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Sample records for critical temperature superconductor

  1. Nonmonotonic critical temperature in superconductor ferromagnet bilayers

    NARCIS (Netherlands)

    Fominov, Ya. V.; Fominov, I.V.; Chtchelkatchev, N.M.; Golubov, Alexandre Avraamovitch

    2002-01-01

    The critical temperature Tc of a superconductor/ferromagnet (SF) bilayer can exhibit nonmonotonic dependence on the thickness df of the F layer. SF systems have been studied for a long time; according to the experimental situation, a ¿dirty¿ limit is often considered which implies that the mean free

  2. Low critical temperature superconductors for electromagnets

    International Nuclear Information System (INIS)

    Devred, A.

    2002-01-01

    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)

  3. Enhancement of critical temperature in fractal metamaterial superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Smolyaninov, Igor I., E-mail: smoly@umd.edu [Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742 (United States); Smolyaninova, Vera N. [Department of Physics Astronomy and Geosciences, Towson University, 8000 York Road, Towson, MD 21252 (United States)

    2017-04-15

    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.

  4. Thermal conductivity in high critical temperature superconductors

    International Nuclear Information System (INIS)

    Castello, D.J.

    1990-01-01

    A measuring procedure to obtain the electrical resistivity, thermal conductivity and thermoelectric power of samples of low conductivity has been developed. The setup was designed to allow the removal of the sample in clean fashion, so that further heat treatments could be performed, and therefore no adhesives were used in the mounting of the thermocouples or heat sinks, etc. The heat equation has been analyzed with time-dependent boundary conditions, with the purpose of developing a dynamic measuring method which avoids the long delays involved in reaching thermal equilibrium above 30K. Based on this analysis, the developed measuring method allows a precise and reliable measurements, in a continuous fashion, for temperatures above 25K. The same setup is used in a stationary mode at low temperatures, so the sample needs to be mounted only once. κ(T) has been measured in two ceramic samples of La 2 CuO 4 : the first semiconducting, the other superconducting (SC) as a consequence of an oxygen annealing. Both exhibit a strong thermal resistivity due to defects, though lower in the SC, where two maxima are observed and are attributed to an AF ordering: T N ' ≅ 40K and T N '' ≅ 240K. The low temperature dependence is T 1 .6 and T 2 .3 respectively. It was interpreted that the former sample presents a greater dispersion due to localized excitations, characteristic of amorphouus materials, 'tunneling two-level systems' (TS). A third syntherized sample of CuO exhibits a typical behaviour of an insulator, with T 2 .6 at low temperatures, a maximum at 40K and a decrease in T -1 at high temperatures. κ(T) in a SC sample of La 1 .85Sr 1 .15CuO 4 with T c =35.5K has also been measured, observing a small increase below T c because of the diminishing of the phonon dispersion due to the condensating electrons. κ(T) is lower than in the previous samples and thus a greater number of defects was inferred. At low temperatures, its dependence is T 1 .4 in agreement with the

  5. On the critical temperature of superconductors

    International Nuclear Information System (INIS)

    Poon, S.J.

    1975-06-01

    An exact expression for the superconducting transition temperature is derived from the Eliashberg equation at T = T/sub c/ taking the energy gap function in the two-square-well form. The expression is improved for self-consistency by using available tunneling data. It is found to give more restricted values of T/sub c/ than the McMillan equation. The prospects of obtaining high T/sub c/ in alloy systems are discussed within the framework of the new equation. (6 figures, 2 tables) (U.S.)

  6. Boundary conditions in Ginsburg Landau theory and critical temperature of high-T superconductors

    Science.gov (United States)

    Lykov, A. N.

    2008-06-01

    New mixed boundary conditions to the Ginsburg-Landau equations are found to limit the critical temperature ( T) of high- T superconductors. Moreover, the value of the pseudogap in these superconductors can be explained by using the method. As a result, the macroscopic approach is proposed to increase T of cuprate superconductors.

  7. Boundary conditions in Ginsburg-Landau theory and critical temperature of high-Tc superconductors

    International Nuclear Information System (INIS)

    Lykov, A.N.

    2008-01-01

    New mixed boundary conditions to the Ginsburg-Landau equations are found to limit the critical temperature (T c ) of high-T c superconductors. Moreover, the value of the pseudogap in these superconductors can be explained by using the method. As a result, the macroscopic approach is proposed to increase T c of cuprate superconductors

  8. 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.

  9. Superconductors with low critical temperature for electro-magnets

    International Nuclear Information System (INIS)

    Devred, A.

    2002-07-01

    Among the superconductors with low critical temperature that are used to build magnets, NbTi has reached a development state that allows a massive production for big equipment of physics and an industrial production in the domain of medicine imaging. The material that might challenge the supremacy of NbTi is Nb 3 Sn but some technical difficulties have yet to be overcome. This report begins with a review of the different industrial processes used to produce superconducting wires based on the NbTi and Nb 3 Sn materials. The transition from the superconducting state to the resistive normal state is described for both materials, the magnetizing of multi-wire superconducting cables is also presented. The author details the different patterns of wires in cables and proposes a formulary that allows the determination, in some simple cases,of energy losses that are generated in a superconducting cable by a variable magnetic field. (A.C.)

  10. Quantum critical point in high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Shaginyan, V.R. [Petersburg Nuclear Physics Institute, RAS, Gatchina 188300 (Russian Federation); Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)], E-mail: vrshag@thd.pnpi.spb.ru; Amusia, M.Ya. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Popov, K.G. [Komi Science Center, Ural Division, RAS, Syktyvkar 167982 (Russian Federation); Stephanovich, V.A. [Opole University, Institute of Mathematics and Informatics, Opole 45-052 (Poland)], E-mail: stef@math.uni.opole.pl

    2009-02-02

    Recently, in high-T{sub c} superconductors (HTSC), exciting measurements have been performed revealing their physics in superconducting and pseudogap states and in normal one induced by the application of magnetic field, when the transition from non-Fermi liquid to Landau-Fermi liquid behavior occurs. We employ a theory, based on fermion condensation quantum phase transition which is able to explain facts obtained in the measurements. We also show, that in spite of very different microscopic nature of HTSC, heavy-fermion metals and 2D {sup 3}He, the physical properties of these three classes of substances are similar to each other.

  11. Low critical temperature superconductors for electromagnets; Supraconducteurs a basse temperature critique pour electroaimants

    Energy Technology Data Exchange (ETDEWEB)

    Devred, A

    2002-07-01

    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)

  12. Micron SR Studies of High Critical Temperature Superconductor Lead

    Science.gov (United States)

    Wu, Wei-Dong

    1995-01-01

    Flux depinning phenomena in the rm Bi_2Sr_2CaCu_2O_8 (Bi2212) and rm Pb_{0.7}Bi_ {1.3}Sr_2CaCu_2O_8 (Pb-Bi2212) systems have been studied using the technique of transverse field (TF) muSR. Comparison of field-cooled (FC) and zero-field-cooled (ZFC) results defines an irreversibility (depinning) temperature T _{rm irr}: the ZFC and FC relaxation rates are essentially identical above T _{rm irr}, while the ZFC relaxation rate is larger than the FC relaxation rate below T_{rm irr}, reflecting the increased inhomogeneity of the local fields in the ZFC measurements due to flux pinning. The irreversibility line T_{irr}(H) of Bi2212 obtained by muSR measurements is compared with those from dc and ac-susceptibility, and mechanical oscillator measurements. I show that the results from muSR and these other techniques can be explained consistently within a framework of the flux creep model. The irreversibility temperature in Pb -Bi2212, determined by muSR measurements, is significantly higher than that in the pure Bi2212 system. This result, together with the larger critical current and the higher activation energy U_0 in the Pb-Bi2212 crystals as found by the dc-susceptibility measurements, suggests an enhancement of flux pinning by the Pb doping. In order to fit the muSR asymmetry measured in Y_{1-x} U_{x}Pd _3, I have performed Monte Carlo simulations for spin glasses with impurity concentration x between 0 and 1; I found that the stretched exponential decay of muon polarisation found empirically in many spin glasses above the spin freezing temperature T_{g } is consistent with a lognormal distribution of the fluctuation rate nu. Our muSR measurements of Y_ {1-x}U_{x}Pd _3 and UPd_4 demonstrate the disappearance of magnetic order with decreasing U concentration x with a threshold U concentration x _{rm th} ~ 0.2. I show that the behavior is consistent with Sherrington's induced spin glass model based on the competition between exchange interaction coupling {cal T } and the

  13. Critical temperature for a model quasi-one-dimensional disordered superconductor

    Science.gov (United States)

    Lin, Yi; Yi, Xiao; Kai-lun, Yao

    1993-06-01

    With the help of the decimation ansatz of the renormlization group, the dependence of critical temperature on a transverse magnetic field is calculated analytically for a quasi-one-dimensional disordered superconductor model, based on the de Gennes-Skal-Shklovskii (dGSS) picture of the large cluster in a percolation system. Our results are in good agreement with those given by Halley's scaling theory.

  14. Superconductors with low critical temperature for electro-magnets; Supraconducteurs a basse temperature critique pour electroaimants

    Energy Technology Data Exchange (ETDEWEB)

    Devred, A

    2002-07-01

    Among the superconductors with low critical temperature that are used to build magnets, NbTi has reached a development state that allows a massive production for big equipment of physics and an industrial production in the domain of medicine imaging. The material that might challenge the supremacy of NbTi is Nb{sub 3}Sn but some technical difficulties have yet to be overcome. This report begins with a review of the different industrial processes used to produce superconducting wires based on the NbTi and Nb{sub 3}Sn materials. The transition from the superconducting state to the resistive normal state is described for both materials, the magnetizing of multi-wire superconducting cables is also presented. The author details the different patterns of wires in cables and proposes a formulary that allows the determination, in some simple cases,of energy losses that are generated in a superconducting cable by a variable magnetic field. (A.C.)

  15. Upper critical field of high temperature Y/sub 1.2/Ba/sub 0.8/CuO/sub 4-δ/superconductor

    International Nuclear Information System (INIS)

    Hor, P.H.; Meng, R.L.; Huang, J.Z.; Chu, C.W.; Huang, C.Y.

    1987-01-01

    An upper critical field is determined for the high temperature, 90-K, superconductor Y/sub 1.2/Ba/sub 0.8/CuO/sub 4-δ/. The temperature dependence of the critical field was established. The sample is found to be a Type-II superconductor

  16. Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors.

    Science.gov (United States)

    Goodrich, L F; Cheggour, N; Stauffer, T C; Filla, B J; Lu, X F

    2013-01-01

    We review variable-temperature, transport critical-current (I c) measurements made on commercial superconductors over a range of critical currents from less than 0.1 A to about 1 kA. We have developed and used a number of systems to make these measurements over the last 15 years. Two exemplary variable-temperature systems with coil sample geometries will be described: a probe that is only variable-temperature and a probe that is variable-temperature and variable-strain. The most significant challenge for these measurements is temperature stability, since large amounts of heat can be generated by the flow of high current through the resistive sample fixture. Therefore, a significant portion of this review is focused on the reduction of temperature errors to less than ±0.05 K in such measurements. A key feature of our system is a pre-regulator that converts a flow of liquid helium to gas and heats the gas to a temperature close to the target sample temperature. The pre-regulator is not in close proximity to the sample and it is controlled independently of the sample temperature. This allows us to independently control the total cooling power, and thereby fine tune the sample cooling power at any sample temperature. The same general temperature-control philosophy is used in all of our variable-temperature systems, but the addition of another variable, such as strain, forces compromises in design and results in some differences in operation and protocol. These aspects are analyzed to assess the extent to which the protocols for our systems might be generalized to other systems at other laboratories. Our approach to variable-temperature measurements is also placed in the general context of measurement-system design, and the perceived advantages and disadvantages of design choices are presented. To verify the accuracy of the variable-temperature measurements, we compared critical-current values obtained on a specimen immersed in liquid helium ("liquid" or I c liq) at 5

  17. Critical-temperature inhomogeneities and resistivity rounding in copper oxide superconductors

    International Nuclear Information System (INIS)

    Maza, J.; Vidal, F.

    1991-01-01

    By using effective-medium approaches, we obtain the onset of the electrical-resistivity rounding, above the normal-superconducting transition, associated with inhomogeneities of the mean-field critical temperature T c0 at scales larger than the superconducting correlation length. These results are compared with available data in single-crystal and single-phase (to within 4%) polycrystalline YBa 2 Cu 3 O 7-δ samples. This comparison shows that the measured resistivity rounding cannot be explained by these types of local T c0 inhomogeneities. Complementarily, our calculations allow us to check some proposals on T c0 inhomogeneities associated with local sample strains or oxygen-content variations. The interplay between T c0 inhomogeneities and superconducting order-parameter fluctuations (SCOPF) leads to the conclusion that in the mean-field-like region (MFR) above the superconducting transition, the T c0 inhomogeneity contribution to the measured resistivity rounding in high-quality (single-phase) cuprate oxide superconductors is negligible. In contrast, our analysis confirms that in the MFR these effects may be explained quantitatively on the grounds of the Lawrence-Doniach theory for SCOPF

  18. 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

  19. High temperature superconductor accelerator magnets

    NARCIS (Netherlands)

    van Nugteren, J.

    2016-01-01

    For future particle accelerators bending dipoles are considered with magnetic fields exceeding 20T. This can only be achieved using high temperature superconductors (HTS). These exhibit different properties from classical low temperature superconductors and still require significant research and

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

    International Nuclear Information System (INIS)

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

    1991-01-01

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

  1. Enhanced critical current density in the pressure-induced magnetic state of the high-temperature superconductor FeSe

    Science.gov (United States)

    Jung, Soon-Gil; Kang, Ji-Hoon; Park, Eunsung; Lee, Sangyun; Lin, Jiunn-Yuan; Chareev, Dmitriy A.; Vasiliev, Alexander N.; Park, Tuson

    2015-01-01

    We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors. PMID:26548444

  2. High Temperature Superconductor Resonator Detectors

    Data.gov (United States)

    National Aeronautics and Space Administration — High Temperature Superconductor (HTS) infrared detectors were studied for years but never matured sufficiently for infusion into instruments. Several recent...

  3. 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.

  4. Thermodynamic Critical Field and Superconducting Fluctuation of Vortices for High Temperature Cuprate Superconductor: La-214

    International Nuclear Information System (INIS)

    Yung Moo Huh

    2001-01-01

    Thermodynamics has been studied systematically for the high temperature cuprate superconductor La 2-x Sr x CuO 4-δ , La-214, in the entire superconductive region from strongly underdoped to strongly overdoped regimes. Magnetization studies with H(parallel)c have been made in order to investigate the changes in free energy of the system as the number of carriers is reduced. Above the superconducting transition temperature, the normal-state magnetization exhibits a two-dimensional Heisenberg antiferromagnetic behavior. Below T c , magnetization data are thermodynamically reversible over large portions of the H-T plane, so the free energy is well defined in these regions. As the Sr concentration is varied over the wide range from 0.060 (strongly underdoped) to 0.234 (strongly overdoped), the free energy change goes through a maximum at the optimum doped in a manner similar to the T c0 vs. x curve. The density of states, N(0), remains nearly constant in the overdoped and optimum doped regimes, taking a broad maximum around x = 0.188, and then drops abruptly towards zero in the underdoped regime. The La 2-x Sr x CuO 4 (La-214) system displays the fluctuating vortex behavior with the characteristic of either 2D or 3D fluctuations as indicated by clearly identifiable crossing points T* close to T c . The dimensional character of the fluctuations depends on both applied magnetic fields and the density of charge carriers. The dimensional crossover from 2D to 3D occurs in the strongly underdoped regime when the c-axis coherence distance ζ c becomes comparable to the spacing between adjacent CuO 2 layers s at sufficiently high magnetic fields near H c2

  5. Thermodynamic Critical Field and Superconducting Fluctuation of Vortices for High Temperature Cuprate Superconductor: La-214

    International Nuclear Information System (INIS)

    Finnemore, Douglas K.

    2001-01-01

    Thermodynamics has been studied systematically for the high temperature cuprate superconductor La 2-x Sr x CuO 4-δ , La-214, in the entire superconductive region from strongly underdoped to strongly overdoped regimes. Magnetization studies with H (parallel) c have been made in order to investigate the changes in free energy of the system as the number of carriers is reduced. Above the superconducting transition temperature, the normal-state magnetization exhibits a two-dimensional Heisenberg antiferromagnetic behavior. Below T c , magnetization data are thermodynamically reversible over large portions of the H-T plane, so the free energy is well defined in these regions. As the Sr concentration is varied over the wide range from 0.060 (strongly underdoped) to 0.234 (strongly overdoped), the free energy change goes through a maximum at the optimum doped in a manner similar to the T c0 vs. x curve. The density of states, N(0), remains nearly constant in the overdoped and optimum doped regimes, taking a broad maximum around x = 0.188, and then drops abruptly towards zero in the underdoped regime. The La 2-x Sr x CuO 4 (La-214) system displays the fluctuating vortex behavior with the characteristic of either 2D or 3D fluctuations as indicated by clearly identifiable crossing points T* close to T c . The dimensional character of the fluctuations depends on both applied magnetic fields and the density of charge carriers. The dimensional crossover from 2D to 3D occurs in the strongly underdoped regime when the c-axis coherence distance ξ c becomes comparable to the spacing between adjacent CuO 2 layers s at sufficiently high magnetic field near H c2

  6. Thermodynamic Critical Field and Superconducting Fluctuation of Vortices for High Temperature Cuprate Superconductor: La-214

    Energy Technology Data Exchange (ETDEWEB)

    Finnemore, Douglas K. [Iowa State Univ., Ames, IA (United States)

    2001-01-01

    Thermodynamics has been studied systematically for the high temperature cuprate superconductor La2-xSrxCuO4-δ, La-214, in the entire superconductive region from strongly underdoped to strongly overdoped regimes. Magnetization studies with H $\\parallel$ c have been made in order to investigate the changes in free energy of the system as the number of carriers is reduced. Above the superconducting transition temperature, the normal-state magnetization exhibits a two-dimensional Heisenberg antiferromagnetic behavior. Below Tc, magnetization data are thermodynamically reversible over large portions of the H-T plane, so the free energy is well defined in these regions. As the Sr concentration is varied over the wide range from 0.060 (strongly underdoped) to 0.234 (strongly overdoped), the free energy change goes through a maximum at the optimum doped in a manner similar to the Tc0 vs. x curve. The density of states, N(0), remains nearly constant in the overdoped and optimum doped regimes, taking a broad maximum around x = 0.188, and then drops abruptly towards zero in the underdoped regime. The La2-xSrxCuO4 (La-214) system displays the fluctuating vortex behavior with the characteristic of either 2D or 3D fluctuations as indicated by clearly identifiable crossing points T* close to Tc. The dimensional character of the fluctuations depends on both applied magnetic fields and the density of charge carriers. The dimensional crossover from 2D to 3D occurs in the strongly underdoped regime when the c-axis coherence distance ξc becomes comparable to the spacing between adjacent CuO2 layers s at sufficiently high magnetic field near Hc2.

  7. Realization of multilayers for superconductors at critical high temperature by chemical method

    International Nuclear Information System (INIS)

    Guibadj, A.

    2009-09-01

    The aim of this research is to study buffer layers made of CeO 2 and La 2 Zr 2 O 7 for high Tc superconductors devoted to energy transportation (coated conductors). We used Metal Organic Decomposition method (MOD) for the synthesis of layers of CeO 2 /SrTiO 3 and La 2 Zr 2 O 7 /LaAlO 3 , because it is a soft and economic method well adapted to manufacture buffers layers for coated conductors. The comparison of various precursors of Cerium was made with the aim of obtaining the adequate precursor for the MOD process. Spin coating was used for depositing precursor solutions of Ce(EH) 3 and LZ(propionic) on various substrates. Thermal analyzes of these precursors allowed to determine their decomposition mode (weight loss analysis) according to the temperature, to estimate the quantity of absorbed moisture by the precursors and to determine the temperature of crystallization of the oxide. It was also used to discuss the mixed nature or not of the lanthanum-zirconium proprionate. The analyses of the microstructure and of the texture of CeO 2 and La 2 Zr 2 O 7 films are established by X-ray diffraction (scans θ-2θ, ω-scan, Φ-scan and pole figures). AFM and MEB allowed us to study roughness, topology and morphology of the surface. Heat treatments of the layers of C(EH) 3 /SrTiO 3 and (La(prop) 3 + Zr(prop) 4 )/LAO, under various atmospheres enabled us to differentiate the poly-crystalline growth from the epitaxial growth. The elimination of residual carbon in the grain boundaries, blocking the grain growth, was carried out by a control of the partial pressure of oxygen at the stage of crystallization; this step makes possible an improvement of the layers' texture. The heating rate has an influence on the nucleation which was studied. Increasing the heating rate favor the heterogeneous nucleation and decreases the number of nuclei, supporting the growth of larger epitaxial grains. Finally, we carried out the multi-layers CeO 2 /La 2 Zr 2 O 7 /LaAlO 3 and YBaCuO/CeO 2

  8. Low-Frequency Optical Studies of High Critical Transition Temperature Superconductors

    Science.gov (United States)

    Voss, Karl Friedrich

    The lattice dynamics and electronic responses of High T_{rm c} Superconductors (HTCSs), as revealed by various methods of optical studies, are presented, analyzed and interpreted. First, some background material is briefly developed. Following this are experimental results of reflection studies on aligned YBa_2Cu_3 O_{7-delta} and on oriented Tl_2Ba_2 CaCu_2O_8 : the former show that HTCSs containing CuO-sheets should be thought of as 2+1-dimensional; the latter indicate that the conductivity of the HTCSs can be modeled as having two-components: a narrow, Drude-like feature in the far -IR (that eventually collapses to a delta -function in a clean limit), and a Lorentz-like mid-IR feature. Using photo-induced absorption studies, this mid -IR feature is traced to polarons shaking off phonons. Our data are consistent with the polaron transport theory developed by Reik in the mid 1960's; fits indicate that the polarons consist of 5-7 phonons, each having a frequency around 200 cm^{-1}. Conventional application of the "classical Bardeen -Cooper-Schrieffer theories" as extended by Mattis-Bardeen --and with the explicit incorporation of the frequency dependence of the electron-phonon interaction due to Eliashberg--fail to predict high enough T_{rm c}s. At the same time, experimental evidence for an anharmonic potential well of the apex oxygen is accumulating. We thus propose that the harmonic phonons of the classical models be replaced with more generalized lattice excitations associated with this anharmonic potential; specifically, we think along the lines of a dynamical Jahn -Teller effect involving the apex oxygens. Various theoretical models that are currently being studied in the literature for this anharmonic potential will be briefly introduced and discussed. Lastly, the role of the intermediate "charge-reservoirs" is studied: by comparing two structures (one with, one without reservoir layers), we find experimentally that the layers not only act as reservoirs, but

  9. High Temperature Superconductor Accelerator Magnets

    CERN Document Server

    AUTHOR|(CDS)2079328; de Rijk, Gijs; Dhalle, Marc

    2016-11-10

    For future particle accelerators bending dipoles are considered with magnetic fields exceeding $20T$. This can only be achieved using high temperature superconductors (HTS). These exhibit different properties from classical low temperature superconductors and still require significant research and development before they can be applied in a practical accelerator magnet. In order to study HTS in detail, a five tesla demonstrator magnet named Feather-M2 is designed and constructed. The magnet is based on ReBCO coated conductor, which is assembled into a $10kA$ class Roebel cable. A new and optimized Aligned Block layout is used, which takes advantage of the anisotropy of the conductor. This is achieved by providing local alignment of the Roebel cable in the coil windings with the magnetic field lines. A new Network Model capable of analyzing transient electro-magnetic and thermal phenomena in coated conductor cables and coils is developed. This model is necessary to solve critical issues in coated conductor ac...

  10. Proximity effect depression of the critical temperature in two-phase Nb-Ti superconductors

    International Nuclear Information System (INIS)

    Meingast, C.; Daeumling, M.; Lee, P.J.; Larbalestier, D.C.

    1987-01-01

    The superconducting critical temperature of high critical current density Nb-Ti composites has been measured at various stages in the critical current optimization process. This process involves heat treatment steps which cause precipitation of normal α-Ti and make the matrix more Nb rich. T/sub c/ rises from 9.1 to 9.5 K during this stage. The final optimization stage involves extensive wire drawing during which the α-Ti precipitates are reduced to less than a coherence length in thickness. This does not result in a reduction in J/sub c/ but T/sub c/ is found to fall from 9.44 to 8.7 K during this step. The depression of T/sub c/ is found to be in fair agreement with the predicted proximity effect suppression of T/sub c/. Wires of optimum transport critical current density are seen to have T/sub c/ of around 9 K

  11. On the critical temperature discontinuity at the theoretical bcc-fcc phase transition in compressed selenium and tellurium superconductors

    Science.gov (United States)

    Szczęśniak, D.; Wrona, I. A.; Drzazga, E. A.; Kaczmarek, A. Z.; Szewczyk, K. A.

    2017-11-01

    Recent hydrides-driven advent in the high-pressure phonon-mediated superconductivity motivates research on chemical elements which compound with hydrogen. It is desired that such elements should allow chemical pre-compression of hydrogen to assure the induction of the superconducting phase with the high transition temperature (T C). Herein, we present detailed theoretical insight into the properties of the superconducting state induced under pressure (p) in two of such component elements, namely selenium (Se) and tellurium (Te) at p=250 GPa and p=70 GPa, respectively. The assumed external pressure conditions allow us to conduct our analysis just above previously theoretically predicted bcc-fcc structural phase transition of Se and Te, and identify the possible associated discontinuity effect of the critical temperature. In particular, our numerical analysis is conducted within Migdal-Eliashberg formalism, due to the confirmed electron-phonon pairing mechanism and relatively high electron-phonon coupling constant in the materials of interest. We predict that T C values in Se and Te equal 8.13 K and 5.96 K, respectively, and mark the highest critical temperature values for these elements within the postulated fcc phase. Additionally, we supplement these results by the estimated maximum values of the superconducting energy band gap and the effective mass of electrons. We predict that all these parameters can be used as a guidelines for experimental observation of the critical temperature discontinuity and the corresponding bcc-fcc phase transition in Se and Te superconductors. Moreover, we show that the thermodynamics of superconducting phase in both elements may exhibit deviations from the conventional estimates of the Bardeen-Cooper-Schrieffer theory, and suggest existence of the strong-coupling and retardation effects. Finally, we note that our results can be also instructive for future screening of chemical elements for applications in superconducting hydrides.

  12. 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...

  13. The critical current of superconductors: an historical review

    International Nuclear Information System (INIS)

    Dew-Hughes, D.

    2001-01-01

    The most important practical characteristic of a superconductor is its critical current density. This article traces the history, both of the experimental discoveries and of the development of the theoretical ideas that have lead to the understanding of those factors that control critical current densities. These include Silsbee's hypothesis, the Meissner effect, London, Ginsburg-Landau and Abrikosov theories, flux pinning and the critical state, and the control of texture in high temperature superconductors

  14. Critical temperatures Tc estimated by Josephson-junction array model of layered high Tc superconductors

    International Nuclear Information System (INIS)

    Kawabata, C.; Shenoy, S.R.; Bishop, A.R.

    1994-11-01

    We model high T c superconductors (HTS) by quantum capacitive Josephson junction arrays (JJA), with Angstrom-scale parameters, to obtain an estimate of Tc trends. The basic idea is as follows. Number (or change) and phase are conjugate variables, with the uncertainty products obeying ΔN · Δ Θ > 1. Thus, in HTS, global phase coherence is opposed by charging-energy induced quantum phase fluctuations, especially across Josephson-coupled CuO 2 planes. These have separation d 1 and effective interplanar dielectric constant ε, e.g. from Y atoms in YBaCuO. Decreasing the interplane charging energy E 0 perpendicular to ∼ d 1 /ε, raises Tc. In Section 1, we motivate a modelling of HTS phase excitations by a quantum capacitive 3D JJA model, with XY planar phases. Section 2 gives a physical picture of the HTS transition, relating the complex layered HTS structure to a simpler ''intermediate level'' quantum 3D JJA/XY model. Section 3 sets up a path integral (3+1)D model that reduces to a previously studied anisotropic 3D XY/JJA model, with constants renormalized in some way, by the capacitance. Postponing a detailed analysis to elsewhere, we make a heuristic estimate for the reduction of the previous Tc, by the charging energy. (author). 30 refs, 8 figs

  15. High temperature superconductor current leads

    Science.gov (United States)

    Hull, John R.; Poeppel, Roger B.

    1995-01-01

    An electrical lead having one end for connection to an apparatus in a cryogenic environment and the other end for connection to an apparatus outside the cryogenic environment. The electrical lead includes a high temperature superconductor wire and an electrically conductive material distributed therein, where the conductive material is present at the one end of the lead at a concentration in the range of from 0 to about 3% by volume, and at the other end of the lead at a concentration of less than about 20% by volume. Various embodiments are shown for groups of high temperature superconductor wires and sheaths.

  16. 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.

  17. The effect of electron density fluctuations on critical temperature in layered superconductors with arbitrary thickness of conducting layer

    Science.gov (United States)

    Askerzade, I. N.

    2018-04-01

    In this work, we analyse the effect of electron density fluctuations of in layered superconductors on the transition temperature Tc. Primarily, we consider the effect of thickness of conducting layer in modelling of superconducting compounds. It is observed that increasing the thickness of conducting layers increases the transition temperature Tc. Also it is shown that, the fluctuations of electron density has negligible character in the case layers with highly different dielectric constants. Obtained results are applicable to Bi2 Sr2 Can - 1 CunO2 n + 4 + δ compounds with n = 1,2,3.

  18. Relationship between effective mass and superconducting critical temperature in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Caulfield, J. [Physics Dept., Univ. of Oxford, Clarendon Lab. (United Kingdom); Lubczynski, W. [Physics Dept., Univ. of Oxford, Clarendon Lab. (United Kingdom); Lee, W. [School of Physics and Materials, Lancaster Univ. (United Kingdom); Singleton, J. [Physics Dept., Univ. of Oxford, Clarendon Lab. (United Kingdom); Pratt, F.L. [Physics Dept., Univ. of Oxford, Clarendon Lab. (United Kingdom); Hayes, W. [Physics Dept., Univ. of Oxford, Clarendon Lab. (United Kingdom); Kurmoo, M. [Royal Institution, London (United Kingdom); Day, P. [Royal Institution, London (United Kingdom)

    1995-03-15

    We report high pressure magnetotransport on the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}. The observation of Shubnikov-de Haas and magnetic breakdown oscillations has allowed the pressure dependences of the Fermi surface topology and quasiparticle effective masses to be deduced and compared with simultaneous measurements of the superconducting critical temperature T{sub c}. The data strongly suggest that the enhancement of the effective mass and the superconducting behaviour are directly connected. The results are fitted by calculations of the linearised Eliashberg equations. (orig.)

  19. High critical magnetic field superconductor La3S4

    International Nuclear Information System (INIS)

    Westerholt, K.; Bach, H.; Wendemuth, R.; Methfessel, S.

    1979-01-01

    A report is presented on electrical conductivity, specific heat and magnetization measurements on La 3 S 4 single crystals. The results show that La 3 S 4 is a strong coupling superconductor with a BCS coherence length of 132 A. This extremely low value makes La 3 S 4 an intrinsic high critical magnetic field superconductor with a Landau-Ginsburg parameter of 20. For the temperature gradient of the upper critical magnetic field at the transition temperature values are found up to 35 kG/K. (author)

  20. Isotopic effect in high temperature superconductors

    International Nuclear Information System (INIS)

    Ohno, Takashi

    2000-01-01

    It is well-known that it essentially contributed to construct the BCB theory that a mechanism on formation of the Cooper pairs was dependent upon a lattice oscillation to change a critical temperature, T(sub c) of a superconductor with isotopic displacement. In this paper, here was, at first, described on an isotopic index actually measured to high temperature superconductors, and was introduced on a study on selective displacement of oxygen position. And then, a detailed measurement of 63-Cu(2) nuclear quadrupole resonance (NQR) at a plane position of YBa2Cu4O8 (Y1248) displaced with 18-O and 16-O, discussion of the isotopic effect on a base of 63-Cu(2) nuclear spin-lattice relaxation ratio, and consideration on the isotopic index according to the isotopic effect were described. As a result of the considerations, it could be concluded that the isotopic effect in a high temperature superconductor proved that antiferromagnetic spin fluctuation was an origin of Cooper pairs cohesive strength. (G.K.)

  1. Risk Mitigaion for HTS Motors: Intermediate Temperature (27 K) Strain Effects in Reinforced Bi-Sr-Ca-Cu-O Superconductors

    National Research Council Canada - National Science Library

    Schwartz, Justin

    2004-01-01

    High temperature superconductors , known for their high critical temperatures, also have very high upper critical fields and thus have received significant attention for superconducting magnets (SCMs...

  2. Studies of high temperature superconductors

    International Nuclear Information System (INIS)

    Narlikar, A.

    1989-01-01

    The high temperature superconductors (HTSCs) discovered are from the family of ceramic oxides. Their large scale utilization in electrical utilities and in microelectronic devices are the frontal challenges which can perhaps be effectively met only through consolidated efforts and expertise of a multidisciplinary nature. During the last two years the growth of the new field has occurred on an international scale and perhaps has been more rapid than in most other fields. There has been an extraordinary rush of data and results which are continually being published as short texts dispersed in many excellent journals, some of which were started to ensure rapid publication exclusively in this field. As a result, the literature on HTSCs has indeed become so massive and so diffuse that it is becoming increasingly difficult to keep abreast with the important and reliable facets of this fast-growing field. This provided the motivation to evolve a process whereby both professional investigators and students can have ready access to up-to- date in-depth accounts of major technical advances happening in this field. The present series Studies of High Temperature Superconductors has been launched to, at least in part, fulfill this need

  3. Passivation Of High-Temperature Superconductors

    Science.gov (United States)

    Vasquez, Richard P.

    1991-01-01

    Surfaces of high-temperature superconductors passivated with native iodides, sulfides, or sulfates formed by chemical treatments after superconductors grown. Passivating compounds nearly insoluble in and unreactive with water and protect underlying superconductors from effects of moisture. Layers of cuprous iodide and of barium sulfate grown. Other candidate passivating surface films: iodides and sulfides of bismuth, strontium, and thallium. Other proposed techniques for formation of passivating layers include deposition and gas-phase reaction.

  4. Transport measurements in superconductors: critical current of granular high TC ceramic superconductor samples

    International Nuclear Information System (INIS)

    Passos, W.A.C.

    2016-01-01

    This work presents a method to obtain critical current of granular superconductors. We have carried out transport measurements (ρxT curves and VxI curves) in a YBa 2 Cu 3 O 7-δ sample to determine critical current density of it. Some specimens reveal a 'semiconductor-like' behavior (electrical resistivity decreases with increasing temperatures above critical temperature T c of material) competing with superconductor behavior. Due to high granular fraction of the sample, these competition is clearly noted in ρxT curves. Measurements carried out from 0 to 8500 Oe of applied field show the same behavior, and the critical current density of the samples is shown. (author)

  5. On the prospects of increasing critical parameters of superconductors

    International Nuclear Information System (INIS)

    Lazarev, B.G.; Pan, V.M.

    1979-01-01

    Noted is the importance of the production of materials with high critical parameters for modern science and technology. Considered are present notions about the nature of high critical densities of critical current. The opinion is expressed that the search of most high-temperature and high-field superconductors should be carried out, in the first place, among compounds based on transition metals displaying structural instability. Noted are prospects of the work over the synthesis of metastabile compounds with A15 structure (e.g. Nb 3 Si), three-component and more complex compounds, and superconductive amorphous systems(metglasses). It is emphasized that the exceeding of the paramagnetic limit of the critical magnetic field is often observed experimentally, and the prospects of critical field increase are sufficiently favourable. Considered is the role of narrow current channels in the formation of critical current density of superconductors

  6. Aeronautical applications of high-temperature superconductors

    Science.gov (United States)

    Turney, George E.; Luidens, Roger W.; Uherka, Kenneth; Hull, John

    1989-01-01

    The successful development of high-temperature superconductors (HTS) could have a major impact on future aeronautical propulsion and aeronautical flight vehicle systems. A preliminary examination of the potential application of HTS for aeronautics indicates that significant benefits may be realized through the development and implementation of these newly discovered materials. Applications of high-temperature superconductors (currently substantiated at 95 k) were envisioned for several classes of aeronautical systems, including subsonic and supersonic transports, hypersonic aircraft, V/STOL aircraft, rotorcraft, and solar, microwave and laser powered aircraft. Introduced and described are the particular applications and potential benefits of high-temperature superconductors as related to aeronautics and/or aeronautical systems.

  7. High Temperature Superconductor Bolometers for Planetary Science

    Data.gov (United States)

    National Aeronautics and Space Administration — This work is a design study of an instrument optimized for JPL's novel high temperature superconductor bolometers. The work involves designing an imaging...

  8. High temperature superconductors and other superfluids

    CERN Document Server

    Alexandrov, A S

    2017-01-01

    Written by eminent researchers in the field, this text describes the theory of superconductivity and superfluidity starting from liquid helium and a charged Bose-gas. It also discusses the modern bipolaron theory of strongly coupled superconductors, which explains the basic physical properties of high-temperature superconductors. This book will be of interest to fourth year graduate and postgraduate students, specialist libraries, information centres and chemists working in high-temperature superconductivity.

  9. 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...

  10. Magnetic Ordering in Layered High Temperature Superconductors

    OpenAIRE

    Sergeeva, G. G.

    1999-01-01

    We discuss the scenario of two-step magnetic ordering in layered high temperature superconductors after charge ordering. As the temperature decreases, the transition from 3D Heisenberg spin behavior to 2D XY coupling of the Cu spins occurs at Berezinskii-Kosterlitz-Thouless temperature in dielectric stripes. Further temperature decreasing leads to the 3D spin glass transition.

  11. 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.

  12. Critical de Broglie wavelength in superconductors

    Science.gov (United States)

    Talantsev, E. F.

    2018-03-01

    There are growing numbers of experimental evidences that the self-field critical currents, Jc(sf,T), are a new instructive tool to investigate fundamental properties of superconductors ranging from atomically thin films [M. Liao et al., Nat. Phys. 6 (2018), https://doi.org/10.1038/s41567-017-0031-6; E. F. Talantsev et al., 2D Mater. 4 (2017) 025072; A. Fete et al., Appl. Phys. Lett. 109 (2016) 192601] to millimeter-scale samples [E. F. Talantsev et al., Sci. Rep. 7 (2017) 10010]. The basic empirical equation which quantitatively accurately described experimental Jc(sf,T) was proposed by Talantsev and Tallon [Nat. Commun. 6 (2015) 7820] and it was the relevant critical field (i.e. thermodynamic field, Bc, for type-I and lower critical field, Bc1, for type-II superconductors) divided by the London penetration depth, λL. In this paper, we report new findings relating to this empirical equation. It is that the critical wavelength of the de Broglie wave, λdB,c, of the superconducting charge carrier which within a numerical pre-factor is equal to the largest of two characteristic lengths of Ginzburg-Landau theory, i.e. the coherence length, ξ, for type-I superconductors or the London penetration depth, λL, for type-II superconductors. We also formulate a microscopic criterion for the onset of dissipative transport current flow: ps ṡ 2ṡλL ln(1+2ṡ(λL ξ )) ≥ 1 2 ṡ ( h 2π), where ps is the charge carrier momentum, h is Planck’s constant and the inequality sign “ <” is reserved for the dissipation-free flow.

  13. Neutron diffraction, structural inorganic chemistry and high-temperature superconductors

    International Nuclear Information System (INIS)

    Hewat, A.W.

    1992-01-01

    This paper discusses neutron diffraction which has been of fundamental importance for the determination of the structure of high-temperature superconductors and for understanding the influence of structure on the critical temperature. This is because the new superconductors are heavy metal oxides; X-rays are mainly scattered by the metal atoms, but thermal neutrons are scattered as strongly by oxygen, which is the atom of most interest in these materials. In fact, for the past 20 yr, neutron diffraction has been steadily gaining ground as an important technique in structural inorganic chemistry

  14. 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...

  15. Critical current density versus normal-state resistivity in granular high-temperature superconductors with different average grain size

    International Nuclear Information System (INIS)

    Curras, S.R.; Veira, J.A.; Maza, J.; Vidal, Felix

    2000-01-01

    The resistivity, ρ, and the critical current density at zero applied magnetic field, J c , of ceramic Y 1 Ba 2 Cu 3 O 7-δ samples with different average grain size, a (from 5 to 14 μm), are reported. These results show that at a given temperature J c depends only on the specific contact resistance of the average grain boundary junction, ρ□, so that the product J c ρ□ is sample independent. The relevance of ρ□ and not of a on J c has been further tested on a subset of samples having very different average grain size but similar ρ□ for which negligible variations of J c are observed. (author)

  16. High temperature crystalline superconductors from crystallized glasses

    Science.gov (United States)

    Shi, Donglu

    1992-01-01

    A method of preparing a high temperature superconductor from an amorphous phase. The method involves preparing a starting material of a composition of Bi.sub.2 Sr.sub.2 Ca.sub.3 Cu.sub.4 Ox or Bi.sub.2 Sr.sub.2 Ca.sub.4 Cu.sub.5 Ox, forming an amorphous phase of the composition and heat treating the amorphous phase for particular time and temperature ranges to achieve a single phase high temperature superconductor.

  17. Improved critical current densities in bulk FeSe superconductor using ball milled powders and high temperature sintering

    Energy Technology Data Exchange (ETDEWEB)

    Muralidhar, M.; Furutani, K.; Murakami, M. [Graduate School of Science and Engineering, Superconducting Materials Laboratory, Shibaura Institute of Technology, Tokyo (Japan); Kumar, Dinesh; Rao, M.S. Ramachandra [Department of Physics, Nano Functional Materials Technology Centre and Materials Science Research Centre, Indian Institute of Technology Madras, Chennai (India); Koblischka, M.R. [Institute of Experimental Physics, Saarland University, Saarbruecken (Germany)

    2016-12-15

    The present study is investigating the effect of high temperature sintering combined with ball milled powders for the preparation of FeSe material via solid state sintering technique. The commercial powders of Fe (99.9% purity) and Se (99.9% purity) were mixed in a nominal ratio Fe:Se = 1:1 and thoroughly ground and ball-milled in a glove box during 6 h. Then, the powder mixture was pressed into pellets of 5 mm in diameter and 2 mm thickness using an uniaxial pressure of 100 MPa. The samples were sealed in quartz tubes and sintered at 600 C for 24 h. Then, the pellets were again thoroughly ground and ball-milled in the glove box and pressed into pellets, and the final sintering was performed at two different temperatures, namely at 900 C for 24 h and at 950 C for 24 h. X-ray diffraction results confirmed that both samples showed mainly of the β-FeSe with tetragonal structure. The temperature dependence of magnetization (M-T) curves revealed a sharp superconducting transition T{sub c,} {sub onset} = 8.16 K for the sample sintered at 900 C. Further, scanning electron microscopy observations proved that samples sintered at 900 C show a platelike grain structure with high density. As a result, improved irreversibility fields around 5 T and the critical current density (J{sub c}) values of 6252 A cm{sup -2} at 5 K and self-field are obtained. Furthermore, the normalized volume pinning force versus the reduced field plots indicated a peak position at 0.4 for the sample sintered at 900 C. Improved flux pinning and the high J{sub c} values are attributed to the textured microstructure of the material, produced by a combination of high temperature sintering and ball milling. (copyright 2016 The Authors. Phys. Status Solidi A published by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Electrochemical investigations of high-Tc superconductors - low-temperature electrochemistry

    International Nuclear Information System (INIS)

    Lorenz, W.J.

    1992-01-01

    This research report presents a summary of results obtained by electrochemical investigations of high-Tc superconductors at room temperature and below the critical temperature (Tc). The studies were to reveal the behaviour of the ceramic superconducting materials at the interface between superconductor and ionic conductor. (MM) With 4 tabs., 8 figs [de

  19. Evidence for self-organized criticality in the Bean critical state in superconductors

    Science.gov (United States)

    Aegerter, C. M.

    1998-08-01

    The time dependence of the magnetization of a type-II superconductor in the Bean critical state is studied. It is found that evolution occurs in the form of bursts, consistent with a model exhibiting self-organized criticality. The distribution of step sizes follows a power law with an exponent of α~= 2. At high temperatures the distribution is Gaussian-like, as would be expected in an equilibrium situation. This may allow the experimental study of the occurrence of criticality.

  20. Time dependence of magnetization of high temperature superconductors

    International Nuclear Information System (INIS)

    Larkin, A.I.; Geshkenbein, V.B.

    1988-10-01

    Magnetization of high T c superconductors logarithmically decreases with time. There is a maximum in the temperature dependence of the coefficient at this logarithm. If one assumes that there do exist two kinds of pinning centers, then this dependence can be described in the Anderson theory of thermal creeps of Abrikosov's vortices. The temperature dependence of the critical current is also discussed. (author). 23 refs

  1. Deformation of high-temperature superconductors

    International Nuclear Information System (INIS)

    Goretta, K.C.; Routbort, J.L.; Miller, D.J.; Chen, N.; Dominguez-Rodriguez, A.; Jimenez-Melendo, M.; De Arellano-Lopez, A.R.

    1994-08-01

    Of the many families of high-temperature superconductors, only the properties of those discovered prior to 1989 - Y-Ba-Cu-O, Tl-Ba(Sr)-Ca-Cu-O, and Bi(Pb)-Sr-Ca-Cu-O - have been studied extensively. Deformation tests have been performed on YBa 2 Cu 3 O x (Y-123), YBa 2 Cu 4 O x (Y-124), TlBa 2 Ca 2 Cu 3 O x (Bi-2223). The tests have revealed that plasticity is generally limited in these compounds and that the rate-controlling diffusional kinetics for creep are very slow. Nevertheless, hot forming has proved to be quite successful for fabrication of bulk high-temperature superconductors, so long as deformation rates are low or large hydrostatic stresses are applied. Steady-state creep data have proved to be useful in designing optimal heat treatments for superconductors and in support of more-fundamental diffusion experiments. The high-temperature superconductors are highly complex oxides, and it is a challenge to understand their deformation responses. In this paper, results of interest and operant creep mechanisms will be reviewed

  2. Technique of Critical Current Density Measurement of Bulk Superconductor with Linear Extrapolation Method

    International Nuclear Information System (INIS)

    Adi, Wisnu Ari; Sukirman, Engkir; Winatapura, Didin S.

    2000-01-01

    Technique of critical current density measurement (Jc) of HTc bulk ceramic superconductor has been performed by using linear extrapolation with four-point probes method. The measurement of critical current density HTc bulk ceramic superconductor usually causes damage in contact resistance. In order to decrease this damage factor, we introduce extrapolation method. The extrapolating data show that the critical current density Jc for YBCO (123) and BSCCO (2212) at 77 K are 10,85(6) Amp.cm - 2 and 14,46(6) Amp.cm - 2, respectively. This technique is easier, simpler, and the use of the current flow is low, so it will not damage the contact resistance of the sample. We expect that the method can give a better solution for bulk superconductor application. Key words. : superconductor, critical temperature, and critical current density

  3. Magnetic memory effects in high temperature superconductors

    International Nuclear Information System (INIS)

    Rockenbauer, A.

    1989-01-01

    Microwave absorption of high temperature oxide superconductors MBa 2 Cu 3 O 7 (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)

  4. Critical state in disk-shaped superconductors

    Science.gov (United States)

    Däumling, M.; Larbalestier, D. C.

    1989-11-01

    We have calculated the magnetic fields and currents occurring in a disk-shaped superconductor (radius >>thickness) in the critical state in a self-consistent way using finite-element analysis. We find that the field shielded (or trapped) in the center of the disk is roughly equal to Jcd, where d is the thickness of the disk. The shielding currents also create radial fields which are or order Jcd/2 on the disk surface. For low applied fields Happltelsa applied field. The field dependence of the calculated magnetic moment in the self-field dominated regime is independent of whether Jc is weakly or strongly (~1/H) dependent on field. The calculations were validated by comparison to both magnetic and resistive measurements on a disk-shaped section in Nb3Sn tape.

  5. High temperature superconductors applications in telecommunications

    International Nuclear Information System (INIS)

    Kumar, A.A.; Li, J.; Zhang, M.F.

    1994-01-01

    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 c superconductors

  6. Magnetic flow dynamics in critical state in discrete superconductor

    International Nuclear Information System (INIS)

    Ginzburg, S.L.; Nakin, A.V.; Savitskaya, N.E.

    2005-01-01

    Theoretic description of avalanche-like magnetic flow dynamics in critical state in discrete second class superconductor is given using model of the 1-D discrete superconductor. In the investigated system self-organizing critical state in a generalized sense is incarnated. This means that critical state consists of a great number of metastatic conditions, transferring one into another by means of avalanches. At the same time leap density of system's total magnetic flux presents a power function

  7. High temperature superconductor cable concepts for fusion magnets

    CERN Document Server

    AUTHOR|(CDS)2078397

    2013-01-01

    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. High temperature superconductor winding packs for fusion magnets are calculated and compared with corresponding low temperature superconductor cases.

  8. Recrystallization of high temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kouzoudis, Dimitris [Iowa State Univ., Ames, IA (United States)

    1996-05-09

    Currently one of the most widely used high Tc superconductors is the Bi-based compounds Bi2Sr2CaCu2Oz and Bi2Sr2Ca2Cu3Oz (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.

  9. Critical fluctuations in topologically massive superconductors

    International Nuclear Information System (INIS)

    Malbouisson, A.P.C.; Nogueira, F.S.; Svaiter, N.F.

    1996-09-01

    We consider a topologically massive Ginzburg-Landau model of superconductivity. In the context of a mean field calculation, we show that there is an increase in the critical temperature driven by the topological term. It is shown that this effect persists even if we take into account the critical fluctuations. The renormalization group analysis gives further insight on this behavior. The fixed point structure is such that the critical exponents tend to their mean field for very large values of the topological mass. In this sense, the topological term stabilizes the critical fluctuations of the order parameters. (author). 13 refs

  10. Quench in high temperature superconductor magnets

    CERN Document Server

    Schwartz, J.

    2013-01-01

    High field superconducting magnets using high temperature superconductors are being developed for high energy physics, nuclear magnetic resonance and energy storage applications. Although the conductor technology has progressed to the point where such large magnets can be readily envisioned, quench protection remains a key challenge. It is well-established that quench propagation in HTS magnets is very slow and this brings new challenges that must be addressed. In this paper, these challenges are discussed and potential solutions, driven by new technologies such as optical fiber based sensors and thermally conducting electrical insulators, are reviewed.

  11. Model for the resistive critical current transition in composite superconductors

    International Nuclear Information System (INIS)

    Warnes, W.H.

    1988-01-01

    Much of the research investigating technological type-II superconducting composites relies on the measurement of the resistive critical current transition. We have developed a model for the resistive transition which improves on older models by allowing for the very different nature of monofilamentary and multifilamentary composite structures. The monofilamentary model allows for axial current flow around critical current weak links in the superconducting filament. The multifilamentary model incorporates an additional radial current transfer between neighboring filaments. The development of both models is presented. It is shown that the models are useful for extracting more information from the experimental data than was formerly possible. Specific information obtainable from the experimental voltage-current characteristic includes the distribution of critical currents in the composite, the average critical current of the distribution, the range of critical currents in the composite, the field and temperature dependence of the distribution, and the fraction of the composite dissipating energy in flux flow at any current. This additional information about the distribution of critical currents may be helpful in leading toward a better understanding of flux pinning in technological superconductors. Comparison of the models with several experiments is given and shown to be in reasonable agreement. Implications of the models for the measurement of critical currents in technological composites is presented and discussed with reference to basic flux pinning studies in such composites

  12. Low-Temperature Synthesis Routes to Intermetallic Superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Schaak, Raymond E

    2008-01-08

    Over the past few years, our group has gained expertise at developing low-temperature solution-based synthetic pathways to complex nanoscale solids, with particular emphasis on nanocrystalline intermetallic compounds. Our synthetic capabilities are providing tools to reproducibly generate intermetallic nanostructures with simultaneous control over crystal structure, composition, and morphology. This DOE-funded project aims to expand these capabilities to intermetallic superconductors. This could represent an important addition to the tools that are available for the synthesis and processing of intermetallic superconductors, which traditionally utilize high-temperature, high-pressure, thin film, or gas-phase vacuum deposition methods. Our current knowledge of intermetallic superconductors suggests that significant enhancements could result from the inherent benefits of low-temperature solution synthesis, e.g. metastable phase formation, control over nanoscale morphology to facilitate size-dependent property studies, robust and inexpensive processability, low-temperature annealing and consolidation, and impurity incorporation (for doping, stoichiometry control, flux pinning, and improving the critical fields). Our focus is on understanding the superconducting properties as a function of synthetic route, crystal structure, crystallite size, and morphology, and developing the synthetic tools necessary to accomplish this. This research program can currently be divided into two classes of superconducting materials: intermetallics (transition metal/post transition metal) and metal carbides/borides. Both involve the development and exploitation of low-temperature synthesis routes followed by detailed characterization of structures and properties, with the goal of understanding how the synthetic pathways influence key superconducting properties of selected target materials. Because of the low-temperature methods used to synthesize them and the nanocrystalline morphologies

  13. Potential aerospace applications of high temperature superconductors

    Science.gov (United States)

    Selim, Raouf

    1994-12-01

    The recent discovery of High Temperature Superconductors (HTS) with superconducting transition temperature, T(sub c), above the boiling point of liquid nitrogen has opened the door for using these materials in new and practical applications. These materials have zero resistance to electric current, have the capability of carrying large currents and as such have the potential to be used in high magnetic field applications. One of the space applications that can use superconductors is electromagnetic launch of payloads to low-earth-orbit. An electromagnetic gun-type launcher can be used in small payload systems that are launched at very high velocity, while sled-type magnetically levitated launcher can be used to launch larger payloads at smaller velocities. Both types of launchers are being studied by NASA and the aerospace industry. The use of superconductors will be essential in any of these types of launchers in order to produce the large magnetic fields required to obtain large thrust forces. Low Temperature Superconductor (LTS) technology is mature enough and can be easily integrated in such systems. As for the HTS, many leading companies are currently producing HTS coils and magnets that potentially can be mass-produced for these launchers. It seems that designing and building a small-scale electromagnetic launcher is the next logical step toward seriously considering this method for launching payloads into low-earth-orbit. A second potential application is the use of HTS to build sensitive portable devices for the use in Non Destructive Evaluation (NDE). Superconducting Quantum Interference Devices (SQUID's) are the most sensitive instruments for measuring changes in magnetic flux. By using HTS in SQUID's, one will be able to design a portable unit that uses liquid nitrogen or a cryocooler pump to explore the use of gradiometers or magnetometers to detect deep cracks or corrosion in structures. A third use is the replacement of Infra-Red (IR) sensor leads on

  14. Influence of anisotropy and pinning centers on critical current properties in Bi-2212 superconductors

    International Nuclear Information System (INIS)

    Haraguchi, T.; Takayama, S.; Kiuchi, M.; Otabe, E.S.; Matsushita, T.; Yasuda, T.; Okayasu, S.; Uchida, S.; Shimoyama, J.; Kishio, K.

    2006-01-01

    The critical current density in Bi-2212 superconductors with various anisotropies irradiated by heavy ions was investigated in the medium temperature region to understand the effects of defect size and the anisotropy of the superconductor. It was found that the critical current density and the irreversibility field were larger for the specimen with larger defect and/or with smaller anisotropy. Introduction of stronger pinning centers and the optimization of the doping condition to improve the dimensionality are desired for further improvement of the critical current properties

  15. Processing of bulk Bi-2223 high-temperature superconductor

    Directory of Open Access Journals (Sweden)

    Alexander Polasek

    2005-12-01

    Full Text Available The Bi2Sr2Ca2Cu3 O10+x (Bi-2223 is one of the main high temperature superconductors for applications. One of these applications is the Superconductor Fault Current Limiter (SCFCL, which is a very promising high temperature superconducting device. SCFCL's can be improved by using bulk superconductors with high critical currents, which requires a sufficiently dense and textured material. In the present work, a process for improving the microstructure of Bi-2223 bulk samples is investigated. Pressed precursor blocks are processed by sintering with a further partial melting step, in order to enhance the Bi-2223 grain texture and to healing cracks induced by pressing. In order to improve the microstructure, the precursor is mixed with silver powder before pressing. Samples with and without silver powder have been studied, with the aim of investigating the influence of silver on the microstructure evolution. The phase contents and the microstructure obtained have been analyzed through XRD and SEM/EDS. The electromagnetic characterization has been performed by Magnetic Susceptibility Analysis. We present and discuss the process and the properties of the superconducting blocks. High fractions of textured Bi-2223 grains have been obtained.

  16. Superconducting critical temperature under pressure

    Science.gov (United States)

    González-Pedreros, G. I.; Baquero, R.

    2018-05-01

    The present record on the critical temperature of a superconductor is held by sulfur hydride (approx. 200 K) under very high pressure (approx. 56 GPa.). As a consequence, the dependence of the superconducting critical temperature on pressure became a subject of great interest and a high number of papers on of different aspects of this subject have been published in the scientific literature since. In this paper, we calculate the superconducting critical temperature as a function of pressure, Tc(P), by a simple method. Our method is based on the functional derivative of the critical temperature with the Eliashberg function, δTc(P)/δα2F(ω). We obtain the needed coulomb electron-electron repulsion parameter, μ*(P) at each pressure in a consistent way by fitting it to the corresponding Tc using the linearized Migdal-Eliashberg equation. This method requires as input the knowledge of Tc at the starting pressure only. It applies to superconductors for which the Migdal-Eliashberg equations hold. We study Al and β - Sn two weak-coupling low-Tc superconductors and Nb, the strong coupling element with the highest critical temperature. For Al, our results for Tc(P) show an excellent agreement with the calculations of Profeta et al. which are known to agree well with experiment. For β - Sn and Nb, we found a good agreement with the experimental measurements reported in several works. This method has also been applied successfully to PdH elsewhere. Our method is simple, computationally light and gives very accurate results.

  17. Theory of the upper critical field in layered superconductors

    International Nuclear Information System (INIS)

    Klemm, R.A.; Luther, A.; Beasley, M.R.

    1975-01-01

    The upper critical field H/subc/ 2 in layered superconductors is calculated from a microscopic theory in which the electrons are assumed to propagate freely within the individual layers subject to scattering off impurities and to propagate via tunneling between the layers. For the magnetic field parallel to the layers, there is a temperature T* 2 /sub parallel/ is thus determined by the combined effects of Pauli paramagnetism and spin-orbit scattering, and for sufficiently strong spin-orbit scattering rates, H/subc/ 2 /sub parallel/(T =0) can greatly exceed the Chandrasekhar-Clogston Pauli limiting field H/subP/. This unusual behavior is found to be most pronounced in the dirty limit for the electron propagation within the layers and when the electrons scatter many times in a given layer before tunneling to an adjacent layer. Our results are also discussed in light of the available experimental data. (auth)

  18. Electron-beam damaged high-temperature superconductor Josephson junctions

    International Nuclear Information System (INIS)

    Pauza, A.J.; Booij, W.E.; Herrmann, K.; Moore, D.F.; Blamire, M.G.; Rudman, D.A.; Vale, L.R.

    1997-01-01

    Results are presented on the fabrication and characterization of high critical temperature Josephson junctions in thin films of YBa 2 Cu 3 O 7-δ produced by the process of focused electron-beam irradiation using 350 keV electrons. The junctions so produced have uniform spatial current densities, can be described in terms of the resistive shunted junction model, and their current densities can be tailored for a given operating temperature. The physical properties of the damaged barrier can be described as a superconducting material of either reduced or zero critical temperature (T c ), which has a length of ∼15nm. The T c reduction is caused primarily by oxygen Frenkel defects in the Cu - O planes. The large beam currents used in the fabrication of the junctions mean that the extent of the barrier is limited by the incident electron-beam diameter, rather than by scattering within the film. The properties of the barrier can be calculated using a superconductor/normal/superconductor (SNS) junction model with no boundary resistance. From the SNS model, we can predict the scaling of the critical current resistance (I c R n ) product and gain insight into the factors controlling the junction properties, T c , and reproducibility. From the measured I c R n scaling data, we can predict the I c R n product of a junction at a given operating temperature with a given current density. I c R n products of ∼2mV can be achieved at 4.2 K. The reproducibility of several junctions in a number of samples can be characterized by the ratio of the maximum-to-minimum critical currents on the same substrate of less than 1.4. Stability over several months has been demonstrated at room and refrigerator temperatures (297 and 281 K) for junctions that have been initially over damaged and then annealed at temperatures ∼380K. (Abstract Truncated)

  19. Electronic phase separation and high temperature superconductors

    International Nuclear Information System (INIS)

    Kivelson, S.A.

    1994-01-01

    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

  20. Rare earth magnetism in high-temperature and borocarbide superconductors

    International Nuclear Information System (INIS)

    Allenspach, P.; Gasser, U.

    2000-01-01

    High-temperature superconductors possess - besides their superconductivity - other fascinating features such as a rich magnetic phase diagram. While it is normally believed that superconductivity and rare-earth magnetism is decoupled in these systems a closer investigation clearly proves that both effects in a very similar manner depend on the doping of charge carriers. An inhomogeneous charge distribution results in inhomogeneous superconductivity and a loss of long-range magnetic order. Magnetic borocarbides are ideal model systems for an investigation into the interaction of superconductivity and (collective) magnetism due to their similar values for the critical temperature of superconductivity and the magnetic ordering temperature. Both lie typically below 15 K and are hence in a comfortable temperature regime for measurements. We will present for both classes of the above substances an analysis based on a wide variety of different measurements (susceptibility, specific heat, neutron diffraction and spectroscopy). This analysis provides an almost universal, phenomenological picture of their magnetic properties. (orig.)

  1. High-temperature superconductors in application - fight for the top

    International Nuclear Information System (INIS)

    Anon.

    1990-01-01

    For the superconductor market two-digit growth rates are predicted until after the year 2000. The decrosslinking of the high temperature superconductors initiated a worldwide race for first applications. The report considers the situation of raw materials and the application potentials in the USA, Japan and Western Europe. (orig.) [de

  2. Surface critical magnetic field Hc3 (T) of a bulk superconductor ...

    Indian Academy of Sciences (India)

    ... surface critical magnetic field Hc3(). It is shown that c3() has the same temperature dependence with c2(), similar to the case of a single-band superconductor, c3()=1.66 c2(). We use an elimination procedure for the decoupling of G–L equations of two-band superconductivity, which eases the calculations.

  3. Self-organizing of critical state in granulated superconductors

    International Nuclear Information System (INIS)

    Ginzburg, S.L.; Savitskaya, N.E.

    2000-01-01

    Critical state in granulated superconductors was studied on the basis of two mathematical models - the system of differential equations for calibration and invariant difference of phases and a simplified model describing the system of associated images and equivalent to the standard models to study self-organizing criticality. The critical state of granulated superconductors in all studied cases was shown to be self-organized. Besides, it is shown that the applied models are practically equivalent ones, that is they both show similar critical behavior and lead to coincidence of noncritical phenomena. For the first time one showed that the occurrence of self-organized critically within the system of nonlinear differential equations and its equivalence to self-organized critically in the standard models [ru

  4. High temperature superconductors: A technological revolution

    Science.gov (United States)

    1990-01-01

    The objectives are to demonstrate the Meissner effect through magnetic levitation, to demonstrate one application of the Meissner effect, the low friction magnetic rotation bearing, and to demonstrate magnetic flux penetration and the Type II nature of ceramic superconductors via the stacking of the superconductor disks. Experimental equipment and procedures are described.

  5. Flux-flow resistivity of three high-temperature superconductors

    International Nuclear Information System (INIS)

    Cha, Y.S.; Evans, D.J.; Hull, J.R.; Seol, S.Y.

    1996-01-01

    Results of experiments on flux-flow resistivity (the relationship of voltage to current) of three high-temperature superconductors are described. The superconductors are a melt-cast BSCCO 2212 rod, a single filament BSCCO powder-in-tube (PIT) tape, and a multifilament PIT tape. The flux-flow resistivity of these superconductors was measured at three temperatures: 77 K (saturated liquid nitrogen), 87 K (saturated liquid argon), and 67 K (subcooled liquid nitrogen). Implications of the present results for practical applications are discussed

  6. 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)

  7. Status of high temperature superconductor development for accelerator magnets

    Science.gov (United States)

    Hirabayashi, H.

    1995-01-01

    High temperature superconductors are still under development for various applications. As far as conductors for magnets are concerned, the development has just been started. Small coils wound by silver sheathed Bi-2212 and Bi-2223 oxide conductors have been reported by a few authors. Essential properties of high T(sub c) superconductors like pinning force, coherent length, intergrain coupling, weak link, thermal property, AC loss and mechanical strength are still not sufficiently understandable. In this talk, a review is given with comparison between the present achievement and the final requirement for high T(sub c) superconductors, which could be particularly used in accelerator magnets. Discussions on how to develop high T(sub c) superconductors for accelerator magnets are included with key parameters of essential properties. A proposal of how to make a prototype accelerator magnet with high T(sub c) superconductors with prospect for future development is also given.

  8. Potential impact of high temperature superconductors on maglev transportation

    Energy Technology Data Exchange (ETDEWEB)

    Hull, J.R.

    1992-02-01

    This report describes the potential impact that high-temperature superconductors (HTSs) may have on transportation by magnetically levitated vehicles. It is not intended as a planning document, but rather as an overview of potential HTS applications to magnetic-levitation (maglev) transportation. The present maglev program in the United States is summarized, and the present status of development of HTSs is described. Areas identified for possible impact on maglev technology are (1) liquid-nitrogen-cooled levitation magnets, (2) magnetic-field shielding of the passenger compartment, (3) superconducting magnetic energy storage for wayside power, (4) superconducting bearings for flywheel energy storage for wayside power, (5) downleads to continuously powered liquid-helium-cooled levitation magnets, and (6) liquid-hydrogen-cooled levitation magnets and linear motor propulsion windings. Major technical issues that remain to be resolved for the use of HTSs in maglev applications include thermal magnetic stability, mechanical properties, and critical current density at liquid-nitrogen temperatures.

  9. Surface critical magnetic field Hc3(T) of a bulk superconductor MgB2 ...

    Indian Academy of Sciences (India)

    Abstract. Two-band Ginzburg–Landau (TB G–L) equations for a bulk MgB2 were solved analyti- cally to determine the temperature dependence of surface critical magnetic field Hc3(T). It is shown that Hc3(T) has the same temperature dependence with Hc2(T), similar to the case of a single-band superconductor, Hc3(T) ...

  10. 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?

  11. Stress analysis in high-temperature superconductors under pulsed field magnetization

    Science.gov (United States)

    Wu, Haowei; Yong, Huadong; Zhou, Youhe

    2018-04-01

    Bulk high-temperature superconductors (HTSs) have a high critical current density and can trap a large magnetic field. When bulk superconductors are magnetized by the pulsed field magnetization (PFM) technique, they are also subjected to a large electromagnetic stress, and the resulting thermal stress may cause cracking of the superconductor due to the brittle nature of the sample. In this paper, based on the H-formulation and the law of heat transfer, we can obtain the distributions of electromagnetic field and temperature, which are in qualitative agreement with experiment. After that, based on the dynamic equilibrium equations, the mechanical response of the bulk superconductor is determined. During the PFM process, the change in temperature has a dramatic effect on the radial and hoop stresses, and the maximum radial and hoop stress are 24.2 {{MPa}} and 22.6 {{MPa}}, respectively. The mechanical responses of a superconductor for different cases are also studied, such as the peak value of the applied field and the size of bulk superconductors. Finally, the stresses are also presented for different magnetization methods.

  12. 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...

  13. Ceramic high temperature superconductor levitating motor with laser commutator

    International Nuclear Information System (INIS)

    Roslan Abd Shukor; Lee Keng Heong

    1996-01-01

    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

  14. Resistive current limiter with high-temperature superconductors. Final report

    International Nuclear Information System (INIS)

    Schubert, M.

    1995-12-01

    Fundamental results of the possibility of using high temperature superconductors (HTSC) in resistive fault current limiters are discussed. Measurement of the homogeneity of BSCCO-powder-in-tube materials were made. In addition, investigations of the transition from superconducting to normalconducting state under AC-current conditions were carried out. Based on these results, simulations of HTSC-materials on ceramic substrate were made and recent results are presented. Important results of the investigations are: 1. Current-limiting without external trigger only possible when the critical current density of HTSC exceeds 10 4 A/cm 2 . 2. Inhomogeneities sometimes cause problems with local destruction. This can be solved by parallel-elements or external trigger. 3. Fast current-limiting causes overvoltages which can be reduced by using parallel-elements. (orig.) [de

  15. Vortex edge barriers and critical current density in granular superconductors

    CERN Document Server

    Belevtsov, L V

    2003-01-01

    Type-II superconductors, even without bulk pinning and in the absence of a macroscopic Bean-Livingston surface barrier for vortex penetration, can exhibit barriers for flux penetration. We investigated some new edge barriers based on the laminar model, that are governed by the anisotropy ratio, grain coupling strength, and grain size. Expressions describing the pinning potential U sub p and critical current density J sub c are derived for magnetic fields near H sub c sub 1. It is shown that edge barrier effects play a substantial role in a realistic description of the critical current density for both MgB sub 2 and high-T sub c superconductors. (Abstract Copyright [2003], Wiley Periodicals, Inc.)

  16. Probing High Temperature Superconductors with Magnetometry in Ultrahigh Magnetic Fields

    Energy Technology Data Exchange (ETDEWEB)

    Li, Lu [Univ. of Michigan, Ann Arbor, MI (United States)

    2017-07-26

    The objective of this research is to investigate the high-field magnetic properties of high temperature superconductors, materials that conduct electricity without loss. A technique known as high-resolution torque magnetometry that was developed to directly measure the magnetization of high temperature superconductors. This technique was implemented using the 65 Tesla pulsed magnetic field facility that is part of the National High Magnetic Field Laboratory at Los Alamos National Laboratory. This research addressed unanswered questions about the interplay between magnetism and superconductivity, determine the electronic structure of high temperature superconductors, and shed light on the mechanism of high temperature superconductivity and on potential applications of these materials in areas such as energy generation and power transmission. Further applications of the technology resolve the novel physical phenomena such as correlated topological insulators, and spin liquid state in quantum magnets.

  17. Transport measurements in superconductors: critical current of granular high TC ceramic superconductor samples; Medidas de transporte em supercondutores: corrente critica de supercondutores granulares de alta temperatura critica

    Energy Technology Data Exchange (ETDEWEB)

    Passos, W.A.C., E-mail: wagner.passos@univasf.edu.br [Universidade Federal do Vale do Sao Francisco (IPCM/UNIVASF), Juazeiro do Norte, BA (Brazil). Instituto de Pesquisas em Ciencia dos Materiais; Silva, E.B. [Companhia Energetica do Sao Francisco (CHESF), Recife, PE (Brazil)

    2016-07-01

    This work presents a method to obtain critical current of granular superconductors. We have carried out transport measurements (ρxT curves and VxI curves) in a YBa{sub 2}Cu{sub 3}O{sub 7-δ} sample to determine critical current density of it. Some specimens reveal a 'semiconductor-like' behavior (electrical resistivity decreases with increasing temperatures above critical temperature T{sub c} of material) competing with superconductor behavior. Due to high granular fraction of the sample, these competition is clearly noted in ρxT curves. Measurements carried out from 0 to 8500 Oe of applied field show the same behavior, and the critical current density of the samples is shown. (author)

  18. The Born-Mayer-Huggins potential in high temperature superconductors

    Science.gov (United States)

    Singh, Hempal; Singh, Anu; Indu, B. D.

    2016-07-01

    The Born-Mayer-Huggins potential which has been found the best suitable potential to study the YBa2Cu3O7-δ type high temperature superconductors is revisited in a new framework. A deeper insight in it reveals that the Born-Mayer parameters for different interactions in high temperature superconductor are not simple quantities but several thermodynamic and spatial functions enter the problem. Based on the new theory, the expressions for pressure, bulk modulus and Born-Mayer parameters have been derived and it is established that these quantities depend upon Gruneisen parameter which is the measure of the strength of anharmonic effects in high temperature superconductors. This theory has been applied to a specific model YBa2Cu3O7-δ crystal for the purpose of numerical estimates to justify the new results.

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

    DEFF Research Database (Denmark)

    Lake, B.; Aeppli, G.; Clausen, K.N.

    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...

  20. Some new aspects of super-high temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Huang, C.Y. (Research and Development Div., Lockheed Missiles and Space Co., Palto Alto, CA (US)); Rabinowitz, M. (Electric Power Research Inst., Palo Alto, CA (USA). Electrical Systems Div.)

    1990-05-01

    The authors review some salient features of the recently observed experimental evidence of ceramic super-high temperature superconductivity (T{sub c} {gt} 200 K). Two theoretical estimates which are capable of accounting for super-high T{sub c} are presented. For comparison, several reports on non-ceramic oxide super-high temperature superconductors are discussed.

  1. Development of high temperature superconductors for magnetic field applications

    International Nuclear Information System (INIS)

    Larbalestier, D.C.

    1991-01-01

    The key requirement for magnetic field applications of high temperature superconductor (HTS) materials is to have conductors with high transport critical current density available for magnet builders. After 3 or 4 years of being without any such object, conductor makers have had recent success in producing simple conductor prototypes. These have permitted the construction of simple HTS magnets having self fields exceeding 1 tesla at 4K. Thus the scientific feasibility of making powerful HTS magnets has been demonstrated. Attention to the technological aspects of making HTS conductors for magnets with strong flux pinning and reduced superconducting granularity is now sensible and attractive. However, extrinsic defects such as filament sausaging, cracking, misaligned grains and other perturbations to long range current flow must be controlled at a low level if the benefit of intrinsic improvements to the critical current density is to be maintained in the conductor form. Due to the great complexity of HTS materials, there is sometimes confusion as to whether a given sample has an intrinsically or extrinsically limited critical current density. Systematic microstructure variation experiments and resistive transition analysis are shown to be particularly helpful in this phase of conductor development

  2. Proceedings, phenomenology and applications of high temperature superconductors

    International Nuclear Information System (INIS)

    Bedell, K.S.

    1991-01-01

    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

  3. PR IN HIGH-TEMPERATURE SUPERCONDUCTORS - INSULATING PLANES, METALLIC CHAINS

    NARCIS (Netherlands)

    KHOMSKII, D

    Critical discussion is given of the properties of Pr-containing high-T(c) superconductors, especially Y1-xPrxBa2Cu3O7. It is argued that the models proposed to explain suppression of T(c) and other properties of this system (pairbreaking; hole filling; strong p-f hybridization) are inadequate and

  4. Pressure induced superconductor quantum critical point in multi-band systems

    Energy Technology Data Exchange (ETDEWEB)

    Padilha, Igor T. [Instituto de Fisica, Universidade Federal Fluminense, Campus da Praia Vermelha, 24210-346 Niteroi, RJ (Brazil); Continentino, Mucio A. [Centro Brasileiro de Pesquisas Fisicas, Rua Dr. Xavier Sigaud 150, Rio de Janeiro, RJ, 22290-180 (Brazil)], E-mail: mucio@if.uff.br

    2009-10-15

    In multi-band superconductors as inter-metallic systems and heavy fermions, external pressure can reduce the critical temperature and eventually destroy superconductivity driving these systems to the normal state. In many cases this transition is continuous and is associated with a superconducting quantum critical point (SQCP). In this work we study a two-band superconductor in the presence of hybridization V. This one-body mixing term is due to the overlap of the different wave-functions. It can be tuned by external pressure and turns out as an important control parameter to study the phase diagram and the nature of the phase transitions. We use a BCS approximation and include both inter- and intra-band attractive interactions. For negligible inter-band interactions, as hybridization (pressure) increases we find a SQCP separating a superconductor from a normal state at a critical value of the hybridization V{sub c}. We obtain the behavior of the electronic specific heat close to the SQCP and the shape of the critical line as V approaches V{sub c}.

  5. Quantum critical scaling at the edge of Fermi liquid stability in a cuprate superconductor.

    Science.gov (United States)

    Butch, Nicholas P; Jin, Kui; Kirshenbaum, Kevin; Greene, Richard L; Paglione, Johnpierre

    2012-05-29

    In the high-temperature cuprate superconductors, the pervasiveness of anomalous electronic transport properties suggests that violation of conventional Fermi liquid behavior is closely tied to superconductivity. In other classes of unconventional superconductors, atypical transport is well correlated with proximity to a quantum critical point, but the relative importance of quantum criticality in the cuprates remains uncertain. Here, we identify quantum critical scaling in the electron-doped cuprate material La(2-x)Ce(x)CuO(4) with a line of quantum critical points that surrounds the superconducting phase as a function of magnetic field and charge doping. This zero-temperature phase boundary, which delineates a metallic Fermi liquid regime from an extended non-Fermi liquid ground state, closely follows the upper critical field of the overdoped superconducting phase and gives rise to an expanse of distinct non-Fermi liquid behavior at finite temperatures. Together with signatures of two distinct flavors of quantum fluctuations, these facts suggest that quantum criticality plays a significant role in shaping the anomalous properties of the cuprate phase diagram.

  6. Survey of potential electronic applications of high temperature superconductors

    International Nuclear Information System (INIS)

    Hammond, R.B.; Bourne, L.C.

    1991-01-01

    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

  7. Temperature Induced Degradation of Nb Ti/Cu Composite Superconductors

    CERN Document Server

    Scheuerlein, C; Senatore, C; Di Michiel, M; Thilly, L; Gerardin, A; Reluner, B; Oberli, L; Willering, G; Bottura, L

    2009-01-01

    The degradation mechanisms of state-of-the-art Nb-Ti/Cu superconductors are described, based on in-situ synchrotron X-ray diffraction measurements during heat treatment. A quantitative description of the Nb-Ti/Cu degradation in terms of critical current density, Cu stabiliser resistivity and mechanical composite strength is presented. In an applied magnetic field a significant critical current degradation is already observed after a 5-minute 400 °C heat treatment, due to variations of a-Ti precipitate size and distribution within the Nb-Ti alloy filaments. A strong degradation of the strand mechanical properties is observed after several minutes heating above 550 °C, which is also the temperature at which the formation of Cu Ti intermetallic phases is detected. Several minutes heating at 250 °C are sufficient to increase the RRR of the strongly cold work strands inside a Rutherford type cable from about 80 to about 240. Heating for several minutes at 400 °C does not cause a significant conductor degradati...

  8. Study of high-temperature superconductors by IBA methods

    Science.gov (United States)

    Chamera, D.; Suchańska, M.; Kozel, V. V.

    1992-02-01

    The ion-induced electron emission (IIEE) technique to study the high- Tc superconductor of the Y 1Ba 2Cu 3O7 - x type was used. The temperature dependence of the IIEE intensity I( T) within the range of 77-300 K was measured. The change of the shape of the I( T) curve at the point 140 K was observed. The ion-induced photon emission technique (IIPE) to study the same high-temperature superconductor was also used. The temperature dependence of the intensity of some emission lines (BaI — 455.5 nm, CuI — 324.7 nm, YI — 467.4 nm) was measured. No anomaly at the point 140 K was observed. The nonmonotonic dependence of the IIEE intensity on the target temperature and the behaviour of the temperature dependence of the IIPE intensity are discussed.

  9. Study of high-temperature superconductors by IBA methods

    Energy Technology Data Exchange (ETDEWEB)

    Chamera, D.; Suchanska, M. (Inst. of Physics, Pedagogical Univ., Kielce (Poland)); Kozel, V.V. (Dept. of Physics, State Univ., Donetsk (USSR))

    1992-02-01

    The ion-induced electron emission (IIEE) technique to study the high-Tc superconductor of the Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-x} type was used. The temperature dependence of the IIEE intensity I(T) within the range of 77-300 K was measured. The change of the shape of the I(T) curve at the point 140 K was observed. The ion-induced photon emission technique (IIPE) to study the same high-temperature superconductor was also used. The temperature dependence of the intensity of some emission lines (BaI - 455.5 nm, CuI - 324.7 nm, YI - 467.4 nm) was measured. No anomaly at the point 140 K was observed. The nonmonotonic dependence of the IIEE intensity on the target temperature and the behaviour of the temperature dependence of the IIPE intensity are discussed. (orig.).

  10. Flux pinning and critical current in layered type-II superconductors in parallel magnetic fields

    International Nuclear Information System (INIS)

    Prokic, V.; Davidovic, D.; Dobrosavljevic-Grujic, L.

    1995-01-01

    We have shown, within the Ginzburg-Landau theory, that the interaction between vortices and normal-metal layers in high-T c superconductor--normal-metal superlattices can cause high critical-current densities j c . The interaction is primarily magnetic, except at very low temperatures T, where the core interaction is dominant. For a lattice of vortices commensurate with an array of normal-metal layers in a parallel magnetic field H, strong magnetic pinning is obtained, with a nonmonotonic critical-current dependence on H, and with j c of the order of 10 7 --10 8 A/cm 2

  11. Pseudogap temperature T* of cuprate superconductors from the Nernst effect

    Science.gov (United States)

    Cyr-Choinière, O.; Daou, R.; Laliberté, F.; Collignon, C.; Badoux, S.; LeBoeuf, D.; Chang, J.; Ramshaw, B. J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Yan, J.-Q.; Cheng, J.-G.; Zhou, J.-S.; Goodenough, J. B.; Pyon, S.; Takayama, T.; Takagi, H.; Doiron-Leyraud, N.; Taillefer, Louis

    2018-02-01

    We use the Nernst effect to delineate the boundary of the pseudogap phase in the temperature-doping phase diagram of hole-doped cuprate superconductors. New data for the Nernst coefficient ν (T ) of YBa2Cu3Oy (YBCO), La1.8 -xEu0.2SrxCuO4 (Eu-LSCO), and La1.6 -xNd0.4SrxCuO4 (Nd-LSCO) are presented and compared with previously published data on YBCO, Eu-LSCO, Nd-LSCO, and La2 -xSrxCuO4 (LSCO). The temperature Tν at which ν /T deviates from its high-temperature linear behavior is found to coincide with the temperature at which the resistivity ρ (T ) deviates from its linear-T dependence, which we take as the definition of the pseudogap temperature T★—in agreement with the temperature at which the antinodal spectral gap detected in angle-resolved photoemission spectroscopy (ARPES) opens. We track T★ as a function of doping and find that it decreases linearly vs p in all four materials, having the same value in the three LSCO-based cuprates, irrespective of their different crystal structures. At low p ,T★ is higher than the onset temperature of the various orders observed in underdoped cuprates, suggesting that these orders are secondary instabilities of the pseudogap phase. A linear extrapolation of T★(p ) to p =0 yields T★(p →0 ) ≃TN (0), the Néel temperature for the onset of antiferromagnetic order at p =0 , suggesting that there is a link between pseudogap and antiferromagnetism. With increasing p ,T★(p ) extrapolates linearly to zero at p ≃pc 2 , the critical doping below which superconductivity emerges at high doping, suggesting that the conditions which favor pseudogap formation also favor pairing. We also use the Nernst effect to investigate how far superconducting fluctuations extend above the critical temperature Tc, as a function of doping, and find that a narrow fluctuation regime tracks Tc, and not T★. This confirms that the pseudogap phase is not a form of precursor superconductivity, and fluctuations in the phase of the

  12. High temperature superconductors in electromagnetic applications

    International Nuclear Information System (INIS)

    Richens, P.E.

    2000-01-01

    The design, construction, and characterization of a High Temperature Superconducting (HTS) magnet is described. The design stage has involved the development of computer software for the calculation of the critical current of a solenoid wound from anisotropic HTS conductor. This calculation can be performed for a variety of problems including those involving magnetic materials such as iron by the incorporation of finite element electromagnetic analysis software. This has enabled the optimization of the magnet's performance. The HTS magnet is wound from 190 m of silver-matrix Bi 2 Sr 2 Ca 2 Cu 3 O 10 powder-in-tube tape conductor supplied by Intermagnetics General Corporation. The dimensions are 70 mm bore and 70 mm length, and it consists of 728 turns. Iron end-plates were utilized in order to reduce the radial magnetic field, and consequently increase the performance by ∼ 20%. The magnet has been operated in liquid cryogens and has achieved engineering current densities of 900 A cm -2 at 77 K and 6680 A cm -2 at 4.2 K. The HTS magnet has been operated by conduction-cooling on a mechanical refrigerator at various temperatures in the range 12 to 50 K. The thermal stability in this relatively low cooling-power system has been assessed. An engineering current density of 5600 A cm -2 was achieved at 12 K. Measurements of the strain dependence of the critical current in a variety of HTS conductors, including powder-in-tube and dip-coated, have been made using a novel single loop tensometer that enables the insertion of a reasonably long length of conductor into the bore of a high-field magnet. (author)

  13. Fermionic spectral functions in backreacting p-wave superconductors at finite temperature

    Energy Technology Data Exchange (ETDEWEB)

    Giordano, G.L.; Grandi, N.E.; Lugo, A.R. [Instituto de Física de La Plata - CONICET & Departamento de Física - UNLP,C.C. 67, 1900 La Plata (Argentina)

    2017-04-14

    We investigate the spectral function of fermions in a p-wave superconducting state, at finite both temperature and gravitational coupling, using the AdS/CFT correspondence and extending previous research. We found that, for any coupling below a critical value, the system behaves as its zero temperature limit. By increasing the coupling, the “peak-dip-hump” structure that characterizes the spectral function at fixed momenta disappears. In the region where the normal/superconductor phase transition is first order, the presence of a non-zero order parameter is reflected in the absence of rotational symmetry in the fermionic spectral function at the critical temperature.

  14. Weak coupling theory of high temperature superconductors

    International Nuclear Information System (INIS)

    Labbe, J.

    1990-01-01

    Many theories of the high T c superconductors are founded on the hypothesis that the electron-electron correlations are so strong in these materials that, in the absence of doping or internal charge transfer, they should be Mott insulators. The authors consider this hypothesis as unlikely for the following reasons. At first, very strong correlations would arise from a very large repulsive Coulomb energy between electrons within each atom. This would be the case only with very strongly localized atomic orbitals, as for instance the f orbitals in the rare earths, leading to very narrow energy bands. But in the copper oxides, the d orbitals of copper, or the p orbitals of oxygen, are not so strongly localized, and thus the intra-atomic repulsive Coulomb energy has no reason to be much larger than in the simple transitional metals or their other compounds

  15. Principles of application of high temperature superconductors to electromagnetic launch technology

    International Nuclear Information System (INIS)

    Oberly, C.E.; Kozlowski, G.; Gooden, C.E.; Lenard, R.X.; Sarkar, A.K.; Maartense, I.

    1991-01-01

    Many recent advances in the performance of bulk high temperature superconductors (HTSC) now permit conductor and magnet development at practical magnetic fields to be pursued for high current applications such as electromagnetic launchers (EML). While early hopes for a superconductor critical temperature (T c ) approaching room temperature have not been fulfilled, numerous HTSC with T c between 60K and 125K exist which can be successfully processed. Some of these HTSC are well enough understood that small conductors and coils may be fabricated for operation near 20K. Numerous physics, magnetic flux mechanics, materials processing and structural support issues remain for resolution before large scale coils made of HTSC can be operated at high energy storage density at temperatures well above 20K. This paper describes the authors' recent results on properties and materials processing of HTSC and their relation to EML applications technology

  16. Cryocooler applications for high-temperature superconductor magnetic bearings

    International Nuclear Information System (INIS)

    Niemann, R. C.

    1998-01-01

    The efficiency and stability of rotational magnetic suspension systems are enhanced by the use of high-temperature superconductor (HTS) magnetic bearings. Fundamental aspects of the HTS magnetic bearings and rotational magnetic suspension are presented. HTS cooling can be by liquid cryogen bath immersion or by direct conduction, and thus there are various applications and integration issues for cryocoolers. Among the numerous cryocooler aspects to be considered are installation; operating temperature; losses; and vacuum pumping

  17. High temperature superconductors in electromagnetic applications

    CERN Document Server

    Richens, P E

    2000-01-01

    powder-in-tube and dip-coated, have been made using a novel single loop tensometer that enables the insertion of a reasonably long length of conductor into the bore of a high-field magnet. The design, construction, and characterization of a High Temperature Superconducting (HTS) magnet is described. The design stage has involved the development of computer software for the calculation of the critical current of a solenoid wound from anisotropic HTS conductor. This calculation can be performed for a variety of problems including those involving magnetic materials such as iron by the incorporation of finite element electromagnetic analysis software. This has enabled the optimization of the magnet's performance. The HTS magnet is wound from 190 m of silver-matrix Bi sub 2 Sr sub 2 Ca sub 2 Cu sub 3 O sub 1 sub 0 powder-in-tube tape conductor supplied by Intermagnetics General Corporation. The dimensions are 70 mm bore and 70 mm length, and it consists of 728 turns. Iron end-plates were utilized in order to reduc...

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

    Energy Technology Data Exchange (ETDEWEB)

    Dunn, Lisa

    2002-03-07

    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 proper- ties 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

  19. Experimental study of flux pinning in NbN films and multilayers: Ultimate limits on critical currents in superconductors

    International Nuclear Information System (INIS)

    Gray, K.E.; Kampwirth, R.T.; Capone, D.W. II; Murduck, J.M.

    1988-08-01

    A flux pinning model is presented which predicts the maximum critical current density attainable in superconductors. That such a limit must exist comes from the realization that flux pinning is strongest in regions of weak superconductivity, but these regions cannot carry a large supercurrent. Since the same regions within the superconductor cannot be used for both pinning and supercurrent conductions, there must be an optimum mix, leading to a maximum J/sub c/. Measurements on films and multilayers of NbN have verified many details of the model including anisotropy effects and a strong reduction in J/sub c/ for defect spacings smaller than the flux core diameter. In an optimized multilayer the pinning force reached /approximately/22% of the theoretical maximum. The implications of these results on the practical applications of NbN films and on the maximum critical current density in the new high temperature superconductors are also discussed. 24 refs., 4 figs

  20. On an Increase of Critical Current in High Temperature Superconductors Doped with $^{238}U$ Due to the Production of Nuclear Photofission Fragment Tracks

    CERN Document Server

    Goncharov, I N

    2001-01-01

    The effect of appreciable increasing J_c(B,T) in HTSC (especially at liquid nitrogen temperatures of 62-78 K and magnetic fields of above 0.5 T) due to the production of fast heavy ion tracks, including those of doped U nuclear fission fragments, is known. The tracks are additional effective pinning-centers. The results described in the literature have been obtained for {235}U doped HTSC after reactor thermal neutron irradiations. Disadvantages of such a method are analyzed in this paper, in particular in case of its use for current-carrying Bi-2223/Ag tape, because a very high radioactivity level slowly decreasing in time arises. The author has suggested to use {238}U nuclear photofission in over a giant resonance energy range (E_gamma ~10-20 MeV). The experimental results obtained after tape irradiation with gamma-quanta (E_gamma \\leq 24 MeV), including a time dependence of radioactivity level, are presented. Possibilities of practical realization of this method are discussed.

  1. Low-energy physics of high-temperature superconductors

    International Nuclear Information System (INIS)

    Emery, V.J.; Kivelson, S.A.

    1992-01-01

    It is argued that the low-energy properties of high temperature superconductors are dominated by the interaction between the mobile holes and a particular class of collective modes, corresponding to local large-amplitude low-energy fluctuations in the hole density. The latter are a consequence of the competition between the effects of long-range Coulomb interactions and the tendency of a low concentration of holes in an antiferromagnet to phase separate. The low-energy behavior of the system is governed by the same fixed point as the two-channel Kondo problem, which accounts for the ''universality'' of the properties of the cuprate superconductors. Predictions of the optical properties and the spin dynamics are compared with experiment. The pairing resonance of the two Kondo problem gives a mechanism of high temperature superconductivity with an unconventional symmetry of the order parameter

  2. Temperature factor for magnetic instability conditions of type – II superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Romanovskii, V., E-mail: vromanovskii@netscape.net

    2014-10-15

    Highlights: • Electrodynamics and thermal diffusion phenomena in superconductors have the fission-chain-reaction nature. • There exist nontrivial relations between stability conditions, allowable losses and stable superconductor’s overheating. • The magnetic stability conditions are direct consequence of the states when the heat releases exceeds the critical energy. • The critical energy of magnetic instability depends on the nature of an external disturbance. • The non-isothermal magnetic instability conditions of the critical state are formulated. - Abstract: The macroscopic development of interrelated electrodynamics and thermal states taking place both before and after instability onset in type-II superconductors are studied using the critical state and the flux creep concepts. The physical mechanisms of the non-isothermal formation of the critical state are discussed solving the set of unsteady thermo-electrodynamics equations taking into consideration the unknown moving penetration boundary of the magnetic flux. To make it, the numerical method, which allows to study diffusion phenomena with unknown moving phase-two boundary, is developed. The corresponding non-isothermal flux jump criteria are written. It is proved for the first time that, first, the diffusion phenomena in superconductors have the fission-chain-reaction nature, second, the stability conditions, losses in superconductor and its stable overheating before instability onset are mutually dependent. The results are compared with those following from the existing magnetic instability theory, which does not take into consideration the stable temperature increase of superconductor before the instability onset. It is shown that errors of isothermal approximation are significant for modes closed to adiabatic ones. Therefore, the well-known adiabatic flux jump criterion limits the range of possible stable superconducting states since a correct determination of their stability states must

  3. Electron spectroscopy on high-temperature superconductors and related compounds

    International Nuclear Information System (INIS)

    Knupfer, M.

    1994-01-01

    In the last two classes of materials have been discovered which distinguish themselves due to a transition into the superconducting state at relatively high temperatures. These are the cuprate superconductors and the alkali metal doped fullerenes. In this work the electronic structure of representatives of these materials, undoped and Ca-doped YBa 2 Cu 4 O 8 and A 3 C 60 (A=K, Rb), has been investigated using electron energy-loss spectroscopy and photoemission spectroscopy. (orig.) [de

  4. American superconductor technology to help CERN to explore the mysteries of matter company's high temperature superconductor wire to be used in CERN's Large Hadron Collider

    CERN Multimedia

    2003-01-01

    American Superconductor Corporation has been selected by CERN, to provide 14,000 meters of high temperature superconductor (HTS) wire for current lead devices that will be used in CERN's Large Hadron Collider (1 page).

  5. The development of research on high temperature superconductors in Malaysia

    International Nuclear Information System (INIS)

    Shaari, A.H.; Hashim, M.; Dalimin, M.N.

    1989-01-01

    The background of the recent discovery of high-temperature oxide superconductor is given. This new discovery has driven scientists of different disciplines from many parts of the world into the race. Even those researchers from the developing countries are able to join the band wagon of the frontier research due to the convenience of working at temperatures well above that of liquid nitrogen. In Malaysia, some aspects of preparations and characterization of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O ceramics are studied. The 90 K transition temperature is observed in Y-Ba-Cu-O. (Auth.). 10 figs.; 5 refs

  6. Neutron scattering from the flux lattice in high temperature superconductors

    International Nuclear Information System (INIS)

    Paul, D.McK.; Forgan, E.M.; Cubitt, R.; Lee, S.L.; Mook, H.A.; Timmins, P.

    1992-01-01

    Neutron scattering has been used to observe diffraction from the flux-line lattice in high temperature superconductors. This technique is particularly useful in such system as it allows observations to be made over a wide range of temperature and magnetic field. Experiments on the systems K 0.4 Ba 0.6 BiO 3 and YBa 2 Cu 3 O 7-δ will be described with applied magnetic fields of up to 4 T and for temperatures from 2 K to Tc. (orig.)

  7. Fracture problem of a nonhomogeneous high temperature superconductor slab based on real fundamental solutions

    Science.gov (United States)

    Gao, Zhiwen; Zheng, Zhiye; Li, Xueyi

    2015-12-01

    To analyze the fracture problem of the nonhomogeneous high temperature superconductor (HTS) slab under electromagnetic force, we derive the real fundamental solutions based on eigenvalue and eigenvector analyses. The superconductor E-J constitutive law is characterized by the Bean model where the critical current density is independent of the flux density. Fracture analysis is performed by the methods of singular integral equations which are solved numerically by Lobatto-Chybeshev collocation method. Numerical results of the stress intensity factor (SIF) are obtained. Moreover, the crack opening displacement (COD) can be obtained by numerical integration dislocation density functions. The effects of the thickness ratio, HTS material nonhomogeneous parameters, applied magnetic field and critical current density on SIF and COD are discussed. The present work could theoretically provide quantitative predictions of the fracture mechanism of the nonhomogeneous HTS.

  8. 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.

  9. Modeling high-temperature superconductors and metallic alloys on the Intel iPSC/860

    International Nuclear Information System (INIS)

    Geist, G.A.; Peyton, B.W.; Shelton, W.A.; Stocks, G.M.

    1990-01-01

    Oak Ridge National Laboratory has embarked on several computational grand Challenges, which require the close cooperation of physicists, mathematicians, and computer scientists. One of these projects is the determination of the material properties of alloys form first principles and, in particular, the electronic structure of high-temperature superconductors. The physical basis for high Tc superconductivity is not well understood. The design of materials with higher critical temperatures and the ability to carry higher current densities can be greatly facilitated by the modeling and detailed study of the electronic structure of existing superconductors. This paper describes the progress to data on this project. We include a description of a self-consistent KKR-CPA method, parallelization of the model, and the incorporation of a dynamic load balancing scheme into the algorithm. We also describe the development and performance of a consolidated KKR-CPA code capable of running on CRAYs, workstations, and several parallel computers without source code modification

  10. The local structure of high-temperature superconductors

    International Nuclear Information System (INIS)

    Mustre de Leon, J.; Conradson, S.D.; Bishop, A.R.; Raistrick, I.D.

    1992-01-01

    We show how x-ray absorption fine structure (XAFS) has been successfully used in the determination of the local crystal structure of high-temperature superconductors, with advantages over traditional diffraction techniques. We review the experimental results that yielded the first evidence for an axial-oxygen-centered lattice instability connected with the superconductivity transition. The interpretation of this instability in terms of a dynamical tunneling model suggests the presence of polarons in these materials. XAFS on Tl 2 Ba 2 CuO 6 and other Tl-based superconductors indicate the presence of local instabilities in the CuO 2 planes of these materials, in addition to axial-oxygen instabilities

  11. Computation of superconductor critical current densities and magnetization curves

    International Nuclear Information System (INIS)

    Hodgdon, M.L.

    1991-01-01

    Using a constitutive law for superconductor hysteresis and the ideas of the critical state model, a system of equations is developed for the critical current density J c , the equilibrium magnetization M e , the upper and lower portions M U and M L of the major hysteresis loop, and their derivatives with respect to the applied field. The constitutive law consists of the differential equation dB/dH=α(H)s(H)[f(H)-B]+g(H) for H≠0, and a rule governing the abrupt changes observed at the turning points of H. For the case presented here in which f, g, and α have analytic forms, the constitutive law yields an easily differentiable expression for the major loop. Hysteresis curves computed from this constitutive law are shown to be in good agreement with experiments. Exponential approximations are given for the critical current densities computed by this method for a polycrystalline sample of YBa 2 Cu 3 O x between 5 and 40 K

  12. In silico optimization of critical currents in superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kimmel, Gregory; Sadovskyy, Ivan A.; Glatz, Andreas

    2017-07-01

    For many technological applications of superconductors the performance of a material is determined by the highest current it can carry losslessly-the critical current. In turn, the critical current can be controlled by adding nonsuperconducting defects in the superconductor matrix. Here we report on systematic comparison of different local and global optimization strategies to predict optimal structures of pinning centers leading to the highest possible critical currents. We demonstrate performance of these methods for a superconductor with randomly placed spherical, elliptical, and columnar defects.

  13. Spins in the Vortices of a High Temperature Superconductor

    OpenAIRE

    Lake, B; Aeppli, G; Clausen, KN; McMorrow, DF; Lefmann, K; Hussey, NE; Mangkorntong, N; Nohara, M; Takagi, H; Mason, TE; Schröder, A

    2002-01-01

    Neutron scattering is used to characterise the magnetism of the vortices for the optimally doped high-temperature superconductor La(2-x)Sr(x)CuO(4) (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 experimen...

  14. Permanent magnets composed of high temperature superconductors

    Science.gov (United States)

    Weinstein, Roy; Chen, In-Gann; Liu, Jay; Lau, Kwong

    1991-01-01

    A study of persistent, trapped magnetic field has been pursued with high-temperature superconducting (HTS) materials. The main effort is to study the feasibility of utilization of HTS to fabricate magnets for various devices. The trapped field, when not in saturation, is proportional to the applied field. Thus, it should be possible to replicate complicated field configurations with melt-textured YBa2Cu3O7 (MT-Y123) material, bypassing the need for HTS wires. Presently, materials have been developed from which magnets of 1.5 T, at 77 K, can be fabricated. Much higher field is available at lower operating temperature. Stability of a few percent per year is readily attainable. Results of studies on prototype motors and minimagnets are reported.

  15. To Crack or Not to Crack: Strain in High Temperature Superconductors

    International Nuclear Information System (INIS)

    Godeke, Arno

    2007-01-01

    Round wire Bi 2212 is emerging as a viable successor of Nb3Sn in High Energy Physics and Nuclear Magnetic Resonance, to generate magnetic fields that surpass the intrinsic limitations of Nb3Sn. Rather bold claims are made on achievable magnetic fields in applications using Bi 2212, due to the materials' estimated critical magnetic field of 100 Tor higher. High transport currents in high magnetic fields, however, lead to large stress on, and resulting large strain in the superconductor. The effect of strain on the critical properties of Bi-2212 is far from understood, and strain is, as with Nb3Sn, often treated as a secondary parameter in the design of superconducting magnets. Reversibility of the strain induced change of the critical surface of Nb3Sn, points to an electronic origin of the observed strain dependence. Record breaking high field magnets are enabled by virtue of such reversible behavior. Strain effects on the critical surface of Bi-2212, in contrast, are mainly irreversible and suggest a non-electronic origin of the observed strain dependence, which appears to be dominated by the formation of cracks in the superconductor volumes. A review is presented of available results on the effects of strain on the critical surface of Bi-2212, Bi-2223 and YBCO. It is shown how a generic behavior emerges for the (axial) strain dependence of the critical current density, and how the irreversible reduction of the critical current density is dominated by strain induced crack formation in the superconductor. From this generic model it becomes clear that magnets using high temperature superconductors will be strain limited far before the intrinsic magnetic field limitations will be approached, or possibly even before the magnetic field limitation of Nb3Sn can be surpassed. On a positive note, in a very promising recent result from NIST on the axial strain dependence of the critical current density in extremely well aligned YBCO, reversible behavior was observed. This

  16. To Crack or Not to Crack: Strain in High TemperatureSuperconductors

    Energy Technology Data Exchange (ETDEWEB)

    Godeke, Arno

    2007-08-22

    Round wire Bi 2212 is emerging as a viable successor ofNb3Sn in High Energy Physics and Nuclear Magnetic Resonance, to generatemagnetic fields that surpass the intrinsic limitations of Nb3Sn. Ratherbold claims are made on achievable magnetic fields in applications usingBi 2212, due to the materials' estimated critical magnetic field of 100 Tor higher. High transport currents in high magnetic fields, however, leadto large stress on, and resulting large strain in the superconductor. Theeffect of strain on the critical properties of Bi-2212 is far fromunderstood, and strain is, as with Nb3Sn, often treated as a secondaryparameter in the design of superconducting magnets. Reversibility of thestrain induced change of the critical surface of Nb3Sn, points to anelectronic origin of the observed strain dependence. Record breaking highfield magnets are enabled by virtue of such reversible behavior. Straineffects on the critical surface of Bi-2212, in contrast, are mainlyirreversible and suggest a non-electronic origin of the observed straindependence, which appears to be dominated by the formation of cracks inthe superconductor volumes. A review is presented of available results onthe effects of strain on the critical surface of Bi-2212, Bi-2223 andYBCO. It is shown how a generic behavior emerges for the (axial) straindependence of the critical current density, and how the irreversiblereduction of the critical current density is dominated by strain inducedcrack formation in the superconductor. From this generic model it becomesclear that magnets using high temperature superconductors will be strainlimited far before the intrinsic magnetic field limitations will beapproached, or possibly even before the magnetic field limitation ofNb3Sn can be surpassed. On a positive note, in a very promising recentresult from NIST on the axial strain dependence of the critical currentdensity in extremely well aligned YBCO, reversible behavior was observed.This result emphasizes the

  17. Electron microscopic observation at low temperature on superconductors

    International Nuclear Information System (INIS)

    Yokota, Yasuhiro; Hashimoto, Hatsujiro; Yoshida, Hiroyuki.

    1991-01-01

    The authors have observed superconducting materials with a high resolution electron microscope at liquid helium temperature. First, observation was carried out on Nb system intermetallic compounds such as Nb 3 Al and Nb 3 Sn of Al 5 type and Nb 3 Ge of 11 type at extremely low temperature. Next, the observation of high temperature superconductive ceramics in the state of superconductivity was attempted. In this paper, first the development of the liquid helium sample holder for a 400 kV electron microscope to realize the observation is reported. Besides, the sample holder of Gatan Co. and an extremely low temperature, high resolution electron microscope with a superconducting lens are described. The purpose of carrying out the electron microscope observation of superconductors at low temperature is the direct observation of the crystalline lattice image in the state of superconductivity. Also the structural transformation from tetragonal crystals to rhombic crystals in Al 5 type superconductors can be observed. The results of observation are reported. (K.I.)

  18. High temperature superconductivity: Concept, preparation and testing of high Tc superconductor compounds, and applications

    International Nuclear Information System (INIS)

    Harara, Wafik

    1992-06-01

    Many studies have been carried out on high temperature superconductors with transition temperature above that of the liquid nitrogen. In this scientific study the concept and the mechanism of this phenomena are discussed, in addition the examples of preparation and testing of high temperature superconductors compounds are shown. Also the most important applications in industry are explained. (author). 15 refs., 2 tabs., 18 figs

  19. Temperature dependence of the kinetic coefficients of superconductors in the intermediate state

    International Nuclear Information System (INIS)

    Gorelik, L.Y.; Kadigrobov, A.M.

    1981-01-01

    It is demonstrated that in the case of a superconductor in the intermediate state at temperature T such that e0/T 0 denoting the characteristic superconductor energy gap) the sound absorption coefficient can be strongly temperature dependent and thermal conductivity along the layers of normal metal can be nonlinearly dependent on the temperature

  20. Microstructures and strucural defects in high-temperature superconductors

    CERN Document Server

    Cai, Zhi Xiong

    1998-01-01

    This book provides an extensive introduction to the microstructures and structural defects in high-temperature superconductors. It illustrates the application of modern experimental techniques as well as theoretical modeling tools in the study of these complex materials.The readers are given an overview of the structure-sensitive properties, such as transport properties, and the effort to develop large-scale (high-current, high-field) applications for these materials. The effects of defects on the superconducting properties of these materials are described when feasible to put the study of mic

  1. Optimum working temperature of power devices based on Bi-2223 superconductors

    International Nuclear Information System (INIS)

    Oomen, M.P.; Haken, B. ten; Leghissa, M.; Rieger, J.

    2000-01-01

    Transformers, motors and magnets based on Bi-2223 tapes have an optimum working temperature where the um of investment and exploitation costs has a minimum. The investment cost is lower at temperatures below 77 K due to the higher critical current of the superconductor. The exploitation cost is mainly determined by the ac loss, which is dominated by the magnetization loss. The magnetization loss of a Bi-2223 tape at 48 Hz is measured for various temperatures between 65 and 77 K. The temperature dependence of the magnetization loss is fully explained by the change in critical current and agrees with the critical-state model. At high magnetic-field amplitudes the magnetization loss normalized with the critical current is independent of the temperature. Nevertheless, at lower temperatures the exploitation cost is higher due to the higher cooling penalty factor. A relation for the optimum temperature is developed, based on realistic expressions for the cooling penalty factor and the critical current as a function of the temperature. The influence of the other relevant parameters is summarized into a single dimensionless number. It is concluded that the optimum temperature of a power device based on Bi-2223 tapes is in the range 65-75 K. (author)

  2. Two decades on[Research into high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Durrani, M. [Physics World (United Kingdom)

    2006-04-15

    Research into high-temperature superconductors should focus on experiment, not theory. While the world looked on in horror at the events unfolding at the Chernobyl nuclear-power plant in the Soviet Union 20 years ago this month, another significant - but far less reported - development in the world of physics had just taken place. On 17 April 1986 a short paper by Georg Bednorz and Alexander Mueller arrived at the offices of Zeitschrift fuer Physik in Heidelberg, Germany. The two physicists, based at IBM's Zurich Research Laboratory in Switzerland, announced they had made a material from barium, lanthanum, copper and oxygen that could conduct electricity without resistance when cooled below a transition temperature, T{sub c}, of about 30 K. It was the world's first 'high-temperature' superconductor. Driven by the dream of materials that can superconduct at room temperature, experimentalists scurried back to their labs. Within a year, a T{sub c} of 90 K in another material had been reported and by October 1987 Bednorz and Mueller had been crowned with a Nobel prize. While papers on high-temperature superconductivity have continued to stream out since those heady days, progress has been slower than expected. Applications like levitating trains and resistance-free power cables are only now starting to come to market. Scientists have been unable to make superconducting wires that work much above 130 K, while a reliable theory of high-temperature superconductivity remains elusive. Even if we had such a theory, it is not clear that it would predict which materials might superconduct at room temperature. After all, the Bardeen-Cooper-Schrieffer theory, which explains the behaviour of low-temperature superconductors with admirable success, said nothing about the superconducting properties of Bednorz and Mueller's copper-oxide ceramics. What successes there have been over the last 20 years - such as the recent discoveries that iron, single crystals

  3. High critical currents in heavily doped (Gd,Y)Ba2Cu3Ox superconductor tapes

    Energy Technology Data Exchange (ETDEWEB)

    Selvamanickam, V; Gharahcheshmeh, MH; Xu, A; Galstyan, E; Delgado, L; Cantoni, C

    2015-01-19

    REBa2Cu3Ox ((REBCO), RE = rare earth) superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50K and fields of 2-30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (J(c)) above 20 MA/cm(2) at 30 K, 3 T in heavily doped (25 mol.% Zr-added) (Gd,Y)Ba2Cu3Ox superconductor tapes, which is more than three times higher than the J(c) typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m(3) have also been attained at 20 K. A composition map of lift factor in J(c) (ratio of J(c) at 30 K, 3 T to the J(c) at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO3 (BZO) nanocolumn defect density of nearly 7 x 10(11) cm(-2) as well as 2-3 nm sized particles rich in Cu and Zr have been found in the high J(c) films. (C) 2015 AIP Publishing LLC.

  4. Hard-Wired Dopant Networks and the Prediction of High Transition Temperatures in Ceramic Superconductors

    International Nuclear Information System (INIS)

    Phillips, J.C.

    2010-01-01

    The review multiple successes of the discrete hard-wired dopant network model ZZIP, and comment on the equally numerous failures of continuum models, in describing and predicting the properties of ceramic superconductors. The prediction of transition temperatures can be regarded in several ways, either as an exacting test of theory, or as a tool for identifying theoretical rules for defining new homology models. Popular first principle methods for predicting transition temperatures in conventional crystalline superconductors have failed for cuprate HTSC, as have parameterized models based on CuO2 planes (with or without apical oxygen). Following a path suggested by Bayesian probability, it was found that the glassy, self-organized dopant network percolative model is so successful that it defines a new homology class appropriate to ceramic superconductors. The reasons for this success in an exponentially complex (non-polynomial complete, NPC) problem are discussed, and a critical comparison is made with previous polynomial (PC) theories. The predictions are successful for the superfamily of all ceramics, including new non-cuprates based on FeAs in place of CuO2.

  5. High-temperature superconductors learn from heavy fermions

    International Nuclear Information System (INIS)

    Varma, C.

    1998-01-01

    Physicists have been intrigued by the nature of high-temperature superconductors since they were discovered 12 years ago. Superconducting materials lose their electrical resistance below a transition temperature, T c , and certain copper-oxide compounds remain superconducting at temperatures up to 160 K. Research into these materials has been driven by fundamental, yet intractable, questions about the basic concepts of condensed-matter physics and the mechanisms of superconductivity. A key question is how the electrons come together to form the Cooper pairs responsible for superconductivity. Physicists at Cambridge University have now studied two heavy-fermion compounds experimentally, and have found that the electron pairing is caused by magnetic effects (N Mathur et al. 1998 Nature 394 39). In this article the author describes their research. (UK)

  6. Oxide glass to high temperature ceramic superconductors - a novel route

    International Nuclear Information System (INIS)

    Chaudhuri, B.K.; Som, K.K.

    1992-01-01

    Recently it has been discovered that many of transition metal oxide (TMO) glasses like Bi-Sr-Ca-Cu-O, Y-Ba-Cu-O, Bi-Pb-Sr-Ca-Cu-O etc. can be directly converted to the corresponding high temperature superconducting phases by properly annealing the respective glasses. In this review recent developements in this field are summarised. The structural, electrical, dielectrical, magnetic, optical, and other properties of these new type of (TMO) glass systems have been elucidated comparing them with the corresponding results of already known (TMO) glasses which do not become superconductors on annealing above their glass transition temperatures (T g ). The electrical properties of this novel glass system have been analysed with reference to the various existing theoretical models based on polaron hopping conduction mechanism. The electrical, magnetic, and other properties of the respective superconductors obtained from their corresponding glass phases by annealing above (T g ) and the possibility of drawing wires, ribbons etc. from these glass matrices and then converting them to their high T c superconducting phases have also been discussed. (author). 107 refs., 32 figs., 5 tabs

  7. Ambient-temperature superconductor symetrical metal-dihalide bis-(ethylenedithio)-tetrathiafulvalene compounds

    Science.gov (United States)

    Williams, Jack M.; Wang, Hsien-Hau; Beno, Mark A.

    1987-01-01

    A new class of organic superconductors having the formula (ET).sub.2 MX.sub.2 wherein ET represents bis(ethylenedithio)-tetrathiafulvalene, M is a metal such as Au, Ag, In, Tl, Rb, Pd and the like and X is a halide. The superconductor (ET).sub.2 AuI.sub.2 exhibits a transition temperature of 5 K. which is high for organic superconductors.

  8. Dynamics of the vortex state in high temperature superconductors

    International Nuclear Information System (INIS)

    Kapitulnik, A.

    1991-01-01

    The large thermal energy available, the strong anisotropy, and short coherence lengths of high temperature superconductors give rise to new phenomena in the mixed state. The author discusses transport and thermodynamic measurements of high-Tc materials and of model systems. In particular, he uses experiments on two dimensional films to compare and isolate two dimensional effects in the cuprates. By using multilayer systems with similar parameters, he identifies decoupling of the superconducting planes in magnetic fields at temperatures much above the irreversibility line. He shows that if the irreversibility line is to be considered a melting transition line, it implies melting of the solid state into a liquid of three dimensional flux lines. He further uses Monte Carlo simulations to study the structure of the vortex state as well as melting

  9. Applications of high-temperature superconductors in power technology

    International Nuclear Information System (INIS)

    Hull, John R

    2003-01-01

    Since the discovery of the first high-temperature superconductors (HTSs) in the late 1980s, many materials and families of materials have been discovered that exhibit superconductivity at temperatures well above 20 K. Of these, several families of HTSs have been developed for use in electrical power applications. Demonstration of devices such as motors, generators, transmission lines, transformers, fault-current limiters, and flywheels in which HTSs and bulk HTSs have been used has proceeded to ever larger scales. First-generation wire, made from bismuth-based copper oxides, was used in many demonstrations. The rapid development of second-generation wire, made by depositing thin films of yttrium-based copper oxide on metallic substrates, is expected to further accelerate commercial applications. Bulk HTSs, in which large single-grain crystals are used as basic magnetic components, have also been developed and have potential for electrical power applications

  10. Characterisation of practical high temperature superconductors in pulsed magnetic fields and development of associated technology

    International Nuclear Information System (INIS)

    Saleh, P.M.

    2000-01-01

    Critical current measurements on state of the art practical high temperature superconductors are presented. Bi 2 Sr 2 CaCu 2 O silver-alloy matrix powder-in-tube and silver-alloy substrate dip-coated tapes, formed into various geometries, have been tested in pulsed magnetic fields of various pulse lengths. These measurements have been compared to tests performed in continuous magnetic fields. A distinct discrepancy between pulsed and continuous measurements has been observed in these silver-alloy, high temperature superconductor composites. The critical current measured in pulsed fields is depressed compared to those measured in continuous fields. Evidence is provided to strongly suggest that eddy current heating in the silver-alloy substrate/sheath of the conductor is responsible for this discrepancy. A model is presented to predict the temperature rise due to eddy current heating. This model shows good agreement with observations. In order to perform measurements on Bi 2 Sr 2 Ca 2 Cu 3 O silver-alloy matrix powder-in-tube conductor, a novel split pulsed magnet has been designed and constructed. This has allowed the first measurements of this kind to be performed on these materials, the results of which are presented in this thesis. The split magnet project itself is presented as a unique engineering project. The design models are compared to magnet test data. Suggestions for possible future improvements of the technique are presented, including a innovative design of a 100ms pulsed magnet solenoid. (author)

  11. Characterisation of practical high temperature superconductors in pulsed magnetic fields and development of associated technology

    CERN Document Server

    Saleh, P M

    2000-01-01

    including a innovative design of a 100ms pulsed magnet solenoid. Critical current measurements on state of the art practical high temperature superconductors are presented. Bi sub 2 Sr sub 2 CaCu sub 2 O silver-alloy matrix powder-in-tube and silver-alloy substrate dip-coated tapes, formed into various geometries, have been tested in pulsed magnetic fields of various pulse lengths. These measurements have been compared to tests performed in continuous magnetic fields. A distinct discrepancy between pulsed and continuous measurements has been observed in these silver-alloy, high temperature superconductor composites. The critical current measured in pulsed fields is depressed compared to those measured in continuous fields. Evidence is provided to strongly suggest that eddy current heating in the silver-alloy substrate/sheath of the conductor is responsible for this discrepancy. A model is presented to predict the temperature rise due to eddy current heating. This model shows good agreement with observations. ...

  12. The onset of dissipation in high-temperature superconductors: Self-field experiments

    Science.gov (United States)

    Talantsev, E. F.; Strickland, N. M.; Wimbush, S. C.; Crump, W. P.

    2017-12-01

    The transport critical current, Ic, is usually defined in terms of a threshold electric field criterion, Ec, with the convention Ec = 1 μV/cm chosen somewhat arbitrarily to provide "reasonably small" electric power dissipation in practical devices. Thus Ic is not fundamentally determined. However, recently it has been shown that the self-field critical current of thin-film superconductors is indeed a fundamental property governed only by the London penetration depth of the material. Here we reconsider the definition of the critical current and resolve this apparent contradiction. We measure the field distribution across the width of both first-generation and second-generation high-temperature superconducting tapes as the transport current is increased from zero to Ic. We identify a threshold current, Ic,surfB, at which the local surface magnetic flux density, Bsurf, abruptly crosses over from a non-linear to a linear dependence on the transport current, as measured at any point on the superconductor surface. This results from the current distribution across the tape width transitioning from non-uniform to uniform. This coincides with the onset of dissipation and immediately precedes the appearance of a measureable electric field. In the present examples Ic,surfB is 12-15% lower than an Ic determined by the Ec criterion. We propose the transition of Bsurf(I) from non-linear to linear as a more fundamental criterion for determining transport critical currents.

  13. High-T(sub c) Superconductor-Normal-Superconductor Junctions with Polyimide-Passivated Ambient Temperature Edge Formation

    Science.gov (United States)

    Barner, J. B.; Kleinsasser, A. W.; Hunt, B. D.

    1996-01-01

    The ability to controllably fabricate High-Temperature Superconductor (HTS) S-Normal-S (SNS) Josephson Juntions (JJ's) enhances the possibilities fro many applications, including digital circuits, SQUID's, and mixers. A wide variety of approaches to fabricating SNS-like junctions has been tried and analyzed in terms of proximity effect behavior.

  14. Status of high temperature superconductor cable and fault current limiter projects at American Superconductor

    Science.gov (United States)

    Maguire, J. F.; Yuan, J.

    2009-10-01

    This paper will describe the status of three key programs currently underway at American Superconductor Corp. The first program is the LIPA project which is a transmission voltage high temperature superconducting cable program, with funding support from the US Department of Energy. The 600 m cable, capable of carrying 574 MVA, was successfully installed and commissioned in LIPA grid on April 22, 2008. An overview of the project, system level design details and operational data will be provided. In addition, the status of the newly awarded LIPA II project will be described. The second program is Project Hydra, with funding support from the US Department of Homeland Security, to design, develop and demonstrate an HTS cable with fault current limiting functionality. The cable is 300 m long and is being designed to carry 96 MVA at a distribution level voltage of 13.8 kV. The cable will be permanently installed and energized in Manhattan, New York in 2010. The initial status of Project Hydra will be presented. The final program to be discussed is a transmission voltage, high temperature superconducting fault current limiter funded by the US DOE. The project encompasses the design, construction and test of a 115 kV FCL for power transmission within a time frame of 4-5 years. Installation and testing are planned for a Southern California Edison substation. A project overview and progress under the first phase will be reported.

  15. EPR spectrometry of high temperature superconductors with temperature modulation

    International Nuclear Information System (INIS)

    Aliev, M.K.; Alimov, G.R.; Muminov, T.M.; Olimov, B.; Sokolov, B.Yh.; Usmanov, R.R.; Kholbaev, I.

    1996-01-01

    The system of thermoregulation through light beam within the temperature range of 77 -2 - 10 -1 K. The root-square temperature instability during 5 minutes does not exceed 0.06 K; the temperature gradient in the sample is approximately 0.01 K/mm by T ∼ 90 K. 10 refs., 2 figs

  16. Microstructure and Properties of High-Temperature Superconductors

    CERN Document Server

    Parinov, I A

    2012-01-01

    The main features of high-temperature superconductors (HTSC) that define their properties are intrinsic brittleness of oxide cuprates, the layered anisotropic structure and the supershort coherence length. Taking into account these features, this treatise presents research into HTSC microstructure and properties, and also explores the possibilities of optimization of the preparation techniques and superconducting compositions. The "composition-technique-experiment-theory-model," employed here, assumes considerable HTSC defectiveness and structure heterogeneity and helps to draw a comprehensive picture of modern representations of the microstructure, strength and the related structure-sensitive properties of the materials considered. Special attention is devoted to the Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O families, which currently offer the most promising applications. Including a great number of illustrations and references, this monograph addresses students, post-graduate students and specialists, taking part in the ...

  17. Microstructure and Properties of High-Temperature Superconductors

    CERN Document Server

    Parinov, Ivan A

    2007-01-01

    The main features of high-temperature superconductors (HTSC) that define their properties are intrinsic brittleness of oxide cuprates, the layered anisotropic structure and the supershort coherence length. Taking into account these features, this treatise presents research into HTSC microstructure and properties, and also explores the possibilities of optimization of the preparation techniques and superconducting compositions. The "composition-technique-experiment-theory-model," employed here, assumes considerable HTSC defectiveness and structure heterogeneity and helps to draw a comprehensive picture of modern representations of the microstructure, strength and the related structure-sensitive properties of the materials considered. Special attention is devoted to the Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O families, which currently offer the most promising applications. Including a great number of illustrations and references, this monograph addresses students, post-graduate students and specialists, taking part in the ...

  18. Low temperature X-ray imaging of magnetic flux patterns in high temperature superconductors

    Science.gov (United States)

    Stahl, Claudia; Ruoß, Stephen; Weigand, Markus; Bechtel, Michael; Schütz, Gisela; Albrecht, Joachim

    2015-05-01

    We present X-ray magnetic circular dichroism (XMCD) microscopy results obtained at liquid nitrogen temperatures on the high-Tc superconductor YBCO (YBa2Cu3O7-δ). The magnetic flux distribution arising from electric currents in the superconductor is detected and visualized using soft-magnetic Co40Fe40B20 (CoFeB) as sensor layer and XMCD as contrast mechanism. It has been shown that the XMCD contrast in the sensor layer directly corresponds to magnetic flux distribution of the superconductor and hence can be used to image magnetic structures in superconductors [Stahl et al., Phys. Rev. B 90, 104515 (2014)]. The existing scanning UHV X-ray microscopy setup MAXYMUS at the synchrotron BESSY II in Berlin has been upgraded for that purpose: we use a nitrogen based MMR Micro Miniature Joule-Thompson Cryostat with temperature range from 75 K to 580 K. The capability of the method is demonstrated on two different superconducting samples, an optimally doped thin film and a melt-textured block.

  19. Fracture problem of a nonhomogeneous high temperature superconductor slab based on real fundamental solutions

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Zhiwen, E-mail: gaozhw@lzu.edu.cn; Zheng, Zhiye; Li, Xueyi

    2015-12-15

    Highlights: • We studied firstly nonhomogeneity fracture in HTS base on real fundamental solutions. • The SIF of nonhomogeneity HTS decrease with nonhomogeneity parameters increasing. • The greater the applied field, the higher the SIF value. • The greater critical current density of the nonhomogeneity HTS is, the smaller values of the SIF. - Abstract: To analyze the fracture problem of the nonhomogeneous high temperature superconductor (HTS) slab under electromagnetic force, we derive the real fundamental solutions based on eigenvalue and eigenvector analyses. The superconductor E-J constitutive law is characterized by the Bean model where the critical current density is independent of the flux density. Fracture analysis is performed by the methods of singular integral equations which are solved numerically by Lobatto–Chybeshev collocation method. Numerical results of the stress intensity factor (SIF) are obtained. Moreover, the crack opening displacement (COD) can be obtained by numerical integration dislocation density functions. The effects of the thickness ratio, HTS material nonhomogeneous parameters, applied magnetic field and critical current density on SIF and COD are discussed. The present work could theoretically provide quantitative predictions of the fracture mechanism of the nonhomogeneous HTS.

  20. High pressure study of high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Souliou, Sofia-Michaela

    2014-09-29

    The current thesis studies experimentally the effect of high external pressure on high-T{sub c} superconductors. The structure and lattice dynamics of several members of the high-T{sub c} cuprate and Fe-based superconductors families were investigated by means of Raman spectroscopy and X-ray diffraction under well-controlled, hydrostatic high pressure and low temperature conditions. The lattice dynamics of the high-T{sub c} superconductor YBa{sub 2}Cu{sub 3}O{sub 6+x} have been investigated systematically by Raman spectroscopy as a function of doping (x = 0.95, 0.75, 0.60, 0.55, and 0.45) and external pressure. Under ambient pressure conditions, in addition to the Raman modes expected from group theory, we observe new Raman active phonons upon cooling the underdoped samples, at temperatures well above the superconducting transition temperature. The doping dependence and the onset temperatures of the new Raman features suggest that they are associated with the incommensurate charge density wave (CDW) state recently discovered in underdoped cuprates using synchrotron X-ray scattering techniques. Under high pressure conditions (from 2 to 12 GPa), our Raman measurements on highly ordered underdoped YBa{sub 2}Cu{sub 3}O{sub 6.55} samples do not show any of the new Raman phonons seen at ambient pressure. High pressure and low temperature Raman measurements have been performed on the underdoped superconductor YBa{sub 2}Cu{sub 4}O{sub 8}. A clear renormalization of some of the Raman phonons is seen below T{sub c} as a result of the changes in the phonon self-energy upon the opening of the superconducting gap, with the most prominent one being that of the B{sub 1g}-like buckling phonon mode. The amplitude of this renormalization strongly increases with pressure, resembling the effect of hole doping in YBa{sub 2}Cu{sub 3}O{sub 6+x}. At ∝ 10 GPa, the system undergoes a reversible pressure-induced structural phase transition to a non-centrosymmmetric structure (space group

  1. Non-universality of critical exponents in the paraconductivity of short-coherence-length superconductors

    International Nuclear Information System (INIS)

    Gauzzi, A.

    1993-01-01

    The Aslamazov-Larkin paraconductivity term is calculated in the case of sufficiently small superconducting coherence length. It is found that the critical exponent of paraconductivity depends on the short-wavelength cut-off of the fluctuation spectrum in the whole Ginzburg-Landau mean-field region. Hence, it is predicted that the Aslamazov-Larkin universal relation between the critical exponent of paraconductivity and the dimensionality of the superconducting state is no longer valid in short-coherence-length superconductors. This prediction is confirmed by paraconductivity measurements on cuprate superconductors. (orig.)

  2. High critical currents in heavily doped (Gd,Y)Ba2Cu3Ox superconductor tapes

    International Nuclear Information System (INIS)

    Selvamanickam, V.; Gharahcheshmeh, M. Heydari; Xu, A.; Galstyan, E.; Delgado, L.; Cantoni, C.

    2015-01-01

    REBa 2 Cu 3 O x ((REBCO), RE = rare earth) superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50 K and fields of 2–30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (J c ) above 20 MA/cm 2 at 30 K, 3 T in heavily doped (25 mol. % Zr-added) (Gd,Y)Ba 2 Cu 3 O x superconductor tapes, which is more than three times higher than the J c typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m 3 have also been attained at 20 K. A composition map of lift factor in J c (ratio of J c at 30 K, 3 T to the J c at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO 3 (BZO) nanocolumn defect density of nearly 7 × 10 11  cm −2 as well as 2–3 nm sized particles rich in Cu and Zr have been found in the high J c films

  3. Eliashberg Analysis of Temperature Dependent Pairing Mechanism in d-Wave Superconductors: Application to High Temperature Superconductivity

    OpenAIRE

    Ahmadi, O.; Coffey, L.

    2012-01-01

    Results are presented for the temperature and frequency dependence of the real and imaginary parts of the diagonal self energy for a d-wave superconductor. An Eliashberg analysis, which has been successful in recent fitting of superconductor-insulator-superconductor tunnel junction conductances for BiSrCaCuO (Bi-2212), is extended to finite temperatures. The effect of the temperature dependence of the 40 meV spin resonance mode, measured in inelastic neutron scattering (INS) in Bi-2212, on th...

  4. Forces of vortice trapping and critical current in type II superconductors

    International Nuclear Information System (INIS)

    Bormio, C.

    1985-12-01

    The vortice-centers interactions of trapping in type II superconductor materials were studied by two theories: thermodynamic (Hampshire-Taylor) and microscopic (Larkin - Ovchinnikov). The study was applied to NbTi with composition of 50% weight of Ti. They are commercial cables containing 361 filaments with final diameter of 0.35 mm for the wire and 9.2 μm foi filaments. The material presents high deformation rate in area and high density of dislocations. These defects actuate as centers of trapping. Variations in themomechanical treatments of superconductor cables modify the interaction mechanisms. The specific mechanism for each treatment type was identified. Measurements of critical current density in function of magnetic field in the range from 1 to 7 Tesla were done, which the usual superconductor parameters as upper critical field and Ginzburg - Landau (Kappa-k) parameter are estimated from literature data. (M.C.K.) [pt

  5. High-Temperature Superconductors as Electromagnetic Deployment and Support Structures in Spacecraft

    Data.gov (United States)

    National Aeronautics and Space Administration — This technique uses the magnetic fields from current passing through coils of high-temperature superconductors (HTSs) to support spacecraft structures and deploy...

  6. Comparison of electromechanical properties and lattice distortions of different cuprate high temperature superconductors

    CERN Document Server

    Scheuerlein, C.; Grether, A; Rikel, M O; Hudspeth, J; Sugano, M; Ballarino, A; Bottura, L

    2016-01-01

    The electromechanical properties of different cuprate high-temperature superconductors, notably two ReBCO tapes, a reinforced and a nonreinforced Bi-2223 tape, and a Bi-2212 wire, have been studied. The axial tensile stress and strain, as well as the transverse compressive stress limits at which an irreversible critical current degradation occurs, are compared. The experimental setup has been integrated in a high-energy synchrotron beamline, and the self-field critical current and lattice parameter changes as a function of tensile stress and strain of a reinforced Bi-2223 tape have been measured simultaneously. Initially, the Bi-2223 filaments exhibit nearly linear elastic behavior up to the strain at which an irreversible degradation is observed. At 77 K, an axial Bi-2223 filament precompression of 0.09% in the composite tape and a Bi-2223 Poisson ratio ν = 0.21 have been determined.

  7. Study of High Temperature Superconductors with Angle-Resolved Photoemission Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Dunn, Lisa

    2003-05-13

    The Angle Resolved Photoemission Spectroscopy (ARPES) recently emerged as a powerful tool for the study of highly correlated materials. This thesis describes the new generation of ARPES experiment, based on the third generation synchrotron radiation source and utilizing very high resolution electron energy and momentum analyzer. This new setup is used to study the physics of high temperature superconductors. New results on the Fermi surfaces, dispersions, scattering rate and superconducting gap in high temperature superconductors are presented.

  8. Comparison between measured and numerically calculated AC losses in second-generation high temperature superconductor pancake coils

    International Nuclear Information System (INIS)

    Zhao, Y.; Fang, J.; Zhang, W.; Zhao, J.; Sheng, L.

    2011-01-01

    The critical current and alternating current loss of HTS coil are not equal in different parts of HTS coil. AC loss inside the magnet forms a certain distribution which makes the winding loss calculation very complex. The analytical expressions are established based on Kim's model and the Clem model. The AC loss of HTS coil is measured by electrical method at 77 K and numerical calculation model is resolved by Matlab. The theoretical results and measurement data were compared and analyzed. As a high temperature superconductor (HTS) coil is a complex electromagnetic system, the critical current and alternating current loss are not equal in different parts of HTS coil. AC loss inside the magnet forms a certain distribution which makes the winding loss calculation very complex. The analytical expressions are established based on Kim's model and the Clem model. The AC loss of high-temperature superconductor pancake coil is generally obtained from experimental measurements and numerical calculations. The AC loss of high-temperature superconductor pancake coil is measured by electrical method at the temperature of liquid nitrogen. Numerical calculation model, which is set up and resolved by Matlab, was given as the theory equation in this study, where the theoretical results and measurement data were compared and analyzed.

  9. An overview of rotating machine systems with high-temperature bulk superconductors

    Science.gov (United States)

    Zhou, Difan; Izumi, Mitsuru; Miki, Motohiro; Felder, Brice; Ida, Tetsuya; Kitano, Masahiro

    2012-10-01

    The paper contains a review of recent advancements in rotating machines with bulk high-temperature superconductors (HTS). The high critical current density of bulk HTS enables us to design rotating machines with a compact configuration in a practical scheme. The development of an axial-gap-type trapped flux synchronous rotating machine together with the systematic research works at the Tokyo University of Marine Science and Technology since 2001 are briefly introduced. Developments in bulk HTS rotating machines in other research groups are also summarized. The key issues of bulk HTS machines, including material progress of bulk HTS, in situ magnetization, and cooling together with AC loss at low-temperature operation are discussed.

  10. Upper critical field of V-Ag multilayered superconductors

    International Nuclear Information System (INIS)

    Kanoda, K.; Mazaki, H.; Hosoito, N.; Shinjo, T.

    1987-01-01

    We report investigations of the upper critical field (H/sub c/ 2 /sub perpendicular/ and H/sub c/ 2 /sub X/) of V-Ag proximity-coupled superconducting multilayer structures, prepared by ultrahigh-vacuum electron-beam evaporation. By means of x-ray diffraction analysis, successful formation of an artificial superstructure is confirmed. From resistivity measurement parallel to the layers, the electron mean free paths in the V and Ag layers are determined. With reference to these transport properties, characterization of H/sub c/ 2 has been made. For three-dimensional multilayer structures, H/sub c/ 2 is analyzed in terms of the temperature dependence of H/sub c/ 2 /sub perpendicular/, the zero-temperature coherence length, and the anisotropy H/sub c/ 2 /sub X//H/sub c2//sub perpendicular/. Our results are in quantitative agreement with the relevant theories. For quasi-two-dimensional multilayer structures, a peculiar temperature dependence has been revealed in both H/sub c/ 2 /sub perpendicular/ and H/sub c/ 2 /sub X/. H/sub c/ 2 /sub perpendicular/ exhibits positive curvature near T/sub c/, and it is continuously enhanced with the increase of multilayer period, as predicted theoretically. In contrast with the monotonic variation in H/sub c/ 2 /sub perpendicular/, a drastic upturn at a certain temperature (dimensional crossover) and an upward inflection at a higher temperature have been observed in H/sub c/ 2 /sub X/. These two types of anomalies in H/sub c/ 2 /sub X/ are discussed in the context of the commensurability between the multilayer structure and the vortex lattice

  11. Improving superconducting properties of YBCO high temperature superconductor by Graphene Oxide doping

    Energy Technology Data Exchange (ETDEWEB)

    Dadras, S., E-mail: dadras@alzahra.ac.ir; Dehghani, S.; Davoudiniya, M.; Falahati, S.

    2017-06-01

    In this research, we report the synthesis and characterization of YBa{sub 2}Cu{sub 3}O{sub 7-δ} (YBCO) high temperature superconductor prepared by sol-gel method and doped with Graphene Oxide (GO) in different weight percentages, 0, 0.1, 0.7 and 1 % wt. The x-ray diffraction (XRD) analysis confirms the formation of orthorhombic phase of superconductivity for all the prepared samples. We found that GO doping reduces the crystalline size of the samples. We evaluated the effects of GO doping on the normal state resistivity (ρ), superconducting transition temperature (T{sub c}) and critical current density (J{sub c}). The results show that the GO doping has a positive effect on these properties. Also, the highest J{sub c} is obtained for the 0.7 %wt GO doped YBCO compound that its critical current density is about 15 times more than the J{sub c} of pure one in 0.4 T magnetic field. The scanning electron microscope (SEM) analysis shows that there are better connections between the grains of GO doped samples. - Highlights: • Graphene Oxide doping increased the YBCO critical current density. • Graphene Oxide creates a better connection between the YBCO grains. • The normal resistivity of samples were decreased by GO doping to YBCO compounds. • Graphene Oxide doping has a positive effect on the critical transition temperature.

  12. Main applications of superconductors

    International Nuclear Information System (INIS)

    Tixador, P.; Brunet, Y.

    2007-01-01

    In 2004, the world market of superconductivity reached 3.65 billion euros and was mainly concerning the NbTi-type superconductors. The high critical temperature superconductors (HCTS) have not reached the industrial maturity yet, both in terms of efficiency and cost, but this situation may change at medium term. Superconductors are mainly used in the industry today to create moderated to high inductions (1.5 to more than 20 T) inside volumes up to several hundreds of m 3 . This article treats of the present day industrial applications of NbTi and Nb 3 Sn superconductors: 1 - specificities of superconductors: persisting mode, AC losses, protection of a superconducting magnet, dimensioning of a superconducting coil; 2 -industrial magnets: NMR imaging, spectroscopy, proton cyclotron; 3 - magnets for research: high energy physics (accelerators-colliders, detectors), fusion facilities (reaction, magnetic confinement, tokamak, ITER), laboratory magnets; 4 - magnets for specific applications: magnetic separation, magnetic levitated train, MHD. (J.S.)

  13. Self-organization of the critical state in Josephson lattices and granulated superconductors

    International Nuclear Information System (INIS)

    Ginzburg, S.L.

    1994-01-01

    A number of models of a Josephson medium and granulated superconductors are studied. It is shown that an important parameter is the quantity V∼j c a 3 /Φ 0 , where j c is the Josephson-current density, a is the granule size, and Φ 0 is the quantum of flux. In the limit V>>1 the continuum approximation is inapplicable. In this case the Josephson medium is transformed into a system in which pinning is realized on elementary loops that incorporate Josephson junctions. Here, nonlinear properties of these junctions obtain. The equations obtained for the currents of the Josephson lattice are identical to the standard formulation in the problem of self-organized criticality, while in granulated superconductors a problem of self-organized criticality with a different symmetry arises-a problem not of sites, but of loop. From the point of view of the critical state in granulated superconductors the concept of self-organized criticality radically changes the entire customary picture. The usual equations of the critical state describe only the average values of the magnetic field in the hydrodynamic approximation. However, it follows from the concept of self-organized criticality that the critical state has an extremely complicated structure, much more complicated than that which follows from the equation of the critical state. In particular, the fluctuations of various quantities in the critical state are much stronger than the ordinary statistical fluctuations, since there are large-scale fluctuations of the currents and fields, with a power-law (scaling) behavior that extends up to scales of the order of the size of the system, as in a turbulent medium. On the other hand, the basic equations in it reflect all the features of pinning - hysteresis and threshold behavior. Therefore, the self-organization of the critical state of a superconductor is a natural realization of this extremely general problem. 15 refs., 4 figs

  14. Critical currents in uranium doped Tl-1223 superconductors

    Science.gov (United States)

    Tönies, S.; Weber, H. W.; Gritzner, G.; Heiml, O.; Eder, M.

    2002-08-01

    Tl-1223 films were doped with small amounts of 235U. Irradiation by thermal neutrons causes fission of uranium into two fission products, which create fission tracks. These defects, which are randomly oriented and homogeneously distributed, significantly improve flux pinning. The superconducting properties of the samples are determined by dc transport measurements in fields up to 6 T at temperatures between 40 and 77 K. Rotation of the sample in the horizontal field of a split-coil magnet allows us also to measure the angular dependence of Jc. Enhancements of the critical current densities and the irreversibility lines as well as a change of the Jc anisotropy are found after irradiation. The results are compared to data on U-doped Bi-2223 tapes.

  15. Singularity of the London penetration depth at quantum critical points in superconductors.

    Science.gov (United States)

    Chowdhury, Debanjan; Swingle, Brian; Berg, Erez; Sachdev, Subir

    2013-10-11

    We present a general theory of the singularity in the London penetration depth at symmetry-breaking and topological quantum critical points within a superconducting phase. While the critical exponents and ratios of amplitudes on the two sides of the transition are universal, an overall sign depends upon the interplay between the critical theory and the underlying Fermi surface. We determine these features for critical points to spin density wave and nematic ordering, and for a topological transition between a superconductor with Z2 fractionalization and a conventional superconductor. We note implications for recent measurements of the London penetration depth in BaFe2(As(1-x)P(x))2 [K. Hashimoto et al., Science 336, 1554 (2012)].

  16. Magnet Lab Highlight: Upper critical field reaches 90 tesla near the Mott transition in fulleride superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Mcdonald, Ross David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-06-05

    The alkali-doped fullerides provide the first example of a transition from a three-dimensional Mott insulator to a superconductor, enabling the effects of both dimensionality and electron correlation on superconductivity to be explored. Chemically the alkali species tunes the superconductivity in the vicinity of the the Mott transition via sample volume. Measuring the relationship between the superconducting transition temperature and upper critical field reveals a crossover from weak- to strong-coupling associated with the dynamical Jahn–Teller effect as the Mott transition is approached. The use of pulsed magnets is required because the upper critical field is enhanced in the vicinity of the Mott insulating phase, reaching 90 T for RbxCs3-xC60 — the highest among cubic crystals. This required close collaboration between Prof Kasahara’s group and the Mag Lab to design rf-measurements compatible with sample encapsulation in an inert atmosphere. The concomitant increase of pairing strength with lattice volume near the Mott transition suggest that the cooperative interplay between molecular electronic structure and strong electron correlations plays a key role in realizing robust superconductivity (with high-TC and high-HC2).

  17. Anisotropic magnetoresistance and thermodynamic fluctuations in high-temperature superconductors

    International Nuclear Information System (INIS)

    Heine, G.

    1999-05-01

    Measurements of the in-plane and out-of-plane resistivity and the transverse and longitudinal in-plane and out-of-plane magnetoresistance above T, are reported in the high-temperature superconductors Bi2Sr2CaCu208+' and YBa2CU307 b . The carrier concentration of the Bi2Sr2CaCu208+' single crystals covers a broad range of the phase diagram from the slightly under doped to the moderately over doped region. The doping concentration of the thin films ranges from strongly under doped to optimally doped. The in-plane resistivities obey a metallic-like temperature dependence with a positive magnetoresistance in the transverse and the longitudinal orientation of the magnetic field. The out-of-plane resistivities show an activated behavior above T, with a metallic region at higher temperatures and negative magnetoresistance. The data were analyzed in the framework of a model for superconducting order parameter fluctuations. The positive in-plane magnetoresistance of the highly anisotropic Bi2Sr2CaCu208+x single crystals is interpreted as the suppression of the fluctuation-conductivity enhancement including orbital and spin contributions, whereas the negative magnetoresistance arises from the reduction of the fluctuation-induced pseudogap in the single-electron density-of-states by the magnetic field. For higher temperatures a transition to the normal-state magnetoresistance occurs for the in-plane transport. In the less anisotropic YBa2CU307 b thin films the positive out-of-plane magnetoresistance near T, changes sign to a negative magnetoresistance at higher temperatures. This behavior is also consistent with predictions from the theory of thermodynamic order-parameter fluctuations. The agreement of the fluctuation theory with the experimental findings is excellent for samples from the over doped side of the phase diagram, but deteriorate with decreasing carrier concentration. This behavior is interpreted by the dominating d-wave symmetry of the superconducting order

  18. Superfluid density and superconducting transition temperature in dirty iron-based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Hartmann, Thomas; Ahn, Felix; Eremin, Ilya [Ruhr-Universitaet Bochum, Bochum (Germany)

    2016-07-01

    Measurements on optimally electron doped LaFeAsO{sub 1-x}F{sub x} samples under pressure up to ∝23 kbar reveal a clear mutual independence between the critical temperature T{sub c} and the ratio of superfluid density over effective band mass of Cooper pairs n{sub s}/m*. The ratio increases about ∝30 % at the maximum pressure whereas T{sub c} remains constant, which clearly implies a breakdown of the Uemura relation in LaFeAsO{sub 1-x}F{sub x}. Here we analyze theoretically this effect by taking into account the effect of nonmagnetic impurities in a multi-band superconductor. We show that the ratio between intra-band and inter-band scattering rates can explain the behaviour of the observables under pressure by only acting on structural parameters while the amount of chemical disorder is still constant.

  19. Superconductors

    International Nuclear Information System (INIS)

    Newkirk, L.R.; Valencia, F.A.

    1977-01-01

    The structural quality of niobium germanide as a high-transition-temperature superconducting material is substantially improved by the presence of about 5 at. percent oxygen. Niobium germanide having this oxygen content may readily be prepared as a bulk coating bonded to a metallic substrate by chemical vapor deposition techniques. 2 figures, 1 table

  20. The study of some physical properties of high temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Ismail, Atif Mahmoud

    2008-07-01

    The phenomenon of superconductivity, the discovery of high temperature superconductivity in the Cuprates and the properties of these materials is described in the introductory chapter. It also includes a discussion of the pseudogap, which has remained a mystery as has the high transition temperature. Possible applications of high temperature superconductivity are reviewed before the theories by Bardeen, Cooper, and Schrieffer (BCS) and Ginzburg and Landau are briefly sketched. The last section gives excerpts of the by now vast literature on this subject, focussing on the role impurities play in this context. The second chapter develops the mathematical tools and the theoretical background for the description of many-body systems. Various Green's functions are introduced which are then used to describe scattering of quasiparticles off defects of arbitrary strength. They are also required to calculate the a.c. conductivity, for which an expression is derived using linear response theory. The convergence problems one encounters when actually calculating the conductivity are briefly discussed. Detailed calculations for the normal state are presented in the third chapter and in the appendix. The third Chapter begins with a detailed presentation of the tight binding model for the energy dispersion because this model appears to give a more accurate description of the electronic properties of high temperature superconductors than the nearly free electron model. The shape of the two-dimensional Fermi surface is calculated and displayed as function of band filling and the next-nearest neighbor hopping integral B, assuming a rigid band. B plays an important role in the formation of so-called hot spots. The quasiparticle density of states and its Hilbert transform F({omega}) are solved by means of complete elliptic integrals formalism. These results are used to obtain impurity bound states. A simple model for the superconductivity in the cuprate materials is developed on

  1. The study of some physical properties of high temperature superconductors

    International Nuclear Information System (INIS)

    Ismail, Atif Mahmoud

    2008-01-01

    The phenomenon of superconductivity, the discovery of high temperature superconductivity in the Cuprates and the properties of these materials is described in the introductory chapter. It also includes a discussion of the pseudogap, which has remained a mystery as has the high transition temperature. Possible applications of high temperature superconductivity are reviewed before the theories by Bardeen, Cooper, and Schrieffer (BCS) and Ginzburg and Landau are briefly sketched. The last section gives excerpts of the by now vast literature on this subject, focussing on the role impurities play in this context. The second chapter develops the mathematical tools and the theoretical background for the description of many-body systems. Various Green's functions are introduced which are then used to describe scattering of quasiparticles off defects of arbitrary strength. They are also required to calculate the a.c. conductivity, for which an expression is derived using linear response theory. The convergence problems one encounters when actually calculating the conductivity are briefly discussed. Detailed calculations for the normal state are presented in the third chapter and in the appendix. The third Chapter begins with a detailed presentation of the tight binding model for the energy dispersion because this model appears to give a more accurate description of the electronic properties of high temperature superconductors than the nearly free electron model. The shape of the two-dimensional Fermi surface is calculated and displayed as function of band filling and the next-nearest neighbor hopping integral B, assuming a rigid band. B plays an important role in the formation of so-called hot spots. The quasiparticle density of states and its Hilbert transform F(ω) are solved by means of complete elliptic integrals formalism. These results are used to obtain impurity bound states. A simple model for the superconductivity in the cuprate materials is developed on the basis

  2. Ternary superconductors

    International Nuclear Information System (INIS)

    Giorgi, A.L.

    1987-01-01

    Ternary superconductors constitute a class of superconducting compounds with exceptional properties such as high transition temperatures (≅ 15.2 K), extremely high critical fields (H c2 >60 Tesla), and the coexistence of superconductivity and long-range magnetic order. This has generated great interest in the scientific community and resulted in a large number of experimental and theoretical investigations in which many new ternary compounds have been discovered. A review of some of the properties of these ternary compounds is presented with particular emphasis on the ternary molybdenum chalcogenides and the ternary rare earth transition metal tetraborides. The effect of partial substitution of a second metal atom to form pseudoternary compounds is examined as well as some of the proposed correlations between the superconducting transition temperature and the structural and electronic properties of the ternary superconductors

  3. High-temperature superconductors. Investigations on Bi-Sr wires and tapes. Final report

    International Nuclear Information System (INIS)

    Weinhold, H.; Huebner, A.; Kurze, B.

    2000-01-01

    ECOFORM Umformtechnik GmbH developed a new combined working and coating system for drawing of extruded shape materials. This permits drawing of superconductors under favourable compression and tension conditions. The application of a concentric hydrostatic pressure (variable) at the entrance into the die enables a homogeneous material flux over the entire die cross-section and increases compression over the tension stress. The optimization of lubrication according to the drawing forces proved of extraordinary importance for attaining superior superconductor properties. The newly developed technique permits to avoid the decrease of mass density of the superconductor phase which was found with conventional drawing procedures. It was even possible to obtain an increase of superconductor mass density in some states of the drawing process. Despite all technological progress the critical current density obtained so far is still smaller than the best values reported in international literature, but further improvements can be expected when optimizing the parameters of pressure-lubrication drawing. (orig.) [de

  4. Equivalent Coil Model for Computing Levitation Forces Between Permanent Magnets and High Temperatures Superconductors

    International Nuclear Information System (INIS)

    Cavia Santos, S.; Garcia-Tabares, L.

    1998-05-01

    A new simple theory has been developed for the study of levitation forces between a permanent magnet and a HTc superconductor. This theory is based on the assumption that both, the magnet and the superconductor, can be modelled by an equivalent coil placed on their surface. While the current flowing through the permanent magnet is constant, the equivalent current through the superconductor can be iether corresponding to screen the overall flux or a constant current corresponding to critical current density when the superconductor is saturated. A test facility has been designed and built for measuring levitation forces at variable approaching speeds. Comparison between theoretical and experimental measurements are presented in the report as well as a general description of the test facility. (Author)

  5. Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2.

    Science.gov (United States)

    Dong, J K; Zhou, S Y; Guan, T Y; Zhang, H; Dai, Y F; Qiu, X; Wang, X F; He, Y; Chen, X H; Li, S Y

    2010-02-26

    The in-plane resistivity rho and thermal conductivity kappa of the FeAs-based superconductor KFe2As2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior rho(T) approximately T{1.5} at H{c{2}}=5 T, and the development of a Fermi liquid state with rho(T) approximately T{2} when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field H{c{2}}. In zero field, there is a large residual linear term kappa{0}/T, and the field dependence of kappa_{0}/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2As2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.

  6. High-temperature superconductors, as seen through the eyes of neutrons

    International Nuclear Information System (INIS)

    Yamani, Z.

    2006-01-01

    Neutron scattering is proved to be a vital probe in unveiling the magnetic properties of high temperature superconductors. Detailed information about the energy and momentum dependence of the magnetic dynamics of high temperature superconductors have been obtained directly by this technique. Over the past decade by improving the crystal growth methods, large and high quality single crystals of high temperature superconductors, which are essential for a neutron scattering experiment, have become available. The results of neutron scattering measurements on such crystals have considerably enhanced our understanding of the magnetism in high temperature superconductors both in the superconducting and normal states. In this review, the neutron scattering results on two main high temperature superconductors families, La 2-x Sr x CuO 4 and YBa 2 CuO 3 O 6+x , are considered with an emphasis on the most prominent properties of these materials that are now widely accepted. These include the presence of strong antiferromagnetic fluctuations even in optimally doped region of the phase diagram. neutron resonance peak that scales with superconducting transition temperature, T,, incommensurate magnetic fluctuations (stripes), and a pseudo gap in the normal state of under doped materials

  7. Microwave impedance of epitaxial high-temperature superconductor films

    International Nuclear Information System (INIS)

    Melkov, G.A.; Malyshev, V.Yu.; Bagada, A.V.

    1995-01-01

    In the 3 cm band dependences of the epitaxial HTS film surface resistance on the magnitude of ac and dc magnetic fields have been measured. YBa 2 Cu 3 O 7-σ films on sapphire were investigated. It was established that alternating magnetic field produces a stronger impact on the surface resistance than dc field. To explain experimental results the assumption is made that a HTS film is not an ideal superconductor and consists of series-connected sections of various types: sections of an ideal superconductor, sections of low and large resistance intragranular Josephson junctions, shunted by the ideal superconductor, and finally, sections of intergranular Josephson junctions few for epitaxial films. In these conditions the dependences of the surface resistance on dc magnetic field are caused by Abrikosov's vortices moving in ideal superconductive sections, and dependences on the amplitude of ac magnetic field are caused by switching of large resistance junctions to a low resistance state

  8. High-Temperature-Superconductor Films In Microwave Circuits

    Science.gov (United States)

    Bhasin, K. B.; Warner, J. D.; Romanofsky, R. R.; Heinen, V. O.; Chorey, C. M.

    1993-01-01

    Report discusses recent developments in continuing research on fabrication and characterization of thin films of high-temperature superconducting material and incorporation of such films into microwave circuits. Research motivated by prospect of exploiting superconductivity to reduce electrical losses and thereby enhancing performance of such critical microwave components as ring resonators, filters, transmission lines, phase shifters, and feed lines in phased-array antennas.

  9. Inhomogeneous magnetic field in AdS/CFT superconductor

    OpenAIRE

    Wen, Wen-Yu

    2008-01-01

    We study the holographically dual description of superconductor in (2+1)-dimensions in the presence of inhomogeneous magnetic field and observe that there exists type I and type II superconductor. A new feature of type changing is observed for type I superconductor near critical temperature.

  10. Application of high temperature ceramic superconductors (CSC) to commercial tokamak reactors

    International Nuclear Information System (INIS)

    Ehst, D.A.; Kim, S.; Gohar, Y.; Turner, L.; Smith, D.L.; Mattas, R.

    1987-10-01

    Ceramic superconductors operating near liquid nitrogen temperature may experience higher heating rates without losing stability, compared to conventional superconductors. This will permit cable design with less stabilizer, reducing fabrication costs for large fusion magnets. Magnet performance is studied for different operating current densities in the superconductor, and cost benefits to commercial tokamak reactors are estimated. It appears that 10 kA . cm -2 (at 77 K and ∼10 T) is a target current density which must be achieved in order for the ceramic superconductors to compete with conventional materials. At current densities around 50 kA . cm -2 most potential benefits have already been gained, as magnet structural steel begins to dominate the cost at this point. For a steady state reactor reductions of ∼7% are forecast for the overall capital cost of the power plant in the best case. An additional ∼3% cost saving is possible for pulsed tokamaks. 9 refs., 4 figs., 8 tabs

  11. Numerical study of a 50 kA current lead using bulk high temperature superconductors

    International Nuclear Information System (INIS)

    Heller, R.

    1993-06-01

    Based on the design of the 30 kA current lead with a low temperature superconductor (LTSC) forseen for the test of a superconducting pulsed model coil (POLO model coil) in the test facility TOSKA at KfK, a 50 kA current lead for the future test of a model coil for the International Thermonuclear Experimental Reactor ITER in the TOSKA facility was proposed resulting in a helium mass flow rate normalized to the current of 0.055 g/(s-kA) at 50 kA resp. of 0.015 g/(s-kA) at zero current. In this paper, the possibility of the use of High Temperature Superconductors (HTSC) for high current carrying current leads cooled by forced flow supercritical helium has been investigated in order to study the capabilities. The current lead behaviour has been theoretically studied under different conditions: zero current operation, nominal current (50 kA) operation, extended current (70 kA) operation, and safety behaviour (loss of helium mass flow). Two design cases which differ in the current sharing and critical temperatures of the HTSC have been investigated in order to look on the amount of helium mass flow reduction. The result is that the reduction of mass flow rate will be 50% at zero current and about 10 to 20% at 50 kA for the two cases. The transient behaviour of the HTSC lead differs considerably from the one of the LTSC lead due to the high electrical resisitivity of the HTSC. (orig.)

  12. Correlation of superconductor strand, cable, and dipole critical currents in CBA magnets

    International Nuclear Information System (INIS)

    Tannenbaum, M.J.; Garber, M.; Sampson, W.B.

    1982-01-01

    A calibration between vendor critical current data for 0.0268'' diameter superconductor strand supplied to Fermilab, and the BNL 10 -12 Ωcm critical current specification is presented. Vendor critical current data for over 400 Fermilab type billets are shown, both as supplied by the vendor and converted to BNL units. Predictions of cable critical current are made using the sum of the critical currents of the 23 strands, where all strands from the same half billet are assigned the same critical current. The measured critical current shows excellent correlation to the predicted value and is approximately 14 +- 2 percent below it. Colliding Beam Accelerator (CBA) full length dipoles reach the conductor critical current limit, essentially without training. Magnet performance is predictable from the measured critical current of a short sample of cable to within 2%

  13. Irradiation damage in superconductors

    International Nuclear Information System (INIS)

    Quere, Y.

    1989-01-01

    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

  14. Quantum critical matter. Quantum phase transitions with multiple dynamics and Weyl superconductors

    International Nuclear Information System (INIS)

    Meng, Tobias

    2012-01-01

    In this PhD thesis, the physics of quantum critical matter and exotic quantum state close to quantum phase transitions is investigated. We will focus on three different examples that highlight some of the interesting phenomena related to quantum phase transitions. Firstly, we discuss the physics of quantum phase transitions in quantum wires as a function of an external gate voltage when new subbands are activated. We find that at these transitions, strong correlations lead to the formation of an impenetrable gas of polarons, and identify criteria for possible instabilities in the spin- and charge sectors of the model. Our analysis is based on the combination of exact resummations, renormalization group techniques and Luttinger liquid approaches. Secondly, we turn to the physics of multiple divergent time scales close to a quantum critical point. Using an appropriately generalized renormalization group approach, we identify that the presence of multiple dynamics at a quantum phase transition can lead to the emergence of new critical scaling exponents and thus to the breakdown of the usual scaling schemes. We calculate the critical behavior of various thermodynamic properties and detail how unusual physics can arise. It is hoped that these results might be helpful for the interpretation of experimental scaling puzzles close to quantum critical points. Thirdly, we turn to the physics of topological transitions, and more precisely the physics of Weyl superconductors. The latter are the superconducting variant of the topologically non-trivial Weyl semimetals, and emerge at the quantum phase transition between a topological superconductor and a normal insulator upon perturbing the transition with a time reversal symmetry breaking perturbation, such as magnetism. We characterize the topological properties of Weyl superconductors and establish a topological phase diagram for a particular realization in heterostructures. We discuss the physics of vortices in Weyl

  15. Low-temperature deuteron irradiation of differently reacted Nb3Sn superconductors

    International Nuclear Information System (INIS)

    Maier, P.; Seibt, E.

    1978-01-01

    Irradiation measurements with 50 MeV deuterons at 18 K and subsequent annealing measurements were performed on Nb 3 Sn single and multifilamentary superconductors at the Helium-Bath Irradiation Facility of the Karlsruhe Cyclotron. The critical current densities jsub(c) of Nb 3 Sn bronze-reacted wire samples at various reaction temperatures (Tsub(R)=650,700,750,800 and 850 0 C) with equal layer thickness were measured for integral deuteron fluxes up to PHIsub(t)=0.7x10 18 cm -2 . After a decrease in jsub(c) of 85% at maximum dose a relatively small annealing effect (4 to 10%) was observed at ambient temperatures. The maximum value of the normalized critical current density, jsub(c)/jsub(c0), at PHIsub(t)approximately=10 17 cm -2 increases with increasing reaction temperature. The difference in volume pinning forces before and after irradiation increases less than linear (approximately√PHIsub(t)) with the irradiation dose. An almost linear dependence between the inverse grain diameter (dsub(K) -1 )) and volume pinning force is obtained both before and after irradiation. (Auth.)

  16. High Temperature Superconductor/Semiconductor Hybrid Microwave Devices and Circuits

    Science.gov (United States)

    Romanofsky, Robert R.; Miranda, Felix A.

    1999-01-01

    Contents include following: film deposition technique; laser ablation; magnetron sputtering; sequential evaporation; microwave substrates; film characterization at microwave frequencies; complex conductivity; magnetic penetration depth; surface impedance; planar single-mode filters; small antennas; antenna arrays phase noise; tunable oscillations; hybrid superconductor/semiconductor receiver front ends; and noise modeling.

  17. Magnetic flux annihilation waves in inhomogeneous high-temperature superconductors

    NARCIS (Netherlands)

    Rudnev, IA; Khodot, AE; Eremin, AV; Mikhailov, BP

    2004-01-01

    The process of magnetic field penetration into polycrystalline high-T-c superconductors of the YBa2Cu3O7 - x and Bi2Sr2Ca2Cu3O10 - x systems has been studied using traditional magnetooptical methods and scanning Hall probe microscopy. It is established that remagnetization of a sample is accompanied

  18. An explanation of the irreversibility behavior in the highly- anisotropic high-temperature superconductors

    International Nuclear Information System (INIS)

    Gray, K.E.; Kim, D.H.

    1991-01-01

    The wide temperature range of the reversible, lossy state of the new high-temperature superconductors in a magnetic field was recognized soon after their discovery. This behavior, which had gone virtually undetected in conventional superconductors, has generated considerable interest, both for a fundamental understanding of the HTS and because it degrades the performance of HTS for finite-field applications. We show that recently proposed explanation of this behavior for the highly-anisotropic high-temperature superconductors, as a dimensional crossover of the magnetic vortices, is strongly supported by recent experiments on a Bi 2 Sr 2 CaCu 2 O x single crystal using the high-Q mechanical oscillator techniques

  19. Ca-Sr-Ga-Nb mixed oxide system for high temperature superconductor substrate applications

    Energy Technology Data Exchange (ETDEWEB)

    Erdei, S.; Cross, L.E.; Ainger, F.W.; Bhalla, A. (Materials Research Lab., The Pennsylvania State Univ., Univ. Park, Pennsylvania (United States))

    1994-05-01

    Twin-free crystals with relatively low melting temperatures are desirable as substrates for high temperature superconductor (HTSC) oxide substrate materials. In the selection of new oxide substrate compositions, special requirements (e.g. suitable dielectric properties for microwave application and perovskite structure with good lattice matching with YBa[sub 2]Cu[sub 3]O[sub 7-[delta

  20. The Neutron Peak in the Interlayer Tunneling Model of High Temperature Superconductors

    International Nuclear Information System (INIS)

    Yin, L.; Chakravarty, S.; Anderson, P.W.

    1997-01-01

    Recent neutron scattering experiments in optimally doped YBCO exhibit an unusual magnetic peak that appears only below the superconducting transition temperature. The experimental observations are explained within the context of the interlayer tunneling theory of high temperature superconductors. copyright 1997 The American Physical Society

  1. PREFACE: Special section featuring selected papers from the 3rd International Workshop on Numerical Modelling of High Temperature Superconductors Special section featuring selected papers from the 3rd International Workshop on Numerical Modelling of High Temperature Superconductors

    Science.gov (United States)

    Granados, Xavier; Sánchez, Àlvar; López-López, Josep

    2012-10-01

    The development of superconducting applications and superconducting engineering requires the support of consistent tools which can provide models for obtaining a good understanding of the behaviour of the systems and predict novel features. These models aim to compute the behaviour of the superconducting systems, design superconducting devices and systems, and understand and test the behavior of the superconducting parts. 50 years ago, in 1962, Charles Bean provided the superconducting community with a model efficient enough to allow the computation of the response of a superconductor to external magnetic fields and currents flowing through in an understandable way: the so called critical-state model. Since then, in addition to the pioneering critical-state approach, other tools have been devised for designing operative superconducting systems, allowing integration of the superconducting design in nearly standard electromagnetic computer-aided design systems by modelling the superconducting parts with consideration of time-dependent processes. In April 2012, Barcelona hosted the 3rd International Workshop on Numerical Modelling of High Temperature Superconductors (HTS), the third in a series of workshops started in Lausanne in 2010 and followed by Cambridge in 2011. The workshop reflected the state-of-the-art and the new initiatives of HTS modelling, considering mathematical, physical and technological aspects within a wide and interdisciplinary scope. Superconductor Science and Technology is now publishing a selection of papers from the workshop which have been selected for their high quality. The selection comprises seven papers covering mathematical, physical and technological topics which contribute to an improvement in the development of procedures, understanding of phenomena and development of applications. We hope that they provide a perspective on the relevance and growth that the modelling of HTS superconductors has achieved in the past 25 years.

  2. Preparation of the YBa2 Cu3O7-x high critical temperature superconductor Phases's characterization in the Y-Ba-Cu-O system using X-ray diffraction

    International Nuclear Information System (INIS)

    Infante, C.E.; Kremer, G.; Zelada, G.; Steinmann, G.; Martin, V.

    1987-01-01

    The fabrication process of the YBa 2 Cu 3 O 7-x superconductor is presented. The phase characterization of the Y-Ba-Cu-O system was investigated and the impurities were identified using X-ray diffraction analysis. Y 2 O 3 , BaCO 3 and Cu O were dried under controlled atmosphere at 900 0 C during 15 hrs and powdered in Agate mortar in hexane. The mixture was heated 900 0 C in a platinum crucible for 15 hours and the product was crushed and reheated in air. The pellets were pressed under a pressure of 5T/cm 2 and sinterized at 1000 0 C during 15 hours followed by slow cooling in the furnace. (M.C.K.)

  3. Critical states and thermomagnetic instabilities in three-dimensional nanostructured superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tamegai, T., E-mail: tamegai@ap.t.u-tokyo.ac.jp [Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Mine, A.; Tsuchiya, Y.; Miyano, S.; Pyon, S. [Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Mawatari, Y.; Nagasawa, S.; Hidaka, M. [National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan)

    2017-02-15

    Highlights: • Critical state field profiles and thermomagnetic instabilities are studied in three-dimensional nanostructured superconductors. • We find that the critical state field profiles in bi-layer systems are not simple superpositions of critical states in the two layers. • We also studied flux avalanches in shifted strip arrays with layer numbers up to six. • Various forms of avalanches either perpendicular or parallel to the strip are observed when the overlap between layers is large. • We find that introduction of asymmetry to shifted strip arrays affects the shape of flux avalanches sensitively. - Abstract: Critical state field profiles and thermomagnetic instabilities are studied in two kinds of three-dimensional nanostructured superconductors. We find that the critical state field profiles in some simple bi-layer systems are not simple superpositions of critical states in the two layers. Competition between the divergence of the local field at the edges of the film and the shielding by the neighboring layer makes novel critical state field profiles. We also studied flux avalanches in shifted strip arrays (SSAs) with layer numbers up to six. Various forms of avalanches either perpendicular or parallel to the strip are observed when the overlap between strips in neighboring layers is large. We also find that introduction of asymmetry in various forms to SSA affects the shape of flux avalanches sensitively.

  4. Comparison study of cable geometries and superconducting tape layouts for high-temperature superconductor cables

    Science.gov (United States)

    Ta, Wurui; Shao, Tianchong; Gao, Yuanwen

    2018-04-01

    High-temperature superconductor (HTS) rare-earth-barium-copper-oxide (REBCO) tapes are very promising for use in high-current cables. The cable geometry and the layout of the superconducting tapes are directly related to the performance of the HTS cable. In this paper, we use numerical methods to perform a comparison study of multiple-stage twisted stacked-tape cable (TSTC) conductors to find better cable structures that can both improve the critical current and minimize the alternating current (AC) losses of the cable. The sub-cable geometry is designed to have a stair-step shape. Three superconducting tape layouts are chosen and their transport performance and AC losses are evaluated. The magnetic field and current density profiles of the cables are obtained. The results show that arrangement of the superconducting tapes from the interior towards the exterior of the cable based on their critical current values in descending order can enhance the cable's transport capacity while significantly reducing the AC losses. These results imply that cable transport capacity improvements can be achieved by arranging the superconducting tapes in a manner consistent with the electromagnetic field distribution. Through comparison of the critical currents and AC losses of four types of HTS cables, we determine the best structural choice among these cables.

  5. Physics and Materials Science of High Temperature Superconductors

    Science.gov (United States)

    1989-08-26

    MEASUREMENTS OF YBaCuO SUPERCONDUCTORS. T. Puig, L. M. Martinez, M. T. Aurell, A. Sanchez, D. X. Chen and J. S. Mufioz, Dept. Fisica (Electromagnetisme...3800 Aveiro, Portugal; and A. P. Gonqalves and M. L. Almeida, Departamento de Quimica ICEN-LNETI, 2686 Sacaven, Portugal. The sintered bulk sample of...I I I I I I, THERMOELECTRIC POWER IN SUPERCONDUCTING CERAMIC OXIDES. ! E. B. Lopes, R. T. Henriques and M. Almeida, Dep. Quimica , ICEN-LNETI, P-2686

  6. Development of MgB2 superconductor wire with high critical current

    International Nuclear Information System (INIS)

    Kim, Chan Joong; Jun, Byung Hyuk; Park, Soon Dong; Kim, Nam Kyu; Kim, Yi Jeong; Yi, Ji Hye; Lee, Ji Hyun; Tan, Kai Sin

    2009-07-01

    The MgB 2 superconductor with smaller grain size could improve its critical properties by providing flux pinning centers with high grain boundary density. The effects of C doping such as charcoal, paper ash and glycerin on the superconducting properties was investigated for in situ processed MgB 2 samples using low purity semi-crystalline B powder. The results show a decrease in Tc and an enhancement of Jc at high fields for the C-doped samples as compared to the un-doped samples. A combined process of a mechanical ball milling and liquid glycerin (C 3 H 8 O 3 ) treatment of B powder has been conducted to enhance the superconducting properties of MgB 2 . The mechanical ball milling was effective for grain refinement, and a lattice disorder was easily achieved by glycerin addition. With the combined process, the critical properties was further increased due to a higher grain boundary density and a greater C substitution. To get fine grain structure of MgB 2 with high critical current properties, mechanical milling for as-received B powder and low temperature solid-state reaction of 550 or 600 .deg. C were attempted to in situ powder-in-tube processed MgB 2 /Fe wires. The critical current properties of the MgB 2 wires using the milled B powder were enhanced due to a smaller grain size and an increased volume of the superconducting phase. The solid-state reaction of a low temperature process for the samples using the milled B powder resulted in a poorer crystallinity with a smaller grain size, which improved superconducting properties. We established the system to measure the transport current properties of the MgB 2 wires. The field dependence of the transport Jc was evaluated for the MgB 2 wires heat-treated at different heat treatment conditions using ball-milled and glycerin-treated B powder. The MgB 2 magnet was developed and the AC loss of MgB 2 wire was also investigated. A conduction cooling device to cool the MgB 2 coil down to 4 K has been fabricated and the

  7. Role of silver addition in the synthesis of high critical current density MgB sub 2 bulk superconductors

    CERN Document Server

    Kumar, D; Narayan, J B; Wang, H; Tiwari, A

    2003-01-01

    Ag-doped MgB sub 2 bulk superconductors have been prepared using a standard solid state processing. The addition of Ag to MgB sub 2 powders during the sintering process has been found to result in an important advantage, namely, the prevention/reduction of loss of Mg, a problem most commonly observed in the sintering of MgB sub 2 bulk samples at elevated temperature and ambient pressures. The Ag-doped MgB sub 2 sample has a distinct superconducting transition temperature around 39 K, while the undoped MgB sub 2 undergoes only a very feeble transition to a diamagnetic superconducting state at around 39 K. The normal conducting silver regions in the MgB sub 2 matrix act as pinning centres resulting in the realization of high critical currents in the presence of magnetic fields.

  8. Anisotropy of the upper critical field in exotic superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Gor' kov, L.P.

    1984-10-25

    While the superconducting order parameter is characterized by a multidimensional representation of the rotation group (a state of the type /sup 3/He-A), the upper critical field near T/sub c/ is anisotropic even in a crystal with a high degree of symmetry. This circumstance can be used to describe the nature of the observed superconductivity. The degeneracy can in principle be lifted by elastic stress.

  9. AC susceptibility response of bulk YBCO superconductors in the presence of a temperature gradient

    International Nuclear Information System (INIS)

    Bodi, A.C.; Kirschner, I.

    1997-01-01

    Low-frequency AC susceptibility measurements on ceramic YBCO superconductors carried out at the presence of a quasi-one-dimensional temperature gradient are compared with those made without the temperature gradient. The values of the different characteristic temperatures measured on samples without and with a temperature gradient are identical but in the second case its characteristic temperature is a medium value. When the temperature gradient is constant on the sample the arithmetic medium value of the local temperatures is the effective characteristic temperature different phenomena. (orig.)

  10. Lower critical field of an anisotropic type-II superconductor

    International Nuclear Information System (INIS)

    Klemm, R.A.; Clem, J.R.

    1980-01-01

    We consider the Ginzburg-Landau free energy of the anisotropic mass form in the presence of a magnetic field of arbitrary fixed direction. It is shown that the free energy may be transformed into the isotropic Ginsburg-Landau form with a kappa that depends upon the direction of the magnetic induction B relative to the crystal lattice. The lower critical field H/sub c/1 is then found for arbitrary direction of B. For highly anisotropic crystals the angular dependence of H/sub c/1 can exhibit a discontinuity or a cusp. The special case of a crystal with uniaxial symmetry is considered in detail

  11. Present status of bulk high temperature superconductors; Baruku koonchodendotai kaihatsu no genjo

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, Masato [Superconductivity Research Laboratory, Tokyo (Japan). Division 3

    1999-03-25

    Recent advancement in materials processing enabled us to grow large single-grain bulk RE-Ba-Cu-O superconductors (RE: rate earth elements) with high critical current densities. These superconductors can exhibit a large electromagnetic force with the interaction of external magnetic fields. Various devices have been developed by utilizing such a force: magnetic bearings, flywheels for energy storage, load transport, hysteresis motors, and several levitation devices. A large magnetic field can also be trapped by bulk superconductors, which can function as a quasi-permanent magnet. Trapped field values have already reached 10 T, thus leading to many novel applications of high trapped field magnets. The final target will be a second-generation Maglev train. (author)

  12. Ceramic high temperature superconductors for high current applications

    Energy Technology Data Exchange (ETDEWEB)

    Christiansen, J.

    1996-12-31

    Composite Reaction Texturing (CRT) is a technique which uses a fine distribution of pre-aligned seeds as nucleating sites for texturing oxide superconductors. It has successfully been applied to the texturing of Bi-2212 compounds. A furhter application of CRT is reported in which Y-123 is biaxially textured using seeds of other Rare Earth-123 compounds with higher melting points as nucleating sites. The resultant textured microstructure exhibits mainly low angle grain boundaries (up to 5 deg. misorientation). Results will be presented on the seed alignment techniques, the development of microstructure during reaction of the composite preform and preliminary measurements of electromagnetic properties. (au). 111 refs.

  13. Ceramic high temperature superconductors for high current applications

    International Nuclear Information System (INIS)

    Christiansen, J.

    1996-01-01

    Composite Reaction Texturing (CRT) is a technique which uses a fine distribution of pre-aligned seeds as nucleating sites for texturing oxide superconductors. It has successfully been applied to the texturing of Bi-2212 compounds. A furhter application of CRT is reported in which Y-123 is biaxially textured using seeds of other Rare Earth-123 compounds with higher melting points as nucleating sites. The resultant textured microstructure exhibits mainly low angle grain boundaries (up to 5 deg. misorientation). Results will be presented on the seed alignment techniques, the development of microstructure during reaction of the composite preform and preliminary measurements of electromagnetic properties. (au)

  14. Analysis of flux-flow curves in superconductors as a function of temperature

    International Nuclear Information System (INIS)

    Boboshko, N.

    1978-01-01

    A phenomenological method to analyse the experimental data of flux-flow resistivity in superconductors as a function of temperature is proposed and successfully applied to existing data for t = kappa >= 0.07. An empirical curve relating the flux-flow resistivity with the Ginsburg-Landau parameter kappa was obtained. (author)

  15. Electronic origin of high-temperature superconductivity in single-layer FeSe superconductor.

    Science.gov (United States)

    Liu, Defa; Zhang, Wenhao; Mou, Daixiang; He, Junfeng; Ou, Yun-Bo; Wang, Qing-Yan; Li, Zhi; Wang, Lili; Zhao, Lin; He, Shaolong; Peng, Yingying; Liu, Xu; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Hu, Jiangping; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

    2012-07-03

    The recent discovery of high-temperature superconductivity in iron-based compounds has attracted much attention. How to further increase the superconducting transition temperature (T(c)) and how to understand the superconductivity mechanism are two prominent issues facing the current study of iron-based superconductors. The latest report of high-T(c) superconductivity in a single-layer FeSe is therefore both surprising and significant. Here we present investigations of the electronic structure and superconducting gap of the single-layer FeSe superconductor. Its Fermi surface is distinct from other iron-based superconductors, consisting only of electron-like pockets near the zone corner without indication of any Fermi surface around the zone centre. Nearly isotropic superconducting gap is observed in this strictly two-dimensional system. The temperature dependence of the superconducting gap gives a transition temperature T(c)~ 55 K. These results have established a clear case that such a simple electronic structure is compatible with high-T(c) superconductivity in iron-based superconductors.

  16. Experimental Consequences of Mottness in High-Temperature Copper-Oxide Superconductors

    Science.gov (United States)

    Chakraborty, Shiladitya

    2009-01-01

    It has been more than two decades since the copper-oxide high temperature superconductors were discovered. However, building a satisfactory theoretical framework to study these compounds still remains one of the major challenges in condensed matter physics. In addition to the mechanism of superconductivity, understanding the properties of the…

  17. Eight-fold quantum states blossom in a high-temperature superconductor

    CERN Multimedia

    2003-01-01

    "Researchers based at Lawrence Berkeley National Laboratory and the University of California at Berkeley have used a scanning tunneling microscope (STM) to reveal eight-fold patterns of quasiparticle interference in the high-temperature superconductor Bi-2212 (bismuth strontium calcium copper oxide)" (2 pages).

  18. ANOMALOUS MICROWAVE-ABSORPTION IN BI-2212 HIGH-TEMPERATURE SUPERCONDUCTORS WITH THE PARAMAGNETIC MEISSNER EFFECT

    NARCIS (Netherlands)

    KATAEV, [No Value; KNAUF, N; BRAUNISCH, W; MULLER, R; BOROWSKI, R; RODEN, B; KHOMSKII, D

    1993-01-01

    The results of the experimental study of an anomaly in low magnetic field microwave absorption in polycrystalline Bi high-temperature superconductors are presented. These results show the presence of the so-called paramagnetic Meissner effect. The data obtained are evidence for the common origin of

  19. Room-temperature-deposited dielectrics and superconductors for integrated photonics.

    Science.gov (United States)

    Shainline, Jeffrey M; Buckley, Sonia M; Nader, Nima; Gentry, Cale M; Cossel, Kevin C; Cleary, Justin W; Popović, Miloš; Newbury, Nathan R; Nam, Sae Woo; Mirin, Richard P

    2017-05-01

    We present an approach to fabrication and packaging of integrated photonic devices that utilizes waveguide and detector layers deposited at near-ambient temperature. All lithography is performed with a 365 nm i-line stepper, facilitating low cost and high scalability. We have shown low-loss SiN waveguides, high-Q ring resonators, critically coupled ring resonators, 50/50 beam splitters, Mach-Zehnder interferometers (MZIs) and a process-agnostic fiber packaging scheme. We have further explored the utility of this process for applications in nonlinear optics and quantum photonics. We demonstrate spectral tailoring and octave-spanning supercontinuum generation as well as the integration of superconducting nanowire single photon detectors with MZIs and channel-dropping filters. The packaging approach is suitable for operation up to 160 °C as well as below 1 K. The process is well suited for augmentation of existing foundry capabilities or as a stand-alone process.

  20. Superconducting magnetic energy storage: Technical considerations and relative capital cost using high-temperature superconductors

    International Nuclear Information System (INIS)

    Loyd, R.J.; Bulc, A.M.; Majumdar, D.

    1992-04-01

    Superconducting magnetic energy storage plants could significantly benefit form using high-temperature superconductors. Benefits would include greatly lowered operation and maintenance expenses and modestly reduced capital costs. The project team compared present HTSC capabilities to the minimum requirements for SMES superconductors. Next, they projected potential cost reductions, assuming one-for-one replacement of conventional low-temperature superconductors with HTSC at equal installed cost. The estimated captial-cost savings from substituting HTSC for conventional superconductors in large-scale SMES plants ranged from 7% for 5000 MWh to 10% for 20 MWh. In addition, HTSC used in SMES plants would provide six design benefits -- better stability, lower refrigeration needs, lower thermal shielding needs, easier cooldown, no helium use, and possibly no vacuum system. Partially offsetting these is the need for more support structure, caused by the lower strength of materials at 77 K versus 4 K, and loss of the cryopumping ability of 4 K surfaces. To realize these benefits, the HTSC primary SMES coil conductor must be robust enough to be formed into a coal, and it must superconduct in a magnetic field of at least 3 tesla at a current density of at least 12,000 A/cm 2

  1. Grain alignment in bulk YBa2Cu3Ox superconductor by a low temperature phase transformation method

    International Nuclear Information System (INIS)

    Selvamanickam, V.; Goyal, A.; Kroeger, D.M.

    1994-01-01

    A quench and directional phase transformation process has been developed to achieve grain alignment in bulk YBa 2 Cu 3 O x superconductors at temperatures about 100 degree C below the peritectic temperature. Isothermal phase transformation of quenched precursors at 890 degree C for 3 min is found to result in the formation of more than 75% of YBa 2 Cu 3 O x phase without any formation of Y 2 BaCuO 5 . Phase transformation at higher temperatures leads to rapid formation of Y 2 BaCuO 5 in addition to YBa 2 Cu 3 O x . A well-aligned microstructure is achieved by directional phase transformation of the quenched compacts as a rate of 10 mm/h. The magnetic field dependence of the critical current density at 77 K of the directionally phase transformed material compares well with that of melt-textured YBCO and is superior to that of magnetically aligned and sintered YBCO

  2. The order parameter of high temperature superconductors, as measured by Andreev Saint-James reflection, Raman and neutron scattering

    OpenAIRE

    Hüfner, Stefan; Müller, Frank

    2010-01-01

    By comparing experiments that use Andreev Saint-James reflection, Raman scattering (B2g) and neutron scattering on the (cuprate) high temperature superconductors, evidence is found, that all of the techniques can measure the order parameter of these superconductors. The order parameter is the energy needed to take a superconducting boson out of the condensate. It has the same temperature and doping dependence as the superconducting transition temperature Tc. This condensation energy is differ...

  3. Nanoscale Stoichiometric Analysis of a High-Temperature Superconductor by Atom Probe Tomography.

    Science.gov (United States)

    Pedrazzini, Stella; London, Andrew J; Gault, Baptiste; Saxey, David; Speller, Susannah; Grovenor, Chris R M; Danaie, Mohsen; Moody, Michael P; Edmondson, Philip D; Bagot, Paul A J

    2017-04-01

    The functional properties of the high-temperature superconductor Y1Ba2Cu3O7-δ (Y-123) are closely correlated to the exact stoichiometry and oxygen content. Exceeding the critical value of 1 oxygen vacancy for every five unit cells (δ>0.2, which translates to a 1.5 at% deviation from the nominal oxygen stoichiometry of Y7.7Ba15.3Cu23O54-δ ) is sufficient to alter the superconducting properties. Stoichiometry at the nanometer scale, particularly of oxygen and other lighter elements, is extremely difficult to quantify in complex functional ceramics by most currently available analytical techniques. The present study is an analysis and optimization of the experimental conditions required to quantify the local nanoscale stoichiometry of single crystal yttrium barium copper oxide (YBCO) samples in three dimensions by atom probe tomography (APT). APT analysis required systematic exploration of a wide range of data acquisition and processing conditions to calibrate the measurements. Laser pulse energy, ion identification, and the choice of range widths were all found to influence composition measurements. The final composition obtained from melt-grown crystals with optimized superconducting properties was Y7.9Ba10.4Cu24.4O57.2.

  4. Magnetic-Field-Induced Soft-Mode Quantum Phase Transition in the High-Temperature Superconductor La1.855Sr0.145CuO4

    DEFF Research Database (Denmark)

    Chang, J.; Christensen, Niels Bech; Niedermayer, C.

    2009-01-01

    Inelastic neutron-scattering experiments on the high-temperature superconductor La1.855Sr0.145CuO4 reveal a magnetic excitation gap Delta that decreases continuously upon application of a magnetic field perpendicular to the CuO2 planes. The gap vanishes at the critical field required to induce lo......-range incommensurate antiferromagnetic order, providing compelling evidence for a field-induced soft-mode driven quantum phase transition....

  5. Visualisation of flux distributions in high-temperature superconductors. Final report; Sichtbarmachung der Flussverteilung in Hochtemperatursupraleitern nach verschiedenen Mikrostrukturaenderungen. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Kuhn, H.; Kronmueller, H.

    1998-05-01

    Theoretical calculation models for current, magnetic and electric field distributions in thin superconductors of arbitrary shape in perpendicular magnetic field were developed. Calculations were done for inhomogeneous and anisotropic critical currents and compared with magnetooptical observations of flux penetration. Nice agreement of theory and experiment was found. Flux-line depinning and motion in superconductors with linear defects was investigated by magneto-optics. Depinning mechanisms were deduced from observations of high-temperature superconductors which are irradiated with swift heavy ions parallel and crosswisely at various angles to the surface normal. Magneto-optical investigations of flux penetration into (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+{delta}} multifilament tapes showed a strong dependence of the current capability on the microstructure of single filaments. The different filament textures which are caused by the inhomogeneous deformation of the tape during thermomechanical treatment results in critical current densities varying by about one order of magnitude. (orig.) [Deutsch] Theoretische Modelle zur Berechnung von Strom-, Magnet- und elektrischen Feldverteilungen wurden fuer duenne Supraleiter beliebiger Geometrie mit inhomogener und anisotroper kritischer Stromdichte im senkrechten Magnetfeld entwickelt und mit magnetooptischen Beobachtungen des Flusseindringens verglichen, wobei eine hervorragende Uebereinstimmung zwischen Theorie und Experiment erzielt wurde. Mit Hilfe von magnetooptischen Untersuchungen des Flusseindringens in schwerionenbestrahlte Hochtemperatursupraleiter, die unter verschiedenen Winkeln zur Oberflaechennormalen parallel und kreuzweise bestrahlt wurden, konnten Bewegungs- und Entankerungsmechanismen von Flusslinien in Supraleitern mit linearen Defekten abgeleitet werden. Magnetooptische Untersuchungen des Flusseindringens in (Bi, Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+{delta

  6. Application of high temperature ceramic superconductors (CSC) to commercial tokamak reactors

    International Nuclear Information System (INIS)

    Ehst, D.A.; Kim, S.; Gohar, Y.; Turner, L.; Smith, D.L.; Mattas, R.

    1988-08-01

    Ceramic superconductors operating near liquid nitrogen temperature may experience higher heating rates without losing stability, compared conventional superconductors. This will permit cable design with less stabilizer, reducing fabrication costs for large fusion magnets. Magnet performance is studied for different operating current densities in the superconductor, and cost benefits to commercial tokamak reactors are estimated. It appears that 10 kA /center dot/ cm/sup /minus/2/ (at 77 K and /approximately/10 T) is a target current density which must be achieved in order for the ceramic superconductors to compete with conventional materials. At current densities around 50 kA /center dot/ cm/sup /minus/2/ most potential benefits have already been gained, as magnet structural steel begins to dominate the cost at this point. For a steady state reactor reductions of /approximately/7% are forecast for the overall capital cost of the power plant in the best case. An additional /approximately/3% cost saving is possible for pulsed tokamaks. 9 refs., 4 figs., 8 tabs

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

    International Nuclear Information System (INIS)

    Foner, S.

    1990-01-01

    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

  8. 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.

  9. 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.

  10. 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.

  11. Far-infrared applications of high-temperature superconductors: Fabry-Perot resonators and fast detectors

    International Nuclear Information System (INIS)

    Renk, K.F.

    1993-01-01

    Far-infrared applications of high temperature superconductors, namely Fabry-Perot resonators and fast detectors, are reported. At terahertz frequencies high finesse (∝60 at 3 THz) is obtained for Fabry-Perot resonators with YBa 2 Cu 3 O 7 -on-MgO reflectors and fast, nonbolometric response with a response time 2 Cu 3 O 7 thin films at frequencies from 0.1 THz to nearly 10 THz. (orig.)

  12. Concepts for using trapped-flux bulk high-temperature superconductor in motors and generators

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R; Strasik, Michael [Boeing Research and Technology, PO Box 3707, MC 2T-50, Seattle, WA 98124-2207 (United States)

    2010-12-15

    We review previous concepts for using bulk high-temperature superconductors (HTSs) in motors and generators and discuss methods for using trapped-flux (TF) HTSs in motors and generators that have been recently investigated in our laboratory. We examine the expected performance of a brushless motor/generator that uses TF bulk HTSs to provide magnetomotive force, where the stator windings are used to create the TF. A key feature is the use of dysprosium for the stator and rotor cores.

  13. Single crystal growth and neutron study of Bi-2212 high temperature superconductor

    International Nuclear Information System (INIS)

    Gu, G.D.; Miles, P.A.; Russell, G. J.; Ivanov, A.; Koshizuka, N.; Kennedy, S.J.

    1999-01-01

    Full text: Many physical properties of the cuprate high temperature superconductors appear to defy the conventional (one-electron) theory of metals. The neutron diffraction and inelastic neutron scattering of the high T c single crystals can provides incisive information about collective magnetic excitations which is required to guide the development of new theories incorporating strong electron correlations. For lack of the suitably large single crystals, inelastic neutron scattering measurements have thus far proven possible for only two of the many families of high temperature superconductors, La 2-x Sr x CuO 4 and YBa 2 Cu 3 O x . While the magnetic pronounced differences that have hampered a unified description of the spin dynamics in the cuprates. In particular, a sharp resonant spin excitation dominates the spectrum in the superconducting state of YBa 2 Cu 3 0 x , but is not found in La 2-x Sr x CuO 4 . We have successfully grown large size Bi-2212 single crystals up to 10*5*1.2 mm 3 by floating zone method, and have studied neutron diffraction and neutron scattering in the single crystals. The Neutron diffraction of the single crystals shows that the crystals are high quality. Here we report the discovery of a magnetic resonance peak in the superconducting state of a third high temperature superconductor of Bi-2212 single crystal by modern neutron optics. The discovery provides evidence of the generality of this unusual phenomenon among the cuprates and greatly extends the empirical basis for its theoretical description. The magnetic resonance peak in Bi-2212 single crystals rules out the possibility or chemical parameters peculiar to YBCO superconductor. Rather, it is an intrinsic feature of the copper oxides whose explanation must be in an integral part of any theory of high temperature superconductivity

  14. Image of the Energy Gap Anisotropy in the Vibrational Spectum of a High Temperature Superconductor

    OpenAIRE

    Flatte, Michael E.

    1992-01-01

    We present a new method of determining the anisotropy of the gap function in layered high-Tc superconductors. Careful inelastic neutron scattering measurements at low temperature of the phonon dispersion curves in the (100) direction in La_(1.85)Sr_(.15)CuO_4 would determine whether the gap is predominately s-wave or d-wave. We also propose an experiment to determine the gap at each point on a quasi-two-dimensional Fermi surface.

  15. Magnetization studies of oxides related to the high temperature cuprate superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhaorong [Iowa State Univ., Ames, IA (United States)

    1995-06-19

    The magnetic properties related to the following high temperature superconductors were measured utilizing a Faraday magnetometer: BaCuO2+x , La2 CuO4 , Sr2 RhO4 , Sr2 VO4, and Sr2 CuO3. Neutron diffraction, magnetic susceptibility, and heat capacity measurements are discussed.

  16. Concepts for using trapped-flux bulk high-temperature superconductor in motors and generators

    International Nuclear Information System (INIS)

    Hull, John R; Strasik, Michael

    2010-01-01

    We review previous concepts for using bulk high-temperature superconductors (HTSs) in motors and generators and discuss methods for using trapped-flux (TF) HTSs in motors and generators that have been recently investigated in our laboratory. We examine the expected performance of a brushless motor/generator that uses TF bulk HTSs to provide magnetomotive force, where the stator windings are used to create the TF. A key feature is the use of dysprosium for the stator and rotor cores.

  17. Microstructure and critical current density in high-Tc metal oxide superconductors

    International Nuclear Information System (INIS)

    Johnson, S.M.; Gusman, M.I.

    1992-03-01

    Superconductor powders in the U-Ba-Cu-O (YBCO) and Bi-Pb-Sr-Ca-Cu-O (BSCCO) systems were synthesized by freeze-drying. Powders were characterized, and processed into samples for evaluation of superconducting behavior. Freeze-drying is attractive because the powders have high purity, are homogeneous, have a small size and are active. YBCO powders can be sintered to high density at 890 degrees C. Many compositions, processing approaches and heat treatments were explored in an effort to understand relations between microstructure and critical density, and to improve the critical current density. Powders were also formed into sputtering targets for coating preparation at Stanford University. The highest critical current density achieved with the YBCO powders was ∼15,000 A/cm 2 at 4.2K and 0.5T using powders treated to prevent carbon contamination. The BSCCO materials with the highest critical current density, ∼30,000 A/cm 2 at the same conditions were formed by heat treating melted and quenched samples. All critical current density measurements were made by Stanford University, a subcontractor to this effort. Stanford University also prepared coatings by off-axis magnetron sputtering

  18. Upper critical field in dirty two-band superconductors: breakdown of the anisotropic Ginzburg-Landau theory

    NARCIS (Netherlands)

    Golubov, Alexandre Avraamovitch; Koshelev, A.E.

    2003-01-01

    We investigate the upper critical field in a dirty two-band superconductor within quasiclassical Usadel equations. The regime of very high anisotropy in the quasi-2D band, relevant for MgB2, is considered. We show that strong disparities in pairing interactions and diffusion constant anisotropies

  19. Oxide superconductors

    International Nuclear Information System (INIS)

    Cava, R.J.

    2000-01-01

    This article briefly reviews ceramic superconductors from historical and materials perspectives. It describes the factors that distinguish high-temperature cuprate superconductors from most electronic ceramics and places them in the context of other families of superconducting materials. Finally, it describes some of the scientific issues presently being actively pursued in the search for the mechanism for high-temperature superconductivity and the directions of research into new superconducting ceramics in recent years

  20. Anisotropic upper critical magnetic fields in Rb 2 Cr 3 As 3 superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Zhang-Tu; Liu, Yi; Bao, Jin-Ke; Xi, Chuan-Ying; Pi, Li; Cao, Guang-Han

    2017-09-13

    Rb2Cr3As3 is a structurally one-dimensional superconductor containing Cr3As3 chains with a superconducting transition temperature of T-c = 4.8 K. Here we report the electrical resistance measurements for Rb2Cr3As3 single crystals, under magnetic fields up to 29.5 T and at temperatures down to 0.36 K, from which the upper critical fields, H-c2(T), can be obtained in a broad temperature range. For field parallel to the Cr3As3 chains, H-c2(parallel to)(T) is paramagnetically limited with an initial slope of mu(0)dH(c2)(parallel to)/dT|T-c = - 16 T K-1 and a zero-temperature upper critical field of mu H-0(c2)parallel to(0) = 17.5 T. For field perpendicular to the Cr3As3 chains, however, H-c2(perpendicular to)(T) is only limited by orbital pair-breaking effect with mu(0)dH(c2)(perpendicular to)/dT|(Tc) = - 3 T K-1. As a consequence, the anisotropy gamma H = H-c2(parallel to)/H-c2(perpendicular to) decreases sharply near T-c and reverses below 2 K. Remarkably, the low- temperature H-c2(perpendicular to)(T) down to 0.075 T-c remains to increase linearly up to over three times the Pauli paramagnetic limit, which strongly suggests dominant spin-triplet superconductivity in Rb2Cr3As3.

  1. Superconductors: The long road ahead

    International Nuclear Information System (INIS)

    Foner, S.; Orlando, T.P.

    1988-01-01

    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

  2. An induction/synchronous motor with high temperature superconductor/normal conductor hybrid double-cage rotor windings

    International Nuclear Information System (INIS)

    Nakamura, T; Nagao, K; Nishimura, T; Matsumura, K

    2009-01-01

    We propose hybrid double-cage rotor windings that consist of a high temperature superconductor (HTS) and a normal conductor, which are introduced into an HTS induction/synchronous motor (HTS-ISM). The motor rotates as a conventional induction motor when the operating temperature of the hybrid rotor is above the critical temperature of the HTS bars, i.e., in the normal conducting state. On the other hand, the HTS-ISM rotates as a synchronous motor when the temperature is below the critical temperature, i.e., in the superconducting (zero resistance) state. In other words, we do not always need to take care of the cooling conditions, if the HTS-ISM is automatically, as well as appropriately, controlled, depending upon the rotation mode. Namely, the above-mentioned hybrid double-cage HTS-ISM is possibly a breakthrough in solving the cooling problems of HTS rotating machines, especially for industrial applications. The experimental results of the aforementioned motor are reported. An example of an operation flowchart of the motor is also presented and discussed.

  3. Planar high temperature superconductor filters with backside coupling

    Science.gov (United States)

    Shen, Zhi-Yuan (Inventor)

    1998-01-01

    An improved high temperature superconducting planar filter wherein the coupling circuit or connecting network is located, in whole or in part, on the side of the substrate opposite the resonators and enables higher power handling capability.

  4. Low-temperature densification of high-Tc superconductors

    International Nuclear Information System (INIS)

    Capone, D.W. II

    1989-01-01

    It is believed that the weak-link behavior in YBa 2 Cu 3 O 7 , 123 bulk materials results from the presence of non-superconducting second phases coating the grain boundaries of sintered 123 compacts. These second phases result from the BaCuO 2 - CuO eutectic, which is a liquid at sintering temperatures above 870 degrees C. Sintering below this temperature results in low densities (ca. 70/% of the theoretical density). Sintering above 870 degrees C produces dense samples via liquid-phase sintering, resulting in the grain boundary phases mentioned above. The authors report the results of a series of low-temperature densification experiments designed to produce 100% dense ceramic samples at temperatures below 870 degrees C. Room-temperature swaging, using standard powder metallurgy techniques, has been used for form fibers having green (unsintered) densities greater than 90% of the theoretical density of the 123. A warm extrusion technique (T ≥ 300 degrees C) has also been used to produce 100% dense 123 compacts. In both cases, after fabrication, the oxygen content of the 123 materials is near 7.0. However, x- ray diffraction experiments show that the cation lattice is disordered, and the materials are not superconducting. These materials can be ordered using suitable posts-annealing techniques. The effect of time and temperature on the degree of ordering and the superconductivity is presented

  5. On the spectral dependence of the critical temperature of superconductors

    International Nuclear Information System (INIS)

    Combescot, R.

    1989-01-01

    The authors have solved analytically the linearized Eliashberg equations for T c in the weak coupling limit. The corrections to their result go to zero in this limit. Their calculation is valid for any spectral shape. They find a smooth dependence of T c on the spectral shape. Only the gross features of the spectrum are relevant. The authors propose for T c an interpolation formula valid for any coupling strength and any spectral shape. This formula is in good agreement with known numerical results. It agrees with all the qualitative behavior obtained from computer work

  6. Design of a high-temperature superconductor current lead for electric utility SMES

    International Nuclear Information System (INIS)

    Niemann, R.C.; Cha, Y.S.; Hull, J.R.; Rey, C.M.; Dixon, K.D.

    1995-01-01

    Current leads that rely on high-temperature superconductors (HTSs) to deliver power to devices operating at liquid helium temperature have the potential to reduce refrigeration requirements to levels significantly below those achievable with conventional leads. The design of HTS current leads suitable for use in near-term superconducting magnetic energy storage (SMES) is in progress. The SMES system has an 0.5 MWh energy capacity and a discharge power of 30 MW. Lead-design considerations include safety and reliability, electrical and thermal performance, structural integrity, manufacturability, and cost. Available details of the design, including materials, configuration, and performance predictions, are presented

  7. Characterization of devices, circuits, and high-temperature superconductor transmission lines by electro-optic testing

    Science.gov (United States)

    Whitaker, John F.

    1991-01-01

    The development of a capability for testing transmission lines, devices, and circuits using the optically-based technique of electro-optics sampling was the goal of this project. Electro-optic network analysis of a high-speed device was demonstrated. The project involved research on all of the facets necessary in order to realize this result, including the discovery of the optimum electronic pulse source, development of an adequate test fixture, improvement of the electro-optic probe tip, and identification of a device which responded at high frequency but did not oscillate in the test fixture. In addition, during the process of investigating patterned high-critical-temperature superconductors, several non-contacting techniques for the determination of the transport properties of high T(sub c) films were developed and implemented. These are a transient, optical pump-probe, time-resolved reflectivity experiment, an impulsive-stimulated Raman scattering experiment, and a terahertz-beam coherent-spectroscopy experiment. The latter technique has enabled us to measure both the complex refractive index of an MgO substrate used for high-T(sub c) films and the complex conductivity of a YBa2Cu3O(7-x) sample. This information was acquired across an extremely wide frequency range: from the microwave to the submillimeter-wave regime. The experiments on the YBCO were conducted without patterning of, or contact to, the thin film. Thus, the need for the more difficult transmission-line experiments was eliminated. Progress in all of these areas was made and is documented in a number of papers. These papers may be found in the section listing the abstracts of the publications that were issued during the course of the research.

  8. Electron-phonon interaction in high temperature superconductors

    Directory of Open Access Journals (Sweden)

    H. Khosroabadi

    2006-09-01

    Full Text Available   We explore the important role of the strong electron-phonon interaction in high temperature superconductivity through the study of the results of some important experiments, such as inelastic neutron and X-ray scattering, angle resolved photoemission spectroscopy, and isotope effects. We also present our computational results of the eigenvalues and eigenvectors of the Ag Raman modes, and the ionic displacement dependence of the electronic band structure by density functional theory. It is clearly evident that the role of phonons in the mechanism behind the high-temperature superconducting state should be seriously considered.

  9. Low temperature superconductor and aligned high temperature superconductor magnetic dipole system and method for producing high magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Ramesh; Scanlan, Ronald; Ghosh, Arup K.; Weggel, Robert J.; Palmer, Robert; Anerella, Michael D.; Schmalzle, Jesse

    2017-10-17

    A dipole-magnet system and method for producing high-magnetic-fields, including an open-region located in a radially-central-region to allow particle-beam transport and other uses, low-temperature-superconducting-coils comprised of low-temperature-superconducting-wire located in radially-outward-regions to generate high magnetic-fields, high-temperature-superconducting-coils comprised of high-temperature-superconducting-tape located in radially-inward-regions to generate even higher magnetic-fields and to reduce erroneous fields, support-structures to support the coils against large Lorentz-forces, a liquid-helium-system to cool the coils, and electrical-contacts to allow electric-current into and out of the coils. The high-temperature-superconducting-tape may be comprised of bismuth-strontium-calcium-copper-oxide or rare-earth-metal, barium-copper-oxide (ReBCO) where the rare-earth-metal may be yttrium, samarium, neodymium, or gadolinium. Advantageously, alignment of the large-dimension of the rectangular-cross-section or curved-cross-section of the high-temperature-superconducting-tape with the high-magnetic-field minimizes unwanted erroneous magnetic fields. Alignment may be accomplished by proper positioning, tilting the high-temperature-superconducting-coils, forming the high-temperature-superconducting-coils into a curved-cross-section, placing nonconducting wedge-shaped-material between windings, placing nonconducting curved-and-wedge-shaped-material between windings, or by a combination of these techniques.

  10. The nature of twin boundaries in the high-temperature superconductor YBa2Cu3O7-δ

    International Nuclear Information System (INIS)

    Zhu, Y.; Welch, D.O.

    1999-01-01

    Twin boundaries are the most commonly observed lattice defect in the high-temperature superconductor YBa 2 Cu 3 O 7-δ . Furthermore, the region around a twin boundary for which the structure and composition are seriously affected is of a scale comparable to the coherence length for the superconducting order parameter. Thus, twin boundaries can be important in the behavior of magnetic vortices and the critical current density in this material. In this paper the authors review the results of a wide range of investigations of twin boundary structure and composition by advanced transmission electron microscopy methods, both imaging and analytical in nature. A simple Landau model of twin boundary energy and width is proposed

  11. Materials process and applications of single grain (RE)-Ba-Cu-O bulk high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Li Beizhan; Zhou Difan; Xu Kun; Hara, Shogo; Tsuzuki, Keita; Miki, Motohiro; Felder, Brice; Deng Zigang [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology (TUMSAT), 2-1-6, Etchu-jima, Koto-ku, Tokyo 135-8533 (Japan); Izumi, Mitsuru, E-mail: izumi@kaiyodai.ac.jp [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology (TUMSAT), 2-1-6, Etchu-jima, Koto-ku, Tokyo 135-8533 (Japan)

    2012-11-20

    This paper reviews recent advances in the melt process of (RE)-Ba-Cu-O [(RE)BCO, where RE represents a rare earth element] single grain high-temperature superconductors (HTSs), bulks and its applications. The efforts on the improvement of the magnetic flux pinning with employing the top-seeded melt-growth process technique and using a seeded infiltration and growth process are discussed. Which including various chemical doping strategies and controlled pushing effect based on the peritectic reaction of (RE)BCO. The typical experiment results, such as the largest single domain bulk, the clear TEM observations and the significant critical current density, are summarized together with the magnetization techniques. Finally, we highlight the recent prominent progress of HTS bulk applications, including Maglev, flywheel, power device, magnetic drug delivery system and magnetic resonance devices.

  12. Materials process and applications of single grain (RE)-Ba-Cu-O bulk high-temperature superconductors

    Science.gov (United States)

    Li, Beizhan; Zhou, Difan; Xu, Kun; Hara, Shogo; Tsuzuki, Keita; Miki, Motohiro; Felder, Brice; Deng, Zigang; Izumi, Mitsuru

    2012-11-01

    This paper reviews recent advances in the melt process of (RE)-Ba-Cu-O [(RE)BCO, where RE represents a rare earth element] single grain high-temperature superconductors (HTSs), bulks and its applications. The efforts on the improvement of the magnetic flux pinning with employing the top-seeded melt-growth process technique and using a seeded infiltration and growth process are discussed. Which including various chemical doping strategies and controlled pushing effect based on the peritectic reaction of (RE)BCO. The typical experiment results, such as the largest single domain bulk, the clear TEM observations and the significant critical current density, are summarized together with the magnetization techniques. Finally, we highlight the recent prominent progress of HTS bulk applications, including Maglev, flywheel, power device, magnetic drug delivery system and magnetic resonance devices.

  13. Magnetometry and electrical transport measurements of high temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Chan, Mun Keat [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-02-13

    Prior to preparing and performing measurements in pulsed magnetic fields, it is necessary to characterize them. For the cuprates such as HgBa2CuO4+δ (Hg1201), measurements of the superconducting temperature is essential. This experiment comprises just such a characterization of Hg1201 crystals to be used for pulsed magnetic field measurements.

  14. Problems of a transformer with high-temperature superconductors

    International Nuclear Information System (INIS)

    Mueller, W.

    1989-01-01

    Fundamental reflections are made on the demands which have to be made on the short-circuit current limitation in the network on the one hand and on the admissible magnetic boundary field strengths of high-temperature superconduction on the other hand. The aim to develop mechanically self-supporting windings led for conventional core-type transformer designs to the construction of concentric-lay winding arrangements with magnetic stray field strengths, which seem to be realizable with regard to material development. Due to the further aim of avoiding core losses, a design study on a coreless high-temperature superconduction transformer was drawn up the windings of which are united in a coaxial cable which is wound up to a toroidal coil. The factors of influence which are relevant for the rating, operating characteristics and the application of a transformer like this are discussed. (orig.) [de

  15. Penetration depth study of high temperature and other novel superconductors

    CERN Document Server

    Manzano, F

    2002-01-01

    penetration depth of lambda sub a (0) = (1100 +- 200)A was yielded. YBa sub 2 Cu sub 4 O sub 8 single crystals were measured to observe any contribution from Andreev boundstates. No evidence for this was found. The penetration depth was seen to decrease at low temperature rather than follow the linear temperature dependence associated with d sub x sub + 2 sub - sub y sub + 2 superconductivity. This low temperature decrease was seen to be increasingly suppressed for magnetic fields above approx 5 mT. The effect was attributed to the suppression of superconductivity along the CuO chains. An attempt was made to separate each of the penetration depth (DELTA lambda sub a (T), DELTA lambda sub b (T) and DELTA lambda sub c (T)) components using geometrical arguments. A high stability LC-oscillator technique was used to perform penetration depth measurements on optimally doped YBa sub 2 Cu sub 3 O sub 7 single crystals, naturally underdoped YBa sub 2 Cu sub 4 O sub 8 single crystals and the novel, newly discovered su...

  16. Possible antipolar pairing mechanism in high-temperature superconductors

    International Nuclear Information System (INIS)

    Cardwell, D.A.; Shorrocks, N.M.

    1989-01-01

    An antipolar pairing mechanism for free charge carriers in high-T c superconducting compounds is proposed qualitatively. This involves the establishment of a two-dimensional (2D) array of effective charge-coupling centers within the superconducting lattice via a specific phonon distortion of cation species along a nonmajor crystallographic direction. A fundamental requirement of this model is that the density of such coupling centers decreases with decreasing temperature. In the case of Y-Ba-Cu-O, it is asserted that charge carriers in a 2D oxygen band adjacent to the phonon-containing plane become localized by the resulting (local) field distortion. Cooper pairs may then form when the charge-coupling-center density falls below the charge-carrier density. Such a mechanism could be mediated by a longitudinal phonon which softens at low temperatures to produce an antipolar state, such as that incipient to an antiferroelectric distortion of the lattice (i.e., in the zero-frequency limiting case). This model, which may be investigated experimentally by low-temperature Raman spectroscopy, isotopic substitution, and x-ray diffractometry at 4.2 K, can be applied to all p-type high-T c systems. In addition, it may account for the observed lattice anisotropy and short coherence length characteristic of these materials

  17. Gap structure of iron-pnictide superconductors from low-temperature heat transport

    Science.gov (United States)

    Reid, Jean-Philippe

    2010-03-01

    The structure of the superconducting gap provides important clues on the symmetry of the order parameter and the pairing mechanism. Here I describe how measurements of the thermal conductivity at very low temperature can be used to determine whether nodes are present in the gap function of a particular superconductor, and how the application of a magnetic field probes the low-energy quasiparticle excitations. Measurements on hole-doped and electron-doped pnictide superconductors, Ba1-xKxFe2As2 [1] and Ba(Fe1-xCox)2As2 [2], reveal a negligible residual linear term at T->0, showing that the gap of these two superconductors has no nodes, at least in the basal plane. In both pnictides, a small field is found to be very effective in exciting quasiparticles, showing that the gap must be very small in some direction on the Fermi surface. In Ba(Fe1-xCox)2As2, the evolution with doping x is as follows: at low x, the gap is large everywhere on the Fermi surface, and beyond optimal doping the minimum gap becomes progressively smaller. I discuss what these features tell us about the nature of the superconducting state in pnictide superconductors. * Measurements of heat transport performed in collaboration with X.-G. Luo, H. Shakeripour, M.A. Tanatar, N. Doiron-Leyraud and L. Taillefer. [1] X.-G. Luo et al., Phys. Rev. B 80, 140503 (2009). [2] M.A. Tanatar et al., arXiv:0907.1276.

  18. Study of the implementation of high temperature superconductors to accelerator magnets

    International Nuclear Information System (INIS)

    Fleiter, Jerome

    2013-01-01

    Particle colliders are the main tool for investigating and understanding the fundamental laws of physics. The CERN Large Hadron Collider (LHC), is a circular accelerator which steers and collides two counter-rotating protons beams. It has four collision points where detectors are placed to analyze the products emerging from the collisions. In a synchrotron machine a magnetic flux density is used to guide and focus particles around the orbit. The maximum energy that a circular machine with a given geometry can achieve is limited by the maximum strength of the dipole magnetic flux density. There is therefore an interest in the particle physics community in searching for dipole magnets with higher strength. The LHC has a beam trajectory radius of 4.3 km and a collision center-of-mass energy of 14 TeV. The accelerator employs 1232 large superconducting Nb-Ti dipole magnets operated at a flux density of up to 8.3 T in a bath of superfluid helium at 1.9 K. Energies higher than that achieved with the LHC require magnets made from superconductors with higher upper critical flux density. Nb 3 Sn is an option for magnets operated up to about 14 T. The level of energies of the type being discussed for a potential energy upgrade of the LHC machine - 33 TeV- would require the use of high temperature superconductors (HTS). Three technical HTS are available today: YBCO, Bi-2212 and Bi-2223. At low temperature YBCO conductors present both irreversible flux density and current density in excess of those measured in Bi-2212 and Bi-2223 conductors. In addition, YBCO can be used as reacted conductor, which makes its use for applications simpler than Bi-2212, which requires heat treatment at high temperature and in oxygen atmosphere after cabling and winding. The level of currents required for application to accelerator magnets, which is above 10 kA at the nominal operating temperature and flux density, excludes the use of single strands. The high current and high current density

  19. Two-loop disorder effects on the nematic quantum criticality in d-wave superconductors

    International Nuclear Information System (INIS)

    Wang, Jing

    2015-01-01

    The gapless nodal fermions exhibit non-Fermi liquid behaviors at the nematic quantum critical point that is supposed to exist in some d-wave cuprate superconductors. This non-Fermi liquid state may be turned into a disorder-dominated diffusive metal if the fermions also couple to a disordered potential that generates a relevant perturbation in the sense of renormalization group theory. It is therefore necessary to examine whether a specific disorder is relevant or not. We study the interplay between critical nematic fluctuation and random chemical potential by performing renormalization group analysis. The parameter that characterizes the strength of random chemical potential is marginal at the one-loop level, but becomes marginally relevant after including the two-loop corrections. Thus even weak random chemical potential leads to diffusive motion of nodal fermions and the significantly critical behaviors of physical implications, since the strength flows eventually to large values at low energies. - Highlights: • The gapless nodal fermions exhibit non-Fermi liquid behaviors at the nematic QCP. • The strength of random chemical potential is marginal at the one-loop level. • The strength becomes marginally relevant after including the two-loop corrections. • The diffusive metallic state is induced by the marginally relevant disorder. • The behaviors of some physical observables are presented at the nematic QCP

  20. Paramagnetic Meissner effect of high-temperature granular superconductors: Interpretation by anisotropic and isotropic models

    International Nuclear Information System (INIS)

    Chen, F.H.; Horng, W.C.; Hsu, H.T.; Tseng, T.Y.

    1995-01-01

    The field-cooled magnetization of high-T c superconducting ceramics measured in low magnetic field exhibits the paramagnetic Meissner effect (PME), i.e., the diamagnetic signal initially increases with decrease in temperature but reaches a maximum at temperature T d and later decreases with decrease in temperature. Even in some samples the signal is ultimately able to transform inversely into a paramagnetic regime once the sample is cooled below a temperature T p as long as the applied field is sufficiently small. This PME has been observed in various high-T c cuprates and is explained by disparate aspects. An anisotropic model, in which the granular superconductors are assumed to be ideally anisotropic, was first alternatively proposed in the present work so as to theoretically account for this effect. On the other hand, an isotropic model, suitable for granular superconductors with randomly oriented grains, was proposed to deal with the samples prepared by a conventional solid-state reaction method. The anomalous magnetization behavior in the present model was demonstrated to be the superposition of the diamagnetic signal, which occurs as a result of the intragranular shielding currents, over the paramagnetic one due to the induction of the intergranular component induced by these currents where the intergranular one behaved as the effective pinning centers. The PME was demonstrated by this model to exist parasitically in granular superconductors. This intergranular effect is therefore worthy of remark when evaluating the volume fraction of superconductivity for the samples from the Meissner signal, in particular, at a low magnetic field

  1. Flux creep characteristics in high-temperature superconductors

    International Nuclear Information System (INIS)

    Zeldov, E.; Amer, N.M.; Koren, G.; Gupta, A.; McElfresh, M.W.; Gambino, R.J.

    1990-01-01

    We describe the voltage-current characteristics of YBa 2 Cu 3 O 7-δ epitaxial films within the flux creep model in a manner consistent with the resistive transition behavior. The magnitude of the activation energy, and its temperature and magnetic field dependences, are readily derived from the experimentally observed power law characteristics and show a (1-T/T c ) 3/2 type of behavior near T c . The activation energy is a nonlinear function of the current density and it enables the determination of the shape of the flux line potential well

  2. Numerical simulation of realistic high-temperature superconductors

    International Nuclear Information System (INIS)

    1997-01-01

    One of the main obstacles in the development of practical high-temperature superconducting (HTS) materials is dissipation, caused by the motion of magnetic flux quanta called vortices. Numerical simulations provide a promising new approach for studying these vortices. By exploiting the extraordinary memory and speed of massively parallel computers, researchers can obtain the extremely fine temporal and spatial resolution needed to model complex vortex behavior. The results may help identify new mechanisms to increase the current-capability capabilities and to predict the performance characteristics of HTS materials intended for industrial applications

  3. High temperature superconductivity the road to higher critical temperature

    CERN Document Server

    Uchida, Shin-ichi

    2015-01-01

    This book presents an overview of material-specific factors that influence Tc and give rise to diverse Tc values for copper oxides and iron-based high- Tc superconductors on the basis of more than 25 years of experimental data, to most of which the author has made important contributions. The book then explains why both compounds are distinct from others with similar crystal structure and whether or not one can enhance Tc, which in turn gives a hint on the unresolved pairing mechanism. This is an unprecedented new approach to the problem of high-temperature superconductivity and thus will be inspiring to both specialists and non-specialists interested in this field.   Readers will receive in-depth information on the past, present, and future of high-temperature superconductors, along with special, updated information on what the real highest Tc values are and particularly on the possibility of enhancing Tc for each member material, which is important for application. At this time, the highest Tc has not been...

  4. Asymptotic Slavery in the Copper Oxide High Temperature Superconductors

    Science.gov (United States)

    Phillips, Philip

    2004-05-01

    Vast progress in theoretical solid state physics has been made by constructing models which mimic the low-energy properties of solids. Essential to the success of this program is the separability of the high and low energy degrees of freedom. While it is hoped that a high energy reduction can be made to solve the problem of high temperature superconductivity in the copper oxide materials, I will show that no consistent theory is possible if the high energy scale is removed. At the heart of the problem is the mixing of all energy scales (that is, UV-IR mixing) in the copper-oxide materials. Optical experiments demonstrate that the number of low-energy degrees of freedom is derived from a high energy scale. The implications of the inseparability of the high and low energy degrees of freedom on the phase diagram of the cuprates is discussed.

  5. Recent neutron scattering results on high-temperature superconductors

    International Nuclear Information System (INIS)

    Mook, H.A.; Dai, P.; Aeppli, G.; Mason, T.E.; Hecker, N.E.; Harvey, J.A.; Armstrong, T.; Salama, K.; Lee, D.

    1994-01-01

    Triple-axis spectrometry has been used to determine the magnetic excitations in YBa 2 Cu 3 O 7 . Polarized measurements at 100 K show the scattering consists of a peak near 40 meV superposed on a small relatively flat background. The 40-meV peak is found to be sharp in energy and anisotropic in momentum occupying a square portion of the Cu-O reciprocal lattice plane. The temperature dependence of the scattering is identical at the square side and corner. Polarized measurements show that the small background scattering observed at 100 K disappears below the superconducting transition. Resonant absorption measurements made to examine the Cu phonons show that no changes in the phonons occur at the superconducting transition

  6. Temperature controlled infrared broadband cloaking with the bilayer coatings of semiconductor and superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiaohua [College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); College of Physics and Electronics, Yancheng Teachers University, Yancheng 224051 (China); Liu, Youwen, E-mail: ywliu@nuaa.edu.cn [College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Feng, Yuncai [College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

    2015-06-15

    Highlights: • We first propose that the cloak is composed of the bilayer of semiconductor and superconductor. • We realize the infrared broadband cloaking based on the scattering cancellation method. • The cloaking frequency can be tuned by external temperature. - Abstract: The infrared broadband tunable cloaking have been proposed and investigated with the bilayer coating materials of semiconductor (n-Ge) and high-temperature superconductor (YBa{sub 2}Cu{sub 3}O{sub 7}), whose cloaking frequency can be controlled by external temperature. The analytical solution is derived based on the scattering cancellation cloaking technique from the Mie scattering theory, and the full-wave numerical simulation is performed by the finite element method. The calculated and simulated results have demonstrated that this invisibility cloak may reduce the total scattering cross section of the composite structure of 90% over a broad frequency band of nearly 20 THz, and the infrared cloaking frequency can be tuned by the external temperature. It can provide a feasible way to design a broadband tunable cloak.

  7. Temperature dependence of the infrared properties of Hg–Ba–Cu–O high-temperature superconductor

    Czech Academy of Sciences Publication Activity Database

    Tomašovičová, N.; Knížek, Karel; Veverka, Miroslav

    378-380, - (2006), s. 455-456 ISSN 0921-4526 Grant - others:VEGA(SK) 2/4060/04; Science and Technology Assistence Agency(SK) APVT-51-027904 Institutional research plan: CEZ:AV0Z10100521 Keywords : mercury superconductors * infrared spectroscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.872, year: 2006

  8. Supercurrent transport properties in Nd substituted TlSr2CaCu2O7 high temperature superconductor

    International Nuclear Information System (INIS)

    Andrew Das Arulsamy; Abd Shukor, R.

    1999-01-01

    The transport critical current density, J ct of TI(Sr 1-x Nd x ) 2 CaCu 2 O 7 (x= 0.1, 0.2 and 0.3) high temperature superconductors were measured at various temperatures. X-ray diffraction patterns indicate that all samples consist of mainly of the 1212 phase. The variation of J ct with Nd concentration, temperature and T c were scaled using a universal function. By plotting J ct versus T n c (x) and [1-(T/T c ) 2 ] m , we can divide the temperature dependencies of J ct into two regions. In each region, a linear relationship is suggested to hold between J ct and [1-(T/T c ) 2 ] m . For x=0.1, a relatively large exponent m in the range 40 - 50 K is observed, but a lower value is observed for a higher temperature range, 55 - 60 K. Average m for x = 0. 1 in the range 40 - 70 K is 1.8 but for x=0.2 and 0.3, m is 0.6 and 1.2, respectively. This can be interpreted as an indication that there is a change in the elementary flux pinning force which is responsible for sustaining the supercurrent. A self-field approximation indicates that Nd substitution lowers the distance between pinning centers (L c ). (author)

  9. Flux Pinning and AC Loss in Second Generation High Temperature Superconductor Wires

    Energy Technology Data Exchange (ETDEWEB)

    Paranthaman, Mariappan Parans [ORNL; Selvamanickam, V. [SuperPower Incorporated, Schenectady, New York

    2007-01-01

    Major advances have been made in the last 18 years in high-temperature superconductor (HTS) reserach and development, resulting in increased use of HTS materials in commerical and pre-commercial electric-power applications. This new and important book addresses the issues related to flux pinning, AC losses and thick YBCO film growth. Written by top most scientists in the world, it presents the current status and issues related to YBCO coated conductors and the need for further fundamental materials science work in YBCO coated conductor. It will be a useful handbook for years to come.

  10. Targets on the basis of ferrites and high-temperature superconductors for ion-plasma sputtering

    International Nuclear Information System (INIS)

    Lepeshev, A.A.; Saunin, V.N.; Telegin, S.V.; Polyakova, K.P.; Seredkin, V.A.; Pol'skij, A.I.

    2000-01-01

    Paper describes a method to produce targets for ion-plasma sputtering using plasma splaying of the appropriate powders on a cooled metal basis. Application of the plasma process was demonstrated to enable to produce complex shaped targets under the controlled atmosphere on the basis of ceramic materials ensuring their high composition homogeneity, as well as, reliable mechanical and thermal contact of the resultant coating with the base. One carried out experiments in ion-plasma sputtering of targets to prepare ferrite polycrystalline films to be used in magnetooptics and to prepare high-temperature superconductor epitaxial films [ru

  11. On the anomalous flicker noise intensity in high-temperature superconductors

    International Nuclear Information System (INIS)

    Kazakov, Kirill A.

    2009-01-01

    The problem of anomalously high levels of flicker noise observed in the normal state of the high-temperature superconductors is addressed. It is argued that the anomaly is the result of incorrect normalization of the power spectra according to the Hooge formula. A careful analysis of the available experimental data is given, which shows that the scaling of the spectral power with sample size is essentially different from the inverse proportionality. It is demonstrated that the measured spectra obey the law given by the recently proposed quantum theory of fundamental flicker noise.

  12. Possibilities of development photodynamic therapy under high temperature superconductor magnetic field

    International Nuclear Information System (INIS)

    Sen, Mihir

    1996-01-01

    After a long extensive research work neutron photon therapy for treatment of acquired immuno-deficiency syndrome (AIDS) was developed. High temperature superconductor magnet was developed and fitted in magnetic resonance imaging system to guide the patient. By this neutron-photon therapy AIDS effected cells are identified prominently. Patient is then injected with light sensitive drug molecules, which only AIDS cell retain. Light from photon (laser) then energizes the drug, which passes that energy to oxygen, which then leads a biochemical attack on the AIDS cells. If all goes well, the AIDS affected cells die. 10 refs., 1 fig

  13. Theory of sinusoidal modulation of the resonant neutron scattering in high-temperature superconductors

    International Nuclear Information System (INIS)

    Li Tao

    2001-01-01

    A model with interlayer pairing is proposed to explain the sinusoidal modulation of the resonant neutron scattering in high-temperature superconductors. It is found that the interlayer pairing has s-wave symmetry in the CuO 2 plane and has comparable magnitude with the d-wave intralayer pairing. It is also found that the interlayer pairing mainly affects momentum close to the hot spots on the Fermi surface while its effect on the gap nodes is negligible. It is pointed out that these characteristics of the interlayer pairing can be understood in a model in which the superconducting pairing originates from the exchange of the antiferromagnetic spin fluctuation

  14. Production of high temperature superconductors and characteristics by infrared and Raman spectroscopy

    International Nuclear Information System (INIS)

    Thomsen, C.

    1991-01-01

    This final report, which is partly kept short, is concerned with electron/phonon interaction and the determination of the band gap in high temperature superconductors (YBa 2 Cu 3 O 7 ). The final report is divided into four parts, which reflect the individual working groups: 1. Raman spectroscopy, 2. IR spectroscopy (reflection measurements, isotope effect, superconducting energy gap, behaviour of infrared active phonons), 3. Magnetic field measurements, and 4. Theory (initial calculation of the metal/isolator transfer in BaBiO 3 ). (MM) [de

  15. ESR spectrometer based setup for microwave investigation of high-temperature superconductors

    CERN Document Server

    Aliev, M K; Muminov, A T; Olimov, B A; Usmanov, R R; Kholbaev, I

    2002-01-01

    The experimental setup adjusted for investigation of non-resonant microwave absorption in high-temperature superconductors has been developed on the basis of ESR spectrometer. Having original temperature system-of-art the setup has made it possible to study not only the field spectrum of detected signal partial deriv R/partial deriv H but the temperature spectrum of one. In the region of superconducting transition the setup allows one to measure the temperature derivative partial deriv R/partial deriv T as well. Using the multi-layer magnetic cylindrical shield ensures the conduction for precise measurements in the weak magnetic fields. Acquisition, processing and visual presentation of experimental data are fulfilled by CAMAC on-line IBM PC. (author)

  16. Critical current measurements of high-temperature superconducting short samples at a wide range of temperatures and magnetic fields

    Science.gov (United States)

    Ma, Hongjun; Liu, Huajun; Liu, Fang; Zhang, Huahui; Ci, Lu; Shi, Yi; Lei, Lei

    2018-01-01

    High-Temperature Superconductors (HTS) are potential materials for high-field magnets, low-loss transmission cables, and Superconducting Magnetic Energy Storage (SMES) due to their high upper critical magnetic field (Hc2) and critical temperature (Tc). The critical current (Ic) of HTS, which is one of the most important parameters for superconductor application, depends strongly on the magnetic fields and temperatures. A new Ic measurement system that can carry out accurate Ic measurement for HTS short samples with various temperatures (4.2-80 K), magnetic fields (0-14 T), and angles of the magnetic field (0°-90°) has been developed. The Ic measurement system mainly consists of a measurement holder, temperature-control system, background magnet, test cryostat, data acquisition system, and DC power supply. The accuracy of temperature control is better than ±0.1 K over the 20-80 K range and ±0.05 K when measured below 20 K. The maximum current is over 1000 A with a measurement uncertainty of 1%. The system had been successfully used for YBa2Cu3O7-x(YBCO) tapes Ic determination with different temperatures and magnetic fields.

  17. In situ observation/analytical technologies of high temperature superconductor for fusion reactor at ultra low temperature

    International Nuclear Information System (INIS)

    Kimoto, Takayoshi; Sun Wei; Fukutomi, Masao; Togano Kazumasa; Saito, Tetsuya; Hiraga, Kenji

    1999-01-01

    The technologies for leveling up the resolving power of electron microscope at ultra low temperature to the level at the room temperature were studied. We developed at first in the world a hardware and software for controlling the current in the electric magnet used for image shift of TEM in order not to drift the TEM image, even if the sample drifts. When the He flow controller controlled the temperature, a clean lattice fringe image of carbon graphite with 3.4 A was obtained at the low temperature by the image shift control method and shift addition of TEM image. A system for introducing the regularity from the electron beam diffraction strength was reconstructed by the application test of high temperature superconductor. At less than about 230 K, the diffraction pattern of CuIr 2 S 4 showed the diffraction spot to indicate the superlattice reflection and the crystal structure transferred at Tc=230 K. (S.Y.)

  18. Radiation behavior of superconductors

    International Nuclear Information System (INIS)

    Scanlan, R.M.; Raymond, E.L.

    1979-01-01

    High energy neutron irradiations have been performed on Nb 3 Sn superconductors to assess their behavior in a fusion reactor environment. Irradiations were performed at 4.2 K and property measurements were made without warming the samples. The critical current I/sub c/ increased with irradiation to a level about 50% above the unirradiated value at the highest fluences reached in our experiments. These results are compared with the results of other low temperature irradiations of Nb 3 Sn

  19. Spatial distribution of Bose condensate in high-temperature superconductors, determined by emission Moessbauer spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Seregin, N.P.; Nasredinov, F.S.; Ali, H.M.; Gordeev, O.A.; Saidov, Ch.S.; Seregin, P.P. [St. Petersburg State Technical University, St. Petersburg (Russian Federation)]. E-mail: nasredinov@tuexph.stu.neva.ru

    2002-08-12

    It has been shown that temperature dependences of the gravity centres of {sup 67}Cu({sup 67}Zn) and{sup 67}Ga({sup 67}Zn) emission Moessbauer spectra of Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4}, La{sub 1.85}Sr{sub 0.15}CuO{sub 4} and Tl{sub 2}Ba{sub 2}Ca{sub 2}CuO{sub 8} superconductors are described by the second-order Doppler shift in the temperature range T{>=}T{sub c}, and Bose condensation of Cooper pairs should be taken into account at T{<=}T{sub c} (T{sub c} is the superconducting transition temperature). The spatial nonuniformity of the electron density created by the Bose condensate has been observed in La{sub 1.85}Sr{sub 0.15}CuO{sub 4}. (author)

  20. Potential for use of high-temperature superconductors in fusion reactors

    International Nuclear Information System (INIS)

    Hull, J.R.

    1991-01-01

    The present rate of development of high-temperature superconductors (HTSs) is sufficiently rapid that there may be opportunities for their use in contemporary fusion devices such as the International Thermonuclear Experimental Reactor (ITER). The most likely 1application is for delivering power to the superconducting magnets, especially in substituting for the current leads between the temperatures of 4 K and 77K. A second possible application of HTSs is as a liquid-nitrogen-cooled power bus, connecting the power supplies to the magnets, thus reducing the ohmic heating losses over these relatively long cables. A third potential application of HTSs is as an inner high-field winding of the toroidal field coils that would operate at ∼20 K. While the use of higher temperature magnets offers significant advantages to the reactor system, it is unlikely that tested conductors of this type will be available within the ITER time frame. 23 refs., 2 figs

  1. Critical-state magnetization of type-II superconductors in rectangular slab and cylinder geometries

    Science.gov (United States)

    Johansen, T. H.; Bratsberg, H.

    1995-04-01

    A scheme is described for analytical calculation of critical-state magnetization M of superconductors in the geometry of long rectangular slabs and cylindrical specimens in a parallel magnetic field. The simplicity of the general scheme is demonstrated by deriving compact expressions for the ascending and descending field branches of M in the exponential model Jc=jc0 exp(-B/B0) and in the Kim, Hempstead, and Strnad model [Phys. Rev. 129, 528 (1963)], Jc=jc0/(1+B/B0). The analyses focus on the vertical width ΔM of large field magnetization hysteresis loops. While Bean's result [Phys. Rev. Lett. 8, 250 (1962)], Jc∝ΔM, today is used extensively to infer the critical current, it is well known that the method lacks consistency when a field dependence is seen in ΔM. For the two models it is shown explicitly that in the expansion of the functional relation ΔM(Jc), Bean's result corresponds to the lowest-order term. Also to the next order in the functional expansion we find a unifying form of expressing the model behaviors. This term contains the second derivative of J2c(B) with a prefactor that depends on the sample geometry. A model-independent proof for the two first terms in the expansion of ΔM(Jc) is also given, which allows the significance of size and shape, i.e., thickness and aspect ratio, to be discussed on a general basis. New methods to extract Jc from ΔM data, one of them without having to invoke specific critical-state models, are indicated.

  2. Development, characterization, and applications of high temperature superconductor nanobridge Josephson junctions

    Energy Technology Data Exchange (ETDEWEB)

    Wendt, J.R.; Tigges, C.P.; Hietala, V.M.; Plut, T.A. [Sandia National Labs., Albuquerque, NM (United States); Martens, J.S.; Char, K.; Johansson, M.E. [Conductus, Inc., Sunnyvale, CA (United States)

    1994-03-01

    A well-controlled, high-yield Josephson junction process in high temperature superconductors (HTS) is necessary for the demonstration of ultra-high-speed devices and circuits which exceed the capabilities of conventional electronics. The authors developed nanobridge Josephson junctions in high quality thin-film YBaCuO with dimensions below 100 nm fabricated using electron-beam nanolithography. They characterized this Josephson junction technology for process yield, junction parameter uniformity, and overall applicability for use in high-performance circuits. To facilitate the determination of junction parameters, they developed a measurement technique based on spectral analysis in the range of 90--160 GHz of phase-locked, oscillating arrays of up to 2,450 Josephson junctions. Because of the excellent yield and uniformity of the nanobridge junctions, they successfully applied the junction technology to a wide variety of circuits. These circuits included transmission-line pulse formers and 32 and 64-bit shift registers. The 32-bit shift register was shown to operate at clock speeds near 100 GHz and is believed to be one of the faster and more complex digital circuit demonstrated to date using high temperature superconductor technology.

  3. Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor.

    Science.gov (United States)

    Charnukha, A; Thirupathaiah, S; Zabolotnyy, V B; Büchner, B; Zhigadlo, N D; Batlogg, B; Yaresko, A N; Borisenko, S V

    2015-05-21

    In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature Tc ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe(0.92)Co(0.08)AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.

  4. Enhancement of superconducting critical current by injection of quasiparticles in superconductor semiconductor devices

    DEFF Research Database (Denmark)

    Kutchinsky, Jonatan; Taboryski, Rafael Jozef; Sørensen, C. B.

    2000-01-01

    We report new measurements on 3-terminal superconductor semiconductor injection devices, demonstrating enhancement of the supercurrent by injection from a superconducting injector electrode. Two other electrodes were used as detectors. Applying a small voltage to the injector, reduced the maximum...

  5. Field-Induced Quantum Critical Point and Nodal Superconductivity in the Heavy-Fermion Superconductor Ce_{2}PdIn_{8}

    Directory of Open Access Journals (Sweden)

    J. K. Dong

    2011-09-01

    Full Text Available The in-plane resistivity ρ and thermal conductivity κ of the heavy-fermion superconductor Ce_{2}PdIn_{8} single crystals were measured down to 50 mK. A field-induced quantum critical point, occurring at the upper critical field H_{c2}, is demonstrated from the ρ(T∼T near H_{c2} and ρ(T∼T^{2} when further increasing the field. The large residual linear term κ_{0}/T at zero field and the rapid increase of κ(H/T at low field give evidence for nodal superconductivity in Ce_{2}PdIn_{8}. The jump of κ(H/T near H_{c2} suggests a first-order-like phase transition at low temperature. These results mimic the features of the famous CeCoIn_{5} superconductor, implying that Ce_{2}PdIn_{8} may be another interesting compound to investigate for the interplay between magnetism and superconductivity.

  6. Flux pinning and phase transitions in model high-temperature superconductors with columnar defects

    Energy Technology Data Exchange (ETDEWEB)

    Lee, K.H.; Stroud, D. (Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States)); Girvin, S.M. (Department of Physics, Indiana University, Bloomington, Indiana 47405 (United States))

    1993-07-01

    We calculate the degree of flux pinning by defects in model high-temperature superconductors (HTSC's). The HTSC is modeled as a three-dimensional network of resistively shunted Josephson junctions in an external magnetic field, corresponding to a HTSC in the extreme type-II limit. Disorder is introduced either by randomizing the coupling between grains (model-[ital A] disorder) or by removing grains (model-[ital B] disorder). Three types of defects are considered: point disorder, random line disorder, and periodic line disorder; but the emphasis is on random line disorder. Static and dynamic properties of the models are determined by Monte Carlo simulations and by solution of the analogous coupled overdamped Josephson equations in the presence of thermal noise. Random line defects considerably raise the superconducting transition temperature [ital T][sub [ital c

  7. Small angle neutron diffraction studies of vortex structures in high temperature superconductors

    DEFF Research Database (Denmark)

    Cubitt, R.; Forgan, E.M.; Wylie, M.T.

    1994-01-01

    We have used neutron scattering to provide direct information about flux structures in the bulk of crystals of the superconductor Bi2Sr2CaCu2O8. Its extremely high effective mass anisotropy, makes the flux lattice susceptable to melting and also to decomposition into 'pancake' vortices, which would...... give a more two-dimensional vortex structure. At low temperatures and fields the scattered intensity is consistent with a three dimensional flux-line structure. At higher fields and temperatures, the scattering from the flux lattice dissapears well below T-c. We can associate this dissappearance...... with the above changes in the vortex structure. We compare the neutron scattering results with macroscopic measurements of magnetisation....

  8. Rotational symmetry breaking in the topological superconductor SrxBi2Se3 probed by upper-critical field experiments.

    Science.gov (United States)

    Pan, Y; Nikitin, A M; Araizi, G K; Huang, Y K; Matsushita, Y; Naka, T; de Visser, A

    2016-06-28

    Recently it was demonstrated that Sr intercalation provides a new route to induce superconductivity in the topological insulator Bi2Se3. Topological superconductors are predicted to be unconventional with an odd-parity pairing symmetry. An adequate probe to test for unconventional superconductivity is the upper critical field, Bc2. For a standard BCS layered superconductor Bc2 shows an anisotropy when the magnetic field is applied parallel and perpendicular to the layers, but is isotropic when the field is rotated in the plane of the layers. Here we report measurements of the upper critical field of superconducting SrxBi2Se3 crystals (Tc = 3.0 K). Surprisingly, field-angle dependent magnetotransport measurements reveal a large anisotropy of Bc2 when the magnet field is rotated in the basal plane. The large two-fold anisotropy, while six-fold is anticipated, cannot be explained with the Ginzburg-Landau anisotropic effective mass model or flux flow induced by the Lorentz force. The rotational symmetry breaking of Bc2 indicates unconventional superconductivity with odd-parity spin-triplet Cooper pairs (Δ4-pairing) recently proposed for rhombohedral topological superconductors, or might have a structural nature, such as self-organized stripe ordering of Sr atoms.

  9. The Physics of High-Field Superconductors: New materials, used in lossless magnets at low temperatures, challenge scientific understanding.

    Science.gov (United States)

    Bean, C P; Schmitt, R W

    1963-04-05

    The recent burst of effort in the area of high-field superconductors has led to the construction of 70,000-oersted coils and the expectation that 100,000-oersted fields will be attained in the near future. The general theory suggests that fields above 300,000 oersteds are conceivable and that current densities of millions of amperes per square centimeter may be attained. Theory and experiment suggest that the upper critical field of materials such as Nb(3)Sn and Nb(.75)Zr(.25) is determined by their tendency to form a mixed state, and that a crucial question concerning their other properties is that of the interaction of this mixed state with imperfections. Lastly, it is possible to make a synthetic high-field superconductor by mechanically subdividing an ideal superconductor.

  10. The role of local repulsive interactions on superconductor quantum critical points

    Energy Technology Data Exchange (ETDEWEB)

    Neto, Francisco Dinóla, E-mail: dinola@if.uff.br [Instituto de Fı´sica, Universidade Federal Fluminense, Campus da Praia Vermelha, Niterói, RJ 24.210-340 (Brazil); Centro Brasileiro de Pesquisas Fı´sicas, Rua Dr. Xavier Sigaud, 150, Urca, Rio de Janeiro, RJ 22290-180 (Brazil); Continentino, Mucio A. [Centro Brasileiro de Pesquisas Fı´sicas, Rua Dr. Xavier Sigaud, 150, Urca, Rio de Janeiro, RJ 22290-180 (Brazil); Lacroix, Claudine [Institut Néel, CNRS-UJF, 25 Avenue des Martyrs, BP 166, 38042 Grenoble Cedex 9 (France)

    2013-02-14

    Highlights: ► In the BEC limit a spread of values of the SC gap is induced by a weak repulsion. ► The Hubbard-I approach was used to treat the strong repulsions case. ► Strong repulsions renormalize the narrow band by a band-filling term. ► The T = 0 phase diagrams shows the attractive interactions as hybridization function. ► The two-band model with a renormalized narrow band is enough to describe the SCES. -- Abstract: The study of superconductivity in multi-band systems is relevant for a variety of materials of actual interest. High T{sub c} cuprates, the new Fe-based materials and heavy fermion superconductors are multi-band systems and this feature must be taken into account for a proper description of their properties. In this paper we study superconductivity in two-band systems. One of the bands is a wide band of conduction electrons. The other is a narrow band of f or d character with an attractive interaction among quasi-particles in neighboring sites and a local repulsive interaction U. These bands are coupled by hybridization, which can be controlled by external pressure allowing to probe the phase diagram of these systems. First, we consider the case of weak repulsive interactions for which a mean-field approximation is satisfactory. We obtain the zero temperature phase diagram for weak and strong attractive interactions. We show that in the presence of U the crossover from the BCS to the Bose–Einstein Condensation (BEC) regime at strong attractive couplings remains smooth. Next we consider the case of strong repulsive U and introduce a Hubbard-I approximation to deal with this interaction. We obtain zero temperature phase diagrams as functions of hybridization and the strength of the repulsive and attractive interactions. We consider the cases of extended s-wave and d-wave symmetry of the order parameter.

  11. Particle-Hole Transformation in Strongly-Doped Iron-Based Superconductors

    OpenAIRE

    Rodriguez, J. P.

    2016-01-01

    An exact particle-hole transformation is discovered in a local-moment description of a single layer in an iron-based superconductor. Application of the transformation to a surface layer of heavily electron-doped FeSe predicts a surface-layer high-temperature superconductor at strong hole doping. Comparison with existing low-T_c iron superconductors suggests that the critical temperature at heavy hole doping can be increased by increasing direct ferromagnetic exchange in between nearest neighb...

  12. Motor models and transient analysis for high-temperature, superconductor switch-based adjustable speed drive applications. Final report

    International Nuclear Information System (INIS)

    Bailey, J.M.

    1996-06-01

    New high-temperature superconductor (HTSC) technology may allow development of an energy-efficient power electronics switch for adjustable speed drive (ASD) applications involving variable-speed motors, superconducting magnetic energy storage systems, and other power conversion equipment. This project developed a motor simulation module for determining optimal applications of HTSC-based power switches in ASD systems

  13. Inverse iron isotope effect on the transition temperature of the (Ba,K)Fe2As2 superconductor.

    Science.gov (United States)

    Shirage, Parasharam M; Kihou, Kunihiro; Miyazawa, Kiichi; Lee, Chul-Ho; Kito, Hijiri; Eisaki, Hiroshi; Yanagisawa, Takashi; Tanaka, Yasumoto; Iyo, Akira

    2009-12-18

    We report that the (Ba,K)Fe(2)As(2) superconductor (transition temperature, T(c) approximately 38 K) has an inverse iron isotope coefficient alpha(Fe) = -0.18(3) (where T(c) approximately M(-alphaFe) and M is the iron isotope mass); i.e., the sample containing the large iron isotope mass depicts a higher T(c). Systematic inverse shifts in T(c) were clearly observed between the samples using three types of Fe isotopes ((54)Fe, natural Fe, and (57)Fe). This indicates the first evidence of the inverse isotope effect in high-T(c) superconductors. This anomalous mass dependence on T(c) implies an exotic coupling mechanism in Fe-based superconductors.

  14. Magnetic Field Gain in Vortex Pinning at Fractal Interfaces of Clusters of High-Temperature Superconductors

    Science.gov (United States)

    Vasyutin, M. A.; Kuz'michev, N. D.; Shilkin, D. A.

    2018-02-01

    The effect of the fractality of the cluster interfaces in the normal phase of a copper-oxide high-temperature superconductor YBCO on the magnetic creep has been studied. The model of a magnetic field dependence of voltage induced by the flux creep for different transport currents has been suggested. The experimental dependences have been approximated using an exponent-hyperbolic function with a current parameter. The empiric magnetic field dependence of the fractal dimensionality of the interfaces of YBCO clusters has been registered. The magnitudes of the magnetic field intensity and fractal dimensionality at which the vortices start to penetrate the granules of the samples have been determined. The connective index of paths of the vortex quench at the percolation threshold has been calculated.

  15. A high temperature superconductor tape RF receiver coil for a low field magnetic resonance imaging system

    International Nuclear Information System (INIS)

    Cheng, M C; Yan, B P; Lee, K H; Ma, Q Y; Yang, E S

    2005-01-01

    High temperature superconductor (HTS) thin films have been applied in making a low loss RF receiver coil for improving magnetic resonance imaging image quality. However, the application of these coils is severely limited by their limited field of view (FOV). Stringent fabrication environment requirements and high cost are further limitations. In this paper, we propose a simpler method for designing and fabricating HTS coils. Using industrial silver alloy sheathed Bi (2-x) Pb x Sr 2 Ca 2 Cu 3 O 10 (Bi-2223) HTS tapes, a five-inch single-turn HTS solenoid coil has been developed, and human wrist images have been acquired with this coil. The HTS tape coil has demonstrated an enhanced FOV over a six-inch YBCO thin film surface coil at 77 K with comparable signal-to-noise ratio

  16. Adaptive Backstepping Control Based on Floating Offshore High Temperature Superconductor Generator for Wind Turbines

    Directory of Open Access Journals (Sweden)

    Feng Yang

    2014-01-01

    Full Text Available With the rapid development of offshore wind power, the doubly fed induction generator and permanent magnet synchronous generator cannot meet the increasing request of power capacity. Therefore, superconducting generator should be used instead of the traditional motor, which can improve generator efficiency, reduce the weight of wind turbines, and increase system reliability. This paper mainly focuses on nonlinear control in the offshore wind power system which is consisted of a wind turbine and a high temperature superconductor generator. The proposed control approach is based on the adaptive backstepping method. Its main purpose is to regulate the rotor speed and generator voltage, therefore, achieving the maximum power point tracking (MPPT, improving the efficiency of a wind turbine, and then enhancing the system’s stability and robustness under large disturbances. The control approach can ensure high precision of generator speed tracking, which is confirmed in both the theoretical analysis and numerical simulation.

  17. Status of high temperature superconductor based magnets and the conductors they depend upon

    CERN Document Server

    Schwartz, J; Chan, W K; Gou, X F; Liu, X T; Phillips, M; Le, Q V; Naderi, G; Turenne, M; Ye, L

    2011-01-01

    This paper reviews the status of high temperature superconductors for high field magnets for future devices such as a high energy LHC or a muon collider. Some of the primary challenges faced for the implementation of systems are discussed. Two conductor technologies, Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ and YBa$_2$Cu$_3$O$_{7-\\delta}$, have emerged as high field conductor options, but their relative advantages and disadvantages for high field magnets are quite different. These are reviewed from an engineering perspective, including coil manufacturing, electromechanical behaviour and quench behaviour. Lastly, the important roles of "system pull" upon conductor and magnet technology development, and of interactions between the materials and magnet communities for accelerating development, are discussed.

  18. Reproducible, large-scale production of thallium-based high-temperature superconductors

    International Nuclear Information System (INIS)

    Gay, R.L.; Stelman, D.; Newcomb, J.C.; Grantham, L.F.; Schnittgrund, G.D.

    1990-01-01

    This paper reports on the development of a large scale spray-calcination technique generic to the preparation of ceramic high-temperature superconductor (HTSC) powders. Among the advantages of the technique is that of producing uniformly mixed metal oxides on a fine scale. Production of both yttrium and thallium-based HTSCs has been demonstrated using this technique. In the spray calciner, solutions of the desired composition are atomized as a fine mist into a hot gas. Evaporation and calcination are instantaneous, yielding an extremely fine, uniform oxide powder. The calciner is 76 cm in diameter and can produce metal oxide powder at relatively large rates (approximately 100 g/h) without contamination

  19. Coasting characteristic of the flywheel system under anisotropy effect of bulk high temperature superconductors

    Science.gov (United States)

    Wu, J. F.; Li, Y.

    2014-10-01

    High-temperature superconductors (HTSCs) array with aligned growth section boundary (GSB) pattern (AGSBP) exhibits larger levitation force and suppression of levitation force decay above a permanent magnet guideway (PMG) compared with misaligned GSB pattern (MGSBP) has been studied in maglev train application (Zheng et al., 2013). This result maybe helpful and support a new way for the HTS bearing design for flywheel systems. So, in this paper, we further examine this growth anisotropy effect on the maglev performance of flywheel system. Levitation force and coasting time were investigated from the point-view of HTS flywheel applications. The GS/GSB alignment of AGSBP bulk HTSCs produces larger levitation force than that of MGSBP, but the coasting time is shorter than that of MGSBP, that is to say, the electric magnetic drag force with AGSBP is larger than that of MGSBP. This result may also exist in the maglev guideline when the maglev train stops freely.

  20. Three-dimensionality of field-induced magnetism in a high-temperature superconductor

    DEFF Research Database (Denmark)

    Lake, B.; Lefmann, K.; Christensen, N.B.

    2005-01-01

    Many physical properties of high-temperature superconductors are two-dimensional phenomena derived from their square-planar CuO(2) building blocks. This is especially true of the magnetism from the copper ions. As mobile charge carriers enter the CuO(2) layers, the antiferromagnetism of the parent...... insulators, where each copper spin is antiparallel to its nearest neighbours(1), evolves into a fluctuating state where the spins show tendencies towards magnetic order of a longer periodicity. For certain charge-carrier densities, quantum fluctuations are sufficiently suppressed to yield static long......-period order(2-6), and external magnetic fields also induce such order(7-12). Here we show that, in contrast to the chemically controlled order in superconducting samples, the field-induced order in these same samples is actually three-dimensional, implying significant magnetic linkage between the CuO(2...

  1. Dopant structural distortions in high-temperature superconductors: an active or a passive role?

    International Nuclear Information System (INIS)

    Haskel, D.; Stern, E.A.; Dogan, F.; Moodenbaugh, A.R.

    2001-01-01

    The parent compounds of high-temperature superconductors, such as YBa 2 Cu 3 O 6 and La 2 CuO 4 , are strongly interacting electron systems, rendering them insulators with Mott-Hubbard gaps of a few electron volts. Charge carriers (holes) are introduced by chemical doping, causing an insulator-metal (IM) transition and, at low temperatures, superconductivity. The role of dopants is widely seen as limited to the introduction of holes into the CuO 2 planes (i.e. occupying electronic states derived from Cu 3d x2-y2 and O 2p x,y atomic orbitals). Most theories of high-T c superconductivity deal with pairing interactions between these planar holes. Local distortions around dopants are poorly understood, because of the experimental difficulty in obtaining such information, particularly at low doping. This has resulted in the neglect, in most theories, of the effect of such distortions on the chemical and electronic structure of high-T c superconductors. Angular-resolved X-ray absorption fine structure (XAFS) spectroscopy on oriented samples is an ideal technique to elucidate the dopant distortions. Element specificity, together with a large orientation dependence of the XAFS signal in these layered structures, allows the local structure around dopants to be resolved. Results are presented here on (Sr, Ba) and Ni dopants, which substitute at the La and Cu sites, respectively, of insulating La 2 CuO 4 . The relevance of the measured local distortions for a complete understanding of the normal and superconducting properties of cuprates is discussed. (au)

  2. Behavior of magnetic superconductors in a magnetic field

    International Nuclear Information System (INIS)

    Buzdin, A.I.

    1984-01-01

    We investigate the behavior in a magnetic field of magnetic superconductors in which the ferromagnetic and superconducting transition temperatures are close together. It is shown that as the temperature is lowered the order of the superconducting transition changes from second to first. The corresponding critical fields and the field and temperature dependences of the magnetization are determined. Attention is focused on a discontinuity in the magnetization in the vortex core in magnetic superconductors. This feature plus the relatively large scattering cross section make magnetic superconductors convenient objects for the study of the superconducting vortex lattice by neutron diffraction

  3. Extreme Technicolor & The Walking Critical Temperature

    DEFF Research Database (Denmark)

    Sannino, Francesco; Järvinen, Matti

    2011-01-01

    We map the phase diagram of gauge theories of fundamental interactions in the flavor- temperature plane using chiral perturbation theory to estimate the relation between the pion decaying constant and the critical temperature above which chiral symmetry is restored. We then investigate the impact...

  4. Higher critical current density achieved in Bi-2223 High-Tc superconductors

    Directory of Open Access Journals (Sweden)

    M.S. Shalaby

    2016-07-01

    Full Text Available Bi2Sr2Ca2Cu3Ox (Bi-2223 were prepared using a solid state reaction method at different sintering times and temperatures. Structural phase identifications have been done using X-Ray analysis and refinement by Reitveld method which proves the coexistence of Bi-2223 and Bi-2212 phases. The critical transition temperature Tc and critical current density Jc values were measured using superconducting quantum interference device magnetometer (SQUID and by the magneto-optics technique. A remarkable rapid decrease to the diamagnetic signal in the magnetization versus temperature M(T at 110 K and Jc around 1.2 × 107 A/m2 at 5 K are confirmed for the Bi-2223 compound.

  5. Bulk superconductivity in Type II superconductors near the second critical field

    DEFF Research Database (Denmark)

    Fournais, Søren; Helffer, Bernard

    2010-01-01

    We consider superconductors of Type II near the transition from the ‘bulk superconducting’ to the ‘surface superconducting’ state. We prove a new L∞ estimate on the order parameter in the bulk, i.e. away from the boundary. This solves an open problem posed by Aftalion and Serfaty [AS]....

  6. Progress in scale-up of second-generation high-temperature superconductors at SuperPower Inc

    International Nuclear Information System (INIS)

    Xie, Y.-Y.; Knoll, A.; Chen, Y.; Li, Y.; Xiong, X.; Qiao, Y.; Hou, P.; Reeves, J.; Salagaj, T.; Lenseth, K.; Civale, L.; Maiorov, B.; Iwasa, Y.; Solovyov, V.; Suenaga, M.; Cheggour, N.; Clickner, C.; Ekin, J.W.; Weber, C.; Selvamanickam, V.

    2005-01-01

    SuperPower is focused on scaling up second-generation (2-G) high-temperature superconductor (HTS) technology to pilot-scale manufacturing. The emphasis of this program is to develop R and D solutions for scale-up issues in pilot-scale operations to lay the foundation for a framework for large-scale manufacturing. Throughput continues to be increased in all process steps including substrate polishing, buffer and HTS deposition. 2-G HTS conductors have been produced in lengths up to 100 m. Process optimization with valuable information provided by several unique process control and quality-control tools has yielded performances of 6000-7000 A m (77 K, 0 T) in 50-100 m lengths using two HTS fabrication processes: metal organic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD). Major progress has been made towards the development of practical conductor configurations. Modifications to the HTS fabrication process have resulted in enhanced performance in magnetic fields. Industrial slitting and electroplating processes have been successfully adopted to fabricate tapes in width of 4 mm and with copper stabilizer for cable and coil applications. SuperPower's conductor configuration has yielded excellent mechanical properties and overcurrent carrying capability. Over 60 m of such practical conductors with critical current over 100 A/cm-width have been delivered to Sumitomo Electric Industries, Ltd. for prototype cable construction

  7. Progress in scale-up of second-generation high-temperature superconductors at SuperPower Inc

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Y.-Y. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States)]. E-mail: yxie@igc.com; Knoll, A. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Chen, Y. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Li, Y. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Xiong, X. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Qiao, Y. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Hou, P. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Reeves, J. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Salagaj, T. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Lenseth, K. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Civale, L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Maiorov, B. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Iwasa, Y. [Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Solovyov, V. [Brookhaven National Laboratory, Upton, NY 11973 (United States); Suenaga, M. [Brookhaven National Laboratory, Upton, NY 11973 (United States); Cheggour, N. [National Institute of Standards and Technology, Boulder, CO 80305 (United States); Clickner, C. [National Institute of Standards and Technology, Boulder, CO 80305 (United States); Ekin, J.W. [National Institute of Standards and Technology, Boulder, CO 80305 (United States); Weber, C. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States); Selvamanickam, V. [SuperPower Inc., 450 Duane Ave., Schenectady, NY 12304 (United States)

    2005-10-01

    SuperPower is focused on scaling up second-generation (2-G) high-temperature superconductor (HTS) technology to pilot-scale manufacturing. The emphasis of this program is to develop R and D solutions for scale-up issues in pilot-scale operations to lay the foundation for a framework for large-scale manufacturing. Throughput continues to be increased in all process steps including substrate polishing, buffer and HTS deposition. 2-G HTS conductors have been produced in lengths up to 100 m. Process optimization with valuable information provided by several unique process control and quality-control tools has yielded performances of 6000-7000 A m (77 K, 0 T) in 50-100 m lengths using two HTS fabrication processes: metal organic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD). Major progress has been made towards the development of practical conductor configurations. Modifications to the HTS fabrication process have resulted in enhanced performance in magnetic fields. Industrial slitting and electroplating processes have been successfully adopted to fabricate tapes in width of 4 mm and with copper stabilizer for cable and coil applications. SuperPower's conductor configuration has yielded excellent mechanical properties and overcurrent carrying capability. Over 60 m of such practical conductors with critical current over 100 A/cm-width have been delivered to Sumitomo Electric Industries, Ltd. for prototype cable construction.

  8. Low temperature London penetration depth and superfluid density in Fe-based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyunsoo [Iowa State Univ., Ames, IA (United States)

    2013-01-01

    The superconducting gap symmetry of the Fe-based superconductors was studied by measurements and analysis of London penetration depth and super uid density. Tunnel diode resonator technique for these measurements was implemented in a dilution refrigerator allowing for the temperatures down to 50 mK. For the analysis of the super uid density, we used both experimental studies of Al-coated samples and original thermodynamic approach based on Rutgers relation. In three systems studied, we found that the superconducting gap at the optimal doping is best described in multi-gap full gap scenario. By performing experiments on samples with arti cially introduced disorder with heavy ion irradiation, we show that evolution of the superconducting transition temperature and of the super uid density are consistent with full-gap sign changing s superconducting state. The superconducting gap develops strong modulation both in the under-doped and the over-doped regimes. In the terminal hole-doped KFe{sub 2}As{sub 2}, both temperature dependence of the super uid density and its evolution with increase of the scattering rate are consistent with symmetry imposed vertical line nodes in the superconducting gap. By comparative studies of hole-doped (Ba,K)Fe{sub 2}As{sub 2} and electron-doped Ca10-3-8, we show that the superconducting gap modulation in the under-doped regime is intrinsic and is not induced by the coexisting static magnetic order.

  9. Nonaqueous slip casting of high temperature ceramic superconductors using an investment casting technique

    Science.gov (United States)

    Hooker, Matthew W. (Inventor); Taylor, Theodore D. (Inventor); Wise, Stephanie A. (Inventor); Buckley, John D. (Inventor); Vasquez, Peter (Inventor); Buck, Gregory M. (Inventor); Hicks, Lana P. (Inventor)

    1993-01-01

    A process for slip casting ceramic articles that does not employ parting agents and affords the casting of complete, detailed, precision articles that do not possess parting lines is presented. This process is especially useful for high temperature superconductors and water-sensitive ceramics. A wax pattern for a shell mold is provided, and an aqueous mixture of a calcium sulfate-bonded investment material is applied as a coating to the wax pattern. The coated wax pattern is then dried, followed by curing to vaporize the wax pattern and leave a shell mold of the calcium sulfate-bonded investment material. The shell mold is cooled to room temperature, and a ceramic slip, created by dispersing a ceramic powder in an organic liquid, is poured therein. After a ceramic shell of desired thickness or a solid article has set up in the shell mold, excess ceramic slip is poured out. The shell mold is misted with water and peeled away from the ceramic article, after which the ceramic is fired to provide a complete, detailed, precision, high temperature superconductive ceramic article without parting lines. The casting technique may take place in the presence of a magnetic field to orient the ceramic powders during the casting process.

  10. Magnetic-field-induced soft-mode quantum phase transition in the high-temperature superconductor La1.855Sr0.145CuO4: an inelastic neutron-scattering study.

    Science.gov (United States)

    Chang, J; Christensen, N B; Niedermayer, Ch; Lefmann, K; Rønnow, H M; McMorrow, D F; Schneidewind, A; Link, P; Hiess, A; Boehm, M; Mottl, R; Pailhés, S; Momono, N; Oda, M; Ido, M; Mesot, J

    2009-05-01

    Inelastic neutron-scattering experiments on the high-temperature superconductor La1.855Sr0.145CuO4 reveal a magnetic excitation gap Delta that decreases continuously upon application of a magnetic field perpendicular to the CuO2 planes. The gap vanishes at the critical field required to induce long-range incommensurate antiferromagnetic order, providing compelling evidence for a field-induced soft-mode driven quantum phase transition.

  11. Magnetic-Field-Induced Soft-Mode Quantum Phase Transition in the High-Temperature Superconductor La1.855Sr0.145CuO4:An Inelastic Neutron-Scattering Study

    OpenAIRE

    Chang, J.; Christensen, Niels Bech; Niedermayer, C.; Lefmann, Kim; Rønnow, H.M.; McMorrow, D.F.; Schneidewind, A.; Link, P.; Hiess, A.; Boehm, M.; Mottl, R.; Pailhes, S.; Momono, N.; Oda, M.; Ido, M.

    2009-01-01

    Inelastic neutron-scattering experiments on the high-temperature superconductor La$_{1.855}$Sr$_{0.145}$CuO$_{4}$ reveal a magnetic excitation gap $\\Delta$ that decreases continuously upon application of a magnetic field perpendicular to the CuO$_2$ planes. The gap vanishes at the critical field required to induce long-range incommensurate antiferromagnetic order, providing compelling evidence for a field-induced soft-mode driven quantum phase transition.

  12. Multilayered cuprate superconductor Ba2Ca5Cu6O12(O1-x,Fx) 2 studied by temperature-dependent scanning tunneling microscopy and spectroscopy

    Science.gov (United States)

    Sugimoto, Akira; Ekino, Toshikazu; Gabovich, Alexander M.; Sekine, Ryotaro; Tanabe, Kenji; Tokiwa, Kazuyasu

    2017-05-01

    Scanning tunneling microscopy/spectroscopy (STM/STS) measurements were carried out on a multilayered cuprate superconductor Ba2Ca5Cu6O12 (O1 -x,Fx )2. STM topography revealed random spot structures with the characteristic length ≤0.5 nm. The conductance spectra d I /d V (V ) show the coexistence of smaller gaps ΔS and large gaps (pseudogaps) ΔL. The pseudogap-related features in the superconducting state were traced with the spatial resolution of ˜0.07 nm. Here, I and V are the tunnel current and bias voltage, respectively. The temperature, T , dependence of ΔS follows the reduced Bardeen-Cooper-Schrieffer (BCS) dependence. The hallmark ratio 2 ΔS(T =0 ) /kBTc equals to 4.9, which is smaller than those of other cuprate superconductors. Here, Tc is the superconducting critical temperature and kB is the Boltzmann constant. The larger gap ΔL survives in the normal state and even increases with T above Tc. The T dependencies of the spatial distributions for both relevant gaps (Δ map), as well as for each gap separately (ΔS and ΔL), were obtained. From the histogram of Δ map, the averaged gap values were found to be Δ¯S=˜24 meV and Δ¯L=˜79 meV. The smaller gap ΔS shows a spatially homogeneous distribution while the larger gap ΔL is quite inhomogeneous, indicating that rather homogeneous superconductivity coexists with the patchy distributed pseudogap. The spatial variation length ξΔ L of ΔL correlates with the scale of the topography spot structures, being approximately 0.4 nm. This value is considerably smaller than the coherence length of this class of superconductors, suggesting that ΔL is strongly affected by the disorder of the apical O/F.

  13. Conceptual design of a forced-flow-cooled 20-kA current lead using Ag-alloy-sheathed Bi-2223 high-temperature superconductors

    International Nuclear Information System (INIS)

    Heller, R.

    1994-11-01

    The use of high-temperature superconductors in current leads to reduce refrigeration power has been investigated by many groups in the past. Most used YBCO and Bi-2212 bulk superconductors, although their critical current density is not very high. In this paper, BI-2223 HTSC tapes sheathed with Ag alloys are used in the design of a 20-kA current lead because of their higher critical current in medium magnetic fields. The lead current of 20 kA is related to the coil current of the planned stellarator WENDELSTEIN 7-X. Forced-now helium cooling has been used in the design, allowing position-independent and well-controlled operation. The design characteristics of the lead are presented and 4-K helium cooling of the whole lead, as well as 60-K helium cooling of the copper part of the lead, is discussed. The power consumption at zero current, and the lead's behaviour in case of loss of coolant flow, are given, The results of the design allow extrapolation to current leads of the 50-kA range

  14. Singularity in the positive Hall coeffcient near pre-onset temperatures in high-Tc superconductors

    Science.gov (United States)

    Vezzoli, G. C.; Chen, M. F.; Craver, F.; Moon, B. M.; Safari, A.; Burke, T.; Stanley, W.

    1990-10-01

    Hall measurements using continuous extremely slow cooling and reheating rates as well as employing eqiulibrium point-by-point conventional techniques reveals a clear anomally in RH at pre-onset temperatures near Tc in polycrystalline samples Y1Ba2Cu3O7 and Bi2Sr2Ca2Cu3O10. The anomaly has the appearance of a singularity of Dirac-delta function which parallels earlier work on La1-xSrxCuO4. Recent single crystal work on the Bi-containing high-Tc superconductor is in accord with a clearcut anomaly. The singularity is tentatively interpreted to be associated (upon cooling) with initially the removal of positive holes from the hopping conduction system of the normal state such as from the increased concentration of bound virtual excitons due to increased exciton and hole lifetimes at low temperature. Subsequently the formation of Cooper pairs by mediation from these centers (bound-holes) and/or bound excitons) may cause an ionization of these bound virtual excitons thereby re-introducing holes and electrons into the conduction system at Tc.

  15. High-temperature superconductors, as seen through the eyes of neutrons

    Directory of Open Access Journals (Sweden)

    Z. Yamani

    2006-09-01

    Full Text Available   Neutron scattering is proved to be a vital probe in unveiling the magnetic properties of high temperature superconductors (HTSC. Detailed information about the energy and momentum dependence of the magnetic dynamics of HTSC have been obtained directly by this technique. Over the past decade by improving the crystal growth methods, large and high quality single crystals of HTSC, which are essential for a neutron scattering experiment, have become available. The results of neutron scattering measurements on such crystals have considerably enhanced our understanding of the magnetism in HTSC both in the superconducting (SC and normal states. In this review, the neutron scattering results on two main HTSC families, La2-xSrxCuO4 (LSCOx and YBa2CuO3O6+x (YBCO6+x, are considered with an emphasis on the most prominent properties of these materials that are now widely accepted. These include the presence of strong antiferromagnetic (AF fluctuations even in optimally doped region of the phase diagram, neutron resonance peak that scales with SC transition temperature, Tc, incommensurate magnetic fluctuations (stripes, and a pseudogap in the normal state of underdoped materials.

  16. Holographic superconductor in the analytic hairy black hole

    International Nuclear Information System (INIS)

    Myung, Yun Soo; Park, Chanyong

    2011-01-01

    We study the charged black hole of hyperbolic horizon with scalar hair (charged Martinez-Troncoso-Zanelli: CMTZ black hole) as a model of analytic hairy black hole for holographic superconductor. For this purpose, we investigate the second order phase transition between CMTZ and hyperbolic Reissner-Nordstroem-AdS (HRNAdS) black holes. However, this transition unlikely occurs. As an analytic treatment for holographic superconductor, we develop superconductor in the bulk and superfluidity on the boundary using the CMTZ black hole below the critical temperature. The presence of charge destroys the condensates around the zero temperature, which is in accord with the thermodynamic analysis of the CMTZ black hole.

  17. High critical currents in heavily doped (Gd,Y)Ba{sub 2}Cu{sub 3}O{sub x} superconductor tapes

    Energy Technology Data Exchange (ETDEWEB)

    Selvamanickam, V., E-mail: selva@uh.edu; Gharahcheshmeh, M. Heydari; Xu, A.; Galstyan, E.; Delgado, L. [Department of Mechanical Engineering and Texas Center for Superconductivity, University of Houston, 4800 Calhoun Rd., Houston, Texas 77204-4006 (United States); Cantoni, C. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37381 (United States)

    2015-01-19

    REBa{sub 2}Cu{sub 3}O{sub x} ((REBCO), RE = rare earth) superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50 K and fields of 2–30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (J{sub c}) above 20 MA/cm{sup 2} at 30 K, 3 T in heavily doped (25 mol. % Zr-added) (Gd,Y)Ba{sub 2}Cu{sub 3}O{sub x} superconductor tapes, which is more than three times higher than the J{sub c} typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m{sup 3} have also been attained at 20 K. A composition map of lift factor in J{sub c} (ratio of J{sub c} at 30 K, 3 T to the J{sub c} at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO{sub 3} (BZO) nanocolumn defect density of nearly 7 × 10{sup 11 }cm{sup −2} as well as 2–3 nm sized particles rich in Cu and Zr have been found in the high J{sub c} films.

  18. Method of producing YBa2Cu3O6+x superconductors with high transition temperatures

    International Nuclear Information System (INIS)

    Rao, A.S.; Arora, O.P.; Aprigliano, L.F.

    1991-01-01

    This patent describes a method for making an improved ceramic superconductor. It comprises: mixing an oxide selected from the group consisting of Y 2 O 3 , Er 2 O 3 , Eu 2 O 3 , Yb 2 O 3 , Dy 2 O 3 and Ho 2 O 3 with barium carbonate and copper oxide powders in a ratio of about 50 grams in the case of Y 2 O 3 , 83 grams for Er 2 O 3 , 76 grams for Eu 2 O 3 , 86 grams of Ho 2 O 3 to about 70 grams of BaCO 3 to about 105 grams of CuO, ball milling the mixture with zironia balls for at least on hour; calcining the mixture at a temperature of 940 degree C + or -degree C with a heating sequence of 2 degree C per minute from room temperature to 200 degree C, maintaining the mixture at the 200 degree C temperature for a least about sixty minutes, heating the mixture at 3 degree C per minute until a temperature of 940 degree C + or -2 degree C is reached, maintaining the mixture at the 940 degree C + or -2 degree C for three hundred minutes, cooling the mixture to room temperature at a rate of 1 degree C per minute, adding silver oxide in powdered form to the mixture an amount of from about 1 to about 20 weight percent, ball milling the mixture containing silver oxide for at least one hour, compacting the mixture, sintering the mixture at 920 degree C + or -2 degree C by heating the mixture at 2 degree C per minute from room temperature 200 degree C, maintaining the temperature at 200 degree C for 60 minutes and then resuming the heating at 3 degree C per minute until a temperature of 920 degree C is reached, (l) maintaining the mixture at 920 degree C + or -2 degree C for three hundred minutes, and (m) cooling the mixture to room temperature at a rate of degree C per minute

  19. High-speed photography of laser ablation plasmas from the high temperature superconductor YBa2Cu3O7-δ

    International Nuclear Information System (INIS)

    Scott, K.; Huntley, J.M.; Phillips, W.A.

    1993-01-01

    The luminous plume formed by laser ablation of the high-temperature superconductor YBa 2 Cu 3 O 7-δ has been investigated using high-speed framing photography. Variation of the background oxygen pressure was found to significantly influence the velocity distribution of the ablated species, leading in particular to shock wave formation and instabilities on the shock front at higher pressures. Spectral characteristics of the plume were studied using optical interference filters, and two distinct regions of emission were identified. (orig.)

  20. Characterization of high temperature superconductor cables for magnet toroidal field coils of the DEMO fusion power plant

    Energy Technology Data Exchange (ETDEWEB)

    Bayer, Christoph M.

    2017-05-01

    Nuclear fusion is a key technology to satisfy the basic demand for electric energy sustainably. The official EUROfusion schedule foresees a first industrial DEMOnstration Fusion Power Plant for 2050. In this work several high temperature superconductor sub-size cables are investigated for their applicability in large scale DEMO toroidal field coils. Main focus lies on the electromechanical stability under the influence of high Lorentz forces at peak magnetic fields of up to 12 T.

  1. Characterization of high temperature superconductor cables for magnet toroidal field coils of the DEMO fusion power plant

    CERN Document Server

    Bayer, Christoph M

    2017-01-01

    Nuclear fusion is a key technology to satisfy the basic demand for electric energy sustainably. The official EUROfusion schedule foresees a first industrial DEMOnstration Fusion Power Plant for 2050. In this work several high temperature superconductor sub-size cables are investigated for their applicability in large scale DEMO toroidal field coils. Main focus lies on the electromechanical stability under the influence of high Lorentz forces at peak magnetic fields of up to 12 T.

  2. Heteroepitaxial growth of strained multilayer thin films of high-temperature superconductors

    International Nuclear Information System (INIS)

    Gross, R.; Gupta, A.; Olsson, E.; Segmueller, A.; Koren, G.

    1991-01-01

    Recently, the heteroepitaxial growth of multilayer structures of different copper oxide superconductors has been reported by several groups. In general, two different types of multilayer structures should be distinguished. The first kind of mulitlayer is formed by high-T c materials having the same crystal structure and almost the same lattice constants, as for example ReBa 2 Cu 3 O 7 (Re=rare earth) multilayers with alternating Re-elements. In these multilayers the two different rare earth copper oxides (Y/Dy, Y/Pr) have the same orthorhombic unit cell. Due to the very similar lattice constants, the misfit strain is easily accommodated without the formation of defects. The second kind of multilayer is formed by layers of materials having different crystal structure and lattice parameters. In these multilayers the misfit can be coherently accommodated below a critical modulation thickness as discussed below. This renders possible the heteroepitaxial growth of strained multilayer structures, both of two copper oxides of different crystal structure, as has been demonstrated recently for the system YBa 2 Cu 3 O 7-δ /Nd 1.83 Ce 0.17 CuO x , and of superconducting copper oxides and insulating materials. For multilayers of different copper oxides, a combination of almost all high-Tc materials should be possible, since the presence of the CuO 2 sheets in these materials results in similar lattice constants in their basal planes ('a' and 'b'). (orig./BHO)

  3. Possibility of the vortex-antivortex transition temperature of a thin-film superconductor being renormalized by disorder

    International Nuclear Information System (INIS)

    Hebard, A.F.; Kotliar, G.

    1989-01-01

    The universal relation between the Kosterlitz-Thouless transition temperature T/sub c/ and the superfluid sheet density of thin-film superconductors with mean-field transition temperature T/sub c/ 0 results in a monotonically decreasing dependence of the ratio T/sub c//T/sub c0/ on the normal-state sheet resistance R/sub n/. Ambiguity in the experimental definition of R/sub n/ in highly disordered thin-film superconductors is addressed by reexamining previously published data on amorphous composite In/InO/sub x/ films. Arguments are presented in favor of using the zero-temperature value of R/sub n/, a quantity obtained by extrapolation. The dependence of T/sub c//T/sub c0/ on R/sub n/ that results from such a choice is in agreement with theory for dirty superconductors and thus suggests that additional corrections to T/sub c/ in the presence of extreme disorder are not required

  4. Review of the critical current densities and magnetic irreversibilities in high T_c superconductors

    Science.gov (United States)

    Senoussi, S.

    1992-07-01

    This review article is concerned with critical current density (J) and magnetic irreversibilities in high-T_c superconductors (HTSC). The apparent J derived from different experimental techniques (transport, hysteresis cycle, ac-susceptibility) are compared. The influence of time (relaxation effects) as well as the macroscopic size of the sample on the criteria defining J are discussed. The dependences of the critical current on grain boundaries (“weaks-links”), texturing and other physical and chemical defects are examined in detail. The role of self fields is clarified. The critical current is strongly influenced by the anisotropy of the layered structure practically whatever the experimental conditions. Intrinsic pinning is lowered by defects. Demagnetizing effects and surface pinnings are reviewed. The usual critical state and flux creep models are recalled emphasizing the physical aspects most specific to HTSC. A theoretical model which takes into account the equilibrium magnetization and sample granularity is developed. It reproduces most of the characteristic features of both the hysteresis cycle and ac-susceptibility. A number of new formulae are introduced. They generalize the Bean model and show how to correct for the dimensions of the grains (granular materials), the macroscopic radius of the sample, anisotropy and demagnetization effects in certain situations. Several limits beyond which the usual critical state breaks down are discussed: (1) the quasi elastic limit where the variable field is too weak to depin the vortices, (2) H≈ H_C1 so that the interaction between vortex lines is exponentially weak and (3) T and H close to the “irreversibility line” where the influence of viscous forces are strong. (4) Hgg H_C1 so that J is governed by collective pinning. Ce papier de revue est consacré aux courant critiques (J) et aux irréversibilités magnétiques dans les nouveaux matériaux supraconducteurs (HTSC). Nous y comparons les densités des

  5. Superconductor electronic device applications

    International Nuclear Information System (INIS)

    VanDuzer, T.

    1989-01-01

    Superconductors are becoming important in many applications where high sensitivity or speed is required. In this paper the authors give brief introduction to superconductive device physics and some comments on the role of high-temperature superconductors. They then present the basic principles of a number of applications in metrology, electromagnetic sensing, and analog and digital circuits. They conclude with the prospects for hybrid semiconductor-superconductor devices, circuits, and systems

  6. Negative magnetic relaxation in superconductors

    Directory of Open Access Journals (Sweden)

    Krasnoperov E.P.

    2013-01-01

    Full Text Available It was observed that the trapped magnetic moment of HTS tablets or annuli increases in time (negative relaxation if they are not completely magnetized by a pulsed magnetic field. It is shown, in the framework of the Bean critical-state model, that the radial temperature gradient appearing in tablets or annuli during a pulsed field magnetization can explain the negative magnetic relaxation in the superconductor.

  7. Homopolar dc motor and trapped flux brushless dc motor using high temperature superconductor materials

    Science.gov (United States)

    Crapo, Alan D.; Lloyd, Jerry D.

    1991-03-01

    Two motors have been designed and built for use with high-temperature superconductor (HTSC) materials. They are a homopolar dc motor that uses HTSC field windings and a brushless dc motor that uses bulk HTSC materials to trap flux in steel rotor poles. The HTSC field windings of the homopolar dc motor are designed to operate at 1000 A/sq cm in a 0.010-T field. In order to maximize torque in the homopolar dc motor, an iron magnetic circuit with small air gaps gives maximum flux for minimum Ampere turns in the field. A copper field winding version of the homopolar dc motor has been tested while waiting for 575 A turn HTSC coils. The trapped flux brushless dc motor has been built and is ready to test melt textured bulk HTSC rings that are currently being prepared. The stator of the trapped flux motor will impress a magnetic field in the steel rotor poles with warm HTSC bulk rings. The rings are then cooled to 77 K to trap the flux in the rotor. The motor can then operate as a brushless dc motor.

  8. Coasting characteristic of the flywheel system under anisotropy effect of bulk high temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Wu, J.F., E-mail: wujf@ciomp.ac.cn; Li, Y.

    2014-10-15

    Highlights: • Coasting time was investigated from the point-view of HTS flywheel applications. • The coasting time of aligned growth section boundary pattern (AGSBP) is shorter than that of MGSBP. • The electric magnetic drag force with AGSBP is larger than that of MGSBP. • This result may also exist in the maglev guideline when the maglev train stops freely. - Abstract: High-temperature superconductors (HTSCs) array with aligned growth section boundary (GSB) pattern (AGSBP) exhibits larger levitation force and suppression of levitation force decay above a permanent magnet guideway (PMG) compared with misaligned GSB pattern (MGSBP) has been studied in maglev train application (Zheng et al., 2013). This result maybe helpful and support a new way for the HTS bearing design for flywheel systems. So, in this paper, we further examine this growth anisotropy effect on the maglev performance of flywheel system. Levitation force and coasting time were investigated from the point-view of HTS flywheel applications. The GS/GSB alignment of AGSBP bulk HTSCs produces larger levitation force than that of MGSBP, but the coasting time is shorter than that of MGSBP, that is to say, the electric magnetic drag force with AGSBP is larger than that of MGSBP. This result may also exist in the maglev guideline when the maglev train stops freely.

  9. Iron based superconductors and related compounds synthesized by solid state metathesis and high temperature reactions

    International Nuclear Information System (INIS)

    Frankovsky, Rainer

    2013-01-01

    The results of this thesis can be divided into three major topics, which can also be seen as different approaches of solid state chemistry to reveal interesting features of known and unknown compounds and to develop alternative synthesis routes. Firstly, known compounds with related structural motifs to the superconducting iron-arsenides were investigated regarding their structural and physical properties. In case of La 3 Pd 4 Ge 4 the influence of Fe doping on the properties was studied, whereas in the series ZrMAs (M=Ti,V) the physical properties have not yet been reported at all and were investigated for the first time. Secondly, an alternative synthesis route has been developed for the synthesis of superconducting LaFeAsO 1-x F x . This solid state metathesis reaction distinctly increased the quality of the samples compared to conventionally prepared products. Furthermore, the reaction pathway was investigated and clarified, which helps to understand the processes during high temperature solid state metathesis reactions in general. Thirdly, this alternative synthesis route was expanded to other systems and new compounds like co-substituted LaFe 1-x Mn x AsO 1-y F y were prepared and thoroughly investigated. This led to a complex study of the interplay of magnetism, electronic and structural conditions and the occurrence of superconducting properties. The investigation and understanding of such complex coherences will probably be decisive for the further understanding of the superconducting mechanism in iron based superconductors.

  10. A high temperature superconductor notch filter for the Sardinia Radio Telescope

    Science.gov (United States)

    Bolli, Pietro; Cresci, Luca; Huang, Frederick; Mariotti, Sergio; Panella, Dario

    2018-03-01

    A High Temperature Superconductor filter operating in the C-band between 4200 and 5600 MHz has been developed for one of the radio astronomical receivers of the Sardinia Radio Telescope. The motivation was to attenuate an interference from a weather radar at 5640 MHz, whose power level exceeds the linear region of the first active stages of the receiver. A very sharp transition after the nominal maximum passband frequency is reached by combining a 6th order band-pass filter with a 6th order stop-band. This solution is competitive with an alternative layout based on a cascaded triplet filter. Three units of the filter have been measured with two different calibration approaches to investigate pros and cons of each, and data repeatability. The final performance figures of the filters are: ohmic losses of the order of 0.15-0.25 dB, matching better than -15 dB, and -30 dB attenuation at 5640 MHz. Finally, a more accurate model of the connection between external connector and microstrip shows a better agreement between simulations and experimental data.

  11. Influence of oxygen doping on critical fields in MgB2 bulk superconductors

    Science.gov (United States)

    Zhang, D.; Li, X.; Wan, F.; Thong, C. J.; Rindfleisch, M. A.; Tomsic, M. J.; Sumption, M. D.; Collings, E. W.

    2017-12-01

    In this work we studied the influence of SnO2 doping on the critical fields and temperatures of MgB2 bulk samples. Bulk samples were made by mixing ex-situ MgB2 powder with 5 wt% SnO2 powder and then pressing the mixed powders into pellets using a pressure of 2000 psi. The bulk pellets were sintered at 900°C in a furnace under flowing Ar. The samples were quenched to room temperature after dwelling at 900°C for 5h. XRD, SEM, and magnetic measurements were made on doped and control samples. XRD showed a decomposition of the SnO2 and very slight reductions in the a-axis and c-axis lattice parameters of the MgB2 phase. M-T (Magnetization-Temperature) curves showed a decrease in Bc2 of approximately 1 T in the temperature range of 24 K - 39 K with SnO2 additions as compared to the control samples.

  12. Transmission using high temperature superconductor cable; Transmissao utilizando cabo supercondutor de alta temperatura

    Energy Technology Data Exchange (ETDEWEB)

    Geschiere, Alex; Piga, Erika [Nuon, Amsterdam (Netherlands); Wille, Dag; Barendregt, Peter [NKT Cables, Brondby (Denmark); NKT Cables, Amsterdam (Netherlands); Royal, John; Lynch, Nancy [Praxair, Danbury, CT (United States)

    2008-04-15

    As energy dutch company intends to install a 6 km 50 kV transmission line with superconductor cable replacing an existent 150 kV circuit which use a pressurized cable at the center of Amsterdam, and so for elevation the line capacity by 2.5 times. This project, the first of a superconductor line with more than a some hundred meters, is considered as the effective beginning market of these cables.

  13. Magnetic refrigeration using flux compression in superconductors

    International Nuclear Information System (INIS)

    Israelsson, U.E.; Strayer, D.M.; Jackson, H.W.; Petrac, D.

    1990-01-01

    The feasibility of using flux compression in high-temperature superconductors to produce the large time-varying magnetic fields required in a field cycled magnetic refrigerator operating between 20 K and 4 K is presently investigated. This paper describes the refrigerator concept and lists limitations and advantages in comparison with conventional refrigeration techniques. The maximum fields obtainable by flux compression in high-temperature superconductor materials, as presently prepared, are too low to serve in such a refrigerator. However, reports exist of critical current values that are near usable levels for flux pumps in refrigerator applications. 9 refs

  14. 15 MeV proton irradiation effects on Bi-based high temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Alinejad, N.; Sohrabi, D. [Nuclear Science and Technology Research Institute, Tehran (Iran, Islamic Republic of). Plasma and Nuclear Fusion Research School; Bolori, F. [Karaj Agricultural, Medical, and Industrial Research School, Karaj (Iran, Islamic Republic of)

    2015-11-15

    Nowadays, superconducting magnetic coils are used in some tokamaks such as EAST, KSTAR, JT-60, and T-15 to generate strong magnetic fields and also in ITER magnetic fields of about 13 tesla will be produced with the help of superconductors. The tokamak superconductors are exposed to the variety of radiations (neutron, ions beam, and gamma) from plasma nuclear reactions which will affect some of the superconductor properties. Therefore, study of the irradiation effects on the superconductor structure and properties are very crucial from technological and scientific point of view. One of the superconductor irradiation effects to be investigated under different conditions of energy and dosage is the potential resistance of the material used in tokamak reactor magnetic coils against activation by radiation. In this work, pellets of high T{sub c} Bi-based superconductors have been prepared and after measurement of parameters, a sample of pellet has been irradiated with 15 MeV protons using Karaj cyclotron facility. The sample's parameters have been measured again after irradiation treatment. X-ray diffraction patterns and SEM images of the sample before and after irradiation treatment have been studied.

  15. Scalar Condensation of Holographic Superconductors using ...

    Indian Academy of Sciences (India)

    Abstract. We study holographic superconductors analytically by using the Ginzburg–Landau action with the γ-quartic term | |4. Our results show that γ-term plays a role in the scalar condensation. It is found that the system displays two kinds of critical temperatures. One is independent of γ. But the other increases with ...

  16. 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.

  17. Calculation of Critical Temperatures by Empirical Formulae

    Directory of Open Access Journals (Sweden)

    Trzaska J.

    2016-06-01

    Full Text Available The paper presents formulas used to calculate critical temperatures of structural steels. Equations that allow calculating temperatures Ac1, Ac3, Ms and Bs were elaborated based on the chemical composition of steel. To elaborate the equations the multiple regression method was used. Particular attention was paid to the collection of experimental data which was required to calculate regression coefficients, including preparation of data for calculation. The empirical data set included more than 500 chemical compositions of structural steel and has been prepared based on information available in literature on the subject.

  18. Towards a 20 kA high temperature superconductor current lead module using REBCO tapes

    Science.gov (United States)

    Heller, R.; Bagrets, N.; Fietz, W. H.; Gröner, F.; Kienzler, A.; Lange, C.; Wolf, M. J.

    2018-01-01

    Most of the large fusion devices presently under construction or in operation consisting of superconducting magnets like EAST, Wendelstein 7-X (W7-X), JT-60SA, and ITER, use high temperature superconductor (HTS) current leads (CL) to reduce the cryogenic load and operational cost. In all cases, the 1st generation HTS material Bi-2223 is used which is embedded in a low-conductivity matrix of AgAu. In the meantime, industry worldwide concentrates on the production of the 2nd generation HTS REBCO material because of the better field performance in particular at higher temperature. As the new material can only be produced in a multilayer thin-film structure rather than as a multi-filamentary tape, the technology developed for Bi-2223-based current leads cannot be transferred directly to REBCO. Therefore, several laboratories are presently investigating the design of high current HTS current leads made of REBCO. Karlsruhe Institute of Technology is developing a 20 kA HTS current lead using brass-stabilized REBCO tapes—as a further development to the Bi-2223 design used in the JT-60SA current leads. The same copper heat exchanger module as in the 20 kA JT-60SA current lead will be used for simplicity, which will allow a comparison of the newly developed REBCO CL with the earlier produced and investigated CL for JT-60SA. The present paper discusses the design and accompanying test of single tape and stack REBCO mock-ups. Finally, the fabrication of the HTS module using REBCO stacks is described.

  19. Clock-frequency and temperature margins of a high-temperature superconductor delay-line memory

    International Nuclear Information System (INIS)

    Hattori, W.; Tahara, S.

    1999-01-01

    We have developed a 10 GHz 32-bit delay-line memory, using a semiconductor crossbar switch and a YBa 2 Cu 3 O 7-δ coplanar delay line. For use in the high-speed (≥10 GHz) cell-buffer storage of large-throughput (≥1 Tbit/s) asynchronous transfer mode (ATM) switching systems, this memory must be fairly reliable. To evaluate the reliability of the operation, therefore, we measured the clock-frequency and temperature margins and the temperature dependence of the bit-error rate. At 64 K, this memory has a capacity of 32 bits with a clock frequency of 9.89±0.11 GHz. In general, clock frequencies of communication systems are strictly managed so that the margins are less than 10 -6 . Therefore, the frequency margin of this memory (∼2x10 -2 )) is wide enough for use in communication systems. The temperature margin was 71.5±4.3 K at 10 GHz and 33 bits. This memory offered error-free operation (BER -13 ) at 71.5 ±3.5 K. These temperature margins are wide enough to be controlled by a cryocooler. These results show that the memory offers reliability and that it can be applied to high-speed ATM cell-buffer storage. (author)

  20. Factors influencing the critical current of Y-Ba-Cu-O superconductor

    International Nuclear Information System (INIS)

    Shi Kexin; Ding Shiying; Yu Zheng; Yan Jialie; Gao Peng

    1990-01-01

    Effects of doping V on the superconducting oxide YBa 2 Cu 3-x V x O y have been studied. It was found that when x≤0.6, there is a decrease, in the superconducting phase ratio of volume to the size of grain and an increase in J c , mass density and hardness of the samples, whereas the sample synthesis conditions, critical temperature T c and superconducting phase structure are not sensitive to the x values. These suggest that the impurity V stays mainly on the grain boundaries and can improve the connection between the grains considerably. In certain cases, it is more important to improve the grain connection than to increase the superconducting phase ratio

  1. The enhancement of critical current density on the bulk of BPSCCO-system superconductor with silver additions

    International Nuclear Information System (INIS)

    Engkir Sukirman; Wisnu Ari Adi; Puji Sulisworo dan W Prasuad

    1999-01-01

    The influence of silver additions on the critical current density (Jc) of BPSCCO-bulk superconductor was investigated, with the aim of getting an increase of its Jc and trying to find out a correlation of Jc and structures of BPSCCO-silver composites. The BPSCCO-system superconductors with nominal composition Bi 1.84 Pb 0.34 Sr 2.00 Ca 2.03 Cu 3.06 O x (2223-phase) were synthesized by using solid state reaction method. The silver added was in the powder-AgO form varied from 0 to 30 wt % AgO. The critical current density, crystal structure, and micro-structure of BPSCCO-silver composites were characterized by means of four-point probe, x-ray diffractometer, and scanning electron microscope that is equipped with a link system energy dispersive spectrometer. It was found that silver additions to BPSCCO cause a reasonable improvement in Jc from 120 to 215 A/cm 2 , and a slight increase in Tc from 92 to 108 K, and lattice parameters of the 2223-phase from a 3.811(3) to 3.820(2) A, and from c = 37.08(3) to 37.15(2) A, with the optimum value occurs at 20 wt % AgO. The AgO powders added to the BPSCCO specimens were converted to Ag 2 O and metallic Ag during the annealing process at 827degC for 96 h in air. The addition of AgO to BPSCCO system does not necessarily lead to decomposition of the 2223-phase. The AgO reacts with and suppresses the 2201-phase. (author)

  2. Effect of irradiation on the critical currents of alloy and compound superconductors

    International Nuclear Information System (INIS)

    Sekula, S.T.

    1977-06-01

    The effects of energetic-particle irradiation on the critical-current density J/sub c/(H) of several superconducting compounds and Nb-Ti alloys have been examined by a number of workers. The irradiations used in the investigations include electrons, fast neutrons, ions, and fission fragments. The results of these studies are reviewed and summarized. In the alloys, changes in J/sub c/(H) on irradiation depend on the metallurgical history of the material and indicate that radiation defects modify the strength of the interaction between the fluxoid array and the sample microstructure. Radiation defects in alloys can also affect J/sub c/(H) through small decreases in T/sub c/, the transition temperature and rho, the normal-state resistivity. Irradiations of A15 compounds up to moderate fluences (dependent on the type and energy of irradiating particle) lead to decreases in T/sub c/ of approximately 1 0 K and increases in J/sub c/(H) with dose for most of the samples investigated. This result can be qualitatively understood as resulting from radiation-induced changes in rho and the pinning force acting on the fluxoids. At higher dose levels, significant depressions of T/sub c/ and possibly gamma, the electronic specific heat coefficient, lead to drastic reductions in J/sub c/(H). The effect of various energetic particles and irradiation temperature on changes in J/sub c/(H) are discussed

  3. Protection of a test magnet wound with a Ag/BSCCO high-temperature superconductor

    International Nuclear Information System (INIS)

    Dresner, L.

    1992-10-01

    The properties of Ag/BSCCO conductor are studied and used to evaluate the feasibility of detecting normal zones in the conductor before the hot-spot temperature reaches critical levels. The results are applied to the protection of a 5-kJ test magnet

  4. Inductively-Charged High-Temperature Superconductors And Methods Of Use

    Science.gov (United States)

    Bromberg, Leslie

    2003-09-16

    The invention provides methods of charging superconducting materials and, in particular, methods of charging high-temperature superconducting materials. The methods generally involve cooling a superconducting material to a temperature below its critical temperature. Then, an external magnetic field is applied to charge the material at a nearly constant temperature. The external magnetic field first drives the superconducting material to a critical state and then penetrates into the material. When in the critical state, the superconducting material loses all the pinning ability and therefore is in the flux-flow regime. In some embodiments, a first magnetic field may be used to drive the superconducting material to the critical state and then a second magnetic field may be used to penetrate the superconducting material. When the external field or combination of external fields are removed, the magnetic field that has penetrated into the material remains trapped. The charged superconducting material may be used as solenoidal magnets, dipole magnets, or other higher order multipole magnets in many applications.

  5. Fabrication of Nb{sub 3}Al superconductor by the optimized mechanical alloying method with low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Y., E-mail: yongzhang@swjtu.cn [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains, Ministry of Education of China, and Superconductivity and New Energy R& D Center, Southwest Jiaotong University, Chengdu 610031 (China); Lin, W.J.; Xu, L.Y.; Yang, D.W.; Chen, Y.L. [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains, Ministry of Education of China, and Superconductivity and New Energy R& D Center, Southwest Jiaotong University, Chengdu 610031 (China); Li, P.Y.; Pan, X.F.; Yan, G. [Western Superconducting Technoligies Co., Ltd., Xi' an 710018 (China); Zhao, Y., E-mail: yzhao@home.swjtu.edu.cn [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains, Ministry of Education of China, and Superconductivity and New Energy R& D Center, Southwest Jiaotong University, Chengdu 610031 (China); School of Materials Science and Engineering, University of New South Wales, Sydney 2052 NSW (Australia)

    2016-11-15

    Highlights: • Due to a much better strain tolerance than Nb{sub 3}Sn, Nb{sub 3}Al has been considered as an excellent candidate for making high field magnets. At present, the Nb{sub 3}Al superconducting wires were prepared mainly by the Jelly-roll method combined with a rapid heating and quenching (RHQ) heat treatment at around 2000 °C. In this study, Nb{sub 3}Al superconductor with T{sub c} of 15.6 K is directly prepared with a mechanical alloying method followed by a low temperature annealing at 800 to 900 °C. Our results hint the possibility that Nb{sub 3}Al superconducting wire with high performance can be prepared below the melting point of Cu (1080 °C) by a conventional powder in tube (PIT) method, thus effectively avoiding high temperature heat treatment and RHQ device. - Abstract: Mechanical alloying was used to synthesize Nb{sub 3}Al superconductor successfully, and the process was optimization under various preparation conditions. In the current study, Nb{sub 3}Al superconductor with T{sub c} of 15.6 K was directly prepared from high quality Nb (Al) solid solution by mechanical alloying method and heat treatment at a low temperature of 800 to 900 °C. The results showed that Nb{sub 3}Al superconducting wire with high performance could be prepared after heat treatment below the melting point of Cu (1080°C) and using Nb (Al) solid solution and conventional powder in tube (PIT) method, thus effectively avoiding ultra-high temperature heat treatment and special rapid heating and quenching(RHQ) device.

  6. Temperature dependence of the phonon structure in the high-temperature superconductor Bi2Sr2CaCu2O8 studied by infrared reflectance spectroscopy

    International Nuclear Information System (INIS)

    Kamaras, K.; Herr, S.L.; Porter, C.D.; Tanner, D.B.; Etemad, S.; Tarascon, J.

    1991-01-01

    We have investigated a ceramic sample of the high-temperature superconductor Bi 2 Sr 2 CaCu 2 O 8 (T c =85 K) by infrared and visible reflectance spectroscopy at several temperatures both below and above the superconducting transition. We find that the temperature variation in the vibrational region is associated with minima or antiresonance features of the optical conductivity, instead of maxima, indicating strong Fano-type electron-phonon interaction and implying that the phonon structure in the infrared is strongly affected by the ab-plane response

  7. Effects of backreaction on power-Maxwell holographic superconductors in Gauss-Bonnet gravity

    Energy Technology Data Exchange (ETDEWEB)

    Salahi, Hamid Reza; Montakhab, Afshin [Shiraz University, Physics Department and Biruni Observatory, College of Sciences, Shiraz (Iran, Islamic Republic of); Sheykhi, Ahmad [Shiraz University, Physics Department and Biruni Observatory, College of Sciences, Shiraz (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), P.O. Box 55134-441, Maragha (Iran, Islamic Republic of)

    2016-10-15

    We analytically and numerically investigate the properties of s-wave holographic superconductors by considering the effects of scalar and gauge fields on the background geometry in five-dimensional Einstein-Gauss-Bonnet gravity. We assume the gauge field to be in the form of the power-Maxwell nonlinear electrodynamics. We employ the Sturm-Liouville eigenvalue problem for analytical calculation of the critical temperature and the shooting method for the numerical investigation. Our numerical and analytical results indicate that higher curvature corrections affect condensation of the holographic superconductors with backreaction. We observe that the backreaction can decrease the critical temperature of the holographic superconductors, while the power-Maxwell electrodynamics and Gauss-Bonnet coefficient term may increase the critical temperature of the holographic superconductors. We find that the critical exponent has the mean-field value β = 1/2, regardless of the values of Gauss-Bonnet coefficient, backreaction and power-Maxwell parameters. (orig.)

  8. Superconductor terahertz metamaterial

    OpenAIRE

    Gu, Jianqiang; Singh, Ranjan; Tian, Zhen; Cao, Wei; Xing, Qirong; Han, Jiaguang; Zhang, Weili

    2010-01-01

    We characterize the behaviour of split ring resonators made up of high-transition temperature YBCO superconductor using terahertz time domain spectroscopy. The superconductor metamaterial shows sharp change in the transmission spectrum at the fundamental inductive-capacitive resonance and the dipole resonance as the temperature dips below the transition temperature. Our results reveal that the high performance of such a metamaterial is limited by material imperfections and defects such as cra...

  9. High temperature superconducting fault current limiter

    Science.gov (United States)

    Hull, John R.

    1997-01-01

    A fault current limiter (10) for an electrical circuit (14). The fault current limiter (10) includes a high temperature superconductor (12) in the electrical circuit (14). The high temperature superconductor (12) is cooled below its critical temperature to maintain the superconducting electrical properties during operation as the fault current limiter (10).

  10. Effect of annealing high-dose heavy-ion irradiated high-temperature superconductor wires

    Science.gov (United States)

    Strickland, N. M.; Wimbush, S. C.; Kluth, P.; Mota-Santiago, P.; Ridgway, M. C.; Kennedy, J. V.; Long, N. J.

    2017-10-01

    Heavy-ion irradiation of high-temperature superconducting thin films has long been known to generate damage tracks of amorphized material that are of close-to-ideal dimension to effectively contribute to pinning of magnetic flux lines and thereby enhance the in-field critical current. At the same time, though, the presence of these tracks reduces the superconducting volume fraction available to transport current while the irradiation process itself generates oxygen depletion and disorder in the remaining superconducting material. We have irradiated commercially available superconducting coated conductors consisting of a thick film of (Y,Dy)Ba2Cu3O7 deposited on a buffered metal tape substrate in a continuous reel-to-reel process. Irradiation was by 185 MeV 197Au ions. A high fluence of 3 × 1011 ions/cm2 was chosen to emphasize the detrimental effects. The critical current was reduced following this irradiation, but annealing at relatively low temperatures of 200 °C and 400 °C substantially restore the critical current of the irradiated material. At high fields and high temperatures there is a net benefit of critical current compared to the untreated material.

  11. Evidence that the reversible strain effect on critical current density and flux pinning in Bi2Sr2Ca2Cu3Ox tapes is caused entirely by the pressure dependence of the critical temperature

    NARCIS (Netherlands)

    van der Laan, D. C.; Douglas, J. F.; Clickner, C. C.; Stauffer, T. C.; Goodrich, L. F.; van Eck, H. J. N.

    2011-01-01

    It is well known that the critical temperature of cuprate-and iron-based high-temperature superconductors changes with pressure. YBa2Cu3O7-delta coated conductors, as well as Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Ox tapes and wires, show a clear reversible effect of strain on their current-carrying

  12. Contamination of YBCO bulk superconductors by samarium and ytterbium

    Czech Academy of Sciences Publication Activity Database

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

    2014-01-01

    Roč. 496, JAN (2014), s. 14-17 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: 0.942, year: 2014

  13. Magnetic-Field-Enhanced Incommensurate Magnetic Order in the Underdoped High-Temperature Superconductor YBa2Cu3O6.45

    DEFF Research Database (Denmark)

    Haug, D.; Hinkov, V.; Suchaneck, A.

    2009-01-01

    We present a neutron-scattering study of the static and dynamic spin correlations in the underdoped high-temperature superconductor YBa2Cu3O6.45 in magnetic fields up to 15 T. The field strongly enhances static incommensurate magnetic order at low temperatures and induces a spectral-weight shift...

  14. X-ray absorption spectroscopy on high-temperature superconductors and related compounds

    International Nuclear Information System (INIS)

    Pellegrin, E.J.H.A.

    1995-07-01

    The electronic structure of the cuprate high-temperature superconductors La 2-x Sr x CuO 4+δ , Tl 2 Ba 2 CaCu 2 O 8 and Tl 2 Ba 2 Ca 2 Cu 3 O 10 has been investigated using polarization-dependent near-edge X-ray absorption fine structure spectroscopy (NEXAFS). In addition, La 2-x Sr x NiO 4+δ has been included in the actual study as an isostructural analogue to the La 2-x Sr x CuO 4+δ system. It appears that the electronic structure of these compounds corresponds to that of a p-type doped charge-transfer insulator including electron-electron interactions on the Cu(Ni) sites and a strong hybridization between Cu(Ni) and O atoms. It is concluded that the low-energy excitations in these compounds can be described on the basis of an effective one-band Mott-Hubbard model. The polarization-dependence of the above spectra gives evidence for the strong in-plane character of the intrinsic and the doped holes. The small amount and the doping-dependence of the out-of-plane character of these charge carriers rule out models for a microscopic mechanism of superconductivity based on a large amount of hole states in the corresponding Apex-O2p z /Cu3d 3z 2 -r 2 orbitals. On the other hand, the reduction of this anisotropy in the overdoped compounds together with similar findings in the macroscopic properties seems to indicate a detrimental influence of non-planar orbitals on the superconducting properties. The differences in the energetic ordering and atomic character of the states close to the Fermi level between the undoped compounds La 2 CuO 4+δ , La 2 NiO 4+δ , and NiO have been determined from the NEXAFS data. It is found that these differences can be explained by the different size of the tetragonal crystal field splitting E Z compared to that of the Hund's rule interaction J H in these systems. This gives evidence for the high-spin d 8 ground state of the undoped nickelates (i.e. J H >E Z ). It is suggested that the polarons in La 2-x Sr x NiO 4+δ can be seen as non

  15. Experimental consequences of Mottness in high-temperature copper-oxide superconductors

    Science.gov (United States)

    Chakraborty, Shiladitya

    It has been more than two decades since the copper-oxide high temperature superconductors were discovered. However, building a satisfactory theoretical framework to study these compounds still remains one of the major challenges in condensed matter physics. In addition to the mechanism of superconductivity, understanding the properties of the normal state is a major puzzle in itself. As these materials are doped Mott insulators, the interaction between electrons is particularly strong. The strong electron correlations are responsible for the breakdown of Fermi-liquid behavior in the normal state. A variety of experimental probes reveal anomalous features in these materials. Such anomalies are reflected in the photoemission spectra as well as transport coefficients such as resistivity, optical conductivity, Hall coefficient, thermoelectric power etc. The objective of this dissertation is to understand the anomalous features as universal features of doped Mott insulators arising entirely as a consequence of strong electron correlations, using the two-dimensional square lattice Hubbard model as the model Hamiltonian. This dissertation is organized into eight chapters. Chapter 1 is an introductory chapter that discusses some key issues. A brief introduction to the superconducting cuprates and their anomalous physical properties is given. Also included is an outline on Mott insulators and the concept of Mottness. Chapter 2 contains a discussion on Cluster Dynamical Mean Field Theory (CDMFT), the principal numerical technique to be implemented in this dissertation. Chapter 3 describes the exact low-energy theory of doped Mott insulators, which largely provides a theoretical framework to this dissertation. In Chapter 4, we compute the spectral function of the two-dimensional Hubbard model using CDMFT and study the origin of the kink feature observed in the electron dispersion measured by ARPES (Angle Resolved Photoemission Spectroscopy). In Chapter 5, the origin of the

  16. Magnetic dipole self-organization of charge carriers in high-temperature superconductors and kinetics of phase transformation

    CERN Document Server

    Voronov, A V; Shuvalov, V V

    2001-01-01

    The phenomenological model, describing the magnetic dipole self-organization of charge carriers (formation of so-called stripe-structures and energy gap in the states spectrum), is designed for interpreting the data on the nonstationary nonlinear spectroscopy of the high-temperature superconductors. It is shown that after fast heating of the superconducting sample the kinetics of the subsequent phase transition depends on the initial temperature T. The destruction of the stripe-structures at low overheating T* < T < T sub m approx = (1.4-1.5)T*, whereby T sub c and T* approx = T sub c are the temperatures of transition into the superconducting state and formation of the stripe-structures occurs slowly (the times above 10 sup - sup 9 s) in spite of practically instantaneous disappearance of the superconductivity

  17. Effect of exciton pairing on the stationary Josephson current in superconductor-semimetal-superconductor junctions

    International Nuclear Information System (INIS)

    Itskovich, I.F.; Shekhter, R.I.

    1983-01-01

    The effect of exciton pairing of charge carriers in a semimetal on the stationary Josephson current in superconductor-semimetal-superconductor junctions is considered. It is shown that the phase transition of the semimetal interlayer into an exciton dielectric state for T/sub γ/< T/sub c/ (T/sub γ/, T/sub c/ are the superconducting and exciton transition temperatures, respectively) is accompanied by a kink on the critical current j/sub c/ versus temperature curve at the point T = T/sub γ/. A sharp nonmonotonic temperature dependence of the reduced current j/sub c//j/sub c/0 (j/sub c/0 is the critical current at T/sub γ/ = 0) is also possible in the range T< T/sub γ/. At low temperatures T<< v/sub 1,2//d<< T/sub γ/ (v/sub 1,2/ are the Fermi velocities of the carriers in the semimetal, d is the thickness of the interlayer) the critical current of the superconductor-semimetal-superconductor junction is exponentially smaller than the current in the absence of exciton pairing

  18. Strain reduced critical current in Bi-2223/Ag superconductors under axial tension and compression

    International Nuclear Information System (INIS)

    Haken, B. ten; Godeke, A.; Kate, H.H.J. ten

    1997-01-01

    The critical current of Ag sheathed Bi(Pb)SrCaCuO-2223 tape conductors is investigated as a function of various strain components. A reduction of the critical current occurs due to both tensile or a compressive strain. The critical current reduction is qualitatively similar with the results as observed in Bi-2212 conductors. An axial compression leads to an immediate critical current reduction. The critical current in an axially elongated sample remains nearly constant up to a certain limit typically close to 0.3% strain. For a larger elongation the critical current reduces rapidly. A transverse pressure acting on the tape surface leads also to an irreversible critical current reduction. This behavior is compared with the influence of an axial compression with an effective Young's modulus. The deformation induced critical current reductions in Bi-2223 conductors can be described by a model that is already proposed for Bi-2212 conductors. This model is based on the irreversible nature of the critical current reduction due to a certain deformation

  19. Characteristics of the Mott transition and electronic states of high-temperature cuprate superconductors from the perspective of the Hubbard model

    Science.gov (United States)

    Kohno, Masanori

    2018-04-01

    A fundamental issue of the Mott transition is how electrons behaving as single particles carrying spin and charge in a metal change into those exhibiting separated spin and charge excitations (low-energy spin excitation and high-energy charge excitation) in a Mott insulator. This issue has attracted considerable attention particularly in relation to high-temperature cuprate superconductors, which exhibit electronic states near the Mott transition that are difficult to explain in conventional pictures. Here, from a new viewpoint of the Mott transition based on analyses of the Hubbard model, we review anomalous features observed in high-temperature cuprate superconductors near the Mott transition.

  20. Can Holstein-Kondo lattice model be used as a candidate for the theory of high transition temperature superconductors

    Directory of Open Access Journals (Sweden)

    R Nourafkan

    2009-08-01

    Full Text Available   It is a common knowledge that the formation of electron pairs is a necessary ingredient of any theoretical work describing superconductivity. Thus, finding the mechanism of the formation of the electron pairs is of utmost importance. There are some experiments on high transition temperature superconductors which support the electron-phonon (e-ph interactions as the pairing mechanism (ARPES, and there are others which support the spin fluctuations as their pairing mechanism (tunneling spectroscopy. In this paper, we introduce the Holstein-Kondo lattice model (H-KLM which incorporates the e-ph as well as the Kondo exchange interaction. We have used the dynamical mean field theory (DMFT to describe heavy fermion semiconductors and have employed the exact-diagonalization technique to obtain our results. The phase diagram of these systems in the parameter space of the e-ph coupling, g, and the Kondo exchange coupling, J, show that the system can be found in the Kondo insulating phase, metallic phase or the bi-polaronic phase. It is shown that these systems develop both spin gap and a charge gap, which are different and possess energies in the range of 1-100 meV. In view of the fact that both spin excitation energies and phonon energies lie in this range, we expect our work on H-KLM opens a way to formalize the theory of the high transition temperature superconductors .

  1. [ital I]-[ital V] characteristics of high-temperature superconductors with columnar defects

    Energy Technology Data Exchange (ETDEWEB)

    Wallin, M.; Girvin, S.M. (Department of Physics, Indiana University, Bloomington, Indiana 47405 (United States))

    1993-06-01

    The vortex glass transition in the presence of columnar defects is studied by Monte Carlo simulations of a vortex loop model, suggested by the analogy to the [ital T]=0 superconductor-insulator transition for dirty bosons in (2+1) dimensions. From finite-size scaling analysis of the [ital I]-[ital V] characteristic we find two dynamical exponents describing the nonequilibrium behavior. We obtain [ital z][sub [perpendicular

  2. Practical superconductor development for electrical power applications

    International Nuclear Information System (INIS)

    Goretta, K.C.

    1991-10-01

    Development of useful high-critical-temperature (high-T c ) 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-T c 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

  3. Practical superconductor development for electrical power applications

    Energy Technology Data Exchange (ETDEWEB)

    Goretta, K.C. (comp.)

    1991-10-01

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

  4. Design, Test and Demonstration of Saturable Reactor High-Temperature Superconductor Fault Current Limiters

    Energy Technology Data Exchange (ETDEWEB)

    Darmann, Frank [Zenergy Power, Inc., Burlingame, CA (United States); Lombaerde, Robert [Zenergy Power, Inc., Burlingame, CA (United States); Moriconi, Franco [Zenergy Power, Inc., Burlingame, CA (United States); Nelson, Albert [Zenergy Power, Inc., Burlingame, CA (United States)

    2012-03-01

    Zenergy Power has successfully designed, built, tested, and installed in the US electrical grid a saturable reactor Fault Current Limiter. Beginning in 2007, first as SC Power Systems and from 2008 as Zenergy Power, Inc., ZP used DOE matching grant and ARRA funds to help refine the design of the saturated reactor fault current limiter. ZP ultimately perfected the design of the saturated reactor FCL to the point that ZP could reliably design a suitable FCL for most utility applications. Beginning with a very basic FCL design using 1G HTS for a coil housed in a LN2 cryostat for the DC bias magnet, the technology progressed to a commercial system that was offered for sale internationally. Substantial progress was made in two areas. First, the cryogenics cooling system progressed from a sub-cooled liquid nitrogen container housing the HTS coils to cryostats utilizing dry conduction cooling and reaching temperatures down to less than 20 degrees K. Large, round cryostats with warm bore diameters of 1.7 meters enabled the design of large tanks to hold the AC components. Second, the design of the AC part of the FCL was refined from a six legged spider design to a more compact and lighter design with better fault current limiting capability. Further refinement of the flux path and core shape led to an efficient saturated reactor design requiring less Ampere-turns to saturate the core. In conclusion, the development of the saturable reactor FCL led to a more efficient design not requiring HTS magnets and their associated peripheral equipment, which yielded a more economical product in line with the electric utility industry expectations. The original goal for the DOE funding of the ZP project Design, Test and Demonstration of Saturable Reactor High-Temperature Superconductor Fault Current Limiters was to stimulate the HTS wire industry with, first 1G, then 2G, HTS wire applications. Over the approximately 5 years of ZP's product development program, the amount of HTS

  5. Why we still don't know the symmetry of the order parameter in high temperature superconductors

    International Nuclear Information System (INIS)

    Klemm, R.A.

    1997-03-01

    One of the most elusive topics in the study of high temperature superconductors (HTCS) is the orbital symmetry of the superconducting order parameter Δ. The low temperature T behavior observed in many experiments suggests that Δ might exhibit line nodes, as expected for d x-y 2 orbital symmetry. However, such behavior also arises from intrinsic proximity coupling and surface states, etc. The paramagnetic Meissner effect, once cited as indirect evidence for a d-wave Δ, was recently observed in Nb. Some phase-sensitive Josephson junction experiments gave strong evidence for a substantial isotropic, or s-wave, component to Δ, whereas others supported the above d-wave form. However, such experiments are intrinsically unreliable in experimental geometries with sample corners, or with meandering grain boundary junctions and stoichiometry inhomogeneities. Finally, the pseudogap observed recently in underdoped HTCS could arise from a charge-density wave

  6. Magneto-Thermal Instabilities in AN Organic Superconductor

    Science.gov (United States)

    Mola, M. M.; Hill, S.; Qualls, J. S.; Brooks, J. S.

    Angle and temperature dependent torque magnetization measurements are reported for the organic superconductor κ-(ET)2Cu(NCS)2, at extremely low temperatures (~ Tc/103). Magneto-thermal instabilities are observed in the form of abrupt magnetization (flux) jumps. We carry out an analysis of the temperature and field orientation dependence of these flux jumps based on accepted models for layered type-II superconductors. Using a simple Bean model, we also find a critical current density of 4 × 108 A/m2 from the remnant magnetization, in agreement with previous measurements.

  7. Electronic structure and superconductivity of FeSe-related superconductors.

    Science.gov (United States)

    Liu, Xu; Zhao, Lin; He, Shaolong; He, Junfeng; Liu, Defa; Mou, Daixiang; Shen, Bing; Hu, Yong; Huang, Jianwei; Zhou, X J

    2015-05-13

    FeSe superconductors and their related systems have attracted much attention in the study of iron-based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced to 37 K at high pressure. On the other hand, its cousin system, FeTe, possesses a unique antiferromagnetic ground state but is non-superconducting. Substitution of Se with Te in the FeSe superconductor results in an enhancement of Tc up to 14.5 K and superconductivity can persist over a large composition range in the Fe(Se,Te) system. Intercalation of the FeSe superconductor leads to the discovery of the AxFe2-ySe2 (A = K, Cs and Tl) system that exhibits a Tc higher than 30 K and a unique electronic structure of the superconducting phase. A recent report of possible high temperature superconductivity in single-layer FeSe/SrTiO3 films with a Tc above 65 K has generated much excitement in the community. This pioneering work opens a door for interface superconductivity to explore for high Tc superconductors. The distinct electronic structure and superconducting gap, layer-dependent behavior and insulator-superconductor transition of the FeSe/SrTiO3 films provide critical information in understanding the superconductivity mechanism of iron-based superconductors. In this paper, we present a brief review of the investigation of the electronic structure and superconductivity of the FeSe superconductor and related systems, with a particular focus on the FeSe films.

  8. Quantum interference in an interfacial superconductor.

    Science.gov (United States)

    Goswami, Srijit; Mulazimoglu, Emre; Monteiro, Ana M R V L; Wölbing, Roman; Koelle, Dieter; Kleiner, Reinhold; Blanter, Ya M; Vandersypen, Lieven M K; Caviglia, Andrea D

    2016-10-01

    The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO) has several intriguing properties that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (T c ; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-T c superconductors. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.

  9. Computational Design of Novel Compounds and Room-temperature Superconductors at High Pressure Conditions

    Science.gov (United States)

    Ma, Yanming

    Pressure, which is a fundamental thermodynamic control on materials' properties, reduces inter-atomic distances and profoundly modifies electronic orbitals and bonding patterns. High pressure has been a versatile tool for creating exotic materials that are not accessible at ambient conditions. Recently, crystal structure prediction has played a leading role in major high-pressure discoveries. Among various structure prediction methods, CALYPSO method (http://www.calypso.cn) is developed on top of swarm-intelligence algorithms by taking the advantage of swarm structures smart learning. Application of CALYPSO into prediction of high-pressure structures has generated a number of exciting discoveries. Examples point to the predicted chemical reactions of Fe/Ni-Xe and Au-Li at high pressures with the formation of unusual compounds Fe3/Ni3Xe and AuLi4/Li5, respectively. Motivated by our theory, the Fe3/Ni3Xe compounds were recently experimentally synthesized, providing a possible solution on ``missing Xe paradox'' towards to Xe storage inside Earth core. Here, Au loses its chemical identity, and acts as a 6p element by achieving high negative oxidation state (>=-2). Our prediction of high-Tc superconductivity on highly compressed H2S initiated the recent experimental observation of record high 200 K superconductivity in H3S. Perspective towards to the design of room-T superconductors in compressed H-rich materials will be presented, including design of high Tc (>100 K) superconductor of TeH4, the highest H-content superconductor in chalcogen hydrides.

  10. Electronic structure of the Y Ba2 Cu3 O7-x high temperature superconductor ceramic

    International Nuclear Information System (INIS)

    Lima, G.A.R.

    1990-01-01

    We investigate the electronic structure of superconductor Y Ba 2 Cu 3 O 7-x through a molecular cluster approach. The calculations are performed self consistently through a semi empirical L.C.A.O. technique, where different charge states are considered. The correlation effects are taken into account by configuration interaction procedure (INDO/CI). The results for the larger cluster yield a density of states showing a strong p-d covalency resulting in a width of around 8,0 eV for the valence band. The optical excitations is analyzed in detail and compared with the experimental data. (author)

  11. Neutron scattering and gravimetric study of BI2Sr2CaCu2O8+x high-temperature superconductors

    International Nuclear Information System (INIS)

    Babaeipour, M

    2005-01-01

    We analysed some of the structural properties of BI 2 Sr 2 CaCu 2 O 8+x superconductors using neutron scattering and intelligent gravimetric analyser instruments from room temperature to 750 deg. C. Both of the experiments showed that the oxygen content of the compound is temperature dependent and decreases as the temperature increases. Neutron experiment results showed that the lattice parameters of the compound are a function of oxygen content and they increase as the oxygen content decreases

  12. An Angle Resolved Photoemission Study of a Mott Insulator and Its Evolution to a High Temperature Superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Ronning, Filip

    2002-03-19

    One of the most remarkable facts about the high temperature superconductors is their close proximity to an antiferromagnetically ordered Mott insulating phase. This fact suggests that to understand superconductivity in the cuprates we must first understand the insulating regime. Due to material properties the technique of angle resolved photoemission is ideally suited to study the electronic structure in the cuprates. Thus, a natural starting place to unlocking the secrets of high Tc would appears to be with a photoemission investigation of insulating cuprates. This dissertation presents the results of precisely such a study. In particular, we have focused on the compound Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}. With increasing Na content this system goes from an antiferromagnetic Mott insulator with a Neel transition of 256K to a superconductor with an optimal transition temperature of 28K. At half filling we have found an asymmetry in the integrated spectral weight, which can be related to the occupation probability, n(k). This has led us to identify a d-wave-like dispersion in the insulator, which in turn implies that the high energy pseudogap as seen by photoemission is a remnant property of the insulator. These results are robust features of the insulator which we found in many different compounds and experimental conditions. By adding Na we were able to study the evolution of the electronic structure across the insulator to metal transition. We found that the chemical potential shifts as holes are doped into the system. This picture is in sharp contrast to the case of La{sub 2-x}Sr{sub x}CuO{sub 4} where the chemical potential remains fixed and states are created inside the gap. Furthermore, the low energy excitations (ie the Fermi surface) in metallic Ca{sub 1.9}Na{sub 0.1}CuO{sub 2}Cl{sub 2} is most well described as a Fermi arc, although the high binding energy features reveal the presence of shadow bands. Thus, the results in this dissertation provide a

  13. AMSAHTS 󈨞: Advances in Materials Science and Applications of High Temperature Superconductors Held in Goddard Space Flight Center, Greenbelt, MD on April 2-6, 1990

    Science.gov (United States)

    1991-01-01

    XES STUDIES OF DENSITY OF STATES OF HIGH TEMPERATURE SUPERCONDUCTORS Gabriel Jasiolek Institute of Physics Polish Academy of Sciences 02-668 Warszawa...Lett. 54 (26), 2719-2721, 1989. 8. R. Adem, L. Martinez, J. Rickards, E. Orozco , J. Fuentes-Maya, J.L. Albarran, A. Mendoza, E. Carrillo, L. Cota, J

  14. Co-current Doping Effect of Nanoscale Carbon and Aluminum Nitride on Critical Current Density and Flux Pinning Properties of Bulk MgB2 Superconductors

    Science.gov (United States)

    Tripathi, D.; Dey, T. K.

    2018-01-01

    The effect of nanoscale aluminum nitride (n-AlN) and carbon (n-C) co-doping on superconducting properties of polycrystalline bulk MgB2 superconductor has been investigated. Polycrystalline pellets of MgB2 , MgB2 + 0.5 wt% AlN (nano), MgB_{1.99}C_{0.01} and MgB_{1.99}C_{0.01} + 0.5 wt% AlN (nano) have been synthesized by a solid reaction process under inert atmosphere. The transition temperature (TC) estimated from resistivity measurement indicates only a small decrease for C (nano) and co-doped MgB2 samples. The magnetic field response of investigated samples has been measured at 4, 10, and 20 K in the field range ± 6 T. MgB2 pellets co-doped with 0.5 wt% n-AlN and 1 wt% n-C display appreciable enhancement in critical current density (J_C ) of MgB2 in both low (≥ 3 times), as well as, high-field region (≥ 15 times). J_C versus H behavior of both pristine and doped MgB2 pellets is well explained in the light of the collective pinning model. Further, the normalized pinning force density f_p(= F_p/F_{pmax}) displays a fair correspondence with the scaling procedure proposed by Eisterer et al. Moreover, the scaled data of the pinning force density (i.e., f_p{-}h data) of the investigated pellets at different temperature are well interpreted by a modified Dew-Hughes expression reported by Sandu and Chee.

  15. Coexistence of magnetic fluctuations and superconductivity in the pnictide high temperature superconductor SmFeAsO1-xFx measured by muon spin rotation.

    Science.gov (United States)

    Drew, A J; Pratt, F L; Lancaster, T; Blundell, S J; Baker, P J; Liu, R H; Wu, G; Chen, X H; Watanabe, I; Malik, V K; Dubroka, A; Kim, K W; Rössle, M; Bernhard, C

    2008-08-29

    Muon spin rotation experiments were performed on the pnictide high temperature superconductor SmFeAsO1-xFx with x=0.18 and 0.3. We observed an unusual enhancement of slow spin fluctuations in the vicinity of the superconducting transition which suggests that the spin fluctuations contribute to the formation of an unconventional superconducting state. An estimate of the in-plane penetration depth lambda ab(0)=190(5) nm was obtained, which confirms that the pnictide superconductors obey an Uemura-style relationship between Tc and lambda ab(0);(-2).

  16. Unusual angular and temperature dependence of the upper critical field in UPt/sub 3/

    Energy Technology Data Exchange (ETDEWEB)

    Shivaram, B.S.; Rosenbaum, T.F.; Hinks, D.G.

    1986-06-01

    We report measurements of the upper critical field, H/sub c2/, inclined at various angles with respect to the c-axis in the heavy fermion superconductor UPt/sub 3/. The angular anisotropy observed near T/sub c/ = 0.53K cannot be explained quantitatively by presently available theoretical expressions which consider either isotropic or anisotropic pairing. In addition, we find that the anisotropy apparently disappears at T /approximately/200 mK, only to reemerge at lower temperatures with an opposite sense. We have also studied H/sub c2/ in the basal lane of this hexagonal crystal and find no angular dependence within the limits of our measurements. 15 refs., 4 figs., 1 tab.

  17. Pressure dependence of critical temperature of bulk FeSe from spin fluctuation theory

    Science.gov (United States)

    Hirschfeld, Peter; Kreisel, Andreas; Wang, Yan; Tomic, Milan; Jeschke, Harald; Jacko, Anthony; Valenti, Roser; Maier, Thomas; Scalapino, Douglas

    2013-03-01

    The critical temperature of the 8K superconductor FeSe is extremely sensitive to pressure, rising to a maximum of 40K at about 10GPa. We test the ability of the current generation of fluctuation exchange pairing theories to account for this effect, by downfolding the density functional theory electronic structure for each pressure to a tight binding model. The Fermi surface found in such a procedure is then used with fixed Hubbard parameters to determine the pairing strength using the random phase approximation for the spin singlet pairing vertex. We find that the evolution of the Fermi surface captured by such an approach is alone not sufficient to explain the observed pressure dependence, and discuss alternative approaches. PJH, YW, AK were supported by DOE DE-FG02-05ER46236, the financial support of MT, HJ, and RV from the DFG Schwerpunktprogramm 1458 is kindly acknowledged.

  18. Chemical effects of alkali atoms on critical temperature in superconducting alkali-doped fullerides

    Science.gov (United States)

    Hetfleisch, F.; Gunnarsson, O.; Srama, R.; Han, J. E.; Stepper, M.; Roeser, H.-P.; Bohr, A.; Lopez, J. S.; Mashmool, M.; Roth, S.

    2018-03-01

    Alkali metal doped fullerides (A3C60) are superconductors with critical temperatures, Tc, extending up to 38 K. Tc is known to depend strongly on the lattice parameter a, which can be adjusted by physical or chemical pressure. In the latter case an alkali atom is replaced by a different sized one, which changes a. We have collected an extensive data base of experimental data for Tc from very early up to recent measurements. We disentangle alkali atom chemical effects on Tc, beyond the well-known consequences of changing a. It is found that Tc, for a fixed a, is typically increased as smaller alkali atoms are replaced by larger ones, except for very large a. Possible reasons for these results are discussed. Although smaller in size than the lattice parameter contribution, the chemical effect is not negligible and should be considered in future physical model developments.

  19. Manufacturing of Superconductors

    DEFF Research Database (Denmark)

    Bech, Jakob Ilsted; Bay, Niels

    tubes containing ceramic powder. The final product is a composite tape, where ceramic superconducting fibres are embedded in a silver matrix. The critical current density Je [kA/cm 2 ] is the primary quality parameter of the product. The quality of the superconducting tape depends very much......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...... of the superconducting ceramic powder Bi2Sr2CaCu2O by a three-point test procedure implying die compaction, diametrical compression and uniaxial compression. · Application of plastic parameters to the constitutive model Drucker/Prager-cap. This model features mean pressure dependent flow stress and volumetric strains...

  20. Magnetic properties of high temperature superconductors. AC susceptibility and magnetostriction studies

    Energy Technology Data Exchange (ETDEWEB)

    Heill, L.K.

    1995-05-01

    The author of this thesis has measured the ac magnetic response function {mu} = {mu}`+i{mu}`` in melt-powder-melt-growth YBa{sub 2}Cu{sub 3}O{sub 7} (Y123) with insulating Y{sub 2}BaCuO{sub 5} (Y211) and in single crystal YBa{sub 2}Cu{sub 3}O{sub 7} (SC) in applied dc fields up to 8 T, oriented both parallel and perpendicular to the crystalline c-axis. Both samples are cubes with sides of about 1 mm. The response of the two samples was mapped out as a function of temperature, excitation field amplitude and frequency, dc field and field orientation. It is found that for both samples the loss peak line (LPL) and hence the irreversibility line (IL) exists at higher temperatures and fields for perpendicular field orientation than for parallel. Strong frequency but weak amplitude dependence is observed for parallel orientation, vice versa for perpendicular orientation. The measured response is strongly non-linear for perpendicular orientation, and intermediate between linear (ohmic) and extremely non-linear (Bean critical state) for parallel orientation. The situation at parallel orientation is close to but above the transition into a vortex solid state, and a power law temperature dependence with exponent 1.5 is obtained for the vortex glass transition line. For perpendicular orientation the response is consistent with that expected in a vortex solid. Pinning barriers are found by means of thermal activation analysis. Anomalous loss peaks {mu}``(T) are observed for the SC sample for intermediate fields in perpendicular orientation. Large magnetostriction is found in a flat single crystal Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} sample at low temperature and fields up to 6 T applied along the c-axis. 332 refs., 59 figs., 7 tabs.

  1. Voltage current characteristics of type III superconductors

    International Nuclear Information System (INIS)

    Dorofejev, G.L.; Imenitov, A.B.; Klimenko, E.Y.

    1980-01-01

    An adequate description of voltage-current characteristics is important in order to understand the nature of high critical current for the electrodynamic construction of type-III superconductors and for commercial superconductor specification. Homogeneous monofilament and multifilament Nb-Ti, Nb-Zr,Nb 3 Sn wires were investigated in different ranges of magnetic field, temperature and current. The shape of the voltage-current characteristics of multifilament wires, and the parameter's dependence on temperature and magnetic field may be explained qualitatively by the longitudinal heterogeneous nature of the filaments. A method of attaining the complete specification of the wire's electro-physical properties is proposed. It includes the traditional description of a critical surface (i.e. the surface corresponding to a certain conventional effective resistivity in T,B,J-space) and a description of any increasing parameter that depends on B and T. (author)

  2. Structural and Transition Temperature of HgPbxBa2Ca2Cu3O8+δ Superconductor

    International Nuclear Information System (INIS)

    Hermiz, G.Y.; Abbass, M.M.

    2005-01-01

    Solid state reaction technique (SSR) was used to prepare high-T c phase in HgPb x Ba 2 Ca 2 Cu 3 O 8+δ superconductors. The effect of additional Pb to HgBa 2 Ca 2 Cu 3 O 8+δ was investigated. It has been found that the maximum transition temperature T c =133K is at x=0.1.X-ray diffraction showed a tetragonal structure with an average value of e=15.816 A . The average value of the valence of copper (v) is equal to 2.025. There is an increasing of density with the enhancement of the concentration of Pb 2

  3. Highly balanced single-layer high-temperature superconductor SQUID gradiometer freely movable within the Earth's magnetic field

    International Nuclear Information System (INIS)

    Schultze, Volkmar; IJsselsteijn, Rob; May, Torsten; Meyer, Hans-Georg

    2003-01-01

    We developed a gradiometer system based on a single-layer high-temperature superconductor dc superconducting quantum interference device (SQUID), which can be freely moved within the Earth's magnetic field during measurement. The problem of circumferential shielding currents in the parallel gradiometer pick-up loop is solved by the use of an appropriately designed magnetometer SQUID integrated on the gradiometer chip. The magnetometer's feedback coil of the flux-locked loop is laid out as a small Helmholtz coil pair, thus keeping the homogeneous magnetic field constant for both the magnetometer and the gradiometer. Therefore, the balance of the directly coupled gradiometer SQUID is enhanced from 100 up to 3800. The noise limited magnetic field gradient resolution of 45 pT m -1 Hz -1/2 is preserved down to frequencies of several Hz even after strong motion in the Earth's magnetic field

  4. 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

  5. Effect of Nb3Sn layer structure and morphology on critical current density of multifilamentary superconductors

    Science.gov (United States)

    Deryagina, I. L.; Popova, E. N.; Patrakov, E. I.; Valova-Zaharevskaya, E. G.

    2017-10-01

    The microstructure and morphology of superconducting Nb3Sn layers in multifilamentary composites differing in the fabrication route (bronze technology and internal-tin method), the shape of Nb filaments (continuous, coupled and tubular) and in the mode of Ti doping (doping of bronze matrix or Nb filaments) have been studied. Significant factors determining critical current density of these wires are the average grain sizes and the fraction of equiaxed grains in the superconducting layers. The minimal grain sizes are characteristic of the composites with tubular Nb filaments, whereas the maximal fraction of equiaxed grains is obtained in the internal-tin wires.

  6. Ambient-pressure organic superconductor

    Science.gov (United States)

    Williams, Jack M.; Wang, Hsien-Hau; Beno, Mark A.

    1986-01-01

    A new class of organic superconductors having the formula (ET).sub.2 MX.sub.2 wherein ET represents bis(ethylenedithio)-tetrathiafulvalene, M is a metal such as Au, Ag, In, Tl, Rb, Pd and the like and X is a halide. The superconductor (ET).sub.2 AuI.sub.2 exhibits a transition temperature of 5 K which is high for organic superconductors.

  7. Toward superconducting critical current by design

    OpenAIRE

    Sadovskyy, I. A.; Jia, Y.; Leroux, M.; Kwon, J.; Hu, H.; Fang, L.; Chaparro, C.; Zhu, S.; Welp, U.; Zuo, J. -M.; Zhang, Y.; Nakasaki, R.; Selvamanickam, V.; Crabtree, G. W.; Koshelev, A. E.

    2015-01-01

    We present the new paradigm of critical current by design. Analogous to materials by design, it aims at predicting the optimal defect landscape in a superconductor for targeted applications by elucidating the vortex dynamics responsible for the bulk critical current. To highlight this approach, we demonstrate the synergistic combination of critical current measurements on commercial high-temperature superconductors containing self-assembled and irradiation tailored correlated defects by using...

  8. Toward Superconducting Critical Current by Design.

    Science.gov (United States)

    Sadovskyy, Ivan A; Jia, Ying; Leroux, Maxime; Kwon, Jihwan; Hu, Hefei; Fang, Lei; Chaparro, Carlos; Zhu, Shaofei; Welp, Ulrich; Zuo, Jian-Min; Zhang, Yifei; Nakasaki, Ryusuke; Selvamanickam, Venkat; Crabtree, George W; Koshelev, Alexei E; Glatz, Andreas; Kwok, Wai-Kwong

    2016-06-01

    A new critical-current-by-design paradigm is presented. It aims at predicting the optimal defect landscape in superconductors for targeted applications by elucidating the vortex dynamics responsible for the bulk critical current. To this end, critical current measurements on commercial high-temperature superconductors are combined with large-scale time-dependent Ginzburg-Landau simulations of vortex dynamics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Magnetic properties of heavy-fermion superconductors

    International Nuclear Information System (INIS)

    Rauchschwalbe, U.

    1986-01-01

    In the present thesis the magnetic properties of heavy-fermion superconductors are investigated. The magnetoresistance and the critical magnetic fields show a variety of anomalous phenomena. The Kondo lattices CeCu 2 Si and CeAl 3 are analysed by magnetoresistance and the field dependence of the resistivitis of UBe 13 , UPt 3 , URu 2 Si 2 and CeRu 3 Si are measured for temperatures < or approx. 1 K. (BHO)

  10. Low-temperature magnetothermal transport investigation of a Ni-based superconductor BaNi2As2: evidence for fully gapped superconductivity.

    Science.gov (United States)

    Kurita, N; Ronning, F; Tokiwa, Y; Bauer, E D; Subedi, A; Singh, D J; Thompson, J D; Movshovich, R

    2009-04-10

    We have performed low-temperature specific heat and thermal conductivity measurements of the Ni-based superconductor BaNi2As2 (T{c}=0.7 K) in a magnetic field. In a zero field, thermal conductivity shows T-linear behavior in the normal state and exhibits a BCS-like exponential decrease below T{c}. The field dependence of the residual thermal conductivity extrapolated to zero temperature is indicative of a fully gapped superconductor. This conclusion is supported by the analysis of the specific heat data, which are well fit by the BCS temperature dependence from T{c} down to the lowest temperature of 0.1 K.

  11. Electrodynamics of Metallic Superconductors

    Directory of Open Access Journals (Sweden)

    M. Dressel

    2013-01-01

    Full Text Available The theoretical and experimental aspects of the microwave, terahertz, and infrared properties of superconductors are discussed. Electrodynamics can provide information about the superconducting condensate as well as about the quasiparticles. The aim is to understand the frequency dependence of the complex conductivity, the change with temperature and time, and its dependence on material parameters. We confine ourselves to conventional metallic superconductors, in particular, Nb and related nitrides and review the seminal papers but also highlight latest developments and recent experimental achievements. The possibility to produce well-defined thin films of metallic superconductors that can be tuned in their properties allows the exploration of fundamental issues, such as the superconductor-insulator transition; furthermore it provides the basis for the development of novel and advanced applications, for instance, superconducting single-photon detectors.

  12. Renormalized phonon frequencies and electric resistivity along the c-axis in single-plane high-temperature superconductors: A double-well analysis

    CERN Document Server

    Georgiev, M; Polyanski, I; Petrova, P T; Tsintsarska, S; Gochev, A

    2001-01-01

    We consider the dynamic interlayer charge transfer across apex oxygens between CuO sub 2 planes in single-layered high-T sub c superconductors. Phonon-coupled axial transfer rates are derived by means of the reaction-rate method. They lead straightforwardly to temperature dependences for the axial resistivity. Doping and temperature dependences are also derived for the renormalized frequencies of phonon modes coupled to the interlayer charge transfer. Our results are compared with experimentally observed dependences. (author)

  13. submitter Quench Protection of Very Large, 50-GJ-Class, and High-Temperature-Superconductor-Based Detector Magnets

    CERN Document Server

    Mentink, Matthias; Mulder, Tim; Van Nugteren, Jeroen; ten Kate, Herman

    2016-01-01

    An investigation is performed on the quench behavior of a conceptual 50-GJ 8-T high-temperature-superconductor-based solenoid. In this design, a 50-kA conductor-on-round-core cable-in-conduit conductor utilizing ReBCO technology is envisioned, operating at 40 K. Various properties such as resistivity, thermal conductivity, and heat capacity are very different at this temperature, which affects the quench behavior. It is found that the envisioned conductor is very stable with a minimum quench energy of about 2 kJ. However, the quench propagation velocity is typically about 20 mm/s, so that creating a wide-spread normal zone throughout the coil is very challenging. Moreover, an extraction voltage exceeding 20 kV would be required to ensure a hot-spot temperature below 100 K once a thermal runaway occurs. A novel concept dubbed “rapid quench transformation” is proposed whereby the superconducting conductor is co-wound with a normal conductor to achieve a high degree of inductive coupling. This geometry allow...

  14. Electronic transport measurements in the electron-doped high-temperature superconductor Praseodymium(2-x) Cerium(x) Copper (II) oxide(4+-delta)

    Science.gov (United States)

    Bach, Paul Leonard

    2011-12-01

    This thesis is composed of four major parts centered around the electron-doped superconductor Pr2-xCexCuO4+/-delta: angular magnetoresistance studies of antiferromagnetism, doping effects of oxygenation, Tc enhancement by the creation of superlattices, and comparison of high-temperature resistivity with the pnictides. The first part focuses on transport measurements of the magnetism in Pr2-xCexCuO4+/-delta and La 2-xCexCuO4+/-delta. It was found that the thermal evolution of the angular dependence of magnetoresistance in Pr 2-xCexCuO4+/-delta can be used to determine the Neel temperature in that material. This angular magnetoresistance technique was also applied to La2-xCexCuO4+/-delta ; evidence for antiferromagnetism in this system was observed as well. This section additionally develops angular magnetoresistance as a useful probe in other cuprate projects here described. The second part investigates over-oxygenated and irradiated Pr2-x CexCuO4+/-delta, in under- and optimal dopings. Resistivity, Hall effect, and angular magnetoresistance measurements show oxygen both doping and disordering the system, in agreement with over-doped films. The evolution of both the Hall effect and angular magnetoresistance shows that over-oxygenation results in significant changes in the number of charge carriers, regardless of the increase in scattering incurred. Additionally, this study indicates that annealing primarily removes apical oxygen, rather than other proposed behaviors. The third part studies multi-layer films of Pr2-xCex CuO4+/-delta and La2-xCexCuO 4+/-delta. These superlattices exhibit a significant Tc enhancement over component layers' T cs. Interface effects are excluded as a source of this Tc increase based upon critical current measurments. The Tc enhancement is found to be due to charge redistribution. Based on Hall and angular magnetoresistance measurements, the result of this redistribution is slightly net-under-doped films. The fourth part uses Pr2-xCexCuO4

  15. Condensation energy density in Bi-2212 superconductors

    International Nuclear Information System (INIS)

    Matsushita, Teruo; Kiuchi, Masaru; Haraguchi, Teruhisa; Imada, Takeki; Okamura, Kazunori; Okayasu, Satoru; Uchida, Satoshi; Shimoyama, Jun-ichi; Kishio, Kohji

    2006-01-01

    The relationship between the condensation energy density and the anisotropy parameter, γ a , has been derived for Bi-2212 superconductors in various anisotropic states by analysing the critical current density due to columnar defects introduced by heavy ion irradiation. The critical current density depended on the size of the defects, determined by the kind and irradiation energy of the ions. A significantly large critical current density of 17.0 MA cm -2 was obtained at 5 K and 0.1 T even for the defect density of a matching field of 1 T in a specimen irradiated with iodine ions. The dependence of the critical current density on the size of the defects agreed well with the prediction from the summation theory of pinning forces, and the condensation energy density could be obtained consistently from specimens irradiated with different ions. The condensation energy density obtained increased with decreasing γ a over the entire range of measurement temperature, and reached about 60% of the value for the most three-dimensional Y-123 observed by Civale et al at 5 K. This gives the reason for the very strong pinning in Bi-2212 superconductors at low temperatures. The thermodynamic critical field obtained decreased linearly with increasing temperature and extrapolated to zero at a certain characteristic temperature, T * , lower than the critical temperature, T c . T * , which seems to be associated with the superconductivity in the block layers, was highest for the optimally doped specimen. This shows that the superconductivity becomes more inhomogeneous as the doped state of a superconductor deviates from the optimum condition

  16. Raising the Bose-Einstein condensation critical temperature using vacancies

    Science.gov (United States)

    Solis, M. A.; Martinez, J. G.; Garcia, J.; Fortes, M.; Salas, P.; Rodriguez, O. A.

    We have studied the thermodynamic properties of an Ideal Bose gas confined within a semi-infinite box with periodic permeable multilayers, in particular we have calculated its BEC critical temperature and isochoric specific heat, where we have always observed a critical temperature Tc smaller than the BEC critical temperature (T0) of an infinite homogeneous ideal Bose gas. However, when we introduce a plane vacancy, a finite gap between the ground and first excited states in the particle energy spectrum is introduced, which increases the critical temperature beyond T0 and generates a specific heat jump at Tc. We expect that these vacancies could lead to a raise in the critical temperature of superfluids within lattice structures. We acknowledge partial support from Grants PAPIIT IN107616 and CONACyT 221030.

  17. Interplay of Phonon and Exciton-Mediated Superconductivity in Hybrid Semiconductor-Superconductor Structures.

    Science.gov (United States)

    Skopelitis, Petros; Cherotchenko, Evgenia D; Kavokin, Alexey V; Posazhennikova, Anna

    2018-03-09

    We predict a strong enhancement of the critical temperature in a conventional Bardeen-Cooper-Schrieffer (BCS) superconductor in the presence of a bosonic condensate of exciton polaritons. The effect depends strongly on the ratio of the cutoff frequencies for phonon and exciton-polariton mediated BCS superconductivity, respectively. We also discuss a possible design of hybrid semiconductor-superconductor structures suitable for the experimental observation of such an effect.

  18. Rotational symmetry breaking in the topological superconductor SrxBi2Se3 probed by upper-critical field experiments

    NARCIS (Netherlands)

    Pan, Y.; Nikitin, A.M.; Araizi, G.K.; Huang, Y.K.; Matsushita, Y.; Naka, T.; de Visser, A.

    2016-01-01

    Recently it was demonstrated that Sr intercalation provides a new route to induce superconductivity in the topological insulator Bi2Se3. Topological superconductors are predicted to be unconventional with an odd-parity pairing symmetry. An adequate probe to test for unconventional superconductivity

  19. Electronic structure of ion arsenic high temperature superconductors studied by angle resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chang [Iowa State Univ., Ames, IA (United States)

    2011-01-01

    The main purpose of the present thesis is to present our ARPES results on the iron arsenic superconductors. As revealed by a series of ARPES measurements on both the AEFe2As2 and the RFeAs(O,F) families (parent compound and carrier-doped systems), the electronic structures of the pnictides are complicated, three dimensional, and closely linked to their superconducting behavior (13; 14; 15; 16; 17; 18; 19). Parent compounds of these materials exhibit the basic hole-electron pocket dual plus an apparent Fermi surface reconstruction caused by long range antiferromagnetism (13; 15). When carriers are introduced, the chemical potential shifts in accordance with the Luttinger theorem and the rigid band shifting picture (13). Importantly, both the appearance and disappearance of the superconducting dome at low and high doping levels have intimate relation with topological changes at the Fermi surfaces, resulting in a specific Fermi topology being favored by superconductivity (15; 16). On the low doping side, superconductivity emerges in the phase diagram once the antiferromagnetic reconstruction disappears below the Fermi level, returning the Fermi surface to its paramagnetic-like appearance. On the high doping side, superconductivity disappears around a doping level at which the central hole pocket vanishes due to increasing electron concentration. Such phenomena are evidence for the governing role the electronic structure plays in their superconducting behavior.

  20. A phenomenological model for the rounding of the electrical conductivity above Tgco in polycrystalline copper oxide superconductors

    International Nuclear Information System (INIS)

    Veira, J.A.; Domarco, G.; Maza, J.; Miguelez, F.; Torron, C.; Vidal, F.

    1989-01-01

    The amplitude and temperature behavior of the electrical resistivity of ceramic superconductors above the mean-field critical temperature of the individual grains is explained by combining the current phenomenological ideas on the electrical conductivity in granular superconductors with the effects of the fluctuations of the superconducting order parameter amplitude. As an example of application, the authors analyze the phase-breaking time in ceramic YBCO samples

  1. Quasiparticle picture of high-temperature superconductors in the frame of a Fermi liquid with the fermion condensate

    Energy Technology Data Exchange (ETDEWEB)

    Amusia, M. Ya.; Shaginyan, V. R.

    2001-06-01

    A model of a Fermi liquid with the fermion condensate (FC) is applied to the consideration of quasiparticle excitations in high-temperature superconductors, in their superconducting and normal states. Within our model the appearance of the fermion condensate presents a quantum phase transition that separates the regions of normal and strongly correlated electron liquids. Beyond the phase transition point the quasiparticle system is divided into two subsystems, one containing normal quasiparticles and the other{emdash}fermion condensate localized at the Fermi surface and characterized by almost dispersionless single-particle excitations. In the superconducting state the quasiparticle dispersion in systems with FC can be presented by two straight lines, characterized by effective masses M{sub FC}{sup *} and M{sub L}{sup *}, respectively, and intersecting near the binding energy, which is of the order of the superconducting gap. This same quasiparticle picture persists in the normal state, thus manifesting itself over a wide range of temperatures as new energy scales. Arguments are presented that fermion systems with FC have features of a {open_quotes}quantum protectorate{close_quotes} [R. B. Laughlin and D. Pines, Proc. Natl. Acad. Sci. U.S.A. >97, 28 (2000); P. W. Anderson, cond-mat/0007185 (unpublished); cond-mat/0007287 (unpublished)].

  2. Quasiparticle picture of high-temperature superconductors in the frame of a Fermi liquid with the fermion condensate

    International Nuclear Information System (INIS)

    Amusia, M. Ya.; Shaginyan, V. R.

    2001-01-01

    A model of a Fermi liquid with the fermion condensate (FC) is applied to the consideration of quasiparticle excitations in high-temperature superconductors, in their superconducting and normal states. Within our model the appearance of the fermion condensate presents a quantum phase transition that separates the regions of normal and strongly correlated electron liquids. Beyond the phase transition point the quasiparticle system is divided into two subsystems, one containing normal quasiparticles and the other-fermion condensate localized at the Fermi surface and characterized by almost dispersionless single-particle excitations. In the superconducting state the quasiparticle dispersion in systems with FC can be presented by two straight lines, characterized by effective masses M FC * and M L * , respectively, and intersecting near the binding energy, which is of the order of the superconducting gap. This same quasiparticle picture persists in the normal state, thus manifesting itself over a wide range of temperatures as new energy scales. Arguments are presented that fermion systems with FC have features of a 'quantum protectorate' [R. B. Laughlin and D. Pines, Proc. Natl. Acad. Sci. U.S.A. >97, 28 (2000); P. W. Anderson, cond-mat/0007185 (unpublished); cond-mat/0007287 (unpublished)

  3. Conductive polymer/superconductor bilayer structures

    International Nuclear Information System (INIS)

    McDevitt, J.T.; Haupt, S.G.; Riley, D.R.; Zhao, J.; Grassi, J.; Lo, R.K.; Jones, C.

    1994-01-01

    The preparation of a hybrid conducting polymer/high-temperature superconductor device consisting of a polypyrrole-coated YBa 2 Cu 3 O 7-∂ 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 YBa 2 Cu 3 O 7-∂ 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 J c , 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

  4. Calculation and analysis of thermodynamical relations for superconductors

    International Nuclear Information System (INIS)

    Nazarenko, A.B.

    1989-01-01

    Absorption of low-frequency and high-frequency sounds, representing a wave of adiabatic periodic volumetric compressions and frequency discharges ω in an isotropic superconductor near transition temperature, are calculated on the basis of the Gizburg-Landau theory. Thermodynamic ratios for sudden changes in thermodynamic values, when transition from normal state to superconducting occurs, analogous Erenfest ratios are obtained. Comparison of the mentioned thermodynamic values with the experimental data given in literature on YBa 2 Cu 3 O 7-δ is carried out. Experiments on ultrasound absorption in new superconductors can give the information about the type of phase transition and thermodynamic ratios for these superconductors, in particular, about dependence of critical temperature on pressure. Similar calculations were carried out for experiments on He2 transition and in ferromagnets. The order parameter in the thermodynamic potential was chosen as isotropic

  5. Epataxial growth of the high-temperature superconductors YBa2Cu3O7-x on silicon single crystals with buffer layers

    International Nuclear Information System (INIS)

    Lubig, A.

    1991-09-01

    In this work the growth of thin films of the high-temperature superconductor YBa 2 Cu 3 O 7-x on Si(001) substrates has been investigated by Rutherford backscattering, channeling, X-ray diffraction, high resolution transmission electron microscopy, and electrical measurements. Epitaxial buffer layers of electrically insulating, pure and yttria-stabilized ZrO 2 ([Y 2 O 3 ] 0.06 [ZrO 2 ] 0.94 = YSZ) as well as of metallic CoSi 2 were employed to largely prevent the interdiffusion and chemical reaction between the superconductor film and the substrate in spite of the high deposition temperatures of the YBa 2 Cu 3 O 7-x in the range of 600 to 800deg C. (orig.)

  6. Revisiting quasiparticle scattering interference in high-temperature superconductors: The problem of narrow peaks

    Science.gov (United States)

    Sulangi, Miguel Antonio; Allan, Milan P.; Zaanen, Jan

    2017-10-01

    We revisit the interpretation of quasiparticle scattering interference in cuprate high-Tc superconductors. This phenomenon has been very successful in reconstructing the dispersions of d -wave Bogoliubov excitations, but the successful identification and interpretation of quasiparticle interference (QPI) in scanning tunneling spectroscopy (STS) experiments rely on theoretical results obtained for the case of isolated impurities. We introduce a highly flexible technique to simulate STS measurements by computing the local density of states using real-space Green's functions defined on two-dimensional lattices with as many as 100 000 sites. We focus on the following question: to what extent can the experimental results be reproduced when various forms of distributed disorder are present? We consider randomly distributed pointlike impurities, smooth "Coulombic" disorder, and disorder arising from random on-site energies and superconducting gaps. We find an apparent paradox: the QPI peaks in the Fourier-transformed local density of states appear to be sharper and better defined in experiment than those seen in our simulations. We arrive at a no-go result for smooth-potential disorder since this does not reproduce the QPI peaks associated with large-momentum scattering. An ensemble of pointlike impurities gets closest to experiment, but this goes hand in hand with impurity cores that are not seen in experiment. We also study the effects of possible measurement artifacts (the "fork mechanism"), which turn out to be of relatively minor consequence. It appears that a more microscopic model of the tunneling process needs to be incorporated in order to account for the sharpness of the experimentally obtained QPI peaks.

  7. Transitions through critical temperatures in nematic liquid crystals

    KAUST Repository

    Majumdar, Apala

    2013-08-06

    We obtain estimates for critical nematic liquid crystal (LC) temperatures under the action of a slowly varying temperature-dependent control variable. We show that biaxiality has a negligible effect within our model and that these delay estimates are well described by a purely uniaxial model. The static theory predicts two critical temperatures: the supercooling temperature below which the isotropic phase loses stability and the superheating temperature above which the ordered nematic states do not exist. In contrast to the static problem, the isotropic phase exhibits a memory effect below the supercooling temperature in the dynamic framework. This delayed loss of stability is independent of the rate of change of temperature and depends purely on the initial value of the temperature. We also show how our results can be used to improve estimates for LC material constants. © 2013 American Physical Society.

  8. Effect of the Temperature, External Magnetic Field, and Transport Current on Electrical Properties, Vortex Structure Evolution Processes, and Phase Transitions in Subsystems of Superconducting Grains and "Weak Links" of Granular Two-Level High-Temperature Superconductor YBa2Cu3O7-δ

    Science.gov (United States)

    Derevyanko, V. V.; Sukhareva, T. V.; Finkel', V. A.

    2018-03-01

    The temperature dependences of the resistivity of granular high-temperature superconductor YBa2Cu3O7-δ ρ( T) are measured at various transverse external magnetic fields 0 ≤ H ext ≤ 100 Oe in the temperature range from the resistivity onset temperature T ρ = 0 to the superconducting transition critical temperature T c at the transport current density from 50 to 2000 mA/cm2. The effect of the external magnetic field and transport current density on the kinetics of phase transitions in both subsystems of granular two-level HTSC ( T = T c2J, T c1g, T c ) is determined. The feasibility of the topological phase transition, i.e., the Berezinsky-Kosterlitz-Thouless transition, in the Josephson medium at T c2J < T BKT < T c1g "in transport current" is established, and its feasibility conditions are studied.

  9. 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.

  10. 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.

  11. Entanglement entropy and complexity for one-dimensional holographic superconductors

    Directory of Open Access Journals (Sweden)

    Mahdi Kord Zangeneh

    2017-08-01

    Full Text Available Holographic superconductor is an important arena for holography, as it allows concrete calculations to further understand the dictionary between bulk physics and boundary physics. An important quantity of recent interest is the holographic complexity. Conflicting claims had been made in the literature concerning the behavior of holographic complexity during phase transition. We clarify this issue by performing a numerical study on one-dimensional holographic superconductor. Our investigation shows that holographic complexity does not behave in the same way as holographic entanglement entropy. Nevertheless, the universal terms of both quantities are finite and reflect the phase transition at the same critical temperature.

  12. Experiment and analysis for a small-sized flywheel energy storage system with a high-temperature superconductor bearing

    Science.gov (United States)

    Kim, Bongsu; Ko, Junseok; Jeong, Sangkwon; Lee, Seung S.

    2006-02-01

    This paper presents a small-sized flywheel energy storage system that uses a high-temperature superconductor (HTS) bearing characterized by a non-contacting bearing with no active control. The small-sized flywheel is made up several magnets for a motor/generator as well as an HTS bearing, and they are fitted into a 34 mm diameter, 3 mm thick aluminium disc. For simplicity and miniaturization of the whole system, the small-sized flywheel takes torque directly from a planar stator, which consists of an axial flux-type brushless DC motor/generator. The small-sized flywheel successfully rotated up to 38 000 rpm in a vacuum while levitated above the stator with a gap of about 1 mm. However, there are some eddy current losses in the stator and non-axisymmetry in the magnetic field causing large drag torque. In order to solve these problems, an improved magnet array in the flywheel, including magnetic screening, is proposed and 3D electromagnetic simulations have been conducted.

  13. Collective oscillations of twin boundaries in high-temperature superconductors as an acoustic analogue of two-dimensional plasmons

    Energy Technology Data Exchange (ETDEWEB)

    Kosevich, Y.A. (All-Union Surface and Vacuum Research Centre, 117334 Moscow, U.S.S.R. (SU)); Syrkin, E.S. (Institute for Low Temperature Physics and Engineering, UkrSSR Academy of Sciences, 310164 Kharkov (USSR))

    1991-01-01

    Low-frequency collective oscillations in a superlattice consisting of alternating highly anisotropic layers are considered. Such superstructure may be formed in the ferroelastic near the structural phase transition by alternation of twins. For the surface waves, propagating along the layers, the conditions and the range of existence of those with the dispersion law {omega}{similar to}{ital k}{sup 1/2}, characteristic for two-dimensional plasmons, have been analyzed for a solid-state system with consideration for elastic anisotropy and retardation of acoustic waves. Such excitations ( dyadons'') were used by Horovitz, Barsch, and Krumhansl (Phys. Rev. B 36, 8895 (1987)) in an attempt to explain the anomalies of low-temperature thermodynamic and kinetic characteristics of high-{ital T}{sub {ital c}} superconductors. We have shown that the similarity of the densities of the matching phases and the retardation of elastic waves in the crystal narrow the range of existence of dyadons, but the high elastic anisotropy of the solid phases enlarges the range of existence of such excitations in solid-state systems. An example of possible crystalline geometry of the phase matching, for which there arise collective excitations of the type under consideration, is found. For transverse and longitudinal waves propagating across the layers, the existence is proved of low-frequency acoustic branches separated by a wide gap from the nearest optical branches.

  14. Collective oscillations of twin boundaries in high-temperature superconductors as an acoustic analogue of two-dimensional plasmons

    Science.gov (United States)

    Kosevich, Yu. A.; Syrkin, E. S.

    1991-01-01

    Low-frequency collective oscillations in a superlattice consisting of alternating highly anisotropic layers are considered. Such superstructure may be formed in the ferroelastic near the structural phase transition by alternation of twins. For the surface waves, propagating along the layers, the conditions and the range of existence of those with the dispersion law ω~k1/2, characteristic for two-dimensional plasmons, have been analyzed for a solid-state system with consideration for elastic anisotropy and retardation of acoustic waves. Such excitations (``dyadons'') were used by Horovitz, Barsch, and Krumhansl [Phys. Rev. B 36, 8895 (1987)] in an attempt to explain the anomalies of low-temperature thermodynamic and kinetic characteristics of high-Tc superconductors. We have shown that the similarity of the densities of the matching phases and the retardation of elastic waves in the crystal narrow the range of existence of dyadons, but the high elastic anisotropy of the solid phases enlarges the range of existence of such excitations in solid-state systems. An example of possible crystalline geometry of the phase matching, for which there arise collective excitations of the type under consideration, is found. For transverse and longitudinal waves propagating across the layers, the existence is proved of low-frequency acoustic branches separated by a wide gap from the nearest optical branches.

  15. Disappearance of nodal gap across the insulator-superconductor transition in a copper-oxide superconductor.

    Science.gov (United States)

    Peng, Yingying; Meng, Jianqiao; Mou, Daixiang; He, Junfeng; Zhao, Lin; Wu, Yue; Liu, Guodong; Dong, Xiaoli; He, Shaolong; Zhang, Jun; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Lee, T K; Zhou, X J

    2013-01-01

    The parent compound of the copper-oxide high-temperature superconductors is a Mott insulator. Superconductivity is realized by doping an appropriate amount of charge carriers. How a Mott insulator transforms into a superconductor is crucial in understanding the unusual physical properties of high-temperature superconductors and the superconductivity mechanism. Here we report high-resolution angle-resolved photoemission measurement on heavily underdoped Bi₂Sr₂-xLaxCuO(₆+δ) system. The electronic structure of the lightly doped samples exhibit a number of characteristics: existence of an energy gap along the nodal direction, d-wave-like anisotropic energy gap along the underlying Fermi surface, and coexistence of a coherence peak and a broad hump in the photoemission spectra. Our results reveal a clear insulator-superconductor transition at a critical doping level of ~0.10 where the nodal energy gap approaches zero, the three-dimensional antiferromagnetic order disappears, and superconductivity starts to emerge. These observations clearly signal a close connection between the nodal gap, antiferromagnetism and superconductivity.

  16. Signatures of mesoscopic Jahn-Teller polaron inhomogeneities in high-temperature superconductors

    CERN Document Server

    Bishop, A R; Leon, J M D

    2003-01-01

    We analyse complementary experimental results in high-temperature superconducting cuprates from x-ray absorption fine structure (XAFS), inelastic neutron scattering (INS) and inelastic x-ray scattering (IXS), Raman spectroscopy (RS), infrared absorption spectroscopy and femtosecond optical spectroscopy in terms of the predictions of a specific fully quantum mechanical calculation of small polaron formation and internal dynamics (phonon-assisted local charge oscillations). These analyses support the scenario in which the pseudogap-associated temperature, T*, marks the onset of an inhomogeneous ground state with polarons, in agreement with several theoretical models which attempt to explain the origin of high-temperature superconductivity in doped cuprates. The change in dynamics, which is observed across the superconducting transition temperature, T sub c in XAFS, INS and RS, indicates an intimate link of the dynamics of these polarons with the mechanism of high-temperature superconductivity. (letter to the ed...

  17. Hybrid High-Temperature Superconductor Current Leads for Space Applications, Phase II

    Data.gov (United States)

    National Aeronautics and Space Administration — The Tai-Yang Research Company (TYRC) proposes to address the need for high temperature superconducting (HTS) current leads used in an adiabatic demagnetization...

  18. Hybrid High-Temperature Superconductor Current Leads for Space Applications, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — The Tai-Yang Research Company (TYRC) of Tallahassee, Florida proposes to build hybrid high-temperature superconducting current leads for space applications,...

  19. Exploring nuclear magnetic resonance at the highest pressure. Closing the pseudogap under pressure in a high temperature superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Meissner, Thomas

    2013-05-13

    In the present work, a novel probe design for high pressure NMR experiments in gem anvil cells (GAC) was used which places a small microcoil inside the high pressure volume as the detection coil. Based on tests carried out at ambient pressure and high pressure of 42 kbar it is demonstrated that this approach is indeed feasible and results in an increase of sensitivity by two orders of magnitude compared to previous GAC-NMR designs. The design was then successfully employed in the investigation of the electronic properties of metallic aluminum and the high temperature superconductor YBa{sub 2}Cu{sub 4}O{sub 8} at pressures of up to 101 kbar. Because of its improved sensitivity and the potential to achieve even higher pressures, the microcoil GAC-NMR setup should prove useful in the investigation of materials under high pressure conditions in the future. In the case of metallic aluminum, the effect of pressure on the electronic density of states at the Fermi level was probed via the Knight-shift K and the spin-lattice relaxation time T{sub 1} at room temperature up to a pressure of 101 kbar, extending the pressure range of previous NMR measurements by a factor of 14 [72]. Most notably, a decrease of K(p) by 11% is detected in the investigated pressure range that is inconsistent with a free electron behavior of the density of states. Numerical band structure calculations that are in excellent agreement with the experimental data suggest that the observed changes of K and T{sub 1} are due to a kink in the electronic states at a Lifshitz-transition at about 75 kbar which has not been observed previously. A further decrease of K by a factor of 2 is predicted to occur in the pressure range up to 300 kbar. In addition, an increase of the NMR linewidths of the metallic aluminum signal was observed above about 42 kbar that is inconsistent with a pure dipolar linewidth. Based on an analysis of the field dependence of this effect it was ascribed to a small additional

  20. New State of Matter: Heavy Fermion Systems, Quantum Spin Liquids, Quasicrystals, Cold Gases, and High-Temperature Superconductors

    Science.gov (United States)

    Shaginyan, V. R.; Stephanovich, V. A.; Msezane, A. Z.; Schuck, P.; Clark, J. W.; Amusia, M. Ya.; Japaridze, G. S.; Popov, K. G.; Kirichenko, E. V.

    2017-12-01

    We report on a new state of matter manifested by strongly correlated Fermi systems including various heavy fermion (HF) metals, two-dimensional quantum liquids such as ^3He films, certain quasicrystals, and systems behaving as quantum spin liquids. Generically, these systems can be viewed as HF systems or HF compounds, in that they exhibit typical behavior of HF metals. At zero temperature, such systems can experience a so-called fermion condensation quantum phase transition (FCQPT). Combining analytical considerations with arguments based entirely on experimental grounds, we argue and demonstrate that the class of HF systems is characterized by universal scaling behavior of their thermodynamic, transport, and relaxation properties. That is, the quantum physics of different HF compounds is found to be universal, emerging irrespective of the individual details of their symmetries, interactions, and microscopic structure. This observed universal behavior reveals the existence of a new state of matter manifest in HF compounds. We propose a simple, realistic model to study the appearance of flat bands in two-dimensional ensembles of ultracold fermionic atoms, interacting with coherent resonant light. It is shown that signatures of these flat bands may be found in peculiarities in their thermodynamic and spectroscopic properties. We also show that the FCQPT, in generating flat bands and altering Fermi surface topology, is an essential progenitor of the exotic behavior of the overdoped high-temperature superconductors represented by La_{2-x}SrxxCuO_4, whose superconductivity differs from that predicted by the classical Bardeen-Cooper-Schrieffer theory. The theoretical results presented are in good agreement with recent experimental observations, closing the colossal gap between these empirical findings and Bardeen-Cooper-Schrieffer-like theories.

  1. Field, temperature, and angle dependent critical current density Jc(H,T,θ) in coated conductors obtained via contact-free methods

    International Nuclear Information System (INIS)

    Thompson, J R; Christen, D K; Zhang Yifei; Zuev, Y L; Cantoni, C; Sinclair, J W; Chen Yimin; Selvamanickam, V

    2010-01-01

    Applications of coated conductors based on high- T c superconductors often require detailed knowledge of their critical current density J c as a function of magnetic field orientation as well as field strength and temperature. This work demonstrates experimental methods for obtaining the angularly dependent J c using contact-free magnetic measurements, and qualifies those methods using several well defined conditions. The studies complement traditional transport techniques and are readily extended to conditions of field and temperature where the current density is very large and transport methods become difficult. Results on representative materials are presented.

  2. Field, temperature, and angle dependent critical current density Jc(H,T, ) in coated conductors obtained via contact-free methods

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, James R [ORNL; Sinclair IV, John W [ORNL; Christen, David K [ORNL; Zhang, Yifei [ORNL; Zuev, Yuri L [ORNL; Cantoni, Claudia [ORNL; Chen, Y [SuperPower Incorporated, Schenectady, New York; Selvamanickam, V. [SuperPower Incorporated, Schenectady, New York

    2010-01-01

    Applications of coated conductors based on high-Tc superconductors often require detailed knowledge of their critical current density Jc as a function of magnetic field orientation as well as field strength and temperature. This work demonstrates experimental methods to obtain the angularly dependent Jc using contact-free magnetic measurements, and qualifies those methods using several well defined conditions. The studies complement traditional transport techniques and are readily extended to conditions of field and temperature where the current density is very large and transport methods become difficult. Results on representative materials are presented.

  3. Field, temperature, and angle dependent critical current density J{sub c}(H,T,{theta}) in coated conductors obtained via contact-free methods

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, J R; Christen, D K; Zhang Yifei; Zuev, Y L; Cantoni, C [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6092 (United States); Sinclair, J W [Department of Physics, University of Tennessee, Knoxville, TN 37996-1200 (United States); Chen Yimin; Selvamanickam, V [SuperPower, Incorporated, 450 Duane Avenue, Schenectady, NY 12304 (United States)

    2010-01-15

    Applications of coated conductors based on high- T{sub c} superconductors often require detailed knowledge of their critical current density J{sub c} as a function of magnetic field orientation as well as field strength and temperature. This work demonstrates experimental methods for obtaining the angularly dependent J{sub c} using contact-free magnetic measurements, and qualifies those methods using several well defined conditions. The studies complement traditional transport techniques and are readily extended to conditions of field and temperature where the current density is very large and transport methods become difficult. Results on representative materials are presented.

  4. Discovery of a superhard iron tetraboride superconductor.

    Science.gov (United States)

    Gou, Huiyang; Dubrovinskaia, Natalia; Bykova, Elena; Tsirlin, Alexander A; Kasinathan, Deepa; Schnelle, Walter; Richter, Asta; Merlini, Marco; Hanfland, Michael; Abakumov, Artem M; Batuk, Dmitry; Van Tendeloo, Gustaaf; Nakajima, Yoichi; Kolmogorov, Aleksey N; Dubrovinsky, Leonid

    2013-10-11

    Single crystals of novel orthorhombic (space group Pnnm) iron tetraboride FeB4 were synthesized at pressures above 8 GPa and high temperatures. Magnetic susceptibility and heat capacity measurements demonstrate bulk superconductivity below 2.9 K. The putative isotope effect on the superconducting critical temperature and the analysis of specific heat data indicate that the superconductivity in FeB4 is likely phonon mediated, which is rare for Fe-based superconductors. The discovered iron tetraboride is highly incompressible and has the nanoindentation hardness of 62(5) GPa; thus, it opens a new class of highly desirable materials combining advanced mechanical properties and superconductivity.

  5. Critical Doping for the Onset of Fermi-Surface Reconstruction by Charge-Density-Wave Order in the Cuprate Superconductor La_{2-x}Sr_{x}CuO_{4}

    Directory of Open Access Journals (Sweden)

    S. Badoux

    2016-04-01

    Full Text Available The Seebeck coefficient S of the cuprate superconductor La_{2-x}Sr_{x}CuO_{4} (LSCO was measured in magnetic fields large enough to access the normal state at low temperatures, for a range of Sr concentrations from x=0.07 to x=0.15. For x=0.11, 0.12, 0.125, and 0.13, S/T decreases upon cooling to become negative at low temperatures. The same behavior is observed in the Hall coefficient R_{H}(T. In analogy with other hole-doped cuprates at similar hole concentrations p, the negative S and R_{H} show that the Fermi surface of LSCO undergoes a reconstruction caused by the onset of charge-density-wave modulations. Such modulations have indeed been detected in LSCO by x-ray diffraction in precisely the same doping range. Our data show that in LSCO this Fermi-surface reconstruction is confined to 0.085critical doping p_{CDW}=0.15±0.005, well below the pseudogap critical doping p^{⋆}≃0.19.

  6. The Role of C-axis Polarized Phonons in High Temperature Superconductors

    International Nuclear Information System (INIS)

    Timusk, T.; Homes, C. C.; Reichardt, W.

    1995-01-01

    We report on the optical conductivity of c-axis phonons in YBa 2 Cu 3 O 7-σ as a function of doping and temperature. At room temperature the frequencies and strengths of the modes are in good agreement with results from shell models based on neutron scattering. We discuss the apical oxygen mode which becomes asymmetric in underdoped materials and argue, with Burns, that the Au mode shifts from 570 cm -1 to 610 cm -1 for the two-fold coordinated copper sites in the chain layer in oxygen depleted materials. At low temperature there is a large transfer of c-axis phonon oscillator strength from O(4) apical and O (2, 3,) plane bending modes, to a very broad at 400 cm -1

  7. Influence of pulse electric current on structure and superconducting properties of high temperature superconductor

    International Nuclear Information System (INIS)

    Rajchenko, A.I.; Flis, A.A.; Chernenko, L.I.; Kryuchkova, N.I.

    1998-01-01

    The influence of high-density pulse current treatment at room temperature on structure and superconducting properties of HTSC Y Ba 2 Cu 3 O x ceramics is studied. The structures of the samples are found to undergo appreciable changes as the density of pulse current is gradually increased from its minimum value; as a certain threshold value is attained, there occurs a melting-off of coarse grains with a partial destroying of intergrain contact areas followed by superconductivity loss. A further increase in the treatment current density results in a restoration of the superconducting properties probably due to the occurrence of aligned-with-current superconducting bridges between the melted-off grains. The superconducting transition temperature in the samples does not charge but subsequent thermal treatment causes this temperature to increase

  8. Vortex-antivortex patterns in mesoscopic superconductors

    International Nuclear Information System (INIS)

    Teniers, Gerd; Moshchalkov, V.V.; Chibotaru, L.F.; Ceulemans, Arnout

    2003-01-01

    We have studied the nucleation of superconductivity in mesoscopic structures of different shape (triangle, square and rectangle). This was made possible by using an analytical gauge transformation for the vector potential A which gives A n =0 for the normal component along the boundary line of the rectangle. As a consequence the superconductor-vacuum boundary condition reduces to the Neumann boundary condition. By solving the linearized Ginzburg-Landau equation with this boundary condition we have determined the field-temperature superconducting phase boundary and the corresponding vortex patterns. The comparison of these patterns for different structures demonstrates that the critical parameters of a superconductor can be manipulated and fine-tuned through nanostructuring

  9. Briefing on superconductor developments

    International Nuclear Information System (INIS)

    Larbalestier, D.

    1987-01-01

    In this paper, the author covers the technology of the new oxide superconductors and how they might relate to the existing superconductors. He discusses old-fashioned superconductors; the material science of superconductors; the new oxide superconductors; and the future of oxide superconductors. 13 figures, 1 table

  10. Relationship of electrical, magnetic, and mechanical properties to processing in high-temperature superconductors

    International Nuclear Information System (INIS)

    Blendell, J.E.; Chiang, C.K.; Cranmer, D.C.

    1987-01-01

    The interrelation between processing, microstructure, and properties is an important factor in understanding the behavior of ceramic materials. This type of understanding will be particularly important in the development of the new high T/sub c/ superconducting ceramic oxides of the type Ba/sub 2/YCu/sub 3/O/sub 7-x/. As an initial effort in understanding these relations, a number of properties have been measured for these superconducting ceramics and related to their microstructure and processing sequence. The Ba/sub 2/YCu/sub 3/O/sub 7-x/ ceramics were prepared by powder processing techniques, followed by dry pressing and sintering in both air and flowing oxygen at various temperatures. The sintered bodies were annealed at various temperatures and environments. Superconducting properties, such as the transition temperature and the width of the transition, were measured by both electrical conductivity and AC magnetic susceptibility; both of these properties show a strong sensitivity to annealing temperature and atmosphere. The microstructure and density were also strongly dependent on processing conditions. In this regard, compositional mapping proved to be an important technique for quantifying microstructural variations. Mechanical properties, such as elastic modulus, hardness, and fracture toughness, which will be important for the reliable use of these materials in large scale structures, were also determined

  11. High temperature superconductors as a technological discontinuity in the power cable industry

    International Nuclear Information System (INIS)

    Beales, T.P.; McCormack, J.S.

    1994-01-01

    The advent of superconductivity above 77 K represents to the power cable industry a technological discontinuity analogous to that seen in the copper telecommunications industry by the arrival of optical fibres. This phenomenon is discussed along with technical criteria and performance targets needed for high temperature superconducting wire to have an economic impact in transmission cables

  12. Energy storage system using superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Chan Joong; Kim, Ki Baek; Park, Hae Woong; Hong, Kye Won [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1995-03-01

    As a result of continuous efforts, high critical current density exceeding 104 A/cm{sup 2} at 77K and strong levitation capacity has been achieved in Y-Ba-Cu-O superconductor which is fabricated by melting technique. Various applications using the levitation properties of high-Tc superconductor is expected to come true in near future. Especially, by utilizing the levitation force between a permanent magnet and the superconductor, a flywheel system which store electrical energy as mechanical energy can be designed. (Author) 11 refs., 7 figs., 5 tabs.

  13. Advantageous grain boundaries in iron pnictide superconductors.

    Science.gov (United States)

    Katase, Takayoshi; Ishimaru, Yoshihiro; Tsukamoto, Akira; Hiramatsu, Hidenori; Kamiya, Toshio; Tanabe, Keiichi; Hosono, Hideo

    2011-08-02

    High critical temperature superconductors have zero power consumption and could be used to produce ideal electric power lines. The principal obstacle in fabricating superconducting wires and tapes is grain boundaries-the misalignment of crystalline orientations at grain boundaries, which is unavoidable for polycrystals, largely deteriorates critical current density. Here we report that high critical temperature iron pnictide superconductors have advantages over cuprates with respect to these grain boundary issues. The transport properties through well-defined bicrystal grain boundary junctions with various misorientation angles (θ(GB)) were systematically investigated for cobalt-doped BaFe(2)As(2) (BaFe(2)As(2):Co) epitaxial films fabricated on bicrystal substrates. The critical current density through bicrystal grain boundary (J(c)(BGB)) remained high (>1 MA cm(-2)) and nearly constant up to a critical angle θ(c) of ∼9°, which is substantially larger than the θ(c) of ∼5° for YBa(2)Cu(3)O(7-δ). Even at θ(GB)>θ(c), the decay of J(c)(BGB) was much slower than that of YBa(2)Cu(3)O(7-δ).

  14. Theoretical study on the two-band degenerate-gaps superconductors: Application to SrPt3P

    Science.gov (United States)

    Huang, Hai; Hou, Li-Chao; Zhao, Bin-Peng

    2016-09-01

    We study the magnetic properties of two-band degenerate-gaps superconductors with two-band isotropic Ginzburg-Landau theory. The exact solutions of upper critical field and London penetration depth are obtained, and the calculations reproduce the experimental data of the recently observed superconducting crystal SrPt3P in a broad temperature range. It directly underlies that SrPt3P is a multi-band superconductor with equal gaps in two Fermi surface sheets.

  15. Devices comprised of discrete high-temperature superconductor chips disposed on a surface

    Energy Technology Data Exchange (ETDEWEB)

    Van Duzer, T.

    1993-06-01

    A structure exposed to electromagnetic radiation is described, comprising: a metal surface and a plurality of discrete elements, each element including an insulating substrate and a high-temperature superconducting material substantially covering a face of said substrate, a portion of said metal surface being substantially covered with said elements with said superconducting material thereof adjacent to and in electrical contact with said metal surface, thereby reducing ohmic losses on exposure of said structure to said electromagnetic radiation.

  16. The improved damping of superconductor bearings for 35 kWh superconductor flywheel energy storage system

    International Nuclear Information System (INIS)

    Han, Y.H.; Park, B.J.; Jung, S.Y.; Han, S.C.; Lee, W.R.; Bae, Y.C.

    2013-01-01

    Highlights: ► We made a 35 kWh superconductor flywheel energy storage system. ► The damping coefficient of the superconductor bearing was increased over 3000 N s/m. ► The source of damping was discussed. -- Abstract: A 35 kWh Superconductor Flywheel Energy Storage system (SFES) using hybrid bearing sets, which is composed of a high temperature superconductor (HTS) bearing and an active magnet damper (AMD), has been developed at KEPCO Research Institute (KEPRI). Damping is a source of energy loss but necessary for the stability of the flywheel system. We found that the damping of HTS bearings can be improved by thermal insulating bolts, which play a role of passive type external damper. To investigate the source of the increased damping, damping coefficients were measured with HTS bearings using insulating bolts made of three kinds of polymer materials. The damping coefficient was raised over 3000 N s/m in the case of PEEK bolts. The value was almost a quarter of the AMD. In this study, thermoelastic and Coulomb friction damping mechanisms are discussed. The main damping mechanism was the thermoelastic damping of the bolts themselves. And interfacial gap between the insulating bolt and metal chamber, which increased during the cooling process, was considered to be the cause of the anisotropic damping coefficients. Finally, the effects of the HTS bearings on the first critical speed are shown

  17. Surface texturing of superconductors by controlled oxygen pressure

    Science.gov (United States)

    Chen, N.; Goretta, K.C.; Dorris, S.E.

    1999-01-05

    A method of manufacture of a textured layer of a high temperature superconductor on a substrate is disclosed. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO{sub 2} atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO{sub 2} atmosphere to cause solidification of the molten superconductor in a textured surface layer. 8 figs.

  18. Charge transfer at the high-temperature superconductor/liquid electrolyte interface

    CERN Document Server

    Le Poul, N

    2001-01-01

    (even in the air) and, consequently, precautions were taken in the low-temperature experiments to avoid contact of the electrode with any water. Studies were also conducted using HTSC electrodes coated by an electropolymerized film of polypyrrole. For the reaction of simple electroactive species at the coated surface, a smooth variation of R sub c sub t and C sub d sub l was observed around T sub c by a.c. impedance analysis (this is taken to indicate that results of similar experiments performed with the uncoated electrode are unaffected by surface corrosion). Polymers covalently modified with electroactive groups (e.g. ferrocene) have also been deposited on the TI,Pb sub 1 sub 2 sub 2 sub 3 electrode, with the aim of increasing the number of electron acceptor/donor species at the electrode, relative to a solution study, and thus favour the transfer of paired electrons. Two such polymers have been studied at low temperatures. Cyclic voltammetry with a TI,Pb sub 1 sub 2 sub 2 sub 3 electrode coated with a fil...

  19. Measuring internal friction at sonic and ultrasonic frequencies in high temperature superconductors

    International Nuclear Information System (INIS)

    Anderson, A.R.; Russell, G.J.

    1996-01-01

    Internal friction measurements provide a sensitive means for probing some structural properties of materials. Defect relaxation processes and phase changes are frequently reflected in internal friction measurements as a function of temperature. Relaxation processes associated with oxygen content have been observed in YBCO and BSCCO (2212). By measuring the internal friction at different frequencies activation energies associated with relaxation processes can be determined. Structural changes are temperature dependent and independent of frequency. The composite bar technique developed employs a piezoelectric quartz bar (with lengths of 2 cm or 3 cm and resonant frequencies of approximately 85 kHz or 120 kHz) with a resonant bar of HTSC attached to one end. The quartz bar is suspended at its nodal points and the system excited electrically using a regenerative feedback system. The composite bar method can also be used at low kilohertz frequencies by attaching the HTSC specimen used in the previous technique to the end of a much longer (e g 30 cm) fused silica rod which has very low damping. The resulting composite bar can be excited electrostatically or electromagnetically at frequencies below 10 kHz. The internal friction can be measured by scanning through the resonant frequency and measuring the bandwidth or by observing the decay of free oscillation in the bar. The advantage of using the two composite bar techniques is that the measurements can be made on the same specimen at different frequencies

  20. The external field dependence of the BCS critical temperature

    DEFF Research Database (Denmark)

    Frank, Rupert L.; Hainzl, Christian; Seiringer, Robert

    2016-01-01

    We consider the Bardeen-Cooper-Schrieffer free energy functional for particles interacting via a two-body potential on a microscopic scale and in the presence of weak external fields varying on a macroscopic scale. We study the influence of the external fields on the critical temperature. We show...... that in the limit where the ratio between the microscopic and macroscopic scale tends to zero, the next to leading order of the critical temperature is determined by the lowest eigenvalue of the linearization of the Ginzburg-Landau equation....

  1. A structural-based microscopic theory on high-temperature cuprate superconductors

    International Nuclear Information System (INIS)

    Wong, K.W.; Ching, W.Y.

    2004-01-01

    Based entirely on the cuprate structure, a microscopic theory for high-temperature superconductivity is proposed. This theory produces quantitative fits to the normal phase properties such as Hall effect, resistivity, thermoelectric power, etc. It also reveals the existence of a pseudo-gap structure that has nodes along the diagonals of the basal plane. In the superconducting phase, an inverse parabolic dependences of T c on hole density is a natural consequence. The optimum T c value derived from the corresponding intrinsic hole density obtained from electronic structure agrees with the value obtained experimentally. This theory can also explain the observation of a strong spin fluctuation near T c in the YBa 2 Cu 3 O 7 (YBCO) and the absence of such in the Bi 2 Sr 2 CaCu 2 O 8 (BiSCCO) system

  2. Recent progress in the melt-process technique of high-temperature superconductors

    CERN Document Server

    Ikuta, H; Mizutani, U

    1999-01-01

    Recently, the performance of high-temperature super conductors prepared by the melt-process technique has been greatly improved. This progress was accomplished by the addition of Ag into the starting materials of the Sm-Ba-CuO $9 system, which prevents the formation of severe macro-sized cracks in the finished samples. The magnetic flux density trapped by this material has now reached 9 T at 25 K, which is comparable to the magnetic flux density produced by $9 ordinary superconducting magnets. The amount of magnetic flux density that can be trapped by the sample is limited by the mechanical strength rather than superconducting properties of the material. The increase in the mechanical $9 strength of the material is important both for further improvement of the material properties and for ensuring reliability of the material in practical applications. (20 refs).

  3. Spiral spin state in high-temperature copper-oxide superconductors: evidence from neutron scattering measurements.

    Science.gov (United States)

    Lindgård, Per-Anker

    2005-11-18

    An effective spiral spin phase ground state provides a new paradigm for the high-temperature superconducting cuprates. It accounts for the recent neutron scattering observations of spin excitations regarding both the energy dispersion and the intensities, including the "universal" rotation by 45 degrees around the resonance energy . The intensity has a 2D character even in a single twin crystal. The value of is related to the nesting properties of the Fermi surface. The excitations above are shown to be due to in-plane spin fluctuations, a testable difference from the stripe model. The form of the exchange interaction function reveals the effects of the Fermi surface, and the unique shape predicts large quantum spin fluctuations in the ground state.

  4. A structural-based microscopic theory on high-temperature cuprate superconductors

    Science.gov (United States)

    Wong, K. W.; Ching, W. Y.

    2004-11-01

    Based entirely on the cuprate structure, a microscopic theory for high-temperature superconductivity is proposed. This theory produces quantitative fits to the normal phase properties such as Hall effect, resistivity, thermoelectric power, etc. It also reveals the existence of a pseudo-gap structure that has nodes along the diagonals of the basal plane. In the superconducting phase, an inverse parabolic dependences of Tc on hole density is a natural consequence. The optimum Tc value derived from the corresponding intrinsic hole density obtained from electronic structure agrees with the value obtained experimentally. This theory can also explain the observation of a strong spin fluctuation near Tc in the YBa 2Cu 3O 7 (YBCO) and the absence of such in the Bi 2Sr 2CaCu 2O 8 (BiSCCO) system.

  5. Shift of the superconducting critical parameters due to correlated disorder

    International Nuclear Information System (INIS)

    Gitterman, M.; Shapiro, I.; Shapiro, B.Ya.

    2012-01-01

    Shift of the critical temperature and second critical magnetic field are calculated for a superconductor with Gaussian correlated disorder. All calculations have been performed in the framework of the stochastic Ginzburg-Landau equation. For uncorrelated disorder the macroscopic critical temperature is determined by the average of the local critical temperature across the sample, while for correlated disorder both the critical temperature and the upper critical magnetic field depend on disorder correlation length. In a nonuniform superconductor with randomly distributed local critical temperature both the macroscopic critical temperature and the upper critical magnetic field strongly depend on the characteristic correlation length ρ 0 of correlated disorder. The shift of the macroscopic critical parameters from those for non-correlated disorder, which does not exist for white noise, is obtained for small ρ 0 in the framework of the Ginzburg-Landau theory.

  6. New Crystal-Growth Methods for Producing Lattice-Matched Substrates for High-Temperature Superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Boatner, L.A.

    2008-06-24

    This effort addressed the technical problem of identifying and growing, on a commercial scale, suitable single-crystal substrates for the subsequent deposition of epitaxial thin films of high temperature semiconductors such as GaN/AlN. The lack of suitable lattice-matched substrate materials was one of the major problem areas in the development of semiconducting devices for use at elevated temperatures as well as practical opto-electronic devices based on Al- and GaN technology. Such lattice-matched substrates are necessary in order to reduce or eliminate high concentrations of defects and dislocations in GaN/AlN and related epitaxial thin films. This effort concentrated, in particular, on the growth of single crystals of ZnO for substrate applications and it built on previous ORNL experience in the chemical vapor transport growth of large single crystals of zinc oxide. This combined expertise in the substrate growth area was further complemented by the ability of G. Eres and his collaborators to deposit thin films of GaN on the subject substrates and the overall ORNL capability for characterizing the quality of such films. The research effort consisted of research on the growth of two candidate substrate materials in conjunction with concurrent research on the growth and characterization of GaN films, i.e. the effort combined bulk crystal growth capabilities in the area of substrate production at both ORNL and the industrial partner, Commercial Crystal Growth Laboratories (CCL), Naples, Florida, with the novel thin-film deposition techniques previously developed in the ORNL SSD.

  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. Effects of cold-working on pinning behaviour and critical current densities in NbTi-based superconductors

    International Nuclear Information System (INIS)

    Yamada, Y.; Murase, S.; Wada, H.; Tachikawa, K.

    1985-01-01

    The effects of cold-working on high-field pinning behaviour at 1.8 K and 4.2 K have been studied for multifilamentary NbTi, NbTiHf and NbTiTa superconductors, which were subjected to cold-working, heat treatment and cold-working, in sequence. It is found that the cold-working, either before or after heat treatment, shifts the peak in pinning force density to a higher field, while the maximum pinning force value is first increased with increasing amount of cold-working, and then decreased. This result can not be predicted by existing pinning theories, and we conclude that for pinning behaviour induced by cold-working, not only the introduction of pinning centres but also their size and spacing must be taken into account. (author)

  9. In situ observation · analytical technologies of high temperature superconductor for fusion reactor at ultra low temperature

    International Nuclear Information System (INIS)

    Kimoto, Takayoshi; Sun, Wei; Fukutomi, Katsuo; Togano, Kazumasa; Saito, Tetsuya; Hiraga, Kenji; Takeda, Toshiyuki

    1998-01-01

    An image installation program of SPARK station 20 was accomplished. It can induce continuously 2.1 MB TEM image at 5 sheet/sec until 160 sheets. An image processing (shift addition) program was developed at first in the world. The program can overlap many sheet of TEM images by shifting them to the correct position. Other image processing programs such as flatfielding and reducing noise processing were developed. High temperature lattice fringe image of superconductive oxide Bi2223 in the drift chamber can be observed at low temperature by using the above image processing programs. New type laser device for filament radiation which consists of argon ion laser was developed as the first step of development of high brightness electron gun. Bi2212 single crystal was determined by the large angle convergent beam electron diffraction. The results showed the crystal structure belonged to Bbmb. (S.Y.)

  10. Field and temperature scaling of the critical current density in commercial REBCO coated conductors

    CERN Document Server

    Senatore, Carmine; Bonura, Marco; Kulich, Miloslav; Mondonico, Giorgio

    2016-01-01

    Scaling relations describing the electromagnetic behaviour of coated conductors (CCs) greatly simplify the design of REBCO-based devices. The performance of REBCO CCs is strongly influenced by fabrication route, conductor architecture and materials, and these parameters vary from one manufacturer to the others. In the present work we have examined the critical surface for the current density, Jc(T,B,θ ), of coated conductors from six different manufacturers: American Superconductor Co. (US), Bruker HTS GmbH (Germany), Fujikura Ltd. (Japan), SuNAM Co. Ltd. (Korea), SuperOx ZAO (Russia) and SuperPower Inc. (US). Electrical transport and magnetic measurements were performed at temperatures between 4.2 K and 77 K and in magnetic field up to 19 T. Experiments were conducted at three different orientations of the field with respect to the crystallographic c-axis of the REBCO layer, θ = 0deg , 45deg and 90deg , in order to probe the angular anisotropy of Jc. In spite of the large variability of CCs performance, ...

  11. On functional integral representations satisfying the constraints in the correlation models of high-temperature superconductors

    International Nuclear Information System (INIS)

    Weller, W.

    1990-01-01

    Functional integral representations are constructed for Fermions with spin 1/2, in which the fields satisfy directly by construction the constraints (e. g., exclusion of double occupancy of a site) appearing in recent models in the theory of high-temperature superconductivity. Thus, the enforcement of the constraints by delta functions in the integration measure is avoided. Perelomov's concept of generalized coherent states is used. However, in constructing such representations, exponential functions of linear combinations of operators (which are difficult to disentangle) are avoided, as is the construction and reduction of the invariant measure. Instead, an ansatz is used for the resolution of the unity operator. This approach also provides more freedom in choosing the appropriate fields. Several new and simple representations with only few elementary fields are given. The representation already used by Wiegmann is recovered. In this case and in any other cases the integration measure is explicitly given. In all these representations, the original Fermi operators are substituted by the product of a spin independent Grassmann field and a spin dependent bosonic (complex) field in accordance with the physical idea of separation of charge and spin degrees of freedom. It is further shown how a change in the integration measure eliminates also zero occupancy (the case of the Heisenberg antiferromagnet). The absence of an explicit delta function constraint in the functional integral is reflected in a special form of the kinetic part of the action. The considered representations are compared with that of the slave boson method. (orig.)

  12. Phase relations study on the melting and crystallization regions of the Bi-2223 high temperature superconductor

    Directory of Open Access Journals (Sweden)

    Polasek Alexander

    2004-01-01

    Full Text Available The melting and solidification behavior of Bi2Sr2Ca2Cu3 O10 (Bi-2223 precursors has been studied. Nominal compositions corresponding to excess of liquid, Ca2CuO3 and CuO have been investigated. Each sample was made by packing a precursor powder into a silver crucible, in order to approximately simulate the situation found in 2223 silver-sheathed tapes. The samples were partially melted and then slow-cooled, being quenched from different temperatures and analyzed through X-ray diffraction (XRD and scanning electron microscopy (SEM/EDS. The precursors decomposed peritectically during melting, forming liquid and solid phases. Very long plates with compositions falling in the vicinity of the 2223 primary phase field formed upon slow-cooling. The 2223 phase may have been formed and the results suggest that long grains of this phase might be obtained by melting and crystallization if the exact peritectic region and the optimum processing conditions are found.

  13. Crystallographic and electrical properties of Pr substituted Gd-123 nanometre sized high temperature superconductors

    International Nuclear Information System (INIS)

    Huse, V.R.; Mote, V.D.; Shah, S.S.; Dole, B.N.; Purushotham, Y.; Dhar, S.K.

    2011-01-01

    The samples of Gd 1-x Pr x Ba 2 Cu 3 O 7-δ with compositions x = 0.0, 0.1 and 0.3 were prepared by ceramic route. The XRD study of all samples is carried out. The XRD studies of the samples prepared by ceramic route show GdPr-123 system have an orthorhombic perovskite structure. The lattice parameters, oxygen content, volume of unit cell, orthorhombic perovskite structure. The lattice parameters, oxygen content, volume of unit cell, orthorhombic distortion, hole concentration in CuO 2 plane and charge on Cu-O plane were evaluated using XRD data. It is found that the lattice parameters, volume of unit cell increase while oxygen content orthorhombic distortion, hole concentration (Psh) and average charge (p) decrease as doping percentage of Pr increases. The resistivity measurement shows the transition temperature decreases while transition width increases with increasing Pr concentration. The suppression of superconductivity may be due to reduction in hole concentration or magnetic pair breaking. We report such qualitative results of Pr substituted Gd-123 in this paper quantitatively. (author)

  14. System and method for quench and over-current protection of superconductor

    Science.gov (United States)

    Huang, Xianrui; Laskaris, Evangelos Trifon; Sivasubramaniam, Kiruba Haran; Bray, James William; Ryan, David Thomas; Fogarty, James Michael; Steinbach, Albert Eugene

    2005-05-31

    A system and method for protecting a superconductor. The system may comprise a current sensor operable to detect a current flowing through the superconductor. The system may comprise a coolant temperature sensor operable to detect the temperature of a cryogenic coolant used to cool the superconductor to a superconductive state. The control circuit is operable to estimate the superconductor temperature based on the current flow and the coolant temperature. The system may also be operable to compare the estimated superconductor temperature to at least one threshold temperature and to initiate a corrective action when the superconductor temperature exceeds the at least one threshold temperature.

  15. The reexamination of thermal expansion of ferromagnetic superconductors and the pressure differential of its superconducting transition temperature-possible application to UGe2

    International Nuclear Information System (INIS)

    Konno, Rikio; Hatayama, Nobukuni

    2011-01-01

    The temperature dependence of thermal expansion of ferromagnetic superconductors below the superconducting transition temperature T scu of a majority spin conduction band is reexamined. In the previous study [to be published in J. M. Phys. B] the volume differential of the kinetic energy of conduction electrons is constant. However, in this study the volume differential of the kinetic energy of conduction electrons is inconstant. The superconducting gap of the majority spin conduction band used in this study has a line node. It is appropriate to UGe 2 . The pressure differential of its superconducting transition temperature is also investigated. We find that the thermal expansion coefficient has the divergence at the superconducting transition temperature. The thermodynamic Grueneisen's relation is satisfied.

  16. Structural disorder and its effect on the superconducting transition temperature in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

    International Nuclear Information System (INIS)

    Su, X.; Zuo, F.; Schlueter, J.A.; Kelly, M.E.; Williams, J.M.

    1998-01-01

    In this paper, we report direct evidence of a structural transition in the organic superconductor κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br near 80 K and the effect of disorder on the superconducting transition temperature. By cooling the sample from above 80 K, the interlayer magnetoresistance displays a bumplike feature, which increases sharply with increasing cooling rate. The rapidly cooled sample has a much larger resistivity and a lower transition temperature, which decreases linearly with increasing resistivity near the transition temperature. We propose that rapid cooling quenches the sample into a disordered state. Localized moments in the disordered state reduce the superconducting transition temperature. copyright 1998 The American Physical Society

  17. Structural studies of ceramic superconductors

    International Nuclear Information System (INIS)

    Hessel Andersen, N.

    1993-12-01

    The structural and superconducting properties of high temperature superconductors have been studied experimentally and by computer simulation technique. The oxygen ordering in the CuO x basal plane of the high temperature superconductor YBa 2 Cu 3 O 6+x has been studied by Monte Carlo computer simulation based on the socalled ASYNNNI model (Asymmetric Next Nearest Neighbor Interaction model), and the formation of specific domains of the two orthorhombic ordered oxygen phases, Ortho-I and Ortho-II, as function of the oxygen stoichiometry, x, has been related to the superconducting transition temperature, T c (x), via a Minimal Model. A similar relation has been established between the temporal variation of T c (t) and structural oxygen ordering during relaxation following a quench from high temperatures. By neutron diffraction studies on single crystalline YBa 2 Cu 3 O 6.4 the presence of short range domains of the Ortho-II type structure has been established, and the degree of ordering has been found to scale with the observed T c according to the expectations from the established Minimal Model. From neutron diffraction studies on Pb 2 Sr 2 Re 1-x Cu 3 O 8 (RE=Y and Ho) the transition from non-superconducting to superconducting samples with increasing Ca-stoichiometry has been related to the change in the Cu bond valence in the superconducting CuO 2 -planes. X-ray diffraction with Euler four-circle technique and TEM (Transmission Electron Microscopy) have been used to identify structural defects in epitaxial YBa 2 Cu 3 O 6+x thin films produced on MgO (1 0 0) and SrTiO 3 (1 0 0) substrates by laser ablation. The results supply an explanation for the differences in the observed critical current densities, and may be used for optimizing the film production process. A computer-controlled gasvolumetric and a gas-mixing flow system for sample preparation of high temperature superconductors, and studies of oxygen equilibrium pressure and bulk oxygen diffusion have been

  18. The high temperature Ising model is a critical percolation model

    NARCIS (Netherlands)

    Meester, R.W.J.; Camia, F.; Balint, A.

    2010-01-01

    We define a new percolation model by generalising the FK representation of the Ising model, and show that on the triangular lattice and at high temperatures, the critical point in the new model corresponds to the Ising model. Since the new model can be viewed as Bernoulli percolation on a random

  19. Noncommutative effects of spacetime on holographic superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Ghorai, Debabrata, E-mail: debanuphy123@gmail.com [S.N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700098 (India); Gangopadhyay, Sunandan, E-mail: sunandan.gangopadhyay@gmail.com [Department of Physics, West Bengal State University, Barasat (India); Inter University Centre for Astronomy & Astrophysics, Pune (India)

    2016-07-10

    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. 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.

  1. Measurement of critical temperature as a function of field

    Science.gov (United States)

    McInturff, A. D.; Ishibashi, K.; Heard, G. D.

    The critical temperature has been measured for various magnet conductors as a function of the perpendicular applied magnetic field. The isothermal environment was provided by a variable temperature cryostat which fits into the bore of a 10 telsa solenoid. The temperature gradient across the sample volume was measured to be less than 25 millikelvins. The superconducting to normal state transition was measured resistively, using sample current densities from 0.01 to 2 A cm -2. The maximum applied magnetic field was 10 T and varied less than 0.5% in the sample volume. The critical transport current range of the samples measured from tens to thousands of amperes in the presence of a 10 T perpendicular magnetic field at 4.2 K.

  2. Temperature range for critical scaling behavior in YBCO thin films

    Science.gov (United States)

    Deak, J.; Darwin, M. J.; McElfresh, M.

    1993-11-01

    The magnetic and transport properties of thin films and single crystals of YBa 2Cu 3O 7-δ are compared. For measurements on thin films, the apparent critical scaling behavior is observed to exist over a temperature range from 87 K down to the vortex-glass transition Tg = 84.2 K at 2.5 kOE and from 83 K to Tg = 70.4 K at 50 kOe. The inflection point ( Tinf) in temperature dependent resistivity measurements R( T) coincides with the highest temperature at which current-voltage ( I-V) characteristics are found to scale. The region between Tg and Tinf shows a behavior characteristics of thermally activated flux motion, while above TinfI-V curves show ohmic behavior. No similar scaling region is observed in some single crystal results, supporting recent claims that the phase transition in some single crystals may not be critical in nature (of order greater than one).

  3. Unusual two-dimensional behavior of iron-based superconductors with low anisotropy

    Science.gov (United States)

    Kalenyuk, A. A.; Pagliero, A.; Borodianskyi, E. A.; Aswartham, S.; Wurmehl, S.; Büchner, B.; Chareev, D. A.; Kordyuk, A. A.; Krasnov, V. M.

    2017-10-01

    We study angular-dependent magnetoresistance in iron-based superconductors Ba1 -xNaxFe2As2 and FeTe1 -xSex . Both superconductors have relatively small anisotropies γ ˜2 and exhibit a three-dimensional (3D) behavior at low temperatures. However, we observe that they start to exhibit a profound two-dimensional behavior at elevated temperatures and in applied magnetic field parallel to the surface. We conclude that the unexpected two-dimensional (2D) behavior of the studied low-anisotropic superconductors is not related to layeredness of the materials, but is caused by appearance of surface superconductivity when magnetic field exceeds the upper critical field Hc 2(T ) for destruction of bulk superconductivity. We argue that the corresponding 3D-2D bulk-to-surface dimensional transition can be used for accurate determination of the upper critical field.

  4. Magnetic pinning in superconductor-ferromagnet multilayers

    International Nuclear Information System (INIS)

    Bulaevskii, L. N.; Chudnovsky, E. M.; Maley, M. P.

    2000-01-01

    We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10 6 -10 7 A/cm 2 at high temperatures (but not very close to T c ) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics

  5. Magnetic pinning in superconductor-ferromagnet multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Bulaevskii, L. N. [Department of Physics and Astronomy, CUNY Lehman College 250 Bedford Park Boulevard West, Bronx, New York 10468-1589 (United States); Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Chudnovsky, E. M. [Department of Physics and Astronomy, CUNY Lehman College, 250 Bedford Park Boulevard West, Bronx, New York 10468-1589 (United States); Maley, M. P. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2000-05-01

    We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10{sup 6}-10{sup 7} A/cm{sup 2} at high temperatures (but not very close to T{sub c}) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics.

  6. Electron energy-loss spectroscopy on n-type doped high-temperature superconductors and related systems

    International Nuclear Information System (INIS)

    Alexander, M.

    1992-08-01

    Electron-enery loss spectroscopy measurements on n-type doped high temperature superconductors, their undoped parent compounds, Y-doped Bi 2 Sr 2 CaCu 2 O 8 and some rare earth oxides are presented. The undoped parent compounds Ln 2 CuO 4 (Ln = Pr, Nd, Sm) are charge transfer insulators with a charge transfer energy gap of 1.4 eV. The conduction band lies in the CuO 2 plane and has mainly Cu3d x 2 -y 2 character. O2p x,y states are slightly hybridized with this band. Upon partially substituting the trivalent Ln ions by tetravalent Ce or Th and monovalent F for the O ions, electron doping of the CuO 2 plane occurs with the electrons having mainly Cu3d character. A rigid band behaviour is proposed by several band structure calculations could be ruled out, as well as the occurence of so called 'mid-gap' states appearing inside the band gap between the valence and conduction bands. The position of the Fermi level was found to be at the bottom of the conduction bands. No measurable influence of the reduction process, necessary to obtain superconductivity, was detected in the unoccupied density of states. Characteristics shifts of the measured oxygen and copper edges were correlated with crossing the metal-insulator transition. These shifts are most probably caused by an improved screening capacity of the free charge carriers. A similar effect was also observed in Y-doped Bi 2 Sr 2 CaCu 2 O 8 . Thus, it was possible to show that the disappearance of the valence band hole states upon doping did not occur in a rigid-band-like manner. The low energy excitations in Nd 1.85 Ce 0.15 CuO 4-δ showed a plasmon like excitation at about 1 eV as well as a reduction and an energy shift of the charge transfer excitation. The dispersion of this plasmon excitation was determined. (orig.)

  7. Anomalous transport phenomena in px+i py superconductors

    Science.gov (United States)

    Li, Songci; Andreev, A. V.; Spivak, B. Z.

    2015-09-01

    Spontaneous breaking of time-reversal symmetry in superconductors with the px+i py symmetry of the order parameter allows for a class of effects which are analogous to the anomalous Hall effect in ferromagnets. These effects exist below the critical temperature, T

  8. Spotlighting quantum critical points via quantum correlations at finite temperatures

    International Nuclear Information System (INIS)

    Werlang, T.; Ribeiro, G. A. P.; Rigolin, Gustavo

    2011-01-01

    We extend the program initiated by T. Werlang et al. [Phys. Rev. Lett. 105, 095702 (2010)] in several directions. Firstly, we investigate how useful quantum correlations, such as entanglement and quantum discord, are in the detection of critical points of quantum phase transitions when the system is at finite temperatures. For that purpose we study several thermalized spin models in the thermodynamic limit, namely, the XXZ model, the XY model, and the Ising model, all of which with an external magnetic field. We compare the ability of quantum discord, entanglement, and some thermodynamic quantities to spotlight the quantum critical points for several different temperatures. Secondly, for some models we go beyond nearest neighbors and also study the behavior of entanglement and quantum discord for second nearest neighbors around the critical point at finite temperature. Finally, we furnish a more quantitative description of how good all these quantities are in spotlighting critical points of quantum phase transitions at finite T, bridging the gap between experimental data and those theoretical descriptions solely based on the unattainable absolute zero assumption.

  9. Developing a high-temperature superconducting bulk magnet for the maglev train of the future

    Science.gov (United States)

    Fujimoto, Hiroyuki

    1998-10-01

    The major applications of high-temperature superconductors have mostly been confined to products in the form of wires and thin films. However, recent developments show that rare-earth REBa2Cu3O7-x and light rare-earth LREBa2Cu3O7-3 superconductors prepared by melt processes have a high critical-current density at 77 K and high magnetic fields. These superconductors will promote the application of bulk high-temperature superconductors in high magnetic fields; the superconducting bulk magnet for the Maglev train is one possible application.

  10. Attempts to test an alternative electrodynamic theory of superconductors by low-temperature scanning tunneling and atomic force microscopy

    Science.gov (United States)

    Peronio, Angelo; Giessibl, Franz J.

    2016-09-01

    We perform an experiment to test between two theories of the electrodynamics of superconductors: the standard London theory and an alternative proposed by J. E. Hirsch [Phys. Rev. B 69, 214515 (2004), 10.1103/PhysRevB.69.214515]. The two alternatives give different predictions with respect to the screening of an electric field by a superconductor, and we try to detect this effect using atomic force microscopy on a niobium sample. We also perform the reverse experiment, where we demonstrate a superconductive tip mounted on a qPlus force sensor. Due to limited accuracy, we are able neither to prove nor to disprove Hirsch's hypothesis. Within our accuracy of 0.17 N/m, the superconductive transition does not alter the atomic-scale interaction between tip and sample.

  11. Epitaxial growth of high temperature superconductors by cathodic sputtering I: thin films of YBaCuO

    International Nuclear Information System (INIS)

    Navacerrada, M.A.; Sefrioui, Z.; Arias, D.; Varela, M.; Loos, G.; Leon, C.; Lucia, M.L.; Santamaria, J.; Sanchez-Quesada, F.

    1998-01-01

    High quality c-oriented YBa 2 Cu 3 O 7 -x thin films have been grown on SrTiO 3 (100)substrates by high pressure sputtering in pure oxygen atmosphere. Low angle X-ray diffraction and atomic force microscopy were performed on films less than 250 angstrom thick showing a plenitude better than one unit cell. Moreover, the structural characterization by means of X ray φ scans showed that growth is epitaxial. The critical temperature has been measured by different ways and was always in the range 89.5-90.5K. the resistance transition is sharper than 1K and the mutual inductance response always shows magnetic losses peaks narrower than 0.3K. Critical current densities are in excess of 10''''6 angstrom/cm''''2 at 77K. (Author) 8 refs

  12. Applications of high-temperature superconductors in power technology[8470 High-current and high-voltage technology: power systems; power transmission lines and cables;

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R [Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439 (United States)

    2003-11-01

    Since the discovery of the first high-temperature superconductors (HTSs) in the late 1980s, many materials and families of materials have been discovered that exhibit superconductivity at temperatures well above 20 K. Of these, several families of HTSs have been developed for use in electrical power applications. Demonstration of devices such as motors, generators, transmission lines, transformers, fault-current limiters, and flywheels in which HTSs and bulk HTSs have been used has proceeded to ever larger scales. First-generation wire, made from bismuth-based copper oxides, was used in many demonstrations. The rapid development of second-generation wire, made by depositing thin films of yttrium-based copper oxide on metallic substrates, is expected to further accelerate commercial applications. Bulk HTSs, in which large single-grain crystals are used as basic magnetic components, have also been developed and have potential for electrical power applications.

  13. Impact of thickness on microscopic and macroscopic properties of Fe-Te-Se superconductor thin films

    Directory of Open Access Journals (Sweden)

    N. Zhang

    2015-04-01

    Full Text Available A series of iron based Fe-Te-Se superconductor thin films depositing on 0.7wt% Nb-doped SrTiO3 at substrate temperatures in the 250°C -450°C range by pulsed laser ablation of a constituents well defined precursor FeTe0.55Se0.55 target sample. We study the possible growth mechanism and its influence on the superconductor properties. Experimental results indicate the superconductive and non-superconductive properties are modulated only by the thickness of the thin films through the temperature range. The films appear as superconductor whenever the thickness is above a critical value ∼30nm and comes to be non-superconductor below this value. Relative ratios of Fe to (Te+Se in the films retained Fe/(Te+Se1 for non-superconductor no matter what the film growth temperature was. The effect of film growth temperature takes only the role of modulating the ratio of Te/Se and improving crystallinity of the systems. According to the experimental results we propose a sandglass film growth mechanism in which the interfacial effect evokes to form a Fe rich area at the interface and Se or Te starts off a consecutive filling up process of chalcogenide elements defect sides, the process is significant before the film thickness reaches at ∼30nm.

  14. Superconductors in the High School Classroom

    Science.gov (United States)

    Lincoln, James

    2017-01-01

    In this article, we discuss the behavior of high-temperature superconductors and how to demonstrate them safely and effectively in the high school or introductory physics classroom. Included here is a discussion of the most relevant physics topics that can be demonstrated, some safety tips, and a bit of the history of superconductors. In an effort…

  15. Electric field effect in superconductor-ferroelectric structures

    Science.gov (United States)

    Lemanov, V. V.

    1995-01-01

    Electric field effect (the E-effect) in superconductors has been studied since 1960 when Glover and Sherill published their results on a shift of the critical temperature T(sub c) about 0.1 mK in Sn and In thin films under the action Off the field E=300 kV/cm. Stadler was the first to study the effect or spontaneous polarization of ferroelectric substrate on the electric properties of superconductors. He observed that the reversal of polarization of TGS substrate under action of external electric field in Sn-TGS structures induced the T(sub c) shift in Sn about 1.3 mK. Since in this case the effect is determined not by the electric field but by the spontaneous polarization, we may call this effect the P-effect. High-T(sub c) superconductors opened the new possibilities to study the E- and P-effects due to low charge carrier density, as compared to conventional superconductors, and to anomalously small coherence length. Experiments in this field began in many laboratories but a breakthrough was made where a shift in T(sub c) by 50 mK was observed in YBCO thin films. Much higher effects were observed in subsequent studies. The first experiments on the P-effect in high-T(sub c) superconductors were reported elsewhere. In this report we shall give a short description of study on the P-effect in high-T(sub c) superconductors.

  16. Hybrid molecule/superconductor assemblies

    International Nuclear Information System (INIS)

    McDevitt, J.T.; Haupt, S.G.; Riley, D.R.; Zhao, J.; Zhou, J.P., Jones, C.

    1993-01-01

    The fabrication of electronic devices from molecular materials has attracted much attention recently. Schottky diodes, molecular transistors, metal-insulator-semiconductor diodes, MIS field effect transistors and light emitting diodes have all been prepared utilizing such substances. The active elements in these devices have been constructed by depositing the molecular phase onto the surface of a metal, semiconductor or insulating substrate. With the recent discovery of high temperature superconductivity, new opportunities now exist for the study of molecule/superconductor interactions as well as for the construction of novel hybrid molecule/superconductor devices. In this paper, methods for preparing the initial two composite molecule/semiconductor devices will be reported. Consequently, light sensors based on dye-coated superconductor junctions as well as molecular switches fashioned from conductive polymer coated superconductor junctions as well as molecular switches fashioned from conductive polymer coated superconductor microbridges will be discussed. Moreover, molecule/superconductor energy and electron transfer phenomena will be illustrated also for the first time

  17. Superconductor Dynamics

    CERN Document Server

    Gömöry, F.

    2014-07-17

    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 ...

  18. Superconductors, analysis and applications, with special reference to the utilisation of bulk (Re)BCO materials

    Energy Technology Data Exchange (ETDEWEB)

    Coombs, T.A., E-mail: tac1000@cam.ac.u [University of Cambridge, Department of Engineering, Trumpington Street, Cambridge CB2 1PZ (United Kingdom)

    2010-11-01

    The Electrical Power and Energy Conversion (EPEC) superconductivity group at Cambridge University has been working on the application of superconductivity to large scale devices. This work is taking place over a range of areas which cover FCLs, motors and generators, SMES, accelerator magnets and MRI. The research is underpinned by advanced modelling techniques using both pure Critical State models and E-J models to analyse the behaviour of the superconductors. As part of the device design we are concentrating on the analysis of AC losses in complicated geometries such as are found in motor windings and the magnetisation of bulk superconductors to enable their full potential to be realised. We are interested in the full range of high-temperature superconductors and have measured and predicted the performance of YBCO, MgB{sub 2} and BSCCO at a range of temperatures and in wire, tape and bulk forms. This paper concentrates on recent work which includes: modelling of coils using formulations based on H and A. A critical state model for the analysis of coils in SMES; crossed field effects in bulk superconductors; a magnetic model together with experimental results which explain and describe the method of flux pumping whereby a bulk superconductor can be magnetised to a high flux density using a repeatedly applied field of low flux density and finally a new configuration for MRI magnets

  19. Superconductor cable

    Science.gov (United States)

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

    1988-01-01

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

  20. Excitations in exotic superconductors

    International Nuclear Information System (INIS)

    Hayden, S.

    1999-01-01

    Neutron scattering has played an important role in unravelling the mysteries of superconductivity. Studies of ordinary or conventional superconductors - materials such as aluminium and lead that lose their electrical resistance when cooled below a certain temperature - have focused on vibrations in the lattice structure of the crystal. In these cases magnetic excitations due to the collective motion of electron spins in the crystal are not particularly important and, moreover, are difficult to see. In contrast, magnetic excitations are thought to be important in the newer, exotic or unconventional superconductors such as heavy fermions and cuprates. Two independent groups working at the Institut Laue-Langevin (ILL) in Grenoble, France, and at the Japan Atomic Energy Research Institute (JAERI) in Tokai have recently observed a new magnetic excitation in the superconducting state of the heavy fermion compound uranium-palladium-aluminium, UPd 2 Al 3 , (Phys. Rev. Lett.1998 81 4244; 1998 80 5417). A similar excitation has been observed in yttrium barium copper oxide (YBa 2 Cu 3 O 6.93 ), a high-temperature superconductor. The results may hold clues about the nature of certain types of unconventional superconductivity. In this article the author describes these latest results. (UK)

  1. p-wave holographic superconductors with Weyl corrections

    Science.gov (United States)

    Momeni, D.; Majd, N.; Myrzakulov, R.

    2012-03-01

    We study the (3+1)-dimensional p-wave holographic superconductors with Weyl corrections both numerically and analytically. We describe numerically the behavior of the critical temperature Tc with respect to charge density ρ in a limited range of Weyl coupling parameter γ and we find in general that the condensation becomes harder with the increase of the parameter γ. In the strong-coupling limit of Yang-Mills theory, we show that the minimum value of Tc obtained from the analytical approach is in good agreement with the numerical results, and finally show how we got remarkably a similar result for the critical exponent \\frac{1}{2} of the chemical potential μ and the order parameterlangJ1xrang with the numerical curves of the superconductors.

  2. High T{sub c} superconductors give new impulse to magnetic levitation

    Energy Technology Data Exchange (ETDEWEB)

    Jung, V. [Forschungszentrum Karlsruhe GmbH Technik und Umwelt (Germany). Inst. fuer Festkoerperphysik

    2001-05-01

    When the new YBaCuO superconductors were developed about 18 years ago, the critical maximum current density, at a magnetic field of 1.0 T and a temperature of 77 K, was still quite low. Roughly 8 years ago, it became possible to raise the critical current density to 106 A/cm{sup 2} at 1.0 T and 77 K. This opened up possibilities for application in self-stabilizing superconducting magnetic bearings and also in maglev trains capable of movement along a track. An important criterion in the high current-carrying capacity of YBaCuO superconductors is the excellent texture of melt-textured YBaCuO moldings, which must also be free of microcracks. Narrow distributions of the a-,b-, and c-axis orientations, in the absence of isotropic fractions, allow almost the entire mirror flux in the superconductor to be induced by permanent magnets. (orig.)

  3. Normal modes of Bi-Sr-Ca-Cu-O high-temperature superconductors: layer-by-layer approach

    International Nuclear Information System (INIS)

    Bush, A.A.; Kitaev, Yu.E.; Limonov, M.F.; Markov, Yu.F.; Novikov, A.A.; Evarestov, R.A.

    1992-01-01

    The non-superconducting Bi 1-x (Sr 1-y Ca y ) x O 1.5-x/2 compounds and the Bi 2 Sr 2 Ca n-1 Cu n O 2n+4 (n=1.2) superconductors have been synthesized and investigated. Using the method of band representations of space groups the complete group symmetry analysis of the normal vibrational modes has been made. Comparing the Raman spectra of the row of bismuth compounds and using the results of the group theory analysis all the strong RSS-lines have been attributed. (orig.)

  4. Percolation effect in thick film superconductors

    International Nuclear Information System (INIS)

    Sali, R.; Harsanyi, G.

    1994-01-01

    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 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 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

  5. Temperature variation of criticality of thermal reactor lattices

    International Nuclear Information System (INIS)

    Velner, S.; Rothenstein, W.

    1975-01-01

    Departures from the asymptotic mode in the experimental setup have been examined in detail for two assemblies, one exponential, the other critical. It was found that the flux shape differed noticeably from the asymptotic mode in the core region especially for the exponential assemblies. On the other hand the departure from the fundamental mode has very little effect on the change of material buckling with temperature. Results of the calculations and their comparison with experiment are presented. The variation of material buckling with temperature is the same for ENDF/B-II and for ENDF/B-IV data, both for asymptotic reactor theory and for the buckling values derived from the flux calculated with the SN code. The results obtained with ENDF/B-IV data for both lattices are shown. In the small exponential assembly the results derived from S-4 calculations are compared with experiment. In the critical assembly the ratio of U-238 to U-235 fissions delta 28 and the relative conversion ratio - the ratio of U-238 captures to U-235 fissions in the lattice compared with the same quantity in a thermal column - are also shown. In both cases the experimental change of buckling with temperature is smaller than the calculated change. (B.G.)

  6. Physical-chemical and technological aspects of the preparation of think layers of the high temperature superconductors Bi-Sr-Ca-Cu-O by method of metal organic vapour phase epitaxy

    International Nuclear Information System (INIS)

    Stejskal, J.; Nevriva, M.; Leitner, J.

    1995-01-01

    The method of metal organic vapour phase epitaxy (MO VPE) was used for preparation of think layers of the high temperature superconductors Bi-Sr-Ca-Cu-O. The suitable chemical precursors (β-diketonates) on the literature data and of the own thermodynamic calculations were selected. The optimal thermodynamic data and thermodynamic stability of the prepared samples were determined

  7. Thermoelectric refrigerator having improved temperature stabilization means

    International Nuclear Information System (INIS)

    Falco, C.M.

    1982-01-01

    A control system for thermoelectric refrigerators is disclosed. The thermoelectric refrigerator includes at least one thermoelectric element that undergoes a first order change at a predetermined critical temperature. The element functions as a thermoelectric refrigerator element above the critical temperature, but discontinuously ceases to function as a thermoelectric refrigerator element below the critical temperature. One example of such an arrangement includes thermoelectric refrigerator elements which are superconductors. The transition temperature of one of the superconductor elements is selected as the temperature control point of the refrigerator. When the refrigerator attempts to cool below the point, the metals become superconductors losing their ability to perform as a thermoelectric refrigerator. An extremely accurate, first-order control is realized

  8. Homes’ law in holographic superconductor with Q-lattices

    International Nuclear Information System (INIS)

    Niu, Chao; Kim, Keun-Young

    2016-01-01

    Homes’ law, ρ s =Cσ DC T c , is an empirical law satisfied by various superconductors with a material independent universal constant C, where ρ s is the superfluid density at zero temperature, T c is the critical temperature, and σ DC is the electric DC conductivity in the normal state close to T c . We study Homes’ law in holographic superconductor with Q-lattices and find that Homes’ law is realized for some parameter regime in insulating phase near the metal-insulator transition boundary, where momentum relaxation is strong. In computing the superfluid density, we employ two methods: one is related to the infinite DC conductivity and the other is related to the magnetic penetration depth. With finite momentum relaxation both yield the same results, while without momentum relaxation only the latter gives the superfluid density correctly because the former has a spurious contribution from the infinite DC conductivity due to translation invariance.

  9. Effect of combined addition of nano-SiC and nano-Ho2O3 on the in-field critical current density of MgB2 superconductor

    Science.gov (United States)

    Varghese, Neson; Vinod, K.; Chattopadhyay, M. K.; Roy, S. B.; Syamaprasad, U.

    2010-01-01

    MgB2 superconducting samples added with nano-Ho2O3 (n-Ho2O3) and/or nano-SiC (n-SiC) have been prepared by an in situ solid state reaction method to investigate and compare the combined and individual effects of n-SiC and n-Ho2O3 on a crystal structure, critical temperature (TC), and critical current density (JC) of MgB2. All the doped samples exhibit significantly enhanced in-field JC and the codoped sample with 2.5 wt % n-Ho2O3 and 5 wt % n-SiC gives the best performance in in-field JC, and the enhancement is around 100 times and 2 times greater than the undoped and monodoped n-SiC samples, respectively, at 5 K and 8 T. For the n-SiC added sample, lattice distortions due to C substitution on the B site and the formation of reacted phase Mg2Si as flux pinners cause enhanced JC up to the maximum field studied (8 T). While in the n-Ho2O3 added sample, a reacted phase HoB4 having a strong magnetic moment forms, without any substitution at the Mg or B site, which acts as a flux pinner in order to enhance the in-field JC. Accordingly the best codoped sample exhibits these combined benefits of n-SiC and n-Ho2O3 in MgB2 superconductor.

  10. Effects of oxygen content on the pinning energy and critical current in the granular (Hg, Re)-1223 superconductors

    International Nuclear Information System (INIS)

    Passos, C.A.C.; Orlando, M.T.D.; Fernandes, A.A.R.; Oliveira, F.D.C.; Simonetti, D.S.L.; Fardin, J.F.; Belich, H.; Ferreira, M.M.

    2005-01-01

    Hg 0.82 Re 0.18 Ba 2 Ca 2 Cu 3 O 8+d polycrystalline samples, with different oxygen content, were investigated by ac resistance measurements under different applied magnetic field (up to 3 A/m) and critical current measurements. The intergrain and intragrain regions have shown an improvement in the pinning energy and critical current density, as considering the precursor preparation with 10% of O 2 and 90% of Ar (optimal doped). In addition, the samples presented S-I-S junctions type as considering Ambegaokar-Baratoff theory

  11. Oriented grained Y-Ba-Cu-O superconductors having high critical currents and method for producing same

    International Nuclear Information System (INIS)

    Salama, K.; Selvamanickam, V.

    1990-01-01

    This patent describes a process for preparing a superconducting metal oxide complex. It comprises: mixing solid compounds containing Y, Ba, Cu and O in amounts appropriate to yield the formula Y 1 Ba 2 Cu 3 O 6 + δ wherein δ has a number value of from about 0.1 to about 1.0; heating the solid compounds in air to a temperature between about 920 degrees C. to about 960 degrees C. for a time sufficient to react the compounds in the solid state quenching the solid state reaction product to ambient temperature in air; compacting the mixture into a solid mass; sintering the solid mass; heating the solid mass; rapidly cooling the mass to a temperature between about 1,020 degrees to about 1,040 degrees C. and then cooling the mass to a steady temperature between about 20 degrees C. to 40 degrees C. below its melting point at a rate of approximately 1 degrees C./hour; maintaining the mass at the steady temperature for a time sufficient for the entire mass to resolidify; cooling the resolidified mass in air from the steady temperature to approximately 550 degrees C. to 650 degrees C. at the rate of approximately 60 degrees C. per hour; additionally cooling the resolidified mass to about 380 degrees C. to about 420 degrees C. at the rate of approximately 30 degrees C. per hour in air; and annealing the resolidified mass

  12. Transient compounds of high alkaline earth metals with custom-made organic ligands as potential precursors for the gas phase separator of high temperature ceramic superconductors

    International Nuclear Information System (INIS)

    Teske, M.

    1993-01-01

    The aim of this work was the representation of new transient custom-made metal/organic compounds of the high alkaline earth metals Ca, Sr and Ba as potential precursors for the gas phase separation (chemical vapour deposition, CVD) of high temperature ceramic superconductors. There is a report on the synthesis and comprehensive characterisation of representatives of the class of compounds of substituted metallocenes and the B diketone compounds of these metals. Some selected compounds were examined as regards their suitability for CVD. The main task was the examination of the effect of structural and electronic parameters of ligands on the properties of the compounds, where the volatility was to the fore. (orig./MM) [de

  13. Field-induced interplanar magnetic correlations in the high-temperature superconductor La1.88Sr0.12CuO4

    DEFF Research Database (Denmark)

    Rømer, A. T.; Jensen, P.; Jacobsen, H.

    2015-01-01

    We present neutron-scattering studies of the interplanar magnetic correlations in the high-temperature superconductor La1.88Sr0.12CuO4 (Tc=27 K). The correlations are studied both in a magnetic field applied perpendicular to the CuO2 planes, and in zero field under different cooling conditions. We...... find that the effect of the magnetic field is to increase the magnetic scattering signal at all values of the out-of-plane wave vector L, indicating an overall increase of the magnetic moments. In addition, weak correlations between the copper oxide planes develop in the presence of a magnetic field....... This effect is not taken into account in previous reports on the field effect of magnetic scattering, since usually only L≈0 is probed. Interestingly, the results of quench-cooling the sample are similar to those obtained by applying a magnetic field. Finally, a small variation of the incommensurate peak...

  14. Tunneling spectroscopy on grain boundary junctions in electron-doped high-temperature superconductors; Tunnelspektroskopie an Korngrenzenkontakten aus elektronendotierten Hochtemperatur-Supraleitern

    Energy Technology Data Exchange (ETDEWEB)

    Welter, B.

    2007-12-07

    Some methods are developed anf presented, by means of which from experimental tunnel spectra, especially on symmetric SIS contacts, informations about the properties of electrodes and tunnel barriers can be obtained. Especially a procedure for the numerical unfolding of symmetric SIS spectra is proposed. Furthermore a series of models is summarized, which can explain the linear background conductivity observed in many spectra on high-temperature superconductors. The results of resistance measurements on film bridges are presented. Especially different methods for the determination of H{sub c2}(T) respectively H{sub c2}(0) are presented and applied to the experimental data. Finally the results of the tunnel-spectroscopy measurements are shown.

  15. Theory of s-wave superconductor containing impurities with retarded interaction with quasiparticles

    International Nuclear Information System (INIS)

    K V Grigorishin

    2014-01-01

    We propose a perturbation theory and diagram technique for a disordered metal when scattering of quasiparticles by nonmagnetic impurities is caused with a retarded interaction. The perturbation theory generalizes a case of elastic scattering in a disordered metal. Eliashberg equations for s-wave superconductivity are generalized for such a disordered superconductor. Anderson's theorem is found to be violated in the sense that embedding of the impurities into an s-wave superconductor increases its critical temperature. We show that the amplification of superconducting properties is a result of nonelastic effects in a scattering by the impurities. (paper)

  16. Superconductors for superconducting magnets

    Science.gov (United States)

    Larbalestier, David

    2011-03-01

    Even in 1913 Kamerlingh Onnes envisioned the use of superconductors to create powerful magnetic fields well beyond the capability provided by cooling normal metals with liquid helium. Only some ``bad places'' in his Hg and Pb wires seemed to impede his first attempts at this dream, one that he imagined would be resolved in a few weeks of effort. In fact, of course, resolution required another 50 years and development of both a true understanding of the difference between type I and type II superconductors and the discovery of compounds such as Nb 3 Sn that could remain superconducting to fields as high as 30 T. And then indeed, starting in the 1960s, Onnes's dreams were comfortably surpassed. In the last 45 years virtually all superconducting magnets have been made from just two Nb-base materials, Nb-Ti and Nb 3 Sn. Now it seems that a new generation of magnets based on cuprate high temperature superconductors with fields well above 30 T are possible using Bi-Sr-Ca-Cu-O and the RE-Ba-Cu-O compounds. We hope that a first demonstration of this possibility will be an all-superconducting 32 T magnet with RE-Ba-Cu-O insert that we are building for NHMFL users. The magnet application potential of this new generation of superconducting conductors will be discussed.

  17. A fluctuating state and the critical behavior of the depinning transition in driven vortex matter in superconductors

    Science.gov (United States)

    Shaw, Gorky; Mandal, Pabitra; Banerjee, S. S.; Niazi, A.; Rastogi, A. K.; Sood, A. K.; Tulapurkar, A.; Ramakrishnan, S.; Grover, A. K.

    2012-06-01

    A status report is presented on explorations in 2H-NbS2 which have revealed a new protocol that generates vortex states corresponding to two limiting ends of critical current density (Jlc(H) and Jhc (H)) for a given vortex density deep in the mixed state. An ordered vortex array set in motion with transport current I (Ilc < I < Ihc) explores its other option of non-moving jammed state of higher end Ihc while steadily enhancing the driving force. Attempts to further unjam the re-pinned state unmask (i) a moving fluctuating state and (ii) the diverging (life) times along with an underlying critical behaviour at the threshold limit of de-pinning the disordered-jammed state, from both below as well as above Ihc.

  18. Visualizing the mechanism that determines the critical current density in polycrystalline superconductors using time-dependent Ginzburg-Landau theory.

    OpenAIRE

    Carty, G. J.; Hampshire, D. P.

    2008-01-01

    In polycrystalline superconducting materials optimized for high critical current density (JC) in high magnetic fields, the mechanism that determines JC has long remained uncertain because of the complicated manner in which the fluxon-fluxon and fluxon-microstructure forces combine. In this work, the time-dependent Ginzburg-Landau equations are used to produce visualizations of fluxons at JC that show the disorder in the pinned part of the flux-line lattice and the motion of those fluxons alon...

  19. Visualizing the mechanism that determines the critical current density in polycrystalline superconductors using time-dependent Ginzburg-Landau theory

    Science.gov (United States)

    Carty, George J.; Hampshire, Damian P.

    2008-05-01

    In polycrystalline superconducting materials optimized for high critical current density (JC) in high magnetic fields, the mechanism that determines JC has long remained uncertain because of the complicated manner in which the fluxon-fluxon and fluxon-microstructure forces combine. In this work, the time-dependent Ginzburg-Landau equations are used to produce visualizations of fluxons at JC that show the disorder in the pinned part of the flux-line lattice and the motion of those fluxons along grain boundaries that cause dissipation. Calculated values of JC are consistent with experimental data.

  20. Superconductors in the high school classroom

    Science.gov (United States)

    Lincoln, James

    2017-11-01

    In this article, we discuss the behavior of high-temperature superconductors and how to demonstrate them safely and effectively in the high school or introductory physics classroom. Included here is a discussion of the most relevant physics topics that can be demonstrated, some safety tips, and a bit of the history of superconductors. In an effort to include first-year physics students in the world of modern physics, a topic as engaging as superconductivity should not be missed. It is an opportunity to inspire students to study physics through the myriad of possible applications that high temperature superconductors hold for the future.