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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.

    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.

  2. 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.

  3. 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.

  4. 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.

  5. Superconductivity: The persistence of pairs

    SciTech Connect

    Edelman, Alex; Littlewood, Peter

    2015-05-20

    Superconductivity stems from a weak attraction between electrons that causes them to form bound pairs and behave much like bosons. These so-called Cooper pairs are phase coherent, which leads to the astonishing properties of zero electrical resistance and magnetic flux expulsion typical of superconducting materials. This coherent state may be qualitatively understood within the Bose–Einstein condensate (BEC) model, which predicts that a gas of interacting bosons will become unstable below a critical temperature and condense into a phase of matter with a macroscopic, coherent population in the lowest energy state, as happens in 4He or cold atomic gases. The successful theory proposed by Bardeen, Cooper and Schrieffer (BCS) predicts that at the superconducting transition temperature Tc, electrons simultaneously form pairs and condense, with no sign of pairing above Tc. Theorists have long surmised that the BCS and BEC models are opposite limits of a single theory and that strong interactions or low density can, in principle, drive the system to a paired state at a temperature Tpair higher than Tc, making the transition to the superconducting state BEC-like (Fig. 1). Yet most superconductors to date are reasonably well described by BCS theory or its extensions, and there has been scant evidence in electronic materials for the existence of pairing independent of the full superconducting state (though an active debate rages over the cuprate superconductors). Writing in Nature, Jeremy Levy and colleagues have now used ingenious nanostructured devices to provide evidence for electron pairing1. Perhaps surprisingly, the material they have studied is a venerable, yet enigmatic, low-temperature superconductor, SrTiO3.

  6. Enhanced superconductivity of fullerenes

    DOEpatents

    Washington, II, Aaron L.; Teprovich, Joseph A.; Zidan, Ragaiy

    2017-06-20

    Methods for enhancing characteristics of superconductive fullerenes and devices incorporating the fullerenes are disclosed. Enhancements can include increase in the critical transition temperature at a constant magnetic field; the existence of a superconducting hysteresis over a changing magnetic field; a decrease in the stabilizing magnetic field required for the onset of superconductivity; and/or an increase in the stability of superconductivity over a large magnetic field. The enhancements can be brought about by transmitting electromagnetic radiation to the superconductive fullerene such that the electromagnetic radiation impinges on the fullerene with an energy that is greater than the band gap of the fullerene.

  7. 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.

  8. 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.

  9. Isotropic superconducting gaps with enhanced pairing on electron Fermi surfaces in FeTe0.55Se0.45

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

    We used angle-resolved photoemission spectroscopy to reveal directly the momentum distribution of the superconducting gap in FeTe1-xSex, which has the simplest structure of all Fe-based superconductors. We found isotropic superconducting gaps on all Fermi surfaces whose sizes can be fitted by a single gap function derived from a strong coupling approach, promoting local antiferromagnetic exchange interactions as a serious candidate for the pairing origin.

  10. Cooper pairsʼ magnetic moment in MCFL color superconductivity

    NASA Astrophysics Data System (ADS)

    Feng, Bo; Ferrer, Efrain J.; de la Incera, Vivian

    2011-12-01

    We investigate the effect of the alignment of the magnetic moments of Cooper pairs of charged quarks that form at high density in three-flavor quark matter. The high-density phase of this matter in the presence of a magnetic field is known to be the Magnetic Color-Flavor-Locked (MCFL) phase of color superconductivity. We derive the Fierz identities of the theory and show how the explicit breaking of the rotational symmetry by the uniform magnetic field opens new channels of interactions and allows the formation of a new diquark condensate. The new order parameter is a spin-1 condensate proportional to the component in the field direction of the average magnetic moment of the pairs of charged quarks. The magnitude of the spin-1 condensate becomes comparable to the larger of the two scalar gaps in the region of large fields. The existence of the spin-1 condensate is unavoidable, as in the presence of a magnetic field there is no solution of the gap equations with nonzero scalar gaps and zero magnetic moment condensate. This is consistent with the fact that the extra condensate does not break any symmetry that has not already been broken by the known MCFL gaps. The spin-1 condensate enhances the condensation energy of pairs formed by charged quarks and the magnetization of the system. We discuss the possible consequences of the new order parameter on the issue of the chromomagnetic instability that appears in color superconductivity at moderate density.

  11. Induced spectral gap and pairing correlations from superconducting proximity effect

    NASA Astrophysics Data System (ADS)

    Chiu, Ching-Kai; Cole, William S.; Das Sarma, S.

    2016-09-01

    We theoretically consider superconducting proximity effect, using the Bogoliubov-de Gennes (BdG) theory, in heterostructure sandwich-type geometries involving a normal s -wave superconductor and a nonsuperconducting material with the proximity effect being driven by Cooper pairs tunneling from the superconducting slab to the nonsuperconducting slab. Applications of the superconducting proximity effect may rely on an induced spectral gap or induced pairing correlations without any spectral gap. We clarify that in a nonsuperconducting material the induced spectral gap and pairing correlations are independent physical quantities arising from the proximity effect. This is a crucial issue in proposals to create topological superconductivity through the proximity effect. Heterostructures of three-dimensional topological insulator (TI) slabs on conventional s -wave superconductor (SC) substrates provide a platform, with proximity-induced topological superconductivity expected to be observed on the "naked" top surface of a thin TI slab. We theoretically study the induced superconducting gap on this naked surface. In addition, we compare against the induced spectral gap in heterostructures of SC with a normal metal or a semiconductor with strong spin-orbit coupling and a Zeeman splitting potential (another promising platform for topological superconductivity). We find that for any model for the non-SC metal (including metallic TI) the induced spectral gap on the naked surface decays as L-3 as the thickness (L ) of the non-SC slab is increased in contrast to the slower 1 /L decay of the pairing correlations. Our distinction between proximity-induced spectral gap (with its faster spatial decay) and pairing correlation (with its slower spatial decay) has important implications for the currently active search for topological superconductivity and Majorana fermions in various superconducting heterostructures.

  12. Pair structure and the pairing interaction in a bilayer Hubbard model for unconventional superconductivity

    SciTech Connect

    Maier, Thomas A

    2011-01-01

    The bilayer Hubbard model with an intralayer hopping t and an interlayer hopping t{sub {lambda}} provides an interesting testing ground for several aspects of what has been called unconventional superconductivity. One can study the type of pair structures which arise when there are multiple Fermi surfaces. One can also examine the pairing for a system in which the structure of the spin-fluctuation spectral weight can be changed. Using a dynamic cluster quantum Monte Carlo approximation, we find that near half filling, if the splitting between the bonding and antibonding bands t{sub {lambda}}/t is small, the gap has B{sub 1g} (d{sub x{sup 2}-y{sup 2}}-wave) symmetry, but when the splitting becomes larger, A{sub 1g} (s{sup {+-}}-wave) pairing is favored. We also find that in the s{sup {+-}} pairing region, the pairing is driven by interlayer spin fluctuations and that T{sub c} is enhanced.

  13. Topological superconductivity and unconventional pairing in oxide interfaces.

    PubMed

    Scheurer, Mathias S; Schmalian, Jörg

    2015-01-28

    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. Enhancing superconductivity in A3C60 fullerides

    NASA Astrophysics Data System (ADS)

    Kim, Minjae; Nomura, Yusuke; Ferrero, Michel; Seth, Priyanka; Parcollet, Olivier; Georges, Antoine

    2016-10-01

    Motivated by the recent experimental report of a possible light-induced superconductivity in K3C60 at high temperature [Mitrano et al., Nature 530, 451 (2016), 10.1038/nature16522], we investigate theoretical mechanisms for enhanced superconductivity in A3C60 fullerenes. We find that an "interaction imbalance" corresponding to a smaller value of the Coulomb matrix element for two of the molecular orbitals in comparison to the third one, efficiently enhances superconductivity. Furthermore, we perform first-principle calculations of the changes in the electronic structure and in the screened Coulomb matrix elements of K3C60 , brought in by the deformation associated with the pumped T1 u intramolecular mode. We find that an interaction imbalance is indeed induced, with a favorable sign and magnitude for superconductivity enhancement. The physical mechanism responsible for this enhancement consists of a stabilization of the intramolecular states containing a singlet pair, while preserving the orbital fluctuations allowing for a coherent interorbital delocalization of the pair. Other perturbations have also been considered and found to be detrimental to superconductivity. The light-induced deformation and ensuing interaction imbalance is shown to bring superconductivity further into the strong-coupling regime.

  15. 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.

  16. Localized Superconductivity in Systems with Inhomogeneous Mass of Cooper Pairs

    NASA Astrophysics Data System (ADS)

    Kopasov, A. A.; Savinov, D. A.; Mel'nikov, A. S.

    2017-04-01

    Within the framework of the Ginzburg-Landau theory, we study the features of the localized nucleation of the order parameter in superconducting systems with inhomogeneous effective mass m of the Cooper pairs, which is due to the spatial modulation of the diffusion coefficient and/or fluctuations in the local anisotropy axis in the sample. In the asymptotics of the weak magnetic fields H, for which the magnetic length [Φ0/(2 πH)]1/2, where Φ0 is the magnetic-flux quantum, is much shorter than the inhomogeneity scale, the spatial scale of the order parameter is determined by the sample-average coherence length and the regular lattice of the Abrikosov vortices is formed in the superconductor. In sufficiently strong magnetic fields H, the order parameter is localized near the minima of the coherence length ξ ∝ m -1/2, which results in an increase in the critical temperature and destruction of the regular lattice of the Abrikosov vortices. Therefore, competition between the two superconductivity-nucleation types is observed during a gradual increase in the magnetic field, which leads to the positive curvature of the phase-transition line. We have also studied the features of the temperature dependences of the upper critical magnetic field for some model spatial mass profiles of the Cooper pairs. The obtained results are in good agreement with direct numerical calculations.

  17. 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

  18. Possible triplet superconducting order in a magnetic superconducting phase induced by paramagnetic pair breaking

    NASA Astrophysics Data System (ADS)

    Hosoya, Ken-ichi; Ikeda, Ryusuke

    2017-06-01

    Motivated by recent thermal conductivity measurements in the superconductor CeCoIn5, we theoretically examine a possible staggered spin-triplet superconducting order to be induced by the coupled spin-density-wave (SDW) and d -wave superconducting (SC) orders in the high-field and low-temperature (HFLT) SC phase peculiar to this material with strong paramagnetic pair-breaking (PPB). It is shown that one type of the π -triplet order is consistent with that explaining the thermal conductivity data and can naturally be incorporated in the picture that the HFLT phase is a consequence of the strong PPB effect inducing the SDW order and the FFLO spatial modulation parallel to the applied magnetic field.

  19. PREFACE: Anisotropic and multiband pairing: from borides to multicomponent superconductivity Anisotropic and multiband pairing: from borides to multicomponent superconductivity

    NASA Astrophysics Data System (ADS)

    Annett, James; Kusmartsev, Feodor; Bianconi, Antonio

    2009-01-01

    In 2001, the discovery of superconductivity in MgB2 rapidly led to the understanding that its complex multi-sheeted Fermi surface had two distinct values of the gap parameter Δ, each with its own characteristic temperature dependence. While the theory of multigap superconductivity had been developed long ago, this was the first well studied example where multigap behaviour was observed clearly, and indeed is essential to understand the full superconducting properties of the material. Following this discovery, evidence for multigap behaviour has appeared in a number of materials, including cuprates, ruthenates, and most recently the iron pnictides. As well as multigap pairing on different Fermi-surface sheets, strong gap anisotropy in k-space and strong modulations of the gap in real space (e.g. stripes and phase separation models) are also important in cuprates. The aim of this special section is to present a selection of high-quality papers from experts in these diverse systems, showing the links and common physical issues arising from the existence of multi-component Cooper pairing. The papers collected together for the special section provide a snapshot of the current state of the understanding of multi-component superconductivity in a wide range of materials. In a model motivated by MgB2, Tanaka and Eschrig describe Abrikosov vortex lattice in a two-gap superconductor, examining how the vortex structure is modified by three-dimensionality or quasi two-dimensionality of the Fermi surface. The multi-sheeted Fermi surfaces of the nickel borocarbides are probed using angle-resolved positron annihilation spectroscopy, described by Dugdale et al, leading to a full three-dimensional picture of the complex Fermi surface in this superconducting material. Possible evidence for multigap superconductivity in the iron pnictides, obtained using Andreev point contact spectroscopy, is described by Samuely et al. The iron pnictides are also the subject of the article by

  20. Higgs modes in the pair density wave superconducting state

    NASA Astrophysics Data System (ADS)

    Soto-Garrido, Rodrigo; Wang, Yuxuan; Fradkin, Eduardo; Cooper, S. Lance

    2017-06-01

    The pair density wave (PDW) superconducting state has been proposed to explain the layer-decoupling effect observed in the La2 -xBaxCuO4 compound at x =1 /8 [E. Berg, E. Fradkin, E.-A. Kim, S. A. Kivelson, V. Oganesyan, J. M. Tranquada, and S. C. Zhang, Phys. Rev. Lett. 99, 127003 (2007), 10.1103/PhysRevLett.99.127003]. In this state the superconducting order parameter is spatially modulated, in contrast with the usual superconducting (SC) state where the order parameter is uniform. In this paper, we study the properties of the amplitude (Higgs) modes in a unidirectional PDW state. To this end we consider a phenomenological model of PDW-type states coupled to a Fermi surface of fermionic quasiparticles. In contrast to conventional superconductors that have a single Higgs mode, unidirectional PDW superconductors have two Higgs modes. While in the PDW state the Fermi surface largely remains gapless, we find that the damping of the PDW Higgs modes into fermionic quasiparticles requires exceeding an energy threshold. We show that this suppression of damping in the PDW state is due to kinematics. As a result, only one of the two Higgs modes is significantly damped. In addition, motivated by the experimental phase diagram, we discuss the mixing of Higgs modes in the coexistence regime of the PDW and uniform SC states. These results should be observable directly in a Raman spectroscopy, in momentum resolved electron energy-loss spectroscopy, and in resonant inelastic x-ray scattering, thus providing evidence of the PDW states.

  1. 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.

  2. Emergent loop current order from pair density wave superconductivity

    NASA Astrophysics Data System (ADS)

    Kashyap, Manoj; Melchert, Drew; Agterberg, Daniel

    2015-03-01

    In addition to charge density wave (CDW) order, there is evidence that the pseudogap phase in the cuprates breaks time reversal symmetry. Here we show that pair density wave (PDW) states give rise to a translational invariant non-superconducting order parameter that breaks time reversal and parity symmetries, but preserves their product. This secondary order parameter has a different origin, but shares the same symmetry properties as a magnetoelectric loop current order that has been proposed earlier in the context of the cuprates to explain the appearance of intra-cell magnetic order. We further show that, due to fluctuations, this secondary loop current order, which represents the breaking of discrete symmetries, can preempt PDW order, which breaks both continuous and discrete symmetries. In such a phase, the emergent loop current order coexists with spatial short range CDW and short range superconducting order. Finally, we propose a PDW phase that accounts for intra-cell magnetic order and the Kerr effect, has CDW order consistent with x-ray scattering and nuclear magnetic resonance observations, and quasi-particle properties consistent with angle resolved photoemission scattering. We acknowledge support from NSF Grant No. DMR-1335215

  3. Enhancement of superexchange pairing in the periodically driven Hubbard model

    NASA Astrophysics Data System (ADS)

    Coulthard, J. R.; Clark, S. R.; Al-Assam, S.; Cavalleri, A.; Jaksch, D.

    2017-08-01

    Recent experiments performed on cuprates and alkali-doped fullerides have demonstrated that key signatures of superconductivity can be induced above the equilibrium critical temperature by optical modulation. These observations in disparate physical systems may indicate a general underlying mechanism. Multiple theories have been proposed, but these either consider specific features, such as competing instabilities, or focus on conventional BCS-type superconductivity. Here we show that periodic driving can enhance electron pairing in strongly correlated systems. Focusing on the strongly repulsive limit of the doped Hubbard model, we investigate in-gap, spatially inhomogeneous, on-site modulations. We demonstrate that such modulations substantially reduce electronic hopping, while simultaneously sustaining superexchange interactions and pair hopping via driving-induced virtual charge excitations. We calculate real-time dynamics for the one-dimensional case, starting from zero- and finite-temperature initial states, and we show that enhanced singlet-pair correlations emerge quickly and robustly in the out-of-equilibrium many-body state. Our results reveal a fundamental pairing mechanism that might underpin optically induced superconductivity in some strongly correlated quantum materials.

  4. Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain

    NASA Astrophysics Data System (ADS)

    Mito, Masaki; Matsui, Hideaki; Tsuruta, Kazuki; Yamaguchi, Tomiko; Nakamura, Kazuma; Deguchi, Hiroyuki; Shirakawa, Naoki; Adachi, Hiroki; Yamasaki, Tohru; Iwaoka, Hideaki; Ikoma, Yoshifumi; Horita, Zenji

    2016-11-01

    Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in Tc. Here we show that this shear strain approach is a new method for enhancing Tc and differs from that using hydrostatic strain. The enhancement of Tc is explained by an increase in net electron–electron coupling rather than a change in the density of states near the Fermi level. The shear strain effect in rhenium could be a successful example of manipulating Bardeen–Cooper–Schrieffer-type Cooper pairing, in which the unit cell volumes are indeed a key parameter.

  5. Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain.

    PubMed

    Mito, Masaki; Matsui, Hideaki; Tsuruta, Kazuki; Yamaguchi, Tomiko; Nakamura, Kazuma; Deguchi, Hiroyuki; Shirakawa, Naoki; Adachi, Hiroki; Yamasaki, Tohru; Iwaoka, Hideaki; Ikoma, Yoshifumi; Horita, Zenji

    2016-11-04

    Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in Tc. Here we show that this shear strain approach is a new method for enhancing Tc and differs from that using hydrostatic strain. The enhancement of Tc is explained by an increase in net electron-electron coupling rather than a change in the density of states near the Fermi level. The shear strain effect in rhenium could be a successful example of manipulating Bardeen-Cooper-Schrieffer-type Cooper pairing, in which the unit cell volumes are indeed a key parameter.

  6. Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain

    PubMed Central

    Mito, Masaki; Matsui, Hideaki; Tsuruta, Kazuki; Yamaguchi, Tomiko; Nakamura, Kazuma; Deguchi, Hiroyuki; Shirakawa, Naoki; Adachi, Hiroki; Yamasaki, Tohru; Iwaoka, Hideaki; Ikoma, Yoshifumi; Horita, Zenji

    2016-01-01

    Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in Tc. Here we show that this shear strain approach is a new method for enhancing Tc and differs from that using hydrostatic strain. The enhancement of Tc is explained by an increase in net electron–electron coupling rather than a change in the density of states near the Fermi level. The shear strain effect in rhenium could be a successful example of manipulating Bardeen–Cooper–Schrieffer-type Cooper pairing, in which the unit cell volumes are indeed a key parameter. PMID:27811983

  7. Superconductivity on a quasiperiodic lattice: Extended-to-localized crossover of Cooper pairs

    NASA Astrophysics Data System (ADS)

    Sakai, Shiro; Takemori, Nayuta; Koga, Akihisa; Arita, Ryotaro

    2017-01-01

    We study a possible superconductivity in quasiperiodic systems by portraying the issue within the attractive Hubbard model on a Penrose lattice. Applying a real-space dynamical mean-field theory to the model consisting of 4181 sites, we find a superconducting phase at low temperatures. Reflecting the nonperiodicity of the Penrose lattice, the superconducting state exhibits an inhomogeneity. According to the type of the inhomogeneity, the superconducting phase is categorized into three different regions which cross over each other. Among them, the weak-coupling region exhibits spatially extended Cooper pairs, which are nevertheless distinct from the conventional pairing of two electrons with opposite momenta.

  8. Emergent loop current order from pair density wave superconductivity

    NASA Astrophysics Data System (ADS)

    Agterberg, D. F.; Melchert, Drew S.; Kashyap, M. K.

    2015-02-01

    There is evidence that the pseudogap phase in the cuprates breaks time-reversal symmetry. Here we show that pair density wave (PDW) states give rise to a translational invariant nonsuperconducting order parameter that breaks time-reversal and parity symmetries, but preserves their product. This secondary order parameter has a different origin, but shares the same symmetry properties as a magnetoelectric loop current order that has been proposed earlier in the context of the cuprates to explain the appearance of intracell magnetic order. We further show that, due to fluctuations, this secondary loop current order, which breaks only discrete symmetries, can preempt PDW order, which breaks both continuous and discrete symmetries. In such a phase, the emergent loop current order coexists with spatial short-range superconducting order and possibly short-range charge density wave (CDW) order. Finally, we propose a PDW phase that accounts for intracell magnetic order and the Kerr effect, has CDW order consistent with x-ray scattering and nuclear magnetic resonance observations, and quasiparticle properties consistent with angle-resolved photoemission scattering.

  9. Electrical Conductivity through a Single Atomic Step Measured with the Proximity-Induced Superconducting Pair Correlation

    NASA Astrophysics Data System (ADS)

    Kim, Howon; Lin, Shi-Zeng; Graf, Matthias J.; Miyata, Yoshinori; Nagai, Yuki; Kato, Takeo; Hasegawa, Yukio

    2016-09-01

    Local disordered nanostructures in an atomically thick metallic layer on a semiconducting substrate play significant and decisive roles in transport properties of two-dimensional (2D) conductive systems. We measured the electrical conductivity through a step of monoatomic height in a truly microscopic manner by using as a signal the superconducting pair correlation induced by the proximity effect. The transport property across a step of a one-monolayer Pb surface metallic phase, formed on a Si(111) substrate, was evaluated by inducing the pair correlation around the local defect and measuring its response, i.e., the reduced density of states at the Fermi energy using scanning tunneling microscopy. We found that the step resistance has a significant contribution to the total resistance on a nominally flat surface. Our study also revealed that steps in the 2D metallic layer terminate the propagation of the pair correlation. Superconductivity is enhanced between the first surface step and the superconductor-normal-metal interface by reflectionless tunneling when the step is located within a coherence length.

  10. 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.

  11. The interplay between topological p-wave superconductivity and odd-frequency pairing in superconducting proximity systems

    NASA Astrophysics Data System (ADS)

    Stanev, Valentin; Galitski, Victor

    2014-03-01

    We study the proximity-induced superconductivity in semiconductor nanowires. The interplay between superconductivity and spin-orbit coupling plays a crucial role in proposals for creating Majorana fermions in semiconducting heterostructures. To further elucidate the physics of such devices we employ the quasiclassical Green's functions methods. We show that the spatial variations of the superconducting order parameter leads to non-trivial effects in the nanowire. We demonstrate the appearance of odd-frequency pairing correlations close to the boundaries, and discuss their effect on the density of states. Work supported by DOE-BES (DESC0001911) and Simons Foundation.

  12. 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.

  13. 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.

  14. Superconducting Pairing Correlations near a Kondo-destruction Quantum Critical Point in Cluster Impurity Models

    NASA Astrophysics Data System (ADS)

    Cai, Ang; Pixley, Jedediah; Si, Qimiao

    Heavy fermion metals represent a canonical system to study superconductivity driven by quantum criticality. We are particularly motivated by the properties of CeRhIn5, which shows the characteristic features of a Kondo destruction quantum critical point (QCP) in its normal state, and has one of the highest Tc's among the heavy fermion superconductors. As a first step to study this problem within a cluster-EDMFT approach, we analyze a four-site Anderson impurity model with the antiferromagnetic spin component of the cluster coupled to a sub-Ohmic bosonic bath. We find a QCP that belongs to the same universality class as the single-site Bose-Fermi Anderson model. Together with previous work on a two-site model, our result suggests that the Kondo destruction QCP is robust as cluster size increases. More importantly, we are able to calculate the d-wave pairing susceptibility, which we find to be enhanced near the QCP. Using this model as the effective cluster model of the periodic Anderson model, we are also able to study the superconducting pairing near the Kondo-destruction QCP of the lattice model; preliminary results will be presented.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  16. 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.

  17. Experimental investigation of the role of the triplet pairing in the superconducting spin-valve effect

    NASA Astrophysics Data System (ADS)

    Leksin, P. V.; Kamashev, A. A.; Garif'yanov, N. N.; Validov, A. A.; Fominov, Ya. V.; Schumann, J.; Kataev, V. E.; Büchner, B.; Garifullin, I. A.

    2016-11-01

    An important role of the morphology of a superconducting layer in the superconducting spin-valve effect has been established. The triplet pairing induced by the superconductor/ferromagnet proximity effect has been experimentally investigated for samples CoO x /Py1/Cu/Py2/Cu/Pb (where Py = Ni0.81Fe0.19) with a smooth superconducting layer. The optimization of the parameters of this structure has demonstrated a complete switching between the normal and superconducting states with a change in the relative orientation of magnetizations of the ferromagnetic layers from the antiparallel to orthogonal orientation. A pure triplet contribution has been observed for the sample with a permalloy layer thickness at which the superconducting spin-valve effect vanishes. A direct comparison of the experimental data with the theoretical calculation of the temperature of the transition to the superconducting state has been performed for the first time.

  18. Superconductivity

    DTIC Science & Technology

    1989-07-01

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

  19. Superconducting pairing of interacting electrons: implications from the two-impurity Anderson model

    NASA Astrophysics Data System (ADS)

    Zhu, Lijun; Zhu, Jian-Xin

    2011-03-01

    We study the non-local superconducting pairing of two interacting Anderson impurities, which has an instability near the quantum critical point from the competition between the Kondo effect and an antiferromagnetic inter-impurity spin exchange interaction. As revealed by the dynamics over the whole energy range, the superconducting pairing fluctuations acquire considerable strength from an energy scale much higher than the characteristic spin fluctuation scale while the low energy behaviors follow those of the staggered spin susceptibility. We argue that the superconducting pairing might not need the spin fluctuations as the glue, but rather originated from the effective Coulomb interaction. On the other hand, critical spin fluctuations in the vicinity of quantum criticality are also crucial to a superconducting pairing instability, by preventing a Fermi liquid fixed point being reached to keep the superconducting pairing fluctuations finite at low energies. A superconducting order, to reduce the accumulated entropy carried by the critical degrees of freedom, may arise favorably from this instability. This work is supported by the U.S. DOE through the LANL/LDRD program.

  20. 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.

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

    DOE PAGES

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

    2016-07-28

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

  2. From Cooper-pair glass to unconventional superconductivity: a unified approach to cuprates and pnictides

    NASA Astrophysics Data System (ADS)

    Sacks, William; Mauger, Alain; Noat, Yves

    2017-05-01

    We report a microscopic model wherein the unconventional superconductivity emerges from an incoherent 'Cooper-pair glass' state. Driven by the pair-pair interaction, a new type of quasi-Bose phase transition is at work. The interaction leads to the unconventional coupling of the quasiparticles to excited pair states, or 'super-quasiparticles', with a non-retarded energy-dependent gap. The model describes quantitatively the quasiparticle excitation spectra of both cuprates and pnictides, including the universal 'peak-dip-hump' signatures, and for the pseudogap phase above Tc. The results show that instantaneous pair-pair interactions account for the SC condensation without a collective mode.

  3. Superconducting pairing in resonant inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Shi, Yifei; Benjamin, David; Demler, Eugene; Klich, Israel

    2016-09-01

    We develop a method to study the effect of the superconducting transition on the resonant inelastic x-ray scattering (RIXS) signal in superconductors with an order parameter with an arbitrary symmetry within a quasiparticle approach. As an example, we compare the direct RIXS signal below and above the superconducting transition for p -wave-type order parameters. For a p -wave order parameter with a nodal line, we show that, counterintuitively, the effect of the gap is most noticeable for momentum transfers in the nodal direction. This phenomenon may be naturally explained as a type of nesting effect.

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

    PubMed

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

    2014-07-11

    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 Bi(2)Sr(2)CaCu(2)O(8+δ) crystals the pairing gap amplitude monotonically extends well beyond Tc, while the phase coherence shows a pronounced power-law divergence as T → T(c), thus showing that phase coherence and gap formation are distinct processes which occur on different timescales.

  5. 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

  6. Superconductivity in just four pairs of (BETS)2GaCl4 molecules.

    PubMed

    Clark, K; Hassanien, A; Khan, S; Braun, K-F; Tanaka, H; Hla, S-W

    2010-04-01

    How small can a sample of superconducting material be and still display superconductivity? This question is relevant to our fundamental understanding of superconductivity, and also to applications in nanoscale electronics, because Joule heating of interconnecting wires is a major problem in nanoscale devices. It has been shown that ultrathin layers of metal can display superconductivity, but any limits on the size of superconducting systems remain a mystery. (BETS)2GaCl4, where BETS is bis(ethylenedithio)tetraselenafulvalene, is an organic superconductor, and in bulk it has a superconducting transition temperature Tc of approximately 8 K and a two-dimensional layered structure that is reminiscent of the high-Tc cuprate superconductors. Here, we use scanning tunnelling spectroscopy to show that a single layer of (BETS)2GaCl4 molecules on an Ag(111) surface displays a superconducting gap that increases exponentially with the length of the molecular chain. Moreover, we show that a superconducting gap can still be detected for just four pairs of (BETS)2GaCl4 molecules. Real-space spectroscopic images directly visualize the chains of BETS molecules as the origin of the superconductivity.

  7. Tuning pairing amplitude and spin-triplet texture by curving superconducting nanostructures

    NASA Astrophysics Data System (ADS)

    Ying, Zu-Jian; Cuoco, Mario; Ortix, Carmine; Gentile, Paola

    2017-09-01

    We investigate the nature of the superconducting (SC) state in curved nanostructures with Rashba spin-orbit coupling (RSOC). In bent nanostructures with inhomogeneous curvature we find a local enhancement or suppression of the SC order parameter, with the effect that can be tailored by tuning either the RSOC strength or the carrier density. Apart from the local SC spin-singlet amplitude control, the geometric curvature generates nontrivial textures of the spin-triplet pairs through a spatial variation of the d ⃗ vector. By employing the representative case of an elliptical quantum ring, we demonstrate that the d ⃗ vector strongly depends on the local curvature and it generally exhibits a three-dimensional profile whose winding is tied to that of the single electron spin in the normal state. Our findings unveil paths to manipulate the quantum structure of the SC state in RSOC nanostructures through their geometry.

  8. Effects of pressure and magnetic field on superconductivity in ZrTe3: local pair-induced superconductivity

    NASA Astrophysics Data System (ADS)

    Tsuchiya, S.; Matsubayashi, K.; Yamaya, K.; Takayanagi, S.; Tanda, S.; Uwatoko, Y.

    2017-06-01

    In this work, the origin of the highly anisotropic superconducting transition in ZrTe3, where the resistance along the a axis, R a , is reduced at 4 K but those along the b axis, R b , and {c}\\prime axis, R c‧, are reduced at 2 K, was explored with the application of a magnetic field and pressure by the electrical resistance measurements. We found that the behavior of the upper critical field and its anisotropy as well as the pressure dependence determined by the R a measurements are quite similar to those of R b . Moreover, the excess conductivity for R b indicates anomalous behavior. These results support an unconventional origin for the anisotropic transition rather than conventional superconducting fluctuation. The reduction in R a is due to filamentary superconductivity (SC) induced by locally bound electron pairs (local pairs), which correspond to bi-polarons, and the transition of R b corresponds to the emergence of bulk SC originating from the Cooper pairs triggered by the transfer of the local pairs.

  9. 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.

  10. Pairing interaction and superconductivity in oxides and hydrides

    NASA Astrophysics Data System (ADS)

    Kulik, I. O.

    1990-05-01

    The existence of a universal mechanism of pairing between holes in electronegative metals is demonstrated. The pairing force arises as a consequence of orbital size dependence upon its filling and is characteristic for electronegative metals with moderate overlap between hole orbitals. This mechanism will not operate at very strong or very weak overlap regimes.

  11. Pair-breaking effects by parallel magnetic field in electric-field-induced surface superconductivity

    NASA Astrophysics Data System (ADS)

    Nabeta, Masahiro; Tanaka, Kenta K.; Onari, Seiichiro; Ichioka, Masanori

    2016-11-01

    We study paramagnetic pair-breaking in electric-field-induced surface superconductivity, when magnetic field is applied parallel to the surface. The calculation is performed by Bogoliubov-de Gennes theory with s-wave pairing, including the screening effect of electric fields by the induced carriers near the surface. Due to the Zeeman shift by applied fields, electronic states at higher-level sub-bands become normal-state-like. Therefore, the magnetic field dependence of Fermi-energy density of states reflects the multi-gap structure in the surface superconductivity.

  12. Macroscopic Einstein-Podolsky-Rosen pairs in superconducting circuits

    SciTech Connect

    Wei, L. F.; Liu Yuxi; Storcz, Markus J.; Nori, Franco

    2006-05-15

    We propose an efficient approach to prepare Einstein-Podolsky-Rosen (EPR) pairs in currently existing Josephson nanocircuits with capacitive couplings. In these fixed coupling circuits, two-qubit logic gates could be easily implemented while, strictly speaking, single-qubit gates cannot be easily realized. For a known two-qubit state, conditional single-qubit operation could still be designed to evolve only the selected qubit and keep the other qubit unchanged; the rotation of the selected qubit depends on the state of the other one. These conditional single-qubit operations allow us to deterministically generate the well-known Einstein-Podolsky-Rosen pairs, represented by EPR-Bell (or Bell) states. Quantum-state tomography is further proposed to experimentally confirm the generation of these states. The decays of the prepared EPR pairs are analyzed using numerical simulations. Possible application of the generated EPR pairs to test Bell's Inequality is also discussed.

  13. Odd-Parity Pairing and Topological Superconductivity in a Strongly Spin-Orbit Coupled Semiconductor

    NASA Astrophysics Data System (ADS)

    Sasaki, Satoshi; Ren, Zhi; Taskin, A. A.; Segawa, Kouji; Fu, Liang; Ando, Yoichi

    2012-11-01

    The existence of topological superconductors preserving time-reversal symmetry was recently predicted, and they are expected to provide a solid-state realization of itinerant massless Majorana fermions and a route to topological quantum computation. Their first likely example, CuxBi2Se3, was discovered last year, but the search for new materials has so far been hindered by the lack of a guiding principle. Here, we report point-contact spectroscopy experiments suggesting that the low-carrier-density superconductor Sn1-xInxTe is accompanied by surface Andreev bound states which, with the help of theoretical analysis, would give evidence for odd-parity pairing and topological superconductivity. The present and previous finding of possible topological superconductivity in Sn1-xInxTe and CuxBi2Se3 suggests that odd-parity pairing favored by strong spin-orbit coupling is likely to be a common underlying mechanism for materializing topological superconductivity.

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

    SciTech Connect

    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).

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

    SciTech Connect

    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).

  16. Enhancing superconducting critical current by randomness.

    SciTech Connect

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

    2016-01-11

    The key ingredient of high critical currents in a type-II superconductor is defect sites that pin vortices. Here, we demonstrate that a random pinscape, an overlooked pinning system in nanopatterned superconductors, can lead to a substantially larger critical current enhancement at high magnetic fields than an ordered array of vortex pin sites. We reveal that the better performance of a random pinscape is due to the variation of the local density of its pinning sites, 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 local density of pinning sites is further enlarged. Our findings highlight the potential of random pinscapes in enhancing the superconducting critical currents of applied superconductors in which random pin sites of nanoscale defects emerging in the materials synthesis process or through ex-situ irradiation are the only practical choice for large-scale production. Our results may also stimulate research on effects of a random pinscape in other complementary systems such as colloidal crystals, Bose-Einstein condensates, and Luttinger liquids.

  17. Enhancing superconducting critical current by randomness

    SciTech Connect

    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.

    2016-01-11

    The key ingredient of high critical currents in a type-II superconductor is defect sites that pin vortices. Here, we demonstrate that a random pinscape, an overlooked pinning system in nanopatterned superconductors, can lead to a substantially larger critical current enhancement at high magnetic fields than an ordered array of vortex pin sites. We reveal that the better performance of a random pinscape is due to the variation of the local density of its pinning sites, 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 local density of pinning sites is further enlarged. Our findings highlight the potential of random pinscapes in enhancing the superconducting critical currents of applied superconductors in which random pin sites of nanoscale defects emerging in the materials synthesis process or through ex-situ irradiation are the only practical choice for large-scale production. Our results may also stimulate research on effects of a random pinscape in other complementary systems such as colloidal crystals, Bose-Einstein condensates, and Luttinger liquids.

  18. Enhancing superconducting critical current by randomness

    DOE PAGES

    Wang, Y. L.; Thoutam, L. R.; Xiao, Z. L.; ...

    2016-01-11

    The key ingredient of high critical currents in a type-II superconductor is defect sites that pin vortices. Here, we demonstrate that a random pinscape, an overlooked pinning system in nanopatterned superconductors, can lead to a substantially larger critical current enhancement at high magnetic fields than an ordered array of vortex pin sites. We reveal that the better performance of a random pinscape is due to the variation of the local density of its pinning sites, which mitigates the motion of vortices. This is confirmed by achieving even higher enhancement of the critical current through a conformally mapped random pinscape, wheremore » the distribution of the local density of pinning sites is further enlarged. Our findings highlight the potential of random pinscapes in enhancing the superconducting critical currents of applied superconductors in which random pin sites of nanoscale defects emerging in the materials synthesis process or through ex-situ irradiation are the only practical choice for large-scale production. Our results may also stimulate research on effects of a random pinscape in other complementary systems such as colloidal crystals, Bose-Einstein condensates, and Luttinger liquids.« less

  19. Microscopic resolution of the interplay of Kondo screening and superconducting pairing: Mn-phthalocyanine molecules adsorbed on superconducting Pb(111)

    NASA Astrophysics Data System (ADS)

    Bauer, Johannes; Pascual, Jose I.; Franke, Katharina J.

    2013-02-01

    Magnetic molecules adsorbed on a superconductor give rise to a local competition of Cooper pair and Kondo singlet formation inducing subgap bound states. For manganese-phthalocyanine molecules on a Pb(111) substrate, scanning tunneling spectroscopy resolves pairs of subgap bound states and two Kondo screening channels. We show in a combined approach of scaling and numerical renormalization group calculations that the intriguing relation between Kondo screening and superconducting pairing is solely determined by the hybridization strength with the substrate. We demonstrate that an effective one-channel Anderson impurity model with a sizable particle-hole asymmetry captures universal and nonuniversal observations in the system quantitatively. The model parameters and disentanglement of the two screening channels are elucidated by scaling arguments.

  20. 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.

  1. Enhanced Superconductivity in Restacked TaS2 Nanosheets.

    PubMed

    Pan, Jie; Guo, Chenguang; Song, Changsheng; Lai, Xiaofang; Li, Hui; Zhao, Wei; Zhang, Hui; Mu, Gang; Bu, Kejun; Lin, Tianquan; Xie, Xiaoming; Chen, Mingwei; Huang, Fuqiang

    2017-04-05

    Since interface superconductivity was discovered at the interface between two insulating layers LaAlO3 and SrTiO3, such interface-induced superconducting systems have been a research hotspot in superconductivity. Here, we report homogeneous interfaces formed by stacking chemically exfoliated monolayer TaS2 nanosheets randomly. Enhanced superconductivity of Tc = 3 K is observed, compared with 0.8 K of parent 2H-TaS2. The measurement of heat capacity shows the increase of electronic specific-heat coefficient γ of restacked TaS2 nanosheets compared to parent 2H-TaS2 crystals. Density functional theory calculations indicate that increase and delocalization of electron states near the Fermi surface due to the homogeneous interfaces effects could account for the enhanced superconductivity.

  2. Triplet pairing and possible weak topological superconductivity in BiS2-based superconductors

    NASA Astrophysics Data System (ADS)

    Yang, Yang; Wang, Wan-Sheng; Xiang, Yuan-Yuan; Li, Zheng-Zao; Wang, Qiang-Hua

    2013-09-01

    We show that the newly discovered BiS2-based superconductors may have a dominant triplet pairing component in addition to a subdominant singlet component arising from the spin-orbital coupling. The pairing respects time-reversal symmetry. The dominant triplet gap causes gap sign changes between the spin-split Fermi pockets. Within a pocket, the gap function respects dx2-y2*-wave symmetry where the asterisk indicates joint spin-lattice rotations. Below the Lifshitz filling level, the gap is nodeless, and the superconducting state is weak topological. Above the Lifshitz points, the gap becomes nodal. The superconducting pairing and the time-reversal symmetry result from the strong spin-orbital coupling and the ferromagneticlike spin fluctuations. The dx2-y2*-wave gap structure follows from the coexisting antiferromagnetic spin fluctuations. The relevance to experiments is discussed.

  3. Topology and zero energy edge states in carbon nanotubes with superconducting pairing

    NASA Astrophysics Data System (ADS)

    Izumida, W.; Milz, L.; Marganska, M.; Grifoni, M.

    2017-09-01

    We investigate the spectrum of finite-length carbon nanotubes in the presence of onsite and nearest-neighbor superconducting pairing terms. A one-dimensional ladder-type lattice model is developed to explore the low-energy spectrum and the nature of the electronic states. We find that zero energy edge states can emerge in zigzag class carbon nanotubes as a combined effect of curvature-induced Dirac point shift and strong superconducting coupling between nearest-neighbor sites. The chiral symmetry of the system is exploited to define a winding number topological invariant. The associated topological phase diagram shows regions with nontrivial winding number in the plane of chemical potential and superconducting nearest-neighbor pair potential (relative to the onsite pair potential). A one-dimensional continuum model reveals the topological origin of the zero energy edge states: a bulk-edge correspondence is proven, which shows that the condition for nontrivial winding number and that for the emergence of edge states are identical. For armchair class nanotubes, the presence of edge states in the superconducting gap depends on the nanotube's boundary shape. For the minimal boundary condition, the emergence of the subgap states can also be deduced from the winding number.

  4. Inductive measurement of the critical pair momentum in thin superconducting films

    NASA Astrophysics Data System (ADS)

    Draskovic, John P.

    This dissertation documents the conception, development, validation, and application of an inductive experimental measurement of the critical Cooper pair momentum in thin superconducting films. A current-carrying (drive) coil of radius much smaller than the film radius induces a highly inhomogeneous screening supercurrent density in the film. The magnitude of the supercurrent is greatest at a radial position corresponding to the coil radius. It is shown that subject to magnetic fields greater than a few mG, the film is in a metastable superconducting state with respect to the formation of flux-bearing vortex-antivortex excitations. Consequently, magnetic coupling to a second (pickup) coil located co-axially on the opposite side of the film is independent of the drive coil current (linear response). As the drive coil current is increased and the highest-momentum Cooper pairs approach a momentum sufficient to break the pairs, the free-energy barrier to vortex-antivortex pair creation is diminished and such pairs appear en masse, detected as a crossover to nonlinear coupling between the coils. A scheme for calculating this critical momentum from the corresponding drive coil field is presented with the empirical assumption that the peak out-of-phase coil coupling corresponds to the upper limit of Meissner state metastability. This assumption is validated by independent measurements of the critical pair momentum and upper critical magnetic field performed on film samples of niobium and molybdenum-germanium alloy. These measurements are connected through the phenomenological superconducting coherence length, and the data show quantitative agreement in these well-studied superconductors. A second experimental study is presented for a collection of cuprate films of varied doping. It is seen that the critical momentum scales roughly with the measured transition temperature, as predicted by a universal model of cuprate superconductivity'.

  5. Superconducting phase and pairing fluctuations in the half-filled two-dimensional Hubbard model.

    PubMed

    Sentef, Michael; Werner, Philipp; Gull, Emanuel; Kampf, Arno P

    2011-09-16

    The two-dimensional Hubbard model exhibits superconductivity with d-wave symmetry even at half-filling in the presence of a next-nearest neighbor hopping. Using plaquette cluster dynamical mean-field theory with a continuous-time quantum Monte Carlo impurity solver, we reveal the non-Fermi liquid character of the metallic phase in proximity to the superconducting state. Specifically, the low-frequency scattering rate for momenta near (π, 0) varies nonmonotonically at low temperatures, and the dc conductivity is T linear at elevated temperatures with an upturn upon cooling. Evidence is provided that pairing fluctuations dominate the normal-conducting state even considerably above the superconducting transition temperature.

  6. Superconductivity in repulsively interacting fermions on a diamond chain: Flat-band-induced pairing

    NASA Astrophysics Data System (ADS)

    Kobayashi, Keita; Okumura, Masahiko; Yamada, Susumu; Machida, Masahiko; Aoki, Hideo

    2016-12-01

    To explore whether a flat-band system can accommodate superconductivity, we consider repulsively interacting fermions on the diamond chain, a simplest possible quasi-one-dimensional system that contains a flat band. Exact diagonalization and the density-matrix renormalization group are used to show that we have a significant binding energy of a Cooper pair with a long-tailed pair-pair correlation in real space when the total band filling is slightly below 1/3, where a filled dispersive band interacts with the flat band that is empty but close to EF. Pairs selectively formed across the outer sites of the diamond chain are responsible for the pairing correlation. At exactly 1/3-filling an insulating phase emerges, where the entanglement spectrum indicates the particles on the outer sites are highly entangled and topological. These come from a peculiarity of the flat band in which "Wannier orbits" are not orthogonalizable.

  7. 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.

  8. 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.

  9. Superconducting pairing and density-wave instabilities in quasi-one-dimensional conductors

    NASA Astrophysics Data System (ADS)

    Nickel, J. C.; Duprat, R.; Bourbonnais, C.; Dupuis, N.

    2006-04-01

    Using a renormalization group approach, we determine the phase diagram of an extended quasi-one-dimensional electron gas model that includes interchain hopping, nesting deviations, and both intrachain and interchain repulsive interactions. d -wave superconductivity, which dominates over the spin-density-wave (SDW) phase at large nesting deviations, becomes unstable to the benefit of a triplet f -wave phase for a weak repulsive interchain backscattering term g1⊥>0 , despite the persistence of dominant SDW correlations in the normal state. Antiferromagnetism becomes unstable against the formation of a charge-density-wave state when g1⊥ exceeds some critical value. While these features persist when both Umklapp processes and interchain forward scattering (g2⊥) are taken into account, the effect of g2⊥ alone is found to frustrate nearest-neighbor interchain d - and f -wave pairing and instead favor next-nearest-neighbor interchain singlet or triplet pairing. We argue that the close proximity of SDW and charge-density-wave phases, singlet d -wave, and triplet f -wave superconducting phases in the theoretical phase diagram provides a possible explanation for recent puzzling experimental findings in the Bechgaard salts, including the coexistence of SDW and charge-density-wave phases and the possibility of a triplet pairing in the superconducting phase.

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

    PubMed

    Erten, Onur; Flint, Rebecca; Coleman, Piers

    2015-01-16

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

  11. 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.

  12. Pairing Symmetry of Heavy Fermion Superconductivity in the Two-Dimensional Kondo—Heisenberg Lattice Model

    NASA Astrophysics Data System (ADS)

    Liu, Yu; Zhang, Guang-Ming; Yu, Lu

    2014-08-01

    In the two-dimensional Kondo—Heisenberg lattice model away from half-filled, the local antiferromagnetic exchange coupling can provide the pairing mechanism of quasiparticles via the Kondo screening effect, leading to the heavy fermion superconductivity. We find that the pairing symmetry strongly depends on the Fermi surface (FS) structure in the normal metallic state. When JH/JK is very small, the FS is a small hole-like circle around the corner of the Brillouin zone, and the s-wave pairing symmetry has a lower ground state energy. For the intermediate coupling values of JH/JK, the extended s-wave pairing symmetry gives the favored ground state. However, when JH/JK is larger than a critical value, the FS transforms into four small hole pockets crossing the boundary of the magnetic Brillouin zone, and the d-wave pairing symmetry becomes more favorable. In that regime, the resulting superconducting state is characterized by either a nodal d-wave or nodeless d-wave state, depending on the conduction electron filling factor as well. A continuous phase transition exists between these two states. This result may be related to the phase transition of the nodal d-wave state to a fully gapped state, which has recently been observed in Yb-doped CeCoIn5.

  13. Nanoantenna Enhancement for Telecom-Wavelength Superconducting Single Photon Detectors

    NASA Astrophysics Data System (ADS)

    Heath, Robert M.; Tanner, Michael G.; Drysdale, Timothy D.; Miki, Shigehito; Giannini, Vincenzo; Maier, Stefan A.; Hadfield, Robert H.

    2015-02-01

    Superconducting nanowire single photon detectors are rapidly emerging as a key infrared photon-counting technology. Two front-side-coupled silver dipole nanoantennas, simulated to have resonances at 1480 nm and 1525 nm, were fabricated in a two-step process. An enhancement of 50% to 130% in the system detection efficiency was observed when illuminating the antennas. This offers a pathway to increasing absorption into superconducting nanowires, creating larger active areas, and achieving more efficient detection at longer wavelengths.

  14. Nanoantenna enhancement for telecom-wavelength superconducting single photon detectors.

    PubMed

    Heath, Robert M; Tanner, Michael G; Drysdale, Timothy D; Miki, Shigehito; Giannini, Vincenzo; Maier, Stefan A; Hadfield, Robert H

    2015-02-11

    Superconducting nanowire single photon detectors are rapidly emerging as a key infrared photon-counting technology. Two front-side-coupled silver dipole nanoantennas, simulated to have resonances at 1480 and 1525 nm, were fabricated in a two-step process. An enhancement of 50 to 130% in the system detection efficiency was observed when illuminating the antennas. This offers a pathway to increasing absorption into superconducting nanowires, creating larger active areas, and achieving more efficient detection at longer wavelengths.

  15. 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.

  16. Paramagnetic and diamagnetic pair-breaking effect in electric-field-induced surface superconductivity under parallel magnetic fields

    NASA Astrophysics Data System (ADS)

    Ichioka, Masanori; Nabeta, Masahiro; Tanaka, Kenta K.; Onari, Seiichiro

    2017-07-01

    Electric-field-induced surface superconductivity is studied by Bogoliubov-de Gennes equation under magnetic fields parallel to the surface. We estimate the pair-breaking effects by the paramagnetic Zeeman shift and by diamagnetic screening current. We find that the depth dependences of pair potential, screening current, spin current, and paramagnetic moment under the magnetic fields reflect the multi-gap superconductivity in the sub-band structure.

  17. Decompression-Driven Superconductivity Enhancement in In2 Se3.

    PubMed

    Ke, Feng; Dong, Haini; Chen, Yabin; Zhang, Jianbo; Liu, Cailong; Zhang, Junkai; Gan, Yuan; Han, Yonghao; Chen, Zhiqiang; Gao, Chunxiao; Wen, Jinsheng; Yang, Wenge; Chen, Xiao-Jia; Struzhkin, Viktor V; Mao, Ho-Kwang; Chen, Bin

    2017-09-01

    An unexpected superconductivity enhancement is reported in decompressed In2 Se3 . The onset of superconductivity in In2 Se3 occurs at 41.3 GPa with a critical temperature (Tc ) of 3.7 K, peaking at 47.1 GPa. The striking observation shows that this layered chalcogenide remains superconducting in decompression down to 10.7 GPa. More surprisingly, the highest Tc that occurs at lower decompression pressures is 8.2 K, a twofold increase in the same crystal structure as in compression. It is found that the evolution of Tc is driven by the pressure-induced R-3m to I-43d structural transition and significant softening of phonons and gentle variation of carrier concentration combined in the pressure quench. The novel decompression-induced superconductivity enhancement implies that it is possible to maintain pressure-induced superconductivity at lower or even ambient pressures with better superconducting performance. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Odd-parity pairing and topological superconductivity in a strongly spin-orbit coupled semiconductor.

    PubMed

    Sasaki, Satoshi; Ren, Zhi; Taskin, A A; Segawa, Kouji; Fu, Liang; Ando, Yoichi

    2012-11-21

    The existence of topological superconductors preserving time-reversal symmetry was recently predicted, and they are expected to provide a solid-state realization of itinerant massless Majorana fermions and a route to topological quantum computation. Their first likely example, Cu(x)Bi(2)Se(3), was discovered last year, but the search for new materials has so far been hindered by the lack of a guiding principle. Here, we report point-contact spectroscopy experiments suggesting that the low-carrier-density superconductor Sn(1-x)In(x)Te is accompanied by surface Andreev bound states which, with the help of theoretical analysis, would give evidence for odd-parity pairing and topological superconductivity. The present and previous finding of possible topological superconductivity in Sn(1-x)In(x)Te and Cu(x)Bi(2)Se(3) suggests that odd-parity pairing favored by strong spin-orbit coupling is likely to be a common underlying mechanism for materializing topological superconductivity.

  19. Mirror nesting and electron-hole asymmetry at repulsive superconducting pairing

    NASA Astrophysics Data System (ADS)

    Belyavsky, V. I.; Kapaev, V. V.; Kopaev, Yu. V.

    2007-11-01

    The dependence of the superconducting order parameter Δ( k) on the momentum of the relative motion of a pair with a large total momentum K is numerically studied for the case of repulsive pairing with allowance for the kinematic and insulator constraints on the momentum transfer at scattering. The Fermi contour with nesting and mirror nesting, which is typical of cuprates and optimal for repulsion-induced superconductivity, lies in an extended vicinity of the saddle points of the dispersion law. A deviation from the mirror nesting cuts off the logarithmic singularity from below and bounds the pre-exponent in Δ( k). The effective coupling constant is determined by the degree of the electron-hole asymmetry. The suppression of the contribution of small momentum transfer processes by the impurity and electron-phonon scattering favors an increase in the order parameter amplitude. The nesting of the Fermi contour causes a Peierls singularity in the Coulomb interaction. The self-consistency equation allows the solutions that may be both antisymmetric and symmetric with respect to the momentum inversion. The maximum-amplitude antisymmetric solution in the case of a singlet pairing can be realized only for K ≠ 0.

  20. Understanding and enhancing superconductivity in FeSe/SrTiO3 by quantum size effects

    NASA Astrophysics Data System (ADS)

    Murta, Bruno; García-García, Antonio M.

    2016-11-01

    Superconductivity in one-atom-layer iron selenide (FeSe) on a strontium titanate (STO) substrate is enhanced by almost an order of magnitude with respect to bulk FeSe. There is recent experimental evidence suggesting that this enhancement persists in FeSe/STO nanoislands. More specifically, for sizes L ˜10 nm, the superconducting gap is a highly nonmonotonic function of L with peaks well above the bulk gap value. This is the expected behavior only for weakly-coupled metallic superconductors such as Al or Sn. Here we develop a theoretical formalism to describe these experiments based on three ingredients: Eliashberg theory of superconductivity in the weak coupling limit, pairing dominated by forward scattering, and periodic orbit theory to model spectral fluctuations. We obtain an explicit analytical expression for the size dependence of the gap that describes quantitatively the experimental results with no free parameters. This is a strong suggestion that superconductivity in FeSe/STO is mediated by STO phonons. We propose that, since FeSe/STO is still a weakly coupled superconductor, quantum size effects can be used to further enhance the bulk critical temperature in this interface.

  1. Cooper-pair insulator phase in superconducting amorphous Bi films induced by nanometer-scale thickness variations

    NASA Astrophysics Data System (ADS)

    Hollen, S. M.; Nguyen, H. Q.; Rudisaile, E.; Stewart, M. D., Jr.; Shainline, J.; Xu, J. M.; Valles, J. M., Jr.

    2011-08-01

    Ultrathin films near the quantum insulator-superconductor transition (IST) can exhibit Cooper-pair transport in their insulating state. This Cooper-pair insulator (CPI) state is achieved in amorphous Bi films evaporated onto substrates with a topography varying on lengths slightly greater than the superconducting coherence length. We present evidence that this topography induces film thickness and corresponding superconducting coupling constant variations that promote Cooper-pair island formation. Analyses of many thickness-tuned ISTs show that weak links between superconducting islands dominate the transport. In particular, the IST occurs when the link resistance approaches the resistance quantum for pairs. These results support conjectures that the CPI is an inhomogeneous state of matter.

  2. Induced spin-triplet pairing in the coexistence state of antiferromagnetism and singlet superconductivity: Collective modes and microscopic properties

    NASA Astrophysics Data System (ADS)

    Almeida, D. E.; Fernandes, R. M.; Miranda, E.

    2017-07-01

    The close interplay between superconductivity and antiferromagnetism in several quantum materials can lead to the appearance of an unusual thermodynamic state in which both orders coexist microscopically, despite their competing nature. A hallmark of this coexistence state is the emergence of a spin-triplet superconducting gap component, called a π triplet, which is spatially modulated by the antiferromagnetic wave vector, reminiscent of a pair density wave. In this paper, we investigate the impact of these π -triplet degrees of freedom on the phase diagram of a system with competing antiferromagnetic and superconducting orders. Although we focus on a microscopic two-band model that has been widely employed in studies of iron pnictides, most of our results follow from a Ginzburg-Landau analysis, and as such should be applicable to other systems of interest, such as cuprates and heavy fermion materials. The Ginzburg-Landau functional reveals not only that the π -triplet gap amplitude couples trilinearly with the singlet gap amplitude and the staggered magnetization magnitude but also that the π -triplet d -vector couples linearly with the magnetization direction. While in the mean-field level this coupling forces the d -vector to align parallel or antiparallel to the magnetization, in the fluctuation regime it promotes two additional collective modes—a Goldstone mode related to the precession of the d -vector around the magnetization and a massive mode, related to the relative angle between the two vectors, which is nearly degenerate with a Leggett-like mode associated with the phase difference between the singlet and triplet gaps. We also investigate the impact of magnetic fluctuations on the superconducting-antiferromagnetic phase diagram, showing that due to their coupling with the π -triplet order parameter the coexistence region is enhanced. This effect stems from the fact that the π -triplet degrees of freedom promote an effective attraction between

  3. 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.

  4. Orbital-Parity Selective Superconducting Pairing Structures of Fe-based Superconductors under Glide Symmetry

    NASA Astrophysics Data System (ADS)

    Lin, Chiahui; Chou, Chung-Pin; Yin, Wei-Guo; Ku, Wei

    2014-03-01

    We show that the superconductivity in Fe-based superconductors consists of zero and finite momentum (π , π , 0) Cooper pairs with the same and different parities of the Fe 3 d orbitals respectively. The former develops the distinct gap structures for each orbital parity, and the latter is characteristic of spin singlet, spacial oddness and time reversal symmetry breaking. This originates from the unit cell containing two Fe atoms and two anions of staggered positioning with respect to the Fe square lattice. The in-plane translation is turned into glide translation, which dictates orbital-parity selective quasiparticles. Such novel pairing structures explain the unusual gap angular modulation on the hole pockets in recent ARPES and STS experiments. Work supported by DOE DE-AC02-98CH10886 and Chinese Academy of Engineering Physics and Ministry of Science and Technology.

  5. 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.

  6. 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.

  7. Generalized Aubry-André-Harper model with p -wave superconducting pairing

    NASA Astrophysics Data System (ADS)

    Zeng, Qi-Bo; Chen, Shu; Lü, Rong

    2016-09-01

    We investigate a generalized Aubry-André-Harper (AAH) model with p -wave superconducting pairing. Both the hopping amplitudes between the nearest-neighboring lattice sites and the on-site potentials in this system are modulated by a cosine function with a periodicity of 1 /α . In the incommensurate case [α =(√{5 }-1 )/2 ] , due to the modulations on the hopping amplitudes, the critical region of this quasiperiodic system is significantly reduced and the system becomes easier to be turned from extended states to localized states. In the commensurate case (α =1 /2 ), we find that this model shows three different phases when we tune the system parameters: Su-Schrieffer-Heeger (SSH)-like trivial, SSH-like topological, and Kitaev-like topological phases. The phase diagrams and the topological quantum numbers for these phases are presented in this work. This generalized AAH model combined with superconducting pairing provides us with a useful test field for studying the phase transitions from extended states to Anderson localized states and the transitions between different topological phases.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. Enhanced spin-triplet superconductivity near dislocations in Sr₂RuO₄.

    PubMed

    Ying, Y A; Staley, N E; Xin, Y; Sun, K; Cai, X; Fobes, D; Liu, T J; Mao, Z Q; Liu, Y

    2013-01-01

    Superconductors with a chiral p-wave pairing are of great interest because they could support Majorana modes that could enable the development of topological quantum computing technologies that are robust against decoherence. Sr₂RuO₄ is widely believed to be a chiral p-wave superconductor. Yet, the mechanism by which superconductivity emerges in this, and indeed most other unconventional superconductors, remains unclear. Here we show that the local superconducting transition temperature in the vicinity of lattice dislocations in Sr₂RuO₄ can be up to twice that of its bulk. This is all the more surprising for the fact that disorder is known to easily quench superconductivity in this material. With the help of a phenomenological theory that takes into account the crystalline symmetry near a dislocation and the pairing symmetry of Sr₂RuO₄, we predict that a similar enhancement should emerge as a consequence of symmetry reduction in any superconductor with a two-component order parameter.

  13. Antagonistic effects of nearest-neighbor repulsion on the superconducting pairing dynamics in the doped Mott insulator regime

    NASA Astrophysics Data System (ADS)

    Reymbaut, A.; Charlebois, M.; Asiani, M. Fellous; Fratino, L.; Sémon, P.; Sordi, G.; Tremblay, A.-M. S.

    2016-10-01

    The nearest-neighbor superexchange-mediated mechanism for dx2-y2 superconductivity in the one-band Hubbard model faces the challenge that nearest-neighbor Coulomb repulsion can be larger than superexchange. To answer this question, we use cellular dynamical mean-field theory (CDMFT) with a continuous-time quantum Monte Carlo solver to determine the superconducting phase diagram as a function of temperature and doping for on-site repulsion U =9 t and nearest-neighbor repulsion V =0 ,2 t ,4 t . In the underdoped regime, V increases the CDMFT superconducting transition temperature Tcd even though it decreases the superconducting order parameter at low temperature for all dopings. However, in the overdoped regime V decreases Tcd. We gain insight into these paradoxical results through a detailed study of the frequency dependence of the anomalous spectral function, extracted at finite temperature via the MaxEntAux method for analytic continuation. A systematic study of dynamical positive and negative contributions to pairing reveals that even though V has a high-frequency depairing contribution, it also has a low frequency pairing contribution since it can reinforce superexchange through J =4 t2/(U -V ) . Retardation is thus crucial to understanding pairing in doped Mott insulators, as suggested by previous zero-temperature studies. We also comment on the tendency to charge order for large V and on the persistence of d -wave superconductivity over extended-s or s +d wave.

  14. Lamb-shift enhancement and detection in strongly driven superconducting circuits.

    PubMed

    Gramich, Vera; Gasparinetti, Simone; Solinas, Paolo; Ankerhold, Joachim

    2014-07-11

    It is shown that strong driving of a quantum system substantially enhances the Lamb shift induced by broadband reservoirs, which are typical for solid-state devices. By varying drive parameters the impact of environmental vacuum fluctuations with continuous spectral distribution onto system observables can be tuned in a distinctive way. This provides experimentally feasible measurement schemes for the Lamb shift in superconducting circuits based on Cooper pair boxes, where it can be detected either in shifted dressed transition frequencies or in pumped charge currents.

  15. Superconductivity in layered materials Pairing theory for projectively translation invariant states

    NASA Astrophysics Data System (ADS)

    Divakaran, P. P.; Rajagopal, A. K.

    1991-06-01

    A mechanism for the superconducting transition in layered bulk substances, based on the existence of (non-plane wave) projective unitary representations (PURs) of their symmetry group and the generalisation of the theory of Cooper pairs to such representations, is proposed and investigated. In the continuum limit, the symmetry group appropriate to layering is a subgroup of the three-dimensional Euclidean group. It has an infinite family of PURs which can be characterised by an arbitrary real central charge in the commutators of momentum components within the layer. Quantum kinematics/dynamics in a sector with nonzero central charge (nontrivial PUR) is studied and the invariant one-particle Hamiltonian and equation of motion are shown to be formally those of a spinless charged particle in a magnetic field normal to the layers (pseudocharge in a pseudomagnetic field) irrespective of the actual charge or spin of the particle. The dielectric response of a gas of electrons in a sector with nonzero central charge is then worked out by standard Green function methods and the nature of the dynamically screened two-particle interaction determined. The influence of the pseudocyclotron frequency makes the effective potential attractive in a regime of wave number and frequency whose extent increases with increasing central charge, thus signalling instability towards the formation of (generalised) Cooper pairs. The general gap equation is then set up and, after a standard simplification, reduced to a form whose solution is known to lead to a critical temperature increasing monotonically with central charge. This model of high-temperature superconductivity is parity and time-reversal invariant and is in qualitative agreement with observations including those on the isotope effect. The fundamental differences between this model and the anion model are commented upon and speculative remarks offered on the physical origin and detection of the central charge.

  16. Superconductivity enhanced by d-density wave: A weak-coupling theory

    NASA Astrophysics Data System (ADS)

    Ha, Kim; Subok, Ri; Ilmyong, Ri; Cheongsong, Kim; Yuling, Feng

    2011-04-01

    Making a revision of mistakes in Ref. [19], we present a detailed study of the competition and interplay between the d-density wave (DDW) and d-wave superconductivity (DSC) within the fluctuation-exchange (FLEX) approximation for the two-dimensional (2D) Hubbard model. In order to stabilize the DDW state with respect to phase separation at lower dopings a small nearest-neighbor Coulomb repulsion is included within the Hartree-Fock approximation. We solve the coupled gap equations for the DDW, DSC, and π-pairing as the possible order parameters, which are caused by exchange of spin fluctuations, together with calculating the spin fluctuation pairing interaction self-consistently within the FLEX approximation. We show that even when nesting of the Fermi surface is perfect, as in a square lattice with only nearest-neighbor hopping, there is coexistence of DSC and DDW in a large region of dopings close to the quantum critical point (QCP) at which the DDW state vanishes. In particular, we find that in the presence of DDW order the superconducting transition temperature Tc can be much higher compared to pure superconductivity, since the pairing interaction is strongly enhanced due to the feedback effect on spin fluctuations of the DDW gap. π-pairing appears generically in the coexistence region, but its feedback on the other order parameters is very small. In the present work, we have developed a weak-coupling theory of the competition between DDW and DSC in 2D Hubbard model, using the static spin fluctuation obtained within FLEX approximation and ignoring the self-energy effect of spin fluctuations. For our model calculations in the weak-coupling limit we have taken U/ t=3.4, since the antiferromagnetic instability occurs for higher values of U/ t.

  17. Peculiarities in the concentration dependence of the superconducting transition temperature in the bipolaron theory of Cooper pairs

    NASA Astrophysics Data System (ADS)

    Lakhno, Victor

    2017-04-01

    It is shown that the bipolaron theory of Cooper pairs suggests that there is a possibility for a superconducting phase to exist at low and high levels of doping and be absent at the intermediate level of doping. The results obtained possibly to imply the universal character of 1/8 anomaly.

  18. Enhanced pinning in superconducting thin films with graded pinning landscapes

    NASA Astrophysics Data System (ADS)

    Motta, M.; Colauto, F.; Ortiz, W. A.; Fritzsche, J.; Cuppens, J.; Gillijns, W.; Moshchalkov, V. V.; Johansen, T. H.; Sanchez, A.; Silhanek, A. V.

    2013-05-01

    A graded distribution of antidots in superconducting a-Mo79Ge21 thin films has been investigated by magnetization and magneto-optical imaging measurements. The pinning landscape has maximum density at the sample border, decreasing linearly towards the center. Its overall performance is noticeably superior than that for a sample with uniformly distributed antidots: For high temperatures and low fields, the critical current is enhanced, whereas the region of thermomagnetic instabilities in the field-temperature diagram is significantly suppressed. These findings confirm the relevance of graded landscapes on the enhancement of pinning efficiency, as recently predicted by Misko and Nori [Phys. Rev. B 85, 184506 (2012)].

  19. Enhanced superconductivity accompanying a Lifshitz transition in electron-doped FeSe monolayer.

    PubMed

    Shi, X; Han, Z-Q; Peng, X-L; Richard, P; Qian, T; Wu, X-X; Qiu, M-W; Wang, S C; Hu, J P; Sun, Y-J; Ding, H

    2017-04-19

    The origin of enhanced superconductivity over 50 K in the recently discovered FeSe monolayer films grown on SrTiO3 (STO), as compared to 8 K in bulk FeSe, is intensely debated. As with the ferrochalcogenides AxFe2-ySe2 and potassium-doped FeSe, which also have a relatively high-superconducting critical temperature (Tc), the Fermi surface (FS) of the FeSe/STO monolayer films is free of hole-like FS, suggesting that a Lifshitz transition by which these hole FSs vanish may help increasing Tc. However, the fundamental reasons explaining this increase of Tc remain unclear. Here we report a 15 K jump of Tc accompanying a second Lifshitz transition characterized by the emergence of an electron pocket at the Brillouin zone centre, which is triggered by high-electron doping following in situ deposition of potassium on FeSe/STO monolayer films. Our results suggest that the pairing interactions are orbital dependent in generating enhanced superconductivity in FeSe.

  20. Enhanced superconductivity accompanying a Lifshitz transition in electron-doped FeSe monolayer

    NASA Astrophysics Data System (ADS)

    Shi, X.; Han, Z.-Q.; Peng, X.-L.; Richard, P.; Qian, T.; Wu, X.-X.; Qiu, M.-W.; Wang, S. C.; Hu, J. P.; Sun, Y.-J.; Ding, H.

    2017-04-01

    The origin of enhanced superconductivity over 50 K in the recently discovered FeSe monolayer films grown on SrTiO3 (STO), as compared to 8 K in bulk FeSe, is intensely debated. As with the ferrochalcogenides AxFe2-ySe2 and potassium-doped FeSe, which also have a relatively high-superconducting critical temperature (Tc), the Fermi surface (FS) of the FeSe/STO monolayer films is free of hole-like FS, suggesting that a Lifshitz transition by which these hole FSs vanish may help increasing Tc. However, the fundamental reasons explaining this increase of Tc remain unclear. Here we report a 15 K jump of Tc accompanying a second Lifshitz transition characterized by the emergence of an electron pocket at the Brillouin zone centre, which is triggered by high-electron doping following in situ deposition of potassium on FeSe/STO monolayer films. Our results suggest that the pairing interactions are orbital dependent in generating enhanced superconductivity in FeSe.

  1. Enhanced superconductivity accompanying a Lifshitz transition in electron-doped FeSe monolayer

    PubMed Central

    Shi, X.; Han, Z-Q; Peng, X-L; Richard, P.; Qian, T.; Wu, X-X; Qiu, M-W; Wang, S. C.; Hu, J. P.; Sun, Y-J; Ding, H.

    2017-01-01

    The origin of enhanced superconductivity over 50 K in the recently discovered FeSe monolayer films grown on SrTiO3 (STO), as compared to 8 K in bulk FeSe, is intensely debated. As with the ferrochalcogenides AxFe2−ySe2 and potassium-doped FeSe, which also have a relatively high-superconducting critical temperature (Tc), the Fermi surface (FS) of the FeSe/STO monolayer films is free of hole-like FS, suggesting that a Lifshitz transition by which these hole FSs vanish may help increasing Tc. However, the fundamental reasons explaining this increase of Tc remain unclear. Here we report a 15 K jump of Tc accompanying a second Lifshitz transition characterized by the emergence of an electron pocket at the Brillouin zone centre, which is triggered by high-electron doping following in situ deposition of potassium on FeSe/STO monolayer films. Our results suggest that the pairing interactions are orbital dependent in generating enhanced superconductivity in FeSe. PMID:28422183

  2. 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

    2016-03-17

    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.

  3. Enhanced superconductivity in atomically thin TaS2

    PubMed Central

    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

  4. Enhanced superconductivity in ThNiAsN

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-Cheng; Shao, Ye-Ting; Wang, Cao; Wang, Zhen; Xu, Zhu-An; Cao, Guang-Han

    2017-06-01

    We report the synthesis and physical properties of a nickel-based arsenide ThNiAsN. The new compound crystallizes in a ZrCuSiAs-type structure (space group P4/nmm ) with lattice parameters a=4.0804(4) \\AA and c=7.9888(6) \\AA . Bulk superconductivity at Tc =4.3 \\text{K} is demonstrated by the measurements of electrical resistivity, dc magnetic susceptibility, and heat capacity. The upper critical field at zero temperature, Hc2(0) , and the specific-heat jump at T c are 6.1 T and 40 \\text{mJ} \\cdot \\text{K}-1\\cdot \\text{mol}-1 , respectively. These two physical quantities, together with the T c value, are the highest among the Ni-based ZrCuSiAs-type materials. We discuss this enhanced superconductivity in terms of the internal chemical pressure in ThNiAsN.

  5. 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.

  6. Thermal transport in topological-insulator-based superconducting hybrid structures with mixed singlet and triplet pairing states.

    PubMed

    Li, Hai; Zhao, Yuan Yuan

    2017-10-02

    In the framework of the Bogoliubov-de Gennes equation, we investigate the thermal transport properties in topological-insulator-based superconducting hybrid structures with mixed spin-singlet and spin-triplet pairing states, and emphasize the different manifestations of the spin-singlet and spin-triplet pairing states in the thermal transport signatures. It is revealed that the temperature-dependent differential thermal conductance strongly depends on the components of the pairing state, and the negative differential thermal conductance only occurs in the spin-singlet pairing state dominated regime. It is also found that the thermal conductance is profoundly sensitive to the components of the pairing state. In the spin-singlet pairing state controlled regime, the thermal conductance obviously oscillates with the phase difference and junction length. With increasing the proportion of the spin-triplet pairing state, the oscillating characteristic of the thermal conductance fades out distinctly. These results suggest an alternative route for distinguishing the components of pairing states in topological-insulator-based superconducting hybrid structures. © 2017 IOP Publishing Ltd.

  7. Enhanced superconductivity by rare-earth metal doping in phenanthrene.

    PubMed

    Wang, X F; Luo, X G; Ying, J J; Xiang, Z J; Zhang, S L; Zhang, R R; Zhang, Y H; Yan, Y J; Wang, A F; Cheng, P; Ye, G J; Chen, X H

    2012-08-29

    We successfully synthesized La- and Sm-doped phenanthrene powder samples and observed superconductivity in them at T(c) around 6 K. The T(c)s are 6.1 K for La(1) phenanthrene and 6.0 K for Sm(1) phenanthrene, which are enhanced by about 1 and 0.5 K compared to those in A(3) phenanthrene (A = K and Rb) and in Ae(1.5) phenanthrene (Ae = Sr and Ba) superconductors, respectively. The superconductive shielding fractions for La(1) phenanthrene and Sm(1) phenanthrene are 46.1% and 49.8% at 2 K, respectively. The small effect of doping with the magnetic ion Sm(3+) on T(c) and the positive pressure dependence coefficient of T(c) strongly suggest unconventional superconductivity in the doped phenanthrene superconductors. The charge transfer to organic molecules from dopants of La and Sm induces a redshift of 7 cm(-1) per electron for the mode at 1441 cm(-1) in the Raman spectra, which is almost the same as those observed in A(3) phenanthrene (A = K and Rb) and Ae(1.5) phenanthrene (Ae = Sr and Ba) superconductors.

  8. Strongly Enhanced Superconductivity in Coupled t-J Segments.

    PubMed

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

    2016-02-12

    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.

  9. Enhancement of superconductivity near a nematic quantum critical point.

    PubMed

    Lederer, S; Schattner, Y; Berg, E; Kivelson, S A

    2015-03-06

    We consider a low T_{c} metallic superconductor weakly coupled to the soft fluctuations associated with proximity to a nematic quantum critical point (NQCP). We show that (1) a BCS-Eliashberg treatment remains valid outside of a parametrically narrow interval about the NQCP, (2) the symmetry of the superconducting state (d wave, s wave, p wave) is typically determined by the noncritical interactions, but T_{c} is enhanced by the nematic fluctuations in all channels, and (3) in 2D, this enhancement grows upon approach to criticality up to the point at which the weak coupling approach breaks down, but in 3D, the enhancement is much weaker.

  10. 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.

  11. 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

  12. Localization and pair breaking parameter in superconducting molybdenum nitride thin films.

    PubMed

    Tsuneoka, Takuya; Makise, Kazumasa; Maeda, Sho; Shinozaki, Bunju; Ichikawa, Fusao

    2017-01-11

    We have investigated the superconductor-insulator transition in molybdenum nitride films prepared by deposition onto MgO substrates. It is indicated that the T c depression from [Formula: see text] for thick films with increase of the normal state sheet resistance [Formula: see text] was well explained by the Finkel'stein formula from the localization theory. Present analysis suggests that the superconducting-insulator transition occurs at a critical sheet resistance [Formula: see text]. It is found that the [Formula: see text] above [Formula: see text] shows different characteristics of [Formula: see text] and [Formula: see text] in the regions [Formula: see text] and [Formula: see text], respectively, where [Formula: see text] is the classical residual resistance and A is a constant. The excess conductance [Formula: see text] due to thermal fluctuation has been analyzed by the sum of the Aslamazov-Larkin and Maki-Thompson correction terms with use of the pair breaking parameter [Formula: see text] in the latter term. The sum agrees well with the data, although the experimental results of the [Formula: see text] dependence of [Formula: see text], that is, [Formula: see text] shows the disagreement with a linear relation [Formula: see text] derived from the localization theory.

  13. 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.

  14. Correlation-induced superconductivity dynamically stabilized and enhanced by laser irradiation

    PubMed Central

    Ido, Kota; Ohgoe, Takahiro; Imada, Masatoshi

    2017-01-01

    Studies on out-of-equilibrium dynamics have paved a way to realize a new state of matter. Superconductor-like properties above room temperatures recently suggested to be in copper oxides achieved by selectively exciting vibrational phonon modes by laser have inspired studies on an alternative and general strategy to be pursued for high-temperature superconductivity. We show that the superconductivity can be enhanced by irradiating laser to correlated electron systems owing to two mechanisms: First, the effective attractive interaction of carriers is enhanced by the dynamical localization mechanism, which drives the system into strong coupling regions. Second, the irradiation allows reaching uniform and enhanced superconductivity dynamically stabilized without deteriorating into equilibrium inhomogeneities that suppress superconductivity. The dynamical superconductivity is subject to the Higgs oscillations during and after the irradiation. Our finding sheds light on a way to enhance superconductivity that is inaccessible in equilibrium in strongly correlated electron systems. PMID:28835923

  15. Correlation-induced superconductivity dynamically stabilized and enhanced by laser irradiation.

    PubMed

    Ido, Kota; Ohgoe, Takahiro; Imada, Masatoshi

    2017-08-01

    Studies on out-of-equilibrium dynamics have paved a way to realize a new state of matter. Superconductor-like properties above room temperatures recently suggested to be in copper oxides achieved by selectively exciting vibrational phonon modes by laser have inspired studies on an alternative and general strategy to be pursued for high-temperature superconductivity. We show that the superconductivity can be enhanced by irradiating laser to correlated electron systems owing to two mechanisms: First, the effective attractive interaction of carriers is enhanced by the dynamical localization mechanism, which drives the system into strong coupling regions. Second, the irradiation allows reaching uniform and enhanced superconductivity dynamically stabilized without deteriorating into equilibrium inhomogeneities that suppress superconductivity. The dynamical superconductivity is subject to the Higgs oscillations during and after the irradiation. Our finding sheds light on a way to enhance superconductivity that is inaccessible in equilibrium in strongly correlated electron systems.

  16. Enhancement of superconductivity near the ferromagnetic quantum critical point in UCoGe.

    PubMed

    Slooten, E; Naka, T; Gasparini, A; Huang, Y K; de Visser, A

    2009-08-28

    We report a high-pressure single crystal study of the superconducting ferromagnet UCoGe. Measurements of the ac susceptibility and resistivity under pressures up to 2.2 GPa show ferromagnetism is smoothly depressed and vanishes at a critical pressure p(c) = 1.4 GPa. Near the ferromagnetic critical point superconductivity is enhanced. Upper-critical field measurements under pressure show B(c2)(0) attains remarkably large values, which provides solid evidence for spin-triplet superconductivity over the whole pressure range. The obtained p-T phase diagram reveals superconductivity is closely connected to a ferromagnetic quantum-critical point hidden under the superconducting "dome."

  17. 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.

  18. Enhanced superconductivity in aluminum-based hyperbolic metamaterials

    NASA Astrophysics Data System (ADS)

    Smolyaninova, Vera N.; Jensen, Christopher; Zimmerman, William; Prestigiacomo, Joseph C.; Osofsky, Michael S.; Kim, Heungsoo; Bassim, Nabil; Xing, Zhen; Qazilbash, Mumtaz M.; Smolyaninov, Igor I.

    2016-09-01

    One of the most important goals of condensed matter physics is materials by design, i.e. the ability to reliably predict and design materials with a set of desired properties. A striking example is the deterministic enhancement of the superconducting properties of materials. Recent experiments have demonstrated that the metamaterial approach is capable of achieving this goal, such as tripling the critical temperature TC in Al-Al2O3 epsilon near zero (ENZ) core-shell metamaterial superconductors. Here, we demonstrate that an Al/Al2O3 hyperbolic metamaterial geometry is capable of a similar TC enhancement, while having superior transport and magnetic properties compared to the core-shell metamaterial superconductors.

  19. Enhanced superconductivity in aluminum-based hyperbolic metamaterials

    PubMed Central

    Smolyaninova, Vera N.; Jensen, Christopher; Zimmerman, William; Prestigiacomo, Joseph C.; Osofsky, Michael S.; Kim, Heungsoo; Bassim, Nabil; Xing, Zhen; Qazilbash, Mumtaz M.; Smolyaninov, Igor I.

    2016-01-01

    One of the most important goals of condensed matter physics is materials by design, i.e. the ability to reliably predict and design materials with a set of desired properties. A striking example is the deterministic enhancement of the superconducting properties of materials. Recent experiments have demonstrated that the metamaterial approach is capable of achieving this goal, such as tripling the critical temperature TC in Al-Al2O3 epsilon near zero (ENZ) core-shell metamaterial superconductors. Here, we demonstrate that an Al/Al2O3 hyperbolic metamaterial geometry is capable of a similar TC enhancement, while having superior transport and magnetic properties compared to the core-shell metamaterial superconductors. PMID:27658850

  20. Interface high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  1. Skyrmionic configuration and half-quantum vortex-antivortex pair in mesoscopic p -wave superconducting noncircular systems

    NASA Astrophysics Data System (ADS)

    Zha, Guo-Qiao

    2017-01-01

    In the framework of the microscopic Bogoliubov-de Gennes theory, we study the topological properties of skyrmionic states under applied magnetic flux in mesoscopic symmetric and asymmetric p -wave superconducting noncircular systems. For a perfect square (rectangular) sample, an enclosed square-loop-like (parallelogram-loop-like) chain comprising four spatially separated one-component vortices emerges for a single-skyrmion state with the topological charge Q =2 . A multiskyrmion state containing two concentric skyrmions can be found in the square case, and more complex skyrmionic structures with Q >2 take place when the superconducting pairing interaction becomes stronger. By contrast, the mesoscopic rectangular geometry favors different arrangements of skyrmions. A novel type of multiskyrmion states with two or three separated skyrmions aligning along the long side of the rectangle becomes stable, accompanied with the half-quantum vortex-antivortex (V-Av) pair in one component of the order parameter. Moreover, for the square loops with a small square hole, the singly quantized vortex always traps in the centered or off-centered hole, while the coreless skyrmion located in the superconducting region tries to restore the centrally symmetric character. For some critical displacement of the off-centered hole, the half-quantum V-Av pair can occur in such asymmetric system.

  2. Implications of the pairing symmetry and the van Hove singularity for the normal and superconducting properties of cuprates

    NASA Astrophysics Data System (ADS)

    Quesada, D.; Pen˜a, R.

    2000-11-01

    The situation concerning the pairing symmetry of cuprates is still controversial. While earlier tunneling measurements pointed out to a dominant d wave symmetry, recent experiments seem to be consistent with a mixing like d+exp⁡(iθ)α, where α = s and s instead. In this communication we address the calculation of the electronic specific heat in the normal and superconducting states for the following pairing channels: s,s,d,d+is,d+is as well as the differential conductance ( dI/dV) for the N - I - N and N - I - S junctions.

  3. 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.

  4. Enhanced Schwinger pair production in many-centre systems

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    Electron-positron pair production is considered for many-centre systems with multiple bare nuclei immersed in a constant electric field. It is shown that there are two distinct regimes where the pair production rate is enhanced. At small interatomic distance, the effective charge of the nuclei approaches the critical charge where the ground state dives into the negative continuum. This facilitates the transition from the negative to the positive energy states, which in turn increases the pair production rate. At larger atomic distance, the enhancement is due to the crossing of resonances and the pair production proceeds by the resonantly enhanced pair production mechanism. These processes are studied within a simple one-dimensional model. A numerical method is developed to evaluate the transmission coefficient in relativistic quantum mechanics, which is required in the calculation of the pair production rate. The latter is evaluated for systems with many (up to five) nuclei. It is shown that the production rate for many-centre systems can reach a few orders of magnitude above Schwinger’s tunnelling result in a static field.

  5. Localization and pair breaking parameter in superconducting molybdenum nitride thin films

    NASA Astrophysics Data System (ADS)

    Tsuneoka, Takuya; Makise, Kazumasa; Maeda, Sho; Shinozaki, Bunju; Ichikawa, Fusao

    2017-01-01

    We have investigated the superconductor-insulator transition in molybdenum nitride films prepared by deposition onto MgO substrates. It is indicated that the T c depression from ≈ 6.6 \\text{K} for thick films with increase of the normal state sheet resistance R\\text{sq}\\text{N} was well explained by the Finkel’stein formula from the localization theory. Present analysis suggests that the superconducting-insulator transition occurs at a critical sheet resistance {{R}\\text{c}}≈ 2 \\text{k} Ω . It is found that the {{R}\\text{sq}}(T) above {{R}\\text{c}} shows different characteristics of {{R}\\text{sq}}(T)={{R}\\text{sq,0}}-A\\ln T and {{R}\\text{sq}}(T)\\propto \\exp ≤ft[{≤ft({{T}0}/T\\right)}1/2}\\right] in the regions {{R}\\text{c}}\\text{sq}\\text{N}<{{R}\\text{Q}}=h/4{{e}2}≈ 6.45 \\text{k} Ω and R\\text{sq}\\text{N}>{{R}\\text{Q}} , respectively, where {{R}\\text{sq,0}} is the classical residual resistance and A is a constant. The excess conductance {{σ\\prime}{}(T) due to thermal fluctuation has been analyzed by the sum of the Aslamazov-Larkin and Maki-Thompson correction terms with use of the pair breaking parameter δ in the latter term. The sum agrees well with the data, although the experimental results of the R\\text{sq}\\text{N} dependence of δ , that is, δ \\propto {{≤ft(R\\text{sq}\\text{N}\\right)}≈ 1.7} shows the disagreement with a linear relation δ \\propto ≤ft(R\\text{sq}\\text{N}\\right) derived from the localization theory.

  6. Quantifying the FIR interaction enhancement in paired galaxies

    NASA Technical Reports Server (NTRS)

    Xu, Cong; Sulentic, Jack W.

    1990-01-01

    The Catalog of Isolated Pairs of Galaxies in the Northern Hemisphere, by Karachentsev (1972), was studied and a well-matched comparison sample taken from the Catalog of Isolated Galaxies, by Karachentseva (1973), in order to quantify the enhanced FIR emission properties of interacting galaxies.

  7. Enhancing Marital Intimacy Through Psychoeducation: The PAIRS Program.

    ERIC Educational Resources Information Center

    Durana, Carlos

    1997-01-01

    Explores intimacy enhancement through a psychoeducational method, the Practical Application of Intimate Relationship Skills (PAIRS) Program. Participants were more distressed and less intimate than general population. Clients' perceptions of intimacy and what maintains intimacy were measured. Findings suggest a multifaceted view of intimacy.…

  8. Yu-Shiba-Rusinov states and topological superconductivity in Ising paired superconductors

    NASA Astrophysics Data System (ADS)

    Sharma, Girish; Tewari, Sumanta

    2016-09-01

    An unusual form of superconductivity, called Ising superconductivity, has recently been uncovered in mono- and few-layered transition metal dichalcogenides. This 2D superconducting state is characterized by the so-called Ising spin-orbit coupling (SOC), which produces strong oppositely oriented effective Zeeman fields perpendicular to the 2D layer in opposite momentum space valleys. We examine the Yu-Shiba-Rusinov (YSR) bound states localized at magnetic impurities in Ising superconductors and show that the unusual SOC manifests itself in unusually strong anisotropy in magnetic field response observable in STM experiments. For a chain of magnetic impurities with moments parallel to the plane of Ising superconductors we show that the low energy YSR band hosts topological superconductivity and Majorana excitations as a direct manifestation of topological effects induced by Ising spin-orbit coupling.

  9. Aligned carbon nanotubes sandwiched in epitaxial NbC film for enhanced superconductivity.

    PubMed

    Zhang, Yingying; Ronning, Filip; Gofryk, Krzysztof; Mara, Nathan A; Haberkorn, Nestor; Zou, Guifu; Wang, Haiyan; Lee, Joon H; Bauer, Eve; McCleskey, Thomas M; Burell, Anthony K; Civale, Leonardo; Zhu, Y T; Jia, Quanxi

    2012-04-07

    Highly aligned carbon nanotube (CNT) ribbons were sandwiched in epitaxial superconducting NbC films by a chemical solution deposition method. The incorporation of aligned long CNTs into NbC film enhances the normal-state conductivity and improves the superconducting properties of the assembly.

  10. Superconductivity:

    NASA Astrophysics Data System (ADS)

    Sacchetti, N.

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

  11. Strong-coupling superconductivity beyond BCS and the key pairing interaction in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Alexandrov, A. S.

    2011-03-01

    It has been now over 20 years since the discovery of the first high temperature superconductor by Georg Bednorz and Alex Müller in 1986 and yet, despite intensive effort, no universally accepted theory exists about the origin of high-temperature superconductivity. A controversial issue on whether the electron-phonon interaction (EPI) is crucial for high-temperature superconductivity or weak and inessential has been one of the most challenging problems of contemporary condensed matter physics. I briefly review our recent theoretical results, which in conjunction with a great number of experimental observations including isotope effects, angle-resolved photoemission (ARPES), pump-probe and tunnelling spectroscopies, normal state diamagnetism and magnetic quantum oscillations provide the definite answer to this fundamental question. The true origin of high-temperature superconductivity is found in a significant finite-range Fröhlich EPI of nonadiabatic polaronic carriers which is beyond the conventional BCS-Migdal-Eliashberg approximation.

  12. Robustness of s-wave pairing symmetry in iron-based superconductors and its implications for fundamentals of magnetically driven high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Hu, Jiangping; Yuan, Jing

    2016-10-01

    Based on the assumption that the superconducting state belongs to a single irreducible representation of lattice symmetry, we propose that the pairing symmetry in all measured iron-based superconductors is generally consistent with the A 1 g s-wave. Robust s-wave pairing throughout the different families of iron-based superconductors at different doping regions signals two fundamental principles behind high- T c superconducting mechanisms: (i) the correspondence principle: the short-range magnetic-exchange interactions and the Fermi surfaces act collaboratively to achieve high- T c superconductivity and determine pairing symmetries; (ii) the magnetic-selection pairing rule: superconductivity is only induced by the magnetic-exchange couplings from the super-exchange mechanism through cation-anion-cation chemical bonding. These principles explain why unconventional high- T c superconductivity appears to be such a rare but robust phenomena, with its strict requirements regarding the electronic environment. The results will help us to identify new electronic structures that can support high- T c superconductivity.

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

    DOE PAGES

    Biswas, P. K.; Guguchia, Z.; Khasanov, R.; ...

    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

  14. Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

    DOE PAGES

    Teknowijoyo, S.; Cho, K.; Tanatar, M. A.; ...

    2016-08-29

    A highly anisotropic superconducting gap is found in single crystals of FeSe by studying the London penetration depth Δλ measured down to 50 mK in samples before and after 2.5 MeV electron irradiation. The gap minimum increases with introduced pointlike disorder, indicating the absence of symmetry-imposed nodes. Surprisingly, the superconducting transition temperature Tc increases by 0.4 K from Tc0 ≈ 8.8 K while the structural transition temperature Ts decreases by 0.9 K from Ts0 ≈ 91.2 K after electron irradiation. Finally, we discuss several explanations for the Tc enhancement and propose that local strengthening of the pair interaction by irradiation-inducedmore » Frenkel defects most likely explains the phenomenon.« less

  15. Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

    SciTech Connect

    Teknowijoyo, S.; Cho, K.; Tanatar, M. A.; Gonzales, J.; Böhmer, A. E.; Cavani, O.; Mishra, V.; Hirschfeld, P. J.; Bud'ko, S. L.; Canfield, P. C.; Prozorov, R.

    2016-08-29

    A highly anisotropic superconducting gap is found in single crystals of FeSe by studying the London penetration depth Δλ measured down to 50 mK in samples before and after 2.5 MeV electron irradiation. The gap minimum increases with introduced pointlike disorder, indicating the absence of symmetry-imposed nodes. Surprisingly, the superconducting transition temperature Tc increases by 0.4 K from Tc0 ≈ 8.8 K while the structural transition temperature Ts decreases by 0.9 K from Ts0 ≈ 91.2 K after electron irradiation. Finally, we discuss several explanations for the Tc enhancement and propose that local strengthening of the pair interaction by irradiation-induced Frenkel defects most likely explains the phenomenon.

  16. Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

    SciTech Connect

    Teknowijoyo, S.; Cho, K.; Tanatar, M. A.; Gonzales, J.; Böhmer, A. E.; Cavani, O.; Mishra, V.; Hirschfeld, P. J.; Bud'ko, S. L.; Canfield, P. C.; Prozorov, R.

    2016-08-29

    A highly anisotropic superconducting gap is found in single crystals of FeSe by studying the London penetration depth Δλ measured down to 50 mK in samples before and after 2.5 MeV electron irradiation. The gap minimum increases with introduced pointlike disorder, indicating the absence of symmetry-imposed nodes. Surprisingly, the superconducting transition temperature Tc increases by 0.4 K from Tc0 ≈ 8.8 K while the structural transition temperature Ts decreases by 0.9 K from Ts0 ≈ 91.2 K after electron irradiation. Finally, we discuss several explanations for the Tc enhancement and propose that local strengthening of the pair interaction by irradiation-induced Frenkel defects most likely explains the phenomenon.

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

    PubMed

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

    2013-12-02

    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-T(c) cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above T(c). 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.

  18. Enhancement of the Superconducting Gap by Nesting in CaKFe4As4 : A New High Temperature Superconductor

    NASA Astrophysics Data System (ADS)

    Mou, Daixiang; Kong, Tai; Meier, William R.; Lochner, Felix; Wang, Lin-Lin; Lin, Qisheng; Wu, Yun; Bud'ko, S. L.; Eremin, Ilya; Johnson, D. D.; Canfield, P. C.; Kaminski, Adam

    2016-12-01

    We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe4 As4 . In contrast to the related CaFe2 As2 compounds, CaKFe4 As4 has a high Tc of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of the Brillouin zone), but are significantly different for each of the Fermi surface (FS) sheets. Most importantly, we find that the momentum dependence of the gap magnitude plotted across the entire Brillouin zone displays a strong deviation from the simple cos (kx)cos (ky) functional form of the gap function, proposed by the scenario of Cooper pairing driven by a short range antiferromagnetic exchange interaction. Instead, the maximum value of the gap is observed on FS sheets that are closest to the ideal nesting condition, in contrast to previous observations in other ferropnictides. These results provide strong support for the multiband character of superconductivity in CaKFe4 As4 , in which Cooper pairing forms on the electron and the hole bands interacting via a dominant interband repulsive interaction, enhanced by band nesting.

  19. Enhancement of the Superconducting Gap by Nesting in CaKFe_{4}As_{4}: A New High Temperature Superconductor.

    PubMed

    Mou, Daixiang; Kong, Tai; Meier, William R; Lochner, Felix; Wang, Lin-Lin; Lin, Qisheng; Wu, Yun; Bud'ko, S L; Eremin, Ilya; Johnson, D D; Canfield, P C; Kaminski, Adam

    2016-12-30

    We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe_{4}As_{4}. In contrast to the related CaFe_{2}As_{2} compounds, CaKFe_{4}As_{4} has a high T_{c} of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of the Brillouin zone), but are significantly different for each of the Fermi surface (FS) sheets. Most importantly, we find that the momentum dependence of the gap magnitude plotted across the entire Brillouin zone displays a strong deviation from the simple cos(k_{x})cos(k_{y}) functional form of the gap function, proposed by the scenario of Cooper pairing driven by a short range antiferromagnetic exchange interaction. Instead, the maximum value of the gap is observed on FS sheets that are closest to the ideal nesting condition, in contrast to previous observations in other ferropnictides. These results provide strong support for the multiband character of superconductivity in CaKFe_{4}As_{4}, in which Cooper pairing forms on the electron and the hole bands interacting via a dominant interband repulsive interaction, enhanced by band nesting.

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

    PubMed

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

    2014-08-12

    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 Ek(α,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.

  1. 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

  2. Assessment of Superconductivity Enhancement Claimed to Occur in Small Particle-Normal Metal Matrix Composite Superconductors,

    DTIC Science & Technology

    1978-02-20

    using current theories, experimental results, and notions of superconductivity of the A15’s and Bl’s. ~Lt Curve 69d10𔄀 SNb3 Sn E 5 o V3 Ga V)~c ._ 0 V3...A10 W4 W~ ESTINGHOUSE RESEARCH AND DEVELOPMENT CENTER PITTSBU-ETC F/6 20/3 I ASSESSMENT OF SUPERCONDUCTIVITY ENHANCEMENT CLAIMED TO OCCUR IN--ETC CU...I FEB 78 N ASHKIN F59020-76-C-0031 UNCLASSIFIED N EE A 1EE1hE ASSESSMENT OF SUPERCONDUCTIVITY ENHANCEMENT CLAIMED TO OCCUR IN SMALL PARTICLE-NORMAL

  3. Superconducting and ferromagnetic phases in SrTiO3/LaAlO3 oxide interface structures: possibility of finite momentum pairing.

    PubMed

    Michaeli, Karen; Potter, Andrew C; Lee, Patrick A

    2012-03-16

    We introduce a model to explain the observed ferromagnetism and superconductivity in LAO/STO oxide interface structures. Because of the polar catastrophe mechanism, 1/2 charge per unit cell is transferred to the interface layer. We argue that this charge localizes and orders ferromagnetically via exchange with the conduction electrons. Ordinarily, this ferromagnetism would destroy superconductivity, but, due to strong spin-orbit coupling near the interface, the magnetism and superconductivity can coexist by forming a Fulde-Ferrell-Larkin-Ovchinikov-type condensate of Cooper pairs at finite momentum, which is surprisingly robust in the presence of strong disorder.

  4. Use of superconducting imaging surfaces to enhance detection of weak magnetic sources by SQUID systems

    SciTech Connect

    Overton, W.C. Jr.; van Hulsteyn, D.B.; Flynn, E.R.

    1989-01-01

    The use of superconducting magnetometers and gradiometers to detect weak magnetic signals is well known. The weak sources produce small field changes in the vicinity of superconducting pickup coil combinations which respond to changes in the local magnetic flux. When coupled to SQUID detectors, these systems can respond to changes as small as 10 ft. However, magnetic noise severely restricts the operation of such systems. We show that combinations of flat and curved superconducting sheets in combination with superconducting pickup coils can enhance the detection capability and improve noise rejection. Surface currents induced in the sheets are represented by the source dipole and its image. They give rise to signals similar to those of the first-order gradiometer. The theory of images is used to analyze the signals. Several configurations of sense coils and superconducting imaging surfaces are analyzed. 15 refs., 28 figs.

  5. Superconducting transition temperatures and coherence length in non-s-wave pairing materials correlated with spin-fluctuation mediated interaction

    NASA Astrophysics Data System (ADS)

    Angilella, G. G.; March, N. H.; Pucci, R.

    2002-03-01

    Following earlier work on electron or hole liquids flowing through assemblies with magnetic fluctuations, we have recently exposed a marked correlation of the superconducting temperature Tc, for non-s-wave pairing materials, with coherence length ξ and effective mass m*. The very recent study of Abanov et al. [Europhys. Lett. 54, 488 (2001)] and the prior investigation of Monthoux and Lonzarich [Phys. Rev. B 59, 14 598 (1999)] have each focused on the concept of a spin-fluctuation temperature Tsf, which again is intimately related to Tc. For the d-wave pairing via antiferromagnetic spin fluctuations in the cuprates, these studies are brought into close contact with our own work, and the result is that kBTsf~ħ2/m*ξ2. This demonstrates that ξ is also determined by such antiferromagnetic spin-fluctuation mediated pair interaction. The coherence length in units of the lattice spacing is then essentially given in the cuprates as the square root of the ratio of two characteristic energies, namely, the kinetic energy of localization of a charge carrier of mass m* in a specified magnetic correlation length to the hopping energy. The quasi-two-dimensional ruthenate Sr2RuO4, with Tc~1.3 K, has p-wave spin-triplet pairing and so is also briefly discussed here.

  6. 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.

  7. 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

  8. 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.

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

    DOE PAGES

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

    2017-04-07

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

  10. Experimental evidence for ferromagnetic spin-pairing superconductivity emerging in UGe2 : A Ge73 -nuclear-quadrupole-resonance study under pressure

    NASA Astrophysics Data System (ADS)

    Harada, A.; Kawasaki, S.; Mukuda, H.; Kitaoka, Y.; Haga, Y.; Yamamoto, E.; Ōnuki, Y.; Itoh, K. M.; Haller, E. E.; Harima, H.

    2007-04-01

    We report that a different type of superconducting order parameter has been realized in the ferromagnetic states in UGe2 via Ge73 -nuclear-quadrupole-resonance experiments performed under pressure (P) . Measurements of the nuclear spin-lattice relaxation rate (1/T1) have revealed an unconventional nature of superconductivity such that the up-spin band is gapped with line nodes, but the down-spin band remains gapless at the Fermi level. This result is consistent with that of a ferromagnetic spin-pairing model in which Cooper pairs are formed among ferromagnetically polarized electrons. The present experiment has shed light on the possible origin of ferromagnetic superconductivity, which is mediated by ferromagnetic spin-density fluctuations relevant to the first-order transition inside the ferromagnetic states.

  11. 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.

  12. 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.

  13. Superconductivity enhancement in the S-doped Weyl semimetal candidate MoTe{sub 2}

    SciTech Connect

    Chen, F. C.; Xiao, R. C.; Luo, X. E-mail: ypsun@issp.ac.cn; Lu, W. J.; Pei, Q. L.; Shao, D. F.; Song, W. H.; Zhang, B.; Yang, H. X.; Li, J. Q.; Zhang, R. R.; Ling, L. S.; Xi, C. Y.; Sun, Y. P. E-mail: ypsun@issp.ac.cn

    2016-04-18

    Two-dimensional transition-metal dichalcogenide (TMDs) MoTe{sub 2} 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 MoTe{sub 2} single crystal can be greatly enhanced by the partial substitution of the Te ions by the S ones. The maximum superconducting temperature T{sub C} of MoTe{sub 1.8}S{sub 0.2} single crystal is about 1.3 K. Compared with the parent MoTe{sub 2} single crystal (T{sub C} = 0.1 K), nearly 13-fold in T{sub C} is improved in the MoTe{sub 1.8}S{sub 0.2} one. The superconductivity has been investigated through the resistivity and magnetization measurements. MoTe{sub 2−x}S{sub x} 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 MoTe{sub 2} single crystals. MoTe{sub 2−x}S{sub x} materials may provide a new platform for our understanding of superconductivity phenomena and topological physics in TMDs.

  14. Observation of enhanced superconductivity in the vicinity of Ar-induced nano-cavities in Pb(111).

    PubMed

    Song, Sang Yong; Seo, Jungpil

    2017-09-22

    Local variations of superconductivity have been studied using scanning tunneling microscopy around nano-cavities formed by Ar ions embedded in Pb(111). Various factors including the density of states at Fermi energy, electron-phonon couplings, and quantum well states, which are known to affect superconductivity, have been examined. We show that the superconductivity is enhanced near the nano-cavities and propose that quantum effects such as quantum confinement, proximity effect and multi-gap effect are possibly involved in determining the superconducting gap of this system. These results have important implications for the characterization and understanding of superconductivity at a nanometer scale.

  15. Superconductivity of the Sr2Ca12Cu24O41 spin-ladder system: are the superconducting pairing and the spin-gap formation of the same origin?

    PubMed

    Fujiwara, Naoki; Môri, Nobuo; Uwatoko, Yoshiya; Matsumoto, Takehiko; Motoyama, Naoki; Uchida, Shinichi

    2003-04-04

    Pressure-induced superconductivity in a spin-ladder cuprate Sr2Ca12Cu24O41 has not been studied on a microscopic level thus far although the superconductivity was already discovered in 1996. We have improved the high-pressure technique using a large high-quality crystal, and succeeded in studying the superconductivity using 63Cu nuclear magnetic resonance. We found that the anomalous metallic state reflecting the spin-ladder structure is realized and the superconductivity possesses an s-wave-like character in the meaning that a finite gap exists in the quasiparticle excitation: At a pressure of 3.5 GPa, we observed two excitation modes in the normal state from the relaxation rate T-11. One gives rise to an activation-type component in T-11, and the other T-linear component linking directly with the superconductivity. This gapless mode likely arises from free motion of holon-spinon bound states appearing by hole doping, and the pairing of them likely causes the superconductivity.

  16. Enhanced antiferromagnetic exchange between magnetic impurities in a superconducting host.

    PubMed

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

    2014-08-22

    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/r(2) 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.

  17. Enhancement of the superconducting gap by nesting in CaKFe4As4: A new high temperature superconductor

    DOE PAGES

    Mou, Daixiang; Kong, Tai; Meier, William R.; ...

    2016-12-28

    We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe4As4. In contrast to the related CaFe2As2 compounds, CaKFe4As4 has a high Tc of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of themore » Brillouin zone), but are significantly different for each of the Fermi surface (FS) sheets. Most importantly, we find that the momentum dependence of the gap magnitude plotted across the entire Brillouin zone displays a strong deviation from the simple cos(kx)cos(ky) functional form of the gap function, proposed by the scenario of Cooper pairing driven by a short range antiferromagnetic exchange interaction. Instead, the maximum value of the gap is observed on FS sheets that are closest to the ideal nesting condition, in contrast to previous observations in other ferropnictides. Finally, these results provide strong support for the multiband character of superconductivity in CaKFe4As4, in which Cooper pairing forms on the electron and the hole bands interacting via a dominant interband repulsive interaction, enhanced by band nesting.« less

  18. Enhanced superconductivity in hole-doped Nb2PdS5

    NASA Astrophysics Data System (ADS)

    Chen, Qian; Yang, Xiaohui; Yang, Xiaojun; Chen, Jian; Shen, Chenyi; Zhang, Pan; Li, Yupeng; Tao, Qian; Xu, Zhu-An

    2017-10-01

    We synthesized a series of Nb2Pd1- x Ru x S5 polycrystalline samples by a solid-state reaction method and systematically investigated the Ru-doping effect on superconductivity by transport and magnetic measurements. It is found that superconductivity is enhanced with Ru doping and is quite robust upon disorder. Hall coefficient measurements indicate that the charge transport is dominated by hole-type charge carriers similar to the case of Ir doping, suggesting multi-band superconductivity. Upon Ru or Ir doping, H c2/ T c exhibits a significant enhancement, exceeding the Pauli paramagnetic limit value by a factor of approximately 4. A comparison of T c and the upper critical field ( H c2) amongst the different doping elements on Pd site, reveals a significant role of spin-orbit coupling.

  19. Potential impact of superconductivity on power quality enhancment

    NASA Astrophysics Data System (ADS)

    McConnell, B. W.

    1992-02-01

    Electric power quality problems are estimated to cost U.S. industry 26 billion dollars per year in lost production. This paper provides a summary of the problem's magnitude, an overview of the underlying causes, discusses the present methods used by industry to reduce the problem's impact and the associated cost, and examines the potential for superconducting technology to effect alternative solutions. The present market for uninterruptible power supplies (UPS) and power conditioners is also discussed and the benefits of applying high temperature superconductors (HTS) are summarized.

  20. Superconducting state of κ-(ET)2CUBr studied by 13C NMR: Evidence for vortex-core-induced nuclear relaxation and unconventional pairing

    NASA Astrophysics Data System (ADS)

    Mayaffre, H.; Wzietek, P.; Jérome, D.; Lenoir, C.; Batail, P.

    1995-11-01

    We present the first 13C NMR measurements carried out in the superconducting state of a two-dimensional organic superconducting single crystal. Spin lattice relaxation rate and Knight shift are reported for magnetic fields parallel and perpendicular to the conducting layers. For perpendicular fields, the relaxation is dominated by the electronic excitations in the vortex cores. From the field dependence of (T1)-1 we obtain the upper critical field. In parallel orientation, the absence of field dependence reveals the existence of a lock-in state, where only relaxation by superconducting excitations is expected. The (T1)-1 then exhibits a T3 law suggesting an unconventional pairing with a very anisotropic gap.

  1. 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.

  2. Enhancing the Superconducting Transition Temperature of BaSi2 by Structural Tuning

    NASA Astrophysics Data System (ADS)

    Flores-Livas, José A.; Debord, Régis; Botti, Silvana; San Miguel, Alfonso; Marques, Miguel A. L.; Pailhès, Stéphane

    2011-02-01

    We present a joint experimental and theoretical study of the superconducting phase of the layered binary silicide BaSi2. Compared with the AlB2 structure of graphite or diboridelike superconductors, in the hexagonal structure of binary silicides the sp3 arrangement of silicon atoms leads to corrugated sheets. Through a high-pressure synthesis procedure we are able to modify the buckling of these sheets, enhancing the superconducting transition temperature from 6 to 8.9 K when the silicon planes flatten out. By performing ab initio calculations based on density-functional theory we explain how the electronic and phonon properties are strongly affected by changes in the buckling. This mechanism is likely present in other intercalated layered superconductors, opening the way to the tuning of superconductivity through the control of internal structural parameters.

  3. Superconducting niobium titanium nitride thin films deposited by plasma-enhanced atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Yemane, Y. T.; Sowa, M. J.; Zhang, J.; Ju, L.; Deguns, E. W.; Strandwitz, N. C.; Prinz, F. B.; Provine, J.

    2017-09-01

    NbTiN has a variety of superconducting applications, ranging from RF cavities to single-photon detectors. Here, we systematically investigated the plasma-enhanced atomic layer deposition (PEALD) of Nb x Ti{}1-x{{N}} with the organometallic precursors (t-butylimido) tris(diethyamido) niobium(V) and tetrakis (dimethylamido) titanium in conjunction with a remote H2/N2 plasma. Deposited film properties have been studied as a function of the ratio of Nb to Ti precursor pulses within each ALD supercycle. PEALD NbTiN films were characterized with spectroscopic ellipsometry (thickness, optical properties), four point probe (resistivity), x-ray photoelectron spectroscopy (composition), x-ray reflectivity (density and thickness), x-ray diffraction (crystallinity), and superconductivity measurements. The PEALD process has shown distinct advantages over deposition of superconducting films via thermal ALD or sputtering, for example a lower processing temperature and more efficient control of film composition. This control of film composition enabled the tuning of electrical and superconducting properties, such as varying the superconducting critical temperature T C between 6.9 and 13.2 K.

  4. Enhanced transition temperature due to tetragonal domains in two-dimensional superconducting strontium titanate

    NASA Astrophysics Data System (ADS)

    Noad, Hilary; Nowack, Katja; Spanton, Eric; Inoue, Hisashi; Kim, Minu; Bell, Chris; Hikita, Yasuyuki; Hwang, Harold Y.; Moler, Kathryn

    2015-03-01

    Strontium titanate (SrTiO3) is a key component in superconducting heterostructures such as LaAlO3/SrTiO3 and monolayer FeSe on SrTiO3, yet superconductivity in bare SrTiO3 is not fully understood. We used a scanning superconducting quantum interference device susceptometer to image the diamagnetic response as a function of temperature in samples of SrTiO3 containing either a 5.5 nm or a 36.9 nm-thick slab of niobium-doped SrTiO3. We find that stripe-like regions remain superconducting at higher temperatures than the rest of the sample. The shape and orientation of the features, as well as their behavior in a subsequent cooldown, are consistent with an origin in the low-temperature tetragonal domain structure of SrTiO3. These results suggest a variety of mechanisms by which the transition temperature could be enhanced and may help constrain theories of superconductivity in SrTiO3.

  5. High-T_{c} Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations.

    PubMed

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

    2017-04-07

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  8. Superconducting pairing and the pseudogap in the nematic dynamical stripe phase of La2-xSrxCuO4.

    PubMed

    Sugai, S; Takayanagi, Y; Hayamizu, N; Muroi, T; Shiozaki, R; Nohara, J; Takenaka, K; Okazaki, K

    2013-11-27

    Fully absorption coefficient corrected Raman spectra were obtained in La2-xSrxCuO4. The B1g spectra have a Fleury-Loudon type two-magnon peak (resonant term) whose energy decreases from 3180 cm(-1) (394 meV) to 440 cm(-1) (55 meV) on increasing the carrier density from x = 0 to 0.25, while the B2g spectra have a 1000-3500 cm(-1) (124-434 meV) hump (hill) whose lower-edge energy increases from x = 0 to 0.115 and then stays constant to x = 0.25. The B2g hump is assigned to the electronic scattering (non-resonant term) of the spectral function with magnetic self-energy. The completely different carrier density dependence arises from anisotropic magnetic excitations of spin-charge stripes. The B1g spectra were assigned to the sum of k ∥  and k⊥ stripe excitations and the B2g spectra to k⊥ stripe excitations according to the calculation by Seibold and Lorenzana (2006 Phys. Rev. B 73 144515). The k ∥  and k⊥ stripe excitations in fluctuating spin-charge stripes were separately detected for the first time. The appearance of only k⊥ stripe excitations in the electronic scattering arises from the charge hopping perpendicular to the stripe. This is the same direction as the Burgers vector of the edge dislocation in metal. The successive charge hopping in the Burgers vector direction across the charge stripes may cause Cooper pairs as predicted by Zaanen et al (2004 Ann. Phys. 310 181). Indeed, this is supported by the experimental fact that the superconducting coherent length coincides with the inter-charge stripe distance in the wide carrier density range. The one-directional charge hopping perpendicular to the stripe causes the flat Fermi surface and the pseudogap near (π,0) and (0,π), but the states around (π/2,π/2) cannot be produced. The low-energy Raman scattering disclosed that the electronic states at the Fermi arc around (π/2,π/2) are coupled to the A1g soft phonon of the tetragonal-orthorhombic phase transition. This suggests that

  9. Optical switching of radical pair conformation enhances magnetic sensitivity

    PubMed Central

    Guerreschi, Gian Giacomo; Tiersch, Markus; Steiner, Ulrich E.; Briegel, Hans J.

    2013-01-01

    The yield of radical pair reactions is influenced by magnetic fields well beyond the levels expected from energy considerations. This dependence can be traced back to the microscopic dynamics of electron spins and constitutes the basis of chemical compasses. Here we propose a new experimental approach based on molecular photoswitches to achieve additional control on the chemical reaction and allow short-time resolution of the spin dynamics. Our proposal enables experiments to test some of the standard assumptions of the radical pair model and improves the sensitivity of a paradigmatic model of chemical magnetometer by up to two orders of magnitude. PMID:25843962

  10. Nodeless pairing in superconducting copper-oxide monolayer films on Bi2Sr2CaCu2O8+δ

    DOE PAGES

    Zhong, Yong; Wang, Yang; Han, Sha; ...

    2016-07-12

    We report that the pairing mechanism of high-temperature superconductivity in cuprates remains the biggest unresolved mystery in condensed matter physics. To solve the problem, one of the most effective approaches is to investigate directly the superconducting CuO2 layers. Here, by growing CuO2 monolayer films on Bi2Sr2CaCu2O8+δ substrates, we identify two distinct and spatially separated energy gaps centered at the Fermi energy, a smaller U-like gap and a larger V-like gap on the films, and study their interactions with alien atoms by low-temperature scanning tunneling microscopy. The newly discovered U-like gap exhibits strong phase coherence and is immune to scattering bymore » K, Cs and Ag atoms, suggesting its nature as a nodeless superconducting gap in the CuO2 layers, whereas the V-like gap agrees with the well-known pseudogap state in the underdoped regime. In conclusion, our results support an s-wave superconductivity in Bi2Sr2CaCu2O8+δ, which, we propose, originates from the modulation-doping resultant two-dimensional hole liquid confined in the CuO2 layers.« less

  11. Three superconducting phases with different categories of pairing in hole- and electron-doped LaFeAs1 -xPxO

    NASA Astrophysics Data System (ADS)

    Miyasaka, S.; Uekubo, M.; Tsuji, H.; Nakajima, M.; Tajima, S.; Shiota, T.; Mukuda, H.; Sagayama, H.; Nakao, H.; Kumai, R.; Murakami, Y.

    2017-06-01

    The phase diagram of the LaFeAs1 -xPxO system has been extensively studied through hole and electron doping as well as As/P substitution. It has been revealed that there are three different superconducting phases with different Fermi surface (FS) topologies and thus with possibly different pairing glues. One of them is well understood as spin fluctuation-mediated superconductivity within a FS nesting scenario. Another one with the FSs in a bad nesting condition must be explained in a different context such as orbital or spin fluctuation in a strongly correlated electronic system. In both phases, T -linear resistivity was commonly observed when the superconducting transition temperature Tc becomes the highest value, indicating that the strength of bosonic fluctuation determines Tc. In the last superconducting phase, the nesting condition of FSs and the related bosonic fluctuation are moderate. Variety of phase diagram characterizes the multiple orbital nature of the iron-based superconductors which are just near the boundary between weak and strong correlation regimes.

  12. Dominant Majorana bound energy and critical current enhancement in ferromagnetic-superconducting topological insulator

    NASA Astrophysics Data System (ADS)

    Khezerlou, Maryam; Goudarzi, Hadi; Asgarifar, Samin

    2017-03-01

    Among the potential applications of topological insulators, we theoretically study the coexistence of proximity-induced ferromagnetic and superconducting orders in the surface states of a 3-dimensional topological insulator. The superconducting electron-hole excitations can be significantly affected by the magnetic order induced by a ferromagnet. In one hand, the surface state of the topological insulator, protected by the time-reversal symmetry, creates a spin-triplet and, on the other hand, magnetic order causes to renormalize the effective superconducting gap. We find Majorana mode energy along the ferromagnet/superconductor interface to sensitively depend on the magnitude of magnetization m zfs from superconductor region, and its slope around perpendicular incidence is steep with very low dependency on m zfs . The superconducting effective gap is renormalized by a factor η( m zfs ), and Andreev bound state in ferromagnet-superconductor/ferromagnet/ferromagnet-superconductor (FS/F/FS) Josephson junction is more sensitive to the magnitude of magnetizations of FS and F regions. In particular, we show that the presence of m zfs has a noticeable impact on the gap opening in Andreev bound state, which occurs in finite angle of incidence. This directly results in zero-energy Andreev state being dominant. By introducing the proper form of corresponding Dirac spinors for FS electron-hole states, we find that via the inclusion of m zfs , the Josephson supercurrent is enhanced and exhibits almost abrupt crossover curve, featuring the dominant zero-energy Majorana bound states.

  13. 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

  14. 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

  15. Pressure Induced Enhancement of Superconductivity in LaRu2P2.

    PubMed

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

    2016-04-18

    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.

  16. Enhancement of superconductivity in FeSe thin crystals induced by biaxial compressive strain

    NASA Astrophysics Data System (ADS)

    Wang, X. F.; Zhang, Z. T.; Wang, W. K.; Zhou, Y. H.; Kan, X. C.; Chen, X. L.; Gu, C. C.; Zhang, L.; Pi, L.; Yang, Z. R.; Zhang, Y. H.

    2017-06-01

    We report on the enhancement of superconductivity in FeSe thin crystals induced by in-plane biaxial compressive strain, with an underlying scotch tape as an in-situ strain generator. It is found that, due to the compressive strain, the superconducting transition temperature Tc ≈ 9 K of FeSe is increased by 30%-40% and the upper critical field Hc2(0) ≈ 14.8 T is increased by ∼ 20%. In parallel, the T*, which characterizes an onset of enhanced spin fluctuations, is raised up from 69 K to 87 K. On the other hand, the structural transition temperature Ts ≈ 94 K, below which an orthorhombic structure and an electronic nematic phase settle in, is suppressed down by ∼ 5 K. These findings reveal clear evolutions of the orders/fluctuations under strain effect in FeSe, the structurally simplest iron-based superconductor where the lattice/spin/charge degrees of freedom are closely coupled to one another. Moreover, the presented research provides a simple and clean way to manipulate the superconductivity in the layered iron compounds and may promote applications in related materials.

  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. 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.

  19. On a mechanism of high-temperature superconductivity: Spin-electron acoustic wave as a mechanism for the Cooper pair formation

    NASA Astrophysics Data System (ADS)

    Andreev, Pavel A.; Polyakov, P. A.; Kuz'menkov, L. S.

    2017-10-01

    We have found the mechanism of the electron Cooper pair formation via the electron interaction by means of the spin-electron acoustic waves. This mechanism takes place in metals with rather high spin polarization, such as ferromagnetic, ferrimagnetic, and antiferromagnetic materials. The spin-electron acoustic wave mechanism leads to transition temperatures 100 times higher than the transition temperature allowed by the electron-phonon interaction. Therefore, spin-electron acoustic waves give the explanation for the high-temperature superconductivity. We find that the transition temperature has strong dependence on the electron concentration and the spin polarization of the electrons.

  20. Dynamical Cooper pairing in nonequilibrium electron-phonon systems

    NASA Astrophysics Data System (ADS)

    Knap, Michael; Babadi, Mehrtash; Refael, Gil; Martin, Ivar; Demler, Eugene

    2016-12-01

    We analyze Cooper pairing instabilities in strongly driven electron-phonon systems. The light-induced nonequilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We demonstrate that the competition between these effects leads to an enhanced superconducting transition temperature in a broad range of parameters. Our results may explain the observed transient enhancement of superconductivity in several classes of materials upon irradiation with high intensity pulses of terahertz light, and may pave new ways for engineering high-temperature light-induced superconducting states.

  1. Dynamical Cooper pairing in nonequilibrium electron-phonon systems

    SciTech Connect

    Knap, Michael; Babadi, Mehrtash; Refael, Gil; Martin, Ivar; Demler, Eugene

    2016-12-08

    In this paper, we analyze Cooper pairing instabilities in strongly driven electron-phonon systems. The light-induced nonequilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We demonstrate that the competition between these effects leads to an enhanced superconducting transition temperature in a broad range of parameters. Finally, our results may explain the observed transient enhancement of superconductivity in several classes of materials upon irradiation with high intensity pulses of terahertz light, and may pave new ways for engineering high-temperature light-induced superconducting states.

  2. Slow-light enhanced correlated photon pair generation in a silicon photonic crystal waveguide.

    PubMed

    Xiong, C; Monat, Christelle; Clark, Alex S; Grillet, Christian; Marshall, Graham D; Steel, M J; Li, Juntao; O'Faolain, Liam; Krauss, Thomas F; Rarity, John G; Eggleton, Benjamin J

    2011-09-01

    We report the generation of correlated photon pairs in the telecom C-band at room temperature from a dispersion-engineered silicon photonic crystal waveguide. The spontaneous four-wave mixing process producing the photon pairs is enhanced by slow-light propagation enabling an active device length of less than 100 μm. With a coincidence to accidental ratio of 12.8 at a pair generation rate of 0.006 per pulse, this ultracompact photon pair source paves the way toward scalable quantum information processing realized on-chip.

  3. Pressure-enhanced superconductivity in Eu3Bi2S4F4

    DOE PAGES

    Luo, Yongkang; Zhai, Hui -Fei; Zhang, Pan; ...

    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. Enhanced superconductivity at the interface of W/Sr 2RuO4 point contacts

    NASA Astrophysics Data System (ADS)

    Wang, He; Lou, Weijian; Luo, Jiawei; Wei, Jian; Liu, Y.; Ortmann, J. E.; Mao, Z. Q.

    2015-05-01

    Differential resistance measurements are conducted for point contacts (PCs) between the Sr2RuO4 (SRO) single crystal and the tungsten tip approaching along the c axis direction of the crystal. Since the contact is made at liquid helium temperature and the tungsten tip is hard enough to penetrate through the surface layer, consistent superconducting features are observed. First, with the tip pushed towards the crystal, the zero-bias conductance peak (ZBCP) due to Andreev reflection at the normal-superconducting interface increases from 3% to more than 20%, much larger than previously reported, and extends to temperatures higher than the bulk transition temperature. Reproducible ZBCP within 0.2 mV may also help determine the gap value of SRO, on which no consensus has been reached. Second, the logarithmic background can be fitted with the Altshuler-Aronov theory of electron-electron interaction for tunneling into quasi-two-dimensional electron systems. Feasibility of such fitting confirms that spectroscopic information such as density of states is probed, and electronic temperature retrieved from such fitting can be important to analyze the PC spectra. Third, at bias much higher than 0.2 mV there are conductance dips due to the critical current effect. These dips persist up to 6.2 K, possibly due to enhanced superconductivity under uniaxial pressure.

  5. 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

  6. Superconductive tunnel junction device with enhanced characteristics and method of manufacture

    SciTech Connect

    Kroger, H.; Jillie, D. W.

    1985-08-20

    A superconductive tunnel junction device comprises first and second superconductive electrodes with a barrier disposed therebetween where the first superconductive electrode and the barrier are formed without interruption in the same vacuum system pump down and with the first superconductive electrode subjected to sputter etching in an argon plasma before the deposition of the barrier for improving the characteristics of the device.

  7. 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

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

    PubMed

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

    2016-01-12

    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.

  9. 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. Copyright © 2015, American Association for the Advancement of Science.

  10. 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

  11. 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.

  12. Off-site repulsion-induced triplet superconductivity: a possibility for chiral p(x+y)-wave pairing in Sr2RuO4.

    PubMed

    Arita, Ryotaro; Onari, Seiichiro; Kuroki, Kazuhiko; Aoki, Hideo

    2004-06-18

    In order to probe the effect of charge fluctuations on triplet pairing, we study the pairing symmetry in the one-band Hubbard model having the off-site Coulomb repulsion (V) on top of the on-site repulsion as a model for the gamma band of Sr2RuO4, a strong candidate for a triplet pairing superconductor. The result, obtained with the dynamical cluster approximation combined with the quantum Monte Carlo method, and confirmed from the fluctuation exchange approximation, shows that while d(x(2)-y(2)) pairing dominates over p in the absence of V, introduction of V makes p(x+y) and d(xy) dominant. The gap function for the chiral p(x+y)+ip(x-y) has nodes that are consistent with the recent measurement of specific heat in rotated magnetic fields in the ruthenate. This suggests that the off-site repulsion may play an essential role in triplet superconductivity in this material.

  13. Stripes and superconductivity in cuprates

    NASA Astrophysics Data System (ADS)

    Tranquada, John M.

    2012-06-01

    Holes doped into the CuO2 planes of cuprate parent compounds frustrate the antiferromagnetic order. The development of spin and charge stripes provides a compromise between the competing magnetic and kinetic energies. Static stripe order has been observed only in certain particular compounds, but there are signatures which suggest that dynamic stripe correlations are common in the cuprates. Though stripe order is bad for superconducting phase coherence, stripes are compatible with strong pairing. Ironically, magnetic-field-induced stripe order appears to enhance the stability of superconducting order within the planes.

  14. Adaptation of a superconducting-solenoid-transporter Si(Li)-Si(Li) spectrometer for in-beam studies of internal-pair transitions

    NASA Astrophysics Data System (ADS)

    Passoja, A.; Tikkanen, P.; Krasznahorkay, A.; Gácsi, Z.; Kibédi, T.; Fényes, T.

    1984-06-01

    The Debrecen superconducting magnetic spectrometer (SMS) has been adapted for in-beam internal-pair studies. Test measurements have been carried out using a 207Bi radioactive source and the 19F(p, αγ) 16O, 23Na(p, αγ) 20Ne, 27Al(p,p'γ) 27Al and 42Ca(p, p'γ) 42Ca reactions (at bombarding energies Ep = 3.5-4.0 MeV). Convenient spectrometer parameters, backscattering of electrons and positrons from one detector to the other, and methods for background reduction have been investigated. Experimental values of (14±3)%, (12±3)%, and (14±2)% for the one-detector pair-line efficiencies were determined for the 20Ne(E2; 1634 keV), 42Ca(E0; 1837 keV) and 27Al(M1 + E2; 2211 keV) transitions, respectively. The observed pair-line detection efficiencies for two detectors operated in sum-coincidence mode were (35 ± 7)% and (34 +-6)% for the 42Ca(E0; 1837 keV) and 27Al(M1 + E2; 2211 keV) transitions, respectively. The energy resolution of the spectrometer was ≈ 0.5% in singles and ≈ o.6% in sum-coincidence measurements for the 2211 keV M1 + E2 pair line of 27Al. Effective pair-formation coefficients for one-detector and opposite two-detector geometries have been calculated theoretically for various multipoles. Different methods for the determination of the multipolarity of internal-pair transitions have been investigated. Optimum multipole discrimination effects have been discussed. The experiments show that a good multipole discrimination power can be achieved with the SMS.

  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. Multimodal plasmon coupling in low symmetry gold nanoparticle pairs detected in surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Dreaden, Erik C.; Near, Rachel D.; Abdallah, Tamer; Talaat, M. Hassan; El-Sayed, Mostafa A.

    2011-05-01

    We report on surface-enhanced Raman scattering of silicon phonon vibrations from arrays of gold nanoprism pairs fabricated by electron beam lithography. We found that resonant excitation of the quadrupolar surface plasmon mode of the nanoprisms increases Raman scattering intensity from the substrate as the distance between the nanoparticle pairs decreases. Finite element modeling and plasmon coupling theory indicate that symmetry is reduced as the nanoparticles approach, resulting in increased dipole-quadrupole coupling. Plasmonic enhancement of the incident and Raman-scattered photons results from the dipolar component of the mixed plasmonic field. This effect is expected to be largest in assemblies/aggregates of nanoparticles.

  17. Design of NbN Superconducting Nanowire Single-Photon Detectors with Enhanced Infrared Detection Efficiency

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Renema, J. J.; Engel, A.; de Dood, M. J. A.

    2017-09-01

    We optimize the design of NbN nanowire superconducting single-photon detectors using the recently discovered position-dependent detection efficiency in these devices. This optimized design of meandering wire NbN detectors maximizes absorption at positions where photon detection is most efficient by altering the field distribution across the wire. In order to calculate the response of the detectors with different geometries, we use a monotonic local detection efficiency from a nanowire and optical absorption distribution via finite-difference-time-domain simulations. The calculations predict a trade-off between average absorption and absorption at the edge, leading to a predicted optimal wire width close to 100 nm for a 1550-nm wavelength, which drops to a 50-nm wire width for a 600-nm wavelength. The absorption at the edges can be enhanced by depositing a silicon nanowire on top of the superconducting nanowire, which improves both the total absorption efficiency and the internal detection efficiency of meandering wire structures. The proposed structure can be integrated in a relatively simple cavity structure to reach absorption efficiencies of 97% for perpendicular and 85% for parallel polarization.

  18. Enhanced Pair Production in Multicenter Systems by SuperIntense Lasers

    NASA Astrophysics Data System (ADS)

    Bandrauk, Andre

    2014-03-01

    Electron-positron(e-e +) pair production is considered for many-center systems with multiple bare nuclei immersed in intense static electric fields corresponding to the extrema of electric fields planned by future super intense laser pulse sources with intensities I > 1024 W/cm2. It is shown analytically using an exactly solvable 1-D delta potential model in a multicenter Dirac equation that there are two distinct regimes where pair production rates are enhanced.At small internuclear distances, the effective nuclear charge approaches the critical charge where the ground state dives into the negative continuum of the Dirac equation. At large atomic distances a new mechanism is predicted, similar to Charge Resonance Enhanced Ionization of molecules by intense, I ~ 1024 W/cm2, laser pulses. Multicenter resonances from the negative energy states are shown to cross into the positive energy states due to large field induced Stark shifts thus resulting in a resonantly enhanced pair production mechanism. A numerical method is developed to calculate the pair production rates from the multicenter Dirac equation. The latter is evaluated for systems (clusters) up to five nuclei of large charge. It is shown that the pair production rate for multicenter systems in superintense electric fields generally exceeds by orders of magnitudes the Schwinger tunneling rate which requires intensities of ~ 1029 W''/cm2. Funded by Canada Research Chair Program.

  19. Evolution of multigap superconductivity in the atomically thin limit: Strain-enhanced three-gap superconductivity in monolayer MgB2

    NASA Astrophysics Data System (ADS)

    Bekaert, J.; Aperis, A.; Partoens, B.; Oppeneer, P. M.; Milošević, M. V.

    2017-09-01

    Starting from first principles, we show the formation and evolution of superconducting gaps in MgB2 at its ultrathin limit. Atomically thin MgB2 is distinctly different from bulk MgB2 in that surface states become comparable in electronic density to the bulklike σ and π bands. Combining the ab initio electron-phonon coupling with the anisotropic Eliashberg equations, we show that monolayer MgB2 develops three distinct superconducting gaps, on completely separate parts of the Fermi surface due to the emergent surface contribution. These gaps hybridize nontrivially with every extra monolayer added to the film owing to the opening of additional coupling channels. Furthermore, we reveal that the three-gap superconductivity in monolayer MgB2 is robust over the entire temperature range that stretches up to a considerably high critical temperature of 20 K. The latter can be boosted to >50 K under biaxial tensile strain of ˜4 % , which is an enhancement that is stronger than in any other graphene-related superconductor known to date.

  20. Using superconducting undulator for enhanced imaging capabilities of MaRIE

    SciTech Connect

    Yampolsky, Nikolai

    2016-09-22

    MaRIE x-ray free electron laser (FEL) is envisioned to deliver a burst of closely spaced in time pulses for enabling the capability of studying the dynamic processes in a sample. MaRIE capability can be largely enhanced using the superconducting undulator, which has the capability of doubling its period. This technology will allow reaching the photon energy as low as ~200-500 eV. As a result, the MaRIE facility will have a broader photon energy range enabling a larger variety of experiments. The soft x-ray capability is more likely to achieve the 3D imaging of dynamic processes in noncrystal materials than the hard x-ray capability alone.

  1. Possible unconventional superconductivity in substituted BaFe2As2 revealed by magnetic pair-breaking studies.

    PubMed

    Rosa, P F S; Adriano, C; Garitezi, T M; Piva, M M; Mydeen, K; Grant, T; Fisk, Z; Nicklas, M; Urbano, R R; Fernandes, R M; Pagliuso, P G

    2014-09-01

    The possible existence of a sign-changing gap symmetry in BaFe2As2-derived superconductors (SC) has been an exciting topic of research in the last few years. To further investigate this subject we combine Electron Spin Resonance (ESR) and pressure-dependent transport measurements to investigate magnetic pair-breaking effects on BaFe1.9M0.1As2 (M = Mn, Co, Cu, and Ni) single crystals. An ESR signal, indicative of the presence of localized magnetic moments, is observed only for M = Cu and Mn compounds, which display very low SC transition temperature (Tc) and no SC, respectively. From the ESR analysis assuming the absence of bottleneck effects, the microscopic parameters are extracted to show that this reduction of Tc cannot be accounted by the Abrikosov-Gorkov pair-breaking expression for a sign-preserving gap function. Our results reveal an unconventional spin- and pressure-dependent pair-breaking effect and impose strong constraints on the pairing symmetry of these materials.

  2. Possible unconventional superconductivity in substituted BaFe2As2 revealed by magnetic pair-breaking studies

    PubMed Central

    Rosa, P. F. S.; Adriano, C.; Garitezi, T. M.; Piva, M. M.; Mydeen, K.; Grant, T.; Fisk, Z.; Nicklas, M.; Urbano, R. R.; Fernandes, R. M.; Pagliuso, P. G.

    2014-01-01

    The possible existence of a sign-changing gap symmetry in BaFe2As2-derived superconductors (SC) has been an exciting topic of research in the last few years. To further investigate this subject we combine Electron Spin Resonance (ESR) and pressure-dependent transport measurements to investigate magnetic pair-breaking effects on BaFe1.9M0.1As2 (M = Mn, Co, Cu, and Ni) single crystals. An ESR signal, indicative of the presence of localized magnetic moments, is observed only for M = Cu and Mn compounds, which display very low SC transition temperature (Tc) and no SC, respectively. From the ESR analysis assuming the absence of bottleneck effects, the microscopic parameters are extracted to show that this reduction of Tc cannot be accounted by the Abrikosov-Gorkov pair-breaking expression for a sign-preserving gap function. Our results reveal an unconventional spin- and pressure-dependent pair-breaking effect and impose strong constraints on the pairing symmetry of these materials. PMID:25176407

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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.

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

    PubMed

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

    2016-02-19

    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.

  5. Enhancement of superconductivity in NbN nanowires by negative electron-beam lithography with positive resist

    NASA Astrophysics Data System (ADS)

    Charaev, I.; Silbernagel, T.; Bachowsky, B.; Kuzmin, A.; Doerner, S.; Ilin, K.; Semenov, A.; Roditchev, D.; Vodolazov, D. Yu.; Siegel, M.

    2017-08-01

    We performed comparative experimental investigation of superconducting NbN nanowires which were prepared by means of positive- and negative electron-beam lithography with the same positive tone Poly-methyl-methacrylate (PMMA) resist. We show that nanowires with a thickness 4.9 nm and widths less than 100 nm demonstrate at 4.2 K higher critical temperature and higher density of critical and retrapping currents when they are prepared by negative lithography. Also the ratio of the experimental critical current to the depairing critical current is larger for nanowires prepared by negative lithography. We associate the observed enhancement of superconducting properties with the difference in the degree of damage that nanowire edges sustain in the lithographic process. A whole range of advantages which is offered by the negative lithography with positive PMMA resist ensures high potential of this technology for improving the performance metrics of superconducting nanowire singe-photon detectors.

  6. 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).

  7. A combination of JND curve property and intensity-pair distribution for image enhancement

    NASA Astrophysics Data System (ADS)

    Zou, Bin; Lu, Yang; Qian, Jun; He, Junfeng; Li, Liangfu; Zhou, Guoliang; Yang, Yizhou; Yan, Haozheng

    2017-02-01

    In recent years, the distribution characteristic of pixel intensity-pairs is proposed, which effectively absorbing the advantages of global and local image enhancement algorithms, avoiding over enhancement, noise amplification and other defects. However, the performance of the algorithm is heavily dependent on the selection of local artificial thresholds. In this paper, by the Just Noticeable Difference(JND) curve from human visual system, dynamic thresholds with visual sense are generated. Then image pixels are divided into different channels for statistical processing, in order to construct mapping functions. Finally, the enhanced image is a weighted fusion of different channels. The experiment results show that the proposed algorithm has better effect and adaptability.

  8. Slow light enhanced correlated photon pair generation in photonic-crystal coupled-resonator optical waveguides.

    PubMed

    Matsuda, Nobuyuki; Takesue, Hiroki; Shimizu, Kaoru; Tokura, Yasuhiro; Kuramochi, Eiichi; Notomi, Masaya

    2013-04-08

    We demonstrate the generation of quantum-correlated photon pairs from a Si photonic-crystal coupled-resonator optical waveguide. A slow-light supermode realized by the collective resonance of high-Q and small-mode-volume photonic-crystal cavities successfully enhanced the efficiency of the spontaneous four-wave mixing process. The generation rate of photon pairs was improved by two orders of magnitude compared with that of a photonic-crystal line defect waveguide without a slow-light effect.

  9. 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.

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

    DOE PAGES

    Patel, Niravkumar D.; Nocera, Alberto; Alvarez, Gonzalo; ...

    2016-08-10

    The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3 [H. Takahashi et al., Nat. Mater. 14, 1008 (2015)] 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 withmore » 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 oneWannier orbital receiving the hole carriers while the other remains half-filled. Lastly, 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.« less

  11. Enhancement of superconductivity by an external magnetic field in magnetic alloys

    NASA Astrophysics Data System (ADS)

    Borycki, Dawid

    2014-05-01

    An infinite-volume limit solution of the thermodynamics of a BCS superconductor containing spin 1/2 and 7/2 magnetic impurities, obtained recently in [D. Borycki, J. Maćkowiak, Supercond. Sci. Technol. 24, 035007 (2011)] is exploited to derive the expressions for critical magnetic field ( T). The credibility of the resulting thermodynamically limited theoretical equations, which depend on the magnetic coupling constant g and impurity concentration c, is verified on the experimental data for the following superconducting alloys: LaCe, ThGd and SmRh4B4. Good quantitative agreement with experimental data is found for sufficiently small values of c. The discrepancies between theoretical and experimental values of ( T) for larger values of c in case of LaCe and ThGd are reduced by introducing the concept of the effective temperature , which accounts for the Coulomb interactions between the electron gas and impurity ions. At low temperatures, the critical magnetic field is found to increase with decreasing temperature T. This enhancement of the critical magnetic field provides evidence of the Jaccarino-Peter effect, which was experimentally observed in the Kondo systems like LaCe, (La1 - x Ce x )Al2 and also in the pseudoternary compounds, including Sn1 - x Eu x Mo6S8, Pb1 - x Eu x Mo6S8 and La1.2 - x Eu x Mo6S8. The effect of an external magnetic field on a BCS superconductor perturbed by magnetic impurities was also studied. On these grounds, by analyzing the dependence of superconducting transition temperature T c on of (La1 - x Ce x )Al2, we have shown, that for certain parameter values, external magnetic field compensates the destructive effect of magnetic impurities.

  12. 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

  13. Enhanced charge stripe order in superconducting La2-xBaxCuO4 in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Huecker, M.; Zimmermann, M. V.; Xu, Z. J.; Wen, J. S.; Gu, G. D.; Tranquada, J. M.

    2013-03-01

    There is mounting evidence for a proximity of the superconducting ground state in the cuprates to competing states with static spin and/or charge density modulations. One such competing state is the spin and charge stripe phase in La2-xBaxCuO4. By means of high energy (100 keV) x-ray diffraction we have studied the effect of a high magnetic field (H||c) on the charge stripe order in a broad range of doping (0.095 <= x <= 0.155). We find that the field can significantly enhance the charge stripe order, but only at temperatures and dopings where it coexists with bulk superconductivity at zero field. The field also increases stripe correlations between the planes, which can result in an enhanced frustration of the interlayer Josephson coupling. Close to the famous x =1/8 compound, where zero field stripe order is pronounced and bulk superconductivity is suppressed, charge stripe order is independent of the field. The results imply that static stripe order and three-dimensionally coherent superconductivity are competing ground states. The work at Brookhaven was supported by the Office of Basic Energy Sciences, Division of Materials Science and Engineering, U.S. Department of Energy (DOE), under Contract No. DE-AC02-98CH10886.

  14. Pressure-induced superconductivity and effective mass enhancement near antiferromagnetic quantum critical point in CePt2In7

    NASA Astrophysics Data System (ADS)

    Bauer, Eric D.; Lee, H. O.; Sidorov, V. A.; Kurita, N.; Gofryk, K.; Ronning, F.; Park, Tuson; Movshovich, R.; Thompson, J. D.

    2010-03-01

    The discovery of the CeMIn5 (M=Co, Rh, Ir) family of heavy fermion superconductors has been a watershed for the field of heavy fermion physics. These materials have not only provided an effective means to explore the rich interplay of magnetism and superconductivity (e.g., CeRhIn5), the development of the heavy fermion state (e.g., Ce1-xLaxCoIn5), and quantum criticality (e.g., CeRhIn5), but have also provided compelling evidence that structural tuning plays an essential role in enhancing their superconducting properties. I will present our discovery of superconductivity in a new, more two-dimensional member of this CemMnIn2m+3n family, CePt2In7, which displays the coexistence of antiferromagnetism and superconductivity and an enhancement of the effective mass under pressure near an antiferromagnetic quantum critical point that is remarkably similar to CeRhIn5.

  15. 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.

  16. Adaptive total variation minimization-based image enhancement from flash and no-flash pairs.

    PubMed

    Yoon, Sang Min; Lee, Yeon Ju; Yoon, Gang-Joon; Yoon, Jungho

    2014-01-01

    We present a novel approach for enhancing the quality of an image captured from a pair of flash and no-flash images. The main idea for image enhancement is to generate a new image by combining the ambient light of the no-flash image and the details of the flash image. In this approach, we propose a method based on Adaptive Total Variation Minimization (ATVM) so that it has an efficient image denoising effect by preserving strong gradients of the flash image. Some numerical results are presented to demonstrate the effectiveness of the proposed scheme.

  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. Cryogenfree superconducting magnets

    NASA Astrophysics Data System (ADS)

    Watanabe, Kazuo; Awaji, Satoshi; Motokawa, Mitsuhiro

    2003-05-01

    Various kinds of cryogenfree superconducting magnets such as a wide bore 8 T, a split-pair 5 T, and a high magnetic field 15 T magnet have been developed successfully at Tohoku University. A cryogenfree 23 T hybrid magnet composed of a cryocooled outer superconducting magnet and a water-cooled inner resistive magnet is being tested for the first time. Further, new construction projects of a cryogenfree 30 T hybrid magnet and a cryogenfree 19 T superconducting magnet have just started.

  19. 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

  20. Enhanced superconductivity in the high pressure phase of SnAs studied from first principles

    NASA Astrophysics Data System (ADS)

    Sreenivasa Reddy, P. V.; Kanchana, V.; Millichamp, T. E.; Vaitheeswaran, G.; Dugdale, S. B.

    2017-01-01

    First principles calculations are performed using density functional theory and density functional perturbation theory for SnAs. Total energy calculations show the first order phase transition from an NaCl structure to a CsCl one at around 37 GPa, which is also confirmed from enthalpy calculations and agrees well with experimental work. Calculations of the phonon structure and hence the electron-phonon coupling, λep, and superconducting transition temperature, Tc, across the phase diagram are performed. These calculations give an ambient pressure Tc, in the NaCl structure, of 3.08 K, in good agreement with experiment whilst at the transition pressure, in the CsCl structure, a drastically increased value of Tc = 12.2 K is found. Calculations also show a dramatic increase in the electronic density of states at this pressure. The lowest energy acoustic phonon branch in each structure also demonstrates some softening effects. Electronic structure calculations of the Fermi surface in both phases are presented for the first time as well as further calculations of the generalised susceptibility with the inclusion of matrix elements. These calculations indicate that the softening is not derived from Fermi surface nesting and it is concluded to be due to a wavevector-dependent enhancement of the electron-phonon coupling.

  1. YSZ buffer layers and YBCO superconducting tapes with enhanced biaxial alignment and properties

    NASA Astrophysics Data System (ADS)

    Savvides, N.; Gnanarajan, S.

    2003-05-01

    Commercial applications of YBa 2Cu 3O 7 (YBCO) superconducting cables require viable and scalable manufacturing processes. We have investigated the evolution of the biaxial alignment of yttria-stabilized zirconia (YSZ) buffer layers with increasing film thickness (50-900 nm) and report on a method of fabricating highly aligned YBCO tapes using a thin epitaxial YSZ buffer layer as template. The method employs magnetron and ion beam assisted deposition (IBAD) techniques followed by epitaxial growth to produce the buffer architectures IBAD-YSZ and epi-YSZ/IBAD-YSZ onto optically polished hastelloy metal substrates. Subsequent in situ deposition of YBCO films is used to determine the biaxial alignment at the surface of the buffer architecture, and to show that 100-200 nm thick epi-YSZ layers suffice to yield YBCO tapes that have enhanced biaxial alignment (Δ φ=9-10°) and high critical current densities: J c(77 K)=(1-2)×10 6 A cm -2 and J c(5 K,1 T)=8×10 6 A cm -2. Atomic force microscopy of the surface microstructure of the YSZ buffer layers and YBCO films reveals some grain coarsening in the epi-YSZ layers compared to the IBAD-YSZ layers while the YBCO tapes show significant outgrowths (∼200 nm) and large grains (800-1200 nm) that are similar to high- Jc YBCO films grown on single crystal MgO(1 0 0) substrates.

  2. Enhancement of crossed Andreev reflection in a superconducting ladder connected to normal metal leads

    NASA Astrophysics Data System (ADS)

    Soori, Abhiram; Mukerjee, Subroto

    2017-03-01

    Crossed Andreev reflection (cAR) is a scattering process that happens in a quantum transport setup consisting of two normal metals (NM) attached to a superconductor (SC), where an electron incident from one NM results in a hole emerging in the other. Typically, electron tunneling (ET) through the superconductor from one NM to the other competes with cAR and masks its signature in the conductance spectrum. We propose a scheme to enhance cAR, in which the SC part of the NM-SC-NM is side coupled to another SC having a different superconducting phase to form a Josephson junction in the transverse direction. At strong enough coupling and for a large enough phase difference, one can smoothly traverse between the highly ET-dominant to the highly cAR-dominant transport regimes by tuning chemical potential, due to the appearance of subgap Andreev states that are extended in the longitudinal direction. We discuss connections to realistic systems.

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

    SciTech Connect

    Wang, Tong

    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

  4. Atomic-resonance-enhanced nonlinear optical frequency conversion with entangled photon pairs

    SciTech Connect

    Du Shengwang

    2011-03-15

    We theoretically study nonlinear optical frequency conversion with time-frequency entangled paired photons whose sum frequency is on two-photon resonance of an atomic ensemble. Assisted by a strong coupling laser, two paired photons with wide spectrum are converted into a single monochromatic photon. The on-resonance nonlinear process is made possible due to the electromagnetically induced transparency that not only eliminates the on-resonance absorption but also enhances the nonlinear interaction between the single photons and atoms. Compared to this quantum-nonlinear conversion, the classical corresponding single-photon counts from accidental two-photon coincidence has a wide spectrum and experiences large absorption. As a result, the system can be used as an efficient two-photon quantum correlator in which the classical accidental coincidences can be suppressed. We perform numerical simulations basing on a Rb atomic vapor cell with realistic operating parameters.

  5. Huperzine-A capsules enhance memory and learning performance in 34 pairs of matched adolescent students.

    PubMed

    Sun, Q Q; Xu, S S; Pan, J L; Guo, H M; Cao, W Q

    1999-07-01

    To study the efficacy of huperzine-A capsules (Hup) on memory and learning performance of adolescent students. Using double-blind and matched pair method, 34 pairs of junior middle school students complaining of memory inadequacy were divided into two groups by normal psychological health inventory (PHI), similar memory quotient (MQ), same sex and class. The Hup group was administrated orally 2 capsules of Hup (each contains Hup 50 micrograms) b.i.d., and the placebo group was given 2 capsules of placebo (starch and lactose inside) b.i.d. for 4 wk. At the end of trial, the Hup group's MQ (115 +/- 6) was more than that of the placebo group (104 +/- 9, P < 0.01), and the scores of Chinese language lesson in the Hup group were elevated markedly too. The Hup capsules enhance the memory and learning performance of adolescent students.

  6. Suppression of superconductivity in the Hubbard model by buckling and breathing phonons.

    PubMed

    Macridin, Alexandru; Moritz, Brian; Jarrell, M; Maier, Thomas

    2012-11-28

    We study the effect of buckling and breathing phonons, relevant for cuprate superconductors, on the d-wave superconductivity in the two-dimensional Hubbard model by employing dynamical cluster Monte Carlo calculations. The interplay of electronic correlations and the electron-phonon interaction produces two competing effects: an enhancement of the effective d-wave pairing interaction, which favors d-wave superconductivity, and a strong renormalization of the single-particle propagator, which suppresses superconductivity. In the region of the parameter space relevant for cuprate superconductors, we find that the buckling and the breathing phonons suppress the superconductivity.

  7. Unconventional superconductivity and novel quantum order.

    PubMed

    Pugh, Emma

    2003-12-15

    Superconductors have many unusual properties not observed in normal metals. The superconducting state is attributed to the pairing of electrons. Conventional forms of superconductivity are produced by distortions in the underlying crystal structure of the material. Recently, it has become evident that not all forms of superconductivity can be explained in this way. The way pairing occurs has to be redressed in these materials. Of particular interest is the interplay between magnetism and superconductivity and the consequences this may have on pair formation.

  8. Enhancement of phase separation and superconductivity in Mn-doped K0.8Fe2-yMnySe2 crystals.

    PubMed

    Li, M T; Chen, L; Li, Z W; Ryu, G H; Lin, C T; Zhang, J C

    2013-08-21

    Single crystals of K0.8Fe2-yMnySe2 with slight Mn doping have been grown by a self-flux method. X-ray diffraction measurements show enhanced phase separation with increasing Mn doping in the compounds. The superconducting transition temperature increases to Tc,onset ∼ 46.1 K for the sample with y ∼ 0.03, as observed by electrical transport measurements. Our results demonstrate that the doping of Mn does not suppress the superconductivity, and on the contrary increases the superconducting shield fraction and transition temperature, an effect which may originate from the Mn dopant's high preference to fill into iron vacancies in the Mn-doped samples. It suggests that the Mn dopant can induce a local lattice strain or distortion that profitably modifies the microstructure of the superconducting/metallic phase, leading to superconductivity of the compound.

  9. Enhanced ultrasonic attenuation of Tl-Ca-Ba-Cu-O at the superconducting transition

    NASA Technical Reports Server (NTRS)

    Sun, K. J.; Winfree, W. P.; Xu, M.-F.; Levy, M.; Sarma, Bimal K.

    1990-01-01

    Temperature-dependent ultrasonic attenuation measurements have been performed on polycrystalline samples of Tl-Ca-Ba-Cu-O at various frequencies. An attenuation anomaly was observed close to the superconducting transition temperature T(c) (103 K) whose temperature position was frequency-independent. The attenuation decreased exponentially with temperature in the superconducting state for both transverse and longitudinal waves. It was also found that the temperature-dependent sound velocity showed a slope change around T(c).

  10. Role of SrTiO3 phonon penetrating into thin FeSe films in the enhancement of superconductivity

    NASA Astrophysics Data System (ADS)

    Zhang, Shuyuan; Guan, Jiaqi; Jia, Xun; Liu, Bing; Wang, Weihua; Li, Fangsen; Wang, Lili; Ma, Xucun; Xue, Qikun; Zhang, Jiandi; Plummer, E. W.; Zhu, Xuetao; Guo, Jiandong

    2016-08-01

    The significant role of interfacial coupling in the enhancement of superconductivity in FeSe films on SrTiO3 has been widely recognized, but the explicit origin of this coupling is yet to be identified. Here, by surface phonon measurements using high-resolution electron energy loss spectroscopy, we found the electric field generated by Fuchs-Kliewer (F-K) phonon modes of SrTiO3 can penetrate into FeSe films and strongly interact with the electrons therein. The mode-specific electron-phonon coupling constant for the ˜92 meV F-K phonon is ˜0.25 in single-layer FeSe on SrTiO3. With increasing FeSe thickness, the penetrating field intensity decays exponentially, which matches well the observed exponential decay of the superconducting gap. It is unambiguously shown that the SrTiO3 F-K phonon penetrating into FeSe is essential for interfacial superconductivity enhancement.

  11. Enhanced charge stripe order of superconducting La2-xBaxCuO4 in a magnetic field

    NASA Astrophysics Data System (ADS)

    Hücker, M.; v. Zimmermann, M.; Xu, Z. J.; Wen, J. S.; Gu, G. D.; Tranquada, J. M.

    2013-01-01

    The effect of a magnetic field on the charge stripe order in La2-xBaxCuO4 has been studied by means of high-energy (100 keV) x-ray diffraction for charge carrier concentrations ranging from strongly underdoped to optimally doped. We find that charge stripe order can be significantly enhanced by a magnetic field applied along the c axis, but only at temperatures and dopings where it coexists with bulk superconductivity at zero field. The field also increases stripe correlations between the planes, which can result in an enhanced frustration of the interlayer Josephson coupling. Close to the famous x=(1)/(8) compound, where zero field stripe order is pronounced and bulk superconductivity is suppressed, charge stripe order is independent of a magnetic field. The results for La2-xBaxCuO4 resemble recent observations in YBa2Cu3O6+δ and, independent of potential differences in the microscopic origin of charge order in these two compounds, imply a very similar competition with three-dimensionally coherent superconductivity.

  12. Galaxy pairs in the Sloan Digital Sky Survey - VI. The orbital extent of enhanced star formation in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Patton, David R.; Torrey, Paul; Ellison, Sara L.; Mendel, J. Trevor; Scudder, Jillian M.

    2013-06-01

    We use pair and environmental classifications of ˜211 000 star-forming galaxies from the Sloan Digital Sky Survey, along with a suite of merger simulations, to investigate the enhancement of star formation as a function of separation in galaxy pairs. Using a new technique for distinguishing between the influence of nearby neighbours and larger scale environment, we find a clear enhancement in star formation out to projected separations of ˜150 kpc, beyond which there is no net enhancement. We find the strongest enhancements at the smallest separations (especially <20 kpc), consistent with earlier work. Similar trends are seen in the simulations, which indicate that the strongest enhancements are produced in highly disturbed systems approaching final coalescence, whereas the more modest enhancements seen at wider separations are the result of starburst activity triggered at first pericentre passage, which persists as the galaxies move to larger separations. The absence of any net enhancement beyond 150 kpc provides reassurance that the detected enhancements are due to galaxy-galaxy interactions, rather than larger scale environmental effects or potential pair selection biases. A rough census indicates that 66 per cent of the enhanced star formation in our pair sample occurs at separations >30 kpc. We conclude that significant interaction-induced star formation is not restricted to merger remnants or galaxies with close companions; instead, a larger population of wider separation pairs exhibit enhanced star formation due to recent close encounters.

  13. Enhancement of high-spin collectivity in N = Z nuclei by the isoscalar neutron-proton pairing

    NASA Astrophysics Data System (ADS)

    Kaneko, K.; Sun, Y.; de Angelis, G.

    2017-01-01

    Pairing from different fermions, neutrons and protons, is unique in nuclear physics. The fingerprint for the isoscalar T = 0 neutron-proton (np) pairing has however remained a question. We study this exotic pairing mode in excited states of rotating N ≈ Z nuclei by applying the state-of-the-art shell-model calculations for 88Ru and the neighboring 90,92Ru isotopes. We show that the T = 0 np pairing is responsible for the distinct rotational behavior between the N = Z and N > Z nuclei. Our calculation suggests a gradual crossover from states with mixed T = 1 and T = 0 pairing near the ground state to those dominated by the T = 0 np pairing at high spins. It is found that the T = 0 np pairing plays an important role in enhancing the high-spin collectivity, thereby reducing shape variations along the N = Z line.

  14. 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’.

  15. Enhanced photoluminescence from condensed electron-hole pairs in trenched Si

    NASA Astrophysics Data System (ADS)

    Cheng, Yung-Chen; Sun, Chi-Yuan; Sun, Edward; Chen, Miin-Jang

    2010-12-01

    In this paper, we report the characteristics of low-temperature photoluminescence (PL) from condensed electron-hole (e-h) pairs in p-type silicon substrates with and without high-aspect-ratio trench structures. The average hole diameters of trenches were 140 and 170 nm, and the depth of trenches were about 5 μm. An Al2O3 surface passivation layer with thickness of 10 nm was grown by atomic layer deposition on surfaces of all samples to reduce nonradiative recombination and provide nucleation centers of condensed e-h pairs at Si/Al2O3 interface. Significant enhancement of PL intensity from e-h liquid/droplet (EHL/EHD) was observed in the trenched silicon at temperature below 30 K. Dominant PL from EHL/EHD at 14 K in the trenched silicon with larger hole diameters may be attributed to stronger spatial confinement of condensed e-h pairs in a smaller volume.

  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. 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.

  18. 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.

  19. Enhanced electron-positron pair production by ultra intense laser irradiating a compound target

    NASA Astrophysics Data System (ADS)

    Liu, Jian-Xun; Ma, Yan-Yun; Yu, Tong-Pu; Zhao, Jun; Yang, Xiao-Hu; Gan, Long-Fei; Zhang, Guo-Bo; Zhao, Yuan; Zhang, Shi-Jie; Liu, Jin-Jin; Zhuo, Hong-Bin; Shao, Fu-Qiu; Kawata, Shigeo

    2016-12-01

    High-energy-density electron-positron pairs play an increasingly important role in many potential applications. Here, we propose a scheme for enhanced positron production by an ultra intense laser irradiating a gas-Al compound target via the multi-photon Breit-Wheeler (BW) process. The laser pulse first ionizes the gas and interacts with a near-critical-density plasma, forming an electron bubble behind the laser pulse. A great deal of electrons are trapped and accelerated in the bubble, while the laser front hole-bores the Al target and deforms its front surface. A part of the laser wave is thus reflected by the inner curved target surface and collides with the accelerated electron bunch. Finally, a large number of γ photons are emitted in the forward direction via the Compton back-scattering process and the BW process is initiated. Dense electron-positron pairs are produced with a maximum density of 6.02× {{10}27} m-3. Simulation results show that the positron generation is greatly enhanced in the compound target, where the positron yield is two orders of magnitude greater than that in only the solid slab case. The influences of the laser intensity, gas density and length on the positron beam quality are also discussed, which demonstrates the feasibility of the scheme in practice.

  20. Nodeless pairing in superconducting copper-oxide monolayer films on Bi2Sr2CaCu2O8+δ

    SciTech Connect

    Zhong, Yong; Wang, Yang; Han, Sha; Lv, Yan-Feng; Wang, Wen-Lin; Zhang, Ding; Ding, Hao; Zhang, Yi-Min; Wang, Lili; He, Ke; Zhong, Ruidan; Schneeloch, John A.; Gu, Gen-Da; Song, Can-Li; Ma, Xu-Cun; Xue, Qi-Kun

    2016-07-12

    We report that the pairing mechanism of high-temperature superconductivity in cuprates remains the biggest unresolved mystery in condensed matter physics. To solve the problem, one of the most effective approaches is to investigate directly the superconducting CuO2 layers. Here, by growing CuO2 monolayer films on Bi2Sr2CaCu2O8+δ substrates, we identify two distinct and spatially separated energy gaps centered at the Fermi energy, a smaller U-like gap and a larger V-like gap on the films, and study their interactions with alien atoms by low-temperature scanning tunneling microscopy. The newly discovered U-like gap exhibits strong phase coherence and is immune to scattering by K, Cs and Ag atoms, suggesting its nature as a nodeless superconducting gap in the CuO2 layers, whereas the V-like gap agrees with the well-known pseudogap state in the underdoped regime. In conclusion, our results support an s-wave superconductivity in Bi2Sr2CaCu2O8+δ, which, we propose, originates from the modulation-doping resultant two-dimensional hole liquid confined in the CuO2 layers.

  1. Nodeless pairing in superconducting copper-oxide monolayer films on Bi2Sr2CaCu2O8+δ

    SciTech Connect

    Zhong, Yong; Wang, Yang; Han, Sha; Lv, Yan-Feng; Wang, Wen-Lin; Zhang, Ding; Ding, Hao; Zhang, Yi-Min; Wang, Lili; He, Ke; Zhong, Ruidan; Schneeloch, John A.; Gu, Gen-Da; Song, Can-Li; Ma, Xu-Cun; Xue, Qi-Kun

    2016-07-12

    We report that the pairing mechanism of high-temperature superconductivity in cuprates remains the biggest unresolved mystery in condensed matter physics. To solve the problem, one of the most effective approaches is to investigate directly the superconducting CuO2 layers. Here, by growing CuO2 monolayer films on Bi2Sr2CaCu2O8+δ substrates, we identify two distinct and spatially separated energy gaps centered at the Fermi energy, a smaller U-like gap and a larger V-like gap on the films, and study their interactions with alien atoms by low-temperature scanning tunneling microscopy. The newly discovered U-like gap exhibits strong phase coherence and is immune to scattering by K, Cs and Ag atoms, suggesting its nature as a nodeless superconducting gap in the CuO2 layers, whereas the V-like gap agrees with the well-known pseudogap state in the underdoped regime. In conclusion, our results support an s-wave superconductivity in Bi2Sr2CaCu2O8+δ, which, we propose, originates from the modulation-doping resultant two-dimensional hole liquid confined in the CuO2 layers.

  2. 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.

  3. 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

    2014-12-04

    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.

  4. 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.

  5. Enhanced magnetic anomaly detection using a nitrogen-cooled superconducting gradiometer

    NASA Astrophysics Data System (ADS)

    Clem, Ted R.; Overway, David J.; Purpura, John W.; Bono, John T.; Carroll, Paul J.; Koch, Roger H.; Rozen, James R.; Keefe, George A.; Willen, Scott; Mohling, Robert A.

    2000-07-01

    During the 1980's the Superconducting Gradiometer/Magnetometer Sensor was demonstrated in the Magnetic and Acoustic Detection of Mines Advanced Technology Demonstration to provide effective mine detection, localization, and classification capabilities, especially against buried mines, and to reduce significantly acoustic false alarms arising from bottom clutter. This sensor utilized Superconducting Quantum Interference Devices manufactured using the low critical temperature (low Tc) superconductor niobium and liquid helium for sensor cooling. This sensor has most recently bee integrated into the Mobile Underwater Debris Survey System and has been demonstrated successfully in a survey to locate unexploded ordnance in coastal waters.

  6. Pairing correlations near a Kondo-destruction quantum critical point

    NASA Astrophysics Data System (ADS)

    Pixley, J. H.; Deng, Lili; Ingersent, Kevin; Si, Qimiao

    2015-05-01

    Motivated by the unconventional superconductivity observed in heavy-fermion metals, we investigate pairing susceptibilities near a continuous quantum phase transition of the Kondo-destruction type. We solve two-impurity Bose-Fermi Anderson models with Ising and Heisenberg forms of the interimpurity exchange interaction using continuous-time quantum Monte Carlo and numerical renormalization-group methods. Each model exhibits a Kondo-destruction quantum critical point separating Kondo-screened and local-moment phases. For antiferromagnetic interimpurity exchange interactions, singlet pairing is found to be enhanced in the vicinity of the transition. Implications of this result for heavy-fermion superconductivity are discussed.

  7. Effect of the three-center terms on the chiral superconducting d-wave pairing of the Hubbard fermions on the triangular lattice

    NASA Astrophysics Data System (ADS)

    Val'kov, V. V.; Val'kova, T. A.; Mitskan, V. A.

    2017-10-01

    Using the diagram technique for the Hubbard operators an integral equation that determines the order parameter of the superconducting phase Δ (p) was obtained in the framework of t-J-V and t-J*-V models on triangular lattice. It is shown that there are two scenarios of formation of superconducting phase with gapless spectrum at the critical concentration of carriers xc. The effect of three-center terms on implementation of this phase was also considered.

  8. 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.

  9. 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.

  10. High critical current density and enhanced irreversibility field in superconducting MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Eom, C. B.; Lee, M. K.; Choi, J. H.; Belenky, L. J.; Song, X.; Cooley, L. D.; Naus, M. T.; Patnaik, S.; Jiang, J.; Rikel, M.; Polyanskii, A.; Gurevich, A.; Cai, X. Y.; Bu, S. D.; Babcock, S. E.; Hellstrom, E. E.; Larbalestier, D. C.; Rogado, N.; Regan, K. A.; Hayward, M. A.; He, T.; Slusky, J. S.; Inumaru, K.; Haas, M. K.; Cava, R. J.

    2001-05-01

    The discovery of superconductivity at 39K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7T at liquid helium temperature (4.2K), significantly lower than about 10T for Nb-Ti (ref. 6) and ~20T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2K greater than 14T. In addition, very high critical current densities at 4.2K are achieved: 1MAcm-2 at 1T and 105Acm-2 at 10T. These results demonstrate that MgB2 has potential for high-field superconducting applications.

  11. Enhancement of the d-wave pairing correlations by charge and spin ordering in the spin-one-half Falicov-Kimball model with Hund and Hubbard coupling

    NASA Astrophysics Data System (ADS)

    Farkašovský, Pavol

    2016-08-01

    The projector quantum Monte Carlo method is used to examine the effects of the spin-independent U fd as well as spin-dependent J z Coulomb interaction between the localized f and itinerant d electrons on the stability of various types of charge/spin ordering and superconducting correlations in the spin-one-half Falicov-Kimball model with Hund and Hubbard coupling. The model is studied for a wide range of f- and d-electron concentrations and it is found that the interband interactions U fd and J z stabilize three basic types of charge/spin ordering, namely, i) the axial striped phases, ii) the regular n-molecular phases and iii) the phase-separated states. It is shown that the d-wave pairing correlations are enhanced within the axial striped and phase-separated states, but not in the regular phases. Moreover, it was found that the antiferromagnetic spin arrangement within the chains further enhances the d-wave paring correlations, while the ferromagnetic one has a fully opposite effect.

  12. Theoretical study of pair density wave superconductors

    NASA Astrophysics Data System (ADS)

    Zheng, Zhichao

    In conventional superconductors, the Cooper pairs are formed from quasiparticles. We explore another type of superconducting state, a pair density wave (PDW) order, which spontaneously breaks some of the translational and point group symmetries. In a PDW superconductor, the order parameter is a periodic function of the center-of-mass coordinate, and the spatial average value of the superconducting order parameter vanishes. In the early 1960s, following the success of the BCS theory of superconductivity, Fulde and Ferrell and Larkin and Ovchinnikov (FFLO) developed theories of inhomogeneous superconducting states. Because of this Zeeman splitting in a magnetic field, the Cooper pairs having a nonzero center-of-mass momentum are more stable than the normal pairing, leading to the FFLO state. Experiments suggest possible occurrence of the FFLO state in the heavy-fermion compound CeCoIn5, and in quasi-low-dimensional organic superconductors. FFLO phases have also been argued to be of importance in understanding ultracold atomic Fermi gases and in the formation of color superconductivity in high density quark matter. In all Fermi superfluids known at the present time, Cooper pairs are composed of particles with spin 1/2. The spin component of a pair wave function can be characterized by its total spin S = 0 (singlet) and S = 1 (triplet). In the discovered broken inversion superconductors CePt3Si, Li2Pt3B, and Li2Pd3B, the magnetic field leads to novel inhomogeneous superconducting states, namely the helical phase and the multiple-q phase. Its order parameter exhibits periodicity similar to FFLO phase, and the consequences of both phases are same: the enhancement of transition temperature as a function of magnetic field. We have studied the PDW phases in broken parity superconductors with vortices included. By studying PDW vortex states, we find the usual Abrikosov vortex solution is unstable against a new solution with fractional vortex pairs. We have also studied the

  13. Motor cortex plasticity induced by paired associative stimulation is enhanced in physically active individuals.

    PubMed

    Cirillo, John; Lavender, Andrew P; Ridding, Michael C; Semmler, John G

    2009-12-15

    Recent evidence indicates that regular physical activity enhances brain plasticity (i.e. the ability to reorganise neural connections) and improves neurocognitive function. However, the effect of regular physical activity on human motor cortex function is unknown. The purpose of this study was to examine motor cortex plasticity for a small hand muscle in highly active and sedentary individuals. Electromyographic recordings were obtained from the left abductor pollicis brevis (APB) muscle of 14 active and 14 sedentary subjects (aged 18-38 yrs). The extent of physical activity was assessed by questionnaire, where the physically active subjects performed >150 min per day moderate-to-vigorous aerobic activity on at least 5 days per week, whereas the sedentary group performed <20 min per day of physical activity on no more than 3 days per week. Transcranial magnetic stimulation (TMS) of the right hemisphere was used to assess changes in APB motor-evoked potentials (MEPs), input-output curve (IO curve), short-interval intracortical inhibition (SICI) and cortical silent period (CSP). Neuroplastic changes were induced using paired-associative stimulation (PAS), which consisted of 90 paired stimuli (0.05 Hz for 30 min) of median nerve electrical stimulation at the wrist followed 25 ms later by TMS to the hand area of motor cortex. The IO curve slope was 35% steeper in individuals with increased physical activity (combined before and after PAS, P < 0.05), suggesting increased motor cortex excitability, although there was no difference in SICI or CSP between groups. PAS induced an increase in MEP amplitude in the physically active subjects (54% increase compared with before, P < 0.01), but no significant facilitation in the sedentary subjects. We conclude that participation in regular physical activity may offer global benefits to motor cortex function that enhances neuroplasticity, which could improve motor learning and neurorehabilitation in physically active individuals.

  14. Superconductivity in type-II Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Alidoust, M.; Halterman, K.; Zyuzin, A. A.

    2017-04-01

    We study superconductivity in a Weyl semimetal with a tilted dispersion around two Weyl points of opposite chirality. In the absence of any tilt, the state with zero momentum pairing between two Fermi sheets enclosing each Weyl point has four point nodes in the superconducting gap function. Moreover, the surface of the superconductor hosts Fermi arc states and Majorana flat bands. We show that a quantum phase transition occurs at a critical value of the tilt, at which two gap nodes disappear by merging at the center of the first Brillouin zone, or by escaping at its edges, depending on the direction of the tilt. The region in the momentum space that the Majorana flat band occupies is found to increase as the tilt parameter is made larger. Additionally, the superconducting critical temperature and electronic specific heat can be enhanced in the vicinity of the quantum phase transition due to the singularity in the electronic density of states.

  15. Enhancing EUV mask blanks usability through smart shift and blank-design pairing optimization

    NASA Astrophysics Data System (ADS)

    Soni, Rakesh Kumar; Paninjath, Sankaranarayanan; Pereira, Mark; Buck, Peter; Thwaite, Peter

    2016-10-01

    EUV Defect avoidance techniques will play a vital role in extreme ultraviolet lithography (EUVL) photomask fabrication with the anticipation that defect free mask blanks won't be available and that cost effective techniques will not be available for defect repairing. In addition, mask shops may not have a large inventory of expensive EUV mask blanks. Given these facts, defect avoidance can be used as cost effective technique to optimize the mask blank and design data (mask data) pair selection across mask blank manufacturers and mask shops so that overall mask blank utilization can be enhanced. In previous work, it was determined that the pattern shift based solution increases the chance that a defective mask blank can be used that would otherwise be discarded [1]. In pattern shift, design data is shifted such that defects are either moved to isolated regions or hidden under the patterns that are written. However pattern shifts techniques don't perform well with masks with higher defect counts. Pattern shift techniques in this form assume all defects to be equally critical. In addition, a defect is critical or important only if it lands on the main pattern. A defect landing on fill, sub-resolution assist feature (SRAF) or fiducial areas may not be critical. In this paper we assess the performance of pattern shift techniques assuming defects that are not critical based upon size or type, as well as defects landing in non-critical areas (smart shift) can be ignored. In a production mask manufacturing environment it is necessary to co-optimize and prioritize blank-design pairing for multiple mask layouts in the queue with the available blanks. A blank-design pairing tool maximizes the utilization of blanks by finding the best pairing between blanks and design data so that the maximum number of mask blanks can be used. In this paper we also propose a novel process which would optimize the usage of costly EUV mask blanks across mask blank manufacturers and mask shops

  16. 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

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

    DOE PAGES

    Casandruc, E.; Nicoletti, D.; Rajasekaran, S.; ...

    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

  18. Enhanced superconductivity, Kondo behavior, and negative-curvature resistivity of oxygen-irradiated thin films of aluminium

    NASA Astrophysics Data System (ADS)

    Sinnecker, E. H. C. P.; Sant'Anna, M. M.; ElMassalami, M.

    2017-02-01

    We followed the evolution of the normal and superconducting properties of Al thin films after each session of various successive oxygen irradiations at ambient temperature. Such irradiated films, similar to the granular ones, exhibit enhanced superconductivity, Kondo behavior, and negative-curvature resistivity. Two distinct roles of oxygen are identified: as a damage-causing projectile and as an implanted oxidizing agent. The former gives rise to the processes involved in the conventional recovery stages. The latter, considered within the context of the Cabrera-Mott model, gives rise to a multistep process which involves charges transfer and creation of stabilized vacancies and charged defects. Based on the outcome of this multistep process, we consider (i) the negative-curvature resistivity as a manifestation of a thermally assisted liberation of trapped electric charges, (ii) the Kondo contribution as a spin-flip scattering from paramagnetic, color-center-type defects, and (iii) the enhancement of Tc as being due to a lattice softening facilitated by the stabilized defects and vacancies. The similarity in the phase diagrams of granular and irradiated films as well as the aging effects are discussed along the same line of reasoning.

  19. 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

    2016-08-18

    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.

  20. 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

  1. Enhancement models of momentum densities of annihilating electron-positron pairs: The many-body picture of natural geminals

    NASA Astrophysics Data System (ADS)

    Makkonen, Ilja; Ervasti, Mikko M.; Siro, Topi; Harju, Ari

    2014-01-01

    The correlated motion of a positron surrounded by electrons is a fundamental many-body problem. We approach this by modeling the momentum density of annihilating electron-positron pairs using the framework of reduced density matrices, natural orbitals, and natural geminals (electron-positron pair wave functions) of the quantum theory of many-particle systems. We find that an expression based on the natural geminals provides an exact, unique, and compact expression for the momentum density. The natural geminals can be used to define and to determine enhancement factors for enhancement models going beyond the independent-particle model for a better understanding of the results of positron annihilation experiments.

  2. 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

  3. Tailoring Superconductivity with Quantum Dislocations.

    PubMed

    Li, Mingda; Song, Qichen; Liu, Te-Huan; Meroueh, Laureen; Mahan, Gerald D; Dresselhaus, Mildred S; Chen, Gang

    2017-08-09

    Despite the established knowledge that crystal dislocations can affect a material's superconducting properties, the exact mechanism of the electron-dislocation interaction in a dislocated superconductor has long been missing. Being a type of defect, dislocations are expected to decrease a material's superconducting transition temperature (Tc) by breaking the coherence. Yet experimentally, even in isotropic type I superconductors, dislocations can either decrease, increase, or have little influence on Tc. These experimental findings have yet to be understood. Although the anisotropic pairing in dirty superconductors has explained impurity-induced Tc reduction, no quantitative agreement has been reached in the case a dislocation given its complexity. In this study, by generalizing the one-dimensional quantized dislocation field to three dimensions, we reveal that there are indeed two distinct types of electron-dislocation interactions. Besides the usual electron-dislocation potential scattering, there is another interaction driving an effective attraction between electrons that is caused by dislons, which are quantized modes of a dislocation. The role of dislocations to superconductivity is thus clarified as the competition between the classical and quantum effects, showing excellent agreement with existing experimental data. In particular, the existence of both classical and quantum effects provides a plausible explanation for the illusive origin of dislocation-induced superconductivity in semiconducting PbS/PbTe superlattice nanostructures. A quantitative criterion has been derived, in which a dislocated superconductor with low elastic moduli and small electron effective mass and in a confined environment is inclined to enhance Tc. This provides a new pathway for engineering a material's superconducting properties by using dislocations as an additional degree of freedom.

  4. Dirac-fermion-induced parity mixing in superconducting topological insulators

    NASA Astrophysics Data System (ADS)

    Mizushima, Takeshi; Yamakage, Ai; Sato, Masatoshi; Tanaka, Yukio

    2014-11-01

    We self-consistently study surface states of superconducting topological insulators. We clarify that, if a topologically trivial bulk s -wave pairing symmetry is realized, parity mixing of the pair potential near the surface is anomalously enhanced by surface Dirac fermions, opening an additional surface gap larger than the bulk one. In contrast to classical s -wave superconductors, the resulting surface density of state hosts an extra coherent peak at the induced gap besides a conventional peak at the bulk gap. We also find that no such extra peak appears for odd-parity superconductors with a cylindrical Fermi surface. Our calculation suggests that the simple U-shaped scanning tunneling microscope spectrum in CuxBi2Se3 does not originate from s -wave superconductivity, but can be explained by odd-parity superconductivity with a cylindrical Fermi surface.

  5. Enhanced superconductivity of SmFeAsO co-doped by Scandium and Fluorine to increase chemical inner pressure

    NASA Astrophysics Data System (ADS)

    Chen, Haijie; Zheng, Ming; Fang, Aihua; Yang, Jianhua; Huang, Fuqiang; Xie, Xiaoming; Jiang, Mianheng

    2012-10-01

    Sm1-x/3Scx/3FeAsO1-xFx (x=0.09-0.27) were synthesized by the mechanical alloying and subsequent low temperature rapid sintering (2 h at 950 °C). The superconducting transition temperature (Tc) increased with the doping level of x. The optimal doping achieved a Tc up to 53.5 K in Sm0.93Sc0.07FeAsO0.79F0.21. The higher Tc value was attributed to the increased chemical inner pressure from local lattice distortion induced by smaller-size dopants, which was further confirmed by Sm1-xScxFeAsO0.88F0.12 (x=0.04, 0.08, 0.12). Accordingly, larger lattice distortion can enhance the superconductivity below the doping limit. Similar phenomenon was also observed in the La1-xYxFeAsO0.8F0.2 (x=0.4, 0.5, 0.6).

  6. Enhanced reduced representation bisulfite sequencing for assessment of DNA methylation at base pair resolution.

    PubMed

    Garrett-Bakelman, Francine E; Sheridan, Caroline K; Kacmarczyk, Thadeous J; Ishii, Jennifer; Betel, Doron; Alonso, Alicia; Mason, Christopher E; Figueroa, Maria E; Melnick, Ari M

    2015-02-24

    DNA methylation pattern mapping is heavily studied in normal and diseased tissues. A variety of methods have been established to interrogate the cytosine methylation patterns in cells. Reduced representation of whole genome bisulfite sequencing was developed to detect quantitative base pair resolution cytosine methylation patterns at GC-rich genomic loci. This is accomplished by combining the use of a restriction enzyme followed by bisulfite conversion. Enhanced Reduced Representation Bisulfite Sequencing (ERRBS) increases the biologically relevant genomic loci covered and has been used to profile cytosine methylation in DNA from human, mouse and other organisms. ERRBS initiates with restriction enzyme digestion of DNA to generate low molecular weight fragments for use in library preparation. These fragments are subjected to standard library construction for next generation sequencing. Bisulfite conversion of unmethylated cytosines prior to the final amplification step allows for quantitative base resolution of cytosine methylation levels in covered genomic loci. The protocol can be completed within four days. Despite low complexity in the first three bases sequenced, ERRBS libraries yield high quality data when using a designated sequencing control lane. Mapping and bioinformatics analysis is then performed and yields data that can be easily integrated with a variety of genome-wide platforms. ERRBS can utilize small input material quantities making it feasible to process human clinical samples and applicable in a range of research applications. The video produced demonstrates critical steps of the ERRBS protocol.

  7. Crystallization and preliminary X-ray analysis of the Pax6 paired domain bound to the Pax6 gene enhancer

    SciTech Connect

    Ito, Makoto Oyama, Takuji; Okazaki, Kenji; Morikawa, Kosuke

    2005-11-01

    The mammalian Pax6 paired domain has been cocrystallizaed with a 25 bp DNA fragment of the Pax6 gene enhancer. Pax6 is a member of the Pax family of transcription factors and is essential for eye development. Pax6 has two DNA-binding domains: the paired domain and the homeodomain. The Pax6 paired domain is involved in Pax6 gene autoregulation by binding to its enhancer. In this study, crystallization and preliminary X-ray diffraction analysis of the mammalian Pax6 paired domain in complex with the Pax6 gene enhancer was attempted. The Pax6 paired domain complexed with an optimized 25 bp DNA fragment was crystallized by the hanging-drop vapour-diffusion method. The crystal diffracted synchrotron radiation to 3.0/3.7 Å resolution and belongs to the monoclinic space group P2{sub 1}, with unit-cell parameters a = 62.21, b = 70.69, c = 176.03 Å, β = 90.54°. Diffraction data were collected to 3.7 Å resolution.

  8. Enhanced superconductivity at the interface of W/Sr2RuO4 point contact

    NASA Astrophysics Data System (ADS)

    Wei, Jian; Wang, He; Lou, Weijian; Luo, Jiawei; Liu, Ying; Ortmann, J. E.; Mao, Z. Q.

    Differential resistance measurements are conducted for point contacts (PCs) between the Sr2RuO4 (SRO) single crystal and the tungsten tip. Since the tungsten tip is hard enough to penetrate through the surface layer, consistent superconducting features are observed. Firstly, with the tip pushed towards the crystal, the zero bias conductance peak (ZBCP) due to Andreev reflection at the normal-superconducting interface increases from 3% to more than 20%, much larger than previously reported, and extends to temperature higher than the bulk transition temperature. Reproducible ZBCP within 0.2 mV may also help determine the gap value of SRO, on which no consensus has been reached. Secondly, the logarithmic background can be fitted with the Altshuler-Aronov theory of electron-electron interaction for tunneling into quasi two dimensional electron system. Feasibility of such fitting confirms that spectroscopic information like density of states is probed, and electronic temperature retrieved from such fitting can be important to analyse the PC spectra. Third, at bias much higher than 0.2 mV there are conductance dips due to the critical current effect and these dips persist up to 6.2 K. For more details see. National Basic Research Program of China (973 Program) through Grant No. 2011CBA00106 and No. 2012CB927400.

  9. 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.

  10. 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…

  11. 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…

  12. 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.

  13. 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…

  14. 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…

  15. 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…

  16. 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…

  17. Enhanced extraordinary optical transmission (EOT) through arrays of bridged nanohole pairs and their sensing applications

    NASA Astrophysics Data System (ADS)

    Yue, Weisheng; Wang, Zhihong; Yang, Yang; Li, Jingqi; Wu, Ying; Chen, Longqing; Ooi, Boon; Wang, Xianbin; Zhang, Xi-Xiang

    2014-06-01

    Extraordinary optical transmission (EOT) through arrays of gold nanoholes was studied with light across the visible to the near-infrared spectrum. The EOT effect was found to be improved by bridging pairs of nanoholes due to the concentration of the electromagnetic field in the slit between the holes. The geometrical shape and separation of the holes in these pairs of nanoholes affected the intensity of the transmission and the wavelength of resonance. Changing the geometrical shapes of these nanohole pairs from triangles to circles to squares leads to increased transmission intensity as well as red-shifting resonance wavelengths. The performance of bridged nanohole pairs as a plasmonic sensor was investigated. The bridged nanohole pairs were able to distinguish methanol, olive oil and microscope immersion oil for the different surface plasmon resonance in transmission spectra. Numerical simulation results were in agreement with experimental observations.

  18. Base pair sensitivity and enhanced ON/OFF ratios of DNA-binding: donor-acceptor-donor fluorophores.

    PubMed

    Wilson, James N; Wigenius, Jens; Pitter, Demar R G; Qiu, Yanhua; Abrahamsson, Maria; Westerlund, Fredrik

    2013-10-10

    The photophysical properties of two recently reported live cell compatible, DNA-binding dyes, 4,6-bis(4-(4-methylpiperazin-1-yl)phenyl)pyrimidin-2-ol, 1, and [1,3-bis[4-(4-methylpiperazin-1-yl)phenyl]-1,3-propandioato-κO, κO']difluoroboron, 2, are characterized. Both dyes are quenched in aqueous solutions, while binding to sequences containing only AT pairs enhances the emission. Binding of the dyes to sequences containing only GC pairs does not produce a significant emission enhancement, and for sequences containing both AT and GC base pairs, emission is dependent on the length of the AT pair tracts. Through emission lifetime measurements and analysis of the dye redox potentials, photoinduced electron transfer with GC pairs is implicated as a quenching mechanism. Binding of the dyes to AT-rich regions is accompanied by bathochromic shifts of 26 and 30 nm, respectively. Excitation at longer wavelengths thus increases the ON/OFF ratio of the bound probes significantly and provides improved contrast ratios in solution as well as in fluorescence microscopy of living cells.

  19. 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. Copyright © 2015, American Association for the Advancement of Science.

  20. Electron-Phonon Coupling and its implication for the superconducting topological insulators

    PubMed Central

    Zhang, Xiao-Long; Liu, Wu-Ming

    2015-01-01

    The recent observation of superconductivity in doped topological insulators has sparked a flurry of interest due to the prospect of realizing the long-sought topological superconductors. Yet the understanding of underlying pairing mechanism in these systems is far from complete. Here we investigate this problem by providing robust first-principles calculations of the role of electron-phonon coupling for the superconducting pairing in the prime candidate CuxBi2Se3. Our results show that electron-phonon scattering process in this system is dominated by zone center and boundary optical modes, with coexistence of phonon stiffening and softening. While the calculated electron-phonon coupling constant λ suggests that Tc from electron-phonon coupling is 2 orders smaller than the ones reported on bulk inhomogeneous samples, suggesting that superconductivity may not come from pure electron-phonon coupling. We discuss the possible enhancement of superconducting transition temperature by local inhomogeneity introduced by doping. PMID:25753813

  1. Superconductivity at 28 K in CaB3C3 predicted from first-principles

    NASA Astrophysics Data System (ADS)

    Chen, Wanjin

    2013-11-01

    The structural parameters, electronic properties, and superconducting state in the graphite-like BxC1-x intercalation compound, CaB3C3, have been studied using pseudopotential density functional theory within the generalized gradient approximation. Electronic and electron-phonon coupling calculations reveal that CaB3C3 is hole conducting and superconducting with critical temperature 28.2 K, which is much higher than that of CaC6 (11.5 K). The excellent superconducting state in CaB3C3 stems from the simultaneous presence of highly mobile and extremely confined conduction electrons, which enhances electron pairing and superconductivity. The current calculations might stimulate further theoretical and experimental investigation in search of new superconducting states in graphite-like BxC1-x intercalated compounds.

  2. Observation of two superconducting domes under pressure in tetragonal FeS

    NASA Astrophysics Data System (ADS)

    Zhang, Jun; Liu, Feng-Liang; Ying, Tian-Ping; Li, Na-Na; Xu, Yang; He, Lan-Po; Hong, Xiao-Chen; Yu, Yun-Jie; Wang, Ming-Xiang; Shen, Jian; Yang, Wen-Ge; Li, Shi-Yan

    2017-09-01

    We investigate the evolution of superconductivity and structure with pressure for the new superconductor FeS (Tc ≈ 4.5 K), a sulfide counterpart of FeSe. A rapid suppression of Tc and vanishing of superconductivity at 4.0 GPa are observed, followed by a second superconducting dome from 5.0 to 22.3 GPa with a 30% enhancement in maximum Tc. An onsite tetragonal to hexagonal phase transition occurs around 7.0 GPa, followed by a broad pressure range of phase coexistence. The residual deformed tetragonal phase is considered as the source of second superconducting dome. The observation of two superconducting domes in iron-based superconductors poses great challenges for understanding their pairing mechanism.

  3. Enhanced superconductivity and superconductor to insulator transition in nano-crystalline molybdenum thin films

    NASA Astrophysics Data System (ADS)

    Sharma, Shilpam; Amaladass, E. P.; Sharma, Neha; Harimohan, V.; Amirthapandian, S.; Mani, Awadhesh

    2017-06-01

    Disorder driven superconductor to insulator transition via intermediate metallic regime is reported in nano-crystalline thin films of molybdenum. The nano-structured thin films have been deposited at room temperature using DC magnetron sputtering at different argon pressures. The grain size has been tuned using deposition pressure as the sole control parameter. A variation of particle sizes, room temperature resistivity and superconducting transition has been studied as a function of deposition pressure. The nano-crystalline molybdenum thin films are found to have large carrier concentration but very low mobility and electronic mean free path. Hall and conductivity measurements have been used to understand the effect of disorder on the carrier density and mobilities. Ioffe-Regel parameter is shown to correlate with the continuous metal-insulator transition in our samples.

  4. Magnetar superconductivity versus magnetism: Neutrino cooling processes

    NASA Astrophysics Data System (ADS)

    Sinha, Monika; Sedrakian, Armen

    2015-03-01

    We describe the microphysics, phenomenology, and astrophysical implication of a B -field induced unpairing effect that may occur in magnetars, if the local B field in the core of a magnetar exceeds a critical value Hc 2. Using the Ginzburg-Landau theory of superconductivity, we derive the Hc 2 field for proton condensate taking into the correction (≤30 % ) which arises from its coupling to the background neutron condensate. The density dependence of pairing of proton condensate implies that Hc 2 is maximal at the crust-core interface and decreases towards the center of the star. As a consequence, magnetar cores with homogenous constant fields will be partially superconducting for "medium-field" magnetars (1015≤B ≤5 ×1016G) whereas "strong-field" magnetars (B >5 ×1016G) will be void of superconductivity. The neutrino emissivity of a magnetar's core changes in a twofold manner: (i) the B -field assisted direct Urca process is enhanced by orders of magnitude, because of the unpairing effect in regions where B ≥Hc 2 ; (ii) the Cooper-pair breaking processes on protons vanish in these regions and the overall emissivity by the pair-breaking processes is reduced by a factor of only a few.

  5. The formation of nano-layered grains and their enhanced superconducting transition temperature in Mg-doped FeSe0.9 bulks

    PubMed Central

    Lan, Feng; Ma, Zongqing; Liu, Yongchang; Chen, Ning; Cai, Qi; Li, Huijun; Barua, Shaon; Patel, Dipak; Hossain, M. Shahriar Al; Kim, Jung Ho; Dou, Shi Xue

    2014-01-01

    To search a proper dopant to further improve superconductivity in 11 type Fe-based superconductors makes sense to both their superconductivity mechanism and possible technological applications. In present work, Mg doped FeSe polycrystalline bulks were obtained by a two-step solid-state reaction method. Even though there are many MgSe and iron impurities existing in the Mg heavy doped FeSe bulks, they exhibit obviously increased Tc compared to undoped FeSe sample. It was found that Mg addition has little effect on the crystal lattice parameters of superconducting β-FeSe, whereas leads to the formation of nano-layered grain structure consisted of MgSe and β-FeSe with similar X-ray diffraction characteristics. Lots of nano-structural interfaces between FeSe and MgSe formed in this homogenous layered grain structure have significant effect on the superconducting properties and are responsible for the enhancement of Tc, as like the case of FeSe thin film on some specific substrates. Our work not only demonstrates a powerful way for raising Tc in bulk superconductors, but also provides a well-defined platform for systematic studies of the mechanism of unconventional superconductivity by considering interface effect. PMID:25257951

  6. The formation of nano-layered grains and their enhanced superconducting transition temperature in Mg-doped FeSe0.9 bulks.

    PubMed

    Lan, Feng; Ma, Zongqing; Liu, Yongchang; Chen, Ning; Cai, Qi; Li, Huijun; Barua, Shaon; Patel, Dipak; Al Hossain, M Shahriar; Kim, Jung Ho; Dou, Shi Xue

    2014-09-26

    To search a proper dopant to further improve superconductivity in 11 type Fe-based superconductors makes sense to both their superconductivity mechanism and possible technological applications. In present work, Mg doped FeSe polycrystalline bulks were obtained by a two-step solid-state reaction method. Even though there are many MgSe and iron impurities existing in the Mg heavy doped FeSe bulks, they exhibit obviously increased Tc compared to undoped FeSe sample. It was found that Mg addition has little effect on the crystal lattice parameters of superconducting β-FeSe, whereas leads to the formation of nano-layered grain structure consisted of MgSe and β-FeSe with similar X-ray diffraction characteristics. Lots of nano-structural interfaces between FeSe and MgSe formed in this homogenous layered grain structure have significant effect on the superconducting properties and are responsible for the enhancement of Tc, as like the case of FeSe thin film on some specific substrates. Our work not only demonstrates a powerful way for raising Tc in bulk superconductors, but also provides a well-defined platform for systematic studies of the mechanism of unconventional superconductivity by considering interface effect.

  7. The formation of nano-layered grains and their enhanced superconducting transition temperature in Mg-doped FeSe0.9 bulks

    NASA Astrophysics Data System (ADS)

    Lan, Feng; Ma, Zongqing; Liu, Yongchang; Chen, Ning; Cai, Qi; Li, Huijun; Barua, Shaon; Patel, Dipak; Hossain, M. Shahriar Al; Kim, Jung Ho; Dou, Shi Xue

    2014-09-01

    To search a proper dopant to further improve superconductivity in 11 type Fe-based superconductors makes sense to both their superconductivity mechanism and possible technological applications. In present work, Mg doped FeSe polycrystalline bulks were obtained by a two-step solid-state reaction method. Even though there are many MgSe and iron impurities existing in the Mg heavy doped FeSe bulks, they exhibit obviously increased Tc compared to undoped FeSe sample. It was found that Mg addition has little effect on the crystal lattice parameters of superconducting β-FeSe, whereas leads to the formation of nano-layered grain structure consisted of MgSe and β-FeSe with similar X-ray diffraction characteristics. Lots of nano-structural interfaces between FeSe and MgSe formed in this homogenous layered grain structure have significant effect on the superconducting properties and are responsible for the enhancement of Tc, as like the case of FeSe thin film on some specific substrates. Our work not only demonstrates a powerful way for raising Tc in bulk superconductors, but also provides a well-defined platform for systematic studies of the mechanism of unconventional superconductivity by considering interface effect.

  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. 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

  10. The role of local repulsion in superconductivity in the Hubbard-Holstein model

    NASA Astrophysics Data System (ADS)

    Lin, Chungwei; Wang, Bingnan; Teo, Koon Hoo

    2017-01-01

    We examine the superconducting solution in the Hubbard-Holstein model using Dynamical Mean Field Theory. The Holstein term introduces the site-independent Boson fields coupling to local electron density, and has two competing influences on superconductivity: The Boson field mediates the effective electron-electron attraction, which is essential for the S-wave electron pairing; the same coupling to the Boson fields also induces the polaron effect, which makes the system less metallic and thus suppresses superconductivity. The Hubbard term introduces an energy penalty U when two electrons occupy the same site, which is expected to suppress superconductivity. By solving the Hubbard-Holstein model using Dynamical Mean Field theory, we find that the Hubbard U can be beneficial to superconductivity under some circumstances. In particular, we demonstrate that when the Boson energy Ω is small, a weak local repulsion actually stabilizesthe S-wave superconducting state. This behavior can be understood as an interplay between superconductivity, the polaron effect, and the on-site repulsion: As the polaron effect is strong and suppresses superconductivity in the small Ω regime, the weak on-site repulsion reduces the polaron effect and effectively enhances superconductivity. Our calculation elucidates the role of local repulsion in the conventional S-wave superconductors.

  11. 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.

  12. Red-shifted luciferase-luciferin pairs for enhanced bioluminescence imaging.

    PubMed

    Yeh, Hsien-Wei; Karmach, Omran; Ji, Ao; Carter, David; Martins-Green, Manuela M; Ai, Hui-Wang

    2017-09-04

    Red-shifted bioluminescence reporters are desirable for biological imaging. We describe the development of red-shifted luciferins based on synthetic coelenterazine analogs and corresponding mutants of NanoLuc that enable bright bioluminescence. One pair in particular showed superior in vitro and in vivo sensitivity over commonly used bioluminescence reporters. We adapted this pair to develop a bioluminescence resonance-energy-based Antares reporter called Antares2, which offers improved signal from deep tissues.

  13. Stripes of increased diamagnetic susceptibility in underdoped superconducting Ba(Fe[subscript 1−x]Co[subscript x])[subscript 2]As[subscript 2] single crystals: Evidence for an enhanced superfluid density at twin boundaries

    SciTech Connect

    Kalisky, B.; Kirtley, J.R.; Analytis, J.G.; Chu, Jiun-Haw; Vailionis, A.; Fisher, I.R.; Moler, K.A.

    2010-10-22

    Superconducting quantum interference device microscopy shows stripes of increased diamagnetic susceptibility in the superconducting state of twinned, orthorhombic, underdoped crystals of Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2}, but not in tetragonal overdoped crystals. These stripes are consistent with enhanced superfluid density on twin boundaries.

  14. Superconductivity without phonons.

    PubMed

    Monthoux, P; Pines, D; Lonzarich, G G

    2007-12-20

    The idea of superconductivity without the mediating role of lattice vibrations (phonons) has a long history. It was realized soon after the publication of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity 50 years ago that a full treatment of both the charge and spin degrees of freedom of the electron predicts the existence of attractive components of the effective interaction between electrons even in the absence of lattice vibrations--a particular example is the effective interaction that depends on the relative spins of the electrons. Such attraction without phonons can lead to electronic pairing and to unconventional forms of superconductivity that can be much more sensitive than traditional (BCS) superconductivity to the precise details of the crystal structure and to the electronic and magnetic properties of a material.

  15. Processing of doped yttrium barium cuprate melt textured bulk single crystals for enhanced superconducting properties

    NASA Astrophysics Data System (ADS)

    Sofie, Stephen Wayne

    2002-08-01

    YBa2Cu3O7-x (123) high temperature superconducting powders were synthesized by mixing Y2O3, CuO, and BaCO3 precursor powders and subsequently reacting them at 920°C in a rotary calciner. The effects of carbon on the critical temperature (Tc), critical current density (Jc), trapped field, as well as the growth of melt textured 123 single crystals were examined as a function of the extent of calcination. Increasing carbon content in the sample resulted in lower and broader transition temperatures, however, J c's were improved showing a high field "fishtail" effect at 77K. Highly porous microstructure were, however, formed with increasing carbon content, thus degrading the properties of the material. To further improve Jc density, non-volatile substitutional and secondary phase dopants were utilized. The addition of 1 wt% CeO 2 (secondary phase particulate) led to an approximate 35% increase in Jc by the formation of ˜1mum BaCeO3 inclusions. Liquid loss was consequently reduced from the CeO2 additions due to increased capillary forces in the semi-solid melt. Nd2O 3 (substitutional dopant) not only substitutes yttrium lattice sites, but also barium lattice sites which can effectively kill superconductivity in a local regions, creating very small flux pinning sites. Additions of less than 0.1mol% Nd2O3 have shown improved high field J c's, however, Nd2O3 additions beyond 1mol% are deleterious to crystal growth due to the formation of Nd123, a higher melting point perovskite, resulting in polycrystalline crystal growth. YBa2Cu3O7-x growth kinetics have been examined to determine factors that may effect particle pushing/entrapment. These factors, such as critical particle radius, critical interface growth velocity, and interfacial energy contributions, are essential for the processing of melt textured single crystals with homogeneous distributions of fine secondary phase dopants. Melt textured single crystals have been grown utilizing an off axis [100] seed which

  16. 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.

  17. 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).

  18. 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.

  19. Enhanced superconductivity in SnSb under pressure: a first principles study.

    PubMed

    Sreenivasa Reddy, P V; Kanchana, V

    2017-07-10

    First principles electronic structure calculations reveal both SnP and SnSb to be stable in the NaCl structure. In SnSb, a first order phase transition from NaCl to CsCl type structure is observed at around 13 GPa, which is also confirmed from enthalpy calculations and agrees well with experimental and other theoretical reports. Calculations of the phonon spectra, and hence the electron-phonon coupling [Formula: see text] and superconducting transition temperature T c, were performed at zero pressure for both the compounds, and at high pressure for SnSb. These calculations report [Formula: see text] of [Formula: see text] K and [Formula: see text] K for SnP and SnSb respectively, in the NaCl structure-in good agreement with experiment-whilst at the transition pressure, in the CsCl structure, a drastically increased value of T c around [Formula: see text] K ([Formula: see text] K at 20 GPa) is found for SnSb, together with a dramatic increase in the electronic density of states at this pressure. The lowest energy acoustic phonon branches in each structure also demonstrate some softening effects, which are well addressed in this work.

  20. Enhanced superconductivity in SnSb under pressure: a first principles study

    NASA Astrophysics Data System (ADS)

    Sreenivasa Reddy, P. V.; Kanchana, V.

    2017-10-01

    First principles electronic structure calculations reveal both SnP and SnSb to be stable in the NaCl structure. In SnSb, a first order phase transition from NaCl to CsCl type structure is observed at around 13 GPa, which is also confirmed from enthalpy calculations and agrees well with experimental and other theoretical reports. Calculations of the phonon spectra, and hence the electron–phonon coupling λep and superconducting transition temperature T c, were performed at zero pressure for both the compounds, and at high pressure for SnSb. These calculations report Tc of 0.614 K and 3.083 K for SnP and SnSb respectively, in the NaCl structure—in good agreement with experiment—whilst at the transition pressure, in the CsCl structure, a drastically increased value of T c around 9.18 K (9.74 K at 20 GPa) is found for SnSb, together with a dramatic increase in the electronic density of states at this pressure. The lowest energy acoustic phonon branches in each structure also demonstrate some softening effects, which are well addressed in this work.

  1. Mn-doping induced ferromagnetism and enhanced superconductivity in Bi4 -xMnxO4S3 (0.075 ≤x ≤0.15 )

    NASA Astrophysics Data System (ADS)

    Feng, Zhenjie; Yin, Xunqing; Cao, Yiming; Peng, Xianglian; Gao, Tian; Yu, Chuan; Chen, Jingzhe; Kang, Baojuan; Lu, Bo; Guo, Juan; Li, Qing; Tseng, Wei-Shiuan; Ma, Zhongquan; Jing, Chao; Cao, Shixun; Zhang, Jincang; Yeh, N.-C.

    2016-08-01

    We demonstrate that Mn doping in the layered sulfides Bi4O4S3 leads to stable Bi4-xMnxO4S3 compounds that exhibit both long-range ferromagnetism and enhanced superconductivity for 0.075 ≤x ≤0.15 , with a possible record superconducting transition temperature (Tc) ˜15 K among all BiS2-based superconductors. We conjecture that the coexistence of superconductivity and ferromagnetism may be attributed to Mn doping in the spacer Bi2O2 layers away from the superconducting BiS2 layers, whereas the enhancement of Tc may be due to excess electron transfer to BiS2 from the Mn4 +/Mn3 + substitutions in Bi2O2 . This notion is empirically corroborated by the increased electron-carrier densities upon Mn doping, and by further studies of the Bi4-xAxO4S3 compounds (A = Co, Ni; x =0.1 , 0.125), where the Tc values remain comparable to that of the undoped Bi4O4S3 system (˜4.5 K) due to lack of 4+ valences in either Co or Ni ions for excess electron transfer to the BiS2 layers. These findings therefore shed new light on feasible pathways to enhance the Tc values of BiS2-based superconductors, although complete elucidation of the interplay between superconductivity and ferromagnetism in these anisotropic layered compounds awaits the development of single crystalline materials for further investigation.

  2. Competing pairing channels in the doped honeycomb lattice Hubbard model

    NASA Astrophysics Data System (ADS)

    Xu, Xiao Yan; Wessel, Stefan; Meng, Zi Yang

    2016-09-01

    Proposals for superconductivity emerging from correlated electrons in the doped Hubbard model on the honeycomb lattice range from chiral d +i d singlet to p +i p triplet pairing, depending on the considered range of doping and interaction strength, as well as the approach used to analyze the pairing instabilities. Here, we consider these scenarios using large-scale dynamic cluster approximation (DCA) calculations to examine the evolution in the leading pairing symmetry from weak to intermediate coupling strength. These calculations focus on doping levels around the van Hove singularity (VHS) and are performed using DCA simulations with an interaction-expansion continuous-time quantum Monte Carlo cluster solver. We calculated explicitly the temperature dependence of different uniform superconducting pairing susceptibilities and found a consistent picture emerging upon gradually increasing the cluster size: while at weak coupling the d +i d singlet pairing dominates close to the VHS filling, an enhanced tendency towards p -wave triplet pairing upon further increasing the interaction strength is observed. The relevance of these systematic results for existing proposals and ongoing pursuits of odd-parity topological superconductivity are also discussed.

  3. Optically induced lattice deformations, electronic structure changes, and enhanced superconductivity in YBa2Cu3O6.48.

    PubMed

    Mankowsky, R; Fechner, M; Först, M; von Hoegen, A; Porras, J; Loew, T; Dakovski, G L; Seaberg, M; Möller, S; Coslovich, G; Keimer, B; Dhesi, S S; Cavalleri, A

    2017-07-01

    Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa2Cu3O6+x induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of the CuO2 planes. The empty chain Cu dy(2)-z(2) orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu L-edge. Femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions.

  4. Optically induced lattice deformations, electronic structure changes, and enhanced superconductivity in YBa2Cu3O6.48

    DOE PAGES

    Mankowsky, R.; Fechner, M.; Forst, M.; ...

    2017-02-28

    Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa2Cu3O6+x induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of the CuO2 planes. Themore » empty chain Cu dy2-z2 orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu L-edge. As a result, femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions.« less

  5. Optically induced lattice deformations, electronic structure changes, and enhanced superconductivity in YBa2Cu3O6.48

    PubMed Central

    Mankowsky, R.; Fechner, M.; Först, M.; von Hoegen, A.; Porras, J.; Loew, T.; Dakovski, G. L.; Seaberg, M.; Möller, S.; Coslovich, G.; Keimer, B.; Dhesi, S. S.; Cavalleri, A.

    2017-01-01

    Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa2Cu3O6+x induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of the CuO2 planes. The empty chain Cu dy2-z2 orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu L-edge. Femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions. PMID:28345009

  6. 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.

  7. Theory of the orbital Kondo effect with assisted hopping in strongly correlated electron systems: Parquet equations, superconductivity, and mass enhancement

    NASA Astrophysics Data System (ADS)

    Penc, K.; Zawadowski, A.

    1994-10-01

    The orbital Kondo effect is treated in a model where, additional to the conduction band, there are localized orbitals close to the Fermi energy. If the hopping between the conduction band and the localized heavy orbitals depends on the occupation of the atomic orbitals in the conduction band, then orbital Kondo correlation occurs. The noncommutative nature of the coupling required for the Kondo effect is formally due to the form factors associated with the assisted hopping, which in the momentum representation depends on the momenta of the conduction electrons involved. The leading logarithmic vertex corrections are due to the local Coulomb interaction between the electrons on the heavy orbital and in the conduction band. The renormalized vertex functions are obtained as a solution of a closed set of differential equations and they show power behavior. The amplitude of large renormalization is determined by an infrared cutoff due to finite energy and dispersion of the heavy particles. The enhanced assisted hopping rate results in mass enhancement and attractive interaction in the conduction band. The superconductivity transition temperature calculated is largest for the intermediate mass enhancement, m*/m~=2-3. For larger mass enhancement the small one-particle weight (Z) in the Green's function reduces the transition temperature, which may be characteristic for other models as well. The theory is developed for different one-dimensional and square-lattice models, but the applicability is not limited to them. In the one-dimensional case charge- and spin-density susceptibilities are also discussed. Good candidates for the heavy orbital are f bands in the heavy fermionic systems and nonbonding oxygen orbitals in high-temperature superconductors and different flatbands in the quasi-one-dimensional organic conductors.

  8. Superconductivity in two-dimensional disordered Dirac semimetals

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Zhao, Peng-Lu; Wang, Jing-Rong; Liu, Guo-Zhu

    2017-02-01

    In two-dimensional Dirac semimetals, Cooper pairing instability occurs only when the attractive interaction strength |u | is larger than some critical value | uc| because the density of states vanishes at Dirac points. Disorders enhance the low-energy density of states but meanwhile shorten the lifetime of fermions, which tend to promote and suppress superconductivity, respectively. To determine which of the two competing effects wins, we study the interplay of Cooper pairing interaction and disorder scattering by means of renormalization group method. We consider three types of disorders, including random mass, random gauge potential, and random chemical potential, and show that the first two suppress superconductivity. In particular, the critical BCS coupling | uc| is increased to certain larger value if the system contains only random mass or random gauge potential, which makes the onset of superconductivity more difficult. In the case of random chemical potential, the effective disorder parameter flows to the strong coupling regime, where the perturbation expansion breaks down and cannot provide a clear answer concerning the fate of superconductivity. When different types of disorder coexist in one system, their strength parameters all flow to strong couplings. In the strong coupling regime, the perturbative renormalization group method becomes invalid, and one needs to employ other methods to treat the disorder effects. We perform a simple gap equation analysis of the impact of random chemical potential on superconductivity by using the Abrikosov-Gorkov diagrammatic approach, and also briefly discuss the possible generalization of this approach.

  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. Photoacoustic signal enhancements from gold nano-colloidal suspensions excited by a pair of time-delayed femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Masim, Frances Camille P.; Hsu, Wei-Hung; Liu, Hao-Li; Yonezawa, Tetsu; Balčytis, Armandas; Juodkazis, Saulius; Hatanaka, Koji

    2017-08-01

    Photoacoustic signal enhancements were observed with a pair of time-delayed femtosecond pulses upon excitation of gold nanosphere colloidal suspension. A systematic experimental investigation of photoacoustic intensity within the delay time, t = 0 to 15 ns, was carried out. The results revealed a significant enhancement factor of ~2 when the pre-pulse energy is 20-30% of the total energy. Pre-pulse and main pulse energy ratios, E(1)p-pol. :E(2)s-pol. were varied to determine the optimal ratio that yields to maximum photoacoustic signal enhancement. This enhancement was ascribed to the initial stage of thermalization and bubble generation in the nanosecond time scale. Pre-pulse scattering intensity measurements and numerical finite-difference time-domain calculations were performed to reveal dynamics and light field enchancement, respectively.

  11. 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.

  12. Theory of Laser-Controlled Competing Superconducting and Charge Orders

    NASA Astrophysics Data System (ADS)

    Sentef, M. A.; Tokuno, A.; Georges, A.; Kollath, C.

    2017-02-01

    We investigate the nonequilibrium dynamics of competing coexisting superconducting (SC) and charge-density wave (CDW) orders in an attractive Hubbard model. A time-periodic laser field A →(t ) lifts the SC-CDW degeneracy, since the CDW couples linearly to the field (A →), whereas SC couples in second order (A→2) due to gauge invariance. This leads to a striking resonance: When the photon energy is red detuned compared to the equilibrium single-particle energy gap, CDW is enhanced and SC is suppressed, while this behavior is reversed for blue detuning. Both orders oscillate with an emergent slow frequency, which is controlled by the small amplitude of a third induced order, namely η pairing, given by the commutator of the two primary orders. The induced η pairing is shown to control the enhancement and suppression of the dominant orders. Finally, we demonstrate that light-induced superconductivity is possible starting from a predominantly CDW initial state.

  13. Acute enhancement of the upper critical field for superconductivity approaching a quantum critical point in URhGe

    NASA Astrophysics Data System (ADS)

    Lévy, F.; Sheikin, I.; Huxley, A.

    2007-07-01

    When a pure material is tuned to the point where a continuous phase-transition line is crossed at zero temperature, known as a quantum critical point (QCP), completely new correlated quantum ordered states can form. These phases include exotic forms of superconductivity. However, as superconductivity is generally suppressed by a magnetic field, the formation of superconductivity ought not to be possible at extremely high field. Here, we report that as we tune the ferromagnet, URhGe, towards a QCP by applying a component of magnetic field in the material's easy magnetic plane, superconductivity survives in progressively higher fields applied simultaneously along the material's magnetic hard axis. Thus, although superconductivity never occurs above a temperature of 0.5K, we find that it can survive in extremely high magnetic fields, exceeding 28T.

  14. Local Quasiparticle Density of States of Superconducting SmFeAsO1-xFx Single Crystals: Evidence for Spin-Mediated Pairing

    NASA Astrophysics Data System (ADS)

    Fasano, Y.; Maggio-Aprile, I.; Zhigadlo, N. D.; Katrych, S.; Karpinski, J.; Fischer, Ø.

    2010-10-01

    We probe the local quasiparticles density of states in micron-sized SmFeAsO1-xFx single crystals by means of scanning tunnelling spectroscopy. Spectral features resemble those of cuprates, particularly a dip-hump-like structure developed at energies larger than the gap that can be ascribed to the coupling of quasiparticles to a collective mode, quite likely a resonant spin mode. The energy of the collective mode revealed in our study decreases when the pairing strength increases. Our findings support spin-fluctuation-mediated pairing in pnictides.

  15. 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.

  16. 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.

  17. 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.

  18. Anharmonic enhancement of superconductivity in metallic molecular Cmca  -  4 hydrogen at high pressure: a first-principles study.

    PubMed

    Borinaga, Miguel; Riego, P; Leonardo, A; Calandra, Matteo; Mauri, Francesco; Bergara, Aitor; Errea, Ion

    2016-12-14

    First-principles calculations based on density-functional theory including anharmonicity within the variational stochastic self-consistent harmonic approximation are applied to understand how the quantum character of the proton affects the candidate metallic molecular Cmca  -  4 structure of hydrogen in the 400-450 GPa pressure range, where metallization of hydrogen is expected to occur. Anharmonic effects, which become crucial due to the zero-point motion, have a large impact on the hydrogen molecules by increasing the intramolecular distance by approximately a 6%. This induces two new electron pockets at the Fermi surface opening new scattering channels for the electron-phonon interaction. Consequently, the electron-phonon coupling constant and the superconducting critical temperature are approximately doubled by anharmonicity and Cmca  -  4 hydrogen becomes a superconductor above 200 K in all the studied pressure range. Contrary to many superconducting hydrides, where anharmoncity tends to lower the superconducting critical temperature, our results show that it can enhance superconductivity in molecular hydrogen.

  19. Anharmonic enhancement of superconductivity in metallic molecular Cmca  -  4 hydrogen at high pressure: a first-principles study

    NASA Astrophysics Data System (ADS)

    Borinaga, Miguel; Riego, P.; Leonardo, A.; Calandra, Matteo; Mauri, Francesco; Bergara, Aitor; Errea, Ion

    2016-12-01

    First-principles calculations based on density-functional theory including anharmonicity within the variational stochastic self-consistent harmonic approximation are applied to understand how the quantum character of the proton affects the candidate metallic molecular Cmca  -  4 structure of hydrogen in the 400-450 GPa pressure range, where metallization of hydrogen is expected to occur. Anharmonic effects, which become crucial due to the zero-point motion, have a large impact on the hydrogen molecules by increasing the intramolecular distance by approximately a 6%. This induces two new electron pockets at the Fermi surface opening new scattering channels for the electron-phonon interaction. Consequently, the electron-phonon coupling constant and the superconducting critical temperature are approximately doubled by anharmonicity and Cmca  -  4 hydrogen becomes a superconductor above 200 K in all the studied pressure range. Contrary to many superconducting hydrides, where anharmoncity tends to lower the superconducting critical temperature, our results show that it can enhance superconductivity in molecular hydrogen.

  20. Odd-Frequency Superconductivity in Sr2RuO4 Measured by Kerr Rotation

    NASA Astrophysics Data System (ADS)

    Komendová, L.; Black-Schaffer, A. M.

    2017-08-01

    We establish the existence of bulk odd-frequency superconductivity in Sr2RuO4 and show that an intrinsic Kerr effect is direct evidence of this state. We use both general two- and three-orbital models, as well as a realistic tight-binding description of Sr2RuO4 to demonstrate that odd-frequency pairing arises due to finite hybridization between different orbitals in the normal state, and is further enhanced by finite interorbital pairing.

  1. 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.

  2. 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

  3. 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

  4. Enhanced trapped field achieved in a superconducting bulk using high thermal conductivity structures following simulated pulsed field magnetization

    NASA Astrophysics Data System (ADS)

    Patel, A.; Glowacki, B. A.

    2012-12-01

    Rapid heat generation is one of the biggest problems faced in carrying out pulsed field magnetization of (RE)BCO superconducting bulks compared to other methods of magnetization. The effects of various thermal conductivities in the ab-plane (kab) and along the c-axis (kc) of a bulk on its trapped field performance following pulsed field magnetization were modelled. The E-J power law was used, coupled with the heat generation, to simulate the effect of anisotropic thermal conductivity combinations on the peak trapped field and total trapped flux. A thermally isolated bulk is not affected so strongly by thermal conductivity, but on cooling the bulk conductively from its base using a cold head, increasing kc significantly enhances both the trapped field and the flux. Embedding highly thermally conducting copper structures in the bulk material was investigated as a practical way to locally increase kab and kc. The structures investigated increased the trapped field and flux by a maximum of around 30% without increasing the size of the bulk. Different structures can be used depending on whether an application requires the highest trapped field or highest total flux.

  5. Fully gapped superconductivity in a nanometre-size YBa2Cu3O(7-δ) island enhanced by a magnetic field.

    PubMed

    Gustafsson, D; Golubev, D; Fogelström, M; Claeson, T; Kubatkin, S; Bauch, T; Lombardi, F

    2013-01-01

    The symmetry of Cooper pairs is central to constructing a superconducting state. The demonstration of a d(x²-y²)-wave order parameter with nodes represented a breakthrough for high critical temperature superconductors (HTSs). However, despite this fundamental discovery, the origin of superconductivity remains elusive, raising the question of whether something is missing from the global picture. Deviations from d(x²-y²)-wave symmetry, such as an imaginary admixture d(x²-y²)+ is (or id(xy)), predict a ground state with unconventional properties exhibiting a full superconducting gap and time reversal symmetry breaking. The existence of such a state, until now highly controversial, can be proved by highly sensitive measurements of the excitation spectrum. Here, we present a spectroscopic technique based on an HTS nanoscale device that allows an unprecedented energy resolution thanks to Coulomb blockade effects, a regime practically inaccessible in these materials previously. We find that the energy required to add an extra electron depends on the parity (odd/even) of the excess electrons on the island and increases with magnetic field. This is inconsistent with a pure d(x²-y²)-wave symmetry and demonstrates a complex order parameter component that needs to be incorporated into any theoretical model of HTS.

  6. Laser drilling: enhancing superconducting joint of GdBa2Cu3O7 - δ coated conductors

    NASA Astrophysics Data System (ADS)

    Park, Y. J.; Lee, M. W.; Oh, Y. K.; Lee, H. G.

    2014-08-01

    While GdBa2Cu3O7 - δ (GdBCO) coated conductors (CCs) have been proposed for superconducting applications, they have not been used in devices with persistent current mode (PCM) operation because of a lack of joining techniques. A superconducting joint of CCs, formed via melting diffusion and oxygenation annealing, offers no electrical resistance between the CCs, thus establishing a superconducting closed loop for PCM operation. Because superconductivity degrades with oxygen out-diffusion during melting diffusion, oxygenation annealing allows oxygen diffusion into the GdBCO lattices. As effective oxygenation annealing requires oxygen pathways in the joint, low solubility and diffusivity of oxygen in the buffer and CC substrate hinder full superconductivity recovery. Here we show a laser-drilling technique to produce microholes as conduits on the surfaces of GdBCO CCs’ to promote oxygen in-diffusion, which resulted in reduced superconductivity recovery time. Superconductivity was fully recovered after laser drilling, melting diffusion at 850 °C for 1 min, and oxygenation annealing at 500 °C for 350 h.

  7. Long Pulse Enhanced Confinement Discharges in the HT-7 Superconducting Tokamak by IBW Heating and LH Wave Current Drive

    NASA Astrophysics Data System (ADS)

    Li, Jiangang

    2002-11-01

    Significant progress has been made on the HT-7 superconducting tokamak in the past year toward obtaining advanced operating modes in steady state. By combining IBW and LHCD, ELM-free limiter H-mode discharges with H_89 2, β _N*H_89 > 3 have been obtained that lasted for 53% τE . A well boronized wall prevented the further impurity accumulation and the large pumping kept the recycling at a very low level. The density kept almost constant with the feedback control. The non-inductive driven current fraction is about 60% and bootstrap fraction is about 18%. The central electron temperature is about 2.6 keV and density above 2 X 10^19 m-3. With reduced plasma parameters of central Te 1.5 keV and n_e0 2 X 10^19 m-3, H_89 1.45, βN 1.1, the improved confinement phase lasts for more than 100τE with the non-inductive driven current fraction 70%. Several technical improvements, especially suitable for teady-state operation, have been made to get these long pulse, enhanced confinement discharges. The new GBST1308 doped graphite coated with a 100 μ m functional gradient coating of SiC film was used as limiter material. The tiles can withstand 5 MW/m^2 heat loads for 30 seconds with water-cooling. Twenty-four pieces of a ferromagnetic material -- ferritic steel -- have been installed to reduce the ripple at the limiter radius from 4% to less than 1.6%. Two large cry-pumps were installed to control particle exhaust. New RF wall coating techniques suitable for superconducting operation, such as RF boronization, siliconization and long-life Li coating, have been developed and routinely used in the HT-7 tokamak. This contributes to the significant reduction of the impurity radiation and edge recycling. Edge turbulence measured by Langmuir probes has been suppressed either by IBW or by LHCD for a low recycling and boronized wall. The edge electric field shear has been modified by IBW and LHCD. Transport analysis of sawtooth heat pulse propagation shows very low electron heat

  8. Superconducting fluctuations and {sup 63}Cu NQR-NMR relaxation in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}: Effect of magnetic field and a test for the pairing-state symmetry

    SciTech Connect

    Carretta, P.; Livanov, D.V.; Rigamonti, A.; Varlamov, A.A. |

    1996-10-01

    Evidence is presented of superconducting fluctuations in the {sup 63}Cu NQR-NMR relaxation rate in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, as obtained from a careful comparison of measurements carried out in the absence and in the presence of a field parallel to the {ital c} axis. It is shown that the field causes a reduction of the relaxation rate {ital W} in a range of about 10 K above {ital T}{sub {ital c}}. This effect is related to the suppression by the magnetic field of the phase-sensitive positive Maki-Thompson contribution while the negative contribution from the DOS fluctuations is almost field independent. Furthermore, it is argued how the fluctuation effects on {ital W} can be used to discuss the pairing state symmetry, at variance with the insensitivity of the transport measurements. It is pointed out that the existence of the Maki-Thompson contribution to {ital W} evidences an {ital s}-wave symmetry component for the pairing in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. {copyright} {ital 1996 The American Physical Society.}

  9. Genome-wide assessment of sequence-intrinsic enhancer responsiveness at single-base-pair resolution.

    PubMed

    Arnold, Cosmas D; Zabidi, Muhammad A; Pagani, Michaela; Rath, Martina; Schernhuber, Katharina; Kazmar, Tomáš; Stark, Alexander

    2017-02-01

    Gene expression is controlled by enhancers that activate transcription from the core promoters of their target genes. Although a key function of core promoters is to convert enhancer activities into gene transcription, whether and how strongly they activate transcription in response to enhancers has not been systematically assessed on a genome-wide level. Here we describe self-transcribing active core promoter sequencing (STAP-seq), a method to determine the responsiveness of genomic sequences to enhancers, and apply it to the Drosophila melanogaster genome. We cloned candidate fragments at the position of the core promoter (also called minimal promoter) in reporter plasmids with or without a strong enhancer, transfected the resulting library into cells, and quantified the transcripts that initiated from each candidate for each setup by deep sequencing. In the presence of a single strong enhancer, the enhancer responsiveness of different sequences differs by several orders of magnitude, and different levels of responsiveness are associated with genes of different functions. We also identify sequence features that predict enhancer responsiveness and discuss how different core promoters are employed for the regulation of gene expression.

  10. Enhancement of electron-positron pair creation due to transient excitation of field-induced bound states

    NASA Astrophysics Data System (ADS)

    Jiang, M.; Lv, Q. Z.; Sheng, Z. M.; Grobe, R.; Su, Q.

    2013-04-01

    We study the creation of electron-positron pairs induced by two spatially separated electric fields that vary periodically in time. The results are based on large-scale computer simulations of the time-dependent Dirac equation in reduced spatial dimensions. When the separation of the fields is very large, the pair creation is caused by multiphoton transitions and mainly determined by the frequency of the fields. However, for small spatial separations a coherence effect can be observed that can enhance or reduce the particle yield compared to the case of two infinitely separated fields. If the travel time for a created electron or positron between both field locations becomes comparable to the period of the oscillating fields, we observe peaks in the energy spectrum which can be explained in terms of field-induced transient bound states.

  11. Method for producing microstructured templates and their use in providing pinning enhancements in superconducting films deposited thereon

    DOEpatents

    Aytug, Tolga; Paranthaman, Mariappan Parans; Polat, Ozgur

    2013-07-16

    The present invention relates to a method for producing a phase-separated layer useful as a flux pinning substrate for a superconducting film, wherein the method includes subjecting at least a first and a second target material to a sputtering deposition technique in order that a phase-separated layer is deposited epitaxially on a primary substrate containing an ordered surface layer. The invention is also directed to a method for producing a superconducting tape containing pinning defects therein by depositing a superconducting film on a phase-separated layer produced by the method described above.

  12. 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

  13. Effect of Fibonacci modulation on superconductivity.

    PubMed

    Gupta, Sanjay; Sil, Shreekantha; Bhattacharyya, Bibhas

    2006-02-15

    We have studied finite-sized single band models with short-range pairing interactions between electrons in the presence of diagonal Fibonacci modulation in one dimension. Two models, namely the attractive Hubbard model and the Penson-Kolb model, have been investigated at half-filling at zero temperature by solving the Bogoliubov-de Gennes equations in real space within a mean-field approximation. The competition between 'disorder' and the pairing interaction leads to a suppression of superconductivity (of usual pairs with zero centre-of-mass momenta) in the strong-coupling limit while an enhancement of the pairing correlation is observed in the weak-coupling regime for both models. However, the dissimilarity of the pairing mechanisms in these two models brings about notable differences in the results. The extent to which the bond-ordered wave and the η-paired (of pairs with centre-of-mass momenta = π) phases of the Penson-Kolb model are affected by the disorder has also been studied in the present calculation. Some finite size effects are also identified.

  14. Huge enhancement of superconductivity in the collapsed tetragonal KFe2As2

    NASA Astrophysics Data System (ADS)

    Ying, Jianjun; Tang, Ling-Yun; Mao, Ho-Kwang; Struzhkin, Viktor; Wang, Ai-Feng; Chen, Xian-Hui; Chen, Xiao-Jia

    2015-03-01

    Recent work on hole-overdoped iron pnictide KFe2As2 indicated a paring symmetry change at pressure of around 1.7 GPa. The investigation for the low-pressure region (below 7 GPa) revealed oscillation of Tc with pressure. Here we report results of high-pressure transport and XRD measurements on KFe2As2 single crystals at high pressures up to 30 GPa. We map out the phase diagram of KFe2As2 and find a huge enhancement of Tc in the collapsed tetragonal phase. The correlation between Tc, electronic and crystal structures is discussed. The strong electronic correlations are proposed to account for such an unexpected Tc enhancement in KFe2As2.

  15. Higgs pair signal enhanced in the 2HDM with two degenerate 125 GeV Higgs bosons

    NASA Astrophysics Data System (ADS)

    Han, Xiao-Fang; Wang, Lei; Yang, Jin Min

    2016-09-01

    We discuss a scenario of the type-II two-Higgs-doublet model (2HDM) in which the bb¯γγ rate of the Higgs pair production is enhanced due to the two nearly degenerate 125 GeV Higgs bosons (h, H). Considering various theoretical and experimental constraints, we figure out the allowed ranges of the trilinear couplings of these two Higgs bosons and calculate the signal rate of bb¯γγ from the productions of Higgs pairs (hh, hH, HH) at the large hadron collider (LHC). We find that in the allowed parameter space some trilinear Higgs couplings can be larger than the Standard Model (SM) value by an order and the production rate of bb¯γγ can be greatly enhanced. We also consider a “decoupling” benchmark point where the light CP-even Higgs has a SM-like cubic self-coupling while other trilinear couplings are very small. With a detailed simulation on the bb¯γγ signal and backgrounds, we find that in such a “decoupling” scenario the hh and hH channels can jointly enhance the statistical significance to 5σ at 14 TeV LHC with an integrated luminosity of 3000 fb-1.

  16. Superconductive wire

    SciTech Connect

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

    1992-12-31

    This invention is comprised of a superconductive article including a first metallic tube having an interior surface and an exterior surface, said interior surface defining an interior hollow cavity, a layer of superconductive material surrounding said exterior surface of said first metallic tube, and, a second metallic tube having an interior surface and an exterior surface, said interior surface adjacent to said layer of superconductive material is provided together with processes of making such a superconductive article including, e.g., 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 and/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.

  17. Enhanced Superconductivity in Close Proximity to the Structural Phase Transition of Sr1-xBaxNi2P2

    NASA Astrophysics Data System (ADS)

    Kudo, Kazutaka; Kitahama, Yutaka; Iba, Keita; Takasuga, Masaya; Nohara, Minoru

    2017-03-01

    The structural evolution and superconductivity of a 122-type solid solution Sr1-xBaxNi2P2 were studied. We found that an orthorhombic-tetragonal structural phase transition takes place at x = 0.5, and is characterized by the P-P dimers breaking. The superconducting transition temperature exhibited its highest value of 2.85 K at x = 0.4.

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

    PubMed

    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(+), Ba(2+)) or PbO- or perovskite-type oxide layers, and also in Fe(1.01)Se (ref. 8) with neutral layers similar in structure to those found in the iron arsenides and no spacer layer. Here we demonstrate the synthesis of Li(x)(NH(2))(y)(NH(3))(1-y)Fe(2)Se(2) (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.

  19. Anisotropic superconductivity driven by kinematic interaction

    NASA Astrophysics Data System (ADS)

    Ivanov, V. A.

    2000-11-01

    We have analysed the effect of kinematic pairing on the symmetry of superconducting order parameter for a square lattice in the frame of the strongly correlated Hubbard model. It is argued that in the first perturbation order the kinematic interaction renormalizes the Hubbard-I dispersions and provides at low doping the mixed singlet (s + s*)-wave superconductivity, giving way at higher doping to the triplet p-wave superconductivity. The obtained phase diagram depends only on the hopping integral parameter. The influence of the Coulomb repulsion on the kinematic superconducting pairing has been estimated. The (s + s*)-wave gap and the thermodynamic critical magnetic field have been derived.

  20. 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.

  1. Suppression of proximity effect and the enhancement of p-wave superconductivity in the Sr2RuO4-Ru system.

    PubMed

    Ying, Y A; Xin, Y; Clouser, B W; Hao, E; Staley, N E; Myers, R J; Allard, L F; Fobes, D; Liu, T; Mao, Z Q; Liu, Y

    2009-12-11

    We report unexpected phenomena observed on the Sr2RuO4-Ru eutectic phase featuring Ru islands embedded in a bulk crystal of the chiral p-wave superconductor Sr2RuO4. It was found that the Sr2RuO4/Ru interface is atomically sharp, terminated uniformly by a Sr/O layer. Surprisingly, the proximity-induced p-wave superconducting energy gap predicted by theory was not detected inside Ru islands. Our results suggest that the previously observed enhancement of superconductivity in this eutectic phase occurs away from rather than near the Sr2RuO4/Ru interface, where dislocations and phonon hardening were found.

  2. 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.

  3. 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.

  4. Intranucleus accumbens amphetamine infusions enhance responding maintained by a stimulus complex paired with oral ethanol self-administration.

    PubMed

    Slawecki, C J; Samson, H H; Chappell, A

    1997-12-01

    Six male Long-Evans rats were trained to self-administer 10% ethanol (v/v) during 30 min operant sessions. A licking response on an empty drinking tube resulted in the presentation of reinforcement from an automatic dipper. During the initiation of ethanol self-administration, a tone-light stimulus complex was paired with all ethanol presentations. When 10% ethanol maintained responding, guide cannulae aimed at the nucleus accumbens (NAcc) were implanted into the brain. The ability of the paired stimulus complex to reinforce a new operant response (i.e., a lever press) was then examined. To test for the development of the new response, responding on one lever resulted in presentation of only the paired tone-light stimulus complex (contingency-associated lever) while responding on an alternate lever had no programmed consequences (no contingency-associated lever). Prior to some new response sessions, amphetamine (5-20 microg/microl) was infused into the NAcc to examine the influence of dopamine on responding maintained by the stimulus complex. Ethanol intake during the sessions prior to new response testing averaged 0.49 +/- 0.07 g/g. During new response sessions no significant differences in lever pressure during no-drug conditions (control, sham, injection or vehicle injection) were observed between the contingency-associated and no contingency-associated levers. Intra-NAcc infusion of amphetamine (5-20 microg/microl) resulted in significant increases in lever pressing only on the contingency-associated lever. These data suggest that increasing NAcc dopamine levels with amphetamine enhanced the ability of the stimulus complex to function as a reinforcer. Further studies examining the ability of potentially more salient stimuli (i.e., taste of ethanol) to function as conditioned reinforcers associated with ethanol self-administration are warranted due to the apparent inability of the paired tone-light stimulus complex to function as a reinforcer without amphetamine

  5. 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.

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

    DOE PAGES

    Tarantini, C.; Sung, Z. -H.; Lee, P. J.; ...

    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

  7. 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.

  8. 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.

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

    PubMed Central

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

    2017-01-01

    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 hyper-stable 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. PMID:27071357

  10. Acute exercise enhances the response to paired associative stimulation-induced plasticity in the primary motor cortex.

    PubMed

    Singh, Amaya M; Neva, Jason L; Staines, W Richard

    2014-11-01

    There is evidence that a single session of aerobic exercise can modulate intracortical inhibition. While decreases in inhibition appear to be a necessary precursor to the induction of long-term potentiation (LTP)-like plasticity, it is not known whether aerobic exercise can enhance the response to LTP induction. We investigated whether the addition of a preceding bout of exercise would modulate the response to paired associative stimulation (PAS) of the upper limb. It was hypothesized that exercise would enhance motor cortical (M1) excitability following PAS compared to a session of PAS alone. Ten healthy individuals underwent a control session involving PAS alone and an exercise session where PAS was preceded by 20 min of moderate-intensity stationary biking. PAS involved 180 pairs of stimuli (right median nerve, left M1) delivered at 0.1 Hz to the right abductor pollicis brevis representation. Excitability changes were measured by the area under a stimulus-response curve, and intracortical circuits were probed by testing short-interval intracortical inhibition (SICI), long-interval intracortical inhibition and intracortical facilitation. Two-way ANOVAs were conducted to compare excitability changes between sessions. PAS-induced increases in M1 excitability were enhanced in the exercise session (p < 0.026). In addition, SICI was differentially modulated between the two sessions, with greater decreases in SICI observed immediately after PAS when it was preceded by the exercise session (p < 0.03). Aerobic exercise enhances the effectiveness of PAS and may be a useful adjunct to traditional therapies and interventions that aim to promote neuroplasticity in cortical networks.

  11. Electronic pairing in exotic superconductors

    SciTech Connect

    Cox, D.L. ); Maple, M.B. )

    1995-02-01

    Superconductivity in heavy-fermion materials and high T[sub c] cuprates may involve electronic pairing with unconventional symmetries and mechanisms. Although there has been no smoking-gun proof, numerous pieces of circumstantial evidence combined with heuristic theoretical arguments make a compelling case that these materials have pairs with exotic symmetry bound by nonphonon glue. 20 refs., 5 figs.

  12. Transition-Metal Oxide Superconductivity

    DTIC Science & Technology

    1988-04-20

    pyramidally coordinated complexes of the 02"- deficient compounds, and (iii) that ordering of the sources that produce the mixed-valence Cu2+ɛ+) ions in...With the strong antiferromagnetic exchange coupling of the Fe2+(3+) pairs in ferrites , no superconducting cells should be anticipated and only normal...I couplings dictate significant antiferromagnetic ordering and little chance of superconductivity. This group includes the common ferrite conduction

  13. Ionization enhancement and suppression by phase-locked ultrafast pulse pairs

    NASA Astrophysics Data System (ADS)

    Foote, David B.; Lin, Y.; Pi, Liang-Wen; Djiokap, J. M. Ngoko; Starace, Anthony F.; Hill, W. T.

    2017-08-01

    We present the results of a study of ionization of Xe atoms by a pair of phase-locked pulses, which is characterized by interference produced by the twin peaks. Two types of interference are considered: ordinary optical interference, which changes the intensity of the composite pulse and thus the ion yield, and a quantum interference, in which the excited electron wave packets interfere. We use the measured Xe+ yield as a function of the temporal delay and/or relative phase between the peaks to monitor the interferences and compare their relative strengths. We model the interference with a pulse intensity function and by calculating the ionization yield with the time-dependent Schrödinger equation. Our results provide insight into optimal control pulses generated with learning algorithms. The results also show that the relative phase between peaks of a control pulse, along with small features such as distortions and imperfections in the wings of an ideal shape, play a significant role in the control process.

  14. Superconducting Cable

    SciTech Connect

    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.

  15. 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.

  16. 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

  17. Itinerant ferromagnetism and p +i p' superconductivity in doped bilayer silicene

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    We study the electronic instabilities of doped bilayer silicene using the random phase approximation. In contrast to the singlet d +i d' superconductivity at the low doping region, we find that the system is an itinerant ferromagnet in the narrow doping regions around the Van Hove singularities, and a triplet p +i p' superconductor in the vicinity of these regions. Adding a weak Kane-Mele spin-orbit coupling to the system further singles out the time-reversal invariant equal-spin helical p +i p' pairing as the leading instability. The triplet pairing identified here is driven by the ferromagnetic fluctuations, which become strong and enhance the superconducting critical temperature remarkably near the phase boundaries between ferromagnetism and superconductivity.

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

    SciTech Connect

    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 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. Finally, this proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra.

  19. Underdoped superconducting cuprates as topological superconductors

    NASA Astrophysics Data System (ADS)

    Lu, Yuan-Ming; Xiang, Tao; Lee, Dung-Hai

    2014-09-01

    Superconductivity in copper oxide (cuprate) high-transition-temperature superconductors follows from the chemical doping of an antiferromagnetic insulating state. The consensus that the wavefunction of the superconducting carrier, the Cooper pair, has dx2-y2 symmetry has long been reached. This pairing symmetry implies the existence of nodes in the superconducting energy gap. Recently, a series of angle-resolved photoemission spectroscopy experiments have revealed that deeply underdoped cuprates exhibit a particle-hole symmetric superconducting-like energy gap at the momentum-space locations where the dx2-y2 gap nodes are expected. Here we discuss the possibility that this phenomenon is caused by a fully gapped topological superconducting state that coexists with the antiferromagnetic order. If experimentally confirmed, this result will completely change our view of how exactly the high-temperature superconductivity state evolves from the insulating antiferromagnet.

  20. Evidence for superconductivity in Li-decorated monolayer graphene.

    PubMed

    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

    2015-09-22

    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.

  1. 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.

  2. 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.

  3. Biological agent identification by nucleic acid base-pair analysis using surface-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Farquharson, Stuart; Smith, Wayne W.; Elliott, Susan; Sperry, Jay F.

    1999-01-01

    Recently, a number of analytical methods have been successfully developed which use nucleic acid sequencing to identify biological warfare agents. However, the effectiveness of these methods, towards the safety and protection of US Armed Forces and their allies are limited by the period required to enumerate the nucleic acid through polymerase chain reactions or culture growth to produce sufficient quantities for analysis. To overcome this limitation, we have been investigating the ability of surface-enhanced Raman spectroscopy to detect nucleic acids with sufficient sensitivity and selectivity to eliminate the need for enumeration. The design of a small volume electrolytic sample cell will be presented along with analysis of the nucleic acid bases and preliminary analysis of model bacteria.

  4. 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.

  5. 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.

  6. 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.

  7. 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

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

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

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

  9. Production of degenerate polarization entangled photon pairs in the telecom-band from a pump enhanced parametric downconversion process.

    PubMed

    Thomas, P J; Chunnilall, C J; Stothard, D J M; Walsh, D A; Dunn, M H

    2010-12-06

    The design and implementation of a novel source of degenerate polarization entangled photon pairs in the telecom band, based on a cavity enhanced parametric downconversion process, is presented. Two of the four maximally entangled Bell states are produced; the remaining two are obtainable by the addition of a half wave plate into the setup. The coincident photon detection rate in the A/D basis between two detectors at the output of the device revealed the production of highly entangled states, resulting in quantum interference visibilities of 0.971 ± 0.041 (ϕ = 0 state) and 0.932 ± 0.036 (ϕ = π state) respectively. The entangled states were found to break the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality by around 6 standard deviations. From the measured coincidence counting rates and the optical system losses, an entangled photon pair production rate of 8.9 × 10(4) s(-1) mW(-1) pump was estimated.

  10. Triplet p + ip pairing correlations in the doped Kane-Mele-Hubbard model: A quantum Monte Carlo study

    DOE PAGES

    Ma, Tianxing; Lin, Hai-Qing; Gubernatis, James E.

    2015-09-01

    By using the constrained-phase quantum Monte Carlo method, we performed a systematic study of the pairing correlations in the ground state of the doped Kane-Mele-Hubbard model on a honeycomb lattice. We find that pairing correlations with d + id symmetry dominate close to half filling, but pairing correlations with p+ip symmetry dominate as hole doping moves the system below three-quarters filling. We correlate these behaviors of the pairing correlations with the topology of the Fermi surfaces of the non-interacting problem. We also find that the effective pairing correlation is enhanced greatly as the interaction increases, and these superconducting correlations aremore » robust against varying the spin-orbit coupling strength. Finally, our numerical results suggest a possible way to realize spin triplet superconductivity in doped honeycomb-like materials or ultracold atoms in optical traps.« less

  11. 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.

  12. 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.

  13. Cooper Pairs in Insulators?!

    ScienceCinema

    James Valles

    2016-07-12

    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. 

  14. Six distinct nuclear factors interact with the 75-base-pair repeat of the Moloney murine leukemia virus enhancer.

    PubMed Central

    Speck, N A; Baltimore, D

    1987-01-01

    Binding sites for six distinct nuclear factors on the 75-base-pair repeat of the Moloney murine leukemia virus enhancer have been identified by an electrophoretic mobility shift assay combined with methylation interference. Three of these factors, found in WEHI 231 nuclear extracts, which we have named LVa, LVb, and LVc (for leukemia virus factors a, b, and c) have not been previously identified. Nuclear factors that bind to the conserved simian virus 40 corelike motif, the NF-1 motif, and the glucocorticoid response element were also detected. Testing of multiple cell lines showed that most factors appeared ubiquitous, except that the NF-1 binding factor was found neither in nuclear extracts from MEL cells nor in the embryonal carcinoma cell lines PCC4 and F9, and core-binding factor was relatively depleted from MEL and F9 nuclear extracts. Images PMID:3561410

  15. Evidence of dynamic pentagon-heptagon pairs in single-wall carbon nanotubes using surface-enhanced Raman scattering.

    PubMed

    Fujimori, Toshihiko; Urita, Koki; Ohba, Tomonori; Kanoh, Hirofumi; Kaneko, Katsumi

    2010-05-19

    Surface-enhanced Raman scattering (SERS) was applied to detecting pentagon-heptagon pairs, the so-called Stone-Wales defect, in single-wall carbon nanotubes (SWCNTs). When a probing laser light was scanned over a SWCNT-dispersed silver surface, two distinct SERS spectra were obtained: (1) temporally stable spectra similar to that of resonance Raman spectra of bulk SWCNTs and (2) temporally fluctuating spectra with additional peaks which were not observed in the non-SERS spectra. The fluctuations in the SERS spectra are discussed in association with dynamic reconstruction of defective structures of SWCNTs (nonhexagonal arrangements of carbon atoms) in the vicinity of SERS-active sites under irradiation of the laser light.

  16. 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

  17. 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.

  18. Superconducting devices

    SciTech Connect

    Ruggiero, S.T. . Dept. of Physics); Rudman, D.A. . Dept. of Materials Science and Engineering)

    1990-01-01

    This book presents a discussion of the theory, fabrication, and qualification of superconducting device elements and integrated circuitry. A look at issues key to the development of practical superconducting devices and systems is presented. Integrated systems, including the fabrication and application of SQUIDs, Josephson arrays, microwave detectors, digital signal processors and computers, and analog signal processors are discussed.

  19. Superconducting Materials

    NASA Technical Reports Server (NTRS)

    1995-01-01

    After working with Lewis Research Center and Jet Propulsion Laboratory, Superconducting Technologies, Inc. (STI) adapted NASA requirements and refined its own standard production recipe. STI uses high temperature superconducting (HTS) materials in its basic products: high quality thin films, circuits and components. Applications include microwave circuits for radar to reduce interference.

  20. 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.

  1. 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.

  2. Global and local superconductivity in boron-doped granular diamond.

    PubMed

    Zhang, Gufei; Turner, Stuart; Ekimov, Evgeny A; Vanacken, Johan; Timmermans, Matias; Samuely, Tomás; Sidorov, Vladimir A; Stishov, Sergei M; Lu, Yinggang; Deloof, Bart; Goderis, Bart; Van Tendeloo, Gustaaf; Van de Vondel, Joris; Moshchalkov, Victor V

    2014-04-02

    Strong granularity-correlated and intragrain modulations of the superconducting order parameter are demonstrated in heavily boron-doped diamond situated not yet in the vicinity of the metal-insulator transition. These modulations at the superconducting state (SC) and at the global normal state (NS) above the resistive superconducting transition, reveal that local Cooper pairing sets in prior to the global phase coherence.

  3. 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.

  4. Superconductivity in Opal-based superconducting nanocomposites

    NASA Astrophysics Data System (ADS)

    Lee, M. K.; Charnaya, E. V.; Chang, L. J.; Kumzerov, Yu. A.; Lin, M. F.

    2015-03-01

    In this study, we investigate superconducting nanocomposites (SCNCs) to elucidate superconductivity in nanostructured type I superconductor. In, Sn and Hg are loaded into opal matrices by high pressure up to 10kbar, in which introducing superconducting metals into templates preserves their own 3D nanostructures. The opal matrices is adopted because it is a well-developed nanoconfinement and widely used in the studies of photonic crystal due to its periodically-superlatticed nanoporous structure. The SCNCs are then measured by Quantum Design MPMS 3 under different external magnetic fields reveal the field dependences of Tc and irreversibility temperature (Tirr). Next, AC susceptibility measurements of SCNCs determine grain coupling, vortex dynamics and field dependence of activation barrier (Ua) as well as Tc. Additionally, the phase diagrams of these SCNCs are analyzed to study superconductivity for a system with similar nanogeometry. Exotic phase diagrams in the opal SCNC studies reveal an enhanced upper critical field (Hc2 (0)) and curvature crossover of upper critical field line. Additionally, according to the field dependence of Ua(H), curvature crossover of the upper critical field line can occur, owing to vortex phase transition.

  5. Junctionless Cooper pair transistor

    NASA Astrophysics Data System (ADS)

    Arutyunov, K. Yu.; Lehtinen, J. S.

    2017-02-01

    Quantum phase slip (QPS) is the topological singularity of the complex order parameter of a quasi-one-dimensional superconductor: momentary zeroing of the modulus and simultaneous 'slip' of the phase by ±2π. The QPS event(s) are the dynamic equivalent of tunneling through a conventional Josephson junction containing static in space and time weak link(s). Here we demonstrate the operation of a superconducting single electron transistor (Cooper pair transistor) without any tunnel junctions. Instead a pair of thin superconducting titanium wires in QPS regime was used. The current-voltage characteristics demonstrate the clear Coulomb blockade with magnitude of the Coulomb gap modulated by the gate potential. The Coulomb blockade disappears above the critical temperature, and at low temperatures can be suppressed by strong magnetic field.

  6. Mechanism of Collaborative Enhancement of Binding of Paired Antibodies to Distinct Epitopes of Platelet Endothelial Cell Adhesion Molecule-1

    PubMed Central

    Greineder, Colin F.; Villa, Carlos H.; Hood, Elizabeth D.; Shuvaev, Vladimir V.; Sun, Jing; Chacko, Ann-Marie; Abraham, Valsamma; DeLisser, Horace M.; Muzykantov, Vladimir R.

    2017-01-01

    Monoclonal antibodies (mAbs) directed to extracellular epitopes of human and mouse Platelet Endothelial Cell Adhesion Molecule-1 (CD31 or PECAM-1) stimulate binding of other mAbs to distinct adjacent PECAM-1 epitopes. This effect, dubbed Collaborative Enhancement of Paired Affinity Ligands, or CEPAL, has been shown to enhance delivery of mAb-targeted drugs and nanoparticles to the vascular endothelium. Here we report new insights into the mechanism underlying this effect, which demonstrates equivalent amplitude in the following models: i) cells expressing a full length PECAM-1 and mutant form of PECAM-1 unable to form homodimers; ii) isolated fractions of cellular membranes; and, iii) immobilized recombinant PECAM-1. These results indicate that CEPAL is mediated not by interference in cellular functions or homophilic PECAM-1 interactions, but rather by conformational changes within the cell adhesion molecule induced by ligand binding. This mechanism, mediated by exposure of partially occult epitopes, is likely to occur in molecules other than PECAM-1 and may represent a generalizable phenomenon with valuable practical applications. PMID:28085903

  7. Mechanism of Collaborative Enhancement of Binding of Paired Antibodies to Distinct Epitopes of Platelet Endothelial Cell Adhesion Molecule-1.

    PubMed

    Kiseleva, Raisa; Greineder, Colin F; Villa, Carlos H; Hood, Elizabeth D; Shuvaev, Vladimir V; Sun, Jing; Chacko, Ann-Marie; Abraham, Valsamma; DeLisser, Horace M; Muzykantov, Vladimir R

    2017-01-01

    Monoclonal antibodies (mAbs) directed to extracellular epitopes of human and mouse Platelet Endothelial Cell Adhesion Molecule-1 (CD31 or PECAM-1) stimulate binding of other mAbs to distinct adjacent PECAM-1 epitopes. This effect, dubbed Collaborative Enhancement of Paired Affinity Ligands, or CEPAL, has been shown to enhance delivery of mAb-targeted drugs and nanoparticles to the vascular endothelium. Here we report new insights into the mechanism underlying this effect, which demonstrates equivalent amplitude in the following models: i) cells expressing a full length PECAM-1 and mutant form of PECAM-1 unable to form homodimers; ii) isolated fractions of cellular membranes; and, iii) immobilized recombinant PECAM-1. These results indicate that CEPAL is mediated not by interference in cellular functions or homophilic PECAM-1 interactions, but rather by conformational changes within the cell adhesion molecule induced by ligand binding. This mechanism, mediated by exposure of partially occult epitopes, is likely to occur in molecules other than PECAM-1 and may represent a generalizable phenomenon with valuable practical applications.

  8. 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

  9. Superconducting electronics

    NASA Astrophysics Data System (ADS)

    Gubankov, V. N.

    The current status and principal trends, recent achievements, and future prospects of superconducting electronics are reviewed. In particular, attention is given to developments in high-temperature superconductivity; contribution of high-temperature superconductors to superconducting electronics; problems associated with high-temperature superconductor devices and recent achievements in this area; and goals in the field of electronics employing high-temperature superconductor components in comparison with the use of traditional superconductors. Applications discussed include ultrasensitive detection of weak electromagnetic radiation, SQUID-based magnetometry; cryogenic logic and memory systems, and measuring instruments.

  10. 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.

  11. Superconductivity in a chiral nanotube

    NASA Astrophysics Data System (ADS)

    Qin, F.; Shi, W.; Ideue, T.; Yoshida, M.; Zak, A.; Tenne, R.; Kikitsu, T.; Inoue, D.; Hashizume, D.; Iwasa, Y.

    2017-02-01

    Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity--unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

  12. Superconductivity in a chiral nanotube.

    PubMed

    Qin, F; Shi, W; Ideue, T; Yoshida, M; Zak, A; Tenne, R; Kikitsu, T; Inoue, D; Hashizume, D; Iwasa, Y

    2017-02-16

    Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity-unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

  13. Correlation of Fe-Based Superconductivity and Electron-Phonon Coupling in an FeAs /Oxide Heterostructure

    NASA Astrophysics Data System (ADS)

    Choi, Seokhwan; Johnston, Steven; Jang, Won-Jun; Koepernik, Klaus; Nakatsukasa, Ken; Ok, Jong Mok; Lee, Hyun-Jung; Choi, Hyun Woo; Lee, Alex Taekyung; Akbari, Alireza; Semertzidis, Yannis K.; Bang, Yunkyu; Kim, Jun Sung; Lee, Jhinhwan

    2017-09-01

    Interfacial phonons between iron-based superconductors (FeSCs) and perovskite substrates have received considerable attention due to the possibility of enhancing preexisting superconductivity. Using scanning tunneling spectroscopy, we studied the correlation between superconductivity and e -ph interaction with interfacial phonons in an iron-based superconductor Sr2VO3FeAs (Tc≈33 K ) made of alternating FeSC and oxide layers. The quasiparticle interference measurement over regions with systematically different average superconducting gaps due to the e -ph coupling locally modulated by O vacancies in the VO2 layer, and supporting self-consistent momentum-dependent Eliashberg calculations provide a unique real-space evidence of the forward-scattering interfacial phonon contribution to the total superconducting pairing.

  14. Enhancement of the superconducting gap by nesting in CaKFe4As4: A new high temperature superconductor

    SciTech Connect

    Mou, Daixiang; Kong, Tai; Meier, William R.; Lochner, Felix; Wang, Lin -Lin; Lin, Qisheng; Wu, Yun; Bud’ko, S. L.; Eremin, Ilya; Johnson, D. D.; Canfield, P. C.; Kaminski, Adam

    2016-12-28

    We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe4As4. In contrast to the related CaFe2As2 compounds, CaKFe4As4 has a high Tc of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of the Brillouin zone), but are significantly different for each of the Fermi surface (FS) sheets. Most importantly, we find that the momentum dependence of the gap magnitude plotted across the entire Brillouin zone displays a strong deviation from the simple cos(kx)cos(ky) functional form of the gap function, proposed by the scenario of Cooper pairing driven by a short range antiferromagnetic exchange interaction. Instead, the maximum value of the gap is observed on FS sheets that are closest to the ideal nesting condition, in contrast to previous observations in other ferropnictides. Finally, these results provide strong support for the multiband character of superconductivity in CaKFe4As4, in which Cooper pairing forms on the electron and the hole bands interacting via a dominant interband repulsive interaction, enhanced by band nesting.

  15. 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.

  16. Superconductivity: Phenomenology

    SciTech Connect

    Falicov, L.M.

    1988-08-01

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

  17. Isotropic quantum scattering and unconventional superconductivity.

    PubMed

    Park, T; Sidorov, V A; Ronning, F; Zhu, J-X; Tokiwa, Y; Lee, H; Bauer, E D; Movshovich, R; Sarrao, J L; Thompson, J D

    2008-11-20

    Superconductivity without phonons has been proposed for strongly correlated electron materials that are tuned close to a zero-temperature magnetic instability of itinerant charge carriers. Near this boundary, quantum fluctuations of magnetic degrees of freedom assume the role of phonons in conventional superconductors, creating an attractive interaction that 'glues' electrons into superconducting pairs. Here we show that superconductivity can arise from a very different spectrum of fluctuations associated with a local (or Kondo-breakdown) quantum critical point that is revealed in isotropic scattering of charge carriers and a sublinear, temperature-dependent electrical resistivity. At this critical point, accessed by applying pressure to the strongly correlated, local-moment antiferromagnet CeRhIn(5), magnetic and charge fluctuations coexist and produce electronic scattering that is maximal at the optimal pressure for superconductivity. This previously unanticipated source of pairing glue opens possibilities for understanding and discovering new unconventional forms of superconductivity.

  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. Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting β-MNCl (M=Hf, Zr).

    PubMed

    Kuroki, Kazuhiko

    2008-12-01

    We investigate the possibility of realizing unconventional superconductivity in doped band insulators on the square and honeycomb lattices. The latter lattice is found to be a good candidate due to the disconnectivity of the Fermi surface. We propose applying the theory to the superconductivity in doped layered nitride β-MNCl (M= Hf, Zr). Finally, we compare two groups of superconductors with disconnected Fermi surface, β-MNCl and the iron pnictides, which have high critical temperature Tc, despite some faults against superconductivity are present.

  20. 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.

  1. Enhanced coherence within the theta band between pairs of brains engaging in experienced versus naïve Reiki procedures.

    PubMed

    Ventura, Anabela Carraca; Persinger, Michael A

    2014-08-01

    The study objective was to discern whether the coherence between brain activities of the "patient" and practitioner differ between Reiki experts and novices. If the physical process associated with Reiki involves "convergence" between the practitioner and subject, then this congruence should be evident in time-dependent shared power within specific and meaningful frequency electroencephalographic bands. Simultaneous quantitative electroencephalogram measures (19 channels) were recorded from 9 pairs of subjects when 1 of the pairs was an experienced Reiki practitioner or had just been shown the procedure. Pairs recorded their experiences and images. The "practitioner" and "patient" pairs were measured within a quiet, comfortable acoustic chamber. Real-time correlations and coherence between pairs of brains for power (μV(2)·Hz(-1)) within the various frequency bands over the 10-min sessions were recorded and analyzed for each pair. Descriptors of experiences were analyzed for word meanings. Only the coherence within the theta range increased over time between the brains of the Reiki pairs relative to the Sham pairs, particularly over the left hemisphere. The pleasantness-unpleasantness rating for the words employed to describe experiences written after the experiment were more congruent for the Reiki pairs compared to the reference pairs. The increased synchronization of the cerebral activity of the participant and the practitioner during proximal therapies involving touch such as Reiki may be an important component of any subsequent beneficial effects.

  2. Enhanced surface losses of organic solar cells induced by efficient polaron pair dissociation at the metal/organic interface

    NASA Astrophysics Data System (ADS)

    Yang, Wenchao; Li, De-Li; Yao, Yao; Hou, Xiaoyuan; Wu, Chang-Qin

    2012-08-01

    As a growing importance is placed on developing more efficient organic solar cells, understanding the behavior of free charge carriers at the metal/organic (M/O) interface is critical. One of the current challenges is understanding surface losses, essentially the loss of free charge carriers at the electrode/organic interface. In this paper, we use device model simulations to study such phenomena and we pay particular attention to the role of polaron pair (PP) M/O interfacial dissociation. The origin of surface losses is through the extraction of free charge carriers from the wrong electrodes, or direct surface recombination of PPs. Through simulation, we find that a high injection barrier leads to a large surface loss. In addition, surface loss increases with both the interfacial dissociation rate and PP diffusivity. Efficient interfacial dissociation can significantly enhance surface losses if the PP diffusivity is relatively large. Furthermore, current voltage characteristics reveal that surface losses undermine the device operating parameters and efficiency. Interlayers inserted at the M/O interface could block wrong electrode carriers, suppress the interfacial dissociation and reduce surface losses.

  3. Enhanced superconductivity in surface-electron-doped iron pnictide Ba(Fe1.94Co0.06)2As2.

    PubMed

    Kyung, W S; Huh, S S; Koh, Y Y; Choi, K-Y; Nakajima, M; Eisaki, H; Denlinger, J D; Mo, S-K; Kim, C; Kim, Y K

    2016-12-01

    The superconducting transition temperature (TC) in a FeSe monolayer on SrTiO3 is enhanced up to 100 K (refs ,,,). High TC is also found in bulk iron chalcogenides with similar electronic structure to that of monolayer FeSe, which suggests that higher TC may be achieved through electron doping, pushing the Fermi surface (FS) topology towards leaving only electron pockets. Such an observation, however, has been limited to chalcogenides, and is in contrast to the iron pnictides, for which the maximum TC is achieved with both hole and electron pockets forming considerable FS nesting instability. Here, we report angle-resolved photoemission characterization revealing a monotonic increase of TC from 24 to 41.5 K upon surface doping on optimally doped Ba(Fe1-xCox)2As2. The doping changes the overall FS topology towards that of chalcogenides through a rigid downward band shift. Our findings suggest that higher electron doping and concomitant changes in FS topology are favourable conditions for the superconductivity, not only for iron chalcogenides, but also for iron pnictides.

  4. Suppression of phase separation and giant enhancement of superconducting transition temperature in FeSe(1-x)Te(x) thin films.

    PubMed

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

    2015-02-17

    We demonstrate the successful fabrication on CaF2 substrates of FeSe(1-x)Tex 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 ofFeSe(1-x)Te(x). We present a complete phase diagram of FeSe(1-x)Te(x) films. Surprisingly, a sudden suppression of Tc is observed at 0:1 < x < 0.2, whereas Tc increases with decreasing x for 0.2 ≤ x < 1. Namely, there is a clear difference between superconductivity realized in x = 0-0.1 and in x ≥ 0.2. To obtain a film of FeSe(1-x)Te(x) with high Tc, the controls of the Te content x and the in-plane lattice strain are found to be key factors.

  5. Enhanced superconductivity in surface-electron-doped iron pnictide Ba(Fe1.94Co0.06)2As2

    NASA Astrophysics Data System (ADS)

    Kyung, W. S.; Huh, S. S.; Koh, Y. Y.; Choi, K.-Y.; Nakajima, M.; Eisaki, H.; Denlinger, J. D.; Mo, S.-K.; Kim, C.; Kim, Y. K.

    2016-12-01

    The superconducting transition temperature (TC) in a FeSe monolayer on SrTiO3 is enhanced up to 100 K (refs ,,,). High TC is also found in bulk iron chalcogenides with similar electronic structure to that of monolayer FeSe, which suggests that higher TC may be achieved through electron doping, pushing the Fermi surface (FS) topology towards leaving only electron pockets. Such an observation, however, has been limited to chalcogenides, and is in contrast to the iron pnictides, for which the maximum TC is achieved with both hole and electron pockets forming considerable FS nesting instability. Here, we report angle-resolved photoemission characterization revealing a monotonic increase of TC from 24 to 41.5 K upon surface doping on optimally doped Ba(Fe1-xCox)2As2. The doping changes the overall FS topology towards that of chalcogenides through a rigid downward band shift. Our findings suggest that higher electron doping and concomitant changes in FS topology are favourable conditions for the superconductivity, not only for iron chalcogenides, but also for iron pnictides.

  6. Pressure-induced superconducting state and effective mass enhancement near the antiferromagnetic quantum critical point of CePt2In7

    NASA Astrophysics Data System (ADS)

    Bauer, E. D.; Lee, H. O.; Sidorov, V. A.; Kurita, N.; Gofryk, K.; Zhu, J.-X.; Ronning, F.; Movshovich, R.; Thompson, J. D.; Park, Tuson

    2010-05-01

    The heavy-fermion antiferromagnet CePt2In7 is a new, structurally more two-dimensional member of the CemMnIn3m+2n family. Applying pressure to CePt2In7 induces a broad dome of superconductivity that coexists with magnetic order for 1≤P≤3GPa . The maximum Tc=2.1K appears near the critical pressure Pc=3.5GPa where the Néel temperature extrapolates to zero temperature. An analysis of the initial slope of the upper critical field, the T2 coefficient of the electrical resistivity, and specific heat indicates an enhancement of the effective mass m∗ as Pc is approached, suggesting that critical fluctuations may mediate superconductivity. Electronic-structure calculations reveal a delicate balance between structural anisotropy and f-d hybridization, which may account for comparable Tc ’s in CePt2In7 and more three-dimensional CeRhIn5 .

  7. Enhanced-recycling H-mode regimes with edge coherent modes achieved by RF heating with lithium-wall conditioning in the EAST superconducting tokamak

    NASA Astrophysics Data System (ADS)

    Wang, H. Q.; Xu, G. S.; Guo, H. Y.; Wan, B. N.; Chen, R.; Ding, S. Y.; Yan, N.; Wang, L.; Gong, X. Z.; Liu, S. C.; Shao, L. M.; Chen, L.; Zhang, W.; Hu, G. H.; Liu, Y. L.; Li, Y. L.; Zhao, N.

    2014-12-01

    Two enhanced-recycling H-mode regimes, named low-enhanced-recycling (LER) and high-enhanced-recycling (HER) H-mode regimes, with edge coherent modes, have been achieved by lower hybrid current drive and ion cyclotron resonance heating with lithium-wall conditioning in the EAST superconducting tokamak. In the LER H-mode regime, the density and radiation increase during the ELM-free phase until the onset of edge-localized modes (ELMs), while in the HER H-mode regime, the density and radiation are well controlled without the presence of ELMs. Both LER and HER H-modes exhibit a low-frequency (frequency <100 kHz) edge quasi-coherent mode (ECM) with an initial frequency chirping down phase, following the L-H transition. In addition, an electromagnetic high-frequency coherent mode (HFM) with frequency >170 kHz appears shortly (<1 ms) after the transition during HER H-modes. Both ECM and HFM propagate in the electron diamagnetic drift direction in the lab frame with a low poloidal wavelength and may be responsible for enhanced recycling during the ELM-free phase. These two enhanced-recycling H-mode regimes may have significant implications for long-pulse high-performance operations in future fusion experiments.

  8. 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.

  9. Renormalization group study of excitonic and superconducting order in doped honeycomb bilayer

    NASA Astrophysics Data System (ADS)

    Murray, James; Vafek, Oskar

    2014-03-01

    We explore the competition between spin-charge order and unconventional superconductivity in the context of the AB stacked bilayer honeycomb lattice, realized experimentally as bilayer graphene, which features approximately parabolically touching electron bands. Using a weak-coupling renormalization group theory, we show that unconventional superconductivity arises generically for repulsively interacting fermions as excitonic order is suppressed by adding charge carriers to the system. We investigate the effects of finite temperature and further-neighbor hopping, the latter of which leads to so-called ``trigonal warping'' and destroys the perfect circular symmetry of the Fermi surfaces. We show that superconductivity survives for a finite range of trigonal warping, and that the nature of the superconducting phase may change as a function of further neighbor hopping. Depending on the range of interactions and the degree of trigonal warping, we find that the most likely superconducting instabilities are to f-wave, chiral d-wave, and pair density wave phases. It is shown that unconventional superconductivity is significantly enhanced by fluctuations in particle-hole channels, with the critical temperature reaching a maximum near the excitonic phase. Supported by the NSF CAREER award under Grant No. DMR-0955561, NSF Cooperative Agreement No. DMR-0654118, and the State of Florida, as well as by ICAM-I2CAM (NSF grant DMR-0844115) and by DoE, Office of Basic Energy Sciences (Award DE-FG02-08ER46544).

  10. Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet

    NASA Astrophysics Data System (ADS)

    Sunwong, P.; Higgins, J. S.; Hampshire, D. P.

    2014-06-01

    We present the designs of probes for making critical current density (Jc) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ˜0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make Jc measurements, made by uniformly ramping the current up to a maximum current (Imax) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b'), and the maximum safe temperature for the critical-current leads (Tmax). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI_{max} /A = [1.46D^{ - 0.18} L^{0.4} (T_{max } - 300)^{0.25D^{ - 0.09} } + 750(b^' /I_{max })D^{10^{ - 3} I_{max } - 2.87b^' }] × 10^6 A m^{ - 1} where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm2 is obtained when Imax = 1000 A, Tmax = 400 K, D = 0.2, b' = 0.3 l h-1 and L = 1.0 m. The optimized helium consumption was found to be 0.7 l h-1. When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/Imax ≈ (1.35 × 10-3)D0.41 l h-1 A-1. A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in our high-field horizontal

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

    NASA Astrophysics Data System (ADS)

    Grether, M.; de Llano, M.

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

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

    NASA Astrophysics Data System (ADS)

    Grether, M.; de Llano, M.

    2007-09-01

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

  13. Superconductive tunneling in junctions with resonant double barrier structures

    NASA Astrophysics Data System (ADS)

    Johansson, Göran; Shumeiko, Vitaly; Bratus, Ekaterina; Wendin, Göran

    1998-03-01

    We calculate the current-voltage characteristics (IVC) of a voltage biased superconducting junction with a double-barrier tunnel junction, having one resonant level, in the normal region. The effect of Coloumb blockade is neglected. Within a simple one-dimensional single-channel model the IVC's dependence on the position and width of the resonance is discussed. Both subgap region and excess current limit is analyzed. Depending on the position of the resonance we see supression of some and enhancement of other features of the subharmonic gap structure. For certain positions of a sharp resonance, the pair current results in a pronounced peak which may dominate over the single particle current, even at voltages much larger than the superconducting gap.

  14. 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

  15. 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.

  16. 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.

  17. Triplet p + ip pairing correlations in the doped Kane-Mele-Hubbard model: A quantum Monte Carlo study

    SciTech Connect

    Ma, Tianxing; Lin, Hai-Qing; Gubernatis, James E.

    2015-09-01

    By using the constrained-phase quantum Monte Carlo method, we performed a systematic study of the pairing correlations in the ground state of the doped Kane-Mele-Hubbard model on a honeycomb lattice. We find that pairing correlations with d + id symmetry dominate close to half filling, but pairing correlations with p+ip symmetry dominate as hole doping moves the system below three-quarters filling. We correlate these behaviors of the pairing correlations with the topology of the Fermi surfaces of the non-interacting problem. We also find that the effective pairing correlation is enhanced greatly as the interaction increases, and these superconducting correlations are robust against varying the spin-orbit coupling strength. Finally, our numerical results suggest a possible way to realize spin triplet superconductivity in doped honeycomb-like materials or ultracold atoms in optical traps.

  18. 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

  19. 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.

  20. Detecting a preformed pair phase: Response to a pairing forcing field

    NASA Astrophysics Data System (ADS)

    Tagliavini, A.; Capone, M.; Toschi, A.

    2016-10-01

    The normal state of strongly coupled superconductors is characterized by the presence of "preformed" Cooper pairs well above the superconducting critical temperature. In this regime, the electrons are paired, but they lack the phase coherence necessary for superconductivity. The existence of preformed pairs implies the existence of a characteristic energy scale associated with a pseudogap. Preformed pairs are often invoked to interpret systems where some signatures of pairing are present without actual superconductivity, but an unambiguous theoretical characterization of a preformed-pair system is still lacking. To fill this gap, we consider the response to an external pairing field of an attractive Hubbard model, which hosts one of the cleanest realizations of a preformed pair phase, and a repulsive model where s -wave superconductivity cannot be realized. Using dynamical mean-field theory to study this response, we identify the characteristic features which distinguish the reaction of a preformed pair state from a normal metal without any precursor of pairing. The theoretical detection of preformed pairs is associated with the behavior of the second derivative of the order parameter with respect to the external field, as confirmed by analytic calculations in limiting cases. Our findings provide a solid test bed for the interpretation of state-of-the-art calculations for the normal state of the doped Hubbard model in terms of d -wave preformed pairs and, in perspective, of nonequilibrium experiments in high-temperature superconductors.

  1. 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.

  2. Pressure induced superconductivity on the border of magnetic order in MnP.

    PubMed

    Cheng, J-G; Matsubayashi, K; Wu, W; Sun, J P; Lin, F K; Luo, J L; Uwatoko, Y

    2015-03-20

    We report the discovery of superconductivity on the border of long-range magnetic order in the itinerant-electron helimagnet MnP via the application of high pressure. Superconductivity with T(sc)≈1  K emerges and exists merely near the critical pressure P(c)≈8  GPa, where the long-range magnetic order just vanishes. The present finding makes MnP the first Mn-based superconductor. The close proximity of superconductivity to a magnetic instability suggests an unconventional pairing mechanism. Moreover, the detailed analysis of the normal-state transport properties evidenced non-Fermi-liquid behavior and the dramatic enhancement of the quasiparticle effective mass near P(c) associated with the magnetic quantum fluctuations.

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

    DOE PAGES

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

    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

  4. Heavy fermion superconductivity

    NASA Astrophysics Data System (ADS)

    Brison, Jean-Pascal; Glémot, Loı̈c; Suderow, Hermann; Huxley, Andrew; Kambe, Shinsaku; Flouquet, Jacques

    2000-05-01

    The quest for a precise identification of the symmetry of the order parameter in heavy fermion systems has really started with the discovery of the complex superconducting phase diagram in UPt 3. About 10 years latter, despite numerous experiments and theoretical efforts, this is still not achieved, and we will quickly review the present status of knowledge and the main open question. Actually, the more forsaken issue of the nature of the pairing mechanism has been recently tackled by different groups with macroscopic or microscopic measurement, and significant progress have been obtained. We will discuss the results emerging from these recent studies which all support non-phonon-mediated mechanisms.

  5. 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

  6. High-temperature superconductivity in one-unit-cell FeSe films

    NASA Astrophysics Data System (ADS)

    Wang, Ziqiao; Liu, Chaofei; Liu, Yi; Wang, Jian

    2017-04-01

    Since the dramatic enhancement of the superconducting transition temperature (T c) was reported in a one-unit-cell FeSe film grown on a SrTiO3 substrate (1-UC FeSe/STO) by molecular beam epitaxy (MBE), related research on this system has become a new frontier in condensed matter physics. In this paper, we present a brief review on this rapidly developing field, mainly focusing on the superconducting properties of 1-UC FeSe/STO. Experimental evidence for high-temperature superconductivity in 1-UC FeSe/STO, including direct evidence revealed by transport and diamagnetic measurements, as well as other evidence from scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), are overviewed. The potential mechanisms of the enhanced superconductivity are also discussed. There are accumulating arguments to suggest that the strengthened Cooper pairing in 1-UC FeSe/STO originates from the interface effects, specifically the charge transfer and coupling to phonon modes in the TiO2 plane. The study of superconductivity in 1-UC FeSe/STO not only sheds new light on the mechanism of high-temperature superconductors with layered structures, but also provides an insight into the exploration of new superconductors by interface engineering.

  7. High-temperature superconductivity in one-unit-cell FeSe films.

    PubMed

    Wang, Ziqiao; Liu, Chaofei; Liu, Yi; Wang, Jian

    2017-04-20

    Since the dramatic enhancement of the superconducting transition temperature (T c) was reported in a one-unit-cell FeSe film grown on a SrTiO3 substrate (1-UC FeSe/STO) by molecular beam epitaxy (MBE), related research on this system has become a new frontier in condensed matter physics. In this paper, we present a brief review on this rapidly developing field, mainly focusing on the superconducting properties of 1-UC FeSe/STO. Experimental evidence for high-temperature superconductivity in 1-UC FeSe/STO, including direct evidence revealed by transport and diamagnetic measurements, as well as other evidence from scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), are overviewed. The potential mechanisms of the enhanced superconductivity are also discussed. There are accumulating arguments to suggest that the strengthened Cooper pairing in 1-UC FeSe/STO originates from the interface effects, specifically the charge transfer and coupling to phonon modes in the TiO2 plane. The study of superconductivity in 1-UC FeSe/STO not only sheds new light on the mechanism of high-temperature superconductors with layered structures, but also provides an insight into the exploration of new superconductors by interface engineering.

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

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

  9. 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.

  10. Pair breaking in multiorbital superconductors: An application to oxide interfaces

    NASA Astrophysics Data System (ADS)

    Scheurer, M. Â. S.; Hoyer, M.; Schmalian, J.

    2015-07-01

    We investigate the impact of impurity scattering on superconductivity in an anisotropic multiorbital model with spin-orbit coupling, which describes the electron fluid at two-dimensional oxide interfaces. As the pairing mechanism is under debate, both conventional and unconventional superconducting states are analyzed. We consider magnetic and nonmagnetic spin-dependent intra- and interorbital scattering and discuss possible microscopic realizations leading to these processes. It is found that, for magnetic disorder, the unconventional superconductor is protected against interband scattering and, thus, it is more robust than the conventional condensate. In case of nonmagnetic impurities, the conventional superconductor is protected as expected from the Anderson theorem and the critical scattering rate of the unconventional state is enhanced by a factor of four due to the spin-orbit coupling and anisotropic masses in oxide interfaces.

  11. Topological superconductivity induced by ferromagnetic metal chains

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  12. Effect of spin-orbit scattering on the magnetic and superconducting properties of nearly ferromagnetic metals: application to granular Pt.

    PubMed

    Fay, D; Appel, J

    2002-09-16

    We calculate the effect of scattering on the static, exchange enhanced, spin susceptibility and show that, in particular, spin-orbit scattering leads to a reduction of the giant moments and spin glass freezing temperature due to dilute magnetic impurities. The harmful spin fluctuation contribution to the intragrain pairing interaction is strongly reduced opening the way for BCS superconductivity. We are thus able to explain the superconducting and magnetic properties recently observed in granular Pt as being due to scattering effects in single small grains.

  13. Effect of Spin-Orbit Scattering on the Magnetic and Superconducting Properties of Nearly Ferromagnetic Metals: Application to Granular Pt

    NASA Astrophysics Data System (ADS)

    Fay, D.; Appel, J.

    2002-08-01

    We calculate the effect of scattering on the static, exchange enhanced, spin susceptibility and show that, in particular, spin-orbit scattering leads to a reduction of the giant moments and spin glass freezing temperature due to dilute magnetic impurities. The harmful spin fluctuation contribution to the intragrain pairing interaction is strongly reduced opening the way for BCS superconductivity. We are thus able to explain the superconducting and magnetic properties recently observed in granular Pt as being due to scattering effects in single small grains.

  14. Chiral magnetic superconductivity

    NASA Astrophysics Data System (ADS)

    Kharzeev, Dmitri E.

    2017-03-01

    Materials with charged chiral quasiparticles in external parallel electric and magnetic fields can support an electric current that grows linearly in time, corresponding to diverging DC conductivity. From experimental viewpoint, this "Chiral Magnetic Superconductivity" (CMS) is thus analogous to conventional superconductivity. However the underlying physics is entirely different - the CMS does not require a condensate of Cooper pairs breaking the gauge degeneracy, and is thus not accompanied by Meissner effect. Instead, it owes its existence to the (temperature-independent) quantum chiral anomaly and the conservation of chirality. As a result, this phenomenon can be expected to survive to much higher temperatures. Even though the chirality of quasiparticles is not strictly conserved in real materials, the chiral magnetic superconductivity should still exhibit itself in AC measurements at frequencies larger than the chirality-flipping rate, and in microstructures of Dirac and Weyl semimetals with thickness below the mean chirality-flipping length that is about 1 - 100 μm. In nuclear physics, the CMS should contribute to the charge-dependent elliptic flow in heavy ion collisions.

  15. Correlation-Enhanced Odd-Parity Interorbital Singlet Pairing in the Iron-Pnictide Superconductor LiFeAs.

    PubMed

    Nourafkan, R; Kotliar, G; Tremblay, A-M S

    2016-09-23

    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 two-Fe Brillouin zone the full frequency-dependent linearized Eliashberg equations to investigate spin-fluctuations mediated Cooper pairing for LiFeAs. 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. The interaction between electrons through Hund's coupling promotes both the intraorbital d_{xz(yz)} and the interorbital magnetic susceptibility. As a consequence, the leading pairing channel, conventional s^{+-}, acquires sizable interorbital d_{xy}-d_{xz(yz)} singlet pairing with odd parity under glide-plane symmetry. The combination of intra- and interorbital components makes the results consistent with available experiments on the angular dependence of the gaps observed on the different Fermi surfaces.

  16. Correlation-Enhanced Odd-Parity Interorbital Singlet Pairing in the Iron-Pnictide Superconductor LiFeAs

    NASA Astrophysics Data System (ADS)

    Nourafkan, R.; Kotliar, G.; Tremblay, A.-M. S.

    2016-09-01

    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 two-Fe Brillouin zone the full frequency-dependent linearized Eliashberg equations to investigate spin-fluctuations mediated Cooper pairing for LiFeAs. 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. The interaction between electrons through Hund's coupling promotes both the intraorbital dx z (y z ) and the interorbital magnetic susceptibility. As a consequence, the leading pairing channel, conventional s+- , acquires sizable interorbital dx y-dx z (y z ) singlet pairing with odd parity under glide-plane symmetry. The combination of intra- and interorbital components makes the results consistent with available experiments on the angular dependence of the gaps observed on the different Fermi surfaces.

  17. Coexistence of superconductivity and ferromagnetism in the d-band metal ZrZn2.

    PubMed

    Pfleiderer, C; Uhlarz, M; Hayden, S M; Vollmer, R; v Löhneysen, H; Bernhoeft, N R; Lonzarich, G G

    2001-07-05

    It has generally been believed that, within the context of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity, the conduction electrons in a metal cannot be both ferromagnetically ordered and superconducting. Even when the superconductivity has been interpreted as arising from magnetic mediation of the paired electrons, it was thought that the superconducting state occurs in the paramagnetic phase. Here we report the observation of superconductivity in the ferromagnetically ordered phase of the d-electron compound ZrZn2. The specific heat anomaly associated with the superconducting transition in this material appears to be absent, and the superconducting state is very sensitive to defects, occurring only in very pure samples. Under hydrostatic pressure superconductivity and ferromagnetism disappear at the same pressure, so the ferromagnetic state appears to be a prerequisite for superconductivity. When combined with the recent observation of superconductivity in UGe2 (ref. 4), our results suggest that metallic ferromagnets may universally become superconducting when the magnetization is small.

  18. 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…

  19. Superconducting magnets

    SciTech Connect

    Not Available

    1994-08-01

    This report discusses the following topics on superconducting magnets: D19B and -C: The next steps for a record-setting magnet; D20: The push beyond 10 T: Beyond D20: Speculations on the 16-T regime; other advanced magnets for accelerators; spinoff applications; APC materials development; cable and cabling-machine development; and high-{Tc} superconductor at low temperature.

  20. Superconducting Microelectronics.

    ERIC Educational Resources Information Center

    Henry, Richard W.

    1984-01-01

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

  1. Superconductivity in a chiral nanotube

    PubMed Central

    Qin, F.; Shi, W.; Ideue, T.; Yoshida, M.; Zak, A.; Tenne, R.; Kikitsu, T.; Inoue, D.; Hashizume, D.; Iwasa, Y.

    2017-01-01

    Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity—unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures. PMID:28205518

  2. Electron Tunneling Studies of MOLYBDENUM(1-X) Rhenium(x): Enhancement of Superconductivity by a Resonance Mode.

    NASA Astrophysics Data System (ADS)

    Shum, Danny Pak-Chum

    It is well-known that a heavy impurity atom in a lattice of light atoms induces a lower frequency in-band resonance mode in the vibrational spectrum. The exact effect of such a mode on the lat- tice spectrum has not previously been reported and effects of such modes on superconductivity have not previously been described. Sputtered thin films of bcc Mo(,1-x)Re(,x), 0.2 < x < 0.4, have been pre- pared for this study because the Re atom is almost twice as heavy as Mo. High quality MoRe/Al(,2)O(,3)/Pb tunnel junctions on these films have been made with an in situ deposited and subsequently oxidized thin Al layer as barrier. Three phonon peaks were observed directly in the dV/dI and d('2)V/dI('2) curves. The (alpha)('2)F((omega)) spectra, determined from the data through the Eliashberg theory of superconductivity, all show an anomalous low energy peak, in addition to the Mo-derived transverse and longitudinal phonon peaks. This peak appears near 14 meV, in agreement with the Brout-Visscher theory and with neu- tron scattering data which first indicated the Re resonance mode in Mo(,.85)Re(,.15). We show that the resonance mode contributes strongly to (alpha)('2)F((omega)) and to strong coupling (delta)(=2(DELTA)/k(,B)T(,c) - 3.53) > 0. (delta) increases with (lamda)(,R), the Re contribution to the electron-phonon coupling con- stant (lamda). The dependences of the anomalous softening and width of the resonance mode on (lamda)(,R) fit the Yu-Anderson theory of local pho- non screening by a Fermi gas of electrons treated as Tomonago. bosons. These results explain the low N(0), high T(,c) behavior of Mo(,.6)Re(,.4). *DOE Report IS-T-1246. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

  3. 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.

  4. Origin of Enhanced Reactivity of a Microsolvated Nucleophile in Ion Pair SN2 Reactions: The Cases of Sodium p-Nitrophenoxide with Halomethanes in Acetone.

    PubMed

    Li, Qiang-Gen; Xu, Ke; Ren, Yi

    2015-04-30

    In a kinetic experiment on the SN2 reaction of sodium p-nitrophenoxide with iodomethane in acetone-water mixed solvent, Humeres et al. (J. Org. Chem. 2001, 66, 1163) found that the reaction depends strongly on the medium, and the fastest rate constant was observed in pure acetone. The present work tries to explore why acetone can enhance the reactivity of the title reactions. Accordingly, we make a mechanistic study on the reactions of sodium p-nitrophenoxide with halomethanes (CH3X, X = Cl, Br, I) in acetone by using a supramolecular/continuum model at the PCM-MP2/6-311+G(d,p)//B3LYP/6-311+G(d,p) level, in which the ion pair nucleophile is microsolvated by one to three acetone molecules. We compared the reactivity of the microsolvated ion pair nucleophiles with solvent-free ion pair and anionic ones. Our results clearly reveal that the microsolvated ion pair nucleophile is favorable for the SN2 reactions; meanwhile, the origin of the enhanced reactivity induced by microsolvation of the nucleophile is discussed in terms of the geometries of transition state (TS) structures and activation strain model, suggesting that lower deformation energies and stronger interaction energies between the deformed reactants in the TS lead to the lower overall reaction barriers for the SN2 reaction of microsolvated sodium p-nitrophenoxide toward halomethanes in acetone.

  5. 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.

  6. On the superconductivity of graphite interfaces

    NASA Astrophysics Data System (ADS)

    Esquinazi, P.; Heikkilä, T. T.; Lysogorskiy, Y. V.; Tayurskii, D. A.; Volovik, G. E.

    2014-11-01

    We propose an explanation for the appearance of superconductivity at the interfaces of graphite with Bernal stacking order. A network of line defects with flat bands appears at the interfaces between two slightly twisted graphite structures. Due to the flat band the probability to find high temperature superconductivity at these quasi one-dimensional corridors is strongly enhanced. When the network of superconducting lines is dense it becomes effectively two-dimensional. The model provides an explanation for several reports on the observation of superconductivity up to room temperature in different oriented graphite samples, graphite powders as well as graphite-composite samples published in the past.

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

    NASA Astrophysics Data System (ADS)

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

    2008-09-01

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

  8. 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 .

  9. 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

  10. Superconducting instability of a non-centrosymmetric system

    NASA Astrophysics Data System (ADS)

    Grzybowska, Dorota; Harań, Grzegorz

    2017-03-01

    The Fermi gas approach to the weak-coupling superconductivity in the non-centrosymmetric systems lead to a conclusion of an approximately spin-orbit coupling independent critical temperature of the singlet states as well as the triplet states defined by the order parameter aligned with the antisymmetric spin-orbit coupling vector. We indicate that the above results follow from a simplified approximation of a density of states by a constant Fermi surface value. Such a scenario does not properly account for the spin-split quasiparticle energy spectrum and reduces the spin-orbit coupling influence on superconductivity to the bare pair-breaking effect of a lifted spin degeneracy. Applying the tight-binding model, which captures the primary features of the spin-split energy band, i.e., its enhanced width and the spin-orbit coupling induced redistribution of the spectral weights in the density of states, we calculate the critical temperature of a non-centrosymmetric superconductor. We report a general tendency of the critical temperature to be suppressed by the antisymmetric spin-orbit coupling. We indicate that, the monotonic decrease of the critical temperature may be altered by the spin-orbit coupling induced van Hove singularities which, when driven to the Fermi level, generate maxima in the phase diagram. Extending our considerations to the intermediate-coupling superconductivity we point out that the spin-orbit coupling induced change of the critical temperature depends on the structure of the electronic energy band and both - the strength and symmetry of the pair potential. Finally, we discuss the mixed singlet-triplet state superconducting instability and establish conditions concerning the symmetry of the singlet and triplet counterparts as well as the range of the spin-orbit coupling energy which make such a phase transition possible.

  11. 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.

  12. 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.

  13. 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.

  14. SUPERCONDUCTING PHOTOINJECTOR

    SciTech Connect

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

    2007-08-26

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

  15. 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.

  16. 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.

  17. 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.

  18. 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

    2014-09-26

    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.

  19. Reentrance phenomenon in superconductor/ferromagnet nanostructures and their application in superconducting spin valves for superconducting electronics

    NASA Astrophysics Data System (ADS)

    Sidorenko, A. S.

    2017-07-01

    In superconductor/ferromagnet layered structures, a Fulde-Ferrell-Larkin-Ovchinnikov-like inhomogeneous superconducting pairing give rise. The singlet and zero-projection triplet components of the pairing oscillate in space, and the presence of interfaces causes interference phenomena. As the result of the interference, the super-conducting critical temperature Tc oscillates as a function of the ferromagnetic layer thicknesses or, even more spectacular, reentrant superconductivity appears. Two ferromagnetic layers can be combined with a superconducting layer into a superconducting spin valve. Proper design and choice of the material parameters give possibility to control superconducting Tc manipulating with magnetic configurations in the system. The conditions to get large spin-valve effect, i.e., a large shift in the critical temperature, are reviewed in the article.

  20. 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

  1. 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

    2013-04-04

    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.

  2. Towards inducing superconductivity into graphene

    NASA Astrophysics Data System (ADS)

    Efetov, Dmitri K.

    Graphenes transport properties have been extensively studied in the 10 years since its discovery in 2004, with ground-breaking experimental observations such as Klein tunneling, fractional quantum Hall effect and Hofstadters butterfly. Though, so far, it turned out to be rather poor on complex correlated electronic ground states and phase transitions, despite various theoretical predictions. The purpose of this thesis is to help understanding the underlying theoretical and experimental reasons for the lack of strong electronic interactions in graphene, and, employing graphenes high tunability and versatility, to identify and alter experimental parameters that could help to induce stronger correlations. In particular graphene holds one last, not yet experimentally discovered prediction, namely exhibiting intrinsic superconductivity. With its vanishingly small Fermi surface at the Dirac point, graphene is a semi-metal with very weak electronic interactions. Though, if it is doped into the metallic regime, where the size of the Fermi surface becomes comparable to the size of the Brillouin zone, the density of states becomes sizeable and electronic interactions are predicted to be dramatically enhanced, resulting in competing correlated ground states such as superconductivity, magnetism and charge density wave formation. Following these predictions, this thesis first describes the creation of metallic graphene at high carrier doping via electrostatic doping techniques based on electrolytic gates. Due to graphenes surface only properties, we are able to induce carrier densities above n>1014 cm-2 (epsilonF>1eV) into the chemically inert graphene. While at these record high carrier densities we yet do not observe superconductivity, we do observe fundamentally altered transport properties as compared to semi-metallic graphene. Here, detailed measurements of the low temperature resistivity reveal that the electron-phonon interactions are governed by a reduced, density

  3. Hydrophobic ion pairing as a method for enhancing structure and activity of lyophilized subtilisin BPN' suspended in isooctane.

    PubMed

    Kendrick, B S; Meyer, J D; Matsuura, J E; Carpenter, J F; Manning, M C

    1997-11-01

    The use of enzymes in low water environments permits reactions to occur that are difficult or impossible in aqueous solution. In this manner, proteases can be used to form, rather than hydrolyze, ester and amide linkages. Presumably, the native-like structure of the enzyme must remain intact for catalysis to transpire. However, little is known regarding the integrity of the overall structure of lyophilized proteins suspended in organic media. In this study, the structural changes that occur during the freeze-drying process and those effected by suspension in the organic solvent were examined. Using Fourier-transform infrared spectroscopy, the secondary structure of lyophilized subtilisin BPN' was monitored and correlated to the level of enzymatic activity when suspended in isooctane. In addition, the ability of ionic detergents to stabilize subtilisin BPN' via ion pairing was evaluated. It was found that subtilisin unfolds to some degree during lyophilization, whether it is ion paired or not. Furthermore, there are structural changes observed when the enzyme is placed in isooctane, although the effects are less with ion-paired subtilisin. This higher level of retention of secondary structure results in increased enzymatic activity.

  4. Unconventional Superconductivity in Bilayer Transition Metal Dichalcogenides.

    PubMed

    Liu, Chao-Xing

    2017-02-24

    Bilayer transition metal dichalcogenides (TMDs) belong to a class of materials with two unique features, the coupled spin-valley-layer degrees of freedom and the crystal structure that is globally centrosymmetric but locally noncentrosymmetric. In this Letter, we will show that the combination of these two features can lead to a rich phase diagram for unconventional superconductivity, including intralayer and interlayer singlet pairings and interlayer triplet pairings, in bilayer superconducting TMDs. In particular, we predict that the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov state can exist in bilayer TMDs under an in-plane magnetic field. We also discuss the experimental relevance of our results and possible experimental signatures.

  5. Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS.

    PubMed

    Adamová, D; Agakichiev, G; Appelshäuser, H; Belaga, V; Braun-Munzinger, P; Cherlin, A; Damjanović, S; Dietel, T; Dietrich, L; Drees, A; Esumi, S I; Filimonov, K; Fomenko, K; Fraenkel, Z; Garabatos, C; Glässel, P; Hering, G; Holeczek, J; Kushpil, V; Lenkeit, B; Maas, A; Marín, A; Milosević, J; Milov, A; Miśkowiec, D; Panebrattsev, Yu; Petchenova, O; Petrácek, V; Pfeiffer, A; Rak, J; Ravinovich, I; Rehak, P; Richter, M; Sako, H; Schmitz, W; Sedykh, S; Seipp, W; Sharma, A; Shimansky, S; Slívová, J; Specht, H J; Stachel, J; Sumbera, M; Tilsner, H; Tserruya, I; Wessels, J P; Wienold, T; Windelband, B; Wurm, J P; Xie, W; Yurevich, S; Yurevich, V

    2003-07-25

    We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2enhanced over the expectation from neutral meson decays by a factor of 5.9+/-1.5(stat)+/-1.2(syst data)+/-1.8(syst meson decays), somewhat larger than previously observed at the higher energy of 158 AGeV. The results are discussed with reference to model calculations based on pi(+)pi(-)-->e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.

  6. 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

  7. 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.

  8. 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

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

    DOE PAGES

    Xu, Zhijun; Stock, C.; Chi, Songxue; ...

    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. Neutron-Scattering Evidence for a Periodically Modulated Superconducting Phase in the Underdoped Cuprate La1.905Ba0.095CuO4

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Stock, C.; Chi, Songxue; Kolesnikov, A. I.; Xu, Guangyong; 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.

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

    PubMed

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

    2014-10-24

    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 La(2-x)Sr(x)CuO(4) and YBa(2)Cu(3)O(6+x).

  12. Plain s-Wave Superconductivity near Magnetic Criticality: Enhancement of Attractive Electron-Boson Coupling Vertex Corrections

    NASA Astrophysics Data System (ADS)

    Tazai, Rina; Yamakawa, Youichi; Tsuchiizu, Masahisa; Kontani, Hiroshi

    2017-07-01

    Recent experiments revealed that the plain s-wave state without any sign-reversal emerges in various metals near magnetic criticality. To understand this counter-intuitive phenomenon, we study the gap equation for the multiorbital Hubbard-Holstein model, by analyzing the vertex correction (VC) due to the higher-order electron-correlation effects. We find that the phonon-mediated orbital fluctuations are magnified by the VC for the susceptibility (χ-VC). In addition, the charge-channel attractive interaction is enlarged by the VC for the coupling-constant (U-VC), which is significant when the interaction has prominent q-dependences; therefore the Migdal theorem fails. Due to both χ-VC and U-VC, the plain s-wave state is caused by the small electron-phonon interaction near the magnetic criticality against the repulsive Coulomb interaction. We find that the direct Coulomb repulsion for the plain s-wave Cooper pair is strongly reduced by the "multiorbital screening effect".

  13. Pair symmetry conversion in driven multiband superconductors

    NASA Astrophysics Data System (ADS)

    Triola, Christopher; Balatsky, Alexander V.

    2017-06-01

    It was recently shown that odd-frequency superconducting pair amplitudes can be induced in conventional superconductors subjected to a spatially nonuniform time-dependent drive. It has also been shown that, in the presence of interband scattering, multiband superconductors will possess bulk odd-frequency superconducting pair amplitudes. In this work we build on these previous results to demonstrate that by subjecting a multiband superconductor with interband scattering to a time-dependent drive, even-frequency pair amplitudes can be converted to odd-frequency pair amplitudes and vice versa. We will discuss the physical conditions under which these pair symmetry conversions can be achieved and possible experimental signatures of their presence.

  14. 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.

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

    PubMed

    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.

  16. 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.

  17. 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.

  18. 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.

  19. Improving model prediction reliability through enhanced representation of wetland soil processes and constrained model auto calibration - A paired watershed study

    NASA Astrophysics Data System (ADS)

    Sharifi, Amirreza; Lang, Megan W.; McCarty, Gregory W.; Sadeghi, Ali M.; Lee, Sangchul; Yen, Haw; Rabenhorst, Martin C.; Jeong, Jaehak; Yeo, In-Young

    2016-10-01

    Process based, distributed watershed models possess a large number of parameters that are not directly measured in field and need to be calibrated, in most cases through matching modeled in-stream fluxes with monitored data. Recently, concern has been raised regarding the reliability of this common calibration practice, because models that are deemed to be adequately calibrated based on commonly used metrics (e.g., Nash Sutcliffe efficiency) may not realistically represent intra-watershed responses or fluxes. Such shortcomings stem from the use of an evaluation criteria that only concerns the global in-stream responses of the model without investigating intra-watershed responses. In this study, we introduce a modification to the Soil and Water Assessment Tool (SWAT) model, and a new calibration technique that collectively reduce the chance of misrepresenting intra-watershed responses. The SWAT model was modified to better represent NO3 cycling in soils with various degrees of water holding capacity. The new calibration tool has the capacity to calibrate paired watersheds simultaneously within a single framework. It was found that when both proposed methodologies were applied jointly to two paired watersheds on the Delmarva Peninsula, the performance of the models as judged based on conventional metrics suffered, however, the intra-watershed responses (e.g., mass of NO3 lost to denitrification) in the two models automatically converged to realistic sums. This approach also demonstrates the capacity to spatially distinguish areas of high denitrification potential, an ability that has implications for improved management of prior converted wetlands under crop production and for identifying prominent areas for wetland restoration.

  20. Quantum anomalies in superconducting Weyl metals

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Hao, Lei; Wang, Baigeng; Ting, C. S.

    2016-05-01

    We theoretically study the quantum anomalies in the superconducting Weyl metals based on the topological field theory. It is demonstrated that the Fermi arc and the surface Andreev bound state, characteristic of the superconducting Weyl metals, are the manifestations of two underlying phenomena, namely, the chiral anomaly and the paritylike anomaly, respectively. The first anomaly is inherited from the Berry curvature around the original Weyl points, while the second is the result of the superconductivity. We show that all the fascinating topological behavior of the superconducting Weyl metals, either the intranode Fulde-Ferrell-Larkin-Ovchinnikov or the internode Bardeen-Cooper-Schrieffer pairing state, can be satisfactorily described and predicted by our topological field theory.

  1. Odd-Parity Superconductivity and the Ferromagnetic Quantum Critical Point

    NASA Astrophysics Data System (ADS)

    Huxley, A. D.; Yates, S. J. C.; Lévy, F.; Sheikin, I.

    2007-05-01

    The study of the emergence of superconductivity close to quantum critical points affords a powerful means to identify the mechanism that drives the formation of unconventional superconductivity in heavy fermion materials. The recent discovery of superconducting states close to quantum critical points in ferromagnets UGe2 and URhGe is reviewed in this light. For URhGe we examine whether the predominant type of magnetic excitations involved are longitudinal excitations, hitherto considered theoretically to be the most promising candidate to mediate equal-spin-paired superconductivity.

  2. STRIPES AND SUPERCONDUCTIVITY IN CUPRATE SUPERCONDUCTORS

    SciTech Connect

    TRANQUADA, J.M.

    2005-08-22

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

  3. Stripes and superconductivity in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Tranquada, J. M.

    2005-08-01

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

  4. Enhanced superconductivity due to forward scattering in FeSe thin films on SrTiO3 substrates

    DOE PAGES

    Rademaker, Louk; Wang, Yan; Berlijn, Tom; ...

    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

  5. Enhanced superconductivity due to forward scattering in FeSe thin films on SrTiO3 substrates

    DOE PAGES

    Rademaker, Louk; Wang, Yan; Berlijn, Tom; ...

    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

  6. Negative U-centers and defect superconductivity

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Yavidov, B.; Makhmudov, N. A.

    1997-04-01

    A connection between the formation of defect bipolarons (i.e. U-centers or U-bipolarons) and superconductivity in high-Tcsuperconductors (HTSC) is considered in two pairing limits of carriers in realr- andk-spaces. The irrelevance ofr-space U-bipolarons to superconductivity is motivated. It is shown that the formation ofk-space U-bipolarons and their subsequent attractive single particle and pair condensation lead to depressed (in comparison with lattice bipolarons) superconductivity due to a large mass of such U-bipolarons. It is argued that the coexistence ofk-space lattice bipolarons andr-space U-bipolarons leads to the shift of the maximum of the concentration dependenceTc(n)to higher carrier concentrations, in accordance with the observations in HTSC.

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

    SciTech Connect

    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 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 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.

  8. 119Sn-NMR investigations on superconducting Ca3Ir4Sn13: Evidence for multigap superconductivity

    DOE PAGES

    Sarkar, R.; Petrovic, C.; Bruckner, F.; ...

    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.

  9. 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

  10. Optical conductivity from pair density waves

    NASA Astrophysics Data System (ADS)

    Dai, Zhehao; Lee, Patrick A.

    2017-01-01

    We present a theory of optical conductivity in systems with finite-momentum Cooper pairs. In contrast to the BCS pairing where ac conductivity is purely imaginary in the clean limit, there is nonzero ac absorption across the superconducting gap for finite-momentum pairing if we break the Galilean symmetry explicitly in the electronic Hamiltonian. Vertex correction is crucial for maintaining the gauge invariance in the mean-field formalism and dramatically changes the optical conductivity in the direction of the pairing momentum. We carried out a self-consistent calculation and gave an explicit formula for optical conductivity in a simple case. This result applies to the Fulde-Ferrell-Larkin-Ovchinnikov state and candidates with pair density waves proposed for high-Tc cuprates. It may help detect pair density waves and determine the pairing gap as well as the direction of the pairing momentum in experiments.

  11. 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.

  12. Spontaneous finite momentum pairing in superconductors without inversion symmetry

    NASA Astrophysics Data System (ADS)

    Steinbok, Aviram; Michaeli, Karen

    2017-05-01

    We analyze the effect of magnetic fluctuations in superconductors with strong spin-orbit coupling and show that they drive a phase transition between two superconducting states: a conventional phase with zero center-of-mass momentum of Cooper pairs, and an exotic phase with nonzero pair momentum. The latter is found to exhibit persistent currents without magnetic field in doubly connected geometries such as rings. Surprisingly, the transition temperature into the superconducting state can be increased by applying a Zeeman magnetic field.

  13. A linkage tournament: affection status, parametric analysis, multivariate traits, and enhancements to variance components and relative pairs.

    PubMed

    Zhang, W; Collins, A; Lonjou, C; Morton, N E

    2002-01-01

    Linkage tests to localize oligogenes have been extended during the past year. Using simulated data and multiplex selection we find that several tests on affected sib pairs have comparable power and type I error. Three variants of SIBPAL2 are favoured when substantial numbers of normal sibs are included, but performance relative to the BETA benchmark degrades rapidly as normal sibs are depleted by selective sampling or typing. Neglect of this fact may explain recent failure of retrospective collaboration to confirm asthma candidates in the 5q cytokine region that are supported by other studies. A fully quantitative trait favours variance components under complete ascertainment and two options in SIBPAL2 under multiplex selection, with substantial gain in power from covariance analysis if the covariate is independent of the candidate locus. A dichotomy and liability threshold give virtually identical results in the SOLAR variance components program. Comparison with single-marker parametric analysis suggests that extension to multiple markers would be competitive with nonparametric methods in power, and superior in depth of genetic analysis. The simulated examples illustrate common problems encountered with linkage scans for oligogenes. They show that nonparametric methods provide no panacea for analytical problems posed by different phenotypes and methods of ascertainment.

  14. Self Powered Highly Enhanced Dual Wavelength ZnO@CdS Core-Shell Nanorod Arrays Photodetector: An Intelligent Pair.

    PubMed

    Sarkar, Sanjit; Basak, Durga

    2015-08-05

    On the face of the impending energy crisis, developing low-energy or even zero-energy photoelectronic devices is extremely important. A multispectral photosensitivity feature of a self-powered device provides an additional powerful tool. We have developed an unprecedented high performance dual wavelength self-powered ZnO@CdS/PEDOT:PSS core-shell nanorods array photodetector through a simple aqueous chemical method wherein a suitable band alignment between an intelligent material pair, i.e. ZnO and CdS, has been utilized. Besides a noteworthy advantage of the devices being that they show a very sharp and prominent dual wavelength photosensitivity, both the ultraviolet and visible light sensitivity (ratio of current under illumination (Iphoto)/current under dark (Idark)) of the device are two orders of higher magnitude than those of pristine ZnO, attaining values of 2.8 × 10(3) and 1.07 × 10(3), respectively. At the same time, temporal responses faster than 20 ms could be achieved with these solution-processed photodetectors. The present study provides a very important direction to engineer core-shell nanostructured devices for dual wavelength high photosensitivity.

  15. 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…

  16. 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…

  17. Evolution of superconducting correlations within magnetic-field-decoupled La2-xBaxCuO4 (x=0.095)

    NASA Astrophysics Data System (ADS)

    Stegen, Z.; Han, Su Jung; Wu, Jie; Pramanik, A. K.; Hücker, M.; Gu, Genda; Li, Qiang; Park, J. H.; Boebinger, G. S.; Tranquada, J. M.

    2013-02-01

    We explore the evolution of superconductivity in La2-xBaxCuO4 with x=0.095 in magnetic fields of up to 35 T applied perpendicular to the CuO2 planes. Previous work on this material has shown that perpendicular fields enhance both charge- and spin-stripe order within the planes. We present measurements of the resistivity parallel and perpendicular to the planes, as well as the Hall effect. Measurements of magnetic susceptibility for fields of up to 15 T applied both parallel and perpendicular to the planes provide complementary measures of the superconductivity. We show that fields sufficient to destroy pair tunneling between the planes do not disrupt the superconducting correlations within the planes. In fact, we observe an onset of large-amplitude but phase-disordered superconductivity within the planes at approximately 30 K that is remarkably insensitive to field. With further cooling, we observe a phase-transition-like drop in the in-plane resistivity to an apparent state of superconductivity despite the lack of phase coherence between the layers. These observations raise interesting questions concerning the identification of the upper critical field, where pairing is destroyed, in underdoped cuprates.

  18. Associative pairing enhances action potential back-propagation in radial oblique branches of CA1 pyramidal neurons

    PubMed Central

    Gasparini, Sonia; Losonczy, Attila; Chen, Xixi; Johnston, Daniel; Magee, Jeffrey C

    2007-01-01

    Back-propagating action potentials (bAPs) are involved in associative synaptic plasticity and the modulation of dendritic excitability. We have used high-speed confocal and two-photon imaging to measure calcium and voltage signals associated with action potential propagation into oblique branches of CA1 pyramidal neurons in adult hippocampal slices. The spatial profile of the bAP-associated Ca2+ influx was biphasic, with an initial increase in the proximity of the branch point followed by a progressive decrease. Voltage imaging in the branches showed that bAP amplitude was initially constant and then steadily declined with distance from the soma. To determine the role of transient K+ channels in this profile, we used external Ba2+ (150 μm) as a channel blocker, after characterizing its effect on A-type K+ channels in the apical trunk. Bath application of Ba2+ significantly reduced the A-type K+ current in outside-out patches and nearly eliminated the distance-dependent decrease in bAP amplitude and its associated Ca2+ signal. Finally, small amplitude bAPs at more distal oblique branch locations could be boosted by simultaneous branch depolarization, such that the paired Ca2+ signal became nearly the same for proximal and distal oblique dendrites. These data suggest that dendritic K+ channels regulate the amplitude of bAPs to create a dendritic Ca2+ signal whose magnitude is inversely related to the electrotonic distance from the soma when bAPs are not associated with a significant amount of localized synaptic input. This distance-dependent Ca2+ signal from bAPs, however, can be amplified and a strong associative signal is produced once the proper correlation between synaptic activation and AP output is achieved. We hypothesize that these two signals may be involved in the regulation of the expression and activity of dendritic voltage- and ligand-gated ion channels. PMID:17272353

  19. In situ synthesis of porous array films on a filament induced micro-gap electrode pair and their use as resistance-type gas sensors with enhanced performances

    NASA Astrophysics Data System (ADS)

    Xu, Zongke; Duan, Guotao; Zhang, Hongwen; Wang, Yingying; Xu, Lei; Cai, Weiping

    2015-08-01

    Resistance-type metal-oxide semiconductor gas sensors with high sensitivity and low detection limit have been explored for practical applications. They require both sensing films with high sensitivity to target gases and an appropriate structure of the electrode-equipped substrate to support the sensing films, which is still challenging. In this paper, a new gas sensor of metal-oxide porous array films on a micro-gap electrode pair is designed and implemented by taking ZnO as a model material. First, a micro-gap electrode pair was constructed by sputtering deposition on a filament template, which was used as the sensor's supporting substrate. Then, the sensing film, made up of ZnO porous periodic arrays, was in situ synthesized onto the supporting substrate by a solution-dipping colloidal lithography strategy. The results demonstrated the validity of the strategy, and the as-designed sensor shows a small device-resistance, an enhanced sensing performance with high resolution and an ultralow detection limit. This work provides an alternative method to promote the practical application of resistance-type gas sensors.Resistance-type metal-oxide semiconductor gas sensors with high sensitivity and low detection limit have been explored for practical applications. They require both sensing films with high sensitivity to target gases and an appropriate structure of the electrode-equipped substrate to support the sensing films, which is still challenging. In this paper, a new gas sensor of metal-oxide porous array films on a micro-gap electrode pair is designed and implemented by taking ZnO as a model material. First, a micro-gap electrode pair was constructed by sputtering deposition on a filament template, which was used as the sensor's supporting substrate. Then, the sensing film, made up of ZnO porous periodic arrays, was in situ synthesized onto the supporting substrate by a solution-dipping colloidal lithography strategy. The results demonstrated the validity of the

  20. A ferroelectric quantum phase transition inside the superconducting dome of Sr1-xCaxTiO3-δ

    NASA Astrophysics Data System (ADS)

    Rischau, Carl Willem; Lin, Xiao; Grams, Christoph P.; Finck, Dennis; Harms, Steffen; Engelmayer, Johannes; Lorenz, Thomas; Gallais, Yann; Fauqué, Benoît; Hemberger, Joachim; Behnia, Kamran

    2017-07-01

    SrTiO3, a quantum paraelectric, becomes a metal with a superconducting instability after removal of an extremely small number of oxygen atoms. It turns into a ferroelectric upon substitution of a tiny fraction of strontium atoms with calcium. The two orders may be accidental neighbours or intimately connected, as in the picture of quantum critical ferroelectricity. Here, we show that in Sr1-xCaxTiO3-δ (0.002 < x < 0.009, δ < 0.001) the ferroelectric order coexists with dilute metallicity and its superconducting instability in a finite window of doping. At a critical carrier density, which scales with the Ca content, a quantum phase transition destroys the ferroelectric order. We detect an upturn in the normal-state scattering and a significant modification of the superconducting dome in the vicinity of this quantum phase transition. The enhancement of the superconducting transition temperature with calcium substitution documents the role played by ferroelectric vicinity in the precocious emergence of superconductivity in this system, restricting possible theoretical scenarios for pairing.