Improvement of persistent magnetic field trapping in bulk Y-Ba-Cu-O superconductors

NASA Technical Reports Server (NTRS)

Chen, In-Gann; Weinstein, Roy

1993-01-01

For type-II superconductors, magnetic field can be trapped due to persistent internal supercurrent. Quasi-persistent magnetic fields near 2 T at 60 K (and 1.4 T at 77 K) have been measured in minimagnets made of proton-irradiated melt-textured Y-Ba-Cu-O (MT-Y123) samples. Using the trapping effect, high-field permanent magnets with dipole, quadrupole, or more complicated configurations can be made of existing MT-Y123 material, thus bypassing the need for high-temperature superconductor (HTS) wires. A phenomenological current model has been developed to account for the trapped field intensity and profile in HTS samples. This model is also a guide to select directions of materials development to further improve field trapping properties. General properties such as magnetic field intensities, spatial distributions, stabilities, and temperature dependence of trapped field are discussed.

The Effect of Oxygen Flow on the Transition Temperature of Hg0.75Pb0.25Sr2-yBayCa2Cu3O8+ δ Superconductors

NASA Astrophysics Data System (ADS)

Jasim, Kareem A.; Al-Khafaji, Raghad S.

2018-05-01

In this paper, there are three different high temperature superconductors which are Hg0.75Pb0.25Sr2-y BayCa2Cu3O8+δ with deferent weight fractions y = 0.10, 0.20 and 0.25 that have been prepared successfully by solid state reaction and the samples have been equipped with/without O2 flow. The optimum calcinations is 1073 K and the sintering process that has been achieved within 1128-1133 K. Transition temperature Tc has been found by using four probe technique through electrical resistivity measurements. The greatest Tc that has been found for Hg0.75Pb0.25Sr1.75 Ba0.25Ca2Cu3O8.31 is 115 oK. Oxygen content (O2) flow exhibits high-phased superconductors that is similar to the samples prepared without O2. Investigation of X-ray diffraction (XRD) is revealed (tetragonal structure) by the c-axis lattice parameter increasing of the samples substituted with Ba. It has been established, from the calculated results, that the Ba variation concentrations of all samples products a modification in the density (ρm), (c/a) and volume fraction (VPh(2223)).

Improvement in trapped fields by stacking bulk superconductors

NASA Astrophysics Data System (ADS)

Suzuki, A.; Wongsatanawarid, A.; Seki, H.; Murakami, M.

2009-10-01

We studied the effects of stacking several bulk superconductor blocks on the field trapping properties. In order to avoid the detrimental effects of the bottom deteriorated parts, bulk Dy-Ba-Cu-O superconductors 45 mm in diameter and 10 mm in thickness were cut from the top parts of as-grown bulk blocks of 25 mm diameter. We stacked the superconductors and measured the field distribution as a function of the gap. The trapped field measurements were performed by field-cooling the samples inserted in between two permanent magnets with liquid nitrogen. It was found that the trapped field values are almost doubled when the number of stacked bulk superconductors increased from two to three. The present results clearly show that one can expect beneficial effects of increasing the ratio of the height to the diameter even in bulk high temperature superconductors.

Effect of grain-alignment on the levitation force of melt-processed YBCO bulk superconductors

NASA Astrophysics Data System (ADS)

Yang, Wan-min; Zhou, Lian; Feng, Yong; Zhang, Ping-xiang; Wu, Min-zhi; Wu, Xiao-zu; Gawalek, W.

1999-07-01

Single-domain YBCO bulk superconductors have been fabricated by Top Seeded Melt Slow Cooling Growth(TSSCG) process. Two typical YBCO cylinder samples with differential grain-alignment were selected for the investigation of the relationship between the grain-alignment and the levitation force under the same testing condition at liquid nitrogen temperature. It is found that the levitation force values is much different for the two samples, the levitation force of the sample with H par c-axis is more than two times higher than that of the samples with H ⊥ c-axis. So it is necessary to take account of this anisotropy in practical applications. The relationship between a magnet and a superconductor can be well described with a double exponential function. All the results are discussed in details.

Positron annihilation study of the high- Tc (Bi,Pb) 2Sr 2Ca 2Cu 3O x superconductor

NASA Astrophysics Data System (ADS)

Lim, H. J.; Byrne, J. G.

1997-03-01

Positron lifetime spectroscopy (PLS) and positron Doppler-broadening spectroscopy (PDBS) were applied to the high- Tc lead-doped Bi 2Sr 2Ca 2Cu 3O x (BPSCCO 2223) superconductor as a function of temperature. Neither positron lifetimes nor Doppler parameters ( S, W, and{S}/{W}) showed significant change through Tc. This may result from having the highest positron density in the open BiO 2 double layers and no significant positron density in the superconducting CuO 2 layers where positrons, if mainly present, are known to be sensitive to the transition in other high- Tc superconductors. Doppler parameters showed that the probability of positron annihilations with core electrons in the lattice slightly increased and that the probability of positron annihilations with conduction electrons slightly decreased as temperature decreased from ambient temperature to 20 K. The lifetime associated with positron annihilations in the perfect lattice of the sample ( τ1) was 209 ps and, due to the annihilations at internal surfaces or voids in the sample ( τ2) was about 540 ps, independent of temperature. Finally, the mean lifetime for BSCCO 2223 was about 307 ps.

Surface texturing of superconductors by controlled oxygen pressure

DOEpatents

Chen, N.; Goretta, K.C.; Dorris, S.E.

1999-01-05

A method of manufacture of a textured layer of a high temperature superconductor on a substrate is disclosed. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO{sub 2} atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO{sub 2} atmosphere to cause solidification of the molten superconductor in a textured surface layer. 8 figs.

Surface texturing of superconductors by controlled oxygen pressure

DOEpatents

Chen, Nan; Goretta, Kenneth C.; Dorris, Stephen E.

1999-01-01

A method of manufacture of a textured layer of a high temperature superconductor on a substrate. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO.sub.2 atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO.sub.2 atmosphere to cause solidification of the molten superconductor in a textured surface layer.

Measuring the interaction force between a high temperature superconductor and a permanent magnet

NASA Astrophysics Data System (ADS)

Valenzuela, S. O.; Jorge, G. A.; Rodríguez, E.

1999-11-01

Repulsive and attractive forces are both possible between a superconducting sample and a permanent magnet, and they can give rise to magnetic levitation or free-suspension phenomena, respectively. We show experiments to quantify this magnetic interaction, which represents a promising field with regard to short-term technological applications of high temperature superconductors. The measuring technique employs an electronic balance and a rare-earth magnet that induces a magnetic moment in a melt-textured YBa2Cu3O7 superconductor immersed in liquid nitrogen. The simple design of the experiments allows a fast and easy implementation in the advanced physics laboratory with a minimum cost. Actual levitation and suspension demonstrations can be done simultaneously as a help to interpret magnetic force measurements.

The phenomenon of voltage controlled switching in disordered superconductors.

PubMed

Ghosh, Sanjib; De Munshi, D

2014-01-15

The superconductor-to-insulator transition (SIT) is a phenomenon occurring in highly disordered superconductors and may be useful in the development of superconducting switches. The SIT has been demonstrated to be induced by different external parameters: temperature, magnetic field, electric field, etc. However, the electric field induced SIT (ESIT), which has been experimentally demonstrated for some specific materials, holds particular promise for practical device development. Here, we demonstrate, from theoretical considerations, the occurrence of the ESIT. We also propose a general switching device architecture using the ESIT and study some of its universal behavior, such as the effects of sample size, disorder strength and temperature on the switching action. This work provides a general framework for the development of such a device.

Thermomagnetic phenomena in the mixed state of high temperature superconductors

NASA Technical Reports Server (NTRS)

Meilikhov, E. Z.

1995-01-01

Galvano- and thermomagnetic-phenomena in high temperature superconductors, based on kinetic coefficients, are discussed, along with a connection between the electric field and the heat flow in superconductor mixed state. The relationship that determines the transport coefficients of high temperature superconductors in the mixed state based on Seebeck and Nernst effects is developed. It is shown that this relationship is true for a whole transition region of the resistive mixed state of a superconductor. Peltier, Ettingshausen and Righi-Leduc effects associated with heat conductivity as related to high temperature superconductors are also addressed.

Advantages of barium peroxide in the powder synthesis of perovskite superconductors

NASA Technical Reports Server (NTRS)

Hepp, A. F.; Gaier, J. R.; Philipp, W. H.; Warner, J. D.; Garlick, R. G.; Pouch, J. J.

1988-01-01

This paper compares reaction chemistry, material processing, and material characteristics for the solid state reaction using BaCO3 or BaO2 in the synthesis of perovskite superconductors. Results are presented for weight loss and X-ray diffraction, sample morphology and homogeneity as monitored by SEM and EDS, and the superconductivity critical temperature and ac susceptibility. Greater mass density, increased sample homogeneity, lower resistance, and improved reproducibility for material are found when BaO32 is used.

High temperature superconductor dc-SQUID microscope with a soft magnetic flux guide

NASA Astrophysics Data System (ADS)

Poppe, U.; Faley, M. I.; Zimmermann, E.; Glaas, W.; Breunig, I.; Speen, R.; Jungbluth, B.; Soltner, H.; Halling, H.; Urban, K.

2004-05-01

A scanning SQUID microscope based on high-temperature superconductor (HTS) dc-SQUIDs was developed. An extremely soft magnetic amorphous foil was used to guide the flux from room temperature samples to the liquid-nitrogen-cooled SQUID sensor and back. The flux guide passes through the pick-up loop of the HTS SQUID, providing an improved coupling of magnetic flux of the object to the SQUID. The device measures the z component (direction perpendicular to the sample surface) of the stray field of the sample, which is rastered with submicron precision in the x-y direction by a motorized computer-controlled scanning stage. A lateral resolution better than 10 µm, with a field resolution of about 0.6 nT Hz-1/2 was achieved for the determination of the position of the current carrying thin wires. The presence of the soft magnetic foil did not significantly increase the flux noise of the SQUID.

Fe substitution and pressure effects on superconductor Re6Hf

NASA Astrophysics Data System (ADS)

Yang, Jinhu; Guo, Yang; Wang, Hangdong; Chen, Bin

2018-04-01

Polycrystalline samples of (Re1-xFex) 6Hf were synthesized by arc-melting method and the phase purity of the samples was confirmed by powder X-ray diffraction method. In this paper, we report the Fe substitution and pressure effect on non-centrosymmetric superconductor Re6Hf. The superconducting transition temperature, TC, is confirmed by the measurements of magnetic susceptibility, electrical resistivity for x ≤ 0.22 samples with the temperature down to 2 K. We find that the TC is suppressed with the increase of Fe content. The upper critical field Hc2 is larger than the value predicted by the WHH theory and shows a linear temperature dependence down to 2 K. When upon the application of external pressure up to 2.5 GPa, the TC decreases monotonically at a rate dlnTC/dP of 0.01 GPa-1.

Fluctuation-induced conductivity in melt-textured Pr-doped YBa2Cu3O7-δ composite superconductor

NASA Astrophysics Data System (ADS)

Opata, Yuri Aparecido; Monteiro, João Frederico Haas Leandro; Siqueira, Ezequiel Costa; Rodrigues, Pedro Júnior; Jurelo, Alcione Roberto

2018-04-01

In this study, the effects of thermal fluctuations on the electrical conductivity in melt-textured YBa2Cu3O7-δ, Y0.95Pr0.05Ba2Cu3O7-δ and (YBa2Cu3O7-δ)0.95-(PrBa2Cu3O7-δ)0.05 composite superconductor were considered. The composite superconductor samples were prepared through the top seeding method using melt-textured NdBa2Cu3O7-d seeds. The resistivity measurements were performed with a low-frequency, low-current AC technique in order to extract the temperature derivative and analyze the influence of the praseodymium ion on the normal superconductor transition and consequently on the fluctuation regimes. The results show that the resistive transition is a two-step process. In the normal phase, above the critical temperature, Gaussian and critical fluctuation regimes were identified, while below the critical temperature, in the regime near the approach to the zero-resistance state, the fluctuation conductivity diverges as expected in a paracoherent-coherent transition.

Analysis of YBCO high temperature superconductor doped with silver nanoparticles and carbon nanotubes using Williamson-Hall and size-strain plot

NASA Astrophysics Data System (ADS)

Dadras, Sedigheh; Davoudiniya, Masoumeh

2018-05-01

This paper sets out to investigate and compare the effects of Ag nanoparticles and carbon nanotubes (CNTs) doping on the mechanical properties of Y1Ba2Cu3O7-δ (YBCO) high temperature superconductor. For this purpose, the pure and doped YBCO samples were synthesized by sol-gel method. The microstructural analysis of the samples is performed using X-ray diffraction (XRD). The crystalline size, lattice strain and stress of the pure and doped YBCO samples were estimated by modified forms of Williamson-Hall analysis (W-H), namely, uniform deformation model (UDM), uniform deformation stress model (UDSM) and the size-strain plot method (SSP). These results show that the crystalline size, lattice strain and stress of the YBCO samples declined by Ag nanoparticles and CNTs doping.

Electronic structure of the bismuth family of high-temperature superconductors

NASA Astrophysics Data System (ADS)

Feng, Donglai

High temperature superconductivity remains the central intellectual problem in condensed matter physics fifteen years after its discovery. Angle resolved photoemission spectroscopy (ARPES) directly probes the electronic structure, and has played an important role in the field of high temperature superconductors. With the recent advances in sample growth and the photoemission technique, we are able to study the electronic structure in great detail, and address regimes that were previously inaccessible. This thesis work contains systematic photoemission studies of the electronic structure of the Bi-family of high temperature superconductors, which include the single-layer system (Bi2201), the bi-layer system (Bi2212), and the tri-layer system (Bi2223). We show that, unlike conventional BCS superconductors, phase coherence information emerges in the single particle excitation spectrum of high temperature superconductors as the superconducting peak in Bi2212. The universality and various properties of this superconducting peak are studied in various systems. We argue that the origin of the superconducting peak may provide the key to understanding the mechanism of High-Tc superconductors. In addition, we identified a new experimental energy scale in the bilayer material, the anisotropic intra-bilayer coupling energy. For a long time, it was predicted that this energy scale would cause bilayer band splitting. We observe this phenomenon, for the first time, in heavily overdoped Bi2212. This new observation requires the revision of the previous picture of the electronic excitation in the Brillouin zone boundary. As the first ARPES study of a trilayer system, various detailed electronic properties of Bi2223 are examined. We show that, comparing with Bi2212, both superconducting gap and relative superconducting peak intensity become larger in Bi2223, however, the strength of the interlayer coupling within each unit cell is possibly weaker. These results suggest that the large superconducting phase transition temperature in a high temperature superconductor is associated with parameters that cause both large pairing strength and strong phase coherence in the system. The number of CuO2 layers in each unit cell is just one of the factors that affect these parameters.

Investigation of magnetic properties of superconductors Y0.98 - x Cax Co0.02 Ba2 Cu3O7 - δ

NASA Astrophysics Data System (ADS)

Pourasad, Sepideh; Shakeripour, Hamideh; Hosseini, SeyedSajad; Salamati, Hadi

2018-06-01

The effect of Co2+, 3+ and Ca2+ substitution in Y3+ site in YBa2Cu3O7-δ superconductor has been studied. The series of high temperature superconducting samples of Y1-y-xCoyCaxBa2Cu3O7-δ with 0 ≤ x ≤ 0.015 and y = 0.020 were prepared by solid-state reaction method. The samples were characterized for phase purity and lattice parameter variations by X-ray diffraction. The AC susceptibility curves, χ'(T), show that in reserving cobalt fixed sample with the optimum Tc, by substitution of divalent Ca2+ at the trivalent Y3+ site no sensitive increasing happen in the superconducting transition temperature.

Vertical Magnetic Levitation Force Measurement on Single Crystal YBaCuO Bulk at Different Temperatures

NASA Astrophysics Data System (ADS)

Celik, Sukru; Guner, Sait Baris; Ozturk, Kemal; Ozturk, Ozgur

Magnetic levitation force measurements of HTS samples are performed with the use of liquid nitrogen. It is both convenient and cheap. However, the temperature of the sample cannot be changed (77 K) and there is problem of frost. So, it is necessary to build another type of system to measure the levitation force high Tc superconductor at different temperatures. In this study, we fabricated YBaCuO superconducting by top-seeding-melting-growth (TSMG) technique and measured vertical forces of them at FC (Field Cooling) and ZFC (Zero Field Cooling) regimes by using our new designed magnetic levitation force measurement system. It was used to investigate the three-dimensional levitation force and lateral force in the levitation system consisting of a cylindrical magnet and a permanent cylindrical superconductor at different temperatures (37, 47, 57, 67 and 77 K).

Single Crystal Synthesis and STM Studies of High Temperature Superconductors

NASA Technical Reports Server (NTRS)

Barrientos, Alfonso

1997-01-01

This is a final report for the work initiated in September of 1994 under the grant NAG8-1085 - NASA/OMU, on the fabrication of bulk and single crystal synthesis, specific heat measuring and STM studies of high temperature superconductors. Efforts were made to fabricate bulk and single crystals of mercury based superconducting material. A systematic thermal analysis on the precursors for the corresponding oxides and carbonates were carried out to synthesized bulk samples. Bulk material was used as seed in an attempt to grow single crystals by a two-step self flux process. On the other hand bulk samples were characterized by x-ray diffraction, electrical resistivity and magnetic susceptibility, We studied the specific heat behavior in the range from 80 to 300 K. Some preliminary attempts were made to study the atomic morphology of our samples. As part of our efforts we built an ac susceptibility apparatus for measuring the transition temperature of our sintered samples.

Magnetic exchange coupling through superconductors: A trilayer study

NASA Astrophysics Data System (ADS)

Sá de Melo, C. A.

2000-11-01

The possibility of magnetic exchange coupling between two ferromagnets (F) separated by a superconductor (S) spacer is analyzed using the functional integral method. For this coupling to occur three prima facie conditions need to be satisfied. First, an indirect exchange coupling between the ferromagnets must exist when the superconductor is in its normal state. Second, superconductivity must not be destroyed due to the proximity to ferromagnetic boundaries. Third, roughness of the F/S interfaces must be small. Under these conditions, when the superconductor is cooled to below its critical temperature, the magnetic coupling changes. The appearance of the superconducting gap introduces a new length scale (the coherence length of the superconductor) and modifies the temperature dependence of the indirect exchange coupling existent in the normal state. The magnetic coupling is oscillatory both above and below the the critical temperature of the superconductor, as well as strongly temperature-dependent. However, at low temperatures the indirect exchange coupling decay length is controlled by the coherence length of the superconductor, while at temperatures close to and above the critical temperature of the superconductor the magnetic coupling decay length is controlled by the thermal length.

Electro-physical properties of superconducting ceramic thick film prepared by partial melting method.

PubMed

Lee, Sang Heon

2013-05-01

BiSrCaCuO superconductor thick films were prepared at several curing temperatures, and their electro-physical properties were determined to find an optimum fabrication conditions. Critical temperatures of the superconductors were decreased with increasing melting temperature, which was related to the amount of equilibrium phases of the superconducting materials with temperature. The critical temperature of BiSrCaCuO bulk and thick film superconductors were 107 K and 96 K, respectively. The variation of susceptibility of the superconductor thick film formed at 950 degrees C had multi-step-type curve for 70 G externally applied field, whereas, a superconductor thick film formed at 885 degrees C had a single step-type curve like a bulk BiSrCaCuO ceramic superconductor in the temperature-susceptibility curves. A partial melting at 865 degrees C is one of optimum conditions for making a superconductor thick film with a relatively homogeneous phase.

Non-Equilibrium Superconductivity and Magnetic Pair Breaking in Perovskite Half-Metallic Ferromagnet-Insulator-Superconductor (F-I-S) Heterostructures

NASA Technical Reports Server (NTRS)

Fu, C.-C.; Yeh, N.-C.; Samoilov, A. V.; Vakili, K.; Li, Y.; Vasquez, R. P.

1999-01-01

The effect of spin-polarized quasiparticle currents on the critical current density (J-c) of cuprate superconductors is studied in perovskite F-I-S heterostructures as a function of insulator thickness and of underlying magnetic materials. A pulsed current technique is employed to minimize extraneous Joule heating on the superconductor. At temperatures near T-c, F-I-S samples with insulator thicknesses\\1e2nm show precipitous decrease in J_c as current injection (I_m) is increased. In contrast, J_c in a controlled sample with a substituted non-magnetic material (N-I-S) exhibit no dependence on I_m. Similarly, a F-I-S sample with a 10 mn insulating barrier also show little J_c effect versus I_m. At low temperatures with I_m = 0, significant suppression of J-c is observed only in the thin barrier F-I-S samples, although T_c and the normal-state resistivity of all samples are comparable. These phenomena can be attributed to the Cooper pair breaking induced by externally-injected and internally-reflected spin-polarized quasiparticle currents. We estimate an order of magnitude range for the spin diffusion length of 100 nm to 100\\ mum.

4He sample probe for combined microwave and dc transport measurements

NASA Astrophysics Data System (ADS)

Dobrovolskiy, Oleksandr V.; Franke, Jörg; Huth, Michael

2015-03-01

Combined microwave and dc electrical transport measurements at low temperatures represent a valuable experimental method in many research areas. In particular, when samples are conventional superconductors, a typical experiment requires a combination of helium temperatures, a wide range of magnetic fields, and the utilization of coaxial lines along with the usual dc wiring. We report on the general design features and the microwave performance of a custom-made low-temperature sample probe, with a measurement bandwidth tested from dc to 20 GHz. Equipped with six coaxial cables, a heater, Hall and temperature sensors, the probe fits into a ⊘32 mm shaft. We present our setup, analyze its microwave performance, and describe two representative experiments enabled by this system. The proposed setup will be essential for a systematic study of the dc and ac response of the vortex dynamics in nanopatterned superconductors subject to combined dc and microwave stimuli. Besides, it will be valuable for the investigation of a broad class of nonlinear stochastic systems where a combination of dc and high-frequency ac driving in a wide temperature range is necessary.

Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors

NASA Technical Reports Server (NTRS)

Vasquez, Richard P. (Inventor); Hunt, Brian D. (Inventor); Foote, Marc C. (Inventor)

1994-01-01

Epitaxial heterojunctions formed between high temperature superconductors and metallic or semiconducting oxide barrier layers are provided. Metallic perovskites such as LaTiO3, CaVO3, and SrVO3 are grown on electron-type high temperature superconductors such as Nd(1.85)Ce(0.15)CuO(4-x). Alternatively, transition metal bronzes of the form A(x)MO(3) are epitaxially grown on electron-type high temperature superconductors. Also, semiconducting oxides of perovskite-related crystal structures such as WO3 are grown on either hole-type or electron-type high temperature superconductors.

Magnetic exchange coupling through superconductors : a trilayer study.

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

Sa de Melo, C. A. R.; Materials Science Division

1997-09-08

The possibility of magnetic exchange coupling between two ferromagnets (F) separated by a superconductor (S) spacer is analyzed using the functional integral method. For this coupling to occur three prima facie conditions need to be satisfied. First, an indirect exchange coupling between the ferromagnets must exist when the superconductor is in its normal state. Second, superconductivity must not be destroyed due to the proximity to ferromagnetic boundaries. Third, roughness of the F/S interfaces must be small. Under these conditions, when the superconductor is cooled to below its critical temperature, the magnetic coupling changes. The appearance of the superconducting gap introducesmore » a new length scale (the coherence length of the superconductor) and modifies the temperature dependence of the indirect exchange coupling existent in the normal state. The magnetic coupling is oscillatory both above and below the critical temperature of the superconductor, as well as strongly temperature-dependent. However, at low temperatures the indirect exchange coupling decay length is controlled by the coherence length of the superconductor, while at temperatures close to and above the critical temperature of the superconductor the magnetic coupling decay length is controlled by the thermal length.« less

Engineered flux-pinning centers in BSCCO TBCCO and YBCO superconductors

DOEpatents

Goretta, Kenneth C.; Lanagan, Michael T.; Miller, Dean J.; Sengupta, Suvankar; Parker, John C.; Hu, Jieguang; Balachandran, Uthamalingam; Siegel, Richard W.; Shi, Donglu

1999-01-01

A method of preparing a high temperature superconductor. A method of preparing a superconductor includes providing a powdered high temperature superconductor and a nanophase material. These components are combined to form a solid compacted mass with the material disposed in the polycrystalline high temperature superconductor. This combined mixture is rapidly heated, forming a dispersion of nanophase size particles without a eutectic reaction. These nanophase particles can have a flat plate or columnar type morphology.

Preparation, structure and superconductivity of high T(c) compounds: Research of high temperature superconductors in Hungary

NASA Technical Reports Server (NTRS)

Kirschner, I.

1995-01-01

In this paper the main directions, methods and results of the investigation of high-T(c) superconductors in Hungary are briefly summarized. The fundamental idea of this research is to study the effect of starting conditions on the microstructure of samples and the influence of the latter one on their superconducting parameters. The investigation concerning technical development is also mentioned.

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.

High-temperature superconductor bulk magnets that can trap magnetic fields of over 17 tesla at 29 K.

PubMed

Tomita, Masaru; Murakami, Masato

2003-01-30

Large-grain high-temperature superconductors of the form RE-Ba-Cu-O (where RE is a rare-earth element) can trap magnetic fields of several tesla at low temperatures, and so can be used for permanent magnet applications. The magnitude of the trapped field is proportional to the critical current density and the volume of the superconductor. Various potential engineering applications for such magnets have emerged, and some have already been commercialized. However, the range of applications is limited by poor mechanical stability and low thermal conductivity of the bulk superconductors; RE-Ba-Cu-O magnets have been found to fracture during high-field activation, owing to magnetic pressure. Here we present a post-fabrication treatment that improves the mechanical properties as well as thermal conductivity of a bulk Y-Ba-Cu-O magnet, thereby increasing its field-trapping capacity. First, resin impregnation and wrapping the materials in carbon fibre improves the mechanical properties. Second, a small hole drilled into the centre of the magnet allows impregnation of Bi-Pb-Sn-Cd alloy into the superconductor and inclusion of an aluminium wire support, which results in a significant enhancement of thermal stability and internal mechanical strength. As a result, 17.24 T could be trapped, without fracturing, in a bulk Y-Ba-Cu-O sample of 2.65 cm diameter at 29 K.

Engineered flux-pinning centers in BSCCO TBCCO and YBCO superconductors

DOEpatents

Goretta, K.C.; Lanagan, M.T.; Miller, D.J.; Sengupta, S.; Parker, J.C.; Hu, J.; Balachandran, U.; Siegel, R.W.; Shi, D.

1999-07-27

A method of preparing a high temperature superconductor is disclosed. A method of preparing a superconductor includes providing a powdered high temperature superconductor and a nanophase material. These components are combined to form a solid compacted mass with the material disposed in the polycrystalline high temperature superconductor. This combined mixture is rapidly heated, forming a dispersion of nanophase size particles without a eutectic reaction. These nanophase particles can have a flat plate or columnar type morphology. 4 figs.

Sealed glass coating of high temperature ceramic superconductors

DOEpatents

Wu, W.; Chu, C.Y.; Goretta, K.C.; Routbort, J.L.

1995-05-02

A method and article of manufacture of a lead oxide based glass coating on a high temperature superconductor is disclosed. The method includes preparing a dispersion of glass powders in a solution, applying the dispersion to the superconductor, drying the dispersion before applying another coating and heating the glass powder dispersion at temperatures below oxygen diffusion onset and above the glass melting point to form a continuous glass coating on the superconductor to establish compressive stresses which enhance the fracture strength of the superconductor. 8 figs.

Sealed glass coating of high temperature ceramic superconductors

DOEpatents

Wu, Weite; Chu, Cha Y.; Goretta, Kenneth C.; Routbort, Jules L.

1995-01-01

A method and article of manufacture of a lead oxide based glass coating on a high temperature superconductor. The method includes preparing a dispersion of glass powders in a solution, applying the dispersion to the superconductor, drying the dispersion before applying another coating and heating the glass powder dispersion at temperatures below oxygen diffusion onset and above the glass melting point to form a continuous glass coating on the superconductor to establish compressive stresses which enhance the fracture strength of the superconductor.

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 Ba_ {1-x}K_ xBiO_3 is nearly temperature independent. This is in contrast to other oxide superconductors, which typically show metallic behavior. We conclude that the BCS theory adequately describes the properties of Ba_{1-x }K_ xBiO_3, as determined in this study.

Contact resistance and normal zone formation in coated yttrium barium copper oxide superconductors

NASA Astrophysics Data System (ADS)

Duckworth, Robert Calvin

2001-11-01

This project presents a systematic study of contact resistance and normal zone formation in silver coated YBa2CU3Ox (YBCO) superconductors. A unique opportunity exists in YBCO superconductors because of the ability to use oxygen annealing to influence the interfacial properties and the planar geometry of this type of superconductor to characterize the contact resistance between the silver and YBCO. The interface represents a region that current must cross when normal zones form in the superconductor and a high contact resistance could impede the current transfer or produce excess Joule heating that would result in premature quench or damage of the sample. While it has been shown in single-crystalline YBCO processing methods that the contact resistance of the silver/YBCO interface can be influenced by post-process oxygen annealing, this has not previously been confirmed for high-density films, nor for samples with complete layers of silver deposited on top of the YBCO. Both the influence of contact resistance and the knowledge of normal zone formation on conductor sized samples is essential for their successful implementation into superconducting applications such as transmission lines and magnets. While normal zone formation and propagation have been studied in other high temperature superconductors, the amount of information with respect to YBCO has been very limited. This study establishes that the processing method for the YBCO does not affect the contact resistance and mirrors the dependence of contact resistance on oxygen annealing temperature observed in earlier work. It has also been experimentally confirmed that the current transfer length provides an effective representation of the contact resistance when compared to more direct measurements using the traditional four-wire method. Finally for samples with low contact resistance, a combination of experiments and modeling demonstrate an accurate understanding of the key role of silver thickness and substrate thickness on the stability of silver-coated YBCO Rolling Assisted Bi-Axially Textured Substrates conductors. Both the experimental measurements and the one-dimensional model show that increasing the silver thickness results in an increased thermal runaway current; that is, the current above which normal zones continue to grow due to insufficient local cooling.

Sample environment for neutron scattering measurements of internal stresses in engineering materials in the temperature range of 6 K to 300 K.

PubMed

Kirichek, O; Timms, J D; Kelleher, J F; Down, R B E; Offer, C D; Kabra, S; Zhang, S Y

2017-02-01

Internal stresses in materials have a considerable effect on material properties including strength, fracture toughness, and fatigue resistance. The ENGIN-X beamline is an engineering science facility at ISIS optimized for the measurement of strain and stress using the atomic lattice planes as a strain gauge. Nowadays, the rapidly rising interest in the mechanical properties of engineering materials at low temperatures has been stimulated by the dynamic development of the cryogenic industry and the advanced applications of the superconductor technology. Here we present the design and discuss the test results of a new cryogenic sample environment system for neutron scattering measurements of internal stresses in engineering materials under a load of up to 100 kN and in the temperature range of 6 K to 300 K. Complete cooling of the system starting from the room temperature down to the base temperature takes around 90 min. Understanding of internal stresses in engineering materials at cryogenic temperatures is vital for the modelling and designing of cutting-edge superconducting magnets and other superconductor based applications.

Sample environment for neutron scattering measurements of internal stresses in engineering materials in the temperature range of 6 K to 300 K

NASA Astrophysics Data System (ADS)

Kirichek, O.; Timms, J. D.; Kelleher, J. F.; Down, R. B. E.; Offer, C. D.; Kabra, S.; Zhang, S. Y.

2017-02-01

Internal stresses in materials have a considerable effect on material properties including strength, fracture toughness, and fatigue resistance. The ENGIN-X beamline is an engineering science facility at ISIS optimized for the measurement of strain and stress using the atomic lattice planes as a strain gauge. Nowadays, the rapidly rising interest in the mechanical properties of engineering materials at low temperatures has been stimulated by the dynamic development of the cryogenic industry and the advanced applications of the superconductor technology. Here we present the design and discuss the test results of a new cryogenic sample environment system for neutron scattering measurements of internal stresses in engineering materials under a load of up to 100 kN and in the temperature range of 6 K to 300 K. Complete cooling of the system starting from the room temperature down to the base temperature takes around 90 min. Understanding of internal stresses in engineering materials at cryogenic temperatures is vital for the modelling and designing of cutting-edge superconducting magnets and other superconductor based applications.

Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

NASA Technical Reports Server (NTRS)

Roth, Don J.; Hepp, Aloysius F.; Deguire, Mark R.; Dolhert, Leonard E.

1991-01-01

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu30(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Spatial variations in ac susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

NASA Technical Reports Server (NTRS)

Roth, Don J.; Deguire, Mark R.; Dolhert, Leonard E.; Hepp, Aloysius F.

1991-01-01

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu3O(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

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

PubMed

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

2018-01-01

High-Temperature Superconductors (HTS) are potential materials for high-field magnets, low-loss transmission cables, and Superconducting Magnetic Energy Storage (SMES) due to their high upper critical magnetic field (H c2 ) and critical temperature (T c ). The critical current (I c ) of HTS, which is one of the most important parameters for superconductor application, depends strongly on the magnetic fields and temperatures. A new I c measurement system that can carry out accurate I c measurement for HTS short samples with various temperatures (4.2-80 K), magnetic fields (0-14 T), and angles of the magnetic field (0°-90°) has been developed. The I c measurement system mainly consists of a measurement holder, temperature-control system, background magnet, test cryostat, data acquisition system, and DC power supply. The accuracy of temperature control is better than ±0.1 K over the 20-80 K range and ±0.05 K when measured below 20 K. The maximum current is over 1000 A with a measurement uncertainty of 1%. The system had been successfully used for YBa 2 Cu 3 O 7-x (YBCO) tapes I c determination with different temperatures and magnetic fields.

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

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

Superconducting magnetic control system for manipulation of particulate matter and magnetic probes in medical and industrial applications

DOEpatents

Cha, Yung Sheng; Hull, John R.; Askew, Thomas R.

2006-07-11

A system and method of controlling movement of magnetic material with at least first and second high temperature superconductors at spaced locations. A plurality of solenoids are associated with the superconductors to induce a persistent currents in preselected high temperature superconductors establishing a plurality of magnetic fields in response to pulsed currents introduced to one or more of the solenoids. Control mechanism in communication with said solenoids and/or said high temperature superconductors are used to demagnetize selected ones of the high temperature superconductors to reduce the magnetic fields substantially to zero. Magnetic material is moved between magnetic fields by establishing the presence thereof and thereafter reducing magnetic fields substantially to zero and establishing magnetic fields in other superconductors arranged in a predetermined configuration.

Influence of the interaction between the inter- and intragranular magnetic responses in the analysis of the ac susceptibility of a granular FeSe0.5Te0.5 superconductor

NASA Astrophysics Data System (ADS)

Mancusi, D.; Polichetti, M.; Cimberle, M. R.; Pace, S.

2015-09-01

The temperature-dependent fundamental ac susceptibility of a granular superconductor in the absence of dc fields has been analyzed by developing a phenomenological model for effective magnetic fields, taking into account the influence of the magnetic interaction between the intergranular and the intragranular magnetizations due to demagnetizing effects. For this purpose a policrystal Fe-based superconductor FeSe0.5Te0.5 sample has been studied. By the frequency dependence of the peaks of the temperature-dependent imaginary part of the fundamental complex susceptibility, the dependence on temperature of the characteristic times both for intergranular and intragranular relaxations of magnetic flux are derived, and the corresponding relaxation processes due to combinations of the flux creep, the flux flow and the thermally activated flux flow regimes are identified on the basis of the effective magnetic fields both at the sample surface and at the grains’ surfaces. Such characteristic times, through the Havriliak-Negami function, determine the temperature and the frequency dependences of the complex susceptibility. The comparison of the numerically obtained curves with the experimental ones confirms the relevance, for identifying the intergranular and intragranular contributions to the ac magnetic response and the corresponding flux dynamical regimes, of the interaction between the intergranular and intragranular magnetizations due to demagnetizing effects.

Electronic structure of the iron-based superconductor (La,Eu)FeAsO1-xFx investigated by laser photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Malaeb, Walid; Awad, Ramadan; Hibino, Taku; Kamihara, Yoichi; Kondo, Takeshi; Shin, Shik

2018-05-01

We have implemented laser photoemission spectroscopy (PES) to investigate the electronic structure of the iron-based superconductor (La,Eu)FeAsO1-xFx (LaEu1111) which is an interesting compound in the "1111" family showing a high value of the superconducting (SC) transition temperature (Tc) due to Eu doping. At least two energy scales were observed from the PES data in the SC compound: One at ∼14 meV closing around Tc and thus corresponding to the SC gap. Another energy scale appears at ∼35 meV and survives at temperatures above Tc which represents the pseudogap (PG). The non-SC sample (La,Eu)FeAsO shows a PG at ∼ 41 meV. These observations in this new superconductor are consistent with the general trend followed by other compounds in the "1111" family.

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

Lombardo, v.; Barzi, E.; Turrioni, D.

Superconducting magnets with magnetic fields above 20 T will be needed for a Muon Collider and possible LHC energy upgrade. This field level exceeds the possibilities of traditional Low Temperature Superconductors (LTS) such as Nb{sub 3}Sn and Nb{sub 3}Al. Presently the use of high field high temperature superconductors (HTS) is the only option available for achieving such field levels. Commercially available YBCO comes in tapes and shows noticeable anisotropy with respect to field orientation, which needs to be accounted for during magnet design. In the present work, critical current test results are presented for YBCO tape manufactured by Bruker. Shortmore » sample measurements results are presented up to 14 T, assessing the level of anisotropy as a function of field, field orientation and operating temperature.« less

Improving magnetic properties of MgB2 bulk superconductors by synthetic engine oil treatment

NASA Astrophysics Data System (ADS)

Taylan Koparan, E.; Savaskan, B.; Yanmaz, E.

2016-08-01

The present study focuses on the effects of standby time of the MgB2 samples immersed in synthetic engine oil on the critical current density (Jc(H)), magnetic field dependence of the pinning force density fp(b) and Tc performances of MgB2 bulk superconductors. Synthetic engine oil was used as a product which is cheap and a rich carbon source. Manufactured MgB2 pellet samples were immersed at different standby time of 30 min, 120 min, 300 min and 1440 min in synthetic engine oil after the first heating process. Finally, MgB2 samples immersed in synthetic engine oil were sintered at 1000 °C and kept for 15 min in Ar atmosphere. The critical current density of all of MgB2 samples immersed at different standby time in engine oil in whole field range was better than that of the pure MgB2 sample because of the number of the pinning centers. The MgB2 sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. The Jc value for the pure sample is 2.0 × 103 A/cm2, whereas for the MgB2 sample immersed at 300 min standby time in engine oil the Jc is enhanced to 4.8 × 103A/cm2 at 5 K and 3 T. The superconducting transition temperature (Tc) did not change with the increasing standby time of the samples in synthetic engine oil at all. The best diamagnetic property was obtained from the sample which kept in synthetic engine oil for 300 min. Synthetic engine oil treatment results in remarkable improvement of the critical current density and pinning force performances of MgB2 superconductors. It was found that all MgB2 samples have a different pinning property at different measuring temperatures. Using synthetic engine oil as a product which is cheap and a rich carbon source in MgB2 bulk superconductors makes MgB2 samples immersed in synthetic engine oil a good candidate for industrial applications.

A new approach to the current distribution in field cooled superconductors disks

NASA Astrophysics Data System (ADS)

Bernstein, P.; Colson, L.; Dupont, L.; Noudem, J.

2018-01-01

The Bean model considers that in field cooled superconducting cylinders with diameter R, the currents flow over all the thickness of the superconductor along circular paths, the minimum radius of which depends on the magnetizing field and the critical current density. A combination of trapped field and levitation force measurements reported recently has shown, however, that in YBCO and MgB2 disks the current flows in fact in a restricted region with thickness t of the superconductor. In this contribution, from measurements carried out on two YBCO and two MgB2 disks, we report the dependence on temperature of t and J p, the current density in this region, as well as that of the field trapped by the samples. The results confirm that t decreases as the temperature decreases. This behaviour is ascribed to the conservation of the magnetic energy stored in the superconductor, which depends on the magnetizing source and not on the measurement temperature. As a consequence, t behaves as {{J}{{p}}}-2/3, while the field trapped along the axis of the cylinder behaves as {{J}{{p}}}1/3. These claims are substantiated by the experimental results. The possibility that J p is equal to the depairing current is investigated.

NMR characterization of sulphur substitution effects in the K xFe 2-ySe 2-zS z high-T c superconductor

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

Torchetti, D. A.; Imai, T.; Lei, H. C.

2012-04-17

We present a⁷⁷ Se NMR study of the effect of S substitution in the high-T c superconductor K xFe 2-ySe 2-zS z in a temperature range up to 250 K. We examine two S concentrations, with z=0.8 (Tc~ 26 K) and z=1.6 (nonsuperconducting). The samples containing sulphur exhibit broader NMR line shapes than the K xFe₂Se₂ sample due to local disorder in the Se environment. Our Knight shift ⁷⁷K data indicate that in all samples, uniform spin susceptibility decreases with temperature, and that the magnitude of the Knight shift itself decreases with increased S concentration. In addition, S substitution progressivelymore » suppresses low-frequency spin fluctuations. None of the samples exhibit an enhancement of low-frequency antiferromagnetic spin fluctuations near T c in 1/T₁T, as seen in FeSe.« less

NMR characterization of sulphur substitution effects in the K xFe 2-ySe 2-xS z high-T c superconductor

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

Torchetti, D. A.; Imai, T.; Lei, H. C.

2012-04-17

We present a 77Se NMR study of the effect of S substitution in the high-T c superconductor K xFe 2-ySe 2-zS z in a temperature range up to 250 K. We examine two S concentrations, with z=0.8 (T c~ 26 K) and z=1.6 (nonsuperconducting). The samples containing sulphur exhibit broader NMR line shapes than the K xFe 2Se 2 sample due to local disorder in the Se environment. Our Knight shift 77K data indicate that in all samples, uniform spin susceptibility decreases with temperature, and that the magnitude of the Knight shift itself decreases with increased S concentration. In addition,more » S substitution progressively suppresses low-frequency spin fluctuations. None of the samples exhibit an enhancement of low-frequency antiferromagnetic spin fluctuations near T c in 1/T 1T, as seen in FeSe.« less

Stabilization of high Tc phase in bismuth cuprate superconductor by lead doping

NASA Technical Reports Server (NTRS)

Gupta, Ram. P.; Pachauri, J. P.; Khokle, W. S.; Nagpal, K. C.; Date, S. K.

1991-01-01

It has been widely ascertained that doping of lead in Bi-Sr-Ca-Cu-O systems promotes the growth of high T sub c (110 K) phase, improves critical current density, and lowers processing temperature. A systematic study was undertaken to determine optimum lead content and processing conditions to achieve these properties. A large number of samples with cationic compositions of Bi(2-x)Pb(x)Sr2Ca2Cu3 (x = 0.2 to 2.0) were prepared by conventional solid state reaction technique. Samples of all compositions were annealed together at a temperature and characterized through resistance temperature (R-T) measurements and x ray diffraction to determine the zero resistance temperature, T sub c(0) and to identify presence of phases, respectively. The annealing temperature was varied between 790 and 880 C to optimize processing parameters. Results are given. In brief, an optimum process is reported along with composition of leaded bismuth cuprate superconductor which yields nearly a high T sub c single phase with highly stable superconducting properties.

Stabilization of high T(sub c) phase in bismuth cuprate superconductor by lead doping

NASA Technical Reports Server (NTRS)

Gupta, Ram. P.; Pachauri, J. P.; Khokle, W. S.; Nagpal, K. C.; Date, S. K.

1990-01-01

It has widely been ascertained that doping of lead in Bi:Sr:Ca:Cu:O systems promotes the growth of high T(sub c) (110 K) phase, improves critical current density, and lowers processing temperature. A systematic investigation is undertaken to determine optimum lead content and processing conditions to achieve these. A large number of samples with cationic compositions of Bi(2-x)Pb(x)Sr2Ca2Cu3 (x = 0.2 to 2.0) were prepared by conventional solid state reaction technique. Samples of all compositions were annealed together at a temperature and characterized through resistance-temperature (R-T) measurements and x ray diffraction (XRD) to determine the zero resistance temperature, T(sub c)(0) and to identify presence of phases, respectively. The annealing temperature was varied between 790 C to optimize processing parameters. Results are given. In brief, an optimum process is reported along with composition of leaded bismuth cuprate superconductor which yields nearly a high T(sub c) single phase with highly stable superconducting properties.

Determination of spin polarization using an unconventional iron superconductor

DOE PAGES

Gifford, J. A.; Chen, B. B.; Zhang, J.; ...

2016-11-21

Here, an unconventional iron superconductor, SmO 0.7F 0.3FeAs, has been utilized to determine the spin polarization and temperature dependence of a highly spin-polarized material, La 0.67Sr 0.33MnO 3, with Andreev reflection spectroscopy. The polarization value obtained is the same as that determined using a conventional superconductor Pb but the temperature dependence of the spin polarization can be measured up to 52 K, a temperature range, which is several times wider than that using a typical conventional superconductor. The result excludes spin-parallel triplet pairing in the iron superconductor.

Trapped field internal dipole superconducting motor generator

DOEpatents

Hull, John R.

2001-01-01

A motor generator including a high temperature superconductor rotor and an internally disposed coil assembly. The motor generator superconductor rotor is constructed of a plurality of superconductor elements magnetized to produce a dipole field. The coil assembly can be either a conventional conductor or a high temperature superconductor. The superconductor rotor elements include a magnetization direction and c-axis for the crystals of the elements and which is oriented along the magnetization direction.

Microstructural control and superconducting properties of YBCO melt textured single crystals

NASA Astrophysics Data System (ADS)

Jongprateep, Oratai

The high temperature superconductor has great potential for practical applications such as superconducting energy storage systems. Since the levitation force, required specifically for these applications, largely depends on the critical current density and loop size of the superconducting current, large-sized single crystals with high critical current density are desired. To achieve the goal in fabricating YBa2Cu3O 7-delta (Y123) samples suitable for the applications, detailed and systematic studies are required to gain further understanding of the crystal growth and flux pinning mechanisms. This research is aimed at constituting a contribution to the knowledge base for the Y123 high temperature superconductor field by extending the study of processing conditions involved in controlling the microstructure of the Y123 superconductors for the enhancement of crystal growth and superconductor properties. Relations among processing parameters, microstructure, crystal growth, and critical current density of Y123 superconductors have been established. The experimental results reveal that low heating rate and short holding time can lead to refinement of Y2BaCuO5 (Y211) particles, which is strongly favorable to enhancement of the crystal growth and electrical properties of the Y123 superconductors. It was observed that relatively large Y123 crystals (17-22 mm in size) can be obtained with fine needle-shaped Y211 particles, processed with low heating rate and short holding time at the maximum temperatures. Additionally, the research also formulated a technique to fabricate Y123 superconductors with improved electrical properties required for the practical applications. By incorporating additives such as BaCeO3, BaSnO 3, Pt and Nd2O3 into Y123 superconductors, refinement of Y211 particles occurs. In addition, secondary phase particles with sizes in sub-micrometer and nanometer range can be formed in the Y123 superconductors. The interfaces between the Y123 matrix and these Y211 or secondary phase particles are believed to act as flux pinning sites and to enhance the critical current density (Jc) in the superconductor. The results showed that formation of secondary phase inclusions in Y123 by doping with BaCeO3, BaSnO 3, Pt or Nd2O3 result in enhancement of J c due to the effective flux pinning.

Application of electrochemical method to microfabricated region in single-crystal device of FeSe1- x Te x superconductors

NASA Astrophysics Data System (ADS)

Okada, Kazuhiro; Takagi, Tomohiro; Kobayashi, Masahiro; Ohnuma, Haruka; Noji, Takashi; Koike, Yoji; Ayukawa, Shin-ya; Kitano, Haruhisa

2018-04-01

The application of an electrochemical method to the iron-based chalcogenide superconductors has great potentials in enhancing their properties such as the superconducting transition temperature. Unfortunately, this method has been limited to polycrystalline powders or thin film samples with a large surface area. Here, we demonstrate that the electrochemical method can be usefully applied to single-crystal devices of FeSe1- x Te x superconductors by combining it with the focused ion beam (FIB) microfabrication techniques. Our results open a new route to developing the high-quality superconducting devices fabricated using layered iron-based chalcogenides, whose properties are electrochemically controlled.

Influence of superconductor film composition on adhesion strength of coated conductors

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

Kesgin, Ibrahim; Khatri, Narayan; Liu, Yuhao

The effect of high temperature superconductor (HTS) film composition on the adhesion strength of rare- earth barium copper oxide coated conductors (CCs) has been studied. It has been found that the mechanical integrity of the superconductor layer is very susceptible to the defects especially those along the ab plane, probably due to the weak interfaces between the defects and the matrix. Gd and Y in the standard composition were substituted with Sm and the number of in-plane defects was drastically reduced. Consequently, a four-fold increase in adhesion or peeling strength in Sm-based CCs was achieved compared to the standard GdYBCOmore » samples.« less

Superconducting and normal-state properties of the layered boride OsB2

NASA Astrophysics Data System (ADS)

Singh, Yogesh; Niazi, A.; Vannette, M. D.; Prozorov, R.; Johnston, D. C.

2007-12-01

OsB2 crystallizes in an orthorhombic structure (Pmmn) which contains alternate boron and osmium layers stacked along the c axis. The boron layers consist of puckered hexagons as opposed to the flat graphite-like boron layers in MgB2 . OsB2 is reported to become superconducting below 2.1K . We report results of the dynamic and static magnetic susceptibilities, electrical resistivity, Hall effect, heat capacity, and penetration depth measurements on arc-melted polycrystalline samples of OsB2 to characterize its superconducting and normal-state properties. These measurements confirmed that OsB2 becomes a bulk superconductor below Tc=2.1K . Our results indicate that OsB2 is a moderate-coupling type-II superconductor with an electron-phonon coupling constant λep≈0.4-0.5 , a small Ginzburg-Landau parameter κ˜1-2 , and an upper critical magnetic field Hc2(0.5K)˜420Oe for an unannealed sample and Hc2(1K)˜330Oe for an annealed sample. The temperature dependence of the superfluid density ns(T) for the unannealed sample is consistent with an s -wave superconductor with a slightly enhanced zero temperature gap Δ(0)=1.9kBTc and a zero temperature London penetration depth λ(0)=0.38(2)μm . The ns(T) data for the annealed sample show deviations from the predictions of the single-band s -wave BCS model. The magnetic, transport, and thermal properties in the normal state of isostructural and isoelectronic RuB2 , which is reported to become superconducting below 1.6K , are also reported.

Simple theory for the dependence of the electrical resistance of the magnetic superconductors TmRh/sub 4/B/sub 4/ and ErRh/sub 4/B/sub 4/ on temperature and field

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

Meijer, H.C.; Andriessen, J.; Postma, H.

1986-04-01

A phenomenological description for the temperature and magnetic field dependence of the electrical resistance R of polycrystalline samples of the reentrant superconductors TmRh/sub 4/B/sub 4/ and ErRh/sub 4/B/sub 4/ is given on the basis of two assumptions: (1) Due to the anisotropic values of the rare-earth ions the critical field of the crystallites depends on the direction of the externally applied field, which leads to an increasing number of normal crystallites with increasing field. For the dependence of the magnetization M on temperature, a molecular field model is used. (2) The bulk resistance R of the sample depends in amore » linear way on the fraction of normal crystallites. There is a qualitative agreement with the experimental results of Hamaker et al. and of Ott et al. It is also shown that an applied field H/sub e/ is equal to the orbital critical field H(/sub c//sub 2/ for the temperature at which R(H/sub e/, T) starts deviating from the resistance of the normal sample.« less

Cryomagnetic Point-Contact Andreev Reflection Spectroscopy on Single Crystal Iron-Chalcogenide Superconductors

NASA Astrophysics Data System (ADS)

Yen, Y. T.; Hu, Rongwei; Petrovic, C.; Yeh, K. W.; Wu, M. K.; Wei, J. Y. T.

2012-02-01

We report on cryomagnetic point-contact Andreev reflection spectroscopy performed on single crystals of superconducting FeTe1-xSx and FeTe1-xSex. The samples are cleaved in-situ and the measurements are carried out at temperatures down to 4.2K and in a field up to 9T. At base temperature and zero field, we observe a cone-shaped hump at lower voltages in the conductance spectra with no dips at zero bias and a linear background at higher voltages. The spectral evolution of gap size, zero-bias conductance, and excess spectral area are analyzed as a function of temperature and field. Further spectral analysis is carried out using theoretical models of conductance spectra in multiband superconductors [1,2] and of gap symmetry in Fe-based superconductors [3]. The role of interstitial iron is also considered, by comparison with atomically-resolved scanning tunneling spectroscopy data.[4pt] [1] V. Lukic and E.J. Nicol, PRB 76, 144508 (2007) [2] A. Golubov et al., PRL 103, 077003 (2009) [3] P.J. Hirschfeld et al., RPP 74, 124508 (2011)

The thermopower in the temperature range T(sub c)-1000K and the bank spectrum of Bi-based superconductors

NASA Technical Reports Server (NTRS)

Gasumyants, V. E.; Vladimirskaya, E. V.; Smirnov, V. I.; Kazanskiy, S. V.

1995-01-01

The temperature dependencies of thermopower, S, in the range T = T(sub c)-1000K as well as of resistivity and Hall coefficient in the range T = T(sub c)-300K for the single-phase ceramic samples Bi2Sr2Ca(1-x)Nd(x)Cu2O(y) have been measured. It was found that the S(T) dependencies in normal phase have three characteristic regions. Despite the fact that the S(T) dependencies in Bi-based high-T(sub c) superconductors (HTSC) differ essentially from ones in Y-based HTSC at T = T(sub c)-300K, the main feature of theirs (S(T) = const at high temperatures) retains in samples investigated at T is greater than 620K. The results obtained have been analyzed on the basis of the narrow-band model with the use of assumption of slight asymmetry of the conductive band. The band spectrum parameters of the samples studied have been calculated. An analysis of the tendencies in these parameters changes with samples composition varying enables to make the conclusion about the similarity of the main features of the conductive band structure in Y- and Bi-based HTSC.

Theoretical modeling of critical temperature increase in metamaterial superconductors

NASA Astrophysics Data System (ADS)

Smolyaninov, Igor I.; Smolyaninova, Vera N.

2016-05-01

Recent experiments have demonstrated that the metamaterial approach is capable of a drastic increase of the critical temperature Tc of epsilon near zero (ENZ) metamaterial superconductors. For example, tripling of the critical temperature has been observed in Al -A l2O3 ENZ core-shell metamaterials. Here, we perform theoretical modeling of Tc increase in metamaterial superconductors based on the Maxwell-Garnett approximation of their dielectric response function. Good agreement is demonstrated between theoretical modeling and experimental results in both aluminum- and tin-based metamaterials. Taking advantage of the demonstrated success of this model, the critical temperature of hypothetic niobium-, Mg B2- , and H2S -based metamaterial superconductors is evaluated. The Mg B2 -based metamaterial superconductors are projected to reach the liquid nitrogen temperature range. In the case of a H2S -based metamaterial Tc appears to reach ˜250 K.

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

DOEpatents

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

1987-01-01

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

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

Corredor, L.T.; Programa de Pós-Graduação em Ciências de Materiais-CCEN, Universidade Federal de Pernambuco, 50670-901 Recife, PE; Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, Bogotá D.C.

Highlights: • We investigated the effect of the dilution of magnetic Ru sub-lattice of RuSr{sub 2}GdCu{sub 2}O{sub 8}. • We synthesized the doped compound Rui{sub x}Re{sub x}Sr{sub 2}GdCu{sub 2}O{sub y}, for 3%, 6%, 9% and 12% Re. • Re would affect the electron coupling: just 3 and 6% samples were superconductor. • Superconductivity emergence strongly affects magnetic properties of 3 and 6% samples. • A weak ferromagnetic component is consistent with a globally antiferromagnetic system. - Abstract: Despite the discovery of new superconductors classes, high-Tc oxides continue to be a current topic, because of their complex phase diagrams and doping-dependantmore » effects (allowing one to investigate the interaction between orbitals), as well as structural properties such as lattice distortion and charge ordering, among many others. Ruthenocuprates are magnetic superconductors in which the magnetic transition temperature is much higher than the critical superconducting temperature, making them unique compounds. With the aim of investigating the dilution of the magnetic Ru sub-lattice, we proposed the synthesis of the Ru{sub 1−x}Re{sub x}Sr{sub 2}GdCu{sub 2}O{sub y} ruthenocuprate-type family, adapting the known two-step process (double perovskite + CuO) by directly doping the double perovskite, thus obtaining the perovskite compound Sr{sub 2}GdRu{sub 1−x}Re{sub x}O{sub y}, which represents a new synthesis process to the best of our knowledge. Our samples were structurally characterized through X-ray diffraction, and the patterns were analysed via Rietveld refinement. A complete magnetic characterization as a function of temperature and applied field, as well as transport measurements were carried out. We discuss our results in the light of the two-lattice model for ruthenocuprates, and a relation between RuO{sub 2} (magnetic) and CuO{sub 2} (superconductor) sub-lattices can clearly be observed.« less

Scanning tunneling microscopy and spectroscopy studies of the heavy-electron superconductor TlNi2Se2

NASA Astrophysics Data System (ADS)

Wilfert, Stefan; Schmitt, Martin; Schmidt, Henrik; Mauerer, Tobias; Sessi, Paolo; Wang, Hangdong; Mao, Qianhui; Fang, Minghu; Bode, Matthias

2018-01-01

We report on the structural and superconducting electronic properties of the heavy-electron superconductor TlNi2Se2 . By using a variable-temperature scanning tunneling microscopy (VT-STM) the coexistence of (√{2 }×√{2 }) R 45∘ and (2 ×1 ) surface reconstructions is observed. Similar to earlier observations on the "122" family of Fe-based superconductors, we find that their respective surface fraction strongly depends on the temperature during cleavage, the measurement temperature, and the sample's history. Cleaving at low temperature predominantly results in the (√{2 }×√{2 }) R 45∘ -reconstructed surface. A detailed analysis of the (√{2 }×√{2 }) R 45∘ -reconstructed domains identifies (2 ×1 ) -ordered dimers, tertramers, and higher order even multimers as domain walls. Higher cleaving temperatures and the warming of low-temperature-cleaved samples increases the relative weight of the (2 ×1 ) surface reconstruction. By slowly increasing the sample temperature Ts inside the VT-STM we find that the (√{2 }×√{2 }) R 45∘ surface reconstructions transforms into the (2 ×1 ) structure at Ts=123 K. We identify the polar nature of the TlNi2Se2 (001) surface as the most probable driving mechanism of the two reconstructions, as both lead to a charge density ρ =0.5 e- , thereby avoiding divergent electrostatic potentials and the resulting "polar catastrophe." Low-temperature scanning tunneling spectroscopy (STS) performed with normal metal and superconducting probe tips shows a superconducting gap which is best fit with an isotropic s wave. We could not detect any correlation between the local surface reconstruction, suggesting that the superconductivity is predominantly governed by TlNi2Se2 bulk properties. Correspondingly, temperature- and field-dependent data reveal that both the critical temperature and critical magnetic field are in good agreement with bulk values obtained earlier from transport measurements. In the superconducting state the formation of an Abrikosov lattice is observed without any zero bias anomaly at the vortex core.

Comparison of the effects of platinum and CeO2 on the properties of single grain, Sm-Ba-Cu-O bulk superconductors

NASA Astrophysics Data System (ADS)

Zhao, Wen; Shi, Yunhua; Radušovská, Monika; Dennis, Anthony R.; Durrell, John H.; Diko, Pavel; Cardwell, David A.

2016-12-01

SmBa2Cu3O7-δ (Sm-123) is a light-rare-earth barium-cuprate (LRE-BCO) high-temperature superconductor (HTS) with significant potential for high field industrial applications. We report the fabrication of large, single grain bulk [Sm-Ba-Cu-O (SmBCO)] superconductors containing 1 wt% CeO2 and 0.1 wt% Pt using a top-seeded melt growth process. The performance of the SmBCO bulk superconductors containing the different dopants was evaluated based on an analysis of their superconducting properties, including critical transition temperature, T c and critical current density, J c , and on sample microstructure. We find that both CeO2 and Pt dopants refine the size of Sm2BaCuO5 (Sm-211) particles trapped in the Sm-123 superconducting phase matrix, which act as effective flux pinning centres, although the addition of CeO2 results in broadly improved superconducting performance of the fully processed bulk single grain. However, 1 wt% CeO2 is significantly cheaper than 0.1 wt% Pt, which has clear economic benefits for use in medium to large scale production processes for these technologically important materials. Finally, the use of CeO2 results generally in the formation of finer Sm-211 particles and to the generation of fewer macro-cracks and Sm-211 free regions in the sample microstructure.

Localization effects in radiationally disordered high-temperature superconductors: Theoretical interpretation

NASA Technical Reports Server (NTRS)

Goshchitskii, B. N.; Davydov, S. A.; Karkin, A. E.; Mirmelstein, A. V.; Sadovskii, M. V.

1990-01-01

Theoretical interpretation of recent experiments on radiationally disordered high-temperature superconductors is presented, based on the concepts of mutual interplay of Anderson localization and superconductivity. Microscopic derivation of Ginzburg-Landau coefficients for the quasi-two-dimensional system in the vicinity of localization transition is given in the framework of the self-consistent theory of localization. The 'minimal metallic conductivity' for the quasi-two-dimensional case is enhanced due to a small overlap of electronic states on the nearest neighbor conducting planes. This leads to a stronger influence of localization effects than in ordinary (three-dimensional) superconductors. From this point of view even the initial samples of high-temperature superconductors are already very close to Anderson transition. Anomalies of H(c2) are also analyzed, explaining the upward curvature of H(c2)(T) and apparent independence of dH(c2)/dT (T = T(sub c)) on the degree of disorder as due to localization effects. Researchers discuss the possible reasons of fast T(sub c) degradation due to the enhanced Coulomb effects caused by the disorder induced decrease of localization length. The appearance and growth of localized magnetic moments is also discussed. The disorder dependence of localization length calculated from the experimental data on conductivity correlates reasonably with the theoretical criterion for suppression of superconductivity in the system with localized electronic states.

Magnetic pinning in a superconducting film by a ferromagnetic layer with stripe domains

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

Mancusi, D.; Di Giorgio, C.; Bobba, F.

2014-10-31

A magnetic study of superconductor/ferromagnet bilayers was performed by hysteresis loops and temperature-dependent magnetization measurements. The superconductor/ferromagnet bilayers consist of a Nb film deposited on a Py film with weak perpendicular magnetic anisotropy. By comparing the temperature-dependent magnetization data obtained on samples with different ferromagnetic layer thickness, a decrease of the magnetic pinning with increasing thickness of the ferromagnetic layer has been found. This is confirmed by the reduction of the Nb film critical current density at low fields extracted by using the magnetic irreversibility of the hysteresis loops. As the ferromagnetic layer exhibits a magnetic structure with stripe domains,more » whose width increases for increasing thickness as observed by magnetic force microscopy (MFM) measurements, we relate the reduction of the superconducting critical current in samples with thicker ferromagnetic layers to a weaker interaction between the vortices guided by the underlying magnetic template.« less

Ultrasonic and elastic properties of Tl- and Hg-Based cuprate superconductors: a review

NASA Astrophysics Data System (ADS)

Abd-Shukor, R.

2018-01-01

This review is regarding the ultrasonic and elastic properties of Tl- and Hg-based cuprate superconductors. The objectives of this paper were to review the ultrasonic attenuation above the transition temperature ?, and sound velocity and elastic anomalies at ? in the Tl- and Hg-based cuprate superconductors. A discontinuity in the sound velocity and elastic moduli is observed near ? for the Hg-based and other cuprate high temperature superconductor but not the Tl-based superconductor. Ultrasonic attenuation peaks are observed between 200 and 250 K in almost all Tl- and Hg-based cuprate superconductors reported. These peaks were attributed to lattice stepping and oxygen ordering in the Tl-O and Hg-O layers. Some Tl- and Hg-based superconductors show attenuation peak near ?. However, this is not a common feature for the cuprate superconductors. The ultrasonic attenuation decrease rate below ? is slower than that expected from a Bardeen-Cooper-Schrieffer (BCS) and pseudo-gapped superconductor.

Method And Apparatus For Evaluatin Of High Temperature Superconductors

DOEpatents

Fishman, Ilya M.; Kino, Gordon S.

1996-11-12

A technique for evaluation of high-T.sub.c superconducting films and single crystals is based on measurement of temperature dependence of differential optical reflectivity of high-T.sub.c materials. In the claimed method, specific parameters of the superconducting transition such as the critical temperature, anisotropy of the differential optical reflectivity response, and the part of the optical losses related to sample quality are measured. The apparatus for performing this technique includes pump and probe sources, cooling means for sweeping sample temperature across the critical temperature and polarization controller for controlling a state of polarization of a probe light beam.

Proximity effects in ferromagnet-superconductor structures

NASA Astrophysics Data System (ADS)

Halterman, Klaus Byron

I present an extensive theoretical investigation of the proximity effects that occur in ferromagnet/superconductor systems. I use a numerical method to solve self consistently the Bogoliubov-de Gennes equations in the continuum. I obtain the pair amplitude and the local density of states (DOS), and use these results to extract the relevant lengths characterizing both the leakage of superconductivity into the magnet and to study spin splitting induced in the superconductor. These phenomena are investigated as a function of parameters such as temperature, magnet polarization, interfacial scattering, sample size and Fermi wave vector mismatch, all of which turn out to have an important influence on the results. These comprehensive results should help characterize and analyze future data, and are shown to be in agreement with existing experiments.

Passivation Of High-Temperature Superconductors

NASA Technical Reports Server (NTRS)

Vasquez, Richard P.

1991-01-01

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

Realization of High-temperature Superconductivity in Nano-carbon Materials and Its Application

DTIC Science & Technology

2015-07-13

hottest topics in condensed matter physics and also for application to zero- emission energy system. In particular, carbon-based superconductors have...ernission energy system. In particular, carbon-based superconductors have attracted significant attention for high transition temperature (T c). In...e-based superconductors have previously shown T c > 40K among various superconductors . In particular, carbon-base new SC exhibited T c < 20K in any

Flux pinning enhancement in thin films of Y3 Ba5 Cu8O18.5 + d

NASA Astrophysics Data System (ADS)

Aghabagheri, S.; Mohammadizadeh, M. R.; Kameli, P.; Salamati, H.

2018-06-01

YBa2Cu3O7 (Y123) and Y3Ba5Cu8O18 (Y358) thin films were deposited by pulsed laser deposition method. XRD analysis shows both films grow in c axis orientation. Resistivity versus temperature analysis shows superconducting transition temperature was about 91.2 K and 91.5 K and transition width for Y358 and Y123 films was about 0.6 K and 1.6 K, respectively. Analysis of the temperature dependence of the AC susceptibility near the transition temperature, employing Bean's critical state model, indicates that intergranular critical current density for Y358 films is more than twice of intergranular critical current density of Y123 films. Thus, flux pining is stronger in Y358 films. Weak links in the both samples is of superconductor-normal-superconductor (SNS) type irrespective of stoichiometry.

A portable magnetic field of >3 T generated by the flux jump assisted, pulsed field magnetization of bulk superconductors

NASA Astrophysics Data System (ADS)

Zhou, Difan; Ainslie, Mark D.; Shi, Yunhua; Dennis, Anthony R.; Huang, Kaiyuan; Hull, John R.; Cardwell, David A.; Durrell, John H.

2017-02-01

A trapped magnetic field of greater than 3 T has been achieved in a single grain GdBa2Cu3O7-δ (GdBaCuO) bulk superconductor of diameter 30 mm by employing pulsed field magnetization. The magnet system is portable and operates at temperatures between 50 K and 60 K. Flux jump behaviour was observed consistently during magnetization when the applied pulsed field, Ba, exceeded a critical value (e.g., 3.78 T at 60 K). A sharp dBa/dt is essential to this phenomenon. This flux jump behaviour enables the magnetic flux to penetrate fully to the centre of the bulk superconductor, resulting in full magnetization of the sample without requiring an applied field as large as that predicted by the Bean model. We show that this flux jump behaviour can occur over a wide range of fields and temperatures, and that it can be exploited in a practical quasi-permanent magnet system.

Superconducting properties of copper oxide high-temperature superconductors

PubMed Central

Chen, Guanhua; Langlois, Jean-Marc; Guo, Yuejin; Goddard, William A.

1989-01-01

The equations for the magnon pairing theory of high-temperature copper-oxide-based superconductors are solved and used to calculate several properties, leading to results for specific heat and critical magnetic fields consistent with experimental results. In addition, the theory suggests an explanation of why there are two sets of transition temperatures (Tc ≈ 90 K and Tc ≈ 55 K) for the Y1Ba2Cu3O6+x class of superconductors. It also provides an explanation of why La2-xSrxCuO4 is a superconductor for only a small range of x (and suggests an experiment to independently test the theory). These results provide support for the magnon pairing theory of high-temperature superconductors. On the basis of the theory, some suggestions are made for improving these materials. PMID:16594038

NMR Characterization of Sulphur Substitution Effects in the KxFe2−ySe2−zSz High-Tc Superconductor

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

Petrovic C.; Torchetti, D.A.; Imai, T.

2012-04-17

We present a {sup 77}Se NMR study of the effect of S substitution in the high-T{sub c} superconductor K{sub x}Fe{sub 2-y}Se{sub 2-z}S{sub z} in a temperature range up to 250 K. We examine two S concentrations, with z = 0.8 (T{sub c} {approx} 26 K) and z = 1.6 (nonsuperconducting). The samples containing sulphur exhibit broader NMR line shapes than the K{sub x}Fe{sub 2}Se{sub 2} sample due to local disorder in the Se environment. Our Knight shift {sup 77}K data indicate that in all samples, uniform spin susceptibility decreases with temperature, and that the magnitude of the Knight shift itselfmore » decreases with increased S concentration. In addition, S substitution progressively suppresses low-frequency spin fluctuations. None of the samples exhibit an enhancement of low-frequency antiferromagnetic spin fluctuations near T{sub c} in 1/T{sub 1}T, as seen in FeSe.« less

High temperature crystalline superconductors from crystallized glasses

DOEpatents

Shi, Donglu

1992-01-01

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

High-Tc SNS Junctions: A New Generation of Proximity-Coupled Josephson Devices

NASA Technical Reports Server (NTRS)

Kleinsasser, A. W.

1997-01-01

This paper reviews this evolution of proximity - coupled Josephson jucntion from the early investigations on low temperature superconductor-normal -superconductor junctions through the introduction of hybrid superconductor-semiconductor devices and the resulting interest in mesoscopic Josephson junctions, to the recent development of high temperature devices.

An explanation for the rise in Tc in the Tl- and Bi-based high temperature superconductors

NASA Technical Reports Server (NTRS)

Bose, S. M.; Longe, P.

1991-01-01

Using the plasmon exchange model for the high T(sub c) superconductor, it is shown that the T(sub c) rises with an increase in the number of CuO layers per unit cell, which is in agreement with recent observations in the Tl- and Bi-based compounds. The calculation also suggests that the sample will become superconducting in successive stages and that there is a saturation effect, i.e., that T(sub c) cannot be raised indefinitely by increasing the number of CuO layers.

A Brief Review of Recent Superconductivity Research at NIST

PubMed Central

Lundy, D. R.; Swartzendruber, L. J.; Bennett, L. H.

1989-01-01

A brief overview of recent superconductivity research at NIST is presented. Emphasis is placed on the new high-temperature oxide superconductors, though mention is made of important work on low-temperature superconductors, and a few historical notes are included. NIST research covers a wide range of interests. For the new high-temperature superconductors, research activities include determination of physical properties such as elastic constants and electronic structure, development of new techniques such as magnetic-field modulated microwave-absorption and determination of phase diagrams and crystal structure. For the low-temperature superconductors, research spans studying the effect of stress on current density to the fabrication of a new Josephson junction voltage standard. PMID:28053408

Can Positron 2D-ACAR Resolve the Electronic Structure of HIGH-Tc Superconductors?

NASA Astrophysics Data System (ADS)

Chan, L. P.; Lynn, K. G.; Harshman, D. R.

We examine the ability of the positron Two-Dimensional Angular Correlation Annihilation Radiation (2D-ACAR) technique to resolve the electronic structures of high-Tc cuprate superconductors. Following a short description of the technique, discussions of the theoretical assumptions, data analysis and experimental considerations, in relation to the high-Tc superconductors, are given. We briefly review recent 2D-ACAR experiments on YBa2Cu3O7-x, Bi2Sr2CaCuO8+δ and La2-xSrxCuO4. The 2D-ACAR technique is useful in resolving the band crossings associated with the layers of the superconductors that are preferentially sampled by the positrons. Together with other Fermi surface measurements (namely angle-resolved photoemission), 2D-ACAR can resolve some of the electronic structures of high-Tc cuprate superconductors. In addition, 2D-ACAR measurements of YBa2Cu3O7-x and Bi2Sr2CaCuO8+δ also reveal an interesting temperature dependence in the fine structures, and a change in the positron lifetime in the former.

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

PubMed

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

2012-07-03

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

Theoretical modeling of critical temperature increase in metamaterial superconductors

NASA Astrophysics Data System (ADS)

Smolyaninov, Igor; Smolyaninova, Vera

Recent experiments have demonstrated that the metamaterial approach is capable of drastic increase of the critical temperature Tc of epsilon near zero (ENZ) metamaterial superconductors. For example, tripling of the critical temperature has been observed in Al-Al2O3 ENZ core-shell metamaterials. Here, we perform theoretical modelling of Tc increase in metamaterial superconductors based on the Maxwell-Garnett approximation of their dielectric response function. Good agreement is demonstrated between theoretical modelling and experimental results in both aluminum and tin-based metamaterials. Taking advantage of the demonstrated success of this model, the critical temperature of hypothetic niobium, MgB2 and H2S-based metamaterial superconductors is evaluated. The MgB2-based metamaterial superconductors are projected to reach the liquid nitrogen temperature range. In the case of an H2S-based metamaterial Tc appears to reach 250 K. This work was supported in part by NSF Grant DMR-1104676 and the School of Emerging Technologies at Towson University.

Microwave heating of a high-Tc YBa2Cu3O6.9 superconductor through a Josephson-junction system

NASA Astrophysics Data System (ADS)

Stankowski, J.; Czyak, B.; Martinek, J.

1990-12-01

An overheating of a Josephson-junction system (JJS) in ceramic YBa2Cu3O6.9 samples was induced by microwave irradiation in a microwave cavity. The amplitude of the Josephson microwave absorption (JMA) was used as a monitor of the local JJS temperature. The difference between the JJS temperature and a sample temperature depends linearly on the power of the microwave field. A thermal hysteresis of Tc for heating and cooling is proportional to the microwave power applied in the JMA experiment.

Transition metal substitutions for Cu in BSCCO: An instructive probe of high temperature superconductivity

NASA Astrophysics Data System (ADS)

Schneider, Clinton W.

1998-12-01

Single crystals of the high temperature superconductor Bisb2Srsb2Casb1(Cusb{1-x}Msb{x})sb2)Osb{8+delta} have been grown for M = Zn, Ni, Co, Fe, and Pd in order to probe the effect of transition metal impurities on superconducting properties. Samples have been characterized by XRD, electron microprobe, and transport measurements. Measurement of resistance is used to determine the depression of Tsb{c} due to the impurities. We determine a value dTsb{c}/dx = -7.8K/at/for all substituents, independent of magnetic moment. Considered in terms of the Abrikosov-Gorkov theory for impurity scattering in superconductors, this result agrees with a d-wave order parameter and strong coupling.

The flux jumps in high Tc Bi(1.7)Pb(0.3)Sr2 Ca2Cu3O(y) bulk superconductor

NASA Astrophysics Data System (ADS)

Cao, Xiaowen; Huang, Sunli

1989-11-01

There were giant flux jumps in high T sub c Bi(1.7)Pb(0.3)Sr2Ca2Cu3O(v) bulk superconductor. The relaxation time, tau, decreased with both the increase of magnetic field and the rise of temperature. The maximum tau was about 40 min. The average -dM/dt increased with both the increase of magnetic field and the rise of temperature. The minimum average -dM/dt was about 4.1 x 10(exp -2) G/min. The flux jump weakened with time. It was dependent on the decrease of gradient of magnetic flux density dn/dx in the sample.

Electrical connection structure for a superconductor element

DOEpatents

Lallouet, Nicolas; Maguire, James

2010-05-04

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

Cryocooler based test setup for high current applications

NASA Astrophysics Data System (ADS)

Pradhan, Jedidiah; Das, Nisith Kr.; Roy, Anindya; Duttagupta, Anjan

2018-04-01

A cryo-cooler based cryogenic test setup has been designed, fabricated, and tested. The setup incorporates two numbers of cryo-coolers, one for sample cooling and the other one for cooling the large magnet coil. The performance and versatility of the setup has been tested using large samples of high-temperature superconductor magnet coil as well as short samples with high current. Several un-calibrated temperature sensors have been calibrated using this system. This paper presents the details of the system along with results of different performance tests.

Local antiferromagnetic exchange and collaborative Fermi surface as key ingredients of high temperature superconductors

PubMed Central

Hu, Jiangping; Ding, Hong

2012-01-01

Cuprates, ferropnictides and ferrochalcogenides are three classes of unconventional high temperature superconductors, who share similar phase diagrams in which superconductivity develops after a magnetic order is suppressed, suggesting a strong interplay between superconductivity and magnetism, although the exact picture of this interplay remains elusive. Here we show that there is a direct bridge connecting antiferromagnetic exchange interactions determined in the parent compounds of these materials to the superconducting gap functions observed in the corresponding superconducting materials: in all high temperature superconductors, the Fermi surface topology matches the form factor of the pairing symmetry favored by local magnetic exchange interactions. We suggest that this match offers a principle guide to search for new high temperature superconductors. PMID:22536479

Flux pinning characteristics and irreversibility line in high temperature superconductors

NASA Technical Reports Server (NTRS)

Matsushita, T.; Ihara, N.; Kiuchi, M.

1995-01-01

The flux pinning properties in high temperature superconductors are strongly influenced by thermally activated flux motion. The scaling relation of the pinning force density and the irreversibility line in various high temperature superconductors are numerically analyzed in terms of the flux creep model. The effect of two factors, i.e., the flux pinning strength and the dimensionality of the material, on these properties are investigated. It is speculated that the irreversibility line in Bi-2212 superconductors is one order of magnitude smaller than that in Y-123, even if the flux pinning strength in Bi-2212 is improved up to the level of Y-123. It is concluded that these two factors are equally important in determination of the flux pinning characteristics at high temperatures.

Synthesis and characterization of iron based superconductor Nd-1111

NASA Astrophysics Data System (ADS)

Alborzi, Z.; Daadmehr, V.

2018-06-01

Polycrystalline sample of NdFeAsO0.8F0.2 was prepared by one-step solid-state reaction method. The structural and electrical properties of sample were characterized through XRD pattern and the 4-probe method. The critical temperature was obtained at 56 K. The crystal structure was tetragonal with P4/nmm:2 symmetry group.

Thermodynamic properties of Dynes superconductors

NASA Astrophysics Data System (ADS)

Herman, František; Hlubina, Richard

2018-01-01

The tunneling density of states in dirty s -wave superconductors is often well described by the phenomenological Dynes formula. Recently we have shown that this formula can be derived, within the coherent potential approximation, for superconductors with simultaneously present pair-conserving and pair-breaking impurity scattering. Here we demonstrate that the theory of such so-called Dynes superconductors is thermodynamically consistent. We calculate the specific heat and critical field of the Dynes superconductors, and we show that their gap parameter, specific heat, critical field, and penetration depth exhibit power-law scaling with temperature in the low-temperature limit. We also show that in the vicinity of a coupling-constant-controlled superconductor to normal metal transition, the Homes law is replaced by a different, pair-breaking-dominated scaling law.

Effect of proton irradiation on the normal-state low-energy excitations of Ba(Fe 1-xRh x) 2As 2 superconductors

DOE PAGES

Moroni, M.; Gozzelino, L.; Ghigo, G.; ...

2017-09-19

Here, we present a 75As nuclear magnetic resonance (NMR) and resistivity study of the effect of 5.5 MeV proton irradiation on the optimal electron doped (x = 0.068) and overdoped (x = 0.107) Ba(Fe 1–xRh x) 2As 2 iron based superconductors. While the proton induced defects only mildly suppress the critical temperature and increase residual resistivity in both compositions, sizable broadening of the NMR spectra was observed in all the irradiated samples at low temperature. The effect is significantly stronger in the optimally doped sample where the Curie Weiss temperature dependence of the line width suggests the onset of ferromagneticmore » correlations coexisting with superconductivity at the nanoscale. 1/T 2 measurements revealed that the energy barrier characterizing the low energy spin fluctuations of these compounds is enhanced upon proton irradiation, suggesting that the defects are likely slowing down the fluctuations between (0,π) and (π,0) nematic ground states.« less

Effect of proton irradiation on the normal-state low-energy excitations of Ba(Fe 1-xRh x) 2As 2 superconductors

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

Moroni, M.; Gozzelino, L.; Ghigo, G.

Here, we present a 75As nuclear magnetic resonance (NMR) and resistivity study of the effect of 5.5 MeV proton irradiation on the optimal electron doped (x = 0.068) and overdoped (x = 0.107) Ba(Fe 1–xRh x) 2As 2 iron based superconductors. While the proton induced defects only mildly suppress the critical temperature and increase residual resistivity in both compositions, sizable broadening of the NMR spectra was observed in all the irradiated samples at low temperature. The effect is significantly stronger in the optimally doped sample where the Curie Weiss temperature dependence of the line width suggests the onset of ferromagneticmore » correlations coexisting with superconductivity at the nanoscale. 1/T 2 measurements revealed that the energy barrier characterizing the low energy spin fluctuations of these compounds is enhanced upon proton irradiation, suggesting that the defects are likely slowing down the fluctuations between (0,π) and (π,0) nematic ground states.« less

Phonon characteristics of high {Tc} superconductors from neutron Doppler broadening measurements

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

Trela, W.J.; Kwei, G.H.; Lynn, J.E.

Statistical information on the phonon frequency spectrum of materials can be measured by neutron transmission techniques if they contain nuclei with low energy resonances, narrow enough to be Doppler-broadened, in their neutron cross sections. The authors have carried out some measurements using this technique for materials of the lanthanum barium cuprate class, La{sub 2{minus}x}Ba{sub x}CuO{sub 4}. Two samples with slightly different concentrations of oxygen, one being superconductive, the other not, were examined. Pure lanthanum cuprate was also measured. Lanthanum, barium and copper all have relatively low energy narrow resonances. Thus it should be possible to detect differences in the phononsmore » carried by different kinds of atom in the lattice. Neutron cross section measurements have been made with high energy resolution and statistical precision on the 59m flight path of LANSCE, the pulsed spallation neutron source at Los Alamos National Laboratory. Measurements on all three materials were made over a range of temperatures from 15K to 300K, with small steps through the critical temperature region near 27K. No significant changes in the mean phonon energy of the lanthanum atoms were observed near the critical temperature of the super-conducting material. It appears however that the mean phonon energy of lanthanum in the superconductor is considerably higher than that in the non-superconductors. The samples used in this series of experiments were too thin in barium and copper to determine anything significant about their phonon spectra.« less

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

Monolithic integrated high-T.sub.c superconductor-semiconductor structure

NASA Technical Reports Server (NTRS)

Barfknecht, Andrew T. (Inventor); Garcia, Graham A. (Inventor); Russell, Stephen D. (Inventor); Burns, Michael J. (Inventor); de la Houssaye, Paul R. (Inventor); Clayton, Stanley R. (Inventor)

2000-01-01

A method for the fabrication of active semiconductor and high-temperature superconducting device of the same substrate to form a monolithically integrated semiconductor-superconductor (MISS) structure is disclosed. A common insulating substrate, preferably sapphire or yttria-stabilized zirconia, is used for deposition of semiconductor and high-temperature superconductor substructures. Both substructures are capable of operation at a common temperature of at least 77 K. The separate semiconductor and superconductive regions may be electrically interconnected by normal metals, refractory metal silicides, or superconductors. Circuits and devices formed in the resulting MISS structures display operating characteristics which are equivalent to those of circuits and devices prepared on separate substrates.

Electronic properties of high-temperature superconductors and novel carbon-based conductors and superconductors

NASA Astrophysics Data System (ADS)

Fuhrer, Michael Sears

This thesis is divided into three sections. The first section discusses the electrical transport properties of a highly anisotropic high temperature superconductor, Bi2Sr2CaCu2O8, in magnetic fields. High temperature superconductivity has greatly expanded the study of vortex matter: the state of the quantized magnetic field excitations, or vortices, in a superconductor. The effects of tilted fields and fields parallel to the planes are studied: striking deviations from the expectations of a simple anisotropic superconductivity model are found, indicating that the layered structure of high temperature superconductors plays a significant role in determining the dynamics and phases of vortex matter. For the case of parallel magnetic fields, the Josephson vortex state, a new phase transition is identified, the melting of the Josephson vortex lattice. A mechanism for Josephson vortex lattice melting is proposed to explain the differences in the phase diagrams from the usual case of Abrikosov vortex lattice melting. The second section discusses experiments on C60-containing solids. A method for growing high quality single crystals of C60 is described. Isotopically pure single crystal samples of the fulleride superconductor Rb3C60 were synthesized in order to measure the carbon isotope effect on superconductivity. By measuring the superconducting transitions in the resistance of single crystals of Rb3C60, the carbon isotope effect was determined with unprecedented accuracy. Measurement of the isotope effect gives essential information for determination of the superconducting parameters, necessary for a complete theoretical picture of superconductivity in this material. New intercalated graphite compounds containing C60, and their electronic properties, are also discussed. The third section discusses the electrical transport and magnetotransport properties of mats of single-walled carbon nanotubes. Single-walled nanotubes are an intriguing new physical system: nanowires of pure carbon with nanometerscale diameters and lengths of microns. The previously unexplained low-temperature properties are shown to be due to localization. The radius of the localized states is determined, and the hopping conduction is found to be three-dimensional in nature. The magnetotransport also agrees with models of variable range hopping in two or greater dimensions, indicating that mats of single-walled nanotubes are well-connected metallic networks.

Preparation of Bi-Sr-Ca-Cu-O superconductors from oxide-glass precursors

DOEpatents

Hinks, David G.; Capone, II, Donald W.

1992-01-01

A superconductor and precursor therefor from oxide mixtures of Ca, Sr, Bi and Cu. Glass precursors quenched to elevated temperatures result in glass free of crystalline precipitates having enhanced mechanical properties. Superconductors are formed from the glass precursors by heating in the presence of oxygen to a temperature below the melting point of the glass.

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

NASA Technical Reports Server (NTRS)

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

1996-01-01

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

Developing Test Apparatus and Measurements of AC Loss of High Temperature Superconductors

DTIC Science & Technology

2012-11-01

temperature of the coil is not raised significantly. The second system, a larger machine, designed with a long term prospective to serve a test bed for...four sample chambers inside the vacuum gap, LN2 – cooled sample holder (currently only one is in use), the laminated back iron, and the outer shell...machine. accommodate a variety of different small coils and linear tapes. This assembly is surrounded by the laminated back iron and the outer shell

Magnetic Exchange Coupling in Ferromagnetic/Superconducting/Ferromagnetic Multilayers

NASA Astrophysics Data System (ADS)

de Melo, C. A. R. Sa

2001-03-01

The possibility of magnetic exchange coupling between ferromagnets (F) separated by superconductor (S) spacers in F/S/F multilayers is analysed theoretically [1,2]. Ideal systems for the observation of magnetic coupling through superconductors are complex oxide multilayers consisting of Colossal Magneto-Resistance (CMR) Ferromagnets and High Critical Temperature Cuprate Superconductors. For this coupling to occur, three "prima facie" conditions need to be satisfied. First, an indirect exchange coupling between the ferromagnets must exist when the superconductor is in its normal state. Second, superconductivity must not be destroyed due to the proximity of ferromagnetic boundaries. Third, roughness of the F/S interfaces must be small. Under these conditions, when the superconductor is cooled below its critical temperature T_c, the magnetic coupling changes. The appearance of the superconducting gap introduces a new length scale (the coherence length of the superconductor) and modifies the temperature dependence of the indirect exchange coupling existent in the normal state. The magnetic coupling is oscillatory both above and below T_c, as well as strongly temperature-dependent. However at low temperatures the indirect exchange coupling decay length is controlled by the coherence length of the superconductor, while at temperatures close to and above Tc the magnetic coupling decay length is controlled by the thermal length. [I would like to thank the Georgia Institute of Technology, NSF (Grant No. DMR-9803111) and NATO (Grant No. CRG-972261) for financial support.] [1] C. A. R. Sa de Melo, Phys. Rev. Lett. 79, 1933 (1997). [2] C. A. R. Sa de Melo, Phys. Rev. B 62, 12303 (2000).

Observation of dx2-y-Like Superconducting Gap in an Electron-Doped High-Temperature Superconductor

NASA Astrophysics Data System (ADS)

Sato, T.; Kamiyama, T.; Takahashi, T.; Kurahashi, K.; Yamada, K.

2001-02-01

High-resolution angle-resolved photoemission spectroscopy of the electron-doped high-temperature superconductor Nd2-xCexCuO4 (x = 0.15, transition temperature Tc = 22 K) has found the quasiparticle signature as well as the anisotropic dx2-y-like superconducting gap. The spectral line shape at the superconducting state shows a strong anisotropic nature of the many-body interaction. The result suggests that the electron-hole symmetry is present in the high-temperature superconductors.

Three dimensional reflectance properties of superconductor-dielectric photonic crystal

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

Pandey, G. N., E-mail: gnpandey@amity.edu; Sancheti, Bhagyashree; Pandey, J. P.

2016-05-06

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

Charge-density study on layered oxyarsenides (LaO)MAs (M = Mn, Fe, Ni, Zn)

NASA Astrophysics Data System (ADS)

Takase, Kouichi; Hiramoto, Shozo; Fukushima, Tetsuya; Sato, Kazunori; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

2017-12-01

Using synchrotron X-ray powder diffraction, we investigate the charge-density distributions of the layered oxypnictides (LaO)MnAs, (LaO)FeAs, (LaO)NiAs, and (LaO)ZnAs, which are an antiferromagnetic semiconductor, a parent material of an iron-based superconductor, a low-temperature superconductor, and a non-magnetic semiconductor, respectively. For the metallic samples, clear charge densities are observed in both the transition-metal pnictide layers and the rare-earth-oxide layers. However, in the semiconducting samples, there is no finite charge density between the transition-metal element and As. These differences in charge density reflect differences in physical properties. First-principles calculations using density functional theory reproduce the experimental results reasonably well.

Universal linear-temperature resistivity: possible quantum diffusion transport in strongly correlated superconductors.

PubMed

Hu, Tao; Liu, Yinshang; Xiao, Hong; Mu, Gang; Yang, Yi-Feng

2017-08-25

The strongly correlated electron fluids in high temperature cuprate superconductors demonstrate an anomalous linear temperature (T) dependent resistivity behavior, which persists to a wide temperature range without exhibiting saturation. As cooling down, those electron fluids lose the resistivity and condense into the superfluid. However, the origin of the linear-T resistivity behavior and its relationship to the strongly correlated superconductivity remain a mystery. Here we report a universal relation [Formula: see text], which bridges the slope of the linear-T-dependent resistivity (dρ/dT) to the London penetration depth λ L at zero temperature among cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+δ and heavy fermion superconductors CeCoIn 5 , where μ 0 is vacuum permeability, k B is the Boltzmann constant and ħ is the reduced Planck constant. We extend this scaling relation to different systems and found that it holds for other cuprate, pnictide and heavy fermion superconductors as well, regardless of the significant differences in the strength of electronic correlations, transport directions, and doping levels. Our analysis suggests that the scaling relation in strongly correlated superconductors could be described as a hydrodynamic diffusive transport, with the diffusion coefficient (D) approaching the quantum limit D ~ ħ/m*, where m* is the quasi-particle effective mass.

High temperature superconducting fault current limiter

DOEpatents

Hull, J.R.

1997-02-04

A fault current limiter for an electrical circuit is disclosed. The fault current limiter includes a high temperature superconductor in the electrical circuit. The high temperature superconductor is cooled below its critical temperature to maintain the superconducting electrical properties during operation as the fault current limiter. 15 figs.

Electronic structure, irreversibility line and magnetoresistance of Cu 0.3Bi 2Se 3 superconductor

DOE PAGES

Hemian, Yi; Gu, Genda; Chen, Chao -Yu; ...

2015-06-01

Cu xBi 2Se 3 is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the Cu xBi 2Se 3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi 2Se 3 topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper criticalmore » field at zero temperature of ~4000 Oe for the Cu 0.3Bi 2Se 3 superconductor with a middle point T c of 1.9K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu 0.3Bi 2Se 3 superconductors up to room temperature. As a result, these observations provide useful information for further study of this possible candidate for topological superconductors.« less

Temperature-and field dependent characterization of a twisted stacked-tape cable

NASA Astrophysics Data System (ADS)

Barth, C.; Takayasu, M.; Bagrets, N.; Bayer, C. M.; Weiss, K.-P.; Lange, C.

2015-04-01

The twisted stacked-tape cable (TSTC) is one of the major high temperature superconductor cable concepts combining scalability, ease of fabrication and high current density making it a possible candidate as conductor for large scale magnets. To simulate the boundary conditions of such a magnets as well as the temperature dependence of TSTCs a 1.16 m long sample consisting of 40, 4 mm wide SuperPower REBCO tapes is characterized using the ‘FBI’ (force-field-current) superconductor test facility of the Institute for Technical Physics of the Karlsruhe Institute of Technology. In a first step, the magnetic background field is cycled while measuring the current carrying capabilities to determine the impact of Lorentz forces on the TSTC sample performance. In the first field cycle, the critical current of the TSTC sample is tested up to 12 T. A significant Lorentz force of up to 65.6 kN m-1 at the maximal magnetic background field of 12 T result in a 11.8% irreversible degradation of the current carrying capabilities. The degradation saturates (critical cable current of 5.46 kA at 4.2 K and 12 T background field) and does not increase in following field cycles. In a second step, the sample is characterized at different background fields (4-12 T) and surface temperatures (4.2-37.8 K) utilizing the variable temperature insert of the ‘FBI’ test facility. In a third step, the performance along the length of the sample is determined at 77 K, self-field. A 15% degradation is obtained for the central part of the sample which was within the high field region of the magnet during the in-field measurements.

SNS Heterojunctions With New Combinations Of Materials

NASA Technical Reports Server (NTRS)

Vasquez, Richard P.; Hunt, Brian D.; Foote, Marc C.

1992-01-01

New combinations of materials proposed for superconductor/normal-metal/superconductor (SNS) heterojunctions in low-temperature electronic devices such as fast switches, magnetometers, and mixers. Epitaxial heterojunctions formed between high-temperature superconductors and either oxide semiconductors or metals. Concept offers alternative to other three-layer heterojunction concepts; physical principles of operation permit SNS devices to have thicker barrier layers and fabricated more easily.

Thermodynamic fluctuation in doped BiSrCaCuO superconductors with 110K phase

NASA Astrophysics Data System (ADS)

Han, S. H.; Andersson, M.

1994-02-01

The resistivity has been carefully measured for four sintered samples of Pb and Pb/Sb doped BiSrCaCuO superconductors with the 110 K phase from zero resistance temperature up to 300 K. The thermodynamical fluctuation have been fitted on the form Δσ∝ε x ( ε=( {T- T c)/ }/{T c}) in the regions -4 < ln ε < -2. By choosing T c in different ways, it is shown that consistent results only could be obtained when T c is defined according to the Lawrence-Doniach theory.

Superconductivity in ThPd2Ge2

NASA Astrophysics Data System (ADS)

Domieracki, Krzysztof; Wiśniewski, Piotr; Wochowski, Konrad; Romanova, Tetiana; Hackemer, Alicja; Gorzelniak, Roman; Pikul, Adam; Kaczorowski, Dariusz

2018-05-01

Our on-going search for unconventional superconductors among the ThTE2Ge2 phases (TE is a d-electron transition metal) revealed that ThPd2Ge2, which crystallizes with a body-centered tetragonal ThCr2Si2-type structure, exhibits superconductivity at low temperatures. In this paper, we report on the electrical transport and thermodynamic properties of a polycrystalline sample of this new superconductor, extended down to 50 mK. The experimental data indicates weakly-coupled type-II superconductivity with Tc = 0.63(2) K and μ0Hc2(0) = 32(2) mT.

73Ge-NMR study on magnetic fluctuations of ferromagnetic superconductor UGe2

NASA Astrophysics Data System (ADS)

Noma, Y.; Kotegawa, H.; Kubo, T.; Tou, H.; Harima, H.; Haga, Y.; Yamamoto, E.; Ōnuki, Y.; Itoh, K. M.; Haller, E. E.; Nakamura, A.; Homma, Y.; Honda, F.; Aoki, D.

2018-05-01

We report 73Ge-NMR measurement on the ferromagnetic superconductor UGe2 at ambient pressure. The observed NMR spectrum supports that the electric field gradient at three inequivalent Ge sites is correctly deduced by a LDA calculation. The temperature dependences of the nuclear spin lattice relaxation rate 1 /T1 for H0 ⊥ a (easy axis) and H0 ∥ a were obtained for the oriented sample. The contrasting behavior in 1 /T1 for H0 ⊥ a and H0 ∥ a reveals that the magnetic fluctuation of UGe2 is highly anisotropic.

Spontaneous Currents in Superconducting Systems with Strong Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Mironov, S.; Buzdin, A.

2017-02-01

We show that Rashba spin-orbit coupling at the interface between a superconductor and a ferromagnet should produce a spontaneous current in the atomic thickness region near the interface. This current is counterbalanced by the superconducting screening current flowing in the region of the width of the London penetration depth near the interface. Such a current-carrying state creates a magnetic field near the superconductor surface, generates a stray magnetic field outside the sample edges, changes the slope of the temperature dependence of the critical field Hc 3 , and may generate the spontaneous Abrikosov vortices near the interface.

High temperature superconducting fault current limiter

DOEpatents

Hull, John R.

1997-01-01

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

The electronic properties of high (Tc) superconductors probed by positron annihilation

NASA Astrophysics Data System (ADS)

Sundar, C. S.; Bharathi, A.; Jean, Y. C.; Hinks, D. G.; Dabrowski, B.; Zheng, Y.; Mitchell, A. W.; Ho, J. C.; Howell, K. H.; Wachs, A. L.

1989-06-01

The discovery of superconductivity at 30 K in Ba(.6)K(.4) BiO3 has generated considerable excitement in view of the contrasting properties of the Ba-K-Bi-O system when compared to the well known Cu-O based high temperature superconductors. Positron annihilation spectroscopy, which is a sensitive local probe of the electronic and defect properties of a solid, was extensively applied in the study of Cu-O based superconductors. The results of positron lifetime as a function of temperature in Ba-K-Bi-O are presented and compared with the known results in the cuprate superconductors. Plausible reasons for the observed temperature dependence of positron lifetime are presented.

Contact spectroscopy of high-temperature superconductors (Review). I - Physical and methodological principles of the contact spectroscopy of high-temperature superconductors. Experimental results for La(2-x)Sr(x)CuO4 and their discussion

NASA Astrophysics Data System (ADS)

Ianson, I. K.

1991-03-01

Research in the field of high-temperature superconductors based on methods of tunneling and microcontact spectroscopy is reviewed in a systematic manner. The theoretical principles of the methods are presented, and various types of contacts are described and classified. Attention is given to deviations of the measured volt-ampere characteristics from those predicted by simple theoretical models and those observed for conventional superconductors. Results of measurements of the energy gap and fine structure of volt ampere characteristic derivatives are presented for La(2-x)Sr(x)CuO4.

Method for making a monolithic integrated high-T.sub.c superconductor-semiconductor structure

NASA Technical Reports Server (NTRS)

Burns, Michael J. (Inventor); de la Houssaye, Paul R. (Inventor); Russell, Stephen D. (Inventor); Garcia, Graham A. (Inventor); Barfknecht, Andrew T. (Inventor); Clayton, Stanley R. (Inventor)

2000-01-01

A method for the fabrication of active semiconductor and high-temperature perconducting devices on the same substrate to form a monolithically integrated semiconductor-superconductor (MISS) structure is disclosed. A common insulating substrate, preferably sapphire or yttria-stabilized zirconia, is used for deposition of semiconductor and high-temperature superconductor substructures. Both substructures are capable of operation at a common temperature of at least 77 K. The separate semiconductor and superconductive regions may be electrically interconnected by normal metals, refractory metal silicides, or superconductors. Circuits and devices formed in the resulting MISS structures display operating characteristics which are equivalent to those of circuits and devices prepared on separate substrates.

Hall viscosity of a chiral two-orbital superconductor at finite temperatures

NASA Astrophysics Data System (ADS)

Yazdani-Hamid, Meghdad; Shahzamanian, Mohammad Ali

2018-06-01

The Hall viscosity known as the anti-symmetric part of the viscosity fourth-rank tensor. Such dissipationless response which appears for systems with broken time reversal symmetry. We calculate this non-dissipative quantity for a chiral two-orbital superconductor placed in a viscoelastic magnetic field using the linear response theory and apply our calculations to the putative multiband chiral superconductor Sr2RuO4. The chirality origin of a multiband superconductor arises from the interorbital coupling of the superconducting state. This feature leads to the robustness of the Hall viscosity against temperature and impurity effects. We study the temperature effect on the Hall viscosity at the one-loop approximation.

The effects of shock wave compaction on the transition temperatures of A15 structure superconductors

NASA Technical Reports Server (NTRS)

Otto, G. H.

1974-01-01

Several superconductors with the A15 structure exhibit a positive pressure coefficient, indicating that their transition temperatures increase with applied pressure. Powders of the composition Nb3Al, Nb3Ge, Nb3(Al0.75Ge0.25), and V3Si were compacted by explosive shock waves. The superconducting properties of these materials were measured before and after compaction and it was found that regardless of the sign of the pressure coefficient, the transition temperature is always lowered. The decrease in transition temperature is associated with a decrease in the particle diameter. The shock wave passage through a 3Nb:1Ge powder mixture leads to the formation of at least one compound (probably Nb5Ge3). However, the formation of the A15 compound Nb3Ge is not observed. Elemental niobium powder can be compacted by converging shock waves close to the expected value of the bulk density. Under special circumstances a partial remelting in the center of the sample is observed.

Fabrication Of High-Tc Superconducting Integrated Circuits

NASA Technical Reports Server (NTRS)

Bhasin, Kul B.; Warner, Joseph D.

1992-01-01

Microwave ring resonator fabricated to demonstrate process for fabrication of passive integrated circuits containing high-transition-temperature superconductors. Superconductors increase efficiencies of communication systems, particularly microwave communication systems, by reducing ohmic losses and dispersion of signals. Used to reduce sizes and masses and increase aiming accuracies and tracking speeds of millimeter-wavelength, electronically steerable antennas. High-Tc superconductors preferable for such applications because they operate at higher temperatures than low-Tc superconductors do, therefore, refrigeration systems needed to maintain superconductivity designed smaller and lighter and to consume less power.

A flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors.

PubMed

Egan, R; Philippe, M; Wera, L; Fagnard, J F; Vanderheyden, B; Dennis, A; Shi, Y; Cardwell, D A; Vanderbemden, P

2015-02-01

We report the design and construction of a flux extraction device to measure the DC magnetic moment of large samples (i.e., several cm(3)) at cryogenic temperature. The signal is constructed by integrating the electromotive force generated by two coils wound in series-opposition that move around the sample. We show that an octupole expansion of the magnetic vector potential can be used conveniently to treat near-field effects for this geometrical configuration. The resulting expansion is tested for the case of a large, permanently magnetized, type-II superconducting sample. The dimensions of the sensing coils are determined in such a way that the measurement is influenced by the dipole magnetic moment of the sample and not by moments of higher order, within user-determined upper bounds. The device, which is able to measure magnetic moments in excess of 1 A m(2) (1000 emu), is validated by (i) a direct calibration experiment using a small coil driven by a known current and (ii) by comparison with the results of numerical calculations obtained previously using a flux measurement technique. The sensitivity of the device is demonstrated by the measurement of flux-creep relaxation of the magnetization in a large bulk superconductor sample at liquid nitrogen temperature (77 K).

New application of superconductors: High sensitivity cryogenic light detectors

NASA Astrophysics Data System (ADS)

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

2017-02-01

In this paper we describe the current status of the CALDER project, which is developing ultra-sensitive light detectors based on superconductors for cryogenic applications. When we apply an AC current to a superconductor, the Cooper pairs oscillate and acquire kinetic inductance, that can be measured by inserting the superconductor in a LC circuit with high merit factor. Interactions in the superconductor can break the Cooper pairs, causing sizable variations in the kinetic inductance and, thus, in the response of the LC circuit. The continuous monitoring of the amplitude and frequency modulation allows to reconstruct the incident energy with excellent sensitivity. This concept is at the basis of Kinetic Inductance Detectors (KIDs) that are characterized by natural aptitude to multiplexed read-out (several sensors can be tuned to different resonant frequencies and coupled to the same line), resolution of few eV, stable behavior over a wide temperature range, and ease in fabrication. We present the results obtained by the CALDER collaboration with 2×2 cm2 substrates sampled by 1 or 4 Aluminum KIDs. We show that the performances of the first prototypes are already competitive with those of other commonly used light detectors, and we discuss the strategies for a further improvement.

Thermoelectric refrigerator having improved temperature stabilization means

DOEpatents

Falco, Charles M.

1982-01-01

A control system for thermoelectric refrigerators is disclosed. The thermoelectric refrigerator includes at least one thermoelectric element that undergoes a first order change at a predetermined critical temperature. The element functions as a thermoelectric refrigerator element above the critical temperature, but discontinuously ceases to function as a thermoelectric refrigerator element below the critical temperature. One example of such an arrangement includes thermoelectric refrigerator elements which are superconductors. The transition temperature of one of the superconductor elements is selected as the temperature control point of the refrigerator. When the refrigerator attempts to cool below the point, the metals become superconductors losing their ability to perform as a thermoelectric refrigerator. An extremely accurate, first-order control is realized.

Fabrication of high temperature superconductors

DOEpatents

Balachandran, Uthamalingam; Dorris, Stephen E.; Ma, Beihai; Li, Meiya

2003-06-17

A method of forming a biaxially aligned superconductor on a non-biaxially aligned substrate substantially chemically inert to the biaxially aligned superconductor comprising is disclosed. A non-biaxially aligned substrate chemically inert to the superconductor is provided and a biaxially aligned superconductor material is deposited directly on the non-biaxially aligned substrate. A method forming a plume of superconductor material and contacting the plume and the non-biaxially aligned substrate at an angle greater than 0.degree. and less than 90.degree. to deposit a biaxially aligned superconductor on the non-biaxially aligned substrate is also disclosed. Various superconductors and substrates are illustrated.

Electrical bushing for a superconductor element

DOEpatents

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

2010-05-04

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

Development of high Tc (greater than 110K) Bi, Tl and Y-based materials as superconducting circuit elements

NASA Technical Reports Server (NTRS)

Haertling, Gene H.; Lee, Burtrand; Grabert, Gregory; Gilmour, Phillip

1991-01-01

This report is presented in two parts. Part 1 deals primarily with Bi-based materials and a small amount of work on a Y-based composition while Part 2 covers work on Tl-based materials. In Part 1, a reliable and reproducible process for producing bulk bismuth-based superconductors has been developed. It is noted however, that a percentage of the tapecast material experiences curling and fracturing after a 30 hour sintering period and is thus in need of further examination. The Bi-Sr-Ca-Cu-O (BSCCO) material has been characterized by critical temperature data, X-ray diffraction data, and surface morphology. In the case of T sub c, it is not critical to anneal the material. It appears that the BSCCO material has the possibility of producing a better grounding strap than that of the 123 material. Attempts to reproduce near room temperature superconductors in the Y-Ba-Cu-O system were unsuccessful. In Part 2, several methods of processing the high temperature superconductor Tl2Ba2Ca2Cu3O10 were investigated; i.e., different precursor compositions were sintered at various sintering times and temperatures. The highest superconductig temperature was found to be 117.8K when fired at 900 C for three hours. Higher sintering temperatures produced a melted sample which was nonsuperconducting at liquid nitrogen temperature. Also, a preliminary study found Li2O substitutions for copper appeared to increase the transition temperature and create fluxing action upon sintering. It was suggested that lower sintering temperatures might be obtained with lithium additions to produce reliable Tl2Ba2Ca2Cu3O10 processing methods.

SQUIDs: microscopes and nondestructive evaluation

NASA Astrophysics Data System (ADS)

Mück, Michael

2005-03-01

SQUIDs (Superconducting Quantum Interference Devices) are magnetic field sensores with unsurpassed sensitivity. They are amazingly versatile, being able to measure all physical quantities which can be converted to magnetic flux. They are routinely fabricated in thin film technology from two classes of superconducting materials: high-temperature superconductors (HTS) which are usually cooled to 77 K, and low-temperature superconductors (LTS), which have to be cooled to 4.2 K. SQUIDs have many applications, two of which shall be discussed in this paper. In SQUID microscopy, a SQUID scans a sample, which preferrably is at room temperature, and measures the two-dimensional magnetic field distribution at the surface of the sample. In order to achieve a relatively high spatial resolution, the stand-off distance between the sample and the SQUID is made as small as possible. SQUIDs show also promising results in the field of nondestructive testing of various materials. For example, ferromagnetic impurities in stainless steel formed by aging processes in the material can be detected with high probability, and cracks in conducting materials, for example aircraft parts, can be located using eddy current methods. Especially for the case of thick, highly conductive, or ferromagnetic materials, as well as sintered materials, it can be shown that a SQUID-based NDE system exhibits a much higher sensitivity compared to conventional eddy current NDE and ultrasonic testing.

Microwave surface resistance of bulk YBa2Cu3O6+x material

NASA Astrophysics Data System (ADS)

Fathy, A.; Kalokitis, D.; Belohoubek, E.; Sundar, H. G. K.; Safari, A.

1988-10-01

Superconducting Y-Ba-Cu-O samples were prepared by conventional solid-state reaction. The microwave surface resistance of 1:2:3 compound superconductor material was measured in a special disk resonator structure at 10 GHz. At liquid-nitrogen temperatures the microwave surface resistance is comparable to that of Au. At lower temperature (~10 K) the surface resistance is an order of magnitude lower than that of Au at the same temperature.

Upper critical and irreversibility fields in Ni- and Co-doped pnictide bulk superconductors

NASA Astrophysics Data System (ADS)

Nikolo, Martin; Singleton, John; Solenov, Dmitry; Jiang, Jianyi; Weiss, Jeremy; Hellstrom, Eric

2018-05-01

A comprehensive study of upper critical and irreversibility magnetic fields in Ba(Fe0.95Ni0.05)2As2 (large grain and small grain samples), Ba(Fe0.94Ni0.06)2As2, Ba(Fe0.92Co0.08)2As2, and Ba(Fe0.92Co0.09)2As2 polycrystalline bulk pnictide superconductors was made in pulsed fields of up to 65 T. The full magnetic field-temperature (H-T) phase diagrams, starting at 1.5 K, were measured. The higher temperature, upper critical field Hc2 data are well described by the one-band Werthamer, Helfand, and Hohenberg (WHH) model. At low temperatures, the experimental data depart from the fitted WHH curves, suggesting an emergence of a new phase that could be attributed to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The large values of the Maki fitting parameter α indicate that the Zeeman pair breaking dominates over the orbital pair breaking and spin-paramagnetic pair-breaking effect is significant in these materials. Possible multi-band structure of these materials is lumped into effective parameters of the single-band model. Table of measured physical parameters allows us to compare these pnictide superconductors for different Co- and Ni- doping levels and granularity.

Control of Y-211 content in bulk YBCO superconductors fabricated by a buffer-aided, top seeded infiltration and growth melt process

NASA Astrophysics Data System (ADS)

Namburi, Devendra K.; Shi, Yunhua; Palmer, Kysen G.; Dennis, Anthony R.; Durrell, John H.; Cardwell, David A.

2016-03-01

Bulk (RE)-Ba-Cu-O ((RE)BCO, where RE stands for rare-earth), single grain superconductors can trap magnetic fields of several tesla at low temperatures and therefore can function potentially as high field magnets. Although top seeded melt growth (TSMG) is an established process for fabricating relatively high quality single grains of (RE)BCO for high field applications, this technique suffers from inherent problems such as sample shrinkage, a large intrinsic porosity and the presence of (RE)2BaCuO5 (RE-211)-free regions in the single grain microstructure. Seeded infiltration and growth (SIG), therefore, has emerged as a practical alternative to TSMG that overcomes many of these problems. Until now, however, the superconducting properties of bulk materials processed by SIG have been inferior to those fabricated using the TSMG technique. In this study, we identify that the inferior properties of SIG processed bulk superconductors are related to the presence of a relatively large Y-211 content (˜41.8%) in the single grain microstructure. Controlling the RE-211 content in SIG bulk samples is particularly challenging because it is difficult to regulate the entry of the liquid phase into the solid RE-211 preform during the infiltration process. In an attempt to solve this issue, we have investigated the effect of careful control of both the infiltration temperature and the quantity of liquid phase powder present in the sample preforms prior to processing. We conclude that careful control of the infiltration temperature is the most promising of these two process variables. Using this knowledge, we have fabricated successfully a YBCO bulk single grain using the SIG process of diameter 25 mm that exhibits a trapped field of 0.69 T at 77 K, which is the largest value reported to date for a sample fabricated by the SIG technique.

Measuring Thermal Diffusivity Of A High-Tc Superconductor

NASA Technical Reports Server (NTRS)

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

1992-01-01

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

The connection characteristics of flux pinned docking interface

NASA Astrophysics Data System (ADS)

Zhang, Mingliang; Han, Yanjun; Guo, Xing; Zhao, Cunbao; Deng, Feiyue

2017-03-01

This paper presents the mechanism and potential advantages of flux pinned docking interface mainly composed of a high temperature superconductor and an electromagnet. In order to readily assess the connection characteristics of flux pinned docking interface, the force between a high temperature superconductor and an electromagnet needs to be investigated. Based on the magnetic dipole method and the Ampere law method, the force between two current coils can be compared, which shows that the Ampere law method has the higher calculated accuracy. Based on the improved frozen image model and the Ampere law method, the force between high temperature superconductor bulk and permanent magnet can be calculated, which is validated experimentally. Moreover, the force between high temperature superconductor and electromagnet applied to flux pinned docking interface is able to be predicted and analyzed. The connection stiffness between high temperature superconductor and permanent magnet can be calculated based on the improved frozen image model and Hooke's law. The relationship between the connection stiffness and field cooling height is analyzed. Furthermore, the connection stiffness of the flux pinned docking interface is predicted and optimized, and its effective working range is defined and analyzed in case of some different parameters.

Thermoelectric properties of FeAs based superconductors, with thick perovskite- and Sm-O fluorite-type blocking layers

NASA Astrophysics Data System (ADS)

Singh, S. J.; Shimoyama, J.; Ogino, H.; Kishio, K.

2015-11-01

The transport properties (electrical resistivity, Hall and Seebeck coefficient, and thermal conductivity) of iron based superconductors with thick perovskite-type oxide blocking layers and fluorine-doped SmFeAsO were studied to explore their possible potential for thermoelectric applications. The thermal conductivity of former compounds depicts the dominated role of phonon and its value decreases rapidly below the Tc, suggesting the addition of scattering of phonons. Both the Seebeck coefficient (S) and Hall coefficient (RH) of all samples were negative in the whole temperature region below 300 K, indicating that the major contribution to the normal state conductivity is by electrons. In addition, the profile of S(T) and RH(T) of all samples have similar behaviours as would be expected for a multi-band superconductors. Although the estimated thermoelectric figure of merit (ZT) of these compounds was much lower than that of practically applicable thermoelectric materials, however its improvement can be expected by optimizing microstructure of the polycrystalline materials, such as densification and grain orientation.

Temperature Evolution of Energy Gap and Band Structure in the Superconducting and Pseudogap States of Bi 2Sr 2CaCu 2O 8+δ Superconductor Revealed by Laser-Based Angle-Resolved Photoemission Spectroscopy

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

Sun, Xuan; Zhang, Wen-Tao; Zhao, Lin

For this study, we carry out detailed momentum-dependent and temperature-dependent measurements on Bi 2Sr 2CaCu 2O 8+δ (Bi2212) superconductor in the superconducting and pseudogap states by super-high resolution laser-based angle-resolved photoemission spectroscopy. The precise determination of the superconducting gap for the nearly optimally doped Bi2212 (T c=91 K) at low temperature indicates that the momentum-dependence of the superconducting gap deviates from the standard d-wave form (cos(2Φ)). It can be alternatively fitted by including a high-order term (cos(6Φ)) in which the next nearest-neighbor interaction is considered. We find that the band structure near the antinodal region smoothly evolves across the pseudogapmore » temperature without a signature of band reorganization which is distinct from that found in Bi 2Sr 2CuO 6+δ superconductors. This indicates that the band reorganization across the pseudogap temperature is not a universal behavior in cuprate superconductors. These results provide new insights in understanding the nature of the superconducting gap and pseudogap in high-temperature cuprate superconductors.« less

Temperature Evolution of Energy Gap and Band Structure in the Superconducting and Pseudogap States of Bi 2Sr 2CaCu 2O 8+δ Superconductor Revealed by Laser-Based Angle-Resolved Photoemission Spectroscopy

DOE PAGES

Sun, Xuan; Zhang, Wen-Tao; Zhao, Lin; ...

2017-12-17

For this study, we carry out detailed momentum-dependent and temperature-dependent measurements on Bi 2Sr 2CaCu 2O 8+δ (Bi2212) superconductor in the superconducting and pseudogap states by super-high resolution laser-based angle-resolved photoemission spectroscopy. The precise determination of the superconducting gap for the nearly optimally doped Bi2212 (T c=91 K) at low temperature indicates that the momentum-dependence of the superconducting gap deviates from the standard d-wave form (cos(2Φ)). It can be alternatively fitted by including a high-order term (cos(6Φ)) in which the next nearest-neighbor interaction is considered. We find that the band structure near the antinodal region smoothly evolves across the pseudogapmore » temperature without a signature of band reorganization which is distinct from that found in Bi 2Sr 2CuO 6+δ superconductors. This indicates that the band reorganization across the pseudogap temperature is not a universal behavior in cuprate superconductors. These results provide new insights in understanding the nature of the superconducting gap and pseudogap in high-temperature cuprate superconductors.« less

Hyper- and hypobaric processing of Tl-Ba-Ca-Cu-O superconductors

NASA Astrophysics Data System (ADS)

Goretta, K. C.; Routbort, J. L.; Shi, Donglu; Chen, J. G.; Hash, M. C.

1989-11-01

Tl-based superconductors of initial composition Tl:Ca:Ba:Cu equal to 2:2:2:3 and 1:3:1:3 were heated in oxygen at pressures of 10(sup 4) to 6 (times) 10(sup 5) Pa. The 2:2:2:3 composition formed primarily the 2-layer superconductor with zero resistance from 77 to 104 K. The 1:3:1:3 composition formed nearly phase pure 3-layer superconductor with a maximum zero resistance temperature of 120 K. Application of hyperbaric pressure influenced phase purities and transition temperatures slightly; phase purities decreased significantly with application of hypobaric pressures.

Superconductors in the high school classroom

NASA Astrophysics Data System (ADS)

Lincoln, James

2017-11-01

In this article, we discuss the behavior of high-temperature superconductors and how to demonstrate them safely and effectively in the high school or introductory physics classroom. Included here is a discussion of the most relevant physics topics that can be demonstrated, some safety tips, and a bit of the history of superconductors. In an effort to include first-year physics students in the world of modern physics, a topic as engaging as superconductivity should not be missed. It is an opportunity to inspire students to study physics through the myriad of possible applications that high temperature superconductors hold for the future.

Observation of Superconductivity in Tetragonal FeS.

PubMed

Lai, Xiaofang; Zhang, Hui; Wang, Yingqi; Wang, Xin; Zhang, Xian; Lin, Jianhua; Huang, Fuqiang

2015-08-19

The possibility of superconductivity in tetragonal FeS has attracted considerable interest because of its similarities to the FeSe superconductor. However, all efforts made to pursue superconductivity in tetragonal FeS have failed so far, and it remains controversial whether tetragonal FeS is metallic or semiconducting. Here we report the observation of superconductivity at 5 K in tetragonal FeS that is synthesized by the hydrothermal reaction of iron powder with sulfide solution. The obtained samples are highly crystalline and less air-sensitive, in contrast to those reported in the literature, which are meta-stable and air-sensitive. Magnetic and electrical properties measurements show that the samples behave as a paramagnetic metal in the normal state and exhibit superconductivity below 5 K. The high crystallinity and the stoichiometry of the samples play important roles in the observation of superconductivity. The present results demonstrate that tetragonal FeS is a promising new platform to realize high-temperature superconductors.

a Study of High Transition Temperature Superconductors: Mercury-Copper Oxide Systems

NASA Astrophysics Data System (ADS)

Kirven, Paul Douglas

1995-01-01

The Hg-based copper-oxides viz., HgBa _2Ca_{n-1}Cu_ nO _{2n+2+delta}, were discovered in 1993. A system consisting of many different, but related, compounds can be synthesized by including or substituting one or more elements in the original compound (e.g. Hg _{1-x}Pb_ x). In this thesis, the superconducting and normal state properties of several of these compounds were investigated. In the normal state electrical resistivity rho(T) is a linear function of temperature (T) and the magnetic susceptibility, X(T), is weakly paramagnetic. Many were observed to superconduct at very high temperatures. At 5 K up to 80% perfect diamagnetic X(T) was measured. The onset transition temperature (T_ c), where a specimen starts to superconduct, is observed to be as high as 135 K. Although T_ c is about 10 K higher than that of any previously known material, in many respects the properties of this new system are similar to that of other type II superconductors. Flux flow behavior and the nature of these type II superconductors was investigated via SQUID measurements and high field longitudinal magneto-resistance R(T,H) as a function of field and temperature. The study of flux motion allows one to observe Anderson-Kim type logarithimic flux creep at low temperature and field (T < 80K and B < 2T) and giant -flux flow at high temperature and field (80 < T < 130; B < 17T). Key parameters were determined. Some of which include reversibility temperature T*(H), critical field Hc, and pinning potential, Uo. Normal state properties which were also measured include the following: Curie constant, Curie-Weiss temperature (15-25 K), temperature independent susceptibility, and Sommerfeld constant (10-25 mJ/mol.Cu K^2). The values of these parameters of the Hg-based superconductors were compared to those of other superconductors. The results of this investigation are expected to yield a better understanding of this newest family of high temperature superconductors.

Low-temperature magnetothermal transport investigation of a Ni-based superconductor BaNi2As2: evidence for fully gapped superconductivity.

PubMed

Kurita, N; Ronning, F; Tokiwa, Y; Bauer, E D; Subedi, A; Singh, D J; Thompson, J D; Movshovich, R

2009-04-10

We have performed low-temperature specific heat and thermal conductivity measurements of the Ni-based superconductor BaNi2As2 (T{c}=0.7 K) in a magnetic field. In a zero field, thermal conductivity shows T-linear behavior in the normal state and exhibits a BCS-like exponential decrease below T{c}. The field dependence of the residual thermal conductivity extrapolated to zero temperature is indicative of a fully gapped superconductor. This conclusion is supported by the analysis of the specific heat data, which are well fit by the BCS temperature dependence from T{c} down to the lowest temperature of 0.1 K.

Electronic evidence of an insulator-superconductor crossover in single-layer FeSe/SrTiO3 films.

PubMed

He, Junfeng; Liu, Xu; Zhang, Wenhao; Zhao, Lin; Liu, Defa; He, Shaolong; Mou, Daixiang; Li, Fangsen; Tang, Chenjia; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

2014-12-30

In high-temperature cuprate superconductors, it is now generally agreed that superconductivity is realized by doping an antiferromagnetic Mott (charge transfer) insulator. The doping-induced insulator-to-superconductor transition has been widely observed in cuprates, which provides important information for understanding the superconductivity mechanism. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic bad metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. No evidence of doping-induced insulator-superconductor transition (or crossover) has been reported in the iron-based compounds so far. Here, we report an electronic evidence of an insulator-superconductor crossover observed in the single-layer FeSe film grown on a SrTiO3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with increasing carrier concentration. In particular, the insulator-superconductor crossover in FeSe/SrTiO3 film exhibits similar behaviors to that observed in the cuprate superconductors. Our results suggest that the observed insulator-superconductor crossover may be associated with the two-dimensionality that enhances electron localization or correlation. The reduced dimensionality and the interfacial effect provide a new pathway in searching for new phenomena and novel superconductors with a high transition temperature.

Electronic evidence of an insulator–superconductor crossover in single-layer FeSe/SrTiO3 films

PubMed Central

He, Junfeng; Liu, Xu; Zhang, Wenhao; Zhao, Lin; Liu, Defa; He, Shaolong; Mou, Daixiang; Li, Fangsen; Tang, Chenjia; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X. J.

2014-01-01

In high-temperature cuprate superconductors, it is now generally agreed that superconductivity is realized by doping an antiferromagnetic Mott (charge transfer) insulator. The doping-induced insulator-to-superconductor transition has been widely observed in cuprates, which provides important information for understanding the superconductivity mechanism. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic bad metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. No evidence of doping-induced insulator–superconductor transition (or crossover) has been reported in the iron-based compounds so far. Here, we report an electronic evidence of an insulator–superconductor crossover observed in the single-layer FeSe film grown on a SrTiO3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with increasing carrier concentration. In particular, the insulator–superconductor crossover in FeSe/SrTiO3 film exhibits similar behaviors to that observed in the cuprate superconductors. Our results suggest that the observed insulator–superconductor crossover may be associated with the two-dimensionality that enhances electron localization or correlation. The reduced dimensionality and the interfacial effect provide a new pathway in searching for new phenomena and novel superconductors with a high transition temperature. PMID:25502774

Temperature- and field-dependent characterization of a conductor on round core cable

NASA Astrophysics Data System (ADS)

Barth, C.; van der Laan, D. C.; Bagrets, N.; Bayer, C. M.; Weiss, K.-P.; Lange, C.

2015-06-01

The conductor on round core (CORC) cable is one of the major high temperature superconductor cable concepts combining scalability, flexibility, mechanical strength, ease of fabrication and high current density; making it a possible candidate as conductor for large, high field magnets. To simulate the boundary conditions of such magnets as well as the temperature dependence of CORC cables a 1.16 m long sample consisting of 15, 4 mm wide SuperPower REBCO tapes was characterized using the ‘FBI’ (force—field—current) superconductor test facility of the Institute for Technical Physics of the Karlsruhe Institute of Technology. In a five step investigation, the CORC cable’s performance was determined at different transverse mechanical loads, magnetic background fields and temperatures as well as its response to swift current changes. In the first step, the sample’s 77 K, self-field current was measured in a liquid nitrogen bath. In the second step, the temperature dependence was measured at self-field condition and compared with extrapolated single tape data. In the third step, the magnetic background field was repeatedly cycled while measuring the current carrying capabilities to determine the impact of transverse Lorentz forces on the CORC cable sample’s performance. In the fourth step, the sample’s current carrying capabilities were measured at different background fields (2-12 T) and surface temperatures (4.2-51.5 K). Through finite element method simulations, the surface temperatures are converted into average sample temperatures and the gained field- and temperature dependence is compared with extrapolated single tape data. In the fifth step, the response of the CORC cable sample to rapid current changes (8.3 kA s-1) was observed with a fast data acquisition system. During these tests, the sample performance remains constant, no degradation is observed. The sample’s measured current carrying capabilities correlate to those of single tapes assuming field- and temperature dependence as published by the manufacturer.

Thermodynamics of Meissner effect and flux pinning behavior in the bulk of single-crystal La 2 - x Sr x CuO 4 ( x = 0.09 )

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

Dhiman, I.; Ziesche, R.; Anand, V. K.

We have studied the magnetic flux pinning behavior and Meissner effect for the high-more » $$T_{\\rm c}$$ single crystal La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ ($x$ = 0.09) superconductor using the polarized neutron imaging method with varying magnetic field and temperature. In the Meissner state expulsion of magnetic field (switched on during the measurements) is visualized, and the signatures of mixed state with increasing temperature are observed. While, for flux pinning behavior between 5 K $$\\leq$$ $T$ $$\\leq$$ 15 K and $$H_{\\rm ext}$$ = 63.5 mT (switched off during the measurements), the evolution of fringe pattern for both 0$$^{o}$$ and 90$$^{o}$$ sample orientation indicates magnetic flux pinning inside the bulk of the sample. At 25 K $$\\leq$$ $T$ $$\\leq$$ 32 K, a continuous decrease of inhomogeneously distribution pinned magnetic flux is observed, with the sample reaching a normal conducting state at $$T_{\\rm c}$$ ($$\\approx$$ 32 K). The flux pinning behavior is also explored as a function of $$H_{\\rm ext}$$, at $T$ = 5 K. As expected, with increasing $$H_{\\rm ext}$$ an increase in fringe density is observed, indicating an increase in magnetic flux pinning in the bulk of the sample. Therefore, in the present work for the first time we report bulk visualization of Meissner effect and flux pinning behavior in high-$$T_{\\rm c}$$ La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ ($x$ = 0.09) superconductor. This study clearly demonstrates the potential of real space polarized neutron imaging technique for the visualization of the superconducting mixed state, particularly in the field of high-$$T_{\\rm c}$$ superconductors.« less

Status of high temperature superconductor development for accelerator magnets

NASA Technical Reports Server (NTRS)

Hirabayashi, H.

1995-01-01

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

Polar Kerr Effect from Time-Reversal Symmetry Breaking in the Heavy-Fermion Superconductor PrOs4Sb12

NASA Astrophysics Data System (ADS)

Levenson-Falk, E. M.; Schemm, E. R.; Aoki, Y.; Maple, M. B.; Kapitulnik, A.

2018-05-01

We present polar Kerr effect measurements of the filled skutterudite superconductor PrOs4 Sb12 . Simultaneous ac susceptibility measurements allow us to observe the superconducting transition under the influence of heating from the optical beam. A nonzero Kerr angle θK develops below the superconducting transition, saturating at ˜300 nrad at low temperatures. This result is repeated across several measurements of multiple samples. By extrapolating the measured θK(T ) to zero optical power, we are able to show that the Kerr angle onset temperature in one set of measurements is consistent with the transition to the B phase at TC 2. We discuss the possible explanations for this result and its impact on the understanding of multiphase and inhomogeneous superconductivity in PrOs4 Sb12 .

Superconductor-normal-superconductor with distributed Sharvin point contacts

DOEpatents

Holcomb, Matthew J.; Little, William A.

1994-01-01

A non-linear superconducting junction device comprising a layer of high transient temperature superconducting material which is superconducting at an operating temperature, a layer of metal in contact with the layer of high temperature superconducting material and which remains non-superconducting at the operating temperature, and a metal material which is superconducting at the operating temperature and which forms distributed Sharvin point contacts with the metal layer.

Pair-breaking mechanisms in superconductor—normal-metal—superconductor junctions

NASA Astrophysics Data System (ADS)

Yang, H. C.; Finnemore, D. K.

1984-08-01

The critical current density Jc has been measured for superconductor—normal-metal—superconductor (S-N-S) junctions over a wide range of temperature and composition in order to determine the depairing effects of magnetic impurities. Junctions, which are in a sandwich geometry with the N layer typically 600 nm thick, show well-defined diffraction patterns indicating that the junctions are of high quality. Below 4.2 K, the temperature dependence of Jc is found to follow a modified bridge theory based on the work of Makeev et al.

Ambient-pressure organic superconductor

DOEpatents

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

1986-01-01

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

Performance of ceramic superconductors in magnetic bearings

NASA Technical Reports Server (NTRS)

Kirtley, James L., Jr.; Downer, James R.

1993-01-01

Magnetic bearings are large-scale applications of magnet technology, quite similar in certain ways to synchronous machinery. They require substantial flux density over relatively large volumes of space. Large flux density is required to have satisfactory force density. Satisfactory dynamic response requires that magnetic circuit permeances not be too large, implying large air gaps. Superconductors, which offer large magnetomotive forces and high flux density in low permeance circuits, appear to be desirable in these situations. Flux densities substantially in excess of those possible with iron can be produced, and no ferromagnetic material is required. Thus the inductance of active coils can be made low, indicating good dynamic response of the bearing system. The principal difficulty in using superconductors is, of course, the deep cryogenic temperatures at which they must operate. Because of the difficulties in working with liquid helium, the possibility of superconductors which can be operated in liquid nitrogen is thought to extend the number and range of applications of superconductivity. Critical temperatures of about 98 degrees Kelvin were demonstrated in a class of materials which are, in fact, ceramics. Quite a bit of public attention was attracted to these new materials. There is a difficulty with the ceramic superconducting materials which were developed to date. Current densities sufficient for use in large-scale applications have not been demonstrated. In order to be useful, superconductors must be capable of carrying substantial currents in the presence of large magnetic fields. The possible use of ceramic superconductors in magnetic bearings is investigated and discussed and requirements that must be achieved by superconductors operating at liquid nitrogen temperatures to make their use comparable with niobium-titanium superconductors operating at liquid helium temperatures are identified.

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

PubMed

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

2015-02-25

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

Bearing design for flywheel energy storage using high-TC superconductors

DOEpatents

Hull, John R.; Mulcahy, Thomas M.

2000-01-01

A high temperature superconductor material bearing system (38) This system (38) includes a rotor (50) having a ring permanent magnet (60), a plurality of permanent magnets (16, 20 and 70) for interacting to generate levitation forces for the system (38). This group of magnets are a push/pull bearing (75). A high temperature superconductor structure (30) interacts with the ting permanent magnet (60) to provide stabilizing forces for the system (38).

Experimental Setup for the Investigation of Superconducting Persistent Current

DTIC Science & Technology

2015-09-01

This documentation is intended to support future investigations of coated conductors in either tape or wire form or for bulk superconductors in an...Introduction Second-generation, high-temperature, coated superconductors , such as yttrium barium copper oxide (Y1Ba2Cu3O7-δ, or REBCO, or RE123), are...source applications.8 In order to push the high-temperature superconductors to a more mature degree, new knowledge and deeper understanding of the

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.

Theory of quantum metal to superconductor transitions in highly conducting systems

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

Spivak, B.

2010-04-06

We derive the theory of the quantum (zero temperature) superconductor to metal transition in disordered materials when the resistance of the normal metal near criticality is small compared to the quantum of resistivity. This can occur most readily in situations in which 'Anderson's theorem' does not apply. We explicitly study the transition in superconductor-metal composites, in an swave superconducting film in the presence of a magnetic field, and in a low temperature disordered d-wave superconductor. Near the point of the transition, the distribution of the superconducting order parameter is highly inhomogeneous. To describe this situation we employ a procedure whichmore » is similar to that introduced by Mott for description of the temperature dependence of the variable range hopping conduction. As the system approaches the point of the transition from the metal to the superconductor, the conductivity of the system diverges, and the Wiedemann-Franz law is violated. In the case of d-wave (or other exotic) superconductors we predict the existence of (at least) two sequential transitions as a function of increasing disorder: a d-wave to s-wave, and then an s-wave to metal transition.« less

Discriminator Stabilized Superconductor/Ferroelectric Thin Film Local Oscillator

NASA Technical Reports Server (NTRS)

Romanofsky, Robert R. (Inventor); Miranda, Felix A. (Inventor)

2000-01-01

A tunable local oscillator with a tunable circuit that includes a resonator and a transistor as an active element for oscillation. Tuning of the circuit is achieved with an externally applied dc bias across coupled lines on the resonator. Preferably the resonator is a high temperature superconductor microstrip ring resonator with integral coupled lines formed over a thin film ferroelectric material. A directional coupler samples the output of the oscillator which is fed into a diplexer for determining whether the oscillator is performing at a desired frequency. The high-pass and lowpass outputs of the diplexer are connected to diodes respectively for inputting the sampled signals into a differential operational amplifier. The amplifier compares the sampled signals and emits an output signal if there is a difference between the resonant and crossover frequencies. Based on the sampled signal, a bias supplied to the ring resonator is either increased or decreased for raising or lowering the resonant frequency by decreasing or increasing, respectively, the dielectric constant of the ferroelectric.

Dynamic stress effects in technical superconductors and the ''training'' problem of superconducting magnets

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

Pasztor, G.; Schmidt, C.

The behavior of NbTi superconductors under dynamic mechanical stress was investigated. A training effect was found in short-sample tests when the conductor was strained in a magnetic field and with a transport current applied. Possible mechanisms are discussed which were proposed to explain training in short samples and in magnets. A stress-induced microplastic as well as an incomplete pseudoelastic behavior of NbTi was detected by monitoring acoustic emission. The experiments support the hypothesis that microplastic or shape memory effects in NbTi involving dislocation processes are responsible for training. The minimum energy needed to induce a normal transition in short-sample testsmore » is calculated with a computer program, which gives the exact solution of the heat equation. A prestrain treatment of the conductor at room temperature is shown to be a simple method of reducing training of short samples and of magnets. This is a direct proof that the same mechanisms are involved in both cases.« less

Method and apparatus for measuring gravitational acceleration utilizing a high temperature superconducting bearing

DOEpatents

Hull, John R.

2000-01-01

Gravitational acceleration is measured in all spatial dimensions with improved sensitivity by utilizing a high temperature superconducting (HTS) gravimeter. The HTS gravimeter is comprised of a permanent magnet suspended in a spaced relationship from a high temperature superconductor, and a cantilever having a mass at its free end is connected to the permanent magnet at its fixed end. The permanent magnet and superconductor combine to form a bearing platform with extremely low frictional losses, and the rotational displacement of the mass is measured to determine gravitational acceleration. Employing a high temperature superconductor component has the significant advantage of having an operating temperature at or below 77K, whereby cooling may be accomplished with liquid nitrogen.

Ground state of underdoped cuprates in vicinity of superconductor-to-insulator transition

DOE PAGES

Wu, Jie; Bollinger, Anthony T.; Sun, Yujie; ...

2016-08-15

When an insulating underdoped cuprate is doped beyond a critical concentration (x c), high-temperature superconductivity emerges. We have synthesized a series of La 2–xSr xCuO 4 (LSCO) samples using the combinatorial spread technique that allows us to traverse the superconductor-to-insulator transition (SIT) in extremely fine doping steps, Δx≈0.00008. We have measured the Hall resistivity (ρ H) as a function of temperature down to 300 mK in magnetic fields up to 9 T. At very low temperatures, ρ H shows an erratic behavior, jumps and fluctuations exceeding 100%, hysteresis, and memory effects, indicating that the insulating ground state is a charge-clustermore » glass (CCG). Furthermore, based on the phase diagram depicted in our experiment, we propose a unified picture to account for the anomalous electric transport in the vicinity of the SIT, suggesting that the CCG is in fact a disordered and glassy version of the charge density wave.« less

Magnetotransport Properties in High-Quality Ultrathin Two-Dimensional Superconducting Mo2C Crystals.

PubMed

Wang, Libin; Xu, Chuan; Liu, Zhibo; Chen, Long; Ma, Xiuliang; Cheng, Hui-Ming; Ren, Wencai; Kang, Ning

2016-04-26

Ultrathin transition metal carbides are a class of developing two-dimensional (2D) materials with superconductivity and show great potentials for electrical energy storage and other applications. Here, we report low-temperature magnetotransport measurements on high-quality ultrathin 2D superconducting α-Mo2C crystals synthesized by a chemical vapor deposition method. The magnetoresistance curves exhibit reproducible oscillations at low magnetic fields for temperature far below the superconducting transition temperature of the crystals. We interpret the oscillatory magnetoresistance as a consequence of screening currents circling around the boundary of triangle-shaped terraces found on the surface of ultrathin Mo2C crystals. As the sample thickness decreases, the Mo2C crystals exhibit negative magnetoresistance deep in the superconducting transition regime, which reveals strong phase fluctuations of the superconducting order parameters associated with the superconductor-insulator transition. Our results demonstrate that the ultrathin superconducting Mo2C crystals provide an interesting system for studying rich transport phenomena in a 2D crystalline superconductor with enhanced quantum fluctuations.

High temperature superconductor current leads

DOEpatents

Hull, John R.; Poeppel, Roger B.

1995-01-01

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

High temperature superconductor current leads

DOEpatents

Hull, J.R.; Poeppel, R.B.

1995-06-20

An electrical lead is disclosed having one end for connection to an apparatus in a cryogenic environment and the other end for connection to an apparatus outside the cryogenic environment. The electrical lead includes a high temperature superconductor wire and an electrically conductive material distributed therein, where the conductive material is present at the one end of the lead at a concentration in the range of from 0 to about 3% by volume, and at the other end of the lead at a concentration of less than about 20% by volume. Various embodiments are shown for groups of high temperature superconductor wires and sheaths. 9 figs.

Levitation Experiment Using a High-Temperature Superconductor Coil for a Plasma Confinement Device

NASA Astrophysics Data System (ADS)

Morikawa, Junji; Ozawa, Daisaku; Ogawa, Yuichi; Yanagi, Nagato; Hamaguchi, Sinji; Mito, Toshiyuki

2001-10-01

Levitation experiments using a high-temperature superconductor coil have been carried out. A coil with a minor radius of 42 mm was fabricated with a Bi-2223 tape conductor, and immersed in the liquid nitrogen. The coil current was induced by the field-cooling method up to the critical current value. The current decay of the coil can be accounted for by the flux flow resistance and the normal resistance at the lap joint. The high-temperature superconductor coil can be levitated for 4 min or more within an accuracy of 25-30 μm.

Phase fluctuations in a strongly disordered s-wave NbN superconductor close to the metal-insulator transition.

PubMed

Mondal, Mintu; Kamlapure, Anand; Chand, Madhavi; Saraswat, Garima; Kumar, Sanjeev; Jesudasan, John; Benfatto, L; Tripathi, Vikram; Raychaudhuri, Pratap

2011-01-28

We explore the role of phase fluctuations in a three-dimensional s-wave superconductor, NbN, as we approach the critical disorder for destruction of the superconducting state. Close to critical disorder, we observe a finite gap in the electronic spectrum which persists at temperatures well above T(c). The superfluid density is strongly suppressed at low temperatures and evolves towards a linear-T variation at higher temperatures. These observations provide strong evidence that phase fluctuations play a central role in the formation of a pseudogap state in a disordered s-wave superconductor.

High current densities above 100 K in the high-temperature superconductor HgBa2CaCu2O6+δ

NASA Astrophysics Data System (ADS)

Krusin-Elbaum, L.; Tsuei, C. C.; Gupta, A.

1995-02-01

THE recent discovery1,2 of a family of mercury-based copper oxide superconductors having transition temperatures1-3 above 130 K is of considerable technological interest. But the viability of high-temperature superconductors for many applications will ultimately depend on the size of the current density, Jc, that they are able to support, not only at high temperatures, but also in high magnetic fields. For the cuprate superconductors, and in particular for Hg-based materials, the combination of high transition temperature1-3 and large mass anisotropy implies that the transport properties will be intrinsically limited by large thermal fluctuations and short superconducting coherence lengths4. Here we report that high-quality c-axis-oriented epitaxial films of the compound HgBa2CaCu6O6+δ (Hg-1212; ref. 5) can support large in-plane current densities at temperatures higher than has been achieved for other superconductors. In low magnetic fields oriented normal to the film surface, we find Jc>~107 A cm-2 at 5 K and Jc~ 105 A cm-2 at 110 K, at least an order of magnitude larger than for Bi- or Tl-based films6-11. For in-plane magnetic fields, the critical current (~108 A cm-2) is close to the theoretical limit even at high fields, indicative of strong intrinsic pinning in this compound.

Relation between resistivity and temperature in the presence of two magnetic flux pinning mechanisms

NASA Astrophysics Data System (ADS)

Hosseinzadeh, Mohammad; Ghorbani, Shaban Reza; Arabi, Hadi

2018-05-01

Moving of vortices in type II superconductors leads to energy dissipation, and therefore pinning of them is a significant problem. Determination of pinning potential and pinning mechanism from experimental data of resistivity is an attractive issue in the phenomenological study of superconductors. A new formalism is suggested to determination of two the δTc and δℓ pinning mechanisms from the resistivity as a function of temperature in type II superconductors.

Non-resonant microwave absorption in high-T c thin films

NASA Astrophysics Data System (ADS)

Durny, R.; Dulcic, A.; Crepeau, R. H.; Freed, J. H.; Kus, P.

1990-11-01

Magnetic-field-dependent non-resonant microwave absorption in thin film samples of various high- Tc superconductors is reported. Complex types of signals were observed as the temperature was lowered from Tc to ≈ 10 K. Possible correlation between the thin film quality and the occurrence of the signals is suggested.

Proceedings, phenomenology and applications of high temperature superconductors

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

Bedell, K.S.

1991-01-01

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

Proceedings, phenomenology and applications of high temperature superconductors

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

Bedell, K.S.

1991-12-31

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

the Characteristic Phase Transitions of Co-doped BaFe2 As2 Synthesized via Flux Growth

NASA Astrophysics Data System (ADS)

Shea, C. H.; Roncaioli, C.; Eckberg, C.; Drye, T.; Sulliavan, M. C.; Paglione, J.

2015-03-01

Since the discovery of a new family of type II superconductors in 2008, the iron pnictides, researches have had suspicions that they might bear similar electronic properties to the well-known (but not easily understood) oxide superconductors. For this reason studies on this family of compounds has been of great interest to the materials science community. Our efforts have been aimed at single crystal growth and measurement of a particular member of this family, BaFe2As2. While this material is not superconducting at standard pressure, the partial substitution of cobalt on the iron site has been shown to suppresses an anti-ferromagnetic phase transition occurring at lower temperatures allowing for the appearance of a superconducting phase. Transport and low field magnetization measurements taken on our samples show clean transitions, indicating Tc's of up to 24 K in optimally doped samples. We will discuss the growth methods and temperature dependent phase transitions of this material at different cobalt concentrations. This work was supported by NSF Grant DMR-1305637.

Epoxy-encapsulated ceramic superconductor microelectrodes

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

Gollmor, R.O.; McDevitt, J.T.; Murray, R.W.

1989-12-01

A procedure is outlined for fabricating well-behaved microelectrodes from ceramic pellets of YBa{sub 2}CU{sub 3}O{sub 7} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} which involves systematic polishing of an epoxy-encapsulated superconductror chip, under Et{sub 4}NCIO{sub 4}/acetonitrile solution, to a potentiometric end point. Voltammetry of the resulting microelectrodes in acetronitrile is illustrated and compared to that arising from alternative superconductor electrode geometries. The microelectrodes have active electrode surface areas ranging from 2 {times} 10 {sup {minus} sup 6} to 3 {times} 10 {sup {minus} sup 4}cm{sup 2}, as characterized electrochemically and microscopically. The results discussed herein are steps toward developing the methodologymore » necessary to study the electrochemical response of high temperature superconductor phases at temperatures below theirtheir superconductor critical temperature.« less

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

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

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.

Effect of magnetic field on the flux pinning mechanisms in Al and SiC co-doped MgB2 superconductor

NASA Astrophysics Data System (ADS)

Kia, N. S.; Ghorbani, S. R.; Arabi, H.; Hossain, M. S. A.

2018-07-01

MgB2 superconductor samples co-doped with 0.02 wt. Al2O3 and 0-0.05 wt. SiC were studied by magnetization - magnetic field (M-H) loop measurements at different temperatures. The critical current density has been calculated by the Bean model, and the irreversibility field, Hirr, has been obtained by the Kramer method. The pinning mechanism of the co-doped sample with 2% Al and 5% SiC was investigated in particular due to its having the highest Hirr. The normalized volume pinning force f = F/Fmax as a function of reduced magnetic field h = H/Hirr has been obtained, and the pinning mechanism was studied by the Dew-Houghes model. It was found that the normal point pinning (NPP), the normal surface pinning (NSP), and the normal volume pinning (NVP) mechanisms play the main roles. The magnetic field and temperature dependence of contributions of the NPP, NSP, and NVP pinning mechanisms were obtained. The results show that the contributions of the pinning mechanisms depend on the temperature and magnetic field. From the temperature dependence of the critical current density within the collective pinning theory, it was found that both the δl pinning due to spatial fluctuations of the charge-carrier mean free path and the δTc pinning due to randomly distributed spatial variations in the transition temperature coexist at zero magnetic field in co-doped samples. Yet, the charge-carrier mean-free-path fluctuation pinning (δl) is the only important pinning mechanism at non-zero magnetic fields.

Second-Generation High-Temperature Superconductor Wires for the Electric Power Grid

NASA Astrophysics Data System (ADS)

Malozemoff, A. P.

2012-08-01

Superconductors offer major advantages for the electric power grid, including high current and power capacity, high efficiency arising from the lossless current flow, and a unique current-limiting functionality arising from a superconductor-to-resistive transition. These advantages can be brought to bear on equipment such as underground power cables, fault current limiters, rotating machinery, transformers, and energy storage. The first round of significant commercial-scale superconductor power-equipment demonstrations, carried out during the past decade, relied on a first-generation high-temperature superconductor (HTS) wire. However, during the past few years, with the recent commercial availability of high-performance second-generation HTS wires, power-equipment demonstrations have increasingly been carried out with these new wires, which bring important advantages. The foundation is being laid for commercial expansion of this important technology into the power grid.

Percolation effect in thick film superconductors

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

Sali, R.; Harsanyi, G.

1994-12-31

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

Percolation effect in thick film superconductors: Using a Bi(Pb)SrCaCuO based paste to prepare a superconducting planar transformer

NASA Technical Reports Server (NTRS)

Sali, Robert; Harsanyi, Gabor

1995-01-01

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

Surface and electronic structure of Bi-Ca-Sr-Cu-O superconductors studied by LEED, UPS and XPS

NASA Astrophysics Data System (ADS)

Shen, Z.-X.; Lindberg, P. A. P.; Wells, B. O.; Lindau, I.; Spicer, W. E.; Mitzi, D. B.; Eom, C. B.; Kapitulnik, A.; Geballe, T. H.; Soukiassian, P.

1989-02-01

Single crystal and polycrystalline samples of Bi2CaSr2Cu2O8 have been studied by various surface sensitive techniques, including low energy electron diffraction (LEED), ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS). The surface structure of the single crystals was characterized by LEED to be consistent with that of the bulk structure. Our data suggest that Bi2CaSr2Cu2O8 single crystals are very stable in the ultrahigh vacuu. No change of XPS spectra with temperature was observed. We have also studied the electronic structure of Bi2Sr2CuO6, which has a lower superconducting transition temperature Tc. Comparing the electronic structure of the two Bi-Ca-Sr-Cu-O superconductors, an important difference in the density of states near EF was observed which seems to be related to the difference in Tc.

Polar Kerr Effect from Time-Reversal Symmetry Breaking in the Heavy-Fermion Superconductor PrOs 4 Sb 12

DOE PAGES

Levenson-Falk, Eli M.; Schemm, E. R.; Aoki, Y.; ...

2018-05-04

Here, we present polar Kerr effect measurements of the filled skutterudite superconductor PrOs 4Sb 12. Simultaneous ac susceptibility measurements allow us to observe the superconducting transition under the influence of heating from the optical beam. A nonzero Kerr angle θ K develops below the superconducting transition, saturating at ~300 nrad at low temperatures. This result is repeated across several measurements of multiple samples. By extrapolating the measured θ K(T) to zero optical power, we are able to show that the Kerr angle onset temperature in one set of measurements is consistent with the transition to the B phase at Tmore » C2. We discuss the possible explanations for this result and its impact on the understanding of multiphase and inhomogeneous superconductivity in PrOs 4Sb 12.« less

Polar Kerr Effect from Time-Reversal Symmetry Breaking in the Heavy-Fermion Superconductor PrOs 4 Sb 12

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

Levenson-Falk, Eli M.; Schemm, E. R.; Aoki, Y.

Here, we present polar Kerr effect measurements of the filled skutterudite superconductor PrOs 4Sb 12. Simultaneous ac susceptibility measurements allow us to observe the superconducting transition under the influence of heating from the optical beam. A nonzero Kerr angle θ K develops below the superconducting transition, saturating at ~300 nrad at low temperatures. This result is repeated across several measurements of multiple samples. By extrapolating the measured θ K(T) to zero optical power, we are able to show that the Kerr angle onset temperature in one set of measurements is consistent with the transition to the B phase at Tmore » C2. We discuss the possible explanations for this result and its impact on the understanding of multiphase and inhomogeneous superconductivity in PrOs 4Sb 12.« less

Magnetically leviated superconducting bearing

DOEpatents

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

1993-01-01

A magnetically levitated superconducting bearing includes a magnet (2) mounted on a shaft (12) that is rotatable around an axis of rotation and a Type II superconductor (6) supported on a stator (14) in proximity to the magnet (2). The superconductor (6) is positioned so that when it is cooled to its superconducting state in the presence of a magnetic field, it interacts with the magnet (2) to produce an attractive force that levitates the magnet (2) and supports a load on the shaft (12). The interaction between the superconductor (6) and magnet(2) also produces surface screening currents (8) that generate a repulsive force perpendicular to the load. The bearing also has means for maintaining the superconductor at a temperature below its critical temperature (16, 18). The bearing could also be constructed so the magnet (2) is supported on the stator (14) and the superconductor (6) is mounted on the shaft (12). The bearing can be operated by cooling the superconductor (6) to its superconducting state in the presence of a magnetic field.

SCDFT Study of High Tc Nitride Superconductors

NASA Astrophysics Data System (ADS)

Arita, R.

Based on the density functional theory for superconductors (SCDFT), we study the pairing mechanism of the layered nitride superconductors, β-LixMNCl (M=Zr, Hf). Recently, it has been shown that SCDFT reproduces experimental superconducting transition temperatures (Tc) of conventional superconductors very accurately. Here we use SCDFT as a "litmus paper" to determine whether the system is a conventional or unconventional superconductor. We show that Tc estimated by SCDFT is less than half of the experimental Tc and its doping dependence is opposite to that observed in the experiments. The present result suggests that β- LixMNCl is not a Migdal-Eliashberg type superconductor.

Method and composition for improving flux pinning and critical current in superconductors

DOEpatents

Morris, Donald E.

1995-01-01

Superconducting materials and methods of forming superconducting materials are disclosed. Highly oxidized superconductors are heated at a relatively high temperature so as to release oxygen, which migrates out of the material, and form a non-superconducting phase which does not diffuse out of grains of the material. The material is then reoxidized at a lower temperature, leaving the non-superconducting inclusions inside a superconducting phase. The non-superconducting inclusions act as pinning centers in the superconductor, increasing the critical current thereof.

Method for preparation of textured YBa.sub.2 Cu.sub.3 O.sub.x superconductor

DOEpatents

Selvamanickam, Venkat; Goyal, Amit; Kroeger, Donald M.

1998-01-01

The present invention relate to textured YBa.sub.2 Cu.sub.3 O.sub.x (Y-123) superconductors and a process of preparing them by directional recrystallization of compacts fabricated from quenched YBCO powders at temperatures about 100.degree. C. below the peritectic temperature to provide a superconductor where more than 75% of the YBa.sub.2 Cu.sub.3 O.sub.x phase is obtained without any Y.sub.2 BaCuO.sub.5 .

Method and composition for improving flux pinning and critical current in superconductors

DOEpatents

Morris, D.E.

1995-07-04

Superconducting materials and methods of forming superconducting materials are disclosed. Highly oxidized superconductors are heated at a relatively high temperature so as to release oxygen, which migrates out of the material, and form a non-superconducting phase which does not diffuse out of grains of the material. The material is then reoxidized at a lower temperature, leaving the non-superconducting inclusions inside a superconducting phase. The non-superconducting inclusions act as pinning centers in the superconductor, increasing the critical current thereof. 14 figs.

Filtering properties of Thue-Morse nano-photonic crystals containing high-temperature superconductor

NASA Astrophysics Data System (ADS)

Talebzadeh, Robabeh; Bavaghar, Mehrdad

2018-05-01

In this paper, we introduced new design of quasi-periodic layered structures by choosing order two of ternary Thue-Morse structure. We considered Superconductor-dielectric photonic crystal with mirror symmetric as (ABSSAB)N(BASSBA)N composed of two kinds of nano-scale dielectric layers (A and B) and high-temperature superconductor layers where N is the number of period. This structure is assumed to be the free space. By using the transfer matrix method and the two fluid model, we theoretically study the transmission spectrum of ternary Thue-Morse superconducting photonic crystals with mirror symmetry and introduce this structure as a narrow optical filter. We showed that transmission peak so-called defect mode appears itself inside the transmission spectrum of suggested structure as same as defective layered structure. Also, we analyzed the influence of various related parameters such as the operating temperature of superconductor layer on position of defect mode. The redshift of defect mode with increasing the operating temperature was observed.

The effect of resolidification on preform optimized infiltration growth processed (Y, Nd, Sm, Gd)BCO, multi-grain bulk superconductor

NASA Astrophysics Data System (ADS)

Pavan Kumar Naik, S.; Seshu Bai, V.

2017-01-01

Controlling the microstructure of superconductors by incorporating the flux pinning centers and reducing the macro-defects to improve high field performance is the topic of recent research. In continuation, the preform optimized infiltration growth (POIG) processed YBa2Cu3O7-δ (YBCO) system, Y-site substituted with three mixed RE (Nd, Sm, Gd) elements is investigated. 20 wt.% of (Nd, Sm, Gd)2BaCuO5 were mixed with Y2BaCuO5 and POIG processed in reduced oxygen atmosphere to obtain YNSG superconductor. No seed is employed for crystal growth; hence the processed samples are multi-grained. Microstructural and compositional investigations on YNSG revealed the presence of different phases in the matrix as well as in precipitates which are of the order of submicron to 4 μm. A large fraction of macro-defects (∼6% of porosity) was observed in the YNSG sample. For reducing the unwanted macro-defects and refine the non-superconducting precipitates, processed YNSG sample is pressed and resolidified (by infiltrating the liquid phases once again) in an argon atmosphere and the structural, microstructural, elemental and superconducting properties are compared with YNSG and undoped samples. Due to spatial scatter in superconducting critical temperatures, caused by the distribution of different REBCO unit cells in YBCO, superconducting transition curve is sharp in YNSG, whereas the resolidified sample showed the broad transition due to solidified liquid phases.

Evidence for Electromagnetic Granularity in the Polycrystalline Iron-Based Superconductor LaO(0.89)F(0.11)FeAs

DTIC Science & Technology

2008-01-01

oriented grain-boundaries. In this work we show considerable evidence for such weak-coupling by study of the dependence of magnetization in bulk and...powdered samples. Bulk sample magnetization curves show very little hysteresis while remanent magnetization shows almost no sample size dependence...K Fig. 2 (Color online) Magnetization hysteresis loops at 5 and 20 K for the bulk LaO0.89F0.11FeAs. Inset shows the temperature dependence of

Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films.

PubMed

Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X J

2016-02-08

The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.

Magnetotransport study of topological superconductor Cu0.10Bi2Se3 single crystal

NASA Astrophysics Data System (ADS)

Li, M. T.; Fang, Y. F.; Zhang, J. C.; Yi, H. M.; Zhou, X. J.; Lin, C. T.

2018-03-01

We report a magnetotransport study of vortex-pinning in Cu0.10Bi2Se3 single crystal. The sample is demonstrated to be in clean limit and absent of Pauli spin-limiting effect. Interestingly, the resistivity versus magnetic field shows an anomalously pronounced increase when approaching the superconducting-normal state boundary for both {{B}app}\\parallel ab and {{B}app}\\parallel c configurations. We have investigated the flux-flowing behavior under various magnetic fields and temperatures, enabling us to establish its anisotropic vortex phase diagram. Our results suggest the Cu0.10Bi2Se3 can be served as one unique material for exploring exotic surface vortex states in topological superconductors.

High temperature superconductor dc SQUID micro-susceptometer for room temperature objects

NASA Astrophysics Data System (ADS)

Faley, M. I.; Pratt, K.; Reineman, R.; Schurig, D.; Gott, S.; Atwood, C. G.; Sarwinski, R. E.; Paulson, D. N.; Starr, T. N.; Fagaly, R. L.

2004-05-01

We have developed a scanning magnetic microscope (SMM) with 25 µm resolution in spatial position for the magnetic features of room temperature objects. The microscope consists of a high-temperature superconductor (HTS) dc SQUID sensor, suspended in vacuum with a self-adjusting standoff, close spaced liquid nitrogen Dewar, X-Y scanning stage and a computer control system. The HTS SQUIDs were optimized for better spatial and field resolutions for operation at liquid nitrogen temperature. Measured inside a magnetic shield, the 10 pT Hz-1/2 typical noise of the SQUIDs is white down to frequencies of about 10 Hz, increasing up to about 20 pT Hz-1/2 at 1 Hz. The microscope is mounted on actively damped platforms, which negate vibrations from the environment as well as damping internal stepper motor noises. A high-resolution video telescope and a 1 µm precision z-axis positioning system allow a close positioning of the sample under the sensor. The ability of the sensors to operate in unshielded environmental conditions with magnetic fields up to about 15 G allowed us to perform 2D mapping of the local ac and dc susceptibility of the objects.

Thermoelectric power of high-pressure synthesized CuBa{sub 2}Ca{sub 3}Cu{sub 4}O{sub 11{minus}{delta}}

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

Liu, C.; Jin, C.; Yamauchi, H.

We report measurements of thermoelectric power (TEP) for high-pressure synthesized CuBa{sub 2}Ca{sub 3}Cu{sub 4}O{sub 11{minus}{delta}} superconductors. The magnitude of TEP for the sample with {ital T}{sub {ital c},zero}=115.9 K is very small and shows a sign crossover at {approximately}160 K. The TEP shows a peak behavior and displays an approximately linear temperature dependence with a negative slope {minus}0.033 {mu}V/K{sup 2} for 120{le}{ital T}{le}240 K. These features resemble those for other known high-{ital T}{sub {ital c}} cuprate superconductors, in particular {ital S}{sub {ital a}} in the {ital a} direction for an untwinned YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} single crystal and polycrystalline Tl-2201more » samples. A brief discussion is given on the TEP behavior in comparison with CuBa{sub 2}YCu{sub 2}O{sub 7{minus}{delta}} cuprate superconductors by considering their similar structure of building blocks and type of charge reservoir. {copyright} {ital 1996 The American Physical Society.}« less

Development of YBCO Superconductor for Electric Systems: Cooperative Research and Development Final Report, CRADA Number CRD-04-150

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

Bhattacharya, R.

2013-03-01

The proposed project will be collaborative in exploration of high temperature superconductor oxide films between SuperPower, Inc. and the National Renewable Energy Laboratory. This CRADA will attempt to develop YBCO based high temperature oxide technology.

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.

Finding new superconductors: the spin-fluctuation gateway to high Tc and possible room temperature superconductivity.

PubMed

Pines, David

2013-10-24

We propose an experiment-based strategy for finding new high transition temperature superconductors that is based on the well-established spin fluctuation magnetic gateway to superconductivity in which the attractive quasiparticle interaction needed for superconductivity comes from their coupling to dynamical spin fluctuations originating in the proximity of the material to an antiferromagnetic state. We show how lessons learned by combining the results of almost three decades of intensive experimental and theoretical study of the cuprates with those found in the decade-long study of a strikingly similar family of unconventional heavy electron superconductors, the 115 materials, can prove helpful in carrying out that search. We conclude that, since Tc in these materials scales approximately with the strength of the interaction, J, between the nearest neighbor local moments in their parent antiferromagnetic state, there may not be a magnetic ceiling that would prevent one from discovering a room temperature superconductor.

Improved ambient-pressure organic superconductor. [Bis(ethylenedithio)TTF-MX/sub 2/

DOEpatents

Williams, J.M.; Wang, Hsien-Hau; Beno, M.A.

1985-05-29

Disclosed is a new class of organic superconductors having the formula (ET)/sub 2/MX/sub 2/ wherein ET represents bis(ethylenedithio)-tetrathiafulvalene, M is a metal such as Au, Ag, In, Tl, Rb, Pd and the like and X is a halide. The superconductor (ET)/sub 2/AuI/sub 2/ exhibits a transition temperature of 5/sup 0/K which is high for organic superconductors.

Construction and performance of a dilution-refrigerator based spectroscopic-imaging scanning tunneling microscope.

PubMed

Singh, U R; Enayat, M; White, S C; Wahl, P

2013-01-01

We report on the set-up and performance of a dilution-refrigerator based spectroscopic imaging scanning tunneling microscope. It operates at temperatures below 10 mK and in magnetic fields up to 14T. The system allows for sample transfer and in situ cleavage. We present first-results demonstrating atomic resolution and the multi-gap structure of the superconducting gap of NbSe(2) at base temperature. To determine the energy resolution of our system we have measured a normal metal/vacuum/superconductor tunneling junction consisting of an aluminum tip on a gold sample. Our system allows for continuous measurements at base temperature on time scales of up to ≈170 h.

High temperature superconductors: A technological revolution

NASA Technical Reports Server (NTRS)

1990-01-01

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

Thermal Expansion of Ferromagnetic Superconductors:. Possible Application to UGe2

NASA Astrophysics Data System (ADS)

Hatayama, Nobukuni; Konno, Rikio

2011-03-01

We investigate the temperature dependence of thermal expansion of the ferromagnetic triplet superconductors and their thermal expansion coefficients below the superconducting transition temperature of a majority spin conduction band. The free energy of the ferromagnetic superconductors derived by Linder et al. is used. The superconducting gaps in the A2 phase of 3He and with a node in UGe2 are considered. By applying Takahashi's method to the free energy, i.e. by taking into account the volume dependence of the free energy explicitly, the temperature dependence of the thermal expansion and the thermal expansion coefficients is studied below the superconducting transition temperature of the majority spin conduction band. We find that we have anomalies of the thermal expansion in the vicinity of the superconducting transition temperatures and that we have divergence of the thermal expansion coefficients are divergent at the superconducting transition temperatures. The Grüneisen's relation between the temperature dependence of the thermal expansion coefficients and the temperature dependence of the specific heat at low temperatures is satisfied.

Thermal Expansion of Ferromagnetic Superconductors:. Possible Application to UGe2

NASA Astrophysics Data System (ADS)

Hatayama, Nobukuni; Konno, Rikio

We investigate the temperature dependence of thermal expansion of the ferromagnetic triplet superconductors and their thermal expansion coefficients below the superconducting transition temperature of a majority spin conduction band. The free energy of the ferromagnetic superconductors derived by Linder et al. is used. The superconducting gaps in the A2 phase of 3He and with a node in UGe2 are considered. By applying Takahashi's method to the free energy, i.e. by taking into account the volume dependence of the free energy explicitly, the temperature dependence of the thermal expansion and the thermal expansion coefficients is studied below the superconducting transition temperature of the majority spin conduction band. We find that we have anomalies of the thermal expansion in the vicinity of the superconducting transition temperatures and that we have divergence of the thermal expansion coefficients are divergent at the superconducting transition temperatures. The Grüneisen's relation between the temperature dependence of the thermal expansion coefficients and the temperature dependence of the specific heat at low temperatures is satisfied.

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

ERIC Educational Resources Information Center

Chakraborty, Shiladitya

2009-01-01

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

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

Nature of the superconductor-insulator transition in disordered superconductors.

PubMed

Dubi, Yonatan; Meir, Yigal; Avishai, Yshai

2007-10-18

The interplay of superconductivity and disorder has intrigued scientists for several decades. Disorder is expected to enhance the electrical resistance of a system, whereas superconductivity is associated with a zero-resistance state. Although superconductivity has been predicted to persist even in the presence of disorder, experiments performed on thin films have demonstrated a transition from a superconducting to an insulating state with increasing disorder or magnetic field. The nature of this transition is still under debate, and the subject has become even more relevant with the realization that high-transition-temperature (high-T(c)) superconductors are intrinsically disordered. Here we present numerical simulations of the superconductor-insulator transition in two-dimensional disordered superconductors, starting from a microscopic description that includes thermal phase fluctuations. We demonstrate explicitly that disorder leads to the formation of islands where the superconducting order is high. For weak disorder, or high electron density, increasing the magnetic field results in the eventual vanishing of the amplitude of the superconducting order parameter, thereby forming an insulating state. On the other hand, at lower electron densities or higher disorder, increasing the magnetic field suppresses the correlations between the phases of the superconducting order parameter in different islands, giving rise to a different type of superconductor-insulator transition. One of the important predictions of this work is that in the regime of high disorder, there are still superconducting islands in the sample, even on the insulating side of the transition. This result, which is consistent with experiments, explains the recently observed huge magneto-resistance peak in disordered thin films and may be relevant to the observation of 'the pseudogap phenomenon' in underdoped high-T(c) superconductors.

Effect of nanosized Co{sub 0.5}Ni{sub 0.5}Fe{sub 2}O{sub 4} on the transport critical current density of Bi{sub 1.6}Pb{sub 0.4}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} superconductor

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

Hafiz, M.; Abd-Shukor, R.

2014-09-03

The effects of nano-sized Co{sub 0.5}Ni{sub 0.5}Fe{sub 2}O{sub 4} addition on the superconducting and transport properties of Bi{sub 1.6}Pb{sub 0.4}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} (Bi-2223) in bulk form has been investigated. Bi-2223 superconductor was fabricated using co-precipitation method and 0.01 – 0.05 wt% of Co{sub 0.5}Ni{sub 0.5}Fe{sub 2}O{sub 4} nanoparticles with average size of 20 nm were added into the samples. The critical temperature (T{sub c}) and critical current density (J{sub c}) of the samples were measured by using the four-point probe method, while the phase formation and microstructure of the samples were examined using x-ray diffraction and SEM respectively.more » It was found that J{sub c} of all samples added with Co{sub 0.5}Ni{sub 0.5}Fe{sub 2}O{sub 4} were higher than non-added sample, with x = 0.01 wt. % sample showing the highest J{sub c}. This study showed that small addition of nano-Co{sub 0.5}Ni{sub 0.5}Fe{sub 2}O{sub 4} can effectively enhance the transport critical current density in Bi-2223 superconductor.« less

The arrival of high temperature superconductors

NASA Astrophysics Data System (ADS)

Chu, Paul C. W.

2011-03-01

The attainment of high temperature superconductivity has been considered a major advancement of modern science. It was the seminal discovery of the first cuprate high temperature superconductor, the Ba-doped La 2 Cu O4 , with a Tc of 35 K in 1986 by Alex Müller and George Bednorz of IBM Zurich Lab, who were awarded the Nobel Prize in 1987, that ushered in the era of cuprate high temperature superconductivity. It was the first liquid nitrogen high temperature superconductor, YBa 2 Cu 3 O7 with a Tc of 93 K discovered in 1987 by Paul C. W. Chu, Maw-Kuen Wu and colleagues in the respective groups at the University of Houston and the University of Alabama at Huntsville that heralded the new era of high temperature superconductivity, drastically changing the psyche of superconductivity research and bringing superconductivity applications a giant step closer to reality. In the ensuing years, many high temperature superconductors have been found, leading to the current record Tc of 134 K which was observed by A. Schilling et al. of ETH in 1993 in HgBa 2 Ca 2 Cu 3 O9 - δ at ambient and later raised to 164 K under 30 GPa by L. Gao et al. In the present talk, I shall briefly recall a few events leading to and during the arrival of high temperature superconductivity. The prospects for future superconductors with higher Tc will also be discussed. Supported in part by U.S. AFOSR, U.S. DoE through ORNL, U.S. AFRL CONTACT through Rice University, the T. L. L. Temple Foundation, the John J. and Rebecca Moores Endowment, and the State of Texas through TCSUH.

High Tc superconductors as thermal radiation shields

NASA Astrophysics Data System (ADS)

Zeller, A. F.

1990-06-01

The feasibility of using high-Tc superconductor films as IR-radiation shields for liquid-helium-temperature dewars is investigated. Calculations show that a Ba-Ca-Sr-Cu-O superconductor with Tc of 110 K, combined with a liquid-nitrogen temperature shield with an emissivity of 0.03 should produce an upper limit to the radiative heat transfer of 15 mW/sq m. The reduction of reflectivity depends on the field level and the extent of field penetration into the superconductor film, whose surface also would provide magnetic shielding for low magnetic fields. Such shields, providing both magnetic and thermal radiation shielding would be useful for spaceborne applications where exposure to the degrading effects of moist air would not be a problem.

Electrical transport properties of sputtered Nd2-xCexCuO4±δ thin films

NASA Astrophysics Data System (ADS)

Guarino, Anita; Leo, Antonio; Avella, Adolfo; Avitabile, Francesco; Martucciello, Nadia; Grimaldi, Gaia; Romano, Alfonso; Pace, Sandro; Romano, Paola; Nigro, Angela

2018-05-01

Thin films of the electron-doped high-temperature superconductor Nd2-xCexCuO4±δ have been deposited by dc sputtering technique on (100) SrTiO3 substrates. A tuning of the oxygen content in the as-grown non-superconducting samples has been achieved by changing the oxygen partial pressure during the growth in the Argon sputtering atmosphere. All samples show the superconducting transition after a suitable two-step thermal treatment in an oxygen-reducing environment. Structural and electrical transport properties on the as-grown as well as on the superconducting samples have been investigated. We find that the structural properties are consistent with a deficiency of the oxygen content with respect to optimally annealed samples, and that the transition to the superconducting phase is always accompanied by an increase of the c-axis lattice parameter. Measurements of the Hall coefficient RH as a function of temperature and in the normal state of our epitaxial films are presented and discussed. RH results negative for all the films regardless of the oxygen content and it decreases with the temperature. In particular, the Hall coefficient is only about 10% lower than the value measured in the as-grown oxygen-deficient phase, in contrast to the results reported in literature. The removal of the excess oxygen in as-grown samples seems not to be the only requirement for triggering the superconducting transition in electron-doped compounds. The microstructural change associated with the increase of the c-axis parameter in our deoxygenated samples could help in understanding the microscopic mechanism underlying the reduction process of n-type superconductors, which is still under debate.

Time-dependent low field microwave absorption in the high temperature superconductors

NASA Astrophysics Data System (ADS)

Owens, F. J.; Iqbal, Z.

1990-11-01

It is observed that the hysteresis in the applied magnetic field position and the intensity at the peak of the low field non-resonant microwave absorption (recorded in an EPR experiment with a modulation amplitude of ∼ 10 G) in the superconducting state of the cuprate superconductors, is time-dependent after the removal of a DC magnetic field sizably greater than the lower critical field. This intrinsic time-dependence, which we attribute to flux creep, is reported here for two copper oxide-based high temperature superconductors.

Nanoscale interplay of strain and doping in a high-temperature superconductor

DOE PAGES

Zeljkovic, Ilija; Gu, Genda; Nieminen, Jouko; ...

2014-11-07

The highest temperature superconductors are electronically inhomogeneous at the nanoscale, suggesting the existence of a local variable which could be harnessed to enhance the superconducting pairing. Here we report the relationship between local doping and local strain in the cuprate superconductor Bi₂Sr₂CaCu₂O₈₊ x. We use scanning tunneling microscopy to discover that the crucial oxygen dopants are periodically distributed, in correlation with local strain. Our picoscale investigation of the intra-unit-cell positions of all oxygen dopants provides essential structural input for a complete microscopic theory.

Effect of processing parameters on the characteristics of high-Tc superconductor YBa2Cu3Oy

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.

1988-01-01

SEM, thermogravimetric analysis, powder X-ray diffraction,and measurements of electrical resistivity and magnetic susceptibility, are presently used to characterize the influence of sintering temperature, sintering and annealing atmospheres, and quench-rate on the properties of the YBa2Cu3Oy superconducting oxide. It is established that annealing in oxygen, together with slow cooling rates, are required for preparation of high-Tc superconductors with sharp transitions; rapid quenching from high temperature does not yield good superconductors, due to low oxygen content.

Maglev system concept using 20-K high-temperature superconductors and hyperconductors

NASA Astrophysics Data System (ADS)

Hull, J. R.; He, Jianliang

A magnetically levitated high-speed ground transportation concept is proposed that uses high-temperature superconductors or hyperconductors, cooled by liquid hydrogen at 20 K, to provide levitation. An on-board hydrogen-powered turbine/generator provides electricity for propulsion by linear induction motors. The liquid hydrogen is used to cool the superconductors and the windings of the generator and motors before combusting in the turbine. The principal advantage of this system is the potential to greatly reduce the cost of the guideway, which is completely passive.

Variation of superconducting transition temperature by proximity effect in NbN/FeN bilayers

NASA Astrophysics Data System (ADS)

Hwang, Tae-Jong; Kim, Dong-Ho

2017-09-01

We report on the proximity effect in superconductor/ferromagnet bilayers made of a new combination of NbN for the superconductor and FeN for the ferromagnet. The bilayers were prepared by reactive magnetron sputtering on a thermally oxidized Si substrate. For a constant NbN layer thickness, the superconducting transition temperatures of the bilayers exhibited a nonmonotonic dependence on the thickness of the FeN layer. The results were interpreted in terms of the proximity effect between the superconductor and ferromagnetic materials.

Thin Film Technology of High-Critical-Temperature Superconducting Electronics.

DTIC Science & Technology

1983-12-05

MD- R136 722 THIN FILM TECHNOLOGY OF HIGH-CRITICAL-TEMPERATURE 1/1 SUPERCONDUCTING ELECTRO..(U) WESTINGHOUSE RESEARCH AND DEVELOPMENT CENTER...critical temperature has been demonstrated. Work will continue in a closed system to eliminate the base superconductor degradation, reduce leakage...a 5% decline in Tc has been demonstrated. Work will continue in a closed system to eliminate the base superconductor degradation, reduce leakage and

Selective Screening of High Temperature Superconductors by Resonant Eddy Current Analysis

DTIC Science & Technology

1990-11-01

observable electronic parameters are both stable and well defined. Further, if the circuit possesses a resonance , then it has well characterized parameters and...Engineers Construction Engineering Research Laboratory - AD-A230 194 Selective Screening of High Temperature Superconductors by Resonant Eddy Current...electrical systems or electronic components from the effects of unwanted electromagnetic energy. With the discovery of High Transition Critical Temperature

Macroscopic phase separation in high-temperature superconductors

PubMed Central

Wen, Hai-Hu

2000-01-01

High-temperature superconductivity is recovered by introducing extra holes to the Cu-O planes, which initially are insulating with antiferromagnetism. In this paper I present data to show the macroscopic electronic phase separation that is caused by either mobile doping or electronic instability in the overdoped region. My results clearly demonstrate that the electronic inhomogeneity is probably a general feature of high-temperature superconductors. PMID:11027323

The effect of B{sub 2}O{sub 3} flux on growth NLBCO superconductor by solid state reaction and wet-mixing methods

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

Suharta, W. G., E-mail: wgsuharta@gmail.com; Wendri, N.; Ratini, N.

The synthesis of B{sub 2}O{sub 3} flux substituted NLBCO superconductor NdBa{sub 1.75}La{sub 0.25}Cu{sub 3}O{sub 7-∂} has been done using solid state reaction and wet-mixing methods in order to obtain homogeneous crystals and single phase. From DTA/TGA characteritations showed the synthesis process by wet-mixing requires a lower temperature than the solid state reaction in growing the superconductor NdBa{sub 1.75}La{sub 0.25}Cu{sub 3}O{sub 7-∂}. Therefore, in this research NdBa{sub 1.75}La{sub 0.25}Cu{sub 3}O{sub 7-∂} sample calcinated at 650°C for wet-mixing method and 820°C for solid state reaction methods. The all samples was sintered at 950°C for ten hours. Crystallinity of the sample was confirmedmore » using X-ray techniques and generally obtained sharp peaks that indicates the sample already well crystallized. Search match analyses for diffraction data gave weight fractions of impurity phase of the solid state reaction method higher than wet-mixing method. In this research showed decreasing the price of the lattice parameter about 1% with the addition of B{sub 2}O{sub 3} flux for the both synthesis process and 2% of wet mixing process for all samples. Characterization using scanning electron microscopy (SEM) showed the distribution of crystal zise for wet-mixing method more homogeneous than solid state reaction method, with he grain size of samples is around 150–250 nm. The results of vibrating sample magnetometer (VSM) showed the paramagnetic properties for all samples.« less

Electronic structure and superconductivity of FeSe-related superconductors.

PubMed

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

2015-05-13

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

Weyl holographic superconductor in the Lifshitz black hole background

NASA Astrophysics Data System (ADS)

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

2016-07-01

We investigate analytically the properties of the Weyl holographic superconductor in the Lifshitz black hole background. We find that the critical temperature of the Weyl superconductor decreases with increasing Lifshitz dynamical exponent, z, indicating that condensation becomes difficult. In addition, it is found that the critical temperature and condensation operator could be affected by applying the Weyl coupling, γ. Moreover, we compute the critical magnetic field and investigate its dependence on the parameters γ and z. Finally, we show numerically that the Weyl coupling parameter γ and the Lifshitz dynamical exponent z together control the size and strength of the conductivity peak and the ratio of gap frequency over critical temperature ω g /T c .

Upper critical field of high temperature Y(1.2)Ba(0.8)CuO(4-delta) superconductor

NASA Technical Reports Server (NTRS)

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

1987-01-01

A 20-T high-field magnet is used to measure electrical resistance as a function of temperature in the Y(1.2)Ba(0.8)CuO(4-delta) superconductor. The temperature dependence of the critical field, Hc2(T), is obtained from the superconduction transition. A Hc2(O) value of 166T is determined which is the highest critical field yet reported. Results show Y(1.2)Ba(0.8)CuO(4-delta) to be a 90K Type-II superconductor, with a lower critical field Hc1(O) of about 0.2T and a penetration depth of about 290 A.

Method for harvesting rare earth barium copper oxide single crystals

DOEpatents

Todt, V.R.; Sengupta, S.; Shi, D.

1996-04-02

A method of preparing high temperature superconductor single crystals is disclosed. The method of preparation involves preparing precursor materials of a particular composition, heating the precursor material to achieve a peritectic mixture of peritectic liquid and crystals of the high temperature superconductor, cooling the peritectic mixture to quench directly the mixture on a porous, wettable inert substrate to wick off the peritectic liquid, leaving single crystals of the high temperature superconductor on the porous substrate. Alternatively, the peritectic mixture can be cooled to a solid mass and reheated on a porous, inert substrate to melt the matrix of peritectic fluid while leaving the crystals melted, allowing the wicking away of the peritectic liquid. 2 figs.

Defects and anharmonicity induced electron spectra of YBa2Cu3O7-δ superconductors

NASA Astrophysics Data System (ADS)

Singh, Anu; Indu, B. D.

2018-05-01

The effects of defects and anharmonicities on the electron density of states (EDOS) have been studied in high-temperature superconductors (HTS) adopting the many body quantum dynamical theory of electron Green's functions via a generalized Hamiltonian that includes the effects of electron-phonon interactions, anharmonicities and point impurities. The automatic emergence of pairons and temperature dependence of EDOS are appear as special feature of the theory. The results thus obtained and their numerical analysis for YBa2Cu3O7-δ superconductors clearly demonstrate that the presence of defects, anharmonicities and electron-phonon interactions modifies the behavior of EDOS over a wide range of temperature.

Method for harvesting rare earth barium copper oxide single crystals

DOEpatents

Todt, Volker R.; Sengupta, Suvankar; Shi, Donglu

1996-01-01

A method of preparing high temperature superconductor single crystals. The method of preparation involves preparing precursor materials of a particular composition, heating the precursor material to achieve a peritectic mixture of peritectic liquid and crystals of the high temperature superconductor, cooling the peritectic mixture to quench directly the mixture on a porous, wettable inert substrate to wick off the peritectic liquid, leaving single crystals of the high temperature superconductor on the porous substrate. Alternatively, the peritectic mixture can be cooled to a solid mass and reheated on a porous, inert substrate to melt the matrix of peritectic fluid while leaving the crystals melted, allowing the wicking away of the peritectic liquid.

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

NASA Astrophysics Data System (ADS)

Kohno, Masanori

2018-04-01

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

Superconductors in the High School Classroom

ERIC Educational Resources Information Center

Lincoln, James

2017-01-01

In this article, we discuss the behavior of high-temperature superconductors and how to demonstrate them safely and effectively in the high school or introductory physics classroom. Included here is a discussion of the most relevant physics topics that can be demonstrated, some safety tips, and a bit of the history of superconductors. In an effort…

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

Li, Lu

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

Improved performance characteristics of a high temperature superconductor bolometer using photo-thermoelectrical feedback

NASA Astrophysics Data System (ADS)

Kaila, M. M.; Russell, G. J.

2000-12-01

We have designed a liquid nitrogen cooled detector where a thermoelectric feedback is combined with electrothermal feedback to produce an improvement of three orders of magnitude in the response time of the detector. We have achieved this by considering a parallel resistance combination of thermoelectric and High Temperature Superconductor (HTSC) material legs of an approximate geometry 1mm /spl times/ 2 mm /spl times/ 1micron operated at 80K. One end of this thermocouple acts as the sensitive area where the radiation is absorbed. The other end remains unexposed and stays basically at substrate temperature. It is found that micron thick films in our bolometer produce characteristics very close to those found for nanometer thick films required in semiconductor detectors and Low Temperature Superconductor (LTSC) bolometers.

REVIEW ARTICLE: Unconventional isotope effects in the high-temperature cuprate superconductors

NASA Astrophysics Data System (ADS)

Zhao, Guo-meng; Keller, H.; Conder, K.

2001-07-01

We review various isotope effects in the high-Tc cuprate superconductors to assess the role of the electron-phonon interaction in the basic physics of these materials. Of particular interest are the unconventional isotope effects on the supercarrier mass, on the charge-stripe formation temperature, on the pseudogap formation temperature, on the electron paramagnetic resonance (EPR) linewidth, on the spin-glass freezing temperature and on the antiferromagnetic ordering temperature. The observed unconventional isotope effects strongly suggest that lattice vibrations play an important role in the microscopic pairing mechanism of high-temperature superconductivity.

Semiconductor-like behavior in superconducting Nb/Al films

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

Greco, M.; Menichetti, E.; Rinaudo, G.

1999-04-20

The authors report here the experimental evidence of semiconductor-superconductor transitions in relatively thick Nb/Al structures. The temperature dependence of resistivity {rho}(T) shows a sharp superconducting transition followed by either a normal metallic behavior in low-resistivity samples, or a semiconducting behavior when the sample resistivity at 10 K is above 100 {mu}{Omega} cm. The authors discuss here the fabrication conditions and the electron localization regime associated with the measured {rho}(T) dependence.

Boundaries of the critical state stability in a hard superconductor Nb3Al in the H-T plane

NASA Astrophysics Data System (ADS)

Chabanenko, V. V.; Vasiliev, S. V.; Nabiałek, A.; Shishmakov, A. S.; Pérez-Rodríguez, F.; Rusakov, V. F.; Szewczyk, A.; Kodess, B. N.; Gutowska, M.; Wieckowski, J.; Szymczak, H.

2013-04-01

The instability of the critical state in a type-II superconductor Nb3Al is studied for the first time for simultaneous consideration of real dependences of thermal and conductive properties of the material on temperature T and magnetic field He. To do this the dependences of specific heat C(T,Hе), magnetization M(T,He) and magnetostriction ΔL(T,He) of the superconductor were investigated experimentally in a strong magnetic field (up to 12 T). The gap width, the coefficient of the linear term, which determines the electronic contribution to the specific heat, the Debye temperature, and other parameters were found using experimental data on the heat capacity in a wide range of temperatures and magnetic fields Hc1 ≤ He ≤ Hc2. From experimental studies of magnetization the dependences of the critical current of the superconductor, Jc(T,He), were reconstructed. The hysteresis loops of magnetization and magnetostriction were calculated using experimental data for temperature and field dependences of the thermal and conductive properties.

Magnetization and transport properties of silver-sheathed (Hg, Re)Ba2Ca2Cu3O8+delta tapes

NASA Astrophysics Data System (ADS)

Su, J. H.; Sastry, P. V. P. S. S.; Schwartz, J.

2003-10-01

(Hg, Re)Ba2Ca2Cu3O8+delta ((Hg, Re)-1223) samples have been fabricated by wrapping Re0.2Ba2Ca2Cu3Oy precursor powder within Ag foil and pressing or rolling. The Ag/precursor composite is then reacted with CaHgO2 in sealed reaction tubes. X-ray diffraction (XRD) patterns showed only one superconducting phase, (Hg, Re)-1223, in agreement with magnetization measurements showing an onset critical temperature (Tc) of 132 K. The magnetization properties were studied by dc magnetic measurements. The irreversibility line (Hirr), deduced from magnetization hysteresis loops, is approximated by a power law, Hirr ~ (1 - T/Tc)n, with n ~ 2.5, indicating moderate coupling between CuO2 layers compared to YBa2Cu3O7 (n ~ 1.5) and Bi/Tl-based superconductors (n ~ 5.5). The temperature dependence of the magnetization hysteresis loop width DeltaM showed three regimes, dominated by weak links at low temperature (regime I), thermally activated depinning of vortices at intermediate temperature (regime II) and giant flux creep at high temperature (regime III), respectively. Two field dependences were found in the intragrain critical current density (Jmagc) versus applied field at various temperatures: a weak one at lower temperature (leq50 K) and a stronger one at high temperature (geq65 K), indicating a transition from vortex lattice to vortex liquid in the tapes. The transport critical current density (Jtranc) of ~3 × 103 A cm-2 at 4.2 K and self-field was comparable to those for bulk Hg-based superconductors, indicating granular nature of the samples, which was confirmed further by XRD, scanning electron microscopy (SEM) and magneto-optical imaging (MOI).

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

Moore, S. A.; Plummer, G.; Fedor, J.

Mapping the distribution of currents inside a superconductor is usually performed indirectly through imaging of the stray magnetic fields above the surface. Here, we show that by direct imaging of the Doppler shift contribution to the quasiparticle excitation spectrum in the superconductor using low temperature scanning tunneling microscopy, we obtain directly the distribution of supercurrents inside the superconductor. We demonstrate the technique at the example of superconductor/ferromagnet hybrid structure that produces intricate current pattern consisting of combination Meissner shielding currents and Abrikosov vortex currents.

Metamaterial superconductors

NASA Astrophysics Data System (ADS)

Smolyaninov, Igor I.; Smolyaninova, Vera N.

2018-05-01

Searching for natural materials exhibiting larger electron-electron interactions constitutes a traditional approach to high-temperature superconductivity research. Very recently, we pointed out that the newly developed field of electromagnetic metamaterials deals with the somewhat related task of dielectric response engineering on a sub-100-nm scale. Considerable enhancement of the electron-electron interaction may be expected in such metamaterial scenarios as in epsilon near-zero (ENZ) and hyperbolic metamaterials. In both cases, dielectric function may become small and negative in substantial portions of the relevant four-momentum space, leading to enhancement of the electron pairing interaction. This approach has been verified in experiments with aluminum-based metamaterials. Metamaterial superconductor with Tc=3.9 K have been fabricated, which is three times that of pure aluminum (Tc=1.2 K), which opens up new possibilities to improve the Tc of other simple superconductors considerably. Taking advantage of the demonstrated success of this approach, the critical temperature of hypothetical niobium, MgB2- and H2S-based metamaterial superconductors is evaluated. The MgB2-based metamaterial superconductors are projected to reach the liquid nitrogen temperature range. In the case of an H2S-based metamaterial, the projected Tc appears to reach 250 K.

Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films

PubMed Central

Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X. J.

2016-01-01

The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors. PMID:26853801

Synthesis and characterization of FeSe1-xTex (x=0, 0.5, 1) superconductors

NASA Astrophysics Data System (ADS)

Zargar, Rayees A.; Hafiz, A. K.; Awana, V. P. S.

2015-08-01

In this study, FeTe1-xSex (x=0,0.5,1) samples were prepared by conventional solid state reaction method and investigated by powder XRD, SEM, Raman and resistivity measurement techniques to reveal the effect of tellurium (Te) substitution in FeSe matrix. Rietveld analysis was performed on room temperature recorded, X-ray diffraction (XRD) patterns of pure FeSe, FeTe and FeSe0.5Te0.5 which shows that all the compounds are crystallized in a tetragonal structure. SEM images show the dense surface morphology. Raman spectra recorded in the range from 100 to 700 cm-1 at ambient temperature has been interpreted by P4/nmm space group of the lattice. The variation in intensity and shift in peak positions of some phonon modes has been discussed on the basis of variation in crystalline field effect by substituting Te in FeSe lattice. The resistivity versus temperature curves reveals that FeSe becomes superconductor at 7 K and FeSe0.5Te0.5 shows superconductivity below 14 K while FeTe is non-superconducting compound.

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

NASA Astrophysics Data System (ADS)

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

1990-10-01

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

JPRS Report, Science & Technology, Europe & Latin America.

DTIC Science & Technology

1987-08-28

Rhine Westfalia) has recently agreed to purchase a new high performance laser which is supposed to • prepare the ground for new processing and...Transition Temperature Lies Within a Very Limited Area"] [Excerpts] VDI-N, Bochum, 15/5/87— High temperature, high current superconductors with a transition...applications of superconductive materials. Dr Kahn was able to produce a high temperature superconductor with high current flow based on the known oxide

Synthesis and electrical properties of (Pb,Co)Sr2(Y,Ca)Cu2Oz

NASA Astrophysics Data System (ADS)

Tashiro, T.; Maeda, T.; Abe, R.; Takechi, S.; Takahashi, T.; Haruta, M.; Horii, S.

One of related materials to high-temperature superconductors (HTSC's) with nominal compositions of (Pb0.5Co0.5)Sr2(Y1xCax)Cu2Oz (x=0∼0.6) is synthesized and characterized. All samples are nearly single-phase, and its crystal structure is likely to be so-called "1-2-1-2" type which is one of typical structures of HTSC's. Electrical resistivity is decreased as x increases. While superconductivity is not observed at temperatures between room-temperature and 20 K for all samples, temperature dependence of the resistivity exhibits metallic behavior down to 150 K for x=0.5. Phase formation and transport behavior are discussed focusing on mixed valence-state of Co2+ and Co3+.

The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)

NASA Technical Reports Server (NTRS)

Mogro-Campero, A.; Turner, L. G.; Bogorad, A.; Herschitz, R.

1990-01-01

The refrigeration of superconductors in space poses a challenging problem. The problem could be less severe if superconducting materials would not have to be cooled when not in use. Thin films of the YBa2Cu3O(7-x) (YBCO) superconductor were subjected to thermal cycling, which was carried out to simulate a large number of eclipses of a low earth orbit satellite. Electrical measurements were performed to find the effect of the temperature cycling. Thin films of YBCO were formed by coevaporation of Y, BaF2, and Cu and postannealing in wet oxygen at 850 C for 3.5 h. The substrates used were (100) SrTiO3, polycrystalline alumina, and oxidized silicon; the last two have an evaporated zirconia layer. Processing and microstructure studies of these types of films have been published. THe zero resistance transition temperatures of the samples used in this study were 91, 82, and 86 K, respectively. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were: the zero resistance transition temperature, the 10 to 90 percent transition width, and the room temperature resistance, normalized to that measured before temperature cycling. The results for two samples are presented. Each sample had a cumulative exposure. Cycling in atmospheric pressure nitrogen was performed at a rate of about 60 cycles per day, whereas in vacuum the rate was only about 10 cycles per day. The results indicate only little or no changes in the parameters measured. Degradation of superconducting thin films of YBCO has been reported due to storage in nitrogen. It is believed that the relatively good performance of films after temperature cycling is related to the fact that BaF2 was used as an evaporation source. The latest result on extended temperature cycling indicates significant degradation. Further tests of extended cycling will be carried out to provide additional data and to clarify this preliminary finding.

Iron isotope effect in the iron arsenide superconductor (Ca0.4Na0.6)Fe2As2

NASA Astrophysics Data System (ADS)

Tsuge, Y.; Nishio, T.; Iyo, A.; Tanaka, Y.; Eisaki, H.

2014-05-01

We report a new sample synthesis technique for polycrystalline (Ca1-xNax)Fe2As2 (0

Superconductivity: Technology meets quantum criticality

NASA Astrophysics Data System (ADS)

Zaanen, Jan

2005-09-01

Superconductivity and antiferromagnetism are in fierce competition in high-temperature superconductors. However, this competition has the unexpected benefit that the antiferromagnetism improves the capacity of the superconductor to resist magnetic fields.

Radio frequency-assisted fast superconducting switch

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

Solovyov, Vyacheslav; Li, Qiang

A radio frequency-assisted fast superconducting switch is described. A superconductor is closely coupled to a radio frequency (RF) coil. To turn the switch "off," i.e., to induce a transition to the normal, resistive state in the superconductor, a voltage burst is applied to the RF coil. This voltage burst is sufficient to induce a current in the coupled superconductor. The combination of the induced current with any other direct current flowing through the superconductor is sufficient to exceed the critical current of the superconductor at the operating temperature, inducing a transition to the normal, resistive state. A by-pass MOSFET maymore » be configured in parallel with the superconductor to act as a current shunt, allowing the voltage across the superconductor to drop below a certain value, at which time the superconductor undergoes a transition to the superconducting state and the switch is reset.« less

Fourth international cryogenic materials conference

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

Reed, R.P.; Clark, A.F.

1982-01-01

In a comprehensive and current collection of 911 papers on a vest range of materials research topics in the field of cryogenic technology, this 924-page volume presents the most recent work of an international spectrum of materials and cyrogenic engineers at industrial and academic laboratories and institutions. The papers are collected under the broad headings of structural alloys; nometallics and composites; flux pinning in superconductors; high field superconductors; A15 superconductors; multiply-connected superconductors; superconductor properties and measurements; strain effects in superconductors; superconductor performance; the fabrication of superconductors; and the fabrication of structural alloys and composits. Ample and adequate photographic, plot, schematic,more » and tabulation illustration are included; the volume is also cross-referenced and has an author, materials, and subject index. It is volume 28 in a series which annually updates the existing knowledge of all areas of low-temperature technology.« less

Magnetic field effect on the electrical resistivity of Y1-xNixBa2Cu3O7-δ superconductor

NASA Astrophysics Data System (ADS)

Hadi-Sichani, Behnaz; Shakeripour, Hamideh; Salamati, Hadi

2018-06-01

The Ni- substituted Y1-xNixBa2Cu3O7-δ high temperature superconducting samples with 0 ≤ x < 0.01 were synthesized by the standard solid-state reaction. The temperature dependent resistivity of the samples was measured under magnetic fields in the range of zero to 1 Tesla, applied perpendicular to the current direction. To study of magnetoresistance is one of the most important ways to investigate the intergranular nature of superconducting materials. The resistive transition is made of two parts. The first- unaffected to applied magnetic field part which is near the onset of superconductivity. This region is due to superconductivity in grains. The second- broaden tail part which is due to the connectivity of the grains. At temperatures close to Tc 0, (ρ = 0), under applied magnetic fields, weak links are affected and the vortices are penetrated and move inside the intergranular and then the tail part is broaden. This broadening part observed in the electrical resistivity, ρ(T), and in the derivative of the electrical resistivity, dρ/dT, becomes too small or even absent in Ni doped samples. For pure sample, Tc 0 was around 90 K; by applying a magnetic field H = 0.3 T it shifted to 40 K. This broadening is 91.4 K to 80 K for x = 0.002 and 91.7 K to 85 K for x = 0.004 samples. We found an optimal value of Ni doping concentration which improves the coupling of the grains. Then, vortices get strongly pinned. These observations suggest that the Ni substitution can reduce the weak links and increase the Jc values of these superconductors.

Low-temperature rapid synthesis and superconductivity of Fe-based oxypnictide superconductors.

PubMed

Fang, Ai-Hua; Huang, Fu-Qiang; Xie, Xiao-Ming; Jiang, Mian-Heng

2010-03-17

Fe-based oxypnictide superconductors were successfully synthesized at lower reaction temperatures and with shorter reaction times made possible by starting with less stable compounds, which provide a larger driving force for reactions. Using ball-milled powders of intermediate compounds, phase-pure superconductors with T(c) above 50 K were synthesized at 1173 K in 20 min. This method is particularly advantageous for retaining F, a volatile dopant that enhances superconductivity. Bulk superconductivity and high upper critical fields up to 392 T in Sm(0.85)Nd(0.15)FeAsO(0.85)F(0.15) were demonstrated.

The pressure coefficient of the Curie temperature of ferromagnetic superconductors

NASA Astrophysics Data System (ADS)

Konno, R.; Hatayama, N.

2012-12-01

The pressure coefficient of the Curie temperature of ferromagnetic superconductors is studied numerically. In our previous study the pressure coefficient of the Curie temperature and that of the superconducting transition temperature were shown based on the Hamiltonian derived by Linder et al. within the mean field approximation about the electron-electron interaction analytically. There have been no numerical results of the pressure coefficient of the Curie temperature derived from the microscopic model. In this study the numerical results are reported. These results are qualitatively consistent with the experimental data in UGe2.

Identifying the genes of unconventional high temperature superconductors.

PubMed

Hu, Jiangping

We elucidate a recently emergent framework in unifying the two families of high temperature (high [Formula: see text]) superconductors, cuprates and iron-based superconductors. The unification suggests that the latter is simply the counterpart of the former to realize robust extended s-wave pairing symmetries in a square lattice. The unification identifies that the key ingredients (gene) of high [Formula: see text] superconductors is a quasi two dimensional electronic environment in which the d -orbitals of cations that participate in strong in-plane couplings to the p -orbitals of anions are isolated near Fermi energy. With this gene, the superexchange magnetic interactions mediated by anions could maximize their contributions to superconductivity. Creating the gene requires special arrangements between local electronic structures and crystal lattice structures. The speciality explains why high [Formula: see text] superconductors are so rare. An explicit prediction is made to realize high [Formula: see text] superconductivity in Co/Ni-based materials with a quasi two dimensional hexagonal lattice structure formed by trigonal bipyramidal complexes.

Cryocoolers for the new high-temperature superconductors

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

Walker, G.; Ellison, W.; Zylstra, S.

1988-06-01

Compact, reliable, low-cost cryocoolers operated simply by closing a switch are an essential requirement for the coming age of superconductivity and cold electronic systems. The advent of high-temperature superconductors has substantially eased the task of those seeking to fill the above need. This article reviews some recent developments in cryocooler systems and examined some prospects for the future.

Alkaline Earth Core Level Photoemission Spectroscopy of High-Temperature Superconductors

NASA Technical Reports Server (NTRS)

Vasquez, R.

1993-01-01

This paper examines photoemission measurements of the alkaline Earth core levels of high-temperature superconductors and related materials, models that seek to explain the large negative shifts observed relative to the corresponding alkaline Earth metals, and the effect of lattice site disorder on the core level spectra and the presence or absence of intrinsic surface peaks.

415th Brookhaven Lecture

ScienceCinema

Ivan Bozovic

2017-12-09

"Atomic-Layer Engineering of Cuprate Superconductors." Copper-oxide compounds, called cuprates, show superconducting properties at 163 degrees Kelvin, the highest temperature of any known superconducting material. Cuprates are therefore among the "high-temperature superconductors" of extreme interest both to scientists and to industry. Research to learn their secrets is one of the hottest topics in the field of materials science.

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.

Localized superconductivity in the quantum-critical region of the disorder-driven superconductor-insulator transition in TiN thin films.

PubMed

Baturina, T I; Mironov, A Yu; Vinokur, V M; Baklanov, M R; Strunk, C

2007-12-21

We investigate low-temperature transport properties of thin TiN superconducting films in the vicinity of the disorder-driven superconductor-insulator transition. In a zero magnetic field, we find an extremely sharp separation between superconducting and insulating phases, evidencing a direct superconductor-insulator transition without an intermediate metallic phase. At moderate temperatures, in the insulating films we reveal thermally activated conductivity with the magnetic field-dependent activation energy. At very low temperatures, we observe a zero-conductivity state, which is destroyed at some depinning threshold voltage V{T}. These findings indicate the formation of a distinct collective state of the localized Cooper pairs in the critical region at both sides of the transition.

The effect of temperature on pinning mechanisms in HTS composites

NASA Astrophysics Data System (ADS)

Sotnikova, A. P.; Rudnev, I. A.

2016-09-01

Pinning mechanism in samples of second generation tapes (2G) of high-temperature superconductors (HTS) was studied The critical current and the pinning force were calculated from the magnetization curves measured in the temperature range of 4.2 - 77 K in magnetic fields up to 14 Tesla using vibration sample magnetometer. To determine the pinning mechanism the dependences of pinning force on magnetic field were constructed according to the Dew-Hughes model and Kramer's rule. The obtained dependences revealed a significant influence of the temperature on effectiveness of different types of pinning. At low temperatures the 2G HTS tapes of different manufacturers demonstrated an equal efficiency of the pinning centers but with temperature increase the differences in pinning mechanisms as well as in properties and effectiveness of the pinning centers become obvious. The influence of the pinning mechanism on the energy losses in HTS tapes was shown.

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

NASA Astrophysics Data System (ADS)

Wong, Chi Ho

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

High pressure low temperature studies on 1-2-2 iron-based superconductors using designer diamond cells

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

Uhoya, Walter O.; Tsoi, Georgiy M.; Vohra, Yogesh K.

In this study, high pressure low temperature electrical resistance measurements were carried out on a series of 122 iron-based superconductors using a designer diamond anvil cell. These studies were complemented by image plate x-ray diffraction measurements under high pressures and low temperatures at beamline 16-BM-D, HPCAT, Advanced Photon Source. A common feature of the 1-2-2 iron-based materials is the observation of anomalous compressibility effects under pressure and a Tetragonal (T) to Collapsed Tetragonal (CT) phase transition under high pressures. Specific studies on antiferromagnetic spin-density-wave Ba 0.5Sr 0.5Fe 2As 2 and Ba(Fe 0.9Ru 0.1) 2As 2 samples are presented to 10more » K and 41 GPa. The collapsed tetragonal phase was observed at a pressure of 14 GPa in Ba 0.5Sr 0.5Fe 2As 2 at ambient temperature. The highest superconducting transition temperature in Ba 0.5Sr 0.5Fe 2As 2 was observed to be at 32 K at a pressure of 4.7 GPa. The superconductivity was observed to be suppressed on transformation to the CT phase in 122 materials.« less

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

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

Kim, Hyunsoo

2013-01-01

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

Synchrotron X-ray Diffraction and High-Pressure Electrical Resistivity Studies for High-Tc Candidate Nd3.5Sm0.5Ni3O8

NASA Astrophysics Data System (ADS)

Uehara, Masatomo; Kobayashi, Kai; Yamamoto, Hiroki; Nakata, Akitoshi; Wakiya, Kazuhei; Umehara, Izuru; Gouchi, Jun; Uwatoko, Yoshiya

2017-11-01

Ln4Ni3O8 (Ln = La, Nd, Sm) has attracted much attention as a candidate for high-Tc superconductor due to its close structural and electrical similarities with high-Tc cuprates. However, Ln4Ni3O8 is not a superconductor and shows semiconducting behavior. Our recent work has revealed that Nd3.5Sm0.5Ni3O8 displays metallic behavior down to 20-40 K upon intercalation and subsequent deintercalation treatments with sulfur, followed by a weak semiconducting tendency at lower temperatures. A synchrotron X-ray diffraction experiment suggests that the structural change induced by sulfur treatment can be explained electrostatically by the removal of additional apical oxygen. High-pressure electrical resistivity measurements up to 8 GPa on a metallic sample show the enhancement of the semiconducting tendency at low temperatures, suggesting that the removal of additional apical oxygen is not totally completed under the present conditions of sulfur treatment.

Experimental Analysis of Critical Current and Alternating Current Losses of High-Temperature Superconductor Tape with Resin and Gallium-Indium-Tin

PubMed Central

Sun, Yajie; Zhang, Huiming; Meng, Yuanzhu

2018-01-01

This paper experimentally analyzes the critical current degradation and AC (alternating current) losses of second-generation (2G) high-temperature superconductor (HTS) tape during the impregnation process. Two impregnation materials were utilized: Gallium-Indium-Tin (GaInSn), and an epoxy resin, Araldite. The critical current of the impregnation materials was measured after different thermal cycles and compared with the tape with no impregnation process. The experimental results show that the critical current of Yttrium Barium Copper Oxide (YBCO) short samples varies between differently impregnated materials. The resin, Araldite, degraded the critical current; however, the GaInSn showed no degradation. Two degradation patterns with Araldite were identified due to the impregnation process, and the corresponding causes were analyzed. We further measured the AC losses of tapes impregnated with liquid metal at different frequencies, up to 600 Hz. Based on the experimental results, GaInSn liquid metal should be the most suitable impregnation material in terms of critical current degradation. PMID:29642490

Experimental Analysis of Critical Current and Alternating Current Losses of High-Temperature Superconductor Tape with Resin and Gallium-Indium-Tin.

PubMed

Yu, Dongmin; Sun, Yajie; Zhang, Huiming; Meng, Yuanzhu; Liu, Huanan

2018-04-08

This paper experimentally analyzes the critical current degradation and AC (alternating current) losses of second-generation (2G) high-temperature superconductor (HTS) tape during the impregnation process. Two impregnation materials were utilized: Gallium-Indium-Tin (GaInSn), and an epoxy resin, Araldite. The critical current of the impregnation materials was measured after different thermal cycles and compared with the tape with no impregnation process. The experimental results show that the critical current of Yttrium Barium Copper Oxide (YBCO) short samples varies between differently impregnated materials. The resin, Araldite, degraded the critical current; however, the GaInSn showed no degradation. Two degradation patterns with Araldite were identified due to the impregnation process, and the corresponding causes were analyzed. We further measured the AC losses of tapes impregnated with liquid metal at different frequencies, up to 600 Hz. Based on the experimental results, GaInSn liquid metal should be the most suitable impregnation material in terms of critical current degradation.

Scaling analysis of field-tuned superconductor-insulator transition in two-dimensional tantalum thin films.

PubMed

Park, Sungyu; Shin, Junghyun; Kim, Eunseong

2017-02-20

The superconductor-insulator (SI) transition in two-dimensional Ta thin films is investigated by controlling both film thickness and magnetic field. An intriguing metallic phase appears between a superconducting and an insulating phase within a range of film thickness and magnetic field. The temperature and electric field scaling analyses are performed to investigate the nature of the SI transition in the thickness-tuned metallic and superconducting samples. The critical exponents product of νz obtained from the temperature scaling analysis is found to be approximately 0.67 in the entire range of film thickness. On the other hand, an apparent discrepancy is measured in the product of ν(z + 1) by the electric filed analysis. The product values are found to be about 1.37 for the superconducting films and about 1.86 for the metallic films respectively. We find that the discrepancy is the direct consequence of electron heating that introduces additional dissipation channels in the metallic Ta films.

Depositing High-T(sub c) Superconductors On Normal-Conductor Wires

NASA Technical Reports Server (NTRS)

Kirlin, Peter S.

1994-01-01

Experiments have demonstrated feasibility of depositing thin layers of high-T(sub c) superconductor on normally electrically conductive wires. Superconductivity evident at and below critical temperature (T{sub c}) of 71 K. OMCVD, organometallic vapor deposition, apparatus coats Ag wire with layer high-T(sub c) superconductor. Superconductive phase of this material formed subsequently by annealing under controlled conditions.

High temperature superconductors applications in telecommunications

NASA Technical Reports Server (NTRS)

Kumar, A. Anil; Li, Jiang; Zhang, Ming Fang

1995-01-01

The purpose of this paper is twofold: (1) to discuss high temperature superconductors with specific reference to their employment in telecommunications applications; and (2) to discuss a few of the limitations of the normally employed two-fluid model. While the debate on the actual usage of high temperature superconductors in the design of electronic and telecommunications devices - obvious advantages versus practical difficulties - needs to be settled in the near future, it is of great interest to investigate the parameters and the assumptions that will be employed in such designs. This paper deals with the issue of providing the microwave design engineer with performance data for such superconducting waveguides. The values of conductivity and surface resistance, which are the primary determining factors of a waveguide performance, are computed based on the two-fluid model. A comparison between two models - a theoretical one in terms of microscopic parameters (termed Model A) and an experimental fit in terms of macroscopic parameters (termed Model B) - shows the limitations and the resulting ambiguities of the two-fluid model at high frequencies and at temperatures close to the transition temperature. The validity of the two-fluid model is then discussed. Our preliminary results show that the electrical transport description in the normal and superconducting phases as they are formulated in the two-fluid model needs to be modified to incorporate the new and special features of high temperature superconductors. Parameters describing the waveguide performance - conductivity, surface resistance and attenuation constant - will be computed. Potential applications in communications networks and large scale integrated circuits will be discussed. Some of the ongoing work will be reported. In particular, a brief proposal is made to investigate of the effects of electromagnetic interference and the concomitant notion of electromagnetic compatibility (EMI/EMC) of high T(sub c) superconductors.

High temperature superconductors applications in telecommunications

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

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

1994-12-31

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

Weak links in high critical temperature superconductors

NASA Astrophysics Data System (ADS)

Tafuri, Francesco; Kirtley, John R.

2005-11-01

The traditional distinction between tunnel and highly transmissive barriers does not currently hold for high critical temperature superconducting Josephson junctions, both because of complicated materials issues and the intrinsic properties of high temperature superconductors (HTS). An intermediate regime, typical of both artificial superconductor-barrier-superconductor structures and of grain boundaries, spans several orders of magnitude in the critical current density and specific resistivity. The physics taking place at HTS surfaces and interfaces is rich, primarily because of phenomena associated with d-wave order parameter (OP) symmetry. These phenomena include Andreev bound states, the presence of the second harmonic in the critical current versus phase relation, a doubly degenerate state, time reversal symmetry breaking and the possible presence of an imaginary component of the OP. All these effects are regulated by a series of transport mechanisms, whose rules of interplay and relative activation are unknown. Some transport mechanisms probably have common roots, which are not completely clear and possibly related to the intrinsic nature of high-TC superconductivity. The d-wave OP symmetry gives unique properties to HTS weak links, which do not have any analogy with systems based on other superconductors. Even if the HTS structures are not optimal, compared with low critical temperature superconductor Josephson junctions, the state of the art allows the realization of weak links with unexpectedly high quality quantum properties, which open interesting perspectives for the future. The observation of macroscopic quantum tunnelling and the qubit proposals represent significant achievements in this direction. In this review we attempt to encompass all the above aspects, attached to a solid experimental basis of junction concepts and basic properties, along with a flexible phenomenological background, which collects ideas on the Josephson effect in the presence of d-wave pairing for different types of barriers.

Application Study of a High Temperature Superconducting Fault Current Limiter for Electric Power System

NASA Astrophysics Data System (ADS)

Naito, Yuji; Shimizu, Iwao; Yamaguchi, Iwao; Kaiho, Katsuyuki; Yanabu, Satoru

Using high temperature superconductor, a Superconducting Fault Current Limiter (SFCL) was made and tested. Superconductor and vacuum interrupter as commutation switch are connected in parallel with bypass coil. When a fault occurs and the excessive current flows, superconductor is first quenched and the current is transferred to bypass coil because on voltage drop of superconductor. At the same time, since magnetic field is generated by current which flows in bypass coil, commutation switch is immediately driven by electromagnetic repulsion plate connected to driving rod of vacuum interrupter, and superconductor is separated from this circuit. Using the testing model, we could separate the superconductor from a circuit due to movement of vacuum interrupter within half-cycle current and transfer all current to bypass coil. Since operation of a commutation switch is included in current limiting operation of this testing model, it is one of helpful circuit of development of SFCL in the future. Moreover, since it can make the consumed energy of superconductor small during fault state due to realization of high-speed switch with simple composition, the burden of superconductor is reduced compared with conventional resistive type SFCL and it is considered that the flexibility of a SFCL design increases. Cooperation with a circuit breaker was also considered, the trial calculation of a parameter and energy of operation is conducted and discussion in the case of installing the SFCL to electric power system is made.

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

PubMed Central

Goodrich, LF; Cheggour, N; Stauffer, TC; Filla, BJ; Lu, XF

2013-01-01

We review variable-temperature, transport critical-current (Ic) measurements made on commercial superconductors over a range of critical currents from less than 0.1 A to about 1 kA. We have developed and used a number of systems to make these measurements over the last 15 years. Two exemplary variable-temperature systems with coil sample geometries will be described: a probe that is only variable-temperature and a probe that is variable-temperature and variable-strain. The most significant challenge for these measurements is temperature stability, since large amounts of heat can be generated by the flow of high current through the resistive sample fixture. Therefore, a significant portion of this review is focused on the reduction of temperature errors to less than ±0.05 K in such measurements. A key feature of our system is a pre-regulator that converts a flow of liquid helium to gas and heats the gas to a temperature close to the target sample temperature. The pre-regulator is not in close proximity to the sample and it is controlled independently of the sample temperature. This allows us to independently control the total cooling power, and thereby fine tune the sample cooling power at any sample temperature. The same general temperature-control philosophy is used in all of our variable-temperature systems, but the addition of another variable, such as strain, forces compromises in design and results in some differences in operation and protocol. These aspects are analyzed to assess the extent to which the protocols for our systems might be generalized to other systems at other laboratories. Our approach to variable-temperature measurements is also placed in the general context of measurement-system design, and the perceived advantages and disadvantages of design choices are presented. To verify the accuracy of the variable-temperature measurements, we compared critical-current values obtained on a specimen immersed in liquid helium (“liquid” or Ic liq) at 5 K to those measured on the same specimen in flowing helium gas (“gas” or Ic gas) at the same temperature. These comparisons indicate the temperature control is effective over the superconducting wire length between the voltage taps, and this condition is valid for all types of sample investigated, including Nb-Ti, Nb3Sn, and MgB2 wires. The liquid/gas comparisons are used to study the variable-temperature measurement protocol that was necessary to obtain the “correct” critical current, which was assumed to be the Ic liq. We also calibrated the magnetoresistance effect of resistive thermometers for temperatures from 4 K to 35 K and magnetic fields from 0 T to 16 T. This calibration reduces systematic errors in the variable-temperature data, but it does not affect the liquid/gas comparison since the same thermometers are used in both cases. PMID:26401435

Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors.

PubMed

Wang, Qisi; Park, J T; Feng, Yu; Shen, Yao; Hao, Yiqing; Pan, Bingying; Lynn, J W; Ivanov, A; Chi, Songxue; Matsuda, M; Cao, Huibo; Birgeneau, R J; Efremov, D V; Zhao, Jun

2016-05-13

An essential step toward elucidating the mechanism of superconductivity is to determine the sign or phase of the superconducting order parameter, as it is closely related to the pairing interaction. In conventional superconductors, the electron-phonon interaction induces attraction between electrons near the Fermi energy and results in a sign-preserved s-wave pairing. For high-temperature superconductors, including cuprates and iron-based superconductors, prevalent weak coupling theories suggest that the electron pairing is mediated by spin fluctuations which lead to repulsive interactions, and therefore that a sign-reversed pairing with an s_{±} or d-wave symmetry is favored. Here, by using magnetic neutron scattering, a phase sensitive probe of the superconducting gap, we report the observation of a transition from the sign-reversed to sign-preserved Cooper-pairing symmetry with insignificant changes in T_{c} in the S-doped iron selenide superconductors K_{x}Fe_{2-y}(Se_{1-z}S_{z})_{2}. We show that a rather sharp magnetic resonant mode well below the superconducting gap (2Δ) in the undoped sample (z=0) is replaced by a broad hump structure above 2Δ under 50% S doping. These results cannot be readily explained by simple spin fluctuation-exchange pairing theories and, therefore, multiple pairing channels are required to describe superconductivity in this system. Our findings may also yield a simple explanation for the sometimes contradictory data on the sign of the superconducting order parameter in iron-based materials.

Advances in superconductivity and Co3O4 nanoparticles as flux pinning center in (Bi, Pb)-2223/Ag superconductor tapes

NASA Astrophysics Data System (ADS)

Abd-Shukor, R.; Jannah, A. N.

2017-09-01

Many new superconducting materials have been discovered in recent years. This includes hydrogen sulfide which superconducts at 203 K under high pressure and Fe-As based materials. To this date the copper oxide-based materials remain as the highest transition temperature superconductor under normal pressure. In this paper we discuss the use of nano-sized particle as pinning center in the Ag-sheathed high temperature superconductor tapes to enhance the transport properties. When the size d of the pinning center is between the coherence length ξ and the penetration depth λ (ξ < d < λ), a stronger interaction between the pinning center and flux lines leading to higher transport critical current density, Jc can be expected. The effect of nanoparticle with size between the coherence length and the penetration depth i.e. ξ < d < λ, Co3O4 on superconductor tapes is discussed in this paper. Three types of Bi(Pb)-Sr-Ca-Cu-O starting materials namely from co-precipitation method without Co3O4 and with 30 nm and 50 nm Co3O4 addition have been prepared. The composition of the 30 nm and 50 nm Co3O4 added samples is (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(Co3O4)0.02 and (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(Co3O4)0.01, respectively. The tapes (˜2-3 cm long) were heated at 845°C for 100 and 150 h. All nanoparticles added tapes showed higher Jc compared to the non-added tapes. By comparing the current results with our previously reported results, the tapes with 30 nm Co3O4 sintered for 50 h showed the highest Jc at all temperatures. This work also showed that smaller magnetic nanoparticles enhanced Jc better than larger particles, A longer sintering time (> 50 h) degraded Jc.

Studies of High Critical Transition Temperature Superconductors

NASA Astrophysics Data System (ADS)

Zhou, Xue Zhi

1990-01-01

In early 1987 the high-T_{ rm c} superconductor, YBa_2 Cu_3O_{7 -delta}, with T_{ rm c} ~eq 90K was successfully made in our laboratory by a standard ceramic technique. Later Tl_2Ca _2Ba_2Cu_3 O_{10} with T _{rm c} ~eq 120K was produced by a special procedure. Structural analysis by x-ray diffraction showed that YBa_2 Cu_3O_{7 -delta} was responsible for the high -T_{rm c}, the so called 123 phase. It is an oxygen deficient perovskite with the orthorhombic structure, space group Pmmm, lattice constant a = 3.8243, b = 3.8862 and c = 11.667 A. Oxygen vacancies are very important to the superconducting properties. An impurity, Y_2BaCuO_5 , with a green colour, was identified as a semiconducting phase. A technique to grow single crystals of YBa _2Cu_3O_ {7-delta} is described. The crystals are rectangular up to 2 x 2 x 0.2 mm^3 in size. Two phases, Tl_2CaBa _2Cu_2O_8 (the 2122 phase) and Tl_2Ca _2Ba_2Cu _3O_{10} (the 2223 phase), are responsible for the high-T _{rm c} in the Tl-system; they have a tetragonal or pseudotetragonal structure with space group I4/mmm. Resistivity and magnetic ac susceptibility results show that high-T_{rm c} materials have a sharp superconducting transition and many properties in common with conventional superconductors. The shielding effect is closely related to the properties of grain boundaries. Magnetic ordering at low temperature (below 10K) of high-T_{rm c} materials was discovered by Mossbauer experiments with ^{57}Fe doped samples. Substitution of Fe for Cu reduced the superconducting transition temperature and the shielding effect. Theories of superconductivity for conventional and the new superconductors are reviewed and related to the experimental results.

Densification of oxide superconductors by hot isostatic pressing

NASA Astrophysics Data System (ADS)

Tien, J. K.; Borofka, J. C.; Hendrix, B. C.; Caulfield, T.; Reichman, S. H.

1988-07-01

Currently, consolidation of high Tc superconductor powders is done by sintering, which is not effective in the reduction of porosity. This work assesses the feasibility of hot isostatic pressing (HIP) to obtain fully dense bulk superconductor using HIP modeling and experimental verification. It is concluded that fully dense YBa2Cu3O7 can be obtained in reasonable times at temperatures down to around 650 °C. The trade-offs between temperature, time, and pressure are examined as well as the effects of powder particle size, powder grain size, and trapped gas pressure. The model has. been verified by experiment under three conditions: 100 MPa HIP at 900 °C for 2 hours, 100 MPa HIP at 750 °C for 2 hours, and sintering at 950 °C for 16 hours. The additional advantages of HIPing oxide superconductors are also discussed.

Current-carrying element based on second-generation high-temperature superconductor for the magnet system of a fusion neutron source

NASA Astrophysics Data System (ADS)

Novikov, M. S.; Ivanov, D. P.; Novikov, S. I.; Shuvaev, S. A.

2015-12-01

Application of current-carrying elements (CCEs) made of second-generation high-temperature superconductor (2G HTS) in magnet systems of a fusion neutron source (FNS) and other fusion devices will allow their magnetic field and thermodynamic stability to be increased substantially in comparison with those of low-temperature superconductor (LTS) magnets. For a toroidal magnet of the FNS, a design of a helical (partially transposed) CCE made of 2G HTS is under development with forced-flow cooling by helium gas, a current of 20-30 kA, an operating temperature of 10-20 K, and a magnetic field on the winding of 12-15 T (prospectively ~20 T). Short-sized samples of the helical flexible heavy-current CCE are being fabricated and investigated; a pilot-line unit for production of long-sized CCE pieces is under construction. The applied fabrication technique allows the CCE to be produced which combines a high operating current, thermal and mechanical stability, manufacturability, and low losses in the alternating modes. The possibility of fabricating the CCE with the outer dimensions and values of the operating parameter required for the FNS (and with a significant margin) using already available serial 2G HTS tapes is substantiated. The maximum field of toroidal magnets with CCEs made of 2G HTS will be limited only by mechanical properties of the magnet's casing and structure, while the thermal stability will be approximately two orders of magnitude higher than that of toroidal magnets with LTS-based CCEs. The helical CCE made of 2G HTS is very promising for fusion and hybrid electric power plants, and its design and technologies of production, as well as the prototype coils made of it for the FNS and other tokamaks, are worth developing now.

Characteristic parameters of superconductor-coolant interaction including high Tc current density limits

NASA Technical Reports Server (NTRS)

Frederking, T. H. K.

1989-01-01

In the area of basic mechanisms of helium heat transfer and related influence on super-conducting magnet stability, thermal boundary conditions are important constraints. Characteristic lengths are considered along with other parameters of the superconducting composite-coolant system. Based on helium temperature range developments, limiting critical current densities are assessed at low fields for high transition temperature superconductors.

Hotspot relaxation dynamics in a current-carrying superconductor

NASA Astrophysics Data System (ADS)

Marsili, F.; Stevens, M. J.; Kozorezov, A.; Verma, V. B.; Lambert, Colin; Stern, J. A.; Horansky, R. D.; Dyer, S.; Duff, S.; Pappas, D. P.; Lita, A. E.; Shaw, M. D.; Mirin, R. P.; Nam, S. W.

2016-03-01

We experimentally studied the dynamics of optically excited hotspots in current-carrying WSi superconducting nanowires as a function of bias current, bath temperature, and excitation wavelength. We observed that the hotspot relaxation time depends on bias current, temperature, and wavelength. We explained this effect with a model based on quasiparticle recombination, which provides insight into the quasiparticle dynamics of superconductors.

Superconductor Particles As The Working Media Of A Heat Engine

NASA Astrophysics Data System (ADS)

Keefe, Peter D.

2011-12-01

A heat engine is presented in which the working media comprises a multiplicity of mutually isolated particles of Type I superconductor which are selectively processed through H-T phase space so as to convert a heat influx from a high temperature heat reservoir into a useful work output, wherein no heat is rejected to a low temperature heat reservoir.

Magnetic-Flux-Compression Cooling Using Superconductors

NASA Technical Reports Server (NTRS)

Strayer, Donald M.; Israelsson, Ulf E.; Elleman, Daniel D.

1989-01-01

Proposed magnetic-flux-compression refrigeration system produces final-stage temperatures below 4.2 K. More efficient than mechanical and sorption refrigerators at temperatures in this range. Weighs less than comparable liquid-helium-cooled superconducting magnetic refrigeration systems operating below 4.2 K. Magnetic-flux-compression cooling stage combines advantages of newly discovered superconductors with those of cooling by magnetization and demagnetization of paramagnetic salts.

Valence, Charge Transfer and Carrier Type for Bi2Sr2Can-1CunO2(n+4+delta) and Related High Temperature Ceramic Superconductors

DTIC Science & Technology

1988-09-30

resistivity and thermoelectric -power measurements. Both of the high temperature superconducting phases reported in the literature, with transition...temperatures near 80K and 110K, have been observed. Evidence from thermoelectric power measurements is presented which shows that this family of ceramic...observed. Evidence from thermoelectric power measurements is presented which shows that this family of ceramic superconductors has contributions to the

Improving NIS Tunnel Junction Refrigerators: Modeling, Materials, and Traps

NASA Astrophysics Data System (ADS)

O'Neil, Galen Cascade

This thesis presents a systematic study of electron cooling with Normal-metal/insulator/superconductor (NIS) tunnel junctions. NIS refrigerators have an exciting potential to simplify 100 mK and 10 mK cryogenics. Rather than using an expensive dilution refrigerator, researchers will be able to use much simpler cryogenics to reach 300 mK and supplement them with mass fabricated thin-film NIS refrigerators to reach 100 mK and below. The mechanism enabling NIS refrigeration is energy selective tunneling. Due to the gap in the superconducting density of states, only hot electrons tunnel from the normal-metal. Power is removed from the normal-metal, that same power and the larger IV power are both deposited in the superconductor. NIS refrigerators often cool less than theory predicts because of the power deposited in the superconductor returns to the normal-metal. When the superconductor temperature is raised, or athermal phonons due to quasiparticle recombination are absorbed in the normal-metal, refrigerator performance will be reduced. I studied the quasiparticle excitations in superconductors to develop the most complete thermal model of NIS refrigerators to date. I introduced overlayer quasiparticle traps, a new method for heatsinking the superconductor. I present measurements on NIS refrigerators with and without quasiparticle traps, to determine their effectiveness. This includes an NIS refrigerator that cools from 300 mK to 115 mK or lower, a large improvement over previous designs. I also looked into reducing the power deposited in the superconductor, by choosing the transition temperature of the superconductor based upon the NIS refrigerator launch temperature. I performed a detailed study of the density of states of superconducting AlMn alloys, demonstrating that Mn impurities behave non-magnetically in Al due to resonant scattering. The density of states remains BCS-like, but my measurements show that the deviations from a BCS density of states harm cooling in NIS refrigerators.

Irreversible magnetization switching at the onset of superconductivity in a superconductor ferromagnet hybrid

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

Curran, P. J.; Bending, S. J.; Kim, J.

2015-12-28

We demonstrate that the magnetic state of a superconducting spin valve, that is normally controlled with an external magnetic field, can also be manipulated by varying the temperature which increases the functionality and flexibility of such structures as switching elements. In this case, switching is driven by changes in the magnetostatic energy due to spontaneous Meissner screening currents forming in the superconductor below the critical temperature. Our scanning Hall probe measurements also reveal vortex-mediated pinning of the ferromagnetic domain structure due to the pinning of quantized stray fields in the adjacent superconductor. The ability to use temperature as well asmore » magnetic field to control the local magnetisation structure raises the prospect of potential applications in magnetic memory devices.« less

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.

Fracture analysis of a transversely isotropic high temperature superconductor strip based on real fundamental solutions

NASA Astrophysics Data System (ADS)

Gao, Zhiwen; Zhou, Youhe

2015-04-01

Real fundamental solution for fracture problem of transversely isotropic high temperature superconductor (HTS) strip is obtained. The superconductor E-J constitutive law is characterized by the Bean model where the critical current density is independent of the flux density. Fracture analysis is performed by the methods of singular integral equations which are solved numerically by Gauss-Lobatto-Chybeshev (GSL) collocation method. To guarantee a satisfactory accuracy, the convergence behavior of the kernel function is investigated. Numerical results of fracture parameters are obtained and the effects of the geometric characteristics, applied magnetic field and critical current density on the stress intensity factors (SIF) are discussed.

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).

The magnitude of the magnetic field near the surface of a high-T(sub c) superconductor with a trapped flux

NASA Technical Reports Server (NTRS)

Overcash, Dan R.

1991-01-01

In 1986, much excitement was caused by the discovery of a class of materials that conducted electricity with zero resistance at temperatures above the boiling temperature of liquid nitrogen. This excitement was checked by the difficulties of manufacturing ceramics and the usefulness of high temperature superconductors that were restricted by their becoming high resistive conductors at small current densities. A lack of pinning of the magnetic field flux caused the return of high resistance as the current was increased in these materials. A study of the magnetic field near the surface of a high temperature superconductor is the first step in the search for a means of pinning the flux lines and increasing their critical current densities. The author found that a comparison between the defects in the surface of the superconductor and the magnetic field showed only a change in the field near the notch and the edge. No correlation was found between the surface grain or structure and the oscillations in the magnetic field. The observed changes in the magnetic field show resonances which may give an indication of the non-flux pinning in these superconductors. A flux pinning mechanism will increase the critical current densities; therefore, other methods of determining this field should be tried. The author proposes using a flux gate magnetometer with a detector wound on a ferrite core to measure the magnitude and direction of the magnetic field.

Forming YBa2Cu3O7-x Superconductors On Copper Substrates

NASA Technical Reports Server (NTRS)

Mackenzie, J. Devin; Young, Stanley G.

1991-01-01

Experimental process forms layer of high-critical-temperature ceramic superconductor YBa2Cu3O7-x on surface of copper substrate. Offers possible solution to problem of finishing ceramic superconductors to required final sizes and shapes (difficult problem because these materials brittle and cannot be machined or bent). Further research necessary to evaluate superconducting qualities of surface layers and optimize process.

Doubling the critical current density in superconducting FeSe 0.5Te 0.5 thin films by low temperature oxygen annealing

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

Zhang, Cheng; Si, Weidong; Li, Qiang

Iron chalcogenide superconducting thin films and coated conductors are attractive for potential high field applications at liquid helium temperature for their high critical current densities J c, low anisotropies, and relatively strong grain couplings. Embedding flux pinning defects is a general approach to increase the in-field performance of superconductors. However, many effective pinning defects can adversely affect the zero field or self-field J c, particularly in cuprate high temperature superconductors. Here, we report the doubling of the self-field J c in FeSe 0.5Te 0.5 films by low temperature oxygen annealing, reaching ~3 MA/cm 2. In-field performance is also dramatically enhanced.more » In conclusion, our results demonstrate that low temperature oxygen annealing is a simple and cost-efficient post-treatment technique which can greatly help to accelerate the potential high field applications of the iron-based superconductors.« less

57Fe Mössbauer study of Lu 2Fe 3Si 5 iron silicide superconductor

DOE PAGES

Ma, Xiaoming; Ran, Sheng; Pang, Hua; ...

2015-03-28

With the advent of Fe–As based superconductivity it has become important to study how superconductivity manifests itself in details of 57Fe Mössbauer spectroscopy of conventional, Fe-bearing superconductors. The iron-based superconductor Lu 2Fe 3Si 5 has been studied by 57Fe Mössbauer spectroscopy over the temperature range from 4.4 K to room temperature with particular attention to the region close to the superconducting transition temperature (T c=6.1 K). Consistent with the two crystallographic sites for Fe in this structure, the observed spectra appear to have a pattern consisting of two doublets over the whole temperature range. Furthermore, the value of Debye temperaturemore » was estimated from temperature dependence of the isomer shift and the total spectral area and compared with the specific heat capacity data. Neither abnormal behavior of the hyperfine parameters at or near T c, nor phonon softening were observed.« less

Doubling the critical current density in superconducting FeSe 0.5Te 0.5 thin films by low temperature oxygen annealing

DOE PAGES

Zhang, Cheng; Si, Weidong; Li, Qiang

2016-11-14

Iron chalcogenide superconducting thin films and coated conductors are attractive for potential high field applications at liquid helium temperature for their high critical current densities J c, low anisotropies, and relatively strong grain couplings. Embedding flux pinning defects is a general approach to increase the in-field performance of superconductors. However, many effective pinning defects can adversely affect the zero field or self-field J c, particularly in cuprate high temperature superconductors. Here, we report the doubling of the self-field J c in FeSe 0.5Te 0.5 films by low temperature oxygen annealing, reaching ~3 MA/cm 2. In-field performance is also dramatically enhanced.more » In conclusion, our results demonstrate that low temperature oxygen annealing is a simple and cost-efficient post-treatment technique which can greatly help to accelerate the potential high field applications of the iron-based superconductors.« less

Superconducting phonon spectroscopy using a low-temperature scanning tunneling microscope

NASA Technical Reports Server (NTRS)

Leduc, H. G.; Kaiser, W. J.; Hunt, B. D.; Bell, L. D.; Jaklevic, R. C.

1989-01-01

The low-temperature scanning tunneling microscope (STM) system described by LeDuc et al. (1987) was used to observe the phonon density of states effects in a superconductor. Using techniques based on those employed in macroscopic tunneling spectroscopy, electron tunneling current-voltage (I-V) spectra were measured for NbN and Pb, and dI/dV vs V spectra were measured using standard analog derivative techniques. I-V measurements on NbN and Pb samples under typical STM conditions showed no evidence for multiparticle tunneling effects.

New permanent magnets

NASA Astrophysics Data System (ADS)

Müller, K.-H.; Krabbes, G.; Fink, J.; Gruß, S.; Kirchner, A.; Fuchs, G.; Schultz, L.

2001-05-01

Permanent magnets play an important role and are widely spread in daily-life applications. Due to their very low costs, large availability of the row materials and their high chemical stability, hard ferrites are still dominant in the permanent magnet market although their relatively poor magnetic properties are a distinct disadvantage. Today's high-performance magnets are mostly made from Nd 2Fe 14B. The aim of research is to combine the large spontaneous magnetization of 3d metals with strong anisotropy fields known from rare-earth transition-metal compounds and, at the same time, to maintain a high value of the Curie temperature. However, the number of iron-rich rare-earth intermetallics is very limited and, consequently, not much success can be noted in this field for the last 10 years. One alternative concept is to use magnetic fields trapped in type II superconductors where much higher fields can be achieved compared to conventional rare-earth magnets. Very recently, we obtained a trapped field as high as 14.4 T in a melt-textured YBCO bulk sample of a few centimeters in diameter. This is the highest value ever achieved in a bulk superconductor. The trapped field of a superconductor is not governed by the Laplace equation and, therefore, levitation works without any additional (active) stabilization. The disadvantage of these magnets is their low working temperature (of liquid nitrogen and below).

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

Local charge-density change and superconductivity: A positron study

NASA Astrophysics Data System (ADS)

Jean, Y. C.; Sundar, C. S.; Bharathi, A.; Kyle, J.; Nakanishi, H.; Tseng, P. K.; Hor, P. H.; Meng, R. L.; Huang, Z. J.; Chu, C. W.; Wang, Z. Z.; Turchi, P. E. A.; Howell, R. H.; Wachs, A. L.; Fluss, M. J.

1990-03-01

The temperature dependence between 10 and 300 K of the positron lifetime was measured in the high-temperature superconductors YBA2(Cu1-xMx)3O6+δ, where M=Zn and Ga with x=0.0 to 0.07 and δ>0.8. In the undoped and Ga-doped samples, the positron lifetime in the Bloch state, τb, was observed to decrease below Tc. In the Zn-doped samples, a dramatic x-dependent temperature variation of τb was observed: from a decrease of Tb below Tc for x=0.01 to an increase of τb for x>0.02. These new experimental results are interpreted in terms of a change in the local charge density of high-Tc oxides associated with the superconducting transition.

L-dependence of low energy spin excitations in FeTe/Se superconductors

NASA Astrophysics Data System (ADS)

Xu, Guangyong; Xu, Zhijun; Schneeloch, John; Wen, Jinsheng; Winn, Barry; Zhao, Yang; Birgeneau, Robert; Gu, Genda; Tranquada, John

We will present neutron scattering measurements on low energy magnetic excitations from FeTe1-xSex (``11'' system) samples. Our work shows that the low energy magnetic excitations are dominated by 2D correlations in the superconducting (SC) compound at low temperature, with the L-dependence well described by the Fe magnetic form factor. However, at temperatures much higher than TC, the magnetic excitations become more three-dimensional with a clear change in the L-dependence. The low energy magnetic excitations from non-superconducting (NSC) samples, on the other hand, always exhibit three-dimensional features for the entire temperature range of our measurements. Our results suggest that in additional to in-plane correlations, the inter-plane spin correlations are also coupled to the superconducting properties in the ``11'' system.

Noncentrosymmetric superconductor BeAu

NASA Astrophysics Data System (ADS)

Amon, A.; Svanidze, E.; Cardoso-Gil, R.; Wilson, M. N.; Rosner, H.; Bobnar, M.; Schnelle, W.; Lynn, J. W.; Gumeniuk, R.; Hennig, C.; Luke, G. M.; Borrmann, H.; Leithe-Jasper, A.; Grin, Yu.

2018-01-01

Mixed spin-singlet and spin-triplet pairing can occur in noncentrosymmetric superconductors. In this respect, a comprehensive characterization of the noncentrosymmetric superconductor BeAu was carried out. It was established that BeAu undergoes a structural phase transition from a low-temperature noncentrosymmetric FeSi structure type to a high-temperature centrosymmetric structure in the CsCl type at Ts=860 K. The low-temperature modification exhibits a superconducting transition below Tc=3.3 K. The values of lower (Hc1=32 Oe) and upper (Hc2=335 Oe) critical fields are rather small, confirming that this type-II (κG-L=2.3 ) weakly coupled (λe-p=0.5 ,Δ Ce/γnTc≈1.26 ) superconductor can be well understood within the Bardeen-Cooper-Schrieffer theory. The muon spin relaxation analysis indicates that the time-reversal symmetry is preserved when the superconducting state is entered, supporting conventional superconductivity in BeAu. From the density functional band structure calculations, a considerable contribution of the Be electrons to the superconducting state was established. On average, a rather small mass renormalization was found, consistent with the experimental data.

Role of the orbital degree of freedom in iron-based superconductors

NASA Astrophysics Data System (ADS)

Yi, Ming; Zhang, Yan; Shen, Zhi-Xun; Lu, Donghui

2017-10-01

Almost a decade has passed since the serendipitous discovery of the iron-based high temperature superconductors (FeSCs) in 2008. The fact that, as in the copper oxide high temperature superconductors, long-range antiferromagnetism in the FeSCs arises in proximity to superconductivity immediately raised the question of the degree of similarity between the two. Despite the great resemblance in their phase diagrams, there exist important differences between the FeSCs and the cuprates that need to be considered in order to paint a full picture of these two families of high temperature superconductors. One of the key differences is the multi-orbital multi-band nature of the FeSCs, which contrasts with the effective single-band nature of the cuprates. Systematic studies of orbital related phenomena in FeSCs have been largely lacking. In this review, we summarize angle-resolved photoemission spectroscopy (ARPES) measurements across various FeSC families that have been reported in literature, focusing on the systematic trends of orbital dependent electron correlations and the role of different Fe 3d orbitals in driving the nematic transition, the spin-density-wave transition, and superconductivity.

Niobium-titanium superconductors produced by powder metallurgy having artificial flux pinning centers

DOEpatents

Jablonski, Paul D.; Larbalestier, David C.

1993-01-01

Superconductors formed by powder metallurgy have a matrix of niobium-titanium alloy with discrete pinning centers distributed therein which are formed of a compatible metal. The artificial pinning centers in the Nb-Ti matrix are reduced in size by processing steps to sizes on the order of the coherence length, typically in the range of 1 to 10 nm. To produce the superconductor, powders of body centered cubic Nb-Ti alloy and the second phase flux pinning material, such as Nb, are mixed in the desired percentages. The mixture is then isostatically pressed, sintered at a selected temperature and selected time to produce a cohesive structure having desired characteristics without undue chemical reaction, the sintered billet is reduced in size by deformation, such as by swaging, the swaged sample receives heat treatment and recrystallization and additional swaging, if necessary, and is then sheathed in a normal conducting sheath, and the sheathed material is drawn into a wire. The resulting superconducting wire has second phase flux pinning centers distributed therein which provide enhanced J.sub.ct due to the flux pinning effects.

Superconductivity, critical current density, and flux pinning in MgB2-x(SiC)x/2 superconductor after SiC nanoparticle doping

NASA Astrophysics Data System (ADS)

Dou, S. X.; Pan, A. V.; Zhou, S.; Ionescu, M.; Wang, X. L.; Horvat, J.; Liu, H. K.; Munroe, P. R.

2003-08-01

We investigated the effect of SiC nanoparticle doping on the crystal lattice structure, critical temperature Tc, critical current density Jc, and flux pinning in MgB2 superconductor. A series of MgB2-x(SiC)x/2 samples with x=0-1.0 were fabricated using an in situ reaction process. The contraction of the lattice and depression of Tc with increasing SiC doping level remained rather small most likely due to the counterbalancing effect of Si and C co-doping. The high level Si and C co-doping allowed the creation of intragrain defects and highly dispersed nanoinclusions within the grains which can act as effective pinning centers for vortices, improving Jc behavior as a function of the applied magnetic field. The enhanced pinning is mainly attributable to the substitution-induced defects and local structure fluctuations within grains. A pinning mechanism is proposed to account for different contributions of different defects in MgB2-x(SiC)x/2 superconductors.

Limitations in cooling electrons using normal-metal-superconductor tunnel junctions.

PubMed

Pekola, J P; Heikkilä, T T; Savin, A M; Flyktman, J T; Giazotto, F; Hekking, F W J

2004-02-06

We demonstrate both theoretically and experimentally two limiting factors in cooling electrons using biased tunnel junctions to extract heat from a normal metal into a superconductor. First, when the injection rate of electrons exceeds the internal relaxation rate in the metal to be cooled, the electrons do not obey the Fermi-Dirac distribution, and the concept of temperature cannot be applied as such. Second, at low bath temperatures, states within the gap induce anomalous heating and yield a theoretical limit of the achievable minimum temperature.

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.

Proximity effect in superconductor/ferromagnet hetero-structures as a function of interface properties

NASA Astrophysics Data System (ADS)

Sarmiento, Julio; Patino, Edgar J.

2014-03-01

Superconductor/ferromagnet heterostructures are currently a subject of strong research due to novel phenomena resulting from the proximity effect. Among the most investigated ones are the oscillations of the critical temperature as function of the ferromagnet thickness. The oscillatory behavior of Tc is theoretically explained as to be result of the generation of the FFLO (Fulde-Ferrel-Larkin-Ovchinnikov) state of Cooper pairs under the presence of the exchange field of the ferromagnet. With the advancement of experimental techniques for S/F bilayers growth new questions regarding the effect of the interface transparency can to be addressed. For instance the influence of the interface roughness on the proximity effect. For studying this phenomenon Nb/Co and Nb/Cu/Co samples were sputtered on SiO2 substrates with different roughness. Characterization of these samples show a significant variation of Tc with the interface roughness. This results point towards a possible relationship between transparency and roughness of the interface. Proyecto Semilla Facultad de Ciencias Universidad de los Andes.

Method of fabricating a (1223) Tl-Ba-Ca-Cu-O superconductor

DOEpatents

Tkaczyk, John Eric; Lay, Kenneth Wilbur; He, Qing

1997-01-01

A method is disclosed for fabricating a polycrystalline <223> thallium-containing superconductor having high critical current at elevated temperatures and in the presence of a magnetic field. A powder precursor containing compounds other than thallium is compressed on a substrate. Thallium is incorporated in the densified powder precursor at a high temperature in the presence of a partial pressure of a thallium-containing vapor.

Unusual two-dimensional behavior of iron-based superconductors with low anisotropy

NASA Astrophysics Data System (ADS)

Kalenyuk, A. A.; Pagliero, A.; Borodianskyi, E. A.; Aswartham, S.; Wurmehl, S.; Büchner, B.; Chareev, D. A.; Kordyuk, A. A.; Krasnov, V. M.

2017-10-01

We study angular-dependent magnetoresistance in iron-based superconductors Ba1 -xNaxFe2As2 and FeTe1 -xSex . Both superconductors have relatively small anisotropies γ ˜2 and exhibit a three-dimensional (3D) behavior at low temperatures. However, we observe that they start to exhibit a profound two-dimensional behavior at elevated temperatures and in applied magnetic field parallel to the surface. We conclude that the unexpected two-dimensional (2D) behavior of the studied low-anisotropic superconductors is not related to layeredness of the materials, but is caused by appearance of surface superconductivity when magnetic field exceeds the upper critical field Hc 2(T ) for destruction of bulk superconductivity. We argue that the corresponding 3D-2D bulk-to-surface dimensional transition can be used for accurate determination of the upper critical field.

Vortices in high-performance high-temperature superconductors

DOE PAGES

Kwok, Wai-Kwong; Welp, Ulrich; Glatz, Andreas; ...

2016-09-21

The behavior of vortex matter in high-temperature superconductors (HTS) controls the entire electromagnetic response of the material, including its current carrying capacity. In this paper, we review the basic concepts of vortex pinning and its application to a complex mixed pinning landscape to enhance the critical current and to reduce its anisotropy. We focus on recent scientific advances that have resulted in large enhancements of the in-field critical current in state-of-the-art second generation (2G) YBCO coated conductors and on the prospect of an isotropic, high-critical current superconductor in the iron-based superconductors. Finally, we discuss an emerging new paradigm of criticalmore » current by design—a drive to achieve a quantitative correlation between the observed critical current density and mesoscale mixed pinning landscapes by using realistic input parameters in an innovative and powerful large-scale time dependent Ginzburg–Landau approach to simulating vortex dynamics.« less

Selenium doping NaCl-type superconductor: SnAs1-xSex (x=0-0.13)

NASA Astrophysics Data System (ADS)

He, Jianqiao; Zhang, Xian; Lai, Xiaofang; Huang, Fuqiang

2017-08-01

Selenium doped NaCl-type superconductor SnAs1-xSex (x=0-0.13) were made through solid state reaction. EDS results show that Se content increases with Se doping until over doped in SnAs0.9Se0.1 and SnAs0.87Se0.13 (around 2.7%). PXRD patterns confirmed the main phase of the six doped samples are SnAs. The cell parameters of doped SnAs were calculated using Rietveld refinements. Their cell parameters increase almost linearly with x until x reaches 13%. Single crystal diffraction measurement results show that there are no interstitial atom in doped SnAs. We conclude that Se atoms are substitutional atoms in SnAs. The superconducting onset temperatures (Tconset, under a magnetic field of 10 Oe) of SnAs increased from 3.8 K to 4.5 K by 10% Se doping. ρ-T curves of 1%, 5% and 10% Se doped samples show that all the three samples are metallic. Upper critical field Hc2(0) of 1%, 5% and 10% Se doped samples are 294 Oe, 649 Oe and 1011 Oe, respectively.

Competing Quantum Orderings in Cuprate Superconductors:

NASA Astrophysics Data System (ADS)

Martin, I.; Ortiz, G.; Balatsky, A. V.; Bishop, A. R.

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra.

Interplay of Phonon and Exciton-Mediated Superconductivity in Hybrid Semiconductor-Superconductor Structures.

PubMed

Skopelitis, Petros; Cherotchenko, Evgenia D; Kavokin, Alexey V; Posazhennikova, Anna

2018-03-09

We predict a strong enhancement of the critical temperature in a conventional Bardeen-Cooper-Schrieffer (BCS) superconductor in the presence of a bosonic condensate of exciton polaritons. The effect depends strongly on the ratio of the cutoff frequencies for phonon and exciton-polariton mediated BCS superconductivity, respectively. We also discuss a possible design of hybrid semiconductor-superconductor structures suitable for the experimental observation of such an effect.

Investigation of the Feasibility of a Superconducting Self-Healing DC Grid on a LNG Carrier

DTIC Science & Technology

2015-06-21

art in High Temperature Superconductor technology is reviewed and an analytical approach of Superconducting DC Power Distribution on a power... Superconductors . I. INTRODUCTION During recent years, the usage of electrical power on- board vessels has grown exponentially. This fact, led...grid. When carrying DC current superconductors are perfectly lossless regardless of the cable length and the power rating of the line [1]. Also

Interplay of Phonon and Exciton-Mediated Superconductivity in Hybrid Semiconductor-Superconductor Structures

NASA Astrophysics Data System (ADS)

Skopelitis, Petros; Cherotchenko, Evgenia D.; Kavokin, Alexey V.; Posazhennikova, Anna

2018-03-01

We predict a strong enhancement of the critical temperature in a conventional Bardeen-Cooper-Schrieffer (BCS) superconductor in the presence of a bosonic condensate of exciton polaritons. The effect depends strongly on the ratio of the cutoff frequencies for phonon and exciton-polariton mediated BCS superconductivity, respectively. We also discuss a possible design of hybrid semiconductor-superconductor structures suitable for the experimental observation of such an effect.

Pressure-temperature phase diagrams of CaK(Fe1 -xNix)4As4 superconductors

NASA Astrophysics Data System (ADS)

Xiang, Li; Meier, William R.; Xu, Mingyu; Kaluarachchi, Udhara S.; Bud'ko, Sergey L.; Canfield, Paul C.

2018-05-01

The pressure dependence of the magnetic and superconducting transitions and that of the superconducting upper critical field are reported for CaK (Fe1-xNix) 4As4 , 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 TN are suppressed upon applying pressure; the superconducting transition temperatures Tc are suppressed by pressure as well, except for x =0.050 in the pressure region where TN and Tc cross. Furthermore, the pressure associated with the crossing of the TN and Tc 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. Finally, at p ˜4 GPa, both Ni-substituted CaK (Fe1-xNix) 4As4 samples likely go through a half-collapsed-tetragonal phase transition, similar to the parent compound CaKFe4As4 .

Hidden phase in parent Fe-pnictide superconductors

NASA Astrophysics Data System (ADS)

Ali, Khadiza; Adhikary, Ganesh; Thakur, Sangeeta; Patil, Swapnil; Mahatha, Sanjoy K.; Thamizhavel, A.; De Ninno, Giovanni; Moras, Paolo; Sheverdyaeva, Polina M.; Carbone, Carlo; Petaccia, Luca; Maiti, Kalobaran

2018-02-01

We investigate the origin of exoticity in Fe-based systems via studying the fermiology of CaFe2As2 employing angle-resolved photoemission spectroscopy. While the Fermi surfaces (FSs) at 200 K and 31 K are observed to exhibit two-dimensional and three-dimensional (3D) topology, respectively, the FSs at intermediate temperatures reveal the emergence of the 3D topology at a temperature much lower than the structural and magnetic phase transition temperature (170 K, for the sample under scrutiny). This leads to the conclusion that the evolution of FS topology is not directly driven by the structural transition. In addition, we discover the existence in ambient conditions of energy bands related to the cT phase. These bands are distinctly resolved in the high-photon energy spectra exhibiting strong Fe 3 d character. They gradually move to higher binding energies due to thermal compression with cooling, leading to the emergence of 3D topology in the Fermi surface. These results reveal the so-far hidden existence of a cT phase under ambient conditions, which is argued to lead to quantum fluctuations responsible for the exotic electronic properties in Fe-pnictide superconductors.

Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

PubMed Central

Guguchia, Z.; Amato, A.; Kang, J.; Luetkens, H.; Biswas, P. K.; Prando, G.; von Rohr, F.; Bukowski, Z.; Shengelaya, A.; Keller, H.; Morenzoni, E.; Fernandes, Rafael M.; Khasanov, R.

2015-01-01

The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap. PMID:26548650

Direct evidence for a pressure-induced nodal superconducting gap in the Ba 0.65Rb 0.35Fe 2As 2 superconductor

DOE PAGES

Guguchia, Z.; Amato, A.; Kang, J.; ...

2015-11-09

The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. Contrasting with other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba 0.65Rb 0.35Fe 2As 2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant.more » More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap.« less

Superconductor cable

DOEpatents

Allais, Arnaud; Schmidt, Frank; Marzahn, Erik

2010-05-04

A superconductor cable is described, having a superconductive flexible cable core (1) , which is laid in a cryostat (2, 3, 4), in which the cable core (1) runs in the cryostat (2, 3, 4) in the form of a wave or helix at room temperature.

Proposal of Magnetic Circuit using Magnetic Shielding with Bulk-Type High Tc Superconductors

NASA Astrophysics Data System (ADS)

Fukuoka, Katsuhiro; Hashimoto, Mitsuo; Tomita, Masaru; Murakami, Masato

Recently, bulk-type high Tc superconductors having a characteristic of critical current density over 104 A/cm2 in liquid nitrogen temperature (77K) on 1T, can be produced. They are promising for many practical applications such as a magnetic bearing, a magnetic levitation, a flywheel, a magnetic shielding and others. In this research, we propose a magnetic circuit that is able to use for the magnetic shield of plural superconductors as an application of bulk-type high Tc superconductors. It is a closed magnetic circuit by means of a toroidal core. Characteristics of the magnetic circuit surrounded with superconductors are evaluated and the possibility is examined. As the magnetic circuit of the ferrite core is surrounded with superconductors, the magnetic flux is shielded even if it leaked from the ferrite core.

Techniques for Connecting Superconducting Thin Films

NASA Technical Reports Server (NTRS)

Mester, John; Gwo, Dz-Hung

2006-01-01

Several improved techniques for connecting superconducting thin films on substrates have been developed. The techniques afford some versatility for tailoring the electronic and mechanical characteristics of junctions between superconductors in experimental electronic devices. The techniques are particularly useful for making superconducting or alternatively normally conductive junctions (e.g., Josephson junctions) between patterned superconducting thin films in order to exploit electron quantum-tunneling effects. The techniques are applicable to both low-Tc and high-Tc superconductors (where Tc represents the superconducting- transition temperature of a given material), offering different advantages for each. Most low-Tc superconductors are metallic, and heretofore, connections among them have been made by spot welding. Most high-Tc superconductors are nonmetallic and cannot be spot welded. These techniques offer alternatives to spot welding of most low-Tc superconductors and additional solutions to problems of connecting most high-Tc superconductors.

Holographic superconductors in the presence of dark matter

NASA Astrophysics Data System (ADS)

Rogatko, Marek; Wysokiński, Karol I.

2017-10-01

The application of the gauge-gravity duality, also known as anti-de Sitter/conformal field theory (AdS/CFT) correspondence to study condensed matter systems has resulted in a number of important findings. Using the analogy, we have studied the phase transitions between a holographic insulator and a metal at zero temperature as well as finite temperature transition between a metal and a holographic superconductor of s- and p-wave symmetry. The main aim of this note is to look in which way the dark matter might affect the properties of superconductors. The hope is that some of the observed modifications could be used to detect this ubiquitous but still elusive component of matter in the Universe.

Dependence of transition temperature on hole concentration per CuO2 sheet in the Bi-based superconductors

NASA Technical Reports Server (NTRS)

Zhao, J.; Seehra, M. S.

1991-01-01

The recently observed variations of the transition temperature (T sub c) with oxygen content in the Bi based (2212) and (2223) superconductors are analyzed in terms of p+, the hole concentration per CuO2 sheet. This analysis shows that in this system, T sub c increases with p+ initially, reaching maxima at p+ = 0.2 approx. 0.3, followed by monotonic decrease of T sub c with p+. The forms of these variations are similar to those observed in the La(2-x)Sr(x)CuO4 and YBa2Cu3Oy systems, suggesting that p+ may be an important variable governing superconductivity in the cuprate superconductors.

Absence of time-reversal symmetry breaking in the noncentrosymmetric superconductor Mo3Al2C

NASA Astrophysics Data System (ADS)

Bauer, E.; Sekine, C.; Sai, U.; Rogl, P.; Biswas, P. K.; Amato, A.

2014-08-01

Zero-field muon spin rotation and relaxation (μSR) studies carried out on the strongly coupled, noncentrosymmetric superconductor Mo3Al2C,Tc=9 K, did not reveal hints of time-reversal symmetry breaking as was found for a number of other noncentrosymmetric systems. Transverse field measurements performed above and below the superconducting transition temperature defined the temperature dependent London penetration depth, which in turn served to derive from a microscopic point of view a simple s-wave superconducting state in Mo3Al2C. The present investigations also provide fairly solid grounds to conclude that time-reversal symmetry breaking is not an immanent feature of noncentrosymmetric superconductors.

One-dimensional backreacting holographic superconductors with exponential nonlinear electrodynamics

NASA Astrophysics Data System (ADS)

Ghotbabadi, B. Binaei; Zangeneh, M. Kord; Sheykhi, A.

2018-05-01

In this paper, we investigate the effects of nonlinear exponential electrodynamics as well as backreaction on the properties of one-dimensional s-wave holographic superconductors. We continue our study both analytically and numerically. In analytical study, we employ the Sturm-Liouville method while in numerical approach we perform the shooting method. We obtain a relation between the critical temperature and chemical potential analytically. Our results show a good agreement between analytical and numerical methods. We observe that the increase in the strength of both nonlinearity and backreaction parameters causes the formation of condensation in the black hole background harder and critical temperature lower. These results are consistent with those obtained for two dimensional s-wave holographic superconductors.

Temperature dependent local atomic displacements in ammonia intercalated iron selenide superconductor

NASA Astrophysics Data System (ADS)

Paris, E.; Simonelli, L.; Wakita, T.; Marini, C.; Lee, J.-H.; Olszewski, W.; Terashima, K.; Kakuto, T.; Nishimoto, N.; Kimura, T.; Kudo, K.; Kambe, T.; Nohara, M.; Yokoya, T.; Saini, N. L.

2016-06-01

Recently, ammonia-thermal reaction has been used for molecular intercalation in layered FeSe, resulting a new Lix(NH3)yFe2Se2 superconductor with Tc ~ 45 K. Here, we have used temperature dependent extended x-ray absorption fine structure (EXAFS) to investigate local atomic displacements in single crystals of this new superconductor. Using polarized EXAFS at Fe K-edge we have obtained direct information on the local Fe-Se and Fe-Fe bondlengths and corresponding mean square relative displacements (MSRD). We find that the Se-height in the intercalated system is lower than the one in the binary FeSe, suggesting compressed FeSe4 tetrahedron in the title system. Incidentally, there is hardly any effect of the intercalation on the bondlengths characteristics, revealed by the Einstein temperatures, that are similar to those found in the binary FeSe. Therefore, the molecular intercalation induces an effective compression and decouples the FeSe slabs. Furthermore, the results reveal an anomalous change in the atomic correlations across Tc, appearing as a clear decrease in the MSRD, indicating hardening of the local lattice mode. Similar response of the local lattice has been found in other families of superconductors, e.g., A15-type and cuprates superconductors. This observation suggests that local atomic correlations should have some direct correlation with the superconductivity.

Mechanism of the high transition temperature for the 1111-type iron-based superconductors R FeAsO (R =rare earth ): Synergistic effects of local structures and 4 f electrons

NASA Astrophysics Data System (ADS)

Zhang, Lifang; Meng, Junling; Liu, Xiaojuan; Yao, Fen; Meng, Jian; Zhang, Hongjie

2017-07-01

Among the iron-based superconductors, the 1111-type Fe-As-based superconductors REFeAs O1 -xFx (RE = rare earth) exhibit high transition temperatures (Tc) above 40 K. We perform first-principles calculations based on density functional theory with the consideration of both electronic correlations and spin-orbit couplings on rare earths and Fe ions to study the underlying mechanism as the microscopic structural distortions in REFeAsO tuned by both lanthanide contraction and external strain. The electronic structures evolve similarly in both cases. It is found that there exist an optimal structural regime that will not only initialize but also optimize the orbital fluctuations due to the competing Fe-As and Fe-Fe crystal fields. We also find that the key structural features in REFeAsO, such as As-Fe-As bond angle, intrinsically induce the modification of the Fermi surface and dynamic spin fluctuation. These results suggest that the superconductivity is mediated by antiferromagnetic spin fluctuations. Simultaneously, we show that the rare-earth 4 f electrons play important roles on the high transition temperature whose behavior might be analogous to that of the heavy-fermion superconductors. The superconductivity of these 1111-type iron-based superconductors with high-Tc is considered to originate from the synergistic effects of local structures and 4 f electrons.

The use of high temperature superconductors to levitate lunar telescope

NASA Technical Reports Server (NTRS)

Brown, Beth A.

1992-01-01

The objective of this paper was to assist in the construction of a lunar telescope mirror model by conducting research on composite materials and other lightweight, rigid materials, and by determining how much weight can be levitated by available superconductors. It is believed that with the construction of four magnets suspended over four bulk superconductors (or vice versa), there should be no problems lifting a model mirror and stabilizing it at different positions. It may be necessary to increase the size and quality of the superconductors and/or magnets in order to achieve this.

"Fluctuoscopy" of Superconductors

NASA Astrophysics Data System (ADS)

Varlamov, A. A.

Study of fluctuation phenomena in superconductors (SCs) is the subject of great fundamental and practical importance. Understanding of their physics allowed to clear up the fundamental properties of SC state. Being predicted in 1968, one of the fluctuation effects, namely paraconductivity, was experimentally observed almost simultaneously. Since this time, fluctuations became a noticeable part of research in the field of superconductivity, and a variety of fluctuation effects have been discovered. The new wave of interest to fluctuations (FL) in superconductors was generated by the discovery of cuprate oxide superconductors (high-temperature superconductors, HTS), where, due to extremely short coherence length and low effective dimensionality of the electron system, superconductive fluctuations manifest themselves in a wide range of temperatures. Moreover, anomalous properties of the normal state of HTS were attributed by many theorists to strong FL in these systems. Being studied in the framework of the phenomenological Ginzburg-Landau theory and, more extensively, in diagrammatic microscopic approach, SC FLs side by side with other quantum corrections (weak localization, etc.) became a new tool for investigation and characterization of such new systems as HTS, disordered electron systems, granular metals, Josephson structures, artificial super-lattices, etc. The characteristic feature of SC FL is their strong dependence on temperature and magnetic fields in the vicinity of phase transition. This allows one to definitely separate the fluctuation effects from other contributions and to use them as the source of information about the microscopic parameters of a material. By their origin, SC FLs are very sensitive to relaxation processes, which break phase coherence. This allows using them for versatile characterization of SC. Today, one can speak about the " fluctuoscopy" of superconductive systems. In review, we present the qualitative picture both of thermodynamic fluctuations close to critical temperature T c0and quantum fluctuations at zero temperature and in vicinity of the second critical field H c2(0). Then in the frameworks of the Ginzburg-Landau theory, we discuss the characteristic crossovers in fluctuation properties of superconductive nanoparticles and layered superconductors. We present the general expression for fluctuation magneto-conductivity valid through all phase diagram of superconductor and apply it to study of the quantum phase transition close to H c2(0). Fluctuation analysis of this transition allows us to present the scenario of fluctuation defragmentation of the Abrikosov lattice.

Composite Ceramic Superconducting Wires for Electric Motor Applications

DTIC Science & Technology

1989-07-07

generators that have been built using NbTi superconducting wire at liquid 3 helium temperature (4.2*K). Most of these magnets , motors, and generators have...temperature superconductors. A magnetic diffusivity value cannot be rigorously determined for the superconductor in the superconducting state when flux jump...cv, FIRST ANNUAL REPORT FOR THE PROJECT "COMPOSITE CERAMIC SUPERCONDUCTING WIRES FOR ELECTRIC MOTOR APPLICATIONS" 2 PRIME CONTRACTOR CERAMICS PROCESS

Method of fabricating a (1223) Tl-Ba-Ca-Cu-O superconductor

DOEpatents

Tkaczyk, J.E.; Lay, K.W.; He, Q.

1997-07-08

A method is disclosed for fabricating a polycrystalline <223> thallium-containing superconductor having high critical current at elevated temperatures and in the presence of a magnetic field. A powder precursor containing compounds other than thallium is compressed on a substrate. Thallium is incorporated in the densified powder precursor at a high temperature in the presence of a partial pressure of a thallium-containing vapor. 2 figs.

Angle dependent defect modes in a photonic crystal filter doped by high and low temperature superconductor defects

NASA Astrophysics Data System (ADS)

Sreejith K., P.; Mathew, Vincent

2018-05-01

We have theoretically investigated the incident angle dependent defect modes in a dual channel photonic crystal filter composed of a high and low temperature superconductor defects. It is observed that the defect mode wavelength can be significantly tuned by incident angle for both polarizations. The angle sensitive defect mode property is of particular application in designing narrow band transmission filter.

Process for preparing high-transition-temperature superconductors in the Nb-Al-Ge system

DOEpatents

Giorgi, A.L.; Szklarz, E.G.

1973-01-30

The patent describes a process for preparing superconducting materials in the Nb-Al-Ge system having transition temperatures in excess of 19K. The process comprises premixing powdered constituents, pressing them into a plug, heating the plug to 1,450-1,800C for 30 minutes to an hour under vacuum or an inert atmosphere, and annealing at moderate temperatures for reasonably long times (approximately 50 hours). High transition-temperature superconductors, including those in the Nb3(Al,Ge) system, prepared in accordance with this process exhibit little degradation in the superconducting transition temperature on being ground to -200 mesh powder. (GRA)

Nearly Perfect Fluidity in a High Temperature Superconductor

DOE PAGES

Rameau, J. D.; Reber, T. J.; Yang, H. -B.; ...

2014-10-13

Perfect fluids are characterized as having the smallest ratio of shear viscosity to entropy density, η/s, consistent with quantum uncertainty and causality. So far, nearly perfect fluids have only been observed in the quark-gluon plasma and in unitary atomic Fermi gases, exotic systems that are amongst the hottest and coldest objects in the known universe, respectively. We use angle resolved photoemission spectroscopy to measure the temperature dependence of an electronic analog of η/s in an optimally doped cuprate high-temperature superconductor, finding it too is a nearly perfect fluid around, and above, its superconducting transition temperature T c.

Nearly perfect fluidity in a high-temperature superconductor

NASA Astrophysics Data System (ADS)

Rameau, J. D.; Reber, T. J.; Yang, H.-B.; Akhanjee, S.; Gu, G. D.; Johnson, P. D.; Campbell, S.

2014-10-01

Perfect fluids are characterized as having the smallest ratio of shear viscosity to entropy density, η /s, consistent with quantum uncertainty and causality. So far, nearly perfect fluids have only been observed in the quark-gluon plasma and in unitary atomic Fermi gases, exotic systems that are amongst the hottest and coldest objects in the known universe, respectively. We use angle resolved photoemission spectroscopy to measure the temperature dependence of an electronic analog of η /s in an optimally doped cuprate high-temperature superconductor, finding it too is a nearly perfect fluid around, and above, its superconducting transition temperature Tc.

Modeling and simulating vortex pinning and transport currents for high temperature superconductors

NASA Astrophysics Data System (ADS)

Sockwell, K. Chad

Superconductivity is a phenomenon characterized by two hallmark properties, zero electrical resistance and the Meissner effect. These properties give great promise to a new generation of resistance free electronics and powerful superconducting magnets. However this possibility is limited by the extremely low critical temperature the superconductors must operate under, typically close to 0K. The recent discovery of high temperature superconductors has brought the critical temperature closer to room temperature than ever before, making the realization of room temperature superconductivity a possibility. Simulations of superconducting technology and materials will be necessary to usher in the new wave of superconducting electronics. Unfortunately these new materials come with new properties such as effects from multiple electron bands, as is the case for magnesium diboride. Moreover, we must consider that all high temperature superconductors are of a Type II variety, which possess magnetic tubes of flux, known as vortices. These vortices interact with transport currents, creating an electrical resistance through a process known as flux flow. Thankfully this process can be prevented by placing impurities in the superconductor, pinning the vortices, making vortex pinning a necessary aspect of our model. At this time there are no other models or simulations that are aimed at modeling vortex pinning, using impurities, in two-band materials. In this work we modify an existing Ginzburg-Landau model for two-band superconductors and add the ability to model normal inclusions (impurities) with a new approach which is unique to the two-band model. Simulations in an attempt to model the material magnesium diboride are also presented. In particular simulations of vortex pinning and transport currents are shown using the modified model. The qualitative properties of magnesium diboride are used to validate the model and its simulations. One main goal from the computational end of the simulations is to enlarge the domain size to produce more realistic simulations that avoid boundary pinning effects. In this work we also implement the numerical software library Trilinos in order to parallelize the simulation to enlarge the domain size. Decoupling methods are also investigated with a goal of enlarging the domain size as well. The One-Band Ginzburg-Landau model serves as a prototypical problem in this endeavor and the methods shown that enlarge the domain size can be easily implemented in the two-band model.

Pressure-decoupled magnetic and structural transitions of the parent compound of iron-based 122 superconductors BaFe2As2

PubMed Central

Wu, J. J.; Lin, Jung-Fu; Wang, X. C.; Liu, Q. Q.; Zhu, J. L.; Xiao, Y. M.; Chow, P.; Jin, Changqing

2013-01-01

The recent discovery of iron ferropnictide superconductors has received intensive concern in connection with magnetically involved superconductors. Prominent features of ferropnictide superconductors are becoming apparent: the parent compounds exhibit an antiferromagnetic ordered spin density wave (SDW) state, the magnetic-phase transition is always accompanied by a crystal structural transition, and superconductivity can be induced by suppressing the SDW phase via either chemical doping or applied external pressure to the parent state. These features generated considerable interest in the interplay between magnetism and structure in chemically doped samples, showing crystal structure transitions always precede or coincide with magnetic transition. Pressure-tuned transition, on the other hand, would be more straightforward to superconducting mechanism studies because there are no disorder effects caused by chemical doping; however, remarkably little is known about the interplay in the parent compounds under controlled pressure due to the experimental challenge of in situ measuring both of magnetic and crystal structure evolution at high pressure and low temperatures. Here we show from combined synchrotron Mössbauer and X-ray diffraction at high pressures that the magnetic ordering surprisingly precedes the structural transition at high pressures in the parent compound BaFe2As2, in sharp contrast to the chemical-doping case. The results can be well understood in terms of the spin fluctuations in the emerging nematic phase before the long-range magnetic order that sheds light on understanding how the parent compound evolves from a SDW state to a superconducting phase, a key scientific inquiry of iron-based superconductors. PMID:24101468

Competing quantum orderings in cuprate superconductors: A minimal model

NASA Astrophysics Data System (ADS)

Martin, I.; Ortiz, G.; Balatsky, A. V.; Bishop, A. R.

2001-02-01

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra.

Transport critical current measurement apparatus using liquid nitrogen cooled high-Tc superconducting magnet with variable temperature insert

NASA Astrophysics Data System (ADS)

Nishijima, G.; Kitaguchi, H.; Tshuchiya, Y.; Nishimura, T.; Kato, T.

2013-01-01

We have developed an apparatus to investigate transport critical current (Ic) as a function of magnetic field and temperature using only liquid nitrogen. The apparatus consists of a (Bi,Pb)2Sr2Ca2Cu3O10 (Bi-2223) superconducting magnet, an outer dewar, and a variable temperature insert (VTI). The magnet, which is operated in depressurized liquid nitrogen, generates magnetic field up to 1.26 T. The sample is also immersed in liquid nitrogen. The pressure in the VTI is controlled from 0.02 to 0.3 MPa, which corresponds to temperature ranging from 66 to 88 K. We have confirmed the long-term stable operation of the Bi-2223 magnet at 1 T. The temperature stability of the sample at high transport current was also demonstrated. The apparatus provides easy-operating Ic measurement environment for a high-Tc superconductor up to 500 A in magnetic fields up to 1 T and in temperatures ranging from 66 to 88 K.

Scanning Probe Microscopies and Their Applications Towards the Study of Superconductors

NASA Astrophysics Data System (ADS)

Helfrich, Jennifer Ann

1995-11-01

The invention of the scanning tunneling microscope (STM) in 1982 made it possible to study surfaces and structures at resolutions previously believed unattainable. Adapting the STM for low temperatures makes it possible to study superconductors with new methods and to obtain valuable information. This thesis describes a novel low temperature STM (LTSTM) that was designed and built at Northwestern University for the purpose of studying superconductors in the mixed state. At low temperatures, this LTSTM has a scan range an order of magnitude larger than other LTSTM's designed elsewhere. It is capable of low temperature imaging and obtaining dI/dV vs. V curves. A detailed study of magnetic force microscopy (MFM) probes is also presented. The fields and forces between probe and surface were computer modeled. These results are compared with results from electron holographs of MFM probes. The final section of the thesis describes an a.c. susceptibility measurement on a UPt_3 sphere. Results are presented and discussed.

Breakdown of single spin-fluid model in the heavily hole-doped superconductor CsFe2As2

NASA Astrophysics Data System (ADS)

Zhao, D.; Li, S. J.; Wang, N. Z.; Li, J.; Song, D. W.; Zheng, L. X.; Nie, L. P.; Luo, X. G.; Wu, T.; Chen, X. H.

2018-01-01

Although Fe-based superconductors are correlated electronic systems with multiorbital, previous nuclear magnetic resonance (NMR) measurement suggests that a single spin-fluid model is sufficient to describe its spin behavior. Here, we first observed the breakdown of single spin-fluid model in a heavily hole-doped Fe-based superconductor CsFe2As2 by site-selective NMR measurement. At high-temperature regime, both Knight shift and nuclear spin-lattice relaxation at 133Cs and 75As nuclei exhibit distinct temperature-dependent behavior, suggesting the breakdown of the single spin-fluid model in CsFe2As2 . This is ascribed to the coexistence of both localized and itinerant spin degree of freedom at 3 d orbitals, which is consistent with the orbital-selective Mott phase. With decreasing temperature, the single spin-fluid behavior is recovered below T*˜75 K due to a coherent state among 3 d orbitals. The Kondo liquid scenario is proposed to understand the low-temperature coherent state.

A novel heat engine for magnetizing superconductors

NASA Astrophysics Data System (ADS)

Coombs, T. A.; Hong, Z.; Zhu, X.; Krabbes, G.

2008-03-01

The potential of bulk melt-processed YBCO single domains to trap significant magnetic fields (Tomita and Murakami 2003 Nature 421 517-20 Fuchs et al 2000 Appl. Phys. Lett. 76 2107-9) at cryogenic temperatures makes them particularly attractive for a variety of engineering applications including superconducting magnets, magnetic bearings and motors (Coombs et al 1999 IEEE Trans. Appl. Supercond. 9 968-71 Coombs et al 2005 IEEE Trans. Appl. Supercond. 15 2312-5). It has already been shown that large fields can be obtained in single domain samples at 77 K. A range of possible applications exist in the design of high power density electric motors (Jiang et al 2006 Supercond. Sci. Technol. 19 1164-8). Before such devices can be created a major problem needs to be overcome. Even though all of these devices use a superconductor in the role of a permanent magnet and even though the superconductor can trap potentially huge magnetic fields (greater than 10 T) the problem is how to induce the magnetic fields. There are four possible known methods: (1) cooling in field; (2) zero field cooling, followed by slowly applied field; (3) pulse magnetization; (4) flux pumping. Any of these methods could be used to magnetize the superconductor and this may be done either in situ or ex situ. Ideally the superconductors are magnetized in situ. There are several reasons for this: first, if the superconductors should become demagnetized through (i) flux creep, (ii) repeatedly applied perpendicular fields (Vanderbemden et al 2007 Phys. Rev. B 75 (17)) or (iii) by loss of cooling then they may be re-magnetized without the need to disassemble the machine; secondly, there are difficulties with handling very strongly magnetized material at cryogenic temperatures when assembling the machine; thirdly, ex situ methods would require the machine to be assembled both cold and pre-magnetized and would offer significant design difficulties. Until room temperature superconductors can be prepared, the most efficient design of machine will therefore be one in which an in situ magnetizing fixture is included. The first three methods all require a solenoid which can be switched on and off. In the first method an applied magnetic field is required equal to the required magnetic field, whilst the second and third approaches require fields at least two times greater. The final method, however, offers significant advantages since it achieves the final required field by repeated applications of a small field and can utilize a permanent magnet (Coombs 2007 British Patent GB2431519 granted 2007-09-26). If we wish to pulse a field using, say, a 10 T magnet to magnetize a 30 mm × 10 mm sample then we can work out how big the solenoid needs to be. If it were possible to wind an appropriate coil using YBCO tape then, assuming an Ic of 70 A and a thickness of 100 µm, we would have 100 turns and 7000 A turns. This would produce a B field of approximately 7000/(20 × 10-3) × 4π × 10-7 = 0.4 T. To produce 10 T would require pulsing to 1400 A! An alternative calculation would be to assume a Jc of say 5 × 108A m-1 and a coil 1 cm2 in cross section. The field would then be 5 × 108 × 10-2 × (2 × 4π × 10-7) = 10 T. Clearly if the magnetization fixture is not to occupy more room than the puck itself then a very high activation current would be required and either constraint makes in situ magnetization a very difficult proposition. What is required for in situ magnetization is a magnetization method in which a relatively small field of the order of millitesla repeatedly applied is used to magnetize the superconductor. This paper describes a novel method for achieving this.

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

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

Shi, Xiaoyan, E-mail: xshi@sandia.gov; Pan, W.; Hawkins, S. D.

2015-10-07

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

Controllable morphology of flux avalanches in microstructured superconductors

NASA Astrophysics Data System (ADS)

Motta, M.; Colauto, F.; Vestgârden, J. I.; Fritzsche, J.; Timmermans, M.; Cuppens, J.; Attanasio, C.; Cirillo, C.; Moshchalkov, V. V.; Van de Vondel, J.; Johansen, T. H.; Ortiz, W. A.; Silhanek, A. V.

2014-04-01

The morphology of abrupt bursts of magnetic flux into superconducting films with engineered periodic pinning centers (antidots) has been investigated. Guided flux avalanches of thermomagnetic origin develop a treelike structure, with the main trunk perpendicular to the borders of the sample, while secondary branches follow well-defined directions determined by the geometrical details of the underlying periodic pinning landscape. Strikingly, we demonstrate that in a superconductor with relatively weak random pinning the morphology of such flux avalanches can be fully controlled by proper combinations of lattice symmetry and antidot geometry. Moreover, the resulting flux patterns can be reproduced, to the finest details, by simulations based on a phenomenological thermomagnetic model. In turn, this model can be used to predict such complex structures and to estimate physical variables of more difficult experimental access, such as the local values of temperature and electric field.

Nondestructive x-ray Scattering Characterization of High Temperature Superconducting Wires

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

Thurston, T R

The purpose of this CRADA was to characterize the structural properties of the superconductor material within the wires in order to determine which processing procedures produce the best superconductor texture and phase development, and hence the best ultimate current carrying capacity.

Emergent Phenomena at Mott Interfaces

DTIC Science & Technology

2016-03-11

that is in quantitative agreement with the transition temperature. The behavior begs a comparison with tunneling experiments in superconductors ...ascribe these peaks to a single superconductor – 54 normal (SN) interface; an SNS junction would give a large 55 superconducting peak at zero bias27. For

Spray-Deposited Superconductor/Polymer Coatings

NASA Technical Reports Server (NTRS)

Wise, Stephanie A.; Tran, Sang Q.; Hooker, Matthew W.

1993-01-01

Coatings that exhibit the Meissner effect formed at relatively low temperature. High-temperature-superconductor/polymer coatings that exhibit Meissner effect deposited onto components in variety of shapes and materials. Simple, readily available equipment needed in coating process, mean coatings produced economically. Coatings used to keep magnetic fields away from electronic circuits in such cryogenic applications as magnetic resonance imaging and detection of infrared, and in magnetic suspensions to provide levitation and/or damping of vibrations.

Disorder-induced inhomogeneities of the superconducting state close to the superconductor-insulator transition.

PubMed

Sacépé, B; Chapelier, C; Baturina, T I; Vinokur, V M; Baklanov, M R; Sanquer, M

2008-10-10

Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconducting titanium nitride thin films reveals strong spatial inhomogeneities of the superconducting gap Delta in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature Tc towards zero, enhancement of spatial fluctuations in Delta, and growth of the Delta/Tc ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.

Acoustic thermometry for detecting quenches in superconducting coils and conductor stacks

NASA Astrophysics Data System (ADS)

Marchevsky, M.; Gourlay, S. A.

2017-01-01

Quench detection capability is essential for reliable operation and protection of superconducting magnets, coils, cables, and machinery. We propose a quench detection technique based on sensing local temperature variations in the bulk of a superconducting winding by monitoring its transient acoustic response. Our approach is primarily aimed at coils and devices built with high-temperature superconductor materials where quench detection using standard voltage-based techniques may be inefficient due to the slow velocity of quench propagation. The acoustic sensing technique is non-invasive, fast, and capable of detecting temperature variations of less than 1 K in the interior of the superconductor cable stack in a 77 K cryogenic environment. We show results of finite element modeling and experiments conducted on a model superconductor stack demonstrating viability of the technique for practical quench detection, discuss sensitivity limits of the technique, and its various applications.

Magnetic suspension using high temperature superconducting cores

NASA Technical Reports Server (NTRS)

Scurlock, R. G.

1992-01-01

The development of YBCO high temperature superconductors, in wire and tape forms, is rapidly approaching the point where the bulk transport current density j vs magnetic field H characteristics with liquid nitrogen cooling will enable its use in model cores. On the other hand, BSCCO high temperature superconductor in wire form has poor j-H characteristics at 77 K today, although with liquid helium or hydrogen cooling, it appears to be superior to NbTi superconductor. Since liquid nitrogen cooling is approx. 100 times cheaper than liquid helium cooling, the use of YBCO is very attractive for use in magnetic suspension. The design is discussed of a model core to accommodate lift and drag loads up to 6000 and 3000 N respectively. A comparison is made between the design performance of a liquid helium cooled NbTi (or BSCCO) superconducting core and a liquid nitrogen cooled YBCO superconducting core.

Variation of transition temperatures and residual resistivity ratio in vapor-grown FeSe

DOE PAGES

Böhmer, A. E.; Taufour, V.; Straszheim, W. E.; ...

2016-07-29

The study of the iron-based superconductor FeSe has blossomed with the availability of high-quality single crystals, obtained through flux/vapor-transport growth techniques below the structural transformation temperature of its tetragonal phase, T≈450°C. Here, we report on the variation of sample morphology and properties due to small modifications in the growth conditions. A considerable variation of the superconducting transition temperature T c, from 8.8 K to 3 K, which cannot be correlated with the sample composition, is observed. Instead, we point out a clear correlation between T c and disorder, as measured by the residual resistivity ratio. Notably, the tetragonal-to-orthorhombic structural transitionmore » is also found to be quite strongly disorder dependent (T s≈72–90K) and linearly correlated with T c.« less

Unconventional superconductivity in Y5Rh6Sn18 probed by muon spin relaxation

PubMed Central

Bhattacharyya, Amitava; Adroja, Devashibhai; Kase, Naoki; Hillier, Adrian; Akimitsu, Jun; Strydom, Andre

2015-01-01

Conventional superconductors are robust diamagnets that expel magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high—temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor Y5Rh6Sn18 ( TC= 3.0 K). The electronic heat capacity of Y5Rh6Sn18 shows a T3 dependence below Tc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu5Rh6Sn18 which is a strong coupling s—wave superconductor. The temperature dependence of the deduced superfluid in density Y5Rh6Sn18 is consistent with a BCS s—wave gap function, while the zero-field muon spin relaxation measurements strongly evidences unconventional superconductivity through a spontaneous appearance of an internal magnetic field below the superconducting transition temperature, signifying that the superconducting state is categorized by the broken time-reversal symmetry. PMID:26286229

Positron annihilation studies in the Nd-Ce-Cu-O superconductor

NASA Astrophysics Data System (ADS)

Sundar, C. S.; Bharathi, A.; Jean, Y. C.; Hor, P. H.; Meng, R. L.; Huang, Z. J.; Chu, C. W.

1990-07-01

In the superconducting Nd1.85Ce0.15CuO3.98, the positron lifetime is observed to decrease from 211 to 205 ps in the temperature range of 150-50 K, whereas in the nonsuperconducting Nd1.85Ce0.15CuO4, having a lifetime value of 231 ps, no significant temperature dependence of lifetime is observed. The difference in the lifetimes of the superconducting and nonsuperconducting samples and their temperature dependencies are understood in terms of positron interaction with the vacancies in the system. Doppler-broadened line shapes of energy spectra are found to show similar results as lifetime measurements. Theoretical calculations are used to show that the oxygen vacancies are weaker traps compared with the vacancies at the Cu and Nd sites. The observed decrease in lifetime in the superconducting sample is interpreted in terms of an increase in the fraction of positrons trapped at the oxygen vacancies as the temperature is lowered. Plausible reasons for the temperature independence of lifetime across Tc in the superconducting sample are discussed.

Measurements of the microwave conductivity of the organic superconductor ET2 (IAuI)

NASA Astrophysics Data System (ADS)

Tanner, D. B.; Jacobsen, C. S.; Williams, J. M.; Wang, H. H.

The microwave conductivity of ET2(IAuI), which is superconducting below 4 K, has been measured between 20 and 300 K. The measurements were done by cavity perturbation at 35 GHz for electric field along the highly conducting direction. The samples were in the skin-depth limit. The room temperature conductivity is quite low, approximately 6 mu/cm. With a decrease in temperature the conductivity increases as T sup -2 reaching nearly 900 mu/cm at 20 K. These values are rather close to extrapolations of the frequency-dependent conductivity determined from far-infrared experiments.

High temperature superconductor analog electronics for millimeter-wavelength communications

NASA Technical Reports Server (NTRS)

Romanofsky, R. R.; Bhasin, K. B.

1991-01-01

The performance of high temperature superconductor (HTS) passive microwave circuits up to X-band was encouraging when compared to their metallic counterparts. The extremely low surface resistance of HTS films up to about 10 GHz enables a reduction in loss by as much as 100 times compared to copper when both materials are kept at about 77 K. However, a superconductor's surface resistance varies in proportion to the frequency squared. Consequently, the potential benefit of HTS materials to millimeter-wave communications requires careful analysis. A simple ring resonator was used to evaluate microstrip losses at Ka-band. Additional promising components were investigated such as antennas and phase shifters. Prospects for HTS to favorable impact millimeter-wave communications systems are discussed.

Topologically protected charge transfer along the edge of a chiral p -wave superconductor

NASA Astrophysics Data System (ADS)

Gnezdilov, N. V.; van Heck, B.; Diez, M.; Hutasoit, Jimmy A.; Beenakker, C. W. J.

2015-09-01

The Majorana fermions propagating along the edge of a topological superconductor with px+i py pairing deliver a shot noise power of 1/2 ×e2/h per eV of voltage bias. We calculate the full counting statistics of the transferred charge and find that it becomes trinomial in the low-temperature limit, distinct from the binomial statistics of charge-e transfer in a single-mode nanowire or charge-2 e transfer through a normal-superconductor interface. All even-order correlators of current fluctuations have a universal quantized value, insensitive to disorder and decoherence. These electrical signatures are experimentally accessible, because they persist for temperatures and voltages large compared to the Thouless energy.

A comparison of superconductor and manganin technology for electronic links used in space mission applications

NASA Technical Reports Server (NTRS)

Caton, R.; Selim, R.; Buoncristiani, A. M.

1992-01-01

The electronic link connecting cryogenically cooled radiation detectors to data acquisition and signal processing electronics at higher temperatures contributes significantly to the total heat load on spacecraft cooling systems that use combined mechanical and cryogenic liquid cooling. Using high transition temperature superconductors for this link has been proposed to increase the lifetime of space missions. Herein, several YBCO (YBa2Cu3O7) superconductor-substrate combinations were examined and total heat loads were compared to manganin wire technology in current use. Using numerical solutions to the heat-flow equations, it is shown that replacing manganin technology with YBCO thick film technology can extend a 7-year mission by up to 1 year.

ESR, SIMS and TEMF of an Y-Ba-Cu-O superconductor

NASA Technical Reports Server (NTRS)

Kirschner, I.; Giber, J.; Halasz, I.

1995-01-01

Superconducting transition comes into being between 92 K and 82 K in the samples having a Meissner's state value of 68 vol. percent. The main material content has an orthorhombic unit cell of Y1Ba2Cu408 accompanied by low quantity CuO and a sporadic phase. A proof of anisotropic superconductivity, an unusually high Cu ion concentration and a temperature dependent transition of charge carriers have been observed.

Gd Ba Cu O bulk superconductors fabricated by a seeded infiltration growth technique under reduced oxygen partial pressure

NASA Astrophysics Data System (ADS)

Iida, K.; Babu, N. H.; Shi, Y. H.; Cardwell, D. A.; Murakami, M.

2006-06-01

Single-grain Gd-Ba-Cu-O (GdBCO) bulk superconductors have been grown by a seeded infiltration and growth (SIG) technique under a 1% O2+N2 atmosphere using a generic MgO-doped Nd-Ba-Cu-O (MgO-NdBCO) seed placed on the sample surface at room temperature (the so-called the cold-seeding method). Partial melting of the MgO-NdBCO seeds fabricated in air under notionally identical thermal processing conditions, however, limited the reliability of this bulk GdBCO single-grain process. The observed seed decomposition is attributed to the dependence of the peritectic temperature Tp of MgO-doped Nd1+xBa2-xCu3Oy solid solution (MgO-doped Nd-123ss, where ss indicates solid solution) compounds on both oxygen partial pressure during the melt process and the level of solid solution (x). The peritectic decomposition temperature of MgO-doped Nd-123ss, with x ranging from 0 to 0.5 under p(O2) = 1.00 atm, was observed to remain constant at 1120 °C. Tp was observed to decrease linearly as a function of solid solution level, on the other hand, under oxygen partial pressures of both p(O2) = 0.21 and 0.01 atm. Based on these results, MgO-doped NdBCO seed crystals should be grown under reduced oxygen partial pressure in order to obtain a stable MgO-doped NdBCO seed crystal suitable for cold-seeding processes of large-grain (RE)BCO bulk superconductors (where RE is a rare earth element).

Possible field-tuned superconductor-insulator transition in high-Tc superconductors: implications for pairing at high magnetic fields.

PubMed

Steiner, M A; Boebinger, G; Kapitulnik, A

2005-03-18

The behavior of some high temperature superconductors (HTSC), such as La(2-x)Sr(x)CuO(4) and Bi(2)Sr(2-x)La(x)CuO(6 + delta), at very high magnetic fields, is similar to that of thin films of amorphous InOx near the magnetic-field-tuned superconductor-insulator transition. Analyzing the InOx data at high fields in terms of persisting local pairing amplitude, we argue by analogy that the local pairing amplitude also persists well into the dissipative state of the HTSCs, the regime commonly denoted as the "normal state" in very high magnetic field experiments.

Critical current and flux dynamics in Ag-doped FeSe superconductor

NASA Astrophysics Data System (ADS)

Galluzzi, A.; Polichetti, M.; Buchkov, K.; Nazarova, E.; Mancusi, D.; Pace, S.

2017-02-01

The measurements of DC magnetization as a function of the temperature M(T), magnetic field M(H), and time M(t) have been performed in order to compare the superconducting and pinning properties of an undoped FeSe0.94 sample and a silver doped FeSe0.94 + 6 wt% Ag sample. The M(T) curves indicate an improvement of the superconducting critical temperature and a reduction of the non-superconducting phase Fe7Se8 due to the silver doping. This is confirmed by the field and temperature dependent critical current density Jc(H,T) extracted from the superconducting hysteresis loops at different temperatures within the Bean critical state model. Moreover, the combined analysis of the Jc(T) and of the pinning force Fp(H/Hirr) indicate that the pinning mechanisms in both samples can be described in the framework of the collective pinning theory. The U*(T, J) curves show a pinning crossover from an elastic creep regime of intermediate size flux bundles, for low temperatures, to a plastic creep regime at higher temperatures for both the samples. Finally, the vortex hopping attempt time has been evaluated for both samples and the results are comparable with the values reported in the literature for high Tc materials.

Chemical stability of high-temperature superconductors

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.

1992-01-01

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

Vortex Escape from Columnar Defect in a Current-Loaded Superconductor

NASA Astrophysics Data System (ADS)

Fedirko, V. A.; Kasatkin, A. L.; Polyakov, S. V.

2018-06-01

The problem of Abrikosov vortices depinning from extended linear (columnar) defect in 3D-anisotropic superconductor film under non-uniformly distributed Lorentz force is studied for the case of low temperatures, disregarding thermal activation processes. We treat it as a problem of mechanical behavior of an elastic vortex string settled in a potential well of a linear defect and exerted to Lorentz force action within the screening layer about the London penetration depth near the specimen surface. The stability problem for the vortex pinning state is investigated by means of numerical modeling, and conditions for the instability threshold are obtained as well as the critical current density j_c and its dependence on the film thickness and magnetic field orientation. The instability leading to vortex depinning from extended linear defect first emerges near the surface and then propagates inside the superconductor. This scenario of vortex depinning mechanism at low temperatures is strongly supported by some recent experiments on high-Tc superconductors and other novel superconducting materials, containing columnar defects of various nature.

Electromagnetic properties of impure superconductors with pair-breaking processes

NASA Astrophysics Data System (ADS)

Herman, František; Hlubina, Richard

2017-07-01

Recently, a generic model was proposed for the single-particle properties of gapless superconductors with simultaneously present pair-conserving and pair-breaking impurity scatterings (the so-called Dynes superconductors). Here we calculate the optical conductivity of the Dynes superconductors. Our approach is applicable for all disorder strengths from the clean limit up to the dirty limit and for all relative ratios of the two types of scattering; nevertheless, the complexity of our description is equivalent to that of the widely used Mattis-Bardeen theory. We identify two optical fingerprints of the Dynes superconductors: (i) the presence of two absorption edges and (ii) finite absorption at vanishing frequencies even at the lowest temperatures. We demonstrate that the recent anomalous optical data on thin MoN films can be reasonably fitted by our theory.

Quasipermanent magnets of high temperature superconductor - Temperature dependence

NASA Technical Reports Server (NTRS)

Chen, In-Gann; Liu, Jianxiong; Ren, Yanru; Weinstein, Roy; Kozlowski, Gregory; Oberly, Charles E.

1993-01-01

We report on persistent field in quasi-permanent magnets of high temperature superconductors. Magnets composed of irradiated Y(1+)Ba2Cu3O7 trapped field Bt = 1.52 T at 77 K and 1.9 T at lower temperature. However, the activation magnet limited Bt at lower temperature. We present data on Jc(H,T) for unirradiated materials, and calculate Bt at various T. Based upon data at 65 K, we calculate Bt in unirradiated single grains at 20 K and find that 5.2 T will be trapped for grain diameter d about 1.2 cm, and 7.9 T for d = 2.3 cm. Irradiated grains will trap four times these values.

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

NASA Astrophysics Data System (ADS)

Giordano, G. L.; Grandi, N. E.; Lugo, A. R.

2017-04-01

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

Analytical assessment of some characteristic ratios for s-wave superconductors

NASA Astrophysics Data System (ADS)

Gonczarek, Ryszard; Krzyzosiak, Mateusz; Gonczarek, Adam; Jacak, Lucjan

2018-04-01

We evaluate some thermodynamic quantities and characteristic ratios that describe low- and high-temperature s-wave superconducting systems. Based on a set of fundamental equations derived within the conformal transformation method, a simple model is proposed and studied analytically. After including a one-parameter class of fluctuations in the density of states, the mathematical structure of the s-wave superconducting gap, the free energy difference, and the specific heat difference is found and discussed in an analytic manner. Both the zero-temperature limit T = 0 and the subcritical temperature range T ≲ T c are discussed using the method of successive approximations. The equation for the ratio R 1, relating the zero-temperature energy gap and the critical temperature, is formulated and solved numerically for various values of the model parameter. Other thermodynamic quantities are analyzed, including a characteristic ratio R 2, quantifying the dynamics of the specific heat jump at the critical temperature. It is shown that the obtained model results coincide with experimental data for low- T c superconductors. The prospect of application of the presented model in studies of high- T c superconductors and other superconducting systems of the new generation is also discussed.

New Fe-based superconductors: properties relevant for applications

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

Putti, M; Pallecchi, I; Bellingeri, E

2009-01-01

Less than two years after the discovery of high temperature superconductivity in oxypnictide LaFeAs(O, F) several families of superconductors based on Fe layers (1111, 122, 11, 111) are available. They share several characteristics with cuprate superconductors that compromise easy applications, such as the layered structure, the small coherence length and unconventional pairing. On the other hand, the Fe-based superconductors have metallic parent compounds and their electronic anisotropy is generally smaller and does not strongly depend on the level of doping, and the supposed order parameter symmetry is s-wave, thus in principle not so detrimental to current transmission across grain boundaries.more » From the application point of view, the main efforts are still devoted to investigate the superconducting properties, to distinguish intrinsic from extrinsic behaviors and to compare the different families in order to identify which one is the fittest for the quest for better and more practical superconductors. The 1111 family shows the highest T{sub c}, huge but also the most anisotropic upper critical field and in-field, fan-shaped resistive transitions reminiscent of those of cuprates. On the other hand, the 122 family is much less anisotropic with sharper resistive transitions as in low temperature superconductors, but with about half the T{sub c} of the 1111 compounds. An overview of the main superconducting properties relevant to applications will be presented. Upper critical field, electronic anisotropy parameter, and intragranular and intergranular critical current density will be discussed and compared, where possible, across the Fe-based superconductor families.« less

Magnetic studies of high Tc superconducting (La0.9Sr0.1)2CuO4-y

NASA Technical Reports Server (NTRS)

Zirngiebl, E.; Thompson, J. D.; Huang, C. Y.; Hor, P. H.; Meng, R. L.

1987-01-01

The magnetic moment of La(0.9Sr0.1)2CuO4-y was measured as a function of temperature and magnetic field, and the onset of superconductivity was found to occur at a temperature of 35 K. At 2 K, the dc magnetic susceptibility was found to reach 83 percent of perfect diamagnetism. Field studies have shown that the sample is a type-II superconductor and that the temperature dependences of the critical fiedls are anomalous. Its critical fields, kappa, and lambda(eff) are much larger than those for (La0.9Ba0.1)2CuO4-y, and their temperature dependences cannot be explained in terms of BCS theory.

Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.

PubMed

Steglich, Frank; Wirth, Steffen

2016-08-01

This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a 'conventional', itinerant QCP can be well understood within Landau's paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an 'unconventional', local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.

Angle-resolved photoemission spectroscopy studies of the Mott insulator to superconductor evolution in calcium-sodium-copper-chloride

NASA Astrophysics Data System (ADS)

Shen, Kyle Michael

The parent compounds of the high-temperature cuprate superconductors are antiferromagnetic Mott insulators. To explain the microscopic mechanism behind high-temperature superconductivity, it is first necessary to understand how the electronic states evolve from the parent Mott insulator into the superconducting compounds. This dissertation presents angle-resolved photoemission spectroscopy (ARPES) studies of one particular family of the cuprate superconductors, Ca 2-xNaxCuO 2Cl2, to investigate how the single-electron excitations develop throughout momentum space as the system is hole doped from the Mott insulator into a superconductor with a transition temperature of 22 K. These measurements indicate that, due to very strong electron-boson interactions, the quasiparticle residue, Z, approaches zero in the parent Mott insulator due to the formation of small lattice polarons. As a result, many fundamental quantities such as the chemical potential, quasiparticle excitations, and the Fermi surface evolve in manners wholly unexpected from conventional weakly-interacting theories. In addition, highly anisotropic interactions have been observed in momentum space where quasiparticle-like excitations persist to low doping levels along the nodal direction of the d-wave super-conducting gap, in contrast to the unusual excitations near the d-wave antinode. This anisotropy may reflect the propensity of the lightly doped cuprates towards forming a competing, charge-ordered state. These results provide a novel and logically consistent explanation of the hole doping evolution of the lineshape, spectral weight, chemical potential, quasiparticle dispersion, and Fermi surface as Ca2- xNaxCuO2Cl2 evolves from the parent Mott insulator into a high-temperature superconductor.

Local Magnetic Measurements of Trapped Flux Through a Permanent Current Path in Graphite

NASA Astrophysics Data System (ADS)

Stiller, Markus; Esquinazi, Pablo D.; Quiquia, José Barzola; Precker, Christian E.

2018-04-01

Temperature- and field-dependent measurements of the electrical resistance of different natural graphite samples suggest the existence of superconductivity at room temperature in some regions of the samples. To verify whether dissipationless electrical currents are responsible for the trapped magnetic flux inferred from electrical resistance measurements, we localized them using magnetic force microscopy on a natural graphite sample in remanent state after applying a magnetic field. The obtained evidence indicates that at room temperature a permanent current flows at the border of the trapped flux region. The current path vanishes at the same transition temperature T_c≈ 370 K as the one obtained from electrical resistance measurements on the same sample. This sudden decrease in the phase is different from what is expected for a ferromagnetic material. Time-dependent measurements of the signal show the typical behavior of flux creep of a permanent current flowing in a superconductor. The overall results support the existence of room-temperature superconductivity at certain regions in the graphite structure and indicate that magnetic force microscopy is suitable to localize them. Magnetic coupling is excluded as origin of the observed phase signal.

Low Cost Cryocoolers for High Temperature Superconductor Communication Filters

NASA Technical Reports Server (NTRS)

Brown, Davina

1998-01-01

This final report describes the work performed by a consortium of Industry and Government to develop low cost cryocoolers. The specific application was for low cost commercial based high temperature superconductor communication filters. This program was initiated in January 1995 and resulted in the successful demonstration of an HTS filter dewar cooled by a low cost pulse tube cryocooler. Further development of this cryocooler technology is proceeding through various contracts underway and proposed at this time.

Making High-Temperature Superconductors By Melt Sintering

NASA Technical Reports Server (NTRS)

Golben, John P.

1992-01-01

Melt-sintering technique applied to YBa2Cu3O7-x system and to Bi/Ca/Sr/Cu-oxide system to produce highly oriented bulk high-temperature-superconductor materials extending to macroscopically usable dimensions. Processing requires relatively inexpensive and simple equipment. Because critical current two orders of magnitude greater in crystal ab plane than in crystal c direction, high degree of orientation greatly enhances critical current in these bulk materials, making them more suitable for many proposed applications.

High-Temperature Superconductors as Electromagnetic Deployment and Support Structures in Spacecraft. [NASA NIAC Phase I

NASA Technical Reports Server (NTRS)

Getliffe, Gwendolyn V.; Inamdar, Niraj K.; Masterson, Rebecca; Miller, David W.

2012-01-01

This report, concluding a one-year NIAC Phase I study, describes a new structural and mechanical technique aimed at reducing the mass and increasing the deployed-to-stowed length and volume ratios of spacecraft systems. This technique uses the magnetic fields generated by electrical current passing through coils of high-temperature superconductors (HTSs) to support spacecraft structures and deploy them to operational configurations from their stowed positions inside a launch vehicle fairing.

What is strange about high-temperature superconductivity in cuprates?

NASA Astrophysics Data System (ADS)

Božović, I.; He, X.; Wu, J.; Bollinger, A. T.

2017-10-01

Cuprate superconductors exhibit many features, but the ultimate question is why the critical temperature (Tc) is so high. The fundamental dichotomy is between the weak-pairing, Bardeen-Cooper-Schrieffer (BCS) scenario, and Bose-Einstein condensation (BEC) of strongly-bound pairs. While for underdoped cuprates it is hotly debated which of these pictures is appropriate, it is commonly believed that on the overdoped side strongly-correlated fermion physics evolves smoothly into the conventional BCS behavior. Here, we test this dogma by studying the dependence of key superconducting parameters on doping, temperature, and external fields, in thousands of cuprate samples. The findings do not conform to BCS predictions anywhere in the phase diagram.

Radiation detector using a bulk high T.sub.c superconductor

DOEpatents

Artuso, Joseph F.; Franks, Larry A.; Hull, Kenneth L.; Symko, Orest G.

1993-01-01

A radiation detector (10) is provided, wherein a bulk high T.sub.c superconducting sample (11) is placed in a magnetic field and maintained at a superconducting temperature. Photons of incident radiation will cause localized heating in superconducting loops of the sample destroying trapped flux and redistributing the fluxons, and reducing the critical current of the loops. Subsequent cooling of the sample in the magnetic field will cause trapped flux redistributed Abrikosov fluxons and trapped Josephson fluxons. The destruction and trapping of the fluxons causes changes in the magnetization of the sample inducing currents in opposite directions in a pickup coil (12) which is coupled by an input coil (15) to an rf SQUID (16).

Radiation detector using a bulk high T[sub c] superconductor

DOEpatents

Artuso, J.F.; Franks, L.A.; Hull, K.L.; Symko, O.G.

1993-12-07

A radiation detector is provided, wherein a bulk high T[sub c] superconducting sample is placed in a magnetic field and maintained at a superconducting temperature. Photons of incident radiation will cause localized heating in superconducting loops of the sample destroying trapped flux and redistributing the fluxons, and reducing the critical current of the loops. Subsequent cooling of the sample in the magnetic field will cause trapped flux redistributed Abrikosov fluxons and trapped Josephson fluxons. The destruction and trapping of the fluxons causes changes in the magnetization of the sample inducing currents in opposite directions in a pickup coil which is coupled by an input coil to an rf SQUID. 4 figures.

Study of Electromagnetic Repulsion Switch to High Speed Reclosing and Recover Time Characteristics of Superconductor

NASA Astrophysics Data System (ADS)

Koyama, Tomonori; Kaiho, Katsuyuki; Yamaguchi, Iwao; Yanabu, Satoru

Using a high-temperature superconductor, we constructed and tested a model superconducting fault current limiter (SFCL). The superconductor and vacuum interrupter as the commutation switch were connected in parallel using a bypass coil. When the fault current flows in this equipment, the superconductor is quenched and the current is then transferred to the parallel coil due to the voltage drop in the superconductor. This large current in the parallel coil actuates the magnetic repulsion mechanism of the vacuum interrupter and the current in the superconductor is broken. Using this equipment, the current flow time in the superconductor can be easily minimized. On the other hand, the fault current is also easily limited by large reactance of the parallel coil. This system has many merits. So, we introduced to electromagnetic repulsion switch. There is duty of high speed re-closing after interrupting fault current in the electrical power system. So the SFCL should be recovered to superconducting state before high speed re-closing. But, superconductor generated heat at the time of quench. It takes time to recover superconducting state. Therefore it is a matter of recovery time. In this paper, we studied recovery time of superconductor. Also, we proposed electromagnetic repulsion switch with reclosing system.

Competing Quantum Orderings in Cuprate Superconductors: A Minimal Model

NASA Astrophysics Data System (ADS)

Martin, Ivar; Ortiz, Gerardo; Balatsky, A. V.; Bishop, A. R.

2001-03-01

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra, and local density of states measurable by STM.

Single ferromagnetic fluctuations in UCoGe revealed by 73Ge- and 59Co-NMR studies

NASA Astrophysics Data System (ADS)

Manago, Masahiro; Ishida, Kenji; Aoki, Dai

2018-02-01

73Ge and 59Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been performed on a 73Ge-enriched single-crystalline sample of the ferromagnetic superconductor UCoGe in the paramagnetic state. The 73Ge NQR parameters deduced from NQR and NMR are close to those of another isostructural ferromagnetic superconductor URhGe. The Knight shifts of the Ge and Co sites are well scaled to each other when the magnetic field is parallel to the b or c axis. The hyperfine coupling constants of Ge are estimated to be close to those of Co. The large difference of spin susceptibilities between the a and b axes could lead to the different response of the superconductivity and ferromagnetism with the field parallel to these directions. The temperature dependence of the nuclear spin-lattice relaxation rates 1 /T1 at the two sites is similar to each other above 5 K. These results indicate that the itinerant U-5 f electrons are responsible for the ferromagnetism in this compound, consistent with previous studies. The similarities and differences in the three ferromagnetic superconductors are discussed.

Method for preparing high transition temperature Nb.sub.3 Ge superconductors

DOEpatents

Newkirk, Lawrence R.; Valencia, Flavio A.

1977-01-01

Bulk coatings of Nb.sub.3 Ge superconductors having transition temperatures in excess of 20 K are readily formed by a chemical vapor deposition technique involving the coreduction of NbCl.sub.5 and GeCl.sub.4 in the presence of hydrogen. The NbCl.sub.5 vapor may advantageously be formed quantitatively in the temperature range of about 250.degree. to 260.degree. C by the chlorination of Nb metal provided the partial pressure of the product NbCl.sub.5 vapor is maintained at or below about 0.1 atm.

Method for preparing high transition temperature Nb/sub 3/Ge superconductors. [Patent application

DOEpatents

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

1975-06-26

Bulk coatings of Nb/sub 3/Ge superconductors having transition temperatures in excess of 20/sup 0/K are readily formed by a chemical vapor deposition technique involving the coreduction of NbCl/sub 5/ and GeCl/sub 4/ in the presence of hydrogen. The NbCl/sub 5/ vapor may advantageously be formed quantitatively in the temperature range of about 250 to 260/sup 0/C by the chlorination of Nb metal provided the partial pressure of the product NbCl/sub 5/ vapor is maintained at or below about 0.1 atm.

Extension of the N-point Padé approximants solution of the Eliashberg equations to T ˜ T c

NASA Astrophysics Data System (ADS)

Leavens, C. R.; Ritchie, D. S.

1985-01-01

Vidberg and Serene introduced a very useful technique for calculating the low temperature (T « T c) gap function of a superconductor which bypasses the real-frequency singular integral equations of Eliashberg. Blashke and Blocksdorf recognized and resolved a difficulty with the technique thereby extending it to higher temperatures. We present a much simpler method of doing essentially the same thing and, for a strong-coupling superconductor at a temperature near T c, compare the gap functions calculated using these methods with the accurate one computed directly from the real-frequency equations.

Growth of Cu 0.5Tl 0.5Ba 2Ca 3Cu 4-yZn yO 12-δ superconductor with optimum carriers

NASA Astrophysics Data System (ADS)

Mumtaz, M.; Khan, Nawazish A.; Khan, E. U.

2010-05-01

We have tried to vary the carriers concentration in Cu 0.5Tl 0.5Ba 2Ca 3Cu 4-yZn yO 12-δ ( y = 0, 1, 1.5, 2, 2.5) superconductor with the help of post-annealing experiments carried out in nitrogen, oxygen and air and to investigate its effects on the superconductivity parameters. The zero resistivity critical temperature [ T c( R = 0)], the magnitude of diamagnetism and critical current [ I c( H = 0)] are found to increase in Zn free samples after post-annealing in oxygen and air, while these superconducting properties have been suppressed after post-annealing in nitrogen at 550 °C for 6 h. The post-annealing of Zn-doped samples in air has marginally increased the superconducting properties, while these properties have been suppressed after post-annealing in nitrogen and oxygen. These studies have led us to the definite conclusion that the Zn-doped material has grown with optimum carriers concentration.

Iron-based superconductors: Unity or diversity?

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

Kivelson, S. A.

2010-02-24

Superconductivity is among the most fascinating properties that a material can show. On the fundamental level, it represents a direct, macroscopic manifestation of coherent quantum mechanical behaviour, and its potential practical importance is almost unlimited, especially if new superconductors can be synthesized or discovered with still higher transition temperatures, Tc.

High Temperature Superconductor/Semiconductor Hybrid Microwave Devices and Circuits

NASA Technical Reports Server (NTRS)

Romanofsky, Robert R.; Miranda, Felix A.

1999-01-01

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

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

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

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.

Processing-property relations in YBa2Cu3O(6+x) superconductors

NASA Astrophysics Data System (ADS)

Safari, A.; Wachtman, J. B., Jr.; Parkhe, V.; Caracciolo, R.; Jeter, D.

Processing of YBa2Cu3O(6+x) superconducting samples by employing different precursor powder preparation techniques such as ball milling, attrition milling, and narrow particle size distribution powder preparation through coprecipitation by spraying will be discussed. CuO coated with oxalates shows the lowest resistance above Tc up to room temperature. The extent of corrosion by water has been studied by employing magnetic susceptibility, XPS, and X-ray diffraction. Superconducting samples are affected to a considerable extent when treated in water at 60 C and the severity of the attack increases with time.

Comprehensive phase diagram of two-dimensional space charge doped Bi2Sr2CaCu2O8+x.

PubMed

Sterpetti, Edoardo; Biscaras, Johan; Erb, Andreas; Shukla, Abhay

2017-12-12

The phase diagram of hole-doped high critical temperature superconductors as a function of doping and temperature has been intensively studied with chemical variation of doping. Chemical doping can provoke structural changes and disorder, masking intrinsic effects. Alternatively, a field-effect transistor geometry with an electrostatically doped, ultra-thin sample can be used. However, to probe the phase diagram, carrier density modulation beyond 10 14  cm -2 and transport measurements performed over a large temperature range are needed. Here we use the space charge doping method to measure transport characteristics from 330 K to low temperature. We extract parameters and characteristic temperatures over a large doping range and establish a comprehensive phase diagram for one-unit-cell-thick BSCCO-2212 as a function of doping, temperature and disorder.

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.

Processing of Bulk YBa2Cu3O(7-x) High Temperature Superconductor Materials for Gravity Modification Experiments and Performance Under AC Levitation

NASA Technical Reports Server (NTRS)

Koczor, Ronald; Noever, David; Hiser, Robert

1999-01-01

We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of bulk-processed high temperature superconductor disks. Others have indicated that large annular disks (on the order of 25cm diameter) and AC levitation fields play an essential role in their observed experiments. We report experiments in processing such large bulk superconductors. Successful results depend on material mechanical characteristics, and pressure and heat treat protocols. Annular disks having rough dimensions of 30cm O.D., 7cm I.D. and 1 cm thickness have been routinely fabricated and tested under AC levitation fields ranging from 45 to 300OHz. Implications for space transportation initiatives and power storage flywheel technology will be discussed.

Nonlinear electrodynamics of high-temperature superconductors

NASA Astrophysics Data System (ADS)

Zutic, Igor

We investigate the effects of nonlinear electrodynamics in unconventional superconductors. These effects can serve as fingerprints to identify the symmetry of the superconducting pairing state and to provide information about the unknown pairing mechanism in High Temperature Superconductors (HTSC). In the Meissner regime, at low temperatures, a nonlinear magnetic response arises from the presence of lines on the Fermi surface where the superconducting energy gap is very small or zero. This can be used to perform "node spectroscopy", that is, as a sensitive bulk probe to locate the angular position of those lines. We first compute the nonlinear magnetic moment as a function of applied field and geometry, assuming d-wave pairing and anisotropic penetration depth, for realistic finite sample. Our novel, numerically implemented, perturbative procedure exploits the small ratio of the penetration depths to the sample size and substantially reduces the computational work required. We next generalize these considerations to other candidates for the energy gap and to perform node spectroscopy. In calculating the nonlinear supercurrent response, we include the effects of orthorhombic distortion and a-b plane anisotropy. Analytic results presented demonstrate a systematic way to experimentally distinguish order parameters of different symmetries, including cases with mixed symmetry (for example, d+s and s+id). We finally extend our findings to the case of low frequency harmonic magnetic field. The nonlinear magnetic response for various physical quantities generates higher harmonics of the frequency of the applied field. We discuss how examination of the field and angular dependences of these harmonics allows determination of the structure of the energy gap. We show how to distinguish nodes from small minima ("quasinodes"). Gaps with nodal lines give rise to universal power law field dependences for the nonlinear magnetic moment and torque. They both have separable temporal and angular dependences. In contrast, with gap functions which only have quasinodes, these quantities do not display power laws in the applied field, and their temporal and angular dependences are not separable. We discuss how to perform measurements so as to maximize the nonlinear signal, and how to determine the gap function symmetry.

Flux line relaxation kinetics following current quenches in disordered type-II superconductors

NASA Astrophysics Data System (ADS)

Chaturvedi, Harshwardhan; Assi, Hiba; Dobramysl, Ulrich; Pleimling, Michel; Täuber, Uwe

We describe the disordered vortex system in type-II superconductors with an elastic line model, whose dynamics we investigate numerically by means of Langevin Molecular Dynamics. A system of driven interacting flux lines in a sample with randomly distributed point pinning centers is subjected to drive quench from a moving non-equilibrium steady state into one of three regimes viz. moving (steady state), pinned (glassy) or depinning (critical). The first yields fast exponential relaxation to the new non-equilibrium stationary state while the second displays algebraically slow relaxation and aging scaling with non-universal exponents. Our most recent work consists of aging and finite temperature scaling studies for drive quenches into the critical depinning regime. This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-09ER46613.

Momentum dependence of the superconducting gap and in-gap states in MgB 2 multiband superconductor

DOE PAGES

Mou, Daixiang; Jiang, Rui; Taufour, Valentin; ...

2015-06-29

We use tunable laser-based angle-resolved photoemission spectroscopy to study the electronic structure of the multiband superconductor MgB 2. These results form the baseline for detailed studies of superconductivity in multiband systems. We find that the magnitude of the superconducting gap on both σ bands follows a BCS-like variation with temperature with Δ 0 ~ 7meV. Furthermore, the value of the gap is isotropic within experimental uncertainty and in agreement with a pure s-wave pairing symmetry. We observe in-gap states confined to k F of the σ band that occur at some locations of the sample surface. As a result, themore » energy of this excitation, ~ 3 meV, was found to be somewhat larger than the previously reported gap on π Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin.« less

Vortex motion and flux-flow resistivity in dirty multiband superconductors

NASA Astrophysics Data System (ADS)

Silaev, Mihail; Vargunin, Artjom

2016-12-01

The conductivity of vortex lattices in multiband superconductors with high concentration of impurities is calculated based on microscopic kinetic theory at temperatures significantly smaller than the critical one. Both the limits of high and low fields are considered, when the magnetic induction is close to or much smaller than the critical field strength Hc 2, respectively. It is shown that in contrast to single-band superconductors, the resistive properties are not universal but depend on the pairing constants and ratios of diffusivities in different bands. The low-field magnetoresistance can strongly exceed the Bardeen-Stephen estimation in a quantitative agreement with experimental data for the two-band superconductor MgB2.

The superconducting state parameters of glassy superconductors

NASA Astrophysics Data System (ADS)

Vora, Aditya M.

2011-11-01

We present theoretical investigations of the superconducting state parameters (SSPs), i.e. the electron-phonon coupling strength, λ, Coulomb pseudopotential, μ*, transition temperature, Tc, isotope effect exponent, α, and effective interaction strength, N0V, of glassy superconductors by employing Ashcroft's well know empty core model potential for the first time using five screening functions proposed by Hartree (H), Taylor, Ichimaru-Utsumi (IU), Farid et al and Sarkar et al. The Tc obtained from the H and IU screening functions is found to be in excellent agreement with available experimental data. Also, the present results confirm the superconducting phase in bulk metallic glass superconductors. A strong dependency of the SSPs of the glassy superconductors on the 'Z' valence is found.

Origin of nonlinear transport across the magnetically induced superconductor-metal-insulator transition in two dimensions.

PubMed

Seo, Y; Qin, Y; Vicente, C L; Choi, K S; Yoon, Jongsoo

2006-08-04

We have studied the effect of perpendicular magnetic fields and temperatures on nonlinear electronic transport in amorphous Ta superconducting thin films. The films exhibit a magnetic field-induced metallic behavior intervening the superconductor-insulator transition in the zero temperature limit. We show that the phase-identifying nonlinear transport in the superconducting and metallic phases arises from an intrinsic origin, not from an electron heating effect. The nonlinear transport is found to accompany an extraordinarily long voltage response time.

Modeling the Effects of Varying the Capacitance, Resistance, Temperature, and Frequency Dependence for HTS Josephson Junctions, DC SQUIDs and DC bi-SQUIDS

DTIC Science & Technology

2014-09-01

junction is a thin layer of insulating material sep- arating two superconductors that is thin enough for electrons to tunnel through. Two Josephson...can sense minute magnetic fields approaching 1015 Tesla. These SQUIDs can be arranged in arrays with different coupling schemes and parameter values to...different material and/or method on the bisecting Josephson junction for high temperature superconductor (HTS) YBa2Cu3O7 (YBCO) bi-SQUIDs. This

Nuclear relaxation rate in layered superconductors with unconventional pairing

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

Maleyev, S.V.; Yashenkin, A.G.; Aristov, D.N.

1994-11-01

The cubic temperature dependence of the nuclear relaxation rate (NRR) in layered superconductors with the order parameter having zeros at the Fermi surface (FS) is found to be universal under quite general conditions. The coefficient in the quasi-Korringa term for the NRR appearing at low temperatures due to impurity scattering is estimated. It is shown that an anisotropy of the gap function over the FS leads to the disappearance of the Hebel-Slichter coherence peak close to [ital T][sub [ital c

The color of polarization in cuprate superconductors

NASA Technical Reports Server (NTRS)

Hoff, H. A.; Osofsky, M. S.; Lechter, W. L.; Pande, C. S.

1991-01-01

A technique for the identification of individual anisotropic grains in a heterogeneous and opaque material involves the observation of grain color in reflected light through crossed polarizers (color of polarization). Such colors are generally characteristic of particular phases. When grains of many members of the class of hole carrier cuprate superconductors are so viewed at room temperature with a 'daylight' source, a characteristic color of polarization is observed. This color was studied in many of these cuprate superconductors and a strong correlation was found between color and the existence of superconductivity. Two members were also examined of the electron cuprate superconductors and it was found that they possess the same color of polarization as the hole carrier cuprate superconductors so far examined. The commonality of the characteristic color regardless of charge carrier indicates that the presence of this color is independent of carrier type. The correlation of this color with the existence of superconductivity in the cuprate superconductors suggests that the origin of the color relates to the origin of superconductivity. Photometric techniques are also discussed.

Thermal mechanisms responsible for the irreversible degradation of superconductivity in commercial superconductors

NASA Astrophysics Data System (ADS)

Romanovskii, V. R.

2017-08-01

Conditions for the irreversible propagation of thermal instabilities in commercial superconductors subjected to intense and soft cooling have been formulated. An analysis has been conducted using two types of the superconductor's I-V characteristics, i.e., an ideal I-V characteristic, which assumes a step superconducting-to-normal transition, and a continuous I-V characteristic, which is described by a power law. The propagation rate of thermal instabilities along the superconducting composite has been determined. Calculations have been made for both subcritical and supercritical values of the current. It has been shown that they propagate along a commercial superconductor in the form of a switching wave. In rapidly cooled commercial superconductors, the steady-state rate of thermal instability propagation in the longitudinal direction can only be positive because there is no region of steady stabilization. It has been proved that, in the case of thermal instability irreversible propagation, the rise in the commercial superconductor temperature is similar to diffusion processes that occur in explosive chain reactions.

Cold SQUIDs and hot samples

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

Lee, T.S.C.

1997-05-01

Low transition temperature (low-{Tc}) and high-{Tc} Superconducting QUantum Interference Devices (SQUIDs) have been used to perform high-resolution magnetic measurements on samples whose temperatures are much higher than the operating temperatures of the devices. Part 1 of this work focuses on measurements of the rigidity of flux vortices in high-{Tc} superconductors using two low-{Tc} SQUIDs, one on either side of a thermally-insulated sample. The correlation between the signals of the SQUIDs is a direct measure of the extent of correlation between the movements of opposite ends of vortices. These measurements were conducted under the previously-unexplored experimental conditions of nominally-zero applied magneticmore » field, such that vortex-vortex interactions were unimportant, and with zero external current. At specific temperatures, the authors observed highly-correlated noise sources, suggesting that the vortices moved as rigid rods. At other temperatures, the noise was mostly uncorrelated, suggesting that the relevant vortices were pinned at more than one point along their length. Part 2 describes the design, construction, performance, and applications of a scanning high-{Tc} SQUID microscope optimized for imaging room-temperature objects with very high spatial resolution and magnetic source sensitivity.« less

Exponential nonlinear electrodynamics and backreaction effects on holographic superconductor in the Lifshitz black hole background

NASA Astrophysics Data System (ADS)

Sherkatghanad, Z.; Mirza, B.; Lalehgani Dezaki, F.

We analytically describe the properties of the s-wave holographic superconductor with the exponential nonlinear electrodynamics in the Lifshitz black hole background in four-dimensions. Employing an assumption the scalar and gauge fields backreact on the background geometry, we calculate the critical temperature as well as the condensation operator. Based on Sturm-Liouville method, we show that the critical temperature decreases with increasing exponential nonlinear electrodynamics and Lifshitz dynamical exponent, z, indicating that condensation becomes difficult. Also we find that the effects of backreaction has a more important role on the critical temperature and condensation operator in small values of Lifshitz dynamical exponent, while z is around one. In addition, the properties of the upper critical magnetic field in Lifshitz black hole background using Sturm-Liouville approach is investigated to describe the phase diagram of the corresponding holographic superconductor in the probe limit. We observe that the critical magnetic field decreases with increasing Lifshitz dynamical exponent, z, and it goes to zero at critical temperature, independent of the Lifshitz dynamical exponent, z.

Routes to High-Temperature Superconductivity: A Lesson from FeSe/SrTiO3

NASA Astrophysics Data System (ADS)

Lee, Dung-Hai

2018-03-01

Raising the superconducting transition temperature to a point where applications are practical is one of the most important challenges in science. In this review, we aim at gaining insights on the Tc controlling factors for a particular high-temperature superconductor family - the FeSe-based superconductors. In particular, we discuss the mechanisms by which the Cooper pairing temperature is enhanced from ˜8 K in bulk FeSe to ˜80 K in the interface between an atomic layer of FeSe and SrTiO3. This includes the experimental hints and the theoretical simulation of the involved mechanisms. We end by applying these insights to suggest some possible high-temperature superconducting systems.

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

NASA Technical Reports Server (NTRS)

Noever, David A.; Koczor, Ronald J.

1998-01-01

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

Superconductor-Mediated Modification of Gravity? AC Motor Experiments with Bulk YBCO Disks in Rotating Magnetic Fields

NASA Technical Reports Server (NTRS)

Noever, David A.; Koczor, Ronald J.; Roberson, Rick

1998-01-01

We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. Podkietnov, et al (Podkietnov, E. and Nieminen, R. (1992) A Possibility of Gravitational Force Shielding by Bulk YBa2 Cu3 O7-x Superconductor, Physica C, C203:441-444.) have indicated that rotating AC fields play an essential role in their observed distortion of combined gravity and barometric pressure readings. We report experiments on large (15 cm diameter) bulk YBCO ceramic superconductors placed in the core of a three-phase, AC motor stator. The applied rotating field produces up to a 12,000 revolutions per minute magnetic field. The field intensity decays rapidly from the maximum at the outer diameter of the superconducting disk (less than 60 Gauss) to the center (less than 10 Gauss). This configuration was applied with and without a permanent DC magnetic field levitating the superconducting disk, with corresponding gravity readings indicating an apparent increase in observed gravity of less than 1 x 10(exp -6)/sq cm, measured above the superconductor. No effect of the rotating magnetic field or thermal environment on the gravimeter readings or on rotating the superconducting disk was noted within the high precision of the observation. Implications for propulsion initiatives and power storage flywheel technologies for high temperature superconductors will be discussed for various spacecraft and satellite applications.

Temperature dependence of differential conductance in Co-based Heusler alloy Co2TiSn and superconductor Pb junctions

NASA Astrophysics Data System (ADS)

Ooka, Ryutaro; Shigeta, Iduru; Umetsu, Rie Y.; Nomura, Akiko; Yubuta, Kunio; Yamauchi, Touru; Kanomata, Takeshi; Hiroi, Masahiko

2018-05-01

We investigated temperature dependence of differential conductance G (V) in planar junctions consisting of Co-based Heusler alloy Co2TiSn and superconductor Pb. Ferromagnetic Co2TiSn was predicted to be half-metal by first-principles band calculations. The spin polarization P of Co2TiSn was deduced to be 60.0% at 1.4 K by the Andreev reflection spectroscopy. The G (V) spectral shape was smeared gradually with increasing temperature and its structure was disappeared above the superconducting transition temperature Tc. Theoretical model analysis revealed that the superconducting energy gap Δ was 1.06 meV at 1.4 K and the Tc was 6.8 K , indicating that both values were suppressed from bulk values. However, the temperature dependent Δ (T) behavior was in good agreement with that of the Bardeen-Cooper-Schrieffer (BCS) theory. The experimental results exhibit that the superconductivity of Pb attached to half-metallic Co2TiSn was kept the conventional BCS mechanism characterized strong-coupling superconductors while its superconductivity was slightly suppressed by the superconducting proximity effect at the Co2TiSn/Pb interface.

Lattice distortion and stripelike antiferromagnetic order in Ca10(Pt3As8)(Fe2As2)5

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

Sapkota, Aashish; Tucker, Gregory S; Ramazanoglu, Mehmet

2014-09-01

Ca10(Pt3As8)(Fe2As2)5 is the parent compound for a class of Fe-based high-temperature superconductors where superconductivity with transition temperatures up to 30 K can be introduced by partial element substitution. We present a combined high-resolution high-energy x-ray diffraction and elastic neutron scattering study on a Ca10(Pt3As8)(Fe2As2)5 single crystal. This study reveals the microscopic nature of two distinct and continuous phase transitions to be very similar to other Fe-based high-temperature superconductors: an orthorhombic distortion of the high-temperature tetragonal Fe-As lattice below TS=110(2) K followed by stripelike antiferromagnetic ordering of the Fe moments below TN=96(2) K. These findings demonstrate that major features of themore » Fe-based high-temperature superconductors are very robust against variations in chemical constitution as well as structural imperfection of the layers separating the Fe-As layers from each other and confirms that the Fe-As layers primarily determine the physics in this class of material.« less

High-performance superconductors for Fusion Nuclear Science Facility

DOE PAGES

Zhai, Yuhu; Kessel, Chuck; Barth, Christian; ...

2016-11-09

High-performance superconducting magnets play an important role in the design of the next step large-scale, high-field fusion reactors such as the fusion nuclear science facility (FNSF) and the spherical tokamak (ST) pilot plant beyond ITER. Here, Princeton Plasma Physics Laboratory is currently leading the design studies of the FNSF and the ST pilot plant study. ITER, which is under construction in the south of France, utilizes the state-of-the-art low temperature superconducting magnet technology based on the cable-in-conduit conductor design, where over a thousand multifilament Nb 3Sn superconducting strands are twisted together to form a high-current-carrying cable inserted into a steelmore » jacket for coil windings. We present design options of the high-performance superconductors in the winding pack for the FNSF toroidal field magnet system based on the toroidal field radial build from the system code. For the low temperature superconductor options, the advanced J cNb 3Sn RRP strands (J c > 1000 A/mm 2 at 16 T, 4 K) from Oxford Superconducting Technology are under consideration. For the high-temperature superconductor options, the rectangular-shaped high-current HTS cable made of stacked YBCO tapes will be considered to validate feasibility of TF coil winding pack design for the ST-FNSF magnets.« less

High-performance superconductors for Fusion Nuclear Science Facility

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

Zhai, Yuhu; Kessel, Chuck; Barth, Christian

High-performance superconducting magnets play an important role in the design of the next step large-scale, high-field fusion reactors such as the fusion nuclear science facility (FNSF) and the spherical tokamak (ST) pilot plant beyond ITER. Here, Princeton Plasma Physics Laboratory is currently leading the design studies of the FNSF and the ST pilot plant study. ITER, which is under construction in the south of France, utilizes the state-of-the-art low temperature superconducting magnet technology based on the cable-in-conduit conductor design, where over a thousand multifilament Nb 3Sn superconducting strands are twisted together to form a high-current-carrying cable inserted into a steelmore » jacket for coil windings. We present design options of the high-performance superconductors in the winding pack for the FNSF toroidal field magnet system based on the toroidal field radial build from the system code. For the low temperature superconductor options, the advanced J cNb 3Sn RRP strands (J c > 1000 A/mm 2 at 16 T, 4 K) from Oxford Superconducting Technology are under consideration. For the high-temperature superconductor options, the rectangular-shaped high-current HTS cable made of stacked YBCO tapes will be considered to validate feasibility of TF coil winding pack design for the ST-FNSF magnets.« less

Effect of heavy-ion and electron irradiation on properties of Fe-based superconductors

NASA Astrophysics Data System (ADS)

Konczykowski, Marcin

2013-03-01

The introduction of defects by particle irradiation is used to reveal the role of disorder in matter, which is unavoidable in all crystalline solids. In superconductors defects introduce flux pinning, controlling critical current, Jc; as well as pair-breaking scattering, limiting the critical temperature, Tc. To elucidate defect related properties of Fe-based superconductors (FBS) we precede in two types of irradiation: heavy ion (6GeV Pb) to create disorder in the form of amorphous tracks and low temperature electron irradiation (2.5MeV at 20K) to create point like defects. Substantial increase of irreversible magnetization and an upward shift of the irreversibility line are observed after heavy ion irradiation of all FBS investigated to date. In BaK 122 , signatures of a Bose-glass vortex state; angular dependence and variable-range hopping flux creep are revealed. Remarkably, heavy ion irradiation does not depress Tc, however, point-like disorder introduced by electron irradiation does substantially. In isovalently substituted Ba(FeAs1 - xPx) 2 and Ba(Fe1 - x Rux As) 2 crystals, Tc decreases linearly with dose. Suppression to 40 % of initial value of Tc was achieved in Ba(FeAs1 - xPx) 2 . An increase of normal state resistivity is observed and correlated to depression of Tc. Change of superconducting gap structure with disorder was determined from penetration depth measurements, λ (T) dependence, at various stages of irradiation. Linear in T variation of pristine samples, indicative of the presence of nodes in gap, turned at low irradiation dose to exponential T variation, indicative of a fully gaped state. T2 variation of λ is observed at higher doses. This behaviour is incompatible with symmetry-imposed nodes of d-wave pairing but consistent with S + / - , S + / + mechanisms. This is the first observation of the impurity-induced node lifting expected in anisotropic s-wave superconductors

Superfluid response in heavy fermion superconductors

NASA Astrophysics Data System (ADS)

Zhong, Yin; Zhang, Lan; Shao, Can; Luo, Hong-Gang

2017-10-01

Motivated by a recent London penetration depth measurement [H. Kim, et al., Phys. Rev. Lett. 114, 027003 (2015)] and novel composite pairing scenario [O. Erten, R. Flint, and P. Coleman, Phys. Rev. Lett. 114, 027002 (2015)] of the Yb-doped heavy fermion superconductor CeCoIn5, we revisit the issue of superfluid response in the microscopic heavy fermion lattice model. However, from the literature, an explicit expression for the superfluid response function in heavy fermion superconductors is rare. In this paper, we investigate the superfluid density response function in the celebrated Kondo-Heisenberg model. To be specific, we derive the corresponding formalism from an effective fermionic large- N mean-field pairing Hamiltonian whose pairing interaction is assumed to originate from the effective local antiferromagnetic exchange interaction. Interestingly, we find that the physically correct, temperature-dependent superfluid density formula can only be obtained if the external electromagnetic field is directly coupled to the heavy fermion quasi-particle rather than the bare conduction electron or local moment. Such a unique feature emphasizes the key role of the Kondo-screening-renormalized heavy quasi-particle for low-temperature/energy thermodynamics and transport behaviors. As an important application, the theoretical result is compared to an experimental measurement in heavy fermion superconductors CeCoIn5 and Yb-doped Ce1- x Yb x CoIn5 with fairly good agreement and the transition of the pairing symmetry in the latter material is explained as a simple doping effect. In addition, the requisite formalism for the commonly encountered nonmagnetic impurity and non-local electrodynamic effect are developed. Inspired by the success in explaining classic 115-series heavy fermion superconductors, we expect the present theory will be applied to understand other heavy fermion superconductors such as CeCu2Si2 and more generic multi-band superconductors.

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

Ovcharov, A. V.; Karateev, I. A.; Mikhutkin, A. A.

The surface microstructure of Ni–W alloy tapes, which are used as substrates to form films of high-temperature superconductors and photovoltaic devices, has been studied. Several samples of a Ni{sub 95}W{sub 5} tape (Evico) annealed under different conditions were analyzed using scanning electron microscopy, energy-dispersive X-ray microanalysis, electron diffraction, and electron energy-loss spectroscopy. NiWO{sub 4} precipitates are found on the surface of annealed samples. The growth of precipitates at a temperature of 950°C is accompanied by the formation of pores on the surface or under an oxide film. Depressions with a wedge-shaped profile are found at the grain boundaries. Annealing inmore » a reducing atmosphere using a specially prepared chamber allows one to form a surface free of nickel tungstate precipitates.« less

Structure and property correlations in FeS

NASA Astrophysics Data System (ADS)

Kuhn, S. J.; Kidder, M. K.; Parker, D. S.; dela Cruz, C.; McGuire, M. A.; Chance, W. M.; Li, Li; Debeer-Schmitt, L.; Ermentrout, J.; Littrell, K. C.; Eskildsen, M. R.; Sefat, A. S.

2017-03-01

For iron-sulfide (FeS), we investigate the correlation between the structural details, including its dimensionality and composition, with its magnetic and superconducting properties. We compare, theoretically and experimentally, the two-dimensional (2D) layered tetragonal (;t-FeS;) phase with the 3D hexagonal ("h-FeS") phase. X-ray diffraction reveals iron-deficient chemical compositions of t-Fe0.93(1)S and h-Fe0.84(1)S that show no low-temperature structural transitions. First-principles calculations reveal a high sensitivity of the 2D structure to the electronic and magnetic properties, predicting marginal antiferromagnetic instability for our compound (sulfur height of zS = 0.252) with an ordering energy of about 11 meV/Fe, while the 3D phase is magnetically stable. Experimentally, h-Fe0.84S orders magnetically well above room temperature, while t-Fe0.93S shows coexistence of antiferromagnetism at TN = 116 and filamentary superconductivity below Tc = 4 K. Low temperature neutron diffraction data reveals antiferromagnetic commensurate ordering with wave vector km = (0.25,0.25,0) and 0.46(2) μB/Fe. Additionally, neutron scattering measurements were used to find the particle size and iron vacancy arrangement of t-FeS and h-FeS. The structure of iron sulfide has a delicate relationship with the superconducting transition; while our sample with a = 3.6772(7) Å is a filamentary superconductor coexisting with an antiferromagnetic phase, previously reported samples with a > 3.68 Å are bulk superconductors with no magnetism, and those with a ≈ 3.674 Å show magnetic properties.

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.

Enhancement of the finite-frequency superfluid response in the pseudogap regime of strongly disordered superconducting films

PubMed Central

Mondal, Mintu; Kamlapure, Anand; Ganguli, Somesh Chandra; Jesudasan, John; Bagwe, Vivas; Benfatto, Lara; Raychaudhuri, Pratap

2013-01-01

The persistence of a soft gap in the density of states above the superconducting transition temperature Tc, the pseudogap, has long been thought to be a hallmark of unconventional high-temperature superconductors. However, in the last few years this paradigm has been strongly revised by increasing experimental evidence for the emergence of a pseudogap state in strongly-disordered conventional superconductors. Nonetheless, the nature of this state, probed primarily through scanning tunneling spectroscopy (STS) measurements, remains partly elusive. Here we show that the dynamic response above Tc, obtained from the complex ac conductivity, is highly modified in the pseudogap regime of strongly disordered NbN films. Below the pseudogap temperature, T*, the superfluid stiffness acquires a strong frequency dependence associated with a marked slowing down of critical fluctuations. When translated into the length-scale of fluctuations, our results suggest a scenario of thermal phase fluctuations between superconducting domains in a strongly disordered s-wave superconductor. PMID:23446946

Observation of antiferromagnetic order collapse in the pressurized insulator LaMnPO

NASA Astrophysics Data System (ADS)

Guo, Jing; Simonson, Jack; Sun, Liling; Wu, Qi; Guo, Peiwen; Zhang, Chao; Gu, Dachun; Kotliar, Gabriel; Aronson, Meigan; Zhao, Zhongxian

2014-03-01

The emergence of superconductivity in the iron pnictide or cuprate high temperature superconductors usually accompanies the suppression of a long-ranged antiferromagnetic (AFM) order state in a corresponding parent compound by doping or pressurizing. A great deal of effort by doping has been made to find superconductivity in Mn-based compounds, which are thought to bridge the gap between the two families of high temperature superconductors, but the AFM order was not successfully suppressed. Here we report the first observations of the pressure-induced elimination of long-ranged AFM order at ~ 34 GPa and a crossover from an AFM insulating to an AFM metallic state at ~ 20 GPa in LaMnPO single crystals that are iso-structural to the LaFeAsO superconductor by in-situ high pressure resistance and ac susceptibility measurements. These findings are of importance to explore potential superconductivity in Mn-based compounds and to shed new light on the underlying mechanism of high temperature superconductivity.

Observation of antiferromagnetic order collapse in the pressurized insulator LaMnPO

NASA Astrophysics Data System (ADS)

Guo, Jing; Simonson, J. W.; Sun, Liling; Wu, Qi; Gao, Peiwen; Zhang, Chao; Gu, Dachun; Kotliar, Gabriel; Aronson, Meigan; Zhao, Zhongxian

2013-08-01

The emergence of superconductivity in the iron pnictide or cuprate high temperature superconductors usually accompanies the suppression of a long-ranged antiferromagnetic (AFM) order state in a corresponding parent compound by doping or pressurizing. A great deal of effort by doping has been made to find superconductivity in Mn-based compounds, which are thought to bridge the gap between the two families of high temperature superconductors, but the AFM order was not successfully suppressed. Here we report the first observations of the pressure-induced elimination of long-ranged AFM order at ~ 34 GPa and a crossover from an AFM insulating to an AFM metallic state at ~ 20 GPa in LaMnPO single crystals that are iso-structural to the LaFeAsO superconductor by in-situ high pressure resistance and ac susceptibility measurements. These findings are of importance to explore potential superconductivity in Mn-based compounds and to shed new light on the underlying mechanism of high temperature superconductivity.

Evidence for a new excitation at the interface between a high- T c superconductor and a topological insulator

DOE PAGES

Zareapour, Parisa; Hayat, Alex; Zhao, Shu Yang F.; ...

2014-12-09

In this research, high-temperature superconductors exhibit a wide variety of novel excitations. If contacted with a topological insulator, the lifting of spin rotation symmetry in the surface states can lead to the emergence of unconventional superconductivity and novel particles. In pursuit of this possibility, we fabricated high critical-temperature (T c ~ 85 K) superconductor/topological insulator (Bi₂Sr₂CaCu₂O₈₊ δ/Bi₂Te₂Se) junctions. Below 75 K, a zero-bias conductance peak (ZBCP) emerges in the differential conductance spectra of this junction. The magnitude of the ZBCP is suppressed at the same rate for magnetic fields applied parallel or perpendicular to the junction. Furthermore, it can stillmore » be observed and does not split up to at least 8.5 T. The temperature and magnetic field dependence of the excitation we observe appears to fall outside the known paradigms for a ZBCP.« less

Observation of antiferromagnetic order collapse in the pressurized insulator LaMnPO.

PubMed

Guo, Jing; Simonson, J W; Sun, Liling; Wu, Qi; Gao, Peiwen; Zhang, Chao; Gu, Dachun; Kotliar, Gabriel; Aronson, Meigan; Zhao, Zhongxian

2013-01-01

The emergence of superconductivity in the iron pnictide or cuprate high temperature superconductors usually accompanies the suppression of a long-ranged antiferromagnetic (AFM) order state in a corresponding parent compound by doping or pressurizing. A great deal of effort by doping has been made to find superconductivity in Mn-based compounds, which are thought to bridge the gap between the two families of high temperature superconductors, but the AFM order was not successfully suppressed. Here we report the first observations of the pressure-induced elimination of long-ranged AFM order at ~ 34 GPa and a crossover from an AFM insulating to an AFM metallic state at ~ 20 GPa in LaMnPO single crystals that are iso-structural to the LaFeAsO superconductor by in-situ high pressure resistance and ac susceptibility measurements. These findings are of importance to explore potential superconductivity in Mn-based compounds and to shed new light on the underlying mechanism of high temperature superconductivity.

Enhancement of the finite-frequency superfluid response in the pseudogap regime of strongly disordered superconducting films.

PubMed

Mondal, Mintu; Kamlapure, Anand; Ganguli, Somesh Chandra; Jesudasan, John; Bagwe, Vivas; Benfatto, Lara; Raychaudhuri, Pratap

2013-01-01

The persistence of a soft gap in the density of states above the superconducting transition temperature Tc, the pseudogap, has long been thought to be a hallmark of unconventional high-temperature superconductors. However, in the last few years this paradigm has been strongly revised by increasing experimental evidence for the emergence of a pseudogap state in strongly-disordered conventional superconductors. Nonetheless, the nature of this state, probed primarily through scanning tunneling spectroscopy (STS) measurements, remains partly elusive. Here we show that the dynamic response above Tc, obtained from the complex ac conductivity, is highly modified in the pseudogap regime of strongly disordered NbN films. Below the pseudogap temperature, T*, the superfluid stiffness acquires a strong frequency dependence associated with a marked slowing down of critical fluctuations. When translated into the length-scale of fluctuations, our results suggest a scenario of thermal phase fluctuations between superconducting domains in a strongly disordered s-wave superconductor.

The Growth and Characterization of the Bismuth Strontium-Calcium 2212 Superconductor

NASA Astrophysics Data System (ADS)

Moulton, Linda Vidale

A miniaturized float zone technique, sometimes referred to as the Laser-heated Pedestal Growth (LHPG) method, was used to produce high quality crystals of the incongruently melting rm Bi_2Sr_2CaCu _2O_{8+delta} (2212) superconductor. The main focus of this research was to (1) produce superconducting samples having different compositions, (2) identify the melt compositions and growth temperatures which produced these samples, and (3) determine the variation of their superconducting transition temperature (T _{rm C}) with composition and processing conditions. The rm Bi_2(Sr,Ca) _3Cu_2O_{8+delta} crystallization experiments were supplemented by a series of similar experiments on the incongruently melting compound rm Ca_3Al_2O_6. The phase equilibria in the CaO-rm Al_2O _3 system has been thoroughly studied, and by analyzing the float-zone growth of this simpler and better-characterized material, it was verified that phase equilibria information and solidification behavior could be extracted from and explained by these solidification experiments. Two different types of nonplanar, crystal/melt interface morphologies were observed in the rm Ca_3Al_2O_6 experiments. Each reflected the influence of the phase equilibria in the CaO-rm Al_2O_3 system and component segregation in the melt. The molten zone compositions were found to approach those predicted by the CaO-rm Al_2O_3 phase diagram as the growth rate decreased, in accordance with the Burton-Prim Slichter relationship. Excellent agreement was obtained between actual phases found to coexist at the rm Ca_3Al_2O_6 /melt interface and the predictions of classical crystal growth theory. Based on the results of the rm Ca _3Al_2O_6 crystallization study, the crystal/melt equilibria in the far more complex rm Bi_2O_3-SrO-CaO-CuO system was evaluated by determining the phases formed during the superconductor growth experiments. The melt compositions were found to be rm Bi_2O_3 -rich and SrO-poor relative to the compositions of the 2212 crystals grown from them. The CaO and CuO segregation coefficients, on the other hand, were observed to be near unity. As one would expect for an incongruently -melting compound, segregation at the solidification front generally decreased with increasing crystallization temperature, but all the segregation coefficients were not observed to simultaneously approach unity. The superconducting transition temperatures (T _{rm C}'s) of six as-crystallized samples having homogeneous crystal compositions were also measured. Sample T_{rm C} was observed to increase with increasing growth temperature and, therefore, change with crystal composition. The results of this study suggested that it is desirable to grow crystals at the highest possible crystallization temperature since they will: (1) have the highest as-grown T_{rm C} 's, and (2) solidify with the least component segregation at the growth interface. In addition, the analysis presented here suggests that such growth is not recommended at higher growth rates, since crystals with mid-range solidus compositions (and consequently, moderate growth temperatures) should crystallize most reliably as single-phase samples at higher growth rates.

Glass formability of high T(sub c) Bi-Sr-Ca-Cu-O superconductors

NASA Technical Reports Server (NTRS)

Kaukler, William F.

1992-01-01

A number of compositions of ceramic oxide high T(sub c) superconductors were evaluated for their glass formation ability by means of rapid thermal analysis during quenching, optical and electron microscopy of the quenched samples, and with subsequent DSC measurements. Correlations between experimental measurements and the methodical composition changes identified the formulations of superconductors that can easily form glass. The superconducting material was first formed as a glass, then with subsequent devitrification it was formed into bulk crystalline superconductor by a series of processing methods.

Photothermal measurements of high Tc superconductors

NASA Astrophysics Data System (ADS)

Fanton, J. T.; Mitzi, D. B.; Kapitulnik, A.; Khuri-Yakub, B. T.; Kino, G. S.; Gazit, D.; Feigelson, R. S.

1989-08-01

We demonstrate a photothermal method for making point measurements of the thermal conductivities of high Tc superconductors. Images made at room temperature on polycrystalline materials show the thermal inhomogeneities. Measurements on single-crystal Bi2Sr2CaCu2Ox compounds reveal a very large anisotropy of about 7:1 in the thermal conductivity.

Optimization of SIS mixer elements

NASA Technical Reports Server (NTRS)

Mattauch, Robert J.

1985-01-01

Superconductor-Insulator-Superconductor (SIS) quantum mixers provide an approach to millimeter wave mixing - potentially offering conversion gain, a low local oscillator power demand, and potential mixer noise temperatures near the quantum limit. The development of a reliable fabrication technology for producing such high quality SIS devices for mixer applications in radio astronomy is the focus of the work.

Heat capacity of high-purity lanthanum

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

Pan, P.H.; Finnemore, D.K.; Bevolo, A.J.

1980-04-01

A study of the specific heat of high-purity single-phase dhcp La shows that this material is an intrinsic type-II superconductor with a kappa of about 2.4. The temperature dependence of the free energy is characteristic of an intermediate coupling superconductor with 2..delta../k/sub B/T/sub c/ approx. = 3.7.

Synthesizing new, high-temperature superconductors

NASA Astrophysics Data System (ADS)

Weaver, Claire; Aronson, Meigan

2015-03-01

Currently, there is no accepted theory behind type-II, high-temperature superconductors, but there is a distinct relationship between anti-ferromagnetism and superconductivity. Our research focuses on synthesizing new superconducting materials by observing the link between atomic structure and magnetic moments of anti-ferromagnetic compounds and attempting to reproduce the molecular physics of these known materials in new compounds. Consider the square-planar arrangement of the transition metal Fe in the Fe-pnictide superconductors of the ZrCuSiAs ``11 11'' and the ThCr2Si2 ``122'' structure types. We believe that the physics behind this superconductor, where Fe has d6 valence electrons, contributes to the superconducting state, not the presence of Fe itself. For this reason, we are synthesizing materials containing neighboring transition metals, like Mn and Co, combined with other elements in similar crystal lattice arrangements, having ionization properties that hopefully impose d6 valence electrons on the transition metals. This project was supported in part by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships Program (SULI).

Nematic quantum critical point without magnetism in FeSe1-xSx superconductors.

PubMed

Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

2016-07-19

In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near [Formula: see text], the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.

Size, Shape and Impurity Effects on Superconducting critical temperature.

NASA Astrophysics Data System (ADS)

Umeda, Masaki; Kato, Masaru; Sato, Osamu

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

Shockwave-Loading-Induced Enhancement of T c in Superconducting Bi 2Sr 2CaCu 2O 8+δ

DOE PAGES

Liu, Tiansheng; He, Chao; Wang, Fengying; ...

2017-07-27

Here, we report a shockwave method for altering the properties of the superconductor material Bi 2Sr 2CaCu 2O 8+δ (Bi2212). We find that the superconducting transition temperature (T c) increases from 84 K for the pristine sample to 94 K for the sample treated at a temperature and pressure of ~1200 K and ~31 GPa, respectively. X-ray diffraction and transmission electron microscopy characterizations indicate that this T c enhancement arises from a phase transition from pristine Bi2212 to a mixture of superconducting Bi2212 and semiconducting Bi 2Sr 2CuO 6+δ (Bi2201) during the shockwave treatment. The shockwave-treated sample exhibits n-type semiconductormore » properties (with an on-off ratio ~5), in contrast to the pure metallic pristine sample. This study offers an alternative route for modifying the superconducting properties via a shockwave treatment. Furthermore, this method may provide a new approach for studying other temperature- and pressure-sensitive materials.« less

Detection of surface impurity phases in high T.sub.C superconductors using thermally stimulated luminescence

DOEpatents

Cooke, D. Wayne; Jahan, Muhammad S.

1989-01-01

Detection of surface impurity phases in high-temperature superconducting materials. Thermally stimulated luminescence has been found to occur in insulating impurity phases which commonly exist in high-temperature superconducting materials. The present invention is sensitive to impurity phases occurring at a level of less than 1% with a probe depth of about 1 .mu.m which is the region of interest for many superconductivity applications. Spectroscopic and spatial resolution of the emitted light from a sample permits identification and location of the impurity species. Absence of luminescence, and thus of insulating phases, can be correlated with low values of rf surface resistance.

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

Emanuela Barzi et al.1

Nb{sub 3}Sn is the superconductor most used in the R and D of high field accelerator magnets by either the wind and react or the react and wind technique. In order to program the low temperature steps of the heat treatment, the growth kinetics of Cu-Sn intermetallics was investigated as a function of duration and temperature. The diffusion constants of {eta}, {var_epsilon} and {delta} phases between 150 and 550 C were evaluated using Cu-Sn model samples. Statistical and systematic errors were thoroughly evaluated for an accurate data analysis. Next the behavior of Internal Tin and Modified Jelly Roll Nb{sub 3}Snmore » composites was compared with the model predictions.« less

A minimal model of striped superconductors

NASA Astrophysics Data System (ADS)

Martin, I.; Ortiz, G.; Balatsky, A. V.; Bishop, A. R.

2001-12-01

We present a minimal model of high-temperature superconductors that simultaneously supports antiferromagnetic stripes and d-wave superconductivity. At the unrestricted mean-field level, the various phases of the cuprates, including weak and strong pseudogap phases, and two different types of superconductivity in the underdoped and the overdoped regimes, find a natural interpretation. We argue that on the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. On the overdoped side, the state is overall homogeneous and the superconductivity is of a classical BCS type.

Aluminum-stabilized NB3SN superconductor

DOEpatents

Scanlan, Ronald M.

1988-01-01

An aluminum-stabilized Nb.sub.3 Sn superconductor and process for producing same, utilizing ultrapure aluminum. Ductile components are co-drawn with aluminum to produce a conductor suitable for winding magnets. After winding, the conductor is heated to convert it to the brittle Nb.sub.3 Sn superconductor phase, using a temperature high enough to perform the transformation but still below the melting point of the aluminum. This results in reaction of substantially all of the niobium, while providing stabilization and react-in-place features which are beneficial in the fabrication of magnets utilizing superconducting materials.

Towards the design of novel cuprate-based superconductors

NASA Astrophysics Data System (ADS)

Yee, Chuck-Hou

The rapid maturation of materials databases combined with recent development of theories seeking to quantitatively link chemical properties to superconductivity in the cuprates provide the context to design novel superconductors. In this talk, we describe a framework designed to search for new superconductors, which combines chemical rules-of-thumb, insights of transition temperatures from dynamical mean-field theory, first-principles electronic structure tools, materials databases and structure prediction via evolutionary algorithms. We apply the framework to design a family of copper oxysulfides and evaluate the prospects of superconductivity.

The disappearing momentum of the supercurrent in the superconductor-to-normal phase transformation

NASA Astrophysics Data System (ADS)

Hirsch, J. E.

2016-06-01

A superconductor in a magnetic field has surface currents that prevent the magnetic field from penetrating its interior. These currents carry kinetic energy and mechanical momentum. When the temperature is raised and the system becomes normal the currents disappear. Where do the kinetic energy and mechanical momentum of the currents go, and how? Here we propose that the answer to this question reveals a key necessary condition for materials to be superconductors, that is not part of conventional BCS-London theory: superconducting materials need to have hole carriers.

Passive microwave device applications of high T(c) superconducting thin films

NASA Astrophysics Data System (ADS)

Lyons, W. G.; Withers, R. S.

1990-11-01

Superconductors with a transition temperature T(c) from 40 K to 125 K are analyzed, with focus placed on their behavior around the boiling point of liquid nitrogen (77 K). It is shown that high-T(c) superconductors are similar to conventional type-II superconductors with paired holes instead of paired electrons. The nature of the electromagnetic response of a superconductor is illustrated with a two-fluid model, and surface resistance and conductor loss are assessed. Several microwave applications of high-T(c) superconductors are outlined including a six-pole dielectric loaded cavity filter used in multiplexers on current communication satellites and a four-pole superconducting filter. An implementation of a chirp filter using superconducting striplines with a cascaded array of backward-wave couplers to achieve a downchirp is presented as well as a 60-GHz phased antenna utilizing microstrip lines in the feed network.

Transport critical current measurement apparatus using liquid nitrogen cooled high-T(c) superconducting magnet with variable temperature insert.

PubMed

Nishijima, G; Kitaguchi, H; Tshuchiya, Y; Nishimura, T; Kato, T

2013-01-01

We have developed an apparatus to investigate transport critical current (I(c)) as a function of magnetic field and temperature using only liquid nitrogen. The apparatus consists of a (Bi,Pb)(2)Sr(2)Ca(2)Cu(3)O(10) (Bi-2223) superconducting magnet, an outer dewar, and a variable temperature insert (VTI). The magnet, which is operated in depressurized liquid nitrogen, generates magnetic field up to 1.26 T. The sample is also immersed in liquid nitrogen. The pressure in the VTI is controlled from 0.02 to 0.3 MPa, which corresponds to temperature ranging from 66 to 88 K. We have confirmed the long-term stable operation of the Bi-2223 magnet at 1 T. The temperature stability of the sample at high transport current was also demonstrated. The apparatus provides easy-operating I(c) measurement environment for a high-T(c) superconductor up to 500 A in magnetic fields up to 1 T and in temperatures ranging from 66 to 88 K.

Local observation of reverse-domain superconductivity in a superconductor-ferromagnet hybrid.

PubMed

Fritzsche, J; Moshchalkov, V V; Eitel, H; Koelle, D; Kleiner, R; Szymczak, R

2006-06-23

Nanoscale magnetic and superconducting properties of the superconductor-ferromagnet Nb/PbFe12O19 hybrid were studied as a function of applied magnetic fields. Low-temperature scanning laser microscopy (LTSLM) together with transport measurements were carried out in order to reveal local variations of superconductivity induced by the magnetic field template produced by the ferromagnetic substrate. Room temperature magnetic force microscopy (MFM) was performed and magnetization curves were taken at room and low temperature to investigate the magnetic properties of the hybrid. Comparative analysis of the LTSLM and the MFM images has convincingly demonstrated the presence of the reverse-domain superconductivity.

A study of enhancing critical current densities (J(sub c)) and critical temperature (T(sub c)) of high-temperature superconductors

NASA Technical Reports Server (NTRS)

Vlasse, Marcus

1992-01-01

The development of pure phase 123 and Bi-based 2223 superconductors has been optimized. The pre-heat processing appears to be a very important parameter in achieving optimal physical properties. The synthesis of pure phases in the Bi-based system involves effects due to oxygen partial pressure, time, and temperature. Orientation/melt-sintering effects include the extreme c-axis orientation of Yttrium 123 and Bismuth 2223, 2212, and 2201 phases. This orientation is conductive to increasing critical currents. A procedure was established to substitute Sr for Ba in Y-123 single crystals.

Topological aspect and the pairing symmetries on spin-triplet chiral p-wave superconductor under strain

NASA Astrophysics Data System (ADS)

Imai, Yoshiki; Sigrist, Manfred

2018-05-01

Motivated by recent experiments on Sr2RuO4, the effect of uniaxial strain on the chiral p-wave superconductor is discussed. We study particularly the relation between the topological indices and different pairing states in the superconducting phase through the thermal Hall conductivity, which is proportional to temperature and the Chern number in the very low-temperature limit. We show that the temperature-dependence of the thermal Hall conductivity under uniaxial strain depends strongly on the form of the pairing state. The obtained result may provide a possible experimental probe for the pairing structure in Sr2RuO4.

Electronic Phase Separation in Iron Selenide (Li,Fe)OHFeSe Superconductor System

NASA Astrophysics Data System (ADS)

Mao, Yiyuan; Li, Jun; Huan, Yulong; Yuan, Jie; Li, Zi-an; Chai, Ke; Ma, Mingwei; Ni, Shunli; Tian, Jinpeng; Liu, Shaobo; Zhou, Huaxue; Zhou, Fang; Li, Jianqi; Zhang, Guangming; Jin, Kui; Dong, Xiaoli; Zhao, Zhongxian

2018-05-01

The phenomenon of phase separation into antiferromagnetic (AFM) and superconducting (SC) or normal-state regions has great implication for the origin of high-temperature (high-Tc) superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the Tc of (Li, Fe)OHFeSe superconductor is questioned. Here we report a systematic study on a series of (Li, Fe)OHFeSe single crystal samples with Tc up to ~41 K. We observe an evident drop in the static magnetization at Tafm ~125 K, in some of the SC (Tc < ~38 K, cell parameter c < ~9.27 {\\AA}) and non-SC samples. We verify that this AFM signal is intrinsic to (Li, Fe)OHFeSe. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal (below Tafm) or SC (below Tc) state in (Li, Fe)OHFeSe. We explain such coexistence by electronic phase separation, similar to that in high-Tc cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of (Li, Fe)OHFeSe, particularly it is never observed in the SC samples of Tc > ~38 K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. It is suggested that the microscopic static phase separation reaches vanishing point in high-Tc (Li, Fe)OHFeSe, by the occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as Tafm reported previously for a (Li, Fe)OHFeSe (Tc ~42 K) single crystal. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-Tc superconductivity.

Study of the second magnetization peak and the pinning behaviour in Ba(Fe0.935Co0.065)2As2 pnictide superconductor

NASA Astrophysics Data System (ADS)

Sundar, Shyam; Mosqueira, J.; Alvarenga, A. D.; Sóñora, D.; Sefat, A. S.; Salem-Sugui, S., Jr.

2017-12-01

Isothermal magnetic field dependence of magnetization and magnetic relaxation measurements were performed for the H\\parallel {{c}} axis on a single crystal of Ba(Fe0.935 Co0.065)2As2 pnictide superconductor having T c = 21.7 K. The second magnetization peak (SMP) for each isothermal M(H) was observed in a wide temperature range from T c to the lowest temperature of measurement (2 K). The magnetic field dependence of relaxation rate R(H), showed a peak (H spt) between H on (onset of SMP in M(H)) and H p (peak field of SMP in M(H)), which is likely to be related to a vortex-lattice structural phase transition, as suggested in the literature for a similar sample. In addition, the magnetic relaxation measured for magnetic fields near H spt showed some noise, which might be the signature of the structural phase transition of the vortex lattice. Analysis of the magnetic relaxation data using Maley’s criterion and the collective pinning theory suggested that the SMP in the sample was due to the collective (elastic) to plastic creep crossover, which was also accompanied by a rhombic to square vortex lattice phase transition. Analysis of the pinning force density suggested a single dominating pinning mechanism in the sample, which did not showing the usual δ {l} and δ {T}{{c}} nature of pinning. The critical current density (J c), estimated using the Bean critical state model, was found to be 5 × 105 A cm- 2 at 2 K in the zero magnetic field limit. Surprisingly, the maximum of the pinning force density was not responsible for the maximum value of the critical current density in the sample.

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

NASA Astrophysics Data System (ADS)

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

2012-10-01

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

Sensitivity of gap symmetry to an incipient band: Application to iron based superconductors

NASA Astrophysics Data System (ADS)

Mishra, Vivek; Scalapino, Douglas; Maier, Thomas

Observation of high temperature superconductivity in iron-based superconductors with a submerged hole band has attracted wide interest. A spin fluctuation mediated pairing mechanism has been proposed as a possible explanation for the high transition temperatures observed in these systems. Here we discuss the importance of the submerged band in the context of the gap symmetry. We show that the incipient band can lead to an attractive pairing interaction and thus have significant effects on the pairing symmetry. We propose a framework to include the effect of the incipient band in the standard multi-orbital spin-fluctuation theories which are widely used for studying various iron-based superconductors. Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.

Effects of magnetic and nonmagnetic impurities on the spin susceptibility of a noncentrosymmetrical superconductor: Application to CePt3Si

NASA Astrophysics Data System (ADS)

Yavari, H.; Mokhtari, M.; Tamaddonpour, M.

2013-10-01

The combined effect of nonmagnetic and magnetic impurities on the spin susceptibility of a noncentrosymmetrical superconductor by considering a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components is investigated. For clean superconductor CePt3Si, the low-temperature dependence (T →0) of spin susceptibility is linear which suggests that the gap function has line nodes, consistent with our gap model. We will show that in the presence of magnetic impurities the susceptibility does not vanish even in the absence of spin orbit coupling and in the region where the energy gap still is finite, and in the low concentration of magnetic impurities the spin susceptibility at zero temperature is proportional to impurity concentration.

Superconductivity between standard types: Multiband versus single-band materials

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

Vagov, A.; Shanenko, A. A.; Milošević, M. V.

In the nearest vicinity of the critical temperature, types I and II of conventional single-band superconductors interchange at the Ginzburg-Landau parameter κ = 1/√2. At lower temperatures this point unfolds into a narrow but finite interval of κ’s, shaping an intertype (transitional) domain in the (κ,T ) plane. In the present work, based on the extended Ginzburg-Landau formalism, we show that the same picture of the two standard types with the transitional domain in between applies also to multiband superconductors. However, the intertype domain notably widens in the presence of multiple bands and can become extremely large when the systemmore » has a significant disparity between the band parameters. It is concluded that many multiband superconductors, such as recently discovered borides and iron-based materials, can belong to the intertype regime.« less

Unconventional iron-based superconductor CsCa2Fe4As4F2: A first-principle study

NASA Astrophysics Data System (ADS)

Singh, Birender; Kumar, Pradeep

2018-05-01

In the present work, we have investigated the structural and electronic properties of newly discovered iron based superconductor CsCa2Fe4As4F2 using first principles calculations. Analysis of the density of states at the Fermi level suggests that Fe-3d states have dominating contribution, and within these 3d states contribution of eg states is significant suggesting multi-band nature of this superconductor. The upper bound of superconducting transition temperature, estimated using electron-phonon coupling constant is found to be ˜2.6 K. To produce the experimental value of transition temperature (28.2 K), a 4-5 times increase in the electron-phonon constant is necessary, hinting that conventional electron-phonon coupling is not enough to explain the origin of superconductivity.

FINAL REPORT. DOE Grant Award Number DE-SC0004062

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

Chiesa, Luisa

With the support of the DOE-OFES Early Career Award and the Tufts startup support the PI has developed experimental and analytical expertise on the electromechanical characterization of Low Temperature Superconductor (LTS) and High Temperature Superconductor (HTS) for high magnetic field applications. These superconducting wires and cables are used in fusion and high-energy physics magnet applications. In a short period of time, the PI has built a laboratory and research group with unique capabilities that include both experimental and numerical modeling effort to improve the design and performance of superconducting cables and magnets. All the projects in the PI’s laboratory exploremore » the fundamental electromechanical behavior of superconductors but the types of materials, geometries and operating conditions are chosen to be directly relevant to real machines, in particular fusion machines like ITER.« less

A Natural Application for High Temperature Superconductors: a Bearing for the Azimuth Mount of a Lunar Telescope

NASA Technical Reports Server (NTRS)

Ma, Ki; Lamb, Mark; Chen, Peter; Wilson, Thomas; Cooley, Rodger; Xia, Harold; Fowler, Clay; Chen, Quark; Chu, Wei-Kan

1995-01-01

A bearing for telescope mounts on the moon has to function in a cold dusty vacuum environment that impairs the operation of almost all traditional bearings, but it is a natural environment for bearings constructed out of magnets and high temperature superconductors. The challenge lies not so much in the weight of the telescope that has to be supported, but in the smoothness of forces required for precision positioning control over a long stretch of time without human intervention. In this paper, we present a design of hybrid superconductor magnet bearings intended for use on the azimuth mount of an altitude-azimuth telescope mount system. In addition to the general features of hybrid super conducting magnet bearings, we will address particular issues connected with the application of these bearings on a telescope mount.

Compact terahertz passive spectrometer with wideband superconductor-insulator-superconductor mixer.

PubMed

Kikuchi, K; Kohjiro, S; Yamada, T; Shimizu, N; Wakatsuki, A

2012-02-01

We developed a compact terahertz (THz) spectrometer with a superconductor-insulator-superconductor (SIS) mixer, aiming to realize a portable and highly sensitive spectrometer to detect dangerous gases at disaster sites. The receiver cryostat which incorporates the SIS mixer and a small cryocooler except for a helium compressor has a weight of 27 kg and dimensions of 200 mm × 270 mm × 690 mm. In spite of the small cooling capacity of the cryocooler, the SIS mixer is successfully cooled lower than 4 K, and the temperature variation is suppressed for the sensitive measurement. By adopting a frequency sweeping system using photonic local oscillator, we demonstrated a spectroscopic measurement of CH(3)CN gas in 0.2-0.5 THz range.

A 0.2-0.5 THz single-band heterodyne receiver based on a photonic local oscillator and a superconductor-insulator-superconductor mixer

NASA Astrophysics Data System (ADS)

Kohjiro, Satoshi; Kikuchi, Kenichi; Maezawa, Masaaki; Furuta, Tomofumi; Wakatsuki, Atsushi; Ito, Hiroshi; Shimizu, Naofumi; Nagatsuma, Tadao; Kado, Yuichi

2008-09-01

We have demonstrated that a superconductor-insulator-superconductor (SIS) mixer pumped by a photonic local oscillator (LO) covers the whole frequency range of 0.2-0.5THz. In the bandwidth of 74% of the center frequency, this single-band receiver exhibits noise temperature of TRX⩽20hf/kB, where h is Planck's constant, f is the frequency, and kB is Boltzmann's constant. Resultant TRX is almost equal to TRX of the identical SIS mixer pumped by three conventional frequency-multiplier-based LOs which share the 0.2-0.5THz band. This technique will contribute to simple, wide-band, and low-noise heterodyne receivers in the terahertz region.

High-temperature superconductor antenna investigations

NASA Technical Reports Server (NTRS)

Karasack, Vincent G.

1990-01-01

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

Nanoscale Investigation of New Fe-Based Superconductors

DTIC Science & Technology

2012-10-15

temperature over 55K in one unit cell FeSe film on SrTiO3 substrate [4]. In addition, a clear diamagnetic signal around 40K was observed in as-grown FeSe nano ...scale. Comparing with other two kinds of nano -scale samples, ultrathin film and Report Documentation Page Form ApprovedOMB No. 0704-0188 Public...unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 nano -particles, crystalline nanowire (NW) in

Quasi permanent superconducting magnet of very high field

NASA Technical Reports Server (NTRS)

Ren, Y.; Liu, J.; Weinstein, R.; Chen, I. G.; Parks, D.; Xu, J.; Obot, V.; Foster, C.

1993-01-01

We report on persistent field in a quasi-permanent magnet made of high temperature superconductor. The material has an average of 40 percent molar excess of Y, relative to Y1Ba2Cu3O7 and has been irradiated with high energy light ions at 200 MeV. The magnet, which traps 1.52 T at 77.3 K, traps nearly 4 T at 64.5 K. No evidence of giant flux jump or sample cracking was observed.

Search for ferromagnetic order in overdoped copper-oxide superconductors

DOE PAGES

Wu, J.; Lauter, V.; Ambaye, H.; ...

2017-04-05

In copper-oxides that show high-temperature superconductivity (HTS), the critical temperature (Tc) has a dome-shaped doping dependence. The cause of demise of both Tc and superfluid density ns on the overdoped side is a major puzzle. A recent study of transport and diamagnetism in a large number of overdoped La2-xSrxCuO4 (LSCO) films shows that this cannot be accounted for by disorder within the conventional Bardeen-Cooper-Schrieffer theory. This brings to focus an alternative explanation — competition of HTS with ferromagnetic order, fluctuating in superconducting samples and static beyond the superconductor-to-metal transition. Here, we examine this proposal by growing single-crystal LSCO thin filmsmore » with doping on both sides of the transition by molecular beam epitaxy, and using polarized neutron reflectometry to measure their magnetic moments. In a heavily overdoped, metallic but non-superconducting LSCO (x = 0.35) film, the spin asymmetry of reflectivity shows a very small static magnetic moment (~2 emu/cm3). Less-doped, superconducting LSCO films show no magnetic moment in neutron reflectivity, both above and below Tc. Therefore, the collapse of HTS with overdoping is not caused by competing ferromagnetic order.« less

Degradation free epoxy impregnation of REBCO coils and cables

NASA Astrophysics Data System (ADS)

Barth, C.; Bagrets, N.; Weiss, K.-P.; Bayer, C. M.; Bast, T.

2013-05-01

In applications utilizing high-temperature superconductors (HTS) under high mechanical loads as high-field magnets or rotors of generators and motors, the rare-earth-barium-copper-oxide (REBCO) tapes have to be stabilized mechanically. This is achieved using support structures of structural materials and filling the voids in the support through the impregnation of the tapes. The impregnation prevents movement of the tapes and distributes mechanical loads evenly. With high mechanical strengths and low sensitivities to rapid temperature changes, epoxy resins are desired materials for the impregnation of superconductor tapes. However, a strong decrease of the current-carrying capabilities was observed in previous epoxy-impregnated REBCO coils. In this work the thermal expansion mismatches between epoxy resins and REBCO tapes are identified as the cause of these degradations. Fillers are used to reduce the thermal expansions of glues and resins. Mixtures with varying filler contents are analyzed systematically. Their thermal expansions and the corresponding degradations of short REBCO tape samples are measured. A mixture of epoxy resin and filler is found which allows degradation-free impregnation of REBCO tapes. This mixture is validated on a 1.2 m long 15 × 5 Roebel-assembled-coated-conductor (RACC) cable from Industrial Research Limited (IRL).

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

PubMed

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

2017-04-01

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

Inhomogeneous Phase Effect of Smart Meta-Superconducting MgB2

NASA Astrophysics Data System (ADS)

Li, Yongbo; Chen, Honggang; Qi, Weichang; Chen, Guowei; Zhao, Xiaopeng

2018-05-01

The inhomogeneous phase of a smart meta-superconductor has a great effect on its superconductivity. In this paper, the effect of concentration, dimensions, electroluminescence (EL) intensity, and distribution of the inhomogeneous phase on the superconducting critical temperature (TC) has been systematically investigated. An ex situ solid sintering was utilized to prepare smart meta-superconducting MgB2 doped with six kinds of electroluminescent materials, such as YVO4{:}Eu^{3+} and Y2O3{:}Eu^{3+} flakes. Elemental mappings through energy dispersive spectroscopy (EDS) show that the inhomogeneous phase is comparatively uniformly dispersed around the MgB2 particles; thus V, Y, and Eu were accumulated at a small area. The measurement results show that the optimum doping concentration of the meta-superconducting MgB2 is 2.0 wt%. The offset temperature (TC^{{ off}}) of the sample doped with 2.0 wt% dopant A is 1.6 K higher than that of pure MgB2. The improvement in TC^{{ off}} is likely related to the sizes, thickness, and EL intensity of the inhomogeneous phase of MgB2 smart meta-superconductor. This experiment provides a novel approach to enhance TC.

Effect of Zn on the structural and electrical properties of high temperature HgBa2Ca2Cu3O8+δ superconductor

NASA Astrophysics Data System (ADS)

Omar, Bilal A.; Fathi, Sabah J.; Jassim, Kareem A.

2018-05-01

Bulk polycrystalline HgBa2Ca2-yZnyCu3O8+δ compound samples with y =0.0, 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3, are synthesized by a solid state reaction process. Study identifies Zinc partial substitution on superconductivity behavior. Structural properties are studied by using X-ray powder pattern, the high temperature phase superconductor (Hg-1223) of the tetragonal structure didn't change with the partial substitution of Zn ions in Ca site, lattice parameters c, c/a are established to vary Zn-substitution. The surface morphology has been studied by using atomic force microscopes (AFM), showed that all specimens have good crystalline and homogeneous surface. Also give a best nano size value is 83.29 nm at y=0.05. Four probe technique is used to measure Tc. The highest Tc and oxygen content were found to be Tc=132 K for y=0.05 after that, Tc decreases from 132 K to 115 K with increasing Zn. In addition, dielectric properties (dielectric constant, dielectric loss factor, and the alternating electrical conductivity) are characterized directly by relating with Zn concentration.

Search for ferromagnetic order in overdoped copper-oxide superconductors

PubMed Central

Wu, J.; Lauter, V.; Ambaye, H.; He, X.; Božović, I.

2017-01-01

In copper-oxides that show high-temperature superconductivity (HTS), the critical temperature (Tc) has a dome-shaped doping dependence. The cause of demise of both Tc and superfluid density ns on the overdoped side is a major puzzle. A recent study of transport and diamagnetism in a large number of overdoped La2−xSrxCuO4 (LSCO) films shows that this cannot be accounted for by disorder within the conventional Bardeen-Cooper-Schrieffer theory. This brings to focus an alternative explanation — competition of HTS with ferromagnetic order, fluctuating in superconducting samples and static beyond the superconductor-to-metal transition. Here, we examine this proposal by growing single-crystal LSCO thin films with doping on both sides of the transition by molecular beam epitaxy, and using polarized neutron reflectometry to measure their magnetic moments. In a heavily overdoped, metallic but non-superconducting LSCO (x = 0.35) film, the spin asymmetry of reflectivity shows a very small static magnetic moment (~2 emu/cm3). Less-doped, superconducting LSCO films show no magnetic moment in neutron reflectivity, both above and below Tc. Therefore, the collapse of HTS with overdoping is not caused by competing ferromagnetic order. PMID:28378795

High Temperature Superconducting Materials Database

National Institute of Standards and Technology Data Gateway

SRD 62 NIST High Temperature Superconducting Materials Database (Web, free access)   The NIST High Temperature Superconducting Materials Database (WebHTS) provides evaluated thermal, mechanical, and superconducting property data for oxides and other nonconventional superconductors.

Superconductor-Insulator Transition in NbTiN Films

NASA Astrophysics Data System (ADS)

Burdastyh, M. V.; Postolova, S. V.; Baturina, T. I.; Proslier, T.; Vinokur, V. M.; Mironov, A. Yu.

2017-12-01

Experimental results indicating a direct disorder-induced superconductor-insulator transition in NbTiN thin films have been reported. It has been shown that an increase in the resistance per square in the normal state is accompanied by the suppression of the critical temperature of the superconducting transition T c according to the fermion mechanism of suppression of superconductivity by disorder. At the same time, the temperature of the Berezinskii-Kosterlitz-Thouless transition is completely suppressed at a nonzero critical temperature and, then, the ground state changes to insulating, which is characteristic of the boson model of suppression of superconductivity by disorder. It has been shown that the temperature dependences of the resistance of insulating films follow the Arrhenius activation law.

Atomic layer epitaxy of YBaCuO for optoelectronic applications

NASA Technical Reports Server (NTRS)

Skogman, R. A.; Khan, M. A.; Van Hove, J. M.; Bhattarai, A.; Boord, W. T.

1992-01-01

An MOCVD-based atomic-layer epitaxy process is being developed as a potential solution to the problems of film-thickness and interface-abruptness control which are encountered when fabricating superconductor-insulator-superconductor devices using YBa2Cu3O(7-x). In initial studies, the atomic-layer MOCVD process yields superconducting YBa2Cu3O(7-x) films with substrate temperatures of 605 C during film growth, and no postdeposition anneal. The low temperature process yields a smooth film surface and can reduce interface degradation due to diffusion.

High-temperature superconductors for space power transmission lines

NASA Astrophysics Data System (ADS)

Hull, John R.; Myers, Ira T.

1989-08-01

Analysis of high temperature superconductors (HTS) for space power transmission lines shows that they have the potential to provide low weight alternatives to conventional power distribution systems, especially for line lengths greater than 100 m. The use of directional radiators, combined with the natural vacuum of space, offers the possibility of reducing or eliminating the heat flux from the environment that dominates loss in terrestrial systems. This leads to scaling laws that favor flat conductor geometries. From a total launch weight viewpoint, HTS transmission lines appear superior, even with presently attainable values of current density.

Magnetic refrigeration using flux compression in superconductors

NASA Technical Reports Server (NTRS)

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

1990-01-01

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

Q factor of megahertz LC circuits based on thin films of YBaCuO high-temperature superconductor

NASA Astrophysics Data System (ADS)

Masterov, D. V.; Pavlov, S. A.; Parafin, A. E.

2008-05-01

High-frequency properties of resonant structures based on thin films of YBa2Cu3O7 δ high-temperature superconductor are studied experimentally in the frequency range 30 100 MHz. The structures planar induction coils with a self-capacitance fabricated on neodymium gallate and lanthanum aluminate substrates. The unloaded Q factor of the circuits exceeds 2 × 105 at 77 K and 40 MHz. Possible loss mechanisms that determine the Q factor of the superconducting resonant structures in the megahertz range are considered.

Passivation of high temperature superconductors

NASA Technical Reports Server (NTRS)

Vasquez, Richard P. (Inventor)

1991-01-01

The surface of high temperature superconductors such as YBa2Cu3O(7-x) are passivated by reacting the native Y, Ba and Cu metal ions with an anion such as sulfate or oxalate to form a surface film that is impervious to water and has a solubility in water of no more than 10(exp -3) M. The passivating treatment is preferably conducted by immersing the surface in dilute aqueous acid solution since more soluble species dissolve into the solution. The treatment does not degrade the superconducting properties of the bulk material.

High-temperature superconductivity using a model of hydrogen bonds.

PubMed

Kaplan, Daniel; Imry, Yoseph

2018-05-29

Recently, there has been much interest in high-temperature superconductors and more recently in hydrogen-based superconductors. This work offers a simple model that explains the behavior of the superconducting gap based on naive BCS (Bardeen-Cooper-Schrieffer) theory and reproduces most effects seen in experiments, including the isotope effect and [Formula: see text] enhancement as a function of pressure. We show that this is due to a combination of the factors appearing in the gap equation: the matrix element between the proton states and the level splitting of the proton.

Processing and property evaluation of metal matrix superconducting materials

NASA Technical Reports Server (NTRS)

Rao, Appajosula S.

1995-01-01

Metal - superconductor (YBCO) systems have been prepared and characterized by resistivity, ac susceptibility and dc SQUID magnetic moment measurements. The silver composites showed superconducting transition for all the composites processed and the superconducting transition temperature tends to depend upon the concentration of the silver in the composite. Aluminum composites showed an unusual resistivity results with two transitions around 90 K and 120 K. The superconducting property of silver composites can be explained qualitatively in terms of the proximity theory that has been suggested for the low temperature superconductors.

Quantum superconductor-metal transition in a proximity array.

PubMed

Feigel'man, M V; Larkin, A I; Skvortsov, M A

2001-02-26

A theory of the zero-temperature superconductor-metal transition is developed for an array of superconductive islands (of size d) coupled via a disordered two-dimensional conductor with the dimensionless conductance g = Planck's over 2 pi/e(2)R(square)>1. At T = 0 the macroscopically superconductive state of the array with lattice spacing b>d is destroyed at g

Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics

NASA Astrophysics Data System (ADS)

Steglich, Frank; Wirth, Steffen

2016-08-01

This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a ‘conventional’, itinerant QCP can be well understood within Landau’s paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an ‘unconventional’, local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.

Critical Current Test of Liquid Hydrogen Cooled HTC Superconductors under External Magnetic Field

NASA Astrophysics Data System (ADS)

Shirai, Yasuyuki; Shiotsu, Masahiro; Tatsumoto, Hideki; Kobayashi, Hiroaki; Naruo, Yoshihiro; Nonaka, Satoshi; Inatani, Yoshifumi

High-Tc (HTC) superconductors including MgB2 will show excellent properties under temperature of Liquid Hydrogen (LH2:20K), which has large latent heat and low viscosity coefficient. In order to design and fabricate the LH2 cooled superconducting energy devices, we must clear the cooling property of LH2 for superconductors, the cooling system and safety design of LH2 cooled superconducting devices and electro-magnetic property evaluation of superconductors (BSCCO, REBCO and MgB2) and their magnets cooled by LH2. As the first step of the study, an experimental setup which can be used for investigating heat transfer characteristics of LH2 in a pool and also in forced flow (circulation loop with a pump), and also for evaluation of electro-magnetic properties of LH2 cooled superconductors under external magnetic field (up to 7 T). In this paper, we will show a short sketch of the experimental set-up, practical experiences in safety operation of liquid hydrogen cooling system and example test results of critical current evaluation of HTC superconductors cooled by LH2.

Structural, electrical and mechanical properties of selenium doped thallium based high-temperature superconductors

NASA Astrophysics Data System (ADS)

Cavdar, S.; Kol, N.; Koralay, H.; Ozturk, O.; Asikuzun, E.; Tasci, A. T.

2016-01-01

In this study, highly-refined chemical powders were synthesized by having them ready in appropriate stoichiometric proportions with conventional solid state reaction method so that they would produce the superconductor TlPb0.3Sr2Ca1-xSexCu2Oy (x = 0; 0.4; 0.6; 1.0). This study aims to understand effect of the selenium doping on the superconducting, structural and mechanical properties of the aforementioned superconducting material. The effect of the doping rates on the structural and electrical properties of the sample has been identified. Electrical characteristics of the TlPb0.3Sr2Ca1-xSexCu2Oy material were measured using standard four point probe method. Structural characteristics were examined with the powder X-ray diffractometer (XRD) and scanning electron microscope (SEM). Mechanical properties were analyzed with Vickers microhardness measurements on the sample surface. According to the results, it was observed that the reflection comes from the (00l) and parallel planes increased with Se doping. Particle size increases with increasing doping ratio. According to results of the mechanical measurements, all samples exhibit indentation size effect (ISE) behavior. Comparing the obtained results with theoretical studies, it was understood that Hays Kendall approach is the best method in determination of mechanical properties and analyzing microhardness of the materials.

Screen printed Y and Bi-based superconductors

NASA Technical Reports Server (NTRS)

Haertling, Gene H.; Hsi, Chi-Shiung

1992-01-01

High T(sub c) superconducting thick film was prepared by screen printing process. Y-based (YBa2Cu3O(7 - x)) superconducting thick films were printed on 211/Al2O3, SNT/Al2O3, and YSZ substrates. Because of poor adhesion of the superconducting thick films to 211/Al2O3 and SNT/Al2O3 substrates, relatively low T(sub c) and J(sub c) values were obtained from the films printed on these substrates. Critical temperatures of YBa2Cu3O(7 - x) thick films deposited on 211/Al2O3 and SNT/Al2O3 substrates were about 80 K. The critical current densities of these films were less than 2 A/cm(exp 2). Higher T(sub c) and J(sub c) films were printed on the YSZ substrates; T(sub c) = 86.4 K and J(sub c) = 50.4 A/cm(exp 2). Multiple lead samples were also prepared on the YSZ substrates. These showed lower T(sub c) and J(sub c) values than plain samples. The heat treatment conditions of the multiple lead samples are still under investigation. Bi-based superconductor thick films have been obtained so far. Improving the superconducting properties of the BSCCO screen printed thick films will be emphasized in future work.

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

Spatially-resolved study of the Meissner effect in superconductors using NV-centers-in-diamond optical magnetometry

NASA Astrophysics Data System (ADS)

Nusran, N. M.; Joshi, K. R.; Cho, K.; Tanatar, M. A.; Meier, W. R.; Bud’ko, S. L.; Canfield, P. C.; Liu, Y.; Lograsso, T. A.; Prozorov, R.

2018-04-01

Non-invasive magnetic field sensing using optically-detected magnetic resonance of nitrogen-vacancy centers in diamond was used to study spatial distribution of the magnetic induction upon penetration and expulsion of weak magnetic fields in several representative superconductors. Vector magnetic fields were measured on the surface of conventional, elemental Pb and Nb, and compound LuNi2B2C and unconventional iron-based superconductors Ba1‑x K x Fe2As2 (x = 0.34 optimal hole doping), Ba(Fe1‑x Co x )2As2 (x = 0.07 optimal electron doping), and stoichiometric CaKFe4As4, using variable-temperature confocal system with diffraction-limited spatial resolution. Magnetic induction profiles across the crystal edges were measured in zero-field-cooled and field-cooled conditions. While all superconductors show nearly perfect screening of magnetic fields applied after cooling to temperatures well below the superconducting transition, T c, a range of very different behaviors was observed for Meissner expulsion upon cooling in static magnetic field from above T c. Substantial conventional Meissner expulsion is found in LuNi2B2C, paramagnetic Meissner effect is found in Nb, and virtually no expulsion is observed in iron-based superconductors. In all cases, good correlation with macroscopic measurements of total magnetic moment is found.

Spatially-resolved study of the Meissner effect in superconductors using NV-centers-in-diamond optical magnetometry

DOE PAGES

Nusran, N. M.; Joshi, K. R.; Cho, K.; ...

2018-04-12

Non-invasive magnetic field sensing using optically-detected magnetic resonance of nitrogen-vacancy centers in diamond was used to study spatial distribution of the magnetic induction upon penetration and expulsion of weak magnetic fields in several representative superconductors. Vector magnetic fields were measured on the surface of conventional, elemental Pb and Nb, and compound LuNi 2B 2C and unconventional iron-based superconductors Ba 1-xK xFe 2As 2 (x = 0.34 optimal hole doping), Ba(Fe 1-xCo x)2As2 (x = 0.07 optimal electron doping), and stoichiometric CaKFe 4As 4, using variable-temperature confocal system with diffraction-limited spatial resolution. Magnetic induction profiles across the crystal edges were measuredmore » in zero-field-cooled and field-cooled conditions. While all superconductors show nearly perfect screening of magnetic fields applied after cooling to temperatures well below the superconducting transition, T c, a range of very different behaviors was observed for Meissner expulsion upon cooling in static magnetic field from above T c. Substantial conventional Meissner expulsion is found in LuNi 2B 2C, paramagnetic Meissner effect is found in Nb, and virtually no expulsion is observed in iron-based superconductors. In all cases, good correlation with macroscopic measurements of total magnetic moment is found.« less

Spatially-resolved study of the Meissner effect in superconductors using NV-centers-in-diamond optical magnetometry

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

Nusran, N. M.; Joshi, K. R.; Cho, K.

Non-invasive magnetic field sensing using optically-detected magnetic resonance of nitrogen-vacancy centers in diamond was used to study spatial distribution of the magnetic induction upon penetration and expulsion of weak magnetic fields in several representative superconductors. Vector magnetic fields were measured on the surface of conventional, elemental Pb and Nb, and compound LuNi 2B 2C and unconventional iron-based superconductors Ba 1-xK xFe 2As 2 (x = 0.34 optimal hole doping), Ba(Fe 1-xCo x)2As2 (x = 0.07 optimal electron doping), and stoichiometric CaKFe 4As 4, using variable-temperature confocal system with diffraction-limited spatial resolution. Magnetic induction profiles across the crystal edges were measuredmore » in zero-field-cooled and field-cooled conditions. While all superconductors show nearly perfect screening of magnetic fields applied after cooling to temperatures well below the superconducting transition, T c, a range of very different behaviors was observed for Meissner expulsion upon cooling in static magnetic field from above T c. Substantial conventional Meissner expulsion is found in LuNi 2B 2C, paramagnetic Meissner effect is found in Nb, and virtually no expulsion is observed in iron-based superconductors. In all cases, good correlation with macroscopic measurements of total magnetic moment is found.« less

Studies of superconducting materials with muon spin rotation

NASA Technical Reports Server (NTRS)

Davis, Michael R.; Stronach, Carey E.; Kossler, W. J.; Schone, H. E.; Yu, X. H.; Uemura, Y. J.; Sternlieb, B. J.; Kempton, J. R.; Oostens, J.; Lankford, W. F.

1989-01-01

The muon spin rotation/relaxation technique was found to be an exceptionally effective means of measuring the magnetic properties of superconductors, including the new high temperature superconductor materials, at the microscopic level. The technique directly measures the magnetic penetration depth (type II superconductors (SC's)) and detects the presence of magnetic ordering (antiferromagnetism or spin-glass ordering were observed in some high temperature superconductor (HTSC's) and in many closely related compounds). Extensive studies of HTSC materials were conducted by the Virginia State University - College of William and Mary - Columbia University collaboration at Brookhaven National Laboratory and TRIUMF (Vancouver). A survey of LaSrCuO and YBaCaCuO systems shows an essentially linear relationship between the transition temperature T(sub c) and the relaxation rate. This appears to be a manifestation of the proportionality between T(sub c) and the Fermi energy, which suggests a high energy scale for the SC coupling, and which is not consistent with the weak coupling of phonon-mediated SC. Studies of LaCuO and YBaCuO parent compounds show clear evidence of antiferromagnetism. YBa2Cu(3-x)CO(x)O7 shows the simultaneous presence of spin-glass magnetic ordering and superconductivity. Three-dimensional SC, (Ba, K) BiO3, unlike the layered CuO-based compounds, shows no suggestion of magnetic ordering. Experimental techniques and theoretical implications are discussed.

Positron Annihilation Measurements of High Temperature Superconductors

NASA Astrophysics Data System (ADS)

Jung, Kang

1995-01-01

The temperature dependence of positron annihilation parameters has been measured for basic YBCO, Dy-doped, and Pr-doped superconducting compounds. The physical properties, such as crystal structure, electrical resistance, and critical temperature, have been studied for all samples. In the basic YBCO and Dy-doped samples, the defect -related lifetime component tau_{2 } was approximately constant from room temperature to above the critical temperature and then showed a step -like decrease in the temperature range 90K { ~} 40K. No significant temperature dependence was found in the short- and long-lifetime components, tau_{1} and tau_{3}. The x-ray diffraction data showed that the crystal structure of these two samples was almost the same. These results indicated that the electronic structure changed below the critical temperature. No transition was observed in the Pr-doped YBCO sample. The advanced computer program "PFPOSFIT" for positron lifetime analysis was modified to run on the UNIX system of the University of Utah. The destruction of superconductivity with Pr doping may be due to mechanisms such as hole filling or hole localization of the charge carriers and may be related to the valence state of the Pr ion. One-parameter analyses like the positron mean lifetime parameter and the Doppler line shape parameter S also have been studied. It was found that a transition in Doppler line shape parameter S was associated with the superconducting transition temperature in basic YBCO, Dy -doped, and 0.5 Pr-doped samples, whereas no transition was observed in the nonsuperconducting Pr-doped sample. The Doppler results indicate that the average electron momentum at the annihilation sites increases as temperature is lowered across the superconducting transition range and that electronic structure change plays an important role in high temperature superconductivity.

Adaptation of superconducting fault current limiter to high-speed reclosing

NASA Astrophysics Data System (ADS)

Koyama, T.; Yanabu, S.

2009-10-01

Using a high temperature superconductor, we constructed and tested a model superconducting fault current limiter (SFCL). The superconductor might break in some cases because of its excessive generation of heat. Therefore, it is desirable to interrupt early the current that flows to superconductor. So, we proposed the SFCL using an electromagnetic repulsion switch which is composed of a superconductor, a vacuum interrupter and a by-pass coil, and its structure is simple. Duration that the current flow in the superconductor can be easily minimized to the level of less than 0.5 cycle using this equipment. On the other hand, the fault current is also easily limited by large reactance of the parallel coil. There is duty of high-speed reclosing after interrupting fault current in the electric power system. After the fault current is interrupted, the back-up breaker is re-closed within 350 ms. So, the electromagnetic repulsion switch should return to former state and the superconductor should be recovered to superconducting state before high-speed reclosing. Then, we proposed the SFCL using an electromagnetic repulsion switch which employs our new reclosing function. We also studied recovery time of the superconductor, because superconductor should be recovered to superconducting state within 350 ms. In this paper, the recovery time characteristics of the superconducting wire were investigated. Also, we combined the superconductor with the electromagnetic repulsion switch, and we did performance test. As a result, a high-speed reclosing within 350 ms was proven to be possible.

Surface impedance and optimum surface resistance of a superconductor with an imperfect surface

NASA Astrophysics Data System (ADS)

Gurevich, Alex; Kubo, Takayuki

2017-11-01

We calculate a low-frequency surface impedance of a dirty, s -wave superconductor with an imperfect surface incorporating either a thin layer with a reduced pairing constant or a thin, proximity-coupled normal layer. Such structures model realistic surfaces of superconducting materials which can contain oxide layers, absorbed impurities, or nonstoichiometric composition. We solved the Usadel equations self-consistently and obtained spatial distributions of the order parameter and the quasiparticle density of states which then were used to calculate a low-frequency surface resistance Rs(T ) and the magnetic penetration depth λ (T ) as functions of temperature in the limit of local London electrodynamics. It is shown that the imperfect surface in a single-band s -wave superconductor results in a nonexponential temperature dependence of Z (T ) at T ≪Tc which can mimic the behavior of multiband or d -wave superconductors. The imperfect surface and the broadening of the gap peaks in the quasiparticle density of states N (ɛ ) in the bulk give rise to a weakly temperature-dependent residual surface resistance. We show that the surface resistance can be optimized and even reduced below its value for an ideal surface by engineering N (ɛ ) at the surface using pair-breaking mechanisms, particularly by incorporating a small density of magnetic impurities or by tuning the thickness and conductivity of the normal layer and its contact resistance. The results of this work address the limit of Rs in superconductors at T ≪Tc , and the ways of engineering the optimal density of states by surface nanostructuring and impurities to reduce losses in superconducting microresonators, thin-film strip lines, and radio-frequency cavities for particle accelerators.

Cooling achieved by rotating an anisotropic superconductor in a constant magnetic field: A new perspective

DOE PAGES

Phan, Manh-Huong; Mandrus, David

2016-12-01

A new type of rotary coolers based on the temperature change (ΔT rot) of an anisotropic superconductor when rotated in a constant magnetic field is proposed.We show that at low temperature the Sommerfeld coefficient (B,Θ) of a single crystalline superconductor, such as MgB 2 and NbS 2, sensitively depends on the applied magnetic field (B) and the orientation of the crystal axis (Θ), which is related to the electronic entropy (S E) and temperature (T) via the expression: S E = T. A simple rotation of the crystal from one axis to one another in a constant magnetic field resultsmore » in a change in and hence S E: ΔSE = ΔγT. A temperature change -ΔT rot ~ 0.94 K from a bath temperature of 2.5 K is achieved by simply rotating the single crystal MgB2 by 90° with respect to the c-axis direction in a fixed field of 2 T. ΔT rot can be tuned by adjusting the strength of B within a wide magnetic field range. Our study paves the way for development of new materials and cryogenic refrigerators that are potentially more energy-efficient, simplified, and compact.« less

Cooling achieved by rotating an anisotropic superconductor in a constant magnetic field: A new perspective

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

Phan, Manh-Huong; Mandrus, David

A new type of rotary coolers based on the temperature change (ΔT rot) of an anisotropic superconductor when rotated in a constant magnetic field is proposed.We show that at low temperature the Sommerfeld coefficient (B,Θ) of a single crystalline superconductor, such as MgB 2 and NbS 2, sensitively depends on the applied magnetic field (B) and the orientation of the crystal axis (Θ), which is related to the electronic entropy (S E) and temperature (T) via the expression: S E = T. A simple rotation of the crystal from one axis to one another in a constant magnetic field resultsmore » in a change in and hence S E: ΔSE = ΔγT. A temperature change -ΔT rot ~ 0.94 K from a bath temperature of 2.5 K is achieved by simply rotating the single crystal MgB2 by 90° with respect to the c-axis direction in a fixed field of 2 T. ΔT rot can be tuned by adjusting the strength of B within a wide magnetic field range. Our study paves the way for development of new materials and cryogenic refrigerators that are potentially more energy-efficient, simplified, and compact.« less