WorldWideScience

Sample records for surface superconductivity effects

  1. Effective field theories for superconducting systems with multiple Fermi surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Braga, P.R., E-mail: pedro.rangel.braga@gmail.com [Departamento de Física Teórica, Instituto de Física, UERJ - Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20550-013 Maracanã, Rio de Janeiro (Brazil); Granado, D.R., E-mail: diegorochagrana@uerj.br [Departamento de Física Teórica, Instituto de Física, UERJ - Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20550-013 Maracanã, Rio de Janeiro (Brazil); Department of Physics and Astronomy, Ghent University, Krijgslaan 281-S9, 9000 Gent (Belgium); Guimaraes, M.S., E-mail: msguimaraes@uerj.br [Departamento de Física Teórica, Instituto de Física, UERJ - Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20550-013 Maracanã, Rio de Janeiro (Brazil); Wotzasek, C., E-mail: clovis@if.ufrj.br [Instituto de Física, Universidade Federal do Rio de Janeiro, 21941-972, Rio de Janeiro (Brazil)

    2016-11-15

    In this work we investigate the description of superconducting systems with multiple Fermi surfaces. For the case of one Fermi surface we re-obtain the result that the superconductor is more precisely described as a topological state of matter. Studying the case of more than one Fermi surface, we obtain the effective theory describing a time reversal symmetric topological superconductor. These results are obtained by employing a general procedure to construct effective low energy actions describing states of electromagnetic systems interacting with charges and defects. The procedure consists in taking into account the proliferation or dilution of these charges and defects and its consequences for the low energy description of the electromagnetic response of the system. We find that the main ingredient entering the low energy characterization of the system with more than one Fermi surface is a non-conservation of the canonical supercurrent triggered by particular vortex configurations.

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

    International Nuclear Information System (INIS)

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

    2016-01-01

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

  3. The effect of plasma etching on the surface topography of niobium superconducting radio frequency cavities

    Science.gov (United States)

    Radjenović, B.; Radmilović-Radjenović, M.

    2014-11-01

    In this letter the evolution of the surface topography of a niobium superconducting radio frequency cavity caused by different plasma etching modes (isotropic and anisotropic) is studied by the three-dimensional level set method. The initial rough surface is generated starting from an experimental power spectral density. The time dependence of the rms roughness is analyzed and the growth exponential factors β are determined for two etching modes (isotropic and anisotropic) assuming that isotropic etching is a much more effective mechanism of smoothing. The obtained simulation results could be useful for optimizing the parameters of the etching processes needed to obtain high quality niobium surfaces for superconducting radio frequency cavities.

  4. Microwave effective surface impedance of structures including a high-Tc superconducting film

    International Nuclear Information System (INIS)

    Hartemann, P.

    1992-01-01

    The microwave effective surface impedances of different stacks made of high-temperature superconducting films, dielectric materials and bulk normal metals were computed. The calculations were based on the two-fluid model of superconductors and the conventional transmission line theory. These effective impedances are compared to the calculated intrinsic surface impedances of the stacked superconducting films. The considered superconducting material has been the oxide YBa 2 Cu 3 O 7 epitaxially grown on crystalline substrates (MgO, LaAlO 3 , SrTiO 3 ), the film thickness ranging from a few nm to 1μm. Discrepancies between the effective surface resistances or reactances and the corresponding intrinsic values were determined at 10 GHz for non resonant or resonant structures. At resonance the surface resistance discrepancy exhibits a sharp peak which reaches 10 4 or more in relative value according to the geometry and the used materials. Obviously the effective surface reactance shows also huge variations about the resonance and may be negative. Moreover geometries allowing to obtain an effective resistance smaller than the film intrinsic value have been found. The effects of the resonance phenomenon on the electromagnetic wave reflectivity and reflection phase shift are investigated. Therefore the reported theoretical results demonstrate that the effective surface impedance of YBCO films with a thickness smaller than 500 nm can be very different from the intrinsic film impedance according to the structures. (Author). 3 refs., 10 figs., 2 tabs

  5. Meissner effect in superconducting microtraps

    OpenAIRE

    Cano, Daniel

    2009-01-01

    This thesis investigates the impact of the Meissner effect on magnetic microtraps for ultracold atoms near superconducting microstructures. This task has been accomplished both theoretically and experimentally. The Meissner effect distorts the magnetic fields near superconducting surfaces, thus altering the parameters of magnetic microtraps. Both computer simulations and experimental measurements demonstrate that the Meissner effect shortens the distance between the magnetic microtrap and the...

  6. Effect of non-uniform surface resistance on the quality factor of superconducting niobium cavity

    Science.gov (United States)

    Tan, Weiwei; Lu, Xiangyang; Yang, Ziqin; Zhao, Jifei; Yang, Deyu; Yang, Yujia

    2016-08-01

    The formula Rs = G /Q0 is commonly used in the calculation of the surface resistance of radio frequency niobium superconducting cavities. The applying of such equation is under the assumption that surface resistance is consistent over the cavity. However, the distribution of the magnetic field varies over the cavity. The magnetic field in the equator is much higher than that in the iris. According to Thermal Feedback Theory, it leads non-uniform distribution of the density of heat flux, which results in a different temperature distribution along the cavity inter surface. The BCS surface resistance, which depends largely on the temperature, is different in each local inner surface. In this paper, the effect of surface non-uniform resistance on the quality factor has been studied, through the calculation of Q0 in the original definition of it. The results show that it is necessary to consider the non-uniform distribution of magnetic field when the accelerating field is above 20 MV/m for TESLA cavities. Also, the effect of inhomogeneity of residual resistance on the quality factor is discussed. Its distribution barely affects the quality factor.

  7. Meissner effect in superconducting microtraps

    International Nuclear Information System (INIS)

    Cano, Daniel

    2009-01-01

    This thesis investigates the impact of the Meissner effect on magnetic microtraps for ultracold atoms near superconducting microstructures. This task has been accomplished both theoretically and experimentally. The Meissner effect distorts the magnetic fields near superconducting surfaces, thus altering the parameters of magnetic microtraps. Both computer simulations and experimental measurements demonstrate that the Meissner effect shortens the distance between the magnetic microtrap and the superconducting surface, reduces the magnetic-field gradients and dramatically lowers the trap depth. A novel numerical method for calculating magnetic fields in atom chips with superconducting microstructures has been developed. This numerical method overcomes the geometrical limitations of other calculation techniques and can solve superconducting microstructures of arbitrary geometry. The numerical method has been used to calculate the parameters of magnetic microtraps in computer-simulated chips containing thin-film wires. Simulations were carried out for both the superconducting and the normal-conducting state, and the differences between the two cases were analyzed. Computer simulations have been contrasted with experimental measurements. The experimental apparatus generates a magnetic microtrap for ultracold Rubidium atoms near a superconducting Niobium wire of circular cross section. The design and construction of the apparatus has met the challenge of integrating the techniques for producing atomic quantum gases with the techniques for cooling solid bodies to cryogenic temperatures. By monitoring the position of the atom cloud, one can observe how the Meissner effect influences the magnetic microtrap. (orig.)

  8. Meissner effect in superconducting microtraps

    Energy Technology Data Exchange (ETDEWEB)

    Cano, Daniel

    2009-04-30

    This thesis investigates the impact of the Meissner effect on magnetic microtraps for ultracold atoms near superconducting microstructures. This task has been accomplished both theoretically and experimentally. The Meissner effect distorts the magnetic fields near superconducting surfaces, thus altering the parameters of magnetic microtraps. Both computer simulations and experimental measurements demonstrate that the Meissner effect shortens the distance between the magnetic microtrap and the superconducting surface, reduces the magnetic-field gradients and dramatically lowers the trap depth. A novel numerical method for calculating magnetic fields in atom chips with superconducting microstructures has been developed. This numerical method overcomes the geometrical limitations of other calculation techniques and can solve superconducting microstructures of arbitrary geometry. The numerical method has been used to calculate the parameters of magnetic microtraps in computer-simulated chips containing thin-film wires. Simulations were carried out for both the superconducting and the normal-conducting state, and the differences between the two cases were analyzed. Computer simulations have been contrasted with experimental measurements. The experimental apparatus generates a magnetic microtrap for ultracold Rubidium atoms near a superconducting Niobium wire of circular cross section. The design and construction of the apparatus has met the challenge of integrating the techniques for producing atomic quantum gases with the techniques for cooling solid bodies to cryogenic temperatures. By monitoring the position of the atom cloud, one can observe how the Meissner effect influences the magnetic microtrap. (orig.)

  9. 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

  10. Last LEP superconducting module travels to surface

    CERN Multimedia

    Patrice Loïez

    2001-01-01

    The last superconducting module is raised from the Large Electron-Positron (LEP) collider tunnel, through the main shaft, to the surface. Superconducting modules were only used in the LEP-2 phase of the accelerator, from 1996 to 2000.

  11. Surface ferromagnetism and superconducting properties of nanocrystalline niobium nitride

    International Nuclear Information System (INIS)

    Shipra, R.; Kumar, Nitesh; Sundaresan, A.

    2013-01-01

    Nanocrystalline δ-NbN x samples have been synthesized by reacting NbCl 5 and urea at three different temperatures. A comparison of their structural, magnetic, transport and thermal properties is reported in the present study. The size of the particles and their agglomeration extent increase with increasing reaction temperature. The sample prepared at 900 °C showed the highest superconducting transition temperature (T c ) of 16.2 K with a transition width, ∼1.8 K, as obtained from the resistivity measurement on cold-pressed bars. Above T c , magnetization measurements revealed the presence of surface ferromagnetism which coexists with superconductivity below T c . Heat capacity measurements confirm superconductivity with strong electron–phonon coupling constant. The sample prepared at 800 °C shows a lower T c (10 K) while that prepared at 700 °C exhibit no superconductivity down to the lowest temperature (3 K) measured. - Highlights: ► Synthesis of δ-NbN nanoparticles by urea nitridation of NbCl 5 . ► Superconducting transition temperature (T c ) is 16.2 K. ► Superconductivity and surface ferromagnetism coexist in the nanoparticles. ► Effect of size and agglomeration on the physical properties of nanoparticles

  12. Topographic power spectral density study of the effect of surface treatment processes on niobium for superconducting radio frequency accelerator cavities

    Science.gov (United States)

    Xu, Chen; Tian, Hui; Reece, Charles E.; Kelley, Michael J.

    2012-04-01

    Microroughness is viewed as a critical issue for attaining optimum performance of superconducting radio frequency accelerator cavities. The principal surface smoothing methods are buffered chemical polish (BCP) and electropolish (EP). The resulting topography is characterized by atomic force microscopy (AFM). The power spectral density (PSD) of AFM data provides a more thorough description of the topography than a single-value roughness measurement. In this work, one dimensional average PSD functions derived from topography of BCP and EP with different controlled starting conditions and durations have been fitted with a combination of power law, K correlation, and shifted Gaussian models to extract characteristic parameters at different spatial harmonic scales. While the simplest characterizations of these data are not new, the systematic tracking of scale-specific roughness as a function of processing is new and offers feedback for tighter process prescriptions more knowledgably targeted at beneficial niobium topography for superconducting radio frequency applications.

  13. Topographic power spectral density study of the effect of surface treatment processes on niobium for superconducting radio frequency accelerator cavities

    International Nuclear Information System (INIS)

    Reece, Charles; Tian, Hui; Kelley, Michael; Xu, Chen

    2012-01-01

    Microroughness is viewed as a critical issue for attaining optimum performance of superconducting radio frequency accelerator cavities. The principal surface smoothing methods are buffered chemical polish (BCP) and electropolish (EP). The resulting topography is characterized by atomic force microscopy (AFM). The power spectral density (PSD) of AFM data provides a more thorough description of the topography than a single-value roughness measurement. In this work, one dimensional average PSD functions derived from topography of BCP and EP with different controlled starting conditions and durations have been fitted with a combination of power law, K correlation, and shifted Gaussian models to extract characteristic parameters at different spatial harmonic scales. While the simplest characterizations of these data are not new, the systematic tracking of scale-specific roughness as a function of processing is new and offers feedback for tighter process prescriptions more knowledgably targeted at beneficial niobium topography for superconducting radio frequency applications.

  14. 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

  15. ATLAS superconducting solenoid on-surface test

    CERN Document Server

    Ruber, Roger J M Y; Doi, Y; Haruyama, T; Haug, F; ten Kate, H H J; Kawai, M; Kondo, T; Kondo, Y; Makida, Y; Mizumaki, S; Olesen, G; Pavlov, O V; Pezzetti, M; Pirotte, O; Sbrissa, E; Yamamoto, A

    2005-01-01

    The ATLAS detector is presently under construction as one of the five LHC experiment set-ups. It relies on a sophisticated magnet system for the momentum measurement of charged particle tracks. The superconducting solenoid is at the center of the detector, the magnet system part nearest to the proton-proton collision point. It is designed for a 2 Tesla strong axial magnetic field at the collision point, while its thin-walled construction of 0.66 radiation lengths avoids degradation of energy measurements in the outer calorimeters. The solenoid and calorimeter have been integrated in their common cryostat, cooled down and tested on-surface. We review the on-surface set-up and report the performance test results.

  16. Topological Superconductivity on the Surface of Fe-Based Superconductors.

    Science.gov (United States)

    Xu, Gang; Lian, Biao; Tang, Peizhe; Qi, Xiao-Liang; Zhang, Shou-Cheng

    2016-07-22

    As one of the simplest systems for realizing Majorana fermions, the topological superconductor plays an important role in both condensed matter physics and quantum computations. Based on ab initio calculations and the analysis of an effective 8-band model with superconducting pairing, we demonstrate that the three-dimensional extended s-wave Fe-based superconductors such as Fe_{1+y}Se_{0.5}Te_{0.5} have a metallic topologically nontrivial band structure, and exhibit a normal-topological-normal superconductivity phase transition on the (001) surface by tuning the bulk carrier doping level. In the topological superconductivity (TSC) phase, a Majorana zero mode is trapped at the end of a magnetic vortex line. We further show that the surface TSC phase only exists up to a certain bulk pairing gap, and there is a normal-topological phase transition driven by the temperature, which has not been discussed before. These results pave an effective way to realize the TSC and Majorana fermions in a large class of superconductors.

  17. 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.

  18. 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.

  19. Aging of residual surface resistance of superconducting lead cavities

    DEFF Research Database (Denmark)

    Danielsen, M.

    1972-01-01

    Measurements of the residual surface resistance of superconducting lead cavities as a function of time during a period of a month showed an oscillating variation. An explanation of the ageing curves is proposed. ©1972 The American Institute of Physics......Measurements of the residual surface resistance of superconducting lead cavities as a function of time during a period of a month showed an oscillating variation. An explanation of the ageing curves is proposed. ©1972 The American Institute of Physics...

  20. Proximity induced ferromagnetism, superconductivity, and finite-size effects on the surface states of topological insulator nanostructures

    Science.gov (United States)

    Sengupta, Parijat; Kubis, Tillmann; Tan, Yaohua; Klimeck, Gerhard

    2015-01-01

    Bi2Te3 and Bi2Se3 are well known 3D-topological insulators (TI). Films made of these materials exhibit metal-like surface states with a Dirac dispersion and possess high mobility. The high mobility metal-like surface states can serve as building blocks for a variety of applications that involve tuning their dispersion relationship and opening a band gap. A band gap can be opened either by breaking time reversal symmetry, the proximity effect of a superconductor or ferromagnet or adjusting the dimensionality of the TI material. In this work, methods that can be employed to easily open a band gap for the TI surface states are assessed. Two approaches are described: (1) Coating the surface states with a ferromagnet which has a controllable magnetization axis. The magnetization strength of the ferromagnet is incorporated as an exchange interaction term in the Hamiltonian. (2) An s-wave superconductor, because of the proximity effect, when coupled to a 3D-TI opens a band gap on the surface. Finally, the hybridization of the surface Dirac cones can be controlled by reducing the thickness of the topological insulator film. It is shown that this alters the band gap significantly.

  1. Superconducting proximity effect in topological materials

    Science.gov (United States)

    Reeg, Christopher R.

    In recent years, there has been a renewed interest in the proximity effect due to its role in the realization of topological superconductivity. In this dissertation, we discuss several results that have been obtained in the field of proximity-induced superconductivity and relate the results to the search for Majorana fermions. First, we show that repulsive electron-electron interactions can induce a non-Majorana zero-energy bound state at the interface between a conventional superconductor and a normal metal. We show that this state is very sensitive to disorder, owing to its lack of topological protection. Second, we show that Rashba spin-orbit coupling, which is one of the key ingredients in engineering a topological superconductor, induces triplet pairing in the proximity effect. When the spin-orbit coupling is strong (i.e., when the characteristic energy scale for spin-orbit coupling is comparable to the Fermi energy), the induced singlet and triplet pairing amplitudes can be comparable in magnitude. Finally, we discuss how the size of the proximity-induced gap, which appears in a low-dimensional material coupled to a superconductor, evolves as the thickness of the (quasi-)low-dimensional material is increased. We show that the induced gap can be comparable to the bulk energy gap of the underlying superconductor in materials that are much thicker than the Fermi wavelength, even in the presence of an interfacial barrier and strong Fermi surface mismatch. This result has important experimental consequences for topological superconductivity, as a sizable gap is required to isolate and detect the Majorana modes.

  2. 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

  3. 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)

  4. Bulk and surface loss in superconducting transmon qubits

    International Nuclear Information System (INIS)

    Dial, Oliver; McClure, Douglas T; Poletto, Stefano; Keefe, G A; Rothwell, Mary Beth; Gambetta, Jay M; Abraham, David W; Chow, Jerry M; Steffen, Matthias

    2016-01-01

    Decoherence of superconducting transmon qubits is purported to be consistent with surface loss from two-level systems on the substrate surface. Here, we present a study of surface loss in transmon devices, explicitly designed to have varying sensitivities to different surface loss contributors. Our experiments also encompass two particular different sapphire substrates, which reveal the onset of a yet unknown additional loss mechanism outside of surface loss for one of the substrates. Tests across different wafers and devices demonstrate substantial variation, and we emphasize the importance of testing large numbers of devices for disentangling different sources of decoherence. (paper)

  5. Fermi surface of superconducting LaFePO determined by quantum oscillations

    Energy Technology Data Exchange (ETDEWEB)

    Mcdonald, Ross D [Los Alamos National Laboratory; Coldea, A I [BRISTOL UNIV; Fletcher, J D [BRISTOL UNIV; Carrington, A [BRISTOL UNIV; Bangura, A F [BRISTOL UNIV; Hussey, N E [BRISTOL UNIV; Analytis, J G [STANFORD UNIV; Chu, J-h [STANFORD UNIV; Erickson, A S [STANFORD UNIV; Fisher, I R [STANFORD UNIV

    2008-01-01

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

  6. 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

  7. Quantum Theory of Conducting Matter Superconductivity and Quantum Hall Effect

    CERN Document Server

    Fujita, Shigeji; Godoy, Salvador

    2009-01-01

    Explains major superconducting properties including zero resistance, Meissner effect, sharp phase change, flux quantization, excitation energy gap, and Josephson effects using quantum statistical mechanical calculations. This book covers the 2D superconductivity and the quantum Hall effects

  8. Investigations of the surface resistance of superconducting materials

    International Nuclear Information System (INIS)

    Junginger, Tobias

    2012-01-01

    In particle accelerators superconducting RF cavities are widely used to achieve high accelerating gradients and low losses. Power consumption is proportional to the surface resistance R S which depends on a number of external parameters, including frequency, temperature, magnetic and electric field. Presently, there is no widely accepted model describing the increase of R S with applied field. In the frame of this project the 400 MHz Quadrupole Resonator has been extended to 800 and 1200 MHz to study surface resistance and intrinsic critical RF magnetic field of superconducting samples over a wide parameter range, establishing it as a world-wide unique test facility for superconducting materials. Different samples were studied and it was shown that R S is mainly caused by the RF electric field in the case of strongly oxidized surfaces. This can be explained by interface tunnel exchange of electrons between the superconductor and localized states in adjacent oxides. For well prepared surfaces, however, the majority of the dissipation is caused by the magnetic field and R S factorizes into field and temperature dependent parts. These different loss mechanisms were correlated to surface topography of the samples and distribution of oxides by using ultrasonic force microscopy and X-ray photon spectroscopy.

  9. Geometrical resonance effects in thin superconducting films

    International Nuclear Information System (INIS)

    Nedellec, P.

    1977-01-01

    Electron tunneling density of states measurements on thick and clear superconducting films (S 1 ) backed by films in the normal or superconducting state (S 2 ) show geometrical resonance effects associated with the spatial variation of Δ(x), the pair potential, near the interface S 1 -S 2 . The present understanding of this so-called 'Tomasch effect' is described. The dispersion relation and the nature of excitations in the superconducting state are introduced. It is shown that the introduction of Green functions give a general description of the superconducting state. The notion of Andreev scattering at the S 1 -S 2 interface is presented and connect the geometrical resonance effects to interference process between excitations. The different physical parameters involved are defined and used in the discussion of some experimental results: the variation of the period in energy with the superconducting thickness is connected to the renormalized group velocity of excitations traveling perpendicular to the film. The role of the barrier potential at the interface on the Tomasch effect is described. The main results discussed are: the decrease of the amplitude of the Tomasch structures with energy is due to the loss of the mixed electron-hole character of the superconducting excitations far away from the Fermi level; the variation of the pair potential at the interface is directly related to the amplitude of the oscillations; the tunneling selectivity is an important parameter as the amplitude as well as the phase of the oscillations are modified depending on the value of the selectivity; the phase of the Tomasch oscillations is different for an abrupt change of Δ at the interface and for a smooth variation. An ambiguity arises due to the interplay between these parameters. Finally, some experiments, which illustrate clearly the predicted effects are described [fr

  10. 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

  11. Correlation effects in superconducting quantum dot systems

    Science.gov (United States)

    Pokorný, Vladislav; Žonda, Martin

    2018-05-01

    We study the effect of electron correlations on a system consisting of a single-level quantum dot with local Coulomb interaction attached to two superconducting leads. We use the single-impurity Anderson model with BCS superconducting baths to study the interplay between the proximity induced electron pairing and the local Coulomb interaction. We show how to solve the model using the continuous-time hybridization-expansion quantum Monte Carlo method. The results obtained for experimentally relevant parameters are compared with results of self-consistent second order perturbation theory as well as with the numerical renormalization group method.

  12. 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

  13. 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

  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. Researches on bake effect on RF superconducting cavities

    International Nuclear Information System (INIS)

    Hao Jiankui; Zhao Kui; Zhu Feng

    2005-01-01

    The Q-slope at high gradient affects the performance of superconducting cavity greatly. Recent researches show that low temperature (100-150) degree C heat treatment (bake) has positive effects on the performance of superconducting cavities. A lot of cavity tests are analyzed based on bake treatment. The average gradient E acc,max and E acc at Q=1 x 10 10 are increased by more than 3.5 MV/m. Q at E acc,max is increased and the Q-slope is improved. Analysis on bake temperature shows that higher bake temperature leads to higher Q value. Comparison of BCP and EP cavities shows that at least 60-80 μm EP is needed for BCP surface. More than 10-15 μm removal of the surface by BCP will degrade the performance of an EP cavity. Oxygen diffusion model is used to illustrate bake effect. (authors)

  16. 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

  17. 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

  18. Niobium thin film deposition studies on copper surfaces for superconducting radio frequency cavity applications

    Energy Technology Data Exchange (ETDEWEB)

    W. M. Roach, D. B. Beringer, J. R. Skuza, W. A. Oliver, C. Clavero, C. E. Reece, R. A. Lukaszew

    2012-06-01

    Thin film coatings have the potential to increase both the thermal efficiency and accelerating gradient in superconducting radio frequency accelerator cavities. However, before this potential can be realized, systematic studies on structure-property correlations in these thin films need to be carried out since the reduced geometry, combined with specific growth parameters, can modify the physical properties of the materials when compared to their bulk form. Here, we present our systematic studies of Nb thin films deposited onto Cu surfaces to clarify possible reasons for the limited success that this process exhibited in previous attempts. We compare these films with Nb grown on other surfaces. In particular, we study the crystal structure and surface morphology and their effect on superconducting properties, such as critical temperature and lower critical field. We found that higher deposition temperature leads to a sharper critical temperature transition, but also to increased roughness indicating that there are competing mechanisms that must be considered for further optimization.

  19. Niobium thin film deposition studies on copper surfaces for superconducting radio frequency cavity applications

    International Nuclear Information System (INIS)

    Roach, W.M.; Beringer, D.B.; Skuza, J.R.; Oliver, W.A.; Clavero, C.; Reece, C.E.; Lukaszew, R.A.

    2012-01-01

    Thin film coatings have the potential to increase both the thermal efficiency and accelerating gradient in superconducting radio frequency accelerator cavities. However, before this potential can be realized, systematic studies on structure-property correlations in these thin films need to be carried out since the reduced geometry, combined with specific growth parameters, can modify the physical properties of the materials when compared to their bulk form. Here, we present our systematic studies of Nb thin films deposited onto Cu surfaces to clarify possible reasons for the limited success that this process exhibited in previous attempts. We compare these films with Nb grown on other surfaces. In particular, we study the crystal structure and surface morphology and their effect on superconducting properties, such as critical temperature and lower critical field. We found that higher deposition temperature leads to a sharper critical temperature transition, but also to increased roughness indicating that there are competing mechanisms that must be considered for further optimization.

  20. 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

  1. Moessbauer effect in superconducting organosol of tin

    International Nuclear Information System (INIS)

    Dekhtyar, I.Ya.; Zhelibo, E.P.; Kushnir, B.G.; Nishchenko, M.M.; Pan, V.M.; Popov, A.G.; Khvorov, M.M.; AN Ukrainskoj SSR, Kiev. Inst. Kolloidnoj Khimii i Khimii Vody)

    1977-01-01

    Structure of disperse particles (approximately 1 μm) of tin organosols have been investigated by means of the Moessbauer effect. A considerable amount of oxides (up to 20%) in amorphous (SnO 2 ) or in metastable crystalline (SnO) states has been discovered. The observed properties of the Moessbauer spectrum of organosols are compared with measurements of their critical temperature. The effect of impurities and of other structural defects on the dynamic and superconducting properties of organosols is observed. Temperature broadening of lines and temperature variation of the Moessbauer effect value for the particle of different dimensions are in a qualitative agreement with the theory of the granular Moessbauer absorbers

  2. 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...

  3. Surface processing for bulk niobium superconducting radio frequency cavities

    Science.gov (United States)

    Kelly, M. P.; Reid, T.

    2017-04-01

    The majority of niobium cavities for superconducting particle accelerators continue to be fabricated from thin-walled (2-4 mm) polycrystalline niobium sheet and, as a final step, require material removal from the radio frequency (RF) surface in order to achieve performance needed for use as practical accelerator devices. More recently bulk niobium in the form of, single- or large-grain slices cut from an ingot has become a viable alternative for some cavity types. In both cases the so-called damaged layer must be chemically etched or electrochemically polished away. The methods for doing this date back at least four decades, however, vigorous empirical studies on real cavities and more fundamental studies on niobium samples at laboratories worldwide have led to seemingly modest improvements that, when taken together, constitute a substantial advance in the reproducibility for surface processing techniques and overall cavity performance. This article reviews the development of niobium cavity surface processing, and summarizes results of recent studies. We place some emphasis on practical details for real cavity processing systems which are difficult to find in the literature but are, nonetheless, crucial for achieving the good and reproducible cavity performance. New approaches for bulk niobium surface treatment which aim to reduce cost or increase performance, including alternate chemical recipes, barrel polishing and ‘nitrogen doping’ of the RF surface, continue to be pursued and are closely linked to the requirements for surface processing.

  4. Chromatic effects in the superconducting accelerator NUCLOTRON

    International Nuclear Information System (INIS)

    Dinev, D.

    1998-01-01

    A systematic study of the chromatic effects in the superconducting heavy ion synchrotron NUCLOTRON in the JINR, Dubna has been performed. The natural chromaticity has been evaluated taking into account the effect of the dipole magnets. The impact of the systematic and random imperfections in the magnetic field of dipoles on the chromaticity and the dependence of the betatron tunes on the amplitude of oscillations have been investigated. The strengths of the sextupole corrections necessary to cancel the chromaticity have been calculated. The chromatic perturbations have been studied by the means of the Montague chromatic functions (author)

  5. A novel approach to characterizing the surface topography of niobium superconducting radio frequency (SRF) accelerator cavities

    Science.gov (United States)

    Tian, Hui; Ribeill, Guilhem; Xu, Chen; Reece, Charles E.; Kelley, Michael J.

    2011-03-01

    As superconducting niobium radio-frequency (SRF) cavities approach fundamental material limits, there is increased interest in understanding the details of topographical influences on realized performance limitations. Micro- and nano-roughness are implicated in both direct geometrical field enhancements as well as complications of the composition of the 50 nm surface layer in which the super-currents typically flow. Interior surface chemical treatments such as buffered chemical polishing (BCP) and electropolishing (EP) used to remove mechanical damage leave surface topography, including pits and protrusions of varying sharpness. These may promote RF magnetic field entry, locally quenching superconductivity, so as to degrade cavity performance. A more incisive analysis of surface topography than the widely used average roughness is needed. In this study, a power spectral density (PSD) approach based on Fourier analysis of surface topography data acquired by both stylus profilometry and atomic force microscopy (AFM) is introduced to distinguish the scale-dependent smoothing effects, resulting in a novel qualitative and quantitative description of Nb surface topography. The topographical evolution of the Nb surface as a function of different steps of well-controlled EP is discussed. This study will greatly help to identify optimum EP parameter sets for controlled and reproducible surface levelling of Nb for cavity production.

  6. A novel approach to characterizing the surface topography of niobium superconducting radio frequency (SRF) accelerator cavities

    International Nuclear Information System (INIS)

    Tian Hui; Ribeill, Guilhem; Xu Chen; Reece, Charles E.; Kelley, Michael J.

    2011-01-01

    As superconducting niobium radio-frequency (SRF) cavities approach fundamental material limits, there is increased interest in understanding the details of topographical influences on realized performance limitations. Micro- and nano-roughness are implicated in both direct geometrical field enhancements as well as complications of the composition of the 50 nm surface layer in which the super-currents typically flow. Interior surface chemical treatments such as buffered chemical polishing (BCP) and electropolishing (EP) used to remove mechanical damage leave surface topography, including pits and protrusions of varying sharpness. These may promote RF magnetic field entry, locally quenching superconductivity, so as to degrade cavity performance. A more incisive analysis of surface topography than the widely used average roughness is needed. In this study, a power spectral density (PSD) approach based on Fourier analysis of surface topography data acquired by both stylus profilometry and atomic force microscopy (AFM) is introduced to distinguish the scale-dependent smoothing effects, resulting in a novel qualitative and quantitative description of Nb surface topography. The topographical evolution of the Nb surface as a function of different steps of well-controlled EP is discussed. This study will greatly help to identify optimum EP parameter sets for controlled and reproducible surface levelling of Nb for cavity production.

  7. Field limit and nano-scale surface topography of superconducting radio-frequency cavity made of extreme type II superconductor

    OpenAIRE

    Kubo, Takayuki

    2014-01-01

    The field limit of superconducting radio-frequency cavity made of type II superconductor with a large Ginzburg-Landau parameter is studied with taking effects of nano-scale surface topography into account. If the surface is ideally flat, the field limit is imposed by the superheating field. On the surface of cavity, however, nano-defects almost continuously distribute and suppress the superheating field everywhere. The field limit is imposed by an effective superheating field given by the pro...

  8. Integrated Surface Topography Characterization of Variously Polished Niobium for Superconducting Particle Accelerators

    International Nuclear Information System (INIS)

    Tian, Hui; Reece, Charles; Kelley, Michael; Ribeill, G.

    2009-01-01

    As superconducting niobium radio-frequency (SRF) cavities approach fundamental material limits, there is increased interest in understanding the details of topographical influences on realized performance limitations. Micro-and nano-roughness are implicated in both direct geometrical field enhancements as well as complications of the composition of the 50 nm surface layer in which the super-currents flow. Interior surface chemical polishing (BCP/EP) to remove mechanical damage leaves surface topography, including pits and protrusions of varying sharpness. These may promote RF magnetic field entry, locally quenching superconductivity, so as to degrade cavity performance. A more incisive analysis of surface topography than the widely-used average roughness is needed. In this study, a power spectral density (PSD) approach based on Fourier analysis of surface topography data acquired by both stylus profilometry and atomic force microscopy (AFM) is being used to distinguish the scale-dependent smoothing effects. The topographical evolution of the Nb surface as a function of different steps of EP is reported, resulting in a novel qualitative and quantitative description of Nb surface topography.

  9. 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.

  10. Improvement and protection of niobium surface superconductivity by atomic layer deposition and heat treatment

    Energy Technology Data Exchange (ETDEWEB)

    Proslier, T.; /IIT, Chicago /Argonne; Zasadzinski, J.; /IIT, Chicago; Moore, J.; Pellin, M.; Elam, J.; /Argonne; Cooley, L.; /Fermilab; Antoine, C.; /Saclay

    2008-11-01

    A method to treat the surface of Nb is described, which potentially can improve the performance of superconducting rf cavities. We present tunneling and x-ray photoemission spectroscopy measurements at the surface of cavity-grade niobium samples coated with a 3 nm alumina overlayer deposited by atomic layer deposition. The coated samples baked in ultrahigh vacuum at low temperature degraded superconducting surface. However, at temperatures above 450 C, the tunneling conductance curves show significant improvements in the superconducting density of states compared with untreated surfaces.

  11. Radiation effects on superconducting fusion magnet components

    International Nuclear Information System (INIS)

    Weber, H.W.

    2011-01-01

    Nuclear fusion devices based on the magnetic confinement principle heavily rely on the existence and performance of superconducting magnets and have always significantly contributed to advancing superconductor and magnet technology to their limits. In view of the presently ongoing construction of the tokamak device ITER and the stellerator device Wendelstein 7X and their record breaking parameters concerning size, complexity of design, stored energy, amperage, mechanical and magnetic forces, critical current densities and stability requirements, it is deemed timely to review another critical parameter that is practically unique to these devices, namely the radiation response of all magnet components to the lifetime fluence of fast neutrons and gamma rays produced by the fusion reactions of deuterium and tritium. I will review these radiation effects in turn for the currently employed standard "technical" low temperature superconductors NbTi and Nb 3 Sn, the stabilizing material (Cu) as well as the magnet insulation materials and conclude by discussing the potential of high temperature superconducting materials for future generations of fusion devices, such as DEMO. (author)

  12. 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

  13. 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

  14. 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

  15. Evidence of incomplete annealing at 800 °C and the effects of 120 °C baking on the crystal orientation and the surface superconducting properties of cold-worked and chemically polished Nb

    Science.gov (United States)

    Sung, Z.-H.; Dzyuba, A.; Lee, P. J.; Larbalestier, D. C.; Cooley, L. D.

    2015-07-01

    High-purity niobium rods were cold-worked by wire-drawing, followed by various combinations of chemical polishing and high-vacuum baking at 120 °C or annealing at 800 °C in order to better understand changes to the surface superconducting properties resulting from typical superconducting radio-frequency cavity processing. AC susceptibility measurements revealed an enhanced upper transition Tc at ˜ 9.3-9.4 K in all samples that was stable through all annealing steps, a value significantly above the accepted Tc of 9.23 K for pure annealed niobium. Corresponding elevations were seen in the critical fields, the ratio of the surface critical field Hc3 to the bulk upper critical field Hc2 rising to 2.3, well above the Ginzburg-Landau value of 1.695. Orientation imaging revealed an extensive dislocation rich sub-grain structure in the as-drawn rods, a small reduction of the surface strain after baking at 120 °C, and a substantial but incomplete recrystallization near the surface after annealing at 800 °C. We interpret these changes in surface superconducting and structural properties to extensive changes in the near-surface interstitial contamination produced by baking and annealing and to synergistic interactions between H and surface O introduced during electropolishing and buffered chemical polishing.

  16. Plasma processing of large curved surfaces for superconducting rf cavity modification

    Directory of Open Access Journals (Sweden)

    J. Upadhyay

    2014-12-01

    Full Text Available Plasma-based surface modification of niobium is a promising alternative to wet etching of superconducting radio frequency (SRF cavities. We have demonstrated surface layer removal in an asymmetric nonplanar geometry, using a simple cylindrical cavity. The etching rate is highly correlated with the shape of the inner electrode, radio-frequency (rf circuit elements, gas pressure, rf power, chlorine concentration in the Cl_{2}/Ar gas mixtures, residence time of reactive species, and temperature of the cavity. Using variable radius cylindrical electrodes, large-surface ring-shaped samples, and dc bias in the external circuit, we have measured substantial average etching rates and outlined the possibility of optimizing plasma properties with respect to maximum surface processing effect.

  17. Thermoelectric flux effect in superconducting indium

    International Nuclear Information System (INIS)

    Van Harlingen, D.J.

    1977-01-01

    In this paper we discuss a thermoelectric effect in superconductors which provides a mechanism for studying quasiparticle relaxation and scattering processes in non-equilibrium superconductors by transport measurements. We report measurements of the thermoelecric flux effect in samples consisting of indium and lead near the In transition temperature; in this temperature range, the contribution to DELTA/sub TAU/ from the Pb is insignificant and so values of OMEGA(T) are obtained for indium. The results of our experiments may be summarized as follows: (1) we have a thermally-generated flux effect in 5 superconducting In-Pb toroidal samples, (2) experimental tests suggest that the observed effect does indeed arise from the proposed thermoelectric flux effect, (3) OMEGA(T) for indium is found to diverge as (T/sub c/ - T)/sup -3/2/ more rapidly than predicted by simple theory, (4) OMEGA(T) at T/T sub c/ = .999 is nearly 10/sup 5/ larger than initially expected, (5) OMEGA (T) roughly correlates with the magnitude of the normal state thermoelectric coefficient for our samples

  18. Effects of insulation on potted superconducting coils

    International Nuclear Information System (INIS)

    Zeller, A.F.; DeKamp, J.C.; Magsig, C.T.; Nolen, J.A.; McInturff, A.D.

    1989-01-01

    Test coils using identical wire but with either Formvar or Polyesterimid insulation were fabricated to determine the effects of insulation on training behavior. It was found that the type of insulation did not affect the training behavior. While considerable attention has been paid to epoxy formulations used for superconducting coils, little study has been devoted to the effects of the wire insulation on training behavior. If the insulation does not bind well with the epoxy, the wires will not be held securely in place, and training will be required to make the coil operate at its design limit. In fact, the coil may never reach its design current, showing considerable degredation. Conversely, if the epoxy-insulation reaction is to soften or weaken the insulation, then shorts and/or training may result. The authors have undertaken a study of the effects of the insulation on potted coils wet wound with Stycast 2850 FT epoxy. The wire was insulated with one of two insulting varnishes: Formvar (a polyvinyl formal resin) or Polyesterimid (a phenolic resin). Formvar is the standard insulation in the United States while Polyesterimid the European standard

  19. Niobium thin film deposition studies on copper surfaces for superconducting radio frequency cavity applications

    Directory of Open Access Journals (Sweden)

    W. M. Roach

    2012-06-01

    Full Text Available Thin film coatings have the potential to increase both the thermal efficiency and accelerating gradient in superconducting radio frequency accelerator cavities. However, before this potential can be realized, systematic studies on structure-property correlations in these thin films need to be carried out since the reduced geometry, combined with specific growth parameters, can modify the physical properties of the materials when compared to their bulk form. Here, we present our systematic studies of Nb thin films deposited onto Cu surfaces to clarify possible reasons for the limited success that this process exhibited in previous attempts. We compare these films with Nb grown on other surfaces. In particular, we study the crystal structure and surface morphology and their effect on superconducting properties, such as critical temperature and lower critical field. We found that higher deposition temperature leads to a sharper critical temperature transition, but also to increased roughness indicating that there are competing mechanisms that must be considered for further optimization.

  20. Effect of Fibonacci modulation on superconductivity

    International Nuclear Information System (INIS)

    Gupta, Sanjay; Sil, Shreekantha; Bhattacharyya, Bibhas

    2006-01-01

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

  1. Substitution effects in magnetic and superconducting materials

    Directory of Open Access Journals (Sweden)

    Peña, O.

    1999-10-01

    Full Text Available Chemical substitutions at very low level have been proved to be a very effective tool to change important physical parameters in many kinds of materials. These modifications may be the result of, for instance, subtle variations of the position of the Fermi level with respect to the density of states, presence of additional electrons which may change the hole carrier concentration, steric effects which impose contraints in the crystallographic lattice, mixed-valence states resultating from the dismutation of chemical components, etc. We review herein three systems in which the substitution effects are at the origin of new physical states : the high-Tc superconductor bismuth cuprate of the 2212 family, the mixed-valence manganese perovskites representative of giant magneto-resistive compounds, and the Chevrel phase materials in which a structural transition may inhibit the superconducting state.

    Las substituciones químicas a un nivel muy pequeño se han probado como una importante herramienta para cambiar los parámetros físicos en una gran variedad de materiales. Estas modificaciones pueden ser el resultado de, por ejemplo, muy ligeras variaciones de la posición del nivel de Fermi con respecto a la densidad de estados, presencia de electrones adicionales que pueden cambiar la concentración de portadores tipo huecos, efectos estéricos que imponen restricciones en la red cristalográfica, estados de valencia mixtos resultantes de la dismutación de los componentes químicos, etc. Aquí se revisan tres sistemas donde los efectos de substitución son el origen de nuevos estados físicos: los superconductores de alta temperatura basados en cupratos de bismuto de la familia 2212, las perovskitas de manganeso de valencia mixta representantes de compuestos con magnetorresistencia gigante, y los materiales con fases de Chevrelt cuya transición estructural puede inhibir el estado superconductor.

  2. Quasiparticle losses at the surface of superconducting tunnel junction detectors

    NARCIS (Netherlands)

    Panteleit, F.; Schroeder, T.; Martin, J.; Huebener, R.P.; Kiewiet, F.B.; Berg, van den M.L.; Korte, P.A.J.

    1999-01-01

    Superconducting tunnel junctions (STJs) are promising as high energy resolution x-ray detectors. However, the theoretical limit of the energy resolution of STJs has not yet been reached for several reasons. In many cases quasiparticle losses limit the energy resolution. We have investigated STJs

  3. Performance of a novel SQUID-based superconducting imaging-surface magnetoencephalography system

    Science.gov (United States)

    Kraus, R. H.; Volegov, P.; Maharajh, K.; Espy, M. A.; Matlashov, A. N.; Flynn, E. R.

    2002-03-01

    Performance for a recently completed whole-head magnetoencephalography system using a superconducting imaging surface (SIS) surrounding an array of 150 SQUID magnetometers is reported. The helmet-like SIS is hemispherical in shape with a brim. Conceptually, the SIS images nearby sources onto the SQUIDs while shielding sensors from distant “noise” sources. A finite element method (FEM) description using the as-built geometry was developed to describe the SIS effect on source fields by imposing B⊥( surface)=0 . Sensors consist of 8×8 mm 2 SQUID magnetometers with 0.84 nT/ Φ0 sensitivity and positions and orientations was found. Good agreement was found between modeled and measured shielding of the SQUIDs from sources external to the array showing significant frequency-independent shielding. Phantom localization precision was better than 0.5 mm at all locations with a mean of better than 0.3 mm.

  4. Surface analyses of electropolished niobium samples for superconducting radio frequency cavity

    International Nuclear Information System (INIS)

    Tyagi, P. V.; Nishiwaki, M.; Saeki, T.; Sawabe, M.; Hayano, H.; Noguchi, T.; Kato, S.

    2010-01-01

    The performance of superconducting radio frequency niobium cavities is sometimes limited by contaminations present on the cavity surface. In the recent years extensive research has been done to enhance the cavity performance by applying improved surface treatments such as mechanical grinding, electropolishing (EP), chemical polishing, tumbling, etc., followed by various rinsing methods such as ultrasonic pure water rinse, alcoholic rinse, high pressure water rinse, hydrogen per oxide rinse, etc. Although good cavity performance has been obtained lately by various post-EP cleaning methods, the detailed nature about the surface contaminants is still not fully characterized. Further efforts in this area are desired. Prior x-ray photoelectron spectroscopy (XPS) analyses of EPed niobium samples treated with fresh EP acid, demonstrated that the surfaces were covered mainly with the niobium oxide (Nb 2 O 5 ) along with carbon, in addition a small quantity of sulfur and fluorine were also found in secondary ion mass spectroscopy (SIMS) analysis. In this article, the authors present the analyses of surface contaminations for a series of EPed niobium samples located at various positions of a single cell niobium cavity followed by ultrapure water rinsing as well as our endeavor to understand the aging effect of EP acid solution in terms of contaminations presence at the inner surface of the cavity with the help of surface analytical tools such as XPS, SIMS, and scanning electron microscope at KEK.

  5. Surface analyses of electropolished niobium samples for superconducting radio frequency cavity

    Energy Technology Data Exchange (ETDEWEB)

    Tyagi, P. V.; Nishiwaki, M.; Saeki, T.; Sawabe, M.; Hayano, H.; Noguchi, T.; Kato, S. [GUAS, Tsukuba, Ibaraki 305-0801 (Japan); KEK, Tsukuba, Ibaraki 305-0801 (Japan); KAKEN Inc., Hokota, Ibaraki 311-1416 (Japan); GUAS, Tsukuba, Ibaraki 305-0801 (Japan) and KEK, Tsukuba, Ibaraki 305-0801 (Japan)

    2010-07-15

    The performance of superconducting radio frequency niobium cavities is sometimes limited by contaminations present on the cavity surface. In the recent years extensive research has been done to enhance the cavity performance by applying improved surface treatments such as mechanical grinding, electropolishing (EP), chemical polishing, tumbling, etc., followed by various rinsing methods such as ultrasonic pure water rinse, alcoholic rinse, high pressure water rinse, hydrogen per oxide rinse, etc. Although good cavity performance has been obtained lately by various post-EP cleaning methods, the detailed nature about the surface contaminants is still not fully characterized. Further efforts in this area are desired. Prior x-ray photoelectron spectroscopy (XPS) analyses of EPed niobium samples treated with fresh EP acid, demonstrated that the surfaces were covered mainly with the niobium oxide (Nb{sub 2}O{sub 5}) along with carbon, in addition a small quantity of sulfur and fluorine were also found in secondary ion mass spectroscopy (SIMS) analysis. In this article, the authors present the analyses of surface contaminations for a series of EPed niobium samples located at various positions of a single cell niobium cavity followed by ultrapure water rinsing as well as our endeavor to understand the aging effect of EP acid solution in terms of contaminations presence at the inner surface of the cavity with the help of surface analytical tools such as XPS, SIMS, and scanning electron microscope at KEK.

  6. Surface studies of niobium chemically polished under conditions for superconducting radio frequency (SRF) cavity production

    Science.gov (United States)

    Tian, Hui; Reece, Charles E.; Kelley, Michael J.; Wang, Shancai; Plucinski, Lukasz; Smith, Kevin E.; Nowell, Matthew M.

    2006-11-01

    The performance of niobium superconducting radiofrequency (SRF) accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially as influenced by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant datasets. We found that the predominant general surface orientation is (1 0 0), but others are also present and at the atomic-level details of surface plane orientation are more complex. The post-etch surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of niobium pentoxide, whose thickness increases with solution flow rate to a maximum of 1.3-1.4 times that resulting from static solution. The standard deviation of the roughness measurements is ±30% and that of the surface composition is ±5%.

  7. Surface studies of niobium chemically polished under conditions for superconducting radio frequency (SRF) cavity production

    Energy Technology Data Exchange (ETDEWEB)

    Tian Hui [Thomas Jefferson National Accelerator Facility and College of William and Mary (United States); Reece, Charles E. [Thomas Jefferson National Accelerator Facility and College of William and Mary (United States); Kelley, Michael J. [Thomas Jefferson National Accelerator Facility and College of William and Mary (United States)]. E-mail: mkelley@jlab.org; Wang Shancai [Department of Physics, Boston University (United States); Plucinski, Lukasz [Department of Physics, Boston University (United States); Smith, Kevin E. [Department of Physics, Boston University (United States); Nowell, Matthew M. [EDAX TSL (United States)

    2006-11-30

    The performance of niobium superconducting radiofrequency (SRF) accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially as influenced by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant datasets. We found that the predominant general surface orientation is (1 0 0), but others are also present and at the atomic-level details of surface plane orientation are more complex. The post-etch surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of niobium pentoxide, whose thickness increases with solution flow rate to a maximum of 1.3-1.4 times that resulting from static solution. The standard deviation of the roughness measurements is {+-}30% and that of the surface composition is {+-}5%.

  8. Surface Studies of Niobium Chemically Polished Under Conditions for Superconducting Radio Frequency (SRF) Cavity Production

    Energy Technology Data Exchange (ETDEWEB)

    Tian,H.; Reece, C.; Kelley, M.; Wang, S.; Plucinski, L.; Smith, K.; Nowell, M.

    2006-01-01

    The performance of niobium superconducting radiofrequency (SRF) accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially as influenced by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant datasets. We found that the predominant general surface orientation is (1 0 0), but others are also present and at the atomic-level details of surface plane orientation are more complex. The post-etch surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of niobium pentoxide, whose thickness increases with solution flow rate to a maximum of 1.3-1.4 times that resulting from static solution. The standard deviation of the roughness measurements is {+-}30% and that of the surface composition is {+-}5%.

  9. 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.

  10. Microscopic examination and elemental analysis of surface defects in LEP superconducting cavities

    International Nuclear Information System (INIS)

    Benvenuti, C.; Cosso, R.; Hauer, M.; Hellgren, N.; Lacarrere, D.

    1996-01-01

    A diagnostic tool, based on a computer controlled surface analysis instrument, incorporating secondary electron imaging, static auger electron spectroscopy and scanning auger mapping has been designed and built at CERN to characterize the inner surface of LEP superconducting cavities with provide unsatisfactory radio-frequency performance. The experimental results obtained to date are reported and discussed. (author)

  11. The HIE-ISOLDE Superconducting Cavities: Surface Treatment and Niobium Thin Film Coating

    CERN Document Server

    Lanza, G; Ferreira, L M A; Gustafsson, A E; Pasini, M; Trilhe, P; Palmieri, V

    2010-01-01

    CERN has designed and prepared new facilities for the surface treatment and niobium sputter coating of the HIE-ISOLDE superconducting cavities. We describe here the design choices, as well as the results of the first surface treatments and test coatings.

  12. Effect of disorder on the superconducting properties of materials

    International Nuclear Information System (INIS)

    Brouers, F.; Derenne, M.

    1982-01-01

    The effect of the variation of the density states at the Fermi level on the critical superconductivity temperature TC of transition metal compounds is studied. This paper suggests using the technique of calculating the 5-fold degenerate d-band density of states from a continued fraction extension of a tight-binding Green function to study the relative importance of one dimensionality chain coupling, three dimensional interactions and the effect of disorder on the electronic and superconducting properties of complex phase and in particular A15 phases. The first results obtained for A15 phases density of states indicate that an extension of the suggested method can be of great interest to analyze the effect of disorder on superconductivity properties of complex phases

  13. The effect of pressure on the charge-density wave and superconductivity in ZrTe sub 3

    CERN Document Server

    Yamaya, K; Yasuzuka, S; Okajima, Y; Tanda, S

    2002-01-01

    The charge-density-wave (CDW) transition temperature, T sub C sub D sub W , of ZrTe sub 3 is found to increase for pressures up to 0.6 GPa, while the superconducting transition temperature, T sub c , decreases with increasing pressure. According to a band calculation, it is found that the pressure-induced enhancement of the CDW and suppression of the superconductivity are not simply explained by the effect of nesting of the Fermi surface, suggesting the possibility of a new relation for the competition between the CDW and superconductivity.

  14. Magnetism, superconductivity and Fermi surfaces of plutonium compounds

    International Nuclear Information System (INIS)

    Haga, Y.; Aoki, D.; Yamagami, H.; Matsuda, T.D.; Nakajima, K.; Arai, Y.; Homma, Y.; Shiokawa, Y.; Yamamoto, E.; Nakamura, A.; Onuki, Y.

    2007-01-01

    Single crystals of plutonium compounds PuRhGa 5 and PuIn 3 are successfully grown. For PuRhGa 5 , anisotropy of the superconducting upper critical field was found and analyzed by the anisotropic mass model, consistent with quasi-two-dimensional electronic states predicted by band calculations. On the other hand, the de Haas-van Alphen oscillation was observed in PuIn 3 . By comparing with the band calculations, it is concluded that 5f electrons are itinerant in PuIn 3

  15. Fermiology and Superconductivity of Topological Surface States in PdTe2

    Science.gov (United States)

    Clark, O. J.; Neat, M. J.; Okawa, K.; Bawden, L.; Marković, I.; Mazzola, F.; Feng, J.; Sunko, V.; Riley, J. M.; Meevasana, W.; Fujii, J.; Vobornik, I.; Kim, T. K.; Hoesch, M.; Sasagawa, T.; Wahl, P.; Bahramy, M. S.; King, P. D. C.

    2018-04-01

    We study the low-energy surface electronic structure of the transition-metal dichalcogenide superconductor PdTe2 by spin- and angle-resolved photoemission, scanning tunneling microscopy, and density-functional theory-based supercell calculations. Comparing PdTe2 with its sister compound PtSe2 , we demonstrate how enhanced interlayer hopping in the Te-based material drives a band inversion within the antibonding p -orbital manifold well above the Fermi level. We show how this mediates spin-polarized topological surface states which form rich multivalley Fermi surfaces with complex spin textures. Scanning tunneling spectroscopy reveals type-II superconductivity at the surface, and moreover shows no evidence for an unconventional component of its superconducting order parameter, despite the presence of topological surface states.

  16. On the theory of type-I superconductor surface tension and twinning-plane-superconductivity

    International Nuclear Information System (INIS)

    Mishonov, T.M.

    1990-01-01

    A correction is found to the surface tension in type-I superconductors which is proportional to the square root of the Ginsburg-Landau parameter. This correction is essential for obtaining the phase diagram and other thermodynamical variables of the narrow superconducting layer arising near the twinning plane in some metals

  17. 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

  18. Effect of increasing disorder on superconductivity of Mo/Nb superlattices

    International Nuclear Information System (INIS)

    Pereiro, Juan; Saerbeck, Thomas; Schuller, Ivan K

    2015-01-01

    We investigated the superconducting properties of Nb/Mo superlattices (SLs). The structural changes as a function of Nb and Mo layer thickness allow us to investigate the effect of disorder on the superconducting properties in a controlled fashion. Systematic structural studies provide quantitative measures of disorder parameters, such as roughness, interdiffusion, and strain, which allow separating their effect on the individual superconducting layers. The Mo critical temperature does not change as the layer thickness decreases below its coherence length. Thus, the SL critical temperatures in the presence of disorder and proximity effects can be modeled by considering only the effects of the Nb mean free path and coherence length. With increasing layer thickness, the SL critical temperatures approach Nb bulk values. Contrary to expectations the T c of Mo remains below the Nb T c . We discuss the results using existing theories based on Coulomb repulsion or changes in the density of states at the Fermi surface as a function of disorder. Questions about current understanding of the effect of disorder on superconductivity arise from the results. (paper)

  19. Effect of increasing disorder on superconductivity of Mo/Nb superlattices

    Science.gov (United States)

    Pereiro, Juan; Saerbeck, Thomas; Schuller, Ivan K.

    2015-08-01

    We investigated the superconducting properties of Nb/Mo superlattices (SLs). The structural changes as a function of Nb and Mo layer thickness allow us to investigate the effect of disorder on the superconducting properties in a controlled fashion. Systematic structural studies provide quantitative measures of disorder parameters, such as roughness, interdiffusion, and strain, which allow separating their effect on the individual superconducting layers. The Mo critical temperature does not change as the layer thickness decreases below its coherence length. Thus, the SL critical temperatures in the presence of disorder and proximity effects can be modeled by considering only the effects of the Nb mean free path and coherence length. With increasing layer thickness, the SL critical temperatures approach Nb bulk values. Contrary to expectations the Tc of Mo remains below the Nb Tc. We discuss the results using existing theories based on Coulomb repulsion or changes in the density of states at the Fermi surface as a function of disorder. Questions about current understanding of the effect of disorder on superconductivity arise from the results.

  20. Chiral d -wave superconductivity in a triangular surface lattice mediated by long-range interaction

    Science.gov (United States)

    Cao, Xiaodong; Ayral, Thomas; Zhong, Zhicheng; Parcollet, Olivier; Manske, Dirk; Hansmann, Philipp

    2018-04-01

    Adatom systems on the Si(111) surface have recently attracted an increasing attention as strongly correlated systems with a rich phase diagram. We study these materials by a single band model on the triangular lattice, including 1 /r long-range interaction. Employing the recently proposed TRILEX method, we find an unconventional superconducting phase of chiral d -wave symmetry in hole-doped systems. Contrary to usual scenarios where charge and spin fluctuations are seen to compete, here the superconductivity is driven simultaneously by both charge and spin fluctuations and crucially relies on the presence of the long-range tail of the interaction. We provide an analysis of the relevant collective bosonic modes and predict how a cumulative charge and spin paring mechanism leads to superconductivity in doped silicon adatom materials.

  1. Investigation of niobium surface structure and composition for improvement of superconducting radio-frequency cavities

    Science.gov (United States)

    Trenikhina, Yulia

    Nano-scale investigation of intrinsic properties of niobium near-surface is a key to control performance of niobium superconducting radio-frequency cavities. Mechanisms responsible for the performance limitations and their empirical remedies needs to be justified in order to reproducibly control fabrication of SRF cavities with desired characteristics. The high field Q-slope and mechanism behind its cure (120°C mild bake) were investigated by comparison of the samples cut out of the cavities with high and low dissipation regions. Material evolution during mild field Q-slope nitrogen treatment was characterized using the coupon samples as well as samples cut out of nitrogen treated cavity. Evaluation of niobium near-surface state after some typical and novel cavity treatments was accomplished. Various TEM techniques, SEM, XPS, AES, XRD were used for the structural and chemical characterization of niobium near-surface. Combination of thermometry and structural temperature-dependent comparison of the cavity cutouts with different dissipation characteristics revealed precipitation of niobium hydrides to be the reason for medium and high field Q-slopes. Step-by-step effect of the nitrogen treatment processing on niobium surface was studied by analytical and structural characterization of the cavity cutout and niobium samples, which were subject to the treatment. Low concentration nitrogen doping is proposed to explain the benefit of nitrogen treatment. Chemical characterization of niobium samples before and after various surface processing (Electropolishing (EP), 800°C bake, hydrofluoric acid (HF) rinsing) showed the differences that can help to reveal the microscopic effects behind these treatments as well as possible sources of surface contamination.

  2. A new quantum interferometer effect in superconducting oxide ceramics

    International Nuclear Information System (INIS)

    Chela Flores, J.; Shehata, L.N.

    1987-08-01

    On the basis of a phenomenological approach to type II high T c superconductivity, we suggest that in the lanthanum compounds the Mercereau effect for a coupled junction pair should display and ex-dependent shift in the period of modulation of the tunnelling current. (author). 14 refs

  3. Effective valence as the control parameter of the superconducting ...

    African Journals Online (AJOL)

    One approach to investigating the superconductivity in the ironbased materials is understanding the chemical and structural parameters that can be used to tune their remarkably high Tc. In this paper, we have demonstrated that the effective valence of iron can be used as the control parameter to tune the Tc of this family of ...

  4. Effect of dislocations on superconductivity. O vliyanii dislokatsiy na sverkhrpovodimost'

    Energy Technology Data Exchange (ETDEWEB)

    Agap' ev, B D; Bytsenko, A A; Sukhanov, S A

    1976-01-01

    Electron-dislocation interaction is analyzed here. The effect of dislocations on the superconductor characteristics is determined according to the Ginzburg-Landau method. Appreciable changes in the stability of the superconductive state are found to occur in the vicinity of dislocations.

  5. Dependence of the residual surface resistance of superconducting radio frequency cavities on the cooling dynamics around T{sub c}

    Energy Technology Data Exchange (ETDEWEB)

    Romanenko, A., E-mail: aroman@fnal.gov; Grassellino, A., E-mail: annag@fnal.gov; Melnychuk, O.; Sergatskov, D. A. [Fermi National Accelerator Laboratory, Batavia, Illinois 60510 (United States)

    2014-05-14

    We report a strong effect of the cooling dynamics through T{sub c} on the amount of trapped external magnetic flux in superconducting niobium cavities. The effect is similar for fine grain and single crystal niobium and all surface treatments including electropolishing with and without 120 °C baking and nitrogen doping. Direct magnetic field measurements on the cavity walls show that the effect stems from changes in the flux trapping efficiency: slow cooling leads to almost complete flux trapping and higher residual resistance, while fast cooling leads to the much more efficient flux expulsion and lower residual resistance.

  6. Dependence of the residual surface resistance of superconducting radio frequency cavities on the cooling dynamics around Tc

    Science.gov (United States)

    Romanenko, A.; Grassellino, A.; Melnychuk, O.; Sergatskov, D. A.

    2014-05-01

    We report a strong effect of the cooling dynamics through Tc on the amount of trapped external magnetic flux in superconducting niobium cavities. The effect is similar for fine grain and single crystal niobium and all surface treatments including electropolishing with and without 120 °C baking and nitrogen doping. Direct magnetic field measurements on the cavity walls show that the effect stems from changes in the flux trapping efficiency: slow cooling leads to almost complete flux trapping and higher residual resistance, while fast cooling leads to the much more efficient flux expulsion and lower residual resistance.

  7. Surface polishing of niobium for superconducting radio frequency (SRF) cavity applications

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Liang [College of William and Mary, Williamsburg, VA (United States)

    2014-08-01

    Niobium cavities are important components in modern particle accelerators based on superconducting radio frequency (SRF) technology. The interior of SRF cavities are cleaned and polished in order to produce high accelerating field and low power dissipation on the cavity wall. Current polishing methods, buffered chemical polishing (BCP) and electro-polishing (EP), have their advantages and limitations. We seek to improve current methods and explore laser polishing (LP) as a greener alternative of chemical methods. The topography and removal rate of BCP at different conditions (duration, temperature, sample orientation, flow rate) was studied with optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Differential etching on different crystal orientations is the main contributor to fine grain niobium BCP topography, with gas evolution playing a secondary role. The surface of single crystal and bi-crystal niobium is smooth even after heavy BCP. The topography of fine grain niobium depends on total removal. The removal rate increases with temperature and surface acid flow rate within the rage of 0~20 °C, with chemical reaction being the possible dominate rate control mechanism. Surface flow helps to regulate temperature and avoid gas accumulation on the surface. The effect of surface flow rate on niobium EP was studied with optical microscopy, atomic force microscopy (AFM), and power spectral density (PSD) analysis. Within the range of 0~3.7 cm/s, no significant difference was found on the removal rate and the macro roughness. Possible improvement on the micro roughness with increased surface flow rate was observed. The effect of fluence and pulse accumulation on niobium topography during LP was studied with optical microscopy, SEM, AFM, and PSD analysis. Polishing on micro scale was achieved within fluence range of 0.57~0.90 J/cm2, with pulse accumulation adjusted accordingly. Larger area treatment was proved possible by

  8. Nanoscale wedge polishing of superconducting thin films-an easy way to obtain depth dependent information by surface analysis techniques

    International Nuclear Information System (INIS)

    Shapoval, T; Engel, S; Gruendlich, M; Meier, D; Backen, E; Neu, V; Holzapfel, B; Schultz, L

    2008-01-01

    A mechanical wedge polishing procedure that offers a simple, cost-effective and rapid way to look into the depth of a thin film with different surface-sensitive scanning techniques has been developed. As an example of its wide applicability, this method was utilized for the investigation of two differently prepared superconducting YBa 2 Cu 3 O 7-δ thin films: an Hf-doped film prepared by chemical solution deposition and an undoped film grown by pulsed laser deposition. Upon polishing, the roughness of the samples was reduced to less than 5 nm (peak-to-valley) without influencing the superconducting properties of the films. Thus, nanoscale polishing opens up a unique possibility for microscopic studies with various surface-sensitive techniques. We demonstrate the successful imaging of flux lines by low temperature magnetic force microscopy after polishing a formerly rough as-prepared film. By applying the wedge polishing procedure to the Hf-doped sample, high resolution electron backscattering diffraction investigations reveal the homogeneous distribution of non-superconducting BaHfO 3 nanoparticles in the whole volume of the film

  9. 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.

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

    International Nuclear Information System (INIS)

    Tong Wang

    2002-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Tong [Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States)

    2002-09-18

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

  12. Radiation effects on insulators for superconducting magnets

    International Nuclear Information System (INIS)

    Kernohan, R.H.; Coltman, R.R. Jr.; Long, C.J.

    1978-01-01

    In order to determine the radiation stability of electrical insulation that could be used in a superconducting magnet for containment of the plasma in a fusion energy device, 55 specimens of eight types of organic insulation were irradiated to a dose of about 2 x 10 8 R (2 x 10 6 J/Kg) at a temperature of 4.8 K in the Low-Temperature Irradiation Facility in the Bulk Shielding Reactor at Oak Ridge National Laboratory. Four of the specimens were monitored for changes in electrical resistivity during the irradiation. The initial resistivities, which were of the order of 10 14 Ω cm, decreased to about 10 13 Ω cm under the influence of a weak radiation field. At full-power reactor operation (2 MW), the resistivities dropped to about 10 11 Ω cm, but changed little during the irradiation. After the irradiation the resistivities increased, but not to the initial values, because of residual radioactivity near or in the experiment assembly. Restoration to near the initial resistivity values was later observed upon warming the specimens to room temperature and purging the irradiation chamber. The latter result may be related to outgassing induced by the irradiation

  13. Study of the skin effect in superconducting materials

    Energy Technology Data Exchange (ETDEWEB)

    Szeftel, Jacob, E-mail: jszeftel@lpqm.ens-cachan.fr [ENS Cachan, LPQM, 61 avenue du Président Wilson, 94230 Cachan (France); Sandeau, Nicolas [Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, F-13013 Marseille (France); Khater, Antoine [Université du Maine, UMR 6087 Laboratoire PEC, F-72000 Le Mans (France)

    2017-05-03

    Highlights: • Comprehensive theoretical study of the skin effect in superconductors. • Based on Newton and Maxwell's equations. • Usual and anomalous skin effects dealt with in the same framework. - Abstract: The skin effect is analyzed to provide the numerous measurements of the penetration depth of the electromagnetic field in superconducting materials with a theoretical basis. Both the normal and anomalous skin effects are accounted for within a single framework, focusing on frequencies less than the superconducting gap. The emphasis is laid on the conditions required for the penetration depth to be equal to London's length, which enables us to validate an assumption widely used in the interpretation of all current experimental results.

  14. 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)

  15. Preparation and handling of surfaces for superconducting radio frequency cavities

    International Nuclear Information System (INIS)

    Bloess, D.

    1988-01-01

    Fortunately, surface treatment for s.c. cavities knows only one simple rule. If one observes this rule strictly one will be successful, if not, one will fail! The rule is CLEANLINESS. This means: clean material (high purity niobium without inclusions), clean (analytical grade) polishing chemicals and solvents, ultraclean (semiconductor grade) rinsing water, ultraclean (class 100) assembly environment. In general, if one applies the same working practice as the semiconductor industry, one will produce surfaces that are less clean than silicon wafers, due to the shape of the cavity (an inner surface is much more difficult to clean than a flat wafer); due to its size and due to the material (niobium is hydrophilic which makes the water with all the dirt in it stick to the surface). 9 references

  16. Superconductivity at high pressures

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, N B; Ginzburg, N I

    1969-07-01

    Work published during the last 3 or 4 yrs concerning the effect of pressure on superconductivity is reviewed. Superconducting modifications of Si, Ge, Sb, Te, Se, P and Ce. Change of Fermi surface under pressure for nontransition metals. First experiments on the influence of pressure on the tunneling effect in superconductors provide new information on the nature of the change in phonon and electron energy spectra of metals under hydrostatic compression. 78 references.

  17. Weak antilocalization effect and noncentrosymmetric superconductivity in a topologically nontrivial semimetal LuPdBi

    KAUST Repository

    Xu, Guizhou; Wang, Wenhong; Zhang, Xiaoming; Du, Yin; Liu, Enke; Wang, Shouguo; Wu, Guangheng; Liu, Zhongyuan; Zhang, Xixiang

    2014-01-01

    A large number of half-Heusler compounds have been recently proposed as three-dimensional (3D) topological insulators (TIs) with tunable physical properties. However, no transport measurements associated with the topological surface states have been observed in these half-Heusler candidates due to the dominating contribution from bulk electrical conductance. Here we show that, by reducing the mobility of bulk carriers, a two-dimensional (2D) weak antilocalization (WAL) effect, one of the hallmarks of topological surface states, was experimentally revealed from the tilted magnetic field dependence of magnetoconductance in a topologically nontrivial semimetal LuPdBi. Besides the observation of a 2D WAL effect, a superconducting transition was revealed at T c ∼ 1.7â.K in the same bulk LuPdBi. Quantitative analysis within the framework of a generalized BCS theory leads to the conclusion that the noncentrosymmetric superconductivity of LuPdBi is fully gapped with a possibly unconventional pairing character. The co-existence of superconductivity and the transport signature of topological surface states in the same bulk alloy suggests that LuPdBi represents a very promising candidate as a topological superconductor.

  18. Weak antilocalization effect and noncentrosymmetric superconductivity in a topologically nontrivial semimetal LuPdBi

    KAUST Repository

    Xu, Guizhou

    2014-07-21

    A large number of half-Heusler compounds have been recently proposed as three-dimensional (3D) topological insulators (TIs) with tunable physical properties. However, no transport measurements associated with the topological surface states have been observed in these half-Heusler candidates due to the dominating contribution from bulk electrical conductance. Here we show that, by reducing the mobility of bulk carriers, a two-dimensional (2D) weak antilocalization (WAL) effect, one of the hallmarks of topological surface states, was experimentally revealed from the tilted magnetic field dependence of magnetoconductance in a topologically nontrivial semimetal LuPdBi. Besides the observation of a 2D WAL effect, a superconducting transition was revealed at T c ∼ 1.7â.K in the same bulk LuPdBi. Quantitative analysis within the framework of a generalized BCS theory leads to the conclusion that the noncentrosymmetric superconductivity of LuPdBi is fully gapped with a possibly unconventional pairing character. The co-existence of superconductivity and the transport signature of topological surface states in the same bulk alloy suggests that LuPdBi represents a very promising candidate as a topological superconductor.

  19. Superconductivity versus quantum criticality: Effects of thermal fluctuations

    Science.gov (United States)

    Wang, Huajia; Wang, Yuxuan; Torroba, Gonzalo

    2018-02-01

    We study the interplay between superconductivity and non-Fermi liquid behavior of a Fermi surface coupled to a massless SU(N ) matrix boson near the quantum critical point. The presence of thermal infrared singularities in both the fermionic self-energy and the gap equation invalidates the Eliashberg approximation, and makes the quantum-critical pairing problem qualitatively different from that at zero temperature. Taking the large N limit, we solve the gap equation beyond the Eliashberg approximation, and obtain the superconducting temperature Tc as a function of N . Our results show an anomalous scaling between the zero-temperature gap and Tc. For N greater than a critical value, we find that Tc vanishes with a Berezinskii-Kosterlitz-Thouless scaling behavior, and the system retains non-Fermi liquid behavior down to zero temperature. This confirms and extends previous renormalization-group analyses done at T =0 , and provides a controlled example of a naked quantum critical point. We discuss the crucial role of thermal fluctuations in relating our results with earlier work where superconductivity always develops due to the special role of the first Matsubara frequency.

  20. Note: Radio frequency surface impedance characterization system for superconducting samples at 7.5 GHz.

    Science.gov (United States)

    Xiao, B P; Reece, C E; Phillips, H L; Geng, R L; Wang, H; Marhauser, F; Kelley, M J

    2011-05-01

    A radio frequency (RF) surface impedance characterization (SIC) system that uses a novel sapphire-loaded niobium cavity operating at 7.5 GHz has been developed as a tool to measure the RF surface impedance of flat superconducting material samples. The SIC system can presently make direct calorimetric RF surface impedance measurements on the central 0.8 cm(2) area of 5 cm diameter disk samples from 2 to 20 K exposed to RF magnetic fields up to 14 mT. To illustrate system utility, we present first measurement results for a bulk niobium sample.

  1. Superconducting spin valve effect in Fe/In based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Leksin, Pavel; Schumann, Joachim; Kataev, Vladislav; Schmidt, Oliver; Buechner, Bernd [Leibniz Institute for Solid State and Materials Research IFW Dresden (Germany); Garifyanov, Nadir; Garifullin, Ilgiz [Zavoisky Physical-Technical Institute, Kazan Scientific Center, Russian Academy of Sciences (Russian Federation)

    2015-07-01

    We report on magnetic and superconducting properties of the spin-valve multilayer system CoOx/Fe1/Cu/Fe2/In. The Superconducting Spin Valve Effect (SSVE) assumes the T{sub c} difference between parallel (P) and antiparallel (AP) orientations of the Fe1 and Fe2 layers' magnetizations. The SSVE value oscillates and changes its sign when the Fe2 layer thickness d{sub Fe2} is varied from 0 to 5 nm. The SSVE value is positive, as expected, in the range 0.4 nm ≤ d{sub Fe2} ≤ 0.8 nm. For a rather broad range of thicknesses 1 nm ≤ d{sub Fe2} ≤ 2.6 nm the SSVE has negative sign assuming the inverse SSVE. Moreover, the magnitude of the inverse effect is larger than that of the positive direct effect. We attribute these oscillations to a quantum interference of the cooper pair wave functions in the magnetic part of the system. For most of the spin-valve samples from this set we experimentally realized the full switching between normal and superconducting states due to direct and inverse SSVE. The analysis of the experimental data has enabled the determination of all microscopic parameters of the studied system.

  2. Current redistribution effects on superconducting d.c, and microwave measurements

    International Nuclear Information System (INIS)

    Barra, M; Cassinese, A; Vaglio, R

    2006-01-01

    In the last two decades, non conventional behavior of the d.c. transport properties of superconductors, with the appearance of anomalous peaks at the transition, have been investigated and interpreted in different ways. In several cases it was recognized that the behavior can be due to current redistribution effects related to the non-homogeneous nature of the measured superconducting sample. In this paper we will briefly review and discuss these effects and, referring to simple concentrated constant equivalent circuits, we will show that sample non-homogeneity can produce the observed features. Then, in the same framework, by performing specific simulations on planar resonators, we will show that anomalous peaks in temperature dependence of the resonant frequency and of the extracted surface reactance can occur at the transition temperature of minority, lower Tc, superconducting phases

  3. Fermi surface of underdoped high-Tc superconducting cuprates

    International Nuclear Information System (INIS)

    Dai, X.; Su, Z.; Yu, L.

    1997-01-01

    The coexistence of a π-flux state and a d-wave resonant-valance-bond (RVB) state is considered in this paper within the slave-boson approach. A critical value of doping concentration δ c is found, below which the coexisting π-flux and d-wave RVB state is favored in energy. The pseudo-Fermi surface of spinons and the physical electron spectral function are calculated. A clear Fermi-level crossing is found along the (0,0) to (π, π) direction, but no such crossing is detected along the (π, 0) to (π, π) direction. Also, an energy gap of d-wave symmetry appears at the Fermi level in our calculation. The above results are in agreement with the angle-resolved photoemission experiments which indicate at a d-wave pseudogap and a half-pocket-like Fermi surface in underdoped cuprates. copyright 1997 The American Physical Society

  4. Free energy surfaces in the superconducting mixed state

    Science.gov (United States)

    Finnemore, D. K.; Fang, M. M.; Bansal, N. P.; Farrell, D. E.

    1989-01-01

    The free energy surface for Tl2Ba2Ca2Cu3O1O has been measured as a function of temperature and magnetic field to determine the fundamental thermodynamic properties of the mixed state. The change in free energy, G(H)-G(O), is found to be linear in temperature over a wide range indicating that the specific heat is independent of field.

  5. Discontinuity of capacitance at the onset of surface superconductivity

    Czech Academy of Sciences Publication Activity Database

    Morawetz, K.; Lipavský, Pavel; Mareš, Jiří J.

    2009-01-01

    Roč. 11, č. 2 (2009), 023032/1-023032/8 ISSN 1367-2630 R&D Projects: GA AV ČR IAA1010404; GA ČR(CZ) GA202/06/0040; GA AV ČR IAA100100712 Institutional research plan: CEZ:AV0Z10100521 Keywords : capacitance * surface supraconductivity Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.312, year: 2009

  6. Superconductivity in technology

    International Nuclear Information System (INIS)

    Komarek, P.

    1976-01-01

    Physics, especially high energy physics and solid state physics was the first area in which superconducting magnets were used but in the long run, the most extensive application of superconductivity will probably be in energy technology. Superconducting power transmission cables, magnets for energy conversion in superconducting electrical machines, MHD-generators and fusion reactors and magnets for energy storage are being investigated. Magnets for fusion reactors will have particularly large physical dimensions, which means that much development effort is still needed, for there is no economic alternative. Superconducting surfaces in radio frequency cavities can give Q-values up to a factor of 10 6 higher than those of conventional resonators. Particle accelerators are the important application. And for telecommunication, simple coaxial superconducting radio frequency cables seem promising. The tunnel effect in superconducting junctions is now being developed commercially for sensitive magnetometers and may soon possibly feature in the memory cells of computer devices. Hence superconductivity can play an important role in the technological world, solving physical and technological problems and showing economic advantages as compared with possible conventional techniques, bearing also in mind the importance of reliability and safety. (author)

  7. Fabrication of Circuit QED Quantum Processors, Part 1: Extensible Footprint for a Superconducting Surface Code

    Science.gov (United States)

    Bruno, A.; Michalak, D. J.; Poletto, S.; Clarke, J. S.; Dicarlo, L.

    Large-scale quantum computation hinges on the ability to preserve and process quantum information with higher fidelity by increasing redundancy in a quantum error correction code. We present the realization of a scalable footprint for superconducting surface code based on planar circuit QED. We developed a tileable unit cell for surface code with all I/O routed vertically by means of superconducting through-silicon vias (TSVs). We address some of the challenges encountered during the fabrication and assembly of these chips, such as the quality of etch of the TSV, the uniformity of the ALD TiN coating conformal to the TSV, and the reliability of superconducting indium contact between the chips and PCB. We compare measured performance to a detailed list of specifications required for the realization of quantum fault tolerance. Our demonstration using centimeter-scale chips can accommodate the 50 qubits needed to target the experimental demonstration of small-distance logical qubits. Research funded by Intel Corporation and IARPA.

  8. Application of a phenomenological model for the surface impedance in high temperature superconducting films

    International Nuclear Information System (INIS)

    Mosquera, A.S.; Landinez Tellez, D.A.; Roa-Rojas, J.

    2007-01-01

    We report the application of a phenomenological model for the microwave surface impedance in high temperature superconducting films. This model is based on the modified two-fluid model, in which the real and imaginary parts of the surface impedance use the modelling parameter γ. This is responsible for the superconducting and normal charge carrier density and is used for the description of the temperature dependence of the London penetration depth λ L (T) including λ L (0). The relaxation time model also uses the γ parameter in combination with the residual resistance parameter α. The parameter δ 1 1 , γ, α, and δ 2 . The parameter δ 2 n (T) is a result of the competition between the increase of the relaxation time and the decrease of the normal charge-carrier density. We applied this model to analyze experimental results of MgB 2 , YBa 2 Cu 3 O 7-δ and GdBa 2 Cu 3 O 7-δ superconducting material. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

    Energy Technology Data Exchange (ETDEWEB)

    Romanenko, A.; Grassellino, A. [Fermi National Accelerator Laboratory, Batavia, Illinois 60510 (United States)

    2013-06-24

    Utilizing difference in temperature dependencies we decoupled Bardeen-Cooper-Schrieffer (BCS) and residual components of the microwave surface resistance of superconducting niobium at all rf fields up to B{sub rf}{approx}115 mT. We reveal that the residual resistance decreases with field at B{sub rf} Less-Than-Or-Equivalent-To 40 mT and strongly increases in chemically treated niobium at B{sub rf}>80 mT. We find that BCS surface resistance is weakly dependent on field in the clean limit, whereas a strong and peculiar field dependence emerges after 120 Degree-Sign C vacuum baking.

  10. Laser Processing on the Surface of Niobium Superconducting Radio-Frequency Accelerator Cavities

    Science.gov (United States)

    Singaravelu, Senthilraja; Klopf, Michael; Krafft, Geoffrey; Kelley, Michael

    2011-03-01

    Superconducting Radio frequency (SRF) niobium cavities are at the heart of an increasing number of particle accelerators.~ Their performance is dominated by a several nm thick layer at the interior surface. ~Maximizing its smoothness is found to be critical and aggressive chemical treatments are employed to this end.~ We describe laser-induced surface melting as an alternative ``greener'' approach.~ Modeling guided selection of parameters for irradiation with a Q-switched Nd:YAG laser.~ The resulting topography was examined by SEM, AFM and Stylus Profilometry.

  11. The Path to High Q-Factors in Superconducting Accelerating Cavities: Flux Expulsion and Surface Resistance Optimization

    Energy Technology Data Exchange (ETDEWEB)

    Martinello, Martina [Illinois Inst. of Technology, Chicago, IL (United States)

    2016-12-01

    causing temperature rising. The physics behind the magnetic flux expulsion is also analyzed, showing that during a fast cooldown the magnetic field structures, called vortices, tend to move in the same direction of the thermal gradient, from the Meissner state region to the mixed state region, minimizing the Gibbs free energy. On the other hand, during a slow cool down, not only the vortices movement is limited by the absence of thermal gradients, but, also, at the end of the superconducting transition, the magnetic field concentrates along randomly distributed normal-conducting region from which it cannot be expelled anymore. The systematic study of the surface resistance components performed for the different surface treatments, reveals that the BCS surface resistance and the trapped flux surface resistance have opposite trends as a function of the surface impurity content, defined by the mean free path. At medium field value, the BCS surface resistance is minimized for nitrogen-doped cavities and significantly larger for standard niobium cavities. On the other hand, Nitrogen-doped cavities show larger dissipation due to trapped flux. This is consequence of the bell-shaped trend of the trapped flux sensitivity as a function of the mean free path. Such experimental findings allow also a better understanding of the RF dissipation due to trapped flux. The best compromise between all the surface resistance components, taking into account the possibility of trapping some external magnetic field, is given by light nitrogen-doping treatments. However, the beneficial effects of the nitrogen-doping is completely lost when large amount of magnetic field is trapped during the cooldown, underlying the importance of both cooldown and magnetic field shielding optimization in high quality factors cryomodules.

  12. The path to high Q-factors in superconducting accelerating cavities: Flux expulsion and surface resistance optimization

    Science.gov (United States)

    Martinello, Martina

    causing temperature rising. The physics behind the magnetic flux expulsion is also analyzed, showing that during a fast cooldown the magnetic field structures, called vortices, tend to move in the same direction of the thermal gradient, from the Meissner state region to the mixed state region, minimizing the Gibbs free energy. On the other hand, during a slow cool down, not only the vortices movement is limited by the absence of thermal gradients, but, also, at the end of the superconducting transition, the magnetic field concentrates along randomly distributed normal-conducting region from which it cannot be expelled anymore. The systematic study of the surface resistance components performed for the different surface treatments, reveals that the BCS surface resistance and the trapped flux surface resistance have opposite trends as a function of the surface impurity content, defined by the mean free path. At medium field value, the BCS surface resistance is minimized for nitrogen-doped cavities and significantly larger for standard niobium cavities. On the other hand, Nitrogen-doped cavities show larger dissipation due to trapped flux. This is consequence of the bell-shaped trend of the trapped flux sensitivity as a function of the mean free path. Such experimental findings allow also a better understanding of the RF dissipation due to trapped flux. The best compromise between all the surface resistance components, taking into account the possibility of trapping some external magnetic field, is given by light nitrogen-doping treatments. However, the beneficial effects of the nitrogen-doping is completely lost when large amount of magnetic field is trapped during the cooldown, underlying the importance of both cooldown and magnetic field shielding optimization in high quality factors cryomodules.

  13. Superconducting proximity effect in mesoscopic superconductor/normal-metal junctions

    CERN Document Server

    Takayanagi, H; Toyoda, E

    1999-01-01

    The superconducting proximity effect is discussed in mesoscopic superconductor/normal-metal junctions. The newly-developed theory shows long-range phase-coherent effect which explaines early experimental results of giant magnetoresistance oscillations in an Andreev interferometer. The theory also shows that the proximity correction to the conductance (PCC) has a reentrant behavior as a function of energy. The reentrant behavior is systematically studied in a gated superconductor-semiconductor junction. A negative PCC is observed in the case of a weak coupling between the normal metal and the external reservoir. Phase coherent ac effect is also observed when rf is irradiated to the junction.

  14. Theory of the isotope effect in superconducting compounds

    International Nuclear Information System (INIS)

    Culetto, F.J.; Rainer, D.

    1978-05-01

    We present a theoretical analysis of the isotope effect on the superconducting transition temperature. Our method is to calculate via formal perturbation theory the response of the transition temperature to small changes of the masses of the various constituents of the compound. We discuss the relation between the isotope effect and various more fundamental parameters in strong coupling superconductors. As illustrative examples, we consider the systems Pd-H(D) alloys and the binary Chevrel phase superconductor Mo 6 Se 8 , and show that analysis of the isotope effect can yield useful information concerning interaction mechanisms in these compounds. (orig.)

  15. Surface Characterization of Impurities in Superconducting Niobium for Radio Frequency (RF) Cavities used in Particle Accelerators

    Science.gov (United States)

    Maheshwari, Prateek

    Niobium (Nb) is the material of choice for Superconducting Radio Frequency (SRF) Cavities used in particle accelerators owing to its high critical temperature (Tc = 9.2 K) and critical magnetic field (≈ 200mT). However, niobium tends to harbor interstitial impurities such as H, C, O and N, which are detrimental to cavity performance. Since the magnetic field penetration depth (lambda) of niobium is 40nm, it is important to characterize these impurities using surface characterization techniques. Also, it is known that certain heat treatments improve cavity efficiency via interstitial impurity removal from the surface of niobium. Thus, a systematic study on the effect of these heat treatments on the surface impurity levels is needed. In this work, surface analysis of both heat treated and non heat treated (120°C-1400°C) large grain (single crystal) bulk niobium samples was performed using secondary ion mass spectrometry (SIMS) and Transmission Electron Microscopy (TEM). Impurity levels were compared on the surface using SIMS after various types of heat treatments expected to improve cavity performance, and the effect of these heat treatments on the surface impurities were examined. SIMS characterization of ion implanted standards of C, N, O, D showed that quantification of C, N and O impurities in Nb is achievable and indicated that H is very mobile in Nb. It was hence determined that quantification of H in Nb is not possible using SIMS due to its high diffusivity in Nb. However, a comparative study of the high temperature heat treated (600°C-1400°C) and non heat treated (control) samples revealed that hydrogen levels decreased by upto a factor of 100. This is attributed to the dissociation of the niobium surface oxide layer, which acts as a passivating film on the surface, and subsequent desorption of hydrogen. Reformation of this oxide layer on cool down disallows any re-absorption of hydrogen, indicating that the oxide acts as a surface barrier for

  16. 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

  17. Magnetization effects in superconducting dipole magnets

    International Nuclear Information System (INIS)

    Ishimoto, H.; Peters, R.E.; Price, M.E.; Yamada, R.

    1977-01-01

    Magnetization effect of superconductors on the field quality was investigated for some of the typical Energy Doubler bending magnets. Calculations were made using the computor program GFUN2D and compared with some measured results. Agreement between them is good. The field quality at low excitation is mainly determined by the magnetization effect. A similar effect due to a stainless collar mechanical support was also calculated, although it is not as big as the first one

  18. Surface temperature measurements on superconducting cavities in superfluid helium

    International Nuclear Information System (INIS)

    Fouaidy, T.; Junquera, T.; Caruette, A.

    1991-01-01

    Two thermometry systems have been developed: a scanning thermometer system routinely used for the 1.5 GHz monocell cavity studies and a fixed thermometer array used to investigate spatial surface resistance distribution on various SC removable endplates of a cylindrical TE011mode cavity. Thermometers used in these systems are thermally insulated from the surrounding HeII bath by an epoxy housing ('epoxy'thermometers). Accurate calibration of the fixed thermometers was conducted by using different test cells and the experimental results were compared to model calculations performed with a finite element computational code. Measured thermometer efficiency and linearity are in good agreement with numerical results. Some typical temperature maps of different Nb samples obtained with the TE011 array (40 epoxy thermometers) are discussed. On the basis of numerical modelling results, a new type of thermometer with an improved efficiency has been designed. The thermal insulation against Helium II has been drastically improved by placing the sensitive part of the thermometer in a small vacuum jacket ('vacuum' thermometers). Two main goals have been reached with the first prototypes: improved efficiency by a factor of 2.5 - 3, and a bath temperature dependence of the thermal response in good agreement with the expected Kapitza conductance behaviour. Fitting experimental results with numerical modelling data, allow us to estimate the Kapitza conductance. The obtained values are in good agreement with the previous results reported by several authors using a different measurement method. The 'vacuum' thermometers are currently used on the TE011 mode cavity with Nb and NbTiN plates and the first results are presented

  19. Unconventional superconductivity and surface pairing symmetry in half-Heusler compounds

    Science.gov (United States)

    Wang, Qing-Ze; Yu, Jiabin; Liu, Chao-Xing

    2018-06-01

    Signatures of nodal line/point superconductivity [Kim et al., Sci. Adv. 4, eaao4513 (2018), 10.1126/sciadv.aao4513; Brydon et al., Phys. Rev. Lett. 116, 177001 (2016), 10.1103/PhysRevLett.116.177001] have been observed in half-Heusler compounds, such as LnPtBi (Ln = Y, Lu). Topologically nontrivial band structures, as well as topological surface states, have also been confirmed by angular-resolved photoemission spectroscopy in these compounds [Liu et al., Nat. Commun. 7, 12924 (2016), 10.1038/ncomms12924]. In this paper, we present a systematical classification of possible gap functions of bulk states and surface states in half-Heusler compounds and the corresponding topological properties based on the representations of crystalline symmetry group. Different from all the previous studies based on the four band Luttinger model, our study starts with the six-band Kane model, which involves both four p-orbital type of Γ8 bands and two s-orbital type of Γ6 bands. Although the Γ6 bands are away from the Fermi energy, our results reveal the importance of topological surface states, which originate from the band inversion between Γ6 and Γ8 bands, in determining surface properties of these compounds in the superconducting regime by combining topological bulk state picture and nontrivial surface state picture.

  20. Field limit and nano-scale surface topography of superconducting radio-frequency cavity made of extreme type II superconductor

    Science.gov (United States)

    Kubo, Takayuki

    2015-06-01

    The field limit of a superconducting radio-frequency cavity made of a type II superconductor with a large Ginzburg-Landau parameter is studied, taking the effects of nano-scale surface topography into account. If the surface is ideally flat, the field limit is imposed by the superheating field. On the surface of cavity, however, nano-defects almost continuously distribute and suppress the superheating field everywhere. The field limit is imposed by an effective superheating field given by the product of the superheating field for an ideal flat surface and a suppression factor that contains the effects of nano-defects. A nano-defect is modeled by a triangular groove with a depth smaller than the penetration depth. An analytical formula for the suppression factor of bulk and multilayer superconductors is derived in the framework of the London theory. As an immediate application, the suppression factor of the dirty Nb processed by electropolishing is evaluated by using results of surface topographic study. The estimated field limit is consistent with the present record field of nitrogen-doped Nb cavities. Suppression factors of surfaces of other bulk and multilayer superconductors, and those after various surface processing technologies, can also be evaluated by using the formula.

  1. 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

  2. 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.

  3. Rf superconducting devices

    International Nuclear Information System (INIS)

    Hartwig, W.H.; Passow, C.

    1975-01-01

    Topics discussed include (1) the theory of superconductors in high-frequency fields (London surface impedance, anomalous normal surface resistance, pippard nonlocal theory, quantum mechanical model, superconductor parameters, quantum mechanical calculation techniques for the surface, impedance, and experimental verification of surface impedance theories); (2) residual resistance (separation of losses, magnetic field effects, surface resistance of imperfect and impure conductors, residual loss due to acoustic coupling, losses from nonideal surfaces, high magnetic field losses, field emission, and nonlinear effects); (3) design and performance of superconducting devices (design considerations, materials and fabrication techniques, measurement of performance, and frequency stability); (4) devices for particle acceleration and deflection (advantages and problems of using superconductors, accelerators for fast particles, accelerators for particles with slow velocities, beam optical devices separators, and applications and projects under way); (5) applications of low-power superconducting resonators (superconducting filters and tuners, oscillators and detectors, mixers and amplifiers, antennas and output tanks, superconducting resonators for materials research, and radiation detection with loaded superconducting resonators); and (6) transmission and delay lines

  4. Transverse ratchet effect and superconducting vortices: simulation and experiment

    International Nuclear Information System (INIS)

    Dinis, L; Parrondo, J M R; Perez de Lara, D; Gonzalez, E M; Vicent, J L; Anguita, J V

    2009-01-01

    A transverse ratchet effect has been measured in magnetic/superconducting hybrid films fabricated by electron beam lithography and magnetron sputtering techniques. The samples are Nb films grown on top of an array of Ni nanotriangles. Injecting an ac current parallel to the triangle reflection symmetry axis yields an output dc voltage perpendicular to the current, due to a net motion of flux vortices in the superconductor. The effect is reproduced by numerical simulations of vortices as Langevin particles with realistic parameters. Simulations provide an intuitive picture of the ratchet mechanism, revealing the fundamental role played by the random intrinsic pinning of the superconductor.

  5. Switching, storage, and erasure effects in a superconducting thin film

    International Nuclear Information System (INIS)

    Testardi, L.R.

    1976-01-01

    Thin niobium films can be switched from a superconducting to a resistive state permanently by application of a short electrical pulse. Application of a short pulse of opposite polarity returns the film to the superconducting state

  6. Analysis of Nb3Sn surface layers for superconducting radio frequency cavity applications

    Science.gov (United States)

    Becker, Chaoyue; Posen, Sam; Groll, Nickolas; Cook, Russell; Schlepütz, Christian M.; Hall, Daniel Leslie; Liepe, Matthias; Pellin, Michael; Zasadzinski, John; Proslier, Thomas

    2015-02-01

    We present an analysis of Nb3Sn surface layers grown on a bulk Niobium (Nb) coupon prepared at the same time and by the same vapor diffusion process used to make Nb3Sn coatings on 1.3 GHz Nb cavities. Tunneling spectroscopy reveals a well-developed, homogeneous superconducting density of states at the surface with a gap value distribution centered around 2.7 ± 0.4 meV and superconducting critical temperatures (Tc) up to 16.3 K. Scanning transmission electron microscopy performed on cross sections of the sample's surface region shows an ˜2 μm thick Nb3Sn surface layer. The elemental composition map exhibits a Nb:Sn ratio of 3:1 and reveals the presence of buried sub-stoichiometric regions that have a ratio of 5:1. Synchrotron x-ray diffraction experiments indicate a polycrystalline Nb3Sn film and confirm the presence of Nb rich regions that occupy about a third of the coating volume. These low Tc regions could play an important role in the dissipation mechanisms occurring during RF tests of Nb3Sn-coated Nb cavities and open the way for further improving a very promising alternative to pure Nb cavities for particle accelerators.

  7. Analysis of Nb{sub 3}Sn surface layers for superconducting radio frequency cavity applications

    Energy Technology Data Exchange (ETDEWEB)

    Becker, Chaoyue [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); High Energy Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Department of Physics, Illinois Institute of Technology, Chicago, Illinois 60616 (United States); Posen, Sam; Hall, Daniel Leslie [Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York 14853 (United States); Groll, Nickolas; Proslier, Thomas, E-mail: prolier@anl.gov [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); High Energy Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Cook, Russell [Nanoscience and Technology Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Schlepütz, Christian M. [X-ray Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Liepe, Matthias [Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York 14853 (United States); Department of Physics, Cornell University, Ithaca, New York 14853 (United States); Pellin, Michael [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Zasadzinski, John [Department of Physics, Illinois Institute of Technology, Chicago, Illinois 60616 (United States)

    2015-02-23

    We present an analysis of Nb{sub 3}Sn surface layers grown on a bulk Niobium (Nb) coupon prepared at the same time and by the same vapor diffusion process used to make Nb{sub 3}Sn coatings on 1.3 GHz Nb cavities. Tunneling spectroscopy reveals a well-developed, homogeneous superconducting density of states at the surface with a gap value distribution centered around 2.7 ± 0.4 meV and superconducting critical temperatures (T{sub c}) up to 16.3 K. Scanning transmission electron microscopy performed on cross sections of the sample's surface region shows an ∼2 μm thick Nb{sub 3}Sn surface layer. The elemental composition map exhibits a Nb:Sn ratio of 3:1 and reveals the presence of buried sub-stoichiometric regions that have a ratio of 5:1. Synchrotron x-ray diffraction experiments indicate a polycrystalline Nb{sub 3}Sn film and confirm the presence of Nb rich regions that occupy about a third of the coating volume. These low T{sub c} regions could play an important role in the dissipation mechanisms occurring during RF tests of Nb{sub 3}Sn-coated Nb cavities and open the way for further improving a very promising alternative to pure Nb cavities for particle accelerators.

  8. Analysis of Nb3Sn surface layers for superconducting radio frequency cavity applications

    International Nuclear Information System (INIS)

    Becker, Chaoyue; Posen, Sam; Hall, Daniel Leslie; Groll, Nickolas; Proslier, Thomas; Cook, Russell; Schlepütz, Christian M.; Liepe, Matthias; Pellin, Michael; Zasadzinski, John

    2015-01-01

    We present an analysis of Nb 3 Sn surface layers grown on a bulk Niobium (Nb) coupon prepared at the same time and by the same vapor diffusion process used to make Nb 3 Sn coatings on 1.3 GHz Nb cavities. Tunneling spectroscopy reveals a well-developed, homogeneous superconducting density of states at the surface with a gap value distribution centered around 2.7 ± 0.4 meV and superconducting critical temperatures (T c ) up to 16.3 K. Scanning transmission electron microscopy performed on cross sections of the sample's surface region shows an ∼2 μm thick Nb 3 Sn surface layer. The elemental composition map exhibits a Nb:Sn ratio of 3:1 and reveals the presence of buried sub-stoichiometric regions that have a ratio of 5:1. Synchrotron x-ray diffraction experiments indicate a polycrystalline Nb 3 Sn film and confirm the presence of Nb rich regions that occupy about a third of the coating volume. These low T c regions could play an important role in the dissipation mechanisms occurring during RF tests of Nb 3 Sn-coated Nb cavities and open the way for further improving a very promising alternative to pure Nb cavities for particle accelerators

  9. High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides

    Science.gov (United States)

    Charnukha, A.; Evtushinsky, D. V.; Matt, C. E.; Xu, N.; Shi, M.; Büchner, B.; Zhigadlo, N. D.; Batlogg, B.; Borisenko, S. V.

    2015-12-01

    In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.

  10. Shielding effectiveness of superconductive particles in plastics

    International Nuclear Information System (INIS)

    Pienkowski, T.; Kincaid, J.; Lanagan, M.T.; Poeppel, R.B.; Dusek, J.T.; Shi, D.; Goretta, K.C.

    1988-09-01

    The ability to cool superconductors with liquid nitrogen instead of liquid helium has opened the door to a wide range of research. The well known Meissner effect, which states superconductors are perfectly diamagnetic, suggests shielding applications. One of the drawbacks to the new ceramic superconductors is the brittleness of the finished material. Because of this drawback, any application which required flexibility (e.g., wire and cable) would be impractical. Therefore, this paper presents the results of a preliminary investigation into the shielding effectiveness of YBa 2 Cu 3 O/sub 7-x/ both as a composite and as a monolithic material. Shielding effectiveness was measured using two separate test methods. One tested the magnetic (near field) shielding, and the other tested the electromagnetic (far field) shielding. No shielding was seen in the near field measurements on the composite samples, and only one heavily loaded sample showed some shielding in the far field. The monolithic samples showed a large amount of magnetic shielding. 5 refs., 5 figs

  11. High-Q operation of superconducting rf cavities: Potential impact of thermocurrents on the rf surface resistance

    Directory of Open Access Journals (Sweden)

    J.-M. Vogt

    2015-04-01

    Full Text Available For many new accelerator applications, superconducting radio frequency systems are the enabling technology. In particular for CW applications, much effort is being expended to minimize the power dissipation (surface resistance of niobium cavities. Starting in 2009, we suggested a means of reducing the residual resistance by performing a thermal cycle [O. Kugeler et al., in Proceedings of the 14th International Conference on RF Superconductivity (2009, p. 352], a procedure of warming up a cavity after initial cooldown to about 20 K and cooling it down again. In subsequent studies [J. M. Vogt, O. Kugeler, and J. Knobloch, Phys. Rev. ST Accel. Beams 16, 102002 (2013], this technique was used to manipulate the residual resistance by more than a factor of 2. It was postulated that thermocurrents during cooldown generate additional trapped magnetic flux that impacts the cavity quality factor. Here, we present a more extensive study that includes measurements of two additional passband modes and that confirms the effect. In this paper, we also discuss simulations that support the claim. While the layout of the cavity LHe tank system is cylindrically symmetric, we show that the temperature dependence of the material parameters results in a nonsymmetric current distribution. Hence a significant amount of magnetic flux can be generated at the rf surface.

  12. Effects of neutron irradiation on a superconducting metallic glass

    International Nuclear Information System (INIS)

    Kramer, E.A.; Johnson, W.L.; Cline, C.

    1979-06-01

    The effects of fast neutron irradiation on a superconducting metallic glass (Mo 6 Ru 4 ) 82 B 18 have been studied. Following irradiation to a total fluence of 10 19 n/cm 2 , T/sub c/ increases from 6.05 K to 6.19 K, and the width of the transition decreases sharply. The density of the material decreases by 1.5%, and the x-ray scattering intensity maxima are broadened. An improvement in the ductility of the samples is observed which together with the other observations suggests the production of defects having atomic scale dimensions and characterized by excess volume

  13. Memory effect in the high-temperature superconducting bulks

    International Nuclear Information System (INIS)

    Zhang, Xing-Yi; Zhou, Jun; Zhou, You-He

    2013-01-01

    Highlights: •Effects of temperature cycles on levitation force relaxation are investigated. •Memory effect of the YBCO bulks is observed in experiments. •With an increase of temperature, memory of the superconductor is gradually lost. -- Abstract: We present an experimental investigation of the relaxation of vertical force components in a high-temperature superconducting levitation system with different temperature cycle processes. For a selected ambient temperature (T 1 ) of the system, the experimental results show that the relaxations of the levitation forces are strongly dependent on the initial temperature. When the sample was submitted to temperature jumps around T 1 , the sample temperature was regulated at T 2 , and there were two cases of the experiments, ΔT = T 2 − T 1 0 (positive temperature cycle). It was found that in the case of negative temperature cycle, the superconducting samples have memory effect. And for the positive temperature cycle, with the experimental temperature increase, the memory effect of samples is gradually losing. Additionally, with the increase of temperature, the influences of the negative and positive temperature cycle on the levitation force relaxation are unsymmetrical. All the results are interpreted by using the characteristics of the free energy ‘ground’ plot of the Spin-glasses qualitatively

  14. Superstrate loading effects on the resonant characteristics of high Tc superconducting circular patch printed on anisotropic materials

    Science.gov (United States)

    Bedra, Sami; Bedra, Randa; Benkouda, Siham; Fortaki, Tarek

    2017-12-01

    In this paper, the effects of both anisotropies in the substrate and superstrate loading on the resonant frequency and bandwidth of high-Tc superconducting circular microstrip patch in a substrate-superstrate configuration are investigated. A rigorous analysis is performed using a dyadic Galerkin's method in the vector Hankel transform domain. Galerkin's procedure is employed in the spectral domain where the TM and TE modes of the cylindrical cavity with magnetic side walls are used in the expansion of the disk current. The effect of the superconductivity of the patch is taken into account using the concept of the complex resistive boundary condition. London's equations and the two-fluid model of Gorter and Casimir are used in the calculation of the complex surface impedance of the superconducting circular disc. The accuracy of the analysis is tested by comparing the computed results with previously published data for several anisotropic substrate-superstrate materials. Good agreement is found among all sets of results. The numerical results obtained show that important errors can be made in the computation of the resonant frequencies and bandwidths of the superconducting resonators when substrate dielectric anisotropy, and/or superstrate anisotropy are ignored. Other theoretical results obtained show that the superconducting circular microstrip patch on anisotropic substrate-superstrate with properly selected permittivity values along the optical and the non-optical axes combined with optimally chosen structural parameters is more advantageous than the one on isotropic substrate-superstrate by exhibiting wider bandwidth characteristic.

  15. Microwave surface resistance of YBa2Cu3O/sub 6.9/ superconducting films

    International Nuclear Information System (INIS)

    Martens, J.S.; Beyer, J.B.; Ginley, D.S.

    1988-01-01

    The microwave surface resistance of an YBa 2 Cu 3 O/sub 6.9/ superconducting thick film was measured over the range 7.0--16.7 GHz at 77 K. This was done by placing a sample in a TE 01 /sub n/ wavemeter cavity and observing the change in selectivity of the cavity. The material's surface resistance is of the same order of magnitude as that of silver at 77 K from 8 to 12 GHz and improves about another order at 4.2 K. The power-law behavior of surface resistance with frequency is probably close to quadratic. This is similar to the behavior of low critical temperature superconductors

  16. High-pressure effects on the superconductivity of β-pyrochlore oxides AOs2O6

    International Nuclear Information System (INIS)

    Muramatsu, Takaki; Takeshita, Nao; Terakura, Chikeko; Takagi, Hidenori; Tokura, Yoshinori; Yonezawa, Shigeki; Muraoka, Yuji; Hiroi, Zenji

    2006-01-01

    High-pressure effects on the superconducting transitions of β-pyrochlore oxide superconductors AOs 2 O 6 (A=Cs, Rb, K) are studied by measuring resistivity under high pressures up to 16 GPa. The superconducting transition temperature T c first increases with increasing pressure in all the compounds and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa) and 10 K (0.6 GPa) for A=Cs, Rb and K, respectively. Finally, the superconductivity is suppressed completely at a critical pressure near 7 and 6 GPa for A=Rb and K and probably above 10 GPa for A=Cs. Characteristic changes in the temperature dependence of resistivity of RbOs 2 O 6 under high pressure. The residual resistivity largely increases with pressure above 4 GPa and, as a result, resistivity indicates small temperature dependence down to 4.2 K at 7 GPa and application of further pressure up to 10 GPa indicates that temperature dependence of resistivity decrease below 100 K. This characteristic behavior in the β-pyrochlore oxides may originate from the nesting of nearly octahedron shape of Fermi surface

  17. Effect of reduction of mechanical losses in AC superconducting coils having various FRP bobbins

    International Nuclear Information System (INIS)

    Sekine, N.; Tada, S.; Higuchi, T.; Takao, T.; Yamanaka, A.; Fukui, S.

    2004-01-01

    We have demonstrated in our previous works that a use of the particular structural material for superconducting coils was effective to mechanical-loss reduction under AC operation. In this study, we measured losses to investigate influence of the mechanical losses in the coils having various fiber reinforced plastics (FRPs) with different thermal expansion coefficients. The losses were small in the coils whose winding tension at coil-operating temperature were strong, on the contrary, the losses of the coil having the weak winding tension were large. The coil having the strongest winding tension at liquid helium temperature showed the smallest loss in all coils, and the loss agreed with a value from the Norris's analysis. We think that the mechanical loss becomes almost zero in this coil since the strong tension can prevent the periodic vibration of the superconducting wire. The dependence of the loss on the difference in surface conditions of the materials of the superconducting coil's bobbins was not observed, however, the mechanical losses in AC coils strongly depended on the winding tensions at cryogenic temperature

  18. Observation of quantum Zeno effect in a superconducting flux qubit

    International Nuclear Information System (INIS)

    Kakuyanagi, K; Baba, T; Matsuzaki, Y; Nakano, H; Saito, S; Semba, K

    2015-01-01

    When a quantum state is subjected to frequent measurements, the time evolution of the quantum state is frozen. This is called the quantum Zeno effect. Here, we observe such an effect by performing frequent discrete measurements in a macroscopic quantum system, a superconducting quantum bit. The quantum Zeno effect induced by discrete measurements is similar to the original idea of the quantum Zeno effect. By using a Josephson bifurcation amplifier pulse readout, we have experimentally suppressed the time evolution of Rabi oscillation using projective measurements, and also observed the enhancement of the quantum state holding time by shortening the measurement period time. This is a crucial step to realize quantum information processing using the quantum Zeno effect. (papers)

  19. Surface characterization of Nb samples electropolished with real superconducting rf accelerator cavities

    Directory of Open Access Journals (Sweden)

    Xin Zhao

    2010-12-01

    Full Text Available We report the results of surface characterizations of niobium (Nb samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris, and the beam pipe. Auger electron spectroscopy was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive x ray for elemental analysis was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S were found covering the samples nonuniformly. Niobium oxide granules with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.

  20. Three-dimensional simulations of the surface topography evolution of niobium superconducting radio frequency cavities

    Directory of Open Access Journals (Sweden)

    Rađenović Branislav M.

    2014-01-01

    Full Text Available This paper contains results of the three-dimensional simulations of the surface topography evolution of the niobium superconducting radio frequency cavities during isotropic and anisotropic etching modes. The initial rough surface is determined from the experimental power spectral density. The simulation results based on the level set method reveal that the time dependence of the root mean square roughness obeys Family-Viscek scaling law. The growth exponential factors b are determined for both etching modes. Exponential factor for the isotropic etching is 100 times lower than that for the anisotropic etching mode reviling that the isotropic etching is very useful mechanism of the smoothing. [Projekat Ministarstva nauke Republike Srbije, br. O171037 i br. III45006

  1. Numerical calculation of transient field effects in quenching superconducting magnets

    International Nuclear Information System (INIS)

    Schwerg, Juljan Nikolai

    2010-01-01

    The maximum obtainable magnetic induction of accelerator magnets, relying on normal conducting cables and iron poles, is limited to around 2 T because of ohmic losses and iron saturation. Using superconducting cables, and employing permeable materials merely to reduce the fringe field, this limit can be exceeded and fields of more than 10 T can be obtained. A quench denotes the sudden transition from the superconducting to the normal conducting state. The drastic increase in electrical resistivity causes ohmic heating. The dissipated heat yields a temperature rise in the coil and causes the quench to propagate. The resulting high voltages and excessive temperatures can result in an irreversible damage of the magnet - to the extend of a cable melt-down. The quench behavior of a magnet depends on numerous factors, e.g. the magnet design, the applied magnet protection measures, the external electrical network, electrical and thermal material properties, and induced eddy current losses. The analysis and optimization of the quench behavior is an integral part of the construction of any superconducting magnet. The dissertation is divided in three complementary parts, i.e. the thesis, the detailed treatment and the appendix. In the thesis the quench process in superconducting accelerator magnets is studied. At first, we give an overview over features of accelerator magnets and physical phenomena occurring during a quench. For all relevant effects numerical models are introduced and adapted. The different models are weakly coupled in the quench algorithm and solved by means of an adaptive time-stepping method. This allows to resolve the variation of material properties as well as time constants. The quench model is validated by means of measurement data from magnets of the Large Hadron Collider. In a second step, we show results of protection studies for future accelerator magnets. The thesis ends with a summary of the results and a critical outlook on aspects which could

  2. Numerical calculation of transient field effects in quenching superconducting magnets

    Energy Technology Data Exchange (ETDEWEB)

    Schwerg, Juljan Nikolai

    2010-07-01

    The maximum obtainable magnetic induction of accelerator magnets, relying on normal conducting cables and iron poles, is limited to around 2 T because of ohmic losses and iron saturation. Using superconducting cables, and employing permeable materials merely to reduce the fringe field, this limit can be exceeded and fields of more than 10 T can be obtained. A quench denotes the sudden transition from the superconducting to the normal conducting state. The drastic increase in electrical resistivity causes ohmic heating. The dissipated heat yields a temperature rise in the coil and causes the quench to propagate. The resulting high voltages and excessive temperatures can result in an irreversible damage of the magnet - to the extend of a cable melt-down. The quench behavior of a magnet depends on numerous factors, e.g. the magnet design, the applied magnet protection measures, the external electrical network, electrical and thermal material properties, and induced eddy current losses. The analysis and optimization of the quench behavior is an integral part of the construction of any superconducting magnet. The dissertation is divided in three complementary parts, i.e. the thesis, the detailed treatment and the appendix. In the thesis the quench process in superconducting accelerator magnets is studied. At first, we give an overview over features of accelerator magnets and physical phenomena occurring during a quench. For all relevant effects numerical models are introduced and adapted. The different models are weakly coupled in the quench algorithm and solved by means of an adaptive time-stepping method. This allows to resolve the variation of material properties as well as time constants. The quench model is validated by means of measurement data from magnets of the Large Hadron Collider. In a second step, we show results of protection studies for future accelerator magnets. The thesis ends with a summary of the results and a critical outlook on aspects which could

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

    Directory of Open Access Journals (Sweden)

    A. Di Bernardo

    2015-11-01

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

  4. Valence skipping driven superconductivity and charge Kondo effect

    International Nuclear Information System (INIS)

    Yanagisawa, Takashi; Hase, Izumi

    2013-01-01

    Highlights: •Valence skipping in metallic compounds can give rise to an unconventional superconductivity. •Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. •The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. •We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. •There is a high temperature region near the boundary. -- Abstract: Valence skipping in metallic compounds can give rise to an unconventional superconductivity. Several elements in the periodic table show valence skipping (or valence missing), for example, Bi forms the compounds in valence states +3 and +5. The doping of valence skipping elements will induce superconductivity and this will lead to a possibility of high temperature superconductivity. We consider the Wolf model with negative-U impurities, and show a phase diagram including superconducting phase. The superconducting state is changed into a metallic state with a local singlet as the attractive interaction |U| increases. There is a high temperature region near the boundary

  5. Effect of superconducting electrons on the energy splitting of tunneling systems

    International Nuclear Information System (INIS)

    Yu, C.C.; Granato, A.V.

    1985-01-01

    We consider the effect of superconducting electrons on the magnitude of the energy splitting of a tunneling system. A specific example is a hydrogen atom tunneling in niobium. We find that in this case the splitting is roughly 20% smaller in the normal state than in the superconducting state. This difference in the splitting should be observable in neutron scattering and ultrasonic measurements

  6. Effect of mild baking on superconducting niobium cavities investigated by sequential nanoremoval

    Directory of Open Access Journals (Sweden)

    A. Romanenko

    2013-01-01

    Full Text Available The near-surface nanostructure of niobium determines the performance of superconducting microwave cavities. Subtle variations in surface nanostructure lead to yet unexplained phenomena such as the dependence of the quality factor of these resonating structures on the magnitude of rf fields—an effect known as the “Q slopes”. Understanding and controlling the Q slopes is of great practical importance for particle accelerators. Here we investigate the mild baking effect—120°C vacuum baking for 48 hours—which strongly affects the Q slopes. We used a hydrofluoric acid rinse alternating with oxidation in water as a tool for stepwise material removal of about 2  nanometers/step from the surface of superconducting niobium cavities. Applying removal cycles on mild baked cavities and measuring the quality factor dependence on the rf fields after one or several such cycles allowed us to explore the distribution of lossy layers within the first several tens of nanometers from the surface. We found that a single HF rinse results in the increase of the cavity quality factor. The low field Q slope was shown to be mostly controlled by the material structure within the first six nanometers from the surface. The medium field Q slope evolution was fitted using linear (∝B peak surface magnetic field and quadratic (∝B^{2} terms in the surface resistance and it was found that best fits do not require the quadratic term. We found that about 10 nanometers of material removal are required to bring back the high field Q slope and about 20–50 nanometers to restore the onset field to the prebaking value.

  7. Mirror-smooth surfaces and repair of defects in superconducting RF cavities by mechanical polishing

    Energy Technology Data Exchange (ETDEWEB)

    Cooper, C. A. [Fermilab; Cooley, L. D. [Fermilab

    2012-11-22

    Mechanical techniques for polishing the inside surface of niobium superconducting radio-frequency (SRF) cavities have been systematically explored. By extending known techniques to fine polishing, mirror-like finishes were produced, with <15 nm RMS (root mean square) roughness over 1 mm2 scan area. This is an order of magnitude less than the typical roughness produced by the electropolishing of niobium cavities. The extended mechanical polishing (XMP) process was applied to several SRF cavities which exhibited equator defects that caused quench at <20 MV m-1 and were not improved by further electropolishing. Cavity optical inspection equipment verified the complete removal of these defects, and minor acid processing, which dulled the mirror finish, restored performance of the defective cells to the high gradients and quality factors measured for adjacent cells when tested with other harmonics. This innate repair feature of XMP could be used to increase manufacturing yield. Excellent superconducting properties resulted after initial process optimization, with quality factor Q of 3 × 1010 and accelerating gradient of 43 MV m-1 being attained for a single-cell TESLA cavity, which are both close to practical limits. Several repaired nine-cell cavities also attained Q > 8 × 109 at 35 MV m-1, which is the specification for the International Linear Collider. Future optimization of the process and pathways for eliminating requirements for acid processing are also discussed.

  8. Introduction to Superconducting RF Structures and the Effect of High Pressure Rinsing

    Energy Technology Data Exchange (ETDEWEB)

    Tajima, Tsuyoshi [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-06-30

    This presentation begins by describing RF superconductivity and SRF accelerating structures. Then the use of superconducting RF structures in a number of accelerators around the world is reviewed; for example, the International Linear Collider (ILC) will use ~16,000 SRF cavities with ~2,000 cryomodules to get 500 GeV e⁺/e⁻ colliding energy. Field emission control was (and still is) a very important practical issue for SRF cavity development. It has been found that high-pressure ultrapure water rinsing as a final cleaning step after chemical surface treatment resulted in consistent performance of single- and multicell superconducting cavities.

  9. Introduction to Superconducting RF Structures and the Effect of High Pressure Rinsing

    International Nuclear Information System (INIS)

    Tajima, Tsuyoshi

    2016-01-01

    This presentation begins by describing RF superconductivity and SRF accelerating structures. Then the use of superconducting RF structures in a number of accelerators around the world is reviewed; for example, the International Linear Collider (ILC) will use ~16,000 SRF cavities with ~2,000 cryomodules to get 500 GeV e@@@/e@@@ colliding energy. Field emission control was (and still is) a very important practical issue for SRF cavity development. It has been found that high-pressure ultrapure water rinsing as a final cleaning step after chemical surface treatment resulted in consistent performance of single- and multicell superconducting cavities.

  10. Cyclic stress effects on transport properties of superconducting composite materials

    International Nuclear Information System (INIS)

    Fisher, E.S.; Kim, S.H.; Turner, A.P.L.

    1976-01-01

    The effects of cyclic stresses at 4.2 0 K on the conductor materials for large superconducting magnets are being investigted in samples of unalloyed copper and of composites containing Nb--Ti or Nb 3 Sn wires in a copper matrix. The samples are constant-strain cycled in pure tension-compression modes. The increase in electrical resistivity of different grades of copper with number and amplitude of cycles is described. The increases can be of the order of the magnetoresistance for 1000 to 2000 cycles at 0.20 percent strain per cycle. The facility for measuring critical current changes with composite cycling is described and the initial results indicate significant I/sub c/ changes as well as unexpected filament fractures. 10 fig

  11. Quantum confinement effects on superconducting properties of Lead nanocrystals

    Science.gov (United States)

    Aubin, Herve; Moreira, Helena; Mahler, Benoit; Dubertret, Benoit

    2008-03-01

    We developed a new chemical synthesis method for producing large quantities of monodispersed lead (Pb) nanocrystals. They are obtained from the alcohol reduction of a mixture of two lead carboxylates with alkyl chains of different lengths, dissolved in a high temperature solvent. The nanocrystals obtained are protected from oxydation and aggregation by long chain fatty acids and their diameter can be tuned to reach values as low as 10 nm. Our results suggest that monodispersed particules are obtained when nucleation and growth occur at distincts temperatures, possibly as a consequence of different reactivities of the two lead carboxylates used in the solution. Owing to the large quantities of monodispersed particles produced, thermodynamics studies as function of particles diameter become possible. In particular, we will present a study of the effect of quantum confinement on superconducting properties of these Pb particles through SQUID magnetometry measurements.

  12. Local switching of two-dimensional superconductivity using the ferroelectric field effect

    Science.gov (United States)

    Takahashi, K. S.; Gabay, M.; Jaccard, D.; Shibuya, K.; Ohnishi, T.; Lippmaa, M.; Triscone, J.-M.

    2006-05-01

    Correlated oxides display a variety of extraordinary physical properties including high-temperature superconductivity and colossal magnetoresistance. In these materials, strong electronic correlations often lead to competing ground states that are sensitive to many parameters-in particular the doping level-so that complex phase diagrams are observed. A flexible way to explore the role of doping is to tune the electron or hole concentration with electric fields, as is done in standard semiconductor field effect transistors. Here we demonstrate a model oxide system based on high-quality heterostructures in which the ferroelectric field effect approach can be studied. We use a single-crystal film of the perovskite superconductor Nb-doped SrTiO3 as the superconducting channel and ferroelectric Pb(Zr,Ti)O3 as the gate oxide. Atomic force microscopy is used to locally reverse the ferroelectric polarization, thus inducing large resistivity and carrier modulations, resulting in a clear shift in the superconducting critical temperature. Field-induced switching from the normal state to the (zero resistance) superconducting state was achieved at a well-defined temperature. This unique system could lead to a field of research in which devices are realized by locally defining in the same material superconducting and normal regions with `perfect' interfaces, the interface being purely electronic. Using this approach, one could potentially design one-dimensional superconducting wires, superconducting rings and junctions, superconducting quantum interference devices (SQUIDs) or arrays of pinning centres.

  13. Ceramic superconductor/metal composite materials employing the superconducting proximity effect

    Science.gov (United States)

    Holcomb, Matthew J.

    2002-01-01

    Superconducting composite materials having particles of superconducting material disposed in a metal matrix material with a high electron-boson coupling coefficient (.lambda.). The superconducting particles can comprise any type of superconductor including Laves phase materials, Chevrel phase materials, A15 compounds, and perovskite cuprate ceramics. The particles preferably have dimensions of about 10-500 nanometers. The particles preferably have dimensions larger than the superconducting coherence length of the superconducting material. The metal matrix material has a .lambda. greater than 0.2, preferably the .lambda. is much higher than 0.2. The metal matrix material is a good proximity superconductor due to its high .lambda.. When cooled, the superconductor particles cause the metal matrix material to become superconducting due to the proximity effect. In cases where the particles and the metal matrix material are chemically incompatible (i.e., reactive in a way that destroys superconductivity), the particles are provided with a thin protective metal coating. The coating is chemically compatible with the particles and metal matrix material. High Temperature Superconducting (HTS) cuprate ceramic particles are reactive and therefore require a coating of a noble metal resistant to oxidation (e.g., silver, gold). The proximity effect extends through the metal coating. With certain superconductors, non-noble metals can be used for the coating.

  14. Phase fluctuations in two coaxial quasi-one-dimensional superconducting cylindrical surfaces serving as a model system for superconducting nanowire bundles

    Energy Technology Data Exchange (ETDEWEB)

    Wong, C.H., E-mail: ch.kh.vong@urfu.ru [Institute of Physics and Technology, Ural Federal University, Clear Water Bay, Kowloon (Russian Federation); Wu, R.P.H., E-mail: pak-hong-raymond.wu@connect.polyu.hk [Department of Applied Physics, The Hong Kong Polytechnic University (Hong Kong); Lortz, R., E-mail: lortz@ust.hk [Department of Physics, Hong Kong University of Science and Technology (Hong Kong)

    2017-03-15

    The dimensional crossover from a 1D fluctuating state at high temperatures to a 3D phase coherent state in the low temperature regime in two coaxial weakly-coupled cylindrical surfaces formed by two-dimensional arrays of parallel nanowires is studied via an 8-state 3D-XY model. This system serves as a model for quasi-one-dimensional superconductors in the form of bundles of weakly-coupled superconducting nanowires. A periodic variation of the dimensional crossover temperature T{sub DC} is observed when the inner superconducting cylindrical surface is rotated in the angular plane. T{sub DC} reaches a maximum when the relative angle between the cylinders is 2.81°, which corresponds to the maximum separation of nanowires between the two cylindrical surfaces. We demonstrate that the relative strength of phase fluctuations in this system is controllable by the rotational angle between the two surfaces with a strong suppression of the fluctuation strength at 2.81°. The phase fluctuations are suppressed gradually upon cooling, before they abruptly vanish below T{sub DC}. Our model thus allows us to study how phase fluctuations can be suppressed in quasi-one-dimensional superconductors in order to achieve a global phase coherent state throughout the nanowire array with zero electric resistance.

  15. Weight-4 Parity Checks on a Surface Code Sublattice with Superconducting Qubits

    Science.gov (United States)

    Takita, Maika; Corcoles, Antonio; Magesan, Easwar; Bronn, Nicholas; Hertzberg, Jared; Gambetta, Jay; Steffen, Matthias; Chow, Jerry

    We present a superconducting qubit quantum processor design amenable to the surface code architecture. In such architecture, parity checks on the data qubits, performed by measuring their X- and Z- syndrome qubits, constitute a critical aspect. Here we show fidelities and outcomes of X- and Z-parity measurements done on a syndrome qubit in a full plaquette consisting of one syndrome qubit coupled via bus resonators to four code qubits. Parities are measured after four code qubits are prepared into sixteen initial states in each basis. Results show strong dependence on ZZ between qubits on the same bus resonators. This work is supported by IARPA under Contract W911NF-10-1-0324.

  16. Defect Detection in Superconducting Radiofrequency Cavity Surface Using C + + and OpenCV

    Science.gov (United States)

    Oswald, Samantha; Thomas Jefferson National Accelerator Facility Collaboration

    2014-03-01

    Thomas Jefferson National Accelerator Facility (TJNAF) uses superconducting radiofrequency (SRF) cavities to accelerate an electron beam. If theses cavities have a small particle or defect, it can degrade the performance of the cavity. The problem at hand is inspecting the cavity for defects, little bubbles of niobium on the surface of the cavity. Thousands of pictures have to be taken of a single cavity and then looked through to see how many defects were found. A C + + program with Open Source Computer Vision (OpenCV) was constructed to reduce the number of hours searching through the images and finds all the defects. Using this code, the SRF group is now able to use the code to identify defects in on-going tests of SRF cavities. Real time detection is the next step so that instead of taking pictures when looking at the cavity, the camera will detect all the defects.

  17. Dai Omega, a large solid angle axial focusing superconducting surface muon channel

    International Nuclear Information System (INIS)

    Miyadera, H.; Nagamine, K.; Shimomura, K.; Nishiyama, K.; Tanaka, H.; Fukuchi, K.; Makimura, S.; Ishida, K.

    2003-01-01

    An axial focusing surface muon channel, Dai Omega, was installed at KEK-MSL in the summer of 2001. Large aperture superconducting coils are utilized instead of quadrupole magnets. Dai Omega adopts an axial focusing beam path using symmetric magnetic fields from four coils. Computer simulations were performed on constructing Dai Omega, and the calculated solid angle acceptance of Dai Omega was larger than 1 sr at the optimum momentum. The momentum acceptance of Dai Omega was 6% FWHM. Dai Omega improved the solid angle acceptance by almost 20 times, in comparison with conventional muon channels. Beam tuning tests of Dai Omega have been carried out, and a beam intensity of 10 6 μ + /s was achieved at KEK-NML (500 MeV, 5 μA), which was almost comparable with that of RAL (800 MeV, 200 μA)

  18. Hall effect of K-doped superconducting thin films

    Energy Technology Data Exchange (ETDEWEB)

    Son, Eunseon; Lee, Nam Hoon; Kang, Won Nam [Dept. of physics, Sungkyunkwan University, Suwon (Korea, Republic of); Hwang, Tae Jong; Kim, Dong Ho [Dept. of physics, Yeungnam University, Gyeongsan(Korea, Republic of)

    2013-09-15

    We have studied Hall effect for potassium (K)-doped BaFe{sub 2}As{sub 2}superconducting thin films by analyzing the relation between the longitudinal resistivity (ρ{sub xy}) and the Hall resistivity (ρ{sub xy}). The thin films used in this study were fabricated on Al{sub O3} (000l) substrates by using an ex-situ pulsed laser deposition (PLD) technique under a high-vacuum condition of ∼10{sup -6} Torr. The samples showed the high superconducting transition temperatures (T{sub C}) of ∼40 K. The ρ{sub xx} and ρ{sub xy}the for K-doped BaFeAs{sub 2} thin films were measured by using a physical property measurement system (PPMS) with a temperature sweep (T-sweep) mode at an applied current density of 100 A/cm{sup 2} and at magnetic fields from 0 up to 9 T. We report the T-sweep results of the ρ{sub xx} and the ρ{sub xy} to investigate Hall scaling behavior on the basis of the relation of ρ{sub xy} = A(ρ{sub xy}){sup β}. The ρ{sub xx} values are 3.0 ± 0.2 in the c-axis-oriented K-doped BaFeAs{sub 2} thin films, whereas the thin films with various oriented-directions like a polycrystal showed slightly lower β than that of c-axis-oriented thin films. Interestingly, the β value is decreased with increasing magnetic fields.

  19. Fermi-surface reconstruction and the origin of high-temperature superconductivity

    International Nuclear Information System (INIS)

    Norman, M.R.

    2010-01-01

    In crystalline lattices, the conduction electrons form waves, known as Bloch states, characterized by a momentum vector k. The defining characteristic of metals is the surface in momentum space that separates occupied from unoccupied states. This 'Fermi' surface may seem like an abstract concept, but it can be measured and its shape can have profound consequences for the thermal, electronic, and magnetic properties of a material. In the presence of an external magnetic field B, electrons in a metal spiral around the field direction, and within a semiclassical momentum-space picture, orbit around the Fermi surface. Physical properties, such as the magnetization, involve a sum over these orbits, with extremal orbits on the Fermi surface, i.e., orbits with minimal or maximal area, dominating the sum (Fig. 1(a)). Upon quantization, the resulting electron energy spectrum consists of Landau levels separated by the cyclotron energy, which is proportional to the magnetic field. As the magnetic field causes subsequent Landau levels to cross through the Fermi energy, physical quantities, such as the magnetization or resistivity, oscillate in response. It turns out that the period of these oscillations, when plotted as a function of 1/B, is proportional to the area of the extremal orbit in a plane perpendicular to the applied field (Fig. 1(b)). The power of the quantum oscillation technique is obvious: By changing the field direction, one can map out the Fermi surface, much like a blind man feeling an elephant. The nature and topology of the Fermi surface in high-T c cuprates has been debated for many years. Soon after the materials were discovered by Bednorz and Mueller, it was realized that superconductivity was obtained by doping carriers into a parent insulating state. This insulating state appears to be due to strong electronic correlations, and is known as a Mott insulator. In the case of cuprates, the electronic interactions force the electrons on the copper ion

  20. Tailoring Surface Impurity Content to Maximize Q-factors of Superconducting Resonators

    Energy Technology Data Exchange (ETDEWEB)

    Martinello, Martina [Illinois Inst. of Technology, Chicago, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Checchin, Mattia [Illinois Inst. of Technology, Chicago, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Grassellino, Anna [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Melnychuk, Oleksandr [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Posen, Sam [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Romanenko, Alexander [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Sergatskov, Dmitri [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Zasadzinski, John [Illinois Inst. of Technology, Chicago, IL (United States)

    2016-06-01

    Quality factor of superconducting radio-frequency (SRF) cavities is degraded whenever magnetic flux is trapped in the cavity walls during the cooldown. In this contribution we study how the trapped flux sensitivity, defined as the trapped flux surface resistance normalized for the amount of flux trapped, depends on the mean free path. A variety of 1.3 GHz cavities with different surface treatments (EP, 120 C bake and different N-doping) were studied in order to cover the largest range of mean free path nowadays achievable, from few to thousands of nanometers. A bell shaped trend appears for the range of mean free path studied. Over doped cavities falls at the maximum of this curve defining the largest values of sensitivity. In addition, we have also studied the trend of the BCS surface resistance contribution as a function of mean free path, revealing that N-doped cavities follow close to the theoretical minimum of the BCS surface resistance as a function of the mean free path. Adding these results together we unveil that optimal N-doping treatment allows to maximize Q-factor at 2 K and 16 MV/m until the magnetic field fully trapped during the cavity cooldown stays below 10 mG.

  1. 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.)

  2. 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}.

  3. 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.

  4. A scanning Auger electron spectrometer for internal surface analysis of Large Electron Positron 2 superconducting radio-frequency cavities

    Science.gov (United States)

    Benvenuti, C.; Cosso, R.; Genest, J.; Hauer, M.; Lacarrère, D.; Rijllart, A.; Saban, R.

    1996-08-01

    A computer-controlled surface analysis instrument, incorporating static Auger electron spectroscopy, scanning Auger mapping, and secondary electron imaging, has been designed and built at CERN to study and characterize the inner surface of superconducting radio-frequency cavities to be installed in the Large Electron Positron collider. A detailed description of the instrument, including the analytical head, the control system, and the vacuum system is presented. Some recent results obtained from the cavities provide examples of the instrument's capabilities.

  5. 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...

  6. Topological superconductivity, topological confinement, and the vortex quantum Hall effect

    International Nuclear Information System (INIS)

    Diamantini, M. Cristina; Trugenberger, Carlo A.

    2011-01-01

    Topological matter is characterized by the presence of a topological BF term in its long-distance effective action. Topological defects due to the compactness of the U(1) gauge fields induce quantum phase transitions between topological insulators, topological superconductors, and topological confinement. In conventional superconductivity, because of spontaneous symmetry breaking, the photon acquires a mass due to the Anderson-Higgs mechanism. In this paper we derive the corresponding effective actions for the electromagnetic field in topological superconductors and topological confinement phases. In topological superconductors magnetic flux is confined and the photon acquires a topological mass through the BF mechanism: no symmetry breaking is involved, the ground state has topological order, and the transition is induced by quantum fluctuations. In topological confinement, instead, electric charge is linearly confined and the photon becomes a massive antisymmetric tensor via the Stueckelberg mechanism. Oblique confinement phases arise when the string condensate carries both magnetic and electric flux (dyonic strings). Such phases are characterized by a vortex quantum Hall effect potentially relevant for the dissipationless transport of information stored on vortices.

  7. 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

  8. Study of first harmonic field effects on beam extraction for VEC K500 superconducting cyclotron

    International Nuclear Information System (INIS)

    Dey, M.K.; Debnath, J.; Mallik, C.; Bhandari, R.K.

    2002-01-01

    In superconducting cyclotron large momentum compaction at extraction region makes the turn separation very small. The first harmonic effects on the He +1 beam using simulated magnetic field for VEC K500 cyclotron is reported

  9. 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

  10. 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

  11. Eddy damping effect of additional conductors in superconducting levitation systems

    Science.gov (United States)

    Jiang, Zhao-Fei; Gou, Xiao-Fan

    2015-12-01

    Passive superconducting levitation systems consisting of a high temperature superconductor (HTSC) and a permanent magnet (PM) have demonstrated several fascinating applications such as the maglev system, flywheel energy storage. Generally, for the HTSC-PM levitation system, the HTSC with higher critical current density Jc can obtain larger magnetic force to make the PM levitate over the HTSC (or suspended below the HTSC), however, the process of the vibration of the levitated PM, provides very limited inherent damping (essentially hysteresis). To improve the dynamic stability of the levitated PM, eddy damping of additional conductors can be considered as the most simple and effective approach. In this article, for the HTSC-PM levitation system with an additional copper damper attached to the HTSC, we numerically and comprehensively investigated the damping coefficient c, damping ratio, Joule heating of the copper damper, and the vibration frequency of the PM as well. Furthermore, we comparatively studied four different arrangements of the copper damper, on the comprehensive analyzed the damping effect, efficiency (defined by c/VCu, in which VCu is the volume of the damper) and Joule heating, and finally presented the most advisable arrangement.

  12. 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.

  13. Miniature scanning electron microscope for investigation of the interior surface of a superconducting Nb radiofrequency accelerating cavity

    International Nuclear Information System (INIS)

    Mathewson, A.G.; Grillot, A.

    1982-01-01

    A miniature scanning electron microscope with an electron beam diameter approx.1 μm has been constructed for high resolution examination at room temperature of the interior surface of a superconducting Nb radiofrequency accelerating cavity. Various objects and surface structures were observed, some of which could be correlated with lossy regions or ''hot spots'' detected previously on the outside surface during cavity operation at < or =4.2 K by a chain of carbon resistors. No internal surface features were observed which could conclusively be correlated with field emitting electron sources

  14. Magnetic field dependence of the superconducting proximity effect in a two atomic layer thin metallic film

    Energy Technology Data Exchange (ETDEWEB)

    Caminale, Michael; Leon Vanegas, Augusto A.; Stepniak, Agnieszka; Oka, Hirofumi; Fischer, Jeison A.; Sander, Dirk; Kirschner, Juergen [Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany)

    2015-07-01

    The intriguing possibility to induce superconductivity in a metal, in direct contact with a superconductor, is under renewed interest for applications and for fundamental aspects. The underlying phenomenon is commonly known as proximity effect. In this work we exploit the high spatial resolution of scanning tunneling spectroscopy at sub-K temperatures and in magnetic fields. We probe the differential conductance along a line from a superconducting 9 ML high Pb nanoisland into the surrounding two layer thin Pb/Ag wetting layer on a Si(111) substrate. A gap in the differential conductance indicates superconductivity of the Pb island. We observe an induced gap in the wetting layer, which decays with increasing distance from the Pb island. This proximity length is 21 nm at 0.38 K and 0 T. We find a non-trivial dependence of the proximity length on magnetic field. Surprisingly, we find that the magnetic field does not affect the induced superconductivity up to 0.3 T. However, larger fields of 0.6 T suppress superconductivity in the wetting layer, where the Pb island still remains superconducting. We discuss the unexpected robustness of induced superconductivity in view of the high electronic diffusivity in the metallic wetting layer.

  15. 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)

  16. Single-particle spectra and magnetic field effects within precursor superconductivity

    International Nuclear Information System (INIS)

    Pieri, P.; Pisani, L.; Strinati, G.C.; Perali, A.

    2004-01-01

    We study the single-particle spectra below the superconducting critical temperature from weak to strong coupling within a precursor superconductivity scenario. The spectral-weight function is obtained from a self-energy that includes pairing-fluctuations within a continuum model representing the hot spots of the Brillouin zone. The effects of strong magnetic fields on the pseudogap temperature are also discussed within the same scenario

  17. Effects of thermal relaxation on an amorphous superconducting Zr--Rh alloy

    International Nuclear Information System (INIS)

    Drehman, A.J.; Johnson, W.L.

    1978-05-01

    The electronic and superconducting properties of an amorphous transition metal alloy are used to evaluate the effects of low temperature annealing. It is observed that the superconducting transition temperature and the electrical resistivity relax exponentially in time from their initial value to a final relaxed value. From this an activation energy for the relaxation process is derived and an explanation is suggested which involves internal stress

  18. 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.

  19. Radiation effects on superconductivity in A15 materials

    International Nuclear Information System (INIS)

    Faehnle, M.

    1981-01-01

    At present the A15 superconductor Nb 3 Sn is one of the most attractive materials for the design of magnet systems for fusion reactors. There the materials are exposed to a high flux of neutrons up to 10 18 to 10 19 n/cm 2 during a continuous fusion reactor operation within ten years. As a result the critical parameters of the superconducting materials are changed which must be taken into account when designing reliable magnet systems. The neutron radiation damage in A15 materials thereby is characterized by small highly disordered regions within a less disordered matrix. The highly disordered regions are responsible for the increase of the critical current density after low-dose neutron irradiation of non-optimized materials and have an influence on the superconducting transition width. In contrast, the change of the superconducting parameters after high-dose irradiation may be understood essentially by considering the properties of the matrix alone. 23 refs

  20. Eddy damping effect of additional conductors in superconducting levitation systems

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Zhao-Fei; Gou, Xiao-Fan, E-mail: xfgou@hhu.edu.cn

    2015-12-15

    Highlights: • In this article, for the eddy current damper attached to the HTSC, we • quantitatively investigated the damping coefficient c, damping ratio, Joule heating of the copper damper, and the vibration frequency of the PM as well. • presented four different arrangements of the copper damper, and comparatively studied their damping effects and Joule heating, and finally proposed the most advisable arrangement. - Abstract: Passive superconducting levitation systems consisting of a high temperature superconductor (HTSC) and a permanent magnet (PM) have demonstrated several fascinating applications such as the maglev system, flywheel energy storage. Generally, for the HTSC–PM levitation system, the HTSC with higher critical current density J{sub c} can obtain larger magnetic force to make the PM levitate over the HTSC (or suspended below the HTSC), however, the process of the vibration of the levitated PM, provides very limited inherent damping (essentially hysteresis). To improve the dynamic stability of the levitated PM, eddy damping of additional conductors can be considered as the most simple and effective approach. In this article, for the HTSC–PM levitation system with an additional copper damper attached to the HTSC, we numerically and comprehensively investigated the damping coefficient c, damping ratio, Joule heating of the copper damper, and the vibration frequency of the PM as well. Furthermore, we comparatively studied four different arrangements of the copper damper, on the comprehensive analyzed the damping effect, efficiency (defined by c/V{sub Cu}, in which V{sub Cu} is the volume of the damper) and Joule heating, and finally presented the most advisable arrangement.

  1. Effect of ion irradiation on surface morphology and superconductivity of BaFe{sub 2}(As{sub 1−x}P{sub x}){sub 2} films

    Energy Technology Data Exchange (ETDEWEB)

    Daghero, D., E-mail: dario.daghero@polito.it [Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Tortello, M. [Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Gozzelino, L. [Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Torino, 10125 Torino (Italy); Gonnelli, R.S. [Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Hatano, T.; Kawaguchi, T.; Ikuta, H. [Department of Crystalline Materials Science, Nagoya University, Nagoya 464-8603 (Japan)

    2017-02-15

    Highlights: • Epitaxial films of BaFe{sub 2}(As,P){sub 2} at optimal doping on MgO substrate have been irradiated by 250 MeV Au ions with different fluences. • Irradiation induces a partial relaxation of the in-plane tensile stress typical of the pristine films. • The residual resistivity increases less than linearly with fluence, tending to saturate; the overall increase is about 60%, but the critical temperature decreases by only 2%. • These results indicate that the substrate and the reduced dimensionality of the films (as compared to the case of single crystals) play an important role in their response to irradiation. - Abstract: We have irradiated epitaxial thin films of BaFe{sub 2}(As{sub 1−x}P{sub x}){sub 2} with x ≃ 0.2 (optimal doping) with Au ions having an energy of 250 MeV. We have used two different fluences, Φ{sub 1} = 2.4 × 10{sup 11} cm{sup −2} and Φ{sub 2} = 7.3 × 10{sup 11} cm{sup −2}, and we have studied the effects of irradiation on the surface morphology, on the resistivity and on the critical temperature. We have found that irradiation progressively destroys the very clear and interconnected growth terraces typical of the pristine surface, leading first to their smoothening – accompanied by the appearance of localized defects – and then to a completely disordered surface. The residual resistivity increases by almost 60%, but the critical temperature decreases very little (i.e. by about 2%) on going from the pristine film to the most irradiated one. The possible role of the substrate in these results is discussed.

  2. Magnetic shield effect simulation of superconducting film shield covering directly coupled HTS dc-SQUID magnetometer

    International Nuclear Information System (INIS)

    Terauchi, N.; Noguchi, S.; Igarashi, H.

    2011-01-01

    A superconducting film shield over a SQUID ring improves the robustness of the SQUID with respect to magnetic noise. Supercurrent in the SQUID magnetometer and the superconducting film shield were simulated. The superconducting film shield reduces the influence of the external magnetic field on the SQUID ring. An HTS SQUID is a high sensitive magnetic sensor. In recent years, the HTS SQUID is widely used in various applications. In some applications, high robustness with respect to magnetic noise is required to realize stable operation at outside of a magnetic shielding room. The target of this paper is a directly coupled HTS dc-SQUID magnetometer. To enhance the robustness of the SQUID magnetometer, use of a superconducting thin film shield has been proposed. The magnetic field directly penetrating the SQUID ring causes the change of the critical current of Josephson junction, and then the SQUID magnetometer transitions into inoperative state. In order to confirm the magnetic shield effect of the superconducting film shield, electromagnetic field simulation with 3D edge finite element method was performed. To simulate the high temperature superconductor, E-J characteristics and c-axis anisotropy are considered. To evaluate the effect of the superconducting film shield, an external magnetic field which is supposed to be a magnetic noise is applied. From the simulation results, the time transition of the magnetic flux penetrating the SQUID ring is investigated and the effect of the superconducting film shield is confirmed. The amplitude of the magnetic flux penetrating the SQUID ring can be reduced to about one-sixth since the superconducting film shield prevents the magnetic noise from directly penetrating the SQUID ring.

  3. Effect of anitiferromagnetism on superconducting gap of cuprates

    International Nuclear Information System (INIS)

    Rout, G.C.; Panda, B.N.; Bishoyi, K.C.

    2000-01-01

    The interplay between superconductivity (SC) and antiferromagnetism (AF) is studied in strongly correlated systems: R 2-x M x CuO 4 (R = Nd, La, Pr, Gd; M = Sr, Ge). It is assumed that superconductivity arises due to BCS pairing mechanism in presence of AF in Cu lattices of Cu-O planes. Temperature dependence of SC gap as well as staggered magnetic field are calculated analytically and solved self-consistently with respect to half-filled band situation for different model parameters λ 1 , and λ 2 being SC and AF coupling parameters respectively. The SC gap is studied in the coexistent phase of SC and AFM. (author)

  4. Study of the surface resistance of superconducting niobium films at 1.5 GHz

    CERN Document Server

    Benvenuti, Cristoforo; Campisi, I E; Darriulat, Pierre; Peck, M A; Russo, R; Valente, A M

    1999-01-01

    A systematic study of superconducting properties of niobium films sputtered on the inner wall of radiofrequency cavities is presented. The measured quantities include in particular the response to 1.5 GHz microwaves, the critical temperature, the penetration depth and the magnetic penetration field. In addition to films grown in different gas discharges (Xe, Kr, Ar and Ar/Ne mixtures) and to films grown on substrates prepared under different conditions, the study also includes bulk niobium cavities. The surface resistance is analysed in terms of its dependence on temperature, on RF field and, when relevant, on the density of trapped fluxons. A simple parameterisation is found to give a good fit to the data. Once allowance for the presence of impurities and defects is made by means of a single parameter, the electron mean free path, good agreement with BCS theory is observed. The fluxon-induced losses are studied in detail and their dependence on RF field, on temperature and on the density of trapped fluxons i...

  5. Roughness analysis applied to niobium thin films grown on MgO(001) surfaces for superconducting radio frequency cavity applications

    OpenAIRE

    D. B. Beringer; W. M. Roach; C. Clavero; C. E. Reece; R. A. Lukaszew

    2013-01-01

    This paper describes surface studies to address roughness issues inherent to thin film coatings deposited onto superconducting radio frequency (SRF) cavities. This is particularly relevant for multilayered thin film coatings that are being considered as a possible scheme to overcome technical issues and to surpass the fundamental limit of ∼50  MV/m accelerating gradient achievable with bulk niobium. In 2006, a model by Gurevich [Appl. Phys. Lett. 88, 012511 (2006)APPLAB0003-695110.1063/1.2162...

  6. Ceramic/metal and A15/metal superconducting composite materials exploiting the superconducting proximity effect and method of making the same

    International Nuclear Information System (INIS)

    Holcomb, M.J.

    1999-01-01

    A composite superconducting material made of coated particles of ceramic superconducting material and a metal matrix material is disclosed. The metal matrix material fills the regions between the coated particles. The coating material is a material that is chemically nonreactive with the ceramic. Preferably, it is silver. The coating serves to chemically insulate the ceramic from the metal matrix material. The metal matrix material is a metal that is susceptible to the superconducting proximity effect. Preferably, it is a NbTi alloy. The metal matrix material is induced to become superconducting by the superconducting proximity effect when the temperature of the material goes below the critical temperature of the ceramic. The material has the improved mechanical properties of the metal matrix material. Preferably, the material consists of approximately 10% NbTi, 90% coated ceramic particles (by volume). Certain aspects of the material and method will depend upon the particular ceramic superconductor employed. An alternative embodiment of the invention utilizes A15 compound superconducting particles in a metal matrix material which is preferably a NbTi alloy

  7. Ceramic/metal and A15/metal superconducting composite materials exploiting the superconducting proximity effect and method of making the same

    Science.gov (United States)

    Holcomb, Matthew J.

    1999-01-01

    A composite superconducting material made of coated particles of ceramic superconducting material and a metal matrix material. The metal matrix material fills the regions between the coated particles. The coating material is a material that is chemically nonreactive with the ceramic. Preferably, it is silver. The coating serves to chemically insulate the ceramic from the metal matrix material. The metal matrix material is a metal that is susceptible to the superconducting proximity effect. Preferably, it is a NbTi alloy. The metal matrix material is induced to become superconducting by the superconducting proximity effect when the temperature of the material goes below the critical temperature of the ceramic. The material has the improved mechanical properties of the metal matrix material. Preferably, the material consists of approximately 10% NbTi, 90% coated ceramic particles (by volume). Certain aspects of the material and method will depend upon the particular ceramic superconductor employed. An alternative embodiment of the invention utilizes A15 compound superconducting particles in a metal matrix material which is preferably a NbTi alloy.

  8. The effect of ammonia intercalation on the superconducting ...

    African Journals Online (AJOL)

    A theoretical investigation of the electronic properties of the relatively high-Tc alkali-metal doped superconducting fullerides when they are further exposed to ammonia molecules as dopants is presented. Our numerical method relies on a group theoretical technique for the formation of molecular orbitals (MO's) for the solid ...

  9. Surface characterization of superconductive Nd1Ba2Cu3Oy thin films using scanning probe microscopes

    International Nuclear Information System (INIS)

    Ting, W.; Badaye, M.; Itti, R.; Morishita, T.; Koshizuka, N.; Tanaka, S.

    1996-01-01

    Recently, superconductive Nd 1 Ba 2 Cu 3 O y (Nd123) thin films with high superconducting transition temperature (T c ) have been successfully fabricated at the authors institute employing the standard laser ablation method. In this paper, they report parts of the results of surface characterization of the Nd123 thin films using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) and an atomic force microscope (AFM) system operated in air. Clear spiral pattern is observed on the surfaces of Nd123 thin films by STM and AFM, suggesting that films are formed by two-dimensional island growth mode at the final growing stage. Contour plots of the spirals show that the step heights of the spirals are not always the integer or half integer numbers of the c-axis parameter of the structure. This implies that the surface natural termination layer of the films may not be unique. Surface atomic images of the as-prepared Nd123 thin films are obtained employing both STM and AFM. STS measurements show that most of the surfaces are semiconductive, or sometimes even metallic. The results of STS measurements together with the fact that they are able to see the surface atomic images using scanning probe microscopes suggest that exposure to air does not cause serious degradation to the as-prepared surfaces of Nd123 thin films

  10. Atomic physics and quantum optics using superconducting circuits: from the Dynamical Casimir effect to Majorana fermions

    Science.gov (United States)

    Nori, Franco

    2012-02-01

    This talk will present an overview of some of our recent results on atomic physics and quantum optics using superconducting circuits. Particular emphasis will be given to photons interacting with qubits, interferometry, the Dynamical Casimir effect, and also studying Majorana fermions using superconducting circuits.[4pt] References available online at our web site:[0pt] J.Q. You, Z.D. Wang, W. Zhang, F. Nori, Manipulating and probing Majorana fermions using superconducting circuits, (2011). Arxiv. J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in a superconducting coplanar waveguide, Phys. Rev. Lett. 103, 147003 (2009). [0pt] J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in superconducting microwave circuits, Phys. Rev. A 82, 052509 (2010). [0pt] C.M. Wilson, G. Johansson, A. Pourkabirian, J.R. Johansson, T. Duty, F. Nori, P. Delsing, Observation of the Dynamical Casimir Effect in a superconducting circuit. Nature, in press (Nov. 2011). P.D. Nation, J.R. Johansson, M.P. Blencowe, F. Nori, Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits, Rev. Mod. Phys., in press (2011). [0pt] J.Q. You, F. Nori, Atomic physics and quantum optics using superconducting circuits, Nature 474, 589 (2011). [0pt] S.N. Shevchenko, S. Ashhab, F. Nori, Landau-Zener-Stuckelberg interferometry, Phys. Reports 492, 1 (2010). [0pt] I. Buluta, S. Ashhab, F. Nori. Natural and artificial atoms for quantum computation, Reports on Progress in Physics 74, 104401 (2011). [0pt] I.Buluta, F. Nori, Quantum Simulators, Science 326, 108 (2009). [0pt] L.F. Wei, K. Maruyama, X.B. Wang, J.Q. You, F. Nori, Testing quantum contextuality with macroscopic superconducting circuits, Phys. Rev. B 81, 174513 (2010). [0pt] J.Q. You, X.-F. Shi, X. Hu, F. Nori, Quantum emulation of a spin system with topologically protected ground states using superconducting quantum circuit, Phys. Rev. A 81, 063823 (2010).

  11. Effect of low temperature baking on the RF properties of niobium superconducting cavities for particle accelerators

    International Nuclear Information System (INIS)

    Gianluigi Ciovati

    2004-01-01

    Radio-frequency superconducting (SRF) cavities are widely used to accelerate a charged particle beam in particle accelerators. The performance of SRF cavities made of bulk niobium has significantly improved over the last ten years and is approaching the theoretical limit for niobium. Nevertheless, RF tests of niobium cavities are still showing some ''anomalous'' losses that require a better understanding in order to reliably obtain better performance. These losses are characterized by a marked dependence of the surface resistance on the surface electromagnetic field and can be detected by measuring the quality factor of the resonator as a function of the peak surface field. A low temperature (100 C-150 C) ''in situ'' bake under ultra-high vacuum has been successfully applied as final preparation of niobium RF cavities by several laboratories over the last few years. The benefits reported consist mainly of an improvement of the cavity quality factor at low field and a recovery from ''anomalous'' losses (so-called ''Q-drop'') without field emission at higher field. A series of experiments with a CEBAF single-cell cavity have been carried out at Jefferson Lab to carefully investigate the effect of baking at progressively higher temperatures for a fixed time on all the relevant material parameters. Measurements of the cavity quality factor in the temperature range 1.37 K-280 K and resonant frequency shift between 6 K-9.3 K provide information about the surface resistance, energy gap, penetration depth and mean free path. The experimental data have been analyzed with the complete BCS theory of superconductivity. The hydrogen content of small niobium samples inserted in the cavity during its surface preparation was analyzed with Nuclear Reaction Analysis (NRA). The single-cell cavity has been tested at three different temperatures before and after baking to gain some insight on thermal conductivity and Kapitza resistance and the data are compared with different models

  12. A comparative study of different processing methods and microwave surface conductivity of 1-2-3 superconducting ceramics

    International Nuclear Information System (INIS)

    Sundar, H.G.K.; Wilson, C.; Horzog, D.

    1988-01-01

    Superconducting YBa/sub 2/Cu/sub 3/O/sub 6+x/ samples were made from powders prepared by different routes: solid state reaction, amorphous citrate and Pechini method. The powders produced by solid state reaction were milled to different degrees, calcined and sintered. Samples were also hot pressed at 875 C and subsequently annealed at different temperatures to regain the superconducting phase. In order to compare the amount of residual carbonate in the final materials prepared by solid state and liquid mix methods, XPS spectra were taken on as calcined powder and on material sintered at different temperatures. To our surprise, the amount of carbonate was quite small in both the methods, but this amount increased with sintering temperature. The microwave surface conductivity of 1-2-3 superconducting material was measured in a disk resonator configuration. At liquid nitrogen temperatures the microwave conductivity was comparable to that of gold and improved with decreasing temperature. At --10K the conductivity was two orders of magnitude greater than that of gold at the same temperature. The surface conductivity of samples obtained by Pechini method was much better than that obtained by solid state method

  13. 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.

  14. The influence of chemical treatments on the superconducting properties of technical niobium materials and their effect on the performance of superconducting radio frequency cavities

    International Nuclear Information System (INIS)

    Roy, S B; Sahni, V C; Myneni, G R

    2009-01-01

    We present the results of a study of superconducting response in the niobium materials used in the fabrication of high accelerating gradient (>25 MV m -1 ) superconducting radio frequency (SC-RF) cavities. These results clearly show that the typical surface chemical treatment deployed during the fabrication of SC-RF cavities affects the superconducting properties of pure niobium materials. Such SC-RF cavities operating at 2 K are often found to show anomalous RF losses, causing either a strong degradation of the quality factor or a thermal breakdown for cavity magnetic fields between 1 and 1.5 kOe. The results of our study suggest a correlation between the field for the first flux-line penetration in these chemically treated technical niobium materials and the reported onset field of anomalous losses in the SC-RF cavities.

  15. The influence of chemical treatments on the superconducting properties of technical niobium materials and their effect on the performance of superconducting radio frequency cavities

    Science.gov (United States)

    Roy, S. B.; Myneni, G. R.; Sahni, V. C.

    2009-10-01

    We present the results of a study of superconducting response in the niobium materials used in the fabrication of high accelerating gradient (>25 MV m-1) superconducting radio frequency (SC-RF) cavities. These results clearly show that the typical surface chemical treatment deployed during the fabrication of SC-RF cavities affects the superconducting properties of pure niobium materials. Such SC-RF cavities operating at 2 K are often found to show anomalous RF losses, causing either a strong degradation of the quality factor or a thermal breakdown for cavity magnetic fields between 1 and 1.5 kOe. The results of our study suggest a correlation between the field for the first flux-line penetration in these chemically treated technical niobium materials and the reported onset field of anomalous losses in the SC-RF cavities.

  16. Magnetic hysteresis effects in superconducting coplanar microwave resonators

    Energy Technology Data Exchange (ETDEWEB)

    Bothner, D.; Gaber, T.; Kemmler, M.; Gruenzweig, M.; Ferdinand, B.; Koelle, D.; Kleiner, R. [Universitaet Tuebingen (Germany); Wuensch, S.; Siegel, M. [Karlsruher Institut fuer Technologie (Germany); Mikheenko, P.; Johansen, T.H. [University of Oslo (Norway)

    2013-07-01

    We present experimental data regarding the impact of external magnetic fields on quality factor and resonance frequency of superconducting microwave resonators in a coplanar waveguide geometry. In particular we focus on the influence of magnetic history and show with the assistance of numerical calculations that the found hysteretic behaviour can be well understood with a highly inhomogeneous microwave current density in combination with established field penetration models for type-II superconducting thin films. Furthermore we have used magneto-optical imaging techniques to check the field distribution which we have assumed in our calculations. Finally, we demonstrate that and how the observed hysteretic behaviour can be used to optimize and tune the resonator performance for possible hybrid quantum sytems in magnetic fields.

  17. Numerical calculation of transient field effects in quenching superconducting magnets

    CERN Document Server

    Schwerg, Nikolai; Russenschuck, Stephan

    2009-01-01

    The maximum obtainable magnetic induction of accelerator magnets, relying on normal conducting cables and iron poles, is limited to around 2 T because of ohmic losses and iron saturation. Using superconducting cables, and employing permeable materials merely to reduce the fringe field, this limit can be exceeded and fields of more than 10 T can be obtained. A quench denotes the sudden transition from the superconducting to the normal conducting state. The drastic increase in electrical resistivity causes ohmic heating. The dissipated heat yields a temperature rise in the coil and causes the quench to propagate. The resulting high voltages and excessive temperatures can result in an irreversible damage of the magnet - to the extend of a cable melt-down. The quench behavior of a magnet depends on numerous factors, e.g. the magnet design, the applied magnet protection measures, the external electrical network, electrical and thermal material properties, and induced eddy current losses. The analysis and optimizat...

  18. Study of thermal effects in superconducting RF cavities

    International Nuclear Information System (INIS)

    Bousson, S.; Caruette, A.; Fouaidy, M.; Hammoudi, N.; Junquera, T.; Lesrel, J.; Yaniche, J.F.

    1999-01-01

    A high speed thermometric system equipped with 64 fixed surface thermometers is used to investigate thermal effects in several 3 GHz cavities. An evaluation of the time response of our thermometers is presented. A method based on RF signal analysis is proposed to evaluate the normal zone propagation rate during thermal breakdown. (authors)

  19. Effect of plasma on the superconductive property of YBCO system

    International Nuclear Information System (INIS)

    Chaudhary, K.A.; Anwar, M.I.; Zakaullah, M.; Alamgir, K.; Murtaza, G.; Haq, A.U.

    1999-01-01

    Oxygen deficient Y/sub 1/Ba/sub 2/Cu 3/O/sub 7-x/ samples are exposed to the rarefied are discharge. The air plasma has gas and electron temperatures as 170 deg. C and 2.1 eV, respectively. As a result of plasma treatment the semiconducting tetragonal phase transformed into superconducting orthorhombic phase with Tc= 84K the phase relating properties have been investigated by monochromated X-ray diffraction and low temperature resistivity measurements. (author)

  20. Radiation-effects limits on copper in superconducting magnets

    Energy Technology Data Exchange (ETDEWEB)

    Guinan, M.W.

    1983-05-25

    The determination of the response of copper stabilizers to neutron irradiation in fusion-reactor superconducting magnets requires information in four areas: (1) neutron flux and spectrum determination, (2) resistivity changes at zero field, (3) resistivity changes at field, and (4) the cyclic irradiation and annealing. Applications of our current understanding of the limits of copper stabilizers in fusion-reactor designs are explored in two examples. Recommendations for future additions to the data base are discussed.

  1. Radiation-effects limits on copper in superconducting magnets

    International Nuclear Information System (INIS)

    Guinan, M.W.

    1983-01-01

    The determination of the response of copper stabilizers to neutron irradiation in fusion-reactor superconducting magnets requires information in four areas: (1) neutron flux and spectrum determination, (2) resistivity changes at zero field, (3) resistivity changes at field, and (4) the cyclic irradiation and annealing. Applications of our current understanding of the limits of copper stabilizers in fusion-reactor designs are explored in two examples. Recommendations for future additions to the data base are discussed

  2. Size and dimensionality effects in superconducting Mo thin films

    International Nuclear Information System (INIS)

    Fabrega, L; Gil, O; Camon, A; Parra-BorderIas, M; Fernandez-MartInez, I; Costa-Kraemer, J L; Briones, F; Sese, J; Gonzalez-Arrabal, R

    2011-01-01

    Molybdenum is a low T c , type I superconductor whose fundamental properties are poorly known. Its importance as an essential constituent of new high performance radiation detectors, the so-called transition edge sensors (TESs) calls for better characterization of this superconductor, especially in thin film form. Here we report on a study of the basic superconducting features of Mo thin films as a function of their thickness. The resistivity is found to rise and the critical temperature decreases on decreasing film thickness, as expected. More relevant, the critical fields along and perpendicular to the film plane are markedly different, thickness dependent and much larger than the thermodynamic critical field of Mo bulk. These results are consistent with a picture of type II 2D superconducting films, and allow estimates of the fundamental superconducting lengths of Mo. The role of morphology in determining the 2D and type II character of the otherwise type I molybdenum is discussed. The possible consequences of this behaviour on the performance of radiation detectors are also addressed.

  3. Remarkable effects of disorder on superconductivity of single atomic layers of lead on silicon

    Science.gov (United States)

    Brun, Christophe

    2015-03-01

    It is well known that conventional superconductivity is very robust against non-magnetic disorder. Nevertheless for thin and ultrathin films the structural properties play a major role in determining the superconducting properties, through a subtle interplay between disorder and Coulomb interactions. Unexpectedly, in 2010 superconductivity was discovered in single atomic layers of lead and indium grown on silicon substrate using scanning tunneling spectroscopy and confirmed later on by macroscopic transport measurements. Such well-controlled and tunable crystalline monolayers are ideal systems for studying the influence of various kinds of structural defects on the superconducting properties at the atomic and mesoscopic scale. In particular, Pb monolayers offer the opportunity of probing new effects of disorder because not only superconductivity is 2D but also the electronic wave functions are 2D. Our study of two Pb monolayers of different crystal structures by very-low temperature STM (300 mK) under magnetic field reveals unexpected results involving new spatial spectroscopic variations. Our results show that although the sheet resistance of the Pb monolayers is much below the resistance quantum, strong non-BCS corrections appear leading to peak heights fluctuations in the dI/dV tunneling spectra at a spatial scale much smaller than the superconducting coherence length. Furthermore, strong local evidence of the signature of Rashba effect on the superconductivity of the Pb/Si(111) monolayer is revealed through filling of in gap states and local spatial variations of this filling. Finally the nature of vortices in a monolayer is found to be very sensitive to the properties of step edges areas. This work was supported by University Pierre et Marie Curie UPMC `Emergence' project, French ANR Project `ElectroVortex,' ANR-QuDec and Templeton Foundation (40381), ARO (W911NF-13-1-0431) and CNRS PICS funds. Partial funding by US-DOE Grant DE-AC02-07CH1.

  4. Chern-Simons gauge theories for the fractional-quantum-Hall-effect hierarchy and anyon superconductivity

    International Nuclear Information System (INIS)

    Ezawa, Z.F.; Iwazaki, A.

    1991-01-01

    It is shown that Chern-Simons gauge theories describe both the fractional-quantum-Hall-effect (FQHE) hierarchy and anyon superconductivity, simply by field-theoretically extracting the effects of vortex excitations. Vortices correspond to Laughlin's quasiparticles or bound states of anyons. Both of these phenomena are explained by the condensations of these vortices. We clarify why the anyon systems become incompressible (FQHE) or compressible (anyon superconductivity) depending on the statistics. It is to be emphasized that we can derive an effective Lagrangian describing fully the FQHE hierarchy from a basic Chern-Simons gauge theory

  5. Stabilized superconducting materials and fabrication process

    International Nuclear Information System (INIS)

    Chevallier, B.; Dance, J.M.; Etourneau, J.; Lozano, L.; Tressaud, A.; Tournier, R.; Sulpice, A.; Chaussy, J.; Lejay, P.

    1989-01-01

    Superconducting ceramics are fluorinated at a temperature ≤ 120 0 C. Are also claimed new superconducting materials with a fluorine concentration gradient decreasing from the surface to the core. Superconductivity is stabilized and/or improved [fr

  6. A contribution to the study of high Tc superconducting coatings and multi-layer coatings electromagnetic properties: surface impedance measurement with a tunnel diode oscillator

    International Nuclear Information System (INIS)

    Omari, A.

    1993-01-01

    A surface impedance measurement system for conducting or superconducting thin films have been developed through the electromagnetic coupling of these films to a tunnel diode oscillator. The electromagnetic response of YBa 2 Cu 3 O 7-δ superconducting films and of id/La 2-x Sr x Cu O 4 multilayers, is studied, showing the 'granular' type of these materials. The intergranular coupling is of the SIS type for the films and of the SNS type for the multilayers. A resistance increase is observed when the temperature decreases in the superconducting phase. 120 p., 45 fig., 60 ref

  7. The superconducting proximity effect in epitaxial Al/Pb nanocomposites

    International Nuclear Information System (INIS)

    Wang, H; Vantomme, A; Temst, K; Picot, T; Houben, K; Moorkens, T; Van Haesendonck, C; Van Bael, M J; Grigg, J; Brown, S A; Biermans, E; Bals, S

    2014-01-01

    We have investigated the superconducting properties of Pb nanoparticles with a diameter ranging from 8 to 20 nm, synthesized by Pb + ion implantation in a crystalline Al matrix. A detailed structural characterization of the nanocomposites reveals the highly epitaxial relation between the Al crystalline matrix and the Pb nanoparticles. The Al/Pb nanocomposites display a single superconducting transition, with the critical temperature T c increasing with the Pb content. The dependence of T c on the Pb/Al volume ratio was compared with theoretical models of the superconducting proximity effect based on the bulk properties of Al and Pb. A very good correspondence with the strong-coupling proximity effect model was found, with an electron–phonon coupling constant in the Pb nanoparticles slightly reduced compared to bulk Pb. Our result differs from other studies on Pb nanoparticle based proximity systems where weak-coupling models were found to better describe the T c dependence. We infer that the high interface quality resulting from the ion implantation synthesis method is a determining factor for the superconducting properties. Critical field and critical current measurements support the high quality of the nanocomposite superconducting films. (paper)

  8. Time variations of fields in superconducting magnets and their effects on accelerators

    Energy Technology Data Exchange (ETDEWEB)

    Herrup, D.A.; Syphers, M.J.; Johnson, D.E.; Johnson, R.P.; Tollestrup, A.V.; Hanft, R.W.; Brown, B.C.; Lamm, M.J.; Kuchnir, M.; McInturff, A.D.

    1988-08-22

    A report on the time dependence of magnetic fields in the superconducting magnets of the Fermilab Tevatron has been published. A field variation of order 1 gauss at the aperture radius is observed. Studies on both full sized Tevatron, dipoles and prototype magnets have been used to elucidate these effects. Explanations based on eddy currents in the coil matrix or on flux creep in the superconducting filaments are explored with these tests. Measurement results and techniques for controlling the effect based on new laboratory tests and the latest accelerator operation are presented. 9 refs., 4 figs.

  9. Time variations of fields in superconducting magnets and their effects on accelerators

    International Nuclear Information System (INIS)

    Herrup, D.A.; Syphers, M.J.; Johnson, D.E.

    1988-01-01

    A report on the time dependence of magnetic fields in the superconducting magnets of the Fermilab Tevatron has been published. A field variation of order 1 gauss at the aperture radius is observed. Studies on both full sized Tevatron, dipoles and prototype magnets have been used to elucidate these effects. Explanations based on eddy currents in the coil matrix or on flux creep in the superconducting filaments are explored with these tests. Measurement results and techniques for controlling the effect based on new laboratory tests and the latest accelerator operation are presented. 9 refs., 4 figs

  10. The effects of filament magnetization in superconducting magnets as calculated by POISSON

    International Nuclear Information System (INIS)

    Caspi, S.; Gilbert, W.S.; Helm, M.; Laslett, L.J.

    1986-09-01

    Magnetization of superconducting material can be introduced into POISSON through a field dependent permeability table (in the same way that iron characteristics are introduced). This can be done by representing measured magnetization data of the increasing and decreasing field by two independent B-γ curves (γ = 1/μ). Magnetization curves of this type were incorporated into the current regions of the program POISSON and their effect on the field coefficients observed. We have used this technique to calculate the effect of magnetization on the multipole coefficients of a SSC superconducting dipole magnet and to compare these coefficients with measured values

  11. Roughness analysis applied to niobium thin films grown on MgO(001) surfaces for superconducting radio frequency cavity applications

    Science.gov (United States)

    Beringer, D. B.; Roach, W. M.; Clavero, C.; Reece, C. E.; Lukaszew, R. A.

    2013-02-01

    This paper describes surface studies to address roughness issues inherent to thin film coatings deposited onto superconducting radio frequency (SRF) cavities. This is particularly relevant for multilayered thin film coatings that are being considered as a possible scheme to overcome technical issues and to surpass the fundamental limit of ˜50MV/m accelerating gradient achievable with bulk niobium. In 2006, a model by Gurevich [Appl. Phys. Lett. 88, 012511 (2006)APPLAB0003-695110.1063/1.2162264] was proposed to overcome this limit that involves coating superconducting layers separated by insulating ones onto the inner walls of the cavities. Thus, we have undertaken a systematic effort to understand the dynamic evolution of the Nb surface under specific deposition thin film conditions onto an insulating surface in order to explore the feasibility of the proposed model. We examine and compare the morphology from two distinct Nb/MgO series, each with its own epitaxial registry, at very low growth rates and closely examine the dynamical scaling of the surface features during growth. Further, we apply analysis techniques such as power spectral density to the specific problem of thin film growth and roughness evolution to qualify the set of deposition conditions that lead to successful SRF coatings.

  12. Roughness analysis applied to niobium thin films grown on MgO(001 surfaces for superconducting radio frequency cavity applications

    Directory of Open Access Journals (Sweden)

    D. B. Beringer

    2013-02-01

    Full Text Available This paper describes surface studies to address roughness issues inherent to thin film coatings deposited onto superconducting radio frequency (SRF cavities. This is particularly relevant for multilayered thin film coatings that are being considered as a possible scheme to overcome technical issues and to surpass the fundamental limit of ∼50  MV/m accelerating gradient achievable with bulk niobium. In 2006, a model by Gurevich [Appl. Phys. Lett. 88, 012511 (2006APPLAB0003-695110.1063/1.2162264] was proposed to overcome this limit that involves coating superconducting layers separated by insulating ones onto the inner walls of the cavities. Thus, we have undertaken a systematic effort to understand the dynamic evolution of the Nb surface under specific deposition thin film conditions onto an insulating surface in order to explore the feasibility of the proposed model. We examine and compare the morphology from two distinct Nb/MgO series, each with its own epitaxial registry, at very low growth rates and closely examine the dynamical scaling of the surface features during growth. Further, we apply analysis techniques such as power spectral density to the specific problem of thin film growth and roughness evolution to qualify the set of deposition conditions that lead to successful SRF coatings.

  13. Roughness analysis applied to niobium thin films grown on MgO(001) surfaces for superconducting radio frequency cavity applications

    Energy Technology Data Exchange (ETDEWEB)

    Beringer, D. B. [College of William and Mary, Williamsburg, VA (United States). Dept. of Physics; Roach, W. M. [College of William and Mary, Williamsburg, VA (United States). Dept. of Applied Science; Clavero, C. [College of William and Mary, Williamsburg, VA (United States). Dept. of Applied Science; Reece, C. E. [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Lukaszew, R. A. [College of William and Mary, Williamsburg, VA (United States). Dept. of Physics; College of William and Mary, Williamsburg, VA (United States). Dept. of Applied Science

    2013-02-05

    This paper describes surface studies to address roughness issues inherent to thin film coatings deposited onto superconducting radio frequency (SRF) cavities. This is particularly relevant for multilayered thin film coatings that are being considered as a possible scheme to overcome technical issues and to surpass the fundamental limit of ~500 MV/m accelerating gradient achievable with bulk niobium. In 2006, a model by Gurevich [ Appl. Phys. Lett. 88 012511 (2006)] was proposed to overcome this limit that involves coating superconducting layers separated by insulating ones onto the inner walls of the cavities. Thus, we have undertaken a systematic effort to understand the dynamic evolution of the Nb surface under specific deposition thin film conditions onto an insulating surface in order to explore the feasibility of the proposed model. We examine and compare the morphology from two distinct Nb/MgO series, each with its own epitaxial registry, at very low growth rates and closely examine the dynamical scaling of the surface features during growth. Further, we apply analysis techniques such as power spectral density to the specific problem of thin film growth and roughness evolution to qualify the set of deposition conditions that lead to successful SRF coatings.

  14. Interplay of antiferromagnetism and superconductivity in cuprates with impurity effect and d-wave pairing

    Energy Technology Data Exchange (ETDEWEB)

    Mohapatra, Rasmita, E-mail: rmrmmohapatra@gmail.com [P.G. Department of Applied Physics and Ballistics, F.M. University, Balasore, Odisha 756019 (India); Rout, G.C., E-mail: gcr@iopb.res.in [Physics Enclave, Plot no-664/4825, Lane-4A, Shree Vihar, Patia, Bhubaneswar, Odisha 751024 (India)

    2015-05-15

    Highlights: • We considered here the interplay of antiferromagnetism (AFM) and Superconductivity (SC) with d-wave pairing symmetry in presence of impurity effect. • The tunneling conductance explains the multiple peaks and dip-hump structure. • It is observed that AFM coupling enhances the superconducting transition temperature. • The low temperature specific heat anomaly due to impurity atoms. - Abstract: We present here a model Hamiltonian to study the interplay between staggered magnetic field and the superconductivity with d-wave pairing symmetry in presence of hybridization between impurity f-electrons of rare-earth ions and 3d-electrons of copper ions. The staggered field and superconducting (SC) gaps are calculated by Green’s function technique and solved self-consistently. The coupling constants are compared using s-wave and d-wave pairings. The strength of hybridization suppresses the magnitude of the gaps; while antiferromagnetic coupling enhances the superconducting transition temperature, but suppresses the Neel temperature. The density of states (DOS) representing tunneling conductance shows complex character with impurity level lying at the Fermi level. The electronic specific heat explains prototype heavy fermion behavior in cuprate systems at low temperatures.

  15. Interplay of antiferromagnetism and superconductivity in cuprates with impurity effect and d-wave pairing

    International Nuclear Information System (INIS)

    Mohapatra, Rasmita; Rout, G.C.

    2015-01-01

    Highlights: • We considered here the interplay of antiferromagnetism (AFM) and Superconductivity (SC) with d-wave pairing symmetry in presence of impurity effect. • The tunneling conductance explains the multiple peaks and dip-hump structure. • It is observed that AFM coupling enhances the superconducting transition temperature. • The low temperature specific heat anomaly due to impurity atoms. - Abstract: We present here a model Hamiltonian to study the interplay between staggered magnetic field and the superconductivity with d-wave pairing symmetry in presence of hybridization between impurity f-electrons of rare-earth ions and 3d-electrons of copper ions. The staggered field and superconducting (SC) gaps are calculated by Green’s function technique and solved self-consistently. The coupling constants are compared using s-wave and d-wave pairings. The strength of hybridization suppresses the magnitude of the gaps; while antiferromagnetic coupling enhances the superconducting transition temperature, but suppresses the Neel temperature. The density of states (DOS) representing tunneling conductance shows complex character with impurity level lying at the Fermi level. The electronic specific heat explains prototype heavy fermion behavior in cuprate systems at low temperatures

  16. High temperature interface superconductivity

    International Nuclear Information System (INIS)

    Gozar, A.; Bozovic, I.

    2016-01-01

    Highlight: • This review article covers the topic of high temperature interface superconductivity. • New materials and techniques used for achieving interface superconductivity are discussed. • We emphasize the role played by the differences in structure and electronic properties at the interface with respect to the bulk of the constituents. - Abstract: High-T_c superconductivity at interfaces has a history of more than a couple of decades. In this review we focus our attention on copper-oxide based heterostructures and multi-layers. We first discuss the technique, atomic layer-by-layer molecular beam epitaxy (ALL-MBE) engineering, that enabled High-T_c Interface Superconductivity (HT-IS), and the challenges associated with the realization of high quality interfaces. Then we turn our attention to the experiments which shed light on the structure and properties of interfacial layers, allowing comparison to those of single-phase films and bulk crystals. Both ‘passive’ hetero-structures as well as surface-induced effects by external gating are discussed. We conclude by comparing HT-IS in cuprates and in other classes of materials, especially Fe-based superconductors, and by examining the grand challenges currently laying ahead for the field.

  17. Pairing fluctuation effects on the single-particle spectra for the superconducting state

    International Nuclear Information System (INIS)

    Pieri, P.; Pisani, L.; Strinati, G.C.

    2004-01-01

    Single-particle spectra are calculated in the superconducting state for a fermionic system with an attractive interaction, as functions of temperature and coupling strength from weak to strong. The fermionic system is described by a single-particle self-energy that includes pairing-fluctuation effects in the superconducting state. The theory reduces to the ordinary BCS approximation in weak coupling and to the Bogoliubov approximation for the composite bosons in strong coupling. Several features of the single-particle spectral function are shown to compare favorably with experimental data for cuprate superconductors

  18. AC Losses and Their Thermal Effect in High Temperature Superconducting Machines

    DEFF Research Database (Denmark)

    Song, Xiaowei (Andy); Mijatovic, Nenad; Zou, Shengnan

    2015-01-01

    In transient operations or fault conditions, high temperature superconducting (HTS) machines suffer AC losses which have an influence on the thermal stability of superconducting windings. In this paper, a method to calculate AC losses and their thermal effect in HTS machines is presented....... The method consists of three sub-models that are coupled only in one direction. The magnetic field distribution is first solved in a machine model, assuming a uniform current distribution in HTS windings. The magnetic fields on the boundaries are then used as inputs for an AC loss model which has...

  19. AC Losses and Their Thermal Effect in High-Temperature Superconducting Machines

    DEFF Research Database (Denmark)

    Song, Xiaowei (Andy); Mijatovic, Nenad; Zou, Shengnan

    2016-01-01

    In transient operations or fault conditions, hightemperature superconducting (HTS) machines suffer ac losses, which have an influence on the thermal stability of superconducting windings. In this paper, a method to calculate ac losses and their thermal effect in HTS machines is presented....... The method consists of three submodels that are coupled only in one direction. The magnetic field distribution is first solved in a machine model, assuming a uniform current distribution in HTS windings. The magnetic fields on the boundaries are then used as inputs for an ac loss model that has a homogeneous...

  20. Measurements of the surface impedance and the ac critical field of superconducting thin tin films at 10 GHz

    International Nuclear Information System (INIS)

    Spencer, G.L.

    1976-01-01

    The surface impedances and ac critical fields of superconducting thin tin films were studied. These experiments were performed using a superconducting frequency stabilized microwave cavity of high Q. Measurements of the power losses in the cavity and the center frequency of the cavity were used to determine the surface impedance and the critical field of a thin film sample placed in the cavity. In this case a theoretical treatment based on a model proposed by I.O. Kulik was used to fit the data. The general agreement between the modified Kulik treatment and the data, obtained in this experiment, was substantial. The second method was to modify the thin film data to correspond to a bulk situation. This modification was accomplished by taking into account the measuring techniques used and the geometric consideration inherent in the experiment. The comparison between the modified experimental data and calculations obtained from the Mattis-Bardeen bulk model was generally very good. One aspect of the results which was not explained was the presence of a slight increase in the surface resistance in the vicinity of the transition temperature. The critical field measurements were compared to the (1 - (T/T/sub c/)/sup 1/2) dependence predicted by Bardeen. If it is assumed that substantial microwave heating took place in the sample near T/sub c/, then remarkable agreement with the Bardeen model can be reached

  1. Possible nucleation of a 2D superconducting phase on WO3 single crystals surface doped with Na+

    International Nuclear Information System (INIS)

    Reich, S.; Tsabba, Y.

    1999-01-01

    WO 3 crystals with a surface composition of Na 0.05 WO 3 were grown. These crystals exhibit a sharp diamagnetic step in magnetization at 91 K, and a magnetic hysteresis below this temperature. As the temperature is lowered below 100 K in transport measurements, a sharp metal to insulator transition is observed, this is followed by a sharp decrease in the resistivity when the temperature is lowered to about 90 K. When the surface of the crystals was covered by gold the depth of the diamagnetic step had decreased considerably. These results indicate a possible nucleation of a superconducting phase on the surface of these crystals. This is a non cuprate system exhibiting a critical temperature in the HTS range. (orig.)

  2. Elementary microscopic treatment of the effect of static disorder on superconductivity

    International Nuclear Information System (INIS)

    Wiecko, Cristina

    1988-01-01

    Dividing explicitely both phonon and electrons in extended and localized excitations, the effect of static disorder on superconductivity is derived by standard treatment. Main increase is obtained from localized levels above ε F which are paired by local phonon modes, in agreement with a previous model derived in mean-field approximation. (Author)

  3. 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...

  4. Effect of the annealing temperature for the hydrogen Q-degradation on superconducting cavities

    International Nuclear Information System (INIS)

    Ota, Tomoko; Sukenobu, Satoru; Tanabe, Yoshio; Onishi, Yoshimichi; Noguchi, Shuichi; Ono, Masaaki; Saito, Kenji; Shishido, Toshio; Yamazaki, Yoshishige

    1997-01-01

    Hydrogen Q-degradation was studied in niobium superconducting cavities prepared by barrel polishing, and electropolishing without annealing, though a fast cooling down of cavities. Cavity performance with various annealing temperature were tested using a 1.3GHz single-cell cavity to compare the effects of annealing temperature for hydrogen Q-degradation. (author)

  5. Effects of disorder on coexistence and competition between superconducting and insulating states

    NARCIS (Netherlands)

    Mostovoy, MV; Marchetti, FM; Simons, BD; Littlewood, PB

    We study effects of nonmagnetic impurities on the competition between the superconducting and electron-hole pairing. We show that disorder can result in coexistence of these two types of ordering in a uniform state, even when in clean materials they are mutually exclusive.

  6. Impact of nitrogen doping of niobium superconducting cavities on the sensitivity of surface resistance to trapped magnetic flux

    Science.gov (United States)

    Gonnella, Dan; Kaufman, John; Liepe, Matthias

    2016-02-01

    Future particle accelerators such as the SLAC "Linac Coherent Light Source-II" (LCLS-II) and the proposed Cornell Energy Recovery Linac require hundreds of superconducting radio-frequency (SRF) niobium cavities operating in continuous wave mode. In order to achieve economic feasibility of projects such as these, the cavities must achieve a very high intrinsic quality factor (Q0) to keep cryogenic losses within feasible limits. To reach these high Q0's in the case of LCLS-II, nitrogen-doping of niobium cavities has been selected as the cavity preparation technique. When dealing with Q0's greater than 1 × 1010, the effects of ambient magnetic field on Q0 become significant. Here, we show that the sensitivity to RF losses from trapped magnetic field in a cavity's walls is strongly dependent on the cavity preparation. Specifically, standard electropolished and 120 °C baked cavities show a sensitivity of residual resistance from trapped magnetic flux of ˜0.6 and ˜0.8 nΩ/mG trapped, respectively, while nitrogen-doped cavities show a higher sensitivity of residual resistance from trapped magnetic flux of ˜1 to 5 nΩ/mG trapped. We show that this difference in sensitivities is directly related to the mean free path of the RF surface layer of the niobium: shorter mean free paths lead to less sensitivity of residual resistance to trapped magnetic flux in the dirty limit (ℓ ≪ ξ0), while longer mean free paths lead to lower sensitivity of residual resistance to trapped magnetic flux in the clean limit (ℓ ≫ ξ0). These experimental results are also shown to have good agreement with recent theoretical predictions for pinned vortex lines oscillating in RF fields.

  7. An introduction to superconductivity. The Meissner effect and the derivation of phenomenological models

    Energy Technology Data Exchange (ETDEWEB)

    Habeney, Lucas

    2016-09-23

    The purpose of this work was to give the reader insight into the topic of conventional superconductors. It started out with defining the superconductive state itself as a state of ideal conductivity and ideal diamagnetism. An important phenomenon to keep in mind in this regard is the Meissner-Ochsenfeld effect. It then went on to attempt to understand those properties on a macroscopic level. This was achieved in the framework of the two major macroscopic theories, the London theory and the Ginzburg-Landau theory. While the London theory focused on the electrodynamic qualities of the superconductive state, the Ginzburg-Landau theory dealt with events close to the superconducting phase transition in a thermodynamic scope. The highlight of this section was the investigation of the Abrikosov lattice, the geometric disposition of the flux tubes in the intermediate Shubnikov phase. We closed with the BCS theory as the premier microscopic theory of superconductivity. Main subjects of this section were the concept of Cooper pairs and the calculation of various energy gap equations. We also looked at real properties of superconductors such as the specific heat to test our rather abstract calculations and came to outstanding agreements. The principles presented in this document should serve as a foundation to work on more advanced problems in superconductivity. Especially the large field of unconventional superconductivity is of huge interest in current research, as most of the high T{sub c} superconductors fall in that category. As unconventional superconductors can not be explained with BCS theory, the search for a uniform theory to describe them is still on-going. Unconventional superconductors include but are not limited to cuprates (T{sub c}

  8. Effect of pressure on the bandstructure and superconductivity in lutetium

    International Nuclear Information System (INIS)

    Asokamani, R.; Natarajan, S.; Rajagopalan, M.; Sundararajan, V.; Suvasini, M.B.; Iyakutti, K.

    1984-08-01

    The detailed bandstructure and superconducting behaviour of lutetium at 230 kbar pressure is reported here. The electronic contribution eta to the electron-phonon mass enhancement lambda is studied within the rigid muffin-tin (RMT) approximation. The pd and df matrix elements are expressed in terms of 'd' bandwidth, Fermi energy and muffin-tin zero. The variations of Grueneisen parameter and Debye temperature with pressure are studied and applied in the calculation of Tsub(c). The calculated Tsub(c) value agrees fairly well with the experimental value. The changes in the conduction bandwidth and the electronic specific heat coefficient with pressure are found to be in agreement with theoretical prediction. (author)

  9. Superconducting proximity effect in MBE grown Nb-InAs junctions

    Science.gov (United States)

    Kan, Carolyn; Xue, Chi; Law, Stephanie; Eckstein, James

    2013-03-01

    Several proposals for the realization of Majorana fermions rely on excellent quality proximity coupling between a superconductor and a high-mobility semiconductor. We examine the long-range proximity coupling between MBE-grown InAs and in situ grown superconducting overlayers by fabricating transport devices, and investigate the effect of substrate choice and growth conditions on the quality of the MBE InAs. GaAs is commonly available as a high quality insulating substrate. Overcoming its lattice mismatch with InAs using GaSb and AlSb layers results in locally smooth terraced surfaces, but global spiral dislocation structures also appear and have a negative impact on the InAs mobility. Growing InAs on homoepitaxial GaSb results in improved morphology and increases the mean free path. We compare the proximity effect in devices made both ways. This material is based upon work supported by the U.S. Department of Energy, Division of Materials Sciences under Award No. DE-FG02 07ER46453, through the Frederick Seitz Materials Research Laboratory at the University of Illinois at Urbana-Champaign.

  10. Origin of photovoltaic effect in superconducting YBa2Cu3O6.96 ceramics

    Science.gov (United States)

    Yang, F.; Han, M. Y.; Chang, F. G.

    2015-01-01

    We report remarkable photovoltaic effect in YBa2Cu3O6.96 (YBCO) ceramic between 50 and 300 K induced by blue-laser illumination, which is directly related to the superconductivity of YBCO and the YBCO-metallic electrode interface. There is a polarity reversal for the open circuit voltage Voc and short circuit current Isc when YBCO undergoes a transition from superconducting to resistive state. We show that there exists an electrical potential across the superconductor-normal metal interface, which provides the separation force for the photo-induced electron-hole pairs. This interface potential directs from YBCO to the metal electrode when YBCO is superconducting and switches to the opposite direction when YBCO becomes nonsuperconducting. The origin of the potential may be readily associated with the proximity effect at metal-superconductor interface when YBCO is superconducting and its value is estimated to be ~10–8 mV at 50 K with a laser intensity of 502 mW/cm2. Combination of a p-type material YBCO at normal state with an n-type material Ag-paste forms a quasi-pn junction which is responsible for the photovoltaic behavior of YBCO ceramics at high temperatures. Our findings may pave the way to new applications of photon-electronic devices and shed further light on the proximity effect at the superconductor-metal interface. PMID:26099727

  11. Temperature dependence of the superconducting proximity effect quantified by scanning tunneling spectroscopy

    Directory of Open Access Journals (Sweden)

    A. Stępniak

    2015-01-01

    Full Text Available Here, we present the first systematic study on the temperature dependence of the extension of the superconducting proximity effect in a 1–2 atomic layer thin metallic film, surrounding a superconducting Pb island. Scanning tunneling microscopy/spectroscopy (STM/STS measurements reveal the spatial variation of the local density of state on the film from 0.38 up to 1.8 K. In this temperature range the superconductivity of the island is almost unaffected and shows a constant gap of a 1.20 ± 0.03 meV. Using a superconducting Nb-tip a constant value of the proximity length of 17 ± 3 nm at 0.38 and 1.8 K is found. In contrast, experiments with a normal conductive W-tip indicate an apparent decrease of the proximity length with increasing temperature. This result is ascribed to the thermal broadening of the occupation of states of the tip, and it does not reflect an intrinsic temperature dependence of the proximity length. Our tunneling spectroscopy experiments shed fresh light on the fundamental issue of the temperature dependence of the proximity effect for atomic monolayers, where the intrinsic temperature dependence of the proximity effect is comparably weak.

  12. Niobium thin film deposition studies on copper surfaces for superconducting radio frequency cavity applications

    OpenAIRE

    W. M. Roach; D. B. Beringer; J. R. Skuza; W. A. Oliver; C. Clavero; C. E. Reece; R. A. Lukaszew

    2012-01-01

    Thin film coatings have the potential to increase both the thermal efficiency and accelerating gradient in superconducting radio frequency accelerator cavities. However, before this potential can be realized, systematic studies on structure-property correlations in these thin films need to be carried out since the reduced geometry, combined with specific growth parameters, can modify the physical properties of the materials when compared to their bulk form. Here, we present our systematic stu...

  13. 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

  14. Framework of collaboration investigation on neutron effect on superconducting magnet materials

    International Nuclear Information System (INIS)

    Nishimura, Arata; Takeuchi, Takao; Nishijima, Shigehiro; Izumi, Yoshinobu; Takakura, Kosuke; Ochiai, Kentaro; Henmi, Tsutomu; Nishijima, Gen; Watanabe, Kazuo; Sato, Isamu; Kurisita, Hiroaki; Narui, Minoru; Shikama, Tatsuo

    2009-01-01

    A fusion reactor will generate D-T neutron and the kinetic energy of the neutron will be converted to the thermal energy and electrical energy. The neutron has huge energy and will be able to penetrate a shielding blanket and stream out of ports for neutral beam injections. The penetrated and streamed out neutrons will reach superconducting magnets and make some damages on the magnet system. To investigate the neutron irradiation effects on the superconducting magnet materials, a collaborative network must be organized and the irradiation researches must be performed. This report will describe the framework of the collaboration investigation which has been established among neutronics, superconducting magnet and fusion system. After showing the collaboration scheme, some new results on 14 MeV neutron irradiation effect are presented. Then, a three years new project which was adopted as one of 'Nuclear basic infrastructure strategy study initiatives' by MEXT will be introduced as an example of collaborative program among superconducting materials, fission reactor and high magnetic field technology. (author)

  15. Effect of superconducting correlation on the localization of quasiparticles in low dimensions

    International Nuclear Information System (INIS)

    Xiang, T.

    1995-01-01

    Localization lengths of superconducting quasiparticles λ s are evaluated and compared with the corresponding normal-state values λ n in one-dimensional (1D) and two-dimensional lattices. The effect of superconducting correlation on the localization of quasiparticles is generally stronger in an off-site pairing state than in an on-site pairing state. The modification of superconducting correlation to λ is strongly correlated with the density of states (DOS) of superconducting quasiparticles. λ s drops within the energy gap but is largely enhanced around energies where DOS peaks appear. For a gapless pairing state in 1D or a d-wave pairing state in 2D, λ s /λ n at the Fermi energy E F is of order 1 and determined purely by the value of gap parameter not by the random potential. For the d-wave pairing state, the localization effect is largely weakened compared with the corresponding normal state and quasiparticles with energies close to E F are more strongly localized than other low-energy quasiparticles

  16. Plasma treatment of bulk niobium surface for superconducting rf cavities: Optimization of the experimental conditions on flat samples

    Directory of Open Access Journals (Sweden)

    M. Rašković

    2010-11-01

    Full Text Available Accelerator performance, in particular the average accelerating field and the cavity quality factor, depends on the physical and chemical characteristics of the superconducting radio-frequency (SRF cavity surface. Plasma based surface modification provides an excellent opportunity to eliminate nonsuperconductive pollutants in the penetration depth region and to remove the mechanically damaged surface layer, which improves the surface roughness. Here we show that the plasma treatment of bulk niobium (Nb presents an alternative surface preparation method to the commonly used buffered chemical polishing and electropolishing methods. We have optimized the experimental conditions in the microwave glow discharge system and their influence on the Nb removal rate on flat samples. We have achieved an etching rate of 1.7  μm/min⁡ using only 3% chlorine in the reactive mixture. Combining a fast etching step with a moderate one, we have improved the surface roughness without exposing the sample surface to the environment. We intend to apply the optimized experimental conditions to the preparation of single cell cavities, pursuing the improvement of their rf performance.

  17. Etching of Niobium Sample Placed on Superconducting Radio Frequency Cavity Surface in Ar/CL2 Plasma

    International Nuclear Information System (INIS)

    Upadhyay, Janardan; Phillips, Larry; Valente, Anne-Marie

    2011-01-01

    Plasma based surface modification is a promising alternative to wet etching of superconducting radio frequency (SRF) cavities. It has been proven with flat samples that the bulk Niobium (Nb) removal rate and the surface roughness after the plasma etchings are equal to or better than wet etching processes. To optimize the plasma parameters, we are using a single cell cavity with 20 sample holders symmetrically distributed over the cell. These holders serve the purpose of diagnostic ports for the measurement of the plasma parameters and for the holding of the Nb sample to be etched. The plasma properties at RF (100 MHz) and MW (2.45 GHz) frequencies are being measured with the help of electrical and optical probes at different pressures and RF power levels inside of this cavity. The niobium coupons placed on several holders around the cell are being etched simultaneously. The etching results will be presented at this conference.

  18. Etching of Niobium Sample Placed on Superconducting Radio Frequency Cavity Surface in Ar/CL2 Plasma

    Energy Technology Data Exchange (ETDEWEB)

    Janardan Upadhyay, Larry Phillips, Anne-Marie Valente

    2011-09-01

    Plasma based surface modification is a promising alternative to wet etching of superconducting radio frequency (SRF) cavities. It has been proven with flat samples that the bulk Niobium (Nb) removal rate and the surface roughness after the plasma etchings are equal to or better than wet etching processes. To optimize the plasma parameters, we are using a single cell cavity with 20 sample holders symmetrically distributed over the cell. These holders serve the purpose of diagnostic ports for the measurement of the plasma parameters and for the holding of the Nb sample to be etched. The plasma properties at RF (100 MHz) and MW (2.45 GHz) frequencies are being measured with the help of electrical and optical probes at different pressures and RF power levels inside of this cavity. The niobium coupons placed on several holders around the cell are being etched simultaneously. The etching results will be presented at this conference.

  19. Surface Characterization of Nb Samples Electro-polished Together With Real Superconducting Radio-frequency Accelerator Cavities

    International Nuclear Information System (INIS)

    Zhao, Xin; Geng, Rong-Li; Tyagi, P.V.; Hayano, Hitoshi; Kato, Shigeki; Nishiwaki, Michiru; Saeki, Takayuki; Sawabe, Motoaki

    2010-01-01

    We report the results of surface characterizations of niobium (Nb) samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris and the beam-pipe. Auger electron spectroscopy (AES) was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive X-ray for elemental analysis (SEM/EDX) was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S) were found covering the samples non-uniformly. Niobium oxide granules with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.

  20. Macroscopic Magnetic Coupling Effect: The Physical Origination of a High-Temperature Superconducting Flux Pump

    Science.gov (United States)

    Wang, Wei; Coombs, Tim

    2018-04-01

    We have uncovered at the macroscopic scale a magnetic coupling phenomenon in a superconducting YBa2Cu3O7 -δ (YBCO) film, which physically explains the mechanism of the high-temperature superconducting flux pump. The coupling occurs between the applied magnetic poles and clusters of vortices induced in the YBCO film, with each cluster containing millions of vortices. The coupling energy is verified to originate from the inhomogeneous field of the magnetic poles, which reshapes the vortex distribution, aggregates millions of vortices into a single cluster, and accordingly moves with the poles. A contrast study is designed to verify that, to provide the effective coupling energy, the applied wavelength must be short while the field amplitude must be strong, i.e., local-field inhomogeneity is the crucial factor. This finding broadens our understanding of the collective vortex behavior in an applied magnetic field with strong local inhomogeneity. Moreover, this phenomenon largely increases the controlled vortex flow rate by several orders of magnitude compared with existing methods, providing motivation for and physical support to a new branch of wireless superconducting dc power sources, i.e., the high-temperature superconducting flux pump.

  1. Signatures of granular superconductivity and Josephson effects in macroscopic measurements: the case of new superconductors

    Directory of Open Access Journals (Sweden)

    S Senoussi

    2006-09-01

    Full Text Available   We report systematic investigations of the magnetic superconducting properties of the new superconducting materials (NS: New high temperature superconductors (HTS, Organic superconductors (OS, fullerenes, carbon nanotubes, MgB2 etc. We show that, contrary to conventional superconductors where the superconducting state can be coherent over several tenths of km, the macroscopic coherence range lc of the NS is often as short as 0.1 to 10 µm typically. As a consequence, the magnetic properties are dominated by granular-like effects as well as Josephson coupling between grains. Here, we concentrate on HTS ceramics and organic superconductors exclusively. In the first case we observe three distinct regimes: (i At very low field (H < 5 Oe to say all the grains are coupled via Josephson effect and lc can be considered as infinite. (2 At intermediate field (5 < H < 50 Oe, typically the grains are gradually decoupled by H and/or T. (iii At higher fields all the grains are decoupled and lc roughly coincides with the diameter of the metallurgical grains. The case of OS is more subtle and is connected with a kind of order-disorder transition that occurs in most of them. For instance, in this study, we exploit quenched disorder (after crossing such a transition in the -(BEDT-TTF2Cu[N(CN2]Br layered organic superconductor to get new insights on both the superconducting state (T £ 11.6 K and the glassy transition at Tg, by studying the superconducting properties as functions of annealing time and annealing temperature around the glassy transition. Our main result is that the data can be described by a percolation molecular cluster model in which the topology and the growth of the molecular clusters obey an Ising spin-glass-like model with Tg ≈ 80 K for the hydrogenated compound and Tg ≈ 55 K for the fully deuterated one.

  2. Radiation effects limits on copper in superconducting magnets

    International Nuclear Information System (INIS)

    Guinan, M.W.

    1984-01-01

    The determination of the response of copper stabilizers to neutron irradiation in fusion reactor superconducting magnets requires information in four areas. (1) Neutron flux and spectrum determination are a major factor in the accuracy with which stabilizer response can be predicted. Since magnet stability depends on the weakest link, calculations must be made in sufficient detail to fully account for steep flux gradients and local pertubations from penetrations. (2) Resistivity changes at zero field in magnet spectra are generally calculated from the damage energy cross-section or the equivalent displacement (dpa) rate. (3) Resistivity changes at field for conceptual designs are generally determined from the changes predicted at zero field by the use of a Kohler plot. The cyclic irradiation and annealing, expected to be characteristic of fusion reactor magnet operation, is presently the largest source of uncertainty in determining the limits of neutron exposure for copper stabilizers. Applications of our current understanding of the limits of copper stabilizers in fusion reactor designs are explored in two examples. Recommendations for future additions to the data base are discussed

  3. Binary circuitry including switching elements utilizing superconductive tunneling effects

    International Nuclear Information System (INIS)

    Baechtold, W.; Gueret, P.L.

    1976-01-01

    Two Josephson gates are connected in series to a low impedance voltage source. Each junction is bridged by a load impedance. The feed voltage is maintained in the order of the gap voltage which correponds to the voltage drop across a Josephson junction when it is in its single-particle-tunneling state. Therefore, only one out of both Josephson elements can exist in the voltage state at a time, and the other junction is forced to assume the superconducting pair-tunneling state. In its symmetric form, the basic circuit can be used as flip-flop or storage means. If asymmetric, the basic circuit shows monostable switching behavior, and it can be used as logic gate. Circuit asymmetry can be caused either by design using different junction areas or electrically by proper bias control currents applied to either or both gates of the basic circuit. The degree of symmetry or asymmetry can even be shifted with electrical means. AND and OR gates and inverting embodiments which perform logic NAND and NOR functions are shown

  4. Conventional proximity effect in bilayers of superconducting underdoped $La_{1.88}Sr_{0.12}CuO_4$ islands coated with non superconducting overdoped $La_{1.65}Sr_{0.35}CuO_4$

    OpenAIRE

    Koren, G.; Millo, O.

    2009-01-01

    Following a recent study by our group in which a large $T_c$ enhancement was reported in bilayers of the non-superconducting $La_{1.65}Sr_{0.35}CuO_4$ and superconducting $La_{1.88}Sr_{0.12}CuO_4$ films [Phys. Rev. Lett. \\textbf{101}, 057005 (2008)], we checked if a similar effect occurs when superconducting $La_{1.88}Sr_{0.12}CuO_4$ islands are coated with a continuous layer of the non superconducting $La_{1.65}Sr_{0.35}CuO_4$. We found that no such phenomenon is observed. The bare supercond...

  5. Energy gap and surface structure of superconducting diamond films probed by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Nishizaki, Terukazu; Takano, Yoshihiko; Nagao, Masanori; Takenouchi, Tomohiro; Kawarada, Hiroshi; Kobayashi, Norio

    2007-01-01

    We have performed scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (1 1 1)-oriented epitaxial films of heavily boron-doped diamond at T = 0.47 K. The STM topography shows two kinds of atomic structures: a hydrogenated 1 x 1 structure, C(1 1 1)1 x 1:H, and an amorphous structure. On the C(1 1 1)1 x 1:H region, the tunneling spectra show superconducting property with the energy gap Δ = 0.83 meV. The obtained gap ratio 2Δ/k B T c = 3.57 is consistent with the weak-coupling BCS theory

  6. Ginzburg-Landau theory of superconducting surfaces under the influence of electric fields

    Czech Academy of Sciences Publication Activity Database

    Lipavský, Pavel; Morawetz, K.; Koláček, Jan; Yang, T.-J.

    2006-01-01

    Roč. 73, č. 5 (2006), 052505/1-052505/4 ISSN 1098-0121 R&D Projects: GA ČR(CZ) GA202/04/0585; GA ČR(CZ) GA202/05/0173; GA AV ČR(CZ) IAA1010312 Grant - others:National Science Consil of Taiwan (TW) NSC 94-2112-M-009-001 Institutional research plan: CEZ:AV0Z10100521 Keywords : superconductivity * thin layers Subject RIV: BE - Theoretical Physics Impact factor: 3.107, year: 2006

  7. Flux pinning by voids in surface-oxidized superconducting niobium and vanadium

    International Nuclear Information System (INIS)

    Meij, G.P. van der.

    1984-01-01

    This thesis describes a study of flux pinning by small voids (roughly 10 nm) in the type II superconductors niobium and vanadium. These voids were created in rectangular foils (with typical dimensions of 30x3x0.2 mm) during an irradiation with fast neutrons in the High Flux Reactor at Petten at temperatures between 400 and 1000 0 C. The pinning force per unit volume is determined from the magnetic properties of the superconducting samples. The experiments were carried out in a slowly ramped magnetic field, as well as in a combination of a static and a much smaller alternating field. (Auth.)

  8. 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

  9. Quenching effect on properties of Bi-Sr-Ca-Cu-O superconducting ceramics of various composition

    International Nuclear Information System (INIS)

    Amitin, E.B.; Gromilov, S.A.; Naumov, V.N.; Royak, A.Ya.; Starikov, M.A.

    1989-01-01

    Bismuth ceramics quenching effect on superconducting properties of samples of various composition is investigated. Two types of quenching effect on sample properties are detected: an increase of superconducting transition temperature T c by 15-20 K; broadening of temperature interval of the phase transition without anynatable T c displacement. X ray diffraction investigations have not detected sufficient differences in diffraction patterns of quenched and non-quenched samples. Within the limits of composition analysis by oxygen (±3%) no change of its content prior to and after quenching is detected. A correlation between the presence of an amorphous phase in a sample and the type of quenching effect is observed: T c increases in ceramics where an amorphous component is detected

  10. 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

  11. Effect of Inhomogeneity on s-wave Superconductivity in the Attractive Hubbard Model

    Energy Technology Data Exchange (ETDEWEB)

    Aryanpour, K. A. [University of California, Davis; Dagotto, Elbio R [ORNL; Mayr, Matthias [Max-Planck-Institut fur Feskorperforschung, Stuttgart, Germany; Paiva, T. [Universidade Federal do Rio de Janeiro, Brazil; Pickett, W. E. [University of California, Davis; Scalettar, Richard T [ORNL

    2006-01-01

    Inhomogeneous s-wave superconductivity is studied in the two-dimensional, square lattice attractive Hubbard Hamiltonian using the Bogoliubov-de Gennes BdG mean field approximation. We find that at weak coupling, and for densities mainly below half-filling, an inhomogeneous interaction in which the on-site interaction Ui takes on two values, Ui=0, 2U results in a larger zero temperature pairing amplitude, and that the superconducting Tc can also be significantly increased, relative to a uniform system with Ui=U on all sites. These effects are observed for stripe, checkerboard, and even random patterns of the attractive centers, suggesting that the pattern of inhomogeneity is unimportant. Monte Carlo calculations which reintroduce some of the fluctuations neglected within the BdG approach see the same effect, both for the attractive Hubbard model and a Hamiltonian with d-wave pairing symmetry.

  12. Interplay of superconductivity and magnetism in presence of inter sub-lattice effect in cuprates

    International Nuclear Information System (INIS)

    Bishoyi, K.C.; Mohapatra, S.P.; Rout, G.C.

    2010-01-01

    In the present communication, we report a model Hamiltonian to study the interplay between the two long range orders of anti-ferromagnetism (AFM) and superconductivity (SC) in cuprate superconductors in presence of the intersite pairing effect. The BCS type but non-phonon pairing mechanism is considered among the electrons of two equivalent Cu sites. The pairing among the electrons of two nearest neighbour non-equivalent Cu sites is included in the Hamiltonian and its effect on the interplay of SC and AFM is investigated. The Hamiltonian is solved by the Green's function method and the corresponding gap equations are calculated and solved self-consistently. The influence of model parameters like AFM coupling (λ), SC coupling (λ 1 ) and the coupling (λ 2 ) for intersite superconducting interactions on the gaps (SC and AFM) are studied numerically and the results are reported. (author)

  13. Method of eliminating the training effect in superconducting coils by post-wind preload

    International Nuclear Information System (INIS)

    Heim, J.R.

    1976-01-01

    The training effect in superconducting coils is eliminated by winding the coil with a composite material that includes both a superconductor and a normal material. Stresses are applied to the wound coil in the direction that electromagnetic stresses will be applied to the coil during normal use. The applied stresses are greater than the calculated magnitude of the greatest electromagnetic stresses to be applied to the coil

  14. Surface Effects in Magnetic Nanoparticles

    CERN Document Server

    Fiorani, Dino

    2005-01-01

    This volume is a collection of articles on different approaches to the investigation of surface effects on nanosized magnetic materials, with special emphasis on magnetic nanoparticles. The book aims to provide an overview of progress in the understanding of surface properties and surface driven effects in magnetic nanoparticles through recent results of different modeling, simulation, and experimental investigations.

  15. Decrease of the surface resistance in superconducting niobium resonator cavities by the microwave field

    Energy Technology Data Exchange (ETDEWEB)

    Ciovati, Gianluigi [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Dhakal, Pashupati [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Gurevich, Alexander V. [Old Dominion University, Norfolk, VA (United States)

    2014-03-03

    Measurements of the quality factor, Q, of Nb superconducting microwave resonators often show that Q increases by {approx_equal} 10%–30% with increasing radio-frequency (rf) field, H, up to {approx} 15-20 mT. Recent high temperature heat treatments can amplify this rf field-induced increase of Q up to {approx_equal} 50%–100% and extend it to much higher fields, but the mechanisms of the enhancement of Q(H) remain unclear. Here, we suggest a method to reveal these mechanisms by measuring temperature dependencies of Q at different rf field amplitudes. We show that the increase of Q(H) does not come from a field dependent quasi-particles activation energy or residual resistance, but rather results from the smearing of the density of state by the rf field.

  16. Fulde-Ferrell state in superconducting core/shell nanowires: role of the orbital effect

    Science.gov (United States)

    Mika, Marek; Wójcik, Paweł

    2017-11-01

    The orbital effect on the Fulde-Ferrell (FF) phase is investigated in superconducting core/shell nanowires subjected to the axial magnetic field. Confinement in the radial direction results in quantization of the electron motion with energies determined by the radial j and orbital m quantum numbers. In the external magnetic field, the twofold degeneracy with respect to the orbital magnetic quantum number m is lifted which leads to the Fermi wave vector mismatch between the paired electrons, (k, j, m, \\uparrow) ≤ftrightarrow (-k, j, -m, \\downarrow) . This mismatch is transferred to the nonzero total momentum of the Cooper pairs, which results in a formation of the FF phase occurring sequentially with increasing magnetic field. By changing the nanowire radius R and the superconducting shell thickness d, we discuss the role of the orbital effect in the FF phase formation in both the nanowire-like (R/d \\ll 1 ) and nanofilm-like (R/d \\gg 1 ) regime. We have found that the irregular pattern of the FF phase which appears for the case of the nanowire-like regime, for the nanofilm-like geometry evolves towards the regular distribution in which the FF phase stability regions emerge periodically between the BCS states. The transition between these two different phase diagrams is explained as resulting from the orbital effect and the multigap character of superconductivity in the core/shell nanowires.

  17. Pressure effect on the superconducting and the normal state of β -B i2Pd

    Science.gov (United States)

    Pristáš, G.; Orendáč, Mat.; Gabáni, S.; Kačmarčík, J.; Gažo, E.; Pribulová, Z.; Correa-Orellana, A.; Herrera, E.; Suderow, H.; Samuely, P.

    2018-04-01

    The pressure effect up to 24.0 kbar on superconducting and normal-state properties of β -B i2Pd single crystal (Tc≈4.98 K at ambient pressure) has been investigated by measurements of the electrical resistivity. In addition, we have performed the heat capacity measurements in the temperature range 0.7-300 K at ambient pressure. The recent calculations of electronic density of states, electron-phonon interaction spectral function, and phonon density of states of β -B i2Pd [Zheng and Margine, Phys. Rev. B 95, 014512 (2017), 10.1103/PhysRevB.95.014512], are used to fit the resistivity and the heat capacity data. In the superconducting state we have focused on the influence of pressure on the superconducting transition temperature Tc and upper critical field Hc 2 and a negative effect with d Tc/d p =-0.025 K /kbar and d Hc 2/d p =-8 mT /kbar is found. A simplified Bloch-Grüneisen model was used to analyze the pressure effect on the temperature dependence of the normal-state resistivity. The obtained results point to a decrease of the electron-phonon coupling parameter λ and to a shift of phonon frequencies to higher values with pressure. Moreover, the temperature dependence of the normal-state resistivity follows a T2 dependence above Tc up to about 25 K. Together with the enhanced value of Sommerfeld coefficient γ =13.23 mJ mo l-1K-2 these results point to a certain role of the electron-electron interaction in the superconducting pairing mechanism in β -B i2Pd .

  18. Resonance of Superconducting Microstrip Antenna with Aperture in the Ground Plane

    Directory of Open Access Journals (Sweden)

    S. Benkouda

    2013-08-01

    Full Text Available This paper presents a rigorous full-wave analysis of a high Tc superconducting rectangular microstrip antenna with a rectangular aperture in the ground plane. To include the effect of the superconductivity of the microstrip patch in the full-wave analysis, a complex surface impedance is considered. The proposed approach is validated by comparing the computed results with previously published data. Results showing the effect of the aperture on the resonance of the superconducting microstrip antenna are given.

  19. Effect of pressure on spin fluctuations and superconductivity in heavy-fermion UPt3

    International Nuclear Information System (INIS)

    Willis, J.O.; Thompson, J.D.; Fisk, Z.; de Visser, A.; Franse, J.J.M.; Menovsky, A.

    1985-01-01

    We have determined the effect of hydrostatic pressure on the susceptibility, on the T 2 temperature dependence of the spin-fluctuation resistivity, and on superconductivity in UPt 3 . The spin-fluctuation temperature T/sub s/, derived from the slope of resistivity versus T 2 , is used within a Fermi-liquid picture to calculate the susceptibility chi at T = 0 K. The depression of this calculated chi with pressure agrees with the directly measured value partial lnchi/partialP = -24 Mbar -1 . Both the superconducting transition temperature T/sub c/ and the initial slope of the upper critical field also decrease under pressure. We find that partial lnT/sub c//partialP = -25 Mbar -1 and speculate upon correlations between chi and T/sub c/

  20. On the proximity effect in a superconductive slab bordered by metal

    International Nuclear Information System (INIS)

    Liniger, W.

    1993-01-01

    The first Ginzburg-Landau equation for the order parameter ψ in the absence of magnetic fields is solved analytically for a superconducting slab of thickness 2d boardered by semi-infinite regions of normal metal at each face. The real-valued normalized wave function f=ψ/ψ ∞ depends only on the transversal spatial coordinate x, normalized with respect to the coherence length ξ of the superconductor, provided the de Gennes boundary condition df/dx=f/b is used. The closed-form solution expresses x as an elliptic integral of f, depending on the normalized parameters d and b. It is predicted theoretically that, for b c =arctan(1/b), the proximity effect is so strong that the superconductivity is completely suppressed. In fact, in this case, the first Ginzburg-Landau equation possesses only the trivial solution f≡0

  1. Exact mapping of the dx2-y2 Cooper-pair wavefunction onto the spin fluctuations in cuprates: the Fermi surface as a driver for 'high Tc' superconductivity

    International Nuclear Information System (INIS)

    McDonald, Ross D; Harrison, Neil; Singleton, John

    2009-01-01

    We propose that the extraordinarily high superconducting transition temperatures in the cuprates are driven by an exact mapping of the d x 2 -y 2 Cooper-pair wavefunction onto the incommensurate spin fluctuations observed in neutron-scattering experiments. This is manifested in the direct correspondence between the inverse of the incommensurability factor δ seen in inelastic neutron-scattering experiments and the measured superconducting coherence length ξ 0 . Strikingly, the relationship between ξ 0 and δ is valid for both La 2-x Sr x CuO 4 and YBa 2 Cu 3 O 7-x , suggesting a common mechanism for superconductivity across the entire hole-doped cuprate family. Using data from recent quantum-oscillation experiments in the cuprates, we propose that the fluctuations responsible for superconductivity are driven by a Fermi-surface instability. On the basis of these findings, one can specify the optimal characteristics of a solid that will exhibit 'high T c ' superconductivity. (fast track communication)

  2. First-principles theory of anharmonicity and the inverse isotope effect in superconducting palladium-hydride compounds.

    Science.gov (United States)

    Errea, Ion; Calandra, Matteo; Mauri, Francesco

    2013-10-25

    Palladium hydrides display the largest isotope effect anomaly known in the literature. Replacement of hydrogen with the heavier isotopes leads to higher superconducting temperatures, a behavior inconsistent with harmonic theory. Solving the self-consistent harmonic approximation by a stochastic approach, we obtain the anharmonic free energy, the thermal expansion, and the superconducting properties fully ab initio. We find that the phonon spectra are strongly renormalized by anharmonicity far beyond the perturbative regime. Superconductivity is phonon mediated, but the harmonic approximation largely overestimates the superconducting critical temperatures. We explain the inverse isotope effect, obtaining a -0.38 value for the isotope coefficient in good agreement with experiments, hydrogen anharmonicity being mainly responsible for the isotope anomaly.

  3. Flux-quantization effects in disordered normal metal rings and superconducting networks

    International Nuclear Information System (INIS)

    Li, Qiming.

    1989-01-01

    The effects of the magnetic flux on the properties of disordered normal metal rings and bond or site diluted two-dimensional superconducting networks are investigated theoretically, with an emphasis on the quantum coherence of the electrons and the localization nature in the disordered systems. The conductance of disordered metal rings in magnetic field is obtained via the Landauer's formula through calculations of the localization length L c . The important role of the ensemble averaging and the self-averaging to obtain the half-flux-quantum h/2e conductance oscillation is demonstrated unambiguously in both rings of a strictly one-dimensional geometry and rings with a finite width. The amplitude of the localization length oscillation is found to follow a universal relation for all the numerical data: Δ(L c /L) = α(L c /L) 2 . L is the radius of the ring. The expected universal conductance fluctuations are observed for L c /L ∼ 1. For L c > L, much larger oscillation amplitudes are obtained. In the case of two-dimensional site or bond percolation superconducting networks, the nature of the eigenstates and the effects on the superconducting-to-normal phase boundary is examined by finite-size transfer matrix calculations within the mean-field Ginzburg-Landau theory of second order phase transitions

  4. Annealing treatment effects on structure and superconductivity in Y1Ba2Cu3O/sub 9-//sub x/

    International Nuclear Information System (INIS)

    Beyers, R.; Lim, G.; Engler, E.M.

    1987-01-01

    We report the effects of heat treatment and ambient on the structure and superconducting properties of Y 1 Ba 2 Cu 3 O/sub 9-//sub x/. The structure undergoes an orthorhombic-to-tetragonal transition on heating at about 700 0 C, caused by oxygen loss and disordering of oxygen vacancies on the copper plane between the barium layers. Heat treatments that promote maximum ordering of the oxygen vacancies result in superior superconducting properties

  5. Development of a theoretical model for polycrystalline superconducting anisotropic using the effective medium approximation

    International Nuclear Information System (INIS)

    Cruz-García, A.; Muné, P; Govea-Alcaide, E.

    2008-01-01

    Full text: In this paper, is a study of the transport properties in anisotropic polycrystalline superconducting. The presence of certain order of orientation of grains in polycrystalline superconducting (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10+delta , is modeled by introducing a probability of orientation, gamma factor. In addition, is included in the model the concentration c, which characterize the contribution of porosity to the decrease in the conductivity of the Crystal, transparent. Assumes that pores and pimples are ellipsoid flattened with similar dimensions and takes into account the values of conductivity of beads in each direction. The calculation is based on the application of a generalization of the approximation of the effective way to the study of heterogeneous media, which is called coherent potential approximation (APC). The results are compared with an empirical model developed recently for samples of YBa 2 Cu 3 O 7 -delta (YBCO) which enriches its employment and applied to ceramic superconducting in general. (author)

  6. Effect of coupling currents on the dynamic inductance during fast transient in superconducting magnets

    Directory of Open Access Journals (Sweden)

    V. Marinozzi

    2015-03-01

    Full Text Available We present electromagnetic models aiming to calculate the variation of the inductance in a magnet due to dynamic effects such as the variation of magnetization or the coupling with eddy currents. The models are studied with special regard to the calculation of the inductance in superconducting magnets which are affected by interfilament coupling currents. The developed models have been compared with experimental data coming from tests of prototype Nb_{3}Sn magnets designed for the new generation of accelerators. This work is relevant for the quench protection study of superconducting magnets: quench is an unwanted event, when part of the magnet becomes resistive; in these cases, the current should be discharged as fast as possible, in order to maintain the resistive zone temperature under a safe limit. The magnet inductance is therefore a relevant term for the description of the current discharge, especially for the high-field new generation superconducting magnets for accelerators, and this work shows how to calculate the correct value during rapid current changes, providing a mean for simulations of the reached temperature.

  7. Effect of superconducting solenoid model cores on spanwise iron magnet roll control

    Science.gov (United States)

    Britcher, C. P.

    1985-01-01

    Compared with conventional ferromagnetic fuselage cores, superconducting solenoid cores appear to offer significant reductions in the projected cost of a large wind tunnel magnetic suspension and balance system. The provision of sufficient magnetic roll torque capability has been a long-standing problem with all magnetic suspension and balance systems; and the spanwise iron magnet scheme appears to be the most powerful system available. This scheme utilizes iron cores which are installed in the wings of the model. It was anticipated that the magnetization of these cores, and hence the roll torque generated, would be affected by the powerful external magnetic field of the superconducting solenoid. A preliminary study has been made of the effect of the superconducting solenoid fuselage model core concept on the spanwise iron magnet roll torque generation schemes. Computed data for one representative configuration indicate that reductions in available roll torque occur over a range of applied magnetic field levels. These results indicate that a 30-percent increase in roll electromagnet capacity over that previously determined will be required for a representative 8-foot wind tunnel magnetic suspension and balance system design.

  8. Co60 and Cs137 gamma radiation effects on textured bscco Superconducting fibers

    International Nuclear Information System (INIS)

    Leyva Fabelo, A.; Bouza Dominguez, J.; Cruz Inclan, Crlos M.

    2001-01-01

    Bi2Sr2CaCu2Ox superconducting fibers synthesized by solid state reaction and textured by the method of zonal laser ablation were irradiated with gamma rays of 1.25 MeV and 662 keV and studied the behavior of some of its properties with the exposition dose. The measurements of dynamic magnetic susceptibility were used for the characterization of the samples. It was observed that for the dose of up to 600 kGy in the case of the Co60 and until 500 mGy for the Cs137, the fibers preserve its superconducting intragrain properties. It is an evidence of the high resistance of the material to the radiacional damage. In all the cases were verified that with the increase of the dose the Ton of the transition grows. Two possible mechanisms that play the most important role in this effect are explained in the text. The ac measurements allowed to verified the increasing behavior of the superconducting volume fraction in the sample with the exposition dose

  9. Thermal coupling effect on the vortex dynamics of superconducting thin films: time-dependent Ginzburg–Landau simulations

    Science.gov (United States)

    Jing, Ze; Yong, Huadong; Zhou, Youhe

    2018-05-01

    In this paper, vortex dynamics of superconducting thin films are numerically investigated by the generalized time-dependent Ginzburg–Landau (TDGL) theory. Interactions between vortex motion and the motion induced energy dissipation is considered by solving the coupled TDGL equation and the heat diffusion equation. It is found that thermal coupling has significant effects on the vortex dynamics of superconducting thin films. Branching in the vortex penetration path originates from the coupling between vortex motion and the motion induced energy dissipation. In addition, the environment temperature, the magnetic field ramp rate and the geometry of the superconducting film also greatly influence the vortex dynamic behaviors. Our results provide new insights into the dynamics of superconducting vortices, and give a mesoscopic understanding on the channeling and branching of vortex penetration paths during flux avalanches.

  10. Current-ripple effect on superconductive dc critical current measurements

    International Nuclear Information System (INIS)

    Goodrich, L.F.; Bray, S.L.; Clark, A.F.

    1988-01-01

    The effect of sample-current power-supply ripple on dc critical current measurement in multifilamentary NbTi superconductors was evaluated. In general the ripple in a current supply became more significant above 500 A because effective filtering was hard to achieve. Ripple also caused noise at the input of the voltmeter used for the measurements. The quantitative effect of current ripple was studied using a battery current supply modified to allow the creation of ripple current with variable frequency and amplitude. Problems common to all large-conductor critical current measurements are discussed

  11. Vortices in superconducting films: Statistics and fractional quantum Hall effect

    International Nuclear Information System (INIS)

    Dziarmaga, J.

    1996-01-01

    We present a derivation of the Berry phase picked up during exchange of parallel vortices. This derivation is based on the Bogolubov endash de Gennes formalism. The origin of the Magnus force is also critically reanalyzed. The Magnus force can be interpreted as an interaction with the effective magnetic field. The effective magnetic field may be even of the order 10 6 T/A. We discuss a possibility of the fractional quantum Hall effect (FQHE) in vortex systems. As the real magnetic field is varied to drive changes in vortex density, the vortex density will prefer to stay at some quantized values. The mere existence of the FQHE does not depend on vortex quantum statistics, although the pattern of the plateaux does. We also discuss how the density of anyonic vortices can lower the effective strengh of the Magnus force, what might be observable in measurements of Hall resistivity. copyright 1996 The American Physical Society

  12. Influence of anisotropy effect and internal stresses upon the superconductive critical temperature of plastically deformed tin

    International Nuclear Information System (INIS)

    Wagner, D.; Stangler, F.

    1976-01-01

    The influence of plastic deformation on the superconductive critical temperature of tin single crystals has been investigated experimentally. It was shown by measurements that the lattice defects produced by plastic deformation lead to an anisotropy effect (according to the theory of Markowitz and Kadanoff), as do impurities in alloyed material. The decrease in T/sub c/ due to this effect can be measured, however, only with samples of certain special orientations. Samples with other orientations show an increase in T/sub c/, which can be explained by the assumption of internal stresses from dislocation pileups. A model is discussed which accounts for the measured rise in T/sub c/

  13. Anharmonic phonons and the isotope effect in superconductivity

    International Nuclear Information System (INIS)

    Crespi, V.H.; Cohen, M.L.; Penn, D.R.

    1991-01-01

    Anharmonic interionic potentials are examined in an Einstein model to study the unusual isotope-effect exponents for the high-T c oxides. The mass dependences of the electron-phonon coupling constant λ and the average phonon frequency √ left-angle ω 2 right-angle are computed from weighted sums over the oscillator levels. The isotope-effect exponent is depressed below 1/2 by either a double-well potential or a potential with positive quadratic and quartic parts. Numerical solutions of Schroedinger's equation for double-well potentials produce λ's in the range 1.5--4 for a material with a vanishing isotope-effect parameter α. However, low phonon frequencies limit T c to roughly 15 K. A negative quartic perturbation to a harmonic well can increase α above 1/2. In the extreme-strong-coupling limit, α is 1/2, regardless of anharmonicity

  14. Effect of low-temperature baking on the radio-frequency properties of niobium superconducting cavities for particle accelerators

    International Nuclear Information System (INIS)

    Ciovati, Gianluigi

    2004-01-01

    Radio-frequency superconducting (SRF) cavities are widely used to accelerate a charged particle beam in particle accelerators. The performance of SRF cavities made of bulk niobium has significantly improved over the last ten years and is approaching the theoretical limit for niobium. Nevertheless, RF tests of niobium cavities are still showing some 'anomalous' losses that require a better understanding in order to reliably obtain better performance. These losses are characterized by a marked dependence of the surface resistance on the surface electromagnetic field and can be detected by measuring the quality factor of the resonator as a function of the peak surface field. A low-temperature (100-150 deg. C) 'in situ' bake under ultrahigh vacuum has been successfully applied as final preparation of niobium RF cavities by several laboratories over the last few years. The benefits reported consist mainly of an improvement of the cavity quality factor at low field and a recovery from 'anomalous' losses (so-called 'Q drop') without field emission at higher field. A series of experiments with a CEBAF single-cell cavity have been carried out at Jefferson Lab to carefully investigate the effect of baking at progressively higher temperatures for a fixed time on all the relevant material parameters. Measurements of the cavity quality factor in the temperature range 1.37-280 K and resonant frequency shift between 6-9.3 K provide information about the surface resistance, energy gap, penetration depth, and mean free path. The experimental data have been analyzed with the complete BCS theory of superconductivity. The hydrogen content of small niobium samples inserted in the cavity during its surface preparation was analyzed with nuclear reaction analysis. The single-cell cavity has been tested at three different temperatures before and after baking to gain some insight on thermal conductivity and Kapitza resistance and the data are compared with different models. This paper

  15. Effect of low-temperature baking on the radio-frequency properties of niobium superconducting cavities for particle accelerators

    Science.gov (United States)

    Ciovati, Gianluigi

    2004-08-01

    Radio-frequency superconducting (SRF) cavities are widely used to accelerate a charged particle beam in particle accelerators. The performance of SRF cavities made of bulk niobium has significantly improved over the last ten years and is approaching the theoretical limit for niobium. Nevertheless, RF tests of niobium cavities are still showing some "anomalous" losses that require a better understanding in order to reliably obtain better performance. These losses are characterized by a marked dependence of the surface resistance on the surface electromagnetic field and can be detected by measuring the quality factor of the resonator as a function of the peak surface field. A low-temperature (100-150°C) "in situ" bake under ultrahigh vacuum has been successfully applied as final preparation of niobium RF cavities by several laboratories over the last few years. The benefits reported consist mainly of an improvement of the cavity quality factor at low field and a recovery from "anomalous" losses (so-called "Q drop") without field emission at higher field. A series of experiments with a CEBAF single-cell cavity have been carried out at Jefferson Lab to carefully investigate the effect of baking at progressively higher temperatures for a fixed time on all the relevant material parameters. Measurements of the cavity quality factor in the temperature range 1.37-280K and resonant frequency shift between 6-9.3K provide information about the surface resistance, energy gap, penetration depth, and mean free path. The experimental data have been analyzed with the complete BCS theory of superconductivity. The hydrogen content of small niobium samples inserted in the cavity during its surface preparation was analyzed with nuclear reaction analysis. The single-cell cavity has been tested at three different temperatures before and after baking to gain some insight on thermal conductivity and Kapitza resistance and the data are compared with different models. This paper describes

  16. Superconducting Meissner effect bearings for cryogenic turbomachines, phase 2

    Science.gov (United States)

    Valenzuela, Javier A.; Martin, Jerry L.

    1994-02-01

    This is the final report of a Phase 2 SBIR project to develop Meissner effect bearings for miniature cryogenic turbomachines. The bearing system was designed for use in miniature cryogenic turboexpanders in reverse-Brayton-cycle cryocoolers. The cryocoolers are designed to cool sensors on satellites. Existing gas bearings for this application run in a relatively warm state. The heat loss from the bearings into the shaft and into the cold process gas imposes a penalty on the cycle efficiency. By using cold Meissner effect bearings, this heat loss could be minimized, and the input power per unit of cooling for these cryocoolers could be reduced. Two bearing concepts were explored in this project. The first used an all-magnetic passive radial suspension to position the shaft over a range of temperatures from room temperature to 77 K. This bearing concept was proven to be feasible, but impractical for the miniature high-speed turbine application since it lacked the required shaft positioning accuracy. A second bearing concept was then developed. In this concept, the Meissner effect bearings are combined with self-acting gas bearings. The Meissner effect bearing provides the additional stiffness and damping required to stabilize the shaft at low temperature, while the gas bearing provides the necessary accuracy to allow very small turbine tip clearances (5mm) and high speeds (greater than 500,000 rpm).

  17. Investigation of Plasma Etching for Superconducting RF Cavities Surface Preparation. Final Report

    International Nuclear Information System (INIS)

    Vuskovic, Leposava

    2009-01-01

    Our results show that plasma-treated samples are comparable or superior to a BCP sample, both in the size of features and sharpness of the boundaries between individual features at the surface. Plasma treatment of bulk Nb cavities is a promising technique for microwave cavities preparation used in particle acceleration application. Etching rates are sufficiently high to enable efficient removal of mechanically damaged surface layer with high reproducibility. No impurities are deposited on the bulk Nb surface during plasma treatment. Surface topology characteristic are promising for complex cavity geometry, since discharge conforms the profile of the reaction chamber. In view of these experimental results, we propose plasma treatment for producing microwave cavities with high Q factor instead of using bulk Nb treated with wet etching process.

  18. 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

  19. Superconducting state mechanisms and properties

    CERN Document Server

    Kresin, Vladimir Z; Wolf, Stuart A

    2014-01-01

    'Superconducting State' provides a very detailed theoretical treatment of the key mechanisms of superconductivity, including the current state of the art (phonons, magnons, and plasmons). A very complete description is given of the electron-phonon mechanism responsible for superconductivity in the majority of superconducting systems, and the history of its development, as well as a detailed description of the key experimental techniques used to study the superconducting state and determine the mechanisms. In addition, there are chapters describing the discovery and properties of the key superconducting compounds that are of the most interest for science, and applications including a special chapter on the cuprate superconductors. It provides detailed treatments of some very novel aspects of superconductivity, including multiple bands (gaps), the "pseudogap" state, novel isotope effects beyond BCS, and induced superconductivity.

  20. 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

  1. Size, Shape and Impurity Effects on Superconducting critical temperature.

    Science.gov (United States)

    Umeda, Masaki; Kato, Masaru; Sato, Osamu

    Bulk superconductors have their own critical temperatures Tc. However, for a nano-structured superconductor, Tc depends on size and shape of the superconductor. Nishizaki showed that the high pressure torsion on bulks of Nb makes Tc higher, because the torsion makes many nano-sized fine grains in the bulks. However the high pressure torsion on bulks of V makes Tc lower, and Nishizaki discussed that the decrease of Tc is caused by impurities in the bulks of V. We studied size, shape, and impurity effects on Tc, by solving the Gor'kov equations, using the finite element method. We found that smaller and narrower superconductors show higher Tc. We found how size and shape affects Tc by studying spacial order parameter distributions and quasi-particle eigen-energies. Also we studied the impurity effects on Tc, and found that Tc decreases with increase of scattering rate by impurities. This work was supported in part of KAKENHI Grant Number JP26400367 and JP16K05460, and program for leading graduate schools of ministry of education, culture, sports, science and technology-Japan.

  2. 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

  3. Observation of weak superconductivity in electrons localized on a film surface

    International Nuclear Information System (INIS)

    Fogel', N.Y.; Kolin'ko, A.E.

    1984-01-01

    We have observed anomalous abrupt resistance changes in thick vanadium films [d>>xi(T)]. We have also observed a number of anomalies in the H--T phase diagrams for these films; these anomalies are most clearly seen when the field is parallel to, or at low angles of incidence with respect to, the film surface. We explain our results by assuming that there are two different electron systems present in the film. One of them is composed of electrons localized near a natural planar defect, the film surface. This subsystem is characterized by extremely small values of the critical current

  4. Preparing last LEP superconducting module for removal

    CERN Multimedia

    Patrice Loïez

    2000-01-01

    The last superconducting module travels along the LEP tunnel towards one of the shafts where it will be lifted to the surface. Superconducting modules were only used in the LEP-2 phase of the accelerator, from 1996 to 2000.

  5. Stacked magnet superconducting bearing

    International Nuclear Information System (INIS)

    Rigney, T.K. II; Saville, M.P.

    1993-01-01

    A superconducting bearing is described, comprising: a plurality of permanent magnets magnetized end-to-end and stacked side-by-side in alternating polarity, such that flux lines flow between ends of adjacent magnets; isolating means, disposed between said adjacent magnets, for reducing flux leakage between opposing sides of said adjacent magnets; and a member made of superconducting material having at least one surface in communication with said flux lines

  6. 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

  7. Valley- and spin-switch effects in molybdenum disulfide superconducting spin valve

    Science.gov (United States)

    Majidi, Leyla; Asgari, Reza

    2014-10-01

    We propose a hole-doped molybdenum disulfide (MoS2) superconducting spin valve (F/S/F) hybrid structure in which the Andreev reflection process is suppressed for all incoming waves with a determined range of the chemical potential in ferromagnetic (F) region and the cross-conductance in the right F region depends crucially on the configuration of magnetizations in the two F regions. Using the scattering formalism, we find that the transport is mediated purely by elastic electron cotunneling (CT) process in a parallel configuration and changes to the pure crossed Andreev reflection (CAR) process in the low-energy regime, without fixing of a unique parameter, by reversing the direction of magnetization in the right F region. This suggests both valley- and spin-switch effects between the perfect elastic CT and perfect CAR processes and makes the nonlocal charge current to be fully valley- and spin-polarized inside the right F region where the type of the polarizations can be changed by reversing the magnetization direction in the right F region. We further demonstrate that the presence of the strong spin-orbit interaction λ and an additional topological term (β ) in the Hamiltonian of MoS2 result in an enhancement of the charge conductance of the CT and CAR processes and make them to be present for long lengths of the superconducting region. Besides, we find that the thermal conductance of the structure with a small length of the highly doped superconducting region exhibits linear dependence on the temperature at low temperatures, whereas it enhances exponentially at higher temperatures. In particular, we demonstrate that the thermal conductance versus the strength of the exchange field (h ) in F region displays a maximum value at h <λ , which moves towards larger exchange fields by increasing the temperature.

  8. Interplay between magnetic quantum criticality, Fermi surface and unconventional superconductivity in UCoGe, URhGe and URu2Si2

    International Nuclear Information System (INIS)

    Bastien, Gael

    2017-01-01

    This thesis is concentrated on the ferromagnetic superconductors UCoGe and URhGe and on the hidden order state in URu 2 Si 2 . In the first part the pressure temperature phase diagram of UCoGe was studied up to 10.5 GPa. Ferromagnetism vanishes at the critical pressure pc≅1 GPa. Unconventional superconductivity and non Fermi liquid behavior can be observed in a broad pressure range around pc. The superconducting upper critical field properties were explained by the suppression of the magnetic fluctuations under field. In the second part the Fermi surfaces of UCoGe and URhGe were investigated by quantum oscillations. In UCoGe four Fermi surface pockets were observed. Under magnetic field successive Lifshitz transitions of the Fermi surface have been detected. The observed Fermi surface pockets in UCoGe evolve smoothly with pressure up to 2.5 GPa and do not show any Fermi surface reconstruction at the critical pressure pc. In URhGe, three heavy Fermi surface pockets were detected by quantum oscillations. In the last part the quantum oscillation study in the hidden order state of URu 2 Si 2 shows a strong g factor anisotropy for two Fermi surface pockets, which is compared to the macroscopic g factor anisotropy extracted from the upper critical field study. (author) [fr

  9. Transport relaxation measurements and glassy state effects in superconducting MgB{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Olutas, M. [Abant Izzet Baysal University, Department of Physics, Turgut Gulez Research Laboratory, 14280 Bolu (Turkey)], E-mail: olutas_m@ibu.edu.tr; Yetis, H.; Altinkok, A.; Kilic, A.; Kilic, K. [Abant Izzet Baysal University, Department of Physics, Turgut Gulez Research Laboratory, 14280 Bolu (Turkey)

    2008-09-15

    Time dependent effects in superconducting MgB{sub 2} have been studied systematically for the first time by transport relaxation measurements (V-t curves) as a function of transport current (I), temperature (T) and external magnetic field (H). At very low dissipation levels (below {approx}1 {mu}V), it was observed that the sample voltage grows up smoothly in time by exhibiting the details of initial stage of relaxation process. At high dissipation levels, steady state corresponding to constant flow rate is maintained within a very short time and monitoring of details of flux dynamic evolving along sample becomes difficult on long time scales. Another interesting behavior is the appearance of voltage peak when the transport current was reduced to a finite value. After peak, it was observed that the sample voltage relaxes smoothly by leveling off within a very short time. The evolution of V-t curves suggests that formation of resistive flow channels along sample develops easily, which is quite similar to that of obtained for the superconducting ceramic samples whose grain boundaries are improved. Time dependent effects were also observed in magnetovoltage measurements (V-H curves) as the field sweep rate (dH/dt) varies. The observations were interpreted mainly in terms of flux trapping in grains.

  10. Transport relaxation measurements and glassy state effects in superconducting MgB2

    International Nuclear Information System (INIS)

    Olutas, M.; Yetis, H.; Altinkok, A.; Kilic, A.; Kilic, K.

    2008-01-01

    Time dependent effects in superconducting MgB 2 have been studied systematically for the first time by transport relaxation measurements (V-t curves) as a function of transport current (I), temperature (T) and external magnetic field (H). At very low dissipation levels (below ∼1 μV), it was observed that the sample voltage grows up smoothly in time by exhibiting the details of initial stage of relaxation process. At high dissipation levels, steady state corresponding to constant flow rate is maintained within a very short time and monitoring of details of flux dynamic evolving along sample becomes difficult on long time scales. Another interesting behavior is the appearance of voltage peak when the transport current was reduced to a finite value. After peak, it was observed that the sample voltage relaxes smoothly by leveling off within a very short time. The evolution of V-t curves suggests that formation of resistive flow channels along sample develops easily, which is quite similar to that of obtained for the superconducting ceramic samples whose grain boundaries are improved. Time dependent effects were also observed in magnetovoltage measurements (V-H curves) as the field sweep rate (dH/dt) varies. The observations were interpreted mainly in terms of flux trapping in grains

  11. Vortex loops in the critical Casimir effect in superfluid and superconducting films

    International Nuclear Information System (INIS)

    Williams, Gary A.

    2004-01-01

    Vortex-loop renormalization techniques are used to calculate the magnitude of the critical Casimir forces in superfluid and superconducting thin films. The force is found to become appreciable when the size of the thermally excited vortex loops is comparable to the film thickness, and the results for T c are found to match very well with perturbative renormalization-group theories that can only be carried out for T>T c . In helium films the Casimir force leads to a change in the film thickness close to T c that has been observed experimentally. A similar effect is predicted to occur near the transition temperature of high-T c superconducting films, which is also a vortex-loop phase transition. In this case the Casimir force takes the form of a voltage difference that will appear at the junction between a thin film and a bulk sample. Estimates show that this voltage can be appreciable (tens of microvolts), and it may be possible to observe the effect by measuring the voltage across two Josephson tunnel junctions to the film and to the bulk, using a SQUID voltmeter

  12. Preparation of MgB2 superconducting microbridges by focused ion beam direct milling

    Science.gov (United States)

    Zhang, Xuena; Li, Yanli; Xu, Zhuang; Kong, Xiangdong; Han, Li

    2017-01-01

    MgB2 superconducting microbridges were prepared by focused ion beam (FIB) direct milling on MgB2 films. The surface topography of the microbridges were observed using SEM and AFM and the superconductivity was measured in this paper. Lots of cracks and holes were found near the milled area. And the superconducting transition temperature was decreased a lot and the bridges prepared were not superconducting due to ion damage after milled with large dose. Through these works, we explored the effect regular of FIB milling and experimental parameters on the performance of microbridges.

  13. Possible room temperature superconductivity in conductors obtained by bringing alkanes into contact with a graphite surface

    Directory of Open Access Journals (Sweden)

    Yasushi Kawashima

    2013-05-01

    Full Text Available Electrical resistances of conductors obtained by bringing alkanes into contact with a graphite surface have been investigated at room temperatures. Ring current in a ring-shaped container into which n-octane-soaked thin graphite flakes were compressed did not decay for 50 days at room temperature. After two HOPG plates were immersed into n-heptane and n-octane at room temperature, changes in resistances of the two samples were measured by four terminal technique. The measurement showed that the resistances of these samples decrease to less than the smallest resistance that can be measured with a high resolution digital voltmeter (0.1μV. The observation of persistent currents in the ring-shaped container suggests that the HOPG plates immersed in n-heptane and n-octane really entered zero-resistance state at room temperature. These results suggest that room temperature superconductor may be obtained by bringing alkanes into contact with a graphite surface.

  14. Effect of lead addition on the formation of superconducting phases in Bi-Sr-Ca-Cu-O ceramics

    International Nuclear Information System (INIS)

    Martinelli, A.E.

    1991-01-01

    Superconducting ceramics with starting composition Bi 2 - x Pb x Sr 2 Ca 2 Cu 3 O y (0,0 ≤ X ≤ 0,6) were prepared in order to investigate the effects of partial substitution of Pb for Bi and sintering time and atmosphere in the formation of superconducting phases. For all samples X-ray diffraction analyses were performed to estimate the amount of superconducting phases; superconductivity was analysed by dc electrical resistance and ac magnetic susceptibility measurements. The main results show that: a) the longer the sintering time (up to 168 h), the larger the volume fraction of superconducting phases with critical temperature (T c ) greater than the temperature of nitrogen liquefaction; b) by partially substituting Pb for Bi it is possible to restrain the formation of 2212 phase (T c = 80 K) and to enhance the amount of 2223 phase (T c = 105 K); C) a heat treatment under oxygen atmosphere before sintering enhances the formation of 2223 phase. (author)

  15. Effect of the magnet insertion on the performance of a superconducting pump

    International Nuclear Information System (INIS)

    Kondo, M.; Inoue, K.; Koshizuka, N.; Seki, H.; Murakami, M.; Hiragushi, M.; Akiyama, S.

    2014-01-01

    Highlights: • Non-contact rotation is possible by using permanent magnets and superconductors. • It is necessary to rotate a superconducting pump stably for practical applications. • We placed a permanent magnet at the bottom to increase the stiffness. • Inserting permanent magnets was effective in increasing the rotational stability. - Abstract: For medical and semiconductor fabrication lines, an ultra-clean and impurity-free environment is often required. In order to realize such a contaminant-free environment, it is desirable to employ a completely non-contact rotating mechanism. Such a non-contact rotation is possible by using a combination of permanent magnets and bulk superconductors. Furthermore, it is necessary to rotate a superconducting pump stably for practical applications. With the aim of increasing the stiffness of rotational parts, we placed a permanent magnet at the bottom such that the superconductors are sandwiched by top and bottom magnets. It was confirmed that the stiffness could surely be improved by arranging lower permanent magnets

  16. Effect of the magnet insertion on the performance of a superconducting pump

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, M., E-mail: mb12021@shibaura-it.ac.jp [Shibaura institute of Technology, Toyosu 3-7-5, Koto-ku, Tokyo 135-8548 (Japan); Inoue, K.; Koshizuka, N. [Shibaura institute of Technology, Toyosu 3-7-5, Koto-ku, Tokyo 135-8548 (Japan); Seki, H. [Awaji Materia, Kanda ogawacho 2-3-13, Chiyoda-ku, Tokyo 101-0045 (Japan); Murakami, M. [Shibaura institute of Technology, Toyosu 3-7-5, Koto-ku, Tokyo 135-8548 (Japan); Hiragushi, M. [Seikow Chemical Engineering and Machinery Ltd., Mizudocho 4-1-31, Amagasaki, Hyogo 661-0026 (Japan); Akiyama, S. [MAG-NEO, Suwa 1-4-23, Saitama Iwatsuki-ku, Saitama 339-0007 (Japan)

    2014-09-15

    Highlights: • Non-contact rotation is possible by using permanent magnets and superconductors. • It is necessary to rotate a superconducting pump stably for practical applications. • We placed a permanent magnet at the bottom to increase the stiffness. • Inserting permanent magnets was effective in increasing the rotational stability. - Abstract: For medical and semiconductor fabrication lines, an ultra-clean and impurity-free environment is often required. In order to realize such a contaminant-free environment, it is desirable to employ a completely non-contact rotating mechanism. Such a non-contact rotation is possible by using a combination of permanent magnets and bulk superconductors. Furthermore, it is necessary to rotate a superconducting pump stably for practical applications. With the aim of increasing the stiffness of rotational parts, we placed a permanent magnet at the bottom such that the superconductors are sandwiched by top and bottom magnets. It was confirmed that the stiffness could surely be improved by arranging lower permanent magnets.

  17. Magnetic field dependence of the critical superconducting current induced by the proximity effect in silicon

    International Nuclear Information System (INIS)

    Nishino, T.; Kawabe, U.; Yamada, E.

    1986-01-01

    The magnetic field dependence of the critical superconducting current induced by the proximity effect in heavily-boron-doped Si is studied experimentally. It is found that the critical current flowing through the p-type-Si-coupled junction decreases with increasing applied magnetic field. The critical current can be expressed as the product of three factors: the current induced by de Gennes's proximity effect, the exponential decrease due to pair breaking by the magnetic field, and the usual diffraction-pattern-like dependence on the magnetic field due to the Josephson effect. The second factor depends on the carrier concentration in the semiconductor. The local critical current shows a rapid decrease at the edge of the electrodes

  18. LT-STM/STS observation of definite superconducting gap states on the multistage crystal surface of Bi2Sr2CaCu2O8+x

    International Nuclear Information System (INIS)

    Murakami, Hironaru; Aoki, Ryozo

    1996-01-01

    Low temperature STM/STS observations have been carried out on cleaved BSCCO crystal surfaces. The authors have succeeded in detection of a special layer, probably a CuO 2 or Ca layer exposed on the surface. The STS spectrum which was reproducibly observed on this special site shows a considerably anisotropic but distinct superconducting gap structure with a definite and flat gap bottom region. This gap structure shows significantly different characteristic from another gap structure observed on the BiO layer, which shows a rounded shape at the gap bottom region without any indication of a finite gap state

  19. Anomalous superconducting spin-valve effect in NbN/FeN/Cu/FeN/FeMn multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Tae Jong; Kim, Dong Ho [Yeungnam University, Gyeongsan (Korea, Republic of)

    2017-09-15

    We have studied magnetic and transport properties of NbN/FeN/Cu/FeN/FeMn spin-valve structure. In-plane magnetic moment exhibited typical hysteresis loops of spin valves in the normal state of NbN film at 20 K. On the other hand, the magnetic hysteresis loop in the superconducting state exhibited more complex behavior in which exchange bias provided by antiferrmagnetic FeMn layer to adjacent FeN layer was disturbed by superconductivity. Because of this, the ideal superconducting spin-valve effect was not detected. Instead the stray field originated from unsaturated magnetic states dominated the transport properties of NbN/FeN/Cu/FeN/FeMn multilayer.

  20. AC/RF Superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Ciovati, G [Jefferson Lab (United States)

    2014-07-01

    This contribution provides a brief introduction to AC/RF superconductivity, with an emphasis on application to accelerators. The topics covered include the surface impedance of normal conductors and superconductors, the residual resistance, the field dependence of the surface resistance, and the superheating field.

  1. AC/RF Superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Ciovati, Gianluigi [JLAB

    2015-02-01

    This contribution provides a brief introduction to AC/RF superconductivity, with an emphasis on application to accelerators. The topics covered include the surface impedance of normal conductors and superconductors, the residual resistance, the field dependence of the surface resistance, and the superheating field.

  2. Ac superconducting articles and a method for their manufacture

    International Nuclear Information System (INIS)

    Meyerhoff, R.W.

    1975-01-01

    A novel ac superconducting article is described comprising 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. (auth)

  3. A study on the effect of tantalum-impurity content on the superconducting properties of niobium materials used for making superconducting radio frequency cavities

    Science.gov (United States)

    Roy, S. B.; Sharath Chandra, L. S.; Chattopadhyay, M. K.; Tiwari, M. K.; Lodha, G. S.; Myneni, G. R.

    2012-11-01

    Niobium materials in highly pure form are used in the fabrication of superconducting radio frequency cavities. We present here a study of the superconducting properties of such niobium materials that have been used in the fabrication of high accelerating gradient superconducting radio frequency cavities after determining their tantalum-impurity contents using a synchrotron-based x-ray fluorescence spectroscopy technique. Our results show that there is a small change in superconducting parameters such as TC,HC1 and HC2 when the tantalum-impurity content varies from ≈150 to ≈1300 ppm. In contrast, a buffered chemical polishing of the same niobium samples changes all these superconducting parameters more significantly. The implications of these results on the performance of niobium superconducting radio frequency cavities are discussed.

  4. A study on the effect of tantalum-impurity content on the superconducting properties of niobium materials used for making superconducting radio frequency cavities

    International Nuclear Information System (INIS)

    Roy, S B; Sharath Chandra, L S; Chattopadhyay, M K; Tiwari, M K; Lodha, G S; Myneni, G R

    2012-01-01

    Niobium materials in highly pure form are used in the fabrication of superconducting radio frequency cavities. We present here a study of the superconducting properties of such niobium materials that have been used in the fabrication of high accelerating gradient superconducting radio frequency cavities after determining their tantalum-impurity contents using a synchrotron-based x-ray fluorescence spectroscopy technique. Our results show that there is a small change in superconducting parameters such as T C ,H C1 and H C2 when the tantalum-impurity content varies from ≈150 to ≈1300 ppm. In contrast, a buffered chemical polishing of the same niobium samples changes all these superconducting parameters more significantly. The implications of these results on the performance of niobium superconducting radio frequency cavities are discussed. (paper)

  5. Itinerant-electron antiferromagnetism and superconductivity in bcc Cr-Re alloys

    International Nuclear Information System (INIS)

    Nishihara, Y.; Yamaguchi, Y.; Kohara, T.; Tokumoto, M.

    1985-01-01

    The magnetic and superconducting properties of bcc Cr-Re alloys with up to 40 at. % Re were studied via measurements of the magnetic susceptibility, electrical resistivity, and nuclear magnetic resonance of the Re nuclei. Antiferromagnetic order coexists with superconductivity above 18 at. % Re. The results were analyzed with the coexistence model of spin-density waves and superconductivity. In the Re-concentration range greater than 18 at. %, about 10% of the Fermi surface satisfies the nesting condition and the rest of it contributes to form the superconducting gap. This model also explains the increase in the superconducting transition temperature and the decrease in the magnetic susceptibility by annealing as a competing effect between spin-density waves and superconductivity

  6. Analysis of the surface resistance of the superconducting accelerating cavities of the S-DALINAC

    Energy Technology Data Exchange (ETDEWEB)

    Brunken, M. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, Darmstadt D-64289 (Germany); Gopych, M. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, Darmstadt D-64289 (Germany); Graef, H.-D. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, Darmstadt D-64289 (Germany); Laier, U. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, Darmstadt D-64289 (Germany)]. E-mail: U.Laier@gsi.de; Mueller, W. [Institut fuer Theorie Elektromagnetischer Felder, Technische Universitaet Darmstadt, Schlossgartenstrasse 8, Darmstadt D-64289 (Germany); Platz, M. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, Darmstadt D-64289 (Germany); Richter, A. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, Darmstadt D-64289 (Germany); Watzlawik, S. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, Darmstadt D-64289 (Germany); Weiland, T. [Institut fuer Theorie Elektromagnetischer Felder, Technische Universitaet Darmstadt, Schlossgartenstrasse 8, Darmstadt D-64289 (Germany)

    2006-08-01

    The quality factors of the 20 cell, 3GHz niobium cavities of the S-DALINAC are smaller by almost a factor of three compared to their design value. Combined with the limited cryogenic power of the helium refrigerator in use, this restricts the maximum electron energy of the S-DALINAC in continuous wave operation. Extensive studies to elaborate the origin of this degradation are presented. A 120{sup -}bar C baking combined with appropriate diagnostic tools for an attempt to improve the Q values has been applied to nine of the 11 cavities. The impact of this treatment on the BCS and residual resistance was evaluated and both were improved. Additionally, quality factor measurements of all modes of the TM{sub 010} passband allowed to derive a spatial distribution of the mean surface resistance. The RF losses in the end cells are systematically higher compared to the inner cells. The studies presented in this article allowed to develop a model describing the Q degradation of the resonators and thereby identifying possible prospects to cure this limitation.

  7. Inhomogeneous superconductivity in a ferromagnet

    International Nuclear Information System (INIS)

    Kontos, T.; Aprili, M.; Lesueur, J.; Genet, F.; Boursier, R.; Grison, X.

    2003-01-01

    We have studied a new superconducting state where the condensate wave function resulting from conventional pairing, is modified by an exchange field. Superconductivity is induced into a ferromagnetic thin film (F) by the proximity effect with a superconducting reservoir (S). We observed oscillations of the superconducting order parameter induced in F as a function of the distance from the S/F interface. They originate from the finite momentum transfer provided to Cooper pairs by the splitting of the spin up and down bands. We measured the superconducting density of states in F by tunneling spectroscopy and the Josephson critical current when F is coupled with a superconducting counter-electrode. Negative values of the superconducting order parameter are revealed by capsized tunneling spectra in F and a negative Josephson coupling (π-junction)

  8. 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

  9. Vortex lattice in effective type-I superconducting films with periodic arrays of submicron holes

    International Nuclear Information System (INIS)

    Berdiyorov, G.R.; Milosevic, M.V.; Peeters, F.M.

    2006-01-01

    The vortex matter and related phenomena in superconducting films with periodic arrays of microholes (antidots) are studied within the nonlinear Ginzburg-Landau (GL) theory. By varying the GL parameter κ, the vortex-vortex interaction is fine tuned, from repulsive to attractive behavior. This interaction is of crucial importance for equilibrium vortex structures, the saturation number of the antidots, and the related quantities, such as critical current. Due to vortex attraction in effectively type-I samples, the giant-vortex state becomes energetically favorable (contrary to the type-II behavior). For the same reason, the number of vortices which can be captured by antidots, increases with decreasing κ. As a result, for given magnetic field, the critical current is larger for effectively type-I superconductors than in conventional type-II cases

  10. Effects of irradiation and mechanical stress on the superconducting properties of candidate magnet conductors

    International Nuclear Information System (INIS)

    Snead, C.L. Jr.; Luhman, T.

    1980-01-01

    The effects of radiation damage on the superconducting critical properties of candidate magnet materials are reviewed. Neutron, and charged-particle irradiation results are covered. The discussion is restricted to effects in NbTi and the A15-compound superconductors. The utility of these conductors in radiation fields is first explored by defining the magnitude of critical-property changes with the fluence of various irradiating particles. The physical mechanisms that couple the irradiation defects to the observed critical-property changes are discussed. Annealing/recovery data on irradiated materials are included where they pertain to the understanding of the physical mechanisms involved, and thereby to the desirability of magnet annealing in actual operating circumstances

  11. Effect of low temperature reactor irradiation on organic insulators in superconducting magnets, (4)

    International Nuclear Information System (INIS)

    Kato, Teruo; Takamura, Saburo

    1983-01-01

    In order to study effects of irradiation at low temperature on insulating materials of superconducting magnets, flexural and impact tests are carried out at 4.2K without warmup after low temperature irradiation for several fiber reinforced plastics. The used materials are glass fiber reinforced epoxies and polyimide, and carbon fiber reinforced epoxies. After irradiation of 1.1 X 10 9 rad, the reduction in flexural strength of G-10 CR is about 70% and that of G-11 CR about 25%. No change are observed in strength of glass fiber reinforced polyimide by low temperature irradiation. Other kinds of glass fiber reinforced epoxies show a reduction in strength but the flexural strength of carbon fiber reinforced epoxies increases a small by irradiation. Irradiation effect of these materials on impact value is similar to that on flexural strength. (author)

  12. Evidence for charge Kondo effect in superconducting Tl-doped PbTe

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, I

    2010-01-11

    We report results of low-temperature thermodynamic and transport measurements of Pb{sub 1-x}Tl{sub x}Te single crystals for Tl concentrations up to the solubility limit of approximately x = 1.5%. For all doped samples, we observe a low-temperature resistivity upturn that scales in magnitude with the Tl concentration. The temperature and field dependence of this upturn are consistent with a charge Kondo effect involving degenerate Tl valence states differing by two electrons, with a characteristic Kondo temperature T{sub K} {approx} 6 K. The observation of such an effect supports an electronic pairing mechanism for superconductivity in this material and may account for the anomalously high T{sub c} values.

  13. Introduction to superconductivity

    CERN Document Server

    Darriulat, Pierre

    1998-01-01

    The lecture series will address physicists, such as particle and nuclear physicists, familiar with non-relativistic quantum mechanics but not with solid state physics. The aim of this introduction to low temperature superconductivity is to give sufficient bases to the student for him/her to be able to access the scientific literature on this field. The five lectures will cover the following topics : 1. Normal metals, free electron gas, chambers equation. 2. Cooper pairs, the BCS ground state, quasi particle excitations. 3. DC superconductivity, Meissner state, dirty superconductors.4. Self consistent approach, Ginsburg Landau equations, Abrikosov fluxon lattice. 5. Josephson effects, high temperature superconductivity.

  14. 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)

  15. Flux pinning by voids in surface-oxidized superconducting niobium and vanadium

    International Nuclear Information System (INIS)

    Meij, G.P. van der.

    1984-03-01

    The volume pinning force in several niobium and vanadium samples with voids is determined at various temperatures. Reasonable agreement is found with the collective pinning theory of Larkin and Ovchinnikov above the field of maximum pinning, if the flux line lattice is assumed to be amorphous in this region and if the elementary pinning force is calculated from the quasi-classical theory of Thuneberg, Kurkijaervi, and Rainer. Also some history and relaxation effects are studied in an alternating field. A qualitative explanation is given in terms of flux line dislocations, which reduce the shear strength of the flux line lattice. (Auth.)

  16. 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.

  17. 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

  18. In vivo MR imaging of the human skin at subnanoliter resolution using a superconducting surface coil at 1.5 Tesla.

    Science.gov (United States)

    Laistler, Elmar; Poirier-Quinot, Marie; Lambert, Simon A; Dubuisson, Rose-Marie; Girard, Olivier M; Moser, Ewald; Darrasse, Luc; Ginefri, Jean-Christophe

    2015-02-01

    To demonstrate the feasibility of a highly sensitive superconducting surface coil for microscopic MRI of the human skin in vivo in a clinical 1.5 Tesla (T) scanner. A 12.4-mm high-temperature superconducting coil was used at 1.5T for phantom and in vivo skin imaging. Images were inspected to identify fine anatomical skin structures. Signal-to-noise ratio (SNR) improvement by the high-temperature superconducting (HTS) coil, as compared to a commercial MR microscopy coil was quantified from phantom imaging; the gain over a geometrically identical coil made from copper (cooled or not) was theoretically deduced. Noise sources were identified to evaluate the potential of HTS coils for future studies. In vivo skin images with isotropic 80 μm resolution were demonstrated revealing fine anatomical structures. The HTS coil improved SNR by a factor 32 over the reference coil in a nonloading phantom. For calf imaging, SNR gains of 380% and 30% can be expected over an identical copper coil at room temperature and 77 K, respectively. The high sensitivity of HTS coils allows for microscopic imaging of the skin at 1.5T and could serve as a tool for dermatology in a clinical setting. © 2013 Wiley Periodicals, Inc.

  19. Orbital Kondo effect due to assisted hopping: Superconductivity, mass enhancement in Cooper oxides with apical oxygen

    International Nuclear Information System (INIS)

    Zawadowski, A.; Penc, K.; Zimanyi, G.

    1991-07-01

    Orbital Kondo effect is treated in a model, where additional to the conduction band there are localized orbitals with energy not very far from the Fermi energy. If the hopping between the conduction band and the localized heavy orbitals depends on the occupation of the conduction band orbital then orbital Kondo correlation occurs. The assisted hopping vertex is enhanced due to the Coulomb interaction between the heavy orbital and the conduction band. The enhanced hopping results in mass enhancement and attractive interaction in the conduction band. The superconductivity transition temperature is calculated. The models of this type can be applied to the high-T c superconductors where the non-bonding oxygen orbitals of the apical oxygens play the role of heavy orbitals. For an essential range of the parameters the T c obtained is about 100K. (author). 22 refs, 9 figs

  20. 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

  1. Irradiation effect of the insulating materials for fusion superconducting magnets at cryogenic temperature

    Science.gov (United States)

    Kobayashi, Koji; Akiyama, Yoko; Nishijima, Shigehiro

    2017-09-01

    In ITER, superconducting magnets should be used in such severe environment as high fluence of fast neutron, cryogenic temperature and large electromagnetic forces. Insulating material is one of the most sensitive component to radiation. So radiation resistance on mechanical properties at cryogenic temperature are required for insulating material. The purpose of this study is to evaluate irradiation effect of insulating material at cryogenic temperature by gamma-ray irradiation. Firstly, glass fiber reinforced plastic (GFRP) and hybrid composite were prepared. After irradiation at room temperature (RT) or liquid nitrogen temperature (LNT, 77 K), interlaminar shear strength (ILSS) and glass-transition temperature (Tg) measurement were conducted. It was shown that insulating materials irradiated at room temperature were much degraded than those at cryogenic temperature.

  2. 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.

  3. Effects of calcium doping on the superconducting properties of top-seeded melt growth processed Y1.5Ba2-xCaxCu3Oy superconductors

    International Nuclear Information System (INIS)

    Park, S.D.; Kim, H.J.; Park, B.J.; Han, Y.H.; Jun, B.-H.; Lee, J.S.; Kim, C.-J.

    2011-01-01

    We study effects of calcium doping in melt processed Y123 superconductors. We examine a superconducting transition temperature and current density. A transition temperature and current density decreases by calcium doping. Calcium doping leads to coarseing of Y211 particles. Y211 refining effect by CeO 2 is disappreared by calcium doping. The effect of calcium doping on the superconducting properties of top seeded melt growth (TSMG) processed Y 1.5 Ba 2-x Ca x Cu 3 O y superconductors was studied in terms of calcium content (X ca ). YBa 2-x Ca x Cu 3 O 7-δ (X ca = 0, 0.005, 0.01, 0.02, 0.04, 0.1, 0.3) powders were synthesized by the powder calcination method. YBa 2-x Ca x Cu 3 O 7-δ powders were mixed with 0.25 mole Y 2 O 3 powder and 1 wt.% CeO 2 as Y 2 BaCuO 5 (Y211) refiner, and finally made into Y 1 . 5 Ba 2-x Ca x Cu 3 O y (Y1.5) + 1 wt.% CeO 2 composition. The single Y123 growth on the top surface was observed up to X ca = 0.1, while the multiple Y123 growth was observed at X ca ≥ 0.1. The superconducting transition temperature (T c ) and critical current density (J c ) of TSMG processed Y1.5 samples were inversely proportional to X ca . The Y211 size increased with increasing X ca due to the enhancement of Y211 coarsening by calcium doping. No Y211 refining effect by CeO 2 was observed in the calcium doped samples. The T c and J c decrease by calcium doping are likely to be due to the calcium incorporation with the Y123 lattice and formation of coarse Y211 particles.

  4. Unexpected nonlinear effects and critical coupling in NbN superconducting microwave resonators

    International Nuclear Information System (INIS)

    Abdo, B.; Buks, E.

    2004-01-01

    Full Text:In this work, we have designed and fabricated several NbN superconducting stripline microwave resonators sputtered on sapphire substrates. The low temperature response exhibits strong and unexpected nonlinear effects, including sharp jumps as the frequency or poser are varied, frequency hysteresis loops changing direction as the input power is varied, and others. Contrary to some other superconducting resonators, a simple model of a one-dimensional Duffing resonator cannot account for the experimental results. Whereas the physical origin of the unusual nonlinear response of our samples remains an open question, our intensive experimental study of these effects under varying conditions provides some important insight. We consider a hypothesis according to which Josephson junctions forming weak links between the grains of the NbN are responsible for the observed behavior. We show that most of the experimental results are qualitatively consistent with such hypothesis. While revealing the underlying physics remains an outstanding challenge for future research, the utilization of the unusual nonlinear response for some novel applications is already demonstrated in the present work. In particular an operate the resonator as an inter modulation amplifier and find that the gain can be as high as 15 dB. To the best of our knowledge, inter modulation gain greater than unity has not been reported before in the scientific literature. In another application we demonstrate for the first time that the coupling between the resonator and its feed line can be made amplitude dependent. This novel mechanism allows us to tune the resonator into critical coupling conditions

  5. Effects of stoichiometry and neutron irradiation in superconducting A-15 compounds

    International Nuclear Information System (INIS)

    Moehlecke, S.

    1978-01-01

    The A-15 (A 3 B) compounds comprise an important class of superconducting compounds. In order to gain a clearer understanding of the parameters influencing the superconductivity in these materials, several A-15 compounds have been prepared and the effects of varying stoichiometry, heat treatment, and irradiation with high energy neutrons (E > 1 MeV) on the superconducting transition temperature T/sub c/, Bragg--William order parameter S, and the lattice parameter a 0 , have been studied. The systems investigated include Nb 3 Ge, Nb 3 Al, Nb 3 Pt, Nb 3 Ir, V 3 Ga, V 3 Si and Mo 3 Os. Some of the results may be summarized as follows: 1) for Nb 3 Al, Nb 3 Pt and V 3 Ga, T/sub c/ is a strong function of composition, reaching a maximum value at the ideal stoichiometric composition of 3A: 1B, if that composition exists in the equilibrium phase diagram, 2) irradiation with high energy neutrons at temperatures of approx.150 0 C results in drastic lowering of T/sub c/ for Nb 3 Al, Nb 3 Pt and Nb 3 Ge, but not for Mo 3 Os, 3) T/sub c/ can be recovered by annealing, the recovery temperature being in the range 300-800 0 C depends on the particular compound, 4) the order parameter S, decreases with increasing neutron fluence (decreasing T/sub c/), and is also recoverable upon annealing at the appropriate temperature, 5) the lattice parameter a 0 , increases with increasing neutron fluence, and isalso restored to its original value by annealing. A simple hard sphere model is developed to calculate the dependence of a 0 on composition within the A-15 phase. Excellent agreement is obtained for the measured values in the Nb--Al, Nb--Pt and V--Ga systems. The results of both compositionally and irradiation induced disorder can be understood on the basis of site-exchange taking placee between the A and B sites in the A-15 structure

  6. Generalized Superconductivity. Generalized Levitation

    International Nuclear Information System (INIS)

    Ciobanu, B.; Agop, M.

    2004-01-01

    In the recent papers, the gravitational superconductivity is described. We introduce the concept of generalized superconductivity observing that any nongeodesic motion and, in particular, the motion in an electromagnetic field, can be transformed in a geodesic motion by a suitable choice of the connection. In the present paper, the gravitoelectromagnetic London equations have been obtained from the generalized Helmholtz vortex theorem using the generalized local equivalence principle. In this context, the gravitoelectromagnetic Meissner effect and, implicitly, the gravitoelectromagnetic levitation are given. (authors)

  7. 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

  8. 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)

  9. Superconductivity of small particles

    International Nuclear Information System (INIS)

    Leavens, C.R.; Fenton, E.W.

    1981-01-01

    The Eliashberg gap equations are used to investigate the contribution of surface-phonon softening to the size dependence of the superconducting transition temperature (T/sub c/) of small metallic particles. Because of our limited quantitative knowledge of phonon spectra and electron-phonon coupling in the surface region, the effect cannot be calculated with certainty. Previous calculations which agree with experiment depend on a fortuitous choice of input parameters which cannot be justified at present. For this reason the absence of any observable size effect for T/sub c/ in Pb is especially important. This null effect is obtained in Pb if the electron-phonon coupling strength is the same in the surface region as in the bulk. This assumption can be tested experimentally because it means that the energy gap of Pb should not be independent of particle size but rather should increase significantly with decreasing radius. Hence, measurement of the size dependence of the energy gap for well-characterized small particles of Pb could provide information regarding the importance of the phonon-softening mechanism, at least for Pb

  10. Genotoxic Effects of Superconducting Static Magnetic Fields (SMFs) on Wheat (Triticum aestivum) Pollen Mother Cells (PMCs)

    International Nuclear Information System (INIS)

    Zhang Pingping; Yin Ruochun; Chen Zhiyou; Wu Lifang; Yu Zengliang

    2007-01-01

    The effects of superconducting static magnetic fields (SMFs) on the pollen mother cells (PMCs) of wheat were investigated in order to evaluate the possible genotoxic effect of such non-ionizing radiation. The seeds of wheat were exposed to static magnetic fields with either different magnetic flux densities (0, 1, 3, 5 and 7 Tesla) for 5 h or different durations (1, 3 and 5 h) at a magnetic flux density of 7 Tesla. The seeds were germinated at 23 o C after exposure and the seedlings were transplanted into the field. The PMCs from young wheat ears were taken and slides were made following the conventional method. The genotoxic effect was evaluated in terms of micronucleus (MN), chromosomal bridge, lagging chromosome and fragments in PMCs. Although the exposed groups of a low field intensity (below 5 Tesla) showed no statistically significant difference in the aberration frequency compared with the unexposed control groups and sham exposed groups, a significant increase in the chromosomal bridge, lagging chromosome, triple-polar segregation or micronucleus was observed at a field strength of 5 Tesla or 7 Tesla, respectively. The analysis of dose-effect relationships indicated that the increased frequency of meiotic abnormal cells correlated with the flux density of the magnetic field and duration, but no linear relationship was observed. Such statistically significant differences indicated a potential genotoxic effect of high static magnetic fields above 5 T

  11. Genotoxic Effects of Superconducting Static Magnetic Fields (SMFs) on Wheat (Triticum aestivum) Pollen Mother Cells (PMCs)

    Science.gov (United States)

    Zhang, Pingping; Yin, Ruochun; Chen, Zhiyou; Wu, Lifang; Yu, Zengliang

    2007-04-01

    The effects of superconducting static magnetic fields (SMFs) on the pollen mother cells (PMCs) of wheat were investigated in order to evaluate the possible genotoxic effect of such non-ionizing radiation. The seeds of wheat were exposed to static magnetic fields with either different magnetic flux densities (0, 1, 3, 5 and 7 Tesla) for 5 h or different durations (1, 3 and 5 h) at a magnetic flux density of 7 Tesla. The seeds were germinated at 23oC after exposure and the seedlings were transplanted into the field. The PMCs from young wheat ears were taken and slides were made following the conventional method. The genotoxic effect was evaluated in terms of micronucleus (MN), chromosomal bridge, lagging chromosome and fragments in PMCs. Although the exposed groups of a low field intensity (below 5 Tesla) showed no statistically significant difference in the aberration frequency compared with the unexposed control groups and sham exposed groups, a significant increase in the chromosomal bridge, lagging chromosome, triple-polar segregation or micronucleus was observed at a field strength of 5 Tesla or 7 Tesla, respectively. The analysis of dose-effect relationships indicated that the increased frequency of meiotic abnormal cells correlated with the flux density of the magnetic field and duration, but no linear relationship was observed. Such statistically significant differences indicated a potential genotoxic effect of high static magnetic fields above 5 T.

  12. Effect of the Tuner on the Field Flatness of SNS Superconducting RF Cavities

    CERN Document Server

    Sun, A

    2004-01-01

    Field flatness in a multi-cell superconducting cavity affects not only the net accelerating voltage, but also the peak surface field and the Lorenz Force detuning coefficient. Our measurement indicates that the field flatness changes both external Q of the Fundamental Power Coupler (FPC) and external Q of the Field Probe (FP). The field amplitude tilts linearly to the distance between the cell center and the cavity’s geometry center (pivot point). The tilt rate has been measured in a cryomodule cold (2 K) test, being about 2%/100 kHz, relative the field flatness at the cavity’s center frequency of 805 MHz. Bead-pull measurements confirmed that the field flatness change is 2.0%/100 kHz for a medium β cavity with helium vessel, and 1.72%/100 kHz without helium vessel. These results matched the predictions of simulations using ANSYS and SUPERFISH. A detailed analysis reveals that longitudinal capacitive gap deformation is the main cause of the frequency change. Field flatness change ...

  13. Possible influence of surface oxides on the optical response of high-purity niobium material used in the fabrication of superconducting radio frequency cavity

    Science.gov (United States)

    Singh, Nageshwar; Deo, M. N.; Roy, S. B.

    2016-09-01

    We have investigated the possible influence of surface oxides on the optical properties of a high-purity niobium (Nb) material for fabrication of superconducting radio frequency (SCRF) cavities. Various peaks in the infrared region were identified using Fourier transform infrared and Raman spectroscopy. Optical response functions such as complex refractive index, dielectric and conductivity of niobium were compared with the existing results on oxides free Nb and Cu. It was observed that the presence of a mixture of niobium-oxides, and probably near other surface impurities, appreciably influence the conducting properties of the material causing deviation from the typical metallic characteristics. In this way, the key result of this work is the observation, identification of vibrational modes of some of surface complexes and study of its influences on the optical responses of materials. This method of spectroscopic investigation will help in understanding the origin of degradation of performance of SCRF cavities.

  14. Possible influence of surface oxides on the optical response of high-purity niobium material used in the fabrication of superconducting radio frequency cavity

    International Nuclear Information System (INIS)

    Singh, Nageshwar; Deo, M.N.; Roy, S.B.

    2016-01-01

    We have investigated the possible influence of surface oxides on the optical properties of a high-purity niobium (Nb) material for fabrication of superconducting radio frequency (SCRF) cavities. Various peaks in the infrared region were identified using Fourier transform infrared and Raman spectroscopy. Optical response functions such as complex refractive index, dielectric and conductivity of niobium were compared with the existing results on oxides free Nb and Cu. It was observed that the presence of a mixture of niobium-oxides, and probably near other surface impurities, appreciably influence the conducting properties of the material causing deviation from the typical metallic characteristics. In this way, the key result of this work is the observation, identification of vibrational modes of some of surface complexes and study of its influences on the optical responses of materials. This method of spectroscopic investigation will help in understanding the origin of degradation of performance of SCRF cavities.

  15. Possible influence of surface oxides on the optical response of high-purity niobium material used in the fabrication of superconducting radio frequency cavity

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Nageshwar [Magnetic and Superconducting Materials Section, Raja Ramanna Centre for Advanced Technology, Indore 452013, M.P. (India); Deo, M.N. [High Pressure & Synchrotron Radiation Physics Division, BARC, Mumbai 400085 (India); Roy, S.B. [Magnetic and Superconducting Materials Section, Raja Ramanna Centre for Advanced Technology, Indore 452013, M.P. (India)

    2016-09-11

    We have investigated the possible influence of surface oxides on the optical properties of a high-purity niobium (Nb) material for fabrication of superconducting radio frequency (SCRF) cavities. Various peaks in the infrared region were identified using Fourier transform infrared and Raman spectroscopy. Optical response functions such as complex refractive index, dielectric and conductivity of niobium were compared with the existing results on oxides free Nb and Cu. It was observed that the presence of a mixture of niobium-oxides, and probably near other surface impurities, appreciably influence the conducting properties of the material causing deviation from the typical metallic characteristics. In this way, the key result of this work is the observation, identification of vibrational modes of some of surface complexes and study of its influences on the optical responses of materials. This method of spectroscopic investigation will help in understanding the origin of degradation of performance of SCRF cavities.

  16. Effects of magnetic non-linearities on a stored proton beam and their implications for superconducting storage rings

    International Nuclear Information System (INIS)

    Cornacchia, M.; Evans, L.

    1985-06-01

    A nonlinear lens may be used to study the effect of high-order multipolar field imperfections on a stored proton beam. Such a nonlinear lens is particulary suitable to simulate field imperfections of the types encountered in coil dominated superconducting magnets. We have studied experimentally at the SPS the effect of high order (5th and 8th) single isolated resonances driven by the nonlinear lens. The width of these resonances is of the order one expects to be caused by field errors in superconducting magnets of the SSC type. The experiment shows that, in absence of tune modulation, these resonances are harmless. Slow crossings of the resonance, on the other hand, have destructive effects on the beam, much more so than fast crossings caused by synchrotron oscillations. In the design of future storage rings, sources of low-frequency tune modulation should be avoided as a way to reduce the harmful effects of high order multipolar field imperfection

  17. Effect of localized electron states on superconductivity of ultrathin beryllium films

    International Nuclear Information System (INIS)

    Tutov, V.I.; Semenenko, E.E.

    1988-01-01

    A wide spectrum of distortions is induced in ultrathin beryllium films of thickness less than 10 A, which are responsible for the system transition from the strong localization state completely suppressing superconductivity (in this case R □ of the layer reaches 97600 Ohm) to the weak localization stae coexisting with superconductivity at comparatively high T c (5 K). The resistance per square R □ of the films decreases more than by an order of magnitude. The superconductivity with T c =1.7 K occurs at rather strong localization, when R □ of the layer is 34000 Ohm

  18. Investigation of the temperature and frequency dependence of the surface resistance of superconducting Nb-resonators between 12 and 18 GHz

    International Nuclear Information System (INIS)

    Meyer, W.

    1978-08-01

    Up to now, all measurements on superconducting niobium cavities are restricted to the frequency range below 12 GHz. This paper reports on the investigation of the temperature and frequency dependence of the surface resistance of superconducting niobium between 12 and 18 GHz. Beside the study of TM modes which are important for accelerators, TE modes have been measured also to be able to separate between different loss mechanisms. The dimensions D = L = 40 mm are choosen so that the cavity is operated in higher order modes. Thereby the fabrication, especially of the coupling, and the handling of the cavity is simplified. We use a fixed magnetic hole coupling. Because the cavity was fabricated in a flanged and in a welded model, the influence of a joint could also be studied. After subtracting the residual resistance Rsub(res) the measured values obtained by the newly installed RF set-up fit in temperature and frequency dependence the superconducting surface resistance Rsub(s1) in the framework of the BCS-theory. The gap parameter Δ/kTsub(c) determined from the temperature dependence lies between 1.94 and 1.98. The frequency dependence of Rsub(s1) shows with Rsub(s1) approximately f 1 . 62 the for Nb expected shape. The highest Q 0 in the flanged cavity was 1.7 x 10 9 (f 0 = 13.260 GHz) and in the welded one 1.8 X 10 9 (f 0 = 13.310 GHz), measured in each case in a TE mode at T = 1.3 K. The residual resistance increases with f 2 and stronger and is especially high in the flanged cavity in modes with currents across the joint. (orig.) 891 WBU [de

  19. Superconducting microtraps for ultracold atoms

    International Nuclear Information System (INIS)

    Hufnagel, C.

    2011-01-01

    Atom chips are integrated devices in which atoms and atomic clouds are stored and manipulated in miniaturized magnetic traps. State of the art fabrication technologies allow for a flexible design of the trapping potentials and consequently provide extraordinary control over atomic samples, which leads to a promising role of atom chips in the engineering and investigation of quantum mechanical systems. Naturally, for quantum mechanical applications, the atomic coherence has to be preserved. Using room temperature circuits, the coherence time of atoms close to the surface was found to be drastically limited by thermal current fluctuations in the conductors. Superconductors offer an elegant way to circumvent thermal noise and therefore present a promising option for the coherent manipulation of atomic quantum states. In this thesis trapping and manipulation of ultracold Rubidium atoms in superconducting microtraps is demonstrated. In this connection the unique properties of superconductors are used to build traps based on persistent currents, the Meissner effect and remanent magnetization. In experiment it is shown, that in superconducting atom chips, thermal magnetic field noise is significantly reduced. Furthermore it is demonstrated, that atomic samples can be employed to probe the properties of superconducting materials. (author) [de

  20. 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.

  1. Parasitic effects in superconducting quantum interference device-based radiation comb generators

    Energy Technology Data Exchange (ETDEWEB)

    Bosisio, R., E-mail: riccardo.bosisio@nano.cnr.it [SPIN-CNR, Via Dodecaneso 33, 16146 Genova (Italy); NEST, Instituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa (Italy); Giazotto, F., E-mail: giazotto@sns.it [NEST, Instituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa (Italy); Solinas, P., E-mail: paolo.solinas@spin.cnr.it [SPIN-CNR, Via Dodecaneso 33, 16146 Genova (Italy)

    2015-12-07

    We study several parasitic effects on the implementation of a Josephson radiation comb generator based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. This system can be used as a radiation generator similarly to what is done in optics and metrology, and allows one to generate up to several hundreds of harmonics of the driving frequency. First we take into account how the assumption of a finite loop geometrical inductance and junction capacitance in each SQUID may alter the operation of the devices. Then, we estimate the effect of imperfections in the fabrication of an array of SQUIDs, which is an unavoidable source of errors in practical situations. We show that the role of the junction capacitance is, in general, negligible, whereas the geometrical inductance has a beneficial effect on the performance of the device. The errors on the areas and junction resistance asymmetries may deteriorate the performance, but their effect can be limited to a large extent by a suitable choice of fabrication parameters.

  2. Effective theory of exotic superconductivity in LaAlO3/SrTiO3 interfaces

    Science.gov (United States)

    Esmailzadeh, Haniyeh; Moghaddam, Ali G.

    2018-05-01

    Motivated by experimental and theoretical works about superconductivity at the oxide interfaces, we provide a simple model for possible unconventional pairings inside the exotic two-dimensional electron gas formed in heterostructures of SrTiO3 and LaAlO3. At the low energy limit, the electron gas at the interfaces is usually modeled with an effective three band model considering of 3d t2g orbitals which are slightly coupled by atomic spin-orbit couplings (SOC). Considering direct superconducting pairing in two higher delocalized bands and by exploiting a perturbative scheme based on canonical transformation, we derive the effective pairing amplitudes with possibly exotic nature inside the localized dxy band as well as various inter-band pairing components. In particular we show that equal-spin triplet pairings are possible between the band dxy and any of other dxz and dyz bands. In addition weaker effective pairings take place inside the localized band itself and between delocalized dxz and dyz bands with singlet and opposite-spin triplet characters. These unconventional effective pairings are indeed mediated by SOC-induced higher order virtual transitions between the bands and particularly into the localized band. Our model suggest that unconventional effective superconductivity is possible at oxide interfaces, simply, due to the special band structure and important role of atomic SOC and perhaps other magnetic effects present at these heterostructures.

  3. 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.

  4. Materials for superconducting cavities

    International Nuclear Information System (INIS)

    Bonin, B.

    1996-01-01

    The ideal material for superconducting cavities should exhibit a high critical temperature, a high critical field, and, above all, a low surface resistance. Unfortunately, these requirements can be conflicting and a compromise has to be found. To date, most superconducting cavities for accelerators are made of niobium. The reasons for this choice are discussed. Thin films of other materials such as NbN, Nb 3 Sn, or even YBCO compounds can also be envisaged and are presently investigated in various laboratories. It is shown that their success will depend critically on the crystalline perfection of these films. (author)

  5. The effects of Fe2O3 nanoparticles on MgB2 superconducting thin films

    International Nuclear Information System (INIS)

    Koparan, E.T.; Sidorenko, A.; Yanmaz, E.

    2013-01-01

    Full text: Since the discovery of superconductivity in binary MgB 2 compounds, extensive studies have been carried out because of its excellent properties for technological applications, such as high transition temperature (T c = 39 K), high upper critical field (H c2 ), high critical current density (J c ). Thin films are important for fundamental research as well as technological applications of any functional materials. Technological applications primarily depend on critical current density. The strong field dependence of J c for MgB 2 necessitates an enhancement in flux pinning performance in order to improve values in high magnetic fields. An effective way to improve the flux pinning is to introduce flux pinning centers into MgB 2 through a dopant having size comparable to the coherence length of MgB 2 . In this study, MgB 2 film with a thickness of about 600 nm was deposited on the MgO (100) single crystal substrate using a 'two-step' synthesis technique. Firstly, deposition of boron thin film was carried out by rf magnetron sputtering on MgO substrates and followed by a post deposition annealing at 850 degrees Celsius in magnesium vapour. In order to investigate the effect of Fe 2 O 3 nanoparticles on the structural and magnetic properties of films, MgB 2 films were coated with different concentrations of Fe 2 O 3 nanoparticles by a spin coating process. The effects of different concentrations of ferromagnetic Fe 2 O 3 nanoparticles on superconducting properties of obtained films were carried out by using structural (XRD, SEM, AFM), electrical (R-T) and magnetization (M-H, M-T and AC Susceptibility) measurements. It was calculated that anisotropic coefficient was about γ = 1.2 and coherence length of 5 nm for the uncoated film. As a result of coherence length, the appropriate diameters of Fe 2 O 3 nanoparticles were found to be 10 nm, indicating that these nanoparticles served as the pinning centers. Based on the data obtained from this study, it can be

  6. Spin currents, relativistic effects and the Darwin interaction in the theory of hole superconductivity

    International Nuclear Information System (INIS)

    Hirsch, J.E.

    2005-01-01

    The existence of macroscopic spin currents in the ground state of superconductors is predicted within the theory of hole superconductivity. Here it is shown that the electromagnetic Darwin interaction is attractive for spin currents and repulsive for charge currents. It is also shown that the mere existence of spin currents implies that some electrons are moving at relativistic speeds in macroscopic superconductors, which in turn implies that the Darwin interaction plays a fundamental role in stabilizing the superconducting state

  7. 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

  8. 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

  9. 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

  10. Superconducting Gap Symmetry of LaFeP(O,F Observed by Impurity Doping Effect

    Directory of Open Access Journals (Sweden)

    Shigeki Miyasaka

    2016-08-01

    Full Text Available We have investigated Mn, Co and Ni substitution effects on polycrystalline samples of LaFePO0.95F0.05 by resistivity and magnetoresistance measurements. In LaFe1-xMxPO0.95F0.05 (M = Mn, Co and Ni, the superconducting transition temperature (Tc monotonously decreases with increasing the impurity doping level of x. There is a clear difference of Tc suppression rates among Mn, Co and Ni doping cases, and the decreasing rate of Tc by Mn doping as a magnetic impurity is larger than those by the nonmagnetic doping impurities (Co/Ni. This result indicates that in LaFePO0.95F0.05, Tc is rapidly suppressed by the pair-breaking effect of magnetic impurities, and the pairing symmetry is a full-gapped s-wave. In the nonmagnetic impurity-doped systems, the residual resistivity in the normal state has nearly the same value when Tc becomes zero. The residual resistivity value is almost consistent with the universal value of sheet resistance for two-dimensional superconductors, suggesting that Tc is suppressed by electron localization in Co/Ni-doped LaFePO0.95F0.05.

  11. Effect of transients on the beam in the Superconducting Supercollider Coupled-Cavity Linac

    International Nuclear Information System (INIS)

    Young, L.M.; Nath, S.

    1992-01-01

    Each module of the Superconducting Super Collider (SSC) Coupled-Cavity Linac (CCL) consists of eight tanks (10 accelerating cells each) coupled with bridge couplers. The radio frequency (rf) power drive is in the center of the module at the bridge coupler between the fourth and fifth tanks. In this simulation of the beam dynamics, the rf power is turned on 10 μs before the beam is turned on. This time lapse allows the fields to build up and stabilize before they are required by the beam. When the beam is turned on, the beam loading causes the fields to change. This transient state of the fields together with their effect on the beam is presented. A model has been developed to calculate field distribution throughout the module as a function of time. Beam dynamics simulations were run with the results of this model at several times during the beam pulse. An estimate of the effect of the transients is given by the results of these simulations

  12. 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.

  13. Basic concepts on the theory of high temperature superconductivity. The importance of the isotope effect. Grundvorstellungen zur Theorie der Hochtemperatur-Supraleitung. Die Rolle des Isotopieeffektes

    Energy Technology Data Exchange (ETDEWEB)

    Der, R.; Schumacher, W. (Zentralinstitut fuer Isotopen- und Strahlenforschung, Leipzig (Germany, F.R.))

    1991-01-01

    With the experimental detection of high temperature superconduction (HTSC) a lot of different new concepts for the explanation of this phenomenon have been developed. After a short reminiscence of the conventional theory of superconduction these new approaches are outlined and discussed. Contrarely to the conventional superconductors the isotopic effect in HTSC is generally very small or absent. The role of the isotopic effects in the investigation of new HTSC mechanisms is discussed. (orig.).

  14. Stabilized superconducting materials and fabrication process. Materiaux supraconducteurs stabilises et leur procede d'obtention

    Energy Technology Data Exchange (ETDEWEB)

    Chevallier, B; Dance, J M; Etourneau, J; Lozano, L; Tressaud, A; Tournier, R; Sulpice, A; Chaussy, J; Lejay, P

    1989-10-06

    Superconducting ceramics are fluorinated at a temperature {le} 120{sup 0}C. Are also claimed new superconducting materials with a fluorine concentration gradient decreasing from the surface to the core. Superconductivity is stabilized and/or improved.

  15. 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.

  16. High Accelerating Field Superconducting Radio Frequency Cavities

    Science.gov (United States)

    Orr, R. S.; Saito, K.; Furuta, F.; Saeki, T.; Inoue, H.; Morozumi, Y.; Higo, T.; Higashi, Y.; Matsumoto, H.; Kazakov, S.; Yamaoka, H.; Ueno, K.; Sato, M.

    2008-06-01

    We have conducted a study of a series of single cell superconducting RF cavities at KEK. These tests were designed to investigate the effect of surface treatment on the maximum accelerating field attainable. All of these cavities are of the ICHIRO shape, based on the Low Loss shape. Our results indicate that accelerating fields as high as the theoretical maximum of 50MV/m are attainable.

  17. Geometric phases and quantum correlations of superconducting two-qubit system with dissipative effect

    International Nuclear Information System (INIS)

    Xue, Liyuan; Yu, Yanxia; Cai, Xiaoya; Pan, Hui; Wang, Zisheng

    2016-01-01

    Highlights: • We find that the Pancharatnam phases include the information of quantum correlations. • We show that the sudden died and alive phenomena of quantum entanglement is original in the transition of Pancharatnam phase. • We find that the faster the Pancharatnam phases change, the slower the quantum correlations decay. • We find that a subspace of quantum entanglement can exist in the Y-state. • Our results provide a useful approach experimentally to implement the time-dependent geometric quantum computation. - Abstract: We investigate time-dependent Pancharatnam phases and the relations between such geometric phases and quantum correlations, i.e., quantum discord and concurrence, of superconducting two-qubit coupling system in dissipative environment with the mixture effects of four different eigenstates of density matrix. We find that the time-dependent Pancharatnam phases not only keep the motion memory of such a two-qubit system, but also include the information of quantum correlations. We show that the sudden died and alive phenomena of quantum entanglement are intrinsic in the transition of Pancharatnam phase in the X-state and the complex oscillations of Pancharatnam phase in the Y-state. The faster the Pancharatnam phases change, the slower the quantum correlations decay. In particular, we find that a subspace of quantum entanglement can exist in the Y-state by choosing suitable coupling parameters between two-qubit system and its environment, or initial conditions.

  18. Effective method to control the levitation force and levitation height in a superconducting maglev system

    International Nuclear Information System (INIS)

    Yang Peng-Tao; Yang Wan-Min; Wang Miao; Li Jia-Wei; Guo Yu-Xia

    2015-01-01

    The influence of the width of the middle magnet in the permanent magnet guideways (PMGs) on the levitation force and the levitation height of single-domain yttrium barium copper oxide (YBCO) bulks has been investigated at 77 K under the zero field cooled (ZFC) state. It is found that the largest levitation force can be obtained in the system with the width of the middle magnet of the PMG equal to the size of the YBCO bulk when the gap between the YBCO bulk and PMG is small. Both larger levitation force and higher levitation height can be obtained in the system with the width of the middle magnet of the PMG larger than the size of the YBCO bulk. The stiffness of the levitation force between the PMG and the YBCO bulk is higher in the system with a smaller width of the middle magnet in the PMG. These results provide an effective way to control the levitation force and the levitation height for the superconducting maglev design and applications. (paper)

  19. Ordinary and triplet superconducting spin valve effect in Fe/Pb based systems

    Energy Technology Data Exchange (ETDEWEB)

    Leksin, Pavel; Schumann, Joachim; Krupskaya, Yulia; Kataev, Vladislav; Hess, Christian; Schmidt, Oliver; Buechner, Bernd [Leibniz Institute for Solid State and Materials Research IFW Dresden (Germany); Garifyanov, Nadir; Garifullin, Ilgiz [Zavoisky Physical-Technical Institute of RAS, Kazan (Russian Federation); Fominov, Yakov [L. D. Landau Institute for Theoretical Physics of RAS, Moscow (Russian Federation)

    2015-07-01

    We report on experimental evidence for the occurrence of the long range triplet correlations (LRTC) of the superconducting (SC) condensate in the spin-valve heterostructures CoO{sub x}/Fe1/Cu/Fe2/Pb. The LRTC generation in this layer sequence is accompanied by a T{sub c} suppression near the orthogonal mutual orientation of the Fe1 and Fe2 layers' magnetization. This T{sub c} drop reaches its maximum of 60mK at the Fe2 layer thickness d{sub Fe2} = 0.6 nm and falls down when d{sub Fe2} is increased. The modification of the Fe/Pb interface by using a thin Cu layer between Fe and Pb layers reduces the SC transition width without preventing the interaction between Pb and Fe2 layers. The dependence of the SSVE magnitude on Fe1 layer thickness d{sub Fe1} reveals maximum of the effect when d{sub Fe1} and d{sub Fe2} are equal and the d{sub Fe2} value is minimal. Using the optimal d{sub Fe1}, d{sub Fe2} and the intermediate Cu layer we realized almost full switching from normal to SC state due to SSVE.

  20. Effect of external magnetic field on superconducting and spin density wave gaps of high-T{sub c} superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Pradhan, B., E-mail: brunda@iopb.res.i [Govt. Science College, Malkangiri 764 048 (India); Raj, B.K. [B.J.B. College, Bhubaneswar 751 014 (India); Rout, G.C., E-mail: gcr@iopb.res.i [Condensed Matter Physics Group P.G. Dept. of Applied Physics and Ballistics, F.M. University, Balasore 756 019 (India)

    2009-07-01

    A theoretical model is addressed here to study the interplay of the superconductivity (SC) and the spin density wave (SDW) long range orders in underdoped region in the vicinity of on-set of superconductivity in presence of an external magnetic field. The order parameters are calculated by using Zubarev's technique of Green's functions and determined numerically self-consistently. The gap parameters are found to be strongly coupled to each other through their coupling constants. The interplay displays BCS type two gaps in the quasi-particle density of states (DOS) which resemble the tunneling conductance of STM experiments. The gap edges in the DOS appear at +-(z+z{sub 1}) and +-(z-z{sub 1}). The applied magnetic field further induces Zeeman splitting which is explained on the basis of spin-filter effect of tunneling experiment.

  1. Effect of external magnetic field on superconducting and spin density wave gaps of high-Tc superconductors

    International Nuclear Information System (INIS)

    Pradhan, B.; Raj, B.K.; Rout, G.C.

    2009-01-01

    A theoretical model is addressed here to study the interplay of the superconductivity (SC) and the spin density wave (SDW) long range orders in underdoped region in the vicinity of on-set of superconductivity in presence of an external magnetic field. The order parameters are calculated by using Zubarev's technique of Green's functions and determined numerically self-consistently. The gap parameters are found to be strongly coupled to each other through their coupling constants. The interplay displays BCS type two gaps in the quasi-particle density of states (DOS) which resemble the tunneling conductance of STM experiments. The gap edges in the DOS appear at ±(z+z 1 ) and ±(z-z 1 ). The applied magnetic field further induces Zeeman splitting which is explained on the basis of spin-filter effect of tunneling experiment.

  2. Effect of crystalline electric fields and long-range magnetic order on superconductivity in rare earth alloys and compounds

    International Nuclear Information System (INIS)

    McCallum, R.W.

    1977-01-01

    The behavior of rare earth ions in a superconducting matrix has been studied in two distinct regimes. First, the effects of crystal field splitting of the 4f levels of a magnetic rare earth ion in the alloy system (LaPr)Sn 3 were investigated in the limit of low Pr 3+ concentration. In this system the rare earth impurity ions occupy random La sites in the crystal lattice. Second, the interaction of long-range magnetic order and superconductivity was explored in the ternary rare earth molybdenum chalcogenide systems. In these compounds the rare earth ions occupy periodic lattice sites in contrast to the random distribution of magnetic ions in dilute impurity alloy systems such as (LaPr)Sn 3

  3. The effect of citric and oxalic acid doping on the superconducting properties of MgB2

    International Nuclear Information System (INIS)

    Ojha, N; Singla, Rashmi; Varma, G D; Malik, V K; Bernhard, C

    2009-01-01

    In this paper we report the effect of carbon doping on the structural and superconducting properties of MgB 2 using citric and oxalic acids as carbon sources. The bulk polycrystalline samples have been synthesized via a standard solid state reaction route with composition MgB 2 +x wt% of citric and oxalic acids (x = 0, 5 and 10). The x-ray diffraction results reveal the formation of dominantly MgB 2 with only a small amount of impurity phase MgO and substitution of C at the B site of MgB 2 for both dopants. Improvements in the upper critical field (H C2 ), irreversibility field (H irr ) and high field (>2.5 T) critical current density (J C ) have been observed on C doping in the samples. The correlations between superconducting properties and structural characteristics of the samples are described and discussed in this paper.

  4. Effects of weak magnetic fields on post-implantation damage in superconducting oxides

    International Nuclear Information System (INIS)

    Khait, Y.L.

    1996-01-01

    Experimentally verifiable effects of weak permanent magnetic fields (PMF's) acting during ion implantation in high-T c superconducting (HTSC) materials at T∼300 K on post-implantation damage (PID) and material parameters are considered. The presence of PMF's of H∼10 3 Oe during ion implantation can enlarge substantially the PID in HTSC materials implanted with ions of moderate energies (e.g. 200-400 keV) and dosage (10 11- 10 12 cm -3 ) at room temperature. The PMF-induced increase in the radiation damage causes the corresponding enhancement in the material resistivity R and reduction in the critical current j cir (measured after the cooling of the HTSC material down to T (L) c after the ion implantation). This is an extension of the PMF effects found experimentally (and explained theoretically) in semiconductors in our previous work. The experimentally verifiable PMF effects on the defect (atomic) migration and radiation damage is a generic consequence of the kinetic electron-related theory of atomic rate processes in solids. The theory links the PMF effects with electron transitions occurring in the nanometer vicinity of atoms overcoming energy barriers which affect exponentially rates of atomic (defect) diffusion. The magnetic field can enhance the number of downward electron transitions that accompany atomic (defect) jumps over energy barriers and synchronize with the jumps. This enhances exponentially the rates of defect migration out of thermal spikes that prevents the defects from fast recombination, and thus, the PMF increases the PID and changes correspondingly R and j cir . (orig.)

  5. Smooth surfaces in very thin GdBa{sub 2}Cu{sub 3}O{sub 7−δ} films for application in superconducting tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Navarro, H., E-mail: henrynavarro@cab.cnea.gov.ar [Instituto Balseiro, Universidad Nacional de Cuyo & CNEA, 8400 Bariloche (Argentina); Centro Atómico Bariloche, Comisión Nacional de Energía Atómica. Av. Bustillo 9500, 8400 San Carlos de Bariloche (Argentina); Sirena, M. [Instituto Balseiro, Universidad Nacional de Cuyo & CNEA, 8400 Bariloche (Argentina); Centro Atómico Bariloche, Comisión Nacional de Energía Atómica. Av. Bustillo 9500, 8400 San Carlos de Bariloche (Argentina); Kim, Jeehoon [Department of Physics, Pohang University of Science and Technology, Pohang (Korea, Republic of); CALDES, Institute for Basic Science, Pohang (Korea, Republic of); Haberkorn, N. [Instituto Balseiro, Universidad Nacional de Cuyo & CNEA, 8400 Bariloche (Argentina); Centro Atómico Bariloche, Comisión Nacional de Energía Atómica. Av. Bustillo 9500, 8400 San Carlos de Bariloche (Argentina)

    2015-03-15

    Highlights: • A detailed study of the morphological properties of GdBa{sub 2}Cu{sub 3}O{sub 7−δ} thin films was realized. • The inclusion of a very thin SrTiO{sub 3} buffer layer modifies the surface of the SrTiO{sub 3} substrates. • The inclusion of the buffer layer suppress the three dimensional nucleation in the GdBa{sub 2}Cu{sub 3}O{sub 7−δ} film. • GdBa{sub 2}Cu{sub 3}O{sub 7−δ} films with large areas free of topological defects and T{sub c} close to liquid nitrogen can be obtained. - Abstract: This paper provides a systematic analysis of the morphology and the superconducting critical temperature obtained in very thin GdBa{sub 2}Cu{sub 3}O{sub 7−δ} films grown on (0 0 1) SrTiO{sub 3} substrates by DC sputtering. We find that the use of a very thin SrTiO{sub 3} buffer layer (≈2 nm) modify the nucleation of GdBa{sub 2}Cu{sub 3}O{sub 7−δ} on the surface of the substrate reducing the formation of 3 dimensional clusters. Our results demonstrate that 16 nm thick GdBa{sub 2}Cu{sub 3}O{sub 7−δ} films with an average root-mean-square (RMS) smaller than 1 nm and large surface areas (up 10 μm{sup 2}) free of 3 dimensional topological defects can be obtained. In films thinner than 24 nm the onset (zero resistance) of superconducting transition of the films is reduced, being close to liquid nitrogen. This fact can be associated with stress reducing the orthorhombicity and slightly drop in oxygen stoichiometry.

  6. Smooth surfaces in very thin GdBa2Cu3O7−δ films for application in superconducting tunnel junctions

    International Nuclear Information System (INIS)

    Navarro, H.; Sirena, M.; Kim, Jeehoon; Haberkorn, N.

    2015-01-01

    Highlights: • A detailed study of the morphological properties of GdBa 2 Cu 3 O 7−δ thin films was realized. • The inclusion of a very thin SrTiO 3 buffer layer modifies the surface of the SrTiO 3 substrates. • The inclusion of the buffer layer suppress the three dimensional nucleation in the GdBa 2 Cu 3 O 7−δ film. • GdBa 2 Cu 3 O 7−δ films with large areas free of topological defects and T c close to liquid nitrogen can be obtained. - Abstract: This paper provides a systematic analysis of the morphology and the superconducting critical temperature obtained in very thin GdBa 2 Cu 3 O 7−δ films grown on (0 0 1) SrTiO 3 substrates by DC sputtering. We find that the use of a very thin SrTiO 3 buffer layer (≈2 nm) modify the nucleation of GdBa 2 Cu 3 O 7−δ on the surface of the substrate reducing the formation of 3 dimensional clusters. Our results demonstrate that 16 nm thick GdBa 2 Cu 3 O 7−δ films with an average root-mean-square (RMS) smaller than 1 nm and large surface areas (up 10 μm 2 ) free of 3 dimensional topological defects can be obtained. In films thinner than 24 nm the onset (zero resistance) of superconducting transition of the films is reduced, being close to liquid nitrogen. This fact can be associated with stress reducing the orthorhombicity and slightly drop in oxygen stoichiometry

  7. Pressure effect on magnetism and superconductivity in CePt{sub 3}Si

    Energy Technology Data Exchange (ETDEWEB)

    Takeuchi, T. [Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043 (Japan) and KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8513 (Japan)]. E-mail: takeuchi@rcem.osaka-u.ac.jp; Shiimoto, M. [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Kohara, H. [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Yasuda, T. [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Hashimoto, S. [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Settai, R. [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Onuki, Y. [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Advanced Science Research Center, JAERI, Tokai, Ibaraki 319-1195 (Japan)

    2006-05-01

    Magnetism and superconductivity in the heavy-fermion superconductor CePt{sub 3}Si have been studied under pressure. The antiferromagnetic and superconducting transition temperatures, T{sub N} and T{sub sc}, respectively, decrease by applying pressure. T{sub N} becomes zero around 0.6-0.7GPa, while the pressure dependence of T{sub sc} exhibits a shoulder-like feature around 0.7GPa, and superconductivity is found to persist in the pressure range up to about 1.5GPa. A broad peak around 5K in the temperature derivative of thermal expansion {alpha}(T) and electrical resistivity d{rho}(T)/dT at ambient pressure begins to shift to higher temperatures above 0.7GPa. These results suggest that a critical pressure exists around 0.6-0.7GPa in CePt{sub 3}Si.

  8. Superconducting ''wiggler'' for the VEPP-3 storage ring and its effect on particle motion

    International Nuclear Information System (INIS)

    Barkov, L.M.; Baryshev, V.B.; Kulipanov, G.N.; Mezentsev, N.A.; Pindyurin, V.F.; Skrinskij, A.N.; Khorev, V.M.; Sheromov, M.A.

    1979-01-01

    To improve characteristics of synchrotron radiation, a superconducting S-type device has been developed and tested, which produces a sign-variable periodic magnetic field with an amplitude of 35 kGs and a half-period of 4.5 cm in the staight section of the VEPP-3 storage ring. The magnetic S-type device comprises 20 superconducting magnets (SCM) connected in series. SCM windings are made of NbTi multicore cables with a diameter of 0.7 mm and a glass fabric impregnated with an epoxy compound. The test results showed that the number of superconductivity disruptions for an operating current of 210 A constitutes 3 or 4 per a SCM, with the magnet critical current increasing from 130-150 A to 210-230 A and reaching a value of 0.9-0.95 of the measured critical current of short superconductor samples

  9. Structure relaxation effect on superconductive properties of amorphous metallic ZrΛ9Λ0BΛ3SiΛ7 alloy

    International Nuclear Information System (INIS)

    Zolotukhin, I.V.; Zheleznyj, V.S.; Rudyj, S.D.; Fedorov, V.M.

    1985-01-01

    The effect of structural relaxation on electronand phonon spectra and electron-phonon interaction of Zr 90 B 3 Si 7 amorphous alloy is investigated. The specific electric conductivity rho 293 , superconducting transition temperature Tsub(c), critical magnetic field Bsub(c) (near Tsub(c)) and the Young modulus E 293 were measured. The Debye temperature THETA sub(D), electron state density on the Fermi surface N(O electron-phonon interaction constant lambda) mean square of a matrix element and the Hopfeld parameter were calculated. Experimental data show that Tsub(c) decreases during the structural relaxation of amorphous alloy in spite of increasing THETA sub(D) and N(O). However, the calculations show that during the structural relaxation the matrix element of the electron-phonon inte raction decreases with a simultaneous lambda decrease and an insignificant change in the Hopfeld parameter

  10. Connectivity and superconductivity

    CERN Document Server

    Rubinstein, Jacob

    2000-01-01

    The motto of connectivity and superconductivity is that the solutions of the Ginzburg--Landau equations are qualitatively influenced by the topology of the boundaries, as in multiply-connected samples. Special attention is paid to the "zero set", the set of the positions (also known as "quantum vortices") where the order parameter vanishes. The effects considered here usually become important in the regime where the coherence length is of the order of the dimensions of the sample. It takes the intuition of physicists and the awareness of mathematicians to find these new effects. In connectivity and superconductivity, theoretical and experimental physicists are brought together with pure and applied mathematicians to review these surprising results. This volume is intended to serve as a reference book for graduate students and researchers in physics or mathematics interested in superconductivity, or in the Schrödinger equation as a limiting case of the Ginzburg--Landau equations.

  11. Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through Tc

    Science.gov (United States)

    Huang, Shichun; Kubo, Takayuki; Geng, R. L.

    2016-08-01

    Recent studies by Romanenko et al. revealed that cooling down a superconducting cavity under a large spatial temperature gradient decreases the amount of trapped flux and leads to reduction of the residual surface resistance. In the present paper, the flux expulsion ratio and the trapped-flux-induced surface resistance of a large-grain cavity cooled down under a spatial temperature gradient up to 80 K /m are studied under various applied magnetic fields from 5 to 20 μ T . We show the flux expulsion ratio improves as the spatial temperature gradient increases, independent of the applied magnetic field: our results support and enforce the previous studies. We then analyze all rf measurement results obtained under different applied magnetic fields together by plotting the trapped-flux-induced surface resistance normalized by the applied magnetic field as a function of the spatial temperature gradient. All the data can be fitted by a single curve, which defines an empirical formula for the trapped-flux-induced surface resistance as a function of the spatial temperature gradient and applied magnetic field. The formula can fit not only the present results but also those obtained by Romanenko et al. previously. The sensitivity rfl of surface resistance from trapped magnetic flux of fine-grain and large-grain niobium cavities and the origin of d T /d s dependence of Rfl/Ba are also discussed.

  12. Annealing effect on superconductivity of La2CuO4 single crystals

    International Nuclear Information System (INIS)

    Tanaka, I.; Takahashi, H.; Kojima, H.

    1992-01-01

    This paper reports that La 2 CuO 4 single crystals grown at an oxygen pressure of 0.2 MPa by TSFZ method are superconducting below 32 K, and show a semiconducting behavior in nonsuperconducting state. The single crystals of La 2 CuO 4 are changed from superconductors to semiconductors by annealing in argon, and are returned to superconductors by annealing at ambient pressure of oxygen. Therefore, superconductivity of the La 2 CuO 4 single crystals is due to excess oxygen

  13. Annealing effect on superconductivity of La2CuO4 single crystals

    International Nuclear Information System (INIS)

    Tanaka, L.; Takahashi, H.; Kojima, H.

    1992-01-01

    La 2 CuO 4 single crystals grown at an oxygen pressure of 0.2 MPa by TSFZ method are superconducting below 32 K, and show a semiconducting behavior in nonsuperconducting state. The single crystals of La 2 CuO 4 are changed from superconductors to semiconductors by annealing in argon, and are returned to superconductors by annealing at ambient pressure of oxygen. Therefore, superconductivity of the La 2 CuO 4 single crystals is due to excess oxygen. (orig.)

  14. 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.

  15. 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

  16. On anyon superconductivity--

    International Nuclear Information System (INIS)

    Chen, Y.-H.; Wilczek, F.; Witten, E.; Halperin, B.I.

    1989-01-01

    We investigate the statistical mechanics of a gas of fractional statistics particles in 2 + 1 dimensions. In the case of statistics very close to Fermi statistics (statistical parameter θ = π(1 - 1/n), for large n), the effect of the statistics is a weak attraction. Building upon earlier RPA calculation for the case n = 2, the authors argue that for large n perturbation theory is reliable and exhibits superfluidity (or superconductivity after coupling to electromagnetism). They describe the order parameter for this superconductng phase in terms of spontaneous breaking of commutativity of translations as opposed to the usual pairing order parameters. The vortices of the superconducting anyon gas are charged, and superconducting order parameters of the usual type vanish. They investigate the characteristic P and T violating phenomenology

  17. Pressure effect on the electrical conductivity and superconductivity of beta-(BDA-TTP)2I3.

    Science.gov (United States)

    Yamada, Jun-Ichi; Fujimoto, Kazuya; Akutsu, Hiroki; Nakatsuji, Shin'ichi; Miyazaki, Akira; Aimatsu, Masashi; Kudo, Satoshi; Enoki, Toshiaki; Kikuchi, Koichi

    2006-03-28

    The pressure-induced electrical conductivity properties of beta-(BDA-TTP)2I3 have been investigated; the salt exhibits a dramatic change in the conductivity behaviour above ca. 10 kbar and undergoes a superconducting transition with an onset near 10 K.

  18. Effect of magnetic field on charge imbalance relaxation of non-equilibrium superconductivity

    International Nuclear Information System (INIS)

    Tsuboi, Kazuki; Yagi, Ryuta

    2010-01-01

    We have studied relaxation of charge imbalance of non-equilibrium superconductivity in magnetic field. We found that excess current due to charge imbalance showed striking dependence on magnitude of magnetic field and its orientation. We discussed origin of the relaxation.

  19. Effect of boron dimers on the superconducting critical temperature inboron-doped diamond

    Czech Academy of Sciences Publication Activity Database

    Šopík, Břetislav; Lipavský, P.

    2012-01-01

    Roč. 21, č. 1 (2012), 77-82 ISSN 0925-9635 R&D Projects: GA ČR GAP204/10/0212 Institutional research plan: CEZ:AV0Z10100521 Keywords : boron * superconductivity * disorder * correlations * dimers Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.709, year: 2012

  20. 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)

  1. 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

  2. New magnetic coherence effect in superconducting La2-xSrxCuO4

    DEFF Research Database (Denmark)

    Mason, T.E.; Schröder, A.; Aeppli, G.

    1996-01-01

    We have used inelastic neutron scattering to examine the magnetic fluctuations at intermediate frequencies in the simplest high temperature superconductor, La2-xSrxCuO4. The suppression of the low energy magnetic response in the superconducting state is accompanied by an increase in the response...

  3. 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

  4. Gambling with Superconducting Fluctuations

    Science.gov (United States)

    Foltyn, Marek; Zgirski, Maciej

    2015-08-01

    Josephson junctions and superconducting nanowires, when biased close to superconducting critical current, can switch to a nonzero voltage state by thermal or quantum fluctuations. The process is understood as an escape of a Brownian particle from a metastable state. Since this effect is fully stochastic, we propose to use it for generating random numbers. We present protocol for obtaining random numbers and test the experimentally harvested data for their fidelity. Our work is prerequisite for using the Josephson junction as a tool for stochastic (probabilistic) determination of physical parameters such as magnetic flux, temperature, and current.

  5. Effective method to control the levitation force and levitation height in a superconducting maglev system

    Science.gov (United States)

    Yang, Peng-Tao; Yang, Wan-Min; Wang, Miao; Li, Jia-Wei; Guo, Yu-Xia

    2015-11-01

    The influence of the width of the middle magnet in the permanent magnet guideways (PMGs) on the levitation force and the levitation height of single-domain yttrium barium copper oxide (YBCO) bulks has been investigated at 77 K under the zero field cooled (ZFC) state. It is found that the largest levitation force can be obtained in the system with the width of the middle magnet of the PMG equal to the size of the YBCO bulk when the gap between the YBCO bulk and PMG is small. Both larger levitation force and higher levitation height can be obtained in the system with the width of the middle magnet of the PMG larger than the size of the YBCO bulk. The stiffness of the levitation force between the PMG and the YBCO bulk is higher in the system with a smaller width of the middle magnet in the PMG. These results provide an effective way to control the levitation force and the levitation height for the superconducting maglev design and applications. Project supported by the National Natural Science Foundation of China (Grant Nos. 51342001 and 50872079), the Key-grant Project of Chinese Ministry of Education (Grant No. 311033), the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120202110003), the Innovation Team in Shaanxi Province, China (Grant No. 2014KTC-18), and the Fundamental Research Funds for the Central Universities, China (Grant Nos. GK201101001 and GK201305014), and the Outstanding Doctoral Thesis Foundation Project of Shaanxi Normal University, China (Grant Nos. X2011YB08 and X2012YB05).

  6. Three-terminal superconducting devices

    International Nuclear Information System (INIS)

    Gallagher, W.J.

    1985-01-01

    The transistor has a number of properties that make it so useful. The authors discuss these and the additional properties a transistor would need to have for high performance applications at temperatures where superconductivity could contribute advantages to system-level performance. These properties then serve as criteria by which to evaluate three-terminal devices that have been proposed for applications at superconducting temperatures. FETs can retain their transistor properties at low temperatures, but their power consumption is too large for high-speed, high-density cryogenic applications. They discuss in detail why demonstrated superconducting devices with three terminals -Josephson effect based devices, injection controlled weak links, and stacked tunnel junction devices such as the superconducting transistor proposed by K. Gray and the quiteron -- each fail to have true transistor-like properties. They conclude that the potentially very rewarding search for a transistor compatible with superconductivity in high performance applications must be in new directions

  7. Interference effects with surface plasmons

    NARCIS (Netherlands)

    Kuzmin, Nikolay Victorovich

    2008-01-01

    A surface plasmon is a purely two-dimensional electromagnetic excitation bound to the interface between metal and dielectric and quickly decaying away from it. A surface plasmon is able to concentrate light on sub-wavelength scales – a feature that is attractive for nano-photonics and integrated

  8. Effect of interstitial impurities on the field dependent microwave surface resistance of niobium

    Science.gov (United States)

    Martinello, M.; Grassellino, A.; Checchin, M.; Romanenko, A.; Melnychuk, O.; Sergatskov, D. A.; Posen, S.; Zasadzinski, J. F.

    2016-08-01

    Previous work has demonstrated that the radio frequency surface resistance of niobium resonators is dramatically reduced when nitrogen impurities are dissolved as interstitial in the material. This effect is attributed to the lowering of the Mattis-Bardeen surface resistance with increasing accelerating field; however, the microscopic origin of this phenomenon is poorly understood. Meanwhile, an enhancement of the sensitivity to trapped magnetic field is typically observed for such cavities. In this paper, we conduct a systematic study on these different components contributing to the total surface resistance as a function of different levels of dissolved nitrogen, in comparison with standard surface treatments for niobium resonators. Adding these results together, we are able to show which is the optimum surface treatment that maximizes the Q-factor of superconducting niobium resonators as a function of expected trapped magnetic field in the cavity walls. These results also provide insights on the physics behind the change in the field dependence of the Mattis-Bardeen surface resistance, and of the trapped magnetic vortex induced losses in superconducting niobium resonators.

  9. Effects of high-energy proton irradiation on the superconducting properties of Fe(Se,Te) thin films

    Science.gov (United States)

    Sylva, G.; Bellingeri, E.; Ferdeghini, C.; Martinelli, A.; Pallecchi, I.; Pellegrino, L.; Putti, M.; Ghigo, G.; Gozzelino, L.; Torsello, D.; Grimaldi, G.; Leo, A.; Nigro, A.; Braccini, V.

    2018-05-01

    In this paper we explore the effects of 3.5 MeV proton irradiation on Fe(Se,Te) thin films grown on CaF2. In particular, we carry out an experimental investigation with different irradiation fluences up to 7.30 · 1016 cm‑2 and different proton implantation depths, in order to clarify whether and to what extent the critical current is enhanced or suppressed, what are the effects of irradiation on the critical temperature, resistivity, and critical magnetic fields, and finally what is the role played by the substrate in this context. We find that the effect of irradiation on superconducting properties is generally small compared to the case of other iron-based superconductors. The irradiation effect is more evident on the critical current density Jc, while it is minor on the transition temperature Tc, normal state resistivity ρ, and on the upper critical field Hc2 up to the highest fluences explored in this work. In more detail, our analysis shows that when protons implant in the substrate far from the superconducting film, the critical current can be enhanced up to 50% of the pristine value at 7 T and 12 K; meanwhile, there is no appreciable effect on critical temperature and critical fields together with a slight decrease in resistivity. On the contrary, when the implantation layer is closer to the film–substrate interface, both critical current and temperature show a decrease accompanied by an enhancement of the resistivity and lattice strain. This result evidences that possible modifications induced by irradiation in the substrate may affect the superconducting properties of the film via lattice strain. The robustness of the Fe(Se,Te) system to irradiation-induced damage makes it a promising compound for the fabrication of magnets in high-energy accelerators.

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  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. 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

  17. Radio-Frequency Illuminated Superconductive Disks: Reverse Josephson Effects and Implications for Precise Measuring of Proposed Gravity Effects

    Science.gov (United States)

    Noever, David A.; Koczor, Ronald J.

    1998-01-01

    We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. It have been indicated three essential components to achieve anomalous gravity effects, namely large, two-layer high-temperature YBCO superconductors, magnetic levitation and AC input in the form of radio-frequency (RF) electromagnetic fields. We report experiments on RF-illuminated (1-15 MHz) superconducting disks with corresponding gravity readings indicating an apparent increase in observed gravity of approximately 3-5 x l0(exp -5)cm/sq s, above and to the side of the superconductor. In this preliminary study, RF- illumination is achieved using a series of large radius (15 cm) spiral antenna with RF power inputs equal to or greater than 90 W. The observed gravitational modification range is significantly lower than the 2.1% gravity modification. The error analyses of thermal and electromagnetic interference in a magnetically shielded gravimeter with vacuum enclosures, Faraday cages and shielded instrument leads, are outlined both experimentally and theoretically. The nearly exact correspondence between the peak gravity effects reported and the well-known peak in AC resistance in superconductors (2-7 MHz, owing to reverse Josephson quantum effects) suggests that electrical resistance will arise in this frequency range and subsequently any trapped magnetic fields in the superconductor may disperse partially into the measuring instrument's local environment. Implications for propulsion initiatives and RF-heating in superconductors will be discussed.

  18. Effect of low temperature baking in nitrogen on the performance of a niobium superconducting radio frequency cavity

    Directory of Open Access Journals (Sweden)

    Pashupati Dhakal

    2018-03-01

    Full Text Available We report the rf performance of a single cell superconducting radiofrequency cavity after low temperature baking in a nitrogen environment. A significant increase in quality factor has been observed when the cavity was heat treated in the temperature range of 120–160 °C with a nitrogen partial pressure of ∼25  m Torr. This increase in quality factor as well as the Q-rise phenomenon (anti-Q-slope is similar to those previously obtained with high temperature nitrogen doping as well as titanium doping. In this study, a cavity N_{2}-treated at 120 °C and at 140 °C showed no degradation in accelerating gradient, however the accelerating gradient was reduced by ∼25% with a 160 °C N_{2} treatment, compared to the baseline tests after electropolishing. Sample coupons treated in the same conditions as the cavity were analyzed by scanning electron microscope, x-ray photoelectron spectroscopy and secondary ion mass spectroscopy revealed a complex surface composition of Nb_{2}O_{5}, NbO and NbN_{(1−x}O_{x} within the rf penetration depth. Furthermore, magnetization measurements showed no significant change on bulk superconducting properties.

  19. Effect of low temperature baking in nitrogen on the performance of a niobium superconducting radio frequency cavity

    Science.gov (United States)

    Dhakal, Pashupati; Chetri, Santosh; Balachandran, Shreyas; Lee, Peter J.; Ciovati, Gianluigi

    2018-03-01

    We report the rf performance of a single cell superconducting radiofrequency cavity after low temperature baking in a nitrogen environment. A significant increase in quality factor has been observed when the cavity was heat treated in the temperature range of 120 - 160 °C with a nitrogen partial pressure of ˜25 m Torr . This increase in quality factor as well as the Q -rise phenomenon (anti-Q -slope) is similar to those previously obtained with high temperature nitrogen doping as well as titanium doping. In this study, a cavity N2 -treated at 120 °C and at 140 °C showed no degradation in accelerating gradient, however the accelerating gradient was reduced by ˜25 % with a 160 °C N2 treatment, compared to the baseline tests after electropolishing. Sample coupons treated in the same conditions as the cavity were analyzed by scanning electron microscope, x-ray photoelectron spectroscopy and secondary ion mass spectroscopy revealed a complex surface composition of Nb2O5 , NbO and NbN(1 -x )Ox within the rf penetration depth. Furthermore, magnetization measurements showed no significant change on bulk superconducting properties.

  20. Critical current density of BiSrCaCuO superconductors: effect of surface barriers

    International Nuclear Information System (INIS)

    Konczykowski, M.; Chikumoto, N.

    1992-01-01

    Effects of surface barriers on vortex motion in BiSrCaCuO-2212 high-temperature superconducting crystals is summarized. Characteristic features of this phenomenon appear in the hysteresis loop (shape of its ascending and descending branches), in the effect of 2.5 MeV electron irradiation, and in flux creep measurements (magnetization dependence to the crystal lateral dimension, size of the flux-creep barrier and the crossover as a function of temperature and time persistent current density). (A.B.). 25 refs., 3 figs

  1. Additional signature of the dynamical Casimir effect in a superconducting circuit

    International Nuclear Information System (INIS)

    Rego, Andreson L.C.; Farina, C.; Silva, Hector O.; Alves, Danilo T.

    2013-01-01

    Full text: The dynamical Casimir effect (DCE) is one of the most fascinating quantum vacuum effects that consists, essentially, on the particle creation as a result of the interaction between a quantized field and a moving mirror. In this sense, particle creation due to external time-dependent potentials or backgrounds, or even time dependent electromagnetic properties of a material medium can also be included in a general definition of DCE. For simplicity, this interaction is simulated, in general, by means of idealized boundary conditions (BC). As a consequence of the particle creation, the moving mirror experiences a dissipative radiation reaction force acting on it. In order to generate an appreciable number of photons to be observed, the DCE was investigated in other contexts, as for example, in the circuit quantum electrodynamics. This theory predicted high photon creation rate by the modulation of the length of an open transmission line coupled to a superconducting quantum interference device (SQUID), an extremely sensitive magnetometer (J.R. Johansson et al, 2009/2010). A time dependent magnetic flux can be applied to the SQUID changing its inductance, leading to a time-dependent BC which simulates a moving boundary It was in the last scenario that the first observation of the DCE was announced by Wilson and collaborators (Wilson et al, 2011). Taking as motivation the experiment that observed the DCE, we investigate the influence of the generalized time-dependent Robin BC, that presents an extra term involving the second order time derivative of the field, in the particle creation via DCE. This kind of BC may appear quite naturally in the context of circuit quantum electrodynamics and the extra term was neglected in the theoretical aspects of the first observation of the DCE. Appropriate adjustments of this new parameter can not only enhance the total number of created particles but also give rise to a non-parabolic shape of the particle creation spectral

  2. Study of thermal effects in superconducting RF cavities; Etude des effets thermiques dans le cavites supraconductrices

    Energy Technology Data Exchange (ETDEWEB)

    Bousson, S.; Caruette, A.; Fouaidy, M.; Hammoudi, N.; Junquera, T.; Lesrel, J.; Yaniche, J.F. [Services Techniques, Inst. de Physique Nucleaire, Paris-11 Univ., 91 - Orsay (France)

    1999-11-01

    A high speed thermometric system equipped with 64 fixed surface thermometers is used to investigate thermal effects in several 3 GHz cavities. An evaluation of the time response of our thermometers is presented. A method based on RF signal analysis is proposed to evaluate the normal zone propagation rate during thermal breakdown. (authors) 2 refs., 3 figs.

  3. The Effect of the Feedback Controller on Superconducting Tokamak AC Losses + AC-CRPP user manual

    International Nuclear Information System (INIS)

    Schaerz, B.; Bruzzone, P.; Favez, J.Y.; Lister, J.B.; Zapretilina, E.

    2001-11-01

    Superconducting coils in a Tokamak are subject to AC losses when the field transverse to the coil current varies. A simple model to evaluate the AC losses has been derived and benchmarked against a complete model used in the ITER design procedure. The influence of the feedback control strategy on the AC losses is examined using this model. An improved controller is proposed, based on this study. (author)

  4. Radiation effects limits on superconducting magnets: Data base for copper stabilizers

    Energy Technology Data Exchange (ETDEWEB)

    Guinan, M.W.

    1986-02-24

    A simple model has been developed which can predict the magnetoresistance of copper as a function of initial purity, the extent of cold work and the presence of both irradiation produced point defects and the extended defects produced by annealing. The remaining area of uncertainty in a complete description of the response of superconducting magnets to irradiation-anneal cycles is the dependence of annealing on dose impurity concentration and cold-work.

  5. Radiation effects limits on superconducting magnets: Data base for copper stabilizers

    International Nuclear Information System (INIS)

    Guinan, M.W.

    1986-01-01

    A simple model has been developed which can predict the magnetoresistance of copper as a function of initial purity, the extent of cold work and the presence of both irradiation produced point defects and the extended defects produced by annealing. The remaining area of uncertainty in a complete description of the response of superconducting magnets to irradiation-anneal cycles is the dependence of annealing on dose impurity concentration and cold-work

  6. 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...

  7. Effects of strain on the superconducting properties of niobium-tin conductors

    International Nuclear Information System (INIS)

    Hoard, R.W.

    1980-11-01

    Investigations were performed to ascertain additional information on the connection between the cubic to tetragonal martensitic phase transformation and the phenomenon of superconductivity in Nb 3 Sn. Of particular interest is the degradation of the critical parameters, such as T/sub c/, H/sub c2/, and J/sub c/, with mechanical straining of the superconductor. These studies yielded information that assisted in the derivation of the critical current-strain scaling laws mentioned above

  8. Titania doping effect on superconducting properties of MgB{sub 2} bulk samples

    Energy Technology Data Exchange (ETDEWEB)

    Serrano, G; Serquis, A [Institute Balseiro - Centra Atomico Bariloche and CONICET, (8400) S. C. de Bariloche, Rio Negro (Argentina); Bridoux, G, E-mail: serranog@ib.cnea.gov.a [Institute Balseiro - Centra Atomico Bariloche, (8400) S. C. de Bariloche, Rio Negro (Argentina)

    2009-05-01

    In this work we study the microstructural and superconducting properties of doped and undoped bulk MgB{sub 2} samples prepared by solid-state reaction, with 0 and 2.5 %at. nominal TiO{sub 2} nanotubes contents, annealed at different temperatures in the 750-900 deg. C range. We discuss the T{sub c}, J{sub c} and H{sub c2} performance and their correlation with the different synthesis parameters.

  9. The Effect of CuSn Intermetallics on the Interstrand Contact Resistance in Superconducting Cables for the Large Hadron Collider (LHC)

    CERN Document Server

    Scheuerlein, C; Jacob, P; Leroy, D; Oberli, L R; Taborelli, M

    2005-01-01

    The LHC superconducting cables are submitted to a 200°C heat-treatment in air in order to increase the resistance between the crossing strands (RC) within the cable. During this treatment the as-applied Sn-Ag alloy strand coating is transformed into a CuSn intermetallic compound layer. The microstructure, the surface topography and the surface chemistry of the non-reacted and reacted coatings have been characterised by different techniques, notably focused ion beam (FIB), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Based on the results obtained by these techniques the different influences that the intermetallics have on RC are discussed. The desired RC is obtained only when a continuous Cu3Sn layer is formed, i.e. a sufficient wetting of the Cu substrate by the tinning alloy is crucial. Among other effects the formation of the comparatively hard intermetallics roughens the surface and, thus, reduces the true contact area and i...

  10. Baking effect on Niobium superconducting RF cavities and its physical interpretation

    Energy Technology Data Exchange (ETDEWEB)

    Saito, K. [High Energy Accelerator Research Organization, Tsukuba, Ibaraki (Japan); Kneisel, P. [Thomas Jefferson Accelerator Facility, VA, (United States)

    2000-07-01

    Recently a very surprising phenomenon has been discovered at JLab and Saclay with chemically polished niobium cavities, which the baking during vacuum evacuation has benefits to improve the cavity performance: high Q and high gradient. We have confirmed the same effect on the electropolished niobium cavities. We have analyzed the temperature dependence of the surface resistance in order to understand this effect in the frame or BCS theory. In this paper these results will be presented. (author)

  11. Pulsed rf superconductivity program at SLAC

    International Nuclear Information System (INIS)

    Campisi, I.E.; Farkas, Z.D.

    1984-08-01

    Recent tests performed at SLAC on superconducting TM 010 caavities using short rf pulses (less than or equal to 2.5 μs) have established that at the cavity surface magnetic fields can be reached in the vicinity of the theoretical critical fields without an appreciable increase in average losses. Tests on niobium and lead cavities are reported. The pulse method seems to be best suited to study peak field properties of superconductors in the microwave band, without the limitations imposed by defects. The short pulses also seem to be more effective in decreasing the causes of field emission by rf processing. Applications of the pulsed rf superconductivity to high-gradient linear accelerators are also possible

  12. Superconductivity in multilayer perovskite. Weak coupling analysis

    International Nuclear Information System (INIS)

    Koikegami, Shigeru; Yanagisawa, Takashi

    2006-01-01

    We investigate the superconductivity of a three-dimensional d-p model with a multilayer perovskite structure on the basis of the second-order perturbation theory within the weak coupling framework. Our model has been designed with multilayer high-T c superconducting cuprates in mind. In our model, multiple Fermi surfaces appear, and the component of a superconducting gap function develops on each band. We have found that the multilayer structure can stabilize the superconductivity in a wide doping range. (author)

  13. SNS superconducting linac

    International Nuclear Information System (INIS)

    Sundelin, Ronald M.

    2001-01-01

    The Spallation Neutron Source (SNS) decided in early 2000 to use superconducting RF (SRF) in the linac at energies above 185 MeV. Since the SNS duty cycle is 6%, the SRF and normal conducting approaches have capital costs which are about the same, but operating costs and future upgradability are improved by using SRF. The current status of cavity and cryomodule development and procurement, including the basis for decisions made, is discussed. The current plan includes use of 805 MHz, 6-cell cavities with geometrical betas of 0.61 and 0.81. There are 33 medium beta and 60 high beta cavities in 11 and 15 cryomodules, respectively. Each cavity (except the 93rd) is powered by a 550 kW pulsed klystron. Issues addressed include choice of peak surface gradient, optimization of cavity shape, selection of a scaled KEK input power coupler, selection of scaled TESLA higher mode couplers, and control of the effects of higher order modes on the beam. (author)

  14. Kondo effect and spin-glass freezing of the magnetic impurities Cr, Mn, and Fe in superconducting palladium hydride

    International Nuclear Information System (INIS)

    van Dongen, J.C.M.; van Dijk, D.; Mydosh, J.A.

    1981-01-01

    Through low-field ac susceptibility measurements we have determined the depression of the superconducting transition temperature T/sub c/ in palladium hydride (T/sub c/0 = 9.3 K) as a function of impurity concentration x for Cr, Mn, and Fe. For Cr and Fe similar values for the initial T/sub c/ depression were found, i.e., -150 K/at. % Cr and -145 K/at. % Fe. From resistivity experiments we are able to estimate the Kondo temperatures T/sub K/, i.e., T/sub K/approx. =10 K for Cr and T/sub K/approx. =5 K for Fe. Since i.e., T/sub K/approx. =10 K for Cr and T/sub K/approx. =5 K for Fe. Since systems exhibits an enhanced pair breaking as described by the theory of Mueller-Hartmann and Zittartz. In contrast, for Mn the initial T/sub c/ depression is -21 K/at. % and T/sub K/<< T/sub c/0, as can be concluded from our resistivity measurements. This means that Mn in PdH exhibits a temperature-independent pair breaking of the Abrikosov and Gor'kov type. However, at larger Mnx values a shoulder appears in T/sub c/(x). We interpret this enhanced superconductivity, according to the theory of Soukoulis and Grest, as being due to the onset of time correlations and short-range antiferromagnetic ordering between the Mn moments. These interaction effects are a precursor to the spin-glass freezing at a lower temperature T/sub f/. Our results suggest a favorable coexistance of superconductivity with the spin-glass state

  15. 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.

  16. 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

  17. Induction shimming: A new shimming concept for superconductive undulators

    Directory of Open Access Journals (Sweden)

    D. Wollmann

    2008-10-01

    Full Text Available Undulators are the most advanced sources for the generation of synchrotron radiation. The photons generated by a single electron add up coherently along the electron trajectory. In order to do so, the oscillatory motion of the electron has to be in phase with the emitted photons along the whole undulator. Small magnetic errors can cause unwanted destructive interferences. In standard permanent magnet undulators, the magnetic errors are reduced by applying shimming techniques. Superconductive undulators have higher magnetic fields than permanent magnet undulators but shimming is more complex. In this paper it is shown that coupled superconductive loops installed along the surface of the superconductive undulator coil can significantly reduce the destructive effect of the field errors. This new idea might allow the building of undulators with a superior field quality.

  18. Gossamer superconductivity, new paradigm?

    Energy Technology Data Exchange (ETDEWEB)

    Won, Hyekyung [Department of Physics, Hallym University, Chuncheon 200-702 (Korea); Haas, Stephan; Parker, David [Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089-0484 (United States); Maki, Kazumi [Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089-0484 (United States); Max-Planck Institute for the Physics of Complex Systems, Noethnitzer Str. 38, 01187 Dresden (Germany); Dora, Balazs [Department of Physics, Budapest University of Technology and Economics, 1521 Budapest (Hungary); Virosztek, Attila [Department of Physics, Budapest University of Technology and Economics, 1521 Budapest (Hungary); Research Institute for Solid State Physics and Optics, P.O. Box 49, 1525 Budapest (Hungary)

    2006-01-01

    We review our recent works on d-wave density wave (dDW) and gossamer superconductivity (i.e. d-wave superconductivity in the presence of dDW) in high-T{sub c} cuprates and CeCoIn{sub 5}. a) We show that both the giant Nernst effect and the angle dependent magnetoresistance (ADMR) in the pseudogap phases of the cuprates and CeCoIn{sub 5} are manifestations of dDW. b) The phase diagram of high-T{sub c} cuprates is understood in terms of mean field theory, which includes two order parameters {delta}{sub 1} and {delta}{sub 2}, where one order paremeter is from dDW and the other from d-wave superconductivity. c) In the optimally to the overdoped region we find the spatially periodic dDW, an analogue of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, becomes more stable. d) In the underdoped region where {delta}{sub 2}/{delta}{sub 1}<<1 the Uemera relation is obtained within the present model. We speculate that the gossamer superconductivity is at the heart of high-T{sub c} cuprate superconductors, the heavy-fermion superconductor CeCoIn{sub 5} and the organic superconductors {kappa}-(ET){sub 2}Cu(NCS){sub 2} and (TMTSF){sub 2}PF{sub 6}. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Superconducting rf development at ATLAS

    Energy Technology Data Exchange (ETDEWEB)

    Shepard, K.W.; Kedzie, M.; Clifft, B.E. [Argonne National Lab., IL (United States); Roy, A.; Potukuchi, P. [Nuclear Science Centre, New Delhi (India); Givens, J.; Potter, J.; Crandall, K. [AccSys Technology, Inc., Pleasanton, CA (United States); Added, N. [Sao Paulo Univ., SP (Brazil)

    1993-12-31

    The ATLAS superconducting heavy-ion linac began operation in 1978 and has operated nearly continuously since that time, while undergoing a series of upgrades and expansions, the most recent being the ``uranium upgrade`` completed earlier this year and described below. In its present configuration the ATLAS linac consists of an array of 64 resonant cavities operating from 48 to 145 MHz, which match a range of particle velocities .007 < {beta} = v/c < .2. The linac provides approximately 50 MV of effective accelerating potential for ions of q/m > 1/10 over the entire periodic table. Delivered beams include 5 {minus} 7 pnA of {sup 238}U{sup 39+} at 1535 MeV. At present more than 10{sup 6} cavity-hours of operation at surface electric fields of 15 MV/m have been accumulated. Superconducting structure development at ATLAS is aimed at improving the cost/performance of existing low velocity structures both for possible future ATLAS upgrades, and also for heavy-ion linacs at other institutions. An application of particular current interest is to develop structures suitable for accelerating radioactive ion beams. Such structures must accelerate very low charge to mass ratio beams and must also have very large transverse acceptance.

  20. Spin-orbit coupling effects, interactions and superconducting transport in nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Schulz, Andreas

    2010-05-15

    In the present thesis we study the electronic properties of several low dimensional nanoscale systems. In the first part, we focus on the combined effect of spin-orbit coupling (SOI) and Coulomb interaction in carbon nanotubes (CNTs) as well as quantum wires. We derive low energy theories for both systems, using the bosonization technique and obtain analytic expressions for the correlation functions that allow us to compute basically all observables of interest. We first focus on CNTs and show that a four channel Luttinger liquid theory can still be applied when SOI effects are taken into account. Compared to previous formulations, the low-energy Hamiltonian is characterized by different Luttinger parameters and plasmon velocities. Notably, the charge and spin modes are coupled. Our theory allows us to compute an asymptotically exact expression for the spectral function of a metallic carbon nanotube. We find modifications to the previously predicted structure of the spectral function that can in principle be tested by photoemission spectroscopy experiments. We develop a very similar low energy description for an interacting quantum wire subject to Rashba spin-orbit coupling (RSOC). We derive a two component Luttinger liquid Hamiltonian in the presence of RSOC, taking into account all e-e interaction processes allowed by the conservation of total momentum. The effective low energy Hamiltonian includes an additional perturbation due to intraband backscattering processes with band flip. Within a one-loop RG scheme, this perturbation is marginally irrelevant. The fixed point model is then still a two channel Luttinger liquid, albeit with a non standard form due to SOI. Again, the charge and spin mode are coupled. Using our low energy theory, we address the problem of the RKKY interaction in an interacting Rashba wire. The coupling of spin and charge modes due to SO effects implies several modifications, e.g. the explicit dependence of the power-law decay exponent of

  1. Spin-orbit coupling effects, interactions and superconducting transport in nanostructures

    International Nuclear Information System (INIS)

    Schulz, Andreas

    2010-05-01

    In the present thesis we study the electronic properties of several low dimensional nanoscale systems. In the first part, we focus on the combined effect of spin-orbit coupling (SOI) and Coulomb interaction in carbon nanotubes (CNTs) as well as quantum wires. We derive low energy theories for both systems, using the bosonization technique and obtain analytic expressions for the correlation functions that allow us to compute basically all observables of interest. We first focus on CNTs and show that a four channel Luttinger liquid theory can still be applied when SOI effects are taken into account. Compared to previous formulations, the low-energy Hamiltonian is characterized by different Luttinger parameters and plasmon velocities. Notably, the charge and spin modes are coupled. Our theory allows us to compute an asymptotically exact expression for the spectral function of a metallic carbon nanotube. We find modifications to the previously predicted structure of the spectral function that can in principle be tested by photoemission spectroscopy experiments. We develop a very similar low energy description for an interacting quantum wire subject to Rashba spin-orbit coupling (RSOC). We derive a two component Luttinger liquid Hamiltonian in the presence of RSOC, taking into account all e-e interaction processes allowed by the conservation of total momentum. The effective low energy Hamiltonian includes an additional perturbation due to intraband backscattering processes with band flip. Within a one-loop RG scheme, this perturbation is marginally irrelevant. The fixed point model is then still a two channel Luttinger liquid, albeit with a non standard form due to SOI. Again, the charge and spin mode are coupled. Using our low energy theory, we address the problem of the RKKY interaction in an interacting Rashba wire. The coupling of spin and charge modes due to SO effects implies several modifications, e.g. the explicit dependence of the power-law decay exponent of

  2. Zinc substitution effects on the superconducting properties of Nd1.85Ce0.15CuO4-δ

    International Nuclear Information System (INIS)

    Garcia-Vazquez, V.; Mazumdar, S.; Falco, C.M.; Barlingay, C.; Risbud, S.H.

    1990-01-01

    With the discovery of the electron superconductors, a new dimension was added to research in the field of high-temperature superconductivity. Studies of these materials should help elucidate the mechanism responsible for high-temperature superconductivity, as well as improve strategies for finding new superconductors. In this paper, we discuss the superconducting structural properties of Nd 1.85 Ce 0.15 (Cu 1-y Zn y )O 4 as a function of the Zn concentration y. Detailed comparisons with previous results of similar substitution studies in the single-CuO 2 -layer hole superconductor La 1.85 Sr 0.15 CuO 4 also are made. We have found that the non-magnetic element Zn has a detrimental effect on the T'-phase electron superconductor, and that this effect is as strong as in the T-phase hole superconductor. Theoretical implications and the question of electron-hole symmetry are also discussed

  3. Method for the manufacture of a superconductive Nb3Sn layer on a niobium surface for high frequency applications

    International Nuclear Information System (INIS)

    Martens, H.

    1978-01-01

    A manufacturing method for depositing an Nb 3 Sn layer on a niobium surface for high frequency applications comprising developing a tin vapor atmosphere which also contains a highly volatile tin compound in the gaseous state, and holding the portions of the surface which are to be provided with the Nb 3 Sn layer at a temperature of between 900 0 and 1500 0 C for a predetermined period of time to form the Nb 3 Sn layer permitting niobium surfaces of any shape to be provided with Nb 3 Sn layers of high uniformity and quality

  4. 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.

  5. Proximity effect bilayer nano superconducting quantum interference devices for millikelvin magnetometry

    Energy Technology Data Exchange (ETDEWEB)

    Blois, A., E-mail: a.blois@ucl.ac.uk; Rozhko, S.; Romans, E. J. [London Centre for Nanotechnology, University College London (UCL), 17-19 Gordon Street, London WC1H 0AH (United Kingdom); Hao, L.; Gallop, J. C. [National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW (United Kingdom)

    2013-12-21

    Superconducting quantum interference devices (SQUIDs) incorporating thin film nanobridges as weak links have sensitivities approaching that required for single spin detection at 4.2 K. However, due to thermal hysteresis they are difficult to operate at much lower temperatures which hinder their application to many quantum measurements. To overcome this, we have developed nanoscale SQUIDs made from titanium-gold proximity bilayers. We show that their electrical properties are consistent with a theoretical model developed for heat flow in bilayers and demonstrate that they enable magnetic measurements to be made on a sample at system temperatures down to 60 mK.

  6. Saturn Rings Origin: Quantum Trapping of Superconducting Iced Particles and Meissner Effect Lead to the Stable Rings System

    Science.gov (United States)

    Viktorovich Tchernyi, Vladimir

    2018-06-01

    Saturn Rings Origin: Quantum Trapping of Superconducting Iced Particles and Meissner Effect Lead to the Stable Rings System Vladimir V. Tchernyi (Cherny), Andrew Yu. Pospelov Modern Science Institute, SAIBR, Moscow, Russia. E-mail: chernyv@bk.ruAbstractIt is demonstrated how superconducting iced particles of the protoplanetary cloud of Saturn are coming to magnetic equator plane and create the stable enough rings disk. There are two steps. First, after appearance of the Saturn magnetic field due to Meissner phenomenon all particles orbits are moving to the magnetic equator plane. Finally they become distributed as rings and gaps like iron particles around magnet on laboratory table. And they are separated from each other by the magnetic field expelled from them. It takes up to few tens of thousands years with ten meters rings disk thickness. Second, due to their quantum trapping all particles become to be trapped within magnetic well at the magnetic equator plane due to Abrikosov vortex for superconductor. It works even when particles have small fraction of superconductor. During the rings evolution some contribution to the disk also could come from the collision-generated debris of the current moon and from the geysers like it happened due to magnetic coupling of Saturn and Enceladus. The rings are relict of the early days of the magnetic field of Saturn system.

  7. 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

  8. Heat conduction in superconducting lead thallium alloys

    International Nuclear Information System (INIS)

    Ho, J.L.N.

    1975-01-01

    The heat conduction of six strong coupling superconducting Pb--Tl alloy specimens (1 to 20 percent wt Tl) was investigated with the emphasis on the effects of impurities upon the phonon thermal conductivity. All the specimens were annealed at 275 0 C for one week. Results show that the superconducting state phonon thermal conductivity of Pb--Tl is in reasonably good agreement with BRT theory. The strong coupling superconductivity of lead alloys can be handled by scaling the gap parameter using a constant factor. The results presented also show that the phonon thermal conductivity at low temperatures of well annealed lead-thallium alloys can be analyzed in terms of phonon scattering by the grain boundaries, point defects, conduction electrons, and other phonons. The phonon-dislocation scattering was found to be unimportant. The phonon relaxation rate due to point defects is in reasonably good agreement with the Klemens theory for the long range strain field scattering introduced by the thallium impurities. At low temperatures, the normal state phonon thermal conductivity showed an increase in the phonon-electron relaxation rate as the thallium concentration increases. The increase of the phonon-electron relaxation rate is attributed to the change of the Fermi surface caused by the presence of thallium impurity. The effect of the strong electron-phonon coupling character upon the phonon-electron relaxation rate has also been considered in terms of the electron-phonon enhancement factor found in the specific heat measurements

  9. Effect of polar surfaces on organic molecular crystals

    Science.gov (United States)

    Sharia, Onise; Tsyshevskiy, Roman; Kuklja, Maija; University of Maryland College Park Team

    Polar oxide materials reveal intriguing opportunities in the field of electronics, superconductivity and nanotechnology. While behavior of polar surfaces has been widely studied on oxide materials and oxide-oxide interfaces, manifestations and properties of polar surfaces in molecular crystals are still poorly understood. Here we discover that the polar catastrophe phenomenon, known on oxides, also takes place in molecular materials as illustrated with an example of cyclotetramethylene tetranitramine (HMX) crystals. We show that the surface charge separation is a feasible compensation mechanism to counterbalance the macroscopic dipole moment and remove the electrostatic instability. We discuss the role of surface charge on degradation of polar surfaces, electrical conductivity, optical band-gap closure and surface metallization. Research is supported by the US ONR (Grants N00014-16-1-2069 and N00014-16-1-2346) and NSF. We used NERSC, XSEDE and MARCC computational resources.

  10. Effect of Sr substitution on superconductivity in Hg2(Ba1-ySry)2YCu2O8-d (part 1): a neutron powder diffraction study

    OpenAIRE

    Toulemonde, P.; Odier, P.; Bordet, P.; Floch, S. Le; Suard, E.

    2002-01-01

    The effect of Sr chemical pressure on superconductivity was investigated in Hg2(Ba1-ySry)2YCu2O8-d. The samples were synthesized at high pressure-high temperature from y = 0.0 to full substitution, y = 1.0. These Sr-substituted compounds are superconducting, without Ca doping on the Y site, and show an increasing Tc with Sr, reaching 42 K for y = 1.0. A detailed neutron powder diffraction study compares the structural changes induced by this chemical Sr/Ba substitution and the mechanical pres...

  11. Magnetically leviated superconducting bearing

    Science.gov (United States)

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

    1993-01-01

    A magnetically levitated superconducting bearing includes a magnet (2) mounted on a shaft (12) that is rotatable around an axis of rotation and a Type II superconductor (6) supported on a stator (14) in proximity to the magnet (2). The superconductor (6) is positioned so that when it is cooled to its superconducting state in the presence of a magnetic field, it interacts with the magnet (2) to produce an attractive force that levitates the magnet (2) and supports a load on the shaft (12). The interaction between the superconductor (6) and magnet(2) also produces surface screening currents (8) that generate a repulsive force perpendicular to the load. The bearing also has means for maintaining the superconductor at a temperature below its critical temperature (16, 18). The bearing could also be constructed so the magnet (2) is supported on the stator (14) and the superconductor (6) is mounted on the shaft (12). The bearing can be operated by cooling the superconductor (6) to its superconducting state in the presence of a magnetic field.

  12. Superconductivity in all its states

    CERN Multimedia

    Globe Info

    2011-01-01

    Temporary exhibition at the Saint-Genis-Pouilly Tourist Office. For the 100th anniversary of its discovery, take a plunge into the amazing world of superconductivity. Some materials, when cooled down to extreme temperatures, acquire a remarkable property -  they become superconducting. Superconductivity is a rare example of a quantum effect that can be witnessed on the macroscopic scale and is today at the heart of much research. In laboratories, researchers try to gain a better understanding of its origins, study new superconducting materials, explore the phenomenon at the nanometric scale and pursue their indefatigable search for new applications. Monday to Friday: 09:00 a.m. to 12:00 and 2:30 p.m. to 6:30 p.m. Saturday: 10:00 a.m. to 12:00 noon » Open to all – Admission free For further information: +33 (0)4 50 42 29 37

  13. 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.

  14. Effect of the time-dependent coupling on a superconducting qubit-field system under decoherence: Entanglement and Wehrl entropy

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Khalek, S., E-mail: sayedquantum@yahoo.co.uk [Mathematics Department, Faculty of Science, Sohag University, 82524 Sohag (Egypt); The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, Miramare-Trieste (Italy); Berrada, K. [The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, Miramare-Trieste (Italy); Al Imam Mohammad Ibn Saud Islamic University (IMSIU), College of Science, Department of Physics, Riyadh (Saudi Arabia); Eleuch, H. [Department of Physics, McGill University, 3600 rue University, Montreal, QC, H3A 2T8 (Canada); Department of Physics, Université de Montréal, 2900 boul. douard-Montpetit, Montreal, QC, H3T 1J4 (Canada)

    2015-10-15

    The dynamics of a superconducting (SC) qubit interacting with a field under decoherence with and without time-dependent coupling effect is analyzed. Quantum features like the collapse–revivals for the dynamics of population inversion, sudden birth and sudden death of entanglement, and statistical properties are investigated under the phase damping effect. Analytic results for certain parametric conditions are obtained. We analyze the influence of decoherence on the negativity and Wehrl entropy for different values of the physical parameters. We also explore an interesting relation between the SC-field entanglement and Wehrl entropy behavior during the time evolution. We show that the amount of SC-field entanglement can be enhanced as the field tends to be more classical. The studied model of SC-field system with the time-dependent coupling has high practical importance due to their experimental accessibility which may open new perspectives in different tasks of quantum formation processing.

  15. Effects of Armature Winding Segmentation with Multiple Converters on the Short Circuit Torque of 10-MW Superconducting Wind Turbine Generators

    DEFF Research Database (Denmark)

    Liu, Dong; Polinder, Henk; Abrahamsen, Asger Bech

    2017-01-01

    Superconducting synchronous generators (SCSGs) are drawing more attention in large direct-drive wind turbine applications. Despite low weight and compactness, the short circuit torque of an SCSG may be too high for wind turbine constructions due to a large magnetic air gap of an SCSG. This paper...... aims at assessing the effects of armature winding segmentation on reducing the short circuit torque of 10-MW SCSGs. A concept of armature winding segmentation with multiple power electronic converters is presented. Four SCSG designs using different topologies are examined. Results show that armature...... winding segmentation effectively reduce the short circuit torque in all the four SCSG designs when one segment is shorted at the terminal....

  16. An effective 2-band eg model of sulfur hydride H3S for high-Tc superconductivity

    Science.gov (United States)

    Nishiguchi, Kazutaka; Teranishi, Shingo; Miyao, Satoaki; Matsushita, Goh; Kusakabe, Koichi

    To understand high transition temperature (Tc) superconductivity in sulfur hydride H3S, we propose an effective 2-band model having the eg symmetry as the minimal model for H3S. Two eg orbitals centered on a sulfur S atom are chosen for the smallest representation of relevant bands with the van-Hove singularity around the Fermi levels except for the Γ-centered small hole pockets by the sulfur 3 p orbitals. By using the maximally localized Wannier functions, we derive the minimal effective model preserving the body-centered cubic (bcc) crystal symmetry of the H3S phase having the highest Tc ( 203 K under pressures) among the other polymorphs of H3S.

  17. Superconducting Accelerator Magnets

    CERN Document Server

    Mess, K H; Wolff, S

    1996-01-01

    The main topic of the book are the superconducting dipole and quadrupole magnets needed in high-energy accelerators and storage rings for protons, antiprotons or heavy ions. The basic principles of low-temperature superconductivity are outlined with special emphasis on the effects which are relevant for accelerator magnets. Properties and fabrication methods of practical superconductors are described. Analytical methods for field calculation and multipole expansion are presented for coils without and with iron yoke. The effect of yoke saturation and geometric distortions on field quality is studied. Persistent magnetization currents in the superconductor and eddy currents the copper part of the cable are analyzed in detail and their influence on field quality and magnet performance is investigated. Superconductor stability, quench origins and propagation and magnet protection are addressed. Some important concepts of accelerator physics are introduced which are needed to appreciate the demanding requirements ...

  18. Effects of Electric and Magnetic Fields on the Performance of a Superconducting Cavity

    International Nuclear Information System (INIS)

    Gianluigi Ciovati; Peter Kneisel; Jacek Sekutowicz; Waldemar Singer

    2005-01-01

    A special two-cell cavity was designed to obtain surface field distributions suitable for investigation of electric and magnetic field effects on cavity performance. The cavity design and preliminary results were presented in a previous contribution. The bulk niobium cavity was heat-treated in a vacuum furnace at 1250 C to improve thermal conductivity. Three seamless hydroformed Nb/Cu cavities of the same design were fabricated to investigate the role of the electron beam welds located in high field areas. This paper will present RF test results at 2 K for the bulk niobium and one of the seamless cavities

  19. Superconducting Ferromagnetic Nanodiamond

    Czech Academy of Sciences Publication Activity Database

    Zhang, G.; Samuely, T.; Xu, Z.; Jochum, J. K.; Volodin, A.; Zhou, S. Q.; May, P. W.; Onufriienko, O.; Kacmarik, J.; Steele, J. A.; Li, J.; Vanacken, J.; Vacík, Jiří; Szabo, P.; Yuan, H. F.; Roeffaers, M. B. J.; Cerbu, D.; Samuely, P.; Hofkens, J.; Moshchalkov, V.V.

    2017-01-01

    Roč. 11, č. 6 (2017), s. 5358-5366 ISSN 1936-0851 R&D Projects: GA ČR(CZ) GBP108/12/G108; GA MŠk LM2015056 Institutional support: RVO:61389005 Keywords : nanodiamond * superconductivity and ferromagnetism * spin fluctuations * giant positive magnetoresistance * anamalous Hall effect Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders OBOR OECD: Nano-materials (production and properties ) Impact factor: 13.942, year: 2016

  20. AC Josephson effect without superconductivity, and other effects of radio frequency quantum nanoelectronics

    Science.gov (United States)

    Waintal, Xavier; Gaury, Benoit; Weston, Joseph

    With single coherent electron sources and electronic interferometers now available in the lab, the time resolved dynamics of electrons can now be probed directly. I will discuss how a fast raise of voltage propagates inside an electronic interferometer and leads to an oscillating current of well controled frequency. This phenomena is the normal counterpart to the AC josephson effect. I will also briefly advertize our software for computing quantum transport properties, Kwant (http://kwant-project.org) and its time-dependent extension T-Kwant.

  1. Surface effects of underground nuclear explosions

    Energy Technology Data Exchange (ETDEWEB)

    Allen, B.M.; Drellack, S.L. Jr.; Townsend, M.J.

    1997-06-01

    The effects of nuclear explosions have been observed and studied since the first nuclear test (code named Trinity) on July 16, 1945. Since that first detonation, 1,053 nuclear tests have been conducted by the US, most of which were sited underground at the Nevada Test Site (NTS). The effects of underground nuclear explosions (UNEs) on their surroundings have long been the object of much interest and study, especially for containment, engineering, and treaty verification purposes. One aspect of these explosion-induced phenomena is the disruption or alteration of the near-surface environment, also known as surface effects. This report was prepared at the request of the Los Alamos National Laboratory (LANL), to bring together, correlate, and preserve information and techniques used in the recognition and documentation of surface effects of UNEs. This report has several main sections, including pertinent background information (Section 2.0), descriptions of the different types of surface effects (Section 3.0), discussion of their application and limitations (Section 4.0), an extensive bibliography and glossary (Section 6.0 and Appendix A), and procedures used to document geologic surface effects at the NTS (Appendix C). Because a majority of US surface-effects experience is from the NTS, an overview of pertinent NTS-specific information also is provided in Appendix B. It is not within the scope of this report to explore new relationships among test parameters, physiographic setting, and the types or degree of manifestation of surface effects, but rather to compile, summarize, and capture surface-effects observations and interpretations, as well as documentation procedures and the rationale behind them.

  2. Field quality of LHC superconducting dipole magnets

    International Nuclear Information System (INIS)

    Mishra, R.K.

    2003-01-01

    The author reports here the main results of field measurements performed so far on the LHC superconducting dipoles at superfluid helium temperature. The main field strength at injection, collision conditions and higher order multipoles are discussed. Superconducting magnets exhibit additional field imperfections due to diamagnetic properties of superconducting cables, apart from geometric error, saturation of iron yoke and eddy currents error. Dynamic effects on field harmonics, such as field decay at injection and subsequent snap back are also discussed. (author)

  3. 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

  4. FY 1999 report on the results of the superconductive energy application technology development/research on a total system, etc. Survey of potentiality of the commercialization of superconductive technology, effects of the introduction, etc. (Future course of the superconductive technology development in Japan); 1999 nendo chodendo denryoku oryokuyo gijutsu kaihatsu total system nado no kenkyu. Chodendo gijutsu no jitsuyoka kanosei oyobi donyu koka nado no chosa (Nippon ni okeru chodendo gijutsu kaihatsu no kongo no hokosei)

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2000-03-01

    By the use of superconductive technology, the following are aimed at: marked reduction in power loss of electrical equipment and power transmission path, and size/weight reduction in electrical devices by high current/magnetic flux density. The superconductive technology has advantages such as great energy saving effect, CO2 reduction and global environmental preservation. As an example, concerning the superconductive generator now being developed under the New Sunshine Project, power loss can be reduced by half, and by the use of high magnetic field, size/weight can be reduced such as reduction in rotor diameter and reduction in weight by half. Further, as an innovative system, cited are the superconducting magnetic energy storage system (SMES) and flywheel energy storage system. The superconducting magnetic levitation railway, medical use MRI, etc. have also innovativity which is difficult to get in the conventional technology. Effects are also expected of introducing the process development using superconducting magnet such as magnetic separation, electromagnetic metallurgy, electromagnetic agitation and monocrytal growth convection control. Also cited is Josephson electronic device. High performance SQUID in bio-magnetic/non-destructive inspection is also expected to be developed. (NEDO)

  5. Spin Hall effect by surface roughness

    KAUST Repository

    Zhou, Lingjun; Grigoryan, Vahram L.; Maekawa, Sadamichi; Wang, Xuhui; Xiao, Jiang

    2015-01-01

    induced by surface roughness subscribes only to the side-jump contribution but not the skew scattering. The paradigm proposed in this paper provides the second, not if only, alternative to generate a sizable spin Hall effect.

  6. Ultrasonic attenuation in superconducting zinc

    International Nuclear Information System (INIS)

    Auluck, S.

    1978-01-01

    The differences in the Zn ultrasonic attenuation data of different workers are analyzed. The superconducting energy gaps deduced from our analysis of the ultrasonic-attenuation data of Cleavelin and Marshall are consistent with the gaps deduced from the knowledge of the Fermi surface and the electron-phonon mass enhancement factor

  7. Neutron irradiation effects on superconducting and stabilizing materials for fusion magnets

    International Nuclear Information System (INIS)

    Maurer, W.

    1984-05-01

    Available low-temperature neutron irradiation data for the superconductors NbTi and Nb 3 Sn and the stabilization materials Cu and Al are collected and maximum tolerable doses for these materials are defined. A neutron flux in a reactor of about 10 9 n/cm 2 s at the magnet position is expected. However, in fusion experiments the flux can be higher by an order of magnitude or more. The energy spectrum is similar to a fission reactor. A fluence of about 10 18 n/cm 2 results during the lifetime of a fusion magnet (about 20 full power years). At this fluence and energy spectrum no severe degradation of the superconducting properties of NbTi and Nb 3 Sn will occur. But the radiation-induced resistivity is for Cu about a twentieth of the room temperature resistivity and a tenth for Al. (orig.) [de

  8. 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

  9. 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

  10. 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

  11. Spin Hall effect by surface roughness

    KAUST Repository

    Zhou, Lingjun

    2015-01-08

    The spin Hall and its inverse effects, driven by the spin orbit interaction, provide an interconversion mechanism between spin and charge currents. Since the spin Hall effect generates and manipulates spin current electrically, to achieve a large effect is becoming an important topic in both academia and industries. So far, materials with heavy elements carrying a strong spin orbit interaction, provide the only option. We propose here a new mechanism, using the surface roughness in ultrathin films, to enhance the spin Hall effect without heavy elements. Our analysis based on Cu and Al thin films suggests that surface roughness is capable of driving a spin Hall angle that is comparable to that in bulk Au. We also demonstrate that the spin Hall effect induced by surface roughness subscribes only to the side-jump contribution but not the skew scattering. The paradigm proposed in this paper provides the second, not if only, alternative to generate a sizable spin Hall effect.

  12. Vortex dynamics in ferromagnetic/superconducting bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Cieplak, M.Z.; Adamus, Z. [Polish Acad Sci, Inst Phys, PL-02668 Warsaw, (Poland); Konczykowski, M. [CEA, DSM, DRECAM, Lab Solides Irradies, Ecole Polytechnique, CNRS-UMR 7642, F-91128 Palaiseau (France); Zhu, L.Y.; Chien, C.L. [Johns Hopkins Univ, Dept Phys and Astron, Baltimore, MD 21218 (United States)

    2008-07-01

    The dependence of vortex dynamics on the geometry of magnetic domain pattern is studied in the superconducting/ferromagnetic bilayers, in which niobium is a superconductor, and Co/Pt multilayer with perpendicular magnetic anisotropy serves as a ferromagnetic layer. Magnetic domain patterns with different density of domains per surface area and different domain size, w, are obtained for Co/Pt with different thickness of Pt. The dense patterns of domains with the size comparable to the magnetic penetration depth (w {>=} {lambda}) produce large vortex pinning and smooth vortex penetration, while less dense patterns with larger domains (w {>=}{>=} {lambda}) enhance pinning less effectively and result in flux jumps during flux motion. (authors)

  13. Effect of processing conditions and methods on residual stress in CeO2 buffer layers and YBCO superconducting films

    International Nuclear Information System (INIS)

    Xiong Jie; Qin Wenfeng; Cui Xumei; Tao Bowan; Tang Jinlong; Li Yanrong

    2006-01-01

    CeO 2 layers have been fabricated by pulsed laser deposition (PLD) technique on (1 1 0 2) sapphire substrate. Microstructure of CeO 2 layers is characterized by X-ray diffraction as functions of substrate temperature. The effects of the substrate temperature on the residual stress have been studied. The results show that residual stress in CeO 2 film decreased with increasing substrate temperature, not the same development tendency as that of thermal stress. This means that the thermal stress is only a fraction of the residual stress. Moreover, YBCO superconducting films were prepared by direct current (DC) sputtering and pulsed laser deposition (PLD) technique. The residual stress and thermal stress of both YBCO films were measured. PLD processing apparently generated higher intrinsic compressive stresses in comparison to DC sputtering

  14. Effect of cooldown and residual magnetic field on the performance of niobium–copper clad superconducting radio-frequency cavity

    International Nuclear Information System (INIS)

    Dhakal, Pashupati; Ciovati, Gianluigi

    2017-01-01

    Here, we present the results of rf measurements on a niobium–copper clad superconducting radio-frequency cavity with different cooldown conditions and residual magnetic field in a vertical test Dewar in order to explore the effect of thermal current induced magnetic field and its trapping on the performance of the cavity. The residual resistance, extracted from the Q 0 (T) curves in the temperature range 4.3–1.5 K, showed no dependence on a temperature gradient along the cavity during the cooldown across the critical temperature up to ~50 K m –1 . The rf losses due to the trapping of residual magnetic field during the cavity cooldown were found to be ~4.3 nΩ μT –1 , comparable to the values measured in bulk niobium cavities. An increase of residual resistance following multiple cavity quenches was observed along with evidence of trapping of magnetic flux generated by thermoelectric currents.

  15. Coupling a single nitrogen-vacancy center with a superconducting qubit via the electro-optic effect

    Science.gov (United States)

    Li, Chang-Hao; Li, Peng-Bo

    2018-05-01

    We propose an efficient scheme for transferring quantum states and generating entangled states between two qubits of different nature. The hybrid system consists of a single nitrogen-vacancy (NV) center and a superconducting (SC) qubit, which couple to an optical cavity and a microwave resonator, respectively. Meanwhile, the optical cavity and the microwave resonator are coupled via the electro-optic effect. By adjusting the relative parameters, we can achieve high-fidelity quantum state transfer as well as highly entangled states between the NV center and the SC qubit. This protocol is within the reach of currently available techniques, and may provide interesting applications in quantum communication and computation with single NV centers and SC qubits.

  16. Pressure effect on crystal structure and superconductivity of La0.8Th0.2FeAsO

    International Nuclear Information System (INIS)

    Kumar, Ravhi S.; Antonio, Daniel; Cornelius, Andrew L.; Zhao, Yusheng; Kanagaraj, M.; Arumugam, S.; Sinogeikin, Stanislav; Prakash, J.; Thakur, Gohil S.; Ganguli, A.K.; Hartmann, Thomas

    2011-01-01

    We have studied the effect of pressure on the superconducting transition temperature (T c ) of thorium doped La 1-x Th x FeAsO (x = 0.2) superconductor under hydrostatic pressures up to 1.6 GPa by resistivity and magnetization experiments. Application of pressure increases the T c to 31 K with a positive pressure coefficient of ∝1 K/GPa. Low temperature X-ray diffraction studies performed at 7.8 K at high pressures show no pressure induced structural changes and the tetragonal P4/nmm structure is found to persist up to 31 GPa. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Nucleation of superconductivity under rapid cycling of an electric field

    International Nuclear Information System (INIS)

    Bandyopadhyay, Malay

    2008-01-01

    The effect of an externally applied high-frequency oscillating electric field on the critical nucleation field of superconductivity in the bulk as well as at the surface of a superconductor is investigated in detail in this work. Starting from the linearized time-dependent Ginzburg-Landau (TDLG) theory, and using the variational principle, I have shown the analogy between a quantum harmonic oscillator with that of the nucleation of superconductivity in the bulk and a quantum double oscillator with that of the nucleation at the surface of a finite sample. The effective Hamiltonian approach of Cook et al (1985 Phys. Rev. A 31 564) is employed to incorporate the effect of an externally applied highly oscillating electric field. The critical nucleation field ratio is also calculated from the ground state energy method. The results obtained from these two approximate theories agree very well with the exact results for the case of an undriven system, which establishes the validity of these two approximate theories. It is observed that the highly oscillating electric field actually increases the bulk critical nucleation field (H c 2 ) as well as the surface critical nucleation field (H c 3 ) of superconductivity as compared to the case of absent electric field (ε 0 = 0). But the externally applied rapidly oscillating electric field accentuates the surface critical nucleation field more than the bulk critical nucleation field, i.e. the increase of H c 3 is 1.6592 times larger than that of H c 2

  18. Effects of ion sputtering on semiconductor surfaces

    International Nuclear Information System (INIS)

    McGuire, G.E.

    1978-01-01

    Ion beam sputtering has been combined with Auger spectroscopy to study the effects of ion beams on semiconductor surfaces. Observations on the mass dependence of ion selective sputtering of two component systems are presented. The effects of ion implantation are explained in terms of atomic dilution. Experimental data are presented that illustrate the super-position of selective sputtering and implantation effects on the surface composition. Sample reduction from electron and ion beam interaction is illustrated. Apparent sample changes which one might observe from the effects of residual gas contamination and electric fields are also discussed. (Auth.)

  19. Superconducting inductive displacement detection of a microcantilever

    Science.gov (United States)

    Vinante, A.

    2014-07-01

    We demonstrate a superconducting inductive technique to measure the displacement of a micromechanical resonator. In our scheme, a type I superconducting microsphere is attached to the free end of a microcantilever and approached to the loop of a dc Superconducting Quantum Interference Device (SQUID) microsusceptometer. A local magnetic field as low as 100 μT, generated by a field coil concentric to the SQUID, enables detection of the cantilever thermomechanical noise at 4.2 K. The magnetomechanical coupling and the magnetic spring are in good agreement with image method calculations assuming pure Meissner effect. These measurements are relevant to recent proposals of quantum magnetomechanics experiments based on levitating superconducting microparticles.

  20. 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

  1. Effects of surfaces on resistor percolation.

    Science.gov (United States)

    Stenull, O; Janssen, H K; Oerding, K

    2001-05-01

    We study the effects of surfaces on resistor percolation at the instance of a semi-infinite geometry. Particularly we are interested in the average resistance between two connected ports located on the surface. Based on general grounds as symmetries and relevance we introduce a field theoretic Hamiltonian for semi-infinite random resistor networks. We show that the surface contributes to the average resistance only in terms of corrections to scaling. These corrections are governed by surface resistance exponents. We carry out renormalization-group improved perturbation calculations for the special and the ordinary transition. We calculate the surface resistance exponents phiS and phiS(infinity) for the special and the ordinary transition, respectively, to one-loop order.

  2. Effect of β-phase decomposition on the superconducting properties of Ti-27 at percent Nb solid solution

    International Nuclear Information System (INIS)

    Hariharan, Y.; Valsakumar, M.C.; Radhakrishnan, T.S.

    1980-01-01

    The effect of β-phase decomposition on the superconducting transition temperature (Tsub(c)) of a Ti-27 at % Nb solid solution has been studied by the resistive technique. The samples were β-quenched from 900deg C and cold rolled to 30%. Annealing at 400deg C for various times upto 15 hours causes Ti-rich phases to precipitate out of the matrix. This decomposition of the β-phase is seen to lead to a progressive enhancement in Tsub(c) from 7.7 K in the β-quenched state to 8.8 K in the sample annealed for 15 hours; further, the width Δ Tsub(c) of the superconducting transition (=90 mK in the β-quenched state) reaches a maximum value (360 mK) for a 10-hour anneal. The conjecture that the enhancement in Tsub(c) occurs as a result of precipitation and the consequent enrichment of the Nb content of the matrix is examined. It is estimated that to account for the large observed enhancement of Tsub(c), the Nb enrichment would have to be of the order of 5-6%; whereas a TEM study has revealed the enrichment to be of the order of 0.2% only. Analysis of the X-ray diffractograms is also not in favour of this hypothesis. Hence alternative mechanisms to account for the Tsub(c) enhancement are currently under investigation. Also discussed is the calculation of Tsub(c) using McMillan's formula for strongly coupled superconductors. (author)

  3. Surface effects in controlled thermonuclear fusion

    International Nuclear Information System (INIS)

    Kaminsky, M.

    1975-08-01

    During the operation of large size plasma facilities and future controlled thermonuclear fusion reactors the surfaces of such major components as container walls, beam limiters, diverter walls and beam-dump walls of the injector region will be exposed to particle and photon bombardment from primary plasma radiations and from secondary radiations. Such radiations can cause, for example, physical and chemical sputtering, blistering, particle- and photon-impact induced desorption, secondary electron and x-ray emission, backscattering, nuclear reactions, photo-decomposition of surface compounds, photocatalysis, and vaporization. Such effects in turn can (a) seriously damage and erode the bombarded surface and (b) release major quantities of impurities which will contaminate the plasma. The effects of some of the major surface phenomena on the operation of plasma facilities and future fusion reactors are discussed

  4. 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.

  5. Vibration of Piezoelectric Nanowires Including Surface Effects

    Directory of Open Access Journals (Sweden)

    R. Ansari

    2014-04-01

    Full Text Available In this paper, surface and piezoelectric effects on the vibration behavior of nanowires (NWs are investigated by using a Timoshenko beam model. The electric field equations and the governing equations of motion for the piezoelectric NWs are derived with the consideration of surface effects. By the exact solution of the governing equations, an expression for the natural frequencies of NWs with simply-supported boundary conditions is obtained. The effects of piezoelectricity and surface effects on the vibrational behavior of Timoshenko NWs are graphically illustrated. A comparison is also made between the predictions of Timoshenko beam model and those of its Euler-Bernoulli counterpart. Additionally, the present results are validated through comparison with the available data in the literature.

  6. Advances in surface treatments: Technology, applications, effects

    International Nuclear Information System (INIS)

    Niku-Lari, A.

    1987-01-01

    An international handbook has been produced to include all aspects of residual stresses, including the theoretical background, effects of residual stresses, measurement and calculation and quantitative assessment of residual stress effects. Techniques for altering residual stresses, particularly surface treatments, are discussed. Up to date information on the state of the art is presented. (UK)

  7. Surface and interface effects in VLSI

    CERN Document Server

    Einspruch, Norman G

    1985-01-01

    VLSI Electronics Microstructure Science, Volume 10: Surface and Interface Effects in VLSI provides the advances made in the science of semiconductor surface and interface as they relate to electronics. This volume aims to provide a better understanding and control of surface and interface related properties. The book begins with an introductory chapter on the intimate link between interfaces and devices. The book is then divided into two parts. The first part covers the chemical and geometric structures of prototypical VLSI interfaces. Subjects detailed include, the technologically most import

  8. Collective modes in superconducting rhombohedral graphite

    Energy Technology Data Exchange (ETDEWEB)

    Kauppila, Ville [O.V. Lounasmaa Laboratory, Aalto University (Finland); Hyart, Timo; Heikkilae, Tero [University of Jyvaeskylae (Finland)

    2015-07-01

    Recently it was realized that coupling particles with a Dirac dispersion (such as electrons in graphene) can lead to a topologically protected state with flat band dispersion. Such a state could support superconductivity with unusually high critical temperatures. Perhaps the most promising way to realize such coupling in real materials is in the surface of rhombohedrally stacked graphite. We consider collective excitations (i.e. the Higgs modes) in surface superconducting rhombohedral graphite. We find two amplitude and two phase modes corresponding to the two surfaces of the graphite where the superconductivity lives. We calculate the dispersion of these modes. We also derive the Ginzburg-Landau theory for this material. We show that in superconducting rhombohedral graphite, the collective modes, unlike in conventional BCS superconductors, give a large contribution to thermodynamic properties of the material.

  9. Effect of impact surface in equestrian falls

    OpenAIRE

    Clark, J. Michio; Post, Andrew; Connor, Thomas A.; Hoshizaki, Thomas Blaine; Gilchrist, M. D.

    2016-01-01

    This study examines the effect of impact surface on head kinematic response and maximum principal strain (MPS) for equestrian falls. A helmeted Hybrid III headform was dropped unrestrained onto three impact surfaces of different stiffness (steel, turf and sand) and three locations. Peak resultant linear acceleration, rotational acceleration and duration of the impact events were measured. A finite element brain model was used to calculate MPS. The results revealed that drops onto steel produc...

  10. Activities on superconductivity cavities at the IPN Orsay, in collaboration with: LAL-CNRS/IN2P3, Orsay; CEA-DAPNIA/SEA, Gif-sur-Yvette; DESY, Hamburg

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1995-12-31

    Different topics concerning superconducting cavity resonators are overviewed. Field emission phenomena and surface effects are discussed in detail. Thermometers, cryostats and radiation mapping instruments are also concerned. 6 items are indexed separately for INIS database. (K.A.).

  11. Activities on superconductivity cavities at the IPN Orsay, in collaboration with: LAL-CNRS/IN2P3, Orsay; CEA-DAPNIA/SEA, Gif-sur-Yvette; DESY, Hamburg

    International Nuclear Information System (INIS)

    1995-01-01

    Different topics concerning superconducting cavity resonators are overviewed. Field emission phenomena and surface effects are discussed in detail. Thermometers, cryostats and radiation mapping instruments are also concerned. 6 items are indexed separately for INIS database. (K.A.)

  12. Effect of Cleaving Temperature on the Surface and Bulk Fermi Surface of Sr2RuO4 Investigated by High Resolution Angle-Resolved Photoemission

    International Nuclear Information System (INIS)

    Liu Shan-Yu; Zhang Wen-Tao; Weng Hong-Ming; Zhao Lin; Liu Hai-Yun; Jia Xiao-Wen; Liu Guo-Dong; Dong Xiao-Li; Zhang Jun; Dai Xi; Fang Zhong; Zhou Xing-Jiang; Mao Zhi-Qiang; Chen Chuang-Tian; Xu Zu-Yan

    2012-01-01

    High resolution angle-resolved photoemission measurements are carried out to systematically investigate the effect of cleaving temperature on the electronic structures and Fermi surfaces of Sr 2 RuO 4 . Unlike previous reports, which found that a high cleaving temperature can suppress the surface Fermi surface, we find that the surface Fermi surface remains obvious and strong in Sr 2 RuO 4 cleaved at high temperature, even at room temperature. This indicates that cleaving temperature is not a key effective factor in suppressing surface bands. On the other hand, the bulk bands can be enhanced in an aged surface of Sr 2 RuO 4 that has been cleaved and held for a long time. We have also carried out laser ARPES measurements on Sr 2 RuO 4 by using a vacuum ultra-violet laser (photon energy at 6.994 eV) and found an obvious enhancement of bulk bands even for samples cleaved at low temperature. This information is important for realizing an effective approach to manipulating and detecting the surface and bulk electronic structure of Sr 2 RuO 4 . In particular, the enhancement of bulk sensitivity, along with the super-high instrumental resolution of VUV laser ARPES, will be advantageous in investigating fine electronic structure and superconducting properties of Sr 2 RuO 4 in the future. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  13. Radiation effects limits on superconducting magnets: data base for copper stabilizers

    International Nuclear Information System (INIS)

    Guinan, M.W.

    1986-01-01

    The objective of this work is to quantify the changes which occur in the magnetoresistivity of coppers (having various purities and pretreatments) at fields up to 12T during the course of sequential neutron irradiations at 4K and anneals to room temperature. In conjunction with work by Klabunde and Coltman at ORNL, the results should lead to engineering design data for the stabilizers of superconducting magnets in fusion reactors. These magnets are expected to be irradiated during reactor operation and warmed to room temperature periodically during maintenance. Two of eight differently prepared copper stabilizer samples, previously irradiated in the RTNS-II at LLNL, the IPNS-1 at ANL, and the BSR at ONRL, have been irradiated to a fluence of 1.33 x 10 22 n/m 2 at RNTS-II. During the course of the irradiation the samples were periodically removed (without warming) for measurements of the transverse magnetoresistance and returned for continued irradiation. This experiment extends the range of neutron irradiation induced resistivity by a factor of five over the previous experiments. A simple model is developed which reproduces the magnetoresistance results of all the experiments to an accuracy of 2.5%

  14. Effect of fluorination on the structure and superconducting properties of the Hg-1201 phase

    International Nuclear Information System (INIS)

    Abakumov, A.M.; Aleshin, V.A.; Antipov, E.V.; Mikhajlova, D.A.; Putilin, S.N.; Rozova, M.G.; Aksenov, V.L.; Balagurov, A.M.

    1997-01-01

    A fluorination of the reduced Hg-1201 phase with T c =61 K carried out with XeF 2 resulted first in an increase in T c up to 97 K and then in a decrease and even a suppression of superconductivity due to overdoping. Neutron power refinement performed on fluorinated HgBa 2 CuO 4 F δ samples showed twice the amount of extra fluorine (δ≅0.24 and 0.32) in comparison with those for the oxygenated Hg-1201 phases with close T c (δ=0.12 and 0.19). This supports the ionic model of the hole doping in the Hg-1201: 2 holes per extra oxygen and 1 hole per extra fluorine. The exchange of extra oxygen for a double amount of fluorine extends the shortening of the apical Cu-O bond distances, while the in-plane distances, as well as T c , do not vary. These results show that the structural nature of T c variation in Hg-1201 under high pressure can be mainly due to the compression of the in-plane Cu-O bond distances

  15. Effect of malic acid doping on the structural and superconducting properties of MgB2

    International Nuclear Information System (INIS)

    Ojha, N.; Sudesh; Stuti Rani; Varma, G.D.

    2010-01-01

    The samples have been prepared via standard solid state reaction route with nominal compositions MgB 2 + x wt% malic acid (x = 0, 5 and 10) by sintering at two different temperatures: 800 and 850 deg C in argon atmosphere. Improvement in upper critical fields (H c2 ) and irreversibility field (H irr ) of doped samples as compared to undoped samples have been observed. At 10 K, critical current densities (J c ) of the 5 and 10 wt% malic acid doped MgB 2 samples sintered at 850 deg C have higher values as compared to undoped sample sintered at the same temperature in the fields greater than 3 T. However, J c values of 5 wt% malic acid doped sample are higher than 10 wt% doped sample in the entire applied field region (0 - 7 T). In case of the samples sintered at 800 deg C improvement in J c values of 5 wt% doped sample have been found in entire field region as compared to undoped sample. On the other hand we see deterioration in J c values of 10 wt% doped samples sintered at 800 deg C as compared to undoped samples sintered at same temperature. The correlations between structural and superconducting properties will be described and discussed in this paper. (author)

  16. Simulations of the effects of a superconducting damping wiggler on a short bunched electron beam at ANKA

    Energy Technology Data Exchange (ETDEWEB)

    Gethmann, Julian; Bernhard, Axel; Blomley, Edmund; Hillenbrand, Steffen; Mueller, Anke-Susanne; Smale, Nigel [Karlsruher Institut fuer Technologie (KIT) (Germany); Zolotarev, Konstantin [Budker Institute of Nuclear Physics (Russian Federation)

    2016-07-01

    (As a part of the CLIC collaboration) A CLIC damping wiggler prototype has been installed at the ANKA synchrotron light source in order to validate the technical design of the 3 T superconducting conduction cooled wiggler and its cryostat and to cary out studies on beam dynamical aspects including collective effects. The latter one will be the main focus in this talk. Collective effects that will occur in damping rings are an issue in ANKA's short bunch operation as well. To simulate these effects the accelerator's model including its insertion device has to be very accurate. Such a model of the ANKA storage ring in short bunch operation mode has been developed in elegant. Simulations with the damping wiggler switched on and off have been performed in order to investigate effects of the wiggler on different machine parameters. These new results will be discussed with regard to the question if on the one hand the wiggler could be used for diagnostic purposes and if on the other hand the wiggler's impact on the beam dynamics is changed by the collective effects.

  17. Superconducting fluctuation effect in CaFe0.88Co0.12AsF

    Science.gov (United States)

    Xiao, H.; Gao, B.; Ma, Y. H.; Li, X. J.; Mu, G.; Hu, T.

    2016-11-01

    Out-of-plane angular dependent torque measurements were performed on CaFe0.88Co0.12AsF single crystals. Superconducting fluctuations, featured by magnetic field enhanced and exponential temperature dependent diamagnetism, are observed above the superconducting transition temperature T c, which is similar to that of cuprate superconductors, but less pronounced. In addition, the ratio of T c versus superfluid density follows well the Uemura line of high-T c cuprates, which suggests the exotic nature of the superconductivity in CaFe0.88Co0.12AsF.

  18. Biofilm Surface Density Determines Biocide Effectiveness

    Directory of Open Access Journals (Sweden)

    Sara Bas

    2017-12-01

    Full Text Available High resistance of biofilms for chemical challenges is a serious industrial and medical problem. In this work a gradient of surface covered with biofilm has been produced and correlated to the effectiveness of different commercially available oxidative biocides. The results for thin Escherichia coli biofilms grown in rich media supplemented with glucose or lactose on glass or poly methyl methacrylate surfaces indicate that the effectiveness of hydrogen peroxide or chlorine dioxide and quaternary ammonium compounds is inversely proportional to the fraction of the surface covered with the biofilm. In areas where biofilm covered more than 90% of the available surface the biocide treatment was inefficient after 60 min of incubation. The combined effect of oxidant and surfactant increased the effectiveness of the biocide. On the other hand, the increased biofilm viscoelasticity reduced biocide effectiveness. The results emphasize differential biocide effectiveness depending on the fraction of the attached bacterial cells. The results suggest that biofilm biocide resistance is an acquired property that increases with biofilm maturation. The more dense sessile structures present lower log reductions compared to less dense ones.

  19. Foreword: Focus on Superconductivity in Semiconductors

    Directory of Open Access Journals (Sweden)

    Yoshihiko Takano

    2008-01-01

    Full Text Available Since the discovery of superconductivity in diamond, much attention has been given to the issue of superconductivity in semiconductors. Because diamond has a large band gap of 5.5 eV, it is called a wide-gap semiconductor. Upon heavy boron doping over 3×1020 cm−3, diamond becomes metallic and demonstrates superconductivity at temperatures below 11.4 K. This discovery implies that a semiconductor can become a superconductor upon carrier doping. Recently, superconductivity was also discovered in boron-doped silicon and SiC semiconductors. The number of superconducting semiconductors has increased. In 2008 an Fe-based superconductor was discovered in a research project on carrier doping in a LaCuSeO wide-gap semiconductor. This discovery enhanced research activities in the field of superconductivity, where many scientists place particular importance on superconductivity in semiconductors.This focus issue features a variety of topics on superconductivity in semiconductors selected from the 2nd International Workshop on Superconductivity in Diamond and Related Materials (IWSDRM2008, which was held at the National Institute for Materials Science (NIMS, Tsukuba, Japan in July 2008. The 1st workshop was held in 2005 and was published as a special issue in Science and Technology of Advanced Materials (STAM in 2006 (Takano 2006 Sci. Technol. Adv. Mater. 7 S1.The selection of papers describe many important experimental and theoretical studies on superconductivity in semiconductors. Topics on boron-doped diamond include isotope effects (Ekimov et al and the detailed structure of boron sites, and the relation between superconductivity and disorder induced by boron doping. Regarding other semiconductors, the superconducting properties of silicon and SiC (Kriener et al, Muranaka et al and Yanase et al are discussed, and In2O3 (Makise et al is presented as a new superconducting semiconductor. Iron-based superconductors are presented as a new series of high

  20. 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

  1. Surface effects on the red giant branch

    Science.gov (United States)

    Ball, W. H.; Themeßl, N.; Hekker, S.

    2018-05-01

    Individual mode frequencies have been detected in thousands of individual solar-like oscillators on the red giant branch (RGB). Fitting stellar models to these mode frequencies, however, is more difficult than in main-sequence stars. This is partly because of the uncertain magnitude of the surface effect: the systematic difference between observed and modelled frequencies caused by poor modelling of the near-surface layers. We aim to study the magnitude of the surface effect in RGB stars. Surface effect corrections used for main-sequence targets are potentially large enough to put the non-radial mixed modes in RGB stars out of order, which is unphysical. Unless this can be circumvented, model-fitting of evolved RGB stars is restricted to the radial modes, which reduces the number of available modes. Here, we present a method to suppress gravity modes (g-modes) in the cores of our stellar models, so that they have only pure pressure modes (p-modes). We show that the method gives unbiased results and apply it to three RGB solar-like oscillators in double-lined eclipsing binaries: KIC 8410637, KIC 9540226 and KIC 5640750. In all three stars, the surface effect decreases the model frequencies consistently by about 0.1-0.3 μHz at the frequency of maximum oscillation power νmax, which agrees with existing predictions from three-dimensional radiation hydrodynamics simulations. Though our method in essence discards information about the stellar cores, it provides a useful step forward in understanding the surface effect in RGB stars.

  2. Surface layer effects on waste glass corrosion

    International Nuclear Information System (INIS)

    Feng, X.

    1993-01-01

    Water contact subjects waste glass to chemical attack that results in the formation of surface alteration layers. Two principal hypotheses have been advanced concerning the effect of surface alteration layers on continued glass corrosion: (1) they act as a mass transport barrier and (2) they influence the chemical affinity of the glass reaction. In general, transport barrier effects have been found to be less important than affinity effects in the corrosion of most high-level nuclear waste glasses. However, they can be important under some circumstances, for example, in a very alkaline solution, in leachants containing Mg ions, or under conditions where the matrix dissolution rate is very low. The latter suggests that physical barrier effect may affect the long-term glass dissolution rate. Surface layers influence glass reaction affinity through the effects of the altered glass and secondary phases on the solution chemistry. The reaction affinity may be controlled by various precipitates and crystalline phases, amorphous silica phases, gel layer, or all the components of the glass. The surface alteration layers influence radionuclide release mainly through colloid formation, crystalline phase incorporation, and gel layer retention. This paper reviews current understanding and uncertainties

  3. 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.

  4. 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

  5. Effect of a pseudogap on Tc and on the superconducting order parameter

    International Nuclear Information System (INIS)

    Rodriguez Nunez, J.J.; Reimer Romero, J.J.; Valera, M.; Schmidt, A.A.

    2007-09-01

    We further develop the pseudogap model proposed by J.L. Tallon and J.W. Loram, Physica C 349, 53-68 (2001). For the pseudogap order parameter we choose a particular form which reproduces the main features of the high temperature superconductor (HTSC) phase diagram which depends on carrier number, n. For fitting the key features of the cuprate oxides we have sensible parameters at our disposal, namely, α, which fixes the density where the pseudogap order parameter is maximum, α' which allows us to display the T c vs n curve and E go which gives us the value of the pseudogap. We have reproduced in a qualitative fashion the main details of the experimental data given in the work of Suryadijaya, T. Sasaqawa, and H. Takagi, Physica C 426-431, 402-406 (2005). Our main results are the following: To have decreased the value of T c with respect to the 'free' case, namely, E go = 0, namely, when the pseudogap order parameter is not present. To have obtained the maximum of T c by choosing α' ≠ 0. To have chosen the minimum value of T c inside the pseudogap region, namely, in the region where the pseudogap parameter is a maximum. To have bounded the region of the superconducting dome by choosing the value of E g. In short, we have proposed a phenomenological form for the pseudogap energy, which depends on carrier number and which reproduces in a qualitative way the results of Suryadijaya, T. Sasaqawa and H. Takagi, Physica C 426-431, 402-406 (2005). Consequently, we conclude that the pseudogap is necessary for HTSC. (author)

  6. Analysis of the effect of imbalanced flow on the KSTAR's superconducting magnet

    International Nuclear Information System (INIS)

    Lee, H. J.; Park, Y. M.; Park, D. S.

    2014-01-01

    The KSTAR superconducting (SC) magnets are cable-in-conduit-conductor (CICC) type magnets, which have a hundred parallel and twisted SC strands in a square conduit with a porosity of 0.36. They are cooled by the forced flow of supercritical helium with a 2 bar pressure drop. A flow imbalance test of the magnet cooling channels, one of the quality assurance processes, was conducted using Ar gas at room temperature during the magnet's manufacture, and was carried out again after assembly. In those tests, the flow imbalance was measured to be within at most ±10% for the all cooling channels, which satisfied the criterion (±20%). During individual tests of the magnets, the tendency of the flow imbalance showed that the mass flow rate of the upper (U) magnets PF1, PF2, PF5, PF6, and PF7 was higher than that of the lower (L) magnets. On the other hand, the mass flow rate of the upper magnets PF3 and PF4 was lower than that of the lower magnets. After assembly, this imbalance became more serious, and the measured mass flow rate of the upper magnets was higher than that of lower magnet at the PF2, PF3 PF4, and PF5 magnets. This imbalance can influence the temperature and the pressure of supercritical helium, as well as accelerate reversal flow and limit operating performance. In this paper, the helium behavior is analyzed and is explained to be due to the flow imbalance in the PF magnet.

  7. 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

  8. 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.

  9. Superconducting augmented rail gun (SARG)

    International Nuclear Information System (INIS)

    Homan, C.G.; Cummings, C.E.; Fowler, C.M.

    1986-01-01

    Superconducting augmentation consists of a superconducting coil operating in the persistent mode closely coupled magnetically with a normally conducting rail gun. A theoretical investigation of the effect of this system on a rail gun has shown that two benefits occur. Projectile velocities and launch efficiencies increase significantly depending on the magnetic coupling between the rail and augmentation circuits. Previous work evaluated an idealized system by neglecting energy dissipation effects. In this paper, the authors extend the analysis to include the neglected terms and show improved actual launch efficiencies for the SARG configuration. In this paper, the authors discuss details of projectile design in depth and present preliminary results of rail gun performance

  10. Color superconductivity in dense quark matter

    International Nuclear Information System (INIS)

    Alford, Mark G.; Schmitt, Andreas; Rajagopal, Krishna; Schaefer, Thomas

    2008-01-01

    Matter at high density and low temperature is expected to be a color superconductor, which is a degenerate Fermi gas of quarks with a condensate of Cooper pairs near the Fermi surface that induces color Meissner effects. At the highest densities, where the QCD coupling is weak, rigorous calculations are possible, and the ground state is a particularly symmetric state, the color-flavor locked (CFL) phase. The CFL phase is a superfluid, an electromagnetic insulator, and breaks chiral symmetry. The effective theory of the low-energy excitations in the CFL phase is known and can be used, even at more moderate densities, to describe its physical properties. At lower densities the CFL phase may be disfavored by stresses that seek to separate the Fermi surfaces of the different flavors, and comparison with the competing alternative phases, which may break translation and/or rotation invariance, is done using phenomenological models. We review the calculations that underlie these results and then discuss transport properties of several color-superconducting phases and their consequences for signatures of color superconductivity in neutron stars.

  11. Effect of impurity modes with quasilocal and local frequencies on the superconducting transition temperature

    International Nuclear Information System (INIS)

    Zhernov, A.P.; Malov, Yu.A.; Panova, G.Kh.

    1975-01-01

    An anisotropic irregular semiconductor is under consideration. It is believed that the effective parameter of the interaction-lambda-which determines electron coupling is less or about 0.5. The Eliashberg integral equation system is solved for T→Tsub(c). A simple analytic expression is obtained for Tsub(c). The character of a varying critical temperature in superconductors with impurity atoms is analyzed in detail. The dependence of the critical temperature on parameters describing the phonon spectrum of an impurity system is investigated. The existence of impurity modes with quasilocal and local frequencies in the phonon spectra can lead both to relatively small and to rather noticeable variations in Tsub(c). The first case is typical of the situation when an impurity atom is practically an isotopic defect. If an impurity atom is very heavy (Msub(I) 1 0 ) or strongly (γ 1 >>γ 0 ) coupled with matrix atoms. A sharp decrease in the effective force constant γ 1 for an impurity atom results in the growth of delta Tsub(c): delta Tsub(c) approximately cγ0/γ 1 (lambda - μsup((0)). On the contrary a rise in the γ 1 value requires a negative correction to Tsub(c), and delta Tsub(c) approximately c/(lambda - μsup((0)), where c - an impurity concentration, μ - matrix element of the Coulomb screened interaction averaged over the Fermi surface and multiplied for the density of normal electron states on the Fermi level. Comparison with experimental data is made. A qualitative description of the Tsub(c) change due to the impurity presence is given for a set of solutions. There is a satisfactory quantitative agreement between calculated and experimental values of delta Tsub(c)

  12. Experiment for transient effects of sudden catastrophic loss of vacuum on a scaled superconducting radio frequency cryomodule

    International Nuclear Information System (INIS)

    Dalesandro, A.; Theilacker, J.; Van Sciver, S.W.

    2011-01-01

    Safe operation of superconducting radio frequency (SRF) cavities require design consideration of a sudden catastrophic loss of vacuum (SCLV) adjacent with liquid helium (LHe) vessels and subsequent dangers. An experiment is discussed to test the longitudinal effects of SCLV along the beam line of a string of scaled SRF cavities. Each scaled cavity includes one segment of beam tube within a LHe vessel containing 2 K saturated LHe, and a riser pipe connecting the LHe vessel to a common gas header. At the beam tube inlet is a fast acting solenoid valve to simulate SCLV and a high/low range orifice plate flow-meter to measure air influx to the cavity. The gas header exit also has an orifice plate flow-meter to measure helium venting the system at the relief pressure of 0.4 MPa. Each cavity is instrumented with Validyne pressure transducers and Cernox thermometers. The purpose of this experiment is to quantify the time required to spoil the beam vacuum and the effects of transient heat and mass transfer on the helium system. Heat transfer data is expected to reveal a longitudinal effect due to the geometry of the experiment. Details of the experimental design criteria and objectives are presented.

  13. 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

  14. Effect of shock pressure on the structure and superconducting properties of Y-Ba-Cu-O in explosively fabricated bulk metal-matrix composites

    Science.gov (United States)

    Murr, L. E.; Niou, C. S.; Pradhan-Advani, M.

    1991-01-01

    While it is now well established that copper-oxide-based power, or virtually any other ceramic superconductor powder, can be consolidated and encapsulated within a metal matrix by explosive consolidation, the erratic superconductivity following fabrication has posed a major problem for bulk applications. The nature of this behavior was found to arise from microstructural damage created in the shock wave front, and the residual degradation in superconductivity was demonstrated to be directly related to the peak shock pressure. The explosively fabricated or shock loaded YBa2Cu3Ox examples exhibit drastically altered rho (or R) - T curves. The deterioration in superconductivity is even more noticeable in the measurement of ac magnetic susceptibility and flux exclusion or shielding fraction which is also reduced in proportion to increasing peak shock pressure. The high frequency surface resistance (in the GHz range) is also correspondingly compromised in explosively fabricated, bulk metal-matrix composites based on YBa2Cu3O7. Transmission electron microscopy (including lattice imaging techniques) is being applied in an effort to elucidate the fundamental (microstructural) nature of the shock-induced degradation of superconductivity and normal state conductivity. One focus of TEM observations has assumed that oxygen displaced from b-chains rather than oxygen-vacancy disorder in the basal plane of oxygen deficient YBa2Cu3Ox may be a prime mechanism. Shock-wave displaced oxygen may also be locked into new positions or interstitial clusters or chemically bound to displaced metal (possibly copper) atoms to form precipitates, or such displacements may cause the equivalent of local lattice cell changes as a result of stoichiometric changes. While the shock-induced suppression of T(sub c) is not desirable in the explosive fabrication of bulk metal-matrix superconductors, it may be turned into an advantage if the atomic-scale distortion can be understood and controlled as local

  15. Linear arrangement of metallic and superconducting defects in a thin superconducting sample

    International Nuclear Information System (INIS)

    Barba-Ortega, J.; Sardella, Edson; Albino Aguiar, J.

    2013-01-01

    Highlights: • We study the influence of superconducting and metallic defects on the vortex configurations in a thin mesoscopic disk. • We found that the vortex–defect interaction leads to interesting vortex configurations. • The first vortex entry is always (never) found sitting on the metallic (superconducting) defect position. -- Abstract: The vortex matter in a superconducting disk with a linear configuration of metallic and superconducting defects is studied. Effects associated to the pinning (anti-pinning) force of the metallic (superconducting) defect on the vortex configuration and on the thermodynamic critical fields are analyzed in the framework of the Ginzburg Landau theory. We calculate the loop of the magnetization, vorticity and free energy curves as a function of the magnetic field for a thin disk. Due to vortex–defect attraction for a metallic defect (repulsion for a superconducting defect), the vortices always (never) are found to be sitting on the defect position

  16. Ab initio molecular-orbital study on electron correlation effects in CuO6 clusters relating to high-Tc superconductivity

    International Nuclear Information System (INIS)

    Yamamoto, S.; Yamaguchi, K.; Nasu, K.

    1990-01-01

    Ab initio molecular-orbital calculations for CuO 6 clusters have been performed to elucidate the electronic structures of undoped and doped copper oxides, which are of current interest in relation to high-T c superconductivity. The electron correlation effects for these species are thoroughly investigated by the full-valence configuration-interaction method and the complete-active-space self-consistent-field method. The electron correlation effect is relatively simple for the A g state (σ hole), whereas pair excitations and spin-flip excitations give sizable contributions to the configuration-interaction wave function for the B state (in-plane π hole). Implications of these results are discussed in relation to the mechanisms of the high-T c superconductivity

  17. Superconductivity and ferromagnetism in topological insulators

    Science.gov (United States)

    Zhang, Duming

    Topological insulators, a new state of matter discovered recently, have attracted great interest due to their novel properties. They are insulating inside the bulk, but conducting at the surface or edges. This peculiar behavior is characterized by an insulating bulk energy gap and gapless surface or edge states, which originate from strong spin-orbit coupling and time-reversal symmetry. The spin and momentum locked surface states not only provide a model system to study fundamental physics, but can also lead to applications in spintronics and dissipationless electronics. While topological insulators are interesting by themselves, more exotic behaviors are predicted when an energy gap is induced at the surface. This dissertation explores two types of surface state gap in topological insulators, a superconducting gap induced by proximity effect and a magnetic gap induced by chemical doping. The first three chapters provide introductory theory and experimental details of my research. Chapter 1 provides a brief introduction to the theoretical background of topological insulators. Chapter 2 is dedicated to material synthesis principles and techniques. I will focus on two major synthesis methods: molecular beam epitaxy for the growth of Bi2Se3 thin films and chemical vapor deposition for the growth of Bi2Se3 nanoribbons and nanowires. Material characterization is discussed in Chapter 3. I will describe structural, morphological, magnetic, electrical, and electronic characterization techniques used to study topological insulators. Chapter 4 discusses the experiments on proximity-induced superconductivity in topological insulator (Bi2Se3) nanoribbons. This work is motivated by the search for the elusive Majorana fermions, which act as their own antiparticles. They were proposed by Ettore Majorara in 1937, but have remained undiscovered. Recently, Majorana's concept has been revived in condensed matter physics: a condensed matter analog of Majorana fermions is predicted to

  18. Total pollution effect of urban surface runoff.

    Science.gov (United States)

    Luo, Hongbing; Luo, Lin; Huang, Gu; Liu, Ping; Li, Jingxian; Hu, Sheng; Wang, Fuxiang; Xu, Rui; Huang, Xiaoxue

    2009-01-01

    For pollution research with regard to urban surface runoff, most sampling strategies to date have focused on differences in land usage. With single land-use sampling, total surface runoff pollution effect cannot be evaluated unless every land usage spot is monitored. Through a new sampling strategy known as mixed stormwater sampling for a street community at discharge outlet adjacent to river, this study assessed the total urban surface runoff pollution effect caused by a variety of land uses and the pollutants washed off from the rain pipe system in the Futian River watershed in Shenzhen City of China. The water quality monitoring indices were COD (chemical oxygen demand), TSS (total suspend solid), TP (total phosphorus), TN (total nitrogen) and BOD (biochemical oxygen demand). The sums of total pollution loads discharged into the river for the four indices of COD, TSS, TN, and TP over all seven rainfall events were very different. The mathematical model for simulating total pollution loads was established from discharge outlet mixed stormwater sampling of total pollution loads on the basis of four parameters: rainfall intensity, total land area, impervious land area, and pervious land area. In order to treat surface runoff pollution, the values of MFF30 (mass first flush ratio) and FF30 (first 30% of runoff volume) can be considered as split-flow control criteria to obtain more effective and economical design of structural BMPs (best management practices) facilities.

  19. The Influence of Grain Boundaries on the Properties of Superconducting Radio Frequency Cavity Niobium

    Science.gov (United States)

    Sung, Zu Hawn

    Grain boundaries (GBs) in niobium are multiply connected defects that may be responsible for significant performance degradation in superconducting radio frequency (RF) cavities. Magneto optical (MO) studies show that early flux penetration often occurs at GBs. One possible mechanism is that a locally reduced superconducting gap (Delta) at the GB reduces the depairing current density (Jb) and thus leads to a local reduction of the critical field. Alternatively vortices may penetrate the GB preferentially because of field enhancement at a GB groove, or for other reasons. In all these cases, the effect of high RF fields is to produce additional power dissipation, which in turn produces a reduction in quality factor (Q 0) and leads to a premature quench of the cavity. To further our understanding of the superconducting properties of SRF-quality Nb, we made extensive superconducting characterizations by magneto-optical imaging, which allowed assessment of the uniformity of properties on scales down to about 5 microm and by direct transport voltage-current methods in single and bi-crystals treated by standard cavity optimization treatments of BCP (buffered chemical treatment) and EP (electropolishing). We correlated these superconducting characterizations to microstructural properties using scanning laser and scanning electron microscopy and then thinned some samples to examine them at the nanometer scale using analytical transmission electron microscopy (TEM). We also developed special metallographic sample preparation techniques that allowed us to apply these experimental approaches to very soft superconducting RF niobium in the polished conditions characteristics of a real inner cavity surface. Using MO imaging, we found that GBs can preferentially admit flux penetration when the plane of a GB is aligned parallel to the vector of the external magnetic field. In DC transport in the superconducting state, we found preferential flux flow at the GB and could detect the

  20. Remarks on superconductive networks

    International Nuclear Information System (INIS)

    Dominguez, D.; Lopez, A.R.N.; Simonin, J.M.

    1989-01-01

    Some remarks on the determination of the normal-superconductor phase boundary in random superconductive networks are made. A recently reported work by Soukoulis, Grest and Li which introduces weak links between nodes as these are removed in the site percolation problem is discussed. By the analysis of two simple geometries, it is shown that this procedure introduces spurious effects which mask the physical properties of the system. These affect in particular the field slope critical index and the sharpness of the normal-superconductor boundary. (Author)