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Sample records for superconducting transition point

  1. Superconductivity in transition metals.

    Science.gov (United States)

    Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  2. Beginning point of metal to insulator transition for Bi-2223 superconducting matrix doped with Eu nanoparticles

    International Nuclear Information System (INIS)

    Yildirim, G.

    2013-01-01

    Highlights: •Standard measurements such as bulk density, ρ-T, J ct , XRD, SEM and EDX examinations for characterization of the samples. •Role of Eu inclusions on the microstructural, electrical and superconducting properties of Bi-2223 phase. •Determination of metal to insulator transition due to Eu impurities in the Bi-2223 superconducting matrix. •From the Eu content level of x = 0.5 onwards, destruction of the superconducting phases. •Constant retrogression of the microstructural and superconducting properties with the Eu individuals. -- Abstract: This comprehensive study examines the change of the microstructural, electrical and superconducting properties of the Eu doped Bi 1.8 Pb 0.4 Eu x Sr 2 Ca 2.2 Cu 3.0 O y ceramic cuprates (with x ⩽ 0.7) produced by the conventional solid state reaction method at the constant annealing temperature of 840 °C for 24 h with the aid of the standard characterization measurements such as bulk density, dc resistivity (ρ-T), transport critical current density (J c ), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron dispersive X-ray (EDX) examinations. For the full characterization of the pure and Eu doped Bi-2223 samples, the degree of granularity (from the bulk density and porosity measurements); the room temperature resistivity, onset–offset critical transition temperature, variation of transition temperature, hole carrier concentration, spin-gap opening temperature and thermodynamic fluctuations (from the dc resistivity experiments); the texturing, crystal structure, crystallite size, phase purity and cell parameters (from the XRD investigations); the variation of the flux pinning centers and the boundary weak-links between the superconducting grains (from the critical current density values); the crystallinity, specimen surface morphology, grain connectivity between the superconducting grains and grain size distribution (from the SEM examinations), the elemental compositions and

  3. Sensing with Superconducting Point Contacts

    Directory of Open Access Journals (Sweden)

    Argo Nurbawono

    2012-05-01

    Full Text Available Superconducting point contacts have been used for measuring magnetic polarizations, identifying magnetic impurities, electronic structures, and even the vibrational modes of small molecules. Due to intrinsically small energy scale in the subgap structures of the supercurrent determined by the size of the superconducting energy gap, superconductors provide ultrahigh sensitivities for high resolution spectroscopies. The so-called Andreev reflection process between normal metal and superconductor carries complex and rich information which can be utilized as powerful sensor when fully exploited. In this review, we would discuss recent experimental and theoretical developments in the supercurrent transport through superconducting point contacts and their relevance to sensing applications, and we would highlight their current issues and potentials. A true utilization of the method based on Andreev reflection analysis opens up possibilities for a new class of ultrasensitive sensors.

  4. Superconducting Metallic Glass Transition-Edge-Sensors

    Science.gov (United States)

    Hays, Charles C. (Inventor)

    2013-01-01

    A superconducting metallic glass transition-edge sensor (MGTES) and a method for fabricating the MGTES are provided. A single-layer superconducting amorphous metal alloy is deposited on a substrate. The single-layer superconducting amorphous metal alloy is an absorber for the MGTES and is electrically connected to a circuit configured for readout and biasing to sense electromagnetic radiation.

  5. Tetracritical point and current circulations in superconducting state

    International Nuclear Information System (INIS)

    Belyavskij, V.I.; Kopaev, Yu.V.; Smirnov, M.Yu.

    2005-01-01

    Phase diagram reflecting the key peculiar features of the standard diagram of the cuprate superconductors was studied in terms of the Ginzburg-Landau phenomenology near the tetracritical point resulting from the competition of superconducting and dielectric channels of pairing. Two-component parameter of order the relative phase of which is associated with antiferromagnetic dielectric ordering corresponds to the superconducting pairing at repulsion. In case of slight doping the dielectric order coexists with superconductivity below the temperature of superconducting phase transition and manifests itself as a slight pseudoslit above the mentioned temperature. A segment of pseudoslit region adjacent to the superconducting state corresponds to the matured fluctuations of the order parameter in the form of quasi-stationary states of noncoherent superconducting pairs and may be interpreted as a region of a strong pseudoslit. At increase of doping one observes a phase transition from the coexistence region and the orbital antiferromagnetism to the conventional superconducting state covering the region of matured fluctuations of the order parameter in the form of quasi-stationary states of the noncorrelated orbital circulation currents adjacent to the line of phase transition [ru

  6. Controlling superconductivity by tunable quantum critical points.

    Science.gov (United States)

    Seo, S; Park, E; Bauer, E D; Ronning, F; Kim, J N; Shim, J-H; Thompson, J D; Park, Tuson

    2015-03-04

    The heavy fermion compound CeRhIn5 is a rare example where a quantum critical point, hidden by a dome of superconductivity, has been explicitly revealed and found to have a local nature. The lack of additional examples of local types of quantum critical points associated with superconductivity, however, has made it difficult to unravel the role of quantum fluctuations in forming Cooper pairs. Here, we show the precise control of superconductivity by tunable quantum critical points in CeRhIn5. Slight tin-substitution for indium in CeRhIn5 shifts its antiferromagnetic quantum critical point from 2.3 GPa to 1.3 GPa and induces a residual impurity scattering 300 times larger than that of pure CeRhIn5, which should be sufficient to preclude superconductivity. Nevertheless, superconductivity occurs at the quantum critical point of the tin-doped metal. These results underline that fluctuations from the antiferromagnetic quantum criticality promote unconventional superconductivity in CeRhIn5.

  7. Superconducting phase transition in STM tips

    Energy Technology Data Exchange (ETDEWEB)

    Eltschka, Matthias; Jaeck, Berthold; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R. [Max Planck Institute for Solid State Research, Stuttgart (Germany); Kern, Klaus [Max Planck Institute for Solid State Research, Stuttgart (Germany); Ecole Polytechnique Federale de Lausanne (Switzerland)

    2015-07-01

    The superconducting properties of systems with dimensions comparable to the London penetration depth considerably differ from macroscopic systems. We have studied the superconducting phase transition of vanadium STM tips in external magnetic fields. Employing Maki's theory we extract the superconducting parameters such as the gap or the Zeeman splitting from differential conductance spectra. While the Zeeman splitting follows the theoretical description of a system with s=1/2 and g=2, the superconducting gaps as well as the critical fields depend on the specific tip. For a better understanding of the experimental results, we solve a one dimensional Usadel equation modeling the superconducting tip as a cone with the opening angle α in an external magnetic field. We find that only a small region at the apex of the tip is superconducting in high magnetic fields and that the order of the phase transition is directly determined by α. Further, the spectral broadening increases with α indicating an intrinsic broadening mechanism due to the conical shape of the tip. Comparing these calculations to our experimental results reveals the order of the superconducting phase transition of the STM tips.

  8. Graphene-based superconducting quantum point contacts

    International Nuclear Information System (INIS)

    Moghaddam, A.G.; Zareyan, M.

    2007-01-01

    We investigate the Josephson effect in the graphene nanoribbons of length L smaller than the superconducting coherence length and an arbitrary width W. We find that in contrast to an ordinary superconducting quantum point contact (SQPC), the critical supercurrent I c is not quantized for the nanoribbons with smooth and armchair edges. For a low concentration of the carriers, I c decreases monotonically with lowering W/L and tends to a constant minimum for a narrow nanoribbon with W c is zero for the smooth edges but eΔ 0 /ℎ for the armchair edges. At higher concentrations of the carriers this monotonic variation acquires a series of peaks. Further analysis of the current-phase relation and the Josephson coupling strength I c R N in terms of W/L and the concentration of carriers revels significant differences with those of an ordinary SQPC. On the other hand for a zigzag nanoribbon, we find that, similar to an ordinary SQPC, I c is quantized but to the half-integer values (n+1/2)4eΔ 0 /ℎ. (orig.)

  9. Geometrical Dynamics in a Transitioning Superconducting Sphere

    Directory of Open Access Journals (Sweden)

    Claycomb J. R.

    2006-10-01

    Full Text Available Recent theoretical works have concentrated on calculating the Casimir effect in curved spacetime. In this paper we outline the forward problem of metrical variation due to the Casimir effect for spherical geometries. We consider a scalar quantum field inside a hollow superconducting sphere. Metric equations are developed describing the evolution of the scalar curvature after the sphere transitions to the normal state.

  10. High transition temperature superconducting integrated circuit

    International Nuclear Information System (INIS)

    DiIorio, M.S.

    1985-01-01

    This thesis describes the design and fabrication of the first superconducting integrated circuit capable of operating at over 10K. The primary component of the circuit is a dc SQUID (Superconducting QUantum Interference Device) which is extremely sensitive to magnetic fields. The dc SQUID consists of two superconductor-normal metal-superconductor (SNS) Josephson microbridges that are fabricated using a novel step-edge process which permits the use of high transition temperature superconductors. By utilizing electron-beam lithography in conjunction with ion-beam etching, very small microbridges can be produced. Such microbridges lead to high performance dc SQUIDs with products of the critical current and normal resistance reaching 1 mV at 4.2 K. These SQUIDs have been extensively characterized, and exhibit excellent electrical characteristics over a wide temperature range. In order to couple electrical signals into the SQUID in a practical fashion, a planar input coil was integrated for efficient coupling. A process was developed to incorporate the technologically important high transition temperature superconducting materials, Nb-Sn and Nb-Ge, using integrated circuit techniques. The primary obstacles were presented by the metallurgical idiosyncrasies of the various materials, such as the need to deposit the superconductors at elevated temperatures, 800-900 0 C, in order to achieve a high transition temperature

  11. Vortex dynamics in superconducting transition edge sensors

    Science.gov (United States)

    Ezaki, S.; Maehata, K.; Iyomoto, N.; Asano, T.; Shinozaki, B.

    2018-02-01

    The temperature dependence of the electrical resistance (R-T) and the current-voltage (I-V) characteristics has been measured and analyzed in a 40 nm thick Ti thin film, which is used as a transition edge sensor (TES). The analyses of the I-V characteristics with the vortex-antivortex pair dissociation model indicate the possible existence of the Berezinskii-Kosterlitz-Thouless (BKT) transition in two-dimensional superconducting Ti thin films. We investigated the noise due to the vortices' flow in TESs. The values of the current noise spectral density in the TESs were estimated by employing the vortex dynamics caused by the BKT transition in the Ti thin films. The estimated values of the current noise spectral density induced by the vortices' flow were in respectable agreement with the values of excess noise experimentally observed in the TESs with Ti/Au bilayer.

  12. Superconductivity Series in Transition Metal Dichalcogenides by Ionic Gating

    NARCIS (Netherlands)

    Shi, Wu; Ye, Jianting; Zhang, Yijin; Suzuki, Ryuji; Yoshida, Masaro; Miyazaki, Jun; Inoue, Naoko; Saito, Yu; Iwasa, Yoshihiro

    2015-01-01

    Functionalities of two-dimensional (2D) crystals based on semiconducting transition metal dichalcogenides (TMDs) have now stemmed from simple field effect transistors (FETs) to a variety of electronic and opto-valleytronic devices, and even to superconductivity. Among them, superconductivity is the

  13. Longitudinal Proximity Effect Superconducting Transition-Edge Sensor

    Data.gov (United States)

    National Aeronautics and Space Administration — Superconducting Transition-Edge Sensors (TESs) hold the highest energy resolving power of any nondispersive spectrometer.   They are used for imaging spectroscopy...

  14. Unexpected Nonlinear Effects in Superconducting Transition-Edge Sensors

    Science.gov (United States)

    Sadleir, John

    2016-01-01

    When a normal metal transitions into the superconducting state the DC resistance drops from a finite value to zero over some finite transition width in temperature, current, and magnetic field. Superconducting transition-edge sensors (TESs) operate within this transition region and uses resistive changes to measure deposited thermal energy. This resistive transition is not perfectly smooth and a wide range of TES designs and materials show sub-structure in the resistive transition (as seen in smooth nonmonotonic behavior, jump discontinuities, and hysteresis in the devices current-voltage relation and derivatives of the resistance with respect to temperature, bias current, and magnetic field). TES technology has advanced to the point where for many applications this structure is the limiting factor in performance and optimization consists of finding operating points away from these structures. For example, operating at or near this structure can lead to nonlinearity in the detectors response and gain scale, limit the spectral range of the detector by limiting the usable resistive range, and degrade energy resolution. The origin of much of this substructure is unknown. This presentation investigates a number of possible sources in turn. First we model the TES as a superconducting weak-link and solve for the characteristic differential equations current and voltage time dependence. We find:(1) measured DC biased current-voltage relationship is the time-average of a much higher frequency limit cycle solution.(2) We calculate the fundamental frequency and estimate the power radiated from the TES treating the bias leads as an antennae.(3) The solution for a set of circuit parameters becomes multivalued leading to current transitions between levels.(4)The circuit parameters can change the measure resistance and mask the true critical current. As a consequence the TES resistance surface is not just a function of temperature, current, and magnetic field but is also a

  15. Search for Superconducting Energy Gap in UPt3 by Point-Contact Spectroscopy

    International Nuclear Information System (INIS)

    Gouchi, Jun; Sumiyama, Akihiko; Yamaguchi, Akira; Motoyama, Gaku; Kimura, Noriaki; Yamamoto, Etsuji; Haga, Yoshinori; Ōnuki, Yoshichika

    2015-01-01

    We have investigated the differential resistance of the point contacts between heavy-fermion superconductor UPt 3 and a normal metal Pt, which were fabricated using a commercial piezo-electric actuator, and retried the observation of the energy gap of UPt 3 . A V-shaped dip is observed in both normal and superconducting states and disappeared around T K ∼ 20 K, suggesting that it is related to the Kondo effect. Below the superconducting transition temperature, a shallow double-minimum structure, which indicates the energy gap, has been observed for the contacts on the faces perpendicular to the a-, b- and c-axes of UPt 3

  16. From superconductivity near a quantum phase transition to superconducting graphite

    Directory of Open Access Journals (Sweden)

    S. S. Saxena

    2006-09-01

    Full Text Available   The collapse of antiferromagnetic order as a function of some quantum tuning parameter such as carrier density or hydrostatic pressure is often accompanied by a region of superconductivity. The corresponding phenomenon in the potentially simpler case of itinerant-electron ferromagnetism, however, remains more illusive. In this paper we consider the reasons why this may be so and summaries evidence suggesting that the obstacles to observing the phenomenon are apparently overcome in a few metallic ferromagnets. A new twist to the problem presented by the recent discoveries in ferroelectric symmetric systems and new graphite intercalate superconductors will also be discussed.

  17. Detection of Resistive Transitions in LHC Superconducting Components

    CERN Document Server

    Denz, R

    2001-01-01

    The LHC has entered the construction phase. It will incorporate a large number of superconducting components like magnets, current leads and busbars. All these components require protection means in case of a transition from the superconducting to the resistive state, the so-called quench. Key elements in the protection system are electronic quench detectors, which have to be able to identify a quench in any state of the powering cycle of the accelerator. According to the different properties and characteristics of the superconducting elements and circuits, a set of quench detectors adapted to their specific tasks has been developed.

  18. Detection of Resistive Transitions in LHC Superconducting Components

    OpenAIRE

    Denz, R; Rodríguez-Mateos, F

    2001-01-01

    The LHC has entered the construction phase. It will incorporate a large number of superconducting components like magnets, current leads and busbars. All these components require protection means in case of a transition from the superconducting to the resistive state, the so-called quench. Key elements in the protection system are electronic quench detectors, which have to be able to identify a quench in any state of the powering cycle of the accelerator. According to the different properties...

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

    Energy Technology Data Exchange (ETDEWEB)

    Levy, F; Huxley, A [CEA, SPSMS, DRFMC, F-38054 Grenoble, (France); Levy, F; Sheikin, I [CNRS, GHMFL, F-38042 Grenoble, (France); Huxley, A [Univ Edinburgh, Scottish Univ Phys Alliance, Sch Phys, Edinburgh EH9 3JZ, Midlothian, (United Kingdom)

    2007-07-01

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

  20. Probing multiband superconductivity by point-contact spectroscopy

    International Nuclear Information System (INIS)

    Daghero, D; Gonnelli, R S

    2010-01-01

    Point-contact spectroscopy was originally developed for the determination of the electron-phonon spectral function in normal metals. However, in the past 20 years it has become an important tool in the investigation of superconductors. As a matter of fact, point contacts between a normal metal and a superconductor can provide information on the amplitude and symmetry of the energy gap that, in the superconducting state, opens up at the Fermi level. In this paper we review the experimental and theoretical aspects of point-contact spectroscopy in superconductors, and we give an experimental survey of the most recent applications of this technique to anisotropic and multiband superconductors. (topical review)

  1. Concurrence of superconductivity and structure transition in Weyl semimetal TaP under pressure

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yufeng; Zhou, Yonghui; Guo, Zhaopeng; Han, Fei; Chen, Xuliang; Lu, Pengchao; Wang, Xuefei; An, Chao; Zhou, Ying; Xing, Jie; Du, Guan; Zhu, Xiyu; Yang, Huan; Sun, Jian; Yang, Zhaorong; Yang, Wenge; Mao, Ho-Kwang; Zhang, Yuheng; Wen, Hai-Hu

    2017-12-01

    Weyl semimetal defines a material with three-dimensional Dirac cones, which appear in pair due to the breaking of spatial inversion or time reversal symmetry. Superconductivity is the state of quantum condensation of paired electrons. Turning a Weyl semimetal into superconducting state is very important in having some unprecedented discoveries. In this work, by doing resistive measurements on a recently recognized Weyl semimetal TaP under pressures up to about 100 GPa, we show the concurrence of superconductivity and a structure transition at about 70 GPa. It is found that the superconductivity becomes more pronounced when decreasing pressure and retains when the pressure is completely released. High-pressure x-ray diffraction measurements also confirm the structure phase transition from I41md to P-6m2 at about 70 GPa. More importantly, ab-initial calculations reveal that the P-6m2 phase is a new Weyl semimetal phase and has only one set of Weyl points at the same energy level. Our discovery of superconductivity in TaP by high pressure will stimulate investigations on superconductivity and Majorana fermions in Weyl semimetals.

  2. Topological defect densities in type-I superconducting phase transitions

    International Nuclear Information System (INIS)

    Paramos, J.; Bertolami, O.; Girard, T.A.; Valko, P.

    2003-01-01

    We examine the consequences of a cubic term added to the mean-field potential of Ginzburg-Landau theory to describe first-order superconducting phase transitions. Constraints on its existence are obtained from experiment, which are used to assess its impact on topological defect creation. We find no fundamental changes in either the Kibble-Zurek or Hindmarsh-Rajantie predictions

  3. Cryogenic particle detectors with superconducting phase transition thermometers

    International Nuclear Information System (INIS)

    Ferger, P.; Colling, P.; Bucci, C.; Nucciotti, A.; Buehler, M.; Cooper, S.; Feilitzsch, F. v.; Forster, G.; Gabutti, A.; Hoehne, J.; Igalson, J.; Kellner, E.; Loidl, M.; Meier, O.; Nagel, U.; Proebst, F.; Rulofs, A.; Schanda, U.; Seidel, W.; Sisti, M.; Stodolsky, L.; Stolovich, A.; Zerle, L.

    1996-01-01

    A tungsten superconducting phase transition thermometer on a 32 g sapphire crystal has given an energy resolution of 100 eV (FWHM) for 1.5 keV X-rays, increasing to 440 eV at 14 keV. A possibility to obtain similar resolution in much larger crystals by using Al films as phonon collectors is presented. (orig.)

  4. Phase transition from nuclear matter to color superconducting quark matter

    Energy Technology Data Exchange (ETDEWEB)

    Bentz, W. E-mail: bentz@keyaki.cc.u-tokai.ac.jp; Horikawa, T.; Ishii, N.; Thomas, A.W

    2003-06-02

    We construct the nuclear and quark matter equations of state at zero temperature in an effective quark theory (the Nambu-Jona-Lasinio model), and discuss the phase transition between them. The nuclear matter equation of state is based on the quark-diquark description of the single nucleon, while the quark matter equation of state includes the effects of scalar diquark condensation (color superconductivity). The effect of diquark condensation on the phase transition is discussed in detail.

  5. Interplay of structural transition and superconductivity in cuprates

    International Nuclear Information System (INIS)

    Ghosh, Haranath; Mitra, Manidipa; Behera, S.N.; Ghatak, S.K.

    1997-01-01

    The presence of lattice distortion is known to suppress the superconducting (SC) transition in the cuprates. It is now accepted that electron correlation plays a dominant role in shaping the properties of these undoped and doped systems. Furthermore, since the Fermi level in these systems lies in a degenerate band of Cu : d and O : p orbitals the structural transition can be modeled as a band Jahn-Teller effect. We study the coexistence of superconductivity and band Jahn-Teller (J-T) distortion, taking into account the electron correlation within the slave boson formalism. It is shown that with increasing dopant concentration (δ), the structural transition temperature (T s ) remains constant up to a certain value and then vanishes, while the SC transition temperature (T c ) increases to a maximum value. The highest value of T c corresponds to that value of δ where T s vanishes. Besides with increasing lattice distortion superconductivity is suppressed. These findings are in qualitative agreement with the experimental results. (author)

  6. New developments on transition radiation detectors using superconducting granules

    International Nuclear Information System (INIS)

    Yuan, L.C.L.

    1977-01-01

    By raising slightly either the temperature or the magnetic field to above that of the critical temperature or the critical magnetic field, the type I superconducting granules would still remain in the superconducting state which becomes a metastable state and is called the superheated superconducting state. If a relativistic charged particle incident on such a granule which is located in a colloidal suspension has imported to it an energy that is above the threshold energy (for state flipping) of the granule then it would flip to the normal state. The threshold energy of a granule is a function of the square of its radius, whereas the energy loss of a charged particle due to ionization is linearly proportional to the radius. The size of the granule can be pre-determined to be such that its threshold energy is slightly above the ionization loss of a relativistic charged particle. Then the traversal of the charged particle through such a granule would not affect the superconducting state of the granule unless a transition x-ray radiation is emitted at the surface of the granule by the traversing particle and the x-ray transition radiation is immediately absorbed either in total or partially by the metallic granule causing it to flip to the normal state. The total intensity of the x-ray transition radiation is linearly proportional to the Lorentz factor γ of the traversing particle, and the number of granules flipped would also be a measure of γ. Three methods for detecting the flipping of granules from the superconducting state to the normal state are described. They include the frequency measuring method, the SQUID method, and the pulse method with low noise amplifier system

  7. Pb induces superconductivity in Bi2Se3 analyzed by point contact spectroscopy

    OpenAIRE

    Arevalo-López, P.; López-Romero, R. E.; Escudero, R.

    2015-01-01

    Some topological insulators become superconducting when doped with Cu and Pd. Superconductivity in a non-superconductor may be induced by proximity effect: i.e. Contacting a non-superconductor with a superconductor. The superconducting macroscopic wave function will induce electronic pairing into the normal compound. In the simplest topological insulator, Bi$_2$Se$_3$, superconductivity may be induced with Pb. We studied with point contact junctions formed by contacting Bi$_2$Se$_3$ crystals ...

  8. Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions.

    Science.gov (United States)

    Weng, Z F; Smidman, M; Jiao, L; Lu, Xin; Yuan, H Q

    2016-09-01

    Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.

  9. Signatures of topological phase transitions in mesoscopic superconducting rings

    International Nuclear Information System (INIS)

    Pientka, Falko; Romito, Alessandro; Duckheim, Mathias; Oppen, Felix von; Oreg, Yuval

    2013-01-01

    We investigate Josephson currents in mesoscopic rings with a weak link which are in or near a topological superconducting phase. As a paradigmatic example, we consider the Kitaev model of a spinless p-wave superconductor in one dimension, emphasizing how this model emerges from more realistic settings based on semiconductor nanowires. We show that the flux periodicity of the Josephson current provides signatures of the topological phase transition and the emergence of Majorana fermions (MF) situated on both sides of the weak link even when fermion parity is not a good quantum number. In large rings, the MF hybridize only across the weak link. In this case, the Josephson current is h/e periodic in the flux threading the loop when fermion parity is a good quantum number but reverts to the more conventional h/2e periodicity in the presence of fermion-parity changing relaxation processes. In mesoscopic rings, the MF also hybridize through their overlap in the interior of the superconducting ring. We find that in the topological superconducting phase, this gives rise to an h/e-periodic contribution even when fermion parity is not conserved and that this contribution exhibits a peak near the topological phase transition. This signature of the topological phase transition is robust to the effects of disorder. As a byproduct, we find that close to the topological phase transition, disorder drives the system deeper into the topological phase. This is in stark contrast to the known behavior far from the phase transition, where disorder tends to suppress the topological phase. (paper)

  10. Localized excitations in superconducting point contacts: probing the Andreev doublet

    International Nuclear Information System (INIS)

    Bretheau, L.

    2013-01-01

    The Josephson effect describes the coherent coupling between superconductors and the resulting supercurrent. Microscopically, it arises from the existence of discrete quasiparticle states, localized at the weak link, the Andreev bound states. They come in doublets in each conduction channel of the weak link, with energies symmetric about the Fermi energy and opposite supercurrents. Each Andreev doublet gives rise to four states: the ground state |-> and the excited state |+>, with even parity, and the excited odd states |↑> and |↓>. Is it possible to address and control Andreev doublets? This thesis describes two sets of experiments designed to answer this question using the most basic Josephson element, a one-atom contact between two superconducting electrodes. In a first experiment, we have observed and characterized the excited odd states |↑> and |↓>. As expected for a spin-degenerate system, they do not carry supercurrent. In this experiment the excitation was uncontrolled and resulted from trapping of spurious quasiparticles. We have measured the lifetime of the odd states: under some condition, it is found to exceed 100 μs. The second experiment is a photon-absorption spectroscopy of the Andreev doublet. It was performed by using a Josephson junction as an integrated on-chip microwave emitter and detector. The observed Andreev transitions correspond to excitation from the ground state |->to the excited even state |+>, and are well accounted for by our quantum model. This result opens the way to coherent manipulation of this two level system. The direct observation of the excited Andreev state, either by quasiparticle-injection or photon-absorption, strongly supports the mesoscopic theory of the Josephson effect. It shows that in addition to the phase difference, each channel of a Josephson weak link possesses an internal fermionic degree of freedom. It could be used to code information in a novel type of superconducting qubit. (author) [fr

  11. Tricritical point of a ferromagnetic transition in UGe2

    International Nuclear Information System (INIS)

    Kabeya, N; Iijima, R; Osaki, E; Ban, S; Imura, K; Deguchi, K; Sato, N K; Aso, N; Homma, Y; Shiokawa, Y

    2010-01-01

    Thermal expansion and magnetostriction measurements of the superconducting ferromagnet UGe 2 under pressure were carried out. The temperature dependence of the thermal expansion coefficient shows a peak at the Curie temperature. When pressure is varied, the peak exhibits a maximum in the vicinity of a tricritical point (TCP), which separates the second-order phase transition from the first-order transition. From results of these measurements, we first construct the magnetic phase diagram including the TCP (P TCP ∼ 12.5 kbar). We also show that two lines characterizing the metamagnetism and the magnetic susceptibility emerge from the TCP. We argue that these magnetic properties in the vicinity of the TCP can be understood within a phenomenological frame of spin fluctuations.

  12. Studies of the Superconducting Transition in the Mo/Au-Bilayer Thin Films

    Science.gov (United States)

    Sadleir, John; Smith, Stephen; Iyomoto, naoko; Bandler, Simon; Chervenak, Jay; Brown, Ari; Brekowsky, Regis; Kilbourne, Caroline; Robinson, Ian

    2007-01-01

    At NASA Goddard, microcalorimeter arrays using superconducting transition edge sensor thermometers (TESs) are under development for high energy resolution X-ray astrophysics applications. We report on our studies of the superconducting transition in our Mo/Au-bilayer TES films including: low current measurements of the superconducting bilayer's resistance transition versus temperature on pixels with different normal metal absorber attachment designs and measured temperature scaling of the critical current and critical magnetic field.

  13. Contribution to the study of superconducting magnets using high transition temperature superconducting materials

    International Nuclear Information System (INIS)

    Lecrevisse, Thibault

    2012-01-01

    The new industrial superconductors using high critical temperature compounds offer new possibilities for superconducting magnetism. Indeed they allow higher magnetic field with the same classical cryogenics at 4.2 K on one hand, and on the other hand they also pave the way for superconducting magnets working between 10 K and 30 K. The high temperature superconductors are then needed in order to produce magnetic fields higher than 16 T (case of HTS dipole insert for Large Hadron Collider at CERN) or to increase the specific density stored in one SMES (Superconducting Magnetic Energy Storage, in the case of the SuperSMES ANR Project).Nevertheless the indisputable assets (critical temperature, critical magnetic field, mechanical stresses) brought by the use of High critical temperature superconductors like YBCO, used in superconducting magnets, require to solve some challenges. Their behavior is still badly understood, especially during the resistive transitions. To succeed in protecting these conductors we need a new reflection on protection schemes designed to avoid the thermal and mechanical damages. The answer to the question: 'Can we use those materials in the long run inside superconducting magnets?' is now inescapable.Some answers are given here. The use of the conductors is approached through various experimental studies to understand the material (electrical characterization and modeling of the critical surface) and to define the key stages of high critical temperature superconducting magnets manufacturing (work on the junctions between conductors and pancakes). This study led to the creation of two coils in order to identify the issues related to the use of YBCO tapes. A numerical thermo-electrical model of the high critical temperature superconductor has been developed and a numerical code based on the CEA software CASTEM (Finish Elements Model) allowed to study the resistive transition (or quench) behavior of those conductor and coil. The code has been

  14. Transition metal borides. Synthesis, characterization and superconducting properties

    Energy Technology Data Exchange (ETDEWEB)

    Kayhan, Mehmet

    2013-07-12

    A systematic study was done on the synthesis and superconducting properties of metal rich transition metal borides. Five different binary systems were investigated including the boride systems of niobium, tantalum, molybdenum, tungsten and rhenium. High temperature solid state methods were used in order to synthesize samples of different transition metal borides of the composition M{sub 2}B, MB, M{sub 3}B{sub 2}, MB{sub 2}, and M{sub 2}B{sub 4}. The reactions were carried out in three different furnaces with different sample containers: the electric arc (copper crucible), the high frequency induction furnace (boron nitride, tantalum or glassy carbon crucibles), and the conventional tube furnace (sealed evacuated quartz ampoules). The products obtained were characterized with X-ray powder diffractometry, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Phase analyses and crystal structure refinements using the Rietveld method and based on structure models known from literature were performed. A neutron diffraction measurement was done for W{sub 2}B{sub 4} to allow for a complete crystal structure determination, because of the presence of a heavy element like tungsten and a light element like boron that made it difficult to determine the accurate determination of the boron atom positions and occupancies from X-ray data. A new structure model for W{sub 2}B{sub 4} was proposed. Magnetic measurements in a SQUID magnetometer down to temperatures as low as 1.8 K were performed to several of the products in order to see if the transition metal borides become superconducting at low temperatures, and the results were compared with data from literature. Superconducting properties were found for the following compounds: NbB{sub 2} (T{sub C} = 3.5 K), β-MoB (T{sub C} = 2.4 K), β-WB (T{sub C} = 2.0 K), α-WB (T{sub C} = 4.3 K), W{sub 2}B{sub 4} (T{sub C} = 5.4 K), Re{sub 7}B{sub 3} (T{sub C} = 2.4 K). A relationship between the superconducting properties

  15. Transition metal borides. Synthesis, characterization and superconducting properties

    International Nuclear Information System (INIS)

    Kayhan, Mehmet

    2013-01-01

    A systematic study was done on the synthesis and superconducting properties of metal rich transition metal borides. Five different binary systems were investigated including the boride systems of niobium, tantalum, molybdenum, tungsten and rhenium. High temperature solid state methods were used in order to synthesize samples of different transition metal borides of the composition M 2 B, MB, M 3 B 2 , MB 2 , and M 2 B 4 . The reactions were carried out in three different furnaces with different sample containers: the electric arc (copper crucible), the high frequency induction furnace (boron nitride, tantalum or glassy carbon crucibles), and the conventional tube furnace (sealed evacuated quartz ampoules). The products obtained were characterized with X-ray powder diffractometry, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Phase analyses and crystal structure refinements using the Rietveld method and based on structure models known from literature were performed. A neutron diffraction measurement was done for W 2 B 4 to allow for a complete crystal structure determination, because of the presence of a heavy element like tungsten and a light element like boron that made it difficult to determine the accurate determination of the boron atom positions and occupancies from X-ray data. A new structure model for W 2 B 4 was proposed. Magnetic measurements in a SQUID magnetometer down to temperatures as low as 1.8 K were performed to several of the products in order to see if the transition metal borides become superconducting at low temperatures, and the results were compared with data from literature. Superconducting properties were found for the following compounds: NbB 2 (T C = 3.5 K), β-MoB (T C = 2.4 K), β-WB (T C = 2.0 K), α-WB (T C = 4.3 K), W 2 B 4 (T C = 5.4 K), Re 7 B 3 (T C = 2.4 K). A relationship between the superconducting properties and the compositional and structural features was discussed for metal diborides. Also it was

  16. Two-step superconducting transition in Cu-V-Si alloys

    International Nuclear Information System (INIS)

    Sharma, R.G.; Krishna, M.M.; Narlikar, A.V.

    1980-01-01

    Copper ternary alloys containing small amounts of vanadium and silicon exhibit a two-step superconducting resistive transition. The first transition occurs around 17 K, the transition temperature of β-W V 3 Si, followed by a plateau and a second transition around 10 K. The resistivity, however, does not drop to zero down to 2.5 K. Reduction of the wire diameter causes the two transitions to shift to lower temperatures. Complete superconductivity in these specimens is absent for two reasons. Firstly, the superconducting volume fraction present in these alloy-wires is below the threshold given by either the effective-medium theory or the site percolation theory. Secondly, the superconducting phase V 3 Si does not precipitate in copper matrix in a fine structure and the proximity effect does not operate strongly. Annealing causes the superconducting particles to coalesce and grow in size and suppresses the proximity effect and superconductivity further in these alloy wires. (author)

  17. Superconducting terahertz mixer using a transition-edge microbolometer

    Science.gov (United States)

    Prober, D. E.

    1993-01-01

    We present a new device concept for a mixer element for THz frequencies. This uses a superconducting transition-edge microbridge biased at the center of its superconducting transition near 4.2 K. It is fed from an antenna or waveguide structure. Power from a local oscillator and an RF signal produce a temperature and resulting resistance variation at the difference frequency. The new aspect is the use of a very short bridge in which rapid (less than 0.1 ns) outdiffusion of hot electrons occurs. This gives large intermediate frequency (IF) response. The mixer offers about 4 GHz IF bandwidth, about 80 ohm RF resistive impedance, good match to the IF amplifier, and requires only 1-20 nW of local oscillator power. The upper RF frequency is determined by antenna or waveguide properties. Predicted mixer conversion efficiency is 1/8, and predicted double-sideband receiver noise temperatures are 260 and 90 K for transition widths of 0.1 and 0.5 Tc, respectively.

  18. Splitting of the resistive transition of copper oxide superconductors: Intrinsic double superconducting transitions versus extrinsic effects

    International Nuclear Information System (INIS)

    Pomar, A.; Curras, S.R.; Veira, J.A.; Vidal, F.

    1996-01-01

    To prove the possible existence of an intrinsic double superconducting transition in the high-temperature copper oxide superconductors (HTSC), an effect recently attributed by various groups to different intrinsic properties of these materials (including unconventional wave pairing), we present in this paper high resolution data of the electrical resistivity, ρ(T), around the superconducting transition of different single crystal and polycrystal YBa 2 Cu 3 O 7-δ samples. The analysis of the temperature derivative of these ρ(T) data strongly suggests that (i) with a temperature resolution well to within 20 mK, the intrinsic resistive transition of the HTSC does not present any double transition anomaly and (ii) the double peak structure observed in dρ(T)/dT by some authors is probably an extrinsic effect (associated with stoichiometric inhomogeneities in some cases, and with experimental artifacts in other cases). copyright 1996 The American Physical Society

  19. Superconductivity

    CERN Document Server

    Poole, Charles P; Creswick, Richard J; Prozorov, Ruslan

    2014-01-01

    Superconductivity, Third Edition is an encyclopedic treatment of all aspects of the subject, from classic materials to fullerenes. Emphasis is on balanced coverage, with a comprehensive reference list and significant graphics from all areas of the published literature. Widely used theoretical approaches are explained in detail. Topics of special interest include high temperature superconductors, spectroscopy, critical states, transport properties, and tunneling. This book covers the whole field of superconductivity from both the theoretical and the experimental point of view. This third edition features extensive revisions throughout, and new chapters on second critical field and iron based superconductors.

  20. Theory of the transition temperature of superconducting amorphous transition metals

    International Nuclear Information System (INIS)

    Zwicknagel, G.

    1979-11-01

    In the present paper first the transition temperature Tsub(c) is shown to be a local quantity, which depends on the (average) short range order, and second it is demonstrated how to calculate local electronic properties in the framework of a short range order model and the transition temperature of amorphous systems based on accepted structure models of the amorphous state. In chapter I the theoretical basis of this work is presented in brief. The model used to study the role of short range order (in periodically ordered as well as in disordered system) is described in chapter II. The results of this model for the periodically ordered case are compared in chapter III with band structure calculations. In chapter IV it is shown how to establish short range order models for disordered systems and what kind of information can be obtained with respect to the electronic properties. Finally in chapter V it is discussed to what extend the interpretation of the transition temperature Tsub(c) as being determined by short range order effects can be supported by the electronic properties, which are calculated in the chapters III and IV. (orig.) [de

  1. Exceptional Points and Dynamical Phase Transitions

    Directory of Open Access Journals (Sweden)

    I. Rotter

    2010-01-01

    Full Text Available In the framework of non-Hermitian quantum physics, the relation between exceptional points,dynamical phase transitions and the counter intuitive behavior of quantum systems at high level density is considered. The theoretical results obtained for open quantum systems and proven experimentally some years ago on a microwave cavity, may explain environmentally induce deffects (including dynamical phase transitions, which have been observed in various experimental studies. They also agree(qualitatively with the experimental results reported recently in PT symmetric optical lattices.

  2. Self-consistent theory of normal-to-superconducting transition

    International Nuclear Information System (INIS)

    Radzihovsky, L.; Chicago Univ., IL

    1995-01-01

    I study the normal-to-superconducting (NS) transition within the Ginzburg-Landau (GL) model, taking into account the fluctuations in the m-component complex order parameter ψ α and the vector potential A in the arbitrary dimension d, for any m. I find that the transition is of second order and that the previous conclusion of the fluctuation-driven first-order transition is a possible artifact of the breakdown of the ε-expansion and the inaccuracy of the 1/m-expansion for physical values ε = 1, m 1. I compute the anomalous η(d, m) exponent at the NS transition, and find η(3, 1) ∼ -0.38. In the m → ∞ limit, η(d, m) becomes exact and agrees with the 1/m-expansion. Near d = 4 the theory is also in good agreement with the perturbative ε-expansion results for m > 183 and provides a sensible interpolation formula for arbitrary d and m. (orig.)

  3. Superconducting energy gap of YB6 studied by point-contact spectroscopy

    International Nuclear Information System (INIS)

    Szabo, Pavol; Kacmarcik, Jozef; Samuely, Peter; Girovsky, Jan; Gabani, Slavomir; Flachbart, Karol; Mori, Takao

    2007-01-01

    Yttrium hexaboride has the second highest critical temperature, T c ∼ 8 K, among all borides. The presented paper deals with the experimental study of its superconducting energy gap established by the method of the point-contact spectroscopy. The temperature dependence of the energy gap and the strength of the superconducting coupling is presented

  4. Calculation of the superconducting transition temperature in niobium

    International Nuclear Information System (INIS)

    Perlov, C.M.

    1982-01-01

    The author presents calculations of the superconducting transition temperature, T/sub c/, the electron-phonon coupling constant, lambda, and the spectral function, α 2 f(ω), for niobium. The author's calculations are based on an empirical pseudopotential method (EPM) band structure. Phonon linewidths are also given for longitudinal and transverse branches along different directions. The necessary electron-phonon matrix elements are evaluated using only the rigid-ion approximation by applying Green's theorem. The calculated value of T/sub c/ is 8.4 K which differs from the measured value by only 9%; the calculated lambda is 1.02. The spectral function and linewidths are compared to experimental and previous theoretical results

  5. Theory of high-T{sub C} superconductivity: transition temperature

    Energy Technology Data Exchange (ETDEWEB)

    Harshman, Dale R [Physikon Research Corporation, Lynden, WA 98264 (United States); Fiory, Anthony T [Department of Physics, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Dow, John D, E-mail: drh@physikon.net [Department of Physics, Arizona State University, Tempe, AZ 85287 (United States)

    2011-07-27

    It is demonstrated that the transition temperature (T{sub C}) of high-T{sub C} superconductors is determined by their layered crystal structure, bond lengths, valency properties of the ions, and Coulomb coupling between electronic bands in adjacent, spatially separated layers. Analysis of 31 high-T{sub C} materials (cuprates, ruthenates, ruthenocuprates, iron pnictides, organics) yields the universal relationship for optimal compounds, k{sub B}T{sub C0} ={beta}/{iota}{zeta}, where {iota} is related to the mean spacing between interacting charges in the layers, {zeta} is the distance between interacting electronic layers, {beta} is a universal constant and T{sub C0} is the optimal transition temperature (determined to within an uncertainty of {+-} 1.4 K by this relationship). Non-optimum compounds, in which sample degradation is evident, e.g. by broadened superconducting transitions and diminished Meissner fractions, typically exhibit reduced T{sub C} < T{sub C0}. It is shown that T{sub C0} may be obtained from an average of the Coulomb interaction forces between the two layers.

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

    Science.gov (United States)

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

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

  7. Superconductivity

    International Nuclear Information System (INIS)

    Narlikar, A.V.

    1993-01-01

    Amongst the numerous scientific discoveries that the 20th century has to its credit, superconductivity stands out as an exceptional example of having retained its original dynamism and excitement even for more than 80 years after its discovery. It has proved itself to be a rich field by continually offering frontal challenges in both research and applications. Indeed, one finds that a majority of internationally renowned condensed matter theorists, at some point of their career, have found excitement in working in this important area. Superconductivity presents a unique example of having fetched Nobel awards as many as four times to date, and yet, interestingly enough, the field still remains open for new insights and discoveries which could undeniably be of immense technological value. 1 fig

  8. Superconductivity

    International Nuclear Information System (INIS)

    Taylor, A.W.B.; Noakes, G.R.

    1981-01-01

    This book is an elementray introduction into superconductivity. The topics are the superconducting state, the magnetic properties of superconductors, type I superconductors, type II superconductors and a chapter on the superconductivity theory. (WL)

  9. Effect of thermal phonons on the superconducting transition temperature

    International Nuclear Information System (INIS)

    Leavens, C.R.; Talbot, E.

    1983-01-01

    There is no consensus in the literature on whether or not thermal phonons depress the superconducting transition temperature T/sub c/. In this paper it is shown by accurate numerical solution of the real-frequency Eliashberg equations for the pairing self-energy phi and renormalization function Z that thermal phonons in the kernel for phi raise T/sub c/ but those in Z lower it by a larger amount so that the net effect is to depress T/sub c/. (A previous calculation which ignored the effect of thermal phonons in phi overestimated the suppression of T/sub c/ by at least a factor of 3.) It is shown how to switch off the thermal phonons in the imaginary-frequency Eliashberg equations, exactly for Z and approximately for phi. The real-frequency and approximate imaginary-frequency results for the depression of T/sub c/ by thermal phonons are in very satisfactory agreement. Thermal phonons are found to depress the transition temperature of Nb 3 Sn by only 2%. It is estimated that the suppression of T/sub c/ by thermal phonons saturates at about 50% in the limit of very strong electron-phonon coupling

  10. Split of the superconducting transition and magnetism in UPt3

    International Nuclear Information System (INIS)

    Marikhin, V.G.

    1992-01-01

    A possible reason for splitting the superconducting phase transition in UPt 3 is discussed. The strong coupling of conduction electrons with uranium atom magnetic moments may be such a cause. The given assertion is based on the simple model described by the two-component order parameter φ Ginzburg -Landau functional. The Ginzburg - Landau functional without coupling has the whole symmetry D 6h of hexagonal crystal. Due to the presence of uranium atom magnetic moments M the symmetry is broken locally with the coupling term γ|Mφ| 2 in the Ginzburg - Landau functional. Averaging over the vector M configurations with the involment of the finite correlation radius a is performed. The inequality a 6h . This means that in a real crystal the hexagonal symmetry is not broken at the scales larger ξ. In the framework of the given theory the expressions for the specific heat jumps and equation combining the upper critical field H c2 and the phase transition split ΔT c with the pressure variation are obtained. The difficulties connencted with the small experimental magnitude of uranium atom magnetic moments are discussed

  11. Current Redistribution around the Superconducting-to-normal Transition in Superconducting Nb-Ti Rutherford Cables

    CERN Document Server

    Willering, G P; ten Kate, H H J

    2008-01-01

    Sufficient thermal-electromagnetic stability against external heat sources is an essential design criterion for superconducting Rutherford cables, especially if operated close to the critical current. Due to the complex phenomena contributing to stability such as helium cooling, inter-strand current and heat transfer, its level is difficult to quantify. In order to improve our understanding, many stability tests were performed on different cable samples, each incorporating several point-like heaters. The current redistribution around the heat front is measured after inducing a local normal zone in one strand of the cable. By using voltage taps, expansion of the normal zone is monitored in the initially quenched strand as well as in adjacent strands. An array of Hall probes positioned at the cable edge is used to scan the selffield generated by the cable by which it becomes possible to estimate the inter-strand current transfer. In this paper it is demonstrated that two different stability regimes can be disti...

  12. The influence of impurity concentration and magnetic fields on the superconducting transition of high-purity titanium

    Energy Technology Data Exchange (ETDEWEB)

    Peruzzi, A.; Gottardi, E.; Peroni, I.; Ponti, G.; Ventura, G

    1999-08-01

    The influence of impurity concentration c and applied magnetic field H on the superconducting transition of high-purity commercial titanium samples was investigated. The superconductive transition temperature T{sub C} was found to be very sensitive to the impurity concentration (dT{sub C}/dc {approx} -0.6 mK/w.ppm) and to the applied magnetic field (dT{sub C}/dH {approx} -1.1 mK/G). A linear dependence of T{sub C} decrease on impurity concentration, as theoretically predicted by various authors, was observed. In the purest sample, a linear decrease of T{sub C} on the applied magnetic field was found. The run-to-run and sample-to-sample reproducibility of the transition of the same sample was evaluated, and its suitability as a thermometric reference point below 1 K was discussed.

  13. Second order phase transition in thermodynamic geometry and holographic superconductivity in low-energy stringy black holes

    Science.gov (United States)

    Rizwan, C. L. Ahmed; Vaid, Deepak

    2018-05-01

    We study holographic superconductivity in low-energy stringy Garfinkle-Horowitz-Strominger (GHS) dilaton black hole background. We finds that superconducting properties are much similar to s-wave superconductors. We show that the second-order phase transition indicated from thermodynamic geometry is not different from superconducting phase transition.

  14. Anomalous properties and coexistence of antiferromagnetism and superconductivity near a quantum critical point in rare-earth intermetallides

    International Nuclear Information System (INIS)

    Val’kov, V. V.; Zlotnikov, A. O.

    2013-01-01

    Mechanisms of the appearance of anomalous properties experimentally observed at the transition through the quantum critical point in rare-earth intermetallides have been studied. Quantum phase transitions are induced by the external pressure and are manifested as the destruction of the long-range antiferromagnetic order at zero temperature. The suppression of the long-range order is accompanied by an increase in the area of the Fermi surface, and the effective electron mass is strongly renormalized near the quantum critical point. It has been shown that such a renormalization is due to the reconstruction of the quasiparticle band, which is responsible for the formation of heavy fermions. It has been established that these features hold when the coexistence phase of antiferromagnetism and superconductivity is implemented near the quantum critical point.

  15. Superconductivity

    CERN Document Server

    Poole, Charles P; Farach, Horacio A

    1995-01-01

    Superconductivity covers the nature of the phenomenon of superconductivity. The book discusses the fundamental principles of superconductivity; the essential features of the superconducting state-the phenomena of zero resistance and perfect diamagnetism; and the properties of the various classes of superconductors, including the organics, the buckministerfullerenes, and the precursors to the cuprates. The text also describes superconductivity from the viewpoint of thermodynamics and provides expressions for the free energy; the Ginzburg-Landau and BCS theories; and the structures of the high

  16. Influence of Superconductivity on Crystal Electric Field Transitions in La1-xTbxAl2

    DEFF Research Database (Denmark)

    Feile, R.; Loewenhaupt, M.; Kjems, Jørgen

    1981-01-01

    Inelastic neutron scattering from the crystal electric field transitions in La1-xTbxAl2 single crystals has revealed an abrupt increase in the lifetimes of these transitions when the system becomes superconducting. An increase in the integrated intensities is also observed. The lifetime effects...... are quantitatively reproduced by existing theories, which take into account the reduced scattering of the conduction electrons by the magnetic ions due to the creation of the superconducting energy gap 2Δ(T)....

  17. Metal-insulator transition and superconductivity in heavily boron-doped diamond and related materials

    Energy Technology Data Exchange (ETDEWEB)

    Achatz, Philipp

    2009-05-15

    During this PhD project, the metal-insulator transition and superconductivity of highly boron-doped single crystal diamond and related materials have been investigated. The critical boron concentration n{sub c} for the metal-insulator transition was found to be the same as for the normal-superconductor transition. All metallic samples have been found to be superconducting and we were able to link the occurence of superconductivity to the proximity to the metal-insulator transition. For this purpose, a scaling law approach based on low temperature transport was proposed. Furthermore, we tried to study the nature of the superconductivity in highly boron doped single crystal diamond. Raman spectroscopy measurements on the isotopically substituted series suggest that the feature occuring at low wavenumbers ({approx} 500 cm{sup -1}) is the A1g vibrational mode associated with boron dimers. Usual Hall effect measurements yielded a puzzling situation in metallic boron-doped diamond samples, leading to carrier concentrations up to a factor 10 higher than the boron concentration determined by secondary ion mass spectroscopy (SIMS). The low temperature transport follows the one expected for a granular metal or insulator, depending on the interplay of intergranular and intragranular (tunneling) conductance. The metal-insulator transition takes place at a critical conductance g{sub c}. The granularity also influences significantly the superconducting properties by introducing the superconducting gap {delta} in the grain and Josephson coupling J between superconducting grains. A peak in magnetoresistance is observed which can be explained by superconducting fluctuations and the granularity of the system. Additionally we studied the low temperature transport of boron-doped Si samples grown by gas immersion laser doping, some of which yielded a superconducting transition at very low temperatures. Furthermore, preliminary results on the LO-phonon-plasmon coupling are shown for the

  18. Metal-insulator transition and superconductivity in heavily boron-doped diamond and related materials

    International Nuclear Information System (INIS)

    Achatz, Philipp

    2009-01-01

    During this PhD project, the metal-insulator transition and superconductivity of highly boron-doped single crystal diamond and related materials have been investigated. The critical boron concentration n c for the metal-insulator transition was found to be the same as for the normal-superconductor transition. All metallic samples have been found to be superconducting and we were able to link the occurence of superconductivity to the proximity to the metal-insulator transition. For this purpose, a scaling law approach based on low temperature transport was proposed. Furthermore, we tried to study the nature of the superconductivity in highly boron doped single crystal diamond. Raman spectroscopy measurements on the isotopically substituted series suggest that the feature occuring at low wavenumbers (∼ 500 cm -1 ) is the A1g vibrational mode associated with boron dimers. Usual Hall effect measurements yielded a puzzling situation in metallic boron-doped diamond samples, leading to carrier concentrations up to a factor 10 higher than the boron concentration determined by secondary ion mass spectroscopy (SIMS). The low temperature transport follows the one expected for a granular metal or insulator, depending on the interplay of intergranular and intragranular (tunneling) conductance. The metal-insulator transition takes place at a critical conductance g c . The granularity also influences significantly the superconducting properties by introducing the superconducting gap Δ in the grain and Josephson coupling J between superconducting grains. A peak in magnetoresistance is observed which can be explained by superconducting fluctuations and the granularity of the system. Additionally we studied the low temperature transport of boron-doped Si samples grown by gas immersion laser doping, some of which yielded a superconducting transition at very low temperatures. Furthermore, preliminary results on the LO-phonon-plasmon coupling are shown for the first time in aluminum

  19. Model for cryogenic particle detectors with superconducting phase transition thermometers

    International Nuclear Information System (INIS)

    Proebst, F.; Frank, M.; Cooper, S.; Colling, P.; Dummer, D.; Ferger, P.; Nucciotti, A.; Seidel, W.; Stodolsky, L.

    1994-09-01

    We present data on a detector composed of an 18 g Si crystal and a superconducting phase transition thermometer which could be operated over a wide temperature range. An energy resolution of 1 keV (FWHM) has been obtained for 60 keV photons. The signals consist of two components: A fast one and a slow one, with decay times of 1.5 ms and 30-60 ms, respectively. In this paper we present a simple model which takes thermal and non-thermal phonon processes into account and provides a description of the observed temperature dependence of the pulse shape. The fast component, which completely dominates the signal at low temperatures, is due to high-frequency non-thermal phonons being absorbed in the thermometer. Thermalization of these phonons then leads to a temperature rise of the absorber, which causes the slow thermal component. At the highest operating temperatures (T∼80 mK) the amplitude of the slow component is roughly as expected from the heat capacity of the absorber. The strong suppression of the slow component at low temperatures is explained mostly as a consequence of the weak thermal coupling between electrons and phonons in the thermometer at low temperatures. (orig.)

  20. Nonempirical Calculation of Superconducting Transition Temperatures in Light-Element Superconductors.

    Science.gov (United States)

    Arita, Ryotaro; Koretsune, Takashi; Sakai, Shiro; Akashi, Ryosuke; Nomura, Yusuke; Sano, Wataru

    2017-07-01

    Recent progress in the fully nonempirical calculation of the superconducting transition temperature (T c ) is reviewed. Especially, this study focuses on three representative light-element high-T c superconductors, i.e., elemental Li, sulfur hydrides, and alkali-doped fullerides. Here, it is discussed how crucial it is to develop the beyond Migdal-Eliashberg (ME) methods. For Li, a scheme of superconducting density functional theory for the plasmon mechanism is formulated and it is found that T c is dramatically enhanced by considering the frequency dependence of the screened Coulomb interaction. For sulfur hydrides, it is essential to go beyond not only the static approximation for the screened Coulomb interaction, but also the constant density-of-states approximation for electrons, the harmonic approximation for phonons, and the Migdal approximation for the electron-phonon vertex, all of which have been employed in the standard ME calculation. It is also shown that the feedback effect in the self-consistent calculation of the self-energy and the zero point motion considerably affect the calculation of T c . For alkali-doped fullerides, the interplay between electron-phonon coupling and electron correlations becomes more nontrivial. It has been demonstrated that the combination of density functional theory and dynamical mean field theory with the ab initio downfolding scheme for electron-phonon coupled systems works successfully. This study not only reproduces the experimental phase diagram but also obtains a unified view of the high-T c superconductivity and the Mott-Hubbard transition in the fullerides. The results for these high-T c superconductors will provide a firm ground for future materials design of new superconductors. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Abrupt onset of a second energy gap at the superconducting transition of underdoped Bi2212

    Energy Technology Data Exchange (ETDEWEB)

    Hussain, Zahid; Lee, W.S.; Vishik, I.M.; Tanaka, K.; Lu, D.H.; Sasagawa, T.; Nagaosa, N.; Devereaux, T.P.; Hussain, Z.; Shen, Z.-X.

    2007-05-26

    he superconducting gap--an energy scale tied to the superconducting phenomena--opens on the Fermi surface at the superconducting transition temperature (Tc) in conventional BCS superconductors. In underdoped high-Tc superconducting copper oxides, a pseudogap (whose relation to the superconducting gap remains a mystery) develops well above Tc (refs 1, 2). Whether the pseudogap is a distinct phenomenon or the incoherent continuation of the superconducting gap above Tc is one of the central questions in high-Tc research3, 4, 5, 6, 7, 8. Although some experimental evidence suggests that the two gaps are distinct9, 10, 11, 12, 13, 14, 15, 16, 17, 18, this issue is still under intense debate. A crucial piece of evidence to firmly establish this two-gap picture is still missing: a direct and unambiguous observation of a single-particle gap tied to the superconducting transition as function of temperature. Here we report the discovery of such an energy gap in underdoped Bi2Sr2CaCu2O8+delta in the momentum space region overlooked in previous measurements. Near the diagonal of Cu?O bond direction (nodal direction), we found a gap that opens at Tc and has a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasi-particles, a classical signature of superconductivity. This is in sharp contrast to the pseudogap near the Cu?O bond direction (antinodal region) measured in earlier experiments19, 20, 21.

  2. Superconductivity and magnetic fluctuations developing in the vicinity of strong first-order magnetic transition in CrAs

    International Nuclear Information System (INIS)

    Kotegawa, H; Matsushima, K; Nakahara, S; Tou, H; Kaneyoshi, J; Nishiwaki, T; Matsuoka, E; Sugawara, H; Harima, H

    2017-01-01

    We report single crystal preparation, resistivity, and nuclear quadrupole resonance (NQR) measurements for new pressure-induced superconductor CrAs. In the first part, we present the difference between crystals made by different thermal sequences and methods, and show the sample dependence of superconductivity in CrAs. In the latter part, we show NQR data focusing the microscopic electronic state at the phase boundary between the helimagnetic and the paramagnetic phases. They suggest strongly that a quantum critical point is absent on the pressure-temperature phase diagram of CrAs, because of the strong first-order character of the magnetic transition; however, the spin fluctuations are observed in the paramagnetic phase. The close relationship between the spin fluctuations and superconductivity can be seen even in the vicinity of the first-order magnetic transition in CrAs. (paper)

  3. Superconductivity

    International Nuclear Information System (INIS)

    Langone, J.

    1989-01-01

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

  4. Superconductivity

    International Nuclear Information System (INIS)

    Onnes, H.K.

    1988-01-01

    The author traces the development of superconductivity from 1911 to 1986. Some of the areas he explores are the Meissner Effect, theoretical developments, experimental developments, engineering achievements, research in superconducting magnets, and research in superconducting electronics. The article also mentions applications shown to be technically feasible, but not yet commercialized. High-temperature superconductivity may provide enough leverage to bring these applications to the marketplace

  5. Chiral and color-superconducting phase transitions with vector interaction in a simple model

    International Nuclear Information System (INIS)

    Kitazawa, Masakiyo; Koide, Tomoi; Kunihiro, Teiji; Nemoto, Yukio

    2002-01-01

    We investigate effects of the vector interaction on chiral and color superconducting (CSC) phase transitions at finite density and temperature in a simple Nambu-Jona-Lasinio model. It is shown that the repulsive density-density interaction coming from the vector term, which is present in the effective chiral models but has been omitted, enhances the competition between the chiral symmetry breaking (χSB) and CSC phase transition, and thereby makes the thermodynamic potential have a shallow minimum over a wide range of values of the correlated chiral and CSC order parameters. We find that when the vector coupling is increased, the first order transition between the χSB and CSC phases becomes weaker, and the coexisting phase in which both the chiral and color-gauge symmetry are dynamically broken comes to exist over a wider range of the density and temperature. We also show that there can exist two endpoints, which are tricritical points in the chiral limit, along the critical line of the first order transition in some range of values of the vector coupling. Although our analysis is based on a simple model, the nontrivial interplay between the χSB and CSC phases induced by the vector interaction is expected to be a universal phenomenon and might give a clue to understanding results obtained with two-color QCD on the lattice. (author)

  6. Strongly correlated electron systems and neutron scattering. Magnetism, superconductivity, structural phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Katano, Susumu [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    1998-03-01

    Neutron scattering experiments in our group on strongly correlated electron systems are reviewed Metal-insulator transitions caused by structural phase transitions in (La{sub 1-x}Sr{sub x}) MnO{sub 3}, a novel magnetic transition in the CeP compound, correlations between antiferromagnetism and superconductivity in UPd{sub 2}Al{sub 3} and so forth are discussed. Here, in this note, the phase transition of Mn-oxides was mainly described. (author)

  7. Effect of point disorder on superconducting properties of ultrathin epitaxial NbN films

    International Nuclear Information System (INIS)

    Jesudasan, John; Bagwe, Vivas; Mondal, Mintu; Chand, Madhavi; Kamlapure, Anand; Pai, S.P.; Raychaudhuri, Pratap; Mishra, Archana

    2009-01-01

    We synthesized homogeneously disordered epitaxial NbN films on MgO(100) substrates using reactive dc magnetron sputtering. The disorder of the films is characterized by the Loffe-Regel parameter k F I. The superconducting properties are studied through transport, ac-susceptibility measurements and electron tunneling. The superconducting transition temperature is studied as a function of thickness for films of different disorder. In the case of the less disordered film, there is a smooth decrease in T c with decreasing thickness but for the more disordered film, the T c shows a sharp decrease to zero at a threshold thickness. The superconducting energy gap is studied via planar tunnel junctions. It is found that for the less disordered films, the temperature dependence of the gap follows the BCS variation but for the more disordered ones, there is a significant deviation from the BCS curve, and the gap remains finite at T c indicating that the superconducting transition is either governed by phase fluctuations or a first order phase transition. (author)

  8. Construction and test of a superconducting phase-transition thermometer for bolometric cryodetectors

    International Nuclear Information System (INIS)

    Meier, H.J.

    1990-10-01

    In the framework of a project for the study of bolometric cryodetectors for the detection of heavy ions a superconducting phase-transition thermometer for the detection of heavy ions was constructed and tested with α particles. The thermometer consists of a 10 nm thick aluminium film, which was evaporated on a sapphire absorber with a typical magnitude of 2.5x2.5 x 0.33 mm 3 . By the method of photolithography the aluminium film was structured in form of a meander. By this at the working point of the thermometer resistances of up to 60 kΩ resulted, so that the signal acquisition was possible with usual readout electronics. Several of these thermometers were constructed, characterized in their properties, and tested. For the study of the detector properties of the thermometers in characterization measurements the width of the phase transitions dT ≅ 2 mK, the temperature dependence of the resistance to dR/dT ≅ 10MΩ/K, the thermal conductivity of the thermal coupling to the cooling bath, and the heat capacity of the bolometers to C ≅ 2 nJ/K were determined.The best energy resolution, which was reached with one of the superconducting phase-transition thermometers, amounts to 50 keV for 5.5 MeV α particles, which corresponds to a relative resolution of 0,9%. By this in the order of magnitude the quality of semiconductor detectors was reached. The best temperature resolution amounts to about 1 μK. (orig./HSI) [de

  9. Pressure controlled transition into a self-induced topological superconducting surface state

    KAUST Repository

    Zhu, Zhiyong; Cheng, Yingchun; Schwingenschlö gl, Udo

    2014-01-01

    Ab-initio calculations show a pressure induced trivial-nontrivial-trivial topological phase transition in the normal state of 1T-TiSe2. The pressure range in which the nontrivial phase emerges overlaps with that of the superconducting ground state. Thus, topological superconductivity can be induced in protected surface states by the proximity effect of superconducting bulk states. This kind of self-induced topological surface superconductivity is promising for a realization of Majorana fermions due to the absence of lattice and chemical potential mismatches. For appropriate electron doping, the formation of the topological superconducting surface state in 1T-TiSe 2 becomes accessible to experiments as it can be controlled by pressure.

  10. Pressure controlled transition into a self-induced topological superconducting surface state

    KAUST Repository

    Zhu, Zhiyong

    2014-02-07

    Ab-initio calculations show a pressure induced trivial-nontrivial-trivial topological phase transition in the normal state of 1T-TiSe2. The pressure range in which the nontrivial phase emerges overlaps with that of the superconducting ground state. Thus, topological superconductivity can be induced in protected surface states by the proximity effect of superconducting bulk states. This kind of self-induced topological surface superconductivity is promising for a realization of Majorana fermions due to the absence of lattice and chemical potential mismatches. For appropriate electron doping, the formation of the topological superconducting surface state in 1T-TiSe 2 becomes accessible to experiments as it can be controlled by pressure.

  11. Superconductivity

    International Nuclear Information System (INIS)

    Andersen, N.H.; Mortensen, K.

    1988-12-01

    This report contains lecture notes of the basic lectures presented at the 1st Topsoee Summer School on Superconductivity held at Risoe National Laboratory, June 20-24, 1988. The following lecture notes are included: L.M. Falicov: 'Superconductivity: Phenomenology', A. Bohr and O. Ulfbeck: 'Quantal structure of superconductivity. Gauge angle', G. Aeppli: 'Muons, neutrons and superconductivity', N.F. Pedersen: 'The Josephson junction', C. Michel: 'Physicochemistry of high-T c superconductors', C. Laverick and J.K. Hulm: 'Manufacturing and application of superconducting wires', J. Clarke: 'SQUID concepts and systems'. (orig.) With 10 tabs., 128 figs., 219 refs

  12. Superconductivity

    International Nuclear Information System (INIS)

    Palmieri, V.

    1990-01-01

    This paper reports on superconductivity the absence of electrical resistance has always fascinated the mind of researchers with a promise of applications unachievable by conventional technologies. Since its discovery superconductivity has been posing many questions and challenges to solid state physics, quantum mechanics, chemistry and material science. Simulations arrived to superconductivity from particle physics, astrophysic, electronics, electrical engineering and so on. In seventy-five years the original promises of superconductivity were going to become reality: a microscopical theory gave to superconductivity the cloth of the science and the level of technological advances was getting higher and higher. High field superconducting magnets became commercially available, superconducting electronic devices were invented, high field accelerating gradients were obtained in superconductive cavities and superconducting particle detectors were under study. Other improvements came in a quiet progression when a tornado brought a revolution in the field: new materials had been discovered and superconductivity, from being a phenomenon relegated to the liquid Helium temperatures, became achievable over the liquid Nitrogen temperature. All the physics and the technological implications under superconductivity have to be considered ab initio

  13. Superconducting and charge density wave transition in single crystalline LaPt2Si2

    Science.gov (United States)

    Gupta, Ritu; Dhar, S. K.; Thamizhavel, A.; Rajeev, K. P.; Hossain, Z.

    2017-06-01

    We present results of our comprehensive studies on single crystalline LaPt2Si2. Pronounced anomaly in electrical resistivity and heat capacity confirms the bulk nature of superconductivity (SC) and charge density wave (CDW) transition in the single crystals. While the charge density wave transition temperature is lower, the superconducting transition temperature is higher in single crystal compared to the polycrystalline sample. This result confirms the competing nature of CDW and SC. Another important finding is the anomalous temperature dependence of upper critical field H C2(T). We also report the anisotropy in the transport and magnetic measurements of the single crystal.

  14. Superconductivity

    CERN Document Server

    Thomas, D B

    1974-01-01

    A short general review is presented of the progress made in applied superconductivity as a result of work performed in connection with the high-energy physics program in Europe. The phenomenon of superconductivity and properties of superconductors of Types I and II are outlined. The main body of the paper deals with the development of niobium-titanium superconducting magnets and of radio-frequency superconducting cavities and accelerating structures. Examples of applications in and for high-energy physics experiments are given, including the large superconducting magnet for the Big European Bubble Chamber, prototype synchrotron magnets for the Super Proton Synchrotron, superconducting d.c. beam line magnets, and superconducting RF cavities for use in various laboratories. (0 refs).

  15. A multiple-field coupled resistive transition model for superconducting Nb3Sn

    Directory of Open Access Journals (Sweden)

    Lin Yang

    2016-12-01

    Full Text Available A study on the superconducting transition width as functions of the applied magnetic field and strain is performed in superconducting Nb3Sn. A quantitative, yet universal phenomenological resistivity model is proposed. The numerical simulation by the proposed model shows predicted resistive transition characteristics under variable magnetic fields and strain, which in good agreement with the experimental observations. Furthermore, a temperature-modulated magnetoresistance transition behavior in filamentary Nb3Sn conductors can also be well described by the given model. The multiple-field coupled resistive transition model is helpful for making objective determinations of the high-dimensional critical surface of Nb3Sn in the multi-parameter space, offering some preliminary information about the basic vortex-pinning mechanisms, and guiding the design of the quench protection system of Nb3Sn superconducting magnets.

  16. A multiple-field coupled resistive transition model for superconducting Nb3Sn

    Science.gov (United States)

    Yang, Lin; Ding, He; Zhang, Xin; Qiao, Li

    2016-12-01

    A study on the superconducting transition width as functions of the applied magnetic field and strain is performed in superconducting Nb3Sn. A quantitative, yet universal phenomenological resistivity model is proposed. The numerical simulation by the proposed model shows predicted resistive transition characteristics under variable magnetic fields and strain, which in good agreement with the experimental observations. Furthermore, a temperature-modulated magnetoresistance transition behavior in filamentary Nb3Sn conductors can also be well described by the given model. The multiple-field coupled resistive transition model is helpful for making objective determinations of the high-dimensional critical surface of Nb3Sn in the multi-parameter space, offering some preliminary information about the basic vortex-pinning mechanisms, and guiding the design of the quench protection system of Nb3Sn superconducting magnets.

  17. Changing electronic density in sites of crystalline lattice under superconducting of phase transition

    International Nuclear Information System (INIS)

    Turaev, N.Yu.; Turaev, E.Yu.; Khuzhakulov, E.S.; Seregin, P.P.

    2006-01-01

    Results of electron density change calculations for sites of the one-dimensional Kronig-Penny lattice at the superconducting phase transition have been presented. The transition from normal state to super conducting one is accompanied by the rise of the electron density at the unit cell centre. It is agreement with Moessbauer spectroscopy data. (author)

  18. Hofstadter's Butterfly and Phase Transition of Checkerboard Superconducting Network in a Magnetic Field

    International Nuclear Information System (INIS)

    Hou Jingmin; Tian, Li-Jim

    2010-01-01

    We study the magnetic effect of the checkerboard superconducting wire network. Based on the de Gennes-Alexader theory, we obtain difference equations for superconducting order parameter in the wire network. Through solving these difference equations, we obtain the eigenvalues, linked to the coherence length, as a function of magnetic field. The diagram of eigenvalues shows a fractal structure, being so-called Hofstadter's butterfly. We also calculate and discuss the dependence of the transition temperature of the checkerboard superconducting wire network on the applied magnetic field, which is related to up-edge of the Hofstadter's butterfly spectrum. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  19. The pressure effect on the superconducting transition temperature of black phosphorus

    CERN Document Server

    Karuzawa, M; Endo, S

    2002-01-01

    We have measured the pressure effect on the superconducting transition temperature T sub c of black phosphorus up to 160 GPa using a superconducting quantum interference device vibrating coil magnetometer. It was found that T sub c had a maximum value of about 9.5 K at about 32 GPa, began decreasing with pressure and reached about 4.3 K at about 100 GPa.

  20. Structural phase transitions and superconductivity in lanthanum copper oxides

    International Nuclear Information System (INIS)

    Crawford, M.K.; Harlow, R.L.; McCarron, E.M.

    1996-01-01

    Despite the enormous effort expended over the past ten years to determine the mechanism underlying high temperature superconductivity in cuprates there is still no consensus on the physical origin of this fascinating phenomenon. This is a consequence of a number of factors, among which are the intrinsic difficulties in understanding the strong electron correlations in the copper oxides, determining the roles played by antiferromagnetic interactions and low dimensionality, analyzing the complex phonon dispersion relationships, and characterizing the phase diagrams which are functions of the physical parameters of temperature and pressure, as well as the chemical parameters of stoichiometry and hole concentration. In addition to all of these intrinsic difficulties, extrinsic materials issues such as sample quality and homogeneity present additional complications. Within the field of high temperature superconductivity there exists a subfield centered around the material originally reported to exhibit high temperature superconductivity by Bednorz and Mueller, Ba doped La 2 CuO 4 . This is structurally the simplest cuprate superconductor. The authors report on studies of phase differences observed between such base superconductors doped with Ba or Sr. What these studies have revealed is a fascinating interplay of structural, magnetic and superconducting properties which is unique in the field of high temperature superconductivity and is summarized in this paper

  1. Subharmonic energy-gap structure and heating effects in superconducting niobium point contacts

    DEFF Research Database (Denmark)

    Flensberg, K.; Hansen, Jørn Bindslev

    1989-01-01

    We present experimental data of the temperature-dependent subharmonic energy-gap structure (SGS) in the current-voltage (I-V) curves of superconducting niobium point contacts. The observed SGS is modified by heating effects. We construct a model of the quasiparticle conductance of metallic...

  2. QUANTUM ELECTRONIC DEVICES: Superconducting Nb3Sn point contact in the submillimeter range of electromagnetic radiation

    Science.gov (United States)

    Belenov, É. M.; Danileĭko, M. V.; Derkach, V. E.; Romanenko, V. I.; Uskov, A. V.

    1988-05-01

    An investigation was made of the influence of submillimeter radiation emitted by an HCN laser operating at a frequency νl = 891 GHz on a superconducting point contact made of Nb3Sn. Three steps of the electric current were recorded. The experimental results indicated that such a contact could be used for frequency multiplication up to 3 THz.

  3. Development of a superconducting transition edge thermometer for calorimetric detection of heavy ions

    Energy Technology Data Exchange (ETDEWEB)

    Meier, J; Boehmer, W; Egelhof, P; Henning, W; Kienlin, A v [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany) Mainz Univ. (Germany). Inst. fuer Physik; Shepard, K W [Argonne National Lab., IL (United States)

    1991-10-01

    A low temperature bolometer for the calorimetric detection of heavy ions was constructed and tested. An aluminium thin-film microstrip, patterned in a meander-line structure by photolithographic techniques, serves as superconducting transition edge thermometer on a sapphire absorber. A transition width {delta}T of the thermometer of the order of some mK, and a resistance of up to R{sub c} = 60 k{Omega} at the working point (T{sub c} {approx equal} 1.5 K) is achieved. In tests with {alpha}-particles signals of typically 1 V pulseheight after the preamplifier and decaytimes around hundred {mu}s were observed. For 5.5 MeV {alpha}-particles the measured energy resolution is {Delta}E = 50 keV, corresponding to a temperature resolution of about 1 {mu}K. First measurements were performed with {sup 20}Ne ions (E = 116 MeV). The dependence of the pulseheight and the FWHM on the working point were investigated and qualitatively explained. The best energy resolution was {Delta}E = 2.6 MeV; most probably the present limitations are determined by the temperature stabilization. (orig.).

  4. On the origin of the double superconducting transition in overdoped YBa2Cu3O x

    International Nuclear Information System (INIS)

    Lortz, R.; Tomita, T.; Wang, Y.; Junod, A.; Schilling, J.S.; Masui, T.; Tajima, S.

    2006-01-01

    The superconducting transition in a single overdoped, detwinned YBa 2 Cu 3 O x (YBCO) crystal is studied using four different probes. Whereas the AC and DC magnetic susceptibilities find a dominant transition at 88 K with a smaller effect near 92 K, the specific heat and electrical resistivity reveal only a single transition at 88 K and 92 K, respectively. Under hydrostatic pressures to 0.60 GPa these two transitions shift in opposite directions, their separation increasing. The present experiments clearly show that the bulk transition lies at 88 K and originates from fully oxygenated YBCO; the 92 K transition likely arises from filamentary superconductivity in a minority optimally doped phase (<1%) of YBCO located at or near the crystal surface

  5. Superconducting states and depinning transitions of Josephson ladders

    International Nuclear Information System (INIS)

    Barahona, M.; Strogatz, S.H.; Orlando, T.P.

    1998-01-01

    We present analytical and numerical studies of pinned superconducting states of open-ended Josephson ladder arrays, neglecting inductances but taking edge effects into account. Treating the edge effects perturbatively, we find analytical approximations for three of these superconducting states emdash the no-vortex, fully frustrated, and single-vortex states emdash as functions of the dc bias current I and the frustration f. Bifurcation theory is used to derive formulas for the depinning currents and critical frustrations at which the superconducting states disappear or lose dynamical stability as I and f are varied. These results are combined to yield a zero-temperature stability diagram of the system with respect to I and f. To highlight the effects of the edges, we compare this dynamical stability diagram to the thermodynamic phase diagram for the infinite system where edges have been neglected. We briefly indicate how to extend our methods to include self-inductances. copyright 1998 The American Physical Society

  6. Nonphonon mechanism of superconductivity in compounds of transition metals

    International Nuclear Information System (INIS)

    Ivanov, V.A.; Zaitsev, R.O.

    1989-01-01

    The kinematical mechanism of superconductivity is applied to the Emery-Hirsch model for the CuO 2 and BiO 3 layers. A superconducting region due to strong kinematic interaction of p- and s, d-electrons are determined as a function of n p and n s,d -degrees of non-filling of 2p 6 ,6s 2 ,3d 10 shells of O 2 - ,Bi 3 + ,Cu + . The T c is calculated taking into account the spin flip relaxation time. Magnetostatic properties of a superconducting state in a weak magnetic field are investigated. Coefficients of the Ginzburg-Landau equation are calculated. The ground state energy of the Emery-Hirsch model is also calculated

  7. Superconductivity

    International Nuclear Information System (INIS)

    Kakani, S.L.; Kakani, Shubhra

    2007-01-01

    The monograph provides readable introduction to the basics of superconductivity for beginners and experimentalists. For theorists, the monograph provides nice and brief description of the broad spectrum of experimental properties, theoretical concepts with all details, which theorists should learn, and provides a sound basis for students interested in studying superconducting theory at the microscopic level. Special chapter on the theory of high-temperature superconductivity in cuprates is devoted

  8. Superconducting transition edge sensors and methods for design and manufacture thereof

    Science.gov (United States)

    Sadleir, John E. (Inventor)

    2013-01-01

    Methods for forming sensors using transition edge sensors (TES) and sensors therefrom are described. The method includes forming a plurality of sensor arrays includes at least one TES device. The TES device includes a TES device body, a first superconducting lead contacting a first portion of the TES device body, and a second superconducting lead contacting of a second portion of the TES device body, where the first and second superconducting leads separated on the TES device body by a lead spacing. The lead spacing can be selected to be different for at least two of the plurality of sensor arrays. The method also includes determining a transition temperature for each of the plurality of sensor arrays and generating a signal responsive to detecting a change in the electrical characteristics of one of the plurality of sensor arrays meeting a transition temperature criterion.

  9. Interval Mathematics Applied to Critical Point Transitions

    Directory of Open Access Journals (Sweden)

    Benito A. Stradi

    2012-03-01

    Full Text Available The determination of critical points of mixtures is important for both practical and theoretical reasons in the modeling of phase behavior, especially at high pressure. The equations that describe the behavior of complex mixtures near critical points are highly nonlinear and with multiplicity of solutions to the critical point equations. Interval arithmetic can be used to reliably locate all the critical points of a given mixture. The method also verifies the nonexistence of a critical point if a mixture of a given composition does not have one. This study uses an interval Newton/Generalized Bisection algorithm that provides a mathematical and computational guarantee that all mixture critical points are located. The technique is illustrated using several example problems. These problems involve cubic equation of state models; however, the technique is general purpose and can be applied in connection with other nonlinear problems.

  10. Superconductivity

    International Nuclear Information System (INIS)

    Caruana, C.M.

    1988-01-01

    Despite reports of new, high-temperature superconductive materials almost every day, participants at the First Congress on Superconductivity do not anticipate commercial applications with these materials soon. What many do envision is the discovery of superconducting materials that can function at much warmer, perhaps even room temperatures. Others hope superconductivity will usher in a new age of technology as semiconductors and transistors did. This article reviews what the speakers had to say at the four-day congress held in Houston last February. Several speakers voiced concern that the Reagan administration's apparent lack of interest in funding superconductivity research while other countries, notably Japan, continue to pour money into research and development could hamper America's international competitiveness

  11. Point contact tunneling spectroscopy apparatus for large scale mapping of surface superconducting properties

    Energy Technology Data Exchange (ETDEWEB)

    Groll, Nickolas; Pellin, Michael J. [Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439 (United States); Zasadzinksi, John F. [Illinois Institute of Technology, Chicago, Illinois 60616 (United States); Proslier, Thomas, E-mail: prolier@anl.gov [Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439 (United States); High Energy Physics Division, Argonne National Laboratory, Lemont, Illinois 60439 (United States)

    2015-09-15

    We describe the design and testing of a point contact tunneling spectroscopy device that can measure material surface superconducting properties (i.e., the superconducting gap Δ and the critical temperature T{sub C}) and density of states over large surface areas with size up to mm{sup 2}. The tip lateral (X,Y) motion, mounted on a (X,Y,Z) piezo-stage, was calibrated on a patterned substrate consisting of Nb lines sputtered on a gold film using both normal (Al) and superconducting (PbSn) tips at 1.5 K. The tip vertical (Z) motion control enables some adjustment of the tip-sample junction resistance that can be measured over 7 orders of magnitudes from a quasi-ohmic regime (few hundred Ω) to the tunnel regime (from tens of kΩ up to few GΩ). The low noise electronic and LabVIEW program interface are also presented. The point contact regime and the large-scale motion capabilities are of particular interest for mapping and testing the superconducting properties of macroscopic scale superconductor-based devices.

  12. Pressure behaviour of the superconducting transition temperature of lanthanum

    International Nuclear Information System (INIS)

    Glocker, R.

    1977-01-01

    The dissertation has the following chapters: 1) Introduction, 2) Fundamentals of the microscopic theory of superconductivity, 3) Calculation of the first momentum of the Eliashberg function, 4) Determination of the average values of frequency, 5) The relativistic cellular method and its application to lanthanum, 6) Results of the calculation of the electron-phonon coupling cosntants for f.c.c. lanthanum, 7) Phonon dispersion and phonon state density. (orig.) [de

  13. Theory of the superconducting proximity effect below the transition temperature

    International Nuclear Information System (INIS)

    Silvert, W.

    1975-01-01

    The form of the low-temperature theory of the superconducting proximity effect depends on whether the non-linear terms are assumed to depend only on the local value of the gap or on its average value over some finite range. The local assumption leads to smaller values of the gap and to unphysical results at low temperatures. The effect of non-locality is significant even in the Ginsburg-Landau regime. (author)

  14. Investigation on maximum transition temperature of phonon mediated superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Fusui, L; Yi, S; Yinlong, S [Physics Department, Beijing University (CN)

    1989-05-01

    Three model effective phonon spectra are proposed to get plots of {ital T}{sub {ital c}}-{omega} adn {lambda}-{omega}. It can be concluded that there is no maximum limit of {ital T}{sub {ital c}} in phonon mediated superconductivity for reasonable values of {lambda}. The importance of high frequency LO phonon is also emphasized. Some discussions on high {ital T}{sub {ital c}} are given.

  15. Superconducting transition in TlBiTe/sub 2/ and TlTe compounds

    Energy Technology Data Exchange (ETDEWEB)

    Kantser, V G; Popovich, N S; Sidorenko, A S

    1985-10-01

    On the basis of zone structure calculation for TlBiTe/sub 2/ and TlTe it is found that TlBiTe/sub 2/ is a narrow-gap semiconductor and TlTe is a p-metal. At Tsub(c)=0.19 K TlTe is found to experience the superconducting transition. In TlBiTe/sub 2/ superconductivity is not observed to occur up to 0.05 K, since there is a possibility of occupying the high density of states zones because they are remote from actual ones. The earlier discovered superconducting transition in TlBiTe/sub 2/ is inherent in the alien phase of TlTe.

  16. Metal-insulator transition and superconductivity induced by Rh doping in the binary pnictides RuPn (Pn=P, As, Sb)

    Science.gov (United States)

    Hirai, Daigorou; Takayama, Tomohiro; Hashizume, Daisuke; Takagi, Hidenori

    2012-04-01

    Binary ruthenium pnictides, RuP and RuAs, with an orthorhombic MnP structure, were found to show a metal to a nonmagnetic insulator transition at TMI = 270 and 200 K, respectively. In the metallic region above TMI, a structural phase transition, accompanied with a weak anomaly in the resistivity and the magnetic susceptibility, indicative of a pseudogap formation, was identified at Ts = 330 and 280 K, respectively. These two transitions were suppressed by substituting Ru with Rh. We found superconductivity with a maximum Tc = 3.7 and 1.8 K in a narrow composition range around the critical point for the pseudogap phase, Rh content xc = 0.45 and 0.25 for Ru1-xRhxP and Ru1-xRhxAs, respectively, which may provide us with a nonmagnetic route to superconductivity at a quantum critical point.

  17. Superconductivity

    CERN Document Server

    Ketterson, John B

    2008-01-01

    Conceived as the definitive reference in a classic and important field of modern physics, this extensive and comprehensive handbook systematically reviews the basic physics, theory and recent advances in the field of superconductivity. Leading researchers, including Nobel laureates, describe the state-of-the-art in conventional and unconventional superconductors at a particularly opportune time, as new experimental techniques and field-theoretical methods have emerged. In addition to full-coverage of novel materials and underlying mechanisms, the handbook reflects continued intense research into electron-phone based superconductivity. Considerable attention is devoted to high-Tc superconductivity, novel superconductivity, including triplet pairing in the ruthenates, novel superconductors, such as heavy-Fermion metals and organic materials, and also granular superconductors. What’s more, several contributions address superconductors with impurities and nanostructured superconductors. Important new results on...

  18. Magnetic fluctuations and the superconducting transition in the heavy-fermion material UPd2Al3

    DEFF Research Database (Denmark)

    Petersen, T.; Mason, T.E.; Aeppli, G.

    1994-01-01

    Inelastic neutron scattering has been performed on single crystals of the heavy-fermion superconductor UPd2Al3. The antiferromagnetically ordered state is characterized by an acoustic spin wave mode with no gap. The low-frequency magnitude excitations are unaffected by the transition to a superco...... to a superconducting state despite coupling to the conduction electrons as evidenced by the significant damping....

  19. Electric field dependence of excess electrical conductivity below transition temperature in thin superconducting lead films

    Energy Technology Data Exchange (ETDEWEB)

    Ashwini Kumar, P K; Duggal, V P [Delhi Univ. (India). Dept. of Physics and Astrophysics

    1976-01-26

    Results of measurements of the electric field dependence of the excess electrical conductivity are reported in thin superconducting lead films below the transition temperature. It is observed that the normal state sheet resistance has some effect on the nonlinearity but the theory of Yamaji still fits well to the experimental data.

  20. Effect of the superconducting transition on amplitude-dependent dislocation internal friction in metals

    International Nuclear Information System (INIS)

    Lomakin, V.V.; Pankrat'eva, G.L.; Roshchupkin, A.M.

    1983-01-01

    In terms of the Granato-Lucke model, an explanation of the amplitude-dependent internal friction change at the superconducting transition is proposed which takes into account the influence of the electronic viscosity on the fluctuation unpinning of dislocations from local obstacles

  1. Pressure dependence of the superconducting transition temperature of Rb3C60 up to 20 kbar

    International Nuclear Information System (INIS)

    Bud'ko, S.L.; Meng, R.L.; Chu, C.W.; Hor, P.H.

    1991-01-01

    AC susceptibility measurements of Rb 3 C 60 under hydrostatic pressure up to 20 kbar are reported. The superconducting transition temperature (T c ) decreases linearly under pressure with the pressure derivative dT c /dP = -0.78 K degrees/kbar

  2. Perturbation theory of a superconducting 0−π impurity quantum phase transition

    Czech Academy of Sciences Publication Activity Database

    Žonda, M.; Pokorný, Vladislav; Janiš, Václav; Novotný, T.

    2015-01-01

    Roč. 5, Mar (2015), s. 8821 ISSN 2045-2322 R&D Projects: GA ČR GCP204/11/J042 Institutional support: RVO:68378271 Keywords : quantum dot * superconductivity * Josephson current * quantum phase transition * perturbation expansion Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 5.228, year: 2015

  3. Review of superconducting transition-edge sensors for x-ray and gamma-ray spectroscopy

    International Nuclear Information System (INIS)

    Ullom, Joel N; Bennett, Douglas A

    2015-01-01

    We present a review of emerging x-ray and gamma-ray spectrometers based on arrays of superconducting transition-edge sensors (TESs). Special attention will be given to recent progress in TES applications and in understanding TES physics. (paper)

  4. Superconducting Sweet-Spot in Microcrystalline Graphite Revealed by Point-Contact Spectroscopy

    Science.gov (United States)

    Arnold, F.; Nyéki, J.; Saunders, J.

    2018-05-01

    In this letter we describe the observation of a magnetic field dependent electronic gap, suggestive of local superconductivity, in the point-contact spectrum of micro-crystalline graphite. Magnetic field dependent point-contact spectroscopy was carried out at a temperature of 1.8K using an etched aluminium tip. At zero field a gap structure in the differential conductance is observed, showing a gap of Δ = 4.2 meV. On applying magnetic fields of up to 500mT, this gap gradually closes, following the theoretical prediction by Ginzburg and Landau for a fully flux-penetrated superconductor. By applying BCS-theory, we infer a critical superconducting temperature of 14K.

  5. Second Law Violation By Magneto-Caloric Effect Adiabatic Phase Transition of Type I Superconductive Particles

    OpenAIRE

    Keefe, Peter

    2004-01-01

    Abstract: The nature of the thermodynamic behavior of Type I superconductor particles, having a cross section less than the Ginzburg-Landau temperature dependent coherence length is discussed for magnetic field induced adiabatic phase transitions from the superconductive state to the normal state. Argument is advanced supporting the view that when the adiabatic magneto-caloric process is applied to particles, the phase transition is characterized by a decrease in entropy in violation of tradi...

  6. Macroscopic weak superconductivity of an NXN Josephson junction array below the Kosterlitz-Thouless transition

    International Nuclear Information System (INIS)

    Shenoy, S.R.; Karlsruhe Univ.

    1983-07-01

    A two-dimensional NXN array of coupled Josephson junctions, each of size tau 0 and Josephson length lambdasub(JO)>>tau 0 , is shown to exhibit macroscopic weak superconductivity. The Josephson phase coherence here extends across the array, vanishing discontinuously at the Kosterlitz-Thouless transition temperature. The transverse size Ntau 0 must be smaller than a few times the effective Josephson screening length lambdasub(J)sup(eff) proportional to lambdasub(JO), for a sharp transition to be seen. (author)

  7. Resistive transition in two-dimensional array of proximity-coupled superconducting weak links

    International Nuclear Information System (INIS)

    Gao Peng; Yu Zheng; Wei Wang; Yao Xi-xian

    1988-01-01

    The Kosterlitz Thouless transition in two-dimensional arrays of proximity-coupled superconducting weak links has been studied in this paper. The samples were prepared by application of the vacuum-evaporation/photoengraving/chemical-etching technique. The experimental results of measurements on some samples of array film showed the existence of the K-T transition in these samples and were consistent with the theory of Lobb, Abraham, and Tinkham

  8. Explore Stochastic Instabilities of Periodic Points by Transition Path Theory

    Science.gov (United States)

    Cao, Yu; Lin, Ling; Zhou, Xiang

    2016-06-01

    We consider the noise-induced transitions from a linearly stable periodic orbit consisting of T periodic points in randomly perturbed discrete logistic map. Traditional large deviation theory and asymptotic analysis at small noise limit cannot distinguish the quantitative difference in noise-induced stochastic instabilities among the T periodic points. To attack this problem, we generalize the transition path theory to the discrete-time continuous-space stochastic process. In our first criterion to quantify the relative instability among T periodic points, we use the distribution of the last passage location related to the transitions from the whole periodic orbit to a prescribed disjoint set. This distribution is related to individual contributions to the transition rate from each periodic points. The second criterion is based on the competency of the transition paths associated with each periodic point. Both criteria utilize the reactive probability current in the transition path theory. Our numerical results for the logistic map reveal the transition mechanism of escaping from the stable periodic orbit and identify which periodic point is more prone to lose stability so as to make successful transitions under random perturbations.

  9. A search for superconductivity below 1 K in transition metal borides

    International Nuclear Information System (INIS)

    Leyarovska, L.; Leyarovski, E.

    1979-01-01

    Some AlB 2 -type (C32 structure) boron compounds were examined for superconductivity down to 0.42 K; the compounds have the formula MeB 2 (Me equivalent to Ti, Zr, Hf, V, Nb, Ta, Cr, Mo) (the atomic ratio of metal to boron was 0.5). Only NbB 2 was found to be superconducting with Tsub(c) = 0.62 K and a surprisingly high value of Hsub(c)(0), about 1600 Oe. Other transition metal as well as non-transition metal boron phases were also tested for superconductivity down to 0.42 K; these compounds were MeB 2 (Me equivalent to Ca, Sr, Ba), W 2 B 5 , CrB, Cr 5 B 3 , UB 2 , UB 4 and UB 12 . None of these compounds proved to be superconducting above 0.42 K; nor was any trace of superconductivity down to 0.42 K observed in MoB and NbB. (Auth.)

  10. Superconducting transition temperature and the formation of closed electron shells in the atoms of superconducting compounds

    International Nuclear Information System (INIS)

    Chapnik, I.M.

    1985-01-01

    The relationship between the regularities in the tansition temperature (T/sub c/) values in analogous compounds (having the same structure and stoichiometry) and the formation of the closed electron shells outside inert gas shells in the atoms of the variable component of the 158 intermetallic superconducting compounds has been discussed. The T/sub c/ data for compounds of the elements from the first long period of the Periodic Table (K to Se) are compared with the T/sub c/ data for the analogous compounds of the elements from the second long period (Rb to Te)

  11. Ecosystem thresholds, tipping points, and critical transitions

    Science.gov (United States)

    Munson, Seth M.; Reed, Sasha C.; Peñuelas, Josep; McDowell, Nathan G.; Sala, Osvaldo E.

    2018-01-01

    Abrupt shifts in ecosystems are cause for concern and will likelyintensify under global change (Scheffer et al., 2001). The terms‘thresho lds’, ‘tipping points’, and ‘critical transitions’ have beenused interchangeably to refer to sudden changes in the integrityor state of an ecosystem caused by environmental drivers(Holling, 1973; May, 1977). Threshold-based concepts havesignific antly aided our capacity to predict the controls overecosystem structure and functioning (Schwinning et al., 2004;Peters et al., 2007) and have become a framework to guide themanagement of natural resources (Glick et al., 2010; Allen et al.,2011). However, our unders tanding of how biotic and abioticdrivers interact to regulate ecosystem responses and of ways toforecast th e impending responses remain limited. Terrestrialecosystems, in particular, are already responding to globalchange in ways that are both transformati onal and difficult topredict due to strong heterogeneity across temporal and spatialscales (Pe~nuelas & Filella, 2001; McDowell et al., 2011;Munson, 2013; Reed et al., 2016). Comparing approaches formeasuring ecosystem performance in response to changingenvironme ntal conditions and for detecting stress and thresholdresponses can improve tradition al tests of resilience and provideearly warning signs of ecosystem transitions. Similarly, com-paring responses across ecosystems can offer insight into themechanisms that underlie variation in threshold responses.

  12. Superconductivity and the structural phase transitions in palladium hydride and palladium deuteride

    International Nuclear Information System (INIS)

    Standley, R.W.

    1980-01-01

    The results of two experimental studies of the superconducting transition temperature, T/sub c/, of palladium hydride, PdH/sub x/, and palladium deuteride, PdD/sub x/, are presented. In the first study, the superconducting transition temperature of PdH/sub x/(D/sub x/) is studied as a function of H(D) concentration, x, in the temperature range from 0.2 K to 4K. The data join smoothly with those reported previously by Miller and Satterthwaite at higher temperatures, and the composite data are described by the empirical relation T/sub c/ = 150.8 (x-x/sub o/) 2 244 , where x/sub o/ = 0.715 for hydride samples and 0.668 for deuteride samples. The results, when compared with the theoretical predictions of Klein and Papaconstantopoulos, et al., raise questions about the validity of their explanation of the reverse isotope effect, which is based solely on a difference in force constants. In the second study, the effect of the order-disorder structural transition associated with the 50 K anomaly on the superconductivity of PdH/sub x/(D/sub x/) is investigated. Samples were quenched to low temperatures in the disordered state, and their transition temperatures measured. The samples were then annealed just below the anomaly temperature, and the ordering process followed by monitoring the change in sample resistance. The transition temperatures in the ordered state were then measured

  13. Mott transition: Low-energy excitations and superconductivity

    International Nuclear Information System (INIS)

    Ioffe, L.B.; Larkin, A.I.

    1988-09-01

    It is possible that metal-dielectric transition does not result in changes of magnetic or crystallographic symmetry. In this case a fermionic spectrum is not changed at the transition, but additional low-energy excitations appear which can be described as a gauge field that has the same symmetry as an electromagnetic one. In the case of a non half-filled band gapless scalar Bose excitations also appear. Due to the presence of additional gauge field the physical conductivity is determined by the lowest conductivity of the Fermi or Bose subsystems. (author). 11 refs

  14. Calculated Changes in the Elastic Properties of MgCNi3 at the Superconducting Transition

    Directory of Open Access Journals (Sweden)

    R. Abd-Shukor

    2013-01-01

    Full Text Available We calculated the elastic properties of MgCNi3 at the superconducting transition ( using various thermodynamic and acoustic data. From the calculations, a step discontinuity of 8 ppm in the bulk modulus, 7 ppm in the Young’s modulus, and 3 ppm in the longitudinal sound velocity ( is expected at . The step discontinuities at the transition temperature indicated the importance of lattice changes to the superconducting mechanism of MgCNi3. The Debye temperature was calculated to be 460 K. The electron-phonon coupling constants calculated in the weak and strong coupling limits of the BCS theory and the van Hove scenario showed that MgCNi3 is a moderately strong coupled superconductor.

  15. Superconductivity suppression near metal-dielectric in transition highly disordered systems

    International Nuclear Information System (INIS)

    Kuchinskij, Eh.Z.; Sadovskij, M.V.; Ehrkabaev, M.A.

    1997-01-01

    The effects of temperature suppression of superconducting transition T c within wide limits of disorders values from low-disordered to highly-disordered ones caused by formation of the Coulomb gap in the states density are studied on the bases of the earlier proposed self consistent theory on the metal-dielectric. It is shown that the proposed theory gives satisfactory description of experimental data for a number of the systems under study

  16. Superconducting transition and low-field magnetoresistance of a niobium single crystal at 4.2 deg. K

    International Nuclear Information System (INIS)

    Perriot, G.

    1967-01-01

    We report the study of the electrical resistance of a niobium single crystal, at 4.2 deg. K, from the beginning of the superconductive transition to 80 kilo oersteds. Critical fieldsH c2 and H c3 have been determined. Influences on superconductive transition of current density, field-current angle, crystal orientation and magnetoresistance have been studied. Variation laws of low-field transverse and longitudinal magneto-resistances have been determined. (author) [fr

  17. Effect of superconductivity on the cubic to tetragonal structural transition due to a two-fold degenerate electronic band

    International Nuclear Information System (INIS)

    Ghatak, S.K.; Khanra, B.C.; Ray, D.K.

    1978-01-01

    The effect of the BCS superconductivity on the cubic to tetragonal structural transition arising from a two-fold degenerate electronic band is investigated within the mean field approximation. The phase diagram of the two transitions is given for a half filled esub(g)-band. Modification of the two transitions when they are close together is also discussed. (author)

  18. Superconductivity

    International Nuclear Information System (INIS)

    Anon.

    1988-01-01

    This book profiles the research activity of 42 companies in the superconductivity field, worldwide. It forms a unique and comprehensive directory to this emerging technology. For each research site, it details the various projects in progress, analyzes the level of activity, pinpoints applications and R and D areas, reviews strategies and provides complete contact information. It lists key individuals, offers international comparisons of government funding, reviews market forecasts and development timetables and features a bibliography of selected articles on the subject

  19. Superconductivity

    International Nuclear Information System (INIS)

    Buller, L.; Carrillo, F.; Dietert, R.; Kotziapashis, A.

    1989-01-01

    Superconductors are materials which combine the property of zero electric resistance with the capability to exclude any adjacent magnetic field. This leads to many large scale applications such as the much publicized levitating train, generation of magnetic fields in MHD electric generators, and special medical diagnostic equipment. On a smaller-scale, superconductive materials could replace existing resistive connectors and decrease signal delays by reducing the RLC time constants. Thus, a computer could operate at much higher speeds, and consequently at lower power levels which would reduce the need for heat removal and allow closer spacing of circuitry. Although technical advances and proposed applications are constantly being published, it should be recognized that superconductivity is a slowly developing technology. It has taken scientists almost eighty years to learn what they now know about this material and its function. The present paper provides an overview of the historical development of superconductivity and describes some of the potential applications for this new technology as it pertains to the electronics industry

  20. Resistive transition of superconducting-wire networks. Influence of pinning and fluctuations

    International Nuclear Information System (INIS)

    Giroud, M.; Buisson, O.; Wang, Y.Y.; Pannetier, B.; Mailly, D.

    1992-01-01

    The authors studied the resistive transition of several 2-D superconducting-wire networks of various coupling strengths, which they characterize in terms of the Kosterlitz-Thouless transition temperature and the ratio ξ/a of the coherence length to the array period. In the extreme strong-coupling limit where the mesh size is of the order of the zero-temperature coherence length, the superconducting behavior is well described by the mean-field properties of the superconducting wave function. Extending to 2-D array, the 1-D phase-slippage model explains the dissipative regime observed above the Ginzburg-Landau depairing critical current. On the other hand, when the coupling is weak, phase fluctuations below the Ginzburg-Landau transition and vortex depinning dominate the resistive behavior. An activated dissipation is observed even below the depairing critical current. Results obtained in this regime for critical temperature, magnetoresistance, or critical current versus temperature, and magnetic field are shown; their periodic oscillations are discussed in terms of depinning of vortices on the array. A simple periodic pinning potential for a vortex in a wire network is calculated, and compared with the case of pinning in Josephson junction arrays. It is shown that this model explains qualitatively the experimental results observed for small ξ/a

  1. Second Law Violation By Magneto-Caloric Effect Adiabatic Phase Transition of Type I Superconductive Particles

    Directory of Open Access Journals (Sweden)

    Peter Keefe

    2004-03-01

    Full Text Available Abstract: The nature of the thermodynamic behavior of Type I superconductor particles, having a cross section less than the Ginzburg-Landau temperature dependent coherence length is discussed for magnetic field induced adiabatic phase transitions from the superconductive state to the normal state. Argument is advanced supporting the view that when the adiabatic magneto-caloric process is applied to particles, the phase transition is characterized by a decrease in entropy in violation of traditional formulations of the Second Law, evidenced by attainment of a final process temperature below that which would result from an adiabatic magneto-caloric process applied to bulk dimensioned specimens.

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

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Shilpam; Amaladass, E.P. [Condensed Matter Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Sharma, Neha [Surface & Nanoscience Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Harimohan, V. [Condensed Matter Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Amirthapandian, S. [Materials Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Mani, Awadhesh, E-mail: mani@igcar.gov.in [Condensed Matter Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)

    2017-06-01

    Disorder driven superconductor to insulator transition via intermediate metallic regime is reported in nano-crystalline thin films of molybdenum. The nano-structured thin films have been deposited at room temperature using DC magnetron sputtering at different argon pressures. The grain size has been tuned using deposition pressure as the sole control parameter. A variation of particle sizes, room temperature resistivity and superconducting transition has been studied as a function of deposition pressure. The nano-crystalline molybdenum thin films are found to have large carrier concentration but very low mobility and electronic mean free path. Hall and conductivity measurements have been used to understand the effect of disorder on the carrier density and mobilities. Ioffe-Regel parameter is shown to correlate with the continuous metal-insulator transition in our samples. - Highlights: • Thin films of molybdenum using DC sputtering have been deposited on glass. • Argon background pressure during sputtering was used to tune the crystallite sizes of films. • Correlation in deposition pressure, disorder and particle sizes has been observed. • Disorder tuned superconductor to insulator transition along with an intermediate metallic phase has been observed. • Enhancement of superconducting transition temperature and a dome shaped T{sub C} vs. deposition pressure phase diagram has been observed.

  3. Superconductivity

    International Nuclear Information System (INIS)

    2007-01-01

    During 2007, a large amount of the work was centred on the ITER project and related tasks. The activities based on low-temperature superconducting (LTS) materials included the manufacture and qualification of ITER full-size conductors under relevant operating conditions, the design of conductors and magnets for the JT-60SA tokamak and the manufacture of the conductors for the European dipole facility. A preliminary study was also performed to develop a new test facility at ENEA in order to test long-length ITER or DEMO full-size conductors. Several studies on different superconducting materials were also started to create a more complete database of superconductor properties, and also for use in magnet design. In this context, an extensive measurement campaign on transport and magnetic properties was carried out on commercially available NbTi strands. Work was started on characterising MgB 2 wire and bulk samples to optimise their performance. In addition, an intense experimental study was started to clarify the effect of mechanical loads on the transport properties of multi-filamentary Nb 3 Sn strands with twisted or untwisted superconducting filaments. The experimental activity on high-temperature superconducting (HTS) materials was mainly focussed on the development and characterisation of YBa 2 Cu 3 O 7-X (YBCO) based coated conductors. Several characteristics regarding YBCO deposition, current transport performance and tape manufacture were investigated. In the framework of chemical approaches for YBCO film growth, a new method, developed in collaboration with the Technical University of Cluj-Napoca (TUCN), Romania, was studied to obtain YBCO film via chemical solution deposition, which modifies the well-assessed metallic organic deposition trifluoroacetate (MOD-TFA) approach. The results are promising in terms of critical current and film thickness values. YBCO properties in films with artificially added pinning sites were characterised in collaboration with

  4. Effect of superconducting transition on microcreep of high-TC ceramics

    International Nuclear Information System (INIS)

    Soldatov, V.P.; Natsik, V.D.; Chajkovskaya, N.M.

    1991-01-01

    Influence of N-S and S-N transition on microplastic deformation kinetics of YBa 2 Cu 3 O 7-δ ceramic samples by there deformation in liquid nitrogen under microscreep conditions is studied. Superconductivity disruption in the sample was achieved by critical value currents. It is shown, that N-S transition increases creep rate,whereas S-N transition slows it down. Microplastic deformation rate by sample state change may very by two-eight times. Influence of heat expansion on creep kinetics as probable associated effect is analyzed. Assumption is expressed, that stimulated transition effect on microplastic deformation of ceramic samples is related to change of their electron state in the area of Josephson contacts between grains

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

    Directory of Open Access Journals (Sweden)

    Romain Maurand

    2012-02-01

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

  6. Multiply Degenerate Exceptional Points and Quantum Phase Transitions

    Czech Academy of Sciences Publication Activity Database

    Borisov, D.; Růžička, František; Znojil, Miloslav

    2015-01-01

    Roč. 54, č. 12 (2015), s. 4293-4305 ISSN 0020-7748 Institutional support: RVO:61389005 Keywords : quantum mechanics * Cryptohermitian observbles * spectra and pseudospectra * real exceptional points * phase transitions Subject RIV: BE - Theoretical Physics Impact factor: 1.041, year: 2015

  7. Two Magnon Raman Scattering as Indicator for Superconducting to Antiferromagnetic Phase Transition Upon Hydrogenation of YBCO

    International Nuclear Information System (INIS)

    Biton, Y.; Shuker, R.

    1999-01-01

    Raman spectra of Hydrogenated YBa 2 Cu 3 O 7-x + H y , where y = 0.45 and 0.19 is the number of Hydrogen atoms per units cell. The spectra exhibit important changes in the electronic scattering. Upon progressive doping with Hydrogen two magnon scattering features emerge. This coincides with the transition of YBa 2 Cu 3 O 7x +H y from superconducting to antiferromagnetic phase. Exchange energy values were obtained from two magnon Raman scattering of the y = 0.45 material. It has been found that for y= 0.19 the sample has not lost its superconductivity, and indeed two-magnon scattering has not been observed. However, the situation changed substantially when the doping of the Hydrogen atoms was 0.45. The two-magnon scattering has been observed at different temperatures down to 20K. The two-magnon energy density exhibits two peak values around 2100cm -1 and 3000cm -1

  8. Investigation of structure, specific heat and superconducting transition in Mg1-xAlxB2(x∼0.5)

    International Nuclear Information System (INIS)

    Xiang, J.Y.; Zheng, D.N.; Lang, P.L.; Zhao, Z.X.; Luo, J.L.

    2004-01-01

    We have carried out structure, magnetic and specific heat measurements on aluminum doped magnetism diboride samples Mg 1-x Al x B 2 in order to investigate possible superconductivity at the x=0.5 concentration. A diamagnetic signal was observed in magnetization measurements accompanied by a decrease in resistivity. However, the diamagnetic signal was extremely small as compared to what expected from full diamagnetism. Also, the transition both in magnetization and resistance was very broad. We propose that the diamagnetism is due to a very small amount of superconducting phase such as MgB 2 and the resistive transition is due to the percolation behavior. Furthermore, we performed specific heat measurements, which are considered as a tool to investigate the bulk nature of superconducting transition, on the x=0.5 sample to verify the existence of superconductivity. We observed no evident superconducting transition in the entire temperature region from 2 to 300 K. The undistinguishable data between 0 and 5 T magnetic fields also indicated the absence of bulk superconductivity in the x=0.5 sample

  9. An approximate method for calculating electron-phonon matrix element of a disordered transition metal and relevant comments on superconductivity

    International Nuclear Information System (INIS)

    Zhang, L.

    1981-08-01

    A method based on the tight-binding approximation is developed to calculate the electron-phonon matrix element for the disordered transition metals. With the method as a basis the experimental Tsub(c) data of the amorphous transition metal superconductors are re-analysed. Some comments on the superconductivity of the disordered materials are given

  10. Two-point entanglement near a quantum phase transition

    International Nuclear Information System (INIS)

    Chen, Han-Dong

    2007-01-01

    In this work, we study the two-point entanglement S(i, j), which measures the entanglement between two separated degrees of freedom (ij) and the rest of system, near a quantum phase transition. Away from the critical point, S(i, j) saturates with a characteristic length scale ξ E , as the distance |i - j| increases. The entanglement length ξ E agrees with the correlation length. The universality and finite size scaling of entanglement are demonstrated in a class of exactly solvable one-dimensional spin model. By connecting the two-point entanglement to correlation functions in the long range limit, we argue that the prediction power of a two-point entanglement is universal as long as the two involved points are separated far enough

  11. Classification of Phase Transitions by Microcanonical Inflection-Point Analysis

    Science.gov (United States)

    Qi, Kai; Bachmann, Michael

    2018-05-01

    By means of the principle of minimal sensitivity we generalize the microcanonical inflection-point analysis method by probing derivatives of the microcanonical entropy for signals of transitions in complex systems. A strategy of systematically identifying and locating independent and dependent phase transitions of any order is proposed. The power of the generalized method is demonstrated in applications to the ferromagnetic Ising model and a coarse-grained model for polymer adsorption onto a substrate. The results shed new light on the intrinsic phase structure of systems with cooperative behavior.

  12. Feedhorn-Coupled Transition-Edge Superconducting Bolometer Arrays for Cosmic Microwave Background Polarimetry

    Science.gov (United States)

    Hubmayr, J.; Austermann, J.; Beall, J.; Becker, D.; Cho, H.-M.; Datta, R.; Duff, S. M.; Grace, E.; Halverson, N.; Henderson, S. W.; hide

    2015-01-01

    NIST produces large-format, dual-polarization-sensitive detector arrays for a broad range of frequencies (30-1400 GHz). Such arrays enable a host of astrophysical measurements. Detectors optimized for cosmic microwave background observations are monolithic, polarization-sensitive arrays based on feedhorn and planar Nb antenna-coupled transition-edge superconducting (TES) bolometers. Recent designs achieve multiband, polarimetric sensing within each spatial pixel. In this proceeding, we describe our multichroic, feedhorn-coupled design; demonstrate performance at 70-380 GHz; and comment on current developments for implementation of these detector arrays in the advanced Atacama Cosmology Telescope receiver

  13. A calorimetric particle detector using an iridium superconducting phase transition thermometer

    International Nuclear Information System (INIS)

    Frank, M.; Dummer, D.; Cooper, S.; Igalson, J.; Proebst, F.; Seidel, W.

    1994-01-01

    We report on a calorimetric particles detector consisting of an 18.3 g silicon crystal and an iridium superconducting phase transition thermometer. The cryogenic calorimeter and the associated apparatus are described in detail. The pulses from irradiation with an α-particle source have a large unexpected overshoot in addition to the component expected from a naive thermal model. The pulse height spectrum displays an energy resolution of 1 percent FWHM at 6 MeV and good linearity. The noise, electrothermal feedback, and position dependence are discussed. (orig.)

  14. Superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Batistoni, Paola; De Marco, Francesco; Pieroni, Leonardo [ed.

    2005-07-01

    Research on superconductivity at ENEA is mainly devoted to projects related to the ITER magnet system. In this framework, ENEA has been strongly involved in the design, manufacturing and test campaigns of the ITER toroidal field model coil (TFMC), which reached a world record in operating current (up to 80 kA). Further to this result, the activities in 2004 were devoted to optimising the ITER conductor performance. ENEA participated in the tasks launched by EFDA to define and produce industrial-scale advanced Nb3Sn strand to be used in manufacturing the ITER high-field central solenoid (CS) and toroidal field (TF) magnets. As well as contributing to the design of the new strand and the final conductor layout, ENEA will also perform characterisation tests, addressing in particular the influence of mechanical stress on the Nb3Sn performance. As a member of the international ITER-magnet testing group, ENEA plays a central role in the measurement campaigns and data analyses for each ITER-related conductor and coil. The next phase in the R and D of the ITER magnets will be their mechanical characterisation in order to define the fabrication route of the coils and structures. During 2004 the cryogenic measurement campaign on the Large Hadron Collider (LHC) by-pass diode stacks was completed. As the diode-test activity was the only LHC contract to be finished on schedule, the 'Centre Europeenne pour la Recherche Nucleaire' (CERN) asked ENEA to participate in an international tender for the cold check of the current leads for the LHC magnets. The contract was obtained, and during 2004, the experimental setup was designed and realised and the data acquisition system was developed. The measurement campaign was successfully started at the end of 2004 and will be completed in 2006.

  15. Transition temperature to the superconducting phase of QCD at high baryon density

    International Nuclear Information System (INIS)

    Brown, William E.; Liu, James T.; Ren, Hai-cang

    2000-01-01

    Recent interest in the study of color superconductivity has focused on the regime of high baryon density where perturbative QCD may be employed. Based on the dominant one-gluon-exchange interaction, both the transition temperature and zero temperature gap have been determined to leading order in the coupling g. While the leading non-BCS behavior T C ∼μg -5 e -κ/g is easily obtained, the pre-exponential factor has proved more difficult to evaluate. Focusing on the transition temperature, we present a perturbative derivation of this factor, exact to leading order in g. This approach is first motivated by the study of a toy model and involves working to second order in the perturbative expansion. We compare this result to the zero temperature gap. Additionally, we extend the analysis to the case of higher angular momentum for longitudinal and transverse quark pairing. (c) 2000 The American Physical Society

  16. Phase transitions in trajectories of a superconducting single-electron transistor coupled to a resonator.

    Science.gov (United States)

    Genway, Sam; Garrahan, Juan P; Lesanovsky, Igor; Armour, Andrew D

    2012-05-01

    Recent progress in the study of dynamical phase transitions has been made with a large-deviation approach to study trajectories of stochastic jumps using a thermodynamic formalism. We study this method applied to an open quantum system consisting of a superconducting single-electron transistor, near the Josephson quasiparticle resonance, coupled to a resonator. We find that the dynamical behavior shown in rare trajectories can be rich even when the mean dynamical activity is small, and thus the formalism gives insights into the form of fluctuations. The structure of the dynamical phase diagram found from the quantum-jump trajectories of the resonator is studied, and we see that sharp transitions in the dynamical activity may be related to the appearance and disappearance of bistabilities in the state of the resonator as system parameters are changed. We also demonstrate that for a fast resonator, the trajectories of quasiparticles are similar to the resonator trajectories.

  17. A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities

    Science.gov (United States)

    Junginger, Tobias; Calatroni, S.; Sublet, A.; Terenziani, G.; Prokscha, T.; Salman, Z.; Suter, A.; Proslier, T.; Zasadzinski, J.

    2017-12-01

    Point contact tunneling and low energy muon spin rotation are used to probe, on the same samples, the surface superconducting properties of micrometer thick niobium films deposited onto copper substrates using different sputtering techniques: diode, dc magnetron and HIPIMS. The combined results are compared to radio-frequency tests performances of RF cavities made with the same processes. Degraded surface superconducting properties are found to correlate to lower quality factors and stronger Q-slope. In addition, both techniques find evidence for surface paramagnetism on all samples and particularly on Nb films prepared by HIPIMS.

  18. Pressure-induced unconventional superconductivity near a quantum critical point in CaFe2As2

    International Nuclear Information System (INIS)

    Kawasaki, S; Tabuchi, T; Zheng Guoqing; Wang, X F; Chen, X H

    2010-01-01

    75 As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe 2 As 2 under pressure. At P = 4.7 and 10.8 kbar, the temperature dependencies of nuclear-spin-lattice relaxation rate (1/T 1 ) measured in the tetragonal phase show no coherence peak just below T c (P) and decrease with decreasing temperature. The superconductivity is gapless at P = 4.7 kbar but evolves to that with multiple gaps at P = 10.8 kbar. We find that the superconductivity appears near a quantum critical point under pressures in the range 4.7 kbar ≤ P ≤ 10.8 kbar. Both electron correlation and superconductivity disappear in the collapsed tetragonal phase. A systematic study under pressure indicates that electron correlations play a vital role in forming Cooper pairs in this compound.

  19. Experimental and Computational Studies of the Superconducting Phase Transition of Quasi 1D Superconductors

    Science.gov (United States)

    Wong, Chi Ho

    In this PhD project, the feasibility of establishing a state with vanishing resistance in quasi-1D superconductors are studied. In the first stage, extrinsic quasi-1D superconductors based on composite materials made by metallic nanowire arrays embedded in mesoporous silica substrates, such as Pb-SBA-15 and NbN-SBA-15 (fabricated by a Chemical Vapor Deposition technique) are investigated. Two impressive outcomes in Pb-SBA-15 are found, including an enormous enhancement of the upper critical field from 0.08T to 14T and an increase of the superconducting transition temperature onset s from 7.2 to 11K. The second stage is to apply Monte Carlo simulations to model the quasi-1D superconductor, considering its penetration depth, coherence length, defects, electron mean free path, tunneling barrier and insulating width between the nanowires. The Monte Carlo results provide a clear picture to approach to stage 3, which represents a study of the intrinsic quasi-1D superconductor Sc3CoC4, which contains parallel arrays of 1D superconducting CoC4 ribbons with weak transverse Josephson or Proximity interaction, embedded in a Sc matrix. According to our previous work, a BKT transition in the lateral plane is believed to be the physics behind the vanishing resistance of quasi-1D superconductors, because it activates a dimensional crossover from a 1D fluctuating superconductivity at high temperature to a 3D bulk phase coherent state in the entire material at low temperatures. Moreover, we decided to study thin 1D Sn nanowires without substrate, which display very similar superconducting properties to Pb-SBA-15 with a strong critical field and Tc enhancement. Finally, a preliminary research on a novel quasi-2D superconductor formed by parallel 2D mercury sheets that are separated by organic molecules is presented. The latter material may represent a model system to study the effect of a layered structure, which is believed to be an effective ingredient to design high temperature

  20. The effect of superconducting transition on macroscopic characteristics of metal and alloy plasticity: fundamental and application aspects

    International Nuclear Information System (INIS)

    Pustovalov, V.V.; Fomenko, V.S.

    2006-01-01

    The results of the papers concerning detection and investigation of the new effect - the changes of macroscopic properties of plastic deformation of metals and alloys at the superconducting transition - are presented. Those papers were the first to demonstrate the efficiency of electron drag of dislocations at low temperature deformation. The review is concerned with the main experimental regularities of the effect - the dependence of plasticity characteristics at the superconducting transition on stress, strain, temperature, strain rate, and doping element concentration in a superconductor. The results suggest the correlation between the effect characteristics and the superconducting properties. The experiments aimed at elucidating the mechanism of the effect are discussed. The theoretical studies into electron retardation of dislocations in metals in normal and superconducting states and the influence of superconducting transition on plasticity are briefly reported. Comparison between theoretical and experimental data is made. The review presents some examples of how the effect can be used as a new method of investigating physical mechanisms of low temperature plastic deformation. Application aspects of the phenomenon are also discussed

  1. Anomalous spectral weight transfer at the superconducting transition of Bi2Sr2CaCu2O8+δ

    International Nuclear Information System (INIS)

    Dessau, D.S.; Wells, B.O.; Shen, Z.; Spicer, W.E.; Arko, A.J.; List, R.S.; Mitzi, D.B.; Kapitulnik, A.

    1991-01-01

    Anomalous spectral weight transfer at the superconducting transition of single-crystalline Bi 2 Sr 2 CaCu 2 O 8+δ was observed by high-resolution angle-resolved photoemission spectroscopy. As the sample goes superconducting, not only is there spectral weight transfer from the gap region to the pileup peak as in BCS theory, but along the Γ-bar M direction there is also some spectral weight transfer from higher binding energies in the form of a dip. In addition, we note that at the superconducting transition there is a decrease (increase) in the occupied spectral weight for the spectra taken along Γ-bar M (Γ-X)

  2. Theory of high-T sub c superconductivity based on the fermion-condensation quantum phase transition

    CERN Document Server

    Amusia, M Ya; Shaginyan, V R

    2001-01-01

    A theory of high temperature superconductivity based on the combination of the fermion-condensation quantum phase transition and the conventional theory of superconductivity is presented. This theory describes maximum values of the superconducting gap which can be as big as DELTA sub 1 approx 0.1 epsilon sub F , with epsilon sub F being the Fermi level. It is shown that the critical temperature 2T sub c approx = DELTA sub 1. If there exists the pseudogap above T sub c then 2T* approx = DELTA sub 1 , and T* is the temperature at which the pseudogap vanished. A discontinuity in the specific heat at T sub c is calculated. The transition from conventional superconductors to high-T sub c ones as a function of the doping level is investigated

  3. Black holes as critical point of quantum phase transition.

    Science.gov (United States)

    Dvali, Gia; Gomez, Cesar

    We reformulate the quantum black hole portrait in the language of modern condensed matter physics. We show that black holes can be understood as a graviton Bose-Einstein condensate at the critical point of a quantum phase transition, identical to what has been observed in systems of cold atoms. The Bogoliubov modes that become degenerate and nearly gapless at this point are the holographic quantum degrees of freedom responsible for the black hole entropy and the information storage. They have no (semi)classical counterparts and become inaccessible in this limit. These findings indicate a deep connection between the seemingly remote systems and suggest a new quantum foundation of holography. They also open an intriguing possibility of simulating black hole information processing in table-top labs.

  4. Transition at the deliquesce point in single salts

    DEFF Research Database (Denmark)

    Rörig-Dalgaard, Inge

    2014-01-01

    Background: Deliquesce points for single salts are in general considered to occur at a specific relative humidity and are also shown as such in phase diagrams. For this reason, salts are used for calibration purpose. According to Gibbs phase rule, the crystalline solid and the saturated solution...... the increasing numbers of thin film water till 20 mbar at 25˚C whereas the deliquescence point is at 24 mbar. These results suggest a stepwise change in the state of the salt. During preparation to salt calibration tests (in a Dynamic Vapour Sorption equipment (DVS)) the author noticed that some single salts...... have a very sudden and accurate change in salt state whereas another salt changed inaccurate as was noticed with NaCl (seen in more than 10 salt preparations). In the present work, the inaccurate transition between the solid NaCl to NaCl in solution was investigated with a cooling stage (CS) in an ESEM...

  5. Development of transition edge superconducting bolometers for the SAFARI Far-Infrared spectrometer on the SPICA space-borne telescope

    NARCIS (Netherlands)

    Mauskopf, P.; Morozov, D.; Glowacka, D.; Goldie, D.; Withington, S.; Bruijn, M.; De Korte, P.; Hoevers, H.; Ridder, M.; Van der Kuur, J.; Gao, J.R.

    2008-01-01

    We describe the optimization of transition edge superconducting (TES) detectors for use in a far-infrared (FIR) Fourier transform spectrometer (FTS) mounted on a cryogenically cooled space-borne telescope (e.g. SPICA). The required noise equivalent power (NEP) of the detectors is approximately 10?19

  6. Introducing Barium in Transition Metal Oxide Frameworks: Impact upon Superconductivity, Magnetism, Multiferroism and Oxygen Diffusion and Storage.

    Science.gov (United States)

    Raveau, Bernard

    2017-06-01

    The role of barium in the structural chemistry of some transition metal oxides of the series "Cu, Mn, Fe,Co" is reviewed, based on its size effect and its particular chemical bonding. Its impact upon various properties, superconductivity, magnetism, multiferroism, oxygen storage is emphasized. © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Upper critical fields and superconducting transition temperatures of some zirconium-base amorphous transition-metal alloys

    International Nuclear Information System (INIS)

    Karkut, M.G.; Hake, R.R.

    1983-01-01

    Superconducting upper critical fields H/sub c/2(T), transition temperatures T/sub c/, and normal-state electrical resistivities rho/sub n/ have been measured in the amorphous transition-metal alloy series Zr/sub 1-z/Co/sub x/, Zr/sub 1-x/Ni/sub x/, (Zr/sub 1-x/Ti/sub x/)/sub 0.78/Ni/sub 0.22/, and (Zr/sub 1-x/Nb/sub x/)/sub 0.78/Ni/sub 0.22/. Structural integrity of these melt-spun alloys is indicated by x-ray, density, bend-ductility, normal-state electrical resistivity, superconducting transition width, and mixed-state flux-pinning measurements. The specimens display T/sub c/ = 2.1--3.8 K, rho/sub n/ = 159--190 μΩ cm, and Vertical Bar(dH/sub c/2/dT)cVertical Bar = 28--36 kG/K. These imply electron mean free paths lroughly-equal2--6 A, zero-temperature Ginzburg-Landau coherence distances xi/sub G/0roughly-equal50--70 A, penetration depths lambda/sub G/0roughly-equal(7--10) x 10 3 A, and extremely high dirtiness parameters xi 0 /lroughly-equal300--1300. All alloys display H/sub c/2(T) curves with negative curvature and (with two exceptions) fair agreement with the standard dirty-limit theory of Werthamer, Helfand, Hohenberg, and Maki (WHHM) for physically reasonable values of spin-orbit-coupling induced, electron-spin-flip scattering time tau/sub so/. This is in contrast to the anomalously elevated H/sub c/2(T) behavior which is nearly linear in T that is observed by some, and the unphysically low-tau/sub so/ fits to WHHM theory obtained by others, for various amorphous alloys

  8. Effect of strain on the martensitic phase transition in superconducting Nb3Sn

    International Nuclear Information System (INIS)

    Hoard, R.W.; Scanlan, R.M.; Smith, G.S.; Farrell, C.L.

    1980-01-01

    The connection between the cubic-to-tetragonal martensitic phase transformation and the phenomenon of superconductivity in A15 compounds is being investigated. The degradation of the critical parameters, such as T/sub c/, H/sub c2/, and J/sub c/, with mechanical straining is of particular interest. Low-temperature x-ray diffraction experiments are performed on Nb 3 Sn ribbons (with the bronze layers etched off) mounted on copper and indium sample stages. The cryostat used is unique in that it has a vacuum mechanical insert which allows the superconductor to be placed under both compressive and tensile strains while at low temperatures. Preliminary results indicate that the martensitic phase transition temperature, T/sub m/, increases with compressive strains. Other effects of strain on tetragonal phase production are also discussed

  9. Phonon-mediated superconducting transition-edge sensor X-ray detectors for use in astronomy

    Science.gov (United States)

    Leman, Steven W.; Martinez-Galarce, Dennis S.; Brink, Paul L.; Cabrera, Blas; Castle, Joseph P.; Morse, Kathleen; Stern, Robert A.; Tomada, Astrid

    2004-09-01

    Superconducting Transition-Edge Sensors (TESs) are generating a great deal of interest in the areas of x-ray astrophysics and space science, particularly to develop them as large-array, imaging x-ray spectrometers. We are developing a novel concept that is based on position-sensitive macro-pixels placing TESs on the backside of a silicon or germanium absorber. Each x-ray absorbed will be position (X/δX and Y/δY ~ 100) and energy (E/δE ~ 1000) resolved via four distributed TES readouts. In the future, combining such macropixels with advances in multiplexing could lead to 30 by 30 arrays of close-packed macro-pixels equivalent to imaging instruments of 10 megapixels or more. We report on our progress to date and discuss its application to a plausible solar satellite mission and plans for future development.

  10. Simulating a topological transition in a superconducting phase qubit by fast adiabatic trajectories

    Science.gov (United States)

    Wang, Tenghui; Zhang, Zhenxing; Xiang, Liang; Gong, Zhihao; Wu, Jianlan; Yin, Yi

    2018-04-01

    The significance of topological phases has been widely recognized in the community of condensed matter physics. The well controllable quantum systems provide an artificial platform to probe and engineer various topological phases. The adiabatic trajectory of a quantum state describes the change of the bulk Bloch eigenstates with the momentum, and this adiabatic simulation method is however practically limited due to quantum dissipation. Here we apply the "shortcut to adiabaticity" (STA) protocol to realize fast adiabatic evolutions in the system of a superconducting phase qubit. The resulting fast adiabatic trajectories illustrate the change of the bulk Bloch eigenstates in the Su-Schrieffer-Heeger (SSH) model. A sharp transition is experimentally determined for the topological invariant of a winding number. Our experiment helps identify the topological Chern number of a two-dimensional toy model, suggesting the applicability of the fast adiabatic simulation method for topological systems.

  11. On the mechanism of high-temperature superconductivity in hydrogen sulfide at 200 GPa: Transition into superconducting anti-adiabatic state in coupling to H-vibrations

    Directory of Open Access Journals (Sweden)

    Pavol Baňacký

    Full Text Available It has been shown that the adiabatic electronic structure of the superconducting phase of sulfur hydride at 200 GPa is unstable toward the vibration motion of H-atoms. A theoretical study indicates that in coupling to H-vibrations, the system undergoes a transition from adiabatic into a stabilized anti-adiabatic multi-gap superconducting state at a temperature that can reach 203 K. Keywords: Superconductivity of sulfur hydride, Electron–phonon coupling in superconductors, Anti-adiabatic theory of superconductivity

  12. Uniaxial strain orientation dependence of superconducting transition temperature (Tc) and critical superconducting pressure (Pc) in β-(BDA-TTP)2I3.

    Science.gov (United States)

    Kikuchi, Koichi; Isono, Takayuki; Kojima, Masayuki; Yoshimoto, Haruo; Kodama, Takeshi; Fujita, Wataru; Yokogawa, Keiichi; Yoshino, Harukazu; Murata, Keizo; Kaihatsu, Takayuki; Akutsu, Hiroki; Yamada, Jun-ichi

    2011-12-14

    Dependence of the superconducting transition temperature (T(c)) and critial superconducting pressure (P(c)) of the pressure-induced superconductor β-(BDA-TTP)(2)I(3) [BDA-TTP = 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] on the orientation of uniaxial strain has been investigated. On the basis of the overlap between the upper and lower bands in the energy dispersion curve, the pressure orientation is thought to change the half-filled band to the quarter-filled one. The observed variations in T(c) and P(c) are explained by considering the degree of application of the pressure and the degree of contribution of the effective electronic correlation at uniaxial strains with different orientations parallel to the conducting donor layer. © 2011 American Chemical Society

  13. Are we getting to the point of understanding high-temperature superconductivity?

    International Nuclear Information System (INIS)

    Huebener, R.P.; Tsuei, C.C.; Newns, D.M.

    1994-01-01

    The model elaborated by van Hove allows a coherent explanation of various anomalies observed with the phenomenon of high-T c superconductivity, including the cause of T c reaching such a high value, or the materials behaving like marginal Fermi liquids. However, there remain other enigma to be solved before it will be possible to fully explain and understand high-T c superconductivity. (DG) [de

  14. The intrinsic crossing point of the magnetization vs. temperature curves in superconducting cuprates in the high-magnetic-field limit

    International Nuclear Information System (INIS)

    Mosqueira, J.; Torron, C.; Veira, J.A.; Vidal, F.

    1998-01-01

    The crossing point of the magnetization vs. temperature curves that appears below T c in highly anisotropic superconducting cuprates was measured in different compounds, with a different number, N, of superconducting CuO 2 layers per periodicity length, s, and also with different values of s. By correcting the measurements from different extrinsic inhomogeneity effects through the Meissner fraction, it is demonstrated experimentally for the first time that in the high-magnetic-field limit the intrinsic crossing point may be explained at a quantitative level in terms of the Tesanovic and coworkers approach based on thermal fluctuations of quasi-2D vortices (pancakes), with an effective periodicity length equal to s, independently of N. (orig.)

  15. Charge Berezinskii-Kosterlitz-Thouless transition in superconducting NbTiN films

    Energy Technology Data Exchange (ETDEWEB)

    Mironov, Alexey Yu.; Silevitch, Daniel M.; Proslier, Thomas; Postolova, Svetlana V.; Burdastyh, Maria V.; Gutakovskii, Anton K.; Rosenbaum, Thomas F.; Vinokur, Valerii V.; Baturina, Tatyana I.

    2018-03-06

    Three decades after the prediction of charge-vortex duality in the critical vicinity of the two-dimensional superconductor-insulator transition (SIT), one of the fundamental implications of this duality-the charge Berezinskii-Kosterlitz-Thouless (BKT) transition that should occur on the insulating side of the SIT-has remained unobserved. The dual picture of the process points to the existence of a superinsulating state endowed with zero conductance at finite temperature. Here, we report the observation of the charge BKT transition on the insulating side of the SIT in 10 nm thick NbTiN films, identified by the BKT critical behavior of the temperature and magnetic field dependent resistance, and map out the magnetic-field dependence of the critical temperature of the charge BKT transition. Finally, we ascertain the effects of the finite electrostatic screening length and its divergence at the magnetic field-tuned approach to the superconductor-insulator transition.

  16. The influence of the s-d(f) Coulomb interaction on the transition element compound superconductive critical temperature

    International Nuclear Information System (INIS)

    Kravtsov, V.E.; Mal'shukov, A.G.

    1978-01-01

    The influence of s-d Coulomb interaction on the superconductive critical temperature Tsub(c) of transition element compounds and their dilute alloys was investigated in the frame of Anderson model. Coulomb interaction of electrons with opposite spins on the same atom was considered in a ladder approximation valid when hybridization is sufficiently small while s-d Coulomb interaction has led to the 'parquet' summation. It is shown that s-d Coulomb interaction results in the decrease of Tsub(c) and hence the electron mechanism of superconductivity seems to be non-effective in systems under consideration. (author)

  17. Effects of a multi-quark interaction on color superconducting phase transition in an extended NJL model

    International Nuclear Information System (INIS)

    Kashiwa, Kouji; Matsuzaki, Masayuki; Kouno, Hiroaki; Yahiro, Masanobu

    2007-01-01

    We study the interplay of the chiral and the color superconducting phase transition in an extended Nambu-Jona-Lasinio model with a multi-quark interaction that produces the nonlinear chiral-diquark coupling. We observe that this nonlinear coupling adds up coherently with the ω 2 interaction to either produce the chiral-color superconductivity coexistence phase or cancel each other depending on its sign. We discuss that a large coexistence region in the phase diagram is consistent with the quark-diquark picture for the nucleon whereas its smallness is the prerequisite for the applicability of the Ginzburg-Landau approach

  18. 1D goes 2D: A Berezinskii-Kosterlitz-Thouless transition in superconducting arrays of 4-Angstrom carbon nanotubes

    KAUST Repository

    Wang, Zhe

    2010-10-01

    We report superconducting resistive transition characteristics for array(s) of coupled 4-Angstrom single wall carbon nanotubes embedded in aluminophosphate-five zeolite. The transition was observed to initiate at 15 K with a slow resistance decrease switching to a sharp, order of magnitude drop between 7.5 and 6.0 K with strong (anisotropic) magnetic field dependence. Both the sharp resistance drop and its attendant nonlinear IV characteristics are consistent with the manifestations of a Berezinskii-Kosterlitz-Thouless transition that establishes quasi long range order in the plane transverse to the c-axis of the nanotubes, leading to an inhomogeneous system comprising 3D superconducting regions connected by weak links. Global coherence is established at below 5 K with the appearance of a well-defined supercurrent gap/low resistance region at 2 K. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Simulations of the L-H transition on experimental advanced superconducting Tokamak

    International Nuclear Information System (INIS)

    Weiland, Jan

    2014-01-01

    We have simulated the L-H transition on the EAST tokamak [Baonian Wan, EAST and HT-7 Teams, and International Collaborators, “Recent experiments in the EAST and HT-7 superconducting tokamaks,” Nucl. Fusion 49, 104011 (2009)] using a predictive transport code where ion and electron temperatures, electron density, and poloidal and toroidal momenta are simulated self consistently. This is, as far as we know, the first theory based simulation of an L-H transition including the whole radius and not making any assumptions about where the barrier should be formed. Another remarkable feature is that we get H-mode gradients in agreement with the α – α d diagram of Rogers et al. [Phys. Rev. Lett. 81, 4396 (1998)]. Then, the feedback loop emerging from the simulations means that the L-H power threshold increases with the temperature at the separatrix. This is a main feature of the C-mod experiments [Hubbard et al., Phys. Plasmas 14, 056109 (2007)]. This is also why the power threshold depends on the direction of the grad B drift in the scrape off layer and also why the power threshold increases with the magnetic field. A further significant general H-mode feature is that the density is much flatter in H-mode than in L-mode

  20. Tunneling measurements in amorphous layers of superconducting transition metals: molybdenum, vanadium, and niobium

    International Nuclear Information System (INIS)

    Roll, U.

    1981-01-01

    Tunneling experiments with amorphous Molybdenum and Vanadium layers are presented, showing no significant increase of the reduced energy gap 2δ(O)/kTsub(c)(δ) compared with the BCS-value, in contrast to all previous measurement on amorphous superconducting materials of simple s-p-metals, showing on enhanced electron-phonon-interaction. This fact may lead to the conclusion that the strong electron-phonon coupling is caused by the amorphous structure of the superconductor. The present results, however, indicate that the strong electron-phonon interaction cannot be explained only ba the amorphous structure of the superconductor. In the measurements of the second derivative d 2 U/dI 2 no phonon-induced structures have been observed for amorphous molybdenum, vanadium and niobium films. Apparently the phonon density of states F(#betta#) of amorphous transition metals has no structure, thus the longitudinal and transverse phonons cannot be identified in the measured (d 2 U/dI 2 )-curves. This particular behaviour of the amorphous transition metals in contrast to the simple s-p-metals may be interpreted by the strongly localized d-electrons. (orig./GG) [de

  1. 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.

  2. Influence of oxygen stoichiometry on the structure and superconducting transition temperature of YBa 2Cu 3O x

    Science.gov (United States)

    Farneth, W. E.; Bordia, R. K.; McCarron, E. M.; Crawford, M. K.; Flippen, R. B.

    1988-06-01

    A detailed study of the superconducting properties and the crystal symmetry of YBa 2Cu 3O x as a function of oxygen content (x) is presented. We correlate the oxygen content, structure and superconducting transition temperature for YBa 2Cu 3O x (6topotactic intercalation/deintercalation of oxygen. It is shown that the orthorhombic to tetragonal phase transition coincides with a loss in superconductivity for samples prepared both by quenching from high temperature and samples prepared by deoxygenation at low temperature. For the orthorhombic phase, T c monotonically decreases as x goes from 7.0 to 6.4 along with a complementary decrease in the extent of orthorhombic distortion. The decrease in T c, however, is not uniform. For quenched samples it shows a plateau for x ˜ 6.75 to 6.55 and then a rather abrupt drop around x ˜ 6.5. Comparison of our data with the literature indicates that the dependence of superconducting properties and crystal structure on the oxygen content can be a complex function of sample processing history. Samples with the same oxygen content but prepared in different ways may have x-ray powder patterns that are indistinguishable, but significantly different electrical properties.

  3. Phase-integral method allowing nearlying transition points

    CERN Document Server

    Fröman, Nanny

    1996-01-01

    The efficiency of the phase-integral method developed by the present au­ thors has been shown both analytically and numerically in many publica­ tions. With the inclusion of supplementary quantities, closely related to new Stokes constants and obtained with the aid of comparison equation technique, important classes of problems in which transition points may approach each other become accessible to accurate analytical treatment. The exposition in this monograph is of a mathematical nature but has important physical applications, some examples of which are found in the adjoined papers. Thus, we would like to emphasize that, although we aim at mathematical rigor, our treatment is made primarily with physical needs in mind. To introduce the reader into the background of this book, we start by de­ scribing the phase-integral approximation of arbitrary order generated from an unspecified base function. This is done in Chapter 1, which is reprinted, after minor changes, from a review article. Chapter 2 is the re...

  4. Point-contact spectroscopic studies on normal and superconducting AFe2As2-type iron pnictide single crystals

    International Nuclear Information System (INIS)

    Lu Xin; Park, W K; Greene, L H; Yuan, H Q; Chen, G F; Luo, G L; Wang, N L; Sefat, A S; McGuire, M A; Jin, R; Sales, B C; Mandrus, D; Gillett, J; Sebastian, Suchitra E

    2010-01-01

    Point-contact Andreev reflection spectroscopy is applied to investigate the gap structure in iron pnictide single-crystal superconductors of the AFe 2 As 2 (A = Ba, Sr) family ('Fe-122'). The observed point-contact junction conductance curves, G(V), can be divided into two categories: one where Andreev reflection is present for both (Ba 0.6 K 0.4 )Fe 2 As 2 and Ba(Fe 0.9 Co 0.1 ) 2 As 2 , and the other with a V 2/3 background conductance universally observed, extending even up to 100 meV for Sr 0.6 Na 0.4 Fe 2 As 2 and Sr(Fe 0.9 Co 0.1 ) 2 As 2 . The latter is also observed in point-contact junctions on the nonsuperconducting parent compound BaFe 2 As 2 and superconducting (Ba 0.6 K 0.4 )Fe 2 As 2 crystals. Mesoscopic phase-separated coexistence of magnetic and superconducting orders is considered to explain distinct behaviors in the superconducting samples. For Ba 0.6 K 0.4 Fe 2 As 2 , double peaks due to Andreev reflection with a strongly sloping background are frequently observed for point contacts on freshly cleaved c-axis surfaces. If normalized using a background baseline and analyzed using the Blonder-Tinkham-Klapwijk model, the data show a gap size of ∼ 3.0-4.0 meV with 2Δ 0 /k B T c ∼ 2.0-2.6, consistent with the smaller gap size reported for the LnFeAsO family ('Fe-1111'). For the Ba(Fe 0.9 Co 0.1 ) 2 As 2 , the G(V) curves typically display a zero-bias conductance peak.

  5. Ginzburg-Landau theory and the superconducting transition in thin, amorphous bismuth films

    International Nuclear Information System (INIS)

    Van Vechten, D.

    1979-01-01

    The Aslamasov-Larkin (AL) theory can be derived from a classical treatment of the conductivity due to short-lived statistical fluctuations into the superconducting state if one truncates the Ginzburg-Landau free energy density expression to read F[psi] = α 0 vertical barpsi vertical bar 2 + c 0 vertical bar del psi vertical bar 2 , where psi is the superconducting order parameter. The next largest term in the GL free energy is (b/2) (vertical bar psi vertical bar 2 ) 2 and is conventionally interpreted as representing the energy associated with interactions between the fluctuations. My dissertation consists of the calculation of the effect of this term on the fluctuation conductivity in three different approximations and the comparison of my predictions to the data of R.E. Glover III and M.K. Chien on thin amorphous bismuth films. The first approximation calculates the contribution to the fluctuations' self energy of the ''tadpole'' diagrams. This approximation yields a 4 parameter equation. Its fits were particularly outstanding for the films deposited on quartz or roughened glass substrates and only for two smooth glass substrates were there non-isolated data points that were not fit at the lowest temperatures measured. (The equation runs into trouble for these films at approximately R(T)/R/sub o/ =.08.) The values of the theoretical equation's fitting parameters were determined by a least squares method and turns out to depend on film thickness in the manner predicted by the theory. The next calculation improves the self energy approximation by including all the ''ring'' diagrams

  6. Properties of a tunnel point contact between aluminum and the superconducting amorphous alloy NiZr2

    International Nuclear Information System (INIS)

    Gantmakher, V.F.; Golubov, A.A.; Osherov, M.V.

    1989-01-01

    The I-V characteristics of a tunnel point contact between aluminum and an amorphous ribbon resembling NiZr 2 in composition differ qualitatively from those of ordinary tunnel junctions between a superconductor and a normal metal. It is demonstrated that the observed curve shapes cannot be explained by accounting solely for one-particle tunneling in conditions of the proximity effect. This is followed by a qualitative discussion of a model in which the current rise at the potential eV equal to the gap width Δ (T) is generated by two-particle electron tunneling through the intermediate state which is manifested as a Cooper pair on the Fermi-level in the thin superconducting layer produced in the aluminum by the proximity effect. The current flowing through the contact will cause a breakdown of superconductivity in the vicinity of the contact at voltages exceeding the gap width. Smallness of the junction plays a decisive role both in inducing superconductivity for eV Δ

  7. Characterization of the microwave properties of superconducting films with high transition temperature

    International Nuclear Information System (INIS)

    Richter, W.; Klinger, M.; Daginnus, M.

    1989-01-01

    In the meantime high quality Y-Ba-Cu-O thin films were produced. The latest results show, that its surface resistances are clearly lower than the values of copper, measured at a temperature of 77 K and up to frequencies of 86 GHz. This examination had the aim to produce high-T c films with a simple and low cost method, to use them as transmission lines at frequencies up to 30 GHz and above. A screen printing process was investigated, and high-T c thick films were fabricated on several substrates. Superconducting transition temperatures up to 80 K (dc zero resistance) were obtained. The films showed no complete magnetic shielding, and its microwave surface resistances were clearly higher than that ones for copper. The a. c. Josephson effect was proved with granular structures of bulk Y-Ba-Cu-O material and with screen printed thick films. Because of its high surface resistances, these thick films are unsuitable for the use as transmission lines at high frequencies. However, the a.c. Josephson effect can be used to manufacture microwave sensors in bulk Y-Ba-Cu-O and screen printed films of Y-Ba-Cu-O, which have a favourable geometric structure. (orig.) With 16 refs., 2 tabs., 24 figs [de

  8. On superconducting double transition in a heavy fermion material UPt3

    International Nuclear Information System (INIS)

    Ozaki, Masa-aki; Machida, Kazushige.

    1992-01-01

    In order to explain phase diagrams independent of field-orientation, which is now evident in UPt 3 , we present a scenario based on a superconducting (SC) class belonging to the one-dimensional representation (1D-REP) with odd-parity. The preexisting antiferromagnetic order (AF) lifts the spin space degeneracy of the pairing function to split T c , which is contrasted with the orbital degeneracy lifting mechanism in the previous 2D-REP scenario. A non-trivial coupling of the two orderings, SC and AF is derived and a GL theory is developed to examine the successive phase transitions. We calculate several quantities, including the upper and lower critical fields, specific heat jumps and derive the phase diagrams under applied fields. It is demonstrated that the present 1D-REP scenario is more consistent with various experiments on UPt 3 than the previous 2D-REP one. We emphasize that the 1D-REP scenario is the only choice remained within the symmetry breaking framework, which is able to consistently explain the experiments. (author)

  9. Evidence of multiband superconductivity in the quaternary borocarbide superconductor YNi2B2C using directional point-contact spectroscopy

    International Nuclear Information System (INIS)

    Raychaudhuri, Pratap; Sheet, Goutam; Mukhopadhyay, Sourin; Takeya, H.

    2007-01-01

    In this paper, we review our recent investigations on the gap anisotropy of the quaternary borocarbide superconductor YNi 2 B 2 C using directional point-contact spectroscopy. Through a detailed study of the temperature and magnetic field dependence of the superconducting energy gaps we show that the gap anisotropy in this material originates from electrons on different Fermi sheets having very different Fermi velocities. The gap anisotropy in this material is therefore well explained through a multiband scenario where electrons in different k-directions have very different electron-phonon coupling strength

  10. Levitation and lateral forces between a point magnetic dipole and a superconducting sphere

    International Nuclear Information System (INIS)

    Al-Khateeb, H M; Alqadi, M K; Alzoubi, F Y; Albiss, B; Hasan, M K; Ayoub, N Y

    2016-01-01

    The dipole–dipole interaction model is employed to investigate the angular dependence of the levitation and lateral forces acting on a small magnet in an anti-symmetric magnet/superconducting sphere system. Breaking the symmetry of the system enables us to study the lateral force which is important in the stability of the magnet above a superconducting sphere in the Meissner state. Under the assumption that the lateral displacement of the magnet is small compared to the physical dimensions of our proposed system, analytical expressions are obtained for the levitation and lateral forces as a function of the geometrical parameters of the superconductor as well as the height, the lateral displacement, and the orientation of the magnetic moment of the magnet. The dependence of the levitation force on the height of the levitating magnet is similar to that in the symmetric magnet/superconducting sphere system within the range of proposed lateral displacements. It is found that the levitation force is linearly dependent on the lateral displacement whereas the lateral force is independent of this displacement. A sinusoidal variation of both forces as a function of the polar and azimuthal angles specifying the orientation of the magnetic moment is observed. The relationship between the stability and the orientation of the magnetic moment is discussed for different orientations. (paper)

  11. 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.

  12. Study on the effect of transition curve to the dynamic characteristics of high-temperature superconducting maglev

    Science.gov (United States)

    Qian, Nan; Zheng, Botian; Gou, Yanfeng; Chen, Ping; Zheng, Jun; Deng, Zigang

    2015-12-01

    High temperature superconducting (HTS) maglev technology is becoming more and more mature, and many key technologies have been deeply studied. However, the transition curve plays a key role in HTS maglev system, and related studies have not been carried out. In this paper series of simulations were conducted to test the lateral and vertical vibration of HTS maglev when passing through curves. Two magnetic guideways, of which one has transition curves but the other does not, are designed to test the vibration characteristics of a mini HTS maglev model running though curves. Results show that after adding transition curves between straight line and circular curve the vibration of HTS maglev model in lateral and vertical directions are all weakened in different degrees. It proves that adding transition curve into HTS maglev system is favorable and necessary.

  13. Antidiabetic Theory of Superconducting State Transition: Phonons and Strong Electron Correlations the Old Physics and New Aspects

    International Nuclear Information System (INIS)

    Banacky, P.

    2010-01-01

    Complex electronic ground state of molecular and solid state system is analyzed on the ab initio level beyond the adiabatic Born-Oppenheimer approximation (BOA). The attention is focused on the band structure fluctuation (BSF) at Fermi level, which is induced by electron-phonon coupling in superconductors, and which is absent in the non-superconducting analogues. The BSF in superconductors results in breakdown of the adiabatic BOA. At these circumstances, chemical potential is substantially reduced and system is stabilized (effect of nuclear dynamics) in the anti adiabatic state at broken symmetry with a gap(s) in one-particle spectrum. Distorted nuclear structure has fluxional character and geometric degeneracy of the anti adiabatic ground state enables formation of mobile bipolarons in real space. It has been shown that an effective attractive e-e interaction (Cooper-pair formation) is in fact correction to electron correlation energy at transition from adiabatic into anti adiabatic ground electronic state. In this respect, Cooper-pair formation is not the primary reason for transition into superconducting state, but it is a consequence of anti adiabatic state formation. It has been shown that thermodynamic properties of system in anti adiabatic state correspond to thermodynamics of superconducting state. Illustrative application of the theory for different types of superconductors is presented.

  14. Positron-annihilation studies of the superconductivity transition in YBa2Cu3O/sub 7-//sub x/

    International Nuclear Information System (INIS)

    Smedskjaer, L.C.; Veal, B.W.; Legnini, D.G.; Paulikas, A.P.; Nowicki, L.J.

    1988-01-01

    Positron-annihilation studies, by Doppler broadening, of the superconducting transition in YBa 2 Cu 3 O/sub 7-//sub x/(x≅0.1) have been made. Below T/sub c/ a large positive temperature dependence of the lineshape parameter is observed, while at (or near) T/sub c/ an almost discontinuous increase in the lineshape parameter takes place. The behavior below T/sub c/ may be consistent with a Bardeen-Cooper-Schrieffer-like theory if an energy band with a small dispersion crosses the Fermi level. The discontinuity is not clearly understood, but may be due to a major change in the electronic structure taking place with the onset of superconductivity

  15. Capacitor energy needed to induce transitions from the superconducting to the normal state

    International Nuclear Information System (INIS)

    Eberhard, P.H.; Ross, R.R.

    1985-08-01

    The purpose of this paper is to describe a technique to turn a long length of superconducting wire normal by dumping a charged capacitor into it and justify some formulae needed in the design. The physical phenomenon is described. A formula for the energy to be stored in the capacitor is given. There are circumstances where the dc in an electrical circuit containing superconducting elements has to be turned off quickly and where the most convenient way to switch the current off is to turn a large portion or all of the superconducting wire normal. Such was the case of the Time Projection Chamber (TPC) superconducting magnet as soon as a quench was detected. The technique used was the discharge of a capacitor into the coil center tap. It turned the magnet winding normal in ten milliseconds or so and provided an adequate quench protection. The technique of discharging a capacitor into a superconducting wire should have many other applications whenever a substantial resistance in a superconducting circuit has to be generated in that kind of time scale. The process involves generating a pulse of large currents in some part of the circuit and heating the wire up by ac losses until the value of the wire critical current is smaller than the dc current. Use of low inductance connections to the circuit is necessary. Then the dc gets turned off due to the resistance of the wire as in a magnet quench

  16. Study of the L–I–H transition with a new dual gas puff imaging system in the EAST superconducting tokamak

    DEFF Research Database (Denmark)

    Xu, G.S.; Shao, L.M.; Liu, S.C.

    2014-01-01

    The intermediate oscillatory phase during the L–H transition, termed the I-phase, is studied in the EAST superconducting tokamak using a newly developed dual gas puff imaging (GPI) system near the L–H transition power threshold. The experimental observations suggest that the oscillatory behaviour...

  17. Third-order gas-liquid phase transition and the nature of Andrews critical point

    Directory of Open Access Journals (Sweden)

    Tian Ma

    2011-12-01

    Full Text Available The main objective of this article is to study the nature of the Andrews critical point in the gas-liquid transition in a physical-vapor transport (PVT system. A dynamical model, consistent with the van der Waals equation near the Andrews critical point, is derived. With this model, we deduce two physical parameters, which interact exactly at the Andrews critical point, and which dictate the dynamic transition behavior near the Andrews critical point. In particular, it is shown that 1 the gas-liquid co-existence curve can be extended beyond the Andrews critical point, and 2 the transition is first order before the critical point, second-order at the critical point, and third order beyond the Andrews critical point. This clearly explains why it is hard to observe the gas-liquid phase transition beyond the Andrews critical point. Furthermore, the analysis leads naturally the introduction of a general asymmetry principle of fluctuations and the preferred transition mechanism for a thermodynamic system. The theoretical results derived in this article are in agreement with the experimental results obtained in (K. Nishikawa and T. Morita, Fluid behavior at supercritical states studied by small-angle X-ray scattering, Journal of Supercritical Fluid, 13 (1998, pp. 143-148. Also, the derived second-order transition at the critical point is consistent with the result obtained in (M. Fisher, Specific heat of a gas near the critical point, Physical Review, 136:6A (1964, pp. A1599-A1604.

  18. Superconducting and Structural Transitions in the β-Pyrochlore Oxide KOs2O6 under High Pressure

    Science.gov (United States)

    Ogusu, Hiroki; Takeshita, Nao; Izawa, Koichi; Yamaura, Jun-ichi; Ohishi, Yasuo; Tsutsui, Satoshi; Okamoto, Yoshihiko; Hiroi, Zenji

    2010-11-01

    Rattling-induced superconductivity in the β-pyrochlore oxide KOs2O6 is investigated under high pressure up to 5 GPa. Resistivity measurements in a high-quality single crystal reveal a gradual decrease in the superconducting transition temperature Tc from 9.7 K at 1.0 GPa to 6.5 K at 3.5 GPa, followed by a sudden drop to 3.3 K at 3.6 GPa. Powder X-ray diffraction experiments show a structural transition from cubic to monoclinic or triclinic at a similar pressure. The sudden drop in Tc is ascribed to this structural transition, by which an enhancement in Tc due to a strong electron-rattler interaction present in the low-pressure cubic phase is abrogated as the rattling of the K ion is completely suppressed or weakened in the high-pressure phase of reduced symmetry. In addition, we find two anomalies in the temperature dependence of resistivity in the low-pressure phase, which may be due to subtle changes in rattling vibration.

  19. Superconductivity: Phenomenology

    International Nuclear Information System (INIS)

    Falicov, L.M.

    1988-08-01

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

  20. Sacral Theater, a code to simulate the propagation of the superconducting magnet LHC atlas barrel toroid transition

    International Nuclear Information System (INIS)

    Gastineau, B.

    2000-06-01

    Sacral Theater has been developed for the toroid magnet Atlas of the CERN LHC project. This three dimensional calculations code calculates the propagation of the transition of a superconducting coil in 25 m long hippodrome. Procedures to study low currents have been included. This work is a part of the magnet safety system because the coils protection is made by warmers activating the quench propagation in case of default detection. This allows the complete dissipation of storage energy that can reach 1080 MJ on Atlas. (N.C.)

  1. A novel transition radiation detector utilizing superconducting microspheres for measuring the energy of relativistic high-energy charged particles

    International Nuclear Information System (INIS)

    Yuan, Luke C.L.; Chen, C.P.; Huang, C.Y.; Lee, S.C.; Waysand, G.; Perrier, P.; Limagne, D.; Jeudy, V.; Girard, T.

    2000-01-01

    A novel transition radiation detector (TRD) utilizing superheated superconducting microspheres of tin of 22-26, 27-32 and 32-38 μm in diameter, respectively, has been constructed which is capable of measuring accurately the energy of relativistic high-energy charged particles. The test has been conducted in a high-energy electron beam facility at the CERN PS in the energy range of 1-10 GeV showing an energy dependence of the TR X-ray photon produced and hence the value γ=E/mc 2 of the charged particle

  2. Relationship between superconducting transition temperature and number of CuO2 layers in mercury-based superconductors

    International Nuclear Information System (INIS)

    Chen Xiaojia; Xu Zhuan; Jiao Zhengkuan; Zhang Qirui

    1997-01-01

    The nonmonotonic dependence of the superconducting transition temperature on the number of CuO 2 layers (n) per unit cell for mercury-based cuprate systems is investigated with the framework of the electrostatic model and the Ginsburg-Landau theory. It is found that the largest value of the normalized density of states is 1.8 when n=3, which corresponds to the highest T c in this series. Using reasonable parameters we predict an upper limit of T c of 160 K. (orig.)

  3. Two gap superconductivity in Ba0.55K0.45Fe2As2 single crystals studied by the directional point-contact Andreev reflection spectroscopy

    International Nuclear Information System (INIS)

    Szabo, P.; Pribulova, Z.; Pristas, G.; Bud'ko, S.L.; Canfield, P.C.; Samuely, P.

    2009-01-01

    First directional point-contact Andreev reflection spectroscopy on the Ba 0.55 K 0.45 Fe 2 As 2 single crystals is presented. The spectra show significant differences when measured in the ab plane in comparison with those measured in the c direction. In the latter case no traces of superconducting energy gap could be found, just a reduced point-contact conductance persisting up to about 100 K and indicating reduced density of states. On the other hand within the ab plane two nodeless superconducting energy gaps Δ S ∼2-5 meV and Δ L ∼9-11 meV are detected.

  4. Novel superconductivity at the magnetic critical point in heavy-fermion systems: a systematic study of NQR under pressure

    International Nuclear Information System (INIS)

    Kitaoka, Y; Kawasaki, S; Kawasaki, Y; Mito, T; Zheng, G-q

    2007-01-01

    We report on the discovery of exotic superconductivity (SC) and novel magnetism in heavy-fermion (HF) compounds, CeCu 2 Si 2 , CeRhIn 5 and CeIn 3 , on the verge of antiferromagnetism (AFM) through nuclear-quadrupole-resonance (NQR) measurements under pressure (P). The exotic SC in a homogeneous CeCu 2 Si 2 (T c = 0.7 K) revealed antiferromagnetic critical fluctuations at the border to AFM or a marginal AFM. Remarkably, it has been found that the application of magnetic field induces a spin-density-wave (SDW) transition by suppressing the SC near the upper critical field. Furthermore, the uniform mixed phase of SC and AFM in CeCu 2 (Si 1-x Ge x ) 2 emerges on a microscopic level, once a tiny amount of 1% Ge (x = 0.01) is substituted for Si to expand its lattice. The application of minute pressure (P∼0.19 GPa) suppresses the sudden emergence of the AFM caused by doping Ge. The persistence of the low-lying magnetic excitations at temperatures lower than T c and T N is ascribed to the uniform mixed phase of SC and AFM. Likewise, the P-induced HF superconductor CeRhIn 5 coexists with AFM on a microscopic level in P = 1.5-1.9 GPa. It is demonstrated that SC does not yield any trace of gap opening in low-lying excitations below the onset temperature, presumably associated with an amplitude fluctuation of superconducting order parameter. The unconventional gapless nature of SC in the low-lying excitation spectrum emerges due to the uniform mixed phase of AFM and SC. By contrast, in CeIn 3 , the P-induced phase separation of AFM and paramagnetism (PM) takes place without any trace for a quantum phase transition. The outstanding finding is that SC sets in at both the phases magnetically separated into AFM and PM in P = 2.28-2.5 GPa. A new type of SC forms the uniform mixed phase with AFM and the HF SC occurs in PM. We propose that the magnetic excitations such as spin-density fluctuations induced by the first-order phase transition from AFM to PM might mediate attractive

  5. Study on the effect of transition curve to the dynamic characteristics of high-temperature superconducting maglev

    International Nuclear Information System (INIS)

    Qian, Nan; Zheng, Botian; Gou, Yanfeng; Chen, Ping; Zheng, Jun; Deng, Zigang

    2015-01-01

    Highlights: • Vibration of a HTS maglev model on two guideways was studied. • Simulation about vibration of HTS maglev on two guideways is accomplished. • Transition curve can weaken vibration of HTS maglev effectively when it running through curves. • Dynamic characteristics of HTS maglev can be enhanced with transition curve. - Abstract: High temperature superconducting (HTS) maglev technology is becoming more and more mature, and many key technologies have been deeply studied. However, the transition curve plays a key role in HTS maglev system, and related studies have not been carried out. In this paper series of simulations were conducted to test the lateral and vertical vibration of HTS maglev when passing through curves. Two magnetic guideways, of which one has transition curves but the other does not, are designed to test the vibration characteristics of a mini HTS maglev model running though curves. Results show that after adding transition curves between straight line and circular curve the vibration of HTS maglev model in lateral and vertical directions are all weakened in different degrees. It proves that adding transition curve into HTS maglev system is favorable and necessary.

  6. Study on the effect of transition curve to the dynamic characteristics of high-temperature superconducting maglev

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Nan [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); Zheng, Botian [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, P R China (China); Gou, Yanfeng [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); Chen, Ping [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, P R China (China); Zheng, Jun [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China); Deng, Zigang, E-mail: deng@swjtu.cn [Applied Superconductivity Laboratory, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P R China (China)

    2015-12-15

    Highlights: • Vibration of a HTS maglev model on two guideways was studied. • Simulation about vibration of HTS maglev on two guideways is accomplished. • Transition curve can weaken vibration of HTS maglev effectively when it running through curves. • Dynamic characteristics of HTS maglev can be enhanced with transition curve. - Abstract: High temperature superconducting (HTS) maglev technology is becoming more and more mature, and many key technologies have been deeply studied. However, the transition curve plays a key role in HTS maglev system, and related studies have not been carried out. In this paper series of simulations were conducted to test the lateral and vertical vibration of HTS maglev when passing through curves. Two magnetic guideways, of which one has transition curves but the other does not, are designed to test the vibration characteristics of a mini HTS maglev model running though curves. Results show that after adding transition curves between straight line and circular curve the vibration of HTS maglev model in lateral and vertical directions are all weakened in different degrees. It proves that adding transition curve into HTS maglev system is favorable and necessary.

  7. Structural, magnetic and superconducting phase transitions in CaFe2As2 under ambient and applied pressure

    International Nuclear Information System (INIS)

    Canfield, P.C.; Bud'ko, S.L.; Ni, N.; Kreyssig, A.; Goldman, A.I.; McQueeney, R.J.; Torikachvili, M.S.; Argyriou, D.N.; Luke, G.; Yu, W.

    2009-01-01

    At ambient pressure CaFe 2 As 2 has been found to undergo a first order phase transition from a high temperature, tetragonal phase to a low-temperature orthorhombic/antiferromagnetic phase upon cooling through T ∼ 170 K. With the application of pressure this phase transition is rapidly suppressed and by ∼0.35 GPa it is replaced by a first order phase transition to a low-temperature collapsed tetragonal, non-magnetic phase. Further application of pressure leads to an increase of the tetragonal to collapsed tetragonal phase transition temperature, with it crossing room temperature by ∼1.7 GPa. Given the exceptionally large and anisotropic change in unit cell dimensions associated with the collapsed tetragonal phase, the state of the pressure medium (liquid or solid) at the transition temperature has profound effects on the low-temperature state of the sample. For He-gas cells the pressure is as close to hydrostatic as possible and the transitions are sharp and the sample appears to be single phase at low temperatures. For liquid media cells at temperatures below media freezing, the CaFe 2 As 2 transforms when it is encased by a frozen media and enters into a low-temperature multi-crystallographic-phase state, leading to what appears to be a strain stabilized superconducting state at low temperatures.

  8. On the origin of the double superconducting transition in overdoped YBa{sub 2}Cu{sub 3}O {sub x}

    Energy Technology Data Exchange (ETDEWEB)

    Lortz, R. [Department of Condensed Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, CH-1211 Geneva 4 (Switzerland)]. E-mail: Rolf.Lortz@physics.unige.ch; Tomita, T. [Department of Physics, Washington University, CB 1105, One Brookings Dr., St. Louis, MO 63130 (United States); Wang, Y. [Department of Condensed Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, CH-1211 Geneva 4 (Switzerland); Junod, A. [Department of Condensed Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, CH-1211 Geneva 4 (Switzerland); Schilling, J.S. [Department of Physics, Washington University, CB 1105, One Brookings Dr., St. Louis, MO 63130 (United States); Masui, T. [Department of Physics, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Tajima, S. [Department of Physics, Osaka University, Toyonaka, Osaka 560-0043 (Japan)

    2006-02-15

    The superconducting transition in a single overdoped, detwinned YBa{sub 2}Cu{sub 3}O {sub x} (YBCO) crystal is studied using four different probes. Whereas the AC and DC magnetic susceptibilities find a dominant transition at 88 K with a smaller effect near 92 K, the specific heat and electrical resistivity reveal only a single transition at 88 K and 92 K, respectively. Under hydrostatic pressures to 0.60 GPa these two transitions shift in opposite directions, their separation increasing. The present experiments clearly show that the bulk transition lies at 88 K and originates from fully oxygenated YBCO; the 92 K transition likely arises from filamentary superconductivity in a minority optimally doped phase (<1%) of YBCO located at or near the crystal surface.

  9. Magnetization relaxation in spin glasses above transition point

    International Nuclear Information System (INIS)

    Zajtsev, I.A.; Minakov, A.A.; Galonzka, R.R.

    1988-01-01

    Magnetization relaxation of Cd 0.6 Zn 0.4 Cr 2 Se 4 and Cd 0.6 Mn 0.4 Te monocrystalline samples with T g =21 K and T g =12 K respectively and magnetic colloid is investigated. It is shown that magnetization inexponential relaxation detected experimentally in spin and dipole glasses is essentially higher than T g temperature transition. It is found that at temperatures higher than T g the essential difference is observed in behaviour of spin glasses with different Z and disorder types

  10. Mid-point review of the German energy transition

    International Nuclear Information System (INIS)

    Lauer, H.; Safa, H.; Guidez, J.

    2017-01-01

    The result of the 2015 review of the German energy transition is lukewarm. First: generating 20 % of the electricity production through wind power and solar energy appears to be very costly in Germany. Secondly there is practically no effect on the reduction of CO_2 releases as coal has been re-introduced to play the role of nuclear energy which was carbon-free to counter-balance the intermittency of renewable energies. Thirdly a necessity to keep all thermal plants ready to operate in order to cope with the intermittency of renewable energies as no adequate means of energy storage is available, appears to be a luxury that only Germany can afford. And fourthly, the cost of electric power for households and small enterprises is all the higher as the government economic policy is to spare German electro-intensive industry. One of the side effects of the German energy transition policy is to disturb the European market of electricity when favourable climate conditions make green electricity very abundant. In this situation electricity prices drop sharply and can even become negative while green electricity is always paid to the producer at a steady price guaranteed by the state. (A.C.)

  11. Integrated high-transition temperature magnetometer with only two superconducting layers

    DEFF Research Database (Denmark)

    Kromann, R.; Kingston, J.J.; Miklich, A.H.

    1993-01-01

    We describe the fabrication and testing of an integrated YBa2Cu3O7-x thin-film magnetometer consisting of a dc superconducting quantum interference device (SQUID), with biepitaxial grain boundary junctions, integrated with a flux transformer on a single substrate. Only two superconducting layers...... are required, the SQUID body serving as the crossunder that completes the multiturn flux transformer. The highest temperature at which any of the magnetometers functioned was 76 K. At 60 K the magnetic field gain of this device was 63, and the magnetic field noise was 160 fT Hz-1/2 at 2 kHz, increasing to 3...

  12. Reply to ''Comment on 'Metal-insulator transition in random superconducting networks' ''

    International Nuclear Information System (INIS)

    Soukoulis, C.M.; Li, Q.; Grest, G.S.

    1990-01-01

    We address the remarks of Dominguez, Lopez, and Simonin [Phys. Rev.B 42, 8665 (1990); preceding paper] on the determination of the normal-to-superconducting (N-S) phase boundary in randomsuperconducting networks. We refute their claims that the disappearanceof the fine structure of the N-S boundary and the change of the critical exponent k for the slope of the critical field on(p-p c ) are due to the introduction of very weak links between nodes in the superconducting networks

  13. Ion-channeling study of anomalous atomic displacements at the superconducting transition in high-Tc materials

    International Nuclear Information System (INIS)

    Rehn, L.E.; Sharma, R.P.; Baldo, P.M.

    1991-01-01

    Ion channeling along the [001] direction in high-quality single crystals of (Y/Er)Ba 2 Cu 3 O 7-x revealed an abrupt change in displace-ments in the a-b plane of the Cu and O atoms at the superconducting transition, T c ; normal 'Debye-like' vibrations were found for the Y/Er and Ba atoms. The anomalous change in Cu-O displacements was found to shift directly with stoichiometry-induced changes in T c , implying a direct link between the observed phonon anomaly and the superconducting transition. Recent measurements of ion-channeling along the [001] axis in (Bi 1.7 Pb 0.3 )Sr 2 Ca 1 Cu 2 O x single-crystals revealed a similar change at T c , suggesting that this phonon anomaly is a general feature of high-T c superconductivity. In order to identify more specifically the crystallographic directions and displacement amplitudes associated with the anomalous phonon behavior, axial channeling scans using RBS, as well as characteristic x-ray production, were taken at several temperatures between 30 and 300K along the [301] and [331] directions of YBa 2 Cu 3 O 7-x single crystals. Twins present in the specimens, and the existing static atomic displacements present along these directions, caused the channeling to be poorer along these axes compared to the (001) direction. Also, a much stronger dependence of the minimum yield on depth was observed. However, since only one twin variant generally dominated over sufficiently wide areas of the specimens, reasonably good (approx 10 percent) minimum yields could be obtained along the appropriate [331] axis, and detwinned crystals produced good results along [301]. (author). 27 refs.; 5 figs

  14. Superconductivity in compensated and uncompensated semiconductors

    Directory of Open Access Journals (Sweden)

    Youichi Yanase and Naoyuki Yorozu

    2008-01-01

    Full Text Available We investigate the localization and superconductivity in heavily doped semiconductors. The crossover from the superconductivity in the host band to that in the impurity band is described on the basis of the disordered three-dimensional attractive Hubbard model for binary alloys. The microscopic inhomogeneity and the thermal superconducting fluctuation are taken into account using the self-consistent 1-loop order theory. The superconductor-insulator transition accompanies the crossover from the host band to the impurity band. We point out an enhancement of the critical temperature Tc around the crossover. Further localization of electron wave functions leads to the localization of Cooper pairs and induces the pseudogap. We find that both the doping compensation by additional donors and the carrier increase by additional acceptors suppress the superconductivity. A theoretical interpretation is proposed for the superconductivity in the boron-doped diamond, SiC, and Si.

  15. Systematics in positron annihilation lifetime analysis of high Tc superconducting transitions

    International Nuclear Information System (INIS)

    Howell, R.H.; Radousky, H.B.; Wachs, A.L.; Fluss, M.J.; Turchi, P.E.A.; Jean, Y.C.; Sunder, C.S.; Chu, C.W.; Peng, J.L.; Folkerts, T.J.; Shelton, R.N.; Hinks, D.G.

    1989-01-01

    Values of the positron lifetime have previously been observed to change with temperature below T c in high T c superconducting oxides. The authors report new measurements on Ba .6 K .4 Bio 3 and Nd 1.85 Ce .15 CuO 4

  16. Superconductivity effects near metal-insulator transition in granular idnium films

    International Nuclear Information System (INIS)

    Belevtsev, B.I.; Komnik, Yu.F.; Fomin, A.V.

    1986-01-01

    The influence of granules superconductivity on the electric properties of granular indium films is investigated under the conditions of partial or full granular localization of electrons. At temperatures below 5 K a minimum of electric resistance and negative magnetoresistance are revealed which are attributed to the competition of hopping conductivity and Josephson intergranular tunneling of electrons

  17. Fermi points and topological quantum phase transitions in a multi-band superconductor.

    Science.gov (United States)

    Puel, T O; Sacramento, P D; Continentino, M A

    2015-10-28

    The importance of models with an exact solution for the study of materials with non-trivial topological properties has been extensively demonstrated. The Kitaev model plays a guiding role in the search for Majorana modes in condensed matter systems. Also, the sp-chain with an anti-symmetric mixing among the s and p bands is a paradigmatic example of a topological insulator with well understood properties. Interestingly, these models share the same universality class for their topological quantum phase transitions. In this work we study a two-band model of spinless fermions with attractive inter-band interactions. We obtain its zero temperature phase diagram, which presents a rich variety of phases including a Weyl superconductor and a topological insulator. The transition from the topological to the trivial superconducting phase has critical exponents different from those of Kitaev's model.

  18. 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

  19. Testing the renormalisation group theory of cooperative transitions at the lambda point of helium

    Science.gov (United States)

    Lipa, J. A.; Li, Q.; Chui, T. C. P.; Marek, D.

    1988-01-01

    The status of high resolution tests of the renormalization group theory of cooperative phase transitions performed near the lambda point of helium is described. The prospects for performing improved tests in space are discussed.

  20. Perturbation theory of a superconducting 0 - π impurity quantum phase transition.

    Science.gov (United States)

    Žonda, M; Pokorný, V; Janiš, V; Novotný, T

    2015-03-06

    A single-level quantum dot with Coulomb repulsion attached to two superconducting leads is studied via the perturbation expansion in the interaction strength. We use the Nambu formalism and the standard many-body diagrammatic representation of the impurity Green functions to formulate the Matsubara self-consistent perturbation expansion. We show that at zero temperature second order of the expansion in its spin-symmetric version yields a nearly perfect agreement with the numerically exact calculations for the position of the 0 - π phase boundary at which the Andreev bound states reach the Fermi energy as well as for the values of single-particle quantities in the 0-phase. We present results for phase diagrams, level occupation, induced local superconducting gap, Josephson current, and energy of the Andreev bound states with the precision surpassing any (semi)analytical approaches employed thus far.

  1. Nonlocal fluctuational electromagnetic response and neutron magnetic scattering near the superconducting transition temperature

    International Nuclear Information System (INIS)

    Barash, Yu.S.; Galaktionov, A.V.

    1992-01-01

    A general expression is found for superconducting fluctuation contribution to transverse permittivity c tr f (Ω, Q) of a standard massive isotopic metal near T c at Ω c and Qζ 0 0 is the coherence length at zero temperature, Q is the external electromagnetic field pulse), depending on frequency and wave vector. Differential cross section of magnetic scattering of neutrons near T c in the region of comparatively small angles is considered

  2. Rounding by disorder of first-order quantum phase transitions: emergence of quantum critical points.

    Science.gov (United States)

    Goswami, Pallab; Schwab, David; Chakravarty, Sudip

    2008-01-11

    We give a heuristic argument for disorder rounding of a first-order quantum phase transition into a continuous phase transition. From both weak and strong disorder analysis of the N-color quantum Ashkin-Teller model in one spatial dimension, we find that, for N > or =3, the first-order transition is rounded to a continuous transition and the physical picture is the same as the random transverse field Ising model for a limited parameter regime. The results are strikingly different from the corresponding classical problem in two dimensions where the fate of the renormalization group flows is a fixed point corresponding to N-decoupled pure Ising models.

  3. Superconducting materials

    International Nuclear Information System (INIS)

    Ruvalds, J.

    1990-01-01

    This report discusses the following topics: Fermi liquid nesting in high temperature superconductors; optical properties of high temperature superconductors; Hall effect in superconducting La 2-x Sr x CuO 4 ; source of high transition temperatures; and prospects for new superconductors

  4. Crossover from normal (N) Ohmic subdivision to superconducting (S) equipartition of current in parallel conductors at the N-S transition: Theory

    OpenAIRE

    Kumar, N.

    2007-01-01

    The recently observed (1) equipartition of current in parallel at and below the Normal-Superconducting (N-S) transition can be understood in terms of a Landau-Ginzburg order-parameter phenomenology. This complements the explanation proposed earlier (1) based on the flux-flow resistance providing a nonlinear negative current feedback towards equipartition when the transition is approached from above. The present treatment also unifies the usual textbook inductive subdivision expected much belo...

  5. Probing chiral superconductivity in Sr_2RuO_4 underneath the surface by point contact measurements

    International Nuclear Information System (INIS)

    Wang, He; Luo, Jiawei; Lou, Weijian

    2017-01-01

    Sr2RuO4 (SRO) is the prime candidate for a chiral p-wave superconductor with critical temperature T_c(SRO)∼1.5 K. Chiral domains with opposite chiralities p_x±ip_y have been proposed, but are yet to be confirmed. We measure the field dependence of the point contact (PC) resistance between a tungsten tip and an SRO–Ru eutectic crystal, where micrometer-sized Ru inclusions are embedded in SRO with an atomically sharp interface. Ruthenium is an s-wave superconductor with T_c(Ru)∼0.5 K; flux pinned near the Ru inclusions can suppress its superconductivity, as reflected in the PC resistance and spectra. This flux pinning effect originates from SRO underneath the surface and is very strong once flux is introduced. To fully remove flux pinning, one needs to thermally cycle the sample above T_c(SRO) or apply alternating fields with decreasing amplitude. With alternating fields, the observed hysteresis in magnetoresistance can be explained by domain dynamics, providing support for the existence of chiral domains. The origin of the strong pinning could be the chiral domains themselves.

  6. Energy Deposition and DPA in the Superconducting Links for the HILUMI LHC Project at the LHC Interaction Points

    CERN Document Server

    AUTHOR|(CDS)2092158; Broggi, Francesco; Santini, C; Ballarino, Amalia; Cerutti, Francesco; Esposito, Luigi Salvatore

    2015-01-01

    In the framework of the upgrade of the LHC machine, the powering of the LHC magnets foresees the removal of the power converters and distribution feedboxes from the tunnel and its location at the surface[1]. The Magnesium Diboride (MgB2) connecting lines in the tunnel will be exposed to the debris from 7+7 TeV p-p interaction. The Superconducting (SC) Links will arrive from the surface to the tunnel near the separation dipole, at about 80 m from the Interaction Point at IP1 and IP5. The Connection Box (where the cables of the SC Links are connected to the NbTi bus bar) will be close to the beam pipe. The debris and its effect on the MgB2 SC links in the connection box (energy deposition and displacement per atom) are presented. The effect of thermal neutrons on the Boron consumption and the contribution of the lithium nucleus and the alpha particle on the DPA are evaluated. The results are normalized to an integrated luminosity of 3000 fb-1, value that represents the LHC High Luminosity lifetime. The dose de...

  7. A New Vacuum Brazing Route for Niobium-316L Stainless Steel Transition Joints for Superconducting RF Cavities

    Science.gov (United States)

    Kumar, Abhay; Ganesh, P.; Kaul, R.; Bhatnagar, V. K.; Yedle, K.; Ram Sankar, P.; Sindal, B. K.; Kumar, K. V. A. N. P. S.; Singh, M. K.; Rai, S. K.; Bose, A.; Veerbhadraiah, T.; Ramteke, S.; Sridhar, R.; Mundra, G.; Joshi, S. C.; Kukreja, L. M.

    2015-02-01

    The paper describes a new approach for vacuum brazing of niobium-316L stainless steel transition joints for application in superconducting radiofrequency cavities. The study exploited good wettability of titanium-activated silver-base brazing alloy (CuSil-ABA®), along with nickel as a diffusion barrier, to suppress brittle Fe-Nb intermetallic formation, which is well reported during the established vacuum brazing practice using pure copper filler. The brazed specimens displayed no brittle intermetallic layers on any of its interfaces, but instead carried well-distributed intermetallic particles in the ductile matrix. The transition joints displayed room temperature tensile and shear strengths of 122-143 MPa and 80-113 MPa, respectively. The joints not only exhibited required hermeticity (helium leak rate high vacuum but also withstood twelve hour degassing heat treatment at 873 K (suppresses Q-disease in niobium cavities), without any noticeable degradation in the microstructure and the hermeticity. The joints retained their leak tightness even after undergoing ten thermal cycles between the room temperature and the liquid nitrogen temperature, thereby establishing their ability to withstand service-induced low cycle fatigue conditions. The study proposes a new lower temperature brazing route to form niobium-316L stainless steel transition joints, with improved microstructural characteristics and acceptable hermeticity and mechanical properties.

  8. Electron mobility, conductivity, and superconductivity near the metal-insulator transition

    International Nuclear Information System (INIS)

    Fiory, A.T.; Hebard, A.F.

    1984-01-01

    The disorder parameter k/sub F/l for amorphous InO/sub x/ is measured by a novel application of the surface electric field effect and is varied by thermal annealing. The normal-state conductivity and superconducting T/sub c/ both vary as (k/sub F/l) -2 and critical disorder occurs at k/sub F/lroughly-equal3/sup 1/2/, as a result of Anderson localization in this low-carrier density material

  9. Calculations of resistivity and superconducting T/sub c/ in transition metals

    International Nuclear Information System (INIS)

    Allen, P.B.; Beaulac, T.P.; Khan, F.S.; Butler, W.H.; Pinski, F.J.; Swihart, J.C.

    1985-01-01

    A survey is given of various electron-phonon effects which have been calculated for the metals Nb, Mo, Ta, Pd, and Cu. These effects include the mass enhancement λ, superconducting T/sub c/, electrical and thermal resistivity, Hall coefficient, magnetoresistance, and the successfully tested predictions of linewidths γ 0 of phonons. The calculations use local density approximations (LDA) energy bands, experimental phonons, and the rigid muffin tin (RMT) approximation. Mesh size noise is less than 1% and the Bloch-Boltzmann integral equation has been solved to unprecedented accuracy

  10. Superconducting current in a bisoliton superconductivity model

    International Nuclear Information System (INIS)

    Ermakov, V.N.; Kruchinin, S.P.; Ponezha, E.A.

    1991-01-01

    It is shown that the transition into a superconducting state with the current which is described by a bisoliton superconductivity model is accompanied by the deformation of the spectrum of one-particle states of the current carriers. The deformation value is proportional to the conducting current force. The residuaby resistance in such state is absent

  11. Enhanced superconductivity of fullerenes

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-06-20

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

  12. From optics to superconductivity. Many body effects in transition metal dichalcogenides

    Energy Technology Data Exchange (ETDEWEB)

    Roesner, Malte; Schoenhoff, Gunnar; Wehling, Tim [Institute for Theoretical Physics, University of Bremen (Germany); Bremen Center for Computational Material Sciences, University of Bremen (Germany); Steinhoff, Alexander; Jahnke, Frank; Gies, Christopher [Institute for Theoretical Physics, University of Bremen (Germany); Haas, Stephan [Department of Physics and Astronomy, University of Southern California, Los Angeles, CA (United States)

    2015-07-01

    We discuss many body effects in MoS{sub 2} ranging from optical properties to the emergence superconductivity (SC) and charge density wave phases (CDW). Combining ab-initio theory and semiconductor Bloch equations we show that excited carriers cause a redshift of the excitonic ground-state absorption line, while higher excitonic lines disappear successively due to a huge Coulomb-induced band gap shrinkage of more than 500 meV and concomitant exciton binding-energy reductions. Upon strong charge doping, we observe a succession of semiconducting, metallic, SC, and CDW regimes. Both, the SC and the CDW instabilities trace back to a Kohn anomaly and related softening of Brillouin zone boundary phonons.

  13. Point Climat no. 29 'Managing France's energy transition while safeguarding economic competitiveness: be productive'

    International Nuclear Information System (INIS)

    Sartor, Oliver; Leguet, Benoit

    2013-01-01

    Among the publications of CDC Climat Research, 'Climate Briefs' presents, in a few pages, hot topics in climate change policy. This issue addresses the following points: - Is the French energy transition compatible with economic growth and a 'competitive' French economy? Our answer is 'yes, with some conditions'. - The French economy is better positioned today for a meaningful energy transition than it has been for over 40 years. At the level of the macro-economy, a steady shift to higher energy prices is now much easier without hurting economic growth than it once was. - A small percentage of energy-intensive sectors may need targeted and temporary assistance with this transition

  14. Electronic Correlations, Jahn-Teller Distortions and Mott Transition to Superconductivity in Alkali-C60 Compounds

    Directory of Open Access Journals (Sweden)

    Alloul H.

    2012-03-01

    Full Text Available The discovery in 1991 of high temperature superconductivity (SC in A3C60 compounds, where A is an alkali ion, has been rapidly ascribed to a BCS mechanism, in which the pairing is mediated by on ball optical phonon modes. While this has lead to consider that electronic correlations were not important in these compounds, further studies of various AnC60 with n=1, 2, 4 allowed to evidence that their electronic properties cannot be explained by a simple progressive band filling of the C60 six-fold degenerate t1u molecular level. This could only be ascribed to the simultaneous influence of electron correlations and Jahn-Teller Distortions (JTD of the C60 ball, which energetically favour evenly charged C60 molecules. This is underlined by the recent discovery of two expanded fulleride Cs3C60 isomeric phases which are Mott insulators at ambient pressure. Both phases undergo a pressure induced first order Mott transition to SC with a (p, T phase diagram displaying a dome shaped SC, a common situation encountered nowadays in correlated electron systems. NMR experiments allowed us to study the magnetic properties of the Mott phases and to evidence clear deviations from BCS expectations near the Mott transition. So, although SC involves an electron-phonon mechanism, the incidence of electron correlations has an importance on the electronic properties, as had been anticipated from DMFT calculations.

  15. The effect of point defects on ferroelastic phase transition of lanthanum-doped calcium titanate ceramics

    International Nuclear Information System (INIS)

    Ni, Yan; Zhang, Zhen; Wang, Dong; Wang, Yu; Ren, Xiaobing

    2013-01-01

    Highlights: ► The effect of point defects on phase transitions in Ca (1−x) La 2x/3 TiO 3 was studied. ► When x = 0.45, normal ferroelastic phase transition happens. ► When x = 0.7, a “glassy-like” frozen process appears. ► Point defects weaken the thermodynamic stability of ferroelastic phase. ► Point defects induce a “glassy-like” frozen process. -- Abstract: In the present paper, La-doped CaTiO 3 is studied to investigate the effect of point defects on ferroelastic phase transition of the ceramics. The dynamic mechanical measurements show that the transition temperature of the orthorhombic to tetragonal phase transition of Ca (1−x) La 2x/3 TiO 3 decreases with increasing dopant (La) concentration x. The samples with the dopant content of x = 0.45 and 0.7 exhibit different structure evolution features during their transition processes as revealed by in situ powder X-ray diffraction (XRD) measurement. Moreover, when x = 0.7, the storage modulus shows a frequency-dependent minimum at T g , which can be well fitted with the Vogel–Fulcher relation, and the corresponding internal friction also exhibits a frequency-dependent peak within the same temperature regime. These results thus indicate that doping La suppresses ferroelastic phase transition in CaTiO 3 and induces a “glassy-like” behavior in Ca (1−x) La 2x/3 TiO 3 , which is similar to “strain glass” in Ni-doped Ti 50−x Ni 50+x

  16. H-point exciton transitions in bulk MoS2

    International Nuclear Information System (INIS)

    Saigal, Nihit; Ghosh, Sandip

    2015-01-01

    Reflectance and photoreflectance spectrum of bulk MoS 2 around its direct bandgap energy have been measured at 12 K. Apart from spectral features due to the A and B ground state exciton transitions at the K-point of the Brillouin zone, one observes additional features at nearby energies. Through lineshape analysis the character of two prominent additional features are shown to be quite different from that of A and B. By comparing with reported electronic band structure calculations, these two additional features are identified as ground state exciton transitions at the H-point of the Brillouin zone involving two spin-orbit split valance bands. The excitonic energy gap at the H-point is 1.965 eV with a valance bands splitting of 185 meV. While at the K-point, the corresponding values are 1.920 eV and 205 meV, respectively

  17. 1D to 3D dimensional crossover in the superconducting transition of the quasi-one-dimensional carbide superconductor Sc3CoC4.

    Science.gov (United States)

    He, Mingquan; Wong, Chi Ho; Shi, Dian; Tse, Pok Lam; Scheidt, Ernst-Wilhelm; Eickerling, Georg; Scherer, Wolfgang; Sheng, Ping; Lortz, Rolf

    2015-02-25

    The transition metal carbide superconductor Sc(3)CoC(4) may represent a new benchmark system of quasi-one-dimensional (quasi-1D) superconducting behavior. We investigate the superconducting transition of a high-quality single crystalline sample by electrical transport experiments. Our data show that the superconductor goes through a complex dimensional crossover below the onset T(c) of 4.5 K. First, a quasi-1D fluctuating superconducting state with finite resistance forms in the [CoC(4)](∞) ribbons which are embedded in a Sc matrix in this material. At lower temperature, the transversal Josephson or proximity coupling of neighboring ribbons establishes a 3D bulk superconducting state. This dimensional crossover is very similar to Tl(2)Mo(6)Se(6), which for a long time has been regarded as the most appropriate model system of a quasi-1D superconductor. Sc(3)CoC(4) appears to be even more in the 1D limit than Tl(2)Mo(6)Se(6).

  18. Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe2As2 close to a first-order phase transition

    Science.gov (United States)

    Fente, Antón; Correa-Orellana, Alexandre; Böhmer, Anna E.; Kreyssig, Andreas; Ran, S.; Bud'ko, Sergey L.; Canfield, Paul C.; Mompean, Federico J.; García-Hernández, Mar; Munuera, Carmen; Guillamón, Isabel; Suderow, Hermann

    2018-01-01

    We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co-substituted CaFe2As2 . We use atomic force, magnetic force, and scanning tunneling microscopy to identify the domains and characterize their properties, finding in particular that tetragonal superconducting domains are very elongated, more than several tens of micrometers long and about 30 nm wide; have the same Tc as unstrained samples; and hold vortices in a magnetic field. Thus, biaxial strain produces a phase-separated state, where each phase is equivalent to what is found on either side of the first-order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of the order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first-order quantum phase transitions lead to nanometric-size phase separation under the influence of strain.

  19. Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe 2

    KAUST Repository

    Zhang, Chendong

    2015-09-21

    By using a comprehensive form of scanning tunneling spectroscopy, we have revealed detailed quasi-particle electronic structures in transition metal dichalcogenides, including the quasi-particle gaps, critical point energy locations, and their origins in the Brillouin zones. We show that single layer WSe surprisingly has an indirect quasi-particle gap with the conduction band minimum located at the Q-point (instead of K), albeit the two states are nearly degenerate. We have further observed rich quasi-particle electronic structures of transition metal dichalcogenides as a function of atomic structures and spin-orbit couplings. Such a local probe for detailed electronic structures in conduction and valence bands will be ideal to investigate how electronic structures of transition metal dichalcogenides are influenced by variations of local environment.

  20. Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe 2

    KAUST Repository

    Zhang, Chendong; Chen, Yuxuan; Johnson, Amber; Li, Ming-yang; Li, Lain-Jong; Mende, Patrick C.; Feenstra, Randall M.; Shih, Chih Kang

    2015-01-01

    By using a comprehensive form of scanning tunneling spectroscopy, we have revealed detailed quasi-particle electronic structures in transition metal dichalcogenides, including the quasi-particle gaps, critical point energy locations, and their origins in the Brillouin zones. We show that single layer WSe surprisingly has an indirect quasi-particle gap with the conduction band minimum located at the Q-point (instead of K), albeit the two states are nearly degenerate. We have further observed rich quasi-particle electronic structures of transition metal dichalcogenides as a function of atomic structures and spin-orbit couplings. Such a local probe for detailed electronic structures in conduction and valence bands will be ideal to investigate how electronic structures of transition metal dichalcogenides are influenced by variations of local environment.

  1. Coupled superconducting qudit-resonator system: Energy spectrum, state population, and state transition under microwave drive

    Science.gov (United States)

    Liu, W. Y.; Xu, H. K.; Su, F. F.; Li, Z. Y.; Tian, Ye; Han, Siyuan; Zhao, S. P.

    2018-03-01

    Superconducting quantum multilevel systems coupled to resonators have recently been considered in some applications such as microwave lasing and high-fidelity quantum logical gates. In this work, using an rf-SQUID type phase qudit coupled to a microwave coplanar waveguide resonator, we study both theoretically and experimentally the energy spectrum of the system when the qudit level spacings are varied around the resonator frequency by changing the magnetic flux applied to the qudit loop. We show that the experimental result can be well described by a theoretical model that extends from the usual two-level Jaynes-Cummings system to the present four-level system. It is also shown that due to the small anharmonicity of the phase device a simplified model capturing the leading state interactions fits the experimental spectra very well. Furthermore we use the Lindblad master equation containing various relaxation and dephasing processes to calculate the level populations in the simpler qutrit-resonator system, which allows a clear understanding of the dynamics of the system under the microwave drive. Our results help to better understand and perform the experiments of coupled multilevel and resonator systems and can be applied in the case of transmon or Xmon qudits having similar anharmonicity to the present phase device.

  2. Lithographed Superconducting Resonator Development for Next-Generation Frequency Multiplexing Readout of Transition-Edge Sensors

    Science.gov (United States)

    Faramarzi, F.; De Haan, T.; Kusaka, A.; Lee, A.; Neuhauser, B.; Plambeck, R.; Raum, C.; Suzuki, A.; Westbrook, B.

    2018-03-01

    Ground-based cosmic microwave background (CMB) experiments are undergoing a period of exponential growth. Current experiments are observing with 1000-10,000 detectors, and the next-generation experiment (CMB stage 4) is proposing to deploy approximately 500,000 detectors. This order of magnitude increase in detector count will require a new approach for readout electronics. We have developed superconducting resonators for next-generation frequency-domain multiplexing (fMUX) readout architecture. Our goal is to reduce the physical size of resonators, such that resonators and detectors can eventually be integrated on a single wafer. To reduce the size of these resonators, we have designed spiral inductors and interdigitated capacitors that resonate around 10-100 MHz, an order of magnitude higher frequency compared to current fMUX readout systems. The higher frequency leads to a wider bandwidth and would enable higher multiplexing factor than the current ˜ 50 detectors per readout channel. We will report on the simulation, fabrication method, characterization technique, and measurement of quality factor of these resonators.

  3. Exceptional points near first- and second-order quantum phase transitions.

    Science.gov (United States)

    Stránský, Pavel; Dvořák, Martin; Cejnar, Pavel

    2018-01-01

    We study the impact of quantum phase transitions (QPTs) on the distribution of exceptional points (EPs) of the Hamiltonian in the complex-extended parameter domain. Analyzing first- and second-order QPTs in the Lipkin-Meshkov-Glick model we find an exponentially and polynomially close approach of EPs to the respective critical point with increasing size of the system. If the critical Hamiltonian is subject to random perturbations of various kinds, the averaged distribution of EPs close to the critical point still carries decisive information on the QPT type. We therefore claim that properties of the EP distribution represent a parametrization-independent signature of criticality in quantum systems.

  4. Turbulence simulations of X point physics on the L-H transitions

    International Nuclear Information System (INIS)

    Xu, X.Q.; Cohen, R.H.; Nevins, W.M.

    2001-01-01

    We show that the resistive X-point mode is the dominant mode in boundary plasmas in X-point divertor geometry. The poloidal fluctuation phase velocity from the simulation results of the resistive X-point turbulence shows experimentally measured structure across separatrix in many fusion devices. The fluctuation phase velocity is larger than ExB velocity both in L and H mode phases. We also demonstrate that there is a strong poloidal asymmetry of particle flux in the proximity of the separatrix. Turbulence suppression in the L-H transition results when sources of energy and particles drive sufficient gradients as in the experiments. (author)

  5. Superconductivity in the actinides

    International Nuclear Information System (INIS)

    Smith, J.L.; Lawson, A.C.

    1985-01-01

    The trends in the occurrence of superconductivity in actinide materials are discussed. Most of them seem to show simple transition metal behavior. However, the superconductivity of americium proves that the f electrons are localized in that element and that ''actinides'' is the correct name for this row of elements. Recently the superconductivity of UBe 13 and UPt 3 has been shown to be extremely unusual, and these compounds fall in the new class of compounds now known as heavy fermion materials

  6. Superconducting Mercury-Based Cuprate Films with a Zero-Resistance Transition Temperature of 124 Kelvin

    Science.gov (United States)

    Tsuei, C. C.; Gupta, A.; Trafas, G.; Mitzi, D.

    1994-03-01

    The synthesis of high-quality films of the recently discovered mercury-based cuprate films with high transition temperatures has been plagued by problems such as the air sensitivity of the cuprate precursor and the volatility of Hg and HgO. These processing difficulties have been circumvented by a technique of atomic-scale mixing of the HgO and cuprate precursors, use of a protective cap layer, and annealing in an appropriate Hg and O_2 environment. With this procedure, a zero-resistance transition temperature as high as 124 kelvin in c axis-oriented epitaxial HgBa_2CaCu_2O6+δ films has been achieved.

  7. Superconducting mercury-based cuprate films with a zero-resistance transition temperature of 124 Kelvin.

    Science.gov (United States)

    Tsuei, C C; Gupta, A; Trafas, G; Mitzi, D

    1994-03-04

    The synthesis of high-quality films of the recently discovered mercury-based cuprate films with high transition temperatures has been plagued by problems such as the air sensitivity of the cuprate precursor and the volatility of Hg and HgO. These processing difficulties have been circumvented by a technique of atomic-scale mixing of the HgO and cuprate precursors, use of a protective cap layer, and annealing in an appropriate Hg and O(2) environment. With this procedure, a zero-resistance transition temperature as high as 124 kelvin in c axis-oriented epitaxial HgBa(2)CaCu(2)O(6+delta) films has been achieved.

  8. A semi-Dirac point and an electromagnetic topological transition in a dielectric photonic crystal

    KAUST Repository

    Wu, Ying

    2014-01-01

    Accidental degeneracy in a photonic crystal consisting of a square array of elliptical dielectric cylinders leads to both a semi-Dirac point at the center of the Brillouin zone and an electromagnetic topological transition (ETT). A perturbation method is deduced to affirm the peculiar linear-parabolic dispersion near the semi-Dirac point. An effective medium theory is developed to explain the simultaneous semi-Dirac point and ETT and to show that the photonic crystal is either a zero-refractive-index material or an epsilon-near-zero material at the semi-Dirac point. Drastic changes in the wave manipulation properties at the semi-Dirac point, resulting from ETT, are described.©2014 Optical Society of America.

  9. Synthesis of metastable A-15 ''Nb3Si'' by ion implantation and on its superconducting transition temperature

    International Nuclear Information System (INIS)

    Clapp, M.T.; Rose, R.M.

    1980-01-01

    The authors have found a new technique for the synthesis of metastable compounds of well-defined composition: namely, ion implantation of a selected element into the desired crystal structure. [M.T. Clapp and R.M. Rose, Appl. Phys. Lett. 33, 205 (1978)]. Starting with a substrate material of A-15 Nb 3 Al/sub 0.9/Si/sub 0.1/, two basic approaches were tried towards the formation of A-15 Nb 3 Si by Si implantation: (1) direct replacement of the Al by Si and (2) implantation into a surface layer depleted of Al. This latter approach proved to be the most successful. It consisted of removing the Al by a diffusion anneal and replacing the Al deficiency by sequential Si implantations. Upon subsequent heat treatment a surface layer of A-15 Nb 3 Al/sub 0.2/Si/sub 0.8/ was produced. Details of the experimental procedure and a discussion of the superconducting transition temperature measurements of the implanted surfaces are presented

  10. Fabrication of close-packed TES microcalorimeter arrays using superconducting molybdenum/gold transition-edge sensors

    Science.gov (United States)

    Finkbeiner, F. M.; Brekosky, R. P.; Chervenak, J. A.; Figueroa-Feliciano, E.; Li, M. J.; Lindeman, M. A.; Stahle, C. K.; Stahle, C. M.; Tralshawala, N.

    2002-02-01

    We present an overview of our efforts in fabricating Transition-Edge Sensor (TES) microcalorimeter arrays for use in astronomical x-ray spectroscopy. Two distinct types of array schemes are currently pursued: 5×5 single pixel TES array where each pixel is a TES microcalorimeter, and Position-Sensing TES (PoST) array. In the latter, a row of 7 or 15 thermally-linked absorber pixels is read out by two TES at its ends. Both schemes employ superconducting Mo/Au bilayers as the TES. The TES are placed on silicon nitride membranes for thermal isolation from the structural frame. The silicon nitride membranes are prepared by a Deep Reactive Ion Etch (DRIE) process into a silicon wafer. In order to achieve the concept of closely packed arrays without decreasing its structural and functional integrity, we have already developed the technology to fabricate arrays of cantilevered pixel-sized absorbers and slit membranes in silicon nitride films. Furthermore, we have started to investigate ultra-low resistance through-wafer micro-vias to bring the electrical contact out to the back of a wafer. .

  11. Enhancement of superconducting transition temperature in FeSe electric-double-layer transistor with multivalent ionic liquids

    Science.gov (United States)

    Miyakawa, Tomoki; Shiogai, Junichi; Shimizu, Sunao; Matsumoto, Michio; Ito, Yukihiro; Harada, Takayuki; Fujiwara, Kohei; Nojima, Tsutomu; Itoh, Yoshimitsu; Aida, Takuzo; Iwasa, Yoshihiro; Tsukazaki, Atsushi

    2018-03-01

    We report on an enhancement of the superconducting transition temperature (Tc) of the FeSe-based electric-double-layer transistor (FeSe-EDLT) by applying the multivalent oligomeric ionic liquids (ILs). The IL composed of dimeric cation (divalent IL) enables a large amount of charge accumulation on the surface of the FeSe ultrathin film, resulting in inducing electron-rich conduction even in a rather thick 10 nm FeSe channel. The onset Tc in FeSe-EDLT with the divalent IL is enhanced to be approaching about 50 K at the thin limit, which is about 7 K higher than that in EDLT with conventional monovalent ILs. The enhancement of Tc is a pronounced effect of the application of the divalent IL, in addition to the large capacitance, supposing preferable interface formation of ILs driven by geometric and/or Coulombic effect. The present finding strongly indicates that multivalent ILs are powerful tools for controlling and improving physical properties of materials.

  12. Anomalous pressure dependence of the superconducting transition temperature in the β-Pyrochlore KOs2O6

    Science.gov (United States)

    Miyoshi, Kiyotaka; Takaichi, Yuta; Takeuchi, Jun

    2009-03-01

    DC magnetic measurements have been performed for β-pyrochlore superconductor KOs2O6 (Tc = 9.6 K) under pressure for the precise determination of the pressure dependence of Tc, using a miniature diamond anvil cell combined with a commercial SQUID magnetometer. It is found that the critical temperature Tc shows a maximum of ~10 K at P=0.5 GPa. The maximum of Tc is higher than that for CsOs2O6 and RbOs2O6, in both of which Tc is known to increase and saturate at Tcm = 8.8 K by the application of pressure, suggesting the enhanced superconductivity due to the rattling of K ions in an oversized cage of Os-O network. For the further application of pressure, Tc decreases linearly but the decreasing rate appears to be suddenly changed at P~2 GPa and Tc~8 K. The sharp bend of the Tc — P line probably corresponds to the transition concerning to the rattling motion which occurs at Tp=7.5 K at ambient pressure, suggesting the positive pressure dependence of Tp.

  13. Superconducting Coset Topological Fluids in Josephson Junction Arrays

    CERN Document Server

    Diamantini, M C; Trugenberger, C A; Sodano, Pasquale; Trugenberger, Carlo A.

    2006-01-01

    We show that the superconducting ground state of planar Josephson junction arrays is a P- and T-invariant coset topological quantum fluid whose topological order is characterized by the degeneracy 2 on the torus. This new mechanism for planar superconductivity is the P- and T-invariant analogue of Laughlin's quantum Hall fluids. The T=0 insulator-superconductor quantum transition is a quantum critical point characterized by gauge fields and deconfined degrees of freedom. Experiments on toroidal Josephson junction arrays could provide the first direct evidence for topological order and superconducting quantum fluids.

  14. Superconductive transition metal carbonitride fibers and method for the preparation thereof

    International Nuclear Information System (INIS)

    Economy, J.; Mason, J.H.; Smith, W.D.

    1976-01-01

    Fine diameter continuous multifilament superconductor yarns comprising niobium carbonitride may be prepared. The fibers of which the yarn is composed possess a very high transition temperature (T/sub c/ of 17 0 K) combined with a good upper critical field (H/sub c2/ of 125 kG) and critical current density (J/sub c/ of 10 5 amps/cm 2 at 40 kG). This invention provides excellent superconductor materials in the form of continuous fine diameter multifilament yarn. 9 claims

  15. Radiation effects on superconductivity

    International Nuclear Information System (INIS)

    Brown, B.S.

    1975-01-01

    The effect of radiation on the superconducting transition temperature (T/sub c/), upper critical field (H/sub c2/), and volume-pinning-force density (F/sub p/) were discussed for the three kinds of superconducting material (elements, alloys, and compounds). 11 figures, 3 tables, 86 references

  16. Signals for the QCD phase transition and critical point in a Langevin dynamical model

    International Nuclear Information System (INIS)

    Herold, Christoph; Bleicher, Marcus; Yan, Yu-Peng

    2013-01-01

    The search for the critical point is one of the central issues that will be investigated in the upcoming FAIR project. For a profound theoretical understanding of the expected signals we go beyond thermodynamic studies and present a fully dynamical model for the chiral and deconfinement phase transition in heavy ion collisions. The corresponding order parameters are propagated by Langevin equations of motions on a thermal background provided by a fluid dynamically expanding plasma of quarks. By that we are able to describe nonequilibrium effects occurring during the rapid expansion of a hot fireball. For an evolution through the phase transition the formation of a supercooled phase and its subsequent decay crucially influence the trajectories in the phase diagram and lead to a significant reheating of the quark medium at highest baryon densities. Furthermore, we find inhomogeneous structures with high density domains along the first order transition line within single events.

  17. Superconducting classes in heavy fermions systems

    International Nuclear Information System (INIS)

    Volovik, G.E.; Gor'kov, L.P.

    1985-01-01

    A mathematical method for constructing of the superconductivity classes for nontrivial superconductors is described. All superconducting phases which can arise directly on transition from the normal state for cubic, hexagonal and tetragonal symmetries are enumerated. It is shown that in the triplet case the types of zeros in the energy gap always correspond to points on the Fermi surface, whereas for signlet pairing the whole zero lines are possible. For the phases with zeros on the lines or points, the low-temperature specific heat varies as T 2 on T 3 respectivelty. The superconducting phases which arise from the multydimensional representations may possess a magnetic moment which induces currents on the surface of a monodomain sample even in the absence of an external magnetic field. The specific case of a domain wall is considered and it is shown that large magnetic currents of magnetization are present in the wall

  18. Is the 10-point agenda of the Federal Government useful for a successful energy transition?

    International Nuclear Information System (INIS)

    Dinther, Clemens van; Renelt, Sven; Strueker, Jens; Terzidis, Orestis; Bretschneider, Peter

    2017-01-01

    With the energy transition, the Federal Government has begun the conversion of the energy supply. Because of the success of the energy transition is essential for the future and competitiveness of Germany as a business location The Federal Association of German Industry (BDI) has already published 2013 Stimulus for a smart energy market, in which are derived five principles which provide a framework for discourse on the measures to be taken. Renewable energies will be the dominant source of electricity in the coming years. This results in new challenges. The Federal Ministry of Economics and Technology (BMWi) has recently adopted a 10-point agenda to address these issues (ZPA) for the central energy projects. To be discussed is to what extent they are in harmony with the five principles of the BDI and at which points adjustments are necessary, so that the conversion of the energy system can succeed. [de

  19. Magnetic-field control of quantum critical points of valence transition.

    Science.gov (United States)

    Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques

    2008-06-13

    We study the mechanism of how critical end points of first-order valence transitions are controlled by a magnetic field. We show that the critical temperature is suppressed to be a quantum critical point (QCP) by a magnetic field, and unexpectedly, the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to the emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be cooperative phenomena of the Zeeman and Kondo effects, which create a distinct energy scale from the Kondo temperature. This mechanism explains the peculiar magnetic response in CeIrIn(5) and the metamagnetic transition in YbXCu(4) for X=In as well as the sharp contrast between X=Ag and Cd.

  20. Search for signatures of phase transition and critical point in heavy ion collisions

    International Nuclear Information System (INIS)

    Tokarev, M.V.; Kechechyan, A.; Alakhverdyants, A.; Zborovsky, I.

    2011-01-01

    The general concepts in the critical phenomena related with the notions of 'scaling' and 'universality' are considered. Behavior of various systems near a phase transition is displayed. Search for clear signatures of the phase transition of the nuclear matter and location of the critical point in heavy ion collisions (HIC) is discussed. The experimental data on inclusive spectra measured in HIC at RHIC and SPS over a wide range of energies s NN 1/2 = 9-200 GeV are analyzed in the framework of z-scaling. A microscopic scenario of the constituent interactions is presented. Dependence of the energy loss on the momentum of the produced hadron, energy and centrality of the collision is studied. Self-similarity of the constituent interactions described in terms of momentum fractions is used to characterize the nuclear medium by 'specific heat' and colliding nuclei by fractal dimensions. Preferable kinematical regions to search for signatures of the phase transition of the nuclear matter produced in HIC are discussed. Discontinuity of the 'specific heat' is assumed to be a signature of the phase transition and the critical point

  1. Vortex-slip transitions in superconducting a-NbGe mesoscopic channels

    Science.gov (United States)

    Kokubo, N.; Sorop, T. G.; Besseling, R.; Kes, P. H.

    2006-06-01

    Intriguing and novel physical aspects related to the vortex flow dynamics have been recently observed in mesoscopic channel devices of a-NbGe with NbN channel edges. In this work we have systematically studied the flow properties of vortices confined in such mesoscopic channels as a function of the magnetic field history, using dc-transport and mode-locking (ML) measurements. As opposed to the field-down situation, in the field-up case a kink anomaly in the dc I-V curves is detected. The mode-locking measurements reveal that this anomaly is, in fact, a flow induced vortex slip transition: by increasing the external drive (either dc or ac) a sudden change occurs from n to n+2 moving vortex rows in the channel. The observed features can be explained in terms of an interplay between field focusing due to screening currents and a change in the predominant pinning mechanism.

  2. Nontrivial transition of transmission in a highly open quantum point contact in the quantum Hall regime

    Science.gov (United States)

    Hong, Changki; Park, Jinhong; Chung, Yunchul; Choi, Hyungkook; Umansky, Vladimir

    2017-11-01

    Transmission through a quantum point contact (QPC) in the quantum Hall regime usually exhibits multiple resonances as a function of gate voltage and high nonlinearity in bias. Such behavior is unpredictable and changes sample by sample. Here, we report the observation of a sharp transition of the transmission through an open QPC at finite bias, which was observed consistently for all the tested QPCs. It is found that the bias dependence of the transition can be fitted to the Fermi-Dirac distribution function through universal scaling. The fitted temperature matches quite nicely to the electron temperature measured via shot-noise thermometry. While the origin of the transition is unclear, we propose a phenomenological model based on our experimental results that may help to understand such a sharp transition. Similar transitions are observed in the fractional quantum Hall regime, and it is found that the temperature of the system can be measured by rescaling the quasiparticle energy with the effective charge (e*=e /3 ). We believe that the observed phenomena can be exploited as a tool for measuring the electron temperature of the system and for studying the quasiparticle charges of the fractional quantum Hall states.

  3. Gauge dependence of the critical dynamics at the superconducting phase transition

    Directory of Open Access Journals (Sweden)

    M.Dudka

    2007-01-01

    Full Text Available The critical dynamics of superconductors in the charged regime is reconsidered within field-theory. For the dynamics, the Ginzburg-Landau model with complex order parameter coupled to the gauge field suggested earlier [Lannert et al. Phys. Rev. Lett. 92, 097004 (2004] is used. Assuming relaxational dynamics for both quantities, the renormalization group functions within one loop approximation are recalculated for different choices of the gauge. A gauge independent result for the divergence of the melectric conductivity is obtained only at the weak scaling fixed point unstable in one loop order where the timescales of the order parameter and the gauge field are different.

  4. Laser activated superconducting switch

    International Nuclear Information System (INIS)

    Wolf, A.A.

    1976-01-01

    A superconducting switch or bistable device is described consisting of a superconductor in a cryogen maintaining a temperature just below the transition temperature, having a window of the proper optical frequency band for passing a laser beam which may impinge on the superconductor when desired. The frequency of the laser is equal to or greater than the optical absorption frequency of the superconducting material and is consistent with the ratio of the gap energy of the switch material to Planck's constant, to cause depairing of electrons, and thereby normalize the superconductor. Some embodiments comprise first and second superconducting metals. Other embodiments feature the two superconducting metals separated by a thin film insulator through which the superconducting electrons tunnel during superconductivity

  5. Effect of stress on the superconducting transition temperature in indium, indium-alloy, tin, and tin-alloy whisker samples

    International Nuclear Information System (INIS)

    Cook, J.W. Jr.; Davis, W.T.; Chandler, J.H.; Skove, M.J.

    1977-01-01

    The dependence of the superconducting transition temperature (T/sub c/) on stress (sigma) for pure In and Sn samples was found to be in qualitative agreement with earlier work. For convenience T/sub c/ is expressed as a function of the experimentally measured strain (epsilon), which is proportional to sigma. The effect of alloying on the initial dependence of the T/sub c/-vs-epsilon curves, (per. delta T/sub c//per. delta epsilon)/sub epsilon = 0/ = eta, was quite different for the In and Sn alloys. The In samples were alloyed with a maximum of 4.8 at.% Tl, 7.9 at.% Sn, and 6.7 at.% Pd; the Sn samples were alloyed with a maximum of 0.3 at.% Cd, 6.0 at.% In, 0.3 at.% Sb, and 2.2 at.% Bi. The addition of impurities had a large effect on eta for the In alloys, with eta reversing sign for some Sn and Pb alloy contents (chi). The T/sub c/-vs-epsilon curves also became nonlinear for some chi. The possible relationship of the In alloy results to changes in the Fermi surface due to the addition of impurities is discussed. For the Sn alloy samples, there was no change in eta with any impurity. The change in room-temperature resistivity with strain was also measured. There was only a slight decrease in the dependence of resistivity on strain for the In--Sn and In--Pb data and no effect on the In--Tl or Sn alloy data

  6. Superconductivity in ternary rare earth transition metal silicides and germanides with the Sc5Co4Si10-type structure

    International Nuclear Information System (INIS)

    Berg, L.S.

    1986-01-01

    A systematic study of the superconducting and normal state properties of some ternary rare earth transition metal silicides and germanides of the Sc 5 Co 4 Si 10 0-type is reported. Low temperature heat capacity measurements indicate the presence of a complicated phonon density of states in these structurally complex compounds. A better description of the phonon spectrum of the high T/sub c/ materials Sc 5 Rh 4 Si 10 , Sc 5 Ir 4 Si 10 , and Y 5 Os 4 Ge 10 , given by a model proposed by Junod et al., is presented and discussed. The large values of ΔC/γ/sub n/T/sub c/ and the electron-phonon coupling constant for these high T/sub c/ compounds indicate that they are strong-coupled superconductors. Relative to other ternary superconductors, many of these materials have large Debye temperatures. DC electrical resistivity measurements on these compounds show resistivity behavior deviating from those exhibited by simple metals. The rho(T) data for Y 5 Ir 4 Si 10 , Lu 5 Ir 4 Si 10 , and Y 5 Os 4 Ge 10 , indicate the presence of anomalies. Static molar magnetic susceptibility measurements performed on these compounds indicate (1) a small effective magnetic moment of 0.26μ/sub B/ on the Co atom and (2) anomalous behaviors in the Lu 5 Rh 4 Si 10 , Lu 5 Ir 4 Si 10 , Y 5 Ir 4 Si 10 , Lu 5 Ir 4 Ge 10 , and Y 5 Rh 4 Ge 10 data. Lastly, upper critical magnetic field measurements were performed on Sc 5 Co 4 Si 10 , Sc 5 Rh 4 Si 10 , Sc 5 Ir 4 Si 10 , Lu 5 Rh 4 Si 10 , Lu 5 Ir 4 Si 10 , and Y 5 Os 4 Ge 10

  7. Transport currents along c-axis and (a,b) planes in YBCO single domain materials. Critical current densities and normal-superconducting transitions

    International Nuclear Information System (INIS)

    Porcar, L.; Bourgault, D.; Chaud, X.; Noudem, J.G.; Tournier, R.; Tixador, P.

    1998-01-01

    High transport currents along the (a,b) planes and along the c-axis have been measured in pulsed current of different pseudo-frequencies. Self field losses and transport current of 8000 A (20000 A cm -2 ) have been measured in Y 1 Ba 2 Cu 3 O 7-δ bars textured by the melting zone technique. Critical currents as high as 500 A (90000 A cm -2 ) along the (a,b) planes or 3000 A (7500 A cm -2 ) along the c-axis have been measured. For both orientations, the transition from the normal state to the superconducting state has been observed. Electric field of 1000 V m -1 and study of the superconducting state recovery are reported. (orig.)

  8. Correlation of the superconducting transition to oxygen stoichiometry in single-crystal Ba1-xKxBiO3-y

    Science.gov (United States)

    Mosley, W. D.; Dykes, J. W.; Klavins, P.; Shelton, R. N.; Sterne, P. A.; Howell, R. H.

    1993-07-01

    Temperature-dependent positron-lifetime experiments have been performed from room temperature to 15 K on single crystals of the oxide superconductor Ba1-xKxBiO3-y. Results indicate that the filling of oxygen vacancies has a marked impact on the superconducting properties of this system. Cation defect concentrations were below the detectable limit of positron-annihilation-analysis techniques in this material, which is in sharp contrast to identical studies on polycrystalline samples. We find that the positron lifetime in these electrochemically deposited single crystals is determined by the oxygen stoichiometry of the lattice, but there is no experimental signature of strong positron localization. By performing a subsequent oxygen anneal on the crystals, the superconducting transition is sharpened and the onset is raised. The observed change in positron lifetime associated with this annealing procedure is in quantitative agreement with theory.

  9. Sound dispersion in a spin-1 Ising system near the second-order phase transition point

    International Nuclear Information System (INIS)

    Erdem, Ryza; Keskin, Mustafa

    2003-01-01

    Sound dispersion relation is derived for a spin-1 Ising system and its behaviour near the second-order phase transition point or the critical point is analyzed. The method used is a combination of molecular field approximation and Onsager theory of irreversible thermodynamics. If we assume a linear coupling of sound wave with the order parameter fluctuations in the system, we find that the dispersion which is the relative sound velocity change with frequency behaves as ω 0 ε 0 , where ω is the sound frequency and ε the temperature distance from the critical point. In the ordered region, one also observes a frequency-dependent velocity or dispersion minimum which is shifted from the corresponding attenuation maxima. These phenomena are in good agreement with the calculations of sound velocity in other magnetic systems such as magnetic metals, magnetic insulators, and magnetic semiconductors

  10. Point-contact spectroscopy of unsaturates oxides of transition metals and the problem of zero anomalies

    International Nuclear Information System (INIS)

    Tulina, N.A.

    1985-01-01

    A study was made of point-contact spectra of oxides WO 2 , ReO 3 , MoO 2 with metallic conductivity. It is shown that zero anomalies often observed in transition metal spectra are due to a higher-type oxide interlayer in the vicinity of a point contact. There are no zero anomalies in the point-contact spectra of heterocontacts Zn-MoO 2 (broken crystal) obtained directly in a helium cryostal. When studying such heterocontacts, major maxima of electron- phonon interaction in MoO 2 were determined on the energy scale hω sub(TA) approximately 28 MeV, hω sub(LA) approximately 41 MeV

  11. Tricritical point in quantum phase transitions of the Coleman–Weinberg model at Higgs mass

    International Nuclear Information System (INIS)

    Fiolhais, Miguel C.N.; Kleinert, Hagen

    2013-01-01

    The tricritical point, which separates first and second order phase transitions in three-dimensional superconductors, is studied in the four-dimensional Coleman–Weinberg model, and the similarities as well as the differences with respect to the three-dimensional result are exhibited. The position of the tricritical point in the Coleman–Weinberg model is derived and found to be in agreement with the Thomas–Fermi approximation in the three-dimensional Ginzburg–Landau theory. From this we deduce a special role of the tricritical point for the Standard Model Higgs sector in the scope of the latest experimental results, which suggests the unexpected relevance of tricritical behavior in the electroweak interactions.

  12. Isotope effect on superconductivity and Raman phonons of Pyrochlore Cd2Re2O7

    Science.gov (United States)

    Razavi, F. S.; Hajialamdari, M.; Reedyk, M.; Kremer, R. K.

    2018-06-01

    Cd2Re2O7 is the only α-Pyrochlore exhibiting superconductivity with a transition temperature (Tc) of ∼ 1 K. In this study, we present the effect of oxygen isotope (18O) as well as combined 18O and cadmium isotope (116Cd) substitution on the superconductivity and Raman scattering spectrum of Cd2Re2O7. The change of Tc and the energy gap Δ(T) are reported using various techniques including point contact spectroscopy. The shift in Raman phonon frequencies upon isotope substitution will be compared with measurement of the isotope effect on the superconducting transition temperature.

  13. Superconducting quantum circuits theory and application

    Science.gov (United States)

    Deng, Xiuhao

    Superconducting quantum circuit models are widely used to understand superconducting devices. This thesis consists of four studies wherein the superconducting quantum circuit is used to illustrate challenges related to quantum information encoding and processing, quantum simulation, quantum signal detection and amplification. The existence of scalar Aharanov-Bohm phase has been a controversial topic for decades. Scalar AB phase, defined as time integral of electric potential, gives rises to an extra phase factor in wavefunction. We proposed a superconducting quantum Faraday cage to detect temporal interference effect as a consequence of scalar AB phase. Using the superconducting quantum circuit model, the physical system is solved and resulting AB effect is predicted. Further discussion in this chapter shows that treating the experimental apparatus quantum mechanically, spatial scalar AB effect, proposed by Aharanov-Bohm, can't be observed. Either a decoherent interference apparatus is used to observe spatial scalar AB effect, or a quantum Faraday cage is used to observe temporal scalar AB effect. The second study involves protecting a quantum system from losing coherence, which is crucial to any practical quantum computation scheme. We present a theory to encode any qubit, especially superconducting qubits, into a universal quantum degeneracy point (UQDP) where low frequency noise is suppressed significantly. Numerical simulations for superconducting charge qubit using experimental parameters show that its coherence time is prolong by two orders of magnitude using our universal degeneracy point approach. With this improvement, a set of universal quantum gates can be performed at high fidelity without losing too much quantum coherence. Starting in 2004, the use of circuit QED has enabled the manipulation of superconducting qubits with photons. We applied quantum optical approach to model coupled resonators and obtained a four-wave mixing toolbox to operate photons

  14. Singular point detection algorithm based on the transition line of the fingerprint orientation image

    CSIR Research Space (South Africa)

    Mathekga, ME

    2009-11-01

    Full Text Available there is another core immediately afterwards, as in fig- ures 1 and 2. Thus, the transition columns where this condition is satisfied is set as the location of the core singular point. a and c or b and f in figure 4 must be comparable as ridges are expected... of Singularities and Pseudo Ridges”, Patt. Recog., Vol. 37, 2004, p 2233– 2243. [9] Msiza, I.S., Leke-Betechuoh, B., Nelwamondo, F.V., and Msimang, N., “A Fingerprint Pattern Classification Ap- proach Based on the Coordinate Geometry of Singulari- ties”, In...

  15. Peculiar thermal points during B2O3 transition from liquid to glass-like state

    International Nuclear Information System (INIS)

    Bartenev, G.M.; Lomovskoj, V.A.

    1992-01-01

    Relaxation transitions in glass-like B 2 O 3 were studied by dynamic methods in vacuum in the temperature range of 70-1070 K and frequency range of 10 -4 -1.2·10 6 Hz. The standard temperature of glass formation is T g =493 K and it corresponds to the standard frequency 5.3·10 -4 Hz. Above T g two special temperature points - T K and T F , position of which does not depend on the frequency, are observed

  16. Quenching of superconductivity in disordered thin films by phase fluctuations

    International Nuclear Information System (INIS)

    Hebard, A.F.; Palaanen, M.A.

    1992-01-01

    The amplitude Ψ 0 and phase Φ of the superconducting order parameter in thin-film systems are affected differently by disorder and dimensionality. With increasing disorder superconducting long range order is quenched in sufficiently thin films by physical processes driven by phase fluctuations. This occurs at both the zero-field vortex-antivortex unbinding transition and at the zero-temperature magnetic-field-tuned superconducting-insulating transition. At both of these transitions Ψ 0 is finite and constant, vanishing only when temperature, disorder, and/or magnetic field are increased further. Experimental results on amorphous-composite InO x films are presented to illustrate these points and appropriate comparisons are made to other experimental systems. (orig.)

  17. Improvement of the superconducting transition and demagnetization factor in YBa2Cu3O7-δ single crystals by laser cutting

    International Nuclear Information System (INIS)

    Bhattacharya, A.; Grupp, D.E.; Goldman, A.M.; Welp, U.

    1996-01-01

    Single crystals of YBa 2 Cu 3 O 7-δ have been cut into disc shapes using an excimer laser. The bulk superconducting transition was found to be sharpened in all cases measured. This is associated with the removal of material at the edges which may be depleted of oxygen or otherwise damaged. The magneto-optical images for one crystal have been correlated with the optical image. The angular dependence of the demagnetizing factor for field applied in the plane was drastically reduced in disc-shaped crystals relative to rectangular ones. The field of first flux entry was also increased. copyright 1996 American Institute of Physics

  18. Phase identification and superconducting transitions in Sr-doped Pr1.85Ce0.15CuO4+δ

    International Nuclear Information System (INIS)

    Varela, A.; Vallet-Regi, M.; Gonazalez-Calbet, J.M.

    1997-01-01

    Sr-doped Pr 1.85 Ce 0.15 CuO 4+δ samples have been prepared with accurate control of the oxygen content. The stability of both T ' and T * phases is strongly dependent on Sr and oxygen content. An electron diffraction study indicates that, in some cases, anionic vacancies are ordered leading to a pseudo-tetragonal superlattice with unit cell parameters 2√2a t xc t . Structural transitions and superconducting phases created by hole doping in such a system are also reported. copyright 1997 Materials Research Society

  19. Dependence of the superconducting transition temperature of the filled skutterudite compound PrPt{sub 4}Ge{sub 12} on hydrostatic pressure

    Energy Technology Data Exchange (ETDEWEB)

    Foroozani, N. [Department of Physics, Washington University, St. Louis, MO 63130 (United States); Hamlin, J.J. [Department of Physics, University of California, San Diego, La Jolla, CA 92093 (United States); Schilling, J.S., E-mail: jss@wuphys.wustl.edu [Department of Physics, Washington University, St. Louis, MO 63130 (United States); Baumbach, R.E.; Lum, I.K.; Shu, L.; Huang, K.; Maple, M.B. [Department of Physics, University of California, San Diego, La Jolla, CA 92093 (United States)

    2013-02-14

    Highlights: ► Superconductivity in the filled skutterudite PrPt{sub 4}Ge{sub 12}. ► Dependence of T{sub c} on purely hydrostatic pressure to 0.6 GPa. ► Comparison of lattice pressure to external pressure effects on superconductivity. ► Evidence for magnetic pair-breaking effects. -- Abstract: The temperature-dependent ac susceptibility of the filled skutterudite superconductor PrPt{sub 4}Ge{sub 12} has been measured under hydrostatic He-gas pressure to 0.58 GPa. The superconducting transition temperature T{sub c} decreases linearly with pressure P from 7.91 K at ambient pressure to 7.83 K at 0.58 GPa, giving the rate dT{sub c}/dP = −0.19 ± 0.03 K/GPa. Evidence is presented that suggests that the value of T{sub c} in this compound is slightly reduced due to magnetic pair-breaking effects from the Pr{sup 3+} cations.

  20. Superconducting transition and low-field magnetoresistance of a niobium single crystal at 4.2 deg. K; Transition supraconductrice et magnetoresistance en champ faible d'un echantillon monocristallin de niobium a 4.2 deg. K

    Energy Technology Data Exchange (ETDEWEB)

    Perriot, G [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires. Service de physique du solide et de resonnance magnetique

    1967-01-01

    We report the study of the electrical resistance of a niobium single crystal, at 4.2 deg. K, from the beginning of the superconductive transition to 80 kilo oersteds. Critical fieldsH{sub c2} and H{sub c3} have been determined. Influences on superconductive transition of current density, field-current angle, crystal orientation and magnetoresistance have been studied. Variation laws of low-field transverse and longitudinal magneto-resistances have been determined. (author) [French] La variation de la resistance electrique d'un monocristal cylindrique de niobium a ete etudiee, a 4,2 deg. K, depuis le debut de la transition supraconductrice jusqu'a 80 kilooersteds. Les champs critiques H{sub c2} et H{sub c3} ont ete determines. On a etudie l'influence de la densite de courant, de l'angle champ-courant, de l'anisotropie cristalline et de la magnetoresistance sur la transition supraconductrice. Les lois de variation des magnetoresistances transversale et longitudinale ont ete determinees dans le domaine des champs faibles. (auteur)

  1. Superconducting transition and low-field magnetoresistance of a niobium single crystal at 4.2 deg. K; Transition supraconductrice et magnetoresistance en champ faible d'un echantillon monocristallin de niobium a 4.2 deg. K

    Energy Technology Data Exchange (ETDEWEB)

    Perriot, G. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires. Service de physique du solide et de resonnance magnetique

    1967-01-01

    We report the study of the electrical resistance of a niobium single crystal, at 4.2 deg. K, from the beginning of the superconductive transition to 80 kilo oersteds. Critical fieldsH{sub c2} and H{sub c3} have been determined. Influences on superconductive transition of current density, field-current angle, crystal orientation and magnetoresistance have been studied. Variation laws of low-field transverse and longitudinal magneto-resistances have been determined. (author) [French] La variation de la resistance electrique d'un monocristal cylindrique de niobium a ete etudiee, a 4,2 deg. K, depuis le debut de la transition supraconductrice jusqu'a 80 kilooersteds. Les champs critiques H{sub c2} et H{sub c3} ont ete determines. On a etudie l'influence de la densite de courant, de l'angle champ-courant, de l'anisotropie cristalline et de la magnetoresistance sur la transition supraconductrice. Les lois de variation des magnetoresistances transversale et longitudinale ont ete determinees dans le domaine des champs faibles. (auteur)

  2. Phenomenological Equations Relating Various Critical Anomalies above a Cubic-to-Tetragonal Phase Transition Point

    Science.gov (United States)

    Hamano, Katsumi; Hirotsu, Shunsuke

    1980-01-01

    Phenomenological equations are derived which interrelate the anomalies in various thermodynamic quantities above the transition point of a cubic-to-tetragonal phase transition caused by an instability of a triply degenerate soft mode. The anomalous part of the Gibbs free energy is assumed to be a simple sum of the three parts which represent the contributions from the three fluctuation components. A cylindrical approximation is adopted to each of the three contributions by taking into account the symmetry of the fluctuations. The theory predicts that the adiabatic elastic compliances, s11s, s12s, and also s11s-s12s should exhibit anomalies proportional to the anomaly in the specific heat at constant pressure. This is in marked contrast with the result of the generalized Pippard equations derived by Garland, and by Janovec. The new equations are successfully tested for KMnF3, CsPbCl3, and CsPbBr3. The β-γ transition of NH4Br is also discussed.

  3. Process for producing clad superconductive materials

    International Nuclear Information System (INIS)

    Cass, R.B.; Ott, K.C.; Peterson, D.E.

    1992-01-01

    This patent describes a process for fabricating superconducting composite wire. It comprises placing a superconductive precursor admixture capable of undergoing self propagating combustion in stoichiometric amounts sufficient to form a superconductive product within an oxygen-porous metal tube; sealing one end of the tube; igniting the superconductive precursor admixture whereby the superconductive precursor admixture endburns along the length of the admixture; and cross-section reducing the tube at a rate substantially equal to the rate of burning of the superconductive precursor admixture and at a point substantially planar with the burnfront of the superconductive precursor mixture, whereby a clad superconductive product is formed in situ

  4. Transition point prediction in a multicomponent lattice Boltzmann model: Forcing scheme dependencies

    Science.gov (United States)

    Küllmer, Knut; Krämer, Andreas; Joppich, Wolfgang; Reith, Dirk; Foysi, Holger

    2018-02-01

    Pseudopotential-based lattice Boltzmann models are widely used for numerical simulations of multiphase flows. In the special case of multicomponent systems, the overall dynamics are characterized by the conservation equations for mass and momentum as well as an additional advection diffusion equation for each component. In the present study, we investigate how the latter is affected by the forcing scheme, i.e., by the way the underlying interparticle forces are incorporated into the lattice Boltzmann equation. By comparing two model formulations for pure multicomponent systems, namely the standard model [X. Shan and G. D. Doolen, J. Stat. Phys. 81, 379 (1995), 10.1007/BF02179985] and the explicit forcing model [M. L. Porter et al., Phys. Rev. E 86, 036701 (2012), 10.1103/PhysRevE.86.036701], we reveal that the diffusion characteristics drastically change. We derive a generalized, potential function-dependent expression for the transition point from the miscible to the immiscible regime and demonstrate that it is shifted between the models. The theoretical predictions for both the transition point and the mutual diffusion coefficient are validated in simulations of static droplets and decaying sinusoidal concentration waves, respectively. To show the universality of our analysis, two common and one new potential function are investigated. As the shift in the diffusion characteristics directly affects the interfacial properties, we additionally show that phenomena related to the interfacial tension such as the modeling of contact angles are influenced as well.

  5. Transition point prediction in a multicomponent lattice Boltzmann model: Forcing scheme dependencies.

    Science.gov (United States)

    Küllmer, Knut; Krämer, Andreas; Joppich, Wolfgang; Reith, Dirk; Foysi, Holger

    2018-02-01

    Pseudopotential-based lattice Boltzmann models are widely used for numerical simulations of multiphase flows. In the special case of multicomponent systems, the overall dynamics are characterized by the conservation equations for mass and momentum as well as an additional advection diffusion equation for each component. In the present study, we investigate how the latter is affected by the forcing scheme, i.e., by the way the underlying interparticle forces are incorporated into the lattice Boltzmann equation. By comparing two model formulations for pure multicomponent systems, namely the standard model [X. Shan and G. D. Doolen, J. Stat. Phys. 81, 379 (1995)JSTPBS0022-471510.1007/BF02179985] and the explicit forcing model [M. L. Porter et al., Phys. Rev. E 86, 036701 (2012)PLEEE81539-375510.1103/PhysRevE.86.036701], we reveal that the diffusion characteristics drastically change. We derive a generalized, potential function-dependent expression for the transition point from the miscible to the immiscible regime and demonstrate that it is shifted between the models. The theoretical predictions for both the transition point and the mutual diffusion coefficient are validated in simulations of static droplets and decaying sinusoidal concentration waves, respectively. To show the universality of our analysis, two common and one new potential function are investigated. As the shift in the diffusion characteristics directly affects the interfacial properties, we additionally show that phenomena related to the interfacial tension such as the modeling of contact angles are influenced as well.

  6. Duality between the Deconfined Quantum-Critical Point and the Bosonic Topological Transition

    Directory of Open Access Journals (Sweden)

    Yan Qi Qin

    2017-09-01

    Full Text Available Recently, significant progress has been made in (2+1-dimensional conformal field theories without supersymmetry. In particular, it was realized that different Lagrangians may be related by hidden dualities; i.e., seemingly different field theories may actually be identical in the infrared limit. Among all the proposed dualities, one has attracted particular interest in the field of strongly correlated quantum-matter systems: the one relating the easy-plane noncompact CP^{1} model (NCCP^{1} and noncompact quantum electrodynamics (QED with two flavors (N=2 of massless two-component Dirac fermions. The easy-plane NCCP^{1} model is the field theory of the putative deconfined quantum-critical point separating a planar (XY antiferromagnet and a dimerized (valence-bond solid ground state, while N=2 noncompact QED is the theory for the transition between a bosonic symmetry-protected topological phase and a trivial Mott insulator. In this work, we present strong numerical support for the proposed duality. We realize the N=2 noncompact QED at a critical point of an interacting fermion model on the bilayer honeycomb lattice and study it using determinant quantum Monte Carlo (QMC simulations. Using stochastic series expansion QMC simulations, we study a planar version of the S=1/2 J-Q spin Hamiltonian (a quantum XY model with additional multispin couplings and show that it hosts a continuous transition between the XY magnet and the valence-bond solid. The duality between the two systems, following from a mapping of their phase diagrams extending from their respective critical points, is supported by the good agreement between the critical exponents according to the proposed duality relationships. In the J-Q model, we find both continuous and first-order transitions, depending on the degree of planar anisotropy, with deconfined quantum criticality surviving only up to moderate strengths of the anisotropy. This explains previous claims of no deconfined

  7. Applied superconductivity

    CERN Document Server

    Newhouse, Vernon L

    1975-01-01

    Applied Superconductivity, Volume II, is part of a two-volume series on applied superconductivity. The first volume dealt with electronic applications and radiation detection, and contains a chapter on liquid helium refrigeration. The present volume discusses magnets, electromechanical applications, accelerators, and microwave and rf devices. The book opens with a chapter on high-field superconducting magnets, covering applications and magnet design. Subsequent chapters discuss superconductive machinery such as superconductive bearings and motors; rf superconducting devices; and future prospec

  8. Submicron superconducting structures

    International Nuclear Information System (INIS)

    Golovashkin, A.I.; Lykov, A.N.

    1986-01-01

    An overview of works concerning superconducting structures of submicron dimensions and a system of such structures is given. It is noted that usage of the above structures in superconducting microelectronics permits, first, to increase the element packing density, to decrease the signal transmission time, capacity, power dissipated in high-frequency applications. Secondly, negligible coherence length in transition metals, their alloys and high-temperature compounds also restrict the dimensions of superconducting weak couplings when the 'classical' Josephson effect is displayed. The most effective methods for production of submicron superconducting structures are the following: lithography, double scribering. Recently the systems of superconducting submicron elements are extensively studied. It is shown that such systems can be phased by magnetic field

  9. The role of Ca substitution on the nature of the superconducting transition of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}

    Energy Technology Data Exchange (ETDEWEB)

    Jaeckel, S.T.; Lopes, L.F.; Nunes, S.E.; Mendonca, A.P.A.; Lopes, R.F.; Vieira, V.N. [Universidade Federal de Pelotas, RS (Brazil). Inst. de Fisica e Matematica; Pureur, P.; Pimentel Junior, J.L.; Rosa, F.M. [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Inst. de Fisica; Ferreira, L.M. [Universidade Federal do ABC (UFABC), Santo Andre, SP (Brazil). Centro de Ciencias Naturais e Humanas

    2012-07-01

    Full text: In this work we report the results of an experimental study about the superconducting transition of Ca- doped YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}samples. Temperature dependent in-plane resistivity measurements were carried out on Y{sub 1-x}Ca{sub x}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} single crystals with Ca content x = 0, 0.01, 0.05, 0.10. The samples were studied under hydrostatic pressure conditions (P {<=}15 kbar) and applied magnetic fields (H {<=} 2500 Oe) with H parallel to the c-axis. From the analysis of the contribution of superconducting fluctuations to the electrical conductivity we identified a fluctuation regime described by the small exponent {lambda}{sub cr} = 0.20 in a narrow temperature range immediately above the critical temperature. The origin of this fluctuation regime is still unclear. A possibility is that it may be a precursor to a weakly first-order pairing transition. The evolution of this super-critical regime with pressure and magnetic field for our Ca-doped samples is distinct from results reported in the literature for pure and other divalent substituted YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}samples. Our results indicate that Ca doping favors the stabilization of the super-critical regime. (author)

  10. Multiple superconducting transition and phase separation in melt-textured YBa{sub 2}Cu{sub 3}O{sub 7−d}

    Energy Technology Data Exchange (ETDEWEB)

    Menegotto Costa, R. [Instituto de Matemática, Estatística e Física, Universidade Federal do Rio Grande (FURG), Campus Carreiros, Rio Grande, RS (Brazil); Dias, F.T. [Instituto de Física e Matemática, Universidade Federal de Pelotas (UFPel), Caixa Postal 354, 96010-900 Pelotas, RS (Brazil); Pureur, P., E-mail: ppureur@if.ufrgs.br [Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS), Caixa Postal 15051, 91501-970 Porto Alegre, RS (Brazil); Obradors, X. [Institut de Ciéncia de Materials de Barcelona, CSIC, Universitat Autònoma de Barcelona, 08193 Bellaterra (Spain)

    2013-12-15

    Highlights: •We report on experimental measurements of the temperature derivative of the resistivity in the region encompassing the superconducting transition in melt-textured samples of the YBa{sub 2}Cu{sub 3}O{sub 7−d} cuprate superconductor. •A complex and subtle multi-peak structure is observed in d{ρ}/dT. •We develop a new method to quantitatively describe the resistive transition of a multi-phased superconductor. •The pseudo-spectral structure observed in d{ρ}/dT is ascribed to a phase separation phenomenon driven by the ordering of labile oxygen atoms in the Cu–O chain substructure. -- Abstract: We report on careful measurements of the temperature derivative of the resistivity, dρ/dT, in the region encompassing the superconducting transition of melt-textured samples of the YBa{sub 2}Cu{sub 3}O{sub 7−d} cuprate superconductor. Measurements were carried out in orientations parallel and perpendicular to the Cu − O{sub 2} atomic planes in the presence of small magnetic fields applied parallel to the current orientation. The dρ/dT results reveal the occurrence of complex multi-peak structures that were analyzed with a new method based on the assumption that a simple series association of conductivities is adequate for describing the resistive transition of multiphased superconductors. We ascribe the multi-peak structure observed in the derivative measurements to a subtle and complex phase separation phenomenon leading to the stabilization of domains having slightly different electronic properties that are related to the ordering of labile oxygen atoms in the YBa{sub 2}Cu{sub 3}O{sub 7−d} chain sub-structure.

  11. Branching points for transition pathways: assessing responses of actors to challenges on pathways to a low carbon future

    International Nuclear Information System (INIS)

    Foxon, Timothy J.; Pearson, Peter J.G.; Arapostathis, Stathis; Carlsson-Hyslop, Anna; Thornton, Judith

    2013-01-01

    This paper describes initial analysis of branching points on a set of transition pathways to a UK low carbon electricity future by 2050. As described in other papers in this special issue, we are exploring and analysing a set of core transition pathways, based on alternative governance patterns in which the ‘logics’ of market actors, government actors and civil society actors, respectively dominate. This core pathway analysis is enhanced by analyses of branching points within and across the pathways, which informs how competition between different logics plays out at key decision points. Branching points are defined as key decision points at which choices made by actors, in response to internal or external stresses or triggers, determine whether and in what ways the pathway is followed. A set of initial branching points for our three core transition pathways is identified through project and stakeholder workshops, and drawing on analysis of actors’ choices and responses at past branching points in energy system transitions. The potential responses of the actors are identified at these branching points, and risk mitigation strategies are formulated for the dominant actors to reinforce that pathway, as well as opportunities for actors to move away from the pathway. - Highlights: Transition Pathways is analysing three potential pathways to a low carbon future. ► Stresses lead to branching points, where actors make choices, creating pathways. ► These choices may lead to path-dependency. ► Differences in governance logics within transition pathways are also analysed. ► Studying branching points adds theoretical understanding and policy relevance to TP.

  12. Bohr model description of the critical point for the first order shape phase transition

    Science.gov (United States)

    Budaca, R.; Buganu, P.; Budaca, A. I.

    2018-01-01

    The critical point of the shape phase transition between spherical and axially deformed nuclei is described by a collective Bohr Hamiltonian with a sextic potential having simultaneous spherical and deformed minima of the same depth. The particular choice of the potential as well as the scaled and decoupled nature of the total Hamiltonian leads to a model with a single free parameter connected to the height of the barrier which separates the two minima. The solutions are found through the diagonalization in a basis of Bessel functions. The basis is optimized for each value of the free parameter by means of a boundary deformation which assures the convergence of the solutions for a fixed basis dimension. Analyzing the spectral properties of the model, as a function of the barrier height, revealed instances with shape coexisting features which are considered for detailed numerical applications.

  13. Bohr model description of the critical point for the first order shape phase transition

    Directory of Open Access Journals (Sweden)

    R. Budaca

    2018-01-01

    Full Text Available The critical point of the shape phase transition between spherical and axially deformed nuclei is described by a collective Bohr Hamiltonian with a sextic potential having simultaneous spherical and deformed minima of the same depth. The particular choice of the potential as well as the scaled and decoupled nature of the total Hamiltonian leads to a model with a single free parameter connected to the height of the barrier which separates the two minima. The solutions are found through the diagonalization in a basis of Bessel functions. The basis is optimized for each value of the free parameter by means of a boundary deformation which assures the convergence of the solutions for a fixed basis dimension. Analyzing the spectral properties of the model, as a function of the barrier height, revealed instances with shape coexisting features which are considered for detailed numerical applications.

  14. Oxidation feature and diffusion mechanism of Zr-based metallic glasses near the glass transition point

    Science.gov (United States)

    Hu, Zheng; Lei, Xianqi; Wang, Yang; Zhang, Kun

    2018-03-01

    The oxidation behaviors of as-cast, pre-deformed, and crystallized Zr47.9Ti0.3Ni3.1Cu39.3Al9.4 metallic glasses (MGs) were studied near the glass transition point. The oxidation kinetics of the crystallized MGs followed a parabolic-rate law, and the as-cast and pre-deformed MGs exerted a typical two-stage behavior above the glass transition temperature (T g). Most interesting, pre-deformed treatment can significantly improve the oxidation rate of MGs, as the initial oxidation appeared earlier than for the as-cast MGs, and was accompanied by much thicker oxide scale. The EDS and XPS results showed that the metal Al acted as the preferred scavenger that absorbed intrinsic oxygen in the near-surface region of as-cast MGs. However, a homogeneous mixed layer without Al was observed in the pre-deformed MGs. We speculated the accelerated diffusion of other elements in the MGs was due to the local increase in the free volume and significant shear-induced dilation of the local structure. The results from this study demonstrate that MGs exhibit controllable atomic diffusion during the oxidation process, which can facilitate use in super-cooled liquid region applications.

  15. Triply degenerate nodal points and topological phase transitions in NaCu3Te2

    Science.gov (United States)

    Xia, Yunyouyou; Li, Gang

    2017-12-01

    Quasiparticle excitations of free electrons in condensed-matter physics, characterized by the dimensionality of the band crossing, can find their elementary-particle analogs in high-energy physics, such as Majorana, Weyl, and Dirac fermions, while crystalline symmetry allows more quasiparticle excitations and exotic fermions to emerge. Using symmetry analysis and ab initio calculations, we propose that the three-dimensional honeycomb crystal NaCu3Te2 hosts triply degenerate nodal points (TDNPs) residing at the Fermi level. Furthermore, in this system we find a tunable phase transition between a trivial insulator, a TDNP phase, and a weak topological insulator (TI), triggered by a symmetry-allowed perturbation and the spin-orbital coupling (SOC). Such a topological nontrivial ternary compound not only serves as a perfect candidate for studying three-component fermions, but also provides an excellent playground for understanding the topological phase transitions between TDNPs, TIs, and trivial insulators, which distinguishes this system from other TDNP candidates.

  16. Hysteresis critical point of nitrogen in porous glass: occurrence of sample spanning transition in capillary condensation.

    Science.gov (United States)

    Morishige, Kunimitsu

    2009-06-02

    To examine the mechanisms for capillary condensation and for capillary evaporation in porous glass, we measured the hysteresis critical points and desorption scanning curves of nitrogen in four kinds of porous glasses with different pore sizes (Vycor, CPG75A, CPG120A, and CPG170A). The shapes of the hysteresis loop in the adsorption isotherm of nitrogen for the Vycor and the CPG75A changed with temperature, whereas those for the CPG120A and the CPG170A remained almost unchanged with temperature. The hysteresis critical points for the Vycor and the CPG75A fell on the common line observed previously for ordered mesoporous silicas. On the other hand, the hysteresis critical points for the CPG120A and the CPG170A deviated appreciably from the common line. This strongly suggests that capillary evaporation of nitrogen in the interconnected and disordered pores of both the Vycor and the CPG75A follows a cavitation process at least in the vicinity of their hysteresis critical temperatures in the same way as that in the cagelike pores of the ordered silicas, whereas the hysteresis critical points in the CPG120A and the CPG170A have origin different from that in the cagelike pores. The desorption scanning curves for the CPG75A indicated the nonindependence of the porous domains. On the other hand, for both the CPG120A and the CPG170A, we obtained the scanning curves that are expected from the independent domain theory. All these results suggest that sample spanning transitions in capillary condensation and evaporation take place inside the interconnected pores of both the CPG120A and the CPG170A.

  17. Superconductivity in doped insulators

    International Nuclear Information System (INIS)

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

    1995-01-01

    It is shown that many synthetic metals, including high temperature superconductors are ''bad metals'', with such a poor conductivity that the usual meanfield theory of superconductivity breaks down because of anomalously large classical and quantum fluctuations of the phase of the superconducting order parameter. It is argued that the supression of a first order phase transition (phase separation) by the long-range Coulomb interaction leads to high temperature superconductivity accompanied by static or dynamical charge inhomogeneIty. Evidence in support of this picture for high temperature superconductors is described

  18. Superconductivity mediated by anharmonic phonons: application to β-pyrochlore oxides

    Science.gov (United States)

    Hattori, Kazumasa; Tsunetsugu, Hirokazu

    2010-03-01

    We investigate three dimensional anharmonic phonons under tetrahedral symmetry and superconductivity mediated by these phonons. Three dimensional anharmonic phonon spectra are calculated directly by solving Schr"odinger equation and the superconducting transition temperature is determined by using the theory of strong coupling superconductivity assuming an isotropic gap function. With increasing the third order anharmonicity b of the tetrahedral potential, we find a crossover in the energy spectrum to a quantum tunneling regime. We obtain strongly enhanced transition temperatures around the crossover point. The first order transition observed in KOs2O6 is discussed in terms of the first excited state energy δ, and the coupling constant λ in the strong coupling theory of superconductivity. Our results suggest that the decrease of λ and increase of δ below the first order transition temperature. We point out that the change in the oscillation amplitude and characterizes this isomorphic transition. The chemical trends of the superconducting transition temperature, λ, and δ in the β-pyrochlore compounds are also discussed.

  19. Rapid characterization of microscopic two-level systems using Landau-Zener transitions in a superconducting qubit

    International Nuclear Information System (INIS)

    Tan, Xinsheng; Yu, Haifeng; Yu, Yang; Han, Siyuan

    2015-01-01

    We demonstrate a fast method to detect microscopic two-level systems in a superconducting phase qubit. By monitoring the population leak after sweeping the qubit bias flux, we are able to measure the two-level systems that are coupled with the qubit. Compared with the traditional method that detects two-level systems by energy spectroscopy, our method is faster and more sensitive. This method supplies a useful tool to investigate two-level systems in solid-state qubits

  20. Electronic structures and superconductivity in LuTE2Si2 phases (TE = d-electron transition metal)

    Science.gov (United States)

    Samsel-Czekała, M.; Chajewski, G.; Wiśniewski, P.; Romanova, T.; Hackemer, A.; Gorzelniak, R.; Pikul, A. P.; Kaczorowski, D.

    2018-05-01

    In the course of our search for unconventional superconductors amidst the 1:2:2 phases, we have re-investigated the LuTE2Si2 compounds with TE = Fe, Co, Ni, Ru, Pd and Pt. In this paper, we present the results of our fully relativistic ab initio calculations of the band structures, performed using the full-potential local-orbital code. The theoretical data are supplemented by the results of low-temperature electrical transport and specific heat measurements performed down to 0.35 K. All the materials studied but LuPt2Si2 crystallize with the body-centered tetragonal ThCr2Si2-type structure (space group I4/mmm). Their Fermi surfaces exhibit a three-dimensional multi-band character. In turn, the Pt-bearing compound adopts the primitive tetragonal CaBe2Ge2-type structure (space group P4/nmm), and its Fermi surface consists of predominantly quasi-two-dimensional sheets. Bulk superconductivity was found only in LuPd2Si2 and LuPt2Si2 (independent of the structure type and dimensionality of the Fermi surface). The key superconducting characteristics indicate a fully-gapped BCS type character. Though the electronic structure of LuFe2Si2 closely resembles that of the unconventional superconductor YFe2Ge2, this Lu-based silicide exhibits neither superconductivity nor spin fluctuations at least down to 0.35 K.

  1. {mu}SR studies of the interplay of magnetic spin stripe order with superconductivity in transition metal oxides

    Energy Technology Data Exchange (ETDEWEB)

    Klauss, Hans-Henning, E-mail: h.klauss@physik.tu-dresden.de [Institute for Solid State Physics, TU Dresden, D-01069 Dresden (Germany)

    2012-11-01

    In this work we review muon spin relaxation experiments on the layered La{sub 2-x}Sr{sub x}NiO{sub 4} nickelate as well as La{sub 2-x}Ba{sub x}CuO{sub 4} and La{sub 2-x}Sr{sub x}CuO{sub 4} cuprate systems to examine spin stripe order. In particular, the interplay of stripe order with superconductivity in Nd and Eu doped La{sub 2-x}Sr{sub x}CuO{sub 4} cuprates is discussed. Detailed studies of the electronic phase diagrams as well as the magnetic and superconducting order parameters for different rare-earth and Sr doping levels in La{sub 2-x-y}RE{sub y}Sr{sub x}CuO{sub 4} revealed the strong correlation of static spin stripe order with the structural distortion in the low temperature tetragonal (LTT) phase and the competition with the superconducting ground state. High magnetic field studies demonstrate the nearly degenerate ground state energy of the different electronic phases. Slow transverse fluctuations of the charge stripes are found in nickelates and cuprates at low temperatures.

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

    Energy Technology Data Exchange (ETDEWEB)

    Weber, F.

    2007-11-02

    The present thesis concentrates on the signatures of strong electron-phonon coupling in phonon properties measured by inelastic neutron scattering. The inelastic neutron scattering experiments were performed on the triple-axis spectrometers 1T and DAS PUMA at the research reactors in Saclay (France) and Munich (Germany), respectively. The work is subdivided into two separate chapters: In the first part, we report measurements of the lattice dynamical properties, i.e. phonon frequency, linewidth and intensity, of the conventional, i.e. phonon-mediated, superconductor YNi{sub 2}B{sub 2}C of the rare-earth-borocarbide family. The detailed check of theoretical predictions for these properties, which were calculated in the theory group of our institute, was one major goal of this work. We measured phonons in the normal state, i.e. T>T{sub c}, for several high symmetry directions up to 70 meV. We were able to extract the full temperature dependence of the superconducting energy gap 2{delta}(T) from our phonon scans with such accuracy that even deviations from the weak coupling BCS behaviour could be clearly observed. By measuring phonons at different wave vectors we demonstrated that phonons are sensitive to the gap anisotropy under the precondition, that different phonons get their coupling strength from different parts of the Fermi surface. In the second part, we investigated the properties of Mn-O bond-stretching phonons in the bilayer manganite La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7}. At the doping level x=0.38 this compound has an ferromagnetic groundstate and exhibits the so-called colossal magnetoresistance effect in the vicinity of the Curie temperature T{sub C}. The atomic displacement patterns of the investigated phonons closely resemble possible Jahn-Teller distortions of the MnO{sub 6} octahedra, which are introduced in this compound by the Jahn-Teller active Mn{sup 3+} ions. We observed strong renormalizations of the phonon frequencies and clear peaks of

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

    International Nuclear Information System (INIS)

    Weber, F.

    2007-01-01

    The present thesis concentrates on the signatures of strong electron-phonon coupling in phonon properties measured by inelastic neutron scattering. The inelastic neutron scattering experiments were performed on the triple-axis spectrometers 1T and DAS PUMA at the research reactors in Saclay (France) and Munich (Germany), respectively. The work is subdivided into two separate chapters: In the first part, we report measurements of the lattice dynamical properties, i.e. phonon frequency, linewidth and intensity, of the conventional, i.e. phonon-mediated, superconductor YNi 2 B 2 C of the rare-earth-borocarbide family. The detailed check of theoretical predictions for these properties, which were calculated in the theory group of our institute, was one major goal of this work. We measured phonons in the normal state, i.e. T>T c , for several high symmetry directions up to 70 meV. We were able to extract the full temperature dependence of the superconducting energy gap 2Δ(T) from our phonon scans with such accuracy that even deviations from the weak coupling BCS behaviour could be clearly observed. By measuring phonons at different wave vectors we demonstrated that phonons are sensitive to the gap anisotropy under the precondition, that different phonons get their coupling strength from different parts of the Fermi surface. In the second part, we investigated the properties of Mn-O bond-stretching phonons in the bilayer manganite La 2-2x Sr 1+2x Mn 2 O 7 . At the doping level x=0.38 this compound has an ferromagnetic groundstate and exhibits the so-called colossal magnetoresistance effect in the vicinity of the Curie temperature T C . The atomic displacement patterns of the investigated phonons closely resemble possible Jahn-Teller distortions of the MnO 6 octahedra, which are introduced in this compound by the Jahn-Teller active Mn 3+ ions. We observed strong renormalizations of the phonon frequencies and clear peaks of the intrinsic phonon linewidth near the order

  4. Implementation of the superfluid helium phase transition using finite element modeling: Simulation of ransient heat transfer and He-I/He-II phase front movement in cooling channels of superconducting magnets

    NARCIS (Netherlands)

    Bielert, Erwin; Verweij, A.P.; ten Kate, Herman H.J.

    2013-01-01

    In the thermal design of high magnetic field superconducting accelerator magnets, the emphasis is on the use of superfluid helium as a coolant and stabilizing medium. The very high effective thermal conductivity of helium below the lambda transition temperature significantly helps to extract heat

  5. Classical generalized transition-state theory. Application to a collinear reaction with two saddle points

    International Nuclear Information System (INIS)

    Garrett, B.C.; Truhlar, D.G.; Grev, R.S.

    1981-01-01

    Accurate classical dynamical fixed-energy reaction probabilities and fixed-temperature rate constants are calculated for the collinear reaction H + FH on a low-barrier model potential energy surface. The calculations cover energies from 0.1 to 100 kcal/mol above threshold and temperatures of 100 to 10,000 K. The accurate results are used to test five approximate theories: conventional transition-state theory (TST), canonical variational theory (CVT), improved canonical variational theory (ICVT), microcanonical variational theory (μVT), and the unified statistical model (US). The first four of these theories involve a single dividing surface in phase space, and the US theory involves three dividing surfaces. The tests are particularly interesting because the potential energy surface has two identical saddle points. At temperatures from 100 to 2000 K, the μVt is the most accurate theory, with errors in the range 11 to 14%; for temperatures from 2000 to 10,000 K, the US theory is the most successful, with errors in the range 3 to 14%. Over the whole range, a factor of 100 in temperature, both theories have errors of 35% or less. Even TST has errors of 47% or less over the whole factor-of-100 temperature range. Although the US model should become exact at threshold for this system, it already underestimates the reaction probability by a factor of 0.64 at 0.1 kcal/mol above threshold. TST and μVT agree with each other within 12% up to an energy 13 kcal/mol above the saddle point energy. 3 figures, 2 tables

  6. Evidence for a vortex-glass transition in superconducting Ba(Fe0.9Co0.1)2As2.

    Science.gov (United States)

    Prando, G; Giraud, R; Aswartham, S; Vakaliuk, O; Abdel-Hafiez, M; Hess, C; Wurmehl, S; Wolter, A U B; Büchner, B

    2013-12-18

    Measurements of magneto-resistivity and magnetic susceptibility were performed on single crystals of superconducting Ba(Fe0.9Co0.1)2As2 close to the conditions of optimal doping. The high quality of the investigated samples allows us to reveal dynamic scaling behaviour associated with a vortex-glass phase transition in the limit of a weak degree of quenched disorder. Accordingly, the dissipative component of the ac susceptibility is reproduced well within the framework of Havriliak-Negami relaxation, assuming a critical power-law divergence for the characteristic correlation time τ of the vortex dynamics. Remarkably, the random disorder introduced by the Fe1-xCox chemical substitution is found to act on the vortices as a much weaker quenched disorder than previously reported for cuprate superconductors such as Y1-xPrxBa2Cu3O7-δ.

  7. Pressure dependence of the Raman spectrum, lattice parameters and superconducting critical temperature of MgB2: evidence for pressure-driven phonon-assisted electronic topological transition

    International Nuclear Information System (INIS)

    Goncharov, A.F.; Struzhkin, V.V.

    2003-01-01

    We overview recent high-pressure studies of high-temperature superconductor MgB 2 by Raman scattering technique combined with measurements of superconducting critical temperature T c and lattice parameters up to 57 GPa. An anomalously broadened Raman band at 620 cm -1 is observed and assigned to the in-plane boron stretching E 2g mode. It exhibits a large Grueneisen parameter indicating that the vibration is highly anharmonic. The pressure dependencies of the E 2g mode and T c reveal anomalies at 15-22 GPa (isotope dependent). The anharmonic character of the E 2g phonon mode, its anomalous pressure dependence, and also that for T c are interpreted as a result of a phonon-assisted Lifshitz electronic topological transition

  8. Superconducting plasmas

    International Nuclear Information System (INIS)

    Ohnuma, Toshiro; Ohno, J.

    1994-01-01

    Superconducting (SC) plasmas are proposed and investigated. The SC plasmas are not yet familiar and have not yet been studied. However, the existence and the importance of SC plasmas are stressed in this report. The existence of SC plasmas are found as follows. There is a fundamental property of Meissner effect in superconductors, which shows a repulsive effect of magnetic fields. Even in that case, in a microscopic view, there is a region of magnetic penetration. The penetration length λ is well-known as London's penetration depth, which is expressed as δ = (m s /μ 0 n s q s 2 ) 1/2 where m s , n s , q s and μ o show the mass, the density, the charge of SC electron and the permeability in free space, respectively. Because this expression is very simple, no one had tried it into more simple and meaningful form. Recently, one of the authors (T.O.) has found that the length can be expressed into more simple and understandable fundamental form as λ = c/ω ps where c = (ε 0 μ 0 ) -1/2 and ω ps = (n s q s 2 /m s ε 0 ) 1/2 are the light velocity and the superconducting plasma frequency. From this simple expression, the penetration depth of the magnetic field to SC is found as a SC plasma skin depth, that is, the fundamental property of SC can be expressed by the SC plasmas. This discovery indicates an importance of the studies of superconducting plasmas. From these points, several properties (propagating modes et al) of SC plasmas, which consist of SC electrons, normal electrons and lattice ions, are investigated in this report. Observations of SC plasma frequency is also reported with a use of Terahertz electromagnet-optical waves

  9. Interpretation of specific-heat and spontaneous-magnetization anomalies at the reentrant superconducting - ferromagnetic transition in (Ho0.6Er0.4)Rh4B4

    International Nuclear Information System (INIS)

    Woolf, L.D.; Johnston, D.C.; Mook, H.A.; Koehler, W.C.; Maple, M.B.; Fisk, Z.

    1981-09-01

    Analysis of neutron-diffraction data on the compound (Ho 0 . 6 Er 0 . 4 )Rh 4 B 4 indicates that the Curie temperature is depressed by about 0.2 K due to the occurrence of superconductivity, in agreement with theoretical predictions. The temperature dependence of the specific heat in the vicinity of the first-order reentrant superconducting - ferromagnetic transition was computed by means of a simple model from the temperature dependence of the spontaneous magnetization of the Ho ions and was found to be in good agreement with the experimental data

  10. Superconductivity - applications

    International Nuclear Information System (INIS)

    The paper deals with the following subjects: 1) Electronics and high-frequency technology, 2) Superconductors for energy technology, 3) Superconducting magnets and their applications, 4) Electric machinery, 5) Superconducting cables. (WBU) [de

  11. Anderson transition on the Cayley tree as a traveling wave critical point for various probability distributions

    International Nuclear Information System (INIS)

    Monthus, Cecile; Garel, Thomas

    2009-01-01

    For Anderson localization on the Cayley tree, we study the statistics of various observables as a function of the disorder strength W and the number N of generations. We first consider the Landauer transmission T N . In the localized phase, its logarithm follows the traveling wave form T N ≅(ln T N )-bar + ln t* where (i) the disorder-averaged value moves linearly (ln(T N ))-bar≅-N/ξ loc and the localization length diverges as ξ loc ∼(W-W c ) -ν loc with ν loc = 1 and (ii) the variable t* is a fixed random variable with a power-law tail P*(t*) ∼ 1/(t*) 1+β(W) for large t* with 0 N are governed by rare events. In the delocalized phase, the transmission T N remains a finite random variable as N → ∞, and we measure near criticality the essential singularity (ln(T ∞ ))-bar∼-|W c -W| -κ T with κ T ∼ 0.25. We then consider the statistical properties of normalized eigenstates Σ x |ψ(x)| 2 = 1, in particular the entropy S = -Σ x |ψ(x)| 2 ln |ψ(x)| 2 and the inverse participation ratios (IPR) I q = Σ x |ψ(x)| 2q . In the localized phase, the typical entropy diverges as S typ ∼( W-W c ) -ν S with ν S ∼ 1.5, whereas it grows linearly as S typ (N) ∼ N in the delocalized phase. Finally for the IPR, we explain how closely related variables propagate as traveling waves in the delocalized phase. In conclusion, both the localized phase and the delocalized phase are characterized by the traveling wave propagation of some probability distributions, and the Anderson localization/delocalization transition then corresponds to a traveling/non-traveling critical point. Moreover, our results point toward the existence of several length scales that diverge with different exponents ν at criticality

  12. The superconducting gaps of C-substituted and Al-substituted MgB2 single crystals by point-contact spectroscopy

    International Nuclear Information System (INIS)

    Daghero, D.; Gonnelli, R.S.; Ummarino, G.A.; Calzolari, A.; Dellarocca, Valeria; Stepanov, V.A.; Zhigadlo, N.; Kazakov, S.M.; Karpinski, J.

    2005-01-01

    We studied the effects of carbon and aluminum substitutions on the gaps of the two-band superconductor MgB 2 by means of point-contact measurements in Mg(B 1-x C x ) 2 and Mg 1-y Al y B 2 single crystals with 0≤x≤0.132 and 0≤y≤0.21. The gap amplitudes, Δ ω and Δ π , were determined by fitting the conductance curves of the point contacts with the standard Blonder-Tinkham-Klapwijk (BTK) model generalized to the two-band case. Whenever possible, their values were confirmed by the independent fit (with a single-band BTK model) of the partial contribution of the two bands to the conductance, separated by means of a suitable magnetic field B*. In C-substituted crystals, the two gaps remain clearly distinct up to x∝0.10, but at x=0.132 we observed for the first time their merging into a single gap Δ≅3 meV with a gap ratio 2Δ=k B T c close to the standard BCS value. In Al-substituted crystals, we found no evidence of this gap merging. Instead, Δ π reaches the value 0.4 meV at y=0.21, where Δ π saturates at about 4 meV. These results are compared with other recent experimental findings in polycrystals and with the predictions of the models for multiband superconductivity. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. The Juvenile Transition: A Developmental Switch Point in Human Life History

    Science.gov (United States)

    Del Giudice, Marco; Angeleri, Romina; Manera, Valeria

    2009-01-01

    This paper presents a new perspective on the transition from early to middle childhood (i.e., human juvenility), investigated in an integrative evolutionary framework. Juvenility is a crucial life history stage, when social learning and interaction with peers become central developmental functions; here it is argued that the "juvenile transition"…

  14. Forecasting of superconducting compounds

    International Nuclear Information System (INIS)

    Savitskii, E.M.; Gribulya, V.G.; Kiseleva, N.N.

    1981-01-01

    In forecasting new superconducting intermetallic compounds of the A15 and Mo 3 Se types most promising from the viewpoint of high critical temperature Tsub(c), high critical magnetic fields Hsub(c), and high critical currents and in estimating their transition temperature it is proposed to apply cybernetic methods of computer learning

  15. High-temperature superconductivity

    International Nuclear Information System (INIS)

    Lynn, J.W.

    1990-01-01

    This book discusses development in oxide materials with high superconducting transition temperature. Systems with Tc well above liquid nitrogen temperature are already a reality and higher Tc's are anticipated. The author discusses how the idea of a room-temperature superconductor appears to be a distinctly possible outcome of materials research

  16. Hydrostatic pressure study of the structural phase transitions and superconductivity in single crystals of (Ba1-xKx)Fe2As2 (x=0 and 0.45) and CaFe2As2

    International Nuclear Information System (INIS)

    Torikachvili, M.S.; Bud'ko, S.L.; Ni Ni; Canfield, P.C.

    2009-01-01

    We studied the effect of hydrostatic pressure (P) on the structural phase transitions and superconductivity in the ternary and pseudo-ternary iron arsenides CaFe 2 As 2 , BaFe 2 As 2 , and (Ba 0.55 K 0.45 )Fe 2 As 2 , by means of measurements of electrical resistivity (ρ) in the 1.8-300 K temperature (T) range, pressures up to 20 kbar, and magnetic fields up to 9 T. CaFe 2 As 2 and BaFe 2 As 2 (lightly doped with Sn) display structural phase transitions near 170 and 85 K, respectively, and do not exhibit superconductivity in ambient pressure, while K-doped (Ba 0.55 K 0.45 )Fe 2 As 2 is superconducting for T 2 As 2 is to shift the onset of the crystallographic transformation down in temperature at the rate of ∼-1.04 K/kbar, while shifting the whole ρ(T) curves downward, whereas its effect on superconducting (Ba 0.55 K 0.45 )Fe 2 As 2 is to shift the onset of superconductivity to lower temperatures at the rate of ∼-0.21 K/kbar. The effect of pressure on CaFe 2 As 2 is first to suppress the crystallographic transformation and induce superconductivity with onset near 12 K very rapidly, i.e., for P c2 ) data in (Ba 0.55 K 0.45 )Fe 2 As 2 and CaFe 2 As 2 are discussed.

  17. Two gap superconductivity in Ba{sub 0.55}K{sub 0.45}Fe{sub 2}As{sub 2} single crystals studied by the directional point-contact Andreev reflection spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Szabo, P.; Pribulova, Z. [Centre of Low Temperature Physics, IEP Slovak Academy of Sciences and P.J.Safarik University, Watsonova 47, SK-04001 Kosice (Slovakia); Pristas, G.; Bud' ko, S.L.; Canfield, P.C. [Ames Laboratory and Iowa State University, Ames, IA 50011 (United States); Samuely, P., E-mail: samuely@saske.s [Centre of Low Temperature Physics, IEP Slovak Academy of Sciences and P.J.Safarik University, Watsonova 47, SK-04001 Kosice (Slovakia)

    2009-10-15

    First directional point-contact Andreev reflection spectroscopy on the Ba{sub 0.55}K{sub 0.45}Fe{sub 2}As{sub 2} single crystals is presented. The spectra show significant differences when measured in the ab plane in comparison with those measured in the c direction. In the latter case no traces of superconducting energy gap could be found, just a reduced point-contact conductance persisting up to about 100 K and indicating reduced density of states. On the other hand within the ab plane two nodeless superconducting energy gaps DELTA{sub S}approx2-5 meV and DELTA{sub L}approx9-11 meV are detected.

  18. Superconductivity and structure of gallium under nanoconfinement

    Energy Technology Data Exchange (ETDEWEB)

    Charnaya, E V; Tien, Cheng; Lee, Min Kai [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Kumzerov, Yu A [A F Ioffe Physico-Technical Institute RAS, St Petersburg, 194021 (Russian Federation)

    2009-11-11

    Superconductivity and crystalline structure were studied for two nanocomposites consisting of gallium loaded porous glasses with different pore sizes. The superconducting transition temperatures were found to differ from those in known bulk gallium modifications. The transition temperatures 7.1 and 6.7 K were ascribed to two new confined gallium structures, iota- and kappa-Ga, observed by synchrotron radiation x-ray powder diffraction. The evolution of superconductivity on decreasing the pore filling with gallium was also studied.

  19. Emergent Higgsless Superconductivity

    Directory of Open Access Journals (Sweden)

    Cristina Diamantini M.

    2017-01-01

    Full Text Available We present a new Higgsless model of superconductivity, inspired from anyon superconductivity but P- and T-invariant and generalizable to any dimension. While the original anyon superconductivity mechanism was based on incompressible quantum Hall fluids as average field states, our mechanism involves topological insulators as average field states. In D space dimensions it involves a (D-1-form fictitious pseudovector gauge field which originates from the condensation of topological defects in compact lowenergy effective BF theories. There is no massive Higgs scalar as there is no local order parameter. When electromagnetism is switched on, the photon acquires mass by the topological BF mechanism. Although the charge of the gapless mode (2 and the topological order (4 are the same as those of the standard Higgs model, the two models of superconductivity are clearly different since the origins of the gap, reflected in the high-energy sectors are totally different. In 2D thi! s type of superconductivity is explicitly realized as global superconductivity in Josephson junction arrays. In 3D this model predicts a possible phase transition from topological insulators to Higgsless superconductors.

  20. Superconducting Fullerene Nanowhiskers

    Directory of Open Access Journals (Sweden)

    Yoshihiko Takano

    2012-04-01

    Full Text Available We synthesized superconducting fullerene nanowhiskers (C60NWs by potassium (K intercalation. They showed large superconducting volume fractions, as high as 80%. The superconducting transition temperature at 17 K was independent of the K content (x in the range between 1.6 and 6.0 in K-doped C60 nanowhiskers (KxC60NWs, while the superconducting volume fractions changed with x. The highest shielding fraction of a full shielding volume was observed in the material of K3.3C60NW by heating at 200 °C. On the other hand, that of a K-doped fullerene (K-C60 crystal was less than 1%. We report the superconducting behaviors of our newly synthesized KxC60NWs in comparison to those of KxC60 crystals, which show superconductivity at 19 K in K3C60. The lattice structures are also discussed, based on the x-ray diffraction (XRD analyses.

  1. Unconventional superconductivity in a two-dimensional repulsive gas of fermions with spin-orbit coupling

    Science.gov (United States)

    Wang, Luyang; Vafek, Oskar

    2014-02-01

    We investigate the superconducting instability of a two-dimensional repulsive Fermi gas with Rashba spin-orbit coupling αR. Using renormalization group approach, we find the superconducting transition temperature as a function of the dimensionless ratio Θ=1}/{2}mαR2/EF where EF = 0 when the smaller Fermi surface shrinks to a (Dirac) point. The general trend is that superconductivity is enhanced as Θ increases, but in an intermediate regime Θ ∼ 0.1, a dome-like behavior appears. At a very small value of Θ, the angular momentum channel jz in which superconductivity occurs is quite high. With increasing Θ, jz decreases with a step of 2 down to jz = 6, after which we find the sequence jz = 6, 4, 6, 2, the last value of which continues to Θ → ∞. In an extended range of Θ, the superconducting gap predominantly resides on the large Fermi surface, while Josephson coupling induces a much smaller gap on the small Fermi surface. Below the superconducting transition temperature, we apply mean field theory to derive the self-consistent equations and find the condensation energies. The state with the lowest condensation energy is an unconventional superconducting state which breaks time-reversal symmetry, and in which singlet and triplet pairings are mixed. In general, these states are topologically nontrivial, and the Chern number of the state with total angular momentum jz is C = 2jz.

  2. Application of a practical method for the isocenter point in vivo dosimetry by a transit signal

    International Nuclear Information System (INIS)

    Piermattei, Angelo; Fidanzio, Andrea; Azario, Luigi

    2007-01-01

    This work reports the results of the application of a practical method to determine the in vivo dose at the isocenter point, D iso , of brain thorax and pelvic treatments using a transit signal S t . The use of a stable detector for the measurement of the signal S t (obtained by the x-ray beam transmitted through the patient) reduces many of the disadvantages associated with the use of solid-state detectors positioned on the patient as their periodic recalibration, and their positioning is time consuming. The method makes use of a set of correlation functions, obtained by the ratio between S t and the mid-plane dose value, D m , in standard water-equivalent phantoms, both determined along the beam central axis. The in vivo measurement of D iso required the determination of the water-equivalent thickness of the patient along the beam central axis by the treatment planning system that uses the electron densities supplied by calibrated Hounsfield numbers of the computed tomography scanner. This way it is, therefore, possible to compare D iso with the stated doses, D iso,TPS , generally used by the treatment planning system for the determination of the monitor units. The method was applied in five Italian centers that used beams of 6 MV, 10 MV, 15 MV x-rays and 60 Co γ-rays. In particular, in four centers small ion-chambers were positioned below the patient and used for the S t measurement. In only one center, the S t signals were obtained directly by the central pixels of an EPID (electronic portal imaging device) equipped with commercial software that enabled its use as a stable detector. In the four centers where an ion-chamber was positioned on the EPID, 60 pelvic treatments were followed for two fields, an anterior-posterior or a posterior-anterior irradiation and a lateral-lateral irradiation. Moreover, ten brain tumors were checked for a lateral-lateral irradiation, and five lung tumors carried out with three irradiations with different gantry angles were

  3. Application of a practical method for the isocenter point in vivo dosimetry by a transit signal

    Energy Technology Data Exchange (ETDEWEB)

    Piermattei, Angelo [UO di Fisica Sanitaria, Centro di Ricerca e Formazione ad Alta Tecnologia nelle Scienze Biomediche dell' Universita Cattolica Sacro Cuore, Campobasso (Italy); Fidanzio, Andrea [Istituto di Fisica, Universita Cattolica del Sacro Cuore, Rome (Italy); Azario, Luigi [Istituto di Fisica, Universita Cattolica del Sacro Cuore, Rome (Italy)] (and others)

    2007-08-21

    This work reports the results of the application of a practical method to determine the in vivo dose at the isocenter point, D{sub iso}, of brain thorax and pelvic treatments using a transit signal S{sub t}. The use of a stable detector for the measurement of the signal S{sub t} (obtained by the x-ray beam transmitted through the patient) reduces many of the disadvantages associated with the use of solid-state detectors positioned on the patient as their periodic recalibration, and their positioning is time consuming. The method makes use of a set of correlation functions, obtained by the ratio between S{sub t} and the mid-plane dose value, D{sub m}, in standard water-equivalent phantoms, both determined along the beam central axis. The in vivo measurement of D{sub iso} required the determination of the water-equivalent thickness of the patient along the beam central axis by the treatment planning system that uses the electron densities supplied by calibrated Hounsfield numbers of the computed tomography scanner. This way it is, therefore, possible to compare D{sub iso} with the stated doses, D{sub iso,TPS}, generally used by the treatment planning system for the determination of the monitor units. The method was applied in five Italian centers that used beams of 6 MV, 10 MV, 15 MV x-rays and {sup 60}Co {gamma}-rays. In particular, in four centers small ion-chambers were positioned below the patient and used for the S{sub t} measurement. In only one center, the S{sub t} signals were obtained directly by the central pixels of an EPID (electronic portal imaging device) equipped with commercial software that enabled its use as a stable detector. In the four centers where an ion-chamber was positioned on the EPID, 60 pelvic treatments were followed for two fields, an anterior-posterior or a posterior-anterior irradiation and a lateral-lateral irradiation. Moreover, ten brain tumors were checked for a lateral-lateral irradiation, and five lung tumors carried out with

  4. Relation between quantum phase transitions and classical instability points in the pairing model

    International Nuclear Information System (INIS)

    Reis, Mauricio; Terra Cunha, M.O.; Oliveira, Adelcio C.; Nemes, M.C.

    2005-01-01

    A quantum phase transition, characterized by an accumulation of energy levels in the espectrum of the model, is associated with a qualitative change in the corresponding classical dynamic obtained upon generalized coherent states of angular momentum

  5. Can magnetism and superconductivity coexist

    International Nuclear Information System (INIS)

    Ishikawa, M.

    1982-01-01

    Recent syntheses of rare earth (RE) ternary superconductors such as (RE)Mo 6 X 8 (X=S or Se) and (RE)Rh 4 B 4 have provided the first opportunity to explore the interaction between magnetism and superconductivity in detail owing to their particular crystal structure. The regular sublattice of the rare-earth ions in these new ternary compounds undergoes a ferro- or antiferromagnetic phase transition in the superconducting state. If the transition is antiferromagnetic, the superconductivity is preserved so that true coexistence results. If it is ferromagnetic, on the other hand, the superconductivity eventually gives way to uniform ferromagnetism at low temperatures. However, recent theories predict several possible states of coexistence even in ferromagnetic superconductors. This article reviews aspects of these new phase transitions in ternary superconductors. (author)

  6. Nonsymmorphic cubic Dirac point and crossed nodal rings across the ferroelectric phase transition in LiOsO3

    Science.gov (United States)

    Yu, Wing Chi; Zhou, Xiaoting; Chuang, Feng-Chuan; Yang, Shengyuan A.; Lin, Hsin; Bansil, Arun

    2018-05-01

    Crystalline symmetries can generate exotic band-crossing features, which can lead to unconventional fermionic excitations with interesting physical properties. We show how a cubic Dirac point—a fourfold-degenerate band-crossing point with cubic dispersion in a plane and a linear dispersion in the third direction—can be stabilized through the presence of a nonsymmorphic glide mirror symmetry in the space group of the crystal. Notably, the cubic Dirac point in our case appears on a threefold axis, even though it has been believed previously that such a point can only appear on a sixfold axis. We show that a cubic Dirac point involving a threefold axis can be realized close to the Fermi level in the nonferroelectric phase of LiOsO3. Upon lowering temperature, LiOsO3 has been shown experimentally to undergo a structural phase transition from the nonferroelectric phase to the ferroelectric phase with spontaneously broken inversion symmetry. Remarkably, we find that the broken symmetry transforms the cubic Dirac point into three mutually crossed nodal rings. There also exist several linear Dirac points in the low-energy band structure of LiOsO3, each of which is transformed into a single nodal ring across the phase transition.

  7. Superconductivity mediated by quantum critical antiferromagnetic fluctuations: The rise and fall of hot spots

    Science.gov (United States)

    Wang, Xiaoyu; Schattner, Yoni; Berg, Erez; Fernandes, Rafael M.

    2017-05-01

    In several unconventional superconductors, the highest superconducting transition temperature Tc is found in a region of the phase diagram where the antiferromagnetic transition temperature extrapolates to zero, signaling a putative quantum critical point. The elucidation of the interplay between these two phenomena—high-Tc superconductivity and magnetic quantum criticality—remains an important piece of the complex puzzle of unconventional superconductivity. In this paper, we combine sign-problem-free quantum Monte Carlo simulations and field-theoretical analytical calculations to unveil the microscopic mechanism responsible for the superconducting instability of a general low-energy model, called the spin-fermion model. In this approach, low-energy electronic states interact with each other via the exchange of quantum critical magnetic fluctuations. We find that even in the regime of moderately strong interactions, both the superconducting transition temperature and the pairing susceptibility are governed not by the properties of the entire Fermi surface, but instead by the properties of small portions of the Fermi surface called hot spots. Moreover, Tc increases with increasing interaction strength, until it starts to saturate at the crossover from hot-spots-dominated to Fermi-surface-dominated pairing. Our work provides not only invaluable insights into the system parameters that most strongly affect Tc, but also important benchmarks to assess the origin of superconductivity in both microscopic models and actual materials.

  8. Superconductivity in graphite intercalation compounds

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Robert P. [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Weller, Thomas E.; Howard, Christopher A. [Department of Physics & Astronomy, University College of London, Gower Street, London WCIE 6BT (United Kingdom); Dean, Mark P.M. [Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY 11973 (United States); Rahnejat, Kaveh C. [Department of Physics & Astronomy, University College of London, Gower Street, London WCIE 6BT (United Kingdom); Saxena, Siddharth S. [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Ellerby, Mark, E-mail: mark.ellerby@ucl.ac.uk [Department of Physics & Astronomy, University College of London, Gower Street, London WCIE 6BT (United Kingdom)

    2015-07-15

    Highlights: • Historical background of graphite intercalates. • Superconductivity in graphite intercalates and its place in the field of superconductivity. • Recent developments. • Relevant modeling of superconductivity in graphite intercalates. • Interpretations that pertain and questions that remain. - Abstract: The field of superconductivity in the class of materials known as graphite intercalation compounds has a history dating back to the 1960s (Dresselhaus and Dresselhaus, 1981; Enoki et al., 2003). This paper recontextualizes the field in light of the discovery of superconductivity in CaC{sub 6} and YbC{sub 6} in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how these relate to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity, and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.

  9. Superconductivity in graphite intercalation compounds

    International Nuclear Information System (INIS)

    Smith, Robert P.; Weller, Thomas E.; Howard, Christopher A.; Dean, Mark P.M.; Rahnejat, Kaveh C.; Saxena, Siddharth S.; Ellerby, Mark

    2015-01-01

    Highlights: • Historical background of graphite intercalates. • Superconductivity in graphite intercalates and its place in the field of superconductivity. • Recent developments. • Relevant modeling of superconductivity in graphite intercalates. • Interpretations that pertain and questions that remain. - Abstract: The field of superconductivity in the class of materials known as graphite intercalation compounds has a history dating back to the 1960s (Dresselhaus and Dresselhaus, 1981; Enoki et al., 2003). This paper recontextualizes the field in light of the discovery of superconductivity in CaC 6 and YbC 6 in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how these relate to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity, and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition

  10. Light scattering by epitaxial VO{sub 2} films near the metal-insulator transition point

    Energy Technology Data Exchange (ETDEWEB)

    Lysenko, Sergiy, E-mail: sergiy.lysenko@upr.edu; Fernández, Felix; Rúa, Armando; Figueroa, Jose; Vargas, Kevin; Cordero, Joseph [Department of Physics, University of Puerto Rico, Mayaguez, Puerto Rico 00681 (United States); Aparicio, Joaquin [Department of Physics, University of Puerto Rico-Ponce, Ponce, Puerto Rico 00732 (United States); Sepúlveda, Nelson [Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan 48824 (United States)

    2015-05-14

    Experimental observation of metal-insulator transition in epitaxial films of vanadium dioxide is reported. Hemispherical angle-resolved light scattering technique is applied for statistical analysis of the phase transition processes on mesoscale. It is shown that the thermal hysteresis strongly depends on spatial frequency of surface irregularities. The transformation of scattering indicatrix depends on sample morphology and is principally different for the thin films with higher internal elastic strain and for the thicker films where this strain is suppressed by introduction of misfit dislocations. The evolution of scattering indicatrix, fractal dimension, surface power spectral density, and surface autocorrelation function demonstrates distinctive behavior which elucidates the influence of structural defects and strain on thermal hysteresis, twinning of microcrystallites, and domain formation during the phase transition.

  11. Modeling spatial variability of sand-lenses in clay till settings using transition probability and multiple-point geostatistics

    DEFF Research Database (Denmark)

    Kessler, Timo Christian; Nilsson, Bertel; Klint, Knud Erik

    2010-01-01

    (TPROGS) of alternating geological facies. The second method, multiple-point statistics, uses training images to estimate the conditional probability of sand-lenses at a certain location. Both methods respect field observations such as local stratigraphy, however, only the multiple-point statistics can...... of sand-lenses in clay till. Sand-lenses mainly account for horizontal transport and are prioritised in this study. Based on field observations, the distribution has been modeled using two different geostatistical approaches. One method uses a Markov chain model calculating the transition probabilities...

  12. Y-junction of superconducting Josephson chains

    International Nuclear Information System (INIS)

    Giuliano, Domenico; Sodano, Pasquale

    2009-01-01

    We show that, for pertinent values of the fabrication and control parameters, an attractive finite coupling fixed point emerges in the phase diagram of a Y-junction of superconducting Josephson chains. The new fixed point arises only when the dimensionless flux f piercing the central loop of the network equals π and, thus, does not break time-reversal invariance; for f≠π, only the strongly coupled fixed point survives as a stable attractive fixed point. Phase slips (instantons) have a crucial role in establishing this transition: we show indeed that, at f=π, a new set of instantons-the W-instantons-comes into play to destabilize the strongly coupled fixed point. Finally, we provide a detailed account of the Josephson current-phase relationship along the arms of the network, near each one of the allowed fixed points. Our results evidence remarkable similarities between the phase diagram accessible to a Y-junction of superconducting Josephson chains and the one found in the analysis of quantum Brownian motion on frustrated planar lattices

  13. Enhancement of superconductivity near the pressure-induced semiconductor-metal transition in the BiS₂-based superconductors LnO₀.₅F₀.₅BiS₂ (Ln = La, Ce, Pr, Nd).

    Science.gov (United States)

    Wolowiec, C T; White, B D; Jeon, I; Yazici, D; Huang, K; Maple, M B

    2013-10-23

    Measurements of electrical resistivity were performed between 3 and 300 K at various pressures up to 2.8 GPa on the BiS2-based superconductors LnO0.5F0.5BiS2 (Ln=Pr, Nd). At lower pressures, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2 exhibit superconductivity with critical temperatures Tc of 3.5 and 3.9 K, respectively. As pressure is increased, both compounds undergo a transition at a pressure Pt from a low Tc superconducting phase to a high Tc superconducting phase in which Tc reaches maximum values of 7.6 and 6.4 K for PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2, respectively. The pressure-induced transition is characterized by a rapid increase in Tc within a small range in pressure of ∼0.3 GPa for both compounds. In the normal state of PrO0.5F0.5BiS2, the transition pressure Pt correlates with the pressure where the suppression of semiconducting behaviour saturates. In the normal state of NdO0.5F0.5BiS2, Pt is coincident with a semiconductor-metal transition. This behaviour is similar to the results recently reported for the LnO0.5F0.5BiS2 (Ln=La, Ce) compounds. We observe that Pt and the size of the jump in Tc between the two superconducting phases both scale with the lanthanide element in LnO0.5F0.5BiS2 (Ln=La, Ce, Pr, Nd).

  14. A simple magnetic balance technique for determining transition temperatures of high T/sub c/ superconducting powders

    International Nuclear Information System (INIS)

    Takamori, T.; Dove, D.B.

    1988-01-01

    A simple arrangement is described that provides a convenient method for determining transition behavior of high Tc superconductors that are in powder form. A single-pan balance was modified so that its deviation from balance could be measured by an inductive displacement transducer. A small magnet was attached to the balance and placed in close proximity above the sample to be measured. As the sample is cooled through the transition, magnetic flux lines are locally excluded resulting in a repulsive force on the magnet attached to the balance. The resulting deflection of the balance has sufficient sensitivity to allow measurements on several mg of powder. This technique provides a convenient method for routine surveying of powder samples during materials development. Example measurements are described

  15. Superconductivity revisited

    CERN Document Server

    Dougherty, Ralph

    2013-01-01

    While the macroscopic phenomenon of superconductivity is well known and in practical use worldwide in many industries, including MRIs in medical diagnostics, the current theoretical paradigm for superconductivity (BCS theory) suffers from a number of limitations, not the least of which is an adequate explanation of high temperature superconductivity. This book reviews the current theory and its limitations and suggests new ideas and approaches in addressing these issues. The central objective of the book is to develop a new, coherent, understandable theory of superconductivity directly based on molecular quantum mechanics.

  16. Controllable manipulation of superconductivity using magnetic vortices

    International Nuclear Information System (INIS)

    Villegas, J E; Schuller, Ivan K

    2011-01-01

    The magneto-transport of a superconducting/ferromagnetic hybrid structure, consisting of a superconducting thin film in contact with an array of magnetic nanodots in the so-called 'magnetic vortex state', exhibits interesting properties. For certain magnetic states, the stray magnetic field from the vortex array is intense enough to drive the superconducting film into the normal state. In this fashion, the normal-to-superconducting phase transition can be controlled by the magnetic history. The strong coupling between superconducting and magnetic subsystems allows characteristically ferromagnetic properties, such as hysteresis and remanence, to be dramatically transferred into the transport properties of the superconductor.

  17. Spin-symmetric solution of an interacting quantum dot attached to superconducting leads: Andreev states and the 0-pi transition

    Czech Academy of Sciences Publication Activity Database

    Janiš, Václav; Pokorný, Vladislav; Žonda, M.

    2016-01-01

    Roč. 89, č. 9 (2016), 1-12, č. článku 197. ISSN 1434-6028 R&D Projects: GA ČR GA15-14259S Institutional support: RVO:68378271 Keywords : mesoscopic and nanoscale systems * And reev bound states * 0-pi transition * perturbation theory Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.461, year: 2016

  18. Effect of He pressure on the superconducting transition temperatures of Na2CsC60 and (NH3)4Na2CsC60

    International Nuclear Information System (INIS)

    Schirber, J.E.; Bayless, W.R.; Rosseinsky, M.J.; Zhou, O.; Fleming, R.M.; Murphy, D.; Fischer, J.E.

    1994-01-01

    The Na based mixed alkali doped C 60 superconductors show anomalous behavior with respect to the ''universal'' superconducting transition temperature T c vs lattice constant a 0 relation followed by most of the fcc A 3 C 60 superconductors. We have measured dt c /dP for Na 2 CsC 60 and (NH 3 ) 4 Na 2 CsC 60 using solid He as the pressure medium to ∼ 6 kbar finding dT c /dP equal to -0.8±(0.01) K/kbar and -1.0(±0.1)K/kbar for Na 2 CsC 60 and Na 2 (NH 3 ) 4 C 60 respectively. Our value for Na 2 CsC 60 differs markedly from that obtained by Mizuki et al of about -1.3 K/kbar. However, using N 2 or Ar, we obtain values for dT c /dP in substantial agreement with Mizuki et al who used fluorinert to generate their pressure. This work emphasizes the need for compressibility measurements with the same pressure medium in the appropriate temperature range so that meaningful comparisons can be made between various pressure measurements and models which are based on lattic spacing

  19. Adiabatic Demagnetization Refrigerator Field Mapping and Shielding Models for a 70 mK Superconducting Transition Edge Sensor Array and Associated Electronics

    Science.gov (United States)

    Ladner, D. R.; Martinez-Galarce, D. S.; McCammon, D.

    2006-04-01

    An X-ray detection instrument to be flown on a sounding rocket experiment (the Advanced Technology Solar Spectroscopic Imager - ATSSI) for solar physics observations is being developed by the Lockheed Martin Solar and Astrophysics Laboratory (LMSAL). The detector is a novel class of microcalorimeter, a superconducting Transition-Edge Sensor (TES), that coupled with associated SQUID and feedback electronics requires high temperature stability at ~70 mK to resolve the energy of absorbed X-ray photons emitted from the solar corona. The cooling system incorporates an existing Adiabatic Demagnetization Refrigerator (ADR) developed at the University of Wisconsin (UW), which was previously flown to study the diffuse cosmic X-ray background. The Si thermistor detectors for that project required 130 K shielded JFET electronic components that are much less sensitive to the external field of the ADR solenoid than are the 1st (~70 mK) and 2nd (~2 K) SQUID stages used with TESs for solar observations. Modification of the Wisconsin ADR design, including TES focal plane and electronics re-positioning, therefore requires a tradeoff between the existing ADR solenoid nulling coil geometry and a low mass passive solenoid shield, while preserving the vibration isolation features of the existing design. We have developed models to accurately compute the magnetic field with and without shielding or nulling coils at critical locations to guide the re-design of the detector subsystem. The models and their application are described.

  20. Study of the variation of the E-I curves in the superconducting to normal transition of Bi-2212 textured ceramics by Pb addition

    Directory of Open Access Journals (Sweden)

    Sotelo, A.

    2006-06-01

    Full Text Available Vitreous cylinders with compositions Bi2-xPbxSr2CaCu2Oy, (x = 0, 0.2, 0.4 and 0.6 were prepared and used as precursors to fabricate textured bars through a laser floating zone melting method (LFZ. The resulting textured cylindrical bars were annealed, followed by their electrical characterization. The microstructure was determined and correlated with the electrical measured properties. The influence of Pb doping on the sharpness of the superconducting to normal transition on the E-I curves has been determined. The sharpest transitions have been obtained for samples doped with 0.4Pb.

    Se han preparado precursores de tipo vítreo en forma de cilindro con composiciones nominales Bi2-xPbxSr2CaCu2Oy, con x = 0, 0.2, 0.4 y 0.6. Estos cilindros se han utilizado como precursores para fabricar barras texturadas por medio de una técnica de fusión zonal inducida por láser (LFZ. Estas barras texturadas se recocieron a diferentes temperaturas y se caracterizaron eléctricamente. Además, se examinó su microestructura para correlacionarla con las propiedades eléctricas medidas. La variación de la transición del estado superconductor al normal se ha relacionado con el dopaje con Pb a través de las curvas E-I. Las mejores transiciones se han obtenido para muestras dopadas con 0.4 Pb.

  1. Comparison of U.S. and Swedish calculation economic transition points

    International Nuclear Information System (INIS)

    Owen, P.S.; Parker, M.B.; Omberg, R.P.

    1979-03-01

    This paper was prepared in response to the view of the Swedish delegation that the U.S. calculation of the economic transitions was in error. The report analyzed the principle differences between the U.S. approach and Swedish approach and concluded that the Swedish results can be reproduced using the U.S. method and Swedish data. Conversely, the U.S. results should be reproducible by Sweden

  2. Magnetic-field induced phase transitions in intermetallic rare-earth ferrimagnets with a compensation point

    Czech Academy of Sciences Publication Activity Database

    Sabdenov, Ch.K.; Davydova, M.D.; Zvezdin, K.A.; Gorbunov, Denis; Tereshina, I. S.; Andreev, Alexander V.; Zvezdin, A. K.

    2017-01-01

    Roč. 43, č. 5 (2017), s. 551-558 ISSN 1063-777X R&D Projects: GA ČR GA16-03593S Institutional support: RVO:68378271 Keywords : rare-earth intermetallics * phase diagram * field-induced transition * magnetic anisotropy * high magnetic fields Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 0.804, year: 2016

  3. Simulating the phosphorus fluid-liquid phase transition up to the critical point

    International Nuclear Information System (INIS)

    Ghiringhelli, Luca M; Meijer, Evert Jan

    2007-01-01

    We report a Car-Parrinello molecular dynamics study of the temperature dependence of the fluid-liquid phase transition in phosphorous, involving the transformation of a molecular fluid phase into a network-like phase. We employed density-functional theory (DFT) with a gradient-corrected functional (B-LYP) to describe the electronic structure and interatomic interactions and performed simulations in a constant pressure ensemble. We spanned a temperature interval ranging from 2500 to 3500 K. With increasing temperature, we found that the structural conversion from the molecular P 4 fluid into the network liquid occurs at decreasing pressures, consistent with experimental observations. At lower temperatures the transition is characterized by a sudden increase of density in the sample. The magnitude of the density change decreases with increasing temperature and vanishes at 3500 K. In the temperature range 3100-3500 K we found signals of near- and super-criticality. We identified local structural changes that serve as seeds triggering the overall structural transition

  4. Superconducting Ferromagnetic Nanodiamond.

    Science.gov (United States)

    Zhang, Gufei; Samuely, Tomas; Xu, Zheng; Jochum, Johanna K; Volodin, Alexander; Zhou, Shengqiang; May, Paul W; Onufriienko, Oleksandr; Kačmarčík, Jozef; Steele, Julian A; Li, Jun; Vanacken, Johan; Vacík, Jiri; Szabó, Pavol; Yuan, Haifeng; Roeffaers, Maarten B J; Cerbu, Dorin; Samuely, Peter; Hofkens, Johan; Moshchalkov, Victor V

    2017-06-27

    Superconductivity and ferromagnetism are two mutually antagonistic states in condensed matter. Research on the interplay between these two competing orderings sheds light not only on the cause of various quantum phenomena in strongly correlated systems but also on the general mechanism of superconductivity. Here we report on the observation of the electronic entanglement between superconducting and ferromagnetic states in hydrogenated boron-doped nanodiamond films, which have a superconducting transition temperature T c ∼ 3 K and a Curie temperature T Curie > 400 K. In spite of the high T Curie , our nanodiamond films demonstrate a decrease in the temperature dependence of magnetization below 100 K, in correspondence to an increase in the temperature dependence of resistivity. These anomalous magnetic and electrical transport properties reveal the presence of an intriguing precursor phase, in which spin fluctuations intervene as a result of the interplay between the two antagonistic states. Furthermore, the observations of high-temperature ferromagnetism, giant positive magnetoresistance, and anomalous Hall effect bring attention to the potential applications of our superconducting ferromagnetic nanodiamond films in magnetoelectronics, spintronics, and magnetic field sensing.

  5. Point-contact spectroscopy of unsaturated transition-metal oxides and the problem of zero-bias anomalies

    International Nuclear Information System (INIS)

    Tulina, N.A.

    1985-01-01

    The point-contact spectra of oxides with metallic conductivity WO 2 , ReO 3 , and MoO 2 are studied. It is shown that the zero-bias anomalies, which are often observed in the spectra of transition metals, are determined by the presence of an interlayer consisting of an oxide of the above type in the region of the point contact. Zero-bias anomalies do not occur in the point-contact spectra of Zn--MoO 2 -chip heterocontacts. In the studies of such heterocontacts the major maxima in the electron--phonon interaction of MoO 2 were determined at the energies hω/sub T/Aapprox.28 meV and hω/sub L/Aapprox.41 meV

  6. Simple description of odd-A nuclei around the critical point of the spherical to axially deformed shape phase transition

    International Nuclear Information System (INIS)

    Zhang Yu; Pan Feng; Liu Yuxin; Luo Yanan; Draayer, J. P.

    2011-01-01

    An analytically solvable model, X(3/2j+1), is proposed to describe odd-A nuclei near the X(3) critical point. The model is constructed based on a collective core described by the X(3) critical point symmetry coupled to a spin-j particle. A detailed analysis of the spectral patterns for cases j=1/2 and j=3/2 is provided to illustrate dynamical features of the model. By comparing theory with experimental data and results of other models, it is found that the X(3/2j+1) model can be taken as a simple yet very effective scheme to describe those odd-A nuclei with an even-even core at the critical point of the spherical to axially deformed shape phase transition.

  7. Recent advances in fullerene superconductivity

    CERN Document Server

    Margadonna, S

    2002-01-01

    Superconducting transition temperatures in bulk chemically intercalated fulleride salts reach 33 K at ambient pressure and in hole-doped C sub 6 sub 0 derivatives in field-effect-transistor (FET) configurations, they reach 117 K. These advances pose important challenges for our understanding of high-temperature superconductivity in these highly correlated organic metals. Here we review the structures and properties of intercalated fullerides, paying particular attention to the correlation between superconductivity and interfullerene separation, orientational order/disorder, valence state, orbital degeneracy, low-symmetry distortions, and metal-C sub 6 sub 0 interactions. The metal-insulator transition at large interfullerene separations is discussed in detail. An overview is also given of the exploding field of gate-induced superconductivity of fullerenes in FET electronic devices.

  8. Superconducting cermets

    International Nuclear Information System (INIS)

    Goyal, A.; Funkenbusch, P.D.; Chang, G.C.S.; Burns, S.J.

    1988-01-01

    Two distant classes of superconducting cermets can be distinguished, depending on whether or not a fully superconducting skeleton is established. Both types of cermets have been successfully fabricated using non-noble metals, with as high as 60wt% of the metal phase. The electrical, magnetic and mechanical behavior of these composites is discussed

  9. Korea's developmental program for superconductivity

    Science.gov (United States)

    Hong, Gye-Won; Won, Dong-Yeon; Kuk, Il-Hyun; Park, Jong-Chul

    1995-04-01

    Superconductivity research in Korea was firstly carried out in the late 70's by a research group in Seoul National University (SNU), who fabricated a small scale superconducting magnetic energy storage system under the financial support from Korea Electric Power Company (KEPCO). But a few researchers were involved in superconductivity research until the oxide high Tc superconductor was discovered by Bednorz and Mueller. After the discovery of YBaCuO superconductor operating above the boiling point of liquid nitrogen (77 K)(exp 2), Korean Ministry of Science and Technology (MOST) sponsored a special fund for the high Tc superconductivity research to universities and national research institutes by recognizing its importance. Scientists engaged in this project organized 'High Temperature Superconductivity Research Association (HITSRA)' for effective conducting of research. Its major functions are to coordinate research activities on high Tc superconductivity and organize the workshop for active exchange of information. During last seven years the major superconductivity research has been carried out through the coordination of HITSRA. The major parts of the Korea's superconductivity research program were related to high temperature superconductor and only a few groups were carrying out research on conventional superconductor technology, and Korea Atomic Energy Research Institute (KAERI) and Korea Electrotechnology Research Institute (KERI) have led this research. In this talk, the current status and future plans of superconductivity research in Korea will be reviewed based on the results presented in interim meeting of HITSRA, April 1-2, 1994. Taejeon, as well as the research activity of KAERI.

  10. Superconducting technology

    International Nuclear Information System (INIS)

    2010-01-01

    Superconductivity has a long history of about 100 years. Over the past 50 years, progress in superconducting materials has been mainly in metallic superconductors, such as Nb, Nb-Ti and Nb 3 Sn, resulting in the creation of various application fields based on the superconducting technologies. High-T c superconductors, the first of which was discovered in 1986, have been changing the future vision of superconducting technology through the development of new application fields such as power cables. On basis of these trends, future prospects of superconductor technology up to 2040 are discussed. In this article from the viewpoints of material development and the applications of superconducting wires and electronic devices. (author)

  11. Search for Pauli exclusion principle violating atomic transitions and electron decay with a p-type point contact germanium detector

    Energy Technology Data Exchange (ETDEWEB)

    Abgrall, N.; Bradley, A.W.; Chan, Y.D.; Mertens, S.; Poon, A.W.P. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Arnquist, I.J.; Hoppe, E.W.; Kouzes, R.T.; LaFerriere, B.D.; Orrell, J.L. [Pacific Northwest National Laboratory, Richland, WA (United States); Avignone, F.T. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); University of South Carolina, Department of Physics and Astronomy, Columbia, SC (United States); Barabash, A.S.; Konovalov, S.I.; Yumatov, V. [National Research Center ' ' Kurchatov Institute' ' Institute for Theoretical and Experimental Physics, Moscow (Russian Federation); Bertrand, F.E.; Galindo-Uribarri, A.; Radford, D.C.; Varner, R.L.; White, B.R.; Yu, C.H. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Brudanin, V.; Shirchenko, M.; Vasilyev, S.; Yakushev, E.; Zhitnikov, I. [Joint Institute for Nuclear Research, Dubna (Russian Federation); Busch, M. [Duke University, Department of Physics, Durham, NC (United States); Triangle Universities Nuclear Laboratory, Durham, NC (United States); Buuck, M.; Cuesta, C.; Detwiler, J.A.; Gruszko, J.; Guinn, I.S.; Leon, J.; Robertson, R.G.H. [University of Washington, Department of Physics, Center for Experimental Nuclear Physics and Astrophysics, Seattle, WA (United States); Caldwell, A.S.; Christofferson, C.D.; Dunagan, C.; Howard, S.; Suriano, A.M. [South Dakota School of Mines and Technology, Rapid City, SD (United States); Chu, P.H.; Elliott, S.R.; Goett, J.; Massarczyk, R.; Rielage, K. [Los Alamos National Laboratory, Los Alamos, NM (United States); Efremenko, Yu. [University of Tennessee, Department of Physics and Astronomy, Knoxville, TN (United States); Ejiri, H. [Osaka University, Research Center for Nuclear Physics, Ibaraki, Osaka (Japan); Finnerty, P.S.; Gilliss, T.; Giovanetti, G.K.; Henning, R.; Howe, M.A.; MacMullin, J.; Meijer, S.J.; O' Shaughnessy, C.; Rager, J.; Shanks, B.; Trimble, J.E.; Vorren, K.; Xu, W. [Triangle Universities Nuclear Laboratory, Durham, NC (United States); University of North Carolina, Department of Physics and Astronomy, Chapel Hill, NC (United States); Green, M.P. [North Carolina State University, Department of Physics, Raleigh, NC (United States); Oak Ridge National Laboratory, Oak Ridge, TN (United States); Triangle Universities Nuclear Laboratory, Durham, NC (United States); Guiseppe, V.E.; Tedeschi, D.; Wiseman, C. [University of South Carolina, Department of Physics and Astronomy, Columbia, SC (United States); Jasinski, B.R. [University of South Dakota, Department of Physics, Vermillion, SD (United States); Keeter, K.J. [Black Hills State University, Department of Physics, Spearfish, SD (United States); Kidd, M.F. [Tennessee Tech University, Cookeville, TN (United States); Martin, R.D. [Queen' s University, Department of Physics, Engineering Physics and Astronomy, Kingston, ON (Canada); Romero-Romero, E. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); University of Tennessee, Department of Physics and Astronomy, Knoxville, TN (United States); Vetter, K. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); University of California, Department of Nuclear Engineering, Berkeley, CA (United States); Wilkerson, J.F. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Triangle Universities Nuclear Laboratory, Durham, NC (United States); University of North Carolina, Department of Physics and Astronomy, Chapel Hill, NC (United States)

    2016-11-15

    A search for Pauli-exclusion-principle-violating K{sub α} electron transitions was performed using 89.5 kg-d of data collected with a p-type point contact high-purity germanium detector operated at the Kimballton Underground Research Facility. A lower limit on the transition lifetime of 5.8 x 10{sup 30} s at 90% C.L. was set by looking for a peak at 10.6 keV resulting from the X-ray and Auger electrons present following the transition. A similar analysis was done to look for the decay of atomic K-shell electrons into neutrinos, resulting in a lower limit of 6.8 x 10{sup 30} s at 90% C.L. It is estimated that the Majorana Demonstrator, a 44 kg array of p-type point contact detectors that will search for the neutrinoless double-beta decay of {sup 76}Ge, could improve upon these exclusion limits by an order of magnitude after three years of operation. (orig.)

  12. Superconducting Super Collider project

    International Nuclear Information System (INIS)

    Perl, M.L.

    1986-04-01

    The scientific need for the Superconducting Super Collider (SSC) is outlined, along with the history of the development of the SSC concept. A brief technical description is given of each of the main points of the SSC conceptual design. The construction cost and construction schedule are discussed, followed by issues associated with the realization of the SSC. 8 refs., 3 figs., 3 tabs

  13. Interface superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Gariglio, S., E-mail: stefano.gariglio@unige.ch [DQMP, Université de Genève, 24 Quai E.-Ansermet, CH-1211 Genève (Switzerland); Gabay, M. [Laboratoire de Physique des Solides, Bat 510, Université Paris-Sud 11, Centre d’Orsay, 91405 Orsay Cedex (France); Mannhart, J. [Max Planck Institute for Solid State Research, 70569 Stuttgart (Germany); Triscone, J.-M. [DQMP, Université de Genève, 24 Quai E.-Ansermet, CH-1211 Genève (Switzerland)

    2015-07-15

    Highlights: • We discuss interfacial superconductivity, a field boosted by the discovery of the superconducting interface between LaAlO. • This system allows the electric field control and the on/off switching of the superconducting state. • We compare superconductivity at the interface and in bulk doped SrTiO. • We discuss the role of the interfacially induced Rashba type spin–orbit. • We briefly discuss superconductivity in cuprates, in electrical double layer transistor field effect experiments. • Recent observations of a high T{sub c} in a monolayer of FeSe deposited on SrTiO{sub 3} are presented. - Abstract: Low dimensional superconducting systems have been the subject of numerous studies for many years. In this article, we focus our attention on interfacial superconductivity, a field that has been boosted by the discovery of superconductivity at the interface between the two band insulators LaAlO{sub 3} and SrTiO{sub 3}. We explore the properties of this amazing system that allows the electric field control and on/off switching of superconductivity. We discuss the similarities and differences between bulk doped SrTiO{sub 3} and the interface system and the possible role of the interfacially induced Rashba type spin–orbit. We also, more briefly, discuss interface superconductivity in cuprates, in electrical double layer transistor field effect experiments, and the recent observation of a high T{sub c} in a monolayer of FeSe deposited on SrTiO{sub 3}.

  14. Superconductivity in inhomogeneous granular metals

    International Nuclear Information System (INIS)

    McLean, W.L.

    1980-01-01

    A model of elongated metal ellipsoids imbedded in a granular metal is treated by an effective medium approach to explain the observed temperature dependence of the normal-state conductivity of superconducting granular aluminum. Josephson tunneling is thus still required to account for the superconductivity. The model predicts the same kind of contrasting behavior on opposite sides of the metal-insulator transition as is found in the recent scaling treatment of Anderson localization

  15. Superconductivity in domains with corners

    DEFF Research Database (Denmark)

    Bonnaillie-Noel, Virginie; Fournais, Søren

    2007-01-01

    We study the two-dimensional Ginzburg-Landau functional in a domain with corners for exterior magnetic field strengths near the critical field where the transition from the superconducting to the normal state occurs. We discuss and clarify the definition of this field and obtain a complete...... asymptotic expansion for it in the large $\\kappa$ regime. Furthermore, we discuss nucleation of superconductivity at the boundary....

  16. Superconductivity in doped semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Bustarret, E., E-mail: Etienne.bustarret@neel.cnrs.fr

    2015-07-15

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

  17. Charge ordering phenomena and superconductivity in underdoped cuprates

    Energy Technology Data Exchange (ETDEWEB)

    Tassini, Leonardo [Bayerische Akademie der Wissenschaften, Muenchen (Germany). Lehrstuhl E23 fuer Technische Physik

    2008-01-16

    In this thesis electronic properties of two prototypical copper-oxygen superconductors were studied with Raman scattering. The underdoped regime including the onset point of superconductivity p{sub sc1} was investigated. Evidence of quasi one-dimensional (1D) dynamical stripes was found. The 1D structures have a universal preferential orientation along the diagonals of the CuO{sub 2} planes below p{sub sc1}. At p{sub sc1}, lattice and electron dynamics change discontinuously. The results show that charge ordering drives the transition at p{sub sc1} and that the maximal transition temperature to superconductivity at optimal doping T{sub c}{sup MAX} depends on the type of ordering at p{sub sc1}. (orig.)

  18. Vortex variable range hopping in a conventional superconducting film

    Science.gov (United States)

    Percher, Ilana M.; Volotsenko, Irina; Frydman, Aviad; Shklovskii, Boris I.; Goldman, Allen M.

    2017-12-01

    The behavior of a disordered amorphous thin film of superconducting indium oxide has been studied as a function of temperature and magnetic field applied perpendicular to its plane. A superconductor-insulator transition has been observed, though the isotherms do not cross at a single point. The curves of resistance versus temperature on the putative superconducting side of this transition, where the resistance decreases with decreasing temperature, obey two-dimensional Mott variable-range hopping of vortices over wide ranges of temperature and resistance. To estimate the parameters of hopping, the film is modeled as a granular system and the hopping of vortices is treated in a manner analogous to hopping of charges. The reason the long-range interaction between vortices over the range of magnetic fields investigated does not lead to a stronger variation of resistance with temperature than that of two-dimensional Mott variable-range hopping remains unresolved.

  19. Hydrostatic pressure dependence of the superconducting transition temperature of HgBa2CaCu2O6+δ and HgBa2Ca2Cu3O8+δ

    International Nuclear Information System (INIS)

    Klehe, A.K.; Schilling, J.S.

    1994-02-01

    The dependence of the superconducting transition temperature T c (P) on purely hydrostatic pressure to 0.9 GPa has been determined in ac susceptibility studies in a He-gas pressure system for optimally doped ceramic samples of HgBa 2 CaCu 2 O 6+δ and HgBa 2 Ca 2 Cu 3 O 8+δ with superconducting transitions at T c (0) ≅ 126.6 K and 133.9 K, respectively. T c increases reversibly under hydrostatic pressure at the rates, d T c /dP ≅ +1.80 ± 0.06 K/GPa and +1.71 ± 0.05 K/GPa, respectively. Within experimental error, these values are the same as found previously for optimally doped single-layered HgBa 2 CuO 4+δ , where d T c /dP ≅ +1.72 ± 0.05 K/GPa. Remarkably, the logarithmic volume derivative of T c is nearly identical for all three compounds, dln T c /dlnV ≅ -1.20 ± 0.05, even though the bulk modulus differs by more than 30%. This provides strong evidence that a common mechanism is responsible for the pressure dependence of the superconducting state in all three compounds

  20. Coexistence of magnetism and superconductivity in the hole doped FeAs-based superconducting compound

    International Nuclear Information System (INIS)

    Lu, T.P.; Wu, C.C.; Chou, W.H.; Lan, M.D.

    2010-01-01

    The magnetic and superconducting properties of the Sm-doped FeAs-based superconducting compound were investigated under wide ranges of temperature and magnetic field. After the systematical magnetic ion substitution, the superconducting transition temperature decreases with increasing magnetic moment. The hysteresis loop of the La 0.87-x Sm x Sr 0.13 FeAsO sample shows a superconducting hysteresis and a paramagnetic background signal. The paramagnetic signal is mainly attributed to the Sm moments. The experiment demonstrates that the coexistence of magnetism and superconductivity in the hole doped FeAs-based superconducting compounds is possible. Unlike the electron doped FeAs-based superconducting compounds SmFeAsOF, the hole doped superconductivity is degraded by the substitution of La by Sm. The hole-doped and electron-doped sides are not symmetric.

  1. Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs.

    Science.gov (United States)

    Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K; Rüegg, Christian; Susner, Michael A; Sefat, Athena S; Zhigadlo, Nikolai D; Morenzoni, Elvezio

    2015-09-08

    The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc(3.2) as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.

  2. Assessing the effects of rural livelihood transition on non-point source pollution: a coupled ABM-IECM model.

    Science.gov (United States)

    Yuan, Chengcheng; Liu, Liming; Ye, Jinwei; Ren, Guoping; Zhuo, Dong; Qi, Xiaoxing

    2017-05-01

    Water pollution caused by anthropogenic activities and driven by changes in rural livelihood strategies in an agricultural system has received increasing attention in recent decades. To simulate the effects of rural household livelihood transition on non-point source (NPS) pollution, a model combining an agent-based model (ABM) and an improved export coefficient model (IECM) was developed. The ABM was adopted to simulate the dynamic process of household livelihood transition, and the IECM was employed to estimate the effects of household livelihood transition on NPS pollution. The coupled model was tested in a small catchment in the Dongting Lake region, China. The simulated results reveal that the transition of household livelihood strategies occurred with the changes in the prices of rice, pig, and labor. Thus, the cropping system, land-use intensity, resident population, and number of pigs changed in the small catchment from 2000 to 2014. As a result of these changes, the total nitrogen load discharged into the river initially increased from 6841.0 kg in 2000 to 8446.3 kg in 2004 and then decreased to 6063.9 kg in 2014. Results also suggest that rural living, livestock, paddy field, and precipitation alternately became the main causes of NPS pollution in the small catchment, and the midstream region of the small catchment was the primary area for NPS pollution from 2000 to 2014. Despite some limitations, the coupled model provides an innovative way to simulate the effects of rural household livelihood transition on NPS pollution with the change of socioeconomic factors, and thereby identify the key factors influencing water pollution to provide valuable suggestions on how agricultural environmental risks can be reduced through the regulation of the behaviors of farming households in the future.

  3. Spin Triplet Nematic Pairing Symmetry and Superconducting Double Transition in U1-xThxBe13

    Science.gov (United States)

    Machida, Kazushige

    2018-03-01

    Motivated by a recent experiment on U1-xThxBe13 with x = 3%, we develop a theory to narrow down the possible pair symmetry to consistently describe the double transition utilizing various theoretical tools, including group theory and Ginzburg-Landau theory. It is explained in terms of the two-dimensional representation Eu with spin triplet. Symmetry breaking causes the degenerate Tc to split into two. The low-temperature phase is identified as the cyclic p wave: d(k) = \\hat{x}kx + ɛ \\hat{y}ky + ɛ 2\\hat{z}kz with ɛ3 = 1, whereas the biaxial nematic phase: d(k) = √{3} (\\hat{x}kx - \\hat{y}ky) is the high-temperature one. This allows us to simultaneously identify the uniaxial nematic phase: d(k) = 2\\hat{z}kz - \\hat{x}kx - \\hat{y}ky for UBe13, which spontaneously breaks the cubic symmetry of the system. Those pair functions are fully consistent with this description and existing data. We comment on the accidental scenario in addition to this degeneracy scenario and the intriguing topological nature hidden in this long-known material.

  4. Point Climat no. 26 'Regional Climate - Air - Energy Plans at the heart of the debate on the energy transition'

    International Nuclear Information System (INIS)

    Bordier, Cecile; Leseur, Alexia

    2013-01-01

    Among the publications of CDC Climat Research, 'Climate Briefs' presents, in a few pages, hot topics in climate change policy. This issue addresses the following points: On the eve of the introduction of the environmental assessment procedure for planning documents, almost all Regional Climate - Air - Energy Plans have now been published. This Climate Brief assesses regional climate strategies, which rely on significant commitment from those involved, including citizens by changing their behaviour, companies by improving their energy efficiency and the banking sector through financial support. Identification of these challenges and areas for action will feed into the national debate on energy transition which began last autumn

  5. Superconductor (Nb)-charge density wave (NbSe sub 3) point-contact spectroscopy

    CERN Document Server

    Sinchenko, A A

    2003-01-01

    Measurements of differential current-voltage (I-V) characteristics of point contacts between Nb and the charge density wave (CDW) conductor NbSe sub 3 formed along the conducting chain direction are reported. Below the superconducting transition of Nb, we have clearly observed Andreev reflection of the gapless electrons of NbSe sub 3. Analysis of the spectra obtained indicates that when the energy of injected particles exceeds the superconducting energy gap, the superconductivity near the S-CDW interface is suppressed because of non-equilibrium effects.

  6. Optical transitions in two-dimensional topological insulators with point defects

    Science.gov (United States)

    Sablikov, Vladimir A.; Sukhanov, Aleksei A.

    2016-12-01

    Nontrivial properties of electronic states in topological insulators are inherent not only to the surface and boundary states, but to bound states localized at structure defects as well. We clarify how the unusual properties of the defect-induced bound states are manifested in optical absorption spectra in two-dimensional topological insulators. The calculations are carried out for defects with short-range potential. We find that the defects give rise to the appearance of specific features in the absorption spectrum, which are an inherent property of topological insulators. They have the form of two or three absorption peaks that are due to intracenter transitions between electron-like and hole-like bound states.

  7. Strong-coupling d-wave superconductivity in PuCoGa.sub.5./sub. probed by point-contact spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Daghero, D.; Tortello, M.; Ummarino, G.A.; Griveau, J.C.; Colineau, E.; Eloirdi, R.; Shick, Alexander; Kolorenč, Jindřich; Lichtenstein, A.I.; Caciuffo, R.

    2012-01-01

    Roč. 3, Apr (2012), "786-1"-"786-8" ISSN 2041-1723 R&D Projects: GA ČR(CZ) GAP204/10/0330; GA AV ČR IAA100100912 Institutional research plan: CEZ:AV0Z10100520 Keywords : superconductivity * PuCoGa 5 * magnetism Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 10.015, year: 2012 http://www.nature.com/ncomms/journal/v3/n4/full/ncomms1785.html

  8. Superconductivity in doped Dirac semimetals

    Science.gov (United States)

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

    2016-07-01

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

  9. Gap features of layered iron-selenium-tellurium compound below and above the superconducting transition temperature by break-junction spectroscopy combined with STS

    Science.gov (United States)

    Ekino, T.; Sugimoto, A.; Gabovich, A. M.

    2018-05-01

    We studied correlations between the superconducting gap features of Te-substituted FeSe observed by scanning tunnelling spectroscopy (STS) and break-junction tunnelling spectroscopy (BJTS). At bias voltages outside the superconducting gap-energy range, the broad gap structure exists, which becomes the normal-state gap above the critical temperature, T c. Such behaviour is consistent with the model of the partially gapped density-wave superconductor involving both superconducting gaps and pseudogaps, which has been applied by us earlier to high-Tc cuprates. The similarity suggests that the parent electronic spectrum features should have much in common for these classes of materials.

  10. Exotic Lifshitz transitions in topological materials

    Science.gov (United States)

    Volovik, G. E.

    2018-01-01

    Topological Lifshitz transitions involve many types of topological structures in momentum and frequency-momentum spaces, such as Fermi surfaces, Dirac lines, Dirac and Weyl points, etc., each of which has its own stability-supporting topological invariant ( N_1, N_2, N_3, {\\tilde N}_3, etc.). The topology of the shape of Fermi surfaces and Dirac lines and the interconnection of objects of different dimensionalities produce a variety of Lifshitz transition classes. Lifshitz transitions have important implications for many areas of physics. To give examples, transition-related singularities can increase the superconducting transition temperature; Lifshitz transitions are the possible origin of the small masses of elementary particles in our Universe, and a black hole horizon serves as the surface of the Lifshitz transition between vacua with type-I and type-II Weyl points.

  11. Organic superconductivity

    International Nuclear Information System (INIS)

    Jerome, D.

    1980-01-01

    We present the experimental evidences for the existence of a superconducting state in the Quasi One Dimensional organic conductor (TMTSF) 2 PF 6 . Superconductivity occuring at 1 K under 12 kbar is characterized by a zero resistance diamagnetic state. The anistropy of the upper critical field of this type II superconductor is consistent with the band structure anistropy. We present evidences for the existence of large superconducting precursor effects giving rise to a dominant paraconductive contribution below 40 K. We also discuss the anomalously large pressure dependence of T sb(s), which drops to 0.19 K under 24 kbar in terms of the current theories. (author)

  12. Realization of superconductive films by screen printing

    International Nuclear Information System (INIS)

    Baudry, H.

    1988-01-01

    Screen printing is a promising method to manufacture superconductive lines making use of superconductive ceramics. An ink has been realized with YBa 2 Cu 3 0 7-x' and the process conditions defined by thermal analysis. A superconductive transition is observed after screen printing on MgO. The firing of the layer is made at 920 0 C followed by a reoxidation step at 420 0 C. The silver electrical contacts are also screen printed [fr

  13. Quantum phase transitions

    International Nuclear Information System (INIS)

    Sachdev, S.

    1999-01-01

    Phase transitions are normally associated with changes of temperature but a new type of transition - caused by quantum fluctuations near absolute zero - is possible, and can tell us more about the properties of a wide range of systems in condensed-matter physics. Nature abounds with phase transitions. The boiling and freezing of water are everyday examples of phase transitions, as are more exotic processes such as superconductivity and superfluidity. The universe itself is thought to have passed through several phase transitions as the high-temperature plasma formed by the big bang cooled to form the world as we know it today. Phase transitions are traditionally classified as first or second order. In first-order transitions the two phases co-exist at the transition temperature - e.g. ice and water at 0 deg., or water and steam at 100 deg. In second-order transitions the two phases do not co-exist. In the last decade, attention has focused on phase transitions that are qualitatively different from the examples noted above: these are quantum phase transitions and they occur only at the absolute zero of temperature. The transition takes place at the ''quantum critical'' value of some other parameter such as pressure, composition or magnetic field strength. A quantum phase transition takes place when co-operative ordering of the system disappears, but this loss of order is driven solely by the quantum fluctuations demanded by Heisenberg's uncertainty principle. The physical properties of these quantum fluctuations are quite distinct from those of the thermal fluctuations responsible for traditional, finite-temperature phase transitions. In particular, the quantum system is described by a complex-valued wavefunction, and the dynamics of its phase near the quantum critical point requires novel theories that have no analogue in the traditional framework of phase transitions. In this article the author describes the history of quantum phase transitions. (UK)

  14. Modern high-temperature superconductivity

    International Nuclear Information System (INIS)

    Ching Wu Chu

    1988-01-01

    Ever since the discovery of superconductivity in 1911, its unusual scientific challenge and great technological potential have been recognized. For the past three-quarters of a century, superconductivity has done well on the science front. This is because sueprconductivity is interesting not only just in its own right but also in its ability to act as a probe to many exciting nonsuperconducting phenomena. For instance, it has continued to provide bases for vigorous activities in condensed matter science. Among the more recent examples are heavy-fermion systems and organic superconductors. During this same period of time, superconductivity has also performed admirably in the applied area. Many ideas have been conceived and tested, making use of the unique characteristics of superconductivity - zero resistivity, quantum interference phenomena, and the Meissner effect. In fact, it was not until late January 1987 that it became possible to achieve superconductivity with the mere use of liquid nitrogen - which is plentiful, cheap, efficient, and easy to handle - following the discovery of supercondictivity above 90 K in Y-Ba-Cu-O, the first genuine quaternary superconductor. Superconductivity above 90 K poses scientific and technological challenges not previously encountered: no existing theories can adequately describe superconductivity above 40 K and no known techniques can economically process the materials for full-scale applications. In this paper, therefore, the author recalls a few events leading to the discovery of the new class of quaternary compounds with a superconducting transition temperature T c in the 90 K range, describes the current experimental status of high-temperature superconductivity and, finally, discusses the prospect of very-high-temperature superconductivity, i.e., with a T c substantially higher than 100 K. 97 refs., 7 figs

  15. Nature of the Blue-Phase-III endash isotropic critical point: An analogy with the liquid-gas transition

    International Nuclear Information System (INIS)

    Anisimov, M.A.; Agayan, V.A.; Collings, P.J.

    1998-01-01

    The analogy with the liquid-gas critical point is analyzed to clarify the nature of the pretransitional behavior of physical properties in the vicinity of the Blue-Phase-III endash isotropic transition in chiral liquid crystalline systems. The analogy is unusual: temperature serves as the ordering field and entropy plays the role of the order parameter. Both mean field and parametric equations of state are formulated in terms of scaling fields. The scaling fields are linear combinations of the physical fields, which are temperature and chirality. It is shown that mixing of the physical field variables naturally leads to a strong asymmetry with respect to the transition temperature in the behavior of the physical properties that cannot be described by simple power laws. While the mean field theory gives a good description of the experimental data, the scaling theory, if one incorporates mixing of the field variables, gives even better agreement with the experimental data, placing this transition in the same universality class as the three-dimensional Ising model. copyright 1998 The American Physical Society

  16. Superconducting linac

    International Nuclear Information System (INIS)

    Bollinger, L.M.; Shepard, K.W.; Wangler, T.P.

    1978-01-01

    This project has two goals: to design, build, and test a small superconducting linac to serve as an energy booster for heavy ions from an FN tandem electrostatic accelerator, and to investigate various aspects of superconducting rf technology. The main design features of the booster are described, a status report on various components (resonators, rf control system, linac control system, cryostats, buncher) is given, and plans for the near future are outlined. Investigations of superconducting-linac technology concern studies on materials and fabrication techniques, resonator diagnostic techniques, rf-phase control, beam dynamics computer programs, asymmetry in accelerating field, and surface-treatment techniques. The overall layout of the to-be-proposed ATLAS, the Argonne Tandem-Linac Accelerator System, is shown; the ATLAS would use superconducting technology to produce beams of 5 to 25 MeV/A. 6 figures

  17. Superconducting materials

    International Nuclear Information System (INIS)

    Kormann, R.; Loiseau, R.; Marcilhac, B.

    1989-01-01

    The invention concerns superconducting ceramics containing essentially barium, calcium and copper fluorinated oxides with close offset and onset temperatures around 97 K and 100 K and containing neither Y nor rare earth [fr

  18. Hole superconductivity

    International Nuclear Information System (INIS)

    Hirsch, J.E.; Marsiglio, F.

    1989-01-01

    The authors review recent work on a mechanism proposed to explain high T c superconductivity in oxides as well as superconductivity of conventional materials. It is based on pairing of hole carriers through their direct Coulomb interaction, and gives rise to superconductivity because of the momentum dependence of the repulsive interaction in the solid state environment. In the regime of parameters appropriate for high T c oxides this mechanism leads to characteristic signatures that should be experimentally verifiable. In the regime of conventional superconductors most of these signatures become unobservable, but the characteristic dependence of T c on band filling survives. New features discussed her include the demonstration that superconductivity can result from repulsive interactions even if the gap function does not change sign and the inclusion of a self-energy correction to the hole propagator that reduces the range of band filling where T c is not zero

  19. Superconducted tour

    Energy Technology Data Exchange (ETDEWEB)

    Anon.

    1988-09-15

    Superconductivity - the dramatic drop in electrical resistance in certain materials at very low temperatures - has grown rapidly in importance over the past two or three decades to become a key technology for high energy particle accelerators. It was in this setting that a hundred students and 15 lecturers met in Hamburg in June for a week's course on superconductivity in particle accelerators, organized by the CERN Accelerator School and the nearby DESY Laboratory.

  20. Transition from the mechanics of material points to the mechanics of structured particles

    Science.gov (United States)

    Somsikov, V. M.

    2016-01-01

    In this paper, necessity of creation of mechanics of structured particles is discussed. The way to create this mechanics within the laws of classical mechanics with the use of energy equation is shown. The occurrence of breaking of time symmetry within the mechanics of structured particles is shown, as well as the introduction of concept of entropy in the framework of classical mechanics. The way to create the mechanics of non-equilibrium systems in the thermodynamic approach is shown. It is also shown that the use of hypothesis of holonomic constraints while deriving the canonical Lagrange equation made it impossible to describe irreversible dynamics. The difference between the mechanics of structured particles and the mechanics of material points is discussed. It is also shown that the matter is infinitely divisible according to the laws of classical mechanics.

  1. Theoretical analyses of superconductivity in iron based ...

    African Journals Online (AJOL)

    This paper focuses on the theoretical analysis of superconductivity in iron based superconductor Ba1−xKxFe2As2. After reviewing the current findings on this system, we suggest that phononexciton combined mechanism gives a right order of superconducting transition temperature (TC) for Ba1−xKxFe2As2 . By developing ...

  2. Spontaneous fluxoid formation in superconducting loops

    DEFF Research Database (Denmark)

    Monaco, R.; Mygind, Jesper; Rivers, R.

    2009-01-01

    We report on the experimental verification of the Zurek-Kibble scenario in an isolated superconducting ring over a wide parameter range. The probability of creating a single flux quantum spontaneously during the fast normal-superconducting phase transition of a wide Nb loop clearly follows...

  3. Superconducting gap anomaly in heavy fermion systems

    Indian Academy of Sciences (India)

    of a pseudo-gap due to superconductivity and the signature of a hybridization gap at the. Fermi level. For the choice of the model parameters, the DOS shows that the HFS is a metal and undergoes a transition to the gap-less superconducting state. Keywords. Heavy fermion superconductor; Narrow band system; Valence ...

  4. INTERLAYER OPTICAL CONDUCTIVITY OF A SUPERCONDUCTING BILAYER

    NARCIS (Netherlands)

    GARTSTEIN, YN; RICE, MJ; VANDERMAREL, D

    1994-01-01

    We employ the Bardeen-Cooper-Schrieffer theory to calculate the frequency-dependent interlayer conductivity of a superconducting bilayer, the two layers of which are coupled by weak single-particle tunneling. The effect of the superconducting transition on the normal-state absorption band is to

  5. Microchip-calorimetry of organic charge transfer complex which shows superconductivity at low temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Muraoka, Yuki [Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043 (Japan); Yamashita, Satoshi [RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198 (Japan); Yamamoto, Takashi [Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043 (Japan); Nakazawa, Yasuhiro, E-mail: nakazawa@chem.sci.osaka-u.ac.jp [Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043 (Japan); Institute for Molecular Science, Nishigonaka 38, Myodaiji, Okazaki 444-8585 (Japan)

    2012-03-20

    Highlights: Black-Right-Pointing-Pointer Organic charge transfer salt of {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br shows superconductivity. Black-Right-Pointing-Pointer We succeeded to detect thermal anomaly microchip device TCG3880. Black-Right-Pointing-Pointer Development details of the calorimeter and the detection system is presented. Black-Right-Pointing-Pointer The magnetic fields dependence shows typical character of layered superconductor. - Abstract: We carried out thermodynamic measurements of organic charge transfer complex of {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene by TCG3880 chip device in order to examine capability of the chip calorimeter at low temperature region and under magnetic fields. TCG3880 chip is mounted on a {sup 3}He cryostat available in combination with a superconductive magnet up to 7 T. Thermal anomalies related to the glass-like freezing of ethylene groups of BEDT-TTF molecules and the superconductive transition were observed. A frequency dependence of the thermal anomaly of the glass formation and a magnetic fields dependence of the thermal anomaly of the superconductive transition are reported. The results presented in this work demonstrate that the TCG3880 is quite useful for thermodynamic investigations of the organic charge transfer complex with much reduced sample quantity as compared with those of relaxation and adiabatic calorimetry.

  6. Superconductivity in doped two-leg ladder cuprates

    International Nuclear Information System (INIS)

    Qin Jihong; Yuan Feng; Feng Shiping

    2006-01-01

    Within the t-J ladder model, superconductivity with a modified d-wave symmetry in doped two-leg ladder cuprates is investigated based on the kinetic energy driven superconducting mechanism. It is shown that the spin-liquid ground-state at the half-filling evolves into the superconducting ground-state upon doping. In analogy to the doping dependence of the superconducting transition temperature in the planar cuprate superconductors, the superconducting transition temperature in doped two-leg ladder cuprates increases with increasing doping in the underdoped regime, and reaches a maximum in the optimal doping, then decreases in the overdoped regime

  7. Multigap superconductivity and strong electron-boson coupling in Fe-based superconductors: a point-contact Andreev-reflection study of Ba(Fe(1-x)Co(x))2As2 single crystals.

    Science.gov (United States)

    Tortello, M; Daghero, D; Ummarino, G A; Stepanov, V A; Jiang, J; Weiss, J D; Hellstrom, E E; Gonnelli, R S

    2010-12-03

    Directional point-contact Andreev-reflection measurements in Ba(Fe(1-x)Co(x))2As2 single crystals (T(c) = 24.5 K) indicate the presence of two superconducting gaps with no line nodes on the Fermi surface. The point-contact Andreev-reflection spectra also feature additional structures related to the electron-boson interaction, from which the characteristic boson energy Ω(b)(T) is obtained, very similar to the spin-resonance energy observed in neutron scattering experiments. Both the gaps and the additional structures can be reproduced within a three-band s ± Eliashberg model by using an electron-boson spectral function peaked at Ω(0) = 12 meV ≃ Ω(b)(0).

  8. Exotic Magnetic Orders and Their Interplay with Superconductivity

    DEFF Research Database (Denmark)

    Christensen, Morten Holm

    Superconductivity represents one of the most important scientific discoveries of the 20th century. The practical applications are numerous ranging from clean energy storage and MRI machines to quantum computers. However, the low temperatures required for superconductivity prohibits many practical...... applications. The more recent discovery of high-temperature superconductors, with superconducting transition temperatures above 100~K, has led to the hope that superconductivity at room-temperature might be achievable, although a complete theoretical understanding of the high-temperature superconductors...

  9. White noise of Nb-based microwave superconducting quantum interference device multiplexers with NbN coplanar resonators for readout of transition edge sensors

    Science.gov (United States)

    Kohjiro, Satoshi; Hirayama, Fuminori; Yamamori, Hirotake; Nagasawa, Shuichi; Fukuda, Daiji; Hidaka, Mutsuo

    2014-06-01

    White noise of dissipationless microwave radio frequency superconducting quantum interference device (RF-SQUID) multiplexers has been experimentally studied to evaluate their readout performance for transition edge sensor (TES) photon counters ranging from near infrared to gamma ray. The characterization has been carried out at 4 K, first to avoid the low-frequency fluctuations present at around 0.1 K, and second, for a feasibility study of readout operation at 4 K for extended applications. To increase the resonant Q at 4 K and maintain low noise SQUID operation, multiplexer chips consisting of niobium nitride (NbN)-based coplanar-waveguide resonators and niobium (Nb)-based RF-SQUIDs have been developed. This hybrid multiplexer exhibited 1 × 104 ≤ Q ≤ 2 × 104 and the square root of spectral density of current noise referred to the SQUID input √SI = 31 pA/√Hz. The former and the latter are factor-of-five and seven improvements from our previous results on Nb-based resonators, respectively. Two-directional readout on the complex plane of the transmission component of scattering matrix S21 enables us to distinguish the flux noise from noise originating from other sources, such as the cryogenic high electron mobility transistor (HEMT) amplifier. Systematic noise measurements with various microwave readout powers PMR make it possible to distinguish the contribution of noise sources within the system as follows: (1) The achieved √SI is dominated by the Nyquist noise from a resistor at 4 K in parallel to the SQUID input coil which is present to prevent microwave leakage to the TES. (2) The next dominant source is either the HEMT-amplifier noise (for small values of PMR) or the quantization noise due to the resolution of 300-K electronics (for large values of PMR). By a decrease of these noise levels to a degree that is achievable by current technology, we predict that the microwave RF-SQUID multiplexer can exhibit √SI ≤ 5 pA/√Hz, i.e., close to √SI of

  10. White noise of Nb-based microwave superconducting quantum interference device multiplexers with NbN coplanar resonators for readout of transition edge sensors

    International Nuclear Information System (INIS)

    Kohjiro, Satoshi; Hirayama, Fuminori; Yamamori, Hirotake; Nagasawa, Shuichi; Fukuda, Daiji; Hidaka, Mutsuo

    2014-01-01

    White noise of dissipationless microwave radio frequency superconducting quantum interference device (RF-SQUID) multiplexers has been experimentally studied to evaluate their readout performance for transition edge sensor (TES) photon counters ranging from near infrared to gamma ray. The characterization has been carried out at 4 K, first to avoid the low-frequency fluctuations present at around 0.1 K, and second, for a feasibility study of readout operation at 4 K for extended applications. To increase the resonant Q at 4 K and maintain low noise SQUID operation, multiplexer chips consisting of niobium nitride (NbN)-based coplanar-waveguide resonators and niobium (Nb)-based RF-SQUIDs have been developed. This hybrid multiplexer exhibited 1 × 10 4  ≤ Q ≤ 2 × 10 4 and the square root of spectral density of current noise referred to the SQUID input √S I  = 31 pA/√Hz. The former and the latter are factor-of-five and seven improvements from our previous results on Nb-based resonators, respectively. Two-directional readout on the complex plane of the transmission component of scattering matrix S 21 enables us to distinguish the flux noise from noise originating from other sources, such as the cryogenic high electron mobility transistor (HEMT) amplifier. Systematic noise measurements with various microwave readout powers P MR make it possible to distinguish the contribution of noise sources within the system as follows: (1) The achieved √S I is dominated by the Nyquist noise from a resistor at 4 K in parallel to the SQUID input coil which is present to prevent microwave leakage to the TES. (2) The next dominant source is either the HEMT-amplifier noise (for small values of P MR ) or the quantization noise due to the resolution of 300-K electronics (for large values of P MR ). By a decrease of these noise levels to a degree that is achievable by current technology, we predict that the microwave RF-SQUID multiplexer can exhibit

  11. Unconventional superconductivity in CaFe0.85Co0.15AsF evidenced by torque measurements

    Science.gov (United States)

    Xiao, Hong; Li, X. J.; Mu, G.; Hu, T.

    Out-of-plane angular dependent torque measurements were performed on CaFe0.85Co0.15AsF single crystals. Abnormal superconducting fluctuation, featured by enhanced diamagnetism with magnetic field, is detected up to about 1.5 times superconducting transition temperature Tc. Compared to cuprate superconductors, the fluctuation effect in iron-based superconductor is less pronounced. Anisotropy parameter γ is obtained from the mixed state torque data and it is found that γ shows both magnetic field and temperature depenence, pointing to multiband superconductivity. The temperature dependence of penetration depth λ (T) suggests unconventional superconductivity in CaFe0.85Co0.15AsF.

  12. Transition from columnar to point pinning in coated conductors: critical currents that are independent of magnetic field direction

    International Nuclear Information System (INIS)

    Zuev, Yuri L; Hun Wee, Sung; Christen, David K

    2012-01-01

    We identify a sharp crossover in the vortex pinning of a high-temperature superconductor with nanocolumnar stacks of precipitates as strong vortex pinning centers. Above a particular, temperature-dependent field B X (T) the vortex response is no longer determined by the nanocolumns, and is instead determined by point-like pinning. This crossover is evident as a change in the dependence of the critical current density on the angle between the applied magnetic field and the nanocolumns. It also leads to the field-orientation-independent power law index n of the E–J curves. Below the transition, there is a strong maximum in J C when the field is aligned parallel to the columns and n depends on field direction. Above the transition, n is independent of the field direction and there is a J C minimum for H parallel to the columns. We discuss a possible mechanism for such behavior change, as well as testing and confirming a prediction that the crossover must become very broad at high temperatures and low fields. (paper)

  13. The effect of correlated and point defects on the vortex lattice melting transition in single-crystal YBa2Cu3O7-δ

    International Nuclear Information System (INIS)

    Kwok, W.K.; Fendrich, J.; Fleshler, S.; Welp, U.; Downey, J.; Crabtree, G.W.; Giapintzakis, J.

    1994-01-01

    The vortex melting transition T m in several untwinned and twinned crystals is measured resistively in fields up to 8T. A Lindemann criterion for vortex lattice melting is obtained in addition to a sharp hysteresis in the magnetoresistance at B m supporting a first-order phase transition. The anisotropy of twin boundary pinning and its reduction of the 'kink' in ρ(T) associated with the first-order melting transition is discussed in samples with very dilute twin boundaries. We also report on the direct suppression of the the melting transition by intrinsic pinning for H parallel ab and by electron-irradiation-induced point defects. (orig.)

  14. The effect of correlated and point defects on the vortex lattice melting transition in single crystal YBa2Cu3O7-δ

    International Nuclear Information System (INIS)

    Kwok, W.K.; Fleshler, S.; Welp, U.; Downey, J.; Crabtree, G.W.; Fendrich, J. Giapintzakis, J.

    1993-08-01

    The vortex melting transition T m in several untwinned and twinned crystals measured resistively in fields up to 8 Tesla. A Lindemann criterion for vortex lattice melting is obtained in addition to a sharp hysteresis in the magnetoresistance at B m supporting a first order phase transition. The anisotropy of twin boundary pinning and its reduction of the ''kink'' in ρ(T) associated with the first order melting transition is discussed in samples with very dilute twin boundaries. We also report on direct suppression of melting transition by intrinsic pinning for H parallel ab and by electron-irradiation-induced point defects

  15. Engineering students at typically invisible transition points: A focus on admissions and the sophomore year

    Science.gov (United States)

    Holloway, Elizabeth M.

    similarity than differences, although the differences indicated that engineering sophomores were less engaged in their learning and less engaged with faculty and advisors. Sophomore engineering women were much more likely than men to be involved in engineering peer mentoring or leadership programs. Multiple regression analysis indicated that the most significant predictor of student satisfaction was satisfaction with peers on campus. The most significant predictor of intention to persist and intention to graduate was surety of major choice. However, there were differences in the most significant predictors when looking at men and women separately. Predictors of success outcomes for engineering sophomores point to the interconnectedness of experiences with faculty, advisors, and peers with individual student traits, characteristics, and preferences, with individual aspects acting as mediating and moderating factors. The overarching results of this research project offer frameworks through which change in the engineering education process can lead to greater participation by women in the engineering field, and increased retention rates for all engineering students.

  16. Critical point of gas-liquid type phase transition and phase equilibrium functions in developed two-component plasma model.

    Science.gov (United States)

    Butlitsky, M A; Zelener, B B; Zelener, B V

    2014-07-14

    A two-component plasma model, which we called a "shelf Coulomb" model has been developed in this work. A Monte Carlo study has been undertaken to calculate equations of state, pair distribution functions, internal energies, and other thermodynamics properties. A canonical NVT ensemble with periodic boundary conditions was used. The motivation behind the model is also discussed in this work. The "shelf Coulomb" model can be compared to classical two-component (electron-proton) model where charges with zero size interact via a classical Coulomb law. With important difference for interaction of opposite charges: electrons and protons interact via the Coulomb law for large distances between particles, while interaction potential is cut off on small distances. The cut off distance is defined by an arbitrary ɛ parameter, which depends on system temperature. All the thermodynamics properties of the model depend on dimensionless parameters ɛ and γ = βe(2)n(1/3) (where β = 1/kBT, n is the particle's density, kB is the Boltzmann constant, and T is the temperature) only. In addition, it has been shown that the virial theorem works in this model. All the calculations were carried over a wide range of dimensionless ɛ and γ parameters in order to find the phase transition region, critical point, spinodal, and binodal lines of a model system. The system is observed to undergo a first order gas-liquid type phase transition with the critical point being in the vicinity of ɛ(crit) ≈ 13(T(*)(crit) ≈ 0.076), γ(crit) ≈ 1.8(v(*)(crit) ≈ 0.17), P(*)(crit) ≈ 0.39, where specific volume v* = 1/γ(3) and reduced temperature T(*) = ɛ(-1).

  17. Atomistic simulation of ideal shear strength, point defects, and screw dislocations in bcc transition metals: Mo as a prototype

    International Nuclear Information System (INIS)

    Xu, W.; Moriarty, J.A.

    1996-01-01

    Using multi-ion interatomic potentials derived from first-principles generalized pseudopotential theory, we have studied ideal shear strength, point defects, and screw dislocations in the prototype bcc transition metal molybdenum (Mo). Many-body angular forces, which are important to the structural and mechanical properties of such central transition metals with partially filled d bands, are accounted for in the present theory through explicit three- and four-ion potentials. For the ideal shear strength of Mo, our computed results agree well with those predicted by full electronic-structure calculations. For point defects in Mo, our calculated vacancy-formation and activation energies are in excellent agreement with experimental results. The energetics of six self-interstitial configurations have also been investigated. The left-angle 110 right-angle split dumbbell interstitial is found to have the lowest formation energy, in agreement with the configuration found by x-ray diffuse scattering measurements. In ascending order, the sequence of energetically stable interstitials is predicted to be left-angle 110 right-angle split dumbbell, crowdion, left-angle 111 right-angle split dumbbell, tetrahedral site, left-angle 001 right-angle split dumbbell, and octahedral site. In addition, the migration paths for the left-angle 110 right-angle dumbbell self-interstitial have been studied. The migration energies are found to be 3 endash 15 times higher than previous theoretical estimates obtained using simple radial-force Finnis-Sinclair potentials. Finally, the atomic structure and energetics of left-angle 111 right-angle screw dislocations in Mo have been investigated. We have found that the so-called open-quote open-quote easy close-quote close-quote core configuration has a lower formation energy than the open-quote open-quote hard close-quote close-quote one, consistent with previous theoretical studies. (Abstract Truncated)

  18. Materials and mechanisms of hole superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Hirsch, J.E., E-mail: jhirsch@ucsd.edu [Department of Physics, University of California, San Diego, La Jolla, CA 92093-0319 (United States)

    2012-01-15

    We study the applicability of the model of hole superconductivity to materials. Both conventional and unconventional materials are considered. Many different classes of materials are discussed. The theory is found suitable to describe all of them. No other theory of superconductivity can describe all these classes of materials. The theory of hole superconductivity proposes that there is a single mechanism of superconductivity that applies to all superconducting materials. This paper discusses several material families where superconductivity occurs and how they can be understood within this theory. Materials discussed include the elements, transition metal alloys, high T{sub c} cuprates both hole-doped and electron-doped, MgB{sub 2}, iron pnictides and iron chalcogenides, doped semiconductors, and elements under high pressure.

  19. Superconducting energy store

    International Nuclear Information System (INIS)

    Elsel, W.

    1986-01-01

    The advantages obtained by the energy store device according to the invention with a superconducting solenoid system consist of the fact that only relatively short superconducting forward and return leads are required, which are collected into cables as far as possible. This limits the coolant losses of the cables. Only one relatively expensive connecting part with a transition of its conductors from room temperature to a low temperature is required, which, like the normal conducting current switch, is easily accessible. As the continuation has to be cooled independently of the upper part solenoid, cooling of this continuation part can prevent the introduction of large quantities of heat into the connected part solenoid. Due to the cooling of the forward and return conductors of the connecting cable with the coolant of the lower part solenoid, there are relatively few separations between the coolant spaces of the part solenoids. (orig./MM) [de

  20. Applied superconductivity. Handbook on devices and applications. Vol. 1 and 2

    Energy Technology Data Exchange (ETDEWEB)

    Seidel, Paul (ed.) [Jena Univ. (Germany). Inst. fuer Festkoerperphysik, AG Tieftemperaturphysik

    2015-07-01

    The both volumes contain the following 12 chapters: 1. Fundamentals; 2. Superconducting Materials; 3. Technology, Preparation, and Characterization (bulk materials, thin films, multilayers, wires, tapes; cooling); 4, Superconducting Magnets; 5. Power Applications (superconducting cables, superconducting current leads, fault current limiters, transformers, SMES and flywheels; rotating machines; SmartGrids); 6. Superconductive Passive Devices (superconducting microwave components; cavities for accelerators; superconducting pickup coils; magnetic shields); 7. Applications in Quantum Metrology (superconducting hot electron bolometers; transition edge sensors; SIS Mixers; superconducting photon detectors; applications at Terahertz frequency; detector readout); 8. Superconducting Radiation and Particle Detectors; 9. Superconducting Quantum Interference (SQUIDs); 10. Superconductor Digital Electronics; 11. Other Applications (Josephson arrays as radiation sources. Tunable microwave devices) and 12. Summary and Outlook (of the superconducting devices).

  1. Applied superconductivity. Handbook on devices and applications. Vol. 1 and 2

    International Nuclear Information System (INIS)

    Seidel, Paul

    2015-01-01

    The both volumes contain the following 12 chapters: 1. Fundamentals; 2. Superconducting Materials; 3. Technology, Preparation, and Characterization (bulk materials, thin films, multilayers, wires, tapes; cooling); 4, Superconducting Magnets; 5. Power Applications (superconducting cables, superconducting current leads, fault current limiters, transformers, SMES and flywheels; rotating machines; SmartGrids); 6. Superconductive Passive Devices (superconducting microwave components; cavities for accelerators; superconducting pickup coils; magnetic shields); 7. Applications in Quantum Metrology (superconducting hot electron bolometers; transition edge sensors; SIS Mixers; superconducting photon detectors; applications at Terahertz frequency; detector readout); 8. Superconducting Radiation and Particle Detectors; 9. Superconducting Quantum Interference (SQUIDs); 10. Superconductor Digital Electronics; 11. Other Applications (Josephson arrays as radiation sources. Tunable microwave devices) and 12. Summary and Outlook (of the superconducting devices).

  2. Superconducting cyclotrons

    International Nuclear Information System (INIS)

    Blosser, H.G.; Johnson, D.A.; Burleigh, R.J.

    1976-01-01

    Superconducting cyclotrons are particularly appropriate for acceleration of heavy ions. A review is given of design features of a superconducting cyclotron with energy 440 (Q 2 /A) MeV. A strong magnetic field (4.6 tesla average) leads to small physical size (extraction radius 65 cm) and low construction costs. Operating costs are also low. The design is based on established technology (from present cyclotrons and from large bubble chambers). Two laboratories (in Chalk River, Canada and in East Lansing, Michigan) are proceeding with construction of full-scale prototype components for such cyclotrons

  3. Two cloud-point phenomena in tetrabutylammonium perfluorooctanoate aqueous solutions: anomalous temperature-induced phase and structure transitions.

    Science.gov (United States)

    Yan, Peng; Huang, Jin; Lu, Run-Chao; Jin, Chen; Xiao, Jin-Xin; Chen, Yong-Ming

    2005-03-24

    This paper reported the phase behavior and aggregate structure of tetrabutylammonium perfluorooctanoate (TBPFO), determined by differential scanning calorimeter, electrical conductivity, static/dynamic light scattering, and rheology methods. We found that above a certain concentration the TBPFO solution showed anomalous temperature-dependent phase behavior and structure transitions. Such an ionic surfactant solution exhibits two cloud points. When the temperature was increased, the solution turned from a homogeneous-phase to a liquid-liquid two-phase system, then to another homogeneous-phase, and finally to another liquid-liquid two-phase system. In the first homogeneous-phase region, the aggregates of TBPFO were rodlike micelles and the solution was Newtonian fluid. While in the second homogeneous-phase region, the aggregates of TBPFO were large wormlike micelles, and the solution behaved as pseudoplastic fluid that also exhibited viscoelastic behavior. We thought that the first cloud point might be caused by the "bridge" effect of the tetrabutylammonium counterion between the micelles and the second one by the formation of the micellar network.

  4. TRANSIT

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. TRANSIT. SYSTEM: DETERMINE 2D-POSITION GLOBALLY BUT INTERMITTENT (POST-FACTO). IMPROVED ACCURACY. PRINCIPLE: POLAR SATELLITES WITH INNOVATIONS OF: GRAVITY-GRADIENT ATTITUDE CONTROL; DRAG COMPENSATION. WORKS ...

  5. Synthesis and superconductivity of In-doped SnTe nanostructures

    Directory of Open Access Journals (Sweden)

    Piranavan Kumaravadivel

    2017-07-01

    Full Text Available InxSn1−xTe is a time-reversal invariant candidate 3D topological superconductor derived from doping the topological crystalline insulator SnTe with indium. The ability to synthesize low-dimensional nanostructures of indium-doped SnTe is key for realizing the promise they hold in future spintronic and quantum information processing applications. But hitherto only bulk synthesized crystals and nanoplates have been used to study the superconducting properties. Here for the first time we synthesize InxSn1−xTe nanostructures including nanowires and nanoribbons, which show superconducting transitions. In some of the lower dimensional morphologies, we observe signs of more than one superconducting transition and the absence of complete superconductivity. We propose that material inhomogeneity, such as indium inhomogeneity and possible impurities from the metal catalyst, is amplified in the transport characteristics of the smaller nanostructures and is responsible for this mixed behavior. Our work represents the first demonstration of InxSn1−xTe nanowires with the onset of superconductivity, and points to the need for improving the material quality for future applications.

  6. Superconducting transformer

    International Nuclear Information System (INIS)

    Murphy, J.H.

    1982-01-01

    A superconducting transformer having a winding arrangement that provides for current limitation when subjected to a current transient as well as more efficient utilization of radial spacing and winding insulation. Structural innovations disclosed include compressed conical shaped winding layers and a resistive matrix to promote rapid switching of current between parallel windings

  7. Superconducting magnets

    International Nuclear Information System (INIS)

    1994-08-01

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

  8. Superconducting magnets

    International Nuclear Information System (INIS)

    Willen, E.

    1996-01-01

    Superconducting dipole magnets for high energy colliders are discussed. As an example, the magnets recently built for the Relativistic Heavy Ion Collider at Brookhaven are reviewed. Their technical performance and the cost for the industry-built production dipoles are given. The cost data is generalized in order to extrapolate the cost of magnets for a new machine

  9. Bipolar superconductivity

    International Nuclear Information System (INIS)

    Pankratov, S.G.

    1987-01-01

    A model of bipolaron superconductivity suggested by Soviet scientist Alexandrov A.S. and French scientist Ranninger is presentes in a popular way. It is noted that the bipolaron theory gives a good explanation of certain properties of new superconductors, high critical temperature, in particular

  10. Superconducting transistor

    International Nuclear Information System (INIS)

    Gray, K.E.

    1978-01-01

    A three film superconducting tunneling device, analogous to a semiconductor transistor, is presented, including a theoretical description and experimental results showing a current gain of four. Much larger current gains are shown to be feasible. Such a development is particularly interesting because of its novelty and the striking analogies with the semiconductor junction transistor

  11. Reorientational dynamics in molecular liquids as revealed by dynamic light scattering: from boiling point to glass transition temperature.

    Science.gov (United States)

    Schmidtke, B; Petzold, N; Kahlau, R; Rössler, E A

    2013-08-28

    We determine the reorientational correlation time τ of a series of molecular liquids by performing depolarized light scattering experiments (double monochromator, Fabry-Perot interferometry, and photon correlation spectroscopy). Correlation times in the range 10(-12) s-100 s are compiled, i.e., the full temperature interval between the boiling point and the glass transition temperature T(g) is covered. We focus on low-T(g) liquids for which the high-temperature limit τ ≅ 10(-12) s is easily accessed by standard spectroscopic equipment (up to 440 K). Regarding the temperature dependence three interpolation formulae of τ(T) with three parameters each are tested: (i) Vogel-Fulcher-Tammann equation, (ii) the approach recently discussed by Mauro et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 19780 (2009)], and (iii) our approach decomposing the activation energy E(T) in a constant high temperature value E∞ and a "cooperative part" E(coop)(T) depending exponentially on temperature [Schmidtke et al., Phys. Rev. E 86, 041507 (2012)]. On the basis of the present data, approaches (i) and (ii) are insufficient as they do not provide the correct crossover to the high-temperature Arrhenius law clearly identified in the experimental data while approach (iii) reproduces the salient features of τ(T). It allows to discuss the temperature dependence of the liquid's dynamics in terms of a E(coop)(T)/E∞ vs. T/E∞ plot and suggests that E∞ controls the energy scale of the glass transition phenomenon.

  12. Superconducting properties of a copper-ternary alloy

    International Nuclear Information System (INIS)

    Sharma, R.G.; Aleksivskii, N.E.

    1975-01-01

    The superconducting properties of a copper-ternary alloy of the type Cu 93 Nb 5 Sn 2 , subjected to a variety of mechanical and heat treatments, are discussed. The as-cast alloy does not turn superconducting down to 4.5K; but the cold-work and subsequent prescribed heat treatments are found to raise the transition temperature Tsub(c) to values as high as 18.1K and the critical current density Jsub(c) (of the Nb 3 Sn formed during annealing) to a value of 3.6x10 5 Acm -2 (at 4.2K and 30kOe). Various possibilities to improve Jsub(c) of this alloy to still higher values are discussed. The as-cast alloy is ductile, easy to draw, and economical from a technical point of view, and the annealed wires and strips are flexible enough for winding. (author)

  13. Rate of tunneling nonequilibrium quasiparticles in superconducting qubits

    International Nuclear Information System (INIS)

    Ansari, Mohammad H

    2015-01-01

    In superconducting qubits the lifetime of quantum states cannot be prolonged arbitrarily by decreasing temperature. At low temperature quasiparticles tunneling between the electromagnetic environment and superconducting islands takes the condensate state out of equilibrium due to charge imbalance. We obtain the tunneling rate from a phenomenological model of non-equilibrium, where nonequilibrium quasiparticle tunnelling stimulates a temperature-dependent chemical potential shift in the superconductor. As a result we obtain a non-monotonic behavior for relaxation rate as a function of temperature. Depending on the fabrication parameters for some qubits, the lowest tunneling rate of nonequilibrium quasiparticles can take place only near the onset temperature below which nonequilibrium quasiparticles dominate over equilibrium one. Our theory also indicates that such tunnelings can influence the probability of transitions in qubits through a coupling to the zero-point energy of phase fluctuations. (paper)

  14. MgB2 superconducting wires basics and applications

    CERN Document Server

    2016-01-01

    The compendium gives a complete overview of the properties of MgB2 (Magnesium Diboride), a superconducting compound with a transition temperature of Tc = 39K, from the fundamental properties to the fabrication of multifilamentary wires and to the presentation of various applications. Written by eminent researchers in the field, this indispensable volume not only discusses superconducting properties of MgB2 compounds, but also describes known preparation methods of thin films and of bulk samples obtained under high pressure methods. A unique selling point of the book is the detailed coverage of various applications based on MgB2, starting with MRI magnets and high current cables, cooled by Helium (He) vapor. High current cables cooled by liquid hydrogen are also highlighted as an interesting alternative due to the shrinking He reserves on earth. Other pertinent subjects comprise permanent magnets, ultrafine wires for space applications and wind generator projects.

  15. Theory of superconductivity

    International Nuclear Information System (INIS)

    Crisan, M.

    1988-01-01

    This book discusses the most important aspects of the theory. The phenomenological model is followed by the microscopic theory of superconductivity, in which modern formalism of the many-body theory is used to treat most important problems such as superconducting alloys, coexistence of superconductivity with the magnetic order, and superconductivity in quasi-one-dimensional systems. It concludes with a discussion on models for exotic and high temperature superconductivity. Its main aim is to review, as complete as possible, the theory of superconductivity from classical models and methods up to the 1987 results on high temperature superconductivity. Contents: Phenomenological Theory of Superconductivity; Microscopic Theory of Superconductivity; Theory of Superconducting Alloys; Superconductors in a Magnetic Field; Superconductivity and Magnetic Order; Superconductivity in Quasi-One-Dimensional Systems; and Non-Conventional Superconductivity

  16. Unconventional superconductivity in heavy fermionic and high-Tc superconductors

    International Nuclear Information System (INIS)

    Volovik, G.E.

    1989-01-01

    Splitting of the superconducting transition and glass spectrum in heavy fermion companies and oxide superconductors are discussed. The multicomponent order parameter leads to splitting of transition due to magnetic field, impurities, orthorhombic distortion, etc... Linear specific heat in oxide superconductors may be explained in terms of the Fermi-surface arising in superconducting state if interband is pairing strong enough

  17. Localized 5f electrons in superconducting PuCoIn5: consequences for superconductivity in PuCoGa5

    International Nuclear Information System (INIS)

    Bauer, E D; Altarawneh, M M; Tobash, P H; Gofryk, K; Ayala-Valenzuela, O E; Mitchell, J N; McDonald, R D; Mielke, C H; Ronning, F; Scott, B L; Thompson, J D; Griveau, J-C; Colineau, E; Eloirdi, R; Caciuffo, R; Janka, O; Kauzlarich, S M

    2012-01-01

    The physical properties of the first In analog of the PuMGa 5 (M = Co, Rh) family of superconductors, PuCoIn 5 , are reported. With its unit cell volume being 28% larger than that of PuCoGa 5 , the characteristic spin-fluctuation energy scale of PuCoIn 5 is three to four times smaller than that of PuCoGa 5 , which suggests that the Pu 5f electrons are in a more localized state relative to PuCoGa 5 . This raises the possibility that the high superconducting transition temperature T c = 18.5 K of PuCoGa 5 stems from the proximity to a valence instability, while the superconductivity at T c = 2.5 K of PuCoIn 5 is mediated by antiferromagnetic spin fluctuations associated with a quantum critical point. (fast track communication)

  18. Earlier and recent aspects of superconductivity

    International Nuclear Information System (INIS)

    Bednorz, J.G.; Muller, K.A.

    1990-01-01

    Contemporary knowledge of superconductivity is set against its historical background in this book. First, the highlights of superconductivity research in the twentieth century are reviewed. Further contributions then describe the basic phenomena resulting from the macroscopic quantum state of superconductivity (such as zero resistivity, the Meissner-Ochsenfeld effect, and flux quantization) and review possible mechanisms, including the classical BCS theory and the more recent alternative theories. The main categories of superconductors - elements, intermetallic phases, chalcogenides, oxides and organic compounds - are described. Common features and differences in their structure and electronic properties are pointed out. This overview of superconductivity is completed by a discussion of properties related to the coherence length

  19. Superconductivity at disordered interfaces

    International Nuclear Information System (INIS)

    Simanek, E.

    1979-01-01

    The increase of the superconducting transition temperature Tsub(c) due to the tunneling of conduction electrons into negative-u centers at a disordered metal-semiconductor interface is calculated. The strong dependence of the experimental increase of Tsub(c) on the Fermi energy of the metal is accounted for by the polaronic reduction of the tunneling matrix elements. The latter reduction is dynamically suppressed by the decreasing lifetime of the localized state as Esub(F) increases. The theoretical enhancement is sufficiently strong to explain the increase of Tsub(c) observed in eutectic alloys. (author)

  20. Superconducting fault current-limiter with variable shunt impedance

    Science.gov (United States)

    Llambes, Juan Carlos H; Xiong, Xuming

    2013-11-19

    A superconducting fault current-limiter is provided, including a superconducting element configured to resistively or inductively limit a fault current, and one or more variable-impedance shunts electrically coupled in parallel with the superconducting element. The variable-impedance shunt(s) is configured to present a first impedance during a superconducting state of the superconducting element and a second impedance during a normal resistive state of the superconducting element. The superconducting element transitions from the superconducting state to the normal resistive state responsive to the fault current, and responsive thereto, the variable-impedance shunt(s) transitions from the first to the second impedance. The second impedance of the variable-impedance shunt(s) is a lower impedance than the first impedance, which facilitates current flow through the variable-impedance shunt(s) during a recovery transition of the superconducting element from the normal resistive state to the superconducting state, and thus, facilitates recovery of the superconducting element under load.

  1. Superconductivity in Ternary Rare-Earth Transition Metal Silicides and Germanides with the SCANDIUM(5) COBALT(4) SILICON(10)-TYPE Structure.

    Science.gov (United States)

    Berg, Linda Sue

    A systematic study of the superconducting and normal state properties of some ternary rare earth transition metal silicides and germanides of the Sc(,5)Co(,4)Si(,10) -type is reported in this work. Low temperature heat capacity measurements indicate the presence of a complicated phonon density of states in these structurally complex compounds. A better description of the phonon spectrum of the high T(,c) materials, Sc(,5)Rh(,4)Si(,10), Sc(,5)Ir(,4)Si(,10), and Y(,5)Os(,4)Ge(,10), given by a model proposed by Junod et al.('1), is presented and discussed. The large values of (DELTA)C/(gamma)(,n)T(,c) and the electron-phonon coupling constant for these high T(,c) compounds indicate that they are strong-coupled superconductors. Relative to other ternary superconductors, many of these materials have large Debye temperatures. The BSC theory does not seem to afford an adequate description of the supercon- ducting state in these compounds. DC electrical resistivity measurements on these compounds show resistivity behaviors deviating from those exhibited by simple metals. The (rho)(T) data for Y(,5)Ir(,4)Si(,10), Lu(,5)Rh(,4)Si(,10), Lu(,5)Ir(,4)Si(,10), and Y(,5)Os(,4)Ge(,10), indicate the presence of anomalies. Static molar magnetic susceptibility measurements performed on these compounds indicate (1) a small effective magnetic moment of 0.26(mu)(,B) on the Co atom and (2) anomalous behaviors in the Lu(,5)Rh(,4)Si(,10), Lu(,5)Ir(,4)Si(,10), Y(,5)Ir(,4)Si(,10), Lu(,5)Ir(,4)Ge(,10), and Y(,5)Rh(,4)Ge(,10) data. It is suggested that the same mechanism, namely, the forma- tion of a charge- or spin-density wave, is causing the anomalous behaviors in both the resistivity and susceptibility data. Lastly, upper critical magnetic field measurements were performed on Sc(,5)Co(,4)Si(,10), Sc(,5)Rh(,4)Si(,10), Sc(,5)Ir(,4)Si(,10), Lu(,5)Rh(,4)Si(,10), Lu(,5)Ir(,4)Si(,10), and Y(,5)Os(,4)Ge(,10). Relative to the other five samples, Y(,5)Os(,4)Ge(,10) exhibits very high values for (-d

  2. Correlation mediated superconductivity in a Spin Peierls Phase of the Hubbard Model

    International Nuclear Information System (INIS)

    Long, M.W.

    1987-08-01

    The author explores the consequences of a mapping of the Hubbard Hamiltonian with a view to finding possible superconducting phases. The transformation pairs up all the sites and is therefore a much more natural starting point for describing a 'Spin Peierls' transition, generating enhanced singlet correlations for this pairing, than it is for describing the 'Resonating Valence Bond' state. It is shown that in the less than half filling case, an effective non-linear hopping Hamiltonian is quite useful in describing half of the electrons. This effective Hamiltonian can show a form of superconducting instability when nearest neighbour hopping is introduced to stabilise it. This superconducting phase seems to be a very unlikely possibility for the standard Hubbard model. (author)

  3. Lighting up superconducting stripes

    Science.gov (United States)

    Ergeçen, Emre; Gedik, Nuh

    2018-02-01

    Cuprate superconductors display a plethora of complex phases as a function of temperature and carrier concentration, the understanding of which could provide clues into the mechanism of superconductivity. For example, when about one-eighth of the conduction electrons are removed from the copper oxygen planes in cuprates such as La2‑xBaxCuO4 (LBCO), the doped holes (missing electrons) organize into one-dimensional stripes (1). The bulk superconducting transition temperature (Tc) is greatly reduced, and just above Tc, electrical transport perpendicular to the planes (along the c axis) becomes resistive, but parallel to the copper oxygen planes, resistivity remains zero for a range of temperatures (2). It was proposed a decade ago (3) that this anisotropic behavior is caused by pair density waves (PDWs); superconducting Cooper pairs exist along the stripes within the planes but cannot tunnel to the adjacent layers. On page 575 of this issue, Rajasekaran et al. (4) now report detection of this state in LBCO using nonlinear reflection of high-intensity terahertz (THz) light.

  4. An aggregate method to calibrate the reference point of cumulative prospect theory-based route choice model for urban transit network

    Science.gov (United States)

    Zhang, Yufeng; Long, Man; Luo, Sida; Bao, Yu; Shen, Hanxia

    2015-12-01

    Transit route choice model is the key technology of public transit systems planning and management. Traditional route choice models are mostly based on expected utility theory which has an evident shortcoming that it cannot accurately portray travelers' subjective route choice behavior for their risk preferences are not taken into consideration. Cumulative prospect theory (CPT), a brand new theory, can be used to describe travelers' decision-making process under the condition of uncertainty of transit supply and risk preferences of multi-type travelers. The method to calibrate the reference point, a key parameter to CPT-based transit route choice model, determines the precision of the model to a great extent. In this paper, a new method is put forward to obtain the value of reference point which combines theoretical calculation and field investigation results. Comparing the proposed method with traditional method, it shows that the new method can promote the quality of CPT-based model by improving the accuracy in simulating travelers' route choice behaviors based on transit trip investigation from Nanjing City, China. The proposed method is of great significance to logical transit planning and management, and to some extent makes up the defect that obtaining the reference point is solely based on qualitative analysis.

  5. Quantum shape phase transitions from spherical to deformed for Bose-Fermi systems: the effect of the odd particle around the critical point

    Directory of Open Access Journals (Sweden)

    Böyükata M.

    2014-03-01

    Full Text Available Quantum phase transitions in odd-nuclei are investigated within the framework of the interacting boson-fermion model with a description based on the concept of intrinsic states. We consider the case of a single j=9/2 odd-particle coupled to an even-even boson core that performs a transition from spherical to deformed prolate and to deformed gamma-unstable shapes varying a control parameter in the boson Hamiltonian. The effect of the coupling of the odd particle to this core is discussed along the shape transition and, in particular, at the critical point.

  6. Role of single-point mutations and deletions on transition temperatures in ideal proteinogenic heteropolymer chains in the gas phase.

    Science.gov (United States)

    Olivares-Quiroz, L

    2016-07-01

    A coarse-grained statistical mechanics-based model for ideal heteropolymer proteinogenic chains of non-interacting residues is presented in terms of the size K of the chain and the set of helical propensities [Formula: see text] associated with each residue j along the chain. For this model, we provide an algorithm to compute the degeneracy tensor [Formula: see text] associated with energy level [Formula: see text] where [Formula: see text] is the number of residues with a native contact in a given conformation. From these results, we calculate the equilibrium partition function [Formula: see text] and characteristic temperature [Formula: see text] at which a transition from a low to a high entropy states is observed. The formalism is applied to analyze the effect on characteristic temperatures [Formula: see text] of single-point mutations and deletions of specific amino acids [Formula: see text] along the chain. Two probe systems are considered. First, we address the case of a random heteropolymer of size K and given helical propensities [Formula: see text] on a conformational phase space. Second, we focus our attention to a particular set of neuropentapeptides, [Met-5] and [Leu-5] enkephalins whose thermodynamic stability is a key feature on their coupling to [Formula: see text] and [Formula: see text] receptors and the triggering of biochemical responses.

  7. TRANSIT TIME THROUGH THE BORDER-CROSSING POINTS: THE CASE STUDY OF THE EU'S ROAD BCP WITH MOLDAVIA

    Directory of Open Access Journals (Sweden)

    Mihaela POPA

    2016-06-01

    Full Text Available . This paper provides an overview on the ACROSSEE project (funded by the ERDF under the SEE program, its objectives, general methodology, and the main results. Moreover, the main survey results are presented as they relate to the Romanian road and rail border-crossing points (BCPs with the Eastern neighbourly country, Moldavia. Results include the actual status of the road BCP, surveys on exiting and entering traffic flows, answers to specific questionnaires of the truck and car drivers in relation with origin-destination of the trips, average waiting time in queue and time required for procedures and controls. Discussion on the mathematical modelling is presented and a provisional simulation model is developed, using ARENA software. The early results are used in order to introduce the need for future assessment of the transit time in a road BCP, with the main purpose: the substantiation of the strategic and operational actions for improvements in trade and transport crossings of the EU borders, considering the need for more vigilant and less time-consuming checks at the outside borders of the EU.

  8. Phase transitions and multicritical points in the mixed spin-32 and spin-2 Ising system with a single-ion anisotropy

    International Nuclear Information System (INIS)

    Bobak, A.; Dely, J.

    2007-01-01

    The effect of a single-ion anisotropy on the phase diagram of the mixed spin-32 and spin-2 Ising system is investigated by the use of a mean-field theory based on the Bogoliubov inequality for the free energy. Topologically different kinds of phase diagrams are achieved by changing values of the parameter in the model Hamiltonian. Besides second-order transitions, lines of first-order transitions terminating either at a tricritical point or an isolated critical point, are found

  9. Modern theories of phase transitions

    International Nuclear Information System (INIS)

    Rajaraman, R.

    1979-01-01

    Modern applications of the ideas of phase transitions to nuclear systems and the modern techniques as applied to familiar phase transitions in solid-state physics are discussed with illustrations. The phenomenon of pion condensation in nuclei and neutron stars, is presented as an example of phase transitions in nuclear systems. The central physical ideas behind this subject as well as techniques used to tackle it are broadly summarised. It is pointed out that unlike familiar examples of ferromagnetism or superconductivity, the order parameter here has spatial variation even in the ground state. Possible experimental consequences are discussed. As an example of the second category, the use of renormalisation group techniques in solid state physics is reviewed. The basic idea behind the renormalisation group in the infra-red (thermodynamic) limit is presented. The observed universality and scaling of critical exponents in second order phase transitions is explained in a model-independent way. (auth.)

  10. Color superconductivity

    International Nuclear Information System (INIS)

    Wilczek, F.

    1997-01-01

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

  11. Color superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Wilczek, F. [Institute for Advanced Study, Princeton, NJ (United States)

    1997-09-22

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

  12. Thermal expansion of coexistence of ferromagnetism and superconductivity

    International Nuclear Information System (INIS)

    Hatayama, Nobukuni; Konno, Rikio

    2010-01-01

    The temperature dependence of thermal expansion of coexistence of ferromag-netism and superconductivity below the superconducting transition temperature T cu of a majority spin conduction band is investigated. Majority spin and minority spin superconducting gaps exist in the coexistent state. We assume that the Curie temperature is much larger than the superconducting transition temperatures. The free energy that Linder et al. [Phys. Rev. B76, 054511 (2007)] derived is used. The thermal expansion of coexistence of ferromagnetism and superconductivity is derived by the application of the method of Takahashi and Nakano [J. Phys.: Condens. Matter 18, 521 (2006)]. We find that we have the anomalies of the thermal expansion in the vicinity of the superconducting transition temperatures.

  13. Dependences on RE of superconducting properties of transition metal co-doped (Ca, RE)FeAs_2 with RE = La–Gd

    International Nuclear Information System (INIS)

    Yakita, H.; Ogino, H.; Sala, A.; Okada, T.; Yamamoto, A.; Kishio, K.; Iyo, A.; Eisaki, H.; Shimoyama, J.

    2015-01-01

    Highlights: • We synthesized Co or Ni co-doped (Ca, RE)FeAs_2 with RE = La–Gd. • Co or Ni co-doping improved superconducting properties of all (Ca, RE)FeAs_2 samples. • T_c of (Ca, RE)FeAs_2 decreased with decreasing ionic radii of RE"3"+. • Eu doped samples showed exceptionally low T_c and long interlayer distance. • Long interlayer distance of Eu doped samples suggested co-existence of Eu"2"+ and Eu"3"+. - Abstract: Dependence of superconducting properties of (Ca, RE)(Fe, TM)As_2 [(Ca, RE)112, TM: Co, Ni)] on RE elements (RE = La–Gd) was systematically investigated. Improvement of superconducting properties by Co or Ni co-doping was observed for all (Ca, RE)112, which is similar to Co-co-doped (Ca, La)112 or (Ca, Pr)112. T_c of Co-co-doped samples decreased from 38 K for RE = La to 29 K for RE = Gd with decreasing ionic radii of RE"3"+. However, Co-co-doped (Ca, Eu)112 showed exceptionally low T_c = 21 K probably due to the co-existence of Eu"3"+ and Eu"2"+ suggested by longer interlayer distance d_F_e_–_F_e of (Ca, Eu)112 than other (Ca, RE)112.

  14. Superconducting magnet

    Science.gov (United States)

    1985-01-01

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

  15. Melt formed superconducting joint between superconducting tapes

    International Nuclear Information System (INIS)

    Benz, M.G.; Knudsen, B.A.; Rumaner, L.E.; Zaabala, R.J.

    1992-01-01

    This patent describes a superconducting joint between contiguous superconducting tapes having an inner laminate comprised of a parent-metal layer selected from the group niobium, tantalum, technetium, and vanadium, a superconductive intermetallic compound layer on the parent-metal layer, a reactive-metal layer that is capable of combining with the parent-metal and forming the superconductive intermetallic compound, the joint comprising: a continuous precipitate of the superconductive intermetallic compound fused to the tapes forming a continuous superconducting path between the tapes

  16. Magnetization Controlled Superconductivity in a Film with Magnetic Dots

    International Nuclear Information System (INIS)

    Lyuksyutov, I.F.; Pokrovsky, V.; Pokrovsky, V.

    1998-01-01

    We consider a superconducting film with a magnetic dots array (MDA) placed upon it. Magnetic moments of the dots are normal to the film and strong enough to create vortices in the superconducting film. Magnetic interaction between dots is negligible. Zero-field cooling leads to random magnetization of the MDA well above the superconducting temperature. With this cooling, the film is in a resistive state below the (expected) superconducting transition. Paradoxically, when field cooled, the film with MDA can be superconducting. copyright 1998 The American Physical Society

  17. Superconductivity and its pressure variation in GaAs

    International Nuclear Information System (INIS)

    Nirmala Louis, C.; Jayam, Sr. Gerardin; Amalraj, A.

    2005-01-01

    The electronic band structure, metallization, phase transition and superconducting transition of gallium arsenide under pressure are studied using TB-LMTO method. Metallization occurs via indirect closing of band gap between Γ and X points. GaAs becomes superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The ground state properties are analyzed by fitting the calculated total energies to the Birch-Murnaghan's equation of state. The superconducting transition temperatures (T c ) obtained as a function of pressure for both the ZnS and NaCl structures and GaAs comes under the class of pressure induced superconductor. When pressure is increased T c increases in both the normal and high pressure structures. The dependence of T c on electron-phonon mass enhancement factor λ shows that GaAs is an electron-phonon-mediated superconductor. Also it is found that GaAs retained in their normal structure under high pressure give appreciably high T c . (author)

  18. 18 January 2011 - Ing. Vittorio Malacalza, ASG Superconductors S.p.A, Italy in the LHC superconducting magnet test hall with Deputy Department Head L. Rossi, in the LHC tunnel at Point 5 and CMS experimental area with Spokesperson G. Tonelli.

    CERN Multimedia

    Maximilien Brice

    2011-01-01

    18 January 2011 - Ing. Vittorio Malacalza, ASG Superconductors S.p.A, Italy in the LHC superconducting magnet test hall with Deputy Department Head L. Rossi, in the LHC tunnel at Point 5 and CMS experimental area with Spokesperson G. Tonelli.

  19. 27 January 2012 - Mitglieder des Stiftungsrates Academia Engelberg und Gesellschaft zum Bettag Luzern Schweiz welcomed by Head of International Relations F. Pauss; visiting LHC tunnel at Point 5 and CMS experimental cavern; in the LHC superconducting magnet test hall SM18.

    CERN Multimedia

    Maximilien Brice

    2012-01-01

    27 January 2012 - Mitglieder des Stiftungsrates Academia Engelberg und Gesellschaft zum Bettag Luzern Schweiz welcomed by Head of International Relations F. Pauss; visiting LHC tunnel at Point 5 and CMS experimental cavern; in the LHC superconducting magnet test hall SM18.

  20. Interactions between superconductivity and quantum criticality in CeCoIn5, URhGe and UCoGe

    International Nuclear Information System (INIS)

    Howald, L.

    2011-01-01

    The subject of this thesis is the analyze of the superconducting upper critical field (Hc2) and the interaction between superconductivity and quantum critical points (QCP), for the compounds CeCoIn 5 , URhGe and UCoGe. In CeCoIn 5 , study by mean of resistivity of the Fermi liquid domain allows us to localize precisely the QCP at ambient pressure. This analyze rule out the previously suggested pinning of Hc2(0) at the QCP. In a second part, the evolution of Hc2 under pressure is analyzed. The superconducting dome is unconventional in this compound with two characteristic pressures: at 1.6 GPa, the superconducting transition temperature is maximum but it is at 0.4 GPa that physical properties (maximum of Hc2(0), maximum of the initial slope dHc2/dT, maximum of the specific heat jump DC/C,... ) suggest a QCP. We explain this antagonism with pair-breaking effects in the proximity of the QCP. With these two experiments, we suggest a new phase diagram for CeCoIn 5 . In a third part, measurements of thermal conductivity on URhGe and UCoGe are presented. We obtained the bulk superconducting phase transition and confirmed the unusual curvature of the slope dHc2/dT observed by resistivity. The temperatures and fields dependence of thermal conductivity allow us to identify a non-electronic contribution for heat transport down to the lowest temperature (50 mK) and probably associated with magnon or longitudinal fluctuations. We also identified two different domains in the superconducting region, These domains are compatible with a two bands model for superconductivity. Thermopower measurements on UCoGe reveal a strong anisotropy to current direction and several anomaly under field applied in the b direction. We suggest a Lifshitz transition to explain our observations in these two compounds. (author) [fr

  1. CERN News: Selection of the type of superconducting coil for the Omega project; New intensity records at the proton synchrotron; Progress with the Spiral Reader film measuring equipment; New technique at transition energy on the proton synchrotron; CERN Courier 10th anniversary; Equipment travelling from and to Serpukhov

    CERN Multimedia

    1969-01-01

    CERN News: Selection of the type of superconducting coil for the Omega project; New intensity records at the proton synchrotron; Progress with the Spiral Reader film measuring equipment; New technique at transition energy on the proton synchrotron; CERN Courier 10th anniversary; Equipment travelling from and to Serpukhov

  2. Fast superconducting magnetic field switch

    Science.gov (United States)

    Goren, Yehuda; Mahale, Narayan K.

    1996-01-01

    The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles.

  3. Fast superconducting magnetic field switch

    International Nuclear Information System (INIS)

    Goren, Y.; Mahale, N.K.

    1996-01-01

    The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. 6 figs

  4. Superconductivity in zirconium-rhodium alloys

    Science.gov (United States)

    Zegler, S. T.

    1969-01-01

    Metallographic studies and transition temperature measurements were made with isothermally annealed and water-quenched zirconium-rhodium alloys. The results clarify both the solid-state phase relations at the Zr-rich end of the Zr-Rh alloy system and the influence upon the superconducting transition temperature of structure and composition.

  5. Nonlinearity in superconductivity and Josephson junctions

    International Nuclear Information System (INIS)

    Lazarides, N.

    1995-01-01

    Within the framework of the Bardeen, Cooper and Schrieffers (BCS) theory, the influence of anisotropy on superconducting states are investigated. Crystal anisotropy exists in un-conventional low temperature superconductors as e.g. U 1-x Th x Be 13 and in high temperature superconductors. Starting from a phenomenological pairing interaction of the electrons or holes, the BCS approach is used to derive a set of coupled nonlinear algebraic equations for the momentum dependent gap parameter. The emphasis is put on bifurcation phenomena between s-, d-wave and mixed s- and d-wave symmetry and the influence on measurable quantities as the electron specific heat, spin susceptibility and Josephson tunnelling. Pitch-fork and perturbed pitch-fork bifurcations have been found separating s- and d-wave superconducting states from mixed s- and d-wave states. The additional superconducting states give rise to jumps in the electron specific heat below the transition temperature. These jumps are rounded in the case of perturbed pitch-fork bifurcations. An experiment to measure the sign of the interlayer interaction using dc SQUIDS is suggested. The Ambegaokar-Baratoff formalism has been used for calculating the quasiparticle current and the two phase coherent tunnelling currents in a Josephson junction made of anisotropic superconductors. It is shown that anisotropy can lead to a reduction in the product of the normal resistance and the critical current. For low voltages across the junction the usual resistively shunted Josephson model can be used. Finally, bunching in long circular Josephson junctions and suppression of chaos in point junctions have been investigated. (au) 113 refs

  6. The end point of the first-order phase transition of the SU(2) gauge-Higgs model on a four-dimensional isotropic lattice

    International Nuclear Information System (INIS)

    Aoki, Y.; Csikor, F.; Fodor, Z.; Ukawa, A.

    1999-01-01

    We report results of a study of the end point of the electroweak phase transition of the SU(2) gauge-Higgs model defined on a four-dimensional isotropic lattice with N t = 2. Finite-size scaling study of Lee-Yang zeros yields λ c = 0.00116(16) for the end point. Combined with a zero-temperature measurement of Higgs and W boson masses, this leads to M H,c = 68.2 ± 6.6 GeV for the critical Higgs boson mass. An independent analysis of Binder cumulant gives a consistent value λ c = 0.00102(3) for the end point

  7. Thermodynamic Green functions in theory of superconductivity

    Directory of Open Access Journals (Sweden)

    N.M.Plakida

    2006-01-01

    Full Text Available A general theory of superconductivity is formulated within the thermodynamic Green function method for various types of pairing mediated by phonons, spin fluctuations, and strong Coulomb correlations in the Hubbard and t-J models. A rigorous Dyson equation for matrix Green functions is derived in terms of a self-energy as a many-particle Green function. By applying the noncrossing approximation for the self-energy, a closed self-consistent system of equations is obtained, similar to the conventional Eliashberg equations. A brief discussion of superconductivity mediated by kinematic interaction with an estimation of a superconducting transition temperature in the Hubbard model is given.

  8. Impurity effects in superconducting UPt3

    International Nuclear Information System (INIS)

    Aronson, M.C.; Vorenkamp, T.; Koziol, Z.; de Visser, A.; Bakker, K.; Franse, J.J.M.; Smith, J.L.

    1991-01-01

    Superconducting UPt 3 is characterized by a novel and complex magnetic field-temperature phase diagram, with two superconducting transitions at T c1 and T c2 in zero field. We have studied the effects of Pd and Y impurities on the zero field superconducting properties of UPt 3 . Resistance measurements show that both dopants increase the residual resistivity and decrease the spin fluctuation temperature in the normal state. T c1 is depressed by both dopants, but more effectively by Pd. |T c1 - T c2 | is essentially unaffected by Y doping, but increases dramatically with Pd doping

  9. Development of magnetic order in superconducting systems

    International Nuclear Information System (INIS)

    Moncton, D.E.; Shirane, G.; Thomlinson, W.

    1979-08-01

    Two different classes of rare-earth (RE) ternary superconductors (RERh 4 B 4 and REMo 6 S 8 , X=S, Se) have provided the first instances in which chemically ordered sublattices of magnetic ions exist in superconductors. Neutron scattering studies show that simple, conventional antiferromagnetism coexists with superconductivity in a number of systems, while destruction of superconductivity occurs with the onset of ferromagnetism. The magnetic structural details are summarized for the coexistent antiferromagnets, and review measurements on the superconducting → ferromagnetic transition in ErRh 4 B 4

  10. Superconductivity in mixed boson-fermion systems

    International Nuclear Information System (INIS)

    Ioffe, L.; Larkin, A.I.; Ovchinnikov, Yu.N.; Yu, L.

    1989-12-01

    The superconductivity of mixed boson-fermion systems is studied using a simple boson-fermion transformation model. The critical temperature of the superconducting transition is calculated over a wide range of the narrow boson band position relative to the Fermi level. The BCS scenario and boson condensation picture are recovered in two limiting cases of high and low positions of boson band, respectively, with modifications due to boson-fermion interaction. (author). 11 refs

  11. Towards inducing superconductivity into graphene

    Science.gov (United States)

    Efetov, Dmitri K.

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

  12. The state of superconductivity

    International Nuclear Information System (INIS)

    Clark, T.D.

    1981-01-01

    The present status of applications based on the phenomena of superconductivity are reviewed. Superconducting materials, large scale applications, the Josephson effect and its applications, and superconductivity in instrumentation, are considered. The influence that superconductivity has had on modern theories of elementary particles, such as gauge symmetry breaking, is discussed. (U.K.)

  13. CLIQ – Coupling-Loss Induced Quench System for Protecting Superconducting Magnets

    CERN Multimedia

    Ravaioli, E; Kirby, G; ten Kate, H H J; Verweij, A P

    2014-01-01

    The recently developed Coupling-Loss-Induced Quench (CLIQ) protection system is a new method for initiating a fast and voluminous transition to the normal state for protecting high energy density superconducting magnets. Upon quench detection, CLIQ is triggered to generate an oscillating current in the magnet coil by means of a capacitive discharge. This in turn introduces a high coupling loss in the superconductor which provokes a quick transition to the normal state of the coil windings. The system is now implemented for the protection of a two meter long superconducting quadrupole magnet and characterized in the CERN magnet test facility. Various CLIQ configurations with different current injection points are tested and the results compared to similar transients lately measured with a not optimized configuration. Test results convincingly show that the newly tested design allows for a more global quench initiation and thus a faster discharge of the magnet energy. Moreover, the performance of CLIQ for reduc...

  14. Approaching the Type-II Dirac Point and Concomitant Superconductivity in Pt-doping Stabilized Metastable 1T-phase IrTe2

    OpenAIRE

    Fei, Fucong; Bo, Xiangyan; Wang, Pengdong; Ying, Jianghua; Chen, Bo; Liu, Qianqian; Zhang, Yong; Sun, Zhe; Qu, Fanming; Zhang, Yi; Li, Jian; Song, Fengqi; Wan, Xiangang; Wang, Baigeng; Wang, Guanghou

    2017-01-01

    Topological semimetal is a topic of general interest in material science. Recently, a new kind of topological semimetal called type-II Dirac semimetal with tilted Dirac cones is discovered in PtSe2 family. However, the further investigation is hindered due to the huge energy difference from Dirac points to Fermi level and the irrelevant conducting pockets at Fermi surface. Here we characterize the optimized type-II Dirac dispersions in a metastable 1T phase of IrTe2. Our strategy of Pt doping...

  15. 100 years of superconductivity

    CERN Document Server

    Rogalla, Horst

    2011-01-01

    Even a hundred years after its discovery, superconductivity continues to bring us new surprises, from superconducting magnets used in MRI to quantum detectors in electronics. 100 Years of Superconductivity presents a comprehensive collection of topics on nearly all the subdisciplines of superconductivity. Tracing the historical developments in superconductivity, the book includes contributions from many pioneers who are responsible for important steps forward in the field.The text first discusses interesting stories of the discovery and gradual progress of theory and experimentation. Emphasizi

  16. High-temperature superconductivity

    International Nuclear Information System (INIS)

    Ginzburg, V.L.

    1987-07-01

    After a short account of the history of experimental studies on superconductivity, the microscopic theory of superconductivity, the calculation of the control temperature and its possible maximum value are presented. An explanation of the mechanism of superconductivity in recently discovered superconducting metal oxide ceramics and the perspectives for the realization of new high-temperature superconducting materials are discussed. 56 refs, 2 figs, 3 tabs

  17. Superconducting accelerator technology

    International Nuclear Information System (INIS)

    Grunder, H.A.; Hartline, B.K.

    1986-01-01

    Modern and future accelerators for high energy and nuclear physics rely increasingly on superconducting components to achieve the required magnetic fields and accelerating fields. This paper presents a practical overview of the phenomenon of superconductivity, and describes the design issues and solutions associated with superconducting magnets and superconducting rf acceleration structures. Further development and application of superconducting components promises increased accelerator performance at reduced electric power cost

  18. Superconductivity theory applied to the periodic table of the elements

    International Nuclear Information System (INIS)

    Elifritz, T.L.

    1994-01-01

    The modern theory of superconductivity, based upon the BCS to Bose-Einstein transition, is applied to the periodic table of the elements, in order to isolate the essential features of high temperature superconductivity and to predict its occurrence within the periodic table. It is predicted that Sodium-Ammonia, Sodium Zinc Phosphide and Bismuth (I) Iodide are promising materials for experimental explorations of high temperature superconductivity

  19. Superconductivity theory applied to the periodic table of the elements

    Energy Technology Data Exchange (ETDEWEB)

    Elifritz, T.L. [Information Corporation, Madison, WI (United States)

    1994-12-31

    The modern theory of superconductivity, based upon the BCS to Bose-Einstein transition, is applied to the periodic table of the elements, in order to isolate the essential features of high temperature superconductivity and to predict its occurrence within the periodic table. It is predicted that Sodium-Ammonia, Sodium Zinc Phosphide and Bismuth (I) Iodide are promising materials for experimental explorations of high temperature superconductivity.

  20. Superconductivity theory applied to the periodic table of the elements

    Science.gov (United States)

    Elifritz, Thomas Lee

    1995-01-01

    The modern theory of superconductivity, based upon the BCS to Bose-Einstein transition is applied to the periodic table of the elements, in order to isolate the essential features of of high temperature superconductivity and to predict its occurrence with the periodic table. It is predicted that Sodium-Ammonia, Sodium Zinc Phosphide and Bismuth (I) Iodide are promising materials for experimental explorations of high temperature superconductivity.

  1. Liquid phase sintered superconducting cermet

    International Nuclear Information System (INIS)

    Ray, S.P.

    1990-01-01

    This patent describes a method of making a superconducting cermet having superconducting properties with improved bulk density, low porosity and in situ stabilization. It comprises: forming a structure of a superconducting ceramic material having the formula RM 2 Cu 3 O (6.5 + x) wherein R is one or more rare earth elements capable of reacting to form a superconducting ceramic, M is one or more alkaline earth metal elements selected from barium and strontium capable of reacting to form a superconducting ceramic, x is greater than 0 and less than 0.5; and a precious metal compound in solid form selected from the class consisting of oxides, sulfides and halides of silver; and liquid phase sintering the mixture at a temperature wherein the precious metal of the precious metal compound is molten and below the melting point of the ceramic material. The liquid phase sintering is carried out for a time less than 36 hours but sufficient to improve the bulk density of the cermet

  2. Some regularities in the occurrence of superconductivity

    International Nuclear Information System (INIS)

    Chapnik, I.M.

    1984-01-01

    The superconducting transition temperatures T/sub c/ of the non-transition elements (NTE) of the first long period of the Periodic Table are compared with those of analogous compounds having NTE components from the second period. In contrast to relations for transition metals (TM) the NTE compounds show a higher T/sub c/ if the NTE component belongs to the first long period. The intermetallic compounds, crystal lattices, and T/sub c/ are listed and discussed

  3. Experimental Investigation of Magnetic Superconducting and other Phase Transitions in Novel f-Electron Materials at Ultra-high Pressures using Designer Diamond Anvils

    International Nuclear Information System (INIS)

    Maple, M. Brian; Jeffries, Jason R.; Ho, Pei-Chun; Butch, Nicholas P.

    2004-01-01

    Pressure is often used as a controlled parameter for the investigation of condensed matter systems. In particular, pressure experiments can provide valuable information into the nature of superconductivity, magnetism, and the coexistence of these two phenomena. Some f-electron, heavy-fermion materials display interesting and novel behavior at moderately low pressures achievable with conventional experimental techniques; however, a growing number of condensed matter systems require ultrahigh pressure techniques, techniques that generate significantly higher pressures than conventional methods, to sufficiently explore their important properties. To that end, we have been funded to develop an ultrahigh pressure diamond anvil cell facility at the University of California, San Diego (UCSD) in order to investigate superconductivity, magnetism, non-Fermi liquid behavior, and other phenomena. Our goals for the first year of this grant were as follows: (a) set up and test a suitable refrigerator; (b) set up a laser and spectrometer fluorescence system to determine the pressure within the diamond anvil cell; (c) perform initial resistivity measurements at moderate pressures from room temperature to liquid helium temperatures (∼1K); (d) investigate f-electron materials within our current pressure capabilities to find candidate materials for high-pressure studies. During the past year, we have ordered almost all the components required to set up a diamond anvil cell facility at UCSD, we have received and implemented many of the components that have been ordered, we have performed low pressure research on several materials, and we have engaged in a collaborative effort with Sam Weir at Lawrence Livermore National Lab (LLNL) to investigate Au4V under ultrahigh pressure in a designer diamond anvil cell (dDAC). This report serves to highlight the progress we have made towards developing an ultrahigh pressure research facility at UCSD, the research performed in the past year, as

  4. Superconducting composites materials

    International Nuclear Information System (INIS)

    Kerjouan, P.; Boterel, F.; Lostec, J.; Bertot, J.P.; Haussonne, J.M.

    1991-01-01

    The new superconductor materials with a high critical current own a large importance as well in the electronic components or in the electrotechnical devices fields. The deposit of such materials with the thick films technology is to be more and more developed in the years to come. Therefore, we tried to realize such thick films screen printed on alumina, and composed mainly of the YBa 2 Cu 3 O 7-δ material. We first realized a composite material glass/YBa 2 Cu 3 O 7-δ , by analogy with the classical screen-printed inks where the glass ensures the bonding with the substrate. We thus realized different materials by using some different classes of glass. These materials owned a superconducting transition close to the one of the pure YBa 2 Cu 3 O 7-δ material. We made a slurry with the most significant composite materials and binders, and screen-printed them on an alumina substrate preliminary or not coated with a diffusion barrier layer. After firing, we studied the thick films adhesion, the alumina/glass/composite material interfaces, and their superconducting properties. 8 refs.; 14 figs.; 9 tabs [fr

  5. Growth of epitaxial Ba2YCu3O(7-delta) thin films and control of their superconducting properties

    International Nuclear Information System (INIS)

    Siegal, M.P.; Phillips, J.M.

    1992-01-01

    The relationship is experimentally defined between the superconducting behavior of Ba2YCu3O(7-delta) (BYCO) films and their structural characteristics. The BYCO films are grown on LaAlO3 100-plane by coevaporating BaF2, Y, and Cu followed by ex situ annealing, and the crystalline quality is tested by Rutherford backscattering ion channeling. SEM is employed to study film morphology, and several techniques are used to measure the transition temperature (Tc), critical current density (Jc), and the penetration length. It is found that point defects and dislocations decrease as the high-temperature stage (Ta) increases; crevices, pinholes, and microcracks are also noted which are related to specific values of Tc, Ta, and penetration length. The results of the present experiments indicate that the material properties of superconducting materials should be examined closely to distinguish between pure superconducting behavior and characteristics related to material structure. 21 refs

  6. Critical endline of the finite temperature phase transition for 2+1 flavor QCD away from the SU(3-flavor symmetric point

    Directory of Open Access Journals (Sweden)

    Nakamura Yoshifumi

    2018-01-01

    Full Text Available We investigate the critical end line of the finite temperature phase transition of QCD away from the SU(3-flavor symmetric point at zero chemical potential. We employ the renormalization-group improved Iwasaki gauge action and non-perturbatively O(a- improved Wilson-clover fermion action. The critical end line is determined by using the intersection point of kurtosis, employing the multi-parameter, multi-ensemble reweighting method at the temporal size NT = 6 and lattice spacing as low as a ≈0.19 fm.

  7. Solvable model of quantum phase transitions and the symbolic-manipulation-based study of its multiply degenerate exceptional points and of their unfolding

    Czech Academy of Sciences Publication Activity Database

    Znojil, Miloslav

    2013-01-01

    Roč. 336, SEP (2013), s. 98-111 ISSN 0003-4916 R&D Projects: GA ČR GAP203/11/1433 Institutional support: RVO:61389005 Keywords : Non-Hermitian quantum Hamiltonian * exceptional point * phase transition * exactly solvable model Subject RIV: BE - Theoretical Physics Impact factor: 3.065, year: 2013 http://www.sciencedirect.com/science/article/pii/S0003491613001267

  8. High field superconducting magnets

    Science.gov (United States)

    Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

    2011-01-01

    A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

  9. Understanding and application of superconducting materials

    International Nuclear Information System (INIS)

    Moon, Byeong Mu; Lee, Chun Heung

    1997-02-01

    This book deals with superconducting materials, which contains from basic theory to application of superconducting materials. The contents of this book are mystery of superconducting materials, properties of superconducting materials, thermodynamics of superconducting materials, theoretical background of superconducting materials, tunnelling and quantum interference, classification and properties of superconducting materials, high temperature superconducting materials, production and analysis of superconducting materials and application of superconducting materials.

  10. Characterization of the insulator barrier and the superconducting transition temperature in GdBa2Cu3O7−δ/BaTiO3 bilayers for application in tunnel junctions

    International Nuclear Information System (INIS)

    Navarro, H.; Sirena, M.; Haberkorn, N.; Yang, Ilkyu; Kim, Jeehoon

    2015-01-01

    The optimization of the superconducting properties in a bottom electrode and the quality of an insulator barrier are the first steps in the development of superconductor/insulator/superconductor tunnel junctions. Here, we study the quality of a BaTiO 3 tunnel barrier deposited on a 16 nm thick GdBa 2 Cu 3 O 7−δ thin film by using conductive atomic force microscopy. We find that the tunnel current is systematically reduced (for equal applied voltage) by increasing the BaTiO 3 barrier thickness between 1.6 and 4 nm. The BaTiO 3 layers present an energy barrier of ≈1.2 eV and an attenuation length of 0.35–0.5 nm (depending on the applied voltage). The GdBa 2 Cu 3 O 7−δ electrode is totally covered by a BaTiO 3 thickness above 3 nm. The presence of ferroelectricity was verified by piezoresponse force microscopy for a 4 nm thick BaTiO 3 top layer. The superconducting transition temperature of the bilayers is systematically suppressed by increasing the BaTiO 3 thickness. This fact can be associated with stress at the interface and a reduction of the orthorhombicity of the GdBa 2 Cu 3 O 7−δ . The reduction in the orthorhombicity is expected by considering the interface mismatch and it can also be affected by reduced oxygen stoichiometry (poor oxygen diffusion across the BaTiO 3 barrier)

  11. Characterization of the insulator barrier and the superconducting transition temperature in GdBa{sub 2}Cu{sub 3}O{sub 7−δ}/BaTiO{sub 3} bilayers for application in tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Navarro, H., E-mail: henrynavarro@cab.cnea.gov.ar; Sirena, M.; Haberkorn, N. [Instituto Balseiro, Universidad Nacional de Cuyo and CNEA, 8400 Bariloche (Argentina); Centro Atómico Bariloche, Comisión Nacional de Energía Atómica. Av. Bustillo 9500, 8400 San Carlos de Bariloche (Argentina); Yang, Ilkyu [Department of Physics, Pohang University of Science and Technology, Pohang (Korea, Republic of); Kim, Jeehoon [Department of Physics, Pohang University of Science and Technology, Pohang (Korea, Republic of); CALDES, Institute for Basic Science, Pohang (Korea, Republic of)

    2015-07-28

    The optimization of the superconducting properties in a bottom electrode and the quality of an insulator barrier are the first steps in the development of superconductor/insulator/superconductor tunnel junctions. Here, we study the quality of a BaTiO{sub 3} tunnel barrier deposited on a 16 nm thick GdBa{sub 2}Cu{sub 3}O{sub 7−δ} thin film by using conductive atomic force microscopy. We find that the tunnel current is systematically reduced (for equal applied voltage) by increasing the BaTiO{sub 3} barrier thickness between 1.6 and 4 nm. The BaTiO{sub 3} layers present an energy barrier of ≈1.2 eV and an attenuation length of 0.35–0.5 nm (depending on the applied voltage). The GdBa{sub 2}Cu{sub 3}O{sub 7−δ} electrode is totally covered by a BaTiO{sub 3} thickness above 3 nm. The presence of ferroelectricity was verified by piezoresponse force microscopy for a 4 nm thick BaTiO{sub 3} top layer. The superconducting transition temperature of the bilayers is systematically suppressed by increasing the BaTiO{sub 3} thickness. This fact can be associated with stress at the interface and a reduction of the orthorhombicity of the GdBa{sub 2}Cu{sub 3}O{sub 7−δ}. The reduction in the orthorhombicity is expected by considering the interface mismatch and it can also be affected by reduced oxygen stoichiometry (poor oxygen diffusion across the BaTiO{sub 3} barrier)

  12. Points of Transition: Understanding the Constructed Identities of L2 Learners/Users across Time and Space

    Science.gov (United States)

    Adawu, Anthony; Martin-Beltran, Melinda

    2012-01-01

    Using sociocultural and poststructuralist theoretical lenses, this study examines the narrative construction of language-learner identity across time and space. We applied cross-narrative methodologies to analyze language-learning autobiographies and interview data from three English users who had recently transitioned to a U.S. context for…

  13. Curriculum on the European Policy Agenda: Global Transitions and Learning Outcomes from Transnational and National Points of View

    Science.gov (United States)

    Sivesind, Kirsten; Wahlström, Ninni

    2016-01-01

    This special issue examines curricula and their histories as they have evolved throughout the 21st century as part of transnational and national education policies. With a specific focus on the policy transitions that are taking place in Europe, the articles demonstrate how curriculum making processes move in different directions, following their…

  14. Disentangling phase transitions and critical points in the proton–neutron interacting boson model by catastrophe theory

    Directory of Open Access Journals (Sweden)

    J.E. García-Ramos

    2014-09-01

    Full Text Available We introduce the basic concepts of catastrophe theory needed to derive analytically the phase diagram of the proton–neutron interacting boson model (IBM-2. Previous studies [1–3] were based on numerical solutions. We here explain the whole IBM-2 phase diagram including the precise order of the phase transitions in terms of the cusp catastrophe.

  15. Magnetic phase transitions in ferrimagnetic DyFe.sub.5./sub.Al.sub.7./sub. near the compensation point

    Czech Academy of Sciences Publication Activity Database

    Mushnikov, N. V.; Rozenfeld, E.V.; Gorbunov, Denis; Andreev, Alexander V.

    2014-01-01

    Roč. 115, č. 3 (2014), s. 257-267 ISSN 0031-918X R&D Projects: GA ČR GAP204/12/0150 Institutional support: RVO:68378271 Keywords : rare- earth intermetallic compounds * ferrimagnetism * compensation temperature * magnetic anisotropy * magnetic phase transition Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.761, year: 2014

  16. UNK superconducting dipole development

    International Nuclear Information System (INIS)

    Ageev, A.I.; Andreev, N.I.; Balbekov, V.I.

    1987-01-01

    For choozing the design of superconducting dipoles (SCD) for the IHEP UNK the test results for SCD with warm and cold iron are given. The main parameters of dipoles are presented. The SCD designs are described. At present works on SP magnet simulation for UNK are carried out in two directions. Tests are conducted on a rig with a chain of series dipoles with a warm magnetic screen. The purpose of these tests is to study heat exchange and hydraulics in magnets, energy and helium evacuation in emergency magnet transition into normal conditions, simulation of possible cooling and heating schemes. Another direction involves production of short and full-scale dipole models with cold iron and their testing on rigs. The final choice of the dipole design for commercial production is planned for 1987

  17. A study on metastable superconducting magnets

    International Nuclear Information System (INIS)

    Koyama, Kenichi

    1976-01-01

    It is important to construct superconducting magnets as cheap as possible. One of the methods to achieve such a purpose is to save the superconducting material and operate the magnets at a high current density. Therefore it is useful to investigate the requirements for the operation of metastable superconducting magnets which can work at a current higher than the recovery current. Using the theory of flux jump, we introduce a ''stable current'' below which no flux jump can occur. On a rough approximation, it is given by I sub(s) =√A P sub(i) H sub(e) T sub(o) f(x)/rho where A : cross-section of the composite conductor. P sub(i) : total perimeter of all the superconducting cores. h sub(e) : effective heat transfer coefficient to the liquid helium through the stabilizer. T sub(o) : a characteristic temperature of the superconducting cores. f(x) : a characteristic function for the relative core radius x. rho : effective resistivity of the composite. Then it is shown that superconducting magnets can operate without unexpected normal transitions in the region enclosed by the two curves of I sub(s) and I sub(c). Next, we discuss the characteristics of our saddle shaped superconducting magnet for an one-KW MHD generator. We found that, 1) the magnet does safely operate in the metastable state; 2) the characteristics of the magnet are consistent with our theoretical results. (auth.)

  18. ac superconducting articles

    International Nuclear Information System (INIS)

    Meyerhoff, R.W.

    1977-01-01

    A noval ac superconducting cable is described. It consists of a composite structure having a superconducting surface along with a high thermally conductive material wherein the superconducting surface has the desired physical properties, geometrical shape and surface finish produced by the steps of depositing a superconducting layer upon a substrate having a predetermined surface finish and shape which conforms to that of the desired superconducting article, depositing a supporting layer of material on the superconducting layer and removing the substrate, the surface of the superconductor being a replica of the substrate surface

  19. The simultaneous measurements of core and outer core density fluctuations in L-H transition using CO2 laser collective scattering diagnostic in the EAST superconducting tokamak

    International Nuclear Information System (INIS)

    Cao, G.M.; Li, Y.D.; Zhang, X.D.; Sun, P.J.; Hu, L.Q.; Li, J.G.; Wu, G.J.

    2013-01-01

    The H-mode is the projected basic operation scenario for the ITER tokamak. The turbulence de-correlation by the synergistic effect of zonal flow and equilibrium ExB flow shear is believed to be the reason for L-H transition, however, the detailed physical mechanism has not been identified so far. Tangential multi-channel CO 2 laser collective scattering diagnostic system (mainly k r measurement) was first installed to investigate electron density fluctuations on EAST tokamak. The measurements in a spontaneous dithering L-H transition show that in core plasma (0 < r/a < 0.5) the low-frequency fluctuations strengthen greatly before L-H transition; meanwhile in outer core plasma (0.2 < r/a < 1) the low-frequency fluctuations strengthen slightly. Bispectral analysis reveals that the coupling strength between low- and high-frequency fluctuations in both core and outer core plasma strengthens greatly before the transition, but the latter is greater than the former. The results indicate that the low-frequency fluctuations of the core and outer core plasma play active, but different, roles in the spontaneous L-H transition. (author)

  20. Abstracts of The First Polish-US Conference on High Temperature Superconductivity

    International Nuclear Information System (INIS)

    1995-01-01

    The current problems in high temperature superconductivity science have been presented at the conference. The two main topics have been mostly represented: superconducting material research and fundamental physical research on superconductivity mechanisms. Superconducting material preparation, chemical composition, magnetic and electrical properties of different type of high temperature superconductors, material structure and its influence on superconducting properties and related problems were included in the first of the general topics. In the range of second general topic of the two listed above, many theoretical models being applied for explanation of superconductivity mechanism in different systems up and below transition temperature were presented

  1. Phase-glass scaling near the coherence transition in granular HoBa{sub 2}Cu{sub 3}O{sub 7-{delta}} superconducting thin films

    Energy Technology Data Exchange (ETDEWEB)

    Roa-Rojas, J.; Landinez Tellez, D.A. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, A. A. 14490, Bogota DC (Colombia); Prieto, P. [Grupo de Peliculas Delgadas, Departamento de Fisica, Universidad del Valle, A. A. 25360, Cali (Colombia)

    2005-07-01

    Systematic measurements of electrical magnetoconductivity near the coherence transition of granular HoBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films are reported. Experiments performed in magnetic fields ranging from 0 to 2500 Oe reveal that close to the coherence transition temperature T{sub c0}(H), the correlation length scales as a power law of temperature with a thermal-dependent critical exponent, {nu}. In low external fields the corresponding value of {nu} is consistent with the two-dimensional phase-glass model, which is in the same dynamical universality class of the so-called vortex-glass model. At applied fields H > 1000 Oe, the vortex dynamics becomes stronger and the coherence transition is not observed. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    Science.gov (United States)

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

    2015-09-01

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

  3. Quasiparticles in the superconducting state of high-Tc metals

    International Nuclear Information System (INIS)

    Amusia, M.Ya.; Shaginyan, V.R.

    2003-01-01

    The behavior of quasiparticles in the superconducting state of high-T c metals within the framework of the theory of superconducting state based on the fermion condensation quantum phase transition is considered. It is shown that the behavior coincides with the behavior of Bogoliubov quasiparticles, whereas the maximum value of the superconducting gap and other exotic properties are determined by the presence of the fermion condensate. If at low temperatures the normal state is recovered by the application of a magnetic field suppressing the superconductivity, the induced state can be viewed as Landau-Fermi liquid. These observations are in good agreement with recent experimental facts [ru

  4. Superconducting magnetic energy storage, possibilities and limitations

    International Nuclear Information System (INIS)

    Bace, M.; Knapp, V.

    1981-01-01

    Energy storage is of great importance for the exploitation of new energy sources as well as for the better utilisation of conventional ones. Several proposals in recent years have suggested that superconducting magnets could be used as energy storage in large electricity networks. It is a purpose of this note to point out that the requirements which have to be met by energy storage in a large electricity network place serious limitation on the possible use of superconducting energy storage. (author)

  5. Strain effects on point defects and chain-oxygen order-disorder transition in 123 cuprate compounds

    International Nuclear Information System (INIS)

    Su Haibin; Welch, David O.; Wong-Ng, Winnie

    2004-01-01

    The energetics of Schottky defects in 123 cuprate superconductor series RBa 2 Cu 3 O 7 (where R=lanthandies) and YA 2 Cu 3 O 7 (A=alkali earths), were found to have unusual relations if one considers only the volumetric strain. Our calculations reveal the effect of nonuniform changes of interatomic distances within the R-123 structures, introduced by doping homovalent elements, on the Schottky defect formation energy. The energy of formation of Frenkel pair defects, which is an elementary disordering event, in 123 compounds can be substantially altered under both stress and chemical doping. Scaling the oxygen-oxygen short-range repulsive parameter using the calculated formation energy of Frenkel pair defects, the transition temperature between orthorhombic and tetragonal phases is computed by quasichemical approximations (QCA's). The theoretical results illustrate the same trend as the experimental measurements in that the larger the ionic radius of R, the lower the orthorhombic/tetragonal phase transition temperature. This study provides strong evidence of the strain effects on order-disorder transition due to oxygens in the CuO chain sites

  6. Transition times between the extremum points of the current–voltage characteristic of a resonant tunneling diode with hysteresis

    Energy Technology Data Exchange (ETDEWEB)

    Grishakov, K. S., E-mail: ksgrishakov@yahoo.com; Elesin, V. F. [National Research Nuclear University “MEPhI” (Russian Federation)

    2016-08-15

    A numerical solution to the problem of transient processes in a resonant tunneling diode featuring a current–voltage characteristic with hysteresis is found for the first time in the context of a coherent model (based on the coupled Schrödinger and Poisson equations) taking into account the Fermi distribution of electrons. The transitions from the high-current to the low-current state and vice versa, which result from the existence of hysteresis and are of great practical importance for ultrafast switches based on resonant tunneling diodes, are studied in detail. It is shown that the transition times for such processes initiated by the application of a small voltage can significantly exceed the characteristic time ℏ/Γ (where G is the width of the resonance level). It is established for the first time that the transition time can be reduced and made as short as the characteristic time ℏ/Γ by applying a sufficiently high voltage. For the parameters of the resonant-tunnelingdiode structure considered in this study, the required voltage is about 0.01 V.

  7. Phase transition and ductile behavior of IrxOs1-xN alloys from theoretical point of view

    Science.gov (United States)

    Sarwan, Madhu; Singh, Sadhna

    2018-05-01

    Present paper reports theoretical investigation of less explored nitrides of Iridium and Osmium using semi-empirical model with charge transfer effect (CTE). This work indicates the presence of structural phase transition in these nitrides from zinc-blend (B3) to rock-salt (B1) structure on application of pressure on them. Transitions occurred at 71 GPa and 86 GPa, with sudden drops in volume of 9.54% and 8.35% in IrN and OsN. The effect of pressure on elastic properties for B3-IrN and B3-OsN is investigated for the first time. On the basis of mechanical properties, it is observed that both compounds are ductile in nature. The present study is extended to investigate transition metal alloy IrxOs1-xN via Vegard's law. To widen the applicability of our model and to explore this alloy we report structural, elastic, mechanical and thermophysical properties. The effect of pressure on Debye temperature with different concentration (x = 0, 0.25, 0.5, 0.75, 1) have also been analyzed. The results are in general in good agreement with available theoretical results.

  8. Pairing and superconductivity from weak to strong coupling in the attractive Hubbard model

    International Nuclear Information System (INIS)

    Toschi, A; Barone, P; Capone, M; Castellani, C

    2005-01-01

    The finite-temperature phase diagram of the attractive Hubbard model is studied by means of the dynamical mean-field theory. We first consider the normal phase of the model by explicitly frustrating the superconducting ordering. In this case, we obtain a first-order pairing transition between a metallic phase and a paired phase formed by strongly coupled incoherent pairs. The transition line ends in a finite temperature critical point, but a crossover between two qualitatively different solutions still occurs at higher temperature. Comparing the superconducting- and the normal-phase solutions, we find that the superconducting instability always occurs before the pairing transition in the normal phase, i.e. T c > T pairing . Nevertheless, the high-temperature phase diagram at T > T c is still characterized by a crossover from a metallic phase to a preformed pair phase. We characterize this crossover by computing different observables that can be used to identify the pseudogap region, like the spin susceptibility, the specific heat and the single-particle spectral function

  9. Transition Processes in Superconducting Magnetic Systems; ПЕРЕХОДНЫЕ ПРОЦЕССЫ В СВЕРХПРОВОДЯЩИХ МАГНИТНЫХ СИСТЕМАХ

    Energy Technology Data Exchange (ETDEWEB)

    Sychev, V. V.; Zenkevich, V. B.; Andrianov, V. V. [Nauchno-Issledovatel' skij Institut Vysokih Temperatur, Moskva, SSSR (Russian Federation)

    1966-12-15

    The prospects for using MHD energy conversion depend in many ways on the feasibility of superconducting magnetic systems. The construction of large, efficient superconducting magnets requires in its turn detailed information about the phenomena occurring in the superconducting windings. The properties of superconducting windings are determined largely by the characteristic features of magnetic field penetration into the volume of the superconductor and by the processes associated with the transition of a part of the windings to the normal state. Accordingly, the programme for the development of a superconducting magnetic system for MHD generation includes investigations of these processes, in which the properties of superconducting windings are brought out most clearly. The experiments were carried out with a small solenoid. The results show that the transition of the superconducting windings to the normal state follows certain patterns. The authors also investigated processes associated with current variations in a superconducting solenoid; for example, they determined experimentally the relationship between the interlinkage of electric and magnetic circuits in the solenoid and the current, the residual interlinkage, the relationship between inductance and current, and the losses when the magnetic polarity of the solenoid is reversed, etc. They also consider the possibility of a theoretical generalization of their results. (author) [Russian] Perspektivnost' magnitogidrodinamicheskogo metoda preobrazovanija jenergii vo mnogom svjazana s vozmozhnost'ju ispol'zovanija sverhprovodjashhej magnitnoj sistemy. Dlja sozdanija bol'shih, jeffektivno rabotajushhih sverhprovodjashhih magnitov neobhodima v svoju ochered' detal'naja informacija o javlenijah, imejushhih mesto v sverhprovodjashhej obmotke. Specifika sverhprovodjashhej obmotki v znachitel'noj mere opredeljaetsja harakternymi osobennostjami proniknovenija magnitnogo polja v ob{sup e}m sverhprovodnika, a takzhe

  10. Superorganismality and caste differentiation as points of no return: how the major evolutionary transitions were lost in translation.

    Science.gov (United States)

    Boomsma, Jacobus J; Gawne, Richard

    2018-02-01

    More than a century ago, William Morton Wheeler proposed that social insect colonies can be regarded as superorganisms when they have morphologically differentiated reproductive and nursing castes that are analogous to the metazoan germ-line and soma. Following the rise of sociobiology in the 1970s, Wheeler's insights were largely neglected, and we were left with multiple new superorganism concepts that are mutually inconsistent and uninformative on how superorganismality originated. These difficulties can be traced to the broadened sociobiological concept of eusociality, which denies that physical queen-worker caste differentiation is a universal hallmark of superorganismal colonies. Unlike early evolutionary naturalists and geneticists such as Weismann, Huxley, Fisher and Haldane, who set out to explain the acquisition of an unmated worker caste, the goal of sociobiology was to understand the evolution of eusociality, a broad-brush convenience category that covers most forms of cooperative breeding. By lumping a diverse spectrum of social systems into a single category, and drawing attention away from the evolution of distinct quantifiable traits, the sociobiological tradition has impeded straightforward connections between inclusive fitness theory and the major evolutionary transitions paradigm for understanding irreversible shifts to higher organizational complexity. We evaluate the history by which these inconsistencies accumulated, develop a common-cause approach for understanding the origins of all major transitions in eukaryote hierarchical complexity, and use Hamilton's rule to argue that they are directly comparable. We show that only Wheeler's original definition of superorganismality can be unambiguously linked to irreversible evolutionary transitions from context-dependent reproductive altruism to unconditional differentiation of permanently unmated castes in the ants, corbiculate bees, vespine wasps and higher termites. We argue that strictly

  11. Analysis of mechanical characteristics of superconducting field coil for 17 MW class high temperature superconducting synchronous motor

    International Nuclear Information System (INIS)

    Kim, J. H.; Park, S. I.; Im, S. H.; Kim, H. M.

    2013-01-01

    Superconducting field coils using a high-temperature superconducting (HTS) wires with high current density generate high magnetic field of 2 to 5 [T] and electromagnetic force (Lorentz force) acting on the superconducting field coils also become a very strong from the point of view of a mechanical characteristics. Because mechanical stress caused by these powerful electromagnetic force is one of the factors which worsens the critical current performance and structural characteristics of HTS wire, the mechanical stress analysis should be performed when designing the superconducting field coils. In this paper, as part of structural design of superconducting field coils for 17 MW class superconducting ship propulsion motor, mechanical stress acting on the superconducting field coils was analyzed and structural safety was also determined by the coupling analysis system that is consists of commercial electromagnetic field analysis program and structural analysis program.

  12. WORKSHOPS: Radiofrequency superconductivity

    International Nuclear Information System (INIS)

    Anon.

    1992-01-01

    In the continual push towards higher energy particle beams, superconducting radiofrequency techniques now play a vital role, highlighted in the fifth workshop on radiofrequency superconductivity, held at DESY from 19 - 24 August 1991

  13. WORKSHOPS: Radiofrequency superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Anon.

    1992-01-15

    In the continual push towards higher energy particle beams, superconducting radiofrequency techniques now play a vital role, highlighted in the fifth workshop on radiofrequency superconductivity, held at DESY from 19 - 24 August 1991.

  14. Extrapolation of radiation thermometry scales for determining the transition temperature of metal-carbon points. Experiments with the Co-C

    Science.gov (United States)

    Battuello, M.; Girard, F.; Florio, M.

    2009-02-01

    Four independent radiation temperature scales approximating the ITS-90 at 900 nm, 950 nm and 1.6 µm have been realized from the indium point (429.7485 K) to the copper point (1357.77 K) which were used to derive by extrapolation the transition temperature T90(Co-C) of the cobalt-carbon eutectic fixed point. An INRIM cell was investigated and an average value T90(Co-C) = 1597.20 K was found with the four values lying within 0.25 K. Alternatively, thermodynamic approximated scales were realized by assigning to the fixed points the best presently available thermodynamic values and deriving T(Co-C). An average value of 1597.27 K was found (four values lying within 0.25 K). The standard uncertainties associated with T90(Co-C) and T(Co-C) were 0.16 K and 0.17 K, respectively. INRIM determinations are compatible with recent thermodynamic determinations on three different cells (values lying between 1597.11 K and 1597.25 K) and with the result of a comparison on the same cell by an absolute radiation thermometer and an irradiance measurement with filter radiometers which give values of 1597.11 K and 1597.43 K, respectively (Anhalt et al 2006 Metrologia 43 S78-83). The INRIM approach allows the determination of both ITS-90 and thermodynamic temperature of a fixed point in a simple way and can provide valuable support to absolute radiometric methods in defining the transition temperature of new high-temperature fixed points.

  15. Structural phases arising from reconstructive and isostructural transitions in high-melting-point oxides under hydrostatic pressure: A first-principles study

    Science.gov (United States)

    Tian, Hao; Kuang, Xiao-Yu; Mao, Ai-Jie; Yang, Yurong; Xu, Changsong; Sayedaghaee, S. Omid; Bellaiche, L.

    2018-01-01

    High-melting-point oxides of chemical formula A B O3 with A =Ca , Sr, Ba and B =Zr , Hf are investigated as a function of hydrostatic pressure up to 200 GPa by combining first-principles calculations with a particle swarm optimization method. Ca- and Sr-based systems: (1) first undergo a reconstructive phase transition from a perovskite state to a novel structure that belongs to the post-post-perovskite family and (2) then experience an isostructural transition to a second, also new post-post-perovskite state at higher pressures, via the sudden formation of a specific out-of-plane B -O bond. In contrast, the studied Ba compounds evolve from a perovskite phase to a third novel post-post-perovskite structure via another reconstructive phase transition. The original characteristics of these three different post-post-perovskite states are emphasized. Unusual electronic properties, including significant piezochromic effects and an insulator-metal transition, are also reported and explained.

  16. The Transition in East Germany: When Is a Ten-Point Fall in the Gender Wage Gap Bad News?

    OpenAIRE

    Jennifer Hunt

    2002-01-01

    Since monetary union with western Germany on 1 July 1990, eastern female monthly wages have risen by 10 percentage points relative to male wages, but female employment has fallen 5 percentage points more than male employment. Using the German Socio-Economic Panel to study the years 1990-1994, I show that along with age, the wage of a worker in 1990 is the most important determinant of the hazard rate from employment. Differences in mean 1990 wages explain more than half of the gender gap in t...

  17. Tailoring Superconductivity with Quantum Dislocations.

    Science.gov (United States)

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

    2017-08-09

    Despite the established knowledge that crystal dislocations can affect a material's superconducting properties, the exact mechanism of the electron-dislocation interaction in a dislocated superconductor has long been missing. Being a type of defect, dislocations are expected to decrease a material's superconducting transition temperature (T c ) by breaking the coherence. Yet experimentally, even in isotropic type I superconductors, dislocations can either decrease, increase, or have little influence on T c . These experimental findings have yet to be understood. Although the anisotropic pairing in dirty superconductors has explained impurity-induced T c reduction, no quantitative agreement has been reached in the case a dislocation given its complexity. In this study, by generalizing the one-dimensional quantized dislocation field to three dimensions, we reveal that there are indeed two distinct types of electron-dislocation interactions. Besides the usual electron-dislocation potential scattering, there is another interaction driving an effective attraction between electrons that is caused by dislons, which are quantized modes of a dislocation. The role of dislocations to superconductivity is thus clarified as the competition between the classical and quantum effects, showing excellent agreement with existing experimental data. In particular, the existence of both classical and quantum effects provides a plausible explanation for the illusive origin of dislocation-induced superconductivity in semiconducting PbS/PbTe superlattice nanostructures. A quantitative criterion has been derived, in which a dislocated superconductor with low elastic moduli and small electron effective mass and in a confined environment is inclined to enhance T c . This provides a new pathway for engineering a material's superconducting properties by using dislocations as an additional degree of freedom.

  18. MICROSTRUCTURE OF SUPERCONDUCTING MGB(2).

    Energy Technology Data Exchange (ETDEWEB)

    ZHU,Y.; LI,Q.; WU,L.; VOLKOV,V.; GU,G.; MOODENBAUGH,A.R.

    2001-07-12

    Recently, Akimitsu and co-workers [1] discovered superconductivity at 39 K in the intermetallic compound MgB{sub 2}. This discovery provides a new perspective on the mechanism for superconductivity. More specifically, it opens up possibilities for investigation of structure/properties in a new class of materials. With the exceptions of the cuprate and C{sub 60} families of compounds, MgB{sub 2} possesses the highest superconducting transition temperature T{sub c}. Its superconductivity appears to follow the BCS theory, apparently being mediated by electron-phonon coupling. The coherence length of MgB{sub 2} is reported to be longer than that of the cuprates [2]. In contrast to the cuprates, grain boundaries are strongly coupled and current density is determined by flux pinning [2,3]. Presently, samples of MgB{sub 2} commonly display inhomogeneity and porosity on the nanoscale, and are untextured. In spite of these obstacles, magnetization and transport measurements show that polycrystalline samples may carry large current densities circulating across many grains [3,4]. Very high values of critical current densities and critical fields have been recently observed in thin films [5,6]. These attributes suggest possible large scale and electronic applications. The underlying microstructure can be intriguing, both in terms of basic science and in applied areas. Subsequent to the discovery, many papers were published [1-13], most dealing with synthesis, physical properties, and theory. There have yet been few studies of microstructure and structural defects [11, 14]. A thorough understanding of practical superconducting properties can only be developed after an understanding of microstructure is gained. In this work we review transmission electron microscopy (TEM) studies of sintered MgB{sub 2} pellets [14]. Structural defects, including second phase particles, dislocations, stacking faults, and grain boundaries, are analyzed using electron diffraction, electron

  19. Proposed experimental test of the theory of hole superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Hirsch, J.E., E-mail: jhirsch@ucsd.edu

    2016-06-15

    Highlights: • The conventional theory of superconductivity predicts no charge flow when the normal-superconductor phase boundary moves. • The theory of hole superconductivity predicts flow and counterflow of charge. • An experiment to measure a voltage is proposed. • No voltage will be measured if the conventional theory is correct. • A voltage will be measured if the theory of hole superconductivity is correct. - Abstract: The theory of hole superconductivity predicts that in the reversible transition between normal and superconducting phases in the presence of a magnetic field there is charge flow in direction perpendicular to the normal-superconductor phase boundary. In contrast, the conventional BCS-London theory of superconductivity predicts no such charge flow. Here we discuss an experiment to test these predictions.

  20. Experimental Investigation of Magnetic Superconducting, and other Phase Transitions in Novel f-Electron Materials at Ultra-high Pressures Using Designer Diamond Anvils

    International Nuclear Information System (INIS)

    Maple, M. Brian

    2005-01-01

    Pressure is a powerful control parameter, owing to its ability to affect crystal and electronic structure without introducing defects, for the investigation of condensed matter systems. Some f-electron, heavy-fermion materials display interesting and novel behavior when exposed to pressures achievable with conventional experimental techniques; however, a growing number of condensed matter systems require extreme conditions such as ultrahigh pressures, high magnetic fields, and ultralow temperatures to sufficiently explore the important properties. To that end, we have been funded to develop an ultrahigh pressure facility at the University of California, San Diego (UCSD) in order to investigate superconductivity, magnetism, non-Fermi liquid behavior, and other phenomena under extreme conditions. Our goals for the second year of this grant were as follows: (a) perform electrical resistivity measurements on novel samples at a myriad of pressures using conventional piston-cylinder techniques, Bridgman anvil techniques, and diamond anvil cell technology; (b) install, commission, and operate an Oxford Kelvinox MX-100 dilution refrigerator for access to ultralow temperatures and high magnetic fields. (c) continue the development of diamond anvil cell (DAC) technology. During the past year, we have successfully installed the Oxford Kelvinox MX-100 dilution refrigerator and verified its operability down to 12 mK. We have begun an experimental program to systematically investigate the f-electron compound URu2Si2 under pressure and in the presence of magnetic fields. We have also continued our collaborative work with Sam Weir at Lawrence Livermore National Laboratory (LLNL) on Au4V and implemented a new corollary study on Au1-xVx using ultrahigh pressures. We have continued developing our DAC facility by designing and constructing an apparatus for in situ pressure measurement as well as designing high pressure cells. This report serves to highlight the progress we have made

  1. On the theory of twinning plane superconductivity

    International Nuclear Information System (INIS)

    Mishonov, T.M.

    1988-01-01

    The thermodynamic potential of the superconducting layer in the twinning plane (TP) vicinity for the type I superconductors is found. The corrections to the surface tension in powers of the Ginsburg-Landau parameter κ are obtained. The corresponding states law for the supercooling field for the type I twinning plane superconductivity (TPS) is obtained, as well as the critical field law for the type II TPS. A review of experimental and theoretical works on TPS and some similar systems is given. The conditions for the Berezinski-Kosterlitz-Thouless transition for the proximity effect are discussed, as well as the possible mechanisms for the conducting phase transition TPS in Nb and the pinning forces close to the twinning plane. The obtained order parameter distribution can be used for description of the superlattices from normal and superconducting metals as well. 6 figs., 44 refs

  2. Renormalization group approach to a p-wave superconducting model

    International Nuclear Information System (INIS)

    Continentino, Mucio A.; Deus, Fernanda; Caldas, Heron

    2014-01-01

    We present in this work an exact renormalization group (RG) treatment of a one-dimensional p-wave superconductor. The model proposed by Kitaev consists of a chain of spinless fermions with a p-wave gap. It is a paradigmatic model of great actual interest since it presents a weak pairing superconducting phase that has Majorana fermions at the ends of the chain. Those are predicted to be useful for quantum computation. The RG allows to obtain the phase diagram of the model and to study the quantum phase transition from the weak to the strong pairing phase. It yields the attractors of these phases and the critical exponents of the weak to strong pairing transition. We show that the weak pairing phase of the model is governed by a chaotic attractor being non-trivial from both its topological and RG properties. In the strong pairing phase the RG flow is towards a conventional strong coupling fixed point. Finally, we propose an alternative way for obtaining p-wave superconductivity in a one-dimensional system without spin–orbit interaction.

  3. Superconducting oxide thin films by ion beam sputtering

    International Nuclear Information System (INIS)

    Kobrin, P.H.; DeNatale, J.F.; Housley, R.M.; Flintoff, J.F.; Harker, A.B.

    1987-01-01

    Superconducting thin films of ternary copper oxides from the Y-Ba-Cu-O and La-Sr-Cu-O systems have been deposited by ion beam sputtering of ceramic targets. Crystallographic orientation of the polycrystalline films has been shown to vary with substrate identity, deposition temperature and annealing temperature. The onset of the superconductive transition occurs near 90K in the Y-Ba-Cu-O system. Fe impurities of < 0.2% have been found to inhibit the superconducting transition, probably by migrating to the grain boundaries

  4. Disappearance of superconductivity and critical resistance in thin indium films

    International Nuclear Information System (INIS)

    Okuma, Satoshi; Nishida, Nobuhiko

    1991-01-01

    In thin granular films composed of two-dimensionally coupled indium particles, we have studied influences of average particle sizes anti d on the superconducting transition. For films with anti d=280A and 224A, superconducting transition temperature stays almost constant with increasing the sheet resistance R n in the normal state, while for a film with anti d=140A, it decreases linearly with R n . This means that the system changes to a dirty superconductor by reducing anti d. With further increasing R n , superconductivity disappears when R n exceeds the value R c of order h/4e 2 , which seems to correlate with anti d. (orig.)

  5. X-points in the spectral emissivity of solid and liquid refractory transition metals measured by multichannel pyrometry. Discussion of the experimental method and physical interpretation

    International Nuclear Information System (INIS)

    Ronchi, C.; Hiernaut, J.P.; Hyland, G.J.

    1993-01-01

    The spectral emissivities of some refractory Transition metals (Hf, Mo, Nb, Re, V, W and Zr) have been measured from about 2500 K up to temperatures above the melting point T m . The experimental method adopted is based on multiwavelength pyrometric measurements, where the determination of the spectral emissivity is implicitly related to the evaluation of temperature through the radiation emission law and an assumed relationship between the spectral emissivity ε and the wavelength λ. Heating was produced with a pulsed laser in times of the order of 100 ms. A specially constructed pyrometer was used which enabled measurements at six different wavelengths to be carried out at time intervals of the order of 0.1 ms. A model for the evaluation of temperature and spectral emissivities has been developed and its limitations due to statistical and systematic errors are discussed. Our experiments confirm the existence of a unique wavelength, λ-x for each metal to which different ε λ -isotherms converge for λ x and from which they diverge for λ>λ x and at which ε λ is independent of T, and thus equal, in particular, to its value at T m , indicate that λ x is preserved through T m and reveal that at T m these metals are effectively 'grey'. Detailed theoretical investigations reveal that the occurrence of the λ x points is intimately connected with the particular T and λ dependences of the interband contribution to the imaginary part of the complex dielectric function entailed by specific features of the electronic band-structure of the Transition metals concerned. Finally, in connection with the 'grey' phenomenon at T m , it should be stressed that this is not found in the case of the Noble metals, although, like Transition metals, they exhibit λ x points, despite their quite different band-structures. (author). 56 refs., 8 figs., 5 tabs

  6. Josephson junction arrays and superconducting wire networks

    International Nuclear Information System (INIS)

    Lobb, C.J.

    1992-01-01

    Techniques used to fabricate integrated circuits make it possible to construct superconducting networks containing as many as 10 6 wires or Josephson junctions. Such networks undergo phase transitions from resistive high-temperature states to ordered low-resistance low-temperature states. The nature of the phase transition depends strongly on controllable parameters such as the strength of the superconductivity in each wire or junction and the external magnetic field. This paper will review the physics of these phase transitions, starting with the simplest zero-magnetic field case. This leads to a Kosterlitz-Thouless transition when the junctions or wires are weak, and a simple mean-field fransition when the junctions or wires are strong. Rich behavior, resulting from frustration, occurs in the presence of a magnetic field. (orig.)

  7. Superconductivity in Medicine

    Science.gov (United States)

    Alonso, Jose R.; Antaya, Timothy A.

    2012-01-01

    Superconductivity is playing an increasingly important role in advanced medical technologies. Compact superconducting cyclotrons are emerging as powerful tools for external beam therapy with protons and carbon ions, and offer advantages of cost and size reduction in isotope production as well. Superconducting magnets in isocentric gantries reduce their size and weight to practical proportions. In diagnostic imaging, superconducting magnets have been crucial for the successful clinical implementation of magnetic resonance imaging. This article introduces each of those areas and describes the role which superconductivity is playing in them.

  8. Superconductivity of high Tc Scientific revolution?

    International Nuclear Information System (INIS)

    Marquina, J.E.; Ridaura, R.; Gomez, R.; Marquina, V.; Alvarez, J.L.

    1997-01-01

    A short history of superconductivity, since its discovery by Bednorz and Muller to the development of new materials with high transition temperatures, is presented. Further evolvements are analyzed in terms of T.s. Kuhn conceptions expressed in his book. The Structure of Scientific Revolutions. (Author) 4 refs

  9. Morphological Transition in the Cellular Structure of Single Crystals of Nickel-Tungsten Alloys near the Congruent Melting Point

    International Nuclear Information System (INIS)

    Azhazha, V.M.; Ladygin, A.N.; Sverdlov, V.Ja.; Zhemanyuk, P.D.; Klochikhin, V.V.

    2005-01-01

    The structure and microhardness of single crystals of nickel-tungsten alloys containing 25-36 wt % W are investigated. The temperature gradient at the crystallization front and the velocity of the crystallization front are the variable parameters of directional crystallization. It is found that, when the velocity of the crystallization front is 4 mm/min, the morphology of the cellular structure of the single crystals grown from nickel-tungsten alloys changes from square cells to hexagonal cells at a tungsten content of greater than or equal to 31 wt %. As the velocity of the crystallization front increases to 10 mm/min, no morphological transition occurs. It is shown that impurities play an important role in the formation of a cellular structure with cells of different types

  10. Three-dimensional superconductivity and vortex glass transition in La1.87Y0.13CuO4

    International Nuclear Information System (INIS)

    Lee, Hyun-Sook; Kim, Heon-Jung; Kim, Hyun-Jung; Jung, Myung-Hwa; Jo, Younghun; Lee, Sung-Ik; Tsukada, Akio; Naito, Michio

    2006-01-01

    The angular dependence of the critical current density (J c (θ)) and the vortex glass transition temperature (T g (θ)) in La 1.87 Y 0.13 CuO 4 were measured at different fields and temperatures. Both J c (θ) and T g (θ) showed a strong angular variation, which is typical for anisotropic superconductors. The angular variation could be described by using the anisotropic three-dimensional Ginzburg-Landau theory. From our analysis, we were able to estimate the anisotropy ratio

  11. Half-metallic superconducting triplet spin multivalves

    Science.gov (United States)

    Alidoust, Mohammad; Halterman, Klaus

    2018-02-01

    We study spin switching effects in finite-size superconducting multivalve structures. We examine F1F2SF3 and F1F2SF3F4 hybrids where a singlet superconductor (S) layer is sandwiched among ferromagnet (F) layers with differing thicknesses and magnetization orientations. Our results reveal a considerable number of experimentally viable spin-valve configurations that lead to on-off switching of the superconducting state. For S widths on the order of the superconducting coherence length ξ0, noncollinear magnetization orientations in adjacent F layers with multiple spin axes leads to a rich variety of triplet spin-valve effects. Motivated by recent experiments, we focus on samples where the magnetizations in the F1 and F4 layers exist in a fully spin-polarized half-metallic phase, and calculate the superconducting transition temperature, spatially and energy resolved density of states, and the spin-singlet and spin-triplet superconducting correlations. Our findings demonstrate that superconductivity in these devices can be completely switched on or off over a wide range of magnetization misalignment angles due to the generation of equal-spin and opposite-spin triplet pairings.

  12. The present role of superconductivity in fusion

    International Nuclear Information System (INIS)

    Shimamoto, S.

    1986-01-01

    After completion of large fusion devices in the world, such as JT-60, JET and TFTR, high temperature plasma is proceeding to critical condition for fusion. The devices up to now use mainly conventional magnet. However, for the next generation machine which demonstrates fusion reaction, deuterium-tritium burning, superconducting magnet system is indispensable from view point of both net energy extraction and capacity limitation of power supply. In order to realize such a large and complicated system, a lot of development works is being carried out. This paper describes required parameters of superconducting magnet and helium refrigerator, the state of plasma condition and superconducting magnet. It is shown that the present technology of superconducting magnet is not so far from realization of fusion experimental reactor

  13. Superconductivity and the environment: a Roadmap

    International Nuclear Information System (INIS)

    Nishijima, Shigehiro; Eckroad, Steven; Marian, Adela; Choi, Kyeongdal; Kim, Woo Seok; Terai, Motoaki; Deng, Zigang; Zheng, Jun; Wang, Jiasu; Umemoto, Katsuya; Du, Jia; Keenan, Shane; Foley, Cathy P; Febvre, Pascal; Mukhanov, Oleg; Cooley, Lance D; Hassenzahl, William V; Izumi, Mitsuru

    2013-01-01

    disasters will be helped by future supercomputer technologies that support huge amounts of data and sophisticated modeling, and with the aid of superconductivity these systems might not require the energy of a large city. We present different sections on applications that could address (or are addressing) a range of environmental issues. The Roadmap covers water purification, power distribution and storage, low-environmental impact transport, environmental sensing (particularly for the removal of unexploded munitions), monitoring the Earth’s magnetic fields for earthquakes and major solar activity, and, finally, developing a petaflop supercomputer that only requires 3% of the current supercomputer power provision while being 50 times faster. Access to fresh water. With only 2.5% of the water on Earth being fresh and climate change modeling forecasting that many areas will become drier, the ability to recycle water and achieve compact water recycling systems for sewage or ground water treatment is critical. The first section (by Nishijima) points to the potential of superconducting magnetic separation to enable water recycling and reuse. Energy. The Equinox Summit held in Waterloo Canada 2011 (2011 Equinox Summit: Energy 2030 http://wgsi.org/publications-resources) identified electricity use as humanity’s largest contributor to greenhouse gas emissions. Our appetite for electricity is growing faster than for any other form of energy. The communiqué from the summit said ‘Transforming the ways we generate, distribute and store electricity is among the most pressing challenges facing society today…. If we want to stabilize CO 2 levels in our atmosphere at 550 parts per million, all of that growth needs to be met by non-carbon forms of energy’ (2011 Equinox Summit: Energy 2030 http://wgsi.org/publications-resources). Superconducting technologies can provide the energy efficiencies to achieve, in the European Union alone, 33–65% of the required reduction in

  14. Superconductivity and the environment: a Roadmap

    Science.gov (United States)

    Nishijima, Shigehiro; Eckroad, Steven; Marian, Adela; Choi, Kyeongdal; Kim, Woo Seok; Terai, Motoaki; Deng, Zigang; Zheng, Jun; Wang, Jiasu; Umemoto, Katsuya; Du, Jia; Febvre, Pascal; Keenan, Shane; Mukhanov, Oleg; Cooley, Lance D.; Foley, Cathy P.; Hassenzahl, William V.; Izumi, Mitsuru

    2013-11-01

    disasters will be helped by future supercomputer technologies that support huge amounts of data and sophisticated modeling, and with the aid of superconductivity these systems might not require the energy of a large city. We present different sections on applications that could address (or are addressing) a range of environmental issues. The Roadmap covers water purification, power distribution and storage, low-environmental impact transport, environmental sensing (particularly for the removal of unexploded munitions), monitoring the Earth’s magnetic fields for earthquakes and major solar activity, and, finally, developing a petaflop supercomputer that only requires 3% of the current supercomputer power provision while being 50 times faster. Access to fresh water. With only 2.5% of the water on Earth being fresh and climate change modeling forecasting that many areas will become drier, the ability to recycle water and achieve compact water recycling systems for sewage or ground water treatment is critical. The first section (by Nishijima) points to the potential of superconducting magnetic separation to enable water recycling and reuse. Energy. The Equinox Summit held in Waterloo Canada 2011 (2011 Equinox Summit: Energy 2030 http://wgsi.org/publications-resources) identified electricity use as humanity’s largest contributor to greenhouse gas emissions. Our appetite for electricity is growing faster than for any other form of energy. The communiqué from the summit said ‘Transforming the ways we generate, distribute and store electricity is among the most pressing challenges facing society today…. If we want to stabilize CO2 levels in our atmosphere at 550 parts per million, all of that growth needs to be met by non-carbon forms of energy’ (2011 Equinox Summit: Energy 2030 http://wgsi.org/publications-resources). Superconducting technologies can provide the energy efficiencies to achieve, in the European Union alone, 33-65% of the required reduction in greenhouse

  15. Routes to High-Temperature Superconductivity: A Lesson from FeSe/SrTiO3

    Science.gov (United States)

    Lee, Dung-Hai

    2018-03-01

    Raising the superconducting transition temperature to a point where applications are practical is one of the most important challenges in science. In this review, we aim at gaining insights on the Tc controlling factors for a particular high-temperature superconductor family - the FeSe-based superconductors. In particular, we discuss the mechanisms by which the Cooper pairing temperature is enhanced from ˜8 K in bulk FeSe to ˜80 K in the interface between an atomic layer of FeSe and SrTiO3. This includes the experimental hints and the theoretical simulation of the involved mechanisms. We end by applying these insights to suggest some possible high-temperature superconducting systems.

  16. High temperature spin-glass-like transition in La0.67Sr0.33MnO3 nanofibers near the Curie point.

    Science.gov (United States)

    Lu, Ruie; Yang, Sen; Li, Yitong; Chen, Kaiyun; Jiang, Yun; Fu, Bi; Zhang, Yin; Zhou, Chao; Xu, Minwei; Zhou, Xuan

    2017-06-28

    The glassy transition of superparamagnetic (SPM) (r glass-like (SGL) behavior near the Curie point (T C ), i.e., T 0 = 330 K, in La 0.67 Sr 0.33 MnO 3 (LSMO) nanofibers (NFs) composed of nanoparticles beyond the SPM size (r ≫ r 0 ), resulting in a significant increase of the glass transition temperature. This SGL transition near the T C of bulk LSMO can be explained to be the scenario of locally ordered clusters embedded in a disordered host, in which the assembly of nanoparticles has a magnetic core-shell model driven by surface spin glass. The presence of a surface spin glass of nanoparticles was proved by the Almeida-Thouless line δT f ∝ H 2/3 , exchange bias, and reduced saturation magnetization of the NF system. Composite dynamics were found - that is, both the SPM and the super-spin-glass (SSG) behavior are found in such an NF system. The bifurcation of the zero-field-cooled (ZFC) and field-cooled (FC) magnetization vs. temperature curves at the ZFC peak, and the flatness of FC magnetization involve SSG, while the frequency-dependent ac susceptibility anomaly follows the Vogel-Fulcher law that implies weak dipole interactions of the SPM model. This finding can help us to find a way to search for high temperature spin glass materials.

  17. From boiling point to glass transition temperature: transport coefficients in molecular liquids follow three-parameter scaling.

    Science.gov (United States)

    Schmidtke, B; Petzold, N; Kahlau, R; Hofmann, M; Rössler, E A

    2012-10-01

    The phenomenon of the glass transition is an unresolved problem in condensed matter physics. Its prominent feature, the super-Arrhenius temperature dependence of the transport coefficients, remains a challenge to be described over the full temperature range. For a series of molecular glass formers, we combined τ(T) collected from dielectric spectroscopy and dynamic light scattering covering a range 10(-12) s < τ(T) < 10(2) s. Describing the dynamics in terms of an activation energy E(T), we distinguish a high-temperature regime characterized by an Arrhenius law with a constant activation energy E(∞) and a low-temperature regime for which E(coop)(T) ≡ E(T)-E(∞) increases exponentially while cooling. A scaling is introduced, specifically E(coop)(T)/E(∞) [proportionality] exp[-λ(T/T(A)-1)], where λ is a fragility parameter and T(A) a reference temperature proportional to E(∞). In order to describe τ(T) still the attempt time τ(∞) has to be specified. Thus, a single interaction parameter E(∞) describing the high-temperature regime together with λ controls the temperature dependence of low-temperature cooperative dynamics.

  18. 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.

  19. Point Climat no. 14 'Financing the transition to a green economy: their word is their (green) bond?'

    International Nuclear Information System (INIS)

    Morel, Romain; Bordier, Cecile

    2012-01-01

    Among the publications of CDC Climat Research, 'Climate Briefs' presents, in a few pages, hot topics in climate change policy. This issue addresses the following points: Responding to climate change involves the implementation of initiatives that require significant up-front capital investment. At a time when bank lending is squeezed, green bonds offer an alternative financing for initiatives with an environmental goal. Lately, the Ile-de-France Region's issuance of environmentally and socially responsible bonds on March 20 2012 demonstrates that an increasing number of players are taking interest in this tool. But green bonds are not, however, the panacea to access to finance issues that mainly depend on the bond issuer's characteristics

  20. Superconducting Sphere in an External Magnetic Field Revisited

    Science.gov (United States)

    Sazonov, Sergey N.

    2013-01-01

    The purpose of this article is to give the intelligible procedure for undergraduate students to grasp proof of the fact that the magnetic field outside the hollow superconducting sphere (superconducting shell) coincides with the field of a point magnetic dipole both when an uniform external magnetic field is applied as when a ferromagnetic sphere…