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Sample records for borocarbide superconductors rni2b2c

  1. Magnetic structures in RNi2B2C (R = Ho, Er) superconductors

    International Nuclear Information System (INIS)

    Single crystal neutron diffraction techniques have been employed to study the evolution of magnetic structures in RNi2B2C compounds in an attempt to understand the relationship between magnetic ordering and superconductivity in several members of this series. For HoNi2B2C, below the superconducting transition (Tc = 8 K), an incommensurate magnetic structure characterized by two wave vectors (0.585 a* and 0.915 c*) is found in a narrow temperature range between 4.7 K and 6 K. This is the same temperature range where bulk measurements find a deep minimum in the upper critical field, Hc2. Below 4.7 K, HoNi2B2C is a simple collinear antiferromagnet. ErNi2B2C (Tc = 11 K) orders in an incommensurate modulated antiferromagnetic state characterized by an ordering wave vector 0.553 a* below 7 K, which coexists with superconductivity

  2. Competition of superconductivity and antiferromagnetism in RNi2B2C (R = Tm, Dy, Ho, Er)

    International Nuclear Information System (INIS)

    Highlights: • Hamiltonian model to study SC and AFM in RNi2B2C. • A competition between SC and AFM. - Abstract: The co-existence of superconductivity (SC) and antiferromagnetism (AFM) in RNi2B2C (R = Tm, Dy, Ho, Er) is reported in this paper. A mean field Hamiltonian model is taken for the system. The order parameters corresponding to SC and AFM are determined and their variation with temperature are studied for these borocarbide superconductors. The interplay of SC and AFM shows BCS type of two gaps in the quasi-particle density of states. Our theoretical study is an attempt to reveal how far the s-wave pairing taken in our model could explain the coexistence properties of SC and AFM in RNi2B2C

  3. Superconducting RNi2B2C(R=Y,Lu) nanoparticles: size effects and weak links

    International Nuclear Information System (INIS)

    The potential of the arc discharge technique for the growth of complex nanocrystalline systems is demonstrated here with the formation of quaternary superconducting nanoparticles belonging to the recently discovered intermetallic boron carbide family RNi2B2C (R = Y, Lu). The nanoparticles, which were embedded in a glassy carbon matrix and had Tc - 15 K, are reported to exhibit magnetic behavior characterized by finite size effects and weak Josephson links between the particles. The formation and characterization of the nanoparticles are detailed. (orig.)

  4. A core level spectroscopic study on RNi2B2C (R=Y,Er) borocarbides

    International Nuclear Information System (INIS)

    Polycrystalline samples of YNi2B2C and magnetic ErNi2B2C were prepared by arc-melting technique with a Tc ∼ 15 K. Core level spectroscopic studies have been performed in order to see the valence of Y, Er and Ni. The results show that Ni and Er exists in 2+ valence state and Y exists in 3+ valence state. (author)

  5. Anisotropic superconducting and normal state magnetic properties of single crystals of RNi*2*B*2*C compounds (R = Y, Gd, Dy, Ho, Er, and Tm)

    International Nuclear Information System (INIS)

    The interaction of superconductivity with magnetism has been one of the most interesting and important phenomena in solid state physics since the 1950's when small amounts of magnetic impurities were incorporated in superconductors. The discovery of the magnetic superconductors RNi2B2C (R = rare earth, Y) offers a new system to study this interaction. The wide ranges of superconducting transition (Tc) and antiferromagnetic (AF) ordering temperatures (TN) (0 K ≤ Tc ≤ 16 K, 0 K ≤ TN ≤ 20 K) give a good opportunity to observe a variety of interesting phenomena. Single crystals of high quality with appropriate size and mass are crucial in examining the anisotropic intrinsic properties. Single crystals have been grown successfully by an unusual high temperature flux method and characterized thoroughly by X-ray, electrical transport, magnetization, neutron scattering, scanning electron microscopy, and other measurements

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

    Science.gov (United States)

    Mazumdar, Chandan; Nagarajan, R.

    2015-07-01

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

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

    International Nuclear Information System (INIS)

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

  8. Discovery and properties of quaternary borocarbide superconductors

    International Nuclear Information System (INIS)

    The discovery of superconductivity in Y-Ni-B-C by Indian scientists has led to a new class of materials, viz, Quaternary Rare Earth Borocarbides, with many interesting properties. Several members of the series show superconductivity with high Tc for intermetallics with the multiphase Y-Pd-B-C system showing a Tc of 23 K which is highest for bulk intermetallics. Some of the magnetic members of the family exhibit the exotic phenomenon of coexistence of superconductivity with high Tc as well as high magnetic ordering temperatures. The two cooperative phenomena occurring at comparable energy scale results in new aspects of interplay of magnetism and superconductivity. In quaternaries, there is ample scope for finding new materials possibly with even higher Tcs and newer phenomena. A glimpse of this new and exciting field is presented here. (author)

  9. Anisotropic superconducting and normal state magnetic properties of single crystals of RNi*2*B*2*C compounds (R = Y, Gd, Dy, Ho, Er, and Tm)

    Energy Technology Data Exchange (ETDEWEB)

    Cho, B.

    1995-11-01

    The interaction of superconductivity with magnetism has been one of the most interesting and important phenomena in solid state physics since the 1950`s when small amounts of magnetic impurities were incorporated in superconductors. The discovery of the magnetic superconductors RNi{sub 2}B{sub 2}C (R = rare earth, Y) offers a new system to study this interaction. The wide ranges of superconducting transition (T{sub c}) and antiferromagnetic (AF) ordering temperatures (T{sub N}) (0 K {le} T{sub c} {le} 16 K, 0 K {le} T{sub N} {le} 20 K) give a good opportunity to observe a variety of interesting phenomena. Single crystals of high quality with appropriate size and mass are crucial in examining the anisotropic intrinsic properties. Single crystals have been grown successfully by an unusual high temperature flux method and characterized thoroughly by X-ray, electrical transport, magnetization, neutron scattering, scanning electron microscopy, and other measurements.

  10. Polarization-dependent X-ray-absorption spectroscopy of $RNi_{2} B_{2}$ C (R=Er $\\to$ Lu) Reduced Ni-3d occupancy in $YbNi_{2} B_{2} C$

    CERN Document Server

    Mazumdar, C; Von Lips, H; Golden, M S; Fink, J; Canfield, P C; Kaindl, G

    2001-01-01

    We present here the results of polarization-dependent X-ray- absorption near-edge structure (XANES) studies at the B-K, C-K, and Ni-L/sub 3/ thresholds of single-crystalline borocarbide compounds RNi/sub 2/B/sub 2/C (with R=Er to Lu) using bulk-sensitive fluorescence yield technique. The Ni-L/sub 3/ XANES spectrum for YbNi /sub 2/B/sub 2/C with photon polarization parallel to the ab plane is significantly more intense than in analogous spectra of other members of this series. This indicates a reduced Ni-3d occupancy in the Ni /sub 2/B/sub 2/ layer in YbNi/sub 2/B/sub 2/C, a fact that might be responsible for the absence of superconductivity in this material. (26 refs).

  11. Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

    Indian Academy of Sciences (India)

    M R Eskildsen; A B Abrahamsen; P L Gammel; D J Bishop; N H Andersen; K Mortensen; P C Canfield

    2002-05-01

    We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi2B2C with the applied field along the - and -axes. For $\\mathbf{H}||\\mathbf{c}$ the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field, 2(), rises sharply, bending away from c2() in contradiction to theoretical predictions of the two merging. For $\\mathbf{H}||\\mathbf{a}$ a first order FLL reorientation transition is observed at tr =3-3.5 kOe. Below tr the FLL nearest neighbor direction is parallel to the -axis, and above tr to the -axis. This transition cannot be explained using nonlocal corrections to the London model.

  12. Small angle neutron scattering studies of the flux line lattices in the borocarbide superconductors

    International Nuclear Information System (INIS)

    This thesis describes small angle neutron scattering studies of the flux line lattice (FLL) in the following members of the borocarbide superconductors: YNi2B2C, ErNi2B2C, TmNi2B2C, LuNi2B2C, Y0.75Lu0.25Ni2B2C and Lu(Ni1-xCOx)2B2C with x = 1.5 - 9%. Of the materials ErN2B2C and TmNi2B2C exhibits coexisting superconductivity and magnetic ordering. Three main conclusions can be derived from the results in this thesis. Existence of a low field hexagonal to square symmetry transition of the FLL, ubiquitous to the superconducting borocarbides, magnetic and non-magnetic alike. This symmetry transition is due to the four-fold anisotropy of the Fermi surface, distorting the screening currents towards a square flow pattern. This four-fold anisotropy together with non-local electrodynamics induces a transition to a square FLL, as the field is increased. Changing the non-locality range shifts the square to hexagonal transition onset field. A static disordering of the FLL in YNi2B2C and LuNi2B2C. In these materials one observes a well ordered FLL, with a longitudinal correlation length exceeding 100 flux line spacings. As the applied field is increased the longitudinal correlation length, increases with field up to H/Hc2 ∼ 0.2. Above this field the FLL correlation length slowly starts to fall off, in contradiction to theoretical models. The existence of complex interactions between the magnetic state and the FLL in TmNi2B2C. This is signalled by coinciding changes in the FLL symmetry and in the magnetic structure. The FLL show a two-step symmetry transition from square to rhombic and then hexagonal with increased field. In addition, the FLL reflectivity shows distinct peaks as the thulium ions orders magnetically at TN and across the field driven magnetic transition. No explanation for this behaviour exists at the present. (au)

  13. Small angle neutron scattering studies of the flux line lattices in the borocarbide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Eskildsen, Morten Ring

    1998-12-01

    This thesis describes small angle neutron scattering studies of the flux line lattice (FLL) in the following members of the borocarbide superconductors: YNi{sub 2}B{sub 2}C, ErNi{sub 2}B{sub 2}C, TmNi{sub 2}B{sub 2}C, LuNi{sub 2}B{sub 2}C, Y{sub 0.75}Lu{sub 0.25}Ni{sub 2}B{sub 2}C and Lu(Ni{sub 1-x}CO{sub x}){sub 2}B{sub 2}C with x = 1.5 - 9%. Of the materials ErN{sub 2}B{sub 2}C and TmNi{sub 2}B{sub 2}C exhibits coexisting superconductivity and magnetic ordering. Three main conclusions can be derived from the results in this thesis. Existence of a low field hexagonal to square symmetry transition of the FLL, ubiquitous to the superconducting borocarbides, magnetic and non-magnetic alike. This symmetry transition is due to the four-fold anisotropy of the Fermi surface, distorting the screening currents towards a square flow pattern. This four-fold anisotropy together with non-local electrodynamics induces a transition to a square FLL, as the field is increased. Changing the non-locality range shifts the square to hexagonal transition onset field. A static disordering of the FLL in YNi{sub 2}B{sub 2}C and LuNi{sub 2}B{sub 2}C. In these materials one observes a well ordered FLL, with a longitudinal correlation length exceeding 100 flux line spacings. As the applied field is increased the longitudinal correlation length, increases with field up to H/H{sub c2} {approx} 0.2. Above this field the FLL correlation length slowly starts to fall off, in contradiction to theoretical models. The existence of complex interactions between the magnetic state and the FLL in TmNi{sub 2}B{sub 2}C. This is signalled by coinciding changes in the FLL symmetry and in the magnetic structure. The FLL show a two-step symmetry transition from square to rhombic and then hexagonal with increased field. In addition, the FLL reflectivity shows distinct peaks as the thulium ions orders magnetically at T{sub N} and across the field driven magnetic transition. No explanation for this behaviour

  14. Solid state chemistry of the quarternary boro-carbide and boro-nitride superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Cava, R.J. [AT and T Bell Labs., Murray Hill, NJ (United States)

    1995-12-31

    The chemistry of copper oxides has been a dominant research topic in the field of new superconducting materials since 1986. Just as the copper oxides opened many new doors after their initial discovery, new doors now to be opened will have to be based on a different kind of material. Several years ago we began to reinvestigate various families of intermetallic materials to explore their potential for superconductivity - an area of exploration largely abandoned since the mid 1970`s. We found a broad new family of materials based on lanthanides, transition metals, and the light elements boron, carbon and nitrogen, one of which has a superconducting transition temperature as high as has ever been observed for an intermetallic compound. These represent the first true quaternary intermetallic superconductors, and show that optimal structural and chemical complexity had not yet been reached in this family of potential superconductors before research on new materials was dropped.

  15. Nested Fermi surfaces and order in the rare earth nickel borocarbides and copper palladium alloys

    International Nuclear Information System (INIS)

    The electronic structure of two systems, each displaying a different type of order believed to derive from their respective Fermi surface topologies, has been investigated using the two-dimensional angular correlation of annihilation radiation (2D-ACAR) technique. A particular topological feature of a generic rare earth nickel borocarbide (general formula RNi2B2C) Fermi surface is popularly believed to be responsible for a particular modulated arrangement of local moments observed in several magnetic borocarbides. Accordingly, c-axis 2D-ACAR spectra were collected from four representative members of the series, namely the Er, Tm, Yb and Lu compounds. A further a-axis projection from LuNi2B2C provides an additional comparison with electronic structure calculations performed for this compound. The c-axis projected k-space electron occupancies reveal a fundamentally similar Fermi surface topology across the measured compounds. The a- and c-axis k-space occupancies obtained from LuNi2B2C showed exceptional qualitative agreement with the corresponding calculated electron occupancy. A number of edge-detection methods were employed to identify the projected Fermi surface, and the existence of the proposed feature was confirmed by direct observation in each of the measured compounds. Calipers of this feature were found to be in good general agreement with those predicted by relevant calculation and expected from indirect experimental evidence. The compositional phase behaviour of copper-palladium solid solutions is believed to be strongly influenced by the shape of their respective Fermi surfaces. In particular, the concentration-dependent positions of diffuse peaks in electron and X-ray diffraction patterns from disordered samples has been associated with the corresponding evolution of flat, parallel areas on the alloy Fermi surface. Electronic structure calculations indicate these areas to be maximal around 40 at. % Pd, and it has been further suggested that the same

  16. μ+SR studies of magnetic properties of boron carbide superconductors

    International Nuclear Information System (INIS)

    Positive-muon spin relaxation (μ+SR) has been carried out in the recently-discovered rare-earth boron carbide superconductors RNi2B2C, R = Ho, Er and Tm. For R = Ho and Er zero-field μ+SR measurements showed a well-defined internal field below the Neel temperatures of 5.5 K coexisting with the superconducting state down to 0.1 K. The observed temperature dependence of the order parameter for Ho is consistent with a 2-dimensional Ising model. For R = Tm a spontaneous internal field appears above 30 K, whose magnitude saturates below about 3 K at a value corresponding to a rare earth moment much smaller than for Ho and Er. Transverse-field micro-SR measurements in R = Tm showed a superconducting penetration depth λ, = 1,200 angstrom. The temperature dependence of λ is consistent with conventional s-wave pairing

  17. Electronic Structure and Fermi Surface of the Quaternary Intermetallic Borocarbide Superconductor YNi2B2C from 2D-ACAR

    Science.gov (United States)

    Hamid, A. S.

    We measured the angular momentum density distribution of YNi2B2C to acquire information about its electronic structure. The measurements were performed using the full-scale utility of the two-dimensional angular correlation of annihilation radiation (2D-ACAR). The measured spectra clarified that Ni (3d) like state, predominantly, affected the Fermi surface of YNi2B2C. Further, s- and p-like-states enhanced its superconducting properties. The Fermi surface of YNi2B2C. was reconstructed using Fourier transformation followed by the LCW (Loucks, Crisp and West) folding procedure. It showed a large and complex surface similar to that of the high temperature superconductors HTS, with anisotropic properties. It also disclosed the effect of d-like state. Nevertheless, the current Fermi surface could deliver the needed topological information to isolate its features. The general layouts of this Fermi surface are; two large electron surfaces running along Γ-Z direction; as well as an additional large electron surface centered on X point; beside one hole surface centered on 100 point. This Fermi surface was interpreted in view of the earlier results.

  18. Possible coexistence of superconductivity and magnetic order in NdPt2B2C

    Indian Academy of Sciences (India)

    S K Dhar; A D Chinchure; E Alleno; C Godart; L C Gupta; R Nagarajan

    2002-05-01

    Coexistence of superconductivity and magnetic order has been one of the exciting aspects of the quaternary borocarbide superconductors. So far, RNi2B2C (R=Tm, Er, Ho and Dy) are the only known magnetic superconductors in this family. Here, we present our resistivity, magnetization and heat capacity studies on NdPt2B2C (nominal composition, NdPt1.5Au0.6B2C and NdPt2.1B2.4C1.2). We find superconductivity in both samples with c,onset∼ 3 K. Bulk magnetic order is found to occur below 1.7 K. We suggest that NdPt2B2C is a possible magnetic superconductor.

  19. Superconductors

    CERN Document Server

    Narlikar, A V

    2014-01-01

    Superconductors is neither about basic aspects of superconductivity nor about its applications, but its mainstay is superconducting materials. Unusual and unconventional features of a large variety of novel superconductors are presented and their technological potential as practical superconductors assessed. The book begins with an introduction to basic aspects of superconductivity. The presentation is readily accessible to readers from a diverse range of scientific and technical disciplines, such as metallurgy, materials science, materials engineering, electronic and device engineering, and chemistry. The derivation of mathematical formulas and equations has been kept to a minimum and, wherever necessary, short appendices with essential mathematics have been added at the end of the text. The book is not meant to serve as an encyclopaedia, describing each and every superconductor that exists, but focuses on important milestones in their exciting development.

  20. Influence of magnetic order on superconductivity and crystal structure of rare earth-nickel-boron carbide compounds

    International Nuclear Information System (INIS)

    Rare-earth nickel borocarbids RNi2B2C are particularly suitable for investigations on one of the most interesting problems in modern solid-state physics: these compounds display competition and coexistence of superconductivity and magnetism. Depending on the R3+ ion, the transition temperatures are in an experimentally easy accessible range of 1 K to 25 K. This thesis presents experimental studies on the interplay of both ordering phenomena. Neutron diffraction is used to determine the magnetic order and the resulting changes of the crystal structure. Experiments are performed on polycrystalline and single crystal samples in dependence on temperature and external magnetic fields. The Ni-B stoichiometry of the tetragonal RNi2B2C compounds is systematically varied and the magnetic R3+ ions are partially substituted by other magnetic or nonmagnetic R'3+ ions. The experimental results are compared with macroscopic magnetic and electrical properties. (orig.)

  1. Unconventional superconductors. Anisotropy and multiband effects

    Energy Technology Data Exchange (ETDEWEB)

    Askerzade, Iman [Ankara Univ. (Turkey). Center of Excellence of Superconductivity Research of Turkey; Azerbaijan National Academy of Sciences (Azerbaijan). Inst. of Physics

    2012-07-01

    This book deals with the new class of materials unconventional superconductors, cuprate compounds, borocarbides, magnesium-diboride and oxypnictides. It gives a systematical review of physical properties of novel superconductors. There is an increasing number of fundamental properties of these compounds which are relevant to future applications, opening new possibilities. The theoretical explanation is presented as generalization of Ginzburg-Landau phenomenology and microscopical Eliashberg theory for multiband and anisotropic superconductors. Various applications of this approaches and time dependent version of two-band Ginzburg-Landau theory are considered. An important topic are fluctuations in two-band and anisotropic superconductors. Significant new results on current problems are presented to stimulate further research. Numerous illustrations, diagrams and tables make this book useful as a reference for students and researchers. (orig.)

  2. Unconventional superconductors anisotropy and multiband effects

    CERN Document Server

    Askerzade, Iman

    2012-01-01

    This book deals with the new class of materials unconventional superconductors, cuprate compounds, borocarbides, magnesium-diboride and oxypnictides. It gives a systematical review of physical properties of novel  superconductors. There is an increasing number of fundamental properties of these compounds which are relevant to future applications, opening new possibilities. The theoretical explanation is presented as generalization of Ginzburg-Landau phenomenology and microscopical Eliashberg theory for multiband and anisotropic superconductors. Various applications of this approachs and time dependent version of two-band Ginzburg-Landau theory are considered. An important topic are fluctuations in two-band and anisotropic superconductors. Significant  new results on current problems are presented to stimulate further research. Numerous illustrations, diagrams and tables make this book useful as a reference for students and researchers.

  3. 11B and 195Pt NMR studies in the Normal State of substituted borocarbide superconductors Y0.98Er0.02Ni2B2C and LaPt1.5Au0.6B2C

    International Nuclear Information System (INIS)

    We report, 11B NMR studies on Y0.98Er0.02Ni2B2C and 11B and 195Pt NMR studies on LaPt1.5Au0.6B2C superconductors. The variation of (1/T1T) with temperature in the normal state of Y0.98Er0.02Ni2B2C shows a similar behaviour as in YNi2B2C. However, its magnitude is one order more than that observed in YNi2B2C. This suggests that T1 is dominated by the thermal fluctuations of Er local moments in this case. From 11B and 195Pt NMR in LaPt1.5Au0.6B2C, we demonstrate that the Pt 5d band is full and the compound exhibits Korringa behaviour as expected for a normal Fermi-liquid. This is in contrast to YNi2B2C where an enhancement of the 11B (1/T1T) is observed at low temperatures along with a deviation from Korringa behaviour, suggesting that the enhancement seen in YNi2B2C could be due to the antiferromagnetic fluctuations from nickel 3d-electrons. (orig.)

  4. X-ray resonant exchange scattering of rare-earth nickel borocarbides

    Energy Technology Data Exchange (ETDEWEB)

    Detlefs, C.

    1997-10-08

    The purpose of this thesis is to investigate the systematics of the microscopic magnetic order within a series of isostructural compounds and, at the same, to develop the relatively young experimental method of x-ray resonant exchange scattering (XRES). In this thesis, the author presents XRES studies of several rare-earth nickel borocarbides, RNi{sub 2}B{sub 2}C. He shows that XRES, similar to the neutron techniques, allows the determination of the orientation of the magnetic moment by measuring the Q-dependence of the scattered intensity of magnetic Bragg reflections. As samples in this study, he chose the recently discovered family of rare-earth nickel borocarbides, RNi{sub 2}B{sub 2}C, which display a wide variety of magnetic structures. Furthermore, in several of these materials, long range magnetic order coexists with superconductivity over some temperature range.

  5. Thermal Low-Temperature Properties of Rare Earth Transition Metal Borocarbides

    OpenAIRE

    Lipp, Dieter

    2002-01-01

    The present work reports on thermal low-temperature properties of rare earth transition metal borocarbides such as specific heat, thermal conductivity and thermopower. The influence of structural disorder, caused by stoichiometric variations and substitutions of the rare earth element or the transition metal, on the thermal and superconducting low-temperature properties is investigated. The structural disorder results in the reduction of the superconducting transition temperature Tc, of the S...

  6. Strong correlations and electron-phonon interaction in superconductors

    International Nuclear Information System (INIS)

    In the last two decades or so, a number of new materials have been discovered which do not comply to the standard theoretical description of their normal and broken symmetry, mainly superconducting, phases. Among them, a unique role is played by the high temperature superconductors (HTS), with their unusual doping dependence of the normal and superconducting properties. Other materials, such as heavy fermion systems and their alloys, alkali metal fullerides, carbon nanotubes, borocarbide superconductors, organic superconductors, etc., also show interesting features. In some of the mentioned systems, clear non-Fermi liquid behavior in the normal state and strong departures from BCS-Eliashberg theory predictions in the superconducting state have been observed. The important issue in this context has been the symmetry of the order parameter, the origin of the pseudogap in the underdoped materials, and the operating mechanism of superconductivity. (orig.)

  7. Vortex dynamics in magnesium-diboride superconductor by using 11B NMR

    International Nuclear Information System (INIS)

    11B nuclear-magnetic-resonance (NMR) measurements were performed to investigate vortex dynamics in the polycrystalline superconductor MgB2. 11B NMR spectrum, shift and transverse relaxation rate 1/T2 were measured down to 4.3 K at ∼1.8 T. The spectrum below Tc exhibits a typical local field distribution for a vortex lattice under a magnetic field. The peak point of the spectrum shifts toward low magnetic field, due to imperfect field penetration. This decrease in the shift starts to appear below the detuning temperature of a NMR resonant circuit, which is measured to match the irreversibility temperature Tirr of magnetization. 1/T2 data, probing the slow motion of vortices, show a single peak with a small change in the rate, in contrast to the results for nickel borocarbides. This strongly suggests that thermal fluctuation of vortices is reduced and the vortex motion is much smaller, compared with nickel borocarbides.

  8. Angular dependant critical field and critical currents of epitaxial holmium nickel borocarbide thin films

    International Nuclear Information System (INIS)

    Epitaxial thin films of HoNi2B2C and related superconducting rare earth borocarbide compounds act as a suitable basis for numerous investigations on structural and superconductive properties such as Tc, Hc2 and Jc. A new batch of HoNi2B2C thin films was grown on ceramic single crystal magnesium oxide substrates under ultra-high vacuum conditions using pulsed laser deposition. A detailed view on the deposition parameters and the physical film properties is presented and angular Hc2- and Jc-measurements are shown. (orig.)

  9. On the crystallographic relationship between monoborides (CrB, α-MoB) and actinide-borocarbides (UBC, ThBC)

    International Nuclear Information System (INIS)

    Previously, (see ibid, vol. 73, p. 198, 1978), a simple geometrical relationship between actinide borocarbides of the formula MBC was derived for the pair ThBC-UBC. Similarity of the metal-boron sublattice within the crystal structures of UBC and CrB was earlier recognized by Toth et al. (1961). A closer inspection of the crystal symmetry relations between transition metal monoborides and actinide borocarbides is the subject of the present work. (Auth.)

  10. Characterisation of electronic and magnetic properties in Rare Earth-Borocarbides

    International Nuclear Information System (INIS)

    This thesis deals with the experimental characterisation of electronic and magnetic properties in single crystalline RE-borocarbides. Measurements of dHvA-oscillations in the nonmagnetic and below Tc = 16.3 K superconducting compound LuNi2B2C result in new insights of the underlying fermi surfaces. Especially one of the measured cross sections shows gapless behavior in the superconducting state. Comparative studies with bandstructure calculations and the related compound YNi2B2C reveal the similarities and differences in the geometry of the fermi surfaces, with tendencies to larger effective masses in LuNi2B2C compared to YNi2B2C. The measured angular dependence Bc2(T, alpha) at low temperatures contradicts the forecasts of an unconventional d-wave-model, which was under consideration to be the responsible mechanism for superconductivity in the borocarbides. The measured Bc2(T)-dependence and the quantitative results of the dHvA-experiments allow a theoretical description of the unusual positive curvature in Bc2(T) in the framework of a two-band model. Magnetisation and neutronen scattering experiments increase the knowledge of the field induced magnetic phases in DyNi2B2C (TN = 10.3 K, Tc = 6.8 K). The neutron scattering experiments confirm the existence of commensurable field induced magnetic structures in DyNi2B2C. The anisotropy and field dependence in the intensity of the fm reflection is interpreted as a multi domain effect

  11. Probing electronic phase transitions with phonons via inelastic neutron scattering: superconductivity in borocarbides, charge and magnetic order in manganites

    International Nuclear Information System (INIS)

    The present thesis concentrates on the signatures of strong electron-phonon coupling in phonon properties measured by inelastic neutron scattering. The inelastic neutron scattering experiments were performed on the triple-axis spectrometers 1T and DAS PUMA at the research reactors in Saclay (France) and Munich (Germany), respectively. The work is subdivided into two separate chapters: In the first part, we report measurements of the lattice dynamical properties, i.e. phonon frequency, linewidth and intensity, of the conventional, i.e. phonon-mediated, superconductor YNi2B2C of the rare-earth-borocarbide family. The detailed check of theoretical predictions for these properties, which were calculated in the theory group of our institute, was one major goal of this work. We measured phonons in the normal state, i.e. T>Tc, for several high symmetry directions up to 70 meV. We were able to extract the full temperature dependence of the superconducting energy gap 2Δ(T) from our phonon scans with such accuracy that even deviations from the weak coupling BCS behaviour could be clearly observed. By measuring phonons at different wave vectors we demonstrated that phonons are sensitive to the gap anisotropy under the precondition, that different phonons get their coupling strength from different parts of the Fermi surface. In the second part, we investigated the properties of Mn-O bond-stretching phonons in the bilayer manganite La2-2xSr1+2xMn2O7. At the doping level x=0.38 this compound has an ferromagnetic groundstate and exhibits the so-called colossal magnetoresistance effect in the vicinity of the Curie temperature TC. The atomic displacement patterns of the investigated phonons closely resemble possible Jahn-Teller distortions of the MnO6 octahedra, which are introduced in this compound by the Jahn-Teller active Mn3+ ions. We observed strong renormalizations of the phonon frequencies and clear peaks of the intrinsic phonon linewidth near the order wave vector of the

  12. Metamaterial superconductors

    CERN Document Server

    Smolyaninov, Igor I

    2014-01-01

    Epsilon near zero (ENZ) conditions have been observed to enhance superconducting properties of a composite metamaterial based on random mixing of superconductor and ferroelectic nanoparticles. Here we analyse several other promising experimental geometries, which may considerably enhance electron pairing interaction in a metamaterial superconductor. The proposed geometries may be fabricated at the current level of nanotechnology development. They enable tuning of both frequency and spatial dispersion of the effective dielectric response function of the metamaterial, thus enabling optimization of the metamaterial superconductor properties.

  13. Thermodynamics of many-band superconductors

    International Nuclear Information System (INIS)

    In the present thesis the microscopical properties of the superconducting state of MgCNi3, MgB2, and some rare earth-transition metal borocarbides are studied by means of measurements of the specific heat. Furthermore the frequency spectrum of the lattice vibrations is estimated. The energy gap of the superconducting state can be determined from the specific heat of the superconducting state, which yields as like as the upper critical mafnetic field Hc2(0) hints on the electron-phonon coupling. From the analysis of these results and the comparison with results from transport measurements as well as the tunnel and point-contact spectroscopy can be concluded, how far the BCS model of superconductivity must be modified in order to be able to describe the superconducting state of the studied compounds. Studies on MgCNi3, which lies near a magnetic instability, show that occurring magnetic fluctuations have a bisection of the superconducting transition temperature TC as consequence. The under this aspect relatively high value of TC=7 K is a consequence of strong electron-phonon coupling, which is essentailly carried by nickel vibrations stabilized by carbon. A for the first time observed distinct anomaly in the specific heat of the classical many-band superconductor MgB2 (here with pure 10B) at about Tc/4=10 K can be understood by means of a two-band model for the case of especially weak coupling between both bands. The analysis of the specific heat of the superconducting phase of the non-magnetic rare earth-nickel borocarbide YNi2B2C and LuNi2B2C leads to the conclusion thet visible effects of the many-band electron system are dependent on the mass on the position both of the rare earth and the transition metal. The signal of the superconducting phase transformation visible in the specific heat of the antiferromagnetic HoNi2B2C is smaller than expected

  14. Nanostructured superconductors

    CERN Document Server

    Moshchalkov, Victor V

    2011-01-01

    The main focus of the book is to present the effects of nanostructuring on superconducting critical parameters. Optimizing systematically flux and condensate confinement in various nanostructured superconductors, ranging from single nano-cells to their hu

  15. Evidence for carbon-boron disorder in YNi210B2C

    International Nuclear Information System (INIS)

    Complete text of publication follows. There has been a tremendous interest in the RNi2B2C (R = rare earth or Y) family of superconductors since their discovery five years ago. This results partly from their relatively high superconducting transition temperatures and partly from the opportunities they offer for the study of the coexistence of superconductivity and long range magnetic order. The compounds crystallise with a modified ThCr2Si2 structure (14/mmm) with carbon occupying the interstitial (0, 0, 1/2) sites. Several authors have reported a marked sensitivity of the electronic properties of the RNi2B2C compounds to thermal treatment and it has been suggested that B-C site disorder may be responsible for the observed behaviour. Whilst natural B and C have closely similar neutron and X-ray scattering lengths, and the low absorption 11B isotope has precisely the same neutron scattering length as C, that of the highly absorbing 10B isotope is significantly different from that of C. Pulsed neutron time-of-flight diffraction has been used to study a sample of isotopically enriched YNi210B2C. Rietveld refinement of the resulting diffraction pattern indeed confirms that the B-C site disorder may be as high as 10% in these compounds. The results of the structural refinement are presented. (author)

  16. Superconductor Dynamics

    CERN Document Server

    Gömöry, F

    2014-01-01

    Superconductors used in magnet technology could carry extreme currents because of their ability to keep the magnetic flux motionless. The dynamics of the magnetic flux interaction with superconductors is controlled by this property. The cases of electrical transport in a round wire and the magnetization of wires of various shapes (circular, elliptical, plate) in an external magnetic field are analysed. Resistance to the magnetic field penetration means that the field produced by the superconducting magnet is no longer proportional to the supplied current. It also leads to a dissipation of electromagnetic energy. In conductors with unequal transverse dimensions, such as flat cables, the orientation with respect to the magnetic field plays an essential role. A reduction of magnetization currents can be achieved by splitting the core of a superconducting wire into fine filaments; however, new kinds of electrical currents that couple the filaments consequently appear. Basic formulas allowing qualitative analyses ...

  17. Chiral superconductors

    Science.gov (United States)

    Kallin, Catherine; Berlinsky, John

    2016-05-01

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

  18. Ferromagnetic superconductors

    International Nuclear Information System (INIS)

    Highlights: • Review of ferromagnetic superconductors. • Covers UGe2, URhGe and UCoGe and briefly other materials. • The focus is on experimental data and the pairing mechanism. - Abstract: The co-existence of superconductivity and ferromagnetism is of potential interest for spintronics and high magnetic field applications as well as a fascinating fundamental state of matter. The recent focus of research is on a family of ferromagnetic superconductors that are superconducting well below their Curie temperature, the first example of which was discovered in 2000. Although there is a ‘standard’ theoretical model for how magnetic pairing might bring about such a state, why it has only been seen in a few materials that at first sight appear to be very closely related has yet to be fully explained. This review covers the current state of knowledge of the magnetic and superconducting properties of these materials with emphasis on how they conform and differ from the behaviour expected from the ‘standard’ model and from each other

  19. Relaxed superconductors

    CERN Document Server

    Andrade, Tomas

    2014-01-01

    Momentum relaxation can be built into many holographic models without sacrificing homogeneity of the bulk solution. In this paper we study two such models: one in which translational invariance is broken in the dual theory by spatially-dependent sources for massless scalar fields and another that features an additional neutral scalar field. We turn on a charged scalar field in order to explore the condensation of a charged scalar operator in the dual theories. After demonstrating that the relaxed superconductors we construct are thermodynamically relevant, we find that the finite DC electrical conductivity of the normal phase is replaced by a superfluid pole in the broken phase. Moreover, when the normal phase possesses a Drude behaviour at low frequencies, the optical conductivity of the broken phase at low frequencies can be described by a two-fluid model that is a sum of a Drude peak and a superfluid pole, as was found recently for inhomogeneous holographic superconductors. We also study cases in which thi...

  20. Ferromagnetic superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Huxley, Andrew D.

    2015-07-15

    Highlights: • Review of ferromagnetic superconductors. • Covers UGe{sub 2}, URhGe and UCoGe and briefly other materials. • The focus is on experimental data and the pairing mechanism. - Abstract: The co-existence of superconductivity and ferromagnetism is of potential interest for spintronics and high magnetic field applications as well as a fascinating fundamental state of matter. The recent focus of research is on a family of ferromagnetic superconductors that are superconducting well below their Curie temperature, the first example of which was discovered in 2000. Although there is a ‘standard’ theoretical model for how magnetic pairing might bring about such a state, why it has only been seen in a few materials that at first sight appear to be very closely related has yet to be fully explained. This review covers the current state of knowledge of the magnetic and superconducting properties of these materials with emphasis on how they conform and differ from the behaviour expected from the ‘standard’ model and from each other.

  1. High-temperature superconductors

    CERN Document Server

    Saxena, Ajay Kumar

    2010-01-01

    The present book aims at describing the phenomenon of superconductivity and high-temperature superconductors discovered by Bednorz and Muller in 1986. The book covers the superconductivity phenomenon, structure of high-Tc superconductors, critical currents, synthesis routes for high Tc materials, superconductivity in cuprates, the proximity effect and SQUIDs, theories of superconductivity and applications of superconductors.

  2. Hall effect in LuNi2B2C and YNi2B2C borocarbides in normal and superconducting mixed states

    International Nuclear Information System (INIS)

    It was shown that the Hall resistivity ρxy for LuNi2B2C and YNi2B2C is negative in the normal and mixed states and has no sign reversal below Tc. In the mixed state the scaling relation ρxy approximately ρxxβ (ρxx is the longitudinal resistivity) was found for both compounds with β ∼ 2.0. In the normal state a distinct nonlinearity in the ρxy(H) dependence, accompanied by a large magnetoresistance, was found below 40 K only for LuNi2B2C. The difference in the behavior of Lu- and Y-based borocarbides seems to be connected with the difference in the Fermi surfaces of these compounds

  3. Superconductor rotor cooling system

    Energy Technology Data Exchange (ETDEWEB)

    Gamble, Bruce B.; Sidi-Yekhlef, Ahmed; Schwall, Robert E.; Driscoll, David I.; Shoykhet, Boris A.

    2004-11-02

    A system for cooling a superconductor device includes a cryocooler located in a stationary reference frame and a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with a rotating reference frame in which the superconductor device is located. A method of cooling a superconductor device includes locating a cryocooler in a stationary reference frame, and transferring heat from a superconductor device located in a rotating reference frame to the cryocooler through a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with the rotating reference frame.

  4. Photothermal measurements of superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kino, G.S.; Studenmund, W.R.; Fishman, I.M. [Stanford Univ., Stanford, CA (United States)

    1996-12-31

    A photothermal technique has been used to measure diffusion and critical temperature in high temperature superconductors. The technique is particularly suitable for determining material quality and inhomogeneity.

  5. Thermodynamics of many-band superconductors; Thermodynamik von Mehrband-Supraleitern

    Energy Technology Data Exchange (ETDEWEB)

    Waelte, A.

    2006-07-01

    In the present thesis the microscopical properties of the superconducting state of MgCNi{sub 3}, MgB{sub 2}, and some rare earth-transition metal borocarbides are studied by means of measurements of the specific heat. Furthermore the frequency spectrum of the lattice vibrations is estimated. The energy gap of the superconducting state can be determined from the specific heat of the superconducting state, which yields as like as the upper critical mafnetic field H{sub c2}(0) hints on the electron-phonon coupling. From the analysis of these results and the comparison with results from transport measurements as well as the tunnel and point-contact spectroscopy can be concluded, how far the BCS model of superconductivity must be modified in order to be able to describe the superconducting state of the studied compounds. Studies on MgCNi{sub 3}, which lies near a magnetic instability, show that occurring magnetic fluctuations have a bisection of the superconducting transition temperature T{sub C} as consequence. The under this aspect relatively high value of T{sub C}=7 K is a consequence of strong electron-phonon coupling, which is essentailly carried by nickel vibrations stabilized by carbon. A for the first time observed distinct anomaly in the specific heat of the classical many-band superconductor MgB{sub 2} (here with pure {sup 10}B) at about T{sub c}/4=10 K can be understood by means of a two-band model for the case of especially weak coupling between both bands. The analysis of the specific heat of the superconducting phase of the non-magnetic rare earth-nickel borocarbide YNi{sub 2}B{sub 2}C and LuNi{sub 2}B{sub 2}C leads to the conclusion thet visible effects of the many-band electron system are dependent on the mass on the position both of the rare earth and the transition metal. The signal of the superconducting phase transformation visible in the specific heat of the antiferromagnetic HoNi{sub 2}B{sub 2}C is smaller than expected.

  6. Development of superconductor bulk for superconductor bearing

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Chan Joong; Jun, Byung Hyuk; Park, Soon Dong (and others)

    2008-08-15

    Current carrying capacity is one of the most important issues in the consideration of superconductor bulk materials for engineering applications. There are numerous applications of Y-Ba-Cu-O (YBCO) bulk superconductors e.g. magnetic levitation train, flywheel energy storage system, levitation transportation, lunar telescope, centrifugal device, magnetic shielding materials, bulk magnets etc. Accordingly, to obtain YBCO materials in the form of large, single crystals without weak-link problem is necessary. A top seeded melt growth (TSMG) process was used to fabricate single crystal YBCO bulk superconductors. The seeded and infiltration growth (IG) technique was also very promising method for the synthesis of large, single-grain YBCO bulk superconductors with good superconducting properties. 5 wt.% Ag doped Y211 green compacts were sintered at 900 .deg. C {approx} 1200 .deg.C and then a single crystal YBCO was fabricated by an infiltration method. A refinement and uniform distribution of the Y211 particles in the Y123 matrix were achieved by sintering the Ag-doped samples. This enhancement of the critical current density was ascribable to a fine dispersion of the Y211 particles, a low porosity and the presence of Ag particles. In addition, we have designed and manufactured large YBCO single domain with levitation force of 10-13 kg/cm{sup 2} using TSMG processing technique.

  7. Tunnelling in organic superconductors

    OpenAIRE

    Bolech, C. J.; Giamarchi, T.

    2005-01-01

    We discuss the possibility of deciding on the symmetry of the superconducting phase in the organic superconductors (Bechgaard salts), using tunnelling experiments. We first briefly review the properties of organic superconductors, and the possibility to have unconventional (triplet) superconductivity in these systems. We then present a simple scheme for computing the full current-voltage characteristics for tunnelling experiments within the framework of the non-equilibrium Keldysh Green funct...

  8. Layered nickel based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Ronning, Filip [Los Alamos National Laboratory; Bauer, Eric D [Los Alamos National Laboratory; Park, Tuson [Los Alamos National Laboratory; Kurita, Nobuyuki [Los Alamos National Laboratory; Klimczuk, T [Los Alamos National Laboratory; Movshovich, R [Los Alamos National Laboratory; Thompson, J D [Los Alamos National Laboratory; Sefat, A S [ORNL; Mandrus, D [ORNL

    2009-01-01

    We review the properties of Ni-based superconductors which contain Ni{sub 2}X{sub 2} (X=As, P, Bi, Si, Ge, B) planes, a common structural element to the recently discovered FeAs superconductors. We also compare the properties ofthe Ni-and Fe-based systems from a perspective ofelectronic structure as well as structure-property relations.

  9. Calculated x-ray dichroic signals and resonant Bragg diffraction structure factors for dysprosium borocarbide (DyB2C2)

    International Nuclear Information System (INIS)

    Low temperature properties of dysprosium borocarbide display evidence of two continuous phase transitions; it has been proposed that the first involves ordering of Dy quadrupole moments and, at a lower temperature, the second involves ordering of Dy magnetic moments. The latter has been established by magnetic neutron diffraction. Insight to the first phase transition, at TQ, has been sought by resonant x-ray Bragg diffraction, which reveals charge-forbidden (Templeton-Templeton) intensities (00l + 1/2) that increase continuously with decreasing temperature. We show that this scattering is absent if the space group is P4/mbm which has been proposed for the high temperature crystal structure. Tanaka et al. (1999) report evidence that at TQ the lattice distorts and the new space group is P42/mnm. The lower point-group symmetry of Dy ions in this space group is shown by us to allow diffraction at (00l + 1/2) and, indeed, in part it is due to Dy quadrupole moments. In the magnetically ordered phase two neighbouring Dy moments along the c-axis are mutually perpendicular and two neighbouring moments in the plane normal to the c-axis are almost oppositely aligned. This magnetic configuration and point-group symmetry 2/m for Dy sites lead us to predict magnetic and charge scattering at reflections (00l + 1/2) in the magnetically ordered phase. At reflections (h0l) and h odd calculated structure factors are purely magnetic. Our finding is consistent with data collected by Hirota et al. (2000) at the reflection (102). We report expressions for circular and linear dichroic signals and structure factors for Bragg scattering for the interpretation of future experiments. The structure factors are appropriate for azimuthal-angle scans in which the crystal is rotated about the (00l + 1/2) or the (h0l) Bragg wavevectors. (author)

  10. Coupling spin qubits via superconductors

    DEFF Research Database (Denmark)

    Leijnse, Martin; Flensberg, Karsten

    2013-01-01

    We show how superconductors can be used to couple, initialize, and read out spatially separated spin qubits. When two single-electron quantum dots are tunnel coupled to the same superconductor, the singlet component of the two-electron state partially leaks into the superconductor via crossed...

  11. High-Temperature Superconductors

    CERN Document Server

    Saxena, Ajay Kumar

    2012-01-01

    This book presents the current knowledge about superconductivity in high Tc cuprate superconductors. There is a large scientific interest and great potential for technological applications. The book discusses all the aspects related to all families of cuprate superconductors discovered so far. Beginning with the phenomenon of superconductivity, the book covers: the structure of cuprate HTSCs, critical currents, flux pinning, synthesis of HTSCs, proximity effect and SQUIDs, possible applications of high Tc superconductors and theories of superconductivity. Though a high Tc theory is still awaited, this book describes the present scenario and BCS and RVB theories. The second edition was  significantly extended by including film-substrate lattice matching and buffer layer considerations in thin film HTSCs, brick-wall microstructure in the epitaxial films, electronic structure of the CuO2 layer in cuprates, s-wave and d-wave coupling in HTSCs and possible scenarios of theories of high Tc superconductivity.

  12. Nonequilibrium distributions in superconductors

    International Nuclear Information System (INIS)

    The nonequilibrium distribution functions of quasiparticles and phonons in superconductors are calculated for various cases. The conditions at which the nonequilibrium distributions exist are found. The dependences of the temperature and concentration of excitations on the pumping intensity, the sample thickness, and other parameters of the superconductor are calculated. In the current state the dependences of these quantities on the superfluid velocity and the current are investigated, and it is found that the dependence T(v/sub s/) has a minimum, and the current for v/sub s/>v/sup(1)/sub s/o becomes negative. It is also shown that in the nonequilibrium superconductor the state with v/sub s/*not =0 and J(v/sub s/*) =0 may exist. We have determined the nonequilibrium distribution function for a tunnel junction and investigated the V-A characteristic at some conditions for which an absolute negative resistance may exist

  13. 373 K Superconductors

    CERN Document Server

    Kostadinov, Ivan Zahariev

    2016-01-01

    Experimental evidence of superconductors with critical temperatures above $373\\:K$ is presented. In a family of different compounds we demonstrate the superconductor state, the transition to normal state above $387\\:K$, an intermediate $242\\:K$ superconductor, susceptibility up to $350\\:K$, $I-V$ curves at $4.2\\:K$ in magnetic field of $12\\:T$ and current up to $60\\:A$, $300\\:K$ Josephson Junctions and Shapiro steps with radiation of $5\\:GHz$ to $21\\:THz$, $300\\:K$ tapes tests with high currents up to $3000\\:A$ and many $THz$ images of coins and washers. Due to a pending patent, the exact chemical characterization and technological processes for these materials are temporarily withheld and will be presented elsewhere.

  14. Bi-based superconductor

    Directory of Open Access Journals (Sweden)

    S E Mousavi

    2009-08-01

    Full Text Available   In this paper, Bi-Sr-Ca-Cu-O (BCSCCO system superconductor is made by the solid state reaction method. The effect of doping Pb, Cd, Sb, Cu and annealing time on the critical temperature and critical current density have been investigated. The microstructure and morphology of the samples have been studied by X-ray diffraction, scanning electron microscope and energy dispersive X-ray. The results show that the fraction of Bi-2223 phase in the Bi- based superconductor, critical temperature and critical current density depend on the annealing temperature, annealing time and the kind and amount of doping .

  15. High temperature superconductors

    International Nuclear Information System (INIS)

    In the years following the discovery of superconductivity in doped lanthanum copper oxide in late 1986 there has been a large, multinational effort in the study of what are now called high Tc superconductors. As a result of this work at least ten discrete phases of superconducting oxides have been identified. The authors felt it would be useful to have a symposium whose focus was to identify and discuss the common structural features of these oxide superconductors. These proceedings hopefully represent a state of the art view of the correlations between crystal chemistry and superconductivity in metal oxide systems

  16. Irradiation damage in superconductors

    International Nuclear Information System (INIS)

    Most superconductors are quite sensitive to irradiation defects. Critical temperatures may be depressed, critical currents may be increased, by irradiation, but other behaviours may be encountered. In compounds, the sublattice in which defects are created is of significant importance. 24 refs

  17. Manufacturing of Superconductors

    DEFF Research Database (Denmark)

    Bech, Jakob Ilsted; Bay, Niels

    Superconducting tapes based on the ceramic high temperature superconductor (HTS) is a new promising product for high current applications such as electro-magnets and current transmission cables. The tapes are made by the oxide powder in tube (OPIT) method implying drawing and rolling of silver tu...

  18. Coupled superconductors and beyond

    International Nuclear Information System (INIS)

    This paper describes the events leading to the discovery of coupled superconductors, the author move in the 1970s to a perspective where mind plays a role comparable to matter, and the remarkable hostility sometimes encountered by those who venture into unconventional areas.

  19. Growth and study of LuNi2B2C single crystals

    International Nuclear Information System (INIS)

    Rare earth-nickel-borocarbides have attracted much interest in the last years because the compounds show the interplay of superconductivity and magnetic ordering. LuNi2B2C can be considered as non-magnetic reference system of such magnetic borocarbides as HoNi2B2C in which superconducting and antiferromagnetic ordering temperatures, Tc and TN, are similar. So far, LuNi2B2C crystals were only prepared by a flux method. For growing larger crystals we used an optical floating zone (FZ) technique, which already was successful in crystal growth of other RNi2B2C (R = Y,Tb,Ho,Tm,Er) compounds. In the case of LuNi2B2C, the primary crystallization field is far from the stoichiometric composition, and adjacent to the properitectic LuB2C2 phase field an extended region of LuNiBC occurs. Systematic studies of polycrystalline samples revealed that samples with nominal compositions LuNi5B3.5C and LuNi5B3C0.5 are free of the properitectic LuB2C2 and LuNiBC phases. Thus in the FZ crystal growth experiments we used a molten zone which corresponds to these compositions. From the grown LuNi2B2C rods single crystalline pieces have been prepared to investigate Fermi surface peculiarities by magneto-resistance measurements and to study the electronic band structure

  20. Platform for engineering topological superconductors: Superlattices on Rashba superconductors

    Science.gov (United States)

    Lu, Yao; He, Wen-Yu; Xu, Dong-Hui; Lin, Nian; Law, K. T.

    2016-07-01

    The search for topological superconductors which support Majorana fermion excitations has been an important topic in condensed matter physics. In this work, we propose an experimental scheme for engineering topological superconductors. In this scheme, by manipulating the superlattice structure of organic molecules placed on top of a superconductor with Rashba spin-orbit coupling, topological superconducting phases can be achieved without or with little fine tuning of the chemical potential. Moreover, superconductors with different Chern numbers can be obtained by changing the superlattice structure of the organic molecules.

  1. Iron pnictide superconductors

    International Nuclear Information System (INIS)

    The scope of this dissertation therefore has not only been the synthesis of various new superconducting and non-superconducting iron pnictides of several structural families but also their in-depth crystallographic and physical characterisation. In Chapters 3 - 6, the family of the ZrCuSiAs-type (1111) compounds is subject of discussion. The solid solution series La(CoxFe1-x)PO is analysed regarding magnetic and superconducting properties and the new compounds EuMnPF and REZnPO, as well as the new superconductor parent compound SrFeAsF are presented. Chapters 7 - 9 are dedicated to the new iron arsenide superconductors of the ThCr2Si2-type (122 family). Therein, also the discovery of the first superconductor in this structural family, Ba0.6K0.4Fe2As2, is unveiled. A detailed examination of the complete solid solution series (Ba1-xKx)Fe2As2 is presented. Moreover, the crystallographic phase transitions of the closely related compounds SrFe2As2 and EuFe2As2 are characterised and the superconductors Sr1-xKxFe2As2 and Ca1-xNaxFe2As2 are examined for magnetic and phononic excitations. In Chapter 10, the redetermined crystal structure of the superconductor Fe(Se1-xTex) (11-type) is presented from a chemist's point of view. Chapters 11 - 14 look into the superconducting and non-superconducting iron arsenides of more complex structural families (32522-type and 21311-type). Therein, crystallographic and magnetic details of Sr3Sc2O5Fe2As2 are presented and Ba2ScO3FeAs and Sr2CrO3FeAs, the first two members of the new 21311-type are portrayed. Sr2CrO3FeAs is looked at in close detail with various methods, so e.g. the spin structure of the magnetically ordered compound is solved and a possible reason for the absence of superconductivity in this compound is given. Finally, the superconductor Sr2VO3FeAs is scrutinised and necessary prerequisites for superconductivity in this compound are suggested. (orig.)

  2. Superconductor stability 90: A review

    International Nuclear Information System (INIS)

    This paper reviews some recent developments in the field of stability of superconductors. The main topics dealt with are hydrodynamic phenomena in cable-in-conduit superconductors, namely, multiple stability, quench pressure, thermal expulsion, and thermal hydraulic quenchback, traveling normal zones in large, composite conductors, such as those intended for SMES, and the stability of vapor-cooled leads made of high-temperature superconductors. 31 refs., 5 figs

  3. Introduction to Holographic Superconductor Models

    CERN Document Server

    Cai, Rong-Gen; Li, Li-Fang; Yang, Run-Qiu

    2015-01-01

    In the last years it has been shown that some properties of strongly coupled superconductors can be potentially described by classical general relativity living in one higher dimension, which is known as holographic superconductors. This paper gives a quick and introductory overview of some holographic superconductor models with s-wave, p-wave and d-wave orders in the literature from point of view of bottom-up, and summarizes some basic properties of these holographic models in various regimes. The competition and coexistence of these superconductivity orders are also studied in these superconductor models.

  4. Experiments on superconductors

    International Nuclear Information System (INIS)

    The book requires no prior knowledge in theoretical physics. It presents fundamental knowledge on superconductors in a clear manner, using experiments ot describe superconductor phenomena so even laymen can understand. The best-known experiment is the suspended magnet experiment based on the Meissner effect. Experiments show how the transition temperature, the critical current, the critical magnetic field strength, the suspension effect and the critical frequency of a HF current can be identified. It is shown how strong magnetic fields can be produced b multifilament HT superconducting wires. The handling of liquid nitrogen and the effects of cryogenic temperatures on electronic components are demonstrated by experiments. Suppliers of materials required for the experiments are listed as well. (orig.)

  5. Vortex cutting in superconductors

    Science.gov (United States)

    Glatz, A.; Vlasko-Vlasov, V. K.; Kwok, W. K.; Crabtree, G. W.

    2016-08-01

    Vortex cutting and reconnection is an intriguing and still-unsolved problem central to many areas of classical and quantum physics, including hydrodynamics, astrophysics, and superconductivity. Here, we describe a comprehensive investigation of the crossing of magnetic vortices in superconductors using time dependent Ginsburg-Landau modeling. Within a macroscopic volume, we simulate initial magnetization of an anisotropic high temperature superconductor followed by subsequent remagnetization with perpendicular magnetic fields, creating the crossing of the initial and newly generated vortices. The time resolved evolution of vortex lines as they approach each other, contort, locally conjoin, and detach, elucidates the fine details of the vortex-crossing scenario under practical situations with many interacting vortices in the presence of weak pinning. Our simulations also reveal left-handed helical vortex instabilities that accompany the remagnetization process and participate in the vortex crossing events.

  6. High-temperature superconductors

    International Nuclear Information System (INIS)

    A number of proposed applications of superconductivity for the electric utility sector are described, the current status of their development is summarized, and the potential impact of successful development of high-temperature superconductors (HTSCs) is discussed in this paper. Performance goals for development of HTSCs are presented and compared with their current status (as of April 1990). Applications discussed include large-scale generators, motors, transmission lines, magnetic storage, transformers, power electronics, and fault-current limiters

  7. Introductory notes on holographic superconductors

    OpenAIRE

    Musso, Daniele

    2014-01-01

    The purpose of these lecture notes is to give a quick and introductory overview of holographic superconductors. Besides the actual description of the standard holographic superconductor, attention is paid to the motivations and the relation with the previous, non-holographic context.

  8. Iron pnictide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tegel, Marcus Christian

    2011-03-22

    The scope of this dissertation therefore has not only been the synthesis of various new superconducting and non-superconducting iron pnictides of several structural families but also their in-depth crystallographic and physical characterisation. In Chapters 3 - 6, the family of the ZrCuSiAs-type (1111) compounds is subject of discussion. The solid solution series La(Co{sub x}Fe{sub 1-x})PO is analysed regarding magnetic and superconducting properties and the new compounds EuMnPF and REZnPO, as well as the new superconductor parent compound SrFeAsF are presented. Chapters 7 - 9 are dedicated to the new iron arsenide superconductors of the ThCr{sub 2}Si{sub 2}-type (122 family). Therein, also the discovery of the first superconductor in this structural family, Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2}, is unveiled. A detailed examination of the complete solid solution series (Ba{sub 1-x}K{sub x})Fe{sub 2}As{sub 2} is presented. Moreover, the crystallographic phase transitions of the closely related compounds SrFe{sub 2}As{sub 2} and EuFe{sub 2}As{sub 2} are characterised and the superconductors Sr{sub 1-x}K{sub x}Fe{sub 2}As{sub 2} and Ca{sub 1-x}Na{sub x}Fe{sub 2}As{sub 2} are examined for magnetic and phononic excitations. In Chapter 10, the redetermined crystal structure of the superconductor Fe(Se{sub 1-x}Te{sub x}) (11-type) is presented from a chemist's point of view. Chapters 11 - 14 look into the superconducting and non-superconducting iron arsenides of more complex structural families (32522-type and 21311-type). Therein, crystallographic and magnetic details of Sr{sub 3}Sc{sub 2}O{sub 5}Fe{sub 2}As{sub 2} are presented and Ba{sub 2}ScO{sub 3}FeAs and Sr{sub 2}CrO{sub 3}FeAs, the first two members of the new 21311-type are portrayed. Sr{sub 2}CrO{sub 3}FeAs is looked at in close detail with various methods, so e.g. the spin structure of the magnetically ordered compound is solved and a possible reason for the absence of superconductivity in this compound

  9. A Dirty Holographic Superconductor

    CERN Document Server

    Arean, Daniel; Zayas, Leopoldo A Pando; Landea, Ignacio Salazar; Scardicchio, Antonello

    2013-01-01

    We implement the effects of disorder on a holographic superconductor by introducing a random chemical potential on the boundary. We consider various realizations of disorder and find that $T_c$ is enhanced. We also present evidence for a precise form of renormalization in this system. Namely, when the random chemical potential is characterized by a power spectrum of the form $k^{-2\\alpha}$ we find that the power spectra of the condensate and the charge density are accurately and universally governed by linear functions of $\\alpha$.

  10. High temperature superconductors

    CERN Document Server

    Paranthaman, Parans

    2010-01-01

    This essential reference provides the most comprehensive presentation of the state of the art in the field of high temperature superconductors. This growing field of research and applications is currently being supported by numerous governmental and industrial initiatives in the United States, Asia and Europe to overcome grid energy distribution issues. The technology is particularly intended for densely populated areas. It is now being commercialized for power-delivery devices, such as power transmission lines and cables, motors and generators. Applications in electric utilities include current limiters, long transmission lines and energy-storage devices that will help industries avoid dips in electric power.

  11. Upper critical field in borocarbides

    International Nuclear Information System (INIS)

    Resistive measurement of superconducting transitions under externally applied magnetic fields in polycrystalline samples of YPd5B3C0.3 and YNi2B2C has revealed a marked positive curvature in the temperature dependence of Hc2, with the slope - dHc2/dT increasing monotonically from Tc to 4.2 K. This observed positive curvature is in marked contrast with the predictions of the conventional theories of upper critical field. It is possible that a compensation mechanism may have to be invoked to account for the observed results. (orig.)

  12. Spin manipulation in nanoscale superconductors

    Science.gov (United States)

    Beckmann, D.

    2016-04-01

    The interplay of superconductivity and magnetism in nanoscale structures has attracted considerable attention in recent years due to the exciting new physics created by the competition of these antagonistic ordering phenomena, and the prospect of exploiting this competition for superconducting spintronics devices. While much of the attention is focused on spin-polarized supercurrents created by the triplet proximity effect, the recent discovery of long range quasiparticle spin transport in high-field superconductors has rekindled interest in spin-dependent nonequilibrium properties of superconductors. In this review, the experimental situation on nonequilibrium spin injection into superconductors is discussed, and open questions and possible future directions of the field are outlined.

  13. Materials design for new superconductors

    Science.gov (United States)

    Norman, M. R.

    2016-07-01

    Since the announcement in 2011 of the Materials Genome Initiative by the Obama administration, much attention has been given to the subject of materials design to accelerate the discovery of new materials that could have technological implications. Although having its biggest impact for more applied materials like batteries, there is increasing interest in applying these ideas to predict new superconductors. This is obviously a challenge, given that superconductivity is a many body phenomenon, with whole classes of known superconductors lacking a quantitative theory. Given this caveat, various efforts to formulate materials design principles for superconductors are reviewed here, with a focus on surveying the periodic table in an attempt to identify cuprate analogues.

  14. Crystalline color superconductors: A review

    CERN Document Server

    Anglani, Roberto; Ciminale, Marco; Gatto, Raoul; Ippolito, Nicola; Mannarelli, Massimo; Ruggieri, Marco

    2013-01-01

    Non-homogenous superconductors and non-homogenous superfluids appear in a variety of contexts which include quark matter at extreme densities, fermionic systems of cold atoms, type-II cuprates and organic superconductors. In the present review we shall focus on the properties of quark matter at high baryonic density which can exist in the interior of compact stars. The conditions that are realized in this stellar objects tend to disfavor standard symmetric BCS pairing and may be in favor of a non-homogenous color superconducting phase. We discuss in details the properties of non-homogenous color superconductors and in particular of crystalline color superconductors. We also review the possible astrophysical signatures associated with the presence of non-homogenous color superconducting phases within the core of compact stars.

  15. Parity violation effects in superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Belov, Nikolay A. [Max Planck Institute for Nuclear Physics, Saupfercheckweg 1, 69117 Heidelberg (Germany); Harman, Zoltan [Max Planck Institute for Nuclear Physics, Saupfercheckweg 1, 69117 Heidelberg (Germany); ExtreMe Matter Institute (EMMI), Planckstrasse 1, 64291 Darmstadt (Germany)

    2013-07-01

    Parity violation effects in a circular superconducting Josephson junction has been investigated in the eighties. That time it appeared that this phenomenon was not significant enough to be experimentally observable. In our work we show, that this rate can be increased in the case of a circular Josephson junction of an unconventional superconductor. Furthermore, this phenomenon can be more significant in the case of the ferromagnetic p-wave unconventional superconductor, since the effect is stronger for polarized pairs.

  16. High temperature superconductor current leads

    International Nuclear Information System (INIS)

    Full text: The use of superconductors in high electrical current applications (magnets, transformers, generators etc.) usually requires cooling with liquid Helium, which is very expensive. The superconductor itself produces no heat, and the design of Helium dewars is very advanced. Therefore most of the heat loss, i.e. Helium consumption, comes from the current lead which connects the superconductor with its power source at room temperature. The current lead usually consists of a pair of thick copper wires. The discovery of the High Temperature Superconductors makes it possible to replace a part of the copper with superconducting material. This drastically reduces the heat losses because a) the superconductor generates no resistive heat and b) it is a very poor thermal conductor compared with the copper. In this work silver-sheathed superconducting tapes are used as current lead components. The work comprises both the production of the tapes and the overall design of the leads, in order to a) maximize the current capacity ('critical current') of the superconductor, b) minimize the thermal conductivity of the silver clad, and c) optimize the cooling conditions

  17. Moessbauer isomer shift anomalies in a superconductor

    International Nuclear Information System (INIS)

    We have investigated the Moessbauer isomer shift in a superconductor within a simple model. Our results are in reasonable agreement with iron dopped superconductors data which has been reported in the literature. (author)

  18. Axion topological field theory of topological superconductors

    OpenAIRE

    Qi, Xiao-Liang; Witten, Edward; Zhang, Shou-Cheng

    2012-01-01

    Topological superconductors are gapped superconductors with gapless and topologically robust quasiparticles propagating on the boundary. In this paper, we present a topological field theory description of three-dimensional time-reversal invariant topological superconductors. In our theory the topological superconductor is characterized by a topological coupling between the electromagnetic field and the superconducting phase fluctuation, which has the same form as the coupling of "axions" with...

  19. Superconductors: The long road ahead

    International Nuclear Information System (INIS)

    Before the discovery of high-temperature superconductors, progress in superconductivity was measured by quite small increases in critical temperature, often of less than one degree. Today, there is no reason to believe that the dramatic leaps in critical temperature inaugurated by superconducting ceramics are over. Researchers may find new high-temperature superconducting materials with less severe technical limitations than the ceramics we know today. And if the day ever comes when a superconductor can be reliably manufactured to operate effectively at room temperature, then superconductors will be incorporated in a broad range of everyday household devices - motors, appliances, even children's toys - with a large consumer market. High-temperature superconductors may also cause us to extensively revise our traditional theories about how superconductivity works. Should it run out that superconductivity in ceramics involves new physical mechanisms, then these mechanisms could lead to applications never considered before. The recent discoveries have already reinvigorated superconductivity research. What was once largely the domain of a relatively small group of scientists has become a genuinely multidisciplinary realm. Now physicists, materials scientists, chemists, metallurgists, ceramists, and solid-state electronics engineers are all focusing on superconductivity. The cross-fertilization of these disciplines should contribute to further discoveries of importance to the practical application of superconductors

  20. Topological semimetals and nodal superconductors

    Science.gov (United States)

    Chang, Po-Yao

    Besides topological band insulators, which have a full bulk gap, there are also gapless phases of matter that belong to the broad class of topological materials, such as topological semimetals and nodal superconductors. We systematically study these gapless topological phases described by the Bloch and Bogoliubov-de Gennes Hamiltonians. We discuss a generalized bulk-boundary correspondence, which relates the topological properties in the bulk of gapless topological phases and the protected zero-energy states at the boundary. We study examples of gapless topological phases, focusing in particular on nodal superconductors, such as nodal noncentrosymmetric superconductors (NCSs). We compute the surface density of states of nodal NCSs and interpret experimental measurements of surface states. In addition, we investigate Majorana vortex-bound states in both nodal and fully gapped NCSs using numerical and analytical methods. We show that different topological properties of the bulk Bogoliubov-quasiparticle wave functions reflect themselves in different types of zero-energy vortex-bound states. In particular, in the case of NCSs with tetragonal point-group symmetry, we find that the stability of these Majorana zero modes is guaranteed by a combination of reflection, time-reversal, and particle-hole symmetries. Finally, by using K-theory arguments and a dimensional reduction procedure from higher-dimensional topological insulators and superconductors, we derive a classification of topologically stable Fermi surfaces in semimetals and nodal lines in superconductors.

  1. Tunneling spectroscopy of novel superconductors

    International Nuclear Information System (INIS)

    Recent discoveries of exciting new superconductors have led to further exciting speculations about novel mechanisms and/or pairing. Tunneling spectroscopy can again play an important role in establishing the applicability of these ideas to specific superconductors. In addition to the traditional role of verifying in detail the electron-phonon coupling through α2F, in many cases the magnitude of the gap compared to the BCS prediction or the crystalline gap anisotropy can reveal direct information about novel mechanisms and/or pairing. Since many of these new materials have only been available as bulk samples, or bulk single-crystal studies are desired, the technique of vacuum tunneling spectroscopy, pioneered by Poppe (1981) for superconductors, is most appropriate. However, thick, nonconducting surface layers are often found which prevent true vacuum tunneling. For these samples, mechanical contact of the tunneling tip is required to break through the surface layer to the superconductor below. The resulting point-contact tunneling can, however, emulate many of the results of true tunneling through a vacuum or insulator. In this paper, they shall briefly review relevant tunneling techniques and some recent experiments on magnetic, organic, heavy fermion and high-T/sub c/ oxide superconductors. Connections are made to theoretical ideas, especially regarding novel mechanisms and/or pairing

  2. Overview of recent magnetic studies of high Tc cuprate parent compounds and related materials

    International Nuclear Information System (INIS)

    Recent studies of the magnetic properties of several high superconducting transition temperature (Tc) cuprate parent compounds and related materials will be reviewed. The observations of a Heisenberg to XY-like crossover upon cooling below ∼ 300 K towards the Neel temperature TN=257 K and a subsequent magnetic field-induced XY-like to Ising-like crossover near TN in single crystals of the K2NiF4-type spin 1/2 model compound Sr2CuO2Cl2 will be described. The spin 1/2 linear chain compound Sr2CuO3, the parent of the Sr2CuO3+δ oxygen-doped superconductors, is found to exhibit classic Bonner-Fisher magnetic behavior, with a large antiferromagnetic Cu-Cu superexchange coupling constant. Studies of the evolution of La2-xSrxCuO4 with Sr doping in the insulating regime (x 2.1, a copper-oxygen cluster compound, exhibits ferromagnetic rather than antiferromagnetic Cu-Cu superexchange interactions. Finally, a summary of the magnetic properties of single crystals of the recently discovered RNi2B2C layered structure superconductors will be given. (orig.)

  3. Chern-Simons Superconductor

    CERN Document Server

    Banerjee, Nabamita; Roychowdhury, Dibakar

    2013-01-01

    We study the effect of a bulk Chern-Simons (CS) term on 3+1 dimensional type II superconductor in the context of the AdS/CFT correspondence. We holographically compute the super-current and find that it is non-local in nature. It receives non trivial corrections due to presence of the CS term. Considering a large limit of a parameter "lambda" (we call this limit as long wave length limit), which is effectively the high temperature limit of the theory, we find that this non-local super-current boils down to a local quantity. The leading term (without the CS term) of this current matches with the result of Ginzburg-Landau (GL) theory. We compute the effect of the CS term on GL current and find that the effect is highly suppressed at large temperature (~1/T^4). Finally, free energy of the vortex configuration has been calculated. The free energy also receives non trivial correction at the order of 1/lambda^2 in the long wave length approximation.

  4. π-0 transition in superconductor-ferromagnetic-superconductor junctions

    International Nuclear Information System (INIS)

    Superconductor-ferromagnetic-superconductor (SFS) Josephson junctions are known to exhibit a transition between π and 0 states. The π-0 phase diagram of an SFS junction depending on the transparency of an intermediate insulating layer is considered. It is shown that in general, the Josephson critical current is nonzero at the π-0 transitions temperature. Contributions to the current from the two spin channels nearly compensate each other and the first harmonic of the Josephson current as a function of phase difference is suppressed. However, higher harmonics give a nonzero contribution to the supercurrent

  5. Thin film superconductor magnetic bearings

    Science.gov (United States)

    Weinberger, Bernard R.

    1995-12-26

    A superconductor magnetic bearing includes a shaft (10) that is subject to a load (L) and rotatable around an axis of rotation, a magnet (12) mounted to the shaft, and a stator (14) in proximity to the shaft. The stator (14) has a superconductor thin film assembly (16) positioned to interact with the magnet (12) to produce a levitation force on the shaft (10) that supports the load (L). The thin film assembly (16) includes at least two superconductor thin films (18) and at least one substrate (20). Each thin film (18) is positioned on a substrate (20) and all the thin films are positioned such that an applied magnetic field from the magnet (12) passes through all the thin films. A similar bearing in which the thin film assembly (16) is mounted on the shaft (10) and the magnet (12) is part of the stator (14) also can be constructed.

  6. Superconductor stability, 1983: a review

    International Nuclear Information System (INIS)

    Three main topics have been discussed in this paper, namely, internally cooled superconductors, cooling by superfluid helium, and metastable magnets. The discussion of each has centered around a dominant idea, and it is fitting to highlight these ideas by way of conclusion. With regard to internally cooled superconductors, most of what we have learned in the last few years centers on the strong motion caused by the thermal expansion of helium. How naive were our early calculations that treated the helium as though it were incompressible. Our discussion of He-II was organized around the Gorter-Mellink relation and the solutions of the nonlinear diffusion equation it gives rise to. And our discussion of metastable magnets revolved around the fruitful concept of the MPZ. These three ideas are sturdy trunks that support much of the thought about superconductor stability that has flowered in the past several years

  7. Heat transport in nonuniform superconductors

    Science.gov (United States)

    Richard, Caroline; Vorontsov, Anton B.

    2016-08-01

    We calculate electronic energy transport in inhomogeneous superconductors using a fully self-consistent nonequilibrium quasiclassical Keldysh approach. We develop a general theory and apply it to a superconductor with an order parameter that forms domain walls of the type encountered in the Fulde-Ferrell-Larkin-Ovchinnikov state. The heat transport in the presence of a domain wall is inherently anisotropic and nonlocal. The bound states in the nonuniform region play a crucial role and control heat transport in several ways: (i) they modify the spectrum of quasiparticle states and result in Andreev reflection processes and (ii) they hybridize with the impurity band and produce a local transport environment with properties very different from those in a uniform superconductor. As a result of this interplay, heat transport becomes highly sensitive to temperature, magnetic field, and disorder. For strongly scattering impurities, we find that the transport across domain walls at low temperatures is considerably more efficient than in the uniform superconducting state.

  8. Hard-gapped holographic superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Basu, Pallab, E-mail: pallab@phas.ubc.c [Department of Physics and Astronomy University of British Columbia, Vancouver, BC V6T 1Z1 (Canada); He Jianyang, E-mail: jyhe@phas.ubc.c [Department of Physics and Astronomy University of British Columbia, Vancouver, BC V6T 1Z1 (Canada); Mukherjee, Anindya, E-mail: anindya@phas.ubc.c [Department of Physics and Astronomy University of British Columbia, Vancouver, BC V6T 1Z1 (Canada); Shieh, H.-H., E-mail: shieh@phas.ubc.c [Department of Physics and Astronomy University of British Columbia, Vancouver, BC V6T 1Z1 (Canada); Perimeter Institute for Theoretical Physics, 31 Caroline Street North Waterloo, Ontario, N2L 2Y5 (Canada)

    2010-05-17

    In this work we discuss the zero temperature limit of a 'p-wave' holographic superconductor. The bulk description consists of a non-Abelian SU(2) gauge fields minimally coupled to gravity. We numerically construct the zero temperature solution which is the gravity dual of the superconducting ground state of the 'p-wave' holographic superconductors. The solution is a smooth soliton with zero horizon size and shows an emergent conformal symmetry in the IR. We found the expected superconducting behavior. Using the near horizon analysis we show that the system has a 'hard gap' for the relevant gauge field fluctuations. At zero temperature the real part of the conductivity is zero for an excitation frequency less than the gap frequency. This is in contrast with what has been observed in similar scalar-gravity-gauge systems (holographic superconductors). We also discuss the low but finite temperature behavior of our solution.

  9. Iron-based superconductors: Foreword

    OpenAIRE

    Alloul, Henri; Cano, Andres

    2016-01-01

    We introduce the thematic (open access) issue published in Comptes Rendus Physique. This issue is focused on the so-called Fe-based superconductors that, since the discovery of superconductivity in F-doped LaFeAsO by Hosono group in 2008, have become one of the latest hot topics in the field of condensed matter. The idea is to give an up-to-date overview of the fundamental properties of this novel family of high-Tc superconductors. First we briefly recall the scientific context of superconduc...

  10. Thin-film ternary superconductors

    International Nuclear Information System (INIS)

    Physical properties and preparation methods of thin film ternary superconductors, (mainly molybdenum chalcogenides) are reviewed. Properties discussed include the superconducting critical fields and critical currents, resistivity and the Hall effect. Experimental results at low temperatures, together with electron microscopy data are used to determine magnetic flux pinning mechanisms in films. Flux pinning results, together with an empirical model for pinning, are used to get estimates for possible applications of thin film ternary superconductors where high current densities are needed in the presence of high magnetic fields. The normal state experimental data is used to derive several Fermi surface parameters, e.g. the Fermi velocity and the effective Fermi surface area. (orig.)

  11. Multifilamentary niobium tin superconductor tape

    Science.gov (United States)

    Brisbin, P. H.; Coles, W. D.

    1975-01-01

    In the method proposed for fabricating multifilamentary Nb3Sn tape, filamentary superconducting paths are produced in standard commercial superconductor tape by chemical milling of separator slots through the Nb3Sn layer. The multifilament configuration features a matrix of ten 1.2 mm wide parallel helical superconducting paths along the length of the tape. The paths are spaced 0.4 mm apart. Tapes tested as small pancake coils demonstrated the integrity and continuity of the matrix, and showed that critical current was sustained in direct proportion to retained superconductor.

  12. Oxygen diffusion in cuprate superconductors

    International Nuclear Information System (INIS)

    Superconducting properties of the cuprate superconductors depend on the oxygen content of the material; the diffusion of oxygen is thus an important process in the fabrication and application of these materials. This article reviews studies of the diffusion of oxygen in La2-xSrxCuO4, YBa2Cu3O7-δ, YBa2Cu4O8, and the Bi2Sr2Can-1CunO2+4 (n = 1, and 2) superconductors, and attempt to elucidate the atomic mechanisms responsible

  13. Plasmons in cuprate superconductors

    International Nuclear Information System (INIS)

    The customary way of determining the complex dielectric constant from the measured reflectance spectra suffers from large uncertainties because of the extrapolations required for the Kramers-Kronig transformation. To avoid these, a method is introduced in which reflectance and ellipsometric data on single crystals and epitaxial films are combined. Utilizing this approach, the spectral functions of YBa2Cu3O7 (Y-Ba-Cu-O) and Bi2Sr2CaCu2O8 (Bi-Sr-Ca-Cu-O) are determined with substantially improved accuracy. This enables the unambiguous identification of optic plasmons at 1.4 eV in Y-Ba-Cu-O and at 1.1 eV in Bi-Sr-Ca-Cu-O. No other low-lying optic plasmons are detected, which likely rules out most plasmon-mediated superconductivity models. Next, the bare plasma frequency is found to be ℎωp=3.2±0.3 eV in Y-Ba-Cu-O and ℎωp=2.4±0.3 eV in Bi-Sr-Ca-Cu-O. These values support ascribing the strong infrared absorption to charge carriers which, however, are not free-electron-like, but rather show characteristic polaronic behavior. Finally, in both Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O, it is found that Im(-1/ε)=βω2 for small ω, and this law is conjectured to be universal for all layered cuprate superconductors. It is again not Drude-like; it may be compatible with the layered electron-gas model. The latter implies existence of a broad band of acoustic plasmon branches

  14. Development of superconductor application technology

    International Nuclear Information System (INIS)

    Fabrication of high Tc bulk superconductor and its application, fabrication of superconducting wire for electric power device and analysis for cryogenic system were carried out for developing superconductor application technologies for electric power system. High quality YBaCuO bulk superconductor was fabricated by controlling initial powder preparation process and prototype flywheel energy storage device was designed basically. The superconducting levitation force measuring device was made to examine the property of prepared superconductor specimen. Systematic studies onthe method of starting powder preparation, mechanical fabrication process, heat treatment condition and analysis of plastic deformation were carried out to increase the stability and reproducibility of superconducting wire. A starting power with good reactivity and fine particle size was obtained by mechanical grinding, control of phase assemblage, and emulsion drying method. Ag/BSCCO tape with good cross sectional shape and Jc of 20,000 A/cm2 was fabricated by applying CIP packing procedure. Multifilamentary wire with Jc of 10,000 A/cm2 was fabricated by rolling method using square billet as starting shape. The joining of the multifilamentary wire was done by etching and pressing process and showed 50% of joining efficiency. Analysis on the heat loss in cryostat for high Tc superconducting device was carried out for optimum design of the future cryogenic system. (author). 66 refs., 104 figs

  15. Testing Superconductor Logic Integrated Circuits

    OpenAIRE

    Joseph, Arun A.; Kerkhoff, Hans G.

    2005-01-01

    Superconductor logic has the potential of extremely low-power consumption and ultra-fast digital signal processing. Unfortunately, the obtained yield of the present processes is low and specific faults occur. This paper deals with fault-modelling, Design-for-Test structures, and ATPG for these integrated circuits.

  16. High Temperature Superconductor Machine Prototype

    DEFF Research Database (Denmark)

    Mijatovic, Nenad; Jensen, Bogi Bech; Træholt, Chresten;

    2011-01-01

    A versatile testing platform for a High Temperature Superconductor (HTS) machine has been constructed. The stationary HTS field winding can carry up to 10 coils and it is operated at a temperature of 77K. The rotating armature is at room temperature. Test results and performance for the HTS field...

  17. Development of superconductor application technology

    Energy Technology Data Exchange (ETDEWEB)

    Hong, G. W.; Kim, C. J.; Lee, H. G.; Lee, H. J.; Kim, K. B.; Won, D. Y.; Jang, K. I.; Kwon, S. C.; Kim, W. J.; Ji, Y. A.; Yang, S. W.; Kim, W. K.; Park, S. D.; Lee, M. H.; Lee, D. M.; Park, H. W.; Yu, J. K.; Lee, I. S.; Kim, J. J.; Choi, H. S.; Chu, Y.; Kim, Y. S.; Kim, D. H.

    1997-09-01

    Fabrication of high Tc bulk superconductor and its application, fabrication of superconducting wire for electric power device and analysis for cryogenic system were carried out for developing superconductor application technologies for electric power system. High quality YBaCuO bulk superconductor was fabricated by controlling initial powder preparation process and prototype flywheel energy storage device was designed basically. The superconducting levitation force measuring device was made to examine the property of prepared superconductor specimen. Systematic studies onthe method of starting powder preparation, mechanical fabrication process, heat treatment condition and analysis of plastic deformation were carried out to increase the stability and reproducibility of superconducting wire. A starting power with good reactivity and fine particle size was obtained by mechanical grinding, control of phase assemblage, and emulsion drying method. Ag/BSCCO tape with good cross sectional shape and Jc of 20,000 A/cm{sup 2} was fabricated by applying CIP packing procedure. Multifilamentary wire with Jc of 10,000 A/cm{sup 2} was fabricated by rolling method using square billet as starting shape. The joining of the multifilamentary wire was done by etching and pressing process and showed 50% of joining efficiency. Analysis on the heat loss in cryostat for high Tc superconducting device was carried out for optimum design of the future cryogenic system. (author). 66 refs., 104 figs.

  18. Chemistry of high temperature superconductors

    CERN Document Server

    1991-01-01

    This review volume contains the most up-to-date articles on the chemical aspects of high temperature oxide superconductors. These articles are written by some of the leading scientists in the field and includes a comprehensive list of references. This is an essential volume for researchers working in the fields of ceramics, materials science and chemistry.

  19. Josephson Current in Superconductor-Ferromagnet/Insulator/d-Wave Superconductor Junctions

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Wei; DONG Zheng-Chao

    2005-01-01

    Solving the Bogoliubov-de Gennes equation, the energy levels of bound states are obtained in the ferromagnetic superconductor. The Josephson currents in a ferromagnetic superconductor/Insulator/d-wave superconductor junction are calculated as a function of the exchange field, temperature, and insulating barrier strength. It is found that the Josephson critical current is always suppressed by the presence of exchange field h and depends on crystalline axis orientation of d-wave superconductor.

  20. Switching effects in superconductor/ferromagnet/superconductor graphene junctions

    International Nuclear Information System (INIS)

    The Josephson effect in the superconductor/ferromagnet/superconductor (SFS) graphene Josephson junction is studied using the Dirac Bogoliubov-de Gennes (DBdG) formalism. It is shown that the SFS graphene junction drives 0—π transition with the increasing of p = h0L/vFħ, which captures the effects of both the exchange field and the length of the junction; the spin-down current is dominant. The 0 state is stable for p < pc (critical value pc ≈ 0.80) and the π state is stable for p > pc, where the free energy minima are at φg = 0 and φg = π, respectively. The coexistence of the 0 and π states appears in the vicinity of pc. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  1. Balanced superconductor-insulator-superconductor mixer on a silicon membrane

    CERN Document Server

    Westig, M P; Stutzki, J; Schultz, M; Justen, M; Honingh, C E

    2011-01-01

    We present a 380-520 GHz balanced superconductor-insulator-superconductor (SIS) mixer on a single silicon substrate. All radio-frequency (RF) circuit components are fabricated on a $9 \\mu$m thick membrane and the intermediate frequency (IF) is separately amplified and combined. The balanced mixer chip, using Nb/Al/Al$_{2}$O$_{3}$/Nb SIS junctions, is mounted in a copper tellurium waveguide block at 4.2 K using Au beam lead contacts. We find uncorrected minimum receiver double-sideband noise temperatures of 70 K and a noise suppression of up to 18 dB, measured within a 440-495 GHz RF and a 4-8 GHz IF band, representing state-of-the-art device performance.

  2. Andreev levels in a Josephson superconductor graphene superconductor nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Manjarrés, Diego A., E-mail: damanjarrnsg@unal.edu.co; Gomez P, S., E-mail: sgomezp@unal.edu.co; Herrera, William J., E-mail: jherreraw@unal.edu.co

    2014-12-15

    We obtain the bound states in superconductor-graphene-superconductor nanostructure, which are responsible for the Josephson effect. The coupling between graphene and each superconducting region is modeled as two different hopping parameters in the respective SG and GS interfaces. With the purpose of determining the local density of states and the spectrum, the Green function of the junction is calculated resolving the Dyson equation. We obtain that the number of levels depends on the width and doping of graphene region and this occurs for the two types of edge (armchair or zigzag). We investigate the behavior of the bound states as a function of the transparency. In the limit of a transparent junction, the results obtained by the Green's function method reproduce those present in the literature. In the tunnel limit the spectrum is different for armchair and zigzag edges.

  3. Andreev levels in a Josephson superconductor graphene superconductor nanostructure

    International Nuclear Information System (INIS)

    We obtain the bound states in superconductor-graphene-superconductor nanostructure, which are responsible for the Josephson effect. The coupling between graphene and each superconducting region is modeled as two different hopping parameters in the respective SG and GS interfaces. With the purpose of determining the local density of states and the spectrum, the Green function of the junction is calculated resolving the Dyson equation. We obtain that the number of levels depends on the width and doping of graphene region and this occurs for the two types of edge (armchair or zigzag). We investigate the behavior of the bound states as a function of the transparency. In the limit of a transparent junction, the results obtained by the Green's function method reproduce those present in the literature. In the tunnel limit the spectrum is different for armchair and zigzag edges

  4. Design for a Superconductor Discovery Engine (SCODEngine)

    Science.gov (United States)

    Isikaku-Ironkwe, O. Paul

    2010-03-01

    One of the grand challenges of superconductivity is achieving a paradigm shift from discovery by serendipity to discovery by design. Periodic Table-based Maps that involve electronegativity, valence electrons and atomic number that correlate with superconducting transition temperature can be used to design novel superconductors. Combining these maps with experimental databases on superconductors, databases of crystal structures and integrating material design software engine, we can re-design many known superconductor families and predict novel systems. By adding search engine technology with a ``knowledge discovery engine'', we produce a superconductor discovery engine (SCODEngine). The SCODEngine enables us to discover novel superconductors with the accelerated speed of a Google search. We have produced a primitive SCODEngine that may revolutionize novel superconductor search and discovery.

  5. Organic Superconductors at Extremely High Magnetic Fields

    International Nuclear Information System (INIS)

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

  6. Holographic Complexity in Gauge/String Superconductors

    OpenAIRE

    Davood Momeni; Seyed Ali Hosseini Mansoori; Ratbay Myrzakulov

    2016-01-01

    Following a methodology similar to \\cite{Alishahiha:2015rta}, we derive a holographic complexity for two dimensional holographic superconductors (gauge/string superconductors) with backreactions. Applying a perturbation method proposed by Kanno in Ref. \\cite{kanno}, we study behaviors of the complexity for a dual quantum system near critical points. We show that when a system moves from the normal phase ($T>T_c$) to the superconductor phase ($T

  7. Holographic complexity in gauge/string superconductors

    Directory of Open Access Journals (Sweden)

    Davood Momeni

    2016-05-01

    Full Text Available Following a methodology similar to [1], we derive a holographic complexity for two dimensional holographic superconductors (gauge/string superconductors with backreactions. Applying a perturbation method proposed by Kanno in Ref. [2], we study behaviors of the complexity for a dual quantum system near critical points. We show that when a system moves from the normal phase (T>Tc to the superconductor phase (T

  8. Holographic complexity in gauge/string superconductors

    Science.gov (United States)

    Momeni, Davood; Mansoori, Seyed Ali Hosseini; Myrzakulov, Ratbay

    2016-05-01

    Following a methodology similar to [1], we derive a holographic complexity for two dimensional holographic superconductors (gauge/string superconductors) with backreactions. Applying a perturbation method proposed by Kanno in Ref. [2], we study behaviors of the complexity for a dual quantum system near critical points. We show that when a system moves from the normal phase (T >Tc) to the superconductor phase (T

  9. Holographic Complexity in Gauge/String Superconductors

    CERN Document Server

    Momeni, Davood; Myrzakulov, Ratbay

    2016-01-01

    Following a methodology similar to \\cite{Alishahiha:2015rta}, we derive a holographic complexity for two dimensional holographic superconductors (gauge/string superconductors) with backreactions. Applying a perturbation method proposed by Kanno in Ref. \\cite{kanno}, we study behaviors of the complexity for a dual quantum system near critical points. We show that when a system moves from the normal phase ($T>T_c$) to the superconductor phase ($T

  10. Recent status of superconductors for accelerator magnets

    International Nuclear Information System (INIS)

    A survey is given of superconductor wire and cable which has been or will be used for construction of dipole magnets for all of the large European and US superconducting accelerator rings. Included is a simplified view of the construction methods and operating requirements of an accelerator dipole magnet, with emphasis on required superconductor performance. The methods of fabricating Nb-Ti superconductors are described, including the critical parameters and materials requirements. The superconductor performance requirements are summarized in an effort to relate why these are important to accelerator designers. Some of the recently observed time dependent effects are covered briefly

  11. Recent progress on carbon-based superconductors

    Science.gov (United States)

    Kubozono, Yoshihiro; Eguchi, Ritsuko; Goto, Hidenori; Hamao, Shino; Kambe, Takashi; Terao, Takahiro; Nishiyama, Saki; Zheng, Lu; Miao, Xiao; Okamoto, Hideki

    2016-08-01

    This article reviews new superconducting phases of carbon-based materials. During the past decade, new carbon-based superconductors have been extensively developed through the use of intercalation chemistry, electrostatic carrier doping, and surface-proving techniques. The superconducting transition temperature T c of these materials has been rapidly elevated, and the variety of superconductors has been increased. This review fully introduces graphite, graphene, and hydrocarbon superconductors and future perspectives of high-T c superconductors based on these materials, including present problems. Carbon-based superconductors show various types of interesting behavior, such as a positive pressure dependence of T c. At present, experimental information on superconductors is still insufficient, and theoretical treatment is also incomplete. In particular, experimental results are still lacking for graphene and hydrocarbon superconductors. Therefore, it is very important to review experimental results in detail and introduce theoretical approaches, for the sake of advances in condensed matter physics. Furthermore, the recent experimental results on hydrocarbon superconductors obtained by our group are also included in this article. Consequently, this review article may provide a hint to designing new carbon-based superconductors exhibiting higher T c and interesting physical features.

  12. Melt processed high-temperature superconductors

    CERN Document Server

    1993-01-01

    The achievement of large critical currents is critical to the applications of high-temperature superconductors. Recent developments have shown that melt processing is suitable for producing high J c oxide superconductors. Using magnetic forces between such high J c oxide superconductors and magnets, a person could be levitated.This book has grown largely out of research works on melt processing of high-temperature superconductors conducted at ISTEC Superconductivity Research Laboratory. The chapters build on melt processing, microstructural characterization, fundamentals of flux pinning, criti

  13. Recent progress on carbon-based superconductors.

    Science.gov (United States)

    Kubozono, Yoshihiro; Eguchi, Ritsuko; Goto, Hidenori; Hamao, Shino; Kambe, Takashi; Terao, Takahiro; Nishiyama, Saki; Zheng, Lu; Miao, Xiao; Okamoto, Hideki

    2016-08-24

    This article reviews new superconducting phases of carbon-based materials. During the past decade, new carbon-based superconductors have been extensively developed through the use of intercalation chemistry, electrostatic carrier doping, and surface-proving techniques. The superconducting transition temperature T c of these materials has been rapidly elevated, and the variety of superconductors has been increased. This review fully introduces graphite, graphene, and hydrocarbon superconductors and future perspectives of high-T c superconductors based on these materials, including present problems. Carbon-based superconductors show various types of interesting behavior, such as a positive pressure dependence of T c. At present, experimental information on superconductors is still insufficient, and theoretical treatment is also incomplete. In particular, experimental results are still lacking for graphene and hydrocarbon superconductors. Therefore, it is very important to review experimental results in detail and introduce theoretical approaches, for the sake of advances in condensed matter physics. Furthermore, the recent experimental results on hydrocarbon superconductors obtained by our group are also included in this article. Consequently, this review article may provide a hint to designing new carbon-based superconductors exhibiting higher T c and interesting physical features. PMID:27351938

  14. Topological properties of ferromagnetic superconductors

    Science.gov (United States)

    Cheung, Alfred K. C.; Raghu, S.

    2016-04-01

    A variety of heavy fermion superconductors, such as UCoGe, UGe2, and URhGe exhibit a striking coexistence of bulk ferromagnetism and superconductivity. In the first two materials, the magnetic moment decreases with pressure, and vanishes at a ferromagnetic quantum critical point (qcp). Remarkably, the superconductivity in UCoGe varies smoothly with pressure across the qcp and exists in both the ferromagnetic and paramagnetic regimes. We argue that in UCoGe, spin-orbit interactions stabilize a time-reversal invariant odd-parity superconductor in the high pressure paramagnetic regime. Based on a simple phenomenological model, we predict that the transition from the paramagnetic normal state to the phase where superconductivity and ferromagnetism coexist is a first-order transition.

  15. Applications of high temperature superconductors

    International Nuclear Information System (INIS)

    On some applications of high temperature superconductivity, recent outlines were described. Bi-series wire materials and fusion bulk materials are commercialized, and various developmental projects on appliances for electric powers and industries are promoted in the world. Such movement is thought to be based on a scope and an expectation that the high temperature superconductive technology will play a large part to overcome future problems on energy and environment. In order to use the high temperature superconductors for a wide range of industrial field in future, the present material is still insufficient at various features. From such meaning, it seems to be necessary to effort furthermore to material development. Here was introduced on some recent states of application development on the high temperature superconductors. (G.K.)

  16. Shielding superconductors with thin films

    CERN Document Server

    Posen, Sam; Catelani, Gianluigi; Liepe, Matthias U; Sethna, James P

    2015-01-01

    Determining the optimal arrangement of superconducting layers to withstand large amplitude AC magnetic fields is important for certain applications such as superconducting radiofrequency cavities. In this paper, we evaluate the shielding potential of the superconducting film/insulating film/superconductor (SIS') structure, a configuration that could provide benefits in screening large AC magnetic fields. After establishing that for high frequency magnetic fields, flux penetration must be avoided, the superheating field of the structure is calculated in the London limit both numerically and, for thin films, analytically. For intermediate film thicknesses and realistic material parameters we also solve numerically the Ginzburg-Landau equations. It is shown that a small enhancement of the superheating field is possible, on the order of a few percent, for the SIS' structure relative to a bulk superconductor of the film material, if the materials and thicknesses are chosen appropriately.

  17. Theoretical studies of unconventional superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Groensleth, Martin Sigurd

    2008-07-01

    This thesis presents four research papers. In the first three papers we have derived analytical results for the transport properties in unconventional superconductors and ferromagnetic systems with multiple broken symmetries. In Paper I and parts of Paper II we have studied tunneling transport between two non-unitary ferromagnetic spin-triplet superconductors, and found a novel interplay between ferromagnetism and superconductivity manifested in the Josephson effect as a spin- and charge-current in the absence of an applied voltage across the junction. The critical amplitudes of these currents can be adjusted by the relative magnetization direction on each side of the junction. Furthermore, in Paper II, we have found a way of controlling a spin-current between two ferromagnets with spin-orbit coupling. Paper III considers a junction consisting of a ferromagnet and a non-unitary ferromagnetic superconductor, and we show that the conductance spectra contains detailed information about the superconducting gaps and pairing symmetry of the Cooper-pairs. In the last paper we present a Monte Carlo study of an effective Hamiltonian describing orbital currents in the CuO2 layers of high-temperature superconductive cuprates. The model features two intrinsically anisotropic Ising models, coupled through an anisotropic next-nearest neighbor interaction, and an Ashkin-Teller nearest neighbor fourth order coupling. We have studied the specific heat anomaly, as well as the anomaly in the staggered magnetization associated with the orbital currents and its susceptibility. We have found that in a limited parameter regime, the specific heat anomaly is substantially suppressed, while the susceptibility has a non-analytical peak across the order-disorder transition. The model is therefore a candidate for describing the breakup of hidden order when crossing the pseudo-gap line on the under-doped side in the phase diagram of high-temperature superconductors. (Author) 64 refs., figs

  18. Quantum rotor in nanostructured superconductors

    OpenAIRE

    Lin, Shi-Hsin; Milošević, M. V.; Covaci, L.; Jankó, B.; Peeters, F.M.

    2014-01-01

    Despite its apparent simplicity, the idealized model of a particle constrained to move on a circle has intriguing dynamic properties and immediate experimental relevance. While a rotor is rather easy to set up classically, the quantum regime is harder to realize and investigate. Here we demonstrate that the quantum dynamics of quasiparticles in certain classes of nanostructured superconductors can be mapped onto a quantum rotor. Furthermore, we provide a straightforward experimental procedure...

  19. Engineering Holographic Superconductor Phase Diagrams

    OpenAIRE

    Chen, Jiunn-Wei; Dai, Shou-Huang; Maity, Debaprasad; Zhang, Yun-Long(State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100190, China)

    2016-01-01

    We study how to engineer holographic models with features of a high temperature superconductor phase diagram. We introduce a field in the bulk which provides a tunable "doping" parameter in the boundary theory. By designing how this field changes the effective masses of other order parameter fields, desired phase diagrams can be engineered. We give examples of generating phase diagrams with phase boundaries similar to a superconducting dome and an anti-ferromagnetic phase by including two ord...

  20. Overview of Crystalline Color Superconductors

    CERN Document Server

    Mannarelli, Massimo

    2015-01-01

    Inhomogeneous phases may appear when a stress is applied to a system and the system can minimize the free energy breaking the rotational invariance. Various examples are known in Nature of this sort, as the paramagnetic to ferromagnetic phase transition, or the fluid/solid phase transition. If the rotational symmetry is broken down to a discrete symmetry, the system is typically named a crystal. We breifly review crystalline color superconductors, which arise in cold quark matter with mismatched Fermi spheres.

  1. Superconductors with Mesoscopic Phase Separation

    OpenAIRE

    Coleman, A.J.; Yukalova, E. P.; V. I. Yukalov

    1997-01-01

    A model of superconductivity is proposed taking into account repulsive particle interaction, mesoscopic phase separation and softening of crystalline lattice. These features are typical of many high-temperature superconductors. The main results obtained for the model are: (i) phase separation is possible only if repulsive forces play a significant role; (ii) the critical temperature as a function of the superconducting phase fraction can have non-monotonic behaviour; (iii) superconductivity i...

  2. Stability Conditions in Gapless Superconductors

    OpenAIRE

    Gubankova, E.

    2006-01-01

    Gapless superconductivity can arise when pairing occurs between fermion species with different Fermi surface sizes, provided there is a sufficiently large mismatch between Fermi surfaces and/or at sufficiently large coupling constant. In gapless states, secondary Fermi surfaces appear where quasiparticle excitation energy vanishes. This work focuses on homogeneous and isotropic superfluids in the s-wave channel, with either zero (conventional superconductor), one, or two spherical Fermi surfa...

  3. Is a color superconductor topological?

    CERN Document Server

    Nishida, Yusuke

    2010-01-01

    A fully gapped state of matter, whether insulator or superconductor, can be asked if it is topologically trivial or nontrivial. Here we investigate topological properties of superconducting Dirac fermions in 3D having a color superconductor as an application. In the chiral limit, when the pairing gap is parity even, the right-handed and left-handed sectors of the free space Hamiltonian have nontrivial topological charges with opposite signs. Accordingly, a vortex line in the superconductor supports localized gapless right-handed and left-handed fermions with the dispersion relations E=+/-vp_z (v is a parameter dependent velocity) and thus propagating in opposite directions along the vortex line. However, the presence of the fermion mass immediately opens up a mass gap for such localized fermions and the dispersion relations become E=+/-v(m^2+p_z^2)^(1/2). When the pairing gap is parity odd, the situation is qualitatively different. The right-handed and left-handed sectors of the free space Hamiltonian in the ...

  4. Material properties of oxide superconductors

    International Nuclear Information System (INIS)

    The differences between the old (inter-) metallic superconductors and the new oxide superconductors are not limited to the much higher values of Tc attainable in the latter. There are many pervasive differences caused directly by oxide chemistry, quasi-perovskite local coordination configurations, and layered metal-semiconductor-metal'-semiconductor-structures. When these differences are ignored, for instance in theoretical models which make effective medium approximations, many experiments appear to present anomalous results. These anomalies largely disappear when account is taken of the real materials properties of the cuprates and other new oxide superconductors, for instance in theoretical models which treat transport as a partially percolative process. This percolative process directly reflects the fact that the highest values of Tc, as well as the most anomalous normal-state transport properties, occur in materials vicinal to a metal-insulator transition. As the metallic and insulating regions alternate even in single-crystal samples, effective medium models, and most effective-medium parameters, lose their significance. Examples of attempts to measure microscopic properties illustrate the importance of filamentary effects on both normal-state and superconductive properties

  5. Edge instabilities of topological superconductors

    Science.gov (United States)

    Hofmann, Johannes S.; Assaad, Fakher F.; Schnyder, Andreas P.

    2016-05-01

    Nodal topological superconductors display zero-energy Majorana flat bands at generic edges. The flatness of these edge bands, which is protected by time-reversal and translation symmetry, gives rise to an extensive ground-state degeneracy. Therefore, even arbitrarily weak interactions lead to an instability of the flat-band edge states towards time-reversal and translation-symmetry-broken phases, which lift the ground-state degeneracy. We examine the instabilities of the flat-band edge states of dx y-wave superconductors by performing a mean-field analysis in the Majorana basis of the edge states. The leading instabilities are Majorana mass terms, which correspond to coherent superpositions of particle-particle and particle-hole channels in the fermionic language. We find that attractive interactions induce three different mass terms. One is a coherent superposition of imaginary s -wave pairing and current order, and another combines a charge-density-wave and finite-momentum singlet pairing. Repulsive interactions, on the other hand, lead to ferromagnetism together with spin-triplet pairing at the edge. Our quantum Monte Carlo simulations confirm these findings and demonstrate that these instabilities occur even in the presence of strong quantum fluctuations. We discuss the implications of our results for experiments on cuprate high-temperature superconductors.

  6. Non-conventional Superconductors and Percolation

    OpenAIRE

    Ni, Xuan Zhong; Jiang, M H

    2011-01-01

    This paper presents a novel theory for understanding the mechanics behind non-conventional superconductors. It presents the hypothesis that non-conventional superconductors are 2D lattices of super-cells and that the superconductivity mechanism involves the ordered hopping of itinerant electrons along with phase transitions in the edge percolations.

  7. Design of high-Tc oxide superconductors

    International Nuclear Information System (INIS)

    The current status of oxide superconductors is briefly reviewed from a crystal structure perspective. Tokura et al. recently classified high-temperature superconductors using a 'block layer (BL)' concept. The present study proposes a new 'layer' concept that specifically classifies this BL. The possibility of obtaining new BLs by reconstructing layers is discussed. A new crystal structure was subsequently discovered. (orig.)

  8. New metallic superconductor makes an immediate impact

    International Nuclear Information System (INIS)

    The recent chance discovery that magnesium diboride becomes superconducting at 40 K - almost twice the temperature of other simple intermetallic compounds - has sparked a race to uncover its basic properties and to process the material for applications. Hot on the heels of the discovery of charge-induced superconductivity at 50 K on the surface of carbon-60 molecules late last year comes the discovery of bulk superconductivity at temperatures approaching 40 K in magnesium diboride. This almost doubles the previous record transition temperature, Tc, of simple intermetallic compounds - previously held by niobium germanium at 23.2 K. This record had not been challenged since the early 1970s, although in 1994 a much more complicated compound - yttrium palladium borocarbide - was found to have a Tc of about 23 K. In bulk materials the transition temperature of magnesium diboride (MgB2) is only exceeded by the much more complicated perovskite cuprate structures. The new discovery provides a salutary reminder of the richness of the solid state and the way that interesting physics can emerge from quite unexpected areas. (U.K.)

  9. Majorana Fermions and Topology in Superconductors

    Science.gov (United States)

    Sato, Masatoshi; Fujimoto, Satoshi

    2016-07-01

    Topological superconductors are novel classes of quantum condensed phases, characterized by topologically nontrivial structures of Cooper pairing states. On the surfaces of samples and in vortex cores of topological superconductors, Majorana fermions, which are particles identified with their own anti-particles, appear as Bogoliubov quasiparticles. The existence and stability of Majorana fermions are ensured by bulk topological invariants constrained by the symmetries of the systems. Majorana fermions in topological superconductors obey a new type of quantum statistics referred to as non-Abelian statistics, which is distinct from bose and fermi statistics, and can be utilized for application to topological quantum computation. Also, Majorana fermions give rise to various exotic phenomena such as "fractionalization", non-local correlation, and "teleportation". A pedagogical review of these subjects is presented. We also discuss interaction effects on topological classification of superconductors, and the basic properties of Weyl superconductors.

  10. Josephson junction microcalorimeter with a superconductor loop

    CERN Document Server

    Yoshihara, F; Shinada, K

    2003-01-01

    We propose a new microcalorimeter in which the critical current of a Josephson junction can be varied by an electron temperature in the normal metal barrier of the superconductor-normal metal-superconductor (SNS) or superconductor-normal metal-insulator-superconductor (SNIS) junctions. In this detector, a Josephson junction with a radiation absorber is included in a superconductor loop and the change of its critical current is converted into a change of magnetic flux in the loop. We estimated the energy resolution of this detector by calculating a noise equivalent power (NEP) of the detector. The estimated energy resolution and dynamic range are 4.2 eV/5.8 eV and 3.1 keV/6.2 keV, respectively with an Ag absorber of 500 x 500 x 2 mu m sup 3 at 100 mK.

  11. The amazing properties of crystalline color superconductors

    International Nuclear Information System (INIS)

    This paper is a brief journey into the amazing realm of crystalline color superconductors. Starting from a qualitative description of superfluids, superconductors and supersolids, we show how inhomogeneous phases may arise when the system is under stress. These basic concepts are then extended to quark matter, in which a richer variety of phases can be realized. The most interesting properties of the crystalline color superconductors are presented. This brief journey ends with a discussion of crystalline color superconductors in compact stars and related astrophysical observables. We aim at providing a pedagogical introduction for nonexpert in the field to a few interesting properties of crystalline color superconductors, without discussing the methods and the technicalities. Thus, the results are presented without a proof. However, we try to give a qualitatively clear description of the main concepts, using standard quantum field theory and analogies with condensed matter systems.

  12. High-temperature oxide superconductors

    International Nuclear Information System (INIS)

    This paper reports that in the high-temperature oxide superconductors of the type Y(Ln)Ba2Cu3O7-δ, structure and oxygen stoichiometry play a crucial role. Thus, this family of high temperature oxide superconductors generally possesses the orthorhombic structure with two- as well as one-dimensional features. Oxygen stoichiometry in YBa2Cu3O7-δ has an important bearing on the structure as well as superconductivity. This is equally true in the La2-xBa2+xCu6O14+δ system of which only the 123 oxide (x = 1) with the orthorhombic structure shows high Tc. Orthorhombicity is also found in La2-x(Sr, Ba)xCuO4 superconductors of the K2NiF4 structure. Orthorhombicity is necessary for the formation of twins in Y(Ln)Ba2Cu3O7. Copper in these cuprates is only in 1+ and 2+ states, thereby making it necessary for oxygen holes to be present. The oxygen holes are responsible for superconductivity of the cuprates. High Tc superconductivity is also found in oxides of the Bi-(ca, SR)-Cu-O and Tl(Ca,Ba)-Cu-O systems of the general formula A2(M', M double-prime)n+1CunO2n+4 (A = Bi,Tl; M' = Ca; M double-prime = Sr,Ba) with Tc's in the range 80-125K depending on the number of Cu-O Layers

  13. Vortex ice in nanostructured superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Reichhardt, Charles [Los Alamos National Laboratory; Reichhardt, Cynthia J [Los Alamos National Laboratory; Libal, Andras J [Los Alamos National Laboratory

    2008-01-01

    We demonstrate using numerical simulations of nanostructured superconductors that it is possible to realize vortex ice states that are analogous to square and kagome ice. The system can be brought into a state that obeys either global or local ice rules by applying an external current according to an annealing protocol. We explore the breakdown of the ice rules due to disorder in the nanostructure array and show that in square ice, topological defects appear along grain boundaries, while in kagome ice, individual defects appear. We argue that the vortex system offers significant advantages over other artificial ice systems.

  14. Intrinsic stability of technical superconductors

    International Nuclear Information System (INIS)

    For the operation of technical superconductors under high current density conditions, the superconducting wires composing high current cables should be intrinsically stabilized. In this report the various important stability criteria are derived and investigated on their validity. An experimental set up is made to check the occurrence of magnetic instabilities if the different applicable criteria are violated. It is found that the observed instabilities can be predicted on the basis of the model given in this report. Production of high current cables based upon composites made by the ECN technique seems to be possible. (Auth.)

  15. Density functional theory for superconductors

    International Nuclear Information System (INIS)

    Superconducting density functional theory (SCDFT) is a fully parameter-free approach to superconductivity. We review the method discussing the main theoretical advantages and disadvantage of the approach as compared to standard Green's functions methods. We present results for several conventional and unconventional superconductors, and in particular we discuss the special case of surface superconductivity considering the case of Pb on Si(111). Then we report on the most recent extensions of the method: to incorporate in a correct way the Migdal's theorem; compute the excitation spectrum; describe a coexistence with magnetism.

  16. Studies of high temperature superconductors

    International Nuclear Information System (INIS)

    With the discovery of Tc ceramic compounds, superconductivity has evolved into a rich and highly competitive field of research of not just condensed matter physics and chemistry but also of diverse engineering disciplines like ceramics, metallurgy and microelectronics. Clearly, significant advances in research and applications of HTSCs are expected only through consolidated efforts requiring among other, the best possible awareness on the part of researchers in these widely differing disciplines. Studies of High Temperature Superconductors looks at the frontal problems and challenges through detailed reviews and extended articles covering fundamental properties, characterization and applications of the new high Tc superconductors. The series is aimed at the professional scantiest and engineer, as well as at graduate students in physics, chemistry, materials science, solid state electronics and engineering. We are back with the sixth volume of Studies which provides in-depth coverage of frontal topics such as growth of HTSC single crystals, thin films, high Tc prospects in other systems, advanced technique for characterizing HTSCs, theoretical models of high Tc and the recent advancements in the high technology of devices

  17. Superconductor bearings, flywheels and transportation

    Science.gov (United States)

    Werfel, F. N.; Floegel-Delor, U.; Rothfeld, R.; Riedel, T.; Goebel, B.; Wippich, D.; Schirrmeister, P.

    2012-01-01

    This paper describes the present status of high temperature superconductors (HTS) and of bulk superconducting magnet devices, their use in bearings, in flywheel energy storage systems (FESS) and linear transport magnetic levitation (Maglev) systems. We report and review the concepts of multi-seeded REBCO bulk superconductor fabrication. The multi-grain bulks increase the averaged trapped magnetic flux density up to 40% compared to single-grain assembly in large-scale applications. HTS magnetic bearings with permanent magnet (PM) excitation were studied and scaled up to maximum forces of 10 kN axially and 4.5 kN radially. We examine the technology of the high-gradient magnetic bearing concept and verify it experimentally. A large HTS bearing is tested for stabilizing a 600 kg rotor of a 5 kWh/250 kW flywheel system. The flywheel rotor tests show the requirement for additional damping. Our compact flywheel system is compared with similar HTS-FESS projects. A small-scale compact YBCO bearing with in situ Stirling cryocooler is constructed and investigated for mobile applications. Next we show a successfully developed modular linear Maglev system for magnetic train operation. Each module levitates 0.25t at 10 mm distance during one-day operation without refilling LN2. More than 30 vacuum cryostats containing multi-seeded YBCO blocks are fabricated and are tested now in Germany, China and Brazil.

  18. Superconductor bearings, flywheels and transportation

    International Nuclear Information System (INIS)

    This paper describes the present status of high temperature superconductors (HTS) and of bulk superconducting magnet devices, their use in bearings, in flywheel energy storage systems (FESS) and linear transport magnetic levitation (Maglev) systems. We report and review the concepts of multi-seeded REBCO bulk superconductor fabrication. The multi-grain bulks increase the averaged trapped magnetic flux density up to 40% compared to single-grain assembly in large-scale applications. HTS magnetic bearings with permanent magnet (PM) excitation were studied and scaled up to maximum forces of 10 kN axially and 4.5 kN radially. We examine the technology of the high-gradient magnetic bearing concept and verify it experimentally. A large HTS bearing is tested for stabilizing a 600 kg rotor of a 5 kWh/250 kW flywheel system. The flywheel rotor tests show the requirement for additional damping. Our compact flywheel system is compared with similar HTS–FESS projects. A small-scale compact YBCO bearing with in situ Stirling cryocooler is constructed and investigated for mobile applications. Next we show a successfully developed modular linear Maglev system for magnetic train operation. Each module levitates 0.25t at 10 mm distance during one-day operation without refilling LN2. More than 30 vacuum cryostats containing multi-seeded YBCO blocks are fabricated and are tested now in Germany, China and Brazil.

  19. Incomplete Andreev reflection in a clean Superconductor/Ferromagnet/Superconductor junction

    OpenAIRE

    Cayssol, J.; Montambaux, G.

    2004-01-01

    We study the Josephson effect in a clean Superconductor-Ferromagnet-Superconductor junction for arbitrarily large spin polarizations. The Andreev reflection at a clean Ferromagnet-Superconductor interface is incomplete, and Andreev channels with a large incidence angle are progressively suppressed with increasing exchange energy. As a result, the critical current exhibits oscillations as a function of the exchange energy and of the length of the ferromagnet and has a temperature dependence wh...

  20. d-wave Holographic Superconductor Vortex Lattice and Non-Abelian Holographic Superconductor Droplet

    OpenAIRE

    Zeng, Hua-Bi; Fan, Zhe-Yong; Zong, Hong-Shi

    2010-01-01

    A d-wave holographic superconductor is studied under a constant magnetic field by perturbation method, we obtain both droplet and triangular vortex lattice solution. The results are the same as the s-wave holographic superconductor. The non-Abelian holographic superconductor with $p+ip$-wave background is also studied under magnetic field, unlike the d-wave and s-wave models, we find that the non-Abelian model has only droplet solution.

  1. A different type of reentrant behavior in superconductor/thin graphite film/superconductor Josephson junctions

    International Nuclear Information System (INIS)

    We experimentally studied current-voltage characteristics of superconductor/thin graphite film/superconductor Josephson junctions. A reentrant behavior in the differential conductance was observed at low bias voltages just above the structure due to supercurrent. The gate voltage dependence of the conductance peak shows that the origin of the reentrant behavior is different from that for the conventional reentrant behavior seen in a disordered normal metal coupled to a superconductor

  2. Spontaneous Josephson spin current in triplet superconductor/ferromagnet/triplet superconductor junctions

    International Nuclear Information System (INIS)

    This paper theoretically studies Josephson spin current through triplet superconductor/ferromagnet/triplet superconductor junctions. At the ferromagnet/superconductor interfaces, the ferromagnetic scattering potential gives rise to coupling between the Andreev bound states and lifts their spin degeneracy. These spin-split Andreev states carry the Josephson spin current through the junctions. The generated spin supercurrent can be controlled by the magnetization of a ferromagnetic thin layer and bias voltage across the junctions. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  3. Electromagnetic properties of metals and superconductors

    International Nuclear Information System (INIS)

    Part 1: Metals. 1. Introduction. 1.1. Normal and anomalous skin effects. 2. Helicons and magneto-plasma waves. 3. Helicon-phonon interaction. 3.1. Magneto-plasma (Alfven) waves. 4. Cyclotron waves. 5. Spin waves in electron system. Part 2: Superconductors. 6. Introduction. 6.1. Response to weak electromagnetic fields. 7. Effect of strong radiation field on superconductors. 8. Laser-induced non-equilibrium state in superconductors. 9. Possibility of photon-induced electron pairing - one-boson processes. 10. Possibility of photon-induced electron pairing -two-boson processes. (author)

  4. Holographic superconductors and superfluids - effect of backreaction

    International Nuclear Information System (INIS)

    Recently, the gravity-gauge theory correspondence has been used to describe so-called holographic superconductors and superfluids with the help of black holes in Anti-de Sitter space-time. In this talk, I discuss holographic superconductors and superfluids away from the probe limit, i.e. taking backreaction of the space-time into account. In the first part of the talk I present our results for Gauss-Bonnet holographic superconductors in (3+1) dimensions, while the second part deals with holographic superfluids in (2+1) dimensions where one of the spatial dimensions is compactified.

  5. Two classes of superconductors discovered in our material research: Iron-based high temperature superconductor and electride superconductor

    International Nuclear Information System (INIS)

    We discovered two new classes of superconductors in the course of material exploration for electronic-active oxides. One is 12CaO . 7Al2O3 crystal in which electrons accomodate in the crystallographic sub-nanometer-sized cavities. This material exhibiting metal-superconductor transition at 0.2 K is the first electride superconductor. The other is iron oxypnicitides with a layered structure. This superconductor is rather different from high Tc cuprates in several respects. The high Tc is emerged by doping carriers to the metallic parent phases which undergo crystallographic transition (tetra to ortho) and Pauli para to antiferromagnetic transition at ∼150 K. The Tc is robust to impurity doping to the Fe sites or is induced by partial substitution of the Fe2+ sites with Co2+ or Ni2+. This article gives a brief summary of these discoveries and recent advances.

  6. De-Sitter spacetime as a superconductor

    CERN Document Server

    Momeni, D

    2016-01-01

    A superconductor is a material with infinite electric conductivity. Superconductivity and magnetism are happening as two opposite phenomena: superconductors need weak external magnetic fields (the Meissner effect) while generally with a strong external magnetic field we loose superconductivity. In \\cite{ref:I}-\\cite{Chernodub:2011tv} , the author showed that a very strong magnetic field can turn an empty space into a superconductor. We extended this idea to the constant curvature spaces, de Sitter (dS) spacetime and by a careful analysis of the modes for a spinor with arbitrary spin, we show that in a very similar condensation scenario as was proposed for flat space, we could transform dS to a superconductor.

  7. Electromagnetic Effects in Superconductors in Gravitational Field

    OpenAIRE

    Ahmedov, B. J.; Kagramanova, V. G.

    2006-01-01

    The general relativistic modifications to the resistive state in superconductors of second type in the presence of a stationary gravitational field are studied. Some superconducting devices that can measure the gravitational field by its red-shift effect on the frequency of radiation are suggested. It has been shown that by varying the orientation of a superconductor with respect to the earth gravitational field, a corresponding varying contribution to AC Josephson frequency would be added by...

  8. High Tc superconductors and the contact properties

    OpenAIRE

    Huang, Hua; Grovenor, C.; Dr. C. R. M. Grovenor

    1992-01-01

    Methods of processing large grained textured superconductor have been successfully developed, based on a melt texturing process. Large grained textured superconductor with grain size over 10mm along the growth direction and Jc over 3600A/cm2 (77K, 0.5 Tesla) has been produced in both one - zone and two - zone furnaces with good reproducibility. Two kinds of design of reactive metal contacts have been proposed and investigated, aiming to make low resistivity contacts with st...

  9. Inhomogeneity and transverse voltage in superconductors

    OpenAIRE

    Segal, A.; Karpovski, M.; Gerber, A

    2011-01-01

    Voltages parallel and transverse to electric current in slightly inhomogeneous superconductors can contain components proportional to the field and temperature derivatives of the longitudinal and Hall resistivities. We show that these anomalous contributions can be the origin of the zero field and even-in-field transverse voltage occasionally observed at the superconductor to normal state transition. The same mechanism can also cause an anomaly in the odd-in-field transverse voltage interferi...

  10. Iron based superconductors: Pnictides versus chalcogenides

    International Nuclear Information System (INIS)

    We present a brief review of the present day situation with studies of high-temperature superconductivity in iron pnictides and chalcogenides. Recent discovery of superconductivity with Tc>30K in AxFe2−x/2Se2 (A=K, Cs, Tl, etc) represents the major new step in the development of new concepts in the physics of Fe-based high-temperature superconductors. We compare LDA and ARPES data on the band structure and Fermi surfaces of novel superconductors and those of the previously studied FeAs superconductors, especially isostructural 122-superconductors like BaFe2As2. It appears that electronic structure of new superconductors is rather different from that of FeAs 122-systems. In particular, no nesting properties of electron and hole-like Fermi surfaces is observed, casting doubts on most popular theoretical schemes of Cooper pairing for these systems. Doping of novel materials is extremely important as a number of topological transitions of Fermi surface near the Γ point in the Brillouin zone are observed for different doping levels. The discovery of Fe vacancies ordering and antiferromagnetic (AFM) ordering at pretty high temperatures (TN>500K), much exceeding superconducting Tc makes these systems unique antiferromagnetic superconductors with highest TN observed up to now. This poses very difficult problems for theoretical understanding of superconductivity. We discuss the role of both vacancies and AFM ordering in transformations of band structure and Fermi surfaces, as well as their importance for superconductivity. In particular, we show that system remains metallic with unfolded Fermi surfaces quite similar to that in paramagnetic state. Superconducting transition temperature Tc of new superconductors is discussed within the general picture of superconductivity in multiple band systems. It is demonstrated that both in FeAs-superconductors and in new FeSe-systems the value of Tc correlates with the value of the total density of states (DOSs) at the Fermi level.

  11. Method of preparing ductile superconductors

    International Nuclear Information System (INIS)

    The invention pertains to a method of producing ductile superconductors consisting of a copper matrix in which a number of superconducting alloys on a vanadium or niobium basis are embedded. According to the invention, the vanadium or niobium base alloy contains between 2 and 15 percent by weight of aluminum, silicon, germanium, gallium, or tin as alloying element. The alloy is quenched from temperatures between 1,5000C and 2,0000C to less than 5000C and then heat-treated between 600 and 1,0000C. By this method, transition temperatures up to 24 K, critical magnetic field strengths up to 200 kG and critical current densities up to 7 x 105A/cm2 could be achieved in the niobium/aluminum system. (HPOE)

  12. Engineering Holographic Superconductor Phase Diagrams

    CERN Document Server

    Chen, Jiunn-Wei; Maity, Debaprasad; Zhang, Yun-Long

    2016-01-01

    We study how to engineer holographic models with features of a high temperature superconductor phase diagram. We introduce a field in the bulk which provides a tunable "doping" parameter in the boundary theory. By designing how this field changes the effective masses of other order parameter fields, desired phase diagrams can be engineered. We give examples of generating phase diagrams with phase boundaries similar to a superconducting dome and an anti-ferromagnetic phase by including two order parameter fields. We also explore whether the pseudo gap phase can be described without adding another order parameter field and discuss the potential scaling symmetry associated with a quantum critical point hidden under the superconducting dome in this phase diagram.

  13. Cuprate high-Tc superconductors

    Directory of Open Access Journals (Sweden)

    Kyle M. Shen

    2008-09-01

    Full Text Available In solid-state physics two different paradigms are typically applied. The first is a local picture, in which one visualizes the quantum states of electrons in atomic orbitals or at impurity atoms in real space (r-space. The second is the momentum or reciprocal space (k-space picture, where electrons are viewed as de Broglie waves completely delocalized throughout the material. Understanding these two separate paradigms is essential for a complete understanding of the physics of condensed matter, but rarely has it been as necessary to combine both pictures as it has been to gain insight into the electronic structure of the high-temperature superconductors (HTSCs. In this article, we review recent developments in the understanding of the relationship between the r-space and k-space electronic spectroscopies used to explore high-temperature superconductivity.

  14. Subgap states in disordered superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Skvortsov, M. A., E-mail: skvor@itp.ac.ru; Feigel' man, M. V., E-mail: feigel@landau.ac.ru [Russian Academy of Sciences, Landau Institute for Theoretical Physics (Russian Federation)

    2013-09-15

    We revise the problem of the density of states in disordered superconductors. Randomness of local sample characteristics translates to the quenched spatial inhomogeneity of the spectral gap, smearing the BCS coherence peak. We show that various microscopic models of potential and magnetic disorder can be reduced to a universal phenomenological random order parameter model, whereas the details of the microscopic description are encoded in the correlation function of the order parameter fluctuations. The resulting form of the density of states is generally described by two parameters: the width {Gamma} measuring the broadening of the BCS peak and the energy scale {Gamma}{sub tail} that controls the exponential decay of the density of subgap states. We refine the existing instanton approaches for determination of {Gamma}{sub tail} and show that they appear as limiting cases of a unified theory of optimal fluctuations in a nonlinear system. The application to various types of disorder is discussed.

  15. Quantum rotor in nanostructured superconductors

    Science.gov (United States)

    Lin, Shi-Hsin; Milošević, M. V.; Covaci, L.; Jankó, B.; Peeters, F. M.

    2014-04-01

    Despite its apparent simplicity, the idealized model of a particle constrained to move on a circle has intriguing dynamic properties and immediate experimental relevance. While a rotor is rather easy to set up classically, the quantum regime is harder to realize and investigate. Here we demonstrate that the quantum dynamics of quasiparticles in certain classes of nanostructured superconductors can be mapped onto a quantum rotor. Furthermore, we provide a straightforward experimental procedure to convert this nanoscale superconducting rotor into a regular or inverted quantum pendulum with tunable gravitational field, inertia, and drive. We detail how these novel states can be detected via scanning tunneling spectroscopy. The proposed experiments will provide insights into quantum dynamics and quantum chaos.

  16. Ultrasonic attenuation in cuprate superconductors

    Indian Academy of Sciences (India)

    T Gupta; D M Gaitonde

    2002-05-01

    We calculate the longitudinal ultrasonic attenuation rate (UAR) in clean d-wave superconductors in the Meissner and the mixed phases. In the Meissner phase we calculate the contribution of previously ignored processes involving the excitation of a pair of quasi-holes or quasi-particles. There is a contribution ∝ in the regime B ≪ F ≪ 0 and a contribution ∝ 1/ in the regime F ≪ B ≪ 0. We find that these contributions to the UAR are large and cannot be ignored. In the mixed phase, using a semi-classical description, we calculate the electronic quasi-particle contribution to the UAR which at very low , has a independent term proportional to $\\sqrt{H}$.

  17. Cooperative phenomena in ternary superconductors

    International Nuclear Information System (INIS)

    A microscopic theory of ferromagnetic superconductors is developed from first principles. Self-consistent equations for the superconducting order parameter Δ and spontaneous magnetization are derived using a Green's function technique and considering the f-d exchange effect up to the second order. The theory is applied to explain the experimental results in the reentrant superconducting ternary system ErRh4B4. The present model explains reentrant behavior, predicts the coexistence of superconductivity and ferromagnetism in a very small range of temperature, the suppression of superconductivity by ferromagnetism, and vice versa. These results are in excellent agreement with the experimental data and predictions of other models. The behavior of the spontaneous magnetization, the superconducting order parameter, the specific heat, and the density of states is also studied

  18. Method of producing a superconductor

    International Nuclear Information System (INIS)

    The invention concerns a method for the production of a superconductor by cold-forming and heating of a copper-covered material consisting of 10 to 60% titanium, 0 to 15% oxygen, 0 to 0.2% nitrogen, 0 to 0.1% carbon, and the rest niobium. According to the invention the cross section after the hot forming is reduced by cold-forming by at least 10%. Then the material is annealed at 100 to 5000C for at least 10 minutes: after that, the cross section is further reduced by cold-forming by at least 5%. Then annealing and cold-forming are repeated until the cross section is reduced by at least 95%. It seems that by cold-forming dislocations are introduced into the atomic lattice serving as traps for stabilizing the magnetic flux. The subsequent annealing treatment evidently makes the network still more efficient. (FW)

  19. Superconductors in the power grid materials and applications

    CERN Document Server

    2015-01-01

    Superconductors offer high throughput with low electric losses and have the potential to transform the electric power grid. Transmission networks incorporating cables of this type could, for example, deliver more power and enable substantial energy savings. Superconductors in the Power Grid: Materials and Applications provides an overview of superconductors and their applications in power grids. Sections address the design and engineering of cable systems and fault current limiters and other emerging applications for superconductors in the power grid, as well as case studies of industrial applications of superconductors in the power grid. Expert editor from highly respected US government-funded research centre Unique focus on superconductors in the power grid Comprehensive coverage

  20. Coincident photoelectron spectroscopy on superconductors

    International Nuclear Information System (INIS)

    Aim of the performed experiments of this thesis was to attempt to detect Cooper pairs as carriers of the superconducting current directly by means of the photoelectric effect. The method of the coincident photoelectron spectroscopy aims thereby at the detection of two coherently emitted electrons by the interaction with a photon. Because electrostatic analyzers typically cover only a very small spatial angle, which goes along with very low coincidence rates, in connection with this thesis a time-of-flight projection system has been developed, which maps nearly the whole spatial angle on a position-resolving detector. The pulsed light source in form of special synchrotron radiation necessary for the measurement has been adjusted so weak, that only single photons could arrive at the sample. Spectroscoped were beside test measurements on silver layers both a lead monocrystal as representative of the classical BCS superconductors and monocrystalline Bi2Sr2CaCu2O8 from the family of the high-temperature superconductors. With excitation energies up to 40 eV could be shown that sufficiently smooth and clean surfaces in the superconducting phase exhibit within the resolving power of about 0.5 eV no recognizable differences in comparison to the normally conducting phase. Beside these studies furthermore the simple photoemission at the different samples and especially in the case of the lead crystal is treated, because here no comparable results are known. Thereby the whole momentum space is discussed and the Fermi surface established as three-dimensional model, by means of which the measurement results are discussed. in the theoretical descriptions different models for the Cooper-pair production are presented, whereby to the momentum exchange with the crystal a special role is attributed, because this can only occur in direct excitations via discrete lattice vectors.

  1. Defect structures in ceramic superconductors

    International Nuclear Information System (INIS)

    The influence of the defect structure on the superconducting properties of high temperature superconductors has been studied experimentally and by computer simulation technique. The relation between defect structure and the superconducting transition temperature, Tc, has been studied in Co-doped YBCO (YBa2Cu3-yCoyO6+x, 0 ≤ y ≤ 0.5), and it has been shown that th model, which has been established to account for the influence of oxygen ordering on Tc in oxygen deficient YBCO (YBa2Cu3O6+x, x 1.85Ce0.15CuO4+x have been carried out in order to elucidate why this material apparently is an electron conductor in the superconducting phase, and not as the other high temperature superconductors, a hole conductor. Structural studies on Pb2Sr2Y1-xCaxCu3O8 (0 ≤ x ≤ 0.5) have been carried out by neutron powder diffraction and it has been shown how the Ca-stoichiometry influence the Cu-valence in the superconducting CuO2-planes. The structural ordering of epitaxial thin films of YBCO and Bi2Sr2CaCu2O8+x deposit on heated substrates of SrTiO3, MgO, LaAlO3 and NdGaO3 has been studied by x-ray diffraction and Rutherford Backscattering spectroscopy, and the structural ordering has been analysed in relation to the superconducting properties. (au) (9 ills., 10 refs.)

  2. Electrochemical interfacial properties of superconductors

    International Nuclear Information System (INIS)

    The first part of the work explains the ionic conduction processes in RbAg4I5 in the temperature range of 10 K ≤ T ≤ 100 K. The low- and high-frequency performance of polycrystalline RbAg4I5 with various microstructures shows a change in the ionic conduction process at a transfer temperature in the range of 60 K ≤ T ≤ 90 K. At temperatures of Tt, the ion transport is observed primarily along the grain boundaries with low activation energies. The second part of the work investigates with a specially developed tripole EIS measuring technique the properties of HTSC/ionic superconductor interfaces as a function of temperature. Through superimposition of an external magnetic field it was possible for the first time to give evidence of the effects of correlated charge carriers in the superconducting phases of HTSC on the observed quantum electrodynamic, kinetic effects at the phase boundary between HTSC and ionic superconductor. The third part explains experiments on pin-pointed application of electrochemical phase boundary reactions for the purpose of local structurisation of surface layers. The tool used is an in-situ scanning probe microscope. In the model system Au(100)/Cu2+ methods have been developed and tested in order to resolve the expected difficulties occurring in the system HTSC/Cu2+. With the process found by the work reported and called ''defect-induced local metal deposition'', it was possible to metallize areas from nanometer size up to the maximum scanning area of the scanning probe microscope. (orig./MM)

  3. Search for Majorana fermions in topological superconductors.

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Wei; Shi, Xiaoyan; Hawkins, Samuel D.; Klem, John Frederick

    2014-10-01

    The goal of this project is to search for Majorana fermions (a new quantum particle) in a topological superconductor (a new quantum matter achieved in a topological insulator proximitized by an s-wave superconductor). Majorana fermions (MFs) are electron-like particles that are their own anti-particles. MFs are shown to obey non-Abelian statistics and, thus, can be harnessed to make a fault-resistant topological quantum computer. With the arrival of topological insulators, novel schemes to create MFs have been proposed in hybrid systems by combining a topological insulator with a conventional superconductor. In this LDRD project, we will follow the theoretical proposals to search for MFs in one-dimensional (1D) topological superconductors. 1D topological superconductor will be created inside of a quantum point contact (with the metal pinch-off gates made of conventional s-wave superconductors such as niobium) in a two-dimensional topological insulator (such as inverted type-II InAs/GaSb heterostructure).

  4. Topological insulators and superconductors from string theory

    Science.gov (United States)

    Ryu, Shinsei; Takayanagi, Tadashi

    2010-10-01

    Topological insulators and superconductors in different spatial dimensions and with different discrete symmetries have been fully classified recently, revealing a periodic structure for the pattern of possible types of topological insulators and superconductors, both in terms of spatial dimensions and in terms of symmetry classes. It was proposed that K theory is behind the periodicity. On the other hand, D-branes, a solitonic object in string theory, are also known to be classified by K theory. In this paper, by inspecting low-energy effective field theories realized by two parallel D-branes, we establish a one-to-one correspondence between the K-theory classification of topological insulators/superconductors and D-brane charges. In addition, the string theory realization of topological insulators and superconductors comes naturally with gauge interactions, and the Wess-Zumino term of the D-branes gives rise to a gauge field theory of topological nature, such as ones with the Chern-Simons term or the θ term in various dimensions. This sheds light on topological insulators and superconductors beyond noninteracting systems, and the underlying topological field theory description thereof. In particular, our string theory realization includes the honeycomb lattice Kitaev model in two spatial dimensions, and its higher-dimensional extensions. Increasing the number of D-branes naturally leads to a realization of topological insulators and superconductors in terms of holography (AdS/CFT).

  5. Impedance conversion using quantum limit nonreciprocity for superconductor-insulator-superconductor mixer compensation

    International Nuclear Information System (INIS)

    It is shown how a superconductor-insulator-superconductor (SIS) mixer when inductively terminated at the if port has inductive reactance at the signal port. This reactance may be used to compensate for the geometric capacitance of a conventionally operated SIS mixer over twice the bandwidth available through signal port resonance techniques

  6. Strong nonequilibrium coherent states in mesoscopic superconductor-semiconductor-superconductor junctions

    DEFF Research Database (Denmark)

    Kutchinsky, Jonatan; Wildt, Morten; Taboryski, Rafael Jozef; Kuhn, Oliver; Sørensen, Claus B.; Hansen, Jørn Bindslev; Lindelof, Poul Erik

    1999-01-01

    A biased superconductor-normal metal-superconductor junction is known to be a strong nonequilibrium system, where Andreev scattering at the interfaces creates a quasiparticle distribution function far from equilibrium, a manifestation of this is the well-known subgap structure in the I...

  7. Superconductor-semiconductor-superconductor planar junctions of aluminium on DELTA-doped gallium arsenide

    DEFF Research Database (Denmark)

    Taboryski, Rafael Jozef; Clausen, Thomas; Kutchinsky, jonatan;

    1997-01-01

    We have fabricated and characterized planar superconductor-semiconductor-superconductor (S-Sm-S) junctions with a high quality (i.e. low barrier) interface between an n++ modulation doped conduction layer in MBE grown GaAs and in situ deposited Al electrodes. The Schottky barrier at the S...

  8. Josephson Current in a Gapped Graphene Superconductor/Barrier/Superconductor Junction: Case of Massive Electrons

    Science.gov (United States)

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

    2011-10-01

    The Josephson effect in a gapped graphene-based superconductor/barrier/superconductor junction is studied. The superconductivity in gapped graphene may be achieved by depositing conventional superconductor on the top of the gapped graphene such as graphene grown on SiC substrate. In gapped graphene system, the carriers exhibit massive Dirac fermions. We focus on the effect of pseudo-Dirac-like mass on the supercurrent. In contrast to that in the gapless graphene superconductor/barrier/superconductor junction, we find that the supercurrent exhibits dependency of the Fermi energy. Also, the massive supercurrent anomalously oscillates as a function of the gate potential. This novel behavior is due to the effect of electrons acquiring mass in gapped graphene.

  9. Vortex and disclination structures in a nematic-superconductor state

    OpenAIRE

    Barci, Daniel G.; Clarim, Rafael V.; Júnior, Nei L. Silva

    2016-01-01

    The nematic-superconductor state, an example of a quantum liquid crystal that breaks gauge as well as rotation invariance, was conjecture to exist in the pseudogap regime of the cuprates high $T_c$ superconductors. We present a detailed study of the structure of topological defects supported by the nematic-superconductor state. By means of a Ginzburg-Landau approach, we study the main relevant imprints on the superconductor order parameter caused by nematicity. Due to a geometrical coupling, ...

  10. Dynamics of superconductor bearings in a cryogenic failure

    International Nuclear Information System (INIS)

    The dynamics of superconductor bearings in a cryogenic failure scenario have been analyzed. As the superconductor warms up, the rotor goes through multiple resonance frequencies, begins to slow down and finally touches down when the superconductor goes through its transition temperature. The bearing can be modelled as a system of springs with axial, radial and cross stiffness. These springs go through various resonant modes as the temperature of the superconductor begins to rise. We have presented possible explanations for such behaviour

  11. Dynamics of superconductor bearings in a cryogenic failure

    Energy Technology Data Exchange (ETDEWEB)

    Rastogi, Amit [Department of Engineering, Cambridge University, Cambridge CB2 1PZ (United Kingdom)]. E-mail: Amit.Rastogi@avizatechnology.com; Campbell, A.M. [Department of Engineering, Cambridge University, Cambridge CB2 1PZ (United Kingdom); Coombs, T.A. [Department of Engineering, Cambridge University, Cambridge CB2 1PZ (United Kingdom)

    2006-08-01

    The dynamics of superconductor bearings in a cryogenic failure scenario have been analyzed. As the superconductor warms up, the rotor goes through multiple resonance frequencies, begins to slow down and finally touches down when the superconductor goes through its transition temperature. The bearing can be modelled as a system of springs with axial, radial and cross stiffness. These springs go through various resonant modes as the temperature of the superconductor begins to rise. We have presented possible explanations for such behaviour.

  12. Rotating superconductor magnet for producing rotating lobed magnetic field lines

    International Nuclear Information System (INIS)

    A rotating superconductor magnet is described for producing a rotating lobed magnetic field, comprising a cryostat; a superconducting magnet in the cryostat having a collar for producing a lobed magnetic field having oppositely directed adjacent field lines; rotatable support means for selectively rotating the superconductor magnet; and means for energizing the superconductor magnet

  13. Superconductivity. Vol. 1. Conventional and unconventional superconductors

    International Nuclear Information System (INIS)

    Conceived as the definitive reference in a classic and important field of modern physics, this extensive and comprehensive handbook systematically reviews the basic physics, theory and recent advances in the field of superconductivity. Leading researchers, including Nobel laureates, describe the state-of-the-art in conventional and unconventional superconductors at a particularly opportune time, as new experimental techniques and field-theoretical methods have emerged. In addition to full-coverage of novel materials and underlying mechanisms, the handbook reflects continued intense research into electron-phonon based superconductivity. Considerable attention is devoted to high-Tc superconductivity, novel superconductivity, including triplet pairing in the ruthenates, novel superconductors, such as heavy-Fermion metals and organic materials, and also granular superconductors. What's more, several contributions address superconductors with impurities and nanostructured superconductors. Important new results on current problems are presented in a manner designed to stimulate further research. Numerous illustrations, diagrams and tables make this book especially useful as a reference work for researchers, students and teachers. Treating the entire superconductivity field, this unparalleled reference resource carefully blends theoretical studies with experimental results to provide the scientist and engineers an indispensable foundation for further research. (orig.)

  14. Conductance spectroscopy of topological superconductor wire junctions

    Science.gov (United States)

    Setiawan, F.; Brydon, Philip; Sau, Jay

    We study the zero-temperature transport properties of one-dimensional normal metal-superconductor (NS) junctions with topological superconductors across their topological transitions. Working within the Blonder-Tinkham-Klapwijk (BTK) formalism generalized for topological NS junctions, we analytically calculate the differential conductance for tunneling into two models of a topological superconductor: a spinless intrinsic p-wave superconductor and a spin-orbit-coupled s-wave superconductor in a Zeeman field. The zero-bias conductance takes nonuniversal values in the nontopological phase while it is robustly quantized at 2e2 / h in the topological regime. Despite this quantization at zero voltage, the zero-bias conductance only develops a peak (or a local maximum) as a function of voltage for sufficiently large interfacial barrier strength, or certain parameter regimes of spin-orbit coupling strength. Our calculated BTK conductance also shows that the conductance is finite inside the superconducting gap region because of the finite barrier transparency, providing a possible mechanism for the observed ``soft gap'' feature in the experimental studies. Work is done in collaboration with Sankar Das Sarma and supported by Microsoft Q, LPS-CMTC, and JQI-NSF-PFC.

  15. Conference summary: Experimnetal

    International Nuclear Information System (INIS)

    The conference is the 1995 International Conference on Strongly Correlated Electron Systems. The summary highlights research on the ''extended'' Doniach model, Kondo insulators, borocarbide superconductors, oxides (including cuprates), other phase transitions, and new materials

  16. Internal stability of technical superconductors

    International Nuclear Information System (INIS)

    Electrical stability and longitudinal quench propagation velocity of technical NbTi superconductors having various matrix compositions was investigated experimentally and theoretically (numerically) for different cooling conditions. Copper, cupro-nickel and both combined were used as matrix materials of the conductors. The measurements were performed between 5 and 8 K in vacuum and at 4.2 K in helium both applying magnetic fields up to 7 T. The quantitative agreement between experiments and calculations was better than a factor of 2 regarding all 8 specimen at the investigated environmental conditions (cooling, temperature, and magnetic field). The remaining uncertainty is mainly conditioned by the accumulation of small inaccuracies in knowledge of the various conductor parameters, but far less to be found in the computer program itself. The accuracy of these parameters cannot be further improved with reasonable effort and expenditure. It is shown, that position and fraction of the cupro-nickel barriers inside the mixed matrix conductors affect strongly quench propagation velocity; stability also is sensible to these parameters. The strong effect on quench propagation velocity may be explained by a feedback mechanism. A way is given, how to change stability and quench propagation velocity of a mixed matrix conductor by constructional measures without implicating an enhancement of the coupling current losses. (orig.)

  17. High-TC ceramic superconductors

    International Nuclear Information System (INIS)

    The mixed-oxides technology allows to prepare high-TC superconductors of the materials classes YBCO and BSCCO, which are characterised by high phase purity and well-defined microstructure. The technology uses as source materials the oxides or cabonates of the metals. Mixing and homogenisation of the source materials powders is done by wet grinding in a plastic drum mill. Chemical conversion is achieved by means of thermal calcination, with the following conditions having proved to be suitable: (1) YBCO: single-step calcination (870deg C, 16h, in room air, in corundum crucibles). (2) BSCCO: two-step calcination. First step: 780deg C, 2h, free cooling in calciner, grinding, drying, second step: 780-800deg C, 16h, chilling. In order to obtain the fine powders required for determining the materials' microstructure during the sintering process, fine grinding is necessary as an intermediate step. For this purpose, the powders are dryly ground in a planetary ball mill. (grinding aids: polyethylene glycol or oleic acid). For compacting and shaping, dry pressing is applied. Sintering to obtain YBCO can be done in free air. A specially designed temperature time programme largely controls the process so as to yield the required microstructure. For the system BSCCO, long-term sintering for a high phase fraction of BSCCO-2223 is inevitable. Controlled microstructure development, as in the system YBCO, is not possible. (orig.)

  18. Transverse acousto-electric effect in superconductors

    Science.gov (United States)

    Lipavský, P.; Koláček, J.; Lin, P.-J.

    2016-06-01

    We formulate a theory based on the time-dependent Ginzburg-Landau (TDGL) theory and Newtonian vortex dynamics to study the transverse acousto-electric response of a type-II superconductor with Abrikosov vortex lattice. When exposed to a transverse acoustic wave, Cooper pairs emerge from the moving atomic lattice and moving electrons. As in the Tolman-Stewart effect in a normal metal, an electromagnetic field is radiated from the superconductor. We adapt the equilibrium-based TDGL theory to this non-equilibrium system by using a floating condensation kernel. Due to the interaction between normal and superconducting components, the radiated electric field as a function of magnetic field attains a maximum value occurring below the upper critical magnetic field. This local increase in electric field has weak temperature dependence and is suppressed by the presence of impurities in the superconductor.

  19. Charge and spin transport in mesoscopic superconductors

    Directory of Open Access Journals (Sweden)

    M. J. Wolf

    2014-02-01

    Full Text Available Background: Non-equilibrium charge transport in superconductors has been investigated intensely in the 1970s and 1980s, mostly in the vicinity of the critical temperature. Much less attention has been paid to low temperatures and the role of the quasiparticle spin.Results: We report here on nonlocal transport in superconductor hybrid structures at very low temperatures. By comparing the nonlocal conductance obtained by using ferromagnetic and normal-metal detectors, we discriminate charge and spin degrees of freedom. We observe spin injection and long-range transport of pure, chargeless spin currents in the regime of large Zeeman splitting. We elucidate charge and spin transport by comparison to theoretical models.Conclusion: The observed long-range chargeless spin transport opens a new path to manipulate and utilize the quasiparticle spin in superconductor nanostructures.

  20. High-temperature superconductor antenna investigations

    International Nuclear Information System (INIS)

    In this paper the use of superconductors to increase antenna radiation efficiency and gain is examined. Although the gain of all normal-metal antennas can be increased through the use of superconductors, some structures have greater potential for practical improvement than others. Some structures suffer a great degradation in bandwidth when replaced with superconductors, while for others the improvement in efficiency is trivial due to the minimal contribution of the conductor loss mechanism to the total losses, or the already high efficiency of the structure. The following antennas and related structures are discussed: electrically small antennas, impedance matching of antennas, microstrip antennas, microwave and millimeter-wave antenna arrays, and superdirective arrays. The greatest potential practical improvements occur for large microwave and millimeter-wave arrays and the impedance matching of antennas

  1. Anomalous Hall effect in Weyl superconductors

    Science.gov (United States)

    Bednik, G.; Zyuzin, A. A.; Burkov, A. A.

    2016-08-01

    We present a theory of the anomalous Hall effect in a topological Weyl superconductor with broken time reversal symmetry. Specifically, we consider a ferromagnetic Weyl metal with two Weyl nodes of opposite chirality near the Fermi energy. In the presence of inversion symmetry, such a metal experiences a weak-coupling Bardeen–Cooper–Schrieffer instability, with pairing of parity-related eigenstates. Due to the nonzero topological charge, carried by the Weyl nodes, such a superconductor is necessarily topologically nontrivial, with Majorana surface states coexisting with the Fermi arcs of the normal Weyl metal. We demonstrate that, surprisingly, the anomalous Hall conductivity of such a superconducting Weyl metal coincides with that of a nonsuperconducting one, under certain conditions, in spite of the nonconservation of charge in a superconductor. We relate this to the existence of an extra (nearly) conserved quantity in a Weyl metal, the chiral charge.

  2. Radiation shielding effectiveness of newly developed superconductors

    Science.gov (United States)

    Singh, Vishwanath P.; Medhat, M. E.; Badiger, N. M.; Saliqur Rahman, Abu Zayed Mohammad

    2015-01-01

    Gamma ray shielding effectiveness of superconductors with a high mass density has been investigated. We calculated the mass attenuation coefficients, the mean free path (mfp) and the exposure buildup factor (EBF). The gamma ray EBF was computed using the Geometric Progression (G-P) fitting method at energies 0.015-15 MeV, and for penetration depths up to 40 mfp. The fast-neutron shielding effectiveness has been characterized by the effective neutron removal cross-section of the superconductors. It is shown that CaPtSi3, CaIrSi3, and Bi2Sr2Ca1Cu2O8.2 are superior shielding materials for gamma rays and Tl0.6Rb0.4Fe1.67Se2 for fast neutrons. The present work should be useful in various applications of superconductors in fusion engineering and design.

  3. Practical superconductor development for electrical power applications

    International Nuclear Information System (INIS)

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

  4. Topological state engineering by potential impurities on chiral superconductors

    Science.gov (United States)

    Kaladzhyan, Vardan; Röntynen, Joel; Simon, Pascal; Ojanen, Teemu

    2016-08-01

    In this work we consider the influence of potential impurities deposited on top of two-dimensional chiral superconductors. As discovered recently, magnetic impurity lattices on an s -wave superconductor may give rise to a rich topological phase diagram. We show that a similar mechanism takes place in chiral superconductors decorated by nonmagnetic impurities, thus avoiding the delicate issue of magnetic ordering of adatoms. We illustrate the method by presenting the theory of potential impurity lattices embedded on chiral p -wave superconductors. While a prerequisite for the topological state engineering is a chiral superconductor, the proposed procedure results in vistas of nontrivial descendant phases with different Chern numbers.

  5. The superconductor revolutions and the (slow) applications evolution

    International Nuclear Information System (INIS)

    The discovery in the 1960's of type 2 superconductors with high critical current densities in high magnetic fields (and the development of NbTi in particular) led to the first revolution. The discovery of high temperature superconductors (HTS) started the second revolution. At this stage ceramists became involved with superconductors. I will assess the status of various superconductor applications, progress of HTS and their possible applications at 4.2K, and near-term needs for superconducting materials operating at 30T in specialized facilities. Reasons for the slow growth of superconductor applications will be reviewed

  6. Physical properties of high temperature superconductors

    CERN Document Server

    Ginsberg, DM

    1998-01-01

    While a great effort has been made to discover new high temperature superconductors, a large-scale, parallel effort has been made to determine the fundamental properties of these fascinating new materials. This is perhaps one of the best books in the field describing these vital properties in an organized and comprehensive manner. The authors are well known for their creative and powerful research on the new superconductors. This volume will be a useful reference for research workers and for graduate students. A subject index is also included for the user's convenience.

  7. Building blocks for correlated superconductors and magnets

    Energy Technology Data Exchange (ETDEWEB)

    Sarrao, J. L.; Ronning, F.; Bauer, E. D.; Batista, C. D.; Zhu, J.-X.; Thompson, J. D. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2015-04-01

    Recent efforts at Los Alamos to discover strongly correlated superconductors and hard ferromagnets are reviewed. While serendipity remains a principal engine of materials discovery, design principles and structural building blocks are beginning to emerge that hold potential for predictive discovery. Successes over the last decade with the so-called “115” strongly correlated superconductors are summarized, and more recent efforts to translate these insights and principles to novel hard magnets are discussed. While true “materials by design” remains a distant aspiration, progress is being made in coupling empirical design principles to electronic structure simulation to accelerate and guide materials design and synthesis.

  8. Electromagnetic Effects in Superconductors in Gravitational Field

    CERN Document Server

    Ahmedov, B J

    2005-01-01

    The general relativistic modifications to the resistive state in superconductors of second type in the presence of a stationary gravitational field are studied. Some superconducting devices that can measure the gravitational field by its red-shift effect on the frequency of radiation are suggested. It has been shown that by varying the orientation of a superconductor with respect to the earth gravitational field, a corresponding varying contribution to AC Josephson frequency would be added by gravity. A magnetic flux (being proportional to angular velocity of rotation $\\Omega$) through a rotating hollow superconducting cylinder with the radial gradient of temperature $\

  9. Long-range spin transport in superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Beckmann, Detlef; Wolf, Michael J. [Institut fuer Nanotechnologie, Karlsruher Institut fuer Technologie (Germany); Huebler, Florian [Institut fuer Festkoerperphysik, Karlsruher Institut fuer Technologie (Germany); Loehneysen, Hilbert von [Institut fuer Festkoerperphysik, Karlsruher Institut fuer Technologie (Germany); Physikalisches Institut, Karlsruher Institut fuer Technologie (Germany)

    2012-07-01

    Recently, there has been some controversy about spin-polarized quasiparticle transport and relaxation in superconductors, with reports of both anomalously short or anomalously long relaxation times as compared to the normal state. Here, we report on non-local transport in multiterminal superconductor-ferromagnet structures. We find signatures of spin transport over distances much larger than the normal-state spin-diffusion length in the presence of a large Zeeman splitting of the quasiparticle states. The relaxation length shows a nearly linear increase with magnetic field, hinting at a freeze-out of spin relaxation by the Zeeman splitting.

  10. Workshop on accelerator magnet superconductors. Proceedings

    International Nuclear Information System (INIS)

    The workshop on accelerator magnet superconductors has gathered 102 registered participants from research laboratories, universities and industry. 8 European companies, active in superconducting materials and cables were present. This workshop has been organized to deal with the status of the world research and development on superconducting materials and cables for high field magnets (B > 10 T). The workshop has also reviewed the status of high temperature superconductors and transmission line cables for potential use in low field superconducting magnets for injectors and beam transfer lines, as well as cables for pulsed magnets that might be used in future hadron colliders or injectors

  11. Multicomponent superconductivity based on multiband superconductors

    International Nuclear Information System (INIS)

    Multicomponent superconductivity is realized in multiband superconductors when an interband pairing interaction is considerably weaker than the intraband interactions. There is a new quantum phase that originates from the interband phase difference in this superconducting condensate. Firstly, we discuss the applicability of this physical viewpoint for known multiband superconductors. Secondly, topics related to the interband phase difference are treated. Finally, we mention that the Bardeen–Cooper–Schrieffer formalism and the Ginzburg–Landau formalism may not be fully guaranteed when we introduce a fluctuation in the interband phase difference mode. We also address plausible new superconducting electronics using the interband phase difference. (review)

  12. Building blocks for correlated superconductors and magnets

    International Nuclear Information System (INIS)

    Recent efforts at Los Alamos to discover strongly correlated superconductors and hard ferromagnets are reviewed. While serendipity remains a principal engine of materials discovery, design principles and structural building blocks are beginning to emerge that hold potential for predictive discovery. Successes over the last decade with the so-called “115” strongly correlated superconductors are summarized, and more recent efforts to translate these insights and principles to novel hard magnets are discussed. While true “materials by design” remains a distant aspiration, progress is being made in coupling empirical design principles to electronic structure simulation to accelerate and guide materials design and synthesis

  13. Order parameter fluctuations in the holographic superconductor

    CERN Document Server

    Plantz, N W M; Vandoren, S

    2015-01-01

    We investigate the effect of order parameter fluctuations in the holographic superconductor. In particular, the fully backreacted spectral functions of the order parameter in both the normal and the superconducting phase are computed. We also present a vector-like large-$N$ version of the Ginzburg-Landau model that accurately describes our long-wavelength results in both phases. The large-$N$ limit of the latter model explains why the Higgs mode and the second-sound mode are not present in the spectral functions. Our results indicate that the holographic superconductor describes a relativistic multi-component superfluid in the universal regime of the BEC-BCS crossover.

  14. Electrical connection structure for a superconductor element

    Science.gov (United States)

    Lallouet, Nicolas; Maguire, James

    2010-05-04

    The invention relates to an electrical connection structure for a superconductor element cooled by a cryogenic fluid and connected to an electrical bushing, which bushing passes successively through an enclosure at an intermediate temperature between ambient temperature and the temperature of the cryogenic fluid, and an enclosure at ambient temperature, said bushing projecting outside the ambient temperature enclosure. According to the invention, said intermediate enclosure is filled at least in part with a solid material of low thermal conductivity, such as a polyurethane foam or a cellular glass foam. The invention is applicable to connecting a superconductor cable at cryogenic temperature to a device for equipment at ambient temperature.

  15. Iron based superconductors: Pnictides versus chalcogenides

    Energy Technology Data Exchange (ETDEWEB)

    Sadovskii, M.V., E-mail: sadovski@iep.uran.ru [Institute for Electrophysics, Russian Academy of Sciences, Ural Branch, Amundsen str. 106, Ekaterinburg 620016 (Russian Federation); Institute for Metal Physics, Russian Academy of Sciences, Ural Branch, S. Kovalevskaya str. 18, Ekaterinburg 620990 (Russian Federation); Kuchinskii, E.Z.; Nekrasov, I.A. [Institute for Electrophysics, Russian Academy of Sciences, Ural Branch, Amundsen str. 106, Ekaterinburg 620016 (Russian Federation)

    2012-10-15

    We present a brief review of the present day situation with studies of high-temperature superconductivity in iron pnictides and chalcogenides. Recent discovery of superconductivity with T{sub c}>30K in A{sub x}Fe{sub 2-x/2}Se{sub 2} (A=K, Cs, Tl, etc) represents the major new step in the development of new concepts in the physics of Fe-based high-temperature superconductors. We compare LDA and ARPES data on the band structure and Fermi surfaces of novel superconductors and those of the previously studied FeAs superconductors, especially isostructural 122-superconductors like BaFe{sub 2}As{sub 2}. It appears that electronic structure of new superconductors is rather different from that of FeAs 122-systems. In particular, no nesting properties of electron and hole-like Fermi surfaces is observed, casting doubts on most popular theoretical schemes of Cooper pairing for these systems. Doping of novel materials is extremely important as a number of topological transitions of Fermi surface near the {Gamma} point in the Brillouin zone are observed for different doping levels. The discovery of Fe vacancies ordering and antiferromagnetic (AFM) ordering at pretty high temperatures (T{sub N}>500K), much exceeding superconducting T{sub c} makes these systems unique antiferromagnetic superconductors with highest T{sub N} observed up to now. This poses very difficult problems for theoretical understanding of superconductivity. We discuss the role of both vacancies and AFM ordering in transformations of band structure and Fermi surfaces, as well as their importance for superconductivity. In particular, we show that system remains metallic with unfolded Fermi surfaces quite similar to that in paramagnetic state. Superconducting transition temperature T{sub c} of new superconductors is discussed within the general picture of superconductivity in multiple band systems. It is demonstrated that both in FeAs-superconductors and in new FeSe-systems the value of T{sub c} correlates with

  16. Workshop on accelerator magnet superconductors. Proceedings

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2004-07-01

    The workshop on accelerator magnet superconductors has gathered 102 registered participants from research laboratories, universities and industry. 8 European companies, active in superconducting materials and cables were present. This workshop has been organized to deal with the status of the world research and development on superconducting materials and cables for high field magnets (B > 10 T). The workshop has also reviewed the status of high temperature superconductors and transmission line cables for potential use in low field superconducting magnets for injectors and beam transfer lines, as well as cables for pulsed magnets that might be used in future hadron colliders or injectors.

  17. Recrystallization of high temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kouzoudis, D.

    1996-05-09

    Currently one of the most widely used high {Tc} superconductors is the Bi-based compounds Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub z} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub z} (known as BSCCO 2212 and 2223 compounds) with {Tc} values of about 85 K and 110 K respectively. Lengths of high performance conductors ranging from 100 to 1000 m long are routinely fabricated and some test magnets have been wound. An additional difficulty here is that although Bi-2212 and Bi-2223 phases exist over a wide range of stoichiometries, neither has been prepared in phase-pure form. So far the most successful method of constructing reliable and robust wires or tapes is the so called powder-in-tube (PIT) technique [1, 2, 3, 4, 5, 6, 7] in which oxide powder of the appropriate stoichiometry and phase content is placed inside a metal tube, deformed into the desired geometry (round wire or flat tape), and annealed to produce the desired superconducting properties. Intermediate anneals are often incorporated between successive deformation steps. Silver is the metal used in this process because it is the most compatible with the reacting phase. In all of the commercial processes for BSCCO, Ag seems to play a special catalytic role promoting the growth of high performance aligned grains that grow in the first few micrometers near the Ag/BSCCO interface. Adjacent to the Ag, the grain alignment is more perfect and the current density is higher than in the center of the tape. It is known that Ag lowers the melting point of several of the phases but the detailed mechanism for growth of these high performance grains is not clearly understood. The purpose of this work is to study the nucleation and growth of the high performance material at this interface.

  18. Giant supercurrent states in a superconductor-InAs/GaSb-superconductor junction

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Xiaoyan, E-mail: xshi@sandia.gov; Pan, W.; Hawkins, S. D.; Klem, J. F. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Yu, Wenlong; Jiang, Zhigang [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Andrei Bernevig, B. [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States)

    2015-10-07

    Superconductivity in topological materials has attracted a great deal of interest in both electron physics and material sciences since the theoretical predictions that Majorana fermions can be realized in topological superconductors. Topological superconductivity could be realized in a type II, band-inverted, InAs/GaSb quantum well if it is in proximity to a conventional superconductor. Here, we report observations of the proximity effect induced giant supercurrent states in an InAs/GaSb bilayer system that is sandwiched between two superconducting tantalum electrodes to form a superconductor-InAs/GaSb-superconductor junction. Electron transport results show that the supercurrent states can be preserved in a surprisingly large temperature-magnetic field (T – H) parameter space. In addition, the evolution of differential resistance in T and H reveals an interesting superconducting gap structure.

  19. Giant supercurrent states in a superconductor-InAs/GaSb-superconductor junction

    International Nuclear Information System (INIS)

    Superconductivity in topological materials has attracted a great deal of interest in both electron physics and material sciences since the theoretical predictions that Majorana fermions can be realized in topological superconductors. Topological superconductivity could be realized in a type II, band-inverted, InAs/GaSb quantum well if it is in proximity to a conventional superconductor. Here, we report observations of the proximity effect induced giant supercurrent states in an InAs/GaSb bilayer system that is sandwiched between two superconducting tantalum electrodes to form a superconductor-InAs/GaSb-superconductor junction. Electron transport results show that the supercurrent states can be preserved in a surprisingly large temperature-magnetic field (T – H) parameter space. In addition, the evolution of differential resistance in T and H reveals an interesting superconducting gap structure

  20. Mobile fluxon qubits in a long superconductor-ferromagnet-superconductor Josephson junction

    International Nuclear Information System (INIS)

    We propose a new type of mobile qubit that utilizes a bound pair of half fluxons in a long superconductor-ferromagnet-superconductor (SFS) Josephson junction. The qubit states are composed of the lowest two levels of the quantized nonlinear internal oscillation of the bound pair. The energy levels are estimated by the numerical quantization based on a collective coordinate method. The qubit operation scheme is discussed, showing an estimate of the interaction strength between a bound pair and a microcircuit

  1. Model of a transverse Josephson effect driven by inhomogeneous magnetization in superconductor/ferromagnet/superconductor junctions

    OpenAIRE

    Yokoyama, Takehito

    2011-01-01

    We investigate transverse charge and spin dc Josephson current in superconductor/ferromagnet/superconductor junction where the ferromagnet has inhomogeneous magnetic structure. The transverse Josephson effect arises from non-trivial structure of the magnetization. The magnetic structure manifested in the transverse charge Josephson effect is essentially different from that discussed in the context of anomalous Hall effect, reflecting the disspationless nature of Josephson current. Possible ca...

  2. Above-gap Conductance Anomaly Studied in Superconductor-graphene-superconductor Josephson Junctions

    OpenAIRE

    Choi, Jae-Hyun; Lee, Hu-Jong; Doh, Yong-Joo

    2011-01-01

    We investigated the electrical transport properties of superconductor-graphene-superconductor (SGS) Josephson junctions. In low voltage bias, we observed conventional proximity-coupled Josephson effect, such as the supercurrent flow through the graphene, sub-gap structure of differential conductance due to Andreev reflection, and periodic modulation of the critical current Ic with perpendicular magnetic field H to the graphene. In high bias above the superconducting gap voltage, however, we a...

  3. Infrared spectra of high temperature superconductors

    International Nuclear Information System (INIS)

    By the advent of high temperature superconductors in 1986, great hope arose in far infrared spectroscopy. Because the energy scale that characterizes superconducting condition extended to the typical far infrared region. However, it has been well known that noteworthy result rarely exists. The physical and technical circumstances as its causes are explained. Recently, the spectra in c-axis direction has become continuously measurable, and the prospect has become better for the electronic structure in normal conduction state and the features of superconduction state. The role of infrared spectroscopy in normal conduction state study is important, and optical conductivity, doping effect and interface (c-axis) spectra are discussed. Whether the superconduction gap of high temperature superconductors is observable with light or not is an important problem, but the gap has not been observable by the experiments, in which high temperature superconductors were changed from the clean limit to the dirty limit. As for superconduction state, c-axis superconduction spectra and Josephson plasma are described. Infrared spectroscopy is the only experimental method that can systematically pursue the change of electronic condition in high temperature superconductors by doping. (K.I.)

  4. Inelastic effects in high Tc superconductors

    International Nuclear Information System (INIS)

    A short review of experimental data on internal friction and ultrasonic attenuation in high temperature superconductors has been given. The vibration frequency varies in the 80 Hz to 600 Hz range. A number of relaxation and nonrelaxation effects has been discussed. (orig.)

  5. Lattice instabilities in heavy fermion superconductors

    International Nuclear Information System (INIS)

    This paper shows that while in nonsuperconducting HF systems such as CeCu6, CeAl3 and stoichiometric CeCu2Si2, the large electronic γ is due to a very narrow f band, in the three HF superconductors UBe13, UPt3 and nonstochiometric CeCu2Si2, it is not. The f band of these systems, as measured by their response to magnetic fields in three different ways, is much wider than suggested by the large γ. According to their actual f band width, the HF superconductors belong into the Bantam Fermion class. It is argued that most of the large γ of the HF superconductors is not of electronic origin and that it is instead caused by the precursor of a martensitic phase transition of the lattice or by a crystallographic phase mixture, i.e., that it is due to the displacive degrees of freedom. This suggests that the superconductivity of all three HF superconductors is caused by some special, low energy phonons rather than by a narrow f band. 52 refs., 4 figs., 3 tabs

  6. Radiation shielding effectiveness of newly developed superconductors

    International Nuclear Information System (INIS)

    Gamma ray shielding effectiveness of superconductors with a high mass density has been investigated. We calculated the mass attenuation coefficients, the mean free path (mfp) and the exposure buildup factor (EBF). The gamma ray EBF was computed using the Geometric Progression (G-P) fitting method at energies 0.015–15 MeV, and for penetration depths up to 40 mfp. The fast-neutron shielding effectiveness has been characterized by the effective neutron removal cross-section of the superconductors. It is shown that CaPtSi3, CaIrSi3, and Bi2Sr2Ca1Cu2O8.2 are superior shielding materials for gamma rays and Tl0.6Rb0.4Fe1.67Se2 for fast neutrons. The present work should be useful in various applications of superconductors in fusion engineering and design. - Highlights: • Radiation shielding properties of superconductors were investigated. • µ/ρ, mean free path, and exposure buildup factor were calculated. • CaPtSi3, CaIrSi3, and Bi2Sr2Ca1Cu2O8.2 were found superior for γ-ray shielding. • Tl0.6Rb0.4Fe1.67Se2 was found superior for fast neutron shielding

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

    Science.gov (United States)

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

    2009-05-01

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

  8. Spin current due to triplet superconductor - ferromagnet interfaces

    International Nuclear Information System (INIS)

    The interface between a superconductor and a ferromagnet is an ideal setting in which to study the complicated interplay of these two phases. Although the relevant physics is now very well understood for a spin singlet pairing state of the superconductor, qualitatively new phenomena can appear for a spin triplet pairing state due to the intrinsic spin structure of the superconductor. One such surprising result is the existence of a bulk spin supercurrent in the triplet superconductor due to spin-flip reflection of triplet Cooper pairs at the superconductor-ferromagnet interface. The resulting spin current displays strong similarities to the spontaneous charge current in a conventional Josephson junction. The dependence of the spin current on a number of relevant parameters is studied e.g. the orbital pairing state of the superconductor and the exchange splitting of the ferromagnet. The possibility of unconventional dynamics of the magnetization of the ferromagnet is discussed.

  9. Transverse effects due to vertex motion in superconductors

    International Nuclear Information System (INIS)

    In type-II superconductors, a magnetic field directed perpendicularly to the surface penetrates the superconductor through a lattice of quantized flux lines (mixed state), each isolated flux line (vortex) containing one quantum of flux. The author investigates two of the transversal effects in the mixed state, i.e. the Ettingshausen effect and the Hall effect. Measurements of these effects in the mixed state of the type-II superconductor Pb40In60 (at.%) are presented. (Auth.)

  10. Nanocomposite RE-Ba-Cu-O bulk superconductors

    OpenAIRE

    Iida, Kazumasa

    2016-01-01

    Nanocomposite oxide high-temperature bulk superconductors can be used as quasi-magnets. Thanks to the recent progress of material processing, quasi-magnet with 26 mm diameter can generate a large field of 17.6 T at 26 K. These results are highly attractive for applications, involving levitation of permanent magnets on the bulk superconductors. Indeed, several other applications such as motors and magnetic resonance microscope using bulk superconductors have been proposed and demonstrated. In ...

  11. Novel electromagnetic effects in high-temperature superconductors

    International Nuclear Information System (INIS)

    We report the first observations at liquid-nitrogen temperatures of parametric inductance behavior, signal up-conversion, and the nondestructive read-out of persistent supercurrent states in a superconductor. These observations have been made using a toroidal transformer with a core of the high-temperature superconductor YBa2Cu3O/sub 6.8/. The effects arise from the field-dependent behavior of the magnetic susceptibility of this superconductor

  12. Josephson super-current in graphene-superconductor junction

    OpenAIRE

    Sarvestani, E.; Jafari, S. A.

    2011-01-01

    Within the tunneling Hamiltonian formulation for the eight-component spinors,the Josephson critical super-current has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intra-valley and inter-valley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical s...

  13. Thermodynamics of anisotropic-gap and multiband clean BCS superconductors

    OpenAIRE

    Mishonov, T.; Penev, E.

    2002-01-01

    The free energy, non-gradient terms of the Ginzburg-Landau expansion, and the jump of the specific heat of a multiband anisotropic-gap clean BCS superconductor are derived in the framework of a separable-kernel approximation. Results for a two-band superconductor, d-wave superconductor, and some recent models for MgB_2 are derived as special cases.

  14. Numerical estimation of AC loss in superconductors with ripple current

    International Nuclear Information System (INIS)

    Highlights: •The loss energy density with ripple current is numerically calculated. •Irie–Yamafuji model is used for magnetic field dependence of critical current. •Calculated result of cylindrical superconductor agrees with theoretical result. •AC loss of strip superconductor becomes large at small ripple current amplitude. •Strip superconductor should be used as a form of hollow cylinder to reduce AC loss. -- Abstract: The loss energy density (AC loss) with ripple current is numerically calculated by finite element method for cylindrical and strip superconductors based on Irie–Yamafuji model in which the magnetic field dependence of the critical current density is taken into account for design of DC transmission cable system. It is confirmed that calculated result of the AC loss in the cylindrical superconductor with the ripple current agrees well with theoretical estimation which was reported in the previous work. On the contrary, the AC loss in the strip superconductor with the ripple current is obtained only by numerical calculation. It is found that the AC loss in the strip superconductor of the ripple current becomes larger than that without DC current at small ripple current amplitude, since the penetration depth of magnetic field becomes large. Therefore, it is recommended that strip superconductor is better to use as cylindrical hollow superconductor for DC transmission cable system to reduce the AC loss

  15. Noncommutative extension of AdS–CFT and holographic superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Pramanik, Souvik, E-mail: souvick.in@gmail.com; Das, Sudipta, E-mail: sudipta_jumaths@yahoo.co.in; Ghosh, Subir, E-mail: subir_ghosh2@rediffmail.com

    2015-03-06

    In this Letter, we consider a Non-Commutative (NC) extension of AdS–CFT correspondence and its effects on holographic superconductors. NC corrections are incorporated via the NC generalization of Schwarzschild black hole metric in AdS with the probe limit. We study NC effects on the relations connecting the charge density and the critical temperature of the Holographic Superconductors. Furthermore, condensation operator of the superconductor has been analyzed. Our results suggest that generically, NC effects increase the critical temperature of the holographic superconductor.

  16. Noncommutative extension of AdS–CFT and holographic superconductors

    International Nuclear Information System (INIS)

    In this Letter, we consider a Non-Commutative (NC) extension of AdS–CFT correspondence and its effects on holographic superconductors. NC corrections are incorporated via the NC generalization of Schwarzschild black hole metric in AdS with the probe limit. We study NC effects on the relations connecting the charge density and the critical temperature of the Holographic Superconductors. Furthermore, condensation operator of the superconductor has been analyzed. Our results suggest that generically, NC effects increase the critical temperature of the holographic superconductor

  17. Noncommutative extension of AdS–CFT and holographic superconductors

    Directory of Open Access Journals (Sweden)

    Souvik Pramanik

    2015-03-01

    Full Text Available In this Letter, we consider a Non-Commutative (NC extension of AdS–CFT correspondence and its effects on holographic superconductors. NC corrections are incorporated via the NC generalization of Schwarzschild black hole metric in AdS with the probe limit. We study NC effects on the relations connecting the charge density and the critical temperature of the Holographic Superconductors. Furthermore, condensation operator of the superconductor has been analyzed. Our results suggest that generically, NC effects increase the critical temperature of the holographic superconductor.

  18. Noncommutative extension of AdS-CFT and holographic superconductors

    Science.gov (United States)

    Pramanik, Souvik; Das, Sudipta; Ghosh, Subir

    2015-03-01

    In this Letter, we consider a Non-Commutative (NC) extension of AdS-CFT correspondence and its effects on holographic superconductors. NC corrections are incorporated via the NC generalization of Schwarzschild black hole metric in AdS with the probe limit. We study NC effects on the relations connecting the charge density and the critical temperature of the Holographic Superconductors. Furthermore, condensation operator of the superconductor has been analyzed. Our results suggest that generically, NC effects increase the critical temperature of the holographic superconductor.

  19. Structural and Chemical Diversity of Tl-Based Cuprate Superconductors

    Institute of Scientific and Technical Information of China (English)

    信赢

    2003-01-01

    The Tl-based cuprate superconductor family is the largest family in crystal structure and chemical composition among all high Tc cuprate superconductors. The Tl family can be divided into two sub-families, the Tl single layer family and the Tl double layer family, based on their crystal structural characteristics. The Tl single layer family is an ideal material for investigating the evolution of crystalline formation, charge carrier density, chemical composition, transport properties, superconductivity and their relationships. The Tl family contains almostall possible crystal structures discovered in high-Tc cuprate superconductors. Tl cuprate superconductors are of great importance not only in studying high-temperature superconductivity but also in commercial applications.

  20. Detecting Fulde–Ferrell superconductors by an Andreev interferometer

    International Nuclear Information System (INIS)

    We propose an Andreev interferometer, based on a branched Y-junction, to detect the finite momentum pairing in Fulde–Ferrell (FF) superconductors. In this interferometer, the oscillation of subgap conductance is a unique function of phase difference between the two channels of the Y-junction, which is determined by the phase modulation of the order parameter in the FF superconductors. This interferometer has the potential not only to determine the magnitude but also the direction of the momentum of Cooper pairs in the FF superconductor. The possible applications of the interferometer in the identification of the finite momentum pairing in non-centrosymmetric superconductors are also discussed. (paper)

  1. Fractional ac Josephson effect in unconventional superconductors

    International Nuclear Information System (INIS)

    For certain orientations of Josephson junctions between two px-wave or two d-wave superconductors, the subgap Andreev bound states produce a 4π-periodic relation between the Josephson current I and the phase difference ψ: I propor to sin(ψ/2) . Consequently, the ac Josephson current has the fractional frequency eV/h where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (not square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs. The fractional ac Josephson effect can be observed experimentally by measuring frequency spectrum of microwave radiation from the junction

  2. Asymmetric Ferromagnet-Superconductor-Ferromagnet Switch

    Energy Technology Data Exchange (ETDEWEB)

    Cadden-Zimansky, P.; Bazaliy, Ya.B.; Litvak, L.M.; Jiang, J.S.; Pearson, J.; Gu, J.Y.; You, Chun-Yeol; Beasley, M.R.; Bader, S.D.

    2011-11-04

    In layered ferromagnet-superconductor-ferromagnet F{sub 1} /S/F{sub 2} structures, the critical temperature T{sub c} of the superconductors depends on the magnetic orientation of the ferromagnetic layers F{sub 1} and F{sub 2} relative to each other. So far, the experimentally observed magnitude of change in T{sub c} for structures utilizing weak ferromagnets has been 2 orders of magnitude smaller than is expected from calculations. We theoretically show that such a discrepancy can result from the asymmetry of F/S boundaries, and we test this possibility by performing experiments on structures where F{sub 1} and F{sub 2} are independently varied. Our experimental results indicate that asymmetric boundaries are not the source of the discrepancy. If boundary asymmetry is causing the suppressed magnitude of T{sub c} changes, it may only be possible to detect in structures with thinner ferromagnetic layers.

  3. Symmetry and topology of noncentrosymmetric superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Samokhin, K.V., E-mail: kirill.samokhin@brocku.ca

    2015-08-15

    We present a detailed analysis of the pairing symmetry and the order parameter topology in superconductors without centre of inversion. Strong spin–orbit coupling of electrons with the crystal lattice leads to a large splitting of the Bloch bands, which makes it necessary to use a multiband description of superconductivity. We identify stable superconducting states and derive the Bogoliubov–de Gennes Hamiltonian, which determines the spectrum of fermionic quasiparticles. To develop a topological classification of the superconducting states we introduce two different types of topological invariants, the Chern numbers and the Maurer–Cartan invariants, and apply them to three-dimensional noncentrosymmetric superconductors, both with and without time reversal symmetry breaking.

  4. Electronic structure of Fe-based superconductors

    Indian Academy of Sciences (India)

    Kalobaran Maiti

    2015-06-01

    Fe-based superconductors have drawn much attention during the last decade due to the presence of superconductivity in materials containing the magnetic element, Fe, and the coexistence of superconductivity and magnetism. Extensive study of the electronic structure of these systems suggested the dominant role of states in their electronic properties, which is significantly different from the cuprate superconductors. In this article, some of our studies of the electronic structure of these fascinating systems employing high-resolution photoemission spectroscopy is reviewed. The combined effect of electron correlation and covalency reveals an interesting scenario in their electronic structure. The contribution of ligand states at the Fermi level is found to be much more significant than indicated in earlier studies. Temperature evolution of the energy bands reveals the signature of transition akin to Lifshitz transition in these systems.

  5. Abrikosov Gluon Vortices in Color Superconductors

    CERN Document Server

    Ferrer, Efrain J

    2010-01-01

    In this talk I will discuss how the in-medium magnetic field can influence the gluon dynamics in a three-flavor color superconductor. It will be shown how at field strengths comparable to the charged gluon Meissner mass a new phase can be realized, giving rise to Abrikosov's vortices of charged gluons. In that phase, the inhomogeneous gluon condensate anti-screens the magnetic field due to the anomalous magnetic moment of these spin-1 particles. This paramagnetic effect can be of interest for astrophysics, since due to the gluon vortex antiscreening mechanism, compact stars with color superconducting cores could have larger magnetic fields than neutron stars made up entirely of nuclear matter. I will also discuss a second gluon condensation phenomenon connected to the Meissner instability attained at moderate densities by two-flavor color superconductors. In this situation, an inhomogeneous condensate of charged gluons emerges to remove the chromomagnetic instability created by the pairing mismatch, and as a ...

  6. Conductive polymer/superconductor bilayer structures

    International Nuclear Information System (INIS)

    The preparation of a hybrid conducting polymer/high-temperature superconductor device consisting of a polypyrrole-coated YBa2Cu3O7-∂ microbridge is reported. Electrochemical techniques are exploited to alter the oxidation state of the polymer and, in doing so, it is found for the first time that superconductivity can be modulated in a controllable and reproducible fashion by a polymer layer. Whereas the neutral (insulating) polypyrrole only slightly influences the electrical properties of the underlying YBa2Cu3O7-∂ film, the oxidized (conductive) polymer depresses Tc by up to 50K. In a similar fashion, the oxidation state of the polymer is found to modulate reversibly the magnitude of Jc, the superconducting critical current. Thus, a new type of molecular switch for controlling superconductivity is demonstrated. Electrochemical, resistance vs. temperature, conact resistance, atomic force microscopy and scanning electron microscopy measurements are utilized to explore the polymer/superconductor interactions

  7. Shot Noise in Ferromagnetic Superconductor Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this paper, the superconducting order parameter and the energy spectrum of the Bogoliubov excitations are obtained from the Bogoliubov-de Gennes (BdG) equation for a ferromagnetic superconductor (FS). Taking into account the rough interface scattering effect, we calculate the shot noise and the differential conductance of the normal- metal insulator ferromagnetic superconductor junction. It is shown that the exchange energy Eh in FS can lead to splitting of the differential shot noise peaks and the conductance peaks. The energy difference between the two splitting peaks is equal to 2Eh. The rough interface scattering strength results in descent of conductance peaks and the shot noise-to-current ratio but increases the shot noise.

  8. Magnetic chains on a triplet superconductor.

    Science.gov (United States)

    Sacramento, P D

    2015-11-11

    The topological state of a two-dimensional triplet superconductor may be changed by an appropriate addition of magnetic impurities. A ferromagnetic magnetic chain at the surface of a superconductor with spin-orbit coupling may eliminate the edge states of a finite system giving rise to localized zero modes at the edges of the chain. The coexistence/competition between the two types of zero modes is considered. The reduction of the system to an effective 1d system gives partial information on the topological properties but the study of the two sets of zero modes requires a two-dimensional treatment. Increasing the impurity density from a magnetic chain to magnetic islands leads to a finite Chern number. At half-filling small concentrations are enough to induce chiral modes. PMID:26459719

  9. Electronic structure of Fe-based superconductors

    International Nuclear Information System (INIS)

    Fe-based superconductors have drawn much attention during the last decade due to the presence of superconductivity in materials containing the magnetic element, Fe, and the coexistence of superconductivity and magnetism. Extensive study of the electronic structure of these systems suggested the dominant role of d states in their electronic properties, which is significantly different from the cuprate superconductors. In this article, some of our studies of the electronic structure of these fascinating systems employing high-resolution photoemission spectroscopy is reviewed. The combined effect of electron correlation and covalency reveals an interesting scenario in their electronic structure. The contribution of ligand p states at the Fermi level is found to be much more significant than indicated in earlier studies. Temperature evolution of the energy bands reveals the signature of transition akin to Lifshitz transition in these systems. (author)

  10. Phases of holographic d-wave superconductor

    CERN Document Server

    Krikun, Alexander

    2015-01-01

    We study different phases in the holographic model of d-wave superconductor. These are described by solutions to the classical equations of motion found in different ansatze. Apart from the known homogeneous d-wave superconducting phase we find three new solutions. Two of them represent two distinct families of the spatially modulated solutions, which realize the charge density wave phases in the dual theory. The third one is the new homogeneous phase with nonzero anapole moment. These phases are relevant to the physics of cuprate high-Tc superconductor in pseudogap region. While the d-wave phase preserves translation, parity and time reversal symmetry, the striped phases break translations spontaneously. Parity and time-reversal are preserved when combined with discrete half-periodic shift of the wave. In anapole phase translation symmetry is preserved, but parity and time reversal are spontaneously broken. All of the considered solutions brake the global $U(1)$. Thermodynamical treatment shows that in the s...

  11. Energy efficiency of adiabatic superconductor logic

    International Nuclear Information System (INIS)

    Adiabatic superconductor logic (ASL), including adiabatic quantum-flux-parametron (AQFP) logic, exhibits high energy efficiency because its bit energy can be decreased below the thermal energy through adiabatic switching operations. In the present paper, we present the general scaling laws of ASL and compare the energy efficiency of ASL with those of other energy-efficient logics. Also, we discuss the minimum energy-delay product (EDP) of ASL at finite temperature. Our study shows that there is a maximum temperature at which the EDP can reach the quantum limit given by ħ/2, which is dependent on the superconductor material and the Josephson junction quality, and that it is reasonable to operate ASL at cryogenic temperatures in order to achieve an EDP that approaches ħ/2. (paper)

  12. Very General Holographic Superconductors and Entanglement Thermodynamics

    CERN Document Server

    Dey, Anshuman; Sarkar, Tapobrata

    2014-01-01

    We construct and analyze holographic superconductors with generalized higher derivative couplings, in single R-charged black hole backgrounds in four and five dimensions. These systems, which we call very general holographic superconductors, have multiple tuning parameters and are shown to exhibit a rich phase structure. We establish the phase diagram numerically as well as by computing the free energy, and then validated the results by calculating the entanglement entropy for these systems. The entanglement entropy is shown to be a perfect indicator of the phase diagram. The differences in the nature of the entanglement entropy in R-charged backgrounds compared to the AdS-Schwarzschild cases are pointed out. We also compute the analogue of the entangling temperature for a subclass of these systems and compare the results with non-hairy backgrounds.

  13. Symmetry and topology of noncentrosymmetric superconductors

    International Nuclear Information System (INIS)

    We present a detailed analysis of the pairing symmetry and the order parameter topology in superconductors without centre of inversion. Strong spin–orbit coupling of electrons with the crystal lattice leads to a large splitting of the Bloch bands, which makes it necessary to use a multiband description of superconductivity. We identify stable superconducting states and derive the Bogoliubov–de Gennes Hamiltonian, which determines the spectrum of fermionic quasiparticles. To develop a topological classification of the superconducting states we introduce two different types of topological invariants, the Chern numbers and the Maurer–Cartan invariants, and apply them to three-dimensional noncentrosymmetric superconductors, both with and without time reversal symmetry breaking

  14. Revisiting holographic superconductors with hyperscaling violation

    CERN Document Server

    Pan, Qiyuan

    2015-01-01

    We reinvestigate the effect of the hyperscaling violation on the holographic superconductors reported recently in J. High Energy Phys. {\\bf 09}, 048 (2013) [arXiv:1305.2000]. Different from the previous findings, we find that the increase of the hyperscaling violation makes it harder first and then easier for the scalar operator to condense, and the mass of the scalar field will not modify the value of the hyperscaling violation which gives the minimum critical temperature. In particular, we improve the Sturm-Liouville method by including the higher order terms in the expansion of the trial function to obtain the analytical results which are completely consistent with the numerical computations. Moreover, we observe that the hyperscaling violation affects the conductivity of the holographic superconductors and changes the expected relation in the gap frequency.

  15. Electrical bushing for a superconductor element

    Science.gov (United States)

    Mirebeau, Pierre; Lallouet, Nicolas; Delplace, Sebastien; Lapierre, Regis

    2010-05-04

    The invention relates to an electrical bushing serving to make a connection at ambient temperature to a superconductor element situated in an enclosure at cryogenic temperature. The electrical bushing passes successively through an enclosure at intermediate temperature between ambient temperature and cryogenic temperature, and an enclosure at ambient temperature, and it comprises a central electrical conductor surrounded by an electrically insulating sheath. According to the invention, an electrically conductive screen connected to ground potential surrounds the insulating sheath over a section that extends from the end of the bushing that is in contact with the enclosure at cryogenic temperature at least as far as the junction between the enclosure at intermediate temperature and the enclosure at ambient temperature. The invention is more particularly applicable to making a connection to a superconductor cable.

  16. Revisiting holographic superconductors with hyperscaling violation

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Qiyuan [Universidade de Sao Paulo, Instituto de Fisica, C.P. 66318, Sao Paulo (Brazil); Hunan Normal University, Department of Physics, Key Laboratory of Low Dimensional Quantum Structures and Quantum Control of Ministry of Education, Changsha, Hunan (China); Institute of Theoretical Physics, Chinese Academy of Sciences, State Key Laboratory of Theoretical Physics, Beijing (China); Zhang, Shao-Jun [Universidade de Sao Paulo, Instituto de Fisica, C.P. 66318, Sao Paulo (Brazil)

    2016-03-15

    We investigate the effect of the hyperscaling violation on the holographic superconductors. In the s-wave model, we find that the critical temperature decreases first and then increases as the hyperscaling violation increases, and the mass of the scalar field will not modify the value of the hyperscaling violation which gives the minimum critical temperature. We analytically confirm the numerical results by using the Sturm-Liouville method with the higher order trial function and improve the previous findings in Fan (J High Energy Phys 09:048, 2013). However, different from the s-wave case, we note that the critical temperature decreases with the increase of the hyperscaling violation in the p-wave model. In addition, we observe that the hyperscaling violation affects the conductivity of the holographic superconductors and changes the expected relation in the gap frequency in both s-wave and p-wave models. (orig.)

  17. Persistent superconductor currents in holographic lattices.

    Science.gov (United States)

    Iizuka, Norihiro; Ishibashi, Akihiro; Maeda, Kengo

    2014-07-01

    We consider a persistent superconductor current along the direction with no translational symmetry in a holographic gravity model. Incorporating a lattice structure into the model, we numerically construct novel solutions of hairy charged stationary black branes with momentum or rotation along the latticed direction. The lattice structure prevents the horizon from rotating, and the total momentum is only carried by matter fields outside the black brane horizon. This is consistent with the black hole rigidity theorem, and it suggests that in dual field theory with lattices, superconductor currents are made up of "composite" fields, rather than "fractionalized" degrees of freedom. We also show that our solutions are consistent with the superfluid hydrodynamics. PMID:25032917

  18. Proximity effects in superconductor-ferromagnet structures

    International Nuclear Information System (INIS)

    In the framework of this theme we study the interaction between superconducting and ferromagnetic metals, which are brought into electric contacts in superconductor-ferromagnet (S/F) layer structures. We want to study and understand, which precisely can happen, when the superconducting electron wave function penetrates into a ferromagnet. In chapter 2 we consider the Josephson effect in a simple model of the multi-domain S/F/S system and calculate the Josephson current through this contact. In chapter 3 we analyze a S/F system with rotating magnetization structure in the ferromagnet for strong and weak magnetic fields. Finally we analyze collective modes in two-band superconductors in the dirty limit

  19. Container-less processing of oxide superconductors

    International Nuclear Information System (INIS)

    The production of bulk oxide superconductors with high current carrying capability has been hindered by weak connectivity along grain boundaries, large property anisotropy, reactivity with all known containing media, oxygen content and control, and difficulties with phase stability. The present work outlines a melt processing technique developed in order to study the melting and solidification behavior of bulk YBa2Cu3O7-x or 1:2:3 superconductor material. By employing a drop tube and a resistance heated muffle furnace, melting and subsequent solidification of sintered 1:2:3 powder is performed in an oxidizing atmosphere, free from container contamination. Preliminary experiments have yielded two distinct microstructure depending on the relative size of the processed sphere. In this paper microstructural studies, x-ray analysis, superconductivity measurements, and TEM studies are presented

  20. Application of High Temperature Superconductors to Accelerators

    CERN Document Server

    Ballarino, A

    2000-01-01

    Since the discovery of high temperature superconductivity, a large effort has been made by the scientific community to investigate this field towards a possible application of the new oxide superconductors to different devices like SMES, magnetic bearings, flywheels energy storage, magnetic shielding, transmission cables, fault current limiters, etc. However, all present day large scale applications using superconductivity in accelerator technology are based on conventional materials operating at liquid helium temperatures. Poor mechanical properties, low critical current density and sensitivity to the magnetic field at high temperature are the key parameters whose improvement is essential for a large scale application of high temperature superconductors to such devices. Current leads, used for transferring currents from the power converters, working at room temperature, into the liquid helium environment, where the magnets are operating, represent an immediate application of the emerging technology of high t...

  1. Soft wall model for a holographic superconductor

    CERN Document Server

    Afonin, S S

    2015-01-01

    We apply the soft wall holographic model from hadron physics to a description of the high-$T_c$ superconductivity. In comparison with the existing bottom-up holographic superconductors, the proposed approach is more phenomenological. On the other hand, it is much simpler and has more freedom for fitting the conductivity properties of the real high-$T_c$ materials. We demonstrate some examples of emerging models and discuss a possible origin of the approach.

  2. Protection considerations for force-cooled superconductors

    International Nuclear Information System (INIS)

    This paper treats some hydrodynamic aspects of protecting magnets wound with force-cooled superconductors, namely, the rise in internal pressure and the forceful expulsion of helium during a quench. Two initial conditions are considered: an entire hydraulic path going normal all at once, and an initially small but nonrecovering normal zone. Formulas are given for the quench pressure and expulsion velocity in both cases and are compared with available experimental data

  3. Superconductor Digital Electronics: -- Current Status, Future Prospects

    Science.gov (United States)

    Mukhanov, Oleg

    2011-03-01

    Two major applications of superconductor electronics: communications and supercomputing will be presented. These areas hold a significant promise of a large impact on electronics state-of-the-art for the defense and commercial markets stemming from the fundamental advantages of superconductivity: simultaneous high speed and low power, lossless interconnect, natural quantization, and high sensitivity. The availability of relatively small cryocoolers lowered the foremost market barrier for cryogenically-cooled superconductor electronic systems. These fundamental advantages enabled a novel Digital-RF architecture - a disruptive technological approach changing wireless communications, radar, and surveillance system architectures dramatically. Practical results were achieved for Digital-RF systems in which wide-band, multi-band radio frequency signals are directly digitized and digital domain is expanded throughout the entire system. Digital-RF systems combine digital and mixed signal integrated circuits based on Rapid Single Flux Quantum (RSFQ) technology, superconductor analog filter circuits, and semiconductor post-processing circuits. The demonstrated cryocooled Digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals, enabling multi-net data links, and performing signal acquisition from HF to L-band with 30 GHz clock frequencies. In supercomputing, superconductivity leads to the highest energy efficiencies per operation. Superconductor technology based on manipulation and ballistic transfer of magnetic flux quanta provides a superior low-power alternative to CMOS and other charge-transfer based device technologies. The fundamental energy consumption in SFQ circuits defined by flux quanta energy 2 x 10-19 J. Recently, a novel energy-efficient zero-static-power SFQ technology, eSFQ/ERSFQ was invented, which retains all advantages of standard RSFQ circuits: high-speed, dc power, internal memory. The

  4. Noncommutative effects of spacetime on holographic superconductors

    OpenAIRE

    Debabrata Ghorai; Sunandan Gangopadhyay

    2016-01-01

    The Sturm–Liouville eigenvalue method is employed to analytically investigate the properties of holographic superconductors in higher dimensions in the framework of Born–Infeld electrodynamics incorporating the effects of noncommutative spacetime. In the background of pure Einstein gravity in noncommutative spacetime, we obtain the relation between the critical temperature and the charge density. We also obtain the value of the condensation operator and the critical exponent. Our findings sug...

  5. Noncommutative effects of spacetime on holographic superconductors

    OpenAIRE

    Ghorai, Debabrata; Gangopadhyay, Sunandan

    2016-01-01

    The Sturm-Liouville eigenvalue method is employed to analytically investigate the properties of holographic superconductors in higher dimensions in the framework of Born-Infeld electrodynamics incorporating the effects of noncommutative spacetime. In the background of pure Einstein gravity in noncommutative spacetime, we obtain the relation between the critical temperature and the charge density. We also obtain the value of the condensation operator and the critical exponent. Our findings sug...

  6. Hydrogen in high-Tc superconductors

    International Nuclear Information System (INIS)

    The role of hydrogen atom doping on the physical properties of high-Tc superconductors is presented. The main features are illustrated by presenting some chosen studies of the thermopower, resistivity, AC losses and Moessbauer effect in the hydrogenated SmBaCuO, YBaCuO and La(Sr)CuO systems. Also a brief survey of the current knowledge in this field is given. (orig.)

  7. Flywheel energy storage with superconductor magnetic bearings

    Science.gov (United States)

    Weinberger, Bernard R.; Lynds, Jr., Lahmer; Hull, John R.

    1993-01-01

    A flywheel having superconductor bearings has a lower drag to lift ratio that translates to an improvement of a factor of ten in the rotational decay rate. The lower drag results from the lower dissipation of melt-processed YBCO, improved uniformity of the permanent magnet portion of the bearings, operation in a different range of vacuum pressure from that taught by the art, and greater separation distance from the rotating members of conductive materials.

  8. Holographic superconductors in a rotating spacetime

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Kai; Abdalla, E. [Universidade de Sao Paulo, Instituto de Fisica, CP 66318, Sao Paulo (Brazil)

    2014-11-15

    We consider holographic superconductors in a rotating black string spacetime. In view of the mandatory introduction of the A{sub φ} component of the vector potential we are left with three equations to be solved. Their solutions show that the rotation parameter a influences the critical temperature T{sub c} and the conductivity σ in a simple but non-trivial way. (orig.)

  9. Unconventional disorder effects in correlated superconductors

    OpenAIRE

    Gastiasoro, Maria N.; Bernardini, Fabio; Andersen, Brian M.

    2016-01-01

    The understanding of disorder has profoundly influenced the development of condensed matter physics, explaining such fundamental effects as, for example, the transition from ballistic to diffusive propagation, and the presence of quantized steps in the quantum Hall effect. For superconductors, the response to disorder reveals crucial information about the internal gap symmetries of the condensate, and thereby the pairing mechanism itself. The destruction of superconductivity by disorder is tr...

  10. Transport properties of high critical temperature superconductors

    International Nuclear Information System (INIS)

    In this paper an overview of transport properties of the new high temperature oxide superconducting materials is presented. In particular the transport critical current in single crystals and sintered material is examined. The intrinsic properties of the new superconductors can be explained in terms of a low pinning energy and of the usual mechanisms of thermally activated flux motion. In sintered samples the superconducting behavior is dominated by the poor intergrain coupling that lead to the formation of Josephson weak links between grains

  11. Interface energy of two band superconductors

    OpenAIRE

    Geyer, Jani; Fernandes, Rafael M.; Kogan, V. G.; Schmalian, Jörg

    2010-01-01

    Using the Ginzburg-Landau theory for two-band superconductors, we determine the surface energy, sigma_s, between coexisting normal and superconducting states at the thermodynamic critical magnetic field. Close to the transition temperature, where the Ginzburg-Landau theory is applicable, we demonstrate that the two-band problem maps onto an effective single band problem. While the order parameters of the two bands may have different amplitudes in the homogeneous bulk, near the critical temper...

  12. Magnetic properties of FeSe superconductor

    OpenAIRE

    Grechnev, G. E.; Panfilov, A.S.; Desnenko, V. A.; Fedorchenko, A. V.; Gnatchenko, S. L.; Chareev, D. A.; Volkova, O. S.; A.N. Vasiliev

    2012-01-01

    A detailed magnetization study for the novel FeSe superconductor is carried out to investigate the behavior of the intrinsic magnetic susceptibility $\\chi$ in the normal state with temperature and under hydrostatic pressure. The temperature dependencies of $\\chi$ and its anisotropy $\\Delta \\chi=\\chi_{|}-\\chi_{\\bot}$ are measured for FeSe single crystals in the temperature range 4.2-300 K, and a substantial growth of susceptibility with temperature is revealed. The observed anisotropy $\\Delta ...

  13. Low angle resistivity anomaly in layered superconductors

    International Nuclear Information System (INIS)

    The pinning effect of vortex lines by the layered structure (intrinsic pinning) on resistivity of high-Tc, superconductors in the mixed state is investigated by means of perturbation theory. A sharp drop in the resistivity at small angles for which vortex lines are almost aligned with the ab-planes is shown to occur even in a high-temperature region where the pinning potential is reduced by thermal fluctuations

  14. Review of holographic superconductors with Weyl corrections

    CERN Document Server

    Momeni, Davood; Myrzakulov, Ratbay

    2014-01-01

    A quick review on the analytical aspects of holographic superconductors (HSC) with Weyl corrections has been presented. Mainly we focus on matching method and variations approaches. Different types of such HSC have been investigated, s-wave, p-wave and St\\'{u}ckelberg ones. We also review the fundamental construction of a p-wave type , in which the non-Abelian gauge field is coupled to the Weyl tensor. The results are compared from numerics to analytical results.

  15. General Relativistic Thermoelectric Effects in Superconductors

    OpenAIRE

    Ahmedov, B. J.

    2007-01-01

    We discuss the general-relativistic contributions to occur in the electromagnetic properties of a superconductor with a heat flow. The appearance of general-relativistic contribution to the magnetic flux through a superconducting thermoelectric bimetallic circuit is shown. A response of the Josephson junctions to a heat flow is investigated in the general-relativistic framework. Some gravitothermoelectric effects which are observable in the superconducting state in the Earth's gravitational f...

  16. Electrostatic field in superconductors I: open questions

    Czech Academy of Sciences Publication Activity Database

    Koláček, Jan; Lipavský, P.

    Singapore : World Scientific Publ. Co, 2010 - (Kusmartsev, F.), s. 557-563 ISBN 978-981-4289-14-6. - (24). [International Workshop on Condensed Matter Theories /32./. Loughborough (GB), 12.08.2008-19.08.2008] Institutional research plan: CEZ:AV0Z10100521 Keywords : superconductor * electric field Subject RIV: BM - Solid Matter Physics ; Magnetism http://eproceedings.worldscinet.com/9789814289153/9789814289153.shtml

  17. Mesoscopic Phase Separation in Anisotropic Superconductors

    OpenAIRE

    V. I. Yukalov; Yukalova, E. P.

    2005-01-01

    General properties of anisotropic superconductors with mesoscopic phase separation are analysed. The main conclusions are as follows: Mesoscopic phase separation can be thermodynamically stable only in the presence of repulsive Coulomb interactions. Phase separation enables the appearance of superconductivity in a heterophase sample even if it were impossible in pure-phase matter. Phase separation is crucial for the occurrence of superconductivity in bad conductors. Critical temperature for a...

  18. High temperature superconductors applications in telecommunications

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, A.A.; Li, J.; Zhang, M.F. [Prairie View A& M Univ., Texas (United States)

    1994-12-31

    The purpose of this paper is twofold: to discuss high temperature superconductors with specific reference to their employment in telecommunications applications; and to discuss a few of the limitations of the normally employed two-fluid model. While the debate on the actual usage of high temperature superconductors in the design of electronic and telecommunications devices-obvious advantages versus practical difficulties-needs to be settled in the near future, it is of great interest to investigate the parameters and the assumptions that will be employed in such designs. This paper deals with the issue of providing the microwave design engineer with performance data for such superconducting waveguides. The values of conductivity and surface resistance, which are the primary determining factors of a waveguide performance, are computed based on the two-fluid model. A comparison between two models-a theoretical one in terms of microscopic parameters (termed Model A) and an experimental fit in terms of macroscopic parameters (termed Model B)-shows the limitations and the resulting ambiguities of the two-fluid model at high frequencies and at temperatures close to the transition temperature. The validity of the two-fluid model is then discussed. Our preliminary results show that the electrical transport description in the normal and superconducting phases as they are formulated in the two-fluid model needs to be modified to incorporate the new and special features of high temperature superconductors. Parameters describing the waveguide performance-conductivity, surface resistance and attenuation constant-will be computed. Potential applications in communications networks and large scale integrated circuits will be discussed. Some of the ongoing work will be reported. In particular, a brief proposal is made to investigate of the effects of electromagnetic interference and the concomitant notion of electromagnetic compatibility (EMI/EMC) of high T{sub c} superconductors.

  19. Superconductor Digital-RF Receiver Systems

    Science.gov (United States)

    Mukhanov, Oleg A.; Kirichenko, Dmitri; Vernik, Igor V.; Filippov, Timur V.; Kirichenko, Alexander; Webber, Robert; Dotsenko, Vladimir; Talalaevskii, Andrei; Tang, Jia Cao; Sahu, Anubhav; Shevchenko, Pavel; Miller, Robert; Kaplan, Steven B.; Sarwana, Saad; Gupta, Deepnarayan

    Digital superconductor electronics has been experiencing rapid maturation with the emergence of smaller-scale, lower-cost communications applications which became the major technology drivers. These applications are primarily in the area of wireless communications, radar, and surveillance as well as in imaging and sensor systems. In these areas, the fundamental advantages of superconductivity translate into system benefits through novel Digital-RF architectures with direct digitization of wide band, high frequency radio frequency (RF) signals. At the same time the availability of relatively small 4K cryocoolers has lowered the foremost market barrier for cryogenically-cooled digital electronic systems. Recently, we have achieved a major breakthrough in the development, demonstration, and successful delivery of the cryocooled superconductor digital-RF receivers directly digitizing signals in a broad range from kilohertz to gigahertz. These essentially hybrid-technology systems combine a variety of superconductor and semiconductor technologies packaged with two-stage commercial cryocoolers: cryogenic Nb mixed-signal and digital circuits based on Rapid Single Flux Quantum (RSFQ) technology, room-temperature amplifiers, FPGA processing and control circuitry. The demonstrated cryocooled digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals in X-band and performing signal acquisition in HF to L-band at ˜30GHz clock frequencies.

  20. Resistivity of multiphase high-Tc superconductors

    International Nuclear Information System (INIS)

    Resistivity versus temperature (ρ-T) behavior of high-Tc superconductors in the normal state was recently modeled semiempirically according to conventional electron hopping theory for mixed-valence metal oxides. One important feature of this work was the interpretation of a resistivity minimum (i.e., the transition between insulator and metal) in the temperature regime near Tc, based on the decrease of activation energies Ehop with increases in magnetic dilution reported in the NiO and CuO systems. Quantitative accuracy has now been established by fitting ρ-T data of the La2-xSrxCuO4 and YBa2Cu3O7 high-Tc compounds, which serve as the basis for interpreting the varying slopes of multiphase superconductors. Calculated curves fitted to reported experimental data show that the metallic slope (∂ρ/∂T>0 above Tc) and the ρ-axis intercept of the linear extrapolation may be used to estimate the volume ratio of effective superconducting phase to normal phase within a particular specimen. From the application of this theory, it is determined that: (i) ρ-axis intercepts of single-phase superconductors are proportional to Ehop(1 - x)/x; (ii) normal phases cause increases in ρ, but decreases in slope of ρ(T)/ρ(300); and (iii) metallic slopes may be achieved with less than 10% effective volume of superconducting phase

  1. High-Tc superconductor quantum interference devices

    International Nuclear Information System (INIS)

    This patent describes a superconductive quantum interferometric device for sensing a characteristic of a magnetic field. It comprises a substrate having a surface, the substrate being selected from the group which consists of strontium titanate, aluminum oxide, sapphire, ZrO2 and mixtures thereof; a coating of MgO on the surface of the substrate; two identical thin-strip films of a high-critical temperature superconductor on the coating, each of the films having a pair of mutually parallel arms in the form of superconductor strips extending toward and aligned with super conductor strips forming corresponding arms of the other thin-strip film, and a crossbar strip connecting the arms of each thin-strip film at right angles to the arms, the high-critical-temperature superconductor being selected from the group which consists of yttrium-barium-calcium-copper-oxides, bismuth-strontium-calcium-copper-oxides, thallium-barium-copper-oxides, thallium-barium-calcium-copper-oxides, barium oxide: potassium oxide: bismuth oxides, and calcium oxide: zinc oxide: iron oxides; and insulating films on the coating between corresponding free ends of the arms thin-strip films, the insulating films being composed of a material selected from the group which consists of silicon dioxide, silicon nitride, magnesium oxide and mixture thereof

  2. Chemical stability of high-temperature superconductors

    Science.gov (United States)

    Bansal, Narottam P.

    1992-01-01

    A review of the available studies on the chemical stability of the high temperature superconductors (HTS) in various environments was made. The La(1.8)Ba(0.2)CuO4 HTS is unstable in the presence of H2O, CO2, and CO. The YBa2Cu3O(7-x) superconductor is highly susceptible to degradation in different environments, especially water. The La(2-x)Ba(x)CuO4 and Bi-Sr-Ca-Cu-O HTS are relatively less reactive than the YBa2Cu3O(7-x). Processing of YBa2Cu3O(7-x) HTS in purified oxygen, rather than in air, using high purity noncarbon containing starting materials is recommended. Exposure of this HTS to the ambient atmosphere should also be avoided at all stages during processing and storage. Devices and components made out of these oxide superconductors would have to be protected with an impermeable coating of a polymer, glass, or metal to avoid deterioration during use.

  3. Free energy of a Lovelock holographic superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Aranguiz, Ligeia [Universidad Tecnica Federico Santa Maria, Valparaiso (Chile); Pontificia Universidad Catolica de Valparaiso, Instituto de Fisica, Valparaiso (Chile); Miskovic, Olivera [Pontificia Universidad Catolica de Valparaiso, Instituto de Fisica, Valparaiso (Chile)

    2014-08-15

    We study thermodynamics of black hole solutions in Lanczos-Lovelock anti-de Sitter gravity in d + 1 dimensions coupled to nonlinear electrodynamics and a Stueckelberg scalar field. This class of theories is used in the context of gauge/gravity duality to describe a high-temperature superconductor in d dimensions. A larger number of coupling constants in the gravitational side is necessary to widen the domain of validity of physical quantities in dual quantum field theory (QFT). We regularize the gravitational action and find the finite conserved quantities for a planar black hole with scalar hair. Then we derive the quantum statistical relation in the Euclidean sector of the theory, and we obtain the exact formula for the free energy of the superconductor in the holographic QFT. Our result is analytic and it includes the effects of backreaction of the gravitational field. We further discuss on how this formula could be used to analyze second order phase transitions through the discontinuities of the free energy, in order to classify holographic superconductors in terms of the parameters in the theory. (orig.)

  4. A Simple Holographic Superconductor with Momentum Relaxation

    CERN Document Server

    Kim, Keun-Young; Park, Miok

    2015-01-01

    We study a holographic superconductor model with momentum relaxation due to massless scalar fields linear to spatial coordinates($\\psi_I = \\beta \\delta_{Ii} x^i$), where $\\beta$ is the strength of momentum relaxation. In addition to the original superconductor induced by the chemical potential($\\mu$) at $\\beta=0$, there exists a new type of superconductor induced by $\\beta$ even at $\\mu=0$. It may imply a new `pairing' mechanism of particles and antiparticles interacting with $\\beta$, which may be interpreted as `impurity'. Two parameters $\\mu$ and $\\beta$ compete in forming superconducting phase. As a result, the critical temperature behaves differently depending on $\\beta/\\mu$. It decreases when $\\beta/\\mu$ is small and increases when $\\beta/\\mu$ is large, which is a novel feature compared to other models. After analysing ground states and phase diagrams for various $\\beta/\\mu$, we study optical electric($\\sigma$), thermoelectric($\\alpha$), and thermal($\\bar{\\kappa}$) conductivities. When the system undergo...

  5. Avoided valence transition in a plutonium superconductor.

    Science.gov (United States)

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

    2015-03-17

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

  6. Topology of nonsymmorphic crystalline insulators and superconductors

    Science.gov (United States)

    Shiozaki, Ken; Sato, Masatoshi; Gomi, Kiyonori

    2016-05-01

    Topological classification in our previous paper [K. Shiozaki and M. Sato, Phys. Rev. B 90, 165114 (2014), 10.1103/PhysRevB.90.165114] is extended to nonsymmorphic crystalline insulators and superconductors. Using the twisted equivariant K theory, we complete the classification of topological crystalline insulators and superconductors in the presence of additional order-two nonsymmorphic space-group symmetries. The order-two nonsymmorphic space groups include half-lattice translation with Z2 flip, glide, twofold screw, and their magnetic space groups. We find that the topological periodic table shows modulo-2 periodicity in the number of flipped coordinates under the order-two nonsymmorphic space group. It is pointed out that the nonsymmorphic space groups allow Z2 topological phases even in the absence of time-reversal and/or particle-hole symmetries. Furthermore, the coexistence of the nonsymmorphic space group with time-reversal and/or particle-hole symmetries provides novel Z4 topological phases, which have not been realized in ordinary topological insulators and superconductors. We present model Hamiltonians of these new topological phases and analytic expressions of the Z2 and Z4 topological invariants. The half-lattice translation with Z2 spin flip and glide symmetry are compatible with the existence of boundaries, leading to topological surface gapless modes protected by the order-two nonsymmorphic symmetries. We also discuss unique features of these gapless surface modes.

  7. Charge of a quasiparticle in a superconductor.

    Science.gov (United States)

    Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas

    2016-02-16

    Nonlinear charge transport in superconductor-insulator-superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e = n, with n = 1-4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD ~ 2Δ, we found a reproducible and clear dip in the extracted charge to q ~ 0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure. PMID:26831071

  8. Comparison between d-wave superconductor with nonmagnetic impurities and s-wave superconductor with magnetic impurities

    International Nuclear Information System (INIS)

    The suppresion of the superconducting transition temperature of both the d-wave superconductor with nonmagnetic impurities and the s-wave one with magnetic impurities are described by the Abrikosov-Gor'kov formula. Unfortunately, this leads to a lot of confusion in high Tc superconductor community. We compute here a few physical quantities of these 2 systems, which can discriminate two cases without ambiguity. In particular, the immediate appearance of the gapless behavior is a clear signature of d-wave superconductor, while the persistence of the energy gap is the one of s-wave superconductor. (orig.)

  9. McMillan-Rowell Like Oscillations in a Superconductor-InAs/GaSb-Superconductor Junction

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Xiaoyan [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Yu, Wenlong [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Hawkins, Samuel D. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Klem, John F. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Pan, Wei [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-08-04

    We fabricated a superconductor (Ta)-InAs/GaSb bilayer-superconductor (Ta) junction device that has a long mean free path and can preserve the wavelike properties of particles (electrons and holes) inside the junction. Differential conductance measurements were also carried out at low temperatures in this device, and McMillan-Rowell like oscillations (MROs) were observed. A much larger Fermi velocity, compared to that from Shubnikov-de Haas oscillations, was obtained from the frequency of MROs. Possible mechanisms are discussed for this discrepancy.

  10. McMillan-Rowell like oscillations in a superconductor-InAs/GaSb-superconductor junction

    International Nuclear Information System (INIS)

    We have fabricated a superconductor (Ta)-InAs/GaSb bilayer-superconductor (Ta) junction device that has a long mean free path and can preserve the wavelike properties of particles (electrons and holes) inside the junction. Differential conductance measurements were carried out at low temperatures in this device, and McMillan-Rowell like oscillations (MROs) were observed. Surprisingly, a much larger Fermi velocity, compared to that from Shubnikov-de Haas oscillations, was obtained from the frequency of MROs. Possible mechanisms are discussed for this discrepancy

  11. Magnetic excitations in iron chalcogenide superconductors

    Directory of Open Access Journals (Sweden)

    Hisashi Kotegawa

    2012-01-01

    Full Text Available Nuclear magnetic resonance and neutron scattering experiments in iron chalcogenide superconductors are reviewed to make a survey of the magnetic excitations in FeSe, FeSe1−xTex and alkali-metal-doped AxFe2−ySe2 (A = K, Rb, Cs, etc. In FeSe, the intimate relationship between the spin fluctuations and superconductivity can be seen universally for the variations in the off-stoichiometry, the Co-substitution and applied pressure. The isovalent compound FeTe has a magnetic ordering with different wave vector from that of other Fe-based magnetic materials. The transition temperature Tc of FeSe increases with Te substitution in FeSe1−xTex with small x, and decreases in the vicinity of the end member FeTe. The spin fluctuations are drastically modified by the Te substitution. In the vicinity of the end member FeTe, the low-energy part of the spin fluctuation is dominated by the wave vector of the ordered phase of FeTe; however, the reduction of Tc shows that it does not support superconductivity. The presence of same wave vector as that of other Fe-based superconductors in FeSe1−xTex and the observation of the resonance mode demonstrate that FeSe1−xTex belongs to the same group as most of other Fe-based superconductors in the entire range of x, where superconductivity is mediated by the spin fluctuations whose wave vector is the same as the nesting vector between the hole pockets and the electron pockets. On the other hand, the spin fluctuations differ for alkali-metal-doped AxFe2−ySe2 and FeSe or other Fe-based superconductors in their wave vector and strength in the low-energy part, most likely because of the different Fermi surfaces. The resonance mode with different wave vector suggests that AxFe2−ySe2 has an exceptional superconducting symmetry among Fe-based superconductors.

  12. A phenomenological approach to high Tc oxide superconductors

    International Nuclear Information System (INIS)

    Oxide superconductors are described in terms of macroscopic wave functions Ψ and Φ corresponding, respectively, to electron pairs of the superconducting and insulating states. In terms of the total free energy of the system, including the effect of interaction, we discuss the electrodynamic responses of the oxide superconductors in relation with the experiments to data. (author). 10 refs

  13. Applications of high-temperature superconductors in electric power supply

    International Nuclear Information System (INIS)

    The author reports on a study in which the characteristics, applications and effects of equipment with high-temperature superconductors in power transmission and distribution networks were investigated. At the present state of the art, it is impossible to say when and in what form high-temperature superconductor materials will be available for low-cost, large-area power supply. (orig.)

  14. Internally-cooled cabled superconductors cooled with helium II

    International Nuclear Information System (INIS)

    Niobium-titanium superconductors maintained at sublambda temperatures provide an alternative to helium cooled niobium-3-tin superconductors operating in the 4.2 to 5 K temperature range. The subject paper examines the replacement of supercritical HeI with subcooled HeII in a slightly modified MIT-12 T test coil. Both steady-state and transient heat loads are considered

  15. Reduction of toroidal ripple by using high Tc superconductors

    International Nuclear Information System (INIS)

    In this paper we present a new method to reduce the toroidal ripple with use of high Tc superconductors. High Tc superconductors can behave as ferromagnetic or diamagnetic materials depending on their magnetic hysteresis. If they are appropriately arranged and magnetized between the toroidal field coils, they possibly decrease the toroidal field ripple. Here, the preliminary design of ITER is taken as an example, and the effect of the high Tc superconductors on the ripple is evaluated. The magnetic induction due to the superconductors is calculated by the current vector potential method based on the critical state model. Several arrangements of the high Tc superconductors were quantitatively examined in order to reduce the ripple. The results obtained by the calculation show that the maximum ripple value can be reduced to be the required value. (orig.)

  16. Optical studies of crystalline organic superconductors under extreme conditions

    CERN Document Server

    McDonald, R D

    2001-01-01

    the aim being to make an optical measurement of the pressure dependence of the charge carrier effective mass. Chapter 4 concentrates on the vibrational modes of kappa-(BEDT-TTF) sub 2 Cu(SCN) sub 2. This chapter reports the first Raman scattering experiments on an organic superconductor at high pressure. Comparison of the infrared reflectance and Raman scattering measurements are used to elucidate the role of electron-phonon coupling in this material's superconductivity. Chapter 5 reports the first non-resonant measurements of the GHz conductivity of an organic molecular superconductor. These experiments probe the unconventional metallic properties of an organic superconductor during the onset of superconductivity. This thesis reports experiments which involve the interaction of light and matter to probe the properties of crystalline organic superconductors. The organic superconductors of the BEDT-TTF family are prototypical correlated electron systems; their low-temperature ground states are dominated by man...

  17. Stable and unstable thermo -current states of high temperature superconductors

    International Nuclear Information System (INIS)

    Formation peculiarities of the stable and unstable states of high-Tc superconductors are discussed. To understand the basic physical trends, which are characteristic for the current penetration mechanism in high temperature superconductors, the operating states of Bi2212 slab without stabilizing matrix placed in DC external magnetic fields at low coolant temperature are theoretically investigated. It is proved that the temperature of a high-Tc superconductor is not equals to the coolant temperature before instability onset. Therefore, the voltage-current characteristic of a high-Tc superconductor has only a positive slope during continuous current charging. As a result, it does not allow one to find the boundary between stable and unstable thermo - current states. This peculiarity has to be considered during experiments at which the critical current of high-Tc superconductors is defined

  18. Development of high temperature superconductors having high critical current density

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Gye Wong; Kim, C. J.; Lee, H.G.; Kwon, S. C.; Lee, H. J.; Kim, K. B.; Park, J. Y.; Jung, C. H

    2000-08-01

    Fabrication of high T{sub c} superconductors and its applications for electric power device were carried out for developing superconductor application technologies. High quality YBCO superconductors was fabricated by melt texture growth, top-seeded melt growth process and multi-seeded melt growth process and the properties was compared. The critical current density of the melt processed YBCO superconductors was about few 10,000 A/cm{sup 2} and the levitation force was 50 N. The processing time needed for the growth of the 123 single grain was greatly reduced by applying multi-seeding without no significant degradation of the levitation force. The multi-seeded melt growth process was confirmed as a time-saving and cost-effective method for the fabrication of bulk superconductors with controlled crystallographic orientation.

  19. Development of high temperature superconductors having high critical current density

    International Nuclear Information System (INIS)

    Fabrication of high Tc superconductors and its applications for electric power device were carried out for developing superconductor application technologies. High quality YBCO superconductors was fabricated by melt texture growth, top-seeded melt growth process and multi-seeded melt growth process and the properties was compared. The critical current density of the melt processed YBCO superconductors was about few 10,000 A/cm2 and the levitation force was 50 N. The processing time needed for the growth of the 123 single grain was greatly reduced by applying multi-seeding without no significant degradation of the levitation force. The multi-seeded melt growth process was confirmed as a time-saving and cost-effective method for the fabrication of bulk superconductors with controlled crystallographic orientation

  20. The Superconducting gap behavior in the antiferromagnetic Nickel-Borocarbide compounds RNi{sub 2}B{sub 2}C (R=Dy, Ho, Er, Tm) studied by point-contacts spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Naidyuk, Yu G; Bobrov, N L; Chernobay, V N; Kvitnitskaya, O E; Yanson, I K [B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 47 Lenin ave., 61103, Kharkiv (Ukraine); Behr, G; Drechsler, S-L; Fuchs, G [Leibniz-Institut fuer Festkoerper- und Werkstoffforschung Dresden, POB 270116, D-01171 Dresden (Germany); Naugle, D G; Rathnayaka, K D D, E-mail: naidyuk@ilt.kharkov.u [Department of Physics, Texas A and M University, College Station TX 77843-4242 (United States)

    2009-03-01

    An general survey of the superconducting (SC) gap study in the title compounds by point-contact (PC) spectroscopy is presented. The SC gap was determined from dV/dI of PCs employing the well-known theory of conductivity for normal metal-superconductor PCs accounting Andreev reflection. The theory was modified by including pair-breaking effects considering the presence of magnetic rare-earth ions. A possible multiband structure of these compounds was also taken into account. The PC study of the gap in the Er-compound (T{sub N} approx = 6 K < T{sub c} approx = 11K) gives evidence for the presence of two SC gaps. Additionally, a distinct decrease of both gaps is revealed for R = Er in the antiferromagnetic (AF) state. For R = Tm (T{sub N} approx =1.5 K < T{sub c} approx =10.5 K) a decrease of the SC gap is observed below 4-5 K, while for R = Dy (T{sub N} approx =10.5 K > T{sub c} approx = 6.5 K) the SC gap has a BCS-like dependence in the AF state. The SC gap for R = Ho (T{sub N} approx =5.2 K < T{sub c} approx = 8.5 K) exhibits below T* approx =5.6 K a single-band BCS-like dependence vanishing above T*, where a specific magnetic order occurs. The difference in the SC gap behavior in the title compounds is attributed to different AF ordering.

  1. Iron-based superconductors via soft chemistry

    International Nuclear Information System (INIS)

    This thesis provides new soft chemistry approaches to Fe-based superconductors. Mild syntheses were demonstrated to be able to overcome difficulties, occurring in conventional synthesis and to enable the access to new metastable phases. A solvent-based metathesis reaction led to β-FeSe exclusively. Contrary to solid state syntheses, the formation of hexagonal α-FeSe could be avoided under mild conditions. The deintercalation of interstitial Fe (by formation of Fe3O4) could be proven by low temperature O2-annealing of Fe1+xTe1-ySey. By using redox (de)intercalations K1-xFe2-ySe2, metastable Na1-xFe2-yAs2 and Na1-x((Fe1-yCoy)1-zAs)2 could successfully be obtained at room temperature. The mild synthesis conditions led to compounds like FeSe and K1-xFe2-ySe2 which exhibited different physical properties than found by conventional high temperature methods. In general, the developed (de)intercalation reactions represent a new, universally applicable tool in order to manipulate the structure along with the properties of Fe-based superconductors. The basic structural features of the characteristic FeX4/4 tetrahedral layers, however, are preserved. Soft chemistry syntheses have been shown to allow the formation of a variety of phases, like Na1-xFe2-yAs2, Na1-x((Fe1-yCoy)1-zAs)2 and K1-xFe2-ySe2. Hence, especially low temperature approaches may enable the realization of complex stacking sequences, potentially leading to the fulfillment of the greatest goal in the research of superconductors - room temperature superconductivity.

  2. Zeeman effects in heavy electron superconductors

    International Nuclear Information System (INIS)

    Understanding the properties of newly discovered strongly correlated electron compounds is a considerable challenge for both fundamental matters and long-term industrial impact. Experimental activity on heavy electron metals and superconductors has lead to highlighting effects that depart from current knowledge. The thesis is aimed at modelling effects that have been observed in response to magnetic field in the heavy electron superconductor CeCoIn5. This consists of two parts. In the first time we deal with the vortex lattice state anomalous local magnetic field space variations as highlighted by small angle neutron scattering and muon spin rotation experiment. On the basis of the Ginzburg-Landau theory with account of spin effect, we analyse the local field inhomogeneity in the vortex lattice and derive expressions for the neutron scattering form factors and muon spin rotation static linewidth. The anomalous experimental data are shown to be result of spin driven supercurrents which circulate around the vortex cores and lead to an increase with external field in the internal field inhomogeneity on a distance of the order of the superconducting coherence length from the vortex axis. The importance of the effect is controlled by a single quantity (the Maki parameter). The second part is on nearly commensurate spin density wave transition in a quasi two-dimensional superconductor. It is motivated by observation of the confinement of spin density wave ordering inside the superconducting state of CeCoIn5 in magnetic field. In the frame of the spin-fermion formulation we propose a mechanism for the ground state transition consisting in the field-induced slowing down of a collective spin density fluctuation mode (spin-exciton) to static ordering. This represents a scenario by which the transition to spin ordering is intrinsically related to superconductivity. (author)

  3. Pseudogap in cuprate and organic superconductors

    OpenAIRE

    Merino, J.; Gunnarsson, O.

    2012-01-01

    We study the pseudogap present in cuprate and organic superconductors. We use the dynamical cluster approximation (DCA), treating a cluster embedded in a bath. As the Coulomb interaction is increased, cluster-bath Kondo states are destroyed and bound cluster states formed. We show that this leads to a pseudogap. Due to weaker coupling to the bath for the anti-nodal point, this happens first for this point, explaining the k-dependence of the pseudogap. The pseudogap can be understood in terms ...

  4. Quasiparticles near domain walls in hexagonal superconductors

    Science.gov (United States)

    Mukherjee, S. P.; Samokhin, K. V.

    2016-02-01

    We calculate the energy spectrum of quasiparticles trapped by a domain wall separating different time-reversal symmetry-breaking ground states in a hexagonal superconductor, such as UPt3. The bound-state energy is found to be strongly dependent on the gap symmetry, the domain-wall orientation, the quasiparticle's direction of semiclassical propagation, and the phase difference between the domains. We calculate the corresponding density of states and show how one can use its prominent features, in particular, the zero-energy singularity, to distinguish between different pairing symmetries.

  5. Detection of infrared photons with a superconductor

    Institute of Scientific and Technical Information of China (English)

    ZHANG LaBao; ZHONG YangYin; KANG Lin; CHEN Jian; JI ZhengMing; XU WeiWei; CAO ChunHai

    2009-01-01

    A superconductor single photon detector based on NbN nanowire was fabricated using electron beam lithography (EBL) and reactive ion etching (RIE) for infrared photon detection. When biased well below its critical current at 4.2 K, NbN nanowire is very sensitive to the incident photons. Typical telecommunication photons with a wavelength of 1550 nm were detected by this detector. Data analysis indicates the repeating rate of the device with 200 nm NbN nanowire may be up to 100 MHz, and the quantum efficiency is about 0.01% when biased at 0.95Ic.

  6. Thermodynamic Properties in Triangular-Lattice Superconductors

    Science.gov (United States)

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

    2016-06-01

    The study of superconductivity arising from doping a Mott insulator has become a central issue in the area of superconductivity. Within the framework of the kinetic-energy-driven superconducting (SC) mechanism, we discuss the thermodynamic properties in the triangular-lattice cobaltate superconductors. It is shown that a sharp peak in the specific heat appears at the SC transition temperature T_c, and then the specific heat varies exponentially as a function of temperature for temperatures Tqualitatively the Bardeen-Cooper-Schrieffer-type temperature dependence, and has the same dome-shaped doping dependence as T_c.

  7. Electronic transport in superconductor-ferromagnet-heterostructures

    International Nuclear Information System (INIS)

    Electronic transport in nanoscale superconductor-ferromagnet (SF) contacts at very low temperature is studied in order to identify non-local Andreev bound states. The samples consist of two parallel ferromagnetic film strips between superconducting leads. The strips are magnetized to exhibit a magnetic field which discourages direct Andreev reflection at the respective SF - interfaces. However, if the magnetization is antiparallel and the distances sufficiently small, the setup allows for a non-local reflection of the electrons in one strip to holes in the other strips and vice versa. This way, a bound state may form, giving rise to a Josephson current across the junction. (orig.)

  8. Inhomogeneous superconductivity in superconductor/ferromagnet heterostructures

    International Nuclear Information System (INIS)

    A strong exchange field acting on the Cooper pairs in the ferromagnetic (F) metal leads to the damping oscillatory behaviour of the superconducting order parameter inside the F layer. In consequence in the superconductor-ferromagnet (S-F) multilayers the critical temperature and Josephson current depend in an oscillatory manner on the exchange field and thickness of ferromagnetic metal. These oscillations are related with the transition into the state where the phase of superconducting order parameter is opposite in S-F-S Josephson junction. The transition to this π-state may occur via the states with an arbitrary ground phase difference

  9. Vortex induced strain effects in anisotropic superconductors

    International Nuclear Information System (INIS)

    Strain in a superconductor, produced by the normal vortex core, can affect both static and dynamic properties of vortices. It causes an additional vortex-vortex interaction which is long-ranged (∼ 1/r2) as compared with finite but much stronger London interaction in the fields far below Hc2. The energy of this magneto-elastic interaction is calculated within London model. The role of strain effects in forming vortex lattice structure is demonstrated for YBa2Cu3O7

  10. High-Tc superconductor coplanar waveguide filter

    Science.gov (United States)

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

    1991-01-01

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

  11. Electric field in type II superconductors

    OpenAIRE

    Kolacek, J.; Lipavsky, P.; Spicka, V.

    1999-01-01

    Generally it is accepted that electric field E in type II superconductors is created by the vortex motion, so that it is proportional to the vortex velocity v_L. This assertion is based on the Josephson relation E = - v_L x B, which was derived and is valid if no transport current is present. We present arguments showing that if transport current is present, static electric field is proportional to the relative velocity of vortices in respect to the velocity of superconducting fluid v_s, so t...

  12. Microwave-induced effects on superconductors

    International Nuclear Information System (INIS)

    We have studied the effects of microwave radiation on superconducting tunnel junctions and on the critical currents of superconducting strips at 2.0 and 10.0 GHz. In the tunnel junctions both quantum mechanical and classical effects (photon-induced tunneling and classical rectification, respectively), were observed, but not gap enhancement. The application of microwave radiation on long, superconducting, thin-film bridges was found to increase their critical current. The microwave magnetic field was found to couple more efficiently to the superconductor. The increase in the critical current was found to be proportional to the square root of the incident power

  13. Non-Abelian Vortices in Holographic Superconductors

    CERN Document Server

    Tallarita, Gianni

    2015-01-01

    We find, by an appropriate extension of the standard holographic superconductor setup, static bulk solutions which describe holographic duals to non-Abelian vortices. In the core of these vortices a scalar field condenses, breaking a non-Abelian global symmetry which leads to additional zero modes called orientational moduli. These moduli appear in the bulk as Goldstone bosons associated to the condensation of a neutral scalar field. We extend this construction to include periodic solutions corresponding to global non-Abelian vortex lattices.

  14. Guided design of copper oxysulfide superconductors

    Science.gov (United States)

    Yee, Chuck-Hou; Birol, Turan; Kotliar, Gabriel

    2015-07-01

    We describe a framework for designing novel materials, combining modern first-principles electronic-structure tools, materials databases, and evolutionary algorithms capable of exploring large configurational spaces. Guided by the chemical principles introduced by Antipov et al., for the design and synthesis of the Hg-based high-temperature superconductors, we apply our framework to screen 333 proposed compositions to design a new layered copper oxysulfide, Hg(CaS)2CuO2. We evaluate the prospects of superconductivity in this oxysulfide using theories based on charge-transfer energies, orbital distillation and uniaxial strain.

  15. Inversion symmetry protected topological insulators and superconductors

    Science.gov (United States)

    Lee, Dung-Hai; Lu, Yuan-Ming

    2015-03-01

    Three dimensional topological insulator represents a class of novel quantum phases hosting robust gapless boundary excitations, which is protected by global symmetries such as time reversal, charge conservation and spin rotational symmetry. In this work we systematically study another class of topological phases of weakly interacting electrons protected by spatial inversion symmetry, which generally don't support stable gapless boundary states. We classify these inversion-symmetric topological insulators and superconductors in the framework of K-theory, and construct their lattice models. We also discuss quantized response functions of these inversion-protected topological phases, which serve as their experimental signatures.

  16. Modeling forces in high-temperature superconductors

    International Nuclear Information System (INIS)

    We have developed a simple model that uses computed shielding currents to determine the forces acting on a high-temperature superconductor (HTS). The model has been applied to measurements of the force between HTS and permanent magnets (PM). Results show the expected hysteretic variation of force as the HTS moves first toward and then away from a permanent magnet, including the reversal of the sign of the force. Optimization of the shielding currents is carried out through a simulated annealing algorithm in a C++ program that repeatedly calls a commercial electromagnetic software code. Agreement with measured forces is encouraging

  17. Minimal Model for an Unbalanced Holographic Superconductor

    CERN Document Server

    Musso, Daniele

    2013-01-01

    We describe the simplest holographic model for an s-wave unbalanced superconductor in 2+1 dimensions. We study its phase diagram and linear response features with particular attention to the possibility of spatially modulated phases (LOFF) and mixed spin-electric properties. The normal phase of the model at hand allows us to analyze a strong-coupling generalization of Mott two-current model for spintronic systems; the superconducting phase features an interesting DC spin-superconductivity without spin-symmetry breaking .

  18. Oxygen diffusion in high-Tc superconductors

    International Nuclear Information System (INIS)

    The cuprate superconductors are fascinating not only because of their technical promise, but also because of their structures, especially the anisotropy of the crystal lattice. There are some structural similarities among these compounds, but also significant differences. Measurements of the oxygen tracer diffusion coefficients have been carried out as a function of temperature, oxygen partial pressure, crystal orientation, and doping in the La-Sr-Cu-0, Y-Ba-Cu-0, and Bi-Sr-Ca-Cu-0 systems. These measurements have revealed a variety of defect mechanisms operating in these compounds; the exact nature of the mechanism depends on the details of the structure

  19. High-temperature superconductors make major progress

    CERN Multimedia

    CERN Bulletin

    2014-01-01

    This month's Nature Materials featured an important breakthrough for high-temperature superconductors. A new method has been found for processing Bi-2212 high-temperature superconducting round wire in order to drastically increase its critical current density. The result confirms that this conductor is a serious candidate for future very-high-field magnets.   This image shows the cross-section of two Bi-2212 wires. The bottom wire has less leakage and void porosity due to a heat treatment done at an overpressure of 100 bar - about 100 times the pressure used to produce the top wire (image from [Nature Materials, Vol. 13 (2014), 10.1038/nmat3887]). The workhorse for building superconducting accelerator magnets has been, so far, the Niobium-Titanium (Nb-Ti) alloy superconductor. But with Nb-Ti having reached its full potential, other conductors must be used to operate in higher magnetic fields beyond those reached with the LHC magnets. Today, the intermetallic Niobium-Tin (Nb3Sn) is th...

  20. Insulation system for high temperature superconductor cables

    Science.gov (United States)

    Michael, P. C.; Haight, A. E.; Bromberg, L.; Kano, K.

    2015-12-01

    Large-scale superconductor applications, like fusion magnets, require high-current capacity conductors to limit system inductance and peak operating voltage. Several cabling methods using high temperature superconductor (HTS) tapes are presently under development so that the unique high-field, high-current-density, high operating temperature characteristics of 2nd generation REBCO coated conductors can be utilized in next generation fusion devices. Large-scale magnets are generally epoxy impregnated to support and distribute electromagnetic stresses through the magnet volume. However, the present generation of REBCO coated conductors are prone to delamination when tensile stresses are applied to the broad surface of REBCO tapes; this can occur during epoxy cure, cooldown, or magnet energization. We present the development of an insulation system which effectively insulates HTS cabled conductors at high withstand voltage while simultaneously preventing the intrusion of the epoxy impregnant into the cable, eliminating degradation due to conductor delamination. We also describe a small-scale coil test program to demonstrate the cable insulation scheme and present preliminary test results.

  1. Electron-phonon properties of pnictide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Boeri, L., E-mail: L.Boeri@fkf.mpg.d [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Dolgov, O.V. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Golubov, A.A. [Faculty of Science and Technology and MESA, Institute for Nanotechnology, University of Twente, 7500 AE Enschede (Netherlands)

    2009-05-01

    In this paper we discuss the normal and superconducting state properties of two pnictide superconductors, LaOFeAs and LaONiAs, using Migdal-Eliashberg theory and density functional perturbation theory. For pure LaOFeAs, the calculated electron-phonon coupling constant lambda=0.21 and logarithmic-averaged frequency omega{sub ln}=206K, give a maximum T{sub c} of 0.8 K, using the standard Migdal-Eliashberg theory. Inclusion of multi-band effects increases the T{sub c} only marginally. To reproduce the experimental T{sub c}, a 5-6 times larger coupling constant would be needed. Our results indicate that standard electron-phonon coupling is not sufficient to explain superconductivity in the whole family of Fe-As based superconductors. At the same time, the electron-phonon coupling in Ni-As based compounds is much stronger and its normal and superconducting state properties can be well described by standard Migdal-Eliashberg theory.

  2. Abrikosov Gluon Vortices in Color Superconductors

    International Nuclear Information System (INIS)

    In this talk I will discuss how the in-medium magnetic field can influence the gluon dynamics in a three-flavor color superconductor. It will be shown how at field strengths comparable to the charged gluon Meissner mass a new phase can be realized, giving rise to Abrikosov's vortices of charged gluons. In that phase, the inhomogeneous gluon condensate anti-screens the magnetic field due to the anomalous magnetic moment of these spin-1 particles. This paramagnetic effect can be of interest for astrophysics, since due to the gluon vortex antiscreening mechanism, compact stars with color superconducting cores could have larger magnetic fields than neutron stars made up entirely of nuclear matter. I will also discuss a second gluon condensation phenomenon connected to the Meissner instability attained at moderate densities by two-flavor color superconductors. In this situation, an inhomogeneous condensate of charged gluons emerges to remove the chromomagnetic instability created by the pairing mismatch, and as a consequence, the charged gluonic currents induce a magnetic field. Finally, I will point out a possible relation between glitches in neutron stars and the existence of the gluon vortices.

  3. Optical conductivity of iron-based superconductors

    International Nuclear Information System (INIS)

    The new family of unconventional iron-based superconductors discovered in 2006 immediately relieved their copper-based high-temperature predecessors as the most actively studied superconducting compounds in the world. The experimental and theoretical effort made in order to unravel the mechanism of superconductivity in these materials has been overwhelming. Although our understanding of their microscopic properties has been improving steadily, the pairing mechanism giving rise to superconducting transition temperatures up to 55 K remains elusive. And yet the hope is strong that these materials, which possess a drastically different electronic structure but similarly high transition temperatures compared to the copper-based compounds, will shed essential new light onto the several-decade-old problem of unconventional superconductivity. In this work we review the current understanding of the itinerant-charge-carrier dynamics in the iron-based superconductors and parent compounds largely based on the optical-conductivity data the community has gleaned over the past seven years using such experimental techniques as reflectivity, ellipsometry, and terahertz transmission measurements and analyze the implications of these studies for the microscopic properties of the iron-based materials as well as the mechanism of superconductivity therein. (topical review)

  4. Holographic Superconductor on Q-lattice

    CERN Document Server

    Ling, Yi; Niu, Chao; Wu, Jian-Pin; Xian, Zhuo-Yu

    2014-01-01

    We construct the simplest gravitational dual model of a superconductor on Q-lattices. We analyze the condition for the existence of a critical temperature at which the charged scalar field will condense. In contrast to the holographic superconductor on ionic lattices, the presence of Q-lattices will suppress the condensate of the scalar field and lower the critical temperature. In particular, when the Q-lattice background is dual to a deep insulating phase, the condensation would never occur for some small charges. Furthermore, we numerically compute the optical conductivity in the superconducting regime. It turns out that the presence of Q-lattice does not remove the pole in the imaginary part of the conductivity, ensuring the appearance of a delta function in the real part. We also evaluate the gap which in general depends on the charge of the scalar field as well as the Q-lattice parameters. Nevertheless, when the charge of the scalar field is relatively large and approaches the probe limit, the gap become...

  5. Percolation effect in thick film superconductors

    International Nuclear Information System (INIS)

    A thick film superconductor paste has been developed to study the properties of granulated superconductor materials, to observe the percolation effect and to confirm the theory of the conducting mechanism in the superconducting thick films. This paste was also applied to make a superconducting planar transformer. Due to high Tc and advantageous current density properties the base of the paste was chosen to be of Bi(Pb)SrCaCuO system. For contacts a conventional Ag/Pt paste was used. The critical temperature of the samples were between 110 K and 115 K depending on the printed layer thickness. The critical current density at the boiling temperature of the liquid He- was between 200-300 A/cm2. The R(T) and V(I) functions were measured with different parameters. The results of the measurements have confirmed the theory of conducting mechanism in the material. The percolation structure model has been built and described. As an application, a superconducting planar thick film transformer was planned and produced. Ten windings of the transformer were printed on one side of the alumina substrate and one winding was printed on the other side. The coupling between the two sides was possible through the substrate. The samples did not need special drying and firing parameters. After the preparation, the properties of the transformer were measured. The efficiency and the losses were determined. Finally, some fundamental advantages and problems of the process were discussed

  6. Percolation effect in thick film superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Sali, R.; Harsanyi, G. [Technical Univ. of Budapest (Hungary)

    1994-12-31

    A thick film superconductor paste has been developed to study the properties of granulated superconductor materials, to observe the percolation effect and to confirm the theory of the conducting mechanism in the superconducting thick films. This paste was also applied to make a superconducting planar transformer. Due to high T{sub c} and advantageous current density properties the base of the paste was chosen to be of Bi(Pb)SrCaCuO system. For contacts a conventional Ag/Pt paste was used. The critical temperature of the samples were between 110 K and 115 K depending on the printed layer thickness. The critical current density at the boiling temperature of the liquid He- was between 200-300 A/cm{sup 2}. The R(T) and V(I) functions were measured with different parameters. The results of the measurements have confirmed the theory of conducting mechanism in the material. The percolation structure model has been built and described. As an application, a superconducting planar thick film transformer was planned and produced. Ten windings of the transformer were printed on one side of the alumina substrate and one winding was printed on the other side. The coupling between the two sides was possible through the substrate. The samples did not need special drying and firing parameters. After the preparation, the properties of the transformer were measured. The efficiency and the losses were determined. Finally, some fundamental advantages and problems of the process were discussed.

  7. Electronic phase separation and high temperature superconductors

    International Nuclear Information System (INIS)

    The authors review the extensive evidence from model calculations that neutral holes in an antiferromagnet separate into hole-rich and hole-poor phases. All known solvable limits of models of holes in a Heisenberg antiferromagnet exhibit this behavior. The authors show that when the phase separation is frustrated by the introduction of long-range Coulomb interactions, the typical consequence is either a modulated (charge density wave) state or a superconducting phase. The authors then review some of the strong experimental evidence supporting an electronically-driven phase separation of the holes in the cuprate superconductors and the related Ni oxides. Finally, the authors argue that frustrated phase separation in these materials can account for many of the anomalous normal state properties of the high temperature superconductors and provide the mechanism of superconductivity. In particular, it is shown that the T-linear resistivity of the normal state is a paraconductivity associated with a novel composite pairing, although the ordered superconducting state is more conventional

  8. Physical properties of high temperature superconductors

    International Nuclear Information System (INIS)

    In this thesis, the magnetic characterization of some Bi1.6Pb0.4Sr2Ca2Cu3O10, Bi1.84Pb0.34Sr1.91Ca2.03Cu2.06O10, Tl2Ba2Ca2Cu3O10 and Bi-2212/Ag high temperature superconductors were given by ac magnetic susceptibility and electrical resistivity measuring techniques. Bi1.6Pb0.4Sr2Ca2Cu3O10 and Bi1.84Pb0.34Sr1.91Ca2.03Cu2.06O10 high temperature superconductors were prepared by liquid ammonium nitrate method, while conventional solid state reaction route was applied to make Tl2Ba2Ca2Cu3O10 superconductor. On the other hand, Powder-In Tube (PIT) technique was used to make multi-filamentary Bi-2212/Ag tapes. Structural characterizations were carried out by X-ray powder diffraction (XRD) patterns and scanning electron microscopy (SEM). Unit cell parameters of Bi1.6Pb0.4Sr2Ca2Cu3O10 and Tl2Ba2Ca2Cu3O10 high temperature superconductors which have tetragonal crystal structure were calculated as a=b=5.3538 AA and c=37.1137 AA, a=b=3.8520 AA and c=35.5970 AA respectively. The results are consistent with the literature. Some information with regards to the grain size and phase content were given by the SEM studies. Fundamental and high order ac susceptibilities, χ=χn'''+iχn''(n=1, 2, 3, 5 and 7) of the samples were measured for the temperature range 15 K-140 K, ac field range 8 A/rn-1600 A/m and the frequency range 11 Hz-2110 Hz. All the susceptibilities exhibit field, frequency and temperature dependences. The observed dependences were analyzed using Bean model. For temperature scaling a function of the form Hp=Hα(l-t)''β was found empirically. The best fitting parameters for the Bi1.6Pb0.4Sr2Ca2Cu3O10 superconductor were found as Hα 3.3x104 A/m and β=2.05. Odd-order harmonic susceptibilities were calculated from the Bean model to make comparison with the experiments. In addition, ac losses were also calculated from the Bean model to compare with the experimentally measured values. At low temperatures and fields, the Bean model is observed to account for the ac losses

  9. Focusing and guiding intense electron beams by a superconductor tube

    International Nuclear Information System (INIS)

    An intense electron beam travelling axially through the opening of a superconductor tube was studied. Model calculations showed that the beam is focused by the superconductor tube when the space-charge effect of the beam electrons is compensated. The tube functions as a lens for electrons injected parallel to the tube axis and also for electrons having a small initial radial velocity component. The electron trajectories were computed, and the focal length of the superconductor tube was estimated. (author). 2 figs., 6 refs

  10. Noncommutative Extension of AdS/CFT and Holographic Superconductors

    CERN Document Server

    Pramanik, Souvik; Ghosh, Subir

    2014-01-01

    In this work, we consider a Non-Commutative (NC) extension of AdS-CFT correspondence and its effects on a Holographic Superconductor. NC corrections enter the model from two very different sectors: the NC generalization of Schwarzschild-AdS Black Hole metric and from NC extension of the abelian gauge theory. We study the NC effects on the relations connecting the charge density, critical temperature and condensation operator of the Holographic Superconductor. Our results suggest that generically, NC effects lower the critical temperature of the holographic superconductor.

  11. Density of states and tunneling characteristics of layered superconductors

    International Nuclear Information System (INIS)

    We have studied the structure of the density-of-states (DOS) curves and tunneling characteristics of layered superconductors with two distinct layers in a unit cell. In general, the peaks of the DOS curves do not correspond to energy gaps of each layer, but depend on the gaps and the interlayer hopping strengths in a complex manner. This makes the interpretation of tunneling data of layered superconductors much less straightforward than isotropic superconductors. Our simulated tunneling characteristics bear certain resemblance to experimental results

  12. Fluxons in thin-film superconductor-insulator superlattices

    DEFF Research Database (Denmark)

    Sakai, S.; Bodin, P.; Pedersen, Niels Falsig

    1993-01-01

    films; in the limit of ultrathin superconductor films it may give a model for describing fluxon motion in layered high-Tc superconductors. Numerical examples of current versus voltage curves to be expected in such an experiment are presented. Journal of Applied Physics is copyrighted by The American......In a system of thin alternating layers of superconductors and insulators the equations describing static and dynamic fluxon solutions are derived. The approach, represented by a useful compact matrix form, is intended to describe systems fabricated for example of niobium or niobium-nitride thin...

  13. 120 K superconductor TlBaCaCu2Oy

    International Nuclear Information System (INIS)

    The author have prepared 120K superconductor in Tl-Ba-Ca-Cu oxide system. This 120K superconductor has been investigated by x-ray diffraction and EDAX micro-analysis. EDAX analysis shows that the composition of this superconductor is very close to TLBa(Ca1-xCux)CuOy(chi - 0.3). Most of the x-ray powder diffractions including all the strong ones can be indexed according to a tetragonal structure with α = 5.46 A and c = 36.2A which means that the sample is nearly a single phase material

  14. Antiferromagnetic topological superconductor and electrically controllable Majorana fermions.

    Science.gov (United States)

    Ezawa, Motohiko

    2015-02-01

    We investigate the realization of a topological superconductor in a generic bucked honeycomb system equipped with four types of mass-generating terms, where the superconductor gap is introduced by attaching the honeycomb system to an s-wave superconductor. Constructing the topological phase diagram, we show that Majorana modes are formed in the phase boundary. In particular, we analyze the honeycomb system with antiferromagnetic order in the presence of perpendicular electric field E(z). It becomes topological for |E(z)|>E(z)(cr) and trivial for |E(z)|scanning tunneling microscope probe. PMID:25699460

  15. Regular Phantom Black Hole and Holography: very high temperature superconductors

    CERN Document Server

    Lin, Kai; Pan, Qiyuan; Abdalla, E

    2015-01-01

    Holographic superconductors containing a non-minimal derivative coupling for scalar field in a regular phantom plane symmetric black hole have been considered. We show that the parameter of the regular black hole $b$ as well as the non-minimal derivative coupling parameter $\\eta$ affect the formation of the condensate as well as the conductivity in the superconductor. Moreover, $b$ has a critical value in which the critical temperature $T_c$ increases without a bound. We argue that an unlimited critical temperature is an evidence that high $T_c$ superconductor must be related to the absence of a singularity in the bulk in the AdS/CFT context.

  16. A general holographic metal/superconductor phase transition model

    CERN Document Server

    Peng, Yan

    2014-01-01

    We study the scalar condensation of a general holographic superconductor model in AdS black hole background away from the probe limit. We find the model parameters together with the scalar mass and backreaction can determine the order of phase transitions completely. In addition, we observe two types of discontinuities of the scalar operator in the case of first order phase transitions. We analyze in detail the effects of the scalar mass and backreaction on the formation of discontinuities and arrive at an approximate relation between the threshold model parameters. Furthermore, we obtain superconductor solutions corresponding to higher energy states and examine the stability of these superconductor solutions.

  17. Josephson spin-current in superconductor-ferromagnetic-superconductor junctions with singlet superconducting leads

    Directory of Open Access Journals (Sweden)

    2010-09-01

    Full Text Available We study numerically the electronic heat capacity, spin and charge current in a diffusive Superconductor-Ferromagnetic-Superconductor systems، with singlet superconducting leads and non-uniform ferromagnetic layer. Specially, we focus on ferromagnetic layer with domain wall and conical structures incorporation the spin-active interfaces. We investigate, how the 0-π transition is influenced by non-uniform magnetization texture and also the appearance of spin-current in such structures. We find that for ferromagnetic layer with domain wall structure, only the one component of spin-current is non-zero and for conical structure, three components of spin-current are non-zero. Also we find that specific heat of such junctions can be tuned by changing the superconducting phase difference. Interestingly, spin-current shows a discontinuous jump at the 0-π transition points of the critical charge current.

  18. Above-gap conductance anomaly studied in superconductor-graphene-superconductor Josephson junctions

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Jae-Hyun; Lee, Hu-Jong [Pohang University of Science and Technology, Pohang (Korea, Republic of); Doh, Yong-Joo [Korea University, Yeongigun (Korea, Republic of)

    2010-07-15

    We investigated the electrical transport properties of superconductor-graphene-superconductor (SGS) Josephson junctions. At low voltage bias, we observed the conventional proximity-coupled Josephson effect, such as supercurrent flow through graphene, a sub-gap structure of differential conductance due to Andreev reflection, and a periodic modulation of the critical current I{sub c} when a perpendicular magnetic field H is applied to the graphene. For high bias above the superconducting gap voltage, however, we observed an anomalous jump of the differential conductance, the voltage position of which is sensitive to the backgate voltage V{sub g}. Our extensive study with varying V{sub g}, temperature, and H reveals that the above-gap structure takes place at a characteristic power P{sup *}, irrespective of V{sub g}, for a given junction. The temperature and the H dependences of P{sup *} are well explained by an increase in the electron temperature in graphene.

  19. Above-gap conductance anomaly studied in superconductor-graphene-superconductor Josephson junctions

    International Nuclear Information System (INIS)

    We investigated the electrical transport properties of superconductor-graphene-superconductor (SGS) Josephson junctions. At low voltage bias, we observed the conventional proximity-coupled Josephson effect, such as supercurrent flow through graphene, a sub-gap structure of differential conductance due to Andreev reflection, and a periodic modulation of the critical current Ic when a perpendicular magnetic field H is applied to the graphene. For high bias above the superconducting gap voltage, however, we observed an anomalous jump of the differential conductance, the voltage position of which is sensitive to the backgate voltage Vg. Our extensive study with varying Vg, temperature, and H reveals that the above-gap structure takes place at a characteristic power P*, irrespective of Vg, for a given junction. The temperature and the H dependences of P* are well explained by an increase in the electron temperature in graphene.

  20. DC and AC Josephson Effect in a Superconductor-Luttinger Liquid-Superconductor System

    OpenAIRE

    Fazio, Rosario; Hekking, F. W. J.; Odintsov, A.A.; RevTex, 11 pages; figures, 9

    1995-01-01

    We calculate both the DC and the AC Josephson current through a one-dimensional system of interacting electrons, connected to two superconductors by tunnel junctions. We treat the (repulsive) Coulomb interaction in the framework of the one-channel, spin-$1/2$ Luttinger model. The Josephson current is obtained for two geometries of experimental relevance: a quantum wire and a ring. At zero temperature, the critical current is found to decay algebraically with increasing distance $d$ between th...

  1. Josephson Current and Noise at a Superconductor-Quantum Spin Hall Insulator-Superconductor Junction

    OpenAIRE

    Fu, Liang; Kane, C. L.

    2008-01-01

    We study junctions between superconductors mediated by the edge states of a quantum spin Hall insulator. We show that such junctions exhibit a fractional Josephson effect, in which the current phase relation has a 4\\pi, rather than a 2\\pi periodicity. This effect is a consequence of the conservation of fermion parity - the number of electrons modulo 2 - in a superconducting junction, and is closely related to the Z_2 topological structure of the quantum spin Hall insulator. Inelastic processe...

  2. A novel heat engine for magnetizing superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Coombs, T A; Hong, Z; Zhu, X [Cambridge University Engineering Department, Trumpington Street, CB2 1PZ (United Kingdom); Krabbes, G [IFW Dresden, Helmholtzstrasse 20, 01069 Dresden (Germany)

    2008-03-01

    The potential of bulk melt-processed YBCO single domains to trap significant magnetic fields (Tomita and Murakami 2003 Nature 421 517-20; Fuchs et al 2000 Appl. Phys. Lett. 76 2107-9) at cryogenic temperatures makes them particularly attractive for a variety of engineering applications including superconducting magnets, magnetic bearings and motors (Coombs et al 1999 IEEE Trans. Appl. Supercond. 9 968-71; Coombs et al 2005 IEEE Trans. Appl. Supercond. 15 2312-5). It has already been shown that large fields can be obtained in single domain samples at 77 K. A range of possible applications exist in the design of high power density electric motors (Jiang et al 2006 Supercond. Sci. Technol. 19 1164-8). Before such devices can be created a major problem needs to be overcome. Even though all of these devices use a superconductor in the role of a permanent magnet and even though the superconductor can trap potentially huge magnetic fields (greater than 10 T) the problem is how to induce the magnetic fields. There are four possible known methods: (1) cooling in field; (2) zero field cooling, followed by slowly applied field; (3) pulse magnetization; (4) flux pumping. Any of these methods could be used to magnetize the superconductor and this may be done either in situ or ex situ. Ideally the superconductors are magnetized in situ. There are several reasons for this: first, if the superconductors should become demagnetized through (i) flux creep, (ii) repeatedly applied perpendicular fields (Vanderbemden et al 2007 Phys. Rev. B 75 (17)) or (iii) by loss of cooling then they may be re-magnetized without the need to disassemble the machine; secondly, there are difficulties with handling very strongly magnetized material at cryogenic temperatures when assembling the machine; thirdly, ex situ methods would require the machine to be assembled both cold and pre-magnetized and would offer significant design difficulties. Until room temperature superconductors can be prepared, the

  3. A novel heat engine for magnetizing superconductors

    International Nuclear Information System (INIS)

    The potential of bulk melt-processed YBCO single domains to trap significant magnetic fields (Tomita and Murakami 2003 Nature 421 517-20; Fuchs et al 2000 Appl. Phys. Lett. 76 2107-9) at cryogenic temperatures makes them particularly attractive for a variety of engineering applications including superconducting magnets, magnetic bearings and motors (Coombs et al 1999 IEEE Trans. Appl. Supercond. 9 968-71; Coombs et al 2005 IEEE Trans. Appl. Supercond. 15 2312-5). It has already been shown that large fields can be obtained in single domain samples at 77 K. A range of possible applications exist in the design of high power density electric motors (Jiang et al 2006 Supercond. Sci. Technol. 19 1164-8). Before such devices can be created a major problem needs to be overcome. Even though all of these devices use a superconductor in the role of a permanent magnet and even though the superconductor can trap potentially huge magnetic fields (greater than 10 T) the problem is how to induce the magnetic fields. There are four possible known methods: (1) cooling in field; (2) zero field cooling, followed by slowly applied field; (3) pulse magnetization; (4) flux pumping. Any of these methods could be used to magnetize the superconductor and this may be done either in situ or ex situ. Ideally the superconductors are magnetized in situ. There are several reasons for this: first, if the superconductors should become demagnetized through (i) flux creep, (ii) repeatedly applied perpendicular fields (Vanderbemden et al 2007 Phys. Rev. B 75 (17)) or (iii) by loss of cooling then they may be re-magnetized without the need to disassemble the machine; secondly, there are difficulties with handling very strongly magnetized material at cryogenic temperatures when assembling the machine; thirdly, ex situ methods would require the machine to be assembled both cold and pre-magnetized and would offer significant design difficulties. Until room temperature superconductors can be prepared, the

  4. Josephson current in a normal-metal nanowire coupled to a superconductor/ferromagnet/superconductor junction

    Science.gov (United States)

    Ebisu, Hiromi; Lu, Bo; Taguchi, Katsuhisa; Golubov, Alexander A.; Tanaka, Yukio

    2016-01-01

    We consider a superconducting nanowire proximity coupled to a superconductor/ferromagnet/superconductor (S/F/S) junction, where the magnetization penetrates into a superconducting segment in a nanowire decaying as ˜exp[-∣n/∣ ξ ] , where n is the site index and the ξ is the decay length. We tune chemical potential and spin-orbit coupling so that the topological superconducting regime hosting the Majorana fermion is realized for long ξ . We find that when ξ becomes shorter, zero energy state at the interface between a superconductor and a ferromagnet splits into two states at nonzero energy. Accordingly, the behavior of the Josephson current is drastically changed due to this "zero mode-nonzero mode crossover." By tuning the model parameters, we find an almost second-harmonic current-phase relation sin2 φ , where φ is the phase difference of the junction. Based on the analysis of Andreev bound state (ABS), we clarify that the current-phase relation is determined by coupling of the states within the energy gap. We find that the emergence of crossing points of ABS is a key ingredient to generate sin2 φ dependence in the current-phase relation. We further study both the energy and φ dependence of pair amplitudes in the ferromagnetic region. For large ξ , an odd-frequency spin-triplet s -wave component is dominant. The magnitude of the odd-frequency pair amplitude is enhanced at the energy level of ABS.

  5. Static Properties of Superconductor Journal Bearing Substator for Superconductor Flywheel Energy Storage System

    Energy Technology Data Exchange (ETDEWEB)

    Park, B. J.; Jung, S. Y.; Lee, J. P.; Park, B. C.; Jeong, N. H.; Sung, T. H.; Han, Y. H. [Korea Electric Power Research Institute, Superconductivity and Application Group, Daejeon (Korea, Republic of)

    2008-10-15

    A Superconductor Flywheel Energy Storage System(SFES) mainly consists of a pair of non-contacting High Temperature Superconductor(HTS) bearings that provide very low frictional losses, a composite flywheel with high energy storage density. The HTS bearings, which offer dynamic stability without active control, are the key technology that distinguishes the SFES from other flywheel energy storage devices, and great effort is being put into developing this technology. The Superconductor Journal Bearing(SJB) mainly consists of HTS bulks and a stator, which holds the HTS bulks and also acts as a cold head. Static properties of HTS bearings provide data to solve problems which may occur easily in a running system. Since stiffness to counter vibration is the main parameter in designing an HTS bearing system, we investigate SJB magnetic force through static properties between the Permanent Magnet(PM) and HTS. We measure stiffness in static condition and the results are used to determine the optimal number of HTS bulks for a 100kWh SFES.

  6. Current-phase relation of a ballistic asymmetric double superconductor-normal-metal-superconductor junction

    International Nuclear Information System (INIS)

    The zero-temperature current-phase (I-φ) relation (CPR) of a mesoscopic, ballistic, and asymmetrically stacked, double superconductor-normal-metal-superconduc tor (SNS) junction is studied. Here φ is the phase difference between the two superconducting end-electrodes. The lack of configuration symmetry in such asymmetric SNSNS junctions forbids a simple choice of values for the phase φ2 of the middle superconductor. We propose to determine the values of φ2 by equating the currents in the two normal regions. Two features in the CPR are found. First, the CPR of the asymmetric junction has a cutoff feature, whose origin is best demonstrated in the long middle superconductor (large L2) cases, when the critical current of the double SNS junction is bounded by the SNS junction that has the longer normal region. This cutoff feature is more pronounced for longer L2 and for higher degree of junction asymmetry. Second, in regions other than the cutoff region, the CPR of the asymmetric junction deviates only within a few percent from the CPR of the symmetric junction which has the same total length LTotal in the normal regions and the same L2. This is in contrast with the greater sensitivity the CPR has to the changes in LTotal or L2. (orig.)

  7. Iron-based superconductors via soft chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Friederichs, Gina Maya

    2015-06-30

    This thesis provides new soft chemistry approaches to Fe-based superconductors. Mild syntheses were demonstrated to be able to overcome difficulties, occurring in conventional synthesis and to enable the access to new metastable phases. A solvent-based metathesis reaction led to β-FeSe exclusively. Contrary to solid state syntheses, the formation of hexagonal α-FeSe could be avoided under mild conditions. The deintercalation of interstitial Fe (by formation of Fe{sub 3}O{sub 4}) could be proven by low temperature O{sub 2}-annealing of Fe{sub 1+x}Te{sub 1-y}Se{sub y}. By using redox (de)intercalations K{sub 1-x}Fe{sub 2-y}Se{sub 2}, metastable Na{sub 1-x}Fe{sub 2-y}As{sub 2} and Na{sub 1-x}((Fe{sub 1-y}Co{sub y}){sub 1-z}As){sub 2} could successfully be obtained at room temperature. The mild synthesis conditions led to compounds like FeSe and K{sub 1-x}Fe{sub 2-y}Se{sub 2} which exhibited different physical properties than found by conventional high temperature methods. In general, the developed (de)intercalation reactions represent a new, universally applicable tool in order to manipulate the structure along with the properties of Fe-based superconductors. The basic structural features of the characteristic FeX{sub 4/4} tetrahedral layers, however, are preserved. Soft chemistry syntheses have been shown to allow the formation of a variety of phases, like Na{sub 1-x}Fe{sub 2-y}As{sub 2}, Na{sub 1-x}((Fe{sub 1-y}Co{sub y}){sub 1-z}As){sub 2} and K{sub 1-x}Fe{sub 2-y}Se{sub 2}. Hence, especially low temperature approaches may enable the realization of complex stacking sequences, potentially leading to the fulfillment of the greatest goal in the research of superconductors - room temperature superconductivity.

  8. New application of superconductors: high sensitivity cryogenic light detectors

    CERN Document Server

    Cardani, L; Casali, N; Casellano, M G; Colantoni, I; Coppolecchia, A; Cosmelli, C; Cruciani, A; D'Addabbo, A; Di Domizio, S; Martinez, M; Tomei, C; Vignati, M

    2016-01-01

    In this paper we describe the current status of the CALDER project, which is developing ultra-sensitive light detectors based on superconductors for cryogenic applications. When we apply an AC current to a superconductor, the Cooper pairs oscillate and acquire kinetic inductance, that can be measured by inserting the superconductor in a LC circuit with high merit factor. Interactions in the superconductor can break the Cooper pairs, causing sizable variations in the kinetic inductance and, thus, in the response of the LC circuit. The continuous monitoring of the amplitude and frequency modulation allows to reconstruct the incident energy with excellent sensitivity. This concept is at the basis of Kinetic Inductance Detectors (KIDs), that are characterized by natural aptitude to multiplexed read-out (several sensors can be tuned to different resonant frequencies and coupled to the same line), resolution of few eV, stable behavior over a wide temperature range, and ease in fabrication. We present the results ob...

  9. Evolution of new superconductors. Past, present and future

    International Nuclear Information System (INIS)

    I present here the past and present situations of new superconductors and also the future prospect. Superconductivity has started since Kamerlingh Onnes first observed the zero resistivity. After that, the critical temperature Tc was gradually increased. In the early stage of superconductive material investigations, main contribution has been made by B. Matthias and his group. In 1986, a new superconductor La-Ba-Cu-O, which belongs to new category in the superconducting society, has been found by Bednorz and Mueller. After that Tc's have been drastically increased, and finally reached to Tc - 164 K in the Hg-compound. Next, I review several new superconductors discovered within 20 years. Finally, I mention my personal perspective to a high-Tc superconductor. (author)

  10. High point for CERN and high-temperature superconductors

    CERN Multimedia

    2007-01-01

    Amalia Ballarino is named the Superconductor Industry Person of the year 2006. Amalia Ballarino showing a tape of high-superconducting material used for the LHC current leads.The CERN project leader for the high-temperature superconducting current leads for the LHC, Amalia Ballarino, has received the award for "Superconductor Industry Person of the Year". This award, the most prestigious international award in the development and commercialization of superconductors, is presented by the leading industry newsletter "Superconductor Week". Amalia Ballarino was selected from dozens of nominations from around the world by a panel of recognized leading experts in superconductivity. "It is a great honour for me," says Amalia Ballarino. "It has been many years of hard work, and it’s a great satisfaction to see that the work has been completed successfully." Amalia Ballarino has been working on high-temperature superconducting materials sin...

  11. Superconductor Materials-A Revolutionary Value Addition to Space Electronics

    Directory of Open Access Journals (Sweden)

    Rathindra Nath Biswas

    2004-04-01

    Full Text Available An early success in low temperature superconductor technology has led to the development of a number of high temperature superconductor (H TS materials, which have critical temperature above 77 K. When the temperature of a solid is lowered below critical temperature, the material loses its electrical resistivity. Because resistance is almost zero, superconductors can carry very high current, generating very large homogeneous magnetic fields. Due to these features, it is possible to design electronic devices with extremely thin profile, offering less weight and low manufacturing cost. Such exceptional properties have made HTS materials useful in military and space sectors, wherc airborne systems have already provided with cryogenic infrastructure which can he used for cooling a high temperature superconductor at no extra cost.

  12. Leaders in high temperature superconductivity commercialization win superconductor industry award

    CERN Multimedia

    2007-01-01

    CERN's Large Hadron Collider curretn leads project head Amalia Ballarino named superconductor industry person of the year 2006. Former high temperature superconductivity program manager at the US Department of energy James Daley wins lifetime achievement award. (1,5 page)

  13. Hybrid layered superconductor/ferromagnet structures for spintronics

    International Nuclear Information System (INIS)

    The advanced technology for production of high-quality superconductor/ferromagnet-hybrids of ultrathin superconducting Nb layers and ferromagnetic CuNi layers for application in spintronics is developed. (authors)

  14. Entanglement Entropy for time dependent two dimensional holographic superconductor

    CERN Document Server

    Mazhari, N S; Myrzakulov, Kairat; Myrzakulov, R

    2016-01-01

    We studied entanglement entropy for a time dependent two dimensional holographic superconductor. We showed that the conserved charge of the system plays the role of the critical parameter to have condensation.

  15. Ceramic high temperature superconductor levitating motor with laser commutator

    International Nuclear Information System (INIS)

    The design of a magnetically levitating motor using a ceramic high temperature superconductor with laser commutator is discussed. A YBa sub 2 Cu sub 3 O sub 7-δ high temperature superconductor with 25 mm diameter and 6 mm thickness is used to levitate a Nd-Fe-B magnet (19.0 mm diameter and 4.8 mm thickness) which is attached symmetrically to a 150 mm long graphite rod. A smaller magnet (5.5 mm diameter and 2.0 mm thickness) is attached at each end of the rod with the appropriate poles arrangements. A suitable laser beam chopper is used to optically drive a solenoid which repels the smaller magnets thus driving the motor. A simple and efficient liquid nitrogen supply system is designed to cool the superconductor. The stability of the bearing is provided by the flux pinning in this type-II superconductor. Some characteristics of the motor are discussed

  16. High temperature superconductor cable concepts for fusion magnets

    International Nuclear Information System (INIS)

    Controlled nuclear fusion can be realized by confining plasma with high magnetic fields. High temperature superconductors have the potential to improve fusion magnets due to their superior mechanical properties, current density and critical temperature. Three concepts of high temperature superconductor cables carrying kA currents (RACC, CORC and TSTC) are investigated, optimized and evaluated in the scope of their applicability as conductor in fusion magnets. The magnetic field and temperature dependence of the cables is measured; the thermal expansion and conductivity of structure, insulation and filling materials are investigated. An improved contacting method is proposed to homogenize the contact resistances and the current distribution within the cables. Degradation-free impregnation with reduced thermal expansion epoxy resin is demonstrated. This technique prevents movement of the tapes and distributes mechanical loads. High temperature superconductor winding packs for fusion magnets are calculated and compared with corresponding low temperature superconductor cases.

  17. Scaling rules for critical current density in anisotropic biaxial superconductors

    Science.gov (United States)

    Li, Yingxu; Kang, Guozheng; Gao, Yuanwen

    2016-06-01

    Recent researches highlight the additional anisotropic crystallographic axis within the superconducting plane of high temperature superconductors (HTS), demonstrating the superconducting anisotropy of HTS is better understood in the biaxial frame than the previous uniaxial coordinates within the superconducting layer. To quantitatively evaluate the anisotropy of flux pinning and critical current density in HTS, we extend the scaling rule for single-vortex collective pinning in uniaxial superconductors to account for flux-bundle collective pinning in biaxial superconductors. The scaling results show that in a system of random uncorrected point defects, the field dependence of the critical current density is described by a unified function with the scaled magnetic field of the isotropic superconductor. The obtained angular dependence of the critical current density depicts the main features of experimental observations, considering possible corrections due to the strong-pinning interaction.

  18. Magnetization process of ferromagnet-superconductor hybrid films

    International Nuclear Information System (INIS)

    Magnetic properties of ferromagnet-superconductor hybrid films were investigated below and above the superconducting critical temperature. Below the superconducting critical temperature, the hybrid films show not only large coercive force but also hysteresis shift. These changes depend on the magnetic state in the ferromagnetic layer at the superconducting critical temperature. Magnetization process of ferromagnet-superconductor hybrid films is discussed in terms of the critical state model for flux pinning in the superconducting layer

  19. Flux periodicities and quantum hair on holographic superconductors.

    Science.gov (United States)

    Montull, Marc; Pujolàs, Oriol; Salvio, Alberto; Silva, Pedro J

    2011-10-28

    Superconductors in a cylindrical geometry respond periodically to a cylinder-threading magnetic flux, with the period changing from hc/2e to hc/e depending on whether the Aharonov-Bohm effects are suppressed. We show that holographic superconductors present a similar phenomenon, and that the different periodicities follow from classical no-hair theorems. We also give the Ginzburg-Landau description of the period-doubling phenomenon. PMID:22107621

  20. Spin nutation effects in molecular nanomagnet$-$superconductor tunnel junctions

    OpenAIRE

    Abouie, J.; Abdollahipour, B.; A. A. Rostami

    2013-01-01

    We study the spin nutation effects of the molecular nanomagnet on the Josephson current through a superconductor$|$molecular nanomagnet$|$superconductor tunnel junction. We explicitly demonstrate that due to the spin nutation of the molecular nanomagnet two oscillatory terms emerge in the $ac$ Josephson current in addition to the conventional $ac$ Josephson current. Some resonances occur in the junction due to the interactions of the transported quasiparticles with the bias voltage and molecu...

  1. Topological field theory and thermal responses of interacting topological superconductors

    OpenAIRE

    Wang, Zhong; Qi, Xiao-Liang; Zhang, Shou-Cheng

    2010-01-01

    We investigate the three-dimensional, time-reversal invariant topological superconductors with generic interaction by their response to external fields. The first description is a gravitational topological field theory, which gives a $Z_2$ classification of topological superconductors, and predicts a half-quantized thermal Hall effect on the surface. The second description introduces an s-wave proximity pairing field on the surface, and the associated topological defects give an integer $Z$ c...

  2. Characterization of YBCO superconductor sintered in CO2-containing atmosphere

    International Nuclear Information System (INIS)

    Stability of the YBCO superconductor toward reacting with CO2 in CO2/O2 gas mixtures during sintering was investigated as a function of the partial pressure of CO2 and temperature. Transport critical current density of the superconductor decreased drastically with increasing concentration of CO2 in the gas mixture. The microstructure and composition of the samples were investigated by transmission electron microscopy and energy-dispersive X-ray spectroscopy

  3. Transition Temperatures of Superconductors estimated from Periodic Table Properties

    OpenAIRE

    Isikaku-Ironkwe, O. Paul

    2012-01-01

    Predicting the transition temperature, Tc, of a superconductor from Periodic Table normal state properties is regarded as one of the grand challenges of superconductivity. By studying the correlations of Periodic Table properties with known superconductors, it is possible to estimate their transition temperatures. Starting from the isotope effect and correlations of superconductivity with electronegativity (\\Chi), valence electron count per atom (Ne), atomic number(Z) and formula weight (Fw),...

  4. New 120 K Tl-Ca-Ba-Cu-O superconductor

    International Nuclear Information System (INIS)

    Electronic and magnetic properties of the new 120 K Tl-Ca-Ba-Cu-O superconductor are presented. Resistance-temperature variations, ac susceptibility, and the (low) magnetic field dependence of the critical current density are reported. The new superconductor can be prepared in a molten state, which should allow processing leading to high critical current density. Preliminary x-ray diffraction data are also presented

  5. Second harmonics and compensation effect in ceramic superconductors

    International Nuclear Information System (INIS)

    The nonlinear ac susceptibility and the compensation effect observed in ceramic superconductors which show the paramagnetic Meissner effect are studied by the Monte Carlo simulations on a three dimensional lattice model of the Josephson array with finite self-conductance. Our study is based on the possible existence of the chiral glass phase in these materials. In agreement with experiments, the compensation effect is demonstrated to be present in d-wave superconductors but not in the s-wave ones. (author)

  6. Pinning by macroscopic spherical cavity in type II superconductor

    International Nuclear Information System (INIS)

    The magnetic field created by a vortex line located near a macroscopic spherical cavity as well as the magnetic field within the superconductor are calculated by solving London equations using the generalized spherical function technique. The interaction energy between the flux line and the cavity and consequently the pinning force were also calculated. It is shown that one possible cause of the pinning is that an attractive image force exists at the superconductor sphere boundary. (author)

  7. Scanning Tunneling Spectroscopy on Electron-Boson Interactions in Superconductors

    OpenAIRE

    Schackert, Michael Peter

    2014-01-01

    This thesis describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  8. Weyl holographic superconductor in the Lifshitz black hole background

    CERN Document Server

    Mansoori, S A Hosseini; Mokhtari, A; Dezaki, F Lalehgani; Sherkatghanad, Z

    2016-01-01

    We investigate analytically the properties of the Weyl holographic superconductor in the Lifshitz black hole background. We find that the critical temperature of the Weyl superconductor decreases with increasing Lifshitz dynamical exponent, $z$, indicating that condensation becomes difficult. In addition, it is found that the critical temperature and condensation operator could be affected by applying the Weyl coupling, $\\gamma$. Finally, we compute the critical magnetic field and investigate its dependence on the parameters $\\gamma$ and $z$.

  9. Enhancement of critical temperature in fractal metamaterial superconductors

    CERN Document Server

    Smolyaninov, Igor I

    2016-01-01

    Fractal metamaterial superconductor geometry has been suggested and analyzed based on the recently developed theoretical description of critical temperature increase in epsilon near zero (ENZ) metamaterial superconductors. Considerable enhancement of critical temperature has been predicted in such materials due to appearance of large number of additional poles in the inverse dielectric response function of the fractal. Our results agree with the recent observation (Fratini et al. Nature 466, 841 (2010)) that fractal defect structure promotes superconductivity.

  10. Probing the energy gap of heavy-fermion superconductors

    International Nuclear Information System (INIS)

    The symmetry of the energy gap in heavy-fermion superconductors has been under intense investigation recently. While the temperature dependence of thermodynamic and transport properties probes the quasiparticle excitation spectrum, point-contact spectra, i.e. current-voltage characteristics, yield information about the energy gap via the mechanism of Andreev reflection. The present review focuses on the latter. Where available, experiments on Josephson effects between heavy-fermion and conventional superconductors will also be reviewed. (orig.)

  11. Charge transport in disordered superconductor-graphene junctions

    International Nuclear Information System (INIS)

    We consider the charge transport through superconductor-graphene tunnel junctions, including the effect of disorder. Coherent scattering on elastic impurities in the graphene layer can give rise to multiple reflections at the graphene-superconductor interface, and can thereby increase the probability of Andreev reflection, leading to an enhancement of the subgap conductance above its classical value. Although the phenomenon is known already from heterostructures involving normal metals, we have studied how graphenes peculiar dispersion relation influences the effect.

  12. AC resistivity of d-wave ceramic superconductors

    OpenAIRE

    Li, Mai Suan; Dominguez, Daniel

    2000-01-01

    We model d-wave ceramic superconductors with a three-dimensional lattice of randomly distributed $\\pi$ Josephson junctions with finite self-inductance. The linear and nonlinear ac resistivity of the d-wave ceramic superconductors is obtained as function of temperature by solving the corresponding Langevin dynamical equations. We find that the linear ac resistivity remains finite at the temperature $T_p$ where the third harmonics of resistivity has a peak. The current amplitude dependence of t...

  13. Structural evolution of superconductor nanowires in biopolymer gels

    International Nuclear Information System (INIS)

    A simple synthesis of superconductor nanowires is carried out by rational design of the synthetic protocol. This technique is based on the selection of a component (in this case BaCO3) that remains invariant throughout the synthesis. A biopolymer matrix ensures antisintering of BaCO3 nanoparticles, leading to single-crystal outgrowth of the superconductor in this most technologically useful of morphologies. (Abstract Copyright [2008], Wiley Periodicals, Inc.)

  14. Scanning tunneling spectroscopy on electron-boson interactions in superconductors

    CERN Document Server

    Schackert, Michael Peter

    2015-01-01

    This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  15. Stability of magnetic tip/superconductor levitation systems

    Institute of Scientific and Technical Information of China (English)

    M. K. Alqadi

    2015-01-01

    The vertical stability of a magnetic tip over a superconducting material is investigated by using the critical state and the frozen image models. The analytical expressions of the stiffness and the vibration frequency about the equilibrium position are derived in term of the geometrical parameters of the magnet/superconductor system. It is found that the stability of the system depends on the shape of the superconductor as well as its thickness.

  16. p-wave superconductors in dilaton gravity

    International Nuclear Information System (INIS)

    In this paper, we study peculiar properties of p-wave superconductors in dilaton gravity. The scale invariance of the bulk geometry is effectively broken due to the existence of a dilaton. By coupling the dilaton to the non-Abelian gauge field, i.e., -1/4 e-βΦFaμνFaμν, we find that the dissipative conductivity of the normal phase decreases and approaches zero at the zero frequency as β increases. Intuitively, the system behaves more and more like an insulator. When the hairy solution is turned on, the system crosses a critical point to the superconducting phase. We find that the critical chemical potential decreases with the increasing of β and the maximum height of the conductivity is suppressed gradually which are consistent with our intuition for insulator/supercondutor transition. (Copyright copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Low critical temperature superconductors for electromagnets

    International Nuclear Information System (INIS)

    After a brief history of the main discoveries in applied superconductivity (section 1), we discuss the structure and properties of NbTi and Nb3 Sn (section 2). Then, we explain why low critical-temperature superconductors are produced under the form of multifilamentary composites (section 3), and we review the manufacturing processes of NbTi and Nb3Sn wires (section 4). We follow by a description of the transition from the superconducting to the normal resistive state of multifilamentary composite wires (section 5) and we detail their magnetization properties section 6). Last, we present the most commonly used cable configurations (section 7) and we provide simple formulae illustrating on a few examples the computation of losses generated under time-varying magnetic fields (section 8). (author)

  18. Noncommutative effects of spacetime on holographic superconductors

    CERN Document Server

    Ghorai, Debabrata

    2016-01-01

    The Sturm-Liouville eigenvalue method is employed to analytically investigate the properties of holographic superconductors in higher dimensions in the framework of Born-Infeld electrodynamics incorporating the effects of noncommutative spacetime. In the background of pure Einstein gravity in noncommutative spacetime, we obtain the relation between the critical temperature and the charge density. We also obtain the value of the condensation operator and the critical exponent. Our findings suggest that higher the value of noncommutative parameter and Born-Infeld parameter make the condensate harder to form. We also observe that the critical temperature depends on the mass of the black hole and higher value of black hole mass is favourable for the formation of the condensate.

  19. Noncommutative effects of spacetime on holographic superconductors

    Science.gov (United States)

    Ghorai, Debabrata; Gangopadhyay, Sunandan

    2016-07-01

    The Sturm-Liouville eigenvalue method is employed to analytically investigate the properties of holographic superconductors in higher dimensions in the framework of Born-Infeld electrodynamics incorporating the effects of noncommutative spacetime. In the background of pure Einstein gravity in noncommutative spacetime, we obtain the relation between the critical temperature and the charge density. We also obtain the value of the condensation operator and the critical exponent. Our findings suggest that the higher value of noncommutative parameter and Born-Infeld parameter make the condensate harder to form. We also observe that the noncommutative structure of spacetime makes the critical temperature depend on the mass of the black hole and higher value of black hole mass is favourable for the formation of the condensate.

  20. Contact characteristics for YBCO bulk superconductors

    Science.gov (United States)

    Yamamoto, Naoki; Sakai, Tomokazu; Sawa, Koichiro; Tomita, Masaru; Murakami, Masato

    2003-10-01

    We have studied the contact characteristics of two resin-impregnated YBCO (a composite of YBa 2Cu 3O y and Y 2BaCuO 5) bulk superconductors in mechanical contact. A switching phenomenon could be observed at a threshold current or a transfer current value in the V- I curves of the YBCO contact. The transfer current exceeded the previous value of 13.5 A at 77 K in the contact when the sample surfaces were carefully polished. The present results suggest that a pair of YBCO blocks might be applicable to the mechanical persistent current switch for superconducting magnetic energy storage and other superconducting systems run in a persistent current mode.

  1. Holographic entanglement entropy in imbalanced superconductors

    International Nuclear Information System (INIS)

    We study the behavior of holographic entanglement entropy (HEE) for imbalanced holographic superconductors. We employ a numerical approach to consider the robust case of fully back-reacted gravity system. The hairy black hole solution is found by using our numerical scheme. Then it is used to compute the HEE for the superconducting case. The cases we study show that in presence of a mismatch between two chemical potentials, below the critical temperature, superconducting phase has a lower HEE in comparison to the AdS-Reissner-Nordström black hole phase. Interestingly, the effects of chemical imbalance are different in the contexts of black hole and superconducting phases. For black hole, HEE increases with increasing imbalance parameter while it behaves oppositely for the superconducting phase. The implications of these results are discussed

  2. Superconducting State Parameters of Binary Superconductors

    Directory of Open Access Journals (Sweden)

    Aditya M. Vora

    2012-05-01

    Full Text Available A well known pseudopotential is used to investigate the superconducting state parameters viz. electron-phonon coupling strength , Coulomb pseudopotential *, transition temperature ТС, isotope effect exponent  and effective interaction strength N0V for the AgxZn1 – x and AgxAl1 – x binary superconductors theoretically for the first time. We have incorporated here five different types of the local field correction functions to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of the various exchange and correlation functions is concluded from the present study. The comparison with other such experimental values is encouraging, which confirms the applicability of the model potential in explaining the superconducting state parameters of binary mixture.

  3. Quench properties of high current superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Garber, M; Sampson, W B

    1980-01-01

    A technique has been developed which allows the simultaneous determination of most of the important parameters of a high current superconductor. The critical current, propagation velocity, normal state resistivity, magnetoresistance, and enthalpy are determined as a function of current and applied field. The measurements are made on non-inductive samples which simulate conditions in full scale magnets. For wide, braided conductors the propagation velocity was found to vary approximately quadratically with current in the 2 to 5 kA region. A number of conductors have been tested including some Nb/sub 3/Sn braids which have critical currents in excess of 10 kA at 5 T, 4.2 K.

  4. Epitaxy of semiconductor-superconductor nanowires

    DEFF Research Database (Denmark)

    Krogstrup, P.; Ziino, N.L.B.; Chang, W.;

    2015-01-01

    Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface...... plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of...... devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are...

  5. High Tc superconductors at microwave frequencies

    International Nuclear Information System (INIS)

    The author discusses various experiments conducted in the micro- and millimeter wave spectral range on thin film and single crystal specimens of the high temperature oxide superconductors. For high quality film the surface resistance Rs is, except at low temperatures, due to thermally excited carriers, with extrinsic effects playing only a secondary role. Because of the low loss various passive microwave components, such as resonators, delay lines and filters, with performance far superior to those made of normal metals can be fabricated. The conductivity measured at millimeter wave frequencies displays a peak below Tc. Whether this is due to coherence factors or due to the change of the relaxation rate when the materials enter the superconducting state remains to be seen

  6. ''Soft'' Anharmonic Vortex Glass in Ferromagnetic Superconductors

    International Nuclear Information System (INIS)

    Ferromagnetic order in superconductors can induce a spontaneous vortex (SV) state. For external field H=0 , rotational symmetry guarantees a vanishing tilt modulus of the SV solid, leading to drastically different behavior than that of a conventional, external-field-induced vortex solid. We show that quenched disorder and anharmoinc effects lead to elastic moduli that are wave-vector dependent out to arbitrarily long length scales, and non-Hookean elasticity. The latter implies that for weak external fields H , the magnetic induction scales universally like B(H)∼B(0)+cHα , with α∼0.72 . For weak disorder, we predict the SV solid is a topologically ordered glass, in the ''columnar elastic glass'' universality class

  7. Josephson junctions based on pnictide superconductors

    International Nuclear Information System (INIS)

    Josephson junctions are a powerful tool for understanding more about the physical behaviour of pnictide superconductors. We built different kinds of Josephson junctions based on pnictide thin films. Planar junctions, edge type junctions, and junctions on bicrystalline substrates were prepared. We present manufacturing techniques and also the electronical properties of the different junctions and compare them. The measurement of I-V-characteristics show a strong excess current. We have to mind this when calculating the IcRN product. The effective IcRN values are 6.5 μV for the grain boundary junction, 7.9 μV for the planar structure, and 7.5 μV for the edge junction.

  8. Generalized Superconductors and Holographic Optics - II

    CERN Document Server

    Mahapatra, Subhash

    2014-01-01

    Using linear response theory, we analyze optical response properties of generalized holographic superconductors, in AdS-Schwarzschild and single R-charged black hole backgrounds in four dimensions. By introducing momentum dependent vector mode perturbations, the response functions for these systems are studied numerically, including the effects of backreaction. This complements and completes the probe limit analysis for these backgrounds initiated in our previous work ({\\tt arXiv : 1305.6273}). Our numerical analysis indicates a negative Depine-Lakhtakia index for both the backgrounds studied, at low enough frequencies. The dependence of the response functions on the backreaction parameter and the model parameters are established and analyzed with respect to similar backgrounds in five dimensions.

  9. Holographic superconductors with hidden Fermi surfaces

    CERN Document Server

    Fan, ZhongYing

    2013-01-01

    In this paper, we investigate a holographic model of superconductor with hidden Fermi surfaces, which was defined by the logarithmic violation of area law of entanglement entropy. We works in fully back-reacted background using standard Einstein-Maxwell-Dilaton action with additional complex scalar filed which was charged under the Maxwell field. Particularly, we analyze the behavior of entanglement entropy during the phase transition. At the critical point, the finite part of the entanglement entropy has a discontinuity of slope and tends to a lower value in the superconducting phase all the way down to the zero temperature limit, indicating the reorganization of degrees of freedom of the system across the phase transition.

  10. Fidelity approach in topological superconductors with disorders

    International Nuclear Information System (INIS)

    We apply the fidelity approach to study the topological superconductivity in spin–orbit coupling nanowire system. The wire is modeled as a one layer lattice chain with Zeeman energy and spin–orbit coupling, which is in proximity to a multi-layer superconductor. In particular, we study the effects of disorders and find that the fidelity susceptibility has multiple peaks. It is revealed that one peak indicates the topological quantum phase transition, while other peaks are signaling the pinning of the Majorana bound states by disorders. - Highlights: • We introduce fidelity approach to study the topological superconducting nanowire with disorders. • We study the quantum phase transition in the wire. • We investigate the disorder pinning of the Majorana bound states in the wire

  11. Holographic p-wave Superconductor with Disorder

    CERN Document Server

    Arean, Daniel; Zayas, Leopoldo A Pando; Landea, Ignacio Salazar; Scardicchio, Antonello

    2014-01-01

    We implement the effects of disorder on a holographic p-wave superconductor by introducing a random chemical potential which defines the local energy of the charge carriers. Since there are various possibilities for the orientation of the vector order parameter, we explore the behavior of the condensate in the parallel and perpendicular directions to the introduced disorder. We clarify the nature of various branches representing competing solutions and construct the disordered phase diagram. We find that moderate disorder enhances superconductivity as determined by the value of the condensate. The disorder we introduce is characterized by its spectral properties, and we also study its influence on the spectral properties of the condensate and charge density. We find fairly universal responses of the resulting power spectra characterized by linear functions of the disorder power spectrum.

  12. High temperature superconductors for fusion magnets

    International Nuclear Information System (INIS)

    Thermonuclear fusion is one of the main challenges of current scientific research. High temperature superconductors are considered to be the most likely candidates to be applied in future fusion power plants. The second generation of high temperature superconducting wires (coated conductors) are the most powerful high temperature superconducting wires. They are usually based on a cuprate structure of yttrium-barium-copper-oxide (YBa2Cu3O7-x), which has a critical temperature of 92 K. The superconducting wires applied in the coils of a fusion reactor have to withstand significant fast neutron fluences. The neutrons are produced directly by the fusion reaction. Therefore, a detailed investigation of fast neutron irradiation on coated conductors was performed in this thesis. The best available commercial coated conductors from the world leading manufacturers (SuperPower, EHTS - Bruker, American Superconductor - AMSC) were chosen as samples. TRIGA Mark II reactor in Vienna was employed as the irradiation facility. The samples were sequentially irradiated and, after each step, fully characterized by direct transport and magnetization measurements. The most complex characterization has been performed on the unirradiated samples. The fast neutrons introduce additional pinning centres into the superconductor, which can significantly change the performance of the superconductor. The critical current densities are often enhanced, but can also be reduced after a certain irradiation level is reached. The discussion and analysis of the results can be divided into two goals: The first is studying the performance with regard to fusion requirements. The samples will be irradiated beyond a fast neutron fluence of 1x1022 m2, which corresponds to the ITER lifetime fluence at the magnet area. The performance of the coated conductors will be then compared with the fusion requirements. The irradiation conditions in fission and fusion reactors are very different. Therefore, a detailed

  13. Point and extended defects in superconductors

    International Nuclear Information System (INIS)

    The effect of point defects created by γ-irradiation and extended defects created by Pb-ion irradiation on the behavior of the critical current density, Jc in several superconductors have been investigated. We have found a limitation of the role of both types of defects on enhancing Jc. We report an explanation of the effect of γ-irradiation and Pb-ion irradiation doses on Jc in these materials. The explanation is based on combining several competing mechanisms of irradiation which we believe to take place mainly in the regions of the grain boundaries. The influences of these mechanisms were found to vary with the irradiation dose level. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Noncommutative effects of spacetime on holographic superconductors

    Directory of Open Access Journals (Sweden)

    Debabrata Ghorai

    2016-07-01

    Full Text Available The Sturm–Liouville eigenvalue method is employed to analytically investigate the properties of holographic superconductors in higher dimensions in the framework of Born–Infeld electrodynamics incorporating the effects of noncommutative spacetime. In the background of pure Einstein gravity in noncommutative spacetime, we obtain the relation between the critical temperature and the charge density. We also obtain the value of the condensation operator and the critical exponent. Our findings suggest that the higher value of noncommutative parameter and Born–Infeld parameter make the condensate harder to form. We also observe that the noncommutative structure of spacetime makes the critical temperature depend on the mass of the black hole and higher value of black hole mass is favourable for the formation of the condensate.

  15. Vibrations in Magnet/Superconductor Levitation Systems

    Institute of Scientific and Technical Information of China (English)

    F. Y. Alzoubi; H. M. Al-khateeb; M. K. Alqadi; N. Y. Ayoub

    2006-01-01

    The problem of a small magnet levitating above a very thin superconducting disc in the Meissner state is analysed. The dipole-dipole interaction model is employed to derive analytical expressions for the interaction energy, levitation force, magnetic stiffness and frequency of small vibrations about the equilibrium position in two different configurations, i.e. with the magnetic moment parallel and perpendicular to the superconductor. The results show that the frequency of small vibrations decreases with the increasing levitation height for a particular radius of the superconducting disc, which is in good agreement with the experimental results. However, the frequency increases monotomcally up to saturation by increasing the radius of the disc for a particular height of the magnet. In addition, the frequency of vibrations is higher when the system is in the vertical configuration than that when the system is in the horizontal configuration.

  16. The role of oxygen in quinternary superconductors.

    Energy Technology Data Exchange (ETDEWEB)

    Beckman, D.R.; Jamieson, D.N. [Melbourne Univ., Parkville, VIC (Australia). School of Physics

    1996-12-31

    The oxygen composition of the new generation of high temperature superconductors (HTSC) has been found to play a crucial role in determining the superconductivity of these materials. However, measurement of the oxygen stoichiometry in such samples has proven difficult due to the small scattering cross section of oxygen, a light element, which has caused the oxygen scattering signal to be overwhelmed by the far larger signals generated off the heavier elements present in the HTSC samples. It is for this reason that previous ion beam analysis of oxide crystals has often either made no attempt to determine the oxygen content or has used O({alpha},{alpha})O resonances such as that at {approx} 3.05 MeV to probe the crystal. This work continues tests of a new technique for probing oxygen which overcomes the problem of an insignificant O BS signal by exploiting the large nuclear resonance found to occur in the O(p,p)O cross-section near an energy of 3.5 MeV in order to produce a significant oxygen edge in the H{sup +} BS spectrum obtained for the HTSC sample. The use of a H{sup +} beam is preferable to a He{sup 2+} beam for such work due to its enhanced sensitivity to light elements. The quinternary superconductor used for this investigation was a good quality pure Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} (BISCO, 2212) crystal. The size of this crystal was 5x5xl mm{sup 3} with the [001] face perpendicular to the surface. Measurements were performed using the University of Melbourne nuclear microprobe. The sample was mounted on an aluminium target holder using a carbon base adhesive which provided good electrical contact and it was oriented inside the target chamber by means of a four axis precision eucentric goniometer. 6 refs., 3 figs.

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

    Science.gov (United States)

    Hosono, Hideo; Ren, Zhi-An

    2009-02-01

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

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

    Science.gov (United States)

    Brandt, E. H.

    1991-01-01

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

  19. Magnetic properties of high-Tc superconductors

    International Nuclear Information System (INIS)

    Magnetic properties of high-Tc superconductors have been studied in order to determine the free-energy surface, the characteristic critical fields, order parameters structure, and the grain size effect on magnetization. Studies of the thermodynamic reversibility for YBa2Cu3O(7-delta) show the rounding in magnetization vs. temperature curves is a reflection of the thermodynamic fluctuations near Tc. Specific heat jump C(0)-C(H) values that have been calculated from the free-energy surfaces show good agreement with the direct calorimetric measurements. Comparative studies of the free-energy surfaces, flux creep and critical currents for both melt-textured and grain-aligned YBa2Cu3O(7-delta) samples have been undertaken in order to evaluate the difference caused by different micro structures in these samples. The free energy per unit length of a vortex is found to be essentially the same in the melt-textured sample as for the single crystals in the grain-aligned sample, suggesting that the line energy is the same for these rather different samples. The specific heat jump values calculated from the free-energy surfaces also show close agreement between the two samples. Magnetic field and temperature dependence of the average Ginzburg-Landau order parameter (f) is evaluated by fitting the magnetization data of grain-aligned YBa2Cu3O(7-delta) to the Hao-Clem model in the region of thermodynamic reversibility. H(sub C)(T) and H(sub c2)(T) were also determined from the fitting along with the kappa(sub c)(T) values. The study reveals the kappa(sub c) is a slowly decreasing function of temperature near T(sub c). Fittings of the same model to Bi2Sr2Ca2Cu3O10 have been carried out. The 2-D nature of bismuth family superconductors introduces some difficulties in applying Hao-Clem model and it is discussed in comparison with YBa2Cu3O(7-delta) results

  20. Current-injection in a ballastic multiterminal superconductor/two-dimensional electron gas Josephson junction

    NARCIS (Netherlands)

    Schäpers, Th.; Guzenko, V.A.; Müller, R.P.; Golubov, A.A.; Brinkman, A.; Crecelius, G.; Kaluza, A.; Lüth, H.

    2003-01-01

    We study the suppression of the critical current in a multi-terminal superconductor/two-dimensional electron gas/superconductor Josephson junction by means of hot carrier injection. As a superconductor Nb is used, while the two-dimensional electron gas is located in a strained InGaAs/InP heterostruc

  1. Anomalous scaling of the penetration depth in nodal superconductors

    Science.gov (United States)

    She, Jian-Huang; Lawler, Michael J.; Kim, Eun-Ah

    2015-07-01

    Recent findings of anomalous superlinear scaling of low-temperature (T ) penetration depth (PD) in several nodal superconductors near putative quantum critical points suggest that the low-temperature PD can be a useful probe of quantum critical fluctuations in a superconductor. On the other hand, cuprates, which are poster child nodal superconductors, have not shown any such anomalous scaling of PD, despite growing evidence of quantum critical points (QCP). Then it is natural to ask when and how can quantum critical fluctuations cause anomalous scaling of PD? Carrying out the renormalization group calculation for the problem of two-dimensional superconductors with point nodes, we show that quantum critical fluctuations associated with a point group symmetry reduction result in nonuniversal logarithmic corrections to the T dependence of the PD. The resulting apparent power law depends on the bare velocity anisotropy ratio. We then compare our results to data sets from two distinct nodal superconductors: YBa2Cu3O6.95 and CeCoIn5. Considering all symmetry-lowering possibilities of the point group of interest, C4 v, we find our results to be remarkably consistent with YBa2Cu3O6.95 being near a vertical nematic QCP and CeCoIn5 being near a diagonal nematic QCP. Our results motivate a search for diagonal nematic fluctuations in CeCoIn5.

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

    International Nuclear Information System (INIS)

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

  3. Superconductor digital electronics: Scalability and energy efficiency issues (Review Article)

    Science.gov (United States)

    Tolpygo, Sergey K.

    2016-05-01

    Superconductor digital electronics using Josephson junctions as ultrafast switches and magnetic-flux encoding of information was proposed over 30 years ago as a sub-terahertz clock frequency alternative to semiconductor electronics based on complementary metal-oxide-semiconductor (CMOS) transistors. Recently, interest in developing superconductor electronics has been renewed due to a search for energy saving solutions in applications related to high-performance computing. The current state of superconductor electronics and fabrication processes are reviewed in order to evaluate whether this electronics is scalable to a very large scale integration (VLSI) required to achieve computation complexities comparable to CMOS processors. A fully planarized process at MIT Lincoln Laboratory, perhaps the most advanced process developed so far for superconductor electronics, is used as an example. The process has nine superconducting layers: eight Nb wiring layers with the minimum feature size of 350 nm, and a thin superconducting layer for making compact high-kinetic-inductance bias inductors. All circuit layers are fully planarized using chemical mechanical planarization (CMP) of SiO2 interlayer dielectric. The physical limitations imposed on the circuit density by Josephson junctions, circuit inductors, shunt and bias resistors, etc., are discussed. Energy dissipation in superconducting circuits is also reviewed in order to estimate whether this technology, which requires cryogenic refrigeration, can be energy efficient. Fabrication process development required for increasing the density of superconductor digital circuits by a factor of ten and achieving densities above 107 Josephson junctions per cm2 is described.

  4. Does the electric power grid need a room temperature superconductor?

    International Nuclear Information System (INIS)

    Highlights: •High temperature superconductor (HTS) wires reach 500 A/cm-width (77 K) over >100 m. •Equipment using HTS wires has been developed for critical needs in the power grid. •Room temperature superconductors (RTS), if discovered, avoid refrigeration in use. •Short coherence length, accelerated flux creep make RTS power applications unlikely. •Given progress in HTS power equipment, power grid does not need RTS. -- Abstract: Superconductivity can revolutionize electric power grids, for example with high power underground cables to open urban power bottlenecks and fault current limiters to solve growing fault currents problems. Technology based on high temperature superconductor (HTS) wire is beginning to meet these critical needs. Wire performance is continually improving. For example, American Superconductor has recently demonstrated long wires with up to 500 A/cm-width at 77 K, almost doubling its previous production performance. But refrigeration, even at 77 K, is a complication, driving interest in discovering room temperature superconductors (RTS). Unfortunately, short coherence lengths and accelerated flux creep will make RTS applications unlikely. Existing HTS technology, in fact, offers a good compromise of relatively high operating temperature but not so high as to incur coherence-length and flux-creep limitations. So – no, power grids do not need RTS; existing HTS wire is proving to be what grids really need

  5. Vortices at planar defects in layered superconductors

    International Nuclear Information System (INIS)

    We propose a self-consistent nonlocal approach for the description of vortices in layered supeconductors that contain planar defects parallel to the layers. The model takes account of interlayer Josephson coupling and of a reduced maximum Josephson current density j0' across the defect as compared to j0 for other interlayer junctions. Analytical formulas that describe the structure of both static and moving vortices, including the nonlinear Josephson core region, are obtained. Within the framework of the model, we have calculated the lower critical field Hc1, vortex mass M, viscous drag coefficient μ, and the nonlinear current-voltage characteristic V(j) for a vortex moving along planar defects. It is shown that for identical junctions (j0'=j0) our approach reproduces results of Clem, Coffey, and Hao [Phys. Rev. B 42, 6209 (1990); 44, 2732 (1991); 44, 6903 (1991)] for μ, M, and Hc1. In the opposite limit j0'0, our model gives an Abrikosov vortex with anisotropic Josephson core described by a nonlocal Josephson electrodynamics. A sign change in the curvature of V(j) is shown to occur due to a crossover between underdamped (Tc) and overdamped T≅Tc dynamics of interlayer junctions as the temperature T is increased. Implications of the results on the c-axis current transport in high-Tc superconductors are discussed. copyright 1996 The American Physical Society

  6. Topological transitions in multi-band superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Continentino, Mucio A., E-mail: mucio@cbpf.br [Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, Urca 22290-180, Rio de Janeiro, RJ (Brazil); Deus, Fernanda, E-mail: fernanda@cbpf.br [Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, Urca 22290-180, Rio de Janeiro, RJ (Brazil); Padilha, Igor T., E-mail: igorfis@ufam.edu.br [Universidade Federal do Amazonas, Campus Capital, 69077-070, Manaus, AM (Brazil); Caldas, Heron, E-mail: hcaldas@ufsj.edu.br [Departamento de Ciências Naturais, Universidade Federal de São João Del Rei, 36301-000, São João Del Rei, MG (Brazil)

    2014-09-15

    The search for Majorana fermions has been concentrated in topological insulators or superconductors. In general, the existence of these modes requires the presence of spin–orbit interactions and of an external magnetic field. The former implies in having systems with broken inversion symmetry, while the latter breaks time reversal invariance. In a recent paper, we have shown that a two-band metal with an attractive inter-band interaction has non-trivial superconducting properties, if the k-dependent hybridization is anti-symmetric in the wave-vector. This is the case, if the crystalline potential mixes states with different parities as for orbitals with angular momentum l and l+1. In this paper we take into account the effect of an external magnetic field, not considered in the previous investigation, in a two-band metal and show how it modifies the topological properties of its superconducting state. We also discuss the conditions for the appearance of Majorana fermions in this system.

  7. Growth and characterization of bulk superconductor material

    CERN Document Server

    Chen, Dapeng; Maljuk, Andrey; Zhou, Fang

    2016-01-01

    This book focuses on recently developed crystal growth techniques to grow large and high quality superconducting single crystals. The techniques applied are traveling solvent floating zone (TSFZ) with infrared image furnace, Bridgeman, solution/flux and top seeded solution growth (TSSG) methods. The materials range from cuprates, cobaltates to pnictides including La2CuO4-based (LCO), YBa2Cu3O7-d (YBCO), Bi2Sr2Can−1CunO2n+4+δ (n=1,2,3) (BSCCO) to NaxCoO2. The modified Bridgman “cold finger” method is devoted to the pnictide system with the best quality (transition width DTc~0.5 K) with highest Tc~38.5 K of Ba0.68K0.32Fe2A2. The book presents various iron-based superconductors with different structures, such as 1111, 122, 111, 11 and 42622,10-3-8. Detailed single crystal growth methods (fluxes, Bridgman, floating zone), the associated procedures and their impact to crystal size and quality are presented. The book also describes the influence of doping on the structure and the electric, magnetic, and supe...

  8. Modelling current voltage characteristics of practical superconductors

    International Nuclear Information System (INIS)

    Based on recent experimental results, and in the light of fundamental physical properties of the magnetic flux in type-II superconductors, we introduce a practical expression for the material law to be applied in numerical modelling of superconducting applications. Focusing on the computational side, in this paper, previous theory is worked out, so as to take the celebrated form of a power-law-like dependence for the current voltage characteristic. However, contrary to the common approach in numerical studies, this proposal suits the general situation of current density flow with components either parallel or perpendicular to the local magnetic field, and different constraints applying on each component. Mathematically, the theory is generated from an elliptic locus defined in terms of the current density vector components. From the physical side, this contour establishes the boundary for the onset of entropy production related to overcritical current flow in different conditions. The electric field is obtained by partial differentiation and points perpendicular to the ellipse. Some numerical examples, inspired by the geometry of a two-layer helical counter-wound cable are provided. Corrections to the widespread use of the implicit isotropic assumption (physical properties only depend on the modulus of the current density vector) are discussed, and essentially indicate that the current carrying capacity of practical systems may be underestimated by using such simplification. (paper)

  9. High temperature superconductors at optimal doping

    Directory of Open Access Journals (Sweden)

    W. E. Pickett

    2006-09-01

    Full Text Available   Intensive study of the high temperature superconductors has been ongoing for two decades. A great deal of this effort has been devoted to the underdoped regime, where the new and difficult physics of the doped Mott insulator has met extra complications including bilayer coupling/splitting, shadow bands, and hot spots. While these complications continue to unfold, in this short overview the focus is moved to the region of actual high-Tc, that of optimal doping. The focus here also is not on the superconducting state itself, but primarily on the characteristics of the normal state from which the superconducting instability arises, and even these can be given only a broad-brush description. A reminder is given of two issues,(i why the “optimal Tc” varies,for n-layered systems it increases for n up to 3, then decreases for a given n, Tc increases according to the ‘basis’ atom in the order Bi, Tl, Hg (ii how does pressure, or a particular uniaxial strain, increase Tc when the zero-strain system is already optimally doped?

  10. Dynamic Quantum Phase Transitions in Holographic Superconductors

    Science.gov (United States)

    Park, Moon Jip; Gilbert, Matthew

    A non-equilibrium quench that crosses a quantum critical point is known to exhibit distinct behavior from trivial quench. This is readily apparent via examination of the Loschmidt echo that contains the Yang-Lee (YL) zeros in the non-equilibrium quench within the vanishing returning rate of ground state when the quantum critical point is crossed. While previous studies on the dynamical quenches are restricted within non-interacting systems, we use of the Loschmidt echo to understand quenches within strongly interacting conformal field theories using holographic mapping. We show that the free energy of the gravitational dual possesses YL zeros at the superconducting critical temperature. We argue that, on the gravitational side, the presence of YL zeros implies that the free energy is invariant under a set of discrete deformations of the metric characterized by the time at which the returning rate vanishes. We illustrate these ideas using a holographic superconductor constructed via the coupling of AdS gravity with a Maxwell field and charged scalar.

  11. Hole-doped cuprate high temperature superconductors

    International Nuclear Information System (INIS)

    Highlights: • Historical discoveries of hole-doped cuprates and representative milestone work. • Several simple and universal scaling laws of the hole-doped cuprates. • A comprehensive classification list with references for hole-doped cuprates. • Representative physical parameters for selected hole-doped cuprates. - Abstract: Hole-doped cuprate high temperature superconductors have ushered in the modern era of high temperature superconductivity (HTS) and have continued to be at center stage in the field. Extensive studies have been made, many compounds discovered, voluminous data compiled, numerous models proposed, many review articles written, and various prototype devices made and tested with better performance than their nonsuperconducting counterparts. The field is indeed vast. We have therefore decided to focus on the major cuprate materials systems that have laid the foundation of HTS science and technology and present several simple scaling laws that show the systematic and universal simplicity amid the complexity of these material systems, while referring readers interested in the HTS physics and devices to the review articles. Developments in the field are mostly presented in chronological order, sometimes with anecdotes, in an attempt to share some of the moments of excitement and despair in the history of HTS with readers, especially the younger ones

  12. Magnetic memory effects in high temperature superconductors

    International Nuclear Information System (INIS)

    Microwave absorption of high temperature oxide superconductors MBa2Cu3O7 (M = Y, Er, Dy, Ho, Lu, Tm, Gd) at 77 K have been studied by ESR. In granular samples diamagnetic zero-field resonance and strong ESR baseline hysteresis have been observed: for increasing field sweep - a high, for decreasing one - a low, while in constant field the baseline approaches the middle position with kinetics typical of spin-glasses. The hysteresis amplitude, i.e. the deviation of high and low baselines, possesses maximum at zero field if the sample is cooled down in zero field. In case of field cooling both the diamagnetic resonance and hysteresis maximum are shifted as a function of relative direction of the fields where the samples are cooled and measured, respectively. The shift is caused by the remanent diamagnetism of trapped fluxons. The hysteresis critically depends on the modulation amplitude of magnetic field, and no hysteresis can be observed if the microwave absorption is detected without field modulation. By applying saw-tooth sweep the spin-glass can be driven between two extreme hysteresis states, and the ESR response is rectangular for large saw-tooth amplitude and linear - for small one, while for intermediate amplitudes the recording shows characteristic memory effects. The hysteresis memory is explained in terms of loop distribution of fluxons. In the single crystal the fluxon absorptions are also detected and the separation of fluxon lines can be related to the hysteresis in granular samples. (author)

  13. Epitaxy of semiconductor-superconductor nanowires

    Science.gov (United States)

    Krogstrup, P.; Ziino, N. L. B.; Chang, W.; Albrecht, S. M.; Madsen, M. H.; Johnson, E.; Nygård, J.; Marcus, C. M.; Jespersen, T. S.

    2015-04-01

    Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are discussed. We formulate the grain growth kinetics of the metal phase in general terms of continuum parameters and bicrystal symmetries. The method realizes the ultimate limit of uniform interfaces and seems to solve the soft-gap problem in superconducting hybrid structures.

  14. Epitaxy of semiconductor-superconductor nanowires.

    Science.gov (United States)

    Krogstrup, P; Ziino, N L B; Chang, W; Albrecht, S M; Madsen, M H; Johnson, E; Nygård, J; Marcus, C M; Jespersen, T S

    2015-04-01

    Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are discussed. We formulate the grain growth kinetics of the metal phase in general terms of continuum parameters and bicrystal symmetries. The method realizes the ultimate limit of uniform interfaces and seems to solve the soft-gap problem in superconducting hybrid structures. PMID:25581626

  15. Tilted loop currents in cuprate superconductors

    International Nuclear Information System (INIS)

    The paper briefly surveys theoretical models for the polar Kerr effect (PKE) and time-reversal symmetry breaking in the pseudogap phase of cuprate superconductors. By elimination, the most promising candidate is the tilted loop-current model, obtained from the Simon–Varma model by tilting one triangular loop up and another one down toward the apical oxygens. The model is consistent with the PKE, spin-polarized neutron scattering, and optical anisotropy measurements. Spontaneous currents in this model flow between the in-plane and apical oxygens in such a manner that each oxygen belongs to one current loop. This loop-current pattern is similar to the spin order in the magnetoelectric antiferromagnet Cr2O3, where the PKE is observed experimentally. By analogy, it should be possible to train the PKE sign in the cuprates magnetoelectrically. Several experiments are proposed to confirm the loop-current order: the magnetic-field-induced polarity, the nonlinear anomalous Hall effect, and the second-harmonic generation

  16. NMR study of high-TC superconductors

    International Nuclear Information System (INIS)

    Recent NMR study of high-TC superconductors carried out by Osaka group is reviewed. NQR frequency νQ, Knight shift K, T1 of 63Cu and 17O were measured over a wide hole doping range from light- to heavy-doped systems, LSCO, YBCO, HBCCO, BSCCO, TBCCO and TBCO, together with impurity and pressure effect. By analysing νQ, K and T1, the local hole numbers of Cu and O at the CuO2 plane, n(Cu) and n(O) the relative magnitude of the uniform susceptibility, χ0 and the low-frequency component of the antiferromagnetic spin fluctuations (AFSF), χQ/Γ (χQ is the staggered susceptibility and Γ is the characteristic energy of the spin fluctuation at q=0) are obtained. The relation between n(Cu), n(O) and χQ, χQ/Γ, TC, etc. were discussed. There are optimum values of n(Cu)/2n(O) and n(Cu)+2n(O) to give maximum TC. The NMR results in the superconducting state are well-explained by d-wave pairing model. The result is consistent with the AFSF mediated superconducting model. (orig.)

  17. Studies of anisotropy of iron based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, Jason A. [Iowa State Univ., Ames, IA (United States)

    2013-01-01

    To study the electronic anisotropy in iron based superconductors, the temperature dependent London penetration depth, Δλ(T), have been measured in several compounds, along with the angular dependent upper critical field, Hc2(T). Study was undertaken on single crystals of Ba(Fe1-xCox)2As2 with x=0.108 and x=0.127, in the overdoped range of the doping phase diagram, characterized by notable modulation of the superconducting gap. Heavy ion irradiation with matching field doses of 6 T and 6.5 T respectively, were used to create columnar defects and to study their effect on the temperature Δλ(T). The variation of the low-temperature penetration depth in both pristine and irradiated samples was fitted with a power-law function Δλ(T) = ATn. Irradiation increases the magnitude of the pre-factor A and decreases the exponent n, similar to the effect on the optimally doped samples. This finding supports the universal s ± scenario for the whole doping range.

  18. Vortex jamming in superconductors and granular rheology

    Energy Technology Data Exchange (ETDEWEB)

    Yoshino, Hajime [Department of Earth and Space Science, Faculty of Science, Osaka University, Toyonaka 560-0043 (Japan); Nogawa, Tomoaki [Division of Physics, Hokkaido University, Sapporo, Hokkaido 060-0810 Japan (Japan); Kim, Bongsoo [Department of Physics, Changwon National University, Changwon 641-773 (Korea, Republic of)], E-mail: yoshino@ess.sci.osaka-u.ac.jp

    2009-01-15

    We demonstrate that a highly frustrated anisotropic Josephson junction array (JJA) on a square lattice exhibits a zero-temperature jamming transition, which shares much in common with those in granular systems. Anisotropy of the Josephson couplings along the horizontal and vertical directions plays roles similar to normal load or density in granular systems. We studied numerically static and dynamic response of the system against shear, i.e. injection of external electric current at zero temperature. Current-voltage curves at various strength of the anisotropy exhibit universal scaling features around the jamming point much as do the flow curves in granular rheology, shear-stress versus shear-rate. It turns out that at zero temperature the jamming transition occurs right at the isotropic coupling and anisotropic JJA behaves as exotic fragile vortex matter: it behaves as a superconductor (vortex glass) in one direction, whereas it is a normal conductor (vortex liquid) in the other direction even at zero temperature. Furthermore, we find a variant of the theoretical model for the anisotropic JJA quantitatively reproduces universal master flow-curves of the granular systems. Our results suggest an unexpected common paradigm stretching over seemingly unrelated fields-the rheology of soft materials and superconductivity.

  19. Production of superconductor/carbon bicomponent fibers

    Science.gov (United States)

    Wise, S. A.; Fain, C. C.; Leigh, H. D.

    1991-01-01

    Certain materials are unable to be drawn or spun into fiber form due to their improper melting characteristics or brittleness. However, fibrous samples of such materials are often necessary for the fabrication of intricate shapes and composites. In response to this problem, a unique process, referred to as the piggyback process, was developed to prepare fibrous samples of a variety of nonspinnable ceramics. In this technique, specially produced C shaped carbon fibers serve as micromolds to hold the desired materials prior to sintering. Depending on the sintering atmosphere used, bicomponent or single component fibers result. While much has been shown worldwide concerning the YBa2Cu3O(7-x) superconductor, fabrication into unique forms has proven quite difficult. However, a variety of intricate shapes are necessary for rapid commercialization of the superconducting materials. The potential for producing fibrous samples of the YBa2Cu3O(7-x) compound by the piggyback process is being studied. Various organic and acrylic materials were studied to determine suspending ability, reactivity with the YBa2Cu3O(7-x) compound during long term storage, and burn out characteristics. While many questions were answered with respect to the interfacial reactions between YBa2Cu3O(7-x) and carbon, much work is still necessary to improve the quality of the sintered material if the fibers produced are to be incorporated into useful composite or cables.

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

    Science.gov (United States)

    Hosono, Hideo; Ren, Zhi-An

    2009-02-01

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

  1. Neutron and Synchrotron X-Ray Scattering Studies of Superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tranquada,J.M.

    2008-09-01

    Superconductors hold the promise for a more stable and efficient electrical grid, but new isotropic, high-temperature superconductors are needed in order to reduce cable manufacturing costs. The effort to understand high-temperature superconductivity, especially in the layered cuprates, provides guidance to the search for new superconductors. Neutron scattering has long provided an important probe of the collective excitations that are involved in the pairing mechanism. For the cuprates, neutron and x-ray diffraction techniques also provide information on competing types of order, such as charge and spin stripes, that appear to be closely connected to the superconductivity. Recently, inelastic x-ray scattering has become competitive for studying phonons and may soon provide valuable information on electronic excitations. Examples of how these techniques contribute to our understanding of superconductivity are presented.

  2. Hysteresis of modulated microwave absorption in hard superconductors

    International Nuclear Information System (INIS)

    The paper discusses the experimental results of investigations into hysteresis effect of microwave (MW) absorption in the following hard superconductors: Nb(poly- and monocrystals with deformation different degree), V3Si, NbSe2, YBa2Cu3O7-x (poly- and monocrystals), La2-xSr2Cu4-y, Tl2Ba2Sa2Cu3Ox, (ET)2Cu(SCN)2 organic superconductor. Definitions of parameters introduced to describe this effect are given. It is shown that MW hysteresis of absorption may be explained on the ground of the effect of Abrikosov vortex redistribution within skin-layer of a hard superconductor at variation of magnetic field scanning direction. 36 refs., 7 figs

  3. Spin injection from a normal metal into a mesoscopic superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Wolf, Michael J.; Kolenda, Stefan [Institut fuer Nanotechnologie, KIT, 76021 Karlsruhe (Germany); Huebler, Florian [Institut fuer Nanotechnologie, KIT, 76021 Karlsruhe (Germany); Center for Functional Nanostructures, KIT, 76131 Karlsruhe (Germany); Institut fuer Festkoerperphysik, KIT, 76021 Karlsruhe (Germany); Loehneysen, Hilbert v. [Center for Functional Nanostructures, KIT, 76131 Karlsruhe (Germany); Institut fuer Festkoerperphysik, KIT, 76021 Karlsruhe (Germany); Physikalisches Institut, KIT, 76128 Karlsruhe (Germany); Beckmann, Detlef [Institut fuer Nanotechnologie, KIT, 76021 Karlsruhe (Germany); Center for Functional Nanostructures, KIT, 76131 Karlsruhe (Germany)

    2013-07-01

    We report on nonlocal transport in superconductor hybrid structures, with ferromagnetic as well as normal-metal tunnel junctions attached to the superconductor. In the presence of a strong Zeeman splitting of the density of states, both charge and spin imbalance is injected into the superconductor. While previous experiments demonstrated spin injection from ferromagnetic electrodes, we show that spin imbalance is also created for normal-metal injector contacts. Using the combination of ferromagnetic and normal-metal detectors allows us to directly discriminate between charge and spin injection, and demonstrate a complete separation of charge and spin imbalance. The relaxation length of the spin imbalance is of the order of several μm and is found to increase with a magnetic field, but is independent of temperature. We further discuss possible relaxation mechanisms for the explanation of the spin relaxation length.

  4. Can nothing be a superconductor and a superfluid?

    CERN Document Server

    Chernodub, M N

    2011-01-01

    A superconductor is a material that conducts electric current with no resistance. Superconductivity and magnetism are known to be antagonistic phenomena: superconductors expel weak external magnetic field (the Meissner effect) while a sufficiently strong magnetic field, in general, destroys superconductivity. In a seemingly contradictory statement, we show that a very strong magnetic field can turn an empty space into a superconductor. The external magnetic field required for this effect should be about 10^{16} Tesla (eB ~ 1 GeV^2). The physical mechanism of the exotic vacuum superconductivity is as follows: in strong magnetic field the dynamics of virtual quarks and antiquarks is effectively one-dimensional because these electrically charged particles tend to move along the lines of the magnetic field. In one spatial dimension a gluon-mediated attraction between a quark and an antiquark of different flavors inevitably leads to formation of a colorless spin-triplet bound state (a vector analogue of the Cooper...

  5. Prospects for utilization of superconductors in the power industry

    International Nuclear Information System (INIS)

    Utilization of superconducting technology is greatly influenced by the discovery of the so-called high-temperature superconductors (HTS). The present report considers to what extent there is a need for HTS in up-to-date engineering and how much they are prepared for practical applications. The work on the practical use of superconductors was started about 30 years ago. As a results, two fields of the high-current superconductivity have emerged. The first category is the field in which other alternatives were inconceivable from techno-economic points of view (magnets of thermo-nuclear installations, MHD generators, inductive energy storage systems, etc.). The second category involves areas where superconductors must demonstrate the ability to compete with existing technologies (electrical devices, magnetic separators, etc.). The present overview discusses developments of various low temperature superconducting devices, estimate their potential and evaluates future applications of HTS based on the experience accumulated in the USSR and other countries. (author)

  6. Spin injection from a normal metal into a mesoscopic superconductor

    International Nuclear Information System (INIS)

    We report on nonlocal transport in superconductor hybrid structures, with ferromagnetic as well as normal-metal tunnel junctions attached to the superconductor. In the presence of a strong Zeeman splitting of the density of states, both charge and spin imbalance is injected into the superconductor. While previous experiments demonstrated spin injection from ferromagnetic electrodes, we show that spin imbalance is also created for normal-metal injector contacts. Using the combination of ferromagnetic and normal-metal detectors allows us to directly discriminate between charge and spin injection, and demonstrate a complete separation of charge and spin imbalance. The relaxation length of the spin imbalance is of the order of several μm and is found to increase with a magnetic field, but is independent of temperature. We further discuss possible relaxation mechanisms for the explanation of the spin relaxation length.

  7. Atomic hydrogen effects on high-Tc superconductors

    International Nuclear Information System (INIS)

    The atomic hydrogen effects on the properties of bulk high-temperature superconductors were investigated. It is shown that the insertion of the atomic hydrogen into the bulk of these materials from a DC plasma leads to the increase of the critical current density Jc for YBaCuO(123) as well as for BiSrCaCuO(2223) high-temperature superconductors. It is found that the hydrogenation of the He implanted samples with following annealing leads to the optically detected blistering on the surface. It means that the textured thin subsurface layers of high-temperature superconductors can be formed by this method. The improvement of superconductivity by atomic hydrogen can be explained by the passivation of dangling bonds and defects on grain boundaries of these materials

  8. Crystal chemistry and structural design of iron-based superconductors

    Institute of Scientific and Technical Information of China (English)

    Jiang Hao; Sun Yun-Lei; Xu Zhu-An; Cao Guang-Han

    2013-01-01

    The second class of high-temperature superconductors (HTSCs),iron-based pnictides and chalcogenides,necessarily contain Fe2X2 (“X” refers to a pnictogen or a chalcogen element) layers,just like the first class of HTSCs which possess the essential CuO2 sheets.So far,dozens of iron-based HTSCs,classified into nine groups,have been discovered.In this article,the crystal-chemistry aspects of the known iron-based superconductors are reviewed and summarized by employing “hard and soft acids and bases (HSAB)” concept.Based on these understandings,we propose an alternative route to exploring new iron-based superconductors via rational structural design.

  9. Spin, charge, and orbital orderings in iron-based superconductors

    Institute of Scientific and Technical Information of China (English)

    Jiang Qing; Kang Yao-Tai; Yao Dao-Xin

    2013-01-01

    In this article,we briefly review spin,charge,and orbital orderings in iron-based superconductors,as well as the multi-orbital models.The interplay of spin,charge,and orbital orderings is a key to understand the high temperature superconductivity.As an illustration,we use the two-orbital model to show the spin and charge orderings in iron-based superconductors based on the mean-field approximation in real space.The typical spin and charge orderings are shown by choosing appropriate parameters,which are in good agreement with experiments.We also show the effect of Fe vacancies,which can introduce the nematic phase and interesting magnetic ground states.The orbital ordering is also discussed in iron-based superconductors.It is found that disorder may play a role to produce the superconductivity.

  10. Signature of electron-phonon interaction in high temperature superconductors

    Directory of Open Access Journals (Sweden)

    Vinod Ashokan

    2011-09-01

    Full Text Available The theory of thermal conductivity of high temperature superconductors (HTS based on electron and phonon line width (life times formulation is developed with Quantum dynamical approach of Green's function. The frequency line width is observed as an extremely sensitive quantity in the transport phenomena of HTS as a collection of large number of scattering processes. The role of resonance scattering and electron-phonon interaction processes is found to be most prominent near critical temperature. The theory successfully explains the spectacular behaviour of high Tc superconductors in the vicinity of transition temperature. A successful agreement between theory and experiment has been obtained by analyzing the thermal conductivity data for the sample La1.8Sr0.2CuO4 in the temperature range 0 − 200K. The theory is equally and successfully applicable to all other high Tc superconductors.

  11. TECHNICAL TRAINING SEMINAR: High Temperature Superconductors: Progress and Issues

    CERN Multimedia

    Davide Vitè

    2002-01-01

    Monday 24 June from 14:30 to 15:30 - Training Centre Auditorium - bldg. 593-11 High Temperature Superconductors: Progress and Issues Prof. Jan Evetts / UNIVERSITY OF CAMBRIDGE, Department of Materials Science and Metallurgy, UK Grappling with grain boundaries: Current transport processes in granular High Temperature Superconductors (HTS) The development of High Temperature Superconductors, seen from a materials scientist's point of view, is relevant to the superconductivity community at CERN: their possible high current applications can include high performance magnets for future accelerators. There is an urgent need to develop a quantitative description of HTS conductors in terms of their complex anisotropy, inhomogeneity and dimensionality. This is essential both for the practical specification of a conductor and for charting routes to conductor optimisation. The critical current, the n-value, dissipation and quenching characteristics are amongst most important parameters that make up an engineering specifi...

  12. Transport current losses in Bi2223 high temperature superconductors

    International Nuclear Information System (INIS)

    Bi2223 high temperature superconductor (HTS) tapes are expected to be used in power industry such as fault current limiter, transformer, magnets, transmission cables. For most of applications of Bi2223 tapes, the superconductor will transport ac current and/or be exposed to applied magnetic field. AC loss is one of important parameters to evaluate the economic feasibility of HTS ceramic superconductors in those applications. Extensive investigations have been done to understand the mechanism of generation of AC loss and minimize it. In this study, AC losses in Bi2223 (HTS) tapes were measured at 77 K. The effects of different factors, such as, current distribution, heat recycling, transport current wave and applied DC magnetic field, were investigated on the AC losses in Bi2223 HTS tapes. Possible explanations were presented in the paper

  13. Phases of holographic superconductors with broken translational symmetry

    CERN Document Server

    Baggioli, Matteo

    2015-01-01

    We consider holographic superconductors in a broad class of massive gravity backgrounds. These theories provide a holographic description of a superconductor with broken translational symmetry. Such models exhibit a rich phase structure: depending on the values of the temperature and the doping the boundary system can be in superconducting, normal metallic or normal pseudo-insulating phases. Furthermore the system supports interesting collective excitations of the charge carriers, which appears in the normal phase, persists in the superconducting phase, but eventually gets destroyed by the superconducting condensate. We also show the possibility of building a phase diagram of a system with the superconducting phase occupying a dome-shaped region, therefore resembling more of a real-world doped high-Tc superconductor.

  14. Influence of thermal gradient in vortex states of mesoscopic superconductors

    International Nuclear Information System (INIS)

    In general, the studies of finite size effects in mesoscopic superconductors have been carried out in such a way that the temperature parameter is constant in the entire system. However, we could have situations where a real sample is near a heater source, as an example. In such situations, gradients of temperature are present. On the other hand, mesoscopic superconductors are interesting systems due to the fact that they present confinement effects which influence all the vortex dynamics. Thus, in this work we studied the influence of thermal gradients on the vortex dynamics in mesoscopic superconductors. For this purposes, we used the time dependent Ginzburg-Landau equations. The thermal gradients produce an asymmetric distribution of the currents around the system which, in turn, yield interesting vortex configurations and difficult the formation of giant vortices

  15. Upper critical field of the noncentrosymmetric superconductor BiPd

    Science.gov (United States)

    Peets, Darren C.; Maldonado, Ana; Enayat, Mostafa; Sun, Zhixiang; Wahl, Peter; Schnyder, Andreas P.

    2016-05-01

    The superconducting parameters and upper critical field of the noncentrosymmetric superconductor BiPd have proven contentious. This material is of particular interest because it is a rare example of a 4 f -electron-free noncentrosymmetric superconductor of which crystals may be grown and cleaved, enabling surface-sensitive spectroscopies. Here, using bulk probes augmented by tunneling data on defects, we establish that the lower of the previously reported upper critical fields corresponds to the bulk transition. The material behaves as a nearly weak-coupled BCS s -wave superconductor, and we report its superconducting parameters as drawn from the bulk upper critical field. Possible reasons behind the order-of-magnitude discrepancy in the reported upper critical fields are discussed.

  16. Coherence effects in a normal-metal--insulator--superconductor junction

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, F.; Spivak, B. [Physics Department, University of Washington, Seattle, Washington 98195 (United States); Zyuzin, A. [Physics Department, University of Cincinnati, Cincinnati, Ohio 45221-0011 (United States)

    1995-08-01

    Coherence effects arising due to Andreev reflections in a superconductor--insulator--normal-metal junction are considered. It is shown that in the absence of electron-electron interaction in the metal at low temperatures, the electrical potential drop on the insulator {ital I}{sub 0}{ital R}{sub {ital I}}, caused by the current density {ital I}{sub 0} through the junction, vanishes, although the resistance of the device {ital R}{sub {infinity}} measured by the two-probe method can be large. The electron-electron interaction determines the zero-temperature value of {ital R}{sub {ital I}}. The implications of these effects for the theory of the superconductor--normal-metal--superconductor junction are discussed.

  17. Josephson supercurrent in a graphene-superconductor junction

    Science.gov (United States)

    Sarvestani, E.; Jafari, S. A.

    2012-01-01

    Within the tunneling Hamiltonian formulation for the eight-component spinors, the Josephson critical supercurrent has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intravalley and intervalley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical supercurrent are completely separable. Therefore, it is possible to consider the effect of the intervalley tunnelings in the critical supercurrent. The incorporation of these type of processes into the tunneling Hamiltonian exposes a special feature of the graphene Josephson junctions. The effect of intervalley tunneling appears in the length dependence plot of critical current in the form of oscillations. We also present the results for temperature dependence of critical supercurrent and compare with experimental results and other theoretical calculations.

  18. Josephson supercurrent in a graphene-superconductor junction

    International Nuclear Information System (INIS)

    Within the tunneling Hamiltonian formulation for the eight-component spinors, the Josephson critical supercurrent has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intravalley and intervalley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical supercurrent are completely separable. Therefore, it is possible to consider the effect of the intervalley tunnelings in the critical supercurrent. The incorporation of these type of processes into the tunneling Hamiltonian exposes a special feature of the graphene Josephson junctions. The effect of intervalley tunneling appears in the length dependence plot of critical current in the form of oscillations. We also present the results for temperature dependence of critical supercurrent and compare with experimental results and other theoretical calculations.

  19. Josephson supercurrent in a graphene-superconductor junction

    Energy Technology Data Exchange (ETDEWEB)

    Sarvestani, Esmaeel [Institute for Advanced Simulation, Forschungszentrum Juelich, 52425 Juelich (Germany); Jafari, Seyed Akbar [Department of Physics, Sharif University of Technology, Tehran 11155-9161 (Iran, Islamic Republic of)

    2013-07-01

    Within the tunneling Hamiltonian formulation for the eight-component spinors, the Josephson critical supercurrent has been calculated in a planar superconductor-normal graphene-superconductor junction. Coupling between superconductor regions and graphene is taken into account by a tunneling Hamiltonian which contains two types of tunneling, intravalley and intervalley tunneling. Within the present tunneling approach, we find that the contributions of two kinds of tunneling to the critical supercurrent are completely separable. Therefore, it is possible to consider the effect of the intervalley tunnelings in the critical supercurrent. The incorporation of these type of processes into the tunneling Hamiltonian exposes a special feature of the graphene Josephson junctions. The effect of intervalley tunneling appears in the length dependence plot of critical current in the form of oscillations. We also present the results for temperature dependence of critical supercurrent and compare with experimental results and other theoretical calculations.

  20. High-Temperature Cuprate Superconductors Experiment, Theory, and Applications

    CERN Document Server

    Plakida, Nikolay Maksimilianovich

    2010-01-01

    High-Temperature Cuprate Superconductors provides an up-to-date and comprehensive review of the properties of these fascinating materials. The essential properties of high-temperature cuprate superconductors are reviewed on the background of their theoretical interpretation. The experimental results for structural, magnetic, thermal, electric, optical and lattice properties of various cuprate superconductors are presented with respect to relevant theoretical models. A critical comparison of various theoretical models involving strong electron correlations, antiferromagnetic spin fluctuations, phonons and excitons provides a background for understanding of the mechanism of high-temperature superconductivity. Recent achievements in their applications are also reviewed. A large number of illustrations and tables gives valuable information for specialists. A text-book level presentation with formulation of a general theory of strong-coupling superconductivity will help students and researches to consolidate their...

  1. Topological Blount's theorem of odd-parity superconductors

    Science.gov (United States)

    Kobayshi, Shingo; Shiozaki, Ken; Sato, Masatoshi; Tanaka, Yukio

    2014-03-01

    Nontrivial nodal structures are one of the most salient features of gap functions of the unconventional superconductors. In a system with spin-orbit coupling and crystal field, the group theory plays a key role to determine the node of the gap function. From the group theoretical ground, Blount proved that the line node is ``vanishingly improbable'' in spin-triplet superconductors. Namely, it is impossible to create a stable line node in odd-parity superconductors. Our motivation is to compare the group theoretical result with topological stability of nodes by K-theory As a result, we found that K-theory not only rebuilds the original Blount's argument but also exhibits counterexamples with the stable line node. In this talk, we will show the physical interpretation of them.

  2. Hybrid electronics based InP and high temperature superconductors

    International Nuclear Information System (INIS)

    Current trend in high speed semiconductor electronics towards 77K operation coupled with the recent discovery of high temperature superconductivity above 77K has the potential of realizing ultra high speed electronics operating at 77K. Depending on the properties of high temperature superconductors, both active and passive hybrid superconductor and semiconductor three terminal devices can be fabricated. Using hybrid superconductor/SrF2/InP/SrF2 resonant tunnel transistor structure and a parallel architecture, the authors have designed a super fast 8 x 8 bit digital multiplier/accumulator operating at 77K with a multiplication/accumulation time of 152 ps, which represent the highest possible speed calculated for any multiplex/accumulation circuit reported to date. Processing of such hybrid devices is quite challenging. In this paper in addition to the theoretical results, the authors present preliminary experimental results of high Tc superconducting thin films formed by rapid isothermal assisted MOCVD technique

  3. Angle-dependent vortex structure in a high anisotropy superconductor

    International Nuclear Information System (INIS)

    Angle-dependent muon spin rotation measurements have been made on the organic superconductor κ-(BEDT-TTF)2Cu(SCN)2. Oscillations are observed in the width of the internal field distribution, which are periodic in the perpendicular component of the applied magnetic field, Bz=B cos θ, with a uniform period over a range of angles and fields. These oscillations are superimposed on the standard cos θ scaling expected for the width in a highly anisotropic superconductor. The oscillation period is of order 2 mT and the amplitude is particularly strong at fields comparable with the period. The origin of this novel phenomenon is discussed in terms of the low field instabilities of tilted vortices in this highly anisotropic superconductor

  4. Possible Measurable Effects of Dark Energy in Rotating Superconductors

    Directory of Open Access Journals (Sweden)

    Clovis Jacinto de Matos

    2009-01-01

    Full Text Available We discuss recent laboratory experiments with rotating superconductors and show that three so far unexplained experimentally observed effects (anomalous acceleration signals, anomalous gyroscope signals, Cooper pair mass excess can be physically explained in terms of a possible interaction of dark energy with Cooper pairs. Our approach is based on a Ginzburg-Landau-like model of electromagnetic dark energy, where gravitationally active photons obtain mass in the superconductor. We show that this model can account simultaneously for the anomalous acceleration and anomalous gravitomagnetic fields around rotating superconductors measured by Tajmar et al. and for the anomalous Cooper pair mass in superconductive Niobium, measured by Cabrera and Tate. It is argued that these three different physical effects are ultimately different experimental manifestations of the simultaneous spontaneous breaking of gauge invariance and of the principle of general covariance in superconductive materials.

  5. Angle-resolved heat capacity of heavy fermion superconductors.

    Science.gov (United States)

    Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige

    2016-09-01

    Owing to a strong Coulomb repulsion, heavy electron superconductors mostly have anisotropic gap functions which have nodes for certain directions in the momentum space. Since the nodal structure is closely related to the pairing mechanism, its experimental determination is of primary importance. This article discusses the experimental methods of the gap determination by bulk heat capacity measurements in a rotating magnetic field. The basic idea is based on the fact that the quasiparticle density of states in the vortex state of nodal superconductors is field and direction dependent. We present our recent experimental results of the field-orientation dependence of the heat capacity in heavy fermion superconductors CeTIn5 (T  =  Co, Ir), UPt3, CeCu2Si2, and UBe13 and discuss their gap structures. PMID:27482621

  6. Time-resolved study of Higgs mode in superconductors

    Science.gov (United States)

    Shimano, Ryo

    The behavior of superconductors far from equilibrium has been intensively studied over decades. Goals of these studies are the elucidation of bosonic fluctuations essential for the pairing mechanisms, the manifestation of competing orders or hidden phases, and the optical manipulation of superconductivity. The study of collective modes is crucially important for these perspectives as it provides the information on the dynamics of order parameters in non-equilibirium states. Generally, collective modes in ordered phases associated with spontaneous symmetry breaking are classified into 1) gapless phase modes and 2) gapped amplitude modes. In superconductors, the phase mode is eaten by gauge field, according to the Anderson-Higgs mechanism. The remaining amplitude mode is recently termed as Higgs mode from its analogy to the Higgs boson in particle physics. Despite its long history of investigation, unambiguous observation of Higgs mode has remained elusive. This is because the Higgs mode does not have a charge nor electric dipole and therefore it does not couple directly to the electromagnetic field. Here we report on our recent observation of Higgs mode in s-wave superconductors by using THz-pump and THz-probe spectroscopy technique. After nonadiabatic excitation near the superconducting gap energy with monocycle THz pulses, Higgs mode was observed as oscillations in the transmission of THz probe pulse. The resonant nonlinear coupling between the Higgs mode and coherent radiation field was also discovered, resulting in an efficient third order harmonic generation of the incident THz radiation. The extension of experiments to multiband superconductors and unconventional superconductors will be discussed. Time-resolved study of Higgs mode in superconductors.

  7. Optical studies of crystalline organic superconductors under extreme conditions

    International Nuclear Information System (INIS)

    This thesis reports experiments which involve the interaction of light and matter to probe the properties of crystalline organic superconductors. The organic superconductors of the BEDT-TTF family are prototypical correlated electron systems; their low-temperature ground states are dominated by many-body interactions and their infrared spectra contain contributions typical of an interacting Fermi liquid: single particle excitations, collective modes and multiparticle excitations. Optical measurements hence provide a unique tool for probing these phenomena. Extreme environments, such as low temperature and high hydrostatic pressure, are used to tune the various interaction strengths, providing a link to the superconducting properties. For example, the superconducting transition temperature in κ-(BEDT- TTF)2Cu(SCN)2 falls from 10 K at ambient pressure to 0 at 0.5 GPa. This thesis presents systematic attempts to identify the many-body interactions responsible for superconductivity on these materials. Chapter 1 introduces the samples under investigation and reviews the relevant background theory pertaining to the interaction of light and matter. Chapter 2 discusses experimental techniques, specifically techniques for carrying out infrared and Raman scattering experiments at high pressure and low temperature. Chapter 3 reports the results of the first high-pressure infrared measurement on an organic superconductor, namely κ-(BEDT-TTF)2Cu(SCN)2, the aim being to make an optical measurement of the pressure dependence of the charge carrier effective mass. Chapter 4 concentrates on the vibrational modes of κ-(BEDT-TTF)2Cu(SCN)2. This chapter reports the first Raman scattering experiments on an organic superconductor at high pressure. Comparison of the infrared reflectance and Raman scattering measurements are used to elucidate the role of electron-phonon coupling in this material's superconductivity. Chapter 5 reports the first non-resonant measurements of the GHz

  8. Physical properties of ultrathin films of high-temperature superconductors

    International Nuclear Information System (INIS)

    Electrical transport measurements were carried out on ultrathin films of high temperature superconductor at extremely low temperatures and in high magnetic fields. These films were fabricated by molecular-beam-epitaxy (MBE). Normal state Hall effect measurements were carried out on both ultrathin and thin films. The Hall number (RH(exp -1)) was a linear function of temperature in thin films and was less temperature dependent in ultrathin films. The Hall angle (cot theta(sub H)) on the other hand exhibited the same T2 dependence in both cases, in accordance with Anderson's Luttinger liquid phenomenology. When the transition temperature decreased to zero the Hall number decreased to a limiting value which corresponded approximately to one pair per coherence volume. The superconductor-insulator transition was studied both in zero magnetic field and in a finite magnetic field. The zero field transition was achieved either by considering a sequence of films of decreasing thicknesses, or by successive thermal cycling of a single film in vacuum. The critical resistance was found to be very close to universal constant h/4e(exp 2) (6.5 k-omega). This result supports the notion that the critical resistance in the superconductor-insulator transition in two dimensions is universal. Anomalous magnetoresistance was observed in films having resistances with values near that of zero-field superconductor-insulator transition. This unusual behavior may result from an interaction between carriers and antiferromagnetically ordered Cu2+ spins of the CuO2 planes. Upon application of a magnetic field three successive superconductor-insulator transitions were found. The first two at low critical fields appear to result from the film sheet resistance being modulated by the applied magnetic field, possibly by scattering of the carriers from reorienting spins. The third one may represent the new type of superconductor-insulator transition proposed by Fisher

  9. Shape of the nuclear magnetic resonance line in anisotropic superconductors with an irregular vortex lattice

    International Nuclear Information System (INIS)

    For high-temperature superconductors the shape of a NMR spectrum line is built regarding for variation of inhomogeneity of irregular vortex lattice magnetic field near superconductor surface. It is shown that the shape of a NMR line is not simply widened but noticeably varies depending on the degree of irregularity of a superconductor vortex lattice. This variation is associated with a local symmetry decrease in an irregular vortex lattice of the superconductor. Taking into account these circumstances may considerably change conclusions about the type of a vortex lattice and superconductor parameters which are commonly gained from NMR line shape analysis

  10. Zeroth order phase transition in a holographic superconductor with single impurity

    Directory of Open Access Journals (Sweden)

    Hua Bi Zeng

    2015-08-01

    Full Text Available We investigate the single normal impurity effect in a superconductor by the holographic method. When the size of impurity is much smaller than the host superconductor, we can reproduce the Anderson theorem, which states that a conventional s-wave superconductor is robust to a normal (non-magnetic impurity with small impurity strength. However, by increasing the size of the impurity in a fixed-size host superconductor, we find a decreasing critical temperature Tc of the host superconductor, which agrees with the results in condensed matter literatures. More importantly, the phase transition at the critical impurity strength (or the critical temperature is of zeroth order.

  11. Zeroth Order Phase Transition in a Holographic Superconductor with Single Impurity

    CERN Document Server

    Zeng, Hua Bi

    2014-01-01

    We studied the single normal impurity effect in superconductor by using the holographic method. When the size of impurity is much smaller compared to the host superconductor, we reproduced the Anderson theorem, which states that a conventional s-wave superconductor is robust to a normal (non-magnetic) impurity with small impurity strength or impurities with small concentration. While by increasing the size of impurity in a fixed host superconductor we also find a decrease $T_c$ of the host superconductor, the phase transition at the critical impurity strength is of zeroth order.

  12. XRD spectra of new YBaCuO superconductors

    Indian Academy of Sciences (India)

    S Sujinnapram; P Udomsamuthirun; T Kruaehong; T Nilkamjon; S Ratreng

    2011-08-01

    XRD spectra of new YBaCuO superconductors were studied. There were 2 phases found in our samples, the superconducting phase and the non-superconducting phase. The more non-superconducting phase, the more anisotropy parameters were found. The amount of impurities have no effect on the value of -axis which has a linear relation to the number of Cu-atoms. So the new formula of YBaCuO are the new types of superconductor in this family that have higher -axis than the Y123.

  13. Proposed experimental test of an alternative electrodynamic theory of superconductors

    International Nuclear Information System (INIS)

    Highlights: • A new experimental test of electric screening in superconductors is proposed. • The electric screening length is predicted to be much larger than in normal metals. • The reason this was not seen in earlier experiments is explained. • This is not predicted by the conventional BCS theory of superconductivity. - Abstract: An alternative form of London’s electrodynamic theory of superconductors predicts that the electrostatic screening length is the same as the magnetic penetration depth. We argue that experiments performed to date do not rule out this alternative formulation and propose an experiment to test it. Experimental evidence in its favor would have fundamental implications for the understanding of superconductivity

  14. Superconductor-insulator transition in the presence of Coulomb disorder

    Science.gov (United States)

    Shklovskii, B. I.

    2007-12-01

    Superconductor-insulator transition driven by the decreasing concentration of electrons n is studied in the case of the disorder potential created by randomly positioned charged impurities. Electrons and Cooper pairs (formed by a non-Coulomb attraction) nonlinearly screen the random potential of impurities. Both electrons and Cooper pairs can be delocalized or localized in the resulting self-consistent potential. The border separating the superconductor and insulator phases in the plane of the concentration of electrons and the length of the Cooper pair is found. For a strong disorder, the central segment of this border follows the Bose-Einstein-Condensation-BCS crossover line defined for a clean sample.

  15. Ultrafast non-equilibrium dynamics in conventional and unconventional superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Schnyder, Andreas; Manske, Dirk [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany)

    2010-07-01

    We present simulations of the ultrafast dynamics of conventional and unconventional superconductors using density-matrix theory. In particular, we study how the optical conductivity evolves in response to ultrashort optical pulses in the frequency range of the superconducting gap, i.e., in the terahertz regime. The dominant relaxation process is assumed to be due to electron-phonon collisions. Employing a second order cluster expansion and assuming that the phonons remain equilibrated, Boltzmann type equations for the dynamics of the quasiparticle occupations and coherences are derived. We apply our theoretical model to the study of non-equilibrium dynamics in the two-gap superconductor MgB{sub 2}.

  16. Permanent magnet with MgB2 bulk superconductor

    Science.gov (United States)

    Yamamoto, Akiyasu; Ishihara, Atsushi; Tomita, Masaru; Kishio, Kohji

    2014-07-01

    Superconductors with persistent zero-resistance currents serve as permanent magnets for high-field applications requiring a strong and stable magnetic field, such as magnetic resonance imaging. The recent global helium shortage has quickened research into high-temperature superconductors (HTSs)—materials that can be used without conventional liquid-helium cooling to 4.2 K. Herein, we demonstrate that 40-K-class metallic HTS magnesium diboride (MgB2) makes an excellent permanent bulk magnet, maintaining 3 T at 20 K for 1 week with an extremely high stability (Tesla-class permanent-magnet applications.

  17. On the critical temperatures of superconductors: a quantum gravity approach

    CERN Document Server

    Gregori, Andrea

    2010-01-01

    We consider superconductivity in the light of the quantum gravity theoretical framework introduced in [1]. In this framework, the degree of quantum delocalization depends on the geometry of the energy distribution along space. This results in a dependence of the critical temperature characterizing the transition to the superconducting phase on the complexity of the structure of a superconductor. We consider concrete examples, ranging from low to high temperature superconductors, and discuss how the critical temperature can be predicted once the quantum gravity effects are taken into account.

  18. Hybrid Crystals of Cuprates and Iron-Based Superconductors

    OpenAIRE

    Dai, Xia; Le, Congcong; Wu, Xianxin; Hu, Jiangping

    2016-01-01

    We propose two possible new compounds, Ba$_2$CuO$_2$Fe$_2$As$_2$ and K$_2$CuO$_2$Fe$_2$Se$_2$, which hybridize the building blocks of two high temperature superconductors, cuprates and iron-based superconductors. These compounds consist of square CuO$_2$ layers and antifluorite-type Fe$_2$X$_2$ (X=As,Se) layers separated by Ba/K. The calculations of binding energies and phonon spectrums indicate that they are dynamically stable, which ensures that they may be experimentally synthesized. The F...

  19. Magnetic response of holographic Lifshitz superconductors: Vortex and Droplet solutions

    Science.gov (United States)

    Lala, Arindam

    2014-07-01

    In this paper a holographic model of s-wave superconductor with anisotropic Lifshitz scaling has been considered. In the presence of an external magnetic field our holographic model exhibits both vortex and droplet solutions. Based on analytic methods we have shown that the anisotropy has no effect on the vortex and droplet solutions whereas it may affect the condensation. Our vortex solution closely resembles the Ginzburg-Landau theory and a relation between the upper critical magnetic field and superconducting coherence length has been speculated from this comparison. Using Sturm-Liouville method, the effect of anisotropy on the critical parameters in insulator/superconductor phase transitions has been analyzed.

  20. Magnetic response of holographic Lifshitz superconductors: Vortex and Droplet solutions

    Energy Technology Data Exchange (ETDEWEB)

    Lala, Arindam, E-mail: arindam.lala@bose.res.in

    2014-07-30

    In this paper a holographic model of s-wave superconductor with anisotropic Lifshitz scaling has been considered. In the presence of an external magnetic field our holographic model exhibits both vortex and droplet solutions. Based on analytic methods we have shown that the anisotropy has no effect on the vortex and droplet solutions whereas it may affect the condensation. Our vortex solution closely resembles the Ginzburg–Landau theory and a relation between the upper critical magnetic field and superconducting coherence length has been speculated from this comparison. Using Sturm–Liouville method, the effect of anisotropy on the critical parameters in insulator/superconductor phase transitions has been analyzed.

  1. Magnetic response of holographic Lifshitz superconductors: Vortex and Droplet solutions

    International Nuclear Information System (INIS)

    In this paper a holographic model of s-wave superconductor with anisotropic Lifshitz scaling has been considered. In the presence of an external magnetic field our holographic model exhibits both vortex and droplet solutions. Based on analytic methods we have shown that the anisotropy has no effect on the vortex and droplet solutions whereas it may affect the condensation. Our vortex solution closely resembles the Ginzburg–Landau theory and a relation between the upper critical magnetic field and superconducting coherence length has been speculated from this comparison. Using Sturm–Liouville method, the effect of anisotropy on the critical parameters in insulator/superconductor phase transitions has been analyzed

  2. New superconductors from granular to high T$_{c}$

    CERN Document Server

    Deutscher, Guy

    2006-01-01

    How new are the high Tc superconductors, as compared to the conventional low Tc ones? In what sense are these oxides different from regular metals in their normal state? How different is the mechanism for high Tc superconductivity from the well-known electron-phonon interaction that explains so well superconductivity in metals and alloys? What are the implications of the new features of the high Tc oxides for their practical applications? This book aims to give some answers to those questions, drawing particularly on similarities between the high Tc oxides and granular superconductors, which also present a maximum of their critical temperature near the metal-insulator transition.

  3. Atomic beam study of a superconductor's magnetic vortex lattice

    International Nuclear Information System (INIS)

    We have developed an atomic beam technique for studying magnetic vortices and vortex lattices of superconductors. Atoms moving near a superconductor's surface see a fluctuating magnetic field as they pass vortices. This field may drive magnetic resonance transitions between hyperfine states. Measuring the magnetic resonance transition probability as a function of atom velocity probes the vortex lattice autocorrelation function. We demonstrate this technique by studying the vortex lattice of a niobium film sample and measuring the sample's penetration depth. We also identify a systematic problem that we think thwarted an earlier attempt to experimentally realize this technique. copyright 1997 The American Physical Society

  4. Spins in the vortices of a high-temperature superconductor

    DEFF Research Database (Denmark)

    Lake, B.; Aeppli, G.; Clausen, K.N.; McMorrow, D.F.; Lefmann, K.; Hussey, N.E.; Mangkorntong, N.; Nohara, M.; Takagi, H.; Mason, T.E.; Schröder, A.

    2001-01-01

    Neutron scattering is used to characterize the magnetism of the vortices for the optimally doped high-temperature superconductor La2-xSrxCuO4 (x = 0.163) in an applied magnetic field. As temperature is reduced, Low-frequency spin fluctuations first disappear with the loss of vortex mobility, but...... then reappear. We find that the vortex state can be regarded as an inhomogeneous mixture of a superconducting spin fluid and a material containing a nearly ordered antiferromagnet. These experiments show that as for many other properties of cuprate superconductors, the important underlying microscopic...

  5. Vortex in holographic two-band superfluid/superconductor

    CERN Document Server

    Wu, Mu-Sheng; Zhang, Hai-Qing

    2015-01-01

    We construct numerically static vortex solutions in a holographic model of two-band superconductor with an interband Josephson coupling in both the superfluid and superconductor regime. We investigate the effect of the interband coupling on the order parameter of each superconducting band, and we find that it has different effects on the two bands. We compute the free energy, critical magnetic field, magnetic penetration length and coherence lengths for the two bands, and we study their dependence on the interband coupling and temperature. Interestingly, we find that the coherence lengths of the two bands are close to identical.

  6. Coherent quantum trasport in ferromagnet-superconductor-ferromagnet graphene junctions

    Directory of Open Access Journals (Sweden)

    M Salehi

    2010-09-01

    Full Text Available In this paper, we investigate the coherent quantum transport in grapheme-based ferromagnet-superconductor-ferromagent junctions within the framework of BCS theory using DBdG quasiparticles equation .The coherency with the finite size of superconductor region has two characteristic features subgap electron transport and oscillations of differential conductance. we show that periodic vanishing of the Andreev reflection at the energies called geometrical resonances above the superconducting gap is a striking consequence of quasiparticles interference. We suggest to make devices that produce polarized spin-current with possible applications in spintronics.

  7. Three dimensional reflectance properties of superconductor-dielectric photonic crystal

    Science.gov (United States)

    Pandey, G. N.; Pandey, J. P.; Pandey, U. K.; Sancheti, Bhagyashree; Ojha, S. P.

    2016-05-01

    In this present communication, we have studied the optical properties of Photonics Crystals with super conducting constituent using the TMM method for a stratified medium. We also studied the three dimensional reflectance property of superconductor-dielectric photonic crystal at different temperature and thickness. From above study we show that the superconductor-dielectric photonic crystal may be used as broad band reflector and omnidirectional reflector at low temperature below to the critical temperature. Such property may be applied to make of the reflector which can be used in low temperature region.

  8. Vortex in holographic two-band superfluid/superconductor

    Science.gov (United States)

    Wu, Mu-Sheng; Wu, Shang-Yu; Zhang, Hai-Qing

    2016-05-01

    We construct numerically static vortex solutions in a holographic model of two-band superconductor with an interband Josephson coupling in both the superfluid and superconductor regime. We investigate the effects of the interband coupling on the order parameter of each superconducting band in the vortex solution, and we find that it is different for each of the two bands. We compute also the free energy, critical magnetic field, magnetic penetration length and coherence lengths for the two bands, and we study their dependence on the interband coupling and temperature. Interestingly, we find that the coherence lengths of the two bands are close to identical.

  9. Thermal analysis in the field of high temperature superconductors

    International Nuclear Information System (INIS)

    The thermo-analytical methods of dilatometry, thermogravimetry and mass spectroscopy were used for the examination of the preparation and oxygen stochiometry of superconductors. A considerable increase of the compression of powder pressed saples of the original carbonate/oxide mixture for YBa2Cu3O7 during the sintering process was achieved in the dilatometer by speed-controlled sintering (rate controlled sintering). The oxygen content of superconductors of the type EuBa2Cu3O7 was examined by thermo-gravimetry and mass spectrometry during preparation, tempering, reduction and oxidation. (MM)

  10. Survey of potential electronic applications of high temperature superconductors

    International Nuclear Information System (INIS)

    In this paper the authors present a survey of the potential electronic applications of high temperature superconductor (HTSC) thin films. During the past four years there has been substantial speculation on this topic. The authors will cover only a small fraction of the potential electronic applications that have been identified. Their treatment is influenced by the developments over the past few years in materials and device development and in market analysis. They present their view of the most promising potential applications. Superconductors have two important properties that make them attractive for electronic applications. These are (a) low surface resistance at high frequencies, and (b) the Josephson effect

  11. Argument for E~j relation of hightemperature superconductors

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In high temperature superconductors (HTSC), when magnetic relaxation approaches the equilibrium state and the superconductor is applied with current, the E~j relation is calculated by considering both forward and backward hopping of thermally activated flux (where backward hopping means hopping from the barriers with low energy to the ones with high energy). It is pointed out that the lnE~lnj curve shows positive curvature. And the results are compared with other models. The discussion on the topic that whether ρ approaches zero as j →0 is carried out.

  12. Ultrasonic Properties of the MgB2 Superconductor

    Institute of Scientific and Technical Information of China (English)

    YU Ri-Cheng; JIN Chang-Qing; LI Shao-Chun; WANG Ru-Ju; LI Feng-Ying; LIU Zhen-Xing; ZHU Jia-Lin

    2001-01-01

    The sound velocities of longitudinal and shear waves are measured on a polycrystalline MgB2 superconductor with Tc of 39 K. The specimen used in the experiments is pressed and heated using the MgB2 powder. The elastic moduli, Debye temperature and specific heat at room temperature are obtained based on sound velocity data. The results indicate that the velocities are much higher than those in the usual materials, while elastic constants remain reasonably soft, which may be due to the high transition temperature of the MgB2 superconductor.

  13. Thermomagnetic effects above and below Tc in the cuprate superconductors

    International Nuclear Information System (INIS)

    Two different thermomagnetic transport quantities, the electrothermal conductivity and the Nernst effect are shown to be powerful probes of high-temperature superconductors. In the vortex state below Tc, the electrothermal conductivity is independent of both the magnetic field and the vortex viscosity because it is sensitive only to the properties of the vortex normal cores. Some new data from cuprate superconductors show a surprising, low-field anomaly in the dilute vortex limit. Above Tc in the normal state, it is shown how the Nernst effect is a probe of transport anisotropy around the Fermi surface

  14. High-T/sub c/ superconductor and its use in superconducting magnets

    International Nuclear Information System (INIS)

    Many of the proposed uses for the high-T/sub c/ superconductor involve the creation of a magnetic field using superconducting coils. This report will assess what is known about the high-T/sub c/ superconductors and take a realistic look at their potential use in various kinds of superconducting magnets. Based on what is known about the high-T/sub c/ superconductors, one can make a ''wish list'' of things that will make such materials useful for magnets. Then, the following question is asked. If one had a high-T/sub c/ superconductor with the same properties as modern niobium-titanium superconductor, how would the superconductor work in a magnet environment? Finally, this report will show the potential impact of the ideal high-T/sub c/ superconductor on: 1) accelerator dipole and quadrupole magnets, 2) superconducting magnets for use in space, and 3) superconducting solenoids for magnetic resonance imaging. 78 refs., 11 tabs

  15. Doping effects in high-Tc superconductors

    International Nuclear Information System (INIS)

    The purpose of the project has been to study how the superconducting and magnetic properties of the high temperature superconductors change as function of oxygen stoichiometry and cation doping. The primary system of investigation has been YBa2Cu3O6+x, which has been studied as function of oxygen stoichiometry, 0 2 planes, that is necessary for superconductivity, is strongly depending on structural ordering. The static properties and the kinetics of the structural ordering process have been studied experimentally by neutron and high energy synchrotron x-ray diffraction, by Raman scattering, and by computer simulation technique. Not only the oxygen stoichiometry but also the cation doping has been shown to influence the magnetic phases, in some cases in an unexpected manner. Thus, by neutron diffraction experiments it has been shown that doping with non-magnetic Al gives rise to a new magnetic phase. A theoretical model, has been developed. The magnetic phases of the Cu and Nd ordering in NdBa2Cu3O6+x, and of the Cu and Pr ordering in PrBa2Cu3O6+x have been studied by neutron diffraction with the main purpose of understanding why PrBa2Cu3O6+x is magnetic and non-superconducting for all oxygen stoichiometries. In NdBa:2Cu3O6+x studies of the magnetic flux lattice have been carried out by Small Angle Neutron Scattering. Additional structural studies of the superconducting and magnetic phases of related materials, of RENi2B2C (RE = rare earth), and of oxidized and cation doped materials based on La2CuO4+δ have been carried out. Methods for structural studies and analyses, and equipment for electrical and magnetic characterization have been developed. (EG) 5 tabs., 46 ills., 35 refs

  16. Nonlocal conductivity in type-II superconductors

    International Nuclear Information System (INIS)

    Multiterminal transport measurements on YBa2Cu2O7 crystals in the vortex liquid regime have shown nonlocal conductivity on length scales up to 50 microns. Motivated by these results we explore the wave vector (k) dependence of the dc conductivity tensor, σμν(k), in the Meissner, vortex lattice, and disordered phases of a type-II superconductor. Our results are based on time-dependent Ginzburg-Landau (TDGL) theory and on phenomenological arguments. We find four qualitatively different types of behavior. First, in the Meissner phase, the conductivity is infinite at k=0 and is a continuous function of k, monotonically decreasing with increasing k. Second, in the vortex-lattice phase, in the absence of pinning, the conductivity is finite (due to flux flow) at k=0; it is discontinuous there and remains qualitatively like the Meissner phase for k>0. Third, in the vortex liquid regime in a magnetic field and at low temperature, the conductivity is finite, smooth and nonmonotonic, first increasing with k at small k and then decreasing at larger k. This third behavior is expected to apply at temperatures just above the melting transition of the vortex lattice, where the vortex liquid shows strong short-range order and a large viscosity. Finally, at higher temperatures in the disordered phase, the conductivity is finite, smooth and again monotonically decreasing with k. This last, monotonic behavior applies in zero magnetic field for the entire disordered phase, i.e., at all temperatures above Tc, while in a field the nonmonotonic behavior may occur in a low-temperature portion of the disordered phase

  17. Electrodeposition on cuprate-based superconductors in nonaqueous media

    International Nuclear Information System (INIS)

    Electrodeposition of metallic protection layers on the Ba2YCu3O7 high -Tc superconductor has been carried out in non-aqueous electrolytes based on the organic solvents acetonitrile, methanol, and propylene carbonate. By lowering the reactivity of the solvent to the strongly oxidized superconductor, the range of potential accessible to cathodic reactions can be extended. In acetonitrile, films of silver, copper, lead, and tin can be deposited, whereas in water it is difficult to achieve more than silver deposits because of the ready reduction of the cuprate compound. Electrochemical techniques with rotating disk and ring-disk electrodes in the nonaqueous electrolytes gave clear voltammetric evidence for the deposition of the metals, their anodic stripping from the substrate, and the ability to cycle the superconductor between plated and uncovered states. Optical microscopy, scanning electron micrographs, and energy dispersive x-ray measurements were used to support the conclusion of high-coverage, microcrystalline metal contacting layers being achieved on the superconductor substrate

  18. Vortex dynamics in the high-temperature superconductors

    International Nuclear Information System (INIS)

    Some fundamental aspects of the structure and dynamics of vortices in the high-temperature superconductors are discussed. New methods for calculating the static and dynamic magnetic field profiles in thin samples in time-varying perpendicular applied magnetic fields are described

  19. Lattice investigation of dual superconductor mechanism of confinement

    International Nuclear Information System (INIS)

    We investigate the dual superconductor mechanism of confinement in lattice SU(2). We focus on the the dual Meissner effect in the maximally abelian gauge. In particular we measure the penetration depth of the maximally Abelian photon fields and the size of flux tube between static quark charges by using the abelian projected links. (orig.)

  20. Recipe for high-Tc transition-metal chalcogenide superconductors

    International Nuclear Information System (INIS)

    The conditions for the occurrence of superconductivity in cuprates are enumerated. There is a minimum of seven, which are discussed in some detail. They may be taken as a recipe in the search for superconductors at elevated temperature with other transition-metal chalcogenide compounds. (orig.)

  1. Spin dynamics in high-$T_C$ superconductors

    OpenAIRE

    Bourges, Ph.; Y. Sidis; Fong, H. F.; Keimer, B.; Regnault, L. P.; Bossy, J.; Ivanov, A. S.; Milius, D. L.; Aksay, I. A.

    1999-01-01

    Key features of antiferromagnetic dynamical correlations in high-$T_C$ superconductors cuprates are discussed. In underdoped regime, the sharp resonance peak, occuring exclusively in the SC state, is accompanied by a broader contribution located around $\\sim$ 30 meV which remains above $T_C$. Their interplay may induce incommensurate structure in the superconducting state.

  2. Plasma resonance in anisotropic layered high-Tc superconductors

    DEFF Research Database (Denmark)

    Sakai, Shigeki; Pedersen, Niels Falsig

    1999-01-01

    The plasma resonance is described theoretically by the inductive coupling model for a large stacked Josephson-junction system such as the intrinsic Josephson-junction array in anisotropic high- T-c superconductors. Eigenmodes of the plasma oscillation are analytically described and a numerical...

  3. Niobium-3-tin internally cooled cabled superconductor (ICCS) technology I

    International Nuclear Information System (INIS)

    Recent work, using tantalum and Incoloy 903 sheathing has demonstrated that internally cooled, cabled superconductors (ICCS) can be compacted without current degradation. This paper compares Inconel 617 sheathing to previous results. Inconel 617 is a practical engineering material with a thermal contraction lying between stainless steel and Incoloy 903

  4. NIOBIUM-3-TIN INTERNALLY COOLED CABLED SUPERCONDUCTOR (ICCS) TECHNOLOGY I

    OpenAIRE

    Hoenig, M.; Steeves, M.; Cyders, C.

    1984-01-01

    Recent work, using tantalum and Incoloy 903 sheathing has demonstrated that internally cooled, cabled superconductors (ICCS) can be compacted without current degradation. This paper compares Inconel 617 sheathing to previous results. Inconel 617 is a practical engineering material with a thermal contraction lying between stainless steel and Incoloy 903.

  5. The mass spectrum of Diquark Boson in the color superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Yamaguchi, K.; Miyamura, O. [Hiroshima Univ., Dept. of Physics, Higashi-Hiroshima, Hiroshima (Japan)

    2000-08-01

    In this work we apply the functional integral method to the study of the color superconducting phase and compute the mass spectrum of the Diquark Boson at finite temperature and nonzero chemical potential. We find the different aspect with QED superconductor. (author)

  6. Fermi surfaces and energy gaps of high-temperature superconductors

    International Nuclear Information System (INIS)

    In this short paper, the authors describe their recent experimental results from high-temperature superconductors. In the normal state, the data reveals interesting features of the Fermi surfaces and low energy excitations near the Fermi level. In the superconducting state, the data shows a very strong anisotropy in the superconducting gap

  7. Organic conductor/high-Tc superconductor bilayer structures

    International Nuclear Information System (INIS)

    Electrochemical techniques are exploited to fabricate conducive polymer/high-Tc superconductor bilayer structures. Scanning electron microscopy and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto YBa2Cu3O7-δ films. In such hybrid polymer/superconductor systems, it is found that when the polymer is oxidized to its conductive state, the transition temperature (Tc) and critical currents (Jc) of the underlying superconductor films are suppressed. Reversible modulation of the values of the transition temperatures of up to 50 K are noted for these structures. Upon reduction of the conductive polymer layer back to its non-conductive form, both Tc and Jc are found to return to values close to those acquired for the underivatized YBa2Cu3O7-δ films. Moreover, measurements as a function of temperature of the polymer/superconductor interface resistance show dramatic decrease in this value at Tc. Also, estimates of superconducting coherence lengths within the organic conductor samples suggest superconducting properties over macroscopically large distances within the organic materials can be expected. Collectively these results are consistent with the first observation of a conductive polymer proximity effect

  8. Effect of barium cuprate on high temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Seyoum, H.M. [Department of Physics, University of the District of Columbia, 4200 Connecticut Avenue N.W., Washington, D.C. 20008 (United States); Melamud, M. [Nuclear Research Center-Negev, Beer-Sheva 84190 (Israel); Wong-Ng, W.; Bennett, L.H.; Swartzendruber, L.J.; Cook, L.; Brown, H.J. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

    1997-04-01

    BaCuO{sub 2} has a pronounced effect on the magnetization data of high-{ital T{sub c}} superconductors. By subtracting the estimated magnetic contribution of BaCuO{sub 2} present in the superconducting samples, the susceptibility is seen to be purely diamagnetic. {copyright} {ital 1997 American Institute of Physics.}

  9. Effect of barium cuprate on high temperature superconductors

    International Nuclear Information System (INIS)

    BaCuO2 has a pronounced effect on the magnetization data of high-Tc superconductors. By subtracting the estimated magnetic contribution of BaCuO2 present in the superconducting samples, the susceptibility is seen to be purely diamagnetic. copyright 1997 American Institute of Physics

  10. Conditions for thermal stabilization of the superconductor's critical state

    Science.gov (United States)

    Romanovskii, V. R.

    2013-05-01

    Conditions for thermal stabilization of the electrodynamic states of a superconductor are studied. The macroscopic states are simulated in the nonisothermal approximation by numerically solving a set of the Fourier and Maxwell equations with the magnetic flux penetration boundary unknown. Stability criteria for the critical state described by the viscous flow model are formulated. The results are compared with those following from the isothermal theory. It is shown that errors inherent in the isothermal approximation are significant for a thermally insulated superconductor. Therefore, the well-known adiabatic criterion of stability formulated in the isothermal approximation limits the domain of stable states, since a correct determination of conditions for the superconducting-normal state transition must take into account the thermal history of the stable superconducting state formation. On the whole, the error of loss calculation in the isothermal approximation increases when the heat transfer coefficient decreases or an external magnetic field sweep and the size of the superconductor's cross section increases. On the other hand, nonisothermal stability conditions expand the variety of allowable states, since they include conditions that links the currently developed theory of thermomagnetic instability, the theory of losses, and the theory of a superconductor's thermal stabilization.

  11. Quantum creep in a highly crystalline two-dimensional superconductor

    Science.gov (United States)

    Saito, Yu; Kasahara, Yuichi; Ye, Jianting; Iwasa, Yoshihiro; Nojima, Tsutomu

    Conventional studies on quantum phase transitions, especially on superconductor-insulator or superconductor-metal-insulator transitions have been performed in deposited metallic thin films such as Bismuth or MoGe. Although the techniques of thin films deposition have been considerably improved, unintentional disorder such as impurities and deficiencies, generating the pinning centers, seems to still exist in such systems. The mechanical exfoliated highly crystalline two-dimensional material can be a good candidate to realize a less-disordered 2D superconductor with extremely weak pinning, combined with transfer method or ionic-liquid gating. We report on the quantum metal, namely, magnetic-field-induced metallic state observed in an ion-gated two-dimensional superconductor based on an ultra-highly crystalline layered band insulator, ZrNCl. We found that the superconducting state is extremely fragile against external magnetic fields; that is, zero resistance state immediately disappears, once an external magnetic field switches on. This is because the present system is relatively clean and the pinning potential is extremely weak, which cause quantum tunneling and flux flow of vortices, resulting in metallic ground state.

  12. Numerical analysis of thermally actuated magnets for magnetization of superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Li Quan; Yan Yu; Rawlings, Colin; Coombs, Tim, E-mail: ql229@cam.ac.u [EPEC Superconductivity Group, Engineering Department, University of Cambridge, Trumpington Street. Cambridge, CB2 1PZ (United Kingdom)

    2010-06-01

    Superconductors, such as YBCO bulks, have extremely high potential magnetic flux densities, comparing to rare earth magnets. Therefore, the magnetization of superconductors has attracted broad attention and contribution from both academic research and industry. In this paper, a novel technique is proposed to magnetize superconductors. Unusually, instead of using high magnetic fields and pulses, repeatedly magnetic waves with strength of as low as rare earth magnets are applied. These magnetic waves, generated by thermally controlling a Gadolinium (Gd) bulk with a rare earth magnet underneath, travel over the flat surface of a YBCO bulk and get trapped little by little. Thus, a very small magnetic field can be used to build up a very large magnetic field. In this paper, the modelling results of thermally actuated magnetic waves are presented showing how to transfer sequentially applied thermal pulses into magnetic waves. The experiment results of the magnetization of YBCO bulk are also presented to demonstrate how superconductors are progressively magnetized by small magnetic field

  13. Controlling the flux dynamics in superconductors by nanostructured magnetic arrays

    Science.gov (United States)

    Kapra, Andrey

    In this thesis we investigate theoretically how the critical current jc of nano-engineered mesoscopic superconducting film can be improved and how one can control the dynamics of the magnetic flux, e.g., the transition from flux-pinned to flux-flow regime, using arrays of magnetic nanostructures. In particularly we investigate: (1) Vortex transport phenomena in superconductors with deposited ferromagnetic structures on top, and the influence of the sample geometry on the critical parameters and on the vortex configurations. Changing geometry of the magnetic bars and magnetization of the bars will affect the critical current jc of the superconducting film. Such nanostructured ferromagnets strongly alter the vortex structure in its neighborhood. The influence of geometry, position and magnetization of the ferromagnet (single bar or regular lattice of the bars) on the critical parameters of the superconductor is investigated. (2) Effect of flux confinement in narrow superconducting channels with zigzag-shaped banks: the flux motion is confined in the transverse (perpendicular) direction of a diamond-cell-shape channel. The matching effect for the magnetic flux is found in the system relevantless of boundary condition. We discuss the dynamics of vortices in the samples and vortex pattern formation in the channel. We show how the inclusion of higher-Tc superconductor into the sample can lead to enhanced properties of the system. By adding an external driving force, we study the vortex dynamics. The different dynamic regimes are discussed. They allowed an effective control of magnetic flux in superconductors.

  14. Proceedings, phenomenology and applications of high temperature superconductors

    International Nuclear Information System (INIS)

    Phenomenology and Applications of High Temperature Superconductors, The Los Alamos Symposium: 1991, was sponsored by the Los Alamos National Laboratory, Center for Materials Science, the Advanced Studies Program on High Temperature Superconductivity Theory (ASP) and the Exploratory Research and Development Center. This is the second symposium in the series. High Temperature Superconductivity, The Los Alamos Symposium: 1989, also published by Addison Wesley, focused on the cutting-edge theoretical and experimental issues in high temperature superconductors. This symposium, with its focus on the phenomenology and applications of high temperature superconductors, gives a complementary review of the aspects of the field closely related to the impact of high temperature superconductors on technology. The objective of ASP is to advance the field on a broad front with no specific point of view by bringing a team of leading academic theorists into a joint effort with the theoretical and experimental scientists of a major DOE national laboratory. The ASP consisted of fellows led by Robert Schrieffer (UCSB and now FSU) joined by David Pines (University of illinois), Elihu Abrahams (Rutgers), Sebastian Doniach (Stanford), and Maurice Rice (ETH, Zurich) and theoretical and experimental staff of Los Alamos National Laboratory. This synergism of academic, laboratory, theoretical and experimental research produced a level of interaction and excitement that would not be possible otherwise. This publication and the previous one in the series are just examples of how this approach to advancing science can achieve significant contributions

  15. Advanced nuclear materials development -Development of superconductor application technology-

    International Nuclear Information System (INIS)

    Fabrication of high Tc bulk superconductor and its application, fabrication of superconducting wire for electric power device and analysis for cryogenic system were carried out for developing superconductor application technologies for electric power system. High quality YBaCuO bulk superconductor was fabricated by controlling initial powder preparation process and prototype fly wheel energy storage device was designed basically. The superconducting levitation force measuring device was made to examine the property of prepared superconductor specimen. Systematic studies on the method of starting powder preparation, mechanical fabrication process, heat treatment condition and analysis of plastic deformation were carried out to increase the stability and reproducibility of superconducting wire. A starting powder with good reactivity and fine particle size was obtained by emulsion drying method. Ag/BSCCO tape with good cross sectional shape and Tc of 16,000 A/cm2 was fabricated by applying CIP packing procedure. Multifilamentary wire with the Jc of approx. 10000 A/cm2 was fabricated by rolling method using square billet as starting shape. The joining of the multifilament wire was done by etching and pressing process and showed 50% of joining efficiency. Analysis on the heat loss in cryostat for high Tc superconducting device was carried out for optimum design of the future cryogenic system. 126 figs, 14 tabs, 214 refs. (Author)

  16. Point-contact spectroscopy on heavy-fermion superconductors

    International Nuclear Information System (INIS)

    Hints at unconventional superconductivity are present in many heavy-fermion superconductors. Among other methods, point-contact spectroscopy is an important tool to study the symmetry and the nodal structure of the energy gap of unconventional superconductors. Andreev reflection of charge carriers at the interface between a normal metal and a superconductor is the main mechanism for a current at low bias through a nanosized constriction, leading to maxima in the differential conductance dI/dV vs. V. The position of the maxima depends not only on the size of the gap along given directions, but also on the order-parameter symmetry, the microscopic details of the contact and the barrier strength. In addition, if the order parameter exhibits a sign change, an Andreev surface bound state leads to a conductance anomaly at zero bias. We will review recent developments in this field and focus particularly on investigations of CeCoIn5, a possible d-wave superconductor

  17. Point-contact spectroscopy on heavy-fermion superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Goll, G. [Physikalisches Institut, Universitaet Karlsruhe, D-76128-Karlsruhe (Germany)]. E-mail: gernot.goll@phys.uni-karlsruhe.de; Brugger, T. [Physikalisches Institut, Universitaet Karlsruhe, D-76128-Karlsruhe (Germany); Marz, M. [Physikalisches Institut, Universitaet Karlsruhe, D-76128-Karlsruhe (Germany); Kontermann, S. [Physikalisches Institut, Universitaet Karlsruhe, D-76128-Karlsruhe (Germany); Loehneysen, H. von [Physikalisches Institut, Universitaet Karlsruhe, D-76128-Karlsruhe (Germany) and Forschungszentrum Karlsruhe, Institut fuer Festkoerperphysik, D-76021 Karlsruhe (Germany); Sayles, T. [Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA 92093 (United States); Maple, M.B. [Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA 92093 (United States)

    2006-05-01

    Hints at unconventional superconductivity are present in many heavy-fermion superconductors. Among other methods, point-contact spectroscopy is an important tool to study the symmetry and the nodal structure of the energy gap of unconventional superconductors. Andreev reflection of charge carriers at the interface between a normal metal and a superconductor is the main mechanism for a current at low bias through a nanosized constriction, leading to maxima in the differential conductance dI/dV vs. V. The position of the maxima depends not only on the size of the gap along given directions, but also on the order-parameter symmetry, the microscopic details of the contact and the barrier strength. In addition, if the order parameter exhibits a sign change, an Andreev surface bound state leads to a conductance anomaly at zero bias. We will review recent developments in this field and focus particularly on investigations of CeCoIn{sub 5}, a possible d-wave superconductor.

  18. Non-conventional Superconductors and diluted Ising Model

    CERN Document Server

    Ni, Xuan Zhong

    2016-01-01

    This paper demonstrates that the results of a Monte Carlo simulation of a diluted 2D Ising antiferromagnetic system corresponds with the phase diagram for non conventional superconductors. An energy gap of this system is defined. We also find a strange phenomenon that when the lattice size of simulation increased the crystal structure becomes more like quasi crystal at the low temperature.

  19. YBCO bulk superconductors doped with gadolinium and samarium

    Czech Academy of Sciences Publication Activity Database

    Volochová, D.; Piovarči, S.; Radušovská, M.; Antal, V.; Kováč, J.; Jurek, Karel; Jirsa, Miloš; Diko, P.

    2013-01-01

    Roč. 494, NOV (2013), s. 36-40. ISSN 0921-4534 Institutional support: RVO:68378271 Keywords : YBCO bulk superconductors * critical temperature * critical current density * peak effect Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.110, year: 2013

  20. Research On Bi-Based High-Temperature Superconductors

    Science.gov (United States)

    Banks, Curtis; Doane, George B., III; Golben, John

    1993-01-01

    Brief report describes effects of melt sintering on Bi-based high-temperature superconductor system, as well as use of vibrating-sample magnetometer to determine hysteresis curves at 77 K for partially melt-sintered samples. Also discussed is production of high-temperature superconducting thin films by laser ablation: such films potentially useful in detection of signals of very low power.

  1. Hard gap in a normal layer coupled to a superconductor

    Science.gov (United States)

    Reeg, Christopher R.; Maslov, Dmitrii L.

    2016-07-01

    The ability to induce a sizable gap in the excitation spectrum of a normal layer placed in contact with a conventional superconductor has become increasingly important in recent years in the context of engineering a topological superconductor. The quasiclassical theory of the proximity effect shows that Andreev reflection at the superconductor/normal interface induces a nonzero pairing amplitude in the metal but does not endow it with a gap. Conversely, when the normal layer is atomically thin, the tunneling of Cooper pairs induces an excitation gap that can be as large as the bulk gap of the superconductor. We study how these two seemingly different views of the proximity effect evolve into one another as the thickness of the normal layer is changed. We show that a fully quantum-mechanical treatment of the problem predicts that the induced gap is always finite but falls off with the thickness of the normal layer d . If d is less than a certain crossover scale, which is much larger than the Fermi wavelength, the induced gap is comparable to the bulk gap. As a result, a sizable excitation gap can be induced in normal layers that are much thicker than the Fermi wavelength.

  2. Do superconductors change as fast as possible when quenched?

    DEFF Research Database (Denmark)

    Rivers, Ray; Monaco, Roberto; Mygind, Jesper; Aarøe, Morten; Koshelets, Valery

    2008-01-01

    If superconductors change as fast as possible as they pass through a phase transition, then the initial domain structure is constrained by causality. We shall see that Josephson junctions do indeed display such behaviour. However, we shall argue that causal bounds arise through the Gaussian nature...

  3. Observation of Antiferromagnetic Resonance in an Organic Superconductor

    DEFF Research Database (Denmark)

    Torrance, J. B.; Pedersen, H. J.; Bechgaard, K.

    1982-01-01

    Anomalous microwave absorption has been observed in the organic superconductor TMTSF2AsF6 (TMTSF: tetramethyltetraselenafulvalene) below its metal-nonmetal transition near 12 K. This absorption is unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin...

  4. Analytic study on backreacting holographic superconductors with dark matter sector

    CERN Document Server

    Nakonieczny, Lukasz

    2014-01-01

    The variational method for Sturm-Liouville eigenvalue problem was employed to study analytically properties of the holographic superconductor with dark matter sector, in which a coupling between Maxwell field and another U(1)-gauge field was considered. The backreaction of the dark matter sector on gravitational background in question was also examined.

  5. Current-Voltage Characteristics of Quasi-One-Dimensional Superconductors

    DEFF Research Database (Denmark)

    Vodolazov, D.Y.; Peeters, F.M.; Piraux, L.; Mátéfi-Tempfli, Stefan; Michotte, S.

    2003-01-01

    The current-voltage (I-V) characteristics of quasi-one-dimensional superconductors were discussed. The I-V characteristics exhibited an unusual S behavior. The dynamics of superconducting condensate and the existence of two different critical currents resulted in such an unusual behavior....

  6. High temperature superconductors wires and cables: technologies of energy conversion

    International Nuclear Information System (INIS)

    Emerging technologies of high temperature superconductors (HTSrs) have an enormous potential for improving capacity of underground and overhead power T and D systems, motors, generators and power plants - because higher Jc and zero resistance of HTSrs reduce losses and can replace losses and can replace conventional conductors. (author)

  7. Conductivity of Holographic Superconductor within Ginzburg–Landau Theory

    Indian Academy of Sciences (India)

    Lei Liao; Yuan Chen

    2014-09-01

    The frequency-dependent conductivity is obtained for the holographic superconductor by using the Ginzburg–Landau theory with a |Ψ|4 term. Our results show that |Ψ|4 term plays a role in the low-temperature behaviour of the conductivity.

  8. Measuring Thermal Diffusivity Of A High-Tc Superconductor

    Science.gov (United States)

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

    1992-01-01

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

  9. Basic thin film processing for high-Tc superconductors

    International Nuclear Information System (INIS)

    Much attention has been paid for the thin films of perovskite-type oxides especially for the thin films of the high-Tc superconducting ceramics. Historically the thin films of the perovskite-type oxides have been studied as a basic research for ferroelectric materials. Thin films of BaTiO3 and PbTiO3 were tried to deposited and there ferroelectricity was evaluated. Recently this kind of perovskite thin films, including PZT (PbTiO3-PbZrO3) and PLZT [(Pb, La) (Zr, T)O3] have been studied in relation to the synthesis of thin film dielectrics, pyroelectrics, piezoelectrics, electro-optic materials, and acousto-optic materials. Thin films of BPB (BaPbO3- BaBiO3) were studied as oxide superconductors. At present the thin films of the rare-earth high-Tc superconductors of LSC (La1-xSrxCuO4) and YBC (YBa2Cu3O7-δ) have been successfully synthesized owing to the previous studies on the ferroelectric thin films of the perovskite- type oxides. Similar to the rare-earth high-Tc superconductors thin films of the rare-earth-free high-Tc superconductors of BSCC (Bi-Sr-Ca-Cu-O)9 and TBCC (Tl- Ba-Ca-Cu-O)10 system have been synthesized. In this section the basic processes for the fabrication of the high- Tc perovskite superconducting thin films are described

  10. Neutron-diffraction investigations of flux-lines in superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Forgan, E.M. [Birmingham Univ. (United Kingdom); Lee, S.L. [Saint Andrews Univ. (United Kingdom); McKPaul, D. [Warwick Univ., Coventry (United Kingdom); Mook, H.A. [Oak Ridge National Lab., TN (United States); Cubitt, R. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

    1997-04-01

    SANS has proved an extremely useful tool for investigating flux-line structures within the bulk of superconductors. With high-T{sub c} materials, the scattered intensities are weak, but careful measurements are giving important new information about flux lattices, flux pinning and flux-lattice melting. (author). 10 refs.

  11. Coherent and correlated spin transport in nanoscale superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Morten, Jan Petter

    2008-03-15

    Motivated by the desire for better understanding of nano electronic systems, we theoretically study the conductance and noise characteristics of current flow between superconductors, ferromagnets, and normal-metals. Such nano structures can reveal information about superconductor proximity effects, spin-relaxation processes, and spintronic effects with potential applications for different areas of mesoscopic physics. We employ the quasiclassical theory of superconductivity in the Keldysh formalism, and calculate the nonequilibrium transport of spin and charge using various approaches like the circuit theory of quantum transport and full counting statistics. For two of the studied structures, we have been able to compare our theory to experimental data and obtain good agreement. Transport and relaxation of spin polarized current in superconductors is governed by energy-dependent transport coefficients and spin-flip rates which are determined by quantum interference effects. We calculate the resulting temperature-dependent spin flow in ferromagnet-superconductor devices. Experimental data for spin accumulation and spin relaxation in a superconducting nano wire is in agreement with the theory, and allows for a spin-flip spectroscopy that determines the dominant mechanism for spin-flip relaxation in the studied samples. A ferromagnet precessing under resonance conditions can give rise to pure spin current injection into superconductors. We find that the absorbed spin current is measurable as a temperature dependent Gilbert damping, which we calculate and compare to experimental data. Crossed Andreev reflection denotes superconducting pairing of electrons flowing from different normal-metal or ferromagnet terminals into a superconductor. We calculate the nonlocal currents resulting from this process in competition with direct electron transport between the normal-metal terminals. We take dephasing into account, and study the nonlocal current when the types of contact in

  12. Unconventional properties of non-centrosymmetric superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Klam, Ludwig

    2010-10-28

    A kinetic theory for non-centrosymmetric superconductors (NCS) is formulated for low temperatures and in the clean limit. The transport equations are solved quite generally for any kind of antisymmetric spin-orbit coupling (ASOC) in an extended momentum and frequency range. The result is a particle-hole symmetric, gauge-invariant and charge conserving description, which is used to calculate the current response, the specific heat capacity, and the Raman response function. A detailed analysis of the gauge invariance and the associated phase fluctuations of the superconducting order parameter revealed two gauge modes: the Anderson-Bogoliubov mode on the one side and a new gauge mode on the other side, which strongly depends on the symmetry of the ASOC. As application of the kinetic theory, the polarization-dependence of the T = 0 electronic Raman response in NCS is studied for two important classes of ASOC with the representative systems CePt{sub 3}Si and Li{sub 2}Pd{sub x}Pt{sub 3-x}B. Analytical expressions for the Raman vertices are derived, and the frequency power laws and pair-breaking peaks are calculated. A characteristic two- peak structure is predicted for NCS and might serve as an indicator for the unknown relative magnitude of the singlet and triplet contributions to the superconducting order parameter. An efficient numerical method is introduced in order to calculate the dynamical spin and charge response of CePt{sub 3}Si, using an itinerant description for the electrons. With a realistic parameterization of the band structure, the nesting function, inelastic neutron scattering cross sections, and Kohn anomalies are calculated for a selected band in the normal non-magnetic state. From the spin and charge susceptibility, a superconducting pairing interaction is constructed for the weak-coupling gap equation. A sign analysis of the decoupled gap equation supports the experimental evidence of a strong triplet contribution to the order parameter in CePt{sub 3

  13. American superconductor: Combining development expertise with market savvy

    International Nuclear Information System (INIS)

    In 1986, scientists at IBM's Zurich Research Laboratory made one of the most important discoveries in science: high temperature superconductors (HS). This new class of ceramic conducts electricity with little or no resistance, at temperatures that are maintainable with existing, convenient cooling technologies. Transforming these brittle ceramic HTS material into commercially viable wires and wire products is the mission of American Superconductor Corporation (ASC), founded in 1987 and now the leading US company in the HTS market. ASC is focusing on the development of superconductor wires and wire products for such applications as power transmission cables, electric motors, and magnetic energy storage devices. Recently American superconductor corporation announced the signing of an agreement with Hoechst AG of Germany that will enable further advances in its techniques for manufacturing of superconductor wires. The company has also joined forces with several national laboratories in a Wire Development Group. This group includes representatives from Argonne, Los Alamos, and Oak Ridge National Laboratories, as well as the University of Wisconsin Applied Superconductivity Center. With this type of support, ASC is realizing dramatic progress. In 1992, the company began daily production of 300-foot long wires; by the end of 1993, ASC expects to produce wires ten times that length. With Pirelli, ASC has produced three-foot long prototype multistrand conductors which already transmit up to 500 Amps of current at 77K, a significant fraction of the operating current anticipated for commercial power transmission cables. By the middle of 1994, the company expects to deliver 100-foot long multistrand conductors operating at 77K, and transmitting 1,000 Amps

  14. Analytical description of AC losses for high temperature superconductors

    International Nuclear Information System (INIS)

    Full text: AC losses for high temperature superconductors have been calculated by considering the effects of the temperature distribution and the flux flow resistance. Maxwell's equations and thermal diffusion equation are used to calculate the distribution of magnetic field and the temperature inside the superconductors, respectively. The flux flow effect on the AC losses is calculated by using the extended critical state model. An analytical expression of the AC losses is obtained using a superposition approximation in which the cases of complete and incomplete magnetic field penetration have been distinguished. The expression can well explain the experimental observations of the frequency dependence of the AC losses per cycle in high temperature superconductors. It is clearly shown from the analytical expression that the effect of the thermal distribution inside the superconductors is different from the effect caused by flux flow resistance. In the case of incomplete magnetic penetration, the temperature distribution results in the increase of the AC losses per cycle upon frequency whereas the flux flow leads to the decrease of the AC losses per cycle upon frequency. In the case of complete magnetic penetration the results are opposite to those in the previous case. Due to the extremely strong flux flow in high temperature superconducting materials, the effect of the flux flow on the AC losses is dominant, and the overall dependence of AC losses per cycle upon frequency is controlled by the flux flow. On the other hand, because the inhomogeneous distribution of the temperature inside the superconductors which is normal higher in the center than near the edge, there is an upper limit for the frequency beyond which the superconductivity will be totally destroyed by AC losses. Analytical expressions for the critical frequency, distributions of magnetic field and critical current density are also obtained

  15. Experimental Signatures of Orbital Fluctuations in Iron Based Superconductors

    Science.gov (United States)

    Lee, Wei-Cheng

    2015-03-01

    Understanding the high temperature superconductivity has been one of main subjects in the condensed matter physics. The discovery of new classes of high-temperature superconductors, iron pnictides in 2008, launched an international wave of research in the past few years. While the magnetic interactions are certainly important in these materials, there have been significant evidences suggesting that the orbital degrees of freedom could play an important role as well. In this talk, I will demonstrate that the orbital degrees of freedom do play a significant role in physical properties of iron-based superconductors. At the level of single particle properties, while the orbital order in the quasi-1D dxz and dyz bands has been proposed to be a possible driving mechanism for the structural phase transition, our study shows that the fluctuations associated with the orbital order could further drive a non-Fermi liquid behavior in the critical region of the orbital ordering phase transition. I will show that this non-Fermi liquid behavior could induce a zero-bias anomaly in the point contact spectroscopy, which has been observed in a variety of iron based superconductors. As for the magnetic properties, we also find that the orbital order and fluctuations can qualitatively change the nature of the spin excitation spectrum, giving rise to the novel incommensurate-to-commensurate transformation observed in a recent neutron scattering measurement. In the superconducting state, we predict that a new collective excitation, termed as orbital resonance mode, could exist generally in the iron-based superconductors, which in principle can be measured by Raman spectroscopy. Our findings offer a new perspective on the pairing mechanism of iron based superconductors, and suggest that orbital degrees of freedom could provide a new route to high temperature superconductivity.

  16. Amplitude control of spin-triplet supercurrent in superconductor/ferromagnet/superconductor Josephson junctions

    Science.gov (United States)

    Martinez, William M.

    When a conventional superconductor (S) is placed in contact with a ferromagnet (F), the decay length of the pair correlations in the ferromagnet is very short, on the order of a nm in a strong ferromagnet such as Co or Fe. This is due to the spin-polarized nature of the ferromagnet, whereas the spins of Cooper pairs in a conventional superconductor are anti-aligned in a spin-singlet state. However, in 2001, theorists predicted that long-range pair correlations in a spin-triplet state could be generated through magnetic inhomogeneity. With parallel spins, the decay length of these correlations extends in principle to that of a superconductor-normal metal system, which can be on the order of a micron at sufficiently low temperature. This effect has been observed experimentally by several groups, commonly through the use of extrinsic magnetic inhomogeneity in samples with multiple magnetic layers. Josephson junction measurements have demonstrated critical currents orders of magnitude larger in samples with this inhomogeneity compared to samples without. However, the ability to reliably control the spin-state of the pair correlations in a single sample has yet to be realized. The goal of this work is to perform measurements on Josephson junctions in which the inhomogeneity can be manipulated. Our approach is to fabricate S/F'/F/F"/S Josephson junctions where we can control the relative magnetization orientations of all three ferromagnetic layers. In order to realize this control, we first had to perform studies to characterize various magnetic materials, most notably a NiFe alloy similar to Permalloy and Co/Ru/Co, a synthetic antiferromagnet. Studies of the NiFe have demonstrated its ability to be used as a spin-triplet generator. Measurements have also been taken of NiFe films to determine how easily its magnetization direction can be rotated in an external field. We have also measured the magnetic hardness of Co/Ru/Co synthetic antiferromagnets as a function of the

  17. Effective Ginzburg-Landau free energy functional for multi-band isotropic superconductors

    Science.gov (United States)

    Grigorishin, Konstantin V.

    2016-04-01

    It has been shown that interband mixing of gradients of two order parameters (drag effect) in an isotropic bulk two-band superconductor plays important role - such a quantity of the intergradients coupling exists that the two-band superconductor is characterized with a single coherence length and a single Ginzburg-Landau (GL) parameter. Other quantities or neglecting of the drag effect lead to existence of two coherence lengths and dynamical instability due to violation of the phase relations between the order parameters. Thus so-called type-1.5 superconductors are impossible. An approximate method for solving of set of GL equations for a multi-band superconductor has been developed: using the result about the drag effect it has been shown that the free-energy functional for a multi-band superconductor can be reduced to the GL functional for an effective single-band superconductor.

  18. Studies of anisotropy of iron based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, Jason [Iowa State Univ., Ames, IA (United States)

    2013-01-01

    To study the electronic anisotropy in iron based superconductors, the temperature dependent London penetration depth, Δλ (T), have been measured in several compounds, along with the angular dependent upper critical field, Hc2(T). Study was undertaken on single crystals of Ba(Fe1-xCox)2As2 with x=0.108 and x=0.127, in the overdoped range of the doping phase diagram, characterized by notable modulation of the superconducting gap. Heavy ion irradiation with matching field doses of 6 T and 6.5 T respectively, were used to create columnar defects and to study their effect on the temperature Δλ (T). The variation of the low-temperature penetration depth in both pristine and irradiated samples was fitted with a power-law function Δλ (T) = ATn. Irradiation increases the magnitude of the pre-factor A and decreases the exponent n, similar to the effect on the optimally doped samples. This finding supports the universal s± scenario for the whole doping range. Knowing that the s± gap symmetry exists across the superconducting dome for the electron doped systems, we next looked at λ (T), in optimally - doped, SrFe2(As1-xPx)2, x =0.35. Both, as-grown (Tc ~ 25 K) and annealed (Tc ~ 35 K) single crystals of SrFe2(As1-xPx)2 were measured. Annealing decreases the absolute value of the London penetration depth from λ(0) = 300 ± 10 nm in as-grown samples to λ (0) = 275±10 nm. At low temperatures, λ (T) ~ T indicates a superconducting gap with line nodes. Analysis of the full-temperature range superfluid density is consistent with the line nodes, but differs from the simple single-gap d-wave. The observed behavior is very similar to that of BaFe2(As1-xPx)2, showing that isovalently substituted pnictides are inherently different from

  19. Electronic Structure of the Bismuth Family of High Temperature Superconductors

    International Nuclear Information System (INIS)

    High temperature superconductivity remains the central intellectual problem in condensed matter physics fifteen years after its discovery. Angle resolved photoemission spectroscopy (ARPES) directly probes the electronic structure, and has played an important role in the field of high temperature superconductors. With the recent advances in sample growth and the photoemission technique, we are able to study the electronic structure in great detail, and address regimes that were previously inaccessible. This thesis work contains systematic photoemission studies of the electronic structure of the Bi-family of high temperature superconductors, which include the single-layer system (Bi2201), the bi-layer system (Bi2212), and the tri-layer system (Bi2223). We show that, unlike conventional BCS superconductors, phase coherence information emerges in the single particle excitation spectrum of high temperature superconductors as the superconducting peak in Bi2212. The universality and various properties of this superconducting peak are studied in various systems. We argue that the origin of the superconducting peak may provide the key to understanding the mechanism of High-Tc superconductors. In addition, we identified a new experimental energy scale in the bilayer material, the anisotropic intra-bilayer coupling energy. For a long time, it was predicted that this energy scale would cause bilayer band splitting. We observe this phenomenon, for the first time, in heavily overdoped Bi2212. This new observation requires the revision of the previous picture of the electronic excitation in the Brillouin zone boundary. As the first ARPES study of a trilayer system, various detailed electronic properties of Bi2223 are examined. We show that, comparing with Bi2212, both superconducting gap and relative superconducting peak intensity become larger in Bi2223, however, the strength of the interlayer coupling within each unit cell is possibly weaker. These results suggest that the

  20. The origin of the Meissner effect in new and old superconductors

    OpenAIRE

    Hirsch, J. E.

    2011-01-01

    It is generally believed that superconducting materials are divided into two classes: `conventional' and `unconventional'. Conventional superconductors (the elements and thousands of compounds including $MgB_2$) are described by conventional London-BCS-Eliashberg electron-phonon theory. There is no general agreement as to what mechanism or mechanisms describe `unconventional' superconductors such as the heavy fermions, organics, cuprate and pnictide families. However all superconductors, whet...