Sample records for x17 superconducting wiggler

  1. Construction and Performance of a Superconducting Multipole Wiggler

    NASA Astrophysics Data System (ADS)

    Hwang, C. S.; Wang, B.; Chen, J. Y.; Chang, C. H.; Chen, H. H.; Fan, T. C.; Lin, F. Y.; Huang, M. H.; Chang, C. C.; Hsu, S. N.; Hsiung, G. Y.; Hsu, K. T.; Chen, J.; Chien, Y. C.; Chen, J. R.; Chen, C. T.

    2004-05-01

    A 3.2 Tesla superconducting multipole wiggler was designed and fabricated as an X-ray source. The magnet assembly, which consists of 32 pairs of racetrack NbTi superconducting coils with a periodic length of 60 mm, provides 28 effective poles. A 1.4056 m long elliptical cold-bore stainless steel beam duct with taper flanges and a wall thickness of 1 mm, was developed and constructed to fit the ultra-high vacuum condition for electron beam. The magnetic field strength was measured in liquid helium using a cryogenic Hall probe, revealing a field behavior very close to behavior consistent with the designed values. A Hall generator and the stretch wire methods are used to determine the transfer function of the peak field, the first and second integrated field distributions, and the good field region of the magnet. The quench protection of the magnet, the control algorithm for automatic filling of liquid helium, and the boil off rate of liquid helium and liquid nitrogen will also be discussed.

  2. Installation of a second superconducting wiggler at SAGA-LS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kaneyasu, T., E-mail: kaneyasu@saga-ls.jp; Takabayashi, Y.; Iwasaki, Y.

    The SAGA Light Source is a synchrotron radiation facility consisting of a 255 MeV injector linac and a 1.4 GeV storage ring with a circumference of 75.6 m. A superconducting wiggler (SCW) with a peak magnetic field of 4 T has been routinely operating for generating hard X-rays since its installation in 2010. In light of this success, it was decided to install a second SCW as a part of the beamline construction by Sumitomo Electric Industries. To achieve this, machine modifications including installation of a new magnet power supply, improvement of the magnet control system, and replacement of themore » vacuum chambers in the storage ring were carried out. Along with beamline construction, installation and commissioning of the second SCW are scheduled to take place in 2015.« less

  3. A New Hard X-ray Wiggler for DORIS III

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tischer, M.; Gumprecht, L.; Pflueger, J.

    2007-01-19

    A 4 m long hard X-ray wiggler has been built and installed in the DORIS III storage ring at DESY. The device replaces an old wiggler especially designed for angiography studies. Future use of this beamline at the HARWI straight section has been dedicated to hard X-ray scattering and diffraction experiments for material science and geological investigations. The required energy range is from 30 keV to about 200 keV with emphasis on the {approx}100 keV spectral range. The magnet configuration corresponds to a hybrid structure with additional side magnets to achieve a 2 T peak field for the specified periodmore » length of 110 mm. The wiggler position in the storage ring has been moved 8 m upstream into the next cell which allowed for reduction of the minimum magnetic wiggler gap to 14 mm.« less

  4. Design and system integration of the superconducting wiggler magnets for the Compact Linear Collider damping rings

    NASA Astrophysics Data System (ADS)

    Schoerling, Daniel; Antoniou, Fanouria; Bernhard, Axel; Bragin, Alexey; Karppinen, Mikko; Maccaferri, Remo; Mezentsev, Nikolay; Papaphilippou, Yannis; Peiffer, Peter; Rossmanith, Robert; Rumolo, Giovanni; Russenschuck, Stephan; Vobly, Pavel; Zolotarev, Konstantin

    2012-04-01

    To achieve high luminosity at the collision point of the Compact Linear Collider (CLIC), the normalized horizontal and vertical emittances of the electron and positron beams must be reduced to 500 and 4 nm before the beams enter the 1.5 TeV linear accelerators. An effective way to accomplish ultralow emittances with only small effects on the electron polarization is using damping rings operating at 2.86 GeV equipped with superconducting wiggler magnets. This paper describes a technical design concept for the CLIC damping wigglers.

  5. Positron production by x rays emitted by betatron motion in a plasma wiggler.

    PubMed

    Johnson, D K; Auerbach, D; Blumenfeld, I; Barnes, C D; Clayton, C E; Decker, F J; Deng, S; Emma, P; Hogan, M J; Huang, C; Ischebeck, R; Iverson, R; Joshi, C; Katsouleas, T C; Kirby, N; Krejcik, P; Lu, W; Marsh, K A; Mori, W B; Muggli, P; O'Connell, C L; Oz, E; Siemann, R H; Walz, D; Zhou, M

    2006-10-27

    Positrons in the energy range of 3-30 MeV, produced by x rays emitted by betatron motion in a plasma wiggler of 28.5 GeV electrons from the SLAC accelerator, have been measured. The extremely high-strength plasma wiggler is an ion column induced by the electron beam as it propagates through and ionizes dense lithium vapor. X rays in the range of 1-50 MeV in a forward cone angle of 0.1 mrad collide with a 1.7 mm thick tungsten target to produce electron-positron pairs. The positron spectra are found to be strongly influenced by the plasma density and length as well as the electron bunch length. By characterizing the beam propagation in the ion column these influences are quantified and result in excellent agreement between the measured and calculated positron spectra.

  6. Magnetic measurements of the 10 T superconducting wiggler for the SPring-8 storage ring

    NASA Astrophysics Data System (ADS)

    Batrakov, A.; Borovikov, V.; Bekhtenev, E.; Fedurin, M.; Hara, M.; Karpov, G.; Kuzin, M.; Mezentsev, N.; Miahara, Y.; Shimada, T.; Shkaruba, V.; Soutome, K.; Tzumaki, K.

    2001-07-01

    In 1999, in the frame of the project ISTC #767 "Budker INP/RIKEN Slow Positron Source", the Budker Institute of Nuclear Physics had made a 10 T Three-pole Superconducting Wiggler. The wiggler will be the keystone of this project by its installation on the SPring-8 storage ring for powerful gamma ray generation ( λ c=450 keV ), that will be used for slow positron production ( Nγ( ɛ>1 MeV)˜10 15, γ/s I e=0.1 A ). A. Ando et al., Proposal of the high magnetic field super conducting WLS for slow positron source at SPring-8, presented at SR1 '97 Conference. In January, 2000, the wiggler was transported to SPring-8, where the last test and measurements were carried out in collaboration with Japan. In this article, the results of measurements of the magnetic field, finding the magnetic field amplitude by an NMR probe, the definition of feed current relations by stretch current wire method, the calibration of a Hall probe in the high magnetic field, and the measurement of the magnetic field profile by a Hall probe are presented.

  7. Development of Superconducting Insertion Device Magnets at NSRRC

    NASA Astrophysics Data System (ADS)

    Hwang, C. S.; Chang, C. H.; Chen, H. H.; Jan, J. C.; Lin, F. Y.; Fan, T. C.; Chen, J.; Hsu, S. N.; Hsu, K. T.; Huang, M. H.; Chang, H. P.; Hsiung, G. Y.; Chien, Y. C.; Chen, J. R.; Kuo, C. C.; Chen, C. T.

    2007-01-01

    A superconducting wavelength shifter (SWLS) with a magnetic field of 6.5 T in cryogen-free operation provides X-rays for high-resolution X-ray microscopy, EXAFS, and medical imaging beamlines. A 32-pole superconducting wiggler (SW) with a period of 6.1 cm and a magnetic field of 3.2 T in a liquid helium bath provides for three dedicated protein crystallography beamlines. Additionally, three 16-pole in-achromatic superconducting wigglers (IASW) with a period of 6.1 cm and a field strength of 3.1 T were constructed in-house and installed between the first and second bending magnets of a TBA arc section. Development of a prototype superconducting undulator (SU15) with a period of 15 mm and a field strength of 1.4 T is currently underway at National Synchrotron Radiation Research Center (MSRRC).

  8. Evaluation of superconducting wiggler designs and free-electron laser support: Final report

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    NONE

    1990-10-12

    This report consists of copies of previous progress reports, and copies of viewgraphs presented in a talk at Los Alamos. The report describes activities carried out as part of a project to evaluate the design and performance of a superconducting wiggler magnet design. It includes work on evaluating the appropriate materials for the magnet coils and poles, and stress evaluations for the design. It includes work on beam optics through the magnet, and design considerations to optimize extraction: work on the cryocooling system; weight minimization efforts; and design work on the vacuum liner for the magnet. A major concern inmore » all of this design work is heat loads which will be dissipated in different parts of the system during operation, as well as transient events.« less

  9. Calculated and measured fields in superferric wiggler magnets

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Blum, E.B.; Solomon, L.

    1995-02-01

    Although Klaus Halbach is widely known and appreciated as the originator of the computer program POISSON for electromagnetic field calculation, Klaus has always believed that analytical methods can give much more insight into the performance of a magnet than numerical simulation. Analytical approximations readily show how the different aspects of a magnet`s design such as pole dimensions, current, and coil configuration contribute to the performance. These methods yield accuracies of better than 10%. Analytical methods should therefore be used when conceptualizing a magnet design. Computer analysis can then be used for refinement. A simple model is presented for the peakmore » on-axis field of an electro-magnetic wiggler with iron poles and superconducting coils. The model is applied to the radiator section of the superconducting wiggler for the BNL Harmonic Generation Free Electron Laser. The predictions of the model are compared to the measured field and the results from POISSON.« less

  10. X-ray grating interferometer for materials-science imaging at a low-coherent wiggler source

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Herzen, Julia; Physics Department and Institute for Medical Engineering, Technische Universitaet Muenchen, 85748 Garching; Donath, Tilman

    2011-11-15

    X-ray phase-contrast radiography and tomography enable to increase contrast for weakly absorbing materials. Recently, x-ray grating interferometers were developed that extend the possibility of phase-contrast imaging from highly brilliant radiation sources like third-generation synchrotron sources to non-coherent conventional x-ray tube sources. Here, we present the first installation of a three grating x-ray interferometer at a low-coherence wiggler source at the beamline W2 (HARWI II) operated by the Helmholtz-Zentrum Geesthacht at the second-generation synchrotron storage ring DORIS (DESY, Hamburg, Germany). Using this type of the wiggler insertion device with a millimeter-sized source allows monochromatic phase-contrast imaging of centimeter sized objects withmore » high photon flux. Thus, biological and materials-science imaging applications can highly profit from this imaging modality. The specially designed grating interferometer currently works in the photon energy range from 22 to 30 keV, and the range will be increased by using adapted x-ray optical gratings. Our results of an energy-dependent visibility measurement in comparison to corresponding simulations demonstrate the performance of the new setup.« less

  11. Current driven wiggler

    NASA Astrophysics Data System (ADS)

    Tournes, C.; Aucouturier, J.; Arnaud, B.; Brasile, J. P.; Convert, G.; Simon, M.

    1992-07-01

    A current-driven wiggler is the cornerstone of an innovative, compact, high-efficiency, transportable tunable free-electron laser (FEL), the feasibility of which is currently being evaluated by Thomson-CSF. The salient advantages are: compactness of the FEL, along with the possibility to accelerate the beam through several successive passes through the accelerating section (the number of passes being defined by the final wavelength of the radiation; i.e. visible, MWIR, LWIR); the wiggler can be turned off and be transparent to the beam until the last pass. Wiggler periodicities as small as 5 mm can be achieved, hence contributing to FEL compactness. To achieve overall efficiencies in the range of 10% at visible wavelengths, not only the wiggler periodicity must be variable, but the strength of the magnetic field of each period can be adjusted separately and fine-tuned versus time during the macropulse, so as to take into account the growing contribution of the wave energy in the cavity to the total ponderomotive force. The salient theoretical point of this design is the optimization of the parameters defining each period of the wiggler for each micropacket of the macropulse. The salient technology point is the mechanical and thermal design of the wiggler which allows the required high currents to achieve magnetic fields up to 2T.

  12. Peculiar phase diagram with isolated superconducting regions in ThFeAsN1‑x O x

    NASA Astrophysics Data System (ADS)

    Li, Bai-Zhuo; Wang, Zhi-Cheng; Wang, Jia-Lu; Zhang, Fu-Xiang; Wang, Dong-Ze; Zhang, Feng-Yuan; Sun, Yu-Ping; Jing, Qiang; Zhang, Hua-Fu; Tan, Shu-Gang; Li, Yu-Ke; Feng, Chun-Mu; Mei, Yu-Xue; Wang, Cao; Cao, Guang-Han

    2018-06-01

    ThFeAsN1‑x O x () system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the T c value decreases rapidly to below 2 K for , and surprisingly, superconductivity re-appears in the range of with a maximum of 17.5 K at x  =  0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x  =  0.4 is , which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN1‑x O x presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.

  13. Peculiar phase diagram with isolated superconducting regions in ThFeAsN1-x O x.

    PubMed

    Li, Bai-Zhuo; Wang, Zhi-Cheng; Wang, Jia-Lu; Zhang, Fu-Xiang; Wang, Dong-Ze; Zhang, Feng-Yuan; Sun, Yu-Ping; Jing, Qiang; Zhang, Hua-Fu; Tan, Shu-Gang; Li, Yu-Ke; Feng, Chun-Mu; Mei, Yu-Xue; Wang, Cao; Cao, Guang-Han

    2018-06-27

    ThFeAsN 1-x O x ([Formula: see text]) system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at [Formula: see text] K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the T c value decreases rapidly to below 2 K for [Formula: see text], and surprisingly, superconductivity re-appears in the range of [Formula: see text] with a maximum [Formula: see text] of 17.5 K at x  =  0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x  =  0.4 is [Formula: see text], which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN 1-x O x presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.

  14. X-ray Synchrotron Radiation in a Plasma Wiggler

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wang, Shuoquin; /UCLA /SLAC, SSRL

    2005-09-27

    A relativistic electron beam can radiate due to its betatron motion inside an ion channel. The ion channel is induced by the electron bunch as it propagates through an underdense plasma. In the theory section of this thesis the formation of the ion channel, the trajectories of beam electrons inside the ion channel, the radiation power and the radiation spectrum of the spontaneous emission are studied. The comparison between different plasma wiggler schemes is made. The difficulties in realizing stimulated emission as the beam traverses the ion channel are investigated, with particular emphasis on the bunching mechanism, which is importantmore » for the ion channel free electron laser. This thesis reports an experiment conducted at the Stanford Linear Accelerator Center (SLAC) to measure the betatron X-ray radiations for the first time. They first describe the construction and characterization of the lithium plasma source. In the experiment, the transverse oscillations of the SLAC 28.5 GeV electron beam traversing through a 1.4 meter long lithium plasma source are clearly seen. These oscillations lead to a quadratic density dependence of the spontaneously emitted betatron X-ray radiation. The divergence angle of the X-ray radiation is measured. The absolute photon yield and the spectral brightness at 14.2 KeV photon energy are estimated and seen to be in reasonable agreement with theory.« less

  15. Hard X-ray Wiggler Front End Filter Design

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Schulte-Schrepping, Horst; Hahn, Ulrich

    2007-01-19

    The front end filter design and implementation for the new HARWI-II hard X-ray wiggler at DORIS-III at HASYLAB/DESY is presented. The device emits a total power of 30 kW at 150mA storage ring current. The beam has a horizontal width of 3.8mrad and a central power density of 54 W/mm2 at 26m distance to the source. The filter section located in the ring tunnel has been introduced to tailor the thermal loads at the downstream optical components. The high power density and the high total power at the filter section are handled with a layered design. Glassy carbon filters convertmore » the absorbed power into thermal radiation to lower the heat load to an acceptable level for water cooled copper filters. The requirements in beam size and filtering are addressed by separating the filter functions in three units which are switched individually into the beam.« less

  16. HARWI---A hard x-ray wiggler beam at DORIS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Graeff, W.; Bittner, L.; Brefeld, W.

    1989-07-01

    The construction of the wiggler W2 at DORIS is described together with the major components of the beamline. Details are given on the assembly and performance of the magnet structure. Three different monochromators are used in the beamline alternatively. One of them, a Laue--Bragg-type monochromator is described in more detail.

  17. Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors

    NASA Technical Reports Server (NTRS)

    Stern, Jeffrey A.; Farr, William H.; Leduc, Henry G.; Bumble, Bruce

    2008-01-01

    Superconducting-nanowire single-photon detectors (SNSPDs) in which Nb(x)Ti(1-x)N (where x<1) films serve as the superconducting materials have shown promise as superior alternatives to previously developed SNSPDs in which NbN films serve as the superconducting materials. SNSPDs have potential utility in optical communications and quantum cryptography. Nb(x)Ti(1-x)N is a solid solution of NbN and TiN, and has many properties similar to those of NbN. It has been found to be generally easier to stabilize Nb(x)Ti(1-x)N in the high-superconducting-transition temperature phase than it is to so stabilize NbN. In addition, the resistivity and penetration depth of polycrystalline films of Nb(x)Ti(1-x)N have been found to be much smaller than those of films of NbN. These differences have been hypothesized to be attributable to better coupling at grain boundaries within Nb(x)Ti(1-x)N films.

  18. Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors

    NASA Technical Reports Server (NTRS)

    Stem, Jeffrey A.; Farr, William H.; Leduc, Henry G.; Bumble, Bruce

    2008-01-01

    Superconducting-nanowire singlephoton detectors (SNSPDs) in which Nb(x)Ti(1-x)N (where x<1) films serve as the superconducting materials have shown promise as superior alternatives to previously developed SNSPDs in which NbN films serve as the superconducting materials. SNSPDs have potential utility in optical communications and quantum cryptography. Nb(x)Ti(1-x)N is a solid solution of NbN and TiN, and has many properties similar to those of NbN. It has been found to be generally easier to stabilize NbxTi1 xN in the high-superconducting-transitiontemperature phase than it is to so stabilize NbN. In addition, the resistivity and penetration depth of polycrystalline films of Nb(x)Ti(1-x)N have been found to be much smaller than those of films of NbN. These differences have been hypothesized to be attributable to better coupling at grain boundaries within Nb(x)Ti(1-x)N films.

  19. Magnetic field error measurement of the CEBAF (NIST) wiggler using the pulsed wire method

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wallace, Stephen; Colson, William; Neil, George

    1993-07-01

    The National Institute for Science and Technology (NIST) wiggler has been loaded to the Continuous Electron Beam Accelerator Facility (CEBAF). The pulsed wire method [R.W. Warren, Nucl. Instr. and Meth. A272 (1988) 267] has been used to measure the field errors of the entrance wiggler half, and the net path deflection was calculated to be Δx ≈ 5.2 m.

  20. Interplay between superconductivity and magnetism in Fe(1-x)Pd(x)Te.

    PubMed

    Karki, Amar B; Garlea, V Ovidiu; Custelcean, Radu; Stadler, Shane; Plummer, E W; Jin, Rongying

    2013-06-04

    The attractive/repulsive relationship between superconductivity and magnetic ordering has fascinated the condensed matter physics community for a century. In the early days, magnetic impurities doped into a superconductor were found to quickly suppress superconductivity. Later, a variety of systems, such as cuprates, heavy fermions, and Fe pnictides, showed superconductivity in a narrow region near the border to antiferromagnetism (AFM) as a function of pressure or doping. However, the coexistence of superconductivity and ferromagnetic (FM) or AFM ordering is found in a few compounds [RRh4B4 (R = Nd, Sm, Tm, Er), R'Mo6X8 (R' = Tb, Dy, Er, Ho, and X = S, Se), UMGe (M = Ge, Rh, Co), CeCoIn5, EuFe2(As(1-x)P(x))2, etc.], providing evidence for their compatibility. Here, we present a third situation, where superconductivity coexists with FM and near the border of AFM in Fe(1-x)Pd(x)Te. The doping of Pd for Fe gradually suppresses the first-order AFM ordering at temperature T(N/S), and turns into short-range AFM correlation with a characteristic peak in magnetic susceptibility at T'(N). Superconductivity sets in when T'(N) reaches zero. However, there is a gigantic ferromagnetic dome imposed in the superconducting-AFM (short-range) cross-over regime. Such a system is ideal for studying the interplay between superconductivity and two types of magnetic (FM and AFM) interactions.

  1. Fast pulsed excitation wiggler or undulator

    DOEpatents

    van Steenbergen, Arie

    1990-01-01

    A fast pulsed excitation, electromagnetic undulator or wiggler, employing geometrically alternating substacks of thin laminations of ferromagnetic material, together with a single turn current loop excitation of the composite assembly, of such shape and configuration that intense, spatially alternating, magnetic fields are generated; for use as a pulsed mode undulator or wiggler radiator, for use in a Free Electron Laser (FEL) type radiation source or, for use in an Inverse Free Electron Laser (IFEL) charged particle accelerator.

  2. Superconductivity and charge density wave in ZrTe 3–xSe x

    DOE PAGES

    Zhu, Xiangde; Ning, Wei; Li, Lijun; ...

    2016-06-02

    Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe 3 when the long range CDW order is gradually suppressed. Superconducting critical temperature T c(x) in ZrTe 3–xSe x (0 ≤ x ≤ 0.1) increases up to 4 K plateau for 0.04 ≤ x ≤ 0.07. Further increase inmore » Se content results in diminishing T c and filametary superconductivity. The CDW modes from Raman spectra are observed in x = 0.04 and 0.1 crystals, where signature of ZrTe 3 CDW order in resistivity vanishes. As a result, the electronic-scattering for high T c crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T = 300 K and contributes to substantial in-plane anisotropy.« less

  3. Electron density distribution in BaPb{sub 1-x}Sb{sub x}O{sub 3} superconducting oxides studied by double nuclear magnetic resonance methods

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Piskunov, Yu. V., E-mail: piskunov@imp.uran.ru; Ogloblichev, V. V.; Arapova, I. Yu.

    2011-11-15

    The effect of charge disorder on the formation of an inhomogeneous state of the electron system in the conduction band in BaPb{sub 1-x}Sb{sub x}O{sub 3} superconducting oxides is investigated experimentally by NMR methods. The NMR spectra of {sup 17}O are measured systematically, and the contributions from {sup 17}O atoms with different cation nearest surroundings are identified. It is found that microscopic regions with an elevated spin density of charge carriers are formed within two coordination spheres near antimony ions. Nuclei of the superconducting phase of the oxide (regions with an elevated antimony concentration) microscopically distributed over the sample are detectedmore » in compounds with x = 0.25 and 0.33. Experiments in which a double resonance signal of the spin echo of {sup 17}O-{sup 207}Pb and {sup 17}O-{sup 121}Sb are measured in the metal phase of BaPb{sub 1-x}Sb{sub x}O{sub 3} oxides are carried out for the first time. The constants of indirect heteronuclear spin-spin {sup 17}O-{sup 207}Pb interaction are determined as functions of the local Knight shift {sub 207}Ks. The estimates of the constants of the indirect interaction between the nuclei of the nearest neighbors (O-Pb and Pb-Pb atoms) and analysis of evolution of the NMR spectra of {sup 17}O upon a change in the antimony concentration are convincing evidence in favor of the development of a microscopically inhomogeneous state of the electron system in the metal phase of BaPb{sub 1-x}Sb{sub x}O{sub 3} oxides.« less

  4. YBa2Cu3O x superconducting nanorods

    NASA Astrophysics Data System (ADS)

    Rieken, William; Bhargava, Atit; Horie, Rie; Akimitsu, Jun; Daimon, Hiroshi

    2018-02-01

    Herein, we report the synthesis of YBa2Cu3O x superconducting nanorods performed by solution chemistry. Initially, a mixture of fine-grained coprecipitated powder was obtained and subsequently converted to YBa2Cu3O x nanorods by heating to 1223 K in oxygen for 12 h. The nanorods are superconducting without the need for any further sintering or oxygenation, thereby providing an avenue for direct application to substrates at room temperature or direct use as formed nanorods. A critical superconducting transition temperature T c of about 92 K was achieved at a critical magnetic field of 10 Oe.

  5. Investigation of superconducting and normal-state properties of the filled-skutterudite system PrPt 4 Ge 12 - x Sb x

    DOE PAGES

    Jeon, I.; Huang, K.; Yazici, D.; ...

    2016-03-07

    We report a study of the superconducting and normal-state properties of the filled-skutterudite system PrPt 4Ge 12 - x Sb x. Polycrystalline samples with Sb concentrations up to x = 5 were synthesized and investigated by means of x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements. We observed a suppression of superconductivity with increasing Sb substitution up to x = 4 , above which no signature of superconductivity was observed down to 140 mK. The Sommerfeld coefficient, γ , of superconducting specimens decreases with increasing x up to x = 3 , suggesting that superconductivity may depend onmore » the density of electronic states in this system. Finally, the specific heat for x = 0.5 exhibits an exponential temperature dependence in the superconducting state, reminiscent of a nodeless superconducting energy gap. Here we observed evidence for a weak “rattling” mode associated with the Pr ions, characterized by an Einstein temperature Θ E ~ 60 K for 0 ≤ x ≤ 5 ; however, the rattling mode may not play any role in suppressing superconductivity.« less

  6. Sharpness of interference pattern of the 3-pole wiggler

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Dejus, Roger J., E-mail: dejus@aps.anl.gov; Kim, Kwang-Je

    2016-07-27

    Due to the small emittance, radiation from neighboring poles of a strong wiggler in future multi-bend achromat-based storage rings can exhibit sharp interference patterns. The spectral-angular distributions of the 3-pole wiggler for the proposed Advanced Photon Source (APS) upgrade were computed and prominent interference patterns were found. In this paper we provide an understanding of such interference patterns. The equations governing the interference pattern are described and computed spectral-angular distributions of a modeled 3-pole wiggler magnetic field using these equations are presented.

  7. Sharpness of Interference Pattern of the 3-Pole Wiggler

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Dejus, Roger J.; Kim, Kwang-Je

    2016-07-02

    Due to the small emittance, radiation from neighboring poles of a strong wiggler in future multi-bend achromat-based storage rings can exhibit sharp interference patterns. The spectral-angular distributions of the 3-pole wiggler for the proposed Advanced Photon Source (APS) upgrade were computed and prominent interference patterns were found. In this paper we provide an understanding of such interference patterns. The equations governing the interference pattern are described and computed spectral-angular distributions of a modeled 3-pole wiggler magnetic field using these equations are presented.

  8. Superconducting order from disorder in 2H-TaSe 2-xS x

    DOE PAGES

    Li, Lijun; Deng, Xiaoyu; Wang, Zhen; ...

    2017-02-24

    Here, we report on the emergence of robust superconducting order in single crystal alloys of TaSe 2$ -$x S x (0 ≤ × ≤2). The critical temperature of the alloy is surprisingly higher than that of the two end compounds TaSe2 and TaS2. The evolution of superconducting critical temperature T c(x) correlates with the full width at half maximum of the Bragg peaks and with the linear term of the high-temperature resistivity. The conductivity of the crystals near the middle of the alloy series is higher or similar than that of either one of the end members 2H-TaSe 2 and/ormore » 2H-TaS 2. It is known that in these materials superconductivity is in close competition with charge density wave order. We interpret our experimental findings in a picture where disorder tilts this balance in favor of superconductivity by destroying the charge density wave order.« less

  9. Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe 3–xSe x

    DOE PAGES

    Cui, Shan; He, Lan -Po; Hong, Xiao -Chen; ...

    2016-06-09

    It was found that selenium doping can suppress the charge-density-wave (CDW) order and induce bulk superconductivity in ZrTe 3. The observed superconducting dome suggests the existence of a CDW quantum critical point (QCP) in ZrTe 3–x Se x near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe 3–x Se x single crystals (x = 0.044 and 0.051) down to 80 mK. For both samples, the residual linear term κ 0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependencemore » of κ 0/T manifests a multigap behavior. Lastly, these results demonstrate multiple nodeless superconducting gaps in ZrTe 3–x Se x, which indicates conventional superconductivity despite of the existence of a CDW QCP.« less

  10. APS undulator and wiggler sources: Monte-Carlo simulation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Xu, S.L.; Lai, B.; Viccaro, P.J.

    1992-02-01

    Standard insertion devices will be provided to each sector by the Advanced Photon Source. It is important to define the radiation characteristics of these general purpose devices. In this document,results of Monte-Carlo simulation are presented. These results, based on the SHADOW program, include the APS Undulator A (UA), Wiggler A (WA), and Wiggler B (WB).

  11. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe 1+yTe 1-xSe x [How does annealing in chalcogen vapor induce superconductivity in Fe 1+yTe -xSe x?

    DOE PAGES

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; ...

    2015-02-27

    Recent investigations have shown that Fe 1+yTe 1-xSe x can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon we performed a combination of magnetic susceptibility, specific heat and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe 1+yTe 1-xSe x treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTe mmore » (m ≥ 1) complexes. We show that the remaining FeTe m complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.« less

  12. The Effects of Wiggler Errors on Free Electron Laser Performance

    DTIC Science & Technology

    1990-04-02

    phase deviation at the end of the wiggler by 113. The detrimental effects of wiggler errors may be reduced by arranging the magent poles in an optimal...fdz6BI. To meet these specifications, the vendor may arrange the mIagnet pole iD an optimum sequence such that If dz6BI is minimized. The present research...zc a- A,,/2. By considering a wiggler in which the error for a given magnet pole is correlated to the errors of the surrounding poles , one may

  13. Two superconducting transitions in single-crystal La 2 - x Ba x CuO 4

    DOE PAGES

    Tee, X. Y.; Ito, T.; Ushiyama, T.; ...

    2017-02-27

    Here, we use spatially-resolved transport techniques to investigate the superconducting properties of single crystals La 2-xBa xCuO 4. We also found a superconducting transition temperature T cs associated with the ab-plane surface region which is considerably higher than the bulk T c. This effect is pronounced in the region of charge carrier doping x with strong spin-charge stripe correlations, reaching T cs = 36 K or 1.64T c.

  14. Interplay between Superconductivity and Magnetism in Fe1-xPdxTe

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Karki, A B; Garlea, Vasile O; Custelcean, Radu

    The love/hate relationship between superconductivity and magnetic ordering has fascinated the condensed matter physics community for a century. In the early days, magnetic impurities doped into a superconductor were found to quickly suppress superconductivity. Later, a variety of systems, such as cuprates, heavy fermions and Fe pnictides, show superconductivity in a narrow region near the border to antiferromagnetism (AFM) as a function of pressure or doping. On the other hand, the coexistence of superconductivity and ferromagnetic (FM) or AFM ordering is found in a few compounds (RRh4B4 (R = Nd, Sm, Tm, Er), R'Mo6X8 (R' = Tb, Dy, Er, Ho,more » and X = S, Se), UMGe (M = Ge, Rh, Co), CeCoIn5, EuFe2(As1-xPx)2 etc.), providing evidence for their compatibility. Here, we present a third situation, where superconductivity coexists with FM and near the border of AFM in Fe1-xPdxTe. The doping of Pd for Fe gradually suppresses the first-order AFM ordering at temperature TN/S, and turns into short-range (SR) AFM correlation with a characteristic peak in magnetic susceptibility at T'N. Superconductivity sets in when T'N reaches zero. However, there is a gigantic ferromagnetic dome imposed in the superconducting-AFM (SR) crossover regime. Such a system is ideal for studying the interplay between superconductivity and two types of magnetic interactions (FM and AFM).« less

  15. Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe3-x Se x

    NASA Astrophysics Data System (ADS)

    Shan, Cui; Lan-Po, He; Xiao-Chen, Hong; Xiang-De, Zhu; Cedomir, Petrovic; Shi-Yan, Li

    2016-07-01

    It was found that selenium doping can suppress the charge-density-wave (CDW) order and induce bulk superconductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point (QCP) in ZrTe3-x Se x near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe3-x Se x single crystals (x = 0.044 and 0.051) down to 80 mK. For both samples, the residual linear term κ 0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ 0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe3-x Se x , which indicates conventional superconductivity despite of the existence of a CDW QCP. Project supported by the National Basic Research Program of China (Grant Nos. 2012CB821402 and 2015CB921401), the National Natural Science Foundation of China (Grant Nos. 91421101, 11422429, and 11204312), the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, China, and STCSM of China (Grant No. 15XD1500200). Work at Brookhaven National Laboratory was supported by the US DOE under Contract No. DESC00112704.

  16. Phase diagram and neutron spin resonance of superconducting NaFe 1 - x Cu x As

    DOE PAGES

    Tan, Guotai; Song, Yu; Zhang, Rui; ...

    2017-02-03

    In this paper, we use transport and neutron scattering to study the electronic phase diagram and spin excitations of NaFe 1-xCu xAs single crystals. Similar to Co- and Ni-doped NaFeAs, a bulk superconducting phase appears near x≈2% with the suppression of stripe-type magnetic order in NaFeAs. Upon further increasing Cu concentration the system becomes insulating, culminating in an antiferromagnetically ordered insulating phase near x≈50%. Using transport measurements, we demonstrate that the resistivity in NaFe 1-xCu xAs exhibits non-Fermi-liquid behavior near x≈1.8%. Our inelastic neutron scattering experiments reveal a single neutron spin resonance mode exhibiting weak dispersion along c axis inmore » NaFe 0.98Cu 0.02As. The resonance is high in energy relative to the superconducting transition temperature T c but weak in intensity, likely resulting from impurity effects. These results are similar to other iron pnictides superconductors despite that the superconducting phase in NaFe 1-xCu xAs is continuously connected to an antiferromagnetically ordered insulating phase near x≈50% with significant electronic correlations. Finally, therefore, electron correlations is an important ingredient of superconductivity in NaFe 1-xCu xAs and other iron pnictides.« less

  17. Superconductivity in layered ZrP2-x Se x with PbFCl-type structure

    NASA Astrophysics Data System (ADS)

    Ishida, Shigeyuki; Fujihisa, Hiroshi; Hase, Izumi; Yanagi, Yousuke; Kawashima, Kenji; Oka, Kunihiko; Gotoh, Yoshito; Yoshida, Yoshiyuki; Iyo, Akira; Eisaki, Hiroshi; Kito, Hijiri

    2016-05-01

    We performed a systematic study of the crystal structure, physical properties, and electronic structure of PbFCl-type ZrP2-x Se x (0.3 ≤ x ≤ 0.9). We successfully synthesized single-phase polycrystalline samples for the Se substitution range of 0.4 ≤ x ≤ 0.8. The crystal structure of the compound is characterized by the alternate stacking of a two-dimensional P square net and a Zr-(P1-x Se x ) network. ZrP2-x Se x exhibits a dome-like superconductivity phase diagram and has a maximum superconducting transition temperature (T c) of 6.3 K for x ≈ 0.6. Resistivity and Hall measurements indicated that electron-phonon scattering plays a dominant role and that electron-type carriers dominate charge transport. Specific heat measurements confirmed that ZrP2-x Se x exhibits bulk superconductivity. Further, the value of the specific heat jump at T c (ΔC/γT c ≈ 1.35) is in keeping with the BCS weak-coupling model. These facts suggest a rather conventional pairing mechanism in ZrP2-x Se x . The x dependence of T c can be explained on the basis of the density of states (DOS) for x ≤ 0.7, whereas the decrease in T c with an increase in the DOS for x = 0.8 needs further investigation. One possible reason for the suppression of superconductivity is that the PbFCl-type structure becomes unstable for x ≥ 0.8. The results of electronic structure calculations agree reasonably well with those of the experimental observations, suggesting that the Zrd band plays a primary role in determining the physical properties. Further, the calculations predict a significant change in the Fermi-surface topology for x ≥ 0.8 this is a probable reason for the decrease in T c as well as the instability of the PbFCl-type structure.

  18. Static charge-density-wave order in the superconducting state of La 2 - x Ba x CuO 4

    DOE PAGES

    Thampy, V.; Chen, X. M.; Cao, Y.; ...

    2017-06-15

    Charge-density-wave (CDW) correlations feature prominently in the phase diagram of the cuprates, motivating competing theories of whether fluctuating CDW correlations aid superconductivity or whether static CDW order coexists with superconductivity in inhomogeneous or spatially modulated states. Here we report Cu L-edge resonant x-ray photon correlation spectroscopy measurements of CDW correlations in superconducting La 2–xBa xCuO 4, x = 0.11. Static CDW order is shown to exist in the superconducting state at low temperatures and to persist up to at least 85% of the CDW transition temperature. As a result, we discuss the implications of our observations for how nominally competingmore » order parameters can coexist in the cuprates.« less

  19. Calculation of the coherent synchrotron radiation impedance from a wiggler

    NASA Astrophysics Data System (ADS)

    Wu, Juhao; Raubenheimer, Tor O.; Stupakov, Gennady V.

    2003-04-01

    Most studies of coherent synchrotron radiation (CSR) have considered only the radiation from independent dipole magnets. However, in the damping rings of future linear colliders, a large fraction of the radiation power will be emitted in damping wigglers. In this paper, the longitudinal wakefield and impedance due to CSR in a wiggler are derived in the limit of a large wiggler parameter K. After an appropriate scaling, the results can be expressed in terms of universal functions, which are independent of K. Analytical asymptotic results are obtained for the wakefield in the limit of large and small distances, and for the impedance in the limit of small and high frequencies.

  20. Composition dependence of superconductivity in YBa2(Cu(3-x)Al(x))O(y)

    NASA Technical Reports Server (NTRS)

    Bansal, N. P.

    1993-01-01

    Eleven different compositions in the system YBa2(Cu(3-x)Al(x))O(y) (x = 0 to 0.3) have been synthesized and characterized by electrical resistivity measurements, powder X-ray diffraction, and scanning electron microscopy. The superconducting transition temperature T sub c (onset) was almost unaffected by the presence of alumina due to its limited solubility in YBa2Cu3O(7-x). However, T sub c(R = 0) gradually decreased, and the resistive tails became longer with increasing Al2O3 concentration. This was probably due to formation of BaAl2O4 and other impurity phases from chemical decomposition of the superconducting phase by reaction with Al2O3.

  1. Tunability enhanced electromagnetic wiggler

    DOEpatents

    Schlueter, Ross D.; Deis, Gary A.

    1992-01-01

    The invention discloses a wiggler used in synchrotron radiation sources and free electron lasers, where each pole is surrounded by at least two electromagnetic coils. The electromagnetic coils are energized with different amounts of current to provide a wide tunable range of the on-axis magnetic flux density, while preventing magnetic saturation of the poles.

  2. STM/STS study of the superconducting gap in SmFeAsO1-xFx

    NASA Astrophysics Data System (ADS)

    Kawashima, Yuki; Ichimura, Koichi; Katono, Kazuhiro; Kurosawa, Tohru; Oda, Migaku; Tanda, Satoshi; Kamihara, Yoichi; Hosono, Hideo

    2015-02-01

    We report an electron tunneling study of SmFeAsO1-xFx in the low doping region (x=0, 0.045, 0.046, 0.069) by low temperature UHV-STM/STS. Superconducting gaps are observed for each superconducting sample x=0.045 (Tc=12.9 K), x=0.046 (Tc=32.9 K) and x=0.069 (Tc=46.9 K). We obtained corresponding superconducting gap size of ΔSC = 9.5 ± 0.5 meV, 9.75±0.25 meV and 11±1 meV. While Tc increases, ΔSC is kept the same. This suggests that the effective attractive interaction is the same and that there is some mechanism that suppresses the superconductivity in the low doping region. On the other hand, similar gap structures were found in a non-superconducting sample with x=0 at 7.8 K. The obtained gap size was ΔN = 8.5 ± 1.5 meV, which is almost the same as the superconducting gap in the superconducting samples (x=0.045, 0.046, 0.069).

  3. Interplay between superconductivity and magnetism in Fe1−xPdxTe

    PubMed Central

    Karki, Amar B.; Garlea, V. Ovidiu; Custelcean, Radu; Stadler, Shane; Plummer, E. W.; Jin, Rongying

    2013-01-01

    The attractive/repulsive relationship between superconductivity and magnetic ordering has fascinated the condensed matter physics community for a century. In the early days, magnetic impurities doped into a superconductor were found to quickly suppress superconductivity. Later, a variety of systems, such as cuprates, heavy fermions, and Fe pnictides, showed superconductivity in a narrow region near the border to antiferromagnetism (AFM) as a function of pressure or doping. However, the coexistence of superconductivity and ferromagnetic (FM) or AFM ordering is found in a few compounds [RRh4B4 (R = Nd, Sm, Tm, Er), R′Mo6X8 (R′ = Tb, Dy, Er, Ho, and X = S, Se), UMGe (M = Ge, Rh, Co), CeCoIn5, EuFe2(As1−xPx)2, etc.], providing evidence for their compatibility. Here, we present a third situation, where superconductivity coexists with FM and near the border of AFM in Fe1−xPdxTe. The doping of Pd for Fe gradually suppresses the first-order AFM ordering at temperature TN/S, and turns into short-range AFM correlation with a characteristic peak in magnetic susceptibility at T′N. Superconductivity sets in when T′N reaches zero. However, there is a gigantic ferromagnetic dome imposed in the superconducting-AFM (short-range) cross-over regime. Such a system is ideal for studying the interplay between superconductivity and two types of magnetic (FM and AFM) interactions. PMID:23690601

  4. Superconductivity in LaPd2Al2-xGax compounds

    NASA Astrophysics Data System (ADS)

    Klicpera, M.; Pásztorová, J.; Javorský, P.

    2014-08-01

    The superconductivity in LaPd2Al2-xGax compounds was studied by means of electrical resistivity and specific heat measurements. The concentration development of the superconducting properties was revealed. The measured data deviate significantly from the Bardeen-Cooper-Schrieffer theory predictions and are discussed in the context of unconventional superconductivity. The electronic specific heat below {{T}_{SC}} follows almost quadratic temperature dependence, which might indicate an axial state with line nodes in the superconducting gap structure.

  5. Superconductivity, pairing symmetry, and disorder in the doped topological insulator Sn 1 - x In x Te for x ≥ 0.10

    DOE PAGES

    Smylie, M. P.; Claus, H.; Kwok, W. -K.; ...

    2018-01-19

    The temperature dependence of the London penetration depth Δλ(T) in the superconducting doped topological crystalline insulator Sn 1-xIn x Te was measured down to 450 mK for two different doping levels, x ≈ 0.45 (optimally doped) and x ≈ 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. The introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance T c, indicating that ferroelectric interactionsmore » do not compete with superconductivity.« less

  6. Superconductivity, pairing symmetry, and disorder in the doped topological insulator Sn 1 - x In x Te for x ≥ 0.10

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Smylie, M. P.; Claus, H.; Kwok, W. -K.

    The temperature dependence of the London penetration depth Δλ(T) in the superconducting doped topological crystalline insulator Sn 1-xIn x Te was measured down to 450 mK for two different doping levels, x ≈ 0.45 (optimally doped) and x ≈ 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. The introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance T c, indicating that ferroelectric interactionsmore » do not compete with superconductivity.« less

  7. Tunability enhanced electromagnetic wiggler

    DOEpatents

    Schlueter, R.D.; Deis, G.A.

    1992-03-24

    The invention discloses a wiggler used in synchrotron radiation sources and free electron lasers, where each pole is surrounded by at least two electromagnetic coils. The electromagnetic coils are energized with different amounts of current to provide a wide tunable range of the on-axis magnetic flux density, while preventing magnetic saturation of the poles. 14 figs.

  8. A multilayered approach to superconducting tunnel junction x ray detectors

    NASA Technical Reports Server (NTRS)

    Rippert, E. D.; Song, S. N.; Ketterson, J. B.; Maglic, S. R.; Lomatch, S.; Thomas, C.; Cheida, M. A.; Ulmer, M. P.

    1992-01-01

    'First generation' superconducting tunnel junction X-ray detectors (characterized by a single tunnel junction in direct contact with its substrate, with totally external amplification) remain more than an order of magnitude away from their theoretical energy resolutions which are in the order of eV's. The difficulties that first generation devices are encountering are being attacked by a 'second generation' of superconducting X-ray detector designs including quasiparticle trapping configurations and Josephson junction arrays. A second generation design concept, the multilayered superconducting tunnel junction X-ray detector, consisting of tens to hundreds of tunnel junctions stacked on top of one another (a superlattice), is presented. Some of the possibilities of this engineered materials approach include the tuning of phonon transmission characteristics of the material, suppression of parasitic quasiparticle trapping and intrinsic amplification.

  9. Technology Development for Tapered-Wiggler Free-Electron Lasers

    DTIC Science & Technology

    1984-04-01

    3-12 . 3-8 Demagnetizing Field for Magnets in Assembled Wiggler, 3-14 the Contour Lines are of g H/M, where K (-B )0r is the Level of Magnetization . 3...of discrepancy may be due to demagnetization at the time of wiggler assembly. The demagnetizing a field for magnets in the presence of the entire... magnetization . The areas of £s0H/M -l- will suf fer Pm. some permanent demagnetization . This loss of magnetization is the reason %! for the slight rolloff

  10. Differences in chemical doping matter: Superconductivity in Ti 1-xTa xSe 2 but not in Ti 1-xNb xSe 2

    DOE PAGES

    Luo, Huixia; Zhu, Yimei; Xie, Weiwei; ...

    2016-02-21

    We report that 1T-TiSe 2, an archetypical layered transition metal dichalcogenide, becomes superconducting when Ta is substituted for Ti but not when Nb is substituted for Ti. This is unexpected because Nb and Ta should be chemically equivalent electron donors. Superconductivity emerges near x = 0.02 for Ti 1–xTa xSe 2, while, for Ti 1–xNb xSe 2, no superconducting transitions are observed above 0.4 K. The equivalent chemical nature of the dopants is confirmed by X-ray photoelectron spectroscopy. ARPES and Raman scattering studies show similarities and differences between the two systems, but the fundamental reasons why the Nb and Tamore » dopants yield such different behavior are unknown. We present a comparison of the electronic phase diagrams of many electron-doped 1T-TiSe 2 systems, showing that they behave quite differently, which may have broad implications in the search for new superconductors. Here, we propose that superconducting Ti 0.8Ta 0.2Se 2 will be suitable for devices and other studies based on exfoliated crystal flakes.« less

  11. Magnetic and Superconducting Properties in Single Crystalline Fe1+δTe1-xSex (x<0.50) System

    NASA Astrophysics Data System (ADS)

    Jinhu Yang,; Mami Matsui,; Masatomo Kawa,; Hiroto Ohta,; Chishiro Michioka,; Chiheng Dong,; Hangdong Wang,; Huiqiu Yuan,; Minghu Fang,; Kazuyoshi Yoshimura,

    2010-07-01

    The spin-fluctuation effect in the Se-substituted single crystalline Fe1+δTe1-xSex (x = 0, 0.05, 0.12, 0.20, 0.30, 0.33, 0.45, and 0.48; 0≤δ≤ 0.12) and the polycrystalline Fe1.11Se has been studied by the measurements of the X-ray diffraction, the magnetic susceptibility under high magnetic fields and the electrical resistivity under magnetic fields up to 14 T. The samples with x = 0.05, 0.12, 0.20, 0.30, 0.33, 0.45, and 0.48 show superconducting transition temperatures in the ranger of 10-14 K. We obtained their intrinsic susceptibilities by the Honda-Owen method. A nearly linear-in-T behavior in magnetic susceptibility of Se-rich superconducting samples was observed, indicating the antiferromagnetic spin fluctuations have a strong link with the superconductivity in this series. The upper critical field μ0Hc2orb for T\\to 0 was estimated to exceed the Pauli paramagnetic limit. The Kadowaki-Woods and Wilson ratios indicate that electrons are strongly correlated in this system. Furthermore, the superconducting coherence length and the electron mean free path were also discussed. These superconducting parameters indicate that the superconductivity in the Fe1+δTe1-xSex system is unconventional.

  12. Superconductivity, pairing symmetry, and disorder in the doped topological insulator Sn 1 - x In x Te for x ≥ 0.10

    DOE PAGES

    Smylie, M. P.; Claus, H.; Kwok, W. -K.; ...

    2018-01-19

    In this paper, the temperature dependence of the London penetration depth Δλ(T) in the superconducting doped topological crystalline insulator Sn 1-xIn xTe was measured down to 450 mK for two different doping levels, x ≈ 0.45 (optimally doped) and x ≈ 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. Finally, the introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance T c, indicatingmore » that ferroelectric interactions do not compete with superconductivity.« less

  13. Superconductivity, pairing symmetry, and disorder in the doped topological insulator Sn 1 - x In x Te for x ≥ 0.10

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Smylie, M. P.; Claus, H.; Kwok, W. -K.

    In this paper, the temperature dependence of the London penetration depth Δλ(T) in the superconducting doped topological crystalline insulator Sn 1-xIn xTe was measured down to 450 mK for two different doping levels, x ≈ 0.45 (optimally doped) and x ≈ 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. Finally, the introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance T c, indicatingmore » that ferroelectric interactions do not compete with superconductivity.« less

  14. Superconductivity, Pairing Symmetry, and Disorder in the Doped Topological Insulator Sn 1-xIn xTe for x >= 0.10.

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Smylie, M. P.; Claus, H.; Kwok, W. -K.

    The temperature dependence of the London penetration depth Delta lambda(T) in the superconducting doped topological crystalline insulator Sn1-xInxTe was measured down to 450 mK for two different doping levels, x approximate to 0.45 (optimally doped) and x approximate to 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. The introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance T-c, indicating that ferroelectric interactions domore » not compete with superconductivity.« less

  15. Wiggler magnetic field assisted third harmonic generation in expanding clusters

    NASA Astrophysics Data System (ADS)

    Vij, Shivani

    2018-04-01

    A simple theoretical model is constructed to study the wiggler magnetic field assisted third harmonic generation of intense short pulse laser in a cluster in its expanding phase. The ponderomotive force of laser causes density perturbations in cluster electron density which couples with wiggler magnetic field to produce a nonlinear current that generates transverse third harmonic. An intense short pulse laser propagating through a gas embedded with atomic clusters, converts it into hot plasma balls via tunnel ionization. Initially, the electron plasma frequency inside the clusters ω pe > \\sqrt{3}{ω }1 (with ω 1 being the frequency of the laser). As the cluster expands under Coulomb force and hydrodynamic pressure, ω pe decreases to \\sqrt{3}{ω }1. At this time, there is resonant enhancement in the efficiency of the third harmonic generation. The efficiency of third harmonic generation is enhanced due to cluster plasmon resonance and by phase matching due to wiggler magnetic field. The effect of cluster size on the expansion rate is studied to observe that the clusters of different radii would expand differently. The impact of laser intensity and wiggler magnetic field on the efficiency of third harmonic generation is also explored.

  16. High-Resolution Hard X-Ray and Gamma-Ray Spectrometers Based on Superconducting Absorbers Coupled to Superconducting Transition Edge Sensors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    van den Berg, M.; Chow, D.; Loshak, A.

    2000-09-21

    We are developing detectors based on bulk superconducting absorbers coupled to superconducting transition edge sensors (TES) for high-resolution spectroscopy of hard X-rays and soft gamma-rays. We have achieved an energy resolution of 70 eV FWHM at 60 keV using a 1 x 1 x 0.25 mm{sup 3} Sn absorber coupled to a Mo/Cu multilayer TES with a transition temperature of 100 mK. The response of the detector is compared with a simple model using only material properties data and characteristics derived from IV-measurements. We have also manufactured detectors using superconducting absorbers with a higher stopping power, such as Pb andmore » Ta. We present our first measurements of these detectors, including the thermalization characteristics of the bulk superconducting absorbers. The differences in performance between the detectors are discussed and an outline of the future direction of our detector development efforts is given.« less

  17. Stripe-like nanoscale structural phase separation in superconducting BaPb 1-xBi xO 3

    DOE PAGES

    Giraldo-Gallo, P.; Zhang, Y.; Parra, C.; ...

    2015-09-16

    The phase diagram of BaPb 1-xBi xO 3 exhibits a superconducting “dome” in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare to the Ginzburg-Landau coherence length. Thus, we find that the maximum T c occurs when the superconducting coherence length matches the width of the partiallymore » disordered stripes, implying a connection between the structural phase separation and the shape of the superconducting dome.« less

  18. New Superconductivity Dome in LaFeAsO1-xFx Accompanied by Structural Transition

    NASA Astrophysics Data System (ADS)

    Yang, Jie; Zhou, Rui; Wei, Lin-Lin; Yang, Huai-Xin; Li, Jian-Qi; Zhao, Zhong-Xian; Zheng, Guo-Qing

    2015-10-01

    High temperature superconductivity is often found in the vicinity of antiferromagnetism. This is also true in LaFeAsO$_{1-x}$F$_{x}$ ($x \\leq$ 0.2) and many other iron-based superconductors, which leads to proposals that superconductivity is mediated by fluctuations associated with the nearby magnetism. Here we report the discovery of a new superconductivity dome without low-energy magnetic fluctuations in LaFeAsO$_{1-x}$F$_{x}$ with 0.25$\\leq x \\leq$0.75, where the maximal critical temperature $T_c$ at $x_{opt}$ = 0.5$\\sim$0.55 is even higher than that at $x \\leq$ 0.2. By nuclear magnetic resonance and Transmission Electron Microscopy, we show that a C4 rotation symmetry-breaking structural transition takes place for $x>$ 0.5 above $T_c$. Our results point to a new paradigm of high temperature superconductivity.

  19. Interface-enhanced high-temperature superconductivity in single-unit-cell FeT e1 -xS ex films on SrTi O3

    NASA Astrophysics Data System (ADS)

    Li, Fangsen; Ding, Hao; Tang, Chenjia; Peng, Junping; Zhang, Qinghua; Zhang, Wenhao; Zhou, Guanyu; Zhang, Ding; Song, Can-Li; He, Ke; Ji, Shuaihua; Chen, Xi; Gu, Lin; Wang, Lili; Ma, Xu-Cun; Xue, Qi-Kun

    2015-06-01

    Recently discovered high-temperature superconductivity in single-unit-cell (UC) FeSe films on SrTi O3 (STO) substrate has stimulated tremendous research interest, both experimental and theoretical. Whether this scenario could be extended to other superconductors is vital in both identifying the enhanced superconductivity mechanism and further raising the critical transition temperature (Tc). Here we successfully prepared single-UC FeT e1 -xS ex(0.1 ≤x ≤0.6 ) films on STO substrates by molecular beam epitaxy and observed U -shaped superconducting gaps (Δ ) up to ˜16.5 meV , nearly ten times the gap value (Δ ˜1.7 meV ) of the optimally doped bulk FeT e0 .6S e0 .4 single crystal (Tc˜14.5 K ). No superconducting gap has been observed on the second UC and thicker FeT e1 -xS ex films at 5.7 K, indicating the important role of the interface. This interface-enhanced high-temperature superconductivity is further confirmed by ex situ transport measurements, which revealed an onset superconducting transition temperature above 40 K, nearly two times higher than that of the optimally doped bulk FeT e0 .6S e0 .4 single crystal. This work demonstrates that interface engineering is a feasible way to discover alternative superconductors with higher Tc.

  20. Harmonic generation with multiple wiggler schemes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bonifacio, R.; De Salvo, L.; Pierini, P.

    1995-02-01

    In this paper the authors give a simple theoretical description of the basic physics of the single pass high gain free electron laser (FEL), describing in some detail the FEL bunching properties and the harmonic generation technique with a multiple-wiggler scheme or a high gain optical klystron configuration.

  1. Superconducting, magnetic and magnetotransport properties of FeTe1-xSex single crystals

    NASA Astrophysics Data System (ADS)

    Kumar, Rohit; Sudesh, Varma, G. D.

    2018-05-01

    The single crystalline samples with compositions FeTe1-xSex (0.25 ≤ x ≤ 0.50) have been prepared via self-flux method and the superconducting, magnetic and magnetotransport properties of the grown crystals were investigated. The superconducting onset temperatures have been determined from the measurements of zero field cooled magnetization and resistance with temperatures. In the present case, highest superconducting transition temperature TC (onset) ˜ 15 K has been obtained for x=0.5. The HC2 (T=0 K) values have been estimated by fitting the experimental HC2 - T plots with WHH model. The highest HC2(0) has been obtained for x=0.5. The activation energy of the thermally activated flux flow has been found from the broadening of superconducting transition in an applied magnetic field using the Arrhenius law. Our results show that the activation energy (U0) decreases with the increasing magnetic field. Furthermore, the magnetization measurements for x=0.4 and 0.5 samples have been performed at T=5 K in the magnetic field range ±7 T to estimate critical current density at different applied magnetic fields using Bean formula. We see that the sample x=0.5 has higher values of JC as compared to that of x=0.4 at all magnetic fields. This is in conformity with the behavior of U0-H plots.

  2. Optical pulse evolution in the Stanford free-electron laser and in a tapered wiggler

    NASA Technical Reports Server (NTRS)

    Colson, W. B.

    1982-01-01

    The Stanford free electron laser (FEL) oscillator is driven by a series of electron pulses from a high-quality superconducting linear accelerator (LINAC). The electrons pass through a transverse and nearly periodic magnetic field, a 'wiggler', to oscillate and amplify a superimposed optical pulse. The rebounding optical pulse must be closely synchronized with the succession of electron pulses from the accelerator, and can take on a range of structures depending on the precise degree of synchronism. Small adjustments in desynchronism can make the optical pulse either much shorter or longer than the electron pulse, and can cause significant subpulse structure. The oscillator start-up from low level incoherent fields is discussed. The effects of desynchronism on coherent pulse propagation are presented and compared with recent Stanford experiments. The same pulse propagation effects are studied for a magnet design with a tapered wavelength in which electrons are trapped in the ponderomotive potential.

  3. Superconductivity at 43K in SmFeAsO1-xFx

    NASA Astrophysics Data System (ADS)

    Chen, X. H.; Wu, T.; Wu, G.; Liu, R. H.; Chen, H.; Fang, D. F.

    2008-06-01

    Since the discovery of high-transition-temperature (high-Tc) superconductivity in layered copper oxides, extensive effort has been devoted to exploring the origins of this phenomenon. A Tc higher than 40K (about the theoretical maximum predicted from Bardeen-Cooper-Schrieffer theory), however, has been obtained only in the copper oxide superconductors. The highest reported value for non-copper-oxide bulk superconductivity is Tc = 39K in MgB2 (ref. 2). The layered rare-earth metal oxypnictides LnOFeAs (where Ln is La-Nd, Sm and Gd) are now attracting attention following the discovery of superconductivity at 26K in the iron-based LaO1-xFxFeAs (ref. 3). Here we report the discovery of bulk superconductivity in the related compound SmFeAsO1-xFx, which has a ZrCuSiAs-type structure. Resistivity and magnetization measurements reveal a transition temperature as high as 43K. This provides a new material base for studying the origin of high-temperature superconductivity.

  4. Coexistence of superconductivity and short-range double-stripe spin correlations in Te-vapor annealed FeTe 1–xSe x with x ≤ 0.2

    DOE PAGES

    Xu, Zhijun; Tranquada, John M.; Schneeloch, J. A.; ...

    2018-06-30

    In as-grown bulk crystals of Fe 1+yTe 1–xSe x with x ≲ 0.3, excess Fe (y > 0) is inevitable and correlates with a suppression of superconductivity. At the same time, t here remains the question as to whether the character of the antiferromagnetic correlations associated wi th the enhanced anion height above the Fe planes in Te-rich samples is compatible with superconductivity. To t est this, we have annealed as-grown crystals with x = 0.1 and 0.2 in Te vapor, effectively reducing the excess Fe and in ducing bulk superconductivity. Inelastic neutron scattering measurements reveal low-energy magnet ic excitationsmore » consistent with short-range correlations of the double-stripe type; nevertheless, cooling int o the superconducting state results in a spin gap and a spin resonance, with the extra signal in the resonance being short-range with a mixed single-stripe/double-stripe character, which is different than other iron-based superconductors. In conclusion, the mixed magnetic character of these superconducting samples does not appear to be trivially explainable by inhomogeneity.« less

  5. Coexistence of superconductivity and short-range double-stripe spin correlations in Te-vapor annealed FeTe 1–xSe x with x ≤ 0.2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Xu, Zhijun; Tranquada, John M.; Schneeloch, J. A.

    In as-grown bulk crystals of Fe 1+yTe 1–xSe x with x ≲ 0.3, excess Fe (y > 0) is inevitable and correlates with a suppression of superconductivity. At the same time, t here remains the question as to whether the character of the antiferromagnetic correlations associated wi th the enhanced anion height above the Fe planes in Te-rich samples is compatible with superconductivity. To t est this, we have annealed as-grown crystals with x = 0.1 and 0.2 in Te vapor, effectively reducing the excess Fe and in ducing bulk superconductivity. Inelastic neutron scattering measurements reveal low-energy magnet ic excitationsmore » consistent with short-range correlations of the double-stripe type; nevertheless, cooling int o the superconducting state results in a spin gap and a spin resonance, with the extra signal in the resonance being short-range with a mixed single-stripe/double-stripe character, which is different than other iron-based superconductors. In conclusion, the mixed magnetic character of these superconducting samples does not appear to be trivially explainable by inhomogeneity.« less

  6. Superconductivity, pairing symmetry, and disorder in the doped topological insulator Sn1 -xInxTe for x ≥0.10

    NASA Astrophysics Data System (ADS)

    Smylie, M. P.; Claus, H.; Kwok, W.-K.; Louden, E. R.; Eskildsen, M. R.; Sefat, A. S.; Zhong, R. D.; Schneeloch, J.; Gu, G. D.; Bokari, E.; Niraula, P. M.; Kayani, A.; Dewhurst, C. D.; Snezhko, A.; Welp, U.

    2018-01-01

    The temperature dependence of the London penetration depth Δ λ (T ) in the superconducting doped topological crystalline insulator Sn1 -xInxTe was measured down to 450 mK for two different doping levels, x ≈0.45 (optimally doped) and x ≈0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. The introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance Tc, indicating that ferroelectric interactions do not compete with superconductivity.

  7. Enhancement of Superconductivity of Lanthanum and Yttrium Sesquicarbide

    DOEpatents

    Krupka, M. C.; Giorgi, A. L.; Krikorian, N. H.; Szklarz, E. G.

    1972-06-22

    A method of enhancing the superconductivity of body-centered cubic lanthanum and yttrium sesquicarbide through formation of the sesquicarbides from ternary alloys of novel composition (N/sub x/M/sub 1-x/)C/sub z/, where N is yttrium or lanthanum, M is thorium, any of the Group IV and VI transition metals, or gold, germanium or silicon, and z is approximately 1.2 to 1.6. These ternary sesquicarbides have superconducting transition temperatures as high as 17.0/sup 0/K.

  8. Enhancement of superconductivity of lanthanum and yttrium sesquicarbide

    DOEpatents

    Krupka, M.C.; Giorgi, A.L.; Krikorian, N.H.; Szklarz, E.G.

    1971-06-22

    A method of enhancing the superconductivity of body-centered cubic lanthanum and yttrium sesquicarbide through formation of the sesquicarbides from ternary alloys of novel composition (N/sub x/M/sub 1-x/)C/sub z/, where N is yttrium or lanthanum, M is thorium, any of the Group IV and VI transition metals, or gold, germanium or silicon, and z is approximately 1.2 to 1.6. These ternary sesquicarbides have superconducting transition temperatures as high as 17.0/sup 0/K.

  9. Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high temperature superconductor La 2-x(Sr;Ba) xCuO 4

    DOE PAGES

    Wagman, J. J.; Carlo, Jeremy P.; Gaudet, J.; ...

    2016-03-14

    We present time-of-flight neutron-scattering measurements on single crystals of La 2-xBa xCuO 4 (LBCO) with 0 ≤ x ≤ 0.095 and La 2-xSr xCuO 4 (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high temperature cuprate superconductivity, ranging from insulating, three dimensional commensurate long range antiferromagnetic order for x ≤ 0.02 to two dimensional (2D) incommensurate antiferromagnetism co-existing with superconductivity for x ≥ 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear resonant enhancement of the inelastic scattering coincident with the low energy crossingsmore » of the highly dispersive spin excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore we show that the low temperature, low energy magnetic spectral weight is substantially larger for samples with non-superconducting ground states relative to any of the samples with superconducting ground states. Lastly spin gaps, suppression of low energy magnetic spectral weight, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO« less

  10. Hard X-ray Sources for the Mexican Synchrotron Project

    NASA Astrophysics Data System (ADS)

    Reyes-Herrera, Juan

    2016-10-01

    One of the principal tasks for the design of the Mexican synchrotron was to define the storage ring energy. The main criteria for choosing the energy come from studying the electromagnetic spectrum that can be obtained from the synchrotron, because the energy range of the spectrum that can be obtained will determine the applications available to the users of the future light source. Since there is a public demand of hard X-rays for the experiments in the synchrotron community users from Mexico, in this work we studied the emission spectra from some hard X-ray sources which could be the best options for the parameters of the present Mexican synchrotron design. The calculations of the flux and the brightness for one Bending Magnet and four Insertion Devices are presented; specifically, for a Superconducting Bending Magnet (SBM), a Superconducting Wiggler (SCW), an In Vacuum Short Period Undulator (IV-SPU), a Superconducting Undulator (SCU) and for a Cryogenic Permanent Magnet Undulator (CPMU). Two commonly available synchrotron radiation programs were used for the computation (XOP and SRW). From the results, it can be concluded that the particle beam energy from the current design is enough to have one or more sources of hard X-rays. Furthermore, a wide range of hard X-ray region can be covered by the analyzed sources, and the choice of each type should be based on the specific characteristics of the X-ray beam to perform the experiments at the involved beamline. This work was done within the project Fomix Conacyt-Morelos ”Plan Estrategico para la construccion y operación de un Sincrotron en Morelos” (224392).

  11. Superconducting order from disorder in 2H-TaSe2-xSx

    NASA Astrophysics Data System (ADS)

    Li, Lijun; Deng, Xiaoyu; Wang, Zhen; Liu, Yu; Abeykoon, Milinda; Dooryhee, Eric; Tomic, Aleksandra; Huang, Yanan; Warren, John B.; Bozin, Emil S.; Billinge, Simon J. L.; Sun, Yuping; Zhu, Yimei; Kotliar, Gabriel; Petrovic, Cedomir

    2017-12-01

    We report on the emergence of robust superconducting order in single crystal alloys of TaSe2-xSx (0 ≤ × ≤ 2). The critical temperature of the alloy is surprisingly higher than that of the two end compounds TaSe2 and TaS2. The evolution of superconducting critical temperature Tc(x) correlates with the full width at half maximum of the Bragg peaks and with the linear term of the high-temperature resistivity. The conductivity of the crystals near the middle of the alloy series is higher or similar than that of either one of the end members 2H-TaSe2 and/or 2H-TaS2. It is known that in these materials superconductivity is in close competition with charge density wave order. We interpret our experimental findings in a picture where disorder tilts this balance in favor of superconductivity by destroying the charge density wave order.

  12. Growth and structural characterization of large superconducting crystals of La 2 - x Ca 1 + x Cu 2 O 6

    DOE PAGES

    Schneeloch, J. A.; Guguchia, Z.; Stone, M. B.; ...

    2017-12-01

    Lmore » arge crystals of a 2 - x Ca 1 + x Cu 2 O 6 (a-Ca-2126) with x = 0:10 and 0.15 have been grown and converted to bulk superconductors by high-pressure oxygen annealing. The superconducting transition temperature, T c, is as high as 55 K; this can be raised to 60 K by post-annealing in air. Here we present structural and magnetic characterizations of these crystals using neutron scattering and muon spin rotation techniques. While the as-grown, non-superconducting crystals are single phase, we nd that the superconducting crystals contain 3 phases forming coherent domains stacked along the c axis: the dominant a-Ca-2126 phase, very thin (1.5 unit-cell) intergrowths of a 2CuO 4, and an antiferromagnetic a 8Cu 8O 20 phase. We propose that the formation and segregation of the latter phases increases the Ca concentration of the a-Ca-2126, thus providing the hole-doping that supports superconductivity.« less

  13. Growth and structural characterization of large superconducting crystals of La 2 - x Ca 1 + x Cu 2 O 6

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Schneeloch, J. A.; Guguchia, Z.; Stone, M. B.

    Lmore » arge crystals of a 2 - x Ca 1 + x Cu 2 O 6 (a-Ca-2126) with x = 0:10 and 0.15 have been grown and converted to bulk superconductors by high-pressure oxygen annealing. The superconducting transition temperature, T c, is as high as 55 K; this can be raised to 60 K by post-annealing in air. Here we present structural and magnetic characterizations of these crystals using neutron scattering and muon spin rotation techniques. While the as-grown, non-superconducting crystals are single phase, we nd that the superconducting crystals contain 3 phases forming coherent domains stacked along the c axis: the dominant a-Ca-2126 phase, very thin (1.5 unit-cell) intergrowths of a 2CuO 4, and an antiferromagnetic a 8Cu 8O 20 phase. We propose that the formation and segregation of the latter phases increases the Ca concentration of the a-Ca-2126, thus providing the hole-doping that supports superconductivity.« less

  14. Generic Superconducting Inhomogeneity in Single Crystal Fe(Te1-xSex) Probed by Nanostructure-transport

    NASA Astrophysics Data System (ADS)

    Yue, Chunlei; Hu, Jin; Liu, Xue; Mao, Zhiqiang; Wei, Jiang

    2015-03-01

    We have investigated the nano-scale electronic properties of the iron-based unconventional superconductor Fe(Te1-xSex) with optimal Se content x = 0.5. Using the microexfoliation method and ion milling thinning, we successfully produced Fe(Te1-xSex) devices with thickness varying from 90nm down to 12nm. Our transport measurements revealed a suppression of superconductivity coinciding with the loss of normal state metallicity. Through the simulation of the formation of superconducting region in nano-scale thin flakes, we show that our observation is in line with the nano-scale inhomogeneity proposed for this material; therefore it provides a more direct evidence for the nano-scale inhomogeneous superconductivity in Fe(Te1-xSex) .

  15. Orbital Selective Spin Excitations and their Impact on Superconductivity of LiFe 1 - x Co x As

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Yu; Yin, Zhiping; Wang, Xiancheng

    We use neutron scattering to study spin excitations in single crystals of LiFe 0.88Co 0.12As, which is located near the boundary of the superconducting phase of LiFe 1-xCo xAs and exhibits non- Fermi-liquid behavior indicative of a quantum critical point. By comparing spin excitations of LiFe 0.88Co 0.12As with a combined density functional theory (DFT) and dynamical mean field theory (DMFT) calculation, we conclude that wave-vector correlated low energy spin excitations are mostly from the dxy orbitals, while high-energy spin excitations arise from the dyz and dxz orbitals. Unlike most iron pnictides, the strong orbital selective spin excitations in LiFeAsmore » family cannot be described by anisotropic Heisenberg Hamiltonian. While the evolution of low-energy spin excitations of LiFe 1-xCo xAs are consistent with electron-hole Fermi surface nesting condition for the dxy orbital, the reduced superconductivity in LiFe 0.88Co 0.12As suggests that Fermi surface nesting conditions for the dyz and dxz orbitals are also important for superconductivity in iron pnictides.« less

  16. Orbital Selective Spin Excitations and their Impact on Superconductivity of LiFe 1 - x Co x As

    DOE PAGES

    Li, Yu; Yin, Zhiping; Wang, Xiancheng; ...

    2016-06-17

    We use neutron scattering to study spin excitations in single crystals of LiFe 0.88Co 0.12As, which is located near the boundary of the superconducting phase of LiFe 1-xCo xAs and exhibits non- Fermi-liquid behavior indicative of a quantum critical point. By comparing spin excitations of LiFe 0.88Co 0.12As with a combined density functional theory (DFT) and dynamical mean field theory (DMFT) calculation, we conclude that wave-vector correlated low energy spin excitations are mostly from the dxy orbitals, while high-energy spin excitations arise from the dyz and dxz orbitals. Unlike most iron pnictides, the strong orbital selective spin excitations in LiFeAsmore » family cannot be described by anisotropic Heisenberg Hamiltonian. While the evolution of low-energy spin excitations of LiFe 1-xCo xAs are consistent with electron-hole Fermi surface nesting condition for the dxy orbital, the reduced superconductivity in LiFe 0.88Co 0.12As suggests that Fermi surface nesting conditions for the dyz and dxz orbitals are also important for superconductivity in iron pnictides.« less

  17. Orbital Selective Spin Excitations and their Impact on Superconductivity of LiFe_{1-x}Co_{x}As.

    PubMed

    Li, Yu; Yin, Zhiping; Wang, Xiancheng; Tam, David W; Abernathy, D L; Podlesnyak, A; Zhang, Chenglin; Wang, Meng; Xing, Lingyi; Jin, Changqing; Haule, Kristjan; Kotliar, Gabriel; Maier, Thomas A; Dai, Pengcheng

    2016-06-17

    We use neutron scattering to study spin excitations in single crystals of LiFe_{0.88}Co_{0.12}As, which is located near the boundary of the superconducting phase of LiFe_{1-x}Co_{x}As and exhibits non-Fermi-liquid behavior indicative of a quantum critical point. By comparing spin excitations of LiFe_{0.88}Co_{0.12}As with a combined density functional theory and dynamical mean field theory calculation, we conclude that wave-vector correlated low energy spin excitations are mostly from the d_{xy} orbitals, while high-energy spin excitations arise from the d_{yz} and d_{xz} orbitals. Unlike most iron pnictides, the strong orbital selective spin excitations in the LiFeAs family cannot be described by an anisotropic Heisenberg Hamiltonian. While the evolution of low-energy spin excitations of LiFe_{1-x}Co_{x}As is consistent with the electron-hole Fermi surface nesting conditions for the d_{xy} orbital, the reduced superconductivity in LiFe_{0.88}Co_{0.12}As suggests that Fermi surface nesting conditions for the d_{yz} and d_{xz} orbitals are also important for superconductivity in iron pnictides.

  18. Emergence of superconductivity from the dynamically heterogeneous insulating state in La(2-x)Sr(x)CuO4.

    PubMed

    Shi, Xiaoyan; Logvenov, G; Bollinger, A T; Božović, I; Panagopoulos, C; Popović, Dragana

    2013-01-01

    A central issue for copper oxides is the nature of the insulating ground state at low carrier densities and the emergence of high-temperature superconductivity from that state with doping. Even though this superconductor-insulator transition (SIT) is a zero-temperature transition, measurements are not usually carried out at low temperatures. Here we use magnetoresistance to probe both the insulating state at very low temperatures and the presence of superconducting fluctuations in La(2-x)Sr(x)CuO(4) films, for doping levels that range from the insulator to the superconductor (x  =  0.03-0.08). We observe that the charge glass behaviour, characteristic of the insulating state, is suppressed with doping, but it coexists with superconducting fluctuations that emerge already on the insulating side of the SIT. The unexpected quenching of the superconducting fluctuations by the competing charge order at low temperatures provides a new perspective on the mechanism for the SIT.

  19. Structural and magnetic phase transitions near optimal superconductivity in BaFe 2(As 1-xP x) 2

    DOE PAGES

    Hu, Ding; Lu, Xingye; Zhang, Wenliang; ...

    2015-04-17

    In this study, we use nuclear magnetic resonance (NMR), high-resolution x-ray and neutron scattering to study structural and magnetic phase transitions in phosphorus-doped BaFe 2(As 1-xP x) 2. Thus, previous transport, NMR, specific heat, and magnetic penetration depth measurements have provided compelling evidence for the presence of a quantum critical point (QCP) near optimal superconductivity at x = 0.3. However, we show that the tetragonal-to-orthorhombic structural (T s) and paramagnetic to antiferromagnetic (AF, T N) transitions in BaFe 2(As 1-xP x) 2 are always coupled and approach to T N ≈ T s ≥ T c (≈ 29 K) formore » x = 0.29 before vanishing abruptly for x ≥ 0.3. These results suggest that AF order in BaFe 2(As 1-xP x) 2 disappears in a weakly first order fashion near optimal superconductivity, much like the electron-doped iron pnictides with an avoided QCP.« less

  20. Influence of substitution, nonstoichiometry and annealing-conditions on superconductivity and normal conductivity of Fe1+δ (Te1‑x Xx ) (X=Se, S)

    NASA Astrophysics Data System (ADS)

    Lima, M. S. L.; ElMassalami, M.; Deguchi, K.; Takeya, H.; Takano, Y.

    2018-03-01

    Thermal evolution of resistivity, ρ(T, x), of as-prepared samples of Fe1+δ Te1‑x S x (δ ≈ 0, x ≤ 0.2 = solubility limit) demonstrate a granular log-in-T character within Ts < T <300K, a Kondo-like resistive contribution within Tc < T < Ts and granular superconductivity at low temperature (Ts = structural transition point of Fe1+δ Te, Tc =superconducting transition point). We attribute the log-in-T character as well as the nonbulk superconducting features of as-prepared samples to their granular superconductor nature. Annealing in oxygen removes Kondo-like contribution, annihilates pair-breaking centres and establishes bulk superconductivity but, in contrast, the high-temperature granular log-in-T character is hardly influenced. This analysis was successfully extended to the isomorphous Fe1+δ Te1‑x Se x as well as to other types of post-synthesis sample-treatment (e.g. annealing in different gas ambient or soaking in particular liquids).

  1. Quantum and superconducting fluctuations effects in disordered Nb 1- xTa x thin films above Tc

    NASA Astrophysics Data System (ADS)

    Giannouri, M.; Papastaikoudis, C.

    1999-05-01

    Disordered Nb 1- xTa x thin films are prepared with e-gun coevaporation. The influence of the β-phase of tantalum in the critical temperature Tc is observed as a function of the substrate temperature. The measurements of transverse magnetoresistance at various isothermals are interpreted in terms of weak-localization and superconducting fluctuations. From the fitting procedure, the phase breaking rate τφ-1 and the Larkin parameter βL are estimated as a function of temperature. Conclusions about the dominant inelastic scattering mechanisms at various temperature regions as well as for the dominant mechanism of superconducting fluctuations near the transition temperature are extracted.

  2. Nanoscale Inhomogeneous Superconductivity in Fe(Te1-xSex) Probed by Nanostructure Transport.

    PubMed

    Yue, Chunlei; Hu, Jin; Liu, Xue; Sanchez, Ana M; Mao, Zhiqiang; Wei, Jiang

    2016-01-26

    Among iron-based superconductors, the layered iron chalcogenide Fe(Te1-xSex) is structurally the simplest and has attracted considerable attention. It has been speculated from bulk studies that nanoscale inhomogeneous superconductivity may inherently exist in this system. However, this has not been directly observed from nanoscale transport measurements. In this work, through simple micromechanical exfoliation and high-precision low-energy ion milling thinning, we prepared Fe(Te0.5Se0.5) nanoflakes with various thicknesses and systematically studied the correlation between the thickness and superconducting phase transition. Our result revealed a systematic thickness-dependent evolution of superconducting transition. When the thickness of the Fe(Te0.5Se0.5) flake is reduced to less than the characteristic inhomogeneity length (around 12 nm), both the superconducting current path and the metallicity of the normal state in Fe(Te0.5Se0.5) atomic sheets are suppressed. This observation provides the first transport evidence for the nanoscale inhomogeneous nature of superconductivity in Fe(Te1-xSex).

  3. Superconductivity of Ba8Si46-xGax clathrates

    NASA Astrophysics Data System (ADS)

    Li, Yang; Zhang, Ruihong; Chen, Ning; Ma, Xingqiao; Cao, Guohui; Luo, Z. P.; Hu, C. R.; Ross, Joseph H., Jr.

    2007-03-01

    We have presented a combined experimental and theoretical study of the effect of Gallium substitution on the superconductivity of the type I clathrate Ba8Si46-xGax. In Ga-doped clathrates, the Ga state is found to be strongly hybridized with the cage conduction-band state. Ga substitution results in a shift toward to a lower energy, a decrease of density of states at Fermi level, a lowering of the carrier concentration and a breakage of integrity of the sp3 hybridized networks. These play key roles in the suppression of superconductivity. For Ba8Si40Ga6, the onset of the superconducting transition occurs at Tc=3.3 K. The investigation of the magnetic superconducting state shows that Ba8Si40Ga6 is a type II superconductor. The critical magnetic fields were measured to be Hc1=35 Oe and Hc2=8.5 kOe. Our estimate of the lectron-phonon coupling reveals that Ba8Si40Ga6 is a moderate phonon-mediated BCS superconductor.

  4. Synthesis and Superconducting Properties of the High Transition Temperature Superconductor BARIUM(1-X) Potassium(x)bismuth Trioxide

    NASA Astrophysics Data System (ADS)

    Folkerts, Timothy John

    A systematic study of Ba_ {1-x}K_ xBiO_3 (BKBO) in the range 0 <= x <= 0.5 is presented in this work, concentrating especially on the superconducting range 0.35 <= x <= 0.5. Samples were studied using powder x-ray diffraction, thermal analysis, magnetization as a function of both temperature and applied field, and resistivity as a function of both temperature and pressure. Particular effort went into producing high quality samples. This proved difficult because of the moisture sensitivity of the starting materials and of the intermediate products, and because of the tendency of the material to phase separate into regions of varying potassium concentrations. Once synthesis techniques were developed which allowed production of high quality samples, systematic studies could be undertaken. The sharpness of the powder x-ray diffraction peaks, along with least squares fits, were used to determine phase purity and to exclude poor quality samples. The lattice parameters of the remaining samples were seen to obey Vegard's Law. Magnetization studies as a function of temperature were used to determine the superconducting transition temperature (T_ c). Onsets for superconductivity were observed as high as 30 K for samples with broad transitions, although samples with sharp transitions had a maximum T_ c of only 28.8 K. This high T_ c, as well as the crystal structure clearly link BKBO to the high T_ c superconductors. Hysteresis measurements were undertaken to determine the upper and lower critical fields, critical currents, and the normal state susceptibility. Estimates of the coherence length, penetration depth, and the electronic contribution to the specific heat based on these measurements agree well with BCS theory. Resistivity data are quit dependent on sample quality, as well as potassium doping. At low potassium concentrations, the material is semiconducting, while at higher potassium concentrations where the material is superconducting, the normal state resistivity of

  5. Coexistence of static magnetism and superconductivity in SmFeAsO(1-x)F(x) as revealed by muon spin rotation.

    PubMed

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

    2009-04-01

    The recent observation of superconductivity with critical temperatures (Tc) up to 55 K in the pnictide RFeAsO(1-x)F(x), where R is a lanthanide, marks the first discovery of a non-copper-oxide-based layered high-Tc superconductor. It has raised the suspicion that these new materials share a similar pairing mechanism to the cuprate superconductors, as both families exhibit superconductivity following charge doping of a magnetic parent material. In this context, it is important to follow the evolution of the microscopic magnetic properties of the pnictides with doping and hence to determine whether magnetic correlations coexist with superconductivity. Here, we present a muon spin rotation study on SmFeAsO(1-x)F(x), with x=0-0.30 that shows that, as in the cuprates, static magnetism persists well into the superconducting regime. This analogy is quite surprising as the parent compounds of the two families have rather different magnetic ground states: itinerant spin density wave for the pnictides contrasted with the Mott-Hubbard insulator in the cuprates. Our findings therefore suggest that the proximity to magnetic order and associated soft magnetic fluctuations, rather than strong electronic correlations in the vicinity of a Mott-Hubbard transition, may be the key ingredients of high-Tc superconductors.

  6. Fermiology of the strongly spin-orbit coupled superconductor Sn(1-x)In(x)Te: implications for topological superconductivity.

    PubMed

    Sato, T; Tanaka, Y; Nakayama, K; Souma, S; Takahashi, T; Sasaki, S; Ren, Z; Taskin, A A; Segawa, Kouji; Ando, Yoichi

    2013-05-17

    We have performed angle-resolved photoemission spectroscopy on the strongly spin-orbit coupled low-carrier density superconductor Sn(1-x)In(x)Te (x = 0.045) to elucidate the electronic states relevant to the possible occurrence of topological superconductivity, as recently reported for this compound based on point-contact spectroscopy. The obtained energy-band structure reveals a small holelike Fermi surface centered at the L point of the bulk Brillouin zone, together with a signature of a topological surface state, indicating that this material is a doped topological crystalline insulator characterized by band inversion and mirror symmetry. A comparison of the electronic states with a band-noninverted superconductor possessing a similar Fermi surface structure, Pb(1-x)Tl(x)Te, suggests that the anomalous behavior in the superconducting state of Sn(1-x)In(x)Te is related to the peculiar orbital characteristics of the bulk valence band and/or the presence of a topological surface state.

  7. Absence of Local Fluctuating Dimers in Superconducting Ir 1-x(Pt,Rh) xTe 2

    DOE PAGES

    Yu, Runze; Banerjee, S.; Lei, H. C.; ...

    2018-06-01

    The compound IrTe2 is known to exhibit a transition to a modulated state featuring Ir-Ir dimers, with large associated atomic displacements. Partial substitution of Pt or Rh for Ir destabilizes the modulated structure and induces superconductivity. It has been proposed that quantum critical dimer fluctuations might be associated with the superconductivity. Here we test for such local dimer correlations and demonstrate their absence. X-ray pair distribution function approach reveals that the local structure of Ir 0.95Pt 0.05Te 2 and Ir 0.8Rh 0.2Te 2 dichalcogenide superconductors with compositions just past the dimer/superconductor boundary is explained well by a dimer-free model downmore » to 10 K, ruling out the possibility of there being nanoscale dimer fluctuations in this regime. This is inconsistent with the proposed quantum-critical-point-like interplay of the dimer state and superconductivity, and precludes scenarios for dimer fluctuations mediated superconducting pairing.« less

  8. Absence of Local Fluctuating Dimers in Superconducting Ir 1-x(Pt,Rh) xTe 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yu, Runze; Banerjee, S.; Lei, H. C.

    The compound IrTe2 is known to exhibit a transition to a modulated state featuring Ir-Ir dimers, with large associated atomic displacements. Partial substitution of Pt or Rh for Ir destabilizes the modulated structure and induces superconductivity. It has been proposed that quantum critical dimer fluctuations might be associated with the superconductivity. Here we test for such local dimer correlations and demonstrate their absence. X-ray pair distribution function approach reveals that the local structure of Ir 0.95Pt 0.05Te 2 and Ir 0.8Rh 0.2Te 2 dichalcogenide superconductors with compositions just past the dimer/superconductor boundary is explained well by a dimer-free model downmore » to 10 K, ruling out the possibility of there being nanoscale dimer fluctuations in this regime. This is inconsistent with the proposed quantum-critical-point-like interplay of the dimer state and superconductivity, and precludes scenarios for dimer fluctuations mediated superconducting pairing.« less

  9. Absence of local fluctuating dimers in superconducting Ir1 -x(Pt,Rh ) xTe2

    NASA Astrophysics Data System (ADS)

    Yu, Runze; Banerjee, S.; Lei, H. C.; Sinclair, Ryan; Abeykoon, M.; Zhou, H. D.; Petrovic, C.; Guguchia, Z.; Bozin, E. S.

    2018-05-01

    The compound IrTe2 is known to exhibit a transition to a modulated state featuring Ir-Ir dimers, with large associated atomic displacements. Partial substitution of Pt or Rh for Ir destabilizes the modulated structure and induces superconductivity. It has been proposed that quantum critical dimer fluctuations might be associated with the superconductivity. Here we test for such local dimer correlations and demonstrate their absence. X-ray pair distribution function approach reveals that the local structure of Ir0 :95Pt0 :05Te2 and Ir0 :8Rh0 :2Te2 dichalcogenide superconductors with compositions just past the dimer/superconductor boundary is explained well by a dimer-free model down to 10 K, ruling out the possibility of there being nanoscale dimer fluctuations in this regime. This is inconsistent with the proposed quantum-critical-point-like interplay of the dimer state and superconductivity, and precludes scenarios for dimer fluctuations mediated superconducting pairing.

  10. Disentangling superconducting and magnetic orders in NaFe1 -xNixAs using muon spin rotation

    NASA Astrophysics Data System (ADS)

    Cheung, Sky C.; Guguchia, Zurab; Frandsen, Benjamin A.; Gong, Zizhou; Yamakawa, Kohtaro; Almeida, Dalson E.; Onuorah, Ifeanyi J.; Bonfá, Pietro; Miranda, Eduardo; Wang, Weiyi; Tam, David W.; Song, Yu; Cao, Chongde; Cai, Yipeng; Hallas, Alannah M.; Wilson, Murray N.; Munsie, Timothy J. S.; Luke, Graeme; Chen, Bijuan; Dai, Guangyang; Jin, Changqing; Guo, Shengli; Ning, Fanlong; Fernandes, Rafael M.; De Renzi, Roberto; Dai, Pengcheng; Uemura, Yasutomo J.

    2018-06-01

    Muon spin rotation and relaxation studies have been performed on a "111" family of iron-based superconductors, NaFe1 -xNixAs , using single crystalline samples with Ni concentrations x =0 , 0.4, 0.6, 1.0, 1.3, and 1.5%. Static magnetic order was characterized by obtaining the temperature and doping dependences of the local ordered magnetic moment size and the volume fraction of the magnetically ordered regions. For x =0 and 0.4%, a transition to a nearly-homogeneous long range magnetically ordered state is observed, while for x ≳0.4 % magnetic order becomes more disordered and is completely suppressed for x =1.5 % . The magnetic volume fraction continuously decreases with increasing x . Development of superconductivity in the full volume is inferred from Meissner shielding results for x ≳0.4 % . The combination of magnetic and superconducting volumes implies that a spatially-overlapping coexistence of magnetism and superconductivity spans a large region of the T -x phase diagram for NaFe1 -xNixAs . A strong reduction of both the ordered moment size and the volume fraction is observed below the superconducting TC for x =0.6 , 1.0, and 1.3%, in contrast to other iron pnictides in which one of these two parameters exhibits a reduction below TC, but not both. The suppression of magnetic order is further enhanced with increased Ni doping, leading to a reentrant nonmagnetic state below TC for x =1.3 % . The reentrant behavior indicates an interplay between antiferromagnetism and superconductivity involving competition for the same electrons. These observations are consistent with the sign-changing s± superconducting state, which is expected to appear on the verge of microscopic coexistence and phase separation with magnetism. We also present a universal linear relationship between the local ordered moment size and the antiferromagnetic ordering temperature TN across a variety of iron-based superconductors. We argue that this linear relationship is consistent with an

  11. Modified magnetism within the coherence volume of superconducting Fe1+δSexTe1-x

    NASA Astrophysics Data System (ADS)

    Leiner, J.; Thampy, V.; Christianson, A. D.; Abernathy, D. L.; Stone, M. B.; Lumsden, M. D.; Sefat, A. S.; Sales, B. C.; Hu, Jin; Mao, Zhiqiang; Bao, Wei; Broholm, C.

    2014-09-01

    Neutron scattering is used to probe magnetic interactions as superconductivity develops in optimally doped Fe1+δSexTe1-x. Applying the first moment sum rule to comprehensive neutron scattering data, we extract the change in magnetic exchange energy Δ [JR -R'] in the superconducting state referenced to the normal state. Oscillatory changes are observed for Fe-Fe displacements |ΔR |<ξ, where ξ =1.3(1) nm is the superconducting coherence length. Dominated by a large reduction in the second nearest neighbor exchange energy [-1.2(2) meV/Fe], the overall reduction in magnetic interaction energy is Δ=-0.31(9) meV/Fe. Comparison to the superconducting condensation energy ΔESC=-0.013(1) meV/Fe, which we extract from specific heat data, suggests the modified magnetism we probe drives superconductivity in Fe1+δSexTe1-x.

  12. Spin-fluctuation-induced non-Fermi-liquid behavior with suppressed superconductivity in LiFe 1-xCo xAs

    DOE PAGES

    Y. M. Dai; Miao, H.; Xing, L. Y.; ...

    2015-09-15

    A series of LiFe 1–xCo xAs compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behavior in LiFe 1–xCo xAs is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFemore » 1–xCo xAs where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.« less

  13. Energy gap evolution across the superconductivity dome in single crystals of (Ba1-x K x )Fe2As2.

    PubMed

    Cho, Kyuil; Kończykowski, Marcin; Teknowijoyo, Serafim; Tanatar, Makariy A; Liu, Yong; Lograsso, Thomas A; Straszheim, Warren E; Mishra, Vivek; Maiti, Saurabh; Hirschfeld, Peter J; Prozorov, Ruslan

    2016-09-01

    The mechanism of unconventional superconductivity in iron-based superconductors (IBSs) is one of the most intriguing questions in current materials research. Among non-oxide IBSs, (Ba 1- x K x )Fe 2 As 2 has been intensively studied because of its high superconducting transition temperature and fascinating evolution of the superconducting gap structure from being fully isotropic at optimal doping ( x ≈ 0.4) to becoming nodal at x > 0.8. Although this marked evolution was identified in several independent experiments, there are no details of the gap evolution to date because of the lack of high-quality single crystals covering the entire K-doping range of the superconducting dome. We conducted a systematic study of the London penetration depth, λ( T ), across the full phase diagram for different concentrations of point-like defects introduced by 2.5-MeV electron irradiation. Fitting the low-temperature variation with the power law, Δλ ~ T n , we find that the exponent n is the highest and the T c suppression rate with disorder is the smallest at optimal doping, and they evolve with doping being away from optimal, which is consistent with increasing gap anisotropy, including an abrupt change around x ≃ 0.8, indicating the onset of nodal behavior. Our analysis using a self-consistent t -matrix approach suggests the ubiquitous and robust nature of s ± pairing in IBSs and argues against a previously suggested transition to a d -wave state near x = 1 in this system.

  14. CDW order and unconventional s-wave superconductivity in Ba1-xNaxTi2Sb2O

    NASA Astrophysics Data System (ADS)

    Kamusella, Sirko; Doan, Phuong; Goltz, Til; Luetkens, Hubertus; Sarkar, Rajib; Guloy, Arnold; Klauss, Hans-Henning

    2014-12-01

    Due to its anticuprate Ti2O layer and its fascinating phase diagram with a large coexistence area of superconductivity and a density wave phase, the new class of titanium based superconductors attracts great scientific interest. In this paper we report μSR investigation on powder samples of Ba1-xNaxTi2Sb2O (x = 0, 0.15, 0.25). Our results exhibit both the presence of a charge density wave and superconductivity in Ba1-xNaxTi2Sb2O. The superconducting order parameter, extracted from a vortex state analysis using the numeric Ginzburg-Landau model, is compatible with a s-wave symmetry. In the universal Uemura classification of superconductors this compound is at the verge of unconventional superconductivity.

  15. Evidence for magnetic-field-induced decoupling of superconducting bilayers in La 2-xCa 1+xCu 2O 6

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhong, Ruidan; Schneeloch, J. A.; Chi, Hang

    We report a study of magnetic susceptibility and electrical resistivity as a function of temperature and magnetic field in superconducting crystals of La 2-xCa 1+xCu 2O 6 with x = 0.10 and 0.15 and transition temperature Tmore » $$m\\atop{c}$$ = 54 K (determined from the susceptibility). When an external magnetic field is applied perpendicular to the CuO 2 bilayers, the resistive superconducting transition measured with currents flowing perpendicular to the bilayers is substantially lower than that found with currents flowing parallel to the bilayers. Intriguingly, this anisotropic behavior is quite similar to that observed for the magnetic irreversibility points with the field applied either perpendicular or parallel to the bilayers. We discuss the results in the context of other studies that have found evidence for the decoupling of superconducting layers induced by a perpendicular magnetic field.« less

  16. Evidence for magnetic-field-induced decoupling of superconducting bilayers in La 2-xCa 1+xCu 2O 6

    DOE PAGES

    Zhong, Ruidan; Schneeloch, J. A.; Chi, Hang; ...

    2018-04-24

    We report a study of magnetic susceptibility and electrical resistivity as a function of temperature and magnetic field in superconducting crystals of La 2-xCa 1+xCu 2O 6 with x = 0.10 and 0.15 and transition temperature Tmore » $$m\\atop{c}$$ = 54 K (determined from the susceptibility). When an external magnetic field is applied perpendicular to the CuO 2 bilayers, the resistive superconducting transition measured with currents flowing perpendicular to the bilayers is substantially lower than that found with currents flowing parallel to the bilayers. Intriguingly, this anisotropic behavior is quite similar to that observed for the magnetic irreversibility points with the field applied either perpendicular or parallel to the bilayers. We discuss the results in the context of other studies that have found evidence for the decoupling of superconducting layers induced by a perpendicular magnetic field.« less

  17. Absorber for wakefield interference management at the entrance of the wiggler of a free electron laser

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Marchlik, Matthew; Biallas, George Herman

    A method for managing the broad band microwave and TeraHertz (THz) radiation in a free electron laser (FEL) having a wiggler producing power in the electromagnetic spectrum. The method includes placement of broadband microwave and TeraHertz (THz) radiation absorbers on the upstream end of the wiggler. The absorbers dampen the bounced back, broad band microwave and THz radiation returning from the surfaces outside the nose of the cookie-cutter and thus preventing broadening of the electron beam pulse's narrow longitudinal energy distribution. Broadening diminishes the ultimate laser power from the wiggler. The broadband microwave and THz radiation absorbers are placed onmore » either side of the slot in the cookie-cutter that shapes the wake field wave of the electron pulse to the slot shape of the wiggler chamber aperture. The broad band microwave and THz radiation absorber is preferably a non-porous pyrolytic grade of graphite with small grain size.« less

  18. Observation of a Charge Density Wave Incommensuration Near the Superconducting Dome in Cu x TiSe 2

    DOE PAGES

    Kogar, A.; de la Pena, G. A.; Lee, Sangjun; ...

    2017-01-11

    X-ray diffraction was employed to study the evolution of the charge density wave (CDW) in Cu xTiSe 2 as a function of copper intercalation in order to clarify the relationship between the CDW and superconductivity. In this paper, the results show a CDW incommensuration arising at an intercalation value coincident with the onset of superconductivity at around x = 0.055(5) . Additionally, it was found that the charge density wave persists to higher intercalant concentrations than previously assumed, demonstrating that the CDW does not terminate inside the superconducting dome. A charge density wave peak was observed in samples up tomore » x = 0.091(6) , the highest copper concentration examined in this study. Lastly, the phase diagram established in this work suggests that charge density wave incommensuration may play a role in the formation of the superconducting state.« less

  19. Electronic disorder and magnetic-field-induced superconductivity enhancement in Fe1+y(Te1-xSex)

    NASA Astrophysics Data System (ADS)

    Hu, Jin; Liu, Tijiang; Qian, Bin; Mao, Zhiqiang

    2012-02-01

    The iron chalcogenide Fe1+y(Te1-xSex) superconductor system exhibits a unique electronic and magnetic phase diagram distinct from those seen in iron pnictides: bulk superconductivity does not appear immediately following the suppression of long-range (π,0) AFM order. Instead, an intermediate phase with weak charge carrier localization appears between AFM order and bulk superconductivity (Liu et al., Nat. Mater. 9, 719 (2010)). In this talk, we report our recent studies on the relationship between the normal state and superconducting properties in Fe1+y(Te1-xSex). We show that the superconducting volume fraction VSC and normal state metallicity significantly increase while the normal state Sommerfeld coefficient γ and Hall coefficient RH drop drastically with increasing Se content in the underdoped superconducting region. Additionally, VSC is surprisingly enhanced by magnetic field in heavily underdoped superconducting samples. The implications of these results will be discussed. Our analyses suggest that the suppression of superconductivity in the underdoped region is associated with electronic disorder caused by incoherent magnetic scattering arising from (π,0) magnetic fluctuations.

  20. Evolution of structure and superconductivity in Ba(Ni 1 -xCox)2As2

    NASA Astrophysics Data System (ADS)

    Eckberg, Chris; Wang, Limin; Hodovanets, Halyna; Kim, Hyunsoo; Campbell, Daniel J.; Zavalij, Peter; Piccoli, Philip; Paglione, Johnpierre

    2018-06-01

    The effects of Co substitution on Ba (Ni1-xCox) 2As2 (0 ≤x ≤0.251 ) single crystals grown out of Pb flux are investigated via transport, magnetic, and thermodynamic measurements. BaNi2As2 exhibits a first-order tetragonal to triclinic structural phase transition at Ts=137 K upon cooling, and enters a superconducting phase below Tc=0.7 K. The structural phase transition is sensitive to cobalt content and is suppressed completely by x ≥0.133 . The superconducting critical temperature, Tc, increases continuously with x , reaching a maximum of Tc=2.3 K at x =0.083 and then decreases monotonically until superconductivity is no longer observable well into the tetragonal phase. In contrast to similar BaNi2As2 substitutional studies, which show an abrupt change in Tc at the triclinic-tetragonal boundary that extends far into the tetragonal phase, Ba (Ni1-xCox) 2As2 exhibits a domelike phase diagram centered around the zero-temperature tetragonal-triclinic boundary. Together with an anomalously large heat capacity jump Δ Ce/γ T ˜2.2 near optimal doping, the smooth evolution of Tc in the Ba (Ni1-xCox) 2As2 system suggests a mechanism for pairing enhancement other than phonon softening.

  1. Impact of Disorder on the Superconducting Phase Diagram in BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Mizukami, Yuta; Konczykowski, Marcin; Matsuura, Kohei; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2017-08-01

    In many classes of unconventional superconductors, the question of whether the superconductivity is enhanced by the quantum-critical fluctuations on the verge of an ordered phase remains elusive. One of the most direct ways of addressing this issue is to investigate how the superconducting dome traces a shift of the ordered phase. Here, we study how the phase diagram of the iron-based superconductor BaFe2(As1-xPx)2 changes with disorder via electron irradiation, which keeps the carrier concentrations intact. With increasing disorder, we find that the magneto-structural transition is suppressed, indicating that the critical concentration is shifted to the lower side. Although the superconducting transition temperature Tc is depressed at high concentrations (x ≳ 0.28), it shows an initial increase at lower x. This implies that the superconducting dome tracks the shift of the antiferromagnetic phase, supporting the view of the crucial role played by quantum-critical fluctuations in enhancing superconductivity in this iron-based high-Tc family.

  2. Wiggler plane focusing in a linear free electron laser

    DOEpatents

    Scharlemann, Ernst T.

    1988-01-01

    Free electron laser apparatus that provides a magnetic centering force to turn or focus a non-axial electron toward the longitudinal axis as desired. The focusing effect is provided by wiggler magnet pole faces that are approximately parabolically shaped.

  3. Anisotropic Pressure Effects on Superconductivity in Fe1+yTe1-xSx

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kazunori; Yamazaki, Teruo; Yamanaka, Takayoshi; Ueta, Daichi; Yoshizawa, Hideki; Yaguchi, Hiroshi

    2018-05-01

    We have investigated the uniaxial and hydrostatic pressure effects on superconductivity in Fe1.07Te0.88S0.12 through magnetic susceptibility measurements down to 1.8 K. The superconducting transition temperature Tc is enhanced by out-of-plane pressure (uniaxial pressure along the c-axis); the onset temperature of the superconductivity reaches 11.8 K at 0.4 GPa. In contrast, Tc is reduced by in-plane pressure (uniaxial pressure along the ab-plane) and hydrostatic pressure. Taking into account these results, it is inferred that the superconductivity of Fe1+yTe1-xSx is enhanced when the lattice constant c considerably decreases. This implies that the relationship between Tc and the anion height for Fe1+yTe1-xSx is similar to that for most iron-based superconductors. We consider the reduction of Tc by hydrostatic pressure to be due to the suppression of spin fluctuations because the system moves away from antiferromagnetic ordering, and the enhancement of Tc by out-of-plane pressure to be due to the anion height effect on Tc.

  4. Polytypism, polymorphism, and superconductivity in TaSe 2 –xTe x

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Luo, Huixia; Xie, Weiwei; Tao, Jing

    2015-03-03

    Polymorphism in materials often leads to significantly different physical properties - the rutile and anatase polymorphs of TiO₂ are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivitymore » of TaSe₂, one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access 2 stable polytypes and 2 stable polymorphs in the TaSe 2-xTe x solid solution, and find that the 3R polytype shows a superconducting transition temperature that is between 6 and 17 times higher than that of the much more commonly found 2H polytype. Thus, the reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of T c on subtle differences in the characteristics of the single layers present, or from a surprising effect of the layer stacking sequence on electronic properties that instead are expected to be dominated by the properties of a single layer in materials of this kind.« less

  5. Structural and magnetic properties and superconductivity in Ba(Fe 1-xTM x) 2As 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Thaler, Alexander

    2012-01-01

    We studied the effects on structural and magnetic phase transitions and the emergence of superconductivity in transition metal substituted BaFe 2As 2. We grew four series of Ba(Fe 1-xTM 2) 2As 2 (TM=Ru, Mn, Co+Cr and Co+Mn) and characterized them by crystallographic, magnetic and transport measurements. We also subjected Ba(Fe 1-xCr x) 2As 2 and Ba(Fe 1-xCo x) 2As 2 to heat treatment to explore what changes might be induced.

  6. The effect of TM doping on the superconducting properties of ZrNi2-xTMxGa (TM = Cu, Co) Heusler compounds

    NASA Astrophysics Data System (ADS)

    Basaula, Dharma Raj; Brock, Jeffrey; Khan, Mahmud

    2018-05-01

    We have explored the structural and superconducting properties of ZrNi2-xTMxGa (TM = Cu, Co) Heusler compounds via x-ray diffraction, scanning electron mi croscopy, electrical resistivity, dc magnetization and ac susceptibility measurements. All samples crystallized in the cubic L21 structure at room temperature. For x ≤ 0.25, all the ZrNi2-xCuxGa compounds showed superconducting properties and a decrease in TC with increasing Cu concentration. The dc magnetization data suggested type-II superconductivity for all the Cu-doped compounds. Contrary to the ZrNi2-xCuxGa compounds, no superconductivity was observed in the ZrNi2-xCoxGa compounds. Substitution of Ni by a small concentration of Co destroyed superconductivity in the Co-doped compounds. The experimental results are discussed and possible explanations are provided.

  7. Universal heat conduction in Ce 1-xYb xCoIn 5: Evidence for robust nodal d-wave superconducting gap

    DOE PAGES

    Xu, Y.; Petrovic, C.; Dong, J. K.; ...

    2016-02-01

    In the heavy-fermion superconductor Ce 1-xYb xCoIn 5, Yb doping was reported to cause a possible change from nodal d-wave superconductivity to a fully gapped d-wave molecular superfluid of composite pairs near x ≈ 0.07 (nominal value x nom = 0.2). Here we present systematic thermal conductivity measurements on Ce 1-xYb xCoIn 5 (x = 0.013, 0.084, and 0.163) single crystals. The observed finite residual linear term κ 0/T is insensitive to Yb doping, verifying the universal heat conduction of the nodal d-wave superconducting gap in Ce 1-xYb xCoIn 5. Similar universal heat conduction is also observed in the CeCo(Inmore » 1–yCd y) 5 system. Furthermore, these results reveal a robust nodal d-wave gap in CeCoIn 5 upon Yb or Cd doping.« less

  8. Observation of direct evolution from antiferromagnetism to superconductivity in C u1 -xL ixFeAs (0 ≤x ≤1.0 )

    NASA Astrophysics Data System (ADS)

    Li, Kunkun; Yuan, Duanduan; Guo, Jiangang; Chen, Xiaolong

    2018-04-01

    We report the structure, antiferromagnetism, and superconductivity in C u1 -xL ixFeAs (0 ≤x ≤1.0 ) samples. A direct evolution from antiferromagnetism to superconductivity is observed as increasing doping level of Li. A phase diagram is constructed to show this evolution, which features no coexistence region between superconductivity and antiferromagnetism. This behavior shows that antiferromagnetic CuFeAs can be regarded as a parent compound to the observed superconductivity by equivalent doping, which is different from the cases with other FeAs-based superconductors. Structural analyses and first-principles calculations indicate that the anion height of F e2A s2 tetrahedral layer plays a crucial role on the physical properties. Moreover, the simple Fermi surface nesting picture adopted to explain the evolution from spin-density wave to superconductor in other FeAs-based superconductors might be not applicable to C u1 -xL ixFeAs .

  9. An electron tunneling study of superconductivity in amorphous Sn(sub 1-x)Cu(sub x) thin films

    NASA Technical Reports Server (NTRS)

    Naugle, D. G.; Watson, P. W., III; Rathnayaka, K. D. D.

    1995-01-01

    The amorphous phase of Sn would have a superconducting transition temperature near 8 K, much higher than that of crystalline Sn with T(sub c) = 3.5 K. To obtain the amorphous phase, however, it is necessary to use a Sn alloy, usually Cu, and quench condense the alloy films onto a liquid He temperature substrate. Alloying with Cu reduces the superconducting transition temperature almost linearly with Cu concentration with an extrapolation of T(sub c) to zero for x = 0.85. Analysis of the tunneling characteristics between a normal metal electrode with an insulating barrier and superconducting amorphous Sn-Cu films provides detailed information on the changes in the electron-phonon coupling which determines T(sub c) in these alloys. The change from very strong electron-phonon coupling to weak-coupling with the increase in Cu content of amorphous Sn-Cu alloys for the range 0.08 is less than or equal to x is less than or equal to 0.41 is presented and discussed in terms of theories of electron-phonon coupling in disordered metals.

  10. Wiggler plane focusing in a linear free electron laser

    DOEpatents

    Scharlemann, E.T.

    1985-11-21

    This disclosure describes a free electron laser apparatus that provides a magnetic centering force to turn or focus a non-axial electron toward the longitudinal axis as desired. The focusing effect is provided by wiggler magnet pole faces that are approximately parabolically shaped.

  11. A doping dependent study of interplay between magnetic and superconducting properties in BaFe2-x Co x As2 single crystals

    NASA Astrophysics Data System (ADS)

    Bag, Biplab; Shaw, Gorky; Banerjee, S. S.; Vinod, K.; Bharathi, A.

    2018-03-01

    We show strong interplay between magnetic and superconducting order in three BaFe2-xCoxAs2 single crystals with different x. Our study reveals the presence of magnetic fluctuations with superconducting order in our samples and the strength of the magnetic fluctuations as well as the pinning properties are found to be the strongest for the optimally doped sample and weakest for the overdoped sample. Using local magnetization measurements, we show that application of an external magnetic field in our samples suppresses the magnetic fluctuations and enhances the diamagnetic response. Further, we show presence of unusual superconducting fluctuations above T c in our samples which we find strongly depends on the strength of the magnetic fluctuations. We believe that our data suggest the possible role of magnetic fluctuations in mediating superconducting fluctuations above Tc in our samples.

  12. Temperature dependence of a superconducting tunnel junction x-ray detector

    NASA Astrophysics Data System (ADS)

    Hiller, Lawrence J.; Labov, Simon E.; Mears, Carl A.; Barfknecht, Andrew T.; Frank, Matthias A.; Netel, Harrie; Lindeman, Mark A.

    1995-09-01

    Superconducting tunnel junctions can be used as part of a high-resolution, energy-dispersive x- ray detector. The energy of the absorbed x ray is used to break superconducting electron pairs, producing on the order of 10(superscript 6) excitations, called quasiparticles. The number of quasiparticles produced is proportional to the energy of the absorbed x ray. When a bias voltage is maintained across the barrier, these quasiparticles produce a net tunneling current. Either the peak tunneling current or the total tunneled charge may be measured to determine the energy of the absorbed x ray. The tunneling rate, and therefore the signal, is enhanced by the use of a quasiparticle trap near the tunnel barrier. The trapping efficiency is improved by decreasing the energy gap, though this reduces the maximum temperature at which the device may operate. In our niobium/aluminum configuration, we can very the energy gap in the trapping layer by varying its thickness. This paper examines the performance of two devices with 50 nm aluminum traps at temperatures ranging from 100 mK to 700 mK. We found that this device has a very good energy resolution of about 12 eV FWHM at 1 keV. This energy resolution is independent of temperature for much of this temperature range.

  13. NMR study of spin fluctuations and superconductivity in LaFeAsO1-xHx

    NASA Astrophysics Data System (ADS)

    Fujiwara, Naoki; Sakurai, Ryosuke; Iimura, Soushi; Matsuishi, Satoru; Hosono, Hideo; Yamakawa, Yoichi; Kontani, Hiroshi

    2013-03-01

    We have performed NMR measurements in LaFeAsO1-xHx, an isomorphic compound of LaFeAsO1-xFx. LaFeAsO1-xHx is most recently known for having double superconducting (SC) domes on H doping. LaFeAsO1-xHx is an electron- doped system, and protons act as H-1 as well as F-1. The first SC dome is very similar between F and H doping, suggesting that H doping supplies the same amount of electrons as F doping. Interestingly, an excess amount of H up to x=0.5 can be replaced with O2-. In the H-overdoped regime (x > 0 . 2), LaFeAsO1-xHx undergoes the second superconducting state. We measured the relaxation rate of LaFeAsO1-xHx for x=0.2 and 0.4, and fond an anomalous electronic state; spin fluctuations measured from 1 /T1 T is enhanced with increasing the doping level from x = 0 . 2 to 0.4. The enhancement of spin fluctuations with increasing carrier doping is a new phenomenon that has not observed in LaFeAsO1-xFx in which the upper limit of the doping level is at most x = 0 . 2 . We will discuss the phenomenon in relation to superconductivity. Grant (KAKENHI 23340101) from the Ministry of Education, Sports and Science, Japan

  14. RbEu (Fe1-xNix) 4As4 : From a ferromagnetic superconductor to a superconducting ferromagnet

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Liu, Ya-Bin; Yu, Ya-Long; Tao, Qian; Feng, Chun-Mu; Cao, Guang-Han

    2017-12-01

    The intrinsically hole-doped RbEuFe4As4 exhibits bulk superconductivity at Tsc=36.5 K and ferromagnetic ordering in the Eu sublattice at Tm=15 K. Here we present a hole-compensation study by introducing extra itinerant electrons via a Ni substitution in the ferromagnetic superconductor RbEuFe4As4 with Tsc>Tm . With the Ni doping, Tsc decreases rapidly, and the Eu-spin ferromagnetism and its Tm remain unchanged. Consequently, the system RbEu (Fe1-xNix) 4As4 transforms into a superconducting ferromagnet with Tm>Tsc for 0.07 ≤x ≤0.08 . The occurrence of superconducting ferromagnets is attributed to the decoupling between Eu2 + spins and superconducting Cooper pairs. The superconducting and magnetic phase diagram is established, which additionally includes a recovered yet suppressed spin-density-wave state.

  15. Effects of laser-polarization and wiggler magnetic fields on electron acceleration in laser-cluster interaction

    NASA Astrophysics Data System (ADS)

    Singh Ghotra, Harjit; Kant, Niti

    2018-06-01

    We examine the electron dynamics during laser-cluster interaction. In addition to the electrostatic field of an individual cluster and laser field, we consider an external transverse wiggler magnetic field, which plays a pivotal role in enhancing the electron acceleration. Single-particle simulation has been presented with a short pulse linearly polarized as well as circularly polarized laser pulses for electron acceleration in a cluster. The persisting Coulomb field allows the electron to absorb energy from the laser field. The stochastically heated electron finds a weak electric field at the edge of the cluster from where it is ejected. The wiggler magnetic field connects the regions of the stochastically heated, ejected electron from the cluster and high energy gain by the electron from the laser field outside the cluster. This increases the field strength and hence supports the electron to meet the phase of the laser field for enhanced acceleration. A long duration resonance appears with an optimized magnetic wiggler field of about 3.4 kG. Hence, the relativistic energy gain by the electron is enhanced up to a few 100 MeV with an intense short pulse laser with an intensity of about 1019 W cm‑2 in the presence of a wiggler magnetic field.

  16. Numerical analysis of THz radiation wave using upper hybrid wave wiggler

    NASA Astrophysics Data System (ADS)

    Malik, Pratibha; Sharma, Suresh C.; Panwar, Jyotsna; Sharma, Rinku

    2018-03-01

    A theory for upper hybrid wave induced by relativistic electron beam in magnetized plasma emits tuneable and coherent terahertz radiation. The nonlinear interaction with REB is used to generate terahertz radiation. The enhancement in the amplitude of THz wave is also observed when pre-bunched REB is used. The ponderomotive force applied on beam electrons due to radiation wave and upper wave wiggler modifies the dispersion relation. By solving the dispersion relation, we have derived the growth rate of the radiation wave. Numerical studies indicate that by increasing the beam energy the growth rate of the radiation wave decreases, while it increases with wiggler frequency. Besides this, the growth rate of the radiation wave increases with beam density and decreases with radiation frequency and static magnetic field.

  17. Superconductivity in the antiperovskite Dirac-metal oxide Sr3−xSnO

    PubMed Central

    Oudah, Mohamed; Ikeda, Atsutoshi; Hausmann, Jan Niklas; Yonezawa, Shingo; Fukumoto, Toshiyuki; Kobayashi, Shingo; Sato, Masatoshi; Maeno, Yoshiteru

    2016-01-01

    Investigations of perovskite oxides triggered by the discovery of high-temperature and unconventional superconductors have had crucial roles in stimulating and guiding the development of modern condensed-matter physics. Antiperovskite oxides are charge-inverted counterpart materials to perovskite oxides, with unusual negative ionic states of a constituent metal. No superconductivity was reported among the antiperovskite oxides so far. Here we present the first superconducting antiperovskite oxide Sr3−xSnO with the transition temperature of around 5 K. Sr3SnO possesses Dirac points in its electronic structure, and we propose from theoretical analysis a possibility of a topological odd-parity superconductivity analogous to the superfluid 3He-B in moderately hole-doped Sr3−xSnO. We envision that this discovery of a new class of oxide superconductors will lead to a rapid progress in physics and chemistry of antiperovskite oxides consisting of unusual metallic anions. PMID:27941805

  18. Control of magnetic, nonmagnetic, and superconducting states in annealed Ca(Fe 1–xCo x)₂As₂

    DOE PAGES

    Ran, S.; Bud'ko, S. L.; Straszheim, W. E.; ...

    2012-06-22

    We have grown single-crystal samples of Co substituted CaFe₂As₂ using an FeAs flux and systematically studied the effects of annealing/quenching temperature on the physical properties of these samples. Whereas the as-grown samples (quenched from 960°C) all enter the collapsed tetragonal phase upon cooling, annealing/quenching temperatures between 350 and 800°C can be used to tune the system to low-temperature antiferromagnetic/orthorhomic or superconducting states as well. The progression of the transition temperature versus annealing/quenching temperature (T-T anneal) phase diagrams with increasing Co concentration shows that, by substituting Co, the antiferromagnetic/orthorhombic and the collapsed tetragonal phase lines are separated and bulk superconductivity ismore » revealed. We established a 3D phase diagram with Co concentration and annealing/quenching temperature as two independent control parameters. At ambient pressure, for modest x and T anneal values, the Ca(Fe₁₋ xCox)₂As₂ system offers ready access to the salient low-temperature states associated with Fe-based superconductors: antiferromagnetic/orthorhombic, superconducting, and nonmagnetic/collapsed tetragonal.« less

  19. Persistence of magnetic excitations in La(2-x)Sr(x)CuO4 from the undoped insulator to the heavily overdoped non-superconducting metal.

    PubMed

    Dean, M P M; Dellea, G; Springell, R S; Yakhou-Harris, F; Kummer, K; Brookes, N B; Liu, X; Sun, Y-J; Strle, J; Schmitt, T; Braicovich, L; Ghiringhelli, G; Božović, I; Hill, J P

    2013-11-01

    One of the most intensely studied scenarios of high-temperature superconductivity (HTS) postulates pairing by exchange of magnetic excitations. Indeed, such excitations have been observed up to optimal doping in the cuprates. In the heavily overdoped regime, neutron scattering measurements indicate that magnetic excitations have effectively disappeared, and this has been argued to cause the demise of HTS with overdoping. Here we use resonant inelastic X-ray scattering, which is sensitive to complementary parts of reciprocal space, to measure the evolution of the magnetic excitations in La(2-x)Sr(x)CuO4 across the entire phase diagram, from a strongly correlated insulator (x = 0) to a non-superconducting metal (x = 0.40). For x = 0, well-defined magnon excitations are observed. These magnons broaden with doping, but they persist with a similar dispersion and comparable intensity all the way to the non-superconducting, heavily overdoped metallic phase. The destruction of HTS with overdoping is therefore caused neither by the general disappearance nor by the overall softening of magnetic excitations. Other factors, such as the redistribution of spectral weight, must be considered.

  20. Emittance and lifetime measurement with damping wigglers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wang, G. M.; Shaftan, T., E-mail: shaftan@bnl.gov; Cheng, W. X.

    National Synchrotron Light Source II (NSLS-II) is a new third-generation storage ring light source at Brookhaven National Laboratory. The storage ring design calls for small horizontal emittance (<1 nm-rad) and diffraction-limited vertical emittance at 12 keV (8 pm-rad). Achieving low value of the beam size will enable novel user experiments with nm-range spatial and meV-energy resolution. The high-brightness NSLS-II lattice has been realized by implementing 30-cell double bend achromatic cells producing the horizontal emittance of 2 nm rad and then halving it further by using several Damping Wigglers (DWs). This paper is focused on characterization of the DW effects inmore » the storage ring performance, namely, on reduction of the beam emittance, and corresponding changes in the energy spread and beam lifetime. The relevant beam parameters have been measured by the X-ray pinhole camera, beam position monitors, beam filling pattern monitor, and current transformers. In this paper, we compare the measured results of the beam performance with analytic estimates for the complement of the 3 DWs installed at the NSLS-II.« less

  1. Conditions for superconductivity in the electron-doped copper-oxide system, (Nd 1-xCe x) 2CuO 4+δ

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Motohashi, T.; Karppinen, M.; Yamauchi, H.

    2008-02-01

    We report systematic studies on the relations among the Ce IV-for-Nd III substitution level ( x), oxygen-partial pressure ( P), oxygen content (4+ δ), lattice parameters ( a, c) and superconductivity characteristics ( Tc, volume fraction) in the (Nd 1-xCe x) 2Cu 1-yO 4+δ system which includes electron-doped superconductors. Independent of the Ce-doping level x, samples synthesized in air are found oxygen deficient, i.e. δ<0. Nevertheless, reductive annealing is needed to induce superconductivity in the air-synthesized samples. At the same time, the amount of oxygen removed upon the annealing is found very small (e.g. 0.004 oxygen atoms per formula unit at x=0.075), and consequently the effect of the annealing on the valence of copper (and thereby also on the electron doping level) is insignificant. Rather, the main function of the reductive annealing is likely to repair the Cu vacancies believed to exist in tiny concentrations ( y) in the air-synthesized samples.

  2. Bulk Superconductivity Induced by In-Plane Chemical Pressure Effect in Eu0.5La0.5FBiS2-xSex

    NASA Astrophysics Data System (ADS)

    Jinno, Gen; Jha, Rajveer; Yamada, Akira; Higashinaka, Ryuji; Matsuda, Tatsuma D.; Aoki, Yuji; Nagao, Masanori; Miura, Osuke; Mizuguchi, Yoshikazu

    2016-12-01

    We have investigated the Se substitution effect on the superconductivity of optimally doped BiS2-based superconductor Eu0.5La0.5FBiS2. Eu0.5La0.5FBiS2-xSex samples with x = 0-1 were synthesized. With increasing x, in-plane chemical pressure is enhanced. For x ≥ 0.6, superconducting transitions with a large shielding volume fraction are observed in magnetic susceptibility measurements, and the highest Tc is 3.8 K for x = 0.8. From low-temperature electrical resistivity measurements, a zero-resistivity state is observed for all the samples, and the highest Tc is observed for x = 0.8. With increasing Se concentration, the characteristic electrical resistivity changes from semiconducting-like to metallic, suggesting that the emergence of bulk superconductivity is linked with the enhanced metallicity. A superconductivity phase diagram of the Eu0.5La0.5FBiS2-xSex superconductor is established.

  3. Superconductivity in pressurized CeRhG e3 and related noncentrosymmetric compounds

    NASA Astrophysics Data System (ADS)

    Wang, Honghong; Guo, Jing; Bauer, Eric D.; Sidorov, Vladimir A.; Zhao, Hengcan; Zhang, Jiahao; Zhou, Yazhou; Wang, Zhe; Cai, Shu; Yang, Ke; Li, Aiguo; Li, Xiaodong; Li, Yanchun; Sun, Peijie; Yang, Yi-feng; Wu, Qi; Xiang, Tao; Thompson, J. D.; Sun, Liling

    2018-02-01

    We report the discovery of superconductivity in pressurized CeRhG e3 , a nonsuperconducting member of the isostructural family of noncentrosymmetric heavy-fermion compounds Ce T X3 (T =Co , Rh, Ir and X =Si , Ge). Superconductivity appears in CeRhG e3 at a pressure of 19.6 GPa and the transition temperature TC reaches a maximum value of 1.3 K at 21.5 GPa. This finding provides an opportunity to establish systematic correlations between superconductivity and material properties within this family. Though ambient-pressure unit-cell volumes and critical pressures for superconductivity vary substantially across the series, all family members reach a maximum TCmax at a common (±1.7%) critical cell volume Vcrit, and TCmax at Vcrit increases with increasing spin-orbit coupling strength of the d electrons. These correlations show that substantial Kondo and spin-orbit couplings favor superconductivity in this family, the latter reflecting the role of broken centrosymmetry.

  4. Observation of multiple superconducting gaps in Fe1+y Se x Te 1-x through Andreev reflection

    NASA Astrophysics Data System (ADS)

    de, Debtanu; Diaz-Pinto, Carlos; Wu, Zheng; Hor, Pei-Herng; Peng, Haibing

    2011-03-01

    Iron-based superconductors have been under intensive study because of the high transition temperature and the intriguing physical mechanisms involving the superconductivity and magnetic orders. Theoretical studies on the role of spin fluctuation suggest unconventional S wave pairing and multiple superconducting (SC) gaps due to the five disjoint Fermi surfaces. However, this multiple SC-gap scenario has yet to be confirmed in experiments. Here we report the experimental observation of five SC gaps in Fe 1+y Se x Te 1-x from Andreev reflection spectra, along with negative differential conductance dips due to the pair breaking related to the largest SC gap. The evolution of the multiple SC gaps is further investigated as a function of both temperature and magnetic field. For the largest SC gap, the Andreev reflection signal persists above bulk Tc, suggesting the existence of phase incoherent Cooper pairs.

  5. Importance of uniaxial compression for the appearance of superconductivity in NdO1-xFxBiS2

    NASA Astrophysics Data System (ADS)

    A, Omachi; T, Hiroi; J, Kajitani; O, Miura; Y, Mizuguchi

    2014-05-01

    We have investigated the crystal structure and superconducting properties of the new layered superconductor NdO1-xFxBiS2. Bulk superconductivity with a Tc above 4.5 K was observed. It was found that the Tc depended on both F concentration and crystal structure. Uniaxial compression along the c axis upon F substitution seemed to be linked with the appearance of bulk superconductivity. Furthermore, we considered that a higher Tc can be achieved when the c/a parameter was optimized in the NdO1-xFxBiS2 system.

  6. The superconducting high-resolution soft X-ray spectrometer at the advanced biological and environmental X-ray facility

    NASA Astrophysics Data System (ADS)

    Friedrich, S.; Drury, O. B.; George, S. J.; Cramer, S. P.

    2007-11-01

    We have built a 36-pixel superconducting tunnel junction X-ray spectrometer for chemical analysis of dilute samples in the soft X-ray band. It offers an energy resolution of ˜10-20 eV FWHM below 1 keV, a solid angle coverage of ˜10 -3, and can be operated at total rates of up to ˜10 6 counts/s. Here, we describe the spectrometer performance in speciation measurements by fluorescence-detected X-ray absorption spectroscopy at the Advanced Biological and Environmental X-ray facility at the ALS synchrotron.

  7. Electron energy and electron trajectories in an inverse free-electron laser accelerator based on a novel electrostatic wiggler

    NASA Astrophysics Data System (ADS)

    Nikrah, M.; Jafari, S.

    2016-06-01

    We expand here a theory of a high-gradient laser-excited electron accelerator based on an inverse free-electron laser (inverse-FEL), but with innovations in the structure and design. The electrostatic wiggler used in our scheme, namely termed the Paul wiggler, is generated by segmented cylindrical electrodes with applied oscillatory voltages {{V}\\text{osc}}(t) over {{90}\\circ} segments. The inverse-FEL interaction can be described by the equations that govern the electron motion in the combined fields of both the laser pulse and Paul wiggler field. A numerical study of electron energy and electron trajectories has been made using the fourth-order Runge-Kutta method. The results indicate that the electron attains a considerable energy at short distances in this device. It is found that if the electron has got sufficient suitable wiggler amplitude intensities, it can not only gain higher energy in longer distances, but also can retain it even after the passing of the laser pulse. In addition, the results reveal that the electron energy gains different peaks for different initial axial velocities, so that a suitable small initial axial velocity of e-beam produces substantially high energy gain. With regard to the transverse confinement of the electron beam in a Paul wiggler, there is no applied axial guide magnetic field in this device.

  8. Dependence of superconductivity in Cu x Bi 2 Se 3 on quenching conditions

    DOE PAGES

    Schneeloch, J. A.; Zhong, R. D.; Xu, Z. J.; ...

    2015-04-20

    Topological superconductivity, implying gapless protected surface states, has recently been proposed to exist in the compound Cu xBi₂Se₃. Unfortunately, low diamagnetic shielding fractions and considerable inhomogeneity have been reported in this compound. In an attempt to understand and improve on the finite superconducting volume fractions, we have investigated the effects of various growth and post-annealing conditions. With a melt-growth (MG) method, diamagnetic shielding fractions of up to 56% in Cu₀̣₃Bi₂Se₃ have been obtained, the highest value reported for this method. We investigate the efficacy of various quenching and annealing conditions, finding that quenching from temperatures above 560°C is essential formore » superconductivity, whereas quenching from lower temperatures or not quenching at all is detrimental. A modified floating zone (FZ) method yielded large single crystals but little superconductivity. Even after annealing and quenching, FZ-grown samples had much less chance of being superconducting than MG-grown samples. Thus, from the low shielding fractions in FZ-grown samples and the quenching dependence, we suggest that a metastable secondary phase having a small volume fraction in most of the samples may be responsible for the superconductivity.« less

  9. Heat capacity jump at T c and pressure derivatives of superconducting transition temperature in the Ba 1 - x Na x Fe 2 As 2 ( 0.1 ≤ x ≤ 0.9 ) series

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bud'ko, Sergey L.; Chung, Duck Young; Bugaris, Daniel

    2014-01-16

    We present the evolution of the initial (up to ~ 10 kbar) hydrostatic pressure dependencies of T c and of the ambient pressure, and the jump in the heat capacity associated with the superconducting transition as a function of Na doping in the Ba1-xNaxFe2As2 family of iron-based superconductors. For Na concentrations 0.15 ≤ x ≤ 0.9, the jump in specific heat at T c, ΔC p| Tmore » $$_c$$, follows the ΔC p ∝ to T 3 (the so-called BNC scaling) found for most BaFe 2As 2 based superconductors. This finding suggests that, unlike the related Ba 1-xK xFe 2As 2 series, there is no significant modification of the superconducting state (e. g., change in superconducting gap symmetry) in the Ba 1-xNa xFe 2As 2 series over the whole studied Na concentration range. Pressure dependencies are nonmonotonic for x = 0.2 and 0.24. For other Na concentrations, T c decreases under pressure in an almost linear fashion. The anomalous behavior of the x = 0.2 and 0.24 samples under pressure is possibly due to the crossing of the phase boundaries of the narrow antiferromagnetic tetragonal phase, unique for the Ba 1-xNa xFe 2As 2 series, with the application of pressure. The negative sign of the pressure derivatives of T c across the whole superconducting dome (except for x = 0.2) is a clear indication of the nonequivalence of substitution and pressure for the Ba 1-xNa xFe 2As 2 series.« less

  10. Energy gap evolution across the superconductivity dome in single crystals of (Ba 1-xK x)Fe 2As 2

    DOE PAGES

    Cho, Kyuil; Konczykowski, Marcin; Teknowijoyo, Serafim; ...

    2016-09-30

    The mechanism of unconventional superconductivity in iron-based superconductors (IBSs) is one of the most intriguing questions in current materials research. Among non-oxide IBSs, (Ba 1$-$xK x)Fe 2As 2 has been intensively studied because of its high superconducting transition temperature and fascinating evolution of the superconducting gap structure from being fully isotropic at optimal doping (x ≈ 0.4) to becoming nodal at x > 0.8. Although this marked evolution was identified in several independent experiments, there are no details of the gap evolution to date because of the lack of high-quality single crystals covering the entire K-doping range of the superconductingmore » dome. In this work, we conducted a systematic study of the London penetration depth, λ(T), across the full phase diagram for different concentrations of point-like defects introduced by 2.5-MeV electron irradiation. Fitting the low-temperature variation with the power law, Δλ ~ T n, we find that the exponent n is the highest and the Tc suppression rate with disorder is the smallest at optimal doping, and they evolve with doping being away from optimal, which is consistent with increasing gap anisotropy, including an abrupt change around x ≃ 0.8, indicating the onset of nodal behavior. Our analysis using a self-consistent t-matrix approach suggests the ubiquitous and robust nature of s ± pairing in IBSs and argues against a previously suggested transition to a d-wave state near x = 1 in this system.« less

  11. Superconductivity in the orthorhombic phase of thermoelectric CsPb{sub x}Bi{sub 4−x}Te{sub 6} with 0.3≤x≤1.0

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, R.X.; Yang, H.X., E-mail: hxyang@iphy.ac.cn; Tian, H.F.

    2015-12-15

    Experimental measurements clearly reveal the presence of bulk superconductivity in the CsPb{sub x}Bi{sub 4−x}Te{sub 6} (0.3≤x≤1.0) materials, i.e. the first member of the thermoelectric series of Cs[Pb{sub m}Bi{sub 3}Te{sub 5+m}], these materials have the layered orthorhombic structure containing infinite anionic [PbBi{sub 3}Te{sub 6}]{sup −} slabs separated with Cs{sup +} cations. Temperature dependences of electrical resistivity, magnetic susceptibility, and specific heat have consistently demonstrated that the superconducting transition in Cs{sub 0.96}Pb{sub 0.25}Bi{sub 3.75}Te{sub 6.04} occurs at T{sub c}=3.1 K, with a superconducting volume fraction close to 100% at 1.8 K. Structural study using aberration-corrected STEM/TEM reveals a rich variety of microstructuralmore » phenomena in correlation with the Pb-ordering and chemical inhomogeneity. The superconducting material Cs{sub 0.96}Pb{sub 0.25}Bi{sub 3.75}Te{sub 6.04} with the highest T{sub c} shows a clear ordered structure with a modulation wave vector of q≈a*/2+c*/1.35 on the a–c plane. Our study evidently demonstrates that superconductivity deriving upon doping of narrow-gap semiconductor is a viable approach for exploration of novel superconductors. - Graphical abstract: Bulk superconductivity is discovered in the orthorhombic Cs{sub 0.96}Pb{sub 0.22}Bi{sub 3.80}Te{sub 6.02} materials with the superconducting transition T{sub c}=3.1 K. The compound shows a clear ordered structure with a modulation wave vector of q≈a*/2+c*/1.35 on the a–c plane. - Highlights: • Bulk superconductivity is discovered in the orthorhombic CsPb{sub x}Bi{sub 4−x}Te{sub 6} materials. • The superconducting transition in Cs{sub 0.96}Pb{sub 0.22}Bi{sub 3.80}Te{sub 6.02} occurs at T{sub c}=3.1 K. • Physical property measurements concerning the bulk superconductivity were present. • Structural modulation due to Pb-ordering was observed.« less

  12. Bulk superconducting phase with a full energy gap in the doped topological insulator Cu(x)Bi₂Se₃.

    PubMed

    Kriener, M; Segawa, Kouji; Ren, Zhi; Sasaki, Satoshi; Ando, Yoichi

    2011-03-25

    The superconductivity recently found in the doped topological insulator Cu(x)Bi₂Se₃ offers a great opportunity to search for a topological superconductor. We have successfully prepared a single-crystal sample with a large shielding fraction and measured the specific-heat anomaly associated with the superconductivity. The temperature dependence of the specific heat suggests a fully gapped, strong-coupling superconducting state, but the BCS theory is not in full agreement with the data, which hints at a possible unconventional pairing in Cu(x)Bi₂Se₃. Also, the evaluated effective mass of 2.6m(e) (m(e) is the free electron mass) points to a large mass enhancement in this material.

  13. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe1 +yTe1 -xSex

    NASA Astrophysics Data System (ADS)

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; Wang, Jun; Berlijn, Tom; Maier, Thomas A.; Kalinin, Sergei V.; Sales, Brian C.; Pan, Minghu

    2015-02-01

    Recent investigations have shown that Fe1 +yTe1 -xSex can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon, we performed a combination of magnetic susceptibility, specific heat, and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe1 +yTe1 -xSex treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTem (m ≥1 ) complexes. We show that the remaining FeTem complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.

  14. Importance of the Fermi-surface topology to the superconducting state of the electron-doped pnictide Ba(Fe 1-xCo x)₂As₂

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liu, Chang; Palczewski, A. D.; Dhaka, R. S.

    We used angle-resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe 1-xCo x)₂As₂ high-temperature superconductor. Our data demonstrate that several Lifshitz transitions—topological changes of the Fermi surface—occur for large x. The central hole barrel changes to ellipsoids that are centered at Z at x~0.11 and subsequently disappear around x~0.2; changes in thermoelectric power occur at similar x values. T c decreases and goes to zero around x~0.15—between the two Lifshitz transitions. Beyond x=0.2 the central pocket becomes electron-like and superconductivity does not exist. Our observations reveal the importance ofmore » the underlying Fermiology in electron-doped iron arsenides. We speculate that a likely necessary condition for superconductivity in these materials is the presence of the central hole pockets rather than nesting between central and corner pockets.« less

  15. Importance of the Fermi-surface topology to the superconducting state of the electron-doped pnictide Ba(Fe 1-xCo x)₂As₂

    DOE PAGES

    Liu, Chang; Palczewski, A. D.; Dhaka, R. S.; ...

    2011-07-25

    We used angle-resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe 1-xCo x)₂As₂ high-temperature superconductor. Our data demonstrate that several Lifshitz transitions—topological changes of the Fermi surface—occur for large x. The central hole barrel changes to ellipsoids that are centered at Z at x~0.11 and subsequently disappear around x~0.2; changes in thermoelectric power occur at similar x values. T c decreases and goes to zero around x~0.15—between the two Lifshitz transitions. Beyond x=0.2 the central pocket becomes electron-like and superconductivity does not exist. Our observations reveal the importance ofmore » the underlying Fermiology in electron-doped iron arsenides. We speculate that a likely necessary condition for superconductivity in these materials is the presence of the central hole pockets rather than nesting between central and corner pockets.« less

  16. Tuning of superconductivity by Ni substitution into noncentrosymmetric ThC o1 -xN ixC2

    NASA Astrophysics Data System (ADS)

    Grant, T. W.; Cigarroa, O. V.; Rosa, P. F. S.; Machado, A. J. S.; Fisk, Z.

    2017-07-01

    The recently discovered noncentrosymmetric superconductor ThCoC2 was observed to show unusual superconducting behavior with a critical temperature of Tc=2.65 K . Here we investigate the effect of nickel substitution on the superconducting state in ThC o1 -xN ixC2 . Magnetization, resistivity, and heat capacity measurements demonstrate Ni substitution has a dramatic effect with critical temperature increased up to Tc=12.1 K for x =0.4 Ni concentration, which is a rather high transition temperature for a noncentrosymmetric superconductor. In addition, the unusual superconducting characteristics observed in pure ThCoC2 appear to be suppressed or tuned with Ni substitution towards a more conventional fully gapped superconductor.

  17. Universal doping evolution of the superconducting gap anisotropy in single crystals of electron-doped Ba(Fe 1–xRh x) 2As 2 from London penetration depth measurements

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kim, Hyunsoo; Tanatar, M. A.; Martin, C.

    Doping evolution of the superconducting gap anisotropy was studied in single crystals of 4d-electron doped Ba(Fe 1–xRh x) 2As 2 using tunnel diode resonator measurements of the temperature variation of the London penetration depth Δλ( T). Single crystals with doping levels representative of an underdoped regime x = 0.039 ( T c = 15.5 K), close to optimal doping x = 0.057 ( T c = 24.4 K) and overdoped x = 0.079 ( T c = 21.5 K) and x = 0.131( T c = 4.9 K) were studied. Superconducting energy gap anisotropy was characterized by the exponent, n,more » by fitting the data to the power-law, Δλ = AT n. The exponent n varies non-monotonically with x, increasing to a maximum n = 2.5 for x = 0.079 and rapidly decreasing towards overdoped compositions to 1.6 for x = 0.131. This behavior is qualitatively similar to the doping evolution of the superconducting gap anisotropy in other iron pnictides, including hole-doped (Ba,K)Fe 2As 2 and 3d-electron-doped Ba(Fe,Co) 2As 2 superconductors, finding a full gap near optimal doping and strong anisotropy toward the ends of the superconducting dome in the T-x phase diagram. The normalized superfluid density in an optimally Rh-doped sample is almost identical to the temperature-dependence in the optimally doped Ba(Fe,Co) 2As 2 samples. In conclusion, our study supports the universal superconducting gap variation with doping and pairing at least in iron based superconductors of the BaFe 2As 2 family.« less

  18. Universal doping evolution of the superconducting gap anisotropy in single crystals of electron-doped Ba(Fe 1–xRh x) 2As 2 from London penetration depth measurements

    DOE PAGES

    Kim, Hyunsoo; Tanatar, M. A.; Martin, C.; ...

    2018-05-08

    Doping evolution of the superconducting gap anisotropy was studied in single crystals of 4d-electron doped Ba(Fe 1–xRh x) 2As 2 using tunnel diode resonator measurements of the temperature variation of the London penetration depth Δλ( T). Single crystals with doping levels representative of an underdoped regime x = 0.039 ( T c = 15.5 K), close to optimal doping x = 0.057 ( T c = 24.4 K) and overdoped x = 0.079 ( T c = 21.5 K) and x = 0.131( T c = 4.9 K) were studied. Superconducting energy gap anisotropy was characterized by the exponent, n,more » by fitting the data to the power-law, Δλ = AT n. The exponent n varies non-monotonically with x, increasing to a maximum n = 2.5 for x = 0.079 and rapidly decreasing towards overdoped compositions to 1.6 for x = 0.131. This behavior is qualitatively similar to the doping evolution of the superconducting gap anisotropy in other iron pnictides, including hole-doped (Ba,K)Fe 2As 2 and 3d-electron-doped Ba(Fe,Co) 2As 2 superconductors, finding a full gap near optimal doping and strong anisotropy toward the ends of the superconducting dome in the T-x phase diagram. The normalized superfluid density in an optimally Rh-doped sample is almost identical to the temperature-dependence in the optimally doped Ba(Fe,Co) 2As 2 samples. In conclusion, our study supports the universal superconducting gap variation with doping and pairing at least in iron based superconductors of the BaFe 2As 2 family.« less

  19. Superconducting properties of under- and over-doped BaxK1‑xBiO3 perovskite oxide

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, D.; Kaczmarek, A. Z.; Szczȩśniak, R.; Turchuk, S. V.; Zhao, H.; Drzazga, E. A.

    2018-06-01

    In this study, we investigate the thermodynamic properties of the BaxK1‑xBiO3 (BKBO) superconductor in the under- (x = 0.5) and over-doped (x = 0.7) regime, within the framework of the Migdal-Eliashberg formalism. The analysis is conducted to verify that the electron-phonon pairing mechanism is responsible for the induction of the superconducting phase in the mentioned compound. In particular, we show that BKBO is characterized by the relatively high critical value of the Coulomb pseudopotential, which changes with doping level and does not follow the Morel-Anderson model. In what follows, the corresponding superconducting band gap size and related dimensionless ratio are estimated to increase with the doping, in agreement with the experimental predictions. Moreover, the effective mass of electrons is found to take on high values in the entire doping and temperature region. Finally, the characteristic dimensionless ratios for the superconducting band gap, the critical magnetic field and the specific heat for the superconducting state are predicted to exceed the limits set within the Bardeen-Cooper-Schrieffer theory, suggesting pivotal role of the strong-coupling and retardation effects in the analyzed compound. Presented results supplement our previous investigations and account for the strong-coupling phonon-mediated character of the superconducting phase in BKBO at any doping level.

  20. Enhanced THz radiation generation by photo-mixing of tophat lasers in rippled density plasma with a planar magnetostatic wiggler and s-parameter

    NASA Astrophysics Data System (ADS)

    Abedi-Varaki, M.

    2018-02-01

    In this paper, the effects of planar magnetostatic wiggler and s-parameter on the terahertz (THz) radiation generation through rippled plasma have been investigated. Efficient THz radiation generation by photo-mixing of tophat lasers for rippled density plasma in the presence of the wiggler field has been presented. Fundamental equations for the analysis of the non-linear current density and THz radiation generation by wiggler magnetostatic field have been derived. It is shown that for the higher order of the tophat lasers, the values of THz amplitude are greater. In fact, the higher order of the tophat lasers has a sharp gradient in the intensity of lasers, which leads to a stronger nonlinear ponderomotive force and, consequently, a stronger current density. In addition, it is seen that by increasing s-parameter, the normalized transverse profile becomes more focused near the axis of y. Furthermore, it is observed that the normalized laser efficiency has a decreasing trend with increasing normalized THz frequency for different values of the wiggler field. Also, it is shown that by employing a greater order of the tophat lasers and a stronger wiggler field, the efficiency of order of 30% can be achieved. Moreover, it is found that we can control focus and intensity of THz radiation emitted in rippled plasma by choosing the appropriate order of the tophat lasers and tuning of the wiggler field.

  1. Controlling superconductivity in La 2-xSr xCuO 4+δ by ozone and vacuum annealing

    DOE PAGES

    Leng, Xiang; Bozovic, Ivan

    2014-11-21

    In this study we performed a series of ozone and vacuum annealing experiments on epitaxial La 2-xSr xCuO 4+δ thin films. The transition temperature after each annealing step has been measured by the mutual inductance technique. The relationship between the effective doping and the vacuum annealing time has been studied. Short-time ozone annealing at 470 °C oxidizes an underdoped film all the way to the overdoped regime. The subsequent vacuum annealing at 350 °C to 380 °C slowly brings the sample across the optimal doping point back to the undoped, non-superconducting state. Several ozone and vacuum annealing cycles have beenmore » done on the same sample and the effects were found to be repeatable and reversible Vacuum annealing of ozone-loaded LSCO films is a very controllable process, allowing one to tune the doping level of LSCO in small steps across the superconducting dome, which can be used for fundamental physics studies.« less

  2. Controlling superconductivity in La 2-xSr xCuO 4+δ by ozone and vacuum annealing

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Leng, Xiang; Bozovic, Ivan

    In this study we performed a series of ozone and vacuum annealing experiments on epitaxial La 2-xSr xCuO 4+δ thin films. The transition temperature after each annealing step has been measured by the mutual inductance technique. The relationship between the effective doping and the vacuum annealing time has been studied. Short-time ozone annealing at 470 °C oxidizes an underdoped film all the way to the overdoped regime. The subsequent vacuum annealing at 350 °C to 380 °C slowly brings the sample across the optimal doping point back to the undoped, non-superconducting state. Several ozone and vacuum annealing cycles have beenmore » done on the same sample and the effects were found to be repeatable and reversible Vacuum annealing of ozone-loaded LSCO films is a very controllable process, allowing one to tune the doping level of LSCO in small steps across the superconducting dome, which can be used for fundamental physics studies.« less

  3. Imaging the coexistence of superconductivity and antiferromagnetism in Fe1+yTe1-xSex (x=0.1) using spin-polarized scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Zhou, Haibiao; Aluru, Ramakrishna; Tsurkan, Vladimir; Loidl, Alois; Deisenhofer, Joachim; Wahl, Peter

    Magnetism has been widely thought to play an important role in unconventional superconductivity. In iron chalcogenide Fe1+yTe, the bicollinear antiferromagnetim (AFM) can be suppressed by Se doping, and consequently superconductivity appears. Though a competition between the two orders is expected, their relation has never been shown in details. Here, using spin-polarized scanning tunneling microscopy, we explore their relation at the atomic scale in an Fe1+yTe1-xSex (x=0.1) single crystal with TC = 10 K, in a regime of the phase diagram where a spin-glass phase has been detected. We clearly observe the short-range AFM order with domains of a lateral size of 10 nm embedded in a non-magnetic matrix. In addition we observe a superconducting gap with prominent coherent peaks in differential conductance spectroscopy with a gap size 2 Δ 4 mV. Surprisingly, no correlation between the superconducting properties (gap size and zero bias conductance) and the local AFM order is observed, while the coherence peaks are weakened by the existence of excess iron atoms. Our observations put constraints on theories that are aimed at explaining the relation between magnetism and unconventional superconductivity.

  4. Effect of Eu substitution on superconductivity in Ba{sub 8−x}Eu{sub x}Al{sub 6}Si{sub 40} clathrates

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liu, Lihua; Bi, Shanli; Peng, Bailu

    2015-05-07

    The silicon clathrate superconductor is uncommon as its structure is dominated by strong Si-Si covalent bonds, rather than the metallic bond, that are more typical of traditional superconductors. To understand the influence of large magnetic moment of Eu on superconductivity for type-I clathrates, a series of samples with the chemical formula Ba{sub 8−x}Eu{sub x}Al{sub 6}Si{sub 40} (x = 0, 0.5, 1, and 2) were synthesised in which Eu occupied Ba sites in cage center. With the increase of Eu content, the cubic lattice parameter decreases monotonically signifying continuous shrinkage of the constituting (Ba/Eu)@Si{sub 20} and (Ba/Eu)@Si{sub 24} cages. The temperature dependence ofmore » magnetization at low temperature revealed that Ba{sub 8}Al{sub 6}Si{sub 40} is superconductive with transition temperature at T{sub C} = 5.6 K. The substitution of Eu for Ba results in a strong superconductivity suppression; Eu-doping largely decreases the superconducting volume and transition temperature T{sub C}. Eu atoms enter the clathrate lattice and their magnetic moments break paired electrons. The Curie-Weiss temperatures were observed at 3.9, 6.6, and 10.9 K, respectively, for samples with x = 0.5, 1.0, and 2.0. Such ferromagnetic interaction of Eu can destroy superconductivity.« less

  5. Superconducting and magnetic properties of RBa/sub 2/Cu/sub 3/O/sub 7-//sub x/ compounds

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shaheen, S.A.; Jisrawi, N.; Lee, Y.H.

    Superconducting properties of RBa/sub 2/Cu/sub 3/O/sub 7-//sub x/ compounds (R = Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb) have been studied by dc electrical resistivity and ac magnetic susceptibility techniques. Except for R = La, which is superconducting below 50 K, RBa/sub 2/Cu/sub 3/O/sub 7-//sub x/ compounds exhibit sharp resistive and inductive transitions in the 90-K range. The nearly constant value of T/sub c/ for magnetic R ions indicates a very weak interaction between R ions, as anticipated from the known crystal structure of these materials. The effects of annealing in oxygen and argon, andmore » air quenching, on the superconducting properties are also discussed.« less

  6. Robust odd-parity superconductivity in the doped topological insulator Nb x Bi 2 Se 3

    DOE PAGES

    Smylie, M. P.; Willa, K.; Claus, H.; ...

    2017-09-15

    We present resistivity and magnetization measurements on proton-irradiated crystals demonstrating that the superconducting state in the doped topological insulator Nb xBi 2Se 3 (x = 0.25) is surprisingly robust against disorder-induced electron scattering. The superconducting transition temperature Tc decreases without indication of saturation with increasing defect concentration, and the corresponding scattering rates far surpass expectations based on conventional theory. The low-temperature variation of the London penetration depth Δλ(T) follows a power law [Δλ(T)~T 2] indicating the presence of symmetry-protected point nodes. Lastly, our results are consistent with the proposed robust nematic E u pairing state in this material.

  7. Method of producing superconducting fibers of YBA2CU30X

    DOEpatents

    Schwartzkopf, Louis A.; Ostenson, Jerome E.; Finnemore, Douglas K.

    1990-11-13

    Fibers of YBa.sub.2 Cu.sub.3 O.sub.x have been produce by pendant drop melt extraction. This technique involves the end of a rod of YBa.sub.2 Cu.sub.3 O.sub.x melted with a hydrogen-oxygen torch, followed by lowering onto the edge of a spinning wheel. The fibers are up to 10 cm in length with the usual lateral dimensions, ranging from 20 .mu.m to 125 .mu.m. The fibers require a heat treatment to make them superconducting.

  8. Development of a ferromagnetic component in the superconducting state of Fe-excess Fe1.12Te1-xSex by electronic charge redistribution

    NASA Astrophysics Data System (ADS)

    Li, Wen-Hsien; Karna, Sunil K.; Hsu, Han; Li, Chi-Yen; Lee, Chi-Hung; Sankar, Raman; Cheng Chou, Fang

    2015-06-01

    The general picture established so far for the links between superconductivity and magnetic ordering in iron chalcogenide Fe1+y(Te1-xSex) is that the substitution of Se for Te directly drives the system from the antiferromagnetic end into the superconducting regime. Here, we report on the observation of a ferromagnetic component that developed together with the superconducting transition in Fe-excess Fe1.12Te1-xSex crystals using neutron and x-ray diffractions, resistivity, magnetic susceptibility and magnetization measurements. The superconducting transition is accompanied by a negative thermal expansion of the crystalline unit cell and an electronic charge redistribution, where a small portion of the electronic charge flows from around the Fe sites toward the Te/Se sites. First-principles calculations show consistent results, revealing that the excess Fe ions play a more significant role in affecting the magnetic property in the superconducting state than in the normal state and the occurrence of an electronic charge redistribution through the superconducting transition.

  9. A practical superconducting-microcalorimeter X-ray spectrometer for beamline and laboratory science

    DOE PAGES

    Doriese, W. B.; Abbamonte, P.; Alpert, B. K.; ...

    2017-05-01

    We describe a series of microcalorimeter X-ray spectrometers designed for a broad suite of measurement applications. The chief advantage of this type of spectrometer is that it can be orders of magnitude more efficient at collecting X-rays than more traditional high-resolution spectrometers that rely on wavelength-dispersive techniques. This advantage is most useful in applications that are traditionally photon-starved and/or involve radiation-sensitive samples. Each energy-dispersive spectrometer is built around an array of several hundred transition-edge sensors (TESs). TESs are superconducting thin films that are biased into their superconducting-to-normal-metal transitions. The spectrometers share a common readout architecture and many design elements, suchmore » as a compact, 65 mK detector package, 8-column time-division-multiplexed superconducting quantum-interference device readout, and a liquid-cryogen-free cryogenic system that is a two-stage adiabatic-demagnetization refrigerator backed by a pulse-tube cryocooler. We have adapted this flexible architecture to mate to a variety of sample chambers and measurement systems that encompass a range of observing geometries. There are two different types of TES pixels employed. The first, designed for X-ray energies below 10 keV, has a best demonstrated energy resolution of 2.1 eV (full-width-at-half-maximum or FWHM) at 5.9 keV. The second, designed for X-ray energies below 2 keV, has a best demonstrated resolution of 1.0 eV (FWHM) at 500 eV. Our team has now deployed seven of these X-ray spectrometers to a variety of light sources, accelerator facilities, and laboratory-scale experiments; these seven spectrometers have already performed measurements related to their applications. Another five of these spectrometers will come online in the near future. We have applied our TES spectrometers to the following measurement applications: synchrotron-based absorption and emission spectroscopy and energy

  10. A practical superconducting-microcalorimeter X-ray spectrometer for beamline and laboratory science

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Doriese, W. B.; Abbamonte, P.; Alpert, B. K.

    We describe a series of microcalorimeter X-ray spectrometers designed for a broad suite of measurement applications. The chief advantage of this type of spectrometer is that it can be orders of magnitude more efficient at collecting X-rays than more traditional high-resolution spectrometers that rely on wavelength-dispersive techniques. This advantage is most useful in applications that are traditionally photon-starved and/or involve radiation-sensitive samples. Each energy-dispersive spectrometer is built around an array of several hundred transition-edge sensors (TESs). TESs are superconducting thin films that are biased into their superconducting-to-normal-metal transitions. The spectrometers share a common readout architecture and many design elements, suchmore » as a compact, 65 mK detector package, 8-column time-division-multiplexed superconducting quantum-interference device readout, and a liquid-cryogen-free cryogenic system that is a two-stage adiabatic-demagnetization refrigerator backed by a pulse-tube cryocooler. We have adapted this flexible architecture to mate to a variety of sample chambers and measurement systems that encompass a range of observing geometries. There are two different types of TES pixels employed. The first, designed for X-ray energies below 10 keV, has a best demonstrated energy resolution of 2.1 eV (full-width-at-half-maximum or FWHM) at 5.9 keV. The second, designed for X-ray energies below 2 keV, has a best demonstrated resolution of 1.0 eV (FWHM) at 500 eV. Our team has now deployed seven of these X-ray spectrometers to a variety of light sources, accelerator facilities, and laboratory-scale experiments; these seven spectrometers have already performed measurements related to their applications. Another five of these spectrometers will come online in the near future. We have applied our TES spectrometers to the following measurement applications: synchrotron-based absorption and emission spectroscopy and energy

  11. A practical superconducting-microcalorimeter X-ray spectrometer for beamline and laboratory science

    NASA Astrophysics Data System (ADS)

    Doriese, W. B.; Abbamonte, P.; Alpert, B. K.; Bennett, D. A.; Denison, E. V.; Fang, Y.; Fischer, D. A.; Fitzgerald, C. P.; Fowler, J. W.; Gard, J. D.; Hays-Wehle, J. P.; Hilton, G. C.; Jaye, C.; McChesney, J. L.; Miaja-Avila, L.; Morgan, K. M.; Joe, Y. I.; O'Neil, G. C.; Reintsema, C. D.; Rodolakis, F.; Schmidt, D. R.; Tatsuno, H.; Uhlig, J.; Vale, L. R.; Ullom, J. N.; Swetz, D. S.

    2017-05-01

    We describe a series of microcalorimeter X-ray spectrometers designed for a broad suite of measurement applications. The chief advantage of this type of spectrometer is that it can be orders of magnitude more efficient at collecting X-rays than more traditional high-resolution spectrometers that rely on wavelength-dispersive techniques. This advantage is most useful in applications that are traditionally photon-starved and/or involve radiation-sensitive samples. Each energy-dispersive spectrometer is built around an array of several hundred transition-edge sensors (TESs). TESs are superconducting thin films that are biased into their superconducting-to-normal-metal transitions. The spectrometers share a common readout architecture and many design elements, such as a compact, 65 mK detector package, 8-column time-division-multiplexed superconducting quantum-interference device readout, and a liquid-cryogen-free cryogenic system that is a two-stage adiabatic-demagnetization refrigerator backed by a pulse-tube cryocooler. We have adapted this flexible architecture to mate to a variety of sample chambers and measurement systems that encompass a range of observing geometries. There are two different types of TES pixels employed. The first, designed for X-ray energies below 10 keV, has a best demonstrated energy resolution of 2.1 eV (full-width-at-half-maximum or FWHM) at 5.9 keV. The second, designed for X-ray energies below 2 keV, has a best demonstrated resolution of 1.0 eV (FWHM) at 500 eV. Our team has now deployed seven of these X-ray spectrometers to a variety of light sources, accelerator facilities, and laboratory-scale experiments; these seven spectrometers have already performed measurements related to their applications. Another five of these spectrometers will come online in the near future. We have applied our TES spectrometers to the following measurement applications: synchrotron-based absorption and emission spectroscopy and energy-resolved scattering

  12. A practical superconducting-microcalorimeter X-ray spectrometer for beamline and laboratory science.

    PubMed

    Doriese, W B; Abbamonte, P; Alpert, B K; Bennett, D A; Denison, E V; Fang, Y; Fischer, D A; Fitzgerald, C P; Fowler, J W; Gard, J D; Hays-Wehle, J P; Hilton, G C; Jaye, C; McChesney, J L; Miaja-Avila, L; Morgan, K M; Joe, Y I; O'Neil, G C; Reintsema, C D; Rodolakis, F; Schmidt, D R; Tatsuno, H; Uhlig, J; Vale, L R; Ullom, J N; Swetz, D S

    2017-05-01

    We describe a series of microcalorimeter X-ray spectrometers designed for a broad suite of measurement applications. The chief advantage of this type of spectrometer is that it can be orders of magnitude more efficient at collecting X-rays than more traditional high-resolution spectrometers that rely on wavelength-dispersive techniques. This advantage is most useful in applications that are traditionally photon-starved and/or involve radiation-sensitive samples. Each energy-dispersive spectrometer is built around an array of several hundred transition-edge sensors (TESs). TESs are superconducting thin films that are biased into their superconducting-to-normal-metal transitions. The spectrometers share a common readout architecture and many design elements, such as a compact, 65 mK detector package, 8-column time-division-multiplexed superconducting quantum-interference device readout, and a liquid-cryogen-free cryogenic system that is a two-stage adiabatic-demagnetization refrigerator backed by a pulse-tube cryocooler. We have adapted this flexible architecture to mate to a variety of sample chambers and measurement systems that encompass a range of observing geometries. There are two different types of TES pixels employed. The first, designed for X-ray energies below 10 keV, has a best demonstrated energy resolution of 2.1 eV (full-width-at-half-maximum or FWHM) at 5.9 keV. The second, designed for X-ray energies below 2 keV, has a best demonstrated resolution of 1.0 eV (FWHM) at 500 eV. Our team has now deployed seven of these X-ray spectrometers to a variety of light sources, accelerator facilities, and laboratory-scale experiments; these seven spectrometers have already performed measurements related to their applications. Another five of these spectrometers will come online in the near future. We have applied our TES spectrometers to the following measurement applications: synchrotron-based absorption and emission spectroscopy and energy-resolved scattering

  13. Ferro-Lattice-Distortions and Charge Fluctuations in Superconducting LaO 1- x F x BiS 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Athauda, Anushika; Hoffmann, Christina; Aswartham, Saicharan

    2017-05-15

    Competing ferroelectric and charge density wave states have been proposed to exist in the electron–phonon coupled LaO1-xFxBiS2 superconductor. The lattice instability is proposed to arise from unstable phonon modes that can break the crystal symmetry. Using single crystal diffraction, a superlattice pattern is observed, that arises from coherent in-plane displacements of the sulfur atoms in the BiS2 superconducting planes. The distortions morph into coordinated ferrodistortive patterns with displacements in the x- and y-directions, that alternate along the c-axis. Diffuse scattering is observed along the (H0L) plane due to stacking faults but not along the (HH0) plane. The ferro-distortive pattern remainsmore » in the superconducting state upon fluorine doping, but the displacements are diminished in magnitude. Moreover, we find that the in-plane distortions give rise to disorder where the (00L) reflections become quite broad. It is possible that charge carriers can get trapped in the lattice deformations reducing the effective number of carriers available for pairing.« less

  14. Origin of Pressure-induced Superconducting Phase in K xFe 2-ySe 2 studied by Synchrotron X-ray Diffraction and Spectroscopy

    DOE PAGES

    Yamamoto, Yoshiya; Yamaoka, Hitoshi; Tanaka, Masashi; ...

    2016-08-08

    Pressure dependence of the electronic and crystal structures of K xFe 2–ySe 2, which has pressure-induced two superconducting domes of SC I and SC II, was investigated by x-ray emission spectroscopy and diffraction. X-ray diffraction data show that compressibility along the c-axis changes around 12 GPa, where a new superconducting phase of SC II appears. This suggests a possible tetragonal to collapsed tetragonal phase transition. X-ray emission spectroscopy data also shows the change in the electronic structure around 12 GPa. These results can be explained by the scenario that the two SC domes under pressure originate from the change ofmore » Fermi surface topology. Lastly, our results here show the pronounced increase of the density of states near the Fermi surface under pressure with a structural phase transition, which can help address our fundamental understanding for the appearance of the SC II phase.« less

  15. Study on superconducting state parameters of Cu1-xZrx metallic glasses using model potentials

    NASA Astrophysics Data System (ADS)

    Jambusarwala, Tasneem S.; Gajjar, P. N.

    2018-05-01

    The superconducting state parameters (SSP) of Cu1-xZrx metallic glasses over the full range of concentration x of Zr have been investigated to study influence of various local pseudopotentials. The study includes the computation of electron-phonon coupling strength (λ), transition temperature (TC), isotope effect exponent (α) and effective interaction strength (N0V) using fourteen different forms of local model potentials. The local field correction function proposed by Taylor (T) is used. The influence of model potential on various parameters is ranging from 6% to 83% for pure Zr and 28% to 84% for pure Cu. The present study confirms that the identification of model potential is vital in studying Superconducting State Parameters.

  16. Site-selective doping and superconductivity in (La1-yPry)(Ba2-xLax)Cu3O7+δ

    NASA Astrophysics Data System (ADS)

    Mitzi, D. B.; Feffer, P. T.; Newsam, J. M.; Webb, D. J.; Klavins, P.; Jacobson, A. J.; Kapitulnik, A.

    1988-10-01

    Samples in the quaternary system (La1-yPry)(Ba2-xLax)Cu3O7+δ have been prepared and characterized using x-ray and neutron diffraction, thermogravimetric analysis, and transport and magnetic measurements. Pr substitutes on the oxygen-depleted La layers for y>0.0, while La substitutes on the Ba sites for x>0.0. The effect of doping on each site is inferred to be primarily local, affecting immediately adjacent Cu-O layers. The similar suppression of superconductivity that accompanies doping on each of the two distinct sites apparently correlates with the degree of oxidation of the Cu-O sheets (and not the chains), indicating that the sheets support the high temperature superconductivity. Comparison of orthorhombic and tetragonal samples with similar Ba:La ratios (and y=0) demonstrates that the orthorhombic phase yields the largest Meissner signals and highest transition temperatures in the La(Ba2-xLax)Cu3O7+δ system. The effect on superconductivity of oxygen-vacancy configuration in the Cu-O chain layers is proposed to derive, indirectly, from their influence on the Cu-O sheets. In addition, optimally superconducting La(Ba2-xLax)Cu3O7+δ samples exhibit interesting normal-state magnetic properties, with a paramagnetic susceptibility that decreases steadily with temperature between 350 K and Tc.

  17. Chemical substitution study on magnetism and superconductivity in Ce1-x SmxCoIn5

    NASA Astrophysics Data System (ADS)

    Pouse, N.; Jang, S.; White, B.; Ran, S.; Maple, M. B.; Almasan, C. C.

    We report electrical resistivity, magnetization, and specific heat measurement measurements on the Ce1- x SmxCoIn5 system for 0 <= x <= 1. Superconductivity in CeCoIn5 is suppressed with increasing Sm concentrations up to x = 0.1, above which there is no evidence for superconductivity from measurements down to 50 mK; antiferromagnetic ordering in SmCoIn5 persists deep into the Ce-rich side, and is not completely suppressed until x = 0.25. We have observed the development of a low-temperature upturn in electrical resistivity for 0.70 <= x <= 0.85 which is consistent with behavior for a single-ion impurity Kondo effect and suggests that the substitution of Sm for Ce causes a change of the relative strength of competing Kondo and Ruderman-Kittel-Kasuya-Yosida energy scales. Research at UCSD is supported by the US DOE BES under Grant No. DE-FG02-04-ER46105, the US NSF under Grant No. DMR-1206553, and research at Kent State U. is supported by NSF under Grant No. DMR-1505826.

  18. 17 CFR 210.1-01 - Application of Regulation S-X (17 CFR part 210).

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 17 Commodity and Securities Exchanges 2 2013-04-01 2013-04-01 false Application of Regulation S-X... POLICY AND CONSERVATION ACT OF 1975 Application of Regulation S-X (17 Cfr Part 210) § 210.1-01 Application of Regulation S-X (17 CFR part 210). (a) This part (together with the Financial Reporting Releases...

  19. 17 CFR 210.1-01 - Application of Regulation S-X (17 CFR part 210).

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 17 Commodity and Securities Exchanges 3 2014-04-01 2014-04-01 false Application of Regulation S-X... POLICY AND CONSERVATION ACT OF 1975 Application of Regulation S-X (17 Cfr Part 210) § 210.1-01 Application of Regulation S-X (17 CFR part 210). (a) This part (together with the Financial Reporting Releases...

  20. 17 CFR 210.1-01 - Application of Regulation S-X (17 CFR part 210).

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 17 Commodity and Securities Exchanges 2 2012-04-01 2012-04-01 false Application of Regulation S-X... POLICY AND CONSERVATION ACT OF 1975 Application of Regulation S-X (17 Cfr Part 210) § 210.1-01 Application of Regulation S-X (17 CFR part 210). (a) This part (together with the Financial Reporting Releases...

  1. 17 CFR 240.17a-19 - Form X-17A-19 Report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 17 Commodity and Securities Exchanges 3 2012-04-01 2012-04-01 false Form X-17A-19 Report by... Certain Stabilizing Activities § 240.17a-19 Form X-17A-19 Report by national securities exchanges and... Corporation such information as is required by § 249.635 of this chapter on Form X-17A-19 within 5 business...

  2. 17 CFR 240.17a-19 - Form X-17A-19 Report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 17 Commodity and Securities Exchanges 3 2013-04-01 2013-04-01 false Form X-17A-19 Report by... Certain Stabilizing Activities § 240.17a-19 Form X-17A-19 Report by national securities exchanges and... Corporation such information as is required by § 249.635 of this chapter on Form X-17A-19 within 5 business...

  3. 17 CFR 240.17a-19 - Form X-17A-19 Report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Form X-17A-19 Report by... Certain Stabilizing Activities § 240.17a-19 Form X-17A-19 Report by national securities exchanges and... Corporation such information as is required by § 249.635 of this chapter on Form X-17A-19 within 5 business...

  4. 17 CFR 240.17a-19 - Form X-17A-19 Report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 17 Commodity and Securities Exchanges 4 2014-04-01 2014-04-01 false Form X-17A-19 Report by... Certain Stabilizing Activities § 240.17a-19 Form X-17A-19 Report by national securities exchanges and... Corporation such information as is required by § 249.635 of this chapter on Form X-17A-19 within 5 business...

  5. 17 CFR 240.17a-19 - Form X-17A-19 Report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 17 Commodity and Securities Exchanges 3 2011-04-01 2011-04-01 false Form X-17A-19 Report by... Certain Stabilizing Activities § 240.17a-19 Form X-17A-19 Report by national securities exchanges and... Corporation such information as is required by § 249.635 of this chapter on Form X-17A-19 within 5 business...

  6. 17 CFR 210.1-01 - Application of Regulation S-X (17 CFR part 210).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 2 2010-04-01 2010-04-01 false Application of Regulation S-X..., INVESTMENT ADVISERS ACT OF 1940, AND ENERGY POLICY AND CONSERVATION ACT OF 1975 Application of Regulation S-X (17 Cfr Part 210) § 210.1-01 Application of Regulation S-X (17 CFR part 210). (a) This part (together...

  7. 17 CFR 210.1-01 - Application of Regulation S-X (17 CFR part 210).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 17 Commodity and Securities Exchanges 2 2011-04-01 2011-04-01 false Application of Regulation S-X..., INVESTMENT ADVISERS ACT OF 1940, AND ENERGY POLICY AND CONSERVATION ACT OF 1975 Application of Regulation S-X (17 Cfr Part 210) § 210.1-01 Application of Regulation S-X (17 CFR part 210). (a) This part (together...

  8. Anomalous 125Te Nuclear Spin Relaxation Coincident with Charge Kondo Behavior in Superconducting Pb1-xTlxTe

    NASA Astrophysics Data System (ADS)

    Mukuda, Hidekazu; Matsumura, Takashi; Maki, Shota; Yashima, Mitsuharu; Kitaoka, Yoshio; Miyake, Kazumasa; Murakami, Hironaru; Giraldo-Gallo, Paula; Geball, Theodore H.; Fisher, Ian R.

    2018-02-01

    We report the results of a 125Te NMR study of single crystalline Pb1-xTlxTe (x = 0, 0.35, 1.0%) as a window on the novel electronic states associated with the thallium impurities in PbTe. The Knight shift is enhanced as x increases, corresponding to an increase in the average density of states (DOS) coupled to a strong spatial variation in the local DOS surrounding each Tl dopant. Remarkably, for the superconducting composition (x = 1.0%), the 125Te nuclear spin relaxation rate (1/T1T) for Te ions that are close to the Tl dopants is unexpectedly enhanced in the normal state below a characteristic temperature of ˜10 K, below which the resistivity experiences an upturn. Such a simultaneous upturn in both the resistivity and (1/T1T) was not suppressed in the high magnetic field. We suggest that these observations are consistently accounted for by dynamical charge fluctuations in the absence of paramagnetism, which is anticipated by the charge Kondo scenario associated with the Tl dopants. In contrast, such anomalies were not detected in the non-superconducting samples (x = 0 and 0.35%), suggesting a connection between dynamical valence fluctuations and the occurrence of superconductivity in Pb1-xTlxTe.

  9. Bulk Superconductivity Induced by Se Substitution in BiCh2-Based Layered Compounds Eu0.5Ce0.5FBiS2-xSex

    NASA Astrophysics Data System (ADS)

    Goto, Yosuke; Sogabe, Ryota; Mizuguchi, Yoshikazu

    2017-10-01

    We report the effect of Se substitution on the crystal structure and superconductivity of BiCh2-based (Ch: S, Se) layered compounds Eu0.5Ce0.5FBiS2-xSex (x = 0-1). Crystal structure analysis showed that both lattice constants, a and c, increased with increasing x, which is different from the related La-doped system Eu0.5La0.5FBiS2-xSex. This is due to Se substitution at both in-plane and out-of-plane Ch sites in the present Ce-doped system. Zero resistivity was observed for x = 0.2-1 above 2 K. The superconducting properties of Eu0.5Ce0.5FBiS2-xSex were investigated by magnetic susceptibility measurement, and the highest superconducting transition temperature of 3.5 K was obtained for x = 0.6 with a large shielding volume fraction. The emergence of bulk superconductivity and metallic conductivity can be qualitatively described in terms of the increased in-plane chemical pressure effect. A magnetic anomaly below 8 K, probably because of the ferromagnetic order of the magnetic moment of Ce3+ ions, coexists with bulk superconductivity in the BiCh2 layer. Since the effect of Se substitution on the magnetic transition temperature is ignorable, we suggest that the coupling between the magnetic order at the (Eu,Ce)F layer and the superconductivity at the Bi(S,Se)2 layer is weak.

  10. Optical probes of symmetry breaking in magnetic and superconducting BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Orenstein, Joseph

    The discovery of iron pnictide superconductors has opened promising new directions in the effort to fully understand the phenomenon of high-Tc, with a focus on the connections between superconductivity, magnetism, and electronic nematicity. The BaFe2(As1-xPx)2 (P:Ba122) system in particular has received attention because isovalent substitution of As for P generates less disorder than doping on the Fe site. The phase diagram of P:Ba122 is characterized by a line of simultaneous antiferromagnetic (AF) and tetragonal-to-orthorhombic transitions, Ts (x) , that penetrates the superconducting dome at x =0.28, just below optimal doping (xopt = 0.30). In this work, we use spatially-resolved optical polarimetry and photomodulated reflectance to detect linear birefringence and therefore breaking of 4-fold rotational (C4) symmetry. In underdoped (x<0.28) samples, birefringence appears at T>Tsand grows continuously with decreasing T . The birefringence is unidirectional in a large (300 μm x300 μm) field of view, suggesting that C4 breaking in this range of T is caused by residual strain that couples to a diverging nematic susceptibility. Birefringence maps just below Ts (x) show the appearance of domains, indicating the onset of spontaneous symmetry breaking to an AF ground state. Surprisingly, in samples with x>0.28, in which the low T phase is superconducting/ tetragonal rather than AF/orthorhombic, C4 breaking is observed as well, with an abrupt onset and domain formation at 55 K. We tentatively associate these features with a transition to an AF phase induced by residual strain, as previously proposed [H.-H. Kuo et al. Phys. Rev. B86, 134507 (2012)] to account for structure in resistivity vs. T. Time-resolved photomodulation allow us to follow the amplitude of the AF order with time following pulsed photoexcitation. Below Tc the AF order at first weakens , but then strengthens in response to the photoinduced weakening of superconductivity. This complex time evolution is

  11. Single-vortex pinning and penetration depth in superconducting NdFeAsO 1-xF x

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, Jessie T.; Kim, Jeehoon; Huefner, Magdalena

    2015-10-12

    We use a magnetic force microscope (MFM) to investigate single vortex pinning and penetration depth in NdFeAsO 1-xF x, one of the highest-T c iron-based superconductors. In fields up to 20 Gauss, we observe a disordered vortex arrangement, implying that the pinning forces are stronger than the vortex-vortex interactions. We measure the typical force to depin a single vortex, F depin ≃ 4.5 pN, corresponding to a critical current up to J c ≃ 7×10 5 A/cm 2. As a result, our MFM measurements allow the first local and absolute determination of the superconducting in-plane penetration depth in NdFeAsO 1-xFmore » x, λ ab = 320 ± 60 nm, which is larger than previous bulk measurements.« less

  12. Evidence for Coexistence of Bulk Superconductivity and Itinerant Antiferromagnetism in the Heavy Fermion System CeCo(In1−xCdx)5

    PubMed Central

    Howald, Ludovic; Stilp, Evelyn; de Réotier, Pierre Dalmas; Yaouanc, Alain; Raymond, Stéphane; Piamonteze, Cinthia; Lapertot, Gérard; Baines, Christopher; Keller, Hugo

    2015-01-01

    In the generic phase diagram of heavy fermion systems, tuning an external parameter such as hydrostatic or chemical pressure modifies the superconducting transition temperature. The superconducting phase forms a dome in the temperature—tuning parameter phase diagram, which is associated with a maximum of the superconducting pairing interaction. Proximity to antiferromagnetism suggests a relation between the disappearance of antiferromagnetic order and superconductivity. We combine muon spin rotation, neutron scattering, and x-ray absorption spectroscopy techniques to gain access to the magnetic and electronic structure of CeCo(In1−xCdx)5 at different time scales. Different magnetic structures are obtained that indicate a magnetic order of itinerant character, coexisting with bulk superconductivity. The suppression of the antiferromagnetic order appears to be driven by a modification of the bandwidth/carrier concentration, implying that the electronic structure and consequently the interplay of superconductivity and magnetism is strongly affected by hydrostatic and chemical pressure. PMID:26224422

  13. Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe 1-xSe x

    DOE PAGES

    Xu, Zhijun; Xu, Guangyong; Schneeloch, J. A.; ...

    2016-03-14

    Imore » t has recently been demonstrated that dynamical magnetic correlations measured by neutron scattering in iron chalcogenides can be described with models of short-range correlations characterized by particular choices of four-spin plaquettes, where the appropriate choice changes as the parent material is doped towards superconductivity. Here we apply such models to describe measured maps of magnetic scattering as a function of two-dimensional wave vectors obtained for optimally superconducting crystals of FeTe 1 ₋ x Se x . We show that the characteristic antiferromagnetic wave vector evolves from that of the bicollinear structure found in underdoped chalcogenides (at high temperature) to that associated with the stripe structure of antiferromagnetic iron arsenides (at low temperature); these can both be described with the same local plaquette, but with different interplaquette correlations. While the magnitude of the low-energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant. The observed change in spin correlations is correlated with the dramatic drop in the electronic scattering rate and the growth of the bulk nematic response upon cooling. n conclusion, we also present powder neutron diffraction results for lattice parameters in FeTe 1 ₋ x Se x indicating that the tetrahedral bond angle tends to increase towards the ideal value upon cooling, in agreement with the increased screening of the crystal field by more itinerant electrons and the correspondingly smaller splitting of the Fe 3d orbitals.« less

  14. Investigation of Pb doping on electrical, structural and superconducting properties of YBa2-xPbxCu3O7-δ superconductors

    NASA Astrophysics Data System (ADS)

    Ezzatpour, S.; Sharifzadegan, L.; Sarvari, F.; Sedghi, H.

    2018-06-01

    In this study the high temperature superconductor YBa2-xPbxCu3O7-δ with doping x = ,0.05,0.1,0.15 were prepared by the standard solid-state reaction method. The effect of Pb substitution on Ba site of YBCO superconducting system, structural, electrical and superconducting properties of Y-based superconductor has been investigated. The measurements of dc resisitivity were performed on all samples with four-probe method using low frequency/lowAC current (4 mA) . The superconducting temperature, Tc, were determined from the resistivity versus temperature (R-T) curves. Results show that Pb doping reduced the cirtical temperature(Tc) and superconductivity properties of our samples. The maximum and the minimum Tc were observed for the samples with x = 0.15 and x = 0.1 respectively. The structure and phase purity of samples were examined by the X-ray powder diffraction technique (XRD) performed by means of D8 Advance Bruker diffractometer with Cu kα radiation. The grain morphology of surface of the samples was analyzed by sacanning electron microscopy (SEM). XRD patterns of polycrystalline materials of composition YBa2-xPbxCu3O7-δ revealed that all prepared samples are orthorhombic. All of the peaks of YBCO and YBa2-xPbxCu3O7-δ have been used for the estimation of volume fractions of the phases and ignored the void peaks.

  15. Temperature-dependent transformation of the magnetic excitation spectrum on approaching superconductivity in Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5).

    PubMed

    Xu, Zhijun; Wen, Jinsheng; Zhao, Yang; Matsuda, Masaaki; Ku, Wei; Liu, Xuerong; Gu, Genda; Lee, D-H; Birgeneau, R J; Tranquada, J M; Xu, Guangyong

    2012-11-30

    Spin excitations are one of the top candidates for mediating electron pairing in unconventional superconductors. Their coupling to superconductivity is evident in a large number of systems, by the observation of an abrupt redistribution of magnetic spectral weight at the superconducting transition temperature, T(c), for energies comparable to the superconducting gap. Here we report inelastic neutron scattering measurements on Fe-based superconductors, Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5) that emphasize an additional signature. The overall shape of the low energy magnetic dispersion changes from two incommensurate vertical columns at T≫T(c) to a distinctly different U-shaped dispersion at low temperature. Importantly, this spectral reconstruction is apparent for temperatures up to ~3T(c). If the magnetic excitations are involved in the pairing mechanism, their surprising modification on the approach to T(c) demonstrates that strong interactions are involved.

  16. Superconducting Generators for Airborne Applications and YBCO-Coated Conductors (Preprint)

    DTIC Science & Technology

    2008-10-01

    Maiorov, M. E. Hawley , M. P. Maley, D. E. Peterson, “Strongly enhanced current densities in superconducting coated conductors of YBa2Cu3O7-x + BaZrO3...ed., New York: Taylor and Francis, 2001. [17] S. P. Ashworth, M. Maley, M. Suenaga, S. R. Foltyn, and J. O. Willis , J. Appl. Phys., vol. 88, p

  17. Enhanced electron-phonon coupling near the lattice instability of superconducting NbC1-xNx from density-functional calculations

    NASA Astrophysics Data System (ADS)

    Blackburn, Simon; Côté, Michel; Louie, Steven G.; Cohen, Marvin L.

    2011-09-01

    Using density-functional theory within the local-density approximation, we study the electron-phonon coupling in NbC1-xNx and NbN crystals in the rocksalt structure. The Fermi surface of these systems exhibits important nesting. The associated Kohn anomaly greatly increases the electron-phonon coupling and induces a structural instability when the electronic density of states reaches a critical value. Our results reproduce the observed rise in Tc from 11.2 to 17.3 K as the nitrogen doping is increased in NbC1-xNx. To further understand the contribution of the structural instability to the rise of the superconducting temperature, we develop a model for the Eliashberg spectral function in which the effect of the unstable phonons is set apart. We show that this model together with the McMillan formula can reproduce the increase of Tc near the structural phase transition.

  18. 17 CFR 249.617 - Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the...

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 17 Commodity and Securities Exchanges 3 2011-04-01 2011-04-01 false Form X-17A-5, information... Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the..., Oct. 29, 1984] Editorial Note: For Federal Register citations affecting Form X-17A-5, see the List of...

  19. 17 CFR 249.617 - Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the...

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 17 Commodity and Securities Exchanges 3 2012-04-01 2012-04-01 false Form X-17A-5, information... Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the..., Oct. 29, 1984] Editorial Note: For Federal Register citations affecting Form X-17A-5, see the List of...

  20. 17 CFR 249.617 - Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the...

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Form X-17A-5, information... Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the..., Oct. 29, 1984] Editorial Note: For Federal Register citations affecting Form X-17A-5, see the List of...

  1. 17 CFR 249.617 - Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the...

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 17 Commodity and Securities Exchanges 3 2013-04-01 2013-04-01 false Form X-17A-5, information... Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the..., Oct. 29, 1984] Editorial Note: For Federal Register citations affecting Form X-17A-5, see the List of...

  2. 17 CFR 249.617 - Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the...

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 17 Commodity and Securities Exchanges 4 2014-04-01 2014-04-01 false Form X-17A-5, information... Form X-17A-5, information required of certain brokers and dealers pursuant to section 17 of the..., Oct. 29, 1984] Editorial Note: For Federal Register citations affecting Form X-17A-5, see the List of...

  3. An X-ray beam position monitor based on the photoluminescence of helium gas

    NASA Astrophysics Data System (ADS)

    Revesz, Peter; White, Jeffrey A.

    2005-03-01

    A new method for white beam position monitoring for both bend magnet and wiggler synchrotron X-ray radiation has been developed. This method utilizes visible light luminescence generated as a result of ionization by the intense X-ray flux. In video beam position monitors (VBPMs), the luminescence of helium gas at atmospheric pressure is observed through a view port using a CCD camera next to the beam line. The beam position, profile, integrated intensity and FWHM are calculated from the distribution of luminescence intensity in each captured image by custom software. Misalignment of upstream apertures changes the image profile making VBPMs helpful for initial alignment of upstream beam line components. VBPMs can thus provide more information about the X-ray beam than most beam position monitors (BPMs). A beam position calibration procedure, employing a tilted plane-parallel glass plate placed in front of the camera lens, has also been developed. The accuracy of the VBPM system was measured during a bench-top experiment to be better than 1 μm. The He-luminescence-based VBPM system has been operative on three CHESS beam lines (F hard-bend and wiggler, A-line wiggler and G-line wiggler) for about a year. The beam positions are converted to analog voltages and used as feedback signals for beam stabilization. In our paper we discuss details of VBPM construction and describe further results of its performance.

  4. Use of the CEBAF Accelerator for IR and UV Free Electron Lasers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yunn, Byung; Sinclair, Charles; Leemann, Christoph

    1992-08-01

    The CEBAF superconducting linac is capable of accelerating electron beams suitable for driving high-power free-electron lasers. The 45 MeV injector linac with a 6 cm period wiggler can produce kilowatt output powers of infrared light (3.6-17 micrometer), while the 400 MeV north linac can produce ultraviolet light (~200 nm) at similar powers. The FELs require the addition of a high-peak intensity electron source (~ 60 A peak current) and extraction beam lines to wigglers with appropriate electron and photon optics. FEL operation is compatible with simultaneous baseline CEBAF nuclear physics operation. A design for a CEBAF-based FEL facility has beenmore » developed. The current status of the FEL project is reported.« less

  5. Universal doping evolution of the superconducting gap anisotropy in single crystals of electron-doped Ba(Fe1‑x Rh x )2As2 from London penetration depth measurements

    NASA Astrophysics Data System (ADS)

    Kim, Hyunsoo; Tanatar, M. A.; Martin, C.; Blomberg, E. C.; Ni, Ni; Bud’ko, S. L.; Canfield, P. C.; Prozorov, R.

    2018-06-01

    Doping evolution of the superconducting gap anisotropy was studied in single crystals of 4d-electron doped Ba(Fe1‑x Rh x )2As2 using tunnel diode resonator measurements of the temperature variation of the London penetration depth . Single crystals with doping levels representative of an underdoped regime x  =  0.039 ( K), close to optimal doping x  =  0.057 ( K) and overdoped x  =  0.079 ( K) and x  =  0.131( K) were studied. Superconducting energy gap anisotropy was characterized by the exponent, n, by fitting the data to the power-law, . The exponent n varies non-monotonically with x, increasing to a maximum n  =  2.5 for x  =  0.079 and rapidly decreasing towards overdoped compositions to 1.6 for x  =  0.131. This behavior is qualitatively similar to the doping evolution of the superconducting gap anisotropy in other iron pnictides, including hole-doped (Ba,K)Fe2As2 and 3d-electron-doped Ba(Fe,Co)2As2 superconductors, finding a full gap near optimal doping and strong anisotropy toward the ends of the superconducting dome in the T-x phase diagram. The normalized superfluid density in an optimally Rh-doped sample is almost identical to the temperature-dependence in the optimally doped Ba(Fe,Co)2As2 samples. Our study supports the universal superconducting gap variation with doping and pairing at least in iron based superconductors of the BaFe2As2 family.

  6. High temperature interfacial superconductivity

    DOEpatents

    Bozovic, Ivan [Mount Sinai, NY; Logvenov, Gennady [Port Jefferson Station, NY; Gozar, Adrian Mihai [Port Jefferson, NY

    2012-06-19

    High-temperature superconductivity confined to nanometer-scale interfaces has been a long standing goal because of potential applications in electronic devices. The spontaneous formation of a superconducting interface in bilayers consisting of an insulator (La.sub.2CuO.sub.4) and a metal (La.sub.1-xSr.sub.xCuO.sub.4), neither of which is superconducting per se, is described. Depending upon the layering sequence of the bilayers, T.sub.c may be either .about.15 K or .about.30 K. This highly robust phenomenon is confined to within 2-3 nm around the interface. After exposing the bilayer to ozone, T.sub.c exceeds 50 K and this enhanced superconductivity is also shown to originate from a 1 to 2 unit cell thick interfacial layer. The results demonstrate that engineering artificial heterostructures provides a novel, unconventional way to fabricate stable, quasi two-dimensional high T.sub.c phases and to significantly enhance superconducting properties in other superconductors. The superconducting interface may be implemented, for example, in SIS tunnel junctions or a SuFET.

  7. Chemical substitution study on magnetism and superconductivity in Ce1-xSmxCoIn5

    NASA Astrophysics Data System (ADS)

    Jang, Sooyoung; White, B. D.; Yazici, D.; Wong, A. S.; Maple, M. B.

    2015-03-01

    We have investigated the system Ce1-xSmxCoIn5 (0 < x < 1) by means of x-ray diffraction, electrical resistivity, specific heat, and magnetization measurements. We observe a crossover from a coherent Kondo lattice exhibiting superconductivity to a single-ion impurity Kondo effect coexisting with magnetic order on the Sm-rich side of the phase diagram. The superconducting transition temperature, Tc, and Kondo lattice coherence temperature, Tcoh, are suppressed near x ~ 0.2 and x ~ 0.5, respectively, which is consistent with the effect of substitution with other rare-earth (RE) ions on CeCoIn5. After Tcoh is suppressed to 0 K, a single-ion impurity Kondo effect is observed for 0.5 < x <= 0.85. The compound SmCoIn5 exhibits three distinct magnetic phase transitions at roughly 8, 10, and 12 K, which are presumably associated with magnetic order; similar features are observed in the related compound SmIn3. These transition temperatures are gradually suppressed by Ce substitution and completely vanish near x ~ 0.2. We establish the phase diagram of the system Ce1-xSmxCoIn5 and compare our results with those obtained from chemical substitution studies of CeCoIn5 involving other RE ions. Research at UCSD was supported by the U.S. Department of Energy, Office of Basic Energy Science, Division of Material Science and Engineering under Grant No. DE-FG02-04-ER46105.

  8. Macroscopic phase separation of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-x Se x revealed by μSR.

    PubMed

    Nikitin, A M; Grinenko, V; Sarkar, R; Orain, J-C; Salis, M V; Henke, J; Huang, Y K; Klauss, H-H; Amato, A; Visser, A de

    2017-12-12

    The compound Sr 0.5 Ce 0.5 FBiS 2 belongs to the intensively studied family of layered BiS 2 superconductors. It attracts special attention because superconductivity at T sc  = 2.8 K was found to coexist with local-moment ferromagnetic order with a Curie temperature T C  = 7.5 K. Recently it was reported that upon replacing S by Se T C drops and ferromagnetism becomes of an itinerant nature. At the same time T sc increases and it was argued superconductivity coexists with itinerant ferromagnetism. Here we report a muon spin rotation and relaxation study (μSR) conducted to investigate the coexistence of superconductivity and ferromagnetic order in Sr 0.5 Ce 0.5 FBiS 2-x Se x with x = 0.5 and 1.0. By inspecting the muon asymmetry function we find that both phases do not coexist on the microscopic scale, but occupy different sample volumes. For x = 0.5 and x = 1.0 we find a ferromagnetic volume fraction of ~8 % and ~30 % at T = 0.25 K, well below T C  = 3.4 K and T C  = 3.3 K, respectively. For x = 1.0 (T sc  = 2.9 K) the superconducting phase occupies most (~64 %) of the remaining sample volume, as shown by transverse field experiments that probe the Gaussian damping due to the vortex lattice. We conclude ferromagnetism and superconductivity are macroscopically phase separated.

  9. Ammoniated alkali fullerides (ND(3))(x)NaA(2)C(60): ammonia specific effects and superconductivity.

    PubMed

    Margadonna, Serena; Aslanis, Efstathios; Prassides, Kosmas

    2002-08-28

    The crystal structure of the superconducting (ND(3))(x)()NaA(2)C(60) (0.7 < or = x < or = 1, A= K, Rb) fullerides (T(c)= 6-15 K) has been studied by synchrotron X-ray and neutron powder diffraction. It is face-centered cubic (fcc) to low temperatures with Na(+)-ND(3) pairs residing in the octahedral interstices. These are disordered over the corners of two "interpenetrating" cubes with the Na(+) ions and the N atoms displaced by approximately 2.0 A and approximately 0.5 A from the center of the site and statically disordered over the corners of the inner and outer cube, respectively. Close contacts between the D atoms of the ND(3) molecules and electron rich 6:6 C-C bonds of neighboring C(60) units provide the signature of weak N-D.pi hydrogen-bonding interactions, which control the intermolecular packing in the crystal and may determine the unusual superconducting properties.

  10. Theoretical band structure of the superconducting antiperovskite oxide Sr3-xSnO

    NASA Astrophysics Data System (ADS)

    Ikeda, Atsutoshi; Fukumoto, Toshiyuki; Oudah, Mohamed; Hausmann, Jan Niklas; Yonezawa, Shingo; Kobayashi, Shingo; Sato, Masatoshi; Tassel, Cédric; Takeiri, Fumitaka; Takatsu, Hiroshi; Kageyama, Hiroshi; Maeno, Yoshiteru

    2018-05-01

    In order to investigate the position of the strontium deficiency in superconductive Sr3-xSnO, we synthesized and measured X-ray-diffraction patterns of Sr3-xSnO (x ∼ 0.5). Because no clear peaks originating from superstructures were observed, strontium deficiency is most likely to be randomly distributed. We also performed first-principles band-structure calculations on Sr3-xSnO (x = 0, 0.5) using two methods: full-potential linearized-augmented plane-wave plus local orbitals method and the Korringa-Kohn-Rostoker Green function method combined with the coherent potential approximation. We revealed that the Fermi energy of Sr3-xSnO in case of x ∼ 0.5 is about 0.8 eV below the original Fermi energy of the stoichiometric Sr3SnO, where the mixing of the valence p and conduction d orbitals are considered to be small.

  11. Raman and fluorescence characteristics of resonant inelastic X-ray scattering from doped superconducting cuprates

    DOE PAGES

    Huang, H. Y.; Jia, C. J.; Chen, Z. Y.; ...

    2016-01-22

    Measurements of spin excitations are essential for an understanding of spin-mediated pairing for superconductivity; and resonant inelastic X-ray scattering (RIXS) provides a considerable opportunity to probe high-energy spin excitations. However, whether RIXS correctly measures the collective spin excitations of doped superconducting cuprates remains under debate. Here we demonstrate distinct Raman- and fluorescence-like RIXS excitations of Bi1.5Pb0.6Sr1.54CaCu2O8+δ. Combining photon-energy and momentum dependent RIXS measurements with theoretical calculations using exact diagonalization provides conclusive evidence that the Raman-like RIXS excitations correspond to collective spin excitations, which are magnons in the undoped Mott insulators and evolve into paramagnons in doped superconducting compounds. In contrast,more » the fluorescence-like shifts are due primarily to the continuum of particle-hole excitations in the charge channel. Our results show that under the proper experimental conditions RIXS indeed can be used to probe paramagnons in doped high-Tc cuprate superconductors.« less

  12. Anomalous electron doping independent two-dimensional superconductivity

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; Xing, Xiangzhuo; Zhao, Haijun; Feng, Jiajia; Pan, Yongqiang; Zhou, Nan; Zhang, Yufeng; Qian, Bin; Shi, Zhixiang

    2017-07-01

    Transition metal (Co and Ni) co-doping effects are investigated on an underdoped Ca0.94La0.06Fe2As2 compound. It is discovered that electron doping from substituting Fe with transition metal (TM = Co, Ni) can trigger high-{T}{{c}} superconductivity around 35 K, which emerges abruptly before the total suppression of the innate spin-density-wave/anti-ferromagnetism (SDW/AFM) state. Remarkably, the critical temperature for the high-{T}{{c}} superconductivity remains constant against a wide range of TM doping levels. And the net electron doping density dependence of the superconducting {T}{{c}} based on the rigid band model can be nicely scaled into a single curve for Co and Ni substitutions, in stark contrast to the case of Ba(Fe1-x TM x )2As2. This carrier density independent superconductivity and the unusual scaling behavior are presumably resulted from the interface superconductivity based on the similarity with the interface superconductivity in a La2-x Sr x CuO4-La2CuO4 bilayer. Evidence of the two-dimensional character of the superfluid by angle-resolved magneto-resistance measurements can further strengthen the interface nature of the high-{T}{{c}} superconductivity.

  13. Universal doping evolution of the superconducting gap anisotropy in single crystals of electron-doped Ba(Fe1-x Rh x )2As2 from London penetration depth measurements.

    PubMed

    Kim, Hyunsoo; Tanatar, M A; Martin, C; Blomberg, E C; Ni, Ni; Bud'ko, S L; Canfield, P C; Prozorov, R

    2018-06-06

    Doping evolution of the superconducting gap anisotropy was studied in single crystals of 4d-electron doped Ba(Fe 1-x Rh x ) 2 As 2 using tunnel diode resonator measurements of the temperature variation of the London penetration depth [Formula: see text]. Single crystals with doping levels representative of an underdoped regime x  =  0.039 ([Formula: see text] K), close to optimal doping x  =  0.057 ([Formula: see text] K) and overdoped x  =  0.079 ([Formula: see text] K) and x  =  0.131([Formula: see text] K) were studied. Superconducting energy gap anisotropy was characterized by the exponent, n, by fitting the data to the power-law, [Formula: see text]. The exponent n varies non-monotonically with x, increasing to a maximum n  =  2.5 for x  =  0.079 and rapidly decreasing towards overdoped compositions to 1.6 for x  =  0.131. This behavior is qualitatively similar to the doping evolution of the superconducting gap anisotropy in other iron pnictides, including hole-doped (Ba,K)Fe 2 As 2 and 3d-electron-doped Ba(Fe,Co) 2 As 2 superconductors, finding a full gap near optimal doping and strong anisotropy toward the ends of the superconducting dome in the T-x phase diagram. The normalized superfluid density in an optimally Rh-doped sample is almost identical to the temperature-dependence in the optimally doped Ba(Fe,Co) 2 As 2 samples. Our study supports the universal superconducting gap variation with doping and [Formula: see text] pairing at least in iron based superconductors of the BaFe 2 As 2 family.

  14. Superconductivity and strong intrinsic defects in LaPd1-xBi2

    NASA Astrophysics Data System (ADS)

    Han, Fei; Malliakas, Christos D.; Stoumpos, Constantinos C.; Sturza, Mihai; Claus, Helmut; Chung, Duck Young; Kanatzidis, Mercouri G.

    2013-10-01

    Two new phases LaPd1-xBi2 and CePd1-xBi2 were obtained by growing single crystals in Bi flux. They adopt the tetragonal ZrCuSi2-type structure and feature Bi-square nets and PbO-type PdBi layers with significant partial Pd occupancy. Bulk superconductivity at 2.1 K and metallic behavior above Tc are observed in LaPd1-xBi2. A small residual resistance ratio (RRR) indicates a strong scattering effect induced by the Pd vacancies, which implies an s-wave pairing symmetry in LaPd1-xBi2. The broadening of the resistivity transition was measured under different magnetic fields demonstrating a high upper critical field of 3 T. Hall effect measurements reveal dominantly electron-like charge carriers and single-band transport behavior in LaPd1-xBi2. The paramagnetic CePd1-xBi2 is nonsuperconducting but shows antiferromagnetic ordering below 6 K.

  15. Energy gap evolution across the superconductivity dome in single crystals of (Ba1−xKx)Fe2As2

    PubMed Central

    Cho, Kyuil; Kończykowski, Marcin; Teknowijoyo, Serafim; Tanatar, Makariy A.; Liu, Yong; Lograsso, Thomas A.; Straszheim, Warren E.; Mishra, Vivek; Maiti, Saurabh; Hirschfeld, Peter J.; Prozorov, Ruslan

    2016-01-01

    The mechanism of unconventional superconductivity in iron-based superconductors (IBSs) is one of the most intriguing questions in current materials research. Among non-oxide IBSs, (Ba1−xKx)Fe2As2 has been intensively studied because of its high superconducting transition temperature and fascinating evolution of the superconducting gap structure from being fully isotropic at optimal doping (x ≈ 0.4) to becoming nodal at x > 0.8. Although this marked evolution was identified in several independent experiments, there are no details of the gap evolution to date because of the lack of high-quality single crystals covering the entire K-doping range of the superconducting dome. We conducted a systematic study of the London penetration depth, λ(T), across the full phase diagram for different concentrations of point-like defects introduced by 2.5-MeV electron irradiation. Fitting the low-temperature variation with the power law, Δλ ~ Tn, we find that the exponent n is the highest and the Tc suppression rate with disorder is the smallest at optimal doping, and they evolve with doping being away from optimal, which is consistent with increasing gap anisotropy, including an abrupt change around x ≃ 0.8, indicating the onset of nodal behavior. Our analysis using a self-consistent t-matrix approach suggests the ubiquitous and robust nature of s± pairing in IBSs and argues against a previously suggested transition to a d-wave state near x = 1 in this system. PMID:27704046

  16. Preparation, Iodometric Analysis, and Classroom Demonstration of Superconductivity in YBa2Cu3O8-x.

    ERIC Educational Resources Information Center

    Harris, Daniel C.; And Others

    1987-01-01

    Described is a student preparation of YBa2Cu3O8-x, a classroom demonstration of its superconductivity, and an analytical chemistry experiment dealing with the oxidation state of copper in the material. (RH)

  17. High-Tc superconductivity near the anion height instability in Fe-based superconductors: analysis of LaFeAsO(1-x)H(x).

    PubMed

    Onari, Seiichiro; Yamakawa, Youichi; Kontani, Hiroshi

    2014-05-09

    The isostructural transition in the tetragonal phase with a sizable change in the anion height, is realized in heavily H-doped LaFeAsO and (La,P) codoped CaFe2As2. In these compounds, the superconductivity with higher Tc (40-50 K) is realized near the isostructural transition. To find the origin of the anion-height instability and the role in realizing the higher-Tc state, we develop the orbital-spin fluctuation theory by including the vertex correction. We analyze LaFeAsO(1-x)H(x) and find that the non-nematic orbital fluctuations, which induce the anion-height instability, are automatically obtained at x∼0.5, in addition to the conventional nematic orbital fluctuations at x∼0. The non-nematic orbital order triggers the isostructural transition, and its fluctuation would be a key ingredient to realize higher-Tc superconductivity of order 50 K.

  18. Superconducting Effects in Optimization of Magnetic Penetration Thermometers for X-ray Microcalorimeters

    NASA Technical Reports Server (NTRS)

    Stevenson, Thomas R.; Balvin, M. A.; Denis, K. L.; Hsieh, W.-T.; Sadleir, J. E.; Bandler, Simon E.; Busch, Sarah E.; Merrell, W.; Kelly, Daniel P.; Nagler, Peter C.; hide

    2012-01-01

    We have made high resolution x-ray microcalorimeters using superconducting MoAu bilayers and Nb meander coils. The temperature sensor is a Magnetic Penetration Thermometer (MPT). Operation is similar to metallic magnetic calorimeters, but instead of the magnetic susceptibility of a paramagnetic alloy, we use the diamagnetic response of the superconducting MoAu to sense temperature changes in an x-ray absorber. Flux-temperature responsivtty can be large for small sensor heat capacity, with enough dynamic range for applications. We find models of observed flux-temperature curves require several effects to explain flux penetration or expulsion in the microscopic devices. The superconductor is non-local, with large coherence length and weak pinning of flux. At lowest temperatures, behavior is dominated by screening currents that vary as a result of the temperature dependence of the magnetic penetration depth, modified by the effect of the nonuniformity of the applied field occurring on a scale comparable to the coherence length. In the temperature regime where responslvity is greatest, spadal variations in the order parameter become important: both local variations as flux enters/leaves the film and an intermediate state is formed, and globally as changing stability of the electrical circuit creates a Meissner transition and flux is expelled/penetrates to minimize free energy.

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

    NASA Astrophysics Data System (ADS)

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

    2004-09-01

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

  20. 17 CFR 249.1200 - Form X-17F-1A-Report for missing, lost, stolen or counterfeit securities.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 17 Commodity and Securities Exchanges 4 2014-04-01 2014-04-01 false Form X-17F-1A-Report for... Reporting and Inquiry With Respect to Missing, Lost, Stolen, or Counterfeit Securities § 249.1200 Form X-17F...] Editorial Note: For Federal Register citations affecting Form X-17F-1A, see the List of CFR Sections...

  1. 17 CFR 249.1200 - Form X-17F-1A-Report for missing, lost, stolen or counterfeit securities.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 17 Commodity and Securities Exchanges 3 2011-04-01 2011-04-01 false Form X-17F-1A-Report for... Reporting and Inquiry With Respect to Missing, Lost, Stolen, or Counterfeit Securities § 249.1200 Form X-17F...] Editorial Note: For Federal Register citations affecting Form X-17F-1A, see the List of CFR Sections...

  2. 17 CFR 249.1200 - Form X-17F-1A-Report for missing, lost, stolen or counterfeit securities.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 17 Commodity and Securities Exchanges 3 2013-04-01 2013-04-01 false Form X-17F-1A-Report for... Reporting and Inquiry With Respect to Missing, Lost, Stolen, or Counterfeit Securities § 249.1200 Form X-17F...] Editorial Note: For Federal Register citations affecting Form X-17F-1A, see the List of CFR Sections...

  3. 17 CFR 249.1200 - Form X-17F-1A-Report for missing, lost, stolen or counterfeit securities.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Form X-17F-1A-Report for... Reporting and Inquiry With Respect to Missing, Lost, Stolen, or Counterfeit Securities § 249.1200 Form X-17F...] Editorial Note: For Federal Register citations affecting Form X-17F-1A, see the List of CFR Sections...

  4. 17 CFR 249.1200 - Form X-17F-1A-Report for missing, lost, stolen or counterfeit securities.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 17 Commodity and Securities Exchanges 3 2012-04-01 2012-04-01 false Form X-17F-1A-Report for... Reporting and Inquiry With Respect to Missing, Lost, Stolen, or Counterfeit Securities § 249.1200 Form X-17F...] Editorial Note: For Federal Register citations affecting Form X-17F-1A, see the List of CFR Sections...

  5. 17 CFR 210.1-02 - Definitions of terms used in Regulation S-X (17 CFR part 210).

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... Regulation S-X (17 CFR part 210). 210.1-02 Section 210.1-02 Commodity and Securities Exchanges SECURITIES AND... POLICY AND CONSERVATION ACT OF 1975 Application of Regulation S-X (17 Cfr Part 210) § 210.1-02 Definitions of terms used in Regulation S-X (17 CFR part 210). Unless the context otherwise requires, terms...

  6. 17 CFR 210.1-02 - Definitions of terms used in Regulation S-X (17 CFR part 210).

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... Regulation S-X (17 CFR part 210). 210.1-02 Section 210.1-02 Commodity and Securities Exchanges SECURITIES AND... POLICY AND CONSERVATION ACT OF 1975 Application of Regulation S-X (17 Cfr Part 210) § 210.1-02 Definitions of terms used in Regulation S-X (17 CFR part 210). Unless the context otherwise requires, terms...

  7. 17 CFR 210.1-02 - Definitions of terms used in Regulation S-X (17 CFR part 210).

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... Regulation S-X (17 CFR part 210). 210.1-02 Section 210.1-02 Commodity and Securities Exchanges SECURITIES AND... POLICY AND CONSERVATION ACT OF 1975 Application of Regulation S-X (17 Cfr Part 210) § 210.1-02 Definitions of terms used in Regulation S-X (17 CFR part 210). Unless the context otherwise requires, terms...

  8. Surprising loss of three-dimensionality in low-energy spin correlations on approaching superconductivity in Fe 1 + y Te 1 - x Se x

    DOE PAGES

    Xu, Zhijun; Schneeloch, J. A.; Wen, Jinsheng; ...

    2017-10-06

    We report inelastic neutron scattering measurements of low-energy ( ℏ ω ≲ 10 meV) magnetic excitations in the “11” system Fe 1+y Te 1-x Se x. The spin correlations are two-dimensional (2D) in the superconducting samples at low temperature, but appear much more three-dimensional (3D) when the temperature rises well above T c ~ 15 K, with a clear increase of the (dynamic) spin correlation length perpendicular to the Fe planes. This behavior is extremely unusual; typically, the suppression of thermal fluctuations at low temperature would favor the enhancement of 3D correlations, or even ordering, and the reversion to 2Dmore » cannot be naturally explained when only the spin degree of freedom is considered. Our results suggest that the low temperature physics in the 11 system, in particular the evolution of low-energy spin excitations towards superconducting pairing, intrinsically involves changes in orbital correlations.« less

  9. Surprising loss of three-dimensionality in low-energy spin correlations on approaching superconductivity in Fe 1 + y Te 1 - x Se x

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Xu, Zhijun; Schneeloch, J. A.; Wen, Jinsheng

    We report inelastic neutron scattering measurements of low-energy ( ℏ ω ≲ 10 meV) magnetic excitations in the “11” system Fe 1+y Te 1-x Se x. The spin correlations are two-dimensional (2D) in the superconducting samples at low temperature, but appear much more three-dimensional (3D) when the temperature rises well above T c ~ 15 K, with a clear increase of the (dynamic) spin correlation length perpendicular to the Fe planes. This behavior is extremely unusual; typically, the suppression of thermal fluctuations at low temperature would favor the enhancement of 3D correlations, or even ordering, and the reversion to 2Dmore » cannot be naturally explained when only the spin degree of freedom is considered. Our results suggest that the low temperature physics in the 11 system, in particular the evolution of low-energy spin excitations towards superconducting pairing, intrinsically involves changes in orbital correlations.« less

  10. Dispersion relation and growth rate of a relativistic electron beam propagating through a Langmuir wave wiggler

    NASA Astrophysics Data System (ADS)

    Zirak, H.; Jafari, S.

    2015-06-01

    In this study, a theory of free-electron laser (FEL) with a Langmuir wave wiggler in the presence of an axial magnetic field has been presented. The small wavelength of the plasma wave (in the sub-mm range) allows obtaining higher frequency than conventional wiggler FELs. Electron trajectories have been obtained by solving the equations of motion for a single electron. In addition, a fourth-order Runge-Kutta method has been used to simulate the electron trajectories. Employing a perturbation analysis, the dispersion relation for an electromagnetic and space-charge waves has been derived by solving the momentum transfer, continuity, and wave equations. Numerical calculations show that the growth rate increases with increasing the e-beam energy and e-beam density, while it decreases with increasing the strength of the axial guide magnetic field.

  11. Indium Substitution Effect on the Topological Crystalline Insulator Family (Pb 1$-$xSn x)1 $-$yInyTe: Topological and Superconducting Properties

    DOE PAGES

    Zhong, Ruidan; Schneeloch, John; Li, Qiang; ...

    2017-02-16

    Topological crystalline insulators (TCIs) have been of great interest in the area of condensed matter physics. We investigated the effect of indium substitution on the crystal structure and transport properties in the TCI system (Pb 1-xSn x) 1-yIn yTe. For samples with a tin concentration x ≤ 50% , the low-temperature resisitivities show a dramatic variation as a function of indium concentration: with up to ~2% indium doping, the samples show weak-metallic behavior similar to their parent compounds; with `6% indium doping, samples have true bulk-insulating resistivity and present evidence for nontrivial topological surface states; with higher indium doping levels,more » superconductivity was observed, with a transition temperature, T c , positively correlated to the indium concentration and reaching as high as 4.7 K. We address this issue from the view of bulk electronic structure modified by the indium-induced impurity level that pins the Fermi level. The current work summarizes the indium substitution effect on (Pb,Sn)Te, and discusses the topological and superconducting aspects, which can be provide guidance for future studies on this and related systems.« less

  12. Indium Substitution Effect on the Topological Crystalline Insulator Family (Pb 1$-$xSn x)1 $-$yInyTe: Topological and Superconducting Properties

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhong, Ruidan; Schneeloch, John; Li, Qiang

    Topological crystalline insulators (TCIs) have been of great interest in the area of condensed matter physics. We investigated the effect of indium substitution on the crystal structure and transport properties in the TCI system (Pb 1-xSn x) 1-yIn yTe. For samples with a tin concentration x ≤ 50% , the low-temperature resisitivities show a dramatic variation as a function of indium concentration: with up to ~2% indium doping, the samples show weak-metallic behavior similar to their parent compounds; with `6% indium doping, samples have true bulk-insulating resistivity and present evidence for nontrivial topological surface states; with higher indium doping levels,more » superconductivity was observed, with a transition temperature, T c , positively correlated to the indium concentration and reaching as high as 4.7 K. We address this issue from the view of bulk electronic structure modified by the indium-induced impurity level that pins the Fermi level. The current work summarizes the indium substitution effect on (Pb,Sn)Te, and discusses the topological and superconducting aspects, which can be provide guidance for future studies on this and related systems.« less

  13. 17 CFR 210.1-02 - Definitions of terms used in Regulation S-X (17 CFR part 210).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... Regulation S-X (17 CFR part 210). 210.1-02 Section 210.1-02 Commodity and Securities Exchanges SECURITIES AND..., INVESTMENT ADVISERS ACT OF 1940, AND ENERGY POLICY AND CONSERVATION ACT OF 1975 Application of Regulation S-X (17 Cfr Part 210) § 210.1-02 Definitions of terms used in Regulation S-X (17 CFR part 210). Unless the...

  14. Magnetism in structures with ferromagnetic and superconducting layers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhaketov, V. D.; Nikitenko, Yu. V., E-mail: nikiten@nf.jinr.ru; Radu, F.

    2017-01-15

    The influence of superconductivity on ferromagnetism in the layered Ta/V/Fe{sub 1–x}V{sub x}/V/Fe{sub 1–x}V{sub x}/Nb/Si structures consisting of ferromagnetic and superconducting layers is studied using polarized neutron reflection and scattering. It is experimentally shown that magnetic structures with linear sizes from 5 nm to 30 μm are formed in these layered structures at low temperatures. The magnetization of the magnetic structures is suppressed by superconductivity at temperatures below the superconducting transition temperatures in the V and Nb layers. The magnetic states of the structures are shown to undergo relaxation over a wide magnetic-field range, which is caused by changes in themore » states of clusters, domains, and Abrikosov vortices.« less

  15. Low-frequency quadrupole impedance of undulators and wigglers

    DOE PAGES

    Blednykh, A.; Bassi, G.; Hidaka, Y.; ...

    2016-10-25

    An analytical expression of the low-frequency quadrupole impedance for undulators and wigglers is derived and benchmarked against beam-based impedance measurements done at the 3 GeV NSLS-II storage ring. The adopted theoretical model, valid for an arbitrary number of electromagnetic layers with parallel geometry, allows to calculate the quadrupole impedance for arbitrary values of the magnetic permeability μ r. Here, in the comparison of the analytical results with the measurements for variable magnet gaps, two limit cases of the permeability have been studied: the case of perfect magnets (μ r → ∞), and the case in which the magnets are fullymore » saturated (μ r = 1).« less

  16. Evidence for a 17-d periodicity from Cyg X-3

    NASA Technical Reports Server (NTRS)

    Holt, S. S.; Boldt, E. A.; Serlemitsos, P. J.; Kaluzienski, L. J.; Pravdo, S. H.; Peacock, A.; Elvis, M.; Watson, M. G.; Pounds, K. A.

    1976-01-01

    Data are presented from the Ariel-V All-Sky Monitor which indicate a 17-day periodicity of the X-ray spectra from Cyg X-3 (3U2030+40). The data are consistent with data from the Ariel V Sky Survey Experiment. Assuming that the high intensity state of Cyg X-3 is well fitted by a structureless black body (Serlemitsos et al., 1975), and that the 17-day maxima correspond to increased electron scattering in the source, it is suggested that the 17-day effect is analogous to the 35-day variation in Her X-1. The possible explanation of this phenomenon as a result of the 17-day orbital period of the binary system containing Cyg X-3 is severely constrained by the stability of the well-known 4.8-hour variation.

  17. Coexistence of superconductivity and magnetism in Ca1 -xNaxFe2As2 : Universal suppression of the magnetic order parameter in 122 iron pnictides

    NASA Astrophysics Data System (ADS)

    Materne, Philipp; Kamusella, Sirko; Sarkar, Rajib; Goltz, Til; Spehling, Johannes; Maeter, Hemke; Harnagea, Luminita; Wurmehl, Sabine; Büchner, Bernd; Luetkens, Hubertus; Timm, Carsten; Klauss, Hans-Henning

    2015-10-01

    We present a detailed investigation of the magnetic and superconducting properties of Ca1 -xNaxFe2As2 single crystals with x =0.00 , 0.35, 0.50, and 0.67 by means of the local probe techniques Mössbauer spectroscopy and muon spin relaxation experiments. With increasing Na-substitution level, the magnetic order parameter is suppressed. For x =0.50 we find a microscopic coexistence of magnetic and superconducting phases accompanied by a reduction of the magnetic order parameter below the superconducting transition temperature Tc. A systematic comparison with other 122 pnictides reveals a square-root correlation between the reduction of the magnetic order parameter and the ratio of the transition temperatures Tc/TN , which can be understood in the framework of a Landau theory. In the optimally doped sample with Tc≈34 K, diluted magnetism is found and the temperature dependence of the penetration depth and superfluid density are obtained, proving the presence of two superconducting s -wave gaps.

  18. Growth, patterning, and weak-link fabrication of superconducting YBa2Cu3O(7-x) thin films

    NASA Astrophysics Data System (ADS)

    Hilton, G. C.; Harris, E. B.; van Harlingen, D. J.

    1988-09-01

    Thin films of the high-temperature superconducting ceramic oxides have been grown, and techniques for fabricating weak-link structures have been investigated. Films of YBa2Cu3O(7-x) grown on SrTiO3 by a combination of dc magnetron sputtering and thermal evaporation from the three sources have been patterned into microbridges with widths down to 2 microns. Evidence is found that the bridges behave as arrays of Josephson-coupled superconducting islands. Further weak-link behavior is induced by in situ modification of the coupling by ion milling through the bridge.

  19. Pressure tuning of structure, superconductivity, and novel magnetic order in the Ce-underdoped electron-doped cuprate T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 ( x = 0.1 )

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Guguchia, Z.; Adachi, T.; Shermadini, Z.

    High-pressure neutron powder diffraction, muon-spin rotation, and magnetization studies of the structural, magnetic, and the superconducting properties of the Ce-underdoped superconducting (SC) electron-doped cuprate system with the Nd 2 CuO 4 (the so-called T ' ) structure T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 with x = 0.1 are reported. A strong reduction of the in-plane and out-of-plane lattice constants is observed under pressure. However, no indication of any pressure-induced phase transition from T ' to the K 2 NiF 4 (the so-called T) structure is observed up to the maximum applied pressure ofmore » p = 11 GPa. Large and nonlinear increase of the short-range magnetic order temperature T so in T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 ( x = 0.1 ) was observed under pressure. Simultaneous pressure causes a nonlinear decrease of the SC transition temperature T c . All these experiments establish the short-range magnetic order as an intrinsic and competing phase in SC T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 ( x = 0.1 ). The observed pressure effects may be interpreted in terms of the improved nesting conditions through the reduction of the in-plane and out-of-plane lattice constants upon hydrostatic pressure.« less

  20. Superconductivity and bandwidth-controlled Mott metal-insulator transition in 1T-TaS2-xSex

    NASA Astrophysics Data System (ADS)

    Ang, R.; Miyata, Y.; Ieki, E.; Nakayama, K.; Sato, T.; Liu, Y.; Lu, W. J.; Sun, Y. P.; Takahashi, T.

    2013-09-01

    We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) of layered chalcogenide 1T-TaS2-xSex to elucidate the electronic states especially relevant to the occurrence of superconductivity. We found a direct evidence for a Ta-5d-derived electron pocket associated with the superconductivity, which is fragile against a Mott-gap opening observed in the insulating ground state for S-rich samples. In particular, a strong electron-electron interaction-induced Mott gap driven by a Ta 5d orbital also exists in the metallic ground state for Se-rich samples, while finite ARPES intensity near the Fermi level likely originating from a Se 4p orbital survives, indicative of the orbital-selective nature of the Mott transition. Present results suggest that effective electron correlation and p-d hybridization play a crucial role to tune the superconductivity and Mott metal-insulator transition.

  1. The hybrid lattice of K(x)Fe(2-y)Se2: where superconductivity and magnetism coexist.

    PubMed

    Louca, Despina; Park, Keeseong; Li, Bing; Neuefeind, Joerg; Yan, Jiaqiang

    2013-01-01

    Much remains unknown of the microscopic origin of superconductivity in atomically disordered systems of amorphous alloys or in crystals riddled with defects. A manifestation of this conundrum is envisaged in the highly defective superconductor of K(x)Fe(2-y)Se2. How can superconductivity survive under such crude conditions that call for strong electron localization? Here, we show that the Fe sublattice is locally distorted and accommodates two kinds of Fe valence environments giving rise to a bimodal bond-distribution, with short and long Fe bonds. The bimodal bonds are present even as the system becomes superconducting in the presence of antiferromagnetism, with the weight continuously shifting from the short to the long with increasing K content. Such a hybrid state is most likely found in cuprates as well while our results point to the importance of the local atomic symmetry by which exchange interactions between local moments materialize.

  2. Coexistence of multiphase superconductivity and ferromagnetism in lithiated iron selenide hydroxide [(L i1 -xF ex) OH ]FeSe

    NASA Astrophysics Data System (ADS)

    Urban, Christian; Valmianski, Ilya; Pachmayr, Ursula; Basaran, Ali C.; Johrendt, Dirk; Schuller, Ivan K.

    2018-01-01

    We present experimental evidence for (a) multiphase superconductivity and (b) coexistence of magnetism and superconductivity in a single structural phase of lithiated iron selenide hydroxide [(L i1 -xF ex )OH]FeSe. Magnetic field modulated microwave spectroscopy data confirms superconductivity with at least two distinct transition temperatures attributed to well-defined superconducting phases at TSC 1=40 ±2 K and TSC 2=35 ±2 K. Magnetometry data for the upper critical fields reveal a change in the magnetic order (TM=12 K) below TSC 1 and TSC 2 that is consistent with ferromagnetism. This occurs because the superconducting coherence length is much smaller than the structural coherence length, allowing for several different electronic and magnetic states on a single crystallite. The results give insight into the physics of complex multinary materials, where several phenomena governed by different characteristic length scales coexist.

  3. Synthesis and superconductivity of In-doped SnTe nanostructures

    DOE PAGES

    Kumaravadivel, Piranavan; Pan, Grace A.; Zhou, Yu; ...

    2017-07-01

    In xSn 1-xTe is a time-reversal invariant candidate 3D topological superconductor derived from doping the topological crystalline insulator SnTe with indium. The ability to synthesize low-dimensional nanostructures of indium-doped SnTe is key for realizing the promise they hold in future spintronic and quantum information processing applications. But hitherto only bulk synthesized crystals and nanoplates have been used to study the superconducting properties. Here for the first time we synthesize In xSn 1-xTe nanostructures including nanowires and nanoribbons, which show superconducting transitions. In some of the lower dimensional morphologies, we observe signs of more than one superconducting transition and the absencemore » of complete superconductivity. We propose that material inhomogeneity, such as indium inhomogeneity and possible impurities from the metal catalyst, is amplified in the transport characteristics of the smaller nanostructures and is responsible for this mixed behavior. Our work represents the first demonstration of In xSn 1-xTe nanowires with the onset of superconductivity, and points to the need for improving the material quality for future applications« less

  4. La 2-xSr xCuO 4-δ superconducting samples prepared by the wet-chemical method

    NASA Astrophysics Data System (ADS)

    Loose, A.; Gonzalez, J. L.; Lopez, A.; Borges, H. A.; Baggio-Saitovitch, E.

    2009-10-01

    In this work, we report on the physical properties of good-quality polycrystalline superconducting samples of La 2-xSr xCu 1-yZn yO 4-δ ( y=0, 0.02) prepared by a wet-chemical method, focusing on the temperature dependence of the critical current. Using the wet-chemical method, we were able to produce samples with improved homogeneity compared to the solid-state method. A complete set of samples with several carrier concentrations, ranging from the underdoped (strontium concentration x≈0.05) to the highly overdoped ( x≈0.25) region, were prepared and investigated. The X-ray diffraction analysis, zero-field cooling magnetization and electrical resistivity measurements were reported on earlier. The structural parameters of the prepared samples seem to be slightly modified by the preparation method and their critical temperatures were lower than reported in the literature. The temperature dependence of the critical current was explained by a theoretical model which took the granular structure of the samples into account.

  5. Metal-insulator transition and superconductivity in the spinel-type Cu(Ir1-xRhx)2S4 system

    NASA Astrophysics Data System (ADS)

    Matsumoto, Nobuhiro; Endoh, Ryo; Nagata, Shoichi; Furubayashi, Takao; Matsumoto, Takehiko

    1999-08-01

    The normal thiospinel CuIr2S4 exhibits a temperature-induced metal-insulator (M-I) transition around 226 K with structural transformation, showing hysteresis on heating and cooling. It has been verified that d electrons of Ir atom on the octahedral B sites have a significant role for the M-I transition. On the other hand, CuRh2S4 is a superconductor with the transition temperature Tc=4.70 K, which is well understood on the basis of the BCS theory. It is important to investigate the effect on the M-I transition by substitution of Rh for Ir. We have systematically studied structural transformation and electrical and magnetic properties of Cu(Ir1-xRhx)2S4. The features of the M-I transition change with Rh concentration x. A phase diagram of temperature versus x will be proposed for the Cu(Ir1-xRhx)2S4 system. The sharp M-I transition temperature varies drastically from 226 to 93 K with x from 0.00 to 0.17 and disappears around x=0.20. In a region of 0.00<=x<=0.20, the magnetic susceptibility begins decreasing at a constant onset temperature 226 K on cooling process and shows rather broad temperature variation, even though the metallic state is kept in the resistivity. The sharp M-I transition can take place after the suppression of magnitude in the susceptibility has sufficiently developed far below 226 K. These experimental results are discussed with emphasis on the intrinsic difference between Cu(Ir1-xRhx)2S4 and CuIr2(S1-xSex)4 systems. Furthermore, we will mention the superconductivity for both systems of Cu(Ir1-xRhx)2S4 with high-Rh concentration region and Cu1-xNixRh2S4.

  6. Superconductivity-localization interplay and fluctuation magnetoresistance in epitaxial BaPb1 -xBixO3 thin films

    NASA Astrophysics Data System (ADS)

    Harris, D. T.; Campbell, N.; Uecker, R.; Brützam, M.; Schlom, D. G.; Levchenko, A.; Rzchowski, M. S.; Eom, C.-B.

    2018-04-01

    BaPb1 -xBixO3 is a superconductor, with transition temperature Tc=11 K, whose parent compound BaBiO3 possesses a charge ordering phase and perovskite crystal structure reminiscent of the cuprates. The lack of magnetism simplifies the BaPb1 -xBixO3 phase diagram, making this system an ideal platform for contrasting high-Tc systems with isotropic superconductors. Here we use high-quality epitaxial thin films and magnetotransport to demonstrate superconducting fluctuations that extend well beyond Tc. For the thickest films (thickness above ˜100 nm ) this region extends to ˜27 K , well above the bulk Tc and remarkably close to the higher Tc of Ba1 -xKxBiO3 (Tc=31 K). We drive the system through a superconductor-insulator transition by decreasing thickness and find the observed Tc correlates strongly with disorder. This material manifests strong fluctuations across a wide range of thicknesses, temperatures, and disorder presenting new opportunities for understanding the precursor of superconductivity near the 2D-3D dimensionality crossover.

  7. Method of producing superconducting fibers of YBa[sub 2]Cu[sub 3]O[sub x

    DOEpatents

    Schwartzkopf, L.A.; Ostenson, J.E.; Finnemore, D.K.

    1990-11-13

    Fibers of YBa[sub 2]Cu[sub 3]O[sub x] have been produce by pendant drop melt extraction. This technique involves the end of a rod of YBa[sub 2]Cu[sub 3]O[sub x] melted with a hydrogen-oxygen torch, followed by lowering onto the edge of a spinning wheel. The fibers are up to 10 cm in length with the usual lateral dimensions, ranging from 20 [mu]m to 125 [mu]m. The fibers require a heat treatment to make them superconducting.

  8. Superconducting six-axis accelerometer

    NASA Technical Reports Server (NTRS)

    Paik, H. J.

    1990-01-01

    A new superconducting accelerometer, capable of measuring both linear and angular accelerations, is under development at the University of Maryland. A single superconducting proof mass is magnetically levitated against gravity or any other proof force. Its relative positions and orientations with respect to the platform are monitored by six superconducting inductance bridges sharing a single amplifier, called the Superconducting Quantum Interference Device (SQUID). The six degrees of freedom, the three linear acceleration components and the three angular acceleration components, of the platform are measured simultaneously. In order to improve the linearity and the dynamic range of the instrument, the demodulated outputs of the SQUID are fed back to appropriate levitation coils so that the proof mass remains at the null position for all six inductance bridges. The expected intrinsic noise of the instrument is 4 x 10(exp -12)m s(exp -2) Hz(exp -1/2) for linear acceleration and 3 x 10(exp -11) rad s(exp -2) Hz(exp -1/2) for angular acceleration in 1-g environment. In 0-g, the linear acceleration sensitivity of the superconducting accelerometer could be improved by two orders of magnitude. The design and the operating principle of a laboratory prototype of the new instrument is discussed.

  9. The hybrid lattice of K xFe 2-ySe 2: where superconductivity and magnetism coexist

    DOE PAGES

    Yang, Junjie; Duan, Chunruo; Huang, Qing; ...

    2013-01-01

    Much remains unknown of the microscopic origin of superconductivity in atomically disordered systems of amorphous alloys or in crystals riddled with defects. A manifestation of this conundrum is envisaged in the highly defective superconductor of K xFe 2-ySe 2. How can superconductivity survive under such crude conditions that call for strong electron localization? Here, we show that the Fe sublattice is locally distorted and accommodates two kinds of Fe valence environments giving rise to a bimodal bond-distribution, with short and long Fe bonds. The bimodal bonds are present even as the system becomes superconducting in the presence of antiferromagnetism, withmore » the weight continuously shifting from the short to the long with increasing K content. Such a hybrid state is most likely found in cuprates as well while our results point to the importance of the local atomic symmetry by which exchange interactions between local moments materialize.« less

  10. Focus on superconducting properties of iron chalcogenides

    NASA Astrophysics Data System (ADS)

    Takano, Yoshihiko

    2012-10-01

    Since the discovery of iron-based superconductors, much attention has been given to the exploration of new superconducting compounds. Numerous superconducting iron compounds have been found and categorized into five groups: LnFeAsO (Ln = lanthanide), BaFe2As2, KFeAs, FeSe and FeAs with perovskite blocking layers. Among them, FeSe has the simplest crystal structure. Since the crystal structure is composed of only superconducting Fe layers, the FeSe family must be the best material to investigate the mechanism of iron-based superconductivity. FeSe shows very strong pressure effects. The superconducting transition temperature (Tc) of FeSe is approximately 8 K at ambient pressure. However Tc dramatically increases up to 37 K under applied pressure of 4-6 GPa. This is the third highest Tc value among binary superconductors, surpassed only by CsC60 under pressure (Tc = 38 K) and MgB2 (Tc = 39 K). On the other hand, despite FeTe having a crystal structure analogous to that of FeSe, FeTe shows antiferromagnetic properties without superconductivity. Doping of small ions, either Se or S, however, can induce superconductivity in FeTe1-xSex or FeTe1-xSx . The superconductivity is very weak for small x values, and annealing under certain conditions is required to obtain strong superconductivity, for instance annealing in oxygen or alcoholic beverages such as red wine. The following selection of papers describe many important experimental and theoretical studies on iron chalcogenide superconductors including preparation of single crystals, bulk samples and thin films; NMR measurements; photoemission spectroscopy; high-pressure studies; annealing effects and research on new BiS2-based superconductors. I hope this focus issue will help researchers understand the frontiers of iron chalcogenide superconductors and assist in the discovery of new phenomena related to iron-based superconductivity.

  11. Transport and superconducting properties of Fe-based superconductors: a comparison between SmFeAsO1-xFx and Fe1+yTe1-xSex

    NASA Astrophysics Data System (ADS)

    Tropeano, M.; Pallecchi, I.; Cimberle, M. R.; Ferdeghini, C.; Lamura, G.; Vignolo, M.; Martinelli, A.; Palenzona, A.; Putti, M.

    2010-05-01

    In this paper we carry out a direct comparison between transport and superconducting properties—namely resistivity, magnetoresistivity, Hall effect, Seebeck effect, thermal conductivity, upper critical field—of two different families of Fe-based superconductors, which can be viewed in many respects as end members: SmFeAsO1 - xFx with the largest Tc and the largest anisotropy and Fe1 + yTe1 - xSex, with the largest Hc2, the lowest Tc and the lowest anisotropy. In the case of the SmFeAsO1 - xFx series, we find that a single-band description allows us to extract an approximate estimation of band parameters such as carrier density and mobility from experimental data, although the behaviour of the Seebeck effect as a function of doping demonstrates that a multiband description would be more appropriate. On the contrary, experimental data for the Fe1 + y(Te1 - x, Sex) series exhibit a strongly compensated behaviour, which can be described only within a multiband model. In the Fe1 + y(Te1 - x, Sex) series, the role of the excess Fe, tuned by Se stoichiometry, is found to be twofold: on one hand it dopes electrons in the system and on the other hand it introduces localized magnetic moments, responsible for Kondo like scattering and likely pairbreaking of Cooper pairs. Hence, Fe excess also plays a crucial role in determining superconducting properties such as the Tc and the upper critical field Hc2. The huge Hc2 values of the Fe1 + yTe1 - xSex samples are described by a dirty limit law, opposed to the clean limit behaviour of the SmFeAsO1 - xFx samples. Hence, magnetic scattering by excess Fe seems to drive the system in the dirty regime, but its detrimental pairbreaking role seems not to be as severe as predicted by theory. This issue has yet to be clarified, addressing the more fundamental issue of the interplay between magnetism and superconductivity.

  12. Molecular mapping of chromosomes 17 and X

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Barker, D.F.

    1991-01-15

    Progress toward the construction of high density genetic maps of chromosomes 17 and X has been made by isolating and characterizing a relatively large set of polymorphic probes for each chromosome and using these probes to construct genetic maps. We have mapped the same polymorphic probes against a series of chromosome breakpoints on X and 17. The probes could be assigned to over 30 physical intervals on the X chromosome and 7 intervals on 17. In many cases, this process resulted in improved characterization of the relative locations of the breakpoints with respect to each other and the definition ofmore » new physical intervals. The strategy for isolation of the polymorphic clones utilized chromosome specific libraries of 1--15 kb segments from each of the two chromosomes. From these libraries, clones were screened for those detecting restriction fragment length polymorphisms. The markers were further characterized, the chromosomal assignments confirmed and in most cases segments of the original probes were subcloned into plasmids to produce probes with improved signal to noise ratios for use in the genetic marker studies. The linkage studies utilize the CEPH reference families and other well-characterized families in our collection which have been used for genetic disease linkage work. Preliminary maps and maps of portions of specific regions of 17 and X are provided. We have nearly completed a map of the 1 megabase Mycoplasma arthritidis genome by applying these techniques to a lambda phage library of its genome. We have found bit mapping to be an efficient means to organize a contiguous set of overlapping clones from a larger genome.« less

  13. Doping influence on Sm1 - x Th x OFeAs superconducting properties: Observation of the effect of intrinsic multiple Andreev reflections and determination of the superconducting parameters

    NASA Astrophysics Data System (ADS)

    Kuzmicheva, T. E.; Kuzmichev, S. A.; Zhigadlo, N. D.

    2014-04-01

    We studied SNS and S-N-S-N-...-S contacts (where S is a superconductor and N is a normal metal) formed by "break-junction" technique in polycrystalline Sm1 - x Th x OFeAs superconductor samples with critical temperatures T C = 34-45 K. In such contacts (intrinsic) multiple Andreev reflections effects were observed. Using spectroscopies based on these effects, we detected two independent bulk order parameters and determined their magnitudes. Theoretical analysis of the large and the small gap temperature dependences revealed superconducting properties of Sm1 - x Th x OFeAs to be driven by intraband coupling, and (where V ij are the electron-boson interaction matrix elements), whereas the ratio between density of states for the bands with the small and the large gap, N 2/ N 1, correspondingly, was roughly of an order. We estimated "solo" BCS-ratio values in a hypothetic case of zero interband coupling ( V i ≠ j = 0) for each condensate as 2ΔL, S/ k B T {C/L,S} ≤ 4.5. The values are constant within the range of critical temperatures studied, and correspond to a case of strong intraband electron-phonon coupling.

  14. Superconductivity in the Sn-Ba-Sr-Y-Cu-O system

    NASA Technical Reports Server (NTRS)

    Aleksandrov, K. S.; Khrustalev, B. P.; Krivomazov, S. N.; Petrov, M. I.; Vasilyev, A. D.; Zwegintsev, S. A.

    1991-01-01

    After the discovery of high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides were synthesized. Here, researchers report the results of the search for superconductivity in the compounds based on tin which has a lone electron pair like Bi, Tl, and Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3O(sub x), Sn1Ba1Ca1Cu3O(sub x), Sn1Ba1Mg1Cu3O(sub x), Sn1Sr1Ca1Cu3O(sub x), Sn1Sr1Mg1Cu3O(sub x), and Sn1Ca1Mg1Cu3O(sub x). The initial components were oxides and carbonates of the appropriate elements. A standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3O(sub x) showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3O(sub x) was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperature undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3O(sub x) ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase, two-valent cations Ba and Sr were partially substituted by univalent (K) and three-valent ones (Y).

  15. Possibility of high temperature superconducting phases in PdH

    NASA Astrophysics Data System (ADS)

    Tripodi, Paolo; Di Gioacchino, Daniele; Borelli, Rodolfo; Vinko, Jenny Darja

    2003-05-01

    Possible new superconducting phases with a high critical transition temperature (Tc) have been found in stable palladium-hydrogen (PdHx) samples for stoichiometric ratio x=H/Pd⩾1, in addition to the well-known low critical transition temperature (0⩽Tc⩽9) when x is in the range (0.75⩽x⩽1.00). Possible new measured superconducting phases with critical temperature in the range 51⩽Tc⩽295 K occur. This Tc varies considerably with every milli part of x when x exceeds unit. A superconducting critical current density Jc⩾6.1×104 A cm-2 has been measured at 77 K with HDC=0 T.

  16. Effect of proton irradiation on superconductivity in optimally doped BaFe 2 ( As 1 - x P x ) 2 single crystals

    DOE PAGES

    Smylie, M. P.; Leroux, M.; Mishra, V.; ...

    2016-03-10

    In this paper, irradiation with 4 MeV protons was used to systematically introduce defects in single crystals of the iron-arsenide superconductor BaFe 2(As 1-xP x) 2, x = 0.33. The effect of disorder on the low-temperature behavior of the London penetration depth λ(T) and transition temperature T c was investigated. In nearly optimally doped samples with T c ~ 29 K, signatures of a superconducting gap with nodes were observed. Contrary to previous reports on electron-irradiated crystals, we do not see a disorder-driven lifting of accidental nodes, and we observe that proton-induced defects are weaker pair breakers than electron-induced defects.more » Finally, we attribute our findings to anisotropic electron scattering caused by proton irradiation defects.« less

  17. Nonaqueous slip casting of YBa2Cu3O(7-x) superconductive ceramics. Ph.D. Thesis - 1993

    NASA Technical Reports Server (NTRS)

    Hooker, Matthew W.; Taylor, Theodore D.

    1994-01-01

    This study investigates the slip casting of YBa2Cu3O(7-x) powders using nonaqueous carrier liquids and fired ceramic molds. The parameters of the process examined here include the rheological properties of YBa2Cu3O(7-x) powder dispersed in various solvent/dispersant systems, the combination of nonaqueous slips with fired ceramic molds to form the superconductive ceramics, the process-property relationships using a four-factor factorial experiment, and the applicability of magnetic fields to align the YBa2Cu3O(7-x) grains during the casting process.

  18. 17 CFR 249.635 - Form X-17A-19, report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 17 Commodity and Securities Exchanges 3 2012-04-01 2012-04-01 false Form X-17A-19, report by national securities exchanges and registered national securities associations of changes in the membership... Certain Exchange Members, Brokers, and Dealers § 249.635 Form X-17A-19, report by national securities...

  19. 17 CFR 249.635 - Form X-17A-19, report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 17 Commodity and Securities Exchanges 3 2011-04-01 2011-04-01 false Form X-17A-19, report by national securities exchanges and registered national securities associations of changes in the membership... Certain Exchange Members, Brokers, and Dealers § 249.635 Form X-17A-19, report by national securities...

  20. 17 CFR 249.635 - Form X-17A-19, report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 17 Commodity and Securities Exchanges 3 2013-04-01 2013-04-01 false Form X-17A-19, report by national securities exchanges and registered national securities associations of changes in the membership... Certain Exchange Members, Brokers, and Dealers § 249.635 Form X-17A-19, report by national securities...

  1. 17 CFR 249.635 - Form X-17A-19, report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 17 Commodity and Securities Exchanges 4 2014-04-01 2014-04-01 false Form X-17A-19, report by national securities exchanges and registered national securities associations of changes in the membership... Certain Exchange Members, Brokers, and Dealers § 249.635 Form X-17A-19, report by national securities...

  2. 17 CFR 249.635 - Form X-17A-19, report by national securities exchanges and registered national securities...

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Form X-17A-19, report by national securities exchanges and registered national securities associations of changes in the membership... Certain Exchange Members, Brokers, and Dealers § 249.635 Form X-17A-19, report by national securities...

  3. Scrutinizing the double superconducting gaps and strong coupling pairing in (Li1−xFex)OHFeSe

    PubMed Central

    Du, Zengyi; Yang, Xiong; Lin, Hai; Fang, Delong; Du, Guan; Xing, Jie; Yang, Huan; Zhu, Xiyu; Wen, Hai-Hu

    2016-01-01

    In the field of iron-based superconductors, one of the frontier studies is about the pairing mechanism. The recently discovered (Li1−xFex)OHFeSe superconductor with the transition temperature of about 40 K provides a good platform to check the origin of double superconducting gaps and high transition temperature in the monolayer FeSe thin film. Here we report a scanning tunnelling spectroscopy study on the (Li1−xFex)OHFeSe single crystals. The tunnelling spectrum mimics that of the monolayer FeSe thin film and shows double gaps at about 14.3 and 8.6 meV. Further analysis based on the quasiparticle interference allows us to rule out the d-wave gap, and for the first time assign the larger (smaller) gap to the outer (inner) Fermi pockets (after folding) associating with the dxy (dxz/dyz) orbitals, respectively. The gap ratio amounts to 8.7, which demonstrates the strong coupling mechanism in the present superconducting system. PMID:26822281

  4. Neutron diffraction study and anomalous negative thermal expansion in non-superconducting PrFe1-xRuxAsO

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yiu, Yuen; Garlea, Vasile O; McGuire, Michael A

    2012-01-01

    Neutron powder diraction has been used to investigate the structural and magnetic behavior of the isoelectronically doped Fe pnictide material PrFe1-xRuxAsO. Substitution of Ru for Fe sup- presses the structural and magnetic phase transitions that occur in the undoped compound PrFeAsO. Contrary to the behavior usually observed in 1111 pnictide materials, the suppression of both the structural and magnetic transitions does not result in the emergence of superconductivity or any other new ground state. Interestingly, PrFeAsO itself shows an unusual negative thermal expansion (NTE) along the c-axis, from 60K down to at least 4K; this does not occur in superconductingmore » samples such as those formed by doping with fluorine on the oxygen site. We nd that NTE is present for all concentrations of PrFe1-xRuxAsO with x ranging from 0.05 to 0.75. These results suggest that the absence of superconductivity in these materials could be related to the presence of NTE.« less

  5. High Temperature Superconductivity in Praseodymium Doped (0%, 2%, 4%) in Melt-Textured Y(1-x)Pr(x)Ba2Cu3O(7-delta) Systems

    NASA Technical Reports Server (NTRS)

    James, Claudell

    1995-01-01

    A study of the magnetic and structural properties of the alloy Y(1-x)Pr(x)Ba2Cu3O(7-delta) of 0%, 2%, and 4% doping of praseodymium is presented. The resulting oxides of the alloy series are a high-temperature superconductor Y-Ba-Cu-O, which has an orthorhombic superconducting crystal-lattice. Magnetic relaxation studies have been performed on the Y-Pr-Ba-CuO bulk samples for field orientation parallel to the c-axis, using a vibrating sample magnetometer. Relaxation was measured at several temperatures to obtain the irreversible magnetization curves used for the Bean model. Magnetization current densities were derived from the relaxation data. Field and temperature dependence of the logarithmic flux-creep relaxation was measured in critical state. The data indicates that the effective activation energy U(eff) increases with increasing T between 77 K and 86 K. Also, the data shows that U(eff)(T) and superconducting transition temperature, Tc, decreased as the lattice parameters increased with increasing Pr ion concentration, x, for the corresponding Y(1-x)Pr(x)Ba(x)Cu3O(7-delta) oxides. One contribution to Tc decrease in this sampling is suspected to be due to the larger ionic radius of the Pr(3+) ion. The upper critical field (H(sub c2)) was measured in the presence of magnetic field parallel to the c axis. A linear temperature dependence with H(sub c2) was obtained.

  6. Structural differences between superconducting and non-superconducting CaCuO2/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Zarotti, Francesca; Di Castro, Daniele; Felici, Roberto; Balestrino, Giuseppe

    2018-06-01

    A study of the interface structure of superconducting and non-superconducting CaCuO2/SrTiO3 heterostructures grown on NdGaO3(110) substrates is reported. Using the combination of high resolution x-ray reflectivity and surface diffraction, the crystallographic structure of superconducting and non-superconducting samples has been investigated. The analysis has demonstrated the excellent sharpness of the CaCuO2/SrTiO3 interface (roughness smaller than one perovskite unit cell). Furthermore, we were able to discriminate between the superconducting and the non-superconducting phase. In the former case, we found an increase of the spacing between the topmost Ca plane of CaCuO2 block and the first TiO2 plane of the overlaying STO block, relative to the non-superconducting case. These results are in agreement with the model that foresees a strong oxygen incorporation in the interface Ca plane in the superconducting heterostructures.

  7. Coulomb-Gas scaling law for a superconducting Bi(2+y)Sr(2-x-y)La(x)CuO(6+delta) thin films in magnetic fields

    PubMed

    Zhang; Deltour; Zhao

    2000-10-16

    The electrical transport properties of epitaxial superconducting Bi(2+y)Sr(2-x-y)La(x)CuO(6+delta) thin films have been studied in magnetic fields. Using a modified Coulomb-gas scaling law, we can fit all the magnetic field dependent low resistance data with a universal scaling curve, which allows us to determine a relation between the activation energy of the thermally activated flux flow resistance and the characteristic temperature scaling parameters.

  8. Superconducting and magnetic properties of Bi 2Sr 2Ca 1- xY xCu 2O y (0≦ x≦1)

    NASA Astrophysics Data System (ADS)

    Yoshizaki, R.; Saito, Y.; Abe, Y.; Ikeda, H.

    1988-07-01

    The effect of substitution of Y atoms for Ca atoms has been studied in the Bi 2Sr 2Ca 1- xY xCu 2O y compound system. For x<0.5, superconductivity is observed and its fractional volume is reduced with increasing x, though the transition temperature of about 85 K is maintained. For x≧0.5 samples, the electrical resistivity behavior can be well described by the three-dimensional variable range hopping conduction, indicating that the system is essentially insulating. In this range of x, magnetic susceptibility shows spin-glass-type cusp at 13 K in the heating process after zero-field cooling and an enhanced cusp at 11 K in the field-cooling process. In the temperature range above about 150 K the Curie-Weiss dependence holds well with a positive paramagnetic Curie temperature, which increases to 40 K with increasing x in the insulating region.

  9. Sputtered superconducting films of Bi sub 2 Sr sub 2 CaCu sub 2 O sub x made by low-temperature, in-situ growth

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kampwirth, R.T.; Gray, K.E.; Andersen, P.H.

    1989-01-01

    Composite target rf magnetron sputtering has previously been successfully employed to make superconducting films of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} in-situ at substrate temperatures T{sub s} < 700{degree}C. We report the successful growth of superconducting films of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} on single crystal MgO substrates by a low-temperature process using dc magnetron sputtering from a Bi-enriched composite target. Using a substrate temperature T{sub s} {approx} 645{degree}C, metallic films with a superconducting onset of 90--100K and an extrapolated T{sub c0} = 56K have been obtained. X-ray diffraction shows the films to be c-axis oriented. Electron microscopy reveals that the filmsmore » are not significantly smoother than films which were post-annealed at 865{degree}C, and that some segregation into nonsuperconducting phases had occurred. The exact mechanism by which crystallization and superconductivity occurs at such low temperatures is not yet known, but it can be speculated that the surface atoms are less constrained and thus have a smaller energy barrier to overcome in forming a crystal structure. 9 refs., 4 figs., 1 tab.« less

  10. Suppression of the antiferromagnetic order when approaching the superconducting state in a phase-separated crystal of K x Fe 2 - y Se 2

    DOE PAGES

    Li, Shichao; Gan, Yuan; Wang, Jinghui; ...

    2017-09-06

    Here, we combined elastic and inelastic neutron scattering techniques, magnetic susceptibility, and resistivity measurements to study single-crystal samples of K xFe 2-ySe 2, which contain the superconducting phase that has a transition temperature of ~31 K. In the inelastic neutron scattering measurements, we also observe both the spin-wave excitations resulting from the block antiferromagnetic ordered phase and the resonance that is associated with the superconductivity in the superconducting phase, demonstrating the coexistence of these two orders. From the temperature dependence of the intensity of the magnetic Bragg peaks, we find that well before entering the superconducting state, the development ofmore » the magnetic order is interrupted, at ~42 K. We consider this result to be evidence for the physical separation of the antiferromagnetic and superconducting phases; the suppression is possibly due to the proximity effect of the superconducting fluctuations on the antiferromagnetic order.« less

  11. Suppression of the antiferromagnetic order when approaching the superconducting state in a phase-separated crystal of K x Fe 2 - y Se 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Shichao; Gan, Yuan; Wang, Jinghui

    Here, we combined elastic and inelastic neutron scattering techniques, magnetic susceptibility, and resistivity measurements to study single-crystal samples of K xFe 2-ySe 2, which contain the superconducting phase that has a transition temperature of ~31 K. In the inelastic neutron scattering measurements, we also observe both the spin-wave excitations resulting from the block antiferromagnetic ordered phase and the resonance that is associated with the superconductivity in the superconducting phase, demonstrating the coexistence of these two orders. From the temperature dependence of the intensity of the magnetic Bragg peaks, we find that well before entering the superconducting state, the development ofmore » the magnetic order is interrupted, at ~42 K. We consider this result to be evidence for the physical separation of the antiferromagnetic and superconducting phases; the suppression is possibly due to the proximity effect of the superconducting fluctuations on the antiferromagnetic order.« less

  12. Disappearance of superconductivity in the solid solution between (Ca4Al2O6)(Fe2As2) and (Ca4Al2O6)(Fe2P2) superconductors.

    PubMed

    Shirage, Parasharam M; Kihou, Kunihiro; Lee, Chul-Ho; Takeshita, Nao; Eisaki, Hiroshi; Iyo, Akira

    2012-09-19

    The effect of alloying the two perovskite-type iron-based superconductors (Ca(4)Al(2)O(6))(Fe(2)As(2)) and (Ca(4)Al(2)O(6))(Fe(2)P(2)) was examined. While the two stoichiometric compounds possess relatively high T(c)'s of 28 and 17 K, respectively, their solid solutions of the form (Ca(4)Al(2)O(6))(Fe(2)(As(1-x)P(x))(2)) do not show superconductivity over a wide range from x = 0.50 to 0.95. The resultant phase diagram is thus completely different from those of other typical iron-based superconductors such as BaFe(2)(As,P)(2) and LaFe(As,P)O, in which superconductivity shows up when P is substituted for As in the non-superconducting "parent" compounds. Notably, the solid solutions in the non-superconducting range exhibit resistivity anomalies at temperatures of 50-100 K. The behavior is reminiscent of the resistivity kink commonly observed in various non-superconducting parent compounds that signals the onset of antiferromagnetic/orthorhombic long-range order. The similarity suggests that the suppression of the superconductivity in the present case also has a magnetic and/or structural origin.

  13. Impacts of Co-doping on the superconductivity and the orbital ordering state in Fe1-xCoxSe single crystal studied by the electrical transport.

    NASA Astrophysics Data System (ADS)

    Urata, Takahiro; Tanabe, Yoichi; Heguri, Satoshi; Tanigaki, Katsumi

    2015-03-01

    In the FeSe with the simplest crystal structure in the Fe-based superconductor families, although both the superconductivity and the orbital ordering states are investigated, the relation between them is still unclear. Here, we report Co doping effects on the superconductivity and the orbital ordering state in Fe1-xCoxSe single crystals. The electrical transport measurements demonstrated that the superconductivity vanishes at 4 % Co doping while the orbital ordering state may be robust against Co doping. Present results suggest that the orbital ordering state is not related to the emergence of the superconductivity in FeSe.

  14. Direct observation of in-plane anisotropy of the superconducting critical current density in Ba (Fe1-xCox) 2As2 crystals

    NASA Astrophysics Data System (ADS)

    Hecher, J.; Ishida, S.; Song, D.; Ogino, H.; Iyo, A.; Eisaki, H.; Nakajima, M.; Kagerbauer, D.; Eisterer, M.

    2018-01-01

    The phase diagram of iron-based superconductors exhibits structural transitions, electronic nematicity, and magnetic ordering, which are often accompanied by an electronic in-plane anisotropy and a sharp maximum of the superconducting critical current density (Jc) near the phase boundary of the tetragonal and the antiferromagnetic-orthorhombic phase. We utilized scanning Hall-probe microscopy to visualize the Jc of twinned and detwinned Ba (Fe1-xCox) 2As2 (x =5 %-8 % ) crystals to compare the electronic normal state properties with superconducting properties. We find that the electronic in-plane anisotropy continues into the superconducting state. The observed correlation between the electronic and the Jc anisotropy agrees qualitatively with basic models, however, the Jc anisotropy is larger than predicted from the resistivity data. Furthermore, our measurements show that the maximum of Jc at the phase boundary does not vanish when the crystals are detwinned. This shows that twin boundaries are not responsible for the large Jc, suggesting an exotic pinning mechanism.

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

    PubMed

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

    2008-08-29

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

  16. MELCOR model for an experimental 17x17 spent fuel PWR assembly.

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cardoni, Jeffrey

    2010-11-01

    A MELCOR model has been developed to simulate a pressurized water reactor (PWR) 17 x 17 assembly in a spent fuel pool rack cell undergoing severe accident conditions. To the extent possible, the MELCOR model reflects the actual geometry, materials, and masses present in the experimental arrangement for the Sandia Fuel Project (SFP). The report presents an overview of the SFP experimental arrangement, the MELCOR model specifications, demonstration calculation results, and the input model listing.

  17. Iron vacancy in tetragonal Fe1-xS crystals and its effect on the structure and superconductivity.

    PubMed

    Guo, Zhongnan; Sun, Fun; Han, Bingling; Lin, Kun; Zhou, Liang; Yuan, Wenxia

    2017-03-29

    Understanding the effects of non-stoichiometry on the structure and physical properties of tetragonal Fe chalcogenides is of great importance, especially for developing fascinating superconductivity in this system, which might be very sensitive to the non-stoichiometry. In this study, a series of Fe 1-x S single crystals were synthesized by a hydrothermal method, which show varying concentrations of Fe vacancies (0 ≤ x ≤ 0.1) in the structure. Based on the crystal samples, the effects of vacancies on the crystal structure and physical properties were studied. The vacancy-free sample (x = 0) showed a metallic state in resistance and superconductivity below 4.5 K, whereas for the samples with Fe vacancies (x ≥ 0.05), the SC was degraded and the sample exhibited semiconducting behavior. Structural analysis showed that the Fe vacancy decreases the lattice parameter a, but elongates c, leading to enhanced tetragonality in Fe 1-x S. Selected-area electron diffraction showed that the vacancy in Fe 1-x S was disordered, which is different from the scenario in FeSe-based materials. On combining the abovementioned results with the first-principles calculations, it was speculated that the disappearance of SC in non-stoichiometric Fe 1-x S resulted from the localization of the 3d electrons of Fe. Moreover, the accompanied metal-insulator transition induced by Fe vacancy mainly belonged to the Mott mechanism because the vacancy did not significantly alter the band structure. These results not only provide deep insight into the effect of Fe vacancy in Fe chalcogenides, but also provide a basis to effectively induce SC in Fe sulfides by decreasing the number of Fe vacancies.

  18. Superconducting compounds and alloys research

    NASA Technical Reports Server (NTRS)

    Otto, G.

    1975-01-01

    Resistivity measurements as a function of temperature were performed on alloys of the binary material system In sub(1-x) Bi sub x for x varying between 0 and 1. It was found that for all single-phase alloys (the pure elements, alpha-In, and the three intermetallic compounds) at temperatures sufficiently above the Debye-temperature, the resistivity p can be expressed as p = a sub o T(n), where a sub o and n are composition-dependent constants. The same exponential relationship can also be applied for the sub-system In-In2Bi, when the two phases are in compositional equilibrium. Superconductivity measurements on single and two-phase alloys can be explained with respect to the phase diagram. There occur three superconducting phases (alpha-In, In2Bi, and In5Bi3) with different transition temperatures in the alloying system. The magnitude of the transition temperatures for the various intermetallic phases of In-Bi is such that the disappearance or occurrence of a phase in two component alloys can be demonstrated easily by means of superconductivity measurements.

  19. Superconductivity in Al-substituted Ba8Si46 clathrates

    NASA Astrophysics Data System (ADS)

    Li, Yang; Garcia, Jose; Chen, Ning; Liu, Lihua; Li, Feng; Wei, Yuping; Bi, Shanli; Cao, Guohui; Feng, Z. S.

    2013-05-01

    There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46-xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed that Ba8Si42Al4 is superconductive with transition temperature at TC = 5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x = 6 sample Ba8Si40Al6, the superconducting transition was observed down to TC = 4.7 K which pointed to a strong suppression of superconductivity with increasing Al content as compared with TC = 8 K for Ba8Si46. Suppression of superconductivity can be attributed primarily to a decrease in the density of states at the Fermi level, caused by reduced integrity of the sp3 hybridized networks as well as the lowering of carrier concentration. These results corroborated by first-principles calculations showed that Al substitution results in a large decrease of the electronic density of states at the Fermi level, which also explains the decreased superconducting critical temperature within the BCS framework. The work provided a comprehensive understanding of the doping effect on superconductivity of clathrates.

  20. The Superconducting Cavity Stabilized Oscillator

    NASA Technical Reports Server (NTRS)

    Turneaure, J. P.; Buchman, Saps; Lipa, John

    1997-01-01

    Superconducting Cavity Stabilized Oscillators (SCSOs) have produced the most stable clocks to date for integration times between 10(exp 2) and 10(exp 3) seconds, achieving a fractional frequency stability of 2 x 10(exp -16) for a sampling time of 100 s. The principal contributors to cavity frequency variations are: (1) acceleration effects due to gravity and vibrations; (2) temperature variations; (3) variations in the energy stored in the cavity; and (4) noise introduced by the frequency stabilization circuit. We discuss the prospects for improvements in all these areas for both ground-based and space-based SCSOs, which may lead to SCSOs with fractional frequency stabilities below 10(exp -17). SCSOs of this frequency stability will be useful for testing fundamental physical principles.

  1. Large magnetic penetration depth and thermal fluctuations in a superconducting Ca10(Pt3As8)[(Fe1 xPtx)2As2]5 (x = 0.097) single crystal

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kim J.; Nazaretski E.; Ronning, F.

    2012-05-18

    We have measured the temperature dependence of the absolute value of the magnetic penetration depth {lambda}(T) in a Ca{sub 10}(Pt{sub 3}As{sub 8})[(Fe{sub 1-x}Pt{sub x}){sub 2}As{sub 2}]{sub 5} (x = 0.097) single crystal using a low-temperature magnetic force microscope (MFM). We obtain {lambda}{sub ab}(0) {approx} 1000 nm via extrapolating the data to T = 0. This large {lambda} and pronounced anisotropy in this system are responsible for large thermal fluctuations and the presence of a liquid vortex phase in this low-temperature superconductor with a critical temperature of 11 K, consistent with the interpretation of the electrical transport data. The superconducting parametersmore » obtained from {lambda} and coherence length {zeta} place this compound in the extreme type II regime. Meissner responses (via MFM) at different locations across the sample are similar to each other, indicating good homogeneity of the superconducting state on a submicron scale.« less

  2. Superconducting gap evolution in overdoped BaFe₂(As 1-xP x)₂ single crystals through nanocalorimetry

    DOE PAGES

    Campanini, D.; Diao, Z.; Fang, L.; ...

    2015-06-18

    We report on specific heat measurements on clean overdoped BaFe₂(As 1-xP x)₂ single crystals performed with a high resolution membrane-based nanocalorimeter. A nonzero residual electronic specific heat coefficient at zero temperature γr=C/T| T→0 is seen for all doping compositions, indicating a considerable fraction of the Fermi surface ungapped or having very deep minima. The remaining superconducting electronic specific heat is analyzed through a two-band s-wave α model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of Δ₀~5.3 me V, corresponding to Δ₀/k BT c ~ 2.2. Increasing the phosphorus concentration x,more » the main gap reduces till a value of Δ₀ ~ 1.9 meV for x = 0.55 and a second weaker gap becomes evident. From the magnetic field effect on γ r, all samples however show similar behavior [γ r(H) - γ r (H = 0)∝ H n, with n between 0.6 and 0.7]. This indicates that, despite a considerable redistribution of the gap weights, the total degree of gap anisotropy does not change drastically with doping.« less

  3. Origin of Pressure-induced Superconducting Phase in KxFe2-ySe2 studied by Synchrotron X-ray Diffraction and Spectroscopy

    NASA Astrophysics Data System (ADS)

    Yamamoto, Yoshiya; Yamaoka, Hitoshi; Tanaka, Masashi; Okazaki, Hiroyuki; Ozaki, Toshinori; Takano, Yoshihiko; Lin, Jung-Fu; Fujita, Hidenori; Kagayama, Tomoko; Shimizu, Katsuya; Hiraoka, Nozomu; Ishii, Hirofumi; Liao, Yen-Fa; Tsuei, Ku-Ding; Mizuki, Jun'Ichiro

    2016-08-01

    Pressure dependence of the electronic and crystal structures of KxFe2-ySe2, which has pressure-induced two superconducting domes of SC I and SC II, was investigated by x-ray emission spectroscopy and diffraction. X-ray diffraction data show that compressibility along the c-axis changes around 12 GPa, where a new superconducting phase of SC II appears. This suggests a possible tetragonal to collapsed tetragonal phase transition. X-ray emission spectroscopy data also shows the change in the electronic structure around 12 GPa. These results can be explained by the scenario that the two SC domes under pressure originate from the change of Fermi surface topology. Our results here show the pronounced increase of the density of states near the Fermi surface under pressure with a structural phase transition, which can help address our fundamental understanding for the appearance of the SC II phase.

  4. Structural, magnetic and magnetocaloric properties of Fe17xMnxPr2 compounds

    NASA Astrophysics Data System (ADS)

    Guo, Yongbin; Ma, Lei; Chen, Tingyi; Zhou, Liang; Wang, Dao; Zhou, Xin; Dong, Peilin

    2018-03-01

    Polycrystalline Fe17xMnxPr2 (x = 0–8) compounds were analyzed by x-ray diffraction (XRD) and vibrating sample magnetometer (VSM) measurements. The results show that Fe17xMnxPr2 compounds exhibited the rhombohedral Th2Zn17-type crystal structure. The lattice parameter and unit cell volume increase with Mn content. The magnetic transition is a typical second-order transition near the T C. The Curie temperature (T C) of Fe17xMnxPr2 compounds decrease sharply in the range of 300–27 K as the Mn content increase. The maximum magnetic entropy change (∣-ΔS M∣) for Fe17xMnxPr2 compounds is 6.25 J · kg‑1·K‑1 in a field of 5 T for the compounds with x = 0. The thermal hysteresis for Fe17xMnxPr2 are 6.59 K at x = 0 and 1.36 K at x = 8, which reduces with the increase in Mn content.

  5. Superconducting thin films on potassium tantalate substrates

    DOEpatents

    Feenstra, Roeland; Boatner, Lynn A.

    1992-01-01

    A superconductive system for the lossless transmission of electrical current comprising a thin film of superconducting material Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-x epitaxially deposited upon a KTaO.sub.3 substrate. The KTaO.sub.3 is an improved substrate over those of the prior art since the it exhibits small lattice constant mismatch and does not chemically react with the superconducting film.

  6. Superconductivity in highly disordered dense carbon disulfide

    PubMed Central

    Dias, Ranga P.; Yoo, Choong-Shik; Struzhkin, Viktor V.; Kim, Minseob; Muramatsu, Takaki; Matsuoka, Takahiro; Ohishi, Yasuo; Sinogeikin, Stanislav

    2013-01-01

    High pressure plays an increasingly important role in both understanding superconductivity and the development of new superconducting materials. New superconductors were found in metallic and metal oxide systems at high pressure. However, because of the filled close-shell configuration, the superconductivity in molecular systems has been limited to charge-transferred salts and metal-doped carbon species with relatively low superconducting transition temperatures. Here, we report the low-temperature superconducting phase observed in diamagnetic carbon disulfide under high pressure. The superconductivity arises from a highly disordered extended state (CS4 phase or phase III[CS4]) at ∼6.2 K over a broad pressure range from 50 to 172 GPa. Based on the X-ray scattering data, we suggest that the local structural change from a tetrahedral to an octahedral configuration is responsible for the observed superconductivity. PMID:23818624

  7. Superconductivity in highly disordered dense carbon disulfide.

    PubMed

    Dias, Ranga P; Yoo, Choong-Shik; Struzhkin, Viktor V; Kim, Minseob; Muramatsu, Takaki; Matsuoka, Takahiro; Ohishi, Yasuo; Sinogeikin, Stanislav

    2013-07-16

    High pressure plays an increasingly important role in both understanding superconductivity and the development of new superconducting materials. New superconductors were found in metallic and metal oxide systems at high pressure. However, because of the filled close-shell configuration, the superconductivity in molecular systems has been limited to charge-transferred salts and metal-doped carbon species with relatively low superconducting transition temperatures. Here, we report the low-temperature superconducting phase observed in diamagnetic carbon disulfide under high pressure. The superconductivity arises from a highly disordered extended state (CS4 phase or phase III[CS4]) at ~6.2 K over a broad pressure range from 50 to 172 GPa. Based on the X-ray scattering data, we suggest that the local structural change from a tetrahedral to an octahedral configuration is responsible for the observed superconductivity.

  8. Radiofrequency amplifier based on a dc superconducting quantum interference device

    DOEpatents

    Hilbert, Claude; Martinis, John M.; Clarke, John

    1986-01-01

    A low noise radiofrequency amplifier (10), using a dc SQUID (superconducting quantum interference device) as the input amplifying element. The dc SQUID (11) and an input coil (12) are maintained at superconductivity temperatures in a superconducting shield (13), with the input coil (12) inductively coupled to the superconducting ring (17) of the dc SQUID (11). A radiofrequency signal from outside the shield (13) is applied to the input coil (12), and an amplified radiofrequency signal is developed across the dc SQUID ring (17) and transmitted to exteriorly of the shield (13). A power gain of 19.5.+-.0.5 dB has been achieved with a noise temperature of 1.0.+-.0.4 K. at a frequency of 100 MHz.

  9. Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystal K xFe 2-ySe 2

    DOE PAGES

    Liu, Yong; Xing, Qingfeng; Straszheim, Warren E.; ...

    2016-02-11

    Here, we report how the superconducting phase forms in pseudo-single-crystal K xFe 2-ySe 2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition.more » It should be emphasized that the phase separation in pseudo-single-crystal K xFe 2-ySe 2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electron microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.« less

  10. Te vacancy-driven superconductivity in orthorhombic molybdenum ditelluride

    NASA Astrophysics Data System (ADS)

    Cho, Suyeon; Kang, Se Hwang; Yu, Ho Sung; Kim, Hyo Won; Ko, Wonhee; Hwang, Sung Woo; Han, Woo Hyun; Choe, Duk-Hyun; Jung, Young Hwa; Chang, Kee Joo; Lee, Young Hee; Yang, Heejun; Wng Kim, Sung

    2017-06-01

    Two-dimensional (2D) transition metal dichalcogenides (TMDs) have received great attentions because of diverse quantum electronic states such as topological insulating (TI), Weyl semimetallic (WSM) and superconducting states. Recently, the superconducting states emerged in pressurized semimetallic TMDs such as MoTe2 and WTe2 have become one of the central issues due to their predicted WSM states. However, the difficulty in synthetic control of chalcogen vacancies and the ambiguous magneto transport properties have hindered the rigorous study on superconducting and WSM states. Here, we report the emergence of superconductivity at 2.1 K in Te-deficient orthorhombic T d-MoTe2-x with an intrinsic electron-doping, while stoichiometric monoclinic 1T‧-MoTe2 shows no superconducting state down to 10 mK, but exhibits a large magnetoresistance of 32 000% at 2 K in a magnetic field of 14 T originating from nearly perfect compensation of electron and hole carriers. Scanning tunnelling spectroscopy and synchrotron x-ray diffraction combined with theoretical calculations clarify that Te vacancies trigger superconductivity via intrinsic electron doping and the evolution of the T d phase from the 1T‧ phase below 200 K. Unlike the pressure-induced superconducting state of monoclinic MoTe2, this Te vacancy-induced superconductivity is emerged in orthorhombic MoTe2, which is predicted as Weyl semimetal, via electron-doping. This chalcogen vacancy induced-superconductivity provides a new route for cultivating superconducting state together with WSM state in 2D van der Waals materials.

  11. Electron acceleration from rest to GeV energy by chirped axicon Gaussian laser pulse in vacuum in the presence of wiggler magnetic field

    NASA Astrophysics Data System (ADS)

    Kant, Niti; Rajput, Jyoti; Singh, Arvinder

    2018-03-01

    This paper presents a scheme of electron energy enhancement by employing frequency - chirped lowest order axicon focussed radially polarised (RP) laser pulse in vacuum under the influence of wiggler magnetic field. Terawatt RP laser can be focussed down to ∼5μm by an axicon optical element, which produces an intense longitudinal electric field. This unique property of axicon focused Gaussian RP laser pulse is employed for direct electron acceleration in vacuum. A linear frequency chirp increases the time duration of laser-electron interaction, whereas, the applied magnetic wiggler helps in improving the strength of ponderomotive force v→ ×B→ and periodically deflects electron in order to keep it traversing in the accelerating phase up to longer distance. Numerical simulations have been carried out to investigate the influence of laser, frequency chirp and magnetic field parameters on electron energy enhancement. It is noticed that an electron from rest can be accelerated up to GeV energy under optimized laser and magnetic field parameters. Significant enhancement in the electron energy gain of the order of 11.2 GeV is observed with intense chirped laser pulse in the presence of wiggler magnetic field of strength 96.2 kG.

  12. Relationship between the Cu-spin fluctuation and superconductivity in La2-xSrxCu1-y(Zn, Ni)yO4 (x = 0.15) studied by the μSR and magnetic-susceptibility

    NASA Astrophysics Data System (ADS)

    Adachi, T.; Oki, N.; Risdiana; Yairi, S.; Koike, Y.; Watanabe, I.

    2007-09-01

    We have investigated effects of Zn and Ni on the Cu-spin dynamics and superconductivity from the zero-field muon-spin-relaxation (ZF-μSR) and magnetic-susceptibility, χ, measurements for the optimally doped La 2- xSr xCu 1- y(Zn, Ni) yO 4 with x = 0.15, changing y finely up to 0.10. The ZF-μSR measurements have revealed that, in the Zn-substituted case, the magnetic correlation between Cu-spins starts to develop at y = 0.01 with increasing y, followed by the formation of a magnetic order at y = 0.02-0.03. In the Ni-substituted case, on the other hand, the magnetic correlation starts to develop at y = 0.02-0.03. These results indicate that the formation of a magnetic order requires a larger amount of Ni than that of Zn, which is consistent with our previous result for x = 0.13. The χ measurements have revealed that the superconducting volume fraction strongly decreases by a small amount of Zn and its decrease is stronger than that by a small amount of Ni. According to the stripe model, therefore, it is concluded that, even for x = 0.15, the dynamical stripe correlations of spins and holes are pinned and stabilized by Zn and Ni, leading to the formation of the static stripe order and the suppression of superconductivity.

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

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

  14. Effect of electron irradiation on superconductivity in single crystals of Ba ( Fe 1 – x Ru x ) 2 As 2 ( x = 0.24 )

    DOE PAGES

    Prozorov, R.; Kończykowski, M.; Tanatar, M. A.; ...

    2014-11-18

    A single crystal of isovalently substituted Ba(Fe 1-xRu x) 2As 2 (x=0.24) is sequentially irradiated with 2.5 MeV electrons up to a maximum dose of 2.1×10 19 e -/cm 2. The electrical resistivity is measured in situ at T=22 K during the irradiation and ex situ as a function of temperature between subsequent irradiation runs. Upon irradiation, the superconducting transition temperature T c decreases and the residual resistivity ρ0 increases. We find that electron irradiation leads to the fastest suppression of T c compared to other types of artificially introduced disorder, probably due to the strong short-range potential of themore » pointlike irradiation defects. As a result, a more detailed analysis within a multiband scenario with variable scattering potential strength shows that the observed T c versus ρ 0 is fully compatible with s ± pairing, in contrast to earlier claims that this model leads to a too rapid suppression of T c with scattering.« less

  15. Enhanced Superconductivity in Sr2CuO(4-x)

    NASA Astrophysics Data System (ADS)

    Geballe, Theodore

    2010-03-01

    The cause of the enhanced Tc of Sr2CuO(4-x) which is almost a factor of two larger than optimally doped La 214 superconductors has remained a challenge since its discovery by Hiroi et al [1]. Lack of progress is due to the difficulties in synthesis which require a strong oxidizing agent at hight pressure and temperature. The resulting superconductor sample is multiphase leading to some ambiguity in interpretation. An unjustified suggestion that the results are spurious is negated by recent experiments in which similar behavior is found but with samples prepared using a different synthesis [2]. This has led us to reconsider the available data in the literature [3]. The experimental value of x = ˜ 0.6 suggests that the superconductivity originates in very heavily overdoped CuO2 layers containing ordered oxygen vacancies. The data support the idea that there is an exciting region of the cuprate phase diagram waiting to be understood but better samples are needed before the possible pairing mechanisms we can think of, or others yet to be determined, can be investigated. [4pt] [1] Z. Hiroi e,t al., Nature 364 (1993) 315 [0pt] [2] Q..Q. Liu et al., Phys Rev B 74 (2006) 100506 [0pt] [3] T.H. Geballe and M. Marezio Physica C 469 (2009) 680

  16. Synthesis and superconductivity of In-doped SnTe nanostructures

    NASA Astrophysics Data System (ADS)

    Kumaravadivel, Piranavan; Pan, Grace A.; Zhou, Yu; Xie, Yujun; Liu, Pengzi; Cha, Judy J.

    2017-07-01

    InxSn1-xTe is a time-reversal invariant candidate 3D topological superconductor derived from doping the topological crystalline insulator SnTe with indium. The ability to synthesize low-dimensional nanostructures of indium-doped SnTe is key for realizing the promise they hold in future spintronic and quantum information processing applications. But hitherto only bulk synthesized crystals and nanoplates have been used to study the superconducting properties. Here for the first time we synthesize InxSn1-xTe nanostructures including nanowires and nanoribbons, which show superconducting transitions. In some of the lower dimensional morphologies, we observe signs of more than one superconducting transition and the absence of complete superconductivity. We propose that material inhomogeneity, such as indium inhomogeneity and possible impurities from the metal catalyst, is amplified in the transport characteristics of the smaller nanostructures and is responsible for this mixed behavior. Our work represents the first demonstration of InxSn1-xTe nanowires with the onset of superconductivity, and points to the need for improving the material quality for future applications.

  17. Phase-incoherent superconducting pairs in the normal state of Ba(Fe(1-x)Co(x))₂As₂.

    PubMed

    Sheet, Goutam; Mehta, Manan; Dikin, D A; Lee, S; Bark, C W; Jiang, J; Weiss, J D; Hellstrom, E E; Rzchowski, M S; Eom, C B; Chandrasekhar, V

    2010-10-15

    The normal state properties of the recently discovered ferropnictide superconductors might hold the key to understanding their exotic superconductivity. Using point-contact spectroscopy we show that Andreev reflection between an epitaxial thin film of Ba(Fe(0.92)Co(0.08))₂As₂ and a silver tip can be seen in the normal state of the film up to temperature T∼1.3T(c), where T(c) is the critical temperature of the superconductor. Andreev reflection far above T(c) can be understood only when superconducting pairs arising from strong fluctuation of the phase of the complex superconducting order parameter exist in the normal state. Our results provide spectroscopic evidence of phase-incoherent superconducting pairs in the normal state of the ferropnictide superconductors.

  18. Development and application of variable-magnification x-ray Bragg optics

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hirano, Keiichi, E-mail: keiichi.hirano@kek.jp; Takahashi, Yumiko; Sugiyama, Hiroshi

    2016-07-27

    A novel x-ray Bragg optics was developed for variable-magnification of an x-ray beam, and was combined with a module of the PILATUS pixel detector. A feasibility test of this optical system was carried out at the vertical-wiggler beamline BL-14B of the Photon Factory. By tuning the magnification factor, we could successfully control the spatial resolution of the optical system between 28 μm and 280 μm. X-ray absorption-contrast images of a leaf were observed at various magnification factors.

  19. Magnetism and Hyperfine Parameters in Iron Rich Gd_2Fe_{17-x}Si_x Intermetallics

    NASA Astrophysics Data System (ADS)

    Nouri, K.; Bartoli, T.; Chrobak, A.; Moscovici, J.; Bessais, L.

    2018-04-01

    Gd_2Fe_{17-x}Si_x (x = 0.25 , 0.5 and 1) samples were synthesized by arc melting and annealed at 1073 K for 1 week. X-ray diffraction analysis by the Rietveld method has shown that these materials crystallize in the rhombohedral Th_2Zn_{17} -type structure (space group R\\bar{3}m ). The Curie temperature increases with Si content x, whereas the unit-cell parameters decrease slightly. The temperature dependence of magnetization data revealed that Gd_2Fe_{17-x}Si_x exhibits a second-order ferromagnetic to paramagnetic phase transition in the vicinity of the Curie temperature. Exchange coupling parameters of R-R, M-M and R-M (R—rare earth, M—transition metal) have been determined from M(T) magnetization curves based on the mean field theory calculation. The magnetic entropy change Δ S_M and the relative cooling power were estimated from isothermal magnetization curves for all samples. In the proximity of {T}_C and in an applied field of 1.56 T, Δ S_M reached a maximum values of 1.38, 1.67 and 3.07 J/kg K for x = 0.25, 0.5 and 1, respectively. We have calculated the magnetic moment per Fe atom from magnetization measurements at 293 K up to 17 kOe, and it decreases with Si content. These results are verified by the Mössbauer spectrometry measurements obtained at the same temperature. The Mössbauer spectra analysis is based on the correlation between the Wigner-Seitz volume and the isomer-shift evolution of each specific site 6c, 9d, 18f, and 18h of the R\\bar{3} m structure. For all Si concentrations, the magnitude of the hyperfine fields are {H_HF}{6c} > {H_HF}{9d} > {H_HF}{18f} > {H_HF}{18h} . The mean hyperfine field decreases with the Si content.

  20. Magnetism and Hyperfine Parameters in Iron Rich Gd_2Fe_{17-x}Si_x Intermetallics

    NASA Astrophysics Data System (ADS)

    Nouri, K.; Bartoli, T.; Chrobak, A.; Moscovici, J.; Bessais, L.

    2018-07-01

    Gd_2Fe_{17-x}Si_x (x = 0.25, 0.5 and 1) samples were synthesized by arc melting and annealed at 1073 K for 1 week. X-ray diffraction analysis by the Rietveld method has shown that these materials crystallize in the rhombohedral Th_2Zn_{17}-type structure (space group R\\bar{3}m). The Curie temperature increases with Si content x, whereas the unit-cell parameters decrease slightly. The temperature dependence of magnetization data revealed that Gd_2Fe_{17-x}Si_x exhibits a second-order ferromagnetic to paramagnetic phase transition in the vicinity of the Curie temperature. Exchange coupling parameters of R- R, M- M and R- M ( R—rare earth, M—transition metal) have been determined from M( T) magnetization curves based on the mean field theory calculation. The magnetic entropy change Δ S_M and the relative cooling power were estimated from isothermal magnetization curves for all samples. In the proximity of {T}_C and in an applied field of 1.56 T, Δ S_M reached a maximum values of 1.38, 1.67 and 3.07 J/kg K for x = 0.25, 0.5 and 1, respectively. We have calculated the magnetic moment per Fe atom from magnetization measurements at 293 K up to 17 kOe, and it decreases with Si content. These results are verified by the Mössbauer spectrometry measurements obtained at the same temperature. The Mössbauer spectra analysis is based on the correlation between the Wigner-Seitz volume and the isomer-shift evolution of each specific site 6 c, 9 d, 18 f, and 18 h of the R\\bar{3}m structure. For all Si concentrations, the magnitude of the hyperfine fields are {H_HF}{6c} > {H_HF}{9d} > {H_HF}{18f} > {H_HF}{18h}. The mean hyperfine field decreases with the Si content.

  1. CSEM-Steel hybrid wiggler/undulator magnetic field studies

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Halbach, K.; Hoyer, E.; Marks, S.

    1985-06-01

    Current design of permanent magnet wiggler/undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing transverse configuration influence on performance, from a combination of models using CSEMs, REC (H/sub c/ = 9.2 KOe) and NdFe (H/sub c/ = 10.7 kOe), different pole widths and end configurations. Results show peak field improvement using NdFe in placemore » of REC in identical models, gap peak field decrease with pole width decrease (all results less than computed 2-D fields), transverse gap field distributions, and importance of CSEM material overhanging the poles in the transverse direction for highest gap fields. 3 refs., 6 figs.« less

  2. Compound formation and superconductivity in Au-Si: X-ray absorption measurements on ion-beam-mixed Au-Si films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jeon, Y.; Jisrawi, N.; Liang, G.

    Multilayered Au-Si thin films have been deposited with the net compositions ''Au/sub 1-//sub x/Si/sub x/,'' x = 0.29, 0.5, and 0.8. After ion-beam mixing these films exhibited superconductivity in the 0.3--1.2 K range despite the nonsuperconducting character of both Au and Si. Near-edge x-ray absorption spectroscopy (XAS) measurements on the Au L/sub 3/ edge in these films indicate that metastable Au-Si compound formation occurs in these ion-mixed materials. Specifically, the XAS measurements indicate changes in Au 5d-orbital occupancy and changes in the local Au structural environment which are both consistent with local compound formation.

  3. Ferromagnetism and superconductivity in CeFeAs1-xPxO (0⩽x⩽40)

    NASA Astrophysics Data System (ADS)

    Jesche, A.; Förster, T.; Spehling, J.; Nicklas, M.; de Souza, M.; Gumeniuk, R.; Luetkens, H.; Goltz, T.; Krellner, C.; Lang, M.; Sichelschmidt, J.; Klauss, H.-H.; Geibel, C.

    2012-07-01

    We report on superconductivity in CeFeAs1-xPxO and the possible coexistence with Ce ferromagnetism (FM) in a small homogeneity range around x=30% with ordering temperatures of TSC≅TC≅4 K. The antiferromagnetic (AFM) ordering temperature of Fe at this critical concentration is suppressed to TNFe≈40 K and does not shift to lower temperatures with a further increase of the P concentration. Therefore, a quantum-critical-point scenario with TNFe→0 K which is widely discussed for the iron based superconductors can be excluded for this alloy series. Surprisingly, thermal expansion and x-ray powder diffraction indicate the absence of an orthorhombic distortion despite clear evidence for short-range AFM Fe ordering from muon-spin-rotation measurements. Furthermore, we discovered the formation of a sharp electron spin resonance signal unambiguously connected with the emergence of FM ordering.

  4. Inhomogeneities and superconductivity in poly-phase Fe-Se-Te systems

    NASA Astrophysics Data System (ADS)

    Hartwig, S.; Schäfer, N.; Schulze, M.; Landsgesell, S.; Abou-Ras, D.; Blum, Ch. G. F.; Wurmehl, S.; Sokolowski, A.; Büchner, B.; Prokeš, K.

    2018-02-01

    The impact of synthesis conditions, post-preparation heating procedure, aging and influence of pressure on the superconducting properties of FeSe0.4Te0.6 crystals is reported. Two FeSe0.4Te0.6 single crystals were used in the study, prepared from stoichiometric melt but cooled down with very different cooling rates, and investigated using magnetic bulk and electrical-resistivity methods. The fast-cooled crystal contains large inclusions of Fe3Se2.1Te1.8 and exhibits bulk superconductivity in its as-prepared state, while the other is homogeneous and shows only traces of superconductivity. AC susceptibility measurements under hydrostatic pressure show that the superconducting transition temperature of the inhomogeneous crystal increases from 12.3 K at ambient pressure to Tsc = 17.9 K at 9 kbar. On the other hand, neither pressure nor mechanically-induced stress is sufficient to induce superconductivity in the homogeneous crystal. However, an additional heat treatment at 673 K followed by fast cooling down and/or long-term aging at ambient conditions leads to the appearance of bulk superconductivity also in the latter sample. This sample remains homogeneous on a scale down to few μm but shows an additional magnetic phase transition around 130 K suggesting that it must be inhomogeneous. For comparison also Fe3Se2.1Te1.8 polycrystals have been prepared and their magnetic properties have been studied. It appears that this phase is not superconducting by itself. It is concluded that nano-scale inhomogeneities that appear in the FeSexTe1-x system due to a spinodal decomposition in the solid state are necessary for bulk superconductivity, possibly due to minor changes in the crystal structure and microstructure. Macroscopic inclusions quenched by fast cooling from high temperatures lead obviously to strain and hence variations in the lattice constants, an effect that is further supported by application of pressure/stress.

  5. Sequentially evaporated thin film YBa2Cu3O(7-x) superconducting microwave ring resonator

    NASA Technical Reports Server (NTRS)

    Rohrer, Norman J.; To, Hing Y.; Valco, George J.; Bhasin, Kul B.; Chorey, Chris; Warner, Joseph D.

    1990-01-01

    There is great interest in the application of thin film high temperature superconductors in high frequency electronic circuits. A ring resonator provides a good test vehicle for assessing the microwave losses in the superconductor and for comparing films made by different techniques. Ring resonators made of YBa2Cu3O(7-x) have been investigated on LaAlO3 substrates. The superconducting thin films were deposited by sequential electron beam evaporation of Cu, Y, and BaF2 with a post anneal. Patterning of the superconducting film was done using negative photolithography. A ring resonator was also fabricated from a thin gold film as a control. Both resonators had a gold ground plane on the backside of the substrate. The ring resonators' reflection coefficients were measured as a function of frequency from 33 to 37 GHz at temperatures ranging from 20 K to 68 K. The resonator exhibited two resonances which were at 34.5 and 35.7 GHz at 68 K. The resonant frequencies increased with decreasing temperature. The magnitude of the reflection coefficients was in the calculation of the unloaded Q-values. The performance of the evaporated and gold resonator are compared with the performance of a laser ablated YBa2Cu3O(7-x) resonator. The causes of the double resonance are discussed.

  6. Multilayer diffraction at 104 keV

    NASA Technical Reports Server (NTRS)

    Krieger, Allen S.; Blake, Richard L.; Siddons, D. P.

    1993-01-01

    We have measured the diffraction peak of a W:Si synthetic multilayer reflector at 104 keV using the High Energy Bonse-Hart Camera at the X-17B hard X-ray wiggler beam line of the National Synchrotron Light Source at Brookhaven National Laboratory. The characteristics of the diffraction peak are described and compared to theory.

  7. The ETA-II linear induction accelerator and IMP wiggler: A high-average-power millimeter-wave free-electron-laser for plasma heating

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Allen, S.L.; Scharlemann, E.T.

    1992-05-01

    We have constructed a 140-GHz free-electron laser to generate high-average-power microwaves for heating the MTX tokamak plasma. A 5.5-m steady-state wiggler (intense Microwave Prototype-IMP) has been installed at the end of the upgraded 60-cell ETA-II accelerator, and is configured as an FEL amplifier for the output of a 140-GHz long-pulse gyrotron. Improvements in the ETA-II accelerator include a multicable-feed power distribution network, better magnetic alignment using a stretched-wire alignment technique (SWAT). and a computerized tuning algorithm that directly minimizes the transverse sweep (corkscrew motion) of the electron beam. The upgrades were first tested on the 20-cell, 3-MeV front end ofmore » ETA-II and resulted in greatly improved energy flatness and reduced corkscrew motion. The upgrades were then incorporated into the full 60-cell configuration of ETA-II, along with modifications to allow operation in 50-pulse bursts at pulse repetition frequencies up to 5 kHz. The pulse power modifications were developed and tested on the High Average Power Test Stand (HAPTS), and have significantly reduced the voltage and timing jitter of the MAG 1D magnetic pulse compressors. The 2-3 kA. 6-7 MeV beam from ETA-II is transported to the IMP wiggler, which has been reconfigured as a laced wiggler, with both permanent magnets and electromagnets, for high magnetic field operation. Tapering of the wiggler magnetic field is completely computer controlled and can be optimized based on the output power. The microwaves from the FEL are transmitted to the MTX tokamak by a windowless quasi-optical microwave transmission system. Experiments at MTX are focused on studies of electron-cyclotron-resonance heating (ECRH) of the plasma. We summarize here the accelerator and pulse power modifications, and describe the status of ETA-II, IMP, and MTX operations.« less

  8. Superconductivity and hybrid soft modes in Ti Se 2

    DOE PAGES

    Maschek, M.; Rosenkranz, S.; Hott, R.; ...

    2016-12-12

    The interplay between superconductivity and charge-density-wave (CDW) order plays a central role in the layered transition-metal dichalcogenides. 1 T-TiSe 2 forms a prime example, featuring superconducting domes on intercalation as well as under applied pressure. Here, we present high energy-resolution inelastic x-ray scattering measurements of the CDW soft phonon mode in intercalated Cu xTiSe 2 and pressurized 1 T-TiSe 2 along with detailed ab-initio calculations for the lattice dynamical properties and phonon-mediated superconductivity. We find that the intercalation-induced superconductivity can be explained by a solely phonon-mediated pairing mechanism, while this is not possible for the superconducting phase under pressure. Wemore » argue that a hybridization of phonon and exciton modes in the pairing mechanism is necessary to explain the full observed temperature-pressure-intercalation phase diagram. Finally, these results indicate that 1 T-TiSe 2 under pressure is close to the elusive state of the excitonic insulator.« less

  9. Experimenting with a Superconducting Levitation Train

    ERIC Educational Resources Information Center

    Miryala, Santosh; Koblischka, M. R.

    2014-01-01

    The construction and operation of a prototype high-"Tc" superconducting train model is presented. The train is levitated by a melt-processed GdBa[subscript 2]Cu[subscript 3]O[subscript x] (Gd-123) superconducting material over a magnetic rail (track). The oval shaped track is constructed in S-N-S or PM3N configuration arranged on an iron…

  10. Substrates suitable for deposition of superconducting thin films

    DOEpatents

    Feenstra, Roeland; Boatner, Lynn A.

    1993-01-01

    A superconducting system for the lossless transmission of electrical current comprising a thin film of superconducting material Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-x epitaxially deposited upon a KTaO.sub.3 substrate. The KTaO.sub.3 is an improved substrate over those of the prior art since the it exhibits small lattice constant mismatch and does not chemically react with the superconducting film.

  11. Fermi Surface Studies and Temperature Dependence of the Electron-Positron Momentum Density in the High Critical Temperature Superconducting Yttrium BARIUM(2) COPPER(3) OXYGEN(7-X) System by Two-Dimensional Acar

    NASA Astrophysics Data System (ADS)

    von Stetten, Eric Carl

    The electron-positron momentum density has been measured by the two dimensional angular correlation of annihilation radiation (2D ACAR) technique for single crystal and polycrystalline (sintered powder) YBa_2 Cu_3O_{7-x} samples. For sintered superconducting and nonsuperconducting samples, the shape and temperature variation of the momentum density was investigated using the high sensitivity 2D ACAR technique. The possible existence of Fermi surfaces (FS's) in the YBa_2Cu _3O_{7-x} system was investigated in high precision 2D ACAR experiments on an oriented (twinned) single crystal superconducting YBa_2Cu _3O_{7-x} (x ~ 0.1) sample, at temperatures above and below the superconducting transition temperature (~85 K). These experiments were performed in the c-axis projection, in order to observe the theoretically predicted cylindrical FS's (if they exist) in a single experiment, without a full reconstruction of the three dimensional momentum density. Large differences were observed between the room temperature 2D ACAR spectra for superconducting and nonsuperconducting sintered powder samples, and smaller differences were observed between the spectra for similarly prepared superconducting samples. For sintered superconducting samples, complex sample dependent temperature variations of the momentum density were observed, in contrast to the small linear temperature variation observed for a sintered powder nonsuperconducting sample. These results are interpreted as manifestations of the theoretically predicted preferential sampling of the linear Cu-O chain region by the positron in the YBa _2Cu_3O _{7-x} system. High precision experiments on the single crystal superconducting sample revealed a nearly isotropic 2D ACAR spectrum, with only four small (~3% of the height at p_{x} = p _{y} = 0) peaks centered along the (110) symmetry lines. A small narrowing of the 2D ACAR spectrum was observed above T_{c}. The Brillouin-zone-reduced momentum density was formed using the "Lock

  12. Anomalous reduction in the long-time flux creep relaxation in superconducting Ca10(Pt4As8)((Fe1‑x Pt x )2As2)5 (x ≈ 0.05) single crystals

    NASA Astrophysics Data System (ADS)

    Haberkorn, N.; Huang, Silu; Jin, R.

    2018-06-01

    We report the vortex dynamics of superconducting a Ca10(Pt4As8)((Fe1‑x Pt x )2As2)5 (x ≈ 0.05) single crystal with T c = 26 K investigated by performing magnetic measurements. The field dependence of the magnetization displays a second peak (SPM), typically related to a crossover between elastic and plastic vortex relaxation in a weak pinning scenario. Long-time flux creep relaxation measurements for fields smaller that of the SPM show that the vortex dynamics can be separated in two different regions. For magnetic fields smaller than the lower end of the SPM, glassy relaxation (with a characteristic glassy exponent μ) is observed. For magnetic fields between the lower end and the SPM, the flux creep rate decreases systematically to values below to the ones predicted by the collective theory. This effect can be understood by considering a stable vortex lattice configuration. As the field position of the SPM can be adjusted by modifying the quenched potential, our results suggest that extremely low flux creep relaxation rate may be tuned in many other superconducting materials.

  13. Site preference, magnetism and lattice vibrations of intermetallics Lu₂Fe 17xT x (T=Cr, Mn, Ru)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Jin-Chun; Qian, Ping, E-mail: qianpinghu@sohu.com; Zhang, Zhen-Feng

    We present an atomistic study on the phase stability, site preference and lattice constants of the rare earth intermetallics Lu₂Fe 17xT x (T=Cr, Mn, Ru). The calculated preferential occupation site of ternary element T is found to be the 4f site. The order of site preference is given as 4f, 12k, 12j and 6g for Lu₂Fe 17xT x. The calculated lattice parameters are corresponding to the experimental results. We have calculated the magnetic moments of Lu₂Fe 17xT x compounds. Results show that the calculated total magnetic moment of Lu₂Fe₁₇ compound is M=37.34 μ B/f.u. In addition, the total and partialmore » phonon densities of states are evaluated first for these complicated structures. - Graphical abstract: The vibrational modes are mostly excited by Fe atoms, Lu contributes to the lower frequencies modes, and the contribution of Ru atoms is the same as Fe atoms. Highlights: • There are no reports on lattice vibrations of Lu₂(Fe, T) 17x (T=Cr, Mn, Ru) compounds. • The phase stability and site preference are evaluated first for the complex structures of Lu₂(Fe, T) 17x (T=Cr, Mn, Ru) compounds. • The lattice inversion method to obtain the interatomic pair potential is the unique one.« less

  14. Microscopic coexistence of magnetism and superconductivity in charge-compensated Ba1-xKx(Fe1-yCoy)2As2

    NASA Astrophysics Data System (ADS)

    Goltz, Til; Zinth, Veronika; Johrendt, Dirk; Rosner, Helge; Pascua, Gwendolyne; Luetkens, Hubertus; Materne, Philipp; Klauss, Hans-Henning

    2014-04-01

    We present a detailed investigation of the electronic phase diagram of effectively charge compensated Ba1-xKx(Fe1-yCoy)2As2 with x /2≈y. Our experimental study by means of x-ray diffraction, Mössbauer spectroscopy, muon spin relaxation and ac-susceptibility measurements on polycrystalline samples is complemented by density functional electronic structure calculations. For low substitution levels of x /2≈y≤0.13, the system displays an orthorhombically distorted and antiferromagnetically ordered ground state. The low-temperature structural and magnetic order parameters are successively reduced with increasing substitution level. We observe a linear relationship between the structural and the magnetic order parameter as a function of temperature and substitution level for x /2≈y≤0.13. At intermediate substitution levels in the range between 0.13 and 0.19, we find superconductivity with a maximum Tc of 15 K coexisting with static magnetic order on a microscopic length scale. For higher substitution levels x /2≈y≥0.25, a tetragonal nonmagnetic ground state is observed. Our DFT calculations yield a significant reduction of the Fe 3d density of states at the Fermi energy and a strong suppression of the ordered magnetic moment in excellent agreement with experimental results. The appearance of superconductivity within the antiferromagnetic state can by explained by the introduction of disorder due to nonmagnetic impurities to a system with a constant charge carrier density.

  15. Molecular mapping of chromosomes 17 and X. Progress report

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Barker, D.F.

    1991-01-15

    Progress toward the construction of high density genetic maps of chromosomes 17 and X has been made by isolating and characterizing a relatively large set of polymorphic probes for each chromosome and using these probes to construct genetic maps. We have mapped the same polymorphic probes against a series of chromosome breakpoints on X and 17. The probes could be assigned to over 30 physical intervals on the X chromosome and 7 intervals on 17. In many cases, this process resulted in improved characterization of the relative locations of the breakpoints with respect to each other and the definition ofmore » new physical intervals. The strategy for isolation of the polymorphic clones utilized chromosome specific libraries of 1--15 kb segments from each of the two chromosomes. From these libraries, clones were screened for those detecting restriction fragment length polymorphisms. The markers were further characterized, the chromosomal assignments confirmed and in most cases segments of the original probes were subcloned into plasmids to produce probes with improved signal to noise ratios for use in the genetic marker studies. The linkage studies utilize the CEPH reference families and other well-characterized families in our collection which have been used for genetic disease linkage work. Preliminary maps and maps of portions of specific regions of 17 and X are provided. We have nearly completed a map of the 1 megabase Mycoplasma arthritidis genome by applying these techniques to a lambda phage library of its genome. We have found bit mapping to be an efficient means to organize a contiguous set of overlapping@ clones from a larger genome.« less

  16. Detection of 17 GHz radio emission from X-ray-bright points

    NASA Technical Reports Server (NTRS)

    Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.

    1994-01-01

    Using observations made with the Nobeyama radio heliograph (NRH) at 17 GHz and the Yohkoh/SXT experiment, we report the first detection of 17 GHz signatures of coronal X-ray-bright points (XBPs). This is also the first reported detection of flaring bright points in microwaves. We have detected four BPs at 17 GHz out of eight identified in SXT data on 1992 July 31, for which we looked for 17 GHz emission. For one XBP located in a quiet mixed-polarity region, the peak times at 17 GHz and X-rays are very similar, and both are long-lasting-about 2 hr in duration. There is a second BP (located near an active region) which is most likely flaring also, but the time profiles in the two spectral domains are not similar. The other two 17 GHz BPs are quiescent with fluctuations superposed upon them. For the quiet region XBP, the gradual, long-lasting, and unpolarized emission suggests that the 17 GHz emission is thermal.

  17. Development of Fe-based superconducting wires for liquid-hydrogen level sensors

    NASA Astrophysics Data System (ADS)

    Ishida, S.; Tsuchiya, Y.; Mawatari, Y.; Eisaki, H.; Nakano, A.; Yoshida, Y.

    2017-07-01

    We developed liquid-hydrogen (LH2) level sensors with Ba(Fe1-x Co x )2As2 superconducting wires (Co-Ba122 wires) as their detection elements. We fabricated Co-Ba122 wires with different Co concentrations x by using the powder-in-tube method. The superconducting transition temperatures of the wires were successfully controlled in the range of 20-25 K by changing x from 0.06 to 0.10. The resistance-temperature curves of the wires exhibited sharp superconducting transitions with widths of 0.5-1.0 K. In addition, we performed an operation test of the Co-Ba122 level sensors with LH2. Close correspondence between the output resistance and the actual LH2 level was observed for a sensor equipped with x = 0.09 wire, demonstrating that this sensor can accurately measure LH2 levels.

  18. Role of the local structure in superconductivity of LaO0.5F0.5BiS2-x Se x system

    NASA Astrophysics Data System (ADS)

    Paris, E.; Mizuguchi, Y.; Hacisalihoglu, M. Y.; Hiroi, T.; Joseph, B.; Aquilanti, G.; Miura, O.; Mizokawa, T.; Saini, N. L.

    2017-04-01

    We have studied the local structure of LaO0.5F0.5BiS2-x Se x by Bi L1-edge extended x-ray absorption fine structure (EXAFS). We find a significant effect of Se substitution on the local atomic correlations with a gradual elongation of average in-plane Bi-S bondlength. The associated mean square relative displacement, measuring average local distortions in the BiS2 plane, hardly shows any change for small Se substitution, but decreases significantly for x≥slant 0.6 . The Se substitution appears to suppress the local distortions within the BiS2 plane that may optimize in-plane orbital hybridization and hence the superconductivity. The results suggest that the local structure of the BiS2-layer is one of the key ingredients to control the physical properties of the BiS2-based dichalcogenides.

  19. Superconductivity in ion-beam-mixed layered Au-Si thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jisrawi, N.M.; McLean, W.L.; Stoffel, N.G.

    The superconducting properties of thin films made by mixing alternating layers of Au and Si using ion-beam bombardment correlate with the formation of metastable metallic phases in what is otherwise a simple eutectic system. Transmission-electron-microscopy measurements reveal the superconducting phases to be amorphous. Compound formation and the nature of Au-Si bonding in these metastable phases are demonstrated from x-ray photoelectron spectroscopy and from a previous study of x-ray-absorption spectroscopy. After mixing with a beam of Xe ions, multilayered films with an average nominal composition Au{sub {ital x}}Si{sub 1{minus}{ital x}}, where {ital x}=0.2, 0.4, 0.5, 0.72, and 0.8, exhibited superconducting transitionmore » temperatures in the range 0.2--1.2 K. A double transition feature in the magnetic field dependence of the resistivity is attributed to the formation of more than one metastable metallic phase in the same sample as the ion dose increases.« less

  20. High quality superconducting titanium nitride thin film growth using infrared pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Torgovkin, A.; Chaudhuri, S.; Ruhtinas, A.; Lahtinen, M.; Sajavaara, T.; Maasilta, I. J.

    2018-05-01

    Superconducting titanium nitride (TiN) thin films were deposited on magnesium oxide, sapphire and silicon nitride substrates at 700 °C, using a pulsed laser deposition (PLD) technique, where infrared (1064 nm) pulses from a solid-state laser were used for the ablation from a titanium target in a nitrogen atmosphere. Structural studies performed with x-ray diffraction showed the best epitaxial crystallinity for films deposited on MgO. In the best films, superconducting transition temperatures, T C, as high as 4.8 K were observed, higher than in most previous superconducting TiN thin films deposited with reactive sputtering. A room temperature resistivity down to ∼17 μΩ cm and residual resistivity ratio up to 3 were observed in the best films, approaching reported single crystal film values, demonstrating that PLD is a good alternative to reactive sputtering for superconducting TiN film deposition. For less than ideal samples, the suppression of the film properties were correlated mostly with the unintended incorporation of oxygen (5–10 at%) in the film, and for high oxygen content films, vacuum annealing was also shown to increase the T C. On the other hand, superconducting properties were surprisingly insensitive to the nitrogen content, with high quality films achieved even in the highly nitrogen rich, Ti:N = 40/60 limit. Measures to limit oxygen exposure during deposition must be taken to guarantee the best superconducting film properties, a fact that needs to be taken into account with other deposition methods, as well.

  1. Electronic state and superconductivity of YBa2Cu3-xO7-y (M=Al,Zn and Sn) systems

    NASA Technical Reports Server (NTRS)

    Zhao, Y.; Zhang, Q. R.; Zhang, H.

    1990-01-01

    A series of YBa2Cu(3-x)MxO(7-y) (M=Al,Zn and Sn) single phase samples were prepared, and the measurements of the crystal structure, oxygen content, electric resistivity, thermoelectric power, Mossbauer spectrum, XPS and superconductivity were performed. The experimental results of X ray powder diffraction, Mossbauer spectrum and oxygen content show that the Zn(2+) and the Al(3+) occupy the Cu(2) site in Cu-O planes and the Cu(1) site in Cu-O chains respectively, but the Sn(4+) occupies both the Cu(1) sites. As regards the properties in superconducting state, both the Zn(2+) and the Al(3+) depress T(sub c) strongly, but the Sn(4+) does not. As for the electronic transport properties in normal state, the system doped by Al(3+) displays a rapid increase of resistivity and some electron localization-like effects, and the thermoelectric power enhances obviously; the series contained Zn(2+) almost shows no changes of electric resistivity but the sign of the thermoelectric power is reversed. Other results are given and briefly discussed.

  2. Superconductivity induced in iron telluride films by low-temperature oxygen incorporation

    NASA Astrophysics Data System (ADS)

    Nie, Y. F.; Telesca, D.; Budnick, J. I.; Sinkovic, B.; Wells, B. O.

    2010-07-01

    We report superconductivity induced in films of the nonsuperconducting, antiferromagnetic parent material FeTe by low-temperature oxygen incorporation in a reversible manner. X-ray absorption shows that oxygen incorporation changes the nominal Fe valence state from 2+ in the nonsuperconducting state to mainly 3+ in the superconducting state. Thus superconductivity in O-doped FeTe occurs in a quite different charge and strain state than the more common FeTe1-xSex . This work also suggests a convenient path for conducting doping experiments in situ with many measurement techniques.

  3. Suppression of 1/f Flux Noise in Superconducting Quantum Circuits

    NASA Astrophysics Data System (ADS)

    Kumar, Pradeep; Freeland, John; Yu, Clare; Wu, Ruqian; Wang, Zhe; Wang, Hui; Shi, Chuntai; Pappas, David; McDermott, Robert

    Low frequency 1/f magnetic flux noise is a dominant contributor to dephasing in superconducting quantum circuits. It is believed that the noise is due to a high density of unpaired magnetic defect states at the surface of the superconducting thin films. We have performed X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) experiments that point to adsorbed molecular oxygen as the dominant source of magnetism in these films. By improving the vacuum environment of our superconducting devices, we have achieved a significant reduction in surface magnetic susceptibility and 1/f flux noise power spectral density. These results open the door to realization of superconducting qubits with improved dephasing times. State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China.

  4. Superconductivity in gallium-substituted Ba8Si46 clathrates

    NASA Astrophysics Data System (ADS)

    Li, Yang; Zhang, Ruihong; Liu, Yang; Chen, Ning; Luo, Z. P.; Ma, Xingqiao; Cao, Guohui; Feng, Z. S.; Hu, Chia-Ren; Ross, Joseph H., Jr.

    2007-02-01

    We report a joint experimental and theoretical investigation of superconductivity in Ga-substituted type-I silicon clathrates. We prepared samples of the general formula Ba8Si46-xGax , with different values of x . We show that Ba8Si40Ga6 is a bulk superconductor, with an onset at TC≈3.3K . For x=10 and higher, no superconductivity was observed down to T=1.8K . This represents a strong suppression of superconductivity with increasing Ga content, compared to Ba8Si46 with TC≈8K . Suppression of superconductivity can be attributed primarily to a decrease in the density of states at the Fermi level, caused by a reduced integrity of the sp3 -hybridized networks as well as the lowering of carrier concentration. These results are corroborated by first-principles calculations, which show that Ga substitution results in a large decrease of the electronic density of states at the Fermi level, which explains the decreased superconducting critical temperature within the BCS framework. To further characterize the superconducting state, we carried out magnetic measurements showing Ba8Si40Ga6 to be a type-II superconductor. The critical magnetic fields were measured to be HC1≈35Oe and HC2≈8.5kOe . We deduce the London penetration depth λ≈3700Å and the coherence length ξc≈200Å . Our estimate of the electron-phonon coupling reveals that Ba8Si40Ga6 is a moderate phonon-mediated BCS superconductor.

  5. Experimental evidence for s-wave pairing symmetry in superconducting Cu(x)Bi2Se3 single crystals using a scanning tunneling microscope.

    PubMed

    Levy, Niv; Zhang, Tong; Ha, Jeonghoon; Sharifi, Fred; Talin, A Alec; Kuk, Young; Stroscio, Joseph A

    2013-03-15

    Topological superconductors represent a newly predicted phase of matter that is topologically distinct from conventional superconducting condensates of Cooper pairs. As a manifestation of their topological character, topological superconductors support solid-state realizations of Majorana fermions at their boundaries. The recently discovered superconductor Cu(x)Bi(2)Se(3) has been theoretically proposed as an odd-parity superconductor in the time-reversal-invariant topological superconductor class, and point-contact spectroscopy measurements have reported the observation of zero-bias conductance peaks corresponding to Majorana states in this material. Here we report scanning tunneling microscopy measurements of the superconducting energy gap in Cu(x)Bi(2)Se(3) as a function of spatial position and applied magnetic field. The tunneling spectrum shows that the density of states at the Fermi level is fully gapped without any in-gap states. The spectrum is well described by the Bardeen-Cooper-Schrieffer theory with a momentum independent order parameter, which suggests that Cu(x)Bi(2)Se(3) is a classical s-wave superconductor contrary to previous expectations and measurements.

  6. Superconductivity of Rock-Salt Structure LaO Epitaxial Thin Film.

    PubMed

    Kaminaga, Kenichi; Oka, Daichi; Hasegawa, Tetsuya; Fukumura, Tomoteru

    2018-06-06

    We report a superconducting transition in a LaO epitaxial thin film with the superconducting transition onset temperature ( T c ) at around 5 K. This T c is higher than those of other lanthanum monochalcogenides and opposite to their chemical trend: T c = 0.84, 1.02, and 1.48 K for LaX (X = S, Se, Te), respectively. The carrier control resulted in a dome-shaped T c as a function of electron carrier density. In addition, the T c was significantly sensitive to epitaxial strain in spite of the highly symmetric crystal structure. This rock-salt superconducting LaO could be a building block to design novel superlattice superconductors.

  7. HiFi-MBQC High Fidelitiy Measurement-Based Quantum Computing using Superconducting Detectors

    DTIC Science & Technology

    2016-04-04

    superconducting nanowire single photon detectors (SNSPDs) which allowed support of quantum photonics experiments leading to 14 peer-reviewed...sampling, and several other areas. 15. SUBJECT TERMS EOARD, photonics, cryostat, superconducting nanowire , SNSPD 16. SECURITY CLASSIFICATION OF: 17...quantum simulations. The main budget contribution was dedicated to develop superconducting nanowire detectors with efficiencies above 93% at telecom

  8. Magnetic preferential orientation of metal oxide superconducting materials

    DOEpatents

    Capone, D.W.; Dunlap, B.D.; Veal, B.W.

    1990-07-17

    A superconductor comprised of a polycrystalline metal oxide such as YBa[sub 2]Cu[sub 3]O[sub 7[minus]X] (where 0 < X < 0.5) exhibits superconducting properties and is capable of conducting very large current densities. By aligning the two-dimensional Cu-O layers which carry the current in the superconducting state in the a- and b-directions, i.e., within the basal plane, a high degree of crystalline axes alignment is provided between adjacent grains permitting the conduction of high current densities. The highly anisotropic diamagnetic susceptibility of the polycrystalline metal oxide material permits the use of an applied magnetic field to orient the individual crystals when in the superconducting state to substantially increase current transport between adjacent grains. In another embodiment, the anisotropic paramagnetic susceptibility of rare-earth ions substituted into the oxide material is made use of as an applied magnetic field orients the particles in a preferential direction. This latter operation can be performed with the material in the normal (non-superconducting) state. 4 figs.

  9. Magnetic preferential orientation of metal oxide superconducting materials

    DOEpatents

    Capone, Donald W.; Dunlap, Bobby D.; Veal, Boyd W.

    1990-01-01

    A superconductor comprised of a polycrystalline metal oxide such as YBa.sub.2 Cu.sub.3 O.sub.7-X (where 0<X<0.5) exhibits superconducting properties and is capable of conducting very large current densities. By aligning the two-dimensional Cu-O layers which carry the current in the superconducting state in the a- and b-directions, i.e., within the basal plane, a high degree of crystalline axes alignment is provided between adjacent grains permitting the conduction of high current densities. The highly anisotropic diamagnetic susceptibility of the polycrystalline metal oxide material permits the use of an applied magnetic field to orient the individual crystals when in the superconducting state to substantially increase current transport between adjacent grains. In another embodiment, the anisotropic paramagnetic susceptibility of rare-earth ions substituted into the oxide material is made use of as an applied magnetic field orients the particles in a preferential direction. This latter operation can be performed with the material in the normal (non-superconducting) state.

  10. Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces.

    PubMed

    Misawa, Takahiro; Nomura, Yusuke; Biermann, Silke; Imada, Masatoshi

    2016-07-01

    Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2-x Sr x CuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices.

  11. Nodeless multiband superconductivity in stoichiometric single-crystalline CaKFe 4 As 4

    DOE PAGES

    Cho, Kyuil; Fente, A.; Teknowijoyo, S.; ...

    2017-03-08

    Measurements of the London penetration depth Δλ(T) and tunneling conductance in single crystals of the recently discovered stoichiometric iron-based superconductor CaKFe 4As 4 (CaK1144) show nodeless, two-effective-gap superconductivity with a larger gap of about 6–10 meV and a smaller gap of about 1–4 meV. Having a critical temperature T c,onset ≈ 35.8 K, this material behaves similar to slightly overdoped (Ba 1–xK x)Fe 2As 2 (e.g., x = 0.54,T c ≈ 34 K), a known multigap s ± superconductor. Here, we conclude that the superconducting behavior of stoichiometric CaK1144 demonstrates that two-gap s± superconductivity is an essential property of high-temperaturemore » superconductivity in iron-based superconductors, independent of the degree of substitutional disorder.« less

  12. Superconducting techniques for gravity survey and inertial navigation

    NASA Technical Reports Server (NTRS)

    Chan, H. A.; Moody, M. V.; Paik, H. J.; Parke, J. W.

    1985-01-01

    A three-axis gravity gradiometer is developed, in which the magnetic fields produced by persistent currents are modulated by motions of superconducting proof masses. The common-acceleration-induced errors are compensated for by a six-axis superconducting accelerometer with a single magnetically levitated proof mass, linear acceleration resolution of 4 x 10 to the -12th m/(s exp 2 Hz exp 1/2), and angular acceleration resolution of 3 x 10 to the -11th rad/(s exp 2 Hz exp 1/2). The testing of a prototype gradiometer revealed that the environment-induced noise limits the noise floor to 7 x 10 to the -10th/(s exp 2 Hz exp 1/2).

  13. Preparation and composition of superconducting copper oxides based on Ga-O layers

    DOEpatents

    Dabrowski, B.; Vaughey, J.T.; Poeppelmeier, K.R.

    1994-12-20

    A high temperature superconducting material with the general formula GaSr[sub 2]Ln[sub 1[minus]x]M[sub x]Cu[sub 2]O[sub 7[+-]w] wherein Ln is selected from the group consisting of La, Ce, Pt, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Y and M is selected from the group consisting of C and Sr, 0.2[<=]x[<=]0.4 and w is a small fraction of one. A method of preparing this high temperature superconducting material is provided which includes heating and cooling a mixture to produce a crystalline material which is subsequently fired, ground and annealed at high pressure and temperature in oxygen to establish superconductivity. 14 figures.

  14. Synthesis of superconducting Nb 3Sn coatings on Nb substrates

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Barzi, E.; Franz, S.; Reginato, F.

    In the present work the electrochemical and thermal syntheses of superconductive Nb 3Sn films are investigated. The Nb 3Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20 to 50 mA/cm 2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb 3Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of aboutmore » 13 μm. Scanning Electron Microscopy (SEM) allowed accurately measuring the thickness of the Nb 3Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction (XRD) patterns confirmed the presence of a cubic Nb 3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained T c was 17.68 K and the B c20 ranged between 22.5 T and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as "Jelly Roll" or "Rod in Tube", or directly used for producing superconducting surfaces. In conclusion, the potential of this method for Superconducting Radiofrequency (SRF) structures is also outlined.« less

  15. Synthesis of superconducting Nb 3Sn coatings on Nb substrates

    DOE PAGES

    Barzi, E.; Franz, S.; Reginato, F.; ...

    2015-12-01

    In the present work the electrochemical and thermal syntheses of superconductive Nb 3Sn films are investigated. The Nb 3Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20 to 50 mA/cm 2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb 3Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of aboutmore » 13 μm. Scanning Electron Microscopy (SEM) allowed accurately measuring the thickness of the Nb 3Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction (XRD) patterns confirmed the presence of a cubic Nb 3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained T c was 17.68 K and the B c20 ranged between 22.5 T and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as "Jelly Roll" or "Rod in Tube", or directly used for producing superconducting surfaces. In conclusion, the potential of this method for Superconducting Radiofrequency (SRF) structures is also outlined.« less

  16. Atomistic origin of an ordered superstructure induced superconductivity in layered chalcogenides.

    PubMed

    Ang, R; Wang, Z C; Chen, C L; Tang, J; Liu, N; Liu, Y; Lu, W J; Sun, Y P; Mori, T; Ikuhara, Y

    2015-01-27

    Interplay among various collective electronic states such as charge density wave and superconductivity is of tremendous significance in low-dimensional electron systems. However, the atomistic and physical nature of the electronic structures underlying the interplay of exotic states, which is critical to clarifying its effect on remarkable properties of the electron systems, remains elusive, limiting our understanding of the superconducting mechanism. Here, we show evidence that an ordering of selenium and sulphur atoms surrounding tantalum within star-of-David clusters can boost superconductivity in a layered chalcogenide 1T-TaS2-xSex, which undergoes a superconducting transition in the nearly commensurate charge density wave phase. Advanced electron microscopy investigations reveal that such an ordered superstructure forms only in the x area, where the superconductivity manifests, and is destructible to the occurrence of the Mott metal-insulator transition. The present findings provide a novel dimension in understanding the relationship between lattice and electronic degrees of freedom.

  17. Superconducting and magneto-transport properties of BiS{sub 2} based superconductor PrO{sub 1-x}F{sub x}BiS{sub 2} (x = 0 to 0.9)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jha, Rajveer; Kishan, Hari; Awana, V. P. S., E-mail: awana@mail.npindia.org

    We report superconducting properties of PrO{sub 1-x}F{sub x}BiS{sub 2} compounds, synthesized by the vacuum encapsulation technique. The synthesized PrO{sub 1-x}F{sub x}BiS{sub 2} (x = 0.1, 0.3, 0.5, 0.7, and 0.9) samples are crystallized in a tetragonal P4/nmm space group. Both transport and DC magnetic susceptibility measurements showed bulk superconductivity below 4 K. The maximum T{sub c} is obtained for x = 0.7 sample. Under applied magnetic field, both T{sub c}{sup onset} and T{sub c} (ρ = 0) decrease to lower temperatures. We estimated highest upper critical field [H{sub c2}(0)] for PrO{sub 0.3}F{sub 0.7}BiS{sub 2} sample to be above 4 T (Tesla). The thermally activated flux flow activation energymore » (U{sub 0}) is estimated 54.63 meV in 0.05 T field for PrO{sub 0.3}F{sub 0.7}BiS{sub 2} sample. Hall measurement results showed that electron charge carriers are the dominating ones in these compounds. Thermoelectric effects (Thermal conductivity and Seebeck coefficient) data suggest strong electron-electron correlations in this material.« less

  18. Status Report on the CEBAF IR and UV FELs

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Leemann, Christoph; Bisognano, Joseph; Douglas, David

    1993-07-01

    The CEBAF five pass recirculating, superconducting linac, being developed as a high power electron source for nuclear physics, is also an ideal FEL driver.The 45 MeV front end linac is presently operational with a CW (low peak current) nuclear physics gun and has met all CEBAF performance specifications including low emittance and energy spread (< 1 * 10^-4). Progress will be reported in commissioning.This experience leads to predictions of excellent FEL performance.Initial designs reported last year have been advanced.Using the output of a high charge DC photoemission gun under development with a 6 cm period wiggler produces kilowatt output powersmore » in the 3.6 to 17 micrometer range in the fundamental.Third harmonic operation extends IR performance down to 1.2 micrometer.Beam at energies up to 400 MeV from the first full CEBAF linac will interact in a similar but longer wiggler to yield kilowatt UV light production at wavelengths as short as 0.15 micrometers.Full power FEL« less

  19. Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe1 -xSex

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Schneeloch, J. A.; Wen, Jinsheng; Božin, E. S.; Granroth, G. E.; Winn, B. L.; Feygenson, M.; Birgeneau, R. J.; Gu, Genda; Zaliznyak, I. A.; Tranquada, J. M.; Xu, Guangyong

    2016-03-01

    It has recently been demonstrated that dynamical magnetic correlations measured by neutron scattering in iron chalcogenides can be described with models of short-range correlations characterized by particular choices of four-spin plaquettes, where the appropriate choice changes as the parent material is doped towards superconductivity. Here we apply such models to describe measured maps of magnetic scattering as a function of two-dimensional wave vectors obtained for optimally superconducting crystals of FeTe1 -xSex . We show that the characteristic antiferromagnetic wave vector evolves from that of the bicollinear structure found in underdoped chalcogenides (at high temperature) to that associated with the stripe structure of antiferromagnetic iron arsenides (at low temperature); these can both be described with the same local plaquette, but with different interplaquette correlations. While the magnitude of the low-energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant. The observed change in spin correlations is correlated with the dramatic drop in the electronic scattering rate and the growth of the bulk nematic response upon cooling. Finally, we also present powder neutron diffraction results for lattice parameters in FeTe1 -xSex indicating that the tetrahedral bond angle tends to increase towards the ideal value upon cooling, in agreement with the increased screening of the crystal field by more itinerant electrons and the correspondingly smaller splitting of the Fe 3 d orbitals.

  20. Theory of the interplay between the superconductivity and the blocked antiferromagnetic order in A(y)Fe(2-x)Se2.

    PubMed

    Jiang, Hong-Min

    2012-09-26

    Based on an effective two-orbital tight-binding model, we examine the possible superconducting states in iron-vacancy-ordered A(y)Fe(2-x)Se(2). In the presence of ordered vacancies and blocked antiferromagnetic order, it is shown that the emergent SC pairing is the nodeless next-nearest-neighbor (NNN)-pairing due to the dominant antiferromagnetic (AFM) interaction between the inter-block NNN sites. In particular, we show that due to the ordered vacancies and the associated blocked AFM order, the interplay between the superconducting and AFM states results in three distinct states in the phase diagram as doping is varied. The divergent experimental observations can be accounted for by considering the different charge carrier concentrations in their respective compounds.

  1. Development of picosecond time-resolved X-ray absorption spectroscopy by high-repetition-rate laser pump/X-ray probe at Beijing Synchrotron Radiation Facility.

    PubMed

    Wang, Hao; Yu, Can; Wei, Xu; Gao, Zhenhua; Xu, Guang Lei; Sun, Da Rui; Li, Zhenjie; Zhou, Yangfan; Li, Qiu Ju; Zhang, Bing Bing; Xu, Jin Qiang; Wang, Lin; Zhang, Yan; Tan, Ying Lei; Tao, Ye

    2017-05-01

    A new setup and commissioning of transient X-ray absorption spectroscopy are described, based on the high-repetition-rate laser pump/X-ray probe method, at the 1W2B wiggler beamline at the Beijing Synchrotron Radiation Facility. A high-repetition-rate and high-power laser is incorporated into the setup with in-house-built avalanche photodiodes as detectors. A simple acquisition scheme was applied to obtain laser-on and laser-off signals simultaneously. The capability of picosecond transient X-ray absorption spectroscopy measurement was demonstrated for a photo-induced spin-crossover iron complex in 6 mM solution with 155 kHz repetition rate.

  2. Anomalous expansion of the copper-apical-oxygen distance in superconducting cuprate bilayers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhou, Hua; Yacoby, Yizhak; Butko, Vladimir Y.

    2010-08-27

    We have introduced an improved x-ray phase-retrieval method with unprecedented speed of convergence and precision, and used it to determine with sub-Angstrom resolution the complete atomic structure of epitaxial La{sub 2-x}Sr{sub x}CuO{sub 4} ultrathin films. We focus on superconducting heterostructures built from constituent materials that are not superconducting in bulk samples. Single-phase metallic or superconducting films are also studied for comparison. The results show that this phase-retrieval diffraction method enables accurate measurement of structural modifications in near-surface layers, which may be critically important for elucidation of surface-sensitive experiments. Specifically we find that, while the copper-apical-oxygen distance remains approximately constant inmore » single-phase films, it shows a dramatic increase from the metallic-insulating interface of the bilayer towards the surface by as much as 0.45 {angstrom}. The apical-oxygen displacement is known to have a profound effect on the superconducting transition temperature.« less

  3. Process for applying a superconductive powder to a wide variety of substrates

    NASA Astrophysics Data System (ADS)

    Hooker, Matthew W.; Wise, Stephanie A.; Tran, Sang Q.

    1992-12-01

    A fine superconducting powder such as YBa2Cu3O(7-x), wherein x is less than one, is blended into a liquid mixture comprising an epoxy resin and a thinner. This liquid mixture with the blended superconducting powder is coated onto a substrate. Next, the thinner is evaporated and the remaining coating cured, resulting in a coating of cured epoxy resin having superconducting powder suspended therein. This coating exhibits the Meissner effect, i.e., it expels a magnetic flux which protects the substrate from external magnetic interference. Since the coated substrate need only be heated for evaporation and curing at relatively low temperatures compared to firing, the superconducting coating can be applied to a wide variety of different materials.

  4. Microwave spectroscopy evidence of superconducting pairing in the magnetic-field-induced metallic state of InO(x) films at zero temperature.

    PubMed

    Liu, Wei; Pan, LiDong; Wen, Jiajia; Kim, Minsoo; Sambandamurthy, G; Armitage, N P

    2013-08-09

    We investigate the field-tuned quantum phase transition in a 2D low-disorder amorphous InO(x) film in the frequency range of 0.05 to 16 GHz employing microwave spectroscopy. In the zero-temperature limit, the ac data are consistent with a scenario where this transition is from a superconductor to a metal instead of a direct transition to an insulator. The intervening metallic phase is unusual with a small but finite resistance that is much smaller than the normal state sheet resistance at the lowest measured temperatures. Moreover, it exhibits a superconducting response on short length and time scales while global superconductivity is destroyed. We present evidence that the true quantum critical point of this 2D superconductor metal transition is located at a field B(sm) far below the conventionally defined critical field B(cross) where different isotherms of magnetoresistance cross each other. The superfluid stiffness in the low-frequency limit and the superconducting fluctuation frequency from opposite sides of the transition both vanish at B≈B(sm). The lack of evidence for finite-frequency superfluid stiffness surviving B(cross) signifies that B(cross) is a crossover above which superconducting fluctuations make a vanishing contribution to dc and ac measurements.

  5. Superconductivity and Magnetism in LaO1-xFxFeAs

    NASA Astrophysics Data System (ADS)

    Buechner, Bernd

    2009-03-01

    Measuring ^75As, ^139La, and ^57Fe Nuclear Magnetic Resonance (NMR) as well as μSR, transport and thermodynamic properties we have determined the phase diagram of LaO1-xFxAsFe superconductors [1-6]. In my talk, I will show experimental studies of the magnetic ordering [2, 5], properties of the superconducting state [1, 3, 5] and the normal state properties [1, 4, 6] in the superconducting regions of the phase diagram. While the temperature dependence of the London penetration as determined from μSR points to an isotropic s wave state [3], our early NMR data suggest singlet pairing and nodes of the order parameter [1]. Extending the NMR work to lower temperatures we find evidence for a deviation of the T^3 behaviour of the spin lattice relaxation, which would agree with the extended s-wave symmetry suggested in recent theoretical work. In the paramagnetic normal state, NMR on all three nuclei shows that the local electronic susceptibility rises with increasing temperature. This had led to suggest the presence of a pseudogap, which I will discuss in detail. The scaling of all NMR shifts with respect to the macroscopic susceptibility indicates that there is no apparent multiband effect through preferential hyperfine couplings. Relaxation measurements indicate a similar temperature-dependence for (T1T)-1, and suggest that the dynamical susceptibility changes uniformly in q space with varying temperature. The transport properties show some striking similarities to the findings in cuprates [6] and, finally, susceptibility [4] as well as NMR studies point to the antiferromagnetic fluctuations, whose relevance is also discussed in many theoretical models of the superconducting pairing mechanism. In collaboration with Hans-Joachim Grafe, Christian Hess, R"udiger Klingeler, G"unter Behr, Agnieszka Kondrat, Norman Leps, and Guillaume Lang, IFW Dresden; Hans-Henning Klauss, TU Dresden; and Hubertus Luetkens, PSI Villigen. [4pt] References: [0pt] [1] H.-J. Grafe et al., Phys

  6. Investigation of Sm substitution on structural and superconducting properties of Y1Ba2-xSmxCu3O7-δ superconductors

    NASA Astrophysics Data System (ADS)

    Sharifzadegan, L.; Sedghi, H.

    2018-07-01

    In this work, samples of a nominal composition Y1 Ba2 - x Smx Cu3O7 - δ With Sm substitution (X = 0.00, 0.01, 0.03, 0.05) were prepared by the solid state reaction method. And the effect of substituting Sm instead of Ba was investigated on the structural and superconducting properties of the samples. Measurement of electrical resistance and critical temperature was done using 4-Probe connection method. Results indicate that Sm substitution affects the YBSCO superconducting samples, decrease the transition temperature of the superconductor and increases the special electrical resistance and the transition width. Also, XRD studies show that in all samples of the Y-123 phase, the formation and structure is orthorhombic. SEM images showed that the porosity in the samples increased with increasing Sm due to disruption in grain growth and instead, increase Sm in the samples cause decreasing the size of the grain.

  7. Enhanced coherent oscillations in the superconducting state of underdoped YB a 2 C u 3 O 6 + x induced via ultrafast terahertz excitation

    DOE PAGES

    Dakovski, Georgi L.; Lee, Wei -Sheng; Hawthorn, David G.; ...

    2015-06-24

    We utilize intense, single-cycle terahertz pulses to induce collective excitations in the charge-density-wave-ordered underdoped cuprate YBa 2Cu 3O 6+x. These excitations manifest themselves as pronounced coherent oscillations of the optical reflectivity in the transient state, accompanied by minimal incoherent quasiparticle relaxation dynamics. The oscillations occur at frequencies consistent with soft phonon energies associated with the charge-density-wave, but vanish above the superconducting transition temperature rather than that at the charge-density-wave transition. These results indicate an intimate relationship of the terahertz excitation with the underlying charge-density-wave and the superconducting condensate itself.

  8. Evidence of Nematicity in K 0.8Fe 1.7Se 2

    DOE PAGES

    Duan, Chunruo; Yang, Junjie; Ye, Feng; ...

    2015-12-11

    We proposed that the superconducting state of K 0.8Fe 1.7Se 2 is phase separated from a non-superconducting magnetic state. These results from a recent neutron diffraction study on a single crystal of K 0.8Fe 1.7Se 2 provide evidence for a continuous transition between the I 4/m m m high temperature phase in which the Fe vacancies are randomly distributed and the I4/m vacancy ordered phase in the temperature range between T (C) and T (S). Upon cooling, the I 4/m phase becomes more populated, increasing the √5 X√5 X 1 superlattice structure, resulting in an enhancement of the (101) superlatticemore » peak. Moreover, the same temperature dependence is observed for the magnetic peak as well. Moreover, due to the Fe site splitting with the transition, its z-coordinate fluctuates, and so must the d xz and d y z orbitals. Finally, the orbital fluctuations couple to the magnetic ordering as seen here and may lead to a realization of nematic order in this system.« less

  9. Chevrel-phase solid solution Mo 6Se 8- xTe x. Study of its superconducting, magnetic and NMR properties

    NASA Astrophysics Data System (ADS)

    Hamard1a, C.; Auffret, V.; Peña, O.; Le Floch, M.; Nowak, B.; Wojakowski, A.

    2000-09-01

    The Chevrel-phase solid solution Mo 6Se 8-Mo 6Te 8 was studied by X-ray diffraction, AC and DC magnetic susceptibility and 77Se and 125Te NMR spectroscopy. From the smooth evolution of the lattice parameters and superconducting critical temperatures, a progressive substitution of selenium atoms by tellurium is shown, on the whole range of composition 0⩽ x⩽8, in the formulation Mo 6Se 8- xTe x: the unit-cell volume increases linearly because of the larger ionic size of tellurium, while Tc decreases rapidly (from 6.45 down to 0 K) because of the different formal oxidation states of the anions and a probable evolution of the Fermi level in the density of states. Results of magnetic susceptibility support this model and suggest the inhibition of the intrinsic metallic behavior with increasing x. The NMR spectra of the binaries Mo 6Se 8 and Mo 6Te 8 reveal two significant features, attributed to two different chalcogen positions in the R 3¯ symmetry. At low Se contents in Mo 6Se 8- xTe x ( x=7.5, 7 and 6), selenium first fills the two X(2) sites along the three-fold axis (2c positions), and then it becomes statistically distributed over the general 6f positions, leading to broad 77Se NMR lines. On the other hand, substitution of Te atoms in Mo 6Se 8 seems to occur in a random way, creating large perturbations on the 125Te NMR spectra, over the whole range of x. Theoretical analysis based on the presence of two anisotropic lines (of axial and non-axial symmetries, respectively) allowed us to estimate their anisotropy factors and to perfectly simulate the frequency response of both Mo 6Se 8 and Mo 6Te 8 binaries. Analysis of the Knight shift anisotropy leads us to conclude about the importance of the molybdenum z 2 molecular orbital contribution which controls the Mo-X dipolar interactions.

  10. Interplay of superconductivity and magnetic fluctuations in single crystals of BaFe2-xCoxAs2

    NASA Astrophysics Data System (ADS)

    Bag, Biplab; Kumar, Ankit; Banerjee, S. S.; Vinod, K.; Bharathi, A.

    2018-04-01

    We report unusual pinning response in optimally doped and overdoped single crystals of BaFe2-xCoxAs2. Here we use magneto-optical imaging technique to measure the local magnetization response which shows an unusual transformation from low temperature diamagnetic state to high temperature positive magnetization response. Our data suggests coexistence of magnetic fluctuation along with superconductivity in the optimally doped crystal. The strength of magnetic fluctuations is the strongest in the optimally doped compound with the highest Tc.

  11. Magnetic field effect in stripe-ordered 214 (La1.6 -xNd0.4) SrxCuO4 and La2 -xBaxCuO4 superconducting cuprates studied by resonant soft x-ray scattering

    NASA Astrophysics Data System (ADS)

    Blanco-Canosa, S.; Schierle, E.; Li, Z. W.; Guo, H.; Adachi, T.; Koike, Y.; Sobolev, O.; Weschke, E.; Komarek, A. C.; Schüßler-Langeheine, C.

    2018-05-01

    We present a study of the charge order of 214 stripe ordered superconducting cuprates (La1.6 -xNd0.4) SrxCuO4 and La2 -xBaxCuO4 for doping levels 0.11 ≤p ≤0.14 by means of resonant x-ray scattering. Up to 6 T, we find no field dependence on either the integrated intensity or the correlation length of the charge modulations, providing evidence for strong stability of charge order under applied fields. The magnetic field data support a strong pinning scenario induced by the low-temperature tetragonal distortion and static disorder, and they highlight the role of the symmetry of the lattice on the stabilization of electronic periodicities.

  12. A hidden pseudogap under the 'dome' of superconductivity in electron-doped high-temperature superconductors.

    PubMed

    Alff, L; Krockenberger, Y; Welter, B; Schonecke, M; Gross, R; Manske, D; Naito, M

    2003-04-17

    The ground state of superconductors is characterized by the long-range order of condensed Cooper pairs: this is the only order present in conventional superconductors. The high-transition-temperature (high-T(c)) superconductors, in contrast, exhibit more complex phase behaviour, which might indicate the presence of other competing ground states. For example, the pseudogap--a suppression of the accessible electronic states at the Fermi level in the normal state of high-T(c) superconductors-has been interpreted as either a precursor to superconductivity or as tracer of a nearby ground state that can be separated from the superconducting state by a quantum critical point. Here we report the existence of a second order parameter hidden within the superconducting phase of the underdoped (electron-doped) high-T(c) superconductor Pr2-xCe(x)CuO4-y and the newly synthesized electron-doped material La2-xCe(x)CuO4-y (ref. 8). The existence of a pseudogap when superconductivity is suppressed excludes precursor superconductivity as its origin. Our observation is consistent with the presence of a (quantum) phase transition at T = 0, which may be a key to understanding high-T(c) superconductivity. This supports the picture that the physics of high-T(c) superconductors is determined by the interplay between competing and coexisting ground states.

  13. Strong Coupling Superconductivity in the Vicinity of the Structural Quantum Critical Point in (CaxSr1-x)3Rh4Sn13

    NASA Astrophysics Data System (ADS)

    Yu, Wing Chi; Cheung, Yiu Wing; Saines, Paul J.; Imai, Masaki; Matsumoto, Takuya; Michioka, Chishiro; Yoshimura, Kazuyoshi; Goh, Swee K.

    The family of the superconducting quasiskutterudites (CaxSr1-x)3Rh4Sn13 features a structural quantum critical point at xc = 0 . 9 , around which a dome-shaped variation of the superconducting transition temperature Tc is found. In this talk, we present the specific heat data for the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching xc, which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2 Δ /kBTc and ΔC / γTc beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. Reference: Wing Chi Yu et al. Phys. Rev. Lett. (in press, 2015) This work was supported by the CUHK (Startup Grant, Direct Grant No. 4053071), UGC Hong Kong (ECS/24300214), Grants-in-Aid from MEXT (22350029 and 23550152), and Glasstone Bequest, Oxford.

  14. Superconductivity by rare earth doping in the 1038-type compounds (Ca1-xREx) 10(FeAs)10(Pt3As8) with RE=Y, La-Nd, Sm-Lu

    NASA Astrophysics Data System (ADS)

    Stürzer, Tobias; Derondeau, Gerald; Bertschler, Eva-Maria; Johrendt, Dirk

    2015-01-01

    We report superconductivity in polycrystalline samples of the 1038-type compounds (Ca1-xREx) 10(FeAs)10(Pt3As8) up to Tc=35 K with RE=Y, La-Nd, Sm, Gd-Lu. The critical temperatures are nearly independent of the trivalent rare earth element used, yielding a common Tc(xRE) phase diagram for electron doping in all these systems. The absence of superconductivity in Eu2+ doped samples, as well as the close resemblance of (Ca1-xREx) 10(FeAs)10(Pt3As8) to the 1048 compound substantiate that the electron doping scenario in the RE-1038 and 1048 phases is analogous to other iron-based superconductors with simpler crystal structures.

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

    NASA Astrophysics Data System (ADS)

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

    1993-07-01

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

  16. Superconducting Detector Arrays for Astrophysics

    NASA Technical Reports Server (NTRS)

    Chervenak, James

    2008-01-01

    The next generation of astrophysics instruments will feature an order of magnitude more photon sensors or sensors that have an order of magnitude greater sensitivity. Since detector noise scales with temperature, a number of candidate technologies have been developed that use the intrinsic advantages of detector systems that operate below 1 Kelvin. Many of these systems employ of the superconducting phenomena that occur in metals at these temperatures to build ultrasensitive detectors and low-noise, low-power readout architectures. I will present one such system in use today to meet the needs of the astrophysics community at millimeter and x-ray wavelengths. Our group at NASA in collaboration with Princeton, NIST, Boulder and a number of other groups is building large format arrays of superconducting transition edge sensors (TES) read out with multiplexed superconducting quantum interference devices (SQUID). I will present the high sensitivity we have achieved in multiplexed x-ray sensors with the TES technology and describe the construction of a 1000-sensor TES/SQUID array for microwave measurements. With our collaboration's deployment of a kilopixel TES array for 2 mm radiation at the Atacarna Cosmology Telescope in November 2007, we have first images of the lensed Cosmic Microwave Background at fine angular scales.

  17. Superconductivity in the Narrow Gap Semiconductor RbBi 11/3Te 6

    DOE PAGES

    Malliakas, Christos D.; Chung, Duck Young; Claus, Helmut; ...

    2016-10-16

    Superconductivity was discovered in the layered compound RbBi 11/3Te 6, featuring Bi vacancies and a narrow band gap of 0.25(2) eV at room temperature. In addition, a sharp superconducting transition at similar to 3.2 K was observed in polycrystalline ingots. The superconducting volume fraction of oriented single crystals is almost 100%, confirming bulk superconductivity. Systematic Se and Sb substitutions in RbBi 11/3-ySb ySe xTe 6-x, revealed a dependence of the superconducting transition on composition that can increase the T c up to similar to 10%. The RbBi 11/3Te 6 system is the first member of the new homologous series Rb[Bimore » 2n+11/3Te 3n+6] with infinite Bi 2Te 3-like layers. Lastly, the large degree of chemical tunability of the electronic structure of the homology via doping and/or substitution gives rise to a new family of superconductors.« less

  18. Physical properties of nanoparticles Nd added Bi1.7Pb0.3Sr2Ca2Cu3Oy superconductors

    NASA Astrophysics Data System (ADS)

    Abbas, Muna; Abdulridha, Ali; Jassim, Amal; Hashim, Fouad

    2018-05-01

    Bi1.7Pb0.3Sr2Ca2Cu3Oy bulks were synthesized, with the addition of Nd2O3 nanoparticles, by the solid state reaction method. The concentrations of Nd were varied from 0.1 to 0.6. The superconducting properties of the samples were investigated and studied to determine the influence of Nd2O3 addition on superconducting properties and microstructural development. The structural characteristics of the synthesized superconductor samples were carried out through X-ray diffractions. DC Four point probe method was used to study the electrical resistivity behavior and to evaluate the transition temperature (TC) for all samples. It was found that: 0.2 weight percentage of Nd2O3 yield the highest TC 123 K for highest volume fraction of 2223-phase, while excessive addition decreased both of them. The results point to compelling indications of correlations between charge carriers and superconductivity. Energy-dispersive X-ray spectroscopy (EDX) analysis for Bi1.7Pb0.3Nd0.2Sr2Ca2Cu3Oy superconductor shows that Nd may be substituted at Ca sites creating point defects, which act as flux pinning centers. Scanning electron microscopy (SEM) was employed to examine the microstructure of some samples. Their results showed precipitation of Nd nanoparticles on the surface as plate-like grains.

  19. Probing the connections between superconductivity, stripe order, and structure in La₁.₉₀₅Ba₀.₀₉₅Cu 1-yZn yO₄

    DOE PAGES

    Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; ...

    2012-04-12

    The superconducting system La 2-xBa xCuO₄ is known to show a minimum in the transition temperature T c at x=1/8 where maximal stripe order is pinned by the anisotropy within the CuO₂ planes that occurs in the low-temperature-tetragonal (LTT) crystal structure. For x=0.095, where T c reaches its maximum value of 32 K, there is a roughly coincident structural transition to a phase that is very close to LTT. Here, we present a neutron scattering study of the structural transition, and demonstrate how features of it correlate with anomalies in the magnetic susceptibility, electrical resistivity, thermal conductivity, and thermoelectric power.more » We also present measurements on a crystal with 1% Zn substituted for Cu, which reduces T c to 17 K, enhances the spin stripe order, but has much less effect on the structural transition. We make the case that the structural transition correlates with a reduction of the Josephson coupling between the CuO₂ layers, which interrupts the growth of the superconducting order. We also discuss evidence for two-dimensional superconducting fluctuations in the normal state, analyze the effective magnetic moment per Zn impurity, and consider the significance of the anomalous thermopower often reported in the stripe-ordered phase.« less

  20. 17. Photocopy of drawing (original 8 x 101/2 inch plate ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    17. Photocopy of drawing (original 8 x 10-1/2 inch plate located in: USDA Forest Service, North Pacific Region, recreation handbook, date unknown). COMMUNITY BLDG., PLATE A-9 (enlarged from a 4x5 negative) - Austin Pass Warming Hut, Washington Highway 542, Glacier, Whatcom County, WA

  1. Characterization of Phase-Slip Centers created in superconducting NbxTi1-xN thin films close to Tc

    NASA Astrophysics Data System (ADS)

    Harrabi, Khalil; Maneval, Jean Paul; Maneval Collaboration

    The dissipative states induced by an over-critical (pair-breaking) current in superconducting NbxTi1-xN strips were investigated and characterized in the vicinity of the critical temperature Tc ( 8.7 K). The suppression of superconductivity then occurs locally and leads to the creation of a phase-slip center (PSC). In the case where the over-critical current is applied as a step pulse, the PSC voltage rise is preceded by a nucleation time td which can be analyzed through a Time-Dependent Ginzburg-Landau theory due to Tinkham. In conformity with previous work, we interpret the effective gap relaxation time of the theory as the film cooling time. By consideration of the respective weights of the electron and phonon specific heats, the phonon escape time can be derived from experiments. It is here found to be 1.8 ns for a 20 nm NbTiN film sputtered on polished crystalline Al2O3\\ King Fahd University of Peroleum and Minerals Saudi Arabia.

  2. Heat load studies of a water-cooled minichannel monochromator for synchrotron x-ray beams

    NASA Astrophysics Data System (ADS)

    Freund, Andreas K.; Arthur, John R.; Zhang, Lin

    1997-12-01

    We fabricated a water-cooled silicon monochromator crystal with small channels for the special case of a double-crystal fixed-exit monochromator design where the beam walks across the crystal when the x-ray energy is changed. The two parts of the cooled device were assembled using a new technique based on low melting point solder. The bending of the system produced by this technique could be perfectly compensated by mechanical counter-bending. Heat load tests of the monochromator in a synchrotron beam of 75 W total power, 3 mm high and 15 mm wide, generated by a multipole wiggler at SSRL, showed that the thermal slope error of the crystal is 1 arcsec/40 W power, in full agreement with finite element analysis. The cooling scheme is adequate for bending magnet beamlines at the ESRF and present wiggler beamlines at the SSRL.

  3. Superconductivity and ferromagnetism in Pd doped Y 9Co 7

    DOE PAGES

    Strychalska, Judyta; Thompson, Joe D.; Cava, Robert J.; ...

    2016-01-15

    The ferromagnetic superconductor Y 9Co 7 was chemically doped to yield the solid solution Y 9Co 7-xPd x for 0 < x < 0.4. The lattice parameter a does not depend on x, whereas c increases with increasing Pd content up to x = 0.2, the palladium solubility limit. The transition from ferromagnetism (T C = 4.25 K) to superconductivity (T sc = 2.4 K) was observed only for the parent Y 9Co 7 compound. For the lowest tested Pd doping level (x = 0.05), ferromagnetism is enhanced strongly (T C = 9.35 K) and superconductivity is not seen abovemore » 1.8 K. Finally, the Curie temperature rapidly increases from 4.25 K to about 10 K for a Pd concentration of x = 0.1 and remains almost unchanged for Y 9Co 6.8Pd 0.2.« less

  4. Technical issues of a high-Tc superconducting bulk magnet

    NASA Astrophysics Data System (ADS)

    Fujimoto, Hiroyuki

    2000-06-01

    Superconducting magnets made of high-Tc superconductors are promising for industrial applications. It is well known that REBa2Cu3O7-x superconductors prepared by melt processes have a high critical current density, Jc, at 77 K and high magnetic fields. The materials are very promising for high magnetic field applications as a superconducting permanent/bulk magnet with liquid-nitrogen refrigeration. Light rare-earth (LRE) BaCuO bulks, compared with REBaCuO bulks, exhibit a larger Jc in high magnetic fields and a much improved irreversibility field, Hirr, at 77 K. In this study, we discuss technical issues of a high-Tc superconducting bulk magnet, namely the aspects of the melt processing for bulk superconductors, their characteristic superconducting properties and mechanical properties, and trapped field properties of a superconducting bulk magnet. One of the possible applications is a superconducting bulk magnet for the magnetically levitated (Maglev) train in the future.

  5. Antiferroic electronic structure in the nonmagnetic superconducting state of the iron-based superconductors.

    PubMed

    Shimojima, Takahiro; Malaeb, Walid; Nakamura, Asuka; Kondo, Takeshi; Kihou, Kunihiro; Lee, Chul-Ho; Iyo, Akira; Eisaki, Hiroshi; Ishida, Shigeyuki; Nakajima, Masamichi; Uchida, Shin-Ichi; Ohgushi, Kenya; Ishizaka, Kyoko; Shin, Shik

    2017-08-01

    A major problem in the field of high-transition temperature ( T c ) superconductivity is the identification of the electronic instabilities near superconductivity. It is known that the iron-based superconductors exhibit antiferromagnetic order, which competes with the superconductivity. However, in the nonmagnetic state, there are many aspects of the electronic instabilities that remain unclarified, as represented by the orbital instability and several in-plane anisotropic physical properties. We report a new aspect of the electronic state of the optimally doped iron-based superconductors by using high-energy resolution angle-resolved photoemission spectroscopy. We find spectral evidence for the folded electronic structure suggestive of an antiferroic electronic instability, coexisting with the superconductivity in the nonmagnetic state of Ba 1- x K x Fe 2 As 2 . We further establish a phase diagram showing that the antiferroic electronic structure persists in a large portion of the nonmagnetic phase covering the superconducting dome. These results motivate consideration of a key unknown electronic instability, which is necessary for the achievement of high- T c superconductivity in the iron-based superconductors.

  6. Superconducting Detectors for Superlight Dark Matter.

    PubMed

    Hochberg, Yonit; Zhao, Yue; Zurek, Kathryn M

    2016-01-08

    We propose and study a new class of superconducting detectors that are sensitive to O(meV) electron recoils from dark matter-electron scattering. Such devices could detect dark matter as light as the warm dark-matter limit, m(X)≳1  keV. We compute the rate of dark-matter scattering off of free electrons in a (superconducting) metal, including the relevant Pauli blocking factors. We demonstrate that classes of dark matter consistent with terrestrial and cosmological or astrophysical constraints could be detected by such detectors with a moderate size exposure.

  7. Magnetic properties and magnetocrystalline anisotropy of Nd 2Fe 17, Nd 2Fe 17X 3, and related compounds

    DOE PAGES

    Pandey, Tribhuwan; Parker, David S.

    2018-02-26

    The electronic and magnetic properties of Nd 2Fe 17 and Nd 2Fe 17X 3 (X = C or N) compounds have been calculated using the first-principles density functional calculations. Among these, the nitrogen and carbon interstitial compounds exhibit all of the required properties such as a saturation moment of 1.6 T, Curie temperature of 700–750 K, however easy magnetic axis lies in the planar direction making them less attractive for permanent magnet applications. The calculated magnetocrystalline anisotropy energy is found to be -2.7 MJ/m 3 for Nd 2Fe 17C 3 and -4.7 MJ/m 3 for Nd 2Fe 17N 3. Finally,more » we further explored the possibility of changing the easy axis direction through La/Ce alloying at Nd site. Although the MAE is found to be smaller in magnitude for all the La/Ce alloys it still maintains planar direction.« less

  8. Molecular mapping of chromosomes 17 and X

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Barker, D.F.

    1989-01-01

    The basic aims of this project are the construction of high density genetic maps of chromosomes 17 and X and the utilization of these maps for the subsequent isolation of a set of physically overlapping DNA segment clones. The strategy depends on the utilization of chromosome specific libraries of small (1--15 kb) segments from each of the two chromosomes. Since the time of submission of our previous progress report, we have refined the genetic map of markers which we had previously isolated for chromosome 17. We have completed our genetic mapping in CEPH reference and NF1 families of 15 markersmore » in the pericentric region of chromosome 17. Physical mapping results with three probes, were shown be in very close genetic proximity to the NF1 gene, with respect to two translocation breakpoints which disrupt the activity of the gene. All three of the probes were found to lie between the centromere and the most proximal translocation breakpoint, providing important genetic markers proximal to the NF1 gene. Our primary focus has shifted to the X chromosome. We have isolated an additional 30 polymorphic markers, bringing the total number we have isolated to over 80. We have invested substantial effort in characterizing the polymorphisms at each of these loci and constructed plasmid subclones which reveal the polymorphisms for nearly all of the loci. These subclones are of practical value in that they produce simpler and stronger patterns on human genomic Southern blots, thus improving the efficiency of the genetic mapping experiments. These subclones may also be of value for deriving DNA sequence information at each locus, necessary for establishing polymerase chain reaction primers specific for each locus. Such information would allow the use of each locus as a sequence tagged site.« less

  9. Coexistence of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-xSex (x = 0.5 and 1.0), a non-U material with Tc < TFM

    PubMed Central

    Thakur, Gohil S.; Fuchs, G.; Nenkov, K.; Haque, Zeba; Gupta, L. C.; Ganguli, A. K.

    2016-01-01

    We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2. Se–doping produces several effects: it suppresses semiconducting–like behavior observed in the undoped Sr0.5Ce0.5FBiS2, the ferromagnetic ordering temperature, TFM, decreases considerably from 7.5 K (in Sr0.5Ce0.5FBiS2) to 3.5 K and the superconducting transition temperature, Tc, gets enhanced slightly to 2.9–3.3 K. Thus in these Se–doped materials, TFM is marginally higher than Tc. Magnetization studies provide evidence of bulk superconductivity in Sr0.5Ce0.5FBiS2-xSex at x ≥ 0.5 in contrast to the undoped Sr0.5Ce0.5FBiS2 (x = 0) where magnetization measurements indicate a small superconducting volume fraction. Quite remarkably, as compared with the effective paramagnetic Ce–moment (~2.2 μB), the ferromagnetically ordered Ce–moment in the superconducting state is rather small (~0.1 μB) suggesting itinerant ferromagnetism. To the best of our knowledge, Sr0.5Ce0.5FBiS2-x Sex (x = 0.5 and 1.0) are distinctive Ce–based bulk superconducting itinerant ferromagnetic materials with Tc < TFM. Furthermore, a novel feature of these materials is that they exhibit a dual and quite unusual hysteresis loop corresponding to both the ferromagnetism and the coexisting bulk superconductivity. PMID:27892482

  10. Impact of concomitant Y and Mn substitution on superconductivity in La1 -yYyFe1 -xMnxAsO0.89F0.11

    NASA Astrophysics Data System (ADS)

    Kappenberger, Rhea; Hammerath, Franziska; Rousse, Pierre; Afrassa, Mesfin Asfaw; Haghighi, M. Hossein; Kamusella, Sirko; Prando, Giacomo; Lamura, Gianrico; Wolter, Anja U. B.; Moroni, Matteo; Sanna, Samuele; Carretta, Pietro; Hess, Christian; Grafe, Hans-Joachim; Klauss, Hans-Henning; Wurmehl, Sabine; Büchner, Bernd

    2018-02-01

    We discuss the impact of concomitant substitution of Fe by Mn and La by Y in optimally F-doped LaFeAsO0.89F0.11 . Mn has a known poisoning effect on superconductivity which is particularly strong in the La1111 system, where 0.2% of Mn were reported to completely suppress superconductivity. Through isovalent substitution of La by the much smaller Y we are able to inflict chemical pressure on the structure, which we show is stabilizing the superconducting state, resulting in a drastically larger amount of Mn needed to completely quench superconductivity. Interestingly, we find that the lattice parameter c changes significantly even for small amounts of Mn substitution within a series, which is unexpected taking only the differences between ionic radii into account. We discuss our findings in the light of electron localization caused by small amounts of paramagnetic Mn impurities in La1 -yYyFe1 -xMnxAsO0.89F0.11 also indicated by resistivity and Mößbauer measurements.

  11. Doping-evolution of the superconducting gap in single crystals of (Ca 1-x La x ) 10 (Pt 3 As 8 )(Fe 2 As 2 ) 5 superconductor from London penetration depth measurements

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cho, K.; Tanatar, M. A.; Ni, N.

    2014-09-19

    The doping-evolution of the superconducting gap structure in iron-based superconductor (Ca 1-xLax)10(Pt3As8)(Fe2As2)5(x = 0.04, 0.06, 0.09, 0.11, and 0.18) was probed by high-resolution measurements of the London penetration depth, λ(T). The samples spanned compositions from underdoped to slightly overdoped with superconducting critical temperatures, Tc, from 12.7 K (x = 0.04) through (optimal) 23.3 K (x = 0.11) to 21.9 K (x = 0.18). The low-temperature variation (up to 0.3 Tc ) of λ(T) was analysed using a power-law function, Δλ = ATn. For compositions close to the optimal doping, (x = 0.09, 0.11, and 0.18), characterized by Tc > 20K,more » Δλ(T) shows a tendency to saturation, indicative of a full gap on the Fermi surface. Fitting over the lowest temperature range (T < 0.1 Tc) gives n = 2.6. This value is well outside the range 1 ≤ n ≤ 2 expected for the line-nodal superconductor. The exponent n decreased to n ~ 2 in the two most underdoped compositions x = 0.04 (Tc = 12.7 K) and 0.06 (Tc = 18.2 K), implying the development of a notable gap anisotropy revealed by the enhanced influence of pair-breaking scattering. This decrease is accompanied by a significant increase of the total variation of the penetration depth Δλ in a fixed temperature interval (e.g., Tmin - 0.3Tc). Both the decrease of the exponent and the increase of the absolute value of Δλ in the underdoped regime are similar to the observations in other charge-doped iron-based superconductors, such as doped BaFe2As2 and NaFeAs, suggesting a universal behavior in iron-based superconductors.« less

  12. Superconducting properties of ion-implanted gold-silicon thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jisrawi, N.M.

    The superconducting properties of thin Au{sub x}Si{sub 1{minus}x}, films prepared by ion beam implantation and ion beam mixing are studied. The films are prepared by evaporation of single Au layers on Si substrates and mixing them with Si, Ar, or Xe, or by Xe beam mixing of alternate multilayers of Au and Si sputtered on Al{sub 2}O{sub 3} substrates. The superconducting transition temperature and upper critical fields are determined by measuring the temperature and magnetic field dependence of resistivity. Temperatures as low as 20mK and magnetic fields as high as 8 T were used. Superconductivity in these films is discussedmore » in connection with metastable metallic phases that are reportedly produced in the Au-Si system by high quenching rate preparation techniques like quenching from the vapor or the melt or ion implantation. Preliminary structural studies provide evidence for the existence of these phases and near-edge X-ray absorption and X-ray photoelectron spectroscopy measurements indicate a metallic type of bonding from which compound formation is inferred. The quality of the films is strongly dependent on the conditions of implantation. The maximum superconducting transition temperature attained is about 1.2 K. The upper critical fields have a maximum of 6T. An unusual double transition in the field dependence of resistivity is observed at low temperatures. The effect is very pronounced at compositions near x = 0.5 where the maximum {Tc} occurs. A model is presented to explain this result which invokes the properties of the metastable metallic phases and assumes the formation of more than two such phases in the same sample as the implantation dose increases. The Si-Au interface plays an important role in understanding the model and in interpreting the results of this thesis in general.« less

  13. Observation of topological superconductivity on the surface of an iron-based superconductor

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, Peng; Yaji, Koichiro; Hashimoto, Takahiro

    Topological superconductors are predicted to host exotic Majorana states that obey non-Abelian statistics and can be used to implement a topological quantum computer. Most of the proposed topological superconductors are realized in difficult-to-fabricate heterostructures at very low temperatures. By using high-resolution spin-resolved and angle-resolved photoelectron spectroscopy, we find that the iron-based superconductor FeTe 1–xSe x (x = 0.45; superconducting transition temperature T c = 14.5 kelvin) hosts Dirac-cone–type spin-helical surface states at the Fermi level; the surface states exhibit an s-wave superconducting gap below T c. Thus, our study shows that the surface states of FeTe 0.55Se 0.45 are topologicallymore » superconducting, providing a simple and possibly high-temperature platform for realizing Majorana states.« less

  14. Observation of topological superconductivity on the surface of an iron-based superconductor

    DOE PAGES

    Zhang, Peng; Yaji, Koichiro; Hashimoto, Takahiro; ...

    2018-03-08

    Topological superconductors are predicted to host exotic Majorana states that obey non-Abelian statistics and can be used to implement a topological quantum computer. Most of the proposed topological superconductors are realized in difficult-to-fabricate heterostructures at very low temperatures. By using high-resolution spin-resolved and angle-resolved photoelectron spectroscopy, we find that the iron-based superconductor FeTe 1–xSe x (x = 0.45; superconducting transition temperature T c = 14.5 kelvin) hosts Dirac-cone–type spin-helical surface states at the Fermi level; the surface states exhibit an s-wave superconducting gap below T c. Thus, our study shows that the surface states of FeTe 0.55Se 0.45 are topologicallymore » superconducting, providing a simple and possibly high-temperature platform for realizing Majorana states.« less

  15. Tuning across the BCS-BEC crossover in superconducting Fe1+ySexTe1-x : An angle-resolved photoemission study

    NASA Astrophysics Data System (ADS)

    Rinott, Shahar; Ribak, Amit; Chashka, Khanan; Randeria, Mohit; Kanigel, Amit

    The crossover from Bardeen-Cooper-Schrieffer (BCS) superconductivity to Bose-Einstein condensation (BEC) was never realized in quantum materials. It is difficult to realize because, unlike in ultra cold atoms, one cannot tune the pairing interaction. We realize the BCS-BEC crossover in a nearly compensated semimetal Fe1+ySexTe1-x by tuning the Fermi energy ɛF via chemical doping, which permits us to systematically change Δ /ɛF from 0 . 16 to 0 . 50 , where Δ is the superconducting (SC) gap. We use angle-resolved photoemission spectroscopy to measure the Fermi energy, the SC gap and characteristic changes in the SC state electronic dispersion as the system evolves from a BCS to a BEC regime. Our results raise important questions about the crossover in multi-band superconductors which go beyond those addressed in the context of cold atoms.

  16. Lighting up superconducting stripes

    NASA Astrophysics Data System (ADS)

    Ergeçen, Emre; Gedik, Nuh

    2018-02-01

    Cuprate superconductors display a plethora of complex phases as a function of temperature and carrier concentration, the understanding of which could provide clues into the mechanism of superconductivity. For example, when about one-eighth of the conduction electrons are removed from the copper oxygen planes in cuprates such as La2‑xBaxCuO4 (LBCO), the doped holes (missing electrons) organize into one-dimensional stripes (1). The bulk superconducting transition temperature (Tc) is greatly reduced, and just above Tc, electrical transport perpendicular to the planes (along the c axis) becomes resistive, but parallel to the copper oxygen planes, resistivity remains zero for a range of temperatures (2). It was proposed a decade ago (3) that this anisotropic behavior is caused by pair density waves (PDWs); superconducting Cooper pairs exist along the stripes within the planes but cannot tunnel to the adjacent layers. On page 575 of this issue, Rajasekaran et al. (4) now report detection of this state in LBCO using nonlinear reflection of high-intensity terahertz (THz) light.

  17. Development of superconducting YBa2Cu3O(x) wires with low resistance electrical contacts

    NASA Technical Reports Server (NTRS)

    Buoncristiani, A. M.; Byvik, C. E.; Caton, R.; Selim, R.; Lee, B. I.; Modi, V.; Sherrill, M.; Leigh, H. D.; Fain, C. C.; Lewis, G.

    1993-01-01

    Materials exhibiting superconductivity above liquid nitrogen temperatures (77 K) will enable new applications of this phenomena. One of the first commercial applications of this technology will be superconducting magnets for medical imaging. However, a large number of aerospace applications of the high temperature superconducting materials have also been identified. These include magnetic suspension and balance of models in wind tunnels and resistanceless leads to anemometers. The development of superconducting wires fabricated from the ceramic materials is critical for these applications. The progress in application of a patented fiber process developed by Clemson University for the fabrication of superconducting wires is reviewed. The effect of particle size and heat treatment on the quality of materials is discussed. Recent advances made at Christopher Newport College in the development of micro-ohm resistance electrical contacts which are capable of carrying the highest reported direct current to this material is presented.

  18. Development of superconducting YBa2Cu3O(x) wires with low resistance electrical contacts

    NASA Astrophysics Data System (ADS)

    Buoncristiani, A. M.; Byvik, C. E.; Caton, R.; Selim, R.; Lee, B. I.; Modi, V.; Sherrill, M.; Leigh, H. D.; Fain, C. C.; Lewis, G.

    Materials exhibiting superconductivity above liquid nitrogen temperatures (77 K) will enable new applications of this phenomena. One of the first commercial applications of this technology will be superconducting magnets for medical imaging. However, a large number of aerospace applications of the high temperature superconducting materials have also been identified. These include magnetic suspension and balance of models in wind tunnels and resistanceless leads to anemometers. The development of superconducting wires fabricated from the ceramic materials is critical for these applications. The progress in application of a patented fiber process developed by Clemson University for the fabrication of superconducting wires is reviewed. The effect of particle size and heat treatment on the quality of materials is discussed. Recent advances made at Christopher Newport College in the development of micro-ohm resistance electrical contacts which are capable of carrying the highest reported direct current to this material is presented.

  19. A study of spin fluctuations and superconductivity in the iron pnictides

    NASA Astrophysics Data System (ADS)

    Gooch, Melissa J.

    In early 2008, Hosono's group published results of their discovery of an iron-based layered superconductor, LaFeAsO1-- xFx (x = 0.11). Their discovery gave new life to condensed matter research, being that it was the first high Tc layered superconductor since the discovery of the cuprates. Within only- a few short months, three additional structures were added to the iron pnictide family. The pnictides share a similar layered structure to that of the cuprates, which sparked questions about what role charge doping plays in the superconductivity of the pnictides. An ideal candidate to investigate the physical properties as the doping varies is KxSr1--xFe 2As2, which forms a solid solution for 0 ≤ x ≤ 1. Upper critical fields, HC2, were investigated for select polycrystalline samples and revealed high HC 2 varies upwards to ˜ 100 T. Pressure measurements revealed similar doping dependent pressure coefficients to the cuprates; however, for the cuprates there is a well understood charge transfer that is induced with the application of pressure. This is not the case for the pnictides where a suppression of the magnetic fluctuations is seen. Resistivity and thermoelectric power measurements provide evidence for a possible hidden magnetic quantum critical point (MQCP). The effects of the MQCP extend up to ˜ 150K and were also seen for K xBa1--xFe 2As2, this suggests that magnetic spin fluctuations may play a crucial role in superconductivity for the pnictides. Superconductivity was seen for KFe2As2, as well as RbFe2As 2, CsFe2As2, and the metastable NaFe2As 2. LiFeAs is an undoped stoichiometric superconductor with a T c = 18 K, but it has been suggested that superconductivity arises from a Li deficiency. These conflicting statements prompted further investigation into the physical properties of LiFeAs. In conclusion, magnetic fluctuations may play a. key role in superconductivity of the pnictides and not charge doping.

  20. Ultrasensitive Superconducting Transition Edge Sensors Based On Electron-Phonon Decoupling

    NASA Technical Reports Server (NTRS)

    Jethava, Nikhil; Chervenak, James; Brown, Ari-David; Benford, Dominic; Kletetschka, Gunther; Mikula, Vilem; U-yen, Kongpop

    2011-01-01

    We have successfully fabricated the superconducting transition edge sensor (TES), bolometer technology that centers on the use of electron-phonon decoupling (EPD) to thermally isolate the bolometer. Along with material characterization for large format antenna coupled bolometer arrays, we present the initial test results of bolometer based on EPD designed for THz detection. We have selected a design approach that separates the two functions of photon absorption and temperature measurement, allowing separate optimization of the performance of each element. We have integrated Molybdenum/Gold (Mo/Au) bilayer TES and ion assisted thermally evaporated (IAE) Bismuth (Bi) films as radiation absorber coupled to a low-loss microstripline from Niobium (Nb) ground plane to a twin-slot antenna structure. The thermal conductance and the time constant of these devices have been measured, and are consistent with our calculations. The device exhibits a single time constant at 0.1 K of approx.160 IlS, which is compatible with readout by a high-bandwidth single SQUID or a time domain SQUID multiplexer. The effects of thermal conductance and electrothermal feedback are major determinants of the time constant, but the electronic heat capacity also plays a major role. The NEP achieved in the device described above is 2.5x10(exp -17)W(gamma)Hz. Our plan is to demonstrate a reduction of the volume in the superconducting element to 5 microns x 5 microns in films of half the thickness at Tc = 60mK. By calculation, this new geometry corresponds to an NEP reduction of two orders of magnitude to 2.5x10(exp -19)W/(gamma)Hz, with a time constant of 130/ls.

  1. Doping - dependent anisotropy of the superconducting gap in underdoped pnictide superconductors

    NASA Astrophysics Data System (ADS)

    Prozorov, Ruslan

    2012-02-01

    The in-plane London penetration depth, δλ(T), was studied in single crystals of Ba1-xKxFe2As2 (``Ba122") and Ca10(Pt3As8)[(Fe1-xPtx)2As2]5 (``10-3-8"). Whereas in Ba122 magnetism and superconductivity coexist in the underdoped regime, the 10-3-8 compound exhibits a clear separation of two order parameters. By comparing the results obtained in these two systems, we could study general features of the superconducting gap structure as function of doping in the underdoped regime. Similar to all other pnictides, the low-temperature variation of London penetration depth exhibits a power-law behavior, δλ(T)= AT^n, in both systems. Moving towards the underdoped edge of the superconducting dome, the exponent n decreases well below scattering - limited value of n=2 and, at the same time, the pre-factor A increases. Both trends indicate an increasing anisotropy of the superconducting gap in more underdoped compounds. These and previous results suggest that the development of the superconducting gap anisotropy towards the underdoped edge of the superconducting dome is an intrinsic property of iron pnictides, similar to the known tendency on the overdoped side where magnetism and superconductivity do not interfere.[4pt] In collboration with M.A. Tanatar, H. Kim, The Ames Laboratory; Bing Shen, Hai-Hu Wen, Nanjing University; and N. Ni, R.J. Cava, Princeton University.

  2. Point-contact spectroscopy of the iron chalcogenide superconductors: interplay between multiband superconductivity and magnetism

    NASA Astrophysics Data System (ADS)

    Park, Wan Kyu; Hunt, C. R.; Arham, H. Z.; Lu, X.; Greene, L. H.; Xu, Z. J.; Wen, J. S.; Lin, Z. W.; Li, Q.; Gu, G.

    2010-03-01

    We report point-contact conductance measurements on the iron chalcogenide superconductors, Fe1+yTe1-xSex. The excess Fe atoms are known to occupy the interstitial sites in the Te-Se plane, affecting the superconductivity as well as the magnetism in this family. For a compound having nominal values of y=0 and x=0.45, a single superconducting transition is observed at 14.2 K. In the superconducting state, BTK-like double peak structures due to Andreev reflection are observed. However, the peak position of different point contacts falls to a wide voltage range, 1.5 -- 4 mV. Additional multiple humps are sometimes observed in a much higher bias voltage range, 8 -- 15 mV. Most strikingly, conductance enhancement persists well above Tc. We will present possible interpretations of these experimental observations in terms of multiband superconductivity and the interplay between superconductivity and magnetism.

  3. Contrast agent choice for intravenous coronary angiography

    NASA Astrophysics Data System (ADS)

    Zeman, H. D.; Siddons, D. P.

    1990-05-01

    The screening of the general population for coronary artery disease would be practical if a method existed for visualizing the extent of occlusion after an intravenous injection of contrast agent. Measurements performed with monochromatic synchrotron radiation X-rays and an iodine-containing contrast agent at the Stanford Synchrotron Radiation Laboratory have shown that such an intravenous angiography procedure would be possible with an adequately intense monochromatic X-ray source. Because of the size and cost of synchrotron radiation facilities it would be desirable to make the most efficient use of the intensity available, while reducing as much as possible the radiation dose experienced by the patient. By choosing contrast agents containing elements with a higher atomic number than iodine, it is possible to both improve the image quality and reduce the patient radiation dose, while using the same synchrotron radiation source. By using Si monochromator crystals with a small mosaic spread, it is possible to increase the X-ray flux available for imaging by over an order of magnitude, without any changes in the storage ring or wiggler magnet. The most critical imaging task for intravenous coronary angiography utilizing synchrotron radiation X-rays is visualizing a coronary artery through the left ventricle or aorta which also contain contrast agent. Calculations have been made of the signal to noise ratio expected for this imaging task for various contrast agents with atomic numbers between that of iodine and bismuth. The X-ray energy spectrum of the X-17 superconduction wiggler beam line at the National Synchrotron Light Source at Brookhaven National Laboratory has been used for these calculations. Both perfect Si crystals and Si crystals with a small mosaic spread are considered as monochromators. Contrast agents containing Gd or Yb seem to have about the optimal calculated signal to noise ratio. Gd-DTPA is already approved for use as a contrast agent for

  4. Interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator

    NASA Astrophysics Data System (ADS)

    Manna, S.; Kamlapure, A.; Cornils, L.; Hänke, T.; Hedegaard, E. M. J.; Bremholm, M.; Iversen, B. B.; Hofmann, Ph.; Wiebe, J.; Wiesendanger, R.

    2017-01-01

    The discovery of high-temperature superconductivity in Fe-based compounds triggered numerous investigations on the interplay between superconductivity and magnetism, and on the enhancement of transition temperatures through interface effects. It is widely believed that the emergence of optimal superconductivity is intimately linked to the suppression of long-range antiferromagnetic (AFM) order, although the exact microscopic picture remains elusive because of the lack of atomically resolved data. Here we present spin-polarized scanning tunnelling spectroscopy of ultrathin FeTe1-xSex (x=0, 0.5) films on bulk topological insulators. Surprisingly, we find an energy gap at the Fermi level, indicating superconducting correlations up to Tc~6 K for one unit cell FeTe grown on Bi2Te3, in contrast to the non-superconducting bulk FeTe. The gap spatially coexists with bi-collinear AFM order. This finding opens perspectives for theoretical studies of competing orders in Fe-based superconductors and for experimental investigations of exotic phases in superconducting layers on topological insulators.

  5. Preparation and composition of superconducting copper oxides based on Ga-O layers

    DOEpatents

    Dabrowski, Bogdan; Vaughey, J. T.; Poeppelmeier, Kenneth R.

    1994-01-01

    A high temperature superconducting material with the general formula GaSr.sub.2 Ln.sub.1-x MxCu.sub.2 O.sub.7.+-.w wherein Ln is selected from the group consisting of La, Ce, Pt, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Y and M is selected from the group consisting of Ca and Sr, 0.2.ltoreq.x.ltoreq.0.4 and w is a small fraction of one. A method of preparing this high temperature superconducting material is provided which includes heating and cooling a mixture to produce a crystalline material which is subsequently fired, ground and annealed at high pressure and temperature in oxygen to establish superconductivity.

  6. Synthesis from separate oxide targets of high quality La2-xSrxCuO4 thin films and dependence with doping of their superconducting transition width

    NASA Astrophysics Data System (ADS)

    Cotón, N.; Mercey, B.; Mosqueira, J.; Ramallo, M. V.; Vidal, F.

    2013-07-01

    A series of superconducting La2-xSrxCuO4 thin films, with 0.09 ≲ x ≲ 0.22, is grown over (100)SrTiO3 substrates by means of a novel pulsed laser deposition method devised to increase the homogeneity and control of doping. We employ two separate parent oxide targets that receive ablation shots at arbitrary computer-controlled relative rates, instead of the conventional procedure that uses a single target whose doping determines the one of the film. We characterize the films both through conventional techniques (XRD, SEM, AFM and EDX) and by measuring their superconducting transition with a high-sensitivity SQUID magnetometer. The latter allows one to determine not only their average critical temperatures {\\bar {T}}_{{c}}(x) but also their dispersions due to inhomogeneities, ΔTc(x). For {\\bar {T}}_{{c}}(x) we obtain the conventional parabolic law centered at x = 0.16, plus a Gaussian depression near x = 1/8 with a {\\bar {T}}_{{c}}-height of about 5 K and x-width about 0.03. For ΔTc(x) we obtain, for all the dopings, values among the lowest reported up to now for La2-xSrxCuO4. The ΔTc(x) dependence can be explained in terms of the unavoidable randomness of the positioning of the Sr ions (the so-called intrinsic chemical inhomogeneity) and a separate residual Tc-inhomogeneity contribution of the order of 0.5 K, this last associated with the samples’ structural inhomogeneities and films’ substrate.

  7. Synthesis of Y1BaCu3O(x) superconducting powders by intermediate phase reactions

    NASA Technical Reports Server (NTRS)

    Moure, C.; Fernandez, J. F.; Tartaj, J.; Recio, P.; Duran, P.

    1991-01-01

    A procedure for synthesizing Y1Ba2Cu3O(x) by solid state reactions was developed. The method is based on the use of barium compounds, previously synthesized, as intermediate phases for the process. The reaction kinetics of this procedure were established between 860 C and 920 C. The crystal structure and the presence of second phases were studied by means of XRD. The sintering behavior and ceramic parameters were also determined. The orthorhombic type-I structure was obtained on the synthesized bodies after a cooling cycle in an air atmosphere. Superconducting transition took place at 91 K. Sintering densities higher than 95 percent D sub th were attained at temperatures below 940 C.

  8. The new HMI beamline MAGS: an instrument for hard X-ray diffraction at BESSY.

    PubMed

    Dudzik, Esther; Feyerherm, Ralf; Diete, Wolfgang; Signorato, Riccardo; Zilkens, Christopher

    2006-11-01

    The Hahn-Meitner-Institute Berlin is operating the new hard X-ray diffraction beamline MAGS at the Berlin synchrotron radiation source BESSY. The beamline is intended to complement the existing neutron instrumentation at the Berlin Neutron Scattering Centre. The new beamline uses a 7 T multipole wiggler to produce photon fluxes in the 10(11)-10(12) photons s(-1) (100 mA)(-1) (0.1% bandwidth)(-1) range at energies from 4 to 30 keV at the experiment. It has active bendable optics to provide flexible horizontal and vertical focusing and to compensate the large heat load from the wiggler source. The experimental end-station consists of a six-circle Huber diffractometer which can be used with an additional (polarization) analyser and different sample environments. The beamline is intended for single-crystal diffraction and resonant magnetic scattering experiments for the study of ordering phenomena, phase transitions and materials science.

  9. Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces

    PubMed Central

    Misawa, Takahiro; Nomura, Yusuke; Biermann, Silke; Imada, Masatoshi

    2016-01-01

    Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2−xSrxCuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices. PMID:27482542

  10. Theoretical studies of superconductivity in doped BaCoSO

    NASA Astrophysics Data System (ADS)

    Qin, Shengshan; Li, Yinxiang; Zhang, Qiang; Le, Congcong; Hu, Jiangping

    2018-06-01

    We investigate superconductivity that may exist in the doped BaCoSO, a multi-orbital Mott insulator with a strong antiferromagnetic ground state. The superconductivity is studied in both t-J type and Hubbard type multi-orbital models by mean field approach and random phase approximation (RPA) analysis. Even if there is no C 4 rotational symmetry, it is found that the system still carries a d-wave like pairing symmetry state with gapless nodes and sign changed superconducting order parameters on Fermi surfaces. The results are largely doping insensitive. In this superconducting state, the three {t_{{2_g}}} orbitals have very different superconducting form factors in momentum space. In particular, the intra-orbital pairing of the {d_{{x^2} - {y^2}}} orbital has an s-wave like pairing form factor. The two methods also predict very different pairing strength on different parts of Fermi surfaces. These results suggest that BaCoSO and related materials can be a new ground to test and establish fundamental principles for unconventional high temperature superconductivity.

  11. Superconductivity and ferromagnetism in Pd doped Y9Co7

    NASA Astrophysics Data System (ADS)

    Klimczuk, Tomasz; Strychalska, Judyta; Thompson, Joe; Cava, Robert

    The ferromagnetic superconductor Y9Co7 was chemically doped with Pd in an attempt to form Y9Co7-xPdx for 0<x<0.4. The lattice parameter a does not depend on x; whereas, c increases with increasing Pd content up to x = 0.2, which turned out to be the palladium solubility limit. Superconductivity (Tsc = 2.4 K) and ferromagnetism (TC = 4.5 K) were observed only for the parent Y9Co7 compound. For the lowest tested Pd doping level (x =0.05), strong enhancement of ferromagnetism is observed (TC = 9.35 K), but superconductivity is not seen above 1.8K. The Curie temperature rapidly increases from 4.5 K to about 10 K for a Pd concentration x =0.1 and remains almost unchanged for Y9Co6.8Pd0.2. Project was financially supported by the National Science Centre (Poland) Grant (DEC-2012/07/E/ST3/00584).

  12. Superconductivity and fusion energy—the inseparable companions

    NASA Astrophysics Data System (ADS)

    Bruzzone, Pierluigi

    2015-02-01

    Although superconductivity will never produce energy by itself, it plays an important role in energy-related applications both because of its saving potential (e.g., power transmission lines and generators), and its role as an enabling technology (e.g., for nuclear fusion energy). The superconducting magnet’s need for plasma confinement has been recognized since the early development of fusion devices. As long as the research and development of plasma burning was carried out on pulsed devices, the technology of superconducting fusion magnets was aimed at demonstrations of feasibility. In the latest generation of plasma devices, which are larger and have longer confinement times, the superconducting coils are a key enabling technology. The cost of a superconducting magnet system is a major portion of the overall cost of a fusion plant and deserves significant attention in the long-term planning of electricity supply; only cheap superconducting magnets will help fusion get to the energy market. In this paper, the technology challenges and design approaches for fusion magnets are briefly reviewed for past, present, and future projects, from the early superconducting tokamaks in the 1970s, to the current ITER (International Thermonuclear Experimental Reactor) and W7-X projects and future DEMO (Demonstration Reactor) projects. The associated cryogenic technology is also reviewed: 4.2 K helium baths, superfluid baths, forced-flow supercritical helium, and helium-free designs. Open issues and risk mitigation are discussed in terms of reliability, technology, and cost.

  13. Synthesis of AlFeCuCrMg{sub x} (x = 0, 0.5, 1, 1.7) alloy powders by mechanical alloying

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Maulik, Ornov; Kumar, Vinod, E-mail: vkt.meta@mnit.ac.in; Adjunct Faculty, Materials Research Centre, Malaviya National Institute of Technology, Jaipur 302017

    2015-12-15

    Novel AlFeCuCrMg{sub x} (x = 0, 0.5, 1, 1.7 mol) high-entropy alloys (HEAs) were synthesized by mechanical alloying. The effect of Mg content on the phase evolution of HEAs was investigated using X-Ray diffractometry (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) pattern analysis. The particle morphology and composition of HEAs were investigated by scanning electron microscopy (SEM). Thermodynamic parameters were calculated and analyzed to explain the formation of a solid solution. XRD analysis revealed BCC as major phase and FCC as a minor phase in as-milled AlFeCuCr and AlFeCuCrMg{sub 0.5} HEAs. Also, XRD analysis of as-milledmore » AlFeCuCrMg, AlFeCuCrMg{sub 1.7} confirmed the formation of two BCC phases (BCC 1 and BCC 2). TEM–SAED analysis of AlFeCuCrMg{sub x} HEAs concurred with XRD results. Microstructural features and mechanism for solid solution formation have been conferred in detail. Phase formation of the present HEAs has been correlated with calculated thermodynamic parameters. Differential thermal analysis (TGA-DTA) of these alloys confirmed that there is no substantial phase change up to 500 °C. - Highlights: • Novel AlFeCuCrMg{sub x} (x = 0, 0.5, 1, 1.7) HEAs were prepared by mechanical alloying. • Phase evolution and lattice parameter were studied by X-Ray Diffraction. • Crystallite size and lattice microstrain calculated failed to obey the Williamson–Hall method. • Criterions for formation of simple solid solution were compared to the thermodynamic parameters of the present HEAs. • Increase in the Mg concentration in AlMg{sub x}FeCuCr (x = 0, 0.5, 1, 1.7) HEAs supports the formation of BCC phase.« less

  14. Evidence for a 17-day periodicity from Cyg-X-3

    NASA Technical Reports Server (NTRS)

    Holt, S. S.; Boldt, E. A.; Serlemitsos, P. J.; Kaluzienski, L. J.; Pravdo, S. H.; Peacock, A.; Elvis, M.; Watson, M. G.; Pounds, K. A.

    1975-01-01

    Data taken from the Ariel-5 All Sky Monitor and the Ariel-5 Sky Survey Experiment are analyzed. It is hypothesized that a periodicity of 17d is characteristic of CygX-3. Results of the analysis are given.

  15. Synergistic effect of heat shock protein 90 inhibitor, 17-allylamino-17-demethoxygeldanamycin and X-rays, but not carbon-ion beams, on lethality in human oral squamous cell carcinoma cells

    PubMed Central

    Musha, Atsushi; Yoshida, Yukari; Takahashi, Takeo; Ando, Koichi; Funayama, Tomoo; Kobayashi, Yasuhiko; Negishi, Akihide; Yokoo, Satoshi; Nakano, Takashi

    2012-01-01

    The purpose of this study is to clarify the effect of a heat shock protein 90 inhibitor, 17-allylamino-17-demethoxygeldanamycin (17-AAG), in combination with X-rays or carbon-ion beams on cell killing in human oral squamous cell carcinoma LMF4 cells. Cell survival was measured by colony formation assay. Cell-cycle distribution was analyzed by flow cytometry. Expression of DNA repair-related proteins was investigated by western blotting. The results showed 17-AAG to have synergistic effects on cell lethality with X-rays, but not with carbon-ion beams. The 17-AAG decreased G2/M arrest induced by X-rays, but not by carbon-ion beams. Both X-ray and carbon-ion irradiation up-regulated expression of non-homologous end-joining-associated proteins, Ku70 and Ku80, but 17-AAG inhibited only X-ray-induced up-regulation of these proteins. These results show that 17-AAG with X-rays releases G2/M phase arrest; cells carrying misrepaired DNA damage then move on to the G1 phase. We demonstrate, for the first time, that the radiosensitization effect of 17-AAG is not seen with carbon-ion beams because 17-AAG does not affect these changes. PMID:22843619

  16. Processing study of high temperature superconducting Y-Ba-Cu-O ceramics

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Safari, A.; Wachtman, J.B. Jr.; Ward, C.

    Processing of the YBa{sub 2}Cu{sub 3}O{sub 6+x} superconducting phase by employing different precursor powder preparation techniques (ball milling, attrition milling) and samples formed by different sintering conditions are discussed. The superconducting phase has been identified by powder x-ray diffraction. The effect of different powder processing and pressing conditions on the structure, density, resistivity and a.c. magnetic susceptibility were studied. Though there is no variation in T{sub c} for all the samples, attrition milled samples show a much lower resistance and less temperature dependence compared to ball milled samples above the superconducting transition temperature up to room temperature. Ball milled samplesmore » were loosely packed with more voids compared to attrition milled samples which are more densely packed with a needle-like structure.« less

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

  18. Infrared Quenched Photoinduced Superconductivity

    NASA Astrophysics Data System (ADS)

    Federici, J. F.; Chew, D.; Guttierez-Solana, J.; Molina, G.; Savin, W.; Wilber, W.

    1996-03-01

    Persistant photoconductivity (PPC) and photoinduced superconductivity (PISC) in oxygen deficient YBa_2Cu_3O_6+x have received recent attention. It has been suggested that oxygen vacancy defects play an important role in the PISC/PPC mechanism.(J. F. Federici, D. Chew, B. Welker, W. Savin, J. Gutierrez-Solana, and T. Fink, Phys. Rev. B), December 1995 Supported by National Science Foundation In this model, defects trap photogenerated electrons so that electron-hole recombination can not occur thereby allowing photogenerated holes to contribute to the carrier density. Nominally, the photoinduced state is long-lived, persisting for days at low temperature. Experiment results will be presented demonstrating that the photoinduced superconductivity state can be quenched using infrared radiation. Implications for the validity of the PISC/PCC defect model will be discussed.

  19. Magnetic properties and microstructure of melt-spun Ce17Fe78-xB6Hfx (x = 0-1.0) alloys

    NASA Astrophysics Data System (ADS)

    Jiang, Qingzheng; Zhong, Minglong; Quan, Qichen; Lei, Weikai; Zeng, Qingwen; Hu, Yongfeng; Xu, Yaping; Hu, Xianjun; Zhang, Lili; Liu, Renhui; Ma, Shengcan; Zhong, Zhenchen

    2017-12-01

    Ce17Fe78-xB6Hfx (x = 0-1.0) alloys were fabricated by a melt-spinning technique in order to study their magnetic properties and microstructure. Magnetic investigations of Ce17Fe78-xB6Hfx (x = 0-1.0) alloys show that the room-temperature coercivity increases linearly from 352 kA/m at x = 0 to 420 kA/m at x = 1.0. The Curie temperature (Tc) decreases monotonically from 424.5 K to 409.1 K. The Ce L3-edge X-ray absorption near edge structure (XANES) spectrums reveal that there is more Ce4+ in ribbons under total electron yield (TEY) than fluorescence yield (FY). Hf addition has no effect on the weight of Ce3+ and Ce4+ in CeFeB-based alloys. The grain refinement and microstructure uniformity are essential for improving the magnetic properties of Hf-doped alloys. This paper may shed light on the further development of the Ce-based magnets and offer a feasible way for using the rare earth resources effectively.

  20. Elastic Properties of Synthetic Pyrope (Mg3Al2Si3O12) to 9 GPa and 1000°C

    NASA Astrophysics Data System (ADS)

    Gwanmesia, G. D.; Zhang, J.; Li, B.; Darling, K.; Kung, J.; Neuville, D.; Raterron, P.; Sullivan, S.; Liebermann, R. C.

    2003-04-01

    We have measured the elastic wave velocities of polycrystalline pyrope (Mg_3Al_2Si_3O12) to 9 GPa and 1000^oC by ultrasonic interferometry, combined with in-situ synchrotron x-ray diffraction and imaging techniques. Fine-grained polycrystalline specimens (99.5% of theoretical density) were hot-pressed from a homogeneous glass starting material in the USSA-2000 apparatus at Stony Brook; the physical properties of the recovered specimens were characterized with density measurements, x-ray diffraction and transmission electron microscopy. Bench-top elastic wave velocities were in excellent agreement with the isotropic averages calculated from single-crystal elastic moduli of Leitner et al. (1980) by the Hashin-Shtrikman method. Travel times of acoustic compressional (P) and shear (S) waves, specimen lengths and PVT equations of state for the specimen and a NaCl standard were measured to 9 GPa and 1000^oC in a DIA-type high pressure apparatus (SAM-85), installed on the superconducting wiggler beamline (X17B) at the National Synchrotron Light Source of the Brookhaven National Laboratory. These data enabled us to determine the pressure and temperature derivatives of the elastic wave velocities and moduli for isotropic pyrope. We compare our new values with those of previous investigators and discuss the implications of these data for interpreting the seismic velocity gradients in the transition zone of the Earth's mantle.

  1. Observation of topological superconductivity on the surface of an iron-based superconductor.

    PubMed

    Zhang, Peng; Yaji, Koichiro; Hashimoto, Takahiro; Ota, Yuichi; Kondo, Takeshi; Okazaki, Kozo; Wang, Zhijun; Wen, Jinsheng; Gu, G D; Ding, Hong; Shin, Shik

    2018-04-13

    Topological superconductors are predicted to host exotic Majorana states that obey non-Abelian statistics and can be used to implement a topological quantum computer. Most of the proposed topological superconductors are realized in difficult-to-fabricate heterostructures at very low temperatures. By using high-resolution spin-resolved and angle-resolved photoelectron spectroscopy, we find that the iron-based superconductor FeTe 1- x Se x ( x = 0.45; superconducting transition temperature T c = 14.5 kelvin) hosts Dirac-cone-type spin-helical surface states at the Fermi level; the surface states exhibit an s-wave superconducting gap below T c Our study shows that the surface states of FeTe 0.55 Se 0.45 are topologically superconducting, providing a simple and possibly high-temperature platform for realizing Majorana states. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  2. Interface-induced superconductivity at ∼25 K at ambient pressure in undoped CaFe2As2 single crystals

    PubMed Central

    Zhao, Kui; Lv, Bing; Deng, Liangzi; Huyan, Shu-Yuan; Xue, Yu-Yi; Chu, Ching-Wu

    2016-01-01

    Superconductivity has been reversibly induced/suppressed in undoped CaFe2As2 (Ca122) single crystals through proper thermal treatments, with Tc at ∼25 K at ambient pressure and up to 30 K at 1.7 GPa. We found that Ca122 can be stabilized in two distinct tetragonal (T) phases at room temperature and ambient pressure: PI with a nonmagnetic collapsed tetragonal (cT) phase at low temperature and PII with an antiferromagnetic orthorhombic (O) phase at low temperature, depending on the low-temperature annealing condition. Neither phase at ambient pressure is superconducting down to 2 K. However, systematic annealing for different time periods at 350 °C on the as-synthesized crystals, which were obtained by quenching the crystal ingot from 850 °C, reveals the emergence of superconductivity over a narrow time window. Whereas the onset Tc is insensitive to the anneal time, the superconductive volume fraction evolves with the time in a dome-shaped fashion. Detailed X-ray diffraction profile analyses further reveal mesoscopically stacked layers of the PI and the PII phases. The deduced interface density correlates well with the superconducting volume measured. The transport anomalies of the T–cT transition, which is sensitive to lattice strain, and the T–O transition, which is associated with the spin-density-wave (SDW) transition, are gradually suppressed over the superconductive region, presumably due to the interface interactions between the nonmagnetic metallic cT phase and the antiferromagnetic O phase. The results provide the most direct evidence to date for interface-enhanced superconductivity in undoped Ca122, consistent with the recent theoretical prediction. PMID:27799564

  3. Spin glass freezing and superconductivity in YBa2(Cu(1-x)Fe(x))3O7 alloys

    NASA Technical Reports Server (NTRS)

    Mirebeau, I.; Hennion, M.; Dianoux, J.; Caignaert, V.; Phillips, T. E.; Moorjani, K.

    1991-01-01

    The dynamics were studied of the iron spins in superconducting YBa2(Cu(0.94)Fe(0.06))3O7 by neutron time of flight measurements. Two samples were studied with slightly different characteristics, as shown by resistivity and neutron diffraction measurements. The same dynamical anomalies are observed by neutrons in both samples. Differences appear qualitative but not quantitative. In the whole temperature range, the q-dependence of the magnetic intensity mainly reflects the magnetic form factor of iron which shows that the iron spins are almost uncorrelated. The elastic and quasielastic intensities strongly vary with temperature. A spin glass like freezing is revealed at low temperature by a sharp decrease of the quasielastic intensity, an increase of the 'elastic' or resolution limited intensity and a minimum in the quasielastic width. The freezing temperature (T sub f - 18 K) corresponds to that already determined by a magnetic splitting in Mossbauer experiments. Above T sub f, the relaxation of the iron spins in the paramagnetic state is modified by the occurrence of superconductivity. An increase was observed of the quasielastic intensity and of the quasielastic width at the superconducting transition.

  4. Pressure-temperature phase diagrams of CaK ( Fe 1 – x Ni x ) 4 As 4 superconductors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Xiang, Li; Meier, William R.; Xu, Mingyu

    Here, the pressure dependence of the magnetic and superconducting transitions and that of the superconducting upper critical field are reported for CaK(Fe 1–xNi x) 4As 4, the first example of an Fe-based superconductor with spin-vortex-crystal-type magnetic ordering. Resistance measurements were performed on single crystals with two substitution levels (x = 0.033,0.050) under hydrostatic pressures up to 5.12 GPa and in magnetic fields up to 9 T. Our results show that, for both compositions, magnetic transition temperatures T N are suppressed upon applying pressure; the superconducting transition temperatures T c are suppressed by pressure as well, except for x = 0.050more » in the pressure region where T N and T c cross. Furthermore, the pressure associated with the crossing of the T N and T c lines also coincides with a minimum in the normalized slope of the superconducting upper critical field, consistent with a likely Fermi-surface reconstruction associated with the loss of magnetic ordering. Lastly, at p ~ 4 GPa, both Ni-substituted CaK(Fe 1–xNi x) 4As 4 samples likely go through a half-collapsed-tetragonal phase transition, similar to the parent compound CaKFe 4As 4.« less

  5. Pressure-temperature phase diagrams of CaK ( Fe 1 – x Ni x ) 4 As 4 superconductors

    DOE PAGES

    Xiang, Li; Meier, William R.; Xu, Mingyu; ...

    2018-05-22

    Here, the pressure dependence of the magnetic and superconducting transitions and that of the superconducting upper critical field are reported for CaK(Fe 1–xNi x) 4As 4, the first example of an Fe-based superconductor with spin-vortex-crystal-type magnetic ordering. Resistance measurements were performed on single crystals with two substitution levels (x = 0.033,0.050) under hydrostatic pressures up to 5.12 GPa and in magnetic fields up to 9 T. Our results show that, for both compositions, magnetic transition temperatures T N are suppressed upon applying pressure; the superconducting transition temperatures T c are suppressed by pressure as well, except for x = 0.050more » in the pressure region where T N and T c cross. Furthermore, the pressure associated with the crossing of the T N and T c lines also coincides with a minimum in the normalized slope of the superconducting upper critical field, consistent with a likely Fermi-surface reconstruction associated with the loss of magnetic ordering. Lastly, at p ~ 4 GPa, both Ni-substituted CaK(Fe 1–xNi x) 4As 4 samples likely go through a half-collapsed-tetragonal phase transition, similar to the parent compound CaKFe 4As 4.« less

  6. Doping evolution of the anisotropic upper critical fields in the iron-based superconductor Ba 1-xK xFe 2As 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tanatar, Makariy A.; Liu, Yong; Jaroszynski, J.

    In-plane resistivity measurements as a function of temperature and magnetic field up to 35 T with precise orientation within the crystallographic ac plane were used to study the upper critical field H c2 of the hole-doped iron-based superconductor Ba 1–xK xFe 2As 2. Compositions of the samples studied spanned from under- doped x=0.17 (T c=12 K) and x=0.22 (T c=20 K), both in the coexistence range of stripe magnetism and superconductivity, through optimal doping x=0.39 (T c=38.4 K) and x=0.47 (T c=37.2 K), to overdoped x=0.65 (T c=22 K) and x=0.83 (T c=10 K). Here, we find notable doping asymmetrymore » of the shapes of the anisotropic H c2(T), suggesting the important role of paramagnetic limiting effects in the H∥a configuration in overdoped compositions and multiband effects in underdoped compositions.« less

  7. Doping evolution of the anisotropic upper critical fields in the iron-based superconductor Ba 1-xK xFe 2As 2

    DOE PAGES

    Tanatar, Makariy A.; Liu, Yong; Jaroszynski, J.; ...

    2017-11-14

    In-plane resistivity measurements as a function of temperature and magnetic field up to 35 T with precise orientation within the crystallographic ac plane were used to study the upper critical field H c2 of the hole-doped iron-based superconductor Ba 1–xK xFe 2As 2. Compositions of the samples studied spanned from under- doped x=0.17 (T c=12 K) and x=0.22 (T c=20 K), both in the coexistence range of stripe magnetism and superconductivity, through optimal doping x=0.39 (T c=38.4 K) and x=0.47 (T c=37.2 K), to overdoped x=0.65 (T c=22 K) and x=0.83 (T c=10 K). Here, we find notable doping asymmetrymore » of the shapes of the anisotropic H c2(T), suggesting the important role of paramagnetic limiting effects in the H∥a configuration in overdoped compositions and multiband effects in underdoped compositions.« less

  8. Stability of an emittance-dominated sheet-electron beam in planar wiggler and periodic permanent magnet structures with natural focusing

    NASA Astrophysics Data System (ADS)

    Carlsten, B. E.; Earley, L. M.; Krawczyk, F. L.; Russell, S. J.; Potter, J. M.; Ferguson, P.; Humphries, S.

    2005-06-01

    A sheet-beam traveling-wave amplifier has been proposed as a high-power generator of rf from 95 to 300 GHz, using a microfabricated rf slow-wave structure [Carlsten et al., IEEE Trans. Plasma Sci. 33, 85 (2005), ITPSBD, 0093-3813, 10.1109/TPS.2004.841172], for emerging radar and communications applications. The planar geometry of microfabrication technologies matches well with the nearly planar geometry of a sheet beam, and the greater allowable beam current leads to high-peak power, high-average power, and wide bandwidths. Simulations of nominal designs using a vane-loaded waveguide as the slow-wave structure have indicated gains in excess of 1 dB/mm, with extraction efficiencies greater than 20% at 95 GHz with a 120-kV, 20-A electron beam. We have identified stable sheet-beam formation and transport as the key enabling technology for this type of device. In this paper, we describe sheet-beam transport, for both wiggler and periodic permanent magnet (PPM) magnetic field configurations, with natural (or single-plane) focusing. For emittance-dominated transport, the transverse equation of motion reduces to a Mathieu equation, and to a modified Mathieu equation for a space-charge dominated beam. The space-charge dominated beam has less beam envelope ripple than an emittance-dominated beam, but they have similar stability thresholds (defined by where the beam ripple continues to grow without bound along the transport line), consistent with the threshold predicted by the Mathieu equation. Design limits are derived for an emittance-dominated beam based on the Mathieu stability threshold. The increased beam envelope ripple for emittance-dominated transport may impact these design limits, for some transport requirements. The stability of transport in a wiggler field is additionally compromised by the beam’s increased transverse motion. Stable sheet-beam transport with natural focusing is shown to be achievable for a 120-kV, 20-A, elliptical beam with a cross section of

  9. ac Modeling and impedance spectrum tests of the superconducting magnetic field coils for the Wendelstein 7-X fusion experiment.

    PubMed

    Ehmler, Hartmut; Köppen, Matthias

    2007-10-01

    The impedance spectrum test was employed for detection of short circuits within Wendelstein 7-X (W7-X) superconducting magnetic field coils. This test is based on measuring the complex impedance over several decades of frequency. The results are compared to predictions of appropriate electrical equivalent circuits of coils in different production states or during cold test. When the equivalent circuit is not too complicated the impedance can be represented by an analytic function. A more detailed analysis is performed with a network simulation code. The overall agreement of measured and calculated or simulated spectra is good. Two types of short circuits which appeared are presented and analyzed. The detection limit of the method is discussed. It is concluded that combined high-voltage ac and low-voltage impedance spectrum tests are ideal means to rule out short circuits in the W7-X coils.

  10. Superconductive wire

    DOEpatents

    Korzekwa, David A.; Bingert, John F.; Peterson, Dean E.; Sheinberg, Haskell

    1995-01-01

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity.

  11. Superconductive wire

    DOEpatents

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

    1995-07-18

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity. 2 figs.

  12. Synchrotron powder X-ray diffraction and structural analysis of Eu0.5La0.5FBiS2-x Se x

    NASA Astrophysics Data System (ADS)

    Nagasaka, K.; Jinno, G.; Miura, O.; Miura, A.; Moriyoshi, C.; Kuroiwa, Y.; Mizuguchi, Y.

    2017-07-01

    Eu0.5La0.5FBiS2-x Se x is a new BiS2-based superconductor system. In Eu0.5La0.5FBiS2-x Se x , electron carriers are doped to the BiS2 layer by the substitution of Eu by La. Bulk superconductivity in this system is induced by increasing the in-plane chemical pressure, which is controlled by the Se concentration (x). In this study, we have analysed the crystal structure of Eu0.5La0.5FBiS2-x Se x using synchrotron powder diffraction and the Rietveld refinement. The precise determination of the structural parameters and thermal factors suggest that the emergence of bulk superconductivity in Eu0.5La0.5FBiS2-x Se x is achieved by the enhanced in-plane chemical pressure and the decrease in in-plane disorder.

  13. Nano Titanium Monoxide Crystals and Unusual Superconductivity at 11 K.

    PubMed

    Xu, Jijian; Wang, Dong; Yao, Heliang; Bu, Kejun; Pan, Jie; He, Jianqiao; Xu, Fangfang; Hong, Zhanglian; Chen, Xiaobo; Huang, Fuqiang

    2018-03-01

    Nano TiO 2 is investigated intensely due to extraordinary photoelectric performances in photocatalysis, new-type solar cells, etc., but only very few synthesis and physical properties have been reported on nanostructured TiO or other low valent titanium-containing oxides. Here, a core-shell nanoparticle made of TiO core covered with a ≈5 nm shell of amorphous TiO 1+ x is newly constructed via a controllable reduction method to synthesize nano TiO core and subsequent soft oxidation to form the shell (TiO 1+ x ). The physical properties measurements of electrical transport and magnetism indicate these TiO@TiO 1+ x nanocrystals are a type-ІІ superconductor of a recorded T c onset = 11 K in the binary Ti-O system. This unusual superconductivity could be attributed to the interfacial effect due to the nearly linear gradient of O/Ti ratio across the outer amorphous layer. This novel synthetic method and enhanced superconductivity could open up possibilities in interface superconductivity of nanostructured composites with well-controlled interfaces. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Spiral magnetic order and pressure-induced superconductivity in transition metal compounds.

    PubMed

    Wang, Yishu; Feng, Yejun; Cheng, J-G; Wu, W; Luo, J L; Rosenbaum, T F

    2016-10-06

    Magnetic and superconducting ground states can compete, cooperate and coexist. MnP provides a compelling and potentially generalizable example of a material where superconductivity and magnetism may be intertwined. Using a synchrotron-based non-resonant X-ray magnetic diffraction technique, we reveal a spiral spin order in MnP and trace its pressure evolution towards superconducting order via measurements in a diamond anvil cell. Judging from the magnetostriction, ordered moments vanish at the quantum phase transition as pressure increases the electron kinetic energy. Spins remain local in the disordered phase, and the promotion of superconductivity is likely to emerge from an enhanced coupling to residual spiral spin fluctuations and their concomitant suppression of phonon-mediated superconductivity. As the pitch of the spiral order varies across the 3d transition metal compounds in the MnP family, the magnetic ground state switches between antiferromagnet and ferromagnet, providing an additional tuning parameter in probing spin-fluctuation-induced superconductivity.

  15. Multigap superconductivity and strong electron-boson coupling in Fe-based superconductors: a point-contact Andreev-reflection study of Ba(Fe(1-x)Co(x))2As2 single crystals.

    PubMed

    Tortello, M; Daghero, D; Ummarino, G A; Stepanov, V A; Jiang, J; Weiss, J D; Hellstrom, E E; Gonnelli, R S

    2010-12-03

    Directional point-contact Andreev-reflection measurements in Ba(Fe(1-x)Co(x))2As2 single crystals (T(c) = 24.5 K) indicate the presence of two superconducting gaps with no line nodes on the Fermi surface. The point-contact Andreev-reflection spectra also feature additional structures related to the electron-boson interaction, from which the characteristic boson energy Ω(b)(T) is obtained, very similar to the spin-resonance energy observed in neutron scattering experiments. Both the gaps and the additional structures can be reproduced within a three-band s ± Eliashberg model by using an electron-boson spectral function peaked at Ω(0) = 12 meV ≃ Ω(b)(0).

  16. Observation of topological superconductivity on the surface of an iron-based superconductor

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Yaji, Koichiro; Hashimoto, Takahiro; Ota, Yuichi; Kondo, Takeshi; Okazaki, Kozo; Wang, Zhijun; Wen, Jinsheng; Gu, G. D.; Ding, Hong; Shin, Shik

    2018-04-01

    Topological superconductors are predicted to host exotic Majorana states that obey non-Abelian statistics and can be used to implement a topological quantum computer. Most of the proposed topological superconductors are realized in difficult-to-fabricate heterostructures at very low temperatures. By using high-resolution spin-resolved and angle-resolved photoelectron spectroscopy, we find that the iron-based superconductor FeTe1–xSex (x = 0.45; superconducting transition temperature Tc = 14.5 kelvin) hosts Dirac-cone–type spin-helical surface states at the Fermi level; the surface states exhibit an s-wave superconducting gap below Tc. Our study shows that the surface states of FeTe0.55Se0.45 are topologically superconducting, providing a simple and possibly high-temperature platform for realizing Majorana states.

  17. Acoustic plane wave preferential orientation of metal oxide superconducting materials

    DOEpatents

    Tolt, Thomas L.; Poeppel, Roger B.

    1991-01-01

    A polycrystalline metal oxide such as YBa.sub.2 Cu.sub.3 O.sub.7-X (where 0<X<0.5) exhibits superconducting properties and is capable of conducting very large current densities. By aligning the two-dimensional Cu-O layers which carry the current in the superconducting state in the a- and b-directions, i.e., within the basal plane, a high degree of crystalline axes alignment is provided between adjacent grains permitting the conduction of high current densities. With the superconducting metal oxide in the form of a ceramic slip which has not yet set, orientation of the crystal basal planes parallel with the direction of desired current flow is accomplished by an applied acoustic plane wave in the acoustic or ultrasonic frequency range (either progressive or standing) in applying a torque to each crystal particle. The ceramic slip is then set and fired by conventional methods to produce a conductor with preferentially oriented grains and substantially enhanced current carrying capacity.

  18. Surprising loss of three-dimensionality in low-energy spin correlations on approaching superconductivity in Fe1 +yTe1 -xSex

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Schneeloch, J. A.; Wen, Jinsheng; Winn, B. L.; Granroth, G. E.; Zhao, Yang; Gu, Genda; Zaliznyak, Igor; Tranquada, J. M.; Birgeneau, R. J.; Xu, Guangyong

    2017-10-01

    We report inelastic neutron scattering measurements of low-energy (ℏ ω ≲10 meV) magnetic excitations in the "11" system Fe1 +yTe1 -xSex . The spin correlations are two-dimensional (2D) in the superconducting samples at low temperature, but appear much more three-dimensional (3D) when the temperature rises well above Tc˜15 K, with a clear increase of the (dynamic) spin correlation length perpendicular to the Fe planes. This behavior is extremely unusual; typically, the suppression of thermal fluctuations at low temperature would favor the enhancement of 3D correlations, or even ordering, and the reversion to 2D cannot be naturally explained when only the spin degree of freedom is considered. Our results suggest that the low temperature physics in the 11 system, in particular the evolution of low-energy spin excitations towards superconducting pairing, intrinsically involves changes in orbital correlations.

  19. Magnetic polarons in antiferromagnetic CaMnO3-x (x<0.01) probed by O17 NMR

    NASA Astrophysics Data System (ADS)

    Trokiner, A.; Verkhovskii, S.; Yakubovskii, A.; Gerashenko, A.; Monod, P.; Kumagai, K.; Mikhalev, K.; Buzlukov, A.; Litvinova, Z.; Gorbenko, O.; Kaul, A.; Kartavtzeva, M.

    2009-06-01

    We study with O17 NMR and bulk magnetization a lightly electron doped CaMnO3-x (x<0.01) polycrystalline sample in the G -type antiferromagnetic state. The O17 NMR spectra show two lines with very different intensities corresponding to oxygen sites with very different local magnetic environments. The more intense unshifted line is due to the antiferromagnetic (AF) matrix. The thermal dependence of the magnetic moment of the AF sublattice deduced from the O17 linewidth is typical of insulating three-dimensional Heisenberg antiferromagnets. The less intense, strongly shifted line directly evidences the existence of ferromagnetic (FM) domains embedded in the AF spin lattice. The extremely narrow line in zero magnetic field indicates a nearly perfect alignment of the manganese spins in the FM domains which also display an unusually weak temperature dependence of their magnetic moment. We show that these FM entities start to move above 40 K in a slow-diffusion regime. These static and dynamic properties bear a strong similarity with those of a small size self-trapped magnetic polaron.

  20. Chemical analysis of superconducting phase in K-doped picene

    NASA Astrophysics Data System (ADS)

    Kambe, Takashi; Nishiyama, Saki; Nguyen, Huyen L. T.; Terao, Takahiro; Izumi, Masanari; Sakai, Yusuke; Zheng, Lu; Goto, Hidenori; Itoh, Yugo; Onji, Taiki; Kobayashi, Tatsuo C.; Sugino, Hisako; Gohda, Shin; Okamoto, Hideki; Kubozono, Yoshihiro

    2016-11-01

    Potassium-doped picene (K3.0picene) with a superconducting transition temperature (T C) as high as 14 K at ambient pressure has been prepared using an annealing technique. The shielding fraction of this sample was 5.4% at 0 GPa. The T C showed a positive pressure-dependence and reached 19 K at 1.13 GPa. The shielding fraction also reached 18.5%. To investigate the chemical composition and the state of the picene skeleton in the superconducting sample, we used energy-dispersive x-ray (EDX) spectroscopy, MALDI-time-of-flight (MALDI-TOF) mass spectroscopy and x-ray diffraction (XRD). Both EDX and MALDI-TOF indicated no contamination with materials other than K-doped picene or K-doped picene fragments, and supported the preservation of the picene skeleton. However, it was also found that a magnetic K-doped picene sample consisted mainly of picene fragments or K-doped picene fragments. Thus, removal of the component contributing the magnetic quality to a superconducting sample should enhance the volume fraction.

  1. {sup 17}O Knight shift study of the superconducting state of Sr{sub 2}RuO{sub 4}

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Mukuda, H.; Ishida, K.; Kitaoka, Y.

    1999-12-01

    {sup 17}O Knight shift measurements in Sr{sub 2}RuO{sub 4} were performed over the wide range of magnetic field 3.2--11.4kOe parallel to the basal RuO{sub 2} planes. The spin susceptibility is totally unchanged through its T{prime}{sub c}, evidencing that the spin-triplet superconducting state is realized in Sr{sub 2}RuO{sub 4}. The results indicates that the Cooper pairs consist of the parallel spin pairs {vert{underscore}bar}{up{underscore}arrow}{up{underscore}arrow}> and {vert{underscore}bar}{down{underscore}arrow}{down{underscore}arrow}> with their quantization axis perpendicular to the c-axis direction. The in-plane 2D nearly ferromagnetic spin fluctuations may play a role for the stabilization of this state among various representations of spin-triplet order parameter.

  2. Superconducting microcircuitry by the microlithographic patterning of superconducting compounds and related materials

    DOEpatents

    Coppa, N.V.

    1993-08-24

    A method is described of producing superconducting microcircuits comprising the steps of: depositing a thin film of Ba[sub 2]Cu[sub 3]O[sub 5+x](O < x < 1) onto a substrate; depositing a thin film of a dopant onto said thin film of Ba[sub 2]Cu[sub 3]O[sub 5+x]; depositing a photoresist onto said thin film of a dopant; shining light through a mask containing a pattern for a desired circuit configuration and onto said photoresist; developing said photoresist to remove portions of said photoresist shined by the light and to selectively expose said dopant film; etching said selectively exposed dopant film from said thin film of Ba[sub 2]Cu[sub 3]O[sub 5+x] to form a pattern of dopant; and heating said substrate at a temperature and for a period of time sufficient to diffuse and react said pattern of dopant with said thin film of Ba[sub 2]Cu[sub 3]O[sub 5+x].

  3. Installation, commissioning and performance of IDs installed at ALBA

    NASA Astrophysics Data System (ADS)

    Campmany, J.; Marcos, J.; Massana, V.; Becheri, F.; Gigante, J. V.; Colldelram, C.; Ribó, Ll

    2013-03-01

    The new synchrotron light source ALBA is currently starting regular operation. Up to 6 beamlines are using light produced by Insertion Devices. There are up to four types of IDs: 2 Apple-II undulators (EU62 and EU71) operating at low energies, one conventional wiggler (MPW80) operating in the range of 2 - 20 keV, two in-vacuum undulators (IVU21) operating in the range 5 - 30 keV and a superconducting wiggler (SCW30) operating in the range of (up to) 40 keV. The main IDs characteristics, their influence on the beam dynamics and a first characterization of their light will be presented.

  4. An X-Ray Source for Lithography Based on a Quasi-Optical Maser Undulator

    DTIC Science & Technology

    1989-05-09

    an electron, c is the speed of light in vacuo, B is the peak magnetic induction and X is the period of the planar undulator or wiggler, the wavelength...relativistic motion is given 11 p = Le’ Y 6 [2 - X )2] (4) where = v/c is the particle velocity normalized to the speAd of light , and § /c, where v = -v is...k0 z + Wt),) (7) where E is the amplitude of the electric field, w is the radian frequency A and k a (0,0,k ) is the wave- vector . ez is a unit vector

  5. Unusual phonon density of states and response to superconducting transition in In-doped topological crystalline insulator Pb 0.5Sn 0.5Te

    DOE PAGES

    Ran, Keijing; Tranquada, John M.; Zhong, Ruidan; ...

    2018-06-30

    Here, we present inelastic neutron scattering results of phonons in (Pb 0.5Sn 0.5) 1–xIn xTe powders, with x = 0, and 0.3.The x = 0 sample is a topological crystalline insulator, and the x = 0 . 3 sample is a superconductor with a bulk superconducting transition temperature T c of 4.7 K. In both samples, we observe unexpected van Hove singularities in the phonon density of states at energies of 1– 2.5 meV, suggestive of local modes. On cooling the superconducting sample through T c, there is an enhancement of these features for energies below twice the superconducting-gap energy.more » We further note that the superconductivity in (Pb 0.5Sn 0.5) 1–xIn xTe occurs in samples with normal-state resistivities of order 10 mΩ cm, indicative of bad-metal behavior. Calculations based on density functional theory suggest that the superconductivity is easily explainable in terms of electron-phonon coupling; however, they completely miss the low-frequency modes and do not explain the large resistivity. While the bulk superconducting state of (Pb 0.5Sn 0.5) 0.7In 0.3Te appears to be driven by phonons, a proper understanding will require ideas beyond simple BCS theor« less

  6. Unusual phonon density of states and response to superconducting transition in In-doped topological crystalline insulator Pb 0.5Sn 0.5Te

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ran, Keijing; Tranquada, John M.; Zhong, Ruidan

    Here, we present inelastic neutron scattering results of phonons in (Pb 0.5Sn 0.5) 1–xIn xTe powders, with x = 0, and 0.3.The x = 0 sample is a topological crystalline insulator, and the x = 0 . 3 sample is a superconductor with a bulk superconducting transition temperature T c of 4.7 K. In both samples, we observe unexpected van Hove singularities in the phonon density of states at energies of 1– 2.5 meV, suggestive of local modes. On cooling the superconducting sample through T c, there is an enhancement of these features for energies below twice the superconducting-gap energy.more » We further note that the superconductivity in (Pb 0.5Sn 0.5) 1–xIn xTe occurs in samples with normal-state resistivities of order 10 mΩ cm, indicative of bad-metal behavior. Calculations based on density functional theory suggest that the superconductivity is easily explainable in terms of electron-phonon coupling; however, they completely miss the low-frequency modes and do not explain the large resistivity. While the bulk superconducting state of (Pb 0.5Sn 0.5) 0.7In 0.3Te appears to be driven by phonons, a proper understanding will require ideas beyond simple BCS theor« less

  7. Low Temperature Magnetometry Measurements of the Heavy Fermion Superconductor Nd1-x Cex CoIn5 with x = 0.98, 0.95, and 0.90

    NASA Astrophysics Data System (ADS)

    Storr, Kevin; Purcell, Kenneth; Rasco, Torrance; Schwartz, Sarah; Petrovic, Cedomir

    2014-03-01

    The Nd1-xCexCoIn5 alloys evolve from local moment magnetism x = 0 to heavy fermion superconductivity x = 1, as the Nd substitution alters the level of 4f-conduction electron coupling. Superconductivity has been shown to exist in Nd concentrations between x = 0 and x = 0.22. We report the temperature and angular dependence of the critical field of the superconducting state of the x = 0.98, 0.95, and 0.90 doping levels at temperatures ranging from 20 - 500 mK, investigating the evolution of the phase diagram for different concentrations of Nd at these previously unexplored low temperatures. No evidence of a low temperature mixed superconducting and magnetic mixed state was observed such that as that seen in CeCoIn5. The suppression of the critical field is more dramatic than the application of pressure and was observed to be rather anisotropic in line with the higher temperature measurements. Department of Defense ARO W911NF1110155.

  8. Present Status of the KSTAR Superconducting Magnet System Development

    NASA Astrophysics Data System (ADS)

    Kim, Keeman; H, K. Park; K, R. Park; B, S. Lim; S, I. Lee; M, K. Kim; Y, Chu; W, H. Chung; S, H. Baek; J Y, Choi; H, Yonekawa; A, Chertovskikh; Y, B. Chang; J, S. Kim; C, S. Kim; D, J. Kim; N, H. Song; K, P. Kim; Y, J. Song; I, S. Woo; W, S. Han; D, K. Lee; Y, K. Oh; K, W. Cho; J, S. Park; G, S. Lee; H, J. Lee; T, K. Ko; S, J. Lee

    2004-10-01

    The mission of Korea Superconducting Tokamak Advanced Research (KSTAR) project is to develop an advanced steady-state superconducting tokamak for establishing a scientific and technological basis for an attractive fusion reactor. Because one of the KSTAR mission is to achieve a steady-state operation, the use of superconducting coils is an obvious choice for the magnet system. The KSTAR superconducting magnet system consists of 16 Toroidal Field (TF) coils and 14 Poloidal Field (PF) coils. Internally-cooled Cable-In-Conduit Conductors (CICC) are put into use in both the TF and PF coil systems. The TF coil system provides a field of 3.5 T at the plasma center and the PF coil system is able to provide a flux swing of 17 V-sec. The major achievement in KSTAR magnet-system development includes the development of CICC, the development of a full-size TF model coil, the development of a coil system for background magnetic-field generation, the construction of a large-scale superconducting magnet and CICC test facility. TF and PF coils are in the stage of fabrication to pave the way for the scheduled completion of KSTAR by the end of 2006.

  9. Crystal Field Excitations Across High Tc Phase Diagram in La1 . 6 - x Nd0 . 4 Srx CuO4

    NASA Astrophysics Data System (ADS)

    Ma, Qianli; Maharaj, Dalini; Buhariwalla, Connor; Kolesnikov, Alexander; Stone, Matthew; Gaulin, Bruce

    The family of high Tc superconductors(SC) La1 . 6 - x Nd0 . 4 Srx CuO4 (Nd-LSCO) has been studied as it displays a complex picture of the canonical hole-doped high Tc phase diagram. It displays static charge and spin stripe order over a range of Sr doping, which are optimized around x=0.125. Nd-LSCO evolves from an AFM insulating phase at x=0, to a region (0.05 <x <0.17) where static charge and spin stripe order co-exist with superconductivity at low temperatures, to an optimally-doped SC(x=0.19) with Tc=20K, and to what is believed to be a conventional non-superconducting Fermi liquid for x > 0 . 25 . Here I present time-of-flight inelastic neutron scattering data of the Nd3+ crystalline electric field (CEF) levels on polycrystalline samples of Nd-LSCO over a range of compositions up to x=0.4. The experiments were performed on the SEQUOIA chopper spectrometer at the Spallation Neutron Source, and observe the evolution of the splitting of the J=9/2 multiplet appropriate to Nd3+ as a function of Sr concentrations (x=0.04,0.12,0.2,0.24 and 0.4) and (4K, 35K and 200K) temperature. We observe sharp CEF transitions near 21 meV and 27 meV at low x, evolve to a single transition near 24meV near x=0.1, in agreement with the onset of a superconducting ground state. NSERC.

  10. Macroscopic character of composite high-temperature superconducting wires

    NASA Astrophysics Data System (ADS)

    Kivelson, S. A.; Spivak, B.

    2015-11-01

    The "d -wave" symmetry of the superconducting order in the cuprate high temperature superconductors is a well established fact [J. Tsuei and J. R. Kirtley, Rev. Mod. Phys. 72, 969 (2000), 10.1103/RevModPhys.72.969 and D. J. Vanharlingen, Rev. Mod. Phys. 67, 515 (1995), 10.1103/RevModPhys.67.515], and one which identifies them as "unconventional." However, in macroscopic contexts—including many potential applications (i.e., superconducting "wires")—the material is a composite of randomly oriented superconducting grains in a metallic matrix, in which Josephson coupling between grains mediates the onset of long-range phase coherence. [See, e.g., D. C. Larbalestier et al., Nat. Mater. 13, 375 (2014), 10.1038/nmat3887, A. P. Malozemoff, MRS Bull. 36, 601 (2011), 10.1557/mrs.2011.160, and K. Heine et al., Appl. Phys. Lett. 55, 2441 (1989), 10.1063/1.102295] Here we analyze the physics at length scales that are large compared to the size of such grains, and in particular the macroscopic character of the long-range order that emerges. While X Y -superconducting glass order and macroscopic d -wave superconductivity may be possible, we show that under many circumstances—especially when the d -wave superconducting grains are embedded in a metallic matrix—the most likely order has global s -wave symmetry.

  11. Simulations of inertial confinement fusion driven by a novel synchrotron-radiation-based x-ray igniter

    NASA Astrophysics Data System (ADS)

    Shlyaptsev, Vyacheslav N.; Tatchyn, Roman O.

    2004-01-01

    The advantages and challenges of using a powerful x-ray source for the fast ignition of compressed Inertial Confinement Fusion (ICF) targets have been considered. The requirements for such a source together with the optics to focus the x-rays onto compressed DT cores lead to a conceptual design based on Energy Recovery Linacs (ERLs) and long wigglers to produce x-ray pulses with the appropriate phase space properties. A comparative assessment of the parameters of the igniter system indicates that the technologies for building it, although expensive, are physically achievable. Our x-ray fast ignition (XFI) scheme requires substantially smaller energy for the initiation of nuclear fusion reactions than other methods.

  12. Chiral plaquette polaron theory of cuprate superconductivity

    NASA Astrophysics Data System (ADS)

    Tahir-Kheli, Jamil; Goddard, William A., III

    2007-07-01

    Ab initio density functional calculations on explicitly doped La2-xSrxCuO4 find that doping creates localized holes in out-of-plane orbitals. A model for cuprate superconductivity is developed based on the assumption that doping leads to the formation of holes on a four-site Cu plaquette composed of the out-of-plane A1 orbitals apical Opz , planar Cud3z2-r2 , and planar Opσ . This is in contrast to the assumption of hole doping into planar Cudx2-y2 and Opσ orbitals as in the t-J model. Allowing these holes to interact with the d9 spin background leads to chiral polarons with either a clockwise or anticlockwise charge current. When the polaron plaquettes percolate through the crystal at x≈0.05 for La2-xSrxCuO4 , a Cudx2-y2 and planar Opσ band is formed. The computed percolation doping of x≈0.05 equals the observed transition to the “metallic” and superconducting phase for La2-xSrxCuO4 . Spin exchange Coulomb repulsion with chiral polarons leads to d -wave superconducting pairing. The equivalent of the Debye energy in phonon superconductivity is the maximum energy separation between a chiral polaron and its time-reversed partner. This energy separation is on the order of the antiferromagnetic spin coupling energy, Jdd˜0.1eV , suggesting a higher critical temperature. An additive skew-scattering contribution to the Hall effect is induced by chiral polarons and leads to a temperature dependent Hall effect that fits the measured values for La2-xSrxCuO4 . The integrated imaginary susceptibility, observed by neutron spin scattering, satisfies ω/T scaling due to chirality and spin-flip scattering of polarons along with a uniform distribution of polaron energy splittings. The derived functional form is compatible with experiments. The static spin structure factor for chiral spin coupling of the polarons to the undoped antiferromagnetic Cud9 spins is computed for classical spins on large two-dimensional lattices and is found to be incommensurate with a

  13. Thermal annealing and pressure effects on BaFe2-xCoxAs2 single crystals.

    PubMed

    Shin, Dongwon; Jung, Soon-Gil; Prathiba, G; Seo, Soonbeom; Choi, Ki-Young; Kim, Kee Hoon; Park, Tuson

    2017-11-26

    We investigate the pressure and thermal annealing effects on BaFe<sub>2-<i>x</i></sub>Co<sub><i>x</i></sub>As<sub>2</sub> (Co-Ba122) single crystals with <i>x</i> = 0.1 and 0.17 via electrical transport measurements. The thermal annealing treatment not only enhances the superconducting transition temperature (<i>T</i><sub>c</sub>) from 9.6 to 12.7 K for <i>x</i> = 0.1 and from 18.1 to 21.0 K for <i>x</i> = 0.17, but also increases the antiferromagnetic transition temperature (<i>T</i><sub>N</sub>). Simultaneous enhancement of <i>T</i><sub>c</sub> and <i>T</i><sub>N</sub> by the thermal annealing treatment indicates that thermal annealing could substantially improve the quality of the Co-doped Ba122 samples. Interestingly, <i>T</i><sub>c</sub> of the Co-Ba122 compounds shows a scaling behavior with a linear dependence on the resistivity value at 290 K, irrespective of tuning parameters, such as chemical doping, pressure, and thermal annealing. These results not only provide an effective way to access the intrinsic properties of the BaFe<sub>2</sub>As<sub>2</sub> system, but also may shed a light on designing new materials with higher superconducting transition temperature. © 2017 IOP Publishing Ltd.

  14. Superconducting coil and method of stress management in a superconducting coil

    DOEpatents

    McIntyre, Peter M.; Shen, Weijun; Diaczenko, Nick; Gross, Dan A.

    1999-01-01

    A superconducting coil (12) having a plurality of superconducting layers (18) is provided. Each superconducting layer (18) may have at least one superconducting element (20) which produces an operational load. An outer support structure (24) may be disposed outwardly from the plurality of layers (18). A load transfer system (22) may be coupled between at least one of the superconducting elements (20) and the outer support structure (24). The load transfer system (22) may include a support matrix structure (30) operable to transfer the operational load from the superconducting element (20) directly to the outer support structure (24). A shear release layer (40) may be disposed, in part, between the superconducting element (20) and the support matrix structure (30) for relieving a shear stress between the superconducting element (20) and the support matrix structure (30). A compliant layer (42) may also be disposed, in part, between the superconducting element (20) and the support matrix structure (30) for relieving a compressive stress on the superconducting element (20).

  15. Doping-dependent anisotropic superconducting gap in Na1-δ(Fe1-xCox)As from London penetration depth

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cho, Kyuil; Tanatar, Makariy A.; Spyrison, Nicholas

    2012-07-30

    The London penetration depth was measured in single crystals of self-doped Na1-δFeAs (from under doping to optimal doping, Tc from 14 to 27 K) and electron-doped Na(Fe1-xCox)As with x ranging from undoped, x=0, to overdoped, x=0.1. In all samples, the low-temperature variation of the penetration depth exhibits a power-law dependence, Δλ(T)=ATn, with the exponent that varies in a domelike fashion from n˜1.1 in the underdoped, reaching a maximum of n˜1.9 in the optimally doped, and decreasing again to n˜1.3 on the overdoped side. While the anisotropy of the gap structure follows a universal domelike evolution, the exponent at optimal doping,more » n˜1.9, is lower than in other charge-doped Fe-based superconductors (FeSCs). The full-temperature range superfluid density, ρs(T)=λ(0)/λ(T)2, at optimal doping is also distinctly different from other charge-doped FeSCs but is similar to isovalently substituted BaFe2(As1-xPx)2, believed to be a nodal pnictide at optimal doping. These results suggest that the superconducting gap in Na(Fe1-xCox)As is highly anisotropic even at optimal doping.« less

  16. Superconducting Cable

    DOEpatents

    Hughey, Raburn L.; Sinha, Uday K.; Reece, David S.; Muller, Albert C.

    2005-03-08

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  17. Superconducting Cable

    DOEpatents

    Hughey, Raburn L.; Sinha, Uday K.; Reece, David S.; Muller, Albert C.

    2005-07-22

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  18. Superconductivity in Bi/Ni bilayer system: Clear role of superconducting phases found at Bi/Ni interface

    NASA Astrophysics Data System (ADS)

    Liu, L. Y.; Xing, Y. T.; Merino, I. L. C.; Micklitz, H.; Franceschini, D. F.; Baggio-Saitovitch, E.; Bell, D. C.; Solórzano, I. G.

    2018-01-01

    Bi/Ni bilayers with varying Bi and Ni layer thicknesses have been prepared by (a) pulsed-laser deposition (PLD) at 300 K and (b) thermal evaporation at 4.2 K. A two-step superconducting transition appears on the electrical transport measurements in the samples prepared by PLD. High-resolution transmission and scanning transmission electron microscopy, supported by energy-dispersive x-ray spectroscopy (EDXS) analysis, reveal that two superconducting intermetallic alloys, namely NiBi and NiBi3, are formed by interdiffusion, if the bilayers are prepared at 300 K. The Tc of the two phases behaves very differently in an external magnetic field and the upper critical magnetic fields at zero temperature [Bc 2(0 ) ] were estimated as 1.1 and 7.4 T, respectively. The lower value corresponds to the Bc 2(0) of NiBi3 phase and the higher one is supposed to be of NiBi. These alloys are responsible for the superconductivity and the two-step transition appearing in the Bi/Ni bilayer system. Surprisingly, the Bi-rich phase (NiBi3) is formed near the Ni layer, while the Ni-rich phase (NiBi) is formed far from the Ni layer. The EDXS analysis at nanometer scale clearly shows an unusual increase of Ni concentration near the interface of Bi/substrate. The limited thickness of Bi layer in the interdiffusion process results in an unexpected distribution of Ni concentration. Samples prepared at 4.2 K after annealing at 300 K do not show any superconductivity, which indicates that a nonepitaxial Bi/Ni interface does not induce superconductivity in the case interdiffusion does not occur. These results offer a deeper understanding of the superconductivity in the Bi/Ni bilayer system.

  19. Superconductivity in a Misfit Phase That Combines the Topological Crystalline Insulator Pb 1-xSn xSe with the CDW-Bearing Transition Metal Dichalcogenide TiSe 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Luo, H.; Yan, K.; Pletikosic, I.

    We report the characterization of the misfit compound (Pb 1-xSn xSe 2)1.16(TiSe 2) 2 for 0 ≤ x ≤ 0.6, in which a [100] rocksalt-structure bilayer of Pb1-xSnxSe, which is a topological crystalline insulator in bulk form, alternates with a double layer of the normally nonsuperconducting transition metal dichalcogenide TiSe 2. The x dependence of Tc displays a weak dome-like shape with a maximum Tc of 4.5 K at x = 0.2; there is only a subtle change in Tc at the composition where the trivial to topological transition occurs in bulk Pb1-xSnxSe. We present the characterization of the superconductormore » at x = 0.4, for which the bulk Pb1-xSnxSe phase is in the topological crystalline insulator regime. For this material, the Sommerfeld parameter γ = 11.06 mJ mol -1 K -2, the Debye temperature Θ D = 161 K, the normalized specific heat jump value ΔC/γT c = 1.38 and the electron-phonon constant value γ ep = 0.72, suggesting that (Pb 0.6Sn 0.4Se) 1.16(TiSe 2) 2 is a BCS-type weak coupling superconductor. This material may be of interest for probing the interaction of superconductivity with the surface states of a topological crystalline insulator.« less

  20. Superconductivity in a Misfit Phase That Combines the Topological Crystalline Insulator Pb 1-xSn xSe with the CDW-Bearing Transition Metal Dichalcogenide TiSe 2

    DOE PAGES

    Luo, H.; Yan, K.; Pletikosic, I.; ...

    2016-05-13

    We report the characterization of the misfit compound (Pb 1-xSn xSe 2)1.16(TiSe 2) 2 for 0 ≤ x ≤ 0.6, in which a [100] rocksalt-structure bilayer of Pb1-xSnxSe, which is a topological crystalline insulator in bulk form, alternates with a double layer of the normally nonsuperconducting transition metal dichalcogenide TiSe 2. The x dependence of Tc displays a weak dome-like shape with a maximum Tc of 4.5 K at x = 0.2; there is only a subtle change in Tc at the composition where the trivial to topological transition occurs in bulk Pb1-xSnxSe. We present the characterization of the superconductormore » at x = 0.4, for which the bulk Pb1-xSnxSe phase is in the topological crystalline insulator regime. For this material, the Sommerfeld parameter γ = 11.06 mJ mol -1 K -2, the Debye temperature Θ D = 161 K, the normalized specific heat jump value ΔC/γT c = 1.38 and the electron-phonon constant value γ ep = 0.72, suggesting that (Pb 0.6Sn 0.4Se) 1.16(TiSe 2) 2 is a BCS-type weak coupling superconductor. This material may be of interest for probing the interaction of superconductivity with the surface states of a topological crystalline insulator.« less

  1. PREFACE: EUCAS '09: The 9th European Conference on Applied Superconductivity (Dresden, Germany, 13-17 September 2009) EUCAS '09: The 9th European Conference on Applied Superconductivity (Dresden, Germany, 13-17 September 2009)

    NASA Astrophysics Data System (ADS)

    Holzapfel, Bernhard; Schultz, Ludwig; Schlörb, Heike

    2010-03-01

    During the 9th European Conference on Applied Superconductivity, 6 plenary, 22 invited, 206 oral and 429 poster contributions were presented on recent developments in the field of applied superconductivity. This issue of Superconductor Science and Technology contains plenary, invited and a selection of contributed oral papers of the four main EUCAS areas: materials, wires and tapes, large scale applications and electronics. The remaining contributed papers that were selected for the conference proceedings will be published in the Journal of Physics: Conference Series. The Dresden EUCAS conference, with 712 participants from 43 countries, continued the tradition of preceding EUCAS conferences of combining basic superconductivity research contributions with the discussion of recent material advances and new developments in large scale and electronic applications. In Dresden, contributions on the recently discovered Fe-based superconductors were presented for the first time during a EUCAS conference and their potential for applications was intensively discussed. Among all the high level papers of this issue we particularly want to highlight the plenary contribution of Praveen Chaudhari on grain boundaries in cuprate superconductors. In his paper Praveen discusses the Jc limitation in HTSC tapes and tunnelling spectroscopy in LSCO thin film bicrystals. Just a few weeks ago we received the sad news that Praveen had passed away on 13 January 2010. Already fighting with his serious illness, Praveen spent all his efforts last fall finishing his plenary talk and paper. This paper will remind us always of his contributions to basic and applied aspects of superconductivity in general and especially his important work on HTSC grain boundaries. Finally we want to acknowledge the help of the International Advisory and National Committees in setting up the scientific program and we would especially like to express our gratitude to all the members of the Local Organization

  2. Superconductivity in palladium-doped 2H-TaS2

    NASA Astrophysics Data System (ADS)

    Zhou, M. H.; Li, X. C.; Dong, C.

    2018-06-01

    A series of Pd x TaS2 (0.01 ≤ x ≤ 0.08) samples were prepared and characterized via scanning electron microscope, x-ray powder diffraction, resistivity, magnetization and specific heat measurements. The lattice parameter c associated with the interlayer distance increases monotonically with the Pd content while the parameter a remains essentially constant. The crystal structure of Pd0.08TaS2 has been determined and refined by Rietveld refinement. Pd0.08TaS2 is hexagonal (space group: P31c) with lattice parameters a = 3.3151(1) Å, c = 12.1497(9) Å. The superconducting transition temperature T c (0.8 K) of TaS2 can be dramatically enhanced by Pd doping, and the maximum T c of 4.2 K, about five times the T c of pure TaS2, is obtained in Pd0.04TaS2. We have determined the superconducting parameters of Pd0.04TaS2, and found that the enhancement of T c can be attributed to the increase of density of states at the Fermi level. The charge density wave (CDW) of TaS2 is gradually suppressed with Pd doping and disappears in Pd0.06TaS2. This suggests that there is a competitive interplay between superconductivity and CDW in this system.

  3. Laboratory demonstrations of superconducting gravity and inertial sensors for space and airborne gravity measurements

    NASA Technical Reports Server (NTRS)

    Paik, Ho J.; Canavan, Edgar R.; Kong, Qin; Moody, M. V.

    1992-01-01

    The paper describes the superconducting gravity gradiometers (SGGs) and superconducting accelerometers being developed at the University of Maryland, which take advantage of many exotic properties of superconductivity to obtain the required low noise, high stability, and large dynamic range. Results of laboratory demonstrations of some of these instruments are presented together with the design and operating principles. Particular attention is given to the three-axis Model II SGG and a six-axis superconducting accelerometer model (Model I SSA). Model II SGG, after a residual common-mode balance, exhibited a noise level of 0.05/sq rt Hz above 0.1 Hz and a 1/f-squared noise below 0.1 Hz. All six channels of Model I SSA operated simultaneously with linear and angular acceleration noise levels of 3 x 10 exp -10 g(E)/sq rt Hz and 5 x 10 exp -8 rad/sec per sec per sq rt Hz, respectively.

  4. Superconducting structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2003-04-01

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  5. Superconducting Structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2005-09-13

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  6. Superconductivity pairing mechanism from cobalt impurity doping in FeSe: Spin (s±) or orbital (s++) fluctuation

    NASA Astrophysics Data System (ADS)

    Urata, T.; Tanabe, Y.; Huynh, K. K.; Yamakawa, Y.; Kontani, H.; Tanigaki, K.

    2016-01-01

    In high-superconducting transition temperature (Tc) iron-based superconductors, interband sign reversal (s±) and sign preserving (s++) s -wave superconducting states have been primarily discussed as the plausible superconducting mechanism. We study Co impurity scattering effects on the superconductivity in order to achieve an important clue on the pairing mechanism using single-crystal Fe1 -xCoxSe and depict a phase diagram of a FeSe system. Both superconductivity and structural transition/orbital order are suppressed by the Co replacement on the Fe sites and disappear above x = 0.036. These correlated suppressions represent a common background physics behind these physical phenomena in the multiband Fermi surfaces of FeSe. By comparing experimental data and theories so far proposed, the suppression of Tc against the residual resistivity is shown to be much weaker than that predicted in the case of general sign reversal and full gap s± models. The origin of the superconducting paring in FeSe is discussed in terms of its multiband electronic structure.

  7. Superconductivity in the lanthanum-yttrium-manganese alloy system

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Stierman, R.J.

    An empirical approach involving lattice instabilities was investigated in the search for new superconducting materials. Pseudo-lanthanide compounds using La and Y were prepared for the system La/sub 1-x/Y/sub x/Mn/sub 2/ by arc melting and subsequent heat treatment. Low temperature magnetic susceptibility and low temperature heat capacity measurements were made. The unit cell lattice parameters were determined from x-ray powder patterns taken on most samples and metallographic examination was carried out on selected samples. Alloys with low La concentrations (x greater than or equal to 0.6) showed RMn/sub 2/ in the cubic C15 Laves phase as the major component with secondmore » phase material present. The magnetic susceptibility and x-ray data indicated a superconducting phase which seemed to be the RMn/sub 2/ phase, but heat capacity measurements showed the second phase material was the superconductor, while the RMn/sub 2/ was not. Failure to form compounds with higher La content was experienced and may be due to the lattice instability expected at x = 0.56. This indicates that perhaps more stingent conditions are required to form pseudo-lanthanide compounds than were previously considered. More systems should be investigated to see if this is true, and to determine the possibilities of this approach.« less

  8. Crystal growth and annealing study of fragile, non-bulk superconductivity in YFe 2Ge 2

    DOE PAGES

    Kim, H.; Ran, S.; Mun, E. D.; ...

    2015-02-05

    In this study, we investigated the occurrence and nature of superconductivity in single crystals of YFe 2Ge 2 grown out of Sn flux by employing X-ray diffraction, electrical resistivity and specific heat measurements. We found that the residual resistivity ratio (RRR) of single crystals can be greatly improved, reaching as high as ~60, by decanting the crystals from the molten Sn at ~350°C and/or by annealing at temperatures between 550°C and 600°C. We found that the samples with RRR ≳ 34 showed resistive signatures of superconductivity with the onset of the superconducting transition T c ≈ 1.4K. RRR values varymore » between 35 and 65 with, on average, no systematic change in value T c, indicating that the systematic changes in RRR do not lead to comparable changes in T c. Specific heat measurements on samples that showed the clear resistive signatures of a superconducting transition did not show any signature of a superconducting phase transition, which suggests that the superconductivity observed in this compound is either some sort of filamentary, strain-stabilized superconductivity associated with small amounts of stressed YFe 2Ge 2 (perhaps at twin boundaries or dislocations) or is a second crystallographic phase that is present at level below detection capability of conventional powder X-ray techniques.« less

  9. Pressure induced superconductivity in very lightly doped LaFeAsO0.975F0.025

    NASA Astrophysics Data System (ADS)

    Miyoshi, K.; Otsuka, K.; Shiota, A.; Shimojo, Y.; Motoyama, G.; Fujiwara, K.; Kitagawa, H.; Nishigori, S.

    2018-05-01

    We have investigated whether or not superconductivity is induced by the application of pressure in very lightly F-doped LaFeAsO1-xFx , which shows spin density wave (SDW) state at ambient pressure, through the measurements of DC magnetization and electrical resistivity under pressure using pulse current sintered (PCS) high density polycrystalline specimens. It has been confirmed that the specimens with x = 0.025 shows superconductivity with Tcdia ∼ 15 K under pressure above ∼ 1.3 GPa. The pressure induced superconductivity can be explained by the lattice compression along c-axis, which enhances the electron doping from LaO layers to FeAs layers.

  10. Superconducting state parameters of bulk amorphous alloys

    NASA Astrophysics Data System (ADS)

    Vora, A. M.

    2012-12-01

    Well recognized empty core pseudopotential of Ashcroft is used to investigate the superconducting state parameters viz; electron-phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature T C , isotope effect exponent α and effective interaction strength N O V of some (Ni33Zr67)1- x V x ( x = 0, 0.05, 0.1, 0.15) bulk amorphous alloys. We have incorporated five different types of local field correction functions, proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of the various exchange and correlation functions is concluded from the present study. The T C obtained from local field correction function proposed by Sarkar et al. (S) is in excellent agreement with available theoretical data. Quadratic T C equation has been proposed providing successfully the T C values of bulk amorphous alloys under consideration. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirm the superconducting phase in the s bulk amorphous alloys.

  11. Metal-insulator quantum critical point beneath the high Tc superconducting dome.

    PubMed

    Sebastian, Suchitra E; Harrison, N; Altarawneh, M M; Mielke, C H; Liang, Ruixing; Bonn, D A; Hardy, W N; Lonzarich, G G

    2010-04-06

    An enduring question in correlated systems concerns whether superconductivity is favored at a quantum critical point (QCP) characterized by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high T(c) cuprates and invoked to explain non-Fermi liquid transport signatures, experimental evidence is lacking for a critical divergence under the superconducting dome. We use ultrastrong magnetic fields to measure quantum oscillations in underdoped YBa(2)Cu(3)O(6+x), revealing a dramatic doping-dependent upturn in quasiparticle effective mass at a critical metal-insulator transition beneath the superconducting dome. Given the location of this QCP under a plateau in T(c) in addition to a postulated QCP at optimal doping, we discuss the intriguing possibility of two intersecting superconducting subdomes, each centered at a critical Fermi surface instability.

  12. Erratum: Evolution of precipitate morphology during heat treatment and its implications for the superconductivity in K x F e 1.6 + y S e 2 single crystals [Phys. Rev. B 86 , 144507 (2012)

    DOE PAGES

    Liu, Y.; Xing, Q.; Dennis, K. W.; ...

    2015-08-14

    In this article, we study the relationship between precipitate morphology and superconductivity in K xFe 1.6+ySe 2 single crystals grown by self-flux method. Scanning electron microscopy (SEM) measurements revealed that the superconducting phase forms a network in the samples quenched above iron vacancy order-disorder transition temperature T s, whereas it aggregates into micrometer-sized rectangular bars and aligns as disconnected chains in the furnace-cooled samples.

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

    DOE PAGES

    Groll, Nickolas; Pellin, Michael J.; Zasadzinksi, John F.; ...

    2015-09-18

    In this paper, 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 C) and density of states over large surface areas with size up to mm 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 canmore » 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. Finally, 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.« less

  14. Superconductivity in Bismuth. A New Look at an Old Problem

    PubMed Central

    2016-01-01

    To investigate the relationship between atomic topology, vibrational and electronic properties and superconductivity of bismuth, a 216-atom amorphous structure (a-Bi216) was computer-generated using our undermelt-quench approach. Its pair distribution function compares well with experiment. The calculated electronic and vibrational densities of states (eDOS and vDOS, respectively) show that the amorphous eDOS is about 4 times the crystalline at the Fermi energy, whereas for the vDOS the energy range of the amorphous is roughly the same as the crystalline but the shapes are quite different. A simple BCS estimate of the possible crystalline superconducting transition temperature gives an upper limit of 1.3 mK. The e-ph coupling is more preponderant in a-Bi than in crystalline bismuth (x-Bi) as indicated by the λ obtained via McMillan’s formula, λc = 0.24 and experiment λa = 2.46. Therefore with respect to x-Bi, superconductivity in a-Bi is enhanced by the higher values of λ and of eDOS at the Fermi energy. PMID:26815431

  15. Superconductivity in Bismuth. A New Look at an Old Problem.

    PubMed

    Mata-Pinzón, Zaahel; Valladares, Ariel A; Valladares, Renela M; Valladares, Alexander

    2016-01-01

    To investigate the relationship between atomic topology, vibrational and electronic properties and superconductivity of bismuth, a 216-atom amorphous structure (a-Bi216) was computer-generated using our undermelt-quench approach. Its pair distribution function compares well with experiment. The calculated electronic and vibrational densities of states (eDOS and vDOS, respectively) show that the amorphous eDOS is about 4 times the crystalline at the Fermi energy, whereas for the vDOS the energy range of the amorphous is roughly the same as the crystalline but the shapes are quite different. A simple BCS estimate of the possible crystalline superconducting transition temperature gives an upper limit of 1.3 mK. The e-ph coupling is more preponderant in a-Bi than in crystalline bismuth (x-Bi) as indicated by the λ obtained via McMillan's formula, λc = 0.24 and experiment λa = 2.46. Therefore with respect to x-Bi, superconductivity in a-Bi is enhanced by the higher values of λ and of eDOS at the Fermi energy.

  16. 17. (4"X5" image enlarged from 2 1/4" negative) Sam Fowler, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    17. (4"X5" image enlarged from 2 1/4" negative) Sam Fowler, Photographer, February 1998 VIEW OF GEORGIA DOT BRIDGE NO. 051-00025D-01986N (JAMES P. HOULIHAN BRIDGE) APPROACH SPAN FENDER - Georgia DOT Bridge No. 051-00025D-01986N, US 17 & State Route 25 Spanning Savannah River, Port Wentworth, Chatham County, GA

  17. Superconductivity in Sm-doped CaFe2As2 single crystals

    NASA Astrophysics Data System (ADS)

    Dong-Yun, Chen; Bin-Bin, Ruan; Jia, Yu; Qi, Guo; Xiao-Chuan, Wang; Qing-Ge, Mu; Bo-Jin, Pan; Tong, Liu; Gen-Fu, Chen; Zhi-An, Ren

    2016-06-01

    In this article, the Sm-doping single crystals Ca1 - x Sm x Fe2As2 (x = 0 ˜ 0.2) were prepared by the CaAs flux method, and followed by a rapid quenching treatment after the high temperature growth. The samples were characterized by structural, resistive, and magnetic measurements. The successful Sm-substitution was revealed by the reduction of the lattice parameter c, due to the smaller ionic radius of Sm3+ than Ca2+. Superconductivity was observed in all samples with onset T c varying from 27 K to 44 K upon Sm-doping. The coexistence of a collapsed phase transition and the superconducting transition was found for the lower Sm-doping samples. Zero resistivity and substantial superconducting volume fraction only happen in higher Sm-doping crystals with the nominal x > 0.10. The doping dependences of the c-axis length and onset T c were summarized. The high-T c observed in these quenched crystals may be attributed to simultaneous tuning of electron carriers doping and strain effect caused by lattice reduction of Sm-substitution. Project supported by the National Natural Science Foundation of China (Grant No. 11474339), the National Basic Research Program of China (Grant Nos. 2010CB923000 and 2011CBA00100), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB07020100).

  18. Superconducting and normal-state anisotropy of the doped topological insulator Sr 0.1Bi 2Se 3

    DOE PAGES

    Smylie, M. P.; Willa, K.; Claus, H.; ...

    2018-05-16

    Sr xBi 2Se 3 and the related compounds Cu xBi 2Se 3 and Nb xBi 2Se 3 have attracted considerable interest, as these materials may be realizations of unconventional topological superconductors. Superconductivity with T c ~3 K in Sr xBi 2Se 3 arises upon intercalation of Sr into the layered topological insulator Bi 2Se 3. Here we elucidate the anisotropy of the normal and superconducting state of Sr 0.1Bi 2Se 3 with angular dependent magnetotransport and thermodynamic measurements. High resolution x-ray diffraction studies underline the high crystalline quality of the samples. We demonstrate that the normal state electronic and magneticmore » properties of Sr 0.1Bi 2Se 3 are isotropic in the basal plane while we observe a large two-fold in-plane anisotropy of the upper critical field in the superconducting state. In conclusion, our results support the recently proposed odd-parity nematic state characterized by a nodal gap of Eu symmetry in Sr xBi 2Se 3.« less

  19. Superconducting and normal-state anisotropy of the doped topological insulator Sr 0.1Bi 2Se 3

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Smylie, M. P.; Willa, K.; Claus, H.

    Sr xBi 2Se 3 and the related compounds Cu xBi 2Se 3 and Nb xBi 2Se 3 have attracted considerable interest, as these materials may be realizations of unconventional topological superconductors. Superconductivity with T c ~3 K in Sr xBi 2Se 3 arises upon intercalation of Sr into the layered topological insulator Bi 2Se 3. Here we elucidate the anisotropy of the normal and superconducting state of Sr 0.1Bi 2Se 3 with angular dependent magnetotransport and thermodynamic measurements. High resolution x-ray diffraction studies underline the high crystalline quality of the samples. We demonstrate that the normal state electronic and magneticmore » properties of Sr 0.1Bi 2Se 3 are isotropic in the basal plane while we observe a large two-fold in-plane anisotropy of the upper critical field in the superconducting state. In conclusion, our results support the recently proposed odd-parity nematic state characterized by a nodal gap of Eu symmetry in Sr xBi 2Se 3.« less

  20. Superconducting and normal-state anisotropy of the doped topological insulator Sr0.1Bi2Se3.

    PubMed

    Smylie, M P; Willa, K; Claus, H; Koshelev, A E; Song, K W; Kwok, W-K; Islam, Z; Gu, G D; Schneeloch, J A; Zhong, R D; Welp, U

    2018-05-16

    Sr x Bi 2 Se 3 and the related compounds Cu x Bi 2 Se 3 and Nb x Bi 2 Se 3 have attracted considerable interest, as these materials may be realizations of unconventional topological superconductors. Superconductivity with T c  ~3 K in Sr x Bi 2 Se 3 arises upon intercalation of Sr into the layered topological insulator Bi 2 Se 3 . Here we elucidate the anisotropy of the normal and superconducting state of Sr 0.1 Bi 2 Se 3 with angular dependent magnetotransport and thermodynamic measurements. High resolution x-ray diffraction studies underline the high crystalline quality of the samples. We demonstrate that the normal state electronic and magnetic properties of Sr 0.1 Bi 2 Se 3 are isotropic in the basal plane while we observe a large two-fold in-plane anisotropy of the upper critical field in the superconducting state. Our results support the recently proposed odd-parity nematic state characterized by a nodal gap of Eu symmetry in Sr x Bi 2 Se 3 .

  1. Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers

    DOE PAGES

    Gong, Xinxin; Kargarian, Mehdi; Stern, Alex; ...

    2017-03-31

    Superconductivity that spontaneously breaks time-reversal symmetry (TRS) has been found, so far, only in a handful of three-dimensional (3D) crystals with bulk inversion symmetry. We report an observation of spontaneous TRS breaking in a 2D superconducting system without inversion symmetry: the epitaxial bilayer films of bismuth and nickel. The evidence comes from the onset of the polar Kerr effect at the superconducting transition in the absence of an external magnetic field, detected by the ultrasensitive loop-less fiber-optic Sagnac interferometer. Because of strong spin-orbit interaction and lack of inversion symmetry in a Bi/Ni bilayer, superconducting pairing cannot be classified as singletmore » or triplet.We propose a theoretical model where magnetic fluctuations in Ni induce the superconducting pairing of the d xy ± id x2-y2 orbital symmetry between the electrons in Bi. In this model, the order parameter spontaneously breaks the TRS and has a nonzero phase winding number around the Fermi surface, thus making it a rare example of a 2D topological superconductor.« less

  2. Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Opačić, M.; Lazarević, N.; Šćepanović, M.

    2015-11-16

    Polarized Raman scattering spectra of superconducting K x Fe2-y Se2 and non-superconducting K0.8Fe1.8Co0.2Se2 single crystals were measured in the temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in the frequency range from 150 to 325 cm-1 in both compounds, suggesting that the K0.8Fe1.8Co0.2Se2 single crystal also has a two-phase nature. The temperature dependence of the Raman mode energy is analyzed in terms of lattice thermal expansion and phonon–phonon interaction. The temperature dependence of the Raman mode linewidth is dominated by temperature-induced anharmonic effects. It is shown that the change in Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. An abrupt change of the A1g mode energy nearmore » $${{T}_{\\text{C}}}$$ was observed in K x Fe2-y Se2, whereas it is absent in non-superconducting K0.8Fe1.8Co0.2Se2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below the critical temperature.« less

  3. Hidden Order as a Source of Interface Superconductivity

    NASA Astrophysics Data System (ADS)

    Moor, Andreas; Volkov, Anatoly; Efetov, Konstantin

    2015-03-01

    We propose a new mechanism of the interfacial superconductivity observed in many heterostructures composed of different materials including high-temperature superconductors. Our proposal is based on the use of the Ginzburg-Landau equations applicable to a wide class of systems. The system under consideration is assumed to have, alongside the superconducting order parameter, also another competing order that might be a charge- or spin-density wave. At certain temperatures or doping level the superconducting state is not realized (thus, ``hidden''), while the amplitude of another order parameter corresponds to a minimum of the free energy. We also assume that at an interface or at a defect, the non-superconducting order parameter is suppressed (strongly or weakly), e.g., due to an enhanced impurity scattering. The local superconductivity is shown to emerge at the interface, and the spatial dependence of the corresponding order parameter is described by the Gross-Pitaevskii equation. The quantized values of the temperature and doping levels, at which Δ (x) arises, are determined by the ``energy'' levels of the linearized Gross-Pitaevskii equation, i.e., of the Schrodinger equation. Interestingly, the local superconductivity arises even at a small suppression of the rival order. We appreciate the support from DFG via the Projekt EF 11/8-1; K. B. E. gratefully acknowledges the financial support of the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST ``MISiS.''

  4. Edge multi-energy soft x-ray diagnostic in Experimental Advanced Superconducting Tokamak

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Y. L.; Xu, G. S.; Wan, B. N.

    A multi-energy soft x-ray (ME-SXR) diagnostic has been built for electron temperature profile in the edge plasma region in Experimental Advanced Superconducting Tokamak (EAST) after two rounds of campaigns. Originally, five preamplifiers were mounted inside the EAST vacuum vessel chamber attached to five vertically stacked compact diode arrays. A custom mechanical structure was designed to protect the detectors and electronics under constraints of the tangential field of view for plasma edge and the allocation of space. In the next experiment, the mechanical structure was redesigned with a barrel structure to absolutely isolate it from the vacuum vessel. Multiple shielding structuresmore » were mounted at the pinhole head to protect the metal foils from lithium coating. The pre-amplifiers were moved to the outside of the vacuum chamber to avoid introducing interference. Twisted copper cooling tube was embedded into the back-shell near the diode to limit the temperature of the preamplifiers and diode arrays during vacuum vessel baking when the temperature reached 150 °C. Electron temperature profiles were reconstructed from ME-SXR measurements using neural networks.« less

  5. High Tc superconducting films from metallo-organic precursors

    NASA Astrophysics Data System (ADS)

    Davison, W. W.; Shyu, S. G.; Buchanan, R. C.

    High Tc superconducting films of heavy metal soaps (derived from carboxylic acid precursors) have been prepared on Si and other substrates. The precursors were synthesized and mixed in appropriate molar ratios to form the high Tc compound YBa2Cu3O(7-x), using a high boiling point common solvent base. The precursor solution was deposited by a spin casting technique on the substrates. Film thicknesses of 0.1-1.0 micron were achieved after heat treatment at 550-850 C at not longer than 4 hours. Films were analyzed as to orientation, appropriate phase, interfacial reaction, and superconducting properties.

  6. Anisotropic superconductivity in β-(BDA-TTP)2SbF6: STM spectroscopy

    NASA Astrophysics Data System (ADS)

    Nomura, K.; Muraoka, R.; Matsunaga, N.; Ichimura, K.; Yamada, J.

    2009-03-01

    We have investigated the gap symmetry in the superconducting phase of β-(BDA-TTP)2SbF6 with use of the scanning tunneling microscope (STM). The tunneling spectra obtained on the conducting surface show a clear superconducting gap structure. Its functional form is of V-shaped similarly to κ-(BEDT-TTF)2X and suggests the anisotropic superconducting gap with line nodes. For lateral surfaces the shape of tunneling spectra varies from the U-shape with relatively large gap to the V-shape with small gap depending on the tunneling direction alternately twice between directional angle 0 and π. From the analysis of conductance curve taking the k dependence of the tunneling probability into account, it is found that the gap has maximum near the a* and c* axes and the nodes appear along near a*+c* and the a-c* directions. These indicate that the d like superconducting pair is formed in this system as the case of κ-(BEDT-TTF)2X. This node direction is consistent with the theoretical prediction based on the spin fluctuation mechanism. However, the zero-bias conductance peak has not been observed yet.

  7. High Pressure Superconductivity in Iron Based Layered Compounds Studied using Designer Diamonds

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Vohra, Yogesh, K.

    High pressure superconductivity in Iron based superconductor FeSe0.5Te0.5 has been studied up to 15 GPa and 10 K using an eight probe designer diamond anvil in a diamond anvil cell device. Four probe electrical resistance measurements show onset of superconductivity (Tc) at 14 K at ambient pressure with Tc increasing with increasing pressure to 19 K at a pressure of 3.6 GPa. At higher pressures beyond 3.6 GPa, Tc decreases and extrapolation suggests non superconducting behavior above 10 GPa. This loss of superconductivity coincides with the pressure induced amorphization of Fe(SeTe)4 tetrahedra reported at 11 GPa in x-ray diffraction studiesmore » at ambient temperature.« less

  8. FOREWORD: Focus on Superconductivity in Semiconductors Focus on Superconductivity in Semiconductors

    NASA Astrophysics Data System (ADS)

    Takano, Yoshihiko

    2008-12-01

    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

  9. Antiferromagnetism and superconductivity in layered organic conductors: Variational cluster approach.

    PubMed

    Sahebsara, P; Sénéchal, D

    2006-12-22

    The kappa-(ET)2X layered conductors (where ET stands for BEDT-TTF) are studied within the dimer model as a function of the diagonal hopping t' and Hubbard repulsion U. Antiferromagnetism and d-wave superconductivity are investigated at zero temperature using variational cluster perturbation theory (VCPT). For large U, Néel antiferromagnetism exists for t' < t(c2)', with t(c2)' approximately 0.9. For fixed t', as U is decreased (or pressure increased), a d(x2-y2) superconducting phase appears. When U is decreased further, then a d(xy) order takes over. There is a critical value of t(c1)' approximately 0.8 of t' beyond which the AF and dSC phases are separated by the Mott disordered phase.

  10. Flux Pinning and Properties of Solid-Solution (Y,Nd)1+xBa2-xCu3O7-delta Superconductors (Preprint)

    DTIC Science & Technology

    2012-02-01

    magnetization , and R is the radius of the superconducting volume roughly approximated as 0.00005 cm for the finely reacted powders [17]. Field...measurements. The superconducting volume percentages were calculated using (%) = 4 v/(1-D*4 v), where v = M/Happl is the measured magnetic ...susceptibility, and D = 1/3 is the demagnetization factor assuming a spherical particle distribution [17]. The applied magnetic field was Happl = 796 A/m

  11. Multiband superconductivity in BiS2-based layered compounds

    NASA Astrophysics Data System (ADS)

    Griffith, M. A.; Puel, T. O.; Continentino, M. A.; Martins, G. B.

    2017-08-01

    A mean-field treatment is presented of a square lattice two-orbital-model for \\text{Bi}{{\\text{S}}2} taking into account intra- and inter-orbital superconductivity. A rich phase diagram involving both types of superconductivity is presented as a function of the ratio between the couplings of electrons in the same and different orbitals (η ={{\\text{V}}\\text{XX}}/{{\\text{V}}\\text{XY}} ) and electron doping x. With the help of a quantity we call orbital-mixing ratio, denoted as R(φ ) , the phase diagram is analyzed using a simple and intuitive picture based on how R(φ ) varies as electron doping increases. The predictive power of R(φ ) suggests that it could be a useful tool in qualitatively (or even semi-quantitatively) analyzing multiband superconductivity in BCS-like superconductors.

  12. Development of a compact superconducting rotating-gantry for heavy-ion therapy

    PubMed Central

    Iwata, Yoshiyuki; Noda, K.; Murakami, T.; Shirai, T.; Furukawa, T.; Fujita, T.; Mori, S.; Sato, S.; Mizushima, K.; Shouda, K.; Fujimoto, T.; Arai, H.; Ogitsu, T.; Obana, T.; Amemiya, N.; Orikasa, T.; Takami, S.; Takayama, S.

    2014-01-01

    An isocentric superconducting rotating-gantry for heavy-ion therapy is being developed [ 1]. This rotating gantry can transport heavy ions having 430 MeV/u to an isocenter with irradiation angles of over ±180°, and is further capable of performing fast raster-scanning irradiation [ 2]. A layout of the beam-transport line for the compact rotating-gantry is presented in Fig. 1. The rotating gantry has 10 superconducting magnets (BM01-10), a pair of the scanning magnets (SCM-X and SCM-Y) and two pairs of beam profile- monitor and steering magnets (ST01-02 and PRN01-02). For BM01-BM06 and BM09-BM10, the combined-function superconducting magnets are employed. Further, these superconducting magnets are designed for fast slewing of the magnetic field to follow the multiple flattop operation of the synchrotron [ 3]. The use of the combined-function superconducting magnets with optimized beam optics allows a compact gantry design with a large scan size at the isocenter; the length and the radius of the gantry will be to be ∼13 and 5.5 m, respectively, which are comparable to those for the existing proton gantries. Furthermore, the maximum scan size at the isocenter is calculated to be as large as ∼200 mm square for heavy-ion beams at the maximum energy of 430 MeV/u. All of the superconducting magnets were designed, and their magnetic fields were calculated using the Opera-3d code [ 4]. With the calculated magnetic fields, beam-tracking simulations were made. The simulation results agreed well with those of the linear beam-optics calculation, proving validity of the final design for the superconducting magnets. The five out of 10 superconducting magnets, as well as the model magnet were currently manufactured. With these magnets, rotation tests, magnetic field measurements and fast slewing tests were conducted. However, we did not observe any significant temperature increase, which may cause a quench problem. Further, results of the magnetic field measurements roughly

  13. High field superconducting magnets

    NASA Technical Reports Server (NTRS)

    Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

    2011-01-01

    A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

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

    PubMed Central

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

    2016-01-01

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

  15. Molecular mapping of chromosomes 17 and X. Progress report

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Barker, D.F.

    1989-12-31

    The basic aims of this project are the construction of high density genetic maps of chromosomes 17 and X and the utilization of these maps for the subsequent isolation of a set of physically overlapping DNA segment clones. The strategy depends on the utilization of chromosome specific libraries of small (1--15 kb) segments from each of the two chromosomes. Since the time of submission of our previous progress report, we have refined the genetic map of markers which we had previously isolated for chromosome 17. We have completed our genetic mapping in CEPH reference and NF1 families of 15 markersmore » in the pericentric region of chromosome 17. Physical mapping results with three probes, were shown be in very close genetic proximity to the NF1 gene, with respect to two translocation breakpoints which disrupt the activity of the gene. All three of the probes were found to lie between the centromere and the most proximal translocation breakpoint, providing important genetic markers proximal to the NF1 gene. Our primary focus has shifted to the X chromosome. We have isolated an additional 30 polymorphic markers, bringing the total number we have isolated to over 80. We have invested substantial effort in characterizing the polymorphisms at each of these loci and constructed plasmid subclones which reveal the polymorphisms for nearly all of the loci. These subclones are of practical value in that they produce simpler and stronger patterns on human genomic Southern blots, thus improving the efficiency of the genetic mapping experiments. These subclones may also be of value for deriving DNA sequence information at each locus, necessary for establishing polymerase chain reaction primers specific for each locus. Such information would allow the use of each locus as a sequence tagged site.« less

  16. Pressure-tuned superconductivity and normal-state behavior in Ba ( Fe 0.943 Co 0.057 ) 2 As 2 near the antiferromagnetic boundary

    DOE PAGES

    Liu, W.; Wu, Y. F.; Li, X. J.; ...

    2018-04-23

    Superconductivity in iron pnictides is unconventional and pairing may be mediated by magnetic fluctuations in the Fe sublattice. Pressure is a clean method to explore superconductivity in iron based superconductors by tuning the ground state continuously without introducing disorder. Here we present a systematic high pressure transport study in Ba (Fe 1 - xCo x) 2 As 2 single crystals with x = 0.057, which is near the antiferromagnetic instability. Resistivity ρ = ρ 0 + AT n was studied under applied pressure up to 7.90 GPa. The parameter n approaches a minimum value of n ≈ 1 at amore » critical pressure P c = 3.65 GPa. Near P c, the superconducting transition temperature T c reaches a maximum value of 25.8 K. In addition, the superconducting diamagnetism at 2 K shows a sudden change around the same critical pressure. Finally, these results may be associated with a possible quantum critical point hidden inside the superconducting dome, near optimum T c.« less

  17. Pressure-tuned superconductivity and normal-state behavior in Ba ( Fe 0.943 Co 0.057 ) 2 As 2 near the antiferromagnetic boundary

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liu, W.; Wu, Y. F.; Li, X. J.

    Superconductivity in iron pnictides is unconventional and pairing may be mediated by magnetic fluctuations in the Fe sublattice. Pressure is a clean method to explore superconductivity in iron based superconductors by tuning the ground state continuously without introducing disorder. Here we present a systematic high pressure transport study in Ba (Fe 1 - xCo x) 2 As 2 single crystals with x = 0.057, which is near the antiferromagnetic instability. Resistivity ρ = ρ 0 + AT n was studied under applied pressure up to 7.90 GPa. The parameter n approaches a minimum value of n ≈ 1 at amore » critical pressure P c = 3.65 GPa. Near P c, the superconducting transition temperature T c reaches a maximum value of 25.8 K. In addition, the superconducting diamagnetism at 2 K shows a sudden change around the same critical pressure. Finally, these results may be associated with a possible quantum critical point hidden inside the superconducting dome, near optimum T c.« less

  18. Low temperature internal friction spectrum of YBa 2Cu 3O x

    NASA Astrophysics Data System (ADS)

    Mi, Y.; Schaller, R.; Berger, H.; Benoit, W.; Sathish, S.

    1991-01-01

    The elastic and anelastic behaviours of polycrystalline YBa 2Cu 3O x specimens have been studied between 80 and 300 K, by means of a resonant bar technique. Three damping peaks have been observed at 90, 115 and 220 K. The stability of these peaks during annealing in vacuum has been carefully examined. The 90 K peak is not related to the superconducting transition because it is still observed after thermal treatments leading to the disappearance of superconductivity. The 115 K is due to a relaxation mechanism. The activation energy is ∼0.17 eV and the frequency factor is ∼10 12s -1. Also this peak is certainly correlated with the excess oxygen atoms, because it disappears with annealing in vacuum. The 220 K maximum, which was also observed by ultrasonic measurements, seems to be affected by the sample preparation, i.e. by the sintering conditions. Finally, a frequency hysteresis has been observed in every superconducting sample, which accounts for an anomalous behaviour of the elastic modulus.

  19. Development and testing of a superconducting link for an IR detector

    NASA Technical Reports Server (NTRS)

    Caton, R.; Selim, R.

    1991-01-01

    The development and testing of a ceramic superconducting link for an infrared detector is summarized. Areas of study included the materials used, the electrical contacts, radiation and temperature cycling effects, aging, thermal conductivity, and computer models of an ideal link. Materials' samples were processed in a tube furnace at temperatures of 840 C to 865 C for periods up to 17 days and transition temperatures and critical current densities were recorded. The project achieved better quality high superconducting transition temperature material through improved processing and also achieved high quality electrical contacts. Studies on effects of electron irradiation, temperature cycling, and aging on superconducting properties indicate that the materials will be suitable for space applications. Various presentations and publications on the study's results are reported.

  20. Electron doping evolution of the neutron spin resonance in NaFe 1-xCo xAs

    DOE PAGES

    Zhang, Chenglin; Song, Yu; Carr, Scott Victor; ...

    2016-05-31

    Neutron spin resonance, a collective magnetic excitation coupled to superconductivity, is one of the most prominent features shared by a broad family of unconventional superconductors including copper oxides, iron pnictides, and heavy fermions. In this paper, we study the doping evolution of the resonances in NaFe 1–xCo xAs covering the entire superconducting dome. For the underdoped compositions, two resonance modes coexist. As doping increases, the low-energy resonance gradually loses its spectral weight to the high-energy one but remains at the same energy. By contrast, in the overdoped regime we only find one single resonance, which acquires a broader width inmore » both energy and momentum but retains approximately the same peak position even when T c drops by nearly a half compared to optimal doping. Furthermore, these results suggest that the energy of the resonance in electron overdoped NaFe 1–xCo xAs is neither simply proportional to T c nor the superconducting gap but is controlled by the multiorbital character of the system and doped impurity scattering effect.« less

  1. Structural, magnetic and Mossbauer studies of TI doped Gd2Fe17-xTix and Gd2Fe16Ga1-xTix (0≤x≤1)

    NASA Astrophysics Data System (ADS)

    Pokharel, G.; Syed Ali, K. S.; Mishra, S. R.

    2015-05-01

    Magnetic compounds of the type Gd2Fe17-xTix and Gd2Fe16Ga1-xTix (x=0.0-1.0) were prepared by arc melting and their structural and magnetic properties were studied by X-ray diffraction (XRD), magnetometery and Mossbauer spectroscopy. The Rietveld analysis of X-ray data shows that these α-Fe free solid-solutions crystallize with Th2Ni17-type structure as main phase along with GdFe2 and TiFe2 as additional phases at higher, x≥0.5 contents. The unit cell volume expands with Ga and Ti content. The Rietveld analysis indicate that both Ti and Ga atoms prefer 12j and 12k sites in both compounds. The effect of Ti and co-substituted Ga-Ti on the bond length are quite different. The saturation magnetization Ms, at 300 K for Gd2Fe17-xTix and Gd2Fe16Ga1-xTix was found to decrease linearly with increasing Ti content. The Ms in both compounds at x=1 reduced by 9% as compared to their parent compounds at x=0. The Curie temperature, Tc, for Gd2Fe17-xTix increased from 513 K (x=0) to 544 K (x=1) while Tc for Gd2Fe16Ga1-xTix reduced from 560 (x=0) to 544 K (x=1) with increase in Ti content. Thus the observed variation in Tc follows Gd2Fe17xTix show high Tc with marginal decline in saturation magnetization. Thus α-Fe free Gd2Fe16Ga1-xTix compounds can be potential candidate for high temperature permanent magnet industrial applications.

  2. Energy Recovery Linacs for Light Source Applications

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    George Neil

    2011-04-01

    Energy Recovery Linacs are being considered for applications in present and future light sources. ERLs take advantage of the continuous operation of superconducting rf cavities to accelerate high average current beams with low losses. The electrons can be directed through bends, undulators, and wigglers for high brightness x ray production. They are then decelerated to low energy, recovering power so as to minimize the required rf drive and electrical draw. When this approach is coupled with advanced continuous wave injectors, very high power, ultra-short electron pulse trains of very high brightness can be achieved. This paper will review the statusmore » of worldwide programs and discuss the technology challenges to provide such beams for photon production.« less

  3. Superconducting levitating bearing

    NASA Technical Reports Server (NTRS)

    Moon, Francis C. (Inventor)

    1996-01-01

    A superconducting bearing assembly includes a coil field source that may be superconducting and a superconducting structure. The coil field source assembly and superconducting structure are positioned so as to enable relative rotary movement therebetween. The structure and coil field source are brought to a supercooled temperature before a power supply induces a current in the coil field source. A Meissner-like effect is thereby obtained and little or no penetration of the field lines is seen in the superconducting structure. Also, the field that can be obtained from the superconducting coil is 2-8 times higher than that of permanent magnets. Since the magnetic pressure is proportioned to the square of the field, magnetic pressures from 4 to 64 times higher are achieved.

  4. Superconductivity in Pristine 2 Ha-MoS2 at Ultrahigh Pressure

    NASA Astrophysics Data System (ADS)

    Chi, Zhenhua; Chen, Xuliang; Yen, Fei; Peng, Feng; Zhou, Yonghui; Zhu, Jinlong; Zhang, Yijin; Liu, Xiaodi; Lin, Chuanlong; Chu, Shengqi; Li, Yanchun; Zhao, Jinggeng; Kagayama, Tomoko; Ma, Yanming; Yang, Zhaorong

    2018-01-01

    As a follow-up of our previous work on pressure-induced metallization of the 2 Hc-MoS2 [Chi et al., Phys. Rev. Lett. 113, 036802 (2014), 10.1103/PhysRevLett.113.036802], here we extend pressure beyond the megabar range to seek after superconductivity via electrical transport measurements. We found that superconductivity emerges in the 2 Ha-MoS2 with an onset critical temperature Tc of ca. 3 K at ca. 90 GPa. Upon further increasing the pressure, Tc is rapidly enhanced beyond 10 K and stabilized at ca. 12 K over a wide pressure range up to 220 GPa. Synchrotron x-ray diffraction measurements evidenced no further structural phase transition, decomposition, and amorphization up to 155 GPa, implying an intrinsic superconductivity in the 2 Ha-MoS2 . DFT calculations suggest that the emergence of pressure-induced superconductivity is intimately linked to the emergence of a new flat Fermi pocket in the electronic structure. Our finding represents an alternative strategy for achieving superconductivity in 2 H -MoS2 in addition to chemical intercalation and electrostatic gating.

  5. X-Band, 17-Watt Solid-State Power Amplifier

    NASA Technical Reports Server (NTRS)

    Mittskus, Anthony; Stone, Ernest; Boger, William; Burgess, David; Honda, Richard; Nuckolls, Carl

    2005-01-01

    An advanced solid-state power amplifier that can generate an output power of as much as 17 W at a design operating frequency of 8.4 GHz has been designed and constructed as a smaller, lighter, less expensive alternative to traveling-wave-tube X-band amplifiers and to prior solid-state X-band power amplifiers of equivalent output power. This amplifier comprises a monolithic microwave integrated circuit (MMIC) amplifier module and a power-converter module integrated into a compact package (see Figure 1). The amplifier module contains an input variable-gain amplifier (VGA), an intermediate driver stage, a final power stage, and input and output power monitors (see Figure 2). The VGA and the driver amplifier are 0.5-m GaAs-based metal semiconductor field-effect transistors (MESFETs). The final power stage contains four parallel high-efficiency, GaAs-based pseudomorphic high-electron-mobility transistors (PHEMTs). The gain of the VGA is voltage-variable over a range of 10 to 24 dB. To provide for temperature compensation of the overall amplifier gain, the gain-control voltage is generated by an operational-amplifier circuit that includes a resistor/thermistor temperature-sensing network. The driver amplifier provides a gain of 14 dB to an output power of 27 dBm to drive the four parallel output PHEMTs, each of which is nominally capable of putting out as much as 5 W. The driver output is sent to the input terminals of the four parallel PHEMTs through microstrip power dividers; the outputs of these PHEMTs are combined by microstrip power combiners (which are similar to the microstrip power dividers) to obtain the final output power of 17 W.

  6. Acoustic identification of the elastic properties of porous and nonporous superconducting materials DyBa2-XSrXCu3O7-δ

    NASA Astrophysics Data System (ADS)

    Sayoud, N.; Lazri, H.; Ogam, E.; Boumaiza, Y.; Boudour, A.

    2018-05-01

    This work involves the development of a method using the principle of acoustic microscopy to determine the elastic properties of high-temperature superconducting materials, the method is applied to analyse the variation of the elastic properties of the superconducting alloy DyBa 2-x Sr x Cu 3 O 7‑δ for different variations of the concentration parameters (x = 0, x = 0.3 and x = 0.6), porosity and temperature. The method is based on the reconstruction of the reflection coefficient calculated from the acoustic signature of the signal received by the microscope during the exploration of the superconducting material for different concentrations. This permitted the determination of the velocities of the surface and volume waves from the modelled reflection coefficient. On the other hand, the elastic parameters of the material such as Young’s, shear and bulk moduli were also deduced.

  7. PREFACE: Superconductivity in ultrathin films and nanoscale systems Superconductivity in ultrathin films and nanoscale systems

    NASA Astrophysics Data System (ADS)

    Bianconi, Antonio; Bose, Sangita; Garcia-Garcia, Antonio Miguel

    2012-12-01

    appears to enhance the critical temperature [4]. This is a hot topic as in the past year many works have clarified the nanoscale phase separation in electron-doped chalcogenides, showing the key role of a complex texture of nanograins and opening new avenues for the fundamental understanding of quantum phenomena in networks of superconducting nanograins. The advances in nanotechnology allow the exploration of the possible existence of superconductivity in single carbon nanotubes [5]. The technological applications presented by Gomez [6] and Lehtinen [7] show the fundamental physics of superconductivity at the nanoscale to promote new advances in quantum devices. We hope that this combination will make these focus papers in Superconductor Science and Technology interesting and promote cross-fertilization among the different sub-branches of the field which all share the same goal of addressing the key questions on nanoscale superconductors. References [1]Croitoru M D, Vagov A, Shanenko A A and Axt V M 2012 The Cooper problem in nanoscale: enhancement of the coupling due to confinement Supercond. Sci. Technol. 25 124001 [2]Perali A, Innocenti A, Valletta A and Bianconi A 2012 Anomalous isotope effect near a 2.5 Lifshitz transition in a multi-band multi-condensate superconductor made of a superlattice of stripes Supercond. Sci. Technol. 25 124002 [3]Zeng S W, Huang Z, Wang X, Lü W M, Liu Z Q, Zhang B M, Dhar S, Venkatesan T and Ariando 2012 The influence of La substitution and oxygen reduction in ambipolar La-doped YBa2Cu3Oy thin films Supercond. Sci. Technol. 25 124003 [4]Poccia N, Bianconi A, Campi G, Fratini M and Ricci A 2012 Size evolution of the oxygen interstitial nanowires in La2CuO4+y by thermal treatments and x-ray continuous illumination Supercond. Sci. Technol. 25 124004 [5]Yang Y, Fedorov G, Zhang J, Tselev A, Shafranjuk S and Barbara P 2012 The search for superconductivity at van Hove singularities in carbon nanotubes Supercond. Sci. Technol. 25 124005 [6]Gomez

  8. A Planar Two-Dimensional Superconducting Bolometer Array for the Green Bank Telescope

    NASA Technical Reports Server (NTRS)

    Benford, Dominic; Staguhn, Johannes G.; Chervenak, James A.; Chen, Tina C.; Moseley, S. Harvey; Wollack, Edward J.; Devlin, Mark J.; Dicker, Simon R.; Supanich, Mark

    2004-01-01

    In order to provide high sensitivity rapid imaging at 3.3mm (90GHz) for the Green Bank Telescope - the world's largest steerable aperture - a camera is being built by the University of Pennsylvania, NASA/GSFC, and NRAO. The heart of this camera is an 8x8 close-packed, Nyquist-sampled detector array. We have designed and are fabricating a functional superconducting bolometer array system using a monolithic planar architecture. Read out by SQUID multiplexers, the superconducting transition edge sensors will provide fast, linear, sensitive response for high performance imaging. This will provide the first ever superconducting bolometer array on a facility instrument.

  9. Charge Fluctuations in the NdO1-xFxBiS2 Superconductors

    NASA Astrophysics Data System (ADS)

    Athauda, Anushika; Mizuguchi, Yoshikazu; Nagao, Masanori; Neuefeind, Joerg; Louca, Despina

    2017-12-01

    The local atomic structure of superconducting NdO1-xFxBiS2 (x = 0.2 and 0.4) is investigated using neutron diffraction and the pair density function analysis technique. In the non-superconducting x = 0.2 composition, ferrodistortive displacements of the pyramidal sulfur ions break the tetragonal symmetry and a superlattice structure emerges with peaks appearing at h + k odd reflections superimposed on the even reflections of the P4/nmm symmetry. In the superconducting x = 0.4 composition, similar ferrodistortive displacements are observed but with different magnitudes coupled with in-plane Bi distortions which are indicative of charge fluctuations.

  10. Absence of superconductivity in LiPdHx

    NASA Astrophysics Data System (ADS)

    Liu, Wenhao; Wang, Enyu; Chen, Guanyu; Zhu, Xiyu; Zhang, Yue; Sheng, Yuzong; Wen, Hai-Hu

    2018-03-01

    Theoretical calculations about LiPdH predict that it may be a superconductor. Using the high-pressure synthesis technique up to 3 GPa, we have successfully fabricated the LiPdH? compound. The sample looks quite pure judging from the refinement of the X-ray diffraction pattern. However, no superconductivity has been detected down to about 2 K. The specific heat measurement shows a small Sommerfeld constant ? = 1.22 mJ mol? K?, which is a bit smaller than the theoretically predicted value. The magnetic susceptibility measured at 1 Tesla reveals a Curie-Weiss law behaviour in the low-temperature region with an estimate of the magnetic moment of 0.08 ?/Pd. The temperature dependence of resistivity has also been measured up to 25.2 GPa, but superconductivity is still not observed above 2 K. The large residual resistivity and small residual-resistivity ratio suggest that the quasiparticle scattering by impurities is quite strong, which might be induced by the hydrogen deficiency, and intimately hinders the occurrence of superconductivity in LiPdH?.

  11. Interplay between magnetism and superconductivity in iron-chalcogenide superconductors: crystal growth and characterizations

    NASA Astrophysics Data System (ADS)

    Wen, Jinsheng; Xu, Guangyong; Gu, Genda; Tranquada, J. M.; Birgeneau, R. J.

    2011-12-01

    In this review, we present a summary of results on single crystal growth of two types of iron-chalcogenide superconductors, Fe1+yTe1-xSex (11), and AxFe2-ySe2 (A = K, Rb, Cs, Tl, Tl/K, Tl/Rb), using Bridgman, zone-melting, vapor self-transport and flux techniques. The superconducting and magnetic properties (the latter gained mainly from neutron scattering measurements) of these materials are reviewed to demonstrate the connection between magnetism and superconductivity. It will be shown that for the 11 system, while static magnetic order around the reciprocal lattice position (0.5, 0) competes with superconductivity, spin excitations centered around (0.5, 0.5) are closely coupled to the materials' superconductivity; this is made evident by the strong correlation between the spectral weight around (0.5, 0.5) and the superconducting volume fraction. The observation of a spin resonance below the superconducting temperature, Tc, and the magnetic-field dependence of the resonance emphasize the close interplay between spin excitations and superconductivity, similar to cuprate superconductors. In AxFe2-ySe2, superconductivity with Tc ~ 30 K borders an antiferromagnetic insulating phase; this is closer to the behavior observed in the cuprates but differs from that in other iron-based superconductors.

  12. Field of a helical Siberian Snake

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Luccio, A.

    1995-02-01

    To preserve the spin polarization of a beam of high energy protons in a circular accelerator, magnets with periodic magnetic field, called Siberian Snakes are being used. Recently, it was proposed to build Siberian Snakes with superconducting helical dipoles. In a helical, or twisted dipole, the magnetic field is perpendicular to the axis of the helix and rotates around it as one proceeds along the magnet. In an engineering study of a 4 Tesla helical snake, the coil geometry is derived, by twisting, from the geometry of a cosine superconducting dipole. While waiting for magnetic measurement data on such amore » prototype, an analytical expression for the field of the helice is important, to calculate the particle trajectories and the spin precession in the helix. This model will also allow to determine the optical characteristics of the snake, as an insertion in the lattice of the accelerator. In particular, one can calculate the integrated multipoles through the magnet and the equivalent transfer matrix. An expression for the field in the helix body, i.e., excluding the fringe field was given in a classical paper. An alternate expression can be found by elaborating on the treatment of the field of a transverse wiggler obtained under the rather general conditions that the variables are separable. This expression exactly satisfies Maxwell`s div and curl equations for a stationary field, {del} {center_dot} B = 0, {del} x B = 0. This approach is useful in that it will allow one to use much of the work already done on the problem of inserting wigglers and undulators in the lattice of a circular accelerator.« less

  13. Evidence for triplet superconductivity in a superconductor-ferromagnet spin valve.

    PubMed

    Leksin, P V; Garif'yanov, N N; Garifullin, I A; Fominov, Ya V; Schumann, J; Krupskaya, Y; Kataev, V; Schmidt, O G; Büchner, B

    2012-08-03

    We have studied the dependence of the superconducting (SC) transition temperature on the mutual orientation of magnetizations of Fe1 and Fe2 layers in the spin valve system CoO(x)/Fe1/Cu/Fe2/Pb. We find that this dependence is nonmonotonic when passing from the parallel to the antiparallel case and reveals a distinct minimum near the orthogonal configuration. The analysis of the data in the framework of the SC triplet spin valve theory gives direct evidence for the long-range triplet superconductivity arising due to noncollinearity of the two magnetizations.

  14. Method of forming superconducting Tl-Ba-Ca-Cu-O films

    DOEpatents

    Wessels, Bruce W.; Marks, Tobin J.; Richeson, Darrin S.; Tonge, Lauren M.; Zhang, Jiming

    1993-01-01

    A method of forming a superconducting Tl-Ba-Ca-Cu-O film is disclosed, which comprises depositing a Ba-Ca-Cu-O film on a substrate by MOCVD, annealing the deposited film and heat-treating the annealed film in a closed circular vessel with TlBa.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x and cooling to form said superconducting film of TlO.sub.m Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+2, wherein m=1,2 and n=1,2,3.

  15. Antiferroic electronic structure in the nonmagnetic superconducting state of the iron-based superconductors

    PubMed Central

    Shimojima, Takahiro; Malaeb, Walid; Nakamura, Asuka; Kondo, Takeshi; Kihou, Kunihiro; Lee, Chul-Ho; Iyo, Akira; Eisaki, Hiroshi; Ishida, Shigeyuki; Nakajima, Masamichi; Uchida, Shin-ichi; Ohgushi, Kenya; Ishizaka, Kyoko; Shin, Shik

    2017-01-01

    A major problem in the field of high-transition temperature (Tc) superconductivity is the identification of the electronic instabilities near superconductivity. It is known that the iron-based superconductors exhibit antiferromagnetic order, which competes with the superconductivity. However, in the nonmagnetic state, there are many aspects of the electronic instabilities that remain unclarified, as represented by the orbital instability and several in-plane anisotropic physical properties. We report a new aspect of the electronic state of the optimally doped iron-based superconductors by using high–energy resolution angle-resolved photoemission spectroscopy. We find spectral evidence for the folded electronic structure suggestive of an antiferroic electronic instability, coexisting with the superconductivity in the nonmagnetic state of Ba1−xKxFe2As2. We further establish a phase diagram showing that the antiferroic electronic structure persists in a large portion of the nonmagnetic phase covering the superconducting dome. These results motivate consideration of a key unknown electronic instability, which is necessary for the achievement of high-Tc superconductivity in the iron-based superconductors. PMID:28875162

  16. Magnetic Penetration Effects in Small Superconducting Devices

    NASA Technical Reports Server (NTRS)

    Stevenson, T. R.; Adams, J. S.; Balvin, M. A.; Bandler, S. R.; Denis, K. L.; Hsieh, W.-T.; Kelly, D. P.; Nagler, P. C.; Porst, J.-P.; Sadleir, J. E.; hide

    2011-01-01

    The temperature dependent behavior of a superconducting body in an applied magnetic field involves flux penetration/expulsion both from screening currents (within a magnetic penetration depth) and variations in the superconducting order parameter (locally to form vortices or a mixed state, or globally in the Meissner effect). The temperature dependence of the magnetic penetration depth, in particular, has been used to make highly sensitive macroscopic thermometers. For the microscopic device volumes required in sensitive low temperature photon detectors, properties of actual thin film materials, non-uniformity of applied magnetic fields, and the influence of measurement circuit dynamics are complicating factors. We discuss the various penetration effects as demonstrated in a particularly promising combination of material and geometry that we have used to make sensitive x-ray microcalorimeters.

  17. Magnetometric mapping of superconducting RF cavities

    NASA Astrophysics Data System (ADS)

    Schmitz, B.; Köszegi, J.; Alomari, K.; Kugeler, O.; Knobloch, J.

    2018-05-01

    A scalable mapping system for superconducting RF (SRF) cavities is presented. Currently, it combines local temperature measurement with 3D magnetic field mapping along the outer surface of the resonator. This allows for the observation of dynamic effects that have an impact on the superconducting properties of a cavity, such as the normal to superconducting phase transition or a quench. The system was developed for a single cell 1.3 GHz TESLA-type cavity, but can be easily adopted to arbitrary other cavity types. A data acquisition rate of 500 Hz for all channels simultaneously (i.e., 2 ms acquisition time for a complete map) and a magnetic field resolution of currently up to 14 mA/m/μ0 = 17 nT have been implemented. While temperature mapping is a well known technique in SRF research, the integration of magnetic field mapping opens the possibility of detailed studies of trapped magnetic flux and its impact on the surface resistance. It is shown that magnetic field sensors based on the anisotropic magnetoresistance effect can be used in the cryogenic environment with improved sensitivity compared to room temperature. Furthermore, examples of first successful combined temperature and magnetic-field maps are presented.

  18. Fluorescence X-ray absorption spectroscopy using a Ge pixel array detector: application to high-temperature superconducting thin-film single crystals.

    PubMed

    Oyanagi, H; Tsukada, A; Naito, M; Saini, N L; Lampert, M O; Gutknecht, D; Dressler, P; Ogawa, S; Kasai, K; Mohamed, S; Fukano, A

    2006-07-01

    A Ge pixel array detector with 100 segments was applied to fluorescence X-ray absorption spectroscopy, probing the local structure of high-temperature superconducting thin-film single crystals (100 nm in thickness). Independent monitoring of pixel signals allows real-time inspection of artifacts owing to substrate diffractions. By optimizing the grazing-incidence angle theta and adjusting the azimuthal angle phi, smooth extended X-ray absorption fine structure (EXAFS) oscillations were obtained for strained (La,Sr)2CuO4 thin-film single crystals grown by molecular beam epitaxy. The results of EXAFS data analysis show that the local structure (CuO6 octahedron) in (La,Sr)2CuO4 thin films grown on LaSrAlO4 and SrTiO3 substrates is uniaxially distorted changing the tetragonality by approximately 5 x 10(-3) in accordance with the crystallographic lattice mismatch. It is demonstrated that the local structure of thin-film single crystals can be probed with high accuracy at low temperature without interference from substrates.

  19. Dielectric properties of (SWCNTs)x GdBa2CuO7-δ superconductor nanocomposites

    NASA Astrophysics Data System (ADS)

    Anas, M.; Ebrahim, S.; Eldeen, I. G.; Awad, R.; Abou-Aly, A. I.

    2017-11-01

    Gd-123 superconducting phase was prepared by solid-state reaction technique. Single-walled carbon nanotubes (SWCNTs) were added in Gd-123 superconducting matrix with different concentrations during the final sintering process to obtain (SWCNTs)x GdBa2Cu3O7-δ (x = 0.0-0.1 wt.%) nanoparticles-superconductor composite. The influence of SWCNTs addition on the phase formation, structural, morphological, superconducting and dielectric properties of Gd-123 phase was investigated. It was found that SWCNTs addition enhance the phase formation and does not change the crystal structure of the host Gd-123 superconducting phase. The superconducting properties of Gd-123 samples were improved after the addition of SWCNTs up to x = 0.06 wt.% due to the enhancement in intergrain connectivity by healing up of micro-cracks and reduction of defects, while these properties were retarded with further increase in x. The dielectric response of (SWCNTs)x Gd-123 superconducting phase with x = 0.0, 0.01, 0.04, 0.05, 0.06 and 0.1 wt.% was measured from 100 KHz to 5 MHz at 77 K. The results reveal that for both real (𝜀‧) and imaginary (𝜀″) parts of dielectric constant, the frequency of dispersion increased by increasing SWCNTs amount up to 0.06 wt.%, then this frequency shifted to lower values for x > 0.06 wt.%. The results were discussed according to the presence and interference of both interfacial and dipolar polarizations.

  20. The soft x-ray beamline at Frascati Labs

    NASA Astrophysics Data System (ADS)

    Cinque, Gianfelice; Burattini, Emilio; Grilli, Antonio; Dabagov, Sultan

    2005-08-01

    DAΦNE-Light is the Synchrotron Radiation laboratory at the Laboratori Nazionali di Frascati (LNF)1. Three beamlines were commissioned since spring 2003 to exploit parasitically the intense photon emission from DAΦNE, the 0.5 1 GeV storage ring routinely circulating over 1 A of electrons. The soft X-ray beamline utilizes a wiggler source and, by a double-crystal fixed-exit monochromator, it is operational in the distinguishing energy window 1.5 - 4 keV range to be extended from the "water window" toward 6 keV. At present, the research activity is focused on X-ray Absorption Spectroscopy (XAS): precisely, X-ray Absorption Near Edge Spectroscopy (XANES) on the inner electronic levels of light elements and transition metals from Al to Ge and both d- and f-shells of higher Z atoms. Preliminary tests of X-ray imaging have been performed in view of applying different focusing optics, namely policapillary systems in trasmission and/or bent mica diffractor in back-reflection, for X-ray microscopy and spectromicroscopy experiments. The use of polycapillary systems (lenses, halflenses, capillaries) for studying features of radiation transportation by such structures (X-ray channelling, focusing, bending, etc.) has been planned.

  1. Controlled synthesis of the antiperovskite oxide superconductor Sr3‑x SnO

    NASA Astrophysics Data System (ADS)

    Hausmann, J. N.; Oudah, M.; Ikeda, A.; Yonezawa, S.; Maeno, Y.

    2018-05-01

    A large variety of perovskite oxide superconductors are known, including some of the most prominent high-temperature and unconventional superconductors. However, superconductivity among the oxidation state inverted material class, the antiperovskite oxides, was recently reported for the first time. In this superconductor, Sr3‑x SnO, the unconventional ionic state Sn4‑ is realized and possible unconventional superconductivity due to a band inversion has been discussed. Here, we discuss an improved facile synthesis method, making it possible to control the strontium deficiency in Sr3‑x SnO. Additionally, a synthesis method above the melting point of Sr3SnO is presented. We show temperature dependence of magnetization and electrical resistivity for superconducting strontium deficient Sr3‑x SnO (T c ∼ 5 K) and for Sr3SnO without a superconducting transition in alternating current susceptibility down to 0.15 K. Further, we reveal a significant effect of strontium raw material purity on the superconductivity and achieve substantially increased M/M Meissner (∼1) compared to the highest value reported so far. More detailed characterizations utilizing powder x-ray diffraction and energy-dispersive x-ray spectroscopy show that a minor cubic phase, previously suggested to be another Sr3‑x SnO phase with a slightly larger lattice parameter, is SrO. The improved characterization and controlled synthesis reported herein enable detailed investigations on the superconducting nature and its dependency on the strontium deficiency in Sr3‑x SnO.

  2. Magnetoresistance oscillations in topological insulator microwires contacted with normal and superconducting leads

    NASA Astrophysics Data System (ADS)

    Konopko, Leonid; Nikolaeva, Albina; Huber, Tito E.; Rogacki, Krzysztof

    2018-05-01

    Recent efforts to detect and manipulate Majorana fermions in solid state devices have employed topological insulator (TI) nanowires proximity coupled to superconducting (SC) leads. This combination holds some promises for the fundamental physics and applications. We studied the transverse magnetoresistance (MR) of polycrystal Bi2Te2Se and single-crystal Bi0.83Sb0.17 TI microwires contacted with superconducting In2Bi leads. Bi2Te2Se has a simple band structure with a single Dirac cone on the surface and a large non-trivial bulk gap of 300 meV. The semiconducting alloy Bi0.83Sb0.17 is a strong topological insulator due to the inversion symmetry of bulk crystalline Bi and Sb. To study the TI/SC interface, we prepared Bi2Te2Se and Bi0.83Sb0.17 glass-coated microwire samples using superconducting alloy In2Bi (Tc = 5.6 K) to provide a contact of one side of the microwires with copper leads and gallium to provide a contact of the other side of microwires with copper leads. The MR oscillations equidistant in a transverse magnetic field (up to 1 T) at the TI/SC interface were observed at various temperatures (4.2 K-1.5 K) in both the Bi2Te2Se and Bi0.83Sb0.17 samples. In the Bi2Te3 sample with a diameter of d = 17 μm, this oscillations exist with a period of ΔB = 18 mT; in the Bi0.83Sb0.17 sample with d = 1.7 μm MR oscillations are characterized by a period of ΔB = 46 mT. The observed oscillations cannot be referred to the Shubnikov de Haas oscillations because they are not periodic in an inverse magnetic field and their amplitude decreases with increasing magnetic field. Most probably, transverse MR oscillations arise owing to the appearance of highly conducting edge states on the planar boundary of SC/TI.

  3. Protective link for superconducting coil

    DOEpatents

    Umans, Stephen D [Belmont, MA

    2009-12-08

    A superconducting coil system includes a superconducting coil and a protective link of superconducting material coupled to the superconducting coil. A rotating machine includes first and second coils and a protective link of superconducting material. The second coil is operable to rotate with respect to the first coil. One of the first and second coils is a superconducting coil. The protective link is coupled to the superconducting coil.

  4. Robust upward dispersion of the neutron spin resonance in the heavy fermion superconductor Ce 1–xYb xCoIn 5

    DOE PAGES

    Song, Yu; Van Dyke, John; Lum, I. K.; ...

    2016-09-28

    Here, the neutron spin resonance is a collective magnetic excitation that appears in copper oxide, iron pnictide, and heavy fermion unconventional superconductors. Although the resonance is commonly associated with a spin-exciton due to the d(s ±)-wave symmetry of the superconducting order parameter, it has also been proposed to be a magnon-like excitation appearing in the superconducting state. Here we use inelastic neutron scattering to demonstrate that the resonance in the heavy fermion superconductor Ce 1–xYb xCoIn 5 with x=0,0.05,0.3 has a ring-like upward dispersion that is robust against Yb-doping. By comparing our experimental data with random phase approximation calculation usingmore » the electronic structure and the momentum dependence of the d x2 –y2-wave superconducting gap determined from scanning tunneling microscopy for CeCoIn 5, we conclude the robust upward dispersing resonance mode in Ce 1–xYb xCoIn 5 is inconsistent with the downward dispersion predicted within the spin-exciton scenari« less

  5. Development of variable-magnification X-ray Bragg optics.

    PubMed

    Hirano, Keiichi; Yamashita, Yoshiki; Takahashi, Yumiko; Sugiyama, Hiroshi

    2015-07-01

    A novel X-ray Bragg optics is proposed for variable-magnification of an X-ray beam. This X-ray Bragg optics is composed of two magnifiers in a crossed arrangement, and the magnification factor, M, is controlled through the azimuth angle of each magnifier. The basic properties of the X-ray optics such as the magnification factor, image transformation matrix and intrinsic acceptance angle are described based on the dynamical theory of X-ray diffraction. The feasibility of the variable-magnification X-ray Bragg optics was verified at the vertical-wiggler beamline BL-14B of the Photon Factory. For X-ray Bragg magnifiers, Si(220) crystals with an asymmetric angle of 14° were used. The magnification factor was calculated to be tunable between 0.1 and 10.0 at a wavelength of 0.112 nm. At various magnification factors (M ≥ 1.0), X-ray images of a nylon mesh were observed with an air-cooled X-ray CCD camera. Image deformation caused by the optics could be corrected by using a 2 × 2 transformation matrix and bilinear interpolation method. Not only absorption-contrast but also edge-contrast due to Fresnel diffraction was observed in the magnified images.

  6. Superconducting characteristics of short MgB2 wires of long level sensor for liquid hydrogen

    NASA Astrophysics Data System (ADS)

    Takeda, M.; Inoue, Y.; Maekawa, K.; Matsuno, Y.; Fujikawa, S.; Kumakura, H.

    2015-12-01

    To establish the worldwide storage and marine transport of hydrogen, it is important to develop a high-precision and long level sensor, such as a superconducting magnesium diboride (MgB2) level sensor for large liquid hydrogen (LH2) tanks on board ships. Three 1.7- m-long MgB2 wires were fabricated by an in situ method, and the superconducting characteristics of twenty-four 20-mm-long MgB2 wires on the 1.7-m-long wires were studied. In addition, the static level-detecting characteristics of five 500-mm-long MgB2 level sensors were evaluated under atmospheric pressure.

  7. Superconductivity, pseudo-gap, and stripe correlations in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Zhang, Zailan; Denis, Sylvain; Lebert, Blair W.; Bertran, Francois; Le Fèvre, Patrick; Taleb-Ibrahimi, Amina; Castellan, John-Paul; Bolloc'h, David Le; Jacques, Vincent L. R.; Sidis, Yvan; Baptiste, Benoît; Decorse, Claudia; Berthet, Patrick; Perfetti, Luca; d'Astuto, Matteo

    2018-05-01

    Under-doped La-214 cuprates show a charge- and spin-modulation known as "stripes" [1]. These stripe modulations are (quasi)-static close to 1/8 hole doping where superconductivity is suppressed. The pseudo-gap phase of other cuprate compounds recently also revealed charge modulation, but interpreted rather as a charge density wave (CDW) [2-4], that possibly competes with superconductivity. In this context, to better understand the interplay between the stripe phase and the superconductivity, we use angle-resolved photoemission spectroscopy to study the electronic band structure and gap in La-214 cuprates near 1/8 doping (La2-x-yNdySrxCuO4 (x = 0.12; y = 0.0 & 0.4)) and compare with the previous results in the same system [5] and La1.86Ba0.14CuO4 [6]. Our data shows a loss of spectral intensity towards the end of the Fermi arcs, that is possibly due to a strong renormalisation, as already pointed out elsewhere [6], with a noisy but still measurable gap. On the nodal direction no gap is observed within our statistics, but a sizeable decrease in intensity with temperature. Moreover, we do not see any shadow band, but our Fermi surface can be well modelled with a single electron band calculation in the tight binding approximation, even very close to the 1/8 doping La2-x-yNdySrxCuO4 with and without Nd substitution.

  8. Additive Manufactured Superconducting Cavities

    NASA Astrophysics Data System (ADS)

    Holland, Eric; Rosen, Yaniv; Woolleet, Nathan; Materise, Nicholas; Voisin, Thomas; Wang, Morris; Mireles, Jorge; Carosi, Gianpaolo; Dubois, Jonathan

    Superconducting radio frequency cavities provide an ultra-low dissipative environment, which has enabled fundamental investigations in quantum mechanics, materials properties, and the search for new particles in and beyond the standard model. However, resonator designs are constrained by limitations in conventional machining techniques. For example, current through a seam is a limiting factor in performance for many waveguide cavities. Development of highly reproducible methods for metallic parts through additive manufacturing, referred to colloquially as 3D printing\\x9D, opens the possibility for novel cavity designs which cannot be implemented through conventional methods. We present preliminary investigations of superconducting cavities made through a selective laser melting process, which compacts a granular powder via a high-power laser according to a digitally defined geometry. Initial work suggests that assuming a loss model and numerically optimizing a geometry to minimize dissipation results in modest improvements in device performance. Furthermore, a subset of titanium alloys, particularly, a titanium, aluminum, vanadium alloy (Ti - 6Al - 4V) exhibits properties indicative of a high kinetic inductance material. This work is supported by LDRD 16-SI-004.

  9. Considerations for NSLS-II Synchrotron Radiation Protection When Operating Damping Wigglers at Low Machine Energy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Seletskiy, S.; Podobedov, B.

    2015-12-30

    The NSLS-II storage ring vacuum chamber, including frontends (FE) and beamlines (BL), is protected from possible damage from synchrotron radiation (SR) emitted from insertion devices (IDs) by a dedicated active interlock system (AIS). The system monitors electron beam position and angle and triggers a beam dump if the beam orbit is outside of the active interlock envelope (AIE). The AIE was calculated under the assumptions of 3 GeV beam energy and ID gaps set to their minimum operating values (i.e. “fully closed”). Recently it was proposed to perform machine studies that would ramp the stored beam energy significantly below themore » nominal operational value of 3 GeV. These studies may potentially include the use of NSLS-II damping wigglers (DWs) for electron beam emittance reduction and control.« less

  10. Superconductivity in the Nb-Ru-Ge σ phase

    DOE PAGES

    Carnicom, Elizabeth M.; Xie, Weiwei; Sobczak, Zuzanna; ...

    2017-12-07

    Here, we show that the previously unreported ternary σ-phase material Nb 20.4Ru 5.7Ge 3.9 (Nb 0.68Ru 0.19Ge 0.13) is a superconductor with a critical temperature of 2.2 K. Temperature-dependent magnetic susceptibility, resistance, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant γ for Nb 20.4Ru 5.7Ge 3.9 is 91 mJ mol-f.u. -1K -2 (~3 mJ mol-atom -1K -2) and the specific heat anomaly at the superconducting transition, ΔC/γT c, is approximately 1.38. The zero-temperature upper critical field (µ 0Hc 2(0)) was estimated to be 2 T by resistance data. Field-dependent magnetization data analysis estimated µmore » 0Hc 1(0) to be 5.5 mT. Thus, the characterization shows Nb 20.4Ru 5.7Ge 3.9 to be a type II BCS superconductor. This material appears to be the first reported ternary phase in the Nb-Ru-Ge system, and the fact that there are no previously reported binary Nb-Ru, Nb-Ge, or Ru-Ge σ-phases shows that all three elements are necessary to stabilize the material. An analogous σ-phase in the Ta-Ru-Ge system did not display superconductivity above 1.7 K, which suggests that electron count cannot govern the superconductivity observed. Preliminary characterization of a possible superconducting σ-phase in the Nb-Ru-Ga system is also reported.« less

  11. Superconductivity enhanced by Se doping in Eu3Bi2(S,Se)4F4

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Zhai, H. F.; Tang, Z. J.; Li, L.; Li, Y. K.; Chen, Q.; Chen, J.; Wang, Z.; Feng, C. M.; Cao, G. H.; Xu, Z. A.

    2015-07-01

    We investigated the negative-chemical-pressure effect of Eu3Bi2S4-x Se x F4 (0 ≤ x ≤ 2.0) by the partial substitution of S with Se. The crystalline lattice substantially expands as Se is doped, suggesting an effective negative chemical pressure. With Se/S doping, the charge-density-wave-like anomaly is suppressed, and meanwhile the superconducting transition temperature (T_c) is enhanced. For x = 2.0 , T c reaches 3.35 K and bulk superconductivity is confirmed by the strong diamagnetic signal, with shielding volume fraction over 90%. Magnetic-susceptibility, specific-heat and Hall-effect measurements reveal that the Se/S doping increases the carrier density, corresponding to the increase of the average Eu valence. Our work provides a rare paradigm of negative-chemical-pressure effect.

  12. Superconductivity Induced by Oxygen Doping in Y2 O2 Bi.

    PubMed

    Cheng, Xiyue; Gordon, Elijah E; Whangbo, Myung-Hwan; Deng, Shuiquan

    2017-08-14

    When doped with oxygen, the layered Y 2 O 2 Bi phase becomes a superconductor. This finding raises questions about the sites for doped oxygen, the mechanism of superconductivity, and practical guidelines for discovering new superconductors. We probed these questions in terms of first-principles calculations for undoped and O-doped Y 2 O 2 Bi. The preferred sites for doped O atoms are the centers of Bi 4 squares in the Bi square net. Several Bi 6p x/y bands of Y 2 O 2 Bi are raised in energy by oxygen doping because the 2p x/y orbitals of the doped oxygen make antibonding possible with the 6p x/y orbitals of surrounding Bi atoms. Consequently, the condition necessary for the "flat/steep" band model for superconductivity is satisfied in O-doped Y 2 O 2 Bi. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Is there a path from cuprates towards room-temperature superconductivity?

    DOE PAGES

    Božović, I.; Wu, J.; He, X.; ...

    2017-09-01

    A brief account is presented of an extensive experiment performed at Brookhaven National Laboratory, aimed at understanding the nature of high-temperature superconductivity in cuprates. Over the course of the last 12 years, over 2000 films of the prototypical high- T c superconductor, La 2-xSr xCuO 4, have been synthesized using atomic-layer-by-layer molecular beam epitaxy (ALL-MBE), characterized by a range of techniques, and patterned into devices. These were then used to measure accurately the key physical parameters in both the superconducting and the normal states, and establish their precise dependence on doping, temperature, and external fields. Our results bring in somemore » great surprises, challenge the commonly held beliefs, rule out many theoretical models, and point to a new path for raising T c even further.« less

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

    DOE PAGES

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

    2016-07-28

    Since the discovery of high-temperature superconductivity in cuprates, proposals have been made that pairing may be local, in particular in underdoped samples. Furthermore, we briefly review evidence for local pairs from our experiments on thin films of La 2–xSr xCuO 4, synthesized by atomic layer-by-layer molecular beam epitaxy (ALL-MBE).

  15. Electrical and magnetic properties of superconducting-insulating Pr-doped GdBa2Cu3O7-y

    NASA Astrophysics Data System (ADS)

    Yamani, Z.; Akhavan, M.

    1997-10-01

    An extensive study of magnetic, electrical transport, and structural properties of the normal and superconducting states of Gd1-xPrxBa2Cu3O7-y (GdPr-123) are presented. Ceramic compounds have been synthesized by the solid-state reaction technique, and characterized by x-ray-diffraction, scanning-electron-microscopy, thermogravimetric, and differential-thermal analyses. The superconducting transition temperature is reduced with increasing Pr content x in a nonlinear manner, in contrast to Abrikosov-Gor'kov pair-breaking theory. Magnetic susceptibility measurements show that the nominal Pr valence is 3.86+, independently of x. A metal-insulator transition is observed at xcr~0.45, similar to that in the oxygen-deficient RBa2Cu3O7-y (R-123) system. Based on this resemblance, we suggest that both Pr doping and oxygen deficiency act through the same mechanism. Hence, the environment surrounding the CuO2 layers is important to high-Tc superconductivity (HTSC). In this sense, HTSC cannot completely be a two-dimentional feature. A chain-plane-correlation effect is plausible.

  16. Superconducting Sr 2- xAxCuO 2F 2+ δ( A=Ca, Ba): Synthetic Pathways and Associated Structural Rearrangements

    NASA Astrophysics Data System (ADS)

    Francesconi, M. G.; Slater, P. R.; Hodges, J. P.; Greaves, C.; Edwards, P. P.; Al-Mamouri, M.; Slaski, M.

    1998-01-01

    The low-temperature fluorination of a range of insulating alkaline earth cuprates Sr2-xAxCuO3(A=Ca (0≤x≤2);A=Ba (0≤x≤0.6)) can result in superconducting oxide fluorides Sr2-xAxCuO2F2+δ. In contrast, conventional high-temperature solid-state reactions produce thermodynamically more stable mixtures of oxides and fluorides. Various soft-chemistry fluorination pathways (utilizing F2gas, NH4F,MF2[M=Cu, Zn, Ni, Ag]) are compared with respect to their efficacy and mechanisms. Attention is also focused on the structural features of the mixed-oxide precursor and the final-oxide fluorides to highlight the remarkable structural rearrangements that occur during the low-temperature fluorination. The effects of fluorination of other Sr-Cu-O systems are used to identify the structural requirements of the precursor oxide in order to achieve such transformations.

  17. In-plane chemical pressure essential for superconductivity in BiCh2-based (Ch: S, Se) layered structure

    PubMed Central

    Mizuguchi, Yoshikazu; Miura, Akira; Kajitani, Joe; Hiroi, Takafumi; Miura, Osuke; Tadanaga, Kiyoharu; Kumada, Nobuhiro; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

    2015-01-01

    BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated. In this study, we investigate the relationship between crystal structure and superconducting properties of the BiCh2-based superconductor family, specifically, optimally doped Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2. We use powder synchrotron X-ray diffraction to determine the crystal structures. We show that the structure parameter essential for the emergence of bulk superconductivity in both systems is the in-plane chemical pressure, rather than Bi-Ch bond lengths or in-plane Ch-Bi-Ch bond angle. Furthermore, we show that the superconducting transition temperature for all REO0.5F0.5BiCh2 superconductors can be determined from the in-plane chemical pressure. PMID:26447333

  18. Competition between magnetism and superconductivity in Eu-based intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Stavinoha, Macy; Green, Lance; Chan, Julia; Morosan, Emilia

    Eu-based intermetallic compounds present a path to discover new correlated electronic behavior in quantum materials. Reports of superconductivity, intermediate valence behavior, and heavy fermions indicate that Eu-based compounds are promising routes to study the relationship between crystallography and electronic properties. The present work is focused on EuGa4, an antiferromagnet with TN = 16 K isostructural with the tetragonal RT2M2 (R = rare earth, T = transition metal, M = metal or metalloid) family that exhibits heavy fermion behavior and unconventional superconductivity. Single crystals of the doped series (Eu1-xLax)Ga4, (Eu1-xCax)Ga4, and Eu(Ga1-xAlx)4 have been grown using the self-flux method and tested for change in unit cell volume and magnetic susceptibility. Results show that doping with Ca (isoelectronic doping) and La (hole doping) reduce TN to 12.4 K and 2.3 K, respectively, for Ca doping up to x = 0.11 and La doping up to x = 0.74 without an associated change in unit cell volume. The series Eu(Ga1-xAlx)4 has shown incommensurate-to-commensurate magnetic transitions. Future studies will aim to further decrease TN and the unit cell volume using physical pressure and chemical pressure through doping. ICAM, Gordon and Betty Moore Foundation.

  19. Control of superconductivity by means of electric-field-induced strain in superconductor/piezoelectric hybrids

    NASA Astrophysics Data System (ADS)

    Stamopoulos, D.; Zeibekis, M.; Zhang, S. J.

    2018-01-01

    The controlled modification of superconductivity by any means, specifically in hybrid systems, has attracted much interest in the recent decades. Here, we present experimental data and phenomenological modeling on the control of TC of superconducting (SC) Nb thin films, with thickness 3 nm ≤ dN b≤50 nm, under the application of in-plane strain, S(Eex) induced by an external out-of-plane electric field, Eex to piezoelectric (PE) single crystals, namely, ( 1 -x )Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT), with x = 0.27 and 0.31. We report experimental modification of TC of Nb by Eex, accurately described by a phenomenological model that incorporates the constitutive relation S(Eex) of PMN-xPT. The systematic experimental-phenomenological modeling approach introduced here is generic and paves the way for an understanding of the underlying physical mechanisms in any SC/PE hybrid.

  20. Fe-vacancy and superconductivity in FeSe-based superconductors

    NASA Astrophysics Data System (ADS)

    Wang, C. H.; Chen, T. K.; Chang, C. C.; Lee, Y. C.; Wang, M. J.; Huang, K. C.; Wu, P. M.; Wu, M. K.

    2018-06-01

    This review summarizes recent advancements in FeSe and related systems. The FeSe and related superconductors are currently receiving considerable attention for the high Tcs observed and for many similar features to the high Tc cuprate superconductors. These similarities suggest that understanding the FeSe based compounds could potentially help our understanding of the cuprates. We shall first review the common features observed in the FeSe-based system. It was found that with a careful control of material synthesizing processes, numerous rich phases have been observed in the FeSe-based system. Detailed studies show that the Fe-vacancy ordered phases found in the FeSe based compounds, which are non-superconducting Mott insulators, are the parent compounds of the superconductors. Superconductivity emerges from the parent phases by disordering the Fe vacancy order, often by a simple annealing treatment. Recent high temperature X-ray diffraction experiments show that the degree of structural distortion associated with the disorder of Fe-vacancy is closely related to volume fraction of the superconductivity observed. These results suggest the strong lattice to spin coupling are important for the occurrence of superconductivity in FeSe based superconductors.