Active superconducting devices formed of thin films

DOEpatents

Martens, Jon S.; Beyer, James B.; Nordman, James E.; Hohenwarter, Gert K. G.

1991-05-28

Active superconducting devices are formed of thin films of superconductor which include a main conduction channel which has an active weak link region. The weak link region is composed of an array of links of thin film superconductor spaced from one another by voids and selected in size and thickness such that magnetic flux can propagate across the weak link region when it is superconducting. Magnetic flux applied to the weak link region will propagate across the array of links causing localized loss of superconductivity in the links and changing the effective resistance across the links. The magnetic flux can be applied from a control line formed of a superconducting film deposited coplanar with the main conduction channel and weak link region on a substrate. The devices can be formed of any type to superconductor but are particularly well suited to the high temperature superconductors since the devices can be entirely formed from coplanar films with no overlying regions. The devices can be utilized for a variety of electrical components, including switching circuits, amplifiers, oscillators and modulators, and are well suited to microwave frequency applications.

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

DTIC Science & Technology

1985-12-11

ANALISIS OF THIN-FILM SUPERCONDUCTORS J. Talvacchio, M. A. Janocko, J. R. Gavaler, and A...in the areas of substrate preparation, niobum nitride, nlobium-tin, and molybdenum-rhenium. AN INTEGRATED DEPOSITION AND ANALISI - FACILITT The four...mobility low (64). The voids are separating 1-3 nm clusters of dense deposit. At low deposition temperatures this microstructure will persist near

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.

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.

Quantum Griffiths singularity of superconductor-metal transition in Ga thin films.

PubMed

Xing, Ying; Zhang, Hui-Min; Fu, Hai-Long; Liu, Haiwen; Sun, Yi; Peng, Jun-Ping; Wang, Fa; Lin, Xi; Ma, Xu-Cun; Xue, Qi-Kun; Wang, Jian; Xie, X C

2015-10-30

The Griffiths singularity in a phase transition, caused by disorder effects, was predicted more than 40 years ago. Its signature, the divergence of the dynamical critical exponent, is challenging to observe experimentally. We report the experimental observation of the quantum Griffiths singularity in a two-dimensional superconducting system. We measured the transport properties of atomically thin gallium films and found that the films undergo superconductor-metal transitions with increasing magnetic field. Approaching the zero-temperature quantum critical point, we observed divergence of the dynamical critical exponent, which is consistent with the Griffiths singularity behavior. We interpret the observed superconductor-metal quantum phase transition as the infinite-randomness critical point, where the properties of the system are controlled by rare large superconducting regions. Copyright © 2015, American Association for the Advancement of Science.

High-Tc superconductor coplanar waveguide filter

NASA Technical Reports Server (NTRS)

Chew, Wilbert; Bajuk, Louis J.; Cooley, Thomas W.; Foote, Marc C.; Hunt, Brian D.; Rascoe, Daniel L.; Riley, A. L.

1991-01-01

Coplanar waveguide (CPW) low-pass filters made of YBa2Cu3O(7-delta) (YBCO) on LaAlO3 substrates, with dimensions suited for integrated circuits, were fabricated and packaged. A complete filter gives a true idea of the advantages and difficulties in replacing thin-film metal with a high-temperature superconductor in a practical circuit. Measured insertion losses in liquid nitrogen were superior to the loss of a similar thin-film copper filter throughout the 0- to 9.5-GHz passband. These results demonstrate the performance of fully patterned YBCO in a practical CPW structure after sealing in a hermetic package.

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.

Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

DOE PAGES

Si, W.; Zhang, C.; Wu, L.; ...

2015-09-01

Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF2 crystalline substrates respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk.more » With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.« less

Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

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

Si, Weidong, E-mail: wds@bnl.gov, E-mail: qiangli@bnl.gov; Zhang, Cheng; Wu, Lijun

2015-08-31

Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF{sub 2} crystalline substrates, respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk. Withmore » large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.« less

Improved superconducting magnet wire

DOEpatents

Schuller, I.K.; Ketterson, J.B.

1983-08-16

This invention is directed to a superconducting tape or wire composed of alternating layers of copper and a niobium-containing superconductor such as niobium of NbTi, Nb/sub 3/Sn or Nb/sub 3/Ge. In general, each layer of the niobium-containing superconductor has a thickness in the range of about 0.05 to 1.5 times its coherence length (which for Nb/sub 3/Si is 41 A) with each copper layer having a thickness in the range of about 170 to 600 A. With the use of very thin layers of the niobium composition having a thickness within the desired range, the critical field (H/sub c/) may be increased by factors of 2 to 4. Also, the thin layers of the superconductor permit the resulting tape or wire to exhibit suitable ductility for winding on a magnet core. These compositions are also characterized by relatively high values of critical temperature and therefore will exhibit a combination of useful properties as superconductors.

Temperature and Microstructural Effects on the Superconducting Properties of Niobium Thin Films

DOE PAGES

Beebe, Melissa R.; Valente-Feliciano, Anne -Marie; Beringer, Douglas B.; ...

2016-11-23

Here, superconducting thin films have a wide range of dc and RF applications, from detectors to superconducting radio frequency. Amongst the most used materials, niobium (Nb) has the highest critical temperature (TC) and highest lower critical field (HC1) of the elemental superconductors and can be deposited on a variety of substrates, making Nb thin films very appealing for such applications. Here, we present temperature-dependent dc studies on the critical temperature and critical fields of Nb thin films grown on copper and r-plane sapphire surfaces. Additionally, we correlate the dc superconducting properties of these films with their microstructure, which allows formore » the possibility of tailoring future films for a specific application.« less

Epitaxial thin films

DOEpatents

Hunt, Andrew Tye; Deshpande, Girish; Lin, Wen-Yi; Jan, Tzyy-Jiuan

2006-04-25

Epitatial thin films for use as buffer layers for high temperature superconductors, electrolytes in solid oxide fuel cells (SOFC), gas separation membranes or dielectric material in electronic devices, are disclosed. By using CCVD, CACVD or any other suitable deposition process, epitaxial films having pore-free, ideal grain boundaries, and dense structure can be formed. Several different types of materials are disclosed for use as buffer layers in high temperature superconductors. In addition, the use of epitaxial thin films for electrolytes and electrode formation in SOFCs results in densification for pore-free and ideal gain boundary/interface microstructure. Gas separation membranes for the production of oxygen and hydrogen are also disclosed. These semipermeable membranes are formed by high-quality, dense, gas-tight, pinhole free sub-micro scale layers of mixed-conducting oxides on porous ceramic substrates. Epitaxial thin films as dielectric material in capacitors are also taught herein. Capacitors are utilized according to their capacitance values which are dependent on their physical structure and dielectric permittivity. The epitaxial thin films of the current invention form low-loss dielectric layers with extremely high permittivity. This high permittivity allows for the formation of capacitors that can have their capacitance adjusted by applying a DC bias between their electrodes.

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

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.

Electric field effect in superconductor-ferroelectric structures

NASA Technical Reports Server (NTRS)

Lemanov, V. V.

1995-01-01

Electric field effect (the E-effect) in superconductors has been studied since 1960 when Glover and Sherill published their results on a shift of the critical temperature T(sub c) about 0.1 mK in Sn and In thin films under the action Off the field E=300 kV/cm. Stadler was the first to study the effect or spontaneous polarization of ferroelectric substrate on the electric properties of superconductors. He observed that the reversal of polarization of TGS substrate under action of external electric field in Sn-TGS structures induced the T(sub c) shift in Sn about 1.3 mK. Since in this case the effect is determined not by the electric field but by the spontaneous polarization, we may call this effect the P-effect. High-T(sub c) superconductors opened the new possibilities to study the E- and P-effects due to low charge carrier density, as compared to conventional superconductors, and to anomalously small coherence length. Experiments in this field began in many laboratories but a breakthrough was made where a shift in T(sub c) by 50 mK was observed in YBCO thin films. Much higher effects were observed in subsequent studies. The first experiments on the P-effect in high-T(sub c) superconductors were reported elsewhere. In this report we shall give a short description of study on the P-effect in high-T(sub c) superconductors.

Vortex pinning properties in Fe-chalcogenides

NASA Astrophysics Data System (ADS)

Leo, A.; Grimaldi, G.; Guarino, A.; Avitabile, F.; Nigro, A.; Galluzzi, A.; Mancusi, D.; Polichetti, M.; Pace, S.; Buchkov, K.; Nazarova, E.; Kawale, S.; Bellingeri, E.; Ferdeghini, C.

2015-12-01

Among the families of iron-based superconductors, the 11-family is one of the most attractive for high field applications at low temperatures. Optimization of the fabrication processes for bulk, crystalline and/or thin film samples is the first step in producing wires and/or tapes for practical high power conductors. Here we present the results of a comparative study of pinning properties in iron-chalcogenides, investigating the flux pinning mechanisms in optimized Fe(Se{}1-xTe x ) and FeSe samples by current-voltage characterization, magneto-resistance and magnetization measurements. In particular, from Arrhenius plots in magnetic fields up to 9 T, the activation energy is derived as a function of the magnetic field, {U}0(H), whereas the activation energy as a function of temperature, U(T), is derived from relaxation magnetization curves. The high pinning energies, high upper critical field versus temperature slopes near critical temperatures, and highly isotropic pinning properties make iron-chalcogenide superconductors a technological material which could be a real competitor to cuprate high temperature superconductors for high field applications.

Thin film growth of the 2122-phase of BCSCO superconductor with high degree of crystalline perfection

NASA Technical Reports Server (NTRS)

Raina, K. K.; Narayanan, S.; Pandey, R. K.

1992-01-01

Thin films of the 80 K-phase of BiCaSrCu-oxide superconductor having the composition of Bi2Ca1.05Sr2.1Cu2.19O(x) and high degree of crystalline perfection have been grown on c-axis oriented twin free single crystal substrates of NdGaO3. This has been achieved by carefully establishing the growth conditions of the LPE experiments. The temperature regime of 850 to 830 C and quenching of the specimens on the termination of the growth period are found to be pertinent for the growth of quasi-single crystalline superconducting BCSCO films on NdGaO3 substrates. The TEM analysis reveals a single crystalline nature of these films which exhibit 100 percent reflectivity in infrared regions at liquid nitrogen temperature.

Laser surface interaction of high-Tc superconductors

NASA Technical Reports Server (NTRS)

Chen, C. H.; Mccann, M. P.; Phillips, R. C.

1991-01-01

During the past two years, one of the most exciting research fields in science has been the study of the newly discovered high-T(sub c) metal oxide superconductors. Although many theoretical models were proposed, there is no general agreement on any theory to explain these materials. One of the peculiar features of these high-T(sub c) materials is the noninteger number of oxygen atoms. The oxygen content is extremely critical to the superconductive properties. Take YBa2Cu3O(7-x) as an example. Its superconductive properties disappear whenever x is larger than 0.5. The existence of Cu(+ 3) was considered to account for x less than 0.5. However, results from mass spectroscopy of laser desorbed species indicate that significant quantities of oxygen molecules are trapped in the bulk of these high-T(sub c) superconductors. It appears that these trapped oxygen molecules may play key roles in superconductive properties. Preparation of superconductive thin films are considered very important for the applications of these new superconductors for the electronics industry. Fluorescence spectra and ion spectra following laser ablation of high-temperature superconductors were obtained. A real time monitor for preparation of superconductive thin films can possibly be developed.

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.

Epitaxial thin film growth in outer space

NASA Technical Reports Server (NTRS)

Ignatiev, Alex; Chu, C. W.

1988-01-01

A new concept for materials processing in space exploits the ultravacuum component of space for thin-film epitaxial growth. The unique LEO space environment is expected to yield 10-ftorr or better pressures, semiinfinite pumping speeds, and large ultravacuum volume (about 100 cu m) without walls. These space ultravacuum properties promise major improvement in the quality, unique nature, and throughput of epitaxially grown materials, including semiconductors, magnetic materials, and thin-film high-temperature 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.

High- and Mid-temperature Superconducting Sensors for Far IR/Sub-mm Applications in Space

NASA Technical Reports Server (NTRS)

Lakew, Brook; Brasunas, J. C.

2004-01-01

In this review paper an overview of the potential applications of high Tc (approx. 90 K) superconductors (HTS) and mid-Tc (approx. 39 K) superconductors (MTS) thin films in far IR/Sub-mm thermal detectors is presented. HTSs (YBCO, GdBCO etc.) were discovered in the late 80s while superconductivity in MgB2, an MTS, was discovered in 2001. The sharp transition in transport properties of HTS has allowed the fabrication of composite infrared thermal detectors (bolometers) with better figures of merit than thermopile detectors - thermopiles are currently on board the CIRS instrument on the Cassini mission to Saturn. The potential for developing even more sensitive sensors for IR/Sub-mm applications using MgB2 thin films is assessed. Current MgB2 thin film deposition techniques and film quality are reviewed.

Thin film superconductor magnetic bearings

DOEpatents

Weinberger, Bernard R.

1995-12-26

A superconductor magnetic bearing includes a shaft (10) that is subject to a load (L) and rotatable around an axis of rotation, a magnet (12) mounted to the shaft, and a stator (14) in proximity to the shaft. The stator (14) has a superconductor thin film assembly (16) positioned to interact with the magnet (12) to produce a levitation force on the shaft (10) that supports the load (L). The thin film assembly (16) includes at least two superconductor thin films (18) and at least one substrate (20). Each thin film (18) is positioned on a substrate (20) and all the thin films are positioned such that an applied magnetic field from the magnet (12) passes through all the thin films. A similar bearing in which the thin film assembly (16) is mounted on the shaft (10) and the magnet (12) is part of the stator (14) also can be constructed.

Fostered Thermomagnetic Stabilities and Boosted Mechanical Reliability Related to High Trapped Field in Composite Bulk YBa2Cu3O(7-δ) Cryomagnets.

PubMed

Kenfaui, Driss; Sibeud, Pierre-Frédéric; Gomina, Moussa; Louradour, Eric; Chaud, Xavier; Noudem, Jacques G

2015-08-06

In the quest of YBa2Cu3O(7-δ) (Y123) bulk superconductors providing strong magnetic fields without failure, it is of paramount importance to achieve high thermal stabilities to safeguard the magnetic energy inside them during the trapping-field process, and sufficient mechanical reliability to withstand the stresses derived from the Lorenz force. Herein, we experimentally demonstrate a temperature rise induced by dissipative flux motion inside an Y123 thin-wall superconductor, and a significant thermal exchange in a composite bulk Y123 cryomagnet realized by embedding this superconductor with high thermal-conductivity metal network. It resulted in stimulating the maximum trapped field Bm, which reached 6.46 T on 15.9 mm-diameter single disk superconductor after magnetization by field cooling to 17 K under 7 T, leading to an improvement of 18% compared to the thin-wall superconductor. The composite cryomagnet particularly revealed the potential to trap stronger fields if larger magnetic activation is available. By virtue of the pore-free and crack-free microstructure of this cryomagnet, its strength σR was estimated to be 363 MPa, the largest one obtained so far for Y123 bulk superconductors, thus suggesting a striking mechanical reliability that seems to be sufficient to sustain stresses derived from trapped fields stronger than any values hitherto reported.

Nonequilibrium restoration of duality symmetry in the vicinity of the superconductor-to-insulator transition

NASA Astrophysics Data System (ADS)

Tamir, I.; Doron, A.; Levinson, T.; Gorniaczyk, F.; Tewari, G. C.; Shahar, D.

2017-09-01

The magnetic field driven superconductor-to-insulator transition in thin films is theoretically understood in terms of the notion of vortex-charge duality symmetry. The manifestation of such symmetry is the exchange of roles of current and voltage between the superconductor and the insulator. While experimental evidence obtained from amorphous indium oxide films supported such duality symmetry, it is shown to be broken, counterintuitively, at low temperatures where the insulating phase exhibits discontinuous current-voltage characteristics. Here, we demonstrate that it is possible to effectively restore duality symmetry by driving the system beyond the discontinuity into its high current, far from equilibrium, state.

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.

Vortices and quasiparticles near the superconductor-insulator transition in thin films.

PubMed

Galitski, Victor M; Refael, G; Fisher, Matthew P A; Senthil, T

2005-08-12

We study the low temperature behavior of an amorphous superconducting film driven normal by a perpendicular magnetic-field (B). For this purpose we introduce a new two-fluid formulation consisting of fermionized field-induced vortices and electrically neutralized Bogoliubov quasiparticles (spinons) interacting via a long-ranged statistical interaction. This approach allows us to access a novel non-Fermi-liquid phase, which naturally interpolates between the low B superconductor and the high B normal metal. We discuss the properties of the resulting "vortex metal" phase.

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

NASA Technical Reports Server (NTRS)

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

1990-01-01

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

A proposal for epitaxial thin film growth in outer space

NASA Technical Reports Server (NTRS)

Ignatiev, Alex; Chu, C. W.

1988-01-01

A new concept for materials processing in space exploits the ultravacuum component of space for thin film epitaxial growth. The unique low earth orbit space environment is expected to yield 10 to the -14th torr or better pressures, semiinfinite pumping speeds, and large ultravacuum volume without walls. These space ultravacuum properties promise major improvement in the quality, unique nature, and the throughput of epitaxially grown materials. Advanced thin film materials to be epitaxially grown in space include semiconductors, magnetic materials, and thin film high temperature superconductors.

Nonlinear microwave response of an MgB2 thin film

NASA Astrophysics Data System (ADS)

Purnell, A. J.; Cohen, L. F.; Zhai, H. Y.; Christen, H. M.; Paranthaman, M. P.; Lowndes, D. H.; Hao, Ling; Gallop, J. C.

2004-04-01

MgB2 is a two-gap superconductor and as a result may manifest unusual physical properties. The performance of MgB2 films at microwave frequencies has so far been rather poor compared to that of Nb alloys and this may result from intrinsic behaviour related to the double-gap structure or extrinsic properties due to non-optimized thin films. Here we give a detailed report on the microwave magnetic field dependent surface impedance of an MgB2 thin film, using a parallel plate resonator, as a function of temperature. We discuss whether the framework used to analyse nonlinear behaviour for other superconductors, both low and high Tc, but single-gap, has any validity for MgB2 and whether the films are limited by intrinsic or extrinsic behaviour. The key result is the observation of junction-type switching effects at high microwave power.

Superconducting RF materials other than bulk niobium: a review

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

Valente-Feliciano, Anne-Marie

For the last five decades, bulk niobium (Nb) has been the material of choice for Superconducting RF (SRF) cavity applications. Thin film alternatives such as Nb and other higher-Tc materials, mainly Nb compounds and A15 compounds, have been investigated with moderate effort in the past. In recent years, RF cavity performance has approached the theoretical limit for bulk Nb. For further improvement of RF cavity performance for future accelerator projects, research interest is renewed towards alternatives to bulk Nb. Institutions around the world are now investing renewed efforts in the investigation of Nb thin films and superconductors with higher transitionmore » temperature Tc for application to SRF cavities. Our paper gives an overview of the results obtained so far and challenges encountered for Nb films as well as other materials, such as Nb compounds, A15 compounds, MgB2, and oxypnictides, for SRF cavity applications. An interesting alternative using a Superconductor-Insulator- Superconductor multilayer approach has been recently proposed to delay the vortex penetration in Nb surfaces. This could potentially lead to further improvement in RF cavities performance using the benefit of the higher critical field Hc of higher-Tc superconductors without being limited with their lower Hc1.« less

Superconducting RF materials other than bulk niobium: a review

DOE PAGES

Valente-Feliciano, Anne-Marie

2016-09-26

For the last five decades, bulk niobium (Nb) has been the material of choice for Superconducting RF (SRF) cavity applications. Thin film alternatives such as Nb and other higher-Tc materials, mainly Nb compounds and A15 compounds, have been investigated with moderate effort in the past. In recent years, RF cavity performance has approached the theoretical limit for bulk Nb. For further improvement of RF cavity performance for future accelerator projects, research interest is renewed towards alternatives to bulk Nb. Institutions around the world are now investing renewed efforts in the investigation of Nb thin films and superconductors with higher transitionmore » temperature Tc for application to SRF cavities. Our paper gives an overview of the results obtained so far and challenges encountered for Nb films as well as other materials, such as Nb compounds, A15 compounds, MgB2, and oxypnictides, for SRF cavity applications. An interesting alternative using a Superconductor-Insulator- Superconductor multilayer approach has been recently proposed to delay the vortex penetration in Nb surfaces. This could potentially lead to further improvement in RF cavities performance using the benefit of the higher critical field Hc of higher-Tc superconductors without being limited with their lower Hc1.« less

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.

Microwave response of high transition temperature superconducting thin films

NASA Technical Reports Server (NTRS)

Miranda, Felix Antonio

1991-01-01

We have studied the microwave response of YBa2Cu3O(7 - delta), Bi-Sr-Ca-Cu-O, and Tl-Ba-Ca-Cu-O high transition temperature superconducting (HTS) thin films by performing power transmission measurements. These measurements were carried out in the temperature range of 300 K to 20 K and at frequencies within the range of 30 to 40 GHz. Through these measurements we have determined the magnetic penetration depth (lambda), the complex conductivity (sigma(sup *) = sigma(sub 1) - j sigma(sub 2)) and the surface resistance (R(sub s)). An estimate of the intrinsic penetration depth (lambda approx. 121 nm) for the YBa2Cu3O(7 - delta) HTS has been obtained from the film thickness dependence of lambda. This value compares favorably with the best values reported so far (approx. 140 nm) in single crystals and high quality c-axis oriented thin films. Furthermore, it was observed that our technique is sensitive to the intrinsic anisotropy of lambda in this superconductor. Values of lambda are also reported for Bi-based and Tl-based thin films. We observed that for the three types of superconductors, both sigma(sub 1) and sigma(sub 2) increased when cooling the films below their transition temperature. The measured R(sub s) are in good agreement with other R(sub S) values obtained using resonant activity techniques if we assume a quadratic frequency dependence. Our analysis shows that, of the three types of HTS films studied, the YBa2Cu3O(7 - delta) thin film, deposited by laser ablation and off-axis magnetron sputtering are the most promising for microwave applications.

C-band superconductor/semiconductor hybrid field-effect transistor amplifier on a LaAlO3 substrate

NASA Technical Reports Server (NTRS)

Nahra, J. J.; Bhasin, K. B.; Toncich, S. S.; Subramanyam, G.; Kapoor, V. J.

1992-01-01

A single-stage C-band superconductor/semiconductor hybrid field-effect transistor amplifier was designed, fabricated, and tested at 77 K. The large area (1 inch x 0.5 inches) high temperature superconducting Tl-Ba-Ca-Cu-O (TBCCO) thin film was rf magnetron sputtered onto a LaAlO3 substrate. The film had a transition temperature of about 92 K after it was patterned and etched. The amplifier showed a gain of 6 dB and a 3 dB bandwidth of 100 MHz centered at 7.9 GHz. An identical gold amplifier circuit was tested at 77 K, and these results are compared with those from the hybrid amplifier.

High-Temperature-Superconductor Films In Microwave Circuits

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

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.

Operating characteristics of superconducting fault current limiter using 24kV vacuum interrupter driven by electromagnetic repulsion switch

NASA Astrophysics Data System (ADS)

Endo, M.; Hori, T.; Koyama, K.; Yamaguchi, I.; Arai, K.; Kaiho, K.; Yanabu, S.

2008-02-01

Using a high temperature superconductor, we constructed and tested a model Superconducting Fault Current Limiter (SFCL). SFCL which has a vacuum interrupter with electromagnetic repulsion mechanism. We set out to construct high voltage class SFCL. We produced the electromagnetic repulsion switch equipped with a 24kV vacuum interrupter(VI). There are problems that opening speed becomes late. Because the larger vacuum interrupter the heavier weight of its contact. For this reason, the current which flows in a superconductor may be unable to be interrupted within a half cycles of current. In order to solve this problem, it is necessary to change the design of the coil connected in parallel and to strengthen the electromagnetic repulsion force at the time of opening the vacuum interrupter. Then, the design of the coil was changed, and in order to examine whether the problem is solvable, the current limiting test was conducted. We examined current limiting test using 4 series and 2 parallel-connected YBCO thin films. We used 12-centimeter-long YBCO thin film. The parallel resistance (0.1Ω) is connected with each YBCO thin film. As a result, we succeed in interrupting the current of superconductor within a half cycle of it. Furthermore, series and parallel-connected YBCO thin film could limit without failure.

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.

Physics and Materials Science of High Temperature Superconductors

DTIC Science & Technology

1989-08-26

30 L. Tessler: Critical Currents in YBaCuO of Thin Films Obtained by Seguential Evaporation 11:30 - 12:00 D. Mitzi : Ogen and Ion Doping~in... Mitzi , L. W. Lombardo and A. Kapitulnik, Department of Applied Physics, Stanford University, U Stanford, CA; and S. S. Laderman, Circuit Technology

Singular temperature dependence of the equation of state of superconductors with spin–orbit interaction in the low-temperature region

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

Ovchinnikov, Yu. N., E-mail: ovc@itp.ac.ru

The equation of state is investigated for a thin superconducting film in a longitudinal magnetic field and with strong spin-orbit interaction at the critical point. As a first step, the state with the maximal value of the magnetic field for a given value of spin–orbit interaction at T = 0 is chosen. This state is investigated in the low-temperature region. The temperature contribution to the equation of state is weakly singular.

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.

High temperature superconductor materials and applications

NASA Technical Reports Server (NTRS)

Doane, George B., III. (Editor); Banks, Curtis; Golben, John

1991-01-01

One of the areas concerned itself with the investigation of the phenomena involved in formulating and making in the laboratory new and better superconductor material with enhanced values of critical current and temperature. Of special interest were the chemistry, physical processes, and environment required to attain these enhanced desirable characteristics. The other area concerned itself with producing high temperature superconducting thin films by pulsed laser deposition techniques. Such films are potentially very useful in the detection of very low power signals. To perform this research high vacuum is required. In the course of this effort, older vacuum chambers were maintained and used. In addition, a new facility is being brought on line. This latter activity has been replete with the usual problems of bringing a new facility into service. Some of the problems are covered in the main body of this report.

Microelectronic superconducting device with multi-layer contact

DOEpatents

Wellstood, Frederick C.; Kingston, John J.; Clarke, John

1993-01-01

A microelectronic component comprising a crossover is provided comprising a substrate, a first high T.sub.c superconductor thin film, a second insulating thin film comprising SrTiO.sub.3 ; and a third high T.sub.c superconducting film which has strips which crossover one or more areas of the first superconductor film. An insitu method for depositing all three films on a substrate is provided which does not require annealing steps. The photolithographic process is used to separately pattern the high T.sub.c superconductor thin films.

Microelectronic superconducting device with multi-layer contact

DOEpatents

Wellstood, F.C.; Kingston, J.J.; Clarke, J.

1993-10-26

A microelectronic component comprising a crossover is provided comprising a substrate, a first high T[sub c] superconductor thin film, a second insulating thin film comprising SrTiO[sub 3] ; and a third high T[sub c] superconducting film which has strips which crossover one or more areas of the first superconductor film. An in situ method for depositing all three films on a substrate is provided which does not require annealing steps. The photolithographic process is used to separately pattern the high T[sub c] superconductor thin films. 14 figures.

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.

Laser ablated YBa2Cu3O(7-x) high temperature superconductor coplanar waveguide resonator

NASA Technical Reports Server (NTRS)

Valco, G. J.; Blemker, A. R.; Bhasin, K. B.

1992-01-01

Several 8.8-GHz coplanar waveguide resonators are fabricated and tested that are made from laser ablated YBa2Cu3O(7-x) thin films on LaAlO3 substrates. A quality factor of 1250 at 77 K was measured. A correlation between the microwave performance of the resonators and the critical temperature and morphology of the films was observed.

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

PubMed Central

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

2016-01-01

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

Superconductor-Insulator transition in sputtered amorphous MoRu and MoRuN thin films

NASA Astrophysics Data System (ADS)

Makise, K.; Shinozaki, B.; Ichikawa, F.

2018-03-01

This work shows the experimental results of the superconductor-insulator (S-I) transition for amorphous molybdenum ruthenium (MoRu) and molybdenum ruthenium nitride (MoRuN) films. These amorphous films onto c-plane sapphire substrates have been interpreted to be homogeneous by XRD and AFM measurements. Electrical and superconducting properties measurements were carried out on MoRu and MoRuN thin films deposited by reactive sputtering technique. We have analysed the data on R sq (T) based on excess conductivity of superconducting films by the AL and MT term and weak localization and electron-electron interaction for the conductance. MoRu films which offer the most homogeneous film morphology, showed a critical sheet resistance of transition, Rc, of ∼ 2 kΩ. This values is smaller than those previously our reported for quench-condensed MoRu films on SiO underlayer held at liquid He temperature.

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.

Fabrication of high-quality superconductor-insulator-superconductor junctions on thin SiN membranes

NASA Technical Reports Server (NTRS)

Garcia, Edouard; Jacobson, Brian R.; Hu, Qing

1993-01-01

We have successfully fabricated high-quality and high-current density superconductor-insulator-superconductor (SIS) junctions on freestanding thin silicon nitride (SIN) membranes. These devices can be used in a novel millimeter-wave and THz receiver system which is made using micromachining. The SIS junctions with planar antennas were fabricated first on a silicon wafer covered with a SiN membrane, the Si wafer underneath was then etched away using an anisotropic KOH etchant. The current-voltage characteristics of the SIS junctions remained unchanged after the whole process, and the junctions and the membrane survived thermal cycling.

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.

Specific heat measurement set-up for quench condensed thin superconducting films.

PubMed

Poran, Shachaf; Molina-Ruiz, Manel; Gérardin, Anne; Frydman, Aviad; Bourgeois, Olivier

2014-05-01

We present a set-up designed for the measurement of specific heat of very thin or ultra-thin quench condensed superconducting films. In an ultra-high vacuum chamber, materials of interest can be thermally evaporated directly on a silicon membrane regulated in temperature from 1.4 K to 10 K. On this membrane, a heater and a thermometer are lithographically fabricated, allowing the measurement of heat capacity of the quench condensed layers. This apparatus permits the simultaneous thermal and electrical characterization of successively deposited layers in situ without exposing the deposited materials to room temperature or atmospheric conditions, both being irreversibly harmful to the samples. This system can be used to study specific heat signatures of phase transitions through the superconductor to insulator transition of quench condensed films.

Proceedings of the 4th International Conference and Exhibition: World Congress on Superconductivity, volume 1

NASA Technical Reports Server (NTRS)

Krishen, Kumar (Editor); Burnham, Calvin (Editor)

1995-01-01

The papers presented at the 4th International Conference Exhibition: World Congress on Superconductivity held at the Marriott Orlando World Center, Orlando, Florida, are contained in this document and encompass the research, technology, applications, funding, political, and social aspects of superconductivity. Specifically, the areas covered included: high-temperature materials; thin films; C-60 based superconductors; persistent magnetic fields and shielding; fabrication methodology; space applications; physical applications; performance characterization; device applications; weak link effects and flux motion; accelerator technology; superconductivity energy; storage; future research and development directions; medical applications; granular superconductors; wire fabrication technology; computer applications; technical and commercial challenges, and power and energy applications.

Proceedings of the 4th International Conference and Exhibition: World Congress on Superconductivity, Volume 2

NASA Technical Reports Server (NTRS)

Krishen, Kumar (Editor); Burnham, Calvin (Editor)

1995-01-01

This document contains papers presented at the 4th International Conference Exhibition: World Congress on Superconductivity held June 27-July 1, 1994 in Orlando, Florida. These documents encompass research, technology, applications, funding, political, and social aspects of superconductivity. The areas covered included: high-temperature materials; thin films; C-60 based superconductors; persistent magnetic fields and shielding; fabrication methodology; space applications; physical applications; performance characterization; device applications; weak link effects and flux motion; accelerator technology; superconductivity energy; storage; future research and development directions; medical applications; granular superconductors; wire fabrication technology; computer applications; technical and commercial challenges; and power and energy applications.

Metal-superconductor transition in low-dimensional superconducting clusters embedded in two-dimensional electron systems

NASA Astrophysics Data System (ADS)

Bucheli, D.; Caprara, S.; Castellani, C.; Grilli, M.

2013-02-01

Motivated by recent experimental data on thin film superconductors and oxide interfaces, we propose a random-resistor network apt to describe the occurrence of a metal-superconductor transition in a two-dimensional electron system with disorder on the mesoscopic scale. We consider low-dimensional (e.g. filamentary) structures of a superconducting cluster embedded in the two-dimensional network and we explore the separate effects and the interplay of the superconducting structure and of the statistical distribution of local critical temperatures. The thermal evolution of the resistivity is determined by a numerical calculation of the random-resistor network and, for comparison, a mean-field approach called effective medium theory (EMT). Our calculations reveal the relevance of the distribution of critical temperatures for clusters with low connectivity. In addition, we show that the presence of spatial correlations requires a modification of standard EMT to give qualitative agreement with the numerical results. Applying the present approach to an LaTiO3/SrTiO3 oxide interface, we find that the measured resistivity curves are compatible with a network of spatially dense but loosely connected superconducting islands.

Ubiquitous long-range antiferromagnetic coupling across the interface between superconducting and ferromagnetic oxides

DOE PAGES

De Luca, G. M.; Ghiringhelli, G.; Perroni, C. A.; ...

2014-11-24

The so-called proximity effect is the manifestation, across an interface, of the systematic competition between magnetic order and superconductivity. This phenomenon has been well documented and understood for conventional superconductors coupled with metallic ferromagnets; however it is still less known for oxide materials, where much higher critical temperatures are offered by copper oxide-based superconductors. In this paper, we show that, even in the absence of direct Cu–O–Mn covalent bonding, the interfacial CuO 2 planes of superconducting La 1.85Sr 0.15CuO 4 thin films develop weak ferromagnetism associated to the charge transfer of spin-polarised electrons from the La 0.66Sr 0.33MnO 3 ferromagnet.more » Theoretical modelling confirms that this effect is general to all cuprate/manganite heterostructures and the presence of direct bonding only affects the strength of the coupling. Finally, the Dzyaloshinskii–Moriya interaction, also at the origin of the weak ferromagnetism of bulk cuprates, propagates the magnetisation from the interface CuO 2 planes into the superconductor, eventually depressing its critical temperature.« less

Oxypnictide SmFeAs(O,F) superconductor: a candidate for high-field magnet applications

NASA Astrophysics Data System (ADS)

Iida, Kazumasa; Hänisch, Jens; Tarantini, Chiara; Kurth, Fritz; Jaroszynski, Jan; Ueda, Shinya; Naito, Michio; Ichinose, Ataru; Tsukada, Ichiro; Reich, Elke; Grinenko, Vadim; Schultz, Ludwig; Holzapfel, Bernhard

2013-07-01

The recently discovered oxypnictide superconductor SmFeAs(O,F) is the most attractive material among the Fe-based superconductors due to its highest transition temperature of 56 K and potential for high-field performance. In order to exploit this new material for superconducting applications, the knowledge and understanding of its electro-magnetic properties are needed. Recent success in fabricating epitaxial SmFeAs(O,F) thin films opens a great opportunity to explore their transport properties. Here we report on a high critical current density of over 105 A/cm2 at 45 T and 4.2 K for both main field orientations, feature favourable for high-field magnet applications. Additionally, by investigating the pinning properties, we observed a dimensional crossover between the superconducting coherence length and the FeAs interlayer distance at 30-40 K, indicative of a possible intrinsic Josephson junction in SmFeAs(O,F) at low temperatures that can be employed in electronics applications such as a terahertz radiation source and a superconducting Qubit.

Oxypnictide SmFeAs(O,F) superconductor: a candidate for high–field magnet applications

PubMed Central

Iida, Kazumasa; Hänisch, Jens; Tarantini, Chiara; Kurth, Fritz; Jaroszynski, Jan; Ueda, Shinya; Naito, Michio; Ichinose, Ataru; Tsukada, Ichiro; Reich, Elke; Grinenko, Vadim; Schultz, Ludwig; Holzapfel, Bernhard

2013-01-01

The recently discovered oxypnictide superconductor SmFeAs(O,F) is the most attractive material among the Fe-based superconductors due to its highest transition temperature of 56 K and potential for high-field performance. In order to exploit this new material for superconducting applications, the knowledge and understanding of its electro-magnetic properties are needed. Recent success in fabricating epitaxial SmFeAs(O,F) thin films opens a great opportunity to explore their transport properties. Here we report on a high critical current density of over 105 A/cm2 at 45 T and 4.2 K for both main field orientations, feature favourable for high-field magnet applications. Additionally, by investigating the pinning properties, we observed a dimensional crossover between the superconducting coherence length and the FeAs interlayer distance at 30–40 K, indicative of a possible intrinsic Josephson junction in SmFeAs(O,F) at low temperatures that can be employed in electronics applications such as a terahertz radiation source and a superconducting Qubit. PMID:23823976

Low-noise submillimeter-wave NbTiN superconducting tunnel junction mixers

NASA Astrophysics Data System (ADS)

Kawamura, Jonathan; Chen, Jian; Miller, David; Kooi, Jacob; Zmuidzinas, Jonas; Bumble, Bruce; LeDuc, Henry G.; Stern, Jeff A.

1999-12-01

We have developed a low-noise 850 GHz superconductor-insulator-superconductor quasiparticle mixer with NbTiN thin-film microstrip tuning circuits and hybrid Nb/AlN/NbTiN tunnel junctions. The mixer uses a quasioptical configuration with a planar twin-slot antenna feeding a two-junction tuning circuit. At 798 GHz, we measured an uncorrected double-sideband receiver noise temperature of TRX=260 K at 4.2 K bath temperature. This mixer outperforms current Nb SIS mixers by a factor of nearly 2 near 800 GHz. The high-gap frequency and low loss at 800 GHz make NbTiN an attractive material with which to fabricate tuning circuits for SIS mixers. NbTiN mixers can potentially operate up to the gap frequency, 2Δ/h˜1.2 THz.

Low-Noise Submillimeter-Wave NbTiN Superconducting Tunnel Junction Mixers

NASA Technical Reports Server (NTRS)

Kawamura, J.; Chen, J.; Miller, D.; Kooi, J.; Zmuidzinas, J.; Bumble, B.; LeDuc, H. G.; Stern, J. A.

1999-01-01

We have developed a low-noise 850 GHz superconductor-insulator-superconductor (SIS) quasi-particle mixer with NbTiN thin-film microstrip tuning circuits and hybrid Nb/AlN/NbTiN tunnel junctions. The mixer uses a quasioptical configuration with a planar twin-slot antenna feeding a two-junction tuning circuit. At 798 GHz, we measured an uncorrected double-sideband receiver noise temperature of T(sub RX) = 260 K at 4.2 K bath temperature. This mixer outperforms current Nb SIS mixers by a factor of nearly 2 near 800 GHz. The high gap frequency and low loss at 800 GHz make NbTiN an attractive material with which to fabricate tuning circuits for SIS mixers. NbTiN mixers can potentially operate up to the gap frequency, 2(delta)/h is approximately 1.2THz.

Magnetic-Field-Tunable Superconducting Rectifier

NASA Technical Reports Server (NTRS)

Sadleir, John E.

2009-01-01

Superconducting electronic components have been developed that provide current rectification that is tunable by design and with an externally applied magnetic field to the circuit component. The superconducting material used in the device is relatively free of pinning sites with its critical current determined by a geometric energy barrier to vortex entry. The ability of the vortices to move freely inside the device means this innovation does not suffer from magnetic hysteresis effects changing the state of the superconductor. The invention requires a superconductor geometry with opposite edges along the direction of current flow. In order for the critical current asymmetry effect to occur, the device must have different vortex nucleation conditions at opposite edges. Alternative embodiments producing the necessary conditions include edges being held at different temperatures, at different local magnetic fields, with different current-injection geometries, and structural differences between opposite edges causing changes in the size of the geometric energy barrier. An edge fabricated with indentations of the order of the coherence length will significantly lower the geometric energy barrier to vortex entry, meaning vortex passage across the device at lower currents causing resistive dissipation. The existing prototype is a two-terminal device consisting of a thin-film su - perconducting strip operating at a temperature below its superconducting transition temperature (Tc). Opposite ends of the strip are connected to electrical leads made of a higher Tc superconductor. The thin-film lithographic process provides an easy means to alter edge-structures, current-injection geo - metries, and magnetic-field conditions at the edges. The edge-field conditions can be altered by using local field(s) generated from dedicated higher Tc leads or even using the device s own higher Tc superconducting leads.

High temperature superconducting YBCO microwave filters

NASA Astrophysics Data System (ADS)

Aghabagheri, S.; Rasti, M.; Mohammadizadeh, M. R.; Kameli, P.; Salamati, H.; Mohammadpour-Aghdam, K.; Faraji-Dana, R.

2018-06-01

Epitaxial thin films of YBCO high temperature superconductor are widely used in telecommunication technology such as microwave filter, antenna, coupler and etc., due to their lower surface resistance and lower microwave loss than their normal conductor counterparts. Thin films of YBCO were fabricated by PLD technique on LAO substrate. Transition temperature and width were 88 K and 3 K, respectively. A filter pattern was designed and implemented by wet photolithography method on the films. Characterization of the filter at 77 K has been compared with the simulation results and the results for a made gold filter. Both YBCO and gold filters show high microwave loss. For YBCO filter, the reason may be due to the improper contacts on the feedlines and for gold filter, low thickness of the gold film has caused the loss increased.

System and method for quench and over-current protection of superconductor

DOEpatents

Huang, Xianrui; Laskaris, Evangelos Trifon; Sivasubramaniam, Kiruba Haran; Bray, James William; Ryan, David Thomas; Fogarty, James Michael; Steinbach, Albert Eugene

2005-05-31

A system and method for protecting a superconductor. The system may comprise a current sensor operable to detect a current flowing through the superconductor. The system may comprise a coolant temperature sensor operable to detect the temperature of a cryogenic coolant used to cool the superconductor to a superconductive state. The control circuit is operable to estimate the superconductor temperature based on the current flow and the coolant temperature. The system may also be operable to compare the estimated superconductor temperature to at least one threshold temperature and to initiate a corrective action when the superconductor temperature exceeds the at least one threshold temperature.

Quantum oscillations from the reconstructed Fermi surface in electron-doped cuprate superconductors

NASA Astrophysics Data System (ADS)

Higgins, J. S.; Chan, M. K.; Sarkar, Tarapada; McDonald, R. D.; Greene, R. L.; Butch, N. P.

2018-04-01

We have studied the electronic structure of electron-doped cuprate superconductors via measurements of high-field Shubnikov–de Haas oscillations in thin films. In optimally doped Pr2‑x Ce x CuO4±δ and La2‑x Ce x CuO4±δ , quantum oscillations indicate the presence of a small Fermi surface, demonstrating that electronic reconstruction is a general feature of the electron-doped cuprates, despite the location of the superconducting dome at very different doping levels. Negative high-field magnetoresistance is correlated with an anomalous low-temperature change in scattering that modifies the amplitude of quantum oscillations. This behavior is consistent with effects attributed to spin fluctuations.

Chiral Majorana fermion modes in a quantum anomalous Hall insulator–superconductor structure

DOE PAGES

He, Qing Lin; Pan, Lei; Stern, Alexander L.; ...

2017-07-21

Majorana fermion is a hypothetical particle that is its own antiparticle. We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantummore » computing.« less

Evolution of High-Temperature Superconductivity from a Low-T_{c} Phase Tuned by Carrier Concentration in FeSe Thin Flakes.

PubMed

Lei, B; Cui, J H; Xiang, Z J; Shang, C; Wang, N Z; Ye, G J; Luo, X G; Wu, T; Sun, Z; Chen, X H

2016-02-19

We report the evolution of superconductivity in an FeSe thin flake with systematically regulated carrier concentrations by the liquid-gating technique. With electron doping tuned by the gate voltage, high-temperature superconductivity with an onset at 48 K can be achieved in an FeSe thin flake with T_{c} less than 10 K. This is the first time such high temperature superconductivity in FeSe is achieved without either an epitaxial interface or external pressure, and it definitely proves that the simple electron-doping process is able to induce high-temperature superconductivity with T_{c}^{onset} as high as 48 K in bulk FeSe. Intriguingly, our data also indicate that the superconductivity is suddenly changed from a low-T_{c} phase to a high-T_{c} phase with a Lifshitz transition at a certain carrier concentration. These results help to build a unified picture to understand the high-temperature superconductivity among all FeSe-derived superconductors and shed light on the further pursuit of a higher T_{c} in these materials.

Study of robust thin film PT-1000 temperature sensors for cryogenic process control applications

NASA Astrophysics Data System (ADS)

Ramalingam, R.; Boguhn, D.; Fillinger, H.; Schlachter, S. I.; Süßer, M.

2014-01-01

In some cryogenic process measurement applications, for example, in hydrogen technology and in high temperature superconductor based generators, there is a need of robust temperature sensors. These sensors should be able to measure the large temperature range of 20 - 500 K with reasonable resolution and accuracy. Thin film PT 1000 sensors could be a choice to cover this large temperature range. Twenty one sensors selected from the same production batch were tested for their temperature sensitivity which was then compared with different batch sensors. Furthermore, the sensor's stability was studied by subjecting the sensors to repeated temperature cycles of 78-525 K. Deviations in the resistance were investigated using ice point calibration and water triple point calibration methods. Also the study of directional oriented intense static magnetic field effects up to 8 Oersted (Oe) were conducted to understand its magneto resistance behaviour in the cryogenic temperature range from 77 K - 15 K. This paper reports all investigation results in detail.

An Introduction to the properties of Superconductors

NASA Astrophysics Data System (ADS)

Letarte, Alec

2001-03-01

A brief introductory presentation of the various properties of superconductors. The discussion will be focussed mainly on the newer ceramic superconductors, but the classic metal ones will also be touched upon. Some of the properties to be considered are: Optical properties, transport properties, persistent currents, coherence length, flux magnetisation, and the ``anti-gravity effect" produced be superconductors Another subject to be looked at will be the recent technological uses and developments of superconductors. For example, they have developed thin superconductors which they are making into a superconducting cable.

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.

Specular Andreev reflection in thin films of topological insulators

NASA Astrophysics Data System (ADS)

Majidi, Leyla; Asgari, Reza

2016-05-01

We theoretically reveal the possibility of specular Andreev reflection in a thin film topological insulator normal-superconductor (N/S) junction in the presence of a gate electric field. The probability of specular Andreev reflection increases with the electric field, and electron-hole conversion with unit efficiency happens in a wide experimentally accessible range of the electric field. We show that perfect specular Andreev reflection can occur for all angles of incidence with a particular excitation energy value. In addition, we find that the thermal conductance of the structure displays exponential dependence on the temperature. Our results reveal the potential of the proposed topological insulator thin-film-based N/S structure for the realization of intraband specular Andreev reflection.

Nematicity, magnetism and superconductivity in FeSe

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

Bohmer, Anna E.; Kreisel, Andreas

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of thesemore » phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. In conclusion, the experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.« less

Nematicity, magnetism and superconductivity in FeSe.

PubMed

Böhmer, Anna E; Kreisel, Andreas

2018-01-17

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c , ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.

Nematicity, magnetism and superconductivity in FeSe

NASA Astrophysics Data System (ADS)

Böhmer, Anna E.; Kreisel, Andreas

2018-01-01

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.

Nematicity, magnetism and superconductivity in FeSe

DOE PAGES

Bohmer, Anna E.; Kreisel, Andreas

2017-12-15

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of thesemore » phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. In conclusion, the experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.« less

Method of manufacturing a high temperature superconductor with improved transport properties

DOEpatents

Balachandran, Uthamalingam; Siegel, Richard W.; Askew, Thomas R.

2001-01-01

A method of preparing a high temperature superconductor. A method of preparing a superconductor includes providing a powdered high temperature superconductor and a nanophase paramagnetic material. These components are combined to form a solid compacted mass with the paramagnetic material disposed on the grain boundaries of the polycrystaline high temperature superconductor.

Temperature dependent pinning landscapes in REBCO thin films

NASA Astrophysics Data System (ADS)

Jaroszynski, Jan; Constantinescu, Anca-Monia; Hu, Xinbo Paul

2015-03-01

The pinning landscapes of REBCO (RE=rare earth elements) thin films have been a topic of study in recent years due to, among other reasons, their high ability to introduce various phases and defects. Pinning mechanisms studies in high temperature superconductors often require detailed knowledge of critical current density as a function of magnetic field orientation as well as field strength and temperature. Since the films can achieve remarkably high critical current, challenges exist in evaluating these low temperature (down to 4.2 K) properties in high magnetic fields up to 30 T. Therefore both conventional transport, and magnetization measurements in a vibrating coil magnetometer equipped with rotating sample platform were used to complement the study. Our results clearly show an evolution of pinning from strongly correlated effects seen at high temperatures to significant contributions from dense but weak pins that thermal fluctuations render ineffective at high temperatures but which become strong at lower temperatures Support for this work is provided by the NHMFL via NSF DRM 1157490

Thermal conductance of Nb thin films at sub-kelvin temperatures.

PubMed

Feshchenko, A V; Saira, O-P; Peltonen, J T; Pekola, J P

2017-02-03

We determine the thermal conductance of thin niobium (Nb) wires on a silica substrate in the temperature range of 0.1-0.6 K using electron thermometry based on normal metal-insulator-superconductor tunnel junctions. We find that at 0.6 K, the thermal conductance of Nb is two orders of magnitude lower than that of Al in the superconducting state, and two orders of magnitude below the Wiedemann-Franz conductance calculated with the normal state resistance of the wire. The measured thermal conductance exceeds the prediction of the Bardeen-Cooper-Schrieffer theory, and demonstrates a power law dependence on temperature as T 4.5 , instead of an exponential one. At the same time, we monitor the temperature profile of the substrate along the Nb wire to observe possible overheating of the phonon bath. We show that Nb can be successfully used for thermal insulation in a nanoscale circuit while simultaneously providing an electrical connection.

Thermal conductance of Nb thin films at sub-kelvin temperatures

NASA Astrophysics Data System (ADS)

Feshchenko, A. V.; Saira, O.-P.; Peltonen, J. T.; Pekola, J. P.

2017-02-01

We determine the thermal conductance of thin niobium (Nb) wires on a silica substrate in the temperature range of 0.1-0.6 K using electron thermometry based on normal metal-insulator-superconductor tunnel junctions. We find that at 0.6 K, the thermal conductance of Nb is two orders of magnitude lower than that of Al in the superconducting state, and two orders of magnitude below the Wiedemann-Franz conductance calculated with the normal state resistance of the wire. The measured thermal conductance exceeds the prediction of the Bardeen-Cooper-Schrieffer theory, and demonstrates a power law dependence on temperature as T4.5, instead of an exponential one. At the same time, we monitor the temperature profile of the substrate along the Nb wire to observe possible overheating of the phonon bath. We show that Nb can be successfully used for thermal insulation in a nanoscale circuit while simultaneously providing an electrical connection.

Electrothermal feedback in kinetic inductance detectors

NASA Astrophysics Data System (ADS)

Guruswamy, T.; Thomas, C. N.; Withington, S.; Goldie, D. J.

2017-06-01

In kinetic inductance detectors (KIDs) and other similar applications of superconducting microresonators, both the large and small-signal behaviour of the device may be affected by electrothermal feedback. Microwave power applied to read out the device is absorbed by and heats the superconductor quasiparticles, changing the superconductor conductivity and hence the readout power absorbed in a positive or negative feedback loop. In this work, we explore numerically the implications of an extensible theoretical model of a generic superconducting microresonator device for a typical KID, incorporating recent work on the power flow between superconductor quasiparticles and phonons. This model calculates the large-signal (changes in operating point) and small-signal behaviour of a device, allowing us to determine the effect of electrothermal feedback on device responsivity and noise characteristics under various operating conditions. We also investigate how thermally isolating the device from the bath, for example by designing the device on a membrane only connected to the bulk substrate by thin legs, affects device performance. We find that at a typical device operating point, positive electrothermal feedback reduces the effective thermal conductance from the superconductor quasiparticles to the bath, and so increases responsivity to signal (pair-breaking) power, increases noise from temperature fluctuations, and decreases the noise equivalent power (NEP). Similarly, increasing the thermal isolation of the device while keeping the quasiparticle temperature constant decreases the NEP, but also decreases the device response bandwidth.

Topological superconductivity in an ultrathin, magnetically-doped topological insulator proximity coupled to a conventional superconductor

NASA Astrophysics Data System (ADS)

Kim, Youngseok; Philip, Timothy M.; Park, Moon Jip; Gilbert, Matthew J.

2016-12-01

As a promising candidate system to realize topological superconductivity, the system of a 3D topological insulator (TI) grown on top of the s -wave superconductor has been extensively studied. To access the topological superconductivity experimentally, the 3D TI sample must be thin enough to allow for Cooper pair tunneling to the exposed surface of TI. The use of magnetically ordered dopants to break time-reversal symmetry may allow the surface of a TI to host Majorana fermion, which are believed to be a signature of topological superconductivity. In this work, we study a magnetically-doped thin film TI-superconductor hybrid system. Considering the proximity induced order parameter in thin film of TI, we analyze the gap closing points of the Hamiltonian and draw the phase diagram as a function of relevant parameters: the hybridization gap, Zeeman energy, and chemical potential of the TI system. Our findings provide a useful guide in choosing relevant parameters to facilitate the observation of topological superconductivity in thin film TI-superconductor hybrid systems. In addition, we further perform numerical analysis on a TI proximity coupled to an s -wave superconductor and find that, due to the spin-momentum locked nature of the surface states in TI, the induced s -wave order parameter of the surface states persists even at large magnitude of the Zeeman energy.

The influence of external factors on the corrosion resistance of high temperature superconductor thin films against moisture

NASA Astrophysics Data System (ADS)

Murugesan, M.; Obara, H.; Yamasaki, H.; Kosaka, S.

2006-12-01

High temperature superconductor (HTS) thin films have been systematically investigated for their corrosion resistance against moisture by studying the role of external factors such as temperature (T), relative humidity (RH), and the type of substrates in the corrosion. In general, (i) the corrosion is progressed monotonously with increasing T as well as RH, (ii) a threshold level of water vapor is needed to cause degradation, and (iii) between T and RH, the influence of T is more dominant. HTS films on SrTiO3 and CeO2 buffered sapphire (cbs) substrates showed better corrosion stability and a low rate of degradation in the critical current density as compared to that of the film grown on MgO substrate. Between DyBa2Cu3Oz (DBCO) and YBa2Cu3Oz, the former is reproducibly found to have many fold higher corrosion resistance against moisture. This observed enhancement in the corrosion resistance in DBCO could be explained by the improved microstructure in the films and the better lattice matching with the substrate. Thus, the dual advantage of DBCO/cbs films, i.e., the enhanced corrosion stability of DBCO and the appropriate dielectric properties of sapphire, can be readily exploited for the use of DBCO/cbs films in the microwave and power devices.

Ceramic superconductor/metal composite materials employing the superconducting proximity effect

DOEpatents

Holcomb, Matthew J.

2002-01-01

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

Giant ultrafast Kerr effect in superconductors

NASA Astrophysics Data System (ADS)

Robson, Charles W.; Fraser, Kieran A.; Biancalana, Fabio

2017-06-01

We study the ultrafast Kerr effect and high-harmonic generation in superconductors by formulating a model for a time-varying electromagnetic pulse normally incident on a thin-film superconductor. It is found that superconductors exhibit exceptionally large χ(3 ) due to the progressive destruction of Cooper pairs, and display high-harmonic generation at low incident intensities, and the highest nonlinear susceptibility of all known materials in the THz regime. Our theory opens up avenues for accessible analytical and numerical studies of the ultrafast dynamics of superconductors.

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.

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.

Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor.

PubMed

He, M Q; Shen, J Y; Petrović, A P; He, Q L; Liu, H C; Zheng, Y; Wong, C H; Chen, Q H; Wang, J N; Law, K T; Sou, I K; Lortz, R

2016-09-02

In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3.

Full superconducting dome of strong Ising protection in gated monolayer WS2.

PubMed

Lu, Jianming; Zheliuk, Oleksandr; Chen, Qihong; Leermakers, Inge; Hussey, Nigel E; Zeitler, Uli; Ye, Jianting

2018-04-03

Many recent studies show that superconductivity not only exists in atomically thin monolayers but can exhibit enhanced properties such as a higher transition temperature and a stronger critical field. Nevertheless, besides being unstable in air, the weak tunability in these intrinsically metallic monolayers has limited the exploration of monolayer superconductivity, hindering their potential in electronic applications (e.g., superconductor-semiconductor hybrid devices). Here we show that using field effect gating, we can induce superconductivity in monolayer WS 2 grown by chemical vapor deposition, a typical ambient-stable semiconducting transition metal dichalcogenide (TMD), and we are able to access a complete set of competing electronic phases over an unprecedented doping range from band insulator, superconductor, to a reentrant insulator at high doping. Throughout the superconducting dome, the Cooper pair spin is pinned by a strong internal spin-orbit interaction, making this material arguably the most resilient superconductor in the external magnetic field. The reentrant insulating state at positive high gating voltages is attributed to localization induced by the characteristically weak screening of the monolayer, providing insight into many dome-like superconducting phases observed in field-induced quasi-2D superconductors.

Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor

PubMed Central

He, M. Q.; Shen, J. Y.; Petrović, A. P.; He, Q. L.; Liu, H. C.; Zheng, Y.; Wong, C. H.; Chen, Q. H.; Wang, J. N.; Law, K. T.; Sou, I. K.; Lortz, R.

2016-01-01

In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3. PMID:27587000

HTS Fabry-Perot resonators for the far infrared

NASA Astrophysics Data System (ADS)

Keller, Philipp; Prenninger, Martin; Pechen, Evgeny V.; Renk, Karl F.

1996-06-01

We report on far infrared (FIR) Fabry-Perot resonators (FPR) with high temperature superconductor (HTS) thin films as mirrors. For the fabrication of FPR we use two parallel MgO plates covered with YBa2Cu3O7-delta thin films on adjacent sides. We have measured the far-infrared transmissivity at 10 K with a Fourier transform infrared spectrometer. Very sharp resonances can be observed for frequencies below 6 THz where the MgO is transparent. The finesse (width of the first order resonance) is comparable to the FPR with metallic meshes as reflectors that are applied in the FIR spectroscopy and astronomy. We have also shown that thin films of gold are not adequate substitute to HTS thin films and not suitable for the fabrication of high-quality FPR due to the ohmic losses.

Process for producing fine and ultrafine filament superconductor wire

DOEpatents

Kanithi, H.C.

1992-02-18

A process for producing a superconductor wire made up of a large number of round monofilament rods is provided for, comprising assembling a multiplicity of round monofilaments inside each of a multiplicity of thin wall hexagonal tubes and then assembling a number of said thin wall hexagonal tubes within an extrusion can and subsequently consolidating, extruding and drawing the entire assembly down to the desired wire size. 8 figs.

Process for producing fine and ultrafine filament superconductor wire

DOEpatents

Kanithi, Hem C.

1992-01-01

A process for producing a superconductor wire made up of a large number of round monofilament rods is provided for, comprising assembling a multiplicity of round monofilaments inside each of a multiplicity of thin wall hexagonal tubes and then assembling a number of said thin wall hexagonal tubes within an extrusion can and subsequently consolidating, extruding and drawing the entire assembly down to the desired wire size.

Bond and flux-disorder effects on the superconductor-insulator transition of a honeycomb array of Josephson junctions

NASA Astrophysics Data System (ADS)

Granato, Enzo

2018-05-01

We study the effects of disorder on the zero-temperature quantum phase transition of a honeycomb array of Josephson junctions in a magnetic field with an average of fo flux quantum per plaquette. Bond disorder due to spatial variations in the Josephson couplings and magnetic flux disorder due to variations in the plaquette areas are considered. The model can describe the superconductor-insulator transition in ultra-thin films with a triangular pattern of nanoholes. Path integral Monte Carlo simulations of the equivalent (2 + 1)-dimensional classical model are used to study the critical behavior and estimate the universal resistivity at the transition. The results show that bond disorder leads to a rounding of the first-order phase transition for fo = 1 / 3 to a continuous transition. For integer fo, the decrease of the critical coupling parameter with flux disorder is significantly different from that of the same model defined on a square lattice. The results are compared with recent experimental observations on nanohole thin films with geometrical disorder and external magnetic field.

High field superconducting properties of Ba(Fe1-xCox)2As2 thin films

NASA Astrophysics Data System (ADS)

Hänisch, Jens; Iida, Kazumasa; Kurth, Fritz; Reich, Elke; Tarantini, Chiara; Jaroszynski, Jan; Förster, Tobias; Fuchs, Günther; Hühne, Ruben; Grinenko, Vadim; Schultz, Ludwig; Holzapfel, Bernhard

2015-11-01

In general, the critical current density, Jc, of type II superconductors and its anisotropy with respect to magnetic field orientation is determined by intrinsic and extrinsic properties. The Fe-based superconductors of the ‘122’ family with their moderate electronic anisotropies and high yet accessible critical fields (Hc2 and Hirr) are a good model system to study this interplay. In this paper, we explore the vortex matter of optimally Co-doped BaFe2As2 thin films with extended planar and c-axis correlated defects. The temperature and angular dependence of the upper critical field is well explained by a two-band model in the clean limit. The dirty band scenario, however, cannot be ruled out completely. Above the irreversibility field, the flux motion is thermally activated, where the activation energy U0 is going to zero at the extrapolated zero-kelvin Hirr value. The anisotropy of the critical current density Jc is both influenced by the Hc2 anisotropy (and therefore by multi-band effects) as well as the extended planar and columnar defects present in the sample.

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.

Chiral Majorana fermion modes in a quantum anomalous Hall insulator-superconductor structure.

PubMed

He, Qing Lin; Pan, Lei; Stern, Alexander L; Burks, Edward C; Che, Xiaoyu; Yin, Gen; Wang, Jing; Lian, Biao; Zhou, Quan; Choi, Eun Sang; Murata, Koichi; Kou, Xufeng; Chen, Zhijie; Nie, Tianxiao; Shao, Qiming; Fan, Yabin; Zhang, Shou-Cheng; Liu, Kai; Xia, Jing; Wang, Kang L

2017-07-21

Majorana fermion is a hypothetical particle that is its own antiparticle. We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantum computing. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Micromachined Millimeter- and Submillimeter-Wave SIS Heterodyne Receivers for Remote Sensing

NASA Technical Reports Server (NTRS)

Hu, Qing

1998-01-01

A heterodyne mixer with a micromachined horn antenna and a superconductor -insulator-superconductor (SIS) tunnel junction as mixing element is tested in the W-band (75-115 GHz) frequency range. Micromachined integrated horn antennas consist of a dipole antenna suspended on a thin Si3N4 dielectric membrane inside a pyramidal cavity etched in silicon. The mixer performance is optimized by using a backing plane behind the dipole antenna to tune out the capacitance of the tunnel junction. The lowest receiver noise temperature of 30+/-3 K without any correction) is measured at 106 GHz with a 3-dB bandwidth of 8 GHz. This sensitivity is comparable to the state-of-the-art waveguide and quasi-optical SIS receivers, showing the potential use of micromachined horn antennas in imaging arrays.

Thermal conductance of Nb thin films at sub-kelvin temperatures

PubMed Central

Feshchenko, A. V.; Saira, O.-P.; Peltonen, J. T.; Pekola, J. P.

2017-01-01

We determine the thermal conductance of thin niobium (Nb) wires on a silica substrate in the temperature range of 0.1–0.6 K using electron thermometry based on normal metal-insulator-superconductor tunnel junctions. We find that at 0.6 K, the thermal conductance of Nb is two orders of magnitude lower than that of Al in the superconducting state, and two orders of magnitude below the Wiedemann-Franz conductance calculated with the normal state resistance of the wire. The measured thermal conductance exceeds the prediction of the Bardeen-Cooper-Schrieffer theory, and demonstrates a power law dependence on temperature as T4.5, instead of an exponential one. At the same time, we monitor the temperature profile of the substrate along the Nb wire to observe possible overheating of the phonon bath. We show that Nb can be successfully used for thermal insulation in a nanoscale circuit while simultaneously providing an electrical connection. PMID:28155895

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.

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.

Magnesium Diboride thin Films, multilayers, and coatings for SRF cavities

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

Xi, Xiaoxing

Superconducting radio frequency (SRF) cavities currently use low-temperature superconductor niobium, and the Nb SRF cavities have approached the performance levels predicted theoretically. Compared to Nb, MgB 2 becomes superconducting at a much higher temperature and promises a better RF performance in terms of higher quality factor Q and higher acceleration capability. An MgB 2 SRF technology can significantly reduce the operating costs of particle accelerators when these potentials are realized. This project aimed to advance the development of an MgB 2 SRF technology. It had two main objectives: (1) materials issues of MgB 2 thin films and multilayers related tomore » their applications in SRF cavities; and (2) coating single-cell cavities for testing at RF frequencies. The key technical thrust of the project is the deposition of high quality clean MgB 2 films and coatings by the hybrid physical-chemical vapor deposition (HPCVD) technique, which was developed in my group. We have achieved technical progress in each of the two areas. For the first objective, we have confirmed that MgB 2 thin film coatings can be used to effectively enhance the vortex penetration field of an SRF cavity. A vortex is a normal region in the shape of spaghetti that threads through a superconductor. Its existence is due to an applied magnetic field that is greater than a so-called lower critical field, H c1. Once a vortex enters the superconductor, its movement leads to loss. This has been shown to be the reason for an SRF cavity to break down. Thus, enhancing the magnetic field for a vortex to enter the superconductor that forms the SRF cavity has be a goal of intense research. To this end, Gurevich proposed that a coating of thin superconductor layer can impede the vortex entrance. In this project, we have done two important experiment to test this concept. One, we showed that the enhancement of H c1 can be achieved by using in both epitaxial and polycrystalline MgB 2 films. Although H c1 is low for bulk MgB 2 samples, about 600 Oe at 5 K, it increases with decreasing film thickness, reaching 1880 Oe when the film thickness is 100 nm. Two, we coated Nb ellipsoids with MgB 2 films to achieve an “inverse cavity” configuration, mimicking the coating of an actual RF cavity. Our results demonstrate that it is indeed possible to increase the vortex penetration field of a cavity by a substantial amount (~600 Oe) by coating it with a thin MgB 2 film. For the second objective, we modified the existing HPCVD system to be able to coat a 3.9 GHz SRF cavity, and using a stainless steel mock cavity showed that a uniform film with good superconducting property can be grown across the cavity interior. Further, we successfully deposited MgB 2 on Cu disc. The two results combined demonstrate that it is possible to coat Cu cavities with high quality MgB 2 films using HPCVD. MgB 2 coated Cu could open up a possibility of using SRF cavities at 20–25 K with cryocoolers.« less

Process for forming epitaxial perovskite thin film layers using halide precursors

DOEpatents

Clem, Paul G.; Rodriguez, Mark A.; Voigt, James A.; Ashley, Carol S.

2001-01-01

A process for forming an epitaxial perovskite-phase thin film on a substrate. This thin film can act as a buffer layer between a Ni substrate and a YBa.sub.2 Cu.sub.3 O.sub.7-x superconductor layer. The process utilizes alkali or alkaline metal acetates dissolved in halogenated organic acid along with titanium isopropoxide to dip or spin-coat the substrate which is then heated to about 700.degree. C. in an inert gas atmosphere to form the epitaxial film on the substrate. The YBCO superconductor can then be deposited on the layer formed by this invention.

High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O

DOEpatents

Ginley, David S.; Hietala, Vincent M.; Hohenwarter, Gert K. G.; Martens, Jon S.; Plut, Thomas A.; Tigges, Chris P.; Vawter, Gregory A.; Zipperian, Thomas E.

1994-10-25

A process for formulating non-hysteretic and hysteretic Josephson junctions using HTS materials which results in junctions having the ability to operate at high temperatures while maintaining high uniformity and quality. The non-hysteretic Josephson junction is formed by step-etching a LaAlO.sub.3 crystal substrate and then depositing a thin film of TlCaBaCuO on the substrate, covering the step, and forming a grain boundary at the step and a subsequent Josephson junction. Once the non-hysteretic junction is formed the next step to form the hysteretic Josephson junction is to add capacitance to the system. In the current embodiment, this is accomplished by adding a thin dielectric layer, LaA1O.sub.3, followed by a cap layer of a normal metal where the cap layer is formed by first depositing a thin layer of titanium (Ti) followed by a layer of gold (Au). The dielectric layer and the normal metal cap are patterned to the desired geometry.

Exploring the performance of thin-film superconducting multilayers as kinetic inductance detectors for low-frequency detection

NASA Astrophysics Data System (ADS)

Zhao, Songyuan; Goldie, D. J.; Withington, S.; Thomas, C. N.

2018-01-01

We have solved numerically the diffusive Usadel equations that describe the spatially varying superconducting proximity effect in Ti-Al thin-film bi- and trilayers with thickness values that are suitable for kinetic inductance detectors (KIDs) to operate as photon detectors with detection thresholds in the frequency range of 50-90 GHz. Using Nam’s extension of the Mattis-Bardeen calculation of the superconductor complex conductivity, we show how to calculate the surface impedance for the spatially varying case, and hence the surface impedance quality factor. In addition, we calculate energy-and spatially-averaged quasiparticle lifetimes at temperatures well-below the transition temperature and compare to calculation in Al. Our results for the pair-breaking threshold demonstrate differences between bilayers and trilayers with the same total film thicknesses. We also predict high quality factors and long multilayer-averaged quasiparticle recombination times compared to thin-film Al. Our calculations give a route for designing KIDs to operate in this scientifically-important frequency regime.

Superconductor-insulator quantum phase transition in disordered FeSe thin films.

PubMed

Schneider, R; Zaitsev, A G; Fuchs, D; V Löhneysen, H

2012-06-22

The evolution of two-dimensional electronic transport with increasing disorder in epitaxial FeSe thin films is studied. Disorder is generated by reducing the film thickness. The extreme sensitivity of the films to disorder results in a superconductor-insulator transition. The finite-size scaling analysis in the critical regime based on the Bose-glass model strongly supports the idea of a continuous quantum phase transition. The obtained value for the critical-exponent product of approximately 7/3 suggests that the transition is governed by quantum percolation. Finite-size scaling with the same critical-exponent product is also substantiated when the superconductor-insulator transition is tuned with an applied magnetic field.

Investigation of superconducting interactions and amorphous semiconductors

NASA Technical Reports Server (NTRS)

Janocko, M. A.; Jones, C. K.; Gavaler, J. R.; Deis, D. W.; Ashkin, M.; Mathur, M. P.; Bauerle, J. E.

1972-01-01

Research papers on superconducting interactions and properties and on amorphous materials are presented. The search for new superconductors with improved properties was largely concentrated on the study of properties of thin films. An experimental investigation of interaction mechanisms revealed no new superconductivity mechanism. The properties of high transition temperature, type 2 materials prepared in thin film form were studied. A pulsed field solenoid capable of providing fields in excess of 300 k0e was developed. Preliminary X-ray measurements were made of V3Si to determine the behavior of cell constant deformation versus pressure up to 98 kilobars. The electrical properties of amorphous semiconducting materials and bulk and thin film devices, and of amorphous magnetic materials were investigated for developing radiation hard, inexpensive switches and memory elements.

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

Performance of Magnetic Penetration Thermometers for X-Ray Astronomy

NASA Technical Reports Server (NTRS)

Nagler, P. C.; Adams, J. S.; Balvin, M. A.; Bandler, S. R.; Denis, K. L.; Hsieh, W. T.; Kelly, D. P.; Porst, J. P.; Sadleir, J. E.; Seidel, G. M.;

Tc depression and superconductor-insulator transition in molybdenum nitride thin films

NASA Astrophysics Data System (ADS)

Ichikawa, F.; Makise, K.; Tsuneoka, T.; Maeda, S.; Shinozaki, B.

2018-03-01

We have studied that the Tc depression and the superconductor-insulator transition (SIT) in molybdenum nitride (MoN) thin films. Thin films were fabricated by reactive DC magnetron sputtering method onto (100) MgO substrates in the mixture of Ar and N2 gases. Several dozen MoN thin films were prepared in the range of 3 nm < thickness d < 60 nm. The resistance was measured by a DC four-probe technique. It is found that Tc decreases from 6.6 K for thick films with increase of the normal state sheet resistance {R}{{sq}}{{N}} and experimental data were fitted to the Finkel’stein formula using the bulk superconducting transition temperature Tc 0 = 6.45 K and the elastic scattering time of electron τ = 1.6 × 10‑16 s. From this analysis the critical sheet resistance Rc is found about 2 kΩ, which is smaller than the quantum sheet resistance R Q. This value of Rc is almost the same as those for 2D NbN films. The value of τ for MoN films is also the similar value for NbN films 1.0 × 10‑16 s, while Tc 0 is different from that for NbN films 14.85 K. It is indicated that the mechanism of SIT for MoN films is similar to that of NbN films, while the mean free path ℓ for MoN films is larger than that for NbN films.

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.

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

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.

Superconductivity of Rock-Salt Structure LaO Epitaxial Thin Film.

PubMed

Kaminaga, Kenichi; Oka, Daichi; Hasegawa, Tetsuya; Fukumura, Tomoteru

2018-06-06

We report a superconducting transition in a LaO epitaxial thin film with the superconducting transition onset temperature ( T c ) at around 5 K. This T c is higher than those of other lanthanum monochalcogenides and opposite to their chemical trend: T c = 0.84, 1.02, and 1.48 K for LaX (X = S, Se, Te), respectively. The carrier control resulted in a dome-shaped T c as a function of electron carrier density. In addition, the T c was significantly sensitive to epitaxial strain in spite of the highly symmetric crystal structure. This rock-salt superconducting LaO could be a building block to design novel superlattice superconductors.

One-dimensional pinning behavior in Co-doped BaFe2As2 thin films

NASA Astrophysics Data System (ADS)

Mishev, V.; Seeböck, W.; Eisterer, M.; Iida, K.; Kurth, F.; Hänisch, J.; Reich, E.; Holzapfel, B.

2013-12-01

Angle-resolved transport measurements revealed that planar defects dominate flux pinning in the investigated Co-doped BaFe2As2 thin film. For any given field and temperature, the critical current depends only on the angle between the crystallographic c-axis and the applied magnetic field but not on the angle between the current and the field. The critical current is therefore limited only by the in-plane component of the Lorentz force but independent of the out-of-plane component, which is entirely balanced by the pinning force exerted by the planar defects. This one-dimensional pinning behavior shows similarities and differences to intrinsic pinning in layered superconductors.

Sequentially evaporated thin Y-Ba-Cu-O superconductor films: Composition and processing effects

NASA Technical Reports Server (NTRS)

Valco, George J.; Rohrer, Norman J.; Warner, Joseph D.; Bhasin, Kul B.

1988-01-01

Thin films of YBa2Cu3O(7-beta) have been grown by sequential evaporation of Cu, Y, and BaF2 on SrTiO3 and MgO substrates. The onset temperatures were as high as 93 K while T sub c was 85 K. The Ba/Y ratio was varied from 1.9 to 4.0. The Cu/Y ratio was varied from 2.8 to 3.4. The films were then annealed at various times and temperatures. The times ranged from 15 min to 3 hr, while the annealing temperatures used ranged from 850 C to 900 C. A good correlation was found between transition temperature (T sub c) and the annealing conditions; the films annealed at 900 C on SrTiO3 had the best T sub c's. There was a weaker correlation between composition and T sub c. Barium poor films exhibitied semiconducting normal state resistance behavior while barium rich films were metallic. The films were analyzed by resistance versus temperature measurements and scanning electron microscopy. The analysis of the films and the correlations are reported.

A Low-noise Micromachined Millimeter-Wave Heterodyne Mixer using Nb Superconducting Tunnel Junctions

NASA Technical Reports Server (NTRS)

DeLange, Gert; Jacobson, Brian R.; Hu, Qing

1996-01-01

A heterodyne mixer with a micromachined horn antenna and a superconductor-insulator-superconductor (SIS) tunnel junction as mixing element is tested in the W-band (75-115 GHz) frequency range. Micromachined integrated horn antennas consist of a dipole antenna suspended on a thin Si3N4 dielectric membrane inside a pyramidal cavity etched in silicon. The mixer performance is optimized by using a backing plane behind the dipole antenna to tune out the capacitance of the tunnel junction. The lowest receiver noise temperature of 30 +/- 3 K (without any correction) is measured at 106 GHz with a 3-dB bandwidth of 8 GHz. This sensitivity is comparable to the state-of-the-art waveguide and quasi-optical SIS receivers, showing the potential use of micromachined horn antennas in imaging arrays.

Thin film superconductors and process for making same

DOEpatents

Nigrey, P.J.

1988-01-21

A process for the preparation of oxide superconductors from high-viscosity non-aqueous solution is described. Solutions of lanthanide nitrates, alkaline earth nitrates and copper nitrates in a 1:2:3 stoichiometric ratio, when added to ethylene glycol containing citric acid solutions, have been used to prepare highly viscous non-aqueous solutions of metal mixed nitrates-citrates. Thin films of these compositions are produced when a layer of the viscous solution is formed on a substrate and subjected to thermal decomposition.

Microelectronic superconducting crossover and coil

DOEpatents

Wellstood, F.C.; Kingston, J.J.; Clarke, J.

1994-03-01

A microelectronic component comprising a crossover is provided comprising a substrate, a first high T[sub c] superconductor thin film, a second insulating thin film comprising SrTiO[sub 3]; and a third high T[sub c] superconducting film which has strips which crossover one or more areas of the first superconductor film. An in situ method for depositing all three films on a substrate is provided which does not require annealing steps and which can be opened to the atmosphere between depositions. 13 figures.

Thin film seeds for melt processing textured superconductors for practical applications

DOEpatents

Veal, Boyd W.; Paulikas, Arvydas; Balachandran, Uthamalingam; Zhong, Wei

1999-01-01

A method of fabricating bulk superconducting material such as RBa.sub.2 Cu.sub.3 O.sub.7-.delta. where R is La or Y comprising depositing a thin epitaxially oriented film of Nd or Sm (123) on an oxide substrate. The powder oxides of RBa.sub.2 Cu.sub.3 O.sub.7-.delta. or oxides and/or carbonates of R and Ba and Cu present in mole ratios to form RBa.sub.2 Cu.sub.3 O.sub.7-.delta., where R is Y or La are heated, in physical contact with the thin film of Nd or Sm (123) on the oxide substrate to a temperature sufficient to form a liquid phase in the oxide or carbonate mixture while maintaining the thin film solid to grow a large single domain 123 superconducting material. Then the material is cooled. The thin film is between 200 .ANG. and 2000 .ANG.. A construction prepared by the method is also disclosed.

Thin film seeds for melt processing textured superconductors for practical applications

DOEpatents

Veal, B.W.; Paulikas, A.; Balachandran, U.; Zhong, W.

1999-02-09

A method of fabricating bulk superconducting material such as RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} where R is La or Y comprising depositing a thin epitaxially oriented film of Nd or Sm (123) on an oxide substrate is disclosed. The powder oxides of RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} or oxides and/or carbonates of R and Ba and Cu present in mole ratios to form RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, where R is Y or La are heated, in physical contact with the thin film of Nd or Sm (123) on the oxide substrate to a temperature sufficient to form a liquid phase in the oxide or carbonate mixture while maintaining the thin film solid to grow a large single domain 123 superconducting material. Then the material is cooled. The thin film is between 200 {angstrom} and 2000 {angstrom}. A construction prepared by the method is also disclosed.

Automatic HTS force measurement instrument

DOEpatents

Sanders, Scott T.; Niemann, Ralph C.

1999-01-01

A device for measuring the levitation force of a high temperature superconductor sample with respect to a reference magnet includes a receptacle for holding several high temperature superconductor samples each cooled to superconducting temperature. A rotatable carousel successively locates a selected one of the high temperature superconductor samples in registry with the reference magnet. Mechanism varies the distance between one of the high temperature superconductor samples and the reference magnet, and a sensor measures levitation force of the sample as a function of the distance between the reference magnet and the sample. A method is also disclosed.

Electrical transport of spin-polarized carriers in disordered ultrathin films.

PubMed

Hernandez, L M; Bhattacharya, A; Parendo, Kevin A; Goldman, A M

2003-09-19

Slow, nonexponential relaxation of electrical transport accompanied by memory effects has been induced in quench-condensed ultrathin amorphous Bi films by the application of a parallel magnetic field. This behavior, which is very similar to space-charge limited current flow, is found in extremely thin films well on the insulating side of the thickness-tuned superconductor-insulator transition. It may be the signature of a collective state that forms when the carriers are spin polarized at low temperatures and in high magnetic fields.

Ultrasonic attenuation in superconducting molybdenum-rhenium alloys.

NASA Technical Reports Server (NTRS)

Ashkin, M.; Deis, D. W.; Gottlieb, M.; Jones, C. K.

1971-01-01

Investigation of longitudinal sound attenuation in superconducting Mo-Re alloys as a function of temperature, magnetic field, and frequency. Evaporated thin film CdS transducers were used for the measurements at frequencies up to 3 GHz. The normal state attenuation coefficient was found to be proportional to the square of frequency over this frequency range. Measurements in zero magnetic field yielded a value of the energy gap parameter close to the threshold value of 3.56 kTc, appropriate to a weakly coupled dirty limit superconductor.

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.

Growth and Structure of High-Temperature Superconducting Thin Films

NASA Astrophysics Data System (ADS)

Achutharaman, Vedapuram Sankar

High temperature superconducting thin films with atomic scale perfection are required for technological applications and scientific studies on the mechanism of superconductivity. Ozone assisted molecular beam epitaxy (MBE) has been shown to produce in-situ superconducting thin films. To obtain a well-controlled and reproducible process, some components such as the substrate heater and the substrate holder have to be designed to be compatible with high oxygen partial pressures. Also, to ensure precise stoichiometry and precipitate-free films, evaporation sources and temperature controllers have to be designed for better temperature stability. The investigation of the MBE process and the thin films grown by MBE are required to obtain a better understanding of the growth parameters such as the composition of the film, substrate surface structure, substrate temperature and ozone partial pressure. This can be obtained by dynamically monitoring the growth process by in-situ characterization techniques such as reflection high energy electron diffraction (RHEED). Intensity oscillations of the specular RHEED beam have been observed during the growth of RBa_2Cu_3 O_7 (R = Y,Dy) films on SrTiO _3. A model for the origin of these RHEED intensity oscillations will be proposed from extensive RHEED intensity studies. A mechanism for growth of these oxides by physical vapor deposition techniques such as MBE and pulsed laser deposition will also be developed. To verify both the models, the growth of the superconductors will be simulated by the Monte Carlo method and compared with experimental RHEED observations.

Onset of two-dimensional superconductivity in space charge doped few-layer molybdenum disulfide

NASA Astrophysics Data System (ADS)

Biscaras, Johan; Chen, Zhesheng; Paradisi, Andrea; Shukla, Abhay

2015-11-01

Atomically thin films of layered materials such as molybdenum disulfide (MoS2) are of growing interest for the study of phase transitions in two-dimensions through electrostatic doping. Electrostatic doping techniques giving access to high carrier densities are needed to achieve such phase transitions. Here we develop a method of electrostatic doping which allows us to reach a maximum n-doping density of 4 × 1014 cm-2 in few-layer MoS2 on glass substrates. With increasing carrier density we first induce an insulator to metal transition and subsequently an incomplete metal to superconductor transition in MoS2 with critical temperature ~10 K. Contrary to earlier reports, after the onset of superconductivity, the superconducting transition temperature does not depend on the carrier density. Our doping method and the results we obtain in MoS2 for samples as thin as bilayers indicates the potential of this approach.

High field superconducting properties of Ba(Fe1−xCox)2As2 thin films

PubMed Central

Hänisch, Jens; Iida, Kazumasa; Kurth, Fritz; Reich, Elke; Tarantini, Chiara; Jaroszynski, Jan; Förster, Tobias; Fuchs, Günther; Hühne, Ruben; Grinenko, Vadim; Schultz, Ludwig; Holzapfel, Bernhard

2015-01-01

In general, the critical current density, Jc, of type II superconductors and its anisotropy with respect to magnetic field orientation is determined by intrinsic and extrinsic properties. The Fe-based superconductors of the ‘122’ family with their moderate electronic anisotropies and high yet accessible critical fields (Hc2 and Hirr) are a good model system to study this interplay. In this paper, we explore the vortex matter of optimally Co-doped BaFe2As2 thin films with extended planar and c-axis correlated defects. The temperature and angular dependence of the upper critical field is well explained by a two-band model in the clean limit. The dirty band scenario, however, cannot be ruled out completely. Above the irreversibility field, the flux motion is thermally activated, where the activation energy U0 is going to zero at the extrapolated zero-kelvin Hirr value. The anisotropy of the critical current density Jc is both influenced by the Hc2 anisotropy (and therefore by multi-band effects) as well as the extended planar and columnar defects present in the sample. PMID:26612567

Optimisation of growth of epitaxial Tl 2Ba 2Ca 1Cu 2O 8 superconducting thin films for electronic device applications

NASA Astrophysics Data System (ADS)

Michael, Peter C.; Johansson, L.-G.; Bengtsson, L.; Claeson, T.; Ivanov, Z. G.; Olsson, E.; Berastegui, P.; Stepantsov, E.

1994-12-01

Epitaxial thin films of Tl 2Ba 2Ca 1Cu 2O 8 (Tl-2212) superconductor have been grown on single crystal (100) lanthanum aluminate (LaAlO 3) substrates by a two stage process: laser ablation of a BaCaCuO (0212) sintered target and post-deposition anneal ex-situ in a thallium environment. The films are c-axis oriented with in-plane epitaxy as determined by x-ray diffraction (XRD θ-2θ and φ-scans). Superconducting transition temperatures as high as 105.5K have been obtained both from four-probe resistance and a.c. magnetic susceptibility measurements. Film morphology and chemical composition have been assessed by scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX). Sensitivity of the precursor film to environmental exposure has proven to be a determining factor in the reproducibility of film growth characteristics. The effect of oxygen partial pressure and substrate temperature used in the precursor film synthesis, as well as the thallium annealing temperature and duration, on the growth of Tl-2212 thin films is reported.

Automatic HTS force measurement instrument

DOEpatents

Sanders, S.T.; Niemann, R.C.

1999-03-30

A device is disclosed for measuring the levitation force of a high temperature superconductor sample with respect to a reference magnet includes a receptacle for holding several high temperature superconductor samples each cooled to superconducting temperature. A rotatable carousel successively locates a selected one of the high temperature superconductor samples in registry with the reference magnet. Mechanism varies the distance between one of the high temperature superconductor samples and the reference magnet, and a sensor measures levitation force of the sample as a function of the distance between the reference magnet and the sample. A method is also disclosed. 3 figs.

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.

Space qualified hybrid superconductor/semiconductor planar oscillator circuit

NASA Technical Reports Server (NTRS)

Miranda, F. A.; Chorey, C. M.; Romanofsky, R. R.; Bhasin, K. B.

1995-01-01

We report on the space qualification of a hybrid superconductor/semiconductor planar local oscillator (LO) at 8.4 GHz. This oscillator was designed, fabricated, and tested as a component for the High Temperature Superconductivity Space Experiment 2 (HTSSE-2). The LO consisted of a GaAs MESFET and microstrip circuitry patterned onto a YBa2Cu3O(7-delta) high temperature superconducting (HTS) thin film on a 1.0 x 1.0 sq cm lanthanum aluminate (LaAlO3) substrate. At 77 K, this oscillator achieved power output levels up to 10 dBm into a 50 Ohm load. When incorporated into a full cryogenic receiver, the LO provided output powers within 0.0-3.0 dBm with less than 50 mW of dc power dissipation. Space qualification data on the sensitivity of the HTS films to the processing steps involved in the fabrication of HTS-based components are presented. Data on ohmic contacts, strength of wire bonds made to such contacts, and aging effects as well as vibration test results are discussed.

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.

Experimental investigations of recent anomalous results in superconductivity

NASA Astrophysics Data System (ADS)

Souw, Victor K.

2000-12-01

This thesis examines three recent anomalous results associated with irreversibility in type-II superconductivity: (1) The magnetic properties of the predicted superconductors LiBeH3 and Li2BeH 4, (2) the paramagnetic transition near T = Tc in Nb, and (3) a noise transition in a YBa2Cu3O7-delta thin film near the vortex-solid transition. The investigation of Li 2BeH4 and LiBeH3 was prompted by theoretical predictions of room-temperature superconductivity for Li2BeH4 and LiBeH3 and a recent report that Li2BeH4 showed magnetic irreversibilities similar to those of type-II superconductors. A modified experimental method is introduced in order to avoid artifacts due to background signals. The resulting data is suggestive of a superparamagnetic impurity from one of the reagents used in the synthesis and after subtracting this contribution, the temperature-dependent susceptibilities of Li2 BeH4 and LiBeH3 are estimated. However, no magnetic irreversibility suggestive of superconductivity is observed. The anomalous paramagnetic transition in Nb is intriguing because Nb does not share the d-wave order parameter symmetry often invoked to explain the phenomenon in other superconductors. A modified experimental method was developed in order to avoid instrumental artifacts known to produce a similar apparently paramagnetic response, but the results of this method indicate that the paramagnetic response is a physical property of the sample. Finally, a very sharp noise transition in a YBa2Cu3O7-delta thin film was found to be distinct from previously reported features in the voltage noise commonly associated with vortex fluctuations near the irreversibility line. In each of these three cases the examination of experimental techniques is an integral part of the investigation of novel vortex behavior near the onset of irreversibility.

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.

High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O

DOEpatents

Ginley, D.S.; Hietala, V.M.; Hohenwarter, G.K.G.; Martens, J.S.; Plut, T.A.; Tigges, C.P.; Vawter, G.A.; Zipperian, T.E.

1994-10-25

A process is disclosed for formulating non-hysteretic and hysteretic Josephson junctions using HTS materials which results in junctions having the ability to operate at high temperatures while maintaining high uniformity and quality. The non-hysteretic Josephson junction is formed by step-etching a LaAlO[sub 3] crystal substrate and then depositing a thin film of TlCaBaCuO on the substrate, covering the step, and forming a grain boundary at the step and a subsequent Josephson junction. Once the non-hysteretic junction is formed the next step to form the hysteretic Josephson junction is to add capacitance to the system. In the current embodiment, this is accomplished by adding a thin dielectric layer, LaA1O[sub 3], followed by a cap layer of a normal metal where the cap layer is formed by first depositing a thin layer of titanium (Ti) followed by a layer of gold (Au). The dielectric layer and the normal metal cap are patterned to the desired geometry. 8 figs.

Detecting stray microwaves and nonequilibrium quasiparticles in thin films by single-electron tunneling

NASA Astrophysics Data System (ADS)

Saira, Olli-Pentti; Maisi, Ville; Kemppinen, Antti; Möttönen, Mikko; Pekola, Jukka

2013-03-01

Superconducting thin films and tunnel junctions are the building blocks of many state-of-the-art technologies related to quantum information processing, microwave detection, and electronic amplification. These devices operate at millikelvin temperatures, and - in a naive picture - their fidelity metrics are expected to improve as the temperature is lowered. However, very often one finds in the experiment that the device performance levels off around 100-150 mK. In my presentation, I will address three common physical mechanisms that can cause such saturation: stray microwaves, nonequilibrium quasiparticles, and sub-gap quasiparticle states. The new experimental data I will present is based on a series of studies on quasiparticle transport in Coulomb-blockaded normal-insulator-superconductor tunnel junction devices. We have used a capacitively coupled SET electrometer to detect individual quasiparticle tunneling events in real time. We demonstrate the following record-low values for thin film aluminum: quasiparticle density nqp < 0 . 033 / μm3 , normalized density of sub-gap quasiparticle states (Dynes parameter) γ < 1 . 6 ×10-7 . I will also discuss some sample stage and chip designs that improve microwave shielding.

Method for forming single phase, single crystalline 2122 BCSCO superconductor thin films by liquid phase epitaxy

NASA Technical Reports Server (NTRS)

Pandey, Raghvendra K. (Inventor); Raina, Kanwal (Inventor); Solayappan, Narayanan (Inventor)

1994-01-01

A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83 K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

Visualizing domain wall and reverse domain superconductivity.

PubMed

Iavarone, M; Moore, S A; Fedor, J; Ciocys, S T; Karapetrov, G; Pearson, J; Novosad, V; Bader, S D

2014-08-28

In magnetically coupled, planar ferromagnet-superconductor (F/S) hybrid structures, magnetic domain walls can be used to spatially confine the superconductivity. In contrast to a superconductor in a uniform applied magnetic field, the nucleation of the superconducting order parameter in F/S structures is governed by the inhomogeneous magnetic field distribution. The interplay between the superconductivity localized at the domain walls and far from the walls leads to effects such as re-entrant superconductivity and reverse domain superconductivity with the critical temperature depending upon the location. Here we use scanning tunnelling spectroscopy to directly image the nucleation of superconductivity at the domain wall in F/S structures realized with Co-Pd multilayers and Pb thin films. Our results demonstrate that such F/S structures are attractive model systems that offer the possibility to control the strength and the location of the superconducting nucleus by applying an external magnetic field, potentially useful to guide vortices for computing application.

Epitaxial layers of 2122 BCSCO superconductor thin films having single crystalline structure

NASA Technical Reports Server (NTRS)

Pandey, Raghvendra K. (Inventor); Raina, Kanwal K. (Inventor); Solayappan, Narayanan (Inventor)

1995-01-01

A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

Visualizing domain wall and reverse domain superconductivity

PubMed Central

Iavarone, M.; Moore, S. A.; Fedor, J.; Ciocys, S. T.; Karapetrov, G.; Pearson, J.; Novosad, V.; Bader, S. D.

2014-01-01

In magnetically coupled, planar ferromagnet-superconductor (F/S) hybrid structures, magnetic domain walls can be used to spatially confine the superconductivity. In contrast to a superconductor in a uniform applied magnetic field, the nucleation of the superconducting order parameter in F/S structures is governed by the inhomogeneous magnetic field distribution. The interplay between the superconductivity localized at the domain walls and far from the walls leads to effects such as re-entrant superconductivity and reverse domain superconductivity with the critical temperature depending upon the location. Here we use scanning tunnelling spectroscopy to directly image the nucleation of superconductivity at the domain wall in F/S structures realized with Co-Pd multilayers and Pb thin films. Our results demonstrate that such F/S structures are attractive model systems that offer the possibility to control the strength and the location of the superconducting nucleus by applying an external magnetic field, potentially useful to guide vortices for computing application. PMID:25164004

Weakly superconducting, thin-film structures as radiation detectors.

NASA Technical Reports Server (NTRS)

Kirschman, R. K.

1972-01-01

Measurements were taken with weakly superconducting quantum structures of the Notarys-Mercereau type, representing a thin superconductor film with a short region that is weakened in the sense that its transition temperature is lower than in the remaining portion of the film. The structure acts as a superconducting relaxation oscillator in which the supercurrent increases with time until the critical current of the weakened section is attained, at which moment the supercurrent decays and the cycle repeats. Under applied radiation, a series of constant-voltage steps appears in the current-voltage curve, and the size of the steps varies periodically with the amplitude of applied radiation. Measurements of the response characteristics were made in the frequency range of 10 to 450 MHz.

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.

Out-of-equilibrium spin transport in mesoscopic superconductors.

PubMed

Quay, C H L; Aprili, M

2018-08-06

The excitations in conventional superconductors, Bogoliubov quasi-particles, are spin-[Formula: see text] fermions but their charge is energy-dependent and, in fact, zero at the gap edge. Therefore, in superconductors (unlike normal metals) spin and charge degrees of freedom may be separated. In this article, we review spin injection into conventional superconductors and focus on recent experiments on mesoscopic superconductors. We show how quasi-particle spin transport and out-of-equilibrium spin-dependent superconductivity can be triggered using the Zeeman splitting of the quasi-particle density of states in thin-film superconductors with small spin-mixing scattering. Finally, we address the spin dynamics and the feedback of quasi-particle spin imbalances on the amplitude of the superconducting energy gap.This article is part of the theme issue 'Andreev bound states'. © 2018 The Author(s).

Attraction between pancake vortices and vortex molecule formation in the crossing lattices in thin films of layered superconductors

NASA Astrophysics Data System (ADS)

Samokhvalov, A. V.; Mel'nikov, A. S.; Buzdin, A. I.

2012-05-01

We study the intervortex interaction in thin films of layered superconductors for the magnetic field tilted with respect to the c axis. In such a case, the crossing lattice of Abrikosov vortices (AVs) and Josephson vortices appears. The interaction between pancake vortices, forming the AVs, with Josephson ones, produces the zigzag deformation of the AV line. This deformation induces a long-range attraction between Abrikosov vortices and, in thin films, it competes with another long-range interaction, i.e., with Pearl's repulsion. This interplay results in the formation of clusters of Abrikosov vortices, which can be considered as vortex molecules. The number of vortices in such clusters depends on field tilting angle and film thickness.

Stress analysis in high-temperature superconductors under pulsed field magnetization

NASA Astrophysics Data System (ADS)

Wu, Haowei; Yong, Huadong; Zhou, Youhe

2018-04-01

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

A Low Noise NbTiN-Based 850 GHz SIS Receiver for the Caltech Submillimeter Observatory

NASA Technical Reports Server (NTRS)

Kooi, J. W.; Kawamura, J.; Chen, J.; Chattopadhyay, G.; Pardo, J. R.; Zmuidzinas, J.; Phillips, T. G.; Bumble, B.; Stern, J.; LeDuc, H. G.

2000-01-01

We have developed a niobium titanium nitride (NbTiN) based superconductor- insulator-superconductor (SIS) receiver to cover the 350 micron atmospheric window. This frequency band lies entirely above the energy gap of niobium (700 GHz), a commonly used SIS superconductor. The instrument uses an open structure twin-slot SIS mixer that consists of two Nb/AlN/NbTiN tunnel junctions, NbTiN thin-film microstrip tuning elements, and a NbTiN ground plane. The optical configuration is very similar to the 850 GHz waveguide receiver that was installed at the Caltech Submillimeter Observatory (CSO) in 1997. To minimize front-end loss, we employed reflecting optics and a cooled beamsplitter at 4 K. The instrument has an uncorrected receiver noise temperature of 205K DSB at 800 GHz and 410K DSB at 900 GHz. The degradation in receiver sensitivity with frequency is primarily due to an increase in the mixer conversion loss, which is attributed to the mismatch between the SIS junction and the twin-slot antenna impedance. The overall system performance has been confirmed through its use at the telescope to detect a wealth of new spectroscopic lines.

What can Andreev bound states tell us about superconductors?

PubMed

Millo, Oded; Koren, Gad

2018-08-06

Zero-energy Andreev bound states, which manifest themselves in the tunnelling spectra as zero-bias conductance peaks (ZBCPs), are abundant at interfaces between superconductors and other materials and on the nodal surface of high-temperature superconductors. In this review, we focus on the information such excitations can provide on the properties of superconductor systems. First, a general introduction to the physics of Andreev bound states in superconductor/normal metal interfaces is given with a particular emphasis on why they appear at zero energy in d -wave superconductors. Then, specific spectroscopic tunnelling studies of thin films, bilayers and junctions are described, focusing on the corresponding ZBCP features. Scanning tunnelling spectroscopy (STS) studies show that the ZBCPs on the c -axis YBa 2 Cu 3 O 7- δ (YBCO) films are correlated with the surface morphology and appear only in proximity to (110) facets. STS on c -axis La 1.88 Sr 0.12 CuO 4 (LSCO) films exhibiting the 1/8 anomaly shows spatially modulated peaks near zero bias associated with the anti-phase ordering of the d -wave order parameter predicted at this doping level. ZBCPs were also found in micrometre-size edge junctions of YBCO/SrRuO 3 /YBCO, where SrRuO 3 is ferromagnetic. Here, the results are consistent with a crossed Andreev reflection effect (CARE) at the narrow domain walls of the SrRuO 3 ZBCPs measured in STS studies of manganite/cuprate bilayers could not be attributed to CARE because the manganite's domain wall is much larger than the coherence length in YBCO, and instead are attributed to proximity-induced triplet-pairing superconductivity with non-conventional symmetry. And finally, ZBCPs found in junctions of non-intentionally doped topological insulator films of Bi 2 Se 3 and the s -wave superconductor NbN are attributed to proximity-induced p x  + ip y triplet order parameter in the topological material.This article is part of the theme issue 'Andreev bound states'. © 2018 The Author(s).

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.

Engineering topological superconductors using surface atomic-layer/molecule hybrid materials

NASA Astrophysics Data System (ADS)

Uchihashi, Takashi

2015-08-01

Surface atomic-layer (SAL) superconductors consisting of epitaxially grown metal adatoms on a clean semiconductor surface have been recently established. Compared to conventional metal thin films, they have two important features: (i) space-inversion symmetry-breaking throughout the system and (ii) high sensitivity to surface adsorption of foreign species. These potentially lead to manifestation of the Rashba effect and a Zeeman field exerted by adsorbed magnetic organic molecules. After introduction of the archetypical SAL superconductor Si(111)-(√7 × √3)-In, we describe how these features are utilized to engineer a topological superconductor with Majorana fermions and discuss its promises and expected challenges.

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.

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

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.

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

Atomic-scale distortions and temperature-dependent large pseudogap in thin films of the parent iron-chalcogenide superconductor Fe1+y Te

NASA Astrophysics Data System (ADS)

Gerbi, Andrea; Buzio, Renato; Kawale, Shrikant; Bellingeri, Emilio; Martinelli, Alberto; Bernini, Cristina; Tresca, Cesare; Capone, Massimo; Profeta, Gianni; Ferdeghini, Carlo

2017-12-01

We investigate with scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT) calculations the surface structures and the electronic properties of Fe1+y Te thin films grown by pulsed laser deposition. Contrary to the regular arrangement of antiferromagnetic nanostripes previously reported on cleaved single-crystal samples, the surface of Fe1+y Te thin films displays a peculiar distribution of spatially inhomogeneous nanostripes. Both STM and DFT calculations show the bias-dependent nature of such features and support the interpretation of spin-polarized tunneling between the FeTe surface and an unintentionally magnetized tip. In addition, the spatial inhomogeneity is interpreted as a purely electronic effect related to changes in hybridization and Fe-Fe bond length driven by local variations in the concentration of excess interstitial Fe cations. Unexpectedly, the surface density of states measured by STS strongly evolves with temperature in close proximity to the antiferromagnetic-paramagnetic first-order transition, and reveals a large pseudogap of 180-250 meV at about 50-65 K. We believe that in this temperature range a phase transition takes place, and the system orders and locks into particular combinations of orbitals and spins because of the interplay between excess interstitial magnetic Fe and strongly correlated d-electrons.

Shielding superconductors with thin films as applied to rf cavities for particle accelerators

DOE PAGES

Posen, Sam; Transtrum, Mark K.; Catelani, Gianluigi; ...

2015-10-29

Determining the optimal arrangement of superconducting layers to withstand large-amplitude ac magnetic fields is important for certain applications such as superconducting radio-frequency cavities. In this paper, we evaluate the shielding potential of the superconducting-film–insulating-film–superconductor (SIS') structure, a configuration that could provide benefits in screening large ac magnetic fields. After establishing that, for high-frequency magnetic fields, flux penetration must be avoided, the superheating field of the structure is calculated in the London limit both numerically and, for thin films, analytically. For intermediate film thicknesses and realistic material parameters, we also solve numerically the Ginzburg-Landau equations. As a result, it is shownmore » that a small enhancement of the superheating field is possible, on the order of a few percent, for the SIS' structure relative to a bulk superconductor of the film material, if the materials and thicknesses are chosen appropriately.« less

Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces.

PubMed

Misawa, Takahiro; Nomura, Yusuke; Biermann, Silke; Imada, Masatoshi

2016-07-01

Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2-x Sr x CuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices.

Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces

PubMed Central

Misawa, Takahiro; Nomura, Yusuke; Biermann, Silke; Imada, Masatoshi

2016-01-01

Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2−xSrxCuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices. PMID:27482542

Construction and performance of a high-temperature-superconductor composite bolometer

NASA Technical Reports Server (NTRS)

Brasunas, J. C.; Moseley, S. H.; Lakew, B.; Ono, R. H.; Mcdonald, D. G.

1989-01-01

A high-Tc superconducting bolometer has been constructed using a YBa2Cu3O(x) thin-film meander line 20 microns wide and 76,000 microns long, deposited on a SrTiO3 substrate. Radiation is absorbed by a thin film of Bi with well-characterized absorption properties deposited on a Si substrate in contact with the SrTiO3. At 1.8 Hz the measured bolometer response to a 500-K blackbody is 5.2 V/W (820 V/W extrapolated to dc). The impact of apparent nonohmic behavior at the transition is discussed, as are ways of reducing the observed 1/f noise. The response time is 32 s and is dominated by the heat capacity of the SrTiO3 substrate.

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.

Aspects of passive magnetic levitation based on high-T(sub c) superconducting YBCO thin films

NASA Technical Reports Server (NTRS)

Schoenhuber, P.; Moon, F. C.

1995-01-01

Passive magnetic levitation systems reported in the past were mostly confined to bulk superconducting materials. Here we present fundamental studies on magnetic levitation employing cylindrical permanent magnets floating above high-T(sub c) superconducting YBCO thin films (thickness about 0.3 mu m). Experiments included free floating rotating magnets as well as well-established flexible beam methods. By means of the latter, we investigated levitation and drag force hysteresis as well as magnetic stiffness properties of the superconductor-magnet arrangement. In the case of vertical motion of the magnet, characteristic high symmetry of repulsive (approaching) and attractive (withdrawing) branches of the pronounced force-displacement hysteresis could be detected. Achievable force levels were low as expected but sufficient for levitation of permanent magnets. With regard to magnetic stiffness, thin films proved to show stiffness-force ratios about one order of magnitude higher than bulk materials. Phenomenological models support the measurements. Regarding the magnetic hysteresis of the superconductor, the Irie-Yamafuji model was used for solving the equation of force balance in cylindrical coordinates allowing for a macroscopic description of the superconductor magnetization. This procedure provided good agreement with experimental levitation force and stiffness data during vertical motion. For the case of (lateral) drag force basic qualitative characteristics could be recovered, too. It is shown that models, based on simple asymmetric magnetization of the superconductor, describe well asymptotic transition of drag forces after the change of the magnet motion direction. Virgin curves (starting from equilibrium, i.e. symmetric magnetization) are approximated by a linear approach already reported in literature only. This paper shows that basic properties of superconducting thin films allow for their application to magnetic levitation or - without need of levitation forces, e.g. microgravity - magnetic damping devices.

Lumped element kinetic inductance detectors based on two-gap MgB2 thin films

NASA Astrophysics Data System (ADS)

Yang, C.; Niu, R. R.; Guo, Z. S.; Cai, X. W.; Chu, H. M.; Yang, K.; Wang, Y.; Feng, Q. R.; Gan, Z. Z.

2018-01-01

Lumped element kinetic inductance detectors (LEKIDs) are made from a single layer superconducting thin film. Because of their low noise and highly multiplexibility, LEKIDs provide a sensitive technology for the detection of millimeter and submillimeter waves. In this work, a 5-pixel 50-nm-thick MgB2 array is made. The microwave properties of the array are measured under dark conditions. We show that the loaded quality factor Q of the resonant circuit is 30 000 at 7.5 K, which is comparable to that of lower-operating-temperature (usually several hundred mK) LEKIDs made from superconductors such as Al and Nb. Moreover, the temperature dependence of resonance frequency gives the two-gap character of MgB2, Δπ (0) = 2.58 meV and Δσ (0) = 8.26 meV. The gap frequency (f = 2Δ/h) indicates that MgB2 LEKIDs have a promising application on terahertz detection.

Onset of two-dimensional superconductivity in space charge doped few-layer molybdenum disulfide

PubMed Central

Biscaras, Johan; Chen, Zhesheng; Paradisi, Andrea; Shukla, Abhay

2015-01-01

Atomically thin films of layered materials such as molybdenum disulfide (MoS2) are of growing interest for the study of phase transitions in two-dimensions through electrostatic doping. Electrostatic doping techniques giving access to high carrier densities are needed to achieve such phase transitions. Here we develop a method of electrostatic doping which allows us to reach a maximum n-doping density of 4 × 1014 cm−2 in few-layer MoS2 on glass substrates. With increasing carrier density we first induce an insulator to metal transition and subsequently an incomplete metal to superconductor transition in MoS2 with critical temperature ≈10 K. Contrary to earlier reports, after the onset of superconductivity, the superconducting transition temperature does not depend on the carrier density. Our doping method and the results we obtain in MoS2 for samples as thin as bilayers indicates the potential of this approach. PMID:26525386

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

Vortex variable range hopping in a conventional superconducting film

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

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.

The Pressure Coefficients of the Superconducting Order Parameters at the Ground State of Ferromagnetic Superconductors

NASA Astrophysics Data System (ADS)

Konno, R.; Hatayama, N.; Chaudhury, R.

2014-04-01

We investigated the pressure coefficients of the superconducting order parameters at the ground state of ferromagnetic superconductors based on the microscopic single band model by Linder et al. The superconducting gaps (i) similar to the ones seen in the thin film of A2 phase in liquid 3He and (ii) with the line node were used. This study shows that we would be able to estimate the pressure coefficients of the superconducting and magnetic order parameters at the ground state of ferromagnetic superconductors.

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

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

Giant asymmetric self-phase modulation in superconductor thin films

NASA Astrophysics Data System (ADS)

Robson, Charles W.; Biancalana, Fabio

2018-04-01

Self-phase modulation (SPM) of light pulses is found to occur strongly, at low incident intensities, in the coupling of light with superconductors. We develop a theory from a synthesis of the time-dependent Ginzburg-Landau (TDGL) equation and basic electrodynamics which shows the strongly non-linear phase accumulated in the interaction. Unusually, the SPM of the pulse in this system is found to be highly asymmetric, producing a strongly redshifted spectrum when interacting with a superconducting thin film, and it develops in just a few nanometers of propagation. In this paper we present theoretical results and simulations in the THz regime, for both hyperbolic secant and supergaussian-shaped pulses.

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.

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.

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.

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.

Final Technical Report Grant No. DE-FG02-97ER45653 Lance E. De Long, Principal Investigator, University of Kentucky Period of Performance: 09/01/97 to 05/14/15

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

De Long, Lance Eric

Prior to 1997, the PI had studied the unusual upper critical magnetic field phase boundaries of several novel or exotic types of superconductors, including charge density wave materials such as NbSe 2, organic superconductors such as κ-(ET) 2Cu[N(CN) 2]Br, high-temperature oxide superconductors such as (Ba,K)BiO 3 and the cuprates, heavy fermion superconductors such as U 6Fe, UBe 13, URu 2Si 2 and UPt 3, and re-entrant Kondo alloys such as (La,Ce)Al 2 and ferromagnetic superconductors such as ErRh 4B 4. Most of these materials exhibited marked positive or negative curvature of H C2(T) which could not be explained by traditionalmore » pair-breaking models. It became clear that many of these materials had very short coherence lengths that made quantized vortices highly mobile (depinned) near the phase boundary, and the fundamental, equilibrium H C2(T) difficult to measure using finite field or current drives. These problems made the underlying physics obscure, and led to erroneous interpretations of experimental data in terms of models of exotic superconducting pairing mechanisms. Around 1995, these issues led the PI to take advantage of modern electron beam lithography techniques for patterning superconducting and ferromagnetic thin films on the nanoscale. Primarily due to strong magnetic shape anisotropy effects, EBL patterning has led to enhanced control of the spatial distribution and dynamics of topological defects such as domain walls and magnetic vortices, which can create serious energy dissipation and other limitations for modern devices. Moreover, finite size and interface effects also strongly alter phase transition temperatures and phase boundaries of superconducting and magnetic films, as well as introduce barriers to equilibration, enhanced fluctuations and alter magnetic relaxation. Geometrical frustration and spin ice behavior can also be systematically controlled in patterned film media. Film patterning thus provides an excellent tool for conducting highly-controlled, fundamental studies of cooperative phases and interactions in artificially structured condensed matter.« less

A Novel Method for Characterization of Superconductors: Physical Measurements and Modeling of Thin Films

NASA Technical Reports Server (NTRS)

Kim, B. F.; Moorjani, K.; Phillips, T. E.; Adrian, F. J.; Bohandy, J.; Dolecek, Q. E.

1993-01-01

A method for characterization of granular superconducting thin films has been developed which encompasses both the morphological state of the sample and its fabrication process parameters. The broad scope of this technique is due to the synergism between experimental measurements and their interpretation using numerical simulation. Two novel technologies form the substance of this system: the magnetically modulated resistance method for characterizing superconductors; and a powerful new computer peripheral, the Parallel Information Processor card, which provides enhanced computing capability for PC computers. This enhancement allows PC computers to operate at speeds approaching that of supercomputers. This makes atomic scale simulations possible on low cost machines. The present development of this system involves the integration of these two technologies using mesoscale simulations of thin film growth. A future stage of development will incorporate atomic scale modeling.

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.

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

He, Qing Lin; Pan, Lei; Stern, Alexander L.

Majorana fermion is a hypothetical particle that is its own antiparticle. We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantummore » computing.« less

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.

Metastable Superconductivity in Two-Dimensional IrTe2 Crystals.

PubMed

Yoshida, Masaro; Kudo, Kazutaka; Nohara, Minoru; Iwasa, Yoshihiro

2018-05-09

Two-dimensional (2D) materials exhibit unusual physical and chemical properties that are attributed to the thinning-induced modification of their electronic band structure. Recently, reduced thickness was found to dramatically impact not only the static electronic structure, but also the dynamic ordering kinetics. The ordering kinetics of first-order phase transitions becomes significantly slowed with decreasing thickness, and metastable supercooled states can be realized by thinning alone. We therefore focus on layered iridium ditelluride (IrTe 2 ), a charge-ordering system that is transformed into a superconductor by suppressing its first-order transition. Here, we discovered a persistent superconducting zero-resistance state in mechanically exfoliated IrTe 2 thin flakes. The maximum superconducting critical temperature ( T c ) was identical to that which is chemically optimized, and the emergent superconductivity was revealed to have a metastable nature. The discovered robust metastable superconductivity suggests that 2D material is a new platform to induce, control, and functionalize metastable electronic states that are inaccessible in bulk crystals.

Characterization of the thin-film NbN superconductor for single-photon detection by transport measurements

NASA Astrophysics Data System (ADS)

Lin, Shi-Zeng; Ayala-Valenzuela, Oscar; McDonald, Ross D.; Bulaevskii, Lev N.; Holesinger, Terry G.; Ronning, Filip; Weisse-Bernstein, Nina R.; Williamson, Todd L.; Mueller, Alexander H.; Hoffbauer, Mark A.; Rabin, Michael W.; Graf, Matthias J.

2013-05-01

The fabrication of high-quality thin superconducting films is essential for single-photon detectors. Their device performance is crucially affected by their material parameters, thus requiring reliable and nondestructive characterization methods after the fabrication and patterning processes. Important material parameters to know are the resistivity, superconducting transition temperature, relaxation time of quasiparticles, and uniformity of patterned wires. In this work, we characterize micropatterned thin NbN films by using transport measurements in magnetic fields. We show that from the instability of vortex motion at high currents in the flux-flow state of the IV characteristic, the inelastic lifetime of quasiparticles can be determined to be about 2 ns. Additionally, from the depinning transition of vortices at low currents, as a function of magnetic field, the size distribution of grains can be extracted. This size distribution is found to be in agreement with the film morphology obtained from scanning electron microscopy and high-resolution transmission electron microscopy images.

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.

Induced Superconductivity and Engineered Josephson Tunneling Devices in Epitaxial (111)-Oriented Gold/Vanadium Heterostructures.

PubMed

Wei, Peng; Katmis, Ferhat; Chang, Cui-Zu; Moodera, Jagadeesh S

2016-04-13

We report a unique experimental approach to create topological superconductors by inducing superconductivity into epitaxial metallic thin film with strong spin-orbit coupling. Utilizing molecular beam epitaxy technique under ultrahigh vacuum conditions, we are able to achieve (111) oriented single phase of gold (Au) thin film grown on a well-oriented vanadium (V) s-wave superconductor film with clean interface. We obtained atomically smooth Au thin films with thicknesses even down to below a nanometer showing near-ideal surface quality. The as-grown V/Au bilayer heterostructure exhibits superconducting transition at around 3.9 K. Clear Josephson tunneling and Andreev reflection are observed in S-I-S tunnel junctions fabricated from the epitaxial bilayers. The barrier thickness dependent tunneling and the associated subharmonic gap structures (SGS) confirmed the induced superconductivity in Au (111), paving the way for engineering thin film heterostructures based on p-wave superconductivity and nano devices exploiting Majorana Fermions for quantum computing.

Stencil lithography of superconducting contacts on MBE-grown topological insulator thin films

NASA Astrophysics Data System (ADS)

Schüffelgen, Peter; Rosenbach, Daniel; Neumann, Elmar; Stehno, Martin P.; Lanius, Martin; Zhao, Jialin; Wang, Meng; Sheehan, Brendan; Schmidt, Michael; Gao, Bo; Brinkman, Alexander; Mussler, Gregor; Schäpers, Thomas; Grützmacher, Detlev

2017-11-01

Topological insulator (Bi0.06Sb0.94)2Te3 thin films grown by molecular beam epitaxy have been capped in-situ with a 2 nm Al film to conserve the pristine topological surface states. Subsequently, a shadow mask - structured by means of focus ion beam - was in-situ placed underneath the sample to deposit a thick layer of Al on well-defined microscopically small areas. The 2 nm thin Al layer fully oxidizes after exposure to air and in this way protects the TI surface from degradation. The thick Al layer remains metallic underneath a 3-4 nm thick native oxide layer and therefore serves as (super-) conducting contacts. Superconductor-Topological Insulator-Superconductor junctions with lateral dimensions in the nm range have then been fabricated via an alternative stencil lithography technique. Despite the in-situ deposition, transport measurements and transmission electron microscope analysis indicate a low transparency, due to an intermixed region at the interface between topological insulator thin film and metallic Al.

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

Fabrication of high T(sub c) superconductor thin film devices: Center director's discretionary fund

NASA Technical Reports Server (NTRS)

Sisk, R. C.

1992-01-01

This report describes a technique for fabricating superconducting weak link devices with micron-sized geometries etched in laser ablated Y1Ba2Cu3O(x) (YBCO) thin films. Careful placement of the weak link over naturally occurring grain boundaries exhibited in some YBCO thin films produces Superconducting Quantum Interference Devices (SQUID's) operating at 77 K.

Progress of research of high-Tc superconductors

NASA Technical Reports Server (NTRS)

Tanaka, Shoji

1991-01-01

Research in the area of of high T(sub c) superconductors has made great progress in the last few years. New materials were found and the systematic investigation of these materials has contributed to understanding the mechanism of high T(sub c) superconductivity. The critical currents in thin films, bulks, and tapes increased drastically, and the origin of flux pinning will be clarified in the near future. The future of high T(sub c) superconductivity, in both the basic and applied research areas, is very optimistic. Recent activities in research of high T(sub c) superconductivity and superconductors in Japan are overviewed.

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.

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).

Two-band induced superconductivity in single-layer graphene and topological insulator bismuth selenide

NASA Astrophysics Data System (ADS)

Talantsev, E. F.; Crump, W. P.; Tallon, J. L.

2018-01-01

Proximity-induced superconductivity in single-layer graphene (SLG) and in topological insulators represent almost ideal examples of superconductivity in two dimensions. Fundamental mechanisms governing superconductivity in the 2D limit are of central interest for modern condensed-matter physics. To deduce fundamental parameters of superconductor/graphene/superconductor and superconductor/bismuth selenide/superconductor junctions we investigate the self-field critical currents in these devices using the formalism of the Ambegaokar-Baratoff model. Our central finding is that the induced superconducting state in SLG and bismuth selenide each exhibits gapping on two superconducting bands. Based on recent results obtained on ultra-thin films of natural superconductors, including single-atomic layer of iron selenide, double and triple atomic layers of gallium, and several atomic layer tantalum disulphide, we conclude that a two-band induced superconducting state in SLG and bismuth selenide is part of a wider, more general multiple-band phenomenology of currently unknown origin.

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.

Thin film metrology and microwave loss characterization of indium and aluminum/indium superconducting planar resonators

NASA Astrophysics Data System (ADS)

McRae, C. R. H.; Béjanin, J. H.; Earnest, C. T.; McConkey, T. G.; Rinehart, J. R.; Deimert, C.; Thomas, J. P.; Wasilewski, Z. R.; Mariantoni, M.

2018-05-01

Scalable architectures characterized by quantum bits (qubits) with low error rates are essential to the development of a practical quantum computer. In the superconducting quantum computing implementation, understanding and minimizing material losses are crucial to the improvement of qubit performance. A new material that has recently received particular attention is indium, a low-temperature superconductor that can be used to bond pairs of chips containing standard aluminum-based qubit circuitry. In this work, we characterize microwave loss in indium and aluminum/indium thin films on silicon substrates by measuring superconducting coplanar waveguide resonators and estimating the main loss parameters at powers down to the sub-photon regime and at temperatures between 10 and 450 mK. We compare films deposited by thermal evaporation, sputtering, and molecular beam epitaxy. We study the effects of heating in a vacuum and ambient atmospheric pressure as well as the effects of pre-deposition wafer cleaning using hydrofluoric acid. The microwave measurements are supported by thin film metrology including secondary-ion mass spectrometry. For thermally evaporated and sputtered films, we find that two-level state are the dominant loss mechanism at low photon number and temperature, with a loss tangent due to native indium oxide of ˜ 5 × 10 - 5 . The molecular beam epitaxial films show evidence of the formation of a substantial indium-silicon eutectic layer, which leads to a drastic degradation in resonator performance.

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.

Processing And Patterning Of Thin Film Superconductors Formed By Metallo-Organic Deposition

NASA Astrophysics Data System (ADS)

Micheli, Adolph L.; Mantese, Joseph V.; Hamdi, Aboud H.

1990-04-01

Thin film superconductors of Y-Ba-Cu and Yb-Ba-Cu were formed by the pyrolysis of neodecanoate solutions of Y, Yb, Ba and Cu which had been deposited onto <100> SrTiO3 substrates [1]. Rapid thermal annealing, in oxygen, of the as-deposited films produced high T films having superconducting onset temperatures above 90 K and zero resistance at 8g K. Scanning Electron Microscopy (SEM) revealed enhancements in grain growth, compared to furnace annealed films, by a factor of 4. X-ray diffraction analysis showed preferred epitaxial grain growth with the c-axis of the films oriented both perpendicular and parallel to the substrate surface. Separate Rutherford Backscattering Spectrometry (RBS) channeling experiments confirmed the formation of preferred epitaxial grain growth. Film composition was determined by RBS and Inductively Coupled Plasma Emission Spectrometry (ICPES). Selective patterning was accomplished by focused beam exposure of the metal neodecanoate films [2-4]. The exposure rendered the neodecanoate film locally insoluble in xylene, thus permitting selective area patterning prior to pyrolysis. Electron, ion and laser beams were used to pattern films on <100> SrTiO3. The finest lines, approximately 5 #m in width and 26 nm thick, were patterned using electron beams whose lines had superconducting onsets above 90 K and zero resistance at 69 K after rapid thermal annealing. Both ion beam and laser patterning had similar superconducting onsets and zero resistance. Neodecanoates of Y, Yb, Ba, and Cu were formed, as previously described [5], by reacting the metal acetates of these materials with either ammonium neodecanoate or tetramethyl ammonium neodecanoate. The carboxylates formed from these reactions were then dissolved in a solution of xylene and pyridine. The individual chemical constituents were combined to produce solutions, Ln:Ba:Cu, in the ratio 1:2:4. Here, Ln is a rare-earth element. Details of the preparation of the metal carboxylates may be found elsewhere [6]. Thin films of Y-Ba-Cu and Yb-Ba-Cu were deposited onto <100> SrTiO by flooding the substrates with the appropriate neodecanoate solutions, then spin drying them at 2000 rpm for 30 s. The substrates were heated rapidly to 500?°C for 5 min in an air oven to pyrolize the metallo organics to their oxides. This process produces thin films about 200 nm thick. The spin coating process was repeated 3-6 times if thicker films were desired. X-ray diffraction analysis of films pyrolized at 500?°C shoed the presence of only microcrystallites. Room temperature resistivities of lx10 0-cm were measured for these films. No superconducting behavior was observed. After the 500?°C pyrolysis the films were further processed by RTA in flowing oxygen. The substrates were placed upon oxidized silicon wafers, rapidly heated to 850?°C for 60 s using infrared radiation produced by a bank of quartz lamps then allowed to cool to room temperature. A second rapid annealing was then performed at 920?°C for 30 s in oxygen. Thin film superconductors formed in the manner described above were very uniform in structure and thickness across the surface of the film. The grains are approximately 1 #m wide and 2 #m long, a factor of 4 larger than the grains found in furnace annealed films formed by MOD [5].

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.

Technology of Producing the Contact Connections of Superconductor Metal-Sheathed Cable

NASA Astrophysics Data System (ADS)

Jakubowski, Andrzej

2017-06-01

The technology of producing the current contact connections on the superconductor cable edges is presented. This lead cable is used as one of the major elements of the magnetic system in thermonuclear reactor construction, actuality for modern world energy. The technology is realized by the radial draft of metal thin-walled tube on the conductor's package. The filling of various profiles by round section wire is optimized. Geometrical characteristics of the dangerous crosssection (as a broken ring) of thin-walled tube injured by the sector cut-out are accounted. The comparative strength calculation of the solid and injured tubes at a longitudinal compression and lateral bending is acted. The radial draft mechanism of cylindrical thin-walled sheath with the wire packing is designed. The necessity to use the nonlinear theory for the sheaths calculate is set. The resilient co-operation of wires as the parallel located cylinders with the contact stripes of rectangular form is considered.

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.

Thin-film metal coated insulation barrier in a Josephson tunnel junction. [Patent application

DOEpatents

Hawkins, G.A.; Clarke, J.

1975-10-31

A highly stable, durable, and reproducible Josephson tunnel junction consists of a thin-film electrode of a hard superconductor, a thin oxide insulation layer over the electrode constituting a Josephson tunnel junction barrier, a thin-film layer of stabilizing metal over the barrier, and a second thin-film hard superconductive electrode over the stabilizing film. The thin stabilizing metal film is made only thick enough to limit penetration of the electrode material through the insulation layer so as to prevent a superconductive short.

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.

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.

Aluminum-Stabilized Magnesium Diboride Superconductors

NASA Astrophysics Data System (ADS)

Dou, S. X.; Collings, E. W.; Shcherbakova, O.; Shcherbakov, A.

2006-03-01

Use of aluminum as stabilizer and iron as reaction barrier for fabrication of MgB2 superconductor wires was studied. The MgB2/Fe/Al or SiC doped MgB2/Fe/Al composite wires were made using Mg+ 2 B powder or SiC doped Mg+2 B powder in Fe/Al tube technique. The composites were processed at 600°C to 650°C for 30 minutes to 3 hours to study the interaction between Fe and Al sheath and the formation of MgB2. No reaction between Fe and Al was found until annealing temperature at 620°C for 30 minutes. A thin layer of alloy, FeAl3 is formed for samples annealed at 620°C for 90 minutes and the reaction layer increases with increasing annealing temperature. Annealing at 650°C resulted in cracks in the Al sheath. Our results show that the Fe/Al sheathed wires achieved the same performance in magnetic and electrical properties as those using an all-Fe sheath. Comparing with the standard NbTi/Cu conductors, the MgB2/Fe/Al conductor having low structural mass, greater thermal conductivity and high efficient stabilization will make a tremendous difference especially for airborne, aerospace, and other applications when weight is important.

A 15-pole high temperature superconductor filter for radar applications

NASA Astrophysics Data System (ADS)

Yu, Xiao; Xi, Weibin; Wu, Songtao

2018-06-01

This paper presents a compact and high first harmonic frequency resonator. The characteristics of this resonator are theoretically analyzed. A highly selective 15-pole Chebyshev high temperature superconducting ultra-high frequency narrowband filter for radar applications was fabricated by using this resonator. The filter has a center frequency of 495 MHz and a fractional bandwidth of 1%. The first harmonic frequency is more than 3.3 times the fundamental frequency. The measured filter shows excellent selectivity, better than 85 dB/1 MHz skirt slopes, and more than 85 dB of rejection at 497.5 MHz from the band edge. The filter was fabricated on a 2 inch YBCO thin film with a 0.5 mm thick MgO substrate. The experimental results are consistent with the simulations.

Improvement of critical current density in thallium-based (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) superconductors

NASA Technical Reports Server (NTRS)

Ren, Z. F.; Wang, C. A.; Wang, J. H.; Miller, D. J.; Goretta, K. C.

1995-01-01

Epitaxial (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) ((Tl,Bi)-1223) thin films on (100) single crystal LaAlO3 substrates were synthesized by a two-step procedure. Phase development, microstructure, and relationships between film and substrate were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Resistance versus temperature, zero-field-cooled and field cooled magnetization, and transport critical current density (J(sub c)) were measured. The zero-resistance temperature was 105-111 K. J(sub c) at 77 K and zero field was greater than 2 x 10(exp 6) A/sq cm. The films exhibited good flux pinning properties.

Thermal-mechanical properties of epoxy-impregnated Bi-2212/Ag composite

DOE PAGES

Li, Pei; Wang, Yang; Fermi National Accelerator Lab.; ...

2014-11-26

In this study, knowledge of the thermal-mechanical properties of epoxy/superconductor/insulation composite is important for designing, fabricating, and operating epoxy impregnated high field superconducting magnets near their ultimate potentials. We report measurements of the modulus of elasticity, Poisson's ratio, and the coefficient of thermal contraction of epoxy-impregnated composite made from the state-of-the-art powder-in-tube multifilamentary Ag/Bi 2Sr 2CaCu 2O x round wire at room temperature and cryogenic temperatures. Stress-strain curves of samples made from single-strand and Rutherford cables were tested under both monotonic and cyclic compressive loads, with single strands insulated using a thin TiO 2 insulation coating and the Rutherford cablemore » insulated with a braided ceramic sleeve.« less

High quality factor, fully switchable terahertz superconducting metasurface

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

Scalari, G., E-mail: scalari@phys.ethz.ch; Maissen, C.; Faist, J.

2014-12-29

We present a complementary THz metasurface realised with Niobium thin film which displays a quality factor Q = 54 and a fully switchable behaviour as a function of the temperature. The switching behaviour and the high quality factor are due to a careful design of the metasurface aimed at maximising the ohmic losses when the Nb is above the critical temperature and minimising the radiative coupling. The superconductor allows the operation of the cavity with high Q and the use of inductive elements with a high aspect ratio. Comparison with three dimensional finite element simulations highlights the crucial role of the inductivemore » elements and of the kinetic inductance of the Cooper pairs in achieving the high quality factor and the high field enhancement.« less

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

GaN/NbN epitaxial semiconductor/superconductor heterostructures

NASA Astrophysics Data System (ADS)

Yan, Rusen; Khalsa, Guru; Vishwanath, Suresh; Han, Yimo; Wright, John; Rouvimov, Sergei; Katzer, D. Scott; Nepal, Neeraj; Downey, Brian P.; Muller, David A.; Xing, Huili G.; Meyer, David J.; Jena, Debdeep

2018-03-01

Epitaxy is a process by which a thin layer of one crystal is deposited in an ordered fashion onto a substrate crystal. The direct epitaxial growth of semiconductor heterostructures on top of crystalline superconductors has proved challenging. Here, however, we report the successful use of molecular beam epitaxy to grow and integrate niobium nitride (NbN)-based superconductors with the wide-bandgap family of semiconductors—silicon carbide, gallium nitride (GaN) and aluminium gallium nitride (AlGaN). We apply molecular beam epitaxy to grow an AlGaN/GaN quantum-well heterostructure directly on top of an ultrathin crystalline NbN superconductor. The resulting high-mobility, two-dimensional electron gas in the semiconductor exhibits quantum oscillations, and thus enables a semiconductor transistor—an electronic gain element—to be grown and fabricated directly on a crystalline superconductor. Using the epitaxial superconductor as the source load of the transistor, we observe in the transistor output characteristics a negative differential resistance—a feature often used in amplifiers and oscillators. Our demonstration of the direct epitaxial growth of high-quality semiconductor heterostructures and devices on crystalline nitride superconductors opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic and piezoelectric properties of the group III/nitride semiconductor family.

GaN/NbN epitaxial semiconductor/superconductor heterostructures.

PubMed

Yan, Rusen; Khalsa, Guru; Vishwanath, Suresh; Han, Yimo; Wright, John; Rouvimov, Sergei; Katzer, D Scott; Nepal, Neeraj; Downey, Brian P; Muller, David A; Xing, Huili G; Meyer, David J; Jena, Debdeep

2018-03-07

Epitaxy is a process by which a thin layer of one crystal is deposited in an ordered fashion onto a substrate crystal. The direct epitaxial growth of semiconductor heterostructures on top of crystalline superconductors has proved challenging. Here, however, we report the successful use of molecular beam epitaxy to grow and integrate niobium nitride (NbN)-based superconductors with the wide-bandgap family of semiconductors-silicon carbide, gallium nitride (GaN) and aluminium gallium nitride (AlGaN). We apply molecular beam epitaxy to grow an AlGaN/GaN quantum-well heterostructure directly on top of an ultrathin crystalline NbN superconductor. The resulting high-mobility, two-dimensional electron gas in the semiconductor exhibits quantum oscillations, and thus enables a semiconductor transistor-an electronic gain element-to be grown and fabricated directly on a crystalline superconductor. Using the epitaxial superconductor as the source load of the transistor, we observe in the transistor output characteristics a negative differential resistance-a feature often used in amplifiers and oscillators. Our demonstration of the direct epitaxial growth of high-quality semiconductor heterostructures and devices on crystalline nitride superconductors opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic and piezoelectric properties of the group III/nitride semiconductor family.

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.

Ultimately short ballistic vertical graphene Josephson junctions

PubMed Central

Lee, Gil-Ho; Kim, Sol; Jhi, Seung-Hoon; Lee, Hu-Jong

2015-01-01

Much efforts have been made for the realization of hybrid Josephson junctions incorporating various materials for the fundamental studies of exotic physical phenomena as well as the applications to superconducting quantum devices. Nonetheless, the efforts have been hindered by the diffusive nature of the conducting channels and interfaces. To overcome the obstacles, we vertically sandwiched a cleaved graphene monoatomic layer as the normal-conducting spacer between superconducting electrodes. The atomically thin single-crystalline graphene layer serves as an ultimately short conducting channel, with highly transparent interfaces with superconductors. In particular, we show the strong Josephson coupling reaching the theoretical limit, the convex-shaped temperature dependence of the Josephson critical current and the exceptionally skewed phase dependence of the Josephson current; all demonstrate the bona fide short and ballistic Josephson nature. This vertical stacking scheme for extremely thin transparent spacers would open a new pathway for exploring the exotic coherence phenomena occurring on an atomic scale. PMID:25635386

Preparation, patterning, and properties of thin YBa2Cu3O(7-delta) films

NASA Astrophysics Data System (ADS)

de Vries, J. W. C.; Dam, B.; Heijman, M. G. J.; Stollman, G. M.; Gijs, M. A. M.

1988-05-01

High T(c) superconducting thin films were prepared on (100) SrTiO3 substrates by dc triode sputtering and subsequent annealing. In these films Hall-bar structures having a width down to 5 microns were patterned using a reactive ion-etching technique. Superconductivity above 77 K was observed. When compared with the original film there is only a small reduction in T(c). The critical current density determined by electrical measurements is substantially reduced. On the other hand, the critical current density in the bulk of the grains as measured by the torque on a film is not reduced by the patterning process. It is suggested that superconductor-normal metal-superconductor junctions between the grains account for this difference.

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.

Assessment of Chemical Solution Synthesis and Properties of Gd2Zr2O7 Thin Films as Buffer Layers for Second-Generation High-Temperature Superconductor Wires (Postprint)

DTIC Science & Technology

2012-02-01

AC05-00OR22725. REFERENCES 1. D.P. Norton, A. Goyal, J.D. Budai, D.K. Christen, D.M. Kroeger, E.D. Specht , Q. He, B. Saffian, M. Paranthaman, C.E...critical current density. Science 274, 755 (1996). 2. A. Goyal, D.P. Norton, J.D. Budai, M. Paranthaman, E.D. Specht , D.M. Kroeger, D.K. Christen, Q...D.K. Christen, M. Paranthaman, E.D. Specht , J.D. Budai, Q. He, B. Saffian, F.A. List, D.F. Lee, E. Hatfield, P.M. Martin, C.E. Klabunde, J. Mathis

Proceedings of the fourth international conference and exhibition: World Congress on superconductivity. Volume 1

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

Krishen, K.; Burnham, C.

1994-12-31

The goals of the World Congress on Superconductivity (WCS) have been to establish and foster the development and commercial application of superconductivity technology on a global scale by providing a non-adversarial, non-advocacy forum where scientists, engineers, businessmen and government personnel can freely exchange information and ideas on recent developments and directions for the future of superconductive research. Sessions were held on: accelerator technology, power and energy, persistent magnetic fields, performance characterization, physical properties, fabrication methodology, superconductive magnetic energy storage (SMES), thin films, high temperature materials, device applications, wire fabrication, and granular superconductors. Individual papers are indexed separately.

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.

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

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.

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.

Cavity mode enhancement of terahertz emission from equilateral triangular microstrip antennas of the high-T c superconductor Bi2Sr2CaCu2O8 + δ.

PubMed

Cerkoney, Daniel P; Reid, Candy; Doty, Constance M; Gramajo, Ashley; Campbell, Tyler D; Morales, Manuel A; Delfanazari, Kaveh; Tsujimoto, Manabu; Kashiwagi, Takanari; Yamamoto, Takashi; Watanabe, Chiharu; Minami, Hidetoshi; Kadowaki, Kazuo; Klemm, Richard A

2017-01-11

We study the transverse magnetic (TM) electromagnetic cavity mode wave functions for an ideal equilateral triangular microstrip antenna (MSA) exhibiting C 3v point group symmetry. When the C 3v operations are imposed upon the antenna, the TM(m,n) modes with wave vectors [Formula: see text] are much less dense than commonly thought. The R 3 operations restrict the integral n and m to satisfy [Formula: see text], where [Formula: see text] and [Formula: see text] for the modes even and odd under reflections about the three mirror planes, respectively. We calculate the forms of representative wave functions and the angular dependence of the output power when these modes are excited by the uniform and non-uniform ac Josephson current sources in thin, ideally equilateral triangular MSAs employing the intrinsic Josephson junctions in the high transition temperature T c superconductor Bi 2 Sr 2 CaCu 2 [Formula: see text], and fit the emissions data from an earlier sample for which the C 3v symmetry was apparently broken.

Exfoliated YBCO filaments for second-generation superconducting cable

NASA Astrophysics Data System (ADS)

Solovyov, Vyacheslav; Farrell, Paul

2017-01-01

The second-generation high temperature superconductor (2G HTS) wire is the most promising conductor for high-field magnets such as accelerator dipoles and compact fusion devices. The key element of the wire is a thin Y1Ba2Cu3O7 (YBCO) layer deposited on a flexible metal substrate. The substrate, which becomes incorporated in the 2G conductor, reduces the electrical and mechanical performance of the wire. This is a process that exfoliates the YBCO layer from the substrate while retaining the critical current density of the superconductor. Ten-centimeter long coupons of exfoliated YBCO layers were manufactured, and detailed structural, electrical, and mechanical characterization were reported. After exfoliation, the YBCO layer was supported by a 75 μm thick stainless steel foil, which makes for a compact, mechanically stronger, and inexpensive conductor. The critical current density of the filaments was measured at both 77 K and 4.2 K. The exfoliated YBCO retained 90% of the original critical current. Similarly, tests in an external magnetic field at 4.2 K confirmed that the pinning strength of the YBCO layer was also retained following exfoliation.

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.

Focus on superconducting properties of iron chalcogenides

NASA Astrophysics Data System (ADS)

Takano, Yoshihiko

2012-10-01

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

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

Inflight resistance measurement on high-T(sub c) superconducting thin films exposed to orbital atomic oxygen on CONCAP-2 (STS-46)

NASA Technical Reports Server (NTRS)

Gregory, J. C.; Raiker, G. N.; Bijvoet, J. A.; Nerren, P. D.; Sutherland, W. T.; Mogro-Camperso, A.; Turner, L. G.; Kwok, Hoi; Raistrick, I. D.; Cross, J. B.

1995-01-01

In 1992, UAH (University of Alabama in Huntsville) conducted a unique experiment on STS-46 in which YBa2Cu3O7 (commonly known as '1-2-3' superconductor) high-T(c) superconducting thin film samples prepared at three different laboratories were exposed to 5 eV atomic oxygen in low Earth orbit on the ambient and 320 C hot plate during the first flight of the CONCAP-2 (Complex Autonomous Payload) experiment carrier. The resistance of the thin films was measured in flight during the atomic oxygen exposure and heating cycle. Superconducting properties were measured in the laboratory before and after the flight by the individual experimenters. Films with good superconducting properties, and which were exposed to the oxygen flux, survived the flight including those heated to 320 C (600 K) with properties essentially unchanged, while other samples which were heated but not exposed to oxygen were degraded. The properties of other flight controls held at ambient temperature appear unchanged and indistinguishable from those of ground controls, whether exposed to oxygen or not.

Strain induced superconductivity in the parent compound BaFe2As2

NASA Astrophysics Data System (ADS)

Engelmann, J.; Grinenko, V.; Chekhonin, P.; Skrotzki, W.; Efremov, D. V.; Oswald, S.; Iida, K.; Hühne, R.; Hänisch, J.; Hoffmann, M.; Kurth, F.; Schultz, L.; Holzapfel, B.

2013-12-01

The discovery of superconductivity with a transition temperature, Tc, up to 65 K in single-layer FeSe (bulk Tc=8 K) films grown on SrTiO3 substrates has attracted special attention to Fe-based thin films. The high Tc is a consequence of the combined effect of electron transfer from the oxygen-vacant substrate to the FeSe thin film and lattice tensile strain. Here we demonstrate the realization of superconductivity in the parent compound BaFe2As2 (no bulk Tc) just by tensile lattice strain without charge doping. We investigate the interplay between strain and superconductivity in epitaxial BaFe2As2 thin films on Fe-buffered MgAl2O4 single crystalline substrates. The strong interfacial bonding between Fe and the FeAs sublattice increases the Fe-Fe distance due to the lattice misfit, which leads to a suppression of the antiferromagnetic spin density wave and induces superconductivity with bulk Tc≈10 K. These results highlight the role of structural changes in controlling the phase diagram of Fe-based superconductors.

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

Influence of Strain on Thermal Conductivity of Silicon Nitride Thin Films

DTIC Science & Technology

2012-03-02

free path of amorphous materials is of the same order as the structural disorder [46], rendering thermal conductivity size independent. Here, the phases...16] Manninen A J, Leivo M M and Pekola J P 1997 Refrigeration of a dielectric membrane by superconductor /insulator/ normal-metal/insulator... superconductor tunneling Appl. Phys. Lett. 70 1885–7 [17] Olson E A et al 2003 The design and operation of a MEMS differential scanning nanocalorimeter for high

Nanostructuring superconductors by ion beams: A path towards materials engineering

NASA Astrophysics Data System (ADS)

Gerbaldo, Roberto; Ghigo, Gianluca; Gozzelino, Laura; Laviano, Francesco; Amato, Antonino; Rovelli, Alberto; Cherubini, Roberto

2013-07-01

The paper deals with nanostructuring of superconducting materials by means of swift heavy ion beams. The aim is to modify their structural, optical and electromagnetic properties in a controlled way, to provide possibility of making them functional for specific applications. Results are presented concerning flux pinning effects (implantation of columnar defects with nanosize cross section to enhance critical currents and irreversibility fields), confined flux-flow and vortex guidance, design of devices by locally tailoring the superconducting material properties, analysis of disorder-induced effects in multi-band superconductors. These studies were carried out on different kinds of superconducting samples, from single crystals to thin films, from superconducting oxides to magnesium diboride, to recently discovered iron-based superconductors.

Thin films of the Bi2Sr2Ca2Cu3O(x) superconductor

NASA Technical Reports Server (NTRS)

Mei, YU; Luo, H. L.; Hu, Roger

1990-01-01

Using RF sputtering technique, thin films of near single phase Bi2Sr2Ca2Cu3O(x) were successfully prepared on SrTiO3(100), MgO(100), and LaAlO3(012) substrates. Zero resistance of these films occurred in the range of 90-105 K.

Vortex pinning in ferromagnet-superconductor bilayer with tunable domain patterns

NASA Astrophysics Data System (ADS)

Cieplak, Marta Z.

2011-03-01

Ferromagnet superconductor hybrids provide a fascinating example of systems in which there is a rich interplay between two seemingly incompatible collective phenomena. Particularly interesting is the impact of the ferromagnet on the dynamics of vortices in the superconductor. The magnetic domains control the location of the vortices. Exquisite control of the dynamics can be achieved by careful tuning of the geometry of the magnetic domains. In this talk I will present the results of recent experiments on superconductor(S)-ferromagnet(F) bilayers with a focus on understanding the hitherto unexplained seemingly unpredictable dependence of the critical current density on the parameters of the experiment. In our experiments the S layer is made of niobium, the F layer is a Co/Pt multilayer with perpendicular magnetic anisotropy, and a thin insulating layer in-between eliminates proximity effect. We use various demagnetization procedures to define different domain patterns in the F layer. We show that some domain patterns produce highly inhomogeneous flux penetration and strong vortex confinement at the sample edge, while for others there is remerkable enhancement of the critical current density in excess of 15. This is the highest value reported to date. We have measured, for the first time in a single tunable structure, the dependence of the activation energy for vortex pinning on the domain width, temperature, and magnetic field. In collaboration with L.Y. Zhu, X. M. Cheng and C. L. Chien (Johns Hopkins), Z. Adamus (Polish Acad. Sci.) and M. Konczykowski (Ecole Polytechnique). Supported by NSF grant DMR05-20491, by the French-Polish Program PICS 4916, and by EU within the European Regional Development Fund, through the Innovative Economy grant POIG.01.01.02-00-108/09.

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.

RF critical field measurement of MgB2 thin films coated on Nb

NASA Astrophysics Data System (ADS)

Tajima, T.; Eremeev, G.; Zou, G.; Dolgashev, V.; Martin, D.; Nantista, C.; Tantawi, S.; Yoneda, C.; Moeckly, B. H.; Campisi, I.

2010-06-01

Niobium (Nb) Superconducting RF (SRF) cavities have been used or will be used for a number of particle accelerators. The fundamental limit of the accelerating gradient has been thought to be around 50 MV/m due to its RF critical magnetic field of around 200 mT. This limit will prevent new projects requiring higher gradient and compact accelerators from considering SRF structures. There is a theory, however, that promises to overcome this limitation by coating thin (less than the penetration depth) superconductors on Nb. We initiated measurements of critical magnetic fields of Nb coated with various thin film superconductors, starting with MgB2 films deposited using reactive evaporation technique, with the goal to apply this coating to SRF cavities. This paper will present first test results of the RF critical magnetic field of a system consisting of a 10 nm B and a 100 nm MgB2 films deposited on a chemically polished 2-inch single grain Nb substrate.

Disappearance of nodal gap across the insulator-superconductor transition in a copper-oxide superconductor.

PubMed

Peng, Yingying; Meng, Jianqiao; Mou, Daixiang; He, Junfeng; Zhao, Lin; Wu, Yue; Liu, Guodong; Dong, Xiaoli; He, Shaolong; Zhang, Jun; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Lee, T K; Zhou, X J

2013-01-01

The parent compound of the copper-oxide high-temperature superconductors is a Mott insulator. Superconductivity is realized by doping an appropriate amount of charge carriers. How a Mott insulator transforms into a superconductor is crucial in understanding the unusual physical properties of high-temperature superconductors and the superconductivity mechanism. Here we report high-resolution angle-resolved photoemission measurement on heavily underdoped Bi₂Sr₂-xLaxCuO(₆+δ) system. The electronic structure of the lightly doped samples exhibit a number of characteristics: existence of an energy gap along the nodal direction, d-wave-like anisotropic energy gap along the underlying Fermi surface, and coexistence of a coherence peak and a broad hump in the photoemission spectra. Our results reveal a clear insulator-superconductor transition at a critical doping level of ~0.10 where the nodal energy gap approaches zero, the three-dimensional antiferromagnetic order disappears, and superconductivity starts to emerge. These observations clearly signal a close connection between the nodal gap, antiferromagnetism and superconductivity.

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.

Preparation of Y-Ba-Cu oxide superconductor thin films using pulsed laser evaporation from high T/sub c/ bulk material

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

Dijkkamp, D.; Venkatesan, T.; Wu, X.D.

We report the first successful preparation of thin films of Y-Ba-Cu-O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO/sub 3/ and Al/sub 2/O/sub 3/ substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the usemore » of ultrahigh vacuum techniques.« less

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.

Improvement of critical current density in thallium-based (Tl,Bi)Sr{sub 1.6}Ba{sub 0.4}Ca{sub 2}Cu{sub 3}O{sub x} superconductors

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

Ren, Z.F.; Wang, C.A.; Wang, J.H.

1994-12-31

Epitaxial (Tl,Bi)Sr{sub 1.6}Ba{sub 0.4}Ca{sub 2}Cu{sub 3}O{sub x} (Tl,Bi)-1223 thin films on (100) single crystal LaAlO{sub 3} substrates were synthesized by a two-step procedure. Phase development, microstructure, and relationships between film and substrate were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Resistance versus temperature, zero-field-cooled and field-cooled magnetization, and transport critical current density (J{sub c}) were measured. The zero-resistance temperature was 105-111 K. J{sub c} at 77 K and zero field was > 2 x 10{sup 6} A/cm{sup 2}. The films exhibited good flux pinning properties.

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.

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.

Decoupling of critical temperature and superconducting gaps in irradiated films of a Fe-based superconductor

NASA Astrophysics Data System (ADS)

Daghero, Dario; Tortello, Mauro; Ummarino, Giovanni A.; Piatti, Erik; Ghigo, Gianluca; Hatano, Takafumi; Kawaguchi, Takahiko; Ikuta, Hiroshi; Gonnelli, Renato S.

2018-07-01

We report on direct measurements of the energy gaps (carried out by means of point-contact Andreev reflection spectroscopy, PCARS) and of the critical temperature in thin, optimally doped, epitaxial films of BaFe2(As1-x P x )2 irradiated with 250 MeV Au ions. The low-temperature PCARS spectra (taken with the current flowing along the c axis) can be fitted by a modified Blonder-Tinkham-Klapwijk model with two nodeless gaps; this is not in contrast with the possible presence of node lines suggested by various experiments in literature. Up to a fluence Φ = 7.3 × 1011 cm-2, we observe a monotonic suppression of the critical temperature and of the gap amplitudes Δ1 and Δ2. Interestingly, while T c decreases by about 3%, the gaps decrease much more (by about 37% and 25% respectively), suggesting a decoupling between high-temperature and low-temperature superconducting properties. An explanation for this finding is proposed within an effective two-band Eliashberg model, in which such decoupling is inherently associated to defects created by irradiation.

Microwave Hybrid Integrated Circuit Applicatins of High Transition Temperature Superconductor

NASA Astrophysics Data System (ADS)

Lu, Shih-Lin

This research work involves microwave characterization of high Tc superconducting (HTS) thin film using microstrip ring resonators, studying the nonlinear properties of HTS thin film transmission lines using two-tone intermodulation technique, coupling mechanisms and coupling factors of microstrip ring resonators side coupled to a microstrip line, two-port S-parameters measurements of GaAs MESFET at low temperature, and the design and implementation of hybrid ring resonator stabilized microwave oscillator using both metal films and superconducting films. A microstrip ring resonators operating at 10 GHz have been fabricated from YBCO HTS thin films deposited on one side of LaAl_2O_3 substrates. Below 60^circ Kelvin the measured unloaded Q of the HTS thin film microstrip ring resonators are more than 1.5 times that of gold film resonators. The two distinct but very close resonance peaks of a ring resonator side coupled to a microstrip line are experimentally identified as due to odd-mode and even-mode coupling. These two mechanisms have different characteristic equivalent circuit models and lead to different coupling coefficients and loaded resonance frequencies. The coupling factors for the two coupling modes are calculated using piecewise coupled line approximations. The two-port S-parameters measurement techniques and GaAs MESFET low temperature DC and microwave characteristics have been investigated. A system errors model including the errors caused by the line constriction at low temperature has been proposed and a temperature errors correction procedure has been developed for the two-port microwave S-parameters measurements at low temperature. The measured GaAs MESFET DC characteristics shows a 20% increase in transconductance at 77^circ K. There is also a 2 db increase in /S21/ at 77^circ K. The microwave oscillator stabilized with both metal and HTS thin film ring resonators have been studied. The tuning ability of the oscillator by a varactor diode has also been investigated. The phase noise performance of one side of the high Tc film oscillator does not show appreciable improvement over the gold film oscillator. With a varactor diode, the oscillator tuning range can be 300 MHz more. Two-tone intermodulation distortion (IMD) at 6.3 GHz in an HTS YBCO superconducting thin film microstrip transmission line on LaAl_2O _3 substrates are experimentally studied. At fixed input power, the 3rd order IMD power as function of temperature shows a minimum at a temperature around 60^circ Kelvin. With DC current applied, the second order IMD is observed and shows a strong functional dependance to the applied DC current and input power.

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.

Experimental formation of a fractional vortex in a superconducting bi-layer

NASA Astrophysics Data System (ADS)

Tanaka, Y.; Yamamori, H.; Yanagisawa, T.; Nishio, T.; Arisawa, S.

2018-05-01

We report the experimental formation of a fractional vortex generated by using a thin superconducting bi-layer in the form of a niobium bi-layer, observed as a magnetic flux distribution image taken by a scanning superconducting quantum interference device (SQUID) microscope. Thus, we demonstrated that multi-component superconductivity can be realized by an s-wave conventional superconductor, because, in these superconductors, the magnetic flux is no longer quantized as it is destroyed by the existence of an inter-component phase soliton (i-soliton).

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.

Superconducting Microwave Electronics at Lewis Research Center

NASA Technical Reports Server (NTRS)

Warner, Joseph D.; Bhasin, Kul B.; Leonard, Regis F.

1991-01-01

Over the last three years, NASA Lewis Research Center has investigated the application of newly discovered high temperature superconductors to microwave electronics. Using thin films of YBa2Cu3O7-delta and Tl2Ca2Ba2Cu3Ox deposited on a variety of substrates, including strontium titanate, lanthanum gallate, lanthanum aluminate and magnesium oxide, a number of microwave circuits have been fabricated and evaluated. These include a cavity resonator at 60 GHz, microstrip resonators at 35 GHz, a superconducting antenna array at 35 GHz, a dielectric resonator at 9 GHz, and a microstrip filter at 5 GHz. Performance of some of these circuits as well as suggestions for other applications are reported.

Superconducting microwave electronics at Lewis Research Center

NASA Astrophysics Data System (ADS)

Warner, Joseph D.; Bhasin, Kul B.; Leonard, Regis F.

Over the last three years, NASA Lewis Research Center has investigated the application of newly discovered high temperature superconductors to microwave electronics. Using thin films of YBa2Cu3O7-delta and Tl2Ca2Ba2Cu3Ox deposited on a variety of substrates, including strontium titanate, lanthanum gallate, lanthanum aluminate and magnesium oxide, a number of microwave circuits have been fabricated and evaluated. These include a cavity resonator at 60 GHz, microstrip resonators at 35 GHz, a superconducting antenna array at 35 GHz, a dielectric resonator at 9 GHz, and a microstrip filter at 5 GHz. Performance of some of these circuits as well as suggestions for other applications are reported.

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…

Electrical and thermal transport properties of the electron-doped cuprate Sm2-x Ce x CuO4-y system

NASA Astrophysics Data System (ADS)

Scanderbeg, D. J.; Taylor, B. J.; Baumbach, R. E.; Paglione, J.; Maple, M. B.

2016-12-01

Electrical and thermal transport measurements were performed on thin films of the electron-doped superconductor Sm2-x Ce x CuO4-y (x  =  0.13  -  0.19) in order to study the evolving nature of the charge carriers from the under-doped to over-doped regime. A temperature versus cerium content (T  -  x) phase diagram has been constructed from the electrical transport measurements, yielding a superconducting region similar to that found for other electron-doped superconductors. Thermopower measurements show a dramatic change from the underdoped region (x  <  0.15) to the overdoped region (x  >  0.15). Application of the Fisher-Fisher-Huse (FFH) vortex glass scaling model to the magnetoresistance data was found to be insufficient to describe the data in the region of the vortex-solid to vortex-liquid transition. It was found instead that the modified vortex glass scaling model of Rydh, Rapp, and Anderson provided a good description of the data, indicating the importance of the applied field on the pinning landscape. A magnetic field versus temperature (H  -  T) phase diagram has also been constructed for the films with x≥slant 0.14 , displaying the evolution of the vortex glass melting lines H g (T) across the superconducting regime.

Random gauge models of the superconductor-insulator transition in two-dimensional disordered superconductors

NASA Astrophysics Data System (ADS)

Granato, Enzo

2017-11-01

We study numerically the superconductor-insulator transition in two-dimensional inhomogeneous superconductors with gauge disorder, described by four different quantum rotor models: a gauge glass, a flux glass, a binary phase glass, and a Gaussian phase glass. The first two models describe the combined effect of geometrical disorder in the array of local superconducting islands and a uniform external magnetic field, while the last two describe the effects of random negative Josephson-junction couplings or π junctions. Monte Carlo simulations in the path-integral representation of the models are used to determine the critical exponents and the universal conductivity at the quantum phase transition. The gauge- and flux-glass models display the same critical behavior, within the estimated numerical uncertainties. Similar agreement is found for the binary and Gaussian phase-glass models. Despite the different symmetries and disorder correlations, we find that the universal conductivity of these models is approximately the same. In particular, the ratio of this value to that of the pure model agrees with recent experiments on nanohole thin-film superconductors in a magnetic field, in the large disorder limit.

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.

Search for New Superconductors for Energy and Power Applications

DTIC Science & Technology

2014-10-21

superconductors, borides , carbides, silicides, and chalcogenides. In addition, a number of thin film systems have been explored: A15s, superlattices, arrays of...YBa2Cu3O7 Bi2Se3 Eu-Si-C ErRh4B4 Bi2Sr2CaCu2O8 (UD, OD) Sb2Se3 V-Si-C (Ga,Mn)As CuO ZrSe2 Sm-Si-C Hf(FeCo)P Y1-xCaxCrO3 Fe-Te-Se BORIDES Hf-Fe-C-P...Physics, Warsaw, Poland Table III New superconductors, discovered by UCSD MURI team. BORIDES Tc (K) Nb0.9Zr0.1B 11.2 ZrNbxB 9.0 ZrVxB 9.0

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.

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.

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

Superconducting NbTiN thin films for superconducting radio frequency accelerator cavity applications

DOE PAGES

Burton, Matthew C.; Beebe, Melissa R.; Yang, Kaida; ...

2016-02-12

Current superconducting radio frequency technology, used in various particle accelerator facilities across the world, is reliant upon bulk niobium superconducting cavities. Due to technological advancements in the processing of bulk Nb cavities, the facilities have reached accelerating fields very close to a material-dependent limit, which is close to 50 MV/m for bulk Nb. One possible solution to improve upon this fundamental limitation was proposed a few years ago by Gurevich [Appl. Phys. Lett. 88, 012511 (2006)], consisting of the deposition of alternating thin layers of superconducting and insulating materials on the interior surface of the cavities. The use of type-IImore » superconductors with Tc > Tc Nb and H c > HcNb, (e.g., Nb 3Sn, NbN, or NbTiN) could potentially greatly reduce the surface resistance (Rs) and enhance the accelerating field, if the onset of vortex penetration is increased above Hc Nb, thus enabling higher field gradients. Although Nb 3Sn may prove superior, it is not clear that it can be grown as a suitable thin film for the proposed multilayer approach, since very high temperature is typically required for its growth, hindering achieving smooth interfaces and/or surfaces. On the other hand, since NbTiN has a smaller lower critical field (H c1) and higher critical temperature (T c) than Nb and increased conductivity compared to NbN, it is a promising candidate material for this new scheme. Here, the authors present experimental results correlating filmmicrostructure with superconducting properties on NbTiN thin film coupon samples while also comparing filmsgrown with targets of different stoichiometry. In conclusion, it is worth mentioning that the authors have achieved thin films with bulk-like lattice parameter and transition temperature while also achieving H c1 values larger than bulk for films thinner than their London penetration depths.« less

The Formation, Transport Properties and Microstructure of 45 Degrees (001) Tilt Grain Boundaries in Yttrium BARIUM(2) COPPER(3) OXYGEN(7-X) Thin Films

NASA Astrophysics Data System (ADS)

Vuchic, Boris Vukan

1995-01-01

Most high angle grain boundaries in high-T _{c} superconductors exhibit weak link behavior. The Josephson-like properties of these grain boundaries can be used for many device applications such as superconducting quantum interference devices (SQUIDs). The structure-property relationship of different types of 45 ^circ (001) YBa_2 Cu_3O_{7-x} thin film grain boundary junctions are examined to study their weak link nature. A technique, termed sputter-induced epitaxy, is developed to form 45^circ (001) tilt grain boundaries in YBa_2Cu _3O_{7-x} thin films on (100) MgO substrates. A low voltage ion bombardment pre-growth substrate treatment is used to modify the epitaxial orientation relationship between the thin film and the substrate in selected regions. By modifying the orientation of the thin film, grain boundary junctions can be placed in any configuration on the substrate. A variety of pre-growth sputtering conditions in conjunction with atomic force microscopy and Rutherford backscatter spectrometry are used to determine the role of the ions in modifying the substrate surface. Sputter-induced epitaxy is extended to a multilayer MgO/LaAlO_3 substrate, allowing integration of the sputter -induced epitaxy junctions into multilayer structures. The low temperature transport properties of the sputter-induced epitaxy junctions and a set of bi-epitaxial grain boundaries are studied. Individual grain boundaries are isolated and characterized for resistance vs. temperature, current vs. voltage as a function of temperature and magnetic field behavior. Resistive and superconducting grain boundaries are compared. Microstructural analysis is performed using scanning electron microscopy, transmission electron microscopy and high resolution electron microscopy (HREM). Marked differences are observed in the microstructure of resistive and superconducting grain boundaries. HREM studies suggest the importance of the local atomic scale structure of the grain boundary in transport properties. A phenomenological grain boundary model is proposed to describe the structure -property relationship of the boundaries.

High-field transport properties of a P-doped BaFe2As2 film on technical substrate

PubMed Central

Iida, Kazumasa; Sato, Hikaru; Tarantini, Chiara; Hänisch, Jens; Jaroszynski, Jan; Hiramatsu, Hidenori; Holzapfel, Bernhard; Hosono, Hideo

2017-01-01

High temperature (high-Tc) superconductors like cuprates have superior critical current properties in magnetic fields over other superconductors. However, superconducting wires for high-field-magnet applications are still dominated by low-Tc Nb3Sn due probably to cost and processing issues. The recent discovery of a second class of high-Tc materials, Fe-based superconductors, may provide another option for high-field-magnet wires. In particular, AEFe2As2 (AE: Alkali earth elements, AE-122) is one of the best candidates for high-field-magnet applications because of its high upper critical field, Hc2, moderate Hc2 anisotropy, and intermediate Tc. Here we report on in-field transport properties of P-doped BaFe2As2 (Ba-122) thin films grown on technical substrates by pulsed laser deposition. The P-doped Ba-122 coated conductor exceeds a transport Jc of 105 A/cm2 at 15 T for main crystallographic directions of the applied field, which is favourable for practical applications. Our P-doped Ba-122 coated conductors show a superior in-field Jc over MgB2 and NbTi, and a comparable level to Nb3Sn above 20 T. By analysing the E − J curves for determining Jc, a non-Ohmic linear differential signature is observed at low field due to flux flow along the grain boundaries. However, grain boundaries work as flux pinning centres as demonstrated by the pinning force analysis. PMID:28079117

High-field transport properties of a P-doped BaFe2As2 film on technical substrate

NASA Astrophysics Data System (ADS)

Iida, Kazumasa; Sato, Hikaru; Tarantini, Chiara; Hänisch, Jens; Jaroszynski, Jan; Hiramatsu, Hidenori; Holzapfel, Bernhard; Hosono, Hideo

2017-01-01

High temperature (high-Tc) superconductors like cuprates have superior critical current properties in magnetic fields over other superconductors. However, superconducting wires for high-field-magnet applications are still dominated by low-Tc Nb3Sn due probably to cost and processing issues. The recent discovery of a second class of high-Tc materials, Fe-based superconductors, may provide another option for high-field-magnet wires. In particular, AEFe2As2 (AE: Alkali earth elements, AE-122) is one of the best candidates for high-field-magnet applications because of its high upper critical field, Hc2, moderate Hc2 anisotropy, and intermediate Tc. Here we report on in-field transport properties of P-doped BaFe2As2 (Ba-122) thin films grown on technical substrates by pulsed laser deposition. The P-doped Ba-122 coated conductor exceeds a transport Jc of 105 A/cm2 at 15 T for main crystallographic directions of the applied field, which is favourable for practical applications. Our P-doped Ba-122 coated conductors show a superior in-field Jc over MgB2 and NbTi, and a comparable level to Nb3Sn above 20 T. By analysing the E - J curves for determining Jc, a non-Ohmic linear differential signature is observed at low field due to flux flow along the grain boundaries. However, grain boundaries work as flux pinning centres as demonstrated by the pinning force analysis.

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.

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.

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

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

Couches minces supraconductrices à haute température critique pour l'électronique

NASA Astrophysics Data System (ADS)

Guilloux-Viry, M.; Perrin, A.

1998-08-01

High critical temperature superconductors (HTCS) are very promising for applications in microelectronics due to the control of high quality epitaxial thin films, in spite of a number of specific constraints. Active and passive devices are already available in various laboratories, prooving that applications are actually expected soon. We report here on the interest of HTCS thin films, on preparation processes including materials and substrates choice, and also on characterization methods which are required in order to chek the quality of the samples. Finally some illustrative examples of applications are presented. Les supraconducteurs à haute température critique ouvrent des perspectives prometteuses dans le domaine de l'électronique en raison de la maîtrise de la croissance de films minces de haute qualité cristalline et physique, malgré des difficultés spécifiques. Des dispositifs, aussi bien actifs que passifs, commencent à être réalisés dans divers laboratoires, montrant que des applications peuvent être effectivement envisagées à relativement court terme.

Applications of Classical and Quantum Mechanical Channeling in Condensed Matter Physics

NASA Astrophysics Data System (ADS)

Haakenaasen, Randi

1995-01-01

The first part of this work involves ion channeling measurements on the high temperature superconductor rm YBa_{2}Cu_{3}O _{7-delta}(YBCO). The experiments were motivated by several previous reports of anomalous behavior in the displacements of the Cu and O atoms in the vicinity of the critical temperature rm(T _{c}) in several high temperature superconductors. Our measurements were complimentary to previous experiments in that we used thin film YBCO (as opposed to bulk single crystals) and focused on a small region around rm T_{c}. We mapped out the channeling parameters chi _{min} and Psi_ {1/2} in a 30 K region around rm T_{c} in 1-2 K steps in thin film YBCO(001) on MgO. Neither of our measurements showed any discontinuities in chi _{min} or Psi_ {1/2} near the superconducting phase transition, and we therefore have no reason to expect anything but a smooth increase in atomic vibrations in this region. We conclude that any anomalous behavior in atomic displacements deduced from previous channeling experiments is not essential to superconductivity. In the second part of the work positrons were used to study quantum mechanical channeling effects. We clearly observed and quantitatively accounted for quantum interference effects, including Bragg diffraction, in the forward transmission of channeled MeV positrons through a single crystal. Experimental scans across the (100), (110), and (111) planes in Si showed excellent agreement with theoretical dynamical diffraction calculations, giving us confidence that we can accurately predict the spatial and momentum distributions of channeled positrons. New experiments are envisioned in which the channeling effect is combined with 2 quantum annihilation in flight measurements to determine valence electron and magnetic spin distributions in a crystal. Since the channeling effect focuses the positrons to the interstices of the crystal, the annihilation rate will reflect the valence electron density. Furthermore, the annihilation rate is sensitive to electron spin polarization, opening up the possibility of making measurements on magnetic materials. Detailed estimates for the count rates of such experiments are presented, indicating the feasibility of developing positron channeling into a new tool in solid state physics.

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

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

Applications of Superconductivity and Impact on U.S. Economy

NASA Astrophysics Data System (ADS)

Selvamanickam, Venkat

2014-03-01

In the past few decades, low temperature superconducting wires (niobium-titanium) have enabled multibillion dollar industries such as magnetic resonance imaging and nuclear magnetic resonance spectroscopy which otherwise would not have been possible. High temperature superconductors (HTS) hold the promise of impacting even a larger market in diverse applications such as energy, health, military, telecommunication, transportation and research. HTS tapes are now being manufactured in quantities of few hundred kilometers annually with current carrying capacity of about 300 times that of copper wire of the same cross section. Power transmission cables up to few kilometers in length made with HTS tapes have already been inserted in the power grid world-wide. In the past few of years, tremendous advancements have occurred in nanoscale defect engineering in these thin film superconducting tapes that has led to a doubling of critical current performance in high magnetic fields and operating temperatures of interest for various applications. Technologies developed in this area have been successfully inserted in production HTS tapes by industry. With the availability of such high performance HTS tapes, a number of coil-based applications are now being aggressively pursued by several institutions. HTS coils enable power devices with high power density with significant weight, size and power benefits. Energy storage, generation, use, transformation and transmission applications as well as magnetic applications such as magnetic shields, plasma confinement, and ultra-high field magnets are becoming possible with the availability of high-performance HTS tapes. An overview of the development and use of superconductors in electric power and magnetic applications will be provided in this presentation.

Crossing fields in thin films of isotropic superconductors

DOE PAGES

Vlasko-Vlasov, V. K.; Colauto, Fabiano; Buzdin, Alexander A.; ...

2016-11-04

We study interactions of perpendicular and longitudinal magnetic fields in niobium films of different thickness in a wide range of temperatures below the superconducting transition temperature ( T C) . In 100 nm Nb film at all temperatures the longitudinal field H || practically does not influence the dynamics of the normal flux. However, in 200nm Nb film, a considerable anisotropy in the vortex motion is found with advanced propagation of the normal flux along H || at T>TC/2 and the preferential jump-wise growth of the thermo-magnetic flux dendrites across H || at T < T C. Appearance of themore » in-plane vortices and their cutting-reconnection with tilted vortices induced by the normal field H || is the reason of the observed anisotropy in the thicker film. Absence of the in-plane vortices and much smaller tilt of vortices generated by H || explain the isotropic normal flux dynamics in the thinner film. Lastly, our results open a new way of manipulating both slow vortex motion and fast thermo-magnetic avalanches.« less

Kinetic Inductance Photodetectors Based on Nonequilibrium Response in Superconducting Thin-Film Structures

NASA Technical Reports Server (NTRS)

Sergeev, A. V.; Karasik, B. S.; Gogidze, I. G.; Mitin, V. V.

2001-01-01

While experimental studies of kinetic-inductance sensors have been limited so far by the temperature range near the superconducting transition, these detectors can be very sensitivity at temperatures well below the transition, where the number of equilibrium quasiparticles is exponentially small. In this regime, a shift of the quasiparticle chemical potential under radiation results in the change of the kinetic inductance, which can be measured by a sensitive SQUID readout. We modeled the kinetic inductance response of detectors made from disordered superconducting Nb, NbC, and MoRe films. Low phonon transparency of the interface between the superconductor and the substrate causes substantial re-trapping of phonons providing high quantum efficiency and the operating time of approximately 1 ms at 1 K. Due to the small number of quasiparticles, the noise equivalent power of the detector determined by the quasiparticle generation-recombination noise can be as small as approximately 10(exp -19) W/Hz(exp 1/2) at He4 temperatures.

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

Reorientation of the diagonal double-stripe spin structure at Fe 1+yTe bulk and thin-film surfaces

DOE PAGES

Hanke, Torben; Singh, Udai Raj; Cornils, Lasse; ...

2017-01-06

Here, establishing the relation between ubiquitous antiferromagnetism in the parent compounds of unconventional superconductors and their superconducting phase is important for understanding the complex physics in these materials. Going from bulk systems to thin films additionally affects their phase diagram. For Fe 1+yTe, the parent compound of Fe 1+ySe 1$-x$Tex superconductors, bulk-sensitive neutron diffraction revealed an in-plane oriented diagonal double-stripe antiferromagnetic spin structure. Here we show by spin-resolved scanning tunnelling microscopy that the spin direction at the surfaces of bulk Fe 1+yTe and thin films grown on the topological insulator Bi 2Te 3 is canted out of the high-symmetry directionsmore » of the surface unit cell resulting in a perpendicular spin component, keeping the diagonal double-stripe order. As the magnetism of the Fe d-orbitals is intertwined with the superconducting pairing in Fe-based materials, our results imply that the superconducting properties at the surface of the related superconducting compounds might be different from the bulk.« less

Reorientation of the diagonal double-stripe spin structure at Fe 1+yTe bulk and thin-film surfaces

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

Hanke, Torben; Singh, Udai Raj; Cornils, Lasse

Here, establishing the relation between ubiquitous antiferromagnetism in the parent compounds of unconventional superconductors and their superconducting phase is important for understanding the complex physics in these materials. Going from bulk systems to thin films additionally affects their phase diagram. For Fe 1+yTe, the parent compound of Fe 1+ySe 1$-x$Tex superconductors, bulk-sensitive neutron diffraction revealed an in-plane oriented diagonal double-stripe antiferromagnetic spin structure. Here we show by spin-resolved scanning tunnelling microscopy that the spin direction at the surfaces of bulk Fe 1+yTe and thin films grown on the topological insulator Bi 2Te 3 is canted out of the high-symmetry directionsmore » of the surface unit cell resulting in a perpendicular spin component, keeping the diagonal double-stripe order. As the magnetism of the Fe d-orbitals is intertwined with the superconducting pairing in Fe-based materials, our results imply that the superconducting properties at the surface of the related superconducting compounds might be different from the bulk.« less

High-temperature superconducting superconductor/normal metal/superconducting devices

NASA Technical Reports Server (NTRS)

Foote, M. C.; Hunt, B. D.; Bajuk, L. J.

1991-01-01

We describe the fabrication and characterization of superconductor/normal metal/superconductor (SNS) devices made with the high-temperature superconductor (HTS) YBa2Cu3O(7-x). Structures of YBa2Cu3O(7-x)/Au/Nb on c-axis-oriented YBa2Cu3O(7-x) were made in both sandwich and edge geometries in order to sample the HTS material both along and perpendicular to the conducting a-b planes. These devices display fairly ideal Josephson properties at 4.2 K. In addition, devices consisting of YBa2Cu3O(7-x)/YBa2Cu3O(y)/YBa2Cu3O(7-x), with a 'normal metal' layer of reduced transition temperature YBa2Cu3O(7-x) were fabricated and show a great deal of promise for applications near 77 K. Current-voltage characteristics like those of the Resistively-Shunted Junction model are observed, with strong response to 10 GHz radiation above 60 K.

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.

Study of the glass formation of high temperature superconductors

NASA Technical Reports Server (NTRS)

Ethridge, Edwin C.; Kaukler, William F.; Rolin, Terry

1992-01-01

A number of compositions of ceramic oxide high T(sub c) superconductors were elevated 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 a bulk crystalline superconductor by a series of processing methods.

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.

Thin Film Approaches to the SRF Cavity Problem: Fabrication and Characterization of Superconducting Thin Films

NASA Astrophysics Data System (ADS)

Beringer, Douglas B.

Superconducting Radio Frequency (SRF) cavities are responsible for the acceleration of charged particles to relativistic velocities in most modern linear accelerators, such as those employed at high-energy research facilities like Thomas Jefferson National Laboratory's CEBAF and the LHC at CERN. Recognizing SRF as primarily a surface phenomenon enables the possibility of applying thin films to the interior surface of SRF cavities, opening a formidable tool chest of opportunities by combining and designing materials that offer greater benefit. Thus, while improvements in radio frequency cavity design and refinements in cavity processing techniques have improved accelerator performance and efficiency - 1.5 GHz bulk niobium SRF cavities have achieved accelerating gradients in excess of 35 MV/m - there exist fundamental material bounds in bulk superconductors limiting the maximally sustained accelerating field gradient (approximately 45 MV/m for Niobium) where inevitable thermodynamic breakdown occurs. With state of the art niobium based cavity design fast approaching these theoretical limits, novel material innovations must be sought in order to realize next generation SRF cavities. One proposed method to improve SRF performance is to utilize thin film superconducting-insulating-superconducting (SIS) multilayer structures to effectively magnetically screen a bulk superconducting layer such that it can operate at higher field gradients before suffering critically detrimental SRF losses. This dissertation focuses on the production and characterization of thin film superconductors for such SIS layers for radio-frequency applications.

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.

Effect of Te doping on FeSe superconductor synthesized by powder-in-tube

NASA Astrophysics Data System (ADS)

Imaduddin, A.; Nisa, K.; Yudanto, S. D.; Nugraha, H.; Siswayanti, B.

2017-04-01

FeSe is a superconducting material, which has the simplest crystal structure among the Fe-based superconductors. It has no arsenic element, which is very harmful to the human body. In this study, we analyzed the effects of milling time and Te doping on FeSe superconductors. The synthesis of the samples were carried out using powder-in-tube method in a SS304 stainless steel tube. After the pressing process, followed by the sintering process at 500° C for 20 hours, the samples were removed from the tubes. Later, we analyzed its crystal structures, surfaces morphology and the superconductivity properties. Δ-FeSe phase (hexagonal, non-superconductor) and β-FeSe (tetragonal, superconductor) were formed in the samples, including minor phases of Fe and Fe3Se4. Te doping changed the crystal structure from β-FeSe and Δ-FeSe into FeSe0.5Te0.5. In addition, the onset critical temperature (TC, onset) shifted to higher temperature.

Cavity mode enhancement of terahertz emission from equilateral triangular microstrip antennas of the high-T c superconductor Bi2Sr2CaCu2O8 + δ

NASA Astrophysics Data System (ADS)

Cerkoney, Daniel P.; Reid, Candy; Doty, Constance M.; Gramajo, Ashley; Campbell, Tyler D.; Morales, Manuel A.; Delfanazari, Kaveh; Tsujimoto, Manabu; Kashiwagi, Takanari; Yamamoto, Takashi; Watanabe, Chiharu; Minami, Hidetoshi; Kadowaki, Kazuo; Klemm, Richard A.

2017-01-01

We study the transverse magnetic (TM) electromagnetic cavity mode wave functions for an ideal equilateral triangular microstrip antenna (MSA) exhibiting C 3v point group symmetry. When the C 3v operations are imposed upon the antenna, the TM(m,n) modes with wave vectors \\propto \\sqrt{{{m}2}+nm+{{n}2}} are much less dense than commonly thought. The R 3 operations restrict the integral n and m to satisfy |m-n| =3p , where p≥slant 0 and p≥slant 1 for the modes even and odd under reflections about the three mirror planes, respectively. We calculate the forms of representative wave functions and the angular dependence of the output power when these modes are excited by the uniform and non-uniform ac Josephson current sources in thin, ideally equilateral triangular MSAs employing the intrinsic Josephson junctions in the high transition temperature T c superconductor Bi2Sr2CaCu2 {{\\text{O}}8+δ} , and fit the emissions data from an earlier sample for which the C 3v symmetry was apparently broken.

Elliptical vortex and oblique vortex lattice in the FeSe superconductor based on the nematicity and mixed superconducting orders

NASA Astrophysics Data System (ADS)

Lu, Da-Chuan; Lv, Yang-Yang; Li, Jun; Zhu, Bei-Yi; Wang, Qiang-Hua; Wang, Hua-Bing; Wu, Pei-Heng

2018-03-01

The electronic nematic phase is characterized as an ordered state of matter with rotational symmetry breaking, and has been well studied in the quantum Hall system and the high-Tc superconductors, regardless of cuprate or pnictide family. The nematic state in high-Tc systems often relates to the structural transition or electronic instability in the normal phase. Nevertheless, the electronic states below the superconducting transition temperature is still an open question. With high-resolution scanning tunneling microscope measurements, direct observation of vortex core in FeSe thin films revealed the nematic superconducting state by Song et al. Here, motivated by the experiment, we construct the extended Ginzburg-Landau free energy to describe the elliptical vortex, where a mixed s-wave and d-wave superconducting order is coupled to the nematic order. The nematic order induces the mixture of two superconducting orders and enhances the anisotropic interaction between the two superconducting orders, resulting in a symmetry breaking from C4 to C2. Consequently, the vortex cores are stretched into an elliptical shape. In the equilibrium state, the elliptical vortices assemble a lozenge-like vortex lattice, being well consistent with experimental results.

Dissipative phases across the superconductor-to-insulator transition

PubMed Central

Couëdo, F.; Crauste, O.; Drillien, A. A.; Humbert, V.; Bergé, L.; Marrache-Kikuchi, C. A.; Dumoulin, L.

2016-01-01

Competing phenomena in low dimensional systems can generate exotic electronic phases, either through symmetry breaking or a non-trivial topology. In two-dimensional (2D) systems, the interplay between superfluidity, disorder and repulsive interactions is especially fruitful in this respect although both the exact nature of the phases and the microscopic processes at play are still open questions. In particular, in 2D, once superconductivity is destroyed by disorder, an insulating ground state is expected to emerge, as a result of a direct superconductor-to-insulator quantum phase transition. In such systems, no metallic state is theoretically expected to survive to the slightest disorder. Here we map out the phase diagram of amorphous NbSi thin films as functions of disorder and film thickness, with two metallic phases in between the superconducting and insulating ones. These two dissipative states, defined by a resistance which extrapolates to a finite value in the zero temperature limit, each bear a specific dependence on disorder. We argue that they originate from an inhomogeneous destruction of superconductivity, even if the system is morphologically homogeneous. Our results suggest that superconducting fluctuations can favor metallic states that would not otherwise exist. PMID:27786260

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.

NbTiN Based SIS Multilayer Structures for SRF Applications

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

Valente, Anne-marie; Eremeev, Grigory; Phillips, H

2013-09-01

For the past three decades, bulk niobium has been the material of choice for SRF cavities applications. RF cavity performance is now approaching the theoretical limit for bulk niobium. For further improvement of RF cavity performance for future accelerator projects, Superconductor Insulator - Superconductor (SIS) multilayer structures (as recently proposed by Alex Gurevich) present the theoretical prospect to reach RF performance beyond bulk Nb, using thinly layered higher-Tc superconductors with enhanced Hc1. Jefferson Lab (JLab) is pursuing this approach with the development of NbTiN and AlN based multilayer SIS structures. This paper presents the results on the characteristics of NbTiNmore » films and the first RF measurements on NbTiN-based multilayer structure on thick Nb films.« less

Using electron-tunneling refrigerators to cool electrons, membranes, and sensors

NASA Astrophysics Data System (ADS)

Miller, Nathan A.

Many cryogenic devices require temperatures near 100 mK for optimal performance, such as thin-film, superconducting detectors. Examples include the submillimeter SCUBA camera on the James Clerk Maxwell Telescope, high-resolution X-ray sensors for semiconductor defect analysis, and a planned satellite to search for polarization in the cosmic microwave background. The cost, size, and complexity of refrigerators used to reach 100 mK (dilution and adiabatic demagnetization refrigerators) are significant and alternative technologies are desirable. We demonstrate work on developing a new option for cooling detectors to 100 mK bath temperatures. Solid-state refrigerators based on Normal metal/Insulator/Superconductor (NIS) tunnel junctions can provide cooling from pumped 3He bath temperatures (˜300 mK) to 100 mK. The cooling mechanism is the preferential tunneling of the highest energy (hottest) electrons from the normal metal through the biased tunnel junctions into the superconductor. When NIS refrigerators are combined with a micro-machined membrane, both the electrons and phonons of the membrane can be cooled. We have developed NIS-cooled membranes with both large temperature reductions and large cooling powers. We have shown the first cooling of a bulk material by cooling a neutron transmutation doped (NTD) thermistor. The fabrication of NIS refrigerators can be integrated with existing detector technology. For the first time, we have successfully integrated NIS refrigerators with both mm-wave and X-ray detectors. In particular, we have cooled X-ray detectors by more than 100 mK and have achieved a resolution of <10 eV at 6 keV at a bath temperature 85 mK above the transition temperature of the detector. The use of integrated NIS refrigerators makes the remarkable performance of cryogenic detectors available from 300 mK platforms. We have also performed preliminary work towards building a general-purpose cooling platform for microelectronics devices on separate chips.

The materials processing research base of the Materials Processing Center

NASA Technical Reports Server (NTRS)

Flemings, M. C.; Bowen, H. K.; Kenney, G. B.

1980-01-01

The goals and activities of the center are discussed. The center activities encompass all engineering materials including metals, ceramics, polymers, electronic materials, composites, superconductors, and thin films. Processes include crystallization, solidification, nucleation, and polymer synthesis.

Saw-tooth pattern from flux jumps observed by high resolution M-H curves in MgB2 thin films

NASA Astrophysics Data System (ADS)

Lee, Jae-Yeap; Lee, Hu-Jong; Jung, Myung-Hwa; Lee, Sung-Ik; Choi, Eun-Mi; Kang, W. N.

2010-08-01

While flux jumps have been observed in the magnetic hysteresis loops of superconductors, a saw-tooth pattern of the flux jump is known to appear only in a bulk superconductor. But in this study, we were able to observe the saw-tooth pattern in MgB2 thin film with the careful data acquisition method enhancing the data taking capability and report the details of the distribution of the field interval between jumps Bfj, and the size of the flux jump, Mfj. The theory based on Bean's model in the adiabatic approach was adapted and it was compared with experimental results. In addition, we observe the cross-over between the saw-tooth pattern and a rounded saw-tooth pattern, as a byproduct. A patterns diagram of the vortex jump was drawn on the H-T plane.

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.

Superconductor-Metal-Insulator transition in two dimensional Ta thin Films

NASA Astrophysics Data System (ADS)

Park, Sun-Gyu; Kim, Eunseong

2013-03-01

Superconductor-insulator transition has been induced by tuning film thickness or magnetic field. Recent electrical transport measurements of MoGe, Bi, Ta thin films revealed an interesting intermediate metallic phase which intervened superconducting and insulating phases at certain range of magnetic field. Especially, Ta thin films show the characteristic IV behavior at each phase and the disorder tuned intermediate metallic phase [Y. Li, C. L. Vicente, and J. Yoon, Physical Review B 81, 020505 (2010)]. This unexpected metallic phase can be interpreted as a consequence of vortex motion or contribution of fermionic quasiparticles. In this presentation, we report the scaling behavior during the transitions in Ta thin film as well as the transport measurements in various phases. Critical exponents v and z are obtained in samples with wide ranges of disorder. These results reveal new universality class appears when disorder exceeds a critical value. Dynamical exponent z of Superconducting sample is found to be 1, which is consistent with theoretical prediction of unity. z in a metallic sample is suddenly increased to be approximately 2.5. This critical exponent is much larger than the value found in other system and theoretical prediction. We gratefully acknowledge the financial support by the National Research Foundation of Korea through the Creative Research Initiatives.

A technique to measure the thermal diffusivity of high Tc superconductors

NASA Technical Reports Server (NTRS)

Powers, Charles E.

1991-01-01

High T(sub c) superconducting electrical current leads and ground straps will be used in cryogenic coolers in future NASA Goddard Space Flight Center missions. These superconducting samples are long, thin leads with a typical diameter of two millimeters. A longitudinal method is developed to measure the thermal diffusivity of candidate materials for this application. This technique uses a peltier junction to supply an oscillatory heat wave into one end of a sample and will use low mass thermocouples to follow the heat wave along the sample. The thermal diffusivity is calculated using both the exponential decay of the heat wave and the phase shift to the wave. Measurements are performed in a cryostat between 10 K and room temperature.

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.

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

Enhanced critical-current in P-doped BaFe2As2 thin films on metal substrates arising from poorly aligned grain boundaries.

PubMed

Sato, Hikaru; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

2016-11-11

Thin films of the iron-based superconductor BaFe 2 (As 1-x P x ) 2 (Ba122:P) were fabricated on polycrystalline metal-tape substrates with two kinds of in-plane grain boundary alignments (well aligned (4°) and poorly aligned (8°)) by pulsed laser deposition. The poorly aligned substrate is not applicable to cuprate-coated conductors because the in-plane alignment >4° results in exponential decay of the critical current density (J c ). The Ba122:P film exhibited higher J c at 4 K when grown on the poorly aligned substrate than on the well-aligned substrate even though the crystallinity was poorer. It was revealed that the misorientation angles of the poorly aligned samples were less than 6°, which are less than the critical angle of an iron-based superconductor, cobalt-doped BaFe 2 As 2 (~9°), and the observed strong pinning in the Ba122:P is attributed to the high-density grain boundaries with the misorientation angles smaller than the critical angle. This result reveals a distinct advantage over cuprate-coated conductors because well-aligned metal-tape substrates are not necessary for practical applications of the iron-based superconductors.

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

Spatial variation of the physical conditions of molecular gas in galaxies

NASA Technical Reports Server (NTRS)

Jackson, James M.; Eckart, Andreas; Wild, Wolfgang; Genzel, Reinhard; Harris, Andrew I.; Downes, Dennis; Jaffe, D. T.; Ho, Paul T. P.

1990-01-01

Multi-line studies of CO-12, CO-13, C-18O, HCN, and HCO(+) at 3 mm, 1.3 mm, and 0.8 mm using the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope, with the IRAM superconductor insulator superconductor (SIS) receivers and the Max Planck Institute for External Physics (MPE) 350 GHz SIS receiver, show that the densities and temperatures of molecular gas in external galaxies change significantly with position. CO-12 measures the densities and temperature of diffuse interclump molecular gas, but not the bulk of the molecular gas. Simple one-component models, with or without external heating, cannot account for the weakness of the CO-12 J = 3 to 2 line relative to J = 2 to 1 and J = 1 to 0. CO-12 does not trace the bulk of the molecular gas, and optical depth effects obviate a straightforward interpretation of CO-12 data. Instead, researchers turned to the optically thin CO isotopes and other molecular species. Isotopic CO lines measure the bulk of the molecular gas, and HCN and HCO(+) pick out denser regions. Researchers find a warm ridge of gas in IC 342 (Eckart et al. 1989), denser gas in the starburst nucleus of IC 342, and a possible hot-spot in NGC 2903. In IC 342, NGC 2146, and NGC 6764, the CO-13 J = 2 to 1 line is subthermally populated, implying gas densities less than or equal to 10(exp 4) cm(-3).

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).

Property and microstructural nonuniformity in the yttrium-barium-copper-oxide superconductor determined from electrical, magnetic, and ultrasonic measurements. Ph.D. Thesis - Case Western Reserve Univ.

NASA Technical Reports Server (NTRS)

Roth, Don J.

1991-01-01

The purpose of this dissertation was the following: (1) to characterize the effect of pore fraction on a comprehensive set of electrical and magnetic properties for the yttrium-barium-copper-oxide (YBCO) high temperature ceramic superconductor; and (2) to determine the viability of using a room-temperature, nondestructive characterization method to aid in the prediction of superconducting (cryogenic) properties. The latter involved correlating ultrasonic velocity measurements at room temperature with property-affecting pore fraction and oxygen content variations. The use of ultrasonic velocity for estimating pore fraction in YBCO is presented, and other polycrystalline materials are reviewed, modeled, and statistically analyzed. This provides the basis for using ultrasonic velocity to interrogate microstructure. The effect of pore fraction (0.10-0.25) on superconductor properties of YBCO samples was characterized. Spatial (within-sample) variations in microstructure and superconductor properties were investigated, and the effect of oxygen content on elastic behavior was examined. Experimental methods used included a.c. susceptibility, electrical, and ultrasonic velocity measurements. Superconductor properties measured included transition temperature, magnetic transition width, transport and magnetic critical current density, magnetic shielding, a.c. loss, and sharpness of the voltage-current characteristics. An ultrasonic velocity image constructed from measurements at 1mm increments across a YBCO sample revealed microstructural variations that correlated with variations in magnetic shielding and a.c. loss behavior. Destructive examination using quantitative image analysis revealed pore fraction to be the varying microstructural feature.

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.

High-field transport properties of a P-doped BaFe2As2 film on technical substrate.

PubMed

Iida, Kazumasa; Sato, Hikaru; Tarantini, Chiara; Hänisch, Jens; Jaroszynski, Jan; Hiramatsu, Hidenori; Holzapfel, Bernhard; Hosono, Hideo

2017-01-12

High temperature (high-T c ) superconductors like cuprates have superior critical current properties in magnetic fields over other superconductors. However, superconducting wires for high-field-magnet applications are still dominated by low-T c Nb 3 Sn due probably to cost and processing issues. The recent discovery of a second class of high-T c materials, Fe-based superconductors, may provide another option for high-field-magnet wires. In particular, AEFe 2 As 2 (AE: Alkali earth elements, AE-122) is one of the best candidates for high-field-magnet applications because of its high upper critical field, H c2 , moderate H c2 anisotropy, and intermediate T c . Here we report on in-field transport properties of P-doped BaFe 2 As 2 (Ba-122) thin films grown on technical substrates by pulsed laser deposition. The P-doped Ba-122 coated conductor exceeds a transport J c of 10 5  A/cm 2 at 15 T for main crystallographic directions of the applied field, which is favourable for practical applications. Our P-doped Ba-122 coated conductors show a superior in-field J c over MgB 2 and NbTi, and a comparable level to Nb 3 Sn above 20 T. By analysing the E - J curves for determining J c , a non-Ohmic linear differential signature is observed at low field due to flux flow along the grain boundaries. However, grain boundaries work as flux pinning centres as demonstrated by the pinning force analysis.

Formation of Y(x)Nd(1-x) Ba2Cu3O(7-delta) (0 = or < x < or = 0.7) Superconductors from an Undercooled Melt Via Aero-Acoustic Levitation

NASA Technical Reports Server (NTRS)

Gustafson, D. E.; Hofmeister, W. H.; Bayuzick, R. J.

2001-01-01

Melt processing of RE123 superconductors has gained importance in recent years. While the first high temperature superconductors (HTSCs) were made using traditional ceramic press and sinter technology, recent fabrication efforts have employed alternate processing techniques including laser ablation and ion beam assisted deposition for thin film fabrication of tapes and wires and melt growth for bulk materials. To optimize these techniques and identify other potential processing strategies, phase relation studies on HTSCs have been conducted on a wide variety of superconducting compounds using numerous processing strategies. This data has enhanced the understanding of these complex systems and allowed more accurate modeling of phase interactions. All of this research has proved useful in identifying processing capabilities for HTSCs but has failed to achieve a breakthrough for wide spread application of these materials. This study examines the role of full to partial substitution of Nd in the Y123 structure under rapid solidification conditions. Aero-acoustic levitation (AAL) was used to levitate and undercool RE123 in pure oxygen binary alloys with RE = Nd an Y along a range of compositions corresponding to Y(x)Nd(1-x) Ba2Cu3O(7-delta) (0 = or < x < or = 0.7) which were melted by a CO2 laser. Higher Y content spheres could not be melted in the AAL and were excluded from this report. Solidification structures were examined using scanning electron microscopy, electron dispersive spectroscopy, and powder x-ray diffraction to characterize microstructures and identify phases.

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

Ultrasonic Attenuation of Surface Acoustic Waves in Thin Films of High Transition Temperature Superconducting Niobium-Tin and Niobium-Nitride

NASA Astrophysics Data System (ADS)

Fredricksen, Hans Peter

The ultrasonic attenuation of 600-700 MHz surface acoustic waves by two high T(,c), cubic crystal structure, superconducting thin films has been investigated. The films studied were two, 0.5 (mu) thin, Nb(,3)Sn samples, electron-beam codeposited on LiNbO(,3) and Quartz, and eleven NbN samples from 3 x 10('3) (ANGSTROM) to <(, )200 (ANGSTROM) thin, sputter deposited on LiNbO(,3). The Nb(,3)Sn (Al5 structure) film on Quartz was difficult to measure due to defects in the Quartz caused by the high deposition temperature ((DBLTURN)700(DEGREES)C) used to make the high T(,c) form of the compound. The Nb(,3)Sn film on LiNbO(,3), however, provided information about the transition temperature and energy gap at T = 0 K when the attenuation was measured as a function of temperature in zero magnetic field. A theory is developed to predict the electron-phonon produced normal state attenuation of surface acoustic waves by a thin, loss producing film on a nonattenuating substrate. Using a viscous drag model for the attenuation, the predictions of the theory are compared to the measured normal state attenuation to find the electron mean-free-path for the Nb(,3)Sn film on LiNbO(,3). The attenuation measured for this film as a function of applied magnetic field for four temperatures below T(,c) showed the sample to be an impurity rich type II superconductor with H(,c(,2)) (T = 0 K) = 85 KG, having GLAG theory constants: (kappa)(,2)(t=1) = 28.5 and (kappa)(t=1) = 29.2. The attenuation curves of the nine thickest NbN samples were non-BCS-like and very similar. Measured as a function of temperature only, because we could not reach the high critical fields of the samples, the attenuation showed an initial drop at T(,c) of about 1-2 dB which then leveled off until the temperature was below 0.5 T(,c), where the rate of decrease was much slower than the initial drop. A qualitative description of this behavior is derived from the Kosterlitz-Thouless vortex-antivortex theory. Although the thinnest NbN film did not show an attenuation change at T(,c), the next thinnest did. In this case, the measured decrease of nearly 40 dB is explained by the change in boundary condition when the substrate surface changes from "open" to "shortened" when the film becomes superconducting.

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.

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.

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.

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.

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.

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.

Thin Film Approaches to the SRF Cavity Problem Fabrication and Characterization of Superconducting Thin Films

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

Beringer, Douglas

Superconducting Radio Frequency (SRF) cavities are responsible for the acceleration of charged particles to relativistic velocities in most modern linear accelerators, such as those employed at high-energy research facilities like Thomas Jefferson National Laboratory’s CEBAF and the LHC at CERN. Recognizing SRF as primarily a surface phenomenon enables the possibility of applying thin films to the interior surface of SRF cavities, opening a formidable tool chest of opportunities by combining and designing materials that offer greater performance benefit. Thus, while improvements in radio frequency cavity design and refinements in cavity processing techniques have improved accelerator performance and efficiency – 1.5more » GHz bulk niobium SRF cavities have achieved accelerating gradients in excess of 35 MV/m – there exist fundamental material bounds in bulk superconductors limiting the maximally sustained accelerating field gradient (≈ 45 MV/m for Nb) where inevitable thermodynamic breakdown occurs. With state of the art Nb based cavity design fast approaching these theoretical limits, novel material innovations must be sought in order to realize next generation SRF cavities. One proposed method to improve SRF performance is to utilize thin film superconducting-insulating-superconducting (SIS) multilayer structures to effectively magnetically screen a bulk superconducting layer such that it can operate at higher field gradients before suffering critically detrimental SRF losses. This dissertation focuses on the production and characterization of thin film superconductors for such SIS layers for radio frequency applications. Correlated studies on structure, surface morphology and superconducting properties of epitaxial Nb and MgB2 thin films are presented.« less

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

ac response of thin superconductors in the flux-creep regime

NASA Astrophysics Data System (ADS)

Gurevich, A.; Brandt, E. H.

1997-05-01

We calculate both analytically and numerically the ac susceptibility χ(ω) and the nonlinear electromagnetic response of thin superconductor strips and disks of constant thickness in a perpendicular time-dependent magnetic field Ba(t)=B0cos ωt, taking account of the strong nonlinearity of the voltage-current characteristics below the irreversibility line. We consider integral equations of nonlinear nonlocal flux diffusion for a wide class of thermally activated creep models. It is shown that thin superconductors, despite being fully in the critical state, exhibit a universal Meissner-like electromagnetic response in the dissipative flux-creep regime. The expression for the linear ac susceptibility during flux creep appears to be similar to the susceptibility of Ohmic conductors, but with the relaxation time constant replaced by the time t elapsed after flux creep has started. This result is independent of any material parameter or temperature or dc field. For ωt>>:1, we obtain χ(ω)~-1+pln (qiωt)/(iωt), where p and q are constants. Above a critical ac amplitude B0=Bl, the local response of the electric field becomes nonlinear, and there are two distinctive nonlinear regimes at B0>Bl, where Bl~s(d/a)1/2Bp, Bp is a characteristic field of full flux penetration, s(T,B)=\\|dln j/dln t\\| is the dimensionless flux-creep rate and d and a are the sample thickness and width, respectively. For BlBh(ω) the ac field causes hysteresis dissipation due to a periodic remagnetization of the critical state that gives rise to the hysteretic magnetic response of the Bean model at B0>>:Bh. Here Bh(ω) weakly depends on ω and is of order (d/a)1/2Bp for a very wide frequency range, well below the irreversibility field, where s(T,B)<<1. Magnetization and ac losses at B0>>:Bh are calculated accounting for the nonlinearity of E(J) at J

Intrinsic superspin Hall current

NASA Astrophysics Data System (ADS)

Linder, Jacob; Amundsen, Morten; Risinggârd, Vetle

2017-09-01

We discover an intrinsic superspin Hall current: an injected charge supercurrent in a Josephson junction containing heavy normal metals and a ferromagnet generates a transverse spin supercurrent. There is no accompanying dissipation of energy, in contrast to the conventional spin Hall effect. The physical origin of the effect is an antisymmetric spin density induced among transverse modes ky near the interface of the superconductor arising due to the coexistence of p -wave and conventional s -wave superconducting correlations with a belonging phase mismatch. Our predictions can be tested in hybrid structures including thin heavy metal layers combined with strong ferromagnets and ordinary s -wave superconductors.

How experimentally to detect a solitary superconductivity in dirty ferromagnet-superconductor trilayers?

NASA Astrophysics Data System (ADS)

Avdeev, Maxim V.; Proshin, Yurii N.

2017-10-01

We theoretically study the proximity effect in the thin-film layered ferromagnet (F) - superconductor (S) heterostructures in F1F2S design. We consider the boundary value problem for the Usadel-like equations in the case of so-called ;dirty; limit. The ;latent; superconducting pairing interaction in F layers taken into account. The focus is on the recipe of experimental preparation the state with so-called solitary superconductivity. We also propose and discuss the model of the superconducting spin valve based on F1F2S trilayers in solitary superconductivity regime.

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.

Stoichiometry and thickness dependence of superconducting properties of niobium nitride thin films

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

Beebe, Melissa R., E-mail: mrbeebe@email.wm.edu; Beringer, Douglas B.; Burton, Matthew C.

2016-03-15

The current technology used in linear particle accelerators is based on superconducting radio frequency (SRF) cavities fabricated from bulk niobium (Nb), which have smaller surface resistance and therefore dissipate less energy than traditional nonsuperconducting copper cavities. Using bulk Nb for the cavities has several advantages, which are discussed elsewhere; however, such SRF cavities have a material-dependent accelerating gradient limit. In order to overcome this fundamental limit, a multilayered coating has been proposed using layers of insulating and superconducting material applied to the interior surface of the cavity. The key to this multilayered model is to use superconducting thin films tomore » exploit the potential field enhancement when these films are thinner than their London penetration depth. Such field enhancement has been demonstrated in MgB{sub 2} thin films; here, the authors consider films of another type-II superconductor, niobium nitride (NbN). The authors present their work correlating stoichiometry and superconducting properties in NbN thin films and discuss the thickness dependence of their superconducting properties, which is important for their potential use in the proposed multilayer structure. While there are some previous studies on the relationship between stoichiometry and critical temperature T{sub C}, the authors are the first to report on the correlation between stoichiometry and the lower critical field H{sub C1}.« less

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.

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.

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.

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.

Engineering of an ultra-thin molecular superconductor by charge transfer

DOEpatents

Hla, Saw Wai; Hassanien, Abdelrahim; Kendal, Clark

2016-06-07

A method of forming a superconductive device of a single layer of (BETS).sub.2GaCl.sub.4 molecules on a substrate surface which displays a superconducting gap that increases exponentially with the length of the molecular chain is provided.

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.

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.

Phase diagram of (Li(1-x)Fe(x))OHFeSe: a bridge between iron selenide and arsenide superconductors.

PubMed

Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian

2015-01-14

Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ∼127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known √5×√5 iron vacancy ordered state, resulting in an AFM order at ∼500 K in AyFe2-xSe2 (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = (1)/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.

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.

The Discovery of a Class of High-Temperature Superconductors.

ERIC Educational Resources Information Center

Muller, K. Alex; Bednorz, J. Georg

1987-01-01

Describes the new class of oxide superconductors, the importance of these materials, and the concepts that led to its discovery. Summarizes the discovery itself and its early confirmation. Discusses the observation of a superconductive glass state in percolative samples. (TW)

The Possibility of Improved and Higher Tc Superconductors in Hybrid Systems

DTIC Science & Technology

2014-10-15

Approved for public release; distribution is unlimited. of the oxygen sub-lattice precisely in thin films and heterostrutures; which plays a pivotal role...to influence the structure-property affair in complex oxide thin films. We have focused our study to effectively control the oxygen position...that by varying precisely the thickness of SCO layers grown on SrTiO3, one can re-arrange the oxygen ions. In particular, we show that it is possible

Superconductor disks and cylinders in an axial magnetic field: II. Nonlinear and linear ac susceptibilities

NASA Astrophysics Data System (ADS)

Brandt, Ernst Helmut

1998-09-01

The ac susceptibility χ=χ'-iχ'' of superconductor cylinders of finite length in a magnetic field applied along the cylinder axis is calculated using the method developed in the preceding paper, part I. This method does not require any approximation of the infinitely extended magnetic field outside the cylinder or disk but directly computes the current density J inside the superconductor. The material is characterized by a general current-voltage law E(J), e.g., E(J)=Ec[J/Jc(B)]n(B), where E is the electric field, B=μ0H the magnetic induction, Ec a prefactor, Jc the critical current density, and n>=1 the creep exponent. For n>1, the nonlinear ac susceptibility is calculated from the hysteresis loops of the magnetic moment of the cylinder, which is obtained by time integration of the equation for J(r,t). For n>>1 these results go over into the Bean critical state model. For n=1, and for any linear complex resistivity ρac(ω)=E/J, the linear ac susceptibility is calculated from an eigenvalue problem which depends on the aspect ratio b/a of the cylinder or disk. In the limits b/a<<1 and b/a>>1, the known results for thin disks in a perpendicular field and long cylinders in a parallel field are reproduced. For thin disks in a perpendicular field, at large frequencies χ(ω) crosses over to the behavior of slabs in parallel geometry since the magnetic field lines are expelled and have to flow around the disk. The results presented may be used to obtain the nonlinear or linear resistivity from contact-free magnetic measurements on superconductors of realistic shape.

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.

Linear ac Response of Thin Superconductors during Flux Creep

NASA Astrophysics Data System (ADS)

Brandt, Ernst Helmut; Gurevich, Alexander

1996-03-01

The linear magnetic susceptibility χ\\(ω\\) of superconducting strips and disks in a transverse magnetic field is calculated in the flux-creep regime. It is shown that χ\\(ω\\) = χ'-iχ'' for ω>>1/t is universal, independent of temperature, dc field, and material parameters, depending only on the sample shape, ac frequency ω/2π, and time t elapsed after creep has started. Qualitatively, χ\\(ω\\) can be obtained from the χ\\(ω\\) of metallic conductors by replacing the Ohmic relaxation time by t. At ωt>>1, which may apply down to rather low frequencies, the dissipative flux-creep state exhibits a nearly Meissner-like response with χ' = -1+0.40/ωt and χ'' = 0.25ln\\(29ωt\\)/ωt for disks.

Gate-tunable electron interaction in high-κ dielectric films

DOE PAGES

Kondovych, Svitlana; Luk’yanchuk, Igor; Baturina, Tatyana I.; ...

2017-02-20

The two-dimensional (2D) logarithmic character of Coulomb interaction between charges and the resulting logarithmic confinement is a remarkable inherent property of high dielectric constant (high-k) thin films with far reaching implications. Most and foremost, this is the charge Berezinskii-Kosterlitz-Thouless transition with the notable manifestation, low-temperature superinsulating topological phase. Here we show that the range of the confinement can be tuned by the external gate electrode and unravel a variety of electrostatic interactions in high-k films. Lastly, our findings open a unique laboratory for the in-depth study of topological phase transitions and a plethora of related phenomena, ranging from criticality ofmore » quantum metal- and superconductor-insulator transitions to the effects of charge-trapping and Coulomb scalability in memory nanodevices.« less

Superconductivity and role of pnictogen and Fe substitution in 112-LaPdxP n2 (P n =Sb ,Bi )

NASA Astrophysics Data System (ADS)

Retzlaff, Reiner; Buckow, Alexander; Komissinskiy, Philipp; Ray, Soumya; Schmidt, Stefan; Mühlig, Holger; Schmidl, Frank; Seidel, Paul; Kurian, Jose; Alff, Lambert

2015-03-01

We report on the epitaxial growth of As-free and phase-pure thin films of the 112-pnictide compounds LaPdxP n2 (P n =Sb ,Bi ) grown on (100) MgO substrates by molecular beam epitaxy. X-ray diffraction, reflection high-energy electron diffraction, and x-ray photoelectron spectroscopy confirm the HfCuSi2 structure of the material with a peculiar pnictogen square net layer. The superconducting transition temperature Tc varies little with Pd concentration. LaPdxSb2 has a higher Tc (3.2 K) by about 20% compared with LaPdxBi2 (2.7 K). Fe substitution of Pd leads to a rapid decay of superconductivity, suggesting that these superconductors are conventional type II.

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.

Temperature dependence of lower critical field of YBCO superconductor

NASA Astrophysics Data System (ADS)

Rani, Poonam; Hafiz, A. K.; Awana, V. P. S.

2018-05-01

We report the detailed study of the temperature dependence of the lower critical field (Hc1) of the YBa2Cu3O7 superconductor by magnetization measurements. The curve shows the multiband gap behavior of the sample. It is found that the sample is not a single BCS type superconductor. Hc1 is measured as the point at which the curve deviates from a Meissner-like linear M(H) curve to a nonlinear path. The Hc1 for YBCO at different temperatures from 10K to 85K has been determined by magnetization measurements M(H) with applied field parallel to the c-axis. The sample phase purity has been confirmed by Rietveld fitted X-ray diffraction data. The amplitude (1-17Oe) dependent AC susceptibility confirms the granular nature of superconducting compound. Using Bean model we calculated the temperature dependency of inter-grain critical current density and Jc(0) is found as 699.14kAcm-2.

Free surfaces recast superconductivity in few-monolayer MgB2: Combined first-principles and ARPES demonstration.

PubMed

Bekaert, J; Bignardi, L; Aperis, A; van Abswoude, P; Mattevi, C; Gorovikov, S; Petaccia, L; Goldoni, A; Partoens, B; Oppeneer, P M; Peeters, F M; Milošević, M V; Rudolf, P; Cepek, C

2017-10-31

Two-dimensional materials are known to harbour properties very different from those of their bulk counterparts. Recent years have seen the rise of atomically thin superconductors, with a caveat that superconductivity is strongly depleted unless enhanced by specific substrates, intercalants or adatoms. Surprisingly, the role in superconductivity of electronic states originating from simple free surfaces of two-dimensional materials has remained elusive to date. Here, based on first-principles calculations, anisotropic Eliashberg theory, and angle-resolved photoemission spectroscopy (ARPES), we show that surface states in few-monolayer MgB 2 make a major contribution to the superconducting gap spectrum and density of states, clearly distinct from the widely known, bulk-like σ- and π-gaps. As a proof of principle, we predict and measure the gap opening on the magnesium-based surface band up to a critical temperature as high as ~30 K for merely six monolayers thick MgB 2 . These findings establish free surfaces as an unavoidable ingredient in understanding and further tailoring of superconductivity in atomically thin materials.

Super Photon Counters

NASA Technical Reports Server (NTRS)

Mather, John

1999-01-01

The perfect photon detector would measure the arrival time, the energy, the polarization, and the position of every arriving quantum, but that is easier said than done. Two groups have now succeeded in doing time-resolved spectroscopy on the Crab Nebula pulsar, measuring everything but the polarization, with reports from Romani et al. at Stanford and from Perryman et al. at ESTEC. Both groups use superconducting detectors to gain the necessary speed and sensitivity. The photon can heat the electrons in a superconductor biased in the middle of its resistive transition, or break bound superconducting electron-hole pairs, which can then be collected. Three years ago, Peacock et al. reported that they had detected single optical photons with a superconducting tunnel junction (STJ), and Paresce wrote a News and Views article. A tunnel junction uses two pieces of conductive material, separated by a tiny gap of insulating material or even vacuum. If the gap is thin enough, electrons can tunnel across anyway, and if the conductors are superconductors, the junction displays very useful quantum mechanical properties and electrical nonlinearities. Amplifiers, detectors, oscillators, and computer circuits can all be made from them. Their special advantage is that they operate at very low temperatures, dissipate very little power, operate very fast, and are very small.

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

Shubnikov-de Haas quantum oscillations reveal a reconstructed Fermi surface near optimal doping in a thin film of the cuprate superconductor Pr 1.86 Ce 0.14 CuO 4 ± δ

DOE PAGES

Breznay, Nicholas P.; Hayes, Ian M.; Ramshaw, B. J.; ...

2016-09-16

In this work, we study magnetotransport properties of the electron-doped superconductor Pr 2-xCe xCuO 4±δ with x = 0.14 in magnetic fields up to 92 T, and observe Shubnikov-de Haas magnetic quantum oscillations. The oscillations display a single frequency F = 255 ± 10 T, indicating a small Fermi pocket that is ~1 % of the two-dimensional Brillouin zone and consistent with a Fermi surface reconstructed from the large holelike cylinder predicted for these layered materials. Despite the low nominal doping, all electronic properties including the effective mass and Hall effect are consistent with overdoped compounds. In conclusion, our studymore » demonstrates that the exceptional chemical control afforded by high quality thin films will enable Fermi surface studies deep into the overdoped cuprate phase diagram.« less

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.

Elastic properties of iron-based superconductor SrFe2(As1-xPx)2

NASA Astrophysics Data System (ADS)

Horikoshi, Keita; Imai, Jo; Nakanishi, Yoshiki; Nakamura, Mitsuteru; Kobayashi, Tatsuya; Adachi, Toru; Miyasaka, Shigeki; Tajima, Setsuko; Yoshizawa, Masahito

2018-05-01

We have measured the transverse elastic constants C44 and C66 of iron-based superconductor SrFe2(As1-xPx)2 (Sr122) single crystals as a function of temperature. Under-doped samples show elastic anomalies towards the structural/magnetic transition temperature. Optimal sample shows an upturn at the superconducting transition temperature in both C44 and C66. These behavior is similar to Ba122, while only C66 shows anomaly for Ba122. The elastic anomalies were analyzed by Jahn-Teller formula, and it was found that the Jahn-Teller energy of C44 is much larger than that of C66. This indicates that monoclinic structural fluctuations exist inherently in Sr122 in addition to the known tetragonal fluctuations. Co-existence of these diverse fluctuations and their cooperation are a key to investigate the mechanism and properties of superconductivity in iron based superconductors.

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.

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

Effect of α-particle irradiation on a NdFeAs(O,F) thin film

NASA Astrophysics Data System (ADS)

Tarantini, C.; Iida, K.; Sumiya, N.; Chihara, M.; Hatano, T.; Ikuta, H.; Singh, R. K.; Newman, N.; Larbalestier, D. C.

2018-07-01

The effect of α-particle irradiation on a NdFeAs(O,F) thin film has been investigated to determine how the introduction of defects affects basic superconducting properties, including the critical temperature T c and the upper critical field H c2, and properties more of interest for applications, like the critical current density J c and the related pinning landscape. The irradiation-induced suppression of the film T c is significantly smaller than on a similarly damaged single crystal. Moreover H c2 behaves differently, depending on the field orientation: for H//c the H c2 slope monotonically increases with increasing disorder, whereas for H//ab it remains constant at low dose and it increases only when the sample is highly disordered. This suggests that a much higher damage level is necessary to drive the NdFeAs(O,F) thin film into the dirty limit. Despite the increase in the low temperature H c2, the effects on the J c(H//c) performances are moderate in the measured temperature and field ranges, with a shifting of the pinning force maximum from 4.5 to 6 T after an irradiation of 2 × 1015 cm-2. On the contrary, J c(H//ab) is always suppressed. The analysis demonstrates that irradiation does introduce point defects (PD) acting as pinning centres proportionally to the irradiation fluence but also suppresses the effectiveness of c-axis correlated pinning present in the pristine sample. We estimate that significant performance improvements may be possible at high field or at temperatures below 10 K. The suppression of the J c(H//ab) performance is not related to a decrease of the J c anisotropy as found in other superconductors. Instead it is due to the presence of PD that decrease the efficiency of the ab-plane intrinsic pinning typical of materials with a layered structure.

Low-frequency Electronic Transport Noise in La2-xBaxCuO4 Nanowires

NASA Astrophysics Data System (ADS)

Weis, Adam; Xin, Yizhou; van Harlingen, Dale

2013-03-01

In the pseudogap regime, high temperature superconductors often exhibit electronic structure, such as charge stripes. Charge stripes pinned to disorder have been predicted to contribute to low-frequency resistance fluctuations when sample dimensions are comparable to the size of stripe domains (Carlson, 2006). We are extending our previous studies of resistance fluctuations in YBa2Cu3O7-δ (Bonetti, 2004; Caplan, 2010) to thin films of La-based cuprates expected to have a more stable stripe phase, particularly in the regime near 1/8-filling. We present measurements of the low-frequency electronic transport in La2-xBaxCuO4 nanowires fabricated by pulsed laser deposition and lithographic techniques. We discuss temperature dependence of the power spectral density and its relevance to correlated electron phases above Tc. This research was supported by the DOE-DMS under grant DE-FG02-07ER46453, through the Frederick Seitz Materials Research Laboratory at the University of Illinois at Urbana-Champaign.

Directed motion of vortices and annihilation of vortex-antivortex pairs in finite-gap superconductors via hot-lattice routes

NASA Astrophysics Data System (ADS)

Gulian, Ellen D.; Melkonyan, Gurgen G.; Gulian, Armen M.

2017-07-01

Using finite gap, time-dependent Ginzburg-Landau equations, generalized to include non-thermal phonons, we report numerical simulations of vortex nucleation, propagation, and annihilation in thin, finite strips of magnetic-impurity free, perfectly homogeneous superconductors. When a steady electric current passes through the strip with either surface defects or nonequilibrium phonon sources (e.g., local ;hotspots;), periodic vortex generation and annihilation is observed even in the absence of external magnetic fields. Local pulses of electric field are produced upon annihilation. The injected phonon lines steer the vortices during their motion within the strip, potentially allowing control of the annihilation site.

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.

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.

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.

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.

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

An ultra-high vacuum scanning tunneling microscope operating at sub-Kelvin temperatures and high magnetic fields for spin-resolved measurements

NASA Astrophysics Data System (ADS)

Salazar, C.; Baumann, D.; Hänke, T.; Scheffler, M.; Kühne, T.; Kaiser, M.; Voigtländer, R.; Lindackers, D.; Büchner, B.; Hess, C.

2018-06-01

We present the construction and performance of an ultra-low-temperature scanning tunneling microscope (STM), working in ultra-high vacuum (UHV) conditions and in high magnetic fields up to 9 T. The cryogenic environment of the STM is generated by a single-shot 3He magnet cryostat in combination with a 4He dewar system. At a base temperature (300 mK), the cryostat has an operation time of approximately 80 h. The special design of the microscope allows the transfer of the STM head from the cryostat to a UHV chamber system, where samples and STM tips can be easily exchanged. The UHV chambers are equipped with specific surface science treatment tools for the functionalization of samples and tips, including high-temperature treatments and thin film deposition. This, in particular, enables spin-resolved tunneling measurements. We present test measurements using well-known samples and tips based on superconductors and metallic materials such as LiFeAs, Nb, Fe, and W. The measurements demonstrate the outstanding performance of the STM with high spatial and energy resolution as well as the spin-resolved capability.

More superconductivity questions than answers.

PubMed

Robinson, A L

1987-07-17

Although making liquid nitrogen-temperature superconductors is easy enough that high school science projects already feature them, researchers still have little idea how the new ceramic oxides work and therefore little guidance for improving them. At the International Workshop on Novel Mechanisms of Superconductivity, held from 22 to 26 June in Berkeley, California, theorists reviewed a host of competing explanations of how these materials come by their remarkable properties, but they could not, get far in sifting through the candidates for the best one. One cause of the unsettled situation is that theorists have not yet pushed their models far enough to make many specific predictions about physical properties and therefore to provide a reason to choose one theory over another. But experimental data for comparison with theory are lacking, too. For example, experimentalists are just now succeeding in being able to grow single crystals and thin films of the ceramic oxide superconductors, whose properties were shown at the workshop to be highly anisotropic. Measurements already made on the polycrystalline sintered material available up to now are difficult to interpret and therefore need to be repeated on good-quality crystals and films, where the variation of properties with crystallographic orientation can be mapped out. Given the high level of Japanese activity in the field, it was surprising that no researchers from industrial laboratories in Japan presented their findings at the workshop. In the light of a budding international competition in commercializing superconductors, some American scientists interpreted the absence as an attempt to protect proprietary advances. A more pleasant surprise was the attendance of a delegation of six Soviet scientists, although one of the fathers of superconductivity theory, Vitaly Ginzburg of the P.N.Lebedev Institute of Physics in Moscow, who was expected, did not come.

CHEMICAL SOLUTION DEPOSITION BASED OXIDE BUFFERS AND YBCO COATED CONDUCTORS

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

Paranthaman, Mariappan Parans

We have reviewed briefly the growth of buffer and high temperature superconducting oxide thin films using a chemical solution deposition (CSD) method. In the Rolling-Assisted Biaxially Textured Substrates (RABiTS) process, developed at Oak Ridge National Laboratory, utilizes the thermo mechanical processing to obtain the flexible, biaxially oriented copper, nickel or nickel-alloy substrates. Buffers and Rare Earth Barium Copper Oxide (REBCO) superconductors have been deposited epitaxially on the textured nickel alloy substrates. The starting substrate serves as a template for the REBCO layer, which has substantially fewer weak links. Buffer layers play a major role in fabricating the second generation REBCOmore » wire technology. The main purpose of the buffer layers is to provide a smooth, continuous and chemically inert surface for the growth of the REBCO film, while transferring the texture from the substrate to the superconductor layer. To achieve this, the buffer layers need to be epitaxial to the substrate, i.e. they have to nucleate and grow in the same bi-axial texture provided by the textured metal foil. The most commonly used RABiTS multi-layer architectures consist of a starting template of biaxially textured Ni-5 at.% W (Ni-W) substrate with a seed (first) layer of Yttrium Oxide (Y2O3), a barrier (second) layer of Yttria Stabilized Zirconia (YSZ), and a Cerium Oxide (CeO2) cap (third) layer. These three buffer layers are generally deposited using physical vapor deposition (PVD) techniques such as reactive sputtering. On top of the PVD template, REBCO film is then grown by a chemical solution deposition. This article reviews in detail about the list of oxide buffers and superconductor REBCO films grown epitaxially on single crystal and/or biaxially textured Ni-W substrates using a CSD method.« less

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.

Microgravity Processing of Oxide Superconductors

NASA Technical Reports Server (NTRS)

Olive, James R.; Hofmeister, William H.; Bayuzick, Robert J.; Vlasse, Marcus

1999-01-01

Considerable effort has been concentrated on the synthesis and characterization of high T(sub c) oxide superconducting materials. The YBaCuO system has received the most intense study, as this material has shown promise for the application of both thin film and bulk materials. There are many problems with the application of bulk materials- weak links, poor connectivity, small coherence length, oxygen content and control, environmental reactivity, phase stability, incongruent melting behavior, grain boundary contamination, brittle mechanical behavior, and flux creep. The extent to which these problems are intrinsic or associated with processing is the subject of controversy. This study seeks to understand solidification processing of these materials, and to use this knowledge for alternative processing strategies, which, at the very least, will improve the understanding of bulk material properties and deficiencies. In general, the phase diagram studies of the YBaCuO system have concentrated on solid state reactions and on the Y2BaCuO(x) + liquid yields YBa2Cu3O(7-delta) peritectic reaction. Little information is available on the complete melting relations, undercooling, and solidification behavior of these materials. In addition, rare earth substitutions such as Nd and Gd affect the liquidus and phase relations. These materials have promising applications, but lack of information on the high temperature phase relations has hampered research. In general, the understanding of undercooling and solidification of high temperature oxide systems lags behind the science of these phenomena in metallic systems. Therefore, this research investigates the fundamental melting relations, undercooling, and solidification behavior of oxide superconductors with an emphasis on improving ground based synthesis of these materials.

Superconducting order parameter fluctuations in NbN/NiCu and NbTiN/NiCu bilayer nanostripes for photon detection

NASA Astrophysics Data System (ADS)

Aichner, Bernd; Jausner, Florian; Zechner, Georg; Mühlgassner, Rita; Lang, Wolfgang; Klimov, Andrii; Puźniak, Roman; Słysz, Wojciech; Guziewicz, Marek; Kruszka, Renata; Wegrzecki, Maciej; Sobolewski, Roman

2017-05-01

Thermodynamic fluctuations of the superconducting order parameter in NbN/NiCu and NbTiN/NiCu superconductor/ferromagnet (S/F) thin bilayers patterned to microbridges are investigated. Plain NbN and NbTiN films served as reference materials for the analyses. The samples were grown using dc-magnetron sputtering on chemically cleaned sapphire single-crystal substrates. After rapid thermal annealing at high temperatures, the superconducting films were coated with NiCu overlays, using co-sputtering. The positive magnetoresistance of the superconducting single layers is very small in the normal state but with a sharp upturn close to the superconducting transition, a familiar signature of superconducting fluctuations. The fluctuation-enhanced conductivity (paraconductivity) of the NbN and NbTiN single layer films is slightly larger than the prediction of the parameter-free Aslamazov-Larkin theory for order-parameter fluctuations in two-dimensional superconductors. The addition of a ferromagnetic top layer, however, changes the magnetotransport properties significantly. The S/F bilayers show a negative magnetoresistance up to almost room temperature, while the signature of fluctuations is similar to that in the plain films, demonstrating the relevance of both ferromagnetic and superconducting effects in the S/F bilayers. The paraconductivity is reduced below theoretical predictions, in particular in the NbTiN/NiCu bilayers. Such suppression of the fluctuation amplitude in S/F bilayers could be favorable to reduce dark counts in superconducting photon detectors and lead the way to enhance their performance.

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

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.

Strongly suppressed proximity effect and ferromagnetism in topological insulator/ferromagnet/superconductor thin film trilayers of Bi2Se3/SrRuO3/underdoped YBa2Cu3O x : a possible new platform for Majorana nano-electronics

NASA Astrophysics Data System (ADS)

Koren, Gad

2018-07-01

We report properties of a topological insulator–ferromagnet–superconductor trilayers comprised of thin films of 20 nm thick {Bi}}2{Se}}3 on 10 nm SrRuO3 on 30 nm {YBa}}2{Cu}}3{{{O}}}x. As deposited trilayers are underdoped and have a superconductive transition with {{T}}{{c}} onset at 75 K, zero resistance at 65 K, {{T}}Cueri} at 150 K and {{T}}* of about 200 K. Further reannealing under vacuum yields the 60 K phase of {YBa}}2{Cu}}3{{{O}}}x which still has zero resistance below about 40 K. Only when 10 × 100 microbridges were patterned in the trilayer, some of the bridges showed resistive behavior all the way down to low temperatures. Magnetoresistance versus temperature of the superconductive ones showed the typical peak due to flux flow against pinning below {{T}}{{c}}, while the resistive ones showed only the broad leading edge of such a peak. All this indicates clearly weak-link superconductivity in the resistive bridges between superconductive {YBa}}2{Cu}}3{{{O}}}x grains via the topological and ferromagnetic cap layers. Comparing our results to those of a reference trilayer (RTL) with the topological {Bi}}2{Se}}3 layer substituted by a non-superconducting highly overdoped {La}}1.65{Sr}}0.35{CuO}}4, indicates that the superconductive proximity effect as well as ferromagnetism in the topological trilayer are actually strongly suppressed compared to the non-topological RTL. This strong suppression could originate in lattice and Fermi levels mismatch as well as in short coherence length and unfavorable effects of strong spin–orbit coupling in {Bi}}2{Se}}3 on the d-wave pairing of {YBa}}2{Cu}}3{{{O}}}x. Proximity induced edge currents in the SRO/YBCO layer could lead to Majorana bound states, a possible signature of which is observed in the present study as zero bias conductance peaks.

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.

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.

Tuning Superconductivity in FeSe Thin Films via Magnesium Doping.

PubMed

Qiu, Wenbin; Ma, Zongqing; Liu, Yongchang; Shahriar Al Hossain, Mohammed; Wang, Xiaolin; Cai, Chuanbing; Dou, Shi Xue

2016-03-01

In contrast to its bulk crystal, the FeSe thin film or layer exhibits better superconductivity performance, which recently attracted much interest in its fundamental research as well as in potential applications around the world. In the present work, tuning superconductivity in FeSe thin films was achieved by magnesium-doping technique. Tc is significantly enhanced from 10.7 K in pure FeSe films to 13.4 K in optimized Mg-doped ones, which is approximately 1.5 times higher than that of bulk crystals. This is the first time achieving the enhancement of superconducting transition temperature in FeSe thin films with practical thickness (120 nm) via a simple Mg-doping process. Moreover, these Mg-doped FeSe films are quite stable in atmosphere with Hc2 up to 32.7 T and Tc(zero) up to 12 K, respectively, implying their outstanding potential for practical applications in high magnetic fields. It was found that Mg enters the matrix of FeSe lattice, and does not react with FeSe forming any other secondary phase. Actually, Mg first occupies Fe-vacancies, and then substitutes for some Fe in the FeSe crystal lattices when Fe-vacancies are fully filled. Simultaneously, external Mg-doping introduces sufficient electron doping and induces the variation of electron carrier concentration according to Hall coefficient measurements. This is responsible for the evolution of superconducting performance in FeSe thin films. Our results provide a new strategy to improve the superconductivity of 11 type Fe-based superconductors and will help us to understand the intrinsic mechanism of this unconventional superconducting 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.

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.

Normal metal - insulator - superconductor thermometers and coolers with titanium-gold bilayer as the normal metal

NASA Astrophysics Data System (ADS)

Räisänen, I. M. W.; Geng, Z.; Kinnunen, K. M.; Maasilta, I. J.

2018-03-01

We have fabricated superconductor - insulator - normal metal - insulator - superconductor (SINIS) tunnel junctions in which Al acts as the superconductor, AlOx is the insulator, and the normal metal consists of a thin Ti layer (5 nm) covered with a thicker Au layer (40 nm). We have characterized the junctions by measuring their current-voltage curves between 60 mK and 750 mK. For comparison, the same measurements have been performed for a SINIS junction pair whose normal metal is Cu. The Ti-Au bilayer decreases the SINIS tunneling resistance by an order of magnitude compared to junctions where Cu is used as normal metal, made with the same oxidation parameters. The Ti-Au devices are much more robust against chemical attacks, and their lower tunneling resistance makes them more robust against static charge. More significantly, they exhibit significantly stronger electron cooling than Cu devices with identical fabrication steps, when biased close to the energy gap of the superconducting Al. By using a self-consistent thermal model, we can fit the current-voltage characteristics well, and show an electron cooling from 200 mK to 110 mK, with a non-optimized device.

Engineering of superconductors and superconducting devices using artificial pinning sites

NASA Astrophysics Data System (ADS)

Wördenweber, Roger

2017-08-01

Vortex matter in superconducting films and devices is not only an interesting topic for basic research but plays a substantial role in the applications of superconductivity in general. We demonstrate, that in most electronic applications, magnetic flux penetrates the superconductor and affects the performance of superconducting devices. Therefore, vortex manipulation turns out to be a useful tool to avoid degradation of superconducting device properties. Moreover, it can also be used to analyze and understand novel and interesting physical properties and develop new concepts for superconductor applications. In this review, various concepts for vortex manipulation are sketched. For example, the use of micro- and nanopatterns (especially, antidots) for guiding and trapping of vortices in superconducting films and thin film devices is discussed and experimental evidence of their vortex guidance and vortex trapping by various arrangements of antidots is given. We demonstrate, that the vortex state of matter is very important in applications of superconductivity. A better understanding does not only lead to an improvement of the performance of superconductor components, such as reduced noise, better power handling capability, or improved reliability, it also promises deeper insight into the basic physics of vortices and vortex matter.

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.

Molecular beam epitaxy growth of SmFeAs(O,F) films with Tc = 55 K using the new fluorine source FeF3

NASA Astrophysics Data System (ADS)

Sakoda, Masahito; Ishii, Akihiro; Takinaka, Kenji; Naito, Michio

2017-07-01

REFeAs(O,F) (RE: rare-earth element) has the highest-Tc (˜58 K) among the iron-based superconductors, but a thin-film growth of REFeAs(O,F) is difficult. This is because it is not only a complex compound consisting of five elements but also requires doping of highly reactive fluorine to achieve superconductivity. We have reported in our previous article that fluorine can be supplied to a film by subliming solid-state fluorides such as FeF2 or SmF3. In this article, we report on the growth of SmFeAs(O,F) using FeF3 as an alternative fluorine source. FeF3 is solid at ambient temperatures and decomposes at temperatures as low as 100-200 °C, and releases fluorine-containing gas during the thermal decomposition. With this alternative fluorine source, we have grown SmFeAs(O,F) films with Tc as high as 55 K. This achievement demonstrates that FeF3 has potential as a fluorine source that can be employed ubiquitously for a thin-film growth of any fluorine containing compounds. One problem specific to FeF3 is that the compound is highly hydroscopic and contains a substantial amount of water even in its anhydrous form. In this article, we describe how to overcome this specific problem.

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.

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.

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.