learning is an essential trait that is expected of every physician. The CanMeds 2005 Physician Competency Framework emphasizes lifelong learning as a key competency that physicians must achieve in becoming better physicians. However, many physicians are not competent at engaging in lifelong learning. The current medical education system is deficient in preparing medical students to develop and carry out their own lifelong learning curriculum upon graduation. Despite understanding how physicians learn at work, medical students are not trained to learn while working. Similarly, although barriers to lifelong learning are known, medical students are not adequately skilled in overcoming these barriers. Learning to learn is just as important, if not more, as acquiring the skills and knowledge required of a physician. The medical undergraduate curriculum lacks a specific learning strategy to prepare medical students in becoming an adept lifelong learner. In this article, we propose a learning strategy for lifelong learning at the undergraduate level. In developing this novel strategy, we paid particular attention to two parameters. First, this strategy should be grounded on literature describing a physician’s lifelong learning process. Second, the framework for implementing this strategy must be based on existing undergraduate learning strategies to obviate the need for additional resources, learner burden, and faculty time. In this paper, we propose a Problem, Analysis, Independent Research Reporting, Experimentation Debriefing (PAIRED) framework that follows the learning process of a physician and serves to synergize the components of problem-based learning and simulation-based learning in specifically targeting the barriers to lifelong learning. PMID:27446767

  3. General Conditions for Proximity-Induced Odd-Frequency Superconductivity in Two-Dimensional Electronic Systems.

    PubMed

    Triola, Christopher; Badiane, Driss M; Balatsky, Alexander V; Rossi, E

    2016-06-24

    We obtain the general conditions for the emergence of odd-frequency superconducting pairing in a two-dimensional (2D) electronic system proximity coupled to a superconductor, making minimal assumptions about both the 2D system and the superconductor. Using our general results we show that a simple heterostructure formed by a monolayer of a group VI transition metal dichalcogenide, such as molybdenum disulfide, and an s-wave superconductor with Rashba spin-orbit coupling exhibits odd-frequency superconducting pairing. Our results allow the identification of a new class of systems among van der Waals heterostructures in which odd-frequency superconductivity should be present. PMID:27391743

  4. General Conditions for Proximity-Induced Odd-Frequency Superconductivity in Two-Dimensional Electronic Systems

    NASA Astrophysics Data System (ADS)

    Triola, Christopher; Badiane, Driss M.; Balatsky, Alexander V.; Rossi, E.

    2016-06-01

    We obtain the general conditions for the emergence of odd-frequency superconducting pairing in a two-dimensional (2D) electronic system proximity coupled to a superconductor, making minimal assumptions about both the 2D system and the superconductor. Using our general results we show that a simple heterostructure formed by a monolayer of a group VI transition metal dichalcogenide, such as molybdenum disulfide, and an s -wave superconductor with Rashba spin-orbit coupling exhibits odd-frequency superconducting pairing. Our results allow the identification of a new class of systems among van der Waals heterostructures in which odd-frequency superconductivity should be present.

  5. Superconductivity in sputtered CuMo6S8

    NASA Technical Reports Server (NTRS)

    Alterovitz, S.; Woollam, J. A.; Kammerdiner, L.; Luo, H.-L.; Martin, C.

    1977-01-01

    The superconducting transition temperature and the superconducting upper critical fields for sputtered films of copper-containing ternary molybdenum chalcogenides (chevrel phases) were determined. The theory presented by Werthamer, Helfand, and Hohenberg (WHH) (1966) was used to make computer-generated plots of the superconducting upper critical field values versus the superconducting transition temperature values for various values of the Maki paramagnetic pair-breaking parameter and the spin-orbit scattering parameter. The interpretation of the graph suggests that the experimental data for at least one sample are above the maximum WHH theoretical limit in the lower temperature range. Possible explanations of this situation are discussed. In other calculations, a scaling law was found suitable for determining pinning force densities; this data was used to calculate critical current values. The relation between resistivity and temperature was studied.

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

    NASA Astrophysics Data System (ADS)

    Hackl, R.; Hanke, W.

    2010-10-01

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

  7. Electron correlation tuned superconductivity in iron chalcogenide superconductors

    NASA Astrophysics Data System (ADS)

    Yi, Ming; Wang, Meng; Lu, Donghui; Kemper, Alexander; Mo, Sung-Kwan; Shen, Zhi-Xun; Birgeneau, Robert

    2015-03-01

    The iron chalcogenide superconductors, AxFe2-ySe2 (A =K, Rb, Cs), is an interesting system where superconductivity occurs without the existence of hole Fermi pockets, hence lacking the nesting conditions needed under a spin fluctuation mediated pairing scenario. It is then important to understand the ingredients needed for superconductivity in these materials. It has been shown that sulfur substitution for selenium in this system can continually reduce the TC from 30K to zero, providing an opportunity for understanding the occurrence of superconductivity in these materials. In this talk, I will present angle-resolved photoemission spectroscopy data on the RbxFe2(Se1-ySy)2 series, where we show that electron correlation strength is the crucial parameter that tunes superconductivity in this family.

  8. Novel Approach to Linear Accelerator Superconducting Magnet System

    SciTech Connect

    Kashikhin, Vladimir; /Fermilab

    2011-11-28

    Superconducting Linear Accelerators include a superconducting magnet system for particle beam transportation that provides the beam focusing and steering. This system consists of a large number of quadrupole magnets and dipole correctors mounted inside or between cryomodules with SCRF cavities. Each magnet has current leads and powered from its own power supply. The paper proposes a novel approach to magnet powering based on using superconducting persistent current switches. A group of magnets is powered from the same power supply through the common, for the group of cryomodules, electrical bus and pair of current leads. Superconducting switches direct the current to the chosen magnet and close the circuit providing the magnet operation in a persistent current mode. Two persistent current switches were fabricated and tested. In the paper also presented the results of magnetic field simulations, decay time constants analysis, and a way of improving quadrupole magnetic center stability. Such approach substantially reduces the magnet system cost and increases the reliability.

  9. Unconventional Superconductivity in YPtBi and Related Topological Semimetals

    NASA Astrophysics Data System (ADS)

    Meinert, Markus

    2016-04-01

    YPtBi, a topological semimetal with a very low carrier density, was recently found to be superconducting below Tc=0.77 K . In conventional theory, the nearly vanishing density of states around the Fermi level would imply a vanishing electron-phonon coupling and would, therefore, not allow for superconductivity. Based on relativistic density-functional theory calculations of the electron-phonon coupling in YPtBi, it is found that carrier concentrations of more than 1021 cm-3 are required to explain the observed critical temperature with the conventional pairing mechanism, which is several orders of magnitude larger than experimentally observed. It is very likely that an unconventional pairing mechanism is responsible for the superconductivity in YPtBi and related topological semimetals with half-Heusler structure.

  10. Unconventional Superconductivity in YPtBi and Related Topological Semimetals.

    PubMed

    Meinert, Markus

    2016-04-01

    YPtBi, a topological semimetal with a very low carrier density, was recently found to be superconducting below T_{c}=0.77  K. In conventional theory, the nearly vanishing density of states around the Fermi level would imply a vanishing electron-phonon coupling and would, therefore, not allow for superconductivity. Based on relativistic density-functional theory calculations of the electron-phonon coupling in YPtBi, it is found that carrier concentrations of more than 10^{21}  cm^{-3} are required to explain the observed critical temperature with the conventional pairing mechanism, which is several orders of magnitude larger than experimentally observed. It is very likely that an unconventional pairing mechanism is responsible for the superconductivity in YPtBi and related topological semimetals with half-Heusler structure. PMID:27081999

  11. Proximity induced Superconductivity in Epitaxial Graphene

    NASA Astrophysics Data System (ADS)

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

    The intimate electrical contact of a superconductor with a normal metal leads to an exchange of carriers through their boundary. Cooper pairs leak into the normal metal via Andreev reflection and enable the normal metal to acquire superconducting-like properties. The electron-hole conversion process in graphene is prominent due to relativistic quantum mechanics governing low energy chiral carriers in a multi-valley system. In the present experiment, we reveal spatial measurements of the proximity effect in graphene from a graphene-superconductor interface. Superconducting aluminum films were grown on epitaxial graphene on SiC. The aluminum films were discontinuous with networks of trenches in the film morphology reaching down to the substrate to exposed graphene terraces. Scanning tunneling spectra measured on the graphene terraces show a clear decay of the superconducting gap width with increasing separation from the graphene-aluminum edges. The decay length for the superconducting energy gap extends beyond 400 nm. Subtle deviations in the exponentially decaying energy gap were also observed on a much smaller length scale of tens of nanometers. Funding from SNSF (project 158468), NIST/CNST Grant 70NANB10H193, and KRF-2010-00349.

  12. Theory of nonequilibrium superconductivity in cuprates

    NASA Astrophysics Data System (ADS)

    Oka, Takashi; Pietilä, Ville

    2013-03-01

    Recently, nonequilibrium properties of Hi Tc superconductors are attracting much interest. This is because new experimental methods such as time resolved ARPES has been applied to cuprates and succeeded in observing the dynamics of photo-excited quasiparticles as well as the temporal evolution of the d-wave superconducting order parameter (e.g.,). One can also realize nonequilibrium states in interfaces between cuprates and metal electrodes and control the superconducting order by changing the applied bias. In order to study the dynamics of superconductivity in strongly correlated systems, we developed a novel numerical method by combining the quantum kinetic equation with the fluctuation exchange approximation (FLEX, self-consistent T-matrix approximation). This method enables us to study the interplay between pair mediating fluctuations, e.g., antiferromagnetic and charge fluctuations, and the dynamics of quasiparticles and superconducting order parameter. In the presentation, we explain the physical insights we obtain by applying this method to nonequilibrium dynamics in d-wave superconductors.

  13. Metal optics and superconductivity

    SciTech Connect

    Golovashkin, A.L.

    1989-01-01

    The articles contained in this collection are dedicated to the study of the electron structure of transition metals and superconducting alloys and compounds based on them. The study of the electron structure of materials is one of the central problems of solid-state physics and defines the solution of a number of problems. One of them is the problem of high-temperature superconductivity which has attracted exceptional attention from physicists in connection with the discovery of new classes of ceramic oxides which are superconducting at liquid-nitrogen temperature. The electron structure is one of the three whales on which all of superconductivity rests. It is frequently our ignorance of the electronic properties of a metal, alloy or compound in its normal state which makes it impossible to predict superconductivity in the material, preventing use from calculating the parameters of the superconducting state. There are now a number of effective methods for investigation of the electron structure of the metals and allows. This collection discusses metal optics, tunneling and magnetic measurements in superconductors. These methods are quite informative and allow us to obtain many important electron characteristics and temperature relations. Various characteristics of the superconducting compounds Nb{sub 3}Ge, Nb{sub 3}Al, nb{sub 3}Sn and Nb{sub 3}Ga with A15 structure and NbN with B1 structure, having rather high critical temperatures, are experimentally studied.

  14. NMR Study of Superconductivity and Spin Fluctuations in Intercalated Iron Selenides AyFe2-xSe2

    NASA Astrophysics Data System (ADS)

    Yu, Weiqiang

    2012-02-01

    The role of spin fluctuations in superconductivity is an essential topic in both cuprate and Fe-based superconductors. NMR works in several Fe-based superconductors proposed that the low-energy antiferromagnetic spin fluctuations (AFSF) is a possible pairing glue for superconductivity. However, studies on other systems such as KFe2As2 and Li1-xFeAs does not support a strong correlation between low-energy spin fluctuations and superconductivity. In the newly discovered AyFe2-xSe2 superconductors with Tc˜ 32 K, our NMR study identifies unambiguously a paramagnetic superconducting phase, which is phase separated from the block antiferromagnetic state. The low-energy AFSF is not seen at all, even though the Tc is high. The AyFe2-xSe2 are singlet superconductors evidenced from the NMR Knight shift K; However, the absence of the coherence peak in the spin-lattice relaxation rate 1/T1 suggests an unconventional behavior of superconductivity. In fact, we found that both the K and the 1/T1T increase dramatically with temperature and follow a a+bT^2 form from Tc up to 300 K. Such behavior is strong evidence for spin fluctuations with a high-energy, local nature in 3D systems, and inconsistent with a band-gap effect. Furthermore, K and 1/T1T saturate above 400 K, indicating an energy scale of 35 meV, which is distinct from the low-energy spin fluctuations. The above temperature enhanced spin fluctuations seem to be universal in Fe-based superconductors. [4pt] References: W. Yu et al., Phys. Rev. Lett. 106, 197001 (2011); Long Ma et al., Phys. Rev. B 83, 174510 (2011); L. Ma et al., arXiv:1103.4960.

  15. A superconducting large-angle magnetic suspension

    NASA Technical Reports Server (NTRS)

    Downer, James R.; Anastas, George V., Jr.; Bushko, Dariusz A.; Flynn, Frederick J.; Goldie, James H.; Gondhalekar, Vijay; Hawkey, Timothy J.; Hockney, Richard L.; Torti, Richard P.

    1992-01-01

    SatCon Technology Corporation has completed a Small Business Innovation Research (SBIR) Phase 2 program to develop a Superconducting Large-Angle Magnetic Suspension (LAMS) for the NASA Langley Research Center. The Superconducting LAMS was a hardware demonstration of the control technology required to develop an advanced momentum exchange effector. The Phase 2 research was directed toward the demonstration for the key technology required for the advanced concept CMG, the controller. The Phase 2 hardware consists of a superconducting solenoid ('source coils') suspended within an array of nonsuperconducting coils ('control coils'), a five-degree-of-freedom positioning sensing system, switching power amplifiers, and a digital control system. The results demonstrated the feasibility of suspending the source coil. Gimballing (pointing the axis of the source coil) was demonstrated over a limited range. With further development of the rotation sensing system, enhanced angular freedom should be possible.

  16. Optical detection of the superconducting proximity effect

    SciTech Connect

    Greene, L.H.; Abeyta, A.C.; Roshchin, I.V.; Robinson, I.K.; Dorsten, J.F.; Tanzer, T.A.; Bohn, P.W.

    1996-12-31

    The authors present the first detection of a superconducting proximity effect by optical techniques. Raman scattering on n{sup +}-InAs is performed through very thin, high-quality, superconducting Nb films grown directly on the (100) InAs surface. The 6 to 10 nm thick Nb films exhibit {Tc}`s of 2.5 to 5.5 K, as measured by electronic transport, and are flat to {approximately}0.5 nm, as measured by x-ray reflectivity. As the Nb/InAs structure is cooled below the superconducting transition temperature, the magnitude of the unscreened LO phonon mode, associated with the surface charge accumulation layer in the InAs, is observed to be enhanced by more than 40%. This reversible change is observed only when the Nb is in good electrical contact with the InAs.

  17. Ultra-Stable Superconducting-Maser Oscillator

    NASA Technical Reports Server (NTRS)

    Strayer, Donald M.; Dick, G. John

    1989-01-01

    Unprecedented stability of frequency in superconducting, triple-cavity ruby maser oscillator achieved by incorporation of amplitude-control subsystem. New design enhances ultra-stable measurements of time by reducing fluctuations to 2 X 10 to negative 19th power routinely, and to as little as 10 to negative 20th power in exceptional cases. Currents induced in superconducting pickup coil by changes in magnetic field in ruby. Currents from coil fed to superconducting quantum-interference device (SQUID) magnetometer, output used to generate control signal for electronically variable attenuator. Attenuator varies pump-signal amplitude in response to magnetic-field fluctuations in ruby. Very high feedback-loop gain used for sensitivity of control and adequate compensation of fluctuations.

  18. Structures behind superconductivity

    SciTech Connect

    Rotman, D.

    1988-07-01

    The previously reported preparation and structures of superconducting materials are reviewed. The two systems, Y-Ba-Cu-O and La-Cu-O, previously reported with high transition temperatures are discussed in some detail. The new systems introduced in 1987 that were not based on a rare earth but including Bi-Sr-Cu-O are also reviewed. Superconductive materials including thallium rather than bismuth that have been reported but not thoroughly studied are discussed briefly. It is pointed out that many superconducting materials have been prepared, but good documentation of the structures and properties of these materials need much more study.

  19. Superconductivity in doped insulators

    SciTech Connect

    Emery, V.J.; Kivelson, S.A.

    1995-12-31

    It is shown that many synthetic metals, including high temperature superconductors are ``bad metals``, with such a poor conductivity that the usual meanfield theory of superconductivity breaks down because of anomalously large classical and quantum fluctuations of the phase of the superconducting order parameter. It is argued that the supression of a first order phase transition (phase separation) by the long-range Coulomb interaction leads to high temperature superconductivity accompanied by static or dynamical charge inhomogeneIty. Evidence in support of this picture for high temperature superconductors is described.

  20. Superconducting active impedance converter

    DOEpatents

    Ginley, D.S.; Hietala, V.M.; Martens, J.S.

    1993-11-16

    A transimpedance amplifier for use with high temperature superconducting, other superconducting, and conventional semiconductors allows for appropriate signal amplification and impedance matching to processing electronics. The amplifier incorporates the superconducting flux flow transistor into a differential amplifier configuration which allows for operation over a wide temperature range, and is characterized by high gain, relatively low noise, and response times less than 200 picoseconds over at least a 10-80 K. temperature range. The invention is particularly useful when a signal derived from either far-IR focal plane detectors or from Josephson junctions is to be processed by higher signal/higher impedance electronics, such as conventional semiconductor technology. 12 figures.

  1. Superconducting active impedance converter

    DOEpatents

    Ginley, David S.; Hietala, Vincent M.; Martens, Jon S.

    1993-01-01

    A transimpedance amplifier for use with high temperature superconducting, other superconducting, and conventional semiconductor allows for appropriate signal amplification and impedance matching to processing electronics. The amplifier incorporates the superconducting flux flow transistor into a differential amplifier configuration which allows for operation over a wide temperature range, and is characterized by high gain, relatively low noise, and response times less than 200 picoseconds over at least a 10-80 K. temperature range. The invention is particularly useful when a signal derived from either far-IR focal plane detectors or from Josephson junctions is to be processed by higher signal/higher impedance electronics, such as conventional semiconductor technology.

  2. Tunneling in superconducting structures

    NASA Astrophysics Data System (ADS)

    Shukrinov, Yu. M.

    2010-12-01

    Here we review our results on the breakpoint features in the coupled system of IJJ obtained in the framework of the capacitively coupled Josephson junction model with diffusion current. A correspondence between the features in the current voltage characteristics (CVC) and the character of the charge oscillations in superconducting layers is demonstrated. Investigation of the correlations of superconducting currents in neighboring Josephson junctions and the charge correlations in neighboring superconducting layers reproduces the features in the CVC and gives a powerful method for the analysis of the CVC of coupled Josephson junctions. A new method for determination of the dissipation parameter is suggested.

  3. Local and global superconductivity in bismuth

    NASA Astrophysics Data System (ADS)

    Baring, Luis A.; da Silva, Robson R.; Kopelevich, Yakov

    2011-10-01

    We performed magnetization M(H, T) and magnetoresistance R(T, H) measurements on powdered (grain size ˜149 μm) as well as highly oriented rhombohedral (A7) bismuth (Bi) samples consisting of single crystalline blocks of size ˜1 × 1 mm in the plane perpendicular to the trigonal c axis. The obtained results revealed the occurrence of (1) local superconductivity in powdered samples with Tc(0) = (8.75 ± 0.05) K, and (2) global superconductivity at Tc(0) = (7.3 ± 0.1) K in polycrystalline Bi triggered by low-resistance ohmic contacts with silver (Ag) normal metal. The results provide evidence that the superconductivity in Bi is localized in a tiny volume fraction, probably at intergrain or Ag/Bi interfaces. On the other hand, the occurrence of global superconductivity observed for polycrystalline Bi can be accounted for by enhancement of the superconducting order parameter phase stiffness induced by the normal metal contacts, the scenario proposed in the context of "pseudogap regime" in cuprates [E. Berg et al., Phys. Rev. B 78, 094509 (2008)].

  4. Enhancing pairwise state-transition weights: A new weighting scheme in simulated tempering that can minimize transition time between a pair of conformational states

    NASA Astrophysics Data System (ADS)

    Qiao, Qin; Zhang, Hou-Dao; Huang, Xuhui

    2016-04-01

    Simulated tempering (ST) is a widely used enhancing sampling method for Molecular Dynamics simulations. As one expanded ensemble method, ST is a combination of canonical ensembles at different temperatures and the acceptance probability of cross-temperature transitions is determined by both the temperature difference and the weights of each temperature. One popular way to obtain the weights is to adopt the free energy of each canonical ensemble, which achieves uniform sampling among temperature space. However, this uniform distribution in temperature space may not be optimal since high temperatures do not always speed up the conformational transitions of interest, as anti-Arrhenius kinetics are prevalent in protein and RNA folding. Here, we propose a new method: Enhancing Pairwise State-transition Weights (EPSW), to obtain the optimal weights by minimizing the round-trip time for transitions among different metastable states at the temperature of interest in ST. The novelty of the EPSW algorithm lies in explicitly considering the kinetics of conformation transitions when optimizing the weights of different temperatures. We further demonstrate the power of EPSW in three different systems: a simple two-temperature model, a two-dimensional model for protein folding with anti-Arrhenius kinetics, and the alanine dipeptide. The results from these three systems showed that the new algorithm can substantially accelerate the transitions between conformational states of interest in the ST expanded ensemble and further facilitate the convergence of thermodynamics compared to the widely used free energy weights. We anticipate that this algorithm is particularly useful for studying functional conformational changes of biological systems where the initial and final states are often known from structural biology experiments.

  5. Enhancing pairwise state-transition weights: A new weighting scheme in simulated tempering that can minimize transition time between a pair of conformational states.

    PubMed

    Qiao, Qin; Zhang, Hou-Dao; Huang, Xuhui

    2016-04-21

    Simulated tempering (ST) is a widely used enhancing sampling method for Molecular Dynamics simulations. As one expanded ensemble method, ST is a combination of canonical ensembles at different temperatures and the acceptance probability of cross-temperature transitions is determined by both the temperature difference and the weights of each temperature. One popular way to obtain the weights is to adopt the free energy of each canonical ensemble, which achieves uniform sampling among temperature space. However, this uniform distribution in temperature space may not be optimal since high temperatures do not always speed up the conformational transitions of interest, as anti-Arrhenius kinetics are prevalent in protein and RNA folding. Here, we propose a new method: Enhancing Pairwise State-transition Weights (EPSW), to obtain the optimal weights by minimizing the round-trip time for transitions among different metastable states at the temperature of interest in ST. The novelty of the EPSW algorithm lies in explicitly considering the kinetics of conformation transitions when optimizing the weights of different temperatures. We further demonstrate the power of EPSW in three different systems: a simple two-temperature model, a two-dimensional model for protein folding with anti-Arrhenius kinetics, and the alanine dipeptide. The results from these three systems showed that the new algorithm can substantially accelerate the transitions between conformational states of interest in the ST expanded ensemble and further facilitate the convergence of thermodynamics compared to the widely used free energy weights. We anticipate that this algorithm is particularly useful for studying functional conformational changes of biological systems where the initial and final states are often known from structural biology experiments. PMID:27389209

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  7. Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Qisi; Park, J. T.; Feng, Yu; Shen, Yao; Hao, Yiqing; Pan, Bingying; Lynn, J. W.; Ivanov, A.; Chi, Songxue; Matsuda, M.; Cao, Huibo; Birgeneau, R. J.; Efremov, D. V.; Zhao, Jun

    2016-05-01

    An essential step toward elucidating the mechanism of superconductivity is to determine the sign or phase of the superconducting order parameter, as it is closely related to the pairing interaction. In conventional superconductors, the electron-phonon interaction induces attraction between electrons near the Fermi energy and results in a sign-preserved s -wave pairing. For high-temperature superconductors, including cuprates and iron-based superconductors, prevalent weak coupling theories suggest that the electron pairing is mediated by spin fluctuations which lead to repulsive interactions, and therefore that a sign-reversed pairing with an s± or d -wave symmetry is favored. Here, by using magnetic neutron scattering, a phase sensitive probe of the superconducting gap, we report the observation of a transition from the sign-reversed to sign-preserved Cooper-pairing symmetry with insignificant changes in Tc in the S-doped iron selenide superconductors KxFe2 -y(Se1-zSz) 2 . We show that a rather sharp magnetic resonant mode well below the superconducting gap (2 Δ ) in the undoped sample (z =0 ) is replaced by a broad hump structure above 2 Δ under 50% S doping. These results cannot be readily explained by simple spin fluctuation-exchange pairing theories and, therefore, multiple pairing channels are required to describe superconductivity in this system. Our findings may also yield a simple explanation for the sometimes contradictory data on the sign of the superconducting order parameter in iron-based materials.

  8. Pairing in a dry Fermi sea

    PubMed Central

    Maier, T. A; Staar, P.; Mishra, V.; Chatterjee, U.; Campuzano, J. C.; Scalapino, D. J.

    2016-01-01

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and −k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability. PMID:27312569

  9. Pairing in a dry Fermi sea

    DOE PAGESBeta

    Maier, Thomas A.; Staar, Peter; Mishra, V.; Chatterjee, Utpal; Campuzano, J. C.; Scalapino, Douglas J.

    2016-06-17

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, wemore » report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.« less

  10. Enhancement of critical currents in (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconducting tapes.

    SciTech Connect

    Balachandran, U.

    1998-11-11

    The performance of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconducting tapes in magnetic fields at 77 K is critical for winding this material into high-field magnets. We have recently enhanced the transport current (I{sub c}) of multifilament Ag-clad Bi-2223 tapes in a self-field at 77 K by increasing the packing density of the precursor powder improving the mechanical deformation, optimizing the conductor design, and adjusting the cooling rate. I{sub c} values of >40 A were obtained repeatedly. However, a transport current of 42 A in a self-field declined to 4 A in a 0.2 T magnetic field applied parallel to the c-axis at 77 K. A new composite tape was then fabricated in which a YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (Y-123) film was deposited on the top of the Ag-sheathed Bi-2223 tape to shield the applied magnetic field and protect the central Bi-2223 filaments. Magnetization measurements showed that the critical current densities of the Y-123-coated, Ag-sheathed Bi-2223 tapes were higher than those of an uncoated tape. These preliminary results may provide the basis for further improving the processing of long-length Bi-2223 tapes for high-field applications.

  11. Weak localization effect in superconducting thin films

    NASA Astrophysics Data System (ADS)

    Kim, Yong-Jihn; Chang, K. J.

    1997-03-01

    It was claimed(1. R. C. Dynes et al., Phys. Rev. Lett. 57), 2195 (1986). that the Eliashberg theory breaks down for two-dimensional superconductivity in weakly disordered systems. From tunneling measurements on Pb films, both the electron-phonon interaction λ and the Coulomb pseudopotential μ^* were suggested to decrease by disordering. In this problem, it was previously noted that the Dyson expansion of Green's function in the presence of impurities is inappropriate.(2. Y.-J. Kim and A. W. Overhauser, Phys. Rev. B47), 8025 (1993). Alternatively, employing time-reversed scattered-state pairs, we note that the phonon-mediated coupling parameter λ is decreased by weak localization. With solving both the BCS and Eliashberg gap equations, we find good agreements between our calculations and existing experimental data. We also discuss the weak localization effect on superconductivity in one- and three-dimensional systems.

  12. Critical parameters of superconducting materials and structures

    SciTech Connect

    Fluss, M.J.; Howell, R.H.; Sterne, P.A.; Dykes, J.W.; Mosley, W.D.; Chaiken, A.; Ralls, K.; Radousky, H.

    1995-02-01

    We report here the completion of a one year project to investigate the synthesis, electronic structure, defect structure, and physical transport properties of high temperature superconducting oxide materials. During the course of this project we produced some of the finest samples of single crystal detwinned YBa{sub 2}Cu{sub 3}O{sub 7}, and stoichiometrically perfect (Ba,K)BiO{sub 3}. We deduced the Fermi surface of YBa{sub 2}Cu{sub 3}O{sub 7}, (La,Sr){sub 2}CuO{sub 4}, and (Ba,K)BiO{sub 3} through the recording of the electron momentum density in these materials as measured by positron annihilation spectroscopy and angle resolved photoemission. We also performed extensive studies on Pr substituted (Y,Pr)Ba{sub 2}Cu{sub 3}O{sub 7} so as to further understand the origin of the electron pairing leading to superconductivity.

  13. Engineering artificial Hamiltonians with parametric superconducting circuits

    NASA Astrophysics Data System (ADS)

    Lu, Yao; Chakram, Srivatsan; Leung, Nelson; Naik, Ravi; Earnest, Nathan; Groszkowski, Peter; Koch, Jens; Kapit, Eliot; Schuster, David

    One major challenge in building a large scale quantum computer is to generate and manipulate interactions between its many qubits. One promising approach is to use parametric flux or voltage modulation to realize effective interactions between different components of superconducting circuits, generating artificial Hamiltonians that are suitable for various quantum computation tasks, which might be difficult to achieve through other means. We propose a parametric superconducting circuit where transmon qubits and resonators are coupled to a flux-modulated parametric coupler. We show that with this device, arbitrary pairs of qubits or resonators in the circuit can be selectively and simultaneously brought into resonance with each other and swap excitations at a controllable rate. This allows for the creation of various artificial circuit Hamiltonians that are suitable for a number of applications such as single qubit state stablization, parametric qubit state readout, autonomous error correction and so on.

  14. The superconducting solenoid magnets for MICE

    SciTech Connect

    Green, Michael A.

    2002-12-22

    The Muon Ionization Cooling Experiment (MICE) is a channel of superconducting solenoid magnets. The magnets in MICE are around the RF cavities, absorbers (liquid or solid) and the primary particle detectors [1], [2]. The MICE superconducting solenoid system consists of eighteen coils that are grouped in three types of magnet assemblies. The cooling channel consists of two complete cell of an SFOFO cooling channel. Each cell consists of a focusing coil pair around an absorber and a coupling coil around a RF cavity that re-accelerates the muons to their original momentum. At the ends of the experiment are uniform field solenoids for the particle detectors and a set of matching coils used to match the muon beam to the cooling cells. Three absorbers are used instead of two in order to shield the detectors from dark currents generated by the RF cavities at high operating acceleration gradients.

  15. Topological Superconductivity with Magnetic Atoms

    NASA Astrophysics Data System (ADS)

    Glazman, Leonid

    2015-03-01

    Chains of magnetic impurities embedded in a conventional s-wave superconductor may induce the formation of a topologically non-trivial superconducting phase. If such a phase is formed along a chain, then its ends carry Majorana fermions. We investigate this possibility theoretically by developing a tight-binding Bogoliubov-de Gennes description, starting from the Shiba bound states induced by the individual magnetic impurities. While the resulting Hamiltonian has similarities with the Kitaev model for one-dimensional spinless p-wave superconductors, there are also important differences, most notably the long-range (power-law) nature of hopping and pairing as well as the complex hopping amplitudes. We develop an analytical theory, complemented by numerical approaches, which accounts for the electron long-range pairing and hopping along the chain, inhomogeneous magnetic order in the chain of embedded impurities or spin-orbit coupling in the host superconductor, and the possibility of direct electron hopping between the impurity atoms. This allows us to elucidate the domain of parameters favoring the formation of a topological phase and to find the spatial structure of Majorana states appearing in that phase. This talk is based on joint work with F. von Oppen, Falko Pientka, and Yang Peng.

  16. Electric field-induced superconducting transition of insulating FeSe thin film at 35 K

    NASA Astrophysics Data System (ADS)

    Hanzawa, Kota; Sato, Hikaru; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2016-04-01

    It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (Tc) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-Tc cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high Tc because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (∼10 nm thick) of FeSe, we report a high Tc of 35 K, which is 4× higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 × 1015 cm-2 (the average volume density of 1.7 × 1021 cm-3), is the origin of the high-Tc superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate Tc for insulating parent materials.

  17. Electric field-induced superconducting transition of insulating FeSe thin film at 35 K.

    PubMed

    Hanzawa, Kota; Sato, Hikaru; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2016-04-12

    It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (Tc) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-Tc cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high Tc because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (∼10 nm thick) of FeSe, we report a high Tc of 35 K, which is 4× higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 × 10(15) cm(-2) (the average volume density of 1.7 × 10(21) cm(-3)), is the origin of the high-Tc superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate Tc for insulating parent materials. PMID:27035956

  18. Superconducting thermoelectric generator

    SciTech Connect

    Metzger, J.D.; El-Genk, M.S.

    1998-05-05

    An apparatus and method for producing electricity from heat is disclosed. The present invention is a thermoelectric generator that uses materials with substantially no electrical resistance, often called superconductors, to efficiently convert heat into electrical energy without resistive losses. Preferably, an array of superconducting elements is encased within a second material with a high thermal conductivity. The second material is preferably a semiconductor. Alternatively, the superconducting material can be doped on a base semiconducting material, or the superconducting material and the semiconducting material can exist as alternating, interleaved layers of waferlike materials. A temperature gradient imposed across the boundary of the two materials establishes an electrical potential related to the magnitude of the temperature gradient. The superconducting material carries the resulting electrical current at zero resistivity, thereby eliminating resistive losses. The elimination of resistive losses significantly increases the conversion efficiency of the thermoelectric device. 4 figs.

  19. Superconducting thermoelectric generator

    SciTech Connect

    Metzger, J.D.; El-Genk, M.S.

    1996-01-01

    An apparatus and method for producing electricity from heat. The present invention is a thermoelectric generator that uses materials with substantially no electrical resistance, often called superconductors, to efficiently convert heat into electrical energy without resistive losses. Preferably, an array of superconducting elements is encased within a second material with a high thermal conductivity. The second material is preferably a semiconductor. Alternatively, the superconducting material can be doped on a base semiconducting material, or the superconducting material and the semiconducting material can exist as alternating, interleaved layers of waferlike materials. A temperature gradient imposed across the boundary of the two materials establishes an electrical potential related to the magnitude of the temperature gradient. The superconducting material carries the resulting electrical current at zero resistivity, thereby eliminating resistive losses. The elimination of resistive losses significantly increases the conversion efficiency of the thermoelectric device.

  20. Superconducting thermoelectric generator

    DOEpatents

    Metzger, John D.; El-Genk, Mohamed S.

    1998-01-01

    An apparatus and method for producing electricity from heat. The present invention is a thermoelectric generator that uses materials with substantially no electrical resistance, often called superconductors, to efficiently convert heat into electrical energy without resistive losses. Preferably, an array of superconducting elements is encased within a second material with a high thermal conductivity. The second material is preferably a semiconductor. Alternatively, the superconducting material can be doped on a base semiconducting material, or the superconducting material and the semiconducting material can exist as alternating, interleaved layers of waferlike materials. A temperature gradient imposed across the boundary of the two materials establishes an electrical potential related to the magnitude of the temperature gradient. The superconducting material carries the resulting electrical current at zero resistivity, thereby eliminating resistive losses. The elimination of resistive losses significantly increases the conversion efficiency of the thermoelectric device.

  1. Supertubes and Superconducting Membranes

    SciTech Connect

    Cordero, Ruben; Miguel-Pilar, Zelin

    2007-02-09

    We show the equivalence between configurations that arise from string theory of type IIA, called supertubes, and superconducting membranes at the bosonic level. We find equilibrium and oscillating configurations for a tubular membrane carrying a current along its axis.

  2. Hybrid superconducting magnetic suspensions

    SciTech Connect

    Tixador, P.; Hiebel, P.; Brunet, Y.

    1996-07-01

    Superconductors, especially high T{sub c} ones, are the most attractive materials to design stable and fully passive magnetic suspensions which have to control five degrees of freedom. The hybrid superconducting magnetic suspensions present high performances and a simple cooling mode. They consist of a permanent magnet bearing, stabilized by a suitable magnet-superconductor structure. Several designs are given and compared in terms of forces and stiffnesses. The design of the magnet bearing plays an important part. The superconducting magnetic bearing participates less in levitation but must provide a high stabilizing stiffness. This is achieved by the magnet configuration, a good material in term of critical current density and field cooling. A hybrid superconducting suspension for a flywheel is presented. This system consists of a magnet thrust bearing stabilized by superconductors interacting with an alternating polarity magnet structure. First tests and results are reported. Superconducting materials are magnetically melt-textured YBaCuO.

  3. Observation of Double-Dome Superconductivity in Potassium-Doped FeSe Thin Films.

    PubMed

    Song, Can-Li; Zhang, Hui-Min; Zhong, Yong; Hu, Xiao-Peng; Ji, Shuai-Hua; Wang, Lili; He, Ke; Ma, Xu-Cun; Xue, Qi-Kun

    2016-04-15

    We report on the emergence of two disconnected superconducting domes in alkali-metal potassium- (K-)doped FeSe ultrathin films grown on graphitized SiC(0001). The superconductivity exhibits hypersensitivity to K dosage in the lower-T_{c} dome, whereas in the heavily electron-doped higher-T_{c} dome it becomes spatially homogeneous and robust against disorder, supportive of a conventional Cooper-pairing mechanism. Furthermore, the heavily K-doped multilayer FeSe films all reveal a large superconducting gap of ∼14  meV, irrespective of film thickness, verifying the higher-T_{c} superconductivity only in the topmost FeSe layer. The unusual finding of a double-dome superconducting phase is a step towards the mechanistic understanding of superconductivity in FeSe-derived superconductors. PMID:27127981

  4. Observation of Double-Dome Superconductivity in Potassium-Doped FeSe Thin Films

    NASA Astrophysics Data System (ADS)

    Song, Can-Li; Zhang, Hui-Min; Zhong, Yong; Hu, Xiao-Peng; Ji, Shuai-Hua; Wang, Lili; He, Ke; Ma, Xu-Cun; Xue, Qi-Kun

    2016-04-01

    We report on the emergence of two disconnected superconducting domes in alkali-metal potassium- (K-)doped FeSe ultrathin films grown on graphitized SiC(0001). The superconductivity exhibits hypersensitivity to K dosage in the lower-Tc dome, whereas in the heavily electron-doped higher-Tc dome it becomes spatially homogeneous and robust against disorder, supportive of a conventional Cooper-pairing mechanism. Furthermore, the heavily K-doped multilayer FeSe films all reveal a large superconducting gap of ˜14 meV , irrespective of film thickness, verifying the higher-Tc superconductivity only in the topmost FeSe layer. The unusual finding of a double-dome superconducting phase is a step towards the mechanistic understanding of superconductivity in FeSe-derived superconductors.

  5. Superconductive ceramic oxide combination

    SciTech Connect

    Chatterjee, D.K.; Mehrotra, A.K.; Mir, J.M.

    1991-03-05

    This patent describes the combination of a superconductive ceramic oxide which degrades in conductivity upon contact of ambient air with its surface and, interposed between the ceramic oxide surface and ambient air in the amount of at least 1 mg per square meter of surface area of the superconductive ceramic oxide, a passivant polymer selected from the group consisting of a polyester ionomer and an alkyl cellulose.

  6. Making Superconducting Welds between Superconducting Wires

    NASA Technical Reports Server (NTRS)

    Penanen, Konstantin I.; Eom, Byeong Ho

    2008-01-01

    A technique for making superconducting joints between wires made of dissimilar superconducting metals has been devised. The technique is especially suitable for fabrication of superconducting circuits needed to support persistent electric currents in electromagnets in diverse cryogenic applications. Examples of such electromagnets include those in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems and in superconducting quantum interference devices (SQUIDs). Sometimes, it is desirable to fabricate different parts of a persistent-current-supporting superconducting loop from different metals. For example, a sensory coil in a SQUID might be made of Pb, a Pb/Sn alloy, or a Cu wire plated with Pb/Sn, while the connections to the sensory coil might be made via Nb or Nb/Ti wires. Conventional wire-bonding techniques, including resistance spot welding and pressed contact, are not workable because of large differences between the hardnesses and melting temperatures of the different metals. The present technique is not subject to this limitation. The present technique involves the use (1) of a cheap, miniature, easy-to-operate, capacitor-discharging welding apparatus that has an Nb or Nb/Ti tip and operates with a continuous local flow of gaseous helium and (2) preparation of a joint in a special spark-discharge welding geometry. In a typical application, a piece of Nb foil about 25 m thick is rolled to form a tube, into which is inserted a wire that one seeks to weld to the tube (see figure). The tube can be slightly crimped for mechanical stability. Then a spark weld is made by use of the aforementioned apparatus with energy and time settings chosen to melt a small section of the niobium foil. The energy setting corresponds to the setting of a voltage to which the capacitor is charged. In an experiment, the technique was used to weld an Nb foil to a copper wire coated with a Pb/Sn soft solder, which is superconducting. The joint was evaluated as

  7. Strongly enhanced vortex pinning from 4 to 77 K in magnetic fields up to 31 T in 15 mol.% Zr-added (Gd, Y)-Ba-Cu-O superconducting tapes

    SciTech Connect

    Xu, A; Delgado, L; Khatri, N; Liu, Y; Selvamanickam, V; Abraimov, D; Jaroszynski, J; Kametani, F; Larbalestier, DC

    2014-04-01

    Applications of REBCO coated conductors are now being developed for a very wide range of temperatures and magnetic fields and it is not yet clear whether vortex pinning strategies aimed for high temperature, low field operation are equally valid at lower temperatures and higher fields. A detailed characterization of the superconducting properties of a 15 mol.% Zr-added REBCO thin film made by metal organic chemical vapor deposition, from 4.2 to 77 K under magnetic fields up to 31 T is presented in this article. Even at a such high level of Zr addition, T-c depression has been avoided (T-c = 91 K), while at the same time an exceptionally high irreversibility field H-irr approximate to 14.8 T at 77 K and a remarkably high vortex pinning force density F-p approximate to 1.7 TN/m(3) at 4.2 K have been achieved. We ascribe the excellent pinning performance at high temperatures to the high density (equivalent vortex matching field similar to 7 T) of self-assembled BZO nanorods, while the low temperature pinning force is enhanced by large additional pinning which we ascribe to strain-induced point defects induced in the REBCO matrix by the BZO nanorods. Our results suggest even more room for further performance enhancement of commercial REBCO coated conductors and point the way to REBCO coil applications at liquid nitrogen temperatures since the critical current density J(c)(H//c) characteristic at 77 K are now almost identical to those of fully optimized Nb-Ti at 4 K. (C) 2014 Author(s).

  8. Superconductive radiofrequency window assembly

    DOEpatents

    Phillips, Harry Lawrence; Elliott, Thomas S.

    1998-01-01

    The present invention is a superconducting radiofrequency window assembly for use in an electron beam accelerator. The srf window assembly (20) has a superconducting metal-ceramic design. The srf window assembly (20) comprises a superconducting frame (30), a ceramic plate (40) having a superconducting metallized area, and a superconducting eyelet (50) for sealing plate (40) into frame (30). The plate (40) is brazed to eyelet (50) which is then electron beam welded to frame (30). A method for providing a ceramic object mounted in a metal member to withstand cryogenic temperatures is also provided. The method involves a new metallization process for coating a selected area of a ceramic object with a thin film of a superconducting material. Finally, a method for assembling an electron beam accelerator cavity utilizing the srf window assembly is provided. The procedure is carried out within an ultra clean room to minimize exposure to particulates which adversely affect the performance of the cavity within the electron beam accelerator.

  9. Superconducting radiofrequency window assembly

    DOEpatents

    Phillips, Harry L.; Elliott, Thomas S.

    1997-01-01

    The present invention is a superconducting radiofrequency window assembly for use in an electron beam accelerator. The srf window assembly (20) has a superconducting metal-ceramic design. The srf window assembly (20) comprises a superconducting frame (30), a ceramic plate (40) having a superconducting metallized area, and a superconducting eyelet (50) for sealing plate (40) into frame (30). The plate (40) is brazed to eyelet (50) which is then electron beam welded to frame (30). A method for providing a ceramic object mounted in a metal member to withstand cryogenic temperatures is also provided. The method involves a new metallization process for coating a selected area of a ceramic object with a thin film of a superconducting material. Finally, a method for assembling an electron beam accelerator cavity utilizing the srf window assembly is provided. The procedure is carried out within an ultra clean room to minimize exposure to particulates which adversely affect the performance of the cavity within the electron beam accelerator.

  10. Superconducting transmission line particle detector

    DOEpatents

    Gray, Kenneth E.

    1989-01-01

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

  11. Superconducting transmission line particle detector

    DOEpatents

    Gray, K.E.

    1988-07-28

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

  12. Two-particle self-consistent approach to unconventional superconductivity

    NASA Astrophysics Data System (ADS)

    Otsuki, Junya

    2012-03-01

    A nonperturbative approach to unconventional superconductivity is developed based on the idea of two-particle self-consistent (TPSC) theory by Vilk and Tremblay. A sum rule, which the momentum-dependent pairing susceptibility satisfies, is derived. An effective pairing interaction between quasiparticles is determined so that the susceptibility should fulfill this exact sum rule, in which fluctuations belonging to different symmetries couple at finite momentum. It is demonstrated that the mode coupling between d-wave and s-wave pairing fluctuations leads to suppression of the d-wave fluctuation near the Mott insulator.

  13. Nuclear pairing at finite temperature and angular momentum

    SciTech Connect

    Dang, N. Dinh; Hung, N. Quang

    2009-01-28

    We propose an approach to nuclear pairing at finite temperature and angular momentum. This approach includes the effects due to the quasiparticle-number fluctuation and dynamic coupling to pair vibrations within the self-consistent quasiparticle random-phase approximation. The pairing gaps, total energies, and heat capacities are calculated within a doubly folded multilevel model as well as several realistic nuclei. The results obtained show that, in the region of moderate and strong couplings, the sharp transition between the superconducting and normal phases is smoothed out. This is manifested in a thermal pairing gap, which does not collapse at a critical temperature predicted by the conventional Bardeen-Cooper-Schrieffer's (BCS) theory, but has a tail extended to high temperatures. Moreover, this approach also predicts the appearance of a thermally assisted pairing at finite angular momentum. The effect of backbending of the momentum of inertia as a function of the square of angular velocity is also discussed.

  14. Prediction of superconductivity in Li-intercalated bilayer phosphorene

    SciTech Connect

    Huang, G. Q.; Xing, Z. W.; Xing, D. Y.

    2015-03-16

    It is shown that bilayer phosphorene can be transformed from a direct-gap semiconductor to a BCS superconductor by intercalating Li atoms. For the Li-intercalated bilayer phosphorene, we find that the electron occupation of Li-derived band is small and superconductivity is intrinsic. With increasing the intercalation of Li atoms, both increased metallicity and strong electron-phonon coupling are favorable for the enhancement of superconductivity. The obtained electron-phonon coupling λ can be larger than 1 and the superconducting temperature T{sub c} can be increased up to 16.5 K, suggesting that phosphorene may be a good candidate for a nanoscale superconductor.

  15. Strong Single-Photon Coupling in Superconducting Quantum Magnetomechanics

    NASA Astrophysics Data System (ADS)

    Via, Guillem; Kirchmair, Gerhard; Romero-Isart, Oriol

    2015-04-01

    We show that the inductive coupling between the quantum mechanical motion of a superconducting microcantilever and a flux-dependent microwave quantum circuit can attain the strong single-photon nanomechanical coupling regime with feasible experimental parameters. We propose to use a superconducting strip, which is in the Meissner state, at the tip of a cantilever. A pickup coil collects the flux generated by the sheet currents induced by an external quadrupole magnetic field centered at the strip location. The position-dependent magnetic response of the superconducting strip, enhanced by both diamagnetism and demagnetizing effects, leads to a strong magnetomechanical coupling to quantum circuits.

  16. Giant enhancement in critical current density, up to a hundredfold, in superconducting NaFe0.97Co0.03 As single crystals under hydrostatic pressure.

    PubMed

    Shabbir, Babar; Wang, Xiaolin; Ghorbani, S R; Wang, A F; Dou, Shixue; Chen, X H

    2015-01-01

    Tremendous efforts towards improvement in the critical current density "Jc" of iron based superconductors (FeSCs), especially at relatively low temperatures and magnetic fields, have been made so far through different methods, resulting in real progress. Jc at high temperatures in high fields still needs to be further improved, however, in order to meet the requirements of practical applications. Here, we demonstrate a simple approach to achieve this. Hydrostatic pressure can significantly enhance Jc in NaFe0.97Co0.03As single crystals by at least tenfold at low field and more than a hundredfold at high fields. Significant enhancement in the in-field performance of NaFe0.97Co0.03As single crystal in terms of pinning force density (Fp) is found at high pressures. At high fields, the Fp is over 20 and 80 times higher than under ambient pressure at12 K and 14 K, respectively, at P = 1 GPa. We believe that the Co-doped NaFeAs compounds are very exciting and deserve to be more intensively investigated. Finally, it is worthwhile to say that by using hydrostatic pressure, we can achieve more milestones in terms of high Jc values in tapes, wires or films of other Fe-based superconductors. PMID:26030085

  17. Giant enhancement in critical current density, up to a hundredfold, in superconducting NaFe0.97Co0.03 As single crystals under hydrostatic pressure

    PubMed Central

    Shabbir, Babar; Wang, Xiaolin; Ghorbani, S. R.; Wang, A. F.; Dou, Shixue; Chen, X. H.

    2015-01-01

    Tremendous efforts towards improvement in the critical current density “Jc” of iron based superconductors (FeSCs), especially at relatively low temperatures and magnetic fields, have been made so far through different methods, resulting in real progress. Jc at high temperatures in high fields still needs to be further improved, however, in order to meet the requirements of practical applications. Here, we demonstrate a simple approach to achieve this. Hydrostatic pressure can significantly enhance Jc in NaFe0.97Co0.03As single crystals by at least tenfold at low field and more than a hundredfold at high fields. Significant enhancement in the in-field performance of NaFe0.97Co0.03As single crystal in terms of pinning force density (Fp) is found at high pressures. At high fields, the Fp is over 20 and 80 times higher than under ambient pressure at12 K and 14 K, respectively, at P = 1 GPa. We believe that the Co-doped NaFeAs compounds are very exciting and deserve to be more intensively investigated. Finally, it is worthwhile to say that by using hydrostatic pressure, we can achieve more milestones in terms of high Jc values in tapes, wires or films of other Fe-based superconductors. PMID:26030085

  18. Paired States of Composite Fermions

    NASA Astrophysics Data System (ADS)

    Bonesteel, N. E.

    2002-03-01

    There is compelling theoretical evidence(R. Morf, Phys. Rev. Lett. 80), 1505 (1998). that the ν=5/2 fractional quantum Hall state is a Moore-Read state(G. Moore and N. Read, Nucl. Phys. B 360), 362 (1991). -- a state which can be viewed as a spin-polarized p-wave `superconductor' of composite fermions. The question remains, how can one test this hypothesis experimentally? To address this we have developed a semi-phenomenological description of this state in which the Halperin-Lee-Read(B.I. Halperin, P.A. Lee, and N. Read, Phys. Rev. B 47), 7312 (1993). theory of the half-filled Landau level is modified by adding a p-wave pairing interaction between composite fermions by hand. The electromagnetic response functions for the resulting mean-field superconducting state are then calculated and used in an RPA calculation of the physical electronic response. For a clean enough sample, and for q << k_f, the transverse electromagnetic response function for composite fermions is governed by type-II coherence factors and shows a `Hebel-Slichter'-like peak as a function of temperature for low enough frequency. The possibility (and potential difficulties) of observing this peak indirectly in surface-acoustic-wave propagation experiments will be discussed. The observation of such a coherence peak would provide strong evidence of BCS pairing in the 5/2 state. Work supported by US DOE Grant No. DE-FG02-97ER45639. Work done in collaboration with K.C. Foster (FSU) and S.H. Simon (Lucent). note

  19. Matched-pair classification

    SciTech Connect

    Theiler, James P

    2009-01-01

    Following an analogous distinction in statistical hypothesis testing, we investigate variants of machine learning where the training set comes in matched pairs. We demonstrate that even conventional classifiers can exhibit improved performance when the input data has a matched-pair structure. Online algorithms, in particular, converge quicker when the data is presented in pairs. In some scenarios (such as the weak signal detection problem), matched pairs can be generated from independent samples, with the effect not only doubling the nominal size of the training set, but of providing the structure that leads to better learning. A family of 'dipole' algorithms is introduced that explicitly takes advantage of matched-pair structure in the input data and leads to further performance gains. Finally, we illustrate the application of matched-pair learning to chemical plume detection in hyperspectral imagery.

  20. Spin-triplet superconducting proximity effect in SrRuO3/Sr2RuO4 hybrids

    NASA Astrophysics Data System (ADS)

    Anwar, Muhammad Shahbaz; Lee, Seungran; Ishiguro, R.; Sugimoto, Y.; Tano, Y.; Kang, S. J.; Shin, Y. J.; Yonezawa, Shingo; Takayanagi, H.; Noh, Tae Won; Maeno, Yoshiteru; Yoshiteru Maeno Team; Tae Won Noh Team; Takayanagi Collaboration

    Spin-triplet superconducting correlations can be induced into a ferromagnet (FM) out of a spin-singlet superconductor (SSC) via magnetic inhomogeneity at the SSC/FM interface. In this case, however, the proximity effect is not readily controllable because spins are quenched. In contrast, superconducting spintronics can be realized by using spin-triplet superconductors (TSCs) and FM hybrids. Theoretically, it has been predicted that spin-triplet proximity effect can be controlled by the relative orientations between the magnetization in the FM and the Cooper pair spin in TSC. We fabricate Au(600-nm)/SrRuO3(15-nm) /Sr2RuO4 junctions by growing epitaxial SrRuO3 FM thin films on Sr2RuO4 TSC single crystals. Differential conductance vs voltage shows the conductance enhancements with superconducting transitions at three different characteristic voltages. These three features can naturally be interpreted as originating from the SC gaps in bulk Sr2RuO4 as well as at two distinct interfaces (Au/SrRuO3 and SrRuO3/Sr2RuO4) . The effect of applied magnetic field reveals that the proximity effect is robust against the loss of magnetic inhomogeneity.